RESUMEN
Retinoic acid (RA), a principal metabolite of vitamin A (retinol), is an essential endogenous regulator of gene transcription and an important therapeutic agent. The catabolism of RA must be well regulated to maintain physiological concentrations of RA. The cytochrome P450 (CYP) gene family CYP26, which encodes RA-4-hydroxylase activity, is strongly implicated in the oxidation of RA. Inflammation alters the expression of numerous genes; however, whether inflammation affects CYP26 expression is not well understood. We investigated the regulation of CYP26A1 and CYP26B1 mRNA levels by RA and LPS in the rat liver, as the liver is centrally involved in retinoid metabolism and the acute-phase response to LPS. Both CYP26A1 and CYP26B1 mRNA were induced in <4 h by a single oral dose of all-trans-RA. RA-induced responses of both CYP26A1 and CYP26B1 were significantly attenuated in rats with LPS-induced inflammation whether LPS was given concurrently with RA or after the RA-induced increase in CYP26A1 and CYP26B1 mRNA levels. When RA and LPS were administered simultaneously (6-h study), LPS alone had little effect on either CYP26A1 or CP26B1 mRNA, but LPS reduced by 80% the RA-induced increase in CYP26A1 mRNA (P<0.02), with a similar trend for CYP26B1 mRNA. When LPS was administered 4 h after RA (16-h study), it abrogated the induction of CYP26A1 (P<0.02) and CYP26B1 (P<0.01). Overall, these results suggest that inflammation can potentially disrupt the balance of RA metabolism and maintenance of RA homeostasis, which may possibly affect the expression of other RA-regulated genes.
Asunto(s)
Sistema Enzimático del Citocromo P-450/biosíntesis , Inflamación/metabolismo , Hígado/enzimología , Tretinoina/metabolismo , Animales , Sistema Enzimático del Citocromo P-450/genética , Modelos Animales de Enfermedad , Relación Dosis-Respuesta a Droga , Inducción Enzimática , Femenino , Inflamación/inducido químicamente , Isoenzimas/biosíntesis , Lipopolisacáridos , Hígado/efectos de los fármacos , Poli I-C , ARN Mensajero/biosíntesis , Ratas , Ratas Sprague-Dawley , Ácido Retinoico 4-Hidroxilasa , Factores de Tiempo , Receptor Toll-Like 3/metabolismo , Transcripción Genética , Tretinoina/farmacologíaRESUMEN
Pyridoxine-5'-beta-D-glucoside (PNG), a glycosylated form of dietary vitamin B-6, is partially hydrolyzed in the small intestine by the cytosolic enzyme pyridoxine-5'-beta-D-glucoside hydrolase (PNG hydrolase) and by the brush border enzyme lactase phlorizin hydrolase (LPH) to release free pyridoxine (PN). This laboratory has previously shown that PNG hydrolase activity is inversely related to dietary vitamin B-6 in rats and guinea pigs. The current investigation was done to examine the effect of dietary PN on PNG hydrolytic activity and its distribution. Nutrient compositional differences between the AIN-76A and AIN-93G purified diets that were unrelated to vitamin B-6 were also examined in relation to PNG hydrolysis in rat small intestinal mucosa. Study one included rats (n = 29) that were fed the AIN-93G diet providing a range of PN concentrations for 5 wk. Rats (n = 49) in study two were fed either AIN-76A or AIN-93G each with graded concentrations of PN. In both studies, rat growth and plasma and liver pyridoxal 5'-phosphate (PLP) concentrations increased (P < 0.05) with increasing concentrations of dietary PN. PNG hydrolytic activity localized to the brush border membrane was five times that measured in the cytosol. Cytosolic PNG hydrolytic activity increased significantly with increasing dietary PN concentration in rats fed the AIN-76A, but not AIN-93G diet. Activity in the mucosal total membrane fraction did not increase in proportion to dietary PN concentration for either diet. Regardless of dietary PN concentration, the basal nutrient composition of the diets affected growth and PNG hydrolytic activity in intestinal mucosa. In contrast to previous results from this laboratory, intestinal hydrolytic activity toward PNG did not increase in vitamin B-6-deficient rats.