Antinociceptive effect of 7-hydroxymitragynine in mice: Discovery of an orally active opioid analgesic from the Thai medicinal herb Mitragyna speciosa

Kratom Alkaloids, Cannabinoids, and Chronic Pain: Basis of Potential Utility and Role in Therapy

Introduction: Chronic neuropathic pain is as a severe detriment to overall quality of life for millions of Americans. Current pharmacological treatment options for chronic neuropathic pain are generally limited in efficacy and may pose serious adverse effects such as risk of abuse, nausea, dizziness, and cardiovascular events. Therefore, many individuals have resorted to methods of pharmacological self-treatment. This narrative review summarizes the existing literature on the utilization of two novel approaches for the treatment of chronic pain, cannabinoid constituents of Cannabis sativa and alkaloid constituents of Mitragyna speciosa (kratom), and speculates on the potential therapeutic benefits of co-administration of these two classes of compounds. Methods: We conducted a narrative review summarizing the primary motivations for use of both kratom and cannabis products based on epidemiological data and summarize the pre-clinical evidence supporting the application of both kratom alkaloids and cannabinoids for the treatment of chronic pain. Data collection was performed using the PubMed electronic database. The following word combinations were used: kratom and cannabis, kratom and pain, cannabis and pain, kratom and chronic pain, and cannabis and chronic pain. Results: Epidemiological evidence reports that the self-treatment of pain is a primary motivator for use of both kratom and cannabinoid products among adult Americans. Further evidence shows that use of cannabinoid products may precede kratom use, and that a subset of individuals concurrently uses both kratom and cannabinoid products. Despite its growing popularity as a form of self-treatment of pain, there remains an immense gap in knowledge of the therapeutic efficacy of kratom alkaloids for chronic pain in comparison to that of cannabis-based products, with only three pre-clinical studies having been conducted to date. Conclusion: There is sufficient epidemiological evidence to suggest that both kratom and cannabis products are used to self-treat pain, and that some individuals actively use both drugs, which may produce potential additive or synergistic therapeutic benefits that have not yet been characterized. Given the lack of pre-clinical investigation into the potential therapeutic benefits of kratom alkaloids against forms of chronic pain, further research is warranted to better understand its application as a treatment alternative.

In Vitro and In Vivo Pharmacokinetic Characterization of 7-Hydroxymitragynine, an Active Metabolite of Mitragynine, in Sprague-Dawley Rats

BACKGROUND AND OBJECTIVES

Kratom, a Southeast Asian tree, has been researched for its potential as a therapeutic for substance use disorders. The most abundant alkaloid in kratom, mitragynine, is being investigated individually for opioid use disorder. However, the active metabolite of mitragynine,7-hydroxymitragynine (7-HMG) has raised concerns because of its high binding affinity to μ-opioid receptors and abuse potential. This study examines various pharmacokinetic parameters of 7-HMG in both in vitro and in vivo models.

METHODS

In vitro pharmacokinetic properties were investigated using human colorectal adenocarcinoma cell monolayers (Caco-2 cells), rat plasma, rat liver microsomes, and rat hepatocytes to determine the permeability, plasma protein binding, and microsomal and hepatocyte stability of 7-HMG, respectively. Oral and intravenous (IV) pharmacokinetic studies of 7-HMG were performed in male Sprague-Dawley rats.

RESULTS

7-HMG exhibits high permeability across Caco-2 cells (19.7 ± 1.0 × 10-6 cm/s), with a relatively low plasma protein binding of 73.1 ± 0.6% to mitragynine. The hepatic extraction ratio was 0.3 and 0.6 in rat liver microsomes and hepatocytes, respectively, indicating that 7-HMG is an intermediate hepatic extraction compound. Oral and IV pharmacokinetic studies were performed in male rats. The volume of distribution was 2.7 ± 0.4 l/kg and the clearance was 4.0 ± 0.3 l/h/kg after IV administration. After oral dosing (5 mg/kg), a Cmax of 28.5 ± 5.0 ng/ml and Tmax of 0.3 ± 0.1 h were observed. However, the oral bioavailability of 7-HMG was only 2.7 ± 0.3%. The results demonstrate 7-HMG is rapidly absorbed but has low oral bioavailability. Mitragynine pseudoindoxyl (MGPI) is a metabolite of 7-HMG that is a more potent µ-opioid agonist than 7-HMG. The parent-to-metabolite ratio for MGPI following IV 7-HMG administration was 0.5 ± 0.1%, indicating very limited systemic exposure to MGPI.

CONCLUSIONS

This study reports the pharmacokinetic parameters of 7-HMG to help with the development of mitragynine, as a therapeutic.

Quantification of 11 kratom alkaloids including mitragynine and its main metabolites in human plasma using LC-MS/MS

Recently in the USA, kratom consumers increasingly report use of the plant for self-treatment of mood ailments, the lack of energy, chronic pain, and opioid withdrawal and dependence. Several alkaloids are present in kratom leaves, but limited data are available on their pharmacokinetics/pharmacodynamics, except for mitragynine. To support clinical studies, a high-performance liquid chromatography-tandem mass spectrometry assay for the simultaneous quantification of 11 kratom alkaloids in human plasma was developed and validated. For calibration standards and quality control samples, human plasma was fortified with alkaloids at varying concentrations, and 200 µL were extracted employing a simple one-step protein precipitation procedure. The extracts were analyzed using LC-MS/MS including electrospray ionization (ESI) in positive multiple reaction monitoring (MRM) mode. The lower limit of quantification was 0.5 ng/mL, and the upper limit of quantification was 400 ng/mL for all analytes. Inter-day analytical accuracy and imprecision ranged from 98.4 to 113% of nominal and from 3.9 to 14.7% (coefficient of variance), respectively. The analysis of plasma samples collected during a clinical trial administering capsules containing kratom leaf extract showed that most samples had quantifiable concentrations of mitragynine, 7-OH-mitragynine, speciogynine, speciociliatine, and paynantheine and that mitragynine, speciogynine, and speciociliatine accumulated in human plasma after daily administration over 15 days. An LC-MS/MS assay for the specific quantification of kratom alkaloids including mitragynine and its main metabolites was developed and successfully validated in human plasma. Human plasma samples collected following multiple oral administrations of a controlled Kratom extract documented accumulation of kratom alkaloids over 15 days.

Kratom: A Narrative Review of the Possible Clinical Uses and Dangers of This Opioid-Like Plant

The term "kratom" refers to a plant species formally known as Mitragyna speciosa. Kratom is composed of over 40 alkaloids, a type of organic compound that contains nitrogen. These compounds work primarily via binding to opioid receptors expressed on neurons, where they stimulate signal transduction mechanisms involving the activation of G proteins. Kratom has been shown to cause both a stimulant-like effect and a sedative effect in humans. These studies have shown that use is highest among European-American, middle-class men living in suburban areas. Additionally, individuals who have a history of opioid misuse are also more likely to take kratom. Kratom is used by many different people in the US for numerous different reasons. Some of the most often cited reasons include treating chronic pain conditions, depression, and anxiety. Individuals who used kratom for these reasons typically consumed kratom daily at a dose of 1-3 grams, with the kratom extracted into a powder to be consumed in a capsule. Additionally, there have been reports of kratom being used to treat opioid withdrawal symptoms, as kratom can bind to some of the same receptors as opioids. This manuscript specifically describes trends regarding the use of kratom in the US, pharmacokinetic and pharmacodynamic properties of kratom, potential therapeutic uses of kratom, adverse events caused by kratom, and case studies in the literature regarding patients using kratom.

An in vitro evaluation on metabolism of mitragynine to 9-O-demethylmitragynine

Kratom (Mitragyna Speciosa Korth.) is an indigenous tree native to Southeast Asia whose leaves have been traditionally ingested as a tea and has seen its popularity increase in the United States. Although kratom and its constituents presently have no approved uses by the Food and Drug Administration, its major alkaloids (e.g., mitragynine) have psychoactive properties that may hold promise for the treatment of opioid cessation, pain management, and other indications. 9-O-demethylmitragynine is a major metabolite formed from mitragynine metabolism (36 % total metabolism) and displays similar pharmacologic activity. Cytochrome P450 (CYP) 3A4 has been identified as a major enzyme involved in mitragynine metabolism; however, the in vitro metabolism parameters of 9-O-demethylmitragynine formation are not well defined and a risk of potential drug interactions exists. Using human liver S9 fractions, 9-O-demethylmitragynine formation was generally linear for enzyme concentrations of 0-0.25 mg/mL and incubation times of 5-20 min. 9-O-demethylmitragynine displayed a Km 1.37 μM and Vmax of 0.0931 nmol/min/mg protein. Known CYP inhibitors and compounds that might be concomitantly used with kratom were assessed for inhibition of 9-O-demethylmitragynine formation. Ketoconazole, a CYP3A index inhibitor, demonstrated a significant effect on 9-O-demethylmitragynine formation, further implicating CYP3A4 as a major metabolic pathway. Major cannabinoids (10 μg/mL) displayed minor inhibition of 9-O-demethylmitragynine formation, while all other compounds had minimal effects. Mixtures of physiological achievable cannabinoid concentrations also displayed minor effects on 9-O-demethylmitragynine formation, making a metabolic drug interaction unlikely; however, further in vitro, in vivo, and clinical studies are necessary to fully exclude any risk.

