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Although information about the occurrence and distribution of retinoids in the environment is scarce, cyanobacterial water blooms have been identified as a significant source of these small molecules. Despite the confirmed presence of retinoids in the freshwater blooms dominated by cyanobacteria and their described teratogenic effects, reliable identification of retinoid producers and the mechanism of their biosynthesis is missing. In this study, the cultures of several taxonomically diverse species of axenic cyanobacteria were confirmed as significant producers of retinoid-like compounds. The consequent bioinformatic analysis suggested that the enzymatic background required for the biosynthesis of all-trans retinoic acid from retinal is not present across phylum Cyanobacteria. However, we demonstrated that retinal conversion into other retinoids can be mediated non-enzymatically by free radical oxidation, which leads to the production of retinoids widely detected in cyanobacteria and environmental water blooms, such as all-trans retinoic acid or all-trans 5,6epoxy retinoic acid. Importantly, the production of these metabolites by cyanobacteria in association with the mass development of water blooms can lead to adverse impacts in aquatic ecosystems regarding the described teratogenicity of retinoids. Moreover, our finding that retinal can be non-enzymatically converted into more bioactive retinoids, also in water, and out of the cells, increases the environmental significance of this process., Competing Interests: P.B. has been a guest editor of this Special Issue. However, he was not involved in the peer review process of this manuscript or in any decisions related to the article. Rest of the authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Background and Objectives: Age-related macular degeneration is a slow-progressing disease in which lipofuscin accumulates in the retina, causing inflammation and apoptosis of retinal pigment epithelial (RPE) cells. This study aimed to identify N -methyl-D-aspartate (NMDA) signaling as a novel mechanism for scavenging N -retinylidene- N -retinylethanolamine (A2E), a component of ocular lipofuscin, in human RPE cells. Materials and Methods: A2E degradation assays were performed in ARPE-19 cells using fluorescently labeled A2E. The autophagic activity in ARPE-19 cells was measured upon blue light (BL) exposure, after A2E treatment. Autophagy flux was determined by measuring LC3-II formation using immunoblotting and confocal microscopy. To determine whether autophagy via the NMDA receptor is involved in A2E clearance, ATG5-deficient cells were used. Results: Ro 25-6981, an NR2B-selective NMDA receptor antagonist, effectively cleared A2E. Ro 25-6981 reduced A2E accumulation in the lysosomes of ARPE-19 cells at sub-cytotoxic concentrations, while increasing the formation of LC3-II and decreasing p62 protein levels in a concentration-dependent manner. The autophagic flux monitored by RFP-GFP-LC3 and bafilomycin A1 assays was significantly increased by Ro 25-6981. A2E clearance by Ro 25-6981 was abolished in ATG5-depleted ARPE-19 cells, suggesting that A2E degradation by Ro 25-6981 was mediated by autophagy. Furthermore, treatment with other NMDA receptor antagonists, CP-101,606 and AZD6765, showed similar effects on autophagy activation and A2E degradation in ARPE-19 cells. In contrast, glutamate, an NMDA receptor agonist, exhibited a contrasting effect, suggesting that both the activation of autophagy and the degradation of A2E by Ro 25-6981 in ARPE-19 cells occur through inhibition of the NMDA receptor pathway. Conclusions: This study demonstrates that NMDA receptor antagonists degrade lipofuscin via autophagy in human RPE cells and suggests that NMDA receptor antagonists could be promising new therapeutics for retinal degenerative diseases.

Retinoids are newly detected compounds in aquatic ecosystems associated with cyanobacterial water blooms. Their potential health risks are only scarcely described despite numerous detections of all-trans retinoic acid (ATRA) and its derivatives in the environment. Besides the known teratogen ATRA there is only little or no information about their potency and namely their effects in vivo. We characterize ATRA and 8 other retinoids reported to occur in the environment for their bioactivity and teratogenicity using four in vitro reporter gene assays and zebrafish (Danio rerio) embryotoxicity assay. Our results document the ability of these compounds to interfere with retinoid signalling and cause teratogenicity at environmentally relevant levels with EC 50 values at nM (hundreds of ng/L) levels and teratogenic indexes ranging from 2.8 (9cis retinoic acid) to 15.8 (retinal). The relative potency of individual compounds for teratogenicity ranged from 0.059 (retinal) to 0.96 (5,6-epoxy ATRA) when compared to ATRA. An environmentally relevant mixture of retinoids was tested showing good predictability of teratogenicity from the in vitro activities and additive toxicity of the mixture. The high teratogenicity of the newly described compounds associated with cyanobacteria presents a concern for developmental stages due to high conservation of the retinoid signalling across vertebrates., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has a marked tropism for the biliary tract; it damages the bile ducts and hepatocytes and can lead to liver decompensation, cirrhosis, and sepsis. The pathogenesis of liver damage and its association with damage to the lung, heart, and brain and to the other protean manifestations of COVID-19 disease are not fully understood. In particular, tissue damage from thinning and leaky blood vessels appears to result from an inflammatory response to the virus rather than the virus itself. This article outlines a new hypothesis of the nature of the inflammatory factor responsible for tissue damage in COVID-19. Review of the literature reveals that COVID-19 disease closely resembles an endogenous form of hypervitaminosis A. We propose that SARS-CoV-2 virus-induced liver damage causes retinoic acid and stored retinyl esters to be released into the circulation in toxic concentrations, unbound to protein, with resulting damage to organs including the lungs, heart, blood vessels, and skin. Several lines of evidence support this model of disease causation. Subject to testing, strategies for the effective treatment and prevention of COVID-19 could include targeting the action and accumulation of retinoids.

The use of genomic approaches in toxicological studies has greatly increased our ability to define the molecular profiles of environmental chemicals associated with developmental neurotoxicity (DNT). Integration of these approaches with adverse outcome pathways (AOPs), a framework that translates environmental exposures to adverse developmental phenotypes, can potentially inform DNT testing strategies. Here, using retinoic acid (RA) as a case example, we demonstrate that the integration of toxicogenomic profiles into the AOP framework can be used to establish a paradigm for chemical testing. RA is a critical regulatory signaling molecule involved in multiple aspects of mammalian central nervous system (CNS) development, including hindbrain formation/patterning and neuronal differentiation, and imbalances in RA signaling pathways are linked with DNT. While the mechanisms remain unresolved, environmental chemicals can cause DNT by disrupting the RA signaling pathway. First, we reviewed literature evidence of RA and other retinoid exposures and DNT to define a provisional AOP related to imbalances in RA embryonic bioavailability and hindbrain development. Next, by integrating toxicogenomic datasets, we defined a relevant transcriptomic signature associated with RA-induced developmental neurotoxicity (RA-DNT) in human and rodent models that was tested against zebrafish model data, demonstrating potential for integration into an AOP framework. Finally, we demonstrated how these approaches may be systematically utilized to identify chemical hazards by testing the RA-DNT signature against azoles, a proposed class of compounds that alters RA-signaling. The provisional AOP from this study can be expanded in the future to better define DNT biomarkers relevant to RA signaling and toxicity., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Lighting is rapidly changing with the introduction of light-emitting diodes (LEDs) in our homes, workplaces, and cities. This evolution of our optical landscape raises major concerns regarding phototoxicity to the retina since light exposure is an identified risk factor for the development of age-related macular degeneration (AMD). In this disease, cone photoreceptors degenerate while the retinal pigment epithelium (RPE) is accumulating lipofuscin containing phototoxic compounds such as A2E. Therefore, it remains unclear if the light-elicited degenerative process is initiated in cones or in the RPE. Using purified cone photoreceptors from pig retina, we here investigated the effect of light on cone survival from 390 to 510 nm in 10 nm steps, plus the 630 nm band. If at a given intensity (0.2 mW/cm²), the most toxic wavelengths are comprised in the visible-to-near-UV range, they shift to blue-violet light (425-445 nm) when exposing cells to a solar source filtered by the eye optics. In contrast to previous rodent studies, this cone photoreceptor phototoxicity is not related to light absorption by the visual pigment. Despite bright flavin autofluorescence of cone inner segment, excitation-emission matrix of this inner segment suggested that cone phototoxicity was instead caused by porphyrin. Toxic light intensities were lower than those previously defined for A2E-loaded RPE cells indicating cones are the first cells at risk for a direct light insult. These results are essential to normative regulations of new lighting but also for the prevention of human retinal pathologies since toxic solar light intensities are encountered even at high latitudes.

