Abstract
Hamster hepatocytes, like human hepatocytes, secrete triacylglycerol (TAG) as very-low-density lipoprotein (VLDL) in association with apolipoprotein (apo) B100, whereas in the rat, TAG is secreted predominantly in association with apoB48. Nevertheless, in hepatocytes from both species, a minimum of between 60% and 70% [69. 1+/-1.4% (hamster), 60.6+/-2.5% (rat)] of the VLDL TAG was secreted following lipolysis and re-esterification of intracellular TAG. The fractional rates of hepatocellular TAG turnover (lipolysis and re-esterification) were similar in both species [1.83+/-0.28 pools/24 h (hamster), 1.39+/-0.23 pools/24 h (rat)]. Comparison of the relative changes in the 3H and 14C specific radioactivities of the VLDL and cellular TAG, pre-labelled with [3H]glycerol and [4C]oleate, suggested that fatty acids released by lipolysis either were recruited directly into a VLDL assembly pool or were recycled to the cellular pool following re-esterification. Recycling in the hamster was somewhat greater than in the rat (66.1+/-5.7% versus 53. 7+/-4.8% of TAG lipolysed respectively). Similarly, a larger proportion of newly synthesized TAG was retained within the cell, rather than secreted as VLDL, in the hamster compared with the rat (37.9+/-2.8% versus 20+/-3.8%, P<0.01). These factors may have contributed to the somewhat lower rate of VLDL TAG secretion in the hamster hepatocytes compared with those from the rat (43.3+/-4.2 versus 96.4+/-3.4 microg/24 h per mg of cell protein). Rat hepatocytes were more sensitive to inhibition of VLDL secretion by insulin than were those from hamster. In neither case did insulin affect total or fractional TAG turnover. The results suggest that assembly of both apoB100 VLDL and apoB48 VLDL is associated with efficient intracellular TAG lipolysis.
Full Text
The Full Text of this article is available as a PDF (188.9 KB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Alexander C. A., Hamilton R. L., Havel R. J. Subcellular localization of B apoprotein of plasma lipoproteins in rat liver. J Cell Biol. 1976 May;69(2):241–263. doi: 10.1083/jcb.69.2.241. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Bartlett S. M., Gibbons G. F. Short- and longer-term regulation of very-low-density lipoprotein secretion by insulin, dexamethasone and lipogenic substrates in cultured hepatocytes. A biphasic effect of insulin. Biochem J. 1988 Jan 1;249(1):37–43. doi: 10.1042/bj2490037. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Borchardt R. A., Davis R. A. Intrahepatic assembly of very low density lipoproteins. Rate of transport out of the endoplasmic reticulum determines rate of secretion. J Biol Chem. 1987 Dec 5;262(34):16394–16402. [PubMed] [Google Scholar]
- Borén J., Rustaeus S., Olofsson S. O. Studies on the assembly of apolipoprotein B-100- and B-48-containing very low density lipoproteins in McA-RH7777 cells. J Biol Chem. 1994 Oct 14;269(41):25879–25888. [PubMed] [Google Scholar]
- Borén J., Wettesten M., Rustaeus S., Andersson M., Olofsson S. O. The assembly and secretion of apoB-100-containing lipoproteins. Biochem Soc Trans. 1993 May;21(2):487–493. doi: 10.1042/bst0210487. [DOI] [PubMed] [Google Scholar]
- Brown A. M., Baker P. W., Gibbons G. F. Changes in fatty acid metabolism in rat hepatocytes in response to dietary n-3 fatty acids are associated with changes in the intracellular metabolism and secretion of apolipoprotein B-48. J Lipid Res. 1997 Mar;38(3):469–481. [PubMed] [Google Scholar]
