Evaluation of toxicity profile of kratom (Mitragyna speciosa Korth) decoction in rats.

Mitragyna speciosa Korth also known as kratom, is an herbal drug preparation for its therapeutic properties and opioid-replacement therapy. Kratom is consumed in a brewed decoction form in Malaysia and to date, no studies have characterized its chemical and toxicity profile. Thus, this study aims to evaluate kratom decoction's safety and toxicity profile after 28 days of treatment. Mitragynine content was quantified in kratom decoction and used as a marker to determine the concentration. Male and female Sprague Dawley rats were orally treated with vehicle or kratom decoction (10, 50 or 150 mg/kg) and two satellite groups were treated with vehicle and kratom decoction (150 mg/kg). Blood and organs were collected for hematology, biochemical and histopathology analysis at the end of treatment. No mortality was found after 28 days of treatment and no significant changes in body weight and hematology profile, except for low platelet count. High amounts of uric acid, AST, ALT and alkaline phosphatase were found in the biochemical analysis. Histological investigation of the heart and lungs detected no alterations except for the kidney, liver and brain tissues. In conclusion, repeated administration of kratom decoction provided some evidence of toxicity in the kidney and liver with no occurrence of mortality.

Inhibition of Advanced Glycation End-Products by Tamarindus indica and Mitragyna inermis Extracts and Effects on Human Hepatocyte and Fibroblast Viability.

Tamarindus indica and Mitragyna inermis are widely used by herbalists to cure diabetes mellitus. The aim of this study is to investigate the inhibitory potential of aqueous and various organic solvent fractions from both plants and some isolated compounds against advanced glycation end-products (AGEs). For this purpose, an in vitro BSA-fructose glycation model was used to evaluate the inhibition of AGE formation. Furthermore, the effects of the fractions on mouse fibroblast (NIH-3T3) and human hepatocyte (HepG2) survival were evaluated. The leaf, stem, and root fractions of both plants exhibited significant inhibition of AGEs formation. The IC50 values appeared to be less than 250 µg/mL; however, all fractions presented no adverse effects on NIH-3T3 up to 500 µg/mL. Otherwise, our phytochemical investigation afforded the isolation of a secoiridoid from the Mitragyna genus named secoiridoid glucoside sweroside (1), along with three known quinovic acid glycosides: quinovic acid-3ß-O-ß-d-glucopyranoside (2), quinovic acid-3-O-ß-d-6-deoxy-glucopyranoside, 28-O-ß-d-glucopyranosyl ester (3), and quinovic acid 3-O-α-l-rhamnopyranosyl-(4→1)-ß-d-glucopyranoside (4). In particular, 1-3 are compounds which have not previously been described in Mitragyna inermis roots. However, the isolated compounds did not exhibit AGE inhibitory activity. Further investigation on these potent antiglycation fractions may allow for the isolation of new antidiabetic drug candidates.

Total Synthesis and Structural Plasticity of Kratom Pseudoindoxyl Metabolites.

Mitragynine pseudoindoxyl, a kratom metabolite, has attracted increasing attention due to its favorable side effect profile as compared to conventional opioids. Herein, we describe the first enantioselective and scalable total synthesis of this natural product and its epimeric congener, speciogynine pseudoindoxyl. The characteristic spiro-5-5-6-tricyclic system of these alkaloids was formed through a protecting-group-free cascade relay process in which oxidized tryptamine and secologanin analogues were used. Furthermore, we discovered that mitragynine pseudoindoxyl acts not as a single molecular entity but as a dynamic ensemble of stereoisomers in protic environments; thus, it exhibits structural plasticity in biological systems. Accordingly, these synthetic, structural, and biological studies provide a basis for the planned design of mitragynine pseudoindoxyl analogues, which can guide the development of next-generation analgesics.

Interactive Effects of µ-Opioid and Adrenergic-α 2 Receptor Agonists in Rats: Pharmacological Investigation of the Primary Kratom Alkaloid Mitragynine and Its Metabolite 7-Hydroxymitragynine.

