Inhibitors of the renal outer medullary potassium channel: A patent review

INTRODUCTION: Hypertension represents a substantial cardiovascular risk factor. Among anti-hypertensive drugs, diuretics play an important role. Nevertheless, they present adverse effects such as hypokalemia or hyperkalemia. In this panorama, inhibitors of the renal outer medullary potassium (ROMK) channels are emerging because they are predicted to give a diuretic/natriuretic activity higher than that provided by loop diuretics, without hypokaliemic and hyperkaliemic side effects. AREAS COVERED: This article reviews the current literature, including all the patents published in the field of inhibitors of the ROMK channels for the treatment of hypertension, heart failure and correlated diseases. The patent examination has been carried out using electronic databases Espacenet. EXPERT OPINION: Although anti-hypertensive drugs armamentarium enumerates a plethora of therapeutic classes, including diuretics, the novel class of ROMK inhibitors may find a place in this crowded market, because of the diuretic/natriuretic effects, devoid of worrying influence on potassium balance. The patent examination highlights, as a strength, the individuation of a successful template: almost all the compounds show noteworthy potency. However, only few selected compounds underwent an in vivo investigation of diuretic and anti-hypertensive activities, and no data on the hERG channel are given in these patents

Mitochondrial Potassium Channels as Pharmacological Target for Cardioprotective Drugs

Brief periods of ischemia are known to confer to the myocardium an increased resistance to the injury due to a later and more prolonged ischemic episode. This phenomenon, known as ischemic preconditioning (IPreC), is ensured by different biological mechanisms. Although an exhaustive comprehension of them has not been reached yet, it is widely accepted that mitochondria are pivotally involved in controlling cell life and death, and thus in IPreC. Among the several signaling pathways involved, as triggers and/or end effectors, in the mitochondrial mechanisms of cardioprotection, an important role is played by the activation of potassium channels located in the mitochondrial inner membrane (mitoK) of cardiomyocytes. Presently, different types of mitoK channels have been recognized in the heart, such as ATP-sensitive (mitoK(ATP)) and calcium-activated (mitoBK(Ca) and mitoSK(Ca)) potassium channels. Consistently, drugs modulating mitoK, on one hand, have been employed as useful experimental tools for early basic studies on IPreC. On the other hand, activators of mitoK are promising and innovative therapeutic agents for limiting the myocardial injury due to ischemic episodes. In this review, we report the experimental evidence supporting the role of mitoK in signaling pathways in the mechanisms of cardioprotection and an overview on the most important molecules acting as modulators of these channels, with their profiles of selectivity. Some innovative pharmaceutical strategies for mitochondriotropic drugs have been also reported. Finally, an appendix describing the main experimental approaches usually employed to study mitoK in isolated mitochondria or in intact cells has been added

Role of hydrogen sulfide in endothelial dysfunction: Pathophysiology and therapeutic approaches

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Hydrogen sulfide releasing capacity of natural isothiocyanates: is it a reliable explanation for the multiple biological effects of brassicaceae?

Hydrogen sulfide is an endogenous pleiotropic gasotransmitter, which mediates important physiological effects in the human body. Accordingly, an impaired production of endogenous hydrogen sulfide contributes to the pathogenesis of important disorders. To date, exogenous compounds, acting as hydrogen sulfide-releasing agents, are viewed as promising pharmacotherapeutic agents. In a recent report, the hydrogen sulfide-releasing properties of some synthetic aryl isothiocyanate derivatives have been reported, indicating that the isothiocyanate function can be viewed as a suitable slow hydrogen sulfide-releasing moiety, endowed with the pharmacological potential typical of this gasotransmitter. Many isothiocyanate derivatives (deriving from a myrosinase-mediated transformation of glucosinolates) are well-known secondary metabolites of plants belonging to the family Brassicaceae, a large botanical family comprising many edible species. The phytotherapeutic and nutraceutic usefulness of Brassicaceae in the prevention of important human diseases, such as cancer, neurodegenerative processes and cardiovascular diseases has been widely discussed in the scientific literature. Although these effects have been largely attributed to isothiocyanates, the exact mechanism of action is still unknown. In this experimental work, we aimed to investigate the possible hydrogen sulfide-releasing capacity of some important natural isothiocyanates, studying it in vitro by amperometric detection. Some of the tested natural isothiocyanates exhibited significant hydrogen sulfide release, leading us to hypothesize that hydrogen sulfide may be, at least in part, a relevant player accounting for several biological effects of Brassicaceae

