A genetic polymorphism of MAO-B modifies the association of cigarette smoking and Parkinson's disease

Risk and protective factors in Parkinson's disease: a simultaneous and prospective study with classical statistical and novel machine learning models

BACKGROUND

Several environmental/lifestyle factors have been individually investigated in previous Parkinson's disease (PD) studies with controversial results. No study has prospectively and simultaneously investigated potential risk/protective factors of PD using both classical statistical and novel machine learning analyses. The latter may reveal more complex associations and new factors that are undetected by merely linear models. To fill this gap, we simultaneously investigated potential risk/protective factors involved in PD in a large prospective population study using both approaches.

METHODS

Participants in the Moli-sani study were enrolled between 2005 and 2010 and followed up until December 2018. Incident PD cases were identified by individual-level record linkage to regional hospital discharge forms, the Italian death registry, and the regional prescription register. Exposure to potential risk/protective factors was assessed at baseline. Multivariable Cox Proportional Hazards (PH) regression models and survival random forests (SRF) were built to identify the most influential factors.

RESULTS

We identified 213 incident PD cases out of 23,901 subjects. Cox PH models revealed that age, sex, dysthyroidism and diabetes were associated with an increased risk of PD. Both hyper and hypothyroidism were independently associated with PD risk. SRF showed that age was the most influential factor in PD risk, followed by coffee intake, daily physical activity, and hypertension.

CONCLUSION

This study sheds light on the role of dysthyroidism, diabetes and hypertension in PD onset, characterized to date by an uncertain relationship with PD, and also confirms the relevance of most factors (age, sex, coffee intake, daily physical activity) reportedly shown be associated with PD. Further methodological developments in SRF models will allow to untangle the nature of the potential non-linear relationships identified.

Early-Onset Parkinson's Disease: Creating the Right Environment for a Genetic Disorder

Parkinson's disease (PD) by its common understanding is a late-onset sporadic movement disorder. However, there is a need to recognize not only the fact that PD pathogenesis expands beyond (or perhaps to) the brain but also that many early-onset patients develop motor signs before the age of 50 years. Indeed, studies have shown that it is likely the protein aggregation observed in the brains of patients with PD precedes the motor symptoms by perhaps a decade. Studies on early-onset forms of PD have shown it to be a heterogeneous disease with multiple genetic and environmental factors determining risk of different forms of disease. Genetic and neuropathological evidence suggests that there are α-synuclein centric forms (e.g., SNCA genomic triplication), and forms that are driven by a breakdown in mitochondrial function and specifically in the process of mitophagy and clearance of damaged mitochondria (e.g., PARKIN and PINK1 recessive loss-of-function mutations). Aligning genetic forms with recognized environmental influences will help better define patients, aid prognosis, and hopefully lead to more accurately targeted clinical trial design. Work is now needed to understand the cross-talk between these two pathomechanisms and determine a sense of independence, it is noted that autopsies studies for both have shown the presence or absence of α-synuclein aggregation. The integration of genetic and environmental data is critical to understand the etiology of early-onset forms of PD and determine how the different pathomechanisms crosstalk.

The Repertoire of Small-Molecule PET Probes for Neuroinflammation Imaging: Challenges and Opportunities beyond TSPO

Neuroinflammation is an adaptive response of the central nervous system to diverse potentially injurious stimuli, which is closely associated with neurodegeneration and typically characterized by activation of microglia and astrocytes. As a noninvasive and translational molecular imaging tool, positron emission tomography (PET) could provide a better understanding of neuroinflammation and its role in neurodegenerative diseases. Ligands to translator protein (TSPO), a putative marker of neuroinflammation, have been the most commonly studied in this context, but they suffer from serious limitations. Herein we present a repertoire of different structural chemotypes and novel PET ligand design for classical and emerging neuroinflammatory targets beyond TSPO. We believe that this Perspective will support multidisciplinary collaborations in academic and industrial institutions working on neuroinflammation and facilitate the progress of neuroinflammation PET probe development for clinical use.

Organoid and pluripotent stem cells in Parkinson's disease modeling: an expert view on their value to drug discovery

Introduction: Parkinson's disease is a devastating neurodegenerative disorder preferentially involving loss of dopaminergic neurons in the substantia nigra, leading to typical motor symptoms. While there are still no therapeutics to modify disease course, recent work using induced pluripotent stem cell (iPSC) and 3D brain organoid models have provided further insight into Parkinson's disease pathogenesis and potential therapeutic targets.Areas covered: This review highlights the generation of iPSC neurons and neural organoids as models for studying Parkinson's disease. It further discusses the recent work using patient-derived neurons from both familial and sporadic forms of Parkinson's to study disease pathogenic phenotypes and pathways. It additionally provides an evaluation of iPSC neurons and organoid models for therapeutic development in Parkinson's.Expert opinion: The use of Parkinson's disease patient-derived neurons and organoids provides us with the exciting opportunity to directly investigate pathogenic mechanisms and test drug compounds in human neurons. Future studies will involve generating more sophisticated models of brain organoids, studying neuronal pathways using larger patient cohorts, and routinely assessing therapeutics in these models.

Polyamines: therapeutic perspectives in oxidative stress and inflammatory diseases

Polyamines are naturally occurring aliphatic compounds, particularly essential elements for biological functions. These compounds play a central role in regulating molecular pathways which are responsible for cellular proliferation, growth, and differentiation. Importantly, excessive polyamine catabolism can lead to a prominent source of oxidative stress which increases inflammatory response and thought to be involved in several diseases including stroke, renal failure, neurological disease, liver disease, and even cancer. Moreover, polyamine supplementation increases life span in model organisms and may encounter oxidative stress via exerting its potential anti-oxidant and anti-inflammatory properties. The revealed literature indicates that an emerging role of polyamine biosynthetic pathway could be a novel target for drug development against inflammatory diseases. In this review, we expand the knowledge on the metabolism of polyamines, and its anti-oxidant and anti-inflammatory activities which might have future implications against inflammatory diseases in humans and animals.

