Separation and characterization of the metabolic products of lappaconitine in rat urine by high-performance liquid chromatography

Design, synthesis, and biological evaluation of low-toxic lappaconitine derivatives as potential analgesics

The C₁₈-diterpenoid alkaloid lappaconitine (LA) is a non-addictive analgesic used in China. The toxicity (LD₅₀ = 11.7 mg/kg) limits its application. Two series of LA derivatives, including amides and sulfonamides (1-93), were designed and synthesized by modification on their C4 acetamidobenzoate side chains in this work. In vivo analgesic activity and toxicity of all derivatives were evaluated, and the structure-activity relationship was summarized. Six lead compounds (35, 36, 39, 49, 70, and 89) exhibited approximate analgesic activity to LA but with significantly reduced toxicity. The therapeutic index of these compounds is 14-30 times that of LA. In vivo metabolism study of the lead compounds 39, 49, 70, and 89 were conducted by UPLC-MS^E, indicating the reason for the low toxicity of the potential derivatives might be they are difficult to metabolize to toxic metabolite N-deacetyllappaconitine compared to LA. The effects of lead compounds on sodium channels and hERG channels were also studied by ion channel reader (ICR) which further revealed their analgesic and toxicity-attenuating mechanisms. Sodium channel assay revealed that the analgesic mechanism of these lead compounds was inhibiting the Na_v 1.7 channels. Taken together, compound 39 was provided as a new analgesic lead compound with significantly low toxicity and comparable activity to LA.

Norditerpenoid alkaloids from Aconitum and Delphinium: structural relevance in medicine, toxicology, and metabolism

Covering: 77 A.D. up to 2020Norditerpenoid alkaloids (NDA), typically N-ethylpiperidine containing C19 or C18 natural product diterpenes, are hexacycles with several contiguous often oxygenated stereocentres. As a function of their structural complexity, they display important pharmacological activities. The processed plants are used as important folk drugs and four NDAs have now been clinically approved. Many metabolism studies on Aconitum alkaloids have been reported as the understanding of their biotransformation in living systems and in cell-free systems is important for the development of these alkaloids as drugs. This Highlight sets out the missing links in NDA biosynthesis, their biological applications, SAR, toxicity, metabolism, and analytical studies.

Hybrides of Alkaloid Lappaconitine with Pyrimidine Motif on the Anthranilic Acid Moiety: Design, Synthesis, and Investigation of Antinociceptive Potency

Convenient and efficient routes to construct hybrid molecules containing diterpene alkaloid lappaconitine and pyrimidine fragments are reported. One route takes place via first converting of lappaconitine to 1-ethynyl-lappaconitine, followed by the Sonogashira cross-coupling-cyclocondensation sequences. The other involves the palladium-catalyzed carbonylative Sonogashira reaction of 5'-iodolappaconitine with aryl acetylene and Mo (CO)6 as the CO source in acetonitrile and subsequent cyclocondensation reaction of the generated alkynone with amidines. The reaction proceeded cleanly in the presence of the PdCl2-(1-Ad)2PBn∙HBr catalytic system. The protocol provides mild reaction conditions, high yields, and high atom and step-economy. Pharmacological screening of lappaconitine-pyrimidine hybrids for antinociceptive activity in vivo revealed that these compounds possessed high activity in experimental pain models, which was dependent on the nature of the substituent in the 2 and 6 positions of the pyrimidine nucleus. Docking studies were undertaken to gain insight into the possible binding mode of these compounds with the voltage-gated sodium channel 1.7. The moderate toxicity of the leading compound 12 (50% lethal dose (LD50) value was more than 600 mg/kg in vivo) and cytotoxicity to cancer cell lines in vitro encouraged the further design of therapeutically relevant analogues based on this novel type of lappaconitine-pyrimidine hybrids.

