Studies were performed to determine if early treatment with an angiotensin II (Ang II) receptor blocker (ARB), olmesartan, prevents the onset of microalbuminuria by attenuating glomerular podocyte injury in Otsuka Long-Evans Tokushima Fatty (OLETF) rats with type 2 diabetes mellitus. OLETF rats were treated with either a vehicle, olmesartan (10 mg/kg/day) or a combination of nonspecific vasodilators (hydralazine 15 mg/kg/day, hydrochlorothiazide 6 mg/kg/day, and reserpine 0.3 mg/kg/day; HHR) from the age of 7–25 weeks. OLETF rats were hypertensive and had microalbuminuria from 9 weeks of age. At 15 weeks, OLETF rats had higher Ang II levels in the kidney, larger glomerular desmin-staining areas (an index of podocyte injury), and lower gene expression of nephrin in juxtamedullary glomeruli, than nondiabetic Long-Evans Tokushima Otsuka (LETO) rats. At 25 weeks, OLETF rats showed overt albuminuria, and higher levels of Ang II in the kidney and larger glomerular desmin-staining areas in superficial and juxtamedullary glomeruli compared to LETO rats. Reductions in mRNA levels of nephrin were also observed in superficial and juxtamedullary glomeruli. Although olmesartan did not affect glucose metabolism, it decreased blood pressure and prevented the renal changes in OLETF rats. HHR treatment also reduced blood pressure, but did not affect the renal parameters. This study demonstrated that podocyte injury occurs in juxtamedullary glomeruli prior to superficial glomeruli in type 2 diabetic rats with microalbuminuria. Early treatment with an ARB may prevent the onset of albuminuria through its protective effects on juxtamedullary glomerular podocytes.
Background. Peritoneal mesothelial cells play an important role in peritoneal dialysis and are often exposed to dialysis fluid containing high glucose levels. Loss of peritoneal function is a major complication associated with long-term peritoneal dialysis. In this study, we hypothesized that high glucose levels induce apoptosis, and that insulin attenuates this apoptosis in peritoneal mesothelial cells. To clarify this hypothesis, we examined the effects of insulin on the phosphatidylinositol 3-kinase/Akt signaling pathway and apoptosis in rat peritoneal mesothelial cells.
Clinical reports indicate that patients with primary aldosteronism commonly have impaired glucose tolerance; however, the relationship between aldosterone and insulin signaling pathway has not been clarified. In this study, we examined the effects of aldosterone treatment on insulin receptor substrate-1 expression and insulin signaling pathway including Akt phosphorylation and glucose uptake in rat vascular smooth muscle cells. Insulin receptor substrate-1 protein expression and Akt phosphorylation were determined by Western blot analysis with anti-insulin receptor substrate-1 and phosphorylated-Akt antibodies, respectively. Glucose metabolism was evaluated using (3)H-labeled 2-deoxy-d-glucose uptake. Aldosterone (1-100 nmol/L) dose-dependently decreased insulin receptor substrate-1 protein expression with a peak at 18 hours (n=4). Aldosterone-induced degradation of insulin receptor substrate-1 was markedly attenuated by treatment with the selective mineralocorticoid receptor antagonist eplerenone (10 micromol/L; n=4). Furthermore, degradation was blocked by the Src inhibitor PP1 (20 micromol/L; n=4). Treatment with antioxidants, N-acetylcysteine (10 mmol/L), or ebselen (40 micromol/L) also attenuated aldosterone-induced insulin receptor substrate-1 degradation (n=4). In addition, proteasome inhibitor MG132 (1 micromol/L) prevented insulin receptor substrate-1 degradation (n=4). Aldosterone treatment abolished insulin-induced Akt phosphorylation (100 nmol/L; 5 minutes; n=4). Furthermore, aldosterone pretreatment decreased insulin-stimulated (100 nmol/L; 60 minutes; n=4) glucose uptake by 50%, which was reversed by eplerenone (10 micromol/L; n=4). These data indicate that aldosterone decreases insulin receptor substrate-1 expression via Src and reactive oxygen species stimulation by proteasome-dependent degradation in vascular smooth muscle cells; thus, aldosterone may be involved in the pathogenesis of vascular insulin resistance via oxidative stress.
Recent basic and clinical data demonstrated that the intrarenal renin-angiotensin system (RAS) plays an important role in the progression of chronic kidney disease (CKD). The urinary angiotensinogen (AGT) excretion rate could be a novel biomarker for the activity of the RAS in the kidney. We previously reported that the healthy volunteers do not have a circadian rhythm of AGT level in urine (Hypertension. 2011;57:e78) or in plasma (Hypertension. 2012;60:A399). However, the circadian rhythm of AGT level in urine and in plasma in patients with CKD has not been reported yet. Therefore, this study was performed to investigate the circadian rhythm of AGT level in urine and in plasma in patients with CKD. We recruited 6 CKD patients with continuous proteinuria admitted to the Kagawa University Hospital from 06/2011 to 10/2011 for the purpose of diagnostic renal biopsy. Plasma samples were collected at 06:00, 12:00, and 18:00. Urine samples were collected at 06:00, 09:00, 12:00, and 18:00. Plasma renin activities (PRAs), plasma and urinary AGT concentrations, and urinary albumin (Alb) concentration were measured using commercially available kits. The urinary concentrations of AGT and Alb were normalized by the urinary concentration of creatinine (Cr) (UAGT/Cr and UAlb/Cr, respectively). PRA (2.07 +/- 0.77 ng of angiotensin I/mL/hr at 06:00, 2.45 +/- 0.77 at 12:00, and 2.58 +/- 0.76 at 18:00, P = 0.8853) or plasma AGT (19.9 +/- 2.4 μg/mL at 06:00, 24.1 +/- 3.1 at 12:00, and 23.0 +/- 3.9 at 18:00, P = 0.6300) did not show a circadian rhythm. Moreover, UAlb/Cr (511 +/- 319 mg/g Cr at 06:00, 827 +/- 459 at 09:00, 1479 +/- 862 at 12:00, and 1370 +/- 818 at 18:00, P = 0.6964) or UAGT/Cr (54 +/- 22 μg/g Cr at 06:00, 119 +/- 41 at 09:00, 350 +/- 194 at 12:00, and 198 +/- 104 at 18:00, P = 0.3035) did not show a circadian rhythm. In conclusion, in addition to healthy volunteers, patients with CKD do not have a circadian rhythm of AGT level in urine or in plasma.
