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1.  A Systems Pharmacology Perspective on the Clinical Development of Fatty Acid Amide Hydrolase Inhibitors for Pain 
The level of the endocannabinoid anandamide is controlled by fatty acid amide hydrolase (FAAH). In 2011, PF-04457845, an irreversible inhibitor of FAAH, was progressed to phase II clinical trials for osteoarthritic pain. This article discusses a prospective, integrated systems pharmacology model evaluation of FAAH as a target for pain in humans, using physiologically based pharmacokinetic and systems biology approaches. The model integrated physiological compartments; endocannabinoid production, degradation, and disposition data; PF-04457845 pharmacokinetics and pharmacodynamics, and cannabinoid receptor CB1-binding kinetics. The modeling identified clear gaps in our understanding and highlighted key risks going forward, in particular relating to whether methods are in place to demonstrate target engagement and pharmacological effect. The value of this modeling exercise will be discussed in detail and in the context of the clinical phase II data, together with recommendations to enable optimal future evaluation of FAAH inhibitors.
doi:10.1038/psp.2013.72
PMCID: PMC3910012  PMID: 24429592
2.  Urinary excretion of phenol, catechol, hydroquinone, and muconic acid by workers occupationally exposed to benzene 
OBJECTIVES: Animal inhalation studies and theoretical models suggest that the pattern of formation of benzene metabolites changes as exposure to benzene increases. To determine if this occurs in humans, benzene metabolites in urine samples collected as part of a cross sectional study of occupationally exposed workers in Shanghai, China were measured. METHODS: With organic vapour monitoring badges, 38 subjects were monitored during their full workshift for inhalation exposure to benzene. The benzene urinary metabolites phenol, catechol, hydroquinone, and muconic acid were measured with an isotope dilution gas chromatography mass spectroscopy assay and strongly correlated with concentrations of benzene air. For the subgroup of workers (n = 27) with urinary phenol > 50 ng/g creatinine (above which phenol is considered to be a specific indicator of exposure to benzene), concentrations of each of the four metabolites were calculated as a ratio of the sum of the concentrations of all four metabolites (total metabolites) and were compared in workers exposed to > 25 ppm v < or = 25 ppm. RESULTS: The median, 8 hour time weighted average exposure to benzene was 25 ppm. Relative to the lower exposed workers, the ratio of phenol and catechol to total metabolites increased by 6.0% (p = 0.04) and 22.2% (p = 0.007), respectively, in the more highly exposed workers. By contrast, the ratio of hydroquinone and muconic acid to total metabolites decreased by 18.8% (p = 0.04) and 26.7% (p = 0.006), respectively. Similar patterns were found when metabolite ratios were analysed as a function of internal benzene dose (defined as total urinary benzene metabolites), although catechol showed a more complex, quadratic relation with increasing dose. CONCLUSIONS: These results, which are consistent with previous animal studies, show that the relative production of benzene metabolites is a function of exposure level. If the toxic benzene metabolites are assumed to be derived from hydroquinone, ring opened products, or both, these results suggests that the risk for adverse health outcomes due to exposure to benzene may have a supralinear relation with external dose, and that linear extrapolation of the toxic effects of benzene in highly exposed workers to lower levels of exposure may underestimate risk.
 
PMCID: PMC1757513  PMID: 9930093
3.  Indirect validation of benzene exposure assessment by association with benzene poisoning. 
Environmental Health Perspectives  1996;104(Suppl 6):1343-1347.
We present a validation study of a quantitative retrospective exposure assessment method used in a follow-up study of workers exposed to benzene. Assessment of exposure to benzene was carried out in 672 factories in 12 cities in China. Historical exposure data were collected for 3179 unique job titles. The basic unit for exposure assessment was a factory/work unit/job title combination over seven periods between 1949 and 1987. A total of 18,435 exposure estimates was developed, using all available historical information, including 8477 monitoring data. Overall, 38% of the estimates were based on benzene monitoring data. The highest time-weighted average exposures were observed for the rubber industry (30.7 ppm) and for rubber glue applicators (52.6 ppm). Because of its recognized link with benzene exposure, the association between a clinical diagnosis of benzene poisoning and benzene exposure was evaluated to validate the assessment method that we used in the cohort study. Our confidence in the assessment method is supported by the observation of a strong positive trend between benzene poisoning and various measures, especially recent intensity of exposure to benzene.
