Abstract 18085: Heparan Sulfate Proteoglycans Only Modestly Affect Postprandial Hepatic Remnant Clearance in Humans

Abstract

Introduction and Methods: Elevated circulating levels of Triglyceride-rich Remnant Lipoproteins (TLR) are strongly associated with increased risk for CVD. The hepatic clearance of TRL involves lipoprotein receptors i.e. the low-density lipoprotein receptor (LDLr) and heparin sulfate proteoglycans (HSPG). The relevance of each pathway in humans remains to be established. To further dissect the relative contribution of each of these receptors, we studied postprandial TRL metabolism with an oral fat tolerance test using cream supplemented with retinyl palmitate (RP) in 1) patients with a heterozygous loss-of-function (LOF) variant in LDLR stratified for a low (n=10) or high (n=10) HSPG gene score; 2) patients with heterozygous LOF variants in EXT1 or EXT2 (n=13), characterised by decreased HSPG chains length but normal sulfation pattern, and compared to matched healthy controls (n=13) and 3) diabetic patients (n=29) stratified for a functional SNP in SULF2, that predisposes to lower SULF2 expression and increased 6-O-sulfation of HSPG chains. Results: Postprandial TRL clearance was significantly delayed in patients with FH compared to controls (AUC-RP FH: 1971±190 vs Con: 646±110 nmol/l/h;P<0.0001 and iAUC-TG FH 6.9±1.0 vs Con 3.8±10 mmol/l/h, P<0.05) supporting the important role of LDLr in TRL clearance. No additional effect was observed if the FH group was stratified for HSPG gene score. Also, in patients with LOF variants in EXT, resulting in shorter HSPG chains, no difference in TRL clearance versus controls could be observed. In contrast, improved 6-O-sulfation due to lower hepatic protein expression of SULF2 resulted in improved fasting and postprandial TG levels and significantly lower iAUC-RP (iAUC-TG AA 6.9±1.1 vs GG 4.1±1.2 mmol/l/h P<0.05; AUC-RP AA 97±15 vs GG 15±2 mg/l/h; P<0.001) Conclusion: Our findings clearly indicate an important role for the LDLr in postprandial TRL clearance in humans. In contrast to murine studies, HSPGs do only modestly contribute to hepatic TRL clearance in humans, and implicate that sulfation of HSPG’s is of more relevance for TRL clearance than HSPG chain length.