Screening of Thai medicinal plant extracts and their active constituents for in vitro antimalarial activity.

To discover antimalarial substances from plants cultivated in Thailand 80%-EtOH extracts from selected plants were screened for in vitro antimalarial activity against the drug resistant K1 strain of Plasmodium falciparum. In total, 86 Thai medicinal plant samples representing 48 species from 35 genera in 16 families were screened and two species (Polyalthia viridis and Goniothalamus marcanii) were found to show notable antimalarial activity (IC50: 10.0 and 6.3 microg/mL). Marcanine A and 16-hydroxycleroda-3,13(14)Z-dien-15,16-olide were identified as the respective major active constituents in P. viridis and G. marcanii, respectively.

Heme-dependent radical generation: possible involvement in antimalarial action of non-peroxide microbial metabolites, nanaomycin A and radicicol.

Antimalarial screening was performed for microbial metabolites that simulate artemisinin in their mode of action, a potent antimalarial component of an herbal remedy with a characteristic peroxide structure. Nanaomycin A was identified in this screen as an antimalarial compound, together with radicicol and several other compounds already reported (J. Antibiotics 51: 153 approximately 160, 1998). Nanaomycin A inhibited in vitro growth of the human malaria parasite Plasmodium falciparum with an IC80 value of 33.1 nM. It was as potent as radicicol and about 1/10 as potent as artemisinin. Studies on the mode of action suggested that the antimalarial action of the two non-peroxides, nanaomycin A and radicicol, involved heme-dependent radical generation, as is for the peroxide artemisinin. Namely, the inhibition of in vitro growth of malaria parasite by nanaomycin A or radicicol was reversed by tocopherol, a radical scavenger added to the assay mixture. Secondly, in a reaction system established for radical detection, in which a test radical donor and beta-alanylhistidine as a radical recipient were incubated with and without hemin, the two compounds caused heme-dependent decreases of beta-alanylhistidine, as did artemisinin. Among the 14 microbial metabolites identified during this screening, a correlation was observed between antimalarial activity and heme-dependent radical generating activity.

Arisugacins, selective acetylcholinesterase inhibitors of microbial origin.

Synthetic inhibitors of acetylcholinesterase (AChE) recently have attracted particular attention for treatment of Alzheimer's disease. By systematic screening of microbial metabolites, we were able to discover the new AChE inhibitors, named arisugacins A and B, from the culture broth of Penicillium sp. FO-4259. The structures of arisugacins are members of the meroterpenoid compounds. Arisugacin A is a potent and highly selective inhibitor of AChE but does not inhibit butyrylcholinesterase in vitro. Arisugacin A is a good candidate as an excellent potential drug for treatment of Alzheimer's disease. Also reviewed is the current status of development of antidementia drugs.

Screening for new antitrichomonal substances of microbial origin and antitrichomonal activity of trichostatin A.

In vitro and in vivo screening methods for new antitrichomonal substances were established. Primary screening is based on in vitro antitrichomonal activities of culture broths of actinomycetes isolated from soil. With secondary screening, after crude materials obtained from the cultured broths were administered orally to mice, excretion of antitrichomonal activity into urine was examined. Tertiary screening was done by examining therapeutic activity for experimental trichomoniasis in mice with Trichomonas foetus. Using the screening systems, a new antibiotic (setamycin)-producing strain was picked out among about six thousands soil isolates, and the therapeutic efficacy of KM-3851, which was identified as trichostatin A, was found. It was active against T. foetus both in vitro and in vivo.

Hygromycin A, an antitreponemal substance. I. Screening method and therapeutic effect for Treponema hyodysenteriae-caused infection in CF-1 mice.

In vitro and in vivo screening methods were established for the discovery of new active substances against Treponema hyodysenteriae. During the screening methods, hygromycin A produced by Streptomyces hygroscopicus KA-355 was found to be active against T. hyodysenteriae. Hygromycin A did not show high antitreponemal activity in in vitro test using the paper disc method on the agar plate inoculated with T. hyodysenteriae. However, the antibiotic exhibited highly therapeutic effect in CF-1 mice, compared with of lincomycin, tiamulin, lankacidin C or olaquindox drinking water. The effective dose (ED50) of hygromycin A was 1.1 micrograms/ml.

Saturated fatty acid-starved cells of Saccharomyces cerevisiae grown in the presence of cerulenin and oleic acid.

Cell growth of Saccharomyces cerevisiae ATCC 12341 inhibited by the antibiotic cerulenin, a specific inhibitor of fatty acid synthesis, was restored by oleic acid (18 : 1) to give saturated fatty acid-starved cells, which could not grow when again transferred into a fresh synthetic medium containing the antibiotic and oleic acid. The growth of the saturated fatty acid-starved cells was restored when they were transferred into a medium supplemented with myristic acid (14 : 0), pentadecanoic acid (15 : 0), and palmitic acid (16 : 0) in the presence of cerulenin and oleic acid. Cellular saturated fatty acid content in the growth-restored cells was also restored to about two-thirds of that of the normal yeast cells. The DNA, RNA, and cell wall synthetic capabilities of the saturated fatty acid-starved cells were almost normal, but the L-leucine uptake and cytochrome pattern were severely impaired. These impairments were reversed on supplying palmitic acid. The decrease of L-leucine uptake of the yeasts was also caused by the addition of cerulenin alone. However, since the decrease occurred later than the inhibition of fatty acid synthesis, it was considered to be a secondary effect. These results, obtained by using the saturated fatty acid-starved cells, indicate that the membranes of S. cerevisiae require certain amounts of saturated fatty acid and that the membrane functions (energy metabolism, transport, and so on) are impaired by starvation of saturated fatty acids.