efsa-opinion-chromium-food-drinking-water

Chromium in food and drinking water
7.2.1.5. Oxidative DNA damage and cytotoxicity
In vitro studies
Levis et al. (1978) studied the cytotoxic effects of Cr(III) and Cr(VI) compounds in cultured hamster
fibroblasts (BHK line) and human epithelial-like cells (HEp line) by measuring as end-points cell
growth and nucleic acid and protein synthesis. The authors concluded that the cytotoxic effects of Cr
can be attributed to the action of Cr(VI) at the plasma membrane level on the mechanisms involved in
nucleoside uptake, and to the interaction of Cr(III) at the intracellular level with nucleophilic targets
on the DNA molecule.
Reactive Oxygen Species (ROS) and DNA fragmentation were measured in murine macrophage cells
following exposure to Cr picolinate and Cr polynicotinate. The induction of oxidative damage was
attributed to the picolinate moiety (Olin et al., 1994).
Oxidative damage was measured in cultured macrophage cells (J774A.1) following exposure to
Cr(III) picolinate and Cr nicotinate (Bagchi et al., 1997). Small dose-dependent increases in lipid
peroxidation, superoxide anion and hydroxyl radical production and DNA fragmentation were
observed with both Cr salts, compared to control, with greater increases in the case of Cr(III)
picolinate in comparison to Cr nicotinate.
Speetjens et al. (1999) reported that in the presence of reductants (ascorbate) and air, Cr(III) picolinate
is capable of generating hydroxyl radicals which in turn can cleave supercoiled plasmid DNA. A
mechanism is proposed where Cr(III) picolinate is reduced by biological reductants to Cr(II)-
containing species that are susceptible to air oxidation, thus resulting in the catalytic generation of
hydroxyl radical. They also reported that in the absence of reductants, hydrogen peroxide can interact
with Cr(III) picolinate to produce hydroxyl radicals by a second, less efficient mechanism.
Human HaCaT keratinocytes were exposed for 24 hrs to Cr(III) complexes and oxidized bases were
measured as 8-hydroxy-2’-deoxyguanosine (Hininger et al., 2007). Concentrations of Cr(III) chloride,
Cr(III) histidinate and Cr(III) picolinate that did not result in cytotoxic effects did not produce
oxidative DNA damage. Cell exposure at LD 50 concentrations (as determined by the MTT test) led to
a significant increase in oxidized bases with Cr(III) chloride but not with Cr(III) histidinate.
Jana et al. (2009) studied the effect of Cr(III) picolinate uptake in peripheral blood lymphocytes by
measuring cytotoxicity and markers of apoptosis. Concentrations of Cr(III) picolinate varying from
5 to 100 μM for different exposure times were tested. The results indicated that Cr(III) picolinate
induces apoptosis in a dose-dependent manner. The involvement of ROS in this phenomenon is
strongly suggested by the inhibition of apoptosis following pretreatment of the cells with the
antioxidant N-acetyl cysteine and by the induction of markers of apoptosis including cytosolic
cytochrome c release that indicate mytocondrial alterations.
In vivo studies
Cupo and Wetherhahn (1985) measured the binding of either sodium dichromate or Cr(III) chloride to
DNA in vivo in rat liver and kidney. Cr was found bound to DNA, nuclear proteins, and RNA protein
fraction in liver and kidney tissues, following an i.p. injection of either sodium dichromate or Cr(III)
chloride. At early times, there was much less Cr binding to chromatin and DNA after Cr(III) treatment
than after Cr(VI) treatment. In addition, after Cr(III) treatment, a large percentage of the Cr bound to
chromatin was associated with protein rather than with the DNA. However, 40 hr after injection there
was no significant difference in the level of Cr binding to DNA after either Cr(VI) or Cr(III)
treatment. In spite of the binding, at this time, DNA damage was found in the kidney only after Cr(VI)
but not Cr(III) treatment, suggesting that while Cr(III) was bioavailable it was not particularly
bioactive.
The ability of some Cr(III) complexes to undergo Fenton-type reactions could also contribute to their
genotoxicity. The generation of oxidative damage by Cr(III) picolinate is suggested by in vivo studies
EFSA Journal 2014;12(3):3595 79