L-cysteine ethylester reverses the adverse effects of morphine on breathing and arterial blood-gas chemistry while minimally affecting antinociception in unanesthetized rats

L-cysteine ethylester (L-CYSee) is a membrane-permeable analogue of L-cysteine with a variety of pharmacological effects. The purpose of this study was to determine the effects of L-CYSee on morphine-induced changes in ventilation, arterial-blood gas (ABG) chemistry, Alveolar-arterial (A-a) gradient (i.e., a measure of the index of alveolar gas-exchange), antinociception and sedation in male Sprague Dawley rats. An injection of morphine (10 mg/kg, IV) produced adverse effects on breathing, including sustained decreases in minute ventilation. L-CYSee (500 μmol/kg, IV) given 15 min later immediately reversed the actions of morphine. Another injection of L-CYSee (500 μmol/kg, IV) after 15 min elicited more pronounced excitatory ventilatory responses. L-CYSee (250 or 500 μmol/kg, IV) elicited a rapid and prolonged reversal of the actions of morphine (10 mg/kg, IV) on ABG chemistry (pH, pCO2, pO2, sO2) and A-a gradient. L-serine ethylester (an oxygen atom replaces the sulfur; 500 μmol/kg, IV), was ineffective in all studies. L-CYSee (500 μmol/kg, IV) did not alter morphine (10 mg/kg, IV)-induced sedation, but slightly reduced the overall duration of morphine (5 or 10 mg/kg, IV)-induced analgesia. In summary, L-CYSee rapidly overcame the effects of morphine on breathing and alveolar gas-exchange, while not affecting morphine sedation or early-stage analgesia. The mechanisms by which L-CYSee modulates morphine depression of breathing are unknown, but appear to require thiol-dependent processes.

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.

Essential role of P-glycoprotein in the mechanism of action of oliceridine

Mu opioid receptor (MOR) agonists comprise the most effective analgesics, but their therapeutic utility is limited by adverse effects. One approach for limiting such effects has been to develop "biased" MOR agonists that show preference for activating G protein over β-Arrestin signaling. However, the notion of biased agonism has been challenged by recent studies. Oliceridine (Olinvyk®, TRV-130, OLC) is a selective MOR agonist approved by the FDA in 2020 for pain management in controlled clinical settings. Oliceridine purportedly demonstrates diminished adverse effects compared to morphine or other MOR agonists, a profile attributed to its biased agonism. However, recent studies suggest that oliceridine does not display biased agonism but instead weak intrinsic efficacy for G protein and β-Arrestin activation. Nevertheless, these insights have been derived from in vitro studies. To better understand oliceridine's in vivo efficacy profile, we performed a comprehensive assessment of its in vitro and in vivo pharmacology using both cultured cells and rodents. In vitro, oliceridine displayed high MOR affinity and weak intrinsic efficacy. In vivo, oliceridine showed impaired brain penetrance and rapid clearance, effects we attributed to its interaction with the P-glycoprotein (P-gp) efflux transporter. Moreover, we found that P-gp was essential for oliceridine's in vivo efficacy and adverse effect profiles. Taken together with prior studies, our results suggest that oliceridine's in vivo efficacy and adverse effect profiles are not attributed solely to its weak intrinsic efficacy or biased agonism but, to a large extent, its interaction with P-gp as well.

Mechanisms of Neurorespiratory Toxicity Induced by Fentanyl Analogs—Lessons from Animal Studies

In 2020, fentanyl and its analogs contributed to ~65% of drug-attributed fatalities in the USA, with a threatening increasing trend during the last ten years. These synthetic opioids used as potent analgesics in human and veterinary medicine have been diverted to recreational aims, illegally produced and sold. Like all opioids, central nervous system depression resulting from overdose or misuse of fentanyl analogs is characterized clinically by the onset of consciousness impairment, pinpoint miosis and bradypnea. However, contrasting with what observed with most opioids, thoracic rigidity may occur rapidly with fentanyl analogs, contributing to increasing the risk of death in the absence of immediate life support. Various mechanisms have been proposed to explain this particularity associated with fentanyl analogs, including the activation of noradrenergic and glutamatergic coerulospinal neurons and dopaminergic basal ganglia neurons. Due to the high affinities to the mu-opioid receptor, the need for more elevated naloxone doses than usually required in morphine overdose to reverse the neurorespiratory depression induced by fentanyl analogs has been questioned. This review on the neurorespiratory toxicity of fentanyl and analogs highlights the need for specific research focused on these agents to better understand the involved mechanisms of toxicity and develop dedicated strategies to limit the resulting fatalities.

