Toxicity evaluation of artesunate and artelinate in Plasmodium berghei-infected and uninfected rats.

A recent therapeutic index study in rats demonstrated that i.v. artesunate (AS) is safer than artelinate (AL). The present study of acute toxicity illustrated an LD(50) of 177 mg/kg and 488 mg/kg for AL and AS, respectively, following daily i.v. injection for 3 days in Plasmodium berghei-infected rats. In uninfected rats, the LD(50) values were 116 mg/kg and 351 mg/kg after a single dose of AL and AS, respectively. This study showed vascular necrosis in 50% of the animals at 13.5 mg/kg AL and at 42.8 mg/kg AS. Animals also showed moderate signs of renal failure at 40 mg/kg AL and 240 mg/kg AS (100 times higher than the therapeutic dose). Histopathological evaluation demonstrated mild to moderate tubular necrosis in uninfected rats treated with 40 mg/kg AL and 240 mg/kg AS; interestingly, fewer pathological lesions were observed in malaria-infected rats. Renal injury was reversible in all cases by Day 8 after cessation of dosing. No neurotoxicity was seen in any case with all i.v. regimens. In conclusion, AL and AS exhibit less toxic effects in P. berghei-infected rats than in uninfected rats. Both agents caused irreversible vascular irritation, reversible nephrotoxicity and no neurotoxicity at high doses. The data indicate that AS is three times safer than AL in rats.

The evaluation of radiolabeled artesunate on tissue distribution in rats and protein binding in humans.

The present study reports the tissue distribution, pharmacokinetics, mass balance, and elimination of [(14)C] artesunate (AS) following single intravenous administration in rats. Protein binding was performed with rat and human plasma. Radioactivity and drug levels in blood, plasma, tissues, urine, and feces up to 192 hours were collected and measured. The mean terminal half-life of plasma (76 h) and blood (105 h) radioactivity was prolonged compared with that of unchanged AS (0.43 h) and dihydroartemisinin (0.75 h), an active metabolite of AS. Drug was widely distributed after 1 hour in select tissues. After 24 hours, the radioactivity rapidly declined in all tissues except spleen until 96 hours. Only 1% of total radioactivity was detected in brain tissue. AS revealed a higher binding capacity with human and rat plasma proteins (73-81%). The radioactivity in whole blood was higher (two to fourfold) than that in plasma throughout the period of the treatment, suggesting that AS binding to RBCs may relate to its powerful antimalarial activity.

Directional specificity and patterning of sensory axons in trigeminal ganglion-whisker pad cocultures.

In the rodent trigeminal pathway, trigeminal axons invade the developing whisker pad from a caudal to rostral direction. We investigated directional specificity of embryonic day (E) 15 rat trigeminal axons within this peripheral target field using explant cocultures. E15 trigeminal axons readily grow into the same age whisker pad explants and form follicle-related patterns along a caudal to rostral direction. They also can grow into this target from its lateral aspects. In contrast, they are unable to invade the whisker pad from the rostral (nasal) pole. We did not find any correlation between the distribution of extracellular matrix molecules and trigeminal axon growth preferences. We also examined age-related changes in trigeminal axon responsiveness to directional cues. E19 trigeminal axons readily grew into E15 whisker pad explants from either the caudal or the rostral pole. These results suggest the presence of growth permissive and repulsive cues that guide sensory axons in the whisker pad. Furthermore, trigeminal axons lose their responsiveness to growth inhibitory cues at later stages of development.

Risk assessment and therapeutic indices of artesunate and artelinate in Plasmodium berghei-infected and uninfected rats.

Artesunate (AS) is being developed as a potential agent for the treatment of severe and complicated malaria. A risk assessment of the therapeutic index and related hematological changes of AS and artelinate (AL) following daily intravenous injection for 3 days was conducted in Plasmodium berghei-infected and uninfected rats. The minimum doses of AS and AL for parasitemia suppression were 2.3 and 2.5 mg/kg, respectively, and the suppressive doses for half parasitemia (SD50) were 7.4 and 8.6 mg/kg, respectively. The maximum tolerated dose (MTD) for AS was 240 mg/kg with a therapeutic index of 32.6. The MTD for AL was 80 mg/kg with a therapeutic index of 9.3. Hematological changes were studied on days 1 and 8 after the final dosing. In both AS- and AL-treated rats, dose-dependent and rapidly reversible hematological changes (significant reductions in RBC, HCT, Hb, and reticulocyte levels) were seen in the peripheral blood. Bone marrow evaluation revealed a statistically significant reduction in the myeloid/erythroid ratio only at the highest dose of AS (240 mg/kg), albeit still within the normal ratio range (1.0-1.5:1.0). Looking at the respective therapeutic indices the authors have concluded that AS is much safer than AL. Both drugs induced hematological changes in rats that parallel the dose-dependent, reversible anemia and reticulocytopenia previously reported in animals and humans. However, no significant bone marrow depression was seen for either agent.