Regulatory effect of Rac1 on vascular reactivity after hemorrhagic shock in rats

We used isolated superior mesenteric arteries (SMAs) from hemorrhagic-shock rats and hypoxia-treated vascular smooth muscle cells (VSMCs; mimicking the shock state) to observe the effects of platelet-derived growth factor (PDGF; Rac1 stimulator) and NSC23766 (Rac1 antagonist) on vascular reactivity and the relationship with the Rho kinase-myosin light-chain phosphatase (MLCP) and p21-activated kinase (PAK)-myosin light-chain kinase (MLCK) signal pathway. The results indicated that the contractile responses of the SMAs and VSMCs were significantly increased at early shock or after transient hypoxia. NSC23766 (Rac1 antagonist) further increased, whereas PDGF (Rac1 stimulator) decreased the contractile responses of SMAs and VSMCs. In the late period of shock or prolonged hypoxia, the contractile responses of SMAs and VSMCs were significantly decreased; NSC23766 increased (whereas PDGF further decreased) the contractile response of the SMAs and VSMCs. Activation of Rac1 with PDGF significantly increased the activity of PAK and MLCP, and decreased Rho kinase and MLCK activity and 20-kDa myosin light-chain phosphorylation in VSMCs. The PAK inhibitor PAK-18 significantly antagonized the PDGF-induced decrease in MLCK activity, whereas the Rho kinase antagonist Y-27632 further enforced the PDGF-induced increase in MLCP activity. Simple fluid resuscitation did not improve but in combination with NSC23766 significantly improved vascular reactivity and animal survival at 24 hours. This suggested that Rac1 has an inhibitory effect on vasoreactivity after shock. Rac1-mediated regulation of vascular reactivity is mainly through activation of PAK, inhibition of MLCK and inhibition of Rho kinase, unpack the inhibition of Rho kinase to MLCP. Rac1 may be a potential target to treat vascular hyporeactivity in many critical conditions.     

Inhibitory effect of streptozotocin-induced diabetes on non-cholinergic motor transmission in rat detrusor and its prevention by sorbinil.

1. Non-cholinergic motor transmission in the urinary bladder of streptozotocin (STZ)-diabetic rats was studied by recording contractile activity of strips of detrusor in vitro. 2. The neurogenic contractile responses to electrical field stimulation (EFS) of atropine-treated detrusor strips were decreased in 4, 8 and 12 week STZ-diabetic rats. The decrease was most marked in 12 week diabetic rats and least in 4 week ones. 3. Concentration-response curves showed no change in sensitivity of the detrusor to acetylcholine (ACh) in diabetic rats. The maximum tension generated by ACh was similar in diabetic and non-diabetic animals. 4. The contractile responses to EFS at frequencies greater than or equal to 1 Hz were not maintained during stimulation. The 'fade' was significantly greater in detrusor strips of diabetic rats. 5. The contractile response of detrusor to EFS was significantly greater in 12 week diabetic rats treated with the aldose reductase inhibitor sorbinil, than in untreated 12 week diabetic rats. The sensitivity to ACh was similar in the two groups. 6. It is concluded that the reduction of the neurogenic non-cholinergic responses of detrusor to EFS in STZ-diabetic rats is probably caused by a reduction in the release of the non-cholinergic motor transmitter. The results are discussed in relation to bladder dysfunction in human diabetes mellitus.     

The effects of adenosine on isolated right atrial preparations from streptozotocin‐diabetic rats

1 The aim of the present study was to investigate the inhibitory effects of adenosine on the contractile force and chronotropic action of isolated right atrial preparations from streptozotocin (STZ)‐diabetic rats. 2 The rats were anaesthetized with diethyl ether and STZ (65 mg kg^?1) was injected intravenously via the tail vein. 3 Adenosine produced concentration‐dependent decreases in the force of contraction and a negative chronotropic action of atria both in control and diabetic groups. The inhibition responses to adenosine were significantly higher in diabetic rat atria than control. 4 Dypiridamole incubation caused a significant potentiation of the inhibitory effect of adenosine on contractile force and chronotropic action of atria in the control group, but not in the diabetic group. In the presence of dipyridamole, the inhibitory effects of adenosine on measured parameters in diabetic rats were not significantly different from those in control rats. 5 These results suggested that atria from 6 weeks STZ‐diabetic rats exhibited a supersensitivity to the negative inotropic and chronotropic effects of adenosine compared with atria from control rats because of an impairment in adenosine uptake mechanism. Altered sensitivity to effects of adenosine might reflect relatively early changes in the course of diabetes.     

