Catechol-O-methyltransferase (COMT) is an enzyme that plays a key role in the modulation of catechol-dependent functions such as cognition, cardiovascular function, and pain processing. Three common haplotypes of the human COMT gene, divergent in two synonymous and one nonsynonymous (val158met) position, designated as low (LPS), average (APS), and high pain sensitive (HPS), are associated with experimental pain sensitivity and risk of developing chronic musculoskeletal pain conditions. APS and HPS haplotypes produce significant functional effects, coding for 3- and 20-fold reductions in COMT enzymatic activity, respectively. In the present study, we investigated whether additional minor single nucleotide polymorphisms (SNPs), accruing in 1 to 5% of the population, situated in the COMT transcript region contribute to haplotype-dependent enzymatic activity. Computer analysis of COMT ESTs showed that one synonymous minor SNP (rs769224) is linked to the APS haplotype and three minor SNPs (two synonymous: rs6267, rs740602 and one nonsynonymous: rs8192488) are linked to the HPS haplotype. Results from in silico and in vitro experiments revealed that inclusion of allelic variants of these minor SNPs in APS or HPS haplotypes did not modify COMT function at the level of mRNA folding, RNA transcription, protein translation, or enzymatic activity. These data suggest that neutral variants are carried with APS and HPS haplotypes, while the high activity LPS haplotype displays less linked variation. Thus, both minor synonymous and nonsynonymous SNPs in the coding region are markers of functional APS and HPS haplotypes rather than independent contributors to COMT activity.
Catechol-O-methyltransferase (COMT) is an ubiquitously expressed enzyme that maintains basic biologic functions by inactivating catechol substrates. In humans, polymorphic variance at the COMT locus has been associated with modulation of pain sensitivity (Andersen & Skorpen, 2009) and risk for developing psychiatric disorders (Harrison & Tunbridge, 2008). A functional haplotype associated with increased pain sensitivity was shown to result in decreased COMT activity by altering mRNA secondary structure-dependent protein translation (Nackley et al., 2006). However, the exact mechanisms whereby COMT modulates pain sensitivity and behavior remain unclear and can be further studied in animal models. We have assessed Comt1 gene expression levels in multiple brain regions in inbred strains of mice and have discovered that Comt1 is differentially expressed among the strains, and this differential expression is cis-regulated. A B2 Short Interspersed Element (SINE) was inserted in the 3′UTR of Comt1 in 14 strains generating a common haplotype that correlates with gene expression. Experiments using mammalian expression vectors of full-length cDNA clones with and without the SINE element demonstrate that strains with the SINE haplotype (+SINE) have greater Comt1 enzymatic activity. +SINE mice also exhibit behavioral differences in anxiety assays and decreased pain sensitivity. These results suggest that a haplotype, defined by a 3′ UTR B2 SINE element, regulates Comt1 expression and some mouse behaviors.
The enzyme catechol-O-methyltransferase (COMT) metabolizes catecholamine neurotransmitters involved in a number of physiological functions including pain perception. Both human and mouse COMT genes possess functional polymorphisms contributing to inter-individual variability in pain phenotypes such as sensitivity to noxious stimuli, severity of clinical pain and response to pain treatment. In this study, we found that the effects of Comt functional variation in mice are modality-specific. Spontaneous inflammatory nociception and thermal nociception behaviors were correlated the most with the presence of the B2 SINE transposon insertion residing in the 3’UTR mRNA region. Similarly, in humans, COMT functional haplotypes were associated with thermal pain perception and with capsaicin-induced pain. Furthermore, COMT genetic variations contributed to pain behaviors in mice and pain ratings in humans in a sex-specific manner. The ancestral Comt variant, without a B2 SINE insertion, was more strongly associated with sensitivity to capsaicin in female versus male mice. In humans, the haplotype coding for low COMT activity increased capsaicin-induced pain perception in women, but not men. These findings reemphasize the fundamental contribution of COMT to pain processes, and provide a fine-grained resolution of this contribution at the genetic level that can be used to guide future studies in the area of pain genetics.
Catechol-O-methyltransferase (COMT), an enzyme that metabolizes catecholamines, has recently been implicated in the modulation of pain. Specifically, low COMT activity is associated with heightened pain perception and development of musculoskeletal pain in humans as well as increased experimental pain sensitivity in rodents.
