Artemisinin enhances heme-catalysed oxidation of lipid membranes.

Artemisinin, a sesquiterpene endoperoxide derived from a traditional Chinese herbal remedy for fevers, is a promising new antimalarial drug, particularly useful against multidrug resistant strains of P. falciparum. Despite widespread clinical use, its mode of action remains uncertain. We investigated whether its antimalarial properties could be explained by an ability to enhance the redox activity of heme, formed in the parasite food vacuole from digested hemoglobin. Artemisinin caused a sustained threefold increase, followed by a gradual decline, in the peroxidase activity of heme. It also enhanced the ability of heme to oxidize membrane lipids about sixfold. An unexpected finding was the potentiation of heme-catalysed membrane lipid oxidation by Vitamin E. The changes in redox-catalytic activity induced by artemisinin were paralleled by major changes in the absorption spectrum of heme, culminating in loss of the Soret band. We propose a model in which artemisinin binds irreversibly to heme in the parasite food vacuole, preventing its polymerization to chemically inert hemozoin, and promoting heme-catalysed oxidation of the vacuolar membrane by molecular oxygen, which leads, ultimately, to vacuole rupture and parasite autodigestion.

National health accounts in developing countries: appropriate methods and recent applications.

Better information on the financing of the health sector is an essential basis for wise policy change in the area of health sector reform. Analysis of health care financing should begin with sound estimates of national health expenditure--total spending, the contributions to spending from different sources and the claims on spending by different uses of the funds. The member countries of the OECD have successfully established such comparative health expenditure accounts in terms of standardized definitions of the uses of funds and breakdowns by public and private sector sources. This has resulted in important research on health system differences which could explain variations in the level and composition of financing. The United States has developed a more detailed approach called National Health Accounts, which expands the OECD method into a more disaggregated 'sources and uses' matrix. In the developing countries, analysis of health expenditures has been much less systematic, despite several decades of calls by international researchers for more attention. This paper reviews previous work done in developing countries and proposes renewed attention to national health expenditures, adapting the recent experience of the United States. Because most developing countries have more pluralistic health financing structures than are found in most industrialized countries, an enhanced and adapted version of the 'sources and uses' matrix method is proposed. This method should be modified to address the relevant categories of expenditures prevalent in the developing countries. Examples of recent applications of such 'national health accounts' from the Philippines, Egypt, India, Mexico, Colombia and Zambia are presented. Experience to date suggests that development of sound estimates using this method in low and middle income countries is feasible and affordable. National health accounts estimates can significantly influence policy. They provide decision makers with a holistic picture of the health sector, showing the actual emphasis of spending and the roles of different payers. They also provide a consistent framework for modelling reforms and for monitoring the effects of changes in financing and provision. An easy to use software tool has been developed for training and data management. Regional networks of collaborating national groups are proposed as a first step in expanding use of the method and to gain both national and cross-national comparative benefits.

The iron environment in heme and heme-antimalarial complexes of pharmacological interest.

Mössbauer spectroscopy has been utilized to probe the electronic environment of iron in a number of Ferriprotoporphyrin IX complexes of relevance to malaria. The markedly different iron environments found for the complexes of hemin with quinine, chloroquine, and the Chinese herbal antimalarial artesunate suggest that these compounds act by protecting the heme from polymerization to insoluble hemozoin, and by facilitating the transport of the protected heme to the food vacuole membrane where it is able to exercise its cytotoxic redox catalytic activity. Mössbauer parameters determined here for purified malaria pigment and synthetic beta-hematin confirm the chemical identical-ness of these species. The Mössbauer spectra of the complexes are discussed in light of the proposed structures of the complexes.

Xanthine oxidase inhibits growth of Plasmodium falciparum in human erythrocytes in vitro.

Malaria parasites, unable to synthesize purine de novo, use host-derived hypoxanthine preferentially as purine source. In a previous study (1990. J. Biol. Chem. 265:6562-6568), we noted that xanthine oxidase rapidly and completely depleted hypoxanthine in human erythrocytes, not by crossing the erythrocyte membrane, but rather by creating a concentration gradient which facilitated hypoxanthine efflux. We therefore investigated the ability of xanthine oxidase to inhibit growth of FCR-3, a chloroquine-resistant strain of Plasmodium falciparum in human erythrocytes in vitro. Parasites were cultured in human group O+ erythrocytes in medium supplemented, as required, with xanthine oxidase or chloroquine. Parasite viability was assessed by uptake of radiolabeled glycine and adenosine triphosphate-derived purine into protein and nucleic acid, respectively, by nucleic acid accumulation, by L-lactate production, and by microscopic appearance. On average, a 90% inhibition of growth was observed after 72 h of incubation in 20 mU/ml xanthine oxidase. Inhibition was notably greater than that exerted by 10(-7) M chloroquine (less than 10%) over a comparable period. The IC50 for xanthine oxidase was estimated at 0.2 mU/ml, compared to 1.5 x 10(-7) M for chloroquine. Inhibition was completely reversed by excess hypoxanthine, but was unaffected by oxygen radical scavengers, including superoxide dismutase and catalase. The data confirms that a supply of host-derived hypoxanthine is critical for nucleic acid synthesis in P. falciparum, and that depletion of erythrocyte hypoxanthine pools of chloroquine-resistant malaria infection in humans. of chloroquine-resistant malaria infection in humans.

Vitamin and mineral status of trained athletes including the effects of supplementation.

We measured serum concentrations of thiamin, riboflavin, nicotinic acid, pyridoxine, folate, cyanocobalamin, ascorbic acid, retinol, tocopherol, zinc, magnesium, copper, iron, and ferritin as well as hemoglobin, hematocrit, percentage transferrin saturation, and total iron-binding capacity in athletes who ingested a multivitamin and mineral supplement for 3 mo. All blood variables were normal and except for pyridoxine and riboflavin there were no significant changes in the blood concentrations of any other vitamins or minerals measured. This may have been due to variable interactions between the vitamins and minerals in the supplement that prevented their being adequately absorbed. There were no signs or symptoms of serious toxic side effects. We conclude that multivitamin and mineral supplementation was without any measurable ergogenic effect and that such supplementation is unnecessary in athletes ingesting a normal diet.