Genetic Profile, Environmental Exposure, and Their Interaction in Parkinson's Disease

The discovery of causative mutations for Parkinson's disease (PD) as well as their functional characterization in cellular and animal models has provided crucial insight into the pathogenesis of this disorder. Today, we know that PD pathogenesis involves multiple related processes including mitochondrial dysfunction, oxidative and nitrative stress, microglial activation and inflammation, and aggregation of α-synuclein and impaired autophagy. However, with the exception of a few families with Mendelian inheritance, the cause of PD in most individuals is yet unknown and the identified genetic susceptibility factors have only small effect size. Epidemiologic studies have found increased risk of PD associated with exposure to environmental toxicants such as pesticides, organic solvents, metals, and air pollutants, while reduced risk of PD associated with smoking cigarettes and coffee consumption. The role of environmental exposure, as well as the contribution of single genetic risk factors, is still controversial. In most of PD cases, disease onset is probably triggered by a complex interplay of many genetic and nongenetic factors, each of which conveys a minor increase in the risk of disease. This review summarizes the current knowledge on causal mutation for PD, susceptibility factors increasing disease risk, and the genetic factors that modify the impact of environmental exposure.

The relationship between monoamine oxidase B (MAOB) A644G polymorphism and Parkinson disease risk: a meta-analysis

BACKGROUND AND OBJECTIVES

Many studies were conducted to assess the relationship between Monoamine oxidase B (MAOB) A644G polymorphism and susceptibility to Parkinson disease (PD). However, the results were inconsistent and inconclusive.

DESIGN AND SETTINGS

A meta-analysis was conducted from all published studies on the associations between monoamine oxidase B (MAOB) A644G polymorphism and Parkinson disease.

METHODS

In this present study, the possible relationship between MAOB A644G polymorphism and PD risk was assessed by a meta-analysis. Eligible articles were identified for the period up to March 2013. Pooled odds ratios (OR) with 95% confidence intervals (CI) were appropriately derived from fixed-effects models.

RESULTS

Twenty case-control studies with a total of 2846 cases and 3508 controls were eligible. In a recessive model, MAOB A644G polymorphism was associated with PD risk (OR=1.32, 95% CI 1.18-1.47, P < .001). Subgroup analyses by ethnicity and gender also found significant relationships between this polymorphism and PD risk.

CONCLUSION

This meta-analysis suggested that MAOB A644G polymorphism may be associated with PD development.

Environmental-genetic interactions in the pathogenesis of Parkinson's disease

To date, numerous case-control studies have shown the complexity of the pathogenesis of Parkinson's disease (PD). In terms of genetic factors, several susceptibility genes are known to contribute to the development of PD, including α-synuclein (SNCA), leucine-rich repeat kinase 2 (LRRK2), and glucocerebrosidase (GBA). In addition, numerous recent epidemiological studies have shown that several environmental factors are either risk factors for PD or protective factors against PD. Risk factors identified include herbicides and pesticides (e.g., paraquat, rotenone, and maneb), metals (e.g., manganese and lead), head trauma, and well water. In contrast, smoking and coffee/caffeine consumption are known to be protective against PD. A recent finding in this field is that environmental-genetic interactions contribute more to the pathogenesis of PD than do genetic factors or environmental factors alone. In this review, I will discuss how these interactions promote the development of PD.

Gene-environment interactions in Parkinson's disease: specific evidence in humans and mammalian models

Interactions between genetic factors and environmental exposures are thought to be major contributors to the etiology of Parkinson's disease. While such interactions are poorly defined and incompletely understood, recent epidemiological studies have identified specific interactions of potential importance to human PD. In this review, the most current data on gene-environment interactions in PD from human studies are critically discussed. Animal models have also highlighted the importance of genetic susceptibility to toxicant exposure and data of potential relevance to human PD are discussed. Goals and needs for the future of the field are proposed.

Genetic polymorphisms involved in dopaminergic neurotransmission and risk for Parkinson's disease in a Japanese population

Background

Parkinson's disease (PD) is characterized by alterations in dopaminergic neurotransmission. Genetic polymorphisms involved in dopaminergic neurotransmission may influence susceptibility to PD.

Methods

We investigated the relationship of catechol-O-methyltransferase (COMT), monoamine oxidase B (MAOB), dopamine receptor (DR) D2 and DRD4 polymorphisms and PD risk with special attention to the interaction with cigarette smoking among 238 patients with PD and 369 controls in a Japanese population.

Results

Subjects with the AA genotype of MAOB rs1799836 showed a significantly increased risk of PD (odds ratio (OR) = 1.70, 95% confidence interval (CI) = 1.12 - 2.58) compared with the AG and GG genotypes combined. The AA genotype of COMT rs4680 was marginally associated with an increased risk of PD (OR = 1.86, 95% CI = 0.98 - 3.50) compared with the GG genotype. The DRD2 rs1800497 and DRD4 rs1800955 polymorphisms showed no association with PD. A COMT -smoking interaction was suggested, with the combined GA and AA genotypes of rs4680 and non-smoking conferring significantly higher risk (OR = 3.97, 95% CI = 2.13 - 7.41) than the AA genotype and a history of smoking (P for interaction = 0.061). No interactions of smoking with other polymorphisms were observed.

Conclusions

The COMT rs4680 and MAOB rs1799836 polymorphisms may increase susceptibility to PD risk among Japanese. Future studies involving larger control and case populations and better pesticide exposure histories will undoubtedly lead to a more thorough understanding of the role of the polymorphisms involved in the dopamine pathway in PD.

