The Role Of Myelin Protein Zero In N-hexane-induced Peripheral Nerve Injury

In recent sereval years, there has been an increasing number of reported cases of n-hexane-induced peripheral neuropathy in China. Because of high incidence, serious harm, and lack of early screening biomarker, n-hexane neuropathy has drawn greater attention by both public and workers. N-hexane is metabolized to a number of compounds, including 2,5-hexanedione (2,5-HD), which is reconigized to be the ultimate neurotoxic agent of it. The pathological alterations of n-hexane-induced chronic peripheral neuropathy including Wallerian-type degeneration and segmental demyelination, but its mechanisms are still not clear. Myelin protein zero (P0) is the major structural element of peripheral myelin that plays a very important role in maintaining the stability of myelin.Based on our previous studies, this paper emphatically discusses the role of P0 in 2,5-HD-induced peripheral nerve demyelination, and the possibility of Po in serum owing to demyelination as a potential marker of n-hexane-induced peripheral neuropathy. Peripheral nerve myelin does not elicit an immune response because of isolation by blood-nerve barrier (BNB), but as the BNB destroyed during the peripheral nerve injury, it can induce immunity response against myelin protein including Po. The effect of immunization participated in pathogenesis of peripheral nerve demyelination was preliminary investigated. For the oxidative damage and other effects induced by m-hexane, extract of ginkgo biloba leaves (Egb761) was also used for intervention study on m-hexane-induced peripheral neuropathy, and the mechanism of 2,5-HD-induced peripheral neuropathy was investigated according to the mechanism of pharmacological actions of Egb761.1. The effect of n-hexane on the level of Po in sciatic nerve To examine the effect of 2,5-HD on the levels of Po in sciatic nerve, Wistar rats were treated with different doses of 2,5-HD (50,100,200,400 mg/kg.d) for 4 weeks, to establish the toxicity model for peripheral nerve injury. Evans-blue (EB),the fluorescent penetrant, was used to study the the blood-nerve barrier (BNB) permeability of the sciatic nerve. Especially the changes in the levels of Po and P0 mRNA in rat sciatic nerves was investigated. The result showed that after given 2,5-HD, the rats weight gain reduced, showed tip-toe walking,foot spay with limb abduction and inability to support body weight. Correspondingly, the peripheral nerve injury was more seriously. There were more EB fluorescence observed in sciatic-tibial nerves of rats treated by 2,5-HD. The level of EB extracted in formamide was determined by fluorimetric spectrophotometry. As the dosage of 2,5-HD increased, the higher level of EB in sciatic-tibial nerves was observed, the permeability of BNB was augmented. The results also showed that the expression of Po mRNA and P0 protein decreased in a dose-dependent manner after treatment with 2,5-HD for 4 weeks. Correlation analysis showed significantly correlation between gait score and body weight, as well as BNB permeability and the level of P0 (P<0.05), and they can indicate the peripheral nerve injury.2. The study of n-hexane on the level of Po protein in serumTo examine the possibility of Po in serum as a potential marker of n-hexane-induced peripheral neuropathy, the serum Po protein of 13 workers were detected by Western blotting. The result demonstrated that 6 of 7 patients were positive, while 2 of 6 control were positive. The level of P0 in serum from different cities was also detected by ELISA. All relative value were expressed as the percentage of control of same city, and the ratios were analyzed. The result showed after exposed to n-hexane more than 6 months, the relative amout of Po protein in workers'serum increased (P<0.05),and the relative level of P0 in 23 n-hexane-induced peripheral neuropathy patients was 1.58, significantly higher (P<0.01)than the control group. And 9 patients were followed up, the result demonstrated that the P0 level could decreased markedly (P<0.05)in the recovery phase after months of treatment.3. The mechanism discussion of immunization in n-hexane induced peripheral neuropathyTo explore the effect of immunization in n-hexane induced peripheral neuropathy, the peripheral nerve myelin and the positive serum taken from the 2,5-HD induced peripheral nerve injury in rats, were respectively injected to the Wistar rats. The result displayed that treatment with myelin could not producing any toxic effects, and positive serum could slightly reduced the rats' body weight gain, but the statistical analysis gave a negative result (P>0.05).4. The protective effect of Ginkgo biloba extract (Egb761) on 2,5-HD-induced toxic peripheral neuropathyTo investigate the role of Egb761 on 2,5-HD-induced peripheral nerve injury, one hour before 400 mg/kg.d 2,5-HD treated, Egb761 (100 mg/kg.d) was pretreated. The signs of neurotoxic symptom induced by 2,5-HD, and the effect of P0 level in sciatic nerve was investigated. The result showed the gait score decreased (P<0.01), and the EB level in sciatic-tibial nerves was reduced. These indicated that pretreatment with Egb761 significantly reduced the signs of neurotoxicity induced by 2,5-HD, and protected the BNB interruption. Egb761 could also inhibited the decreasing tendency of Po and mRNA (P<0.05). P0 constitutes more than 50% of the total peripheral myelin protein, and it is the major adhesive and structural element of peripheral myelin. Combining the above results, it can be concluded that the change of P0 expression may play an important role in the toxic peripheral neuropathy induced by 2,5-HD, Egb761 has protective effects on P0 expression, and by which Egb761 reduce the 2,5-HD-induced peripheral neurotoxicity in rats.Conclusions (1) The alteration of Po may be an important mechanism of the toxic peripheral neuropathy induced by n-hexane, and by damaging the expression of Po, n-hexane induced demyelination.(2) The serum Po level may be a good biomarker of peripheral neuropathy induced n-hexane. (3) Egb761 reduced the damage of BNB permeability and Po expression induced by 2,5-HD, and has a protective effect against 2,5-HD-induced peripheral neurotoxicity in rats.