RESUMEN
Understanding the influence of ubiquitously present plant steroids on mammalian cell biology is currently of interest. Feedback inhibition of HMGCoA reductase (HMGCR) catalytic activity in the transformation of HMG-CoA to mevalonate is a significant regulatory step in sterol biosynthetic pathway. To assess the role of dietary steroids in this biochemical transformation, the phytosteroid isoform 28-homobrassinolide (28-HB), 90 % pure, obtained from Godrej Agrovet (India) was used to determine its effect on mammalian HMG-CoA reductase. Photometric assay of pure human and select rat tissue HMGCR post 28-HB oral feed, PCR-HMGCR gene expression, and in silico docking of 28-HB and HMGCoA on HMGCR protein template were carried out. Using an oral feed regimen of pure 28-HB, we noted a decrease of 16 % in liver, 17.1 % in kidney and 9.3 % in testicular HMGCR enzyme activity, 25 % in HMGCR gene expression and 44 % in the activity of pure human HMGCR due to this plant oxysterol. In silico docking studies yielded binding metrics for 28-HB-HMGCR lower than for HMGCoA-HMGCR, indicating stronger binding of HMGCR by this ligand. 28-HB exerts differential effects on rat tissue HMGCR, down regulates liver HMGCR gene expression and significantly inhibits HMGCR activity.
Asunto(s)
Colestanonas/administración & dosificación , Regulación hacia Abajo , Hidroximetilglutaril-CoA Reductasas/metabolismo , Riñón/enzimología , Hígado/enzimología , Testículo/enzimología , Acilcoenzima A/metabolismo , Animales , Colestanonas/farmacología , Humanos , Hidroximetilglutaril-CoA Reductasas/química , Hidroximetilglutaril-CoA Reductasas/genética , Masculino , Ácido Mevalónico/metabolismo , Simulación del Acoplamiento Molecular , Ratas , EstereoisomerismoRESUMEN
Cholesterol is the template for steroid hormone biosynthesis. Cholesterol homeostasis is regulated by Cyt-P450 oxygenated cholesterols acting as ligands on LXR-α and LXR-ß transcription factors that are now emerging as drug targets. Heterodimerization of LXRs with retinoic acid receptor is considered a prerequisite for target gene activation. Dietary plant oxysterol 28-homobrassinolide (28-HB) is a proven antihyperglycemic and a pro-steroidogenic agent in the rat. Whether 28-HB has a role in LXR gene expression was therefore investigated using oral gavage (15 days) of 28-HB (333 µg/kg b w) to normal and diabetic rat. PCR amplified LXR-α and ß mRNA transcripts from treated rat liver and testis exhibited quantitative differences in their expression. Conformational differences in 28-HB docking to LXR-α and ß binding domains were also noted through in silico studies, LXR-ß adopting lesser specificity. We report that 28-HB transactivates LXR genes in the rat tissues.