Antiprotozoal screening and cytotoxicity of extracts and fractions from the leaves, stem bark and root bark of Alstonia congensis

Antiplasmodial, antimalarial activities and toxicity of African medicinal plants: a systematic review of literature

BACKGROUND

Malaria still constitutes a major public health menace, especially in tropical and subtropical countries. Close to half a million people mainly children in Africa, die every year from the disease. With the rising resistance to frontline drugs (artemisinin-based combinations), there is a need to accelerate the discovery and development of newer anti-malarial drugs. A systematic review was conducted to identify the African medicinal plants with significant antiplasmodial and/or anti-malarial activity, toxicity, as wells as assessing the variation in their activity between study designs (in vitro and in vivo).

METHODS

Key health-related databases including Google Scholar, PubMed, PubMed Central, and Science Direct were searched for relevant literature on the antiplasmodial and anti-malarial activities of African medicinal plants.

RESULTS

In total, 200 research articles were identified, a majority of which were studies conducted in Nigeria. The selected research articles constituted 722 independent experiments evaluating 502 plant species. Of the 722 studies, 81.9%, 12.4%, and 5.5% were in vitro, in vivo, and combined in vitro and in vivo, respectively. The most frequently investigated plant species were Azadirachta indica, Zanthoxylum chalybeum, Picrilima nitida, and Nauclea latifolia meanwhile Fabaceae, Euphorbiaceae, Annonaceae, Rubiaceae, Rutaceae, Meliaceae, and Lamiaceae were the most frequently investigated plant families. Overall, 248 (34.3%), 241 (33.4%), and 233 (32.3%) of the studies reported very good, good, and moderate activity, respectively. Alchornea cordifolia, Flueggea virosa, Cryptolepis sanguinolenta, Zanthoxylum chalybeum, and Maytenus senegalensis gave consistently very good activity across the different studies. In all, only 31 (4.3%) of studies involved pure compounds and these had significantly (p = 0.044) higher antiplasmodial activity relative to crude extracts. Out of the 198 plant species tested for toxicity, 52 (26.3%) demonstrated some degree of toxicity, with toxicity most frequently reported with Azadirachta indica and Vernonia amygdalina. These species were equally the most frequently inactive plants reported. The leaves were the most frequently reported toxic part of plants used. Furthermore, toxicity was observed to decrease with increasing antiplasmodial activity.

CONCLUSIONS

Although there are many indigenous plants with considerable antiplasmodial and anti-malarial activity, the progress in the development of new anti-malarial drugs from African medicinal plants is still slothful, with only one clinical trial with Cochlospermum planchonii (Bixaceae) conducted to date. There is, therefore, the need to scale up anti-malarial drug discovery in the African region.

A review on antimicrobial botanicals, phytochemicals and natural resistance modifying agents from Apocynaceae family: Possible therapeutic approaches against multidrug resistance in pathogenic microorganisms

Accelerated emergence of drug- resistant pathogenic microbes, their unbeatable virulence and a gradual loss of efficacy of currently used antimicrobial agents over the last decade, have expanded the scope of herbal medicine to combat this emerging challenge to have a wide spectrum of activity to develop effective medicines with lesser untoward side effects. Plant-based natural products should be of utmost interest to today's pharmaceutical industries since they are a primary source of new chemical entities directed at new drug targets. Apocynaceae or 'Dogbane' family has attained a global reputation as a source of some life-saving plant-derived products and novel compounds. Members of this family have also been extensively investigated against several nosocomial pathogenic microbes through in vitro and in vivo experimental settings. Several plant-derived components obtained from members of this family have also exhibited remarkable microbial growth inhibitory properties. Popular and widely accepted international databases such as PubMed, Science Direct, ResearchGate, Scopus, Google Scholar, JSTOR and more were searched using the various search strings such as Apocynaceae, antimicrobials, multidrug resistance, resistance modifying agents and pathogenic microorganisms were used in various combinations to retrieve several citations related to the topic. The current review encompasses recent developments in experimental studies and phytochemical analyses which correlates with antimicrobial efficacy of selected Apocynaceous plants along with synergistic mechanism and structural details. The present review recognizes and leverages the importance of Apocynaceae plants, which could be of significant interest in the development of more effective and less toxic antimicrobial drugs which may surmount multidrug resistance. Three different paradigm models harnessing clinical antimicrobial resistance (AMR) including the plant family Apocynaceae, Gram-positive and Gram-negative bacterial species have been broadly discussed in this review. In a nutshell, the present review represents a comprehensive account on the antimicrobials and resistance modifying agents obtained from the members of the plant family Apocynaceae and derived phytochemicals. It also gives an insight into the underlying mode of action of these phytochemicals against an array of pathogenic bacteria, their mechanism of antibiosis, plant parts from which the phytochemicals were isolated or the extracts was prepared with a critical discussion on the botanically-derived antibiotics as a template for antimicrobial drug development.

