Biomedical subjects

P T Strickland

Publications and source records attributed to P T Strickland.

At least 19 recordsLinked to original sources

PubMed2005

Golestan cohort study of oesophageal cancer: feasibility and first results.

To investigate the incidence of oesophageal cancer (EC) in the Golestan province of North-East Iran, we invited 1349 rural and urban inhabitants of Golestan province aged 35-80 to undergo extensive lifestyle interviews and to provide biological samples. The interview was repeated on a subset of 130 participants to assess reliability of questionnaire and medical information. Temperature at which tea was consumed was measured on two occasions by 110 subjects. Samples of rice, wheat and sorghum were tested for fumonisin contamination. An active follow-up was carried out after 6 and 12 months. A total of 1057 subjects (610 women and 447 men) participated in this feasibility study (78.4% participation rate). Cigarette smoking, opium and alcohol use were reported by 163 (13.8%), 93 (8.8%) and 39 (3.7%) subjects, respectively. Tobacco smoking was correlated with urinary cotinine (kappa = 0.74). Most questionnaire data had kappa > 0.7 in repeat measurements; tea temperature measurement was reliable (kappa = 0.71). No fumonisins were detected in the samples analysed. During the follow-up six subjects were lost (0.6%), two subjects developed EC (one dead, one alive); in all, 13 subjects died (with cause of death known for 11, 84.6%). Conducting a cohort study in Golestan is feasible with reliable information obtained for suspected risk factors; participants can be followed up for EC incidence and mortality.

Adult↗

PubMed2005

Exposure to traffic exhausts and oxidative DNA damage.

AIMS: To assess the relations between exposure to traffic exhausts and indicators of oxidative DNA damage among highway toll station workers. METHODS: Cross-sectional study of 47 female highway toll station workers exposed to traffic exhausts and 27 female office workers as a reference group. Exposure assessment was based on average and cumulative traffic density and a biomarker of exposure, urinary 1-hydroxypyrene-glucuronide (1-OHPG). Urinary 8-hydroxydeoxyguanosine (8-OHdG) was used as a biomarker of oxidative DNA damage. Plasma nitric oxide (NO) was measured as an indicator of oxidative stress related to traffic exhaust exposure. RESULTS: The mean concentration of urinary 8-OHdG was substantially higher among the exposed non-smokers (13.6 microg/g creatinine) compared with the reference non-smokers (7.3 microg/g creatinine; difference 6.3, 95% CI 3.0 to 9.6). The mean concentration of NO among the exposed (48.0 micromol/l) was also higher compared with the reference non-smokers (37.6 micromol/l; difference 10.4, 95% CI -0.4 to 21.2). In linear regression adjusting for confounding, a change in log(8-OHdG) was statistically significantly related to a unit change in log(1-OHPG) (beta = 0.372, 95% CI 0.081 to 0.663). CONCLUSIONS: Results indicate that exposure to traffic exhausts increases oxidative DNA damage. Urinary 8-OHdG is a promising biomarker of traffic exhaust induced oxidative stress.

8-Hydroxy-2'-Deoxyguanosine↗

PubMed2001

Concentration of 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP) in urine and alkali-hydrolyzed urine after consumption of charbroiled beef.

Heterocyclic amines (HAs) and polycyclic aromatic hydrocarbons are carcinogenic products formed during the cooking of meat at moderate to high temperatures. We have previously shown that the urinary concentration of 1-hydroxypyrene-glucuronide, a metabolite of pyrene, increased significantly in ten subjects who had ingested charbroiled ground beef. We now report the time course and interindividual variation of 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP) concentration in the urine samples from these ten subjects. PhIP concentration was determined in both untreated and alkali-hydrolyzed urine to obtain estimates of the proportion of conjugated PhIP metabolites in each subject. PhIP was measured by gas chromatography-negative ion chemical ionization-mass spectrometry after derivatization with pentafluorobenzyl bromide. Ten healthy non-smoking males consumed identical amounts of broiled beef on five consecutive days. The morning after the first day of broiled beef consumption, urinary concentration of PhIP increased 14-38 fold above mean pre-feed concentration of PhIP in individual alkali-hydrolyzed urine samples. Following cessation of broiled beef consumption, urinary PhIP concentration declined to near pre-feed levels within 48-72 hrs. The ratio of total alkali-labile PhIP metabolites to unmetabolized PhIP varied by about 2.7-fold among subjects, ranging from 18:1 to 48:1, suggesting that interindividual differences in PhIP metabolism occur and can be detected by this method. This study of urinary PhIP following ingestion of meat cooked by charbroiling, that contains both HAs and polycyclic aromatic hydrocarbons, extends previous studies of ingestion of pan-fried meat that contains primarily HAs. The results indicate that significant amounts of PhIP are bioavailable from ingestion of charbroiled ground beef and that measurement of proportions of alkali-labile PhIP metabolites and parent PhIP in human urine may yield information on individual metabolism of ingested PhIP.

