Antimalarial properties of green tea

Plants as Sources of Natural and Recombinant Antimalaria Agents

Malaria is one of the severe infectious diseases that has victimized about half a civilization billion people each year worldwide. The application of long-lasting insecticides is the main strategy to control malaria; however, a surge in antimalarial drug development is also taking a leading role to break off the infections. Although, recurring drug resistance can compromise the efficiency of both conventional and novel antimalarial medicines. The eradication of malaria is significantly contingent on discovering novel potent agents that are low cost and easy to administer. In this context, plant metabolites inhibit malaria infection progression and might potentially be utilized as an alternative treatment for malaria, such as artemisinin. Advances in genetic engineering technology, especially the advent of molecular farming, have made plants more versatile in producing protein drugs (PDs) to treat infectious diseases, including malaria. These recent developments in genetic modifications have enabled the production of native pharmaceutically active compounds and the accumulation of diverse heterologous proteins such as human antibodies, booster vaccines, and many PDs to treat infectious diseases and genetic disorders. This review will discuss the pivotal role of a plant-based production system that expresses natural antimalarial agents or host protein drugs to cure malaria infections. The potential of these natural and induced compounds will support modern healthcare systems in treating malaria infections, especially in developing countries to mitigate human fatalities.

The protein aggregation inhibitor YAT2150 has potent antimalarial activity in Plasmodium falciparum in vitro cultures

Background

By 2016, signs of emergence of Plasmodium falciparum resistance to artemisinin and partner drugs were detected in the Greater Mekong Subregion. Recently, the independent evolution of artemisinin resistance has also been reported in Africa and South America. This alarming scenario calls for the urgent development of new antimalarials with novel modes of action. We investigated the interference with protein aggregation, which is potentially toxic for the cell and occurs abundantly in all Plasmodium stages, as a hitherto unexplored drug target in the pathogen.

Results

Attempts to exacerbate the P. falciparum proteome’s propensity to aggregation by delivering endogenous aggregative peptides to in vitro cultures of this parasite did not significantly affect their growth. In contrast, protein aggregation inhibitors clearly reduced the pathogen’s viability. One such compound, the bis(styrylpyridinium) salt YAT2150, exhibited potent antiplasmodial activity with an in vitro IC₅₀ of 90 nM for chloroquine- and artemisinin-resistant lines, arresting asexual blood parasites at the trophozoite stage, as well as interfering with the development of both sexual and hepatic forms of Plasmodium. At its IC₅₀, this compound is a powerful inhibitor of the aggregation of the model amyloid β peptide fragment 1-40, and it reduces the amount of aggregated proteins in P. falciparum cultures, suggesting that the underlying antimalarial mechanism consists in a generalized impairment of proteostasis in the pathogen. YAT2150 has an easy, rapid, and inexpensive synthesis, and because it fluoresces when it accumulates in its main localization in the Plasmodium cytosol, it is a theranostic agent.

Conclusions

Inhibiting protein aggregation in Plasmodium significantly reduces the parasite’s viability in vitro. Since YAT2150 belongs to a novel structural class of antiplasmodials with a mode of action that potentially targets multiple gene products, rapid evolution of resistance to this drug is unlikely to occur, making it a promising compound for the post-artemisinin era.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01374-4.

In Vivo Antimalarial Activity of the Leaf Extract of Osyris quadripartita Salzm. ex Decne and Its Major Compound (-) Catechin

Background

The leaves of Osyris quadripartita Salzm. ex Decne, endemic to Ethiopia, are traditionally used for the treatment of malaria. Previous phytochemical investigations of Osyris species showed the presence of flavonoids, anthracene derivatives, and sesquiterpene lactones as the main constituents. The aim of the present study was to investigate the antimalarial activity of the leaf extract of O. quadripartita and its isolated constituent against mice infected with Plasmodium berghei.

Methods

Isolation of a compound was carried out on silica gel column chromatography of the extract eluting with gradient mixtures of CHCl3/MeOH. Structural elucidation of the isolated compound was achieved by ESI-MS and 1D-and 2D-NMR spectral data. Peter's 4-day suppressive test method was used to determine the antimalarial activity of the test substances. Level of parasitemia, survival time, and body weight change were used to determine the antimalarial activity of the test substances.

Results

(-) Catechin was isolated and characterized from the hydroalcoholic extract of O. quadripartita. At a concentration of 400 mg/kg, both the extract and (-) catechin exhibited antimalarial activity with the highest chemosuppression values of 70.61% and 64.26%, respectively.

Conclusion

These findings indicate that O. quadripartita is endowed with genuine antimalarial activity attributed in part, to its (-) catechin content. Hence, the present study may validate the traditional use of the plant for the treatment of malaria.

