Enric Condom

Protocol renal allograft biopsies and the design of clinical trials aimed to prevent or treat chronic allograft nephropathy

BACKGROUND The minimum sample size to perform a clinical trial aimed to modify the natural history of chronic allograft nephropathy (CAN) is very large. Since the presence of chronic tubulointerstitial damage in renal protocol biopsy specimens is an independent predictor of late outcome, we evaluated whether protocol biopsies could facilitate the design of trials aimed to prevent or treat CAN. METHODS Two hundred eighty-two protocol biopsy specimens were obtained 3 months after transplantation in 280 patients with serum creatinine levels <300 micromol/L, proteinuria <1000 mg/day, and stable function. The specimens were evaluated according to the Banff criteria. RESULTS Graft survival depended on the presence of CAN and renal transplant vasculopathy (RTV). Thus, biopsy specimens were classified as: (a) no CAN (n=174); (b) CAN without RTV (n=87); and (c) CAN with RTV (n=21). Graft survival at 10 years was 95%, 82%, and 41%, respectively (P=0.001). Total serum cholesterol before transplantation was 4.5+/-1.1, 4.6+/-1.1, and 5.3+/-1.6 mmol/L, respectively (P=0.009) and it was the only predictor of RTV. Power analysis (beta=20%, alpha=5%) was done to evaluate whether protocol biopsies can facilitate the design of clinical trials aimed either to prevent or treat CAN. We showed that the most feasible approach would be to use the presence of CAN as the primary efficacy end point in a prevention trial. To demonstrate a 50% reduction in the incidence of CAN at 3 months, 570 patients would be required. CONCLUSIONS Protocol biopsies may allow a reduction of sample size and especially the time of follow-up in a trial aimed to prevent CAN.

Do Alloreactivity and Prolonged Cold Ischemia Cause Different Elementary Lesions in Chronic Allograft Nephropathy

This study assesses the individual contributions of the nonalloreactive factor, cold ischemia (CI), and alloreactivity to late functional and structural renal graft changes, and examines the effect of the association of both factors on the progression of chronic allograft nephropathy. Lewis rats acted as receptors of kidneys from either Lewis or Fischer rats. For CI, kidneys were preserved for 5 hours. The rats were divided into four groups: Syn, syngeneic graft; SynI, syngeneic graft and CI; Allo, allogeneic graft; AlloI, allogeneic graft and CI. Renal function was assessed every 4 weeks for 24 weeks. Grafts were evaluated for acute inflammatory response at 1 week and for chronic histological damage at 24 weeks. Only when CI and allogenicity were combined did immediate posttransplant mortality occur, while survivors showed accelerated renal insufficiency that induced further mortality at 12 weeks after transplant. Solely ischemic rats developed renal insufficiency. Renal structural damage in ischemic rats was clearly tubulointerstitial, while significant vasculopathy and glomerulosclerosis appeared only in the allogeneic groups. There was increased infiltration of macrophages and expression of mRNA-transforming growth factor-beta1 in the ischemic groups, irrespective of the allogeneic background. The joint association of CI plus allogenicity significantly increased cellular infiltration at both early and late stages, aggravating tubulointerstitial and vascular damage considerably. In summary, CI is mainly responsible for tubulointerstitial damage, whereas allogenicity leads to vascular lesion. The association of both factors accelerates and aggravates the progression of experimental chronic allograft nephropathy.

Effect of a platelet-activating factor (PAF) receptor antagonist on hyperacute xenograft rejection; evaluation in a pig kidney-human blood xenoperfusion model

In pig to human discordant xenotransplantation, PAF may contribute to the pathogenesis of hyperacute xenograft rejection (HXR). We examined the release of PAF and the effect of a PAF receptor antagonist (BN 52021) on HXR in a pig kidney–human blood xenoperfusion model. Pig kidneys were perfused with porcine blood (AUTO group, n = 5), human blood (HETER group, n = 6) or human blood plus BN 52021 (BN group, n = 4), respectively. In contrast to HETER kidneys that never produced urine and were rejected in 15–30 min, the administration of BN 52021 induced a partial recovery of glomerular filtration rate and allowed kidneys to function until the end of the study. The release of PAF and soluble P‐selectin, as well as endothelial P‐selectin expression and tissue myeloperoxidase (MPO), were much higher in the HETER than in the AUTO group. HETER and BN kidneys displayed similar natural xenoantibody titres, CH50, PAF, soluble P‐selectin as well as renal immunoglobulin (IgM, IgG, IgA) and complement (C3, C1q) deposition. However, HETER kidneys displayed a full histologic picture of HXR (mainly interstitial haemorrhage and vascular microthrombi) and BN kidneys had only endothelial cell swelling. Also, BN 52021 administration attenuated glomerular and vascular P‐selectin expression and renal tissue MPO activity. We conclude that in the pig kidney–human blood xenoperfusion model, PAF is produced in higher amounts than in the pig kidney–pig blood autologous combination. The administration of BN 52021 exerts a protective effect by means of attenuating the acute inflammatory response and blocking vascular microthrombi formation.

Cold ischemia in the absence of alloreactivity induces chronic transplant nephropathy through a process mediated by the platelet-activating factor.

