Cardiovascular Protection of Activating KATP Channel During Ischemia-Reperfusion Acidosis

New Drug Targets and Preclinical Modelling Recommendations for Treating Acute Myocardial Infarction

Acute myocardial infarction (AMI) is the leading cause of morbidity and mortality worldwide and the primary underlying risk factor for heart failure. Despite decades of research and clinical trials, there are no drugs currently available to prevent organ damage from acute ischaemic injuries of the heart. In order to address the increasing global burden of heart failure, drug, gene, and cell-based regeneration technologies are advancing into clinical testing. In this review we highlight the burden of disease associated with AMI and the therapeutic landscape based on market analyses. New studies revealing the role of acid-sensitive cardiac ion channels and other proton-gated ion channels in cardiac ischaemia are providing renewed interest in pre- and post-conditioning agents with novel mechanisms of action that may also have implications for gene- and cell-based therapeutics. Furthermore, we present guidelines that couple new cell technologies and data resources with traditional animal modelling pipelines to help de-risk drug candidates aimed at treating AMI. We propose that improved preclinical pipelines and increased investment in drug target identification for AMI is critical to stem the increasing global health burden of heart failure.

KATP Channel Blocker Glibenclamide Prevents Radiation-Induced Lung Injury and Inhibits Radiation-Induced Apoptosis of Vascular Endothelial Cells by Increased Ca2+ Influx and Subsequent PKC Activation

Radiation-induced lung injury (RILI) is a common and severe side effect of thoracic radiotherapy, which compromises patients' quality of life. Recent studies revealed that early vascular injury, especially microvascular damage, played a central role in the development of RILI. For this reason, early vascular protection is essential for RILI therapy. The ATP-sensitive K⁺ (K_ATP) channel is an ATP-dependent K⁺ channel with multiple subunits. The protective role of the K_ATP channel in vascular injury has been demonstrated in some published studies. In this work, we investigated the effect of K_ATP channel on RILI. Our findings confirmed that the K_ATP channel blocker glibenclamide, rather than the K_ATP channel opener pinacidil, remitted RILI, and in particular, provided protection against radiation-induced vascular injury. Cytology experiments verified that glibenclamide enhanced cell viability, increased the potential of proliferation after irradiation and attenuated radiation-induced apoptosis. Involved mechanisms included increased Ca²⁺ influx and PKC activation, which were induced by glibenclamide pretreatment. In conclusion, the K_ATP channel blocker glibenclamide remitted RILI and inhibited the radiation-induced apoptosis of vascular endothelial cells by increased Ca²⁺ influx and subsequent PKC activation.

Exendin-4 improves cardiovascular function and survival in flow-induced pulmonary hypertension

OBJECTIVES

Systemic left-to-right shunting causes pulmonary arteriopathy, leading to progressive cardiopulmonary failure and a poor prognosis. In this study, we examined the extraglycemic effect of a synthetic glucagon-like peptide, exendin-4, on pulmonary arteriopathy regression and cardiopulmonary function in nondiabetic rats.

METHODS

Pulmonary hypertension (PH) was induced by monocrotaline (60 mg/kg, subcutaneous) injection followed by the creation of an aortocaval fistula. After 4 weeks, exendin-4 (1 μg/kg/day) was administered intraperitoneally for 3 consecutive weeks, followed by an assessment of cardiopulmonary function, pulmonary artery vasoreactivity, tissue and blood biochemistry, and lung histology.

RESULTS

Exendin-4 significantly reduced right ventricle mass and pulmonary artery pressure, which improved right ventricle function and the survival rate in rats with PH. Tissue and blood interleukin-1β levels decreased, whereas pulmonary artery cyclic adenosine monophosphate levels were restored by exendin-4. Smooth muscle-myosin heavy chain-II and α-smooth muscle actin protein levels increased in the pulmonary arteries of exendin-4-treated rats. Histology showed that exendin-4 decreased the main and intra-acinar pulmonary artery medial thickness.

CONCLUSIONS

Exendin-4 treatment improved pulmonary artery function in flow-induced PH via its direct vasoactive properties, anti-inflammatory effects, and vascular smooth muscle cell phenotypic modulation. Mitigation of pulmonary arteriopathy further potentiated right ventricle performance and reduced overall mortality. These responses were associated with suppressed expression and activity of interleukin-1β and its downstream signaling molecules. Glucagon-like peptide analogs may possess pleiotropic therapeutic potential in flow-induced PH.

