Azelnidipine down-regulates renal angiotensin-converting enzyme and mineralocorticoid receptor mRNA in diabetic hypertensive rats

Effects of a new lipophilic L-type calcium channel blocker, azelnidipine, on the expression of molecular components of the renin-angiotensin-aldosterone system (RAAS) were assessed. Male Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of diabetes with hypertension, and their lean littermates, Long-Evans Tokushima Otsuka (LETO) rats, were treated with azelnidipine for 2 weeks. The renal cortical mineralocorticoid receptor mRNA in OLETF was higher than in LETO, but was suppressed (P<0.05) by azelnidipine. Renal cortical angiotensin-converting enzyme mRNA of OLETF was lower than that of LETO rats, and it was further suppressed by azelnidipine (P<0.05). Azelnidipine can down-regulate the gene expression of molecular components of RAAS.     

Effect of enalapril on diabetic nephropathy in OLETF rats: the role of an anti-oxidative action in its protective properties

1. We have evaluated the effects of the angiotensin-converting enzyme inhibitor enalapril on renal function and oxidative status in the kidney of Otsuka Long-Evans Tokushima Fatty (OLETF) rats, an animal model of spontaneous onset of type 2 diabetes mellitus. 2. Enalapril (5 mg/kg) or vehicle (distilled water) was given once daily by gavage to 22-week-old male OLETF rats for 32 weeks. Long-Evans Tokushima Otsuka (LETO) rats, the control animals for OLETF rats, received vehicle alone (n = 10 in each group). 3. Enalapril attenuated the rise in blood pressure mildly, but significantly. Enalapril significantly blunted the development of proteinuria without a significant effect on creatinine clearance. At the end of the study period, the lipid peroxide content in the renal cortex was significantly increased in OLETF compared with LETO rats, in which enalapril had no effect on lipid peroxide content. Enalapril enhanced the activity of catalase in the renal cortex of OLETF rats, but had no effect on the activity of either superoxide dismutase or glutathione peroxidase. 4. These results suggest that oxidative stress may be involved in the development of nephropathy in type 2 diabetes. Enalapril exhibited renoprotective effects without changing lipid peroxides in the kidney, suggesting that the beneficial effects of the compound on diabetic renal damage in OLETF rats may not be mediated through an anti-oxidative action.     

Olmesartan ameliorates a dietary rat model of non-alcoholic steatohepatitis through its pleiotropic effects

Insulin resistance is a major pathological condition associated with obesity and metabolic syndrome. Insulin resistance and the renin-angiotensin system are intimately linked. We evaluated the role of the renin-angiotensin system in the pathogenesis of insulin resistance-associated, non-alcoholic steatohepatitis by using the angiotensin II type 1 receptor blocker olmesartan medoxomil in a diabetic rat model. The effects of olmesartan on methionine- and choline-deficient (MCD) diet-induced steatohepatitis were investigated in obese, diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats and control Long-Evans Tokushima Otsuka (LETO) rats. Components of the renin-angiotensin system were up-regulated in the livers of OLETF rats, compared with LETO rats. In OLETF, but not LETO, rats, oral administration of olmesartan for 8 weeks ameliorated insulin resistance. Moreover, olmesartan suppressed MCD diet-induced hepatic steatosis and the hepatic expression of lipogenic genes (sterol regulatory element-binding protein-1c and fatty acid synthase) in OLETF, but not LETO, rats. In both OLETF and LETO rats, olmesartan inhibited hepatic oxidative stress (4-hydroxy-2-nonenal-modified protein) and expression of NADPH oxidase. Olmesartan also inhibited hepatic fibrosis, stellate cell activation, and expression of fibrogenic genes (transforming growth factor-beta, alpha 1 [I] procollagen, plasminogen activator inhibitor-1) in both OLETF and LETO rats. In conclusion, pharmacological blockade of the angiotensin II type 1 receptor slows the development of steatohepatitis in the OLETF rat model. This angiotensin II type 1 receptor blocker may exert insulin resistance-associated effects against hepatic steatosis and inflammation as well as direct effects against the generation of reactive oxygen species and fibrogenesis.     

