Lipid balance in HepG2 cells: active synthesis and impaired mobilization

G F Gibbons,R Khurana,A Odwell,M C Seelaender

doi:10.1016/s0022-2275(20)39775-3

Abstract

The human hepatoma cell line HepG2 in culture medium synthesized fatty acids de novo (144 +/- 9 nmol fatty acid/mg protein per 24 h) at a rate similar to that observed in freshly prepared rat hepatocytes (192 +/- 8 nmol/mg per 24 h) and in primary cultures of rat hepatocytes (165.4 +/- 29.3 nmol/mg per 24 h). In HepG2 cells, fatty acid synthesis was inhibited by extracellular oleate (0.75 mM), and, to a lesser extent, by glucagon (10(-7) M). Insulin (7.8 x 10(-8) M) had a mild stimulatory effect. Fatty acid synthesis was not influenced by lipogenic precursors (lactate plus pyruvate), substances which, in rat hepatocytes, had pronounced stimulatory effects. Fatty acid synthesis rates were also unchanged in the presence of prostaglandin E2 (PGE2). In general, compared to rat hepatocytes, fatty acid synthesis in HepG2 cells was less sensitive to manipulation of the culture medium in vitro. HepG2 cells had a high capacity for triacylglycerol synthesis from extracellular oleate (469 +/- 43 nmol triacylglycerol/mg protein per 24 h) but phospholipid synthesis was relatively low (15.8 +/- 0.4% of total glycerolipids). Very little of the above newly synthesized triacylglycerol was secreted as lipoprotein (4.62 +/- 0.88 nmol triacylglycerol/mg protein per 24 h) resulting in a large intracellular accumulation of triacylglycerol. This was exacerbated by the absence of any detectable ketogenesis. The secretion of triacylglycerol produced from de novo synthesized fatty acids was also very low in HepG2 compared to that observed in primary cultures of rat hapatocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Highlights

IntroductionT h e secretion of triacylglycerol produced from de novo synthesized fatty acids was very low in HepG2 compared to that observed in primary cultures of rat hepatocytes
In the absence of hormones or of lipogenic precursors, the rate of fatty acid synthesis in HepG2 amounted to 144 9 nmol/mg protein per 24 h
T h e rate of TAG synthesis in HepG2 is comparable to that observed in normal rat hepatocytes

Summary

Introduction

T h e secretion of triacylglycerol produced from de novo synthesized fatty acids was very low in HepG2 compared to that observed in primary cultures of rat hepatocytes. In contrast to rat hepatocytes, most of the lipoprotein triacylglycerol in HepGZ was secreted without prior lipolysis and re-esterification of intracellular triacylglycerol. This reflected a very low overall rate of intracellular triacylglycerol lipolysis in HepG2. L), there have been no studies of the regulation of fatty acid synthesis or of the reciprocal control of fatty acid disposal via the oxidative and esterification pathways [2] All these factors contribute to the maintenance of hepatic triacylglycerol (TAG) homeostasis. The reason(s) for this uncoupling of apoB and TAG secretion in HepG2 remains obscure a defect in the so-called “second stage” transfer of TAG to the nascent lipoprotein has been implicated [8]

Methods

Results

Conclusion