Phenols are the substrate for the enzyme phenolsulphotransferase (PST), which exists in two forms and is particularly active in the gut: PST-M, which inactivates phenolic monoamines such as tyramine and dopamine, and PST-P, which degrades phenol itself and
p-cresol. Ethyl acetate extracts of red wine contained very potent inhibitors of PST, particularly the P form, but also white wine and other drinks (spirits and vodka) show some degree of this activity [
46]. The main difference between red and white wine is their flavonoid component: red wine contains typically 1,200 mg/l, while white wine only 50 mg/l. This fraction inhibits potently and specifically PST-P, at a dilution consistent with a consumption in vivo of a single glass. Catechins and anthocyanins (responsible for the color of red wine), which comprise about 30% of flavonoid fraction and are absorbed through the gastrointestinal tract, are potent inhibitors of PST-P in vitro. To study if red wine also has this metabolic effect in vivo,
p-cresol that is a specific substrate of PST-P was determined in urine after the oral challenge with red wine, vodka or water:
p-cresol increased significantly after red wine with respect to controls. This suggests the possibility that red wine inhibition of conjugation by PST-P of
p-cresol and other phenols could result in a build up of free phenols in the circulation, which may be toxic in several ways [
9]. In dietary migraine, a deficit of PST-P was identified [
47]. Other studies show that in migraine patients, the activity of PST-M responsible for inactivation of dopamine and 5HT was reduced, but not that of PST-P, without any significant difference in dietary migraine. Moreover, the selective inhibition of PST-P by red wine is much more potent than previously thought, with 2,000-fold dilution of dealcoholized red wine having the ability to inhibit sulphation by this enzyme by 50% [
48]. Phenol flavonoids were contained in beer [
49] and also in the chocolate, which impair endothelial function [
50].