Biomedical subjects
M A Mehlman
Publications and source records attributed to M A Mehlman.
Dangerous and cancer-causing properties of products and chemicals in the oil refining and petrochemical industry. VIII. Health effects of motor fuels: carcinogenicity of gasoline--scientific update.
1. Significant increases in tumors of kidney, liver, and other tissues and organs following exposure to gasoline provide sufficient evidence of carcinogenicity. 2. Benzene, a significant component of gasoline, has been established without question as a human carcinogen by IARC, EPA, and WHO. 3. 1,3-Butadiene, a component of gasoline, is a powerful carcinogen in both animals and humans. 4. Sufficient evidence for the carcinogenicity of alkyl benzenes, very significant components of gasoline, has also been established. 5. Human epidemiologic studies show important increases in cancers of the kidney, stomach, brain, pancreas, prostate, lung, and skin as well as hematopoietic and lymphatic leukemias as a result of exposure to gasoline, its components, and its vapors. 6. Stage 2 controls are being implemented to reduce exposure of the human population to gasoline vapors.
Dangerous and cancer-causing properties of products and chemicals in the oil-refining and petrochemical industries. Part IX: Asbestos exposure and analysis of exposures.
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Benzene health effects: unanswered questions still not addressed.
Data which could have helped answer many of the scientific questions posed in 1983 concerning the carcinogenicity of benzene are not yet available. Since we do not know of any safe level above zero, the problems that have been plaguing the health protection process relative to benzene can perhaps be best resolved by setting current recommended maximum levels of exposure to 0.004 to 0.1 ppm, and, to the extent possible, avoiding any exposure at all to benzene and benzene-containing products.
Dangerous and cancer-causing properties of products and chemicals in the oil refining and petrochemical industry--Part II: Carcinogenicity, mutagenicity, and developmental toxicity of 1,3-butadiene.
1,3-butadiene (BD) is present in synthetic rubber and motor fuels (gasoline). BD is shown to cause lymphocytic lymphomas, heart hemangiosarcomas, lung alveolar bronchiolar cancers, forestomach-squamous cell cancers, harderian gland neoplasms, preputial gland adenoma or carcinoma, liver-hepatocellular cancers, mammary gland acinar cell carcinomas, ovary-glanulosa cell carcinoma, brain cancers, pancreas adenoma and carcinoma, testis-Leydig cell tumors, thyroid follicular adenoma and carcinoma, and zymbal gland carcinoma in rodents and to date no exposure level has been established at which this chemical does not cause cancers. In humans BD causes increase in lymphomas, leukemias, and other cancers of hematopoietic systems and organs. BD is also a potent alkylating agent, directly toxic to developing embryos and damages progeny after parental exposure.
Dangerous properties of petroleum-refining products: carcinogenicity of motor fuels (gasoline).
Gasoline contains large numbers of dangerous and cancer-causing chemicals such as benzene, butadiene, toluene, ethylbenzene, xylene, trimethyl pentane, methyltertbutylether (MTBE) and many others. For the U.S. alone approximately 140 billion gallons of gasoline were consumed in 1989. An increase in only ten cents per gallon in price of gasoline generates 14 billion dollars in extra profit per year for oil industry cartel. Laboratory animals exposed to gasoline developed cancers in different tissues and organs. A number of epidemiological studies in humans provide evidence of increased cancer risk of leukemia, kidney, liver, brain, lymphosarcoma, lymphatic tissue pancreas and other tissues and organs.
A report on methods to reduce, refine and replace animal testing in industrial toxicology laboratories.
The Committee to Promote Principles of Reduction, Refinement and Replacement of Animal Testing in Industrial Toxicology Laboratories was established in 1987 to work toward industrywide improvements in laboratory animal testing methods. The committee's goals are to gather information about effective nonanimal testing techniques and other methods of conserving and improving the care of laboratory animals, to work toward the systematic validation of nonanimal alternatives, and to disseminate useful information about progressive programs and policies throughout the industrial toxicology community. This is the first in a continuing series of reports the committee plans to produce as part of an ongoing program to promote communication among industrial toxicologists about successful methods of reducing, refining and replacing animal testing. Here are some of the report's major findings: (1) Animal care and use committees charged with the oversight of laboratory animal use are a universal practice at the companies surveyed. (2) Significant reductions in the number of animals used for acute toxicity testing have taken place at all the companies during the last 5- to 10-year period. (3) Structure-activity relationships (predicting a test compound's properties based on the known properties of familiar chemicals with similar structures) are widely used to minimize, but not replace, the use of animals. (4) Tissue and organ culture systems are being used with increasing frequency for screening and mechanistic studies, but are not completely replacing animal evaluations as a final step. (5) There is a pressing need for the systematic and scientifically sound validation of nonanimal alternative techniques to reduce the use of animals in toxicology testing while satisfying requirements for the protection of public safety.
Developmental toxicity of Clarified Slurry Oil applied dermally to rats.
