Covariation of human microsomal protein per gram of liver with age: absence of influence of operator and sample storage may justify interlaboratory data pooling.

Scaling of metabolic clearance values from liver microsomal data or recombinantly expressed cytochrome P450 enzymes to predict human hepatic clearance requires knowledge of the amount of microsomal protein per gram of liver (MPPGL). Identification of physiological covariates of MPPGL requires analysis of values from large diverse populations, which necessitates pooling of data from numerous sources. To ensure compatibility between results obtained within and between studies, the impact of interoperator differences and sample storage on values of MPPGL was investigated. With use of triplicate samples from one liver (HL86), no statistically significant difference was detected between values of MPPGL prepared from samples stored at -80 degrees C (23.5 +/- 1.2 mg g(-1)) and those determined using fresh tissue (21.9 +/- 0.3 mg g(-1)). Although there was a significant difference in the yield of microsomal protein obtained from another liver sample (HL43) by three different operators (17 +/- 1, 19 +/- 2, and 24 +/- 1 mg g(-1); p = 0.004, analysis of variance), no difference was observed in the estimated MPPGL after application of appropriate correction factors for each operator (28 +/- 1, 30 +/- 5, and 31 +/- 4 mg g(-1)). The result provided justification for pooling reported values of MPPGL for use in covariate analysis. Investigation of the relationship between age and MPPGL provided preliminary evidence that MPPGL values increase from birth to a maximum of 40 mg g(-1) [95% confidence interval for the geometric mean (95% CI mean(geo)): 37-43 mg g(-1) at approximately 28 years followed by a gradual decrease in older age (mean of 29 mg g(-1) at 65 years; 95% CI mean(geo): 27-32 mg g(-1)). Accordingly, appropriate age-adjusted scaling factors should be used in extrapolating in vitro clearance values to clinical studies.

Simultaneous measurement of specific serum IgG responses to five select agents.

Select Agents are defined by CDC and the USDA Animal and Plant Health Inspection Service (APHIS) as biological agents or toxins deemed a threat to public, animal, or plant health, or to animal or plant products. They are classified on the basis of their ease of dissemination, mortality/morbidity rate, and potential for social disruption. A subset of these agents includes Bacillus anthracis, Yersinia pestis, Francisella tularensis, ricin toxin (RT), and staphylococcal enterotoxin B (SEB). Infection or intoxication with these agents has been shown to elicit an antigen-specific serum IgG response. We describe a fluorescent covalent microsphere immunoassay (FCMIA) for measurement of specific IgG antibodies to seven different antigens from five different select agents; B. anthracis [protective antigen (PA) and lethal factor (LF)], Y. pestis (F1 and V antigens), F. tularensis, RT and SEB simultaneously in human B. anthracis vaccinee sera (containing anti-PA and anti-LF IgG) which had been spiked with animal specific IgG antibodies to the other select agents. Inter-assay and intra-assay coefficients of variation were 6.5 and 13.4%, respectively (N = 4). There were no significant differences (P > 0.70) between assay responses when the assays were performed individually or multiplexed. When the observed versus expected interpolated concentrations were compared, highly linear relationships were observed (r2 values from 0.981 to 0.999, P < 0.001). Minimum detectable concentrations (MDC) ranged from 0.3 ng mL(-1) (Y. pestis F1) to 300 ng mL(-1) (RT). Finally, the curves showed responses were linear for most analytes from their MDC to 125 (SEB) to 1,300 (Y. pestis F1) x their MDC. These data indicate that multiplexed FCMIA is a sensitive and accurate method for simultaneous measurement of specific IgG in serum to CDC select agents and may be of value in screening either decontamination workers or the general population for exposure to/infection with these agents.

Determination of serum IgG antibodies to Bacillus anthracis protective antigen in environmental sampling workers using a fluorescent covalent microsphere immunoassay.

