In vitro metabolism study of Strychnos alkaloids using high-performance liquid chromatography combined with hybrid ion trap/time-of-flight mass spectrometry

Exploration by molecular networking of Strychnos alkaloids reveals the unexpected occurrence of strychnine in seven Strychnos species

INTRODUCTION

Plants of the Strychnos genus, which include about 200 species, are used for multiple traditional purposes as hunting poison, for example, and have shown interesting pharmacological properties, especially curarizing and tetanizing, but also against malaria. Many monoterpene indole alkaloids have already been isolated and identified. Among them, there is strychnine, a famous alkaloid that can cause death by asphyxiation.

OBJECTIVE

Investigate alkaloidic molecular diversity from Strychnos genus using molecular networking technique and study the Strychnos genus from a chemotaxonomic point of view.

MATERIAL AND METHODS

Twenty-eight different species and different plant parts were ground into powder using a grinder. The methanolic extracts were carried out using a pressurized solvent extraction and the alkaloid extract was performed manually with a separating funnel. The extracts were analyzed by HPLC-ESI(+)-Q/TOF. The data were processed using MZmine 2 software and the molecular network was generated on the GNPS platform. The study of the generated molecular network allowed the detection of various alkaloids. Among these is the famous strychnine which has been detected in 7 new Strychnos species not yet described as strychnine producers. This identification was investigated using orthogonal approaches, namely TLC, NMR, HPLC-UV and UHPLC-ESI(+)-Q/TOF analyses. The LOD by HPLC-UV of strychnine was also determined.

RESULTS

Further analyses allowed to confirm the presence of strychnine in S. densiflora trunk barks but also to show the presence of strychnine with high probability in the trunk barks of S. camptoneura, S. congolana, S. boonei, and S. tchibangensis, and in the leaves of S. usambarensis. About the trunk barks of S. tricalyisoides, the probability of a strychnine content remains low.

CONCLUSION

This work exemplified the efficiency of molecular networking in identifying known metabolites (major and minor alkaloids) involved in the chemotaxonomic study of plants from Strychnos genus.

Strychnine and its mono- and dimeric analogues: a pharmaco-chemical perspective

Covering: up to November 2021Since its isolation in 1818, strychnine has attracted the attention of a plethora of chemists and pharmacologists who have established its structure, developed total syntheses, and examined its complex pharmacology. While numerous reviews on structure elucidation and total synthesis of strychnine are available, reports on structure-activity relationships (SARs) of this fascinating alkaloid are rare. In this review, we present and discuss structures, synthetic approaches, metabolic transformations, and the diverse pharmacological actions of strychnine and its mono- and dimeric analogues. Particular attention is given to its SARs at glycine receptors (GlyRs) in light of recently published high-resolution structures of strychnine-GlyR complexes. Other pharmacological actions of strychnine and its derivatives, such as their antagonistic properties at nicotinic acetylcholine receptors (nAChRs), allosteric modulation of muscarinic acetylcholine receptors as well as anti-cancer and anti-plasmodial effects are also critically reviewed, and possible future developments in the field are discussed.

The Production and Evaluation of an Electrochemical Sensors for Strychnine and Its Main Metabolite Strychnine N-Oxide for Their Use in Biological Samples

Strychnine (STN) and its major metabolite Strychnine N-Oxide (SNO) were examined electrochemically. Both parent compounds and its major metabolite showed electroactivity on glassy carbon electrodes using CV and DPV techniques. One oxidation peak at 1008 mV was observed for STN with the optimum peak intensity at pH 7. SNO produced two oxidation peaks, at 617 mV and 797 mV, at pH 5. The peaks demonstrated irreversible behaviour and the irreversibility of the system was confirmed at different scan rates. A calibration curve was produced for both CV and DPV measurements and the sensitivity of the proposed EC method was good compared with previous electrochemical and non-electrochemical methods. The precision of oxidation peak of STN using the STN-MIP method produced a maximum value of 11.5% and 2.32% for inter-day and intraday %RSD, respectively. The average% recovery was around 92%. The electrochemical method has been successfully applied to the determination of STN in spiked plasma and urine samples. For SNO, both anodic peaks of SNO demonstrated irreversible behaviour. A different sweep rate was used for calculating the number of ‘transfer electrons’ in the system; based on this, the mechanism of oxidation reaction was proposed. Calibration curves for both oxidative peaks were produced using DPV measurements. The second anodic peak demonstrated high linearity and precision with %RSD < 1.96%.