Adult↗

PubMed2001

Effect of photoreactivating light on UV radiation-induced alterations in human skin.

BACKGROUND/AIMS: Photoreactivating light (PRL) after ultraviolet radiation (UVR) exposure causes photoreversal of cyclobutane pyrimidine dimers through the activation of photolyase. Although photoreversal has been demonstrated in the "three kingdoms of life," its existence in man remains controversial. We sought evidence for photoreversal in man. METHODS AND RESULTS: Seven subjects were spot-irradiated at two sites with 4 minimal erythema doses (MED) of solar-simulating UVR. Of the two sites, one was then immediately exposed to a PRL source. Epidermal biopsies were taken immediately after exposure. No significant difference in the quantity of pyrimidine dimers was detected comparing the "UVR only" site to the "UVR, PRL-exposed" site. Biopsies were repeated 24 h later and no significant difference in p53 protein expression or dendritic cell number was detected. However, the "UVR, PRL-exposed" site showed a greater reduction in pyrimidine dimer quantity. CONCLUSIONS: We found no evidence for a direct effect of PRL causing photoreversal of UVR-induced pyrimidine dimers in man. Our results do, however, suggest that some indirect effect of PRL may enhance pyrimidine dimer repair in the 24-h period following UVR exposure.

Adult↗

PubMed2001

COMT genotype, micronutrients in the folate metabolic pathway and breast cancer risk.

Catechol-O-methyltransferase (COMT) catalyzes the O-methylation of catechol estrogens (CEs), using S-adenosylmethionine (SAM) as a methyl donor. Several studies have indicated that the val108met COMT polymorphism, which results in a 3-4-fold decrease in activity, is associated with increased breast cancer risk. Folate, whose intake levels have also been associated with breast cancer risk, and other micronutrients in the folate metabolic pathway influence levels of SAM and S-adenosylhomocysteine (SAH), a COMT inhibitor generated by the demethylation of SAM. Because these micronutrients have been shown to alter SAM and SAH levels, we hypothesized that they could also affect COMT-catalyzed CE methylation. Although measurements of SAM and SAH were not initially collected, a secondary analysis of data from two nested case-control studies was performed to examine whether serum levels of folate, vitamin B12 (B12), pyridoxal 5'-phosphate (PLP), cysteine and homocysteine, in conjunction with COMT genotype, were associated with breast cancer risk. COMT(HH) (high activity COMT homozygote) breast cancer cases had statistically significantly lower levels of homocysteine (P = 0.05) and cysteine (P = 0.04) and higher levels of PLP (P = 0.02) than COMT(HH) controls. In contrast, COMT(LL) (low activity COMT homozygote) cases had higher levels of homocysteine than COMT(LL) controls (P = 0.05). No associations were seen between B12, COMT genotype, and breast cancer risk. An increasing number of COMT(L) alleles was significantly associated with increased breast cancer risk in women with below median levels of folate (P(trend) = 0.05) or above median levels of homocysteine (P(trend) = 0.02). These findings are consistent with a role for certain folate pathway micronutrients in mediating the association between COMT genotype and breast cancer risk.

Breast Neoplasms↗

PubMed2001

Associations of lead exposure and dose measures with erythrocyte protein kinase C activity in 212 current Korean lead workers.

