Background: Diabetic nephropathy is associated with increased albuminuria and accumulation of extracellular matrix proteins within the kidney. Clinical studies have shown some beneficial effects of calcium channel blockers (CCB) on diabetic nephropathy, even though they are generally considered to be less renoprotective than agents that interrupt the renin angiotensin system. However, effects of CCBs on renal injury, and in particular, expression of extracellular matrix proteins in a model of normotensive diabetic nephropathy, are poorly characterized.
Methods: Experimental diabetes was induced by injection of streptozocin in Sprague-Dawley rats. Amlodipine, a CCB which blocks the L channel, and mibefradil, a CCB blocking the T as well as the L channels, were given to diabetic rats for six months. Albumin excretion rate (AER), pathologic injury, and expression of the extracellular matrix proteins, collagen I, and fibronectin were assessed.
Results: Increased AER in diabetic rats (13.2 x//1.3 mg/d, geometric mean x// tolerance factor) was attenuated by either amlodipine (3.2 x// 1.4 mg/d) or mibefradil (2.6 x// 1.4 mg/d). Increased glomerulosclerosis and tubulointerstitial injury in diabetic animals were attenuated by amlodipine and mibefradil. There was increased collagen accumulation in the kidney of diabetic rats as assessed by picro-sirius red staining. Gene expression of both collagen I and fibronectin were also increased in the kidneys from diabetic animals, as assessed by reverse transcription-polymerase chain reaction (RT-PCR). These markers of fibrosis were attenuated by treatment with either amlodipine or mibefradil. Blood pressure in diabetic rats (136 +/- 2 mm Hg) was modestly reduced by amlodipine (126 +/- 3 mm Hg) but not by mibefradil treatment (134 +/- 3 mm Hg).
Conclusion: Calcium channel blockers attenuated albuminuria, pathologic injury, and accumulation of extracellular matrix proteins in this normotensive model of diabetic nephropathy. These findings suggest that CCBs may be useful in preventing pathologic injury in the diabetic kidney.