Metabolism of Fentanyl and Acetylfentanyl in Human-Induced Pluripotent Stem Cell-Derived Hepatocytes

In vitro metabolism of seven arolyl-derived fentanyl-type new psychoactive substances

Over the past decade, fentanyl-type new psychoactive substances (F-NPS) have emerged as the most representative synthetic opioids in third-generation drugs. These substances are characterized by their "low" fatal dose and parent drug levels in biological matrices, "fast" rates of derivatization and metabolism, and "many" derivatization sites and analogs. The low levels of parent fentanyl NPS in biological matrices complicate their detection, necessitating the use of characteristic metabolites as biomarkers for forensic analysis. Moreover, the ongoing emergence of arolyl-derived F-NPS further challenges forensic laboratories in accurately identifying the parent drug from its metabolites. To address this issue, in this study, the in vitro phase I metabolism of seven arolyl-derived F-NPS was studied using a human liver microsome model. Metabolites were analyzed by liquid chromatography-ion trap tandem time-of-flight mass spectrometry. Using density functional theory, the structural characteristics and their effects on amide hydrolysis, N-dealkylation, and oxidation metabolism were clarified. Amide hydrolysis was influenced by the positive charge of the carbonyl carbon and the 2-substituent effect on the aryl groups. N-dealkylation, β-monohydroxylation, N-oxidation, and phenyl group monohydroxylation in the tail were less affected by structural changes in the head. The former two were the major metabolites and exhibited competition. The relative contents of N-oxidation and phenyl group monohydroxylation in the tail were relatively stable at 4% and 13%, respectively. Furthermore, the β-C adjacent to the nitrogen on the piperidine ring was susceptible to oxidation, leading to the formation of the monohydroxylation metabolite. The results of this study may enhance our understanding of the in vitro metabolism of arolyl-derived F-NPS, and potentially all F-NPS, providing important data and theoretical support for predicting their in vivo metabolism in the future.

The synthetic opioid fentanyl increases HIV replication in macrophages

BACKGROUND

The illicit use of synthetic opioids such as fentanyl has led to a serious public health crisis in the US. People with opioid use disorder are more likely to contract infections such as HIV and viral hepatitis and experience more severe disease. While several drugs of abuse are known to enhance viral replication and suppress immunologic responses, the effects of synthetic opioids on HIV pathogenesis have not been investigated thoroughly. Thus, we examined the impact of fentanyl on HIV replication and chemokine receptor expression in the U937 cell line and monocyte-derived macrophages (MDMs).

METHODS

U937 cells were exposed to varying concentrations of fentanyl. Expression levels of the CXCR4 and CCR5 chemokine receptors were measured in cell lysates. HIV p24 antigen was quantified in culture supernatants by ELISA, and HIV proviral DNA was quantified in cells using SYBR real-time PCR targeting the pol gene. RNAseq was performed to characterize cellular gene regulation in the presence of fentanyl.

RESULTS

Fentanyl induced HIV p24 expression and proviral DNA levels in U937 cells and in primary MDMs. The opioid antagonist naltrexone blocked the effect of fentanyl and reversed the expression of HIV protein and proviral DNA. Fentanyl led to a non-significant decrease in CXCR4 and CCR5 protein levels in U937 cells. RNA sequencing identified several differentially expressed genes in cells infected with HIV and exposed to fentanyl compared to infected cells with no drug exposure. Several microRNAs were also differentially expressed upon fentanyl exposure but not at a statistically significant level.

CONCLUSION

These data demonstrate that the synthetic opioid fentanyl can promote HIV replication in macrophages. As higher HIV levels lead to accelerated disease progression and a higher risk of transmission to others, further research is needed to better understand opioid-virus interactions and to develop new and/or optimized treatment strategies for people living with HIV and opioid use.

Balancing acts: The dual faces of fentanyl in medicine and public health

Fentanyl is a potent synthetic opioid widely used in medicine for its effective analgesic properties, particularly in surgical procedures and in the treatment of severe, chronic pain. In recent decades, however, there has been a worrying increase in the illicit use of fentanyl, particularly in North America. This rise in illicit use is concerning because fentanyl is associated with polydrug abuse, which adds layers of complexity and dangerous. This review provides a comprehensive examination of fentanyl, focusing on its synthesis and medical use. It also discusses the significance of the piperidine ring in medicinal chemistry as well as the critical role of fentanyl in pain management and anesthesia. Furthermore, it addresses the challenges associated with the abuse potential of fentanyl and the resulting public health concerns. The study aims to strike a balance between the clinical benefits and risks of fentanyl by advocating for innovative uses while addressing public health issues. It examines the chemistry, pharmacokinetics and pharmacodynamics of fentanyl and highlights the importance of personalized medicine in the administration of opioids. The review underscores the necessity of continuous research and adaptation in both clinical use and public health strategies.

Comparative analysis of the metabolites and biotransformation pathways of fentanyl in the liver and brain of zebrafish

The rise of fentanyl has introduced significant new challenges to public health. To improve the examination and identification of biological samples in cases of fentanyl misuse and fatalities, this study utilized a zebrafish animal model to conduct a comparative investigation of the metabolites and biotransformation pathways of fentanyl in the zebrafish's liver and brain. A total of 17 fentanyl metabolites were identified in the positive ion mode using ultra-high-pressure liquid chromatography Q Exactive HF Hybrid Quadrupole-Orbitrap mass spectrometry (UHPLC-QE HF MS). Specifically, the zebrafish's liver revealed 16 fentanyl metabolites, including 6 phase I metabolites and 10 phase II metabolites. Conversely, the zebrafish's brain presented fewer metabolites, with only 8 detected, comprising 6 phase I metabolites and 2 phase II metabolites. Notably, M'4, a metabolite of dihydroxylation, was found exclusively in the brain, not in the liver. Through our research, we have identified two specific metabolites, M9-a (monohydroxylation followed by glucuronidation) and M3-c (monohydroxylation, precursor of M9-a), as potential markers of fentanyl toxicity within the liver. Furthermore, we propose that the metabolites M1 (normetabolite) and M3-b (monohydroxylation) may serve as indicators of fentanyl metabolism within the brain. These findings suggest potential strategies for extending the detection window and enhancing the efficiency of fentanyl detection, and provide valuable insights that can be referenced in metabolic studies of other new psychoactive substances.

