Parkinson's disease, CYP2D6 polymorphism, and age

Quantitative and causal analysis for inflammatory genes and the risk of Parkinson's disease

Background

The dysfunction of immune system and inflammation contribute to the Parkinson's disease (PD) pathogenesis. Cytokines, oxidative stress, neurotoxin and metabolism associated enzymes participate in neuroinflammation in PD and the genes involved in them have been reported to be associated with the risk of PD. In our study, we performed a quantitative and causal analysis of the relationship between inflammatory genes and PD risk.

Methods

Standard process was performed for quantitative analysis. Allele model (AM) was used as primary outcome analysis and dominant model (DM) and recessive model (RM) were applied to do the secondary analysis. Then, for those genes significantly associated with the risk of PD, we used the published GWAS summary statistics for Mendelian Randomization (MR) to test the causal analysis between them.

Results

We included 36 variants in 18 genes for final pooled analysis. As a result, IL-6 rs1800795, TNF-α rs1799964, PON1 rs854560, CYP2D6 rs3892097, HLA-DRB rs660895, BST1 rs11931532, CCDC62 rs12817488 polymorphisms were associated with the risk of PD statistically with the ORs ranged from 0.66 to 3.19 while variants in IL-1α, IL-1β, IL-10, MnSOD, NFE2L2, CYP2E1, NOS1, NAT2, ABCB1, HFE and MTHFR were not related to the risk of PD. Besides, we observed that increasing ADP-ribosyl cyclase (coded by BST1) had causal effect on higher PD risk (OR[95%CI] =1.16[1.10-1.22]) while PON1(coded by PON1) shown probably protective effect on PD risk (OR[95%CI] =0.81[0.66-0.99]).

Conclusion

Several polymorphisms from inflammatory genes of IL-6, TNF-α, PON1, CYP2D6, HLA-DRB, BST1, CCDC62 were statistically associated with the susceptibility of PD, and with evidence of causal relationships for ADP-ribosyl cyclase and PON1 on PD risk, which may help understand the mechanisms and pathways underlying PD pathogenesis.

Parkinson's Disease and Melanoma: Co-Occurrence and Mechanisms

Parkinson's disease (PD) is a neurodegenerative disorder that is characterized by loss of dopaminergic neurons in the substantia nigra pars compacta, depletion of dopamine in the striatum and the presence of Lewy bodies. Cancer is uncontrolled growth of cells in the body and migration of these cells from their site of origin to other parts of the body. PD and cancer are two opposite diseases, one arising from cell proliferation and the other from cell degeneration. This fundamental difference is consistent with inverse comorbidity between most cancers and neurodegenerative diseases. However, a positive association of PD and melanoma has been reported which has recently become of significant interest. A link between PD and cancer has been supported by many epidemiological studies, most of which show that PD patients have a lower risk of developing most cancers than the general population. However, the mechanisms underlying this epidemiological observation are not known. In this review we focus on epidemiological studies correlating PD and melanoma and the possible mechanisms underlying the co-occurrence of the two diseases. We explore possible explanations for the important observations that more PD patients develop melanoma that would otherwise be expected and vice-versa.

Cytochrome P450 2D6 and Parkinson's Disease: Polymorphism, Metabolic Role, Risk and Protection

Cytochrome P450 (CYP) 2D6 is one of the most highly active, oxidative and polymorphic enzymes known to metabolize Parkinsonian toxins and clinically established anti-Parkinson's disease (PD) drugs. Albeit CYP2D6 gene is not present in rodents, its orthologs perform almost the similar function with imprecise substrate and inhibitor specificity. CYP2D6 expression and catalytic activity are found to be regulated at every stage of the central dogma except replication as well as at the epigenetic level. CYP2D6 gene codes for a set of alternate splice variants that give rise to a range of enzymes possessing variable catalytic activity. Case-control studies, meta-analysis and systemic reviews covering CYP2D6 polymorphism and PD risk have demonstrated that poor metabolizer phenotype possesses a considerable genetic susceptibility. Besides, ultra-rapid metabolizer offers protection against the risk in some populations while lack of positive or inverse association is also reported in other inhabitants. CYP2D6 polymorphisms resulting into deviant protein products with differing catalytic activity could lead to inter-individual variations, which could be explained to certain extent on the basis of sample size, life style factors, food habits, ethnicity and tools used for statistical analysis across various studies. Current article describes the role played by polymorphic CYP2D6 in the metabolism of anti-PD drugs/Parkinsonian toxins and how polymorphisms determine PD risk or protection. Moreover, CYP2D6 orthologs and their roles in rodent models of Parkinsonism have also been mentioned. Finally, a perspective on inconsistency in the findings and futuristic relevance of CYP2D6 polymorphisms in disease diagnosis and treatment has also been highlighted.

