Wenhua Han

Association between KCNJ6 (GIRK2) Gene Polymorphisms and Postoperative Analgesic Requirements after Major Abdominal Surgery

Opioids are commonly used as effective analgesics for the treatment of acute and chronic pain. However, considerable individual differences have been widely observed in sensitivity to opioid analgesics. We focused on a G-protein-activated inwardly rectifying potassium (GIRK) channel subunit, GIRK2, that is an important molecule in opioid transmission. In our initial polymorphism search, a total of nine single-nucleotide polymorphisms (SNPs) were identified in the whole exon, 5′-flanking, and exon-intron boundary regions of the KCNJ6 gene encoding GIRK2. Among them, G-1250A and A1032G were selected as representative SNPs for further association studies. In an association study of 129 subjects who underwent major open abdominal surgery, the A/A genotype in the A1032G SNP and -1250G/1032A haplotype were significantly associated with increased postoperative analgesic requirements compared with other genotypes and haplotypes. The total dose (mean±SEM) of rescue analgesics converted to equivalent oral morphine doses was 20.45±9.27 mg, 10.84±2.24 mg, and 13.07±2.39 mg for the A/A, A/G, and G/G genotypes in the A1032G SNP, respectively. Additionally, KCNJ6 gene expression levels in the 1032A/A subjects were significantly decreased compared with the 1032A/G and 1032G/G subjects in a real-time quantitative PCR analysis using human brain tissues, suggesting that the 1032A/A subjects required more analgesics because of lower KCNJ6 gene expression levels and consequently insufficient analgesic effects. The results indicate that the A1032G SNP and G-1250A/A1032G haplotype could serve as markers that predict increased analgesic requirements. Our findings will provide valuable information for achieving satisfactory pain control and open new avenues for personalized pain treatment.

Association of μ-Opioid Receptor Gene Polymorphism A118G with Alcohol Dependence in a Japanese Population

Ethanol is considered to activate the brain reward system by increasing the release of an endogenous opioid receptor ligand, β-endorphin. The polymorphism A118G in the µ-opioid receptor gene (OPRM1) causes the amino acid change Asn40Asp and has been reported to affect the affinity of the ligand for the receptor. The association of this polymorphism with the vulnerability to alcohol dependence has been studied in many populations, but not yet in Japanese people. In the present study, we compared the frequencies of the polymorphism OPRM1 A118G between patients with alcohol dependence and healthy control subjects living in a Japanese provincial prefecture. We also genotyped a polymorphism, G1510A, in the acetaldehyde dehydrogenase 2 gene (ALDH2), in which the A allele causes poor metabolism of acetaldehyde, a major metabolite of alcohol. Both OPRM1 118G and ALDH2 1510G were significantly associated with alcohol dependence. These results suggest that OPRM1 118G in addition to ALDH2 1510G might be one of the risk factors for alcohol dependence in Japanese people.

Essential Role of NMDA Receptor Channel ε4 Subunit (GluN2D) in the Effects of Phencyclidine, but Not Methamphetamine

Phencyclidine (PCP), a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, increases locomotor activity in rodents and causes schizophrenia-like symptoms in humans. Although activation of the dopamine (DA) pathway is hypothesized to mediate these effects of PCP, the precise mechanisms by which PCP induces its effects remain to be elucidated. The present study investigated the effect of PCP on extracellular levels of DA (DAex) in the striatum and prefrontal cortex (PFC) using in vivo microdialysis in mice lacking the NMDA receptor channel ε1 or ε4 subunit (GluRε1 [GluN2A] or GluRε4 [GluN2D]) and locomotor activity. PCP significantly increased DAex in wildtype and GluRε1 knockout mice, but not in GluRε4 knockout mice, in the striatum and PFC. Acute and repeated administration of PCP did not increase locomotor activity in GluRε4 knockout mice. The present results suggest that PCP enhances dopaminergic transmission and increases locomotor activity by acting at GluRε4.

A Possible Genetic Mechanism Underlying Individual and Interstrain Differences in Opioid Actions: Focus on the Mu Opioid Receptor Gene

Abstract: Individual differences in responses to opioids limit effective pain treatment with these drugs. Identifying the mechanism could help to improve the analgesic effects of them. Since the molecular cloning of the mu opioid receptor (muOR) gene, substantial advances in opioid research have been made, including the discoveries that muOR plays a mandatory role in the analgesic effects of opioids and that the sequence of the muOR gene varies from one individual to another. It is conceivable that the differences in the muOR gene cause individual differences in opioid actions. The present review summarizes the recent advances made in research on human and mouse muOR genes and proposes that the variances in the 3′ untranslated region (39‐UTR) of the muOR gene might participate in the variability of the opioid response.