AIMS: To evaluate potential exposure to Bacillis anthracis (Ba) spores in sampling/decontamination workers in the aftermath of an anthrax terror attack. METHODS: Fifty six serum samples were obtained from workers involved in environmental sampling for Ba spores at the American Media, Inc. (AMI) building in Boca Raton, FL after the anthrax attack there in October 2001. Nineteen sera were drawn from individuals both pre-entry and several weeks after entrance into the building. Nine sera each were drawn from unique individuals at the pre-entry and follow up blood draws. Thirteen donor control sera were also evaluated. Individuals were surveyed for Ba exposure by measurement of serum Ba anti-protective antigen (PA) specific IgG antibodies using a newly developed fluorescent covalent microsphere immunoassay (FCMIA). RESULTS: Four sera gave positive anti-PA IgG results (defined as anti-PA IgG concentrations > or = the mean microg/ml anti-PA IgG from donor control sera (n = 13 plus 2 SD which were also inhibited > or = 85% when the serum was pre-adsorbed with PA). The positive sera were the pre-entry and follow up samples of two workers who had received their last dose of anthrax vaccine in 2000. CONCLUSION: It appears that the sampling/decontamination workers of the present study either had insufficient exposure to Ba spores to cause the production of anti-PA IgG antibodies or they were exposed to anthrax spores without producing antibody. The FCMIA appears to be a fast, sensitive, accurate, and precise method for the measurement of anti-PA IgG antibodies.

Development of a sensitivity enhanced multiplexed fluorescence covalent microbead immunosorbent assay (FCMIA) for the measurement of glyphosate, atrazine and metolachlor mercapturate in water and urine.

Body burdens from exposures to pesticides may be estimated from urinary analyses of pesticide parent/metabolite concentrations. Pesticide applicators and others are often exposed to numerous unrelated pesticides, either sequentially or simultaneously. Classically, body burdens of pesticides are analyzed using chemical/instrumental analysis (CIM) or enzyme immunoassays (EIAs). Both of these technologies can usually be used to quantitate one analyte (or closely related groups of analytes) per analysis. Alternatively, multiple analytes can be measured simultaneously using a multiplexed fluorescence covalent microbead immunoassay (FCMIA). We developed a multiplexed FCMIA to simultaneously measure glyphosate (Gly), atrazine (Atz), and metolachlor mercapturate (MM) in water and urine. The assay had least detectable doses (LDDs) in water/diluted urine of 0.11/0.09 ng/ml (Gly, water/urine LDD), 0.10/0.07 ng/ml (Atz) and 0.09/0.03 ng/ml (MM). The sensitivity for the measurement of Gly was enhanced by derivatization. All assays gave linear responses from the LDDs for each respective pesticide to 300 ng/ml. There was no cross-reactivity between the three analytes. Using a 96-well microplate and an autosampler, as many as 288 separate analyses can be completed in approximately 120 min with precision, sensitivity, and specificity equivalent to, if not better, than that found when these same analytes are measured by CIM or EIA.

Interindividual variance of cytochrome P450 forms in human hepatic microsomes: correlation of individual forms with xenobiotic metabolism and implications in risk assessment.

Differences in biotransformation activities may alter the bioavailability or efficacy of drugs, provide protection from certain xenobiotic and environmental agents, or increase toxicity of others. Cytochrome P450 (CYP450) enzymes are responsible for the majority of oxidation reactions of drugs and other xenobiotics and differences in their expression may directly produce interindividual differences in susceptibility to compounds whose toxicity is modulated by these enzymes. To rapidly quantify CYP450 forms in human hepatic microsomes, we developed, and applied, an ELISA to 40 samples of microsomes from adult human organ donors. The procedure was reliable and the results were reproducible within normal limits. Protein content for CYP1A, CYP2E1, and CYP3A positively correlated with suitable marker activities. CYP1A, CYP2B, CYP2C6, CYP2C11, CYP2E1, and CYP3A protein content demonstrated 36-, 13-, 11-, 2-, 12-, and 22-fold differences between the highest and lowest samples and the values were normally distributed. Of the forms examined, CYP3A was expressed in the highest amount and it was the only form whose content was correlated with total CYP450 content. Content of other forms was independent of total CYP450. We further determined the contribution of specific forms to the biotransformation of trichloroethylene as a model substrate. CYP2E1 was strongly correlated with chloral hydrate formation from trichloroethylene; CYP2B displayed the strongest correlation with trichloroethanol formation. These data describing the expression and distribution of these forms in human microsomes can be used to extrapolate in vitro derived metabolic rates for toxicologically important reactions, when form selectivity and specific activity are known. This approach may be applied to refine estimates of human interindividual differences in susceptibility for application in human health risk assessment.

Induction of stress proteins in rat cardiac myocytes by antimony.

