Disruption of neuronal circuitry following exposure to chlorinated organophosphate flame retardants: Implications for neurological disease Open Access

Abstract

Introduction: Many environmental contaminants are proven or suspected to cause neurotoxicity resulting in brain damage, neurobehavioral issues, memory and motor dysfunction, decreased reaction times, and other neurological symptoms. Chemicals such as PCBs and PBDEs have been banned or phased out from use as they are suspected as neurotoxicants. TDCPP was introduced to replace these flame-retardants. TDCPP is detected in as it leaches from various products and accumulates in the environment and human tissue. The neurotoxic potential of TDCPP is unknown.

Objective: This study is designed to determine whether chlorinated organophosphate flame retardant exposure disrupts neuronal circuitry and contributes to the onset of neurological disease.

Methods: I exposed three chlorinated organophosphate flame retardant compounds to SK-N-SH cells to assess cytotoxicity, and TDCPP was selected for further study. I exposed primary culture neurons from the ventral mesencephalon and frontal cortex to TDCPP, followed by a 30-day animal study using 30mg/kg/day TDCPP by oral gavage to adult male mice. Animals were challenged with MPTP to evaluate TDCPP's impact to the dopaminergic neurons of the striatum.

Results: Exposure of SK-N-SH cells to TDCPP resulted in a dose-dependent cytotoxicity, with significant reduction in cell viability. Primary neuron cultures from the ventral mesencephalon were more susceptible to damage by TDCPP and also showed a dose-dependent toxicity. Primary neurons from the frontal cortex were also susceptible and showed significant reduction in neurite length, whereas VMES neurite length was not affected. The animal study showed that while MPTP alone elicited a significant reduction in DAT expression in the striatum, MPTP challenge following TDCPP exposure resulted in even greater reduction in DAT, suggesting that TDCPP exposure compromises the neurons.

Discussion: This study demonstrates that exposure of in vitro models to TDCPP causes a dose-dependent cytotoxic effect as seen in reduction of viable SK-N-SH cells and in reduction of TH+ and MAP+ neurons in primary culture. MPTP exposure in vivo also results in reductions in TH and DAT, which are exacerbated by treatment with TDCPP. These results suggest that TDCPP may be a neurotoxicant and warrants further investigation to better understand pathways of exposure and neuronal damage.

Table of Contents

INTRODUCTION.................................................................1 Anatomy..................................................................1 Dopamine........................................................1 Dopamine synthesis...........................................1 Pathways.........................................................2 Oxidative Stress................................................2 MPTP...............................................................2 Environmental Exposure.......................................4

Environmental contaminants................................4

PCBs................................................................4 PBDEs..............................................................5 Chlorinated Organophosphates.............................6 TDCPP..............................................................7 METHODS.................................................................9

Selection of TDCPP for treatment..................................9

Cytotoxicity assay......................................................9 Primary culture..........................................................10 Immunochemistry.......................................................10

Detection of Reactive Oxygen Species...........................10

Animal Study.............................................................11

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)......11

Western Blot Analysis.................................................12 Immunohistochemistry................................................12 RESULTS..........................................................................13 Selection of TDCPP....................................................13

Analysis of TDCPP toxicity in SK-N-SH cell line................14

Analysis of Oxidative Stress.........................................14

Analysis of TDCPP toxicity in primary cell culture..............14

Ventral mesencephalic expression.........................14 Cortical expression.............................................15 Analysis of TDCPP toxicity in adult mice..........................16

Immunohistochemical expression..........................16

DISCUSSION......................................................................16 FIGURES...........................................................................21 REFERENCES......................................................................28

About this Master's Thesis

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School	Rollins School of Public Health
Department	Environmental Health
Degree	MPH
Submission	Master's Thesis
Language	English
Research Field	Health Sciences, Public Health
Keyword	TDCPP dopamine toxicology neurotoxicology organochlorine brain
Committee Chair / Thesis Advisor	Caudle, William Michael, Emory University
Committee Members	Tolbert, Paige, Emory University
Partnering Agencies	Emory University schools, faculty or affiliated programs

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