Lead can replace calcium in enzyme assays that measure protein kinase C activity and lead activates protein kinase C in human erythrocytes after exposure to lead in vitro. To examine the relevance of these observations to lead exposure in humans, we studied the associations of lead found in blood or tibia with activation of protein kinase C in erythrocytes isolated from workers in the lead industry. We examined erythrocytes among 212 lead workers, with a mean (+/-SD) age of 39.1 (10.0) years and exposure duration of 8.1 (6.5) years and measured protein kinase C activation by an in vitro back-phosphorylation assay. After adjustment for potential confounding factors (age and sex), tibia lead and exposure duration were significantly associated with erythrocyte protein kinase C activation (both p values < 0.05). No associations were observed between protein kinase C activation and blood-lead or zinc-protoporphyrin levels. These findings suggest that human exposure to lead results in activation of erythrocyte protein kinase C, which may be directly relevant to the neurotoxicity of lead.

Adult↗

PubMed2001

Relationship between the Val158Met polymorphism of catechol O-methyl transferase and breast cancer.

A case-control study was performed to assess the potential influence of catechol O-methyl transferase (COMT) genotype on the risk of breast cancer in Korean women. One hundred and sixty-three histologically confirmed incident breast cancer cases and 163 age- and menopausal status-matched control individuals with no present or previous history of cancer were selected as study subjects. COMT genetic polymorphism was determined by gel electrophoresis after NlaIII enzyme digestion of amplified DNA. Odds ratios and 95% confidence intervals were estimated by unconditional logistic regression after adjustment for known or suspected risk factors of breast cancer. Women with at least one COMT lower enzyme activity associated allele (COMT-L) were at elevated risk for breast cancer (OR = 1.7, 95% CI = 1.04-2.78) compared with those homozygous for high enzyme activity associated COMT-H alleles. Among women with low (> or = 23.1) body mass index the COMT-L allele containing genotypes posed a marginally significant increased risk of breast cancer compared to the COMT-HH genotype (OR = 1.8, 95% CI = 0.95-3.48). Women with at least one COMT-L allele who had experienced a full-term pregnancy when aged over 30 years or were nulliparous had 2.7-fold increased risk; however, this increase did not reach statistical significance (OR = 2.7, 95% CI = 0.64-11.35). Furthermore, never-drinking and never-smoking women with at least one COMT-L allele were at increased risk of breast cancer compared to those with COMT-HH genotype with ORs of 2.0 (95% CI = 1.23-3.38) and 1.7 (95% CI = 1.04-2.62), respectively. These results are consistent with studies showing that COMT genotype of lower enzyme activity might be related to increase in risk of breast cancer, and extend this finding to Korean women.

Adult↗

PubMed2001

Development of aflatoxin B(1)-lysine adduct monoclonal antibody for human exposure studies.

Mouse monoclonal antibodies were developed against a synthetic aflatoxin B(1) (AFB)-lysine-cationized bovine serum albumin conjugate. The isotype of one of these antibodies, IIA4B3, has been classified as immunoglobulin G1(lambda). The affinity and specificity of IIA4B3 were further characterized by a competitive radioimmunoassay. The affinities of IIA4B3 for AFB and its associated adducts and metabolites are ranked as follows: AFB-lysine > 8,9-dihydro-8-(2,6-diamino-4-oxo-3,4-dihydropyrimid-5-yl formamido)-9-hydroxy-AFB > AFB = 8,9-dihydro-8-(N(7)-guanyl)-9-hydroxy-AFB > aflatoxin M(1) > aflatoxin Q(1). IIA4B3 had about a 10-fold higher affinity for binding to AFB-lysine adduct than to AFB when (3)H-AFB-lysine was used as the tracer. The concentration for 50% inhibition for AFB-lysine was 0.610 pmol; that for AFB was 6.85 pmol. IIA4B3 had affinities at least sevenfold and twofold higher than those of 2B11, a previously developed antibody against parent AFB, for the major aflatoxin-DNA adducts 8,9-dihydro-8-(N(7)-guanyl)-9-hydroxy-AFB and 8,9-dihydro-8-(2,6-diamino-4-oxo-3,4-dihydropyrimid-5-yl formamido)-9-hydroxy-AFB, respectively. An analytical method based on a competitive radioimmunoassay with IIA4B3 and (3)H-AFB-lysine was validated with a limit of detection of 10 fmol of AFB-lysine adduct. The method has been applied to the measurement of AFB-albumin adduct levels in human serum samples collected from the residents of areas at high risk for liver cancer.

