Abstract
AbstractGallium arsenide (GaAs), a chemical compound of gallium and arsenic, is widely used material in various semiconductor products. While cytotoxic effects of individual gallium and arsenic were well documented, the direct investigation of cytotoxic effects of mere gallium arsenide compound is largely unexplored. We have previously shown in our laboratory that short-term exposure of human fibroblast cells to gallium arsenide exhibits genotoxic micronuclei (MN) formation while of Chinese hamster oocyte (CHO) cells impacts on regulation of cell cycle. In this study, I used CHO-K1 cells to investigate both the cytotoxic and genotoxic mechanisms of the short-term effect of gallium arsenide treatment and to delineate the possible inductive pathway(s) involved. Oxidative stress is the prompt cellular response for many metal stimuli. The oxidative process contributes to glutathione depletion, DNA and/or protein damage, and lipid peroxidation through production of intermediate reactive nitrogen species (RNS) and/or reactive oxygen species (ROS) and finally leads to cell damage or apoptosis. To investigate the involvement of oxidative stress in gallium arsenide treatment, the DAN assay was used to detect a stable product of nitric oxide (NO) in GaAs-treated CHO-K1 cells. The induction of nitrite level was concentration- and time-dependent suggesting the induction is GaAs-specific. The DAN assay was then challenged against pathway-specific inhibitors. Treatment with NO synthase (NOS) inhibitor, either N□-nitro-L-arginine methyl ester (NAME) or S-methyl-L-thiocitrullin (MTC), inhibits the GaAs-induced nitric oxide (NO) production, suggesting the involvement and the necessity of RNS intermediates in GaAs induction. Likewise, 6-hyroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) scavenging hydroxyl radical –OH. and perooxynitrite ONOO- also suppressed the increase of nitrite level, suggesting the involvement and the necessity of ROS intermediates in GaAs induction. Consistent results were also obtained independently by the DCF assay with those of the DAN assay in a concomitantly increase of DCF fluorescence intensity and in the pathway-specific inhibitor experiments using Trolox and either NAME or MTC. In the genotoxic aspect, GaAs induced micronuclei (MN) formation and it is also mediated by ROS and RNS. As cell viability was tested, 0-80 % of cells was killed as examined by Sulforhodamine B (SRB) assay. These results indicated that GaAs possesses cytotoxic and genotoxic effects and both RNS and ROS are involved and required for GaAs stimulation in micronuclei (MN) formation. PageChinese Abstract……………..………………………………………01English Abstract……………………………………………………...02Introduction…………………………………………………………..03Material and Methods..……………………………………………….07Results………………………………………………………………..10Discussion……………………………………………………………14References...………………………………………………………….17Figures………………………………………………………………..21