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Oxidation–reduction (redox) reactions are central to the existence of life. Reactive species of oxygen, nitrogen and sulfur mediate redox control of a wide range of essential cellular processes. Yet, excessive levels of oxidants are associated with ageing and many diseases, including cardiological and neurodegenerative diseases, and cancer. Hence, maintaining the fine-tuned steady-state balance of reactive species production and removal is essential. Here, we discuss new insights into the dynamic maintenance of redox homeostasis (that is, redox homeodynamics) and the principles underlying biological redox organization, termed the ‘redox code’. We survey how redox changes result in stress responses by hormesis mechanisms, and how the lifelong cumulative exposure to environmental agents, termed the ‘exposome’, is communicated to cells through redox signals. Better understanding of the molecular and cellular basis of redox biology will guide novel redox medicine approaches aimed at preventing and treating diseases associated with disturbed redox regulation.

A robust database shows that dietary supplements of vitamins E and C are safe for the general population. Because these nutrients supply antioxidant and other functions for homeostasis and protection against free radical damage, supplementation has been intensively studied. Because of perceived benefits, many persons consume quantities of vitamins E and C well above the recommended dietary allowances. As safety guidance, tolerable upper intake levels have been established by the Food and Nutrition Board, Institute of Medicine, at 1000 mg for vitamin E and 2000 mg for vitamin C in adults. Many clinical trials with these vitamins have involved subjects with various diseases, and no consistent pattern of adverse effects has occurred at any intake. Numerous studies of vitamin C supplementation have provided no pattern of evidence to support concerns about safety other than occasional gastrointestinal upset or mild diarrhea resulting from the osmotic effects of unabsorbed quantities of vitamin C. Evidence of bleeding effects and other potential adverse effects of high vitamin E intakes in humans is not convincing. Evidence of adverse effects of vitamin C that result from its effects on iron absorption and metabolism has not been confirmed in clinical trials. Thus, we conclude from clinical trial evidence that vitamin E supplements appear safe for most adults in amounts [less than or equal to] 1600 IU (1073 mg RRR-[alpha]-tocopherol or the molar equivalent of its esters) and that vitamin C supplements of [less than or equal to] 2000 mg/d are safe for most adults. KEY WORDS Vitamin E, [alpha]-tocopherol, tocopherol, vitamin C, ascorbic acid, risk assessment, safety, clinical trials

‘Reactive oxygen species’ (ROS) is a generic term that defines a wide variety of oxidant molecules with vastly different properties and biological functions that range from signalling to causing cell damage. Consequently, the description of oxidants needs to be chemically precise to translate research on their biological effects into therapeutic benefit in redox medicine. This Expert Recommendation article pinpoints key issues associated with identifying the physiological roles of oxidants, focusing on H2O2and O2.–. The generic term ROS should not be used to describe specific molecular agents. We also advocate for greater precision in measurement of H2O2, O2.–and other oxidants, along with more specific identification of their signalling targets. Future work should also consider inter-organellar communication and the interactions of redox-sensitive signalling targets within organs and whole organisms, including the contribution of environmental exposures. To achieve these goals, development of tools that enable site-specific and real-time detection and quantification of individual oxidants in cells and model organisms are needed. We also stress that physiological O2levels should be maintained in cell culture to better mimic in vivo redox reactions associated with specific cell types. Use of precise definitions and analytical tools will help harmonize research among the many scientific disciplines working on the common goal of understanding redox biology.

Reactive oxygen species are thought to be implicated in the pathogenesis of various human diseases. They are generated endogenously under physiological and pathological conditions but also upon exposure to exogenous [...]

Lycopene bioavailability from a single dose of fresh tomatoes or tomato paste (23 mg lycopene) ingested together with 15 g corn oil was compared by analyzing carotenoid concentrations in the chylomicron fraction. The lycopene isomer pattern was the same in both fresh tomatoes and tomato paste. The triacylglycerol response in chylomicrons was not significantly different after both treatments. Ingestion of tomato paste was found to yield 2.5-fold higher total and all-trans-lycopene peak concentrations (P [is less than] 0.05 and P [is less than] 0.005, respectively) and 3.8-fold higher area under the curve (AUC) responses (P [is less than] 0.001) than ingestion of fresh tomatoes. The same was calculated for lycopene cis-isomers, but only the AUC response for the cis-isomers was significantly higher after ingestion of tomato paste (P [is less than] 0.005). No difference was observed in the [Alpha]- and [Beta]-carotene response. Thus, in humans, the bioavailability of lycopene is greater from tomato paste than from fresh tomatoes. Am J Clin Nutr 1997;66:116-22.

The occurrence of reactive oxygen species, known as pro-oxidants, is an attribute of normal aerobic life. The steady-state formulation of pro-oxidants is balanced by a similar rate of their consumption by antioxidants that are enzymatic and/or nonenzymatic. 'Oxidative stress' results from imbalance in this pro-oxidant-antioxidant equilibrium in favor of the pro-oxidants. A number of diseases are associated with oxidative stress, being the basis of antioxidant therapy. Current evidence in clinical research does not show unequivocal distinction between causal or associative relationships of pro-oxidants to the disease process.

Free radicals (unstable atoms with unpaired electrons) are by-products of certain biochemical reactions occurring within the body's cells. These free radicals are highly reactive (reactive oxygen species) and can damage DNA, proteins and cell membranes. Antioxidants such as carotenoids (including vitamin A precursors), tocopherols (vitamin E) and thiols (compounds containing sulfur) protect tissues from damage by inactivating reactive oxygen species. The ability of antioxidants to act as scavengers (inactivators) of free radicals may be important in explaining the possible anti-cancer properties of beta-carotene, a form of vitamin A and a carotenoid. Tocopherols are fat-soluble antioxidants that provide the greatest protection for cell membranes from destruction by oxygen radicals. The concentration of vitamin E in a cell membrane determines the susceptibility of the membrane to damage by free radicals. Glutathione is the most important cellular thiol for scavenging free radicals. Carotenoids, tocopherols and thiols are the natural defense mechanisms of the cell, protecting it from the damaging effects of free radicals. (Consumer Summary produced by Reliance Medical Information, Inc.)