The role of the efflux transporter, P-glycoprotein, at the blood-brain barrier in drug discovery

The blood-brain barrier (BBB) expresses a high abundance of transporters, particularly P-glycoprotein (P-gp), that regulate endogenous and exogenous molecule uptake and removal of waste. This review discusses key drug metabolism and pharmacokinetic considerations for the efflux transporter P-gp at the BBB in drug discovery and development. We highlight the differences in P-gp expression and protein levels across species but the limited observations of species-specific substrates. Given the impact of age and disease on BBB biology, we summarise the modulation of P-gp for several neurological disorders and ageing and exemplify several disease-specific hurdles or opportunities for drug exposure in the brain. Furthermore, the review includes observations of CNS-related drug-drug interactions due to the inhibition or induction of P-gp at the BBB in animal studies and humans and the need for continued evaluation especially for compounds with a narrow therapeutic window. This review focusses primarily on small molecules but also considers the impact of new chemical entities, particularly beyond Ro5 molecules and their potential to be recognised as P-gp substrates as well as advanced drug delivery systems which offer an alternative approach to achieve and sustain central nervous system exposure.

The Impact of P-Glycoprotein on Opioid Analgesics: What's the Real Meaning in Pain Management and Palliative Care?

Opioids are widely used in cancer and non-cancer pain management. However, many transporters at the blood-brain barrier (BBB), such as P-glycoprotein (P-gp, ABCB1/MDR1), may impair their delivery to the brain, thus leading to opioid tolerance. Nonetheless, opioids may regulate P-gp expression, thus altering the transport of other compounds, namely chemotherapeutic agents, resulting in pharmacoresistance. Other kinds of painkillers (e.g., acetaminophen, dexamethasone) and adjuvant drugs used for neuropathic pain may act as P-gp substrates and modulate its expression, thus making pain management challenging. Inflammatory conditions are also believed to upregulate P-gp. The role of P-gp in drug-drug interactions is currently under investigation, since many P-gp substrates may also act as substrates for the cytochrome P450 enzymes, which metabolize a wide range of xenobiotics and endobiotics. Genetic variability of the ABCB1/MDR1 gene may be accountable for inter-individual variation in opioid-induced analgesia. P-gp also plays a role in the management of opioid-induced adverse effects, such as constipation. Peripherally acting mu-opioid receptors antagonists (PAMORAs), such as naloxegol and naldemedine, are substrates of P-gp, which prevent their penetration in the central nervous system. In our review, we explore the interactions between P-gp and opioidergic drugs, with their implications in clinical practice.

L-cysteine methyl ester overcomes the deleterious effects of morphine on ventilatory parameters and arterial blood-gas chemistry in unanesthetized rats

We are developing a series of thiolesters that produce an immediate and sustained reversal of the deleterious effects of opioids, such as morphine and fentanyl, on ventilation without diminishing the antinociceptive effects of these opioids. We report here the effects of systemic injections of L-cysteine methyl ester (L-CYSme) on morphine-induced changes in ventilatory parameters, arterial-blood gas (ABG) chemistry (pH, pCO₂, pO₂, sO₂), Alveolar-arterial (A-a) gradient (i.e., the index of alveolar gas-exchange within the lungs), and antinociception in unanesthetized Sprague Dawley rats. The administration of morphine (10 mg/kg, IV) produced a series of deleterious effects on ventilatory parameters, including sustained decreases in tidal volume, minute ventilation, inspiratory drive and peak inspiratory flow that were accompanied by a sustained increase in end inspiratory pause. A single injection of L-CYSme (500 μmol/kg, IV) produced a rapid and long-lasting reversal of the deleterious effects of morphine on ventilatory parameters, and a second injection of L-CYSme (500 μmol/kg, IV) elicited pronounced increases in ventilatory parameters, such as minute ventilation, to values well above pre-morphine levels. L-CYSme (250 or 500 μmol/kg, IV) also produced an immediate and sustained reversal of the deleterious effects of morphine (10 mg/kg, IV) on arterial blood pH, pCO₂, pO₂, sO₂ and A-a gradient, whereas L-cysteine (500 μmol/kg, IV) itself was inactive. L-CYSme (500 μmol/kg, IV) did not appear to modulate the sedative effects of morphine as measured by righting reflex times, but did diminish the duration, however, not the magnitude of the antinociceptive actions of morphine (5 or 10 mg/kg, IV) as determined in tail-flick latency and hindpaw-withdrawal latency assays. These findings provide evidence that L-CYSme can powerfully overcome the deleterious effects of morphine on breathing and gas-exchange in Sprague Dawley rats while not affecting the sedative or early stage antinociceptive effects of the opioid. The mechanisms by which L-CYSme interferes with the OR-induced signaling pathways that mediate the deleterious effects of morphine on ventilatory performance, and by which L-CYSme diminishes the late stage antinociceptive action of morphine remain to be determined.