Key Targets for Multi-Target Ligands Designed to Combat Neurodegeneration

HIGHLIGHTS Compounds that interact with multiple targets but minimally with the cytochrome P450 system (CYP) address the many factors leading to neurodegeneration.Acetyl- and Butyryl-cholineEsterases (AChE, BChE) and Monoamine Oxidases A/B (MAO A, MAO B) are targets for Multi-Target Designed Ligands (MTDL).ASS234 is an irreversible inhibitor of MAO A >MAO B and has micromolar potency against the cholinesterases.ASS234 is a poor CYP substrate in human liver, yielding the depropargylated metabolite.SMe1EC2, a stobadine derivative, showed high radical scavenging property, in vitro and in vivo giving protection in head trauma and diabetic damage of endothelium.Control of mitochondrial function and morphology by manipulating fission and fusion is emerging as a target area for therapeutic strategies to decrease the pathological outcome of neurodegenerative diseases. Growing evidence supports the view that neurodegenerative diseases have multiple and common mechanisms in their aetiologies. These multifactorial aspects have changed the broadly common assumption that selective drugs are superior to "dirty drugs" for use in therapy. This drives the research in studies of novel compounds that might have multiple action mechanisms. In neurodegeneration, loss of neuronal signaling is a major cause of the symptoms, so preservation of neurotransmitters by inhibiting the breakdown enzymes is a first approach. Acetylcholinesterase (AChE) inhibitors are the drugs preferentially used in AD and that one of these, rivastigmine, is licensed also for PD. Several studies have shown that monoamine oxidase (MAO) B, located mainly in glial cells, increases with age and is elevated in Alzheimer (AD) and Parkinson's Disease's (PD). Deprenyl, a MAO B inhibitor, significantly delays the initiation of levodopa treatment in PD patients. These indications underline that AChE and MAO are considered a necessary part of multi-target designed ligands (MTDL). However, both of these targets are simply symptomatic treatment so if new drugs are to prevent degeneration rather than compensate for loss of neurotransmitters, then oxidative stress and mitochondrial events must also be targeted. MAO inhibitors can protect neurons from apoptosis by mechanisms unrelated to enzyme inhibition. Understanding the involvement of MAO and other proteins in the induction and regulation of the apoptosis in mitochondria will aid progress toward strategies to prevent the loss of neurons. In general, the oxidative stress observed both in PD and AD indicate that antioxidant properties are a desirable part of MTDL molecules. After two or more properties are incorporated into one molecule, the passage from a lead compound to a therapeutic tool is strictly linked to its pharmacokinetic and toxicity. In this context the interaction of any new molecules with cytochrome P450 and other xenobiotic metabolic processes is a crucial point. The present review covers the biochemistry of enzymes targeted in the design of drugs against neurodegeneration and the cytochrome P450-dependent metabolism of MTDLs.

The association between Parkinson's disease and melanoma: a systematic review and meta-analysis

Objective

To assess the association between Parkinson’s disease (PD) and melanoma via systematic review and meta-analysis.

Methods

Comprehensive search in PubMed, Web of Science, Embase and four China databases (SinoMed, WanFang data, CNKI and VIP database) of epidemiologic evidences on PD and melanoma published before April 30, 2015. Studies which reported risk estimates of melanoma among PD patients or risk estimates of PD in patients with melanoma were included. Pooled odds ratios (ORs) with 95 % confidence intervals (CIs) were calculated by random-effects models. Heterogeneity across studies was assessed using Cochran Q and I² statistics. Subgroup analyses and sensitivity analyses were conducted to evaluate sources of heterogeneity. Subgroup analyses were done according to temporal relationship, geographic region and gender respectively. We assessed publication bias using the Begg and Egger test. In addition, study appraisal was done using a scale for observational studies to ensure the quality of evidence.