Nanostructured lipid carriers for percutaneous administration of alkaloids isolated from Aconitum sinomontanum

BACKGROUND

Lipid-based nanosystems have great potential for transdermal drug delivery. In this study, nanostructured lipid carriers (NLCs) for short-acting alkaloids lappacontine (LA) and ranaconitine (RAN) isolated from Aconitum sinomontanum (AAS) at 69.47 and 9.16% (w/w) yields, respectively, were prepared to enhance percutaneous permeation. Optimized NLC formulations were evaluated using uniform design experiments. Microstructure and in vitro/in vivo transdermal delivery characteristics of AAS-loaded NLCs and solid lipid nanoparticles (SLNs) were compared. Cellular uptake of fluorescence-labeled nanoparticles was probed using laser scanning confocal microscopy and fluorescence-activated cell sorting. Nanoparticle integrity during transdermal delivery and effects on the skin surface were also investigated.

RESULTS

NLC formulations were less cytotoxic than the AAS solution in HaCaT and CCC-ESF cells. Moreover, coumarin-6-labeled NLCs showed biocompatibility with HaCaT and CCC-ESF cells, and their cellular uptake was strongly affected by cholesterol and lipid rafts. Significantly greater cumulative amounts of NLC-associated LA and RAN than SLN-associated alkaloids penetrated the rat skin in vitro. In vivo microdialysis showed higher area under the concentration-time curve (AUC)0-t for AAS-NLC-associated LA and RAN than for AAS-SLN-associated alkaloids.

CONCLUSIONS

NLC formulations could be good transdermal systems for increasing biocompatibility and decreasing cytotoxicity of AAS. AAS-NLCs showed higher percutaneous permeation than the other preparations. These findings suggest that NLCs could be promising transdermal delivery vehicles for AAS.

Comparative metabolism of Lappaconitine in rat and human liver microsomes and in vivo of rat using ultra high-performance liquid chromatography-quadrupole/time-of-flight mass spectrometry

Lappaconitine (LAP), a non-addictive potent analgesic drug, is broadly used to treat cancer and postoperative pain in many countries, and it also has antibiotic activity against Pseudomonas aeruginosa and Salmonella Typhi. Despite its widespread usage and potential for expanded use, its metabolism was poorly investigated. In this work, the metabolic fate of LAP in liver microsomes of the rat and human was compared, and after oral administration, the metabolites in the rat were investigated using ultra high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-Q/TOF-MS). As a result, a total of 51 metabolites were identified, including 48 metabolites that were reported here for the first time. Based on accurate MS/MS spectra and the known structure of LAP, the metabolites structures and their fragment ions were readily characterized. The biotransformations of LAP in vitro and in vivo were shown to involve hydroxylation, N-deacetylation, O-demethylation, N-deethylation, and hydrolysis. Furthermore, the results indicated a quantitative species difference in the metabolites for LAP between the rat and human. However, 16-DMLAP, DAL and 5'-OH-DAL were the main in vitro and in vivo metabolites. This work provides the LAP metabolite profiles in rat and human, which will help better understand the pharmacological and toxicological activities of LAP.

Analysis of the metabolites of mesaconitine in rat blood using ultrafast liquid chromatography and electrospray ionization mass spectrometry

BACKGROUND

Mesaconitine is the main active component of genus aconitum plants that are widely used in clinics in China. However, little has been known about the metabolic pathway of mesaconitine.

OBJECTIVE

To explore the metabolites and propose the pathway of mesaconitine.

MATERIALS AND METHODS

In the present study, mesaconitine (4 mg kg(-1)) was orally administered to male rats. Then, blood samples collected were pretreated using solid-phase extraction technique with C18 cartridges, and analyzed using LC/MS/MS method with electrospray ionization. Both positive ion mode and collision induced dissociation (CID) were used to elucidate the structures of the major metabolites of mesaconitine.

