ROLE OF INTRACELLULAR DEOXYNUCLEOSIDE TRIPHOSPHATES IN LEVELS IN DNA DAMAGE IN HUMAN PERIPHERAL BLOOD LYMPHOCYTES: 37

Abstract

The effect of deoxynucleosides on single strand chromosomal breaks in peripheral blood lymphocytes (PBL) were measured both by the sucrose gradient nucleoid sedimentation method and by alkaline unwinding followed by fluorimetric measurement of etidium bromide binding to double stranded DNA. Extracellular deoxyadenosine (0.3-10 μM) in the presence of deoxycoformycin (1 μM) cause extensive DNA damage in PBL in a concentration dependent manner. The appearance of DNA damage following deoxyadenosine addition to PBL correlated with the accumulation of intracellular dATP levels. Extracellular deoxycytidine (50 μM) inhibited the accumulation of intracellular dATP from deoxyadenosine and in parallel prevented the DNA damage caused by deoxyadenosine in PBL. On the other hand, addition of extracellular deoxyguanosine (50 μM) or thymidine (50 μM) also completely prevented the DNA damage by deoxyadenosine but without interferring with dATP accumulation. Measurements of intracellular deoxynucleoside triphosphates levels in PBL show extremely low levels of dGTP, dCTP and TTP and higher levels of dATP. It is possible that the marked increase of intracellular dATP levels combined with the extremelylow levels of the other deoxynucleoside triphosphates interfer with DNA repair process in resting PBL resulting in the appearance of single stranded breaks. Thymocytes, which contain higher levels of deoxynucleoside triphosphates, did not show DNA damage in the presence of deoxyadenosine.