Abstract  Upper respiratory tract (URT) absorption of several compounds with differing water solubilities and potentials to cause lesions of the nasal mucosa were studied in rats. Absorption of propylene glycol monomethyl ether (PGME), PGME acetate (PGMEAc), ethyl acrylate (EA), epichiorohydrin (EPI), styrene (STY), nitroethane (NE), ethylene dibromide (EDB), and methylene chloride (MeCl2) vapors by the isolated URT was compared to that by the isolated lower respiratory tract (LRT) and the intact animal. Neatly all PGME and PGMEAc and 30-70% of EA, EPI, STY, NE, and EDB were absorbed when passed through the. URT. In general, similar levels were absorbed by both the isolated LRT and intact animal. It was estimated that intact animals received more than 90% of their total dose of PGME and PGMEAc. and 50% of EA, NE, EPI, and EDB via the URT. Further, the dosage per Unit of surface area in the URT may be 5000-6000 times that of the LRT. However, the extent of URT absorption was not related to the ability to cause lesions of the nasal mucosa. Absorption of compounds by the URT was not a simple function of water solubility or of blood or water/air partitioning coefficients suggesting that a more complex mechanism for controlling absorption may exist. In one case. it was demonstrated that URT enzymatic activity could influence the absorption of certain compounds by the URT.

Abstract  Methylene chloride was less mutagenic in Salmonella typhimurium TA100/NG-11 (glutathione-deficient) compared to TA100, indicating that glutathione is involved in the activation of methylene chloride to a mutagen in bacteria. In rodents, the pathway of methylene chloride metabolism utilizing glutathione produces formaldehyde via a postulated S-chloromethylglutathione conjugate (GSCH2Cl). Formaldehyde is known to cause DNA-protein cross-links, and GSCH2Cl may act as a monofunctional DNA alkylator by analogy with the glutathione conjugates of 1,2-dihaloalkanes. The lack of sensitivity of Salmonella TA100 towards formaldehyde (Schmid et al., Mutagenesis, 1 (1986) No. 6, 427-431) suggests that GSCH2Cl is responsible for methylene chloride mutagenicity in Salmonella. In Escherichia coli K12 (AB1157), formaldehyde was mutagenic only in the wild-type, a characteristic shared with cross-linking agents, whereas 1,2-dibromoethane (1,2-DBE) was more mutagenic in uvrA cells (AB1886). Methylene chloride, activated by S9 from mouse liver, was mutagenic only in wild-type cells, suggesting a mutagenic role for metabolically derived formaldehyde in E. coli. Mouse-liver S9 also enhanced the cell-killing effect of methylene chloride in the uvrA, and a recA/uvrA double mutant (AB2480) which is very sensitive to DNA damage. This pattern was consistent with formaldehyde damage. However, a mutagenic role in bacteria for the glutathione conjugate of methylene chloride cannot be ruled out by these E. coli experiments because S9 fractions did not increase 1,2-DBE mutagenicity, suggesting lack of cell wall penetration by this reactive species. Rat-liver S9 did not activate methylene chloride to a bacterial mutagen or enhance methylene chloride-induced cell-killing, which is consistent with the carcinogenicity difference between the species.

Abstract  Glutathione-S-transferase-mediated metabolism of methylene chloride (MC) generates S-chloromethylglutathione, which has the potential to react with DNA, and formaldehyde, which is a known mutagen. MC-induced mutations in the HPRT gene of Chinese hamster ovary cells have been sequenced and compared with the mutations induced by 1, 2-dibromoethane (1,2-DEB), which is known to act through a glutathione conjugate, and formaldehyde. All three compounds induced primarily point mutations, with a small number of insertion and deletion events. The most common point mutations induced by MC were GC-->AT transitions (4/8), with two GC-->CG transversions and two AT-->TA transversions. This pattern of mutations showed greater similarity with 1,2-DBE, where the dominant point mutations were GC-->AT transitions (7/9), than formaldehyde, where all mutations were single base transversions and 5/6 occurred from AT base pairs. The mutation sequence results for MC suggest that S-chloromethylglutathione plays a major role in MC mutagenesis, with only a limited contribution from formaldehyde. The involvement of a glutathione (GSH) conjugate in MC mutagenicity would be analogous to the well-characterized pathway of activation of 1,2-DBE.

