Effects of Everolimus on Tacrolimus-Accelerated Progression of Renal Interstitial Fibrosis in Subtotal Nephrectomized Rats

Chronic kidney disease (CKD) is characterized by progressive glomerulosclerosis and interstitial fibrosis, ultimately leading to irreversible renal dysfunction. Tacrolimus, a calcineurin inhibitor widely used after kidney transplantation, is known to accelerate chronic renal injury, whereas everolimus has been introduced as a calcineurin inhibitor–sparing agent. However, their direct effects on renal fibrogenesis remain incompletely defined. In this study, we established a chronic renal failure model using 5/6 nephrectomized rats to evaluate tacrolimus-accelerated renal interstitial fibrosis and the impact of concomitant everolimus treatment. Low-dose tacrolimus (1 mg/kg every other day) administered for two weeks starting four weeks after nephrectomy markedly accelerated interstitial fibrotic progression, accompanied by histological deterioration and increased albuminuria. Co-administration of low-dose everolimus (1 mg/kg every other day) significantly attenuated tacrolimus-accelerated fibrosis and improved functional and structural renal parameters. Histological analyses demonstrated reduced interstitial fibrosis and glomerular alterations in the everolimus-treated group. Although α-smooth muscle actin expression was not significantly suppressed, everolimus restored autophagic activity, as indicated by normalization of the LC3-II/LC3-I ratio in both in vivo and in vitro experiments. These findings indicate that tacrolimus accelerates renal fibrogenesis in a remnant kidney model and that concomitant low-dose everolimus effectively mitigates this progression, providing a time- and cost-efficient experimental platform for evaluating antifibrotic strategies in CKD.