Human histamine N-methyltransferase pharmacogenetics: common genetic polymorphisms that alter activity

Amitriptyline affects histamine-N-methyltransferase and diamine oxidase activity in rats and guinea pigs

Histamine participates in numerous physiological and patophysiological processes. Drugs which interfere with the histamine actions are antagonists and agonists of histamine receptors. Histamine degrading enzymes as a possible target for modifying histamine action have so far not been extensively studied. Therefore we examined in vivo and in vitro effects of amitriptyline on two histamine degrading enzymes - diamine oxidase and histamine-N-methyltransferase. We were interested in the in vivo effects of amitriptyline on the diamine oxidase release into guinea pig plasma after heparin stimulation and in effects on the activity and gene expression of both histamine degrading enzymes in different guinea pig tissues. Amitriptyline's in vitro effects on the diamine oxidase and histamine-N-methyltransferase activities were measured in guinea pig and also in rat. Enzyme activities were determined with the radiometric micro-assay. The results showed that amitriptyline in vivo changed the profile of the heparin-induced diamine oxidase release, which could be due to changes in at least three processes: diamine oxidase release into plasma, protein synthesis and enzyme activity at the molecular level. Amitriptyline in some tissues (lung and spleen) amplified the mRNA expression of histamine degrading enzymes. Furthermore, the activities of these enzymes were increased in most examined tissues of amitriptyline treated guinea pigs. In vitro studies indicate that amitriptyline differently affects diamine oxidase and histamine-N-methyltransferase in two different rodent species, guinea pig and rat. Our study proved that amitriptyline enhances the histamine degrading processes in guinea pig, what might importantly contribute to lower histamine levels.

Histamine and histamine intolerance

Histamine intolerance results from a disequilibrium of accumulated histamine and the capacity for histamine degradation. Histamine is a biogenic amine that occurs to various degrees in many foods. In healthy persons, dietary histamine can be rapidly detoxified by amine oxidases, whereas persons with low amine oxidase activity are at risk of histamine toxicity. Diamine oxidase (DAO) is the main enzyme for the metabolism of ingested histamine. It has been proposed that DAO, when functioning as a secretory protein, may be responsible for scavenging extracellular histamine after mediator release. Conversely, histamine N-methyltransferase, the other important enzyme inactivating histamine, is a cytosolic protein that can convert histamine only in the intracellular space of cells. An impaired histamine degradation based on reduced DAO activity and the resulting histamine excess may cause numerous symptoms mimicking an allergic reaction. The ingestion of histamine-rich food or of alcohol or drugs that release histamine or block DAO may provoke diarrhea, headache, rhinoconjunctival symptoms, asthma, hypotension, arrhythmia, urticaria, pruritus, flushing, and other conditions in patients with histamine intolerance. Symptoms can be reduced by a histamine-free diet or be eliminated by antihistamines. However, because of the multifaceted nature of the symptoms, the existence of histamine intolerance has been underestimated, and further studies based on double-blind, placebo-controlled provocations are needed. In patients in whom the abovementioned symptoms are triggered by the corresponding substances and who have a negative diagnosis of allergy or internal disorders, histamine intolerance should be considered as an underlying pathomechanism.

Association of THR105Ile, a functional polymorphism of histamine N-methyltransferase (HNMT), with alcoholism in German Caucasians

BACKGROUND

CNS histamine has been shown to have an inhibitory effect on reward and it is implicated in the etiology of addiction and stress. Histamine N-methyltransferase (HNMT) is believed to be the sole pathway for termination of the neurotransmitter action of histamine in mammalian brain. A common, functional polymorphism, a C314T transition in the HNMT gene, results in a Thr105Ile substitution of the protein encoded. A recent study has shown that the frequency of the Ile105 allele was significantly lower in alcoholics compared to that in non-alcoholics in Finns and Plains American Indians. Following up these results, we tested whether the Thr105Ile polymorphism was associated with alcoholism in German Caucasians.

METHODS

Thr105Ile was genotyped in n=366 psychiatrically interviewed German Caucasian ICD-10 lifetime alcoholics, along with n=200 ethnically matched controls.

RESULTS

No significant difference was found in the frequency of the Ile105 allele between alcoholics (0.11) and controls (0.10) (chi(2)=0.21, d.f.=1, p=0.647). Likewise, genotype distributions did not differ significantly. However, the frequency of the Ile105 allele was significantly lower in male alcoholics with a family history of alcoholism compared to that in male alcoholics without a family history of alcoholism (chi(2)=4.07, d.f.=1, p=0.044).

CONCLUSIONS

In German Caucasians the association of the HNMT Thr105Ile polymorphism with alcoholism was not replicated per se, but a congruent association was found between the Ile105 allele and family history of alcoholism supporting the protective role of the Ile105 allele against alcoholism.

Histamine and Schizophrenia

With the availability of an increased number of experimental tools, for example potent and brain-penetrating H1-, H2-, and H3-receptor ligands and mutant mice lacking the histamine synthesis enzyme or the histamine receptors, the functional roles of histaminergic neurons in the brain have been considerably clarified during the recent years, particularly their major role in the control of arousal, cognition, and energy balance. Various approaches tend to establish the implication of histaminergic neurons in schizophrenia. A strong hyperactivity of histamine neurons is induced in rodent brain by administration of methamphetamine or NMDA-receptor antagonists. Histamine neuron activity is modulated by typical and atypical neuroleptics. H3-receptor antagonists/inverse agonists display antipsychotic-like properties in animal models of the disease. Because of the limited predictability value of most animal models and the paucity of drugs affecting histaminergic transmission that were tried so far in human, the evidence remains therefore largely indirect, but supports a role of histamine neurons in schizophrenia.

Altered methylprednisolone pharmacodynamics in healthy subjects with histamine N-methyltransferase C314T genetic polymorphism

This study investigated the potential differences in methylprednisolone pharmacodynamics between healthy subjects with different histamine N-methyltransferase (HNMT) C314T genotypes. Six individuals with C/C genotype and 4 with C/T genotype were administered a single intravenous dose of methylprednisolone 0.6 mg/kg ideal body weight in a randomized 2-period manner. Methylprednisolone plasma concentrations were fitted with a 1-compartment model. Cortisol and whole blood histamine suppression were assessed by indirect response models, with circadian baseline cortisol analyzed by Fourier analysis. The area between the baseline and effect curve and the area under the effect versus time curve suppression ratio were used to characterize plasma histamine suppression. Methylprednisolone pharmacokinetics and plasma and whole blood histamine suppression were similar between the 2 genotype groups. Median nadir of cortisol and the 50% inhibitory concentration for cortisol were significantly higher in subjects with C/T genotype than those with C/C genotype (P=.031 and .033, respectively, Wilcoxon rank sum test). Subjects who are heterozygous for the T314 variant allele thus appeared less sensitive to the suppressive effects of methylprednisolone on cortisol secretion.

Pharmacogenetics and Pharmacogenomics: Development, Science, and Translation

Pharmacogenetics and pharmacogenomics involve the study of the role of inheritance in individual variation in drug response, a phenotype that varies from potentially life-threatening adverse drug reactions to equally serious lack of therapeutic efficacy. This discipline evolved from the convergence of rapid advances in molecular pharmacology and genomics. Originally, pharmacogenetic studies focused on monogenic traits, often involving genetic variation in drug metabolism. However, contemporary studies increasingly involve entire "pathways" encoding proteins that influence both pharmacokinetics--factors that influence the concentration of a drug reaching its target(s)--and pharmacodynamics, the drug target itself, as well as genome-wide approaches. Pharmacogenomics is also increasingly moving across the "translational interface" into the clinic and is being incorporated into the drug development process and the governmental regulation of that process. However, significant challenges remain to be overcome if pharmacogenetics-pharmacogenomics is to achieve its full potential as a major medical application of genomic science.