Objective: Retinoic acid (RA) is a ligand for nuclear receptors that modulate gene transcription and cell differentiation. Whether RA controls ectopic calcification in humans is unknown. We tested the hypothesis that RA regulates osteogenic differentiation of human arterial smooth muscle cells and aortic valvular interstitial cells that participate in atherosclerosis and heart valve disease, respectively. Approach and Results: Human cardiovascular tissue contains immunoreactive RAR (RA receptor)-a retinoid-activated nuclear receptor directing multiple transcriptional programs. RA stimulation suppressed primary human cardiovascular cell calcification while treatment with the RAR inhibitor AGN 193109 or RARα siRNA increased calcification. RA attenuated calcification in a coordinated manner, increasing levels of the calcification inhibitor MGP (matrix Gla protein) while decreasing calcification-promoting TNAP (tissue nonspecific alkaline phosphatase) activity. Given that nuclear receptor action varies as a function of distinct ligand structures, we compared calcification responses to cyclic retinoids and the acyclic retinoid peretinoin. Peretinoin suppressed human cardiovascular cell calcification without inducing either secretion of APOC3 (apolipoprotein-CIII), which promotes atherogenesis, or reducing CYP7A1 (cytochrome P450 family 7 subfamily A member 1) expression, which occurred with cyclic retinoids all- trans RA, 9- cis RA, and 13- cis RA. Additionally, peretinoin did not suppress human femur osteoblast mineralization, whereas all- trans RA inhibited osteoblast mineralization., Conclusions: These results establish retinoid regulation of human cardiovascular calcification, provide new insight into mechanisms involved in these responses, and suggest selective retinoid modulators, like acyclic retinoids may allow for treating cardiovascular calcification without the adverse effects associated with cyclic retinoids.

In animals, retinoic acids (RAs), one of the main derivatives of vitamin A, are crucial for a variety of physiological processes. RAs, including all-trans-RA, 9-cis-RA, 13-cis-RA, and their corresponding metabolites (i.e., all-trans-4-oxo-RA, 9-cis-4-oxo-RA and 13-cis-4-oxo-RA) can be excreted through urination from humans and animals. Sewage treatment plants (STPs) are a significant source of RAs and 4-oxo-RAs into aquatic environments. RAs and 4-oxo-RAs can be identified and quantified by use of liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). RAs and 4-oxo-RAs have been reported in various environmental matrices including rivers, lakes, reservoirs and coastal marine environments as well as in sewage effluents discharged from STPs. Greater concentrations of RAs and 4-oxo-RAs have been observed during blooms of cyanobacteria and microalgae, suggesting that cyanobacteria and microalgae are natural sources of RAs and 4-oxo-RAs in aquatic environments. These potential sources of RAs and 4-oxo-RAs raise concerns about their concentrations and risks in aquatic environments because excessive intake of these chemicals can result in abnormal morphological development in animals. Teratogenic effects were observed in amphibians, fish embryos, gastropods, mammals and birds when exposed to RAs. This review summarizes sources, concentrations, adverse effects and ecological risks of RAs and 4-oxo-RAs in aquatic environments. An interim, predicted no-effect concentration (PNEC) of RAs (in terms of at-RA) for freshwater environments was determined to be 3.93 ng/L at-RA equivalents. Based on limited data on concentrations of RAs in freshwater ecosystems, their hazard quotients were found to range from zero to 16.41, depending on the environmental conditions of receiving waters. Ecological risks of RAs in marine environments are yet to be explored due to the paucity of data related to both their concentrations in marine environment and toxic potencies to marine species. This review updates current knowledge of RAs and 4-oxo-RAs in aquatic environments and calls for more studies on their concentrations and fate in aquatic environments, especially estuarine and coastal marine environments with a view to enabling a comprehensive assessment of their ecological risks around the globe., Competing Interests: Declaration of Competing Interest We declare that we have no conflict of interest., (Copyright © 2020 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Age-related macular degeneration (AMD) is a late-onset retinal disease and the leading cause of central vision loss in the elderly. Degeneration of retinal pigment epithelial cells (RPE) is a crucial contributing factor responsible for the onset and progression of AMD. The toxic fluorophore N-retinyl-N-retinylidene ethanolamine (A2E), a major lipofuscin component, accumulates in RPE cells with age. Phytochemicals with antioxidant properties may have a potential role in both the prevention and treatment of this age-related ocular disease. Particularly, there is an increased interest in the therapeutic effects of resveratrol (RSV), a naturally occurring polyphenol (3,4',5-trihydroxystilbene). However, the underlying mechanism of the RSV antioxidative effect in ocular diseases has not been well explored. We hypothesized that this bioactive compound may have beneficial effects for AMD. To this end, to investigate the potential profits of RSV against A2E-provoked oxidative damage, we used human RPE cell line (ARPE-19). RSV (25 µM) attenuates the cytotoxicity and the typical morphological characteristics of apoptosis observed in 25 µM A2E-laden cells. RSV pretreatment strengthened cell monolayer integrity through the preservation of the transepithelial electrical resistance and reduced the fluorescein isothiocyanate (FITC)-dextran diffusion rate as well as cytoskeleton architecture. In addition, RSV exhorts protective effects against A2E-induced modifications in the intracellular redox balance. Finally, RSV also prevented A2E-induced mitochondrial network fragmentation. These findings reinforce the idea that RSV represents an attractive bioactive for therapeutic intervention against ocular diseases associated with oxidative stress such as AMD.

Cyanobacteria routinely release potentially harmful bioactive compounds into the aquatic environment. Several recent studies suggested a potential link between the teratogenicity of effects caused by cyanobacteria and production of retinoids. To investigate this relationship, we analysed the teratogenicity of field-collected cyanobacterial bloom samples by means of an in vivo zebrafish embryo test, an in vitro reporter gene bioassay and by the chemical analysis of retinoids. Extracts of biomass from cyanobacterial blooms with the dominance of Microcystis aeruginosa and Aphanizomenon klebahnii were collected from water bodies in the Czech Republic and showed significant retinoid-like activity in vitro, as well as high degrees of teratogenicity in vivo. Chemical analysis was then used to identify a set of retinoids in ng per gram of dry weight concentration range. Subsequent fractionation and bioassay-based characterization identified two fractions with significant in vitro retinoid-like activity. Moreover, in most of the retinoids eluted from these fractions, teratogenicity with malformations typical for retinoid signalling disruption was observed in zebrafish embryos after exposure to the total extracts and these in vitro effective fractions. The zebrafish embryo test proved to be a sensitive toxicity indicator of the biomass extracts, as the teratogenic effects occurred at even lower concentrations than those expected from the activity detected in vitro. In fact, teratogenicity with retinoid-like activity was detected at concentrations that are commonly found in biomasses and even in bulk water surrounding cyanobacterial blooms. Overall, these results provide evidence of a link between retinoid-like activity, teratogenicity and the retinoids produced by cyanobacterial water blooms in the surrounding environment., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

