Summary
To understand the changes in the metabolome of hepatitis C virus (HCV)‐infected persons, we conducted a metabolomic investigation in both plasma and urine of 30 HCV‐positive individuals using ...plasmas from 30 HCV‐negative blood donors and urines from 30 healthy volunteers. Samples were analysed by gas chromatography–mass spectrometry and data subjected to multivariate analysis. The plasma metabolomic phenotype of HCV‐positive persons was found to have elevated glucose, mannose and oleamide, together with depressed plasma lactate. The urinary metabolomic phenotype of HCV‐positive persons comprised reduced excretion of fructose and galactose combined with elevated urinary excretion of 6‐deoxygalactose (fucose) and the polyols sorbitol, galactitol and xylitol. HCV‐infected persons had elevated galactitol/galactose and sorbitol/glucose urinary ratios, which were highly correlated. These observations pointed to enhanced aldose reductase activity, and this was confirmed by real‐time quantitative polymerase chain reaction with AKR1B10 gene expression elevated sixfold in the liver. In contrast, AKR1B1 gene expression was reduced 40% in HCV‐positive livers. Interestingly, persons who were formerly HCV infected retained the metabolomic phenotype of HCV infection without reverting to the HCV‐negative metabolomic phenotype. This suggests that the effects of HCV on hepatic metabolism may be long lived. Hepatic AKR1B10 has been reported to be elevated in hepatocellular carcinoma and in several premalignant liver diseases. It would appear that HCV infection alone increases AKR1B10 expression, which manifests itself as enhanced urinary excretion of polyols with reduced urinary excretion of their corresponding hexoses. What role the polyols play in hepatic pathophysiology of HCV infection and its sequelae is currently unknown.
1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxin is a chemical inducer of Parkinson's disease (PD) whereas
N-methylated β-carbolines and isoquinolines are naturally occurring analogues ...of MPTP involved in PD. This research has studied the oxidation of MPTP by human CYP2D6 (CYP2D6*1 and CYP2D6*10 allelic variants) as well as by a mixture of cytochrome P450s-resembling HLM, and the products generated compared with those afforded by human monoamine oxidase (MAO-B). MPTP was efficiently oxidized by CYP2D6 to two main products: MPTP-OH (
p-hydroxylation) and PTP (
N-demethylation), with turnover numbers of 10.09 min
−
1
and
K
m of 79.36
±
3 μM (formation of MPTP-OH) and 18.95 min
−
1
and
K
m 69.6
±
2.2 μM (PTP). Small amounts of dehydrogenated toxins MPDP
+ and MPP
+ were also detected. CYP2D6 competed with MAO-B for the oxidation of MPTP. MPTP oxidation by MAO-B to MPDP
+ and MPP
+ toxins (bioactivation) was up to 3-fold higher than CYP2D6 detoxification to PTP and MPTP-OH. Several
N-methylated β-carbolines and isoquinolines were screened for
N-demethylation (detoxification) that was not significantly catalyzed by CYP2D6 or the P450s mixture. In contrast, various β-carbolines were efficiently hydroxylated to hydroxy-β-carbolines by CYP2D6. Thus,
N(2)-methyl-1,2,3,4-tetrahydro-β-carboline (a close MPTP analog) was highly hydroxylated to 6-hydroxy-
N(2)-methyl-1,2,3,4-tetrahydro-β-carboline and a corresponding 7-hydroxy-derivative. Thus, CYP2D6 could participate in the bioactivation and/or detoxification of these neuroactive compounds by an active hydroxylation pathway. The CYP2D6*1 enzymatic variant exhibited much higher metabolism of both MPTP and
N(2)-methyl-1,2,3,4-tetrahydro-β-carboline than the CYP2D6*10 variant, highlighting the importance of CYP2D6 polymorphism in the oxidation of these toxins. Altogether, these results suggest that CYP2D6 can play an important role in the metabolic outcome of both MPTP and β-carbolines.
A study was conducted to examine whether the association between the presence of a single CYP2A6 reduced activity allele and lower prevalence of smoking held among 460 people enrolled in a ...case-control study of lung cancer.
Xenobiotics are encountered by humans on a daily basis and include drugs, environmental pollutants, cosmetics, and even components of the diet. These chemicals undergo metabolism and detoxication to ...produce numerous metabolites, some of which have the potential to cause unintended effects such as toxicity. They can also block the action of enzymes or receptors used for endogenous metabolism or affect the efficacy and/or bioavailability of a coadministered drug. Therefore, it is essential to determine the full metabolic effects that these chemicals have on the body. Metabolomics, the comprehensive analysis of small molecules in a biofluid, can reveal biologically relevant perturbations that result from xenobiotic exposure. This review discusses the impact that genetic, environmental, and gut microflora variation has on the metabolome, and how these variables may interact, positively and negatively, with xenobiotic metabolism.
