Abstract. The effects of combining four dihydroethanoanthracenic (DEA) derivatives and chloroquine were assessed in vitro against Plasmodium falciparum chloroquine resistant parasites W2, Palo Alto, FCR3, and Bres1. Like verapamil or promethazine, the four dihydroethanoanthracenic derivatives tested can be added to the growing list of agents that show capability in enhancing the activity of chloroquine against resistant parasites. The structurally related tricyclic antihistaminic compounds examined in this study exerted different intrinsic antimalarial activity, but the same chloroquine-potentiating activity as verapamil or promethazine. They may act both on the rate of chloroquine accumulation and on its access to ferriprotoporphyrin IX. The reversal mechanism would be assumed to result from competition between DEA derivatives and chloroquine for efflux translocation sites, thus causing an increase in steadystate accumulation of chloroquine and a return to susceptibility. Restoration of therapeutic efficacy of chloroquine against resistant parasites by the administration of an additional drug available at relatively low cost may be a more effective strategy than the introduction of another antimalarial drug at the national level.

No abstract

An alternate procedure has been developed for the processing of whole blood for the estimation of benzoylecgonine with the use of the Abbott ADx reagents and analyzer. This procedure allows for handling of relatively large numbers of samples without the need to evaporate extraction solvent. Blood samples were diluted with an equal volume of phosphate buffer-methanol (80:20 v/v), and the proteins were removed by centrifugation through a membrane filter device. A comparison of the proposed method with an acetone solvent extraction procedure has been made, and results were shown to be equivalent. Recoveries of 94-105% benzoylecgonine were obtained for added concentrations of 25-500 ng/mL.

A negative ion chemical ionization (NICI) mass spectrometric procedure has been developed to measure phenylethylamine in human urine as the pentafluorobenzoyl derivative. The aromatic amine was isolated from alkaline urine by hexane and ethyl acetate extraction followed by a back-extraction into diluted acid. The acid extract was lyophilized and the residue derivatized with (2,3,4,5,6)-pentafluorobenzoyl chloride. Quantification was achieved by comparing the peak areas of the [M-HF]- ion to a ratio of internal and external standards. The phenylethylamine levels excreted by normal subjects and patients with phenylketonuria were found to be consistent with previous reports.

Enzymatic conversion of retinal to retinoic acid in rat liver cytosol was detected using a rapid and sensitive assay based on high pressure liquid chromatography (HPLC). This retinal oxidase assay system did not require extraction steps or any other manipulation of the sample mixture once the sample vial was sealed for incubation. The product (retinoic acid) and the reactant (retinal) were separated by HPLC in 14.0 min with a sensitivity of 15 and 40 pmol per injection for retinoic acid and retinal, respectively. Enzymatic activity was observed to be linear with protein concentration (0-2.4 mg/mL) and time (0-30 min) and displayed a broad pH maximum of 7.7-9.7. The enzyme exhibited Michaelis-Menten single-substrate kinetics with an apparent Km of 0.25 mM. The average specific activity in nine normal rats was 35.6 +/- 3.3 nmol retinoic acid formed/h per mg protein. Incubation of the enzyme with zinc did not affect the rate of retinoic acid synthesis. Dithiothreitol inhibited the reaction. Both NAD and NADH stimulated retinoic acid formation. Formation of retinol was also observed when these pyridine nucleotides were added to the reaction mixture, indicating the presence of retinal reductase activity. The results of kinetic studies suggest that NADH may act indirectly to stimulate retinoic acid formation.