- Bruce J. S., Salter A. M. Metabolic fate of oleic acid, palmitic acid and stearic acid in cultured hamster hepatocytes. Biochem J. 1996 Jun 15;316(Pt 3):847–852. doi: 10.1042/bj3160847. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Cartwright I. J., Higgins J. A. Intracellular events in the assembly of very-low-density-lipoprotein lipids with apolipoprotein B in isolated rabbit hepatocytes. Biochem J. 1995 Sep 15;310(Pt 3):897–907. doi: 10.1042/bj3100897. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Coussons P. J., Bourgeois C. S., Wiggins D., Gibbons G. F. Selective recruitment of ApoB-48 for the assembly of VLDL in rat triacylglycerol-enriched hepatocytes. Arterioscler Thromb Vasc Biol. 1996 Jul;16(7):889–897. doi: 10.1161/01.atv.16.7.889. [DOI] [PubMed] [Google Scholar]
- Davis R. A., Boogaerts J. R., Borchardt R. A., Malone-McNeal M., Archambault-Schexnayder J. Intrahepatic assembly of very low density lipoproteins. Varied synthetic response of individual apolipoproteins to fasting. J Biol Chem. 1985 Nov 15;260(26):14137–14144. [PubMed] [Google Scholar]
- Dixon J. L., Ginsberg H. N. Regulation of hepatic secretion of apolipoprotein B-containing lipoproteins: information obtained from cultured liver cells. J Lipid Res. 1993 Feb;34(2):167–179. [PubMed] [Google Scholar]
- Duerden J. M., Bartlett S. M., Gibbons G. F. Long-term maintenance of high rates of very-low-density-lipoprotein secretion in hepatocyte cultures. A model for studying the direct effects of insulin and insulin deficiency in vitro. Biochem J. 1989 Nov 1;263(3):937–943. doi: 10.1042/bj2630937. [DOI] [PMC free article] [PubMed] [Google Scholar]
- FOLCH J., LEES M., SLOANE STANLEY G. H. A simple method for the isolation and purification of total lipides from animal tissues. J Biol Chem. 1957 May;226(1):497–509. [PubMed] [Google Scholar]
- Gibbons G. F. A comparison of in-vitro models to study hepatic lipid and lipoprotein metabolism. Curr Opin Lipidol. 1994 Jun;5(3):191–199. doi: 10.1097/00041433-199405030-00006. [DOI] [PubMed] [Google Scholar]
- Gibbons G. F., Bartlett S. M., Sparks C. E., Sparks J. D. Extracellular fatty acids are not utilized directly for the synthesis of very-low-density lipoprotein in primary cultures of rat hepatocytes. Biochem J. 1992 Nov 1;287(Pt 3):749–753. doi: 10.1042/bj2870749. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Gibbons G. F., Khurana R., Odwell A., Seelaender M. C. Lipid balance in HepG2 cells: active synthesis and impaired mobilization. J Lipid Res. 1994 Oct;35(10):1801–1808. [PubMed] [Google Scholar]
- Gibbons G. F., Wiggins D. Intracellular triacylglycerol lipase: its role in the assembly of hepatic very-low-density lipoprotein (VLDL). Adv Enzyme Regul. 1995;35:179–198. doi: 10.1016/0065-2571(94)00006-o. [DOI] [PubMed] [Google Scholar]
- Goldfarb S., Barber T. A., Pariza M. W., Pugh T. D. Lipid synthesis and ultrastructure of adult rat hepatocytes during their first twenty-four hours in culture. Exp Cell Res. 1978 Nov;117(1):39–46. doi: 10.1016/0014-4827(78)90425-1. [DOI] [PubMed] [Google Scholar]
- Gretch D. G., Sturley S. L., Wang L., Lipton B. A., Dunning A., Grunwald K. A., Wetterau J. R., Yao Z., Talmud P., Attie A. D. The amino terminus of apolipoprotein B is necessary but not sufficient for microsomal triglyceride transfer protein responsiveness. J Biol Chem. 1996 Apr 12;271(15):8682–8691. doi: 10.1074/jbc.271.15.8682. [DOI] [PubMed] [Google Scholar]
