Association Of PPARα Rs4253728G>A Genetic Polymorphism With Fentanyl Intravenous Analgesic Effect

BackgroundFentanyl is a widely used synthetic narcotic opioid. It works fast, maintains ashort time, has no histamine release effect and slightly influences breathing andcirculation function. Therefore, fentanyl has been the most common opioid forinduction and maintenance of anesthesia and postoperative intravenous analgesia inour country at present. However, clinical studies have found that the significant doseof fentanyl for postoperative pain control varies greatly among individuals. Researchconfirmed that genetic factor was the main reason that caused the difference. It affectthe pharmacokinetics and pharmacodynamics of opioids by changing the metabolicenzymes activity or expression level in vivo. Fentanyl is metabolized predominantlyinto norepinephrine fentanyl by the cytochrome P4503A4(CYP3A4) in the liver. Theindividual differences of fentanyl pharmacokinetics prompt that the difference of theintravenous analgesia effect is closely related with CYP3A4. Genetic variation maycontribute to the interindividual variability in drug metabolism. Our previousexperiment reported that CYP3A4*1G is a high-frequency allele in Chinese, whichchanged the fentanyl pharmacokinetic parameters in vivo and influenced its analgesiceffect. Currently, the reports about the regulation of CYP3A4*1G geneticpolymorphism on CYP3A4are controversial. In addition, recent studies suggestedthat the majority of CYP3A4single nucleotide polymorphisms (SNP) mutation frequency was relatively low and it had slightly impact on the phenotype. An obviousbut less investigated possibility is that trans-acting genes encoding regulatorytranscription factors or proteins that modulate mono-oxygenase activity in other wayscontribute to CYP3A4variation.Peroxisome proliferator-activated receptor-alpha (PPARα) is a ligand-activatedtranscriptional factor that belongs to the subfamily of nuclear receptors. Recentresearch reported that PPARα influenced CYP3A4enzyme activity, among whichrs4253728single nucleotide polymorphism was one of the most influential factors on it.Due to the importance of PPARα in the regulation of the CYP3A4enzyme activity, weconducted this study to determine the impact of PPARα rs4253728geneticpolymorphism on fentanyl intravenous analgesia effect. The present study aims atproviding an theoretical evidence and clinical foundation for individualizedmedication in postoperative pain management.Materials and Methods1Patients ProfileBetween March2013and November2013, one hundred and sixty-eight femalepatients aged20to50-year-old, American Society of Anesthesiologists (ASA)physical status of I or II. All patients were within±20%of ideal body weight index anddiagnosed as uterine fibroids and underwent selective abdominal myomectomy or totalhysterectomy were enrolled. All patients underwent patient-controlled intravenousanalgesia (PCIA) after the surgery. Patients were divided into three groups accordingto their genotypes. Exclusion criteria: known history of alcohol or drug abuse;significant hepatic or renal dysfunction, combine with cardiovascular disease, mentaldisease, diabetes mellitus or chronic analgesic use; patients who had consumed drugsknown to inhibit or induce the expression of CYP3A4enzymes one month prior to thesurgery; pregnancy or nursing.2Anesthesia and Postoperative AnalgesiaThe study was approved by the Institutional Ethics Committee of the FirstAffiliated Hospital of Zhengzhou University. All patients and their family members signed informed consents. All patients did not obtain any preoperative drugs. After theburglary, continuous monitoring of electrocardiograph (ECG), heart rate (HR),non-invasive blood pressure (NIBP), respiratory rate (RR) and pulse oxygensaturation (SpO2). A standardized total intravenous anesthesia (TIVA) protocol wasimplemented for all patients: for induction of anesthesia, intravenous midazolam0.1mg/kg, remifentanil2μg/kg, propofol0.5mg/kg and succinylcholine1.5mg/kg.The patients were assigned to receive6to8mg/kg/h propofol and0.1to0.2μg/kg/min remifentanil to maintain anaesthesia. Atracurium0.6mg/kg wasadministered intravenously as an initial dosage immediately after the trachealintubation was confirmed and intermittently administered0.1to0.2mg/kg atracuriumto maintain muscle relaxants. At the end of surgery stopped transfusing all intravenousanesthetics. Pull out the endotracheal tube when patients’ consciousness, spontaneousbreathing and myodynamia recovered.Visual analogue scale(VAS) was delivered immediately after extubation. If theVAS>3, intravenous fentanyl20ug per5min until the VAS≤3, recorded thetitration dosage of fentanyl. PCIA was