Mode of Cell Death in Mouse Brain Following Early Exposure to Low-Dose Trichloroethane: Apoptosis or Necrosis

The goal of this study was to investigate, in-vivo , the predominant mechanism of cell death, apoptosis versus necrosis, in the mature mouse brain exposed early to a ubiquitous environmental toxicant trichloroethane (TCE). A subset of male albino mice was injected intraperitoneally twice weekly for three weeks with TCE (100 and 400µg/kg). All animals were followed up for signs of toxicity and mortality. Changes in neural tissues were histpathologically evaluated. Biomarkers of brain cell number were also studied. The results showed that TCE insult triggered significant alterations in the microstructure of the brain tissues compared to controls. Mitotic figures and apoptotic changes such as chromatin condensation and nuclear fragments were also identified. Cell death analysis demonstrates that cell apoptosis with necrosis was evident in the TCE-treated groups. The percent of necrosis was quantified as 20.09 ± 2.57% at 100µg/kg TCE, 30.57 ± 5.18% at 400µg/kg TCE, and 12.67 ± 1.25% in controls. However, the percent of apoptosis was quantified as 29.18 ± 1.51% at 100µg/kg TCE, 20.14 ± 2.12% at 400µg/kg TCE, and 8 ± 1.25% in controls. There was also a significant reduction in the brain DNA content in the TCE-treated groups. Agarose gel electrophoresis is also provided further biochemical evidence of apoptosis by showing internucleosomal DNA fragmentation. These results correlated with neurobehavioral impairment. These findings indicate that TCE induces degeneration and apoptotic cell death in mouse brain, suggesting a crucial role played by apoptosis in TCE neurotoxicity.