Murine Model Of Acute Toxoplasmosis Research Articles

Imidazo[1,2-b]pyridazines targeting Toxoplasma gondii calcium-dependent protein kinase 1 decrease the parasite burden in mice with acute toxoplasmosis

The current therapeutic arsenal for toxoplasmosis is restricted to drugs non-specific to the parasite which cause important side effects. Development of more efficient and specific anti-Toxoplasma compounds is urgently needed. Imidazo[1,2-b]pyridazines designed to inhibit the calcium-dependent protein kinase 1 of Toxoplasma gondii (TgCDPK1) and effective against tachyzoite growth in vitro at submicromolar ranges were modified into hydrochloride salts to be administered in vivo in a mouse model of acute toxoplasmosis. All protonated imidazo[1,2-b]pyridazine salts (SP230, SP231 and SP232) maintained their activity on TgCDPK1 and T. gondii tachyzoites. Rat and mouse liver microsomes were used to predict half-life and intrinsic clearance, and the pharmacokinetic profile of the most rapidly degraded imidazo[1,2b]pyridazine salt (SP230) was determined in serum, brain and lungs of mice after a single administration of 50 mg/kg. Compounds were then tested in vivo in a murine model of acute toxoplasmosis. Mice infected with tachyzoites of the ME49 strain of T. gondii were treated for 4, 7 or 8 days with 25 or 50 mg/kg/day of SP230, SP231 or SP232. The parasite burdens were strongly diminished (>90% reduction under some conditions) in the spleen and the lungs of mice treated with imidazo[1,2-b]pyridazine salts compared with untreated mice, without the need for pre-treatment. Moreover, no increases in the levels of hepatic and renal toxicity markers were observed, demonstrating no significant signs of short-term toxicity. To conclude, imidazo[1,2-b]pyridazine salts have strong efficacy in vivo on acute toxoplasmosis and should be further tested in a model of mouse congenital toxoplasmosis.

Deletion of mitogen-activated protein kinase 1 inhibits development and growth of Toxoplasma gondii.

Mitogen-activated protein kinases (MAPKs) regulate key signaling events in a variety of eukaryotic cells. Toxoplasma gondii, the causative agents of toxoplasmosis, possesses a p38α MAPK homologue, MAPK1, which is an important manipulator of host immunity and virulence in mice. In this work, we showed an increased transcript level of MAPK1 in T. gondii during bradyzoite differentiation induced by alkaline treatment and heat shock in vitro, suggesting that MAPK1 may be associated with bradyzoite differentiation. The biological roles of MAPK1 of T. gondii were investigated by construction of a MAPK1 deletion mutant (Δmapk1) and a complementation mutant with restored MAPK1 expression using a type I strain. Knockout of MAPK1 resulted in markedly defective bradyzoite differentiation, host-cell attachment and parasite replication in vitro, and the inability to cause lethal infection in a murine model of acute toxoplasmosis, with lower parasite burden in infected tissues, showing that MAPK1 is associated with the acute virulence of parasite in mice. Complementation of MAPK1-deficient parasites restored bradyzoite development, attachment, replication, and virulence. Our findings demonstrate that MAPK1 is involved in asexual development and growth of T. gondii.

Development of new highly potent imidazo[1,2-b]pyridazines targeting Toxoplasma gondii calcium-dependent protein kinase 1

Using a structure-based design approach, we have developed a new series of imidazo[1,2-b]pyridazines, targeting the calcium-dependent protein kinase-1 (CDPK1) from Toxoplasma gondii. Twenty derivatives were thus synthesized. Structure-activity relationships and docking studies confirmed the binding mode of these inhibitors within the ATP binding pocket of TgCDPK1. Two lead compounds (16a and 16f) were then identified, which were able to block TgCDPK1 enzymatic activity at low nanomolar concentrations, with a good selectivity profile against a panel of mammalian kinases. The potential of these inhibitors was confirmed in vitro on T. gondii growth, with EC50 values of 100 nM and 70 nM, respectively. These best candidates also displayed low toxicity to mammalian cells and were selected for further in vivo investigations on murine model of acute toxoplasmosis.