RESULTS

Ten compounds were identified, among which seven were new metabolites, and the metabolic pathway was proposed. The protonated molecular ions of seven new metabolites were at m/z 648, 618, 616, 602, 572, 468, and 542, multistage fragment ions with neutral loss of 28 u (CO), 60 u (CH3COOH), 18 u (H2O), and 32 u (CH3OH). These new metabolites detected firstly in vivo, were named 10-hydroxyl-mesaconitine, hypaconitine, dehydrated mesaconitine 16-O-demethylmesaconitine, 16-O-demethylhypaconitine, and 16-O-demethyl-dehydrated hypaconitine, respectively. Furthermore, the breaking sequence of methoxyl was obtained using quantum chemistry.

CONCLUSION

The study proved that the method of solid-phase extraction technique coupled with MS and quantum chemistry can be applied to the analysis of metabolites in plasma quickly and conveniently.

Separation and identification of Aconitum alkaloids and their metabolites in human urine

To study the safety of Aconitum medicinal herbs in clinic and identify Aconitum alkaloids poisoning in forensic medicine, Aconitum alkaloids and their metabolites were separated and identified in human urine by liquid chromatography-electrospray ionization-multi-stage mass spectrometry (LC-ESI-MS(n)) and chemical pathway of metabolism was investigated. The alkaloids and their metabolites in the urine sample were extracted with solid-phase cartridges and separated by HPLC with acetonitrile-water-formic acid (40:60:0.5) mobile phase. Structures of five metabolites and three parent Aconitum alkaloids were identified with multi-stage mass spectrometry data through comparison with authentic substances as aconitine (M(1)), mesaconitine (M(2)), hypaconitine (M(3)), benzoylaconine (M(4)), benzoylmesaconine (M(5)), benzoylhypaconine (M(6)), 16-O-demethylaconitine (M(7)) and 16-O-demethylhypaconitine (M(8)), respectively. Among them, M(8) was identified and reported for the first time. Metabolic pathways of Aconitum alkaloids in human body were proposed.

Mechanisms of photoinduced electron transfer reactions of lappaconitine with aromatic amino acids. Time-resolved CIDNP study

CIDNP techniques were applied to the investigation of the elementary mechanism of photoinduced interaction between anti-arrhythmic drug lappaconitine and amino acids tyrosine and tryptophan. It has been shown that the reactions involve the formation of lappaconitine radical anion. Lappaconitine radical anion is unstable and rapidly eliminates N-acetyl anthranilic acid via protonation and ether bond cleavage. The rate constant of ether bond cleavage was estimated to be equal to 4 x 10(5) s(-1). The role of single electron transfer is discussed in the light of the model of drug-receptor interactions.

Structure-dependent differences in the effects of the Aconitum alkaloids lappaconitine, N-desacetyllappaconitine and lappaconidine in rat hippocampal slices

Lappaconitine, a C19 diterpenoid alkaloid from Aconitum sinomontanum has been reported to possess analgesic and antiinflammatory properties in vivo and to inhibit neuronal activity in brain slices. In the present study the effect of lappaconitine has been compared with the effects of its main metabolite N-desacetyllappaconitine and the structurally related alkaloid lappaconidine. For comparison of drug effects population spikes and field excitatory postsynaptic potentials (EPSPs) evoked by stimulation of stratum radiatum or the alveus were studied in normal rat hippocampal slices and in slices treated with low Mg2+-medium. At concentrations of 3-100 microM, both lappaconitine and N-desacetyllappaconitine inhibited population spikes elicited by stratum radiatum and alvear stimulation as well as the field EPSP recorded in CA1 stratum radiatum. The drug-induced depression of field potential responses was increased with rising stimulus frequency, indicating an activity-dependent mode of action. The effect of N-desacetyllappaconitine on each parameter investigated was significantly stronger than the effect of lappaconitine. Despite the structural relationship, lappaconidine failed to affect neuronal excitability in concentration below 100 microM, and an increase in stimulus frequency did not potentiate its effect. Moreover, lappaconitine and N-desacetyllappaconitine suppressed epileptiform activity induced by bicuculline or by omission of Mg2+ from the bathing medium.