The primary kratom alkaloid mitragynine is proposed to act through multiple mechanisms, including actions at µ-opioid receptors (MORs) and adrenergic-α 2 receptors (Aα 2Rs), as well as conversion in vivo to a MOR agonist metabolite (i.e., 7-hydroxymitragynine). Aα 2R and MOR agonists can produce antinociceptive synergism. Here, contributions of both receptors to produce mitragynine-related effects were assessed by measuring receptor binding in cell membranes and, in rats, pharmacological behavioral effect antagonism studies. Mitragynine displayed binding affinity at both receptors, whereas 7-hydroxymitragynine only displayed MOR binding affinity. Compounds were tested for their capacity to decrease food-maintained responding and rectal temperature and to produce antinociception in a hotplate test. Prototypical MOR agonists and 7-hydroxymitragynine, but not mitragynine, produced antinociception. MOR agonist and 7-hydroxymitragynine rate-deceasing and antinociceptive effects were antagonized by the opioid antagonist naltrexone but not by the Aα 2R antagonist yohimbine. Hypothermia only resulted from reference Aα 2R agonists. The rate-deceasing and hypothermic effects of reference Aα 2R agonists were antagonized by yohimbine but not naltrexone. Neither naltrexone nor yohimbine antagonized the rate-decreasing effects of mitragynine. Mitragynine and 7-hydroxymitragynine increased the potency of the antinociceptive effects of Aα 2R but not MOR reference agonists. Only mitragynine produced hypothermic effects. Isobolographic analyses for the rate-decreasing effects of the reference Aα 2R and MOR agonists were also conducted. These results suggest mitragynine and 7-hydroxymitragynine may produce antinociceptive synergism with Aα 2R and MOR agonists. When combined with Aα 2R agonists, mitragynine could also produce hypothermic synergism. SIGNIFICANCE STATEMENT: Mitragynine is proposed to target the µ-opioid receptor (MOR) and adrenergic-α2 receptor (Aα2R) and to produce behavioral effects through conversion to its MOR agonist metabolite 7-hydroxymitragynine. Isobolographic analyses indicated supra-additivity in some dose ratio combinations. This study suggests mitragynine and 7-hydroxymitragynine may produce antinociceptive synergism with Aα2R and MOR agonists. When combined with Aα2R agonists, mitragynine could also produce hypothermic synergism.

Kratom (Mitragyna speciosa) Validation: Quantitative Analysis of Indole and Oxindole Alkaloids Reveals Chemotypes of Plants and Products.

Many consumers are turning to kratom (Mitragyna speciosa) to self-manage pain and opioid addiction. In the United States, an array of capsules, powders, and loose-leaf kratom products are readily available. Additionally, several online sites supply live kratom plants. A prerequisite to establishing quality control and quality assurance standards for the kratom industry, or understanding how alkaloid levels effect clinical outcomes, is the identification and quantitation of major and minor alkaloid constituents within available products and preparations. To this end, an ultra-high performance liquid chromatography-high resolution mass spectrometry method was developed for the analysis of 8 indole alkaloids (7-hydroxymitragynine, ajmalicine, paynantheine, mitragynine, speciogynine, isopaynantheine, speciociliatine, and mitraciliatine) and 6 oxindole alkaloids (isomitraphylline, isospeciofoleine, speciofoline, corynoxine A, corynoxeine, and rhynchophylline) in US-grown kratom plants and commercial products. These commercial products shared a qualitatively similar alkaloid profile, with 12 - 13 detected alkaloids and high levels of the indole alkaloid mitragynine (13.9 ± 1.1 - 270 ± 24 mg/g). The levels of the other major alkaloids (paynantheine, speciociliatine, speciogynine, mitraciliatine, and isopaynantheine) and the minor alkaloids varied in concentration from product to product. The alkaloid profile of US-grown M. speciosa "Rifat" showed high levels of the indole alkaloid speciogynine (7.94 ± 0.83 - 11.55 ± 0.18 mg/g) and quantifiable levels of isomitraphylline (0.943 ± 0.033 - 1.47 ± 0.18 mg/g). Notably, the alkaloid profile of a US-grown M. speciosa seedling was comparable to the commercial products with a high level of mitragynine (15.01 ± 0.20 mg/g). This work suggests that there are several M. speciosa chemotypes.

