Increased macrophage activation inhibited by tacrolimus in the kidney of diabetic rats.

Background/aims: Accumulating evidence suggests that macrophage-induced inflammation may be the mechanism of development and progression of diabetic nephropathy. A previous study by our group has shown that tacrolimus, like cyclosporin A, has a renoprotective effect in diabetic rats. The present study aimed to elucidate the underlying molecular events.

Methods: Diabetic rats were induced by using streptozotocin. Diabetic rats were subjected to oral tacrolimus treatment at a dose of 0.5 or 1.0 mg/kg daily for 4 weeks. Body weight, blood glucose, hemoglobin A(1c) (HbA(1c)) and renal pathology were assessed, followed by analyses of renal calcineurin (CaN) expression, changes in renal macrophage infiltration, proliferation and activation, and detection of renal TLR2+ and TLR4+ as well as NF-κB-p-p65+ in macrophages.

Results: Diabetic rats had a reduced body weight and increased blood glucose and HbA(1c) levels, whereas tacrolimus treatment did not affect body weight or blood glucose and HbA(1c). Increased relative kidney weight was only significantly reduced by tacrolimus treatment at a dose of 1.0 mg/kg, while the elevated albumin excretion rate was markedly attenuated after treatment with tacrolimus (0.5 and 1.0 mg/kg) in diabetic rats. Elevated glomerular volume was significantly attenuated by tacrolimus treatment with 0.5 and 1.0 mg/kg, and increased indices for tubulointerstitial injury were only ameliorated by tacrolimus treatment with 1.0 mg/kg. Western blot data showed that expression of CaN protein was induced 2.4-fold in the kidneys of positive control diabetic rats, whereas tacrolimus treatment at 0.5 and 1.0 mg/kg doses reduced the increased expression of CaN protein by 38.0 and 73.2%, respectively. Histologically there was a marked accumulation of ED-1+ cells (macrophages) in diabetic kidneys and tacrolimus treatment failed to inhibit it. In contrast, tacrolimus treatment at 0.5 and 1.0 mg/kg doses significantly inhibited the elevated ED-1+/PCNA+ cells and ED-1+/iNOS+ cells in the kidneys of diabetic rats, while tacrolimus treatment at a dose of 0.5 or 1.0 mg/kg significantly suppressed the increased ED-1+/TLR2+ cells, ED-1+/TLR4+ cells and ED-1+/NF-κB-p-p65+ cells in the kidneys of diabetic rats.

Conclusion: The data from the current study demonstrated that tacrolimus could ameliorate early renal injury through a mechanism to suppress macrophage activation.