Abstract  Numerous epidemiological studies have associated episodes of increased air pollution with increased incidence of respiratory disease, including pneumonia, croup, and bronchitis. Trichloroethylene (TCE) and chloroform are among 33 hazardous air pollutants identified by the U.S. Environmental Protection Agency as presenting the greatest threat to public health in the largest number of urban areas. Also, both are common indoor air pollutants. Here, we assessed the potential effects of TCE and chloroform on resistance to pulmonary bacterial infection and related alveolar macrophage (AM) function. CD-1 mice were exposed by inhalation to filtered air (control) or concentrations of TCE ranging from 5 to 200 ppm, or concentrations of chloroform ranging from 100 to 2000 ppm. Immediately following exposure, mice were challenged with an aerosol of Streptococcus zooepidemicus and monitored for clearance of bacteria from the lung and mortality. In separate experiments, exposed mice were injected intratracheally with viable bacteria and phagocytic function was evaluated in macrophages obtained from lung washes 30 min later. The NOEL for enhanced mortality to infection was 25 ppm for TCE and 500 ppm for chloroform. Relative to the air controls, differences in clearance of bacteria from the lung were noted in mice exposed to TCE (NOEL = 50 ppm) and to chloroform (NOEL 100 ppm), and differences in AM phagocytic index were noted for TCE (NOEL = 100 ppm) and for chloroform (NOEL < 100 ppm). The data support the utility of the S. zooepidemicus infectivity model in assessing potential increased risk of respiratory infection and suggest that delayed clearance of bacteria from the lung or decreased phagocytosis are viable alternatives to mortality as an endpoint. Collectively, these endpoints are among the most sensitive health effects reported for TCE.

Abstract  In a recent report, we found an elevated risk of cancer of the central nervous system (CNS) in several occupations and industries, and a modest association with exposure to solvents and to contact with the public.

To further explore the occupational risk of CNS cancer among women, we extended the analysis of the previous death certificate-based case-control study, including 12,980 female cases (ICD-9 codes 191 and 192) in 24 US states in 1984-1992 and 51,920 female controls who died from diseases other than malignancies and neurological disorders. We applied newly designed job-exposure matrices for 11 occupational hazards, previously reported as brain cancer risk factors, to the occupation and industry codes in the death certificates. We also conducted a separate analysis of 161 meningioma cases (ICD-9 codes 192.1 and 192.3), a tumor more frequent among women, particularly in the postmenopausal age group.

Overall, CNS cancer risk showed a 20-30% increase among women exposed to electromagnetic fields (EMF), methylene chloride, insecticides and fungicides, and contact with the public. Risk for meningioma was elevated among women exposed to lead (OR = 1.9; 95% CI 1.0, 3.9). CNS cancer did not show a clear pattern of risk increase by probability and intensity of exposure to any of the explored risk factors. Cross-classification by probability and intensity of exposure did not reveal any significant trend. Cases were too few to explore trends of meningioma by probability and intensity of exposure to lead.

We did not find evidence of a strong contribution of 11 occupational hazards to the etiology of CNS cancer. However, limitations of the occupational information might have reduced our ability to detect clear patterns of risk.

Abstract  Methylene chloride has been the subject of recent toxicological and carcinogenesis studies because of significant human exposure and widespread use in industrial processing, food preparation and agriculture. In this study, liver and lung tumors, induced in female B6C3F1 mice by inhalation of 2000 p.p.m. methylene chloride (6 h/day, 5 days/week continuous exposure), were examined for the presence of activated ras proto-oncogenes. DNA was isolated from 49 spontaneous and 50 methylene chloride-induced liver tumors and screened by oligonucleotide hybridization of PCR amplified H-ras gene fragments for codon 61 mutations. In the chemically induced tumors, 38 mutations were detected, 16 C to A transversions in base 1, 16 A to G transitions in base 2 and 6 A to T transversions in base 2. This mutation profile was similar to that identified for the H-ras gene in the spontaneous liver tumors and suggests that methylene chloride acts in liver by promoting cells with spontaneous lesions. Tumors in which H-ras codon 61 mutations were not detected were examined for the presence of transforming genes by the nude mouse tumorigenicity assay. Except for activated K-ras genes detected in DNA from two methylene chloride induced tumors and one spontaneous tumor, no other transforming genes were identified. DNA from 54 lung tumors was screened by direct sequencing of PCR amplified DNA fragments of the K-ras gene for first and second exon mutations, and 12 mutations were identified, 5 in exon one and 7 in exon 2. The low number of spontaneous tumors available in this study limits the interpretation of the data, and thus the frequency and spectrum of K-ras activation in the methylene chloride induced tumors was not significantly different from that in the seven spontaneous tumors analyzed. Since K-ras activation was not detected in 80% of the tumors, the nude mouse tumorigenicity assay was used to examine the lung tumors for the presence of other transforming genes. At present no transforming genes other than ras genes were identified in either liver or lung tumors.