Sulfobutylation of Beta-Cyclodextrin Enhances the Complex Formation with Mitragynine: An NMR and Chiroptical Study.

Mitragynine (MTR), the main indole alkaloid of the well-known plant kratom (Mitragyna speciosa), is one of the most studied natural products nowadays, due to its remarkable biological effects. It is a partial agonist on the opioid receptors, and as such relieves pain without the well-known side-effects of the opioids applied in the clinical practice. MTR and its derivatives therefore became novel candidates for drug development. The poor aqueous solubility and low bioavailability of drugs are often improved by cyclodextrins (CyDs) as excipients through host-guest type complex formation. Among the wide variety of CyDs, sulfobutylether-beta-cyclodextrin (SBEßCyD) is frequently used and official in the European and U.S. Pharmacopoeia. Herein, the host-guest complexation of MTR with ßCyD and SBEßCyD was studied using chiroptical and NMR spectroscopy. It was found by NMR measurements that MTR forms a rather weak (logß11 = 0.8) 1:1 host-guest complex with ßCyD, while the co-existence of the 2MTR∙SBEßCyD and MTR∙SBEßCyD species was deducted from 1H NMR titrations in the millimolar MTR concentration range. Sulfobutylation of ßCyD significantly enhanced the affinity towards MTR. The structure of the formed inclusion complex was extensively studied by circular dichroism spectroscopy and 2D ROESY NMR. The insertion of the indole moiety was confirmed by both techniques.

Predicted Mode of Binding to and Allosteric Modulation of the µ-Opioid Receptor by Kratom's Alkaloids with Reported Antinociception In Vivo.

Pain management devoid of serious opioid adverse effects is still far from reach despite vigorous research and development efforts. Alternatives to classical opioids have been sought for years, and mounting reports of individuals finding pain relief with kratom have recently intensified research on this natural product. Although the composition of kratom is complex, the pharmacological characterization of its most abundant alkaloids has drawn attention to three molecules in particular, owing to their demonstrated antinociceptive activity and limited side effects in vivo. These three molecules are mitragynine (MG), its oxidized active metabolite, 7-hydroxymitragynine (7OH), and the indole-to-spiropseudoindoxy rearrangement product of MG known as mitragynine pseudoindoxyl (MP). Although these three alkaloids have been shown to preferentially activate the G protein signaling pathway by binding and allosterically modulating the µ-opioid receptor (MOP), a molecular level understanding of this process is lacking and yet important for the design of improved therapeutics. The molecular dynamics study and experimental validation reported here provide an atomic level description of how MG, 7OH, and MP bind and allosterically modulate the MOP, which can eventually guide structure-based drug design of improved therapeutics.

Pharmacokinetics of Eleven Kratom Alkaloids Following an Oral Dose of Either Traditional or Commercial Kratom Products in Rats.

