Woon-Gye Chung

Prevention of nitric oxide-mediated 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinson's disease in mice by tea phenolic epigallocatechin 3-gallate.

In animal models of Parkinsons disease (PD), the toxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is mediated by oxidative stress, especially by nitric oxide (NO). Inhibition of NO synthase (NOS) activity in the brain produces a neuroprotective effect against PD induced by MPTP Green tea containing high levels of (-)-epigallocatechin 3-gallate (EGCG) was administered to test whether EGCG attenuates MPTP-induced PD in mice through the inhibition of NOS expression. Both tea and the oral administration of EGCG prevented the loss of tyrosine hydroxylase (TH)-positive cells in the substantia nigra (SN) and of TH activity in the striatum. These treatments also preserved striatal levels of dopamine and its metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid (HVA). Both tea and EGCG decreased expressions of nNOS in the substantia nigra. Also tea plus MPTP and EGCG plus MPTP treatments decreased expressions of neuronal NO synthase (nNOS) at the similar levels of EGCG treatment group. Therefore, the preventive effects of tea and EGCG may be explained by the inhibition of nNOS in the substantia nigra.

Phenotypes of flavin-containing monooxygenase activity determined by ranitidine N-oxidation are positively correlated with genotypes of linked FM03 gene mutations in a Korean population.

A non-invasive urine analysis method to determine the in-vivo flavin-containing mono-oxygenase (FMO) activity catalysing N-oxidation of ranitidine (RA) was developed and used to phenotype a Korean population. FMO activity was assessed by the molar concentration ratio of RA and RANO in the bulked 8 h urine. This method was used to determine the FMO phenotypes of 210 Korean volunteers (173 men and 37 women, 110 nonsmokers and 100 smokers). Urinary RA/RANO ratio, representing the metabolic ratio and the reciprocal index of FMO activity, ranged from 5.67-27.20 (4.8-fold difference) and was not different between men and women (P = 0.76) or between smokers and nonsmokers (P = 0.50). The frequencies of RA/RANO ratios were distributed in a trimodal fashion. Among the 210 Korean subjects, 93 (44.3%) were fast metabolizers, 104 (49.5%) were intermediate metabolizers and 13 (6.2%) were slow metabolizers. Subsequently, the relationship between the ranitidine N-oxidation phenotypes and FMO3 genotypes, determined by the presence of two previously identified mutant alleles (Glu158Lys: FMO3/Lys158 and Glu308Gly: FMO3/Gly308 alleles) commonly found in our Korean population was examined. The results showed that subjects who were homozygous and heterozygous for either one or both of the FMO3/Lys158 and FMO3/Gly308 mutant alleles had significantly lower in-vivo FMO activities than those with homozygous wild-type alleles (FMO3/Glu158 and FMO3/Glu308) (P < 0.001, Mann-Whitney U-test). Furthermore, the FMO activities of subjects with either FMO3/Lys158 or FMO3/Gly308 mutant alleles were almost identical to those having both FMO3 mutant alleles (FMO3/Lys158 and FMO3/Gly308). These two mutant alleles located, respectively, at exons 4 and 7 in the FMO3 gene appeared to be strongly linked by cis-configuration in Koreans. Therefore, we concluded that presence of FMO3/Lys158 and FMO3/Gly308 mutant alleles in FMO3 gene is responsible for the low ranitidine N-oxidation (FMO3 activity) in our Korean population.

Involvement of CYP3A1, 2B1, and 2E1 in C-8 hydroxylation and CYP 1A2 and flavin-containing monooxygenase in N-demethylation of caffeine: identified by using inducer treated rat liver microsomes that are characterized with testosterone metabolic patterns