β'-Phenylfentanyl Metabolism in Primary Human Hepatocyte Incubations: Identification of Potential Biomarkers of Exposure in Clinical and Forensic Toxicology

From 2014 onwards, illicit fentanyl and analogues have caused numerous intoxications and fatalities worldwide, impacting the demographics of opioid-related overdoses. The identification of cases involving fentanyl analogues is crucial in clinical and forensic settings to treat patients, elucidate intoxications, address drug use disorders and tackle drug trends. However, in analytical toxicology, the concentration of fentanyl analogues in biological matrices is low, making their detection challenging. Therefore, the identification of specific metabolite biomarkers is often required to document consumption. β'-Phenylfentanyl (N-phenyl-N-[1-(2-phenylethyl)-4-piperidinyl]-benzenepropanamide) is a fentanyl analogue that was first detected in Sweden in 2017 and has recently reemerged onto the American illicit drug market. There is little data available on β'-phenylfentanyl effects and toxicokinetics and its metabolism is yet to be studied. We aimed to investigate β'-phenylfentanyl human metabolism to identify potential biomarkers of use. To assist in β'-phenylfentanyl metabolite identification, a list of putative reactions was generated using in silico predictions with GLORYx freeware. β'-phenylfentanyl was incubated with cryopreserved 10-donor-pooled human hepatocytes, analyses were performed by liquid chromatography-high-resolution tandem mass spectrometry (LC-HRMS-MS) and data were processed using a partially automated targeted/untargeted approach with Compound Discoverer. We identified 26 metabolites produced by N-dealkylation, oxidation, hydroxylation, O-glucuronidation, O-methylation and combinations thereof. We suggest β'-phenylnorfentanyl (N-phenyl-N-4-piperidinyl-benzenepropanamide) and further metabolites 1-oxo-N-phenyl-N-4-piperidinyl-benzenepropanamide and 1-hydroxy-N-phenyl-N-4-piperidinyl-benzenepropanamide as major biomarkers of β'-phenylfentanyl use. In silico predictions were mostly wrong, and β'-phenylfentanyl metabolic fate substantially differed from that of a closely related analogue incubated in the same conditions, highlighting the value of the experimental assessment of new psychoactive substance human metabolism. In vivo data are necessary to confirm the present results. However, the present results may be necessary to help analytical toxicologists identify β'-phenylfentanyl-positive cases to provide authentic samples.

Hepatic and renal toxicities and metabolism of fentanyl analogues in rats

New synthetic opioids continue to emerge in the illicit market, and among them, fentanyl analogues pose a serious threat to the public health with their abuse and trafficking. We investigated the toxicity of fentanyl analogues on the liver and kidneys mediated by the µ-opioid receptor (MOR). Our study focused on 4-fluoro-isobutyrylfentanyl (4F-iBF), which is classified as a "narcotic" in Japan; structurally similar analogues 4-chloro-isobutyrylfentanyl (4Cl-iBF) and isobutyrylfentanyl (iBF) were also investigated. Rats that were intraperitoneally administered 4F-iBF (5 mg/kg (12.3 μmol/kg)) or iBF (12.3 μmol/kg) displayed hepatic and renal ischemic-like damage, but 4Cl-iBF (12.3 μmol/kg) did milder renal damage only. We found that the agonist activity of 4F-iBF, at MORs was approximately 7.2 times that of 4Cl-iBF, and that pretreatment with MOR antagonist naltrexone (0.8 mg/kg) alleviated liver and kidney injuries caused by 4F-iBF. These results suggested that 4F-iBF might cause ischemic damage to the liver and kidneys, induced by respiratory depression mediated by MORs. Furthermore, to elucidate the metabolism of fentanyl analogues, we investigated the change over time in the amount of 4F-iBF, 4Cl-iBF, iBF (6.15 μmol/kg, respectively), and their respective metabolites in serum after intraperitoneal administration to rats. The results showed that in 24-h post-dose serum, 4Cl-iBF and iBF were substantially eliminated while 4F-iBF remained at about 30% of the maximum level, and each of the N-dephenylethylated metabolites of 4F-iBF, 4Cl-iBF, and iBF was detected in 2-h post-dose serum. The results from this study revealed information on the hepatic and renal toxicities and metabolism related to fentanyl analogues.

The synthetic opioid fentanyl increases HIV replication and chemokine co-receptor expression in vitro

The US is experiencing a major public health crisis that is fueled by the illicit use of synthetic opioids including fentanyl. While several drugs of abuse can enhance viral replication and/or antagonize immune responses, the impact of specific synthetic opioids on HIV pathogenesis is poorly understood. Thus, we evaluated the effects of fentanyl on HIV replication in vitro. HIV-susceptible or HIV-expressing cell lines were incubated with fentanyl. HIV p24 synthesis and chemokine receptor levels were quantified by ELISA in culture supernatants and cell lysates, respectively. Addition of fentanyl resulted in a dose-dependent increase in HIV replication. Fentanyl enhanced expression of the HIV chemokine co-receptors CXCR4 and CCR5 and caused a dose-dependent decrease in cell viability. The opioid antagonist naltrexone blocked the effect of fentanyl on HIV replication and CCR5 receptor levels but not CXCR4 receptor levels. TLR9 expression was induced by HIV; however, fentanyl inhibited TLR9 expression in a dose-dependent manner. These data demonstrate that the synthetic opioid fentanyl can promote HIV replication in vitro. As increased HIV levels are associated with accelerated disease progression and higher likelihood of transmission, additional research is required to enhance the understanding of opioid-virus interactions and to develop new and/or optimized treatment strategies for persons with HIV and opioid use disorder.