Kratom, Mitragyna speciosa Korth., is being widely consumed in the United States for pain management and the reduction of opioid withdrawal symptoms. The central nervous system (CNS) active alkaloids of kratom, including mitragynine, 7-hydroxymitragynine, and numerous additional compounds, are believed to derive their effects through opioid receptor activity. There is no literature describing the systemic exposure of many of these alkaloids after the consumption of kratom. Therefore, we have developed and validated a bioanalytical method for the simultaneous quantitation of 11 kratom alkaloids (mitragynine, 7-hydroxymitragynine, corynantheidine, speciogynine, speciociliatine, paynantheine, corynoxine, corynoxine-B, mitraphylline, ajmalicine, and isospeciofoline) in rat plasma. The validated method was used to analyze oral pharmacokinetic study samples of lyophilized kratom tea (LKT) and a marketed product, OPMS liquid shot, in rats. Among the 11 alkaloids, only mitragynine, 7-hydroxymitragynine, speciociliatine, and corynantheidine showed systemic exposure 8 h postdose, and the dose-normalized systemic exposure of these four alkaloids was higher (1.6-2.4-fold) following the administration of the commercial OPMS liquid. Paynantheine and speciogynine levels were quantifiable up to 1 h postdose, whereas none of the other alkaloids were detected. In summary, the method was successfully applied to quantify the exposure of individual kratom alkaloids after an oral dose of traditional or commercial products. This information will contribute to understanding the role of each alkaloid in the overall pharmacology of kratom and elucidating the pharmacokinetic differences between traditional and commercial kratom products.

Exploring the Chemistry of Alkaloids from Malaysian Mitragyna speciosa (Kratom) and the Role of Oxindoles on Human Opioid Receptors.

Ten indole and oxindole alkaloids (1-10) were isolated from the freshly collected leaves of Malaysian Mitragyna speciosa (Kratom). The chemical structures of these compounds were established on the basis of extensive 1D and 2D NMR and HRMS data analysis. The spectroscopic data of mitragynine oxindole B (4) are reported herein for the first time. The spatial configuration of mitragynine oxindole B (4) was confirmed by single-crystal X-ray diffraction. Simultaneous quantification of the isolated alkaloids in the M. speciosa leaf specimens collected from different locations in the northern region of Peninsular Malaysia was also performed using UPLC-MS/MS. The oxindole alkaloids (1-4) and the indole alkaloid (10) were assessed for binding affinity at opioid receptors. Corynoxine (1) showed high binding affinity to µ-opioid receptors with a Ki value of 16.4 nM. Further, corynoxine (1) was 1.8-fold more potent than morphine in rats subjected to a nociceptive hot plate assay. These findings have important implications for evaluating the combined effects of the minor oxindole alkaloids in the overall therapeutic activity of M. speciosa.

Accelerated Solvent Extractions (ASE) of Mitragyna speciosa Korth. (Kratom) Leaves: Evaluation of Its Cytotoxicity and Antinociceptive Activity.

Mitragyna speciosa Korth (kratom) is known for its psychoactive and analgesic properties. Mitragynine is the primary constituent present in kratom leaves. This study highlights the utilisation of the green accelerated solvent extraction technique to produce a better, non-toxic and antinociceptive active botanical extract of kratom. ASE M. speciosa extract had a dry yield (0.53-2.91 g) and showed a constant mitragynine content (6.53-7.19%) when extracted with organic solvents of different polarities. It only requires a shorter extraction time (5 min) and a reduced amount of solvents (less than 100 mL). A substantial amount of total phenolic (407.83 ± 2.50 GAE mg/g and flavonoids (194.00 ± 5.00 QE mg/g) were found in ASE kratom ethanol extract. The MTT test indicated that the ASE kratom ethanolic leaf extract is non-cytotoxic towards HEK-293 and HeLa Chang liver cells. In mice, ASE kratom ethanolic extract (200 mg/kg) demonstrated a better antinociceptive effect compared to methanol and ethyl acetate leaf extracts. The presence of bioactive indole alkaloids and flavonols such as mitragynine, paynantheine, quercetin, and rutin in ASE kratom ethanolic leaf extract was detected using UHPLC-ESI-QTOF-MS/MS analysis supports its antinociceptive properties. ASE ethanolic leaf extract offers a better, safe, and cost-effective choice of test botanical extract for further preclinical studies.

The Chemistry of Kratom [Mitragyna speciosa]: Updated Characterization Data and Methods to Elucidate Indole and Oxindole Alkaloids.

