Active and passive smoking and risk of Parkinson's disease

Cholinergic Receptor Modulation as a Target for Preventing Dementia in Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative condition characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) in the midbrain resulting in progressive impairment in cognitive and motor abilities. The physiological and molecular mechanisms triggering dopaminergic neuronal loss are not entirely defined. PD occurrence is associated with various genetic and environmental factors causing inflammation and mitochondrial dysfunction in the brain, leading to oxidative stress, proteinopathy, and reduced viability of dopaminergic neurons. Oxidative stress affects the conformation and function of ions, proteins, and lipids, provoking mitochondrial DNA (mtDNA) mutation and dysfunction. The disruption of protein homeostasis induces the aggregation of alpha-synuclein (α-SYN) and parkin and a deficit in proteasome degradation. Also, oxidative stress affects dopamine release by activating ATP-sensitive potassium channels. The cholinergic system is essential in modulating the striatal cells regulating cognitive and motor functions. Several muscarinic acetylcholine receptors (mAChR) and nicotinic acetylcholine receptors (nAChRs) are expressed in the striatum. The nAChRs signaling reduces neuroinflammation and facilitates neuronal survival, neurotransmitter release, and synaptic plasticity. Since there is a deficit in the nAChRs in PD, inhibiting nAChRs loss in the striatum may help prevent dopaminergic neurons loss in the striatum and its pathological consequences. The nAChRs can also stimulate other brain cells supporting cognitive and motor functions. This review discusses the cholinergic system as a therapeutic target of cotinine to prevent cognitive symptoms and transition to dementia in PD.

Preventive treatments to slow substantia nigra damage and Parkinson's disease progression: A critical perspective review

Restoring the lost physiological functions of the substantia nigra in Parkinson's disease (PD) is an important goal of PD therapy. The present article reviews a) novel drug targets that should be targeted to slow PD progression, and b) clinical and experimental research data reporting new treatments targeting immune-inflammatory and oxidative pathways. A systematic search was performed based on the major databases, i.e., ScienceDirect, Web of Science, PubMed, CABI Direct databases, and Scopus, on relevant studies performed from 1900 to 2020. This review considers the crucial roles of mitochondria and immune-inflammatory and oxidative pathways in the pathophysiology of PD. High levels of oxidative stress in the substantia nigra, as well as modifications in glutathione regulation, contribute to mitochondrial dysfunction, with a decline in complex I of the mitochondrial electron transport chain reported in PD patients. Many papers suggest that targeting antioxidative systems is a crucial aspect of preventive and protective therapies, even justifying the utilization of N-acetylcysteine (NAC) supplementation to fortify the protection afforded by intracellular glutathione. Dietary recommended panels including ketogenetic diet, muscular exercise, nutraceutical supplementation including NAC, glutathione, nicotine, caffeine, melatonin, niacin, and butyrate, besides to nonsteroidal anti-inflammatory drugs (NSAIDs), and memantine treatment are important aspects of PD therapy. The integration of neuro-immune, antioxidant, and nutritional approaches to treatment should afford better neuroprotection, including by attenuating neuroinflammation, nitro-oxidative stress, mitochondrial dysfunction, and neurodegenerative processes. Future research should clarify the efficacy, and interactions, of nicotine receptor agonists, gut microbiome-derived butyrate, melatonin, and NSAIDs in the treatment of PD.

The impact of long-term exposure to ambient air pollution and second-hand smoke on the onset of Parkinson disease: a review and meta-analysis

OBJECTIVES

Long-term exposure to particulate and gaseous air pollution (AP) may trigger the development of Parkinson disease (PD), but this association remains controversial. The relationship between second-hand smoke (SS) and PD risk is also inconclusive. We aimed to systematically review epidemiological studies investigating the association between these AP exposures and PD risk.

STUDY DESIGN

This was a systematic review and meta-analysis of studies investigating the relationship of ambient AP and SS with PD risk.

METHODS

PubMed, Embase, Web of Science, Cochrane Library, and Google Scholar databases were searched. We used a random-effects model to derive pooled estimates of relative risk (RR) and corresponding 95% confidence intervals (CIs) per increment in pollutant concentration. The studied AP included particulate matter with aerodynamic diameter <2.5 μm (PM_2.5), <10 μm (PM₁₀), nitrogen dioxides (NO_2, NO_x), ozone (O₃), and carbon monoxide (CO).

