Megumi Tagami

Analgesic requirements after major abdominal surgery are associated with OPRM1 gene polymorphism genotype and haplotype

AIMS The association between SNPs of the human OPRM1 gene encoding the micro-opioid receptor and postoperative analgesic requirements in surgical patients remains controversial. Here, we evaluate whether any of the five tag SNPs (A118G, IVS2+G691C, IVS3+G5953A, IVS3+A8449G and TAA+A2109G) representing the four linkage disequilibrium blocks of the OPRM1 gene influences postoperative analgesic requirements. MATERIALS & METHODS We studied 138 adult Japanese patients who underwent major open abdominal surgery under combined general and epidural anesthesia and received continuous postoperative epidural analgesia with opioids. RESULTS The 118G homozygous (GG) patients required 24-h postoperative analgesics more than 118A homozygous (AA) and heterozygous (AG) patients. Tag SNP haplotypes also were associated with 24-h postoperative analgesic requirements. CONCLUSIONS These results suggest that OPRM1 gene tag SNP genotypes and haplotypes can primarily contribute to prediction of postoperative analgesic requirements in individual patients undergoing major open abdominal surgery.

Association between OPRM1 gene polymorphisms and fentanyl sensitivity in patients undergoing painful cosmetic surgery

ABSTRACT Individual differences in sensitivity to fentanyl, a widely used opioid analgesic, can hamper effective pain treatment. Still controversial is whether the single nucleotide polymorphisms (SNPs) of the human OPRM1 gene encoding the μ‐opioid receptor influence the analgesic effects of opioids. We examined associations between fentanyl sensitivity and the two SNPs, A118G and IVS3+A8449G, in the human OPRM1 gene in 280 Japanese patients undergoing painful orofacial cosmetic surgery, including bone dissection. Regarding the A118G SNP in exon 1, in a cold pressor‐induced pain test before surgery, less analgesic effects of fentanyl were shown in subjects carrying the minor G allele of the A118G SNP (median of difference between pain perception latencies before and after fentanyl injection [PPLpost–PPLpre]: 12 s) compared with subjects not carrying this allele (PPLpost–PPLpre: 15 s, p = 0.046). Furthermore, the IVS3+A8449G SNP in intron 3, which represents a complete linkage disequilibrium block with more than 30 SNPs from intron 3 to the 3′ untranslated region, was associated with 24‐h postoperative fentanyl requirements. Subjects carrying the minor G allele of the IVS3+A8449G SNP required significantly less fentanyl for 24‐h postoperative pain control (median: 1.5 μg/kg) compared with subjects not carrying this allele (median: 2.5 μg/kg, p = 0.010). Although further validation is needed, the present findings shed light on the involvement of OPRM1 3′ untranslated region polymorphisms in fentanyl sensitivity in addition to the A118G SNP and open new avenues for personalized pain treatment with fentanyl.

Genome-wide association study identifies a potent locus associated with human opioid sensitivity

Opioids, such as morphine and fentanyl, are widely used as effective analgesics for the treatment of acute and chronic pain. In addition, the opioid system has a key role in the rewarding effects of morphine, ethanol, cocaine and various other drugs. Although opioid sensitivity is well known to vary widely among individual subjects, several candidate genetic polymorphisms reported so far are not sufficient for fully understanding the wide range of interindividual differences in human opioid sensitivity. By conducting a multistage genome-wide association study (GWAS) in healthy subjects, we found that genetic polymorphisms within a linkage disequilibrium block that spans 2q33.3–2q34 were strongly associated with the requirements for postoperative opioid analgesics after painful cosmetic surgery. The C allele of the best candidate single-nucleotide polymorphism (SNP), rs2952768, was associated with more analgesic requirements, and consistent results were obtained in patients who underwent abdominal surgery. In addition, carriers of the C allele in this SNP exhibited less vulnerability to severe drug dependence in patients with methamphetamine dependence, alcohol dependence, and eating disorders and a lower ‘Reward Dependence’ score on a personality questionnaire in healthy subjects. Furthermore, the C/C genotype of this SNP was significantly associated with the elevated expression of a neighboring gene, CREB1. These results show that SNPs in this locus are the most potent genetic factors associated with human opioid sensitivity known to date, affecting both the efficacy of opioid analgesics and liability to severe substance dependence. Our findings provide valuable information for the personalized treatment of pain and drug dependence.

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.

Intravenous midazolam suppresses noxiously evoked activity of spinal wide dynamic range neurons in cats.