Endogenous histamine and cortisol levels in subjects with different histamine N-methyltransferase C314T genotypes : a pilot study

BACKGROUND

Histamine N-methyltransferase (HNMT) catalyzes the methylation of histamine and plays an important role in histamine biotransformation in bronchial epithelium. Enzymatic activity of HNMT has been shown to be regulated by genetic factors, including polymorphisms in the HNMT gene. In this pilot study we determined endogenous levels of histamine and cortisol in plasma and whole blood samples from subjects with different genotypes for the HNMT C314T polymorphism, and investigated whether these parameters differed between individuals with the HNMT CC genotype and those with the CT genotype.

METHODS

Blood samples were collected from 48 unrelated volunteers (36 males, 12 females), aged 21-40 years, who participated in the study. PCR-restriction fragment length polymorphism analysis was used to determine HNMT C314T genotypes. Erythrocyte HNMT activity was determined as well as plasma and whole blood levels of histamine and cortisol. Two-group comparisons of the various parameters were analyzed by Blocked Wilcoxon test and Wilcoxon Rank Sum test as appropriate.

RESULTS

Thirty-seven subjects (24 Caucasians, three African Americans, one Middle Eastern, five Indians, three Chinese, and one Filipino) were found to have the homozygous CC genotype. Ten subjects (eight Caucasians, one Middle Eastern, and one Chinese) were heterozygous and one individual (Pakistani) was homozygous for the variant 314T allele. The frequency of HNMT CT heterozygotes in the small Caucasian cohort was 0.125. Median enzyme activity was significantly lower in subjects with the heterozygous CT genotype than in those with the homozygous CC genotype (485 vs 631 U/mL of red blood cells; p=0.023). A broad range of histamine levels in plasma and whole blood was observed for all subjects. Whereas the median plasma histamine level was found to be higher in heterozygotes for the wild-type 314C allele than homozygotes (3.32 vs 2.30 nmol/L; p=0.021), there was no difference between the two groups in histamine levels in whole blood. Cortisol levels were similar between individuals with the homozygous CC genotype and those with the heterozygous CT genotype.

CONCLUSION

Wide variability of plasma and whole-blood histamine levels was observed in subjects with different HNMT C314T genotypes. Endogenous levels of histamine are likely to be affected by various genes and polymorphisms.

A systematic analysis of disease-associated variants in the 3' regulatory regions of human protein-coding genes II: the importance of mRNA secondary structure in assessing the functionality of 3' UTR variants

In an attempt both to catalogue 3' regulatory region (3' RR)-mediated disease and to improve our understanding of the structure and function of the 3' RR, we have performed a systematic analysis of disease-associated variants in the 3' RRs of human protein-coding genes. We have previously analysed the variants that have occurred in two specific domains/motifs of the 3' untranslated region (3' UTR) as well as in the 3' flanking region. Here we have focused upon 83 known variants within the upstream sequence (USS; between the translational termination codon and the upstream core polyadenylation signal sequence) of the 3' UTR. To place these variants in their proper context, we first performed a comprehensive survey of known cis-regulatory elements within the USS and the mechanisms by which they effect post-transcriptional gene regulation. Although this survey supports the view that RNA regulatory elements function within the context of specific secondary structures, there are no general rules governing how secondary structure might exert its influence. We have therefore addressed this question by systematically evaluating both functional and non-functional (based upon in vitro reporter gene and/or electrophoretic mobility shift assay data) USS variant-containing sequences against known cis-regulatory motifs within the context of predicted RNA secondary structures. This has allowed us not only to establish a reliable and objective means to perform secondary structure prediction but also to identify consistent patterns of secondary structural change that could potentiate the discrimination of functional USS variants from their non-functional counterparts. The resulting rules were then used to infer potential functionality in the case of some of the remaining functionally uncharacterized USS variants, from their predicted secondary structures. This not only led us to identify further patterns of secondary structural change but also several potential novel cis-regulatory motifs within the 3' UTRs studied.

Pharmacogenomics: catechol O-methyltransferase to thiopurine S-methyltransferase

1. Pharmacogenomics is the study of the role of inheritance in variation in the drug response phenotype-a phenotype that can vary from adverse drug reactions at one end of the spectrum to lack of therapeutic efficacy at the other. 2. The thiopurine S-methyltransferase (TPMT) genetic polymorphism represents one of the best characterized and most clinically relevant examples of pharmacogenomics. This polymorphism has also served as a valuable "model system" for studies of the ways in which variation in DNA sequence might influence function. 3. The discovery and characterization of the TPMT polymorphism grew directly out of pharmacogenomic studies of catechol O-methyltransferase (COMT), an enzyme discovered by Julius (Julie) Axelrod and his coworkers. 4. This review will outline the process by which common, functionally significant genetic polymorphisms for both COMT and TPMT were discovered and will use these two methyltransferase enzymes to illustrate general principles of pharmacogenomic research-both basic mechanistic and clinical translational research-principles that have been applied to a series of genes encoding methyltransferase enzymes.

Evidence for a reduced histamine degradation capacity in a subgroup of patients with atopic eczema

BACKGROUND

A diminished histamine degradation based on a reduced diaminoxidase activity is suspected as a reason for non-IgE-mediated food intolerance caused by histamine. Atopic eczema (AE) is often complicated by relapses triggered by IgE-mediated allergy to different kinds of food. However, in a subgroup of patients with AE, allergy testing proves negative, although these patients report a coherence of food intake and worsening of AE and describe symptoms that are very similar to histamine intolerance (HIT).

OBJECTIVES

It was the aim of our study to evaluate symptoms of HIT in combination with diaminoxidase levels in a total of 360 individuals consisting of patients with AE (n = 162) in comparison with patients with HIT (n = 124) without AE and healthy control volunteers (n = 85).

METHODS

Histamine plasma level was determined with an ELISA and diaminoxidase serum activity with the help of radio extraction assays using [3H]-labeled putrescine-dihydrochloride as a substrate. Detailed clinical evaluations of characteristic features of AE and HIT were performed.

RESULTS

Reduced diaminoxidase serum levels leading to occurrence of HIT symptoms like chronic headache, dysmenorrhea, flushing, gastrointestinal symptoms, and intolerance of histamine-rich food and alcohol were significantly more common in patients with AE than in controls. Reduction of both symptoms of HIT and Severity Scoring of Atopic Dermatitis could be achieved by a histamine-free diet in the subgroup of patients with AE and low diaminoxidase serum levels.

CONCLUSION

Higher histamine plasma levels combined with a reduced histamine degradation capacity might influence the clinical course of a subgroup of patients with AE.

CLINICAL IMPLICATIONS

As HIT emerges in a subgroup of patients with AE, a detailed anamnestic evaluation of food intolerance and HIT symptoms complemented by an allergological screening for food allergy, a diet diary, and, in confirmed suspicion of HIT, measurement of diaminoxidase activity and a histamine-free diet should be undertaken.

Severity of ulcerative colitis is associated with a polymorphism at diamine oxidase gene but not at histamine N-methyltransferase gene

AIM: To analyse the role of two common polymorphisms in genes coding for histamine metabolising enzymes as it relates to the risk to develop ulcerative colitis (UC) and the clinical course of these patients.

METHODS: A cohort of 229 unrelated patients with UC recruited from a single centre and 261 healthy volunteers were analysed for the presence of Thr105Ile and His645Asp amino acid substitutions at histamine N-methyltransferase (HNMT) and diamine oxidase (ABP1) enzymes, respectively, by amplification-restriction procedures. All patients were phenotyped and followed up for at least 2 years (mean time 11 years).

