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Modulation of lipoprotein lipase activity by apolipoproteins. Effect of apolipoprotein C-III.
From a total of 22 hypertriglyceridemic subjects tested, 14 subjects were selected on the basis of normal postheparin plasma lipoprotein lipase ( LPL) levels and the presence of LPL inhibitory activity in their fasting plasma. The inhibitory activity was detected in both the lipoprotein fraction (d less than 1.25 g/ml) and the lipoprotein-deficient fraction (d greater than 1.25 g/ml). Correlational analyses of LPL inhibitory activity and apolipoprotein levels present in the lipoprotein fraction (d less than 1.25 g/ml) indicated that only apolipoprotein C-III ( ApoC-III) was significantly correlated (r = 0.602, P less than 0.05) with the inhibition activity of the lipoprotein fraction. Furthermore, it was found that LPL-inhibitory activities of the plasma lipoprotein fraction and lipoprotein-deficient fraction were also correlated (r = 0.745, P less than 0.005), though the activity in the lipoprotein-deficient plasma was not related to the ApoC-III or apolipoprotein E levels. Additional correlational analyses indicated that the LPL levels in the postheparin plasma of these subjects were inversely related to the levels of plasma apolipoproteins C-II, C-III, and E. To explain some of these observations, we directly examined the in vitro effect of ApoC-III on LPL activity. The addition of ApoC-III-2 resulted in a decreased rate of lipolysis of human very low density lipoproteins by LPL. Kinetic analyses indicated that ApoC-III-2 was a noncompetitive inhibitor of LPL suggesting a direct interaction of the inhibitor with LPL. Results of these studies suggest that ApoC-III may represent a physiologic modulator of LPL activity levels and that the incidence of LPL inhibitory activity in the plasma of hypertriglyceridemic subjects is more common than previously recognized.[1]References
- Modulation of lipoprotein lipase activity by apolipoproteins. Effect of apolipoprotein C-III. Wang, C.S., McConathy, W.J., Kloer, H.U., Alaupovic, P. J. Clin. Invest. (1985)
