Gamma Tocotrienol Regulates HMG-CoA Reductase

Byron's Comments:

Basic tocotrienol and cholesterol science.

Study Title:

Tocotrienols regulate cholesterol production in mammalian cells by post-transcriptional suppression of 3-hydroxy-3-methylglutaryl-coenzyme A reductase.

Study Abstract:

Tocotrienols are natural farnesylated analogues of tocopherols which decrease hepatic cholesterol production and reduce plasma cholesterol levels in animals. For several cultured cell types, incubation with gamma-tocotrienol inhibited the rate of [14C]acetate but not [3H] mevalonate incorporation into cholesterol in a concentration- and time-dependent manner, with 50% inhibition at approximately 2 microM and maximum approximately 80% inhibition observed within 6 h in HepG2 cells. 3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase total activity and protein levels assayed by Western blot were reduced concomitantly with the decrease in cholesterol synthesis. In HepG2 cells, gamma-tocotrienol suppressed reductase despite strong blockade by inhibitors at several steps in the pathway, suggesting that isoprenoid flux is not required for the regulatory effect. HMG-CoA reductase protein synthesis rate was moderately diminished (57% of control), while the degradation rate was increased 2.4-fold versus control (t1/2 declined from 3.73 to 1.59 h) as judged by [35S]methionine pulse-chase/immunoprecipitation analysis of HepG2 cells treated with 10 microM gamma-tocotrienol. Under these conditions, the decrease in reductase protein levels greatly exceeded the minor decrease in mRNA (23 versus 76% of control, respectively), and the low density lipoprotein receptor protein was augmented. In contrast, 25-hydroxycholesterol strongly cosuppressed HMG-CoA reductase protein and mRNA levels and the low density lipoprotein receptor protein. Thus, tocotrienols influence the mevalonate pathway in mammalian cells by post-transcriptional suppression of HMG-CoA reductase, and appear to specifically modulate the intracellular mechanism for controlled degradation of the reductase protein, an activity that mirrors the actions of the putative non-sterol isoprenoid regulators derived from mevalonate.

Study Information:

Parker RA, Pearce BC, Clark RW, Gordon DA, Wright JJ. Tocotrienols regulate cholesterol production in mammalian cells by post-transcriptional suppression of 3-hydroxy-3-methylglutaryl-coenzyme A reductase. J Biol Chem.  1993 May 25;268(15):11230-8.
Department of Metabolic Diseases, Bristol-Myers Squibb Pharmaceutical Research Institute, Princeton, New Jersey 08543.

Full Study:

http://www.jbc.org/content/268/15/11230.long

Most Popular News:


Connect with Wellness Resources:

Connect on Facebook Follow us on Twitter Wellness Resources on Pinterest Wellness Resources YouTube Channel Get RSS News Feeds
Telecourse
bookstore
Thyroid and Metabolism
podcast
autoship