Results

We identified 24 eligible studies on PD and melanoma with a total number of 292,275 PD patients: the pooled OR was 1.83 (95 % CI 1.46–2.30) overall, subgroup analyses by temporal relationship showed that risk of melanoma after PD diagnosis was significantly higher (OR 2.43, 95 % CI 1.77–3.32), but not before the diagnosis of PD (OR 1.09, 95 % CI 0.78–1.54). Subgroup analysis by geographic region showed that increased risk of melanoma in PD was found both in Europe (OR 1.44, 95 % CI 1.22–1.70) and in North America (OR 2.64, 95 % CI 1.63–4.28). Gender-specific subgroup analyses did not show difference between men (OR 1.64, 95 % CI 1.27–2.13) and women (OR 1.38, 95 % CI 1.04–1.82) in the risk of melanoma. In addition, we found the risk of non-melanoma skin cancers in PD was slightly higher (OR 1.20, 95 % CI 1.11–1.29) than general population. It was impossible to evaluate the association between PD and melanoma according to use of levodopa or gene polymorphism via meta-analysis since few observational or cohort studies have focused on it.

Conclusions

An association between PD and melanoma was confirmed. Most of the evidences were of high quality, and the conclusion was robust. Further research is needed to explore the mechanisms underlying this relationship.

Electronic supplementary material

The online version of this article (doi:10.1186/s40035-015-0044-y) contains supplementary material, which is available to authorized users.

Recent examples on the clinical relevance of the CYP2D6 polymorphism and endogenous functionality of CYP2D6

The cytochrome P450 2D6 (CYP2D6) belongs to a group of CYPs considered of utmost importance in the metabolism of xenobiotics. Despite being of only minor abundance in the liver, it is involved in the clearance of >25% of marketed drugs. Accordingly, CYP2D6 can be very efficiently inhibited by a couple of commonly used drugs such as some antidepressants, although induction by any drug has not been observed thus far. CYP2D6 was also one of the first enzymes for which a highly polymorphic expression could be shown leading to a widespread range of functionality, from a complete lack of a functional enzyme to overexpression due to multiplication of active alleles. A clear relationship between the CYP2D6 genotype and adverse events during treatment with CNS-active drugs such as codeine, antidepressants, or antipsychotics could be demonstrated. More recently, some new aspects emerged about the potential endogenous function of CYP2D6 in terms of behavior and brain disorders.

CYP2D6*4 allele polymorphism increases the risk of Parkinson's disease: evidence from meta-analysis

Background

Many epidemiological studies have been conducted to explore the association between a single CYP2D6 gene polymorphism and Parkinson’s disease (PD) susceptibility. However, the results remain controversial.

Objectives

To clarify the effects of a single CYP2D6 gene polymorphism on the risk of PD, a meta-analysis of all available studies relating to CYP2D6*4 polymorphism and the risk of PD was conducted.

Methods

A comprehensive literature search of PubMed, EMBASE, and the China National Knowledge Infrastructure (CNKI) up to September 1, 2013 was conducted. Data were extracted by two independent authors and pooled odds ratio (OR) with 95% confidence interval (CI) were calculated. Meta-regression, Galbraith plots, subgroup analysis, sensitivity analysis, and publication bias analysis were also performed.

Results

Twenty-two separate comparisons consisting of 2,629 patients and 3,601 controls were included in our meta-analysis. The pooled analyses showed a significant association between CYP2D6*4G/A polymorphism and PD risk in all of the comparisons (A vs. G allele: OR = 1.28, 95% CI = 1.14–1.43, P = 0.001; AA vs. GG: OR = 1.43, 95% CI = 1.06–1.93, P = 0.018; AG vs. GG: OR = 1.22, 95% CI = 1.06–1.40, P = 0.006; AG+AA vs. GG: OR = 1.26, 95% CI = 1.10–1.44, P = 0.001; AA vs. AG+GG: OR = 1.37, 95% CI = 1.02–1.83, P = 0.036). In subgroup analysis stratified by ethnicity, significant associations were also demonstrated in Caucasians but not in Asians. No significant association was found in subgroup analysis stratified by age of onset or disease form.

