The quercetin metabolite 4-methylcatechol causes vasodilation via voltage-gated potassium (KV) channels.

Dietary polyphenols have been associated with many beneficial cardiovascular effects. However, these effects are rather attributed to small phenolic metabolites formed by the gut microbiota, which reach sufficient concentrations in systemic circulation. 4-Methylcatechol (4-MC) is one such metabolite. As it is shown to possess considerable vasorelaxant effects, this study aimed to unravel its mechanism of action. To this end, experimental in vitro and in silico approaches were employed. In the first step, isometric tension recordings were performed on rat aortic rings. 4-MC potentiated the effect of cyclic nucleotides, but the effect was not mediated by either soluble guanylyl cyclase (sGC), modification of cyclic adenosine monophosphate levels, or protein kinase G. Hence, downstream targets such as calcium or potassium channels were considered. Inhibition of voltage-gated K+ channels (KV) markedly decreased the effect of 4-MC, and vasodilation was partly decreased by inhibition of the KV7 isoform. Contrarily, other types of K+ channels or L-type Ca2+ channels were not involved. In silico reverse docking confirmed that 4-MC binds to KV7.4 through hydrogen bonding and hydrophobic interactions. In particular, it interacts with two crucial residues for KV7.4 activation: Trp242 and Phe246. In summary, our findings suggested that 4-MC exerts vasorelaxation by opening KV channels with the involvement of KV7.4.

3-methoxycatechol causes vasodilation likely via KV channels: ex vivo, in silico docking and in vivo study.

Substituted catechols include both natural and synthetic compounds found in the environment and foods. Some of them are flavonoid metabolites formed by the gut microbiota which are absorbed afterwards. Our previous findings showed that one of these metabolites, 4-methylcatechol, exerts potent vasorelaxant effects in rats. In the current study, we aimed at testing of its 22 structural congeners in order to find the most potent structure and to investigate the mechanism of action. 3-methoxycatechol (3-MOC), 4-ethylcatechol, 3,5-dichlorocatechol, 4-tert-butylcatechol, 4,5-dichlorocatechol, 3-fluorocatechol, 3-isopropylcatechol, 3-methylcatechol and the parent 4-methylcatechol exhibited high vasodilatory activities on isolated rat aortic rings with EC50s ranging from ∼10 to 24 µM. Some significant sex-differences were found. The most potent compound, 3-MOC, relaxed also resistant mesenteric artery but not porcine coronary artery, and decreased arterial blood pressure in both male and female spontaneously hypertensive rats in vivo without affecting heart rate. It potentiated the vasodilation mediated by cAMP and cGMP, but did not impact L-type Ca2+-channels. By using two inhibitors, activation of voltage-gated potassium channels (KV) was found to be involved in the mechanism of action. This was corroborated by docking analysis of 3-MOC with the KV7.4 channel. None of the most active catechols decreased the viability of the A-10 rat embryonic thoracic aorta smooth muscle cell line. Our findings showed that various catechols can relax vascular smooth muscles and hence could provide templates for developing new antihypertensive vasodilator agents without affecting coronary circulation.

Biological Properties of Vitamins of the B-Complex, Part 1: Vitamins B1, B2, B3, and B5.

This review summarizes the current knowledge on essential vitamins B1, B2, B3, and B5. These B-complex vitamins must be taken from diet, with the exception of vitamin B3, that can also be synthetized from amino acid tryptophan. All of these vitamins are water soluble, which determines their main properties, namely: they are partly lost when food is washed or boiled since they migrate to the water; the requirement of membrane transporters for their permeation into the cells; and their safety since any excess is rapidly eliminated via the kidney. The therapeutic use of B-complex vitamins is mostly limited to hypovitaminoses or similar conditions, but, as they are generally very safe, they have also been examined in other pathological conditions. Nicotinic acid, a form of vitamin B3, is the only exception because it is a known hypolipidemic agent in gram doses. The article also sums up: (i) the current methods for detection of the vitamins of the B-complex in biological fluids; (ii) the food and other sources of these vitamins including the effect of common processing and storage methods on their content; and (iii) their physiological function.

3-Hydroxyphenylacetic Acid: A Blood Pressure-Reducing Flavonoid Metabolite.

