The Experts below are selected from a list of 123 Experts worldwide ranked by ideXlab platform
Robert S. H. Liu - One of the best experts on this subject based on the ideXlab platform.
-
Probing for the threshold energy for visual transduction: red-shifted visual pigment analogs from 3-methoxy-3-Dehydroretinal and related compounds.
Photochemistry and photobiology, 1999Co-Authors: Hiroo Imai, Akihisa Terakita, Rong-liang Chen, Takahiro Hirano, Yoshinori Shichida, Rajeev S. Muthyala, Leticia U. Colmenares, Robert S. H. LiuAbstract:— While azulenic retinal analogs failed to yield a red-shifted visual pigment analog, the 9-cis isomers of the push-pull polyenals 3-methoxy-3-Dehydroretinal and 14F-3-me-thoxy-3-Dehydroretinal yielded iodopsin pigment analogs with absorption maxima at, respectively, 663 and 720 nm. The former gave a relatively stable batho product (700 nm) and was able to activate transducin. A lower activity was observed for the latter. One possible explanation for the combined results is that the excitation energies of these red-shifted pigments are approaching the threshold energy for visual transduction (although at this time we cannot rigorously exclude a role of the added F-atom in reducing the transducin activity).
-
New hindered isomers of 3-Dehydroretinal (vitamin A2)
Tetrahedron, 1996Co-Authors: Rong-liang Chen, Robert S. H. LiuAbstract:Abstract The preparation of six new isomers (7-cis, 7,9-dicis, 7,11-dicis, 7,13-dicis, 7,9,11-tricis and 7,9,13-tricis) of 3-Dehydroretinal ( 1 , vitamin A 2 ), and their spectroscopic properties are reported. Because of the unexpected 1,7-H migration in photo-sensitized isomerization of the smaller building blocks in the dehydro-series, the introduction of the 7-cis geometry in the synthesis of new hindered isomers of 3-Dehydroretinal required construction of this cis-double bond prior to that of the 3,4-double bond.
-
PHOTOSTATIONARY STATE COMPOSITIONS OF RETINAL AND RELATED COMPOUNDS INCLUDED IN BETA -LACTOGLOBULIN. EFFECTS OF PROTEIN HOST ON ISOMER DISTRIBUTION OF POLYENE SUBSTRATES
Photochemistry and photobiology, 1995Co-Authors: Robert S. H. LiuAbstract:— The UV-visible absorption spectra and photostationary state compositions of retinal (or the related C-18 ketone, 3-Dehydroretinal and the C-22 aldehyde) imbedded in the binding cavity of (3-lactoglobulin (BLG) are consistent with the view that the carbonyl group of these polyenes are hydrogen-bonded with the protein host, most likely with the lone protonated lysine residue in the binding pocket. Patterns of variation in photochemical behavior of the imbedded chromophore versus that in solution are discussed in terms of possible specific protein-substrate interactions. The results are also compared with that of the methyl ether of retinol where similar hydrogen bonding is not possible.
-
7-cis- and 7,9-dicis-3-Dehydroretinal. Hindered isomers of vitamin A2 aldehyde☆
Tetrahedron Letters, 1994Co-Authors: Rong-liang Chen, Robert S. H. LiuAbstract:Successful synthesis of the hindered 7-cis and 7,9-dicis isomers of 3-Dehydroretinal from β-ionone is reported. The procedure, involving introduction of the hindered 7-cis geometry prior to the 3,4-double bond, should be applicable to preparation of other unknown isomers of Vitamin A2 aldehyde.
Rong-liang Chen - One of the best experts on this subject based on the ideXlab platform.
-
Probing for the threshold energy for visual transduction: red-shifted visual pigment analogs from 3-methoxy-3-Dehydroretinal and related compounds.
