The effect of exogenous dihydroxyacetone and methylglyoxal on growth, anthocyanin accumulation, and the glyoxalase system in Arabidopsis.

Dihydroxyacetone (DHA) occurs in wide-ranging organisms, including plants, and can undergo spontaneous conversion to methylglyoxal (MG). While the toxicity of MG to plants is well-known, the toxicity of DHA to plants remains to be elucidated. We investigated the effects of DHA and MG on Arabidopsis. Exogenous DHA at up to 10 mm did not affect the radicle emergence, the expansion of green cotyledons, the seedling growth, or the activity of glyoxalase II, while DHA at 10 mm inhibited the root elongation and increased the activity of glyoxalase I. Exogenous MG at 1.0 mm inhibited these physiological responses and increased both activities. Dihydroxyacetone at 10 mm increased the MG content in the roots. These results indicate that DHA is not so toxic as MG in Arabidopsis seeds and seedlings and suggest that the toxic effect of DHA at high concentrations is attributed to MG accumulation by the conversion to MG.

In search of the perfect tan: Chemical activity, biological effects, business considerations, and consumer implications of dihydroxyacetone sunless tanning products.

As the desire and popularity of a tanned appearance continues, the social effects of UV-free tanning are becoming more important. Dihydroxyacetone (DHA) has seen extensive use as the main tanning agent in sunless tanners. The DHA-induced tan is a result of brown melanoidins formed by a non-enzymatic Maillard reaction between DHA and amino acid species found in the stratum corneum. DHA, thereby, provides a safer route to a tanned appearance compared with exposure to ultraviolet radiation. However, DHA is a highly reactive molecule, posing a multitude of challenges for potential product formulations. With their increased use, the safety considerations of topically applied DHA tanners have been investigated. Many different vehicles have been used for topical delivery of DHA, and they are becoming increasingly multifunctional. This review provides a holistic overview of dihydroxyacetone sunless tanning products.

Dihydroxyacetone suppresses mTOR nutrient signaling and induces mitochondrial stress in liver cells.

Dihydroxyacetone (DHA) is the active ingredient in sunless tanning products and a combustion product from e-juices in electronic cigarettes (e-cigarettes). DHA is rapidly absorbed in cells and tissues and incorporated into several metabolic pathways through its conversion to dihydroxyacetone phosphate (DHAP). Previous studies have shown DHA induces cell cycle arrest, reactive oxygen species, and mitochondrial dysfunction, though the extent of these effects is highly cell-type specific. Here, we investigate DHA exposure effects in the metabolically active, HepG3 (C3A) cell line. Metabolic and mitochondrial changes were evaluated by characterizing the effects of DHA in metabolic pathways and nutrient-sensing mechanisms through mTOR-specific signaling. We also examined cytotoxicity and investigated the cell death mechanism induced by DHA exposure in HepG3 cells. Millimolar doses of DHA were cytotoxic and suppressed glycolysis and oxidative phosphorylation pathways. Nutrient sensing through mTOR was altered at both short and long time points. Increased mitochondrial reactive oxygen species (ROS) and mitochondrial-specific injury induced cell cycle arrest and cell death through a non-classical apoptotic mechanism. Despite its carbohydrate nature, millimolar doses of DHA are toxic to liver cells and may pose a significant health risk when higher concentrations are absorbed through e-cigarettes or spray tanning.

A colorimetric comparison of sunless with natural skin tan.

The main ingredient of sunless tanning products is dihydroxyacetone (DHA). DHA reacts with the protein and amino acid composition in the surface layers of the skin, producing melanoidins, which changes the skin colour, imitating natural skin tan caused by melanin. The purpose of this study was to characterise DHA-induced skin colour changes and to test whether we can predict the outcome of DHA application on skin tone changes. To assess the DHA-induced skin colour shift quantitatively, colorimetric and spectral measurements of the inner forearm were obtained before, four hours and 24 hours after application of a 7.5% concentration DHA gel in the experimental group (n = 100). In a control group (n = 60), the same measurements were obtained on both the inner forearm (infrequently sun-exposed) and the outer forearm (frequently sun-exposed); the difference between these two areas was defined as the naturally occurring tan. Skin colour shifts caused by DHA tanning and by natural tanning were compared in terms of lightness (L*), redness (a*) and yellowness (b*) in the standard CIELAB colour space. Naturalness of the DHA-induced skin tan was evaluated by comparing the trajectory of the chromaticity distribution in (L*, b*) space with that of naturally occurring tan. Twenty-four hours after DHA application, approximately 20% of the skin colour samples became excessively yellow, with chromaticities outside the natural range in (L*, b*) space. A principal component analysis was used to characterise the tanning pathway. Skin colour shifts induced by DHA were predicted by a multiple regression on the chromaticities and the skin properties. The model explained up to 49% of variance in colorimetric components with a median error of less than 2 ΔE. We conclude that the control of both the magnitude and the direction of the colour shift is a critical factor to achieve a natural appearance.