Regular intake of polyphenol-rich food has been associated with a wide variety of beneficial health effects, including the prevention of cardiovascular diseases. However, the parent flavonoids have mostly low bioavailability and, hence, their metabolites have been hypothesized to be bioactive. One of these metabolites, 3-hydroxyphenylacetic acid (3-HPAA), formed by the gut microbiota, was previously reported to exert vasorelaxant effects ex vivo. The aim of this study was to shed more light on this effect in vivo, and to elucidate the mechanism of action. 3-HPAA gave rise to a dose-dependent decrease in arterial blood pressure when administered i.v. both as a bolus and infusion to spontaneously hypertensive rats. In contrast, no significant changes in heart rate were observed. In ex vivo experiments, where porcine hearts from a slaughterhouse were used to decrease the need for laboratory animals, 3-HPAA relaxed precontracted porcine coronary artery segments via a mechanism partially dependent on endothelium integrity. This relaxation was significantly impaired after endothelial nitric oxide synthase inhibition. In contrast, the blockade of SKCa or IKCa channels, or muscarinic receptors, did not affect 3-HPAA relaxation. Similarly, no effects of 3-HPAA on cyclooxygenase nor L-type calcium channels were observed. Thus, 3-HPAA decreases blood pressure in vivo via vessel relaxation, and this mechanism might be based on the release of nitric oxide by the endothelial layer.

Biochanin A, the Most Potent of 16 Isoflavones, Induces Relaxation of the Coronary Artery Through the Calcium Channel and cGMP-dependent Pathway.

The dietary intake of flavonoids seems to be inversely related to cardiovascular mortality. The consumption of isoflavonoids is increasing in the general population, especially due to the use of food supplements and a variety of isoflavonoid-rich foods. However, detailed studies on the vascular influence of individual pure isoflavonoids are mostly missing. For this study, 16 isoflavonoids were initially screened for their vasorelaxant properties on rat aortas. The 2 most potent of them, biochanin A and glycitein, were further tested for the mechanism of action on porcine coronary arteries. They both induced an endothelium independent vascular relaxation, with EC50 below 6 and 17 µM, respectively. Biochanin A, but not glycitein, was able to block the vasoconstriction caused by KCl, CaCl2, serotonin, and U46619 in a dose-dependent manner. Another series of experiments suggested that the major mechanism of action of biochanin A was the inhibition of L-type calcium channels. Moreover, biochanin A in relatively small concentrations (2 - 4 µM) interfered with the cGMP, but not cAMP, pathway in isolated coronary arteries. These results indicate that some isoflavonoids, in particular biochanin A, are able to have vasodilatory effects in micromolar concentrations, which is of potential clinical interest for the management of cardiovascular pathologies.

The pharmacokinetics of flavanones.

The intake of flavanones, the predominant flavonoid in the Citrus genus in human diets is variable but considerable. It is thus unsurprising that they have attracted interest for their claimed positive effects on health. However, to substantiate any purported impact on health and decipher the underlying mechanism(s), knowledge of pharmacokinetics is crucial. The aim of this article is to review currently known aspects of the fate of flavanones in the organism including absorption, metabolism, distribution, and excretion as well as possible kinetic interactions with clinically used drugs. There are three principal keynotes: (1) The level of parent flavanones in plasma is negligible. The major reason for this is that although flavanones are absorbed into enterocytes after oral intake, they are rapidly metabolized, in particular, into conjugates, sulfates and glucuronides, which are the major forms circulating in plasma. (2) A large fraction reaches the colon where it is efficiently metabolized into small absorbable phenolics. (3) The form (aglycone vs. glycoside) and species (e.g. human vs. rat) have important impact. In conclusion, knowledge of the pharmacokinetics of flavanones, in particular of metabolites, their achievable plasma concentration and half-lives, should be borne in mind when their biological effects are investigated.

The Effect of Silymarin Flavonolignans and Their Sulfated Conjugates on Platelet Aggregation and Blood Vessels Ex Vivo.

Silymarin is a traditional drug and food supplement employed for numerous liver disorders. The available studies indicate that its activities may be broader, in particular due to claimed benefits in some cardiovascular diseases, but the contributions of individual silymarin components are unclear. Therefore, we tested silymarin flavonolignans as pure diastereomers as well as their sulfated metabolites for potential vasorelaxant and antiplatelet effects in isolated rat aorta and in human blood, respectively. Eleven compounds from a panel of 17 tested exhibited a vasorelaxant effect, with half maximal effective concentrations (EC50) ranging from 20 to 100 µM, and some substances retained certain activity even in the range of hundreds of nM. Stereomers A were generally more potent as vasorelaxants than stereomers B. Interestingly, the most active compound was a metabolite-silychristin-19-O-sulfate. Although initial experiments showed that silybin, 2,3-dehydrosilybin, and 2,3-dehydrosilychristin were able to substantially block platelet aggregation, their effects were rapidly abolished with decreasing concentration, and were negligible at concentrations ≤100 µM. In conclusion, metabolites of silymarin flavonolignans seem to have biologically relevant vasodilatory properties, but the effect of silymarin components on platelets is low or negligible.

Two flavonoid metabolites, 3,4-dihydroxyphenylacetic acid and 4-methylcatechol, relax arteries ex vivo and decrease blood pressure in vivo.