Physiological characteristics of diabetic neuropathy in sucrose-fed Otsuka Long-Evans Tokushima fatty rats

Diabetic neuropathy is a very common complication of diabetes mellitus, and animal studies have contributed tremendously to its understanding. The aim of this study was to estimate the neuropathic alterations in the Otsuka Long-Evans Tokushima fatty (OLETF) rats, an animal model of human type 2 diabetes mellitus. For this purpose, four groups of animals were used: untreated OLETF rats, sucrose-fed for 2 months OLETF rats, untreated Long-Evans Tokushima Otsuka (LETO) nondiabetic rats as genetic controls of OLETF, and sucrose-fed LETO rats. All were examined at baseline, at the end of the sucrose treatment, and during a washout period. The following parameters were evaluated: motor nerve conduction velocity (MNCV), sensitivity to noxious thermal and mechanical stimuli using the tail-flick (TF) and tail-pressure (TP) tests, and blood glucose (BG) and HbA1c levels. Our results showed that BG and HbA1c were significantly higher in OLETF rats when compared with those in control LETO rats. Sucrose caused remarkable increase of BG and HbA1c in the OLETF rats, but not in the sucrose-fed LETO rats. MNCV and thermal nociception significantly decreased in OLETF rats in their 10th month, while the values of the TP test did not differ compared with those from LETO rats. Sucrose administration significantly decreased the MNCV, and increased the pain threshold evaluated by the TF and TP tests, compared with those in the control OLETF rats. The studied parameters were not significantly altered in sucrose-fed LETO rats. In conclusion, our findings show that signs of diabetic neuropathy appear late in the individual development of the OLETF rats, and MNCV and thermal nociception are selectively affected in this strain. Sucrose deteriorated the diabetic state, decreased MNCV, and caused thermal and mechanical hypoalgesia.     

Mechanisms underlying the impaired EDHF-type relaxation response in mesenteric arteries from Otsuka Long-Evans Tokushima Fatty (OLETF) rats

We previously reported that in mesenteric arteries from streptozotocin-induced diabetic rats, the endothelium-derived hyperpolarizing factor (EDHF)-type relaxation is impaired, possibly due to a reduced action of cAMP. Here, we observed an impairment of acetylcholine-induced EDHF-type relaxation in mesenteric arteries from a type 2 diabetic model, Otsuka Long-Evans Tokushima Fatty (OLETF) rats [vs. age-matched control Long-Evans Tokushima Otsuka (LETO) rats], and we investigated the mechanism underlying this impairment. In the LETO group, this EDHF-type relaxation was attenuated by 18alpha-glycyrrhetinic acid (a gap-junction inhibitor) and by a protein kinase A (PKA) inhibitor. In both groups (OLETF and LETO), it was enhanced by 3-isobutyl-1-methylxanthine, a cAMP-phosphodiesterase (PDE) inhibitor, but following these enhancements it was still weaker in OLETF rats than in LETO rats. The relaxations induced by cilostamide (a selective PDE3 inhibitor) and 8-bromo-cAMP (a cell-permeant cAMP analog) were reduced in OLETF rats, as was PKA activity. The relaxations induced by two activators of Ca(2+)-activated K(+) channels (K(Ca)) [1-ethyl-2-benzimidazolinone (1-EBIO), intermediate-conductance K(Ca) channel (IK(Ca)) activator, and riluzole, small-conductance K(Ca) channel (SK(Ca)) activator] were also impaired in OLETF rats. We conclude that the impairment of EDHF-type relaxation seen in OLETF rats may be attributable not only to a reduction in cAMP/PKA signaling, but also to reduced endothelial K(Ca) channel activities.     

The calcium channel antagonist benidipine reduces plasma and cardiac endothelin-1 levels in type II diabetic rat model

Cardiovascular complications are the central feature of type 2 diabetes mellitus, and insulin resistance is an early clinical manifestation of type 2 diabetes mellitus. Calcium channel blockers are widely used to treat cardiovascular diseases in diabetic patients; however, it remains unknown how endothelin-1 (ET-1) is altered and associated with cardiac lesions at the insulin-resistant early stage of type 2 diabetes mellitus, and, if so, whether calcium channel blockers can reverse such alterations. We examined plasma and cardiac expression of ET-1 in male Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a spontaneous model of human type 2 diabetes mellitus. At 8 weeks of age, OLETF rats were treated for 12 weeks with a long acting calcium channel blocker, benidipine (3 mg/kg per day p.o.) (BEN, n = 15), or with vehicle (OLETF, n = 15), and age-matched genetic control, male Long-Evans Tokushima Otsuka (LETO) rats were also used (n = 15). Blood pressure was significantly higher in OLETF than LETO rats, and benidipine treatment of OLETF rats for 12 weeks did not reduce their blood pressure significantly. Plasma and cardiac levels of ET-1 were significantly higher in OLETF compared with LETO rats (both P < 0.01), and were reversed after benidipine treatment. Our results suggest that ET-1 plays a pivotal role in the pathogenesis of cardiac complications at the insulin-resistant stage of diabetes mellitus, and that benidipine treatment may have a beneficial effect on these complications.     