Inhibition of prostate smooth muscle contraction and prostate stromal cell growth by the inhibitors of Rac,NSC23766 and EHT1864

Background and Purpose

Medical therapy of lower urinary tract symptoms (LUTS) suggestive of benign prostatic hyperplasia (BPH) targets smooth muscle contraction in the prostate, or prostate growth. However, current therapeutic options are insufficient. Here, we investigated the role of Rac in the control of smooth muscle tone in human prostates and growth of prostate stromal cells.

Experimental Approach

Experiments were performed using human prostate tissues from radical prostatectomy and cultured stromal cells (WPMY-1). Expression of Rac was examined by Western blot and fluorescence staining. Effects of Rac inhibitors (NSC23766 and EHT1864) on contractility were assessed in the organ bath. The effects of Rac inhibitors were assessed by pull-down, cytotoxicity using a cell counting kit, cytoskeletal organization by phalloidin staining and cell growth using an 5-ethynyl-2′-deoxyuridine assay.

Key Results

Expression of Rac1–3 was observed in prostate samples from each patient. Immunoreactivity for Rac1–3 was observed in the stroma, where it colocalized with the smooth muscle marker, calponin. NSC23766 and EHT1864 significantly reduced contractions of prostate strips induced by noradrenaline, phenylephrine or electrical field stimulation. NSC23766 and EHT1864 inhibited Rac activity in WPMY-1 cells. Survival of WPMY-1 cells ranged between 64 and 81% after incubation with NSC23766 (50 or 100 μM) or EHT1864 (25 μM) for 24 h. NSC23766 and EHT1864 induced cytoskeletal disorganization in WPMY-1 cells. Both inhibitors impaired the growth of WPMY-1 cells.

Conclusions and Implications

Rac may be a link connecting the control of prostate smooth muscle tone with proliferation of smooth muscle cells. Improvements in LUTS suggestive of BPH by Rac inhibitors appears possible.     

Total flavonoids of Epimedium ameliorates testicular damage in streptozotocin‐induced diabetic rats by suppressing inflammation and oxidative stress

Testicular damage is the anomaly that will often accompany diabetes mellitus. Thus, this study aimed to investigate the role that total flavonoids of Epimedium (TFE) played against streptozotocin (STZ)‐induced diabetic testicular dysfunction and to elucidate the mechanism of action. The diabetic rat model was induced by vein injection of STZ in healthy rats. Thirty male healthy Spraque‐Dawley rats were randomly divided into following groups: the control group, the diabetic group, and the diabetic + TFE group. Gastrointestinal administration begins at fifth week of TFE for 6 weeks. After TFE administration, all animals were euthanized. Testicular tissue samples and blood samples of rats were collected for histopathological examination and for determination of levels of various biomarkers including blood glucose, testosterone, testicular enzymes, and oxidative stress indicators. All testes were weighted to calculate the testicular organ index. Hematoxylin‐eosin staining was used for observing the testis and epididymis pathological changes. Protein expression (monocyte chemoattractant protein‐1, transforming growth factor‐beta‐1, interleukin‐6, and 3‐beta‐hydroxysteroid dehydrogenase) was detected by immunohistochemistry and western blot techniques. There was a significant difference in the changes between the diabetes group and the control group. As a result of treat with TFE, the blood glucose decreased but there was no significant difference, and other indicators showed significant improvement. TFE may protect against STZ‐induced testicular injury by suppressing inflammation and oxidative stress.     