Caffeine (CA) is oxidized by rat liver microsomal enzymes to theobromine (TB), paraxanthine (PX), and theophylline (TP) by N-demethylation and to trimethylurate (TMU) by C-8 hydroxylation, In order to identify the specific enzymes responsible for productions of these primary CA metabolites, liver microsomes enriched with various isoforms of cytochrome P450 (CYP) and flavin-containing monooxygenase (FMO) are prepared by pretreatment of rats with several inducers. The specific increases in various CYP or FMO activities are identified with the diagnostic testosterone metabolic patterns or the thiobenzamide S-oxidation assay. They are then employed to metabolize the CA. Liver microsomes isolated from rats pretreated with phenobarbital (PB-microsomes) did not have increased FMO activity but had increased activities for hydroxylating the testosterone at 6 beta-(CYP3A1), 16 beta-(CYP2B1), and 2 beta-(CYP3A1) positions. This PB-microsomes had increased activity for TMU production from CA (result of C-8 hydroxylation). Liver microsomes isolated from rats pretreated with acetone (AC-microsomes) had a normal level of FMO activity but had enhanced rates of 6 beta-(CYP3A1) and 2 beta-(CYP3A1) hydroxylations of testosterone. The AC-microsomes again had increased activity for production of TMU. Similarly, the liver microsomes isolated from rats pretreated with dexamethasone (DEX-microsomes) had a normal level of FMO activity but had enhanced rates of forming 6 beta-and 2 beta-hydroxytestosterone (Cyp3A1) as well as androstenedione (CYP3A1). The DEX-microsomes again had increased activity for production of TMU only. Liver microsomes isolated from rats pretreated with 3-methylcholanthrene (MC-microsomes), however, had increased FMO activity and also enhanced rates of forming the 7 alpha-(CYP1A1/2, and 2A1), 6 beta-(CYP3A1), and 2 beta-(CYP3A1) hydroxytestosterone. The MC-microsomes had increased activity for producing all of the four primary metabolites of CA, i.e. the N-demethylation metabolites like TB, PX. and TP, as well as the C-8 hydroxylation metabolite TMU. By the process of association of the obtained results, liver microsomes with increased contents of CYP2B1, 3A1, and 2E1 could catalyze the C-8 hydroxylation at an increased rate producing increased amount of TMU. Increased productions of CA N-demethylation metabolites (TB, PX, and TP) are, however, catalyzed by the increased activities of CYP1A2 and FMO which are associated uniquely with the MC-microsomes.

Induction of the procarcinogen-activating CYP1A2 by a herbal dietary supplement in rats and humans

Herbal dietary supplements to promote health may be double-edge swords. A herbal dietary supplement, FastOne, which contains extracts of kola nut, grape, green tea and Ginkgo biloba, and is used as an agent for weight management, was administered to rats to test whether it induced CYP1A2, a procarcinogen-activating enzyme. Western blot analysis indicated that treatments with 0.15, 0.3, 0.5, 1 and 2 g/kg of the supplement for 3 days increased CYP1A2 expression in rat liver microsomes in a dose-dependent manner. The 0.3, 0.5, 1 and 2 g/kg treatments increased rat liver microsomal CYP1A2 activity measures as the conversion of caffeine to paraxanthine to 166, 212, 331 and 473% of normal, respectively. In humans, the intake of 2 and 4 capsules of the supplement for 3 days increased CYP1A2 activity to 194 and 203%, respectively, as assessed by the change in the urinary ratio of 1,7-dimethylxanthine plus paraxanthine to unmetabolized caffeine. Intake of the herbal supplement increased CYP1A2 activity to levels higher than that observed from smoking (179%). This study suggests that the long-term intake of the dietary supplement inducing CYP1A2 may increase the incidence of colorectal cancers caused by procarcinogens activated by CYP1A2 in rapid N-acetyltransferase-2 acetylators and of lung adenocarcinoma in slow acetylators.

Decreased formation of ethoxyacetic acid from ethylene glycol monoethyl ether and reduced atrophy of testes in male rats upon combined administration with toluene and xylene.