‘Reactive oxygen species’ (ROS) is an umbrella term for an array of derivatives of molecular oxygen that occur as a normal attribute of aerobic life. Elevated formation of the different ROS leads to molecular damage, denoted as ‘oxidative distress’. Here we focus on ROS at physiological levels and their central role in redox signalling via different post-translational modifications, denoted as ‘oxidative eustress’. Two species, hydrogen peroxide (H2O2) and the superoxide anion radical (O2·−), are key redox signalling agents generated under the control of growth factors and cytokines by more than 40 enzymes, prominently including NADPH oxidases and the mitochondrial electron transport chain. At the low physiological levels in the nanomolar range, H2O2is the major agent signalling through specific protein targets, which engage in metabolic regulation and stress responses to support cellular adaptation to a changing environment and stress. In addition, several other reactive species are involved in redox signalling, for instance nitric oxide, hydrogen sulfide and oxidized lipids. Recent methodological advances permit the assessment of molecular interactions of specific ROS molecules with specific targets in redox signalling pathways. Accordingly, major advances have occurred in understanding the role of these oxidants in physiology and disease, including the nervous, cardiovascular and immune systems, skeletal muscle and metabolic regulation as well as ageing and cancer. In the past, unspecific elimination of ROS by use of low molecular mass antioxidant compounds was not successful in counteracting disease initiation and progression in clinical trials. However, controlling specific ROS-mediated signalling pathways by selective targeting offers a perspective for a future of more refined redox medicine. This includes enzymatic defence systems such as those controlled by the stress-response transcription factors NRF2 and nuclear factor-κB, the role of trace elements such as selenium, the use of redox drugs and the modulation of environmental factors collectively known as the exposome (for example, nutrition, lifestyle and irradiation).

Background: Carotenoids and tocopherols, known to be efficient antioxidants and capable of scavenging reactive oxygen species generated during photooxidative stress, may protect the skin from ultraviolet light-induced erythema. [Beta]-Carotene is widely used as an oral sun protectant but studies on its protective effects are scarce. Objective: The objective of this study was to investigate the protective effects of oral supplementation with carotenoids and a combination of carotenoids and vitamin E against the development of erythema in humans. Design: A carotenoid supplement (25 mg total carotenoids/d) and a combination of the carotenoid supplement and vitamin E [335 mg (500 IU) RRR-[Alpha]-tocopherol/d] were given for 12 wk to healthy volunteers. Erythema was induced by illumination with a blue-light solar simulator. Serum [Beta]-carotene and [Alpha]-tocopherol concentrations and skin carotenoid levels were assessed by HPLC and reflection photometry. Results: Serum [Beta]-carotene and [Alpha]-tocopherol concentrations increased with supplementation. Erythema on dorsal skin (back) was significantly diminished (P [is less than] 0.01) after week 8, and erythema suppression was greater with the combination of carotenoids and vitamin E than with carotenoids alone. Conclusion: The antioxidants used in this study provided protection against erythema in humans and may be useful for diminishing sensitivity to ultraviolet light. Am J Clin Nutr 2000;71:795-8. KEY WORDS Carotenoids, tocopherol, sunburn, skin, erythema, healthy adults, ultraviolet light

Oxidative stress as a concept in redox biology and medicine has witnessed fulminant development of the past 30-odd years. It is a global concept, defined as “an imbalance between oxidants and antioxidants in favor of the oxidants, leading to a disruption of redox signaling and control and/or molecular damage”(Sies H, Jones DP: Oxidative stress. In Encyclopedia of stress, 2nd Ed., Fink G, Editor. Amsterdam: Elsevier; 2007:45–48). Physiological (low-level) oxidative stress is used in redox signaling and redox regulation, termed oxidative eustress, whereas higher burden (supraphysiological) leads to disrupted redox signaling and/or oxidative damage to biomolecules, termed oxidative distress. There are powerful oxidative stress response systems. The challenge for the future is to design methods to obtain detailed information on spatiotemporal redox patterns and their regulation for application in specific settings.

Viral and bacterial infections are often associated with deficiencies in macronutrients and micronutrients, including the essential trace element selenium. In selenium deficiency, benign strains of Coxsackie and influenza viruses can mutate to highly pathogenic strains. Dietary supplementation to provide adequate or supranutritional selenium supply has been proposed to confer health benefits for patients suffering from some viral diseases, most notably with respect to HIV and influenza A virus (IAV) infections. In addition, selenium-containing multimicronutrient supplements improved several clinical and lifestyle variables in patients coinfected with HIV and Mycobacterium tuberculosis. Selenium status may affect the function of cells of both adaptive and innate immunity. Supranutritional selenium promotes proliferation and favors differentiation of naive CD4-positive T lymphocytes toward T helper 1 cells, thus supporting the acute cellular immune response, whereas excessive activation of the immune system and ensuing host tissue damage are counteracted through directing macrophages toward the M2 phenotype. This review provides an up-to-date overview on selenium in infectious diseases caused by viruses (e.g., HIV, IAV, hepatitis C virus, poliovirus, West Nile virus) and bacteria (e.g., M. tuberculosis, Helicobacter pylori). Data from epidemiologic studies and intervention trials, with selenium alone or in combination with other micronutrients, and animal experiments are discussed against the background of dietary selenium requirements to alter immune functions.

Recent observational and clinical studies have raised interest in the potential health effects of cranberry consumption, an association that appears to be due to the phytochemical content of this fruit. The profile of cranberry bioactives is distinct from that of other berry fruit, being rich in A-type proanthocyanidins (PACs) in contrast to the B-type PACs present in most other fruit. Basic research has suggested a number of potential mechanisms of action of cranberry bioactives, although further molecular studies are necessary. Human studies on the health effects of cranberry products have focused principally on urinary tract and cardiovascular health, with some attention also directed to oral health and gastrointestinal epithelia. Evidence suggesting that cranberries may decrease the recurrence of urinary tract infections is important because a nutritional approach to this condition could lower the use of antibiotic treatment and the consequent development of resistance to these drugs. There is encouraging, but limited, evidence of a cardioprotective effect of cranberries mediated via actions on antioxidant capacity and lipoprotein profiles. The mixed outcomes from clinical studies with cranberry products could result from interventions testing a variety of products, often uncharacterized in their composition of bioactives, using different doses and regimens, as well as the absence of a biomarker for compliance to the protocol. Daily consumption of a variety of fruit is necessary to achieve a healthy dietary pattern, meet recommendations for micronutrient intake, and promote the intake of a diversity of phytochemicals. Berry fruit, including cranberries, represent a rich source of phenolic bioactives that may contribute to human health.

Criteria for assessing the purported protection by flavanol-rich foods against vascular dysfunction and oxidative damage to biomolecules was the subject of the 27th Hohenheim Consensus Conference held on July 11, 2011. State-of-the-art evidence was put into perspective, focusing on several questions that were followed by a consensus answer. Among the topics addressed were the major sources of flavanols in the human diet, the bioavailability of flavanols, biomarkers for “health benefit,” and the biological function of flavanols. Consensus was reached on these topics. No conclusion was reached on the design of randomized, controlled trials for substantiation of health claims for flavanol-rich foods as to the necessity of a study arm with an isolated pharmacologically active compound, e.g., (−)-epicatechin.

A single-dose ingestion of flavanol-rich cocoa acutely reverses endothelial dysfunction. To investigate the time course of endothelial function during daily consumption of high-flavanol cocoa, we determined flow-mediated dilation (FMD) acutely (for up to 6 hours after single-dose ingestion) and chronically (administration for 7 days). The study population represented individuals with smoking-related endothelial dysfunction; in addition to FMD, plasma nitrite and nitrate were measured. The daily consumption of a flavanol-rich cocoa drink (3 × 306 mg flavanols/d) over 7 days (n = 6) resulted in continual FMD increases at baseline (after overnight fast and before flavanol ingestion) and in sustained FMD augmentation at 2 hours after ingestion. Fasted FMD responses increased from 3.7 ± 0.4% on day 1 to 5.2 ± 0.6%, 6.1 ± 0.6%, and 6.6 ± 0.5% (each P< 0.05) on days 3, 5, and 8, respectively. FMD returned to 3.3 ± 0.3% after a washout week of cocoa-free diet (day 15). Increases observed in circulating nitrite, but not in circulating nitrate, paralleled the observed FMD augmentations. The acute, single-dose consumption of cocoa drinks with 28 to 918 mg of flavanols led to dose-dependent increases in FMD and nitrite, with a maximal FMD at 2 hours after consumption. The dose to achieve a half-maximal FMD response was 616 mg (n = 6). Generally applied biomarkers for oxidative stress (plasma, MDA, TEAC) and antioxidant status (plasma ascorbate, urate) remained unaffected by cocoa flavanol ingestion. The daily consumption of flavanol-rich cocoa has the potential to reverse endothelial dysfunction in a sustained and dose-dependent manner.

Endothelial dysfunction is the pathophysiologic principle involved in the initiation and progression of arteriosclerosis, thus endothelial function serves as a “barometer” for cardiovascular health that can be used for the evaluation of new therapeutic strategies. This review provides an introduction to the concept of endothelial dysfunction, and it explores the importance of this prognostic marker in the context of clinical, dietary interventions in humans. Moreover, we summarize and evaluate the findings of various clinical trials that demonstrated an improvement of endothelial dysfunction in subjects with cardiovascular risk factors after the acute and chronic consumption of flavanol-rich foods, including cocoa products, red wine, and tea.

Plant constituents such as carotenoids and flavonoids are involved in the light-protecting system in plants and contribute to the prevention of UV damage in humans. As micronutrients they are ingested with the diet and are distributed into light-exposed tissues where they provide systemic photoprotection. β-Carotene is an endogenous photoprotector, and its efficacy to prevent UV-induced erythema formation has been demonstrated in intervention studies. Lycopene is the major carotenoid of the tomato and is a very efficient singlet oxygen quencher in the group of carotenoids. Following ingestion of lycopene or tomato-derived products rich in lycopene, photoprotective effects have been demonstrated. After 10-12 weeks of intervention a decrease in the sensitivity towards UV-induced erythema was observed in volunteers. Dietary carotenoids may contribute to life-long protection against harmful UV radiation.

Carotenoids are suitable photoprotectants, and β-carotene supplements are used for protection against ultraviolet (UV) light-induced erythema. Protective effects are also observed when carotenoids are provided with the diet. Here, we investigated the photoprotective effects of synthetic lycopene in comparison with a tomato extract (Lyc-o-Mato®) and a drink containing solubilized Lyc-o-Mato® (Lyc-o-Guard-Drink). With these different sources, the volunteers ingested similar amounts of lycopene (about 10 mg/day). After 12 weeks of supplementation, significant increases in lycopene serum levels and total skin carotenoids were observed in all groups. Significant increases in the serum levels of phytofluene and phytoene occurred in the Lyc-o-Mato and the Lyc-o-Guard-Drink group. At weeks 0, 4, and 12 an erythema was induced with a solar light simulator. Dorsal skin of each subject was irradiated with 1.25 minimal erythemal dose (MED). Reddening of the skin was evaluated before and 24 hours after irradiation by chromametry and expressed as positive a-values (red/green-axis). Δ a-values (difference of a-value before irradiation and after 24 hours) were used as an index of erythema intensity. A decrease in the Δ a-value from week 0 to week 12, indicating prevention of erythema formation, was observed in all groups. Compared to week 0, the Δ a-value at week 12 was 25% lower in the synthetic lycopene group. The protective effect was more pronounced in the Lyc-o-Mato (38%) and Lyc-o-Guard-Drink (48%) groups. In the two latter groups, phytofluene and phytoene may have contributed to protection. Both of these carotenoids exhibit absorption maxima at wavelengths of UV light. Absorption of UV light protects skin from photodamage and might explain the differences observed between groups.

Photooxidative processes play a role in the pathobiochemistry of various disorders of light-exposed tissue. After irradiation of skin with UV light, erythema (sunburn) is an initial effect suitable for monitoring the direct biological response. Carotenoids are efficient in photoprotection, scavenging singlet oxygen and peroxyl radicals. Intervention studies with supplements or a carotenoid-rich diet documented efficiency in systemic photoprotection, measuring a decreased sensitivity against UV-induced erythema. For successful intervention, treatment with carotenoids is needed for a period of at least ten weeks. An increased consumption of carotenoids may contribute to life-long protection against UV-induced damage.

Both UVB (280–320 nm) and UVA (320–400 nm) radiation lead to an enhanced expression of cyclooxygenase-2 (COX-2) in epidermal cells in various in-vitroand in-vivomodels. It is demonstrated here that the expression of COX-2 is induced in artificial human epidermis exposed to simulated solar light (>290 nm). Employing filters eliminating specified regions from the simulated solar spectrum, the UVB and UVA-2 (320–350 nm) regions are shown to fully account for induction of COX-2 mRNA and protein as well as the enhanced production of prostaglandin E2after irradiation. At the protein level, approximately 70% of the total induction by solar light is due to light in the UVA-2 region. UVA-1 (350–400 nm), visible light and IR radiation are practically ineffective. COX-2 induction by simulated solar light is attenuated in the presence of inhibitors of p38MAPKor of c-Jun-N-terminal kinases (JNK), whereas COX-2 induction by UVA is blocked only by inhibition of JNK. UV-induced COX-2 expression is not affected by inhibition of the MEK 1,2/ERK 1,2 pathways.