Photochemistry and photobiology, 1999Co-Authors: Hiroo Imai, Akihisa Terakita, Rong-liang Chen, Takahiro Hirano, Yoshinori Shichida, Rajeev S. Muthyala, Leticia U. Colmenares, Robert S. H. LiuAbstract:— While azulenic retinal analogs failed to yield a red-shifted visual pigment analog, the 9-cis isomers of the push-pull polyenals 3-methoxy-3-Dehydroretinal and 14F-3-me-thoxy-3-Dehydroretinal yielded iodopsin pigment analogs with absorption maxima at, respectively, 663 and 720 nm. The former gave a relatively stable batho product (700 nm) and was able to activate transducin. A lower activity was observed for the latter. One possible explanation for the combined results is that the excitation energies of these red-shifted pigments are approaching the threshold energy for visual transduction (although at this time we cannot rigorously exclude a role of the added F-atom in reducing the transducin activity).
-
New hindered isomers of 3-Dehydroretinal (vitamin A2)
Tetrahedron, 1996Co-Authors: Rong-liang Chen, Robert S. H. LiuAbstract:Abstract The preparation of six new isomers (7-cis, 7,9-dicis, 7,11-dicis, 7,13-dicis, 7,9,11-tricis and 7,9,13-tricis) of 3-Dehydroretinal ( 1 , vitamin A 2 ), and their spectroscopic properties are reported. Because of the unexpected 1,7-H migration in photo-sensitized isomerization of the smaller building blocks in the dehydro-series, the introduction of the 7-cis geometry in the synthesis of new hindered isomers of 3-Dehydroretinal required construction of this cis-double bond prior to that of the 3,4-double bond.
-
7-cis- and 7,9-dicis-3-Dehydroretinal. Hindered isomers of vitamin A2 aldehyde☆
Tetrahedron Letters, 1994Co-Authors: Rong-liang Chen, Robert S. H. LiuAbstract:Successful synthesis of the hindered 7-cis and 7,9-dicis isomers of 3-Dehydroretinal from β-ionone is reported. The procedure, involving introduction of the hindered 7-cis geometry prior to the 3,4-double bond, should be applicable to preparation of other unknown isomers of Vitamin A2 aldehyde.
Patrice Couture - One of the best experts on this subject based on the ideXlab platform.
-
temporal variations in kidney metal concentrations and their implications for retinoid metabolism and oxidative stress response in wild yellow perch perca flavescens
Aquatic Toxicology, 2018Co-Authors: Michel A Defo, Louis Bernatchez, Peter G C Campbell, Patrice CoutureAbstract:The objective of this study was to determine if temporal variations in tissue metal concentrations are related to biomarkers of retinoid metabolism and oxidative stress responses in juvenile yellow perch (Perca flavescens). To this end, kidney metal (Cd, Cu and Zn) concentrations were measured in fish sampled in spring and fall 2012 in four lakes representing a wide range of water and sediment metal contamination in the Rouyn-Noranda (Quebec) region. Lakes Opasatica and Helene were considered as reference lakes while lakes Dufault and Marlon were metal-contaminated. Kidney concentrations of Cd, Cu and Zn varied widely between spring and fall in fish from both clean and metal-contaminated lakes. An inter-lake difference in renal metal concentrations was only observed for Cd, with fish from Lake Marlon consistently displaying higher concentrations. In the spring, the concentrations of liver dehydroretinol, dehydroretinyl palmitate and total vitamin A esters were higher in fish sampled in the most contaminated lake. Strong temporal variations in the concentrations of these metabolites, as well as in the percentage of liver free dehydroretinol and the epidermal retinol dehydrogenase 2 transcription levels, were observed in fish living in the most metal-impacted lake, with generally higher values in the spring. In contrast to liver, in muscle, no clear seasonal variations in the concentrations of dehydroretinol, dehydroretinyl stearate or in the percentage of free dehydroretinol were observed in fish captured in the most contaminated lake. Temporal variations of traditional biomarkers of oxidative stress response were also observed in the most metal-impacted lake. For example, the transcription level of the gene encoding Cu/Zn superoxide dismutase-1 in liver and muscle catalase activity of perch sampled in the most contaminated lake were higher in spring than in fall. Positive relationships were found between kidney Cd concentrations and the transcription level of the gene encoding glucose 6-phosphate dehydrogenase, and all forms of retinoid concentrations in liver in spring, except with the percentage of free dehydroretinol where the correlation was negative. Our results translate to a state of stress caused by Cd and illustrate that temporal variations in tissue metal concentrations affect retinoid metabolism and antioxidant capacities in juvenile wild yellow perch. Overall this study contributes to highlight the importance of considering temporal variations when investigating the consequences of metal contamination on the physiology of wild fish.
