Journal of Pharmacy And Bioallied Sciences
Journal of Pharmacy And Bioallied Sciences Login  | Users Online: 126  Print this pageEmail this pageSmall font sizeDefault font sizeIncrease font size 
    Home | About us | Editorial board | Search | Ahead of print | Current Issue | Past Issues | Instructions | Online submission




 
 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 12  |  Issue : 6  |  Page : 787-803  

Influence of DRD2 polymorphisms on the clinical outcomes of opioiddependent patients on methadone maintenance therapy


1 Faculty of Pharmacy, Universiti Sultan Zainal Abidin (UniSZA), Besut Campus, Terengganu, Malaysia; Pharmacogenetics and Novel Therapeutics Cluster, Institute for Research in Molecular Medicine (INFORMM), Universiti Sains Malaysia (USM), Kelantan, Malaysia
2 Emergency and Trauma Department, Hospital Sultanah Aminah, Johor, Malaysia
3 Pharmacogenetics and Novel Therapeutics Cluster, Institute for Research in Molecular Medicine (INFORMM), Universiti Sains Malaysia (USM), Kelantan, Malaysia; Department of Pharmacology and Toxicology, College of Pharmacy, Hawler Medical University, Hawler, Iraq
4 Pharmacogenetics and Novel Therapeutics Cluster, Institute for Research in Molecular Medicine (INFORMM), Universiti Sains Malaysia (USM), Kelantan, Malaysia; Human Genome Center, School of Medical Sciences, Universiti Sains Malaysia (USM), Kelantan, Malaysia
5 Pharmacogenetics and Novel Therapeutics Cluster, Institute for Research in Molecular Medicine (INFORMM), Universiti Sains Malaysia (USM), Kelantan, Malaysia; Department of Psychiatry, School of Medical Sciences, Universiti Sains Malaysia (USM), Kelantan, Malaysia
6 School of Medical Sciences, Universiti Sains Malaysia (USM), Kelantan, Malaysia
7 Pharmacogenetics and Novel Therapeutics Cluster, Institute for Research in Molecular Medicine (INFORMM), Universiti Sains Malaysia (USM), Kelantan, Malaysia
8 Pharmacogenetics and Novel Therapeutics Cluster, Institute for Research in Molecular Medicine (INFORMM), Universiti Sains Malaysia (USM), Kelantan, Malaysia; Centre for Research in Addiction (CentRenA), Universiti Sultan Zainal Abidin (UniSZA), Gong Badak Campus, Terengganu, Malaysia
9 Pharmacogenetics and Novel Therapeutics Cluster, Institute for Research in Molecular Medicine (INFORMM), Universiti Sains Malaysia (USM), Kelantan, Malaysia; Faculty of Medicine, Universiti Sultan Zainal Abidin (UniSZA), Medical Campus, Terengganu, Malaysia

Date of Submission03-Nov-2019
Date of Decision21-Jan-2020
Date of Acceptance08-Mar-2020
Date of Web Publication05-Nov-2020

Correspondence Address:
Dr. Zalina Zahari
Faculty of Pharmacy, Universiti Sultan Zainal Abidin (UniSZA), Besut Campus, 22200 Besut, Terengganu.
Malaysia
Login to access the Email id

Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jpbs.JPBS_248_19

Rights and Permissions
   Abstract 

Introduction: Dopamine receptor D2 (DRD2) is one of the dopamine receptors that have been studied in relation to opioid dependence. It is possible, therefore, that DRD2 gene (DRD2) polymorphisms influence treatment outcomes of patients with opioid dependence. The objective of this study was to investigate the influence of DRD2 polymorphisms on the clinical outcomes of opioid-dependent patients on methadone maintenance therapy (MMT). Materials and Methods: Patients with opioid dependence (n = 148) were recruited from MMT clinics. Pain sensitivity, severity of the opiate withdrawal syndrome, and sleep quality were assessed using cold pressor test (CPT), Subjective Opiate Withdrawal Scale (SOWS-M), and Pittsburgh Sleep Quality Index (PSQI)-Malay, respectively. Deoxyribonucleic acid (DNA) was extracted from whole blood, and then was used for genotyping of Val96Ala, Leu141Leu, Val154Ile, Pro310Ser, Ser311Cys, TaqI A, -141C Ins/Del, and A-241G polymorphisms. Results: Among 148 patients, 8.1% (n = 12), 60.8% (n = 90), 27.7% (n = 41), and 29.1% (n = 43) had at least one risk allele for Ser311Cys, TaqI A, -141C Ins/Del, and A-241G polymorphisms, respectively. There were no significant differences in pain responses (pain threshold, tolerance, and intensity), SOWS, and PSQI scores between DRD2 polymorphisms. Conclusion: The common DRD2 polymorphisms are not associated with pain sensitivity, severity of the opiate withdrawal syndrome, and sleep quality in patients with opioid dependence on MMT. However, this may be unique for Malays. Additional research should focus on investigating these findings in larger samples and different ethnicity.

Keywords: Dopamine receptor D2, pain sensitivity, severity of the opiate withdrawal syndrome, sleep quality


How to cite this article:
Zahari Z, Lee CS, Ibrahim MA, Musa N, Mohd Yasin MA, Lee YY, Tan SC, Mohamad N, Ismail R. Influence of DRD2 polymorphisms on the clinical outcomes of opioiddependent patients on methadone maintenance therapy. J Pharm Bioall Sci 2020;12, Suppl S2:787-803

How to cite this URL:
Zahari Z, Lee CS, Ibrahim MA, Musa N, Mohd Yasin MA, Lee YY, Tan SC, Mohamad N, Ismail R. Influence of DRD2 polymorphisms on the clinical outcomes of opioiddependent patients on methadone maintenance therapy. J Pharm Bioall Sci [serial online] 2020 [cited 2020 Nov 26];12, Suppl S2:787-803. Available from: https://www.jpbsonline.org/text.asp?2020/12/6/787/299977




