Methionine deficiency in rats fed soy protein induces hypercholesterolemia and potentiates lipoprotein susceptibility to peroxidation.
A number of studies have provided evidence that plant proteins, especially soy protein, have a cholesterol-lowering effect as compared with casein. However, dietary supply of sulfur amino acids may be deficient when soy protein is present in the diet at a suboptimal level, which could affect lipid metabolism. Accordingly, in rats fed 13% protein diets, soy protein feeding resulted in a cholesterol-increasing effect (+18%), which could be counteracted by methionine supplementation (0.4%). In contrast, soy protein was effective in decreasing plasma triglyceride, as compared with levels in rats fed casein; this triglyceride-lowering effect was entirely abolished by methionine supplementation. The hypercholesterolemic effect of soy protein was characterized by a higher cholesterol content in low-density lipoprotein (LDL) and high-density lipoprotein 1 (HDL1) fractions, together with a marked induction of hepatic hydroxymethyl glutaryl coenzyme A (HMG CoA) reductase activity and to a lesser extent cholesterol 7 alpha-hydroxylase. There was practically no induction of these enzymes, as compared with levels in rats fed casein diets, when the soy protein diet was supplemented with methionine. Very-low-density lipoprotein (VLDL) plus LDL susceptibility to peroxidation was higher in rats fed soy protein than in casein-fed rats, which could reflect in part the lack of sulfur amino acid availability, since methionine supplementation led to a partial recovery of lipoprotein resistance to peroxidation. These findings suggest that amino acid imbalance could be atherogenic by increasing circulating cholesterol and leading to a higher lipoprotein susceptibility to peroxidation.
Moundras
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Laboratoire des Maladies Métaboliques, Institute National de la Recherche Agronomique de Clermont-Ferrand/Theix, St Genès Champanelle, France.
Rémésy
C
C
Levrat
M A
MA
Demigné
C
C
D000818:Animals; D002364:Caseins / Q000008:administration & dosage; D002784:Cholesterol / Q000097:blood; D002790:Cholesterol 7-alpha-Hydroxylase / Q000096:biosynthesis; D008076:Cholesterol, HDL / Q000097:blood; D004044:Dietary Proteins / Q000008:administration & dosage*; D006903:Hydroxymethylglutaryl CoA Reductases / Q000096:biosynthesis; D006937:Hypercholesterolemia / Q000209:etiology*; D015227:Lipid Peroxidation; D008099:Liver / Q000201:enzymology; D008297:Male; D008715:Methionine / Q000008:administration & dosage / Q000172:deficiency*; D014674:Plant Proteins, Dietary / Q000008:administration & dosage*; D051381:Rats; D017208:Rats, Wistar; D030262:Soybean Proteins; D014280:Triglycerides / Q000097:blood
D002364:Caseins; D008076:Cholesterol, HDL; D004044:Dietary Proteins; D014674:Plant Proteins, Dietary; D030262:Soybean Proteins; D014280:Triglycerides; D002784:Cholesterol; D008715:Methionine; D006903:Hydroxymethylglutaryl CoA Reductases; D002790:Cholesterol 7-alpha-Hydroxylase