An overview of the Plasmodium falciparum hexose transporter and its therapeutic interventions

Despite intense elimination efforts, human malaria, caused by the infection of five Plasmodium species, remains the deadliest parasitic disease in the world. Even worse, with the emergence and spreading of the first-line drug-resistant Plasmodium parasites, therapeutic interventions based on novel plasmodial drug targets are more necessary than ever. Given that the blood-stage parasites primarily rely on glycolysis for their energy supply, blocking glucose uptake, the rate-limiting step of ATP generation, was considered a promising approach to kill these parasites. To achieve this goal, characterization of the plasmodial hexose transporter and development of selective inhibitors have been pursued for decades. Here, we review the identification and characterization of the Plasmodium falciparum hexose transporter (PfHT1) and summarize current advances in its inhibitor development.

Ethanolic extract of Camellia sinensise licited hypoglycemic but lacked antimalarial properties in Plasmodium berghei-infected diabetic mice

The in vivo antimalarial and antidiabetic activity of extract of Camellia sinensis (ECS) in alloxan-induced diabetic and Plasmodium berghei-infected mice were investigated. Eighty-four BALB/c mice divided into sets 1 & 2 infected with P. berghei and 2 & 3 injected with alloxan received either distilled water, ECS (300mg/kg), Chloroquine (CQ-10mg/kg) or Metformin (250mg/kg). Results showed significant increases (p<0.05) in percentage parasitaemia of P. berghei-infected mice treated with ECS and P. berghei-diabetic mice. Furthermore, ECS significantly decreased (p<0.05) blood glucose and PCV in diabetic and P. berghei-diabetic mice.  ECS regenerated pancreatic islet cells in P. berghei-infected-diabetes but lacked appreciable antimalarial activity.

New insights into the role of the Nrf2 signaling pathway in green tea catechin applications

Nuclear factor-erythroid 2-related factor 2 (Nrf2) is a transcriptional signaling pathway that plays a crucial role in numerous clinical complications. Pivotal roles of Nrf2 have been proved in cancer, autoimmune diseases, neurodegeneration, cardiovascular diseases, diabetes mellitus, renal injuries, respiratory conditions, gastrointestinal disturbances, and general disorders related to oxidative stress, inflammation, apoptosis, gelatinolysis, autophagy, and fibrogenesis processes. Green tea catechins as a rich source of phenolic compounds can deal with various clinical problems and manifestations. In this review, we attempted to focus on intervention between green tea catechins and Nrf2. Green tea catechins especially epigallocatechin gallate (EGCG) elucidated the protective role of Nrf2 and its downstream molecules in various disorders through Keap-1, HO-1, NQO-1, GPx, GCLc, GCLm, NF-kB cross-link, kinases, and apoptotic proteins. Subsequently, we compiled an updated expansions of the Nrf2 role as a gate to manage and protect different disorders and feasible indications of green tea catechins through this signaling pathway. The present review highlighted recent evidence-based data in silico, in vitro, and in vivo studies on an outline for future clinical trials.

Catechins as Model Bioactive Compounds for Biomedical Applications

Research regarding polyphenols has gained prominence over the years because of their potential as pharmacological nutrients. Most polyphenols are flavanols, commonly known as catechins, which are present in high amounts in green tea. Catechins are promising candidates in the field of biomedicine. The health benefits of catechins, notably their antioxidant effects, are related to their chemical structure and the total number of hydroxyl groups. In addition, catechins possess strong activities against several pathogens, including bacteria, viruses, parasites, and fungi. One major limitation of these compounds is low bioavailability. Catechins are poorly absorbed by intestinal barriers. Some protective mechanisms may be required to maintain or even increase the stability and bioavailability of these molecules within living organisms. Moreover, novel delivery systems, such as scaffolds, fibers, sponges, and capsules, have been proposed. This review focuses on the unique structures and bioactive properties of catechins and their role in inflammatory responses as well as provides a perspective on their use in future human health applications.

In vitro activity of Camellia sinensis (green tea) against trophozoites and cysts of Acanthamoeba castellanii

The effect of Camellia sinensis (green tea) on the growth of Acanthamoeba castellanii trophozoites was examined using a microplate based-Sulforhodamine B (SRB) assay. C. sinensis hot and cold brews at 75% and 100% concentrations significantly inhibited the growth of trophozoites. We also examined the structural alterations in C. sinensis-treated trophozoites using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). This analysis showed that C. sinensis compromised the cell membrane integrity and caused progressive destruction of trophozoites. C. sinensis also significantly inhibited the parasite's ability to form cysts in a dose-dependent manner and reduced the rate of excystation from cysts to trophozoites. C. sinensis exhibited low cytotoxic effects on primary corneal stromal cells. However, cytotoxicity was more pronounced in SV40-immortalized corneal epithelial cells. Chromatographic analysis showed that both hot and cold C. sinensis brews contained the same number and type of chemical compounds. This work demonstrated that C. sinensis has anti-acanthamoebic activity against trophozoite and cystic forms of A. castellanii. Further studies are warranted to identify the exact substances in C. sinensis that have the most potent anti-acanthamoebic effect.