   Introduction Top


Opioid dependence is a chronic disease, which represents a significant problem, with heroin being the most commonly abused opiate.[1],[2] In Malaysia, methadone maintenance therapy (MMT) has been used since 2005 as one of the harm reduction programs designed to reduce human immunodeficiency virus (HIV) transmission indirectly by treating patients who have problems with opioid dependence, such as heroin and morphine.[2] Patients on MMT were mainly male of Malay ethnicity.[2],[3],[4] Methadone treatment appears to be successful in eliminating withdrawal symptoms, although control of cravings and seeking behaviors cannot be achieved in all patients.[2],[3] Patients on MMT have been shown to have methadone-related heightened pain sensitivity and poor sleep quality.[1],[5],[6],[7],[8]

The outcomes of MMT may be influenced by a combination of environmental, drug-induced, and genetic factors. Genetic association studies in addiction research aim to characterize genetic differences and variation in the processes that contribute to addiction and response to treatment. Attention has been directed to the genetic factors that might influence treatment outcomes of MMT.[9],[10],[11],[12],[13],[14],[15],[16],[17],[18],[19] Variation in addiction-related genes (such as dopamine receptor D2 gene, DRD2) due to polymorphisms in the genetic sequence may explain interindividual differences in clinical outcomes of patients on MMT.[9],[10],[11],[12],[13],[14],[15],[16],[17],[18],[19]

DRD2 contains polymorphisms that might affect DRD2 expression, density of the receptor, and signal transduction. Polymorphisms in dopamine-related genes have been shown to contribute to interindividual differences in pain sensitivity among healthy subjects and patients, susceptibility to migraine, and response to analgesics.[20],[21],[22] The Val96Ala polymorphism in the exon 3, which resides at the second transmembrane domain, was expected to affect the ligand binding pocket of the DRD2 receptor;[23] Pro310Ser and Ser311Cys (dbSNP rs1801028) polymorphisms in the exon 7 at third cytoplasmic domain were expected to affect the interaction with G proteins, and therefore DRD2 signal transduction via cyclic adenosine monophosphate (cAMP) inhibition.[23],[24] The -141C Ins/Del (dbSNP rs1799732) polymorphism in the promoter region of the DRD2 was directly related to DRD2 expression.[25] DRD2/ANKK1 TaqI A (also known as DRD2 Taq1A, dbSNP rs1800497, referred to here as TaqI A) polymorphism is thought to be associated with the number of spiperone-binding sites, which may have functional pharmacological relevance. Individuals with TaqI A1 allele seem to have lower striatal DRD2 density compared to those without this allele.[26],[27]

DRD2 is one of the dopamine receptors genes that have been studied in relation to opioid dependence.[28],[29] The latest meta-analysis by Deng et al.[28] supported the previous meta-analysis study by Chen et al.,[29] which demonstrated that the DRD2/ANKK1 TaqI A (also known as DRD2 Taq1A, dbSNP rs1800497, referred to here as TaqI A) polymorphism played an important roles in the development of opioid dependence. In addition, Chen et al.[29] found that the -141C Ins/Del (dbSNP rs1799732) polymorphism was significantly associated with increased risk of opioid dependence. It is possible, therefore, that variations in the DRD2 influence clinical outcomes of patients with opioid dependence on MMT.

There has been little information on the effect of DRD2 polymorphisms on methadone treatment outcomes. There are however studies that investigated the impact of genetic polymorphisms of DRD2 on patient’s dose requirements[14],[16] and efficacy[15],[17],[18],[19] of methadone therapy. However, to the best of our knowledge, data on Ser311Cys (dbSNP rs1801028) and -141C Ins/Del (dbSNP rs1799732) polymorphisms among patients with opioid dependence on MMT are still unavailable for references because information about the relationship between these polymorphisms and methadone outcomes was not reported in the previous studies.[14],[15],[16],[17],[18],[19] Dopamine receptor D2 (DRD2) is one of the dopamine receptors that have been studied in relation to pain sensitivity.[30] DRD2 binding in the brain is associated with individual responses to painful stimulation and pain modulatory capacity.[31] Healthy humans with low DRD2 availability in the striatum are associated with a higher cold pain threshold.[31]

Relationship between pain sensitivity, severity of the opiate withdrawal syndrome, and sleep quality with genetic polymorphisms of DRD2 has not been previously reported in patients with opioid dependence on MMT. We aimed in this study to test the hypothesis that DRD2 is associated with interindividual variation in clinical outcomes of patients with opioid dependence on MMT.


   Materials and Methods Top


Subjects

We have reported detailed methods of this study sample previously.[1],[5],[6],[7],[8],[9],[10],[11],[12],[32],[33],[34] Data used in this study were collected as part of the study to evaluate the application of personalized methadone therapy among patients on MMT. In this cross-sectional study, a total of 148 subjects were recruited from 11 outpatient methadone clinics in Kelantan, Malaysia between March and October 2013. In this study, all subjects were stabilized in treatment, defined as having been enrolled in the program for more than 1 month with no change of methadone dosage over the past 1 month.

This study was approved by the Human Research Ethics Committee (HREC), Universiti Sains Malaysia (USM) in Kelantan, Malaysia (Reference number: USMKK/PPP/JEPeM (253.3 [14]) and the Medical Research and Ethics Committee at the Ministry of Health, Malaysia (Reference number: NMRR-13-524-16614), and was conducted in accordance with the Declaration of Helsinki.

We recruited only male subjects who were of Malay ethnicity to minimize the possible effects that gender and ethnicity had on pain sensitivity[35],[36],[37] and sleep,[38],[39] and because more than 90% of the patients on MMT in Malaysia are Malay males.[2],[3],[4] All subjects fulfilled inclusion and exclusion criteria and gave informed consent. Inclusion criteria included: (1) subjects aged more than 18 years; (2) free of acute medical, surgical, and psychiatric illness; (3) free of acute or chronic medical, surgical, and psychiatric illness that requires concurrent medical, surgical, or psychiatric therapy; (4) free of regular use of alcohol; (5) free of intoxication; (6) able to understand study protocols and to follow simple study instructions; and (7) willing to sign written informed consent. Alcohol use and intoxication were carefully evaluated during interview and clinical assessment by a physician who assisted the author in this study.

