Evidence for zinc protection against 2,5-hexanedione toxicity by co-exposure of rats to zinc chloride

Role of N-acetylcysteine in protecting against 2,5-hexanedione neurotoxicity in a rat model: changes in urinary pyrroles levels and motor activity performance

The interference of N-acetylcysteine (NAC) on 2,5-hexanedione (2,5-HD) neurotoxicity was evaluated through behavioral assays and the analysis of urinary 2,5-HD, dimethylpyrrole norleucine (DMPN), and cysteine-pyrrole conjugate (DMPN NAC), by ESI-LC-MS/MS, in rats exposed to 2,5-HD and co-exposed to 2,5-HD and NAC. Wistar rats were treated with 4 doses of: 400mg 2,5-HD/kg bw (group I), 400mg 2,5-HD/kg bw+200mg NAC/kg bw (group II), 200mg NAC/kg bw (group III) and with saline (group IV). The results show a significant decrease (p<0.01) in urinary DMPN and free 2,5-HD, a significant increase (p<0.01) in DMPN NAC excretion, and a significant recovery (p<0.01) on motor activity in rats co-exposed to 2,5-HD+NAC, as compared with rats exposed to 2,5-HD alone. Taken together, our findings suggest that at the studied conditions NAC protects against 2,5-HD neurotoxicity and DMPN may be proposed as a new sensitive and specific biomarker of 2,5-HD neurotoxicity in animals treated with a toxic amount of 2,5-hexanedione.

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.

Evidence of zinc protection against 2,5-hexanedione neurotoxicity: correlation of neurobehavioral testing with biomarkers of excretion

Risk prevention of human exposure against n-hexane neurotoxicity is relevant towards the protective measures to be proposed in occupational toxicology. Metabolic studies have identified 2,5-hexanedione (2,5-HD) as the main neurotoxic metabolite of n-hexane, which reacts with amino groups of lysine in axonal neurofilaments forming 2,5-dimethylpyrrole adducts, which are responsible for n-hexane neurotoxicity. In the present study, we have investigated the interaction of zinc with 2,5-HD, by correlating the decrease of pyrrole derivatives excretion with changes of neurobehavioral effects. Two subchronic experiments (11 and 8 weeks of exposure) were performed in Wistar rats exposed to different doses of 2,5-HD (200, 400 mg/kg per day) and to the mixture of 2,5-HD + zinc acetate (200 + 300 mg/kg per day) and (400 + 500 mg/kg per day). The results obtained show a significant increase in the excretion of pyrroles in the groups exposed to 2,5-HD alone as compared to controls, and a significant decrease in the excretion of pyrrole derivatives in the groups of rats co-exposed to 2,5-HD + zinc acetate when compared to the rats exposed to 2,5-HD alone. These biochemical changes were immediately evident after the first day of exposure. Simultaneously, neurobehavioral testing (rearing and ambulation in open field) was performed weekly in the same groups of rats. The results demonstrated a significant decrease in neurobehavioral dysfunction in rats co-exposed to 2,5-HD and zinc acetate. At the end of the exposure period, pyrroles levels returned to control values progressively, and the recovery of the neurotoxic effects was gradually established depending on the dose of exposure. The results suggest that zinc is a potential chemo-protector against 2,5-HD neurotoxicity which was identified by neurobehavioral testing. Moreover, pyrrole derivatives are good predictive biochemical biomarkers of 2,5-HD exposure and could be used as a complementary tool to characterize its neurotoxic effects.

Interaction of zinc on biomarker responses in rats exposed to 2,5-hexanedione by two routes of exposure

The interaction of zinc(II) on the toxicokinetics of 2,5-hexanedione (2,5-HD), the ultimate toxic metabolite of n-hexane, was performed by quantifying the changes of two urinary biomarkers, free 2,5-HD and pyrrole derivatives, in rats exposed to 2,5-HD and to 2,5-HD plus zinc acetate. Eight groups of Wistar rats were exposed for 4 days (dietary and intraperitoneally) to 2,5-HD, zinc acetate and 2,5-HD plus zinc acetate and the 24 h urine was used to determine the excretion of these biomarkers. On comparing the results obtained by the two routes of exposure with different doses of 2,5-HD and zinc acetate, it was observed that there was a significant decrease (P<0.05) in the excretion of free 2,5-HD and pyrroles derivatives in rats exposed to the chemical mixture, when compared with the excretion of these biomarkers in rats exposed to 2,5-HD alone. To evaluate the mechanism of this interaction, further experiments were performed using one group of rat dietary pre-exposed to zinc acetate followed by 2,5-HD exposure. The results of our experiment suggest that zinc protect proteins of pyrrolization by coordination to amino groups, with the subsequent inhibition of protein cross-linking responsible by 2,5-HD neurotoxicity.