D-Cysteine Ethyl Ester Reverses the Deleterious Effects of Morphine on Breathing and Arterial Blood-Gas Chemistry in Freely-Moving Rats

Cell-penetrant thiol esters including the disulfides, D-cystine diethyl ester and D-cystine dimethyl ester, and the monosulfide, L-glutathione ethyl ester, prevent and/or reverse the deleterious effects of opioids, such as morphine and fentanyl, on breathing and gas exchange within the lungs of unanesthetized/unrestrained rats without diminishing the antinociceptive or sedative effects of opioids. We describe here the effects of the monosulfide thiol ester, D-cysteine ethyl ester (D-CYSee), on intravenous morphine-induced changes in ventilatory parameters, arterial blood-gas chemistry, alveolar-arterial (A-a) gradient (i.e., index of gas exchange in the lungs), and sedation and antinociception in freely-moving rats. The bolus injection of morphine (10 mg/kg, IV) elicited deleterious effects on breathing, including depression of tidal volume, minute ventilation, peak inspiratory flow, and inspiratory drive. Subsequent injections of D-CYSee (2 × 500 μmol/kg, IV, given 15 min apart) elicited an immediate and sustained reversal of these effects of morphine. Morphine (10 mg/kg, IV) also A-a gradient, which caused a mismatch in ventilation perfusion within the lungs, and elicited pronounced changes in arterial blood-gas chemistry, including pronounced decreases in arterial blood pH, pO2 and sO2, and equally pronounced increases in pCO2 (all responses indicative of decreased ventilatory drive). These deleterious effects of morphine were immediately reversed by the injection of a single dose of D-CYSee (500 μmol/kg, IV). Importantly, the sedation and antinociception elicited by morphine (10 mg/kg, IV) were minimally affected by D-CYSee (500 μmol/kg, IV). In contrast, none of the effects of morphine were affected by administration of the parent thiol, D-cysteine (1 or 2 doses of 500 μmol/kg, IV). Taken together, these data suggest that D-CYSee may exert its beneficial effects via entry into cells that mediate the deleterious effects of opioids on breathing and gas exchange. Whether D-CYSee acts as a respiratory stimulant or counteracts the inhibitory actions of µ-opioid receptor activation remains to be determined. In conclusion, D-CYSee and related thiol esters may have clinical potential for the reversal of the adverse effects of opioids on breathing and gas exchange, while largely sparing antinociception and sedation.

Fentanyl alleviates intestinal mucosal barrier damage in rats with severe acute pancreatitis by inhibiting the MMP-9/FasL/Fas pathway

BACKGROUND

Fentanyl is an analgesic used against pancreatitis-related pain, while whether it ameliorates severe acute pancreatitis (SAP) has yet to be checked. The present study aims to determine fentanyl-delivered effect on SAP and the mechanism underlying this effect.

METHODS

Rat SAP models were established, following fentanyl treatment. The serum activity of amylase (AMY), lipase (LIP) and diamine oxidase (DAO) was detected by enzyme-linked immunosorbent assay. Histological examination was performed in the pancreatic and intestinal tissues with hematoxylin-eosin staining. After transfection with matrix metalloproteinase (MMP)9 overexpression plasmids, Caco-2 monolayers were treated with fentanyl and subsequently exposed to lipopolysaccharide (LPS). The transepithelial electrical resistance (TEER) value was determined in rat intestinal mucosa through an Ussing chamber assisted by Analyze & Acquire, and in Caco-2 cell monolayers through a voltohmmeter. Intestinal mucosa and paracellular permeabilities were determined by fluorescein isothiocyanate (FITC)-labeled dextran assay. The expressions of ZO-1, Occludin, MMP9, Fas and Fas ligand (FasL) in rat intestinal mucosa and/or Caco-2 monolayers were analyzed by qRT-PCR or/and western blot.

