Identification and biochemical characterization of an ATP-dependent dihydroxyacetone kinase from Trypanosoma cruzi.

Dihydroxyacetone (DHA) can be used as an energy source by many cell types; however, it is toxic at high concentrations. The enzyme dihydroxyacetone kinase (DAK) has shown to be involved in DHA detoxification and osmoregulation. Among protozoa of the genus Trypanosoma, T. brucei, which causes sleeping sickness, is highly sensitive to DHA and does not have orthologous genes to DAK. Conversely, T. cruzi, the etiological agent of Chagas Disease, has two putative ATP-dependent DAK (TcDAKs) sequences in its genome. Here we show that T. cruzi epimastigote lysates present a DAK specific activity of 27.1 nmol/min/mg of protein and that this form of the parasite is able to grow in the presence of 2 mM DHA. TcDAK gene was cloned and the recombinant enzyme (recTcDAK) was expressed in Escherichia coli. An anti-recTcDAK serum reacted with a protein of the expected molecular mass of 61 kDa in epimastigotes. recTcDAK presented maximal activity using Mg+2, showing a Km of 6.5 µM for DHA and a K0.5 of 124.7 µM for ATP. As it was reported for other DAKs, recTcDAK activity was inhibited by FAD with an IC50 value of 0.33 mM. In conclusion, TcDAK is the first DAK described in trypanosomatids confirming another divergent metabolism between T. brucei and T. cruzi.

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

PURPOSE: 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. MATERIALS AND METHODS: Normal Human Epidermal Keratinocytes (NHEK) were used to determine any potential in vitro 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. RESULTS: 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 10 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. CONCLUSION: DHA treatment had a significant and negative effect on primary keratinocytes consistent with in vitro cultured cell outcomes; however, more information is needed to draw conclusions about the biological effect of DHA in human skin.

Exogenous exposure to dihydroxyacetone mimics high fructose induced oxidative stress and mitochondrial dysfunction.

Dihydroxyacetone (DHA) is a three-carbon sugar that is the active ingredient in sunless tanning products and a by-product of electronic cigarette (e-cigarette) combustion. Increased use of sunless tanning products and e-cigarettes has elevated exposures to DHA through inhalation and absorption. Studies have confirmed that DHA is rapidly absorbed into cells and can enter into metabolic pathways following phosphorylation to dihydroxyacetone phosphate (DHAP), a product of fructose metabolism. Recent reports have suggested metabolic imbalance and cellular stress results from DHA exposures. However, the impact of elevated exposure to DHA on human health is currently under-investigated. We propose that exogenous exposures to DHA increase DHAP levels in cells and mimic fructose exposures to produce oxidative stress, mitochondrial dysfunction, and gene and protein expression changes. Here, we review cell line and animal model exposures to fructose to highlight similarities in the effects produced by exogenous exposures to DHA. Given the long-term health consequences of fructose exposure, this review emphasizes the pressing need to further examine DHA exposures from sunless tanning products and e-cigarettes.

Assessing the respiratory toxicity of dihydroxyacetone using an in vitro human airway epithelial tissue model.

Dihydroxyacetone (DHA) is an approved color additive used in sunless tanning lotions. Recently, there has been an increased use of DHA in sunless tanning booths in a manner that could result in its inhalation during application. In the present study, we have evaluated the potential for DHA causing toxicity via inhalation using a human air-liquid-interface (ALI) in vitro airway epithelial tissue model. ALI airway models have a close structural and functional resemblance to the in vivo airway epithelium, and thus data generated in these models may have relevance for predicting human responses. To simulate in vivo exposure conditions, we employed a method for liquid aerosol generation that mimics the physical form of inhaled chemicals and used doses of DHA and an exposure frequency reflecting human respiratory exposures during tanning sessions. Compared to the vehicle control, cilia beating frequency (CBF) and MUC5AC secretion were significantly decreased after each exposure. However, time-course studies indicated that both CBF and MUC5AC secretion returned to normal levels within 3 days after the treatment. Matrix metalloproteinase (MMP) release, on the other hand, was decreased 24 h after the first exposure and its level returned to baseline after 5 exposures. No significant morphological changes occurred in the DHA-treated cultures after 5 weekly exposures. Our findings indicate that DHA, at concentrations likely to be experienced by humans, has transient toxic effects on human airway ALI cultures.