As a part of the aging process, N-retinylidene-N-retinylethanolamine (A2E) accumulates in the retina to activate autophagy in retinal pigmented epithelial cells. However, the effect of A2E photoactivation on autophagy, which is more clinically relevant, still remains unclear. Here, we investigated the effect of blue light (BL)-activated A2E on autophagy in human retinal pigmented epithelial cells, ARPE-19. A significant increase in LC3-II protein was observed when BL was irradiated on ARPE-19 cells containing A2E. The mammalian target of rapamycin (mTOR) pathway was examined to verify whether autophagy was activated, but no change in AKT, mTOR, and 4EBP phosphorylation was observed. Transcription factor EB (TFEB) target gene expression, which is another pathway involved in autophagy, was also not altered by A2E and BL. However, intracellular p62 protein levels were significantly increased, which represented the inhibition of autophagic flux. To investigate the mechanism of the suppressed autophagic flux, the lysosomal state was observed. After BL irradiation, lysosomal damage was induced in A2E-treated ARPE-19 cells, and this phenomenon was prevented by treatment with the antioxidant, N-acetylcysteine. Our results suggest that A2E photoactivation compromises autophagy in ARPE-19 cells and that reactive oxygen species (ROS) play an important role in this process., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Discharge of partially treated effluent from sewage treatment plants (STPs) is a significant source of chemical contaminants, such as retinoids and oestrogenic endocrine disrupting chemicals (EDCs), which are continuously input into the marine environments of densely populated and urbanized coastal cities. In this study, we successfully developed three analytical methods to detect and qualify retinoic acids (at-RA, 13c-RA & 9c-RA), their metabolites (at-4-oxo-RA, 13c-4-oxo-RA & 9c-4-oxo-RA), and oestrogenic EDCs using high pressure liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Using these methods, we found that the total concentrations of retinoids in the influents and effluents of three saline STPs in Hong Kong were 7.1-29 ng/L and 3.7-9.1 ng/L, respectively, and those of EDCs were 3107-5829 ng/L and 1225-2638 ng/L, respectively. Retinoids were dominated by at-4-oxo-RA or 13c-4-oxo-RA in wastewater, whereas at-RA and 13c-RA were the most abundant in sludge. Alkylphenols and bisphenol A were the dominant EDCs in wastewater, whilst alkylphenols, triclosan, and triclocarban were dominant in sludge. Overall, the sewage treatment processes in the STPs of Hong Kong were not highly efficient in the removal of retinoids and EDCs from wastewater influents, with removal efficiencies in the aqueous phase of 41-82% and 31-79%, respectively. The removals were attributed mainly to sorption and degradation. Due to such limited removal, the effluents from STPs and the adjacent seawaters (i.e., receiving water bodies) still exhibited relatively high concentrations of retinoids (2.0-4.3 ng/L in seawaters) and EDCs (71-260 ng/L in seawaters), which posed medium ecological risks to the coastal marine ecosystem of Hong Kong (i.e., hazard quotients: 0.1-1)., (Copyright © 2019 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Numerous studies have focused on the deteriorate role of amyloid-β (Aβ) on retina, implying the potential pathogenic mechanism underlying age-related macular degeneration (AMD). However, the mechanism underlying the Aβ deposition in AMD patients remains unknown. Beta-site amyloid precursor protein-cleaving enzyme 1 (BACE1), rate-limiting enzyme for Aβ production, plays an important role in Aβ deposition in the brain. In the current study, we aimed to clarify the regulation mechanism of BACE1 and explore potential drug targets using a lipofuscinfluorophore A2E-mediated photo-oxidation model. In this model, Aβ 1-40 and Aβ 1-42 levels increased simultaneously with the enhanced BACE1 expression. These changes were associated with the hypomethylation of specific loci within the BACE1 gene promoter and the decreased levels of DNA methyltransferase 1 (DNMT1). Furthermore, we noticed overlapping regions of differentially methylated CpG islands and specificity protein (Sp1) binding sites within the BACE1 promoter. We employed chromatin immunoprecipitation (ChIP) assay to verify that the decreased BACE1 promoter methylation by DNMT1 enabled increased binding between Sp1 and the BACE1 promoter, which further enhanced BACE1 transcription. The inhibition of Sp1 with mithramycin A (MTM) could down-regulate the expression of BACE1 as well as alleviate the RPE barrier morphology and function impairment. Our results for the first time show the competitive regulation of BACE1 by transcription factor Sp1 and DNMT1 after photo-oxidation and confirm the potential novel protective role of MTM on RPE cells., (Copyright © 2018. Published by Elsevier Ltd.)

A challenge in the treatment of Staphylococcus aureus infections is the high prevalence of methicillin-resistant S. aureus (MRSA) strains and the formation of non-growing, dormant 'persister' subpopulations that exhibit high levels of tolerance to antibiotics and have a role in chronic or recurrent infections. As conventional antibiotics are not effective in the treatment of infections caused by such bacteria, novel antibacterial therapeutics are urgently required. Here we used a Caenorhabditis elegans-MRSA infection screen to identify two synthetic retinoids, CD437 and CD1530, which kill both growing and persister MRSA cells by disrupting lipid bilayers. CD437 and CD1530 exhibit high killing rates, synergism with gentamicin, and a low probability of resistance selection. All-atom molecular dynamics simulations demonstrated that the ability of retinoids to penetrate and embed in lipid bilayers correlates with their bactericidal ability. An analogue of CD437 was found to retain anti-persister activity and show an improved cytotoxicity profile. Both CD437 and this analogue, alone or in combination with gentamicin, exhibit considerable efficacy in a mouse model of chronic MRSA infection. With further development and optimization, synthetic retinoids have the potential to become a new class of antimicrobials for the treatment of Gram-positive bacterial infections that are currently difficult to cure.

In the retinal pigment epithelium of patients with age-related macular degeneration (AMD), excess N-retinylidene-N-retinylethanolamine (A2E), a dimer of all-trans-retinal, accumulats to induce inflammatory cytokine secretion and phototoxic effects. Therefore, the reduction of intracellular A2E is a promising approach for the prevention and treatment of AMD. In this study, acid-labile β-cyclodextrin (β-CD)-threaded polyrotaxanes (PRXs) were synthesized and investigated their effects on the removal of A2E accumulated in retinal pigment epithelium cells (ARPE-19) in comparison to nonlabile PRXs and 2-hydroxypropyl β-CD (HP-β-CD) were examined. GC-MS and HPLC studies strongly suggest that the acid-labile PRXs dissociated into their constituent molecules in cells by lysosomal acidification and threaded β-CDs were considered to be released from the PRXs. The released β-CDs formed an inclusion complex with A2E, which promoted the excretion of A2E. Indeed, the acid-labile PRXs effectively reduced intracellular A2E level at approximately a 10-fold lower concentration than HP-β-CD. Accompanied with A2E removal, the toxicity and phototoxicity of A2E were attenuated by treatment with acid-labile PRXs. Because the nonlabile PRX failed to reduce intracellular A2E level and attenuate phototoxicity, intracellular release of threaded β-CDs from the acid-labile PRX might contribute to reducing intracellular A2E. We conclude that acid-labile PRXs are promising candidates for the treatment of macular diseases through the removal of toxic metabolites.

Aim: To establish a mouse model for the study of congenital defects, using exposure of pregnant females to the teratogen BMS-189453, a multiple retinoic acid competitive antagonist.We found not less than 60% of fetuses had transposition of the great arteries and l5% had other congenital heart defects such as double outlet right ventricle, tetralogy of Fallot, truncus and right aortic arch. Newborns exposed in utero to BMS-189453 were affected by thymus aplasia or hypoplasia, and severe congenital anomalies of the central nervous system due to neural tube defects. An anterior rotation of the right lung was also frequently present in our model. We also report a case of murine congenital diaphragmatic hernia associated with thymic aplasia and transposition of the great arteries., Conclusion: These findings support the hypothesis that the combination of diaphragmatic hernia and congenital heart defects may be related to an alteration of the retinoic acid signaling pathways.

Previous studies have shown that N(1),N(12)-bis(all-trans-retinoyl)spermine (RASP), a retinoid analog, inhibits RNase P activity and angiogenesis in the chicken embryo chorioallantoic membrane, demonstrates anti-tumor activity on prostate cancer cells, and acts as anti-inflammatory agent, being more effective and less toxic than all-trans retinoic acid. In an attempt to further characterize the biological profile of RASP, we tested its effects on organ toxicity and teratogenicity by daily oral gavage of RASP at a level of 50 mg/Kg of body weight in two generations of rats. We found that this compound does not induce changes to the body growth, the appearance of physical features, and the animal's reflexes. Additionally, no substantial histopathological lesions were found in brain, heart, lung, thymus, liver, thyroid gland, adrenal gland, pituitary gland, kidneys, spleen, skin, femora, prostate, testis, epididymis, vagina, uterus, and ovaries of RASP-treated animals. These results suggest RASP, as a promising lead compound for the treatment of several dermatological disorders and certain cancer types, has apparently minimal toxic side-effects as revealed in this two-generation reproduction study in rats., (© 2016 Wiley Periodicals, Inc.)

