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

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

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

Cholinesterase-like organocatalysis by imidazole and imidazole-bearing molecules

Organocatalysis, which is mostly explored for its new potential industrial applications, also represents a chemical event involved in endogenous processes. In the present study, we provide the first evidence that imidazole and imidazole derivatives have cholinesterase-like properties since they can accelerate the hydrolysis of acetylthiocholine and propionylthiocholine in a concentration-dependent manner. The natural imidazole-containing molecules as L-histidine and histamine show a catalytic activity, comparable to that of imidazole itself, whereas synthetic molecules, as cimetidine and clonidine, were less active. In the experimental conditions used, the reaction progress curves were sigmoidal and the rational of such unexpected behavior as well as the mechanism of catalysis is discussed. Although indirectly, findings of the present study suggests that imidazolic compounds may interfere with the homeostasis of the cholinergic system in vivo

The citrus flavanone naringenin produces cardioprotective effects in hearts from 1 year old rat, through activation of mitoBK channels

Background and Purpose: Incidence of cardiovascular disorders increases with age, because of a dramatic fall of endogenous self-defense mechanisms and increased vulnerability of myocardium. Conversely, the effectiveness of many cardioprotective drugs is blunted in hearts of 1 year old rat. The Citrus flavanone naringenin (NAR) was reported to promote cardioprotective effects against ischemia/reperfusion (I/R) injury, through the activation of mitochondrial large conductance calcium-activated potassium channel (mitoBK). These effects were observed in young adult rats, but no data are available about the possible cardioprotective effects of NAR in aged animals. Experimental Approach: This study aimed at evaluating the potential cardioprotective effects of NAR against I/R damage in 1 year old rats, and the possible involvement of mitoBK. Key Results: Naringenin protected the hearts of 1 year old rats in both ex vivo and in vivo I/R protocols. Noteworthy, these effects were antagonized by paxilline, a selective BK-blocker. The cardioprotective effects of NAR were also observed in senescent H9c2 cardiomyoblasts. In isolated mitochondria from hearts of 1 year old, NAR exhibited the typical profile of a mitoBK opener. Finally, Western Blot analysis confirmed a significant (albeit reduced) presence of BK-forming alpha and beta subunits, both in cardiac tissue of 1 year old rats and in senescent H9c2 cells. Conclusion and Implications: This is the first work reporting cardioprotective effects of NAR in 1 year old rats. Although further studies are needed to better understand the whole pathway involved in the NAR-mediated cardioprotection, these preliminary data represent a promising perspective for a rational nutraceutical use of NAR in aging

Different patterns of H2S/NO activity and cross-talk in the control of the coronary vascular bed under normotensive or hypertensive conditions

Hydrogen sulfide (H2S) and nitric oxide (NO) play pivotal roles in the cardiovascular system. Conflicting results have been reported about their cross-talk. This study investigated their interplays in coronary bed of normotensive (NTRs) and spontaneously hypertensive rats (SHRs). The effects of H2S- (NaHS) and NO-donors (sodium nitroprusside, SNP) on coronary flow (CF) were measured in Langendorff-perfused hearts of NTRs and SHRs, in the absence or in the presence of propargylglycine (PAG, inhibitor of H2S biosynthesis), L-NAME (inhibitor of NO biosynthesis), ODQ (inhibitor of guanylate cyclase), L-Cysteine (substrate for H2S biosynthesis) or L-Arginine (substrate for NO biosynthesis). In NTRs, NaHS and SNP increased CF; their effects were particularly evident in Angiotensin II (AngII)-contracted coronary arteries. The dilatory effects of NaHS were abolished by L-NAME and ODQ; conversely, PAG abolished the effects of SNP. In SHRs, high levels of myocardial ROS production were observed. NaHS and SNP did not reduce the oxidative stress, but produced clear increases of the basal CF. In contrast, in AngII-contracted coronary arteries of SHRs, significant hyporeactivity to NaHS and SNP was observed. In SHRs, the vasodilatory effects of NaHS were only modestly affected by L-NAME and ODQ; PAG poorly influenced the effects of SNP. Then, in NTRs, the vascular actions of H2S required NO and vice versa. By contrast, in SHRs, the H2S-induced actions scarcely depend on NO release; as well, the NO effects are largely H2S-independent. These results represent the first step for understanding pathophysiological mechanisms of NO/H2S interplays under both normotensive and hypertensive conditions

Application of a pharmacokinetic/pharmacogenetic approach to assess the nicotine metabolic profile of smokers in the real-life setting

The nicotine metabolite ratio, i.e., the ratio 3-hydroxycotinine/cotinine, is used to assess the nicotine metabolic status and has been proven to predict the response to smoking cessation treatments in randomized clinical trials. In the current study, a pharmacokinetic-pharmacogenetic integrated approach is described, based on the development of a liquid chromatography–tandem mass spectrometry (LC/MS/MS) method for nicotine metabolite ratio assay in plasma and a real-time PCR analysis for fast genotyping of CYP2A6. The pharmacokinetic-pharmacogenetic approach was validated in 66 subjects with different smoking status. The LC/MS/MS assay was rapid and sensitive enough to detect plasma cotinine levels also in second-hand exposed abstainers. In the cohort of patients of the present study the following results were obtained: (i) the frequencies of CYP2A6 genetic variants were comparable with those from clinical trials carried out in Caucasian populations; (ii) all the subjects carrying the CYP2A6 deficient allele also had a slow metabolizer phenotype; (iii) slow metabolizers had mean nicotine metabolite ratio approximately 50% of that of the normal/fast metabolizers; (iv) women had higher nicotine metabolite ratio than men; and (v) salivary nicotine metabolite ratio measures were comparable to plasma levels. Overall, the findings of the current study demonstrate that the simultaneous assessment of nicotine metabolite ratio and CYP2A6 genotype from human blood samples is feasible and accurate and could be used in a smoking cessation program to optimize treatments and identify those smokers who inherit metabolically deficient CYP2A6 alleles

Cytotoxic Activity of Oleocanthal Isolated from Virgin Olive Oil on Human Melanoma Cells

Oleocanthal is one of the phenolic compounds of extra virgin olive oil with important anti-inflammatory properties. Although its potential anticancer activity has been reported, only limited evidence has been provided in cutaneous malignant melanoma. The present study is aimed at investigating the selective in vitro antiproliferative activity of oleocanthal against human malignant melanoma cells. Since oleocanthal is not commercially available, it was obtained as a pure standard by direct extraction and purification from extra virgin olive oil. Cell viability experiments carried out by WST-1 assay demonstrated that oleocanthal had a remarkable and selective activity for human melanoma cells versus normal dermal fibroblasts with IC50s in the low micromolar range of concentrations. Such an effect was paralleled by a significant inhibition of ERK1/2 and AKT phosphorylation and downregulation of Bcl-2 expression. These findings may suggest that extra virgin olive oil phenolic extract enriched in oleocanthal deserves further investigation in skin cancer