Rubratoxin B elicits antioxidative and DNA repair responses in mouse brain

Abstract

Rubratoxin B (RB) is a mycotoxin with potential neurotoxic effects that have not yet been characterized. Based on existing evidence that RB interferes with mitochondrial electron transport to produce oxidative stress in peripheral tissues, we hypothesized that RB would produce oxidative damage to macromolecules in specific brain regions. Parameters of oxidative DNA damage and repair, lipid peroxidation, and superoxide dismutase (SOD) activity were measured across six mouse brain regions 24 h after administration of a single dose of RB. Lipid peroxidation and oxidative DNA damage were either unchanged or decreased in all brain regions in RB-treated mice compared with vehicle-treated mice. Concomitant with these decreased indices of oxidative macromolecular damage, SOD activity was significantly increased in all brain regions. Oxyguanosine glycosylase activity (OGG1), a key enzyme in the repair of oxidized DNA, was significantly increased in three brain regions--cerebellum (CB), caudate/putamen (CP), and cortex (CX)--but not in the hippocampus (HP), midbrain (MB), and pons/medulla (PM). The RB-enhanced OGG1 catalytic activity in these brain regions was not due to increased OGG1 protein expression, but was a result of enhanced catalytic activity of the enzyme. In conclusion, specific brain regions responded to an acute dose of RB by significantly altering SOD and OGG1 activities to maintain the degree of oxidative DNA damage equal to, or less than, that of normal steady-state levels.

Figure 1

Content of TBARS in different regions of mouse brain exposed to RB (striped bars) in comparison with control (opened bars). All values represent mean ± SE. The significantly (p < 0.05) different levels of TBARS in comparison with control are indicated by asterisks.

Figure 2

Relationship between relative indices of OGG1 activity and accumulation of 8-oxodG in various regions of mouse brain. Relative indices represent values normalized to the correspondent controls.

Figure 3

OGG1 expression in different regions of mouse brain. The Western blot lanes depicted by C_CB–C_PM array show the level of OGG1 in control mouse, and lanes from R_CB to R_PM represent OGG1 expression in the brain of RB-intoxicated animal. Pure enzyme presented as a positional marker for OGG1 identification.

Figure 4

Determination of OGG1 on native PAGE. Enzymatic activity of OGG1 was assayed in every single fraction by using ³²P-duplex oligonucleotide. Upper panel represents ³²P-duplex oligonucleotide products visualized with Biorad-363 Phosphoimager System. Lower panel represent the averaged data of three experiments with OGG1 extracted from HP of control mouse. OGG1 activity was calculated as the percent of radioactivity in the band of specifically cleaved product over the total radioactivity in the lane.

Figure 5

Kinetic behavior of OGG1 extracted from different regions of brain. Circles represent OGG1 obtained from CP of mouse exposed to RB. Squares represent OGG1 obtained from CP of control mouse. Data expressed by means of three replications.