Two separate commercial products of kratom [Mitragyna speciosa (Korth.) Havil. Rubiaceae] were used to generate reference standards of its indole and oxindole alkaloids. While kratom has been studied for over a century, the characterization data in the literature for many of the alkaloids are either incomplete or inconsistent with modern standards. As such, full 1H and 13C NMR spectra, along with HRESIMS and ECD data, are reported for alkaloids 1-19. Of these, four new alkaloids (7, 11, 17, and 18) were characterized using 2D NMR data, and the absolute configurations of 7, 17, and 18 were established by comparison of experimental and calculated ECD spectra. The absolute configuration for the N(4)-oxide (11) was established by comparison of NMR and ECD spectra of its reduced product with those for compound 7. In total, 19 alkaloids were characterized, including the indole alkaloid mitragynine (1) and its diastereoisomers speciociliatine (2), speciogynine (3), and mitraciliatine (4); the indole alkaloid paynantheine (5) and its diastereoisomers isopaynantheine (6) and epiallo-isopaynantheine (7); the N(4)-oxides mitragynine-N(4)-oxide (8), speciociliatine-N(4)-oxide (9), isopaynantheine-N(4)-oxide (10), and epiallo-isopaynantheine-N(4)-oxide (11); the 9-hydroxylated oxindole alkaloids speciofoline (12), isorotundifoleine (13), and isospeciofoleine (14); and the 9-unsubstituted oxindoles corynoxine A (15), corynoxine B (16), 3-epirhynchophylline (17), 3-epicorynoxine B (18), and corynoxeine (19). With the ability to analyze the spectroscopic data of all of these compounds concomitantly, a decision tree was developed to differentiate these kratom alkaloids based on a few key chemical shifts in the 1H and/or 13C NMR spectra.

Lateral Flow Assessment and Unanticipated Toxicity of Kratom.

The leaves of the Mitragynine speciosia tree (also known as Kratom) have long been chewed, smoked, or brewed into a tea by people in Southeastern Asian countries, such as Malaysia and Thailand. Just this past year, the plant Kratom gained popularity in the United States as a "legal opioid" and scheduling it as a drug of abuse is currently pending. The primary alkaloid found in Kratom is a µ-opioid receptor agonist, mitragynine, whose structure contains a promising scaffold for immunopharmacological use. Although Kratom is regarded as a safe opioid alternative, here we report the LD50 values determined for its two main psychoactive alkaloids, mitragynine and 7-hydroxymitragynine, as comparable to heroin in mice when administered intravenously. Given Kratom's recent emergence in the U.S., there is currently no diagnostic test available for law enforcement or health professionals, so we sought to design such an assay. Mitragynine was used as a starting point for hapten design, resulting in a hapten with an ether linker extending from the C9 position of the alkaloid. Bacterial flagellin (FliC) was chosen as a carrier protein for active immunization in mice, yielding 32 potential monoclonal antibodies (mAbs) for assay development. Antimitragynine mAbs in the range of micro- to nanomolar affinities were uncovered and their utility in producing a convenient lateral flow detection assay of human fluid samples was examined. Antibodies were screened for binding to mitragynine, 7-hydroxymitragynine, and performance in lateral flow assays. Two monoclonal antibodies were subcloned and further purified with 93 and 362 nM affinity to mitragynine. Test strip assays were optimized with a detection cut off of 0.5 µg/mL for mitragynine in buffer and urine (reflecting projected clinically relevant levels of drug in urine), which could be beneficial to law enforcement agencies and health professionals as the opioid epidemic in America continues to evolve.

Risk of death associated with kratom use compared to opioids.

