The cellular toxicology of mitragynine, the dominant alkaloid of the narcotic-like herb, Mitragyna speciosa Korth

Abstract

Toxicology ResearchDear Editor, Thank you for the reviews on our submission. The reviewers make some very good suggestions that we have incorporated into the text and the revised manuscript is now much stronger. I shall address the reviewers' comments on a point by point basis. Referee 1This is a well written paper and the experiments described, though fairly basic, are well performed and analysed. The work explores the mechanism of toxicity of mitragynine, the active alkaloid constituent of the herb Mitragyna speciosa Korth, and suggests a key molecular initiating event (MIE) that triggers the toxicity cascade.We thank the reviewer for the supportive words. The dose level at which toxicity was seen is 75µM that is some 75,000 to 750fold higher that that found in fairly high level users of the herb. This needs to be included in the abstract.We do mention this fact in the discussion along with the problems of extrapolating in vitro data to the situation in humans. To put our data in context, we also comment upon the human fatalities associated with Kratom consumption. In line with the comment and taking into consideration the reviewer's point 2, we now include new statements in the abstract and expand on this in the discussion. This is a great point. In fact references 9-11 in our manuscript give details of plasma levels of mitragynine in human fatalities associated with Kratom use. The plasma mitragynine concentrations in these individuals varied between 0.45 -1.5 microM, which is 50 fold less than the concentrations used in our studies. We have therefore included a review of these reports in our revised discussion. It Shown in both the cytoxicity assays (fig 2B) and clonogenic assays (Fig 2D) the lower doses show a marked cell proliferation. This is not commented on and some text should be included to deal with this.We have amended the text to comment on this. The reviewer makes an important point and we have reviewed the literature around this. We note that there is clear evidence in the literature of opiate mediated cell toxicity, particularly around morphine. In the revised submission we now reference reports of similar observations to ours, regarding naloxone effects on morphine toxicity and their speculation on the role of the µ receptor. Clearly the role of opioid receptors in opiate cellular toxicity remains controversial. The authors looked at the mechanism and hypothesised that the key molecular event could be interaction with the opiate receptors. This was tested using antagonists against these receptors. Naloxone that has activity particularly against the µ and ҝ receptors showed activity in reducing the toxicity but naltrindole (active against the δ receptor) did not show activity in Minor comments a. The resolution of figure 1 needs to be improved. This figure has clearly been cut and pasted from elsewhere.We have redrawn the figure using Chem-Draw. b. Figures 2A and 2B require error bars.We apologise for this oversight. The error bars have been added. Referee: 2Comments to the Author The results f...

Biochemical Benefits, Diagnosis, and Clinical Risks Evaluation of Kratom

“…The study found cytotoxicity was preceded by cell cycle arrest mainly at G1 and S phase. Although, the study demonstrated that the concentration of Mitragyna required to reduce the relative cell number by 50% (IC50) following 24 h treatment of SH-SY5Y cells was 7.5 × 10 −5 M ( 35 ), the author also note a low doses of Mitragyna (3 × 10 −7 M) could stimulate cell proliferation. The evidence remains that Mitragynine can cause cellular toxicity ( 35 ).…”

“…Saidin et al ( 35 ) studied the cellular toxicity of M. speciosa Korth on human cell (human neuronal SH-SY5Y cell line lines). The study found cytotoxicity was preceded by cell cycle arrest mainly at G1 and S phase.…”

“…The antileukemic property of Mitragyna that we reviewed seems to be more anecdotal than being substantiated by the literature. M. speciosa requires further study; however, individuals taking large quantities of these opiate-like ( 35 ) materials may be at risk ( 46 ), especially those who have a high CYP2E1 activity, such as heavy alcohol users ( 35 ). In case of liver injury, the liver damage may be due to the presence of contaminant or error in identification or preparation of the herbal product ( 42 ).…”

“…considers the plant to be minimally toxic, and research evaluating its toxic effects on humans is limited ( 5 ). Saidin et al ( 35 ) estimated the daily human use of M. speciosa is to be about 17 mg, which is about 20 leaves consumption of 20 leaves per day, at this dose, the consumption is said to be regular, and the potential plasma concentration is estimated to be 10 −9 to 10 −7 M ( 35 ). Fatalities after kratom consumption have been reported to occur in individuals with blood mitragynine concentrations of between 0.45 and 1.0 μM ( 35 ), substantially lower than the threshold of toxicity predicted from this in vitro report ( 35 ).…”

“…Saidin et al ( 35 ) estimated the daily human use of M. speciosa is to be about 17 mg, which is about 20 leaves consumption of 20 leaves per day, at this dose, the consumption is said to be regular, and the potential plasma concentration is estimated to be 10 −9 to 10 −7 M ( 35 ). Fatalities after kratom consumption have been reported to occur in individuals with blood mitragynine concentrations of between 0.45 and 1.0 μM ( 35 ), substantially lower than the threshold of toxicity predicted from this in vitro report ( 35 ). Saidin et al recommended further study and advised that individual taking large doses of Mitragynine may be at risk of toxicity in association with heavy use of alcohol ( 35 ).…”