RESULTS: There were no significant differences in the distribution of ABP1 alleles between ulcerative colitis patients and healthy individuals [OR (95% CI) for variant alleles = 1.22 (0.91-1.61)]. However, mutated ABP1 alleles were present with higher frequency among the 58 patients that required immunosuppresive drugs [OR (95 % CI) for carriers of mutated alleles 2.41 (1.21-4.83; P = 0.006)], with a significant gene-dose effect (P = 0.0038). In agreement with the predominant role of ABP1 versus HNMT on local histamine metabolism in human bowel, the frequencies for carriers of HNMT genotypes or mutated alleles were similar among patients, regardless clinical evolution, and control individuals.

CONCLUSION: The His645Asp polymorphism of the histamine metabolising enzyme ABP1 is related to severity of ulcerative colitis.

Human arsenic methyltransferase (AS3MT) pharmacogenetics: gene resequencing and functional genomics studies

Arsenic contaminates ground water worldwide. Methylation is an important reaction in the biotransformation of arsenic. We set out to study the pharmacogenetics of human arsenic methyltransferase (AS3MT, previously CYT19). After cloning the human AS3MT cDNA, we annotated the human gene and resequenced its 5'-flanking region, exons, and splice junctions using 60 DNA samples from African-American (AA) and 60 samples from Caucasian-American (CA) subjects. We observed 26 single nucleotide polymorphisms (SNPs), including 3 non-synonymous cSNPs, as well as a variable number of tandem repeats in exon 1 within an area encoding the cDNA 5'-untranslated region. The nonsynonymous cSNPs included T860C (M287T) with frequencies of 10.8 and 10% in AA and CA subjects, respectively, as well as C517T (A173W) in one AA and C917T (T306I) in one CA sample. Haplotype analysis showed that Ile(306) was linked to Thr(287), so this double variant allozyme was also studied functionally. After expression in COS-1 cells and correction for transfection efficiency, the Trp(173) allozyme displayed 31%, Thr(287) 350%, Ile(306) 4.8%, and Thr(287)/Ile(306) 6.2% of the activity of the wild type (WT) allozyme, with 20, 190, 4.4, and 7.9% of the level of WT immunoreactive protein, respectively. Apparent K(m) values for S-adenosyl-l-methionine were 4.6, 3.1, and 11 mum for WT, Trp(173), and Thr(287) allozymes, with K(m) values for sodium arsenite with the same allozymes of 11.8, 8.9, and 4.5mum. The Ile(306) and Thr(287)/Ile(306) allozymes expressed too little activity for inclusion in the substrate kinetic studies. Expression of reporter gene constructs for the 5'-flanking region and the variable number of tandem repeats in the 5'-untranslated region demonstrated cell line-dependent variation in reporter gene expression, with shorter repeats associated with increased transcription in HepG2 cells. These results raise the possibility that inherited variation in AS3MT may contribute to variation in arsenic metabolism and, perhaps, arsenic-dependent carcinogenesis in humans.

Thiopurine S-methyltransferase pharmacogenetics: variant allele functional and comparative genomics

Thiopurine S-methyltransferase (TPMT) catalyses the S-methylation of thiopurine drugs. Genetic polymorphisms for TPMT are a major factor responsible for large individual variations in thiopurine toxicity and therapeutic effect. The present study investigated the functional effects of human TPMT variant alleles that alter the encoded amino acid sequence of the enzyme, TPMT*2, *3A, *3B, *3C and *5 to *13. After expression in COS-1 cells and correction for transfection efficiency, allozymes encoded by these alleles displayed levels of activity that varied from virtually undetectable (*3A,*3B and *5) to 98% (*7) of that observed for the wild-type allele. Although some allozymes had significant elevations in apparent Km values for 6-mercaptopurine and S-adenosyl-L-methionine (i.e. the two cosubstrates for the reaction), the level of enzyme protein was the major factor responsible for variation in activity. Quantitative Western blot analysis demonstrated that the level of enzyme protein correlated closely with level of activity for all allozymes except TPMT*5. Furthermore, protein levels correlated with rates of TPMT degradation. TPMT amino acid sequences were then determined for 16 non-human mammalian species and those sequences (plus seven reported previously, including two nonmammalian vertebrate species) were used to determine amino acid sequence conservation. Most human TPMT variant allozymes had alterations of residues that were highly conserved during vertebrate evolution. Finally, a human TPMT homology structural model was created on the basis of a Pseudomonas structure (the only TPMT structure solved to this time), and the model was used to infer the functional consequences of variant allozyme amino acid sequence alterations. These studies indicate that a common mechanism responsible for alterations in the activity of variant TPMT allozymes involves alteration in the level of enzyme protein due, at least in part, to accelerated degradation.

Lack of association of histamine-N-methyltransferase (HNMT) polymorphisms with asthma in the Indian population

Histamine plays a major role in allergic disorders, including asthma. A major pathway of histamine biotransformation in the lungs is mediated by histamine N-methyltransferase (HNMT). We investigated the association of a functional SNP C314T; a SNP A929G, a (CA)n repeat in intron 5, and a novel (CA)n repeat (BV677277), 7.5 kb downstream of the HNMT gene with asthma and its associated traits such as total serum IgE levels in a case-control as well as in a family-based study design. In contrast to a previous study, no association was observed for the polymorphisms investigated with asthma (P>0.05). When haplotypes were constructed for these loci and compared, no significant difference was observed in the distribution between cases and controls. In the family-based design, no biased transmission was observed for any of the polymorphisms and haplotypes with asthma using the additive model of inheritance in family-based association test (FBAT). Thus, consistent with the case-control findings, the polymorphisms and haplotypes in the HNMT gene are not associated with asthma in the Indian population.

Polymorphisms of high-affinity IgE receptor and histamine-related genes in patients with ASA-induced urticaria/angioedema

The pathogenic mechanism of ASA-induced urticaria/angioedema (AIU) is still poorly understood, but it has been known that histamine releasing by cutaneous mast cell activation is considered to be an important role. Considering the importance of histamine in AIU, we speculated that a genetic abnormality of histamine-related genes such as a high-affinity IgE receptor, a metabolic enzyme of histamines and histamine receptors, may be involved in the development of AIU. Enrolled in the study were 110 patients with AIU, 53 patients without ASA hypersensitivity who had various drug allergies presenting as exanthematous skin symptoms, and 99 normal healthy controls (NC). Eleven single nucleotide polymorphisms (SNPs) of the beta chain of the high-affinity IgE receptor (FCER1B) and three histamine-related genes-histamine N-methyltransferase (HNMT), histamine H1 receptor (HRH1), histamine H2 receptor (HRH2)-were screened using the SNP-IT assay based on a single base extension method. No significant differences were observed in allele and genotype frequencies, and haplotype frequencies of all the SNPs of FCER1B, HNMT, HRH1, and HRH2 among the three groups (p>0.05, respectively). These results suggest that the polymorphisms of FCER1B and the three histamine-related genes may not contribute to the development of AIU phenotype in the Korean population.

Thr105Ile, a Functional Polymorphism of Histamine N-Methyltransferase, Is Associated with Alcoholism in Two Independent Populations

BACKGROUND

Histamine is expressed in cortical and limbic areas that are involved in emotion and cognition and modulates these behaviors. H1 receptor antagonists are sedative. Histamine N-methyltransferase (HNMT) catalyzes the Ntau methylation of histamine, the sole pathway for termination of the neurotransmitter action of histamine in mammalian brain. A common and functionally significant polymorphism, a C314T transition in exon 4 of the HNMT gene results in a Thr105Ile substitution of the protein encoded. The Thr105 allele is associated with approximately 2-fold higher enzyme activity, leading to the prediction that it might be associated with diminished histamine levels, resulting in differences in anxiety, cognition, and sedation that play important roles in alcoholism. In two ethnically distinct populations, we tested whether the Thr105Ile polymorphism was associated with alcoholism and with harm avoidance, a dimensional measure of anxious personality.

