Critical review of the evidence for a causal association between exposure to asbestos and esophageal cancer.

Esophageal cancers comprise about 1% of all cancers diagnosed in the US but are more prevalent in other regions of the world. Several regulatory agencies have classified asbestos as a known human carcinogen, and it is linked to multiple diseases and malignancies, including lung cancer and mesothelioma. In a 2006 review of the epidemiological literature, the Institute of Medicine (IOM) did not find sufficient evidence to demonstrate a causal relationship between asbestos exposure and esophageal cancer. To reevaluate this conclusion, we performed a critical review of the animal toxicological, epidemiological, and mechanism of action literature on esophageal cancer and asbestos, incorporating studies published since 2006. Although there is some evidence in the epidemiological literature for an increased risk of esophageal cancer in asbestos-exposed occupational cohorts, these studies generally did not control for critical esophageal cancer risk factors (e.g. smoking, alcohol consumption). Furthermore, data from animal toxicological studies do not indicate that asbestos exposure increases esophageal cancer risk. Based on our evaluation of the literature, and reaffirming the IOM's findings, we conclude that there is insufficient evidence to demonstrate a causal link between asbestos exposure and esophageal cancer.

CNS tau efflux via exosomes is likely increased in Parkinson's disease but not in Alzheimer's disease.

INTRODUCTION: Alzheimer's disease (AD) and Parkinson's disease (PD) involve tau pathology. Tau is detectable in blood, but its clearance from neuronal cells and the brain is poorly understood. METHODS: Tau efflux from the brain to the blood was evaluated by administering radioactively labeled and unlabeled tau intracerebroventricularly in wild-type and tau knock-out mice, respectively. Central nervous system (CNS)-derived tau in L1CAM-containing exosomes was further characterized extensively in human plasma, including by single molecule array technology with 303 subjects. RESULTS: The efflux of Tau, including a fraction via CNS-derived L1CAM exosomes, was observed in mice. In human plasma, tau was explicitly identified within L1CAM exosomes. In contrast to AD patients, L1CAM exosomal tau was significantly higher in PD patients than controls and correlated with cerebrospinal fluid tau. CONCLUSIONS: Tau is readily transported from the brain to the blood. The mechanisms of CNS tau efflux are likely different between AD and PD.

Mortalin is Expressed by Astrocytes and Decreased in the Midbrain of Parkinson's Disease Patients.

Mortalin, an essential mitochondrial chaperone protein, has previously been implicated in the pathogenesis of a wide array of diseases, including neurodegenerative conditions such as Parkinson's disease (PD) and Alzheimer's disease. Previous reports have consistently described mortalin protein levels to be lower in the brain tissue of patients with neurodegenerative disease, with expression demonstrated to be lower in neurons of post-mortem PD brain specimens. However, to date, mortalin expression has not yet been evaluated in astrocytes of post-mortem brain tissue from either normal or PD subjects. Mortalin expression was demonstrated in mouse primary astrocyte cultures by Western blot and quantitative polymerase chain reaction (PCR). Furthermore, confocal microscopy studies in human post-mortem tissue indicated co-localization of mortalin within astrocytes. Utilizing a quantitative immunofluorescence staining approach, the protein was found to be moderately reduced (∼35%) in this cell type in the substantia nigra pars compacta, but not structures of the corpus striatum, in PD subjects as compared to age-/gender-matched controls. These findings highlight the potential contribution of disrupted astroglial function in the pathogenesis of PD.

Blood α-synuclein in agricultural pesticide handlers in central Washington State.

Epidemiologic studies suggest that occupational exposure to pesticides might increase Parkinson disease risk. Some pesticides, such as the organophosphorus insecticide chlorpyrifos, appear to increase the expression of α-synuclein, a protein critically involved in Parkinson disease. Therefore, we assessed total blood cell α-synuclein in 90 specimens from 63 agricultural pesticide handlers, mainly Hispanic men from central Washington State, who participated in the state's cholinesterase monitoring program in 2007-2010. Additionally, in age-adjusted linear regression models for repeated measures, we assessed whether α-synuclein levels were associated with butyrylcholinesterase-chlorpyrifos adducts or cholinesterase inhibition measured in peripheral blood, or with self-reported pesticide exposure or paraoxonase (PON1) genotype. There was no evidence by any of those indicators that exposure to chlorpyrifos was associated with greater blood α-synuclein. We observed somewhat greater α-synuclein with the PON1-108T (lower paraoxonase enzyme) allele, and with ≥ 10 h of exposure to cholinesterase inhibiting insecticides in the preceding 30 days, but neither of these associations followed a clear dose-response pattern. These results suggest that selected genetic and environmental factors may affect α-synuclein blood levels. However, longitudinal studies with larger numbers of pesticide handlers will be required to confirm and elucidate the possible associations observed in this exploratory cross-sectional study.

