Targeted screening of the synergistic components in Artemisia annua L. leading to enhanced antiplasmodial potency of artemisinin based on a "top down" PD-PK approach

ETHNOPHARMACOLOGICAL RELEVANCE

Artemisinin (ART) showed enhanced antimalarial potency in the herb Artemisia annua L. (A. annua), from which ART is isolated. Increased absorption of ART with inhibited metabolism in the plant matrix is an underlying mechanism. Several synergistic components have been reported based on a "bottom-up" approach, i.e., traditional isolation followed by pharmacokinetic and/or pharmacodynamic evaluation.

AIM OF THE STUDY

In this study, we employed a "top-down" approach based on in vivo antimalarial and pharmacokinetic studies to identify synergistic components in A. annua.

MATERIALS AND METHODS

Two A. annua extracts in different chemical composition were obtained by extraction using ethyl acetate (EA) and petroleum ether (PE). The synergistic antimalarial activity of ART in two extracts was compared both in vitro (Plasmodium falciparum) and in vivo (murine Plasmodium yoelii). For the PD-PK correlation analysis, the pharmacokinetic profiles of ART and its major metabolite (ART-M) were investigated in healthy rats after a single oral administration of pure ART (20 mg/kg) or equivalent ART in each A. annua extract. A liquid chromatography-tandem high-resolution mass spectrometry (LC-HRMS)-based analytical strategy was then applied for efficient component classification and structural characterization of the differential components in the targeted extract with a higher antimalarial potency. Major components isolated from the targeted extract were then evaluated for their synergistic effect in the same proportion.

RESULTS

Compared with pure ART (ED50, 5.6 mg/kg), ART showed enhanced antimalarial potency in two extracts in vivo (ED50 of EA, 2.9 mg/kg; ED50 of PE, 1.6 mg/kg), but not in vitro (IC50, 15.0-20.0 nM). A significant increase (1.7-fold) in ART absorption (AUC0-t) was found in rats after a single oral dose of equivalent ART in PE but not in EA; however, no significant change in the metabolic capability (AUCART-M/AUCART) was found for ART in either extract. The differential component analysis of the two extracts showed a higher composition of sesquiterpene compounds, especially component AB (3.0% in PE vs. 0.9% in EA) and component AA (14.1% in PE vs. 5.1% in EA). Two target sesquiterpenes were isolated and identified as arteannuin B (AB) and artemisinic acid (AA). The synergism between ART and AB/AA in the same proportion with PE extract (20:1.6:7.6, mg/kg) was verified by a pharmacokinetic study in rats.

CONCLUSIONS

A "top-down" strategy based on PD-PK studies was successfully employed to identify synergistic components for ART in A. annua. Two sesquiterpene compounds (arteannuin B and artemisinic acid) could enhance the antimalarial potency of ART by increasing its absorption.

Identification of chemosensitizing agents of colorectal cancer in Rauvolfia vomitoria using an NMR-based chemometric approach

Searching for new adjuvants of conventional chemotherapeutic approaches against colorectal cancer cells is extremely urgent. In current research, a non-targeted analytical approach was established by combining proton nuclear magnetic resonance spectroscopy with a chemometrics data mining tool to identify chemosensitizing agents from Rauvolfia vomitoria. This approach enabled the identification of potential active constituents in the initial fractionation process and provided their structural information. This strategy was validated by its application to Rauvolfia vomitoria extract exhibiting chemosensitizing activity on 5-fluorouracil against colorectal cancer cells. After the workflow, the biochemometrics analysis showed that at least 15 signals (Variable influence on projection (VIP) > 1) could have contributions in the differentiation of various fractions. Through systematic literature and database searches, we found that the most active fraction (fraction 7) exhibited the highest presence of sabazin-type and armaniline-type alkaloids, which were potential chemosensitizers as previously reported. To validate the results of the strategy, the effect of 5-FU and compounds isolated from fraction seven incubation on HCT-8 and LoVo cell vialibilty were evaluated. These results evidenced that compound β-carboline (3), 1-methyl-β-carboline (4), and lochnerine (6) could enhance the cytotoxicity of 5-fluorouracil against to Colorectal cancer cells. Besides, 21 compounds including two new compounds were isolated from Rauvolfia vomitoria. The experimental results verify the reliability of the method, and this approach provides a new and efficient tool to overcome some of the bottlenecks in natural products drug discovery.