Voltage-operated potassium (Kv) channels contribute to endothelium-dependent vasorelaxation of carvacrol on rat aorta

OBJECTIVES: Carvacrol, a monoterpene widely present in nature, is commonly used in the food industry and in cosmetics, besides to possess a plethora of pharmacological properties, among these also in vitro vasorelaxing effects and in vivo hypotensive responses. Although in rat aortic rings carvacrol evoked a vasodilatation both in the presence and in the absence of endothelium, in preparations with intact endothelial layer its vasoactive response markedly improved. METHODS: This study aimed at investigating the mechanism of action responsible for the endothelial component of the carvacrol-induced vasorelaxing response observed in rat isolated aortic rings. KEY FINDINGS: Pharmacological characterization led us to exclude the involvement of NO pathway (neither L-NAME, NO biosynthesis inhibitor, nor ODQ, guanylate cyclase inhibitor, was able to modify the vascular effects of carvacrol) and of arachidonic acid cascade (no inhibitor intercepting the cascade influenced the endothelial-dependent vasodilatation of the monoterpene). Moreover, endothelial TRP channels were also not involved, as capsazepine did not antagonize vasorelaxing effect. Finally, endothelial potassium channels were considered as possible targets of carvacrol; indeed, two voltage-operated potassium (Kv) channel blockers, 4-aminopyridine and quinine, significantly reduced carvacrol potency and efficacy indices. CONCLUSIONS: Kv channels seem to be responsible for vascular effects of the monoterpene typical of Labiatae family

Advances in Technologies for Highly Active Omega-3 Fatty Acids from Krill Oil: Clinical Applications

Euphausia superba, commonly known as krill, is a small marine crustacean from the Antarctic Ocean that plays an important role in the marine ecosystem, serving as feed for most fish. It is a known source of highly bioavailable omega-3 polyunsaturated fatty acids (eicosapentaenoic acid and docosahexaenoic acid). In preclinical studies, krill oil showed metabolic, anti-inflammatory, neuroprotective and chemo preventive effects, while in clinical trials it showed significant metabolic, vascular and ergogenic actions. Solvent extraction is the most conventional method to obtain krill oil. However, different solvents must be used to extract all lipids from krill because of the diversity of the polarities of the lipid compounds in the biomass. This review aims to provide an overview of the chemical composition, bioavailability and bioaccessibility of krill oil, as well as the mechanisms of action, classic and non-conventional extraction techniques, health benefits and current applications of this marine crustacean

The Citrus Flavanone Naringenin Protects Myocardial Cells against Age-Associated Damage

In recent years, the health-promoting effects of the citrus flavanone naringenin have been examined. The results have provided evidence for the modulation of some key mechanisms involved in cellular damage by this compound. In particular, naringenin has been revealed to have protective properties such as an antioxidant effect in cardiometabolic disorders. Very recently, beneficial effects of naringenin have been demonstrated in old rats. Because aging has been demonstrated to be directly related to the occurrence of cardiac disorders, in the present study, the ability of naringenin to prevent cardiac cell senescence was investigated. For this purpose, a cellular model of senescent myocardial cells was set up and evaluated using colorimetric, fluorimetric, and immunometric techniques. Relevant cellular senescence markers, such as X-gal staining, cell cycle regulator levels, and the percentage of cell cycle-arrested cells, were found to be reduced in the presence of naringenin. In addition, cardiac markers of aging-induced damage, including radical oxidative species levels, mitochondrial metabolic activity, mitochondrial calcium buffer capacity, and estrogenic signaling functions, were also modulated by the compound. These results suggested that naringenin has antiaging effects on myocardial cells