Strategies for developing μ opioid receptor agonists with reduced adverse effects

Opioids are currently the most effective and widely used painkillers in the world. Unfortunately, the clinical use of opioid analgesics is limited by serious adverse effects. Many researchers have been working on designing and optimizing structures in search of novel μ opioid receptor(MOR) agonists with improved analgesic activity and reduced incidence of adverse effects. There are many strategies to develop MOR drugs, mainly focusing on new low efficacy agonists (potentially G protein biased agonists), MOR agonists acting on different Gα subtype, targeting opioid receptors in the periphery, acting on multiple opioid receptor, and targeting allosteric sites of opioid receptors, and others. This review summarizes the design methods, clinical applications, and structure-activity relationships of small-molecule agonists for MOR based on these different design strategies, providing ideas for the development of safer novel opioid ligands with therapeutic potential.

Effects of Itraconazole on Pharmacokinetics of Mitragynine and 7-Hydroxymitragynine in Healthy Volunteers

CYP3A4-mediated metabolic conversion of mitragynine to 7-hydroxymitragynine (7OH) has been demonstrated in human liver microsomes, and in rodents. Pharmacokinetics (PK) of mitragynine and 7OH in humans is still limited. We aimed to examine the pharmacokinetics of mitragynine and the formation of 7OH in healthy volunteers. To elucidate involvement of CYP3A4 in 7OH formation, inhibition by itraconazole was implemented. Two study periods with PK study of mitragynine alone in period 1, followed by period 2 including itraconazole pretreatment was conducted. Freshly prepared kratom tea consisting of 23.6 mg of mitragynine was given to participants in both study periods. Serial blood samplings were performed for 72 hours, and analyzed using a validated LCMS in multiple reaction monitoring mode. The median Cmax for mitragynine of 159.12 ± 8.68 ng/mL was attained in 0.84 h. While median Cmax for 7OH of 12.81 ± 3.39 ng/mL was observed at 1.77 h. In period 1, Cmax and AUC 0-inf of 7OH accounted for 9% and 20 %, respectively, of those parameters for mitragynine. The geometric mean ratio of AUC0-72 for 7OH/mitragynine (metabolic ratio, MR) was 13.25 ± 1.07. Co-administration of itraconazole 200 mg per day orally for 4 days (period 2) decreased 7OH exposure by 56% for Cmax and 43% for AUC0-72 after a single oral dose of kratom tea. While the Cmax of mitragynine increased by 1.5 folds without a significant change in Tmax. The geometric mean metabolic ratio was 3.30 ± 1.23 (period 2), indicating the attenuation for the formation of 7OH by the pretreatment with itraconazole. This suggested the CYP3A4-mediated formation of 7OH from mitragynine in healthy volunteers. This study provides the first evidence of metabolic conversion of mitragynine to 7OH in humans.

An insight review on the neuropharmacological effects, mechanisms of action, pharmacokinetics and toxicity of mitragynine

Mitragynine is one of the main psychoactive alkaloids in Mitragyna speciosa Korth. (kratom). It has opium-like effects by acting on μ-, δ-, and κ-opioid receptors in the brain. The compound also interacts with other receptors, such as adrenergic and serotonergic receptors and neuronal Ca2+ channels in the central nervous system to have its neuropharmacological effects. Mitragynine has the potential to treat diseases related to neurodegeneration such as Alzheimer's disease and Parkinson's disease, as its modulation on the opioid receptors has been reported extensively. This review aimed to provide an up-to-date and critical overview on the neuropharmacological effects, mechanisms of action, pharmacokinetics and safety of mitragynine as a prospective psychotropic agent. Its multiple neuropharmacological effects on the brain include antinociceptive, anti-inflammatory, antidepressant, sedative, stimulant, cognitive, and anxiolytic activities. The potential of mitragynine to manage opioid withdrawal symptoms related to opioid dependence, its pharmacokinetics and toxic effects were also discussed. The interaction of mitragynine with various receptors in the brain produce diverse neuropharmacological effects, which have beneficial properties in neurological disorders. However, further studies need to be carried out on mitragynine to uncover its complex mechanisms of action, pharmacokinetics, pharmacodynamic profiles, addictive potential, and safe dosage to prevent harmful side effects.

Kratom: A Bibliometric Analysis of Scientific Publications

Kratom has caught the attention of governments, policymakers, and academicians due to its unique characteristics. This paper explores the scholarly works related to the different aspects of Kratom to elucidate its research progress and identify future research agendas. We reviewed existing publications on Kratom using a bibliometric methodology. By analyzing 431 scientific publications, we identified publication sources, document analysis, countries analysis, and research keywords, which helped us understand the research locus on Kratom. After reviewing the publications, we discovered significant disagreements in categorizing and defining Kratom amongst authors based on their nationalities. We also showed the knowledge structure of existing publications via thematic analysis, illustrating that the studies focused on the opioid nature of Kratom. Also, drug abuse-related issues evolved as the motor theme of research, while other aspects are prevalent as niche or emerging research themes. This paper contributes to the literature by providing a broad idea of existing literature and offering a comprehensive outlook on Kratom, which could be helpful for policy formulation in the future.

An update on the clinical pharmacology of kratom: uses, abuse potential, and future considerations

INTRODUCTION

Kratom (Mitragyna speciosa) has generated substantial clinical and scientific interest as a complex natural product. Its predominant alkaloid mitragynine and several stereoisomers have been studied for activity in opioid, adrenergic, and serotonin receptors. While awaiting clinical trial results, the pre-clinical evidence suggests a range of potential therapeutic applications for kratom with careful consideration of potential adverse effects.

AREAS COVERED

The focus of this review is on the pharmacology, pharmacokinetics, and potential drug-drug interactions of kratom and its individual alkaloids. A discussion on the clinical pharmacology and toxicology of kratom is followed by a summary of user surveys and the evolving concepts of tolerance, dependence, and withdrawal associated with kratom use disorder.

EXPERT OPINION

With the increasing use of kratom in clinical practice, clinicians should be aware of the potential benefits and adverse effects associated with kratom. While many patients may benefit from kratom use with few or no reported adverse effects, escalating dose and increased use frequency raise the risk for toxic events in the setting of polysubstance use or development of a use disorder.

[Kratom (Mitragyna Speciosa): a Psychoactive Plant with Opportunities and Risks]

Kratom is an evergreen tree that is native to Southeast Asia. Its leafs are traditionally used as a stimulant, a remedy for various health problems and for religious purposes. Especially in the US (in a lesser extent also in Europe) kratom use is significantly prevalent. In Western countries, kratom is used predominantly as an analgesic and stimulant, for the treatment of opioid use disorders, and for improving mental health (e. g., in depression, anxiety disorders). Main molecular constituents of kratom are alkaloids of which mitragynine and 7-hydroxymitragynine appear to be most important. Pharmacodynamics and -kinetics of kratom are complex and insufficiently studied. It is known that mitragynine and 7-hydroxymitragynine are partial agonist at human μ-opioid receptors and antagonists at κ- and δ-opioid receptors with additional effects at other central receptors. Tolerability of kratom is presumably better than that of classical opioids; this is probably due to missing effects of kratom on β-arrestin and discussed as a starting point for the development of opioids with improved tolerability. Some alkaloids of kratom are inhibitors of CYP26 and to a somewhat lesser degree of CYP2C19 and CYP3A4. The addictive potential of kratom appears to be lower than that of classical opioids; however, corresponding data is limited and kratom use disorders appear to occur primarily in Western countries. Several cases of severe health-related problems and deaths are known in the US; in these cases, however, polysubstance use was usually present. Kratom use is likely associated with hepatotoxicity and cardiotoxicity. Kratom-associated mortality and morbidity in Western countries are quantitatively significantly different from Southeast Asia, where kratom use is no public health problem. The reasons for this may be the combined use of substances (which is more prevalent in Western countries), higher dosages of consumed kratom, adulterations and contaminations of commercially available kratom in Western countries, pharmacokinetic interactions, and higher concentrations of 7-hydroxymitragynine in dried kratom leafs (that are typically consumed in Western countries) in comparison to fresh leafs (that are typically consumed in Southeast Asia).

