Search

The biocide tetrakis(hydroxymethyl)phosphonium sulphate (THPS) and other members of the tetrakis(hydroxymethyl) phosphonium salts (THPX) family are associated with liver toxicity in several mammalian species and teratogenicity in rabbits. Malformations include skeletal changes and abnormalities in eye development and are very similar to those seen with vitamin A deficiency or excess. For this reason, it was hypothesized that teratogenicity of THPS(X) might be attributed to disturbances in retinol availability and/or metabolism as a result of maternal toxicity, for example, either due to insufficient dietary intake by the mothers or due to liver toxicity. Therefore, in the present study, liver toxicity and vitamin A homeostasis were studied in pregnant rabbits that were exposed to 13.8 or 46.0 mg/kg THPS during organogenesis and in precision‐cut liver slices of rats and rabbits exposed to 0–70 μM THPS. Results show that in vivo exposure to THPS leads to a marked reduction of food intake, increased plasma concentrations of γ‐glutamytransferase, degenerative changes in the liver and to changes in retinoid content in liver and plasma in the rabbits during organogenesis. In addition, THPS, both in vivo and ex vivo, caused a change in expression of proteins related to vitamin A metabolism and transport. Together, these observations could explain the birth defects observed in earlier teratogenicity studies. Pregnant rabbits and liver slices of rats and rabbits were exposed to tetrakis(hydroxymethyl)phosphonium sulphate (THPS) to investigate its interaction with vitamin A homeostasis. In the rabbits, this resulted in substantial reduction of food intake, adverse liver effects, and reduced retinol concentrations in liver and plasma. In vivo and in liver slices, THPS changed the expression of proteins related to retinoid metabolism and transport. The interference with vitamin A homeostasis could act in synergy with food deprivation leading to birth defects in rabbits following THPS exposure. [ABSTRACT FROM AUTHOR]

The close packing of vertebrate photoreceptors presents a challenge to the exchange of molecules between the outer segments, retinal pigmented epithelium (RPE), and Müller glia. An extracellular hyaluronan scaffold separates these cells while soluble interphotoreceptor matrix (IPM) proteins traffic visual cycle retinoids, fatty acids, and other molecules between them. In the IPM, retinoids and fatty acids are carried by interphotoreceptor retinoid-binding protein (IRBP). The fact that much of the retina's IRBP can be extracted by saline wash has led to the notion that IRBP does not bind to the retina, but freely distributes itself within the subretinal space. In this study, we challenge this idea by asking if there are specialized IPM domains that bind IRBP, perhaps facilitating its ability to target delivery/uptake of its ligands. Xenopus is an ideal animal model to study the role of the IPM in RPE-photoreceptor interactions. Here, we took advantage of the large size of its photoreceptors, ability to detach the retina in light, sustainability of the retina in short term organ culture, and the availability of recombinant full-length Xenopus IRBP and antisera directed against Xenopus IRBP. We compared the distribution of wash resistant native IRBP, and that of IRBP-Alexa 647 binding in Xenopus retina. IRBP and cone opsin were localized using anti-Xenopus IRBP serum, and monoclonal COS-1 respectively. Cone matrix sheath proteoglycans were localized with wheat germ agglutinin (WGA), and diffuse IPM proteoglycans with peanut agglutinin (PNA). Wholemounts and frozen sections were compared by immunofluorescence from retinas detached under Ringer's followed by additional washes, or detached directly under 4% paraformaldehyde without Ringer's wash. Undetached Lowicryl embedded retinas were subjected to IRBP immunogold electron microscopy (EM). Immunogold labeled a diffuse network of filamentous structures, and a separate distinct flocculant material directly coating the outer segments, filling the rod periciliary ridge, and associated with Müller microvilli. By immunofluorescence, Ringer's wash removed most of the diffuse IRBP, but not that coating the outer segments. IRBP-Alexa 647 bound to the cone outer segments and Müller villi region, and comparably less to rod outer segments. Co-incubation with unlabeled IRBP markedly reduced this binding; ovalbumin-Alexa 647 and Alexa 647 dye alone showed no binding. Our data suggest that the pericellular matrix of the cone outer segments and Müller microvilli provide specialized domains that facilitate IRBP's functions. [ABSTRACT FROM AUTHOR]

Animals acquire carotenoids from the diet and convert them to retinoids. These lipids must be distributed in the body to support retinoid signaling in peripheral tissues and photoreceptor function in the eyes. However, the hydrophobicity of carotenoids and retinoids limit their diffusion in the aqueous environment of the body. Therefore, membrane proteins and cellular binding proteins transport these lipids between extra- and intracellular compartments and facilitate their metabolism. Mutations in genes encoding these transport proteins are associated with a wide spectrum of blinding disorders. Here, we describe approaches used by our laboratories that have proven successful in expressing these proteins and examining their biochemical properties in the test tube and in cell-based assays. These assays can be utilized for screening of small molecule modulators of their activities to correct pathologies associated with retinoid metabolism., (Copyright © 2022 Elsevier Inc. All rights reserved.)

