Laboratory Investigation

Kidney International (1993) 44, 789–794; doi:10.1038/ki.1993.313

Studies of alteration of hepatic cholesterol metabolism in puromycin-induced nephrotic syndrome in rats

Mohamed A E H Thabet1, Anna Challa1, James C M Chan1, William M Pandak1, Douglas M Heuman1 and Z Reno Vlahc caronevic caron1

1Departments of Pediatrics and Internal Medicine, and the Nephrology Division, Children's Medical Center, Medical College of Virginia, Health Sciences Division of Virginia Commonwealth University, Richmond, Virginia, USA

Correspondence: James C M Chan MD, Box 498 MCV Station, Richmond, Virginia 23298-0498, USA.

Received 9 December 1992; Revised 24 March 1993; Accepted 19 May 1993.

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Abstract

Studies of alteration of hepatic cholesterol metabolism in puromycin-induced nephrotic syndrome in rats. Hypercholesterolemia frequently accompanies the nephrotic syndrome, but the mechanism responsible for elevation of plasma cholesterol is poorly understood. Specifically, the contribution of abnormal hepatic cholesterol metabolism to elevated concentrations of serum cholesterol has never been studied in depth. The objective of the present study was to define the alteration of hepatic cholesterol metabolism in puromycin induced nephrotic syndrome in rats. Studies involved measurements of specific activities of four enzymes participating in the maintenance of hepatic cholesterol metabolism: HMG-CoA-reductase, the rate limiting enzyme of cholesterol synthesis; cholesterol 7alpha-hydroxylase, the rate limiting enzyme in bile acid synthesis; acyl CoA:cholesterol acyltransferase, the enzyme responsible for esterification of cholesterol; and cholesterol ester hydrolase (CEH), an enzyme which hydrolyzes cholesterol. Multiple injections of puromycin resulted in a production of nephrotic syndrome with massive proteinuria, hypoalbuminemia, hypercholesterolemia, ascites and edema. HMG-CoA-reductase (nmol/hr/mg protein) and cholesterol 7alpha-hydroxylase activities (nmol/hr/mg protein) in rats with nephrotic syndrome were not statistically significant as compared to control rats (4.0 plusminus 0.7 and 2.0 plusminus 0.6 vs. 3.3 plusminus 0.4 and 1.6 plusminus 0.2), respectively. Our results also demonstrate, for the first time, that the normal diurnal rhythm in HMG-CoA reductase activity is no longer present in the nephrotic animals. The activities in the nephrotics in the day was 4.0 nmol/hr/mg and at night, 3.9 nmol/hr/day, compared to the control values of 3.3 nmol/hr/mg in the day and 6.9 nmol/hr/mg at night. ACAT activities were 428 plusminus 78 versus 302 plusminus 64 pmol/min/mg/protein (P = NS). CEH activity was markedly increased in the nephrotic syndrome 3.4 plusminus 0.7 versus 1.1 plusminus0.1 nmol/hr/mg protein in control rats. There was a 25% increase in microsomal free cholesterol in rats with nephrotic syndrome (P < 0.01). [14C]-leucine incorporation in TCA precipitable fraction was not affected by puromycin injection in the first 12 days of the experiment, suggesting that the determinations of enzyme activities were not affected by puromycin, a known inhibitor of protein synthesis. We conclude that the hypercholesterolemia in nephrotic syndrome is not due to a marked alteration of hepatic cholesterol synthesis or degradation. A marked threefold increase in CEH was observed, but its role in the genesis of hypercholesterolemia is uncertain.

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