Clarified Slurry Oil (CSO), the heavy residual fraction from the fluidized catalytic cracker, was applied to the shaven backs of groups of 10 pregnant rats at doses of 0, 4, 8, 30, 125, and 250 mg/kg/day. All groups received the test material on gestation days 0-19. CSO was applied undiluted and left uncovered on the skin; collars were placed on the rats to minimize ingestion of the test material. Signs of maternal toxicity, some of which were seen at dose levels as low as 8 mg/kg/day, included vaginal bleeding, decreased body weight gain, reduced food consumption, death, increased relative liver weights, atrophy of the thymus, and aberrant serum chemistry. The number of fetal resorptions/deaths was markedly increased and the number of viable offspring decreased by CSO at dosages of 30 mg/kg/day and above. The group receiving 250 mg/kg/day carried no viable offspring. Fetuses from pregnant females exposed to CSO at dose levels in excess of 8 mg/kg/day were smaller than those from control and 4 mg/kg/day groups, and their skeletons showed decreased ossification. Abnormal external development and visceral development were observed in living and dead fetuses exposed in utero to CSO at dose levels as low as 8 mg/kg/day. Based on these data, 4 mg/kg/day represents the No-Observed-Adverse-Effect-Level for both maternal and developmental toxicity.
Pharmacokinetics and metabolism of benzene in Zymbal gland and other key target tissues after oral administration in rats.
Solid tumors have been reported in the Zymbal gland, oral and nasal cavities, and mammary gland of Sprague-Dawley rats following chronic oral administration of benzene. The cause for the specificity of such lesions remains unclear, but it is possible that tissue-specific metabolism or pharmacokinetics of benzene is responsible. Metabolism and pharmacokinetic studies were carried out in our laboratory with 14C-benzene at oral doses of 0.15 to 500 mg/kg to ascertain tissue retention, metabolite profile, and elimination kinetics in target and nontarget organs and in blood. Findings from those studies indicate the following: a) the Zymbal gland is not a sink or a site of accumulation for benzene or its metabolites even after a single high dose (500 mg/kg) or after repeated oral administration; b) the metabolite profile is quantitatively different in target tissues (e.g., Zymbal gland, nasal cavity), nontarget tissues and blood; and (c) pharmacokinetic studies show that the elimination of radioactivity from the Zymbal gland is biphasic.
A method for in vitro culture of rat Zymbal gland: use in mechanistic studies of benzene carcinogenesis in combination with 32P-postlabeling.
Zymbal glands were excised bilaterally from the ear ducts of female Sprague-Dawley rats (three/group), minced into approximately four fragments per gland, and transferred into a microtiter plate containing 1.5 mL per well of Waymouth's tissue culture medium supplemented with fetal calf serum, hydrocortisone, insulin, and gentamicin. After addition of a test compound or solvent vehicle, plates were incubated for 6, 24, 48, or 96 hr at 37 degrees C in a humidified atmosphere of 5% CO2 in air. Tissue in culture for 6 hr was histologically indistinguishable from the freshly excised tissue, while that in culture for 24, 48, and 96 hr showed a progressive deterioration often with necrosis and/or squamous metaplasia. More pronounced deterioration was noted in samples treated with 750 or 1500 micrograms/mL of benzene. Using a nuclease P1-enhanced 32P-postlabeling assay, aromatic DNA adducts were detected in cultured Zymbal glands exposed for 48 hr to benzene and its derivatives, as well as to 7,12-dimethylbenzanthracene (DMBA) and 2-acetylaminofluorene (AAF). Benzene produced very low levels of adducts (0.5 adducts per 10(9) nucleotides), whereas its congeners produced relatively high levels of adducts (50-2000 lesions per 10(9) nucleotides), which decreased in the order benzoquinone greater than hydroquinone greater than phenol greater than benzenetriol greater than catechol. Each adduct profile overall was characteristic for the compound studied, suggesting the formation of compound-specific electrophiles. AAF and DMBA adducts were identical to those formed in vivo in animals. Our results show that the Zymbal glands are capable of metabolizing different carcinogens to DNA-reactive intermediates, a process that may be causally associated with tumor formation in vivo in this organ.
32P analysis of DNA adducts in tissues of benzene-treated rats.
Solid tumors have been reported in the Zymbal gland, oral and nasal cavities, liver, and mammary gland of Sprague-Dawley rats following chronic, high-dose administration of benzene. The carcinogenic activity of benzene is thought to be caused by activation to toxic metabolites that can interact with DNA, forming covalent adducts. A nuclease P1-enhanced 32P-postlabeling assay, having a sensitivity limit of 1 adduct in 10(9-10) DNA nucleotides, was found suitable for measuring aromatic DNA adducts derived in vitro from catechol, benzenetriol (BT), phenol, hydroquinone (HQ), and benzoquinone (BQ), potential metabolites of benzene. When DNA specimens isolated from tissues of female Sprague-Dawley rats at 24 hr after an oral gavage dose of 200 to 500 mg/kg, 5 days/week, in olive oil (3 mL/kg) for 1 day, 1 week, 5 weeks, and 10 weeks were analyzed by the 32P-postlabeling procedure, no aromatic adducts were detected unequivocally with DNA samples of liver, kidney, bone marrow, and mammary gland. With Zymbal gland DNA, three weak spots at levels totaling four lesions per 10(9) DNA nucleotides were seen only after 10 weeks of treatment, and these adducts did not correspond chromatographically to major adducts in vitro from the above specified compounds. Consequently, this finding requires confirmatory experiments. This distinct adduct pattern may relate to tumor induction in this organ following benzene administration. Our results also indicate that DNA adducts derived from catechol, BT, phenol, HQ, and BQ are either not formed in vivo with benzene or formed at levels below the detection limit of 1 adduct per 10(9-10) DNA nucleotides.