Antiplasmodial activity of Cocos nucifera leaves in Plasmodium berghei-infected mice

Plasmodium falciparum (P. falciparum) malaria presents serious public health problems worldwide. The parasite´s resistance to antimalarial drugs has proven to be a significant hurdle in the search for effective treatments against the disease. For this reason, the study of natural products to find new antimalarials remains a crucial step in the fight against malaria. In this study, we aimed to study the in vivo performance of the decoction of C. nucifera leaves in P. berghei-infected mice. We analyzed the effectiveness of different routes of administration and the acute toxicity of the extract. Additionally, we determined the suppressive, curative and prophylactic activity of the extract. The results showed that the decoction of leaves of C. nucifera is most effective when administered intramuscularly to mice in comparison to intraperitoneal, subcutaneous and intragastric methods. We also found that organ signs of acute toxicity appear at 2000 mg/kg/day as evidenced by necropsy examination. Additionally, we found that the prophylactic effect of the extract is of 48% inhibition, however, there is no curative effect. Finally, in a 4-day suppressive assay, we found that the extract can inhibit the growth of the parasite by up to 54% at sub-toxic doses when administered intramuscularly.

Antiplasmodial natural products: an update

Background

Malaria remains a significant public health challenge in regions of the world where it is endemic. An unprecedented decline in malaria incidences was recorded during the last decade due to the availability of effective control interventions, such as the deployment of artemisinin-based combination therapy and insecticide-treated nets. However, according to the World Health Organization, malaria is staging a comeback, in part due to the development of drug resistance. Therefore, there is an urgent need to discover new anti-malarial drugs. This article reviews the literature on natural products with antiplasmodial activity that was reported between 2010 and 2017.

Methods

Relevant literature was sourced by searching the major scientific databases, including Web of Science, ScienceDirect, Scopus, SciFinder, Pubmed, and Google Scholar, using appropriate keyword combinations.

Results and Discussion

A total of 1524 compounds from 397 relevant references, assayed against at least one strain of Plasmodium, were reported in the period under review. Out of these, 39% were described as new natural products, and 29% of the compounds had IC₅₀ ≤ 3.0 µM against at least one strain of Plasmodium. Several of these compounds have the potential to be developed into viable anti-malarial drugs. Also, some of these compounds could play a role in malaria eradication by targeting gametocytes. However, the research into natural products with potential for blocking the transmission of malaria is still in its infancy stage and needs to be vigorously pursued.

Inhibitory effects of Syzygium aromaticum and Camellia sinensis methanolic extracts on the growth of Babesia and Theileria parasites

Currently, chemotherapeutics against piroplasmosis are also associated with toxicity and the emergence of drug-resistant parasites. Therefore, the discovery of new drug compounds is necessary for the effective control of bovine and equine piroplasms. Syzygium aromaticum (clove) and Camellia sinensis (green tea) have several documented medicinal properties. In the present study, the growth-inhibiting effects of S. aromaticum and C. sinensis methanolic extracts were evaluated in vitro and in vivo. The half-maximal inhibitory concentration (IC₅₀) values for methanolic S. aromaticum against Babesia bovis, B. bigemina, B. divergens, B. caballi, and Theileria equi were 109.8 ± 3.8, 8.7 ± 0.09, 76.4 ± 4.5, 19.6 ± 2.2, and 60 ± 7.3 μg/ml, respectively. Methanolic C. sinensis exhibited IC₅₀ values of 114 ± 6.1, 71.3 ± 3.7, 35.9 ± 6.8, 32.7 ± 20.3, and 60.8 ± 7.9 μg/ml against B. bovis, B. bigemina, B. divergens, B. caballi, and T. equi, respectively. The toxicity assay on Madin-Darby bovine kidney (MDBK), mouse embryonic fibroblast (NIH/3T3), and human foreskin fibroblast (HFF) cell lines showed that methanolic S. aromaticum and methanolic C. sinensis affected only the viability of the MDBK cell line with half-maximal effective concentrations (EC₅₀) of 894.7 ± 4.9 and 473.7 ± 7.4 μg/ml, respectively, while the viability of NIH/3T3 and HFF cell lines was not affected even at 1000 μg/ml. In the in vivo experiment, methanolic S. aromaticum and methanolic C. sinensis oral treatments at 150 mg/kg inhibited the growth of Babesia microti in mice by 69.2% and 42.4%, respectively. These findings suggest that methanolic S. aromaticum and methanolic C. sinensis extracts have the potential as alternative remedies for treating piroplasmosis.