Abstract  The activity of cytochrome P450 (CYP) enzymes, which determine the rate of elimination of lipid-soluble drugs, demonstrates considerable interindividual variability. The extent to which age and sex influence CYP activity remains unclear in humans. Our objectives were to determine whether in vivo activity of selected CYP enzymes is affected by age or sex and to evaluate sex bioequivalence in a large sample size.

We have assessed in vivo activity of the CYP1A2, 2C19, 2D6, 2E1, and 3A4 enzymes in 161 normal subjects (51% female subjects and 40% aged >50 years). After simultaneous administration of a cocktail of selective probes (caffeine, mephenytoin, debrisoquin [INN, debrisoquine], chlorzoxazone, and dapsone, respectively), phenotypic indices for metabolism of these drugs were used as measures of individual CYP activity. Sex bioequivalence analysis used the bootstrap method.

There were no sex differences associated with CYP1A2 activity. A significant negative correlation (r = -0.572, P < .01) between enzyme activity and age was observed for CYP2C19, but there were no sex differences. CYP2D6 activity showed no dependence on age or sex. In contrast, CYP2E1 activity showed an age-associated increase (r = 0.393, P < .01), which developed earlier in life in male subjects compared with female subjects. These results were further supported by the sex bioequivalence analysis of CYP phenotypic activity, which revealed that sexes were equivalent with respect to CYP2C19 (90% confidence interval [CI], 0.874-1.04), CYP3A4 (90% CI, 0.95-1.176), and CYP2D6 (90% CI, 0.928-1.09) phenotype and just exceeded the 0.8 to 1.25 limits to be equivalent with respect to CYP2E1 (90% CI, 0.785-1.08) and CYP1A2 (90% CI, 0.736-1.03) phenotype.

These observations suggest that the presence of selective mechanisms of regulation for individual CYP enzymes can be influenced by age and sex. However, we suggest that sex has a limited ability to explain intersubject variation of activity for these phenotypic measures of CYP enzyme activity.

Abstract  This study examined the relationship between birthweight and exposure to emissions of methylene chloride (DCM) from manufacturing processes of the Eastman Kodak Company at Kodak Park in Rochester, Monroe County, New York. County census tracts were categorized as exposed to high, moderate, low or no DCM based on the Kodak Air Monitoring Program (KAMP) model, a theoretical dispersion model of DCM developed by Eastman Kodak Company. Birthweight and information on variables known to influence birthweight were obtained from 91,302 birth certificates of white singleton births to Monroe County residents from 1976 to 1987. No significant adverse effects of exposure to DCM on birthweight were found. Adjusted birthweight in high exposure census tracts was 18.7 g less than in areas with no exposure (95% confidence interval for the difference between high and no exposure - 51.6, 14.2 g). Problems inherent in the method of estimation of exposure, which may decrease power or bias the results, are discussed. Better methods to estimate exposure to emissions from multiple industrial point sources are needed.

Abstract  Dichloromethane dehalogenase from Methylophilus sp. DM11 is a glutathione S-transferase homolog that is specifically active with dihalomethane substrates. This bacterial enzyme and rat liver glutathione S-transferases were purified to investigate their relative reactivity with CH2Cl2 and related substrates. Rat liver alpha class glutathione transferases were inactive and mu class enzymes showed low activity (7-23 nmol/min/mg of protein) with CH2Cl2. theta class glutathione transferase 5-5 from rat liver and Methylophilus sp. dichloromethane dehalogenase showed specific activities of > or = 1 mumol/min/mg of protein. Apparent Kcat/Km were determined to be 3.3 x 10(4) and 6.0 x 10(4) L M-1 S-1 for the two enzymes, respectively. Dideutero-dichloromethane was processed to dideutereo-formaldehyde, consistent with a nucleophilic halide displacement mechanism. The possibility of a GSCH2X reaction intermediate (GS, glutathione; X, halide) was probed using CH2ClF to generate a more stable halomethylglutathione species (GSCH2F). The reaction of CH2ClF with dichloromethane dehalogenase produced a kinetically identifiable intermediate that decomposed to formaldehyde at a similar rate to synthetic HOCH2CH2SCH2F. 19F-NMR revealed the transient formation of an intermediate identified as GSCH2F by its chemical shift, its triplet resonance, and H-F coupling constant consistent with a fluoromethylthioether. Its decomposition was matched by a stoichiometric formation of fluoride. These studies indicated that the bacterial dichloromethane dehalogenase directs a nucleophilic attack of glutathione on CH2Cl2 to produce a halomethylthioether intermediate. This focuses attention on the mechanism used by theta class glutathione transferases to generate a halomethylthioeter from relatively unreactive dihalomethanes.

