INTRODUCTION: It is well known that platelets from diabetic patients can be resistant to clinically used antiplatelet drugs. METHODS: To assess the phenomenon in more detail, 50 adult patients suffering from type 1 diabetes mellitus (T1D) were recruited and their responses to 7 platelet aggregation inducers, as well as to 3 clinically used antiplatelet drugs (acetylsalicylic acid /ASA/, ticagrelor and vorapaxar) and one experimental compound, 4-methylcatechol, were assessed ex vivo. A control group of 50 generally healthy age-matched controls was also included for comparison. RESULTS: T1D patients exhibited a lower aggregation reaction to 3 inducers but were conversely more resistant to the effect of ASA and vorapaxar than controls. Ticagrelor tended to be less active in T1D as well. On the other hand, 4-methylcatechol was equally or even more potent in T1D than in healthy controls. Plasma glucose levels above 7 mM were associated with lower platelet aggregation responses to four aggregation inducers. In contrast, the effect of 4-methylcatechol, unlike that of ASA, did not appear to be strongly influenced by glycemia. Further subanalyses, excluding hypertensive patients and significantly more frequently administered drugs, did not substantially modify the results. CONCLUSION: Conclusively, 4-methylcatechol seems to be a prototypical antiplatelet compound with a strong effect even in diabetic patients.

• Keywords
• 4-methylcatechol, Aggregation, Diabetes mellitus, Platelets,
• MeSH
• Platelet Aggregation * drug effects   MeSH
• Aspirin * therapeutic use   pharmacology   adverse effects   MeSH
• Diabetes Mellitus, Type 1 * blood   diagnosis   drug therapy   MeSH
• Adult MeSH
• Platelet Aggregation Inhibitors * therapeutic use   adverse effects   pharmacology   MeSH
• Catechols * therapeutic use   pharmacology   MeSH
• Blood Glucose metabolism   drug effects   MeSH
• Lactones * therapeutic use   pharmacology   MeSH
• Drug Resistance MeSH
• Middle Aged MeSH
• Humans MeSH
• Young Adult MeSH
• Pyridines * therapeutic use   pharmacology   MeSH
• Case-Control Studies MeSH
• Ticagrelor therapeutic use   MeSH
• Blood Platelets * drug effects   metabolism   MeSH
• Treatment Outcome MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Young Adult MeSH
• Male MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Comparative Study MeSH
• Names of Substances
• Aspirin * MeSH
• Platelet Aggregation Inhibitors * MeSH
• Catechols * MeSH
• Blood Glucose MeSH
• Lactones * MeSH
• Pyridines * MeSH
• Ticagrelor MeSH
• vorapaxar MeSH Browser

The human body is regularly exposed to simple catechols and small phenols originating from our diet or as a consequence of exposure to various industrial products. Several biological properties have been associated with these compounds such as antioxidant, anti-inflammatory, or antiplatelet activity. Less explored is their potential impact on the endocrine system, in particular through interaction with the alpha isoform of the estrogen receptor (ERα). In this study, human breast cancer cell line MCF-7/S0.5 was employed to investigate the effects on ERα of 22 closely chemically related compounds (15 catechols and 7 phenols and their methoxy derivatives), to which humans are widely exposed. ERα targets genes ESR1 (ERα) and TFF1, both on mRNA and protein level, were chosen to study the effect of the tested compounds on the mentioned receptor. A total of 7 compounds seemed to impact mRNA and protein expression similarly to estradiol (E2). The direct interaction of the most active compounds with the ERα ligand binding domain (LBD) was further tested in cell-free experiments using the recombinant form of the LBD, and 4-chloropyrocatechol was shown to behave like E2 with about 1/3 of the potency of E2. Our results provide evidence that some of these compounds can be considered potential endocrine disruptors interacting with ERα.

• Keywords
• catechol, cytotoxicity, endocrine disruptor, estrogenicity, xenobiotic,
• MeSH
• Estrogen Receptor alpha * metabolism   genetics   MeSH
• Endocrine Disruptors * pharmacology   toxicity   MeSH
• Trefoil Factor-1 metabolism   genetics   MeSH
• Phenols * pharmacology   chemistry   MeSH
• Humans MeSH
• MCF-7 Cells MeSH
• Breast Neoplasms metabolism   MeSH
• Check Tag
• Humans MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Estrogen Receptor alpha * MeSH
• Endocrine Disruptors * MeSH
• ESR1 protein, human MeSH Browser
• Trefoil Factor-1 MeSH
• Phenols * MeSH
• TFF1 protein, human MeSH Browser