Loss of gap junctional intercellular communication (GJIC) is a characteristic of cancer cells. Since a coordinated interaction of epithelial tumor cells with stromal cells is a prerequisite for tumor invasion and metastasis, the present study was designed to test the hypothesis that skin-derived tumor cells may modulate homologous and heterologous GJIC. While homologous GJIC of human dermal fibroblasts as well as epidermal keratinocytes was detected, no communication was measured between SCL-1 cells derived from squamous cell carcinoma of human skin. Interestingly, co-cultures of dermal fibroblasts and SCL-1 tumor cells in serum-containing medium resulted in a 52-70% lowering of the number of communicating fibroblasts. Furthermore, incubation of confluent fibroblast cultures with serum-free supernatant fractions (20-30 kDa) from tumor cells, termed the 20/30 fraction, lowered the homologous gap junction communication of fibroblasts by >90%. This novel aspect of down-regulated homologous GJIC of dermal fibroblasts, which is reversible, was neither mediated by alteration of the expression of connexin43, the major gap junctional protein of dermal fibroblasts, nor by aberrant localization of connexin43 in the plasma membrane. Furthermore, post-translational modifications of connexins, such as phosphorylation, was not measured by mobility shift studies. Tumor cell-mediated GJIC down-regulation between fibroblasts was suppressed using EGTA-containing serum-free tumor cell-derived supernatants suggesting that calcium ions (Ca2+) might mediate the transduction of this effect. The involvement of Ca2+ in down-regulation of homologous GJIC of fibroblasts was supported by an increase in fluorescence intensity of the intracellular calcium-sensitive indicator Fura-2 upon treatment of fibroblasts with the active 20/30 fraction. In conclusion, these data establish homologous GJIC of (stromal) fibroblasts as a parameter modulated by a paracrine acting factor(s) of epithelial tumor cells during tumor-stroma interaction of skin cells.

Schwefel und Selen kommen in Proteinen als Bestandteile der Aminosäuren Cystein, Methionin, Selenocystein und Selenomethionin vor, deren Ausnahmestellung in neueren Arbeiten unterstrichen wird. Ihre Redoxeigenschaften unter physiologischen Bedingungen ermöglichen eine erstaunliche Vielfalt posttranslationaler Proteinmodifikationen, metallfreier Redoxreaktionen und ungewöhnlicher Chalkogenredoxzustände. Wie keine andere Aminosäure kann das “Redox-Chamäleon” Cystein an so unterschiedlichen Redoxreaktionen wie Atom-, Elektronen- und Hydridtransfer sowie Radikal- und Austauschreaktionen beteiligt sein. Es kommt im menschlichen Körper in zahlreichen Oxidationsstufen vor, von denen jede mit charakteristischen chemischen (z. B. Redox- und Metallbindungs-) und biologischen Eigenschaften verknüpft ist. Durch die Position des Selens im Periodensystem der Elemente zwischen Metallen und Nichtmetallen werden Selenoproteine zu idealen Katalysatoren einer Vielzahl biologischer Redoxumwandlungen, sodass die chalkogenhaltigen Aminosäuren Cystein, Methionin, Selenocystein und Selenomethionin und ihre einzigartige Biochemie Gegenstand eines vielversprechenden Forschungsgebietes sind.

Sulfur and selenium occur in proteins as constituents of the amino acids cysteine, methionine, selenocysteine, and selenomethionine. Recent research underscores that these amino acids are truly exceptional. Their redox activity under physiological conditions allows an amazing variety of posttranslational protein modifications, metal free redox pathways, and unusual chalcogen redox states that increasingly attract the attention of biological chemists. Unlike any other amino acid, the “redox chameleon” cysteine can participate in several distinct redox pathways, including exchange and radical reactions, as well as atom-, electron-, and hydride-transfer reactions. It occurs in various oxidation states in the human body, each of which exhibits distinctive chemical properties (e.g. redox activity, metal binding) and biological activity. The position of selenium in the periodic table between the metals and the nonmetals makes selenoproteins ideal catalysts for many biological redox transformations. It is therefore apparent that the chalcogen amino acids cysteine, methionine, selenocysteine, and selenomethionine exhibit a unique biological chemistry that is the source of exciting research opportunities.

Pharmaceutical preparations derived from natural sources such as vegetables often contain compounds that contribute to the antioxidant defence system and apparently play a role in the protection against degenerative diseases. In the present study, commercial preparations containing extracts of turmeric, artichoke, devil's claw and garlic or salmon oil were investigated. The products were divided into fractions of different polarity, and their antioxidant activity was determined using the Trolox equivalent antioxidant capacity (TEAC) assay. This test is based on the efficacy of the test material to scavenge 2,2′‐azino‐bis(3‐ethylbenzthiazoline‐6‐sulfonic acid) (ABTS) derived radicals. Total phenols were determined in all fractions as well as specific carotenoids in the most lipophilic fraction to assess their contribution to the antioxidant activity. For comparison, the radical scavenging effect of selected constituents of the extracts such as curcumin, luteolin, kaempferol, chlorogenic acid, harpagoside, β‐carotene and α‐tocopherol was investigated and compared with that of Trolox. Curcumin, luteolin, kaempferol, chlorogenic acid and β‐carotene showed an antioxidant activity superior to Trolox in the TEAC assay; harpagoside was barely active. All fractions of the turmeric extract preparation exhibited pronounced antioxidant activity, which was assigned to the presence of curcumin and other polyphenols. The antioxidant activity corresponding to the artichoke leaf extract was higher in the aqueous fractions than in the lipophilic fractions. Similarly, devil's claw extract was particularly rich in water‐soluble antioxidants. Harpagoside, a major compound in devil's claw, did not contribute significantly to its antioxidant activity. The antioxidant capacity of the garlic preparation was poor in the TEAC assay. That of salmon oil was mainly attributed to vitamin E, which is added to the product for stabilization. In all test preparations, the antioxidant activity was significantly correlated with the content of total phenolic compounds.

Singlet oxygen, an electronically excited form of molecular oxygen, may be generated photochemically or in dark reactions in vivo. Singlet oxygen is not only toxic to cells and impairs signaling events but is also capable of eliciting a cellular stress response. The signaling processes initiated in this response include the activation of mitogen-activated protein kinases. Two possible activation mechanisms of signaling pathways by singlet oxygen are the generation of positive regulators as well as the inactivation of negative regulators.

