Molecular mechanisms of cold-induced CYP1A activation in rat liver microsomes

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Cytochrome P4501A (the CYP1A1 and CYP1A2 enzymes) is known to metabolize anthropogenic xenobiotics to carcinogenic and mutagenic compounds. CYP1A1 transcriptional activation is regulated via the aryl hydrocarbon receptor (AhR)-dependent signal transduction pathway. CYP1A2 activation may occur through the AhR-dependent or AhR-independent signal transduction pathways. We used male Wistar rats to explore possible mechanisms of CYP1A activation induced by exposure to cold and the effects of the protein-tyrosine kinase inhibitors genistein, herbimycin A, and geldanamycin on the properties of hepatic CYP1A1 and CYP1A2 proteins following exposure to cold and to classic CYP1A inducers. The molecular mechanisms of cold-induced CYP1A1 and CYP1A2 activation are different. The CYP1A2 activation apparently occurs at the post-transcriptional level. The CYP1A1 activation, whether caused by exposure to cold or by classic CYP1A inducers, is AhR-dependent and occurs at the transcriptional level. Protein tyrosine kinase inhibitors have no effect on benzo(a)pyrene-induced CYP1A expression but alter cold-induced CYP1A1 activity and theCYP1A1 mRNA level. Thus, treatment with herbimycin A or geldanamycin leads to an increase in CYP1A1 activity, while treatment with genistein increases CYP1A1 mRNA expression and decreases CYP1A2 activity. These data elucidate the molecular mechanisms of cold-induced CYP1A activation and the role of protein kinases in the regulation of CYP1A during exposure to cold. Our results can also help identify the differences between the molecular mechanisms underlying the effects of the classic CYP1A inducers and the effects of cooling (AU)

Nueva singladura clínica y toxicológica de la gammaglutamiltranspeptidasa / New clinical and toxicological scenario of gammaglutamyltranspeptidase

Desde su descubrimiento en 1950 por Hanes, la enzima gammaglutamiltranspeptidasa, al menos en medicina clínica, se ha vinculado casi en exclusiva, al valor de su aumento en la toxicidad por etanol y, en menor medida, de la existencia de ciertas neoplasias y de bloqueo de la vía biliar. Más recientemente, menudean trabajos acerca de su papel metabólico, mediando la neutralización de radicales libres de oxígeno y aprovisionando de glutatión a las células. El nivel sérico de gammaglutamiltranspeptidasa es expresivo de estrés oxidativo aumentado y se ha asociado a diversos factores de riesgo cardiovascular y a componentes del síndrome de resistencia a la insulina, de modo que sería un biomarcador precoz para el desarrollo de diabetes. Por otro lado numerosos fármacos inducen la enzima tisular (microsomas) pudiendo dar elevaciones séricas que no suponen daño estructural a nivel hepático. Su ubicuidad anátomo-citológica hace que pueda aumentar en suero en numerosos procesos, siendo por ello en ocasiones dificultoso patentizar su origen. Finalmente, desde un ángulo epidemiológico y toxicológico, siendo que el glutatión es necesario para conjugar diversas sustancias químicas, la enzima resultaría un biomarcador, entre otros, de numerosas sustancias nocivas medioambientales. Se incide en conjunto en este ensanchamiento del significado clínico y diagnóstico de una enzima que se creía suficientemente conocida desde hace medio siglo en que se descubrió(AU)

