Hypoxia-induced generation of methane in mitochondria and eukaryotic cells: an alternative approach to methanogenesis.
OBJECTIVE
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.


CONCLUSIONS
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.
Ghyczy
Miklós
M
Cologne, Germany.
Torday
Csilla
C
Kaszaki
József
J
Szabó
Andrea
A
Czóbel
Miklós
M
Boros
Mihály
M
D000818:Animals; D002417:Cattle; D015687:Cell Hypoxia / Q000187:drug effects; D002478:Cells, Cultured; D002794:Choline / Q000494:pharmacology; D045304:Cytochromes c / Q000378:metabolism; D004285:Dogs; D004579:Electron Transport / Q000187:drug effects; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism; D005057:Eukaryotic Cells / Q000187:drug effects / Q000378:metabolism*; D006098:Granulocytes / Q000187:drug effects / Q000378:metabolism; D008163:Luminescent Measurements; D008697:Methane / Q000096:biosynthesis*; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism*; D010084:Oxidation-Reduction / Q000187:drug effects; D051381:Rats; D013367:Submitochondrial Particles / Q000187:drug effects / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D045304:Cytochromes c; D002794:Choline; D013755:Tetradecanoylphorbol Acetate; D008697:Methane