Structure-function based design of small molecule inhibitors targeting Rho family GTPases

Rho GTPases of the Ras superfamily are involved in the regulation of multiple cell functions and have been implicated in the pathology of various human diseases including cancer. They are attractive drug targets in future targeted therapy. A wealth of structure-function information made available by high resolution structures and mutagenesis studies has laid out the foundation for the derivation of a mechanism-based targeting strategy. Here we describe the rational design and characterizations of a first generation Rac-specific small molecule inhibitor. Based on the structure-function information of Rac interaction with GEFs, in a computer based Virtual Screening we have identified NSC23766, a highly soluble and membrane permeable compound, as a specific inhibitor of a subset of GEF binding to Rac and therefore Rac activation. In fibroblast cells NSC23766 inhibited Rac1 GTP-loading without affecting Cdc42 or RhoA activity and suppressed the Rac-GEF, Tiam1, and oncogenic Ras induced cell growth and transformation. NSC23766 also potently inhibited the prostate PC-3 cancer cell proliferation and invasion induced by Rac hyperactivation. Intraperitoneal administration of NSC23766 to laboratory mice resulted in effective Rac GTPase suppression and hematopoietic stem cell mobilization from the bone marrow to the peripheral blood, similar to the effects of genetically targeted disruption of Rac GTPases in the animals. A co-crystal structure of NSC23766 bound to Rac1 provided further insight for future medicinal chemistry modification and improvement of this lead Rac-specific inhibitor. Thus, structure-function based rational design may represent a new avenue for generating lead small molecule inhibitors of Ras superfamily GTPases that are useful for modulating pathological conditions in which the small GTPase deregulation may play a role.     

二烯丙基二硫下调TGF-β1/Rac1通路抑制人胃癌细胞β-catenin表达

目的研究二烯丙基二硫(diallyl disulfide,DADS)是否通过下调TGF-β1/Rac1通路抑制人胃癌MGC803细胞β-catenin表达。方法实验组分为6组,对照组(Control),DADS处理组,TGF-β1处理组,TGF-β1+SB431542组,TGF-β1+DADS组,TGF-β1+NSC23766组。RT-PCR、Western blot分别检测TGF-β1、Rac1、β-catenin、E-cadherin和vimentin mRNA和蛋白水平。结果DADS下调TGF-β1、Rac1、β-catenin和vimentin,上调E-cadherin表达。TGF-β1受体阻断剂SB431542和Rac1抑制剂NSC23766下调β-catenin和vi-mentin,上调E-cadherin表达。结论DADS通过下调TGF-β1/Rac1通路抑制人胃癌MGC803细胞β-catenin表达。     

Deep sea minerals ameliorate diabetic‐induced inflammation via inhibition of TNFα signaling pathways

It has been well‐documented that the consumption of deep sea water (DSW) has beneficial effects on myocardial hypertrophy and cardiac apoptosis induced by hypercholesterolemia. However, the molecular mechanisms for the anti‐inflammatory effects of DSW on diabetic cardiomyopathy are still largely unclear. The main purpose of this present study was to test the hypothesis that DSW exerts anti‐inflammatory effects through the suppression of the TNF‐α‐mediated signaling pathways. IP injection of streptozotocin (STZ) at the dose of 65 mg/kg was used to establish a diabetes rat model. DSW mineral extracts that diluted in desalinated water were prepared in three different dosages and administered to the rats through gavages for 4 weeks. These dosages are DSW‐1X (equivalent to 37 mg Mg²⁺/kg/day), 2X (equivalent to 74 mg Mg²⁺/kg/day) and 3X (equivalent to 111 mg Mg²⁺ mg/kg/day). Immunofluorescence staining and Western blot showed that the protein expression level of TNF‐α was markedly higher in the STZ‐induced diabetic rat hearts than in the control group. Consequently, the phosphorylation levels of the TNF‐α‐modulated downstream signaling molecules and P38 mitogen‐activated protein kinases (MAPKs) were notably elevated in heart tissues of STZ‐induced diabetes. These higher phosphorylation levels subsequently upregulated NF‐κB‐modulated inflammatory mediators, such as cyclooxygenase (COX)‐II and inducible nitric oxide synthase (iNOS). However, treatment with DSW as well as MgSO₄, the main mineral in DSW, significantly reversed all the alterations. These findings suggest that DSW has potential as a therapeutic agent for preventing diabetes‐related cardiovascular diseases.     

