EFFECTS OF DIETARY-PROTEIN SOURCE ON PLASMA-LIPIDS, HMG COA REDUCTASE-ACTIVITY, AND HEPATIC GLUTATHIONE LEVELS IN GERBILS

It has recently been postulated that soy protein-induced hypocholesterolemia is induced by increased production of reduced glutathione (GSH). The objective of the current study was to determine the influences of dietary proteins and amino acids on plasma lipid concentrations, hepatic GSH, and HMG CoA reductase activity. Twenty-eight adult male, inbred gerbils were fed diets similar in all respects except that dietary protein source was from either soy protein isolate (SOY), casein (CAS), L-amino acid patterned after SOY (SAA), or L-amino acid patterned after CAS (CAA). Results indicated that gerbils fed SOY had lower plasma total cholesterol concentrations than gerbils fed CAS or CAA. Low density lipoprotein-cholesterol was also lowest in SOY-fed animals compared with all other groups. High density lipoprotein (HDL)-cholesterol concentrations were highest in CAA-fed animals. Plasma triglycerides were unaffected by dietary treatment. Hepatic GSH concentrations were lowest in SOY-fed gerbils, but were not different between SAA- and CAA-fed groups. HMG CoA reductase activity was highest in gerbils fed SOY compared with CAS; however, when amino acids were fed the opposite occurred-reductase activity was higher in gerbils fed CAA compared with animals fed SAA. Correlation analysis showed no association between GSH and HMG CoA reductase activity. Positive correlations were present between GSH and total and HDL-cholesterol concentrations. These results indicate that lipid metabolism is influenced by dietary protein source, but these changes are not likely to be mediated by a GHS-mediated modification of cholesterol biosynthesis.