Inhibition mechanism of 3-hydroxy-3-methyl-glutaryl-CoA reductase by tocotrienol-rich rice bran fraction optimally extracted with ultrasonic energy.

Tocotrienols (T3) are vitamin E components that inhibit 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGR), a primary target for cholesterol management. T3 was extracted from rice bran (RBE) using ultrasonic energy keeping solute: solvent ratio, power and time on specific energy and T3 concentration as responses as per Box-Behnken Design. The lowest specific energy (52.38 ± 0.14 J mL) uptake by the sample was most effective in enhancing the concentration of T3 in RBE (199.34 ± 0.63 μg mL). In vitro HMGR kinetics and in silico binding interactions of the identified α-, δ- and γ-T3 fractions were studied. Enzyme kinetic studies revealed an uncompetitive mode of inhibition by α-T3, γ-T3, and RBE and a mixed mode of inhibition for δ-T3. γ-T3 showed lowest IC concentration (11.33 μg mL) followed by α-T3 (16.73 μg mL), RBE (20.45 μg mL) and δ-T3 (23.16 μg mL). Molecular docking studies highlighted the hydrogen bonding of δ-T3 with Gln766 and α- and γ-T3 with Met655 and Val805 amino acid residues at the NADPH binding site of HMGR. Results indicate the potential use of T3 enriched RBE optimally extracted using ultrasound as potent HMGR inhibitor.