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Biomedical subjects

T Green

Publications and source records attributed to T Green.

At least 73 records · Page 4Linked to original sources
PubMed1996

The inhalation toxicology, genetic toxicology, and metabolism of difluoromethane in the rat.

Difluoromethane (HFC32) is under development as a replacement for chlorofluorocarbons (CFCs) in some refrigeration applications. It has been evaluated by standard studies of toxicity, developmental toxicity, and genotoxicity. In addition, the metabolism and disposition of HFC32 was investigated and a physiologically based pharmacokinetic (PB-PK) model constructed. Inhalation of HFC32 (up to 50,000 ppm) caused no organ-specific effects, but resulted in slight maternal toxicity to the pregnant rat and rabbit and some fetotoxicity to the rat. HFC32 did not sensitize the heart to adrenaline. The pharmacokinetics of [14C]difluoromethane (10,000 to 50,000 ppm/6 hr) revealed that about 2.1% of the inhaled HFC32 was absorbed and that steady state blood levels were achieved within 2 hr and were proportional to dose. Carbon dioxide was the major metabolite of HFC32 at all exposure levels. Carbon monoxide was not detected. The in vivo data were used to validate a PB-PK model to describe the uptake and metabolism of HFC32. Absorption and distribution are adequately described using rat blood:air and tissue:air partition coefficients. Metabolism, which was linear across the dose range, was described by a first order rate constant (Kf = 8.98 hr-1). Of the absorbed HFC32, about 63% was metabolized at all doses; however, when metabolism was expressed as a percentage of the inhaled dose it was much lower, being about 1.4% of the HFC32 entering the airways. Overall, the results indicate that HFC32 is of very low toxicity and should be an acceptable alternative to CFCs.

Animals↗
PubMed1996

In vitro T-lymphocyte response and house dust mite-induced bronchoconstriction.

BACKGROUND: There is considerable evidence that T cells may play an important role in asthma. The purpose of this study was to determine whether the responsiveness of T lymphocytes to mite allergen stimulation in vitro is a determinant of bronchial response to house dust mite (HDM) allergen challenge in subjects who are allergic to HDM. METHODS: Peripheral blood was taken from seven healthy nonatopic subjects and 23 subjects with positive skin test reactions to HDM. Of the subjects in the latter group, 16 had an asthmatic reaction on inhalation challenge with HDM extract (HDM-responders), whereas the remaining seven had a negative reaction (HDM allergic). The proportion of subsets of T lymphocytes and their activation and the amount of IL-2, IL-4, IL-5, and interferon-gamma released in the supernatants with and without stimulation with the HDM extract were determined. RESULTS: Without stimulation, the proportions of subsets of T lymphocytes and their activation were similar between groups. When stimulated with the HDM allergen, the proportion of CD4+CD25+ cells from HDM responders was significantly higher than those in the control group. Comparison within groups of cell cultures with and without stimulation with the mite allergen showed that the proportion of CD4+, CD4+CD25+, CD4+/CD8+, and CD3+HLADR+ cells were significantly increased in HDM responders with stimulation; there was a trend for CD4+CD25+ cells to be increased in the HDM-allergic subjects; no increase in any T-lymphocyte subsets was found in the control subjects. The release of IL-5 was significantly greater in HDM responsers than in the other two groups. The severity of the immediate asthmatic reaction was significantly associated with the degree of nonallergic bronchial hyperresponsiveness and the amount of IL-5 released but not with the level of specific IgE to the mite allergen or subsets of T lymphocytes with and without stimulation. CONCLUSION: The findings suggest that responsiveness of T lymphocytes to allergen challenge in vitro may play a role in determining the bronchial response to the allergen in vivo.

Animals↗
PubMed1996

DNA sequence analysis of methylene chloride-induced HPRT mutations in Chinese hamster ovary cells: comparison with the mutation spectrum obtained for 1,2-dibromoethane and formaldehyde.