Spectroscopic methodologies and molecular docking studies on the interaction of antimalarial drug piperaquine and its metabolites with human serum albumin

Artemisinin-based combination therapy is widely used for the treatment of uncomplicated Plasmodium falciparum malaria, and piperaquine (PQ) is one of the important partner drugs. During the biotransformation of PQ, M1 (N-oxidation product), M2 (N-oxidation product), M3 (carboxylic acid product), M4 (N-dealkylation product), and M5 (N-oxidated product of M4) are formed by cytochrome P450 pathways. Despite decades of clinical use, the interactions between PQ and its main metabolites (PQs) with human serum albumin (HSA) have not been reported. In the present study, the binding of PQs with HSA under physiological conditions was investigated systematically through fluorescence, circular dichroism (CD) spectroscopy, and molecular docking methods. The experimental results show that the intrinsic fluorescence quenching of HSA was induced by those compounds resulting from the formation of stable HSA-compound complexes. The main forces involved in the interactions between PQ, M1, and M2 which bind to HSA were hydrogen s and van der Waals forces, while the interactions of M3, M4, and M5 were driven by hydrophobic forces. The main binding sites of the compounds to HSA were also examined by classical fluorescent marker experiments and molecular docking studies. Binding constants (K_b) revealed that the affinities of the PQ, M1, M2, M3, and M4 to HSA were stronger than that of M5. Additionally, the binding rates of PQs with HSA were determined by ultrafiltration methods. Consistent with the binding constant results, the binding rate of M5 was lower than the binding rates of PQ, M1, M2, M3, and M4. Furthermore, PQs binding to HSA led to conformational and structural alterations of HSA, as revealed by multi-spectroscopic studies. In order to investigate one possible mechanism by which PQs inhibit the growth of malaria-causing Plasmodium parasites, ¹H NMR spectroscopy was performed to investigate the interaction of the PQs with heme. This study is beneficial to enhance our understanding of the ecotoxicology and environmental behaviors of PQ and its metabolites.

Investigation of the component in Artemisia annua L. leading to enhanced antiplasmodial potency of artemisinin via regulation of its metabolism

ETHNOPHARMACOLOGICAL RELEVANCE

The chemical matrix of the herb Artemisia annua L. (A. annua), from which artemisinin (QHS) is isolated, can enhance both the bioavailability and efficacy of QHS. However, the exact mechanism of this synergism remains unknown. The biotransformation of QHS and potential "enzyme inhibitors" in plant matrix could be of great importance in understanding the improved efficacy of QHS in A. annua, which has been limited to the synergism with flavonoid components.

AIM OF THE STUDY

To investigate the component in A. annua extracts (MAE) leading to enhanced antiplasmodial potency of QHS via regulation of its metabolism. The efficacy of QHS in combination with the synergistic component was also evaluated.

MATERIALS AND METHODS

The total MAE extract and its three MAE fractions (MAE-I eluted using 3% methanol, MAE-II eluted using 50% methanol and MAE-III eluted using 85% methanol) were obtained from dry plant materials and prepared after lyophilization. The pharmacokinetic profiles of QHS and its major phase I metabolite monohydroxylated artemisinin (QHS-M) were investigated in healthy rats after a single oral administration of QHS in each MAE extract. Major components isolated from the target MAE fraction were evaluated for their enzyme inhibition. The antimalarial activity of QHS in combination with the potential synergistic component against Plasmodium falciparum was studied in vivo (murine Plasmodium yoelii). The recrudescence and survival time of infected mice were also recorded after drug treatment.

RESULTS

Compared to pure QHS, a 2-fold increase in QHS exposure (AUC and C_max) was found in healthy rats after a single oral dose of QHS in the total MAE extract or its fraction MAE-III. In addition, metabolic biotransformation of QHS to the metabolite QHS-M (mediated by CYP3A) was inhibited by MAE or MAE-III. Among nine major components isolated from MAE-III (five sesquiterpenenes, three flavonoids and one phenolic acid), only arteannuin B (AB) showed an inhibition of CYP3A4 (IC₅₀ 1.2μM). The synergism between QHS and AB was supported using in vivo antiplasmodial assay and a pharmacokinetic study in mice. Unfortunately, the synergism cannot reduce the rate of recrudescence.

CONCLUSIONS

AB was one of main contributors in A. annua leading to enhanced antiplasmodial potency of QHS via regulation of its metabolism. The final recrudescence indicated the careful use of A. annua for malaria treatment unless additional contributing components or antiplasmodial mechanism were found.

Investigation of the active components in Tripterygium wilfordii leading to its acute hepatotoxicty and nephrotoxicity

ETHNOPHARMACOLOGICAL RELEVANCE

The traditional herbal medicine Tripterygium wilfordii Hook. f. (TW) has been widely used for the treatment of rheumatoid arthritis and autoimmune disease in the clinic. However, adverse reactions of TW including hepatotoxicity and nephrotoxicity have been frequently reported. Terpenes and alkaloids are among the most important active components in TW. Triptolide (TP), a major terpene in TW, has been found to induce toxicity, and metabolic pathways could lead to detoxification of TP. In this study, whether other major terpenes or alkaloids in TW contribute to its toxicity was investigated. The role of metabolic eliminations in their potential detoxification process was also evaluated.