Conclusions

We concluded that the CYP2D6*4G/A polymorphism denotes an increased genetic susceptibility to PD in the overall population, especially in Caucasians. Further large and well-designed studies are needed to confirm this association.

Postural instability/gait disturbance in Parkinson's disease has distinct subtypes: an exploratory analysis

OBJECTIVE

To test the hypothesis that postural instability with falling (PIF) and freezing of gait (FOG) are distinct subtypes of the postural instability/gait disturbance (PIGD) form of Parkinson's disease (PD).

METHODS

499 PD subjects from the NeuroGenetics Research Consortium were studied using logistic regression to examine, in a cross sectional analysis, predictors of FOG and PIF. Potential predictors were from four spheres; demographic, clinical motor, clinical non-motor and genetic.

RESULTS

FOG and PIF were both associated with greater gait subscores and lower tremor subscores on the Unified Parkinson's Disease Rating Scale (p ≤ 0.02). However, they differed with regard to demographic, non-motor and genetic predictors. FOG was associated with greater duration of disease, with ORs of 3.01 (95% CI 1.35 to 6.72) and 4.91 (95% CI 2.29 to 10.54) for third and fourth quartiles of duration, respectively, versus the lowest half of duration. The risk of having psychotic symptoms was also significantly increased (OR 3.02, 95% CI 1.41 to 6.49; p=0.004). FOG was inversely associated with the presence of the CYP2D6*4 allele (OR 0.41, 95% CI 0.21 to 0.80; p=0.009) suggesting a protective effect. PIF was associated with depression (OR 1.08, 95% CI 1.01 to 1.15; p<0.02) and was inversely associated with APOE ε4 (OR 0.21, 95% CI 0.05 to 0.87; p=0.03), again suggesting a protective effect.

CONCLUSION

FOG and PIF have different demographic, non-motor and genetic predictors suggesting that they may be pathophysiologically distinct subtypes of PIGD. These findings have implications in the discovery of therapeutic targets for these disabling features as well as for predicting outcomes of PD.

The association between Parkinson's disease and melanoma

Parkinson's disease (PD) is a neurodegenerative disorder characterized by a loss of melanin-positive, dopaminergic neurons in the substantia nigra. Although there is convincing epidemiologic evidence of a negative association between PD and most cancers, a notable exception to this is that melanoma, a malignant tumor of melanin-producing cells in skin, occurs with higher-than-expected frequency among subjects with PD and that melanoma patients are more likely to have PD. A clear biological explanation for this epidemiological observation is lacking. Here, we present a comprehensive review of published literature exploring the association between PD and melanoma. On the basis of published findings, we conclude that (i) changes in pigmentation including melanin synthesis and/or melanin synthesis enzymes, such as tyrosinase and tyrosine hydroxylase, play important roles in altered vulnerability for both PD and melanoma; (ii) changes of PD-related genes such as Parkin, LRRK2 and α-synuclein may increase the risk of melanoma; (iii) changes in some low-penetrance genes such as cytochrome p450 debrisoquine hydroxylase locus, glutathione S-transferase M1 and vitamin D receptor could increase the risk for both PD and melanoma and (iv) impaired autophagy in both PD and melanoma could also explain the association between PD and melanoma. Future studies are required to address whether altered pigmentation, PD- or melanoma-related gene changes and/or changes in autophagy function induce oncogenesis or apoptosis. From a clinical point of view, early diagnosis of melanoma in PD patients is critical and can be enhanced by periodic dermatological surveillance, including skin biopsies.

Association between polymorphisms in Wnt signaling pathway genes and bone mineral density in postmenopausal Korean women

OBJECTIVE

The purpose of this study was to investigate the association between single nucleotide polymorphisms in Wnt signal pathway genes and circulating osteoprotegerin (OPG), soluble receptor activator of the nuclear factor-κB ligand (sRANKL) levels, bone turnover markers, and bone mineral density (BMD) in postmenopausal Korean women.

