Inhibition of ceramide-redox signaling pathway blocks glomerular injury in hyperhomocysteinemic rats

Ceramide-activated NAD(P)H oxidase has been reported to participate in homocysteine (Hcys)-induced abnormal metabolism of the extracellular matrix (ECM) in rat glomerular mesangial cells. However, it remains unknown whether this ceramide-redox signaling pathway contributes to glomerular injury induced by hyperhomocysteinemia (hHcys) in vivo. The present study was designed to address this question, defining the role of ceramide and activated NAD(P)H oxidase in the development of hHcys-induced glomerular injury. Uninephrectomized Sprague-Dawley rats were fed a folate-free diet for 8 weeks to produce hHcys and the de novo ceramide synthesis inhibitor myriocin or the NAD(P)H oxidase inhibitor apocynin was administrated. Rats with folate-free diet significantly increased plasma Hcys levels, renal ceramide levels, and NAD(P)H oxidase activity accompanied by marked glomerular injury. Treatment of rats with myriocin significantly reduced ceramide levels and improved glomerular injury, as shown by decreased urinary albumin excretion and reduced glomerular damage index. ECM components changed towards to normal levels with decreased tissue inhibitor of metalloproteinase-1 and increased matrix metalloproteinase-1 activity. NAD(P)H oxidase activity and Rac GTPase activity were reduced by 69 and 66%, respectively. In rats treated with apocynin, similar beneficial effects in protecting glomeruli from hHcys-induced injury were observed. These results support the view that de novo ceramide production is involved in Hcys-induced NAD(P)H oxidase activity in the kidney of hHcys rats and indicate the important role of ceramide-mediated redox signaling in hHcys-induced glomerular injury in rats.