Cytotoxic, genotoxic, and toxicogenomic effects of dihydroxyacetone in human primary keratinocytes

Dihydroxyacetone (DHA) is the only ingredient approved by the U.S. FDA as a colour additive in sunless tanning (self-tanning) products. Consumer sunless tanning products available for retail purchase contain 1–15% DHA. Although originally thought to only interact with the stratum corneum, more recent research has shown that DHA penetrates beyond the stratum corneum to living keratinocytes indicating a possible route of exposure in the epidermis. Normal Human Epidermal Keratinocytes (NHEK) were used to determine any potential <i>in vitro</i> toxicological effects of DHA in the epidermis. NHEK cells exposed to DHA concentrations up to 0.90% (100 mM) in dosing media were evaluated for viability, genotoxicity (Comet Assay), and gene expression changes by microarray analysis. Cell viability significantly decreased ∼50% after 3-h exposure to 50 and 100 mM DHA. DNA damage was only found to be significantly increased in cells exposed to cytotoxic DHA concentrations. A subtoxic dose of DHA induced significant gene expression changes. Particularly, expression of cyclin B1, CDK1, and six other genes associated with the G2/M cell cycle checkpoint was significantly decreased which correlates well with a G2/M block reported in the existing literature. Advanced Glycation End Product (AGE) formation significantly increased after 24 h of DHA exposure at and above 5 mM. In summary, these data show that DHA is cytotoxic above 25 mM in primary keratinocytes. Genotoxicity was detected only at cytotoxic concentrations, likely indicative of non-biologically relevant DNA damage, while subtoxic doses induce gene expression changes and glycation. DHA treatment had a significant and negative effect on primary keratinocytes consistent with <i>in vitro</i> cultured cell outcomes; however, more information is needed to draw conclusions about the biological effect of DHA in human skin.