MDI 301 is a novel 9-cis retinoic acid derivative in which the terminal carboxylic acid group has been replaced by a picolinate ester. MDI 301, a retinoic acid receptor-α - agonist, suppressed the growth of several human myeloid leukemia cell lines (HL60, NB4, OCI-M2, and K562) in vitro and induced cell-substrate adhesion in conjunction with upregulation of CD11b. Tumor growth in HL60-injected athymic nude mice was reduced. In vitro, MDI 301 was comparable to all-trans retinoic acid (ATRA) whereas in vivo, MDI 301 was slightly more efficacious than ATRA. Most importantly, unlike what was found with ATRA treatment, MDI 301 did not induce a cytokine response in the treated animals and the severe inflammatory changes and systemic toxicity seen with ATRA did not occur. A retinoid with these characteristics might be valuable in the treatment of promyelocytic leukemia, or, perhaps, other forms of myeloid leukemia.

Vitamin A and its derivatives, the retinoids, are micronutrient necessary for the human diet in order to maintain several cellular functions from human development to adulthood and also through aging. Furthermore, vitamin A and retinoids are utilized pharmacologically in the treatment of some diseases, as, for instance, dermatological disturbances and some types of cancer. In spite of being an essential micronutrient with clinical application, vitamin A exerts several toxic effects regarding redox environment and mitochondrial function. Moreover, decreased life quality and increased mortality rates among vitamin A supplements users have been reported. However, the exact mechanism by which vitamin A elicits its deleterious effects is not clear yet. In this review, the role of mitochondrial dysfunction in the mechanism of vitamin A-induced toxicity is discussed.

Retinoic acids and their derivatives have been recently identified by chemical analyses in cyanobacteria and algae. Given the essential role of retinoids for vertebrate development this has raised concerns about a potential risk for vertebrates exposed to retinoids during cyanobacterial blooms. Our study focuses on extracellular compounds produced by phytoplankton cells (exudates). In order to address the capacity for the production of retinoids or compounds with retinoid-like activity we compared the exudates of ten cyanobacteria and algae using in vitro reporter gene assay. Exudates of three cyanobacterial species showed retinoid-like activity in the range of 269-2,265 ng retinoid equivalents (REQ)/L, while there was no detectable activity in exudates of the investigated algal species. The exudates of one green alga (Desmodesmus quadricaudus) and the two cyanobacterial species with greatest REQ levels, Microcystis aeruginosa and Cylindrospermopsis raciborskii, were selected for testing of the potential relation of retinoid-like activity to developmental toxicity in zebrafish embryos. The exudates of both cyanobacteria were indeed provoking diverse teratogenic effects (e.g. tail, spine and mouth deformation) and interference with growth in zebrafish embryos, while such effects were not observed for the alga. Fish embryos were also exposed to all-trans retinoic acid (ATRA) in a range equivalent to the REQ concentrations detected in exudates by in vitro bioassays. Both the phenotypes and effective concentrations of exudates corresponded to ATRA equivalents, supporting the hypothesis that the teratogenic effects of cyanobacterial exudates are likely to be associated with retinoid-like activity. The study documents that some cyanobacteria are able to produce and release retinoid-like compounds into the environment at concentrations equivalent to those causing teratogenicity in zebrafish. Hence, the characterization of retinoid-like and teratogenic potency should be included in the assessment of the potential adverse effects caused by the release of toxic and bioactive compounds during cyanobacterial blooms., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Aims: Age-related lipofuscin N-retinylidene-N-retinylethanolamine (A2E) accumulated in human retinal pigment epithelium (RPE) cells confers susceptibility to blue light-mediated damage, which represents one pathogenesis of age-related macular degeneration. This study investigated the expression of 2 best-characterized endoplasmic reticulum (ER) stress markers, glucose-related protein 78 (GRP78) and C/EBP homologous protein (CHOP), as well as their regulation by oxidative stress after blue light-mediated damage of A2E-containing RPE cells., Methods: ARPE-19 cells were incubated with A2E (10, 25, 50 μM) for 2 h and exposed to blue light for 20 min. A2E distributions in RPE cells were assessed via laser scanning confocal microscope and liquid chromatography-mass spectrometry. Cell viability was measured by a Cell Titer 96 Aqueous One Solution cell proliferation assay. The quantity of intracellular reactive oxygen species (ROS) was detected by dihydroethidium fluorescence using flow cytometry. Expressions of GRP78 and CHOP were measured at both mRNA and protein levels. To examine the role of oxidative stress in regulating GRP78 and CHOP expression, RPE cells were pretreated with the antioxidant N-acetylcysteine (NAC) for 2 h. RNA interference of GRP78 performed by short hairpin RNA was used to evaluate the effect of GRP78 in blue light-mediated damage of RPE cells., Results: After blue light exposure, A2E-treated RPE cells showed a gradual decrease in cell viability and a particular increase in ROS levels. Meanwhile, the expressions of GRP78 and CHOP in A2E-treated RPE cells were significantly increased at different time points after illumination. Pretreatment with NAC attenuated the expression of 2 ER stress markers, especially CHOP in A2E and blue light-treated RPE cells. Silencing of GRP78 by RNA interference upregulated CHOP and caspase-12 expression as well as aggravated the blue light-mediated damage of A2E-laden RPE cells., Conclusion: RPE cells exhibited ROS accumulation and subsequent elevation of GRP78 and CHOP expression after A2E and blue light-induced damage. The ROS scavenger NAC diminished ER stress protein expression, suggesting a connection between ER and oxidative stress in blue light-mediated damage of A2E-containing RPE cells. Besides, GRP78 may play a protective role in it., (© 2014 S. Karger AG, Basel.)

Adarotene belongs to the so-called class of atypical retinoids. The presence of the phenolic hydroxyl group on Adarotene structure allows a rapid O-glucuronidation as a major mechanism of elimination of the drug, favoring a fast excretion of its glucuronide metabolite in the urines. A series of ether, carbamate and ester derivatives was synthesized. All of them were studied and evaluated for their stability at different pH. The cytotoxic activity in vitro on NCI-H460 non-small cell lung carcinoma and A2780 ovarian tumor cell lines was also tested. A potential back-up of Adarotene has been selected to be evaluated in tumor models., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

The present study determines the relative developmental toxicity potencies of retinoids in the embryonic stem (ES)-D3 cell differentiation assay of the embryonic stem cell test, and compares the outcomes with their relative potencies in in vivo and two other in vitro assays for developmental toxicity. The results reveal that the potency ranking obtained in the ES-D3 cell differentiation assay is similar to the reported potency rankings in the two other in vitro assays for developmental toxicity. TTNPB ((E)-4[2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)-1-propenyl]benzoic acid) was the most potent retinoid, whereas etretinate and retinol had the lowest potency. All-trans-retinoic acid, 13-cis-retinoic acid, 9-cis-retinoic acid and acitretin showed an intermediate potency. In vivo potency rankings of the developmental toxicity of retinoids appear to be dependent on the species and/or exposure regimens used. The obtained in vitro potency ranking does not completely correspond with the in vivo potency rankings, although TTNPB is correctly predicted to be the most potent and retinol the least potent congener. The lack of in vivo kinetic processes in the ES-D3 cell differentiation assay might explain the deviating potency predictions of some retinoids. Therefore, knowledge on the species-dependent in vivo kinetics is essential when using in vitro toxicity data for the estimation of in vivo developmental toxicity potencies within series of related compounds., (Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.)