Association of morphine-induced antinociception with variations in the 5'flanking and 3' untranslated regions of the μ opioid receptor gene in 10 inbred mouse strains

Objective Genetic factors are hypothesized to be involved in interindividual differences in opioid sensitivity. Inbred mouse strains that are genetically different and isogenic within each strain are useful for elucidating the genetic mechanisms underlying the interindividual differences in opioid-induced analgesia. Methods We examined the effects of morphine in 10 inbred mouse strains, including wild-derived strains that have a wide range of genetic diversity, including BLG2, CHD, KJR, MSM, NJL, PGN2, and SWN. We also performed full sequencing of the 5′ flanking region and exons of the mouse μ opioid receptor gene Oprm1 and analyzed the association between genotypes and phenotypes in these mice. Results The effects of morphine on locomotor activation and antinociception varied among the inbred strains. The nucleotide differences that cause amino acid substitutions were not found in the Oprm1 gene in the inbred strains analyzed in this study. In the 5′ flanking region and 3′ untranslated region of the Oprm1 gene, four highly variable regions containing novel short tandem repeat polymorphisms (GA, T, TA, and CA/CT) were identified. The GA, T, and TA repeat numbers were significantly associated with morphine-induced antinociception. Conclusion These results suggest that the short tandem repeats in the 5′ flanking and 3′ untranslated regions of the μ opioid receptor gene are involved in interstrain differences in opioid sensitivity in mice. Wild-derived inbred mouse strains with different numbers of these repeats may be useful models for examining interindividual differences in opioid sensitivity.

Involvement of the 3′ non‐coding region of the mu opioid receptor gene in morphine‐induced analgesia

Abstract  The mu opioid receptor (MOR) is known to play an essential role in morphine‐induced analgesia. MOR‐1 mRNA, the major MOR transcript, possesses a long 3′ untranslated region (3′UTR) in both mouse and human species. The sequence of the MOR‐1 3′UTR, especially that of its 3′ end region, is conserved between mice and humans. In the MOR‐1 3′UTR, AU‐rich elements (AREs) are densely localized at the 3′ end region, suggesting low stability of this mRNA. Numerous putative transcription factor‐binding motifs are located in the 3′ non‐coding regions of the mouse and human MOR genes. The CXBK mouse strain, known as a MOR‐deficient strain, possesses a decreased amount of MOR‐1 mRNA containing an abnormally long MOR‐1 3′UTR with a long nucleotide insertion. This insert might disrupt the stability of the MOR‐1 mRNA or might reduce the transcription of the MOR‐1 mRNA by separating the transcription factor‐binding motifs in the 3′ non‐coding region of the MOR gene, thereby decreasing MOR‐1 mRNA expression and attenuating morphine‐induced analgesia in CXBK mice. These recent findings suggest that the MOR‐1 3′UTR is involved in mRNA expression and in the difference in response to morphine. This possible genetic mechanism may provide a good starting point for designing effective pain treatments with opiates.

Inhibitory Role of Inducible cAMP Early Repressor (ICER) in Methamphetamine-Induced Locomotor Sensitization

Background The inducible cyclic adenosine monophosphate (cAMP) early repressor (ICER) is highly expressed in the central nervous system and functions as a repressor of cAMP response element-binding protein (CREB) transcription. The present study sought to clarify the role of ICER in the effects of methamphetamine (METH). Methods and Findings We tested METH-induced locomotor sensitization in wildtype mice, ICER knockout mice, and ICER I-overexpressing mice. Both ICER wildtype mice and knockout mice displayed increased locomotor activity after continuous injections of METH. However, ICER knockout mice displayed a tendency toward higher locomotor activity compared with wildtype mice, although no significant difference was observed between the two genotypes. Moreover, compared with wildtype mice, ICER I-overexpressing mice displayed a significant decrease in METH-induced locomotor sensitization. Furthermore, Western blot analysis and quantitative real-time reverse transcription polymerase chain reaction demonstrated that ICER overexpression abolished the METH-induced increase in CREB expression and repressed cocaine- and amphetamine-regulated transcript (CART) and prodynorphin (Pdyn) expression in mice. The decreased CART and Pdyn mRNA expression levels in vivo may underlie the inhibitory role of ICER in METH-induced locomotor sensitization. Conclusions Our data suggest that ICER plays an inhibitory role in METH-induced locomotor sensitization.