Beneficial effect of TGF beta antagonism in treating diabetic nephropathy depends on when treatment is started

Background: In diabetic rats with maximal activation of RAS induced by uninephrectomy, late treatment with anti-TGF beta antibody limited renal injury only when combined with ACE inhibitor. We investigated whether in a two-kidney diabetic model the time at which treatment started predicted the response to TGF beta antagonist. Methods: 27 weeks after streptozotocin injection, animals had mild proteinuria and were randomized to receive irrelevant antibody, anti-TGF beta antibody (1D11) or enalapril till 52 weeks ( early treatment). The effect of agents alone or combined was also evaluated at the time of overt proteinuria ( late treatment, 52 - 61 weeks). Results: When given early, 1D11 displayed marked antihypertensive and antiproteinuric effects. Glomerulosclerosis was reduced to the extent that a remarkable percentage of glomeruli without sclerosis appeared after treatment. Podocyte number was normalized. Renoprotection of 1D11 was comparable to enalapril. Despite control of blood pressure, in late treatment single agents did not reduce proteinuria significantly. Glomerulosclerosis and podocyte loss were partially limited by 1D11 or enalapril, but full protection was achieved by combination. Conclusions: Renoprotective effect of TGF beta antagonism crucially depends on the time at which treatment started. Effectiveness of early treatment with 1D11 would indicate that TGF beta is a major mediator of damage in early diabetes. To tackle the renal damage in the phase of advanced disease, a combined treatment with ACE inhibitor is needed. Copyright (c) 2006 S. Karger AG, Basel.