METHODS

Wnt9a c256G>A; low-density lipoprotein receptor-related protein (LRP) 5 c266A>G, c2245C>G, c3893C>T, and c4099G>A; secreted frizzled-related protein (sFRP) 4 c1019G>A; axin II c148C>T and c1615G>A; glycogen synthase kinase binding protein (GBP) c455C>A; β-catenin c94G>T and c101G>T; T-cell factor 1 c663G>T, c734C>T, and c766G>A; and adenomatous polyposis coli c5465T>A polymorphisms were analyzed in 392 postmenopausal Korean women. Serum levels of OPG, sRANKL, and bone turnover markers were measured, and BMDs at the lumbar spine and femoral neck were examined.

RESULTS

Wnt9a c256G>A, LRP5 c2245C>G and c4099G>A, axin II c1615G>A, GBP c455C>A, β-catenin c94G>T and c101G>T, and T-cell factor 1 c663G>T and c734C>T single nucleotide polymorphisms were not observed. Among the genes showing polymorphisms, only the sFRP4 c1019G>A polymorphism was associated with BMD. The AA genotype in the sFRP4 c1019G>A polymorphism showed significantly lower lumbar spine BMD and a higher serum bone alkaline phosphatase level than did the GG genotype and showed a 6.39 times higher risk for osteoporosis at the lumbar spine compared with the GG genotype. No significant differences in bone turnover markers, OPG, and sRANKL were detected among the other single genotypes or the LRP haplotype genotype.

CONCLUSIONS

Our results suggest that the sFRP4 c1019G>A polymorphism may be one of the genetic factors affecting lumbar spine BMD in postmenopausal Korean women.

Association between polymorphisms in tumor necrosis factor (TNF) and TNF receptor genes and circulating TNF, soluble TNF receptor levels, and bone mineral density in postmenopausal Korean women

OBJECTIVE

The aim of the present study was to investigate the relationship of polymorphisms in the tumor necrosis factor (TNF)-alpha, TNF-beta, and TNF receptor (TNFR) genes to circulating TNF, soluble TNFR (sTNFR) levels, and bone mineral density (BMD) in women.

METHODS

The TNF-alpha G(-308)A, C(-857)T, C(-863)A, T(-1031)C, TNF-beta A252G, TNFRI A36G, TNFRII T676G, A1663G, A1668G, and C1690T polymorphisms were analyzed in 377 postmenopausal Korean women. The levels of serum TNF-alpha, TNF-beta, sTNFRI, sTNFRII, and bone turnover markers were measured. BMD was examined by dual energy x-ray absorptiometry.

RESULTS

After adjustment for age, body mass index, and years since menopause, no significant differences in BMD of the lumbar spine and femoral neck and serum levels of bone turnover markers were detected, according to single polymorphisms in TNF and TNFR genes and combined polymorphisms. However, the frequencies of the TT genotype of TNF-alpha T(-1031)C polymorphism, the non-AA genotype of TNF-beta A252G polymorphism, and the GG genotype of TNFRII A1663G polymorphism were significantly higher in osteoporotic women than in women with normal BMD, respectively (P < 0.05). The TNFRII T676G polymorphism affected the serum sTNFRI and sTNFRII levels. The serum sTNFRII levels in the CC genotype of TNFRII C1690T polymorphism were the highest, with a G or C allele dose effect, and the TNFRII G676C/C1690T haplotype genotype also affected serum sTNFRII levels.

CONCLUSIONS

TNF-alpha T(-1031)C, TNF-beta A252G, and TNFRII A1663G polymorphisms may be genetic factors for osteoporosis in Korean postmenopausal women, and the TNFRII T676G and C1690T polymorphisms and their combined polymorphism affected serum sTNFRII levels. The TNFRII T676G polymorphism also affected the serum sTNFRI levels.

