THE EFFECT OF L-CARNITINE AND ACETYL-L-CARNITINE ON THE DISAPPEARANCEOF DNA SINGLE-STRAND BREAKS IN HUMAN PERIPHERAL-BLOOD LYMPHOCYTES

DNA single-strand breaks (SSBs) and their disappearance during repair incubation were determined by alkaline filter elution in freshly isola ted human peripheral blood lymphocytes (PBLs) after in vitro treatment with either the oxygen radical-generating system of xanthine oxidase (XOD) plus hypoxanthine (HYP) or the alkylating agent N-ethyl-N'-nitro sourea (ENU). The elution curves obtained with DNA from PBLs treated w ith XOD/HYP were markedly non-linear, possibly as a result of a nonran dom induction of SSBs along the DNA strands. The disappearance of XOD/ HYP-induced SSBs during the initial repair period was quite slow; only 20 +/- 7% (n = 6) of the induced SSBs had disappeared after a 2 1/2 h repair incubation. However, by 24 h the elution curves obtained with DNA from treated PBLs were indistinguishable from those obtained with DNA from non-treated control cells, indicating complete repair. Treatm ent of PBLs with ENU resulted in linear elution curves. Approximately 50% of the total amount of ENU-induced SSBs had disappeared within 1 h in PBLs from most donors; the additional SSBs were found to be persis tent (Beorrigter, M.E.T.I., Mullaart,E., Berends,F. and Vijg,J. (1991) Induction and disappearance of DNA strand breaks and/or alkali-labile sites in human lymphocytes exposed to N-ethyl-N'-nitrosoureas. Carcin ogenesis, 12, 77-82). Preincubation of PBLs with 5 m.M L-carnitine, a trans-mitochondrial carrier of acetyl and long-chain acyl groups, or 5 mM acetyl-L-carnitine, resulted in a more rapid disappearance of XOD/ HYP-induced SSBs (48 +/- 23% and 48 +/- 30% respectively). Preincubati on of PBLs with different doses of L-carnitine, before exposure to 0.5 mM ENU, increased SSB disappearance dependent on the dose and donor P BLs. In conclusion, these studies suggest that treatment with L-carnit ine accelerates the disappearance of SSBs induced by oxygen radicals a nd alkylating agents.