Background: There is limited evidence regarding the efficacy and safety of retinoids in different psoriasis subtypes., Objective: To systematically review the available literature on: (i) modalities of administration and prescription of oral retinoids as single agent or combined therapy for the treatment of plaque-type psoriasis (PV), nail psoriasis and localized and generalized pustular psoriasis : initial and optimal dosage; (ii) skeletal toxicity of retinoid for the treatment of psoriasis., Methods: A systematic literature search was carried out in MEDLINE, EMBASE, and Cochrane Library databases from 1975 to 2010 searching for randomized controlled trials and observational studies evaluating 1) various dosages of retinoid in psoriasis and 2) skeletal toxicity of retinoid in psoriasis. Articles were limited to human subjects and English/French languages., Results: Efficacy of retinoids in psoriasis. Among 1348 identified references, 44 published studies were included. Starting daily dosages between 10 and 25 mg and stepwise escalation were associated with higher clinical efficacy and lower incidence of adverse events in comparison with higher doses and regimens rapidly reaching optimal dose. Retinoids as single agent therapy appeared to show limited efficacy in PV, while the good clinical efficacy reported in pustular forms should be cautiously considered, given the spontaneously remitting course of the disease. Combining retinoids with phototherapy appeared to be highly effective in patients with PV. Potential skeletal toxicity of retinoids. 15 published studies out of 105 identified references were included. There is no strong evidence of an increased risk of skeletal abnormalities in psoriasis patients treated with retinoids., Conclusion: Acitretin appears to provide better efficacy in pustular psoriasis than in PV as a single agent treatment. There is no evidence for skeletal toxicity of retinoids in the setting of psoriasis, and accordingly monitoring this risk through X-ray is not warranted., (© 2011 The Authors. JEADV © 2011 European Academy of Dermatology and Venereology.)

Some forms of blinding macular disease are associated with excessive accumulation of bisretinoid lipofuscin in retinal pigment epithelial (RPE) cells of the eye. This material is refractory to lysosomal enzyme degradation. In addition to gene and drug-based therapies, treatments that reverse the accumulation of bisretinoid would be beneficial. Thus, we have examined the feasibility of degrading the bisretinoids by delivery of exogenous enzyme. As proof of principle we report that horseradish peroxidase (HRP) can cleave the RPE bisretinoid A2E. In both cell-free and cell-based assays, A2E levels were decreased in the presence of HRP. HRP-associated cleavage products were detected by ultraperformance liquid chromatography (UPLC) coupled to electrospray ionization mass spectrometry, and the structures of the aldehyde-bearing cleavage products were elucidated by 18O-labeling and 1H NMR spectroscopy and by recording UV−vis absorbance spectra. These findings indicate that RPE bisretinoids such as A2E can be degraded by appropriate enzyme activities.

Jaws are formed by cephalic neural crest (CNCCs) and mesodermal cells migrating to the first pharyngeal arch (PA1). A complex signaling network involving different PA1 components then establishes the jaw morphogenetic program. To gather insight on this developmental process, in this study, we analyze the teratogenic effects of brief (1-15 min) pulses of low doses of retinoic acid (RA: 0.25-2 µM) or RA agonists administered to early Xenopus laevis (X.l.) embryos. We show that these brief pulses of RA cause permanent craniofacial defects specifically when treatments are performed during a 6-hr window (developmental stages NF15-NF23) that covers the period of CNCCs maintenance, migration, and specification. Earlier or later treatments have no effect. Similar treatments performed at slightly different developmental stages within this temporal window give rise to different spectra of malformations. The RA-dependent teratogenic effects observed in Xenopus can be partially rescued by folinic acid. We provide evidence suggesting that in Xenopus, as in the mouse, RA causes craniofacial malformations by perturbing signaling to CNCCs. Differently from the mouse, where RA affects CNCCs only at the end of their migration, in Xenopus, RA has an effect on CNCCs during all the period ranging from their exit from the neural tube until their arrival in the PA1. Our findings provide a conceptual framework to understand the origin of individual facial features and the evolution of different craniofacial morphotypes., (© 2010 Wiley-Liss, Inc.)

Low resting heart rate is a strong and consistent predictor of conduct disorder and chronic aggression. Explanations such as fearlessness and low arousal-induced stimulus-seeking have been offered, assuming a causal association between the phenomena, but the origin of low heart rate and its significance for understanding aggression and violence remain obscure. Retinoids (vitamin A and its congeners) play important roles in embryogenesis and neural development. Several lines of evidence also suggest a causal role of retinoids in aggression as well as cognitive and mood disorders. The hypothesis is proposed that retinoid overexpression in utero induces, via a noradrenergic-to-cholinergic switch, alterations in cardiac functioning and hemodynamics resulting in low resting heart rate, brain structural and functional changes, minor physical anomalies, and persistent aggression. Retinoid toxicity occurring early in pregnancy could represent a final common pathway by which various prenatal challenges result in conduct disorder and chronic aggression (e.g., maternal cigarette smoking, alcohol consumption, drug use, exposure to environmental chemicals, stress, trauma or infection). Implications of the model for understanding related aspects of chronic aggression are discussed, as well as strategies for prevention and treatment.

Purpose: Cell death can be induced by exogenous reactive oxygen species (ROS). Endogenous ROS can also play a role in cell death triggered by agents that are not themselves ROS. One of the most potent ROS-generating systems is the iron-catalyzed Fenton reaction. Herein, the authors tested whether iron plays an important role in cell death induced by diverse stimuli in retinal pigment epithelial (RPE) cells., Methods: The ability of the iron chelator salicylaldehyde isonicotinoyl hydrazone (SIH) to chelate intracellular labile iron was tested in the human cell line ARPE-19. The ability of SIH to protect against RPE cell death induced by hydrogen peroxide, staurosporine, anti-Fas, and exposure to A2E plus blue light was determined. ROS production by staurosporine was assessed in the presence and absence of SIH. The protective activity of SIH was compared with that of other iron chelators and an antioxidant., Results: Acute exposure to SIH was nontoxic and at least partially protective against cell death induced by all tested agents. On a molar basis, SIH was more protective against hydrogen peroxide than other iron chelators and an antioxidant. SIH decreased levels of staurosporine-induced ROS., Conclusions: Iron chelation with SIH can decrease levels of ROS and protect RPE cells against cell death induced by diverse stimuli. These results suggest a central role for iron in cell death pathways, potentially involving the generation of oxidative stress. SIH or related iron chelators may prove useful for protection against diseases involving RPE death, such as AMD.

Introduction: Periconceptional supplementation with multivitamins containing folic acid reduces the risk of congenital malformations. We have previously investigated the effect on the murine development of a multiple retinoic acid competitive antagonist, Bristol-Myers-Squibb 189453, showing that treated fetuses were affected with heart defects, thymus aplasia or hypoplasia, and severe anomalies of the central nervous system. Hereby, we analyzed the effects of nutritive therapy involving folic acid and methionine on teratogen-induced congenital defects in mice., Materials and Methods: A total of 132 outbred CD1 litters were studied. Pregnant mice were divided into four experimental groups, and an oral supplementation of H(2)O or folic acid, or methionine, or folic acid+methionine was administered from 0.5 days postcoitum until the end of pregnancy. At 7.5 days postcoitum, mice from all these groups were administered Bristol-Myers-Squibb 189453 to induce the teratogenic effect. At the end of pregnancy, fetuses were dissected and tissues were analyzed by histology and flow cytometric assays., Results: Folic acid reduces congenital heart diseases from 81.3% to 64.8%, neural tube defects from 20.3% to 3.7%, and thymus abnormalities from 98.4% to 27.8%, restoring a normal number of differentiated thymus cells. Methionine is less effective in contrasting congenital heart diseases and neural tube defects, and induces thymus cell proliferation but not differentiation. Folic acid+methionine weakly reduce congenital heart diseases and neural tube defects, but consistently reduce the incidence of fetuses affected with thymus pathologies from 98.4% to 67.7%., Conclusions: Our results suggest that folic acid and methionine periconceptional supplementations may influence the incidence of congenital defects and may probably induce negative selection of embryos presenting developmental anomalies.