Molecular docking and ADME properties of bioactive molecules against human acid-beta-glucosidase enzyme, cause of Gaucher's disease

Gaucher disease is one of the common lysosomal storage diseases widespread all over the world. It is divided into three types such as type 1 (non-neuropathic), type 2 (acute infantile neuropathic) and type 3 (chronic neuropathic). This is caused by the deficiency of glucocerebrosidases from the midpoint nervous system. Recent years, computational tools are very important and play a vital role in identifying new leads for disease treatment. This study was performed to screen the effective bioactive molecules against glucocerebrosidases. In this study, Molecular docking and ADME profiles of bioactive molecules were found with the help of Schrödinger software. Results showed that, (-)-epicatechin are having best docking score and good binding affinity than other ligands. Hence, we concluded that the (-)-epicatechin may be a better drug candidate for gaucher disease which can be explored further.

Effect of (-)-epicatechin, a flavonoid on the NO and NOS activity of Raillietina echinobothrida

(-)-Epicatechin, a natural flavonoid reportedly has huge pharmacological properties. In this study the cestocide effect of (-)-epicatechin is demonstrated in Raillietina echinobothrida. Although the antiparasitic activity of (-)-epicatechin has been demonstrated against protozoa, helminths and ectoparasites, in the present study the cestocide activity of (-)-epicatechin is shown to be related to a decrease in nitric oxide synthase (NOS) activity and nitric oxide (NO) production. On exposure to 0.53mg/ml each of epicatechin, reference drug praziquantel and Ѡ Nitro-l- Arginine Methyl Ester (NOS inhibitor), the parasites attained paralysis at 10.15, 0.27 and 11.21h followed by death at 30.15, 1.21 and 35.18h respectively. Biochemical analysis showed a significant decrease in activity of NOS (57.360, 36.040 and 44.615%) and NO (41.579, 19.078 and 24.826%) in comparison to the controls. NADPH-diaphorase histochemical staining (a selective marker for NOS in neuronal tissue) demonstrated a pronounced decline in the visible staining activity in the tegument, subtegument and the peripheral nerve regions following exposure to the treatments. Strong binding affinity of (-)-epicatechin with NOS protein was also revealed through docking studies. The results strongly define the probable anthelmintic activity of our compound through its influence on the NOS activity.

Antiplasmodial Activity of Isolated Polyphenols from Alectryon serratus Leaves Against 3D7 Plasmodium falciparum

Background:

Alectryon serratus was selected from a screening program devoted to search naturally occurring antimalarial compound from plants in Alas Purwo National Park, Banyuwangi, East Java, Indonesia. The previous studies showed that ethanol extract of A. serratus leaves contains some polyphenol compounds.

Objective:

This study was designed to isolate and investigate antiplasmodial activity of polyphenol compounds.

Material and Methods:

The ethanol extract of A. serratus leaves was fractioned using liquid–liquid fractionation and column chromatography. Isolated compounds were identified using High-performance liquid chromatography, ultraviolet-visible, nuclear magnetic resonance, and compared with references. The isolates were tested in vitro for antiplasmodial activity against chloroquine-sensitive 3D7 strain of Plasmodium falciparum. Thin blood smears were used to assess the levels of parasitemia and growth inhibition of the isolates.

Result:

Half maximal Inhibitory concentration of Gallic acid (1), methyl gallate (2), and kempferol-3-O-rhamnoside (3) were 0.0722 μM, 0.0128 μM, and 3.4595 μM, respectively.

Conclusion:

The results suggest that gallic acid, methyl gallate, and kempferol-3-O-rhamnoside isolated from A. serratus leaves have antiplasmodial activity and are potential to be developed as antimalarial drugs.

SUMMARY

The ethanol extract of Alectryon serratus leaves was successively fractionated in CH₂Cl₂, EtOAc, and n-butanol. EtOAc fraction was fractionated using column chromatography and purified using preparative thin-layer chromatography (TLC). Isolates were studied for their antiplasmodial activity on parasites culture of chloroquine-sensitive 3D7 strain of Plasmodium falciparum. Parasitemia percentages, growth percentages, and inhibition percentages of each group were calculated. The half maximal inhibitory concentration (IC₅₀) values that represent the concentration required to inhibit 50% of Plasmodium growth were calculated from a calibration curve using linear regression. The results suggest that isolates have antiplasmodial activity and are responsible in the antimalarial activity of Alectryon serratus leaves.