Effects of sunlight have fascinated researchers for decades because nearly every living thing on earth is likely to be exposed to sunlight and the ultraviolet (UV) fraction of it. In addition to detrimental long-term effects such as immunosuppression and skin cancer, premature aging of the skin (photoaging) is a well-documented consequence of exposure to UVA and UVB. Photoaged skin is biochemically characterized by an overgrowth of abnormal elastic fibers in the dermis and by a dramatic decrease of distinct collagen types. Ultraviolet irradiation induces delayed UV-responsive genes, among them matrix metalloproteinases, which degrade macromolecules of the extracellular matrix, a hallmark in carcinogenesis and aging. We are interested in UVB-triggered initial events and in subsequent signaling resulting in enhanced expression of two major members of the matrix metalloproteinase family, the interstitial collagenase (MMP-1) and stromelysin-1 (MMP-3), in human dermal fibroblasts. Especially, these skin cells play a central role in connective tissue breakdown in photoaging and as stromal cells in tumor invasion and metastasis by means of their capability to produce matrix metalloproteinases. In this review, we will focus on UVB-triggered induction of matrix metalloproteinases, the so far identified components of the UVB-modulated signal transduction pathway(s), and the UVB irradiation-associated generation of reactive oxygen species (ROS). Finally, a potentially novel aspect in UVB irradiation-mediated expression of interstitial collagenase and stromelysin-1-namely, the involvement of reactive nitrogen species (RNS)-is discussed.

AbstractUpon exposure to UV light photooxidative reactions are initiated which are damaging to biomolecules and affect the integrity of cells and tissues. Photooxidative damage plays a role in pathological processes and is involved in the development of disorders affecting the skin. When skin is exposed to UV light, erythema is observed as an initial reaction. Carotenoids like β-carotene or lycopene are efficient antioxidants scavenging singlet molecular oxygen and peroxyl radicals generated in during photooxidation. When β-carotene was applied as such or in combination with α-tocopherol for 12 weeks, erythema formation induced with a solar light simulator was diminished from week 8 on. Similar effects were also achieved with a diet rich in lycopene. Ingestion of tomato paste corresponding to a dose of 16 mg lycopene/ day over 10 weeks led to increases in serum levels of lycopene and total carotenoids in skin. At week 10, erythema formation was significantly lower in the group that ingested the tomato paste as compared to the control group. No significant difference was found at week 4 of treatment. Thus, protection against UV light-induced erythema can be achieved by ingestion of a commonly consumed dietary source of lycopene. Such protective effects of carotenoids were also demonstrated in cell culture. The in-vitro data indicate that there is an optimal level of protection for each carotenoid.Copyright © 2002 S. Karger AG, Basel

Enhanced expression of matrix metalloproteinase (MMP)-1/interstitial collagenase and MMP-3/stromelysin-1 in skin fibroblasts and subsequent damage of dermal connective tissue in the context of sun-induced premature aging and skin tumour progression is causally linked to UVB irradiation. Here, we were interested in identifying components of the complex signal-transduction pathway underlying UVB-mediated up-regulation of these delayed UV-responsive genes and focused on components maximally activated early after irradiation. A 2.3-fold increase in protein kinase CK2 activity was measured at 20–40min after low-dose UVB irradiation (at 10mJ/cm2) of dermal fibroblasts. This UVB-mediated increase in CK2 activity was abrogated by pharmacological approaches using non-toxic concentrations of the CK2 inhibitor 5,6-dichloro-1-β-d-ribofuranosylbenzimidazole (DRB). Preincubation of fibroblasts with DRB prior to UVB irradiation lowered MMP-1 by 49–69% and MMP-3 protein levels by 55–63% compared with UVB-irradiated controls. By contrast, the CK2 inhibitor did not affect the UVB-triggered transcription of MMPs. Furthermore, UVB irradiation of fibroblasts overexpressing a kinase-inactive mutant of CK2 (CK2α-K68A-HA) resulted in lowering of the protein levels of MMP-1 by 25% and MMP-3 by 22% compared with irradiated fibroblasts transfected with the vector control. This reduction in MMP protein levels correlated with the transfection efficiency. Taken together, we describe a novel aspect of protein kinase CK2, namely its inducible activity by UVB irradiation, and provide evidence that CK2 is an early mediator of the UVB-dependent up-regulation of MMP-1 and MMP-3 translation, whereas their major tissue inhibitor of matrix metalloproteinase-1 is not affected by CK2.

Exposure of living organisms to UV light leads to photooxidative reactions. Peroxyl radicals are involved in the propagation of lipid peroxidation. Carotenoids are dietary antioxidants and show photoprotective effects in human skin, efficiently scavenging peroxyl radicals and inhibiting lipid peroxidation. Cultured human skin fibroblasts were used to examine the protective effects of the carotenoids, lycopene, ?-carotene and lutein on UVB-induced lipid peroxidation. The carotenoids were delivered to the cells using liposomes as the vehicle. The cells were exposed to UVB light for 20 min. Lycopene, ?-carotene and lutein were capable of decreasing UV-induced formation of thiobarbituric acid-reactive substances at 1 h to levels 40-50 of controls free of carotenoids. The amounts of carotenoid needed for optimal protection were divergent at 0.05, 0.40 and 0.30 nmolmg protein for lycopene, ?-carotene and lutein, respectively. Beyond the optimum levels, further increases of carotenoid levels in cells led to prooxidant effects.

During inflammatory reactions, cells are under nitrosative and/or oxidative stress. The zinc finger transcription factors vitamin D receptor (VDR) and retinoid X receptor (RXR) were used as a model system to characterize effects of NO⋅and/or reactive oxygen species on zinc finger-dependent gene expression. Nitric oxide (NO⋅) as well as H2O2, singlet oxygen (1O2), peroxyl radicals (ROO⋅), and peroxynitrite (ONOO−), respectively, were shown to inhibit VDR/RXR-DNA complex formation in vitroin a dose-dependent manner. While NO-induced inhibition of VDR/RXR-DNA complex formation could be restored nearly completely by subsequent treatment with dithiothreitol, inhibition by H2O2proved to be only partially reversible, and inhibition by 1O2, ROO⋅or ONOO−was found to be irreversible. In cells transiently transfected with VDR and RXR, subtoxic concentrations of NO⋅or hydroperoxides and intracellular generation of superoxide anion radicals inhibited VDR/RXR-dependent reporter gene activity in a dose-dependent manner. Interestingly, cells can repair the zinc fingers of VDR and RXR after nitrosative stress but not after oxidative stress. The results indicate that, among the reactive species investigated, only NO⋅may act sufficiently gentle to be considered as a regulator and not only as an inhibitor of gene expression via zinc finger transcription factors.

