In Vivo Efficacy and Metabolism of the Antimalarial Cycleanine and Improved In Vitro Antiplasmodial Activity of Semisynthetic Analogues

Aqueous extract of Enantia chlorantha Oliv. demonstrates antimalarial activity and improves redox imbalance and biochemical alterations in mice

BACKGROUND

Malaria is an infectious disease, which has continued to cause inconceivable loss of lives every year, almost unabatedly. Currently, it has become more difficult to treat the disease due to the emergence and spread of resistance to recommended antimalarial drugs. This situation necessitates an urgent search for antimalarial compounds with unique modes of action. Here, we investigate the antimalarial activity, antioxidant and anti-inflammatory capacity of Enantia chlorantha aqueous stem bark extract (EcASBE) in vivo.

METHODS

The extract was screened for selected phytoconstituents including alkaloids and flavonoids. We evaluated the antimalarial activity of EcASBE against Plasmodium berghei NK65 infection in mice, using curative, prophylactic, and suppressive antimalarial test models, respectively. In addition, the antioxidant and anti-inflammatory activities of the extract were assessed.

RESULTS

The EcASBE significantly (p < 0.05) inhibited parasitaemia dose-dependently, with the highest inhibition (80.4%) and prolonged survival (MST = 20) observed in the curative test. Our findings reveal significant (p < 0.05) improvement of serum ALT, AST, ALP, GGT, and levels of TNF-α, creatinine and urea following extract administration. Furthermore, the extract led to a significant (p < 0.05) rise in the levels of CAT, SOD, GPx, and GSH, with a concomitant reduction in NO and MDA levels.

CONCLUSION

The antimalarial, antioxidative, antiperoxidative, and inflammatory-inhibiting properties of the plant in infected mice demonstrate its great value for therapeutic intervention, and substantiate its use in traditional medicine for malaria treatment. Hence, further investigation to identify the repertoire of the active antimalarial components is warranted.

In vitro and in vivo antimalarial activity and chemical profiling of sugarcane leaves

Saccharum officinarum Linn. (sugarcane, Family-Poaceae) is employed in Ibibio traditional medicine for the treatment of various infections and diseases such as malaria. We This study aims to assess the antiplasmodial effect of the leaf extract and fractions on human malaria parasite (Plasmodium falciparum) in vitro, and rodent malaria parasite (P. berghei) in vivo, and analyse the bioactive components of the active fraction(s). The leaf extract and fractions of S. officinarum were prepared and their growth inhibitory effects tested against the chloroquine resistant P. falciparum strain (Dd2) and P. berghei infection in mice. An acute toxicity of the extract was determined. A combination of gas chromatography and liquid chromatography-mass spectrometry, and nuclear magnetic resonance spectroscopy was applied for metabolites profiling of crude extract and active fractions. The leaf extract and fractions demonstrated moderate activity against P. falciparum with the dichloromethane fraction producing the most potent activity (EC50 = 15.4 µg/mL). The leaf extract (170-510 mg/kg, p.o., LD50 = 1732 mg/kg) and fractions demonstrated significant (p < 0.05-0.001) effect on P. berghei infection in prophylactic  tests as well as in established infection with n-butanol fractions producing the highest effect. An unusual sulphur-containing compound, dilaurylthiodipropionate, fatty acids, phenolic acids, flavonoid and flavonoid glycoside were identified in the active fractions. These results give credence to the use of sugarcane leaves as malarial remedy locally by confirming the in vitro and in vivo antiplasmodial potential of leaf extract/fractions of S. officinarum.

Biotransformation of artemisinin to a novel derivative via ring rearrangement by Aspergillus niger

Abstract

Artemisinin is a component part of current frontline medicines for the treatment of malaria. The aim of this study is to make analogues of artemisinin using microbial transformation and evaluate their in vitro antimalarial activity. A panel of microorganisms were screened for biotransformation of artemisinin (1). The biotransformation products were extracted, purified and isolated using silica gel column chromatography and semi-preparative HPLC. Spectroscopic methods including LC-HRMS, GC–MS, FT-IR, 1D and 2D NMR were used to elucidate the structure of the artemisinin metabolites.¹H NMR spectroscopy was further used to study the time-course biotransformation. The antiplasmodial activity (IC₅₀) of the biotransformation products of 1 against intraerythrocytic cultures of Plasmodium falciparum were determined using bioluminescence assays. A filamentous fungus Aspergillus niger CICC 2487 was found to possess the best efficiency to convert artemisinin (1) to a novel derivative, 4-methoxy-9,10-dimethyloctahydrofuro-(3,2-i)-isochromen-11(4H)-one (2) via ring rearrangement and further degradation, along with three known derivatives, compound (3), deoxyartemisinin (4) and 3-hydroxy-deoxyartemisinin (5). Kinetic study of the biotransformation of artemisinin indicated the formation of artemisinin G as a key intermediate which could be hydrolyzed and methylated to form the new compound 2. Our study shows that the anti-plasmodial potency of compounds 2, 3, 4 and 5 were ablated compared to 1, which attributed to the loss of the unique peroxide bridge in artemisinin (1). This is the first report of microbial degradation and ring rearrangement of artemisinin with subsequent hydrolysis and methoxylation by A.niger.

