Selected indole-based kratom alkaloids were evaluated for their opioid and adrenergic receptor binding and functional effects, in vivo antinociceptive effects, plasma protein binding, and metabolic ...stability. Mitragynine, the major alkaloid in
(kratom), had higher affinity at opioid receptors than at adrenergic receptors while the vice versa was observed for corynantheidine. The observed polypharmacology of kratom alkaloids may support its utilization to treat opioid use disorder and withdrawal.
Relationships between
-opioid receptor (MOR) efficacy and effects of mitragynine and 7-hydroxymitragynine are not fully established. We assessed in vitro binding affinity and efficacy and ...discriminative stimulus effects together with antinociception in rats. The binding affinities of mitragynine and 7-hydroxymitragynine at MOR (K
values 77.9 and 709 nM, respectively) were higher than their binding affinities at
-opioid receptor (KOR) or
-opioid receptor (DOR).
Sguanosine 5'-
-
-thiotriphosphate stimulation at MOR demonstrated that mitragynine was an antagonist, whereas 7-hydroxymitragynine was a partial agonist (E
= 41.3%). In separate groups of rats discriminating either morphine (3.2 mg/kg) or mitragynine (32 mg/kg), mitragynine produced a maximum of 72.3% morphine-lever responding, and morphine produced a maximum of 65.4% mitragynine-lever responding. Other MOR agonists produced high percentages of drug-lever responding in the morphine and mitragynine discrimination assays: 7-hydroxymitragynine (99.7% and 98.1%, respectively), fentanyl (99.7% and 80.1%, respectively), buprenorphine (99.8% and 79.4%, respectively), and nalbuphine (99.4% and 98.3%, respectively). In the morphine and mitragynine discrimination assays, the KOR agonist U69,593 produced maximums of 72.3% and 22.3%, respectively, and the DOR agonist SNC 80 produced maximums of 34.3% and 23.0%, respectively. 7-Hydroxymitragynine produced antinociception; mitragynine did not. Naltrexone antagonized all of the effects of morphine and 7-hydroxymitragynine; naltrexone antagonized the discriminative stimulus effects of mitragynine but not its rate-decreasing effects. Mitragynine increased the potency of the morphine discrimination yet decreased morphine antinociception. Here we illustrate striking differences in MOR efficacy, with mitragynine having less than 7-hydroxymitragynine. SIGNIFICANCE STATEMENT: At human
-opioid receptor (MOR) in vitro, mitragynine has low affinity and is an antagonist, whereas 7-hydroxymitragynine has 9-fold higher affinity than mitragynine and is an MOR partial agonist. In rats, intraperitoneal mitragynine exhibits a complex pharmacology including MOR agonism; 7-hydroxymitragynine has higher MOR potency and efficacy than mitragynine. These results are consistent with 7-hydroxymitragynine being a highly selective MOR agonist and with mitragynine having a complex pharmacology that combines low efficacy MOR agonism with activity at nonopioid receptors.
Rationale
Mitragyna speciosa
(kratom) may hold promise as both an analgesic and treatment for opioid use disorder. Mitragynine, its primary alkaloid constituent, is an opioid receptor ligand. ...However, the extent to which the in vivo effects of mitragynine are mediated by opioid receptors, or whether mitragynine interacts with other opioid agonists, is not fully established.
Objectives
The effects of mitragynine and the prototypical opioid agonist morphine were compared for their capacity to decrease operant responding for food delivery, and to increase response latency to a thermal stimulus.
Methods
Male and female Sprague-Dawley rats responded under a multiple cycle fixed ratio 10 schedule of food delivery and were tested on a hot plate (52 °C) immediately after each cycle. Morphine and mitragynine were administered alone, in combination with each other, and in combination with the opioid antagonist naltrexone.
Results
Morphine and mitragynine dose-dependently decreased schedule-controlled responding; the ED
50
values were 7.3 and 31.5 mg/kg, respectively. Both drugs increased thermal antinociception; the ED
50
value for morphine was 18.3. Further, doses of naltrexone that antagonized morphine did not antagonize mitragynine. Mitragynine (17.8 mg/kg) did not alter the rate-decreasing or antinociceptive effects of morphine.
Conclusions
The antinociceptive effects of mitragynine and morphine occur at doses larger than those that disrupt learned behavior. Opioid receptors do not appear to mediate the disruptive effects of mitragynine on learned behavior. Mitragynine had lesser antinociceptive effects than morphine, and these did not appear to be mediated by opioid receptors. The pharmacology of mitragynine includes a substantial non-opioid mechanism.