An in vitro evaluation of kratom (Mitragyna speciosa) on the catalytic activity of carboxylesterase 1 (CES1)

Kratom, (Mitragyna Speciosa Korth.) is a plant indigenous to Southeast Asia whose leaves are cultivated for a variety of medicinal purposes and mostly consumed as powders or tea in the United States. Kratom use has surged in popularity with the lay public and is currently being investigated for possible therapeutic benefits including as a treatment for opioid withdrawal due to the pharmacologic effects of its indole alkaloids. A wide array of psychoactive compounds are found in kratom, with mitragynine being the most abundant alkaloid. The drug-drug interaction (DDI) potential of mitragynine and related alkaloids have been evaluated for effects on the major cytochrome P450s (CYPs) via in vitro assays and limited clinical investigations. However, no thorough assessment of their potential to inhibit the major hepatic hydrolase, carboxylesterase 1 (CES1), exists. The purpose of this study was to evaluate the in vitro inhibitory potential of kratom extracts and its individual major alkaloids using an established CES1 assay and incubation system. Three separate kratom extracts and the major kratom alkaloids mitragynine, speciogynine, speciociliatine, paynantheine, and corynantheidine displayed a concentration-dependent reversible inhibition of CES1. The experimental Ki values were determined as follows for mitragynine, speciociliatine, paynantheine, and corynantheidine: 20.6, 8.6, 26.1, and 12.5 μM respectively. Speciociliatine, paynantheine, and corynantheidine were all determined to be mixed-type reversible inhibitors of CES1, while mitragynine was a purely competitive inhibitor. Based on available pharmacokinetic data, determined Ki values, and a physiologically based inhibition screen mimicking alkaloid exposures in humans, a DDI mediated via CES1 inhibition appears unlikely across a spectrum of doses (i.e., 2-20g per dose). However, further clinical studies need to be conducted to exclude the possibility of a DDI at higher and extreme doses of kratom and those who are chronic users.

Cannabinoid mechanisms contribute to the therapeutic efficacy of the kratom alkaloid mitragynine against neuropathic, but not inflammatory pain

AIMS

Mitragynine (MG) is an alkaloid found in Mitragyna speciosa (kratom), a plant used to self-treat symptoms of opioid withdrawal and pain. Kratom products are commonly used in combination with cannabis, with the self-treatment of pain being a primary motivator of use. Both cannabinoids and kratom alkaloids have been characterized to alleviate symptoms in preclinical models of neuropathic pain such as chemotherapy-induced peripheral neuropathy (CIPN). However, the potential involvement of cannabinoid mechanisms in MG's efficacy in a rodent model of CIPN have yet to be explored.

MAIN METHODS

Prevention of oxaliplatin-induced mechanical hypersensitivity and formalin-induced nociception were assessed following intraperitoneal administration of MG and CB1, CB2, or TRPV1 antagonists in wildtype and cannabinoid receptor knockout mice. The effects of oxaliplatin and MG exposure on the spinal cord endocannabinoid lipidome was assessed by HPLC-MS/MS.

KEY FINDINGS

The efficacy of MG on oxaliplatin-induced mechanical hypersensitivity was partially attenuated upon genetic deletion of cannabinoid receptors, and completely blocked upon pharmacological inhibition of CB1, CB2, and TRPV1 channels. This cannabinoid involvement was found to be selective to a model of neuropathic pain, with minimal effects on MG-induced antinociception in a model of formalin-induced pain. Oxaliplatin was found to selectively disrupt the endocannabinoid lipidome in the spinal cord, which was prevented by repeated MG exposure.

SIGNIFICANCE

Our findings suggest that cannabinoid mechanisms contribute to the therapeutic efficacy of the kratom alkaloid MG in a model of CIPN, which may result in increased therapeutic efficacy when co-administered with cannabinoids.

Phytochemistry and biological activities of corynanthe alkaloids

Medicinal plants constitute a source for designing clinically useful drugs targeting diseases through various mechanisms. Plant secondary metabolites can be used as lead compounds of drugs. Corynanthe alkaloids are highly abundant natural bioactive substances of various core structures possessing important properties such as nerve excitation and antimalarial and analgesic effects. In this review, we summarize and review the state-of-the-art corynanthe-type alkaloid research focusing on phytochemistry, pharmacology, and structural chemistry. Approximately 120 articles reporting 231 alkaloids classified into simple corynanthe, yohimbine, oxindole corynanthe, mavacurane, sarpagine, akuammiline, strychnos, and ajmaline-type groups were compiled. Relevant biological properties discussed include antiviral, antibacterial, anti-inflammatory, antimalarial, muscle-relaxant, vasorelaxant, and analgesic activities and activities affecting the main nervous and cardiac systems, as well as NF-κB inhibitory and Na⁺-glucose cotransporter inhibitory properties. This review provides insights and a reference for future studies, thus paving the way for the discovery of drugs based on corynanthe alkaloids.

Pharmacokinetic and Pharmacodynamic Consequences of Cytochrome P450 3A Inhibition on Mitragynine Metabolism in Rats

Mitragynine, an opioidergic alkaloid present in Mitragyna speciosa (kratom), is metabolized by cytochrome P450 3A (CYP3A) to 7-hydroxymitragynine, a more potent opioid receptor agonist. The extent to which conversion to 7-hydroxymitragynine mediates the in vivo effects of mitragynine is unclear. The current study examined how CYP3A inhibition (ketoconazole) modifies the pharmacokinetics of mitragynine in rat liver microsomes in vitro. The study further examined how ketoconazole modifies the discriminative stimulus and antinociceptive effects of mitragynine in rats. Ketoconazole [30 mg/kg, oral gavage (o.g.)] increased systemic exposure to mitragynine (13.3 mg/kg, o.g.) by 120% and 7-hydroxymitragynine exposure by 130%. The unexpected increase in exposure to 7-hydroxymitragynine suggested that ketoconazole inhibits metabolism of both mitragynine and 7-hydroxymitragynine, a finding confirmed in rat liver microsomes. In rats discriminating 3.2 mg/kg morphine from vehicle under a fixed-ratio schedule of food delivery, ketoconazole pretreatment increased the potency of both mitragynine (4.7-fold) and 7-hydroxymitragynine (9.7-fold). Ketoconazole did not affect morphine's potency. Ketoconazole increased the antinociceptive potency of 7-hydroxymitragynine by 4.1-fold. Mitragynine (up to 56 mg/kg, i.p.) lacked antinociceptive effects both in the presence and absence of ketoconazole. These results suggest that both mitragynine and 7-hydroxymitragynine are cleared via CYP3A and that 7-hydroxymitragynine is formed as a metabolite of mitragynine by other routes. These results have implications for kratom use in combination with numerous medications and citrus juices that inhibit CYP3A. SIGNIFICANCE STATEMENT: Mitragynine is an abundant kratom alkaloid that exhibits low efficacy at the μ-opioid receptor (MOR). Its metabolite, 7-hydroxymitragynine, is also an MOR agonist but with higher affinity and efficacy than mitragynine. Our results in rats demonstrate that cytochrome P450 3A (CYP3A) inhibition can increase the systematic exposure of both mitragynine and 7-hydroxymitragynine and their potency to produce MOR-mediated behavioral effects. These data highlight potential interactions between kratom and CYP3A inhibitors, which include numerous medications and citrus juices.

Kratom: The analytical challenge of an emerging herbal drug

Mitragyna speciosa or kratom is emerging worldwide as a "legal" herbal drug of abuse. An increasing number of papers is appearing in the scientific literature regarding its pharmacological profile and the analysis of its chemical constituents, mainly represented by alkaloids. However, its detection and identification are not straightforward as the plant material is not particularly distinctive. Hyphenated techniques are generally preferred for the identification and quantification of these compounds, especially the main purported psychoactive substances, mitragynine (MG) and 7-hydroxymitragynine (7-OH-MG), in raw and commercial products. Considering the vast popularity of this recreational drug and the growing concern about its safety, the analysis of alkaloids in biological specimens is also of great importance for forensic and toxicological laboratories. The review addresses the analytical aspects of kratom spanning the extraction techniques used to isolate the alkaloids, the qualitative and quantitative analytical methods and the strategies for the distinction of the naturally occurring isomers.

Directed Biosynthesis of Mitragynine Stereoisomers

Mitragyna speciosa ("kratom") is used as a natural remedy for pain and management of opioid dependence. The pharmacological properties of kratom have been linked to a complex mixture of monoterpene indole alkaloids, most notably mitragynine. Here, we report the central biosynthetic steps responsible for the scaffold formation of mitragynine and related corynanthe-type alkaloids. We illuminate the mechanistic basis by which the key stereogenic center of this scaffold is formed. These discoveries were leveraged for the enzymatic production of mitragynine, the C-20 epimer speciogynine, and fluorinated analogues.

