Methionine-induced elevation of plasma homocysteine concentration is associated with an increase of plasma cholesterol in adult rats.
OBJECTIVE
Dietary methionine affects cholesterol metabolism in growing rats. Methionine effects on adult rats and mechanisms by which methionine alters the lipid metabolism are not fully elucidated. We investigated possible mechanisms by which dietary methionine acts on lipid metabolism of adult rats.


METHODS
Male adult rats were divided into three groups (n=10) and were fed casein-based diets differing in methionine concentration (low-methionine diet: 0.96 g/kg; adequate-methionine diet: 2.22 g/kg, high-methionine diet: 6.82 g/kg) for 4 weeks. Concentrations of triacylglycerols and cholesterol in plasma and lipoproteins, concentration of homocysteine in plasma, concentration of cholesterol in liver, fecal lipid excretion, expression of hepatic HMG-CoA reductase, phosphatidylethanolamine N-methyltransferase 2 (PEMT-2) and of LDL receptor were measured.


RESULTS
Rats fed the high-methionine diet had higher plasma homocysteine concentrations than rats fed the low-methionine diet (p<0.05). Although concentrations of cholesterol in plasma and lipoproteins were not different between the groups, there was a distinct positive correlation between circulating plasma homocysteine and plasma cholesterol (R(2)=0.55, p<0.001). The fecal excretion of cholesterol and bile acids was not altered by dietary methionine. The relative mRNA concentration of HMG-CoA reductase and of LDL receptor remained unaffected by dietary methionine. Gene expression of PEMT-2 was higher in rats fed the high-methionine diet than in rats fed the other diets (p<0.05).


CONCLUSIONS
The results demonstrate that dietary methionine contributes to a rise in circulating homocysteine concentration which positively correlates with the concentration of plasma cholesterol. However, the effects of methionine on cholesterol metabolism of adult rats were relatively weak.
Hirche
Frank
F
Institut fur Ernahrungswissenschaften, Martin-Luther-Universitat Halle-Wittenberg, Halle/Saale, Germany.
Schroder
Arlette
A
Knoth
Berit
B
Stangl
Gabriele I
GI
Eder
Klaus
K
D000704:Analysis of Variance; D000818:Animals; D002784:Cholesterol / Q000097:blood*; D004305:Dose-Response Relationship, Drug; D005243:Feces / Q000737:chemistry; D006710:Homocysteine / Q000097:blood* / Q000187:drug effects; D006903:Hydroxymethylglutaryl CoA Reductases / Q000235:genetics / Q000378:metabolism; D050356:Lipid Metabolism / Q000187:drug effects*; D008074:Lipoproteins / Q000032:analysis / Q000737:chemistry; D008297:Male; D008715:Methionine / Q000008:administration & dosage / Q000494:pharmacology*; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley
D008074:Lipoproteins; D006710:Homocysteine; D002784:Cholesterol; D008715:Methionine; D006903:Hydroxymethylglutaryl CoA Reductases