Abstract
Purpose : To investigate the effect of Betong watercress and phenethyl isothiocyanate (PEITC) on the N-demethylation of caffeine (CF) in rats Methods : Male Wistar rats were subjected to 2 phases of experiment. Phase I, they received a single oral dose of CF (10 mg/kg), while in phase II, they were pretreated with the following regimens: 10 mg/kg fluvoxamine, i.p.; a single oral dose of 2, 10, and 20 mg/kg PEITC; 2, 10, and 20 mg/kg PEITC, once daily for five days; single oral dose of 800 mg/kg Betong watercress; 800 mg/kg Betong watercress once daily for five days, before receiving the same dose of CF as in phase I. Serum concentrations of CF and its metabolites after 3 h of CF administration were measured. Caffeine metabolic ratios (CMRs) and ratio of serum concentration of metabolites to that of CF were calculated and compared. Results : CMRs were decreased by a single pretreatment \with fluvoxamine (30 – 40%), PEITC (2 - 20 mg/kg) (40 – 55%), and Betong watercress (9 – 22%). The decreases caused by 10 and 20 mg/kg PEITC were significantly greater than those by fluvoxamine. CMRs were also decreased after five days of pretreatment with all doses of PEITC (43 – 69%) and Betong watercress (28 – 44%). The reduction in metabolic ratio after single- and multiple PEITC pretreatments was dose- and time-independent. Conclusion : Betong watercress and PEITC inhibit N-demethylation of CF in rats. Such an effect indicates that they have inhibitory activity on CYP1A2 and CYP2C. Keywords : Watercress, Phenethyl isothiocyanate, Caffeine, N-demethylation, Fluvoxamine, Cytochrome
Highlights
Watercress (Nasturtium officinale R.Br.) and other members of the Cruciferae (Brassicaceae) contain glucosinolates which can be hydrolysed by myrosinase to isothiocyanates (ITCs) after chewing
The derivative product of phenethyl isothiocyanate (PEITC) was eluted at 3.91 min and it was well separated with no interference
CF is primarily metabolized via N-demethylation to TB (1-N position), PX (3N position), and TP (7-N position), and via C-8hydroxylation to trimethyluric acid (TMU)
Summary
Watercress (Nasturtium officinale R.Br.) and other members of the Cruciferae (Brassicaceae) contain glucosinolates which can be hydrolysed by myrosinase to isothiocyanates (ITCs) after chewing. Watercress contains the largest amounts of ITCs, mostly phenethyl isothiocyanate (PEITC) [1] which is a dietary substance that has a protective effect against chemical carcinogen-induced tumors in animals [2]. Watercress and PEITC influence phases I & II drug metabolizing enzymes. Watercress inhibits the CYP2E1-mediated metabolism of some drugs [3, 4], but higher doses enhance the activity of ethoxyresorufin-O-deethylase (EROD; CYP1A), and NAD(P)H-quinonereductase, in a dose-dependent manner [5]. The effect of the PEITC on CYP1A expression and activity is still unclear. An in vitro study has demonstrated that CYP1A2 and other isoforms are inhibited by PEITC [6]. An animal study has shown inconsistent effects of PEITC on CYP1A activity [7]
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