Contribution of CYP2D6 Functional Activity to Oxycodone Efficacy in Pain Management: Genetic Polymorphisms, Phenoconversion, and Tissue-Selective Metabolism

Validation studies and multiomics analysis of Zhx2 as a candidate quantitative trait gene underlying brain oxycodone metabolite (oxymorphone) levels and behavior

Sensitivity to the subjective reinforcing properties of opioids has a genetic component and can predict addiction liability of opioid compounds. We previously identified Zhx2 as a candidate gene underlying increased brain concentration of the oxycodone (OXY) metabolite oxymorphone (OMOR) in BALB/cJ (J) versus BALB/cByJ (By) females that could increase OXY state-dependent reward. A large structural intronic variant is associated with a robust reduction of Zhx2 expression in J mice, which we hypothesized enhances OMOR levels and OXY addiction-like behaviors. We tested this hypothesis by restoring the Zhx2 loss-of-function in J mice (mouse endogenous retroviral element knockout) and modeling the loss-of-function variant through knocking out the Zhx2 coding exon (exon 3 knockout [E3KO]) in By mice and assessing brain OXY metabolite levels and behavior. Consistent with our hypothesis, Zhx2 E3KO females showed an increase in brain OMOR levels and OXY-induced locomotor activity. However, contrary to our hypothesis, state-dependent expression of OXY conditioned place preference decreased in E3KO females and increased in E3KO males. We also overexpressed Zhx2 in the livers and brains of J mice and observed Zhx2 overexpression in select brain regions that was associated with reduced OXY state-dependent learning. Integrative transcriptomic and proteomic analysis of E3KO mice identified astrocyte function, cell adhesion, extracellular matrix properties, and endothelial cell functions as pathways influencing brain OXY metabolite concentration and behavior. These results support Zhx2 as a quantitative trait gene underlying brain OMOR concentration that is associated with changes in OXY behavior and implicate potential quantitative trait mechanisms that together inform our overall understanding of Zhx2 in brain function. SIGNIFICANCE STATEMENT: This study validated Zhx2 as a gene whose dysfunction increases brain levels of a highly potent and addictive metabolite of oxycodone, oxymorphone, in a female-specific manner. This result has broad implications for understanding the role of oxycodone metabolism and brain oxymorphone levels in the addiction liability of oxycodone (the active ingredient in OxyContin) and highlights the need for the study of sex differences in opioid metabolism as it relates to the addiction liability of opioids and opioid use disorder.

Validating the accuracy of mathematical model-based pharmacogenomics dose prediction with real-world data

OBJECTIVE

The study aims to verify the usage of mathematical modeling in predicting patients' medication doses in association with their genotypes versus real-world data.

METHODS

The work relied on collecting, extracting, and using real-world data on dosing and patients' genotypes. Drug metabolizing enzymes, i.e., cytochrome CYP 450, were the focus. A total number of 1914 subjects from 26 studies were considered, and CYP2D6 and CYP2C19 gene polymorphisms were used for the verification.

RESULTS

Results show that the mathematical model was able to predict the reported optimal dosing of the values provided in the considered studies. Predicting patients' optimal doses circumvents trial and error in patients' treatments.

DISCUSSION

The authors discussed the advantages of using a mathematical model in patients' dosing and identified multiple issues that would hinder the usability of raw data in the future, especially in the era of artificial intelligence (AI). The authors recommend that researchers and healthcare professionals use simple descriptive metabolic activity terms for patients and use allele activity scores for drug dosing rather than phenotype/genotype classifications.

CONCLUSION

The authors verified that a mathematical model could assist in providing data for better-informed decision-making in clinical settings and drug research and development.

Role Assessment of Water-Soluble Pharmaceutical Form of Phosphatidylcholine on the Catalytic Activity of Cytochrome P450 2C9 and 2D6

This study aimed to investigate whether the water-soluble pharmaceutical form of phosphatidylcholine nanoparticles (wPC) stimulated the catalytic activity of CYP enzymes 2C9 and 2D6. We have shown that electroenzymatic CYP2C9 catalysis to nonsteroidal anti-inflammatory drug naproxen as a substrate was enhanced from 100% to 155% in the presence of wPC in media. Electroenzymatic CYP2D6 activity in the presence of the adrenoceptor-blocking agent bisoprolol as a substrate was elevated significantly from 100% to 144% when wPC was added to potassium phosphate buffer solution. These results indicate the ability of wPC in the form of the phospholipid ultra-small nanoparticles to work as a membrane additive and crowding agent to accelerate the electroenzymatic reactions of cytochrome P450.