METHODS

A 5' exonuclease assay (TaqMan) was used to genotype Thr105Ile in psychiatrically interviewed Finnish Caucasian (n = 218) and Plains American Indian (n = 186) alcoholics, along with ethnically matched, psychiatrically interviewed, controls (Finns: n = 313, Plains Indian: n = 140).

RESULTS

Ile105 allele frequencies were significantly lower in alcoholics compared with nonalcoholics in both populations (Finns: 0.12 vs. 0.17, chi(2) = 6, p = 0.015; Plains Indians: 0.03 vs. 0.08, chi(2) = 5, p = 0.023). Genotype distributions also differed significantly. In Finns, Ile105 showed borderline significance for an association with lower harm avoidance (p = 0.070) after correcting for alcoholism diagnosis.

CONCLUSIONS

Decreased levels of brain histamine consequent to the Thr105 allele may result in higher levels of anxiety and, as a consequence, vulnerability to alcoholism.

No association of histamine- N-methyltransferase polymorphism with asthma or bronchial hyperresponsiveness in two German pediatric populations

Histamine plays an important role in the allergic inflammation. Histamin N-Methyltransferase (HNMT) catalyses the major pathway of histamine metabolism in the human lung. A common functional single nucleotide polymorphism (SNP) within the HNMT gene (C314T) was recently related to asthma. We tested this SNP for associations with asthma and asthma associated traits in two German pediatric populations (1. MAS-cohort, n=888, 85 children with asthma; 2. asthmatic children from Freiburg, n=176). Non-asthmatic (n=515) and non-atopic (n=211) children from the MAS-cohort were used as controls. For genotyping melting curve analyses (Light Cycler System) were applied. In contrast to a previous study, no association of the HNMT 314T allele with asthma, bronchial hyperresponsiveness (BHR) or other asthma related phenotypes could be observed in either study population. We conclude that this SNP might not play a major role in the pathogenesis of asthma or BHR in German children.

Alcoholism: genes and mechanisms

Alcoholism is a chronic relapsing/remitting disease that is frequently unrecognized and untreated, in part because of the partial efficacy of treatment. Only approximately one-third of patients remain abstinent and one-third have fully relapsed 1 year after withdrawal from alcohol, with treated patients doing substantially better than untreated [1]. The partial effectiveness of strategies for prevention and treatment, and variation in clinical course and side effects, represent a challenge and an opportunity to better understand the neurobiology of addiction. The strong heritability of alcoholism suggests the existence of inherited functional variants of genes that alter the metabolism of alcohol and variants of other genes that alter the neurobiologies of reward, executive cognitive function, anxiety/dysphoria, and neuronal plasticity. Each of these neurobiologies has been identified as a critical domain in the addictions. Functional alleles that alter alcoholism-related intermediate phenotypes include common alcohol dehydrogenase 1B and aldehyde dehydrogenase 2 variants that cause the aversive flushing reaction; catechol-O-methyltransferase (COMT) Val158Met leading to differences in three aspects of neurobiology: executive cognitive function, stress/anxiety response, and opioid function; opioid receptor μ1 (OPRM1) Asn40Asp, which may serve as a gatekeeper molecule in the action of naltrexone, a drug used in alcoholism treatment; and HTTLPR, which alters serotonin transporter function and appears to affect stress response and anxiety/dysphoria, which are factors relevant to initial vulnerability, the process of addiction, and relapse.

Human SULT1A3 pharmacogenetics: gene duplication and functional genomic studies

Sulfotransferase (SULT) 1A3 catalyzes the sulfate conjugation of catecholamines. Inheritance is an important factor responsible for individual variation in SULT1A3 activity, and gene resequencing studies have shown the presence of one functionally significant SULT1A3 nonsynonymous cSNP. However, following completion of the Human Genome Project, it appeared that SULT1A3 might be duplicated. We used specific PCR-based assays and fluorescence in situ hybridization to verify that 2 SULT1A3 genes-SULT1A3 and SULT1A4-were present on chromosome 16 in all human DNA samples studied. Furthermore, reanalysis of previous gene resequencing data confirmed the presence of the SULT1A3 SNPs identified previously, but also revealed 11 novel polymorphisms, including 3 nonsynonymous cSNPs. Functional genomic studies showed that two of those cSNPs, C302T, and C302A, resulted in decreased enzyme activity without striking changes in substrate kinetics but with parallel changes in levels of immunoreactive protein. In addition, RT-PCR revealed that both SULT1A3 and SULT1A4 can be transcriptionally active. The duplication of SULT1A3 will have to be taken into account in future efforts to understand individual variation in SULT1A3 activity or properties.

Human catechol O-methyltransferase genetic variation: gene resequencing and functional characterization of variant allozymes

Catechol O-methyltransferase (COMT) plays an important role in the metabolism of catecholamines, catecholestrogens and catechol drugs. A common COMT G472A genetic polymorphism (Val108/158Met) that was identified previously is associated with decreased levels of enzyme activity and has been implicated as a possible risk factor for neuropsychiatric disease. We set out to 'resequence' the human COMT gene using DNA samples from 60 African-American and 60 Caucasian-American subjects. A total of 23 single nucleotide polymorphisms (SNPs), including a novel nonsynonymous cSNP present only in DNA from African-American subjects, and one insertion/deletion were observed. The wild type (WT) and two variant allozymes, Thr52 and Met108, were transiently expressed in COS-1 and HEK293 cells. There was no significant change in level of COMT activity for the Thr52 variant allozyme, but there was a 40% decrease in the level of activity in cells transfected with the Met108 construct. Apparent K(m) values of the WT and variant allozymes for the two reaction cosubstrates differed slightly, but significantly, for 3,4-dihydroxybenzoic acid but not for S-adenosyl-L-methionine. The Met108 allozyme displayed a 70-90% decrease in immunoreactive protein when compared with WT, but there was no significant change in the level of immunoreactive protein for Thr52. A significant decrease in the level of immunoreactive protein was also observed in hepatic biopsy samples from patients homozygous for the allele encoding Met108. These observations represent steps toward an understanding of molecular genetic mechanisms responsible for variation in COMT level and/or properties, variation that may contribute to the pathophysiology of neuropsychiatric disease.

Human catecholamine sulfotransferase (SULT1A3) pharmacogenetics: functional genetic polymorphism

Sulfotransferase (SULT) 1A3 catalyzes the sulfate conjugation of catecholamines and structurally related drugs. As a step toward studies of the possible contribution of inherited variation in SULT1A3 to the pathophysiology of human disease and/or variation in response to drugs related to catecholamines, we have resequenced all seven coding exons, three upstream non-coding exons, exon-intron splice junctions and the 5'-flanking region of SULT1A3 using DNA samples from 60 African-American (AA) and 60 Caucasian-American (CA) subjects. Eight single nucleotide polymorphisms (SNPs) were observed in AA and five in CA subjects, including one non-synonymous cSNP (Lys234Asn) that was observed only in AA subjects with an allele frequency of 4.2%. This change in amino acid sequence resulted in only 28 +/- 4.5% (mean +/- SEM) of the enzyme activity of the wild-type (WT) sequence after transient expression in COS-1 cells, with a parallel decrease (54 +/- 2.2% of WT) in level of SULT1A3 immunoreactive protein. Substrate kinetic studies failed to show significant differences in apparent Km values of the two allozymes for either dopamine (10.5 versus 10.2 micro m for WT and variant, respectively) or the cosubstrate 3'-phosphoadenosine 5'-phosphosulfate (0.114 versus 0.122 micro m, respectively). The decrease in level of immunoreactive protein in response to this single change in amino acid sequence was due, at least in part, to accelerated SULT1A3 degradation through a proteasome-mediated process. These observations raise the possibility of ethnic-specific inherited alterations in catecholamine sulfation in humans.