THE EFFECT OF CLINDAMYCIN AND SULFADIAZINE ON EXPERIMENTAL MURINE MODEL WITH ACUTE TOXOPLASMOSIS

Toxoplasmosis has zoonotic importance among human and domestic animals. It causes diseases in both man and animals through ingestion of oocysts that passed in faeces of cat or by ingestion of cysts in undercooked meat.The present study was designed to clarify the effect of Clindamycin (CLI) combined with Sulfadiazine (SD) on a murine model of acute toxoplasmosis. Albino Swiss mice were intraperitoneally infected with 103 tachyzoites of the RH strain of Toxoplasma gondii and were per orally treated with either drug alone (SD) or (CLI) or both combined. Starting with day 1 for 14 days. Survival was monitored during 8 weeks. Residual infection was assessed by a bioassay of representative 4-week survivors and by parasite DNA detection using PCR for representative 8-week survivors. An effect of treatment was shown in all treated groups compared to untreated control mice. Among mice infected with parasite, SD and CLI at any dose combination protected more animals. However, treatment with SD plus CLI at 25 plus 25, 25 plus 50, and 50 plus 50 mg/kg/day protected 25, 37, and 81% of mice, respectively, thus demonstrating a significant synergistic effect of SD and CLI against T. gondii especially in cases of acute infection.

Toxoplasma MIC2 Is a Major Determinant of Invasion and Virulence

Like its apicomplexan kin, the obligate intracellular protozoan Toxoplasma gondii actively invades mammalian cells and uses a unique form of gliding motility. The recent identification of several transmembrane adhesive complexes, potentially capable of gripping external receptors and the sub-membrane actinomyosin motor, suggests that the parasite has multiple options for host-cell recognition and invasion. To test whether the transmembrane adhesin MIC2, together with its partner protein M2AP, participates in a major invasion pathway, we utilized a conditional expression system to introduce an anhydrotetracycline-responsive mic2 construct, allowing us to then knockout the endogenous mic2 gene. Conditional suppression of MIC2 provided the first opportunity to directly determine the role of this protein in infection. Reduced MIC2 expression resulted in mistrafficking of M2AP, markedly defective host-cell attachment and invasion, the loss of helical gliding motility, and the inability to support lethal infection in a murine model of acute toxoplasmosis. Survival of mice infected with MIC2-deficient parasites correlated with lower parasite burden in infected tissues, an attenuated inflammatory immune response, and induction of long-term protective immunity. Our findings demonstrate that the MIC2 protein complex is a major virulence determinant for Toxoplasma infection and that MIC2-deficient parasites constitute an effective live-attenuated vaccine for experimental toxoplasmosis.

Evaluation of two inhibitors of invasion: LY311727 [3-(3-acetamide-1-benzyl-2-ethyl-indolyl-5-oxy)propane phosphonic acid] and AEBSF [4-(2-aminoethyl)-benzenesulphonyl fluoride] in acute murine toxoplasmosis

We examined the effect of an inhibitor of secretory phospholipase A2 type II (LY311727) and of a specific inhibitor of serine proteases (AEBSF) in a murine model of acute toxoplasmosis. LY311727 did not afford any significant protection and produced earlier mortality compared with untreated mice at a dose of 100 mg/kg. In contrast, AEBSF demonstrated a significant increase in length of survival, and this effect was enhanced when AEBSF was administered with non-protective doses of pyrimethamine.

Synergistic effect of clindamycin and atovaquone in acute murine toxoplasmosis.