Polymorphic CYP2D6 is the enzyme that activates the opioid analgesic tramadol by O-demethylation to its active metabolite O-demethyltramadol (M1). Our objective was to determine the opioid effects ...measured by pupillary response to tramadol of CYP2D6 genotyped volunteers in relation to the disposition of tramadol and M1 in plasma. Tramadol displayed phenotypic pharmacokinetics and it was possible to identify poor metabolizers (PM) with >99% confidence from the metabolic ratio (MR) in a single blood sample taken between 2.5 and 24 h post-dose. Homozygous extensive metabolizers (EM) differed from PM subjects by an almost threefold greater (P=0.0014) maximal pupillary constriction (Emax). Significant correlations between the AUC and Cmax values of M1 versus pupillary constriction were found. The corresponding correlations of pharmacokinetic parameters for tramadol itself were weaker and negative. The strongest correlations were for the single-point metabolic ratios at all sampling intervals versus the effects, with rs ranging from 0.85 to 0.89 (p<0.01). It is concluded that the concept of dual opioid/non-opioid action of the drug, though considerably stronger in EMs, is valid for both EM and PM subjects. This is the theoretical basis for the frequent use and satisfactory efficacy of tramadol in clinical practice when given to genetically non-selected population.
2-Amino-1-methyl-6-phenylimidazo4,5-bpyridine (PhIP) carcinogenesis is initiated by N2-hydroxylation, mediated by several cytochromes P450, including CYP1A1. However, the role of CYP1A1 in PhIP ...metabolic activation in vivo is unclear. In this study, Cyp1a1-null and wild-type (WT) mice were used to investigate the potential role of CYP1A1 in PhIP metabolic activation in vivo. PhIP N2-hydroxylation was actively catalyzed by lung homogenates of WT mice, at a rate of 14.9 ± 5.0 pmol/min/g tissue, but <1 pmol/min/g tissue in stomach and small intestine, and almost undetectable in mammary gland and colon. PhIP N2-hydroxylation catalyzed by lung homogenates of Cyp1a1-null mice was ∼10-fold lower than that of WT mice. In contrast, PhIP N2-hydroxylation activity in lung homogenates of Cyp1a2-null versus WT mice was not decreased. Pretreatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin increased lung Cyp1a1 mRNA and lung homogenate PhIP N2-hydroxylase activity ∼50-fold in WT mice, where the activity was substantially inhibited (70%) by monoclonal antibodies against CYP1A1. In vivo, 30 min after oral treatment with PhIP, PhIP levels in lung were similar to those in liver. After a single dose of 0.1 mg/kg 14CPhIP, lung PhIP-DNA adduct levels in Cyp1a1-null mice, but not in Cyp1a2-null mice, were significantly lower (P = 0.0028) than in WT mice. These results reveal that mouse lung has basal and inducible PhIP N2-hydroxylase activity predominantly catalyzed by CYP1A1. Because of the high inducibility of human CYP1A1, especially in cigarette smokers, the role of lung CYP1A1 in PhIP carcinogenesis should be considered. (237 words).
A group of human cytochrome P450 genes encompassing the CYP2A, CYP2B, and CYP2F subfamilies were cloned and assembled into a 350-kb contig localized on the long arm of chromosome 19. Three complete ...CYP2A genes--CYP2A6, CYP2A7, and CYP2A13--plus two pseudogenes truncated after exon 5, were identified and sequenced. A variant CYP2A6 allele that differed from the corresponding CYP2A6 and CYP2A7 cDNAs previously sequenced was found and was designated CYP2A6v2. Sequence differences in the CYP2A6v2 gene are restricted to regions encompassing exons 3, 6, and 8, which bear sequence relatedness with the corresponding exons of the CYP2A7 gene, located downstream and centromeric of CYP2A6v2, suggesting recent gene-conversion events. The sequencing of all the CYP2A genes allowed the design of a PCR diagnostic test for the normal CYP2A6 allele, the CYP2A6v2 allele, and a variant--designated CYP2A6v1--that encodes an enzyme with a single inactivating amino acid change. These variant alleles were found in individuals who were deficient in their ability to metabolize the CYP2A6 probe drug coumarin. The allelic frequencies of CYP2A6v1 and CYP2A6v2 differed significantly between Caucasian, Asian, and African-American populations. These studies establish the existence of a new cytochrome P450 genetic polymorphism.