Fentanyl enhances HIV infection in vitro

Acquired immunodeficiency syndrome (AIDS) caused by Human immunodeficiency virus type 1 (HIV-1) has a high tendency among illicit drug abusers. Recently, it is reported that abuse of fentanyl, a potent synthetic μ receptor-stimulating opioid, is an independent risk factor for HIV-1 infection. However, the mechanism of action in augmenting HIV-1 infection still remains elusive. In this study, we found that fentanyl enhanced infection of HIV-1 in MT2 cells, primary macrophages and Jurkat C11 cells. Fentanyl up-regulated CXCR4 and CCR5 receptor expression, which facilitated the entry of virion into host cells. In addition, it down-regulated interferon-β (IFN-β) and interferon-stimulated genes (APOBEC3F, APOBEC3G and MxB) expression in MT2 cells. Our findings identify an essential role of fentanyl in the positive regulation of HIV-1 infection via the upregulation of co-receptors (CXCR4/CCR5) and downregulation of IFN-β and ISGs, and it may have an important role in HIV-1 immunopathogenesis.

The metabolism of valerylfentanyl using human liver microsomes and zebrafish larvae

Valerylfentanyl, a novel synthetic opioid less potent than fentanyl, has been reported in biological samples, but there are limited studies on its pharmacokinetic properties. The goal of this study was to elucidate the metabolism of valerylfentanyl using an in vitro human liver microsome (HLM) model compared with an in vivo zebrafish model. Nineteen metabolites were detected with N-dealkylation-valeryl norfentanyl and hydroxylation as the major metabolic pathways. The major metabolites in HLMs were also detected in 30 day postfertilization zebrafish. An authentic liver specimen that tested positive for valerylfentanyl, among other opioids and stimulants, revealed the presence of a metabolite that shared transitions and retention time as the hydroxylated metabolite of valerylfentanyl but could not be confirmed without an authentic standard. 4-Anilino-N-phenethylpiperidine (4-ANPP), a common metabolite to other fentanyl analogs, was also detected. In this study, we elucidated the metabolic pathway of valerylfentanyl, confirmed two metabolites using standards, and demonstrated that the zebrafish model produced similar metabolites to the HLM model for opioids.

In Vitro and In Vivo Analysis of Fentanyl and Fentalog Metabolites using Hyphenated Chromatographic Techniques: A Review

Fentanyl and fentanyl analogues (also called fentalogs) are used as medical prescriptions to treat pain for a long time. Apart from their pharmaceutical applications, they are misused immensely, causing the opioid crisis. Fentanyl and its analogues are produced in clandestine laboratories and sold over dark Web markets to different parts of the world, leading to a rise in the death rate due to drug overdose. This is because the users are unaware of the lethal effects of the newer forms of fentalogs. Unlike other drugs, these fentalogs cannot be detected easily, as very little data are available, and this is one of the major reasons for the risk of life-threatening poisoning or deaths. Hence, rigorous studies of these drugs and their possible metabolites are required. It is also necessary to develop techniques for the detection of minute traces of metabolites in biological fluids. This Review provides an overview of the application of hyphenated chromatographic techniques used to analyze multiple novel fentalogs, using in vivo and in vitro methods. The article focuses on the metabolites formed in phase I and phase II processes in biological specimens obtained in recent cases of drug abuse and overdose deaths that could be useful for the detection and differentiation of multiple fentalogs.

In silico prediction, LC-HRMS/MS analysis, and targeted/untargeted data-mining workflow for the profiling of phenylfentanyl in vitro metabolites

Illicit fentanyl and analogues have been involved in many fatalities and cases of intoxication across the United States over the last decade, and are becoming a health concern in Europe. New potent analogues emerge onto the drug market every year to circumvent analytical detection and legislation, and little pharmacological/toxicological data are available when the substances first appear. However, pharmacokinetic data are crucial to determine specific biomarkers of consumption in clinical and forensic settings, considering the low active doses and the rapid metabolism of fentanyl analogues. Phenylfentanyl is a novel analogue that was first detected in seized material in 2017, and little is currently known about this substance and its metabolism. We studied phenylfentanyl metabolic fate using in silico predictions with GLORYx freeware, human hepatocyte incubations, and liquid chromatography-high-resolution tandem mass spectrometry (LC-HRMS/MS). We applied a specific targeted/untargeted workflow using data-mining software to allow the rapid and partially automated screening of LC-HRMS/MS raw data. Approximately 90,000 substances were initially individuated after 3-h incubation with hepatocytes, and 115 substances were automatically selected for a manual check by the operators. Finally, 13 metabolites, mostly produced by N-dealkylation, amide hydrolysis, oxidation, and combinations thereof, were identified. We suggest phenylnorfentanyl as the main biological marker of phenylfentanyl use, and we proposed the inclusion of its fragmentation pattern in mzCloud and HighResNPS online libraries. Other major metabolites include N-Phenyl-1-(2-phenylethyl)-4-piperidinamine (4-ANPP), 1-(2-phenylethyl)-4-piperidinol, and other non-specific metabolites. Phase II transformations were infrequent, and the hydrolysis of the biological samples is not required to increase the detection capability of non-conjugated metabolites. The overall workflow is easily adaptable for the metabolite profiling of other novel psychoactive substances.