Exclusion criteria were: (1) subjects who were currently taking illicit benzodiazepines, cannabinoids, and barbiturates; (2) subjects with chronic or ongoing acute pain; (3) subjects with a history of analgesic ingestion within 3 days before the cold pressor test (CPT); and (4) subjects with severe cognitive impairment, which may interfere with pain assessments and/or communication.

Urine drug screens for morphine, tetrahydrocannabinol, amphetamines, and benzodiazepines were performed using drugs of abuse rapid test, F.A.C.T.S 4 in 1 Combo Dipcard Rapid Test (MOR/THC/AMP/BZO) (Scientifacts Sdn. Bhd., Selangor, Malaysia) twice in one week at least 3 days apart before the study. Subjects with two consecutive negative urine tests were included in the study. They were instructed to avoid analgesics of any type within 72 h before CPT test day. They have been instructed not to ingest methadone from their MMT clinic on the test morning. Subjects who fulfilled all criteria were interviewed to obtain sociodemographic data and other relevant information.

Cold pressor test, Subjective Opiate Withdrawal Scale, and Pittsburgh Sleep Quality Index–Malay

CPT was performed to assess pain threshold, pain tolerance, and pain intensity. Details on CPT methods have been described in our previous articles.[40],[41],[42],[43],[44] The times elapsed between the immersion of hand to pain detection (threshold) and hand withdrawal (tolerance) were quantified in seconds. Immediately after hand withdrawal, subjects were asked to subjectively score their maximal pain intensity using 0–100 visual analog scale (VAS), where zero (0) represented no pain and a hundred (100) represented the worst pain imaginable. The CPT was performed six times over 24 h. The first test was performed approximately 30 min before their morning dose of methadone (0 h), and at 2, 4, 8, 12, and 24 h after the dose.

Patients’ opioid withdrawal symptoms were assessed using the translated and validated Malay version of the Subjective Opiate Withdrawal Scale (SOWS-M).[10],[45] The SOWS-M is a self-administered scale, which contains 16 symptoms. Patients were asked to rate each symptom according to severity. Each item was rated on a four-point Likert scale where zero (0) was “not at all,” one (1) was “a little,” two (2) was “moderately,” three (3) was “quite a bit,” and four (4) was “extremely,” with a total score of 0–64. As this was a patient self-evaluation, the researcher’s role was only to assist the patient to complete the task, not to do it for them or interpret their symptomology. For most patients, the 16-item SOWS-M took less than 10 min to complete. The SOWS-M was administered six times over a 24-h period at 0 h (i.e., immediately [approximately 30 min] before taking their morning dose of methadone), and at 2, 4, 8, 12, and 24 h after the dose intake.

Sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI)-Malay.[46],[47] The PSQI-M contains 19 items that are included in scoring. The 19 individual items were used to generate seven component scores: subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleep medications, and daytime dysfunction. The sum of these seven component scores yields one global score of subjective sleep quality with a potential range of 0–21, with higher scores representing poorer subjective sleep quality.

Genotyping of DRD2 polymorphisms

For genotyping, 2 mL of venous blood from each subject was collected. Deoxyribonucleic acid (DNA) was extracted using the QIAamp DNA Blood Mini Kit (Qiagen, Hilden, Germany) according to the manufacturer’s instructions with slight modifications. The quantity and quality of the extracted total genomic DNA was determined on the NanoDrop ND-1000 Spectrophotometer (NanoDrop Technologies, Wilmington, Delaware). Genotyping of eight DRD2 polymorphisms of our research interest (Val96Ala, Leu141Leu, Val154Ile, Pro310Ser, Ser311Cys, TaqI A, -141C Ins/Del, and A-241G) was performed according to previously developed nested allele-specific multiplex polymerase chain reaction (PCR) methods with slight modifications[48] (methods are available on request).

Statistical analysis

Sample size was calculated prior the start of the study based on the Cohen sample size table,[49] using medium population effect size (ES) assuming a two-tailed 5% type I error rate and 80% power. The required sample size per group was 64 alleles or subjects for comparisons of mean values of two groups (under allelic additive model and genotype dominant and recessive model). Allele, genotype, haplotype, and diplotype frequencies were calculated using the program SVS 7.3.1 (GOLDEN HELIX, SNP, and VARIATION SUITE 7) based on an expectation-maximization (EM) algorithm for the following procedures: (a) the calculation of DRD2 alleles and genotypes frequencies; (b) the estimation of heterozygosity in each polymorphism in Hardy–Weinberg proportion; and (c) the estimation of maximum-likelihood haplotype frequency. Assuming a mutant-type allele was a high-risk allele, genotype frequencies under dominant and recessive model were determined for the presently observed polymorphisms of DRD2.[50] Data analysis was carried out after all genotyping of the subjects was completed. Repeated measures analysis of variance (RM-ANOVA), independent t test, or one-way ANOVA test was used to examine the effects of presently observed DRD2 polymorphisms on cold pressor pain responses and SOWS and PSQI scores under genotype and allelic additive model, genotype dominant and recessive model, and haplotypes and diplotypes analysis. Haplotypes and diplotypes with frequencies less than 10% were pooled. The statistical analysis was carried out using Statistical Package for the Social Sciences (SPSS)/Win software (version 24.0, SPSS, Chicago, Illinois). All confidence intervals (CIs) were computed at the 95% level. A probability of <0.05 was considered to be significant for statistical comparison.


   Results Top


Samples demographics

Of the initial 169 subjects who were invited to participate, 21 subjects were excluded from the study (health reasons = 12, scheduling conflicts = 3, and miscellaneous reasons = 6). The average age was 36.86 (standard deviation [SD] = 6.13, range: 25–55) years and the average daily dose of methadone was 72.70 (SD = 28.25, range: 20–160) mg/day with an average duration in MMT of 2.82 (SD = 2.02, range: 0.33–9.00) years.