SCOPE: The flavonoid quercetin reduces arterial blood pressure in animals and humans but the mechanisms remains elusive. The aim of this study was to test the activity of flavonoid microbial metabolites, which can participate on the final vasorelaxant effect. METHODS AND RESULTS: Both ex vivo (isolated rat thoracic aorta and mesenteric artery) and in vivo (normotensive and spontaneously hypertensive rats) approaches were used in this study. 4-methylcatechol and 3,4-dihydroxyphenylacetic acid (DHPA) had greater vasorelaxant effects on mesenteric artery than 3-(3-hydroxyphenyl)propionic acid, the previously reported metabolite with vasorelaxant effect. In vivo testing confirmed their blood pressure decreasing effect given both as bolus and slow infusion. Their mechanism at molecular level was different. CONCLUSIONS: This study is the first to show that flavonoid metabolites DHPA and 4-methylcatechol decrease arterial blood pressure and hence a mixture of microbial metabolites formed in the gastrointestinal tract may be responsible for or contribute to the effect of orally ingested quercetin.

Comprehensive review of cardiovascular toxicity of drugs and related agents.

Cardiovascular diseases are a leading cause of morbidity and mortality in most developed countries of the world. Pharmaceuticals, illicit drugs, and toxins can significantly contribute to the overall cardiovascular burden and thus deserve attention. The present article is a systematic overview of drugs that may induce distinct cardiovascular toxicity. The compounds are classified into agents that have significant effects on the heart, blood vessels, or both. The mechanism(s) of toxic action are discussed and treatment modalities are briefly mentioned in relevant cases. Due to the large number of clinically relevant compounds discussed, this article could be of interest to a broad audience including pharmacologists and toxicologists, pharmacists, physicians, and medicinal chemists. Particular emphasis is given to clinically relevant topics including the cardiovascular toxicity of illicit sympathomimetic drugs (e.g., cocaine, amphetamines, cathinones), drugs that prolong the QT interval, antidysrhythmic drugs, digoxin and other cardioactive steroids, beta-blockers, calcium channel blockers, female hormones, nonsteroidal anti-inflammatory, and anticancer compounds encompassing anthracyclines and novel targeted therapy interfering with the HER2 or the vascular endothelial growth factor pathway.

Flavonoid metabolite 3-(3-hydroxyphenyl)propionic acid formed by human microflora decreases arterial blood pressure in rats.

There are reports of positive effects of quercetin on cardiovascular pathologies, however, mainly due to its low biovailability, the mechanism remains elusive. Here, we report that one metabolite formed by human microflora (3-(3-hydroxyphenyl)propionic acid)relaxed isolated rat aorta and decreased arterial blood pressure in rats.

Oral administration of quercetin is unable to protect against isoproterenol cardiotoxicity.

Catecholamines are endogenous amines that participate in the maintenance of cardiovascular system homeostasis. However, excessive release or exogenous administration of catecholamines is cardiotoxic. The synthetic catecholamine, isoprenaline (isoproterenol, ISO), with non-selective ß-agonistic activity has been used as a viable model of acute myocardial toxicity for many years. Since the pathophysiology of ISO-cardiotoxicity is complex, the aim of this study was to elucidate the effect of oral quercetin pretreatment on myocardial ISO toxicity. Wistar-Han rats were randomly divided into four groups: solvent or quercetin administered orally by gavage in a dose of 10 mg kg(-1) daily for 7 days were followed by s.c. water for injection or ISO in a dose of 100 mg kg(-1). Haemodynamic, ECG and biochemical parameters were measured; effects on blood vessels and myocardial histology were assessed, and accompanying pharmacokinetic analysis was performed. Quercetin was unable to protect the cardiovascular system against acute ISO cardiotoxicity (stroke volume decrease, cardiac troponin T release, QRS-T junction elevation and histological impairment). The sole positive effect of quercetin on catecholamine-induced cardiotoxicity was the normalization of increased left ventricular end-diastolic pressure caused by ISO. Quercetin did not reverse the increased responsiveness of rat aorta to vasoconstriction in ISO-treated animals, but it decreased the same parameter in the control animals. Accompanying pharmacokinetic analysis showed absorption of quercetin and its metabolite 3-hydroxyphenylacetic acid formed by bacterial microflora. In conclusion, a daily oral dose of 10 mg kg(-1) of quercetin for 7 days did not ameliorate acute ISO-cardiovascular toxicity in rats despite minor positive cardiovascular effects.

Novel bronchodilatory quinazolines and quinoxalines: synthesis and biological evaluation.

A series of heterocyclic derivatives analogous to (-)vasicinone, in which the vasicinone C-ring was replaced with alkyl chain terminated by tertiary amine was prepared. N3, C4-O, C4-S or C4-N were used as the sites of attachment. The 4-[3-(1-piperidyl)propylsulfanyl]derivatives displayed bronchodilatory effect at low micromolar concentrations on isolated rat trachea, and low toxicity both on Balb/c 3T3 mouse fibroblast cells and in mice.

