Effects of Excess Dietary <i>L</i>-Cystine on the Rat Plasma Lipoproteins

Abstract

The effects of excess dietary cystine on the cholesterol and protein contents of rat plasma lipoproteins are described. 5 % L-cystine was added to a semisynthetic diet containing 23% casein and 0.05% cholesterol, to the same diet enriched with 1 % cholesterol or containing tristearin instead of lard. Rats were fed the diets during 2 months. The addition of cystine led to an increase in the plasma cholesterol level of the rats fed with the basal diet (from 0.92 to 1.56 mg/mi). But it produced a reduction of this level in cholesterol-fed rats (from 1.71 to 1.49 mg/ml). These different changes in the total plasma cholesterol level are explained by the specific effects of cystine on each lipoprotein: whatever the diet, cystine supplementation reduced the chylomicron and VLDL cholesterol contents and increased that of LDL (especially LDL2: density 1.040–1.063) and HDL. This study allowed us to compare 2 conditions which lead to hypercholesterolemia but which have opposite effects on hepatic cholesterogenesis: the supplementation of the same basal diet with 1 % cholesterol or 5% cystine. In cholesterol-fed rats, the major part (49%) of plasma cholesterol was found in the chylomicrons and VLDL while the LDL2 cholesterol content was low (0.07 mg/ml plasma). Conversely, cystine-fed rats had a low chylomicron and VLDL plasma content (both enriched in apoprotein E), whereas up to 33% of the plasma cholesterol were carried by LDL2. Thus the production of LDL2 in cholesterol and cystine-fed rats could be related to hepatic cholesterogenesis.

Alaska pollock (Gadus chalcogrammus) proteins and hydrolysed polypeptides: a systematic review of their potential bioactivities

“…Although it is unclear, the activities of APP as a cholesterol‐lowering agent are influenced by a number of factors, including amino acid composition and the intradigestive tract effect. Several studies have proven that certain amino acids, for example, Gly, Met and Cys possess cholesterol‐lowering activity, and the ratio of Lys/Arg is related to lower cholesterol activity (Katan et al ., 1982; Serougne et al ., 1984; Sugiyama et al ., 1986; Spielmann et al ., 2008). Moreover, cholesterol metabolism in the intradigestive tract is related to physicochemical characteristics of digestive tract products and how faster the dietary proteins to be digested (Terpstra & Sanchez‐Muniz, 1981).…”

Dietary ε-Polylysine Decreased Serum and Liver Lipid Contents by Enhancing Fecal Lipid Excretion Irrespective of Increased Hepatic Fatty Acid Biosynthesis-Related Enzymes Activities in Rats

“…The reduction of serum cholesterol content due to several dietary proteins compared with that of casein was found to depend on their amino acid composition and the digestive tract effects of their digestion products ( 3 , 42 ). One of these factors is the amino acid composition of the protein, in particular the ratio of lysine/arginine ( 43 ), and its content of specific amino acids, namely, methionine ( 44 ), cysteine ( 45 ), and glycine ( 46 ). In this study, however, the amino acid composition of the EPL diet proved to be similar to that of the LYS-AA diet, so the difference could not be explained in terms of differences in lysine/arginine, methionine, cysteine, and glycine contents.…”