RESULTS

Fentanyl alleviated SAP-related histological alterations in the pancreas and intestines, reduced the elevated levels of SAP-related AMY, LIP and DAO, but promoted the levels of ZO-1 and Occludin. In SAP rats and Caco-2 monolayers, SAP-related or LPS-induced TEER value decreases, permeability increases, and increases in the expressions of MMP9, Fas and FasL were reversed partly by fentanyl. Notably, MMP9 overexpression could reverse the above fentanyl-delivered in vitro effects.

CONCLUSION

Fentanyl alleviates intestinal mucosal barrier damage in rats with SAP by inhibiting the MMP9/FasL/Fas pathway.

Encapsulated Escitalopram and Paroxetine Intranasal Co-Administration: In Vitro/In Vivo Evaluation

Depression is a common mental disorder. Its treatment with selective serotonin reuptake inhibitors (SSRIs) is effective only in a fraction of patients, and pharmacoresistance is increasing steadily. Intranasal (IN) drug delivery to the brain stands out as a promising strategy to improve current therapeutic approaches by operating as a shuttle to overcome the blood–brain barrier. This work aimed to simultaneously administer escitalopram and paroxetine by IN route to mice. For this purpose, three nanostructured lipid carriers (NLC1, NLC2, and BorNLC) and one nanoemulsion (NE) were tested for drug loading. After their characterization, investigation of their impact on nasal cell viability and SSRI permeability assays were performed, using a human nasal RPMI 2650 cell line in air–liquid interface. In vitro assays demonstrated that NLCs, including borneol (BorNLC), significantly increased escitalopram permeability (p < 0.01) and paroxetine recovery values (p < 0.05) in relation to the other formulations and non-encapsulated drugs. IN and intravenous (IV) pharmacokinetic studies performed in vivo with a single dose of 2.38 mg/kg demonstrated similar results for escitalopram brain-to-plasma ratios. IN administrations delayed escitalopram peak concentrations in the brain for 15–60 min and no direct nose-to-brain delivery was detected. However, encapsulation with BorNLC considerably decreased escitalopram exposure in the lungs (124 μg min/g) compared with free escitalopram by IN (168 μg min/g) and IV (321 μg min/g) routes. Surprisingly, BorNLC IN instillation increased concentration levels of paroxetine in the brain by five times and accelerated brain drug delivery. Once again, lung exposure was considerably lower with BorNLC (AUC_t = 0.433 μg min/g) than that with IV administration (AUC_t = 1.01 μg min/g) and non-encapsulated IN formulation (AUC_t = 2.82 μg min/g). Direct nose-to-brain delivery was observed for paroxetine IN administration with a direct transport percentage (DTP) of 56.9%. If encapsulated, it increases to 74.2%. These results clearly emphasize that nose-to-brain delivery and lung exposure depend on the formulation and on the characteristics of the drug under investigation. NLCs seem to be an advantageous strategy for nose-to-brain delivery of lipophilic molecules, since they reduce systemic and lung exposure, thereby decreasing adverse effects. For hydrophilic compounds, NLCs are particularly important to decrease lung exposure after IN administration.

Predicting Maternal-Fetal Disposition of Fentanyl Following Intravenous and Epidural Administration Using Physiologically Based Pharmacokinetic Modeling

