S-Adenosylhomocysteine Metabolism in Different Cell Lines: Effect of Hypoxia and Cell Density

Abstract

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.

Hypoxia Induces Genomic DNA Demethylation through the Activation of HIF-1α and Transcriptional Upregulation of MAT2A in Hepatoma Cells

“…However, Hermes and colleagues (32) observed that hypoxia leads to increased SAM and decreased SAH levels in HepG2 cells. This difference may be due to alterations in the cell density of cultured cells (33).…”

Expression and Localization of S-Adenosylhomocysteine-Hydrolase in the Rat Kidney Following Carbon Monoxide Induced Hypoxia

“…Since it was previously shown that hypoxia decreases AdoHcy-hydrolase expression in HepG2 cells [5,31] we also examined in this study the effect of hypoxia on the AdoHcy-hydrolase mRNA content in rat kidneys. CO exposure decreased the mRNA content of AdoHcy-hydrolase in the rat kidney by 64%.…”

S-Adenosylhomocysteine Hydrolase Overexpression in HEK-293 Cells: Effect on Intracellular Adenosine Levels, Cell Viability, and DNA Methylation

“…Prior to all other experiments cells were rinsed with PBS and then cultured with serumfree MEM for 24 h. This allows us to compare our results to previous studies [3,10,21].…”

“…Therefore, the aim of the present study was to evaluate whether elevated AdoHcyase activity might also lead to changes in AdoHcy metabolism and thus, influence energy metabolism, cell viability, growth rate, and DNA methylation. As a model system, we used HEK-293 cells stably overexpressing AdoHcyase to different extents, because HEK-293 cells exhibit high intracellular AdoHcy levels and a low AdoMet/AdoHcy ratio compared to other established cell lines [21].…”