The effect of clindamycin (CLI) combined with autovaquone (ATO) was examined in a murine model of acute toxoplasmosis. Swiss Webster mice intraperitoneally infected with 10(2) or 10(4) tachyzoites of the RH strain of Toxoplasma gondii were perorally treated with either drug alone (for ATO, 5, 25, 50, or 100 mg/kg of body weight/day; for CLI, 25, 50, or 400 mg/kg/day) or both combined (for ATO plus CLI, respectively, 5 plus 25, 25 plus 25, 25 plus 50, 50 plus 50, or 100 plus 400 mg/kg/day) starting with day 1 for 14 days. Survival was monitored during 7 weeks. Residual infection was assessed by a bioassay of representative 4-week survivors and by parasite DNA detection by PCR for representative 7-week survivors. An effect of treatment was shown in all treatment groups compared to untreated control mice (P = 0.0000). Among mice infected with 10(2) parasites, ATO and CLI at any dose combination protected significantly more animals than ATO alone (P = 0.0000), but compared to CLI alone, given its good effect, the combined drugs were no more effective (P > 0.05). For mice infected with 10(4) parasites, the drugs combined at the lowest and highest doses (5 plus 25 and 100 plus 400 mg/kg/day) were, similarly, more effective than ATO alone (P = 0.035 and 0.000, respectively) but not than CLI alone (P > 0. 05). However, treatment with ATO plus CLI at 25 plus 25, 25 plus 50, and 50 plus 50 mg/kg/day protected 20, 33, and 78% of mice, respectively, compared to virtually no survivals among those treated with either drug alone (P < 0.0005), thus demonstrating a significant synergistic effect of ATO and CLI against T. gondii. Furthermore, the dose of ATO at a given dose of CLI was shown to be critical to the effect. Moreover, the absence of residual infection in some survivors shows the potential of this drug combination to eliminate the parasite.

Effect of clindamycin in a model of acute murine toxoplasmosis.

OBJECTIVE: To characterize the antitoxoplasma activity of clindamycin in a murine model of acute toxoplasmosis. METHODS: Rates of survival and mean survival times of Swiss Webster mice infected intraperitoneally with 106-102 tachyzoites of the RH strain of Toxoplasma gondii treated with clindamycin or sulfamethoxazole (positive control) or untreated (negative control) were compared. Survivors were submitted to examination of untreated brain tissue preparations, intraperitoneal and peroral subinoculations of brain tissue homogenates into fresh mice, and to pathohistology, including immunohistochemistry, of brain and lungs. RESULTS: The effect of clindamycin treatment (400 mg/kg/day) on infected Swiss Webster mice was inoculum size dependent, ranging from no survivals in animals infected with 106 parasites, to 100% survivals with an inoculum of 102. Treatment initiated 24 h before and at time of infection prolonged mean survival times comparably to sulfamethoxazole, and significantly when compared to untreated controls. In contrast, treatment initiated 48 h postinfection with an inoculum of 106 did not postpone death. In the clindamycin-treated survivors, there was no biological or histologic evidence for the persistence of toxoplasma. CONCLUSIONS: The results obtained show that at an appropriate parasite dose/drug dose ratio, clindamycin is strongly toxoplasmacidal in a murine model of acute toxoplasmosis.

In vitro and in vivo effects of rifabutin alone or combined with atovaquone against Toxoplasma gondii.