Fentanyl is an opioid analgesic used to treat obstetrical pain in parturient women through epidural or intravenous route, and unfortunately can also be abused by pregnant women. Fentanyl is known to cross the placental barrier, but how the route of administration and time after dosing affects maternal-fetal disposition kinetics at different stages of pregnancy is not well characterized. To address this knowledge gap, we developed a maternal-fetal physiologically based pharmacokinetic (mf-PBPK) model for fentanyl to evaluate the feasibility to predict the maternal and fetal plasma concentration-time profiles of fentanyl after various dosing regimens. As fentanyl is typically given via the epidural route to control labor pain, an epidural dosing site was developed using alfentanil as a reference drug and extrapolated to fentanyl. Fetal hepatic clearance of fentanyl was predicted from CYP3A7-mediated norfentanyl formation in fetal liver microsomes (intrinsic clearance = 0.20 ± 0.05 µl/min/mg protein). The developed mf-PBPK model successfully captured fentanyl maternal and umbilical cord concentrations after epidural dosing and was used to simulate the concentrations after intravenous dosing (in a drug abuse situation). The distribution kinetics of fentanyl were found to have a considerable impact on the time course of maternal:umbilical cord concentration ratio and on interpretation of observed data. The data show that mf-PBPK modeling can be used successfully to predict maternal disposition, transplacental distribution, and fetal exposure to fentanyl. SIGNIFICANCE STATEMENT: This study establishes the modeling framework for predicting the time course of maternal and fetal exposures of fentanyl opioids from mf-PBPK modeling. The model was validated based on fentanyl exposure data collected during labor and delivery after intravenous or epidural dosing. The results show that mf-PBPK modeling is a useful predictive tool for assessing fetal exposures to fentanyl opioid therapeutic regimens and potentially can be extended to other drugs of abuse.

A Large-Scale Observational Study on the Temporal Trends and Risk Factors of Opioid Overdose: Real-World Evidence for Better Opioids

Background

The USA is in the midst of an opioid overdose epidemic. To address the epidemic, we conducted a large-scale population study on opioid overdose.

Objectives

The primary objective of this study was to evaluate the temporal trends and risk factors of inpatient opioid overdose. Based on its patterns, the secondary objective was to examine the innate properties of opioid analgesics underlying reduced overdose effects.

Methods

A retrospective cross-sectional study was conducted based on a large-scale inpatient electronic health records database, Cerner Health Facts^®, with (1) inclusion criteria for participants as patients admitted between 1 January, 2009 and 31 December, 2017 and (2) measurements as opioid overdose prevalence by year, demographics, and prescription opioid exposures.

Results

A total of 4,720,041 patients with 7,339,480 inpatient encounters were retrieved from Cerner Health Facts^®. Among them, 30.2% patients were aged 65+ years, 57.0% female, 70.1% Caucasian, 42.3% single, 32.0% from the South, and 80.8% in an urban area. From 2009 to 2017, annual opioid overdose prevalence per 1000 patients significantly increased from 3.7 to 11.9 with an adjusted odds ratio (aOR): 1.16, 95% confidence interval (CI) 1.15–1.16. Compared to the major demographic counterparts, being in (1) age group: 41–50 years (overall aOR 1.36, 95% CI 1.31–1.40) or 51–64 years (overall aOR 1.35, 95% CI 1.32–1.39), (2) marital status: divorced (overall aOR 1.19, 95% CI 1.15–1.23), and (3) census region: West (overall aOR 1.32, 95% CI 1.28–1.36) were significantly associated with a higher odds of opioid overdose. Prescription opioid exposures were also associated with an increased odds of opioid overdose, such as meperidine (overall aOR 1.09, 95% CI 1.06–1.13) and tramadol (overall aOR 2.20, 95% CI 2.14–2.27). Examination on the relationships between opioid analgesic properties and their association strengths, aORs, and opioid overdose showed that lower aOR values were significantly associated with (1) high molecular weight, (2) non-interaction with multi-drug resistance protein 1 or interaction with cytochrome P450 3A4, and (3) non-interaction with the delta opioid receptor or kappa opioid receptor.

Conclusions

The significant increasing trends of opioid overdose at the inpatient care setting from 2009 to 2017 suggested an ongoing need for efforts to combat the opioid overdose epidemic in the USA. Risk factors associated with opioid overdose included patient demographics and prescription opioid exposures. Moreover, there are physicochemical, pharmacokinetic, and pharmacodynamic properties underlying reduced overdose effects, which can be utilized to develop better opioids.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40801-021-00253-8.