We report that the proinflammatory cytokine tumor necrosis factor α (TNFα) downregulates COMT mRNA and protein in astrocytes. Examination of the distal COMT promoter (P2-COMT) reveals a putative binding site for nuclear factor κB (NF-κB), the pivotal regulator of inflammation and the target of TNFα. Cell culture assays and functional deletion analyses of the cloned P2-COMT promoter demonstrate that TNFα inhibits P2-COMT activity in astrocytes by inducing NF-κB complex recruitment to the specific κB binding site.
Collectively, our findings provide the first evidence for NF-κB-mediated inhibition of COMT expression in the central nervous system, suggesting that COMT contributes to the pathogenesis of inflammatory pain states.
Catechol O-methyltransferase (COMT) is expressed as both soluble (S) and membrane-bound (MB) isoforms, with S-COMT predominantly expressed in liver. A common nonsynonymous SNP, 472G>A (108/158Val>Met, S/MB), has been associated with variation in levels of COMT enzyme activity and thermal stability. We set out to test the hypothesis that additional COMT polymorphisms might also be associated with phenotypic variation.
We phenotyped 268 liver biopsy samples for S-COMT activity and thermal stability, resequenced a portion of the gene that had not previously been resequenced, and genotyped DNA from these same samples for 16 COMT polymorphisms.
There was a significant association between the two COMT phenotypes and genotype at the codon 108 SNP. A haplotype-based approach was then used to assess the possible association of other polymorphisms with phenotype. Specifically, codon 108 SNP explained 20.4% of variance in activity (P<10−6), and 59% of variance in thermal stability (P<10−6). Haplotypes that included SNPs at cDNA nucleotides 408 and 472 explained additional variance in enzyme activity (up to 24.4%), and the addition to the haplotype of a SNP at intron 2 (51) explained a total of 27.5% of the variance. However, no SNPs beyond that at nucleotide 472G>A polymorphism were associated with variation in thermal stability. We also observed a three-fold variation in the ability of reporter gene constructs for “proximal promoter” haplotypes to drive transcription.
The common COMT 108Val>Met polymorphism is associated with human liver S-COMT activity and thermal stability, but additional COMT SNPs also contribute to variation in activity.
catechol O-methyltransferase; COMT; genetic polymorphism; SNP; haplotype; thermal stability
Catechol-O-Methyltransferase (COMT) plays a key role in dopamine and estrogen metabolism. Recently, COMT haplotypes rather than the single polymorphism Val158Met have been reported to underlie differences in protein expression by modulating mRNA secondary structure. So far, studies investigating the epigenetic variability of the S-COMT (soluble COMT) promoter region mainly focused on phenotypical aspects, and results have been controversial.
We assessed S-COMT promoter methylation in saliva and blood derived DNA with regard to early pre- and postnatal growth as well as to genotype for polymorphisms rs6269, rs4633, and rs4680 (Val158Met) in 20 monozygotic twin pairs (mean age 4 years), who were discordant for intrauterine development due to severe feto-fetal-transfusion syndrome. Methylation levels of two previously reported partially methylated cytosines were determined by the quantitative SIRPH (SNuPE- IP RP HPLC) assay.
Overall, we observed a high variability of S-COMT promoter methylation, which did not correlate with individual differences in the pre- or postnatal growth pattern. Within the twin pairs however we noted a distinct similarity that could be linked to underlying COMT genotypes. This association was subsequently confirmed in a cohort of 93 unrelated adult controls. Interestingly, 158Val-alleles were found at both ends of the epigenotypical range, which is in accordance with a recently proposed model of COMT haplotypes corresponding to a continuum of phenotypical variability.
The strong heritable component of S-COMT promoter methylation found in our study needs to be considered in future approaches that focus on interactions between COMT epigenotype and phenotype.