-
Waterborne cadmium and nickel impact oxidative stress responses and retinoid metabolism in yellow perch.
Aquatic toxicology (Amsterdam Netherlands), 2014Co-Authors: Michel A Defo, Louis Bernatchez, Peter G C Campbell, Patrice CoutureAbstract:In this experiment, we studied the transcriptional and functional (enzymatic) responses of yellow perch (Perca flavescens) to metal stress, with a focus on oxidative stress and vitamin A metabolism. Juvenile yellow perch were exposed to two environmentally relevant concentrations of waterborne cadmium (Cd) and nickel (Ni) for a period of 6 weeks. Kidney Cd and Ni bioaccumulation significantly increased with increasing metal exposure. The major retinoid metabolites analyzed in liver and muscle decreased with metal exposure except at high Cd exposure where no variation was reported in liver. A decrease in free plasma dehydroretinol was also observed with metal exposure. In the liver of Cd-exposed fish, both epidermal retinol dehydrogenase 2 transcription level and corresponding enzyme activities retinyl ester hydrolase and lecithin dehydroretinyl acyl transferase increased. In contrast, muscle epidermal retinol dehydrogenase 2 transcription level decreased with Cd exposure. Among antioxidant defences, liver transcription levels of catalase, microsomal glutathione-S-transferase-3 and glucose-6-phosphate dehydrogenase were generally enhanced in Cd-exposed fish and this up-regulation was accompanied by an increase in the activities of corresponding enzymes, except for microsomal glutathione-S-transferase. No consistent pattern in antioxidant defence responses was observed between molecular and biochemical response when fish were exposed to Ni, suggesting a non-synchronous response of antioxidant defence in fish exposed to waterborne Ni. There was a general lack of consistency between muscle transcription level and enzyme activities analyzed. The overall findings from this investigation highlight the usefulness of transcriptional and biochemical endpoints in the identification of oxidative stress and vitamin A metabolism impairment biomarkers and the potential use of multi-level biological approaches when assessing environmental risk in fish.
-
Evidence for metabolic imbalance of vitamin A2 in wild fish chronically exposed to metals
Ecotoxicology and environmental safety, 2012Co-Authors: Michel A Defo, Louis Bernatchez, Peter G C Campbell, Fabien Pierron, Philip A. Spear, Patrice CoutureAbstract:In a recent study on indigenous yellow perch chronically exposed to metals, we reported a negative correlation between liver metal concentration and liver transcription levels of genes encoding for enzymes involved in the metabolism of retinoids. We therefore speculated that metals, and especially the non-essential metal Cd, could alter the metabolism of retinoids in wild fish. Thus the present field study investigates the impact of in situ metal exposure on retinoid storage. A total of 55 yellow perch (Perca flavescens) were sampled in six lakes representing a metal contamination gradient (8≤N≤10 per lake). Our results show that yellow perch from Cd-contaminated lakes had significantly higher concentrations of liver dehydroretinol and dehydroretinyl esters than did fish from reference lakes. However, the increase in retinyl ester stores with increasing Cd concentrations was quantitatively much more important than the increase in free dehydroretinol. As a result, a significant decrease in the percentage of hepatic free dehydroretinol with increasing renal Cd concentrations was observed. These results suggest that the enzymes and the binding proteins involved in vitamin A homeostasis are inhibited by the presence of Cd. Alternatively, the increase in tissue vitamin A (antioxidant) levels could serve to better counteract the oxidative stress engendered by Cd exposure. Overall our findings illustrate that vitamin A(2) homeostasis can be altered as a consequence of chronic exposure to low Cd concentrations. Thus, in the context of environmental risk assessment, the percentage of liver free dehydroretinol can be considered as a biomarker of for in situ Cd exposure.