PMCID: PMC1469750  PMID: 9118918
4.  Excretion of 1,2,4-benzenetriol in the urine of workers exposed to benzene. 
Urine samples were collected from 152 workers (64 men, 88 women) who had been exposed to benzene, 53 workers (men only) exposed to a mixture of benzene and toluene, and 213 non-exposed controls (113 men, 100 women). The samples were analysed for 1,2,4-benzentriol (a minor metabolite of benzene) by high performance liquid chromatography. The time weighted average solvent exposure of each worker was monitored by diffusive sampling technique. The urinary concentration of 1,2,4-benzentriol related linearly to the intensity of exposure to benzene both in men and women among workers exposed to benzene, and was suppressed by toluene co-exposure among male workers exposed to a mixture of benzene and toluene. A cross sectional balance study in men at the end of the shift of a workday showed that only 0.47% of benzene absorbed will be excreted into urine as 1,2,4-benzenetriol, in close agreement with previous results in rabbits fed benzene. The concentration of 1,2,4-benzenetriol in urine was more closely related to the concentration of quinol than that of catechol. The fact that phenol and quinol, but not catechol, are precursors of 1,2,4-benzentriol in urine was further confirmed by the intraperitoneal injection of the three phenolic compounds to rats followed by urine analysis for 1,2,4-benzenetriol.
PMCID: PMC1009826  PMID: 2775675
5.  A retrospective cohort study of leukemia and other cancers in benzene workers 
A retrospective cohort study was carried out in 1982–1983 among 28,460 benzene-exposed workers (15,643 males, 12,817 females) from 233 factories and 28,257 control workers (16,621 males, 12,366 females) from 83 factories in 12 large cities in China. All-cause mortality was significantly higher among the exposed (265.46/100,000 person-years) than among the unexposed (139.06/100,000 person-years), as was mortality from all malignant neoplasms (123.21/100,000 versus 54.7/100,000, respectively). For certain cancers, increased mortality was noted among benzene-exposed males in comparison with that among unexposed males; the standardized mortality ratios (SMR) were elevated for leukemia (SMR = 5.74), lung cancer (SMR = 2.31), primary hepatocarcinoma (SMR = 1.12), and stomach cancer (SMR = 1.22). For females only leukemia occurred in excess among the exposed. Risk of leukemia rose as duration to exposure to benzene increased up to 15 years, and then declined with additional years of exposure. Leukemia occurred among some workers with as little as 6 to 10 ppm average exposure and 50 ppm-years (or possibly less) cumulative lifetime exposure (based on all available measurements for the exposed work units). Among the 30 leukemia cases identified in the exposed cohort, the proportion of subjects with acute lymphocytic leukemia was substantially lower and the proportion with acute nonlymphocytic leukemias was higher than in the general population. During 1972 to 1981, the annual incidence of leukemia ranged from 5.83 to 28.33 per 100,000 with higher rates occurring in the interval 1977 to 1981 than in the earlier years of the study period. Future studies should evaluate more precisely the relationship between exposure levels, job title, and development of leukemia among cases and noncases within the exposed cohort.
PMCID: PMC1568128  PMID: 2792042
6.  Urinary t,t-muconic acid as an indicator of exposure to benzene. 
A method for rapidly determining t,t-muconic acid (MA) by high performance liquid chromatography was developed and successfully applied to urine samples from 152 workers exposed to benzene (64 men, 88 women) and 213 non-exposed controls (113 men, 100 women). The MA concentrations in urine correlated linearly with time weighted average benzene concentrations in the breath zone air of workers. A cross sectional balance study showed that about 2% of benzene inhaled is excreted into the urine as MA. The MA concentrations in the urine of the non-exposed was below the detection limit (less than 0.1 mg/l) in most cases, and the 95% lower confidence limit of MA for those exposed to benzene at 5 ppm (5.0 mg/l as a non-corrected value) was higher than the 97.5%-tile values for the non-exposed (1.4 mg/l). In practice, it was possible to separate those exposed to 6-7 ppm benzene from the non-exposed by means of urine analysis for MA. The urinary MA concentration was suppressed by coexposure to toluene.