administered when the VAS score≤3. PCIAdevice: a computer controlled infusion pump (CADD-Legacy6300). Drug formula:droperidol5mg and fentanyl1mg in100ml normal saline. PCIA settings:background dose0.5ml/h, extra dose2ml/h, lockout time5min, maximum dosage145μg/h. Successful analgesia was defined as the VAS score≤3. If the fentanylconsumption had achieved the maximum limit (145g/h) and it still could not meet thedemand of analgesia (VAS score>3), other analgesic drugs would be supplementedand the case was weed out from the experiment.3Analgesia effect evaluationRecorded the VAS score immediately after extubation,24h,48h after thesurgery. Incidence of any postoperative adverse effects such as dizzy, nausea, sedation,vomiting, respiratory depression and skin itching were recorded.4Genotyping assays for PPARα polymorphismsBlood samples were collected during the surgery. DNA was extracted through astandard phenol/chloroform procedure. Gene segment was amplified using the polymerase chain reaction (PCR). Genotyping of PPARα rs4253728allele wasconducted by direct sequence analysis technique.5Evaluation of CYP3A4activityWe chose midazolam (MDZ) as the probe drug detecting the CYP3A4enzymeactivity and use the ratio of1-hydroxy midazolam (1’-OH MDZ) to MDZ as measureindex of CYP3A4enzyme activity. Test method: intravenous midazolam0.1mg/kg forinduction of anesthesia. Peripheral venous blood sample was collected from eachpatient60minutes after induction of anesthesia. The plasma concentration of1’-OHMDZ and MDZ were measured by liquid chromatography mass spectrometry(LC-MS)procedure.6Statistical analysisSPSS17.0software was used for statistical analyses. Values were reported asx s. Chi-square test was used to verify Hardy-Weinberg equilibrium. One-wayanalysis of variance was used to assess whether significant differences exist betweenthe three genotypes. Data for postoperative fentanyl consumption were compared usingone-way analysis of variance between groups. Multiple comparisons was performedafter adjusted for weight, age and remifentanil consumption during the surgery. Theincidences of any adverse effect were analyzed using Fisher exact test or Chi-squaretest. A two tailed P-value of <0.05was considered statistically significant.Results1General informationWe included168female patients. The VAS pain scores immediately afterextubation,24h,48h after the surgery were (5.9±1.3)，（2.3±0.6），(1.1±0.5). All patientsachieved effective postoperative analgesia. The postoperative fentanyl consumption inthe first and second24h were（379.5±213.6）μ g and（182.3±51.7） μg. Threepatients experienced giddy, twenty-seven patients experienced nausea and vomiting,three patients experienced mild sedation and one patient experienced pruritus. Theincidence of postoperative giddy, nausea and vomiting, mild sedation and pruritus were1.79%，27.98%，1.79%，0.60%, respectively. None of the patients meet other adverse reactions in our postoperative follow-up.2Frequency of PPARα rs4253728(G>A) alleleThe frequency of PPARα rs4253728(G>A) allele in Chinese gynecologicpatients was20.4%. The Gene mutation frequency was in accordance withHardy-Weinberg equilibrium (P>0.05). The frequency of PPARα rs4253728(G>A)allele in this study was higher than that of African-Americans(20.4%vs7.2%) and itwas lower than that of Caucasians(20.4%vs27.3%). The allelic frequency washomogeneous to what had been reported in the cited reference (P>0.05).3Effect of PPARα genetic polymorphism on CYP3A4enzyme activity andfentanyl postoperative analgesic effectAccording to the genotypes, the patients were divided into three groups: GG, GAand AA. For the purpose of this study we compared age, gender, weight, height, bodymass index, ASA status, diagnosis, the operation time, the differences were notstatistically significant (P>0.05). The differences of VAS pain scores detectedimmediately after extubation,24h and48h after the surgery were not statisticallysignificant (P>0.05) across genotypes. Three groups of patients’ fentanyl consumptionat the first24h were not statistically significant(P>0.05). In the second24h, fentanylconsumption was lower in AA than those of GG and GA(P<0.05). The difference ofCYP3A4enzyme activity among three groups was statistically significant(P<0.05).The incidence of adverse reactions among the different genotype groups was not notstatistically significant (P>0.05).Conclusions1．The frequency of PPARα rs4253728(G>A) allele in Chinese gynecologicpatients is20.4%.2．PPARα rs4253728(G>A) genetic polymorphism is associated with CYP3A4enzyme activity or fentanyl intravenous analgesic effect. It is a genetic marker thatmay affect the difference of fentanyl intravenous analgesic effect in Chinesegynecologic patients.