Investigating the Impact of Kratom (Mitragyna speciosa) Use Upon Male Sexual Health

Purpose

Kratom (Mitragyna speciosa) exhibits μ-receptor agonism and is used as an opioid substitute. While opioids are known to inhibit sexual behavior, less is known regarding kratom. We conducted a pilot study to assess the subjective impact of kratom upon male sexual health including erectile and ejaculatory function.

Patients and Methods

Twitter and Reddit (r/Kratom) were accessed to disseminate our survey featuring validated instruments (the International Index of Erectile Function, IIEF, and the premature ejaculation diagnostic tool, PEDT). Sexual health prior to and after 4 weeks of kratom use was assessed.

Results

Most males surveyed (n = 165) were 18-40 years old (84.9%), with 95.8% of respondents using it at least weekly and 82.4% using kratom for ≥1 year. Reasons for use included treating pain (39.4%), and mental health conditions (63.6%). Kratom was associated with a positive (37.7%) and negative (20.5%) impact on sexual health. Kratom subjectively increased time to ejaculation in 104 (66.6%) patients, perceived as positive by 62 (59.6%). Seventy-eight patients answered questions about premature ejaculation. The median (with interquartile range, IQR, following;) pre-kratom and kratom use scores were 13.0; 8.0 and 6.5; 5.0, respectively (p < 0.001). Ejaculation before 5 minutes improved after kratom (51.3% vs 12.8%) (p < 0.0001). Following kratom use, patients reported lack of frustration with ejaculation prior to desire (21.8% vs 61.5%) (p < 0.001). The erectile function domain of the IIEF was statistically significantly different however - clinically similar pre-kratom use (29.0; 5.75) versus 27.0; 6.75 during kratom use (p = 0.037).

Conclusion

Clinicians treating male sexual health should be aware of kratom and its potential effect on ejaculatory and erectile function.

Comparative metabolomics analysis reveals alkaloid repertoires in young and mature Mitragyna speciosa (Korth.) Havil. Leaves

The fresh leaves of Mitragyna speciosa (Korth.) Havil. have been traditionally consumed for centuries in Southeast Asia for its healing properties. Although the alkaloids of M. speciosa have been studied since the 1920s, comparative and systematic studies of metabolite composition based on different leaf maturity levels are still lacking. This study assessed the secondary metabolite composition in two different leaf stages (young and mature) of M. speciosa, using an untargeted liquid chromatography-electrospray ionisation-time-of-flight-mass spectrometry (LC-ESI-TOF-MS) metabolite profiling. The results revealed 86 putatively annotated metabolite features (RT:m/z value) comprising 63 alkaloids, 10 flavonoids, 6 terpenoids, 3 phenylpropanoids, and 1 of each carboxylic acid, glucoside, phenol, and phenolic aldehyde. The alkaloid features were further categorised into 14 subclasses, i.e., the most abundant class of secondary metabolites identified. As per previous reports, indole alkaloids are the most abundant alkaloid subclass in M. speciosa. The result of multivariate analysis (MVA) using principal component analysis (PCA) showed a clear separation of 92.8% between the young and mature leaf samples, indicating a high variance in metabolite levels between them. Akuammidine, alstonine, tryptamine, and yohimbine were tentatively identified among the many new alkaloids reported in this study, depicting the diverse biological activities of M. speciosa. Besides delving into the knowledge of metabolite distribution in different leaf stages, these findings have extended the current alkaloid repository of M. speciosa for a better understanding of its pharmaceutical potential.

Controversial usages of kratom (Mitragyna speciosa): For good or for evil

Kratom (Mitragyna speciosa) is a plant that grows well in tropical climates such as in Southeast Asia. Traditionally, people discovered it possessed a stimulating effect that relieved tiredness. Furthermore, it contains analgesic and medicinal properties for the treatment of pain, diarrhea, muscle discomfort, and blood pressure and to enhance stamina. Nevertheless, long term or regular consumption of kratom leads to addiction. This is because the main alkaloid of kratom, mitragynine, binds to opioid receptors and exerts a euphoric effect similar to that of morphine, which may lead to death. Due to this reason, kratom has been listed as a regulated substance in many countries including the United States, Thailand, Malaysia, Bhutan, Finland, Lithuania, Denmark, Poland, Sweden, Australia, and Myanmar. Usages of kratom carry two pharmacological effects depending on dosage. Low-dose kratom exerts a stimulating effect that refreshes the user. High-dose kratom exerts sedative effects that can lead to addiction similar to that of morphine. Despite the euphoric effect of kratom, the beneficial values of kratom to human health is indisputable. Therefore, a complete banning of kratom may cause a loss to pharmaceutical industry. Rather, a controlled or selective usage of kratom will be a better choice.

Kratom as an opioid alternative: harm, or harm reduction? A systematic review of literature

Background: Kratom (Mitragyna speciosa Korth.) products are increasingly endorsed for self-management of multiple ailments, including as opioid substitution. The FDA has expressed that there is no evidence to indicate that this botanical is safe or effective for any medical use.Objective: We systematically review the current state of the literature concerning the impact of kratom and its alkaloids in all paradigms that involve opioids.Methods: A keyword search of online literature databases identified 16 preclinical studies, 25 case reports, and 10 observational studies meeting our pre-selected criteria.Results: All rodent models support alkaloids' action on opioid receptors, translating in their ability to mitigate opioid withdrawal. Some studies found mitragynine (MG) to have less reinforcing properties than morphine, and possessing tolerance-sparing properties when coadministered with morphine. Two studies that assessed 7-hydroxymitragynine (7OHMG) found it to substitute for morphine with potential for tolerance and dependence. Aside from addiction development, case reports outline a variety of confounding toxicities. Ten surveys of users, some conducted with assistance from pro-kratom lobbying organizations, find a high self-reported efficacy as an opioid substitute, with minimal reported adverse effects.Conclusion: With no reported controlled human clinical trials, in the light of rising concerns surrounding kratom's liabilities, there is insufficient evidence to allow any conclusions to be drawn. Case reports and observational studies carry significant bias toward harm and efficacy, respectively. Existing animal studies are heterogeneous in methodology and ultimately findings, with concern for interspecies variability and human translatability. Further research should investigate the safety and efficacy of using kratom alkaloids as opioid substitutes.

Kratom alkaloid mitragynine: Inhibition of chemotherapy-induced peripheral neuropathy in mice is dependent on sex and active adrenergic and opioid receptors

Mitragynine (MG) is an alkaloid found in Mitragyna speciosa (kratom) that is used as an herbal remedy for pain relief and opioid withdrawal. MG acts at μ-opioid and α-adrenergic receptors in vitro, but the physiological relevance of this activity in the context of neuropathic pain remains unknown. The purpose of the present study was to characterize the effects of MG in a mouse model of chemotherapy-induced peripheral neuropathy (CIPN), and to investigate the potential impact of sex on MG's therapeutic efficacy. Inhibition of oxaliplatin-induced mechanical hypersensitivity was measured following intraperitoneal administration of MG. Both male and female C57BL/6J mice were used to characterize potential sex-differences in MG's therapeutic efficacy. Pharmacological mechanisms of MG were characterized through pretreatment with the opioid and adrenergic antagonists naltrexone, prazosin, yohimbine, and propranolol (1, 2.5, 5 mg/kg). Oxaliplatin produced significant mechanical allodynia of equal magnitude in both male and females, which was dose-dependently attenuated by repeated MG exposure. MG was more potent in males vs females, and the highest dose of MG (10 mg/kg) exhibited greater anti-allodynic efficacy in males. Mechanistically, activity at µ-opioid, α₁- and α₂-adrenergic receptors, but not β-adrenergic receptors contributed to the effects of MG against oxaliplatin-induced mechanical hypersensitivity. Repeated MG exposure significantly attenuated oxaliplatin-induced mechanical hypersensitivity with greater potency and efficacy in males, which has crucial implications in the context of individualized pain management. The opioid and adrenergic components of MG indicate that it shares pharmacological properties with clinical neuropathic pain treatments.

Acute Renal Insufficiency Associated With Consumption of Hydrocodone- and Morphine-Adulterated Kratom (Mitragyna Speciosa)

BACKGROUND

Kratom (Mitragyna speciosa), an evergreen tree native to Southeast Asia, contains alkaloids that cause both stimulant and opioid-like effects. In the United States, its use continues to grow. Kratom products, however, are unregulated and nonstandardized, and reports of adulteration have been described previously.