Abstract  Cytochrome P4502E1 (CYP2E1) is expressed in human peripheral blood lymphocytes (PBLs), and previous reports have suggested the possibility of using this readily available tissue as a reporter of CYP2E1 status. To further explore the relevance of this approach we assessed CYP2E1 expression in PBLs in two contrasting conditions, chronic hepatitis C and insulin-dependent diabetes (IDD), illustrating an organ and a systemic disease, respectively.

Total RNA was isolated from extracted PBLs (hepatitis C patients + IDD) and by percutaneous needle biopsy (hepatitis C patients only). Gene expression for CYP2E1 was determined by real-time reverse-transcription polymerase chain reaction. Histological changes in liver tissue were assessed according to Ludwig's criteria.

In patients with chronic hepatitis C a clear relationship was found between CYP2E1 expression in the liver and the progression of hepatic disease (both lobular inflammation and fibrosis indices), and observed variations were consistent with the preferential distribution of CYP2E1 in the lobular zone. No effect of the liver disease was, however, found at the PBL level. A statistically significant increase in mean CYP2E1 expression level was observed in the lymphocytes from poorly controlled IDD subjects compared to controls.

Taken together, our data indicate that the measurement of CYP2E1 expression in PBLs is not useful in liver diseases. However, in a systemic condition (IDD) this measurement can be proposed for monitoring the CYP2E1 induction in a relatively noninvasive manner. This tool should therefore be further validated in clinical field or experimental studies for CYP2E1 phenotyping purposes.

Abstract  Despite the very wide recognition that carbon monoxide (CO) is a significant neurotoxicant, the level at which subtle effects occur, and the existence of sensitive periods in development for such toxicity, has been undetermined. In terms of risk to the fetus, a potentially susceptible sub-population, there is concern, first, that the level of exposure at which neurotoxicity occurs may be different from the adult, and second, that the site of toxic action and subsequent neurotoxic effects of CO may be different in the immature and mature brain. The investigator studied the susceptibility of the developing brain to moderate levels of CO maintained chronically through the period of neuronal proliferation, and into the period of synapse formation. Carbon monoxide may be thought of as both a prototypical hypoxic agent, and a significant public health hazard in its own right. Carbon monoxide is a ubiquitous toxic agent that accounts for large numbers of deaths and significant morbidity in human populations. Subtle neurotoxic effects of this agent may be even more common, but they may go largely undetected, or fail to be associated with CO exposure. We have shown that prenatal CO exposure at moderate levels can produce significant neurotoxic effects in rats. The data obtained from the cerebellum and neostriatum, in particular, suggest that chronic, moderate perinatal CO exposure may disrupt neuronal proliferation and, perhaps, may disrupt certain markers for neurochemical transmission.

Abstract  The purpose of this study of 3211 cellulose-fiber production workers was to evaluate earlier findings of excess biliary tract and liver cancer in a similarly exposed cohort reported in 1990. Mortality from biliary tract and liver cancer was not increased in this study population, and there was no excess mortality from pancreatic cancer. Mortality was not elevated for cancers of the lung or liver, sites at which tumors were induced in experimental animals exposed to methylene chloride. Men with 20 or more years of employment exhibited increased mortality from prostate cancer, whereas women who also had 20 or more years of employment experienced higher-than-expected mortality from cervical cancer. Although these apparent increases in mortality are difficult to interpret biologically and are not consistent with previous studies, they require further investigation.