Renal protective effect of YM598, a selective endothelin ET(A) receptor antagonist,against diabetic nephropathy in OLETF rats

We have investigated the effect of potassium (E)-N-[6-methoxy-5-(2-methoxyphenoxy)-2-(pyrimidin-2-yl) pyrimidin-4-yl]-2-phenylenthenesulfonamidate (YM598), a selective endothelin ET(A) receptor antagonist, on renal function in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, an animal model of type II diabetes. YM598 (0.1 or 1 mg kg(-1)), enalapril (5 mg kg(-1)), an angiotensin-converting enzyme inhibitor, or vehicle was administered once daily by gastric gavage to 22-week-old male Otsuka Long-Evans Tokushima Fatty rats for 32 weeks. Enalapril but not YM598 mildly lowered blood pressure in the diabetic rats. YM598 blunted the development of albuminuria in a dose-dependent manner. High dose of YM598 reduced albuminuria comparable to enalapril. Urinary endothelin-1 excretion was greater in the diabetic than in the control rats, and was not substantially influenced by the agents. These data suggest that endothelin is involved in the progression of diabetic nephropathy in Otsuka Long-Evans Tokushima Fatty rats, and an endothelin ET(A) receptor antagonist may be useful for the treatment of diabetic nephropathy.     

Long-term treatment with Hachimi-jio-gan attenuates kidney damage in spontaneously diabetic WBN/Kob rats

Diabetes mellitus is now the most common cause of end-stage renal failure. In this study, the effects of Hachimi-jio-gan on diabetic kidney damage in spontaneously diabetic WBN/Kob rats were examined. Oral administration of Hachimi-jio-gan to WBN/Kob rats for 25 weeks significantly suppressed urinary protein excretion. It did not affect body weight loss or blood glucose levels, whereas it reversed the increase in kidney weight of WBN/Kob rats. Hachimi-jio-gan also reduced fibronectin and transforming growth factor beta1 (TGF-beta1) protein expression in the renal cortex. Furthermore, renal lipid peroxidation levels of WBN/Kob rats given Hachimi-jio-gan were significantly lower than those of untreated controls. Renal superoxide dismutase activity was elevated by Hachimi-jio-gan treatment in a dose-dependent manner. These results suggested that Hachimi-jio-gan could prevent diabetic kidney damage by reducing renal oxidative injury and expression of fibronectin and TGF-beta1 proteins, which are all involved in the pathophysiology of diabetic nephropathy.     

Sildenafil, a phosphodiesterase type 5 inhibitor, attenuates diabetic nephropathy in non-insulin-dependent Otsuka Long-Evans Tokushima Fatty rats

BACKGROUND

It is well established that the pathogenesis of diabetic nephropathy is associated with abnormalities of renal nitric oxide (NO) generation. Many of the biological actions of NO are mediated by cGMP, which is rapidly degraded by phosphodiesterases. In this study, we evaluated the renoprotective effects of sildenafil (SIL), an inhibitor of phosphodiesterase-5, in type 2 diabetic rats.

METHODS

Male Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a non-insulin-dependent diabetes model, and Long-Evans Tokushima Otsuka rats, a non-diabetic control, were treated with either SIL (2.5 mg·kg⁻¹ in drinking water) or undosed water for 28 weeks, starting at 30 weeks of age.