Chronotoxicity of Semen Strychni is associated with circadian metabolism and transport in mice

OBJECTIVES

We aimed to determine the circadian responses of mice to Semen Strychni and to investigate the role of pharmacokinetics in generating chronotoxicity.

METHODS

Total extract of Semen Strychni was administered by oral gavage to wild-type (WT) and Bmal1-/- (a circadian clock-deficient model) mice at different circadian time points for toxicity (including survival) and pharmacokinetic characterization. Nephrotoxicity and neurotoxicity were evaluated by measuring plasma creatinine and creatine kinase BB (CK-BB), respectively. Drug metabolism and transport assays were performed using liver/intestine microsomes and everted gut sacs, respectively.

KEY FINDINGS

Semen Strychni nephrotoxicity and neurotoxicity as well as animal survival displayed significant circadian rhythms (the highest level of toxicity was observed at ZT18 and the lowest level at ZT2 to ZT6). According to pharmacokinetic experiments, herb dosing at ZT18 generated higher plasma concentrations (and systemic exposure) of strychnine and brucine (two toxic constituents) compared with ZT6 dosing. This was accompanied by reduced formation of both dihydroxystrychnine and strychnine glucuronide (two strychnine metabolites) at ZT18. Bmal1 ablation sensitized mice to Semen Strychni-induced toxicity (with increased levels of plasma creatinine and CK-BB) and abolished the time dependency of toxicity. Metabolism of Semen Strychni (strychnine and brucine) in the liver and intestine microsomes of WT mice was more extensive at ZT6 than at ZT18. These time differences in hepatic and intestinal metabolism were lost in Bmal1-/- mice. Additionally, the intestinal efflux transport of Semen Strychni (strychnine and brucine) was more extensive at ZT6 than ZT18 in WT mice. However, the time-varying transport difference was abolished in Bmal1-/- mice.

CONCLUSIONS

Circadian responses of mice to Semen Strychni are associated with time-varying efflux transport and metabolism regulated by the circadian clock (Bmal1). Our findings may have implications for optimizing phytotherapy with Semen Strychni via timed delivery.

Renoprotective Effects of Total Glucosides from Paeony against Nephrotoxicity Induced by Total Alkaloids from Semen Strychni

Semen Strychni have been shown to have therapeutic effect in improving blood circulation, relieving rheumatic pain, and treating cancer. However, Semen Strychni could cause severe nephrotoxicity. The present study was designed to evaluate whether treatment with total glucosides from paeony (TGP) has renoprotective effect against nephrotoxicity induced by total alkaloids from Semen Strychni (TAS). The levels of blood urea nitrogen (BUN) and creatinine (Cr) were determined and histopathological changes were also examined to evaluate renal injury. Moreover, a HPLC-MS method was developed and validated to investigate the comparative toxicokinetics of strychnine and brucine in rats plasma after oral administration of TAS and pretreatment with TGP. Results demonstrated that the levels of BUN and Cr were significantly increased (p < 0.05) in TAS group, together with tubule epithelium cloudy swelling, degeneration, and glomerular atrophy in rats' kidneys. The TAS-induced kidney damage was alleviated after pretreatment with TGP. Besides, T_max of strychnine and brucine were increased and T_1/2 of strychnine and brucine were decreased after pretreatment with TGP. The toxicokinetics study showed that pretreatment with TGP could attenuate the absorption of strychnine and brucine, as well as accelerate their elimination. These results suggest that TGP possesses renoprotective effects.