Vitamin A derivatives modulate gene expression through retinoic acid and rexinoid receptor (RAR/RXR) heterodimers and are indispensable for limb development. Of particular interest, RARgamma is highly expressed in cartilage, a target affected following retinoid-induced limb insult. The goal of this study was to examine how selective activation of RARgamma affects limb development. Forelimbs from E12.5 CD-1 mice were cultured for 6 days in the presence of all-trans RA (pan-RAR agonist; 0.1 or 1.0 microM) or BMS-189961 (BMS961, RARgamma-selective agonist; 0.01 or 0.1 microM) and limb morphology assessed. Untreated limbs developed normal cartilage elements whereas pan-RAR or RARgamma agonist-treated limbs exhibited reductive effects on chondrogenesis. Retinoid activity was assessed using RAREbeta2 (retinoic acid response element beta2)-lacZ reporter limbs; after 3 h of treatment, both drugs increased retinoid activity proximally. To elucidate the expression profiles of a subset of genes important for development, limbs were cultured for 3 h and cRNA hybridized to osteogenesis-focused microarrays. Two genes, matrix GLA protein (Mgp; chondrogenesis inhibitor) and growth differentiation factor-10 (Gdf10/Bmp3b) were induced by RA and BMS-189961. Real-time PCR was done to validate our results and whole mount in situ hybridizations against Mgp and Gdf10 localized their upregulation to areas of cartilage and programmed cell death, respectively. Thus, our results illustrate the importance of RARgamma in mediating the retinoid-induced upregulation of Mgp and Gdf10; determining their roles in chondrogenesis and cell death will help further unravel mechanisms underlying retinoid teratogenicity.

Vitamin A-derived retinoic acids (RAs) are known to exert a variety of biological actions, including modulatory effects on cell differentiation and apoptosis. A recent study has demonstrated that 13-cis-RA and all-trans-RA suppressed neurogenesis in the dentate gyrus of the hippocampus in adult mice. The present experiments were performed to see whether 13-cis-RA and all-trans-RA could alter the dendritic morphology of cultured hippocampal neurons via RA receptors: retinoic acid receptor (RAR) and retinoid X receptor (RXR). High doses of 13-cis-RA and all-trans-RA exerted a negative effect on the cultured hippocampal neurons, while a low dose of 13-cis-RA but not all-trans-RA caused a positive effect. The negative changes induced by 13-cis-RA and all-trans-RA were antagonized by RXR antagonists and RAR antagonists, respectively. The positive changes induced by a low dose of 13-cis-RA were blocked by both RXR antagonists and RAR antagonists. These results suggest that RAs at high concentrations cause a negative effect on the dendritic morphology of cultured hippocampal neurons through RA receptors, while RAs at low concentrations exert a positive influence on cultured hippocampal neurons.

Integrity of retinal pigment epithelial cells is necessary for photoreceptor survival and vision. The essential omega-3 fatty acid, docosahexaenoic acid, attains its highest concentration in the human body in photoreceptors and is assumed to be a target for lipid peroxidation during cell damage. We have previously shown, in contrast, that docosahexaenoic acid is also the precursor of neuroprotectin D1 (NPD1), which now we demonstrate, acts against apoptosis mediated by A2E, a byproduct of phototransduction that becomes toxic when it accumulates in aging retinal pigment epithelial (RPE) cells and in some inherited retinal degenerations. Furthermore, we show that neurotrophins, particularly pigment epithelium-derived factor, induce NPD1 synthesis and its polarized apical secretion. Moreover, docosahexaenoic acid (DHA) elicits a concentration-dependent and selective potentiation of pigment epithelial-derived factor-stimulated NPD1 synthesis and release through the apical RPE cell surface. The bioactivity of signaling activated by pigment epithelium-derived factor and DHA uncovered synergistic cytoprotection with concomitant NPD1 synthesis when cells were challenged with oxidative stress. Also, DHA and pigment epithelium-derived factor synergistically modify the expression of Bcl-2 family members, activating antiapoptotic proteins and decreasing proapoptotic proteins, and by attenuating caspase 3 activation during oxidative stress. Thus, our findings demonstrate that DHA-derived NPD1 protects against RPE cell damage mediated by aging/disease-induced A2E accumulation. Also, our results identify neurotrophins as regulators of NPD1 and of its polarized apical efflux from RPE cells. Taken together, these findings imply NPD1 may elicit autocrine actions on RPE cells and paracrine bioactivity in cells located in the proximity of the interphotoreceptor matrix.

Vitamins A and D are the first group of substances that have been reported to exhibit properties of skin hormones, such as organized metabolism, activation, inactivation, and elimination in specialized cells of the tissue, exertion of biological activity, and release in the circulation. Vitamin A and its two important metabolites, retinaldehyde and retinoic acids, are fat-soluble unsaturated isoprenoids necessary for growth, differentiation and maintenance of epithelial tissues, and also for reproduction. In a reversible process, vitamin A is oxidized IN VIVO to give retinaldehyde, which is important for vision. The dramatic effects of vitamin A analogues on embryogenesis have been studied by animal experiments; the clinical malformation pattern in humans is known. Retinoic acids are major oxidative metabolites of vitamin A and can substitute for it in vitamin A-deficient animals in growth promotion and epithelial differentiation. Natural vitamin A metabolites are vitamins, because vitamin A is not synthesized in the body and must be derived from carotenoids in the diet. On the other hand, retinoids are also hormones - with intracrine activity - because retinol is transformed in the cells into molecules that bind to and activate specific nuclear receptors, exhibit their function, and are subsequently inactivated. The mechanisms of action of natural vitamin A metabolites on human skin are based on the time- and dose-dependent influence of morphogenesis, epithelial cell proliferation and differentiation, epithelial and mesenchymal synthetic performance, immune modulation, stimulation of angiogenesis and inhibition of carcinogenesis. As drugs, vitamin A and its natural metabolites have been approved for the topical and systemic treatment of mild to moderate and severe, recalcitrant acne, photoaging and biologic skin aging, acute promyelocytic leukaemia and Kaposi's sarcoma. On the other hand, the critical importance of the skin for the human body's vitamin D endocrine system is documented by the fact that the skin is both the site of vitamin D (3)- and 1,25-dihydroxyvitamin D (3) [1, 25(OH) (2)D (3)]-synthesis and a target organ for 1,25(OH) (2)D (3). 1,25(OH) (2)D (3) is not only essential for mineral homeostasis and bone integrity, but also for numerous further physiologic functions including regulation of growth and differentiation in a broad variety of normal and malignant tissues, including cells derived from prostate, breast and bone. In keratinocytes and other cell types, 1,25(OH) (2)D (3) regulates growth and differentiation. Consequently, vitamin D analogues have been introduced for the treatment of the hyperproliferative skin disease psoriasis. Other newly detected functions of vitamin D analogues include profound effects on the immune system as well as protection against cancer and other diseases, including autoimmune and infectious diseases, in various tissues. Current investigation of the biological effects of vitamin D analogues are likely to lead to new therapeutic applications that, besides cancer prevention, may include the prevention and treatment of infectious as well as of inflammatory skin diseases. This review summarizes existing knowledge on vitamins A and D, the major vitamin-hormones of the skin.

Background: The morphogenetic mechanisms that are responsible for the transposition of the great arteries are still largely unknown, mainly because this malformation is very difficult to experimentally reproduce. The aim of the present study was to test the effect of BMS-189453, a retinoic acid antagonist, on murine heart morphogenesis., Methods: We administered this drug at 5 mg/kg body weight (twice, at a 12-h interval) to pregnant mice on 6.25/6.75 days postcoitum (dpc) (Group A), 6.75/7.25 dpc (Group B), 7.25/7.75 dpc (Group C), 7.75/8.25 dpc (Group D), or 8.25/8.75 dpc (Group E). At birth, the anatomical features of fetuses were evaluated by stereomicroscopic examination., Results: In Group A (18 fetuses), cardiovascular anatomy was normal in 10 (56%) cases, and 8 (44%) fetuses presented with transposition of the great arteries. In Group B, no fetuses were obtained. In Group C (78 fetuses), cardiovascular anatomy was normal in 19 (24%) cases, while 59 (76%) mice presented with various types of cardiac defects, including 48 transpositions of the great arteries (61%). In Group D (80 fetuses), cardiac defects were seen in 22 (27%) mice: 14 of these (17%) were transpositions of the great arteries. In Group E (72 fetuses), cardiovascular anatomy was normal in all cases. Of 248 fetuses analyzed, 87% presented with thymic aplasia or hypoplasia, and 20% presented with meroanencephalia and/or rachischisis., Conclusions: Transposition of the great arteries can be consistently reproduced in mice by administration of a retinoic acid competitive antagonist on 7.5 dpc.