Abbreviations Used: S.F: Subfraction, EGCG: Epigallocatechingallate, EGC: Epigallocatechin

(-)-Epigallocatechin-3-Gallate Inhibits the Chaperone Activity of Plasmodium falciparum Hsp70 Chaperones and Abrogates Their Association with Functional Partners

Heat shock proteins (Hsps), amongst them, Hsp70 and Hsp90 families, serve mainly as facilitators of protein folding (molecular chaperones) of the cell. The Hsp70 family of proteins represents one of the most important molecular chaperones in the cell. Plasmodium falciparum, the main agent of malaria, expresses six Hsp70 isoforms. Two (PfHsp70-1 and PfHsp70-z) of these localize to the parasite cytosol. PHsp70-1 is known to occur in a functional complex with another chaperone, PfHsp90 via a co-chaperone, P. falciparum Hsp70-Hsp90 organising protein (PfHop). (-)-Epigallocatechin-3-gallate (EGCG) is a green tea constituent that is thought to possess antiplasmodial activity. However, the mechanism by which EGCG exhibits antiplasmodial activity is not fully understood. A previous study proposed that EGCG binds to the N-terminal ATPase domain of Hsp70. In the current study, we overexpressed and purified recombinant forms of two P. falciparum cytosol localized Hsp70s (PfHsp70-1 and PfHsp70-z), and PfHop, a co-chaperone of PfHsp70-1. Using the surface plasmon resonance approach, we demonstrated that EGCG directly binds to the two Hsp70s. We further observed that binding of EGCG to the two proteins resulted in secondary and tertiary conformational changes. In addition, EGCG inhibited the ATPase and chaperone function of the two proteins. Furthermore, EGCG abrogated association of the two Hsp70s with their functional partners. Using parasites cultured in vitro at the blood stages, we observed that 2.9 µM EGCG suppressed 50% P. falciparum parasite growth (IC₅₀). Our findings demonstrate that EGCG directly binds to PfHsp70-1 and PfHsp70-z to inhibit both the ATPase and chaperone functions of the proteins. Our study constitutes the first direct evidence suggesting that the antiplasmodial activity of EGCG is at least in part accounted for by its inhibition of Hsp70 function.

Tea (Camellia sinensis) infusions ameliorate cancer in 4TI metastatic breast cancer model

BACKGROUND

Tea (Camellia sinensis) infusions are widely consumed beverages with numerous health benefits. However, physiological and molecular responses mediating these activities are poorly understood.

METHOD

Three replicates of 4TI cancer cell suspension (2.0 × 105 cells/ml) were challenged in vitro with various concentrations of green, black and purple tea infusions to asseses their cytoxicity and associated differentially expressed genes in the cells. Inhibitory activity was tested by using serial dilutions of respective tea infusions in a 96 well ELISA plate.

RESULTS

Green tea had the highest inhibition on 4TI cells proliferation at a concentration of IC50 = 13.12 μg/ml. Further analysis of the 4TI cancer cell line treated with tea using 454 pyrosequencing generated 425,696 reads with an input mean length of 286.54. Trimmed sequences were imported on a CLC genomic workbench v7.03 and annotated on a reference mouse genome (Mus musculus strain C57BL/6 J). Results revealed a differential expression of apoptosis related genes in the transcriptome. Casp8, Casp9, Casp3, Casp6, Casp8AP2, Aifm1, Aifm2 and Apopt1 genes were significantly upregulated indicating the process of apoptosis was initiated and executed.

CONCLUSION

These findings on caspases offer valuable information on the mechanism of tea as an anticancer agent and will contribute to further research in future novel treatments.

Strategies to enhance biologically active-secondary metabolites in cell cultures of Artemisia - current trends

The genus Artemisia has been utilized worldwide due to its immense potential for protection against various diseases, especially malaria. Artemisia absinthium, previously renowned for its utilization in the popular beverage absinthe, is gaining resurgence due to its extensive pharmacological activities. Like A. annua, this species exhibits strong biological activities like antimalarial, anticancer and antioxidant. Although artemisinin was found to be the major metabolite for its antimalarial effects, several flavonoids and terpenoids are considered to possess biological activities when used alone and also to synergistically boost the bioavailability of artemisinin. However, due to the limited quantities of these metabolites in wild plants, in vitro cultures were established and strategies have been adopted to enhance medicinally important secondary metabolites in these cultures. This review elaborates on the traditional medicinal uses of Artemisia species and explains current trends to establish cell cultures of A. annua and A. absinthium for enhanced production of medicinally important secondary metabolites.

Human cathelicidin LL-37 enhance the antibiofilm effect of EGCG on Streptococcus mutans

BACKGROUND

Streptococcus mutans forms biofilms as a resistance mechanism against antimicrobial agents in the human oral cavity. We recently showed that human cathelicidin LL-37 exhibits inhibitory effects on biofilm formation of S. mutans through interaction with lipoteichoic acid (LTA), but without antibacterial or biofilm dispersal abilities. (-)-Epigallocatechin gallate (EGCG) is the most abundant constituent of tea catechins that has the greatest anti-infective potential to inhibit the growth of various microorganisms and biofilm formation. Therefore, in this study, we evaluated whether LL-37 interacts with EGCG to enhance the antibiofilm effect of EGCG on S. mutans biofilm formation.

