title: The impact of the catechol-O-methyltransferase genotype on the acute responsiveness of vascular reactivity to a green tea extract.
abstract: The beneficial effects of green tea catechins, such as the proposed improvement in endothelial function, may be influenced by phase II metabolism during and after absorption. The methylation enzyme, catechol-O-methyltransferase (COMT), has a missense mutation rs4680 (G to A), proposed to result in a 40 % reduction in enzyme activity. In the present pilot study, twenty subjects (ten of each homozygous COMT genotype) were recruited. Green tea extract capsules (836 mg green tea catechins) were given in a fasted state, and a high-carbohydrate breakfast was given after 60 min. Blood samples and vascular function measurements were taken at regular intervals. The change in digital volume pulse stiffness index (SI) from baseline was shown to be different between genotype groups at 120 and 240 min, with a lower SI in the GG individuals (P ≤ 0·044). The change in blood pressure from baseline also differed between genotype groups, with a greater increase in systolic (P = 0·023) and diastolic (P = 0·034) blood pressure at 120 min in the GG group. The GG [corrected] group was shown to have a greater increase in insulin concentrations at 120 min (P = 0·019) and 180 min (P = 0·008) compared with baseline, despite similar glucose profiles. No genotypic differences were found in vascular reactivity measured using laser Doppler iontophoresis, total nitrite, lipids, plasma total antioxidant capacity or inflammatory markers after ingestion of the green tea extract. In conclusion, SI and insulin response to the glucose load differed between the COMT genotype groups, and this may be suggestive of a green tea extract and genotype interaction.
authors.affiliation: Department of Food and Nutritional Sciences, University of Reading, Whiteknights, PO Box 226, Reading, Berkshire RG6 6AP, UK. r.j.moore@reading.ac.uk
authors.forename: Rosalind J
authors.initials: RJ
authors.lastname: Miller
authors.forename: Kim G
authors.initials: KG
authors.lastname: Jackson
authors.forename: Tony
authors.initials: T
authors.lastname: Dadd
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Mayes
authors.forename: A Louise
authors.initials: AL
authors.lastname: Brown
authors.forename: Anne M
authors.initials: AM
authors.lastname: Minihane
mesh_terms: D000328:Adult; D000368:Aged; D001786:Blood Glucose / Q000032:analysis; D001794:Blood Pressure / Q000235:genetics; D028241:Camellia sinensis / Q000737:chemistry*; D002392:Catechin / Q000008:administration & dosage; D002394:Catechol O-Methyltransferase / Q000235:genetics*; D004040:Dietary Carbohydrates / Q000008:administration & dosage; D019587:Dietary Supplements; D004730:Endothelium, Vascular / Q000503:physiopathology*; D005260:Female; D056726:Genetic Association Studies; D006801:Humans; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance / Q000235:genetics; D008297:Male; D008875:Middle Aged; D020125:Mutation, Missense; D050177:Overweight / Q000097:blood / Q000378:metabolism / Q000503:physiopathology; D010865:Pilot Projects; D010936:Plant Extracts / Q000008:administration & dosage*; D019518:Postprandial Period; D006113:United Kingdom; D014655:Vascular Resistance / Q000235:genetics
chemical_list: D001786:Blood Glucose; D004040:Dietary Carbohydrates; D007328:Insulin; D010936:Plant Extracts; D002392:Catechin; D002394:Catechol O-Methyltransferase