Cannabinoid-2 Agonism with AM2301 Mitigates Morphine-Induced Respiratory Depression

CB 1 Cannabinoid Receptor Agonists Induce Acute Respiratory Depression in Awake Mice

Recreational use of synthetic cannabinoid agonists (i.e., "Spice" compounds) that target the Cannabinoid Type 1 receptor (CB 1 ) can cause respiratory depression in humans. However, Δ 9 -tetrahydrocannabinol (THC), the major psychoactive phytocannabinoid in cannabis, is not traditionally thought to interact with CNS control of respiration, based largely upon sparse labeling of CB1 receptors in the medulla and few reports of clinically significant respiratory depression following cannabis overdose. The respiratory effects of CB 1 agonists have rarely been studied in vivo , suggesting that additional inquiry is required to reconcile the conflict between conventional wisdom and human data. Here we used whole body plethysmography to examine the respiratory effects of the synthetic high efficacy CB 1 agonist CP55,940, and the low efficacy CB 1 agonist Δ 9 -tetrahydrocannabinol in male and female mice. CP55,940 and THC, administered systemically, both robustly suppressed minute ventilation. Both cannabinoids also produced sizable reductions in tidal volume, decreasing both peak inspiratory and expiratory flow - measures of respiratory effort. Similarly, both drugs reduced respiratory frequency, decreasing both inspiratory and expiratory time while markedly increasing expiratory pause, and to a lesser extent, inspiratory pause. Respiratory suppressive effects occurred at lower doses in females than in males, and at many of the same doses shown to produce cardinal behavioral signs of CB 1 activation. We next used RNAscope in situ hybridization to localize CB 1 mRNA to glutamatergic neurons in the medullary pre-Bötzinger Complex, a critical nucleus in controlling respiration. Our results show that, contrary to previous conventional wisdom, CB 1 mRNA is expressed in glutamatergic neurons in a brain region essential for breathing and CB 1 agonists can cause significant respiratory depression.

Δ9-Tetrahydrocannabinol Effects on Respiration and Heart Rate Across Route of Administration in Female and Male Mice

The physiological impact of cannabinoid receptor agonists is of great public health interest due to their increased use in recreational and therapeutic contexts. However, the body of literature on cannabinoid receptor agonists includes multiple confounding variables that complicate comparisons across studies, including route of administration, timeline across which phenotypes are observed, agonist dose, and sex of the study cohort. In this study, we characterized the impact of sex and route of administration on Δ9-tetrahydrocannabinol (THC)-induced changes in cardiopulmonary phenotypes in mice. Using noninvasive plethysmography and telemetry, we monitored heart rate and respiration in the same cohort of animals across aerosol, oral gavage, subcutaneous, and intraperitoneal administrations of THC (0-30 mg/kg THC for oral gavage, subcutaneous, and intraperitoneal, and 0-300 mg/ml THC for aerosol). All routes of THC administration altered respiratory minute volume and heart rate, with the direction of effects typically being consistent across dependent measures. THC primarily decreased respiration and heart rate, but females given oral gavage THC showed increased heart rate. Intraperitoneal and subcutaneous THC produced the longest-lasting effects, including THC-induced alterations in physiological parameters for up to 10 h, whereas effects of aerosolized THC were short lived. The fastest onset of effects of THC occurred for aerosolized and intraperitoneal THC. Altogether, the work herein establishes the impact of dosing route on THC-induced heart rate and respiratory alteration in male and female mice. This study highlights important differences in the timeline of cardiopulmonary response to THC following the most common preclinical routes of administration.

Simultaneous fatal poisoning of two victims with 4F-MDMB-BINACA and ethanol

PURPOSE

Methyl-2-(1-(4-fluorobutyl)-1H-indazole-3-carboxamido)-3,3-dimethylbutanoate (4F-MDMB-BINACA) is a newly emerging synthetic cannabinoid receptor agonists (SCRA) first described in 2018 in both Europe and the United States. Two fatal cases are reported caused by simultaneous consumption of 4F-MDMB-BINACA and ethanol.

METHODS

The victims were brothers who were both found deceased after consuming 4F-MDMB-BINACA and ethanol. Post-mortem toxicological analyses of blood and urine were carried out by supercritical fluid chromatography tandem mass spectrometry (SFC-MS/MS) and headspace gas chromatography with flame ionization detection (HS-GC-FID).

RESULTS

The concentration of 4F-MDMB-BINACA in the postmortem blood was 2.50 and 2.34 ng/mL, and blood alcohol concentration was 2.11 and 2.49 g/L, respectively.

CONCLUSION

According to the reported cases and reviews of the scientific literature, concurrent ethanol consumption should amplify the toxicity of SCRAs. The threshold SCRA concentration for fatal overdose can be estimated ng/mL level (0.37-4.1 ng/mL according to the reported cases) in cases in which 1.5-2.5 g/L of ethanol is present in the blood.