The flavanol (−)-epicatechin is known to protect against peroxynitrite-induced nitration and oxidation reactions. This study investigated the protection afforded by (−)-epicatechin against both these reaction types on one target molecule, the aminoacid tyrosine, in a hydrophilic milieu as well as with a lipophilic tyrosine derivative, N-t-BOC l-tyrosine tert-butyl ester (BTBE), bound to liposomes. The flavanol efficiently attenuated both tyrosine nitration and tyrosine dimerization (which is based on an initial oxidation reaction) and was active in the hydrophilic and hydrophobic systems at similar IC50 values, ≈0.02–0.05 mol (−)-epicatechin/mol peroxynitrite. Related procyanidin oligomers of different chain-length (dimer to octamer) were also tested for their protective properties, and exhibited protection that, on a monomer basis, was in the same order of magnitude as those for (−)-epicatechin.

AbstractSome cocoas and chocolates are rich in ()epicatechin and its related oligomers, the procyanidins. Fractions of these compounds, isolated from the seeds of Theobroma cacao, caused dosedependent inhibition of isolated rabbit 15-lipoxygenase-1 with the larger oligomers being more active; the decamer fraction revealed an IC 50 of 0.8 M. Among the monomeric flavanols, epigallocatechin gallate (IC 50 = 4 M) and epicatechin gallate (5 M) were more potent than ()epicatechin (IC50 = 60 M). ()Epicatechin and procyanidin nonamer also inhibited the formation of 15-hydroxyeicosatetraenoic acid from arachidonic acid in rabbit smooth muscle cells transfected with human 15-lipoxygenase-1. In contrast, inhibition of the lipoxygenase pathway in J774A.1 cells transfected with porcine leukocytetype 12- lipoxygenase (another representative of the 12/15- lipoxygenase family) was only observed upon sonication of the cells, suggesting a membrane barrier for flavanols in these cells. Moreover, epicatechin (IC50 approx. 15 M) and the procyanidin decamer inhibited recombinant human platelet 12-lipoxygenase. These observations suggest general lipoxygenase inhibitory potency of flavanols and procyanidins that may contribute to their putative beneficial effects on the cardiovascular system in man. Thus, they may provide a plausible explanation for recent literature reports indicating that procyanidins decrease the leukotriene/prostacyclin ratio in humans and human aortic endothelial cells.

The flavanol (−)-epicatechin has been found to protect against damage inflicted by peroxynitrite, an inflammatory intermediate. Here, epicatechin was tested in systems of increasing complexity. The compound efficiently protected against nitration of protein tyrosine residues by peroxynitrite (IC50 ≈ 0.02 mol epicatechin/mol peroxynitrite). However, at epicatechin concentrations completely preventing nitration of tyrosine by peroxynitrite, protection against the oxidative inactivation of glyceraldehyde-3-phosphate dehydrogenase or soybean lipoxygenase-1 was marginal (IC50 > 1 mol epicatechin/mol peroxynitrite), approximately two orders of magnitude less. Likewise, epicatechin was relatively ineffective against oxidation of thiols in cell lysates, and against the oxidation of 2′,7′-dichlorodihydrofluorescein in cultured cells. The activation of the kinases Akt/protein kinase B, ERK1/2 and p38-MAPK by peroxynitrite in murine aorta endothelial cells was not altered by epicatechin, suggesting that activation of these kinases is due to processes other than tyrosine nitration.

AbstractRecently, γglutamyl transpeptidase, which initiates cleavage of extracellular glutathione, has been shown to promote oxidative damage to cells. Here we examined a murine disease model of glomerulosclerosis, involving loss of the Mpv17 gene coding for a peroxisomal protein. In Mpv17[/] cells, enzyme activity and mRNA expression (examined by quantitative RTPCR) of membranebound γglutamyl transpeptidase were increased, while plasma glutathione peroxidase and superoxide dismutase levels were lowered. Superoxide anion production in these cells was increased as documented by electron spin resonance spectroscopy. In the presence of Mn(III)tetrakis(4- benzoic acid)porphyrin, the activities of γglutamyl transpeptidase and plasma glutathione peroxidase were unchanged, suggesting a relationship between enzyme expression and the amount of reactive oxygen species. Inhibition of γglutamyl transpeptidase by acivicin reverted the lowered plasma glutathione peroxidase and superoxide dismutase activities, indicating reciprocal control of gene expression for these enzymes.

Lutein and zeaxanthin are the predominant carotenoids in the human macula lutea. Epidemiological data suggest that an increased intake of a lutein-rich diet correlates with a diminished risk for age-related macular degeneration, a major cause of impaired vision in the elderly. Filtering of blue light has been proposed as a possible mechanism of protection. Here, the blue light filter efficacy of carotenoids was investigated in unilamellar liposomes loaded in the hydrophilic core space with a fluorescent dye, Lucifer yellow, excitable by blue light. Carotenoids were incorporated into the lipophilic membrane. Fluorescence emission in carotenoid-containing liposomes was lower than in carotenoid-free controls when exposed to blue light, indicating a filter effect. Filter efficacy was in the order lutein > zeaxanthin > β-carotene > lycopene. Some of the difference in blue light filter efficacy of carotenoids is attributable to differences in extinction coefficients, and a major further contribution is suggested to be related to the orientation of the incorporated molecules in the liposomal membrane.

Photodynamic therapy (PDT) is being used clinically for the treatment of skin cancers. One concept of delivering the employed photosensitizer directly to target cells is to stimulate cellular synthesis of sensitizers such as porphyrins. ALA (5-aminolevulinate) is applied as a precursor of porphyrins which then serve as endogenous photosensitizers. Upon irradiation, reactive oxygen species, predominantly singlet oxygen, are generated, leading to cell death. ALA–PDT using red light (550–750 nm) is known to lead to the activation of stress kinases, such as c-Jun-N-terminal kinase and p38. These kinases are also activated by UVA (320–400 nm), whose biological effects are mediated in part by singlet oxygen. In the present study, the efficiency of a combination of both treatment strategies, ALA–PDT and UVA, in cytotoxicity and activation of stress kinases was investigated taking human skin fibroblasts as a model. Compared with the commonly used ALA–PDT with red light (LD50 = 13.5 J/cm2), UVA–ALA–PDT was 40-fold more potent in killing cultured human skin fibroblasts (LD50 = 0.35 J/cm2) and still 10-fold more potent than ALA–PDT with green light (LD50 = 4.5 J/cm2). Its toxicity relied on the formation of singlet oxygen, as was shown employing modulators of singlet oxygen lifetime. In line with these data, strong activation of the stress kinase p38 was obtained in ALA-pretreated cells irradiated with UVA at doses two orders of magnitude lower than necessary for a comparable activation of p38 by UVA in control cells. Taken together, these data suggest UVA–ALA–PDT as a potentially interesting new approach in the photodynamic treatment of skin diseases.