RESULTS

In total, 21 studies with 222,051 patients with PD were eligible for inclusion. We found marginally significant increased risk of PD with per 10-μg/m³ increase in concentration of PM_2.5 (RR = 1.08, 95% CI = 0.98-1.19), NO₂ (RR = 1.03, 95% CI = 0.99-1.07), and O₃ (RR = 1.01, 95% CI = 1.00-1.02). A positive but non-significant association was also detected for CO (RR = 1.32, 95% CI = 0.82-2.11). Furthermore, an inverse PD-SS relationship was noted irrespective of exposure occasions and timing (at home: RR = 0.73, 95% CI = 0.56-0.95; at work: RR = 0.82, 95% CI = 0.57-1.17; in children: RR = 0.91, 95% CI = 0.76-1.08). Both sensitivity and subgroup analyses generated results comparable with those of the overall analyses.

CONCLUSIONS

Our study suggested that exposure to PM_2.5, NO₂, and O₃ might contribute to higher risk of PD, whereas SS conferring reduced PD risk. Public and environmental health strategies that aim at reducing outdoor AP levels might reduce the burden of PD. More prospective cohort studies with personal exposure measurements are warranted in the future.

The Changing Landscape of Parkinson Epidemiologic Research

Despite recent successes in understanding the genetics of Parkinson’s disease (PD), the causes of late-onset sporadic PD remain elusive. Many of the epidemiologic findings on PD etiology have been challenged by alternative explanations such as reverse causation. This is mainly because PD often takes decades to develop before it can be diagnosed late in life. Convincing evidence shows that this prodromal stage of PD is characterized by various prodromal symptoms such as olfactory impairment and rapid-eye-movement sleep behavior disorder (RBD). As they likely reflect PD pathogenesis years, if not decades, before nigrostriatal involvement, research on these symptoms may represent an unprecedented opportunity to dissect the etiology of PD. Using PD prodromal symptoms as intermediate phenotypes, we may be able to identify factors that contribute to the development of these symptoms and factors that modify their progression to clinical PD. Further, this line of research will also enable examinations of novel etiological hypotheses of PD development such as the microbiome and prion hypotheses. In this article, the author used olfactory impairment and RBD as examples to illustrate the promises and challenges of epidemiologic research on prodromal symptoms to understand PD etiology.

Exploring causality of the association between smoking and Parkinson's disease

BACKGROUND

The aim of this paper is to investigate the causality of the inverse association between cigarette smoking and Parkinson's disease (PD). The main suggested alternatives include a delaying effect of smoking, reverse causality or an unmeasured confounding related to a low-risk-taking personality trait.

METHODS

A total of 715 incident PD cases were ascertained in a cohort of 220 494 individuals from NeuroEPIC4PD, a prospective European population-based cohort study including 13 centres in eight countries. Smoking habits were recorded at recruitment. We analysed smoking status, duration, and intensity and exposure to passive smoking in relation to PD onset.

RESULTS

Former smokers had a 20% decreased risk and current smokers a halved risk of developing PD compared with never smokers. Strong dose-response relationships with smoking intensity and duration were found. Hazard ratios (HRs) for smoking <20 years were 0.84 [95% confidence interval (CI) 0.67-1.07], 20-29 years 0.73 (95% CI 0.56-0.96) and >30 years 0.54 (95% CI 0.43-0.36) compared with never smokers. The proportional hazard assumption was verified, showing no change of risk over time, arguing against a delaying effect. Reverse causality was disproved by the consistency of dose-response relationships among former and current smokers. The inverse association between passive smoking and PD, HR 0.70 (95% CI 0.49-0.99) ruled out the effect of unmeasured confounding.

CONCLUSIONS

These results are highly suggestive of a true causal link between smoking and PD, although it is not clear which is the chemical compound in cigarette smoking responsible for the biological effect.