Thirteen Cases of Valeryl Fentanyl in Michigan: A Call for Expanding Opioid Testing

ABSTRACT

In this report, we describe 13 cases of drug overdose in Michigan in which valeryl fentanyl was found in postmortem blood. Valeryl fentanyl is a schedule I opioid that is rarely found in drug overdoses in the United States. Although little data exist on the mortality and morbidity associated with valeryl fentanyl, its molecular structure indicates that it would be less potent than fentanyl.When analyzing blood samples for valeryl fentanyl, samples from peripheral sites were sometimes negative for quantitative levels; however, samples from central sites in the same decedent were positive. This could indicate unique pharmacokinetics for valeryl fentanyl, which could have implications for other fentanyl analogs. Given the paucity of pharmacodynamic information, the prohibition of its use, the potential to buttress law enforcement efforts in monitoring drug trafficking trends, and to determine the efficacy of current regulations, laboratories should test for valeryl fentanyl. When testing for valeryl fentanyl, and likely other fentanyl analogs, the site of sample collection is important: central sources of blood are preferred to peripheral sources.

Untargeted Metabolomics in Forensic Toxicology: A New Approach for the Detection of Fentanyl Intake in Urine Samples

The misuse of fentanyl, and novel synthetic opioids (NSO) in general, has become a public health emergency, especially in the United States. The detection of NSO is often challenged by the limited diagnostic time frame allowed by urine sampling and the wide range of chemically modified analogues, continuously introduced to the recreational drug market. In this study, an untargeted metabolomics approach was developed to obtain a comprehensive "fingerprint" of any anomalous and specific metabolic pattern potentially related to fentanyl exposure. In recent years, in vitro models of drug metabolism have emerged as important tools to overcome the limited access to positive urine samples and uncertainties related to the substances actually taken, the possible combined drug intake, and the ingested dose. In this study, an in vivo experiment was designed by incubating HepG2 cell lines with either fentanyl or common drugs of abuse, creating a cohort of 96 samples. These samples, together with 81 urine samples including negative controls and positive samples obtained from recent users of either fentanyl or "traditional" drugs, were subjected to untargeted analysis using both UHPLC reverse phase and HILIC chromatography combined with QTOF mass spectrometry. Data independent acquisition was performed by SWATH in order to obtain a comprehensive profile of the urinary metabolome. After extensive processing, the resulting datasets were initially subjected to unsupervised exploration by principal component analysis (PCA), yielding clear separation of the fentanyl positive samples with respect to both controls and samples positive to other drugs. The urine datasets were then systematically investigated by supervised classification models based on soft independent modeling by class analogy (SIMCA) algorithms, with the end goal of identifying fentanyl users. A final single-class SIMCA model based on an RP dataset and five PCs yielded 96% sensitivity and 74% specificity. The distinguishable metabolic patterns produced by fentanyl in comparison to other opioids opens up new perspectives in the interpretation of the biological activity of fentanyl.

Identification of herbal components as TRPA1 agonists and TRPM8 antagonists

Transient receptor potential (TRP) channels are non-selective cation channels that are implicated in analgesia, bowel motility, wound healing, thermoregulation, vasodilation and voiding dysfunction. Many natural products have been reported to affect the activity of TRP channels. We hypothesize that numerous traditional herbal medicines (THMs) might exert their pharmacological activity through modulating the activity of TRP channels. The present study aimed to evaluate the effects of flavonoid aglycones and their glycosides, which are the main components of many THMs, on the TRP channel subtypes. A Ca²⁺ influx assay was performed using recombinant human TRPA1, TRPV1, TRPV4 and TRPM8 cell lines. Our findings showed that flavonoid aglycones and glycycoumarin activated TRPA1. In particular, isoflavone and chalcone compounds displayed potent TRPA1 agonistic activity. Furthermore, flavone aglycones showed concomitant potent TRPM8 inhibiting activity. Indeed, flavone, isoflavone aglycones, non-prenylated chalcones and glycycoumarin were found to be TRPM8 inhibitors. Hence, flavonoid aglycones metabolized by lactase-phlorizin hydrolase and β-glucosidase in the small intestine or gut microbiota of the large intestine could generate TRPA1 agonists and TRPM8 antagonists.

The synthetic opioid fentanyl enhances viral replication in vitro

The US is in the midst of a major drug epidemic fueled in large part by the widespread recreational use of synthetic opioids such as fentanyl. Persons with opioid use disorder are at significant risk for transmission of injection-associated infections such as hepatitis B virus (HBV) and hepatitis C virus (HCV). Commonly abused substances may antagonize immune responses and promote viral replication. However, the impact of synthetic opioids on virus replication has not been well explored. Thus, we evaluated the impact of fentanyl and carfentanil using in vitro systems that replicate infectious viruses. Fentanyl was used in cell lines replicating HBV or HCV at concentrations of 1 ng, 100 ng, and 10 ug. Viral protein synthesis was quantified by ELISA, while apoptosis and cell death were measured by M30 or MTT assays, respectively. HCV replicative fitness was evaluated in a luciferase-based system. RNAseq was performed to evaluate cellular gene regulation in the presence of fentanyl. Low dose fentanyl had no impact on HCV replication in Huh7.5JFH1 hepatocytes; however, higher doses significantly enhanced HCV replication. Similarly, a dose-dependent increase in HCV replicative fitness was observed in the presence of fentanyl. In the HepG2.2.15 hepatocyte cell line, fentanyl caused a dose-dependent increase in HBV replication, although only a higher doses than for HCV. Addition of fentanyl resulted in significant apoptosis in both hepatocyte cell lines. Cell death was minimal at low drug concentrations. RNAseq identified a number of hepatocyte genes that were differentially regulated by fentanyl, including those related to apoptosis, the antiviral / interferon response, chemokine signaling, and NFκB signaling. Collectively, these data suggest that synthetic opioids promote viral replication but may have distinct effects depending on the drug dose and the viral target. As higher viral loads are associated with pathogenesis and virus transmission, additional research is essential to an enhanced understanding of opioid-virus pathogenesis and for the development of new and optimized treatment strategies.

