Background: Several experimental and clinical studies have implicated a role for transforming growth factor-beta (TGF-beta) in mediating the nephrotoxic effects of cyclosporine (CsA). To test this hypothesis, we administered neutralizing anti-TGF-beta antibodies (alpha-TGF-beta) in a well-described rat model of chronic CsA nephrotoxicity.
Methods: We studied three groups (N = 9 per group) of adult, male Sprague-Dawley rats that received a low-salt diet (0.05% sodium). Normal controls were given vehicle subcutaneously and an alternate-day intraperitoneal injection of 3 mg of nonspecific mouse IgG (MIgG) for 28 days. The CsA group received 15 mg/kg/day of CsA subcutaneously and 3 mg of MIgG intraperitoneally on alternate days for 28 days. The CsA/alpha-TGF-beta group received CsA and alternate-day alpha-TGF-beta (3 mg) for 28 days. At the end of 28 days, creatinine clearance was measured by 24-hour urine collection. Histologic assessment was performed for tubulointerstitial damage and arteriolar hyalinosis. Northern analysis was performed for alpha 1(I) collagen and TGF-beta 1 gene expression, and quantitative reverse transcription-polymerase chain reaction was performed to measure levels of tissue inhibitor of metalloproteinase-1 (TIMP-1), TIMP-2, plasminogen activator inhibitor-1 (PAI-1), matrix metalloproteinase-2 (MMP-2), and MMP-9.
Results: CsA-treated rats had significantly lower creatinine clearance as compared with normal controls (0.43 +/- 0.07 vs. 0.67 +/- 0.14 mL/min, P = 0.0002), increased interstitial damage and afferent arteriolar hyalinosis (P = 0.0001), and increased alpha1(I) collagen (4-fold) and TGF-beta 1 (2.5-fold) mRNA expression. CsA-treated rats also had significantly increased TIMP-1 (7.4-fold, P < 0.001), MMP-2, and PAI-1 (all approximately 2-fold, P < 0.02) and decreased MMP-9 (85% reduction, P < 0.001) as compared with controls. Treatment with alpha-TGF-beta in CsA-treated rats significantly prevented the reduction in creatinine clearance (0.58 +/- 0.03 mL/min, P = 0.009 vs. CsA alone), the increase in afferent arteriolar hyalinosis (P < 0.05 vs. CsA alone), normalized alpha 1(I) collagen mRNA levels, and attenuated CsA effects on TGF-beta1, TIMP-1, and MMP-9.
Conclusions: In this rat model of CsA-induced nephrotoxicity, renal insufficiency and characteristic histologic changes are associated with altered expression of matrix and matrix-regulating molecules. Based on our results with alpha-TGF-beta antibodies, many but not all of these nephrotoxic effects of CsA are mediated by TGF-beta.