The ocular lenses of several genera of strictly diurnal dwarf geckos contain the monomeric ι-crystallin, which is closely related to the cellular retinol-binding protein type I (CRBP I). The contents of ι-crystallin vary between 2 and 12% of the total amount of crystallins depending on species. The endogenous ligand of ι-crystallin of all species investigated so far turns out to be 3,4-didehydroretinol (vitamin A2). No other lenticular retinoids were detected. In lenses of Old World species ( Lygodactylus, Pristurus, Quedenfeldtia), this ligand occurs exclusively in the all- trans form. In lenses of species of the neotropical genus Gonatodes, however, it occurs in two isomeric forms: all- trans and 11- cis. ι-Crystallin of Gonatodes is the first CRBP-like protein which naturally binds an 11- cis isomer of vitamin A. All- trans 3,4-didehydroretinol and its ester are present in eye cups of Lygodactylus. In contrast, eye cups of nocturnal geckos without ι-crystallin lack these retinoids. The retinal pigment epithelium is suggested to be the site of conversion of retinol to 3,4-didehydroretinol, which finally serves as ligand of ι-crystallin. [ABSTRACT FROM AUTHOR]

In the adult, as well as in the embryo, a number of specific extra- and intracellular binding proteins such as the plasma retinol binding protein (RBP), the cellular retinol binding protein type I (CRBP I), and also the cellular receptors for RBP are thought to regulate transport and metabolism of retinol (vitamin A). Since the regulation of materno-fetal transport of vitamin A is not well understood, we examined the localization of these proteins during the development of the mouse chorio-allantoic and yolk sac placentas. The labyrinthine region of the chorio-allantoic placenta, where exchange of substances can occur between the maternal and fetal circulations, did not contain RBP (mRNA or protein) or antigen(s) similar to the bovine RBP-receptor p63, whereas the visceral endoderm of the yolk sac placenta, the second site for materno-fetal transport, did. Furthermore, only the endodermal cells of the visceral yolk sac appeared to strongly accumulate radiolabelled retinoids. The cellular retinol binding protein (CRBP I) was detected both in the trophoblast layer of the placental labyrinth closest to the fetal endothelium (layer III), and in the visceral endoderm of the yolk sac. Together, these findings suggest that the yolk sac placenta mediates retinol transfer to the embryo/fetus throughout the entire gestation. The chorio-allantoic placenta, on the other hand, does not appear to have this capacity, while the presence of CRBP I does suggest a retinol-metabolizing capability. [ABSTRACT FROM AUTHOR]

Retinoic acid, one of the most potent of the naturally occurring retinoids (retinol and derivatives), is required for the maintenance of epithelial cell growth. This study describes the pattern of expression of nuclear retinoic acid receptors (RARs and RXRs), and cellular binding proteins for retinol and retinoic acid (CRBP I, CRABP I and II), in endometrial epithelial cells. The effects of retinoic acid on the expression of these receptors in endometrial epithelial cells have also been studied and compared with its effects in endometrial stromal cells. Messenger RNA for RAR-α, RAR-β, RAR-γ, RXR-α, CRBP I and CRABP II was detected by Northern blotting of total RNA extracted from cultured epithelial cells. In comparison with stromal cell RNA that was used as an internal standard, CRBP I appeared to be more abundant in epithelial cells, whereas CRABP II appeared to be more abundant in the stromal cells. This implies that the intracellular concentration of retinoic acid may be maintained at higher levels in epithelial cells compared to stromal cells. In addition, the response of the two cell types to retinoic acid differs: RAR-β is induced in stromal cells treated with all-trans retinoic acid but not in epithelial cells. From these data we suggest that retinoid physiology differs between endometrial epithelial and stromal cells.Furthermore, by analogy with other studies, we propose that retinoic acid may be maintained at a higher intracellular concentration in endometrial epithelial cells to facilitate differentiation to a glandular phenotype. Since RAR-β is induced by retinoic acid in endometrial stromal cells but not endometrial epithelial cells, retinoic acid may also play a role in mediating stromal-epithelial cell interactions in endometrial differentiation. [ABSTRACT FROM PUBLISHER]

A survey is presented of model building techniques and computer-assisted quantum-chemical and molecular-dynamics simulations, as applied to the study of protease and receptor design, to the determination of the properties of related effectors, agonist and antagonist molecules, and to the design of fatty-acid transport proteins and molecular carriers. Studies covering integral membrane protein design have been reviewed: they include porins, ion channels and G protein coupled receptors. In the transport molecule class, hydrophobic ligand transporters, such as serum and cellular retinoid binding proteins, have been reviewed. [ABSTRACT FROM AUTHOR]