Effects of 1,1,1-trichloroethane on the cGMP metabolism in mouse brain

Final Report on the Safety Assessment of Trichloroethane

Trichloroethane functions in cosmetics as a solvent. Although Trichloroethane has been reported to the Food and Drug Administration (FDA) to be used in cosmetic products, an industry survey found that it is not in current use in the cosmetic industry. Trichloroethane is considered a Class I ozone-depleting substance by the Environmental Protection Agency (EPA) and its use is prohibited in the United States, unless considered essential. The FDA has stated that Trichloroethane's use in cosmetics is considered nonessential. Trichloroethane is detected by gas chromatography, gas chromatography-mass spectrometry, and gas-liquid chromatography. In rats, Trichloroethane, whether inhaled or injected, is mostly expelled intact from the body through exhalation. A very small percentage is excreted in the urine. In humans, Trichloroethane is rapidly absorbed through the skin and eliminated in exhaled air and a very small percentage is excreted in urine. Inhaled Trichloroethane is eliminated in exhaled air. Acute oral LD50 values have been reported as follows: 12.3 g/kg in male rats; 10.3 g/kg in female rats; 11.24 g/kg in female mice; 5.66 g/kg in female rabbits; and 9.47 g/kg in male guinea pigs. Acute toxicity studies using other routes of exposure, including subcutaneous injection and inhalation, produced no evidence of significant toxicity, except at very high exposure levels. Continuous inhalation exposure of rabbits to 750 mg/m3 for 90 days did not produce any signs of toxicity. Continuous exposure of rats, guinea pigs, rabbits, and monkeys to 500 ppm Trichloroethane for 6 months did not produce any signs of toxicity. Other short-term and subchronic inhalation exposures confirmed acute and short-term exposure findings that the toxic effects of inhalation were a function of both concentration and time. Rats receiving 750 or 1500 mg/kg day–1 Trichloroethane in corn oil by oral gavage 5 days per week for 78 weeks had reduced body weights and early mortality. Reduced body weights, decreased survival rates, and early mortality (in females) were found in mice dosed with 3000 or 6000 mg/kg day–1 (over the last 58 weeks; lower doses were administered for the first 20 weeks). Mice exposed to prolonged periods of Trichloroethane in an inhalation chamber had increased motor activity at levels up to 5000 ppm. Further increase of concentration of exposure resulted in less of an increase of motor activity until motor activity began to fall below normal at 10,000 ppm. Adverse effects on motor activity in rats were seen at exposures as low as 3000 ppm for 4 h. Rabbits had slight reddening and scaling after 10 24-h applications to abdominal skin of Trichloroethane mixed with 2.4% to 3.0% dioxane, and slight to moderate erythema, slight edema, and slight exfoliation was observed when 75% Trichloroethane and 25% tetrachloroethylene were applied to rabbit ears for 11 days. Undiluted Trichloroethane applied to the clipped backs of guinea pigs produced histopathologic damage in the epidermis. A primary irritation index of 5.22 (out of 8) was reported in rabbits. Trichloroethane applied to the eyes of rabbits resulted in transient irritation and apparent pain, but no corneal damage. There was no effect on gestation, pup survival, or growth in mice given Trichloroethane in drinking water at up to 5.83 mg/ml during mating and/or gestation. Rats exhibited no or minimal effects of ingestion of Trichloroethane up to 30 ppm in drinking water during mating and/or gestation. There was no effect on gestation, pup survival, or growth in mice or rats inhaling 875 ppm Trichloroethane. However, prenatal exposure of rodents to Trichloroethane can produce developmental toxicity in the form of delayed development in the offspring. Trichloroethane has been found to be mutagenic in the Ames assay in some studies and not mutagenic in others. Trichloroethane induced transformations in Fischer rat embryo cell system at 99 μM, was not mutagenic using the mouse lymphoma assay at up to 0.51 μg/ml, was equivocal in that assay when tested with S9, and was also equivocal in a sister-chromatid exchange assay using Chinese hamster ovarian (CHO) cells with and without S9. Mice ingesting 80,000 ppm Trichloroethane in their drinking water had an increase in the frequency of micronucleated normochromatic erythrocytes. A peripheral blood micronucleus test in female mice was negative. Trichloroethane was not carcinogenic to rats when administered 1500 mg/kg by oral gavage 5 days/week for 78 weeks or in mice administered 6000 mg/kg. Exposure to 1500 ppm Trichloroethane vapor for 6 h/day, 5 days/week for 2 years likewise gave no indications of oncogenic effects in rats or mice. People who have been exposed to Trichloroethane have reported dizziness, lassitude, unconsciousness, respiratory depression, peripheral vascular collapse, impaired postural control, mild encephalopathy, perioral tingling, burning on the tongue and discomfort in the hands and feet. The Cosmetic Ingredient Review (CIR) Expert Panel recognizes that Trichloroethane (1,1,1-Trichloroethane) has been declared a Class I ozone-depleting substance by the EPA and its use is limited to essential products. The FDA has determined that use of Trichloroethane in aerosol cosmetic products is considered nonessential. At issue for this assessment is the safety of direct exposure to individuals as a result of exposure to cosmetic products that may contain Trichloroethane. The Expert Panel found the available data to be sufficient to support the safety of Trichloroethane as a solvent in cosmetic products.

