S-adenosylhomocysteine metabolism in different cell lines: effect of hypoxia and cell density.

BACKGROUND/AIMS The methylation potential (MP) is defined as the ratio of S-adenosylmethionine (AdoMet) to S-adenosylhomocysteine (AdoHcy). It was shown recently that hypoxia increases AdoMet/AdoHcy ratio in HepG2 cells (Hermes et al., Exp Cell Res 294: 325-334, 2004). In the present study, we compared AdoMet/AdoHcy ratio and energy metabolism in HepG2, HEK-293, HeLa, MCF-7 and SK-HEP-1 cell lines under normoxia and hypoxia. METHODS Metabolite concentrations were measured by HPLC. In addition, AdoHcy hydrolase (AdoHcyase) activity was determined photometrically. RESULTS Under normoxia HepG2 cells show the highest AdoMet/AdoHcy ratio of 53.4 +/- 3.3 followed by MCF-7 and SK-HEP-1 cells with a AdoMet/AdoHcy ratio of 14.4 +/- 1.1 and 21.1 +/- 1.3, respectively. The lowest AdoMet/AdoHcy ratios are exhibited by HeLa and HEK-293 cells (6.6 +/- 0.7 and 7.1 +/- 0.3). Hypoxia does not significantly change the MP in MCF-7 and HeLa cells, but alters the MP in HepG2, HEK-293 and SK-HEP-1 cells. These alterations are dependent on the cell density. Under normoxia HepG2 cells exhibit AdoHcyase activity of 2.5 +/- 0.2 nmol min(-1) mg(-1) protein. All other cell lines show 3-5 times lower enzyme activity. Interestingly, hypoxia affects AdoHcyase activity only in HepG2 cells. CONCLUSIONS Our data clearly show that the cell lines are characterized by different MP and different behavior under hypoxia. That implies that a lower MP is not necessarily associated with impaired transmethylation activity and cellular function.