Key points

• Aspergillus niger CICC 2487 was found to be efficient for biotransformation of artemisinin

• A novel and unusual artemisinin derivative was isolated and elucidated

• The peroxide bridge in artemisinin is crucial for its high antimalarial potency

• The pathway of biotransformation involves the formation of artemisinin G as a key intermediate

Supplementary Information

The online version contains supplementary material available at 10.1007/s00253-022-11888-0.

Complete biosynthesis of the bisbenzylisoquinoline alkaloids guattegaumerine and berbamunine in yeast

This work demonstrates microbial biosynthesis of bisbenzylisoquinoline (bisBIA) alkaloids. We show that several didomain epimerases can function in yeast to epimerize the nonnative substrate N-methylcoclaurine, an essential step in bisBIA biosynthesis. The N-methylcoclaurine epimerase activity was increased 10-fold by combining individual reductase and oxidase domains from different plant species. Strain engineering and optimization of media and growth conditions increased the bisBIA titer over 10,000-fold. We show that strains can be engineered to primarily produce one bisBIA product by selection of the cytochrome P450 variant that couples the monomer BIA subunits. We then leverage our bisBIA biosynthetic strain as a platform for the screening of other plant enzymes to produce two additional plant natural products de novo in a heterologous host.

Benzylisoquinoline alkaloids (BIAs) are a diverse class of medicinal plant natural products. Nearly 500 dimeric bisbenzylisoquinoline alkaloids (bisBIAs), produced by the coupling of two BIA monomers, have been characterized and display a range of pharmacological properties, including anti-inflammatory, antitumor, and antiarrhythmic activities. In recent years, microbial platforms have been engineered to produce several classes of BIAs, which are rare or difficult to obtain from natural plant hosts, including protoberberines, morphinans, and phthalideisoquinolines. However, the heterologous biosyntheses of bisBIAs have thus far been largely unexplored. Here, we describe the engineering of yeast strains that produce the Type I bisBIAs guattegaumerine and berbamunine de novo. Through strain engineering, protein engineering, and optimization of growth conditions, a 10,000-fold improvement in the production of guattegaumerine, the major bisBIA pathway product, was observed. By replacing the cytochrome P450 used in the final coupling reaction with a chimeric variant, the product profile was inverted to instead produce solely berbamunine. Our highest titer engineered yeast strains produced 108 and 25 mg/L of guattegaumerine and berbamunine, respectively. Finally, the inclusion of two additional putative BIA biosynthesis enzymes, SiCNMT2 and NnOMT5, into our bisBIA biosynthetic strains enabled the production of two derivatives of bisBIA pathway intermediates de novo: magnocurarine and armepavine. The de novo heterologous biosyntheses of bisBIAs presented here provide the foundation for the production of additional medicinal bisBIAs in yeast.

Clerodane Diterpenoids from an Edible Plant Justicia insularis: Discovery, Cytotoxicity, and Apoptosis Induction in Human Ovarian Cancer Cells

OBJECTIVES

The toxicity of chemotherapeutic anticancer drugs is a serious issue in clinics. Drug discovery from edible and medicinal plants represents a promising approach towards finding safer anticancer therapeutics. Justicia insularis T. Anderson (Acanthaceae) is an edible and medicinal plant in Nigeria. This study aims to discover cytotoxic compounds from this rarely explored J. insularis and investigate their underlying mechanism of action.

METHODS

The cytotoxicity of the plant extract was evaluated in human ovarian cancer cell lines and normal human ovarian surface epithelia (HOE) cells using a sulforhodamine B assay. Bioassay-guided isolation was carried out using column chromatography including HPLC, and the isolated natural products were characterized using GC-MS, LC-HRMS, and 1D/2D NMR techniques. Induction of apoptosis was evaluated using Caspase 3/7, 8, and 9, and Annexin V and PI based flow cytometry assays. SwissADME and SwissTargetPrediction web tools were used to predict the molecular properties and possible protein targets of identified active compounds. Key finding: The two cytotoxic compounds were identified as clerodane diterpenoids: 16(α/β)-hydroxy-cleroda-3,13(14)Z-dien-15,16-olide (1) and 16-oxo-cleroda-3,13(14)E-dien-15-oic acid (2) from the Acanthaceous plant for the first time. Compound 1 was a very abundant compound (0.7% per dry weight of plant material) and was shown to be more potent than compound 2 with IC₅₀ values in the micromolar range against OVCAR-4 and OVCAR-8 cancer cells. Compounds 1 and 2 were less cytotoxic to HOE cell line. Both compounds induced apoptosis by increasing caspase 3/7 activities in a concentration dependent manner. Compound 1 further increased caspase 8 and 9 activities and apoptosis cell populations. Compounds 1 and 2 are both drug like, and compound 1 may target various proteins including a kinase.

CONCLUSIONS

Clerodane diterpenoids (1 and 2) in J. insularis were identified as cytotoxic to ovarian cancer cells via the induction of apoptosis, providing an abundant and valuable source of hit compounds for the treatment of ovarian cancer.