title: Exposure to high levels of fumarate and succinate leads to apoptotic cytotoxicity and altered global DNA methylation profiles in vitro.
abstract: In the Krebs cycle, succinate is oxidized to fumarate by succinate dehydrogenase (SDH), followed by the conversion of fumarate to malate by fumarate hydratase (FH). In cells with defective SDH and FH, the Krebs cycle is congested, respiration impaired and fumarate and succinate accumulates. Several studies have indicated that the accumulation of these substrates are associated with cytotoxicity and oncogenesis. High levels of succinate and fumarate induce hypoxia inducible factor (HIF1A) hydroxylases, leading to the activation of oncogenic HIF pathways. However, the role of HIF as primary inducer of oncogenic change has been questioned, as other non-enzymatic mechanisms have been shown to interfere with cellular metabolism, cell signalling as well as disrupting protein function. Owing to the essential roles that SDH and FH play in cellular energy metabolism, and their associated tumor suppressor capacity, it is vital to understand the biochemical effects resulting from the accumulation of their associated metabolites. Therefore, in this study, we investigated the effect of high concentrations of succinate and fumarate exposure on cell viability, genome integrity and global DNA methylation using a human hepatocellular carcinoma (HepG2) cell culture model. It was found that relatively high concentrations of succinate and fumarate cause a loss of cell viability, which seems to be orchestrated through an apoptotic pathway. Cells exposed to high levels of succinate also presented with elevated caspase 3 and/or caspase 7 levels. In addition, elevated levels of fumarate lead to extensive DNA fragmentation, which may contribute pathophysiologically by inducing chromosomal instability, while succinate demonstrated lower genotoxicity. Furthermore, both succinate and fumarate altered the global DNA methylation patterns via significant DNA hypermethylation. Since numerous studies have reported correlations between aberrant DNA methylation and oncogenesis, hypermethylation may contribute to the oncogenesis observed in cells exposed to high concentrations of these metabolites.
authors.affiliation: Centre of Excellence for Pharmaceutical Sciences (PHARMACEN), North-West University, Potchefstroom 2520, South Africa. Electronic address: 20134045@nwu.ac.za.
authors.forename: Johannes F
authors.initials: JF
authors.lastname: Wentzel
authors.affiliation: Centre of Excellence for Pharmaceutical Sciences (PHARMACEN), North-West University, Potchefstroom 2520, South Africa.
authors.forename: Angélique
authors.initials: A
authors.lastname: Lewies
authors.affiliation: Centre for Human Metabolomics, Biochemistry Division, North-West University, Potchefstroom 2520, South Africa.
authors.forename: Abel J
authors.initials: AJ
authors.lastname: Bronkhorst
authors.affiliation: Centre for Human Metabolomics, Biochemistry Division, North-West University, Potchefstroom 2520, South Africa.
authors.forename: Etresia
authors.initials: E
authors.lastname: van Dyk
authors.affiliation: Centre of Excellence for Pharmaceutical Sciences (PHARMACEN), North-West University, Potchefstroom 2520, South Africa.
authors.forename: Lissinda H
authors.initials: LH
authors.lastname: du Plessis
authors.affiliation: Centre for Human Metabolomics, Biochemistry Division, North-West University, Potchefstroom 2520, South Africa.
authors.forename: Piet J
authors.initials: PJ
authors.lastname: Pretorius
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3 / Q000378:metabolism; D053179:Caspase 7 / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D020552:Comet Assay; D004249:DNA Damage / Q000187:drug effects; D019175:DNA Methylation / Q000187:drug effects*; D005434:Flow Cytometry; D005650:Fumarates / Q000494:pharmacology*; D056945:Hep G2 Cells; D006801:Humans; D019802:Succinic Acid / Q000494:pharmacology*
chemical_list: D005650:Fumarates; D019802:Succinic Acid; D053148:Caspase 3; D053179:Caspase 7
keywords: Apoptosis; Cancer; DNA methylation; Fumarate; Methylation sensitive comet assay; Succinate