Occupational exposures and movement abnormalities among Japanese-American men: the Honolulu-Asia Aging Study

Mercury and Parkinson's Disease: Promising Leads, but Research Is Needed

Environmental toxicants are thought to play a major role in the pathogenesis of Parkinson's disease. In reviewing the literature on heavy metals known to be toxicants, we noted several recent studies on mercury suggesting a possible role in the etiology of some cases of this disease. We therefore undertook a review of this association, focusing especially on peer-reviewed articles to avoid the bias inherent in much of the literature regarding mercury. For most people, our contemporary exposure to mercury comes from dental amalgam tooth restorations and from eating fish contaminated with mercury. In both cases, mercury is known to get into the brain in utero and at all ages. It remains in the brain for many years and is known to produce permanent neuropsychological deficits. Mercury toxicity can produce tremors and other Parkinsonian clinical symptoms. It can also produce neurochemical and neuropathological changes similar to those found in Parkinson's disease, including the loss of dopamine neurons, degeneration of tubulin and axons, dysfunction of mitochondria, and the aggregation of alpha-synuclein. Relatively few studies have assessed mercury in parkinsonian patients, but almost all reported a statistically significant association. Published studies suggest some promising leads in the relationship between mercury exposure and Parkinson's disease. However, studies of patients are relatively few, and the need for research is clear. A search of Parkinsonian research studies currently funded by the US National Institutes of Health, Parkinson's Foundation, and the Michael J Fox Foundation yielded no studies on mercury. We believe such studies should be supported.

Coherent and Contradictory Facts, Feats and Fictions Associated with Metal Accumulation in Parkinson's Disease: Epicenter or Outcome, Yet a Demigod Question

Unwarranted exposure due to liberal use of metals for maintaining the lavish life and to achieve the food demand for escalating population along with an incredible boost in the average human life span owing to orchestrated progress in rejuvenation therapy have gradually increased the occurrence of Parkinson's disease (PD). Etiology is albeit elusive; association of PD with metal accumulation has never been overlooked due to noteworthy similitude between metal-exposure symptoms and a few cardinal features of disease. Even though metals are entailed in the vital functions, a hysterical shift, primarily augmentation, escorts the stern nigrostriatal dopaminergic neurodegeneration. An increase in the passage of metals through the blood brain barrier and impaired metabolic activity and elimination system could lead to metal accumulation in the brain, which eventually makes dopaminergic neurons quite susceptible. In the present article, an update on implication of metal accumulation in PD/Parkinsonism has been provided. Moreover, encouraging and paradoxical facts and fictions associated with metal accumulation in PD/Parkinsonism have also been compiled. Systematic literature survey of PD is performed to describe updated information if metal accumulation is an epicenter or merely an outcome. Finally, a perspective on the association of metal accumulation with pesticide-induced Parkinsonism has been explained to unveil the likely impact of the former in the latter.

Solvents and Parkinson disease: a systematic review of toxicological and epidemiological evidence

Parkinson disease (PD) is a debilitating neurodegenerative motor disorder, with its motor symptoms largely attributable to loss of dopaminergic neurons in the substantia nigra. The causes of PD remain poorly understood, although environmental toxicants may play etiologic roles. Solvents are widespread neurotoxicants present in the workplace and ambient environment. Case reports of parkinsonism, including PD, have been associated with exposures to various solvents, most notably trichloroethylene (TCE). Animal toxicology studies have been conducted on various organic solvents, with some, including TCE, demonstrating potential for inducing nigral system damage. However, a confirmed animal model of solvent-induced PD has not been developed. Numerous epidemiologic studies have investigated potential links between solvents and PD, yielding mostly null or weak associations. An exception is a recent study of twins indicating possible etiologic relations with TCE and other chlorinated solvents, although findings were based on small numbers, and dose-response gradients were not observed. At present, there is no consistent evidence from either the toxicological or epidemiologic perspective that any specific solvent or class of solvents is a cause of PD. Future toxicological research that addresses mechanisms of nigral damage from TCE and its metabolites, with exposure routes and doses relevant to human exposures, is recommended. Improvements in epidemiologic research, especially with regard to quantitative characterization of long-term exposures to specific solvents, are needed to advance scientific knowledge on this topic.

Associations of welding and manganese exposure with Parkinson disease: review and meta-analysis

OBJECTIVE

To examine associations of welding and manganese exposure with Parkinson disease (PD) using meta-analyses of data from cohort, case-control, and mortality studies.

METHODS

Epidemiologic studies related to welding or manganese exposure and PD were identified in a PubMed search, article references, published reviews, and abstracts. Inclusion criteria were 1) cohort, case-control, or mortality study with relative risk (RR), odds ratio (OR), or mortality OR (MOR) and 95 confidence intervals (95% CI); 2) RR, OR, and MOR matched or adjusted for age and sex; 3) valid study design and analysis. When participants of a study were a subgroup of those in a larger study, only results of the larger study were included to assure independence of datasets. Pooled RR/OR estimates and 95% CIs were obtained using random effects models; heterogeneity of study effects were evaluated using the Q statistic and I(2) index in fixed effect models.

RESULTS

Thirteen studies met inclusion criteria for the welding meta-analysis and 3 studies for the manganese exposure meta-analysis. The pooled RR for the association between welding and PD for all study designs was 0.86 (95% CI 0.80-0.92), with absence of between-study heterogeneity (I(2) = 0.0). Effect measures for cohort, case-control, and mortality studies were similar (0.91, 0.82, 0.87). For the association between manganese exposure and PD, the pooled OR was 0.76 (95% CI 0.41-1.42).

CONCLUSIONS

Welding and manganese exposure are not associated with increased PD risk. Possible explanations for the inverse association between welding and PD include confounding by smoking, healthy worker effect, and hormesis.

Potential risk factors for incident glioblastoma multiforme: the Honolulu Heart Program and Honolulu-Asia Aging Study

Glioblastoma multiforme (GBM) is the most common adult primary malignant brain tumor. Ninety percent of adult GBM patients die within 24 months after diagnosis. The etiology of GBM is unknown. The Honolulu Heart Program (HHP) and Honolulu-Asia Aging Study (HAAS) are prospective, cohort studies of cardiovascular and neurodegenerative disease based on 8,006 Japanese-American men followed since 1965. The Japan Hawaii Cancer Study provides data on incident cancer cases in the HHP/HAAS cohort. We used data from these studies to obtain epidemiologic information about GBM. GBM cases were identified by searching the 1965-1998 databases using International Classification of Diseases (ICD-9) codes. Nine histologically confirmed GBM cases, 58-80 years old, were identified. The incidence rate was 6.2/100,000 person-years. Records of each case were reviewed. Selected variables from the first three examinations (1965-1968; 1968-1970; 1971-1974) were used to identify potential candidate GBM risk factors. A multivariate Cox proportional hazards model showed sugar intake and occupational exposure to carbon tetrachloride were independently and significantly associated with development of GBM.