Cat Red Blood Cell ThiopurineS-Methyltransferase: Companion Animal Pharmacogenetics

A common genetic polymorphism for thiopurine S-methyltransferase (TPMT) is a major factor responsible for individual variation in the toxicity and therapeutic efficacy of thiopurine drugs in humans. We set out to determine whether inheritance might also influence the level of TPMT activity in the domestic cat, Felis domesticus. As a first step, red blood cell (RBC) TPMT activity was measured in blood samples from 104 cats. The average level of cat RBC TPMT activity was lower than that observed in humans and was not related to either age or sex of the animal. We then cloned and characterized the F. domesticus TPMT cDNA and gene. Genotype-phenotype correlation analysis was performed by resequencing the cat TPMT gene using DNA samples from 12 animals with high and 12 with low levels of RBC TPMT activity. Thirty-one single nucleotide polymorphisms (SNPs) were observed in these 24 DNA samples, including five that altered the encoded amino acid, resulting in nine allozymes (six observed and three inferred). Twelve of the 31 feline TPMT SNPs were associated, collectively, with 56% of the variation in level of RBC TPMT activity in these 24 animals. When those 12 SNPs were assayed in all 89 cats for which DNA was available, 30% of the variation in level of RBC TPMT activity was associated with these 12 polymorphisms. After expression in COS-1 cells, five of the eight variant cat allozymes displayed decreased levels of both TPMT activity and immunoreactive protein compared with the wild-type allozyme. These observations are compatible with the conclusion that inheritance is an important factor responsible for variation in levels of RBC TPMT activity in the cat. They also represent a step toward the application of pharmacogenetic principles to companion animal thiopurine drug therapy.

Human estrogen sulfotransferase (SULT1E1) pharmacogenomics: gene resequencing and functional genomics

1. Estrogens are used as drugs and estrogen exposure is a risk factor for hormone-dependent diseases such as breast cancer. Sulfate conjugation is an important pathway for estrogen metabolism. The sulfotransferase (SULT) enzyme SULT1E1 has the lowest K(m) values for estrogens and catecholestrogens of the 10 known human SULT isoforms. 2. We previously cloned and characterized the human SULT1E1 cDNA and gene as steps toward pharmacogenetic studies. In the present experiments, we set out to determine whether common, functionally significant genetic polymorphisms might exist for SULT1E1. As a first step, we 'resequenced' the eight SULT1E1 exons and exon-intron splice junctions as well as portions of the 5'-flanking region using DNA from 60 African-American and 60 Caucasian-American subjects. 3. In all, 23 polymorphisms, 22 single nucleotide polymorphisms (SNPs) and one insertion deletion were observed. There were three nonsynonymous coding SNPs (cSNPs) that altered the following encoded amino acids: Asp22Tyr, Ala32Val and Pro253His. Among these, 12 pairs of SNPs were tightly linked. In addition, 12 unambiguous SULT1E1 haplotypes were identified, including six that were common to both populations studied. 4. Transient expression in COS-1 cells of constructs containing the three nonsynonymous cSNPs showed significant decreases in SULT1E1 activity for the Tyr22 and Val32 allozymes, with corresponding decreases in levels of immunoreactive protein. There were no changes in levels of either activity or immunoreactive protein for the His253 allozyme. Apparent K(m) values of the Val32 allozyme for the two cosubstrates for the reaction, 17beta-estradiol and 3'-phosphoadenosine 5'-phosphosulfate, were not significantly different from those of the wild-type enzyme, but there was a two- to three-fold increase in K(m) values for the His253 allozyme and a greater than five-fold increase for the Tyr22 allozyme. 5. These observations raise the possibility that genetically determined variation in SULT1E1-catalyzed estrogen sulfation might contribute to the pathophysiology of estrogen-dependent diseases as well as variation in the biotransformation of exogenously administered estrogens.

Effects of amphotericin B and caspofungin on histamine expression

STUDY OBJECTIVE

To determine the effects of amphotericin B deoxycholate and caspofungin on the release of histamine from human peripheral blood cells, mononuclear cells, and mast cells.

DESIGN

In vitro cell culture experiments.

SETTING

University medical center.

MATERIAL

Cultured human mononuclear (THP-1) and mast (HMC-1) cells from five healthy volunteers.

MEASUREMENTS AND MAIN RESULTS

The cultured cells were incubated with increasing concentrations of amphotericin B deoxycholate, diphenhydramine, amphotericin B deoxycholate plus diphenhydramine, caspofungin, caspofungin plus diphenhydramine, and the calcium ionophore A23187 for up to 24 hours. Histamine concentrations and histamine N-methyltransferase activity were determined at various time points throughout exposure. Cell viability was assessed by exclusion of erythrocin B. The A23187 increased histamine concentrations from baseline in peripheral blood and HMC-1 cells. No change in histamine concentrations was observed in response to amphotericin B deoxycholate, whereas caspofungin induced a significant increase in histamine release in peripheral blood cells and HMC-1 cells. No change in histamine concentrations was observed in THP-1 cells in response to any pharmacologic agent tested. Similarly, histamine N-methyltransferase activity in peripheral blood was not affected by amphotericin B deoxycholate, but was significantly decreased by caspofungin.

CONCLUSION

Amphotericin B deoxycholate does not affect histamine concentrations or histamine N-methyltransferase activity in whole blood or HMC-1 cells, suggesting that the amphotericin B-induced infusion-related reaction is not a histamine-mediated event. Conversely, caspofungin increased histamine concentrations in whole blood and HMC-1 cells and inhibited histamine N-methyltransferase activity. These data suggest that infusion-related reactions associated with caspofungin may be mediated by histamine release secondary to caspofungin.

Histamine N-methyltransferase gene polymorphisms in Chinese and their relationship with enzyme activity in erythrocytes

The aim of this study was to identify polymorphisms in the histamine N-methyltransferase (HNMT) gene in Chinese and to assess their relationship with HNMT activity. One hundred and ninety-two unrelated subjects were recruited. HNMT polymorphisms were screened by direct sequencing with purified polymerase chain reaction products comprising all six exons, plus splice junctions, as well as approximately 2 kb of the 5'-flanking region (5'-FR). Erythrocyte HNMT activity was previously measured by radiochemical microassay. A total of 11 single nucleotide polymorphisms (SNPs) were identified, among which six SNPs had variant allele frequencies greater than 5%. Of the six common SNPs, three (-1637T>C, -463T>C and -411C>T) were located in 5'-FR, one (314C>T) in coding exons, and two (939A>G and 1097A>T) in the 3'-untranslated region (3'-UTR). Most of these common SNPs were in linkage disequilibrium. Genotype-phenotype correlation analyses were performed for those common SNPs in 5'-FR and 3'-UTR. In males, no significant association was found between HNMT activity and these non-coding SNPs. However, in females, the -1637T>C or -463T>C tended to be associated with decreased HNMT activity, whereas the 939A>G or 1097A>T appeared to be correlated with increased enzymatic activity. HNMT polymorphisms differ considerably between Chinese and American. The common SNPs in 5'-FR (-1637T>C and -463T>C) and 3'-UTR (939A>G and 1097A>T) might conditionally regulate the activity of HNMT, or might be genetically linked to unknown mutation(s) underlying the HNMT phenotypic variance.

