Pharmacokinetics and behavioral effects of an extended-release, liposome-encapsulated preparation of oxymorphone in rhesus macaques

Mesoporous Polydopamine Nanoparticles Attenuate Morphine Tolerance in Neuropathic Pain Rats by Inhibition of Oxidative Stress and Restoration of the Endogenous Antioxidant System

Oxidative stress resulting from reactive oxygen species (ROS) is known to play a key role in numerous neurological disorders, including neuropathic pain. Morphine is one of the commonly used opioids for pain management. However, long-term administration of morphine results in morphine antinociceptive tolerance (MAT) through elevation of ROS and suppression of natural antioxidant defense mechanisms. Recently, mesoporous polydopamine (MPDA) nanoparticles (NPS) have been known to possess strong antioxidant properties. We speculated that morphine delivery through an antioxidant nanocarrier might be a reasonable strategy to alleviate MAT. MPDAs showed a high drug loading efficiency of ∼50%, which was much higher than conventional NPS. Spectral and in vitro studies suggest a superior ROS scavenging ability of NPS. Results from a rat neuropathic pain model demonstrate that MPDA-loaded morphine (MPDA@Mor) is efficient in minimizing MAT with prolonged analgesic effect and suppression of pro-inflammatory cytokines. Additionally, serum levels of liver enzymes and levels of endogenous antioxidants were measured in the liver. Treatment with free morphine resulted in elevated levels of liver enzymes and significantly lowered the activities of endogenous antioxidant enzymes in comparison with the control and MPDA@Mor-treated group. Histopathological examination of the liver revealed that MPDA@Mor can significantly reduce the hepatotoxic effects of morphine. Taken together, our current work will provide an important insight into the development of safe and effective nano-antioxidant platforms for neuropathic pain management.

Liposome-Encapsulated Morphine Affords a Prolonged Analgesia While Facilitating Extinction of Reward and Aversive Memories

Morphine is thoroughly used for pain control; however, it has a high addictive potential. Opioid liposome formulations produce controlled drug release and have been thoroughly tested for pain treatment although their role in addiction is still unknown. This study investigated the effects of free morphine and morphine encapsulated in unilamellar and multilamellar liposomes on antinociception and on the expression and extinction of the positive and negative memories associated with environmental cues. The hot plate test was used to measure central pain. The rewarding effects of morphine were analyzed by the conditioned-place preference (CPP) test, and the aversive aspects of naloxone-precipitated morphine withdrawal were evaluated by the conditioned-place aversion (CPA) paradigm. Our results show that encapsulated morphine yields prolonged antinociceptive effects compared with the free form, and that CPP and CPA expression were similar in the free- or encapsulated-morphine groups. However, we demonstrate, for the first time, that morphine encapsulation reduces the duration of reward and aversive memories, suggesting that this technological process could transform morphine into a potentially less addictive drug. Morphine encapsulation in liposomes could represent a pharmacological approach for enhancing extinction, which might lead to effective clinical treatments in drug addiction with fewer side effects.

New drug candidates for liposomal delivery identified by computer modeling of liposomes' remote loading and leakage

Remote drug loading into nano-liposomes is in most cases the best method for achieving high concentrations of active pharmaceutical ingredients (API) per nano-liposome that enable therapeutically viable API-loaded nano-liposomes, referred to as nano-drugs. This approach also enables controlled drug release. Recently, we constructed computational models to identify APIs that can achieve the desired high concentrations in nano-liposomes by remote loading. While those previous models included a broad spectrum of experimental conditions and dealt only with loading, here we reduced the scope to the molecular characteristics alone. We model and predict API suitability for nano-liposomal delivery by fixing the main experimental conditions: liposome lipid composition and size to be similar to those of Doxil® liposomes. On that basis, we add a prediction of drug leakage from the nano-liposomes during storage. The latter is critical for having pharmaceutically viable nano-drugs. The "load and leak" models were used to screen two large molecular databases in search of candidate APIs for delivery by nano-liposomes. The distribution of positive instances in both loading and leakage models was similar in the two databases screened. The screening process identified 667 molecules that were positives by both loading and leakage models (i.e., both high-loading and stable). Among them, 318 molecules received a high score in both properties and of these, 67 are FDA-approved drugs. This group of molecules, having diverse pharmacological activities, may be the basis for future liposomal drug development.

