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At least 685 records · Page 38Linked to original sources
PubMed1993

Inhibition of phospholipase A2 purified from human herniated disc.

The effect on human herniated intervertebral disc phospholipase A2 (HD-PLA2) of a number of retinoids, antirheumatic drugs and reported PLA2 inhibitors was evaluated using autoclaved [1-14C]-oleate-labeled Escherichia coli membranes as the substrate. Dexamethasone, non-steroidal antiinflammatory drugs, aristolochic acid and retinol were inactive, whereas a marked inhibition was found for manoalide, retinal, nordihydroguaiaretic acid and p-bromophenacyl bromide after preincubation with the enzyme (IC50 values 0.25, 4, 5 and 5 microM, respectively). The results are parallel to those obtained with the PLA2 purified from human synovial fluid.

Acetophenones↗
PubMed1994

Retinal dehydrogenation and retinoic acid 4-hydroxylation in rat hepatic microsomes: developmental studies and effect of foreign compounds on the activities.

All-trans-retinoic acid (RA) regulates the transcription of a number of mammalian genes and is therefore important in the control of many cellular processes. RA is formed and deactivated within the cell so that biotransformation modulates RA availability. This study investigate the relationship between the formation of RA from retinal and its metabolism by 4-hydroxylation in rat hepatic microsomes. From kinetic studies the Michaelis constants for RA formation and 4-hydroxylation were 52 and 24 microM, respectively, and the maximal reaction velocities were 33 and 136 pmol/min/mg protein, respectively. Thus, 4-hydroxylation was the more efficient process. In microsomes from 1-week-old rats, RA formation was very low (approximately 2 pmol/min/mg protein) but was several-fold greater in adults of both sexes (approximately 10 pmol/min/mg protein). In contrast, 4-hydroxylation was quantitatively more significant at all ages examined between 1 and 15 weeks; by 10 and 15 weeks a sexual dimorphism was apparent (M > F). Thus, the ratio of RA 4-hydroxylation to RA formation was comparatively large in microsomes from 1-week-old rats and declined to a stable value around 4-6 weeks of age. With the exception of dexamethasone, which decreased the activity, administration of foreign compounds to male rats had little effect on RA formation. Both dexamethasone and phenobarbital induced RA 4-hydroxylation but DMSO and beta-naphthoflavone were without effect. From these findings, 4-hydroxylation, particularly in very young animals, may be an effective means of controlling RA production. RA 4-hydroxylation, like other cytochrome P450 activities, was inducible in rat liver but no evidence was found for induction of the microsomal retinal dehydrogenase.

Aging↗
PubMed1995

Biotransformation of all-trans-retinol and all-trans-retinal to all-trans-retinoic acid in rat conceptal homogenates.