Use of CYP2D6 Inhibitors with CYP2D6 Opioids: Association with Emergency Department Visits for Pain

Hydrocodone, tramadol, codeine, and oxycodone are commonly prescribed opioids that rely on activation by cytochrome P450 2D6 (CYP2D6). CYP2D6 inhibitors can significantly decrease CYP2D6 activity, leading to reduced generation of active metabolites, and impairing pain control. To understand this impact, we assessed emergency department (ED) visits in patients initiating these CYP2D6-dependent opioids while on CYP2D6-inhibitor antidepressants vs. antidepressants that do not inhibit CYP2D6. This retrospective cohort study included adult patients prescribed CYP2D6-dependent opioids utilizing electronic health records data from the University of Florida Health (2015-2021). The association between ED visits and inhibitor exposure was tested using multivariable logistic regression. The primary analysis had 12,118 patients (72% female; mean (SD) age, 55 (13.4)) in the hydrocodone/tramadol/codeine cohort and 5,547 patients (64% female; mean (SD) age, 53.6 (14.2)) in the oxycodone cohort. Hydrocodone/tramadol/codeine-treated patients exposed to CYP2D6-inhibitor antidepressants (n = 7,043) had a higher crude rate of pain-related ED visits than those taking other antidepressants (n = 5,075) (3.28% vs. 1.87%), with an adjusted odds ratio (aOR) of 1.75 (95% CI: 1.36 to 2.24). Similarly, in the oxycodone cohort, CYP2D6-inhibitor antidepressant-exposed individuals (n = 3,206) had a higher crude rate of ED visits than individuals exposed to other antidepressants (n = 2,341) (5.02% vs. 3.37%), with aOR of 1.70 (95% CI: 1.27-2.27). Similar findings were observed in secondary and sensitivity analyses. Our findings suggest patients with concomitant use of hydrocodone/tramadol/codeine or oxycodone and CYP2D6 inhibitors have more frequent ED visits for pain, which may be due to inadequate pain control.

Validation studies and multi-omics analysis of Zhx2 as a candidate quantitative trait gene underlying brain oxycodone metabolite (oxymorphone) levels and behavior

Sensitivity to the subjective reinforcing properties of opioids has a genetic component and can predict addiction liability of opioid compounds. We previously identified Zhx2 as a candidate gene underlying increased brain concentration of the oxycodone (OXY) metabolite oxymorphone (OMOR) in BALB/cJ (J) versus BALB/cByJ (By) females that could increase OXY state-dependent reward. A large structural intronic variant is associated with a robust reduction of Zhx2 expression in J mice, which we hypothesized enhances OMOR levels and OXY addiction-like behaviors. We tested this hypothesis by restoring the Zhx2 loss-of-function in Js (MVKO) and modeling the loss-of-function variant through knocking out the Zhx2 coding exon (E3KO) in Bys and assessing brain OXY metabolite levels and behavior. Consistent with our hypothesis, Zhx2 E3KO females showed an increase in brain OMOR levels and OXY-induced locomotor activity. However, contrary to our hypothesis, state-dependent expression of OXY-CPP was decreased in E3KO females and increased in E3KO males. We also overexpressed Zhx2 in the livers and brains of Js and observed Zhx2 overexpression in select brain regions that was associated with reduced OXY state-dependent learning. Integrative transcriptomic and proteomic analysis of E3KO mice identified astrocyte function, cell adhesion, extracellular matrix properties, and endothelial cell functions as pathways influencing brain OXY metabolite concentration and behavior. These results support Zhx2 as a quantitative trait gene underlying brain OMOR concentration that is associated with changes in OXY behavior and implicate potential quantitative trait mechanisms that together inform our overall understanding of Zhx2 in brain function.

