Ray L. Fernando

Differential ability of cells to promote oxidation of low density lipoproteins in vitro

Atherosclerosis and focal segmental glomerulosclerosis share some common histological features and it is speculated that they result from similar pathobiological mechanisms. There is strong evidence that oxidation of low density lipoprotein (LDL) may be an initiating event in atherogenesis and that oxidised LDL may also be involved in the glomerulosclerotic process. In vitro studies have demonstrated that cells present in the arterial intima and kidney-derived cells promote LDL oxidation. The aim of this study was to compare LDL oxidation by kidney-derived human mesangial cells and proximal tubular cells, with human umbilical vein endothelial cells and the human monocyte cell line THP-1. We used the thiobarbituric acid assay and agarose gel electrophoresis to measure the extent of LDL oxidation. Our results demonstrate that all of the cell types used had the ability to oxidise LDL significantly more than cell-free controls and that endothelial cells induced the highest degree of oxidative modification of LDL under our experimental conditions.

Intraperitoneal Nitric Oxide Production in Patients Treated by Continuous Ambulatory Peritoneal Dialysis

Background: Nitric oxide (NO) generation within the peritoneum could potentially affect peritoneal transport by increasing capillary vasodilatation, and increase peritoneal permeability during episodes of bacterial peritonitis. As peritoneal mesothelial cells have a common embryological derivation with endothelial cells, then mesothelial cells could potentially be a major source of locally produced NO. Methods: NO was measured using the Griess reaction in fresh and spent dialysate effluent (SPDE) from uninfected CAPD patients, and from those during episodes of bacterial peritonitis. Human peritoneal mesothelial cells (HPMC) were cultured and NO production determined in the presence of SPDE and the effect of a potential NO substrate, L-arginine, and NO synthase inhibitor, L-NMMA. NO production by peritoneal macrophages (MØ), obtained from SPDE and the effect of staphylococci was also determined. RNA for inducible nitric oxide synthase (iNOS) was sought using Northern blotting technique following combination stimulation with lipopolysaccharide and cytokines (IL-1β, TNF-α and γ-INF, and/or spent dialysate from patients with bacterial peritonitis). Results: Whereas fresh CAPD dialysate was nitrite-free, SPDE from the day time exchange contained 41 ± 3 µM (nitrite and nitrate), and that from the overnight dwell 91 ± 8 µM. During CAPD peritonitis, dialysate nitrite and nitrate increased from 9.3 ±0.8 to 17.5 ± 2.4 µM/l·h, for the first CAPD bag at presentation, and 15.2 ± 1.8 for the second and 16.2 ± 2.4 for the third exchange (p < 0.01 compared to non-infected control). By the second day, levels had returned to baseline, 7.3 ± 0.9 µM/l·h. HPMC produced 261 nmol nitrate and nitrite/mg cell protein, and this increased in a dose-dependent manner with the addition of spent uninfected CAPD dialysate, to 365 nmol/mg with 1:10 dilution and 655 nmol/mg with 1:2 dilution, p < 0.001. The addition of the substrate, L-arginine, resulted in a 10% increase in nitrite and nitrate production, whereas the addition of L-NMMA produced a 10% reduction. Peritoneal MØ obtained from SPDE produced similar quantities of nitrite and nitrate to peritoneal mesothelial cells, and cultures of Staphylococcus aureus resulted in a reduction in nitrite and nitrate levels, as they were used as a growth requirement. However, we could not demonstrate RNA production for iNOS by HPMC following cytokine or SPDE stimulation. Conclusions: This suggests that HPMC may be an important source of locally generated NO within the peritoneal cavity under basal conditions, but as they do not contain iNOS, the increased NO produced during episodes of acute bacterial peritonitis is more likely due to a combination of increased NO production by peritoneal endothelial cells and transmigrating macrophages.

Do glomerular atherosclerosis and lipid-mediated tubulo-interstitial disease cause progressive renal failure in man ?

The nephrotic syndrome presents the kidney with a new environment in which blood vessels, glomerular structures and tubules are exposed over substantial periods of time to lipoproteins. LDL has charge affinity with glomerular basement membrane glycosaminoglycans, so potentially increases or maintains albumin loss. This in turn stimulates LDL synthesis. HDL is small enough to be passed by the glomerular filter in substantial amounts and has been found to stimulate endothelin-1 production by human proximal tubular cells in culture. LDL also inhibits nitric oxide vasodilatory responses, an action which when added to that of endothelin-1 may result in decreased renal tissue oxygenation. Taken together, these aspects of the nephrotic syndrome broaden conventional definitions of atherosclerosis and offer a number of targets for therapy in progressive renal disease.