Background. Ischemia-reperfusion injury is considered a risk factor for the development of chronic transplant nephropathy (CTN) although the mechanisms that mediate its effects have not been completely established. We have previously shown that treatment with a platelet-activating factor (PAF) receptor antagonist (UR12670) protected kidneys from the progression to chronic nephropathy induced by warm ischemia. Here we examine the contribution of cold ischemia to the development of late functional and structural kidney changes in rats subjected to syngeneic renal transplantation and the role of PAF in this chronic nephropathy. Subjects and Methods. Lewis rats were used as kidney donors and recipients, which were transplanted either immediately or after a cold ischemia period of 5 hr. Contralateral nephrectomy was performed on the seventh day after transplantation. Cyclosporine was administered for 15 days after transplantation. Groups were as follows: Sy, immediate transplantation; SyI, transplantation after 5 hr of cold ischemia; SyIUr, transplantation after 5 hr of cold ischemia plus UR12670 from the transplantation day to the end of the study, at 24 weeks. Serum creatinine, creatinine clearance, and proteinuria were determined every 4 weeks. Urinary PAF excretion was determined in the 24th week. At the end of the study, kidney tissue was processed for histological study (number of infiltrating macrophages, tubulointerstitial damage, and percentage of interstitial area). Results. Rats grafted with ischemic kidneys (SyI) developed renal insufficiency and proteinuria, increased their urinary PAF excretion, and had histological lesions that resemble CTN. In contrast, rats grafted with nonischemic kidneys (Sy) maintained a stable renal function, without proteinuria, and showed no histological abnormalities in the kidney. Long-term treatment with UR12670 (SyIUr) ameliorated renal function, lowered urinary PAF excretion, and reduced the number of infiltrating macrophages, tubulointerstitial damage, and the percentage of interstitial area. Conclusions. In the absence of alloreactivity, cold ischemia induces CTN, which is associated with enhanced urinary PAF excretion. The protecting effect of UR12670 confirms that PAF is involved in the progression to CTN.

Fibronectin (FN) decreases glomerular lesions and synthesis of tumour necrosis factor‐alpha (TNF‐α), platelet‐activating factor (PAF) and FN in proliferative glomerulonephritis

We have studied the effect of therapy with plasma FN on glomerular synthesis of PAF, TNF‐α and FN, in experimental proliferative glomerulonephritis. Glomerular PAF, TNF‐α and FN production were increased in rats with nephritis. Peak glomerular PAF production preceded, while peak glomerular TNF‐α bioactivity coincided with maximal proteinuria. Rats treated with FN (5 mg/kg per 48 h) for 15 days had less proteinuria, glomerular and interstitial cell infiltration and glomerular PAF, TNF‐α and FN synthesis than non‐treated rats. In order to characterize further the mechanisms of action of FN, healthy rats were injected with either FN or saline. Peripheral blood mononuclear cells and neutrophils from healthy rats injected with FN secreted less TNF‐α and PAF, respectively, than those obtained from saline‐treated rats. Our data suggest that the beneficial effect of FN may be related to decreased number of glomerular leucocytes and decreased synthesis of inflammatory mediators and extracellular matrix.

Functional and pathologic outcome after complement inactivation in a pig kidney-human blood xenoperfusion model

Abstract In pig to human discordant xenotransplantation there is evidence that hyperacute rejection (HAR) is mediated by the binding of natural xenoantibodies (NxAb) to endothelial xenoantigens with subsequent complement system activation. 1 Hence, prolonged graft survival using complement inhibitors such as cobra venom factor, 2 sCR1, 3 or transgenic animals expressing human complement regulatory proteins such as DAF 4 or CD59, 5 has been observed. Thus, complement plays a pivotal role in endothelial barrier disruption and in the development of HAR. 6 Ex vivo organ perfusion is accepted as a useful tool to study HAR in the pig to human discordant combination. 7 Most of the xenoperfusion experiments in this combination have been performed using pig hearts or pig livers; there is less experience in the functional evaluation of pig kidneys perfused with human blood. We designed this work in order to evaluate the functional and pathologic findings in pig kidneys perfused with complement-inactivated human blood.

Effect of human natural xenoantibody depletion and complement inactivation on early pig kidney function.

Preformed xenoreactive natural antibodies (XNA) and complement mediate hyperacute xenograft rejection (HXR) in pig-to-human discordant xenotransplantation. In a pig kidney-human blood xenoperfusion model, we investigated whether XNA depletion and/or human complement inactivation preserved early pig kidney function. Pig kidneys were perfused for 180 min with pig blood (AUTO group, n = 8), human blood (HETER group, n = 6), complement-inactivated human blood (COMi group, n = 5), XNA-depleted human blood (ABd group, n = 5) or complement-inactivated and XNA-depleted human blood (ABd&COMi group, n = 5). HETER kidneys were rejected after 15–30 min and showed vascular microthrombi and interstitial hemorrhages. XNA depletion and/or complement inactivation prevented HXR. The glomerular filtration rate in ABd, COMi and ABd&COMi groups was significantly lower than in the AUTO group. Also, beyond 60 min, the COMi group showed a significantly lower glomerular filtration rate than that observed in ABd and ABd&COMi groups. Kidneys from ABd, COMi and ABd&COMi groups displayed endothelial cell edema, as well as higher soluble P-selectin levels and a higher renal myeloperoxidase content than the AUTO group kidneys. COMi and ABd&COMi groups had a significantly lower renal myeloperoxidase level than the HETER group. Also, in contrast to HETER and ABd groups, these complement-inactivated groups failed to show a positive correlation between P-selectin and renal myeloperoxidase. We also investigated platelet-activating factor (PAF) as possible mediator for these functional and pathologic changes. We found that blood PAF levels were similar in HETER, ABd, COMi and ABd&COMi groups and significantly higher than in the AUTO group. Also, when PAF was added to porcine endothelial cell monolayers, morphological changes due to cytoskeleton contraction were observed, and these changes were prevented by preincubation with a PAF receptor antagonist. In conclusion, although depletion of XNA and/or complement inactivation prevent HXR, the pig kidney function is not preserved at the level of the autologous combination. The PAF overproduction observed in the xenogenic combination, which is independent of the presence of XNA and complement, may be, at least in part, responsible for early endothelial cell morphological changes still present when HXR is prevented.