The efficacy of rifabutin (RIFA) alone or in combination with atovaquone (ATO) was examined in vitro and in a murine model of acute toxoplasmosis. In vitro studies were performed with MRC5 fibroblast tissue cultures, with quantification of Toxoplasma growth by enzyme-linked immunosorbent assay. For in vivo studies, mice were acutely infected with 10(4) tachyzoites of the virulent RH strain and were then treated perorally for 10 days from day 1 or day 4 postinfection. The efficacy of each drug regimen was assessed by determination of survival rates and sequential titration of parasites in blood, brain, and lungs by a tissue culture method. In vitro, RIFA was inhibitory for Toxoplasma growth at concentrations between 0.5 and 20 micrograms/ml; the 50% inhibitory concentration was estimated to be 1.68 micrograms/ml. When RIFA and ATO were combined, synergistic effects were noted for RIFA at 20 micrograms/ml combined with ATO at 0.01 or 0.02 microgram/ml and RIFA at 1, 2, or 5 micrograms/ml combined with ATO at 0.02 microgram/ml. In vivo, administration of RIFA at 200 mg/kg of body weight per day from day 1 to day 10 resulted in a 100% protection during treatment, with clearance of parasites from the blood, brain, and lungs. After the cessation of therapy, relapses occurred in the brain and lungs; the mortality was 46% at the end of the experiment (day 30). Among the mice treated with RIFA at 200 mg/kg/day from day 4 to day 14, no death was recorded during the treatment period and a marked reduction in parasite burdens was observed in blood and tissues; however, relapses occurred and 10% of mice survived until day 30. Administration of RIFA at 200 mg/kg/day in combination with ATO at 100 mg/kg/day resulted in a marked prolongation of survival compared with that for mice that received ATO or RIFA alone. However, in mice receiving the combination, parasite burdens in blood and organs were similar to those in mice treated with RIFA alone. These results confirmed the activity of RIFA in the treatment of acute toxoplasmosis and the potential of the combination of RIFA-ATO since the two drugs act synergistically against Toxoplasma gondii.

Trovafloxacin is active against Toxoplasma gondii.

Drugs currently used for treatment of toxoplasmosis in pregnant women, congenital infections, immunocompromised patients, and patients with the ocular disease are not always effective or may be dangerous to use; therefore, there is a need for more-effective and less-toxic drugs. Recently, we examined a group of fluoroquinolones for in vitro and in vivo activities against Toxoplasma gondii. Among those examined in vitro (ciprofloxacin, fleroxacin, ofloxacin, temafloxacin, and trovafloxacin), only trovafloxacin significantly inhibited intracellular replication of T. gondii without significant toxicity for host cells. In a murine model of acute toxoplasmosis, 100 or 200 mg of trovafloxacin per kg of body weight per day for 10 days protected 100% of infected mice against death. A dose of 50 mg/kg/day protected 90% of the mice, and a dose of 25 mg/kg/day effected prolongation of time to death. The other fluoroquinolones did not have such in vivo activities. These results indicate that trovafloxacin may be useful for treatment of toxoplasmosis in humans.

Protective effect of low doses of an anti‐IL‐4 monoclonal antibody in a murine model of acute toxoplasmosis

Treatment with an anti-IL-4 monoclonal antibody protected susceptible C57BL/6 mice against challenge with an avirulent strain of T. gondii. Antibody therapy with 100 micrograms on days 0 and 7 post infection resulted in 100% survival of C57/BL6 mice infected orally. Survival was dose-dependent. Treatment prolonged parasitaemia but did not alter tissue parasite load. Increased serum IgG2a and IFN-gamma levels, together with low levels of IgG1, in mice treated with anti-IL-4 or an isotype control, indicated a trend towards a predominant Th1 response in all survivors. The persistence of an IgE response after treatment suggests that endogenous IL-4 was only partly neutralized or that other factors can induce the production of IgE in murine toxoplasmosis.

In-vitro and in-vivo activities of roxithromycin in combination with pyrimethamine or sulphadiazine against Toxoplasma gondii.

The efficacy of roxithromycin alone or in combination with pyrimethamine or sulphadiazine was examined in vitro and in a murine model of acute toxoplasmosis. In-vitro studies were performed with MRC5 fibroblast tissue cultures, with quantification of toxoplasma growth by an enzyme-linked immunosorbent assay. For in-vivo studies, mice were infected with 10(4) tachyzoites of the virulent RH strain and then treated perorally for 10 days from day 1 after infection. The efficacy of each drug regimen was assessed by determination of survival rates and sequential titration of parasites in blood, brain and lungs, using a tissue culture method. In vitro, roxithromycin inhibited toxoplasma growth at a concentration of > or = 0.02 mg/L; the 50% inhibitory concentration was estimated to be 1.34 mg/L. No synergistic effect was observed when it was combined with pyrimethamine or sulphadiazine. In vivo, roxithromycin alone at 50 or 200 mg/kg/day slightly prolonged survival compared with untreated mice, but a striking synergistic effect was observed when roxithromycin was administered in combination with pyrimethamine or sulphadiazine at subtherapeutic doses, i.e., 12.5 and 100 mg/kg/day, respectively. Combination regimens consistently resulted in a marked reduction fo the parasite burdens in blood and tissue, compared with those in mice treated with any of the agents alone. These results suggest that in-vivo activities of either pyrimethamine or sulphadiazine against T. gondii are reinforced by roxithromycin and such combinations should be considered in development of alternative treatments for human toxoplasmosis.

