Examination of low-incidence brain tumor responses in F344 rats following chemical exposures in National Toxicology Program carcinogenicity studies.
(1/21)
Neoplasms in the brain are uncommon in control Fischer 344 (F344) rats; they occur at a rate of less than 1% in 2-yr toxicity/carcinogenicity studies. Furthermore, only 10 of nearly 500 studies conducted by the National Toxicology Program (NTP) showed any evidence of chemically related neoplastic effects in the brain. Generally, the brain tumor responses were considered equivocal, because the characteristics of potential neurocarcinogenic agents (such as statistically significant increased incidences, decreased latency and/or survival, and demonstration of dose-response relationships) were not observed. A thorough examination, including comparisons with a well-established historical database, is often critical in evaluating rare brain tumors. Chemicals that gave equivocal evidence of brain tumor responses were generally associated with carcinogenicity at other sites, and many chemicals were mutagenic when incubated with metabolic activating enzymes. Other factors that were supportive of the theory that marginal increases in brain tumor incidence were related to chemical exposure were that (a) some of the tumors were malignant, (b) no brain neoplasms were observed in concurrent controls from some studies, and/or (c) brain tumors were also seen following exposure to structurally related chemicals. In 2-yr studies in F344 rats (studies conducted by the NTP), equivocal evidence of carcinogenicity was observed for the following 9 chemicals: isoprene, bromoethane, chloroethane, 3,3'-dimethylbenzidine dihydrochloride, 3,3'-dimethoxybenzidine dihydrochloride, furosemide, C.I. direct blue 15, diphenhydramine hydrochloride, and 1-H-benzotriazole. Glycidol was the only chemical evaluated by the NTP with which there was clear evidence of brain tumor induction in F344 rats. Clarification of the potential neurocarcinogenic risks of chemicals that produce equivocal evidence of a brain tumor response in conventional 2-yr rodent studies may be aided by the use of transgenic mouse models that exhibit genetic alterations that reflect those present in human brain tumors as well as by the use of in utero exposures. (+info)
Warm air sensation for assessment of block after spinal anaesthesia.
(2/21)
We have evaluated a new method of assessing dermatomal sensory levels after regional anaesthesia based on warm sensation. Sensory levels were assessed in 30 patients after spinal anaesthesia using a respiratory gas humidifier, adapted to deliver a constant flow of warm air at 40 +/- 0.2 degrees C. This was compared with the cold sensation from ethyl chloride spray. The frequency distribution of the dermatomal differences showed 96.6% of the comparisons were between +1 and -1 dermatomes. The median difference in dermatomal levels between the two methods of assessment was 0 (interquartile range 0-1) (P = 0.65). We conclude that the warm air method compares favourably with ethyl chloride spray and both can be used interchangeably. (+info)
Commensal interactions in a dual-species biofilm exposed to mixed organic compounds.
(3/21)
There is limited knowledge of interspecies interactions in biofilm communities. In this study, Pseudomonas sp. strain GJ1, a 2-chloroethanol (2-CE)-degrading organism, and Pseudomonas putida DMP1, a p-cresol-degrading organism, produced distinct biofilms in response to model mixed waste streams composed of 2-CE and various p-cresol concentrations. The two organisms maintained a commensal relationship, with DMP1 mitigating the inhibitory effects of p-cresol on GJ1. A triple-labeling technique compatible with confocal microscopy was used to investigate the influence of toxicant concentrations on biofilm morphology, species distribution, and exopolysaccharide production. Single-species biofilms of GJ1 shifted from loosely associated cell clusters connected by exopolysaccharide to densely packed structures as the p-cresol concentrations increased, and biofilm formation was severely inhibited at high p-cresol concentrations. In contrast, GJ1 was abundant when associated with DMP1 in a dual-species biofilm at all p-cresol concentrations, although at high p-cresol concentrations it was present only in regions of the biofilm where it was surrounded by DMP1. Evidence in support of a commensal relationship between DMP1 and GJ1 was obtained by comparing GJ1-DMP1 biofilms with dual-species biofilms containing GJ1 and Escherichia coli ATCC 33456, an adhesive strain that does not mineralize p-cresol. Additionally, the data indicated that only tower-like cell structures in the GJ1-DMP1 biofilm produced exopolysaccharide, in contrast to the uniform distribution of EPS in the single-species GJ1 biofilm. (+info)
Acute, subacute, and subchronic oral toxicity studies of 1,1-dichloroethane in rats: application to risk evaluation.