A hypothesis for examining dihydroxyacetone, the active component in sunless tanning products, as a topical prophylactic against SARS-COV-2 transmission.

This hypothesis raises the interesting prospect that dihydroxyacetone (DHA), the key ingredient in self-tanning creams, when applied daily to the face and hands may have prophylactic action against SARS-COV-2 transmission and infection. The scientific and mechanistic basis for this hypothesis is elaborated based on our understanding of the chemical reactivity of DHA with proteins to afford advanced glycation products. This piece ends with a proposal for doing key experiments that can be run to test this hypothesis. As more than 30 million people have been infected with this disease world-wide, a safe method for stopping spread is worthy of consideration. Publication of this hypothesis would enable the scientific community at large to test this in a clinically meaningful setting to address the potential for DHA-based prophylaxis. Given the calamity of this crisis, it is anticipated that the publication of this hypothesis, which is supported by key studies on protein and nucleoside glycation, can be disseminated to as many researchers as possible.

Successful treatment of aluminium phosphide poisoning by dihydroxyacetone: A two-case report study.

WHAT IS KNOWN AND OBJECTIVE: Aluminium phosphide (AlP) is an agricultural fumigant which produces phosphine gas in the presence of moisture. Phosphine inhibits oxidative phosphorylation and causes cell death by inhibiting cytochrome C oxidase. Clinical manifestations of AlP poisoning are refractory hypotension, tachycardia, low oxygen saturation and severe metabolic acidosis. CASE SUMMARY: Two cases received dihydroxyacetone (DHA) in addition to routine management of AlP poisoning. Administration of DHA (7 gr in 50 mL sodium bicarbonate, gavage) 2 times at a 1-hour interval improved the clinical signs. WHAT IS NEW AND CONCLUSION: This is the first case report to highlight the safe and successful treatment of AlP poisoning with DHA. However, more clinical studies are recommended to determine the precise mechanism of DHA action.

Metformin lowers glucose 6-phosphate in hepatocytes by activation of glycolysis downstream of glucose phosphorylation.

The chronic effects of metformin on liver gluconeogenesis involve repression of the G6pc gene, which is regulated by the carbohydrate-response element-binding protein through raised cellular intermediates of glucose metabolism. In this study we determined the candidate mechanisms by which metformin lowers glucose 6-phosphate (G6P) in mouse and rat hepatocytes challenged with high glucose or gluconeogenic precursors. Cell metformin loads in the therapeutic range lowered cell G6P but not ATP and decreased G6pc mRNA at high glucose. The G6P lowering by metformin was mimicked by a complex 1 inhibitor (rotenone) and an uncoupler (dinitrophenol) and by overexpression of mGPDH, which lowers glycerol 3-phosphate and G6P and also mimics the G6pc repression by metformin. In contrast, direct allosteric activators of AMPK (A-769662, 991, and C-13) had opposite effects from metformin on glycolysis, gluconeogenesis, and cell G6P. The G6P lowering by metformin, which also occurs in hepatocytes from AMPK knockout mice, is best explained by allosteric regulation of phosphofructokinase-1 and/or fructose bisphosphatase-1, as supported by increased metabolism of [3-3H]glucose relative to [2-3H]glucose; by an increase in the lactate m2/m1 isotopolog ratio from [1,2-13C2]glucose; by lowering of glycerol 3-phosphate an allosteric inhibitor of phosphofructokinase-1; and by marked G6P elevation by selective inhibition of phosphofructokinase-1; but not by a more reduced cytoplasmic NADH/NAD redox state. We conclude that therapeutically relevant doses of metformin lower G6P in hepatocytes challenged with high glucose by stimulation of glycolysis by an AMP-activated protein kinase-independent mechanism through changes in allosteric effectors of phosphofructokinase-1 and fructose bisphosphatase-1, including AMP, Pi, and glycerol 3-phosphate.

