Biomedical subjects
Publications and source records attributed to E Deharo.
24 hours after an intra-peritoneal inoculation of frozen blood infected with Plasmodium yoelii nigeriensis, the malarial infection is non detectable in most starved mice while it is patent in mice fed 2 hours before the inoculation. It is assumed that the post feeding lymphatic flow brings to the blood the latent merozoites.
The youngest (rings and young trophozoites) erythrocytic stages of Plasmodium yoelii nigeriensis and P. yoelii killicki, two rodent malaria subspecies developing very asynchronously in the blood, were separated from the other stages using a discontinuous Percoll-glucose gradient. They were inoculated into mice and the subsequent infection remained synchronous for two generations. The duration of the asexual cycle was found to be 18 h.
Cedronin was isolated from Simaba cedron Planchon (Simaroubaceae), a species popularly believed in South America to have antimalarial properties. It was examined for in vitro and in vivo antimalarial activities and for cytotoxicity against KB cells. Experimental results showed that cedronin was active against chloroquine-sensitive and resistant strain, with an IC50 of 0.25 micrograms/ml (0.65 mumol/ml). It was also found to be active in vivo against Plasmodium vinkei with an IC50 of 1.8 mg/kg (4.7 nM/kg) in the classic 4-day test. Cedronin belongs to the small group of quassinoids with a C19 basic skeleton and shows a rather low cytotoxicity against KB cells (IC50 = 4 micrograms/ml, 10.4 microM) as compared with C20 biologically active quassinoids; however its toxic/therapeutic ratio (10/1.8) remains lower than chloroquine (10/0.5).
The biological rhythms of Plasmodium vinckei vinckei, P. v. lentum and P. yoelii yoelii i.e. synchronicity, duration of the erythrocytic cycle, timing of the schizogony and of the penetration of merozoites into red blood cells, were studied in the Swiss white mouse. Two different methods of synchronisation were used: the freezing-thawing of parasitized blood and the inoculation of a single parasitic stage, separated from the other stages by centrifugation through a Percoll-Glucose gradient. The duration of the schizogonic cycle of P. v. vinckei and P. v. lentum, two highly synchronous subspecies, was 24 hours. With P. v. vinckei the timing of the schizogony was independent of the circadian rhythm of the host and was set by the time of inoculation. With P. v. lentum the timing of the schizogony and merozoites penetration into red blood cells depended both, on the hosts rhythm and the time of inoculation of frozen-thawed blood: schizogony occurred at 18:00 if the inoculum was injected at 06:00 or 12:00 and at 06:00 if injected at 18:00 or 00:01. P. y. yoelii a naturally asynchronous parasite was synchronized by means of a Percoll-Glucose gradient. The duration of its intraerythrocytic cycle was found to be 18 hours, similar to that of the other subspecies of P. yoelii.
Several procedures were employed to try to specify the schizogonic cycle of Plasmodium yoelii nigeriensis. The Percoll-glucose gradient technique for concentrating the very young stages (rings and young trophozoites), allowing a very precise follow up of the development of the parasitaemia during the first schizogonic cycles. A method for studying the prepatencies, providing an approximation of the number of merozoites inoculated. A comparison between the numbers of merozoites present in the blood, after--firstly simple dilutions in saline, revealing the total number of merozoites,--secondly dilutions in saline after a passage of a few hours in the organism of a mouse, revealing the number of latent merozoites. It was shown that the infection, during the first two cycles, varies according to the time of inoculation. In all cases the increase of the parasitaemia occurred mainly from 00:01 to 06:00. This increase of parasitaemia in mice inoculated with the Percoll concentrated parasites was significantly high during the first cycle in mice inoculated at 06:00 and 09:00 and during the second cycle in those inoculated at 12:00, 15:00 and 18:00. However, differences were rapidly compensated and parasitaemias became comparable at the 3rd or 4th cycle when they ceased to be dependent on the time of inoculation.
The antimalarial activity of the fatty alcohol, n-hentriacontanol, isolated from the bolivian Solanaceae, Cuatresia sp, is investigated in vivo through a classical four-day suppressive test against Plasmodium berghei and P. vinckei in mice. This product markedly reduced the virulence of experimentally induced P. vinckei infection. n-Hentriacontanol belongs to a new class of antimalarial natural compounds to be exploited for therapeutic purposes.
With the recent development of numerous low molecular weight heparins (LMWHs), a certain amount of concern has become evident as to the equivalency of each agent. In a comprehensive study, we have taken the seven available LMWHs to directly compare their in vitro and in vivo (subcutaneous) antithrombotic properties in one laboratory setting. Where possible, various batches of one LMWH were evaluated. Our findings were that variations of in vivo activity were observed between the LMWHs studied. Some activities were significantly different from placebo, whereas others were not. Depending on the assay chosen significant differences could also be observed for the in vitro activity.
Hirudin, a potent inhibitor of blood coagulation, differs in its antithrombotic activity according to the source of isolation. It was therefore of interest to study recombinant hirudin. Hirudin was obtained by a genetic process from E. coli. Its antithrombotic action was investigated in an experimental (rat) model of venous thrombosis and was compared to heparin whose results are known. Heparin (400 micrograms/kg) and hirudin (12.5, 25 and 50 micrograms/kg) present an antithrombotic effect and limit the extension of an existing thrombus (p less than 0.05). Higher heparin dosages increase the bleeding time mean value (p less than 0.05) whereas hirudin does not. So, recombinant hirudin presents the same antithrombotic action as heparin but with very inferior dosage. This activity seems not dose-dependent and is associated to weak hemorrhagic effects.
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The apparition in the 80's of low molecular weight heparins (LMWHs) obtained by chemical or enzymatical splitting, modified the fields of prophylactic treatment of thromboembolic diseases. These drugs present on heparin numerous advantages: equal antithrombotic activity with a smaller bleeding risk, higher bioavailability, longer pharmacokinetic, which simplify their use. The definite mode of action remains unknown, but LMWH act at different steps like coagulation (by AT III), fibrinolysis, blood cells, endothelial cells. Further, like heparin, they can be neutralized by protamine. However the right, simple, specific biological assay which presents a good correlation with the antithrombotic activity, remained to be established.