Retinoids are widely used in the treatment of photoaging to stimulate dermal repair. However, retinoids also induce epidermal hyperplasia, which can lead to excessive scaling. Scaling is the major deterrent to topical retinoid therapy. Keratinocyte growth is strongly stimulated via ligand activation of EGFR. We examined regulation of EGFR ligands by retinoids and the role of EGFR in retinoid-induced hyperplasia in human skin in vivo. Topical treatment of human skin with all-trans retinoic acid (tRA) induces EGFR ligands heparin-binding (HB)-EGF and amphiregulin (AR), and reduces betacellulin mRNA levels. Laser capture microdissection-coupled real-time reverse transcription-PCR reveals that tRA increases HB-EGF mRNA throughout the epidermis, whereas AR induction is limited to basal keratinocytes. Topical tRA activates extracellular signal-regulated kinase 1/2 (Erk1/2) downstream EGFR effectors in human skin in vivo. tRA increases the soluble forms of AR and HB-EGF proteins, and induces epidermal hyperplasia, in human skin organ culture. Neutralization of HB-EGF or AR with specific antibodies strongly reduces tRA-induced epidermal hyperplasia. Finally, inhibition of EGFR activation by genistein reduces epidermal hyperplasia caused by topical retinoid treatment. These data demonstrate the central role of EGFR activation in retinoid-induced epidermal hyperplasia, and suggest that EGFR inhibitors can mitigate retinoid-induced scaling.

Retinoic acid (RA) is involved in vertebrate morphogenesis, growth, cellular differentiation, and tissue homeostasis. The use of in vitro systems initially led to the identification of nuclear receptor RXR/RAR heterodimers as possible transducers of the RA signal. To unveil the physiological functions of RARs and RXRs, genetic and pharmacological studies have been performed in the mouse. Together, their results demonstrate that (a) RXR/RAR heterodimers in which RXR is either transcriptionally active or silent are involved in the transduction of the RA signal during prenatal development, (b) specific RXRalpha/RAR heterodimers are required at many distinct stages during early embryogenesis and organogenesis, (c) the physiological role of RA and its receptors cannot be extrapolated from teratogenesis studies using retinoids in excess. Additional cell type-restricted and temporally controlled somatic mutagenesis is required to determine the functions of RARs and RXRs during postnatal life.

Retinoids consist of a family of naturally occuring compounds including all-trans retinoic acid (ATRA), retinal, retinol (vitamin A), 9-cis retinoic acid, 13-cis retinoic acid as well as a large number of synthetic derivatives. Retinoids are known to elicit diverse pharmacological profiles such as controlling cell differentiation/proliferation and modulating specific premalignant lesions and reducing second primary tumors in patients. Clinical use of retinoids is limited due to their toxicity. Three benzimidazole retinoid derivatives (BITN, BITNm, BITNe) were synthesized and were examined in terms of genotoxicity towards human lymphocyte cultures by sister chromatid exchange (SCE) analysis. It has been found that BITN decreased the number of SCEs 20% at 10(-6) M, but had no effect at 10(-5) M. No significant effect on SCEs was observed for BITNm and BITNe at both concentrations. ATRA increased the SCEs (35%) at 10(-5) M but had no effect at 10(-6) M. The results have shown that benzimidazole retinoids did not induce SCE significantly. Besides this, BITN reduced the SCEs and had a protective effect at low concentration. Since the induction of glutathione S-transferase (GST) is associated with anticancer drug resistance, the effects of BITN, BITNm, BITNe and ATRA on human lymphocyte GSTs were also investigated using CDNB as substrate. BITN and BITNm induced GST activities 54% and 49% respectively at 10(-5) M, but had no effect at 10(-6) M. BITNe induced GST activity 62% at 10(-5) M and 35% at 10(-6) M. ATRA had no effect on GST activity at 10(-5) M.

The maximum effective dose of retinyl ascorbate and its potential therapeutic benefits against induced oxidative damage were assessed in vitro using cultured human epidermal keratinocytes. RA-AsA exhibited toxic effects at concentrations >6 microM. The findings indicate to the potency of RA-AsA as free radical scavenger and cell proliferation regulator.

Purpose: Extracellular matrix (ECM) plays an important role in the regulation of cell function. The aging process may involve chemical modifications to ECM proteins, which may contribute to the aging of the Bruch membrane and pathogenesis of age-related macular degeneration (AMD). The purpose of this study is to investigate nitrite modification of basement membrane-like proteins on RPE cell behavior as a model for the aging of the Bruch membrane in age-related eye diseases. As a comparison, retinal pigment epithelium (RPE) cell behavior on glycolaldehyde-modified matrices (GMM) was also studied., Methods: Growth factor reduced Matrigel was reacted with nitrite or glycolaldehyde for 1 week or 12 hr, respectively. Calf RPE cells were plated on the modified matrices and examined in several ways. Attachment rates, proliferation rates, apoptosis, and necrosis were determined. Cell morphology and cell susceptibility to A2E-mediated damage was also monitored., Results: Nitrite-modified matrices (NMMs) inhibited cell attachment by 65% and proliferation by 33.7% compared to 69.6% and 21.7%, respectively, by GMM. Proliferation inhibition was not significant when cells were plated at high density on GMM (3.47%) but significant on NMM (20.9%). NMM induced cell apoptosis and necrosis, but GMM induced cell apoptosis only. Both modifications inhibited RPE differentiation. RPE cells on both matrices were more susceptible to blue light mediated damage by A2E, but damage was greater on NMM., Conclusions: NMM has significant damaging effects on RPE cell function and viability that is similar to the damaging effects of GMM. These studies may have relevance to the RPE dysfunction observed during the progression of AMD.

Sunlight is a known human carcinogen. Many cosmetics contain retinoid-based compounds, such as retinyl palmitate (RP), either to protect the skin or to stimulate skin responses that will correct skin damaged by sunlight. However, little is known about the photodecomposition of some retinoids and the toxicity of these retinoids and their sunlight-induced photodecomposition products on skin. Thus, studies are required to test whether topical application of retinoids enhances the phototoxicity and photocarcinogenicity of sunlight and UV light. Mechanistic studies are needed to provide insight into the disposition of retinoids in vitro and on the skin, and to test thoroughly whether genotoxic damage by UV-induced radicals may participate in any toxicity of topically applied retinoids in the presence of UV light. This paper reports the update information and our experimental results on photostability, photoreactions, and phototoxicity of the natural retinoids including retinol (ROH), retinal, retinoid acid (RA), retinyl acetate, and RP (Figure 1).

The aim of the present study was to evaluate the in vivo effects of the RAR-alpha selective antagonist Ro 41-5253 on a xenograft animal model for breast cancer. Our observations indicate a lack of toxic side effects of the drug, even when used at high dosages. It is interesting to note that using Ro 41-5253 at dosages of 10, 30 and 100 mg/kg/die resulted in a slight, but significant inhibition of cell growth. The data obtained in this study represents the basis for a further evaluation of Ro 41-5253 anti-neoplastic activity on transgenic breast cancer animal models.