Dihydroxyacetone Exposure Alters NAD(P)H and Induces Mitochondrial Stress and Autophagy in HEK293T Cells.

Dihydroxyacetone phosphate (DHAP) is the endogenous byproduct of fructose metabolism. Excess DHAP in cells can induce advanced glycation end products and oxidative stress. Dihydroxyacetone (DHA) is the triose precursor to DHAP. DHA is used as the active ingredient in sunless tanning products, including aerosolized spray tans, and is formed by the combustion of solvents found in electronic cigarettes. Human exposure to DHA has been increasing as the popularity of sunless tanning products and electronic cigarettes has grown. Topically applied DHA is absorbed through the viable layers of the skin and into the bloodstream. Exogenous exposure to DHA is cytotoxic in immortalized keratinocytes and melanoma cells with cell cycle arrest induced within 24 h and cell death occurring by apoptosis at consumer-relevant concentrations of DHA within 72 h. Less is known about systemic exposures to DHA that occur following absorption through skin, and now through inhalation of the aerosolized DHA used in spray tanning. In the present study, HEK293T cells were exposed to consumer-relevant concentrations of DHA to examine the cytotoxicity of systemic exposures. HEK293T cells were sensitive to consumer-relevant doses of DHA with an IC50 value of 2.4 ± 0.3 mM. However, cell cycle arrest did not begin until 48 h after DHA exposure. DHA-exposed cells showed altered metabolic activity with decreased mitochondrial function and decreased lactate and ATP production observed within 24 h of exposure. Autofluorescent imaging and NAD+ sensors also revealed an imbalance in the redox cofactors NAD+/NADH within 24 h of exposure. Cell death occurred by autophagy indicated by increases in LC3B and SIRT1. Despite DHA's ability to be converted to DHAP and integrated into metabolic pathways, the metabolic dysfunction and starvation responses observed in the HEK293T cells indicate that DHA does not readily contribute to the energetic pool in these cells.

Kinetic Analysis of Hepatic Metabolism Using Hyperpolarized Dihydroxyacetone.

Hyperpolarized carbon-13 magnetic resonance (HP-MR) is a new metabolic imaging method the does not use ionizing radiation. Due to the inherent chemical specificity of MR, not only tracer uptake but also downstream metabolism of the agent is detected in a straightforward manner. HP [2-13C] dihydroxyacetone (DHA) is a promising new agent that directly interrogates hepatic glucose metabolism. DHA has three metabolic fates in the liver: glucose production, glycerol production and potential inclusion into triglycerides, and oxidation in the tricarboxylic acid cycle. Each pathway is regulated by flux through multiple enzymes. Using Duhamel's formula, the kinetics of DHA metabolism is modeled, resulting in estimates of specific reaction rate constants. The multiple enzymatic steps that control DHA metabolism make more simplified methods for extracting kinetic data less than satisfactory. The described modeling paradigm effectively identifies changes in metabolism between gluconeogenic and glycogenolytic models of hepatic function.

[Self-tanning and sunless tanning products]. / Autobronzants et bronzants artificiels.

Practically all currently available self-tanning products have as their active ingredient dihydroxyacetone (DHA), which may or may not be combined with erythrulose, tyrosine derivatives, and occasionally a naphthoquinone. The resulting skin tone, which resembles a natural tan, is due to chemical combination of the DHA with amino acids in the skin through the Maillard reaction. Polymer pigments known as melanoidins are formed and are fixed in the stratum corneum, where they remain until corneocyte desquamation occurs. The colouring thus achieved is semi-permanent and is well tolerated by skin. While the formulation of such products is complex and their storage difficult, no other substances provide more satisfactory or more lasting results.

A novel methanol-free Pichia pastoris system for recombinant protein expression.