In vitro and in vivo antiplasmodial activity of extracts and isolated constituents of Alstonia congensis root bark

ETHNOPHARMACOLOGICAL RELEVANCE

An aqueous decoction of root bark of Alstonia congensis Engl. (Apocynaceae) is used in several African countries to treat various ailments including malaria.

MATERIALS AND METHODS

Extracts of different polarity and isolated constituents were tested in vitro for their antiplasmodial activity against the chloroquine-resistant strain Plasmodium falciparum K1 and the chloroquine-sensitive strain P. falciparum NF54A19A, as well as for their cytotoxic effects againt MRC-5 cells (human lung fibroblasts). Extracts and fractions were evaluated in vivo against the chloroquine-resistant strain P. yoelii N67 and the chloroquine-sensitive strain P. berghei berghei ANKA.

RESULTS

The aqueous extract, the 80% methanol extract and the alkaloid-enriched extract exhibited strong antiplasmodial activity against P. falciparum K1 with IC₅₀ values < 10 µg/ml and against P. falciparum NF54 A19A with IC₅₀ values < 0.02 µg/ml. In vivo against P. yoelii N67, at the highest oral dose of 400 mg/kg body weight, all extracts produced 70-73% chemosuppression, while against P. berghei berghei, more than 75% chemosuppression was observed. With regard to the isolated constituents, boonein was inactive in vitro against P. falciparum K-1 (IC₅₀ > 64 µM), while echitamine, 6,7-seco-angustilobine B and β-amyrin exhibited moderate activity (IC₅₀ < 30 µM). Against P. falciparum NF54 A19A, boonein was inactive (IC₅₀ > 64 µM), while echitamine, 6,7-secoangustilobine and β-amyrin showed moderate IC₅₀ values of 11.07, 21.26 and 40.70 µM, respectively.

CONCLUSION

These results demonstrated that all extracts from A. congensis root bark possessed antiplasmodial activity in vitro and in vivo. They can be used as raw materials for the preparation of ameliorated remedies for the treatment of uncomplicated malaria. The observed antiplasmodial activity may be due in part to the presence of indole alkaloids.

Antiparasitic phytotherapy perspectives, scope and current development

Tropical protozoan diseases are currently a major public health problem throughout the world and are strongly linked with poverty, this combined with a lack of commercial markets for potential drugs has created a large burden on the health and economic development of low-income and middle-income countries in Africa, Asia, and the Americas. Due to the low research interest and the high increase of resistance against the existing treatments, as well as increasing inefficiency, toxicity, prolonged treatment schedules and costs, there is an urgent need for cost-effective, safe and easy-to-administer, new effective compounds with novel mechanisms of action. Several studies of crude plant extracts have already identified potential compounds to treat Chagas’ disease, Leishmaniasis, Toxoplasmosis, Giardiasis, and Malaria among other protozoan parasites. Natural compounds of medicinal plants have shown lower toxicity together with higher specificity, creating an optimistic view of new treatments for diseases. Out of 1010 new active substances approved as drugs for medical conditions by regulatory agencies during the past 25 years, 490(48.5%) were from a natural origin.

Apocynaceae species with antiproliferative and/or antiplasmodial properties: a review of ten genera

Apocynaceae is a large family of tropical trees, shrubs and vines with most species producing white latex. Major metabolites of species are triterpenoids, iridoids, alkaloids and cardenolides, which are known for a wide range of biological and pharmacological activities such as cardioprotective, hepatoprotective, neuroprotective, anti-inflammatory, anticancer and antimalarial properties. Prompted by their anticancer and antimalarial properties, the current knowledge on ten genera (Allamanda, Alstonia, Calotropis, Catharanthus, Cerbera, Dyera, Kopsia, Nerium, Plumeria and Vallaris) is updated. Major classes of metabolites are described using some species as examples. Species with antiproliferative (APF) and/or antiplasmodial (APM) properties have been identified. With the exception of the genus Dyera, nine genera of 22 species possess APF activity. Seven genera (Alstonia, Calotropis, Catharanthus, Dyera, Kopsia, Plumeria and Vallaris) of 13 species have APM properties. Among these species, Alstonia angustiloba, Alstonia macrophylla, Calotropis gigantea, Calotropis procera, Catharanthus roseus, Plumeria alba and Vallaris glabra displayed both APF and APM properties. The chemical constituents of these seven species are compiled for assessment and further research.

Ethnomedicinal survey of plants used in the treatment of malaria in Southern Nigeria

ETHNOPHARMACOLOGICAL RELEVANCE

Malaria is one of the most severe public health problems worldwide. It is a leading cause of death and disease in many developing countries, where young children and pregnant women are the groups most affected. Spread of multidrug-resistant strains of Plasmodium and the adverse side effects of the existing anti-malarial drugs have necessitated the search for novel, well tolerated and more efficient antimalarial drugs. This ethnomedicinal study surveyed the different types of medicinal plants used for the treatment of malaria in Southern Nigeria with the intent of identifying plants that are traditionally employed in the treatment of malaria across geopolitical boundaries.