The effects of intravenously (IV) administered midazolam on noxiously evoked activity of spinal wide dynamic range (WDR) neurons were investigated in decerebrate, spinal-cord-transected cats. Extracellular, single-unit recordings were measured during stimulation by pinching the receptive field on the hind paw and the effect of midazolam at doses of 0.25, 0.5, 1, 2, and 4 mg/kg were measured. Two series of experiments were performed to characterize the analgesic effects of midazolam. In the first, dose-response experiments (n = 59) demonstrated a dose-dependent suppression of the noxiously evoked activity of spinal WDR neurons after midazolam administration. This effect of midazolam was maximal at a dose of 1 mg/kg IV. The second series of experiments (n = 14) demonstrated that a benzodiazepine antagonist, flumazenil (n = 8), promptly reversed the effect of midazolam, while an opioid antagonist, naloxone (n = 6), had no effect on the effect of midazolam. The present study demonstrates that IV administered midazolam suppresses noxiously evoked activity of spinal WDR neurons that is reversible by a benzodiazepine antagonist. This is consistent with an analgesic action of midazolam. (Anesth Analg 1995;80:58-63)

Zonal differences in effects of HGF/SF and EGF on DNA synthesis in hepatocytes under fed or starved conditions

Zonal differences of DNA synthesis in hepatocytes induced by hepatocyte growth factor and/or scatter factor (HGF/SF) and epidermal growth factor (EGF) were investigated using male Wistar rats under fed or starved conditions. Overall, DNA synthesis was greater in fed rats than in starved rats. The predominance of EGF in periportal hepatocytes (PPH) on zonal DNA synthesis was reversed by starved conditions, but the predominance of HGF/SF on zonal DNA synthesis in perivenous hepatocytes (PVH) was not influenced by nutritional conditions. 125I-labeled EGF and 125I-labeled HGF/SF-receptor binding studies revealed no significant difference between PPH and PVH in starved or fed rats. To investigate the mechanism of the signal transduction pathway, we used genistein, an inhibitor of tyrosine kinase. Genistein had different effects on zonal difference in EGF and HGF/SF. In EGF, 1 microgram/ml genistein abolished zonal differences, but in HGF/SF 1 microgram/ml genistein did not abolish zonal differences. These data suggest that, in contrast to HGF/SF, zonal difference of DNA synthesis by EGF was dependent on nutritional conditions and DNA synthesis induced by HGF/SF and EGF might be related to tyrosine kinase, but the influence of tyrosine kinase on DNA synthesis was different between HGF/SF and EGF.Zonal differences of DNA synthesis in hepatocytes induced by hepatocyte growth factor and/or scatter factor (HGF/SF) and epidermal growth factor (EGF) were investigated using male Wistar rats under fed or starved conditions. Overall, DNA synthesis was greater in fed rats than in starved rats. The predominance of EGF in periportal hepatocytes (PPH) on zonal DNA synthesis was reversed by starved conditions, but the predominance of HGF/SF on zonal DNA synthesis in perivenous hepatocytes (PVH) was not influenced by nutritional conditions.125I-labeled EGF and125I-labeled HGF/SF-receptor binding studies revealed no significant difference between PPH and PVH in starved or fed rats. To investigate the mechanism of the signal transduction pathway, we used genistein, an inhibitor of tyrosine kinase. Genistein had different effects on zonal difference in EGF and HGF/SF. In EGF, 1 μg/ml genistein abolished zonal differences, but in HGF/SF 1 μg/ml genistein did not abolish zonal differences. These data suggest that, in contrast to HGF/SF, zonal difference of DNA synthesis by EGF was dependent on nutritional conditions and DNA synthesis induced by HGF/SF and EGF might be related to tyrosine kinase, but the influence of tyrosine kinase on DNA synthesis was different between HGF/SF and EGF.

Association between 5-hydroxytryptamine 2A receptor gene polymorphism and postoperative analgesic requirements after major abdominal surgery

Although the serotonin (5-hydroxytryptamine (5-HT)) 2A receptor has been reported to be associated with pain, no relationship has been found between single nucleotide polymorphisms in the 5-HT2A receptor gene and analgesic requirements. To clarify the mechanism of individual differences in analgesic requirements, we investigated the relationship between the 5-HT2A 102T/C gene polymorphism and analgesic requirements in 135 patients who underwent major open abdominal surgery and were managed with continuous epidural analgesia with opioids after surgery. Genotyping was performed using polymerase chain reaction-restriction fragment length polymorphism. We found that the 102T/C polymorphism had significant main effects with regard to analgesic requirements. In addition, significant interaction effects were found between the 102T/C polymorphism and sex in terms of analgesic requirements. Among female subjects, patients with the T/T genotype of the 102T/C polymorphism had more analgesic requirements than those with the other genotypes. This finding suggests that the linkage disequilibrium block, which includes the 102T/C polymorphism of the 5-HT2A receptor gene, is involved in individual differences in analgesic requirements in women.