Glutathione ethyl ester reverses the deleterious effects of fentanyl on ventilation and arterial blood-gas chemistry while prolonging fentanyl-induced analgesia

There is an urgent need to develop novel compounds that prevent the deleterious effects of opioids such as fentanyl on minute ventilation while, if possible, preserving the analgesic actions of the opioids. We report that L-glutathione ethyl ester (GSHee) may be such a novel compound. In this study, we measured tail flick latency (TFL), arterial blood gas (ABG) chemistry, Alveolar-arterial gradient, and ventilatory parameters by whole body plethysmography to determine the responses elicited by bolus injections of fentanyl (75 μg/kg, IV) in male adult Sprague-Dawley rats that had received a bolus injection of GSHee (100 μmol/kg, IV) 15 min previously. GSHee given alone had minimal effects on TFL, ABG chemistry and A-a gradient whereas it elicited changes in some ventilatory parameters such as an increase in breathing frequency. In vehicle-treated rats, fentanyl elicited (1) an increase in TFL, (2) decreases in pH, pO₂ and sO₂ and increases in pCO₂ (all indicative of ventilatory depression), (3) an increase in Alveolar-arterial gradient (indicative of a mismatch in ventilation-perfusion in the lungs), and (4) changes in ventilatory parameters such as a reduction in tidal volume, that were indicative of pronounced ventilatory depression. In GSHee-pretreated rats, fentanyl elicited a more prolonged analgesia, relatively minor changes in ABG chemistry and Alveolar-arterial gradient, and a substantially milder depression of ventilation. GSHee may represent an effective member of a novel class of thiolester drugs that are able to prevent the ventilatory depressant effects elicited by powerful opioids such as fentanyl and their deleterious effects on gas-exchange in the lungs without compromising opioid analgesia.

Tolerance to Opioid-Induced Respiratory Depression in Chronic High-Dose Opioid Users: A Model-Based Comparison With Opioid-Naïve Individuals

Chronic opioid consumption is associated with addiction, physical dependence, and tolerance. Tolerance results in dose escalation to maintain the desired opioid effect. Intake of high-dose or potent opioids may cause life-threatening respiratory depression, an effect that may be reduced by tolerance. We performed a pharmacokinetic-pharmacodynamic analysis of the respiratory effects of fentanyl in chronic opioid users and opioid-naïve subjects to quantify tolerance to respiratory depression. Fourteen opioid-naïve individuals and eight chronic opioid users received escalating doses of intravenous fentanyl (opioid-naïve subjects: 75-350 µg/70 kg; chronic users: 250-700 µg/70 kg). Isohypercapnic ventilation was measured and the fentanyl plasma concentration-ventilation data were analyzed using nonlinear mixed-effects modeling. Apneic events occurred in opioid-naïve subjects after a cumulative fentanyl dose (per 70 kg) of 225 (n = 3) and 475 µg (n = 6), and in 7 chronic opioid users after a cumulative dose of 600 (n = 2), 1,100 (n = 2), and 1,800 µg (n = 3). The time course of fentanyl's respiratory depressant effect was characterized using a biophase equilibration model in combination with an inhibitory maximum effect (Emax ) model. Differences in tolerance between populations were successfully modeled. The effect-site concentration causing 50% ventilatory depression, was 0.42 ± 0.07 ng/mL in opioid-naïve subjects and 1.82 ± 0.39 ng/mL in chronic opioid users, indicative of a 4.3-fold sensitivity difference. Despite higher tolerance to fentanyl-induced respiratory depression, apnea still occurred in the opioid-tolerant population indicative of the potential danger of high-dose opioids in causing life-threatening respiratory depression in all individuals, opioid-naïve and opioid-tolerant.

Reversing P-Glycoprotein-Associated Multidrug Resistance of Breast Cancer by Targeted Acid-Cleavable Polysaccharide Nanoparticles with Lapatinib Sensitization

For reversing the treatment failure in P-glycoprotein (P-gp)-associated MDR (multidrug resistance) of breast cancer, a high dose of Lapatinib (Lap), a substrate of breast cancer-resistant protein, was encapsulated into safe and effective acid-cleavable polysaccharide-doxorubicin (Dox) conjugates to form targeted HPP-Dox/Lap nanoparticles with an optimal drug ratio and appropriate nanosize decorated with oligomeric hyaluronic acid (HA) for specially targeting overexpressed CD44 receptors of MCF-7/ADR. The markedly increased cellular uptake and the strongest synergetic cytotoxicity revealed the enhanced reversal efficiency of HPP-Dox/Lap nanoparticles with reversal multiples at 29.83. This was also verified by the enhanced penetrating capacity in multicellular tumor spheroids. The reinforced Dox retention and substantial down-regulation of P-gp expression implied the possible mechanism of MDR reversal. Furthermore, the efficient ex vivo accumulation and distribution of nanoparticles in the tumor site and the high tumor growth inhibition (93%) even at a lower dosage (1 mg/kg) as well as lung metastasis inhibition in vivo with negligible side effects revealed the overwhelming advantages of targeted polysaccharide nanoparticles and Lap-sensitizing effect against drug-resistant tumor. The development of an efficient and nontoxic-targeted polysaccharide delivery system for reversing MDR by synergistic therapy might provide a potential clinical application value.

