Glucose does not stimulate apoprotein B secretion from HepG2 cells because of insufficient stimulation of triglyceride synthesis

Hongshi Jiang,Henry N Ginsberg,Xujun Wu

doi:10.1016/s0022-2275(20)32483-4

Abstract

We have previously demonstrated a close relationship between oleic acid (OA)-stimulated triglyceride (TG) synthesis and apolipoprotein B (apoB) secretion in HepG2 cells. However, other investigators studying the association between glucose-stimulated TG synthesis and apoB secretion have reported variable results. The present study was carried out to answer the question: does TG derived from glucose have different effects on apoB secretion from HepG2 cells compared to TG derived from oleate? We observed that incubations of HepG2 cells for as long as 48 h in 30 mm glucose did not increase apoB secretion. We then demonstrated that the failure of glucose to stimulate apoB secretion from HepG2 cells results from insufficient stimulation of TG synthesis by glucose. Thus, incorporation of [3H]glycerol into [3H]TG in the presence of 30 mm glucose for up till 48 h was not increased compared to basal conditions. The inability of glucose to stimulate TG synthesis was also evidenced by the inability of both 8-h and 24-h incubations with 30 mm glucose to increase cell TG mass; similar incubations with OA increased TG mass 50–100“%. Additional studies demonstrated that glucose conversion to either glycerol or fatty acids was minimal; this accounted for the lack of stimulation of TG synthesis. We conclude that in HepG2 cells, availability of high glucose levels in the media for as long as 48 h does not stimulate triglyceride synthesis, and that this is the basis for the failure of glucose to stimulate apoB secretion. —Jiang, H., H. N. Ginsberg, and X. Wu. Glucose does not stimulate apolipoprotein B secretion from HepG2 cells because of insufficient stimulation of triglyceride synthesis. J. Lipid Res. 1998. 39: 2277–2285.

Highlights

We have previously demonstrated a close relationship between oleic acid (OA)-stimulated triglyceride (TG) synthesis and apolipoprotein B secretion in HepG2 cells
When compared to Bovine serum albumin (BSA) (1.5%) alone, 30 mm glucose treatment caused no we carried out a series of experiments to determine whether glucose stimulated TG synthesis in HepG2 cells
A time-dependent increase in [3H]TG synthesis was observed when HepG2 cells were incubated with 0.4 mm OA (P Ͻ 0.01, OA vs. BSA at every time point). [3H]TG secretion after 8 h labeling was not increased by glucose (Fig. 2B; P ϭ NS, glucose vs. BSA)

Summary

Introduction

We have previously demonstrated a close relationship between oleic acid (OA)-stimulated triglyceride (TG) synthesis and apolipoprotein B (apoB) secretion in HepG2 cells. We demonstrated that the failure of glucose to stimulate apoB secretion from HepG2 cells results from insufficient stimulation of TG synthesis by glucose. Additional studies demonstrated that glucose conversion to either glycerol or fatty acids was minimal; this accounted for the lack of stimulation of TG synthesis. We conclude that in HepG2 cells, availability of high glucose levels in the media for as long as 48 h does not stimulate triglyceride synthesis, and that this is the basis for the failure of glucose to stimulate apoB secretion.—Jiang, H., H. Wu. Glucose does not stimulate apolipoprotein B secretion from HepG2 cells because of insufficient stimulation of triglyceride synthesis.

Methods

Results

Conclusion