Elevated low-density lipoprotein (LDL) cholesterol levels lead to atherosclerosis and platelet hyperaggregability, both of which are known culprits of arterial thrombosis. Normalization of LDL cholesterol in familial hypercholesterolemia (FH) is not an easy task and frequently requires specific treatment, such as regularly performed lipid apheresis and/or novel drugs such as proprotein convertase subtilisin kexin 9 monoclonal antibodies (PCSK9Ab). Moreover, a high resistance rate to the first-line antiplatelet drug acetylsalicylic acid (ASA) stimulated research of novel antiplatelet drugs. 4-methylcatechol (4-MC), a known metabolite of several dietary flavonoids, may be a suitable candidate. The aim of this study was to analyse the antiplatelet effect of 4-MC in FH patients and to compare its impact on two FH treatment modalities via whole-blood impedance aggregometry. When compared to age-matched, generally healthy controls, the antiplatelet effect of 4-MC against collagen-induced aggregation was higher in FH patients. Apheresis itself improved the effect of 4-MC on platelet aggregation and blood from patients treated with this procedure and pretreated with 4-MC had lower platelet aggregability when compared to those solely treated with PCKS9Ab. Although this study had some inherent limitations, e.g., a low number of patients and possible impact of administered drugs, it confirmed the suitability of 4-MC as a promising antiplatelet agent and also demonstrated the effect of 4-MC in patients with a genetic metabolic disease for the first time.

• Keywords
• 4-methylcathechol, familial hypercholesterolemia, lipid apheresis, platelet,
• MeSH
• Hyperlipoproteinemia Type II * drug therapy   MeSH
• Cholesterol, LDL MeSH
• Humans MeSH
• Antibodies, Monoclonal pharmacology   therapeutic use   MeSH
• Proprotein Convertase 9 MeSH
• Proprotein Convertases therapeutic use   MeSH
• Blood Component Removal * methods   MeSH
• Subtilisin MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• 4-methylcatechol MeSH Browser
• Cholesterol, LDL MeSH
• Antibodies, Monoclonal MeSH
• Proprotein Convertase 9 MeSH
• Proprotein Convertases MeSH
• Subtilisin MeSH

A polyphenol-rich diet has beneficial effects on cardiovascular health. However, dietary polyphenols generally have low bioavailability and reach low plasma concentrations. Small phenolic metabolites of these compounds formed by human microbiota are much more easily absorbable and could be responsible for this effect. One of these metabolites, 4-methylcatechol (4-MC), was suggested to be a potent anti-platelet compound. The effect of 4-MC was tested ex vivo in a group of 53 generally healthy donors using impedance blood aggregometry. The mechanism of action of this compound was also investigated by employing various aggregation inducers/inhibitors and a combination of aggregometry and enzyme linked immunosorbent assay (ELISA) methods. 4-MC was confirmed to be more potent than acetylsalicylic acid on both arachidonic acid and collagen-triggered platelet aggregation. Its clinically relevant effect was found even at a concentration of 10 μM. Mechanistic studies showed that 4-MC is able to block platelet aggregation caused by the stimulation of different pathways (receptors for the von Willebrand factor and platelet-activating factor, glycoprotein IIb/IIIa, protein kinase C, intracellular calcium elevation). The major mechanism was defined as interference with cyclooxygenase-thromboxane synthase coupling. This study confirmed the strong antiplatelet potential of 4-MC in a group of healthy donors and defined its mechanism of action.

• Keywords
• aggregation, blood, flavonoid, human, metabolite, platelet,
• MeSH
• Phenols MeSH
• Immunologic Tests * MeSH
• Catechols * pharmacology   MeSH
• Humans MeSH
• Polyphenols MeSH
• Platelet Function Tests MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• 4-methylcatechol MeSH Browser
• Phenols MeSH
• Catechols * MeSH
• Polyphenols MeSH

Flavonoids are associated with positive cardiovascular effects. However, due to their low bioavailability, metabolites are likely responsible for these properties. Recently, one of these metabolites, 4-methylcatechol, was described to be a very potent antiplatelet compound. This study aimed to compare its activity with its 22 close derivatives both of natural or synthetic origin in order to elucidate a potential structure-antiplatelet activity relationship. Blood from human volunteers was induced to aggregate by arachidonic acid (AA), collagen or thrombin, and plasma coagulation was also studied. Potential toxicity was tested on human erythrocytes as well as on a cancer cell line. Our results indicated that 17 out of the 22 compounds were very active at a concentration of 40 μM and, importantly, seven of them had an IC50 on AA-triggered aggregation below 3 μM. The effects of the most active compounds were confirmed on collagen-triggered aggregation too. None of the tested compounds was toxic toward erythrocytes at 50 μM and four compounds partly inhibited proliferation of breast cancer cell line at 100 μM but not at 10 μM. Additionally, none of the compounds had a significant effect on blood coagulation or thrombin-triggered aggregation. This study hence reports four phenol derivatives (4-ethylcatechol, 4-fluorocatechol, 2-methoxy-4-ethylphenol and 3-methylcatechol) suitable for future in vivo testing.

