Poor metabolization of n-hexane in Parkinson's disease

Although genomic screening studies have identified several genes associated with Parkinson's disease (PD), there is evidence that environmental factors are also involved in the pathogenesis of the disease and that hydrocarbon-solvents may be one of them. The genetic component is less evident in late-onset PD. To assess whether age and PD may affect the catabolism of the hydrocarbon n-hexane, a two-part study was performed. In the first part the urinary levels of its main metabolites, 2,5-hexanedione and 2,5-dimethylpyrroles, were measured in 108 patients and 108 healthy controls, matched by age and sex. Metabolite urinary excretion was significantly reduced in PD patients as compared with controls and was inversely related to age in both groups. In the second part the same comparison was made between 24 non-smoking and 10 smoking patients, matched to controls, after smoking of a hydrocarbon-rich cigarette. In these subjects also n-hexane and 2,5-hexanedione blood levels were measured. There was no appreciable difference in n-hexane blood levels between patients and controls in non-smokers, whereas there was a significant increase in patients over controls in smokers (p < 0.01). 2,5-hexanedione blood levels were significantly lower in patients than in healthy controls, both in non-smokers and in smokers, but the reduction was more pronounced in smokers (-46.3% versus - 10.7%). The same was true for 2,5-hexanedione and 2,5-dimethylpyrrole urinary levels. This study suggests that aging and PD may be associated with a reduction in the capacity to eliminate the hydrocarbon n-hexane. This metabolic alteration may play a role in the pathogenesis of PD.