Whole-body plethysmography (WBP) in unrestrained, non-anesthetized rodents is a preclinical method to assess the respiratory depressant effects of opioids, the leading cause of opioid overdose death ...in humans. However, low baseline respiration rates under normocapnic conditions (i.e., “floor” effect) can render the measurement of respiratory decreases challenging. We assessed hypercapnia-induced increases in respiration as a strategy to assess opioid-induced decreases in respiration in rats.
WBP was used to assess respiration frequency, tidal volume and minute volume in the presence of normocapnic and hypercapnic (8% CO2) conditions in rats during the rat diurnal period of the light cycle. The mu-opioid receptor agonist fentanyl was administered intravenously, and the hot plate test was used to assess acute antinociception.
Hypercapnia-induced increases in respiratory parameters (frequency, minute volume, and tidal volume) were decreased by fentanyl at doses that did not decrease the same parameters under the normocapnic conditions. These findings show that hypercapnia increases sensitivity to respiratory depressant effects of fentanyl, as compared with assessments during the rat diurnal period when activity and breathing rate are generally low, i.e., there is a floor effect. The current approach is highly sensitive to opioid-induced respiratory depression, and therefore provides a useful method for assessment in a pre-clinical setting.
Abstract only
There is an overdose epidemic associated with the use of illicitly manufactured as well as prescription mu‐opioid receptor agonists. Sigma
1
receptor (σ
1
R) antagonists in combination ...with other drugs may provide a viable, safer pharmacological option than opioids alone for treating pain. The present study compared pharmacological effects of the σ
1
R antagonist CM304 alone and in combination with high (fentanyl and morphine) and low (buprenorphine) efficacy opioid agonists and the cannabinoid CB (CP55,940 and THC) receptor agonists in C57BL/6J mice. Rectal temperature, tail withdrawal latency (10‐seconds cutoff) from warm water of various temperatures (45°C, 50°C and 55°C) and counts of unhabituated locomotor activity were measured in this order. Basal latency for tail withdrawal systematically decreased from 10 seconds at 45°C to 1.3 seconds at 55°C. Morphine, fentanyl and buprenorphine dose‐dependently increased maximum possible effects (MPEs) up to 100% at 55°C (ED
50
values: 7.50, 0.068, and 1.13 mg/kg, respectively), whereas CP55,940 and THC were less effective at 55°C (E
max
values: 56.6% and 58.2%, respectively). CM304 (56 mg/kg, i.p.) produced an upward shift in the CP55,940 dose‐effect function such that 100% MPE was achieved at 3.2 mg/kg CP55,940, while CM304 (56 mg/kg) produced a 3‐fold leftward shift in the dose‐effect curve of THC. On the other hand, CM304 did not enhance the antinociceptive effects of morphine and fentanyl but enhanced the effects of buprenorphine. In contrast to tail withdrawal latency, there were no consistent effects of CM304 on cannabinoid‐induced decreases in rectal temperature or locomotor activity. The present results may support the development of a σ
1
R antagonist as an adjunct to cannabinoid and low efficacy μ‐opioid receptor agonists for the treatment of acute pain.
Support or Funding Information
This work was supported by National Institute on Drug Abuse grants DA23205 and DA48353.
Abstract only
Mitragyna speciosa
(kratom) has been used as a treatment for opioid use disorder in Southeast Asia. The primary kratom alkaloid mitragynine has received much attention due to its opioid ...pharmacology. One of the
in vivo
metabolites of mitragynine, 7‐hydroxymitragynine, is a more potent μ‐opioid receptor agonist than mitragynine; this has led to the hypothesis that mitragynine is a prodrug that exerts opioid agonist activity, in part, through metabolic conversion to 7‐hydroxymitragynine. Here, we investigated this hypothesis by comparing mitragynine and 7‐hydroxymitragynine for 1)
in vitro
binding affinity (
3
