Visceral leishmaniasis in the BALB/c mouse: sodium stibogluconate treatment during acute and chronic stages of infection: II. Changes in tissue drug distribution

Oxidative stress in mice treated with antileishmanial meglumine antimoniate

In order to improve the understanding of the toxicity of pentavalent antimony (Sb(V)), we investigated the acute effects of meglumine antimoniate (MA) on the oxidative stress in heart, liver, kidney, spleen and brain tissue of mice. Levels of lipoperoxidation and protein carbonylation were measured to evaluate the oxidative status, whereas superoxide dismutase/catalase activity and glutathione levels were recorded to examine the antioxidative status. We observed that MA caused significant protein carbonylation in the heart, spleen and brain tissue. Increased lipoperoxidation was found in the liver and brain tissue. An imbalance between superoxide dismutase and catalase activities could be observed in heart, liver, spleen and brain tissue. Our results suggest that MA causes oxidative stress in several vital organs of mice. This indicates that the production of highly reactive oxygen and nitrogen species induced by MA might be involved in some of its toxic adverse effects.

Canine Leishmaniasis

Canine leishmaniasis is caused by Leishmania infantum (syn. L. chagasi, in America) and is transmitted by the bite of phlebotomine sand flies. Infected dogs constitute the main domestic reservoir of the parasite and play a key role in transmission to humans, in which the parasite produces visceral leishmaniasis. The increasing awareness that control of the human disease depends on effective control of canine leishmaniasis has promoted, in the last few years, research into leishmanial infection in dogs. Newly available specific reagents and molecular tools have been applied to the detailed investigation of canine leishmaniasis and important advances have been made in elucidating the epidemiology and pathology of the disease. These new findings have led to better understanding of the disease, and have also helped in the development of new diagnostic methods and control measures against the infection, such as insecticide-impregnated collars for dogs, new drugs and treatment protocols, and second generation vaccines, with the hope of not only reducing the heavy burden of the disease among dogs but also reducing the incidence of human visceral leishmaniasis.

Pharmacokinetics, toxicities, and efficacies of sodium stibogluconate formulations after intravenous administration in animals

The pharmacokinetics and toxicities of free sodium stibogluconate (SSG) and two vesicular formulations of this drug (a nonionic surfactant vesicular formulation of SSG [SSG-NIV] and SSG-NIV-dextran) were determined after treatment with a single intravenous dose in healthy dogs and were related to their antileishmanial efficacies in mice. Analysis of the curves of the concentrations in plasma after intravenous administration of SSG and SSG-NIV in dogs showed that both formulations produced similar antimony (Sb) pharmacokinetics. In contrast, treatment with SSG-NIV-dextran significantly modified the pharmacokinetics of the drug. The elimination half-life was four times longer (280 min) than that observed after administration of SSG (71 min) (P = 0.01), and the volume of distribution at steady state (V(SS)) was also increased (V(SS) for SSG, 0.21 liters/kg; V(SS) for SSG-NIV-dextran, 0.34 liters/kg [P = 0.02]), thus indicating that drug encapsulation favors the distribution of Sb into organs and increases its residence time in tissues. This would explain the superior antileishmanial efficacy of this formulation compared to those of the free drug in mice. No signs of toxicity were found in dogs after SSG and SSG-NIV administration. However, SSG-NIV-dextran treatment was associated with short-term toxicity, demonstrated by the development of chills and diarrhea, which cleared by 24 h postdosing, and hepatic dysfunction at 24 h postdosing (P < 0.05). The levels of all the biochemical parameters had returned to normal at 1 month postdosing. No signs of toxicity were observed in mice treated with all three formulations.

Efficacies of vesicular and free sodium stibogluconate formulations against clinical isolates of Leishmania donovani

In this study, the in vitro and in vivo efficacies of free sodium stibogluconate (SSG) and a nonionic surfactant vesicular formulation of SSG (SSG-NIV) against a laboratory strain of Leishmania donovani (MHOM/ET/67:LV82) and different clinical isolates of L. donovani were determined. Treatment with SSG-NIV was more effective against intramacrophage amastigotes than treatment with SSG. In vivo murine studies showed that there was interstrain variability in the infectivity of the different L. donovani strains, with two of the strains (20001 and 20003) giving low parasite burdens. In addition, interstrain variability in the antileishmanial efficacy of SSG in a single dose containing 300 mg of Sb(V)/kg of body weight was observed. This dose of free drug either caused a >97% reduction in liver parasite burdens or had no significant effect on parasite burdens compared with the result with the respective control. In some instances, treatment with this free SSG dose also caused a significant reduction in spleen (strain 20006) or bone marrow (strains 20001 and 20009) parasite burdens. Treatment with SSG-NIV was more effective than that with SSG against all of the strains tested. In SSG-responsive strains, the reduction in liver parasite burdens by SSG-NIV treatment was similar to that caused by free SSG. In SSG-nonresponsive strains, SSG-NIV treatment caused at least a 95% reduction in liver parasite burdens. Overall, these results indicate that the use of a vesicular formulation of SSG is likely to increase its clinical efficacy against visceral leishmaniasis.

