Malaria, quinine and red cell lysis

Desbutylhalofantrine: evaluation of QT prolongation and other cardiovascular effects after intravenous administration in vivo

Desbutylhalofantrine (Hfm) is an active and equipotent metabolite of halofantrine (Hf). Both compounds are effective in the treatment of sensitive and multidrug-resistant and In vitro data and interpretation of some clinical studies of Hf have suggested that, unlike Hf, Hfm may be devoid of adverse cardiac effects. The aim of these investigations was to provide the first in vivo examination of the intrinsic capacity of Hfm to affect repolarization in the heart, using an anesthetized rabbit model. Using a dose-rising regimen, Hfm was administered IV at doses of 1, 1, 2, 4, and 8 mg/kg and the baseline rate-corrected QT interval (QTc) value of 377 +/- 13 ms rose to 394 +/- 16, 396 +/- 12, 429 +/- 18, 433 +/- 16, and 489 +/- 15 ms, respectively. There were no significant changes in blood pressure, heart rate, or PR or QRS intervals. The Hfm plasma concentrations were quantitated after high-performance liquid chromatographic analysis, the results indicating a significant correlation between Hfm plasma concentration and QT(c) prolongation. The study also identified a concentration-dependent hemolysis of erythrocytes after administration of Hfm. The conclusions from this study are that IV administration of Hfm does cause a significant prolongation of the QT(c) interval in a rabbit model.

The mechanisms of action of antiprotozoal and anthelmintic drugs in man

The mechanisms of action of antiprotozoal and anthelmintic drugs are reviewed according to: (1) drugs interfering with metabolic processes; (2) drugs interfering with reproduction and larval physiology; and (3) drugs interfering with neuromuscular physiology of parasites.

Charge transfer and oxy radicals in antimalarial action. Quinones, dapsone metabolites, metal complexes, iminium ions, and peroxides

A mechanism of action is proposed that encompasses almost all of the main categories of antimalarial agents: quinones and precursors, dapsone metabolites, metal complexes of thiosemicarbazones and biguanides, iminium-type ions from acridines and quinolines, and peroxides. The toxic effect of the drugs is believed to result from the generation of reactive oxygen radicals that usually arise via charge transfer. Electrochemical studies (reduction potential and reversibility) were performed on a number of these agents. Reduction potentials range from -0.23 to -1.52 V. It is likely that the in vivo values are appreciably more positive in certain cases.

Aspects of helminth metabolism

‘Each organism must be examined as a biochemical entity before any reasonable understanding of helminth metabolism can be attained’ (Saz, 1969).

Changes in the membrane microviscosity of mouse red blood cells infected with Plasmodium berghei detected using n-(9-anthroyloxy) fatty acid fluorescent probes

A set of n-(9-anthroyloxy) fatty acids (n = 2, 6, 9, 12, 16) have been used as fluorescent probes to examine the lipid environment at different depths in the outer membrane of normal mouse erythrocytes and red blood cells from Plasmodium berghei-infected blood. Fluorescent polarization experiments with normal mouse erythrocytes have demonstrated a typical gradient in microviscosity from the surface to the centre of the bilayer as a consequence of the motional properties of the C-atoms of the phospholipid acyl chains. The fluorescent probes rotate faster in the membrane of purified pluriparasitized cells (greater than 90% purity) than with the remaining fraction of red blood cells from infected blood (20--40% immature, infected red cells, and uninfected red cells), or normal mouse erythrocytes. This increase in fluidity with heavily infected cells occurs predominantly at the centre of the lipid bilayer, rather than at the membrane surface. A comparison of the polarization values of intact and lysed infected cells indicates that the fluorescent fatty acids preferentially label the plasma membrane rather than the internal membranes of infected cells. The results suggest that P. berghei infection causes a change in the composition and/or organization of the outer membrane of pluriparasitized cells which produces a decrease in membrane microviscosity.

Octadecenoic fatty acids and their association with hemolysis in malaria

Octadecenoic fatty acids have been implicated in prehemolytic and hemolytic phenomena associated with malaria. Oleic [18:1 (n-9)] and cis-vaccenic [18:1 (n-7)] acids were found and quantified in the major neutral and phospholipids of the erythrocytes and plasmas of normal and Plasmodium lophurae-infected ducks, and in the parasite itself. The octadecenoic fatty acids were elevated over normal values in the major phospholipid classes of infected erythrocytes, in the erythrocyte-specific alkoxy phosphatidylethanolamine of infected erythrocytes, and in the plasma unesterified fatty acids, triacylglycerols, cholesterol esters and phosphatidlycholine of infected ducklings. Oleic acid was the major fatty acid of P. lophurae (33% total lipid fatty acid). Theoretical considerations of octadecenoic fatty acid modifications of erythrocyte membrane structure and function in malaria are discussed.