A Novel Loading Method for Doxycycline Liposomes for Intracellular Drug Delivery: Characterization of In Vitro and In Vivo Release Kinetics and Efficacy in a J774A.1 Cell Line Model of Mycobacterium smegmatis Infection

Doxycycline (doxy) is used in treating intracellular and extracellular infections. Liposomal (LE) antibiotics allow low-frequency dosing and extended efficacy compared with standard (STD) formulations. We developed a novel sulfuric acid-loading method for doxycycline liposomes (LE-doxy). We hypothesized that a single s.c. injection of LE-doxy would be detectable in serum for at least 2 weeks at concentrations equal to or better than STD-doxy and would be bactericidal in an in vitro Mycobacterium smegmatis infection of J774A.1 macrophage cells. Liposomes were encapsulated by sulfuric acid gradient loading, and release kinetics were performed in vitro and in vivo. LE-doxy made using 8.25 mg/ml doxycycline loaded for 24 hours achieved 97.77% capture in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 43.87% in sphingomyelin (sphing). Rats were injected s.c. with 50 mg/kg LE-doxy or 5 mg/kg STD-doxy, and serial blood samples were collected. Pharmacokinetics were analyzed using high-performance liquid chromatography. Liver and injection site skin samples were collected at euthanasia (4 weeks postinjection). Minimal histologic tissue reactions occurred after injection of STD (nonliposomal), DPPC, or sphing-doxy. DPPC-doxy had slightly faster in vitro leakage than sphing liposomes, although both were detectable at 264 hours. The mean residence time for DPPC was the highest (111.78 hours), followed by sphing (56.00 hours) and STD (6.86 hours). DPPC and sphing-doxy were detectable at 0.2 μg/ml in serum at 336 hours postadministration. LE-doxy was not toxic to J774A.1 cells in vitro and produced inhibition of viable Mycobacterium smegmatis at 24 and 48 hours. LE-doxy will require further testing in in vivo infection models.

Pharmacokinetics of 2 formulations of buprenorphine in macaques (Macaca mulatta and Macaca fascicularis)

Buprenorphine is the cornerstone of pain management in nonhuman primates, but the pharmacokinetics of this widely used drug are unknown. The purpose of this study was to evaluate the pharmacokinetic profiles of buprenorphine (0.01 and 0.03 mg/kg IM) and sustained-release buprenorphine (0.2 mg/kg SC) in 2 macaque species (M. mulatta and M. fascicularis) by using mass spectrometry. The pharmacokinetics did not differ significantly between species, and buprenorphine was dose-proportional at the tested doses. The low and high doses of buprenorphine had elimination half-lives of 2.6 ± 0.7 and 5.3 ± 2.0 h, respectively, but the low-dose data were constrained by the sensitivity of the analytical method. Sustained-release buprenorphine had an elimination half-life of 42.6 ± 26.2 h. The AUC0-Tlast of buprenorphine were 9.1 ± 4.3 and 39.0 ± 25.1 ng × h/mL for the low and high doses, respectively, and sustained-release buprenorphine had an AUC0-Tlast of 177 ± 74 ng × h/mL. Assuming a hypothesized therapeutic buprenorphine plasma concentration threshold of 0.1 ng/mL in macaques, these results suggest that buprenorphine doses of 0.01 mg/kg IM should be administered every 6 to 8 h, whereas doses of 0.03 mg/kg IM can be administered every 12 h. These results further demonstrate that a single 0.2-mg/kg SC injection of sustained-release buprenorphine maintains plasma concentrations above 0.1 ng/mL for 5 d in macaques. These findings support a new dosing strategy using sustained-release buprenorphine to improve pain management, decrease animal stress, improve animal welfare, and simplify the postoperative management of nonhuman primates in laboratory animal and zoological settings.

Quantitative structure-property relationship modeling of remote liposome loading of drugs

Remote loading of liposomes by trans-membrane gradients is used to achieve therapeutically efficacious intra-liposome concentrations of drugs. We have developed Quantitative Structure Property Relationship (QSPR) models of remote liposome loading for a data set including 60 drugs studied in 366 loading experiments internally or elsewhere. Both experimental conditions and computed chemical descriptors were employed as independent variables to predict the initial drug/lipid ratio (D/L) required to achieve high loading efficiency. Both binary (to distinguish high vs. low initial D/L) and continuous (to predict real D/L values) models were generated using advanced machine learning approaches and 5-fold external validation. The external prediction accuracy for binary models was as high as 91-96%; for continuous models the mean coefficient R(2) for regression between predicted versus observed values was 0.76-0.79. We conclude that QSPR models can be used to identify candidate drugs expected to have high remote loading capacity while simultaneously optimizing the design of formulation experiments.

Pharmacokinetics and behavioral effects of liposomal hydromorphone suitable for perioperative use in rhesus macaques

INTRODUCTION

This study aims to evaluate the pharmacokinetic, behavioral, and motor effects of a liposomal preparation of hydromorphone hydrochloride (LE-hydro) in rhesus monkeys. We administered either 2 mg/kg of LE-hydro (n = 8) subcutaneous (s.c.) or 0.1 mg/kg of standard pharmaceutical hydromorphone HCl (hydro) preparation either intravenous (i.v.; n = 4) or s.c. (n = 5).