After the discovery of gammaglutamyltranspeptidase in 1950 by Hanes, the significance of its increased levels in clinical practice has mainly been focused on ethanol toxicity, and also some neoplasms and biliary tract obstruction. More recently, attention has swift to the metabolic functions of this enzyme, as a neutralizer of oxygen free radicals and as a glutathione donor to the cell. High serum levels of gammaglutamyltranspeptidase is known to occur when oxidative stress is increased, or associated with several vascular risk factors and the insulin resistance syndrome, as an early marker of diabetes. There are also a number of drugs that induce the expression of the tissue enzyme (microsomes) with the result of high serum levels without structural damage to the liver. Because it is a ubiquitous enzyme, a very high number of causes can be involved, that may be difficult to recognize. Finally, because glutathione is necessary to conjugate a number of chemical compounds, from an epidemiological and toxicological perspective, the enzyme might be useful as a biomarker of seve - ral ambient toxins. In this review we want to emphasize the increasing clinical and diagnostic significance of this enzyme discovered half a century ago(AU)

Peroxidación lipídica de microsomas obtenidos del hígado y riñón de rata: efecto del isómero CIS- 9, TRANS-11 del ácido linoléico / Lipid peroxidation of microsomes obtained from rat liver and kidney: effect of CIS-9, TRANS-11_ conjugated linoleic acid isomer

La composición de ácidos grasos, la quimioluminescencia y el índice de peroxidabilidad de microsomas obtenidos de hígado y riñón de rata fueron estudiados después de la administración oral del isómero ácido linoleico conjugado-9-cis, 11-trans (c9-t11-ALC). Mediante la incubación de microsomas en un sistema ascorbato-Fe++ (120 minutos en 37°C), se observó que las cuentas totales por minuto/mg de proteína, originadas por la quimioluminiscencia, eran más bajas en microsomas de hígado y riñón pertenecientes al grupo c9-t11-ALC que en los microsomas obtenidos de grupo control. El efecto de c9-t11-ALC sobre la composición de ácidos grasos poli-insaturados de microsomas hepáticos nativos fue evidenciado por una disminución estadísticamente significativa p<0.007 del ácido linoleico C18:2 n6. Cuando los microsomas peroxidados obtenidos de hígado y riñón, de ambos grupos (control y c9-t11-ALC), fueron comparados con sus respectivos nativos, se observó que C18:2 n6, C20: 4 n6 disminuyeron en todas las membranas microsomales usadas en este trabajo, mientras que en los microsomas obtenidos de hígado del grupo c9-t11-ALC y grupo control también disminuyó C22: 6n3. Por consiguiente, el índice del peroxidabilidad – parámetro basado en el índice máximo de oxidación de ácidos grasos – mostró cambios significativos en microsomas de hígado y riñón. Estos cambios fueron menos pronunciados en las membranas microsomales obtenidas de las ratas que recibieron c9-t11-ALC por vía oral. Nuestros resultados confirmarían y ampliarían observaciones anteriores que indicaron que ALC podría actuar como antioxidante, protegiendo las membranas contra efectos dañinos (AU)

The polyunsaturated fatty acid composition, chemiluminescence and peroxidizability index of microsomes obtained from rat liver and kidney were studied after oral administration of cis-9, trans-11-conjugated linoleic acid isomer (c9-t11-CLA). After incubation of microsomes in an ascorbate Fe++ system (120 min at 37°C) it was observed that the total counts per min/mg protein originated from light emission: chemiluminescence was lower in liver and kidney microsomes in the c9-t11-CLA group than in the microsomes obtained from control group. The effect of c9-t11-CLA on the polyunsaturated fatty acid composition of native liver microsomes was evidenced by a statistically significant p<0.007 decrease of linoleic acid C18:2 n6. When peroxidized microsomes obtained from liver and kidney of both groups (control and c9-t11-CLA) were compared with respective natives, it was observed that C18:2 n6, C20:4 n6 decreased in all membranes used in this work, whereas in microsomes obtained from liver c9-t11-CLA and control groups C22:6 n3 also decreased. As a consequence, the peroxidizability index – a parameter based on the maximal rate of oxidation of fatty acids – showed significant changes in liver and kidney microsomes. These changes were less pronounced in membranes derived from rats receiving c9-t11-CLA per os. Our results would confirm and extend previous observations which indicated that CLA could act as an antioxidant, protecting membranes from deleterious effects (AU)