Journal of the American Society of Nephrology 193 Uremic Serum Subtraction Inhibits Apolipoprotein A-I Production by a Human Hepatoma Cell Lin& Vaijinath S. Kamanna, Moti L. Kashyap, Rama Pai, Dung T. Bui, Fu-You Jin, Daeyoung Dave Roh, Gaurang M. Shah, and Michael A. Kirschenbaum2 V.5. Kamanna, 1?. Pai, DI. Bui, D.D. Roh, G.M. Shah. MA. Kirschenbaum, Section of Nephrology, Depart- ment of Veterans Affairs Medical Center, and the Department of Medicine, University of California. Irvine. Long Beach, CA ML. Kashyap, F-V. Jin, Section of Gerontology and the Cholesterol Center, Department of Veterans Af- fairs Medical Center and Department of Medicine, University of California, Irvine, CA (J. Am. Soc. Nephrol. 1994; 5:193-200) ABSTRACT Abnormalities in lipoprotein metabolism are corn- mon in uremic patients and may represent an addi- tional risk factor for the development of atheroscle- rosis. Despite the frequent occurrence of lipoprotein abnormalities, the role of various serum toxins and subtractions that accumulate in urernic patients on lipoprotein metabolism is not clearly understood. This study addressed the role of uremic toxins on lipopro- tein metabolism by examining the effect of a 500 to 2,000-d subfraction obtained from the serum of uremic and control subjects on the synthesis of apo- lipoprotein (apo) A-I in a human hepatoma cell line (Hep-G2). Serum subtractions obtained from uremic patients inhibited apo A-I synthesis and secretion by Hep-G2 cells in a dose-dependent manner as meas- ured by (3H)leucine incorporation into apo A-I, im- munoprecipitation, and ELISA. The uremic serum subtraction decreased the mRNA expression for apo A-I in Hep-G2 cells when compared with controls. These observations suggest that a component of uremic serum can have the potential to inhibit he- patic apo A-I synthesis and may adversely influence high-density lipoprotein metabolism, thus increasing the risk for the development of atherosclerotic vas- cular complications in uremic patients. Key Words: ESRD, uremic toxins, atherosclerosis, high-density Ii’poproteins I ReceIved Februay 14, 1994. Accepted March 25. 1994. 2 Correspondence to Dr. MA. Kirschenbaum, Nephrotogy Section (1 1 IN), De- portm#{149}nt of veterans AffaIrs Mdlcal Center, 5901 East Seventh Street. Long Beach, CA 90822. 1046.6673/0502-0193$03.00/0 Journal of the American Society of Nephrology Copyright C 1994 by the American SOciety of Nephrology A lthough atherosclerotic cardiovascular disease is commonly observed in patients with ESRD (1), hypercholesterolemia. and increased serum low- density hipoprotein (LDL) cholesterol, conventionally accepted risk factors for the development of athero- sclerosis in the general population may not be con- sistently found (2-4) in these patients whose serum triglycerides are often elevated and whose high-den- sity lipoprotein (HDL) cholesterol is often decreased (2,3,5,6). In this regard, previous studies using apo- hipoprotein (apo) measurements in patients with chronic renal disease showed decreased concentra- tions of apo A-I and A-Il and increased apo C-Ill, suggesting abnormalities in very law-density hipapro- tein (VLDL) and HDL metabolism (2,7). Additionally, patients with chronic renal disease often exhibit di- minished apo A-I and HDL synthetic and fractional catabolic rates, which have been thought to contrib- ute to their lowered levels of HDL and apo A-I (8). Although the association between lipids and progres- sive renal disease is not clearly understood, there exist sufficient data to suggest that abnormalities in hipoprateins and apo in uremic patients may contrib- ute to their increased risk for developing atherascle- rotic cardiovascular disease. Multiple factors have been proposed to influence the dyslipidemias seen in patients with chronic renal disease including coexisting diabetes, hypertension, liver disease, electrolyte imbalances, hemostatic ab- normahities, and the potential effect of circulating serum components that accumulate in uremia. The accumulation of toxins in the serum of uremic pa- tients has been proposed to contribute to same of the metabolic disturbances associated with chronic renal disease (9, 1 0). Despite speculation, the role of the serum subfractians that accumulate in uremic pa- tients in altering hipoprotein and apo metabolism and possibly contributing to the development of systemic atherosclerosis remains unclear. In this study. the effect of uremic serum subfrac- tians on apo A-I synthetic capacity and secretion was examined in a human hepatoma cell line (Hep-G2) that has previously been reported to possess many normal hepatic cell functions. including the synthe- sis of serum lipoproteins and apo ( 11 , 1 2). In recent years, these cells have been used extensively to study various aspects of lipoprotein metabolism. The re- sults of this study indicated that a uremic serum subfraction could reduce the hepatic synthetic ca-