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 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.

The influence of microbial isoflavonoid specific metabolites on platelets and transition metals iron and copper.

BACKGROUND: Isoflavonoids seem to possess positive cardiovascular and other beneficial effects in humans. HYPOTHESIS: Their low bioavailability, however, indicates that small isoflavonoid metabolites formed by human microflora can significantly contribute to these activities. STUDY DESIGN: Testing antiplatelet activity ex vivo in human blood and interaction with transition metals in vitro. METHODS: The effect on platelet aggregation induced by different triggers (arachidonic acid, collagen, ADP, TRAP-6), and interactions with transition metals (iron and copper chelation/reduction) were evaluated against four isoflavonoid-specific metabolites: S-equol; O-desmethylangolensin; 2-(4-hydroxyphenyl) propionic acid (HPPA); and 4-ethylphenol. RESULTS: S-equol, 4-ethylphenol and O-desmethylangolensin blocked platelet aggregation induced by arachidonic acid and collagen. S-equol even matched the potency of acetylsalicylic acid in the case of collagen, which is the most physiological inducer of aggregation. Moreover, their effects in general seemed to be biologically relevant and attainable at achievable plasma concentrations, with the exception of HPPA which was ineffective. While only O-desmethylangolensin mildly chelated iron and copper, all four compounds markedly reduced cupric ions. Their direct free radical scavenging effects seem to have little clinical relevance. CONCLUSION: This study has shown that S-equol, O-desmethylangolensin and 4-ethylphenol, arising from isoflavonoid intake, can have biologically relevant effects on platelet aggregation.

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.

Aqueous injection of quercetin: An approach for confirmation of its direct in vivo cardiovascular effects.

Potential positive effects of flavonol quercetin on humans were suggested by many studies. However, it is not clear if these effects are mediated by quercetin or its metabolites. The in vivo confirmation of quercetin effects is largely hindered by its low water solubility and thus impossibility to test directly its impact. Therefore, a solid dispersion of quercetin with polyvinylpyrrolidone (PVP) was developed to prepare an injectable formulation of water-soluble quercetin. The optimized formulation provided a 20,000-fold increase in quercetin solubility. This formulation was tested on conventional and spontaneously hypertensive rats; it lowered their blood pressure in both short- and long-term basis. Pharmacokinetic data are also provided. This study reports for the first time an injectable water-soluble formulation of quercetin suitable for confirmation of its vascular effect in vivo.

The Stoichiometry of Isoquercitrin Complex with Iron or Copper Is Highly Dependent on Experimental Conditions.

Interaction of flavonoids with transition metals can be partially responsible for their impact on humans. Stoichiometry of the iron/copper complex with a flavonoid glycoside isoquercitrin, a frequent component of food supplements, was assessed using competitive and non-competitive methods in four (patho)physiologically-relevant pH values (4.5. 5.5, 6.8, and 7.5). Isoquercitrin chelated all tested ions (Fe2+, Fe3+, Cu2+, and Cu⁺) but its affinity for Cu⁺ ions proved to be very low. In general, the chelation potency dropped with pH lowering. Metal complexes of 1:1 stoichiometry were mostly formed, however, they were not stable and the stoichiometry changed depending on conditions. Isoquercitrin was able to reduce both Cu2+ and Fe3+ ions at low ratios, but its reducing potential was diminished at higher ratios (isoquercitrin to metal) due to the metal chelation. In conclusion, this study emphasizes the need of using multiple different methods for the assessment of chelation potential in moderately-active metal chelators, like flavonoids.