Genotoxicity of microcystin-LR in mammalian cells: Implication from peroxynitrite produced by mitochondria

Area of Science:

• Hepatotoxicity
• Genotoxicity
• Cellular Biology

Background:

• Microcystin-LR (MC-LR) is a potent hepatotoxin linked to liver cancer.
• Increasing cyanobacteria blooms raise concerns about MC-LR exposure.
• Understanding MC-LR's genotoxic mechanisms is crucial for public health.

Purpose of the Study:

• To investigate the effects of MC-LR on DNA damage in HepG2 cells.
• To identify the specific free radicals and their sources contributing to MC-LR genotoxicity.
• To elucidate the role of mitochondrial dysfunction in MC-LR-induced DNA damage.

Main Methods:

• MC-LR exposure to HepG2 cells with varying concentrations and durations.
• Assessment of DNA double-strand breaks (DSBs) and γ-H2AX expression.
• Utilized scavengers for reactive oxygen species (ROS) and reactive nitrogen species (RNS), including mitochondrial O2•−, mitochondrial NOS, and peroxynitrite (ONOO−).
• Measured mitochondrial membrane potential (MMP).

Main Results:

• MC-LR induced a concentration- and time-dependent increase in DSBs.
• γ-H2AX protein expression and immunofluorescence staining significantly elevated after MC-LR exposure.
• Mitochondrial-derived peroxynitrite (ONOO−) was identified as a major contributor to MC-LR genotoxicity.
• A significant decrease in MMP was observed, indicating mitochondrial dysfunction.

Conclusions:

• MC-LR induces significant DNA damage, specifically DSBs, in HepG2 cells.
• Mitochondrial peroxynitrite plays a critical role in mediating MC-LR's genotoxic effects.
• MC-LR exposure disrupts mitochondrial function, contributing to its overall toxicity.