Kratom use appears to be increasing across the United States, increasing attention to deaths in which kratom use was detected. Most such deaths have been ascribed to fentanyl, heroin, benzodiazepines, prescription opioids, cocaine and other causes (e.g., homicide, suicide and various preexisting diseases). Because kratom has certain opioid-like effects (e.g., pain relief), and is used by some people as a substitute for opioids for pain or addiction, kratom has been compared to "narcotic-like opioids" (e.g., morphine) with respect to risk of death despite evidence that its primary alkaloid, mitragynine, carries little of the signature respiratory depressing effects of morphine-like opioids. This commentary summarizes animal toxicology data, surveys and mortality data associated with opioids and kratom to provide a basis for estimating relative mortality risk. Population-level mortality estimates attributed to opioids as compared to kratom, and the per user mortality risks of opioids as compared to kratom are provided. By any of our assessments, it appears that the risk of overdose death is >1000 times greater for opioids than for kratom. The limitations of the mortality risk estimate warrants caution in individuals with unknown factors such as use of other substances and medications, or other preexisting conditions. More research on kratom safety and risks is needed, as is regulation of commercial kratom products to ensure that consumers are informed by FDA labeling and that kratom products are not contaminated or adulterated with other substances.

Metabolite profiling and identification of enzymes responsible for the metabolism of mitragynine, the major alkaloid of Mitragyna speciosa (kratom).

1. Mitragynine is the major indole-based alkaloid of Mitragyna speciosa (kratom). Decoctions (teas) of the plant leaves have been used traditionally for cough, diarrhoea, pain, hypertension and for the treatment of opioid addiction. In the West, kratom has become increasingly utilized for mood elevation, pain treatment and as a means of self-treating opioid addiction. 2. Metabolic pathways of mitragynine were identified in human liver microsomes (HLM) and S9 fractions. A total of thirteen metabolites were identified, four oxidative metabolites and a metabolite formed by demethylation at the 9-methoxy group were the major metabolites of mitragynine. 3. The cytochrome P450 enzymes involved in the metabolism of mitragynine were identified using selective chemical inhibitors of HLM and recombinant cytochrome P450. The metabolism of mitragynine was predominantly carried out through the CYP3A4 with minor contributions by CYP2D6 and CYP2C9. The formation of five oxidative metabolites (Met2, Met4, Met6, Met8 and Met11) was catalyzed by the CYP3A4. 4. In summary, mitragynine was extensively metabolized in HLM primarily to O-demethylated and mono-oxidative metabolites. The CYP3A4 enzyme plays a predominant role in the metabolic clearance of mitragynine and also in the formation of 7-hydroxymitragynine (Met2), a known active minor alkaloid identified in the leaf material.

Comparative Pharmacokinetics of Mitragynine after Oral Administration of Mitragyna speciosa (Kratom) Leaf Extracts in Rats.

Kratom (Mitragyna speciosa) has been examined for its opioid activity, especially for the treatment of opioid withdrawal and pain. Mitragynine, the most abundant alkaloid in kratom, is thought to be the major psychoactive alkaloid. An HPLC method was developed for the quantification of mitragynine in kratom leaf extracts. In addition, a multiple reaction mode based UPLC-MS/MS method was developed and validated for the quantification of mitragynine in rat plasma. Pharmacokinetic studies were performed by comparing a single intravenous dose of mitragynine (5 mg/kg, mitragynine hydrochloride) to a single oral dose of mitragynine (20 mg/kg, mitragynine hydrochloride), lyophilized kratom tea, and the organic fraction of the lyophilized kratom tea at an equivalent mitragynine dose of 20 mg/kg in rats. After intravenous administration, mitragynine exhibited a biexponential decrease in the concentration-time profile, indicating the fast distribution of mitragynine from the systemic circulation or central compartment to the peripheral compartments. Mitragynine hydrochloride, lyophilized kratom tea, and the lyophilized kratom tea organic fraction were dosed orally and the absolute oral bioavailability of mitragynine in rats was found to be 1.5- and 1.8-fold higher than that of mitragynine dosed alone. The results provide evidence that an equivalent oral dose of the traditional preparation (lyophilized kratom tea) and formulated/manufactured products (organic fraction) of kratom leaves provide better systemic exposure of mitragynine than that of mitragynine dosed alone.

In vitro anthelmintic effects of Bridelia ferruginea, Combretum glutinosum, and Mitragyna inermis leaf extracts on Haemonchus contortus, an abomasal nematode of small ruminants.