Prostanoid release and constrictor responses to noradrenaline in the rat mesenteric vascular bed in non‐insulin‐dependent diabetes mellitus

1 The administration of streptozotocin (STZ) to 2‐day old rats induced a non‐insulin‐dependent diabetes mellitus (NIDDM)‐like state, with mild hyperglycaemia and no alterations in body weight at the adult age. 2 In the isolated and perfused mesenteric vascular bed of NIDDM animals, the constrictor responses to either noradrenaline (NA) or potassium chloride (KCl) were not modified as compared with age‐matched non‐diabetic controls. 3 The reduction in NA contractions induced by the cyclooxygenase inhibitor, 10 μM indomethacin in the control group was absent in the NIDDM rats. 4 The increase in the NA‐induced contractions caused by endothelium removal was suppressed by indomethacin in the controls but not in the NIDDM group. 5 The prostanoid release from the mesenteric vascular beds of NIDDM rats was markedly reduced as compared with non‐diabetic controls. Noradrenaline increased production of the constrictor prostaglandin (PG) F₂α in control but not in NIDDM rats. 6 In summary, these results show that in STZ‐induced NIDDM rats, there is an impairment of the prostanoid production, as well as a suppression of the role of prostanoids in the contractile effects of NA in the mesenteric vascular bed. These alterations are more severe than those previously observed in a model of insulin‐dependent diabetes mellitus (IDDM), in which hyperglycaemia and reduction of body weight were more marked. The conclusion is that, in these models of diabetes and in the preparation studied, vascular alterations and modifications of glycaemia and body weight are not closely related.     

Rac对失血性休克大鼠血管反应性的调节作用

目的探讨Rac在失血性休克大鼠血管反应性调节中的作用。方法采用SD大鼠复制休克模型,取离体血管环,观察休克早期和晚期血管反应性的变化以及Rac激动剂和特异性抑制剂对休克早期和晚期血管反应性的影响;通过酶消化法培养原代血管平滑肌细胞（vascular smoot hmuscle cell,VSMC）,采用双室培养方式分别观察VSMC缺氧10min和90min后VSMC对去甲肾上腺素（norepinephrine,NE）的收缩反应性变化,同时观察Rac活性调节剂对缺氧后VSMC收缩反应性的影响。结果在休克早期和短暂缺氧后,离体血管环和VSMC对NE收缩反应性均有所升高,Rac的激动剂血小板衍生生长因子（platelet derived growth factor,PDGF）可部分降低休克早期或短暂缺氧后血管反应性,Rac特异性抑制剂NSC23766可拮抗由PDGF所引起的血管反应性的变化,而在休克晚期或长时间缺氧后,离体血管环和VSMC对NE收缩反应性明显降低,NSC23766对休克晚期或长时间缺氧所致血管反应性降低有升高作用。结论休克后血管反应性呈双相变化,休克早期升高,休克晚期降低,Rac参与了休克血管反应性的调节。     

The effect of hypercholesterolemia on carbachol-induced contractions of the detrusor smooth muscle in rats: increased role of L-type Ca2+ channels

To investigate a possible relation between hypercholesterolemia and detrusor smooth muscle function, we studied the contractile response to potassium challenge, carbachol (CCh), and the components of CCh-induced contractile mechanism in high-cholesterol diet-fed rats. Adult male Sprague–Dawley rats were fed with standard (control group, N?=?17) or 4?% cholesterol diet (hypercholesterolemia group (HC), N?=?16) for 4?weeks. Spontaneous contractions of detrusor muscle strips and their responses to potassium chloride (KCl) or cumulative dose–contraction curves to CCh were recorded. The effects of muscarinic receptor antagonists (methoctramin and/or 4-diphenylacetoxy-N-methylpiperidine), L-type Ca⁺² channel blocker (nifedipine), and/or rho-kinase inhibitor Y-27632 were investigated. Blood cholesterol level was increased in the HC group with no sign of atherosclerosis. The KCl-induced detrusor smooth muscle contractions were higher in HC, whereas spontaneous and CCh-induced responses were similar in both groups. Preincubation with receptor antagonist for M₃ but not for M₂ attenuated contraction significantly, shifting the dose–response curve to the right. This response was similar in both groups. Among two effector mechanisms of M₃-mediated detrusor smooth muscle contraction, rho-kinase pathway was not affected by hypercholesterolemia, whereas blockade of L-type Ca⁺² channels potently reduced contractions. The results of this study point out a relation between hypercholesterolemia and contractile mechanism of detrusor smooth muscle likely to change urinary bladder function, via altering L-type Ca⁺² channels. Taken together with escalating incidence of hypercholesterolemia and lower urinary tract symptoms, it is a field which deserves to be investigated further.     

