Lipids and progression of renal disease: role of modified low density lipoprotein and lipoprotein(a).

Atherogenic lipoproteins accumulate in the arterial wall as well as within the glomerulus and may accelerate vascular and glomerular injury. We therefore assessed whether oxidized low density lipoprotein (LDL) and lipoprotein(a) [Lp(a)] influence three major systems: (i) endothelium-dependent vasodilation, (ii) renin release of juxtaglomerular (JG) cells, and (iii) proliferation and viability of mesangial cells (MC). Lipoproteins were prepared from human plasma. Renal arteries were obtained from rabbits and JG as well as MC cells from mouse, rat and human kidneys. Dilator responses were detected in isolated arterial segments by a photoelectric device. Renin activity of JG cells was measured in culture supernatants and cells and DNA synthesis by 3H-thymidine incorporation in MC. Acetylcholine-induced, endothelium-dependent dilator responses of renal arteries were not significantly attenuated after incubation with native Lp(a). However, exposure to in vitro oxidized Lp(a) suppressed dilator responses in a dose-dependent manner. Using a chemiluminescence assay, we could detect increased O2- production by arteries pretreated with oxidized Lp(a), which suggested that enhanced nitric oxide (NO) inactivation by O2- might be the underlying mechanism of impairment of endothelium-dependent dilations. In general, oxidized Lp(a) was far more potent than oxidized LDL in this effect. In JG cells, both oxidized LDL and Lp(a) dose-dependently stimulated renin release. Coincubation with HDL significantly suppressed oxidized LDL and Lp(a) stimulated renin release and O2- production. In MC native and oxidized Lp(a) were poor ligands for the LDL receptor, but bound more tightly to extracellular matrix than native LDL. Native and oxidized Lp(a) elicited proliferation or toxicity of MC in a dose-dependent fashion. Stimulation of DNA synthesis in MC or renin release in JG cells was partly blunted or eliminated when cells were incubated with oxidized LDL and Lp(a) in the presence of superoxide dismutase and catalase, enzymes removing O2- and H2O2. These dat suggest a common underlying mechanism. Atherogenic lipoproteins induce formation of oxygen radicals not only in arteries, but also in glomeruli and JG cells, causing an inhibition of nitric oxide mediated vasodilation, stimulation of renin release, and modulation of mesangial cell growth and proliferation. The damaging effect of the lipoproteins can be prevented by antioxidative enzymes and HDL.