Catecholamine signaling pathways in the peripheral and central nervous systems (PNS, CNS, respectively) utilize catechol-O-methyltransferase (COMT) as a major regulatory enzyme responsible for deactivation of dopamine (DA), norepinephrine (NE) and epinephrine (E). Accordingly, homeostasis of COMT gene expression is hypothesized to be functionally linked to regulation of autonomic control of normotensive vascular events. Recently, we demonstrated that morphine administration in vitro resulted in decreased cellular concentrations of COMT-encoding mRNA levels, as compared to control values. In contrast, cells treated with E up regulated their COMT gene expression. In sum, these observations indicate a potential reciprocal linkage between end product inhibition of COMT gene expression by E and morphine. Interestingly, the observed effects of administered E on COMT gene expression suggest an enhancement of its own catabolism or, reciprocally, a stimulation morphine biosynthesis.
endogenous morphine; catecholamines; epinephrine; catechol-O-methyltransferase
Catechol-O-methyltransferase (COMT) is a key enzyme responsible for the degradation of dopamine and norepinephrine. COMT activity influences cognitive and emotional states in humans and aggression and drug responses in mice. This study identifies the key sequence variant that leads to differences in Comt mRNA and protein levels among mice, and that modulates synaptic function and pharmacological and behavioral traits.
We examined Comt expression in multiple tissues in over 100 diverse strains and several genetic crosses. Differences in expression map back to Comt and are generated by a 230 nt insertion of a B2 short interspersed element (B2 SINE) in the proximal 3′ UTR of Comt in C57BL/6J. This transposon introduces a premature polyadenylation signal and creates a short 3′ UTR isoform. The B2 SINE is shared by a subset of strains, including C57BL/6J, A/J, BALB/cByJ, and AKR/J, but is absent in others, including DBA/2J, FVB/NJ, SJL/J, and wild subspecies. The short isoform is associated with increased protein expression in prefrontal cortex and hippocampus relative to the longer ancestral isoform. The Comt variant causes downstream differences in the expression of genes involved in synaptic function, and also modulates phenotypes such as dopamine D1 and D2 receptor binding and pharmacological responses to haloperidol.
We have precisely defined the B2 SINE as the source of variation in Comt and demonstrated that a transposon in a 3′ UTR can alter mRNA isoform use and modulate behavior. The recent fixation of the variant in a subset of strains may have contributed to the rapid divergence of inbred strains.
Genetic variation contributes to differences in pain sensitivity and response to different analgesics. Catecholamines are involved in the modulation of pain and are partly metabolized by the catechol-O-methyltransferase (COMT) enzyme. Genetic variability in the COMT gene may therefore contribute to differences in pain sensitivity and response to analgesics. It is shown that a polymorphism in the COMT gene, Rs4680 (Val158Met), influence pain sensitivity in human experimental pain and the efficacy for morphine in cancer pain treatment. In this study we wanted to investigate if variability in other regions in the COMT gene also contributes to interindividual variability in morphine efficacy.
We genotyped 11 single nucleotide polymorphisms (SNPs) throughout the COMT gene, and constructed haplotypes from these 11 SNPs, which were in Hardy-Weinberg equilibrium. We compared both genotypes and haplotypes against pharmacological, demographical and patient symptoms measurements in a Caucasian cancer patient cohort (n = 197) receiving oral morphine treatment for cancer pain. There were two frequent haplotypes (34.5% and 17.8%) in our cohort. Multivariate analyses showed that patients carrying the most frequent haplotype (34.5%) needed lower morphine doses than patients not carrying the haplotype, with a reduction factor of 0.71 (p = 0.005). On the allele level, carriers of alleles for six of the SNPs show weak associations in respect to morphine dose and the alleles associated with the lowest morphine doses constitute part of the most frequent haplotype.
This study suggests that genetic variability in the COMT gene influence the efficacy of morphine in cancer patients with pain, and that increased understanding of this variability is reached by expanding from analyses of single SNPs to haplotype construction and analyses.
Three common haplotypes in the gene encoding catechol-O-methyltransferase (COMT) have been associated with pain modulation and the risk of developing chronic musculoskeletal pain, namely temporomandibular disorder (TMD). Haplotypes coding for higher enzymatic activity were correlated with lower pain perception. Rodent studies showed that COMT inhibition increases pain sensitivity via β2/3-adrenergic receptors. We hypothesized that the non-selective β-adrenergic antagonist propranolol will reduce clinical and experimental pain in TMD patients in a manner dependent on the subjects’ COMT diplotype.