Genetic polymorphism in cytochrome P450 2D6 (CYP2D6): Population distribution of CYP2D6 activity

Cytochrome P-450 2D6 (CYP2D6) is involved in the metabolism of many therapeutic drugs even though the enzyme represents a small proportion of the total CYP content of human liver. In vivo phenotyping with probe drug substrates such as debrisoquine and dextromethorphan showed a clear separation between poor metabolizers (PM) and extensive metabolizers (EM). This polymorphism may affect susceptibility to environmental disease, as suggested by molecular epidemiologic studies that found an association between CYP2D6 metabolizer phenotype and cancer risk; however, this association is not consistent. There are only a few examples of CYP2D6 involvement in toxicant mechanism of action, but this has not been extensively studied. Gene probe studies documented a number of genetic polymorphisms that underlie CYP2D6 metabolizer phenotypes. The EM group carries the wild-type (*1) or active (*2) variant alleles, while the PM group carries the *3, *4, *5, or *6 alleles, all of which code for a protein that has lower or null CYP2D6 activity. The current analysis characterizes (a) influence of genotype on phenotype based upon in vivo metabolism studies of probe drugs and (b) frequency of the major genotypes in different population groups is also characterized. These data were then incorporated into Monte Carlo modeling to simulate population distributions of CYP2D6 activity. This analysis reproduced the bimodal distributions commonly seen in phenotyping studies of Caucasians and found extensive population variability in enzyme activity, as indicated by the 9- to 56-fold difference between the PM modal median and the total population median CYP2D6 activity. This substantial degree of interindividual variability in CYP function indicates that assessments involving CYP2D6 substrates need to consider the full distribution of enzyme activity in refining estimates of internal dose in health assessments of xenobiotics.

Polymorphisms of catechol-0-methyltransferase (COMT), monoamine oxidase B (MAOB), N-acetyltransferase 2 (NAT2) and cytochrome P450 2D6 (CYP2D6) gene in patients with early onset of Parkinson’s disease

The aim of the present study was to evaluate the contribution of MAOB, COMT, NAT2 and CYP2D6 gene polymorphisms to early onset Parkinson's disease (PD). The study enrolled 134 patients with Parkinson's disease (early onset-EOPD--67 patients, and late onset--LOPD--patients), and 66 healthy individuals. Polymerane chain reaction restriction fragment length polymorphism (PCR-RFLP) methods were used for genotyping. Univariate analysis revealed a significant two-fold higher EOPD risk among carriers of MAOB allele A or AA genotype. Multivariate analysis revealed that MAOB allele A was an independent factor predisposing to EOPD. It was shown that neither NAT2, CYP2D6 nor COMT genotype was associated with PD.

Polymorphism in semaphorin 5A (Sema5A) gene is not a marker of Parkinson's disease risk

A SNP rs7702187 within the semaphorin 5A gene (Sema5A) has been recently associated with sporadic Parkinson's disease (PD) risk in American Caucasians. In the present study frequencies of rs7702187 was determined in two independent populations involving 427 sporadic PD patients (235 Polish Caucasians and 192 Asians from Singapore) and 412 healthy controls (220 Caucasians and 192 Asians), with the use of PCR-RFLP assay. The frequencies of the minor allele were found to be very similar in PD patients and healthy controls in both populations studied: 0.147 versus 0.143 in Caucasian, and 0.224 versus 0.221 in Asian, respectively. Our research does not confirm the previous observation, as no relationship was found between polymorphism within Sema5A gene and the risk of PD. It can be concluded that rs7702187 SNP in Sema5a gene is not a marker of PD risk in the studied populations.

Environmental health research in the post-genome era: new fields, new challenges, and new opportunities

The human genome sequence provides researchers with a genetic framework to eventually understand the relationships of gene-environment interactions. This wealth of information has led to the birth of several related areas of research, including proteomics, functional genomics, pharmacogenomics, and toxicogenomics. Developing techniques such as DNA/protein microarrays, small-interfering RNA (siRNA) applications, two-dimensional gel electrophoresis, and mass spectrometry in conjunction with advanced analysis software and the availability of Internet databases offers a powerful set of tools to investigate an individual's response to specific stimuli. This review summarizes these emerging scientific fields and techniques focusing specifically on their applications to the complexities of gene-environment interactions and their potential role in environ-mental biosecurity.