Dihydroxyacetone induces G2/M arrest and apoptotic cell death in A375P melanoma cells.

The active ingredient in sunless tanning products (STPs) is a simple sugar, dihydroxyacetone (DHA). Several studies have demonstrated that DHA is absorbed within the viable layers of skin and not fully contained within the stratum corneum. Additionally, spray tanning and other aerosolized application methods have increased the risk of internal exposure through mucous membranes and inhalation. Beyond its presence in STPs, DHA also occurs as an endogenous by-product of fructose metabolism, and an excess of DHA in cells can induce advanced glycation end (AGE) products and oxidative stress. Therefore, exogenous and endogenous exposures to DHA may be harmful to cells, and it has already been demonstrated that exogenous exposure to DHA is cytotoxic in immortalized keratinocytes. Still, little is known about the exogenous DHA exposure effects on other skin components. In this study, we explore the effects of exogenous DHA exposure in a human melanoma cell line, A375P. Melanoma cells were sensitive to DHA and displayed a transient burst of reactive oxygen species within an hour of exposure. Cell cycle arrest at G2/M was observed within 24 h of exposure, and apoptosis, monitored by the cleavage of PARP-1 and Caspase-3, was detected within 72 h of exposure to DHA. Together, these demonstrate that exogenous exposure to DHA has cytotoxic effects in our selected cell model and indicates the need to further investigate the exogenous exposure effects of DHA in other relevant exposure models.

Contact dermatitis caused by sunless tanning treatment with dihydroxyacetone in hairless descendants of Mexican hairless dogs.

Dihydroxyacetone (DHAT) is a color additive that is added to sunless tanning products to produce an artificial tan. Although this agent has been used extensively as safe sunless tanning, no published data are available to judge whether the abuse of DHAT causes a potential hazard to the human skin. The purpose of this study was to clarify whether frequent treatment with DHAT solutions had a deleterious effect on the wide skin surface of hairless descendants of Mexican hairless dogs. The skin reactions to the DHAT-treatment were investigated by daily clinical observations and histopathological examinations (21 and 42 days after the beginning of the DHAT-treatment). Clinical observations showed that skin color changes were apparent within 6 h after the first treatment with 5% DHAT solutions, with maximal darkening between 12 and 24 h. Twenty-one days after the beginning of the treatment with 5% DHAT solutions, the skin developed irritant dermatitis, and then the skin lesions gradually became severe during this study. Histopathological examinations showed entire epidermal thickening, 21 days after the beginning of the treatment with 5% DHAT solutions. Forty-two days after the beginning of the treatment with 5% DHAT solutions, the skin exhibited remarkable epidermal degeneration (hyperplastic and dyskeratotic changes) and moderate inflammatory reactions in the dermis. In severe dermatitic sites, I found focal epidermal necrosis or interepidermal blister formation beneath the thickened parakeatotic corneum. Throughout this study, there were no clinical and histopathological changes in the sites treated with vehicle alone. These results revealed that the skin coloring generated by frequent wide treatments with DHAT caused severe contact dermatitis which was associated with the damaged stratum corneum.

Dihydroxyacetone-induced death is accompanied by advanced glycation endproduct formation in selected proteins of Saccharomyces cerevisiae and Caenorhabditis elegans.

Advanced glycation endproduct (AGE) formation is an important mechanism for protein deterioration during diabetic complications and ageing. The effects on AGE formation following dihydroxyacetone (DHA) stress were studied in two model organisms, the yeast Saccharomyces cerevisiae and the nematode Caenorhabditis elegans. Total protein AGEs, detected using an anti-N(epsilon)-carboxyalkyllysine-specific monoclonal antibody, displayed a strong correlation to DHA-induced yeast cell mortality in the wild-type and hypersensitive as well as resistant mutant strains. During DHA-induced cell death we also detected AGEs as the formation of acidic protein modifications by 2-D PAGE. Furthermore, we confirmed AGE targets immunologically on 2-D gel-separated protein extracted from DHA-treated cells. AGE modification of several metabolic enzymes (Eno2p, Adh1p, Met6 and Pgk1p) and actin (Act1p) displayed a strong correlation to DHA-induced cell death. DHA was toxic to C. elegans even at low concentration and also in this organism AGE formation accompanied death. We propose the use of DHA as a model AGE-generating substance for its apparent lack of a clear oxidative stress connection, and yeast and worm as model organisms to identify genetic determinants of protein AGE formation.

