Chemico-Biological Interactions 115 (1998) 85 – 107
Protection of DNA in HL-60 cells from damage
generated by hydroxyl radicals produced by
reaction of H
2
O
2
with cell iron by
zinc-metallothionein
Wael G. Elgohary, Sarfraz Sidhu, Susan O. Krezoski,
David H. Petering, Robert W. Byrnes *
Department of Chemistry, P.O. Box 413, Uni6ersity of Wisconsin -Milwaukee, Milwaukee,
WI 53201, USA
Received 20 February 1998; received in revised form 26 May 1998; accepted 11 June 1998
Abstract
Scavenging of hydroxyl radicals (
OH) by the zinc form of metallothionein (ZnMT) was
studied in HL-60 cells and in nuclei from such cells previously treated with ZnCl
2
(ZnMT
cells). Cells were grown for 48 h to label DNA for alkaline elusion experiments. During the
last 24 h 0.1 mM ZnMT was included to induce ZnMT. Generation of DNA single-strand
breaks (SSBs) by H
2
O
2
in cells (5 ×10
5
/ml) treated at 4° was increased by approximately
70% in Zn-treated cells by comparison with control cells. These cells had grown from an
initial concentration of 5 ×10
5
/ml to a concentration at harvest of 16 ×10
5
/ml. Cells started
at 6 ×10
5
/ml and growing to a final concentration of 20 ×10
5
/ml did not exhibit a similar
increase in SSBs. This elevation in SSBs was traced to an increase in cell Fe content which
exhibited a sharp dependence upon concentrations of cells and of ZnCl
2
at the time of
addition. The diffusion distance (d ) from Fe to DNA of ZnMT cells treated with H
2
O
2
was
found to be 3.4 nm. This compares with a distance of 6.1 nm in control cells. SSB generation
by hydroxyl radicals formed by
137
Cs-g rays in Zn-treated cells decreased by 12%, accompa-
Abbre6iations: DMSO, dimethyl sulfoxide; DRF, dose reduction factor; NEB, nuclear extraction
buffer; NEM, N-ethylmaleimide; NTB, nuclear treatment buffer; MT, metallothionein; SSB, single
strand break.
* Corresponding author. Present address: 3950 Mahaila Avenue, Apt. J-15, San Diego, CA 92122,
USA. Tel: +1 619 6239756
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