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

Animals↗
PubMed1996

Lack of neurotoxic effect of diethylpropion in crack-cocaine abusers.

Dopamine agonists have been used with some success in treating cocaine addiction. However, both cocaine and psychostimulants have been reported to produce neurotoxic effects. We evaluated the effect of the stimulant diethylpropion on cognitive performance in a double-blind, placebo-controlled trial. Forty-six abstinent crack-cocaine users received either placebo, 25-mg, 50-mg, or 75-mg doses of diethylpropion. Patients were tested at baseline and again after 9-14 days of medication. There were no differences between placebo and medication groups on any test, indicating that, within the time frame studied, diethylpropion does not produce neurotoxic effects that can be detected with standardized neuropsychological tests.

Adult↗
PubMed1996

Granulomatous disease in common variable immunodeficiency: effect on immunoglobulin replacement therapy and response to steroids and splenectomy.

A 40 year old white woman with common variable immunodeficiency of four years duration presented with rapidly increasing splenomegaly. Despite high dose, weekly intravenous immunoglobulin, it was impossible to raise the trough serum IgG concentration to within the normal range. While waiting for a diagnostic splenectomy, low dose corticosteroids were started, leading to a decrease in the size of the spleen and an increase in the trough IgG concentration. Both spleen and liver showed non-caseating granulomas. Following splenectomy, the corticosteroids were tailed off and the trough IgG was maintained well into the normal range on a reduced, fortnightly dose of intravenous immunoglobulin and a low dose of oral corticosteroid.

Adult↗
PubMed1996

Adverse psychological events occurring in the first year after predictive testing for Huntington's disease. The Canadian Collaborative Study Predictive Testing.

A total of 135 participants in the Canadian predictive testing programme for HD were followed for at least one year in one of four study groups: increased risk (n = 37), decreased risk ( n = 58), uninformative (n = 17), or not tested (n = 23). Clinical criteria for an adverse event were a suicide attempt or formulation of a suicide attempt plan, psychiatric hospitalisation, depression lasting longer than two months, a marked increase in substance abuse, and the breakdown of important relationships. Quantitative criteria, as measured by changes on the General Severity Index of the Symptom Checklist 90-R and the Beck Depression Inventory, were also used to identify people who had adverse events. Twenty of the 135 participants (14.8%) had an adverse event. There were no significant differences between those with or without an adverse event with respect to age, sex, marital status, education, psychiatric history, general psychiatric distress, or social supports at baseline. However, evidence for depression was associated with an increased frequency of adverse events (p < 0.04). The adverse events were similar and seen with equivalent frequency in those receiving an increased risk or decreased risk and persons at risk who did not receive a modification of risk. However, a significant difference was found in the timing of adverse events for the increased and decreased risk groups (p < 0.0002). In the increased risk group all of the adverse events occurred within 10 days after results whereas, in the decreased risk group, all of the adverse events occurred six months or later after reviewing test results. These results suggest that people entering into predictive testing with some evidence of clinical depression warrant special vigilance and also suggest that counselling and support should be available for all participants in predictive testing irrespective of the direction of test results.

Adolescent↗
PubMed1996

Metabolism and disposition of difluoromethane (HFC32) in the mouse.