Nicotine promotes neuron survival and partially protects from Parkinson's disease by suppressing SIRT6

Parkinson’s disease is characterized by progressive death of dopaminergic neurons, leading to motor and cognitive dysfunction. Epidemiological studies consistently show that the use of tobacco reduces the risk of Parkinson’s. We report that nicotine reduces the abundance of SIRT6 in neuronal culture and brain tissue. We find that reduction of SIRT6 is partly responsible for neuroprotection afforded by nicotine. Additionally, SIRT6 abundance is greater in Parkinson’s patient brains, and decreased in the brains of tobacco users. We also identify SNPs that promote SIRT6 expression and simultaneously associate with an increased risk of Parkinson’s. Furthermore, brain-specific SIRT6 knockout mice are protected from MPTP-induced Parkinson’s, while SIRT6 overexpressing mice develop more severe pathology. Our data suggest that SIRT6 plays a pathogenic and pro-inflammatory role in Parkinson’s and that nicotine can provide neuroprotection by accelerating its degradation. Inhibition of SIRT6 may be a promising strategy to ameliorate Parkinson’s and neurodegeneration.

Air pollution and Parkinson's disease - evidence and future directions

Parkinson's disease (PD) is a neurodegenerative disease of unknown etiology that is thought to be caused by a complex combination of environmental and/or genetic factors. Air pollution exposure is linked to numerous adverse effects on human health, including brain inflammation and oxidative stress, processes that are believed to contribute to the development and progression of PD. This review provides an overview of recent advances in the epidemiology of air pollution and PD, including evidence of the effects of various pollutants (ozone, PM10, PM2.5, PM2.5-10, NOx, NO2, CO, traffic air pollution, second-hand smoking) on PD risk. Based on this evidence, promising opportunities for future research are outlined, including: (1) studies of smaller particle sizes that cross the blood-brain barrier, (2) studies of the effects of air pollution on PD mortality and/or progression; (3) studies of interactions of air pollution with gene environment and other environmental factors.

Association between Parkinson's Disease and Cigarette Smoking, Rural Living, Well-Water Consumption, Farming and Pesticide Use: Systematic Review and Meta-Analysis

Objective

Bradford Hill’s viewpoints were used to conduct a weight-of-the-evidence assessment of the association between Parkinson’s disease (PD) and rural living, farming and pesticide use. The results were compared with an assessment based upon meta-analysis. For comparison, we also evaluated the association between PD and cigarette smoking as a “positive control” because a strong inverse association has been described consistently in the literature.

Methods

PubMed was searched systematically to identify all published epidemiological studies that evaluated associations between Parkinson’s disease (PD) and cigarette smoking, rural living, well-water consumption, farming and the use of pesticides, herbicides, insecticides, fungicides or paraquat. Studies were categorized into two study quality groups (Tier 1 or Tier 2); data were abstracted and a forest plot of relative risks (RRs) was developed for each risk factor. In addition, when available, RRs were tabulated for more highly exposed individuals compared with the unexposed. Summary RRs for each risk factor were calculated by meta-analysis of Tier 1, Tier 2 and all studies combined, with sensitivity analyses stratified by other study characteristics. Indices of between-study heterogeneity and evidence of reporting bias were assessed. Bradford Hill’s viewpoints were used to determine if a causal relationship between PD and each risk factor was supported by the weight of the evidence.

Findings

There was a consistent inverse (negative) association between current cigarette smoking and PD risk. In contrast, associations between PD and rural living, well-water consumption, farming and the use of pesticides, herbicides, insecticides, fungicides or paraquat were less consistent when assessed quantitatively or qualitatively.

Conclusion

The weight of the evidence and meta-analysis support the conclusion that there is a causal relationship between PD risk and cigarette smoking, or some unknown factor correlated with cigarette smoking. There may be risk factors associated with rural living, farming, pesticide use or well-water consumption that are causally related to PD, but the studies to date have not identified such factors. To overcome the limitations of research in this area, future studies will have to better characterize the onset of PD and its relationship to rural living, farming and exposure to pesticides.