BACKGROUND: As one of the most popular expression systems, recombinant protein expression in Pichia pastoris relies on the AOX1 promoter (P AOX1 ) which is strongly induced by methanol. However, the toxic and inflammatory nature of methanol restricts its application, especially in edible and medical products. Therefore, constructing a novel methanol-free system becomes necessary. The kinases involved in P AOX1 activation or repression by different carbon sources may be promising targets. RESULTS: We identified two kinase mutants: Δgut1 and Δdak, both of which showed strong alcohol oxidase activity under non-methanol carbon sources. Based on these two kinases, we constructed two methanol-free expression systems: Δgut1-HpGCY1-glycerol (P AOX1 induced by glycerol) and Δdak-DHA (P AOX1 induced by DHA). By comparing their GFP expression efficiencies, the latter one showed better potential. To further test the Δdak-DHA system, three more recombinant proteins were expressed as examples. We found that the expression ability of our novel methanol-free Δdak-DHA system was generally better than the constitutive GAP promoter, and reached 50-60 % of the traditional methanol induced system. CONCLUSIONS: We successfully constructed a novel methanol-free expression system Δdak-DHA. This modified expression platform preserved the favorable regulatable nature of P AOX1 , providing a potential alternative to the traditional system.

Prevention of phosphine-induced cytotoxicity by nutrients in HepG2 cells.

BACKGROUND & OBJECTIVES: Phosphides used as an insecticide and rodenticide, produce phosphine (PH3) which causes accidental and intentional poisoning cases and deaths. There is no specific treatment or antidote available for PH3poisoning. It is suggested that PH3-induced toxicity is associated with adenosine triphosphate (ATP) depletion; therefore, in this study the effect of some nutrients was evaluated on PH3cytotoxicity in a cell culture model. METHODS: PH3was generated from reaction of zinc phosphide (10 mM) with water in the closed culture medium of HepG2 cells, and cytotoxicity was measured after one and three hours of incubation. ATP, glutathione (GSH) and lipid peroxidation were also assessed at one or three hours post-incubation. ATP suppliers including dihydroxyacetone, glyceraldehyde and fructose were added to the culture medium 10 min before PH3generation to prevent or reduce phosphine-induced cytotoxicity. RESULTS: Phosphine caused about 30 and 66 per cent cell death at one and three hours of incubation, respectively. ATP content of the cells was depleted to 14.7 per cent of control at one hour of incubation. ATP suppliers were able to prevent cytotoxicity and ATP depletion induced by PH3. Dihydroxyacetone, α-ketoglutarate, fructose and mannitol restored the ATP content of the cells from 14.7 per cent to about 40 , 34 , 32 and 30 per cent, respectively. Lipid peroxidation and GSH depletion were not significantly induced by zinc phosphide in this study. INTERPRETATION & CONCLUSIONS: The results supported the hypothesis that phosphine-induced cytotoxicity was due to decrease of ATP levels. ATP suppliers could prevent its toxicity by generating ATP through glycolysis. α-keto compounds such as dihydroxyacetone and α-ketoglutarate may bind to phosphine and restore mitochondrial respiration.

Fructose 2,6-bisphosphate is essential for glucose-regulated gene transcription of glucose-6-phosphatase and other ChREBP target genes in hepatocytes.

Glucose metabolism in the liver activates the transcription of various genes encoding enzymes of glycolysis and lipogenesis and also G6pc (glucose-6-phosphatase). Allosteric mechanisms involving glucose 6-phosphate or xylulose 5-phosphate and covalent modification of ChREBP (carbohydrate-response element-binding protein) have been implicated in this mechanism. However, evidence supporting an essential role for a specific metabolite or pathway in hepatocytes remains equivocal. By using diverse substrates and inhibitors and a kinase-deficient bisphosphatase-active variant of the bifunctional enzyme PFK2/FBP2 (6-phosphofructo-2-kinase-fructose-2,6-bisphosphatase), we demonstrate an essential role for fructose 2,6-bisphosphate in the induction of G6pc and other ChREBP target genes by glucose. Selective depletion of fructose 2,6-bisphosphate inhibits glucose-induced recruitment of ChREBP to the G6pc promoter and also induction of G6pc by xylitol and gluconeogenic precursors. The requirement for fructose 2,6-bisphosphate for ChREBP recruitment to the promoter does not exclude the involvement of additional metabolites acting either co-ordinately or at downstream sites. Glucose raises fructose 2,6-bisphosphate levels in hepatocytes by reversing the phosphorylation of PFK2/FBP2 at Ser32, but also independently of Ser32 dephosphorylation. This supports a role for the bifunctional enzyme as the phosphometabolite sensor and for its product, fructose 2,6-bisphosphate, as the metabolic signal for substrate-regulated ChREBP-mediated expression of G6pc and other ChREBP target genes.