(4/21)
1,1-Dichloroethane (DCE) is a solvent that is often found as a contaminant of drinking water and a pollutant at hazardous waste sites. Information on its short- and long-term toxicity is so limited that the U.S. EPA and ATSDR have not established oral reference doses or minimal risk levels for the volatile organic chemical (VOC). The acute oral LD(50) in male Sprague-Dawley (S-D) rats was estimated in the present study to be 8.2 g/kg of body weight (bw). Deaths appeared to be due to CNS depression and respiratory failure. In an acute/subacute experiment, male S-D rats were given 0, 1, 2, 4, or 8 g DCE/kg in corn oil by gavage for 1, 5, or 10 consecutive days. The animals were housed in metabolism cages for collection of urine and sacrificed for blood and tissue sampling 24 h after their last dose. There were decreases in body weight gain and relative liver weight at all dosage levels, as well as increased renal nonprotein sulfhydryl levels at 2 and 4 g/kg after 5 and 10 days. Elevated serum enzyme levels, histopathological changes, and abnormal urinalyses were not manifest. For the subchronic study, adult male S-D rats were gavaged with 0.5, 1, 2, or 4 g DCE/kg 5 times weekly for up to 13 weeks. Animals receiving 4 g/kg exhibited pronounced CNS depression, with more than one-half dying by week 11. The 2-g/kg rats exhibited moderate CNS depression. One 2-g/kg rat died during week 6. There were very few manifestations of organ damage in animals that succumbed or in survivors at any dosage level. Decreases in bw gain and transient increases in enzymuria were noted at 2 and 4 g/kg. Serum enzyme levels and blood urea nitrogen were not elevated, nor were glycosuria or proteinuria present. Chemically induced histological changes were not seen in the liver, kidney, lung, brain, adrenal, spleen, stomach, epididymis, or testis. Hepatic microsomal cytochrome P450 experiments revealed that single, high oral doses of DCE did not alter total P450 levels, but did induce CYP2E1 levels and activity and inhibit CYP1A1 activity. These effects were reversible and regressed with repeated DCE exposure. There was no apparent progression of organ damage during the 13-week subchronic study, nor appearance of adverse effects not seen in the short-term exposures. One g/kg orally (po) was found to be the acute, subacute, and subchronic LOAEL for DCE, under the conditions of this investigation. In each instance, 0.5 g/kg was the NOAEL. (+info)
Venous cannulation and topical ethyl chloride in patients receiving nitrous oxide.
(5/21)
The purpose of this study was to evaluate the effect of ethyl chloride spray on the anxiety and pain associated with placing an intravenous catheter in patients sedated with nitrous oxide. Eighty-eight patients scheduled for dental surgery with a combination of intravenous and nitrous oxide sedation were randomly assigned to have ethyl chloride spray or a placebo, water spray, applied before cannulation of a vein. Anxiety and pain were reported using a 10.0-cm visual analog scale before nitrous oxide administration, after nitrous oxide sedation, following application of the spray, and following venous cannulation. The first 2 assessments measured overall levels of patient anxiety and pain and confirmed that nitrous oxide sedation reduced anxiety without changing already low levels of pain. The second 2 assessments of anxiety and pain measured the reaction toward the spray and cannulation. The application of ethyl chloride spray produced significantly more anxiety and pain than did the placebo. The results of this study demonstrate that ethyl chloride spray does not significantly reduce the anxiety and pain associated with venous cannulation in patients sedated with nitrous oxide. (+info)
Chlorozotocin, 2-(3-(2-chloroethyl)-3-nitrosoureido)-D-glucopyranose, an antitumor agent with modified bone marrow toxicity.