40 female Caucasian participants meeting the Research Diagnostic Criteria for TMD were genotyped for COMT polymorphisms and completed a randomized, double–blind, placebo-controlled, two-period crossover pilot study. Each period consisted of a baseline assessment week followed by an intervention week (propranolol or placebo). Changes in clinical pain ratings, psychological status, and responses to heat and pressure stimuli between baseline and intervention weeks were compared across periods.
The number of patients reporting a reduction in pain intensity rating was greater during propranolol treatment (p=0.014) compared with placebo. Propranolol significantly reduced a composite pain index (p=0.02) but did not decrease other clinical and experimental pain ratings. When stratified by the COMT high activity haplotype, a beneficial effect of propranolol on pain perception was noted in subjects not carrying this haplotype, a diminished benefit was observed in the heterozygotes, and no benefit was noted in the homozygotes.
COMT haplotypes may serve as genetic predictors of propranolol treatment outcome, identifying a subgroup of TMD patients who will benefit from propranolol therapy.
propranolol; β-blockers; pharmacogenetics; chronic pain; temporomandibular joint disorder (TMD); catechol-O-methyltransferase (COMT); polymorphism
A single nucleotide polymorphism in the human COMT (catechol-O-methyltransferase) gene has been associated with increased risk for breast cancer and several CNS diseases and disorders. The G to A polymorphism causes a valine (val) to methionine (met) substitution at codon 108 soluble- (S)/ 158 membrane- (MB) COMT, generating alleles encoding high and low activity forms of the enzyme, COMTH and COMTL, respectively. Tissues and cells with a COMTLL genotype have decreased COMT activity compared to COMTHH cells. Previously, we reported that the decreased activity was due to decreased amounts of S-COMTL protein in human hepatocytes. In this study, we investigated the role of S-COMT protein synthesis and turnover as determinates of reduced COMT protein in COMTLL compared to COMTHH cells. No association between S-COMT protein synthesis and COMT genotype was detected. Using a pulse-chase protocol, the half-life of S-COMTH was determined to be 4.7 days, which was considerably longer than expected from the half-lives of other phase 2 enzyme proteins. The half-life of S-COMTL compared to S-COMTH protein was significantly shorter at 3.0 days, but the difference was affected by the medium used during the chase period. These results suggest that increased turnover may contribute to reduced COMT activity in cells and tissues from COMTLL individuals. Subtle differences appear to be able to affect the stability of the S-COMTL protein, and this may contribute to the differences observed in epidemiological studies on the association of this polymorphism with breast cancer risk.
Catechol-O-methyltransferase (COMT); COMT polymorphism; protein synthesis; protein turnover; human breast epithelial cell lines
Heavy drinking can cause chronic hypertension, possibly due to effects on the autonomic nervous system. Catechol-O-methyltransferase (COMT) inactivates catecholamines, and a G to A substitution in codon 108 in the soluble COMT mRNA (or codon 158 in the membrane bound form) substitutes methionine for valine and alters enzyme activity.
We evaluated the association of COMT genotype at this locus with blood pressure in 839 alcohol dependent individuals before and during participation in an alcoholism treatment trial. Hierarchical linear models were used to account for within-subject correlation on repeated blood pressure measurements, and findings were adjusted for age, gender, ethnicity, alcohol use, body-mass index, current smoking, hypertension history, and study site.
Relative to those with the val-val genotype, those with the met-met genotype had higher adjusted systolic (+4.9 mm Hg, p<0.01) and diastolic (+3.2 mm Hg, p<0.01) blood pressure at baseline. Those with the val-met genotype did not significantly differ from the val-val genotype. Changes in blood pressure between baseline and 4 weeks of alcohol treatment also differed by genotype. Relative to the val-val genotype, the met-met genotype had a greater reduction in adjusted systolic pressure (-3.9 mm Hg, p<0.01) and diastolic pressure (-2.8 mm Hg, p<0.01). Corresponding relative reductions for the val-met genotype were -2.2 mm Hg systolic (p=0.070) and -1.5 mm Hg diastolic (p<0.05).
Findings suggest that alcohol-induced blood pressure elevation may be related to the effects of catecholamines and their genetically determined inactivation.