HDAMGO) and efficacy (GTPgS) at the μ‐opioid receptor, 2) plasma levels following p.o. mitragynine using a UPLC‐MS/MS method, and 3) potency and effectiveness to produce acute antinociception in the hotplate assay at 52° C. In the hotplate assay, the i.v. route of administration was used to minimize the conversion of mitragynine to 7‐hydroxymitragynine in order to directly compare the pharmacology of the two alkaloids. The binding affinity of 7‐hydroxymitragynine at the human μ‐opioid receptor (Ki=78 nM) was 22‐fold lower than morphine and 9.0‐fold higher than mitragynine. The % maximum GTPgS stimulations of 7‐hydroxymitragynine and morphine at the μ‐opioid receptor were 45% (up to 30 μM) and 90% (up to 30 μM), respectively. In contrast, mitragynine (up to 100 μM) did not significantly stimulate GTPgS. Following p.o. administration of mitragynine (HCl salt, 55 mg/kg), the Cmax value of 7‐hydroxymitragynine (85 ng/mL) was 14‐fold less than that of mitragynine. The Tmax values of 7‐hydroxymitragynine and mitragynine were 30 and 84 minutes, respectively. The % metabolite ratio (AUC
7‐hydroxymitragynine
/AUC
mitragynine
)*100 was 8%. The % maximum possible effects (MPE, ED
50
values in mg/kg, i.v.) of 7‐hydroxymitragynine (up to 0.1 mg/kg), morphine (up to 1.0 mg/kg) and mitragynine (up to 17.8 mg/kg) were 100% (1.9), 100% (5.1) and 34% (>17.8). In addition, 32 mg/kg mitragynine was lethal. Finally, drug discrimination was used as a pharmacologically selective measure of μ‐opioid receptor agonism
in vivo
. In rats discriminating morphine (3.2 mg/kg, i.p.) from vehicle, the discriminative stimulus effects of mitragynine were assessed 90 minutes after p.o. administration to correspond to its Tmax. Mitragynine (up to 178 mg/kg) produced 76% morphine‐lever responding (ED
50
=51 mg/kg). Though the conversion rate of 7‐hydroxymitragynine from p.o. mitragynine is low, 7‐hydroxymitragynine is a more potent and efficacious μ‐opioid receptor agonist than mitragynine, suggesting that conversion to this metabolite may contribute to the
in vivo
μ‐opioid activity of mitragynine.
Support or Funding Information
Supported by NIDA grants DA23205 and DA48353.
Abstract only
Opioid overdose is one of the leading causes of death in the United States in people under 50 years, which has resulted in a decline in life expectancy in the United States. Thus, there ...is a need for an alternative to prescription mu‐opioid agonists for pain treatment. Delta (9)‐tetrahydrocannabinol (THC), a cannabinoid (CB) agonist, has been shown to produce antinociceptive effects albeit less effectively than mu‐opioid receptor agonists. Sigma
1
receptor (σ
1
R) antagonists in combination with THC may provide a viable and safe pharmacological alternative to prescription opioids for pain treatment. The present study compared the pharmacological effects of the σ
1
R antagonist CM304 alone and in combination with THC in Sprague Dawley rats. Hotplate latency was determined at 52°C followed by rectal temperature measurement and the drugs were administered intravenously (i.v.) and in cumulative doses every 5 min. THC dose‐dependently increased maximum possible effects (MPEs) up to 84% which were reversed by 10 mg/kg rimonabant (cannabinoid CB
1
receptor antagonist). CM304 alone up to a dose of 10 mg/kg did not produce significant antinociceptive or hypothermic effects, but CM304 (1.0 and 3.2 mg/kg, i.v.) dose‐dependently left‐shifted the dose‐effect functions of the antinociceptive (7.3‐fold at 3.2 mg/kg CM304) and hypothermic effects of THC. In rats discriminating 3.2 mg/kg THC i.p. from vehicle under a fixed ratio (FR) 10 schedule of food delivery, the cannabinoid CB
1
receptor agonist CP55,940 fully substituted for THC, whereas CM304 i.p. produced a maximum of 27 % THC‐lever responding at 17.8 mg/kg. CM304, at doses of 32 and 56 mg/kg, decreased response rate to 24 and 9 %, respectively. No dose of BD1063 (σ
1
R antagonist), rimonabant, SR144528 (cannabinoid CB
2
receptor antagonist), morphine (μ‐opioid receptor agonist), or naltrexone (opioid antagonist) produced greater than 30% THC‐lever responding. Pretreatment with rimonabant (1.78 mg/kg) produced a rightward shift in the dose effect curve of THC (4.5‐fold) and CP55940 (4.5‐fold) while pretreatment with CM304, BD1063, SR144528, and naltrexone had no significant effect on the dose effect curve of THC. The present results may support the development of a σ
1
R antagonist as an adjunct to cannabinoids for treatment of acute pain without enhancing an undesirable side effect of THC.
Support or Funding Information
This work was supported by National Institute on Drug Abuse grants DA23205 and DA48353.
Objectives
Determine whether levels of anxiety and depression, cognitive ability, and self-quarantining during and prior to the pandemic predict decreases in perceived functional ability.
Design and ...Setting
Longitudinal data collected from the Canadian Longitudinal Study on Aging (CLSA) COVID-19 Questionnaire Study (2020) and core CLSA study (Follow-Up 1; 2014-2018).