METHODS

Clinical S. mutans strains (n = 10) isolated from children's saliva were tested in a biofilm formation assay. The antibiofilm effect of EGCG with and without LL-37 was analyzed by the minimum biofilm eradication concentration assay and confirmed using field emission-scanning electron microscopy. In addition, the interaction among EGCG, LL-37, and LTA of S. mutans was determined using quartz crystal microbalance analysis.

RESULTS

EGCG killed 100 % of planktonic S. mutans within 5 h, inhibited biofilm formation within 24 h, and reduced bacteria cells in preformed biofilms within 3 h at a concentration of 0.2 mg/mL. However, EGCG did not appear to interact with LTA. LL-37 effectively enhanced the bactericidal activity of EGCG against biofilm formation and preformed biofilms as determined by quantitative crystal violet staining and field emission-scanning electron microscopy. In addition, quartz crystal microbalance analysis revealed that LL-37 interacted with EGCG and promoted binding between EGCG and LTA of S. mutans.

CONCLUSIONS

We show that LL-37 enhances the antibiofilm effect of EGCG on S. mutans. This finding provides new knowledge for dental treatment by using LL-37 as a potential antibiofilm compound.

COMPUTATIONAL MODELING OF ANTIMALARIAL 10-SUBSTITUTED DEOXOARTEMISININS

Nineteen 10-substitued deoxoartemisinin derivatives and artemisinin with activity against D-6 strains of malarial falciparum designated as Sierra Leone are studied. We use molecular electrostatic potential maps in an attempt to identify key structural features of the artemisinins that are necessary for their activities and molecular docking to investigate the interaction with the molecular receptor (heme). Chemometric modeling: Principal Component Analysis (PCA), Hierarchical Cluster Analysis (HCA), K-Nearest Neighbor (KNN), Soft Independent Modeling of Class Analogy (SIMCA) and Stepwise Discriminant Analysis (SDA) are employed to reduce dimensionality and investigate which subset of descriptors are responsible for the classification between more active (MA) and less active (LA) artemisinins. The PCA, HCA, KNN, SIMCA and SDA studies showed that the descriptors LUMO (Lowest Unoccupied Molecular Orbital) energy, DFeO1 (Distance between the O 1 atom from ligand and iron atom from heme), X1A (Average Connectivity Index Chi-1) and Mor15u (Molecular Representation of Structure Based on Electron Diffraction) code of signal 15, unweighted, are responsible for separating the artemisinins according to their degree of antimalarial activity. The prediction study was done with a new set of eight artemisinins by using the chemometric methods and five of them were predicted as active against D-6 strains of falciparum malaria. In order to verify if the key structural features that are necessary for their antimalarial activities were investigated for the interaction with the heme, we also carried out calculations of the molecular electrostatic potential (MEP) and molecular docking. MEP maps and molecular docking were analyzed for more active compounds of the prediction set.

Medicinal plants used by various tribes of bangladesh for treatment of malaria

It has been estimated that 300-500 million malaria infections occur on an annual basis and causes fatality to millions of human beings. Most of the drugs used for treatment of malaria have developed drug-resistant parasites or have serious side effects. Plant kingdom has throughout the centuries proved to be efficient source of efficacious malarial drugs like quinine and artemisinin. Since these drugs have already developed or in the process of developing drug resistance, it is important to continuously search the plant kingdom for more effective antimalarial drugs. In this aspect, the medicinal practices of indigenous communities can play a major role in identification of antimalarial plants. Bangladesh has a number of indigenous communities or tribes, who because of their living within or in close proximity to mosquito-infested forest regions, have high incidences of malaria. Over the centuries, the tribal medicinal practitioners have treated malaria with various plant-based formulations. The objective of the present study was to conduct an ethnomedicinal survey among various tribes of Bangladesh to identify the plants that they use for treatment of the disease. Surveys were conducted among seven tribes, namely, Bawm, Chak, Chakma, Garo, Marma, Murong, and Tripura, who inhabit the southeastern or northcentral forested regions of Bangladesh. Interviews conducted with the various tribal medicinal practitioners indicated that a total of eleven plants distributed into 10 families were used for treatment of malaria and accompanying symptoms like fever, anemia, ache, vomiting, and chills. Leaves constituted 35.7% of total uses followed by roots at 21.4%. Other plant parts used for treatment included barks, seeds, fruits, and flowers. A review of the published scientific literature showed that a number of plants used by the tribal medicinal practitioners have been scientifically validated in their uses. Taken together, the plants merit further scientific research towards possible discovery of novel compounds that can be used to successfully treat malaria with less undesirable sideeffects.