Sensitivity of KATP channels to cellular metabolic disorders and the underlying structural basis

AIM

ATP-sensitive potassium (KATP) channels formed by a combination of SUR/Kir6.x subunits play a crucial role in protection against hypoxic or ischemic injuries resulting from cell metabolic disorders. In this study we investigated the effects of Na-azide, a metabolic inhibitor, on KATP channels expressed in Xenopus oocytes, and explored the structure basis for their sensitivity to cell metabolic disorders.

METHODS

Six subtypes of KATP channels (wild SUR1/Kir6.2, SUR2B/Kir6.2, SUR1/Kir6.1, SUR2B/Kir6.1, SUR2A/Kir6.2 and SUR2A/Kir6.1), as well as eleven subtypes of KATP channels with mutant subunits were expressed in Xenopus oocytes. KATP currents were recorded using a two-electrode voltage clamp recording technique. The drugs were applied through bath.

RESULTS

Except SUR2A/Kir6.1, five subtypes of KATP channels were activated by Na-azide (3 mmol/L) with an order of the responses: SUR1/Kir6.2>SUR2B/Kir6.2>SUR1/Kir6.1>SUR2B/Kir6.1>SUR2A/Kir6.2, and the opening rate (t1/2) was SUR1/Kir6.x>SUR2B/Kir6.x>SUR2A/Kir6.2. Furthermore, Kir6.2, rather than Kir6.1, had intrinsic sensitivity to Na-azide, and the residues involved in ATP-binding (R50 and K185) or pH-sensing (H175) were associated with the sensitivity of the Kir6.2 subunit to Na-azide. Moreover, the residues (K707 and K1348) within the Walker A (WA) motifs of two nucleotide-binding domains (NBDs) were essential for SUR2B/Kir6.x (especially SUR2B/Kir6.1) channel activation by Na-azide, suggesting a key role for Mg-adenine nucleotide binding and/or hydrolysis in the SUR2B subunit.

CONCLUSION

Among the six subtypes of KATP channels, SUR1/Kir6.2 is the most sensitive, whereas SUR2A/Kir6.1 is insensitive, to cell metabolic disorders. The Kir6.2 subunit, rather than the Kir6.1 subunit, has intrinsic sensitivity to cell metabolic disorders. The residues (K707 and K1348) within the WA motifs of SUR2B are important for the sensitivity of SUR2B/Kir6.x channels to cell metabolic disorders.

Selenium attenuates adriamycin-induced cardiac dysfunction via restoring expression of ATP-sensitive potassium channels in rats

The possible mechanism of adriamycin (ADR) and/or selenium (Se) deficiency-induced cardiac dysfunction, and cardioprotective effects of Se against ADR-induced cardiac toxicity were investigated in this study. Cardiac function was evaluated by plasma brain natriuretic peptide level and echocardiographic and hemodynamic parameters. Cardiac glutathione peroxidase (GPx) activity was assessed spectrophotometrically. Expression of ATP-sensitive potassium channels (KATP) subunits-SUR2A and Kir6.2-were examined by real-time PCR and Western blotting. The results showed that cardiac function and cardiac GPx activity decreased remarkably after administration of ADR or Se deficiency; more dramatic impairment of cardiac function and cardiac GPx activity were observed after co-administration of ADR and Se deficiency. Mechanically, it is novel for us to find down-regulation of KATP subunits gene expression in cardiac tissue after administration of ADR or Se deficiency, and more significant inhibition of cardiac KATP gene expression was identified after co-administration of ADR and Se deficiency. Furthermore, cardiac toxicity of ADR was found alleviated by Se supplementation, accompanied by restoring of cardiac GPx activity and cardiac KATP gene expression. These results indicate that decreased expression of cardiac KATP is involved in adriamycin and/or Se deficiency-induced cardiac dysfunction; Se deficiency exacerbates adriamycin-induced cardiac dysfunction by future inhibition of KATP expression; Se supplementation seems to protect against adriamycin-induced cardiac dysfunction via restoring KATP expression, showing potential clinical application in cancer chemotherapy.