Aflatoxin B1↗

PubMed2000

Phage display of ScFv peptides recognizing the thymidine(6-4)thymidine photoproduct.

Solar ultraviolet (UV) radiation induces DNA photoproducts in skin cells and is the predominant cause of human skin cancers. To understand human susceptibility to skin cancer and to facilitate the development of prevention measures, highly specific reagents to detect and quantitate UV-induced DNA adducts in human skin will be needed. One approach towards this end is the use of monoclonal antibody-based molecular dosimetry methods. To facilitate the development of photoproduct-specific antibody reagents we have: (i) cloned and sequenced a single chain variable fragment (ScFv) gene coding for one such high affinity monoclonal antibody, [alpha]UVssDNA-1 (mAb C3B6), recognizing the thymidine(6-4)thymidine photoproduct; (ii) expressed and displayed the cloned ScFv gene on the surface of phage; (iii) selected functional recombinant phage by panning; (iv) purified the ScFv peptide; (v) shown that the purified ScFv peptide binds to UV-irradiated polythymidylic acid but not unirradiated polythymidylic acid. This is the first demonstration of the use of phage display to select a ScFv recognizing DNA damage. In addition, this is the initial step towards immortalizing the antibody gene for genetic manipulation, structure-function studies and application to human investigations.

Amino Acid Sequence↗

PubMed2000

An automated, handheld biosensor for aflatoxin.

A new immunoaffinity fluorometric biosensor has been developed for detecting and quantifying aflatoxins, a family of potent fungi-produced carcinogens that are commonly found in a variety of agriculture products. They have also been cited as a biological agent under weapons development. The handheld, self-contained biosensor is fully automatic, highly sensitive, quick, quantitative, and requires no special storage. Approximately 100 measurements can be made before refurbishment is required, and concentrations from 0.1 parts per billion (ppb) to 50 ppb can be determined in <2 min with a 1 ml sample volume. The device operates on the principles of immunoaffinity for specificity and fluorescence for a quantitative assay. The analytic procedure is flexible so that other chemical and biological analytes could be detected with minor modifications to the current device. Advances in electro-optical components, electronics, and miniaturized fluidics were combined to produce this reliable, small, and versatile instrument.

Aflatoxins↗

PubMed2000

Alcohol consumption, glutathione S-transferase M1 and T1 genetic polymorphisms and breast cancer risk.

To evaluate the potential association between GSTM1 and GSTT1 genotypes and development of breast cancer, a hospital based case-control study was conducted in a South Korean study population consisting of 189 histologically confirmed incident breast cancer cases and their 189 age-matched control subjects with no present or previous history of cancer. A multiplex polymerase chain reaction method was used for the genotyping analyses and statistical evaluations were performed by unconditional logistic regression model. The GSTM1 null genotype was significantly associated with breast cancer risk in premenopausal women [odds ratio (OR) = 2.0, 95% confidence interval (CI) = 1-3.7], but not in the postmenopausal women (OR = 0.9, 95% CI = 0.5-1.9), nor in all women grouped together (OR = 1.3, 95% CI = 0.8-1.1). The GSTT1 null genotype posed a similar risk of breast cancer with an OR of 1.6 (95% CI = 1.0-2.5) for the total breast cancer group, OR of 1.7 (95% CI = 0.9-3.2) for pre-menopausal women, and OR of 1.3 (95% CI = 0.6-2.8) for post-menopausal women. The breast cancer risk associated with concurrent lack of both GSTM1 and GSTT1 genes was 2.2 (95% CI = 1.1-4.5), and the risk increased as the number of null genotype increased (P for trend = 0.03). When the data were stratified by the known risk factors of breast cancer, a significant interaction was observed between the GSTM1 genotypes and alcohol consumption (P for interaction = 0.03). An especially remarkable risk of breast cancer was observed for alcohol-consuming premenopausal women lacking both the GSTM1 and GSTT1 genes (OR = 5.3, 95% CI = 1.0-27.8) compared to those with both of the genes. Our findings thus suggest a novel gene-environment interaction which plays an important role in the individual susceptibility to breast cancer. p6

