*3.3.3 Effect of Ni (II) on formation of DNA adduct 8-OHdG*

After an 8-OHdG analysis was performed on the rats' urine samples of group C (rats given exposure to BPA and Ni (II) metals), a chromatogram was obtained with results as in **Figure 8**. 8-OHdG in rats' urine samples exposed to BPA and Ni (II) metals were detected at retention time of 0.733 min.

Exposure to BPA and Ni (II) metals may also have an effect that may lead to the formation of an 8-OHdG DNA adduct. As shown in **Figure 9**, 8-OHdG levels in mice exposed to BPA and Ni (II) metals were greater than those of controls.

The 8-OHdG concentration in mice given exposure to BPA and Ni (II) at a dosage of 0.1 μg/kg bw also increased from exposure time of 1st to 4th week ie from 26.185 ng/mL to 28.696 ng/mL. In this condition, the concentration of 8-OHdG is also above the LOD value. This is sufficient to prove that 8-OHdG can be formed and detected due to exposure to BPA and metal Ni (II) in vivo.

### **Figure 7.**

*Possible BPA mechanism in the human body (reprocessed). 1: Cytochrome P450; 2: Cytochrome P450 reductase. (Source: Atkinson and Roy [18]).*

**Figure 8.** *Chromatogram of mouse urine samples given exposure to BPA and Ni (II).*

*In Vivo Study of DNA Adduct (8-OHdG) Formation of* Rattus novergicus *Using Bisphenol… DOI: http://dx.doi.org/10.5772/intechopen.99432*

One of the harmful effects of the nickel mechanism in the body is to induce the formation of ROS and increase lipid peroxidation in the cells [21]. Given that nickel is not an essential element for humans, it is not yet clear how nickel compounds go through the metabolic phase.

However, the resulting 8-OHdG levels of rats given exposure to BPA and Ni (II) were smaller than the 8-OHdG levels produced by rats given BPA exposure alone. The results can be seen in **Figure 10**.

This may be due to metabolic differences between rats and also because the doses given to mice are too small. A dose of 0.1 μg/kg bb resulted in an 8-OHdG increase each week in rats, but the levels remained smaller than the 8-OHdG levels obtained from rats given BPA exposure.

Oxidative stress of DNA of transition metals can possibly occurred due to the presence of free radicals produced by Fenton or Fenton-like reaction [22]. The major form of free radicals are hydroxyl radicals [17]. Nickel (II) at the excessive


### **Figure 9.**

*The comparison graph of 8-OHdG concentrations in control and mouse rats given exposure to BPA and Ni (II).*

### **Figure 10.**

*Graph of comparison of 8-OHdG levels in rats given exposure to BPA and rats given exposure to BPA and Ni (II).*

levels has a role in Fenton-like reaction to the formation of free radicals. Nickel (II) exposure in rats can cause a significant increase in lipid peroxidation, and a decrease of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH) [23].

Ni2+ is the largest nickel ionic species in the cell. There is the possibility of a Fenton-like reaction with nickel but only with the Ni2+ interaction with certain ligands, such as Gli-Gli-His (Glycyl-Glycyl-Histidin) or imidazole nitrogen from histidine [24]. The binding of Ni2+ to these ligands eliminates the oxidation potential of Ni2+ in which hydrogen peroxide can catalyze the oxidation of nickel to a higher oxidation state. This reaction produces a radical but the reaction depends on the binding of Ni2+ with certain ligands [25]. Thus, although nickel can produce oxidative stress in cells and oxidize the DNA bases, certain nickel compounds with carcinogenic potentials exhibit weak mutagenic activity in some mutation tests. However, chromosomal damage that causes mutations of a detectable gene produced by some nickel compounds may contribute to its carcinogenesis properties [26]. One interesting feature of the nickel compound is its synergistic nature with other compounds or agents that can cause cancer by its mutagenic mechanism. For example, synergic nickel with benzo [a]pirene, UV, and radiation [11]. It can also explain the absence of synergistic effects between BPA and Ni (II).
