Gentamicin and amikacin repress the growth of Plasmodium falciparum in culture, probably by inhibiting a parasite acid phospholipase

Human erythrocytes were loaded with either gentamicin or amikacin and subsequently infected with the human malarial parasite Plasmodium falciparum and grown in culture. Parasite invasion of erythrocytes was unaffected by the drugs, but subsequent development was retarded. The digestion of host cell cytosol in ring-stage parasites was inhibited by the drugs. A substantial acid, Ca2+-independent phospholipase activity could be monitored in parasite cytosol and was found to be inhibited by the drugs. These results imply that phospholipases are involved in the feeding mechanism of the parasite and that gentamicin and amikacin exert their inhibitory activity by affecting these enzymes.     

A serotonergic system in the brain of the Antarctic fish, Trematomus bernacchii

The immunohistochemical distribution of serotonin-containing nerve fibres and cells has been described in the brain of the Antarctic fish, Trematomus bernacchii. The largest serotonergic system was associated with the diencephalic and rhombencephalic ventricles. In particular, serotonin-positive cells have been found in the lateral recess and neuropile zone of the diencephalic ventricle, where we have identified the serotonergic portion of the paraventricular organ. Numerous serotonin cells were localized in the dorsal nucleus of the raphe, the dorsal tegmental nucleus and the central gray. Two large cell groups, arranged in a pair of well-defined columns and connecting the central gray with the dorsal reticular formation, were immunostained in the region of the trigeminal nuclei. In addition, few positive cells have been found in the preoptic area and the cerebellar valvula, and few serotonergic nerve fibres, probably belonging to the lateral lemniscus, have been identified. The distribution of serotonin elements in the brain of T. bernacchii has been compared with that described in other fish, where it showed some modifications in the immunoreactive pattern. Finally, the lack of a serotonergic system at the level of the reticular superior formation has been reported; however, it was not possible to rule out a phylogenetic or environmental explanation.     

The effect of ferriprotoporphyrin IX and chloroquine on phospholipid monolayers and the possible implications to antimalarial activity

Ferriprotoporphyrin IX intercalates into phospholipid membranes, as evidenced from its effect on the surface pressure of monolayers composed of different phospholipids. Ferriprotoporphyrin intercalation is enhanced by membrane hydrophobicity and decreased by negative surface potential. Chloroquine enhances the effect of ferriprotoporphyrin in relatively hydrophobic membranes but reduces it in monolayers composed of highly unsaturated phospholipids. These results are consistent with the differential effect of chloroquine on ferriprotoporphyrin-induced lysis of erythrocytes and of malarial parasites, thus supporting the membrane-lesion hypothesis of antimalarial action.     

Some reflections concerning host erythrocyte-malarial parasite interrelationships

During the intraerythrocytic development of the malarial parasite, the host cell's structure and function are altered to such an extent that the infected red blood cell may be regarded as a finely tuned, although imperfect, symbiotic organism. Problems such as the control of the parasite's life and cell cycles, volume regulation of the malaria-infected erythrocyte, the energy metabolism of the malaria-infected red blood cell, and the possible metabolic purpose for parasite oxidative stressing of its host cell, seem worth addressing at the outset.     

Studies on new,centrally active and reversible acetylcholinesterase inhibitors

We have synthesized the tertiary amines of pyridostigmine and neostigmine, 3-pyridinol dimethylcarbamate (norpyridostigmine) and 3-dimethylaminophenol dimethylcarbamate (norneostigmine) respectively, and we have tested their abilities to cross the blood-brain barrier and inhibit mouse brainAChE activity. The in vivo inhibition of AChE activity by norpyridostigmine reaches 72% at 10 minutes which is comparable to that seen with physostigmine (73% at 10 minutes). Inhibition by norneostigmine is less effective (50% at 10 minutes) and approaches that obtained with tetrahydroaminoacridine (57% at 10 minutes). These data show that both norpyridostigmine and norneostigmine cross the blood-brain barrier and that they are effective inhibitors of mouse brain AChE activity. These drugs could be useful in the treatment of memory, impairment associated with Alzheimer's disease, and other memory disorders.     

C-terminal peptide identification by fast atom bombardment mass spectrometry.

A previously described technique [Rose, Simona, Offord, Prior, Otto & Thatcher (1983) Biochem. J. 215, 273-277] permits the identification of the C-terminal peptide of a protein as the only peptide that does not incorporate any 18O upon partial enzymic hydrolysis in 18O-labelled water. Formation of chemical derivatives followed by combined g.l.c.-m.s. was used in this earlier work. We now describe the isolation from protein digests, by reversed-phase h.p.l.c., of labelled and unlabelled polypeptides and their direct analysis by fast atom bombardment mass spectrometry. Under the conditions used, the 18O label is retained throughout the separation and analysis, thus permitting assignments of C-terminal peptides to be made. Enzyme-catalysed exchange of label into the terminal carboxy group was found to occur in some cases without hydrolysis of a peptide bond. This effect, which may be exploited to prepare labelled peptides, does not prevent application of the method (two separate digests must then be used). We have applied our method to the analysis of enzymic partial hydrolysates of glucagon, insulin and of several proteins produced by expression of recombinant DNA.     

Compartment analysis of ATP in malaria-infected erythrocytes

The ATP concentration of malaria-infected erythrocytes changes substantially with parasite development. These alterations have been attributed to a decline in host cell [ATP], but have not been tested critically hitherto. A method for the compartmental analysis of ATP in malaria (Plasmodium falciparum)-infected human red blood cells has been developed using Sendai virus to permeabilize the host erythrocyte membrane. Permeabilization and release of host cytosol was complete within 6 to 8 minutes and ATP was measured by the luciferin-luciferase bioluminescence assay in the lysate and in the pellet. Equal ATP concentrations were found in host and parasite compartments at the trophozoite and schizont stages. Both were lower than those detected in uninfected cells. Other methods for compartment analysis of ATP are presented and discussed.