In vitro antifungal activity of dihydroxyacetone against causative agents of dermatomycosis.

Dihydroxyacetone (DHA), a three-carbon sugar, is the browning ingredient in commercial sunless tanning formulations. DHA preparations have been used for more than 50 years and are currently highly popular for producing temporary pigmentation resembling an ultraviolet-induced tan. In this work, the in vitro antifungal activity of dihydroxyacetone was tested against causative agents of dermatomycosis, more specifically against dermatophytes and Candida spp. The antifungal activity was determined by the broth microdilution method according to the Clinical and Laboratory Standards Institute guidelines for yeasts and filamentous fungi. The data obtained show that the fungicidal activity varied from 1.6 to 50 mg ml(-1). DHA seems to be a promising substance for the treatment of dermatomycosis because it has antifungal properties at the same concentration used in artificial suntan lotions. Therefore, it is a potential low-toxicity antifungal agent that may be used topically because of its penetration into the corneal layers of the skin.

Influence of reducing carbohydrates on (6S)-5-methyltetrahydrofolic acid degradation during thermal treatments.

The mechanism and kinetics of the degradation of (6S)5-methyl-5,6,7,8-tetrahydrofolic acid in an aqueous solution in the presence of reducing carbohydrates such as glucose and fructose were investigated for thermal treatments. Preliminary experiments indicated that the presence of reducing carbohydrates, especially fructose (1.6 mM-1.5 M), strongly enhanced folate degradation at moderate temperatures (50-90 degrees C, 0-60 min). Identification of the predominant folate degradation products by LC-MS and NMR pointed to the formation of N(2alpha)-[1-(carboxyethyl)]-5-methyl-5,6,7,8-tetrahydrofolic acid diastereomers besides other folate degradation products upon prolonged heating (24 h, 100 degrees C) of (6S)5-methyl-5,6,7,8-tetrahydrofolic acid in fructose or dihydroxyacetone solutions. Using a Bayesian multiresponse kinetic modeling approach, kinetic characterization and elucidation of the degradation mechanism in the presence of equimolar amounts of dihydroxyacetone, fructose, and glucose were achieved. On the basis of the established degradation mechanism for (6S)5-methyl-5,6,7,8-tetrahydrofolic acid oxidation in the literature, it was shown that nonenzymatic glycation occurred due to reaction of dihydroxyacetone with 5-methyl-7,8-dihydrofolic acid. During thermal treatments (85-110 degrees C, 0-60 min), the nonenzymatic glycation reaction was characterized by an activation energy of 61.3 +/- 9.3 and 77.6 +/- 7.8 kJ mol(-1) in the presence of, respectively, dihydroxyacetone and fructose. Addition of L-ascorbic acid (1.13 mM) to folate samples (0.04 mM) with equimolar amounts of fructose prior to heating (100 degrees C, 0-45 min) was shown to retard the formation of 5-methyl-7,8-dihydrofolic acid and hence prevented the formation of the carboxyethylated derivatives under the investigated conditions.

Novel therapeutic targets in Plasmodium falciparum: aquaglyceroporins.

BACKGROUND: Malaria is caused by the intracellular parasite Plasmodium falciparum. The constant need for novel malaria therapies is due to the development of resistance against existing drugs. OBJECTIVE: To summarise attempts to investigate parasitic aquaporins as drug targets in malaria. METHODS: Starting with a summary of the history of malaria we present aquaporin structure and function relationships. Potential interactions of inhibitors with plasmodial AQP (PfAQP) are discussed. PfAQP blockage is examined in the light of recent work on knock-out parasites. Since PfAQP is able to transport other small solutes the parasites are sensitive to other compounds which are harmless to the human host. RESULTS/CONCLUSIONS: Total blockage of PfAQP may not lead to the death of the parasite but application of PfAQP as a vehicle for toxic substances may be a further pathway for research.

Camouflaging vitiligo with dihydroxyacetone.

Dihydroxyacetone (DHA), the active ingredient in sunless tanning agents, can provide cosmetically acceptable camouflage for some vitiligo patients.

