Hypoxia-Induced Generation of Methane in Mitochondria and Eukaryotic Cells - An Alternative Approach to Methanogenesis

Abstract

Background/Aims: Electrophilic methyl groups bound to positively charged nitrogen moieties may act as electron acceptors, and this mechanism could lead to the generation of methane from choline. The aims were to characterize the methanogenic potential of phosphatidylcholine metabolites, and to define the in vivo relevance of this pathway in hypoxia-induced cellular responses. Methods: The postulated reaction was investigated (1) in model chemical experiments, (2) in rat mitochondrial subfractions and (3) in bovine endothelial cell cultures under hypoxic conditions and in the presence of hydroxyl radical generation. The rate of methane formation was determined by gas chromatography with flame-ionisation detectors. The lucigenin-enhanced chemiluminescence assay was used to determine the reactive oxygen species-scavenging capacity of the choline metabolites. Results: Significant methane generation was demonstrated in all three series of experiments. Phosphatidylcholine metabolites with alcoholic moiety in the molecule (i.e. choline, N,N-dimethylethanolamine and N-methylethanolamine), inhibited oxygen radical production both in vitro and in vivo, and displayed an effectiveness proportional to the amount of methane generated and the number of methyl groups in the compounds. Conclusion: Methane generation occurs in aerobic systems. Phosphatidylcholine metabolites containing both electron donor and acceptor groups may have a function to counteract intracellular oxygen radical production.

Evidence for methane production by saprotrophic fungi

“…This is in accordance with the findings of Ghyczy et al 9,12 who demonstrated that endothelial cells from rat liver produced CH 4 when exposed to site-specific inhibitors of the ETC. It would seem that aerobic CH 4 formation is not only a result of chemical formation from dead biomass as previously shown by several studies 8,11 but might also have a physiological role in eukaryotic groups such as fungi, animals and plants.…”

“…Traditionally, biogenic CH 4 was thought to be formed only by prokaryotic microorganisms (methanogens; archaea) under strictly anoxic conditions in wetland soils and rice paddies, the intestines of termites and ruminants, and human and agricultural waste 6 . However, recently CH 4 formation was also reported to occur under oxic conditions in terrestrial vegetation 7,8 and in animals 9 .…”

“…Less well known are the findings of Ghyczy et al 9,12 who demonstrated that endothelial cells from rat liver produced CH 4 when exposed to site-specific inhibitors of the electron transport chain (ETC). A similar observation has been made for plant cell cultures grown under sterile and oxic conditions 13 .…”

A novel pathway of direct methane production and emission by eukaryotes including plants, animals and fungi: An overview

“…Hypoxic mitochondrial CH 4 production was found in rats (Ghyczy et al, 2003;Tuboly et al, 2013b), and such CH 4 -generating capacity has proved to be independent of the methanogenic flora because it persists after antibiotic treatment targeting the gastrointestinal methanogenic archaea. CH 4 production can occur not only in rat mitochondria but also in bovine endothelial cells under hypoxic conditions (Ghyczy et al, 2008a). CH 4 emissions were found by whole-body measurements in rats and exhaled air measurements in humans with the reliable method of diode laser-based photoacoustic spectroscopy; furthermore, a measurable level of CH 4 was still observed after antibiotic treatment in rats (Tuboly et al, 2013a).…”

“…In vivo and in vitro studies have provided persuasive evidence of animal CH 4 production under stress conditions (Ghyczy et al, 2003(Ghyczy et al, , 2008aTuboly et al, 2013a;Tuboly et al, 2013b). Sodium azide (NaN 3 ) administration is a widely used method to cause mitochondrial dysfunction (Ghyczy et Fungous Methionine a Postulated reaction schemes for CH 4 production in plants and fungi (reaction ①) as well as animals (reaction ②).…”