The effects of nonlethal concentrations of potassium antimonyl tartrate (PAT) were examined in cultured neonatal rat cardiac myocytes. PAT (5, 10 microM) significantly increased cellular reduced glutathione (GSH) and heme oxygenase activity after 18 h. GSH levels and heme oxygenase activity were increased 2.5- and 5.4-fold, respectively, by 10 microM PAT after 18 h. In addition, total cytochrome P450 levels were decreased by PAT after an 18-h exposure. PAT exposures were associated with the induction of specific stress proteins. Nonlethal concentrations of PAT produced a dose-dependent increase in HO-1, HSP70, and HSP25/27 protein levels but did not increase HSP60 levels. Pretreatment of cardiac myocytes with low concentrations of PAT (0.5-10 microM) protected against a subsequent lethal concentration of PAT (200 microM). This protection was blocked if cells were treated with the protein synthesis inhibitor cycloheximide. Results demonstrate that low concentrations of PAT increase GSH levels and stress protein synthesis, which may be responsible for the protection that low-level PAT exposure offers against the subsequent toxicity of higher concentrations of PAT.

Characterization of cytochrome P450 and glutathione S-transferase activity and expression in male and female ob/ob mice.

OBJECTIVE: To characterize the effect(s) of gender, age (glycemic status) and obese state, on hepatic biotransformation activities, expression of cytochrome P450 (CYP450) mRNAs and glutathione transferase activity in the ob/ob mouse. DESIGN: Male and female, ob/ob or ob/+ mice were killed at 3-4 months or 7-8 months of age. Hepatic microsomes, cytosol and RNA were prepared from each animal. ANIMALS: Male and female ob/ob and ob/+ mice, 3-4 or 7-8 months of age. MEASUREMENTS: CYP450 form-specific activities of CYP1A1/1A2, CYP3A and CYP2B were estimated by determining the 0-dealkylation of alkoxyresorufin substrates (ethoxy-EROD, benzoxy-BROD and pentoxy-resorufin, PROD, respectively). CYP2E1-dependent, 4-nitrophenol hydroxylase (PNP-OH) and CYP3A-dependent erythromycin N-demethylase (ERY-DM) were also measured in hepatic microsomes. CYP1A2, CYP2E1 and CYP3A protein in microsomal fractions was determined by ELISA. Glutathione transferase activity (GST) was determined in hepatic cytosol and CYP1A2 and CYP2E1 mRNA was estimated by Northern blot analysis. RESULTS: Female mice, regardless of glycemic status, showed an obesity enhanced level of CYP2E1-dependent PNP-OH activity and CYP2E1 protein as shown by ELISA. These increases were observed to be independent of the diabetic state, since 7-8 month-old mice had blood glucose levels identical to lean mice. The mRNA level of CYP2E1 in female mice also exhibited age-and obesity-influenced decreases in expression. No significant differences in CYP2E1 activity or expression were observed in male mice. CYP3A-dependent ERY-DM activity was significantly higher in young males, regardless of phenotype. CYP3A and CYP2B activities did not differ among any animals; however, CYP1A activity, while depressed in obese animals of both genders, was significantly different in old animals. Glutathione S-transferase activity was lower in obese male mice, whereas no difference was observed between lean and obese females CONCLUSION: This study supports earlier observations in man and rats that the obese state produces alterations in the expression of important oxidation and conjugation pathways. In addition, this report more thoroughly examines the role of gender and glycemic status on biotransformation activities in the ob/ob mouse as demonstrated by increased CYP2E1 protein and CYP2E1-dependent activity in obese females, decreased CYP1A2 protein and CYP1A2-dependent activity in obese animals, and obesity had no effect of glutathione transferase in female mice, in contrast with the previously reported obesity-dependent decrease of this activity in male mice.

Effect of magnetic field exposure on anchorage-independent growth of a promoter-sensitive mouse epidermal cell line (JB6).