Genotypic profile

All the DNA samples from the subjects were successfully genotyped. The Val96Ala, Leu141Leu, Val154Ile, and Pro310Ser polymorphisms were not detected in any subject. Allele, genotype, haplotype, and diplotype distributions of presently observed DRD2 polymorphisms are presented in [Supplementary Table 1 [Additional file 1]]. All the detected polymorphisms were in Hardy–Weinberg equilibrium (HWE) distribution (P > 0.300).

Frequencies of the mutant-type allele for Ser311Cys, TaqI A, -141C Ins/Del, and A-241G polymorphisms were 4.1%, 39.2%, 15.2%, and 16.2%, respectively. There was no subject with 311 Cys/Cys genotype in this study.

When considering loci Ser311Cys, TaqI A, -141C Ins/Del, and A-241G, we observed eight haplotypes in our subjects. Two of them had a frequency higher than 30.0%. The most frequent estimated haplotype was the haplotype no. 1 (CGCA or 311 Ser/TaqI A2/-141C Ins/-241A) (n = 100, 33.8%), followed by the haplotype composed of only wild-type alleles, no. 2 (CACA or 311 Ser/TaqI A1/-141C Ins/-241A) (n = 92, 31.1%). The haplotype composed of only mutant-type alleles (GAAG or 311 Cys/TaqI A1/-141C Del/-241G) was not detected in any subject.

Among the 22 estimated diplotypes, the most common haplotype pair (i.e., diplotype) was diplotype no. 1 (CACA/CGCA) (n = 27, 18.2%) and diplotype no. 2 (CGCA/CGCA) (n = 27, 18.2%) followed by diplotype no. 3 (CGAA/CACA) (n = 13, 8.8%).

Cold pressor test responses, Subjective Opiate Withdrawal Scale, and Pittsburgh Sleep Quality Index–Malay scores among DRD2 polymorphisms

Results showed no significant differences in pain responses (pain threshold, tolerance, and intensity), SOWS, and PSQI scores between presently observed DRD2 polymorphisms (Ser311Cys, TaqI A, -141C Ins/Del, and A-241G) under genotype and allelic additive model, genotype dominant and recessive model, and haplotypes and diplotypes analysis [Table 1][Table 2][Table 3][Table 4][Table 5].
Table 1: Influences of presently observed DRD2 polymorphisms on cold pressor pain threshold

Click here to view
Table 2: Influences of presently observed DRD2 polymorphisms on cold pressor pain tolerance

Click here to view
Table 3: Influences of presently observed DRD2 polymorphisms on cold pressor pain intensity

Click here to view
Table 4: Influences of presently observed DRD2 polymorphisms on total Subjective Opiate Withdrawal Scale scores

Click here to view
Table 5: Influences of presently observed DRD2 polymorphisms on global Pittsburgh Sleep Quality Index scores

Click here to view



   Discussion Top


In this paper, we explored the influence of DRD2 polymorphisms on clinical outcomes of methadone treatment. We were unable to find any association between these specific DRD2 polymorphisms with pain sensitivity, severity of the opiate withdrawal syndrome, and sleep quality during treatment.

In our current study, we genotyped eight DRD2 polymorphisms among 148 opioid-dependent Malay males on MMT. We found that all of the patients were noncarriers of mutant-type alleles for Val96Ala, Leu141Leu, Val154Ile, and Pro310Ser (dbSNP rs1800496) polymorphisms, which were similar to those found among 93 intravenous heroin addicts by Teh et al.[51] and 152 Malay male opioid naive healthy volunteers in our previous study.[40] Genotype distribution for Ser311Cys in our patients was also similar to that observed in the previous study.[40] Among the presently observed mutant-type alleles, the most frequently observed was TaqI A1 (39.2%, 95% CI: 33.6, 44.8), followed by -241G (16.2%, 95% CI: 12.0, 20.4). The frequencies of TaqI A1 and -241G alleles resembled those reported earlier in healthy Malay males (TaqI A1 [38.5%, 95% CI: 33.0, 44.0] and -241G [12.8%, 95% CI: 9.1, 16.6])[40] and in 596 healthy Japanese males (TaqI A1 [34.1%, 95% CI: 31.4, 36.8] and -241G [11.7%, 95% CI: 8.9, 14.5]).[52] We obtained a -141C Del allelic frequency of 15.2% (95% CI: 11.1, 19.3) and 4.1% (95% CI: 1.8, 6.3) for 311 Cys allele, which were within the range reported for healthy Malay subjects (-141C Del [15.5%, 95% CI: 11.4, 19.5] and 311 Cys [6.6%, 95% CI: 3.8, 9.4])[40] and healthy Japanese subjects (-141C Del [17.0%, 95% CI: 14.9, 19.2] and 311 Cys [2.8%, 95% CI: 1.4, 4.2]).[52]

We recently evaluated the roles of the cytochrome P450 family 2 subfamily B member 6 (CYP2B6),[10] opioid receptor mu 1 (OPRM1),[12] and P-glycoprotein (P-gp) efflux transporter (ABCB1)[9] gene polymorphisms on pain sensitivity, and found that these genetic factors were significantly associated with pain threshold and pain tolerance among patients with opioid dependence on MMT. The CYP2B6*6 allele has previously been shown to be associated with a lower pain threshold and lower pain tolerance.[10] Interestingly, previous study found that the IVS2+691 CC genotype and AC/AG diplotype of 118A>G and IVS2+691G>C polymorphisms of OPRM1 seem to have opposing roles in pain tolerance.[12] Analysis of relationship between ABCB1 and cold pressor pain response showed that the 2677G>T/A polymorphism and CGC haplotype for the 1236C>T, 2677G>T/A, and 3435C>T polymorphisms of ABCB1 are associated with pain sensitivity among patients with opioid dependence on MMT.[9]

DRD2 has been studied in relation to pain sensitivity.[30] The binding of DRD2 in the brain has been shown to be associated with individual responses to painful stimulation and pain modulatory capacity.[31] In healthy human, low DRD2 availability in the striatum is associated with a higher cold pain threshold.[31] Recently, Jääskeläinen et al.[21] suggested that variation in the DRD2 plays a key role in human pain, thus supporting the hypothesis that 957C>T polymorphism influences dopaminergic pain processing in the striatum, and thereby predicts individual variation of the thermal pain sensitivity.