MATERIALS AND METHODS

Serial blood samples were drawn after injection and analyzed for serum hydro concentration by liquid chromatography/mass spectrometry. Following s.c. injection of 0.1 mg/kg hydro or 2 mg/kg LE-hydro, behavioral evaluations were conducted in groups of rhesus monkeys (n = 10/group) in the presence of a compatible stimulus animal and motor skills were also evaluated (n = 10/group). The motor skills test consisted of removing a food reward (carrot ring) from either a straight peg (simple task) or a curved peg (difficult task).

RESULTS

LE-hydro (MRT(0-INF) = 105.9 h) demonstrated extended-release pharmacokinetics compared to hydro when administered by either i.v. (MRT(0-INF) =1.1 h) or s.c. (MRT(0-INF) =1.3 h) routes. Hydro did not affect motor performance of the simpler task, but the monkeys' performance deteriorated on the more difficult task at 0.5 and 1 h after injection. LE-hydro had no effect on motor skills in either the simpler or more difficult task.

CONCLUSIONS

The results of these studies indicate that LE-hydro has a pharmacokinetic and behavioral side effects profile consistent with an analgesic that could be tested for surgical use in animals. Our studies also expand the use of rhesus monkeys as a translational behavioral pharmacodynamics model for testing extended-release opioid medication.

Epidural administration of liposome-encapsulated hydromorphone provides extended analgesia in a rodent model of stifle arthritis

Liposome encapsulation of opioids by using an ammonium-sulfate-gradient loading technique significantly slows the release time of the drug. This study evaluated the duration of analgesia in a rodent model of monoarthritis after epidural administration of liposome-encapsulated hydromorphone (LE-hydromorphone; prepared by ammonium-sulfate-gradient loading) compared with standard hydromorphone and a negative control of blank liposomes. Analgesia was assessed by changes in thermal withdrawal latency, relative weight-bearing, and subjective behavioral scoring. Analgesia in arthritic rats was short-lived after epidural hydromorphone; increases in pain threshold were observed only at 2 h after administration. In contrast, thermal pain thresholds after epidural LE-hydromorphone were increased for as long as 72 h, and subjective lameness scores were lower for as long as 96 h after epidural administration. Injection of LE-hydromorphone epidurally was associated with various mild changes in CNS behavior, and 2 rats succumbed to respiratory depression and death. In conclusion, LE-hydromorphone prolonged the duration of epidural analgesia compared with the standard formulation of hydromorphone, but CNS side effects warrant careful administration of this LE-hydromorphone in future studies.

Pharmacokinetics of oxymorphone in titi monkeys (Callicebus spp.) and rhesus macaques (Macaca mulatta)

Oxymorphone is a pure μ-opioid receptor agonist that is commonly used in nonhuman primate medicine and surgery to minimize pain ranging in intensity from moderate to severe. We compared pharmacokinetic profiles and physiologic and behavioral responses to oxymorphone between titi monkeys (Callicebus spp.) and rhesus macaques (Macaca mulatta). Titi monkeys (n = 4) and rhesus macaques (n = 4) were injected intravenously with either a bolus of 0.075 mg/kg oxymorphone or placebo on multiple occasions, with a minimal washout period of 14 d between trials. Blood collection was limited to no more than 3 samples per trial, with samples collected at multiple time points until 10 h after injection. Collection periods, animal order, and testing day were randomized. In addition, macaques underwent a single serial collection at all time points to validate study design. A 2-compartment model best described the disposition of oxymorphone in both species. Clearance was faster in macaques than titi monkeys, in which terminal half-life was longer. Statistically significant physiologic differences were found between species and between treatments within species. Apart from these effects, oxymorphone did not significantly change physiologic parameters over time. After oxymorphone treatment, macaques demonstrated behaviors reflecting pruritis, whereas titi monkeys exhibited sedation. Despite its mild side effects, we recommend the consideration of oxymorphone for pain management protocols in both Old and New World nonhuman primates.

A mathematical relationship for hydromorphone loading into liposomes with trans-membrane ammonium sulfate gradients

We have studied the loading of the opioid hydromorphone into liposomes using ammonium sulfate gradients. Unlike other drugs loaded with this technique, hydromorphone is freely soluble as the sulfate salt, and, consequently, does not precipitate in the liposomes after loading. We have derived a mathematical relationship that can predict the extent of loading based on the ammonium ion content of the liposomes and the amount of drug added for loading. We have adapted and used the Berthelot indophenol assay to measure the amount of ammonium ions in the liposomes. Plots of the inverse of the fraction of hydromorphone loaded versus the amount of hydromorphone added are linear, and the slope should be the inverse of the amount of ammonium ions present in the liposomes. The inverse of the slopes obtained closely correspond to the amount of ammonium ions in the liposomes measured with the Berthelot indophenol assay. We also show that loading can be less than optimal under conditions where osmotically driven loss of ammonium ions or leakage of drug after loading may occur.