Analysis of the C314T and A595G mutations in histamine N-methyltransferase gene in a Chinese population

BACKGROUND

Histamine N-methyltransferase (HNMT) plays an important role in the metabolism of histamine, a biogenic amine that has many physiologic and pathological roles in human tissues. A missense mutation C314T (Thr105Ile) in the HNMT gene has been identified to represent a common functional polymorphism in Caucasians, whereas an A595G (Ile199Val) variant has been reported in one HNMT cDNA from a Japanese subject.

METHODS

By using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay, the point mutations C314T and A595G within HNMT were both detected in 352 unrelated Chinese Han subjects.

RESULTS

None of the 352 subjects contained the A595G mutation, whereas 40 (11.6%) heterozygotes and 1 (0.3%) homozygote for the variant T314 allele were detected. The frequency of the variant T314 allele in this Chinese population was 0.060 (95% CI: 0.042-0.078), not different from Japanese but significantly lower than American Caucasians.

CONCLUSIONS

The C314T mutation represents a common functional genetic polymorphism in the Chinese Han population with a variant T314 allele frequency similar to Japanese but lower than American Caucasians, whereas the A595G mutation does not appear to exist in this population.

Canine red blood cell thiopurine S-methyltransferase: companion animal pharmacogenetics

Thiopurine S-methyltransferase (TPMT) plays an important role in the metabolism of thiopurine drugs. In humans, a common genetic polymorphism for TPMT is a major factor responsible for individual variation in the toxicity and therapeutic efficacy of these drugs. Dogs (Canis familiaris) are also treated with thiopurine drugs and, similar to humans, they display large individual variations in thiopurine toxicity and efficacy. We set out to determine whether dogs might also display genetically determined variation in TPMT activity. As a first step, we observed that canine red blood cell (RBC) TPMT activity in samples from 145 dogs varied over a nine-fold range. That variation was not associated with either the age or sex of the animal. Subsequently, we cloned the canine TPMT cDNA and gene. The canine cDNA encoded a protein that was 81.2% identical to the enzyme encoded by the most common TPMT allele in humans. A genotype-phenotype correlation analysis was performed by resequencing the canine gene using DNA samples from 39 animals selected for high, low or intermediate levels of RBC TPMT activity. We observed nine polymorphisms in these 39 DNA samples, including three insertion/deletion events and six single nucleotide polymorphisms (SNPs), one of which was a nonsynonymous cSNP (Arg97Gln). However, when the variant allozyme at codon 97 was expressed in COS-1 cells, it did not display significant differences in either basal levels of TPMT activity or in substrate kinetics compared with the wild-type allozyme. Six of the nine canine TPMT polymorphisms were associated with 67% of the variation in level of RBC TPMT activity in these 39 blood samples. When those six SNPs were assayed using DNA from all 145 animals studied, 40% of the phenotypic variance in the entire population sample could be explained by these polymorphisms. Therefore, inheritance is a major factor involved in the regulation of variation in RBC TPMT in the dog, just as it is in humans. These observations represent a step towards the application of pharmacogenetic and pharmacogenomic principles to companion animal drug therapy.

Human sulfotransferase SULT2A1 pharmacogenetics: genotype-to-phenotype studies

SULT2A1 catalyzes the sulfate conjugation of dehydroepiandrosterone (DHEA) as well as other steroids. As a step toward pharmacogenetic studies, we have 'resequenced' SULT2A1 using 60 DNA samples from African-American and 60 samples from Caucasian-American subjects. All exons, splice junctions and approximately 370 bp located 5' of the site of transcription initiation were sequenced. We observed 15 single nucleotide polymorphisms (SNPs), including three non-synonymous coding SNPs (cSNPs) that were present only in DNA from African-American subjects. Linkage analysis revealed that two of the nonsynonymous cSNPs were tightly linked. Expression constructs were created for all nonsynonymous cSNPs observed, including a 'double variant' construct that included the two linked cSNPs, and those constructs were expressed in COS-1 cells. SULT2A1 activity was significantly decreased for three of the four variant allozymes. Western blot analysis demonstrated that decreased levels of immunoreactive protein appeared to be the major mechanism responsible for decreases in activity, although apparent Km values also varied among the recombinant allozymes. In addition, the most common of the nonsynonymous cSNPs disrupted the portion of SULT2A1 involved with dimerization, and this variant allozyme behaved as a monomer rather than a dimer during gel filtration chromatography. These observations indicate that common genetic polymorphisms for SULT2A1 can result in reductions in levels of both activity and enzyme protein. They also raise the possibility of ethnic-specific pharmacogenetic variation in SULT2A1-catalyzed sulfation of both endogenous and exogenous substrates for this phase II drug-metabolizing enzyme.

Membrane-bound histamine N-methyltransferase in mouse brain: possible role in the synaptic inactivation of neuronal histamine

In the CNS, histamine is a neurotransmitter that is inactivated by histamine N-methyltransferase (HNMT), a soluble enzyme localized to the cytosol of neurons and endothelial cells. However, it has not been established how extracellular histamine, a charged molecule at physiological pH, reaches intracellular HNMT. Present studies investigated two potential routes of histamine inactivation in mouse brain nerve terminal fractions (synaptosomes): (i) histamine uptake and (ii) histamine metabolism by HNMT. Intact synaptosomes demonstrated a weak temperature-dependent histamine uptake (0.098 pmol/min-mg protein), but contained a much greater capacity to metabolize histamine by HNMT (1.4 pmol/min-mg protein). Determination of the distribution of HNMT within synaptosomes revealed that synaptosomal membranes (devoid of soluble HNMT) contribute HNMT activity equivalent to intact synaptosomes (14.3 +/- 2.2 and 18.2 +/- 4.3 pmol/min-tube, respectively) and suggested that histamine-methylating activity is associated with the membrane fraction. Additional experimental findings that support this hypothesis include: (i) the histamine metabolite tele-methylhistamine (tMH) was found exclusively in the supernatant fraction following an HNMT assay with intact synaptosomes; (ii) the membrane-bound HNMT activity was shown to increase 6.5-fold upon the solubilization of the membranes with 0.1% Triton X-100; and (iii) HNMT activity from the S2 fraction, ruptured synaptosomes, and synaptosomal membranes displayed different stability profiles when stored over 23 days at - 20 degrees C. Taken together, these studies demonstrate functional evidence for the existence of membrane-bound HNMT. Although molecular studies have not yet identified the nature of this activity, the present work suggests that levels of biologically active histamine may be controlled by an extracellular process.

Human histamine N-methyltransferase pharmacogenetics: gene resequencing, promoter characterization, and functional studies of a common 5'-flanking region single nucleotide polymorphism (SNP)

Histamine N-methyltransferase (HNMT) catalyzes one of two major metabolic pathways for histamine. The levels of HNMT activity and immunoreactive protein in human tissues are regulated primarily by inheritance. Previous studies of HNMT identified two common single nucleotide polymorphisms (SNPs), including a functionally significant nonsynonymous coding SNP (cSNP), (C314T, Thr105Ile), but that polymorphism did not explain all of the phenotypic variation. In the present study, a genotype-to-phenotype strategy was used to search for additional genetic factors that might contribute to the regulation of human HNMT activity. Specifically, we began by resequencing the human HNMT gene using 90 ethnically anonymous DNA samples from the Coriell Cell Repository and identified a total of eight SNPs, including the two that had been reported previously. No new nonsynonymous cSNPs were observed, but three of the six novel SNPs were located in the 5'-flanking region (5'-FR) of the gene-including a third common polymorphism with a frequency of 0.367 (36.7%). That observation directed our attention to possible genetic effects on HNMT transcription. As a first step in testing that possibility, we created and studied a series of reporter gene constructs for the initial 1kb of the HNMT 5'-FR. The core promoter and possible regulatory regions were identified and verified by electrophoresis mobility shift assays. We then studied the possible functional implications of the new common HNMT 5'-FR SNP. However, on the basis of reporter gene studies, that SNP appeared to have little effect on transcription. Phenotype-genotype correlation analysis performed with 112 human kidney biopsy samples that had been phenotyped for their level of HNMT activity confirmed that the common 5'-FR SNP was not associated with the level of HNMT activity in vivo. In summary, this series of experiments resulted in the identification of several novel HNMT polymorphisms, identification of the HNMT core promoter, and a comprehensive functional genomic study of a common HNMT 5'-FR SNP. These results represent an additional step in the definition of molecular genetic mechanisms involved in the regulation of this important autacoid-metabolizing enzyme in humans.

