H. Luo et al., ROLE OF CHROMIUM(IV) IN THE CHROMIUM(VI)-RELATED FREE-RADICAL FORMATION, DG HYDROXYLATION, AND DNA-DAMAGE, Journal of inorganic biochemistry, 64(1), 1996, pp. 25-35
A reactive Cr(IV) ester was synthesized from a reaction of CrO3 with 2
,4-dimethyl-2,4-pentanediol as verified by electron spin resonance (ES
R) and magnetic susceptibility measurements. ESR spin trapping studies
demonstrate that the Cr(IV) ester is capable of generating hydroxyl f
ree radical ((OH)-O-.) through a Fenton-like mechanism (Cr(IV) + H2O2
--> Cr(V)+ (OH)-O-. + OH-) with a concomitant generation of Cr(V) spec
ies (g = 1.9787). Cr(IV) caused DNA strand breaks as measured by elect
rophoretic assays. H2O2 enhanced the DNA strand breaks via (OH)-O-. fo
rmation by a Cr(IV)-mediated Fenton-like reaction. In the Cr(IV)/H2O2
system, formate did not block Cr(V) formation, but prevented DNA damag
e, indicating that (OH)-O-. radicals, and not Cr(V), caused the DNA da
mage. Reaction of Cr(VI) with ascorbate was also used as a source of C
r(IV). Incubation of Cr(VI), ascorbate, and DNA caused DNA strand brea
ks. A free radical trap, 5,5-dimethyl-1-pyrroline (DMPO), only slightl
y inhibited the DNA damage. Addition of Mn(II), which inhibited Cr(IV)
, caused significant protection. H2O2 enhanced the DNA damage via Cr(I
V)-mediated (OH)-O-. radical generation and Mn(II) inhibited the damag
e, again showing that Cr(IV) and its related (OH)-O-. generation cause
d DNA strand breaks. HPLC measurements showed that (OH)-O-. radicals g
enerated by a Cr(IV)-mediated Fenton-like reaction generated 8-hydroxy
-2'-deoxyguanosine from 2'-deoxyguanosine. The results demonstrate tha
t Cr(IV) and its generated (OH)-O-. radicals are capable of damaging D
NA. Moreover, in comparison with Cr(V), Cr(IV) is a more potent DNA da
maging agent.