The anchorage-independent growth of mouse epidermal cells (JB6) exposed to 60-Hz magnetic fields (MF) was investigated. Promotion-responsive JB6 cells were suspended in agar (10(4)cells/plate) and exposed continuously to 0.10 or 0.96 mT, 60-Hz magnetic fields for 10-14 days, with or without concurrent treatment with the tumor promoter tetradecanoylphorbol acetate (TPA). Exposures to MF were conducted in a manner such that the experimenter was blind to the treatment group of the cells. At the end of the exposure period, the anchorage-independent growth of JB6 cells on soft agar was examined by counting the number of colonies larger than 60 microm (minimum of 60 cells). The use of a combined treatment of the cells with both MF and TPA was to provide an internal positive control to estimate the success of the assay and to allow evaluation of co-promotion. Statistical analysis was performed by a randomized block design analysis of variance to examine both the effect of TPA treatment (alone and in combination with MF exposure) and the effect of intra-assay variability. Transformation frequency of JB6 cells displayed a dose-dependent response to increasing concentrations of TPA. Coexposure of cells to both TPA and 0.10 or 0.96 mT, 60-Hz MF did not result in any differences in transformation frequency for any TPA concentrations tested (0-1 ng/ml). These data indicate that exposure to a 0.10 or 0.96 mT, 60-Hz MF does not act as a promoter or co-promoter in promotion-sensitive JB6 cell anchorage-independent growth.

Repeat exposure to incremental doses of acetaminophen provides protection against acetaminophen-induced lethality in mice: an explanation for high acetaminophen dosage in humans without hepatic injury.

In studies designed to simulate a clinical observation in which an individual became tolerant to normally lethal doses of acetaminophen (APAP), mice were pretreated with increasing doses of APAP for 8 days and challenged on day 9 with normally supralethal doses of APAP. These animals developed minimal hepatotoxicity after a challenge dose with a fourfold increase in LD50 to 1,350 mg/kg. The pretreatment regimen resulted in hepatic changes including: centrilobular localization of 3-(cysteine-S-yl)APAP protein adducts, selective down-regulation of cytochrome P4502E1 (CYP2E1) and CYP1A2 that produced the toxic metabolite, N-acetyl-p-benzoquinone imine, higher levels of reduced glutathione (GSH), centrilobular inflammation, and a fourfold increase in hepatocellular proliferation. The protection against the lethal APAP doses afforded by pretreatment is secondary to these changes and to the associated regional shift in the bioactivation of the APAP challenge dose from centrilobular to periportal regions where CYP2E1 is not found, protective GSH is more abundant, and where cell-proliferative responses are better able to sustain repair. This shift in APAP bioactivation results in less-intense covalent binding that is more diffuse and spread uniformly throughout the hepatic lobe, most likely contributing to protection by delaying the early onset of liver injury that has been generally associated with centrilobular localization of the adducts. Intervention of APAP pretreatment-induced cell division in mice with colchicine left them resistant to a 500-mg/kg (normally lethal) dose of APAP, but unable to survive a 1,000-mg/kg APAP challenge dose. The data demonstrate multiple mechanistic components to the protection afforded by APAP pretreatment. Whereas metabolic and physiological changes not dependent on cell proliferation are adequate to protect against 500 mg/kg APAP, these changes plus a potentiated cell-proliferative response are necessary for protection against the supralethal 1,000-mg/kg APAP dose. Furthermore, the data document an uncoupling of the traditional association between covalent binding and toxicity, and suggest that the assessment of toxicity following repeated or chronic APAP exposure must consider altered drug interactions and parameters besides those historically used to assess acute APAP overdose.

Immunochemical, 32P-postlabeling, and GC/MS detection of 4-aminobiphenyl-DNA adducts in human peripheral lung in relation to metabolic activation pathways involving pulmonary N-oxidation, conjugation, and peroxidation.

