Role of Lipoprotein-Bound NEFAs in Enhancing the Specific Activity of Plasma CETP in the Nephrotic Syndrome

Abstract

Abstract Plasma cholesteryl ester transfer protein (CETP) activity, evaluated by the transfer of radiolabeled cholesteryl esters from a tracer dose of tritiated HDL to the plasma apolipoprotein B–containing lipoproteins, was significantly higher in patients with untreated idiopathic nephrotic syndrome (n=15) than in normolipidemic control subjects (n=22) (81.5±8.4 versus 43.1±3.1 μg CE · mL −1 · h −1 , respectively; P <.001). The increased CETP activity in nephrotic plasma was explained by a significant rise in both the CETP mass concentration (3.2±0.2 versus 2.1±0.1 mg/L; P <.001), and the specific CETP activity, calculated as the ratio of CETP activity to CETP mass (25.3±1.7 versus 20.4±1.6 μg CE · mg −1 · h −1 ; P <.05). Elevated CETP activity in nephrotic patients was shown to be associated with a significant decrease in the mean size of LDL (24.4±0.5 versus 26.3±0.5 nm; P <.0001) as well as in the relative abundance of HDL 2a (29.6±1.6% versus 34.8±1.1%; P <.05). The nephrotic syndrome was characterized by a significant increase in the relative proportion of lipoprotein-bound nonesterified fatty acids (NEFAs) (35.4±7.7% versus 7.6±3.0% of total; P <.01), leading to a significant increase in the electronegative charge of LDL (−4.3±0.1 versus −3.9±0.1 mV; P <.05) and HDL (−11.5±0.1 versus −11.1±0.2 mV; P <.05). Compared with native, nonsupplemented plasma, removal of lipoprotein-bound NEFAs by addition of fatty acid–poor albumin to total plasma from nephrotic patients or control subjects significantly decreased CETP activity and specific CETP activity. Specific CETP activity no longer differed between nephrotic and control groups after albumin supplementation (19.7±1.5 versus 17.7±1.5 μg CE · mg −1 · h −1 ; NS). It is concluded that, in addition to elevated CETP mass concentration, lipoprotein-bound NEFAs, by increasing the negative electrostatic charge of nephrotic lipoproteins, can facilitate the CETP-mediated neutral-lipid transfer reaction in total plasma from nephrotic patients.