RESULTS

Sildenafil treatment significantly decreased albuminuria, attenuated glomerular hyperfiltration and resulted in a decrease in glomerular hypertrophy, in addition to a reduced glomerulosclerosis score and a dramatic decrease in the number of glomerular and tubulointerstitial proliferating cell nuclear antigen-positive cells in OLETF rats. This was accompanied by a significant reduction in renal cortical mRNA levels of collagen types I and III. The increased mRNA levels of matrix metalloproteinase (MMP)-2, MMP-9, tissue inhibitors of MMPs (TIMP)-1 and TIMP-2 in the OLETF rats were significantly or partially attenuated by SIL treatment.

CONCLUSIONS

This study suggests that SIL attenuated diabetic nephropathy due to its potent antiproliferative effects and its regulatory effects on extracellular matrix. This latter effect is thought to be a result of its ability to affect the balance between MMPs and their inhibitors.     

Hematological alterations in the Otsuka Long-Evans Tokushima fatty (OLETF) rats--a model of type 2 diabetes mellitus

The OLETF rat develops microangiopathic complications similar to human diabetes and is considered a useful model of Type 2 DM. Erythrocyte, platelet and leucocyte abnormalities described in diabetic patients are thought to play a role in the development of diabetic microangiopathy. This study was designed to investigate whether OLETF rats show hematological alterations and the effect of sucrose treatment on metabolic and blood parameters. Hematological parameters, body weight, food and water intake, fasting and non-fasting blood glucose (BG) and HbA1c were measured in OLETF rats treated for two months with 30% sucrose added to drinking water. Non-treated OLETF rats and non-diabetic Long-Evans Tokushima Otsuka (LETO) rats were used as controls. In the control OLETF rats the number of platelets (Plt) and red blood cells (RBC) was higher, while the mean cell volume (MCV) and the mean cell hemoglobin content (MCH) were lower compared with LETO. Mean cell hemoglobin concentration (MCHC) was significantly higher in the diabetic rats. Sucrose administration decreased food intake and body weight and increased fasting blood glucose and HbA1c. It resulted in a decrease of RBC, Hb, Hct, MCV and MCH compared with control OLETF, while Plt count increased significantly. Our results point to significant alterations in erythrocyte count and morphology and Plt count in diabetic OLETF rats compared with non-diabetic LETO. Sucrose administration accelerated the development of diabetes, affected blood cells inducing the suppression of RBC and an increase in Plt count and some of its effects persisted after sucrose withdrawal.     

Dilazep hydrochloride,an antiplatelet drug,prevents progression of diabetic nephropathy in Otsuka Long-Evans Tokushima fatty rats

Diabetic nephropathy is a leading cause of end-stage renal disease in industrialized countries. Although the mechanisms for the development and progression of diabetic nephropathy are not fully understood, platelet activation may participate in its pathogenesis by promoting microthrombus formation. In this study, we investigated the effects of dilazep hydrochloride, an antiplatelet agent, on the development and progression of diabetic nephropathy in Otsuka Long-Evans Tokushima fatty (OLETF) rats, a type 2 diabetes mellitus animal model. Administration of dilazep hydrochloride significantly reduced the increase of urinary protein excretions and N-acetyl-beta-D-glucosaminidase (NAG) activity in OLETF rats. Furthermore, dilazep hydrochloride treatment prevented glomerulosclerosis and tubular atrophy and reduced positive staining for type IV collagen in the glomeruli of diabetic rats. These results indicate that platelet activation plays a dominant role in the development and progression of diabetic nephropathy. Our study suggests that dilazep hydrochloride is a valuable new drug for the treatment of diabetic patients with nephropathy.     

Lowered entrainment function in the suprachiasmatic nucleus of Otsuka Long Evans Tokushima Fatty (OLETF) rats.

The entrainment function in the suprachiasmatic nucleus (SCN) of young non-diabetic Otsuka Long Evans Tokushima Fatty (OLETF) rats was studied. OLETF rats significantly needed more days for re-entrainment to a new light-dark cycle than control Long Evans Tokushima Otsuka (LETO) rats. We also assessed Fos expression in the SCN induced by dim light exposure. The number of Fos-immunoreactive cells was significantly decreased in 5- to 13-week-old OLETF rats compared with LETO rats. Moreover, the effect of glutamate on neuronal activity in the SCN of OLETF rats were investigated. In young non-diabetic OLETF rats, the phase delay in the SCN neuronal firing rhythm induced by 1 microM glutamate was significantly less than that in LETO rats. These results suggested that the entrainment function is reduced in OLETF rats before the onset of diabetes.     

