ABSTRACT
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.
Subject(s)
Cholestanones/administration & dosage , Down-Regulation , Hydroxymethylglutaryl CoA Reductases/metabolism , Kidney/enzymology , Liver/enzymology , Testis/enzymology , Acyl Coenzyme A/metabolism , Animals , Cholestanones/pharmacology , Humans , Hydroxymethylglutaryl CoA Reductases/chemistry , Hydroxymethylglutaryl CoA Reductases/genetics , Male , Mevalonic Acid/metabolism , Molecular Docking Simulation , Rats , StereoisomerismABSTRACT
Brassinosteroids are plant-derived polyhydroxylated derivatives of 5a-cholestane, structurally similar to cholesterol-derived animal steroid hormones and insect ecdysteroids, with no known function in mammals. 28-Homobrassinolide (HB), a steroidal lactone with potent plant growth-promoting property, stimulated protein synthesis and inhibited protein degradation in L6 rat skeletal muscle cells (EC(50) 4 µM) mediated in part by PI3K/Akt signaling pathway. Oral administration of HB (20 or 60 mg/kg/d for 24 d) to healthy rats fed normal diet (protein content 23.9%) increased food intake, body weight gain, lean body mass, and gastrocnemius muscle mass as compared with vehicle-treated controls. The effect of HB administration increased slightly in animals fed a high-protein diet (protein content 39.4%). Both oral (up to 60 mg/kg) and subcutaneous (up to 4 mg/kg) administration of HB showed low androgenic activity when tested in the Hershberger assay. Moreover, HB showed no direct binding to the androgen receptor in vitro. HB treatment was also associated with an improved physical fitness of untrained healthy rats, as evident from a 6.7% increase in lower extremity strength, measured by grip test. In the gastrocnemius muscle of castrated animals, HB treatment significantly increased the number of type IIa and IIb fibers and the cross-sectional area of type I and type IIa fibers. These findings suggest that oral application of HB triggers selective anabolic response with minimal or no androgenic side-effects and begin to elucidate the putative cellular targets for plant brassinosteroids in mammals.
Subject(s)
Anabolic Agents/pharmacology , Cholestanones/pharmacology , Muscle, Skeletal/drug effects , Anabolic Agents/administration & dosage , Animals , Body Composition/drug effects , Cells , Cholestanones/administration & dosage , Dietary Proteins , Lethal Dose 50 , Male , Molecular Structure , Muscle Fibers, Skeletal/drug effects , Muscle, Skeletal/cytology , Orchiectomy , Rats , Rats, WistarABSTRACT
The subchronic effect of the plant hormone homobrassinolide, a dietary constituent of vegetables and green leaves, was investigated in male albino Wistar strain rats. Blood sugar and serum insulin content, tissue hexokinase enzyme activity, and mRNA expression were studied using homobrassinolide administered orally by gavage at 50 µg (333 µg/kg body weight) for 15 consecutive days. Selected tissue responses were determined at 16 days post administration in control and experimental animals employing established methods. Homobrassinolide reduced the circulating blood sugar and increased the serum insulin level significantly. Hexokinase activity in the brain, heart, liver, kidney, and testis of experimental rats was found elevated. Hexokinase mRNA expression detected employing polymerase chain reaction (PCR) technique was found significantly increased in the brain and liver compared to other tissues. It is suggested that this plant hormone is a transcriptional activator of hexokinase gene, promoting enhanced hexokinase mRNA synthesis in vivo in rat tissues.
