Nitric oxide modulates vascular endothelial growth factor and receptors in chronic cyclosporine nephrotoxicity

Background. Vascular endothelial growth factor (VEGF) is involved in angiogenesis, wound healing, and inflammation and exerts its effect via tyrosine kinase receptors, fms -like tyrosine kinase (Flt-1) and fetal liver kinase (Flk-1 or KDR). We have previously shown that VEGF is up-regulated in a model of chronic cyclosporine (CsA) nephrotoxicity and that L-arginine (L-Arg) improved while N-nitro-L-arginine-methyl ester (L-NAME) worsened fibrosis. We examined the role of nitric oxide modulation on VEGF in this model. Methods. Pair-fed salt-depleted rats were administered CsA, CsA + L-NAME, CsA +L-Arg, vehicle (VH), VH + L-NAME or VH +L-Arg and were sacrificed at 7 or 28 days. Physiologic and histologic changes were studied in addition to the mRNA expression of VEGF and its receptors Flt-1 and KDR/Flk-1 by Northern blot and the protein expression of VEGF by Western blot and immunohistochemical staining. Results. While L-NAME worsened renal function and histology, L-Arg had the opposite beneficial effect in CsA-treated rats. VEGF mRNA and protein expressions increased with CsA, further increased with L-NAME and became significantly reduced with L-Arg. Flt-1 expression was similar in all groups. On the other hand, KDR/Flk-1 mRNA expression was modulated in a fashion similar to VEGF. Also, nitric oxide modulation did not have an effect on VH-treated rats. Conclusions. VEGF expression in chronic CsA nephrotoxicity is increased by nitric oxide blockade and decreased by nitric oxide enhancement. Moreover, VEGF probably exerted its effect via the KDR/Flk-1 receptor. The actions of VEGF in this model remain speculative, but it is probable that VEGF plays a role, either independently or through nitric oxide, in CsA-induced fibrosis.