Recent laboratory studies in chemical carcinogenesis: gasoline.
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Benzene: evaluation of control measures not competitive with basic research requirements.
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Toxicity and biochemical mechanisms of ozone.
Ozone is a reactive environmental oxidant molecule whose deleterious effects are enhanced by interaction with other photochemical oxidants. While the pulmonary system is the primary target for ozone toxicity, at a morphological and biochemical level, extrapulmonary toxic effects are well documented. The consequences of exposure to ozone depend on its concentration and are influenced by genetic and host factors. Ozone damage is in part mediated via free radicals formed in the processes of direct peroxidation of polyunsaturated fatty acids by ozone and oxidation of proteins, amines, and thiols. Antidoxidants such as Vitamin E which scavenge the chain-propagating free radicals and stop antioxidation serve as protectors in ozone-induced toxicity.
Health risk assessment of chemical mixtures.
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Systemic toxicity from subchronic dermal exposure, chemical characterization, and dermal penetration of catalytically cracked clarified slurry oil.
Clarified slurry oil (CSO), the heavy residual fraction from the fluidized catalytic cracker, was applied to the shaven backs of groups of 10 male and 10 female Sprague-Dawley rats 5 days/week for 13 weeks at doses of 8, 30, 125, or 500 mg/kg/day, and to another group for 2 weeks at doses of 2000 mg/kg/day. The rats were fitted with cardboard Elizabethan collars to minimize the ingestion of the test material, which was applied undiluted and remained uncovered on the skin. A similar group of rats served as controls; they were treated in the same manner except that no CSO was applied to their skin. There was a dose-related mortality and depression of body weight gain in the rats treated with CSO at doses of 30 mg/kg/day or greater; none of the rats dosed at 2000 mg/kg/day survived more than 2 weeks. The primary target organs of CSO toxicity were the liver, thymus, and bone marrow. The effects on the liver included increased weight (250% at 500 mg/kg/day), cholangiolitis, diffuse liver cell degeneration and hypertrophy, necrosis, fibrosis, decreased serum glucose, increased levels of alkaline phosphatase, aspartate aminotransferase, alanine amino transferase, bilirubin, and triglycerides. The thymus was found to be small and upon microscopic examination to be atrophic or hypoplastic. Erythroid hypoplasia was found in the bone marrow of some of the rats dosed at 30 mg/kg/day and increased in severity with increasing dose. The erythroid hypoplasia was accompanied by a dose-related anemia. Even in the rats dosed at 8 mg/kg/day, very slight abnormalities in the bile ducts were observed upon microscopic examination of the liver. Chromatographic separation and analyses demonstrated that CSO contains about 58% 3- to 5-ring polycyclic aromatic hydrocarbons (PAHs) and approximately 8-10% carbazole derivatives. In vitro and in vivo skin penetration studies demonstrated that the carbazole materials penetrate through the skin to a considerable extent (about 44%); less penetration was observed with 2- or 3-ring (8-13%) or 5-ring PAHs (3%).
Inhibition of the effects of thyroid hormone on rat liver by 5,5'-diphenylthiohydantoin.
Metabolites were measured in freeze-clamped livers from rats that had been maintained for 3 weeks on a stock diet supplemented with 0.1% 5,5'-diphenylthiohydantoin (DPTH). Compared with control animals, DPTH-treated animals had lower levels of phosphoenolypyruvate and 3-phosphoglycerate and elevated ratios of [ATP]/[ADP][Pi] and [NADP+]/[NADPH], suggesting mild hypothyroidism. Conversely, the administration of thyroxine (T4) for 5 days to animals fed the control diet resulted in elevated levels of phosphoenolpyruvate, 3-phosphoglycerate, and ketone bodies and lowered ratios of [ATP]/[ADP][Pi] and [NADP+]/[NADPH], consistent with the known effects of thyroid hormones on liver tissues. In animals simultaneously treated with DPTH and T4, the effects of thyroxine on the [NADP+]/[NADPH] ratio and the levels of phosphoenolypyruvate, 2-phosphoglycerate and ketone bodies were reversed. However, the calculated free cytoplasmic [ATP]/[ADP][Pi] ratio and the calculated cytochrome c3+/cytochrome c2+ ratio did not return to control values. This suggests that those actions of thyroid hormone which are mediated by potentiation of adrenergic effects are reversed by DPTH. These actions include a decrease in peripheral lipolysis, a reduction of the free cytoplasmic [NADP+]/[NADPH] ratio, and an apparent inhibition of the pyruvate kinase reaction, but DPTH apparently does not reverse the effects of thyroid hormone on mitochondrial O2 consumption and ATP generation.
Toxic air pollutants (TAP).
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