Structure Elucidation of Urinary Metabolites of Fentanyl and Five Fentanyl Analogs using LC-QTOF-MS, Hepatocyte Incubations and Synthesized Reference Standards

Fentanyl analogs constitute a particularly dangerous group of new psychoactive compounds responsible for many deaths around the world. Little is known about their metabolism, and studies utilizing liquid chromatography–quadrupole time-of-flight mass spectrometry (LC–QTOF-MS) analysis of hepatocyte incubations and/or authentic urine samples do not allow for determination of the exact metabolite structures, especially when it comes to hydroxylated metabolites. In this study, seven motifs (2-, 3-, 4- and β-OH as well as 3,4-diOH, 4-OH-3-OMe and 3-OH-4-OMe) of fentanyl and five fentanyl analogs, acetylfentanyl, acrylfentanyl, cyclopropylfentanyl, isobutyrylfentanyl and 4F-isobutyrylfentanyl were synthesized. The reference standards were analyzed by LC–QTOF-MS, which enabled identification of the major metabolites formed in hepatocyte incubations of the studied fentanyls. By comparison with our previous data sets, major urinary metabolites could tentatively be identified. For all analogs, β-OH, 4-OH and 4-OH-3-OMe were identified after hepatocyte incubation. β-OH was the major hydroxylated metabolite for all studied fentanyls, except for acetylfentanyl where 4-OH was more abundant. However, the ratio 4-OH/β-OH was higher in urine samples than in hepatocyte incubations for all studied fentanyls. Also, 3-OH-4-OMe was not detected in any hepatocyte samples, indicating a clear preference for the 4-OH-3-OMe, which was also found to be more abundant in urine compared to hepatocytes. The patterns appear to be consistent across all studied fentanyls and could serve as a starting point in the development of methods and synthesis of reference standards of novel fentanyl analogs where nothing is known about the metabolism.

Analysis of 17 fentanyls in plasma and blood by UPLC-MS/MS with interpretation of findings in surgical and postmortem casework

The opioid crisis is linked to an increased misuse of fentanyl as well as fentanyl analogs that originate from the illicit drug market. Much of our current understanding of fentanyl and fentanyl analog use in our communities comes from postmortem toxicology findings. In the clinical settings of addiction medicine and pain management, where the opioid abuse potential is high, the use of fentanyl, as well as specific fentanyl analogs, may be underestimated due to limited plasma testing and limited availability of assays with suitable analytical sensitivity and selectivity to detect misuse of fentanyls. We report plasma and blood assays for 17 fentanyls (these include fentanyl, fentanyl analogs, fentanyl metabolites and synthetic precursors) in clinical, and medical examiner, casework. A mixed-mode solid phase extraction of diluted plasma or precipitated blood was optimized for maximum recovery of the fentanyls with minimized matrix effects. Analysis was performed using a Waters ACQUITY UPLC I-Class interfaced with a Waters Xevo TQ-S micro tandem quadrupole mass spectrometer. Method parameters were optimized and validated for precision, accuracy, carryover, linearity and matrix effects. Application studies were performed in postmortem blood obtained in 44 fentanyl-related fatalities and in serial plasma samples from 18 surgical patients receiving intravenous fentanyl therapy while undergoing parathyroidectomy. Fentanyls found in postmortem cases included fentanyl, norfentanyl, despropionyl-fentanyl (4-ANPP), beta-hydroxy fentanyl (β-OH fentanyl), acetyl fentanyl, acetyl norfentanyl, methoxyacetyl fentanyl, furanyl fentanyl, cyclopropyl fentanyl, and para-fluorobutyryl fentanyl, with fentanyl, norfentanyl, 4-ANPP and β-OH fentanyl predominating in frequency. Fentanyl concentrations ranged from 0.2 to 56 ng/mL and fentanyl was nearly always found with 4-ANPP, norfentanyl and β-OH fentanyl. Concentrations of other fentalogs ranged from <1 to 84 ng/mL (extrapolated). In the surgical cases, fentanyl was detected and quantified along with norfentanyl and β-OH fentanyl, but without detection of 4-ANPP in any of the samples. The association and relative concentrations of β-OH fentanyl, fentanyl and norfentanyl in the postmortem and clinical studies indicated a metabolic, rather than an illicit, source of β-OH fentanyl.

Interpol review of toxicology 2016-2019

This review paper covers the forensic-relevant literature in toxicology from 2016 to 2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/content/download/14458/file/Interpol%20Review%20.Papers%202019.pdf.