Physiologically-Based Pharmacokinetic (PBPK) Modeling Providing Insights into Fentanyl Pharmacokinetics in Adults and Pediatric Patients

Fentanyl is widely used for analgesia, sedation, and anesthesia both in adult and pediatric populations. Yet, only few pharmacokinetic studies of fentanyl in pediatrics exist as conducting clinical trials in this population is especially challenging. Physiologically-based pharmacokinetic (PBPK) modeling is a mechanistic approach to explore drug pharmacokinetics and allows extrapolation from adult to pediatric populations based on age-related physiological differences. The aim of this study was to develop a PBPK model of fentanyl and norfentanyl for both adult and pediatric populations. The adult PBPK model was established in PK-Sim® using data from 16 clinical studies and was scaled to several pediatric subpopulations. ~93% of the predicted AUClast values in adults and ~88% in pediatrics were within 2-fold of the corresponding value observed. The adult PBPK model predicted a fraction of fentanyl dose metabolized to norfentanyl of ~33% and a fraction excreted in urine of ~7%. In addition, the pediatric PBPK model was used to simulate differences in peak plasma concentrations after bolus injections and short infusions. The novel PBPK models could be helpful to further investigate fentanyl pharmacokinetics in both adult and pediatric populations.

Quality Control of Psoralea corylifolia L. Based on High-Speed Countercurrent Chromatographic Fingerprinting

Traditional Chinese medicine (TCM)has played an important role in promoting the health of Chinese people. The TCM Psoralea corylifolia L. has been used in the treatment of various kinds of diseases including enuresis, vitiligo, and calvities. However, therapeutic effects of P. corylifolia L. have often influenced by the quality of plants. So, it is very important to control the quality of P. corylifolia L. In this study, analytical high-speed countercurrent chromatography (HSCCC) was successfully used to fingerprint P. corylifolia L. Samples of P. corylifolia L. were extracted by ultrasonic extraction. n-hexane-ethyl acetate–methanol–water at a ratio of 5:5.5:6.5:5 (v/v) was selected as a two-phase solvent system and the condition of HSCCC were optimized in order to good separation. And the method of HSCCC was verified (reproducibility, precision, and stability). HSCCC chromatograms exhibited six common peaks, which were selected as indicator compounds for the quality control of P. corylifolia L. Within 20 types of medicinal materials, chemical components are similar, but the levels of components are quite different in HSCCC fingerprint. The present results demonstrate that the HSCCC method provides a reliable basis for the quality control of P. corylifolia L. and can also be applied to confirm the authenticity of plant materials.

Modulation of Opioid Transport at the Blood-Brain Barrier by Altered ATP-Binding Cassette (ABC) Transporter Expression and Activity

Opioids are highly effective analgesics that have a serious potential for adverse drug reactions and for development of addiction and tolerance. Since the use of opioids has escalated in recent years, it is increasingly important to understand biological mechanisms that can increase the probability of opioid-associated adverse events occurring in patient populations. This is emphasized by the current opioid epidemic in the United States where opioid analgesics are frequently abused and misused. It has been established that the effectiveness of opioids is maximized when these drugs readily access opioid receptors in the central nervous system (CNS). Indeed, opioid delivery to the brain is significantly influenced by the blood-brain barrier (BBB). In particular, ATP-binding cassette (ABC) transporters that are endogenously expressed at the BBB are critical determinants of CNS opioid penetration. In this review, we will discuss current knowledge on the transport of opioid analgesic drugs by ABC transporters at the BBB. We will also examine how expression and trafficking of ABC transporters can be modified by pain and/or opioid pharmacotherapy, a novel mechanism that can promote opioid-associated adverse drug events and development of addiction and tolerance.