PARK16 polymorphisms, interaction with smoking, and sporadic Parkinson's disease in Japan

Epidemiological evidence on the relationships between PARK16 single nucleotide polymorphisms (SNPs) and Parkinson's disease (PD) is inconsistent. We examined this issue in Japan. Included were 229 cases within six years of PD onset. Controls were 356 patients without neurodegenerative disease. Compared with subjects with the AA genotype of SNP rs823128, those with the AG genotype, but not the GG genotype, had a significantly reduced risk of sporadic PD. Compared with the AA genotype of SNP rs947211, both the AG genotype and the GG genotype were significantly related to an increased risk of sporadic PD. Using subjects with the AA genotype of SNP rs823156 as a reference group, there were significant inverse relationships under the additive and dominant models. No significant relationships were found between SNPs rs16856139 or rs11240572 and sporadic PD. The CAAAC, the TGAGA, and the CAGAC haplotypes were significantly related to sporadic PD. The additive interaction between SNP rs823128 and smoking affecting sporadic PD was significant, although the multiplicative interaction was not significant. The PARK16 SNPs rs823128, rs947211, and rs823156 and the CAAAC, TGAGA, and CAGAC haplotypes may be significantly associated with sporadic PD in Japan. New evidence of an additive interaction between SNP rs823156 and smoking is suggested.

6-OHDA-Induced Changes in Parkinson's Disease-Related Gene Expression are not Affected by the Overexpression of PGAM5 in In Vitro Differentiated Embryonic Mesencephalic Cells

LUHMES cells, a recently established line of immortalized embryonic mesencephalic cells, are the novel in vitro model for studying Parkinson's disease (PD) and dopaminergic neuron biology. Phosphoglyceromutase 5 (PGAM5) is a mitochondrial protein involved in mitophagy, mitochondria dynamics, and other processes important for PD pathogenesis. We tested the impact of lentiviral overexpression of PGAM5 protein in LUHMES cells on their differentiation and expression of 84 PD-related genes. LUHMES cells were transduced with PGAM5 or mock and treated with 100 μM 6-hydroxydopamine (6-OHDA), a model PD neurotoxin. Real-Time PCR analysis revealed that the treatment with 6-OHDA-induced changes in expression of 44 PD-related genes. PGAM5 transduction alone did not cause alternations in PD-related genes expression, nor it affected changes in gene expression mediated by 6-OHDA. The 6-OHDA-induced PD-related gene expression profile of LUHMES cells is presented for the first time and widely discussed.

Do physical exercise and reading reduce the risk of Parkinson's disease? a cross-sectional study on factors associated with Parkinson's disease in elderly Chinese veterans

BACKGROUND

The purpose of this study was to investigate risk factors for and factors protecting against Parkinson's disease (PD) in elderly Chinese veterans.

METHODS

Using a database containing detailed information on the health status of the nervous system in elderly Chinese veterans, univariate and multivariate analyses of factors that may be associated with PD were performed. Univariate analysis of qualitative data was done using the Pearson Chi-square and Fisher's exact tests, and the Mann-Whitney U nonparametric test was used for univariate analysis of quantitative data. Multivariate logistic regression analysis was used to identify independent risk factors for and factors protecting against PD in elderly Chinese veterans.

RESULTS

A total of 9,676 elderly Chinese veterans were enrolled, including 228 cases with PD and 183 cases with Parkinson's syndrome, with 9,265 non-PD subjects serving as controls. Age (odds ratio [OR] 1.343, 95% confidence interval [CI] 1.028-1.755) and medical history of essential tremor (OR 1.228, 95% CI 1.081-1.396) were identified as independent risk factors for PD, with age being the most important risk factor. Physical exercise (OR 0.478, 95% CI 0.355-0.643) and reading (OR 0.513, 95% CI 0.357-0.735) were identified as independent factors protecting against PD, and physical exercise showed better protection against PD relative to reading. Smoking, alcohol use, anemia, cerebral trauma, education level, and electromagnetic field exposure showed no association with PD.

CONCLUSION

Physical exercise and reading may be independent factors that protect against PD among elderly Chinese veterans, while advancing age and medical history of essential tremor may be independent risk factors for PD. This study was cross-sectional, so further research is needed to confirm its results.

Quitting smoking: an early non-motor feature of Parkinson's disease?

INTRODUCTION

Epidemiological studies report a 60-70% reduced risk of Parkinson's disease (PD) in smokers as compared to non-smokers. However, relationships between former smoking and PD have been poorly investigated.

METHODS

We recruited 116 de novo PD subjects, and investigated current, former and never smoking, and reasons for smoking cessation among former smokers. Two hundred and thirty-two controls were matched by Propensity Score.