LC-QTOF-MS Identification of Major Urinary Cyclopropylfentanyl Metabolites Using Synthesized Standards

Cyclopropylfentanyl is a fentanyl analog implicated in 78 deaths in Europe and over 100 deaths in the United States, but toxicological information including metabolism data about this drug is scarce. The aim of this study was to provide the exact structure of abundant and unique metabolites of cyclopropylfentanyl along with synthesis routes. In this study, metabolites were identified in 13 post-mortem urine samples using liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS). Samples were analyzed with and without enzymatic hydrolysis, and seven potential metabolites were synthesized in-house to provide the identity of major metabolites. Cyclopropylfentanyl was detected in all samples, and the most abundant metabolite was norcyclopropylfentanyl (M1) that was detected in 12 out of 13 samples. Reference materials were synthesized (synthesis routes provided) to identify the exact structure of the major metabolites 4-hydroxyphenethyl cyclopropylfentanyl (M8), 3,4-dihydroxyphenethyl cyclopropylfentanyl (M5) and 4-hydroxy-3-methoxyphenethyl cyclopropylfentanyl (M9). These metabolites are suitable urinary markers of cyclopropylfentanyl intake as they are unique and detected in a majority of hydrolyzed urine samples. Minor metabolites included two quinone metabolites (M6 and M7), not previously reported for fentanyl analogs. Interestingly, with the exception of norcyclopropylfentanyl (M1), the metabolites appeared to be between 40% and 90% conjugated in urine. In total, 11 metabolites of cyclopropylfentanyl were identified, including most metabolites previously reported after hepatocyte incubation.

Evaluation of Acetylfentanyl Following Suspected Heroin Overdose When Complicated by the Presence of Toxic Fentanyl and Alprazolam Concentrations

A 34-year-old male was reported to be snorting a white powder that was believed to contain heroin. Toxicological analysis revealed free morphine (356 μg/L), fentanyl (34.7 μg/L), alprazolam (64.9 μg/L), and acetylfentanyl (32.9 μg/L) in femoral blood and 6-monoacetylmorphine (6-MAM, <10.0 μg/L) in vitreous fluid. Norfentanyl was only detected in stomach contents (<1.00 μg/total). Heroin, fentanyl, and acetylfentanyl were also detected in solid dose evidence submitted by law enforcement. The fentanyl and alprazolam concentrations might normally be associated with a fatal outcome and are supported with the distribution of fentanyl and alprazolam being consistent with an acute intoxication. In addition, the presence of 6-MAM and a free versus total morphine ratio of 67.9% provide supporting evidence of a rapid death following intranasal (IN) administration. However, the presence of illicit acetylfentanyl complicates toxicologic interpretation due to overlapping recreational and fatal concentrations of this compound reported in the literature as well as a potential for postmortem redistribution (PMR). Reported acetylfentanyl concentrations have also varied when presented with significant fentanyl concentrations and underscore the need to consider a wide range of illicit opioid compounds when investigating drug-related deaths. Based on our comprehensive toxicologic analysis, the results suggest an acute intoxication primarily by IN administration of acetylfentanyl and fentanyl. In addition, we suggest the presence of alprazolam, 6-MAM, and a percentage free morphine is also consistent with rapid death. The cause of death was officially attributed to an acute combined intoxication of acetylfentanyl, fentanyl, alprazolam, and heroin, with the manner of death as accidental.

Metabolism of a new synthetic opioid tetrahydrofuranylfentanyl in fresh isolated human hepatocytes: Detection and confirmation of ring-opened metabolites

The metabolism of a new synthetic opioid tetrahydrofuranylfentanyl (THF-fentanyl) was investigated using fresh human hepatocytes. Fourteen metabolites of THF-fentanyl, such as tetrahydrofuran ring-opened metabolites, desphenethylated metabolites, hydroxylated metabolites, and hydroxylated and methoxylated metabolites and their glucuronides, were detected in the culture medium of hepatocytes incubated with THF-fentanyl. Six metabolites, i.e. desphenethylated metabolite, 4'-hydroxy-THF-fentanyl, β-hydroxy-THF-fentanyl, 4'-hydroxy-3'-methoxy-THF-fentanyl, ring-opened alcohol metabolite, and ring-opened carboxylic acid metabolite, were identified via chemically synthesized authentic standards. A ring-opened alcohol metabolite and a ring-opened carboxylic acid metabolite are thought to be formed by reduction or oxidation of the intermediate aldehyde, which was formed by ring-opening of the metabolite hydroxylated at the carbon atom adjacent to the oxygen atom of the tetrahydrofuran ring. A ring-opened carboxylic acid metabolite was the main metabolite of THF-fentanyl based on the peak intensity.

Studies on the in vitro and in vivo metabolism of the synthetic opioids U-51754, U-47931E, and methoxyacetylfentanyl using hyphenated high-resolution mass spectrometry

New Synthetic Opioids (NSOs) are one class of New Psychoactive Substances (NPS) enjoying increasing popularity in Europe. Data on their toxicological or metabolic properties have not yet been published for most of them. In this context, the metabolic fate of three NSOs, namely, trans-3,4-dichloro-N-[2-(dimethylamino)cyclohexyl]-N-methyl-benzenacetamide (U-51754), trans-4-bromo-N-[2-(dimethylamino)cyclohexyl]-N-methyl-benzamide (U-47931E), and 2-methoxy-N-phenyl-N-[1-(2-phenylethyl)piperidin-4-yl] acetamide (methoxyacetylfentanyl), was elucidated by liquid chromatography high-resolution mass spectrometry after pooled human S9 fraction (phS9) incubations and in rat urine after oral administration. The following major reactions were observed: demethylation of the amine moiety for U-51754 and U-47931E, N-hydroxylation of the hexyl ring, and combinations thereof. N-dealkylation, O-demethylation, and hydroxylation at the alkyl part for methoxyacetylfentanyl. Except for U-47931E, parent compounds could only be found in trace amounts in rat urine. Therefore, urinary markers should preferably be metabolites, namely, the N-demethyl-hydroxy and the hydroxy metabolite for U-51754, the N-demethylated metabolite for U-47931E, and the N-dealkylated metabolite as well as the O-demethylated one for methoxyacetylfentanyl. In general, metabolite formation was comparable in vitro and in vivo, but fewer metabolites, particularly those after multiple reaction steps and phase II conjugates, were found in phS9. These results were consistent with those of comparable compounds obtained from human liver microsomes, human hepatocytes, and/or human case studies.