Despite the important central role of DRD2 in the dopaminergic pain processing, our study did not find any association between the common DRD2 polymorphisms (Ser311Cys, TaqI A, -141C Ins/Del, and A-241G) and cold pressor pain sensitivity, even without the multiple testing corrections. Our findings are in line with our previous study, the only study to examine the role of DRD2 polymorphisms on the interindividual differences in cold pressor pain threshold, pain tolerance, and pain intensity among healthy volunteers.[40] To the best of our knowledge, no prior study has specifically investigated the association of Val96Ala, Leu141Leu, Val154Ile, Pro310Ser, Ser311Cys, TaqI A, -141C Ins/Del, and A-241G polymorphisms and pain sensitivity as a measurement of adverse effects to methadone (i.e., hyperalgesia), thus data of individual polymorphisms are not yet available for comparison.

Does withdrawal symptoms in patients on MMT depend, in part, on polymorphism of the DRD2? In terms of withdrawal symptoms, we were unable to confirm a role of dopaminergic systems in pharmacodynamic effects of methadone. No significant associations were found between DRD2 polymorphisms and the severity of the opiate withdrawal syndrome as rated by 16-item SOWS-M.

Concerning genetic factors for sleep disturbance–related side effects of opioids, thus far, only two studies have been conducted among opioid-addicted individuals during methadone treatment. In both studies (i.e., by Wang et al.[13] and Zahari et al.[11]), the OPRM1 polymorphisms have been shown to be associated with methadone-related sleep problems. Wang et al.[13] reported a significant association of OPRM1 polymorphisms with insomnia side effects in a Taiwanese MMT cohort. In our previous study, we found that the AC/AG diplotype for the 118A>G and IVS2+691G>C polymorphisms of OPRM1 is associated with better sleep quality among opioid-dependent Malay males on MMT.[11]

Strong biological support for gene-level effects of DRD2 on sleep and circadian rhythm phenotypes have been reported in the literature.[53] In mice, both DRD2 presynaptic autoreceptors and post-synaptic heteroreceptors influence dopamine expression levels,[54] and DRD2 knockout mice show significant differences in wakefulness, non-rapid eye movement sleep, and sleep latency.[55] In human, the first large-scale genetic analysis to show an association between DRD2 variants and sleep in a multiethnic sample was reported in 2016.[53] This study involved seven Candidate Gene Association Resource (CARe) cohorts of over 25,000 individuals of African, Asian, European, and Hispanic American ancestry. The finding showed that rs17601612 polymorphism of DRD2 was significantly associated with self-reported, habitual sleep duration. An association was also observed for rs17601612 with polysomnographically determined sleep latency. These findings support a role for DRD2 in influencing sleep duration. Their work motivates us to examine the association between DRD2 polymorphisms and clinical outcomes in our Malay males with opioid dependence on MMT. However, our current study did not find any association between DRD2 polymorphisms and sleep disturbance–related side effects of methadone. The comparison of their study and ours is difficult as the studies are designed differently. However, this may in part be explained by differences in ethnicity of the study populations,[38],[39] sample size, the types of DRD2 polymorphisms investigated in each study, and characteristics of study participants whether the subjects are opioid dependent owing to chronic treatment or are opioid naive.

The findings of our current study have a number of practical implications for future research. Because of the ethnic diversity in Malaysian population, and also because different ethnic groups show differences in pain sensitivity[35],[36],[37] and sleep,[38],[39] we suggest that the association of polymorphisms in the DRD2 with cold pressor pain sensitivity and sleep quality also be investigated in other races. Besides DRD2 polymorphisms, it is possible that mutation of dopamine-related genes, which regulate other subtypes of dopamine receptors and dopamine transporters, could explain the large interindividual variation in clinical outcomes of patients on MMT. Thus, future genetic studies of pain and sleep should consider other dopamine-related genes. The clinical impact of DRD2 polymorphism on clinical outcomes of opioid dependent patients on MMT are largely unknown. The results of this study suggested that interindividual differences in clinical outcomes of patients on MMT were not explained by the polymorphisms in the genetic sequence of DRD2. Therefore, identifying DRD2 genotypes for Ser311Cys, TaqI A, -141C Ins/Del, and A-241G polymorphisms among opioid-dependent patients on MMT may have no great impact on the personalized medicine to individualize and optimize methadone substitution treatment, which would be of particular importance during the management of withdrawal symptoms in this patient population.

Limitations of our study deserve consideration. First, the frequencies of 311Cys, -141C Del, and -241G alleles in the study samples were low, thus limiting the interpretation of their influence on clinical outcomes of patients on MMT, although the respective allelic frequencies in our samples were similar to those previously described.[40],[51],[52] Second, this study recruited only male subjects who were of Malay ethnicity to control for possible confounding effects that gender and ethnicity had on pain and sleep. Unfortunately, we are not able to address potential sex- and ethnic-specific effects of variations of DRD2 on pain and sleep in our study. Therefore, it is not possible for us to extend the conclusion of no association of DRD2 genetic variations on pain and sleep to female subjects or other ethnicities.


   Conclusion Top


The DRD2 polymorphisms we studied were not associated with differences in pain sensitivity, severity of the opiate withdrawal syndrome, and sleep quality. However, this may be unique for Malays. Other polymorphisms may be more relevant for Malays. Further investigations in larger numbers, other populations, and polymorphisms are required to confirm these findings.