Astrocytic dynamin-like protein 1 regulates neuronal protection against excitotoxicity in Parkinson disease.

Mitochondrial dynamics has recently become an area of piqued interest in neurodegenerative disorders, including Parkinson disease (PD); however, the contribution of astrocytes to these disorders remains unclear. Here, we show that the level of dynamin-like protein 1 (Dlp1; official name DNM1L), which promotes mitochondrial fission, is lower in astrocytes from the brains of PD patients, and that decreased astrocytic Dlp1 likely represents a relatively early event in PD pathogenesis. In support of this conclusion, we show that Dlp1 knockdown dramatically affects mitochondrial morphological characteristics and localization in astrocytes, impairs the ability of astrocytes to adequately protect neurons from the excitotoxic effects of glutamate, and increases intracellular Ca(2+) in response to extracellular glutamate, resulting from compromised intracellular Ca(2+) buffering. Taken together, our results suggest that astrocytic mitochondrial Dlp1 is a key protein in mitochondrial dynamics and decreased Dlp1 may interfere with neuron survival in PD by disrupting Ca(2+)-coupled glutamate uptake.

Plasma exosomal α-synuclein is likely CNS-derived and increased in Parkinson's disease.

Extracellular α-synuclein is important in the pathogenesis of Parkinson's disease (PD) and also as a potential biomarker when tested in the cerebrospinal fluid (CSF). The performance of blood plasma or serum α-synuclein as a biomarker has been found to be inconsistent and generally ineffective, largely due to the contribution of peripherally derived α-synuclein. In this study, we discovered, via an intracerebroventricular injection of radiolabeled α-synuclein into mouse brain, that CSF α-synuclein was readily transported to blood, with a small portion being contained in exosomes that are relatively specific to the central nervous system (CNS). Consequently, we developed a technique to evaluate the levels of α-synuclein in these exosomes in individual plasma samples. When applied to a large cohort of clinical samples (267 PD, 215 controls), we found that in contrast to CSF α-synuclein concentrations, which are consistently reported to be lower in PD patients compared to controls, the levels of plasma exosomal α-synuclein were substantially higher in PD patients, suggesting an increased efflux of the protein to the peripheral blood of these patients. Furthermore, although no association was observed between plasma exosomal and CSF α-synuclein, a significant correlation between plasma exosomal α-synuclein and disease severity (r = 0.176, p = 0.004) was observed, and the diagnostic sensitivity and specificity achieved by plasma exosomal α-synuclein were comparable to those determined by CSF α-synuclein. Further studies are clearly needed to elucidate the mechanism involved in the transport of CNS α-synuclein to the periphery, which may lead to a more convenient and robust assessment of PD clinically.

Biomarkers of Parkinson's disease: current status and future perspectives.

This review summarizes major advances in biomarker discovery for diagnosis, differential diagnosis and progression of Parkinson's disease (PD), with emphasis on neuroimaging and biochemical markers. Potential strategies to develop biomarkers capable of predicting PD in the prodromal stage before the appearance of motor symptoms or correlating with nonmotor symptoms, an active area of research, are also discussed.

DJ-1 isoforms in whole blood as potential biomarkers of Parkinson disease.

DJ-1 is a multifunctional protein that plays an important role in oxidative stress, cell death, and synucleinopathies, including Parkinson disease. Previous studies have demonstrated that total DJ-1 levels decrease in the cerebrospinal fluid, but do not change significantly in human plasma from patients with Parkinson disease when compared with controls. In this study, we measured total DJ-1 and its isoforms in whole blood of patients with Parkinson disease at various stages, Alzheimer disease, and healthy controls to identify potential peripheral biomarkers of PD. In an initial discovery study of 119 subjects, 7 DJ-1 isoforms were reliably detected, and blood levels of those with 4-hydroxy-2-nonenal modifications were discovered to be altered in late-stage Parkinson disease. This result was further confirmed in a validation study of another 114 participants, suggesting that, unlike total DJ-1 levels, post-translationally modified isoforms of DJ-1 from whole blood are candidate biomarkers of late-stage Parkinson disease.