[Study of the Metabolism of New Drugs of Abuse]

Human hepatocytes possess a wider range of phase I and II drug-metabolizing enzyme activities than other liver tissue-derived products, such as human liver microsomes. Thus, hepatocytes may be useful for predicting the in vivo metabolic fate of new drugs of abuse in humans. Recently, new types of human hepatocytes have been made commercially available for use in drug metabolism studies, such as a liver tumor-derived cell line (HepaRG), and a human induced pluripotent stem cell-derived hepatocyte (h-iPS-HEP). In our laboratory, HepaRG has been used to elucidate the metabolic pathways of XLR-11, a synthetic cannabinoid, and its thermal degradant. In addition, the potential of h-iPS-HEP to metabolize drugs was assessed using fentanyl as a model drug, and indeed, h-iPS-HEP exhibited a pattern for fentanyl metabolite formation similar to that observed in vivo. In addition, the phase I and II drug-metabolizing enzyme activities of HepaRG, h-iPS-HEP, liver-humanized mouse-derived hepatocytes (PXB-cellsTM), and human primary hepatocytes were evaluated and compared. HepaRG showed high phase I and II drug metabolism activities; however, the CYP2D6 activity in these cells was quite low, and therefore h-iPS-HEP lacked O-methylation and conjugation activities. PXB-cells provided optimal results, i.e., these cells are extremely easy to use, and they possess higher phase I and II drug-metabolizing enzyme activities than the other cells tested. Although PXB-cells are contaminated with mouse-derived cells up to a concentration of several percent, this cell system appears to be promising for the prediction of in vivo human metabolism of new drugs of abuse.

Metabolic Pathways and Potencies of New Fentanyl Analogs

Up to now, little is known about the metabolic pathways of new fentanyl analogs that have recently emerged on the drug markets worldwide with high potential for producing addiction and severe adverse effects including coma and death. For some of the compounds, limited information on the metabolism has been published, however, for others so far no information is available. Considering the well characterized metabolism of the pharmaceutically used opioid fentanyl and the so far available data, the metabolism of the new fentanyl analogs can be anticipated to generally involve reactions like hydrolysis, hydroxylation (and further oxidation steps), N- and O-dealkylation and O-methylation. Furthermore, phase II metabolic reactions can be expected comprising glucuronide or sulfate conjugate formation. When analyzing blood and urine samples of acute intoxication cases or fatalities, the presence of metabolites can be crucial for confirmation of the uptake of such compounds and further interpretation. Here we present a review on the metabolic profiles of new fentanyl analogs responsible for a growing number of severe and fatal intoxications in the United States, Europe, Canada, Australia, and Japan in the last years, as assessed by a systematic search of the scientific literature and official reports.

Ultra-High-Performance Liquid Chromatography-Tandem Mass Spectrometry Assay for Quantifying Fentanyl and 22 Analogs and Metabolites in Whole Blood, Urine, and Hair

Recently, synthetic opioid-related overdose fatalities, led by illicitly manufactured fentanyl and analogs, increased at an alarming rate, posing a global public health threat. New synthetic fentanyl analogs have been constantly emerging onto the drug marked for the last few years, to circumvent the laws and avoid analytical detection. Analytical methods need to be regularly updated to keep up with the new trends. In this study, we aimed to develop a new method for detecting the newest fentanyl analogs with a high sensitivity, in whole blood, urine, and hair. The method is intended to provide to clinical and forensic toxicologists a tool for documenting consumption. We developed a comprehensive ultra-high-performance liquid chromatography-tandem mass spectrometry method for quantifying fentanyl and 22 analogs and metabolites. Urine samples were simply diluted before injection; a liquid-liquid extraction was performed for blood testing; and a solid phase extraction was performed in hair. The chromatographic separation was short (8 min). The method was validated with a high sensitivity; limits of quantifications ranged from 2 to 6 ng/L in blood and urine, and from 11 to 21 pg/g in hair. The suitability of the method was tested with 42 postmortem blood, urine, or hair specimens from 27 fatalities in which fentanyl analogs were involved. Average blood concentrations (±SD) were 7.84 ± 7.21 and 30.0 ± 18.0 μg/L for cyclopropylfentanyl and cyclopropyl norfentanyl, respectively (n = 8), 4.08 ± 2.30 μg/L for methoxyacetylfentanyl, (n = 4), 40.2 ± 38.6 and 44.5 ± 21.1 μg/L for acetylfentanyl and acetyl norfentanyl, respectively (n = 3), 33.7 and 7.17 μg/L for fentanyl and norfentanyl, respectively (n = 1), 3.60 and 0.90 μg/L for furanylfentanyl and furanyl norfentanyl, respectively (n = 1), 0.67 μg/L for sufentanil (n = 1), and 3.13 ± 2.37 μg/L for 4-ANPP (n = 9). Average urine concentrations were 47.7 ± 39.3 and 417 ± 296 μg/L for cyclopropylfentanyl and cyclopropyl norfentanyl, respectively (n = 11), 995 ± 908 μg/L for methoxyacetylfentanyl, (n = 3), 1,874 ± 1,710 and 6,582 ± 3,252 μg/L for acetylfentanyl and acetyl norfentanyl, respectively (n = 5), 146 ± 318 and 300 ± 710 μg/L for fentanyl (n = 5) and norfentanyl (n = 6), respectively, 84.0 and 23.0 μg/L for furanylfentanyl and furanyl norfentanyl, respectively (n = 1), and 50.5 ± 50.9 μg/L for 4-ANPP (n = 10). Average hair concentrations were 2,670 ± 184 and 82.1 ± 94.7 ng/g for fentanyl and norfentanyl, respectively (n = 2), and 10.8 ± 0.57 ng/g for 4-ANPP (n = 2).