Approval of ethical committees

This study was approved by the Human Research Ethics Committee (HREC), Universiti Sains Malaysia (USM) in Kelantan, Malaysia (Reference number: USMKK/PPP/JEPeM (253.3 [14]) and the Medical Research and Ethics Committee at the Ministry of Health, Malaysia (Reference number: NMRR-13-524-16614), and was conducted in accordance with the Declaration of Helsinki.

Acknowledgements

We are grateful to Nur Amalina Che Rahim and Wan Izzati Mariah Binti Wan Hassan from the Department of Pharmacy, Hospital Universiti Sains Malaysia, Kubang Kerian, Kelantan, Malaysia; Wan Nor Arifin Wan Harun from Biostatistics and Research Methodology Unit, School of Medical Sciences, Universiti Sains Malaysia, Kelantan, Malaysia; and all the members of Pharmacogenetics and Novel Therapeutics Cluster, Institute for Research in Molecular Medicine (INFORMM), Universiti Sains Malaysia (USM), Kelantan, Malaysia, for their support and valuable suggestions during the study.

Financial support and sponsorship

The study was supported by the Universiti Sains Malaysia (USM) grant under the “Research University Cluster (RUC)” Grant No. 1001.PSK.8620014, under the project; Application of Personalised Methadone Therapy Methadone Maintenance Therapy (PMT for MMT).

Conflicts of interest

There are no conflicts of interest.



 
   References Top

1.
Zahari Z, Siong LC, Musa N, Mohd Yasin MA, Choon TS, Mohamad N, et al. Report: demographic profiles and sleep quality among patients on methadone maintenance therapy (MMT) in Malaysia. Pak J Pharm Sci 2016;29:239-46.  Back to cited text no. 1
    
2.
Ali N, Aziz SA, Nordin S, Mi NC, Abdullah N, Paranthaman V, et al. Evaluation of methadone treatment in Malaysia: findings from the Malaysian methadone treatment outcome study (MYTOS). Subst Use Misuse 2018;53:239-48.  Back to cited text no. 2
    
3.
Almeman AA, Ismail R, Mohamad N Methadone maintenance therapy (MMT) in Malaysia: an observational clinical study. Australas Med J 2017;10:314-21.  Back to cited text no. 3
    
4.
Malini C, Abdul Wahab NA, Shamsuddin AF Effectiveness of methadone maintenance therapy (MMT) and life style improvement among opiate dependent patients registered. Jurnal Sains Kesihatan Malaysia 2019;17:51-6.  Back to cited text no. 4
    
5.
Zahari Z, Lee CS, Tan SC, Mohamad N, Lee YY, Ismail R Relationship between cold pressor pain-sensitivity and sleep quality in opioid-dependent males on methadone treatment. Peer J 2015;3:e839.  Back to cited text no. 5
    
6.
Zahari Z, Lee CS, Mohamad N, Musa N, Mohd Yasin MA, Tan SC, et al Association between perceived sleep disorders and sleep-related factors among patients on methadone maintenance therapy (MMT) in Malaysia. Int Med J 2016;23:134-7.  Back to cited text no. 6
    
7.
Zahari Z, Lee CS, Ibrahim MA, Musa N, Mohd Yasin MA, Lee YY, et al. Comparison of pain tolerance between opioid dependent patients on methadone maintenance therapy (MMT) and opioid naive individuals. J Pharm Pharm Sci 2016;19:127-36.  Back to cited text no. 7
    
8.
Zahari Z, Inrahim MA, Tan SC, Mohamad N, Ismail R Sleep quality in opioid-naive and opioid-dependent patients on methadone maintenance therapy in Malaysia. Turk J Med Sci 2016;46:1743-8.  Back to cited text no. 8
    
9.
Zahari Z, Lee CS, Ibrahim MA, Musa N, Mohd Yasin MA, Lee YY, et al. ABCB1 polymorphisms and cold pressor pain responses: opioid-dependent patients on methadone maintenance therapy. Nurs Res 2017;66:134-44.  Back to cited text no. 9
    
10.
Zahari Z, Lee CS, Ibrahim MA, Musa N, Mohd Yasin MA, Lee YY, et al. Relationship between CYP2B6*6 and cold pressor pain sensitivity in opioid dependent patients on methadone maintenance therapy (MMT). Drug Alcohol Depend 2016;165:143-50.  Back to cited text no. 10
    
11.
Zahari Z, Lee CS, Ibrahim MA, Musa N, Mohd Yasin MA, Lee YY, et al. The AC/AG diplotype for the 118A>G and IVS2+691G>C polymorphisms of OPRM1 gene is associated with sleep quality among opioid-dependent patients on methadone maintenance therapy. Pain Ther 2016;5:43-54.  Back to cited text no. 11
    
12.
Zahari Z, Lee CS, Ibrahim MA, Musa N, Yasin MA, Lee YY, et al. The opposing roles of IVS2+691 CC genotype and AC/AG diplotype of 118A>G and IVS2+691G>C of OPRM1 polymorphisms in cold pain tolerance among opioid-dependent Malay males on methadone therapy. Pain Ther 2015;4:179-96.  Back to cited text no. 12
    
13.
Wang SC, Tsou HH, Chen CH, Chen YT, Ho IK, Hsiao CF, et al. Genetic polymorphisms in the opioid receptor mu1 gene are associated with changes in libido and insomnia in methadone maintenance patients. Eur Neuropsychopharmacol 2012;22:695-703.  Back to cited text no. 13
    
14.
Levran O, Peles E, Randesi M, Shu X, Ott J, Shen PH, et al. Association of genetic variation in pharmacodynamic factors with methadone dose required for effective treatment of opioid addiction. Pharmacogenomics 2013;14:755-68.  Back to cited text no. 14
    