RESULTS

PD subjects and controls were found to be current smokers (7.7 vs. 39.6%), former smokers (43.9 vs. 6.5%) and never smokers (48.2 vs. 53.9%). Logistic regression showed that current smokers were less likely to have PD (p < 0.001; OR: 0.22; 95% CI: 0.10-0.46), while former smokers were more likely to have PD (p < 0.001; OR: 7.6; 95% CI: 4.09-15.75), as compared to never smokers. Fifty-one PD patients reported quitting smoking before PD diagnosis (mean time since cessation 9.4 ± 7.3 years). Most important reasons to quit smoking in PD group were illness different from PD (26 subjects, 51.0%), knowledge of the harmful effects of smoking (24 subjects, 47.0%), and physician's advice (1 subject, 2.0%).

CONCLUSION

The reduced prevalence of current smokers among PD subjects as compared to healthy controls is consistent with previous findings, suggesting a possible neuroprotective effect of smoking. However, it could be due, at least in part, to the increased prevalence of former smokers among PD patients, that were more prone to quit smoking as compared to healthy controls. We suggest that smoking cessation could be an early preclinical condition occurring in PD.

Inflammation and oxidative stress induced by cigarette smoke in Lewis rat brains

Exposure to cigarette smoke has been associated with an increased risk of neurological diseases such as stroke, Alzheimer's disease and multiple sclerosis. In these studies, serum and brain sections from Lewis rats or those exposed to cigarette smoke and control rats were examined for evidence of increased inflammation and oxidative stress. Immunocytochemical staining of brain sections from CS-exposed rats showed increased expression of class II MHC and, in ELISA, levels of IFN-gamma and TNF-α were higher than for non-exposed rats. In polymerase chain reaction assays there was increased interferon-gamma, TNF-α, IL-1α, IL-1β, IL-23, IL-6, IL-23, IL-17, IL-10, TGF-β, T-bet and FoxP3 gene expression with CS exposure. There was also markedly elevated MIP-1α/CCL3, less prominent MCP-1/CCL2 and no elevation of SDF-1α gene expression. Analysis of samples from CS-exposed and control rats for anti-oxidant expression showed no significant difference in serum levels of glutathione and, in brain, similar levels of superoxide dismutase and decreased thioredoxin gene expression. In contrast, there was increased brain gene expression for the pro-oxidants iNOS and the NADPH components NOX4, dual oxidase 1 and p22(phox). Nrf2 expression, which is typically triggered as a secondary response to oxidative stress, was also increased in brains from CS-exposed rats with nuclear translocation of this protein from cytoplasm demonstrated in astrocytes in association with increased expression of the aryl hydrocarbon receptor gene, an Nrf2 target. These studies, therefore, demonstrate that CS exposure in these animals can trigger multiple immune and oxidative responses that may have important roles in the pathogenesis of CNS inflammatory neurological diseases.

Lack of association between BST1 polymorphisms and sporadic Parkinson's disease in a Japanese population

Several genome-wide association studies and case-control studies have investigated the relationships between single nucleotide polymorphisms (SNPs) in the BST1 gene and Parkinson's disease (PD), but the results have been inconsistent. We examined the relationships between SNPs rs11931532, rs12645693, and rs11724635 and the risk of sporadic PD in Japan. Included were 229 cases within 6years of onset of PD as defined according to the UK PD Society Brain Bank clinical diagnostic criteria. Controls were 357 inpatients and outpatients without neurodegenerative disease. SNPs rs11931532 and rs12645693 were not significantly related to sporadic PD. Compared with a reference group of subjects with the CC genotype of SNP rs11724635, those with the AA genotype had a marginally significantly increased risk of sporadic PD: the adjusted OR was 1.57 (95% CI: 0.95-2.61, P=0.08). No significant interactions were found between BST1 SNP rs11724635 and smoking or caffeine intake with respect to sporadic PD. The current study failed to detect significant relationships between BST1 SNPs rs11931532, rs12645693, and rs11724635 and sporadic PD; however, the relationship between SNP rs11724635 and sporadic PD was of borderline significance. We do not find evidence for interactions between smoking or caffeine intake and SNP rs11724635 affecting sporadic PD.

