Very-low-density lipoprotein subfraction composition and metabolism by adipose tissue☆

Abstract 

Lipoprotein lipase (LPL) plays a pivotal role in very—low-density lipoprotein (VLDL) metabolism. Within the circulation, the VLDL population is heterogeneous with respect to both size and composition. Several studies have investigated the action of LPL in vitro on different VLDL subfractions, but little is known of the action of LPL in vivo. To investigate this, arterial and adipose tissue venous plasma samples were obtained from 16 normal male healthy volunteers (aged 24.4 ± 1.8 years; body mass index, 23.5 ± 0.7 kg · m⁻²) following an overnight fast. VLDL subfractions were isolated (VLDL₁ of S_f 60 to 400 and VLDL₂ of S_f 20 to 60) and characterized in terms of triacylglycerol (TAG) and apolipoprotein (apo) B, E, CI, CII, and CIII content. The apolipoprotein content of VLDL₁ differed from that of VLDL₂: the VLDL₂ fraction contained significantly more apo B (0.018 ± 0.004 v 0.011 ± 0.003 μmol · L⁻¹, P = .001) but the ratios of TAG:apo B and apo CI:B, CII:B, and CIII:B were significantly higher in VLDL₁ (48,200 ± 7,960 v 13,860 ± 2,420, 22.7 ± 5.5 v 12.5 ± 2.2, 45.0 ± 6.3 v 14.9 ± 2.0, and 0.434 ± 0.077 v 0.357 ± 0.054, respectively, molar ratios, all P < .05). The venous blood draining an adipose tissue depot contained less VLDL₁-TAG than arterial blood (328 ± 68 v 381 ± 83 μmol · L⁻¹, respectively, P < .01), whereas VLDL₂-TAG exhibited an opposite tendency (199 ± 46 v 172 ± 31 μmol · L⁻¹, NS). Concentrations of VLDL₁-apo B, -apo CII, and -apo CIII were significantly less in adipose tissue venous blood compared with arterial blood (0.011 ± 0.004 v 0.013 ± 0.004, 0.38 ± 0.08 v 0.43 ± 0.10, and 1.33 ± 0.35 v 1.58 ± 0.38 μmol · L⁻¹, respectively, all P < .05). These studies demonstrated novel differences in VLDL₁ and VLDL₂ in terms of composition and metabolism by human adipose tissue LPL in vivo.

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