S-hydroxymethylglutathione limits formaldehyde toxicity

MORELLATO, AGUSTÍN E.; UMANSKY, CARLA; LUCAS B. PONTEL

Simposio; Cancer Metabolism Showcase Discovery 2022; 2022

Formaldehyde (FA) is a ubiquitous metabolite classified as a human carcinogen by the World Health Organization (WHO). This classification is based on its strong reactivity against DNA and proteins, likely underlying cancer onset and some phenotypes observed in inherited conditions such as the Fanconi Anemia.Endogenously, FA can be produced during normal metabolic processes like histone and nucleic acid demethylation reactions or the one-carbon cycle. FA can also be obtained from the metabolization of dietary products and from polluted air. Overall, contributing to blood circulating FA levels that are in the micromolar range. To prevent FA accumulation, our cells evolved a main pathway centered on the enzyme alcohol dehydrogenase 5 (ADH5). Interestingly, in the last years, biallelic mutations in the gene coding for ADH5 together with dominant negative mutations in the mitochondrial aldehyde dehydrogenase ALDH2 have been identified as drivers of a severe form of inherited bone marrow failure syndrome (IBMFS). This condition develops even in presence of functional DNA repair, raising the question of whether FA causes relevant cellular damage beyond genotoxicity.In this work, we evaluated cellular targets of FA toxicity beyond DNA damage. Initially, we focused on determining the accumulation of reactive oxygen species by chemical probes such as 2′,7′- dichlorodihydrofluorescein diacetate (H2DCFDA) and dihydroethidium (DHE), by measuring cellular peroxides by electron spin resonance (ESR), and by determining GSH-related species by high-resolution mass spectrometry (UPLC-HRMS). Our results indicate that cellular FA can react with the redox-active thiol group of glutathione (GSH), altering the GSH:GSSG redox balance and triggering oxidative stress. To prevent these effects, cells evolved the enzyme ADH5, which metabolizes the product formed by the reaction between FA and GSH (S-hydroxymethyl-GSH). Lacking ADH5 sensitizes preB leukemia and colorectal carcinoma cells against blood levels of FA. Moreover, we have identified the ortholog gene coding for ADH5 in Caenorbaetis elegans (re-named as adh-5). Inactivation of Adh-5 renders C. elegans hypersensitive to FA and triggers oxidative stress markers.Finally, we show that GSH synthesis is required to limit FA toxicity in hematopoietic, liver and colorectal carcinoma-derived cell lines.Overall, supporting an intimate relationship between FA and GSH metabolism that might be relevant for human health.