Implementing a pragmatic clinical trial to tailor opioids for chronic pain on behalf of the IGNITE ADOPT PGx investigators

Chronic pain is a prevalent condition with enormous economic burden. Opioids such as tramadol, codeine, and hydrocodone are commonly used to treat chronic pain; these drugs are activated to more potent opioid receptor agonists by the hepatic CYP2D6 enzyme. Results from clinical studies and mechanistic understandings suggest that CYP2D6-guided therapy will improve pain control and reduce adverse drug events. However, CYP2D6 is rarely used in clinical practice due in part to the demand for additional clinical trial evidence. Thus, we designed the ADOPT-PGx (A Depression and Opioid Pragmatic Trial in Pharmacogenetics) chronic pain study, a multicenter, pragmatic, randomized controlled clinical trial, to assess the effect of CYP2D6 testing on pain management. The study enrolled 1048 participants who are taking or being considered for treatment with CYP2D6-impacted opioids for their chronic pain. Participants were randomized to receive immediate or delayed (by 6 months) genotyping of CYP2D6 with clinical decision support (CDS). CDS encouraged the providers to follow the CYP2D6-guided trial recommendations. The primary study outcome is the 3-month absolute change in the composite pain intensity score assessed using Patient-Reported Outcomes Measurement Information System (PROMIS) measures. Follow-up will be completed in July 2024. Herein, we describe the design of this trial along with challenges encountered during enrollment.

Chronic Pain Management in a CYP2D6 Poor Metabolizer: A Case Report for Oxycodone

The objective of this case report is to illustrate pharmacogenomics (PGx)-guided oxycodone treatment, given the conflicting data on the analgesic response from oxycodone in Cytochrome P450 (CYP)2D6 poor metabolizers (PMs). PGx-guided therapy can help improve treatment outcomes. This case report describes a 58-year-old patient who was prescribed oxycodone for chronic pain management. The patient presented with a history of inadequate pain control despite analgesic treatment with oxycodone (morphine milliequivalent [MME] = 22.5). Pharmacogenetic testing revealed that the patient was a CYP2D6 Poor Metabolizer (PM), which may shed light on the observed lack of analgesic response to oxycodone. The clinical pharmacist recommended switching to an alternative opioid not metabolized via the CYP2D6 pathway. The patient was subsequently switched to hydromorphone (MME = 16), resulting in improved pain control and fewer side effects. The newer hydromorphone dose accounted for a 30% MME dose reduction. The patient's initial average and worst pain score were 7 and 9 out of 10, respectively, per the numeric rating scale (NRS). Upon follow-up with the patient in two weeks, her average and worst pain scores improved to 3 and 3.5 out of 10, respectively, per the NRS. Further PGx testing results led to an overall positive outcome, such as her willingness to participate in physical therapy as a result of improved pain scores. This case highlights the importance of considering individual variability in drug metabolism when prescribing medications, particularly opioids such as oxycodone, to ensure optimal therapeutic outcomes and minimize the risk of adverse events in CYP2D6 PMs.

Exploring the impact of CYP2D6 and UGT2B7 gene-drug interactions, and CYP-mediated DDI on oxycodone and oxymorphone pharmacokinetics using physiologically-based pharmacokinetic modeling and simulation