CASE REPORT

A 21-year-old African-American woman with a history of occasional headaches and self-treatment with internet-purchased kratom presented to the emergency department with the chief symptoms of nausea, vomiting, and left flank pain. Laboratory tests showed a markedly elevated serum creatinine of 4.25 mg/dL (reference range 0.6-1.2 mg/dL) and proteinuria. A computed tomography scan of the abdomen and pelvis was unrevealing. A standard urine screen for drugs of abuse was positive for opiates. A confirmatory testing revealed the presence of hydrocodone and morphine in the urine. Hydrocodone, morphine, and mitragynine were identified in a sample of kratom leaves provided by the patient. The patient's renal function improved with supportive care and normalized 1 month post discharge after kratom discontinuation. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Despite widespread use, relatively little is known about kratom's adverse effects, particularly regarding its potential to cause renal insufficiency. This case illustrates the vital importance of recognizing that adulteration of unregulated products is certainly a possibility and clinicians may continue to see a rise in adverse effects, given kratom's increasing popularity.

Need for clarity and context in case reports on kratom use, assessment, and intervention

This Letter to the Editor is a response to Broyan and colleagues who recently published a Case Report presenting data on 28 patients in the United States who identified kratom as their primary substance of use and who were subsequently induced on buprenorphine/naloxone for a reported diagnosis of kratom use disorder. We applaud the authors for helping to advance the science on kratom and recognize the difficulties in conducting kratom-related clinical assessment and research. However, a number of inconsistences and generalizations were identified in this Case Report, which also lacked some critical context. Importantly, such inconsistencies and generalizations can be observed throughout kratom-specific case reports. We feel this is now an important opportunity to highlight these issues that are present in the Broyan and colleagues Case report but emphasize that they are not unique to it. We do this with the hope that by acknowledging these issues it can help inform editors, clinicians, and researchers who may not be familiar with kratom and, as a result of this unfamiliarity, may inadvertently present findings in a manner that could confuse readers and even misinform clinical researchers and practitioners.

Acute, Sublethal, and Developmental Toxicity of Kratom (Mitragyna speciosa Korth.) Leaf Preparations on Caenorhabditis elegans as an Invertebrate Model for Human Exposure

Kratom (Mitragyna speciosa Korth.) is a tree native to Southeast Asia with stimulant and opioid-like effects which has seen increased use in Europe and North America in recent years. Its safety and pharmacological effects remain under investigation, especially in regard to developmental and generational toxicity. In the current study, we investigated commercial kratom preparations using the nematode Caenorhabditis elegans as a translational model for toxicity and pharmacological effects. The pure alkaloids mitragynine and 7-hydroxymitragynine as well as aqueous, ethanolic, and methanolic extracts of three commercial kratom products were evaluated using a battery of developmental, genotoxic, and opioid-related experiments. As determined previously, the mitragynine and 7-hydroxymitragynine content in kratom samples was higher in the alcoholic extracts than the aqueous extracts. Above the human consumption range equivalent of 15-70 µg/mL, kratom dose-dependently reduced brood size and health of parent worms and their progeny. 7-hydroxymitragynine, but not mitragynine, presented with toxic and developmental effects at very high concentrations, while the positive control, morphine, displayed toxic effects at 0.5 mM. Kratom and its alkaloids did not affect pumping rate or interpump interval in the same way as morphine, suggesting that kratom is unlikely to act primarily via the opioid-signalling pathway. Only at very high doses did kratom cause developmental and genotoxic effects in nematodes, indicating its relative safety.

The respiratory depressant effects of mitragynine are limited by its conversion to 7-OH mitragynine

Background and Purpose

Mitragynine, the major alkaloid in Mitragyna speciosa (kratom), is a partial agonist at the μ opioid receptor. CYP3A‐dependent oxidation of mitragynine yields the metabolite 7‐OH mitragynine, a more efficacious μ receptor agonist. While both mitragynine and 7‐OH mitragynine can induce anti‐nociception in mice, recent evidence suggests that 7‐OH mitragynine formed as a metabolite is sufficient to explain the anti‐nociceptive effects of mitragynine. However, the ability of 7‐OH mitragynine to induce μ receptor‐dependent respiratory depression has not yet been studied.

Experimental Approach

Respiration was measured in awake, freely moving, male CD‐1 mice, using whole body plethysmography. Anti‐nociception was measured using the hot plate assay. Morphine, mitragynine, 7‐OH mitragynine and the CYP3A inhibitor ketoconazole were administered orally.

Key Results

The respiratory depressant effects of mitragynine showed a ceiling effect, whereby doses higher than 10 mg·kg⁻¹ produced the same level of effect. In contrast, 7‐OH mitragynine induced a dose‐dependent effect on mouse respiration. At equi‐depressant doses, both mitragynine and 7‐OH mitragynine induced prolonged anti‐nociception. Inhibition of CYP3A reduced mitragynine‐induced respiratory depression and anti‐nociception without affecting the effects of 7‐OH mitragynine.

Conclusions and Implications

Both the anti‐nociceptive effects and the respiratory depressant effects of mitragynine are partly due to its metabolic conversion to 7‐OH mitragynine. The limiting rate of conversion of mitragynine into its active metabolite results in a built‐in ceiling effect of the mitragynine‐induced respiratory depression. These data suggest that such ‘metabolic saturation’ at high doses may underlie the improved safety profile of mitragynine as an opioid analgesic.

Clinical Pharmacokinetic Assessment of Kratom (Mitragyna speciosa), a Botanical Product with Opioid-like Effects, in Healthy Adult Participants

Increasing use of the botanical kratom to self-manage opioid withdrawal and pain has led to increased kratom-linked overdose deaths. Despite these serious safety concerns, rigorous fundamental pharmacokinetic knowledge of kratom in humans remains lacking. We assessed the pharmacokinetics of a single low dose (2 g) of a well-characterized kratom product administered orally to six healthy participants. Median concentration-time profiles for the kratom alkaloids examined were best described by a two-compartment model with central elimination. Pronounced pharmacokinetic differences between alkaloids with the 3S configuration (mitragynine, speciogynine, paynantheine) and alkaloids with the 3R configuration (mitraciliatine, speciociliatine, isopaynantheine) were attributed to differences in apparent intercompartmental distribution clearance, volumes of distribution, and clearance. Based on noncompartmental analysis of individual concentration-time profiles, the 3S alkaloids exhibited a shorter median time to maximum concentration (1–2 vs. 2.5–4.5 h), lower area under the plasma concentration-time curve (430–490 vs. 794–5120 nM × h), longer terminal half-life (24–45 vs. ~12–18 h), and higher apparent volume of distribution during the terminal phase (960–12,700 vs. ~46–130 L) compared to the 3R alkaloids. Follow-up mechanistic in vitro studies suggested differential hepatic/intestinal metabolism, plasma protein binding, blood-to-plasma partitioning, and/or distribution coefficients may explain the pharmacokinetic differences between the two alkaloid types. This first comprehensive pharmacokinetic characterization of kratom alkaloids in humans provides the foundation for further research to establish safety and effectiveness of this emerging botanical product.

A systematic review of (pre)clinical studies on the therapeutic potential and safety profile of kratom in humans

INTRODUCTION

Kratom (Mitragyna speciosa) is a tropical plant traditionally used as an ethnomedicinal remedy for several conditions in South East Asia. Despite the increased interest in its therapeutical benefits in Western countries, little scientific evidence is available to support such claims, and existing data remain limited to kratom's chronic consumption.

OBJECTIVE

Our study aims to investigate (pre)clinical evidence on the efficacy of kratom as a therapeutic aid and its safety profile in humans.

METHODS

A systematic literature search using PubMed and the Medline database was conducted between April and November 2020.

RESULTS

Both preclinical (N = 57) and clinical (N = 18) studies emerged from our search. Preclinical data indicated a therapeutic value in terms of acute/chronic pain (N = 23), morphine/ethanol withdrawal, and dependence (N = 14), among other medical conditions (N = 26). Clinical data included interventional studies (N = 2) reporting reduced pain sensitivity, and observational studies (N = 9) describing the association between kratom's chronic (daily/frequent) use and safety issues, in terms of health consequences (e.g., learning impairment, high cholesterol level, dependence/withdrawal).

CONCLUSIONS

Although the initial (pre)clinical evidence on kratom's therapeutic potential and its safety profile in humans is encouraging, further validation in large, controlled clinical trials is required.

