Document Type

Thesis

Date of Award

5-2004

School/College

College of Science, Engineering, and Technology (COSET)

Degree Name

MS in Biology

First Advisor

Professor Fawzia Abdel-Rahman

Abstract

Occupational workers who are exposed to manganese (Mn2+) manifest neural degeneration resembling Parkinson's disease (PD). In the treatments of PD, the \" manipulation of dopamine (DA) concentrations is often utilized. Such manipulations seem to increase DA turnover, but increased DA may also have a deleterious effect. In several cell culture models, it has been shown that Mn2+ interacts with cellular DA and caused dopaminergic cell death. Thus, DA modulation at cellular level induced change in Mn2+and DA interaction eventually causes cell death in vulnerable brain areas. Mn2+ in cell culture model appears to induce DNA fragmentation and cell death through oxidative stress. However, DA modulation-induced change in Mn2+ and DA interaction and the underlying mechanism(s) that increased dopaminergic cell's vulnerability remain unclear. In the present study, we showed that Mn2+ exposure (0-500 11M) to mesencephalic cells for 24 hrs induced minimal apoptotic cell death. However, in cell 2 cultures 2 hrs pre-exposure to DA (200 u M) potentiated Mn2+ -induced apoptotic cell death remarkably in which oxidative stress was involved. The ability of Mn2+ -induced apoptotic cell death to DA was determined by the measuring lactate dehydrogenase (LDH) and Apoptag TUNEL staining (terminaldeoxynucleotidyl transferase DNA labeling). This was further confirmed by the mitochondrial cell viability assay (MTT). This supports our hypothesis that greater level of DA interacts with Mn2+ and may cause cells to be more susceptible. The involvement of oxidative stress during Mn2+ and DA interaction was revealed through measurement of reactive oxygen species which was potentiated in the presence of DA than Mn2+ alone. DNA extraction following Mn2+ and DA treatment further revealed that DA enhanced Mn2+ induced oxidative DNA damage which was significantly prevented by various antioxidants (superoxide dismutase, catalase and vitamin E) supplementation. In addition, co-incubation of SOD, catalase or vitamin E with Mn2+ and DA significantly protected the cells from apoptotic cell death and LDH activity, which indicates the involvement of oxidative stress during Mn2+ and DA interaction induced dopaminergic cell death. These studies support our hypothesis that greater level of DA interacts with Mn2+, and causes dopaminergic cells to be more susceptible to oxidative DNA damage.

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