Metabolic clearance of select opioids and opioid antagonists using hepatic spheroids and recombinant cytochrome P450 enzymes.

The opioid crisis is a pressing public health issue, exacerbated by the emergence of more potent synthetic opioids, particularly fentanyl and its analogs. While competitive antagonists exist, their efficacy against synthetic opioids is largely unknown. Furthermore, due to the short durations of action of current antagonists, renarcotization remains a concern. In this study, metabolic activity was characterized for fentanyl-class opioids and common opioid antagonists using multiple in vitro systems, namely, cytochrome P450 (CYP) enzymes and hepatic spheroids, after which an in vitro-in vivo correlation was applied to convert in vitro metabolic activity to predictive in vivo intrinsic clearance. For all substrates, intrinsic hepatic metabolism was higher than the composite of CYP activities, due to fundamental differences between whole cells and single enzymatic reactions. Of the CYP isozymes investigated, 3A4 yielded the highest absolute and relative metabolism across all substrates, with largely negligible contributions from 2D6 and 2C19. Comparative analysis highlighted elevated lipophilicity and diminished CYP3A4 activity as potential considerations for the development of more efficacious opioid antagonists. Finally, antagonists with a high degree of molecular similarity exhibited comparable clearance, providing a basis for structure-metabolism relationships. Together, these results provide multiple screening criteria for early stage drug discovery involving opioid countermeasures.

Cardiopulmonary effects of phosphine poisoning: A preliminary evaluation of milrinone.

Exposure to phosphine (PH3) presents with a host of diverse, non-specific symptoms that span multiple organ systems and is characterized by a high mortality rate. While a comprehensive mechanism for PH3 poisoning remains inconclusive, prior studies have implicated cardiac failure and circulatory compromise as potential pathways central to PH3-induced mortality. In this study, milrinone (MLR), a phosphodiesterase-3 inhibitor used to treat cardiac failure, was investigated as a potential countermeasure for PH3 poisoning. Lethality, physiological responses, and behavioral changes were evaluated in telemetrized female rats pretreated with water (sham) or one of three doses of MLR (40, 200, or 600 µg/kg) and exposed to PH3 (660 ppm for 25-40 min; 16,500-26,400 ppm × min). Animals receiving prophylactic administration of 600 µg/kg of MLR had nominally improved survivability compared to sham animals, although median lethal concentration-time and time of death did not differ substantially between treatment groups. Changes in respiration and behavior induced by PH3 appeared largely unaffected by MLR pretreatment, regardless of dose. Conversely, MLR pretreatment alleviated some aspects of PH3-induced cardiac function impairment, with slight dose-dependent effects observed for cardiac contractility, mean arterial pressure, and QRS duration. Together, these results illustrate the importance of circulatory compromise in PH3 poisoning and highlight the potential viability of MLR as a potential countermeasure option or part of a countermeasure regimen when administered prophylactically at 600 µg/kg.

Assessment of naloxone as a therapeutic for inhaled carfentanil in the ferret.

Carfentanil is a powerful synthetic opioid that is approximately 100 times more potent than fentanyl and 10,000 times more potent than morphine. Carfentanil was originally intended to be used as a sedative for big game animals in a veterinary setting, but it is becoming increasingly recognized as a public health concern. We set out to investigate the effectiveness of naloxone against a potentially lethal dose of inhaled carfentanil in male ferrets. Ferrets were implanted with telemetry devices to study cardiac parameters and exposed to aerosolized carfentanil in a whole-body plethysmography chamber to record respiratory parameters. We observed profound respiratory depression in exposed animals, which led to apneic periods constituting 24-31 % of the exposure period. Concomitant with these apneic periods, we also observed cardiac abnormalities in the form of premature junctional contractions (PJCs). At our acute exposure dose, lethal in 3 % of our animals, naïve ferrets were unresponsive and incapacitated for a total of 126.1 ± 24.6 min. When administered intramuscularly at human equivalent doses (HEDs) of either 5 mg or 10 mg, naloxone significantly reduced the time that ferrets were incapacitated following exposure, although we observed no significant difference in the reduction of time that the animals were incapacitated between the treatment groups. Naloxone was able to quickly resolve the respiratory depression, significantly reducing the frequency of apneic periods in carfentanil-exposed ferrets. Our results suggest that naloxone, when administered via intramuscular injection following incapacitation, is a viable treatment against the effects of a potentially lethal dose of inhaled carfentanil.

Methylene blue and monosodium glutamate improve neurologic signs after fluoroacetate poisoning.