Plasmodial sugar transporters as anti-malarial drug targets and comparisons with other protozoa

Glucose is the primary source of energy and a key substrate for most cells. Inhibition of cellular glucose uptake (the first step in its utilization) has, therefore, received attention as a potential therapeutic strategy to treat various unrelated diseases including malaria and cancers. For malaria, blood forms of parasites rely almost entirely on glycolysis for energy production and, without energy stores, they are dependent on the constant uptake of glucose. Plasmodium falciparum is the most dangerous human malarial parasite and its hexose transporter has been identified as being the major glucose transporter. In this review, recent progress regarding the validation and development of the P. falciparum hexose transporter as a drug target is described, highlighting the importance of robust target validation through both chemical and genetic methods. Therapeutic targeting potential of hexose transporters of other protozoan pathogens is also reviewed and discussed.

Whole plant extracts versus single compounds for the treatment of malaria: synergy and positive interactions

Background

In traditional medicine whole plants or mixtures of plants are used rather than isolated compounds. There is evidence that crude plant extracts often have greater in vitro or/and in vivo antiplasmodial activity than isolated constituents at an equivalent dose. The aim of this paper is to review positive interactions between components of whole plant extracts, which may explain this.

Methods

Narrative review.

Results

There is evidence for several different types of positive interactions between different components of medicinal plants used in the treatment of malaria. Pharmacodynamic synergy has been demonstrated between the Cinchona alkaloids and between various plant extracts traditionally combined. Pharmacokinetic interactions occur, for example between constituents of Artemisia annua tea so that its artemisinin is more rapidly absorbed than the pure drug. Some plant extracts may have an immunomodulatory effect as well as a direct antiplasmodial effect. Several extracts contain multidrug resistance inhibitors, although none of these has been tested clinically in malaria. Some plant constituents are added mainly to attenuate the side-effects of others, for example ginger to prevent nausea.

Conclusions

More clinical research is needed on all types of interaction between plant constituents. This could include clinical trials of combinations of pure compounds (such as artemisinin + curcumin + piperine) and of combinations of herbal remedies (such as Artemisia annua leaves + Curcuma longa root + Piper nigum seeds). The former may enhance the activity of existing pharmaceutical preparations, and the latter may improve the effectiveness of existing herbal remedies for use in remote areas where modern drugs are unavailable.

Flavonoids from Artemisia annua L. as antioxidants and their potential synergism with artemisinin against malaria and cancer

Artemisia annua is currently the only commercial source of the sesquiterpene lactone artemisinin. Since artemisinin was discovered as the active component of A. annua in early 1970s, hundreds of papers have focused on the anti-parasitic effects of artemisinin and its semi-synthetic analogs dihydroartemisinin, artemether, arteether, and artesunate. Artemisinin per se has not been used in mainstream clinical practice due to its poor bioavailability when compared to its analogs. In the past decade, the work with artemisinin-based compounds has expanded to their anti-cancer properties. Although artemisinin is a major bioactive component present in the traditional Chinese herbal preparations (tea), leaf flavonoids, also present in the tea, have shown a variety of biological activities and may synergize the effects of artemisinin against malaria and cancer. However, only a few studies have focused on the potential synergistic effects between flavonoids and artemisinin. The resurgent idea that multi-component drug therapy might be better than monotherapy is illustrated by the recent resolution of the World Health Organization to support artemisinin-based combination therapies (ACT), instead of the previously used monotherapy with artemisinins. In this critical review we will discuss the possibility that artemisinin and its semi-synthetic analogs might become more effective to treat parasitic diseases (such as malaria) and cancer if simultaneously delivered with flavonoids. The flavonoids present in A. annua leaves have been linked to suppression of CYP450 enzymes responsible for altering the absorption and metabolism of artemisinin in the body, but also have been linked to a beneficial immunomodulatory activity in subjects afflicted with parasitic and chronic diseases.

Synergistic and additive effects of epigallocatechin gallate and digitonin on Plasmodium sporozoite survival and motility

BACKGROUND

Most medicinal plants contain a mixture of bioactive compounds, including chemicals that interact with intracellular targets and others that can act as adjuvants to facilitate absorption of polar agents across cellular membranes. However, little is known about synergistic effects between such potential drug candidates and adjuvants. To probe for such effects, we tested the green tea compound epigallocatechin gallate (EGCG) and the membrane permeabilising digitonin on Plasmodium sporozoite motility and viability.

