Trichloroethylene and its metabolite TaClo lead to degeneration of substantia nigra dopaminergic neurones: Effects in wild type and human A30P mutant α-synuclein mice

Abstract

Parkinson's disease (PD) is characterised pathologically by degeneration of the dopaminergic (DA) neurones of the substantia nigra pars compacta (SNpc) and the presence of α-synuclein containing Lewy body inclusions. Trichloroethylene (TCE) has been suggested as a potential environmental chemical that may contribute to the development of PD, via conversion to the neurotoxin, 1-Trichloromethyl-1,2,3,4-tetrahydro-β-carboline (TaClo). We investigated the effect of an 8 week exposure to TCE or TaClo on wild type and, as an experimental model of PD, A30P mutant α-synuclein overexpressing mice using a combination of behaviour and pathology. TCE or TaClo exposure caused significant DA neuronal loss within the SNpc in both wild type and transgenic mice. Cell numbers were lower in A30P animals than wild type, however, no additive effect of TCE or TaClo exposure and A30P overexpression was found. TCE or TaClo did not appear to lead to acceleration of motor or cognitive deficits in either wild type or A30P mutant mice, potentially because of the modest reductions of DA neuronal number in the SNpc. Our results do however suggest that TCE exposure could be a possible factor in development of PD like changes following exposure.

Keywords: Neurodegeneration; Parkinson’s disease; TaClo; Trichloroethylene; α-Synuclein.

Fig. 1

Effect of TCE and TaClo on A30P α-synuclein and wild type C57BL/6 Mice on Motor Function Using Rotarod. Average fall latency (sec) of vehicle (10 ml/kg olive oil), TCE (100 mg/kg) or TaClo (2 mg/kg), treated wild type or A30P C57BL/6 mice over time, triplicate trials. Data presented as mean ± SEM (n = 8–10). Significant difference over time (p < 0.05, p < 0.001 respectively), No significant difference between treatment groups or of treatment over time, Two-Way (treatment, time) Repeated Measures ANOVA.

Fig. 2

Effect of TCE and TaClo on wild type and A30P α-synuclein C57BL/6 Mice as Assessed by the Pole Test. Average (A) total time, and (B) Number of falls per trial of vehicle (10 ml/kg olive oil), TCE (100 mg/kg) or TaClo (2 mg/kg), treated wild type or A30P α-synuclein overexpressing C57BL/6 mice over time, triplicate trials. Data presented as mean ± SEM (n = 8–10 animals per group). A significant effect of time was seen on time to complete the task for all groups (p < 0.05). No significant difference between treatment groups or of treatment over time was observed, Two-Way (time, treatment) Repeated Measures ANOVA.

Fig. 3

Effect of TCE and TaClo on wild type and A30P α-synuclein overexpressing C57BL/6 Mouse Spatial Learning Assessed by the Barnes Maze. Average (A) primary latency, (B) total latency (both sec), (C) primary errors and (D) total errors to find target of vehicle (10 ml/kg olive oil), TCE (100 mg/kg) or TaClo (2 mg/kg), treated wild type or A30P α-synuclein overexpressing C57BL/6 mice over time, quadruplicate trials. Data presented as mean ± SEM (n = 8–10). (A and B) Significant difference over time (p < 0.001), No significant difference between treatment groups or of treatment over time, Two-Way Repeated Measures ANOVA.

Fig. 4

Effect of TCE and TaClo on SNpc DA Neuron Number and Density in A30P α-synuclein overexpressing and wild type C57BL/6 Mice. Total (A) number and (B) density of TH-positive cells in the SNpc of TCE (1000 mg/kg), TaClo (2 mg/kg) and vehicle (olive oil) treated wild type (wt) and A30P overexpressing C57BL/6 mice wer assessed using a stereological approach. Analysis of all data and variables showed a significant overall effect F(4, 58) = 5.217, p < 0.001, Wilks' Lambda=0.425 (MANOVA). Post hoc analysis on the outcome variables revealed a significant effect on cell density F(5, 29) = 7.361, p < 0.003 and cell number F(5, 29) = 4.236, p = 0.043. Data presented as mean ± SD (n=5/6). ***p < 0.001, **p < 0.01, *p < 0.05 when compared to strain vehicle, +p < 0.05 when compared to same treatment wt group (univariate ANOVA). No significant effect was seen on treatment between strains.