The endocannabinoid system and breathing

Recent changes in cannabis accessibility have provided adjunct therapies for patients across numerous disease states and highlights the urgency in understanding how cannabinoids and the endocannabinoid (EC) system interact with other physiological structures. The EC system plays a critical and modulatory role in respiratory homeostasis and pulmonary functionality. Respiratory control begins in the brainstem without peripheral input, and coordinates the preBötzinger complex, a component of the ventral respiratory group that interacts with the dorsal respiratory group to synchronize burstlet activity and drive inspiration. An additional rhythm generator: the retrotrapezoid nucleus/parafacial respiratory group drives active expiration during conditions of exercise or high CO₂. Combined with the feedback information from the periphery: through chemo- and baroreceptors including the carotid bodies, the cranial nerves, stretch of the diaphragm and intercostal muscles, lung tissue, and immune cells, and the cranial nerves, our respiratory system can fine tune motor outputs that ensure we have the oxygen necessary to survive and can expel the CO₂ waste we produce, and every aspect of this process can be influenced by the EC system. The expansion in cannabis access and potential therapeutic benefits, it is essential that investigations continue to uncover the underpinnings and mechanistic workings of the EC system. It is imperative to understand the impact cannabis, and exogenous cannabinoids have on these physiological systems, and how some of these compounds can mitigate respiratory depression when combined with opioids or other medicinal therapies. This review highlights the respiratory system from the perspective of central versus peripheral respiratory functionality and how these behaviors can be influenced by the EC system. This review will summarize the literature available on organic and synthetic cannabinoids in breathing and how that has shaped our understanding of the role of the EC system in respiratory homeostasis. Finally, we look at some potential future therapeutic applications the EC system has to offer for the treatment of respiratory diseases and a possible role in expanding the safety profile of opioid therapies while preventing future opioid overdose fatalities that result from respiratory arrest or persistent apnea.

Brain Penetrant, but not Peripherally Restricted, Synthetic Cannabinoid 1 Receptor Agonists Promote Morphine-Mediated Respiratory Depression

Introduction: Cannabis acceptance and use continues to rise despite the gaps in knowledge regarding the mechanisms of cannabinoids and the endocannabinoid system in many physiological functions, including respiratory influence. Methods: With recent evidence of cannabinoid receptor 1 (CB1R) presence in the collection of respiratory neurons in the brainstem, as well as in the peripheral lung tissue, it is vital that the mechanisms involved in central and peripheral CB1R modulation of respiratory function be delineated. In this study we sought to define the roles of central versus peripheral CB1R activation on respiratory depression alone and in combination with morphine using whole body plethysmography. Results: We show that the peripherally restricted CB1 agonist (4-{2-[-(1E)-1[(4-propylnaphthalen-1-yl)methylidene]-1H-inden-3yl]ethyl}morpholine [PrNMI] 0.3, 0.6, and 1 mg/kg) does not induce respiratory depression, while our previous studies showed that a central penetrating synthetic cannabinoid does induce respiratory depression. Significantly, the combination of morphine with the peripheral CB1 agonist, PrNMI, attenuated morphine-induced respiratory depression. Conclusions: These studies support that a peripherally restricted CB1R agonist may be a unique strategy to attenuate the respiratory depression associated with opioid therapy.

Cannabinoids, the endocannabinoid system, and pain: a review of preclinical studies

ABSTRACT

This narrative review represents an output from the International Association for the Study of Pain's global task force on the use of cannabis, cannabinoids, and cannabis-based medicines for pain management, informed by our companion systematic review and meta-analysis of preclinical studies in this area. Our aims in this review are (1) to describe the value of studying cannabinoids and endogenous cannabinoid (endocannabinoid) system modulators in preclinical/animal models of pain; (2) to discuss both pain-related efficacy and additional pain-relevant effects (adverse and beneficial) of cannabinoids and endocannabinoid system modulators as they pertain to animal models of pathological or injury-related persistent pain; and (3) to identify important directions for future research. In service of these goals, this review (1) provides an overview of the endocannabinoid system and the pharmacology of cannabinoids and endocannabinoid system modulators, with specific relevance to animal models of pathological or injury-related persistent pain; (2) describes pharmacokinetics of cannabinoids in rodents and humans; and (3) highlights differences and discrepancies between preclinical and clinical studies in this area. Preclinical (rodent) models have advanced our understanding of the underlying sites and mechanisms of action of cannabinoids and the endocannabinoid system in suppressing nociceptive signaling and behaviors. We conclude that substantial evidence from animal models supports the contention that cannabinoids and endocannabinoid system modulators hold considerable promise for analgesic drug development, although the challenge of translating this knowledge into clinically useful medicines is not to be underestimated.

History of Respiratory Stimulants

The interest in substances that stimulate respiration has waxed and waned throughout the years, intensifying following the introduction of a new class of drugs that causes respiratory depression, and diminishing when antidotes or better drug alternatives are found. Examples include the opioids--deaths increasing during overprescribing, diminishing with wider availability of the opioid receptor antagonist naloxone, increasing again during COVID-19; the barbiturates--until largely supplanted by the benzodiazepines; propofol; and other central nervous system depressants. Unfortunately, two new troubling phenomena force a reconsideration of the status-quo: (1) overdoses due to highly potent opioids such as fentanyl, and even more-potent licit and illicit fentanyl analogs, and (2) overdose due to polysubstance use (the combination of an opioid plus one or more non-opioid drug, such as a benzodiazepine, sedating antidepressant, skeletal muscle relaxant, or various other agents). Since these now represent the majority of cases, new solutions are again needed. An interest in respiratory stimulants has been revived. This interest can be informed by a short review of the history of this interesting class of medications. We present a short history of the trajectory of advances toward more selective and safer respiratory stimulants.