- Hoang V. Q., Pearce N. J., Suckling K. E., Botham K. M. Evaluation of cultured hamster hepatocytes as an experimental model for the study of very low density lipoprotein secretion. Biochim Biophys Acta. 1995 Jan 3;1254(1):37–44. doi: 10.1016/0005-2760(94)00160-z. [DOI] [PubMed] [Google Scholar]
- LOWRY O. H., ROSEBROUGH N. J., FARR A. L., RANDALL R. J. Protein measurement with the Folin phenol reagent. J Biol Chem. 1951 Nov;193(1):265–275. [PubMed] [Google Scholar]
- Leiper J. M., Bayliss J. D., Pease R. J., Brett D. J., Scott J., Shoulders C. C. Microsomal triglyceride transfer protein, the abetalipoproteinemia gene product, mediates the secretion of apolipoprotein B-containing lipoproteins from heterologous cells. J Biol Chem. 1994 Sep 2;269(35):21951–21954. [PubMed] [Google Scholar]
- Lewis G. F. Fatty acid regulation of very low density lipoprotein production. Curr Opin Lipidol. 1997 Jun;8(3):146–153. doi: 10.1097/00041433-199706000-00004. [DOI] [PubMed] [Google Scholar]
- Marsh J. B., Sparks C. E. The effect of fasting on the secretion of lipoproteins and two forms of apo B by perfused rat liver. Proc Soc Exp Biol Med. 1982 Jun;170(2):178–181. doi: 10.3181/00379727-170-41415. [DOI] [PubMed] [Google Scholar]
- Mayes P. A. Control of hepatic triacylglycerol metabolism. Biochem Soc Trans. 1976;4(4):575–580. doi: 10.1042/bst0040575. [DOI] [PubMed] [Google Scholar]
- McLeod R. S., Wang Y., Wang S., Rusiñol A., Links P., Yao Z. Apolipoprotein B sequence requirements for hepatic very low density lipoprotein assembly. Evidence that hydrophobic sequences within apolipoprotein B48 mediate lipid recruitment. J Biol Chem. 1996 Aug 2;271(31):18445–18455. doi: 10.1074/jbc.271.31.18445. [DOI] [PubMed] [Google Scholar]
- Michalopoulos G., Pitot H. C. Primary culture of parenchymal liver cells on collagen membranes. Morphological and biochemical observations. Exp Cell Res. 1975 Aug;94(1):70–78. doi: 10.1016/0014-4827(75)90532-7. [DOI] [PubMed] [Google Scholar]
- Ontko J. A., Cheng Q., Yamamoto M. Metabolic factors underlying high serum triglycerides in the normal hamster. J Lipid Res. 1990 Nov;31(11):1983–1992. [PubMed] [Google Scholar]
- Owen M. R., Corstorphine C. C., Zammit V. A. Overt and latent activities of diacylglycerol acytransferase in rat liver microsomes: possible roles in very-low-density lipoprotein triacylglycerol secretion. Biochem J. 1997 Apr 1;323(Pt 1):17–21. doi: 10.1042/bj3230017. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Patel S. B., Grundy S. M. Interactions between microsomal triglyceride transfer protein and apolipoprotein B within the endoplasmic reticulum in a heterologous expression system. J Biol Chem. 1996 Aug 2;271(31):18686–18694. doi: 10.1074/jbc.271.31.18686. [DOI] [PubMed] [Google Scholar]
- Patsch W., Gotto A. M., Jr, Patsch J. R. Effects of insulin on lipoprotein secretion in rat hepatocyte cultures. The role of the insulin receptor. J Biol Chem. 1986 Jul 25;261(21):9603–9606. [PubMed] [Google Scholar]
- Pease R. J., Leiper J. M. Regulation of hepatic apolipoprotein-B-containing lipoprotein secretion. Curr Opin Lipidol. 1996 Jun;7(3):132–138. doi: 10.1097/00041433-199606000-00004. [DOI] [PubMed] [Google Scholar]
- Rusiñol A., Verkade H., Vance J. E. Assembly of rat hepatic very low density lipoproteins in the endoplasmic reticulum. J Biol Chem. 1993 Feb 15;268(5):3555–3562. [PubMed] [Google Scholar]
- Rustaeus S., Lindberg K., Borén J., Olofsson S. O. Brefeldin A reversibly inhibits the assembly of apoB containing lipoproteins in McA-RH7777 cells. J Biol Chem. 1995 Dec 1;270(48):28879–28886. doi: 10.1074/jbc.270.48.28879. [DOI] [PubMed] [Google Scholar]