Epidemiology and etiology of Parkinson's disease: a review of the evidence

The etiology of Parkinson's disease (PD) is not well understood but likely to involve both genetic and environmental factors. Incidence and prevalence estimates vary to a large extent-at least partly due to methodological differences between studies-but are consistently higher in men than in women. Several genes that cause familial as well as sporadic PD have been identified and familial aggregation studies support a genetic component. Despite a vast literature on lifestyle and environmental possible risk or protection factors, consistent findings are few. There is compelling evidence for protective effects of smoking and coffee, but the biologic mechanisms for these possibly causal relations are poorly understood. Uric acid also seems to be associated with lower PD risk. Evidence that one or several pesticides increase PD risk is suggestive but further research is needed to identify specific compounds that may play a causal role. Evidence is limited on the role of metals, other chemicals and magnetic fields. Important methodological limitations include crude classification of exposure, low frequency and intensity of exposure, inadequate sample size, potential for confounding, retrospective study designs and lack of consistent diagnostic criteria for PD. Studies that assessed possible shared etiological components between PD and other diseases show that REM sleep behavior disorder and mental illness increase PD risk and that PD patients have lower cancer risk, but methodological concerns exist. Future epidemiologic studies of PD should be large, include detailed quantifications of exposure, and collect information on environmental exposures as well as genetic polymorphisms.

Exploration of new scaffolds as potential MAO-A inhibitors using pharmacophore and 3D-QSAR based in silico screening

Monoamine oxidase-A (MAO-A) inhibitors are of particular importance in the treatment of depressive disorders. Herein described is pharmacophore generation and atom-based 3D-QSAR analysis of previously reported pyrrole based MAO-A inhibitors in order to get insight into their structural requirements responsible for high affinity. The best pharmacophore model generated consisted of four features DHHR: a hydrogen bond donor (D), two hydrophobic groups (H) and an aromatic ring (R). Based on model generated, a statistically valid 3D-QSAR with good predictability was developed. Derived pharmacophore was used as a query to search Zinc 'clean drug-like' database. Hits retrieved were passed progressively through filters like fitness score, predicted activity and docking scores. The survived hits present new scaffolds with a potential for MAO-A inhibition.

Smoking, genes encoding dopamine pathway and risk for Parkinson's disease

Smoking has been reported to be inversely associated with Parkinson's disease (PD) in many studies, but a recent study in China found that smoking increased the risk of PD. Variants in genes associated with dopamine metabolism found to increase the risk for PD have also been associated with smoking behavior. To investigate the association between smoking and PD in a Chinese population and determine whether the genetic variants of genes involved in dopamine metabolism influence the relationship between smoking and risk for PD. Chinese PD patients were recruited from Xuanwu Hospital. Controls were sampled from community. Detailed information on life-long smoking behavior was collected by face-to-face interview. Genotypes were determined for SLC6A3 VNTR, COMT Val108/158Met and MAO-B intron13 A/G polymorphisms by PCR-RFLP, DHPLC and sequencing. Chi-square and logistic regression model were used in the analysis. 176 PD cases and 354 controls were enrolled in this study. 23.9% cases are smokers, compared to 48.0% in controls. Ever smoking is inversely associated with PD (odds ratio=0.14, 95% CI 0.08-0.26, adjusted for age and gender). None of the above-mentioned genetic polymorphisms was associated with PD risk or smoking. When each variant was included in the logistic regression model, the inverse association between smoking and PD remained the same, and the interactions between smoking and variants were not significant in the model. Our data support a reduction of PD risk associated with smoking in a Chinese population. These variants of genes associated with DA uptake and metabolism do not affect the inverse association between smoking and PD.

Potential anticancer application of polyamine oxidation products formed by amine oxidase: a new therapeutic approach

The polyamines spermine, spermidine and putrescine are ubiquitous cell components. These molecules are substrates of a class of enzymes that includes monoamine oxidases, diamine oxidases, polyamine oxidases and copper-containing amine oxidases. Amine oxidases are important because they contribute to regulate levels of mono- and polyamines. In tumors, polyamines and amine oxidases are increased as compared to normal tissues. Cytotoxicity induced by bovine serum amine oxidase (BSAO) and spermine is attributed to H(2)O(2) and aldehydes produced by the reaction. This study demonstrated that multidrug-resistant (MDR) cancer cells (colon adenocarcinoma and melanoma) are significantly more sensitive than the corresponding wild-type (WT) ones to H(2)O(2) and aldehydes, the products of BSAO-catalyzed oxidation of spermine. Transmission electron microscopy (TEM) observations showed major ultrastructural alterations of the mitochondria. These were more pronounced in MDR than in WT cells. Increasing the incubation temperature from 37 to 42 degrees Celsius enhances cytotoxicity in cells exposed to spermine metabolites. The combination BSAO/spermine prevents tumor growth, particularly well if the enzyme has been conjugated to a biocompatible hydrogel polymers. Since both wild-type and MDR cancer cells after pre-treatment with MDL 72527, a lysosomotropic compound, are sensitized to subsequent exposure to BSAO/spermine, it is conceivable that combined treatment with a lysosomotropic compound and BSAO/spermine would be effective against tumor cells. It is of interest to search for such novel compounds, which might be promising for application in a therapeutic setting.