Polymorphic cytochrome P450 2D6: humanized mouse model and endogenous substrates

Cytochrome P450 2D6 (CYP2D6) is the first well-characterized polymorphic phase I drug-metabolizing enzyme, and more than 80 allelic variants have been identified for the CYP2D6 gene, located on human chromosome 22q13.1. Human debrisoquine and sparteine metabolism is subdivided into two principal phenotypes--extensive metabolizer and poor metabolizer--that arise from variant CYP2D6 genotypes. It has been estimated that CYP2D6 is involved in the metabolism and disposition of more than 20% of prescribed drugs, and most of them act in the central nervous system or on the heart. These drug substrates are characterized as organic bases containing one nitrogen atom with a distance about 5, 7, or 10 A from the oxidation site. Aspartic acid 301 and glutamic acid 216 were determined as the key acidic residues for substrate-enzyme binding through electrostatic interactions. CYP2D6 transgenic mice, generated using a lambda phage clone containing the complete wild-type CYP2D6 gene, exhibits enhanced metabolism and disposition of debrisoquine. This transgenic mouse line and its wild-type control are models for human extensive metabolizers and poor metabolizers, respectively, and would have broad application in the study of CYP2D6 polymorphism in drug discovery and development, and in clinical practice toward individualized drug therapy. Endogenous 5-methoxyindole- thylamines derived from 5-hydroxytryptamine were identified as high-affinity substrates of CYP2D6 that catalyzes their O-demethylations with high enzymatic capacity and specificity. Thus, polymorphic CYP2D6 may play an important role in the interconversions of these psychoactive tryptamines, including a crucial step in a serotonin-melatonin cycle.

Potential role of cerebral cytochrome P450 in clinical pharmacokinetics: modulation by endogenous compounds

Cytochrome P450 (CYP) enzymes catalyse phase I metabolic reactions of psychotropic drugs. The main isoenzymes responsible for this biotransformation are CYP1A2, CYP2D6, CYP3A and those of the subfamily CYP2C. Although these enzymes are present in the human brain, their specific role in this tissue remains unclear. However, because CYP enzymatic activities have been reported in the human brain and because brain microsomes have been shown to metabolise the same probe substrates used to assess specific hepatic CYP activities and substrates of known hepatic CYPs, local drug metabolism is believed to be likely. There are also indications that CYP2D6 is involved in the metabolism of endogenous substrates in the brain. This, along with the fact that several neurotransmitters modulate CYP enzyme activities in human liver microsomes, indicates that CYP enzymes present in brain could be under various regulatory mechanisms and that those mechanisms could influence drug pharmacokinetics and, hence, drug response. In this paper we review the presence of CYP1A2, CYP2C9, CYP2D6 and CYP3A in brain, as well as the possible existence of local brain metabolism, and discuss the putative implications of endogenous modulation of these isoenzymes by neurotransmitters.

Dementia with lewy bodies: molecular pathogenesis and implications for classification

Dementia with Lewy bodies results from the accumulation from Lewy-type pathology (Lewy bodies, Lewy neurites), secondary cellular injury, and apoptotic neurodegeneration. The severity of dementia correlates with the abundance of Lewy bodies in the cortex. Dementia with Lewy bodies co-occurs with 2 specific syndromes, one beginning with dementia complicated by visual hallucinations and parkinsonism; the other beginning with Parkinson's disease and progressing to a parkinsonian-dementia syndrome. Clinical syndromes associated with these 2 pathways to dementia share many clinical features including the type of cognitive impairment, fluctuating attentional disturbances, prominent visual hallucinations and psychosis, depression, and rapid eye movement sleep behavior disorder. Lewy pathology results from protein misfolding and the accumulation of alpha-synuclein in the cell cytoplasm. Dementia with Lewy bodies is one of many neurodegenerative disorders linked to protein misfolding. Identification of clinical symptoms indicative of the presence of a specific protein disturbance will assist in choosing therapies when protein-specific disease-modifying treatments are available. Classification systems based on symptom complexes related to the presence of protein misfolding will assist therapeutic decisions.