In vitro and in vivo pharmacology of kratom

Kratom products have been historically and anecdotally used in south Asian countries for centuries to manage pain and opioid withdrawal. The use of kratom products has dramatically increased in the United States. More than 45 kratom alkaloids have been isolated, yet the overall pharmacology of the individual alkaloids is still not well characterized. The purpose of this chapter is to summarize in vitro and in vivo opioid activities of the primary kratom alkaloid mitragynine and its more potent metabolite 7-hydroxymitragynine. Following are experimental procedures described to characterize opioid receptor activity; receptor binding and functional assays, antinociceptive assays, operant conditioning assays, and respiratory plethysmography. The capacity of kratom alkaloids to confer tolerance and physical dependence as well as their pharmacokinetic properties are also summarized. The data reviewed here suggest that kratom products and mitragynine possess low efficacy agonist activity at the mu-opioid receptor in vivo. In addition, kratom products and mitragynine have been demonstrated to antagonize the effects of high efficacy mu-opioid agonists. The data further suggest that 7-hydroxymitragynine formed in vivo by metabolism of mitragynine may be minimally involved in the overall behavioral profile of mitragynine and kratom, whereas 7-hydroxymitragynine itself, at sufficiently high doses administered exogenously, shares many of the same abuse- and dependence-related behavioral effects associated with traditional opioid agonists. The apparent low efficacy of kratom products and mitragynine at mu-opioid receptors supports the development of these ligands as effective and potentially safe medications for opioid use disorder.

Evaluation of Kratom Opioid Derivatives as Potential Treatment Option for Alcohol Use Disorder

Background and Purpose:Mitragyna speciosa extract and kratom alkaloids decrease alcohol consumption in mice at least in part through actions at the δ-opioid receptor (δOR). However, the most potent opioidergic kratom alkaloid, 7-hydroxymitragynine, exhibits rewarding properties and hyperlocomotion presumably due to preferred affinity for the mu opioid receptor (µOR). We hypothesized that opioidergic kratom alkaloids like paynantheine and speciogynine with reduced µOR potency could provide a starting point for developing opioids with an improved therapeutic window to treat alcohol use disorder.

Experimental Approach: We characterized paynantheine, speciociliatine, and four novel kratom-derived analogs for their ability to bind and activate δOR, µOR, and κOR. Select opioids were assessed in behavioral assays in male C57BL/6N WT and δOR knockout mice.

Key Results: Paynantheine (10 mg∙kg⁻¹, i.p.) produced aversion in a limited conditioned place preference (CPP) paradigm but did not produce CPP with additional conditioning sessions. Paynantheine did not produce robust antinociception but did block morphine-induced antinociception and hyperlocomotion. Yet, at 10 and 30 mg∙kg⁻¹ doses (i.p.), paynantheine did not counteract morphine CPP. 7-hydroxypaynantheine and 7-hydroxyspeciogynine displayed potency at δOR but limited µOR potency relative to 7-hydroxymitragynine in vitro, and dose-dependently decreased voluntary alcohol consumption in WT but not δOR in KO mice. 7-hydroxyspeciogynine has a maximally tolerated dose of at least 10 mg∙kg⁻¹ (s.c.) at which it did not produce significant CPP neither alter general locomotion nor induce noticeable seizures.

Conclusion and Implications: Derivatizing kratom alkaloids with the goal of enhancing δOR potency and reducing off-target effects could provide a pathway to develop novel lead compounds to treat alcohol use disorder with an improved therapeutic window.

Clinical Pharmacology of the Dietary Supplement, Kratom (Mitragyna speciosa)

Kratom (Mitragyna speciosa) consists of over 40 alkaloids with two of them, mitragynine (MG) and 7-OH-mitragynine (7-OH-MG) being the main psychoactive compounds. MG and 7-OH-MG each target opioid receptors and have been referred to as atypical opioids. They exert their pharmacologic effects on the μ, δ, and κ opioid receptors. In addition, they affect adrenergic, serotonergic, and dopaminergic pathways. Kratom has been touted as an inexpensive, legal alternative to standard opioid replacement therapy such as methadone and buprenorphine. Other uses for kratom include chronic pain, attaining a "legal high," and numerous CNS disorders including anxiety depression and post-traumatic stress disorder (PTSD). Kratom induces analgesia and mild euphoria with a lower risk of respiratory depression or adverse central nervous system effects compared to traditional opioid medications. Nonetheless, kratom has been associated with both physical and psychological dependence with some individuals experiencing classic opioid withdrawal symptoms upon abrupt cessation. Kratom use has been linked to serious adverse effects including liver toxicity, seizures, and death. These risks are often compounded by poly-substance abuse. Further, kratom may potentiate the toxicity of coadministered medications through modulation of cytochrome P450, P-glycoprotein, and uridine diphosphate glucuronosyltransferase enzymes (UGDT). In 2016 the U.S. Drug Enforcement Administration (DEA) took steps to classify kratom as a federal schedule 1 medication; however, due to public resistance, this plan was set aside. Until studies are conducted that define kratom's role in treating opioid withdrawal and/or other CNS conditions, kratom will likely remain available as a dietary supplement for the foreseeable future. This article is protected by copyright. All rights reserved.

A Novel Mitragynine Analog with Low-Efficacy Mu Opioid Receptor Agonism Displays Antinociception with Attenuated Adverse Effects

Mitragynine and 7-hydroxymitragynine (7OH) are the major alkaloids mediating the biological actions of the psychoactive plant kratom. To investigate the structure-activity relationships of mitragynine/7OH templates, we diversified the aromatic ring of the indole at the C9, C10, and C12 positions and investigated their G-protein and arrestin signaling mediated by mu opioid receptors (MOR). Three synthesized lead C9 analogs replacing the 9-OCH3 group with phenyl (4), methyl (5), or 3'-furanyl [6 (SC13)] substituents demonstrated partial agonism with a lower efficacy than DAMGO or morphine in heterologous G-protein assays and synaptic physiology. In assays limiting MOR reserve, the G-protein efficacy of all three was comparable to buprenorphine. 6 (SC13) showed MOR-dependent analgesia with potency similar to morphine without respiratory depression, hyperlocomotion, constipation, or place conditioning in mice. These results suggest the possibility of activating MOR minimally (G-protein Emax ≈ 10%) in cell lines while yet attaining maximal antinociception in vivo with reduced opioid liabilities.

The Antidepressant-Like and Analgesic Effects of Kratom Alkaloids are accompanied by Changes in Low Frequency Oscillations but not ΔFosB Accumulation

Mitragyna speciosa (“kratom”), employed as a traditional medicine to improve mood and relieve pain, has shown increased use in Europe and North America. Here, the dose-dependent effects of a purified alkaloid kratom extract on neuronal oscillatory systems function, analgesia, and antidepressant-like behaviour were evaluated and kratom-induced changes in ΔFosB expression determined. Male rats were administered a low or high dose of kratom (containing 0.5 or 1 mg/kg of mitragynine, respectively) for seven days. Acute or repeated low dose kratom suppressed ventral tegmental area (VTA) theta oscillatory power whereas acute or repeated high dose kratom increased delta power, and reduced theta power, in the nucleus accumbens (NAc), prefrontal cortex (PFC), cingulate cortex (Cg) and VTA. The repeated administration of low dose kratom additionally elevated delta power in PFC, decreased theta power in NAc and PFC, and suppressed beta and low gamma power in Cg. Suppressed high gamma power in NAc and PFC was seen selectively following repeated high dose kratom. Both doses of kratom elevated NAc-PFC, VTA-NAc, and VTA-Cg coherence. Low dose kratom had antidepressant-like properties whereas both doses produced analgesia. No kratom-induced changes in ΔFosB expression were evident. These results support a role for kratom as having both antidepressant and analgesic properties that are accompanied by specific changes in neuronal circuit function. However, the absence of drug-induced changes in ΔFosB expression suggest that the drug may circumvent this cellular signaling pathway, a pathway known for its significant role in addiction.

Kratom Alkaloids as Probes for Opioid Receptor Function: Pharmacological Characterization of Minor Indole and Oxindole Alkaloids from Kratom

Dry leaves of kratom (mitragyna speciosa) are anecdotally consumed as pain relievers and antidotes against opioid withdrawal and alcohol use disorders. There are at least 54 alkaloids in kratom; however, investigations to date have focused around mitragynine, 7-hydroxy mitragynine (7OH), and mitragynine pseudoindoxyl (MP). Herein, we probe a few minor indole and oxindole based alkaloids, reporting the receptor affinity, G-protein activity, and βarrestin-2 signaling of corynantheidine, corynoxine, corynoxine B, mitraciliatine, and isopaynantheine at mouse and human opioid receptors. We identify corynantheidine as a mu opioid receptor (MOR) partial agonist, whereas its oxindole derivative corynoxine was an MOR full agonist. Similarly, another alkaloid mitraciliatine was found to be an MOR partial agonist, while isopaynantheine was a KOR agonist which showed reduced βarrestin-2 recruitment. Corynantheidine, corynoxine, and mitraciliatine showed MOR dependent antinociception in mice, but mitraciliatine and corynoxine displayed attenuated respiratory depression and hyperlocomotion compared to the prototypic MOR agonist morphine in vivo when administered supraspinally. Isopaynantheine on the other hand was identified as the first kratom derived KOR agonist in vivo. While these minor alkaloids are unlikely to play the majority role in the biological actions of kratom, they represent excellent starting points for further diversification as well as distinct efficacy and signaling profiles with which to probe opioid actions in vivo.