Genome-wide and candidate gene association study of cigarette smoking behaviors

The contribution of common genetic variation to one or more established smoking behaviors was investigated in a joint analysis of two genome wide association studies (GWAS) performed as part of the Cancer Genetic Markers of Susceptibility (CGEMS) project in 2,329 men from the Prostate, Lung, Colon and Ovarian (PLCO) Trial, and 2,282 women from the Nurses' Health Study (NHS). We analyzed seven measures of smoking behavior, four continuous (cigarettes per day [CPD], age at initiation of smoking, duration of smoking, and pack years), and three binary (ever versus never smoking, < or = 10 versus > 10 cigarettes per day [CPDBI], and current versus former smoking). Association testing for each single nucleotide polymorphism (SNP) was conducted by study and adjusted for age, cohabitation/marital status, education, site, and principal components of population substructure. None of the SNPs achieved genome-wide significance (p<10(-7)) in any combined analysis pooling evidence for association across the two studies; we observed between two and seven SNPs with p<10(-5) for each of the seven measures. In the chr15q25.1 region spanning the nicotinic receptors CHRNA3 and CHRNA5, we identified multiple SNPs associated with CPD (p<10(-3)), including rs1051730, which has been associated with nicotine dependence, smoking intensity and lung cancer risk. In parallel, we selected 11,199 SNPs drawn from 359 a priori candidate genes and performed individual-gene and gene-group analyses. After adjusting for multiple tests conducted within each gene, we identified between two and five genes associated with each measure of smoking behavior. Besides CHRNA3 and CHRNA5, MAOA was associated with CPDBI (gene-level p<5.4x10(-5)), our analysis provides independent replication of the association between the chr15q25.1 region and smoking intensity and data for multiple other loci associated with smoking behavior that merit further follow-up.

Genetic influences on smoking cessation and relapse in pregnant women

Cigarette smoking during pregnancy continues to be a significant public health concern. Maternal smoking during pregnancy has been associated with low birth weight (<2500 g), fetal growth restriction, placental problems, pre-term delivery and spontaneous abortion. Mothers who smoke during pregnancy are twice as likely to give birth to low birth weight infants, and smoking during pregnancy is estimated to be responsible for 20-30% of all low birth weight infants. Smoking during pregnancy not only affects placental function, thus causing obstetrical complications, but nicotine also crosses the placenta and acts as a neuroteratogen. This in turn, elevates the risk of cognitive and auditory processing deficits, and has also been found to be negatively associated with long-term consequences on offspring behaviour. In addition, smoking has negative long-term health consequences for both mother and child, including respiratory conditions, cancer and cardiovascular problems. This review provides insight into the genetic influences on smoking behaviour in pregnant women. In particular, the roles of genes in the neurotransmitter pathways are highlighted. It also emphasises the need for further research in this area, and provides rationale for the importance of focusing on pregnant women who are highly motivated to quit when researching smoking behaviours in women.

The functional polymorphism of the hemoglobin-binding protein haptoglobin influences susceptibility to idiopathic Parkinson's disease

Oxidative stress and iron have been widely implicated in the etiology of Parkinson's disease (PD). Hemoglobin is the richest source of iron in the body. The human Haptoglobin (Hp) protein is a plasma alpha-2 glycoprotein that removes free Hemoglobin from the circulation and tissues and is important in protection from oxidative stress, in immune system regulation, and angiogenesis. A common genetic polymorphism of Hp exists in the population, where the Hp 1-1, Hp 2-1, and Hp 2-2 forms exhibit profound functional differences. In this study, the Hp genotype corresponding to phenotypes Hp 1-1, 2-1 and 2-2 was determined in 312 idiopathic PD patients and 420 normal control subjects. A significant increase in the number of subjects carrying the Hp 2-1 genotype was present among PD patients. The distribution of Hp genotypes among PD patients (16.0% Hp 1-1, 56.4% Hp 2-1, 27.6% Hp 2-2) was significantly different from the distribution in controls (15.2% Hp 1-1, 48.1% Hp 2-1, 36.7% Hp 2-2) (chi(2) = 6.99, P = 0.030). The odds ratios for PD risk for Hp 2-1 and Hp 1-1 versus Hp 2-2 genotype were 1.51 (1.07-2.12) and 1.36 (0.86-2.15), respectively. Overall, the association of Hp-1 allele with PD resulted stronger among subjects who were never-smokers as compared to ever-smokers. Also, among ever-smokers, Hp genotypes were significantly associated with PD only among women, but not men, indicating the presence of a gene x gender x smoking interaction. To our knowledge, this is the first study that investigates the association of Hp genotypes with the risk of PD.

Family-based case-control study of MAOA and MAOB polymorphisms in Parkinson disease

Monoamine oxidase (MAO) is an enzyme regulating metabolism of neurotransmitters such as dopamine. Two distinct forms of enzyme, encoded by genes MAOA and MAOB located on the X chromosome, have been considered as possible factors in the pathogenesis of Parkinson disease (PD). Previous association studies of PD and MAO genes reported inconsistent results. In this study, we used a large family-based data set to test associations between MAO genes and a risk of PD. The data set includes 298 female discordant sibpairs and 348 male discordant sibpairs. For this study, all subjects analyzed were white and families with known parkin mutations were removed. We analyzed 15 single nucleotide polymorphisms (SNPs) and a dinucleotide repeat marker in the MAO genes. Association was found with the intron 13 SNP of MAOB in the female subset (P = 0.02). No significant association was found in the male subset. Our results add to the evidence of involvement of MAOB in PD and suggest that the effect may be stronger in women.

New pyrrole inhibitors of monoamine oxidase: synthesis, biological evaluation, and structural determinants of MAO-A and MAO-B selectivity

A series of new pyrrole derivatives have been synthesized and evaluated for their monoamine oxidase (MAO) A and B inhibitory activity and selectivity. N-Methyl,N-(benzyl),N-(pyrrol-2-ylmethyl)amine (7) and N-(2-benzyl),N-(1-methylpyrrol-2-ylmethyl)amine (18) were the most selective MAO-B (7, SI = 0.0057) and MAO-A (18, SI = 12500) inhibitors, respectively. Docking and molecular dynamics simulations gave structural insights into the MAO-A and MAO-B selectivity. Compound 18 forms an H-bond with Gln215 through its protonated amino group into the MAO-A binding site. This H-bond is absent in the 7/MAO-A complex. In contrast, compound 7 places its phenyl ring into an aromatic cage of the MAO-B binding pocket, where it forms charge-transfer interactions. The slightly different binding pose of 18 into the MAO-B active site seems to be forced by a bulkier Tyr residue, which replaces a smaller Ile residue present in MAO-A.

