Changes of free amino acid content in rat brain after exposure to trichloroethylene and tetrachloroethylene

Early lifestage exposure and potential developmental susceptibility to tetrachloroethylene

BACKGROUND

Tetrachloroethylene, also known as perchloroethylene or "perc", is a highly volatile and lipophilic solvent widely used in dry cleaning, textile processing, and metal-cleaning operations. The limited epidemiological and toxicological data available for exposure to perc during developmental lifestages, as well as the evidence for critical windows of exposure, highlight early life as a period of potential susceptibility.

METHODS

A literature search was performed to identify all peer-reviewed epidemiological and toxicologial studies examining outcomes from early lifestage exposure to perc, and reviewed by developmental stage for both exposure and outcome.

RESULTS

Exposure scenarios to perc unique to early lifestages include transplacental and breast milk intake, along with inhalation, ingestion, or dermal exposure. Toxicokinetics factors that may influence early lifestage susceptibility to perc, along with existing physiologically based pharmacokinetic (PBPK) models, are described. Adverse outcomes examined include: reproductive outcomes examined prior to conception including reduced fertility, adverse effects on sperm, or altered reproductive hormones; prenatal outcomes examined after exposure prior to conception or prenatally including fetal death, birth defects, and decreased birth weight; postnatal outcomes examined after exposure prior to conception, prenatally, or during childhood including neurotoxicity, immunotoxicity, cancer, hepatotoxicity, congential anomalies and mortality; and adult schizophrenia examined after exposure prior to conception.

CONCLUSIONS

The limited evidence on early lifestage exposure to perc does not provide sufficient evidence of this sensitive period as being more or less important than exposure at a later lifestage, such as during adulthood. However, there are a number of adverse health effects observed uniquely in early lifestages, and increased sensitivity to visual system deficits is suggested in children. Other outcomes observed in adults may not have been adequately assessed in children to directly compare sensitivity.

Alteration of brain neurotransmitters in female rat offspring induced by prenatal administration of 16 and 64 mg/kg of 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153)

PCB153 (2,2',4,4',5,5'-hexachlorobiphenyl), a non-coplanar PCB and the congener most widely distributed in the environment, was orally administered to pregnant Sprague-Dawley (Crj: CD (SD) IGS) rats from gestation day 10 through 16 at doses of 0 (control), 16 and 64 mg/kg body weight. Female pups were sacrificed at 1, 3, 6, and 9 wk, and at 1 yr of age to evaluate the differences in brain neurotransmitters and their metabolites between PCB153-exposed and control groups. Brain levels of norepinephrine (NE), 3-methoxy-4-hydroxyphenylglycol (MHPG), dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), serotonin (5HT), 5-hydroxyindoleacetic acid (5HIAA), acetylcholine (ACh), and choline (Ch) in discrete brain regions or in whole brain were measured. At 1 to 3 wk after birth, brain levels of DA, DOPAC, HVA, 5HT and 5HIAA in PCB-exposed groups were higher than those of the control group. At 9 wk after birth, DA turnover was reduced in half of the four brain areas examined (forebrain and hindbrain), and 5HIAA levels were increased in all brain areas in the PCB-treated group compared to those of the control group. At 1 yr after birth, the levels of DA, DOPAC, and HVA in the hippocampus, hypothalamus, and medulla oblongata were lower in the PCB-exposed groups than in the control group. Prenatal exposure to PCB153 stimulated the turnover of 5HT neurons in the brain of female offspring at early stages (1 to 9 wk) of development. On the other hand, the turnover of DA neurons in the PCB-exposed groups was reduced in late stages (9 wk to 1 yr) of development compared with that of the control group. The brain neurotransmitters of dams treated with PCB were assayed at 3 wk after delivery (15 wk old), and decreases in DA, DOPAC, and HVA were observed. PCB153 reduced the activity of DA neurons in the brain of dams. These results are discussed in relation to health effects observed in humans exposed to PCBs.