UCHL1 S18Y variant is a risk factor for Parkinson's disease in Japan

Background

A recent meta-analysis on the UCHL1 S18Y variant and Parkinson’s disease (PD) showed a significant inverse association between the Y allele and PD; the individual studies included in that meta-analysis, however, have produced conflicting results. We examined the relationship between UCHL1 S18Y single nucleotide polymorphism (SNP) and sporadic PD in Japan.

Methods

Included were 229 cases within 6 years of onset of PD, defined according to the UK PD Society Brain Bank clinical diagnostic criteria. Controls were 357 inpatients and outpatients without neurodegenerative disease. Adjustment was made for sex, age, region of residence, smoking, and caffeine intake.

Results

Compared with subjects with the CC or CA genotype of UCHL1 S18Y SNP, those with the AA genotype had a significantly increased risk of sporadic PD: the adjusted OR was 1.57 (95 % CI: 1.06 − 2.31). Compared with subjects with the CC or CA genotype of UCHL1 S18Y and the CC or CT genotype of SNCA SNP rs356220, those with the AA genotype of UCHL1 S18Y and the TT genotype of SNP rs356220 had a significantly increased risk of sporadic PD; the interaction, however, was not significant. Our previous investigation found significant inverse relationships between smoking and caffeine intake and PD in this population. There were no significant interactions between UCHL1 S18Y and smoking or caffeine intake affecting sporadic PD.

Conclusions

This study reveals that the UCHL1 S18Y variant is a risk factor for sporadic PD. We could not find evidence for interactions affecting sporadic PD between UCHL1 S18Y and SNCA SNP rs356220, smoking, or caffeine intake.

Long-lasting transcriptional refractoriness triggered by a single exposure to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrimidine

Parkinson's disease (PD) is a progressive neurodegenerative disorder whose etiology is thought to have environmental (toxin) and genetic contributions. The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrimidine (MPTP) induces pathological features of PD including loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and striatal dopamine (DA) depletion. We previously described the striatal transcriptional response following acute MPTP administration in MPTP-sensitive C57BL/6J mice. We identified three distinct phases: early (5h), intermediate (24h) and late (72h) and reported that the intermediate and late responses were absent in MPTP-resistant Swiss-Webster (SWR) mice. Here we show that C57BL/6J mice pre-treated with a single 40 mg/kg dose of MPTP and treated 9 days later with 4×20 mg/kg MPTP, display a striatal transcriptional response similar to that of MPTP-resistant SWR mice, i.e. a robust acute response but no intermediate or late response. Transcriptional refractoriness is dependent upon the dose of the priming challenge with as little as 10mg/kg MPTP being effective and can persist for more than 28 days. Priming of SWR mice has no effect on their response to subsequent challenge with MPTP. We also report that paraquat, another free radical producer, also elicits striatal transcriptional alterations but these are largely distinct from those triggered by MPTP. Paraquat-induced changes are also refractory to priming with paraquat. However neither paraquat nor MPTP elicits cross-attenuation. Thus exposure to specific toxins triggers distinct transcriptional responses in striatum that are influenced by prior exposure to the same toxin. The prolonged refractory period described here for MPTP could explain at the molecular level the reported discrepancies between different MPTP administration regimens and may have implications for our understanding of the relationship between environmental toxin exposure and PD.

Inflammation in Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disease that is characterized by the degeneration of dopaminergic neurons in the substantia nigra pars compacta. Inflammatory responses manifested by glial reactions, T cell infiltration, and increased expression of inflammatory cytokines, as well as other toxic mediators derived from activated glial cells, are currently recognized as prominent features of PD. The consistent findings obtained by various animal models of PD suggest that neuroinflammation is an important contributor to the pathogenesis of the disease and may further propel the progressive loss of nigral dopaminergic neurons. Furthermore, although it may not be the primary cause of PD, additional epidemiological, genetic, pharmacological, and imaging evidence support the proposal that inflammatory processes in this specific brain region are crucial for disease progression. Recent in vitro studies, however, have suggested that activation of microglia and subsequently astrocytes via mediators released by injured dopaminergic neurons is involved. However, additional in vivo experiments are needed for a deeper understanding of the mechanisms involved in PD pathogenesis. Further insight on the mechanisms of inflammation in PD will help to further develop alternative therapeutic strategies that will specifically and temporally target inflammatory processes without abrogating the potential benefits derived by neuroinflammation, such as tissue restoration.