DNA microarray analysis of type 2 diabetes-related genes co-regulated between white blood cells and livers of diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats

In a previous study, we hypothesized that some type 2 diabetes mellitus susceptible genes may be up/down-regulated in white blood cells (WBC) of Otsuka Long-Evans Tokushima Fatty (OLETF) rats, reflecting their up/down-regulation in major insulin-target tissues such as the liver before the onset of diabetes. We identified 57 potential candidate genes for predicting diabetes. In this study, we examined this hypothesis further by extending the experimental conditions from before the onset (6 weeks) to after the onset (24 weeks) of diabetes that type 2 diabetes mellitus susceptible genes are co-regulated in WBC, reflecting their expression in the liver. Using rat oligo DNA microarrays, we found that 48 genes are up/down-regulated in OLETF rats compared to control Long-Evans Tokushima Otsuka (LETO) rats in WBC and liver under fasting or insulin administration conditions. Twenty nine and 33 genes were up/down-regulated in both WBC and livers, respectively, under fasting and insulin administration conditions, respectively. Eight out of 29 genes in fasting condition and 12 out of 33 genes in insulin administration conditions have been reported to be type 2 diabetes mellitus susceptible genes and the remainder have not been reported to be related to type 2 diabetes mellitus. These results support our hypothesis that the expression levels of type 2 diabetes mellitus related genes in WBC are reflective of those in the liver after the onset of diabetes.     

自发性2型糖尿病大鼠肺组织α平滑肌肌动蛋白表达的变化及罗格列酮对其影响

目的 探讨自发性2型糖尿病(OLETF)大鼠肺组织α-平滑肌肌动蛋白(α-SMA)表达的变化及罗格列酮对其影响.方法 30周龄雄性OLETF大鼠16只,分为OLETF组和OLETF/L组每组8只,对照组为8只LETO组大鼠.OLETF/L组大鼠给予罗格列酮3 mg/(kg·d)灌胃12周后处死大白鼠,应用免疫组织化学和免疫蛋白印迹法检测各组大鼠肺组织α-SMA蛋白表达.结果 各组大鼠肺组织α-SMA主要表达于肌成纤维细胞、血管平滑肌细胞、小气道平滑肌,OLETF组大鼠肺组织α-SMA蛋白表达(2.03±0.64)明显高于LETO组(1.18±0.35),P<0.05];OLETF/L组明显减少(1.34±0.40),差异均有统计学意义(均P<0.05).结论 OLETF大鼠肺组织肌成纤维细胞生成增多,罗格列酮可抑制成纤维细胞向肌成纤维细胞的转化,早期改善糖尿病肺纤维化.

Abstract：

Objective To investigate the changes of expression of α—smooth muscle actin(α-SMA)in lung of spontaneous type 2 diabetes Otsuka Long-Evans Tokushima Fatty(OLETF)rats and the effect by tlle rosiglitazone.Methods Totally 16 male OLETF rats in 30 weeks old were divided into OLETF group and OLETF／L group.The Long Evans Tokushima Otsuka(LETO)rats were in control group.Thle OLtErI’F.rats were given gastric lavage bymsiglitazone 3 ms／(kg·d)then were killed after 12 weeks.The levels of ct-SMA in lung of three groups were detected by immunohistochemistry and western blotting.Results α-SMA in lung of three groups mainly expressed in myofibmblast.vascular smooth muscle cells and small airway smootII muscle.Compared to control group,tlle levels of α-SMA in lung of OIJETF group were increased obviously(2.03-4-0.64 VS 1.18 4-0.35,P<0.05).Compared to OLETF group,the levels of α-SMA in lung of OLETF／L group were decreased obviously(1.34 ±0.40 VS 2.03 ±0.64.P<0.05).Conclusion Myofibroblast increases in lung of OLETF rats.Rosiglitazone can inhibit the transformation from fibroblast to myofibroblast and improve pulmonary fibrosis in diabetes in early stage.     