4-Aminobiphenyl (ABP) is a recognized human bladder carcinogen, whose presence in cigarette smoke results in DNA adduct formation in the human urothelium. Since preliminary studies indicated that even higher levels of ABP-DNA adducts may be present in human peripheral lung, we utilized a sensitive immunochemical assay, in combination with 32P-postlabeling, to quantify the major 4-aminobiphenyl (ABP)-DNA adduct, N-(guan-8-yl)-ABP, in surgical samples of peripheral lung tissue from smokers and ex-smokers. No differences in adduct levels were detected between smokers and ex-smokers by immunoassay. In contrast, the 32P-postlabeling method showed statistically significant differences between adduct levels in smokers and ex-smokers; however, a relatively high background of smoking-related adducts chromatograph near the major ABP adducts and may compromise estimation of the level of ABP-DNA adducts in smokers. Furthermore, the levels measured by 32P-postlabeling were 20- to 60-fold lower than that measured by immunoassay. Since 32P-postlabeling may underestimate and immunochemical assays may overestimate adduct levels in the lung, selected samples were also evaluated by GC/MS. The immunochemical and GC/MS data were concordant, leading us to conclude that N-(guan-8-yl)-ABP adducts were not related to smoking status. Since ABP-DNA adduct levels in human lung did not correlate with smoking status as measured by immunoassay and GC/MS, the metabolic activation capacity of human lung microsomes and cytosols was examined to determine if another exposure (e.g., 4-nitrobiphenyl) might be responsible for the adduct. The rates of microsomal ABP N-oxidation were below the limit of detection, which was consistent with a lack of detectable cytochrome P4501A2 in human lung. N-Hydroxy-ABP O-acetyltransferase (but not sulfotransferase) activity was detected in cytosols and comparative measurements of N-acetyltransferase (NAT) using p-aminobenzoic acid and sulfamethazine indicated that NAT1 and NAT2 contributed to this activity. 4-Nitrobiphenyl reductase activity was found in lung microsomes and cytosols, with the reaction yielding ABP and N-hydroxy-ABP. Lung microsomes also demonstrated high peroxidative activation of ABP, benzidine, 4,4'-methylene-bis(2-chloroaniline), 2-aminofluorene, and 2-naphthylamine. The preferred co-oxidant was hydrogen peroxide and the reaction was strongly inhibited by sodium azide but not by indomethacin or eicosatetraynoic acid, which suggested the primary involvement of myeloperoxidase rather than prostaglandin H synthase or lipoxygenase. This was confirmed by immunoinhibition and immunoprecipitation studies using solubilized human lung microsomes and antisera specific for myeloperoxidase. These data suggest that ABP-DNA adducts in human lung result from some environmental exposure to 4-nitrobiphenyl. The bioactivation pathways appear to involve: (1) metabolic reduction to N-hydroxy-ABP and subsequent O-acetylation by NAT1 and/or NAT2; and (2) metabolic reduction to ABP and subsequent peroxidation by myeloperoxidase. The myeloperoxidase activity appears to be the highest peroxidase activity measured in mammalian tissue and is consistent with the presence of neutrophils and polymorphonuclear leukocytes surrounding particulate matter derived from cigarette smoking.

Antimony-induced alterations in thiol homeostasis and adenine nucleotide status in cultured cardiac myocytes.

Cultured cardiac myocytes were exposed for up to 4 h to 50 and 100 microM potassium antimonyl tartrate (PAT). After 4 h, 50 and 100 microM PAT killed 14 and 33% respectively of the cardiac myocytes. PAT-induced alterations in both protein and nonprotein thiol homeostasis. Transient increases in oxidized glutathione disulfide (GSSG) levels were detected after cells were treated with 100 microM PAT for 2 h. After 4 h, both concentrations of PAT significantly depleted reduced glutathione (GSH) levels. Protein thiols levels were also decreased after a 2-h exposure to 50 and 100 microM PAT. Cells treated with 50 microM and 100 microM PAT had a 15% and 40% reduction respectively in protein thiols after 4 h. PAT also significantly inhibited glutathione peroxidase and pyruvate dehydrogenase activity in cardiac myocytes. Pyruvate dehydrogenase activity levels were inhibited as early as 1 h after cells were treated with both concentrations of PAT. Cardiac myocyte ATP levels were also decreased by PAT, but only after a 4-h exposure to 50 microM and 100 microM PAT. Decreases in cellular ATP levels paralleled PAT toxicity put appeared to be secondary to other cellular changes initiated by PAT exposure.

Cytochrome P450-dependent metabolism of trichloroethylene: interindividual differences in humans.