Histamine genomics in silico: polymorphisms of the human genes involved in the synthesis, action and degradation of histamine

BACKGROUND

Histamine is a ubiquitous biogenic amine involved in the regulation of numerous basic physiological and pathophysiological processes. The DNA sequences of the genes encoding proteins (enzymes and receptors) that participate in the synthesis, degradation and cellular binding of histamine are already identified.

OBJECTIVE

We analyzed the in silico available human sequences to find genetic polymorphisms in histamine-related genes (L-histidine decarboxylase, histamine receptors, histamine N-methyl transferase and diamine-oxidase), and compared these data with findings concerning structure-function relationships in order to get information about the possible pathophysiological relevance of these polymorphisms.

METHODS

Sequence analysis was performed at the National Center for Biotechnology Information Database. The search tool BLAST was applied.

RESULTS

Several sequence variations were found, and it is conceivable that some of these genetic polymorphisms may be related to various pathological conditions. Among sequence variations, variants with no amino acid change, variants resulting in amino acid alterations, and many nucleotide changes involving non-coding sequences were revealed.

CONCLUSIONS

Histamine genomics may provide a new tool for medical prediction and drug design in the future.

Pharmacogenomics: the inherited basis for interindividual differences in drug response

It is well recognized that most medications exhibit wide interpatient variability in their efficacy and toxicity. For many medications, these interindividual differences are due in part to polymorphisms in genes encoding drug metabolizing enzymes, drug transporters, and/or drug targets (e.g., receptors, enzymes). Pharmacogenomics is a burgeoning field aimed at elucidating the genetic basis for differences in drug efficacy and toxicity, and it uses genome-wide approaches to identify the network of genes that govern an individual's response to drug therapy. For some genetic polymorphisms (e.g., thiopurine S-methyltransferase), monogenic traits have a marked effect on pharmacokinetics (e.g., drug metabolism), such that individuals who inherit an enzyme deficiency must be treated with markedly different doses of the affected medications (e.g., 5%-10% of the standard thiopurine dose). Likewise, polymorphisms in drug targets (e.g., beta adrenergic receptor) can alter the sensitivity of patients to treatment (e.g., beta-agonists), changing the pharmacodynamics of drug response. Recognizing that most drug effects are determined by the interplay of several gene products that govern the pharmacokinetics and pharmacodynamics of medications, pharmacogenomics research aims to elucidate these polygenic determinants of drug effects. The ultimate goal is to provide new strategies for optimizing drug therapy based on each patient's genetic determinants of drug efficacy and toxicity. This chapter provides an overview of the current pharmacogenomics literature and offers insights for the potential impact of this field on the safe and effective use of medications.

Human 3'-phosphoadenosine 5'-phosphosulfate synthetase 2 (PAPSS2) pharmacogenetics: gene resequencing, genetic polymorphisms and functional characterization of variant allozymes

3'-Phosphoadenosine 5'-phosphosulfate (PAPS) is the sulfate donor cosubstrate for all sulfotransferase (SULT) enzymes. SULTs catalyze the sulfate conjugation of many endogenous and exogenous compounds, including drugs and other xenobiotics. In humans, PAPS is synthesized from adenosine 5'-triphosphate (ATP) and inorganic sulfate (SO2-4) by two isoforms, PAPSS1 and PAPSS2. Rare mutations that inactivate PAPSS2 are associated with human spondyloepimetaphyseal dysplasia and murine brachymorphism. To determine whether more common genetic polymorphisms that do not completely inactivate the enzyme might be one factor responsible for individual differences in sulfate conjugation, we previously cloned the human PAPSS2 gene. In the present studies, we 'resequenced' all twelve PAPSS2 exons and splice junctions, as well as approximately 500 bp of the 5'-flanking region, using 90 Polymorphism Discovery Resource (PDR) DNA samples from the Coriell Cell Repository. Twenty-two single nucleotide polymorphisms (SNPs) were observed, including four nonsynonymous coding region SNPs (cSNPs) that altered the following amino acids: Glu10Lys, Met281Leu,Val291Met and Arg432Lys. We also observed four insertions/deletions, including one sample that was homozygous for an 81-bp deletion in the 5'-flanking region 286 bp upstream from the site of transcription initiation. Transient expression studies showed that two of the nonsynonymous cSNPS, those that resulted in Glu10Lys and Val291Met alterations in encoded amino acids, showed significant decreases in levels of PAPSS activity. In the case of Glu10Lys, decreased activity was paralleled by a decrease in immunoreactive protein, while the Val291Met allozyme displayed a significant decrease in affinity for both ATP and Na2SO4 when compared to 'wild-type' enzyme, but without a significant alteration in level of immunoreactive protein. It will now be possible to test the hypothesis that these common, functionally significant PAPSS2 genetic polymorphisms might contribute to variations in sulfate conjugation in vivo.

Human sulfotransferase SULT1C1 pharmacogenetics: gene resequencing and functional genomic studies

Sulfotransferase (SULT) enzymes catalyze an important phase II reaction in the biotransformation of many drugs and other xenobiotics. We previously cloned the human SULT1C1 cDNA and gene as steps toward pharmacogenetic studies. We have now 'resequenced' the exons, portions of introns flanking exons and approximately 315 bp of the 5' flanking region of SULT1C1 in 89 DNA samples from Caucasian subjects to identify common genetic polymorphisms. Nineteen separate polymorphisms were observed, including four nonsynonymous coding region single nucleotide polymorphisms (cSNPs) and five insertions/deletions. These data were also used to determine and/or infer common SULT1C1 haplotypes. Three of the four nonsynonymous cSNPs had allele frequencies greater than 1%, including one with a frequency of 6.7%. Expression constructs were created for all of the nonsynonymous cSNPs observed, and those constructs were used to transfect COS-1 cells. Three of the four SULT1C1 variant allozymes had significantly reduced enzyme activity when compared with the wild-type enzyme. Among the variant allozymes, apparent Km values for 3'-phosphoadenosine 5'-phosphosulfate (PAPS), the sulfate donor for the reaction, varied 7-fold, and quantitative Western blot analysis showed variable levels of immunoreactive protein when compared to the wild-type enzyme. Therefore, mechanisms responsible for decreased activity involved both alterations in levels of enzyme protein and alterations in substrate kinetics. In summary, application of a 'genotype to phenotype' strategy has resulted in the identification of a series of functionally significant common genetic polymorphisms for SULT1C1. It will now be possible to evaluate the possible contribution of these polymorphisms to variation in the sulfate conjugation of drugs, other xenobiotics and/or disease pathophysiology.