Profiling and Distribution of Metabolites of Procyanidin B2 in Mice by UPLC-DAD-ESI-IT-TOF-MSn Technique

The metabolite profiles and distributions of procyanidin B2 were qualitatively described using UPLC-DAD-ESI-IT-TOF-MSn without help of reference standards, and a possible metabolic pathway was proposed in the present study. Summarily, 53 metabolites (24 new metabolites) were detected as metabolites of procyanidin B2, and 45 of them were tentatively identified. Twenty seven metabolites were assigned as similar metabolites of (-)-epicatechin by scission of the flavanol interflavanic bond C4-C8, including 16 aromatic metabolites, 5 conjugated metabolites, 3 ring-cleavage metabolites, and 2 phenylvalerolactone metabolites. Additionally, 14 metabolites were conjugates of free procyanidin B2, comprising 9 methylation metabolites, 8 sulfation metabolites, 5 hydration metabolites, 2 hydroxylation metabolites, 1 hydrogenation metabolites, and 1 glucuronidation metabolites. The results of metabolite distributions in organs indicated that the conjugated reaction of free procyanidin B2 mainly occurred in liver and diversified metabolites forms were observed in small intestine. The metabolic components of procyanidin B2 identified in mice provided useful information for further study of the bioactivity and mechanism of its action.

Identification of the toxic components in Semen Strychni and their metabolites in rat serum by high performance liquid chromatography coupled with a Q Exactive high-resolution benchtop quadrupole Orbitrap mass spectrometer

Scheme of the identification of components in vitro and in vivo.

A study of Semen Strychni-induced renal injury and herb-herb interaction of Radix Glycyrrhizae extract and/or Rhizoma Ligustici extract on the comparative toxicokinetics of strychnine and brucine in rats

Recently, the renal injury caused by Semen strychni and its major toxic constituents, strychnine and brucine, was reported in many clinical cases. Hence, this study was conducted to investigate the renal injury induced by Semen Strychni and the protective effects of Radix Glycyrrhizae and Rhizoma Ligustici. The protective mechanisms were related to the comparative toxicokinetics of strychnine and brucine. Serum and urine uric acid and creatinine were used as renal function markers to evaluate the condition of kidney, and renal injury was directly reflected by histopathological changes. Compared with rats in blank group and protective herb groups, rats in Semen Strychni high-dose group showed significant differences in the results of renal function markers, and various glomerular and tubular degenerations were found in the histopathological study. The decreased AUC (only strychnine) and Cmax, the increased Tmax by Radix Glycyrrhizae and the decreased T1/2 by Radix Glycyrrhizae and Rhizoma Ligustici were found in model groups. Results indicated that high dose of Semen Strychni might induce renal injury. Radix Glycyrrhizae and Rhizoma Ligustici might work together and have effects on the elimination of strychnine and brucine. The protective effects of Radix Glycyrrhizae might also be explained by the slow absorption of the alkaloids.

Metabolism of brucine: the important metabolic pathways of dihydroindole-type alkaloid for excretion in rats

Background: Brucine is a widely prescribed glycine antagonist, but a complete understanding of its metabolic pathway is still lacking. The present work represents the first investigation of in vivo metabolism of brucine in rats using LC–ESI-ion trap-TOF-MS. Results: A total of 12 Phase I and five Phase II metabolites were tentatively identified. Brucine can be metabolized by hydrolysis, demethylation and methoxylation, in addition to diverse oxidations in a Phase I manner followed by glucuronidation in Phase II metabolism. Both the renal and biliary routes were observed for the excretion of brucine and its metabolites. Conclusion: Our results update the metabolism and disposition data on brucine, which provides basic information for better understanding of the pharmacological and toxicological activities of brucine-containing medicines.