Platelet-activating factor (PAF) increase intracellular lipid accumulation by increasing both LDL and scavenger receptors in human mesangial cells.

Intra- and extracellular lipid accumulation and the production of inflammatory mediators by renal and accessory cells may play an important role in the initiation and progression of these lesions. Platelet activating factor (PAF) is a biologically active phospholipid that is produced by various cells upon activation by different stimuli. It has been suggested that PAF plays a role in atherogenesis, and several studies indicated its participation in the pathogenesis of renal diseases. The aim of this study is to investigate the role of PAF on intracellular lipid accumulation and gene regulation of lipoprotein receptors in human mesangial cells (HMCs). A human mesangial cell line (HMC) was used to study the effects of PAF on foam cell formation by Oil red O staining and on the expression of LDLr, SR-AI, and PAF-R mRNA using RT-PCR. Native LDL caused foam cell formation in HMC in the presence of PAF. PAF enhanced LDLr expression and overrode LDL receptor suppression induced by a high concentration of LDL. Moreover, it enhanced SR-AI expression. PAF also caused increase in PAF-R expression. The above data suggest that PAF enhances its own receptor expression and then increases lipid accumulation by dysregulating LDL receptor regulation and inducing scavenger receptor expression in HMCs. These results suggest that PAF has a potential role in lipid mediated renal injury.

Intraperitoneal nitric oxide production in patients treated by continuous ambulatory peritonal 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-1beta, TNF-alpha and gamma-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 microM (nitrite and nitrate), and that from the overnight dwell 91 +/- 8 microM. During CAPD peritonitis, dialysate nitrite and nitrate increased from 9.3 +/-0.8 to 17.5 +/- 2.4 microM/l x 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 microM/l x 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.