Malaria is one of the most prevalent infectious diseases in the world. Treatment for malaria is commonly inadequate due to the lack of quality assured effective drugs. The effectiveness of these drugs is declining at an ever accelerating rate, with consequent increase in malaria related morbidity and mortality. The newest antiplasmodial drug from plants is needed to overcome this problem. Numerous mangroves and mangal associates are used as folklore medicine to treat various human diseases. The mangrove plant species are a good source of potential bioactive entities which exhibits many therapeutic properties. The present study was carried out to test the antiplasmodial activity of five mangrove plant species distributed along the South East coast of India. Bruguiera cylindrica, Ceriops decandra, Lumnitzera racemosa, Rhizophora apiculata, and Rhizophora mucronata mangrove plant extracts exhibited in vitro antiplasmodial activity against chloroquine-sensitive Plasmodium falciparum. Of which, the ethanolic bark extract of R. mucronata exhibited high antiplasmodial activity (IC(50)=62.18 μg.ml(-1)). Statistical analysis reveals that, significant antiplasmodial activity (P<0.05) was observed between the concentrations and time of exposure. The chemical injury to erythrocytes was also carried out and it shows that no morphological differences in erythrocytes by the ethanolic extract of mangrove plants after 48 h of incubation. The screening for phytochemical constituents in the mangrove plants were carried out and it reveals that, the presence of alkaloids, triterpenes, flavonoids, tannins, catachin, anthroquinone, phenols, sugars, and proteins. This study shows that the mangrove plants had a source of lead compounds for the development of new drugs for the treatment of malaria.

The ocean covers more than 70% of earth surface and hosts most 300,000 described species of plants and animals to use, which have been virtually unexploited for the development of medicines. Marine plants are the good source of biologically active entities which exhibit therapeutic properties, when applied single or in combination of different plant extracts (polyherbal). Polyherbal preparations are always a complex mixture of different forms and thus different compounds, which might act as agonistic, synergistic, complementary, antagonistic or toxic way. The present study was initially carried out to test the antiplasmodial activity of 13 mangrove plants and eight seaweeds species distributed along the coast of south India. Of these, mangrove species Aegiceras corniculatum and the seaweed species Chaetomorpha antennina have shown maximum antiplasmodial activity. Hence, the present study was mooted out to increase the percentage of antiplasmodial activity when applied as polyherbal preparations. The effect of marine polyherbal preparations from the methanolic extracts of two marine plants A. corniculatum and C. antennina for their antiplasmodial activity was tested. It shows that the polyherbal extract showed 63.50 ± 0.408% suppression of parasitaemia against Plasmodium falciparum at 1.5 mg ml⁻¹ concentration. In vivo test was carried out with rat animal model to find out the effectiveness of the polyherbal extracts in the live system, which reveals that polyherbal extracts have exhibited remarkable antiplasmodial activity (50.57 ± 0.465%) against Plasmodium berghei at 120 mg kg⁻¹ bw. This study shows that combinations of mangrove plants and seaweeds extracts had a source of lead compounds for the development of new drugs for the treatment of malaria.

The ethanolic leaf extracts of O. sanctum possess lead compounds for the development of antiplasmodial drugs.

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The problems of resistant lines of Plasmodium falciparum are escalating. Twelve seaweeds species belong to five different families (Sargassaceae, Gracilariaceae, Hypneaceae, Corallinaceae and Halimedaceae) were collected from Mandapam coastal area, and the seaweeds extracts were tested for in vitro antiplasmodial activity against P. falciparum. Among the tested seaweeds, Gracilaria verrucosa (IC(50) 5.55 μg.ml(-1)) and Hypnea espera (IC(50) 8.94 μg.ml(-1)) showed good antiplasmodial activity, and these results are comparable with positive controls such as artemether (IC(50) 4.09 μg.ml(-1)) and chloroquine (IC(50) 19.59 μg.ml(-1)), respectively. Turbinaria conoides, Sargassum myriocystem, Hypnea valentiae and Jania rubens extracts showed IC(50) values between 5 to 50 μg.ml(-1). Sargassum sp., Turbinaria decurrens and Halimeda gracilis extracts showed IC(50) values between 50 to 100 μg.ml(-1). Gracilaria corticata, Jania adherens and Halimeda opuntia extracts showed IC(50) value of more than 100 μg.ml(-1). Statistical analysis reveals that significant in vitro antiplasmodial activity (P < 0.05) was observed between the concentrations and time of exposure. The chemical injury to erythrocytes was also carried out, and it shows that no morphological changes in erythrocytes by the ethanolic extract of seaweeds extracts after 48 h of incubation. The in vitro antiplasmodial activity might be due to the presence of sugars, proteins, phenols and carboxylic acid in the ethanolic extracts of seaweeds. It is concluded from the present study that the ethanolic extracts of seaweeds of G. verrucosa and Hypnea espera possess lead compounds for development of antiplasmodial drugs.