Effects of Troponoids on Mitochondrial Function and Cytotoxicity

Area of Science:

• Biochemistry
• Virology
• Toxicology

Background:

• Alpha-hydroxytropolones (αHTs) are troponoid compounds that inhibit hepatitis B virus (HBV) replication by targeting HBV RNase H.
• Related troponoids, including tropones and tropolones, have demonstrated cytotoxicity in cell lines, potentially linked to mitochondrial respiration inhibition.

Purpose of the Study:

• To investigate the effects of 35 diverse troponoids on mitochondrial function, genome ratios, cytotoxicity, and reactive oxygen species (ROS) production.
• To evaluate the safety and efficacy of troponoids as potential therapeutic agents for HBV infection.

Main Methods:

• Screening of 35 troponoids for effects on mitochondrial function, mitochondrial/nuclear genome ratios, cytotoxicity (MTS assay), and ROS production.
• Assessment of troponoid impact on cellular respiration and glycolysis.
• Testing cytotoxicity in hepatic cell lines and primary human hepatocytes, with and without the ROS scavenger N-acetylcysteine.

Main Results:

• Troponoids, as a class, did not inhibit respiration or glycolysis, except for the α-ketotropolone subclass.
• No impact on mitochondrial DNA/nuclear DNA ratio was observed after 3 days of exposure.
• Potent HBV RNase H inhibitors among the tested troponoids were not cytotoxic in primary human hepatocytes.
• Tropolones and αHTs increased ROS production at cytotoxic concentrations but not at concentrations effective for HBV inhibition.
• Troponoid-induced cytotoxicity was significantly reduced by the ROS scavenger N-acetylcysteine.

Conclusions:

• Troponoids can induce cytotoxicity in cell lines at high concentrations by increasing ROS production, but they are not cytotoxic in primary hepatocytes.
• The findings suggest that αHTs could be developed as HBV therapeutics, but strategies to mitigate ROS production, such as compound design modification or co-administration with ROS antagonists, may be necessary.