Adult↗

PubMed1999

Comparison of three analytical methods for 1-hydroxypyrene glucuronide in urine after non-occupational exposure to polycyclic aromatic hydrocarbons.

Urinary pyrene metabolites, 1-OHP and 1-OHPG, have been used as biomarkers for the assessment of occupational and environmental exposure to PAHs. This study compares the sensitivity and applicability of the different analytical methods of 1-OHPG for human biomonitoring of low level exposure to PAHs. Three analytical methods were compared: (1) HPLC method from that reported by Singh et al. (Singh, R., Tucek, M., Maxa, K., Tenglerova, J., Weyand, E.H., 1995. A rapid and simple method for the analysis of 1-hydroxypyrene glucuronide: a potential biomarker for polycyclic aromatic hydrocarbon exposure. Carcinogenesis 16, 2909-2915); (2) IAC-SFS method: the rapid and simple assay using IAC purification using monoclonal antibody specific for PAH-DNA adduct and PAH metabolites and SFS quantitation; and (3) IAC-HPLC method: IAC and HPLC separation and quantitation. The correlation between the IAC-SFS method, HPLC method, and the IAC-SFS method was determined in 20 first year-grade junior high school students (age 12-13) from Yochon, Korea who participated in a nationwide survey for the environmental disease surveillance projects in Korea. Chromatograms obtained by the IAC purification and HPLC quantitation method were clear with no interfering peaks adjacent to 1-OHPG, thus 1-OHPG could be easily quantitated. However, the HPLC method produced chromatogram profiles with many interfering peaks adjacent to 1-OHPG peak. The concentrations of 1-OHPG in 20 urine samples were similar when analyzed by all three analytical methods. The correlation coefficient between the IAC-HPLC and IAC-SFS methods was 0.915, and between the IAC-HPLC and HPLC methods was 0.844, and between the IAC-SFS and HPLC methods was 0.805. The analytical methods for 1-OHPG compared in this study showed a good correlation with one another. These results suggest that any of the methods can be applied to human biomonitoring of PAH exposure. However, SFS quantitation after IAC purification is rapid and simple because this method does not need HPLC separation of 1-OHPG.

Adolescent↗

PubMed1999

Plasma 5-aminolevulinic acid concentration and lead exposure in children.

The relationship between concentration of 5-aminolevulinic acid in plasma (ALAP) and other biomarkers of lead exposure and effect was investigated in lead-exposed children. We measured ALAP by chemical derivatization and high-performance liquid chromatography with fluorescence detection. The study population consisted of 103 children: 78 from a referral clinic for children with lead poisoning and 25 from a general pediatric clinic. Blood lead concentration (PbB), age, and ALAP were higher in lead clinic subjects than in general clinic subjects. ALAP was significantly correlated with PbB (Spearman r=0.38, P=0.0007) and free erythrocyte protoporphyrin concentration (r=0.41, P=0.0002) in lead clinic subjects. PbB was a significant predictor of ALAP (P=0.0001) by multiple linear regression in all subjects. The average PbB in the 3- to 12-month period prior to blood collection correlated with ALAP to the same degree that current PbB correlated with ALAP. Possible associations between ALAP and adverse health outcomes, particularly neurobehavioral effects, should be investigated in children to assess the predictive value of ALAP for these endpoints.

Aminolevulinic Acid↗

PubMed1999

Serum concentrations of organochlorine compounds and the subsequent development of breast cancer.