Fluoroacetate (FA) is a tasteless, odorless, water-soluble metabolic poison with severe toxicological effects. Characterized in the mid-1900s, it has been used as a rodenticide but is comparably lethal to all mammals. Many countries have restricted its use, and modern-day accidental human exposures are rare, but recently, concerns have been raised about its application as a chemical weapon with no known antidote. A combined treatment of methylene blue (MB), an antioxidant, and monosodium glutamate (MSG), a precursor of the citric acid cycle substrate alpha-ketoglutarate, has been recommended as an effective countermeasure; however, no peer-reviewed articles documenting the efficacy of this therapy have been published. Using a rodent model, we assessed the effects of MB and MSG on the neurologic, cardiac, and pulmonary systems. Transcriptomic analysis was used to elucidate inflammatory pathway activation and guide bioassays, which revealed the advantages and disadvantages of these candidate countermeasures. Results show that MB and MSG can reduce neurologic signs observed in rats exposed to sodium FA and improve some effects of intoxication. However, while this strategy resolved some signs of intoxication, ultimately it was unable to significantly reduce lethality.

A sex-balanced rodent model for evaluating phosphine inhalation toxicity.

Exposure to phosphine (PH3 ), a common grain fumigant, is characterized by diverse nonspecific symptoms and a high mortality rate. Although PH3 poisoning is thought to target oxidative respiration, the exact mechanism of action remains largely unknown, resulting in limited treatment options. In our study, the effects of PH3 on female rats were assessed to elucidate potential sex-specific differences and obtain a more comprehensive understanding of PH3 toxicity. Lethality, physiology, and behavior were evaluated in female rats exposed to gaseous PH3 (13,200-26,400 ppm × min), and results were compared with corresponding findings in male rats. Median lethal concentration-time (LCt50 ) and time of death (tTOD ) did not differ significantly between the sexes. Cardiopulmonary changes induced by PH3 were also of comparable magnitude, although temporally, respiratory responses occurred earlier and cardiovascular variations manifested later in female rats. Behavioral observations corroborated physiological findings and indicated a response to hypoxic conditions and low cardiac output. Together, these results provided insights on the toxic mechanisms of PH3 , in particular, its potential interference with oxygen transport and circulation.

Changes in murine respiratory dynamics induced by aerosolized carfentanil inhalation: Efficacy of naloxone and naltrexone.

Carfentanil (CRF) is an extremely potent opioid capable of inducing fatal respiratory depression. Naloxone (NX) and naltrexone (NTX) are opioid antagonists for which the efficacy against CRF remains largely unexplored. In this study, the effects of aerosolized CRF on respiratory function were investigated using adult male CD-1 mice. Mice were exposed to 0.4 mg/m3 of CRF for 15 min using custom whole-body plethysmograph units. Minute volume (MV), respiratory frequency (f), duty cycle (DC), and tidal volume (TV) were monitored and compared to control animals exposed to aerosolized H2O. CRF exposure induced respiratory depression, characterized by a marked decrease in MV, which was sustained throughout 24 h post-exposure. Prophylactic and therapeutic treatment with intramuscular (i.m.) NX marginally improved MV, with slight dose-dependent effects. Analogous treatment with i.m. NTX returned MV to baseline levels, with all doses and intervention times performing similarly. Despite improvements in MV, treatment administration did not reverse changes in DC, a measure of respiratory timing. Overall, NX and NTX administration alleviated volumetric aspects of opioid-induced respiratory toxicity, while changes in respiratory timing remained unresolved throughout post-exposure observation. These sustained changes and differences in recovery between two aspects of respiratory dynamics may provide insights for further exploration into the underlying mechanism of action of opioids and opioid antagonists.

Chemical and cellular oxidant production induced by naphthalene secondary organic aerosol (SOA): effect of redox-active metals and photochemical aging.

Exposure to air pollution is a leading global health risk. Secondary organic aerosol (SOA) constitute a large portion of ambient particulate matter (PM). In this study, the water-soluble oxidative potential (OP) determined by dithiothreitol (DTT) consumption and intracellular reactive oxygen and nitrogen species (ROS/RNS) production was measured for SOA generated from the photooxidation of naphthalene in the presence of iron sulfate and ammonium sulfate seed particles. The measured intrinsic OP varied for aerosol formed using different initial naphthalene concentrations, however, no trends were observed between OP and bulk aerosol composition or seed type. For all experiments, aerosol generated in the presence of iron-containing seed induced higher ROS/RNS production compared to that formed in the presence of inorganic seed. This effect was primarily attributed to differences in aerosol carbon oxidation state [Formula: see text]. In the presence of iron, radical concentrations are elevated via iron redox cycling, resulting in more oxidized species. An exponential trend was also observed between ROS/RNS and [Formula: see text] for all naphthalene SOA, regardless of seed type or aerosol formation condition. This may have important implications as aerosol have an atmospheric lifetime of a week, over which [Formula: see text] increases due to continued photochemical aging, potentially resulting in more toxic aerosol.