Vasodilatory activity of human quercitin metabolites.

A large number of studies confirmed antihypertensive effect of quercetin. However, due to its low bioavailability, the mechanism of action has been remaining vague and is not likely associated with its antioxidant effect. This study was designed to determinate if quercetin metabolites might be responsible for the activity. During the in vitro study, the vasorelaxant potency of different quercetin metabolites including small phenolic acids formed by bacterial microflora was tested. Metabolites at concentration 10(-7) to 10(-3) M were tested for relaxation of rat thoracic aorta rings precontracted by phenylephrine. Subsequently the most active structure was selected for in vivo experiments, when the effect on blood pressure and heart rate was monitored after i.v. administration in dose range from 0,2mg/kg to 25mg/kg. The most active structure, 3-(3-hydroxyphenyl)propionic acid, initiated vasorelaxation in concentration of 100nM while quercetin at 500nM. The major quercetin metabolite formed by human enzymes, 3-glucuronide, was almost inactive. During the in vivo study the 3-(3-hydroxyphenyl)propionic acid decreased systolic blood pressure even at dose of 1mg/kg without having an effect on heart rate at this dose. In conclusion, some of quercetin metabolites may have be partly responsible for vasorelaxant activity of orally administered quercetin.

Metabolic profiling of a potential antifungal drug, 3-(4-bromophenyl)-5-acetoxymethyl-2,5-dihydrofuran-2-one, in mouse urine using high-performance liquid chromatography with UV photodiode-array and mass spectrometric detection.

3-(4-bromophenyl)-5-acetyloxymethyl-2,5-dihydrofuran-2-one (LNO-18-22) is a representative member of a novel group of potential antifungal drugs, derived from a natural 3,5-disubstituted butenolide, (-)incrustoporine, as a lead structure. This lipophilic compound is characterized by high in vitro antifungal activity and low acute toxicity. For the purpose of in vivo studies, a new bioanalytical high-performance liquid chromatographic method with UV photodiode-array and mass spectrometric detection (HPLC-PDA-MS), involving a direct injection of diluted mouse urine was developed and used in the evaluation of the metabolic profiling of this drug candidate. The separation of LNO-18-22 and its phase I metabolites was performed in 37 min on a 125 mmx4 mm chromatographic column with Purospher RP-18e using an acetonitrile-water gradient elution. Scan mode of UV detection (195-380 nm) was employed for the identification of the parent compound and its biotransformation products in the biomatrix. Finally, the identity of LNO-18-22 and its metabolites was confirmed using HPLC-MS analyses of the eluate. These experiments demonstrated the power of a comprehensive analytical approach based on the combination of xenobiochemical methods and the results from tandem HPLC-PDA-MS (chromatographic behaviour, UV and MS spectra of native metabolites versus synthetic standards). The chemical structures of five phase I LNO-18-22 metabolites and one phase II metabolite were elucidated in the mouse urine, with two of these metabolites having very unexpected structures.

Effects of oral alpha-tocopherol on lung response in rat model of allergic asthma.

OBJECTIVE AND BACKGROUND: Asthma is a chronic inflammatory disease in which an oxidant/antioxidant imbalance plays an important role. d-alpha-tocopherol (biologically the most active form of vitamin E) has redox properties and by scavenging the free radicals can act as an antioxidant. The aim of this study was to examine the effects of orally administered alpha-tocopherol in a rat model of allergic asthma. METHODOLOGY: Actively sensitized rats (OA) were treated with alpha-tocopherol (400 mg/kg/day for 10 days) or vehicle; 1 h after the last dose, they were challenged with antigen aerosol. The antigen-induced airway hyperresponsiveness to direct bronchoconstrictor (serotonin), the inflammatory cell infiltrate and histological changes were determined 1 or 24 h after the antigen challenge. RESULTS: Alpha-tocopherol pretreatment was not significantly effective at reducing the studied parameters when compared with controls, even though there was a tendency to a reduction in bronchial responsiveness and in eosinophil and neutrophil infiltration. CONCLUSION: Alpha-tocopherol when administered in the chosen study design in an animal model of asthma had no major effect on airway inflammation. The effect of antioxidants deserves further evaluation.

In vitro activities of 3-(halogenated phenyl)-5-acyloxymethyl- 2,5-dihydrofuran-2-ones against common and emerging yeasts and molds.

Three 3-(halogenated phenyl)-5-acyloxymethyl-2,5-dihydrofuran-2-ones were evaluated for activity against 191 strains of common and emerging yeasts and Aspergillus species by the broth microdilution test performed according to NCCLS guidelines. The furanone derivatives displayed broad-spectrum in vitro activity against potentially pathogenic yeasts and molds, especially Aspergillus spp. (MIC