A nested case-control study was conducted to examine the association between serum concentrations of 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE), the primary metabolite of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT), and polychlorinated biphenyls (PCBs) and the development of breast cancer up to 20 years later. Cases (n = 346) and controls (n = 346) were selected from cohorts of women who donated blood in 1974, 1989, or both, and were matched on age, race, menopausal status, and month and year of blood donation. Analyses were stratified by cohort participation because median DDE and PCB concentrations among the controls were 59 and 147% higher in 1974 than 1989, respectively. Median concentrations of DDE were lower among cases than controls in both time periods [11.7% lower in 1974 (P = 0.06) and 8.6% lower in 1989 (P = 0.41)]. Median concentrations of PCBs were similar among cases and controls [P = 0.21 for 1974 and P = 0.37 for 1989 (Wilcoxon signed rank test)]. The risk of developing breast cancer among women with the highest concentrations of DDE was roughly half that among women with the lowest concentrations, whether based on concentrations in 1974 [odds ratio (OR), 0.50; 95% confidence interval (CI), 0.27-0.89; P(trend) = 0.02] or in 1989 (OR, 0.53; 95% CI, 0.24-1.17; P(trend) = 0.08). The associations between circulating concentrations of PCBs and breast cancer were less pronounced but still in the same direction (1974: OR, 0.68; 95% CI, 0.36-12.9; P(trend) = 0.2; and 1989: OR, 0.73; 95% CI, 0.37-1.46; P(trend) = 0.6). Adjustment for family history of breast cancer, body mass index, age at menarche or first birth, and months of lactation did not materially alter these associations. These associations remained consistent regardless of lactation history and length of the follow-up interval, with the strongest inverse association observed among women diagnosed 16-20 years after blood drawing. Results from this prospective, community-based nested case-control study are reassuring. Even after 20 years of follow-up, exposure to relatively high concentrations of DDE or PCBs showed no evidence of contributing to an increased risk of breast cancer.

Adult↗

PubMed1998

Association between glutathione S-transferase M1, P1, and T1 genetic polymorphisms and development of breast cancer.

BACKGROUND: Glutathione S-transferases (GSTs) are encoded by a superfamily of genes and play a role in the detoxification of potential carcinogens. In a nested case-control study, we investigated associations between genetic variability in specific GST genes (GSTM1, GSTT1, and GSTP1) and susceptibility to breast cancer. METHODS: In 1989, a total of 32 898 individuals donated blood samples to a research specimen bank established in Washington County, MD. Genotypes of blood specimen DNA were determined for 110 of 115 women with incident cases of breast cancer diagnosed during the period from 1990 through 1995 and up to 113 of 115 control subjects. Associations between specific genotypes and the development of breast cancer were examined by use of logistic regression to calculate odds ratios (ORs) and 95% confidence intervals (CIs). RESULTS: The GSTM1 homozygous null genotype was associated with an increased risk of developing breast cancer (OR = 2.10; 95% CI = 1.22-3.64), principally due to an association with postmenopausal breast cancer (OR = 2.50; 95% CI = 1.34-4.65). For GSTP1, the data were suggestive of a trend of increasing risk with higher numbers of codon 105 valine alleles (compared with isoleucine alleles); a 1.97-fold increased risk of breast cancer (95% CI = 0.77-5.02) was associated with valine/valine homozygosity. The risk of breast cancer associated with the GSTT1 homozygous null genotype was 1.50 (95 % CI = 0.76-2.95). The risk of breast cancer increased as the number of putative high-risk genotypes increased (P for trend <.001) (OR = 3.77; 95% CI = 1.10-12.88 for a combined genotype of GSTM1 null, GSTT1 null, and either GSTP1 valine heterozygosity or GSTP1 valine homozygosity). CONCLUSIONS: Our findings suggest that genetic variability in members of the GST gene family may be associated with an increased susceptibility to breast cancer.

Breast Neoplasms↗

PubMed1998

Genotyping by mass spectrometric analysis of short DNA fragments.

