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Nature Metabolism Sep 2020The mechanistic target of rapamycin complex 1 (mTORC1) kinase regulates cell growth by setting the balance between anabolic and catabolic processes. To be active, mTORC1...
The mechanistic target of rapamycin complex 1 (mTORC1) kinase regulates cell growth by setting the balance between anabolic and catabolic processes. To be active, mTORC1 requires the environmental presence of amino acids and glucose. While a mechanistic understanding of amino acid sensing by mTORC1 is emerging, how glucose activates mTORC1 remains mysterious. Here, we used metabolically engineered human cells lacking the canonical energy sensor AMP-activated protein kinase to identify glucose-derived metabolites required to activate mTORC1 independent of energetic stress. We show that mTORC1 senses a metabolite downstream of the aldolase and upstream of the GAPDH-catalysed steps of glycolysis and pinpoint dihydroxyacetone phosphate (DHAP) as the key molecule. In cells expressing a triose kinase, the synthesis of DHAP from DHA is sufficient to activate mTORC1 even in the absence of glucose. DHAP is a precursor for lipid synthesis, a process under the control of mTORC1, which provides a potential rationale for the sensing of DHAP by mTORC1.
Topics: AMP-Activated Protein Kinases; Dihydroxyacetone; Dihydroxyacetone Phosphate; Energy Metabolism; Fructose-Bisphosphate Aldolase; Glucose; Glycolysis; HEK293 Cells; Humans; Lipid Metabolism; Phosphotransferases (Alcohol Group Acceptor); TOR Serine-Threonine Kinases
PubMed: 32719541
DOI: 10.1038/s42255-020-0250-5 -
Nature Medicine Sep 2018Metformin, the universal first-line treatment for type 2 diabetes, exerts its therapeutic glucose-lowering effects by inhibiting hepatic gluconeogenesis. However, the...
Metformin, the universal first-line treatment for type 2 diabetes, exerts its therapeutic glucose-lowering effects by inhibiting hepatic gluconeogenesis. However, the primary molecular mechanism of this biguanide remains unclear, though it has been suggested to act, at least partially, by mitochondrial complex I inhibition. Here we show that clinically relevant concentrations of plasma metformin achieved by acute intravenous, acute intraportal or chronic oral administration in awake normal and diabetic rats inhibit gluconeogenesis from lactate and glycerol but not from pyruvate and alanine, implicating an increased cytosolic redox state in mediating metformin's antihyperglycemic effect. All of these effects occurred independently of complex I inhibition, evidenced by unaltered hepatic energy charge and citrate synthase flux. Normalizing the cytosolic redox state by infusion of methylene blue or substrates that contribute to gluconeogenesis independently of the cytosolic redox state abrogated metformin-mediated inhibition of gluconeogenesis in vivo. Additionally, in mice expressing constitutively active acetyl-CoA carboxylase, metformin acutely decreased hepatic glucose production and increased the hepatic cytosolic redox state without altering hepatic triglyceride content or gluconeogenic enzyme expression. These studies demonstrate that metformin, at clinically relevant plasma concentrations, inhibits hepatic gluconeogenesis in a redox-dependent manner independently of reductions in citrate synthase flux, hepatic nucleotide concentrations, acetyl-CoA carboxylase activity, or gluconeogenic enzyme protein expression.
Topics: Acetyl-CoA Carboxylase; Adenylate Kinase; Animals; Blood Glucose; Diabetes Mellitus, Type 2; Dihydroxyacetone; Disease Models, Animal; Gluconeogenesis; Injections, Intravenous; Lipid Metabolism; Liver; Male; Metformin; Mice; Oxidation-Reduction; Phosphorylation; Pyruvic Acid; Rats, Sprague-Dawley; Streptozocin
PubMed: 30038219
DOI: 10.1038/s41591-018-0125-4 -
ACS Omega Dec 2022Sunless tanning has become incredibly prevalent due to the increasing fashionable demand and the awareness of photodamage risks. The brown pigments are induced by...
Sunless tanning has become incredibly prevalent due to the increasing fashionable demand and the awareness of photodamage risks. The brown pigments are induced by dihydroxyacetone (DHA) and amino groups in the stratum corneum (SC) of skin via the Maillard reaction. While most studies concerning sunless tanning reactions have focused on free amino acids (AAs), little information is available on the impact of the side chain of AAs or proteins on this important reaction in cosmetic chemistry. To explore the reactivity and color development kinetics of different types of amino groups, three basic free AAs (Arg, His, and Lys) and three Nα-protected AAs (Boc-Arg-OH, Boc-His-OH, and Boc-Lys-OH) were used to react with DHA using a simplified model system at different reaction times, pH, and temperatures. Full factorial experiments were employed to design and analyze the effects of these three factors. The browning intensity and color characteristics were quantitatively evaluated. The factorial experiments showed that temperature had the most significant influence on the browning intensity and played a dominant role in the interactions with the reaction time and pH. It was found, for the first time, that Arg and His reacted with DHA more rapidly than Boc-Arg-OH and Boc-His-OH, while Boc-Lys-OH developed a stronger color than Lys under the same conditions, suggesting that ε-NH of a lysine residue in peptides or proteins of SC may play a crucial role in the color development of DHA tanning. This study not only clearly illustrates the capability of the side chain of AAs to produce colored compounds but also provides a deeper understanding of DHA tanning.
PubMed: 36530253
DOI: 10.1021/acsomega.2c06124 -
Chemical Research in Toxicology Apr 2022Dihydroxyacetone (DHA) is a major byproduct of e-cigarette combustion and is the active ingredient in sunless tanning products. Mounting evidence points to its damaging...
Dihydroxyacetone (DHA) is a major byproduct of e-cigarette combustion and is the active ingredient in sunless tanning products. Mounting evidence points to its damaging effects on cellular functions. While developing a simple synthetic route to monomeric [C]DHA for flux metabolic studies that compared DHA and glyceraldehyde (GA) metabolism, we uncovered that solid DHA ages upon storage and differences in the relative abundance of each of its isomer occur when reconstituted in an aqueous solution. While all three of the dimeric forms of DHA ultimately resolve to the ketone and hydrated forms of monomeric DHA once in water at room temperature, these species require hours rather than minutes to reach an equilibrium favoring the monomeric species. Consequently, when used in bolus or flux experiments, the relative abundance of each isomer and its effects at the time of application is dependent on the initial DHA isomeric composition and concentration, and time of equilibration in solution before use. Here, we make recommendations for the more consistent handling of DHA as we report conditions that ensure that DHA is present in its monomeric form while in solutions, conditions used in an isotopic tracing study that specifically compared monomeric DHA and GA metabolism in cells.
Topics: Dihydroxyacetone; Electronic Nicotine Delivery Systems; Isomerism; Solutions
PubMed: 35324152
DOI: 10.1021/acs.chemrestox.1c00403 -
Dihydroxyacetone suppresses mTOR nutrient signaling and induces mitochondrial stress in liver cells.PloS One 2022Dihydroxyacetone (DHA) is the active ingredient in sunless tanning products and a combustion product from e-juices in electronic cigarettes (e-cigarettes). DHA is...
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.
Topics: Dihydroxyacetone; Electronic Nicotine Delivery Systems; Reactive Oxygen Species; Mitochondria; Liver
PubMed: 36472985
DOI: 10.1371/journal.pone.0278516 -
Environmental and Molecular Mutagenesis Mar 2021Dihydroxyacetone (DHA) is a three-carbon sugar that is the active ingredient in sunless tanning products and a by-product of electronic cigarette (e-cigarette)... (Review)
Review
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.
Topics: Dihydroxyacetone; Dihydroxyacetone Phosphate; Fructose; Humans; Metabolic Networks and Pathways; Mitochondria; Oxidative Stress; Phosphorylation
PubMed: 33496975
DOI: 10.1002/em.22425 -
Chemical Research in Toxicology Aug 2019Dihydroxyacetone phosphate (DHAP) is the endogenous byproduct of fructose metabolism. Excess DHAP in cells can induce advanced glycation end products and oxidative...
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 IC 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.
Topics: Autophagy; Cell Cycle Checkpoints; Dihydroxyacetone; Dose-Response Relationship, Drug; Glutathione; HEK293 Cells; Humans; Mitochondria; NAD; Structure-Activity Relationship; Tumor Cells, Cultured
PubMed: 31328504
DOI: 10.1021/acs.chemrestox.9b00230 -
World Journal of Microbiology &... Jun 2022Gluconobacter oxydans is a well-known acetic acid bacterium that has long been applied in the biotechnological industry. Its extraordinary capacity to oxidize a variety... (Review)
Review
Gluconobacter oxydans is a well-known acetic acid bacterium that has long been applied in the biotechnological industry. Its extraordinary capacity to oxidize a variety of sugars, polyols, and alcohols into acids, aldehydes, and ketones is advantageous for the production of valuable compounds. Relevant G. oxydans industrial applications are in the manufacture of L-ascorbic acid (vitamin C), miglitol, gluconic acid and its derivatives, and dihydroxyacetone. Increasing efforts on improving these processes have been made in the last few years, especially by applying metabolic engineering. Thereby, a series of genes have been targeted to construct powerful recombinant strains to be used in optimized fermentation. Furthermore, low-cost feedstocks, mostly agro-industrial wastes or byproducts, have been investigated, to reduce processing costs and improve the sustainability of G. oxydans bioprocess. Nonetheless, further research is required mainly to make these raw materials feasible at the industrial scale. The current shortage of suitable genetic tools for metabolic engineering modifications in G. oxydans is another challenge to be overcome. This paper aims to give an overview of the most relevant industrial G. oxydans processes and the current strategies developed for their improvement.
Topics: Acetic Acid; Biotechnology; Fermentation; Gluconobacter oxydans; Metabolic Engineering
PubMed: 35688964
DOI: 10.1007/s11274-022-03310-8 -
FEBS Letters Sep 2017The biosynthesis of plasmalogens in anaerobic bacteria differs fundamentally from that in animal cells. Firstly, the formation of the alk-1'-enyl ether bond in animal... (Review)
Review
The biosynthesis of plasmalogens in anaerobic bacteria differs fundamentally from that in animal cells. Firstly, the formation of the alk-1'-enyl ether bond in animal cells is oxygen dependent. Secondly, the first step in plasmalogen formation in animal cells is an acylation of dihydroxyacetone phosphate, which has been ruled out as a precursor in anaerobes. In bacteria the alk-1'-enyl ether bond is formed after the fully formed acyl glycerolipids are synthesized. Evidence will be presented for the conversion of the sn-1 acyl-linked chain to an O-alk-1'-enyl ether by an as yet unknown mechanism.
Topics: Acylation; Anaerobiosis; Animals; Clostridium beijerinckii; Dihydroxyacetone Phosphate; Plasmalogens
PubMed: 28617934
DOI: 10.1002/1873-3468.12714 -
Canadian Medical Association Journal Nov 1925
PubMed: 20315582
DOI: No ID Found