Catalysis of the oxidation of all-trans-retinol (vitamin A1) or of all-trans-retinal to all-trans-retinoic acid (all-trans-RA) by rat conceptal enzymes was investigated during organogenesis. Products of the reaction were identified and quantified with HPLC by comparing their elution times with those of authentic standard retinoids. Under the incubation and assay conditions utilized, all-trans-retinol and all-trans-retinal were converted to readily detectable quantities of all-trans-RA. Rat conceptal homogenates from gestational days 10.5, 11.5 and 12.5 each exhibited enzymatic activity for oxidation of all-trans-retinol and all-trans-retinal to all-trans-RA. Enzymatic catalysis was verified by showing that: (1) both reactions were coenzyme dependent; (2) the rates of reactions increased as concentrations of conceptal protein increased; (3) both reactions were abolished by heating the tissue homogenates (100 degrees, 5 min); and (4) both reactions exhibited substrate saturation. Under the same experimental conditions, formation of all-trans-RA from all-trans-retinol was much slower than from all-trans-retinal, suggesting that oxidation of all-trans-retinol to all-trans-retinal was the rate-limiting step for biotransformation of all-trans-retinol to all-trans-RA in embryonic tissues. When NAD or NADP were replaced by NADH or NADPH, the rate of oxidation of all-trans-retinol was reduced markedly, indicating that the reaction was catalyzed primarily by an NAD/NADP-dependent dehydrogenase(s). Carbon monoxide (CO:O2 = 90:10) did not inhibit the reaction. NAD appeared to be a more effective cofactor than NADP in catalyzing oxidation of all-trans-retinal to all-trans-RA. When NAD was omitted, formation of all-trans-RA from all-trans-retinal was reduced by approximately 55%. Replacing NAD by NADH or NADPH also reduced the conversion of all-trans-retinal to all-trans-RA by about 60%. These observations suggested at least two pathways for the generation of all-trans-RA from all-trans-retinal in embryos: oxidation catalyzed by an NAD/NADP-dependent dehydrogenase(s) and oxidation catalyzed by an oxidase(s) that did not require NAD, NADH, NADP or NADPH. Conversion of all-trans-retinol to all-trans-RA was inhibited strongly by low concentrations of citral, but not by high concentrations of sodium azide, 4-methylpyrazole, or metyrapone. Similarly, oxidation of all-trans-retinal was inhibited strongly by citral but not by metyrapone.(ABSTRACT TRUNCATED AT 400 WORDS)

Acyclic Monoterpenes↗
PubMed1985

Chromophores in the extraretinal photoreceptor (pineal organ) of teleosts.

We have demonstrated, using a highly sensitive high performance liquid chromatography technique, that the pineal organ (epiphysis cerebri) of the rainbow trout contains both 11-cis-retinal and 11-cis-3-dehydroretinal. These compounds were assumed to be the chromophores of pineal photopigments, because they were isomerized to all-trans forms by light-adaptation. The quantity of chromophores in the dark-adapted pineal organ was extremely low (9.2-29.1 pmol/pineal), corresponding to approximately 1/300-1/1000 of that of the retina.

Animals↗
PubMed1992

Ibotenic acid lesions in the amygdaloid central nucleus but not in the lateral subthalamic area prevent the acquisition of differential Pavlovian conditioning of bradycardia in rabbits.

The present study examined the effect of ibotenic acid lesions in the amygdaloid central nucleus (ACe) or in the lateral zona incerta of the subthalamus (LZI) on the acquisition of differential Pavlovian conditioning of bradycardia in rabbits. Previous work has shown that bilateral electrolytic lesions in either ACe or LZI abolished the retention of conditioned heart rate (HR) responses. In order to determine whether these findings were due to destruction of cells intrinsic to ACe or LZI, ibotenic acid lesions were placed bilaterally in either structure or in control sites. Following recovery, animals were subjected to differential Pavlovian conditioning in which one tone (CS+) was paired with periorbital shock and a second tone (CS-) was presented alone. It was found that destruction of cell bodies in ACe, but not LZI, prevented the acquisition of the differential bradycardiac conditioned response. In addition, ACe lesions did not interfere with baseline HR, the HR orienting response, the HR unconditioned response to shock, or the concomitantly conditioned corneoretinal potential. The results of this study suggest that destruction of cells intrinsic to ACe selectively prevents the acquisition of differentially conditioned HR, and perhaps other conditioned responses related to conditioned arousal, but does not affect unlearned HR responses or specific somatomotor conditioned responses.

Amygdala↗
PubMed1990

Electron spin resonance study of free radicals generated from retinyl- and ionyl-derivatives.

Free radicals generated from alpha- and beta-ionyl bromides gave well resolved ESR spectra, but retinyl bromide and chloride gave only broad signals. Delocalised radicals were also spectroscopically observed on hydrogen abstraction from alpha-ionane, alpha-ionyltrimethylsilylether and buten-3-ynyl-2,6,6-trimethyl-2-cyclohexene. Retinyl and beta-ionyl radicals, derived from the corresponding xanthates, were successfully spin trapped with nitrosodurene. The results suggested that the secondary sites C(7) and C(9) were the most reactive in the beta-ionyl radical and that the secondary sites C(7) and C(11) and probably the primary site C(15) were the most reactive in the retinyl radical.