Takaharu Seki - One of the best experts on this subject based on the ideXlab platform.
-
Retinals and retinols induced by estrogen in the blood plasma of Xenopus laevis
The Journal of experimental biology, 1993Co-Authors: Masami Azuma, Toshiaki Irie, Takaharu SekiAbstract:Injection of estrogen into male Xenopus laevis induced the appearance of retinals (retinal and 3-Dehydroretinal) and a considerable increase in the amount of retinols (retinol and 3-dehydroretinol) in the blood plasma. These retinoids were mainly in the all-trans form. Without estrogen injection, retinols were normally found in the blood plasma of both males and females, but only trace amounts of retinals were detected and these were restricted to the plasma of females. The proteins in the blood plasma of estrogen-injected males were separated into two fractions. One fraction included vitellogenin, the precursor of egg yolk proteins, and the other contained some plasma proteins other than vitellogenin. Retinals were detected in the former and retinols in the latter. It is suggested that retinals are bound to vitellogenin and are taken up into oocytes in the process of vitellogenesis.
Michel A Defo - One of the best experts on this subject based on the ideXlab platform.
-
temporal variations in kidney metal concentrations and their implications for retinoid metabolism and oxidative stress response in wild yellow perch perca flavescens
Aquatic Toxicology, 2018Co-Authors: Michel A Defo, Louis Bernatchez, Peter G C Campbell, Patrice CoutureAbstract:The objective of this study was to determine if temporal variations in tissue metal concentrations are related to biomarkers of retinoid metabolism and oxidative stress responses in juvenile yellow perch (Perca flavescens). To this end, kidney metal (Cd, Cu and Zn) concentrations were measured in fish sampled in spring and fall 2012 in four lakes representing a wide range of water and sediment metal contamination in the Rouyn-Noranda (Quebec) region. Lakes Opasatica and Helene were considered as reference lakes while lakes Dufault and Marlon were metal-contaminated. Kidney concentrations of Cd, Cu and Zn varied widely between spring and fall in fish from both clean and metal-contaminated lakes. An inter-lake difference in renal metal concentrations was only observed for Cd, with fish from Lake Marlon consistently displaying higher concentrations. In the spring, the concentrations of liver dehydroretinol, dehydroretinyl palmitate and total vitamin A esters were higher in fish sampled in the most contaminated lake. Strong temporal variations in the concentrations of these metabolites, as well as in the percentage of liver free dehydroretinol and the epidermal retinol dehydrogenase 2 transcription levels, were observed in fish living in the most metal-impacted lake, with generally higher values in the spring. In contrast to liver, in muscle, no clear seasonal variations in the concentrations of dehydroretinol, dehydroretinyl stearate or in the percentage of free dehydroretinol were observed in fish captured in the most contaminated lake. Temporal variations of traditional biomarkers of oxidative stress response were also observed in the most metal-impacted lake. For example, the transcription level of the gene encoding Cu/Zn superoxide dismutase-1 in liver and muscle catalase activity of perch sampled in the most contaminated lake were higher in spring than in fall. Positive relationships were found between kidney Cd concentrations and the transcription level of the gene encoding glucose 6-phosphate dehydrogenase, and all forms of retinoid concentrations in liver in spring, except with the percentage of free dehydroretinol where the correlation was negative. Our results translate to a state of stress caused by Cd and illustrate that temporal variations in tissue metal concentrations affect retinoid metabolism and antioxidant capacities in juvenile wild yellow perch. Overall this study contributes to highlight the importance of considering temporal variations when investigating the consequences of metal contamination on the physiology of wild fish.
