© 2005 Oxford University Press
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Contribution of hMTH1 to the Maintenance of 8-Oxoguanine Levels in Lung DNA of Non–Small-Cell Lung Cancer Patients
bieta Speina
skaski
aw T. Ku
mierek
Affiliations of authors: Department of Molecular Biology, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawiskiego 5a, 02-106 Warsaw, Poland (ES, KDA, MZ, BT, JTK); Department of Clinical Biochemistry (DG, AS, RO) and Department and Clinic of Thoracic Surgery and Tumours (JK), The Ludwik Rydygier Medical University in Bydgoszcz, Karowicza 24, 85-092 Bydgoszcz, Poland
Correspondence to: Jarosaw T. Kumierek, Ph.D., Department of Molecular Biology, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawiskiego 5a, 02-106 Warsaw, Poland (e-mail: jareq{at}ibb.waw.pl).
Background: The level of 8-oxoguanine (8-oxoG), a general marker of oxidative DNA damage, in DNA is the result of both an equilibrium between the rates of its formation and removal from DNA by DNA repair enzymes and the removal of 8-oxodGTP from the cellular nucleotide pool by hydrolysis to 8-oxodGMP, preventing its incorporation into DNA. To determine the contribution of each component to the level of 8-oxoG in DNA, we compared 8-oxoG–excising activity (encoded by hOGG1), 8-oxodGTPase activity (encoded by hMTH1), and 8-oxoG levels in DNA from tumors and surrounding normal lung tissues from non–small-cell lung cancer patients. Methods: We measured the level of 8-oxoG in DNA of 47 patients by high-performance liquid chromatography/electrochemical detection (HPLC/ECD), hOGG1 activity in tissue extracts of 56 patients by the nicking assay using an oligodeoxynucleotide containing a single 8-oxoG, and hMTH1 activity in tissue extracts of 33 patients by HPLC/UV detection. All statistical tests were two-sided. Results: The 8-oxoG level was lower in tumor DNA than in DNA from normal lung tissue (geometric mean: 5.81 versus 10.18 8-oxoG/106 G, geometric mean of difference = 1.75; P<.001). The hOGG1 activity was also lower in tumor than in normal lung tissue (geometric mean: 8.76 versus 20.91 pmol/h/mg protein, geometric mean of difference = 2.39; P<.001), whereas the hMTH1 activity was higher in tumor than in normal lung tissue (geometric mean: 28.79 versus 8.94 nmol/h/mg protein, geometric mean of difference = 0.31; P<.001). The activity of hMTH1 was three orders of magnitude higher than that of hOGG1 (nanomoles versus picomoles per hour per milligram of protein, respectively). Conclusions: Several different components contribute to the maintenance of 8-oxoG levels in human DNA, with the greatest contributor being the removal of 8-oxodGTP from the cellular nucleotide pool by hMTH1.
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