Diazoxide对乳鼠窦房结细胞模拟缺血-再灌注时的保护作用研究

目的 为探讨KATP通道开放剂Diazoxide对模拟缺血 再灌注时培养乳鼠窦房结细胞的保护作用及其可能机制。方法 分离乳鼠窦房结细胞 ,纯化培养 2d后进行实验。随机分为对照组、模拟缺血 再灌注组 (I/R)、KATP通道开放剂Diazoxide干预组 (D +I/R)及KATP通道阻断剂 5 HD干预组 (5 HD +D +I/R及 5 HD +I/R)。以流式细胞计检测各组窦房结细胞存活率 ;用激光共聚焦显微镜测定各组窦房结细胞内钙。并采用全细胞膜片钳技术测定各组细胞L型钙 (L ICa)电流密度。结果 ①D +I/R组窦房结细胞存活率 6 1.4 3%± 5 .14 %较I/R组显著增加 ;而 5 HD +D +I/R组 5 2 .35 %± 4 .94 %及 5 HD +I/R组 5 3.16 %±5 .35 %均较D +I/R组明显降低。②D +I/R组窦房结细胞相对荧光值较I/R显著降低 ;5 HD +D +I/R及5 HD +I/R两组均较D +I/R组显著增高。③D +I/R组窦房结细胞L ICa密度较I/R组显著增加。 5 HD +D +I/R组与 5 HD +I/R组的L ICa密度较D +I/R组明显减低。结论 KATP通道开放剂Diazoxide降低窦房结细胞内钙负荷 ,对模拟缺血 再灌注时的窦房结细胞有保护作用 ,并可对抗模拟缺血 再灌注对窦房结细胞L型钙电流的影响 。

Neuroprotective effects of a mitochondrial K^+-ATP channel opener (diazoxide) are mediated by Bcl-2 expression upregulation

Mitochondrial K＋-ATP （mito-KATP） channels play an important role in cellular function and survival following ischemic stress. The present results revealed that intervention with diazoxide, a mito-KATP channel opener, led to an increase in Bcl-2 expression in the cerebral cortex of rats subjected to cerebral ischemia reperfusion injury. In addition, the intervention also led to clear improvements in neuronal mitochondrial morphology and consciousness post-injury. Glibenclamide a mito-KATP channel blocker, exhibited the converse effects. Both diazoxide and glibenclamide exerted dose-dependent effects （in particular, at 18 mg/kg diazoxide and 25 mg/kg glibenclamide）. These findings suggest that diazoxide exerts a neuroprotective effect on cerebral ischemia reperfusion injury by opening mito-KATP channels and upregulating Bcl-2 expression.

Diazoxide preconditioning antagonizes cytotoxicity induced by epileptic seizures

Diazoxide, an activator of mitochondrial ATP-sensitive potassium channels, can protect neurons and astrocytes against oxidative stress and apoptosis. In this study, we established a cellular mode of epilepsy by culturing hippocampal neurons in magnesium-free medium, and used this to investigate effects of diazoxide preconditioning on the expression of inwardly rectifying potassium channel （Kir） subunits of the ATP-sensitive potassium. We found that neuronal viability was significantly reduced in the epileptic cells, whereas it was enhanced by diazoxide preconditioning. Double immunofluorescence and western blot showed a significant increase in the expression of Kir6.1 and Kir6.2 in epileptic cells, especially at 72 hours after seizures. Diazoxide pretreatment completely reversed this effect at 24 hours after seizures. In addition, Kir6.1 expression was significantly upregulated compared with Kir6.2 in hippocampal neurons after seizures. These findings indicate that diazoxide pretreatment may counteract epileptiform discharge-induced cytotoxicity by suppressing the expression of Kir subunits.

Cardioprotective Effects of Diazoxide on Myocardial Ischemia/Reperfusion Injury in Rats

In order to study the cardioprotective effects of diazoxide on the myocardial ischemia/reperfusion injury of rats and mechanisms, the healthy SD rats were randomly divided into 2 groups： the rats in the experimental group were injected with diazoxide for preconditioning with the dosage of 12.5 mg/kg through the right femoral vein and those in the control group was only administered with the equal volume of media. After 10 rain, a left thoracotomy was performed and the left anterior descending branch was occluded for 2 h. Two h later, the left anterior descending branch was reperfused for 2 h and then the heart was quickly excised to be used for measurement of MDA, SOD and the infarct size, in situ cell apoptosis detection and observation of the cell ultrastructure by electron microscopy. The results showed that as compared with the control group, MDA, the infarct size and cell apoptosis in the experimental group were greatly reduced （P〈0.05）. And the cell ultrastructure was obviously improved, But the activity of SOD had no change （P〉0.05）. It was concluded that diazoxide could protect the rats from myocardial ischemia/reperfusion injury, which might be contributed to the reduction of lipid peroxidation and cell apoptosis.

