The role of platelets in progressive glomerulosclerosis: mechanisms for intraglomerular platelet activation and pathogenetic consequences

Haemolytic uraemic syndrome is an immune-mediated disease: role of anti-CD36 antibodies

Haemolytic uraemic syndrome (HUS) is a disorder in which platelet microthrombi are formed that have a particular propensity to deposit in the kidney microvasculature, resulting in impaired renal function and thrombocytopenia. The mechanism of formation of these microthrombi is not known. In this study, we showed that plasma from five adult and six paediatric cases of HUS caused aggregation and release of adenosine triphosphate from normal platelets. The plasma reacted against platelet lysate in a protein blot and all samples showed reactivity against a band at 88 kDa, corresponding to the membrane antigen CD36. This was confirmed by probing with Mo91, a monoclonal antibody to CD36. CD36 was also identified in the immune complex formed by incubation of patient plasmas with normal platelet lysate. In other studies, bands of 32 and 7.7 kDa were obtained when purified verotoxin was protein blotted and probed with either patient plasma or with anti-CD36 antibody Mo91 suggesting structural homologies between CD36 and verotoxin. While a direct cause-effect relationship is not yet established, the data support the concept of an immunological pathogenesis for HUS and suggest that molecular mimicry involving one or both of the homologous domains in membrane-bound CD36 and verotoxin lead to the development of antibodies capable of inducing the pathophysiological events characteristic of HUS.

Role of interstitial ATP and adenosine in the regulation of renal hemodynamics and microvascular function

The role of adenosine in the regulation of renal hemodynamics and function has been studied extensively; however, another purine agent, ATP, is also gaining recognition for its paracrine role in the kidney. Adenosine and ATP bind to specific membrane-bound P1 and P2 purinoceptors, respectively, and initiate a variety of biological effects on renal microvascular tone, mesangial cell function, and renal epithelial transport. The purpose of this review is to summarize the potential roles of interstitial ATP and adenosine as regulators of renal hemodynamics and microcirculation. In vitro blood-perfused juxtamedullary nephron preparation was used to assess the roles of ATP and adenosine in the regulation of renal microvascular tone. This approach mimics the adventitial exposure of renal microvascular smooth muscle to ATP and adenosine synthesized locally and released into the interstitial fluid. ATP selectively vasoconstricts afferent but not efferent arterioles via P2X and P2Y receptors, whereas, adenosine vasoconstricts both vascular segments via activation of adenosine A(1) receptors. Furthermore, selective P2X and P2Y receptor stimulation increases intracellular calcium concentration in vascular smooth muscle cells that are freshly isolated from the preglomerular microvasculature. These data support the hypothesis that interstitial ATP plays a critical role in the control of renal microvascular function through mechanisms that are independent of adenosine receptors. We have recently developed a renal microdialysis method to determine the dynamics of ATP and adenosine levels in the renal cortical interstitium. In this review, we also summarize current knowledge pertaining to the alterations in renal interstitial ATP and adenosine in some pathophysiological conditions.

Role of ticlopidine on adriamycin-induced nephropathy

The effect of ticlopidine on rats with adriamycin nephropathy was observed during 26 weeks. In the ticlopidine-treated nephrotic animals (TNG), proteinuria was less than in the untreated nephrotic animals (NG), but this difference was significant only at week 6 (TNG = 47.27 +/- 16.52 versus NG = 100.08 +/- 13.83 mg/24 h, p < 0.01) and week 26 (TNG = 157.00 +/- 28.73 versus NG = 217.00 +/- 21.73 mg/24 h, p < 0.01) after ADR injection. NG presented severe tubulointerstitial abnormalities with a tubulointerstitial lesion index of 3+. No difference in glomerular lesions was observed among the groups (NG median = 6%, TNG median = 4% and TCG median = 2%). The tubulointerstitial lesion index of TNG was less intense (median = 2+) but not different from those of the control groups (CG median = 1+; TCG median = 0+) nor NG (median = 3+). We concluded that the treatment with ticlopidine produced some partially beneficial effects but did not prevent the development of adriamycin-induced nephropathy.

Platelet behaviour and haemostatic variables in type 1 (insulin-dependent) diabetic patients with and without albuminuria

Abnormalities of haemostasis have been implicated in the development of both large and small vessel disease in diabetes. Platelet behaviour and coagulation factors were studied in 28 non-diabetic control subjects and 81 Type 1 diabetic patients with different degrees of albuminuria. Twenty-four (30%) patients had macro- or micro-albuminuria. These patients had elevated levels of beta-thromboglobulin compared with normo-albuminuric patients and control subjects (macro-albuminuric 113 (range 60-314), micro-albuminuric 88 (50-220), normo-albuminuric 55 (13-273), control 52 (18-210) micrograms l-1, p less than 0.001). Similar results were found for platelet factor 4 (macro-albuminuric 57 (9-350), micro-albuminuric 78 (12-205), normo-albuminuric 10 (2-135), control 9 (3-95) micrograms l-1, p less than 0.001). There were decreased beta-thromboglobulin:platelet factor 4 ratios in the albuminuric patients compared with control subjects and normo-albuminuric patients (p less than 0.001). There is abnormal platelet activity in Type 1 diabetic patients with elevated albumin excretion rates.