Corticosteroids augment cyclosporine nephrotoxicity in pediatric nephrotic syndrome: potential role of alternatively activated macrophages.

Background: Cyclosporine A (CsA) is an effective steroid-sparing agent for steroid-dependent nephrotic syndrome (SDNS); however, long-term administration of CsA can induce chronic kidney injury (CsA nephropathy). We previously reported that alternatively activated macrophages (M2-type macrophages) are closely linked to the pathogenesis of interstitial fibrosis in progressive kidney disease. In this study, we investigated the possible involvement of M2-type macrophages in CsA nephropathy in SDNS. Materials and Methods: A total of 33 children diagnosed with SDNS and who were treated with CsA for more than 2 years were investigated. Fourteen biopsy specimens from age-matched SDNS children who had not received CsA treatment were used as the control. Renal fibrosis was assessed by Masson chrome staining of biopsy sections. Sections were also stained for α-smooth muscle actin (α-SMA), type I collagen, CD68 (total macrophages), CD163 (M2 marker) and CCL2. Urine levels of CCL2 were measured by cytometric bead array kit. Results: The CsA-treated group showed significant interstitial fibrosis (12.2±7.3 vs 7.6±2.1%, p<0.001) with accumulation of interstitial CD163 ⁺ CD68 ⁺ macrophages (10.8 vs 7.9/HPF; p<0.001) compared with SDNS control patients. There was a significant correlation between the degree of interstitial fibrosis and the number of interstitial CD163 ⁺ cells (p<0.001), and between interstitial fibrosis and the cumulative steroid dose used during CsA treatment (p<0.001), while no correlation was found between the cumulative steroid dose used before CsA treatment and histological changes. Immunostaining revealed significant expression of CCN2 and CCL2 in biopsies from the CsA group which co-localized with CD163 ⁺ macrophages. In addition, the urinary CCL2/creatinine ratio was significantly elevated in the CsA group compared to controls, both at relapse (1012±641.2 vs. 239.9±226.9 pg/mg; p = 0.02) and at remission (202.0±178.4 vs. 77.7±127.3 pg/mg; p = 0.04). Conclusion: Our findings suggest that CD163 ⁺ M2-type macrophages may participate in the development of interstitial fibrosis induced by CsA. Steroid treatment during CsA treatment appears to augment CsA nephrotoxicity through the production of pro-fibrotic factors.