- Sessions V. A., Salter A. M. Low density lipoprotein binding to monolayer cultures of hepatocytes isolated from hamsters fed different dietary fatty acids. Biochim Biophys Acta. 1995 Aug 24;1258(1):61–69. doi: 10.1016/0005-2760(95)00081-m. [DOI] [PubMed] [Google Scholar]
- Sharp D., Blinderman L., Combs K. A., Kienzle B., Ricci B., Wager-Smith K., Gil C. M., Turck C. W., Bouma M. E., Rader D. J. Cloning and gene defects in microsomal triglyceride transfer protein associated with abetalipoproteinaemia. Nature. 1993 Sep 2;365(6441):65–69. doi: 10.1038/365065a0. [DOI] [PubMed] [Google Scholar]
- Sparks J. D., Sparks C. E. Insulin modulation of hepatic synthesis and secretion of apolipoprotein B by rat hepatocytes. J Biol Chem. 1990 May 25;265(15):8854–8862. [PubMed] [Google Scholar]
- Sparks J. D., Sparks C. E. Insulin regulation of triacylglycerol-rich lipoprotein synthesis and secretion. Biochim Biophys Acta. 1994 Nov 17;1215(1-2):9–32. doi: 10.1016/0005-2760(94)90088-4. [DOI] [PubMed] [Google Scholar]
- Swift L. L. Assembly of very low density lipoproteins in rat liver: a study of nascent particles recovered from the rough endoplasmic reticulum. J Lipid Res. 1995 Mar;36(3):395–406. [PubMed] [Google Scholar]
- Van Harken D. R., Dixon C. W., Heimberg M. Hepatic lipid metabolism in experimental diabetes. V. The effect of concentration of oleate on metabolism of triglycerides and on ketogenesis. J Biol Chem. 1969 May 10;244(9):2278–2285. [PubMed] [Google Scholar]
- Wang C. N., Hobman T. C., Brindley D. N. Degradation of apolipoprotein B in cultured rat hepatocytes occurs in a post-endoplasmic reticulum compartment. J Biol Chem. 1995 Oct 20;270(42):24924–24931. doi: 10.1074/jbc.270.42.24924. [DOI] [PubMed] [Google Scholar]
- Wiggins D., Gibbons G. F. Origin of hepatic very-low-density lipoprotein triacylglycerol: the contribution of cellular phospholipid. Biochem J. 1996 Dec 1;320(Pt 2):673–679. doi: 10.1042/bj3200673. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Wiggins D., Gibbons G. F. The lipolysis/esterification cycle of hepatic triacylglycerol. Its role in the secretion of very-low-density lipoprotein and its response to hormones and sulphonylureas. Biochem J. 1992 Jun 1;284(Pt 2):457–462. doi: 10.1042/bj2840457. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Wu X., Shang A., Jiang H., Ginsberg H. N. Low rates of apoB secretion from HepG2 cells result from reduced delivery of newly synthesized triglyceride to a "secretion-coupled" pool. J Lipid Res. 1996 Jun;37(6):1198–1206. [PubMed] [Google Scholar]
- Yang L. Y., Kuksis A., Myher J. J. Biosynthesis of chylomicron triacylglycerols by rats fed glyceryl or alkyl esters of menhaden oil fatty acids. J Lipid Res. 1995 May;36(5):1046–1057. [PubMed] [Google Scholar]
- Yang L. Y., Kuksis A., Myher J. J., Steiner G. Contribution of de novo fatty acid synthesis to very low density lipoprotein triacylglycerols: evidence from mass isotopomer distribution analysis of fatty acids synthesized from [2H6]ethanol. J Lipid Res. 1996 Feb;37(2):262–274. [PubMed] [Google Scholar]
- Yang L. Y., Kuksis A., Myher J. J., Steiner G. Origin of triacylglycerol moiety of plasma very low density lipoproteins in the rat: structural studies. J Lipid Res. 1995 Jan;36(1):125–136. [PubMed] [Google Scholar]
- Yao Z., Tran K., McLeod R. S. Intracellular degradation of newly synthesized apolipoprotein B. J Lipid Res. 1997 Oct;38(10):1937–1953. [PubMed] [Google Scholar]