Up‐regulation of Rac1 in the bronchial smooth muscle of murine experimental asthma

There has been considerable research on the involvement of RhoA/Rho kinase signalling in smooth muscle contractions. However, only a few reports have addressed the specific role of Rac1, which is a member of the Rho GTPase superfamily. Therefore, this study investigated the role of Rac1‐related pathways in bronchial smooth muscle (BSM) contractions. Bronchial rings isolated from mice were suspended in an organ bath, and the isometric contractions of circular smooth muscles were monitored. The phosphorylation of myosin light chains (MLCs) was analysed by immunoblotting. The Rac1 inhibitor EHT1864 inhibited carbachol (CCh)‐induced BSM contractions, although high K⁺ depolarization‐induced BSM contractions were not significantly attenuated by EHT1864. Moreover, high K⁺‐ and phorbol 12,13‐dibutyrate (PDBu; PKC activator)‐induced contractions were not attenuated by Rac1 inhibition, whereas sodium fluoride (NaF)‐induced force development was inhibited by EHT1864. The gene and protein expression of Rac1 was increased in the BSM of a murine model with antigen‐induced airway hyper‐responsiveness (AHR). In addition, an increased force of the BSM contractions in AHR was suppressed by EHT1864 treatment, suggesting that the up‐regulation of Rac1 is involved in AHR. These findings suggest that an increase in Rac1‐mediated signalling is involved in the augmented contractions of BSMs in antigen‐induced AHR mice.     

Tiam1/Rac1 signaling pathway mediates palmitate-induced, ceramide-sensitive generation of superoxides and lipid peroxides and the loss of mitochondrial membrane potential in pancreatic β-cells

The phagocytic NADPH oxidase [NOX] has been implicated in the generation of superoxides in the pancreatic β-cell. Herein, using normal rat islets and clonal INS 832/13 cells, we tested the hypothesis that activation of the small G-protein Rac1, which is a member of the NOX holoenzyme, is necessary for palmitate [PA]-induced generation of superoxides in pancreatic β-cells. Incubation of isolated β-cells with PA potently increased the NOX activity culminating in a significant increase in the generation of superoxides and lipid peroxides in these cells; such effects of PA were attenuated by diphenyleneiodonium [DPI], a known inhibitor of NOX. In addition, PA caused a transient, but significant activation [i.e., GTP-bound form] of Rac1 in these cells. NSC23766, a selective inhibitor of Rac1, but not Cdc42 or Rho activation, inhibited Rac1 activation and the generation of superoxides and lipid peroxides induced by PA. Fumonisin B-1 [FB-1], which inhibits de novo synthesis of ceramide [CER] from PA, also attenuated PA-induced superoxide and lipid peroxide generation and NOX activity implicating intracellularly generated CER in the metabolic effects of PA; such effects were also demonstrable in the presence of the cell-permeable C2-CER. Further, NSC23766 prevented C2-CER-induced Rac1 activation and production of superoxides and lipid peroxides. Lastly, C2-CER, but not its inactive analogue, significantly reduced the mitochondrial membrane potential, which was prevented to a large degree by NSC23766. Together, our findings suggest that Tiam1/Rac1 signaling pathway regulates PA-induced, CER-dependent superoxide generation and mitochondrial dysfunction in pancreatic β-cells.     

The effect of streptozotocin-induced diabetes on cholinergic motor transmission in the rat urinary bladder.