Reduction of Food Intake by Fenofibrate is Associated with Cholecystokinin Release in Long-Evans Tokushima Rats

Fenofibrate is a selective peroxisome proliferator-activated receptor α (PPARα) activator and is prescribed to treat hyperlipidemia. The mechanism through which PPARα agonists reduce food intake, body weight, and adiposity remains unclear. One explanation for the reduction of food intake is that fenofibrate promotes fatty acid oxidation and increases the production of ketone bodies upon a standard experimental dose of the drug (100~300 mg/kg/day). We observed that low-dose treatment of fenofibrate (30 mg/kg/day), which does not cause significant changes in ketone body synthesis, reduced food intake in Long-Evans Tokushima (LETO) rats. LETO rats are the physiologically normal controls for Otsuka Long-Evans Tokushima Fatty (OLETF) rats, which are obese and cholecystokinin (CCK)-A receptor deficient. We hypothesized that the reduced food intake by fenofibrate-treated LETO rats may be associated with CCK production. To investigate the anorexic effects of fenofibrate in vivo and to determine whether CCK production may be involved, we examined the amount of food intake and CCK production. Fenofibrate-treated OLETF rats did not significantly change their food intake while LETO rats decreased their food intake. Treatment of fenofibrate increased CCK synthesis in the duodenal epithelial cells of both LETO and OLETF rats. The absence of a change in the food intake of OLETF rats, despite the increase in CCK production, may be explained by the absence of CCK-A receptors. Contrary to the OLETF rats, LETO rats, which have normal CCK receptors, presented a decrease in food intake and an increase in CCK production. These results suggest that reduced food intake by fenofibrate treatment may be associated with CCK production.     

Altered endothelium-dependent responsiveness in the aortas and renal arteries of Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of non-insulin-dependent diabetes mellitus

We examined endothelium-dependent relaxation in the aortas and renal arteries of Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of non-insulin-dependent diabetes mellitus, in comparison with non-diabetic Long-Evans Tokushima Otsuka rats as controls. Acetylcholine-induced relaxation in both arteries was attenuated, and the attenuation was restored to the control level by indomethacin. The relaxation was inhibited completely in the aortas, but only partially in renal arteries by N(G)-nitro-L-arginine methyl ester, and the degree of the latter inhibition was greater in OLETF rats than in the controls. The relaxation was inhibited by aminoguanidine in both arteries of OLETF rats but not in the controls. Serum NO(2) plus NO(3) levels significantly increased in OLETF rats. These results suggest that impairment of relaxation in OLETF rat arteries is due to increased release of contractile factors but not decreased release of nitric oxide.     

Renal protective effect of YM598, a selective endothelin type A receptor antagonist

We have investigated the protective effect of YM598, a selective endothelin type A receptor antagonist, against an endothelin-1-induced proliferation of rat mesangial cells and renal function in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, an animal model of type II diabetes. YM598, but not K-8794, a selective endothelin type B receptor antagonist, inhibited the endothelin-1-induced proliferation of cultured mesangial cells derived from intact Wistar rats in a concentration-dependent manner. YM598 (0.1 or 1 mg/kg), enalapril (5 mg/kg), an angiotensin- converting enzyme inhibitor, or vehicle was administered once daily by gastric gavage to 22-week-old male OLETF rats for 32 weeks. YM598 blunted the development of albuminuria in a dose-dependent manner. A higher dose of YM598 reduced albuminuria comparable with enalapril. Urinary endothelin-1 excretion was greater in the diabetic rats than in the control rats, and was not substantially influenced by the agents. Enalapril, but not YM598, mildly lowered the blood pressure in the diabetic rats, indicating that blood pressure reduction is not involved in the major mechanism of the renoprotective effect of YM598 in OLETF rats. These data suggest that endothelin is involved in the progression of diabetic nephropathy in OLETF rats, and an endothelin type A antagonist is promising for the treatment of diabetic nephropathy.     

Vildagliptin blocks vascular injury in thoracic aorta of diabetic rats by suppressing advanced glycation end product–receptor axis