Abstract  DNA single-strand (ss) breaks were detected in the livers of B6C3F1 mice immediately following exposure to 4000-8000 p.p.m. methylene chloride (MC) for 6 h. This damage was undetectable 2 h after exposure, suggesting an active DNA repair process. Similarly, DNA ss breaks were detected in whole lung homogenates taken from mice exposed to 2000-6000 p.p.m. MC. The DNA of mouse Clara cells incubated in vitro with MC was also damaged at concentrations of 5 mM MC and above. Pre-treatment of mice with the glutathione depletor buthionine sulphoximine (BSO) caused a decrease in the amount of DNA damage detected, suggesting a GST-mediated mechanism. DNA damage was also reduced in Clara cells when incubated in vitro with MC in the presence of BSO. In CHO cells induction of DNA damage was dependent upon exogenous MC metabolism by mouse liver S100 fraction (but not microsomes) in the presence of GSH. DNA ss breaks were not induced by MC in hamster hepatocytes in vitro at concentrations from 5 to 90 mM MC, nor in eight individual samples of normal human hepatocytes exposed to MC at similar concentrations. The ability of MC to induce DNA ss breaks in the four species studied is entirely compatible with the known carcinogenicity of this chemical in animals and offers experimental evidence to suggest that humans would not be susceptible to MC-induced liver cancer. The DNA ss breaks correlate with the metabolism of MC by the GST pathway and provide an explanation for the lack of sensitivity of hamsters and rats to MC-induced liver cancer.

Abstract  Some cytochrome P450 catalyzed reactions show atypical kinetics, and these kinetic processes can be grouped into five categories: activation, autoactivation, partial inhibition, substrate inhibition, and biphasic saturation curves. A two-site model in which the enzyme can bind two substrate molecules simultaneously is presented which can be used to describe all of these observed kinetic properties. Sigmoidal kinetic characteristics were observed for carbamazepine metabolism by CYP3A4 and naphthalene metabolism by CYPs 2B6, 2C8, 2C9, and 3A5 as well as dapsone metabolism by CYP2C9. Naphthalene metabolism by CYP3A4 and naproxen metabolism by CYP2C9 demonstrated nonhyperbolic enzyme kinetics suggestive of a low Km, low Vmax component for the first substrate molecule and a high Km, high Vmax component for the second substrate molecule. 7, 8-Benzoflavone activation of phenanthrene metabolism by CYP3A4 and dapsone activation of flurbiprofen and naproxen metabolism by CYP2C9 were also observed. Furthermore, partial inhibition of 7, 8-benzoflavone metabolism by phenanthrene was observed. These results demonstrate that various P450 isoforms may exhibit atypical enzyme kinetics depending on the substrate(s) employed and that these results may be explained by a model which includes simultaneous binding of two substrate molecules in the active site.

Abstract  Mortality ascertainment was extended through 1990 for a cohort of 1271 workers involved in the production of cellulose triacetate fiber at a plant in Rock Hill, South Carolina. Each subject was employed for at least three months between 1 January 1954 and 1 January 1977 in jobs that entailed exposure to the highest concentrations of methylene chloride. Median exposures in 1977 ranged from 140 to 745 ppm (8-h time-weighted average). The observed numbers of deaths from specific causes were compared with the expected numbers of deaths computed from rates in York County, South Carolina. For most causes of death, there was little if any association with employment. Among causes of particular interest, no new deaths were observed from cancer of the liver and biliary tract, although the excess from the earlier study persisted (4 observed, 1.34 expected). No excess mortality was observed for cancer of the pancreas (2 observed, 2.42 expected) or for ischemic heart disease (43 observed, 47.8 expected).

Abstract  The objective of this study was to compare the human immunodeficiency virus (HIV) viral load (VL) and CD4 counts in patients infected with HIV with and without cervical cancer. The authors hypothesized that HIV-positive women with cervical cancer would have a greater risk of immune suppression.

A case-control study was conducted that included all HIV-positive patients who were seen at the authors' institution from January 1, 1995 to April 20, 2006 with invasive cervical cancer (cases) and without invasive cervical cancer (controls). Patients were included only if they had a CD4 count recorded<6 months before or<3 months after their diagnosis of invasive cervical cancer (cases) or at their last gynecologic examination (controls). Controls were matched to cases on a 4:1 ratio according to current smoking history. Patients were considered immunocompetent if they had both a CD4 count>200 cells/microL and a VL<10,000 copies/mL.