Environmental tobacco smoke and Parkinson's disease

BACKGROUND

Parkinson's disease is inversely associated with cigarette smoking, but its relation with passive smoking or environmental tobacco smoke exposure is rarely examined.

METHODS

Within a case-control study, we assessed the association between Parkinson's disease and living or working with active smokers. Cases were newly diagnosed with idiopathic Parkinson's disease (n = 154) from western Washington State in 2002-2008. Age- and sex-matched controls (n = 173) were neurologically normal and unrelated to cases.

RESULTS

Compared with never active or passive tobacco smokers, we observed reduced Parkinson's disease risks for ever passive only smokers (OR, 0.34; 95% CI, 0.16-0.73), similar to those for ever active smokers (OR, 0.35; 95% CI, 0.17-0.73). Among persons whose only tobacco smoke exposure was passive smoking at home, risk was inversely associated with years exposed.

CONCLUSIONS

These observations parallel those well established for active smoking. However, it remains unresolved whether a true protective effect of tobacco smoke, generally detrimental to health, underlies these associations.

Dietary intake of antioxidant vitamins and risk of Parkinson's disease: a case-control study in Japan

BACKGROUND

antioxidant vitamins are expected to protect cells from oxidative damage by neutralizing the effects of reactive oxygen species. However, epidemiological evidence regarding the associations between antioxidant vitamin intake and Parkinson's disease (PD) is limited and inconsistent. We investigated the relationship between dietary intake of selected antioxidant vitamins, vegetables and fruit and the risk of PD in Japan using data from a multicenter hospital-based case-control study.

METHODS

included were 249 patients within 6 years of onset of PD. Controls were 368 inpatients and outpatients without a neurodegenerative disease. Information on dietary factors was collected using a validated self-administered diet history questionnaire. Adjustment was made for sex, age, region of residence, pack-years of smoking, years of education, body mass index, dietary intake of cholesterol, alcohol, total dairy products, and coffee and the dietary glycemic index.

RESULTS

higher consumption of vitamin E and β-carotene was significantly associated with a reduced risk of PD after adjustment for confounders under study: the adjusted odds ratio in the highest quartile was 0.45 (95% confidence interval [CI]: 0.25-0.79, P for trend = 0.009) for vitamin E and 0.56 (95% CI: 0.33-0.97, P for trend = 0.03) for β-carotene. Stratified by sex, such inverse associations were significant only in women. No material relationships were shown between intake of vitamin C, α-carotene, cryptoxanthin, green and yellow vegetables, other vegetables, or fruit and the risk of PD.

CONCLUSIONS

higher intake of vitamin E and β-carotene may be associated with a decreased risk of PD.

Dietary intake of metals and risk of Parkinson's disease: a case-control study in Japan

Metals are involved in several important functions in the nervous system. Zinc and iron are increased and copper is decreased in the substantia nigra in Parkinson's disease (PD). However, epidemiological evidence for the association of dietary intake of metals with the risk of PD is limited. We investigated the relationship between metal consumption and the risk of PD in Japan using data from a multicenter hospital-based case-control study. Included were 249 cases within 6 years of onset of PD based on the UK PD Society Brain Bank clinical diagnostic criteria. Controls were 368 inpatients and outpatients without a neurodegenerative disease. Information on dietary factors was collected using a self-administered diet history questionnaire. Higher intake of iron, magnesium, and zinc was independently associated with a reduced risk of PD: the adjusted OR in the highest quartile was 0.24 (95% CI: 0.10-0.57, P for trend=0.0003) for iron, 0.33 (95% CI: 0.13-0.81, P for trend=0.007) for magnesium and 0.50 (95% CI: 0.26-0.95, P for trend=0.055) for zinc. There were no relationships between the intake of copper or manganese and the risk of PD. Higher intake of iron, magnesium, and zinc may be protective against PD.