-
Waterborne cadmium and nickel impact oxidative stress responses and retinoid metabolism in yellow perch.
Aquatic toxicology (Amsterdam Netherlands), 2014Co-Authors: Michel A Defo, Louis Bernatchez, Peter G C Campbell, Patrice CoutureAbstract:In this experiment, we studied the transcriptional and functional (enzymatic) responses of yellow perch (Perca flavescens) to metal stress, with a focus on oxidative stress and vitamin A metabolism. Juvenile yellow perch were exposed to two environmentally relevant concentrations of waterborne cadmium (Cd) and nickel (Ni) for a period of 6 weeks. Kidney Cd and Ni bioaccumulation significantly increased with increasing metal exposure. The major retinoid metabolites analyzed in liver and muscle decreased with metal exposure except at high Cd exposure where no variation was reported in liver. A decrease in free plasma dehydroretinol was also observed with metal exposure. In the liver of Cd-exposed fish, both epidermal retinol dehydrogenase 2 transcription level and corresponding enzyme activities retinyl ester hydrolase and lecithin dehydroretinyl acyl transferase increased. In contrast, muscle epidermal retinol dehydrogenase 2 transcription level decreased with Cd exposure. Among antioxidant defences, liver transcription levels of catalase, microsomal glutathione-S-transferase-3 and glucose-6-phosphate dehydrogenase were generally enhanced in Cd-exposed fish and this up-regulation was accompanied by an increase in the activities of corresponding enzymes, except for microsomal glutathione-S-transferase. No consistent pattern in antioxidant defence responses was observed between molecular and biochemical response when fish were exposed to Ni, suggesting a non-synchronous response of antioxidant defence in fish exposed to waterborne Ni. There was a general lack of consistency between muscle transcription level and enzyme activities analyzed. The overall findings from this investigation highlight the usefulness of transcriptional and biochemical endpoints in the identification of oxidative stress and vitamin A metabolism impairment biomarkers and the potential use of multi-level biological approaches when assessing environmental risk in fish.
-
Evidence for metabolic imbalance of vitamin A2 in wild fish chronically exposed to metals
Ecotoxicology and environmental safety, 2012Co-Authors: Michel A Defo, Louis Bernatchez, Peter G C Campbell, Fabien Pierron, Philip A. Spear, Patrice CoutureAbstract:In a recent study on indigenous yellow perch chronically exposed to metals, we reported a negative correlation between liver metal concentration and liver transcription levels of genes encoding for enzymes involved in the metabolism of retinoids. We therefore speculated that metals, and especially the non-essential metal Cd, could alter the metabolism of retinoids in wild fish. Thus the present field study investigates the impact of in situ metal exposure on retinoid storage. A total of 55 yellow perch (Perca flavescens) were sampled in six lakes representing a metal contamination gradient (8≤N≤10 per lake). Our results show that yellow perch from Cd-contaminated lakes had significantly higher concentrations of liver dehydroretinol and dehydroretinyl esters than did fish from reference lakes. However, the increase in retinyl ester stores with increasing Cd concentrations was quantitatively much more important than the increase in free dehydroretinol. As a result, a significant decrease in the percentage of hepatic free dehydroretinol with increasing renal Cd concentrations was observed. These results suggest that the enzymes and the binding proteins involved in vitamin A homeostasis are inhibited by the presence of Cd. Alternatively, the increase in tissue vitamin A (antioxidant) levels could serve to better counteract the oxidative stress engendered by Cd exposure. Overall our findings illustrate that vitamin A(2) homeostasis can be altered as a consequence of chronic exposure to low Cd concentrations. Thus, in the context of environmental risk assessment, the percentage of liver free dehydroretinol can be considered as a biomarker of for in situ Cd exposure.