METHODOLOGY/PRINCIPAL FINDINGS

Green fluorescent P. berghei sporozoites were imaged using a recently developed visual screening methodology. Motility and viability parameters were automatically analyzed and IC50 values were calculated, and the synergism of drug and adjuvant was assessed by the fractional inhibitory concentration index. Validating our visual screening procedure, we showed that sporozoite motility and liver cell infection is inhibited by EGCG at nontoxic concentrations. Digitonin synergistically increases the cytotoxicity of EGCG on sporozoite survival, but shows an additive effect on sporozoite motility.

CONCLUSIONS/SIGNIFICANCE

We proved the feasibility of performing highly reliable visual screens for compounds against Plasmodium sporozoites. We thereby could show an advantage of administering mixtures of plant metabolites on inhibition of cell motility and survival. Although the effective concentration of both drugs is too high for use in malaria prophylaxis, the demonstration of a synergistic effect between two plant compounds could lead to new avenues in drug discovery.

Comparison of effects of green tea catechins on apicomplexan hexose transporters and mammalian orthologues

Here we have investigated the inhibitory properties of green tea catechins on the Plasmodium falciparum hexose transporter (PfHT), the Babesia bovis hexose transporter 1 (BboHT1) and the mammalian facilitative glucose transporters, GLUT1 and GLUT5, expressed in Xenopus laevis oocytes. (-)-Epicatechin-gallate (ECG) and (-)-epigallocatechin-gallate (EGCG) inhibited D-glucose transport by GLUT1 and PfHT, and D-fructose transport by GLUT5, with apparent K(i) values between 45 and 117 microM. BboHT1 was more potently inhibited by the ungallated catechins (-)-epicatechin (EC) and (-)-epigallocatechin (EGC), with apparent K(i) values of 108 and 168 microM, respectively. Site-directed mutagenesis experiments provided little further support for previously reported models of catechin binding to hexose transporters. Furthermore, P. falciparum growth inhibition by catechins was not affected by the external D-glucose concentration. Our results provide new data on the inhibitory action of catechins against sugar transporters but were unable to elucidate the antimalarial mechanism of action of these agents.

Phytochemical licochalcone A enhances antimalarial activity of artemisinin in vitro

Resistance to synthetic first-line antimalarial drugs is considered to be a major cause of increased malaria morbidity and mortality. Use of artemisinin-based combination therapies (ACTs) is being encouraged to reduce the malaria mortality in areas of falciparum resistance. Artemisinin is a natural product at times in short supply. With projected rise in demand of artemisinin there is an unmet need for alternate ACTs. Novel compounds that reduce dependence on artemisinin are required. In vitro cultures of Plasmodium falciparum provide a screen system for identifying and evaluating new drug combinations. Interactions of two phytochemicals, artemisinin and licochalcone A, has been studied against synchronized erythrocytic stages of chloroquine-sensitive 3D7 and chloroquine-resistant RKL 303 strains of P. falciparum. These two compounds in combination show synergistic antiplasmodial activity in vitro on these strains. Artemisinin but not licochalcone A interferes with hemozoin formation. Neither of the phytochemicals alone or in combination obstructs sorbitol-induced hemolysis.

Antiplasmodial Effects of a few Selected Natural Flavonoids and their Modulation of Artemisinin Activity

The direct antiplasmodial effects of five structurally-related flavonoids, namely quercetin, rutin, eriodictyol, eriodictyolchalcone and catechin, were analyzed in vitro on P. falciparum. Notably, all these flavonoids, with the only exception of rutin, caused relevant inhibition of P. falciparum growth when given at 1 mM concentration. In addition, they were found to affect greatly the potent antiplasmodial activity of artemisinin, leading to significant additive and even synergistic effects. In particular, quercetin induced a pronounced synergistic effect. The observed synergisms might be conveniently exploited to design new and/or more effective combination therapies.

1968–2008: 40 Years of Franco F. Vincieri's Natural Products Research

This paper presents an overview of Prof. Vincieri's accomplishments in his career as a researcher in the field of pharmacognosy (pharmaceutical biology), analytical phytochemistry and pharmaceutical technology applied to herbal drug preparations at the Department of Pharmaceutical Sciences of the University of Florence. This article is a recognition of his valuable contributions to these research fields, especially for his outstanding and innovative interdisciplinary studies on the quality control of herbal drugs, herbal drug preparations, herbal medicinal products, botanical food supplements, and some “special foods” such as grapes, wines, olives and olive oil.

Heme activates artemisinin more efficiently than hemin, inorganic iron, or hemoglobin

Artemisinin derivatives appear to mediate their anti-malarial through an initial redox-mediated reaction. Heme, inorganic iron, and hemoglobin have all been implicated as the key molecules that activate artemisinins. The reactions of artemisinin with different redox forms of heme, ferrous iron, and deoxygenated and oxygenated hemoglobin were analyzed under similar in vitro conditions. Heme reacted with artemisinin much more efficiently than the other iron-containing molecules, supporting the role of redox active heme as the primary activator of artemisinin.