1. The effect of streptozotocin (STZ)-induced diabetes on cholinergic motor transmission in the rat urinary bladder was investigated by recording contractile activity of detrusor strips in vitro. 2. The Ca(2+)-channel antagonist, nifedipine, was found to be more effective in blocking the noncholinergic motor transmission than P2-purinoceptor desensitization by alpha,beta-methylene ATP. 3. The neurogenic contractile responses to electrical field stimulation in the presence of nifedipine (cholinergic) were larger in the diabetic detrusor than in the non-diabetic controls. The potentiation of the cholinergic transmission was more evident at higher frequencies. 4. Concentration-response curves for acetylcholine were identical in detrusors from diabetic and non-diabetic animals, thus excluding a postsynaptic supersensitivity to acetylcholine being responsible for the potentiation of cholinergic motor transmission. 5. It is concluded that the potentiation of cholinergic motor transmission is due to enhanced release of acetylcholine in diabetic detrusor. Possible reasons for this enhancement are discussed in relation to diabetes.     

Deep sea minerals prolong life span of streptozotocin‐induced diabetic rats by compensatory augmentation of the IGF‐I‐survival signaling and inhibition of apoptosis

Consumption of deep sea minerals (DSM), such as magnesium, calcium, and potassium, is known to reduce hypercholesterolemia‐induced myocardial hypertrophy and cardiac‐apoptosis and provide protection against cardiovascular diseases. Heart diseases develop as a lethal complication among diabetic patients usually due to hyperglycemia‐induced cardiac‐apoptosis that causes severe cardiac‐damages, heart failure, and reduced life expectancy. In this study, we investigated the potential of DSM and its related cardio‐protection to increase the life expectancy in diabetic rats. In this study, a heart failure rat model was developed by using streptozotocin (65 mg kg^?1) IP injection. Different doses of DSM‐1× (37 mg kg^?1 day^?1), 2× (74 mg kg^?1 day^?1) and 3× (111 mg kg^?1 day^?1), were administered to the rats through gavages for 4 weeks. The positive effects of DSM on the survival rate of diabetes rats were determined with respect to the corresponding effects of MgSO₄. Further, to understand the mechanism by which DSM enhances the survival of diabetic rats, their potential to regulate cardiac‐apoptosis and control cardiac‐dysfunction were examined. Echocardiogram, tissue staining, TUNEL assay, and Western blotting assay were used to investigate modulations in the myocardial contractile function and related signaling protein expression. The results showed that DSM regulate apoptosis and complement the cardiomyocyte proliferation by enhancing survival mechanisms. Moreover DSM significantly reduced the mortality rate and enhanced the survival rate of diabetic rats. Experimental results show that DSM administration can be an effective strategy to improve the life expectancy of diabetic subjects by improving cardiac‐cell proliferation and by controlling cardiac‐apoptosis and associated cardiac‐dysfunction. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 769–781, 2016.     

Effects of coffee and caffeine on bladder dysfunction in streptozotocin-induced diabetic rats

AIM: To explore the effects and mechanisms of caffeine and coffee on bladder dysfunction in streptozotocin-induced diabetic rats. METHODS: Sprague-Dawley male rats were divided randomly into 4 groups: control, diabetes mellitus (DM), DM with coffee treatment, and DM with caffeine treatment. The diabetic rat was induced by intraperitoneal injection of streptozotocin (60 mg/kg). After 7 weeks of treatment with coffee and caffeine, cystometrogram, contractile responses to electrical field stimulation (EFS) and acetylcholine (ACh), and cyclic AMP (cAMP) concentration of the bladder body and base were measured. RESULTS: The bladder weight, volume threshold for micturition and post-void residual volume (PVR) in the diabetic rats were significantly higher compared to those in the control animals. Coffee or caffeine treatment significantly reduced the bladder weight, bladder capacity and PVR in the diabetic rats. DM caused significant decreases in cAMP concentration of the bladder and coffee and caffeine caused upregulation of cAMP content in the diabetic bladder. In addition, coffee and caffeine tended to normalize the altered detrusor contractile responses to EFS and ACh in the diabetic rats. CONCLUSION: These results indicate that caffeine and coffee may have beneficial effects on bladder dysfunction in the early stage of diabetes by increasing cAMP content in the lower urinary tract, recovering the micturition reflex and improving the detrusor contractility.     

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.     

