A tipping point in dihydroxyacetone exposure: mitochondrial stress and metabolic reprogramming alter survival in rat cardiomyocytes H9c2 cells.

Exogenous exposures to the triose sugar dihydroxyacetone (DHA) occur from sunless tanning products and electronic cigarette aerosol. Once inhaled or absorbed, DHA enters cells, is converted to dihydroxyacetone phosphate (DHAP), and incorporated into several metabolic pathways. Cytotoxic effects of DHA vary across the cell types depending on the metabolic needs of the cells, and differences in the generation of reactive oxygen species (ROS), cell cycle arrest, and mitochondrial dysfunction have been reported. We have shown that cytotoxic doses of DHA induced metabolic imbalances in glycolysis and oxidative phosphorylation in liver and kidney cell models. Here, we examine the dose-dependent effects of DHA on the rat cardiomyocyte cell line, H9c2. Cells begin to experience cytotoxic effects at low millimolar doses, but an increase in cell survival was observed at 2 mM DHA. We confirmed that 2 mM DHA increased cell survival compared to the low cytotoxic 1 mM dose and investigated the metabolic differences between these two low DHA doses. Exposure to 1 mM DHA showed changes in the cell's fuel utilization, mitochondrial reactive oxygen species (ROS), and transient changes in the glycolysis and mitochondrial energetics, which normalized 24 h after exposure. The 2 mM dose induced robust changes in mitochondrial flux through acetyl CoA and elevated expression of fatty acid synthase. Distinct from the 1 mM dose, the 2 mM exposure increased mitochondrial ROS and NAD(P)H levels, and sustained changes in LDHA/LDHB and acetyl CoA-associated enzymes were observed. Although the cells were exposed to low cytotoxic (1 mM) and non-cytotoxic (2 mM) acute doses of DHA, significant changes in mitochondrial metabolic pathways occurred. Further, the proliferation increase at the acute 2 mM DHA dose suggests a metabolic adaption occurred with sustained consequences in survival and proliferation. With increased exogenous exposure to DHA through e-cigarette aerosol, this work suggests cell metabolic changes induced by acute or potentially chronic exposures could impact cell function and survival.

Acute exposure to dihydroxyacetone promotes genotoxicity and chromosomal instability in lung, cardiac, and liver cell models.

Inhalation exposures to dihydroxyacetone (DHA) occur through spray tanning and e-cigarette aerosols. Several studies in skin models have demonstrated that millimolar doses of DHA are cytotoxic, yet the genotoxicity was unclear. We examined the genotoxicity of DHA in cell models relevant to inhalation exposures. Human bronchial epithelial cells BEAS-2B, lung carcinoma cells A549, cardiomyocyte Ac16, and hepatocellular carcinoma HepG3 were exposed to DHA, and low millimolar doses of DHA were cytotoxic. IC90 DHA doses induced cell cycle arrest in all cells except the Ac16. We examined DHA's genotoxicity using strand break markers, DNA adduct detection by Repair Assisted Damage Detection (RADD), metaphase spreads, and a forward mutation assay for mutagenesis. Similar to results for skin, DHA did not induce significant levels of strand breaks. However, RADD revealed DNA adducts were induced 24 h after DHA exposure, with BEAS-2B and Ac16 showing oxidative lesions and A549 and HepG3 showing crosslink-type lesions. Yet, only low levels of reactive oxygen species or advanced glycation end products were detected after DHA exposure. Metaphase spreads revealed significant increases in chromosomal aberrations in the BEAS-2B and HepG3 with corresponding changes in ploidy. Finally, we confirmed the mutagenesis observed using the supF reporter plasmid. DHA increased the mutation frequency, consistent with methylmethane sulfonate, a mutagen and clastogen. These data demonstrate DHA is a clastogen, inducing cell-specific genotoxicity and chromosomal instability. The specific genotoxicity measured in the BEAS-2B in this study suggests that inhalation exposures pose health risks to vapers, requiring further investigation.