Date of Award

December 2012

Degree Type

Thesis

Degree Name

Master of Science

Department

Biological Sciences

First Advisor

Michael Carvan

Committee Members

Chuck Wimpee, Reinhold Hutz

Keywords

Biomarker, Gene Expression, Malathion, Organophosphate, Rainbow Trout, Salmonid

Abstract

Understanding the early life stage toxic effects of environmental organophosphate exposure on organism health is crucial to identifying biomarkers that can be used for preventative care. Malathion, a potent organophosphate, is one of the most widely used organophosphates in agriculture and pest eradication. Due to its widespread use, pesticide runoff into area bodies of water poses a great threat to aquatic life and human inhabitants. Acute exposure to high concentrations of malathion causes neurological abnormalities and can result in respiratory failure, muscle spasms, and mental confusion in humans.

In the present study, the effects of malathion are observed following acute, low-level exposure; however, most diagnostic tests require sustained exposure to concentrations high enough to induce acetylcholinesterase inhibition. There is a direct relationship between AChE inhibition and acute exposure to malathion, that results in systematic disturbances in neural function and elicits overt toxicity. While disrupted AChE activity serves as a biomarker, it is not sensitive to low levels of malathion exposure. Therefore, it is necessary to identify novel biomarkers that are more sensitive to malathion exposure so that steps can be taken to ensure the safety of humans and aquatic life before the neurological complications can develop.

Here were we report the discovery of two new potential biomarkers that are expressed following acute, low-concentration malathion exposure. We used two early life stages of rainbow trout (sac fry and swim-up fry) exposed to varying malathion levels (3-100 parts per billion, ppb) over 48 hours. At these levels, swim-up fry had heightened mortality rates compared to sac fry, indicating that they may exhibit change in gene expression. To identify transcriptional biomarkers, a 16K salmonid cDNA microarray was used; 349 genes were found to be differentially expressed at concentrations as low as 10 ppb. Additionally, we further analyzed malathion responsive genes using qPCR, network and ontologic analysis. The results from qPCR revealed that the gene encoding for a small heat shock protein, HSP30, was robustly upregulated. A second gene put forth as a candidate biomarker in this study is cytochrome P4501A3 (CYP1A3); this study also shows paralog CYP1A1 was not found to be malathion inducible in either life stage. Network and ontologic analysis suggested changes in expression of genes involved in metal ion binding, catalytic activity, transport, oxidation-reduction, metabolism and stress response. The novel findings of this study contribute to the construction of a repertoire of predictive biomarkers, induced by malathion exposure, that may also be used as tools to survey fish population health.

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