Atropine reverses antinociception induced by 2,5-hexanedione in rats

Exposure to 2,5-hexanedione is accompanied by ovarian and uterine oxidative stress and disruption of endocrine balance in rats

2,5-Hexanedione (2,5-HD) is an aliphatic diketone identified as the main neurotoxic metabolite of the industrial chemicals n-hexane and methyl-n-butyl ketone. Considering the dearth of information on the female reproductive toxicity effects of 2,5-HD in the literature, we assessed the potential oxidative stress mechanisms of 2,5-HD in the ovary and uterus of Wistar rats. A total of 32 female rats were randomly allotted to four groups, in which rats were exposed to 2,5-HD at doses of 0% (control), 0.25%, 0.5% and 1.0% respectively in their drinking water for 21 days. The results showed that 2,5-HD significantly increased ovarian and uterine malondialdehyde (MDA) and hydrogen peroxide (H2O2) levels (p < 0.05). Additionally, while significant decreases in ovarian catalase, superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione-S-transferase (GST) activities occurred in all the 2,5-HD-treated groups, uterine catalase, GST, and GPx activities increased. Further, 2,5-HD increased follicle stimulating hormone, but decreased estrogen levels in all the 2,5-HD-treated groups, while prolactin increased in the 0.5, and 1.0% 2,5-HD-treated rats compared with the control (p < 0.05). Thus, these data imply that 2,5-HD exposure disrupts hormonal homeostasis and induces oxidative stress in the ovary and uterus of rats. These findings may therefore have toxicological implications in women occupationally exposed to n-hexane and methyl-n-butyl ketone.

2,5-Hexanedione induced reduction in protein content and mRNA expression of neurofilament in rat cerebral cortex

Exposure chronically to n-hexane produces central-peripheral axonopathy mediated by 2,5-hexanedione (HD). Studies have shown neurofilament (NF) subunit proteins are decreased substantially in cerebral cortices, optic axons, spinal cords, and sciatic nerves from HD-exposed rats. To deeply investigate the alterations in NF contents in HD neuropathy, the relative levels of NF-L, NF-M, and NF-H in rat cerebral cortex were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. HD was administrated to Wistar rats by intraperitoneal injection at dosage of 200 or 400mg/kg. Rats were sacrificed after 6 weeks of treatment, and cerebral cortices were dissected, homogenized, and used for the determination of NF subunit proteins. The results, except for supernatant NF-L and NF-M that could not be assayed, showed HD intoxication resulted in significant decreases by 32-67% (P<0.01) in NF subunits in both of the pellet and supernatant fractions of cerebral cortex homogenate. As an initial investigation to determine how such changes in NF proteins might occur, the gene expression of NF-L, NF-M, and NF-H subunit mRNA was quantified using reverse transcription-polymerase chain reaction (RT-PCR). Statistical analysis revealed that HD exposure caused a significant reduction in the expression of NF-L and NF-H gene (P<0.05 or P<0.01), while the levels of NF-M mRNA kept unaffected (P>0.05). These suggest that the observed reduction in NF gene expression might be related to diminished levels of subunit proteins, while the actual contribution might be uncertain. The functional significance of the reduced protein contents and the regulation of gene expression remain to be determined.

2,5-Hexanedione inhibits rat brain acetylcholinesterase activity in vitro

A number of C(4)-C9 aliphatic ketones, including 2,5-hexanedione (2,5-HD), are acetylcholinesterase (AChE; EC 3.1.1.7) inhibitors. In the previous work, we demonstrated that antinociception induced by 2,5-HD was partially reversed by atropine. Since cholinergic system seems to be affected by hexacarbon compounds, in the present study we examined the effect of 2,5-HD on AChE activity of rat brain in vitro. The results demonstrated that both Km and Vmax were altered by 2,5-HD. At 5 mM 2,5-HD, there were no significant changes in Km or Vmax parameters, but at concentrations higher than 10 mM an increase in Km and a decrease in Vmax was observed. The Ki plot was linear and the curves intersect on the left of the 1/V versus [I] plot. These data characterize an inhibition of the mixed type. Although the 2,5-HD concentration that inhibited AChE activity is high compared to that attainable in occupationally exposed workers, these data are useful in understanding the neurotoxicity of this compound. Furthermore, the effect of 2,5-HD on AChE activity must not be a consequence of its effects as an organic solvent on protein structure, because total inhibition induced by 2,5-HD was partially reversed by increasing substrate concentration.

Early spatial memory deficit induced by 2,5-hexanedione in the rat

2,5-Hexanedione (2,5-HD), the major common neurotoxic metabolite of n-hexane and methyl n-butyl ketone, causes a delayed neuropathy with associated sensorimotor impairments. The question arises as to whether specific cognitive deficits occur even prior to changes in sensorimotor ability. The present experiments examined the effects of 2,5-HD on spatial navigation of rats in a water maze at levels/times that did not affect spontaneous exploratory motor activity in an open field holeboard apparatus. Exposure to 1% 2,5-HD in the drinking water for 2 weeks did not significantly affect escape learning, as measured by latency to find a hidden platform. However, 2,5-HD treated animals were impaired in the use of a spatial strategy during a recall test. A similar impairment in spatial memory was observed after i.p. injection of 500 mg/kg/day 2,5-HD for 4 days, in the absence of significant changes in sensorimotor ability or weight loss. Thus 2,5-HD may mediate some of the cognitive effects of hexacarbons and these changes can occur prior to the development of motor symptoms.