Vildagliptin is a stable inhibitor of dipeptidyl peptidase-IV, a responsible enzyme that mainly inactivates glucagon-like peptide-1, and now one of the widely used agents for the treatment of diabetes. However, effects of vildagliptin on vascular injury in diabetes are largely unknown. Since advanced glycation end products (AGEs) and their receptor RAGE axis are reported to contribute to vascular complications in diabetes, we investigated here whether vildagliptin inhibits vascular damage in thoracic aorta of Otsuka Long-Evans Tokushima Fatty rats (OLETF rats), an animal model of type 2 diabetes with obesity, by blocking the AGEs-RAGE axis. OLETF and control LETO rats at 22 weeks old were given vehicle or 3 mg/kg of vildagliptin for another 12 weeks. Vildagliptin treatment decreased fasting plasma glucose and heart rate in OLETF rats. Compared with control LETO rats, levels of AGEs, RAGE mRNA and protein, an oxidative stress marker, 8-hydroxydeoxyguanosine, two membrane components of NADPH oxidase, p22 and gp91phox mRNAs, and phospho-NF-κB p65 in thoracic aorta were significantly enhanced in OLETF rats, all of which were inhibited by the treatment with vildagliptin. Vildagliptin significantly reduced both mRNA and protein levels of monocyte chemoattractant protein-1, vascular cell adhesion molecule-1 and plasminogen activator inhibitor-1 in thoracic aorta of OLETF rats. Enhanced expression of transforming growth factor-β in the aorta of diabetic rats was also suppressed by vildagliptin. Our present data suggest that vildagliptin could play a protective role against vascular injury in diabetes partly by attenuating the deleterious effects of AGEs-RAGE-oxidative stress axis.     

Alterations of voltage‐dependent K+ channels in the mesenteric artery during the early and chronic phases of diabetes

This study investigated the alteration of voltage‐dependent K⁺ (Kv) channels in mesenteric arterial smooth muscle cells from control (Long‐Evans Tokushima Otsuka [LETO]) and diabetic (Otsuka Long‐Evans Tokushima Fatty [OLETF]) rats during the early and chronic phases of diabetes. We demonstrated alterations in the mesenteric Kv channels during the early and chronic phase of diabetes using the patch‐clamp technique, the arterial tone measurement system, and RT‐PCR in Long‐Evans Tokushima (LETO; for control) and Otsuka Long‐Evans Tokushima Fatty (OLETF; for diabetes) type 2 diabetic model rats. In the early phase of diabetes, the amplitude of mesenteric Kv currents induced by depolarizing pulses was greater in OLETF rats than in LETO rats. The contractile response of the mesenteric artery induced by the Kv inhibitor, 4‐aminopyridine (4‐AP), was also greater in OLETF rats. The expression of most Kv subtypes‐ including Kv1.1, Kv1.2, Kv1.4, Kv1.5, Kv1.6, Kv2.1, Kv3.2, Kv4.1, Kv4.3, Kv5.1, Kv6.2, Kv8.1, Kv9.3, and Kv10.1‐were increased in mesenteric arterial smooth muscle from OLETF rats compared with LETO rats. However, in the chronic phase of diabetes, the Kv current amplitude did not differ between LETO and OLETF rats. In addition, the 4‐AP‐induced contractile response of the mesenteric artery and the expression of Kv subtypes did not differ between the two groups. The increased Kv current amplitude and Kv channel‐related contractile response were attributable to the increase in Kv channel expression during the early phase of diabetes. The increased Kv current amplitude and Kv channel‐related contractile response were reversed during the chronic phase of diabetes.     

Lithospermic acid B ameliorates the development of diabetic nephropathy in OLETF rats

Lithospermic acid B (LAB), an active component isolated from Salvia miltiorrhizae, has been reported to have renoprotective effects in type 1 diabetic animal models. In the present study we investigated the effects of LAB on the prevention of diabetic nephropathy in type 2 diabetic Otsuka Long-Evans-Tokushima Fatty (OLETF) rats. LAB (20 mg/kg) was given orally once daily to 10-week-old male OLETF rats for 28 weeks. Treatment of OLETF rats with LAB had little effects on body weight and blood glucose levels. Treatment with LAB resulted in significant reduction in blood pressure. LAB markedly attenuated albuminuria and significantly lowered levels of lipid peroxidation, monocyte chemoattractant protein-1 (MCP-1), and transforming growth factor-beta (TGF-beta1) expression in renal tissues of OLETF rats. In addition, LAB inhibited the progression of glomerular hypertrophy, mesangial expansion, and expansion of the extracellular matrix in the renal cortex. Collectively, these results suggest that LAB has beneficial effects on the diabetic nephropathy in OLETF rats by decreasing blood pressure, oxidative stress, and MCP-1 expression. Our results suggest that LAB might be a new therapeutic agent for the prevention of nephropathy in type 2 diabetes.