Epidemiology of Parkinson's disease

This chapter discusses the epidemiology of Parkinson's disease (PD). Classically, PD refers to progressive parkinsonism caused by loss of pigmented aminergic brainstem neurons without an identifiable cause, while parkinsonism refers simply to the syndrome of bradykinesia, resting tremor, rigidity and postural reflex impairment. Over nearly two centuries, Parkinson's clinical description has provided the framework for clinical investigations, including epidemiologic ones. Descriptions of PD were limited to selected clinical settings until the middle of the 20th century. Since then, epidemiologic approaches have been used not only to investigate the population distribution of PD, but also as a way to glean clues as to the cause of this “idiopathic” disorder. Because PD is relatively infrequent, a large base population must be surveyed to identify sufficient numbers of cases for a study. In some instances, PD cases can be identified through health service rosters within defined geographic areas or in enumerated populations. In others, cases of PD are sought independently of the health care system, such as through door-to-door surveys. While the latter approach is theoretically least likely to exclude cases, the time and cost involved are also greatest using this approach.

Monoamine oxidase and tobacco dependence

Tobacco smoking is a leading cause of preventable death around the world, and there are major public health and research efforts in many countries aimed at reducing its usage. However, the molecular mechanisms underlying tobacco dependence are still not completely understood. Nicotine's action on nicotinic acetylcholine receptors, and the downstream release of dopamine, is believed to be the major pathway underlying tobacco dependence. However there is mounting evidence indicating that non-nicotinic components of tobacco smoke also play a role by inhibiting monoamine oxidase (MAO) and subsequently altering neurotransmitter levels. This article provides a review of the current knowledge of the association between MAO and tobacco dependence and suggests that further research into this topic is likely to lead to more effective pharmacotherapies for smoking cessation.

Héritabilité et gènes candidats dans le tabagisme

HERITABILITY INDICATORS: Genetic studies of tobacco use can be useful to understand the physiopathology of nicotine dependence and potentially to prevent it. Twin and adoption studies have clearly shown the role of genetic factors in tobacco use at different stages. Genetic factors account for 55% (range: 11-84%) of the smoking initiation and 61% (range: 52-71%) for persistence. Age at onset and intensity of smoking are also influenced by genetic factors. Estimation of the heritability of initiation/persistence of smoking varies by gender. It is estimated as 66%/61% for women and 49%/61% for men respectively. In adolescent twin studies, heritability estimated the liability of lifetime or current use of tobacco to be more than 80%, while the heritability for initiation being between 11% and 59%. Heavy smoking is also influenced by genetic factors, especially when patients are co-abusing alcohol or coffee. Genetics findings - Advances in molecular genetics identified different candidate genes for tobacco use mainly involving neurotransmission of neuromodulators. Because of the brain reward effects of nicotine on the mesolimbic system, the genes involved in the dopaminergic transmission receive specific attention. Genetic polymorphisms of the dopamine D1, D2, D4 and D5 receptors, dopamine transporter (DAT1) and dopamine B-hydroxylase (DBH) have been associated at least once with clinical aspects of tobacco use (initiation, dependence and intensity) and temperament traits as novelty seeking, the latter being lower in smokers and thus considered as a vulnerable marker in accordance with the reinforcement effect of nicotine. Regarding interaction between nicotine use and anxiety and depression, the gene encoding for the serotonin transporter (5-HTT) may constitute a candidate gene. Because of interindividual bioavailability of nicotine, genetic polymorphisms of metabolism enzymes have also been analysed. Some variants of the cytochrome P450 seem to be more frequent among dependent smokers than controls or ever smokers (CYP2A6) and heavier smokers (CYP2D6). Genetic research might be suitable for a therapeutic approach and identify subjects at high risk for nicotine dependence.

Relationship between impulsive sensation seeking traits, smoking, alcohol and caffeine intake, and Parkinson's disease

BACKGROUND

An inverse relation exists between smoking and coffee intake and Parkinson's disease (PD). The present study explored whether this is explained by low sensation seeking, a personality trait believed to characterise PD.

METHODS

A total of 106 non-demented patients with PD and 106 age and sex matched healthy controls completed a short version of Zuckerman's Sensation Seeking Scale (SSS), the Geriatric Depression Scale, and the Trait Anxiety Inventory. Data were collected on past and current cigarette smoking, and participants also completed food frequency questionnaires to estimate current caffeine and alcohol intake.

RESULTS

Patients with PD had lower sensation seeking and higher depression and anxiety scores. They were also less likely to have ever smoked, and had lower caffeine and alcohol intakes. Analysis of the data using conditional logistic regression suggested that the inverse association of PD risk with sensation seeking was independent of smoking, and caffeine and alcohol intake. Moreover, low sensation seeking explained some of the apparent effect of caffeine and alcohol intake on PD. However, the effect of smoking was weakened only slightly when SSS was included in the regression model.

CONCLUSION

This study raises the possibility that there is a neurobiological link between low sensation seeking traits--which might underlie the parkinsonian personality--and the hypothetical protective effect of cigarette smoking and caffeine consumption on PD.

