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

Sigma1-Receptor Agonism Protects against Renal Ischemia-Reperfusion Injury

Mechanisms of renal ischemia-reperfusion injury remain unresolved, and effective therapies are lacking. We previously showed that dehydroepiandrosterone protects against renal ischemia-reperfusion injury in male rats. Here, we investigated the potential role ofsigma1-receptor activation in mediating this protection. In rats, pretreatment with either dehydroepiandrosterone or fluvoxamine, a high-affinitysigma1-receptor agonist, improved survival, renal function and structure, and the inflammatory response after sublethal renal ischemia-reperfusion injury. In human proximal tubular epithelial cells, stimulation by fluvoxamine or oxidative stress caused thesigma1-receptor to translocate from the endoplasmic reticulum to the cytosol and nucleus. Fluvoxamine stimulation in these cells also activated nitric oxide production that was blocked bysigma1-receptor knockdown or Akt inhibition. Similarly, in the postischemic rat kidney,sigma1-receptor activation by fluvoxamine triggered the Akt-nitric oxide synthase signaling pathway, resulting in time- and isoform-specific endothelial and neuronal nitric oxide synthase activation and nitric oxide production. Concurrently, intravital two-photon imaging revealed prompt peritubular vasodilation after fluvoxamine treatment, which was blocked by thesigma1-receptor antagonist or various nitric oxide synthase blockers. In conclusion, in this rat model of ischemia-reperfusion injury,sigma1-receptor agonists improved postischemic survival and renal functionviaactivation of Akt-mediated nitric oxide signaling in the kidney. Thus,sigma1-receptor activation might provide a therapeutic option for renoprotective therapy

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

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

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

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

The role of sigma-1 receptor and brain-derived neurotrophic factor in the development of diabetes and comorbid depression in streptozotocin-induced diabetic rats

RATIONALE: Depression is highly prevalent in diabetes (DM). Brain-derived neurotrophic factor (BDNF) which is mainly regulated by the endoplasmic reticulum chaperon sigma-1 receptor (S1R) plays a relevant role in the development of depression. OBJECTIVES: We studied the dose-dependent efficacy of S1R agonist fluvoxamine (FLU) in the prevention of DM-induced depression and investigated the significance of the S1R-BDNF pathway. METHODS: We used streptozotocin to induce DM in adult male rats that were treated for 2 weeks p.o. with either different doses of FLU (2 or 20 mg/bwkg) or FLU + S1R antagonist NE100 (1 mg/bwkg) or vehicle. Healthy controls were also enrolled. Metabolic, behaviour, and neuroendocrine changes were determined, and S1R and BDNF levels were measured in the different brain regions. RESULTS: In DM rats, immobility time was increased, adrenal glands were enlarged, and thymuses were involuted. FLU in 20 mg/bwkg, but not in 2 mg/bwkg dosage, ameliorated depression-like behaviour. S1R and BDNF protein levels were decreased in DM, while FLU induced SIR-BDNF production. NE100 suspended all effects of FLU. CONCLUSIONS: We suggest that disturbed S1R-BDNF signaling in the brain plays a relevant role in DM-induced depression. The activation of this cascade serves as an additional target in the prevention of DM-associated depression