Aldosterone Antagonists in Monotherapy Are Protective against Streptozotocin-Induced Diabetic Nephropathy in Rats

Angiotensin converting enzyme inhibitors (ACEi) and angiotensin II receptor blockers (ARB) are the standard clinical therapy of diabetic nephropathy (DN), while aldosterone antagonists are only used as adjuncts. Previously in experimental DN we showed that Na/K ATPase (NKA) is mislocated and angiotensin II leads to superimposed renal progression. Here we investigated the monotherapeutic effect of aldosterone blockers on the progression of DN and renal NKA alteration in comparison to ACEi and ARBs. Streptozotocin-diabetic rats developing DN were treated with aldosterone antagonists; ACEi and ARB. Renal function, morphology, protein level and tubular localization of NKA were analyzed. To evaluate the effect of high glucose per se; HK-2 proximal tubular cells were cultured in normal or high concentration of glucose and treated with the same agents. Aldosterone antagonists were the most effective in ameliorating functional and structural kidney damage and they normalized diabetes induced bradycardia and weight loss. Aldosterone blockers also prevented hyperglycemia and diabetes induced increase in NKA protein level and enzyme mislocation. A monotherapy with aldosterone antagonists might be as, or more effective than ACEi or ARBs in the prevention of STZ-induced DN. Furthermore the alteration of the NKA could represent a novel pathophysiological feature of DN and might serve as an additional target of aldosterone blockers

Renal histopathology in control, diabetic and treated diabetic rats.

<p>Aldosterone antagonists were the most effective in attenuating the structural lesions of DN. Representative PAS staining of kidney sections (40x magnification; scale bar –50 μm): non-diabetic control (A), STZ-induced diabetic (B), Enalapril (E), Losartan (F), Spironolactone (G) and Eplerenone (H) treated diabetic rats (n = 8–10/group). Long, wide headed arrows point on mesangial matrix; long, narrow headed arrows on arterioles. Armanni-Ebstein lesions are marked with short, wide headed arrows. <i>C</i>: Mesangial fractional volume values (Vv) are defined by the ratio of mesangial area/glomerular tuft area. The mesangial area is determined by assessment of PAS-positive and nucleus-free areas in the mesangium. *p<0.05 <i>vs</i> Control; §p<0.05 <i>vs</i> Diabetes, respectively; (bars show means ± SD). <i>D</i>: Arteriolar hyalinosis is defined by the average of hyalinized quarters of arterioles. The hyalin is determined by assessment of PAS-positive and nucleus-free areas within the arterioles. *p<0.05 <i>vs</i> Control; §p<0.05 <i>vs</i> Diabetes, respectively; (bars show means ± SD).</p

Confocal images of control, diabetic and treated diabetic rats.

<p>Aldosterone inhibitors prevented the mislocation of NKA induced by diabetes in proximal tubules. Representative pictures of immunofluorescence staining of kidney sections for Na/K ATPase (NKA, green) in control (A), streptozotocin-diabetic (B) and diabetic, Enalapril (C), Losartan (D), Spironolactone (E) and Eplerenone (F) treated rats (63x magnification; scale bar–10 μm). Nuclei are stained blue with Hoechst. PT-proximal tubule, DT-distal tubule, Bm-basal membrane, Lu – apical membrane at the lumen and Nucl – nuclei. Fluorescent signal intensity of NKA (green) generated from a line shown as red arrow in the merged image are shown on the bottom right of each panel.</p

Western blot analysis of Na/K ATPase (NKA).

<p>Aldosterone antagonists were the most effective in decreasing diabetes and hyperglycemia induced elevation of tubular NKA protein level. Top panel: Representative examples of Western blot analysis. Lower panels: <i>A</i>: Densitometric analysis of NKA protein levels in kidney homogenates of control, diabetic and treated diabetic rats. <i>B</i>: Densitometric analysis of NKA protein levels in HK-2 tubular cells. Bar graph represents densitometric analysis from multiple experiments. Data represent means ± SD; *p<0.05 <i>vs</i> Control; §p<0.05 <i>vs</i> Diabetes, respectively; (bars show means±SD; n = 8–10/group). IOD – integrated optical density.</p

Metabolic and renal parameters of control, diabetic and treated diabetic rats.

<p>Data are means ± SD, n = 8–10/group, ^*p<0.05 vs. C; ^§p<0.05 vs. D, ^**p<0.01 vs. C; ^§§p<0.01 vs. D, ^***p<0.001 vs. C; ^§§§p<0.001 vs. D; respectively. UD–undetectable.</p