Synthesis and evaluation of multi-functional NO-donor/insulin-secretagogue derivatives for the treatment of type II diabetes and its cardiovascular complications

Although there is a significant effort in the discovery of effective therapies to contrast both the pathological endocrine and metabolic aspects of diabetes and the endothelial dysfunction associated with this disease, no hypoglycemic drug has been proven to defeat the cardiovascular complications associated with type II diabetes. The aim of this research was to design new compounds exhibiting a double profile of hypoglycemic agents/NO-donors. The synthesis of molecules obtained by the conjunction of NO-donor moieties with two oral insulin-secretagogue drugs (repaglinide and nateglinide) was reported. NO-mediated vasorelaxing effects of the synthesized compounds were evaluated by functional tests on isolated endothelium-denuded rat aortic rings. The most potent molecule (4) was tested to evaluate the hypoglycemic and the anti-ischemic cardioprotective activities. This study indicates that 4 should represent a new insulin-secretagogue/NO-donor prodrug with an enhanced cardiovascular activity, which may contrast the pathological aspects of diabetes and endowed of cardioprotective activity

Searching for novel hydrogen sulfide donors: The vascular effects of two thiourea derivatives

The gasotransmitter hydrogen sulfide (H2S) is involved in the regulation of the vascular tone and an impairment of its endogenous production may play a role in hypertension. Thus, the administration of exogenous H2S may be a possible novel and effective strategy to control blood pressure. Some natural and synthetic sulfur compounds are suitable H2S-donors, exhibiting long-lasting H2S release; however, novel H2S-releasing agents are needed to improve the pharmacological armamentarium for the treatment of cardiovascular diseases. For this purpose, N-phenylthiourea (PTU) and N,N'-diphenylthiourea (DPTU) compounds have been investigated as potential H2S-donors. The thioureas showed long-lasting H2S donation in cell free environment and in human aortic smooth muscle cells (HASMCs). In HASMCs, DPTU caused membrane hyperpolarization, mediated by activation of KATP and Kv7 potassium channels. The thiourea derivatives promoted vasodilation in rat aortic rings, which was abolished by KATP and Kv7 blockers. The vasorelaxing effects were also observed in angiotensin II-constricted coronary vessels. In conclusion, thiourea represents an original H2S-donor functional group, which releases H2S with slow and long lasting kinetic, and promotes typical H2S-mediated vascular effects. Such a moiety will be extremely useful for developing original cardiovascular drugs and new chemical tools for investigating the pharmacological roles of H2S

A Nutraceutical Strategy to Slowing Down the Progression of Cone Death in an Animal Model of Retinitis Pigmentosa

Retinitis pigmentosa (RP) is an inherited retinal dystrophy characterized by progressive degeneration of the visual cells and abnormalities in retinal pigment epithelium, the vision is lost slowly, and the final outcome is total blindness. RP primarily affects rods, but cones can also be affected as a secondary effect. Photoreceptor cell death is usually triggered by apoptosis, however the molecular mechanisms linking the rod degeneration to the secondary cone death are poorly understood. Possible causes of the secondary cone death are oxidative stress and/ or the release of toxic factors from dying rods. The aim of this study is to analyze the effect of nutraceutical molecules with antioxidant properties, on the progression of the disease in an established animal model of RP, and rd10 mice. We show that chronic treatment per os with a flavanone (naringenin) or a flavonol (quercetin) present in citrus fruits, grapes and apples, preserves retinal morphology, and ameliorates functionality. These actions are associated with a significant reduction of stress-oxidative markers, such as the detoxifying enzymes Sod1 and Sod2. In addition, naringenin and quercetin treatment reduces the levels of acrolein staining associated with a reduction of ROS in the cellular environment. The study demonstrates the beneficial effects of naringenin and quercetin, two molecules that possess antioxidant properties, limiting neurodegeneration, and thus preventing cone damage