Butylated Hydroxytoluene↗
PubMed1990

Distribution of retinoids in the chick limb bud: analysis with monoclonal antibody.

Retinoic acid induces anteroposterior duplicate formation in developing chick limb bud, and it may be a natural morphogen involved in limb pattern formation. Retinoic acid is produced from retinol locally in the limb bud via retinal, and thus, to elucidate the distribution of these retinoids in the limb bud seems to be important for the understanding of the morphogen formation. We produced a monoclonal antibody against the retinoids with BSA-RA (bovine serum albumin-retinoic acid) conjugate for antigen, and investigated the distribution of retinoids in the chick limb bud. The antibody predominantly bound to retinoic acid, but weakly to retinol and retinal. Retinoids appeared in the limb bud at stage 18 and were distributed through stages 20-24, when the pattern formation in distal mesoderm was in progress. Initially they were found evenly in the whole mesoderm, but disappeared gradually from core mesoderm and remained only in the region of peripheral mesoderm at stage 24. At stage 26, retinoids were detected only in ectoderm. These results support the idea that the retinoids actually play roles in limb pattern formation and suggest that the retinoids in the peripheral mesoderm are important for pattern formation. Further, the role of retinoids in epidermis development at later limb bud stages is also suggested.

Animals↗
PubMed1989

The actions of retinal and retinoic acid on histamine release from rat peritoneal mast cells.

Histamine release from rat peritoneal mast cells induced by anti-IgE was potentiated by the retinoids: retinoic acid 2-10 microM and retinal 1-5 microM. Retinal also produced a concentration-dependent increase in anti-IgE-stimulated 45Ca uptake by these mast cells. A similar potentiating action of both retinoids was observed on histamine release induced by 12-O-tetradecanoylphorbol-13-acetate (TPA). For both anti-IgE- and TPA-induced histamine release, the potentiating effect of the two retinoids was only observed in the presence of extracellular calcium. In contrast, histamine release induced by compound 48/80 was inhibited by retinal 1-5 microM and by retinoic acid 10-50 microM and the inhibition was the same in the presence as in the absence of extracellular calcium 1 mM. Histamine release induced by calcium and the calcium ionophore A 23187 was inhibited by retinoid acid 2-10 microM and by retinal 10 microM. Inhibitions of compounds 48/80-induced histamine release by cromoglycate and by retinal were additive. It is concluded that while the actions of retinoids on rat peritoneal mast cells are consistent with the inhibition of protein kinase C, another action of these compounds, unrelated to this enzyme, may explain the data.

Animals↗
PubMed1989

Growth factors and hormones which affect survival, growth, and differentiation of the MCF-7 stem cells and their descendants.

The human breast tumor cell line was separated by Percoll density gradient centrifugation into six different subpopulations, A to F, one of which (E) appears to contain the stem cells on the basis of several criteria (M. Resnicoff et al. 1987, Proc. Natl. Acad. Sci. USA 84, 7295. We now analyzed the response of the isolated subpopulations to insulin, thrombin, PGF2 alpha, estradiol, and 13-cis-retinal. We demonstrate that the first two growth factors stimulate [3H]thymidine incorporation in the more differentiated subpopulations (D and F), while PGF2 alpha has mitogenic activity in subpopulations C and D. In the absence of any added growth factor, estradiol has the extreme and transient capacity of allowing the stem cell to detach from the tissue culture dish and to grow in suspension as multicellular aggregates (MCF-7/SE cells). 13-cis-Retinal acts as a negative modulator of differentiation and protects the cells from the inhibitory and differentiation activity of Na-butyrate.

Breast Neoplasms↗