Site selective C-H functionalization of Mitragyna alkaloids reveals a molecular switch for tuning opioid receptor signaling efficacy

Mitragynine (MG) is the most abundant alkaloid component of the psychoactive plant material "kratom", which according to numerous anecdotal reports shows efficacy in self-medication for pain syndromes, depression, anxiety, and substance use disorders. We have developed a synthetic method for selective functionalization of the unexplored C11 position of the MG scaffold (C6 position in indole numbering) via the use of an indole-ethylene glycol adduct and subsequent iridium-catalyzed borylation. Through this work we discover that C11 represents a key locant for fine-tuning opioid receptor signaling efficacy. 7-Hydroxymitragynine (7OH), the parent compound with low efficacy on par with buprenorphine, is transformed to an even lower efficacy agonist by introducing a fluorine substituent in this position (11-F-7OH), as demonstrated in vitro at both mouse and human mu opioid receptors (mMOR/hMOR) and in vivo in mouse analgesia tests. Low efficacy opioid agonists are of high interest as candidates for generating safer opioid medications with mitigated adverse effects.

Kratom-induced transaminitis with subsequent precipitated opioid withdrawal following naltrexone

Kratom is an herbal supplement that has gained popularity for recreational use within the United States. Kratom exerts opioid-like effects and, although not US FDA approved, is commonly used for self-treatment of pain, withdrawal management from opioids, and euphoria. Drug-related hepatic injury has been associated with kratom use. All of this raises concern for patient safety and monitoring. The potential for additive liver toxicity must be considered when kratom is used concurrently with hepatotoxic, over-the-counter, herbal, and prescription medications. This case report describes a case of kratom-induced liver inflammation complicated by opioid withdrawal that was precipitated by initiation of IM naltrexone. To our knowledge, there are no published case reports related to opioid withdrawal following naltrexone administration in patients using kratom (without other opioids). The purpose of this case report is to demonstrate potential complications that may arise with kratom use and considerations that should be taken prior to initiation of naltrexone in kratom users.

Natural Products for the Treatment of Pain: Chemistry and Pharmacology of Salvinorin A, Mitragynine, and Collybolide

Pain remains a very pervasive problem throughout medicine. Classical pain management is achieved through the use of opiates belonging to the mu opioid receptor (MOR) class, which have significant side effects that hinder their utility. Pharmacologists have been trying to develop opioids devoid of side effects since the isolation of morphine from papaver somniferum, more commonly known as opium by Sertürner in 1804. The natural products salvinorin A, mitragynine, and collybolide represent three nonmorphinan natural product-based targets, which are potent selective agonists of opioid receptors, and emerging next-generation analgesics. In this work, we review the phytochemistry and medicinal chemistry efforts on these templates and their effects on affinity, selectivity, analgesic actions, and a myriad of other opioid-receptor-related behavioral effects.

Oral Pharmacokinetics in Beagle Dogs of the Mitragynine Metabolite, 7-Hydroxymitragynine

BACKGROUND AND OBJECTIVES

7-Hydroxymitragynine (7-HMG) is an oxidative metabolite of mitragynine, the most abundant alkaloid in the leaves of Mitragyna speciosa (otherwise known as kratom). While mitragynine is a weak partial µ-opioid receptor (MOR) agonist, 7-HMG is a potent and full MOR agonist. It is produced from mitragynine by cytochrome P450 (CYP) 3A, a drug-metabolizing CYP isoform predominate in the liver that is also highly expressed in the intestine. Given the opioidergic potency of 7-HMG, a single oral dose pharmacokinetic and safety study of 7-HMG was performed in beagle dogs.

METHODS

Following a single oral dose (1 mg/kg) of 7-HMG, plasma samples were obtained from healthy female beagle dogs. Concentrations of 7-HMG were determined using ultra-performance liquid chromatography coupled with a tandem mass spectrometer (UPLC-MS/MS). Pharmacokinetic parameters were calculated using a model-independent non-compartmental analysis of plasma concentration-time data.

RESULTS

Absorption of 7-HMG was rapid, with a peak plasma concentration (C_max, 56.4 ± 1.6 ng/ml) observed within 15 min post-dose. In contrast, 7-HMG elimination was slow, exhibiting a mono-exponential distribution and mean elimination half-life of 3.6 ± 0.5 h. Oral dosing of 1 mg/kg 7-HMG was well tolerated with no observed adverse events or significant changes to clinical laboratory tests.

CONCLUSIONS

These results provide the first pharmacokinetic and safety data for 7-HMG in the dog and therefore contribute to the understanding of the putative pharmacologic role of 7-HMG resulting from an oral delivery of mitragynine from kratom.

Influence of G protein-biased agonists of μ-opioid receptor on addiction-related behaviors

Opioid analgesics remain a gold standard for the treatment of moderate to severe pain. However, their clinical utility is seriously limited by a range of adverse effects. Among them, their high-addictive potential appears as very important, especially in the context of the opioid epidemic. Therefore, the development of safer opioid analgesics with low abuse potential appears as a challenging problem for opioid research. Among the last few decades, different approaches to the discovery of novel opioid drugs have been assessed. One of the most promising is the development of G protein-biased opioid agonists, which can activate only selected intracellular signaling pathways. To date, discoveries of several biased agonists acting via μ-opioid receptor were reported. According to the experimental data, such ligands may be devoid of at least some of the opioid side effects, such as respiratory depression or constipation. Nevertheless, most data regarding the addictive properties of biased μ-opioid receptor agonists are inconsistent. A global problem connected with opioid abuse also requires the search for effective pharmacotherapy for opioid addiction, which is another potential application of biased compounds. This review discusses the state-of-the-art on addictive properties of G protein-biased μ-opioid receptor agonists as well as we analyze whether these compounds can diminish any symptoms of opioid addiction. Finally, we provide a critical view on recent data connected with biased signaling and its implications to in vivo manifestations of addiction.

Chemical composition and biological effects of kratom (Mitragyna speciosa): In vitro studies with implications for efficacy and drug interactions

The safety and efficacy of kratom (Mitragyna speciosa) for treatment of pain is highly controversial. Kratom produces more than 40 structurally related alkaloids, but most studies have focused on just two of these, mitragynine and 7-hydroxymitragynine. Here, we profiled 53 commercial kratom products using untargeted LC-MS metabolomics, revealing two distinct chemotypes that contain different levels of the alkaloid speciofoline. Both chemotypes were confirmed with DNA barcoding to be M. speciosa. To evaluate the biological relevance of variable speciofoline levels in kratom, we compared the opioid receptor binding activity of speciofoline, mitragynine, and 7-hydroxymitragynine. Mitragynine and 7-hydroxymitragynine function as partial agonists of the human µ-opioid receptor, while speciofoline does not exhibit measurable binding affinity at the µ-, δ- or ƙ-opioid receptors. Importantly, mitragynine and 7-hydroxymitragynine demonstrate functional selectivity for G-protein signaling, with no measurable recruitment of β-arrestin. Overall, the study demonstrates the unique binding and functional profiles of the kratom alkaloids, suggesting potential utility for managing pain, but further studies are needed to follow up on these in vitro findings. All three kratom alkaloids tested inhibited select cytochrome P450 enzymes, suggesting a potential risk for adverse interactions when kratom is co-consumed with drugs metabolized by these enzymes.

Pharmacology of Herbal Sexual Enhancers: A Review of Psychiatric and Neurological Adverse Effects

Sexual enhancers increase sexual potency, sexual pleasure, or libido. Substances increasing libido alter the concentrations of specific neurotransmitters or sex hormones in the central nervous system. Interestingly, the same pathways are involved in the mechanisms underlying many psychiatric and neurological disorders, and adverse reactions associated with the use of aphrodisiacs are strongly expected. However, sexual enhancers of plant origin have gained popularity over recent years, as natural substances are often regarded as a safer alternative to modern medications and are easily acquired without prescription. We reviewed the psychiatric and neurological adverse effects associated with the consumption of herbal aphrodisiacs Areca catechu L., Argemone Mexicana L., Citrus aurantium L., Eurycoma longifolia Jack., Lepidium meyenii Walp., Mitragyna speciosa Korth., Panax ginseng C. A. Mey, Panax quinquefolius L., Pausinystalia johimbe (K. Schum.) Pierre ex Beille, Piper methysticum G. Forst., Ptychopetalum olacoides Benth., Sceletium tortuosum (L.) N. E. Brown, Turnera diffusa Willd. ex. Schult., Voacanga africana Stapf ex Scott-Elliot, and Withania somnifera (L.) Dunal. A literature search was conducted on the PubMed, Scopus, and Web of Science databases with the aim of identifying all the relevant articles published on the issue up to June 2020. Most of the selected sexual enhancers appeared to be safe at therapeutic doses, although mild to severe adverse effects may occur in cases of overdosing or self-medication with unstandardized products. Drug interactions are more concerning, considering that herbal aphrodisiacs are likely used together with other plant extracts and/or pharmaceuticals. However, few data are available on the side effects of several plants included in this review, and more clinical studies with controlled administrations should be conducted to address this issue.

