Iptakalim: A novel multi-utility potassium channel opener

Potassium Channels in Parkinson's Disease: Potential Roles in Its Pathogenesis and Innovative Molecular Targets for Treatment

Parkinson's disease (PD) is a neurodegenerative disorder characterized by selective loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) region of the midbrain. The loss of neurons results in a subsequent reduction of dopamine in the striatum, which underlies the core motor symptoms of PD. To date, there are no effective treatments to stop, slow, or reverse the pathologic progression of dopaminergic neurodegeneration. This unfortunate predicament is because of the current early stages in understanding the biologic targets and pathways involved in PD pathogenesis. Ion channels have become emerging targets for new therapeutic development for PD due to their essential roles in neuronal function and neuroinflammation. Potassium channels are the most prominent ion channel family and have been shown to be critically important in PD pathology because of their roles in modulating neuronal excitability, neurotransmitter release, synaptic transmission, and neuroinflammation. In this review, members of the subfamilies of voltage-gated K+ channels, inward rectifying K+ channels, and Ca2+-activated K+ channels are described. Evidence of the role of these channels in PD etiology is discussed together with the latest views on related pathologic mechanisms and their potential as biologic targets for developing neuroprotective drugs for PD. SIGNIFICANCE STATEMENT: Parkinson's disease (PD) is the second most common neurodegenerative disorder, featuring progressive degeneration of dopaminergic neurons in the midbrain. It is a multifactorial disease involving multiple risk factors and complex pathobiological mechanisms. Mounting evidence suggests that ion channels play vital roles in the pathogenesis and progression of PD by regulating neuronal excitability and immune cell function. Therefore, they have become "hot" biological targets for PD, as demonstrated by multiple clinical trials of drug candidates targeting ion channels for PD therapy.

Iptakalim improves cerebral microcirculation in mice after ischemic stroke by inhibiting pericyte contraction

Pericytes are present tight around the intervals of capillaries, play an essential role in stabilizing the blood-brain barrier, regulating blood flow and immunomodulation, and persistent contraction of pericytes eventually leads to impaired blood flow and poor clinical outcomes in ischemic stroke. We previously show that iptakalim, an ATP-sensitive potassium (K-ATP) channel opener, exerts protective effects in neurons, and glia against ischemia-induced injury. In this study we investigated the impacts of iptakalim on pericytes contraction in stroke. Mice were subjected to cerebral artery occlusion (MCAO), then administered iptakalim (10 mg/kg, ip). We showed that iptakalim administration significantly promoted recovery of cerebral blood flow after cerebral ischemia and reperfusion. Furthermore, we found that iptakalim significantly inhibited pericytes contraction, decreased the number of obstructed capillaries, and improved cerebral microcirculation. Using a collagen gel contraction assay, we demonstrated that cultured pericytes subjected to oxygen-glucose deprivation (OGD) consistently contracted from 3 h till 24 h during reoxygenation, whereas iptakalim treatment (10 μM) notably restrained pericyte contraction from 6 h during reoxygenation. We further showed that iptakalim treatment promoted K-ATP channel opening via suppressing SUR2/EPAC1 complex formation. Consequently, it reduced calcium influx and ET-1 release. Taken together, our results demonstrate that iptakalim, targeted K-ATP channels, can improve microvascular disturbance by inhibiting pericyte contraction after ischemic stroke. Our work reveals that iptakalim might be developed as a promising pericyte regulator for treatment of stroke.

The Pharmacology of ATP-Sensitive K+ Channels (KATP)

ATP-sensitive K⁺ channels (K_ATP) are inwardly-rectifying potassium channels, broadly expressed throughout the body. K_ATP is regulated by adenine nucleotides, characteristically being activated by falling ATP and rising ADP levels thus playing an important physiological role by coupling cellular metabolism with membrane excitability. The hetero-octameric channel complex is formed of 4 pore-forming inward rectifier Kir6.x subunits (Kir6.1 or Kir6.2) and 4 regulatory sulfonylurea receptor subunits (SUR1, SUR2A, or SUR2B). These subunits can associate in various tissue-specific combinations to form functional K_ATP channels with distinct electrophysiological and pharmacological properties. K_ATP channels play many important physiological roles and mutations in channel subunits can result in diseases such as disorders of insulin handling, cardiac arrhythmia, cardiomyopathy, and neurological abnormalities. The tissue-specific expression of K_ATP channel subunits coupled with their rich and diverse pharmacology makes K_ATP channels attractive therapeutic targets in the treatment of endocrine and cardiovascular diseases.

Iptakalim ameliorates hypoxia-impaired human endothelial colony-forming cells proliferation, migration, and angiogenesis via Akt/eNOS pathways

Hypoxia-associated pulmonary hypertension is characterized by pulmonary vascular remodeling. Pulmonary arterial endothelial cells dysfunction is considered as the initial event. As precursor of endothelial cells, endothelial colony-forming cells (ECFCs) play significant roles in maintenance of endothelium integrity and restoration of normal endothelial cell function. Accumulating data have indicated that hypoxia leads to a decrease in the number and function of ECFCs with defective capacity of endothelial regeneration. Previous studies have reported that the activation of ATP-sensitive potassium channels (K_ATP) shows therapeutic effects in pulmonary hypertension. However, there have been few reports focusing on the impact of K_ATP on ECFC function under hypoxic condition. Therefore, the aim of this study was to investigate whether the opening of K_ATP could regulate hypoxia-induced ECFC dysfunction. Using ECFCs derived from adult peripheral blood, we observed that Iptakalim (Ipt), a novel K_ATP opener (KCO), significantly promoted ECFC function including cellular viability, proliferation, migration, angiogenesis, and apoptosis compared with ECFCs exposed to hypoxia. Glibenclamide (Gli), a nonselective K_ATP blocker, could eliminate the effects. The protective role of Ipt is attributed to an increased production of nitric oxide (NO), as well as an enhanced activation of angiogenic transduction pathways, containing Akt and endothelial nitric oxide synthase. Our observations demonstrated that K_ATP activation could improve ECFC function in hypoxia via Akt/endothelial nitric oxide synthase pathways, which may constitute increase ECFC therapeutic potential for hypoxia-associated pulmonary hypertension treatment.