Catechol-O-methyltransferase; genotype; SNP; blood pressure; alcoholism
Autonomic dysfunction is frequent in patients with fibromyalgia (FM). Heart rate variability analyses have demonstrated signs of ongoing sympathetic hyperactivity. Catecholamines are sympathetic neurotransmitters. Catechol-O-methyltransferase (COMT), an enzyme, is the major catecholamine-clearing pathway. There are several single-nucleotide polymorphisms (SNPs) in the COMT gene associated with the different catecholamine-clearing abilities of the COMT enzyme. These SNPs are in linkage disequilibrium and segregate as 'haplotypes'. Healthy females with a particular COMT gene haplotype (ACCG) producing a defective enzyme are more sensitive to painful stimuli. The objective of our study was to define whether women with FM, from two different countries (Mexico and Spain), have the COMT gene haplotypes that have been previously associated with greater sensitivity to pain. All the individuals in the study were female. Fifty-seven Mexican patients and 78 Spanish patients were compared with their respective healthy control groups. All participants filled out the Fibromyalgia Impact Questionnaire (FIQ). Six COMT SNPs (rs2097903, rs6269, rs4633, rs4818, rs4680, and rs165599) were genotyped from peripheral blood DNA. In Spanish patients, there was a significant association between three SNPs (rs6269, rs4818, and rs4680) and the presence of FM when compared with healthy controls. Moreover, in Spanish patients with the 'high pain sensitivity' haplotype (ACCG), the disease, as assessed by the FIQ, was more severe. By contrast, Mexican patients displayed only a weak association between rs6269 and rs165599, and some FIQ subscales. In our group of Spanish patients, there was an association between FM and the COMT haplotype previously associated with high pain sensitivity. This association was not observed in Mexican patients. Studies with a larger sample size are needed in order to verify or amend these preliminary results.
To establish the zebrafish as a model for investigating the methylation pathway of drug metabolism, we embarked on the molecular cloning of the zebrafish catechol O-methyltransferase (COMT). By searching the GenBank database, a zebrafish nucleotide sequence encoding a putative COMT was identified. Based on the sequence information, we designed and synthesized oligonucleotides corresponding to its 5’- and 3’-coding regions of this zebrafish COMT. Using the first-strand cDNA reverse-transcribed from the total RNA isolated from a 3-month-old adult female zebrafish as the template, the cDNA encoding the zebrafish COMT was PCR-amplified. The recombinant zebrafish COMT protein was subsequently expressed in and purified from BL21 (DE3) Escherichia coli cells transformed with the pGEX-2TK expression vector harboring the zebrafish COMT cDNA. Upon enzymatic characterization, purified COMT displayed methylating activity toward dopamine, dopa, and catecholestrogens, as well as three representative catechol drugs, methyldopa, dobutamine, and isoproterenol. A reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed developmental stage-dependent expression of the zebrafish COMT during embryonic development and throughout the larval stage onto maturity. These results provide a foundation for investigating the involvement of COMT-mediated methylation in protection against the adverse effects of catechol drugs and other xenobiotic catechols during the developmental process.
Catechol O-methyltransferase; developmental expression; methylation; molecular cloning; zebrafish
Polycystic ovary syndrome (PCOS) is an endocrine disorder that affects 5–8% of reproductive age women. The primary features of PCOS are hyperandrogenemia, chronic anovulation and infertility. It has been suggested that defects in ovarian steroid metabolism contribute to the follicular growth arrest and abnormal production of ovarian steroid hormones that are characteristic of PCOS. 2-methoxyestradiol (2-ME) is formed by the action of catechol-O-methyltransferase (COMT) on 2-hydroxyestradiol. COMT expression is increased in the follicles and ovarian stroma of women with PCOS. Moreover, 2-ME decreases granulosa cell proliferation and steroidogenesis, raising the possibility that ovarian dysfunction associated with PCOS is due, in part, to increased synthesis of 2-ME resulting from increased COMT activity. Four single-nucleotide polymorphisms (SNPs) (rs6269, rs4633, rs4818, rs4680) in the COMT gene characterize haplotypes, which are associated with large variations in COMT enzymatic activity. The aim of this study was to determine whether individual COMT SNPs and the COMT haplotypes are associated with PCOS using a family-based test of association and linkage. Additionally, we examined the relationships between COMT SNPs and haplotypes with quantitative variables usually assessed in the evaluation of women with PCOS. There were no significant correlations between genotype and total testosterone, non-SHBG bound testosterone and BMI. However, we found that the prolactin level in women with PCOS varied significantly with COMT haplotype, and suggest that this association reflects a genetic factor influencing the stress response. Our findings suggest that common variants and haplotypes of the COMT gene are not major contributors to risk for PCOS, but that COMT genotype may influence prolactin levels.