In total, 15 cases and 60 controls were identified. The median CD4 count for cases was 208 cells/microL (range, 18-1102 cells/microL) compared with 445 cells/microL (range, 20-1201 cells/microL) for controls (P=.03). The median VL was 16,918 copies/mL (range, 50-214,915 copies/mL) for cases compared with 1430 copies/mL (range, 50-571,000 copies/mL) for controls (P=.15). Only 1 of 14 cases (7%) was immunocompetent compared with 35 of 55 controls (64%; odds ratio, 0.04; 95% confidence interval, 0-0.37; P<.001). This significance was maintained after adjusting for other factors (P=.002).

Women with HIV who were diagnosed with invasive cervical cancer appeared to have a much greater degree of immunosuppression than women with HIV without invasive cervical cancer.

Abstract  More than a million workers are at risk for methylene chloride exposure. Aerosol sprays and paint stripping may also cause significant nonoccupational exposures. After methylene chloride inhalation, significant amounts of carbon monoxide are formed in vivo as a metabolic by-product. Poisoning predominantly affects the central nervous system and results from both carboxyhemoglobin formation and direct solvent-related narcosis. In this report, we describe a case of methylene chloride intoxication probably complicated by exogenous carbon monoxide exposure. The worker's presentation of intermittent headaches was consistent with both methylene chloride intoxication and carbon monoxide poisoning. The exposures and symptoms were corroborated by elevated carboxyhemoglobin saturations and a workplace inspection that documented significant exposures to both methylene chloride and carbon monoxide. When both carbon monoxide and methylene chloride are inhaled, additional carboxyhemoglobin formation is expected. Preventive efforts should include education, air monitoring, and periodic carboxyhemoglobin determinations. Methylene chloride should never be used in enclosed or poorly ventilated areas because of the well-documented dangers of loss of consciousness and death.

Abstract  The literature contains only one report of methylene chloride poisoning after ingestion. Unfortunately carboxyhaemoglobin (COHb) levels were not obtained in this case. We now describe a fatal case where a similar amount of the solvent was ingested and after which toxicology screening was done.

Abstract  A retrospective cohort mortality study was conducted among men employed for one or more years, between 1940 and 1969, at an operating division of a large chemical company. Vital status follow-up for the cohort of 1,919 men was determined through 1979 and identified 390 deaths. Overall mortality in the study group and in each of eight employment subgroups was less than that of the corresponding United States white male population. Additionally, standardized mortality ratios were not significantly elevated for any of the examined cause-of-death categories. Cause-specific mortality comparisons were also made among the employment subgroups and by duration of employment in the company division using an internal analysis method. There were no relationships observed for employment duration. Several significant differences (p less than 0.05) by employment subgroup were noted; however, neither the decreases nor increases presently could be ascribed to identifiable environmental factors.

Abstract  Pairs of forward and reverse primers and TaqMan probes specific to each human cytochrome P450 isoform were prepared. Analysis of the mRNA level of each CYP isoform in total RNA from pooled specimens of various human organs was performed by real-time reverse transcription PCR using an ABI PRISM 7700 sequence detector system. The expression of CYP3A4 mRNA was similar to that of CYP3A7 mRNA in the fetal liver, and CYP3A4 mRNA levels in the fetal liver were about 0.1 times lower than in the adult liver. CYP2E1 showed the highest level of mRNA expression in the liver. The mRNA expression of 30 CYP isoforms (CYP1A1, 1A2, 1B1, 2A6, 2A7, 2B6, 2C8, 2C9, 2C18, 2C19, 2D6, 2E1, 2J2, 3A4, 3A5, 3A7, 4A11, 4F2, 4F3, 5A1, 7B1, 8A1, 8B1, 17, 26A1, 27, 27B1, 39A1, 46, and 51) in the liver was successfully detected by this method. CYP2F1, 4B1, 4F8, 11s (11A, 11B1, and 11B2), 19, and 24 mRNA levels were the highest in the lung, lung, prostate, adrenal gland, placenta, and kidney, respectively; however, the mRNA expression of these eight CYP isoforms in the liver was not detected by this method. The mRNA levels of the CYP isoforms determined in various human tissues were in good agreement with previously reported data. The method described here has the advantages of high specificity and excellent quantification over a wide range of mRNA concentrations, making it suitable for the evaluation of a large number of samples in the assessment of the expression profile of drug-metabolizing enzymes.