Characterization of the in vitro transcriptional activity of polymorphic alleles of the human monoamine oxidase-B gene

The activity of monoamine oxidase-B (MAO-B) enzyme has a high degree of heritability, although no common genetic polymorphisms are present in the MAO-B coding region. The only known polymorphisms in MAO-B gene are a C-1,114T in the 5' region, a variable number of GT repeats in intron 2, and a G/A change in intron 13. The genetically determined differences in MAO-B activity among subjects most likely derive from functional differences conferred by these three MAO-B genetic polymorphisms, or by polymorphisms in trans-acting factors that regulate MAO-B expression. In order to identify differences in transcriptional activity conferred by the MAO-B genetic variants, we cloned alternative alleles at the three polymorphic loci in -1,114, intron 2 and intron 13, and tested them in transfection-luciferase assays in HepG2 hepatoma and 1321N1 astrocytoma cells. The mutant -1,114 allele T had higher activity than allele C in both cell lines, when cloned in pGL3Enhancer. Significant differences in trascriptional activity by intron 2 GT repeat allele were also observed, and varied by cell type and reporter construct. Allele G of intron 13 had significantly higher activity than allele A in both cell lines. These results indicate transcriptional activity differences between MAO-B variant alleles that are naturally occurring in the population.

Catechol-O-Methyltransferase and Monoamine Oxidase B Genes and Susceptibility to Sporadic Parkinson’s Disease in a Polish Population

Recent reports have proved that genetic factors play a role in the pathogenesis of sporadic Parkinson's disease (PD). It has been suggested that polymorphisms in monoamine oxidase B (MAOB) and catechol-O-methyltransferase (COMT) might increase the risk of PD. A total of 210 Polish patients with sporadic PD and 152 healthy controls were studied. The MAOB and COMT polymorphisms were identified using the polymerase chain reaction-restriction fragment length polymorphism method. The MAOB allele and genotype frequencies in PD patients did not differ significantly from the controls. A statistically lower frequency of the COMTLL genotype in patients with parkinsonism was found. The combined haplotype of the MAOB G (G/G) and COMTHL genotype showed a fourfold increase (p < 0.05) in the risk of PD in female patients in this Polish population.

Comparison of age of onset and development of motor complications between smokers and non-smokers in Parkinson's disease

BACKGROUND

There is growing evidence from case-control and from cohort studies that smoking is inversely related to the risk of developing Parkinson's disease (PD). However, it is still controversial if PD starts at an older age in ever-smoking patients compared to never-smoking ones.

PATIENTS AND METHODS

The present retrospective study compares in a large series of 512 out-patients, collected over the last 24 years, the age of onset of the complaints, the age at which PD was diagnosed and the start of levodopa treatment between ever- and never-smokers. Also, the occurrence of long-term side-effects of the drug was evaluated. 184 PD patients with a history of smoking were compared with 328 who had never smoked. The subgroups with and without a family history of PD were analysed separately.

RESULTS

In the overall ever-smoking group, as well as in the subgroup without a family history, the onset of the disease and the time of the diagnosis of PD and the time at which levodopa was started occurred at an older age than in the never-smoking group. This difference could not be demonstrated in the patients with a family history, due to the low number of cases and the lack of statistical power. Although the follow-up period was the same in both study groups, motor fluctuations and dyskinesia were more frequent and appeared earlier after levodopa treatment in the non-smoking compared to the ever-smoking PD patients. Only for cognitive impairment there was a non-significant trend in the smoking group.

CONCLUSION

The present study confirms the protective action of smoking on PD and also suggests some modulating effect of smoking on the dopaminergic system.

The effect of monoamine oxidase B (MAOB) and catechol-O-methyltransferase (COMT) polymorphisms on levodopa therapy in patients with sporadic Parkinson's disease

OBJECTIVES

The etiology of sporadic idiopathic Parkinson's disease (PD) is considered multifactorial with both genetic and environmental factors modifying the disease expression. Recent studies suggest that polymorphism in monoamine oxidase B (MAOB) and catechol-O-methyltransferase (COMT) might influence the risk and treatment of PD. The aim of the study was to evaluate the effect of MAOB and COMT genetic polymorphism on effective daily dose of levodopa applied during the first 5 years of treatment, and to find out if a relationship exists between MAOB and COMT haplotypes and motor disturbances onset in PD patients treated with levodopa preparations.

MATERIALS AND METHODS

A total of 95 patients (40 females and 55 males) of Polish origin diagnosed with sporadic PD were enrolled into the study, and were divided into two groups. Group 1 - patients treated with doses of levodopa below 500 mg/day during the first 5 years of treatment. Group 2 - patients requiring levodopa doses exceeding 500 mg/24 h during the first 5 years of treatment. Low activity alleles of MAOB and COMT, i.e. MAOB allele A and COMT(L) as well as high activity ones, i.e. MAOB allele G and COMT(H), were determined using PCR-RFLP method.

RESULTS

No statistically significant differences were found in MAOB and COMT allele distribution in the two groups. However, the frequency of COMT(L/L) homozygotes was higher in the group treated with low doses of levodopa when compared with the second group. MAOB and COMT AG-HH haplotype predominated in the group of females treated with high daily doses of levodopa when compared with AG-LL haplotype in the group of females treated with low daily doses of levodopa (<500 mg/24 h).

CONCLUSION

The results of the study suggest that patients with COMT(L/L) genotype and possibly MAOB genotype A may benefit from more efficient and safer levodopa therapy.

Genetic contributions to Parkinson's disease

Sporadic Parkinson's disease (PD) is a common neurodegenerative disorder, characterized by the loss of midbrain dopamine neurons and Lewy body inclusions. It is thought to result from a complex interaction between multiple predisposing genes and environmental influences, although these interactions are still poorly understood. Several causative genes have been identified in different families. Mutations in two genes [alpha-synuclein and nuclear receptor-related 1 (Nurr1)] cause the same pathology, and a third locus on chromosome 2 also causes this pathology. Other familial PD mutations have identified genes involved in the ubiquitin-proteasome system [parkin and ubiquitin C-terminal hydroxylase L1 (UCHL1)], although such cases do not produce Lewy bodies. These studies highlight critical cellular proteins and mechanisms for dopamine neuron survival as disrupted in Parkinson's disease. Understanding the genetic variations impacting on dopamine neurons may illuminate other molecular mechanisms involved. Additional candidate genes involved in dopamine cell survival, dopamine synthesis, metabolism and function, energy supply, oxidative stress, and cellular detoxification have been indicated by transgenic animal models and/or screened in human populations with differing results. Genetic variation in genes known to produce different patterns and types of neurodegeneration that may impact on the function of dopamine neurons are also reviewed. These studies suggest that environment and genetic background are likely to have a significant influence on susceptibility to Parkinson's disease. The identification of multiple genes predisposing to Parkinson's disease will assist in determining the cellular pathway/s leading to the neurodegeneration observed in this disease.