Trichloroethylene (TRI) is an industrial solvent with a history of use in anesthesia, and is a common groundwater contaminant. Cytochrome P450 (CYP)-dependent metabolism of TRI produces chloral hydrate (CH) and is rate limiting in the ultimate production of trichloro- and/or dichloroacetic acid from TRI. Exposure of rodents to TRI results in lung and liver tumors (mice) and nephrotoxicity (rats). The toxicity is exacerbated by pretreatment of mice with CYP inducers. We report significant variability in TRI metabolism in a sample of 23 human hepatic microsomal samples and demonstrate the dependence of TRI metabolism on CYP2E1. K(m) values in this limited sample population are not normally distributed. We have correlated microsomal CH formation with the activity toward routine CYP2E1 substrates and with immunologically detectable CYP2E1 protein. Further, TRI metabolism in microsomes from lymphoblastoid cell lines expressing CYP2E1, CYP1A1, CYP1A2, or CYP3A4 indicated minimal involvement of the latter forms, with CYP2E1 catalyzing more than 60% of total microsomal TRI metabolism. These results indicate that humans are not uniform in their capacity for CYP-dependent metabolism of TRI and increased CYP2E1 activity may increase susceptibility to TRI-induced toxicity in the human.

Loss of CYP2E1 and CYP1A2 activity as a function of acetaminophen dose: relation to toxicity.

The effect of acetaminophen (APAP) dose on the cytochrome P450s responsible for its bioactivation was examined in control mice and mice treated with acetone to induce CYP2E1, or beta-napthaflavone to induce CYP1A2. In non-induced mice, 150 mg/kg APAP caused minimal hepatotoxicity and loss of CYP2E1- but not CYP1A2-dependent activity. In contrast, 400 mg/kg APAP was hepatotoxic and diminished both CYP2E1 and CYP1A2 activities. In acetone-pretreated mice, the 150 and 400 mg/kg APAP doses caused similar depletion of CYP2E1 activity and similar levels of covalent binding of APAP to liver proteins. In beta-napthaflavone-pretreated mice, CYP1A2 activity was decreased only by the high dose of APAP, and covalent binding was > 2-fold higher at the high APAP dose. The data indicate CYP2E1 is important in the bioactivation of APAP at the low dose with little additional contribution at the high dose, whereas CYP1A2 contributes more to the bioactivation and toxicity APAP at high doses.

Cryopreservation and long-term storage of primary rat hepatocytes: effects on substrate-specific cytochrome P450-dependent activities and unscheduled DNA synthesis.

The effects of cryopreservation and long-term storage on substrate-specific cytochrome P450-dependent activities and unscheduled DNA synthesis were studied in freshly isolated and cryopreserved hepatocytes derived from adult male Fischer 344 and Sprague-Dawley rats. Primary rat hepatocytes were isolated via an in situ collagenase perfusion technique, cryopreserved at -196 degrees C, and thawed at 5 weeks and 104 and 156 weeks post-freezing. In Fischer 344 and Sprague-Dawley rats, cryopreserved hepatocytes were equivalent or similar to freshly isolated hepatocytes in substrate-specific activities for 7-ethoxyresorufin-O-deethylase and dimethylnitrosamine-N-demethylase and unscheduled DNA synthesis responses. No significant differences in activities toward 7-ethoxyresorufin-O-deethylase and dimethylnitrosamine-N-demethylase, the substrate-specific activities for cytochromes P4501A1 and P4501A2 and cytochrome P4502E1, respectively, were observed between freshly isolated and cryopreserved hepatocytes. Similar unscheduled DNA synthesis responses, a measure of DNA damage and repair, were observed after exposure to the genotoxic carcinogens 2-acetylamino-fluorene, 7,12-dimethylbenz[a]anthracene, and dimethylnitrosamine; although some decreases were also observed in Fischer 344 hepatocytes after 104 weeks and Sprague-Dawley hepatocytes after 156 weeks in the highest concentrations tested. These results suggest that cryopreserved hepatocytes, stored for extended periods of time in liquid nitrogen, are metabolically equivalent to freshly isolated hepatocytes in their ability to activate precarcinogens.

Osteolathyrogenic effects of malathion in Xenopus embryos.

Malathion, an organophosphorus insecticide, has been found previously to cause developmental defects such as enlargement of the atria and aorta and bent notochord in Xenopus laevis. Since these defects are similar to those caused by known lathyrogens, the effects of malathion on collagen biochemistry and structure were studied. Embyros were exposed to malathion or its metabolite malaoxon during the first 4 days of development. Notochords of malathion- and malaoxon-treated embryos were bent ventrally between the third and sixth somites and were enlarged. Ultrastructural examination of the postanal tail notochord showed that the elastic externa was disorganized and less dense and the sheath had fewer, more disorganized fibers. Embryos exposed in culture displayed a concentration-dependent reduction in ascorbate and hydroxyproline. Malathion and malaoxon inhibited the activities of lysyl oxidase (I50s of 0.7 and 8.7 nM, respectively) and proline hydroxylase (I50s of 58 microM and 49.9 nM, respectively) in homogenates of Xenopus embryos. These data suggest that malathion and malaoxon alter posttranslational modification of collagen, with resultant morphological defects in connective tissue.