(6/21)
Chlorozotocin, 2-(3-(2-chloroethyl)-3-nitrosoureido)-D-glucopyranose, is a newly synthesized, water-soluble nitrosourea antitumor agent that is active against L1210 leukemia in mice. A 701% and a 401% increase in life-span were attained with a dose that was lethal to 10% of the animals (15 to 20 mg/kg, i.p.) in mice treated on Day 2 or Day 6 of L1210 tumor growth, respectivley. Sixity % of Day 2-treated mice and 30% of Day 6-treated mice survived for 90 days. At the maximally effective dose against L1210, chlorozotocin produced no significant depression in normal bone marrow DNA synthesis nor in peripheral neutrophil count, in contrast to a sustained greater than 90% inhibition in L1210 ascites cell DNA synthesis. If the antitumor activity and reduced bone marrow toxicity of chlorozotocin are confirmed in man the use of this compound would facilitate treatment of patients with neoplastic disease who have preexisting abnormal bone marrow function or would allow for the more effective use of a nitrosourea agent in combination with anticancer agents possessing more potent myelosuppressive properties. (+info)
Microbial dehalorespiration with 1,1,1-trichloroethane.
(7/21)
1,1,1-Trichloroethane (TCA) is a ubiquitous environmental pollutant because of its widespread use as an industrial solvent, its improper disposal, and its substantial emission to the atmosphere. We report the isolation of an anaerobic bacterium, strain TCA1, that reductively dechlorinates TCA to 1,1-dichloroethane and chloroethane. Strain TCA1 required H2 as an electron donor and TCA as an electron acceptor for growth, indicating that dechlorination is a respiratory process. Phylogenetic analysis indicated that strain TCA1 is related to gram-positive bacteria with low DNA G+C content and that its closest relative is Dehalobacter restrictus, an obligate H2-oxidizing, chloroethene-respiring bacterium. (+info)
Biological and biochemical properties of 1-(2-chloroethyl)-3-(beta-D-glucopyranosyl)-1-nitrosourea (NSC D 254157), a nitrosourea with reduced bone marrow toxicity.
(8/21)
1-(2-Chloroethyl)-3-(beta-D-glucopyranosyl)-1-nitrosourea (GANU), a water-soluble nitrosourea, differs from 2-[3-(2-chloroethyl)-3-nitrosoureido]-D-glucopyranose (chlorozotocin) by the placement of the cytotoxic group on C-1 of glucose. Its biological and biochemical properties are compared with those of chlorozotocin. At a 10% lethal dose (10 mg/kg i.p.), GANU demonstrates minimal myelosuppression. This dose failed to depress normal bone marrow DNA synthesis, in contrast to a 96% inhibition in L1210 DNA synthesis. In L1210 cell suspension, equimolar doses of GANU and chlorozotocin produced equivalent degrees of inhibition in DNA synthesis. GANU has significant L1210 activity in BALB/c X DBA/2 F1 mice treated on Day 2 of tumor growth. A 117% increased life-span and 15% 45-day survivors are atained with 15 mg/kg i.p., a 50% lethal dose. However, in concurrent studies using randomly selected littermate groups of mice, GANU proved less active than chlorozotocin which produced a 306% increased life-span (15 mg/kg i.p.). GANU and chlorozotocin have similar in vitro alkylating activity but the in vitro carbamoylating activity of GANU is sevenfold that of chlorozotocin. On a molar basis, the lethal toxicity of GANU is twice that of chlorozotocin. The significant carbamoylating activity of GANU may contribute to its greater toxicity and therefore limit the mumoles of alkylating agent that can be administered to the tumor. These structure-activity studies further confirm that the addition of a glucose carrier to a cytotoxic nitrosourea moiety can selectively reduce bone marrow toxicity while retaining antitumor activity. (+info)