• Keywords
• 4-methylcatechol, aggregation, catechol, flavonoid, platelet, whole blood,
• MeSH
• Platelet Aggregation * MeSH
• Phenol * MeSH
• Phenols pharmacology   MeSH
• Platelet Aggregation Inhibitors pharmacology   MeSH
• Humans MeSH
• Thrombin pharmacology   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Phenol * MeSH
• Phenols MeSH
• Platelet Aggregation Inhibitors MeSH
• Thrombin MeSH

Flavonoids are abundant polyphenols in nature. They are extensively biotransformed in enterocytes and hepatocytes, where conjugated (methyl, sulfate, and glucuronide) metabolites are formed. However, bacterial microflora in the human intestines also metabolize flavonoids, resulting in the production of smaller phenolic fragments (e.g., hydroxybenzoic, hydroxyacetic and hydroxycinnamic acids, and hydroxybenzenes). Despite the fact that several colonic metabolites appear in the circulation at high concentrations, we have only limited information regarding their pharmacodynamic effects and pharmacokinetic interactions. Therefore, in this in vitro study, we investigated the interactions of 24 microbial flavonoid metabolites with human serum albumin and cytochrome P450 (CYP2C9, 2C19, and 3A4) enzymes. Our results demonstrated that some metabolites (e.g., 2,4-dihydroxyacetophenone, pyrogallol, O-desmethylangolensin, and 2-hydroxy-4-methoxybenzoic acid) form stable complexes with albumin. However, the compounds tested did not considerably displace Site I and II marker drugs from albumin. All CYP isoforms examined were significantly inhibited by O-desmethylangolensin; nevertheless, only its effect on CYP2C9 seems to be relevant. Furthermore, resorcinol and phloroglucinol showed strong inhibitory effects on CYP3A4. Our results demonstrate that, besides flavonoid aglycones and their conjugated derivatives, some colonic metabolites are also able to interact with proteins involved in the pharmacokinetics of drugs.

• Keywords
• CYP450 enzymes, O-desmethylangolensin, colonic flavonoid metabolites, pharmacokinetic interaction, phloroglucinol, polyphenols, resorcinol, serum albumin,
• MeSH
• Erythrocytes enzymology   MeSH
• Flavonoids * chemistry   metabolism   MeSH
• Hepatocytes enzymology   MeSH
• Humans MeSH
• Serum Albumin, Human * chemistry   metabolism   MeSH
• Cytochrome P-450 Enzyme System * chemistry   metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Flavonoids * MeSH
• Serum Albumin, Human * MeSH
• Cytochrome P-450 Enzyme System * MeSH

Quercetin is proven to decrease arterial blood pressure when given orally. Its bioavailability is, however, low and, therefore, its metabolites could rather be responsible for this effect. In particular, the colonic metabolites of quercetin, 3,4-dihydroxyphenylacetic acid (DHPA), 4-methylcatechol (4MC), and 3-(3-hydroxyphenyl)propionic acid (3HPPA), have been previously shown to decrease the blood pressure in spontaneously hypertensive rats (SHR). Interestingly, the mechanisms of action of these three metabolites are different. The aim of this study is hence to investigate if these metabolites can potentiate each other and thus decrease blood pressure in reduced doses. Three double-combinations of previously mentioned metabolites were administered to SHR as infusions to mimic a real biological situation. All combinations significantly decreased the blood pressure in SHR but there were important differences. The effect of DHPA and 4MC was mild and very short. A combination of DHPA with 3HPPA caused more pronounced effects, which were also rather short-lived. The last combination of 3HPPA and 4MC caused a long-lasting effect. In conclusion, certain combinations of quercetin metabolites have a more pronounced antihypertensive effect than single metabolites.

• Keywords
• blood pressure, in vivo, infusion, phenolic, quercetin, rat,
• MeSH
• Antihypertensive Agents pharmacokinetics   MeSH
• Biological Availability MeSH
• Phenols pharmacokinetics   MeSH
• Hypertension drug therapy   MeSH
• Catechols pharmacokinetics   MeSH
• Blood Pressure drug effects   MeSH
• Rats MeSH
• 3,4-Dihydroxyphenylacetic Acid pharmacokinetics   MeSH
• Coumaric Acids pharmacokinetics   MeSH
• Disease Models, Animal MeSH
• Rats, Inbred SHR MeSH
• Quercetin chemistry   MeSH
• Dose-Response Relationship, Drug MeSH
• Animals MeSH
• Check Tag
• Rats MeSH
• Male MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• 4-methylcatechol MeSH Browser
• Antihypertensive Agents MeSH
• dihydro-3-coumaric acid MeSH Browser
• Phenols MeSH
• Catechols MeSH
• 3,4-Dihydroxyphenylacetic Acid MeSH
• Coumaric Acids MeSH
• Quercetin MeSH