Oxycodone is one of the most commonly used opioids to treat moderate to severe pain. It is metabolized mainly by CYP3A4 and CYP2D6, while only a small fraction of the dose is excreted unchanged into the urine. Oxymorphone, the metabolite primarily formed by CYP2D6, has a 40- to 60-fold higher mu-opioid receptor affinity than the parent compound. While CYP2D6-mediated gene-drug-interactions (GDIs) and drug-drug interactions (DDIs) are well-studied, they only account for a portion of the variability in oxycodone and oxymorphone exposure. The combined impact of CYP2D6-mediated GDIs and DDIs, CYP3A4-mediated DDIs, and UGT2B7 GDIs is not fully understood yet and hard to study in head-to-head clinical trials given the relatively large number of scenarios. Instead, we propose the use of a physiologically-based pharmacokinetic model that integrates available information on oxycodone's metabolism to characterize and predict the impact of DDIs and GDIs on the exposure of oxycodone and its major, pharmacologically-active metabolite oxymorphone. To this end, we first developed and verified a PBPK model for oxycodone and its metabolites using published clinical data. The verified model was then applied to determine the dose-exposure relationship of oxycodone and oxymorphone stratified by CYP2D6 and UGT2B7 phenotypes respectively, and administered perpetrators of CYP-based drug interactions. Our simulations demonstrate that the combination of CYP2D6 UM and a UGT2B7Y (268) mutation may lead to a 2.3-fold increase in oxymorphone exposure compared to individuals who are phenotyped as CYP2D6 NM / UGT2B7 NM. The extent of oxymorphone exposure increases up to 3.2-fold in individuals concurrently taking CYP3A4 inhibitors, such as ketoconazole. Inhibition of the CYP3A4 pathway results in a relative increase in the partial metabolic clearance of oxycodone to oxymorphone. Oxymorphone is impacted to a higher extent by GDIs and DDIs than oxycodone. We predict oxymorphone exposure to be highest in CYP2D6 UMs/UGT2B7 PMs in the presence of ketoconazole (strong CYP3A4 index inhibitor) and lowest in CYP2D6 PMs/UGT2B7 NMs in the presence of rifampicin (strong CYP3A4 index inducer) covering a 55-fold exposure range.

Oxycodone: A Current Perspective on Its Pharmacology, Abuse, and Pharmacotherapeutic Developments

Oxycodone, a semisynthetic derivative of naturally occurring thebaine, an opioid alkaloid, has been available for more than 100 years. Although thebaine cannot be used therapeutically due to the occurrence of convulsions at higher doses, it has been converted to a number of other widely used compounds that include naloxone, naltrexone, buprenorphine, and oxycodone. Despite the early identification of oxycodone, it was not until the 1990s that clinical studies began to explore its analgesic efficacy. These studies were followed by the pursuit of several preclinical studies to examine the analgesic effects and abuse liability of oxycodone in laboratory animals and the subjective effects in human volunteers. For a number of years oxycodone was at the forefront of the opioid crisis, playing a significant role in contributing to opioid misuse and abuse, with suggestions that it led to transitioning to other opioids. Several concerns were expressed as early as the 1940s that oxycodone had significant abuse potential similar to heroin and morphine. Both animal and human abuse liability studies have confirmed, and in some cases amplified, these early warnings. Despite sharing a similar structure with morphine and pharmacological actions also mediated by the μ-opioid receptor, there are several differences in the pharmacology and neurobiology of oxycodone. The data that have emerged from the many efforts to analyze the pharmacological and molecular mechanism of oxycodone have generated considerable insight into its many actions, reviewed here, which, in turn, have provided new information on opioid receptor pharmacology. SIGNIFICANCE STATEMENT: Oxycodone, a μ-opioid receptor agonist, was synthesized in 1916 and introduced into clinical use in Germany in 1917. It has been studied extensively as a therapeutic analgesic for acute and chronic neuropathic pain as an alternative to morphine. Oxycodone emerged as a drug with widespread abuse. This article brings together an integrated, detailed review of the pharmacology of oxycodone, preclinical and clinical studies of pain and abuse, and recent advances to identify potential opioid analgesics without abuse liability.

Association of CYP2D6 genotype predicted phenotypes with oxycodone requirements and side effects in children undergoing surgery

Background

Oxycodone is a commonly used oral opioid in children for treating postoperative pain. Highly polymorphic gene CYP2D6 metabolizes oxycodone into its more potent metabolite, oxymorphone. We hypothesized that altered activity due to CYP2D6 polymorphisms will influence oxycodone requirements {relative oxycodone use [oxycodone morphine equivalents (MEq)/total MEq] to maintain analgesia} (primary outcome) and risk for oxycodone induced side-effects such as respiratory depression (RD) and emesis (secondary outcomes). We also explored the influence of genotype availability and provider guidance on oral opioid prescription patterns.