MATERIALS AND METHODS

The toxicity of TW and its five major active components (one terpene and four alkaloids) in mice was evaluated in terms of mortality and blood biochemical levels (ALT, AST, BUN and CREA). TP was used as a positive control. Metabolic pathways leading to potential detoxification of TW or its two representative components (triptonide and wilforgine) were evaluated in glutathione (GSH)-depleted (treated with L-buthionine-S,R-sulfoxinine, BSO) and aminobenzotriazole (ABT; a nonspecific inhibitor for P450s)-treated mice.

RESULTS

In normal mice, the major metabolic pathways for the terpene compounds TP and triptonide (TN) were hydroxylation and cysteine conjugation, and the alkaloid wilforgine (WG) mainly underwent oxidative metabolism and hydrolysis. In ABT/BSO-treated mice, the hydroxylated metabolites of TP, TN and WG were found at a lower level than normal mice, and the level of cysteine conjugates of TN increased probably due to the stress response. Compared with normal mice, mortality and levels of ALT (but not BUN) were significantly higher (P<0.01) in TW (or TP)-treated mice (1.2 mg kg(-1)), indicating the acute toxicity (may not nephrotoxicity) of TW and its active component TP. Pretreatment with ABT and/or BSO increased the acute toxicity (including hepatotoxicity and nephrotoxicity) caused by TW or TP. No significant toxicity was found for TN or four alkaloids in normal mice or ABT/BSO-treated mice.

CONCLUSIONS

TP was probably the main contributor to the toxicity of TW, and the terpene TN and alkaloids in TW may be of no toxicological concern at dosage levels up to 20-fold of the therapeutic dose. Metabolic eliminations to less reactive metabolites implied a high potential for detoxification of TW, and caution should be taken for TW clinical use during co-administration with other CYP inhibitors or GSH-depleting agents.

Effects of diacetyl guan-fu base A on pacemaker cells in sinoatrial node of rabbits

AIM

To study the electrophysiological effects of diacetyl guan-fu base A (DGFA) on pacemaker cells in sinoatrial (SA) node.

METHODS

Intracellular microelectrode method was used to record parameters of action potential (AP) in SA node of rabbits.

RESULTS

DGFA could not only slow down spontaneous firing frequency (SFF), mean rate of repolarization (MRR), and rate of diastolic depolarization (RDD), but also prolong diastolic interval (DI) and duration of action potential (APD) in a concentration-dependent manner in SA node. Furthermore, DGFA markedly decreased the maximum rate of depolarization (MRD) with a slight reduce of the amplitude of action potential (APA) and there was no significant effect on the maximal diastolic potential (MDP). The decrease in SFF caused by DGFA was not affected by atropine (0.05 mg/L).

CONCLUSION

The effects might be due to the reduction of calcium influx and potassium efflux, and the muscarinic receptors were not involved.

Effects of inhaled low molecular weight heparin on airway allergic inflammation in aerosol-ovalbumin-sensitized guinea pigs

Low molecular weigh, heparin (LMWH) possesses multiple nonanticoagulant properties. In the present study, we observed its anti-airway allergic inflammatory effects by bronchoalveolar lavage in guinea pigs. Guinea pigs were sensitized by repeatedly inhaling aerosolized ovalbumin. LMWH (400 u/l, 800 u/l), dexamethasone (1.2 mg/1) or vehicle (normal saline) was inhaled for 7 days. Then the animals were sacrificed under anesthesia and then lavaged with ice-cold Hank's buffer immediately; bronchoalveolar lavage fluid (BALF) was prepared 24 h after the animals were challenged by antigen exposure. The effects of LMWH on total cell counts, absolute eosinophil counts and cell catalogues in BALF were studied; effects on the activity of eosinophil peroxidase (EPO) and the contents of histamine and eosinophil cationic protein (ECP) in BALF supernatant were detected. Our results showed that compared with the vehicle group, LMWH at 400 u/l and 800 u/1 could significantly reduce total cell counts, absolute eosinophil counts and percentage of eosinophils in BALF (P<0.05 and P<0.01, respectively); LMWH at 800 u/l markedly inhibited the activity of EPO in BALF supernatant (P<0.05); LMWH at 400 u/l and 800 u/l remarkably reduced the content of histamine in BALF supernatant (P<0.05 and P<0.01, respectively), LMWH at 800 u/l decreased the content of ECP (P<0.05) significantly. It suggested that LMWH exerted anti-airway allergic inflammatory action by inhibiting infiltration of inflammatory cells and reducing release of inflammatory mediators, as well as antagonizing their activities, and that LMWH could be developed as a potential anti-bronchial asthmatic drug.