Peripheral sensory neuropathy associated with 1,1,1-trichloroethane

A case is described of peripheral sensory neuropathy in a woman who had daily exposure to 1,1,1-trichloroethane, used as a degreasing agent. Although previous reviews of the health effects of 1,1,1-trichloroethane have not indicated long-term neurotoxicity, there are recent animal studies that suggest chronic central neurotoxic effects and previous case reports of peripheral neuropathy in three exposed workers in one plant. Our case provides additional evidence that 1,1,1-trichloroethane exposure may be associated with peripheral sensory neuropathy. Reporting of similar cases is encouraged and investigation of the neurotoxic effects of 1,1,1-trichloroethane is recommended.

The use of experimental studies to reveal suspected neurotoxic chemicals as occupational hazards: acute and chronic exposures to organic solvents

The nervous system differs from many other body organs by its central control of vital functions and its low regeneration capacity. Organic solvents have, as a group, been suspected to have neurotoxic effects. Because of their similar physical properties and the fact that in industrial uses, they are often present in various mixtures, organic solvents have also been regarded, unfortunately, to induce common neurotoxic effects. However, it is evident from experimental studies using specified exposure conditions that different organic solvents have very diverse neurotoxic effects and also that the toxic mechanism may differ between acute and chronic exposure. No specific method used to describe a neurotoxic effect or single toxic response can be used for the overall occupational risk assessment of all organic solvents. Each solvent has to be considered as having its own unique toxic effects.

Effects of 1,1,1-trichloroethane on synaptosomal calcium accumulation in mouse brain

Addition of 1,1,1-trichloroethane (TCE), in vitro to synaptosomes isolated from the mouse cerebellum and cerebral cortex inhibited the slow phase of K+-stimulated 45Ca2+ influx and the net 45Ca2+ influx (delta k). In the brain stem, however, TCE increased the fast and slow phases of calcium uptake under depolarizing conditions and also delta k. The non-depolarized calcium influx was not altered by TCE added in vitro. Two hours after injection of TCE (2.4 g/kg) the calcium accumulation in the presence of high K+ was lowered in the cerebellar synaptosomes, while it was increased in brain stem synaptosomes. TCE administered in vivo did not alter the calcium influx into cerebrocortical synaptosomes nor did it affect the non-depolarization-induced 45Ca2+ influx. Thus, these data indicate that TCE may influence voltage-dependent calcium channels in mouse brain synaptosomes.

Actions of 1,1,1-trichloroethane on the cAMP metabolism in mouse brain

Inhalation or intraperitoneal administration of 1,1,1-trichloroethane (TCE) increased the cAMP content in the brain stem in a dose-related and time-dependent fashion. TCE had no effect on the cAMP level in the cerebellum and hippocampus, but slightly reduced that in the cerebral cortex. Following intraperitoneal administration of TCE the activity of norepinephrine- and F- -activated adenylate cyclase (AC) in a brain stem homogenate was enhanced, while the serotonin-stimulated AC activity was decreased. Neither the basal AC activity nor the guanine nucleotide- and forskolin-activated enzyme was affected by TCE. TCE had no effect on the soluble cAMP-dependent phosphodiesterase activity. It is suggested that the increased cAMP content in the brain stem induced by TCE may be mediated via adrenoreceptor interaction with the guanine nucleotide-binding regulatory component, resulting in activation of the catalytic unit of the adenylate cyclase and thereby an increase in the cAMP level.