Lipoprotein receptor mediated metabolism of [14C]arachidonic acid labeled chylomicron remnants by Hep G2 cells

During lipolysis of chylomicron triacylglycerol by lipoprotein lipase, arachidonic acid (AA) esters are hydrolyzed at a slower rate than the predominant 16–18 carbon fatty acid esters. The further metabolism of the AA that is hereby enriched in the chylomicron remnant acylglycerols has not been investigated. In the present study, we examined the low density lipoprotein (LDL) dependent and independent metabolism of ¹⁴C]AA present in chylomicron remnants in the human hepatoma cell line Hep G2. Mesenteric duct cannulated rats were fed ¹⁴C]AA and ³H]cholesterol in corn oil, and the chyle obtained was injected intravenously into hepatectomized rats to form chylomicron remnants labeled with ¹⁴C]AA in the triacylglycerol (TG) and with³H in the cholesteryl ester portion. The remnants were then incubated with Hep G2 cells. The uptake of ¹⁴C]AA within 2–4 h was similar to that of ³H]cholesteryl ester. After uptake into the cells, ¹⁴C]AA was preferentially incorporated into phospholipids, a high proportion being found in phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol. ¹⁴C]AA and ³H]cholesteryl ester uptake were influenced to similar extents by factors unknown to regulate the LDL receptor and by an anti-LDL receptor antibody. Addition of compactin thus increased the uptake of ¹⁴C]AA by 50% in 4 h and mevalonolactone decreased the uptake by 86%. Using an anti-LDL receptor antibody, 25.0% of ³H]cholesterol/cholesteryl ester and 37.7% of ¹⁴C]AA binding to the cells at 4°C were blocked. There was no lipolysis of ¹⁴C]TG or ¹⁴C]diacylglycerol by lipase secreted into the medium during incubations. The study shows that after the uptake of chylomicron remnants by Hep G2 cells, which in part occursvia the LDL receptor, AA is liberated from the acylglycerols and is preferentially incorporated into phospholipids.