Case-only study of interactions between genetic polymorphisms of GSTM1, P1, T1 and Z1 and smoking in Parkinson’s disease

Current opinion contends that complex interactions between genetic and environmental factors play a role in the etiology of Parkinson's disease (PD). Cigarette smoking is thought to reduce risk of PD, and emerging evidence suggests that genetic factors may modulate smoking's effect. We used a case-only design, an approach not previously used to study gene-environment interactions in PD, specifically to study interactions between glutathione-S-transferase (GST) gene polymorphisms and smoking in relation to PD. Four-hundred PD cases (age at onset: 60.0 +/- 10.7 years) were genotyped for common polymorphisms in GSTM1, P1, T1 and Z1 using well-established methods. Smoking exposure data were collected in face-to-face interviews. The independence of the studied GST genotypes and smoking exposure was confirmed by studying 402 healthy, aged individuals. No differences were observed in the distributions of GSTM1, T1 or Z1 polymorphisms between ever-smoked and never-smoked PD cases using logistic regression (all P > 0.43). However, GSTP1 *C haplotypes were over-represented among PD cases who ever smoked (odds ratio for interaction (ORi) = 2.00 (95% CI: 1.11-3.60, P = 0.03)). Analysis revealed that ORi between smoking and the GSTP1-114Val carrier status increased with increasing smoking dose (P = 0.02 for trend). These data suggest that one or more GSTP1 polymorphisms may interact with cigarette smoking to influence the risk for PD.

DNA sequence analysis of monoamine oxidase B gene coding and promoter regions in Parkinson's disease cases and unrelated controls

The allele G of the intron 13 G/A polymorphism of the monoamine oxidase B gene (MAO-B) has been associated with Parkinson's disease (PD) in several studies. Apart from a potential direct effect on splicing processes, the association of this intronic polymorphism with PD is due possibly to linkage disequilibrium with other mutations in the coding or promoter regions of the gene. We addressed this latter hypothesis by determining the DNA sequence of the entire MAO-B coding region comprising 15 exons and partial intronic sequences flanking each exon, in 33 cases with idiopathic PD and 38 unrelated controls. The promoter region of MAO-B gene up to base -1,369 from ATG (start point of mRNA translation) was also sequenced to identify variants with potential functional effects on gene transcription. In the promoter region, a new polymorphism consisting of a C to T single base change was detected in position -1,114 from ATG, with an allelic frequency of 3.5%, but it was not associated with PD risk. No commonly occurring (>10%) polymorphisms were found in the exons or the intronic sequences flanking the exons, although several rare variants were detected in the coding and promoter regions.

Monoamine oxidase B polymorphism, cigarette smoking and risk of Parkinson's disease: a study in an Asian population

Cigarette smoking is associated with reduced monoamine oxidase B (MAO B) activity. Polymorphisms of the MAO B gene may modify the relationship between smoking and Parkinson's Disease (PD). We examined the association of MAO B intron 13 G/A polymorphism and risk of PD, and the modulation of the polymorphism on smoking and PD in an Asian study population in Singapore. Two hundred and thirty PD patients (mean age 66.0 +/- 9.4 years, 63% men) and 241 age, gender, and race matched controls (mean age 64 +/- 9.2 years, 58.9% males) were studied. The frequency of G and A alleles in PD and controls was; 66/315 (21.0%) vs. 73/340 (21.5%) and 249/315 (79.0%) vs. 267/340 (78.5%). For women, the genotype frequency in PD and controls was; GG: 7/85 (8.2%) vs. 8/99 (8.1%); GA: 25/85 (29.4%) vs. 27/99 (27.3%); AA: 53/85 (62.4%) vs. 64/99 (64.6%). For men, allele frequency in PD and controls was; A: 118/145 (81.4%) vs. 112/142 (78.9%) and G: 27/145 (18.6%) vs. 30/142 (21.1%). The allele and genotype frequencies were not significantly different between young and late onset PD. The frequency of "ever" smokers in PD and controls was 31/230 (13.5%) vs. 52/241 (21.6%), P = 0.02. A stepwise logistic regression analysis did not reveal any interaction of smoking and the G allele and risk of PD. The MAO B G/A genotype frequency in our Asian population was quite different from Caucasians suggesting that ethnicity specific effects need to be considered in evaluating gene-environmental interaction.

Genetic and environmental risk factors and their interactions for Parkinson's disease in a Chinese population

The interaction between genetic and environmental factors for PD was examined in a Chinese population. It was found that although the intron 2 MAOB (GT)(n) repeat polymorphism was not associated with PD in the population, a relationship might have been masked by the "protective effect" of tea drinking. In individuals who did not drink tea (<1 cup/day), the possession of short length < or = 178 bp (GT)(n) alleles conferred a borderline significant increased risk for PD (adjusted OR=1.47; C.I.=1.03-2.1). As the extent of tea consumption increased, the association between the < or = 178 bp allele and PD disappeared. This result suggests that the MAOB gene may be associated with PD in Chinese if the putative protective effect of tea drinking is taken into account. The significance of this finding is unclear as the study may be limited because of its marginal significance and limited numbers. However, it does demonstrate the importance of considering putative positive and negative environmental risk factors in any examination of genetic risk factors for PD.