Biased Opioid Ligands

Achieving effective pain management is one of the major challenges associated with modern day medicine. Opioids, such as morphine, have been the reference treatment for moderate to severe acute pain not excluding chronic pain modalities. Opioids act through the opioid receptors, the family of G-protein coupled receptors (GPCRs) that mediate pain relief through both the central and peripheral nervous systems. Four types of opioid receptors have been described, including the μ-opioid receptor (MOR), κ-opioid receptor (KOR), δ-opioid receptor (DOR), and the nociceptin opioid peptide receptor (NOP receptor). Despite the proven success of opioids in treating pain, there are still some inherent limitations. All clinically approved MOR analgesics are associated with adverse effects, which include tolerance, dependence, addiction, constipation, and respiratory depression. On the other hand, KOR selective analgesics have found limited clinical utility because they cause sedation, anxiety, dysphoria, and hallucinations. DOR agonists have also been investigated but they have a tendency to cause convulsions. Ligands targeting NOP receptor have been reported in the preclinical literature to be useful as spinal analgesics and as entities against substance abuse disorders while mixed MOR/NOP receptor agonists are useful as analgesics. Ultimately, the goal of opioid-related drug development has always been to design and synthesize derivatives that are equally or more potent than morphine but most importantly are devoid of the dangerous residual side effects and abuse potential. One proposed strategy is to take advantage of biased agonism, in which distinct downstream pathways can be activated by different molecules working through the exact same receptor. It has been proposed that ligands not recruiting β-arrestin 2 or showing a preference for activating a specific G-protein mediated signal transduction pathway will function as safer analgesic across all opioid subtypes. This review will focus on the design and the pharmacological outcomes of biased ligands at the opioid receptors, aiming at achieving functional selectivity.

Metabolism of a Kratom Alkaloid Metabolite in Human Plasma Increases Its Opioid Potency and Efficacy

Kratom is widely consumed in the United States for self-treatment of pain and opioid withdrawal symptoms. Mitragynine is the most abundant alkaloid in kratom and is a μ-opioid receptor agonist. 7-Hydroxymitragynine (7-HMG) is a mitragynine metabolite that is a more potent and efficacious opioid than its parent mitragynine. 7-HMG contributes to mitragynine's antinociceptive effects in mice, but evidence suggests it may also have a higher abuse potential. This in vitro study demonstrates that 7-HMG is stable in rodent and monkey plasma but is unstable in human plasma. Surprisingly, in human plasma 7-HMG is converted to mitragynine pseudoindoxyl, an opioid that is even more potent than either mitragynine or 7-HMG. This novel metabolite is formed in human plasma to a much greater extent than in the preclinical species tested (mouse, rat, dog, and cynomolgus monkey) and due to its μ-opioid potency may substantially contribute to the pharmacology of kratom in humans to a greater extent than in other tested species.

Development of an ELISA for detection of mitragynine and its metabolites in human urine

An enzyme-linked immunosorbent assay for detection of mitragynine, other closely related Kratom alkaloids and metabolites was developed using polyclonal antibodies. Mitragynine was conjugated to a carrier protein, cationized-bovine serum albumin using Mannich reaction. The synthesized antigen was injected into rabbits to elicit specific polyclonal antibodies against mitragynine. An enzyme conjugate was synthesized for evaluating its performance with the antibodies produced. The assay had an IC₅₀ of 7.3 ng/mL with a limit of detection of 15 ng/mL for mitragynine. Antibody produced have high affinity for mitragynine (100%), other closely related Kratom alkaloids such as paynantheine (54%), speciociliatine (63%), 7α-hydroxy-7H-mitragynine (83%) and cross-reacted with metabolites 9-O-demethyl mitragynine (79%), 16-carboxy mitragynine (103%), 9-O-demethyl mitragynine sulfate (263%), 9-O-demethyl mitragynine glucuronide (60%), 16-carboxy mitragynine glucuronide (60%), 9-O-demethyl-16-carboxy mitragynine sulfate (270%) and 17-O-demethyl-16,17-dihydro mitragynine glucuronide (34%). It showed cross-reactivity less than 0.01% to reserpine, codeine, morphine, caffeine, methadone, amphetamine, and cocaine. Ten-fold dilution urine was used in the assay to reduce the matrix effects. The recovery ranged from 83% to 112% with variation coefficients in intraday and interday less than 8% and 6%, respectively. The ELISA turned out to be a convenient tool to diagnose mitragynine, other closely related Kratom alkaloids and metabolites in human urine samples.

Kratom-Pharmacology, Clinical Implications, and Outlook: A Comprehensive Review

Kratom, or Mitragyna, is a tropical plant indigenous to Southeast Asia, with unique pharmacological properties. It is commonly consumed by preparing the leaves into decoction or tea, or by grinding them into a powder. Recent evidence has revealed that kratom has physiological effects similar to opioids, including pain relief and euphoria, as well as stimulant properties, which together raise potential concern for dependence and addiction. Moreover, growing evidence suggests that the prevalence of kratom use is increasing in many parts of the world, raising important considerations for healthcare providers. This manuscript will discuss the most current epidemiology, pharmacology, toxicity, and management related to kratom, while seeking to provide a contemporary perspective on the issue and its role in the greater context of the opioid epidemic.

G protein-biased kratom-alkaloids and synthetic carfentanil-amide opioids as potential treatments for alcohol use disorder

BACKGROUND AND PURPOSE

Mitragyna speciosa, more commonly known as kratom, is a plant that contains opioidergic alkaloids but is unregulated in most countries. Kratom is used in the self-medication of chronic pain and to reduce illicit and prescription opioid dependence. Kratom may be less dangerous than typical opioids because of the stronger preference of kratom alkaloids to induce receptor interaction with G proteins over β-arrestin proteins. We hypothesized that kratom (alkaloids) can also reduce alcohol intake.

EXPERIMENTAL APPROACH

We pharmacologically characterized kratom extracts, kratom alkaloids (mitragynine, 7-hydroxymitragynine, paynantheine, and speciogynine) and synthetic carfentanil-amide opioids for their ability to interact with G proteins and β-arrestin at μ, δ, and κ opioid receptors in vitro. We used C57BL/6 mice to assess to which degree these opioids could reduce alcohol intake and whether they had rewarding properties.

KEY RESULTS

Kratom alkaloids were strongly G protein-biased at all three opioid receptors and reduced alcohol intake, but kratom and 7-hydroxymitragynine were rewarding. Several results indicated a key role for δ opioid receptors, including that the synthetic carfentanil-amide opioid MP102-a G protein-biased agonist with modest selectivity for δ opioid receptors-reduced alcohol intake, whereas the G protein-biased μ opioid agonist TRV130 did not.

CONCLUSION AND IMPLICATIONS

Our results suggest that kratom extracts can decrease alcohol intake but still carry significant risk upon prolonged use. Development of more δ opioid-selective synthetic opioids may provide a safer option than kratom to treat alcohol use disorder with fewer side effects.

Kratom and Future Treatment for the Opioid Addiction and Chronic Pain: Periculo Beneficium?

Kratom (Mitragyna speciosa), a naturally existing plant found in South-East Asia, is traditionally used as a herb to help elevate a person's energy and also to treat numerous medical ailments. Other than the analgesic property, kratom has been used as an agent to overcome opioid withdrawal as it contains natural alkaloids, i.e. mitragynine, 7-hydroxymitragynine, and MGM-9, which has agonist affinity on the opioid receptors, including mu (µ) and kappa (κ). The role of neural reward pathways linked to µ-opioid receptors and both dopaminergic and gamma-Aminobutyric acid (GABA)-ergic interneurons that express µ-opioid receptors were deliberated. However, kratom has been reported to be abused together with other illicit substances with high risk of potential addiction. There are also anecdotes of adverse effects and toxicity of kratom, i.e. tremor, fatigue, seizure, and death. Different countries have distinctive regulation and policy on the plantation and use of this plant when most of the countries banned the use of it because of its addiction problems and side effects. The aim of this review is to highlight on the potential use of kratom, unique 'herbs" as a substitution therapy for chronic pain and opioid addiction, based on the neurobiological perspective of pain and the underlying mechanism of actions of drug addiction.