1. Difluoromethane (HFC32) is under development as a replacement for chlorofluorocarbons (CFCs) in some refrigeration applications. 2. The metabolism and disposition of [14C]-difluoromethane ([14C]-HFC32) was determined in male Swiss mice as a consequence of a single 6 h inhalation exposure to atmospheres of 10 000 p.p.m. 3. Of the inhaled dose, about 1-2% was recovered in expired air, urine, faeces and carcass suggesting that systemic absorption of this hydrofluorocarbon from the alveolar air space of the lung into blood is poor. Upon cessation of exposure the majority of the systemically absorbed HFC32 was exhaled within 1 h. 4. Carbon dioxide was a major metabolite of HFC32. Carbon dioxide measured post-exposure accounted for about 0.3% of the inhaled dose. Urinary and faecal excretion of non-volatile metabolites accounted for about 0.34% and 0.07% of the inhaled dose, respectively. 5. Carbon monoxide could not be detected. 6. Total metabolism, measured as the sum of the radioactivity recovered in urine, faeces, as carbon dioxide and that retained in the carcass, amounted to about 0.8% of the inhaled dose, equivalent to 64% of the total radioactivity recovered. 7. Analysis of a range of tissues at 4 days post-exposure showed a relatively uniform distribution of radioactivity with the highest concentration in the lung, liver and kidney. There was no evidence of a specific retention in any organ or tissue.

Absorption↗
PubMed1996

Evaluation of the potential carcinogenicity and genetic toxicity to humans of the herbicide acetochlor.

Comprehensive toxicological studies of the herbicide acetochlor are presented and discussed. Although it gave a negative profile of responses in the many toxicity tests conducted there were some findings that prompted further investigation. First, although non-mutagenic in the Salmonella assay, acetochlor was clastogenic to mammalian cells treated in vitro. This clastogenic potential was not expressed in vivo in four rodent cytogenetic assays (bone marrow and germ cells). Second, although acetochlor gave a negative response in rat liver UDS assays when tested at the acute MTD, gavage administration of a single, supra-MTD dose (2000 mg/kg) gave a weak positive assay response. This dose-level (2000 mg/kg) was necrotic to the liver, depressed hepatic glutathione levels by up to approximately 80%, altered the metabolism of acetochlor, and was associated with up to 33% lethality. In contrast, reference liver genotoxins such as DMN, DMH and 2AAF were shown to elicit UDS in the absence of such effects, and at approximately 400 x lower dose-levels. Finally, microscopic nasal polypoid adenomas were induced in the rat when acetochlor was administered for two years at the maximum tolerated dose (MTD). The tumours were not life-threatening, they did not metastasize, and no DNA damage was induced in the nasal cells of rats maintained on a diet containing the MTD of acetochlor for either 1 or 18 weeks (comet assay). In order to probe the mechanism of action of these high dose toxicities a series of chemical and genetic toxicity studies was conducted on acetochlor and a range of structural analogues. These revealed the chloroacetyl substructure to be the clastogenic species in vitro. Although relatively inert, this substituent is preferentially reactive to sulphydryl groupings, most evidently, to glutathione (GSH). Similar chemical reactivity and clastogenicity in vitro was observed for two related chemicals bearing a chloroacetyl group, both of which have been defined as non-carcinogens in studies reported by the US.NTP. These collective observations indicate that the source of the clastogenicity of acetochlor in vitro is also the source of its rapid detoxification in the rat in vivo, via reaction with GSH. Metabolic studies of acetochlor are described which reveal the formation of a series of GSH-associated biliary metabolites in the rat that were not produced in the mouse. The metabolism of acetochlor in the rat changes with increasing dose-levels, probably because of depletion of hepatic GSH. It is most likely that a rat-specific metabolite is responsible for the rat nasal tumours observed uniquely at elevated dose-levels. The absence of genetic toxicity to the nasal epithelium of rats exposed acutely or subchronically to acetochlor favours a non-genotoxic mechanism for the induction of these adenomas. The observation of a time- and dose-related increase in S-phase cells in the nasal epithelium is consistent with this conclusion. Despite some confusion caused by the early use of perilethal gavage administrations of acetochlor to rodents, and supra-MTD dietary concentrations in some of the chronic studies, the available MTD data are consistent with acetochlor not posing a genetic or carcinogenic hazard to humans.

Adenomatous Polyps↗
PubMed1995

The incorporation of radiolabelled sulphur from captan into protein and its impact on a DNA binding study.