The cured immune phenotype achieved by treatment of visceral leishmaniasis in the BALB/c mouse with a nonionic surfactant vesicular formulation of sodium stibogluconate does not protect against reinfection

Single-dose treatment with sodium stibogluconate solution (SSG) and treatment with a nonionic surfactant vesicular formulation of sodium stibogluconate (SSG-NIV) were compared for the ability to protect BALB/c mice against infection with Leishmania donovani. Prophylactic treatment with SSG-NIV protected against infection, although its effects were time and organ dependent; protection was not obtained with SSG. Protection against reinfection with L. donovani was observed only in mice cured by treatment with SSG-NIV. However, this protective effect was probably due to the presence of residual drug rather than an immune effect, since prophylactic SSG-NIV treatment gave similar results. Transfer of enriched spleen T-cell populations from L. donovani-infected mice or from infected SSG-NIV-treated mice gave no protection against L. donovani infection in the recipients. T cells from infected mice, but not from infected SSG-NIV-treated mice, were infectious to recipients. SSG-NIV treatment was equally effective against visceral leishmaniasis in immunocompetent and SCID mice, whereas SSG treatment was less effective in the latter. The results of this study suggest that the high antileishmanial activity of SSG-NIV is due to favorable modification of SSG delivery and does not require a fully functional immune response. Cure of visceral leishmaniasis by SSG-NIV treatment in the BALB/c mouse did not protect against reinfection.

Immune responses of Leishmania donovani infected BALB/c mice following treatment with free and vesicular sodium stibogluconate formulations

The anti-parasitic efficacy of free and a non-ionic surfactant vesicular (NIV) sodium stibogluconate (SSG) formulation of the drug, and their effect on the immune responses of Leishmania donovani infected BALB/c mice, was compared. The SSG NIV formulation maintained a significant suppression of splenic, hepatic and bone marrow parasite burdens (P < 0.005) compared to control values throughout the study. Infected controls and drug treated animals had high levels of L. donovani specific antibodies by day 14 of the study and the titre of these antibodies increased throughout the study for infected controls and free SSG treated animals. Initially SSG NIV treated animals had significantly higher specific IgG2a levels (P < 0.01, day 16) compared with infected controls and free SSG treated mice, but by day 31 the levels of this isotype and other antibodies (IgG1, IgG3 and IgM) were significantly lower (P < 0.05) than values for the other two groups. There was no difference in the proliferative responses of spleen cells taken from infected controls and drug treated animals to both specific and non-specific stimulation at day 16 of the study. On day 31, only spleen cells taken from infected mice given SSG NIV displayed a significant proliferative response to parasite antigen preparations and Concanavalin A stimulation (P < 0.01). No IL4 was detected in supernatants from in vitro spleen cells cultures. Significant levels of IFN-gamma was induced by stimulation of cells from vesicular drug treated animals with a frozen parasite preparation compared with medium controls (P < 0.05) on day 49 but not day 16. Similar stimulation did not induce IFN gamma production in spleen cells from infected controls or free drug treated animals. Only SSG NIV treated animals gave a significant positive DTH response to an L. donovani parasite preparation (P < 0.05) given on day 31. The results of this study indicate that there was a formulation dependent qualitative difference in the post-treatment immune responses of L. donovani infected animals, with SSG NIV animals displaying immune responses expected for a cured phenotype.

Strategies for immune intervention in visceral leishmaniasis

Therapeutic intervention remains a major tool for control of visceral leishmaniasis (VL). Studies in murine models of VL have demonstrated the efficacy of various cytokines, either alone or in conjunction with antimony chemotherapy. Here, some basic aspects of the models used to study VL are summarized and the recent data in this field are reviewed. Finally, alternative strategies to harnessing the protective potential of the host immune response, based on augmenting communication between antigen-presenting cells and T cells, are discussed.

The distribution of free and non-ionic vesicular sodium stibogluconate in the dog

The pharmacokinetics and tissue distribution of antimony after the administration of sodium stibogluconate in a free form or entrapped in vesicles prepared from non-ionic surfactant were studied in the dog. Animals were given either one or two intravenous bolus injection(s) equivalent to 45 mg Sb kg-1 as free drug or 0.625 or 0.685 mg Sb kg-1 as vesicular drug. Blood samples were taken at various times after dosing and antimony levels in various tissues were determined at 3 h, 48 h and 6 days after dosing. After free stibogluconate antimony clearance from the blood occurred in a rapid elimination phase with a blood half-life of 0.58 +/- 0.08 h. This rapid elimination phase did not occur after vesicular drug. Both drug preparations gave similar antimony levels in the spleen, liver and femur and humerus bone marrow at all time points assessed even though the vesicular dose was one-seventieth of the free drug dose. After the free drug there was marked urinary excretion of antimony and, as a result, increased kidney loading at the expense of other tissue. Vesicle-mediated drug delivery suppressed renal excretion and a much greater proportion of the antimony dose was recovered from tissue than was obtained after free drug. A hypothesis is presented to account for the differences in tissue antimony concentrations produced by the two formulations.