Kumiko Kaifu

Aldosterone Suppresses Insulin Signaling Via the Downregulation of Insulin Receptor Substrate-1 in Vascular Smooth Muscle 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 3H-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 &mgr;mol/L; n=4). Furthermore, degradation was blocked by the Src inhibitor PP1 (20 &mgr;mol/L; n=4). Treatment with antioxidants, N-acetylcysteine (10 mmol/L), or ebselen (40 &mgr;mol/L) also attenuated aldosterone-induced insulin receptor substrate-1 degradation (n=4). In addition, proteasome inhibitor MG132 (1 &mgr;mol/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 &mgr;mol/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.

Early Treatment With Olmesartan Prevents Juxtamedullary Glomerular Podocyte Injury and the Onset of Microalbuminuria in Type 2 Diabetic Rats

Background 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. Methods 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. Results 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. Conclusions 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.

Insulin attenuates apoptosis induced by high glucose via the PI3-kinase/Akt pathway in rat peritoneal mesothelial cells

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. METHODS Phosphorylated insulin receptor and Akt were detected by western blot analysis. Apoptosis was evaluated by measuring caspase 3 activity and by TUNNEL staining. RESULTS Insulin (100 nmol/L) increased tyrosine phosphorylation of insulin receptor in peritoneal mesothelial cells. Furthermore, insulin (1-100 nmol/L) dose-dependently stimulated Akt phosphorylation. Treatment with the phosphatidylinositol 3-kinase inhibitors wortmannin (100 nmol/L) and LY294002 (10 micromol/L) attenuated insulin-induced Akt phosphorylation, indicating that insulin phosphorylates Akt via a phosphatidylinositol 3-kinase-dependent pathway. Insulin attenuated caspase 3 activity and decreased the number of TUNNEL-positive cells. The phosphatidylinositol 3-kinase inhibitors and overexpression of a dominant-negative mutant of Akt inhibited the effect of insulin on apoptosis. CONCLUSIONS The present data indicate that insulin attenuates high glucose-induced apoptosis via the phosphatidylinositol 3-kinase/Akt signaling pathway in peritoneal mesothelial cells. Therefore, the insulin signaling pathway may play a protective role in peritoneal function.

Low-density lipoprotein apheresis for haemodialysis patients with peripheral arterial disease reduces reactive oxygen species production via suppression of NADPH oxidase gene expression in leucocytes

BACKGROUND Peripheral arterial disease (PAD) is a major complication of haemodialysis (HD), especially in patients with diabetes mellitus. Although previous reports have indicated that low-density lipoprotein apheresis (LDL-A) improves arteriosclerosis in PAD patients, the mechanism by which LDL-A affects PAD is still unclear. In this study, we tested the hypothesis that LDL-A attenuates reactive oxygen species (ROS) production in HD patients with PAD. METHODS Twenty HD patients with PAD were investigated in this study. Clinical effects were evaluated by thermography and angiography. Oxidative stress in serum was evaluated by thiobarbituric acid reactive substances (TBARS) and expression of p22phox mRNA. RESULTS Ischaemic symptoms due to PAD were gradually improved in 13 patients (65%) after LDL-A. One session of LDL-A removed approximately 75% of LDL from serum. Some patients exhibited dramatic improvement of severe symptoms of PAD such as skin ulcers after serial performance of LDL-A. The levels of LDL cholesterol, malondialdehyde-modified LDL, high-sensitivity C-reactive protein, vascular endothelial growth factor, international normalized ratio of pro-thrombin time and bradykinin were decreased after a single session of LDL-A, although there were no additional changes after 10 sessions of LDL-A. The levels of fibrinogen and p22phox mRNA were decreased by a single session of LDL-A, and these decreases continued over the entire period of treatment. TBARS was decreased after a course of LDL-A. CONCLUSIONS LDL-A improved ischaemic symptoms in HD patients with PAD by reducing ROS production in leucocytes. We conclude that LDL-A is an effective therapy for patients with HD complicated by PAD.

Angiotensin II Shifts Insulin Signaling Into Vascular Remodeling From Glucose Metabolism in Vascular Smooth Muscle Cells

BACKGROUND To clarify the role of angiotensin II (Ang II) in insulin-induced arteriosclerosis, we examined the effects of Ang II on insulin-induced mitogen-activated protein (MAP) kinase activation and cellular hypertrophy in rat vascular smooth muscle cells (VSMCs). METHODS Phosphorylated MAP kinases were detected with western blot analysis. Cellular hypertrophy and glucose uptake were evaluated from incorporation of [(3)H]-labeled-leucine and -deoxy-D-glucose, respectively. Cell sizes were measured by Coulter counter. RESULTS While Ang II (100 nmol/l, 18 h) augmented cellular hypertrophy by insulin (10 nmol/l, 24 h), insulin alone did not affect hypertrophy without Ang II pretreatment. Insulin increased p38MAP kinase and c-Jun N-terminal kinase (JNK) phosphorylation; in the presence of Ang II, p38MAP kinase, and JNK were further activated by insulin. Treatment of a p38MAP kinase inhibitor, SB203580 (10 µmol/l), and a JNK inhibitor, SP600125 (20 µmol/l), abrogated the [(3)H]-leucine incorporation by insulin in the presence of Ang II. Both the Ang II receptor blocker, RNH-6270 (100 nmol/l), and an antioxidant, ebselen (40 µmol/l), inhibited vascular cell hypertrophy. Specific depletion of insulin receptor substrate-1 with small interfering RNA increased [(3)H]-leucine incorporation by insulin (10 nmol/l, 24 h); pretreatment with Ang II attenuated insulin (10 nmol/l, 30 min)-induced glucose uptake. CONCLUSIONS Ang II attenuates insulin-stimulated glucose uptake and enhances vascular cell hypertrophy via oxidative stress- and MAP kinase-mediated pathways in VSMCs. Ang II may also cause insulin signaling to diverge from glucose metabolism into vascular remodeling, affecting insulin-induced arteriosclerosis in hypertension.

Circadian rhythm of plasma and urinary angiotensinogen in healthy volunteers and in patients with chronic kidney disease

The urinary angiotensinogen (AGT) excretion rate could be a novel biomarker for the intrarenal activity of the renin-angiotensin system. Little is known about the circadian rhythm of AGT levels in plasma or urine. In this short article, making use of data in plasma and urine of healthy volunteers and patients with chronic kidney diseases, we first report that we were unable to find evidence for a circadian rhythm of AGT under any condition. Next we critically discuss to what degree elevated urinary AGT levels might be considered an independent biomarker that is not simply the non-specific consequence of proteinuria.