Repeated administration of high doses of captan is known to produce tumours specifically in the duodenum of mice. Captan is not carcinogenic in the rat. In this study, DNA purified from the liver, stomach, duodenum and jejenum of mice dosed with 35S radiolabelled captan was found to contain radioactivity equivalent to Covalent Binding Indices in the range 38-91; that from the bone marrow had a CBI of 2.8. The distribution of radioactivity between the various tissues did not reflect the target organ specificity of captan. Attempts to further purify the DNA samples using caesium chloride gradients resulted in partial separation of the radioactivity from the DNA suggesting that covalent binding to the DNA may not have occurred. A study of the chemical breakdown of captan showed that captan is unstable, producing a variety of potentially reactive species containing sulphur. Evidence was further obtained to show that the sulphur of captan is incorporated into endogenous amino acids and protein. Hepatic DNA from mice dosed with 35S radiolabelled N-acetylcysteine, and two thiazolidine derivatives which are analogous to known metabolites of captan, was radiolabelled to a similar extent to that from captan treated mice. Furthermore, the DNA from each of these treatments had similar properties on caesium chloride gradients. It was concluded that the radioactivity associated with DNA in the captan DNA binding study was present in the low levels of protein which are always associated with purified DNA samples.

Acetylcysteine↗
PubMed1995

Expression of recombinant homo-oligomeric 5-hydroxytryptamine3 receptors provides new insights into their maturation and structure.

A recombinant baculovirus containing a mouse 5-hydroxytryptamine3 (5-HT3) receptor subunit cDNA under the control of the polyhedrin promoter was shown to direct the production of large amounts of functional 5-HT3 receptor in insect cells, as assayed by Western blotting and ligand binding. After solubilization, the receptor was purified to homogeneity by affinity chromatography and characterized pharmacologically. The ligand binding characteristics of the recombinant receptor were essentially identical to those of the native receptor, both before and after purification. Only fully glycosylated receptors bound to the ligand affinity resin, although subsequent removal of the sugar did not affect ligand binding. Visualization of the purified receptor using electron microscopy showed that the receptor preparation contained a homogeneous population of pentameric doughnut-shaped particles. The general appearance of the recombinant homo-oligomeric channels was indistinguishable from that of native 5-HT3 receptors. Yields of purified receptors were of the order of 200 micrograms/3 liters of original culture. The amount and homogeneity of the purified receptor are sufficient to begin preliminary crystallization trials.

Animals↗
PubMed1995

Methylene chloride-induced DNA damage: an interspecies comparison.

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

Animals↗
PubMed1995

Identification and quantification of fluorine-containing metabolites of 1-chloro-2,2,2-trifluoroethane (HCFC133A) in the rat by 19F-NMR spectroscopy.

1-Chloro-2,2,2-trifluorethane (HCFC133a) causes a reduction in testis weight and germinal epithelial cell atrophy in the rat following exposure by inhalation at concentrations of 10,000 ppm and above. Following administration by gavage, an increased incidence of Leydig cell tumors of the testis was seen. The metabolism of HCFC133a has been investigated in respect to the known toxicity of this compound. Male rats were exposed by inhalation to an atmosphere of 50,000 ppm HCFC133a for a period of 6 hr. Analysis of urine, collected during the exposure period and up to 48 hr following exposure, by 19F-NMR spectroscopy identified 2,2,2-trifluoroethanol (TFE; and its beta-glucuronide), trifluoroacetaldehyde (TFAA; as its hydrate and urea adduct), and trifluoroacetic acid (TFA) as fluorine-containing metabolites of HCFC133a. Of the total amount of metabolite eliminated in urine, 83% was excreted within 24 hr postdose, establishing a rapid elimination of metabolites by this route. TFAA, an established testicular toxicant, was the major metabolite accounting for 57% of the total fluorinated metabolites eliminated in urine, whereas TFA and TFE accounted for 29% and 14%, respectively. The presence of these metabolites in urine is consistent with an oxidative route of metabolism of this fluorocarbon.