Ramipril and resveratrol co‐treatment attenuates RhoA/ROCK pathway‐regulated early‐stage diabetic nephropathy‐associated glomerulosclerosis in streptozotocin‐induced diabetic rats

Clinical studies have shown that hyperglycemia can induce early‐stage diabetic nephropathy (DN). Furthermore, oxidative stress, tubular epithelial‐mesenchymal transition and extracellular matrix accumulation promote the progression of DN to chronic kidney disease and tubulointerstitial fibrosis. It is necessary to initiate treatment at the early stages of DN or even during the early stages of diabetes. In this work, rats with streptozotocin (STZ)‐induced diabetes mellitus (DM) presented early DN symptoms within 45 days, and collagen accumulation in the glomerulus of the rats was primarily mediated through the RhoA/ROCK pathway instead of the TGF‐β signaling pathway. Resveratrol (15 mg/kg/day) and ramipril (10 mg/kg/day) co‐treatment of STZ‐induced DN rats showed that glomerulosclerosis in early‐stage DN was reversible (P < .05 compared with that in STZ‐induced DM rats). The results of this study support early intervention in diabetes or DN as a more efficient therapeutic strategy.     

Regulatory roles for Tiam1, a guanine nucleotide exchange factor for Rac1, in glucose-stimulated insulin secretion in pancreatic β-cells

Using various biochemical, pharmacological and molecular biological approaches, we have recently reported regulatory roles for Rac1, a small G-protein, in glucose-stimulated insulin secretion (GSIS). However, little is understood with respect to localization of, and regulation by, specific regulatory factors of Rac1 in GSIS. Herein, we investigated regulatory roles for Tiam1, a specific nucleotide exchange factor (GEF) for Rac1, in GSIS in pancreatic β-cells. Western blot analysis indicated that Tiam1 is predominantly cytosolic in distribution. NSC23766, a specific inhibitor of Tiam1-mediated activation of Rac1, markedly attenuated glucose-induced, but not KCl-induced insulin secretion in INS 832/13 cells and normal rat islets. Further, NSC23766 significantly reduced glucose-induced activation (i.e. GTP-bound form) and membrane association of Rac1 in INS 832/13 cells and rat islets. Moreover, siRNA-mediated knock-down of Tiam1 markedly inhibited glucose-induced membrane trafficking and activation of Rac1 in INS 832/13 cells. Interestingly, however, in contrast to the inhibitory effects of NSC23766, Tiam1 gene depletion potentiated GSIS in these cells; such a potentiation of GSIS was sensitive to extracellular calcium. Together, our studies present the first evidence for a regulatory role for Tiam1/Rac1-sensitive signaling step in GSIS. They also provide evidence for the existence of a potential Rac1/Tiam1-independent, but calcium-sensitive component for GSIS in these cells.     

Regulatory roles for Tiam1, a guanine nucleotide exchange factor for Rac1, in glucose-stimulated insulin secretion in pancreatic beta-cells

Using various biochemical, pharmacological and molecular biological approaches, we have recently reported regulatory roles for Rac1, a small G-protein, in glucose-stimulated insulin secretion (GSIS). However, little is understood with respect to localization of, and regulation by, specific regulatory factors of Rac1 in GSIS. Herein, we investigated regulatory roles for Tiam1, a specific nucleotide exchange factor (GEF) for Rac1, in GSIS in pancreatic beta-cells. Western blot analysis indicated that Tiam1 is predominantly cytosolic in distribution. NSC23766, a specific inhibitor of Tiam1-mediated activation of Rac1, markedly attenuated glucose-induced, but not KCl-induced insulin secretion in INS 832/13 cells and normal rat islets. Further, NSC23766 significantly reduced glucose-induced activation (i.e. GTP-bound form) and membrane association of Rac1 in INS 832/13 cells and rat islets. Moreover, siRNA-mediated knock-down of Tiam1 markedly inhibited glucose-induced membrane trafficking and activation of Rac1 in INS 832/13 cells. Interestingly, however, in contrast to the inhibitory effects of NSC23766, Tiam1 gene depletion potentiated GSIS in these cells; such a potentiation of GSIS was sensitive to extracellular calcium. Together, our studies present the first evidence for a regulatory role for Tiam1/Rac1-sensitive signaling step in GSIS. They also provide evidence for the existence of a potential Rac1/Tiam1-independent, but calcium-sensitive component for GSIS in these cells.