Alteration of brain levels of neurotransmitters and amino acids in male F344 rats induced by three-week repeated inhalation exposure to 1-bromopropane

The present study investigated the effects of 1-bromopropane (1BP) on brain neuroactive substances of rats to determine the extent of its toxicity to the central nervous system (CNS). We measured the changes in neurotransmitters (acetylcholine, catecholamine, serotonin and amino acids) and their metabolites or precursors in eight brain regions after inhalation exposure to 1BP at 50 to 1,000 ppm for 8 h per day for 7 d per week for 3 wk. Rats were sacrificed at 2 h (Case 1), or at 19 h (Case 2) after the end of exposure. In Case 1, the level of 5-hydroxyindoleacetic acid (5HIAA) was lowered in some brain regions by 1BP exposure. The decrease of 5HIAA in the frontal cortex was statistically significant at 50 ppm 1BP exposure. In Case 2, gamma-amino butyric acid (GABA) and taurine were decreased in many brain regions of exposed rats, and a significant decrease of taurine in the midbrain occurred at 50 ppm 1BP exposure. In both cases of 2-h and 19-h intervals from the end of exposure to sacrifice, aspartate and glutamine levels were elevated in many brain regions, but the acetylcholine level did not change in any brain region. Three-week repeated exposure to 1BP produced significantly changes in amino acid contents of rat brains, particularly at 1,000 ppm.

Chronic trichloroethylene intoxication: a new approach by trigeminal-evoked potentials?

Trigeminal nerve impairment is frequently seen in chronic trichlorethylene intoxication (TRI). A total of 104 occupationally exposed subjects were selected for study because they were employed at a highly exposed workplace. They were studied by clinical examination and by trigeminal somatosensory evoked potentials (TSEP). Normal values for TSEP were obtained from the study of 52 healthy nonexposed subjects. Facial hypoesthesia, when present, was global and predominant in the mandibular and maxillary nerve areas, associated or not with absent reflexes. A disturbed TSEP was found in 40 subjects which was predictable from their clinical symptoms. Correlation with exposure parameters (duration of exposure, trichlorethanol, and trichloracetic acid urinary rates) was mainly observed in subjects presenting both clinical and electrical alterations. Electrical alterations alone were less predictive. An abnormal TSEP may thus provide objective determination of risk assessment in the absence of clinical signs.

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

Administration of 1,1,1-trichloroethane (TCE) to mice by inhalation or intraperitoneally reduced the cGMP contents of the brain stem, cerebral cortex, and vermis anterior, including the hemispheres. Following intraperitoneal administration the cGMP contents of the vermis posterior and hippocampus were also reduced. To investigate the mechanism underlying these changes, the effects of TCE on brain guanylate cyclase (GC) and phosphodiesterase (PDE) activities were examined after intraperitoneal administration in mice. The basal GC activities in the particulate and soluble fractions of the homogenates of the cerebellum, brain stem and cerebral cortex were not altered by TCE. In the cerebellum TCE treatment inhibited sodium azide-stimulated GC activity in the particulate and soluble fractions, while in the brain stem it enhanced the particulate GC activity induced by Ca2+. TCE treatment increased the rate of cGMP hydrolysis in the cerebral cortex and this was further accelerated by addition of Ca2+. Ca2+ also increased the rate of cGMP hydrolysis in the brain stem. However, in the cerebellum TCE enhanced the Ca2+-independent PDE activity as well as the enzyme activity in the presence of Ca2+ and exogenous calmodulin. These results indicate that the reduction of the cGMP content in the brain stem and cerebral cortex in vivo on exposure to TCE is due to changes in the rate of cGMP hydrolysis. In the cerebellum the TCE reduced cGMP content may be regulated by increased rate of cGMP hydrolysis as well as effects on the guanylate cyclase.

Changes in free amino acid contents of rat brain induced by exposure to methyl bromide

Rats were exposed to methyl bromide (MB) for 24 h at 10-120 ppm or for 3 weeks at 1-10 ppm. Changes in free amino acid contents of rat midbrain were measured by high-performance liquid chromatography (HPLC). MB increased glutamine and aspartic acid contents dose-dependently by short-and long-term exposure. Alanine content was markedly increased by long-term exposure to 10 ppm MB. Glycine was dose-dependently increased, except at 120 ppm. The harmful effect of MB on the central nervous system is discussed in relation to the changes in amino acid metabolism.