Plasma NGAL Is An Early Biomarker of Graft Function, Calcineurin Inhibitor Nephrotoxicity and Tubular Regeneration in Kidney Transplantation from Extended Criteria Donors

Abstract

Delayed graft function (DGF) is an early complication of kidney transplantation (KT) usually defined as the need for dialysis in the first week after the procedure. The main cause of DGF is ischemia-reperfusion injury and the incidence of DGF has been increasing in the last years for the use of kidneys from extended criteria donors (ECD). Moreover, DGF is associated with an increased risk of acute rejection due to enhanced tissue immunogenicity and to a premature loss of kidney graft function. Plasma Neutrophil Gelatinase Associated Lipocalin (NGAL) is a 25 kDa protein belonging to the lipocalin family secreted by leukocytes and different epithelia including renal tubular epithelial cells. NGAL has been proposed as early biomarker of ischemic and toxic acute kidney injury and of DGF in kidney graft. The aims of this study were to evaluate: 1) plasma NGAL in 50 patients in the first 24h after KT from ECD; 2) the relationship between plasma NGAL and DGF, slow graft function (SGF) and immediate graft function (IGF); 3) the trend of serum creatinine (sCr) and plasma NGAL in the first 5 days after KT; 4) plasma NGAL before and after the introduction of calcineurin inhibitors (CNI, tacrolimus or cyclosporine); 5) the in vitro role of NGAL in tubular regeneration after ischemic injury. Fifty patients were enrolled in the study (immunosuppression with basiliximab, MMF and steroids: CNI introduced when sCr < 2.5 mg/dl). Patients were divided in 3 groups: DGF, SGF (sCr >3 mg/dl at day 6 after KT) and IGF (sCr < 3 mg/dl at day 6 after KT). Plasma NGAL levels were measured by a fluorimetric method (Alere, San Diego, CA). Protein and mRNA NGAL levels, proliferation and apoptosis were evaluated in isolated human tubular cells cultured under hypoxia or with therapeutic doses of tacrolimus/cyclosporine. Patients' demographics and characteristics were: male 67%, recipient age 57.65 yr, donor age 65 yr, cold ischemia time 16.8 h, HLA mismatches 3.46, recipient BMI 24.2, donor hypertension 64.4%, donor eGFR 88.66 ml/min. The incidence of DGF was 28%: in the 72% of patients without DGF, SGF occurred in 55%, IGF in 45%. Plasma NGAL levels (< 24h after KT) were significantly higher in DGF than in SGF and IGF groups (DGF 654.94 ng/ml; SGF 439.75 ng/ml; IGF 357.37 ng/ml). A decline of plasma NGAL but not of sCr was detectable at day 2 after KT with a further decrease at day 3, 4 and 5. By contrast, NGAL increased after 24 hr from CNI introduction (before CNI: 120.12 ng/ml; after CNI: 188.25 ng/ml). Human tubular cells cultured under hypoxia or in presence of tacrolimus/cyclosporine showed enhanced mRNA/protein levels of NGAL. In addition, recombinant NGAL induced a dosedependent decrease of tubular cell apoptosis via caspase inactivation and triggering of P-Akt/Akt pathway. In conclusion, the results of the present study suggest that NGAL is an early predictor of graft function and CNI nephrotoxicity after KT from ECD. These data sustain the role of NGAL as potential autocrine factor involved in tubular regeneration after ischemia-reperfusion and nephrotoxic injury.