Exposure of proteins to oxidants leads to increased oxidation followed by preferential degradation by the proteasomal system. The role of the biologically occurring oxidants singlet oxygen and peroxynitrite in oxidation of proteins in living cells and enhanced degradation of these proteins was examined in this study. Subsequent to treatment of an isolated model protein, ferritin, with singlet oxygen or peroxynitrite, there was enhanced degradation by the isolated 20S proteasome. Treatment of clone 9 liver cells (normal liver epithelia) with two different singlet oxygen-generating systems or peroxynitrite leads to a concentration-dependent increase in cellular protein turnover. At high concentrations of these oxidants, the protein turnover decreases without significant loss of cell viability and proteasome activity. To compare the increase of intracellular protein turnover with that obtained with other oxidants, cells were exposed to hydrogen peroxide or xanthine/xanthine oxidase. The maximal increase in protein turnover was similar with the various oxidants. The oxidized protein moieties were removed by enhanced protein turnover. Removal of singlet oxygen- or peroxynitrite-damaged proteins is dependent on the proteasomal system, as suggested by the sensitivity to lactacystin. Our results provide evidence that the proteasomal system is able to selectively recognize and degrade proteins modified by singlet oxygen or peroxynitrite in vitro as well as in living cells.

In fluorescence diagnosis and photodynamic therapy of neoplastic tissues 5-aminolevulinic acid is used to synthesize endogenous porphyrins as photosensitizers. The efficacy of neoplastic tissues to fluorescence diagnosis and photodynamic therapy is thought to be dependent on the total level of intralesional formed porphyrins. The available profiles of porphyrin metabolites in normal and in neoplastic cell lines after administration of 5-aminolevulinic acid vary considerably. Thus, this is the first in-vitro study which compares the porphyrin biosynthesis in normal skin cells (HaCaT, fibroblasts) with melanoma cells (Bro, SKMel-23, SKMel-28). After incubation with 1 mM 5-aminolevulinic acid, kinetics of porphyrin levels and metabolites were determined in the cells and the corresponding supernatants. Exogenous 5-aminolevulinic acid induced porphyrin formation in all cells with maximum values after an incubation period of 16–36 h. Increase of porphyrin levels varied from 10- to 80-fold (SKMel-28>HaCaT>fibroblasts>SKMel-23&z.Gt;Bro) with minimum 1.5 times higher levels of porphyrins in the supernatants than in the cells. In cells and supernatants protoporphyrin and coproporphyrin were the predominantly formed porphyrin metabolites. Metastatic melanoma cells (SKMel-23, SKMel-28) accumulated much higher porphyrin levels than primary melanoma cells (Bro). In conclusion, by optimizing the treatment modalities, especially the light source, topical photodynamic therapy (PDT) could become a treatment alternative of melanoma metastases in progressive disease.

Peroxynitrite is a potent oxidizing and nitrating species formed in a diffusion-limited reaction between nitrogen monoxide and superoxide. It induces apoptosis through unknown mechanisms and is believed to interfere with receptor tyrosine kinase signalling through nitration of tyrosine residues. One pathway emanating from receptor tyrosine kinases is that leading to activation of the anti-apoptotic kinase Akt. In the present study we provide evidence that peroxynitrite, administered to cells using two different delivery systems, results in the dose- and time-dependent activation of Akt. Akt activation is rapid and followed by phosphorylation of glycogen synthase kinase-3, an established substrate of Akt. Akt activation is inhibited in the presence of the phosphoinositide 3-kinase (PI-3K) inhibitors wortmannin and LY294002, and by treatment with the platelet-derived growth factor (PDGF) receptor (PDGFR) inhibitor AG1295, indicating a requirement for PDGFR and PI-3K in mediating peroxynitrite-induced Akt activation. Accordingly, the PDGFR-A and PDGFR-B isoforms were shown to undergo rapid tyrosine phosphorylation on treatment with peroxynitrite. Prior exposure of cells to peroxynitrite interferes with PDGF-induced Akt phosphorylation. Our findings suggest that Akt activation occurs as an acute response to peroxynitrite treatment and could play an important role in influencing cell survival and/or alter the cellular response to other growth regulatory signals.

AbstractThyroid hormones stimulate gap junctional communication in rat liver WB-F344 epithelial cells, elevating connexin43 mRNA and protein levels. In the present work we analysed connexin43 expression in liver and heart samples from thyroid hormone-treated Wistar rats. Connexin43 mRNA was elevated 2.1-fold in rat liver samples as compared to controls, while there was no change in heart. Thyroid hormone response elements in the rat connexin43 promoter region were examined; a candidate sequence, including a binding site for ligand-dependent transcription factors, was identified at position −480 to −464. This putative regulatory element, rCx−480, contains a direct repeat structure separated by three base pairs (DR3-type element). In electrophoretic mobility shift assays using in vitrotranslated proteins, the rCx−480element formed stronger complexes with thyroid hormone receptor α/retinoid X receptor α heterodimers than with vitamin D receptor/retinoid X receptor α heterodimers. In transfected Cos-7 cells, promoter activation was observed via this element after treatment with 3,3′,5-triiodo-L-thyronine. Loss of binding was seen when the 3′ half-site or the spacer region of the rCx−480element were experimentally mutated, while a stronger binding was observed with mutations introduced in the 5′ halfsite.

Heme oxygenase-1, an inducible heat shock protein, is upregulated by oxidative stress, and its expression is modulated by proinflammatory cytokines such as IL-1 and IL-6. In the present study, we investigated the effects of postlesional, orally applied ebselen, a neuroprotective antioxidant, on serum levels of IL-6 and cerebral heme oxygenase-1 expression following focal ischemia induced by photothrombosis. Ebselen (50 mg/kg body weight) was given 30 min postlesion to male Wistar rats. Animals were divided into four groups: sham-operated vehicle control (n = 9), sham-operated ebselen control (n = 8), lesioned vehicle control (n = 14), and lesioned ebselen-treated (n = 17). Ebselen treatment resulted in a significant lowering of IL-6 plasma levels (26 ± 5 pg/ml) as compared with that seen in lesioned vehicle controls (48 ± 9 pg/ml) at 24 h postlesion. In sham-operated rats IL-6 was not detectable. Heme oxygenase-1-positive glial cells were quantitated within topographically determined perilesional brain regions. Within the 0.5-mm-wide rim region directly associated with the lesion core, no differences in the amount of heme oxygenase-1-positive glial cells were found. However, in the more remote ipsilateral perilesional cortex, significantly fewer heme oxygenase-1-positive glial cells were present within the supragranular cortical layers of lesioned ebselen-treated rats compared to lesioned vehicle controls (P < 0.001). In sham-operated rats, no glial heme oxygenase-1 induction occurred. The results indicate that postlesional ebselen treatment lowered plasma IL-6 levels subsequent to a photothrombotic lesion concomitant with a lowering of the heme oxygenase-1 response in glial cells.