Animals↗
PubMed1994

Methylene chloride: an inhalation study to investigate toxicity in the mouse lung using morphological, biochemical and Clara cell culture techniques.

Single exposures of mice to methylene chloride (MC) cause vacuolation and necrosis of the bronchiolar Clara cells which subsequently recover normal morphology on continued exposure. Both cytochrome P-450 (CYP)- and glutathione S-transferase (GST)-dependent metabolism of MC are known to occur. The current studies have investigated the metabolism of MC in mouse lung using inhibitors of both GST and CYP-dependent routes of metabolism, the consequences of metabolic inhibition on the Clara cell vacuolation, and any changes in cell proliferation, assessed in vitro, in Clara cells cultured from exposed individuals. Vacuolated bronchiolar cells were seen in mice exposed to 2000 and 4000 ppm MC but were not seen at lower concentrations, while addition of the CYP inhibitor, piperonyl butoxide, significantly reduced the bronchiolar cell vacuolation seen following exposure to 2000 ppm MC. Treatment of mice with the glutathione depletor, buthionine sulphoximine, had no effect on the number of vacuolated bronchiolar cells following MC. Exposure of mice to 1000 ppm MC and above for 6 h caused a burst of DNA synthesis in bronchiolar Clara cells cultured in vitro from the lungs of exposed animals. The results suggest that the Clara cell vacuolation following MC exposure is mediated via CYP metabolism, that depression of the CYP metabolic pathway occurs following exposure, and that Clara cell vacuolation may have a priming role in stimulating cell proliferation in the unaffected cell population.

Administration, Inhalation↗
PubMed1994

The role of formaldehyde and S-chloromethylglutathione in the bacterial mutagenicity of methylene chloride.

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

Animals↗
PubMed1994

Relationship between hepatic DNA damage and methylene chloride-induced hepatocarcinogenicity in B6C3F1 mice.

Methylene chloride (MC) induced DNA damage in freshly isolated hepatocytes from mice and rats, which was detectable as single-strand (ss) breaks by alkaline elution. The lowest in vitro concentration of MC needed to induce DNA damage in mouse hepatocytes (0.4 mM) was much lower than for rat hepatocytes (30 mM), and is close to the calculated steady-state concentration of MC in the mouse liver (1.6 mM) at a carcinogenic dose (4000 p.p.m. by inhalation). DNA ss breaks were also detectable in hepatocyte DNA from mice which had inhaled 4000 p.p.m. MC for 6 h, but not in hepatocyte DNA from rats similarly exposed. In studies with hepatocytes cultured overnight in the presence of buthionine sulfoximine to deplete glutathione (GSH), subsequent exposure to MC resulted in less DNA damage in the GSH-depleted cells. This shows that conjugation of MC with GSH is important in its activation of DNA-damaging species in the liver. The GSH pathway of MC metabolism produces two potential DNA-damaging species, formaldehyde and S-chloromethylglutathione (GSCH2Cl). Formaldehyde is known to cause DNA ss breaks in cells. However, the lowest concentration of formaldehyde required to induce a significant amount of DNA ss breaks in mouse hepatocytes (0.25 mM) is unlikely to be formed following in vitro or in vivo metabolism of MC at concentrations that induce similar amounts of DNA damage. That formaldehyde does not play a role in this DNA damage has been confirmed in experiments with CHO cells exposed to MC and an exogenous activation system from mouse liver (S9 fraction). Formaldehyde was responsible for the DNA- protein cross-linking effect of MC, but did not cause the DNA damage leading to ss breaks. These DNA ss breaks are likely to be caused by GSCH2Cl. The results suggest a genotoxic mechanism for MC carcinogenicity in the mouse liver, and support the proposal that the observed species differences in liver carcinogenicity result from differences in the amount of MC metabolism via the GSH pathway in the target organ.

Animals↗