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Mercury-induced externalization of phosphatidylserine and caspase 3 activation in human liver carcinoma (HepG2) cells
Dwayne J Sutton1, Paul B Tchounwou
1Molecular Toxicology Research laboratory, NIH-Center for Environmental Health, College of Science, Engineering and Technology, Jackson State University, 1400 Lynch Street, Box 18540 Jackson, Mississippi 39217, USA.
Abstract:
Apoptosis arises from the active initiation and propagation of a series of highly orchestrated specific biochemical events leading to the demise of the cell. It is a normal physiological process, which occurs during embryonic development as well as in the maintenance of tissue homeostasis. Diverse groups of molecules are involved in the apoptosis pathway and it functions as a mechanism to eliminate unwanted or irreparably damaged cells. However, inappropriate induction of apoptosis by environmental agents has broad ranging pathologic implications and has been associated with several diseases including cancer. The toxicity of several heavy metals such as mercury has been attributed to their high affinity to sulfhydryl groups of proteins and enzymes, and their ability to disrupt cell cycle progression and/or apoptosis in various tissues. The aim of this study was to assess the potential for mercury to induce early and late-stage apoptosis in human liver carcinoma (HepG2) cells. The Annexin-V and Caspase 3 assays were performed by flow cytometric analysis to determine the extent of phosphatidylserine externalization and Caspase 3 activation in mercury-treated HepG2 cells. Cells were exposed to mercury for 10 and 48 hours respectively at doses of 0, 1, 2, and 3 microg/mL based on previous cytotoxicity results in our laboratory indicating an LD50 of 3.5 +/- 0.6 microg/mL for mercury in HepG2 cells. The study data indicated a dose response relationship between mercury exposure and the degree of early and late-stage apoptosis in HepG2 cells. The percentages of cells undergoing early apoptosis were 0.03 +/- 0.03%, 5.19 +/- 0.04%, 6.36 +/- 0.04%, and 8.84 +/- 0.02% for 0, 1, 2, and 3 microg/mL of mercury respectively, indicating a gradual increase in apoptotic cells with increasing doses of mercury. The percentages of Caspase 3 positive cells undergoing late apoptosis were 3.58 +/- 0.03%, 17.06 +/- 0.05%, 23.32 +/- 0.03%, and 34.51 +/- 0.01% for 0, 1, 2, and 3 microg/mL of mercury respectively, also indicating a gradual increase in Caspase positive cells with increasing doses of mercury.
Insights
This study shows that mercury exposure induces apoptosis, a programmed cell death, in human liver cancer cells (HepG2). Increased mercury doses led to a dose-dependent rise in both early and late-stage apoptosis, highlighting mercury
Area of Science:
- Toxicology
- Cell Biology
- Biochemistry
Background:
- Apoptosis is a critical physiological process for tissue homeostasis and development.
- Environmental toxins, including heavy metals like mercury, can inappropriately induce apoptosis, contributing to disease.
- Mercury toxicity is linked to its affinity for sulfhydryl groups, disrupting cellular functions.
Purpose of the Study:
- To investigate the capacity of mercury to induce early and late-stage apoptosis in human liver carcinoma (HepG2) cells.
- To establish a dose-response relationship between mercury exposure and apoptotic markers in HepG2 cells.
Main Methods:
- HepG2 cells were exposed to varying concentrations of mercury (0-3 microg/mL) for 10 and 48 hours.
- Annexin-V and Caspase 3 assays were conducted using flow cytometry.
- Analysis focused on phosphatidylserine externalization and Caspase 3 activation.
Main Results:
- A dose-dependent increase in early-stage apoptosis was observed with mercury exposure.
- Percentages of early apoptotic cells increased from 0.03% (control) to 8.84% at 3 microg/mL mercury.
- Late-stage apoptosis, indicated by Caspase 3 activation, also showed a dose-dependent rise, from 3.58% to 34.51%.
Conclusions:
- Mercury exposure significantly induces both early and late-stage apoptosis in HepG2 cells.
- The observed effects demonstrate a clear dose-response relationship between mercury concentration and apoptosis induction.
- These findings underscore the apoptotic potential of mercury in liver cancer cells.