Methods

Patients who underwent Nuss procedure and spine fusion with CYP2D6 genotyping results available preoperatively were included. Data on demographics, genotypes, oral opioids, pain scores, RD and emesis were collected. Univariate and multivariable regression for comparison of CYP2D6 genotype predicted poor, ultrarapid, intermediate metabolizers (PM, UM and IM) phenotype with normal metabolizers (NM) for outcomes were performed. Stratified logistic regression was conducted in low (oxycodone/total MEq <0.5) and high (and oxycodone/total MEq >0.5) oxycodone use groups for RD and emesis, with application of firth correction due to quasi-complete separations. Breslow-Day test was used to evaluate odds ratios for prescribing genotype directed opioid between control group (2012-15) (where providers were alerted to genotyping results availability but not directed to use them while prescribing) and genotype directed groups (2016-18) (where providers were directed to use the genotyping results available to them while prescribing oxycodone after surgery).

Results

Of 193 subjects (age 15.9±0.25 years, 28.5% female, 93.78% White; 101 NM, 76 IM, 10 PM and 6 UM), 77.72% underwent pectus surgery. CYP2D6 phenotype was associated with oxycodone MEq/total MEq requirements (P<0.001). Both PM and UM phenotypes had lower oxycodone requirements compared to NM [-0.316 (SE 0.098), P=0.005 and -0.432 (SE 0.113), P<0.001 respectively]. CYP2D6 phenotype was associated with RD in high use oxycodone group (P=0.018) but not low use oxycodone groups (P=0.634). No phenotype association was found for emesis. Oxycodone was prescribed to 91.24% of NM/IM vs. 66.67% of PM/UM (P=0.129) in control group and 94.64% of NM/IM vs. 28.57% of PM/UM (P<0.001) in the genotype-directed group. PM/UM phenotypes in genotype directed group had a lower chance of being prescribed oxycodone (effect size =-2.775; SE 1.566; P=0.076).

Conclusions

Our findings suggest CYP2D6 genotypes are associated with oxycodone requirements for analgesia and may influence risk for RD. Genotype availability and guidance likely influence oral opioid prescription pattern after surgery. Our findings are limited by small sample size for UM/PM groups.

Utilizing Pharmacogenomics Results to Determine Opioid Appropriateness and Improve Pain Management in a Patient with Osteoarthritis

The opioid epidemic in the United States has exposed the need for providers to limit opioid dispensing and identify at-risk patients prior to prescribing opioids. With pharmacogenomic testing, clinicians can analyze hundreds of medications—including commonly prescribed opioids—against genetic results to understand and predict risk and response. Moreover, knowledge of genotypic variants and altered function can help decrease trial and error prescribing, identify patients at-risk for adverse drug events, and improve pain control. This patient case demonstrates how pharmacogenomic test results identified drug–gene interactions and provided insight about a patient’s inadequate opioid therapy response. With pharmacogenomic information, the patient’s healthcare team discontinued opioid therapy and selected a more appropriate regimen for osteoarthritis (ie, celecoxib), resulting in improved pain control and quality of life.

Effect of Combined Methamphetamine and Oxycodone Use on the Synaptic Proteome in an In Vitro Model of Polysubstance Use

Polysubstance use (PSU) generally involves the simultaneous use of an opioid along with a stimulant. In recent years, this problem has escalated into a nationwide epidemic. Understanding the mechanisms and effects underlying the interaction between these drugs is essential for the development of treatments for those suffering from addiction. Currently, the effect of PSU on synapses-critical points of contact between neurons-remains poorly understood. Using an in vitro model of primary neurons, we examined the combined effects of the psychostimulant methamphetamine (METH) and the prescription opioid oxycodone (oxy) on the synaptic proteome using quantitative mass-spectrometry-based proteomics. A further ClueGO analysis and Ingenuity Pathway Analysis (IPA) indicated the dysregulation of several molecular functions, biological processes, and pathways associated with neural plasticity and structural development. We identified one key synaptic protein, Striatin-1, which plays a vital role in many of these processes and functions, to be downregulated following METH+oxy treatment. This downregulation of Striatin-1 was further validated by Western blot. Overall, the present study indicates several damaging effects of the combined use of METH and oxy on neural function and warrants further detailed investigation into mechanisms contributing to synaptic dysfunction.