15.
Lawford BR, Young RM, Noble EP, Sargent J, Rowell J, Shadforth S, et al. The D(2) dopamine receptor A(1) allele and opioid dependence: association with heroin use and response to methadone treatment. Am J Med Genet 2000;96:592-8.  Back to cited text no. 15
    
16.
Hung CC, Chiou MH, Huang BH, Hsieh YW, Hsieh TJ, Huang CL, et al. Impact of genetic polymorphisms in ABCB1, CYP2B6, OPRM1, ANKK1 and DRD2 genes on methadone therapy in Han Chinese patients. Pharmacogenomics 2011;12:1525-33.  Back to cited text no. 16
    
17.
Crettol S, Besson J, Croquette-Krokar M, Hämmig R, Gothuey I, Monnat M, et al. Association of dopamine and opioid receptor genetic polymorphisms with response to methadone maintenance treatment. Prog Neuropsychopharmacol Biol Psychiatry 2008;32:1722-7.  Back to cited text no. 17
    
18.
Bawor M, Dennis BB, Tan C, Pare G, Varenbut M, Daiter J, et al. Contribution of BDNF and DRD2 genetic polymorphisms to continued opioid use in patients receiving methadone treatment for opioid use disorder: an observational study. Addict Sci Clin Pract 2015;10:19.  Back to cited text no. 18
    
19.
Barratt DT, Coller JK, Somogyi AA Association between the DRD2 A1 allele and response to methadone and buprenorphine maintenance treatments. Am J Med Genet B Neuropsychiatr Genet 2006;141B:323-31.  Back to cited text no. 19
    
20.
Fernandez F, Colson N, Quinlan S, MacMillan J, Lea RA, Griffiths LR Association between migraine and a functional polymorphism at the dopamine beta-hydroxylase locus. Neurogenetics 2009;10:199-208.  Back to cited text no. 20
    
21.
Jääskeläinen SK, Lindholm P, Valmunen T, Pesonen U, Taiminen T, Virtanen A, et al. Variation in the dopamine D2 receptor gene plays a key role in human pain and its modulation by transcranial magnetic stimulation. Pain 2014;155:2180-7.  Back to cited text no. 21
    
22.
Treister R, Pud D, Ebstein RP, Eisenberg E Dopamine transporter genotype dependent effects of apomorphine on cold pain tolerance in healthy volunteers. PLoS One 2013;8:e63808.  Back to cited text no. 22
    
23.
Gejman PV, Ram A, Gelernter J, Friedman E, Cao Q, Pickar D, et al. No structural mutation in the dopamine D2 receptor gene in alcoholism or schizophrenia. Analysis using denaturing gradient gel electrophoresis. JAMA 1994;271:204-8.  Back to cited text no. 23
    
24.
Cravchik A, Sibley DR, Gejman PV Functional analysis of the human D2 dopamine receptor missense variants. J Biol Chem 1996;271:26013-7.  Back to cited text no. 24
    
25.
Arinami T, Gao M, Hamaguchi H, Toru M A functional polymorphism in the promoter region of the dopamine D2 receptor gene is associated with schizophrenia. Hum Mol Genet 1997;6:577-82.  Back to cited text no. 25
    
26.
Jönsson EG, Nöthen MM, Grünhage F, Farde L, Nakashima Y, Propping P, et al. Polymorphisms in the dopamine D2 receptor gene and their relationships to striatal dopamine receptor density of healthy volunteers. Mol Psychiatry 1999;4:290-6.  Back to cited text no. 26
    
27.
Thompson J, Thomas N, Singleton A, Piggott M, Lloyd S, Perry EK, et al. D2 dopamine receptor gene (DRD2) Taq1 A polymorphism: reduced dopamine D2 receptor binding in the human striatum associated with the A1 allele. Pharmacogenetics 1997;7:479-84.  Back to cited text no. 27
    
28.
Deng XD, Jiang H, Ma Y, Gao Q, Zhang B, Mu B, et al. Association between DRD2/ANKK1 TaqIA polymorphism and common illicit drug dependence: evidence from a meta-analysis. Hum Immunol 2015;76:42-51.  Back to cited text no. 28
    
29.
Chen D, Liu F, Shang Q, Song X, Miao X, Wang Z Association between polymorphisms of DRD2 and DRD4 and opioid dependence: evidence from the current studies. Am J Med Genet B Neuropsychiatr Genet 2011;156B:661-70.  Back to cited text no. 29
    
30.
Martikainen IK, Hagelberg N, Mansikka H, Hietala J, Någren K, Scheinin H, et al. Association of striatal dopamine D2/D3 receptor binding potential with pain but not tactile sensitivity or placebo analgesia. Neurosci Lett 2005;376:149-53.  Back to cited text no. 30
    
31.
Hagelberg N, Martikainen IK, Mansikka H, Hinkka S, Någren K, Hietala J, et al. Dopamine D2 receptor binding in the human brain is associated with the response to painful stimulation and pain modulatory capacity. Pain 2002;99:273-9.  Back to cited text no. 31
    
32.
Zahari Z, Ibrahim MA, Lee CS, Musa N, Tan SC, Mohamad N, et al Comparison of QTc interval between opioid dependent patients on methadone maintenance therapy (MMT) and opioid naive individuals. Int Med J 2019;26:96-100.  Back to cited text no. 32
    
33.
Zahari Z, Lee CS, Ibrahim MA, Musa N, Mohd Yasin MA, Lee YY, et al. Relationship between serum methadone concentration and cold pressor pain sensitivity in patients undergoing methadone maintenance therapy. Iran J Pharm Res 2018;17:8-16.  Back to cited text no. 33
    
34.
Zahari Z, Lee CS, Ibrahim MA, Musa N, Mohd Yasin MA, Lee YY, et al Relationship between ABCB1 polymorphisms and serum methadone concentration in patients undergoing methadone maintenance therapy (MMT). Am J Drug Alcohol Abuse2016;42:587-96.  Back to cited text no. 34
    