A method has been developed to produce small DNA fragments from PCR products for analysis of defined DNA variations by mass spectrometry. The genomic region to be analyzed is PCR-amplified with primers containing a sequence for the type IIS restriction endonuclease Bpml. Bpml digestion of the resultant PCR products yields fragments as small as seven bases, which are then analyzed by electrospray ionization mass spectrometry. The approach was validated using seven different variants within the APC tumor suppressor gene, in which a perfect correlation was obtained with DNA sequencing. Both the sense and antisense strands were analyzed independently, and several variants can be analyzed simultaneously. These results provide the basis for a generally applicable and highly accurate method that directly queries the mass of variant DNA sequences.

Base Sequence↗

PubMed1998

Metabolism of benzo[a]pyrene and benzo[a]pyrene-7,8-diol by human cytochrome P450 1B1.

Benzo[a]pyrene (B[a]P), a ubiquitous environmental, tobacco and dietary carcinogen, has been implicated in human cancer etiology. The role of human cytochrome P450 1B1 in the metabolism of B[a]P is poorly understood. Using microsomal preparations of human P450 1A1, 1A2 and 1B1 expressed in baculovirus-infected insect cells, as well as human and rat P450 1B1 expressed in yeast, we have determined the metabolism of B[a]P, with and without the addition of exogenous epoxide hydrolase, and B[a]P-7,8-dihydrodiol (7,8-diol), each substrate at a concentration of 10 microM. HPLC analysis detected eight major metabolites of B[a]P and four metabolites of the 7,8-diol. The results of these studies indicate that cytochrome P450 1B1 carries out metabolism of B[a]P along the pathway to the postulated ultimate carcinogen, the diol epoxide 2, at rates much higher than P450 1A2 but less than P450 1A1. The rates of formation of the 7,8-diol metabolite in incubations with epoxide hydrolase are 0.17 and 0.38 nmol/min/nmol P450 for human P450 1B1 and 1A1, respectively, and undetectable for 1A2. The rates of total tetrol metabolite formation from the 7,8-diol, which are indicative of diol epoxide formation, are 0.60, 0.43 and 2.58 nmol/min/nmol P450 for 1B1, 1A2 and 1A1 respectively. In agreement with other reports of rat P450 1B1 activity, our data show this rat enzyme to be very active for B[a]P and 7,8-diol, with rates higher than human P450 1B1. In addition to the established role of P450 1A1 in B[a]P metabolism, P450 1B1 may significantly contribute to B[a]P and 7,8-diol metabolism and carcinogenesis in rodent tumor models and in humans.

Animals↗

PubMed1998

Metabolism of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine by human cytochrome P4501A1, P4501A2 and P4501B1.

While the metabolic activation of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) by N-hydroxylation has been well documented, the relative roles of the human cytochrome P450 (CYP) enzymes that catalyze this reaction have not been established. Previous studies indicated that the mutagenic activation product, 2-hydroxyamino-PhIP (N2-OH-PhIP), is produced primarily by CYP1A2, and to a lesser extent by CYP1A1. We recently reported that human CYP1B1 also produces N2-OH-PhIP (Carcinogenesis, 18, 1793-1798, 1997). In the present study, we examined PhIP metabolism by microsomes containing recombinant human CYP1A1, 1A2 or 1B1 expressed in Sf9 insect cells and compared the kinetic values for PhIP metabolite formation. PhIP metabolites were analyzed by high pressure liquid chromatography with fluorescence and absorbance detection. Vmax values for N2-OH-PhIP formation were 90, 16 and 0.2 nmol/min/nmol P450, and the apparent Km values were 79, 5.1 and 4.5 microM for human CYP1A2, 1A1 and 1B1, respectively. The non-mutagenic metabolite, 4'-hydroxy-PhIP, was also formed by all three CYP enzymes with Vmax values of 1.5, 7.8 and 0.3 nmol/ min/nmol P450 and apparent Km values of 43, 8.2 and 2.2 microM for human CYP1A2, 1A1 and 1B1, respectively. Although the Vmax for N2-OH-PhIP production was highest for CYP1A2, the catalytic efficiency (Vmax/Km) of CYP1A1 was greater than that of CYP1A2. These results suggest that, for humans, extrahepatic CYP1A1 may be more important than previously thought for the metabolic activation of the dietary carcinogen PhIP.

Animals↗