Association Of CYP3AP-44>A Gene Polymorphiam With Fentanyl Intravenous Analgesic Effect

Background and ObjectiveFentanyl, a synthetic opioid analgesic with potent and rapid analgesic effect, is commonly used clinically in postoperative pain management in China. The consumption of fentanyl required to achieve adequate analgesia postoperatively varies markedly among individuals, which challenges the safe use of fentanyl for analgesia therapy. This mechanism responsible for the variability is due, at least in large part, to genetic polymorphisms of drug-metabolizing enzymes involved in fentanyl disposition. Fentanyl is metabolized by the oxidative enzyme cytochrome P450 (CYP) 3A, mainly by CYP3A4/5 in liver microsomes in vivo after intravenous administration. The human CYP3A locus contains a pseudogene CYP3AP1. Previously reported CYP3AP1 and CYP3A4 variants as well as CYP3AP1 and CYP3A5 variants were in linkage disequilibrium. Moreover, the CYP3AP1-44G>A genotype has been shown to be associated with CYP3A expression and it has therefore been suggested that CYP3AP1-44G>A may be considered a strong indicator of low CYP3A metabolic activity. Our previous study have found genetic polymorphisms of CYP3A4*1G and CYP3A5*3 affected fentanyl analgesic effect. However, there was no reports on the association of CYP3AP1-44G>A polymorphism with fentanyl analgesic effect in Chinese gynecologic patients. We conducted this study to observe the impact of CYP3AP1 -44G>A polymorphism on fentanyl effect for intravenous analgesia. The present study provides an important foundation and theoretical evidence for individualization of medication in the pain treatment.Materials and Methods1. Patient ProfileA total of 203 women undergoing selective abdominal total hysterectomy or myomectomy under general anesthesia were recruited in the Department of Anesthesiology, First Affiliated Hospital, Zhengzhou University. The study protocol was approved by the Institutional Ethics Committee of Zheng Zhou University, and all subjects gave their written informed consent. All patients were of Han nationality. Patients were 20 to 50 years old, within±20% of ideal body weight, and had a physical status ofⅠorⅡaccording to the American Society of Anesthesiologists. Exclusion criteria included a history of psychiatric diseases, cardiovascular diseases, hepatic or renal dysfunction, diabetes mellitus, alcohol or drug abuse, or chronic analgesic use. Patients who were pregnant or nursing were excluded. Patients who had used drugs known to inhibit or induce the expression of CYP3A enzymes in the previous 2 weeks were also excluded.2. Anesthetic Procedure and Postoperative Pain AssessmentPatients did not receive premedication. Blood pressure monitoring, electrocardiography and pulse oximetry were performed in the operating room. An intravenous cannula was inserted into a forearm vein. A standardized general anesthesia technique was used for all patients. General anesthesia was induced with midazolam, propofol and remifentanil, injected intravenously. Neuromuscular block was produced with atracurium, administered intravenously. Patients were intubated, and mechanical ventilation was adjusted to maintain end-tidal CO2 between 35 and 40 mmHg. Then atracurium was administered in repeated boluses to maintain muscle relaxation. During the operation, remifentanil, and propofol were infused intravenously to maintain anesthesia. At the end of the surgery, neuromuscular blockade was reversed by neostigmine and atropine. Patients were extubated if awake and with adequate spontaneous breathing. A handheld slide rule-type visual analog scale (VAS) with values from 0 (no pain) to 10 mm (unbearable pain) was used to assess the immediate postoperative pain as soon as patients were conscious and able to talk. For VAS score>3, fentanyl,20μg/5 min, was given intravenously. For VAS score≤3, patients immediately began to receive fentanyl by patient-controlled intravenous analgesia (PCIA) administered intravenously.PCIA with fentanyl was provided for adequate analgesia postoperatively as soon as the patient was alert enough to use the PCIA pump, The analgesic solution in the PCA pump (6300 CADD-Legacy, USA) contained fentanyl,1 mg, and droperidol,5 mg, in 100 ml saline. The program of the PCIA pump was set as 2 ml bolus of fentanyl solution per time, lock time 5 min, background infusion rate 0.5 ml/h, and maximal fentanyl infusion rate 145μg/h. The fentanyl dose delivered was recorded by the pump automatically.3. Assessment of fentanyl analgesic effectPain at rest during PCIA was assessed by the VAS. VAS score≤3 was defined as satisfactory analgesia. An alternative analgesic was chosen to establish pain control with VAS score> 3, even under the maximum dose of fentanyl, and data for such patients were excluded from the analysis. The VAS, fentanyl consumption and occurrence of any adverse effects in the first and second 24 h postoperatively were recorded.4. Genotyping for CYP3AP1-44G>AGenomic DNA was extracted from whole blood samples taken by a conventional phenol-chloroform method. Purified genomic DNA was stored at -70℃until use. PCR followed by restriction fragment length polymorphism was used for genotyping CYP3AP1 -44G>A. The results for each genotype were confirmed in randomly selected individuals by direct sequence analysis.5. Evaluation of CYP3A activityEthylenediaminetetraacetic-acid-containing tubes were used to take blood samples. Plasma was separated immediately. Level of midazolam (MDZ) and its metabolite 1'-hydroxymidazolam (1'-OH-MDZ) was determined by liquid chromatography-mass spectrometry (LC-MS). CYP3A activity was measured by plasma ratio of 1'-OH-MDZ to MDZ at 1 h after intravenous administration of midazolam,0.1 mg/kg, for induction of anesthesia.6. Statistical analysisStatistical analysis involved use of SPSS v.11.0 for Windows (SPSS Inc, Chicago, IL, USA). The chi-square test was used to verify Hardy-Weinberg equilibrium. Data for numerical variables are expressed as mean and SD after assessment for normality with the Kolmogorov-Smirnov test. One-way ANOVA was used to assess significant differences among groups for normally distributed numerical variables, and the Kruskal-Wallis rank sum test was used for numerical variables with skewed distributions. Between-group comparisons such as for the VAS score involved the Mann-Whitney test U test. Data for fentanyl dose delivered via PCIA were analysed for the groups by one-way ANOVA with post-hoc analysis. The incidences of any adverse effects were analyzed using Chi-square test or Fisher exact test. A P< 0.05 (two-sided) was considered statistically significant.Results1. General informationIn total,203 women were included. The VAS score immediately after surgery was 5.5±1.6. At 24 h after surgery, it was 2.3±0.8. The fentanyl consumption was 361.9±206.7μg and 198.4±111.8μg in the postoperative first and second 24 h, respectively. The incidence of postoperative nausea and vomiting was 28.6%. The incidences of pruritus and mild sedation in our study were 0.49% and 1.48%, respectively.2. Distribution of CYP3AP1-44G>A alleleThe overall frequency of CYP3AP1-44G>A allele in gynecologic patients was 71.4%. The allele frequency was in Hardy-Weinberg equilibrium (P>0.05), which indicates that the patient pool was likely representative of the population being studied. The allelic frequency of CYP3AP1-44G>A was similar to that reported in Indian (67.8%), Africian American (64.6%) and South Asian (63.5%). (P>0.05) 3. Association of CYP3AP1 -44G>A polymorphism with CYP3A activity and fentanyl analgesic effectPatients were divided into three genotypes, GG, GA and AA, according to the genotype of CYP3AP1 -44G>A. There were no significant differences in general information among the three genotype groups (P>0.05). No statistical differences in postoperative VAS pain scores, fentanyl consumption at 24 h amd CYP3A activity were detected across genotypes (P>0.05). There was no significant difference in incidences of adverse events among the different genotype groups (P>0.05), either.Conclusions1. The frequency of CYP3A4*1 G allele in gynecologic patients is 71.4%.2. CYP3AP1-44G>A is not associated with CYP3A activity and fentanyl analgesic effect. It is not a genetic marker that can affect the fentanyl analgesic effect in gynecologic patients.