No abstract

The immunosuppressive activity of cyclosporine is mediated by inhibiting calcineurin phosphatase. However, calcineurin is widely distributed in other tissues. We examined the degree of calcineurin inhibition by cyclosporine in various tissues. In vitro, the cyclosporine concentration inhibiting 50% (IC50) of calcineurin was ϳ10 ng/mL in human and mouse leukocytes suspensions. In vitro and in vivo IC50s of cyclosporine in homogenates of mouse kidney, heart, liver, testis, and spleen were also comparable (9-48 ng/mL). The maximum calcineurin inhibition by cyclosporine varied, from 83 to 95% of calcineurin activity in spleen, kidney, liver, and testis to 60% in heart and only 10% in brain. Maximum calcineurin inhibition was increased by the addition of cyclophilin A, indicating that cyclophilin concentrations were limiting in some tissues, at least in this assay. Western analysis of mouse tissues showed significantly less cyclophilin in heart than other tissues. cyclosporine concentrations per weight of tissue protein were highest in kidney and liver and lowest in brain and testis after oral dosing, with intermediate levels in spleen, heart, and whole blood. Thus each cyclosporine dose produces rapid and widespread inhibition of calcineurin in tissues, with differences in total susceptibility of each tissue.

Enteric hyperoxalosis is a recognized complication of bariatric surgery, with consequent oxalate nephropathy leading to chronic kidney disease and occasionally end-stage renal failure. In patients with prior gastrointestinal bypass surgery, renal allografts are also at risk of oxalate nephropathy. Further, transplant recipients may be exposed to additional causes of hyperoxalosis. We report two cases of renal allograft oxalate nephropathy in patients with remote histories of bariatric surgery. Conservative management led to improvement of graft function in one patient, while the other patient returned to dialysis. Interpretation of serologic, urine and biopsy studies is complicated by oxalate accumulation in chronic renal failure, and heightened excretion in the early posttransplant period. A high index of suspicion and careful clinicopathologic correlation on the part of transplant nephrologists and renal pathologists are required to recognize and treat allograft oxalate nephropathy. As the incidence of obesity and pretransplant bariatric surgery increases in the transplant population, allograft oxalate nephropathy is likely to be an increasing cause of allograft dysfunction.

Cyclosporine (CsA) is both a clinical immunosuppressive drug and a probe to dissect intracellular signaling pathways. In vitro, CsA inhibits lymphocyte gene activation by inhibiting the phosphatase activity of calcineurin (CN). In clinical use, CsA treatment inhibits 50-75% of CN activity in circulating leukocytes. We modeled this degree of CN inhibition in primary human leukocytes in vitro in order to study the effect of partial CN inhibition on the downstream signaling events that lead to gene activation. In CsA-treated leukocytes stimulated by calcium ionophore, the degree of reduction in CN activity was accompanied by a similar degree of inhibition of each event tested: dephosphorylation of nuclear factor of activated T cell proteins, nuclear DNA binding, activation of a transfected reporter gene construct, IFN-␥ and IL-2 mRNA accumulation, and IFN-␥ production. Furthermore, the degree of CN inhibition was reflected by a similar degree of reduction in lymphocyte proliferation and IFN-␥ production in the allogeneic mixed lymphocyte cultures. These data support the conclusion that CN activity is rate-limiting for the activation of primary human T lymphocytes. Thus, the reduction of CN activity observed in CsA-treated patients is accompanied by a similar degree of reduction in lymphocyte gene activation, and accounts for the immunosuppression observed. ( J. Clin. Invest. 1997.

Abstract. To devise objective criteria for early diagnosis of delayed graft function (DGF), 59 adult living donor kidney transplants with immediate graft function (IGF) and 51 cadaveric kidney transplants were investigated for creatinine reduction ratio (CRR2) from posttransplant day 1 to day 2 and 24-h urine creatinine excretion (UC2) on day 2. The mean CRR2 in living donor transplants was 53% (SD Ϯ 11); the distribution of CRR2 was gaussian, and all of them had UC2 Ͼ1000 mg. Criteria for DGF were developed on the basis of living donor transplant: CRR2 Յ30% (2SD below 53%) Ϯ UC2 Յ1000 mg. Overall, 24 cadaver transplant recipients (47%) developed DGF (CRR2 Յ30%); 13 patients (25%) had mild DGF (UC2 Ͼ1000 mg), and the remaining 11 (22%) had severe DGF (UC2 Յ1000 mg). All the patients with severe DGF had a measured creatinine clearance Ͻ25 ml/min on day 7, and 8 of 11 were dialyzed within the first week of transplantation. Patients with IGF and mild DGF had a creatinine clearance of Ն25 ml/min on or before day 7, and none of them were dialyzed. Calcineurin inhibitors were avoided or delayed in five patients with mild DGF and all patients with severe DGF. In conclusion, diagnosing DGF within 48-h after transplantation is simple and may be valuable in the management of these patients.