Dihydroxyacetone detoxification in Saccharomyces cerevisiae involves formaldehyde dissimilation.

To investigate Saccharomyces cerevisiae physiology during growth on the conditionally toxic triose dihydroxyacetone (DHA), protein expression was studied in strains overexpressing either of the two dihydroxyacetone kinase isogenes, DAK1 or DAK2, that grow well utilizing DHA as a carbon and energy source. DHA metabolism was found mostly similar to ethanol utilization, involving a strong component of glucose derepression, but also involved DHA-specific regulatory changes. A specific and strong (10- to 30-fold induction of formaldehyde dehydrogenase, Fdhlp, indicated activation of the formaldehyde dissimilation pathway in DHA medium. The importance of this pathway was further supported by impaired adaptation to DHA growth and DHA survival in a glutathione-dependent formaldehyde dehydrogenase (SFA1) deletion mutant. Glutathione synthase (GSH1) deletion led to decreased DHA survival in agreement with the glutathione cofactor requirement for the SFA1-encoded activity. DHA toxicity did, however, not solely appear related to formaldehyde accumulation, because SFA1 overexpression only enhanced formaldehyde but not DHA tolerance. In further agreement with a low DHA-to-formaldehyde flux, GSH supplements in the low microM range also fully suppressed the DHA sensitivity of a gsh1Delta strain. Under growth reduction on high (100 mM) DHA medium we report increased levels of advanced glycation end-product (AGE) formation on total protein. Under these high-DHA conditions expression of several stress-related proteins, e.g. a heat-shock protein (Hsp104p) and the oxidative stress indicator, alkyl hydroperoxide reductase (Ahp1p) was also found induced. However, hallmark determinants of oxidative stress tolerance (e.g. YAP1, SKN7, HYR1/GPX3 and SOD2) were redundant for DHA tolerance, thus indicating mechanisms of DHA toxicity largely independent of central oxidative stress defence mechanisms. We conclude that mechanisms for DHA growth and detoxification appear complex and that the evolutionary strive to minimize detrimental effects of this intracellular metabolite links to both formaldehyde and glutathione metabolism.

Dihydroxyacetone, the active browning ingredient in sunless tanning lotions, induces DNA damage, cell-cycle block and apoptosis in cultured HaCaT keratinocytes.

Dihydroxyacetone (DHA), the active substance in sunless tanning lotions reacts with the amino groups of proteins to form a brown-colored complex. This non-enzymatic glycation, known as the Maillard reaction, can also occur with free amino groups in DNA, raising the possibility that DHA may be genotoxic. To address this issue we investigated the effects of DHA on cell survival and proliferation of a human keratinocyte cell line, HaCaT. Dose- and time-dependent morphological changes, chromatin condensation, cytoplasmic budding and cell detachment were seen in cells treated with DHA. Several dead cells were observed after long-time (24 h) incubation with 25 mM DHA or more. Furthermore, an extensive decline in proliferation was observed 1 day after DHA exposure for 24 h. When applied in different concentrations (5-50 mM) and for different time periods (1, 3 or 24 h) DHA caused a G(2)/M block after the cyclin B(1) restriction point. Exit from this cell-cycle block was associated with massive apoptosis, as revealed by a clonogenic assay, TUNEL staining and electron microscopy. Furthermore, DHA caused DNA damage as revealed by the alkaline comet assay. Preincubation with antioxidants prevented the formation of DNA strand breaks. The DHA toxicity may be caused by direct redox reactions, with formation of ROS as the crucial intermediates. The genotoxic capacity of DHA raises a question about the long-term clinical consequences of treatment of the skin with this commonly used compound.