AbstractThe binding of selenoprotein P to glycosaminoglycans using heparin as a model compound was studied by surface plasmon resonance. It was found that heparin contains two binding sites for selenoprotein P, a highaffinity, lowcapacity site (K[tilde operator]1n) and a lowaffinity, highcapacity site (K [tilde operator] 140n). Binding at both sites is sensitive to pH and ionic strength, and the highaffinity site is abolished by histidine carbethoxylation with diethylpyrocarbonate. The pH and salt dependence of binding suggests electrostatic interactions with heparin. The concentrations of selenoprotein P in plasma ([tilde operator]50n) are sufficiently high to facilitate binding of selenoprotein P to proteoglycans on the vascular endothelium, and this may contribute to the formation of a protective barrier against oxidants such as peroxynitrite or hydroperoxides.

Stroke occurs due to haemorrhage or occlusive injury and results in ischaemia and reperfusion injury. A variety of destructive mechanisms are involved including oxygen radical generation, calcium overload, cytotoxicity and apoptosis as well as the generation of inflammatory mediators. Ebselen, 2-phenyl-1,2-benzisoselenazol-3(2H)-one (PZ 51, DR3305), is a mimic of GSH peroxidase which also reacts with peroxynitrite and can inhibit enzymes such as lipoxygenases, NO synthases, NADPH oxidase, protein kinase C and H+/K+-ATPase. Ebselen is in a late stage of development for the treatment of stroke. The molecular actions of ebselen contribute to its anti-inflammatory and anti-oxidant properties, which have been demonstrated in a variety of in vivo models. Numerous in vitro experiments using isolated LDL, liposomes, microsomes, isolated cells and organs have established that ebselen protects against oxidative challenge. Unlike many inorganic and aliphatic selenium compounds, ebselen has low toxicity as metabolism of the compound does not liberate the selenium moiety, which remains within the ring structure. Subsequent metabolism involves methylation, glucuronidation and hydroxylation. Experimental studies in rats and dogs have revealed that ebselen is able to inhibit both vasospasm and tissue damage in stroke models, which correlates with its inhibitory effects on oxidative processes. Results from randomised, placebo-controlled, double-blind clinical studies on the neurological consequences of acute ischaemic stroke, subarachnoid haemorrhage and acute middle cerebral artery occlusion, have revealed that ebselen significantly enhances outcome in patients who have experienced occlusive cerebral ischaemia of limited duration. The benefit achieved with ebselen is closely related to the rapidity with which the treatment is initiated, following the onset of the stroke attack. Safety and tolerability are good and no adverse effects have become apparent. Ebselen is currently at the pre-registration stage for subarachnoid haemorrhage and stroke in Japan.

AbstractPeroxynitrite (ONOO−), a potent oxidizing and nitrating species, has been linked to covalent modifications of biomolecules in a number of pathological conditions. In S. cerevisiae, a model eukaryotic cell system, ONOO−was found to be more potent than hydrogen peroxide in oxidizing thiols, inducing heat shock proteins (Hsp70) and enhancing the ubiquitination of proteins. As identified by microsequence analysis following immunoprecipitation with anti-nitrotyrosine antibodies, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) was especially susceptible to nitration by ONOO−in yeast cells. The activity of this enzyme was strongly inhibited upon steady-state exposure of the cells to low doses of ONOO−in yeast and in cultured rat astrocytes. Thus, ONOO−is a potent stressor in yeast capable of inducing oxidative damage and protein nitration, with GAPDH being a preferential target protein that is efficiently inactivated.

Experimental evidence is provided that selenomethionine oxide (MetSeO) is more readily reducible than its sulfur analogue, methionine sulfoxide (MetSO). Pulse radiolysis experiments reveal an efficient reaction of MetSeO with one-electron reductants, such as e-aq(k= 1.2 ×× 1010M-1s-1), CO··-2(k= 5.9 ×× 108M-1s-1) and (CH3)2) C··OH (k= 3.5 ×× 107M-1s-1), forming an intermediate selenium-nitrogen coupled zwitterionic radical with the positive charge at an intramolecularly formed Se∴∴N 2σσ/1σσ* three-electron bond, which is characterized by an optical absorption with λλmaxat 375 nm, and a half-life of about 70 μμs. The same transient is generated upon HO··radical-induced one-electron oxidation of selenomethionine (MetSe). This radical thus constitutes the redox intermediate between the two oxidation states, MetSeO and MetSe. Time-resolved optical data further indicate sulfur-selenium interactions between the Se∴∴N transient and GSH. The Se∴∴N transient appears to play a key role in the reduction of selenomethionine oxide by glutathione.

Carotenoids and retinoids stimulate gap junctional communication (GJC), thought to be related to cancer-preventive properties. Lycopene, a nonprovitamin A carotenoid and its possible oxidation product, acyclo-retinoic acid, were tested for their effect on GJC, on stabilization of connexin43 mRNA, and on the transactivation of the RAR-β2-promoter in vitro. In human fetal skin fibroblasts, GJC was stimulated by lycopene and acyclo-retinoic acid. Lycopene was effective at a concentration of 0.1 μM, whereas higher amounts of acyclo-retinoic acid (1 μM) were needed for comparable stimulation. Stabilizing effects of acyclo-retinoic acid on the mRNA of connexin43 via elements located in the 3′-UTR were weak. In comparison to retinoic acid (0.1 μM), considerably higher concentrations of the acyclo analog (50 μM) were required for similar effects; lycopene (0.1 μM) was not active in this system. Likewise, unphysiologically high levels of acyclo-retinoic acid (50 μM) were necessary to transactivate the RAR-β2 promoter. The data demonstrate that acyclo-retinoic acid is much less active than retinoic acid with respect to GJC and retinoid-related signaling. Therefore, we conclude that lycopene affects GJC independent of the formation of acyclo-retinoic acid.