A fraction derived from brewer's yeast inhibits cholesterol synthesis by rat liver preparations in vitro

Abstract

Brewer's yeast was grown on a defined medium containing tracer51Cr with or without added chromium. The two batches of yeast contained 10 μg/g (high-Cr) or 80 ng/g (low-Cr). Extracts were prepared and fractionated. A third batch of yeast (third batch) was grown with added Cr, and fractionated. Rats were reared on either rat cubes (normal diet) or on a low-Cr diet (low-Cr), or on rat cubes with added cholestyramine (cholestyramine diet). Preparations of rat liver, both cell-free and intact hepatocytes, incorporated acetate-carbon into fatty acids and cholesterol. These processes were inhibited by a yeast fraction containing small, neutral, water-soluble compounds. The degree of inhibition was the same whether the liver came from normal rats or rats fed on the low-Cr diet. Similarly the inhibitory effect was found with identical amounts of extracts from low- or high-Cr yeasts. Therefore, Cr compounds do not appear to account for the inhibitory effects of brewer's yeast. Use of other substrates indicated that the site of inhibition of sterol synthesis was apparently between acetyl-CoA and mevalonate. One inhibitory substance was isolated from yeast and was found to be nicotinamide riboside. This may have been produced from NAD(P) during the preparation of yeast extracts, and it may be produced from dietary yeast supplements during digestion in vivo. Nicotinamide riboside may be partly responsible for the reported effects of yeast supplements on plasma lipids in humans.

Chromium: celebrating 50 years as an essential element?

“…28 However, Cr 3+ has been demonstrated repeatedly to be separable from agents in yeast responsible for in vitro stimulation of glucose metabolism in adipocytes. [29][30][31][32][33][34][35] Thus, the component of yeast that is active in the bioassays apparently does not contain Cr. The characterization of a Cr fraction from yeast was performed on a mixture that contained multiple Cr-containing species and other components, and the Cr-containing components of the mixture probably do not reflect what bound Cr initially in the intact yeast.…”

Mass Spectrometric and Spectroscopic Studies of the Nutritional Supplement Chromium(III) Nicotinate

“…This proposal, which has been reiterated numerous times in reviews and textbooks as the structure of the biologically active form of chromium, "GTF," clearly has absolutely no basis. Finally, Cr 3+ has been demonstrated repeatedly to be separable from agents in yeast responsible for in vitro stimulation of glucose metabolism in adipocytes [8][9][10][11][12][13].…”

Carcass Characteristics, Plasma Biochemical Profile and Faecal Microbial Count of Crossbred Pigs Supplemented With Probiotic, Prebiotic and Synbiotic

“…Piva et al (2005) also reported similar (P>0.05) concentration of plasma Ca (2.42 vs 2.64 m mol/l) and total protein (61.2 vs 63.2 g/l) in pigs fed diet supplemented with synbiotic (Lactitol + Lactic acid bacteria) on comparison with those fed basal diet. It has been reported (Holdsworth et al, 1991) that yeast supplementation inhibited liver cholesterol synthesis and lowered the plasma total cholesterol level in rats. This effect is attributed to compounds such as pantethine and nicotinamide riboside, which inhibit cholesterol synthesis by inhibiting incorporation of acetyl groups into nonsaponifiable lipid.…”