Damage to mitochondrial DNA induced by the quinolone Bay y 3118 in embryonic turkey liver

Quinolones are a class of antibiotics that induce damage to and lass of DNA from bacteria. The structural organization of bacterial DNA is more simila r to eukaryotic mitochondrial DNA (mtDNA) than to eukaryotic chromosomal or nuclear DNA (nDNA). Antibiotics affecting the bacterial genome may therefo re preferentially damage mtDNA rather than nDNA. We investigated the effect of a quinolone on mtDNA in avian embryonic hepatocytes in ovo. The quinolo ne Bay y 3118 (1-cyclopropyl-7-(2,8-diazabicyclo[4.3.0]non-8-yl) 6-fluoro-8 -chloro-1,4-dihydro-4-oxo-3-quinolinecarboxylic acid hydrochloride, chemica l structure see Bremm et al. [K.D. Bremm, U. Petersen, K.G. Metzger, R. End ermann, In vitro evaluation of Bay-y 3118, a new full-spectrum fluoroquinol one, Chemotherapy 38 (1992) 376-387] was injected into fertilized turkey eg gs 8 days before hatching at doses of 1, 3, 10 and 30 mg per egg. The embry os were removed from the eggs after 4 days and liver samples were shock fro zen. Mitochondrial DNA was purified from samples of the embryonic Liver. Th e integrity of mtDNA was investigated by electrophoresis on agarose gels wi th native mtDNA and with ribonuclease-treated mtDNA. Fluorescent staining o f the electrophoresis gels allows the densitometric quantification of the m tDNA of the regular band at 16 kilobases (kb) and the amount of DNA fragmen ts of irregular size (smear). The genotoxic nitrosamine nitrosodiethylamine (NDEA) has previously been shown to reduce the content of mtDNA of the reg ular size of 16 kb and to induce the occurrence of smaller fragments of mtD NA [H. Enzmann, C. Kuhlem, E. Loser, P. Bannasch, Damage to mitochondrial D NA induced by the hepatocarcinogen, diethylnitrosamine in ovo, Mutation Res , 329 (1995) 113-120]. After exposure to 10 and 30 mg Bay y 118, a dose-dep endent induction of damage to the mtDNA was found, whereas exposure to 3 an d 1 mg showed no effect. NDEA (25 mg) was used as positive control. Testing chemical compounds in the in ovo model is a simple and rapid approach for investigations on chemically induced alterations of mtDNA. (C) 1999 Elsevie r Science B.V. All rights reserved.