Male painters are commonly exposed to ethylene glycol monoethyl ether (EGE), a well known reproductive toxic agent causing testicular atrophy, in the form of solvent mixture containing toluene (TOL) and xylene (XYL). This study was carried out to determine the effect of exposing male rats to solvent mixture containing TOL and XYL on the EGE (200 mg/kg) on testicular atrophy and production of toxic metabolite, ethoxyacetic acid (EAA) from EGE. Compared to the extent of testes atrophy observed upon EGE administration alone, the combined administration of EGE (200 mg/kg) with TOL (250 mg/kg) and XYL (500 mg/kg) for 4 weeks has reduced the extent of testes atrophy by 25%. The combined administration delayed the time for appearance of the highest plasma concentration (t(max)) of EAA from 3 to 6 h and also decreased the highest concentration (Cmax) as well as the total amount of plasma EAA (AUC(0-18 h)) by 45 and 29%, respectively. This explained the diminished testicular atrophy in male rats observed when EGE was administered in a solvent mixture containing TOL and XYL. This study suggested that testicular toxicity observed in male painters caused by EGE may be decreased when they are exposed to EGE in the form of solvent mixture containing TOL and XYL.

Co-administration of toluene and xylene antagonized the testicular toxicity but not the hematopoietic toxicity caused by ethylene glycol monoethyl ether in Sprague–Dawley rats

Occupational painters are exposed to ethylene glycol monoethyl ether (EGEE), a widely used emulsifying solvent known to cause testicular degeneration and bone marrow depression, together with toluene (TOL) and xylene (XYL) as a mixture. In the previous study (Chung et al., Tox. Lett. 104:143, 1999), testicular atrophy caused by EGEE (200 mg/kg) was shown to be antagonized by co-administration of TOL (250 mg/kg) and XYL (500 mg/kg). This study was conducted to provide histological support for the previously observed antagonistic protective effect of TOL + XYL on EGEE inducible testicular toxicity and to determine whether a similar antagonistic effect can be demonstrated against the EGEE derived hematopoietic toxicity. Compared to the extent of seminiferous tubule degeneration caused by EGEE (150 mg/kg, six times per week for 4 weeks), testes of rats given co-administration of TOL (250 mg/kg) + XYL (500 mg/kg) showed dramatically reduced tubular degeneration. Hyperplasia of Leydig cells in the interstitium was observed in both EGEE and EGEE + TOL + XYL-treated rats. Although a minimal dose of EGEE causing testicular atrophy was used, WBC and platelet counts were decreased significantly. In the TOL + XYL-treated control group, the WBC and platelet counts were not decreased. However, the bone marrow depression caused by EGEE was not reversed by the combined administration of TOL + XYL. In all experimental groups (EGEE alone, TOL + XYL, EGEE + TOL + XYL), plasma levels of creatinine and alkaline phosphatase were significantly decreased. In addition to the marked testicular atrophy, EGEE also decreased the weights of adrenal glands and epididymis. In conclusion, while the testicular degeneration caused by EGEE was antagonized by TOL + XYL, the EGEE derived hematopoietic suppression was not reversed.

Metabolism of subtoxic level of selenite by double-perfused small intestine in rats

Intestinal metabolism of the subtoxic level of selenite in rats was investigated using a double-perfusion system, which is an in situ, in vitro preparation in which the intestinal lumen and its vasculature are perfused simultaneously. The toxicity of sodium selenite was determined by inhibition of 3-O-methyl glucose (3MG) absorption and by histological examination. Levels of 1.2 mM selenite were required to significantly (p<0.05) reduce 3MG intestinal absorption (58±11%, mean±SD). Cation-exchange chromatography was used to determine the chemical forms of Se from selenite after using luminal concentrations of 1–200 µM in vascular perfusates. The chemical forms were selenite, selenodiglutathione (GS-Se-SG), mixed selenoglutathione plus cysteine (GS-Se-CYS), selenodicysteine (CYS-Se-CYS), protein-bound Se, and unidentified selenocompounds. Selenite was the predominant selenocompound found in vascular perfusate, but protein-bound Se was the predominant metabolite from selenite present in the vascular effuents. There was a corresponding increase of all metabolites with increased levels of selenite with time of absorption, but not with increased concentration of luminal selenite.

Ethnic differences of FMO3 gene mutant alleles

Clinical Pharmacology & Therapeutics (1999) 65, 184–184; doi:

Correlation between phenotypes of FMO obtained by ranitidine N‐oxidation and genotypes of FMO3 in a Korean population

Clinical Pharmacology & Therapeutics (1999) 65, 183–183; doi: