Identification and characterization of reaction products of 5-hydroxytryptamine with methylglyoxal and glyoxal by liquid chromatography/tandem mass spectrometry

Superoxide anion radical induced phototoxicity of 2,4,5,6-Tetraminopyrimidine sulfate via mitochondrial-mediated apoptosis in human skin keratinocytes at ambient UVR exposure

2,4,5,6-Tetraaminopyrimidine sulfate (TAPS) is worldwide the most commonly used developer in hair dyes. As skin is the major organ, which is directly exposed to these permanent hair dyes, a comprehensive dermal safety assessment is needed. Hereto, we studied the photosensitization potential and mechanism involved in dermal phototoxicity of TAPS exposed to the dark and UVA/UVB/Sunlight by using different in-chemico and mammalian (HaCaT) cells, as test systems. Our experimental outcomes illustrate that TAPS get photodegraded (LC-MS/MS) and specifically generated superoxide anion radical (O₂^•-) under UVA and UVB via type-I photodynamic reaction. The phototoxic potential of TAPS is measured through MTT, NRU, and LDH assays that depicted a significant reduction in cell viability at the concentration of 25 μg/ml and higher. Different cellular stainings (PI uptake, AO/EB, JC-1, NR uptake) suggested the role of mitochondrial-mediated apoptosis. Further, the transcriptomics study revealed upregulation of Apaf-1, Bax, Caspase 3, Caspase 9, Cytochrome c and downregulation of Bcl-2 and Catalase by TAPS treated cells that strengthen our findings. Thus, the above findings suggest that chronic application of TAPS may be hazardous for human skin and promote various skin diseases.

Methylglyoxal-Mediated Dopamine Depletion, Working Memory Deficit, and Depression-Like Behavior Are Prevented by a Dopamine/Noradrenaline Reuptake Inhibitor

Methylglyoxal (MGO) is an endogenous toxin, mainly produced as a by-product of glycolysis that has been associated to aging, Alzheimer's disease, and inflammation. Cell culture studies reported that MGO could impair the glyoxalase, thioredoxin, and glutathione systems. Thus, we investigated the effect of in vivo MGO administration on these systems, but no major changes were observed in the glyoxalase, thioredoxin, and glutathione systems, as evaluated in the prefrontal cortex and the hippocampus of mice. A previous study from our group indicated that MGO administration produced learning/memory deficits and depression-like behavior. Confirming these findings, the tail suspension test indicated that MGO treatment for 7 days leads to depression-like behavior in three different mice strains. MGO treatment for 12 days induced working memory impairment, as evaluated in the Y maze spontaneous alternation test, which was paralleled by low dopamine and serotonin levels in the cerebral cortex. Increased DARPP32 Thr75/Thr34 phosphorylation ratio was observed, suggesting a suppression of phosphatase 1 inhibition, which may be involved in behavioral responses to MGO. Co-treatment with a dopamine/noradrenaline reuptake inhibitor (bupropion, 10 mg/kg, p.o.) reversed the depression-like behavior and working memory impairment and restored the serotonin and dopamine levels in the cerebral cortex. Overall, the cerebral cortex monoaminergic system appears to be a preferential target of MGO toxicity, a new potential therapeutic target that remains to be addressed.

Characterization of Reaction Products and Mechanisms between Serotonin and Methylglyoxal in Model Reactions and Mice

Serotonin is an important endogenous regulatory neurotransmitter and has also been found in fruits, vegetables, and nuts. Methylglyoxal (MGO) is a reactive dicarbonyl metabolite and also a food toxin that modifies protein and DNA to cause the development of many chronic diseases. The objective of this study is to understand the reaction mechanisms between serotonin and MGO and determine whether serotonin could trap MGO in vivo. Five products were detected in phosphate buffer (pH 7.4) at 37 °C. Four products (compounds 2 and 4-6) were purified from the reaction mixture, and their structures were characterized by the analysis of their high-resolution mass and one- and two-dimensional nuclear magnetic resonance spectra. One product (compound 3), as a result of its instability, could not be properly purified and was tentatively characterized on the basis of its high-resolution mass spectrum and corresponding mass fragments. On the basis of the structures of these five products, two reaction pathways were proposed. Compounds 2, 3, 5, and 6 were produced through the Pictet-Spengler condensation pathway between the primary amine of serotonin and the ketone of MGO, and compound 3 was identified as the intermediate product to form products 2, 5, and 6, whereas compound 4 was formed through nucleophilic substitution by the benzene ring of serotonin, which is a new reaction pathway between biogenic amines and reactive carbonyl species. More importantly, the detection of adducts 2 and 4-6 in mice supports our hypothesis that the reaction between serotonin and MGO also happens in vivo through the same pathways as those in model reactions, suggesting that dietary or endogenous serotonin has the capacity to trap MGO in vivo.