Interrelation between the inhibition of glycolytic flux by silibinin and the lowering of mitochondrial ROS production in perifused rat hepatocytes.

Silibinin, the most biologically active component of the polyphenolic extract from milk thistle seeds, is widely used to prevent many types of hepatobiliary disorders. Recent evidence suggests new applications for this ancient medication, notably for the treatment of type 2 diabetes owing to its antihyperglycemic properties. As we have lately demonstrated that silibinin lowered glucose production from various gluconeogenic substrates in perifused rat hepatocytes, the aim of this study was to examine the effect of silibinin on both oxidative glucose utilization and reactive oxygen species (ROS) generation since the release of ROS secondary to an increased mitochondrial metabolism may contribute to diabetic damage. We found that silibinin dose-dependently reduced glycolysis from carbohydrates in a cell perifusion system via an inhibitory effect targeted on pyruvate kinase activity. Furthermore, a dramatic effect upon oxidative phosphorylation was shown, as evidenced by a fall in ATP-to-ADP ratio, together with an increase in lactate-to-pyruvate ratio. The most attractive finding was that silibinin, at a concentration as low as 10 microM, fully mitigated the rise in metabolic flow-driven ROS formation. In addition, studies on isolated liver mitochondria revealed that this low dose of silibinin depressed ROS production linked to the electron transfer chain activity. From these results, one may tentatively suggest that interesting activities for silibinin, beyond its general antioxidant status, could be expected from its potential clinical use, especially in pathological conditions when mitochondrial ROS formation is severely enhanced.

Role of GldA in dihydroxyacetone and methylglyoxal metabolism of Escherichia coli K12.

The metabolic pathway involving dihydroxyacetone is poorly characterized although novel enzymes associated with this metabolite have recently been demonstrated. The role of GldA in dihydroxyacetone and methylglyoxal metabolism was investigated by purifying the enzyme and characterizing its catalytic ability using nuclear magnetic resonance (NMR) spectroscopy. At neutral pH, the enzyme exhibits much higher affinities towards dihydroxyacetone, methylglyoxal, and glycolaldehyde than glycerol with K(m) values of 0.30, 0.50, 0.85, and 56 mM, respectively. This is consistent with NMR data with crude extracts, showing that the conversion from dihydroxyacetone to glycerol by GldA is far more efficient than the reverse reaction. Dihydroxyacetone was found to be lethal at higher concentration with an LC(50) value of 28 mM compared with 0.4 mM of methylglyoxal, while lactaldehyde was found to exhibit significant growth inhibition in Escherichia coli cells. The toxicity of dihydroxyacetone appears to be due to its intracellular conversion to an aldehyde compound, presumably methylglyoxal, since the glyoxalase mutant becomes sensitive to dihydroxyacetone. Based on information that gldA is preceded in an operon by the ptsA homolog and talC gene encoding fructose 6-phosphate aldolase, this study proposes that the primary role of gldA is to remove toxic dihydroxyacetone by converting it into glycerol.

UV-generated free radicals (FR) in skin: their prevention by sunscreens and their induction by self-tanning agents.

In the past few years, the cellular effects of ultraviolet (UV) irradiation induced in skin have become increasingly recognized. Indeed, it is now well known that UV irradiation induces structural and cellular changes in all the compartments of skin tissue. The generation of reactive oxygen species (ROS) is the first and immediate consequence of UV exposure and therefore the quantitative determination of free radical reactions in the skin during UV radiation is of primary importance for the understanding of dermatological photodamage. The RSF method (radical sun protection factor) herein presented, based on electron spin resonance spectroscopy (ESR), enables the measurement of free radical reactions in skin biopsies directly during UV radiation. The amount of free radicals varies with UV doses and can be standardized by varying UV irradiance or exposure time. The RSF method allows the determination of the protective effect of UV filters and sunscreens as well as the radical induction capacity of self-tanning agents as dihydroxyacetone (DHA). The reaction of the reducing sugars used in self-tanning products and amino acids in the skin layer (Maillard reaction) leads to the formation of Amadori products that generate free radicals during UV irradiation. Using the RSF method three different self-tanning agents were analyzed and it was found, that in DHA-treated skin more than 180% additional radicals were generated during sun exposure with respect to untreated skin. For this reason the exposure duration in the sun must be shortened when self-tanners are used and photoaging processes are accelerated.