Oxygen-dependent injury by a human plasma factor associated with minimal change disease

The mechanism by which a human plasma factor associated with proteinuria is able to cause experimental glomerular albumin leakage is unknown. This factor (called 100KF) is able to induce glomerular alterations in the rat kidney, similar to those seen in minimal change disease, including loss of glomerular sialoglycoproteins and decreased expression of glomerular ecto-ATPase. It was previously shown that 100KF is able to stimulate release of reactive oxygen species in inflammatory cells in vitro. This prompted us to test whether 100KF-induced injury is oxygen dependent. The expression of glomerular sialoglycoproteins and ecto-ATPase was evaluated by standard histochemistry and computerized image analysis and expressed in arbitrary units. Rat kidney sections were incubated with or without 100KF under normal or oxygen-poor, i.e., nitrogen, conditions, or with supplementation of superoxide dismutase (SOD, 100 U/ml). The effect of 100KF on glomerular ecto-ATPase was oxygen dependent (32.98+/-2.14 under air vs. 65.20+/-5.53 under nitrogen, P less than or equal to 0.01), in contrast to the 100KF-induced loss of glomerular sialoglycoproteins that was not significantly altered under nitrogen (62.67+/-10.08 under air vs. 61.74+/-26.05 under nitrogen). Supplementation of SOD to 100KF solution under normal incubation conditions also suggested oxygen-dependent impairment of glomerular ecto-ATPase. Alternate perfusion ex vivo of the rat kidney with 100KF followed by diluted plasma showed that enhanced leakage of plasma proteins could be inhibited with SOD, indicating oxygen dependency of this 100KF-induced enhanced permeability (60.25+/-19.32 mu g urinary albumin/ml after 100KF perfusion vs. 25.23+/-12.05 mu g/ml after 100KF plus SOD, P less than or equal to 0.01). We conclude that the action of 100KF upon specific glomerular matrix molecules is oxygen dependent, as is the albumin leakage induced by 100KF in the present ex vivo model

INTRAGLOMERULAR THROMBOTIC TENDENCY AND GLOMERULAR ADPASE - UNILATERAL IMPAIRMENT OF ADPASE ELICITS A PROAGGREGATORY MICROENVIRONMENT IN EXPERIMENTAL GLOMERULONEPHRITIS

It has been proposed, predominantly from ex vivo studies, that glomerular ADPase may function as an antithrombotic principle within the rat kidney. Therefore, intraglomerular platelet aggregation was studied in vivo in rats after impairment of glomerular ADPase activity using local X-irradiation (20 Gy). Biochemical assays in suspensions of glomeruli obtained from rats 24 hours after local X-irradiation (group I) demonstrated a significant reduction in ADPase activity as compared to sham treated rats (group II; p <0.01). Cytochemical observations at the ultrastructural level showed that this reduction in glomerular enzyme activity represents in particular ADPase activity detectable in the basement membrane. Following X-irradiation, intraglomerular platelet aggregation was quantitatively studied in two groups of rats. Both groups received X-irradiation of the left kidney (20 Gy). Twenty-four hours after X-irradiation, animals received an intravenous injection of either 0.5 ml of saline (group III; N = 6) or 0.5 ml of heterologous nephrotoxic serum (NTS; group IV; N = 6). Subsequently, 24 hours after this injection, platelet aggregation in left kidneys was compared with aggregation in contralateral non-X-irradiated kidneys. The results showed that while X-irradiation per se did not induce intraglomerular platelet aggregation as compared with the contralateral kidney (0.20 +/- 0.08% versus 0.17 +/- 0.06% platelet aggregation/glomerulus), a significant increase in platelet aggregation could be demonstrated in X-irradiated kidneys in the early phase of nephrotoxic serum nephritis as compared with the contralateral nephritic kidney (2.45 +/- 0.66% versus 1.37 +/- 0.35% platelet aggregation per glomerulus; p <0.005). A potential effect of altered influx of inflammatory cells after X-irradiation could be excluded since no difference in H2O2 producing cells was observed between left and right kidneys. Thus, while ADPase impairment by X-irradiation does not induce platelet aggregation per se, it is clear that in proaggregatory conditions, like in NTS nephritis, the thrombotic tendency, due to decreased glomerular ADPase, is enhanced. These results demonstrate the functional significance of glomerular ADPase activity as an antithrombotic principle following platelet activation in vivo