Excess of Vitamin A (retinol) and related compounds (retinoids) induces bone fragility and is associated with increased hip fracture incidence in humans. Yet, their impact on the adult skeleton has been studied in relatively little detail. It is assumed that they induce generalized bone loss and decrease long-bone thickness due to reduction of radial bone growth. Here we characterized early skeletal responses of adult rodents to retinoid treatment, revealing novel aspects of retinoid action on the mature skeleton. The retinoid Ro 13-6298, given subcutaneously for 4 days, induced bone loss in the hind limbs of 12- and 56-week-old rats and of 15-week-old mice. In vivo monitoring of bone mass and geometry changes by peripheral quantitative computed tomography demonstrated that bone mass decline was due to subperiosteal cortical bone loss, which induced a shrinkage of bone diameter, whilst cancellous bone mass was preserved. We observed that the native retinoic acid isomer all-trans RA induced an identical pattern of bone loss. Histomorphometric evaluation revealed that increased subperiosteal osteoclastic bone resorption caused the cortical bone destruction. Interestingly, bone resorption was suppressed in cancellous bone, which was in agreement with reduced in vitro formation of osteoclasts from bone marrow cells that were derived from the proximity of cancellous bone. The retinoid-induced increase in subperiosteal bone resorption could be blocked by bisphosphonate as direct potent inhibitor of osteoclast action, but not by estradiol. Retinoid treatment induced a reduction of bone-forming surfaces at the subperiosteal site, but not in cancellous bone. In vitro osteoblast performance was also reduced or unchanged, depending on the cellular system used and assay type/duration. In conclusion, our studies revealed that the impact of retinoids on bone is highly bone-compartment-specific at early treatment phases. Furthermore, we showed that bone diameter shrinks in the adult skeleton after retinoid treatment due to subperiosteal osteoclastic bone resorption. Thus, retinoid-induced bone thinning is not only due to reduced radial bone growth as previously assumed. Our findings might explain why high intake of retinol is associated with increased hip fracture risk in the elderly and suggest a therapy to prevent such potential negative effects.

Retinoic acid can induce teratogenesis of the fetus of many animals including human, and its biological activities are induced by a serious of different retinoic acid accepters and their ligands. The retinoic acid acceptor RAR plays key roles in the teratogenesis, and the ligands of RAR are strong teratogens. The intensity sequence of the relative teratogenesis is ligandalpha, ligandbeta and ligandgamma. The ligands of the retinoic acid acceptor RXR cannot induce teratogenesis, but they can enhance the teratogenesis of the RAR stimulus. The retinoic acid acceptors can also affect the development of the fetus by adjusting the expression of the other genes. The relations between the gene mutation of the retinoic acid acceptor, various retinoic acid acceptors and their ligands and teratogenesis of retinoic acid are summarized in this article. In addition, the regulations of the retinoic acid acceptors to the other genes are also discussed.

The role that nutritional factors play in mammalian development has received renewed attention over the past two decades, as the scientific literature exploded with reports of retinoid compounds disrupting craniofacial development, and with other reports that folic acid supplementation in the periconceptional period can protect embryos from highly significant malformations. As was often the case, the situation became far more complicated, as the interaction between nutritional factors with selected genes was recognized. In this review, we attempt to summarize a complex clinical and experimental literature of nutritional factors, their biological transport mechanisms, and the impact that they have during early embryogenesis. Although not exhaustive, our goal was to provide an overview of important gene-nutrient interactions and a framework for their investigation.

The retinal pigment epithelial cell (RPE cell) layer protects the photoreceptors of the retina against oxidative stress. The decline of this capacity is believed to be a major factor in the impairment of vision in age-related macular degeneration. Exposure of human adult RPE cells to UV light at predominantly 320-400 nm (UVA light) in the presence of all-trans-retinaldehyde results in photooxidative cytotoxicity. Significant protection of RPE cells was obtained by prior treatment with phase 2 gene inducers, such as the isothiocyanate sulforaphane or a bis-2-hydroxybenzylideneacetone Michael reaction acceptor. The degree of protection was correlated with the potencies of these inducers in elevating cytoprotective glutathione levels and activities of NAD(P)H:quinone oxidoreductase. In embryonic fibroblasts derived from mice in which the genes for the transcription factor Nrf2, the repressor Keap1, or both Nrf2 and Keap1 were disrupted, the magnitude of resistance to photooxidative damage paralleled the basal levels of glutathione and NAD(P)H:quinone oxidoreductase in each cell type. Demonstration of protection of RPE cells against photooxidative damage by induction of phase 2 proteins may shed light on the role of oxidative injury in ocular disease. Moreover, the finding that dietary inducers provide indirect antioxidant protection suggests novel strategies for preventing chronic degenerative diseases, such as age-related macular degeneration.

Retinoids are natural and synthetic derivatives of vitamin A that have great promise for cancer therapy and chemoprevention. Of the retinoids developed so far, 4-(N-hydroxyphenyl)retinamide (4-HPR or fenretinide) appears to have the best therapeutic potential in vitro and in vivo and is currently being tested in clinical trials for cancer prevention and therapy. To develop other potentially potent antitumor agents, we synthesized 85 retinoid derivatives. In an initial screening of these synthetic retinoids using the HCT116 colon cancer cell line, we found that 4-amino-2-(butyrylamino)phenyl(2E,4E,6E,8E)-3,7-dimethyl-9-(2,6,6-trimethyl-1-cyclohexenyl)-2,4,6,8-nonatetraenoate (ABPN or CBG41) induced the greatest growth inhibition, with an IC(50) value of 0.6 microM. Subsequent studies in other cancer cell lines indicated that ABPN was much more growth-inhibitory than all-trans retinoic acid or 4-HPR. Compared to 4-HPR, ABPN induced 5.5- to 70.0-fold more growth inhibition in most cancer cells, with the exception of gynecologic cancer cells. In these cells, the antiproliferative effect was only 1.5- to 2.8-fold more than 4-HPR. We examined the molecular mechanism underlying the difference in growth inhibition between 4-HPR and ABPN. DAPI staining, DNA fragmentation, FACS and Western blotting analyses suggest that ABPN induced apoptosis by activating caspase-3 and -8, which may result in increased PARP cleavage. Unlike 4-HPR, ABPN activated all 3 RAR isotypes to an extent similar to AtRA. In addition, ABPN significantly inhibited AP-1 transcriptional activity and thus greatly suppressed the expression of the matrix metalloproteinase -1, -2 and -3 genes, which are involved in tumor invasion. These results suggest that ABPN may be a promising retinoid derivative offering not only enhanced cytotoxicity, but also increased inhibition of tumor invasiveness., (Copyright 2003 Wiley-Liss, Inc.)

Sunlight is a human carcinogen. Many retinoid-containing cosmetics are used to protect damages caused by sunlight irradiation. Since retinol is thermally unstable and retinyl palmitate (RP) s relatively more stable, RP is also widely used as an ingredient in cosmetic formulations. In general, little is known about the photodecomposition of retinoids and the toxicity of retinoids and their photodecomposition products on the skin's responses to sunlight. This review focuses on the update information on photoreactions, phototoxicity, and photocarcinogenicity of the natural retinoids including retinol, retinal, retinoid acid (RA), retinyl acetate, and RP.

Tazarotene is an acetylenic retinoid which is metabolised to tazarotenic acid and which binds selectively to the retinoid receptors RARbeta and RARgamma. The safety, toxicity and pharmacokinetics of oral tazarotene were determined over 12 weeks of treatment in 34 patients with advanced cancer. Commonly seen toxicities were mucocutaneous symptoms, musculoskeletal pain and headache. Dose-limiting toxicities were hypercalcaemia, hypertriglyceridaemia and musculoskeletal pain. The maximum tolerated dose of tazarotene in this schedule is 25.2 mg day(-1). Plasma concentrations of tazarotenic acid were found to peak rapidly within 1-3 h of dosing and thereafter declined quickly. The C(max) and AUC values on day 0, and weeks 2 and 4 were similar indicating no drug accumulation. The dose-normalised C(max) and AUC values at different dose levels and different study days appeared to be similar indicating linear pharmacokinetics. No objective responses were seen, although stable disease was seen in six out of eight evaluable patients receiving the three highest dose levels of tazarotene (16.8, 25.2 or 33.4 mg day(-1)). We conclude that oral tazarotene is well tolerated when administered daily for 12 weeks, has a favourable toxicity profile compared with other retinoids and merits further investigation as an anticancer therapy.