Participants
17 541 CLSA participants.
Measurements
Self-quarantining behaviours from questionnaires administered at Baseline (April 2020), Monthly, and Exit (December 2020) time points of the CLSA COVID-19 Questionnaire Study, levels of anxiety and depression at Baseline, perceived change in functional ability at Exit, and performance on neuropsychological tests (Rey Auditory Verbal Learning Task, Mental Alternation Task, Animal Fluency Test) and functional ability (Older Americans Resources and Services OARS Multidimensional Assessment Questionnaire) from the core CLSA study.
Results
Greater cognitive ability pre-pandemic (B = −.003, P < .01), higher levels of anxiety (B = −.024, P < .01) and depressive symptoms (B = −.110, P < .01) at Baseline, and higher frequency of engaging in self-quarantining throughout the COVID-19 survey period (B = −.098, P < .01) were associated with perceived loss in functional ability at Exit. Self-quarantining behaviour was associated with perceived loss in functional ability only at average and high levels of depressive symptoms (B = −.013, P < .01).
Conclusions
Older adults with higher cognitive and lower functional ability prior to the pandemic were at greater risk of decreased perceived functional ability during the first year of the pandemic, as were those who experienced greater levels of anxiety and depressive symptoms during the pandemic. Strategies/interventions to preserve functional ability in older adults with cognitive independence prior to future pandemics are warranted.
Introduction
Adjuvant chemotherapy is recommended in patients with stage II colon cancer with high-risk features (HRF). However, there is no quantification of the amount of risk conferred by each HRF ...or the overall survival (OS) benefit gained by chemotherapy based on the risk factor.
Objective
To assess survival benefits associated with adjuvant chemotherapy among stage II colon cancer patients having one or more HRF T4 tumors, less than 12 lymph nodes examined (< 12LN), positive margins, high-grade tumor, perineural invasion (PNI), and lymphovascular invasion (LVI).
Methods
Patients diagnosed with stage II colon cancer between 2010 and 2013 were identified from California Cancer Registry. Propensity score weighted all-cause mortality hazard ratios (HR) were calculated for combinations of HRF.
Results
A total of 5160 stage II colon cancer patients were identified, of which 2398 had at least one HRF and 510 of 2398 (21%) received adjuvant chemotherapy. Compared with patients with a single HRF, presence of any 2 or ≥ 3 HRF showed increasingly poorer survival HR 1.42, 95% confidence interval (CI) 1.16–1.73 and HR 2.50, 95% CI 1.96–3.20, respectively. Chemotherapy was associated with improved overall survival only among patients with T4 as the single HRF (HR 0.51, 95% CI 0.34–0.78) or combinations involving T4 as T4/< 12 LN (HR 0.31, 95% CI 0.11–0.90), T4/high grade (HR 0.26, 95% CI 0.11–0.61), and T4/LVI (HR 0.16, 95% CI 0.04–0.61).
Conclusions
Not all high-risk features have similar adverse effects on OS. T4 tumors and their combination with other HRF achieve the most survival benefit with adjuvant therapy. Type and number of high-risk features should be taken into consideration when recommending adjuvant chemotherapy in stage II colon cancer.
CONTEXT: More than a century of forest and fire management of Inland Pacific landscapes has transformed their successional and disturbance dynamics. Regional connectivity of many terrestrial and ...aquatic habitats is fragmented, flows of some ecological and physical processes have been altered in space and time, and the frequency, size and intensity of many disturbances that configure these habitats have been altered. Current efforts to address these impacts yield a small footprint in comparison to wildfires and insect outbreaks. Moreover, many current projects emphasize thinning and fuels reduction within individual forest stands, while overlooking large-scale habitat connectivity and disturbance flow issues. METHODS: We provide a framework for landscape restoration, offering seven principles. We discuss their implication for management, and illustrate their application with examples. RESULTS: Historical forests were spatially heterogeneous at multiple scales. Heterogeneity was the result of variability and interactions among native ecological patterns and processes, including successional and disturbance processes regulated by climatic and topographic drivers. Native flora and fauna were adapted to these conditions, which conferred a measure of resilience to variability in climate and recurrent contagious disturbances. CONCLUSIONS: To restore key characteristics of this resilience to current landscapes, planning and management are needed at ecoregion, local landscape, successional patch, and tree neighborhood scales. Restoration that works effectively across ownerships and allocations will require active thinking about landscapes as socio-ecological systems that provide services to people within the finite capacities of ecosystems. We focus attention on landscape-level prescriptions as foundational to restoration planning and execution.
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