Catechol-O-Methyltransferase; COMT; polycystic ovary syndrome; prolactin5
Cannabis use confers a two-fold increase in risk for psychosis, with adolescent use conferring an even greater risk. A high-low activity polymorphism in catechol-O-methyltransferase (COMT), a gene encoding the COMT enzyme involved in dopamine clearance in the brain, may interact with adolescent cannabis exposure to increase risk for schizophrenia. The impact of such an interaction on central neurotransmitter pathways implicated in schizophrenia is unknown. Male mice with knockout of the COMT gene were treated chronically with delta-9-tetrahydrocannabinol (THC) during adolescence (postnatal day 32–52). We measured the size and density of GABAergic cells and the protein expression of cannabinoid receptor 1 (CB1R) in the prefrontal cortex (PFC) and hippocampus (HPC) in knockout mice relative to heterozygous mutants and wild-type controls. Size and density of dopaminergic neurons was also assessed in the ventral tegmental area (VTA) across the genotypes. COMT genotype × THC treatment interactions were observed for: (1) dopaminergic cell size in the VTA, (2) CB1R protein expression in the HPC, and (3) parvalbumin (PV) cell size in the PFC. No effects of adolescent THC treatment were observed for PV and dopaminergic cell density across the COMT genotypes. COMT genotype modulates the effects of chronic THC administration during adolescence on indices of neurotransmitter function in the brain. These findings illuminate how COMT deletion and adolescent cannabis use can interact to modulate the function of neurotransmitters systems implicated in schizophrenia.
delta-9-tetrahydrocannabinol; COMT; dopamine; GABA; gene × environment interaction; animal models; dopamine; animal models; cannabinoids; GABA; delta-9-tetrahydrocannabinol; COMT
The occurrence of catechol-O-methyltransferase (COMT) in presynaptic neurons remains controversial. This study utilized dopaminergic and noradrenergic toxins to assess the presence of COMT in the presynaptic neurons originating from the substantia nigra, ventral tegmental area or locus coeruleus. Destruction of dopaminergic and noradrenergic neurons was assessed by measuring the dopamine and noradrenaline content in the projection areas of these neurons. Additionally, COMT protein expression and activity were examined in several projection areas to determine whether there are any changes in COMT values. Colocalization studies were done to identify COMT-containing postsynaptic neurons. Despite successful lesioning of dopaminergic and noradrenergic neurons, no changes in COMT protein expression or activity could be noted. These results strongly suggest that COMT is not present in presynaptic dopaminergic and noradrenergic neurons. There was a high colocalization of COMT with the GABAergic marker of short neurons both in the striatum and cortex but only a weak, if any, with the cholinergic marker in the cortex.
Catechol-O-methyltransferase (COMT) degrades catecholamines, such as dopamine and epinephrine, by methylating them in the presence of a divalent metal cation (usually Mg(II)), and S-adenosyl-L-methionine. The enzymatic activity of COMT is known to be vitally dependent on the nature of the bound metal: replacement of Mg(II) with Ca(II) leads to a complete deactivation of COMT; Fe(II) is slightly less than potent Mg(II), and Fe(III) is again an inhibitor. Considering the fairly modest role that the metal plays in the catalyzed reaction, this dependence is puzzling, and to date remains an enigma. Using a quantum mechanical / molecular mechanical dynamics method for extensive sampling of protein structure, and first principle quantum mechanical calculations for the subsequent mechanistic study, we explicate the effect of metal substitution on the rate determining step in the catalytic cycle of COMT, the methyl transfer. In full accord with experimental data, Mg(II) bound to COMT is the most potent of the studied cations and it is closely followed by Fe(II), whereas Fe(III) is unable to promote catalysis. In the case of Ca(II), a repacking of the protein binding site is observed, leading to a significant increase in the activation barrier and higher energy of reaction. Importantly, the origin of the effect of metal substitution is different for different metals: for Fe(III) it is the electronic effect, whereas in the case of Ca(II) it is instead the effect of suboptimal protein structure.
