Background: This study focused on the effects of hemodialysis on the atherogenic properties of low density lipoprotein (LDL) in patients with end-stage renal disease (ESRD). The impact of cholesterol ester transfer protein (CETP) activity and lipolysis on LDL composition, particularly the changes during hemodialysis, was investigated.
Methods: Blood was drawn from 15 normotriglyceridemic (NTG) and 15 hypertriglyceridemic patients [HTG; triglycerides (TG) < 2.2 mmol/liter] before hemodialysis, during (1.5 hr after the beginning of anticoagulation) and at the end of treatment. In each sample, lipid values and CETP activity were measured. LDL was prepared and characterized by its components and diameters (2 to 16% PAGGE). To investigate the functional properties of LDL, fractions obtained from NTG and HTG patients were incubated with human skin fibroblasts and a cell line of murine macrophages (P388), and cholesterol ester formation rates were measured.
Results: In comparison to LDL from NTG patients at baseline, HTG-LDL were enriched in triglycerides (P < 0.02), depleted in cholesterol proportion (P < 0.01) and small in size (P < 0.001). These LDL induced the cholesterol esterification rates (50 micrograms/mL LDL-protein) in a twofold greater unsaturation in macrophages when compared to LDL from NTG patients (P < 0.04). The rates in fibroblasts were reduced by approximately half (P < 0.05). During hemodialysis, LDL were decreased in size (P < 0.001) and depleted in TG (P < 0.01), particularly in the hypertriglyceridemic state. Although CETP activity increased during hemodialysis (P < 0.001), the cholesterol content remained unchanged. When HTG-LDL obtained during hemodialysis were incubated with cells, esterification rates particularly in macrophages were markedly accelerated in comparison to the unmodified lipoprotein at baseline (P < 0.05).
Conclusion: LDL from HTG patients with ESRD was TG-enriched, CH-depleted and smaller in size. As the intracellular esterification rates induced by LDL were related to the cellular uptake, these LDL were a superior substrate for murine macrophages with the tendency of intracellular accumulation, and an inferior substrate for fibroblasts suggesting a decreased uptake by the specific receptor pathway. TG-depletion of LDL during hemodialysis, particularly in HTG patients due to a lipase-mediated TG-hydrolysis, increased these effects in macrophages. We suggest that the alterations of LDL that occur during repeated hemodialysis in vivo could contribute to the high prevalence of premature atherosclerosis found in HTG patients with ESRD.