ABCC9/SUR2 in the brain: Implications for hippocampal sclerosis of aging and a potential therapeutic target

The ABCC9 gene and its polypeptide product, SUR2, are increasingly implicated in human neurologic disease, including prevalent diseases of the aged brain. SUR2 proteins are a component of the ATP-sensitive potassium ("KATP") channel, a metabolic sensor for stress and/or hypoxia that has been shown to change in aging. The KATP channel also helps regulate the neurovascular unit. Most brain cell types express SUR2, including neurons, astrocytes, oligodendrocytes, microglia, vascular smooth muscle, pericytes, and endothelial cells. Thus it is not surprising that ABCC9 gene variants are associated with risk for human brain diseases. For example, Cantu syndrome is a result of ABCC9 mutations; we discuss neurologic manifestations of this genetic syndrome. More common brain disorders linked to ABCC9 gene variants include hippocampal sclerosis of aging (HS-Aging), sleep disorders, and depression. HS-Aging is a prevalent neurological disease with pathologic features of both neurodegenerative (aberrant TDP-43) and cerebrovascular (arteriolosclerosis) disease. As to potential therapeutic intervention, the human pharmacopeia features both SUR2 agonists and antagonists, so ABCC9/SUR2 may provide a "druggable target", relevant perhaps to both HS-Aging and Alzheimer's disease. We conclude that more work is required to better understand the roles of ABCC9/SUR2 in the human brain during health and disease conditions.

Emergence of Chinese drug discovery research: impact of hit and lead identification

The identification of hits and the generation of viable leads is an early and yet crucial step in drug discovery. In the West, the main players of drug discovery are pharmaceutical and biotechnology companies, while in China, academic institutions remain central in the field of drug discovery. There has been a tremendous amount of investment from the public as well as private sectors to support infrastructure buildup and expertise consolidation relative to drug discovery and development in the past two decades. A large-scale compound library has been established in China, and a series of high-impact discoveries of lead compounds have been made by integrating information obtained from different technology-based strategies. Natural products are a major source in China's drug discovery efforts. Knowledge has been enhanced via disruptive breakthroughs such as the discovery of Boc5 as a nonpeptidic agonist of glucagon-like peptide 1 receptor (GLP-1R), one of the class B G protein-coupled receptors (GPCRs). Most of the original hit identification and lead generation were carried out by academic institutions, including universities and specialized research institutes. The Chinese pharmaceutical industry is gradually transforming itself from manufacturing low-end generics and active pharmaceutical ingredients to inventing new drugs.

The role of ATP-sensitive potassium channels in cellular function and protection in the cardiovascular system

ATP-sensitive potassium channels (K(ATP)) are widely distributed and present in a number of tissues including muscle, pancreatic beta cells and the brain. Their activity is regulated by adenine nucleotides, characteristically being activated by falling ATP and rising ADP levels. Thus, they link cellular metabolism with membrane excitability. Recent studies using genetically modified mice and genomic studies in patients have implicated K(ATP) channels in a number of physiological and pathological processes. In this review, we focus on their role in cellular function and protection particularly in the cardiovascular system.

Kir6.2 knockout aggravates lipopolysaccharide-induced mouse liver injury via enhancing NLRP3 inflammasome activation

BACKGROUND

ATP-sensitive potassium (K-ATP) channels couple cellular metabolism to electric activity. Although Kir6.2-composed K-ATP channel (Kir6.2/K-ATP channel) has been demonstrated to regulate inflammation, a common cause of most liver diseases, its role in liver injury remains elusive.

METHODS

Kir6.2 knockout mice were used to prepared LPS-induced liver injury model so as to investigate the role of Kir6.2/K-ATP channels in the injury. Histochemistry was applied to evaluate the extent of liver injury. Proinflammatory cytokines were analyzed by ELISA. Endoplasmic reticulum (ER) stress and autophagy were assessed by western blotting.

RESULTS

We showed that Kir6.2 knockout markedly promoted the infiltration of lymphocytes and neutrophils in liver and significantly elevated serum levels of alanine transaminase (ALT) in respond to LPS treatment. We further found that Kir6.2 deficiency enhanced the activation of NF-κB and NLRP3 inflammasome following LPS challenge, and thereby increased the levels of pro-inflammatory cytokines IL-1β, IL-18 and TNF-α. Treatment of wild-type mice with the K-ATP channel opener iptakalim (IPT) could protect against LPS-induced liver injury through attenuating NLRP3 inflammasome-mediated inflammatory responses. Furthermore, Kir6.2 knockout-induced activation of NLRP3 inflammasome aggravated endoplasmic reticulum (ER) stress, autophagy and subsequent hepatocyte death.

CONCLUSION

Kir6.2 deficiency exacerbated LPS-induced liver injury by enhancing NLRP3 inflammasome-mediated inflammatory response. Thus, Kir6.2/K-ATP channel may be a potential candidate target for the treatment and prevention of liver injury.