PMCID: PMC1009737  PMID: 2923822
7.  Determination of catechol and quinol in the urine of workers exposed to benzene. 
Time weighted average concentrations of benzene in breathing zone air (measured by diffusive sampling coupled with FID gas chromatography) and concentrations of catechol and quinol in the urine (collected at about 1500 in the second half of a working week and analysed by high performance liquid chromatography) were compared in 152 workers who were exposed to benzene (64 men, 88 women). The concentration of urinary metabolites was also determined in 131 non-exposed subjects (43 men, 88 women). There was a linear relation between the benzene concentrations in the breathing zone and the urinary concentrations of catechol and quinol (with or without correction for urine density) in both sexes. Neither catechol nor quinol concentration was able to separate those exposed to benzene at 10 ppm from those without exposure. The data indicated that when workers were exposed to benzene at 100 ppm about 25% of benzene absorbed was excreted into the urine as phenolic metabolites, of which 13.2%, 1.6%, and 10.2% are phenol, catechol, and quinol, respectively.
PMCID: PMC1009634  PMID: 3395585
8.  Leukaemia in benzene workers: a retrospective cohort study. 
A retrospective cohort study was conducted in 233 benzene factories and 83 control factories in 12 cities in China. The benzene cohort and the control cohort consisted of 28,460 benzene exposed workers (178,556 person-years in 1972-81) and 28,257 control workers (199,201 person-years). Thirty cases of leukaemia (25 dead and 5 alive) were detected in the former and four cases (all dead) in the latter. The leukaemia mortality rate was 14/100,000 person-years in the benzene cohort and 2/100,000 person-years in the control cohort; the standardized mortality ratio was 5.74 (p less than 0.01 by U test). The average latency of benzene leukaemia was 11.4 years. Most (76.6%) cases of benzene leukaemia were of the acute type. The mortality due to benzene leukaemia was high in organic synthesis plants followed by painting and rubber synthesis industries. The concentration of benzene to which patients with a leukaemia were exposed ranged from 10 to 1000 mg/m3 (mostly from 50 to 500 mg/m3). Of the 25 cases of leukaemia, seven had a history of chronic benzene poisoning before the leukaemia developed.
PMCID: PMC1007793  PMID: 3814544
9.  Quantitative relation of urinary phenol levels to breathzone benzene concentrations: a factory survey. 
Urine samples were collected from 64 men and 88 women in shoe factories and printing plants at the end of a seven hour day shift in the latter half of a week in spring. Urine samples were also taken from 43 men and 88 women in the same factories but who were not exposed to solvents. Exposure to benzene during the shift was monitored by passive dosimeters. Both phenol in urine and benzene in activated carbon were analysed with FID gas chromatographs. The urinary concentrations of phenol were linearly related to the time weighted average concentrations of benzene in the breathzone air; the variation was so small that those exposed to 10 ppm benzene could be separated from the non-exposed at least on a group basis when the phenol concentration was corrected either for creatinine concentration or for specific gravity. The urinary phenol concentrations corresponding to 10 ppm benzene were 47.5 mg/l (as observed), 57.9 mg/g creatinine, or 46.6 mg/l (specific gravity 1.016).
PMCID: PMC1007738  PMID: 3778839
10.  Mortality among benzene-exposed workers in China. 
Environmental Health Perspectives  1996;104(Suppl 6):1349-1352.
A large cohort of 74,828 benzene-exposed and 35,805 nonexposed workers employed between 1972 and 1987 in 12 cities in China was followed to determine mortality from all causes. Benzene-exposed study subjects were employed in a variety of occupations including coating applications, and rubber, chemical, and shoe production. Mortality was slightly increased among workers with greater cumulative exposure to benzene (ptrend < 0.05), but this excess was largely due to cancer deaths (ptrend < 0.01). Deaths due to lymphatic and hematopoietic malignancies (ptrend = 0.01) and lung cancer (ptrend = 0.01) increased with increasing cumulative exposure to benzene. Investigations continue to relate benzene exposure to specific lymphatic and hematopoietic malignancies and other causes of death.
PMCID: PMC1469764  PMID: 9118919
11.  An expanded cohort study of cancer among benzene-exposed workers in China. Benzene Study Group. 
Environmental Health Perspectives  1996;104(Suppl 6):1339-1341.