MATERIALS AND METHODS

Data were collected from 79 respondents composed of 50 traditional herbsellers and 29 herbal practitioners using a semi-structured questionnaire. Data was analyzed using frequency and percentages.

RESULTS

Of the 79 respondents interviewed, 24% were males while 76% were females. A total of 156 species belonging to 60 families were reported being used to treat malaria in the study area. Fabaceae was the most represented family having fourteen (14) plant species. Of the plants identified during the survey, Azadirachta indica was the species of highest relative frequency of citation (RFC - 1.0). The dominant plant parts used in the preparation of remedies were leaves (50.50%) and Decoction was the main method of preparation. Analysis of regional plant occurrence revealed that South-Western Nigeria represented the region with the highest plant occurrence (60.7%) followed by South-South (24%) and South-East (15.3%). Regional occurrence of plants used in the treatment of malaria in Southern Nigeria is reported here for the first time.

CONCLUSION

This study has documented a great diversity of plants used in the treatment of malaria in Southern Nigeria. Extracts prepared strictly according to the practitioners' recipes should therefore be screened for antiplasmodial activity and toxicity by in vitro and in vivo standard tests to justify their local usage. These studies might lead to the isolation and possible identification of potentially active compounds, which may be regarded as future promising phytomedicines in the treatment of malaria. Conservation of these plant species is also recommended to ensure their continuous availability for future use.

Antimalarial activity of medicinal plants from the Democratic Republic of Congo: A review

ETHNOPHARMACOLOGICAL RELEVANCE

Malaria is the most prevalent parasitic disease and the foremost cause of morbidity and mortality in the Democratic Republic of Congo. For the management of this disease, a large Congolese population recourses to traditional medicinal plants. To date the efficacy and safety of many of these plants have been validated scientifically in rodent malaria models. In order to generate scientific evidence of traditional remedies used in the Democratic Republic of Congo for the management of malaria, and show the potential of Congolese plants as a major source of antimalarial drugs, this review highlights the antiplasmodial and toxicological properties of the Congolese antimalarial plants investigated during the period of 1999-2014. In doing so, a useful resource for further complementary investigations is presented. Furthermore, this review may pave the way for the research and development of several available and affordable antimalarial phytomedicines.

MATERIALS AND METHODS

In order to get information on the different studies, a Google Scholar and PubMed literature search was performed using keywords (malaria, Congolese, medicinal plants, antiplasmodial/antimalarial activity, and toxicity). Data from non-indexed journals, Master and Doctoral dissertations were also collected.

RESULTS

Approximately 120 extracts and fractions obtained from Congolese medicinal plants showed pronounced or good antiplasmodial activity. A number of compounds with interesting antiplasmodial properties were also isolated and identified. Some of these compounds constituted new scaffolds for the synthesis of promising antimalarial drugs. Interestingly, most of these extracts and compounds possessed high selective activity against Plasmodium parasites compared to mammalian cells. The efficacy and safety of several plant-derived products was confirmed in mice, and a good correlation was observed between in vitro and in vivo antimalarial activity. The formulation of several plant-derived products also led to some clinical trials and license of three plant-derived drugs (Manalaria(®), Nsansiphos(®), and Quinine Pharmakina(®)).

CONCLUSION

The obtained results partly justify and support the use of various medicinal plants to treat malaria in folk medicine in the Democratic Republic of Congo. Antimalarial plants used in Congolese traditional medicine represent an important source for the discovery and development of new antimalarial agents. However, in order to ensure the integration of a larger number of plant-derived products in the Congolese healthcare system, some parameters and trends should be considered in further researches, in agreement with the objectives of the "Traditional Medicine Strategy" proposed by the World Health Organization in 2013. These include evaluation of geographical and seasonal variation, investigation of reproductive biology, assessment of prophylactic antimalarial activity, evaluation of natural products as adjuvant antioxidant therapy for malaria, development of plant-based combination therapies and monitoring of herbal medicines in pharmacovigilance systems.

Bioactive indole alkaloids isolated from Alstonia angustifolia

Bioassay-guided fractionation was conducted on a CHCl₃-soluble extract of the stem bark of Alstonia angustifolia (Apocynaceae) collected in Vietnam using the HT-29 human colon cancer cell line, and led to the isolation of a new sarpagine-type indole alkaloid (1), together with nine known alkaloids, including four macroline-derived alkaloids (2-5), a sarpagine-type alkaloid (6), and four macroline-pleiocarpamine bisindole alkaloids (7-10). The structure of the new compound (1) was determined on the basis of spectroscopic data interpretation. Compounds 1-10 were evaluated in vitro for their NF-κB (p65) inhibitory activity against the Hela cells in an ELISA assay. The new sarpagine alkaloid, N(4)-methyltalpinine (1), was found to show significant NF-κB inhibitory activity (ED₅₀ = 1.2 µM). Furthermore, all the isolates (1-10) were evaluated in vitro for their antileishmanial activity, and compounds (1-4, 6 and 8-10) exhibited leishmaniacidal activity against promastigotes of Leishmania mexicana.