Simple, potent, and selective pyrrole inhibitors of monoamine oxidase types A and B

N-Benzyl- and N-propargyl-1H-pyrrole-2-carboxyamides and some related methylenamines were synthesized and tested for their monoamine oxidase types A and B inhibitory activity. 2-(N-Methyl-N-propargylaminomethyl)-1H-pyrrole (24) was the most potent MAO-A inhibitor of the series [K(i)(MAO-A) = 0.0054 microM], but it was not selective. Inhibitors N-4-fluorobenzyl-1H-pyrrole-2-carboxamide (12) and N-cyclohexylmethyl-1H-pyrrole-2-carboxamide (25) showed the highest MAO-A selectivity indexes (SI) corresponding to 2025 and >2500, respectively, while 2-(N-methyl-N-benzylaminomethyl)-1H-pyrrole (21) was the most selective MAO-B inhibitor, having an SI of 0.0057.

Monoamine oxidase polymorphisms and smoking behaviour in Japanese

Although nicotine dependence is one of the primary reasons why smokers cannot quit smoking, nicotine cannot explain all of the psychopharmacological effects of tobacco smoke. Accumulating evidence points to potent inhibition of monoamine oxidase (MAO) which metabolizes neurotransmitters relating to additive behaviour. We have therefore investigated the association between smoking behaviour and MAO ( variable number of tandem repeat in the promoter region and A644G) polymorphisms. The genotypes were examined in 504 Japanese outpatients (217 men and 287 women) who visited Aichi Cancer Centre Hospital. The age-adjusted odds ratios (aORs) were estimated by a logistic model. Among males, we did not find a significant association of the smoking habit with either of the polymorphisms. The median Fargastrom test for nicotine dependence (FTND) score among male current smokers was significantly higher with than without the 4-repeat allele (5.8 and 4.7, respectively). The aOR of FTND 6 versus FTND 6 was 2.72 (95% confidence interval 1.13-6.50) for males with the 4-repeat allele. Among females, the aOR of being current smokers compared to never smokers was 0.49 (0.26-0.93) for individuals with the 4-repeat allele. Our results indicate that the polymorphisms of influence the smoking habit for female, as well as the nicotine dependence and smoking initiation for male smokers. These findings among male smokers support the view that MAO affects a smokers' requirement for nicotine and may explain why some people are predisposed to tobacco addiction and why some individuals find it difficult to stop smoking.

Gender difference in the interaction of smoking and monoamine oxidase B intron 13 genotype in Parkinson's disease

We tested for gender-specific interactions between smoking and genetic polymorphisms of monoamine oxidase B (MAO-B) intron 13 (G or A allele), monoamine oxidase A (MAO-A) EcoRV (Yor N allele), and dopamine D2 recepor (DRD2) Taq1B (B1 or B2 allele) in a case-control study of 186 incident idiopathic Parkinson's disease (PD) cases and 296 age- and gender-matched controls. The odds ratios (ORs) for PD risk for ever smokers versus never smokers were 0.27 (95% CI: 0.13-0.58) for men of genotype G, and 1.26 (0.60-2.63) for men of genotype A (interaction chi2 = 8.14, P = 0.004). In contrast, for women, the OR for ever smokers versus never smokers were 0.62 (95% CI: 0.25-1.34) and 0.64 (95% CI: 0.18-2.21) for women of genotype GG/GA and AA, respectively (interaction chi2 = 0.001, P = 0.975). No interactions were detected between smoking and either MAO-A EcoRV or DRD2 Taq1B genotypes. These results suggest that a strong gender difference exists with respect to the modifying effect of MAO-B genotype on the smoking association with PD.

The genetic basis of Parkinson's disease

Although the mechanisms underlying neurodegeneration in Parkinson's disease are not fully understood, considerable evidence suggests that genetic factors can influence susceptibility to the disease. In this article, we critically review this evidence and examine studies estimating patterns of inheritance. In a few families, Parkinson's disease is clearly inherited in a Mendelian fashion, and in some of these the disease causing genes have already been identified. Possible pathogenic mechanisms by which these genes cause Parkinson's disease are discussed. Further candidate genes and systematic efforts to identify genes influencing susceptibility to the disease in general are also summarised. The identification of such susceptibility genes will eventually enable us to more accurately classify this complex disease.

Occupational and environmental risk factors for Parkinson's disease

The etiology of Parkinson's disease (PD) remains obscure. Current research suggests that a variety of occupational and environmental risk factors may be linked to PD. This paper provides an overview of major occupational and environmental factors that have been associated with the development of PD and tries to assess current thinking about these factors and their possible mechanisms of operation. While clear links to rural living, dietary factors, exposure to metals, head injury, and exposure to infectious diseases during childhood have not been established, there is general agreement that smoking and exposure to pesticides affect the probability of developing PD.

Pharmacogenomics of neurodegenerative diseases

Current knowledge of sporadic degenerative disorders suggests that, despite their multifactorial etiopathogenesis, genetics plays a primary role in orchestrating the pathological events, and even dramatically changes the disease phenotype from patient to patient. Genes may act as susceptibility factors, increasing the risk of disease development, or may operate as regulatory factors, modulating the magnitude and severity of pathogenic processes or the response to drug treatment. The goal of pharmacogenomics is the application of this knowledge to elaborate more specific and effective treatments and to tailor therapies to individual patients according to their genetic profile. Here, we outline the leading theories on the etiopathogenesis of neurodegenerative diseases, including amyotrophic lateral sclerosis, Parkinson's disease, and Alzheimer disease, and we review the potential role of genetic variations, such as gene mutations and polymorphisms, in each context. We also suggest potential targets for new therapeutic approaches and variability factors for current treatments based on genotype features. Finally, we propose a few options of preventive therapeutic interventions in patients with a high genetic risk of disease.