An expanded cohort study of 74,828 benzene-exposed and 35,805 unexposed workers were followed during 1972 to 1987, based on a previous study in 12 cities in China. A small increase was observed in total cancer mortality among benzene-exposed compared with unexposed workers (relative risk [RR] = 1.2). Statistically significant excesses were noted for leukemia (RR = 2.3), malignant lymphoma (RR = 4.5), and lung cancer (RR = 1.4). When risks were evaluated by leukemia subtype, only acute myelogenous leukemia was significantly elevated (RR = 3.1), although nonsignificant excesses were also noted for chronic myelogenous leukemia (RR = 2.6) and acute lymphocytic leukemia (RR = 2.3). A significant excess was also found for aplastic anemia.
PMCID: PMC1469739  PMID: 9118917
12.  Clinical features of hematopoietic malignancies and related disorders among benzene-exposed workers in China. Benzene Study Group. 
Environmental Health Perspectives  1996;104(Suppl 6):1353-1364.
Previous occupational cohort studies of benzene-exposed workers have for the most part used only death certificates to validate diagnoses of workers developing leukemia and other hematopoietic and lymphoproliferative malignancies and related disorders (HLD). In a follow-up study of 74,828 benzene-exposed workers and a comparison group of 35,805 nonexposed workers from 12 cities in China, we sought to characterized clinicopathologically and to confirm diagnoses of all cases of HLD. Using medical records, laboratory hematology results, and histopathology, U.S. and Chinese expert hematopathologists, blinded to exposure status, carried out a detailed review using standardized evaluation forms. Key among the findings were a notable diversity of malignant and nonneoplastic hematopoietic and lymphoproliferative disorders, documentation of excess myelodysplastic syndromes among benzene workers, and widespread dyspoiesis involving all hematopoietic cell lines. As sophisticated clinicopathologic characterization and corresponding classification schemes for HLD become increasingly widespread, it is recommended that future epidemiologic investigations of benzene workers incorporate similarly detailed morphologic evaluation. In extending follow-up of this cohort of young workers, we will continue to use all available clinical, laboratory hematology, and pathology data as well as cytogenetic and biochemical markers to characterized various HLD outcomes. These careful surveillance mechanisms should also provide additional insight into carcinogenic mechanisms of benzene and allow comparison of the molecular pathogenesis of HLD induced by benzene versus chemotherapy, radiation, or other exposure.
PMCID: PMC1469722  PMID: 9118920
13.  An epidemiologic study of early biologic effects of benzene in Chinese workers. 
Environmental Health Perspectives  1996;104(Suppl 6):1365-1370.
Benzene is a recognized hematotoxin and leukemogen, but its mechanisms of action in humans are still uncertain. To provide insight into these processes, we carried out a cross-sectional study of 44 healthy workers currently exposed to benzene (median 8-hr time-weighted average; 31 ppm), and unexposed controls in Shanghai, China. Here we provide an overview of the study results on peripheral blood cells levels and somatic cell mutation frequency measured by the glycophorin A (GPA) gene loss assay and report on peripheral cytokine levels. All peripheral blood cells levels (i.e., total white blood cells, absolute lymphocyte count, platelets, red blood cells, and hemoglobin) were decreased among exposed workers compared to controls, with the exception of the red blood cell mean corpuscular volume, which was higher among exposed subjects. In contrast, peripheral cytokine levels (interleukin-3, interleukin-6, erythropoietin, granulocyte colony-stimulating factor, tissue necrosis factor-alpha) in a subset of the most highly exposed workers (n = 11) were similar to values in controls (n = 11), suggesting that benzene does not affect these growth factor levels in peripheral blood. The GPA assay measures stem cell or precursor erythroid cell mutations expressed in peripheral red blood cells of MN heterozygous subjects, identifying NN variants, which result from loss of the GPA M allele and duplication of the N allele, and N phi variants, which arise from gene inactivation. The NN (but not N phi) GPA variant cell frequency was elevated in the exposed workers compared with controls (mean +/- SD, 13.9 +/- 8.4 mutants per million cells versus 7.4 +/- 5.2 per million cells, (respectively; p = 0.0002), suggesting that benzene produces gene-duplicating but not gene-inactivating mutations at the GPA locus in bone marrow cells of exposed humans. These findings, combined with ongoing analyses of benzene macromolecular adducts and chromosomal aberrations, will provide an opportunity to comprehensively evaluate a wide range of early biologic effects associated with benzene exposure in humans.
PMCID: PMC1469765  PMID: 9118921

Results 1-13 (13)