Postmortem Toxicology of New Synthetic Opioids

One hundred fifteen Americans die every day from opioid overdose. These overdose fatalities have been augmented by the increased availability of potent synthetic opioids, such as fentanyl and its derivatives. The death rate of synthetic opioids, other than methadone, increased by 72.2% from 2014 to 2015, and doubled from 2015 to 2016, situating the USA in the midst of an opioid overdose epidemic. The analytical identification of these opioids in postmortem samples and the correct toxicological data interpretation is critical to identify and implement preventive strategies. This article reviews the current knowledge of postmortem toxicology of synthetic opioids and the chemical and pharmacological factors that may affect drug concentrations in the different postmortem matrices and therefore, their interpretation. These factors include key chemical properties, essential pharmacokinetics parameters (metabolism), postmortem redistribution and stability data in postmortem samples. Range and ratios of concentrations reported in traditional and non-traditional postmortem specimens, blood, urine, vitreous humor, liver and brain, are summarized in tables. The review is focused on fentanyl and derivatives (e.g., acetyl fentanyl, butyryl fentanyl, carfentanil, furanyl fentanyl, 4-methoxybutyrylfentanyl, 4-fluorobutyrylfentanyl, ocfentanil) and non-traditional opioid agonists (e.g., AH-7921, MT-45, U-47700). All of these data are critically compared to postmortem data, and chemical and pharmacological properties of natural opioids (morphine), semi-synthetic (oxycodone, hydrocodone, hydromorphone, and oxymorphone), and synthetic opioids (methadone and buprenorphine). The interpretation of drug intoxication in death investigation is based on the available published literature. This review serves to facilitate the evaluation of cases where synthetic opioids may be implicated in a fatality through the critical review of peer reviewed published case reports and research articles.

Correlations between metabolism and structural elements of the alicyclic fentanyl analogs cyclopropyl fentanyl, cyclobutyl fentanyl, cyclopentyl fentanyl, cyclohexyl fentanyl and 2,2,3,3-tetramethylcyclopropyl fentanyl studied by human hepatocytes and LC-QTOF-MS

Recently, a number of fentanyl analogs have been implicated in overdose deaths in Europe and in the US. So far, little is known of the molecular behavior of the structurally related subgroup; the alicyclic fentanyls. In this study, reference standards of cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and 2,2,3,3-tetramethylcyclopropyl fentanyl (TMCPF) at a final concentration of 5 µM were incubated with cryopreserved human hepatocytes (1 × 10⁶ cells/mL) for 0, 1, 3 and 5 h. The metabolites formed were identified by liquid chromatography-quadrupole time-of-flight mass spectrometry analysis. The most abundant biotransformation found was N-dealkylation (formation of normetabolites) and oxidation of the alicyclic rings. As ring size increased, the significance of N-dealkylation decreased in favor of alicyclic ring oxidation. An example of this was cyclopropyl fentanyl, with a three-carbon ring, whose normetabolite covered 82% of the total metabolic peak area and no oxidation of the alicyclic ring was observed. In contrast, TMCPF, with a seven-carbon ring structure, rendered as much as 85% of its metabolites oxidized on the alicyclic ring. Other biotransformations found included oxidation of the piperidine ethyl moiety and/or the phenethyl substructure, glucuronidation as well as amide hydrolysis to form metabolites identical to despropionyl fentanyl. Taken together, this study provides a base for understanding the metabolism of a number of structurally related fentanyl analogs formed upon intake.

Use of hepatocytes isolated from a liver-humanized mouse for studies on the metabolism of drugs: application to the metabolism of fentanyl and acetylfentanyl

Purpose

The usefulness of hepatocytes isolated from a liver-humanized mouse (PXB-cells) as a model in vitro system for the prediction of the in vivo metabolism of new drugs of abuse was evaluated.

Methods

For the drug metabolism study, fentanyl, a powerful synthetic opioid, and acetylfentanyl, an N-acetyl analog of fentanyl, were selected as model drugs. PXB-cells were cultured with the drug for 24–48 h and then the media were collected and analyzed by liquid chromatography/mass spectrometry after deproteinization with acetonitrile.

Results

The main metabolite formed from fentanyl by PXB-cells was the desphenethylated metabolite (nor-fentanyl), and the other major metabolites formed were 4′-hydroxy-fentanyl, β-hydroxy-fentanyl and (ω-1)-hydroxy-fentanyl. ω-Hydroxy-fentanyl and 4′-hydroxy-3′-methoxy-fentanyl were the minor metabolites. Similar results were obtained for acetylfentanyl. The metabolite profile of fentanyl in PXB-cells was consistent with the in vivo metabolite profile of fentanyl reported previously. Most of the 4′-hydroxy- and 4′-hydroxy-3′-methoxy-metabolites of fentanyl and acetylfentanyl were conjugated in PXB-cells, indicating that PXB-cells had high conjugation enzyme activities. From experiments using human liver microsomes and anti-CYP antibodies, it was revealed that CYP3A4 was involved in the production of nor-fentanyl, β-hydroxy-fentanyl and (ω-1)-hydroxy-fentanyl, while CYP2D6 was partially involved in the production of 4′-hydroxy-fentanyl.

Conclusions

Our results indicated that PXB-cells have high activities of phase I and phase II drug-metabolizing-enzymes, can be stably supplied, and are easy to use; thus, PXB-cells are highly useful for the prediction of the in vivo metabolism of drugs of abuse.