Patient Perceptions and Potential Utility of Pharmacogenetic Testing in Chronic Pain Management and Opioid Use Disorder in the Camden Opioid Research Initiative

Pharmacogenetics (PGx) has the potential to improve opioid medication management. Here, we present patient perception data, pharmacogenetic data and medication management trends in patients with chronic pain (arm 1) and opioid use disorder (arm 2) treated at Cooper University Health Care in Camden City, NJ. Our results demonstrate that the majority of patients in both arms of the study (55% and 65%, respectively) are open to pharmacogenetic testing, and most (66% and 69%, respectively) believe that genetic testing has the potential to improve their medical care. Our results further support the potential for CYP2D6 PGx testing to inform chronic pain medication management for poor metabolizers (PMs) and ultrarapid metabolizers (UMs). Future efforts to implement PGx testing in chronic pain management, however, must address patient concerns about genetic test result access and genetic discrimination.

CYP2D6 phenotypes and opioid metabolism: the path to personalized analgesia

INTRODUCTION

Opioids play a fundamental role in chronic pain, especially considering when 1 of 5 Europeans adults, even more in older females, suffer from it. However, half of them do not reach an adequate pain relief. Could pharmacogenomics help to choose the most appropriate analgesic drug?

AREAS COVERED

The objective of the present narrative review was to assess the influence of cytochrome P450 2D6 (CYP2D6) phenotypes on pain relief, analgesic tolerability, and potential opioid misuse. Until December 2021, a literature search was conducted through the MEDLINE, PubMed database, including papers from the last 10 years. CYP2D6 plays a major role in metabolism that directly impacts on opioid (tramadol, codeine, or oxycodone) concentration with differences between sexes, with a female trend toward poorer pain control. In fact, CYP2D6 gene variants are the most actionable to be translated into clinical practice according to regulatory drug agencies and international guidelines.

EXPERT OPINION

CYP2D6 genotype can influence opioids' pharmacokinetics, effectiveness, side effects, and average opioid dose. This knowledge needs to be incorporated in pain management. Environmental factors, psychological together with genetic factors, under a sex perspective, must be considered when you are selecting the most personalized pain therapy for your patients.

Pharmacogenomic Testing and Patient Perception Inform Pain Pharmacotherapy

(1) Background: Chronic pain is one of the most common reasons for individuals to seek medications. Historically, opioids have been the mainstay of chronic pain management. However, in some patient populations, opioids fail to demonstrate therapeutic efficacy, whereas in other populations, opioids may cause toxic effects, even at lower doses. Response to pain medication is affected by many factors, including an individual's genetic variations. Pharmacogenomic testing has been designed to help achieve optimal treatment outcomes. This study aimed at assessing the impact of CYP2D6 pharmacogenomic testing on physicians' choice in prescribing chronic pain medications and patient pain control. (2) Methods: This retrospective study reviewed 107 patient charts from a single site pain management center. All 107 patients received pharmacogenomic testing. The outcomes of interest were confirmation that the optimal pain medication is being administered or a change in the chronic pain medication is warranted as a result of the pharmacogenomic testing. The main independent variable was the pharmacogenomic test result. Other independent variables included patient gender, race, and comorbidities. The retrospective study was reviewed and approved by the Touro College and University System IRB, HSIRB1653E. (3) Results: Patients self-reported pain intensity on a scale of 1-10 before and after pharmacogenomic testing. Then, 100% of patients in the retrospective study were tested for their pain pharmacogenomic profile. Of the 107 patients participating in the study, more than 50% had their medications altered as a result of the pharmacogenomic testing. The percentage of patients with intense pain were decreased post-pharmacogenomic testing (5.6%) as compared to pre-pharmacogenomic testing (10.5%). Patients with intense, moderate, and mild pain categories were more likely to receive changes in pain medications. In contrast, patients with severe pain were less likely to receive a change in pain medication. Hispanic ethnicity was associated with a statistically significantly decrease in a pain scale category. Illegal drug abuse was associated with a decrease in pain scale category. Change in medication dose was associated with a decrease in pain scale category. (4) Conclusion: In this retrospective study, implementation of pharmacogenomic testing demonstrated significant benefits to patients with intense pain undergoing treatment.