The effect of differing immunosuppressive regimes on the functional and morphologic changes in a rat renal allograft model of chronic rejection

Establishment of an experimental rat model of tacrolimus-induced kidney injury accompanied by interstitial fibrosis

Nephrotoxicity is the major adverse reaction to tacrolimus; however, the underlying mechanisms remain to be fully elucidated. Although several tacrolimus-induced nephrotoxicity animal models have been reported, most renal injury rat models contain factors other than tacrolimus. Here, we report the development of a new nephrotoxicity with interstitial fibrosis rat model induced by tacrolimus administration. Thirty Wistar rats were randomly divided into four groups: sham-operated (Sham), vehicle-treated ischemia reperfusion (I/R) injury (IRI), tacrolimus treated (TAC) and tacrolimus treated I/R injury (TAC + IRI). Rats subjected to IR injury and treated with tacrolimus for 2 weeks showed higher serum creatinine (Scr), blood urea nitrogen (BUN), serum magnesium (Mg) and serum potassium (K), indicating decreased renal function. In addition, tacrolimus treatment combined with IR injury increased histological injury (tubular vacuolation, glomerulosclerosis and interstitial fibrosis), as well as α-smooth muscle actin (α-SMA), transforming growth factor-β (TGF-β), and kidney injury molecule-1 (KIM-1) expression in the renal cortex. In summary, we have developed a tacrolimus-induced kidney injury rat model with interstitial fibrosis within 2 weeks by creating conditions mimicking renal transplantation via tacrolimus administration following ischemia-reperfusion.

Expressions of Angiopoietin-1, Angiopoietin-2, and Tie2 and their roles in rat renal allografts with chronic allograft nephropathy

OBJECTIVE

Angiopoietin-1 (Ang1) and -2(Ang2) are 2 ligands for the endothelium-specific tyrosine kinase Tie2. Previous studies have shown that reciprocal regulation of Ang1, Ang2, and Tie2 plays an important role in chronic cardiac allograft vasculopathy. This study investigated the expressions of Ang1, Ang2, and Tie2 in rat renal allografts undergoing chronic allograft nephropathy (CAN).

MATERIALS AND METHODS

Renal transplantations following the procedure of Kamada with our modification were orthotopically performed using Fisher (F344, RT1(1v1)) rats as both donors and recipients in the autograft group. Fisher and Lewis (LEW, RT1(1)) rats were used as donors and recipients in the allograft group, respectively, which was treated with cyclosporine (CsA; 10 mg/kg/d x 10 d). At 4w, 8w, and 12 weeks posttransplantation, serum creatinine (SCr) was measured and pathologic changes assessed according to the Banff 97 criteria. The mRNA (Deltact) and protein expressions of Ang1, Ang2, and Tie2 were localized by real-time fluorescence quantitative polymerase chain reaction (PCR) and by immunohistochemistry.

RESULTS

The elevation in SCr and the pathologic changes in CAN were observed in all allografts at 8 and 12 weeks. The expressions of Ang1 and Ang2 were localized to epithelial cells and endothelium of the vascular bundles of the glomeruli; Tie2 was specifically expressed in endothelium of vessels both in auto- and allografts at all time points posttransplantation. At 4 weeks, the differences in mRNA expression of Ang1, Ang2, and Tie2 between the 2 groups were not significant (P > .05). Compared with autografts, the mRNA expression of Ang1 decreased significantly (P = .008 and .003 for 8 and 12 weeks, respectively), and the mRNA expressions of Ang2 and Tie2 significantly increased (P = .001/.006 and .005/.001 for 8 and 12 weeks, respectively). The changes in expression of all 3 genes showed significant correlation with the Banff score in the allografts.

CONCLUSION

This study suggested that the abnormal expression and reciprocal regulation of Ang1, Ang2, and Tie2 may play important roles in the development of CAN in rat renal allografts.

Effects of Everolimus on Cellular and Humoral Immune Processes Leading to Chronic Allograft Nephropathy in a Rat Model with Sensitized Recipients

BACKGROUND

Chronic allograft nephropathy (CAN) remains the most common cause of late graft loss especially in sensitized patients. The aim of this study is to evaluate the therapeutic effect of everolimus on cellular and humoral mechanisms of chronic allograft damage in a rat model with sensitized recipients.

METHODS

F344 kidneys were transplanted to LEW.RNU rats. The athymic recipients were reconstituted with 3.5 x 10(7) or 5 x 10(7) presensitized CD4+T-lymphocytes. In the treatment group, everolimus was introduced five weeks posttransplantation. Rats were monitored for peripheral blood lymphocytes, renal function, histological changes in the graft, and the development of donor-specific alloantibodies.

RESULTS

Rats developed cell dose-dependent renal failure. Increased urinary albumin excretion and glomerulopathy were frequently accompanied by the development of donor-specific major histocompatibility complex (MHC) alloantibodies. In the everolimus group, five of six animals survived for 20 weeks with stable serum creatinine and displayed neither acute cellular rejection nor CAN. Prolonged survival was accompanied with significantly reduced tubulointerstitial cell infiltrate in the graft. Increased urinary albumin excretion was present in all, acute tubular necrosis in five of six, and glomerular sclerosis in two grafts. MHC alloantibodies were found in four of six animals.

CONCLUSION

The used rat model offers the opportunity to study the influence of everolimus on the interaction of humoral and cellular mechanisms involved in chronic renal damage. Everolimus leads to a prolongation of allograft survival, reduced cell infiltrate in the graft, and prevents tubular atrophy and interstitial fibrosis. The development of alloantibodies and albuminuria was not prevented. These data suggest that although cellular rejection is clearly suppressed, humoral mechanisms of CAN cannot be completely controlled by everolimus treatment in the sensitized rat model.