Two novel assays for the detection of haemin-binding properties of antimalarials evaluated with compounds isolated from medicinal plants.

Forty-two compounds isolated from nine plants used within South America for the treatment of malaria were tested for haemin binding using two novel, rapid screening methods. The data obtained were analysed with respect to IC(50) values for in vitro toxicity to Plasmodium falciparum trophozoites. One method, a multiwell assay based on the inhibition of the interaction of haemin with glutathione (GSH), is sensitive in the 10 microM range, takes c. 1 h and is suitable for either a high throughput screen or rapid assay during natural product isolation. Of 19 compounds showing antiplasmodial activity (IC(50) 40% inhibition of GSH-haemin reaction. The sensitivity and specificity of the assay were 0.85 and 0.82, respectively. The positive predictive value was 0.81 and the negative predictive value 0.86. A more sensitive assay (0.1 microM range) is based on the reversal by haemin-binding compounds of the haemin inhibition of the L-dopachrome-methyl ester tautomerase activity of human macrophage migration inhibitory factor. This assay gives a better idea of the affinity of interaction and uses very small amounts of test compound. The log[RI(50)] of eight of the compounds that tested positive in the above assays together with those of quinine and chloroquine showed a positive correlation with log[antiplasmodial IC(50)] for strain T9-96 (r = 0.824) and strain K1 (r = 0.904). Several of the antimalarial compounds that bind haemin are isoquinolines, a class not shown previously to interact with haemin

Bioactive Compounds of Camu-Camu (Myrciaria dubia (Kunth) McVaugh)

Camu-camu is a shrub, native to the Amazon that thrives in areas where flooding is frequent. Genetically, the plant is characterized by a diploid genome and moderate genetic diversity. Several parts of the plant are used in traditional folk medicine to treat a variety of acute and chronic diseases. For over 50 years, the exceptionally high vitamin C content of camu-camu has attracted worldwide attention that continues today because of the recent discovery of several health-promoting phytochemicals with corroborated biological activities (e.g., antioxidant, anti-obesity, antidiabetic). All of these beneficial attributes are well supported by in vitro and in vivo studies as well as human clinical trials. The metabolic precursors of these phytochemicals are synthesized in key metabolic pathways (i.e., the shikimate pathway, the mevalonate pathway). Of these metabolic pathways, we show details for the biosynthesis of betulinic acid, trans-resveratrol, and syringic acid. In conclusion, camu-camu is an exceptional plant for its ability to produce and accumulate significant amounts of a variety of health-promoting phytochemicals. Although several metabolic pathways responsible for the biosynthesis of these phytochemicals have been reconstructed based on fruit and seedling transcriptomes, detailed knowledge of the vast majority of metabolic pathways and their molecular regulatory mechanisms is lacking. Consequently, we must increase our knowledge of the metabolic processes using multi-omic approaches so that we can acquire the skills necessary to develop genetically improved varieties of camu-camu and implement biotechnological applications for the production of these bioactive phytochemicals