The etiology of preeclampsia is complex, with susceptibility being attributable to multiple environmental factors and a large genetic component. Although many candidate genes for preeclampsia have been suggested and studied, the specific causative genes still remain to be identified. Catechol-O-methyltransferase (COMT) is an enzyme involved in catecholamine and estrogen degradation and has recently been ascribed a role in development of preeclampsia. In the present study, we have examined the COMT gene by genotyping the functional Val108/158Met polymorphism (rs4680) and an additional single-nucleotide polymorphism, rs6269, predicting COMT activity haplotypes in a large Norwegian case/control cohort (ncases= 1135, ncontrols= 2262). A low COMT activity haplotype is associated with recurrent preeclampsia in our cohort. This may support the role of redox-regulated signaling and oxidative stress in preeclampsia pathogenesis as suggested by recent studies in a genetic mouse model. The COMT gene might be a genetic risk factor shared between preeclampsia and cardiovascular diseases.
preeclampsia; catechol-O-methyltransferase; COMT; Val108/158Met; haplotypes
The extensive methylation of green tea polyphenols (GTPs) in vivo may limit their chemopreventive potential. We investigated whether quercetin, a natural inhibitor of catechol-O-methyltransferase (COMT) and multidrug resistance proteins (MRPs), will differentially increase the intracellular concentration and decrease the methylation of GTPs in different cancer cell lines. Intrinsic COMT activity was lowest in lung cancer A549 cells, intermediate in kidney 786-O cells and highest in liver HepG2 cells. Quercetin increased the cellular absorption of epigallocatechin gallate (EGCG) four-fold in A549 cells with a decreased methylation rate from 63% to 19%, 2-fold in 786-O cells with a decreased methylation from 97% to 56%, while no significant effect was observed in HepG2 cells. The combination significantly decreased the activity and protein expression of COMT and decreased the protein expression of MRP1 compared to individual treatments. The combination exhibited the strongest increase in antiproliferation in A549 cells, an intermediate effect in 786-O cells and lowest effect in HepG2 cells. The effect of quercetin on bioavailability and metabolism of GTPs was confirmed in vivo. SCID mice were administered brewed green tea (GT) and a diet supplemented with 0.4% quercetin alone or in combination for 2 weeks. We observed a 2 to 3-fold increase of total and non-methylated EGCG in lung and kidney and a trend to increase in liver. In summary, combining quercetin with GT provides a promising approach to enhance the chemoprevention of GT. Responses of different cancers to the combination may vary by tissue depending on the intrinsic COMT and MRP activity.
Green tea polyphenols; quercetin; methylation; catechol-O-methyltransferase
Genetic variation at the Catechol-O-metyltransferase (COMT) gene has been significantly associated with risk for various neuropsychiatric conditions such as schizophrenia, panic disorder, bipolar disorders, anorexia nervosa, and others. It has also been associated with nicotine dependence, sensitivity to pain, and cognitive dysfunctions especially in schizophrenia. The non-synonymous SNP in exon 4 - Val108/158Met - is the most studied SNP at COMT and the basis for most associations. It is not, however, the only variation in the gene; several haplotypes exist across the gene. Some studies indicate that the haplotypic combinations of alleles at the Val108/158Met SNP with those in the promoter region and in the 3' untranslated region are responsible for the associations with disorders and not the non-synonymous SNP by itself.
We have now studied DNA samples from 45 populations for 63 SNPs in a region of 172kb across the region of 22q11.2 encompassing the COMT gene. We focused on 28 SNPs spanning the COMT coding region and immediately flanking DNA, and found that the haplotypes are from diverse evolutionary lineages that could harbor as yet undetected variants with functional consequences. Future association studies should be based on SNPs that define the common haplotypes in the population(s) being studied.