Human populations are thought to metabolize coumarin almost exclusively by 7-hydroxylation. We have identified an individual who is homozygous for a single amino acid substitution (Leul60His) in the ...cytochrome
P450 CYP2A6 arising from the variant
CYP2A6∗2 allele. On administration of coumarin (2 mg orally) no detectable 7-hydroxycoumarin was excreted in the 0–8-hr urine, rather, approximately 50% of the dose was eliminated as 2-hydroxyphenylacetic acid, the end-product of coumarin 3-hydroxylation. His immediate family members, who were heterozygous for the
CYP2A6∗2 allele, excreted little 2-hydroxyphenylacetic acid and mainly 7-hydroxycoumarin, when similarly tested. These findings raise a question regarding human risk evaluations for environmental coumarin exposures, since 7-hydroxylation is regarded as a detoxication pathway, but 3-hydroxylation as the process required to lead to macromolecular covalent binding of coumarin. Persons homozygous for the
CYP2A6∗2 allele may constitute 1–25% of various populations.
Nasopharyngeal carcinoma occurs disproportionately among individuals of Chinese descent. The cytochrome P450 2E1 enzyme (CYP2E1) is known to activate nitrosamines and other carcinogens that are ...possibly involved in the development of this disease. Certain alleles of the CYP2E1 gene are thought to be more highly expressed than others, and their distribution varies between Asian and Caucasian populations. We conducted a case-control study to investigate whether such variations affect the risk of developing nasopharyngeal cancer.
Three hundred sixty-four patients with nasopharyngeal carcinoma (96% of 378 eligible patients) and 320 control subjects (86% of 374 eligible subjects) were studied. A risk factor questionnaire was administered to participants to assess factors postulated to be linked to nasopharyngeal carcinoma. Peripheral blood was obtained from all subjects and DNA was purified from nucleated cells. A polymerase chain reaction-based restriction fragment length polymorphism assay that used the restriction enzymes Rsa I and Dra I was used to detect wild-type and variant forms of the CYP2E1 gene.
Individuals homozygous for an allele of the CYP2E1 gene that is detected by Rsa I digestion (c2 allele) were found to have an increased risk of nasopharyngeal carcinoma (relative risk RR = 2.6; 95% confidence interval CI = 1.2-5.7); this effect was limited to nonsmokers (RR = 9.3; 95% CI = 2.7-32) and was not affected by alcohol consumption.
Our findings suggest that the CYP2E1 genotype is a determinant of nasopharyngeal carcinoma risk.
Glutathione S-transferase M1 (GSTM1) is active in the detoxication of a number of carcinogens, including polyaromatic hydrocarbons, such as those present in cigarette smoke. In about 30%-55% of ...individuals, depending on the ethnic group, there is a virtual absence of GSTM1 enzyme activity due to deletion of both copies of the GSTM1 gene (GSTM1 null genotype). This genetic polymorphism of the GSTM1 gene locus has been proposed as a risk factor for lung cancer. However, results across studies are inconsistent.
We conducted a case-control study of patients with incident lung cancer and population control subjects to examine the association between homozygous deletion of the GSTM1 gene and lung cancer risk among African-Americans and Caucasians.
At 35 hospitals in Los Angeles County, California, we identified patients with a first diagnosis of lung cancer between September 1, 1990, and January 6, 1994. Of the 859 potentially eligible case patients, 207 had died by the time their physicians had received our request for permission to contact them. We enrolled 356 eligible case patients (167 African-Americans and 189 Caucasians) and 731 eligible control subjects (258 African-Americans and 473 Caucasians, all residents of Los Angeles County). Samples of white blood cell DNA sufficient for determination of the GSTM1 genotype by a polymerase chain reaction-based assay were obtained from 342 case patients and 716 control subjects. The odds ratios (ORs) and 95% confidence intervals (CIs) for lung cancer associated with homozygous deletion of the GSTM1 gene, in total and after stratification by a number of relevant characteristics, were estimated by logistic regression analysis.
For patients with all lung cancers combined, the GSTM1 null genotype was associated with an OR of 1.29 (95% CI = 0.94-1.77). The OR was similar among African-Americans (OR = 1.20; 95% CI = 0.72-2.00) and Caucasians (OR = 1.37; 95% CI = 0.91-2.06). The association was strongest for squamous cell carcinoma (OR = 1.57; 95% CI = 0.93-2.63). We observed an OR of 1.77 (95% CI = 1.11-2.82) for the GSTM1 null genotype in relation to lung cancer risk among smokers of less than 40 pack-years, but no association among heavier smokers (OR = 0.90; 95% CI = 0.56-1.44).
Our data do not support a substantial association between homozygous deletion of the GSTM1 gene and the risk of lung cancer overall in this population. However, our data do suggest an elevated risk for lighter smokers with this genotype.
Because the power of our analyses within strata of lifetime smoking history was limited, larger studies will be needed to confirm these findings.
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