Gastrointestinal nematodes remain a major constraint on the health, welfare, and production of small ruminants. This study was conducted to evaluate three plant extracts (from Bridelia ferruginea, Combretum glutinosum, and Mitragyna inermis) as effective remedies against gastrointestinal parasites of small ruminants. Phytochemical screening was conducted on the plant leaves, and the potential anthelmintic properties of these plants were tested in vitro on Haemonchus contortus using the egg hatch, larval migration, and adult worm motility assays. The phytochemical screening of the leaves revealed the presence of several bioactive components in all the plants. The number of eggs that hatched was reduced in a concentration-dependent manner (p < 0.01) upon treatment with the methanol extract of B. ferruginea and the acetone extracts of C. glutinosum and M. inermis. The inhibitory effect of the acetone extract of B. ferruginea and the methanol extracts of C. glutinosum and M. inermis was not concentration-dependent (p > 0.05). There was a significant difference (p < 0.05) in the reduction in larval migration between the lowest concentrations (75 to 150 µg/mL) and the highest concentrations (300 to 1200 µg/mL) of plant extracts. The ability of plant extracts to affect the mobility of the adult worms was not concentration-dependent (p > 0.05); however, it was dependent on the time of incubation (p < 0.01). At the highest concentration (2400 µg/mL), all adult worms were motionless after 24 h of exposure, while at the lowest concentration (< 150 µg/mL), this occurred after 48 h of exposure. M. inermis and C. glutinosum extracts were more effective than B. ferruginea extracts (p < 0.05). Overall, these results suggest that these plants used by small-scale farmers possess antiparasitic properties useful for helminthiasis control. However, the effects of the plants remain to be confirmed via in vivo assays and toxicity tests in further studies.

Nature's first "atypical opioids": Kratom and mitragynines.

WHAT IS KNOWN AND OBJECTIVE: Advances in pain research have led to an understanding that many pains are driven by more than one underlying (patho)physiologic cause (ie, they are "multimechanistic") and that better pain relief is obtained with fewer adverse effects when an analgesic is correspondingly multimechanistic. At least two of the more-modern analgesics combine opioid and non-opioid mechanisms, and have become known as "atypical opioids." Less well known is that just as Nature evolved opioids, it also evolved atypical opioids, presaging modern drug discovery efforts. COMMENT: Traditional (typical) opioids are extracts or analogs of substances derived from the poppy plant. They produce their analgesic and adverse effects primarily through a single, opioid mechanism (albeit with individual differences). Two most recent analgesics were developed to have both an opioid mechanism and, a second, non-opioid mechanism of action (inhibition of monoamine neurotransmitter reuptake). Little known is that Nature had already evolved a plant source of compounds with the same properties. WHAT IS NEW AND CONCLUSION: As debate about the use and abuse potential of kratom swirls, conflicting, often contradicting, opinions are expressed. A review of the basic pharmacology of kratom reveals the explanation for the bifurcation in viewpoints: kratom has both opioid and non-opioid properties. Fascinatingly, just as the poppy plant (Papaver) evolved the typical opioids, Mitragyna evolved the mitragynines-Nature's "atypical opioids."

PXR mediated induction of CYP3A4, CYP1A2, and P-gp by Mitragyna speciosa and its alkaloids.

Kratom (Mitragyna speciosa), a native herb of Southeast Asia, is widely known for its psychoactive properties. Recent increase in the use of kratom as a recreational drug has increased the risk of its interaction with conventional drugs if taken concomitantly. A few reports are available related to the effects of kratom on the activity of cytochrome P450 enzymes (CYPs), but there are no reports of its effects on pregnane X receptor (PXR), a transcription factor that regulates the expression of CYPs and P-glycoprotein (P-gp). This study was carried out to evaluate the effects of a methanolic extract of kratom leaves, an alkaloid rich fraction and its 5 indole and 4 oxindole alkaloids on PXR activation and the resulting changes in the mRNA expression of PXR target genes (CYP3A4, CYP1A2, and P-gp). A significant activation of PXR was observed by the extract (3-fold), alkaloidal fraction (4-fold) and all 9 alkaloids (4- to 6-fold) that was associated with an increased mRNA expression which resulted into an increase in the activity of CYP3A4, CYP1A2, and P-gp. These results indicate that high consumption of Mitragyna speciosa extract along with the conventional drugs may lead to potential herb-drug interactions due to its effects on PXR.