Effects of Diazoxide Treatments on Electrophysiologyic Properties in Guinea Pig Papillary Muscles Undergoing Ischemia/Reperfusion

The effects of diazoxide treatments on electrophysiologyic properties in guinea pig papillary muscles undergoing ischemia/reperfusion was studied using intracellular microelectrode technique. Twenty-four guinea pigs were randomly divided into three groups (n=8 in each group). In control group, St.Thomas solution was given. In experimental group, St.Thomas solution with diazoxide (100 mol/L) was given. In pretreatment group, the muscle was treated with diazoxide 20 min before arrested with St.Thomas cardioplegia. The results showed that the APD_50 and APD_90 in experimental and pretreatment groups were significantly shorter after 5 and 10 min reperfusion (P<0.01, P<0.05), but longer after 30 min reperfusion (P<0.01, P<0.05) than in control group. In experimental and pretreatment groups, APA, OS, Vmax recovered more quickly than those in control group. The time to re-systole after reperfusion in control group was longer than that in experimental and pretreatment groups. There was no significant difference in RP among three groups. The time of arrest in pretreatment group was longer than that in experimental and pretreatment group (P<0.05). This study indicates that protective effects of St.Thomas solution with diazoxide is better than that of pretreatment with diazoxide or St.Thomas solution alone.

Diazoxide preconditioning plus subsequent hypothermia increased resistance of rat cultured hippocampal neurons against hypoxia-reoxygenation injury

Background Cerebral ischemia-reperfusion/hypoxia-reoxygenation insult triggers lots of pathophysiological and biochemical events that separately affect the evolution of cerebral damage. Accordingly, all known effective neuroprotective measures should be taken to get the optimal efficacy of therapy. This study was undertaken to investigate whether diazoxide （DZ） preconditioning combined with the following hypothermia could contribute to synergistic neuroprotection compared with either hypothermia or DZ preconditioning alone. Methods Cultured for 9-10 days in vitro, the hippocampal neurons of SD rats were preconditioned with DZ 0 pmol/L or DZ 250 pmol/L for 1 hour per day and this treatment lasted for 3 days. Subsequently, neurons were subjected to deprivation of oxygen for 4 hours at 37°0, 34°C, 30℃ and 22℃, respectively. This experiment consisted of 8 groups （4 temperature groups and 4 combination groups） and each group contained 12-well or 2-dish cells. Survival rate, expression of Bcl-2, fluorescence magnitude of intracellular calcium, and concentration of malondialdehyde （MDA） were determined at 24 hours after reoxygenation. Results The survival rate and expression of Bcl-2 were both increased in individually hypothermic conditions compared with those at 370G （P〈0.05）, whereas intracellular calcium and MDA did the opposite exhibition simultaneously （P〈0.05）. 22℃ contributed to a higher survival rate and greater expression of Bcl-2 in comparison with other hypothermia （P〈0.05）. Preceding administration of 250 pmol/L DZ took the similar effects on the neurons like hypothermia. Moreover, compared with individual hypothermia or DZ preconditioning, the neuronal survival rate and expression of Bcl-2 in the combination group were increased significantly （P〈0.05）, whereas the calcium fluorescence density and concentration of MDA were reduced further （P〈0.05）. 250 Iamol/L DZ preconditioning combined with 22℃ provided a maximal neuroprotection. Conclusions Compared with either individual hypothermia or DZ preconditioning, the combination of both treatments conferred synergistic protection for cultured hippocampal neurons in vitro against hypoxia- reoxygenation insult.

