Study On Biomarkers For Chronic Peripheral Neurotoxicity Of N-hexane

Objective:To study on the time-course changes of peripheral neurotoxicity induced by n-hexane, to demnonstrate the feasibility of 2,5-HD as the exposure biomarker through occupational epidemiological survey, and to search for early neurotoxic effect biomarkers of N-hexane.Method:①9 hospitalized patients with N-hexane poisoning were investigated, all the medical histories and occupational histories were collected, neurological examinations and ENMG were taken periodically, and the exposed chemicals at workplace was identified. Results of examination were analyzed using statistic software to describe the characteristics.②Characteristics of N-hexane exposure of workers engaged in work processing were studied. Workers exposed to N-hexane in a furniture factory in Minhang district, Shanghai were recruited, questionnaires were completed by workers, area sampling for air N-hexane were taken at workplaces and spot urine samples were collected from workers after shifts. Air samples and urinary samples were assayed by gas chromatography. Correlations between TWAg of air N-hexane and urinary 2,5-HD levels were analyzed.③Rats were sub-chronically administered with N-hexane by gavage at a dose of 0,104mg/kg/d,417mg/kg,1667mg/kg/d seperately. Peripheral nerve injury was verified by specific symptoms and neuropathological examinations. Electrophysiological tests were carried dynamically in multiple time points during administration on rat tail sensory and motor nerve potential amplitude, latency, conduction velocity and other indicators were recorded. Time-course changes of these indicators were analyzed. Simultaneously several possible early effect biomarkers named myelin basic protein (MBP), neuron-specific enolase (NSE), nerve growth factor (NGF), neurofilament (NF) levels in serum of rats were detected.Results:①Achilles tendon reflex, knee reflex, radial periosteal reflex, biceps reflex reduced or lost in neurological exams. ENMG of the cases showed increased muscle spontaneous potential, abnormal wave phase in muscle contraction, decreased nerve conduction velocity (p<0.01), extended distal latency (p<0.01), decreased wave amplitude (p<0.05). After neurotrophic treatment plus supplemented physical exercise, condition of patients have significantly improved (p<0.01).②Airborne N-hexane TWA8 levels in workshop ranged from 1.8-9.9mg/m3.206 workers were recruited and urine samples were taken from 95.15% of them. The arithmetic mean (AM) and geometric mean (GM) of specific-gravity-adjusted urinary 2,5-HD levels were 0.50μg/ml and 0.33μg/ml respectively. Urinary 2,5-HD level was significantly correlated with TWA8 concentration of airborne N-hexane (coefficient= 0.174, p=0.015) and total personal exposure amount of airborne n-hexane (coefficient= 0.280, p=0.000). Subjective symptoms score of workers was correlated with total personal exposure amount of airborne N-hexane too (coefficient=0.159,p=0.045).③After 18 weeks N-hexane exposure, rats with the dose of 1667mg/kg·d were paralyzed in hind limb, with a ratio of 81.2%, body weight were lost significantly, typical peripheral nerve poisoning symptoms were manifested. Neural atrophy, attenuated nerve, sparse neuraxon, increased gap and demyelination were revealed by histopathological examination. Nerve conduction velocity examination showed that sensory nerve distal latency extended by 78.78% (P<0.05), conduction velocity declined by 64.26%(P<0.05), potential amplitude declined partially. Notable changes occurred from the 4th week of administration. Motor nerve distal latency extended by 264.02%(P<0.05). Conduction velocity declined by 51.95%(P<0.05). Potential amplitude declined by 62.86%. Notable changes occurred from the 2rd week of administration. Serum NSE,NF levels increased in N-hexane exposed rats, P<0.05, the maximum rise were 122.94% and 193.35% respectively. There were no significant change in MBP levels (P>0.05). Serum NGF levels decreased in certain time points, respectively (P<0.05).Conclusion:①ENMG of chronic occupational n-hexane poisoning showed peripheral nerve injury, which was worse in lower limbs than in upper limbs. and the motor nerves were more vulnerable than the sensory nerves. Meanwhile these patients had better recoveries after treatments. After months of disengaging with N-hexane, the patient condition had been still getting worse. ENMG manifestations were not exactly parallel with clinical manifestations. Clinical recovery preceded the improvements of ENMG. Neurotrophic therapy should be the primary way to cure the disease with rather favourable prognosis.②Workers in furniture factory in Minhang District we surveyed were occupationally exposed to n-hexane at fairly low levels. Workers in adhesive spraying workshop were exposed to the highest concentration of N-hexane, resulting in an increase in the urinary 2,5-HD. It would be effective to control N-hexane exposure focusing on this tache. There was a very slight adverse influence on body at this exposure level. Workers can be protected for health under current occupational exposure limits.③Peripheral nerve of rats could be damaged by N-hexane. Motor nerve was damaged earlier and more obviously than sensory nerve. Neurophysiologic indicators preceded actual symptom and had good correlation with neurobehavioral symptoms. Nerve conduction velocity and distal latency were sensitive indicators. Serums NSE, NF were the most sensitive indicators, which increase preceded the symptom of animals and changed substantially, could be used as good biomarkers of toxic effect induced by N-hexane. Significance of MBP and NGF used as neurotoxic effect biomarker induced by N-hexane were remained to be verified.