Synthetic and Receptor Signaling Explorations of the Mitragyna Alkaloids: Mitragynine as an Atypical Molecular Framework for Opioid Receptor Modulators.

Mu-opioid receptor agonists represent mainstays of pain management. However, the therapeutic use of these agents is associated with serious side effects, including potentially lethal respiratory depression. Accordingly, there is a longstanding interest in the development of new opioid analgesics with improved therapeutic profiles. The alkaloids of the Southeast Asian plant Mitragyna speciosa, represented by the prototypical member mitragynine, are an unusual class of opioid receptor modulators with distinct pharmacological properties. Here we describe the first receptor-level functional characterization of mitragynine and related natural alkaloids at the human mu-, kappa-, and delta-opioid receptors. These results show that mitragynine and the oxidized analogue 7-hydroxymitragynine, are partial agonists of the human mu-opioid receptor and competitive antagonists at the kappa- and delta-opioid receptors. We also show that mitragynine and 7-hydroxymitragynine are G-protein-biased agonists of the mu-opioid receptor, which do not recruit ß-arrestin following receptor activation. Therefore, the Mitragyna alkaloid scaffold represents a novel framework for the development of functionally biased opioid modulators, which may exhibit improved therapeutic profiles. Also presented is an enantioselective total synthesis of both (-)-mitragynine and its unnatural enantiomer, (+)-mitragynine, employing a proline-catalyzed Mannich-Michael reaction sequence as the key transformation. Pharmacological evaluation of (+)-mitragynine revealed its much weaker opioid activity. Likewise, the intermediates and chemical transformations developed in the total synthesis allowed the elucidation of previously unexplored structure-activity relationships (SAR) within the Mitragyna scaffold. Molecular docking studies, in combination with the observed chemical SAR, suggest that Mitragyna alkaloids adopt a binding pose at the mu-opioid receptor that is distinct from that of classical opioids.

The pharmacology and toxicology of kratom: from traditional herb to drug of abuse.

Mitragyna speciosa (Rubiaceae), commonly known as kratom, is a tropical tree with a long history of traditional use in parts of Africa and Southeast Asia. In recent years, kratom has gained popularity for use as a recreational drug across the globe. Relatively new to the illicit market and used in a manner different from its traditional applications, preparations of kratom are touted by many as a safe and legal psychoactive product that improves mood, relieves pain, and may provide benefits in opiate addiction. Available literature was reviewed for M. speciosa via PubMed, Google Scholar, CINAHL, and EBSCO to summarize its traditional uses, phytochemical composition, pharmacology and toxicology of proposed active constituents, and potential for misuse and abuse. Research has demonstrated that both stimulant and sedative dose-dependent effects do exist, but a growing concern for the drug's effects and safety of use has resulted in national and international attention primarily due to an increase in hospital visits and deaths in several countries that are said to have been caused by extracts of the plant. The main active alkaloid substances in kratom, mitragynine and 7-hydroxymitragynine, present with a range of CNS stimulant and depressant effects mediated primarily through monoaminergic and opioid receptors. Recently, Palm Beach County, located in the southeastern corridor of Florida, has considered regulating kratom due to public safety concerns following the death of a young adult. At the local, state, and even federal levels, governments are now being confronted with the task of determining the safety and the possible regulation of kratom extracts. There are currently no standard analytical screening techniques for mitragynine and its metabolites following ingestion limiting its detection to more sophisticated techniques like liquid chromatography-mass spectrometry to determine kratom use. The growing concern of the abuse potential of kratom requires careful evaluation of its benefits and potential toxicities.