Beneficial effects of adenosine triphosphate-sensitive K^+ channel opener on liver ischemia/reperfusion injury

AIM:To investigate the effect of diazoxide administration on liver ischemia/reperfusion injury.METHODS:Wistar male rats underwent partial liver ischemia performed by clamping the pedicle from the medium and left anterior lateral segments for 1 h under mechanical ventilation.They were divided into 3 groups:Control Group,rats submitted to liver manipulation,Saline Group,rats received saline,and Diazoxide Group,rats received intravenous injection diazoxide(3.5 mg/kg) 15 min before liver reperfusion.4 h and 24 h after reperfusion,blood was collected for determination of aspartate transaminase(AST),alanine transaminase(ALT),tumor necrosis factor(TNF-α),interleukin-6(IL-6),interleukin-10(IL-10),nitrite/nitrate,creatinine and tumor growth factor-β1(TGF-β1).Liver tissues were assembled for mitochondrial oxidation and phosphorylation,malondialdehyde(MDA) content,and histologic analysis.Pulmonary vascular permeability and myeloperoxidase(MPO) were also determined.RESULTS:Four hours after reperfusion the diazoxide group presented with significant reduction of AST(2009 ± 257 U/L vs 3523 ± 424 U/L,P = 0.005); ALT(1794 ± 295 U/L vs 3316 ± 413 U/L,P = 0.005); TNF-α(17 ± 9 pg/mL vs 152 ± 43 pg/mL,P = 0.013; IL-6(62 ± 18 pg/mL vs 281 ± 92 pg/mL); IL-10(40 ± 9 pg/mL vs 78 ± 10 pg/mL P = 0.03),and nitrite/nitrate(3.8 ± 0.9 μmol/L vs 10.2 ± 2.4 μmol/L,P = 0.025) when compared to the saline group.A significant reduction in liver mitochondrial dysfunction was observed in the diazoxide group compared to the saline group(P < 0.05).No differences in liver MDA content,serum creatinine,pulmonary vascular permeability and MPO activity were observed between groups.Twenty four hours after reperfusion the diazoxide group showed a reduction of AST(495 ± 78 U/L vs 978 ± 192 U/L,P = 0.032); ALT(335 ± 59 U/L vs 742 ± 182 U/L,P = 0.048),and TGF-β1(11 ± 1 ng/mL vs 17 ± 0.5 ng/mL,P = 0.004) serum levels when compared to the saline group.The control group did not present alterations when compared to the diazoxide and saline groups.CONCLUSION:Diazoxide maintains liver mitochondrial function,increases liver tolerance to ischemia/reperfusion injury,and reduces the systemic inflammatory response.These effects require further evaluation for using in a clinical setting.

Cardioprotective effects of mitochondrial K_(ATP) channels activated at different time

Backgroud Recent studies in adult hearts have indicated that K ATP channels in the inner mitochondrial membrance are responsible for the protection. And we investigated whether opening of mitochondrial K ATP channels (mK ATP ) could provide myocardial protection for immature rabbits and determined its role in cardioprotection Methods Thirty-four 3-4-week-old rabbits, weighing 300-350 g, were divided randomly into five groups: Group Ⅰ (control group, n=8); Group Ⅱ [diazoxide preconditioning group; n=8; the hearts were pretreated with 100 μmol/L diazoxide for 5 minutes followed by 10-minute wash out with Krebs-Henseleit buffer (KHB)]; Group Ⅲ ; Group Ⅲ [diazoxide+5-hydroxydeconate (5-HD) preconditioning group; n=5; the hearts were pretreated with 100 μmol/L diazoxide and 100 μmol/L 5-HD); Group Ⅳ (diazoxide+cardioplegia group; n=8; cardioplegia containing 100 μmol/L diazoxide perfused the hearts for 5 minutes before ischemia); Group Ⅴ (diazoxide+5-HD+cardioplegia group; n=5; the cardioplegia contained 100 μmol/L diazoxide and 100 μmol/L 5-HD) All hearts were excised and connected to langendrff perfusion system and passively perfused with KHB at 38℃ under a pressure of 70 cmH 2O After reperfusion, the recovery rate of left ventricular diastolic pressure (LVDP), ±dp/dt max , coronary flow (CF), the creatinine kinase (CK), lactate dehydrogenase (LDH), aspartate aminotransferase (AST) in coronary sinus venous effluent and the tissue ATP were measured Mitochondria were evaluated semiquantitatively by morphology Results After ischemia and reperfusion (I/R), the two groups that were treated by diazoxide only (Groups Ⅱ and Ⅳ) had a significant improvement in LVDP, ±dp/dt max , and CF recovery AST, LDH, and CK were decreased, and the levels of tissue ATP in the two groups were higher Mitochondria was protected better in Group Ⅳ than in other groups Conclusions Activating mK ATP channels before and during ischemia can similarly protect immature rabbit hearts, and the mechanism is related to the direct protective effect on mitochondria Opening of mK ATP channel during ischemia provides a better protection for mitochondria than it does before ischemia