35.
Etherton J, Lawson M, Graham R Individual and gender differences in subjective and objective indices of pain: gender, fear of pain, pain catastrophizing and cardiovascular reactivity. Appl Psychophysiol Biofeedback 2014;39:89-97.  Back to cited text no. 35
    
36.
Racine M, Tousignant-Laflamme Y, Kloda LA, Dion D, Dupuis G, Choinière M A systematic literature review of 10 years of research on sex/gender and experimental pain perception—part 1: are there really differences between women and men? Pain 2012;153:602-18.  Back to cited text no. 36
    
37.
Shavers VL, Bakos A, Sheppard VB Race, ethnicity, and pain among the U.S. adult population. J Health Care Poor Underserved 2010;21:177-220.  Back to cited text no. 37
    
38.
Stepnowsky CJ Jr, Moore PJ, Dimsdale JE Effect of ethnicity on sleep: complexities for epidemiologic research. Sleep 2003;26:329-32.  Back to cited text no. 38
    
39.
Grandner MA, Williams NJ, Knutson KL, Roberts D, Jean-Louis G Sleep disparity, race/ethnicity, and socioeconomic position. Sleep Med2016;18:7-18.  Back to cited text no. 39
    
40.
Zahari Z, Lee CS, Ibrahim MA, Musa N, Mohd Yasin MA, Lee YY, et al Polymorphisms in the dopamine receptor D2 (DRD2) gene and cold pressor pain sensitivity. Int Med J 2019;26:86-95.  Back to cited text no. 40
    
41.
Zahari Z, Lee CS, Lee YY, Tan SC, Mohamad N, Ismail R Cold-pressor pain responses in healthy opioid-naive males of Malay ethnicity. Int Med J 2018;25:296-8.  Back to cited text no. 41
    
42.
Zahari Z, Lee CS, Ibrahim MA, Musa N, Mohd Yasin MA, Lee YY, et al CYP2D6 gene polymorphisms and cold pressor pain sensitivity among Malay males. Int Med J 2018;25:157-62.  Back to cited text no. 42
    
43.
Zahari Z, Lee CS, Ibrahim MA, Musa N, Mohd Yasin MA, Lee YY, et al. Relationship between ABCB1 polymorphisms and cold pain sensitivity among healthy opioid-naive Malay males. Pain Pract 2017;17:930-40.  Back to cited text no. 43
    
44.
Zahari Z, Lee CS, Lee YY, Ibrahim MA, Musa N, Mohd Yasin MA, et al 118A>G and IVS2+691G>C polymorphisms of OPRM1 gene have no influence on cold-pain sensitivity among healthy opioid-naive Malay males. Int J Pharm Pharm Sci 2016;8:73-80.  Back to cited text no. 44
    
45.
Mohamed Nazar NI Therapeutic drug monitoring in methadone maintenance therapy (MMT): an evaluation of genetic factors influencing clinical outcomes and serum concentrations of methadone. In: Pusat Pengajian Sains Perubatan: Ph. D Thesis. Kelantan, Malaysia: Universiti Sains Malaysia, 2013.  Back to cited text no. 45
    
46.
Zahari Z, Ibrahim MA, Musa N, Tan SC, Mohamad N, Ismail R Sleep quality and OPRM1 polymorphisms: a cross-sectional study among opioid-naive individuals. Brazil J Pharm Sci 2018;54:e17217.  Back to cited text no. 46
    
47.
Buysse DJ, Reynolds CF 3rd, Monk TH, Berman SR, Kupfer DJ The Pittsburgh Sleep Quality Index: a new instrument for psychiatric practice and research. Psychiatry Res 1989;28:193-213.  Back to cited text no. 47
    
48.
Zahari Z, Salleh MR, Zahri Johari MK, Musa N, Ismail R A nested allele-specific multiplex polymerase chain reaction method for the detection of DRD2 polymorphisms. Malays J Med Sci 2011;18:44-57.  Back to cited text no. 48
    
49.
Cohen J A power primer. Psychol Bull 1992;112:155-9.  Back to cited text no. 49
    
50.
Lewis CM, Knight J Introduction to genetic association studies. Cold Spring Harb Protoc 2012;2012:297-306.  Back to cited text no. 50
    
51.
Teh LK, Izuddin AF, M H FH, Zakaria ZA, Salleh MZ Tridimensional personalities and polymorphism of dopamine D2 receptor among heroin addicts. Biol Res Nurs 2012;14:188-96.  Back to cited text no. 51
    
52.
Hibino H, Tochigi M, Otowa T, Kato N, Sasaki T No association of DRD2, DRD3, and tyrosine hydroxylase gene polymorphisms with personality traits in the Japanese population. Behav Brain Funct 2006;2:32.  Back to cited text no. 52
    
53.
Cade BE, Gottlieb DJ, Lauderdale DS, Bennett DA, Buchman AS, Buxbaum SG, et al. Common variants in DRD2 are associated with sleep duration: the care consortium. Hum Mol Genet 2016;25:167-79.  Back to cited text no. 53
    
54.
Anzalone A, Lizardi-Ortiz JE, Ramos M, De Mei C, Hopf FW, Iaccarino C, et al. Dual control of dopamine synthesis and release by presynaptic and postsynaptic dopamine D2 receptors. J Neurosci 2012;32:9023-34.  Back to cited text no. 54
    
55.
Qu WM, Xu XH, Yan MM, Wang YQ, Urade Y, Huang ZL Essential role of dopamine D2 receptor in the maintenance of wakefulness, but not in homeostatic regulation of sleep, in mice. J Neurosci 2010;30:4382-9.  Back to cited text no. 55
    



 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

Top
 
 
  Search
 
    Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
    Access Statistics
    Email Alert *
    Add to My List *
* Registration required (free)  

 
  In this article
    Abstract
   Introduction
    Materials and Me...
   Results
   Discussion
   Conclusion
    References
    Article Tables

 Article Access Statistics
    Viewed165    
    Printed4    
    Emailed0    
    PDF Downloaded2    
    Comments [Add]    

Recommend this journal