Combination Irbesartan/Amlodipine versus Irbesartan/Cilnidipine for Attenuation of Albuminuria in Rats with Streptozotocin-Induced Diabetic Nephropathy

Abstract

Background: Excessive urinary albumin excretion is associated with hypertension and diabetic nephropathy. Calcium channel blockers (CCBs) used as antihypertensives suppress such albuminuria with variable efficacy. While hypertension benefits from the addition of angiotensin receptor blockers (ARBs), it is unknown if ARBs alter the effects of CCBs on albuminuria. Objective: This study compared the efficacy of combined ARB irbesartan with either CCB amlodipine or CCB cilnidipine on albuminuria associated with experimental diabetic nephropathy. Methods: Male Sprague-Dawley rats with streptozotocin-induced diabetes were treated with a CCB alone (amlodipine 2.0 mg/kg/d or cilnidipine 2.0 mg/kg/d), an ARB alone (irbesartan 20.0 mg/kg/d), or combinations. In the acute protocol, changes in glomerular afferent and efferent arteriole diameters were examined by a charge-coupled device video microscope following single doses. In the chronic protocol, urinary albumin excretion, glomerular reactive oxygen species, and endothelial surface layer (ESL) condition were evaluated after 2 weeks of daily treatment. Results: In the acute protocol, cilnidipine mono therapy caused a greater dilation in glomerular efferent arterioles than amlodipine monotherapy, while combination therapy with irbesartan induced comparable efferent arteriole dilation. In the chronic protocol, cilnidipine mono therapy suppressed albuminuria, reduced glomerular oxidative stress, and protected the glomerular ESL against degeneration to a much greater extent that amlodipine monotherapy. However, addition of irbesartan reduced albumin excretion, oxidative stress, and ESL degeneration to the same extent in both groups. Conclusions: While cilnidipine is more effective alone, the combinations of irbesartan with cilnidipine or amlodipine are equally effective for reducing albuminuria and other pathological sequela of experimental diabetic nephropathy.