A simple and inexpensive haemozoin-based colorimetric method to evaluate anti-malarial drug activity

BACKGROUND: The spread of drug resistance in malaria parasites and the limited number of effective drugs for treatment indicates the need for new anti-malarial compounds. Current assays evaluating drugs against Plasmodium falciparum require expensive materials and equipment, thus limiting the search for new drugs, particularly in developing countries. This study describes an inexpensive procedure that is based on the advantage of a positive correlation between the haemozoin level of infected erythrocytes and parasite load. METHODS: The relationship between parasitaemia and the haemozoin level of infected erythrocytes was investigated after converting haemozoin into monomeric haem. The 50% inhibitory concentration (IC(50)) values of chloroquine, quinine, artemisinin, quinidine and clotrimazole against P. falciparum K1 and 9A strains were determined using the novel assay method. RESULTS: The haemozoin of parasites was extracted and converted into monomeric haem, allowing the use of a colorimeter to efficiently and rapidly measure the growth of the parasites. There was a strong and direct linear relationship between the absorbance of haem converted from haemozoin and the percentage of the parasite (R(2) = 0.9929). Furthermore, the IC(50) values of drugs were within the range of the values previously reported. CONCLUSION: The haemozoin-based colorimetric assay can be considered as an alternative, simple, robust, inexpensive and convenient method, making it applicable in developing countries.