SNP; haplotype; population; association; lineage; evolution
With synthetic gene services, molecular cloning is as easy as ordering a pizza. However choosing the right RNA code for efficient protein production is less straightforward, more akin to deciding on the pizza toppings. The possibility to choose synonymous codons in the gene sequence has ignited a discussion that dates back 50 years: Does synonymous codon use matter? Recent studies indicate that replacement of particular codons for synonymous codons can improve expression in homologous or heterologous hosts, however it is not always successful. Furthermore it is increasingly apparent that membrane protein biogenesis can be codon-sensitive. Single synonymous codon substitutions can influence mRNA stability, mRNA structure, translational initiation, translational elongation and even protein folding. Synonymous codon substitutions therefore need to be carefully evaluated when membrane proteins are engineered for higher production levels and further studies are needed to fully understand how to select the codons that are optimal for higher production.
There is much evidence that schizophrenia patients have an increased risk for aggression and violent behavior, including homicide. The neurobiological basis and correlates of this risk have not been much studied. While genome-wide association studies are lacking, a number of candidate genes have been investigated. By far, the most intensively studied is the catechol-O-methyltransferase (COMT) gene on chromosome 22. COMT is involved in the metabolism of dopamine, a key neurotransmitter in schizophrenia pathophysiology. Several studies suggest that the Val158Met polymorphism of this gene affects COMT activity. Methionine (Met)/Met homozygote schizophrenia patients show 4- to 5-fold lower COMT activity than valine (Val)/Val homozygotes, and some but not all studies have found an association with aggression and violence. Recently, a new functional single-nucleotide polymorphism in the COMT gene, Ala72Ser, was found to be associated with homicidal behavior in schizophrenia, but this finding warrants further replication. Studies published so far indicate that an association with the monoamine oxidase A, B, or tryptophan hydroxylase 1 genes is unlikely. Data for the brain-derived neurotrophic factor gene are conflicting and limited. Data from the limited number of neuroimaging studies performed to date are interesting. Frontal and temporal lobe abnormalities are found consistently in aggressive schizophrenia patients. Positron emission tomography and single photon-emission computed tomography (SPECT) data indicate deficits also in the orbitofrontal and temporal cortex. Some functional magnetic resonance imaging studies found a negative association of violent behavior with frontal and right-sided inferior parietal activity. Neuroimaging studies may well help further elucidate the interrelationship between neurocognitive functioning, personality traits, and antisocial and violent behavior.
aggression; genetics; violence; neurobiology; neuroimaging; schizophrenia
The intrarenal natriuretic hormone dopamine (DA) is metabolised by catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO). Inhibition of COMT, as opposed to MAO, results in a potent natriuretic response in the rat. The present study in anaesthetized homozygous and heterozygous COMT gene deleted mice attempted to further elucidate the importance of COMT in renal DA and sodium handling. After acute intravenous isotonic sodium loading, renal function was followed.
COMT activity in heterozygous mice was about half of that in wild type mice and was zero in the homozygous mice. MAO activity did not differ between the genotypes. Urinary sodium excretion increased 10-fold after sodium loading in wild type mice. In heterozygous and homozygous mice, the natriuretic effects of sodium loading were only 29 % and 39 %, respectively, of that in wild type mice. Arterial pressure and glomerular filtration rate did not differ between genotypes. Baseline norepinephrine and DA excretions in urine were elevated in the homozygous, but not in heterozygous, COMT gene deleted mice. Urinary DA excretion increased after isotonic sodium loading in the wild type mice but not in the COMT gene deleted mice.
Mice with reduced or absent COMT activity have altered metabolism of catecholamines and are unable to increase renal DA activity and produce normal natriuresis in response to acute sodium loading. The results support the hypothesis that COMT has an important role in the DA-mediated regulation of renal sodium excretion.
Catechol O-methyltransferase (COMT) metabolizes catechol moieties by methylating a single hydroxyl group at the meta- or para- hydroxyl position. Hydrophobic amino acids near the active site of COMT influence the regioselectivity of this reaction. Our sequence analysis highlights their importance by showing that these residues are highly conserved throughout evolution. Reaction barriers calculated in the gas phase reveal a lower barrier during methylation at the meta- position, suggesting that the observed meta-regioselectivity of COMT can be attributed to the substrate itself, and that COMT has evolved residues to orient the substrate in a manner that increases the rate of catalysis.