Recent developments in the genetics of asthma

Asthma is a complex genetic disease with multiple genes involved in the pathogenesis. Some of these genes have been investigated to determine whether they influence an individual's response to asthma medication. We summarise the recent developments in the genetics of asthma as they pertain to the three main treatments available - inhaled glucocorticoids (GCs), (2)-agonists and leukotriene modulators. It has been shown that polymorphisms in the (2)-adrenergic receptor ((2)AR) gene influence responsiveness to (2)-agonists. Polymorphisms in the 5-lipoxygenase (5-LO) gene and the leukotriene C(4) (LTC4) synthase gene have been associated with response to medications that target the LT pathway. However, no polymorphisms have been identified that influence response to anticholinergics or are involved in steroid resistance. In the future, knowledge of an individual's genotype may help us tailor treatment to make it the most appropriate form for that asthmatic individual.

Theoretical 3D model of histamine N-methyltransferase: insights into the effects of a genetic polymorphism on enzymatic activity and thermal stability

Histamine N-methyltransferase (HNMT) catalyzes the N-methylation of histamine in mammals. The experimentally determined HNMT three-dimensional (3D) structure is not available. However, there is a common genetic polymorphism for human HNMT (Thr105Ile) that reduces enzymatic activity and is a risk factor for asthma. To obtain insights into mechanisms responsible for the effects of that polymorphism on enzymatic activity and thermal stability, we predicted the 3D structure of HNMT using the threading method and molecular dynamics simulations in water. Herein, we report a theoretical 3D model of human HNMT which reveals that polymorphic residue Thr105Ile is located in the turn between a beta strand and an alpha helix on the protein surface away from the active site of HNMT. Ile105 energetically destabilizes folded HNMT because of its low Chou-Fasman score for forming a turn conformation and the exposure of its hydrophobic side chain to aqueous solution. It thus promotes the formation of misfolded proteins that are prone to the clearance by proteasomes. This information explains, for the first time, how genetic polymorphisms can cause enhanced protein degradation and why the thermal stability of allozyme Ile105 is lower than that of Thr105. It also supports the hypothesis that the experimental observation of a significantly lower level of HNMT enzymatic activity for allozyme Ile105 than that with Thr105 is due to a decreased concentration of allozyme Ile105, but not an alternation of the active-site topology of HNMT caused by the difference at residue 105.

Two polymorphic forms of human histamine methyltransferase: structural, thermal, and kinetic comparisons

BACKGROUND

Histamine plays important biological roles in cell-to-cell communication; it is a mediator in allergic responses, a regulator of gastric acid secretion, a messenger in bronchial asthma, and a neurotransmitter in the central nervous system. Histamine acts by binding to histamine receptors, and its local action is terminated primarily by methylation. Human histamine N-methyltransferase (HNMT) has a common polymorphism at residue 105 that correlates with the high- (Thr) and low- (Ile) activity phenotypes.

RESULTS

Two ternary structures of human HNMT have been determined: the Thr105 variant complexed with its substrate histamine and reaction product AdoHcy and the Ile105 variant complexed with an inhibitor (quinacrine) and AdoHcy. Our steady-state kinetic data indicate that the recombinant Ile105 variant shows 1.8- and 1.3-fold increases in the apparent K(M) for AdoMet and histamine, respectively, and slightly (16%) but consistently lower specific activity as compared to that of the Thr105 variant. These differences hold over a temperature range of 25 degrees C-45 degrees C in vitro. Only at a temperature of 50 degrees C or higher is the Ile105 variant more thermolabile than the Thr105 enzyme.

CONCLUSIONS

HNMT has a 2 domain structure including a consensus AdoMet binding domain, where the residue 105 is located on the surface, consistent with the kinetic data that the polymorphism does not affect overall protein stability at physiological temperatures but lowers K(M) values for AdoMet and histamine. The interactions between HNMT and quinacrine provide the first structural insights into a large group of pharmacologic HNMT inhibitors and their mechanisms of inhibition.

Histamine N-methyltransferase functional polymorphism: lack of association with schizophrenia

Histamine is a central nervous system (CNS) neurotransmitter that has been implicated in the pathophysiology of schizophrenia. Histamine N-methyltransferase (HNMT) terminates the neurotransmitter actions of histamine in the mammalian CNS, and levels of HNMT activity in human tissues are controlled, in part, by inheritance. A common C314T polymorphism in the HNMT gene causes a Thr105Ile change in encoded amino acid. The T314 allele results in decreased levels of both HNMT enzyme activity and immunoreactive protein. There is also a polymorphic CA repeat in intron 5 of the HNMT gene. The frequencies of alleles for the functional C314T polymorphism and the polymorphic CA repeat were compared between 171 schizophrenia cases and 171 ethnically matched controls to test for possible disease association. No significant difference was found between the two groups in the frequency of the T314 allele in patients with schizophrenia and controls (0.068 vs. 0.078, respectively). Allele frequencies for the polymorphic HNMT CA repeat also failed to show significant differences between cases and matched controls.

Histamine N-methyltransferase pharmacogenetics: association of a common functional polymorphism with asthma

Histamine is involved in the pathophysiology of asthma, and histamine N-methyltransferase (HNMT) plays the dominant role in histamine metabolism in human bronchial epithelium. Levels of HNMT activity in human tissues are controlled, in part, by inheritance. A common C314T polymorphism within the HNMT gene results in a Thr105Ile change in encoded amino acid, and the T314 allele is associated with decreased levels of both HNMT enzymatic activity and immunoreactive protein. Therefore, presence of the T314 allele would be expected to result in reduced histamine metabolism and increased bronchoconstriction. We characterized this common, functionally significant polymorphism in DNA samples from 237 randomly selected Caucasian control subjects and 192 samples from Caucasian asthmatic patients. Allele frequencies for the T314 HNMT allele were 0.08 in the control samples and 0.14 in samples from Caucasian asthmatic patients (odds ratio = 1.9, P < 0.01), indicating a significant increase in the frequency of subjects with low HNMT activity among asthmatics. The association between a common, functionally significant genetic polymorphism for HNMT and asthma suggests that individual variation in histamine metabolism might contribute to the pathophysiology and/or response to therapy of this disease.

Methylation pharmacogenetics: catechol O-methyltransferase, thiopurine methyltransferase, and histamine N-methyltransferase

Methyl conjugation is an important pathway in the biotransformation of many exogenous and endogenous compounds. Pharmacogenetic studies of methyltransferase enzymes have resulted in the identification and characterization of functionally important common genetic polymorphisms for catechol O-methyltransferase, thiopurine methyltransferase, and histamine N-methyltransferase. In recent years, characterization of these genetic polymorphisms has been extended to include the cloning of cDNAs and genes, as well as a determination of the molecular basis for the effects of inheritance on these methyltransferase enzymes. The thiopurine methyltransferase genetic polymorphism is responsible for clinically significant individual variations in the toxicity and therapeutic efficacy of thiopurine drugs such as 6-mercaptopurine. Phenotyping for the thiopurine methyltransferase genetic polymorphism represents one of the first examples in which testing for a pharmacogenetic variant has entered standard clinical practice. The full functional implications of pharmacogenetic variation in the activities of catechol O-methyltransferase and histamine N-methyltransferase remain to be determined. Finally, experimental strategies used to study methylation pharmacogenetics illustrate the rapid evolution of biochemical, pharmacologic, molecular, and genomic approaches that have been used to determine the role of inheritance in variation in drug metabolism, effect, and toxicity.

Pharmacogenomics - it's not just pharmacogenetics

New technologies in both combinatorial chemistry and combinatorial biology promise to unlock new opportunities for drug discovery and lead optimisation. Using such genome-based technologies to measure the dynamic properties of pharmacological systems, pharmacogenomics can now provide an objective measure of a drug's biological efficacy, including its potential adverse effects.