HepG2 cells: an in vitro model for P450-dependent metabolism of acetaminophen.

The human hepatoma cell line, HepG2, retains many cellular functions often lost by cells in culture. This research examined the constitutive bioactivation of acetaminophen and P450-dependent activity in microsomes from HepG2 cells and the effect of 0.1% acetone pretreatment on these activities. Low levels of acetaminophen bioactivation, P450 IIE1 activity, and P450 IA1-IA2 activity were demonstrated in non-induced HepG2 microsomes. Acetone increased acetaminophen bioactivation and IIE1-dependent metabolism but not P450 IA1-IA2-dependent activity. Thus, HepG2 cells may provide an in vitro model for assessing human xenobiotic metabolism of acetaminophen and other drugs.

The effect of propylene glycol on the P450-dependent metabolism of acetaminophen and other chemicals in subcellular fractions of mouse liver.

Propylene glycol (PG) decreases the hepatotoxicity of acetaminophen (APAP). To elucidate the mechanism for this response, we measured the effect of PG on the in vitro metabolism of APAP by subcellular liver fractions from 6-10 week-old male B6C3F1 mice. The fractions were assayed for their ability to bioactivate APAP to N-acetyl-p-benzoquinone imine, which was trapped as APAP-glutathione conjugates or APAP-protein adducts, and for dimethyl-nitrosamine-N-demethylase (DMN), 4-nitrophenol hydroxylase (4-NPOH), and phenacetin-O-deethylase (PAD) activities. Activity in the crude mitochondrial-rich (10,000 x g pellet) fraction was low and PG had no effect. PG inhibited DMN and 4-NPOH, indicators of IIE1-dependent activity, and the formation of APAP-glutathione conjugates and APAP-protein adducts in both heavy (15,000 x g pellet) and light (100,000 x g pellet) microsomes. PAD, a measure of IA2-dependent activity, was not inhibited. These data demonstrate that PG selectively inhibits IIE1 activity, including the bioactivation of APAP, and implicates this as the mechanism for PG-mediated protection of APAP hepatotoxicity in mice.

Target site bioactivation of the neurotoxic organophosphorus insecticide parathion in partially hepatectomized rats.

Target organ bioactivation of phosphorothionate insecticides to their potent anticholinesterase oxon metabolites (for example, parathion to paraoxon) may be extremely important in toxicity because liver and blood provide so much potential protection by a variety of mechanisms, such as the aliesterases which serve as alternate phosphorylation sites. To determine whether the brain can produce sufficient oxon in vivo to contribute to toxicity, male rats were partially hepatectomized and injected i.v. with 1.5 mg/kg parathion. After 30 minutes, brain AChE was inhibited 68% whereas liver and plasma aliesterases were unaffected. Because aliesterases are far more sensitive to paraoxon inhibition than is brain AChE, these results indicate that neither the liver nor extra-hepatic tissues were contributing oxon into the blood stream. Thus target site activation of parathion occurred in vivo at sufficient levels to contribute substantially to toxicity.

Critical time periods and the effect of tryptophan in malathion-induced developmental defects in Xenopus embryos.

Xenopus laevis embryos were exposed to the organophosphorus insecticide malathion or its metabolite malaoxon during the first four days of development. The compounds produced the following defects in a dose dependent manner: reduced size, abnormal pigmentation, abnormal gut, enlargement of the atria and aorta, bent notochord and lowered NAD+ levels. Notochords were bent downward between the third and sixth somites with concurrent compression of the somites. Anterior intestine diameter was increased with a concurrent reduction in the number of intestinal loops. When tryptophan was administered along with malathion, NAD+ was measured at control levels or above, yet neither severity nor incidence of defects were reduced. The reduction of NAD+ does not seem to be responsible for the defects seen in Xenopus as occurs for some defects in avian species. In experiments to determine critical time of exposure, the final 48 h, which follow organogenesis and are primarily devoted to growth and development, seem most critical.