Polymorphism in candidate genes: implications for the risk and treatment of idiopathic Parkinson's disease

Idiopathic Parkinson's disease (IPD) is a progressive neurodegenerative disorder for which no restorative or neuroprotective therapy is available. Interest has recently been directed to association studies on polymorphisms of various genes, mainly those related to dopamine metabolism and transport, and their effect on response to PD, which includes primarily levodopa and dopaminomimetics. Approximately 15-20% of patients with PD do not respond to levodopa, and the majority of those who do respond develop adverse fluctuations in motor response, primarily levodopa-induced dyskinesias. This review summarizes the influence of polymorphisms in various genes on the relative risk of IPD and on levodopa efficacy. It focuses on the importance of well-designed polymorphism studies that include large samples of patients with IPD and tightly matched controls and use identical methodologies. Valid data on such polymorphisms might increase the efficacy of levodopa, decrease its side effects, and reduce the occurrence of levodopa-induced dyskinesias. They might also provide a novel diagnostic tool for PD.

Progress in clinical neurosciences: Parkinson's disease with dementia and dementia with Lewy bodies

Dementia occurs in up to 30% of people with Parkinson's disease and is a major cause of disability. Pathologically, Parkinson's dementia, where dementia follows the onset of parkinsonism by at least one year, overlaps with dementia with Lewy bodies. We review the functional impact, definitions, neuropsychology, epidemiology and pathophysiology of Parkinson's dementia, dementia with Lewy bodies and their overlap. Associated psychiatric and imaging findings are also considered. Lastly, current and emerging approaches to assessment and treatment in patients with these Lewy body associated dementias are presented.

Rapid and Reliable Method for Cytochrome P450 2D6 Genotyping

Background: Single-nucleotide polymorphisms and single-base deletions within the cytochrome P450 2D6 (CYP2D6) gene have been associated with a poor metabolizer (PM) phenotype and display a frequency of 7–10% in the Caucasian population.

Methods: We developed a reliable and rapid procedure to identify five major PM-associated mutations (CYP2D6*4, *7, and *8) and deletions (CYP2D6*3 and *6) by real-time PCR with subsequent fluorometric melting point analysis of the PCR product. These polymorphisms within the CYP2D6 gene were detected by use of two primer pairs and five different pairs of hybridization probes. DNA extracted from whole blood of 323 individuals was analyzed, and results were compared with genotypes obtained by allele-specific multiplex PCR. In case of uncertain results, additional sequence analysis was performed.

Results: Genotyping results by real-time PCR were 100% reliable, whereas conventional allele-specific multiplex PCR produced uncertain results for 12.1% of samples, as confirmed by sequence analysis. Costs for reagents and consumables were considerably higher for the real-time PCR technology, but labor time was reduced by 2 h compared with allele-specific PCR. The allele frequencies in the population investigated were 0.186 for allele *4, 0.026 for allele *5, 0.009 for allele *3, 0.031 for allele *6, and 0.002 for allele *8. The defective CYP2D6*7 allele was not found. In addition, three additional mutations were detected, one of them displaying a PM genotype.

Conclusion: Genotyping of CYP2D6 by real-time PCR with fluorometric melting point analysis is a rapid and reliable method.

ACT and UCH-L1 polymorphisms in Parkinson's disease and age of onset

alpha1-Antichymotrypsin (ACT) and ubiquitin carboxy-terminal hydrolase L1 (UCH-L1) have been suggested as susceptibility factors for Parkinson's disease (PD). We replicated these findings in a Chinese case-control sample consisting of 160 PD cases and 160 carefully matched control subjects. Genotypes were determined using polymerase chain reaction and BstN1 or Rsa1 restriction enzyme assay. Analysis showed no significant difference between PD patients and controls for genotype or allele frequencies of the ACT and UCH-L1 S18Y polymorphisms. UCH-L1 S18Y polymorphism carriers, however, were found to be significantly less frequent in early-onset PD patients with a reduced risk of 0.557 (95% C.I. = 0.314-0.985; P = 0.043). These data suggest that ACT polymorphism does not influence the risk for developing PD. UCH-L1 S18Y polymorphism, however, may be a weak protective factor against early-onset PD.