Associations between the orexin (hypocretin) receptor 2 gene polymorphism Val308Ile and nicotine dependence in genome-wide and subsequent association studies

BackgroundMany genetic and environmental factors are involved in the etiology of nicotine dependence. Although several candidate gene variations have been reported by candidate gene studies or genome-wide association studies (GWASs) to be associated with smoking behavior and the vulnerability to nicotine dependence, such studies have been mostly conducted with subjects with European ancestry. However, genetic factors have rarely been investigated for the Japanese population as GWASs. To elucidate genetic factors involved in nicotine dependence in Japanese, the present study comprehensively explored genetic contributors to nicotine dependence by using whole-genome genotyping arrays with more than 200,000 markers in Japanese subjects.ResultsThe subjects for the GWAS and replication study were 148 and 374 patients, respectively. A two-stage GWAS was conducted using the Fagerström Test for Nicotine Dependence (FTND), Tobacco Dependence Screener (TDS), and number of cigarettes smoked per day (CPD) as indices of nicotine dependence. For the additional association analyses, patients who underwent major abdominal surgery, patients with methamphetamine dependence/psychosis, and healthy subjects with schizotypal personality trait data were recruited. Autopsy specimens with various diseases were also evaluated. After the study of associations between more than 200,000 marker single-nucleotide polymorphisms (SNPs) and the FTND, TDS, and CPD, the nonsynonymous rs2653349 SNP (located on the gene that encodes orexin [hypocretin] receptor 2) was selected as the most notable SNP associated with FTND, with a p value of 0.0005921 in the two-stage GWAS. This possible association was replicated for the remaining 374 samples. This SNP was also associated with postoperative pain, the initiation of methamphetamine use, schizotypal personality traits, and susceptibility to goiter.ConclusionsAlthough the p value did not reach a conventional genome-wide level of significance in our two-stage GWAS, we obtained significant results in the subsequent analyses that suggest that the rs2653349 SNP (Val308Ile) could be a genetic factor that is related to nicotine dependence and possibly pain, schizotypal personality traits, and goiter in the Japanese population.

Effects of Acetaldehyde on Action Potentials and Ca2+ Currents in Single Atrial Myocytes from the Bullfrog

Aim: The purpose of the present study was to examine the effects of acetaldehyde on the contractile force and membrane potentials and currents in the bullfrog heart. Methods: Contractile force was recorded using right atrial tissues, and membrane potentials and currents were measured by using whole cell patch clamp methods in right atrial myocytes. Results: Acetaldehyde at 500 µmol/l and 1 mmol/l increased the contractile force significantly. Acetaldehyde at 300 and 500 µmol/l increased the overshoot and the plateau of electrically induced action potentials in a concentration-dependent and reversible manner, while the resting membrane potential did not change. The duration of the action potential (APD90) measured at the 90% repolarization level was shortened. The L-type Ca2+ current (ICa) increased significantly when 300 and 500 µmol/l were applied. The fast transient inward current, the inward rectifying potassium current and the outward delayed-rectifier potassium current were not changed following acetaldehyde application (500 µmol/l or 1 mmol/l). Conclusion: These results suggest that acetaldehyde increased the ICa, thereby increased the contractile force, the overshoot and the plateau of action potentials. The shortening of APD90 may be due to the acceleration of the current decay during the ICa inactivation phase.

Suppressive effect of spinal dorsal-horn neuronal activity by local spinal-cord cooling is reversed by naloxone in cats

AbstractPurpose. The purpose of this study was to assess the effect of local spinal cord cooling on spinal dorsal-horn neuronal activity, with special emphasis on the role of endogenous opioid. Methods. Decerebrate, spinal-cord-transected cats (n= 30) were subjected to local spinal-cord irrigation, using 0.9 N saline solution (15°C; n= 15, and 35°C; n= 15) for 90 min. The extracellular, single-cell activity of spinal dorsal-horn neurons responding to noxious stimulation was recorded. Sixty-one minutes after induction of local spinal-cord irrigation, naloxone (0.1 mg·kg−1) was administered intravenously. Local spinal-cord blood flow was measured using the hydrogen clearance technique. Results. Local spinal cord cooling produced significant suppression of both spontaneous and evoked activity (33.1 ± 7.7% and 31.4 ± 5.5%, respectively; mean ± SE). Naloxone reversed this suppression immediately. Local spinal-cord blood flow was significantly reduced during spinal-cord cooling, but naloxone did not change local spinal-cord blood flow. Conclusion. The results demonstrate that endogenous opioids may play an important role in dorsal-horn neuronal suppression induced by local spinal-cord cooling.