Apo B variant composition of triglyceride-rich lipoproteins (TRL) has an influence on the catabolic fate of the lipoprotein (Lp) particle. Although differences in apo BH (higher Mr apo B) and apo BL (lower Mr apo B) metabolism have been reported, reasons for the heterogeneity remain to be explored. Receptor-mediated Lp removal has been studied extensively and recent evidence suggests that apo BL does not interact with the chylomicron (CM) remnant receptor pathway in the liver. Thus, reasons for heterogenous apo B metabolism probably occur prior to receptor events and are a property of particles. Rats, in contrast to rabbits and humans, have both apo B variants in hepatically synthesized TRL. TRL modification by lipases (lipoprotein lipase and/or hepatic lipase) is necessary before preferential hepatic apo BL clearance is observed. Other factors which determine Lp clearance include apo C composition, apo CIII:CII ratio, apo E content, triglyceride vs. cholesterol ester content, physical size, and metabolic state. What is not known is how these events alter Lp structure in a way as to affect the subsequent catabolic fate of the Lp. The hypothesis to be tested is that observed heterogeneous metabolism of apo B-containing Lps relates to apo B expression which in turn is influenced by particle lipid and apoprotein composition. Study of hepatic clearance of Lp apo B is proposed stressing pre-receptor events (synthetic and lipolytic) which alter Lp composition. Favorable apoprotein composition for hepatic clearance of Lps will be determined and will be related to hepatic clearance pathways. We have developed monoclonal antibodies (mAbs) to rat apoproteins which will be used to isolate subpopulations of Lps of unique epitope composition for catabolic studies. Other mAbs will also be used in sensitive immunoassays for conformational epitopes present on Lps to allow development of two site assays in order to determine other apo B epitopes and apoprotein epitopes present on particles. Proposed experiments will continue studies of apo B turnover in vivo and in liver perfusion. Models of altered metabolic circumstances will include the streptozotocin diabetic, PAN-nephrotic and cholesterol-fed rat and we will extend catabolic studies to primary rat and rabbit hepatocyte cultures. Particle composition of apo B Lps is seen as critical to hepatic clearance. Studies assume importance considering the relationship of apo B-Lps as positive risk factors in atherogenesis.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL029837-06
Application #
3340891
Study Section
Metabolism Study Section (MET)
Project Start
1983-04-01
Project End
1990-03-31
Budget Start
1988-07-01
Budget End
1990-03-31
Support Year
6
Fiscal Year
1988
Total Cost
Indirect Cost
Name
University of Rochester
Department
Type
School of Medicine & Dentistry
DUNS #
208469486
City
Rochester
State
NY
Country
United States
Zip Code
14627
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Sparks, J D; Phung, T L; Bolognino, M et al. (1998) Lipoprotein alterations in 10- and 20-week-old Zucker diabetic fatty rats: hyperinsulinemic versus insulinopenic hyperglycemia. Metabolism 47:1315-24
Van Mater, D; Sowden, M P; Cianci, J et al. (1998) Ethanol increases apolipoprotein B mRNA editing in rat primary hepatocytes and McArdle cells. Biochem Biophys Res Commun 252:334-9
Sparks, J D; Collins, H L; Sabio, I et al. (1997) Effects of fatty acids on apolipoprotein B secretion by McArdle RH-7777 rat hepatoma cells. Biochim Biophys Acta 1347:51-61
Phung, T L; Mooney, R A; Kulas, D T et al. (1997) Suppression of the protein tyrosine phosphatase LAR reduces apolipoprotein B secretion by McA-RH7777 rat hepatoma cells. Biochem Biophys Res Commun 237:367-71
Phung, T L; Roncone, A; Jensen, K L et al. (1997) Phosphoinositide 3-kinase activity is necessary for insulin-dependent inhibition of apolipoprotein B secretion by rat hepatocytes and localizes to the endoplasmic reticulum. J Biol Chem 272:30693-702
Schock, D; Kuo, S R; Steinburg, M F et al. (1996) An auxiliary factor containing a 240-kDa protein complex is involved in apolipoprotein B RNA editing. Proc Natl Acad Sci U S A 93:1097-102
Sparks, J D; Phung, T L; Bolognino, M et al. (1996) Insulin-mediated inhibition of apolipoprotein B secretion requires an intracellular trafficking event and phosphatidylinositol 3-kinase activation: studies with brefeldin A and wortmannin in primary cultures of rat hepatocytes. Biochem J 313 ( Pt 2):567-74
Phung, T L; Sowden, M P; Sparks, J D et al. (1996) Regulation of hepatic apolipoprotein B RNA editing in the genetically obese Zucker rat. Metabolism 45:1056-8
Sparks, J D; Sparks, C E (1996) Chromatographic method for isolation and quantification of apolipoproteins B-100 and B-48. Methods Enzymol 263:104-20

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