Lack of association of dairy food, calcium, and vitamin D intake with the risk of Parkinson's disease: a case-control study in Japan

Three previous cohort studies in the USA reported that dairy product consumption was significantly associated with an increased risk of Parkinson's disease (PD) in men, but not in women. We examined the relationship between consumption of dairy products, calcium, and vitamin D and the risk of PD using data from a multicenter hospital-based case-control study in Japan. Included were 249 cases within 6 years of onset of PD based on the UK PD Society Brain Bank clinical diagnostic criteria. Controls were 368 inpatients and outpatients without a neurodegenerative disease. Information on dietary factors was collected using a validated self-administered diet history questionnaire. Adjustment was made for sex, age, region of residence, pack-years of smoking, years of education, body mass index, and dietary factors including cholesterol, dietary glycemic index, vitamin E, β-carotene, vitamin B(6), caffeine, iron, and alcohol. Total dairy product consumption was not materially associated with the risk of PD (P for trend = 0.62). No evident relationships were observed between intake of milk, yogurt, cheese, or ice cream and the risk of PD (P for trend = 0.75, 0.63, 0.59, and 0.35, respectively). There were no measurable associations between consumption of calcium or vitamin D and PD (P for trend = 0.37 and 0.69, respectively). No significant interactions were observed between the dietary exposures and sex regarding PD. Our results suggest that intake of dairy products, calcium, and vitamin D was not related to PD, regardless of sex. However, such null relationships might be a consequence of PD.

Alcohol drinking and risk of Parkinson's disease: a case-control study in Japan

Background

Although some epidemiologic studies found inverse associations between alcohol drinking and Parkinson's disease (PD), the majority of studies found no such significant associations. Additionally, there is only limited research into the possible interactions of alcohol intake with aldehyde dehydrogenase (ALDH) 2 activity with respect to PD risk. We examined the relationship between alcohol intake and PD among Japanese subjects using data from a case-control study.

Methods

From 214 cases within 6 years of PD onset and 327 controls without neurodegenerative disease, we collected information on "peak", as opposed to average, alcohol drinking frequency and peak drinking amounts during a subject's lifetime. Alcohol flushing status was evaluated via questions, as a means of detecting inactive ALHD2. The multivariate model included adjustments for sex, age, region of residence, smoking, years of education, body mass index, alcohol flushing status, presence of selected medication histories, and several dietary factors.

Results

Alcohol intake during peak drinking periods, regardless of frequency or amount, was not associated with PD. However, when we assessed daily ethanol intake separately for each type of alcohol, only Japanese sake (rice wine) was significantly associated with PD (adjusted odds ratio of ≥66.0 g ethanol per day: 3.39, 95% confidence interval: 1.10-11.0, P for trend = 0.001). There was no significant interaction of alcohol intake with flushing status in relation to PD risk.

Conclusions

We did not find significant associations between alcohol intake and PD, except for the daily amount of Japanese sake. Effect modifications by alcohol flushing status were not observed.

LRRK2 Gly2385Arg polymorphism, cigarette smoking, and risk of sporadic Parkinson's disease: a case-control study in Japan

Previous case-control studies in Japanese and ethnic Chinese populations reported that the LRRK2 Gly2385Arg variant is a risk factor for Parkinson's disease (PD). We aimed to validate the previous findings and investigate whether cigarette smoking influences the relationship between the Gly2385Arg variant and PD. Included were 229 cases within 6years of onset of sporadic PD. Controls were 358 inpatients and outpatients without a neurodegenerative disease. The frequency of the heterozygous genotype was 13.1% of cases and 6.4% of controls: adjusted OR for the GA genotype was 2.06 (95% CI: 1.15-3.69). Compared with subjects with the GG genotype who had ever smoked, those with the GA genotype who had never smoked had a 5.8-fold increased risk of sporadic PD. The multiplicative interaction between the SNP and smoking was not statistically significant. With respect to the additive interaction, the estimated attributable proportion due to interaction (AP), but not relative excess risk due to interaction or the synergy index, was statistically significant (AP=0.50, 95% CI: 0.05-0.94), suggesting the presence of a biological interaction. The present study confirms that the LRRK2 Gly2385Arg variant is a risk factor for sporadic PD. In addition, we provide new evidence for the biological interaction between the polymorphism and smoking with regard to the risk of sporadic PD.