In vitro and in vivo activities of the hydroxynaphthoquinone atovaquone alone or combined with pyrimethamine, sulfadiazine, clarithromycin, or minocycline against Toxoplasma gondii.

The efficacy of atovaquone alone or combined with pyrimethamine, sulfadiazine, clarithromycin, and minocycline was examined in vitro and in a murine model of acute toxoplasmosis. In vitro studies were performed with MRC5 fibroblast tissue cultures, with quantification of Toxoplasma growth by an enzyme-linked immunosorbent assay. For in vivo studies, mice were acutely infected intraperitoneally with 10(4) tachyzoites of the virulent RH strain and then treated perorally for 10 days from day 1 postinfection. The following drug regimens were investigated: atovaquone at 100 and 50 mg/kg of body weight per day and the combinations of atovaquone at 50 mg/kg with sulfadiazine at 200 mg/kg, pyrimethamine at 12.5 mg/kg, clarithromycin at 200 mg/kg, or minocycline at 50 mg/kg. Efficacy was assessed by determination of survival rates and sequential determination of parasite burdens in blood, brain, and lungs. In vitro, atovaquone inhibited Toxoplasma growth at a concentration of > or = 0.02 mg/liter; the 50% inhibitory concentration was estimated to be 0.023 mg/liter. No synergistic effect was observed when it was combined with sulfadiazine, clarithromycin, or minocycline, whereas a significant antagonistic effect was noted for the combination of atovaquone with pyrimethamine. In vivo, administration of atovaquone at 100 or 50 mg/kg/day for 10 days resulted in prolonged survival compared with that in untreated mice; this survival was associated with a reduction of parasite burdens in blood and tissues during the course of treatment. The combinations of atovaquone with pyrimethamine, clarithromycin, or sulfadiazine were more efficient than each drug administered alone, in terms of survival, but parasite burdens in blood and organs were not reduced compared with those in mice treated with any of the agents alone. These experimental results confirmed the activity of atovaquone against Toxoplasma gondii, but no marked improvement in efficacy was observed in vitro and in vivo when this drug was combined with pyrimethamine, sulfadiazine, minocycline, or clarithromycin.

Synergistic activity of clarithromycin and minocycline in an animal model of acute experimental toxoplasmosis.

The efficacy of clarithromycin in a murine model of acute toxoplasmosis was studied. Clarithromycin was administered alone and concurrently with minocycline, and efficacy was assessed by survival rates and sequential determination of parasite burden in blood, brains, and lungs. Limited protection resulted from administration of each drug alone, whereas a remarkable synergistic effect followed concurrent administration. Survival of mice treated with 200 mg of clarithromycin plus 20 mg of minocycline per kg of body weight daily was 95%; that of mice treated with 50 mg of clarithromycin plus 50 mg of minocycline per kg daily was 93%. The parasite burden in the blood and organ tissues of these mice was markedly reduced compared with that in mice treated with a single agent. In mice treated with 200 mg of clarithromycin plus 50 mg of minocycline per kg per day, survival was 100% during the 30-day experiment; no parasites were found in blood and tissues.

Synergistic activity of azithromycin and pyrimethamine or sulfadiazine in acute experimental toxoplasmosis.

The efficacy of azithromycin administered alone or combined with pyrimethamine or sulfadiazine was examined in a murine model of acute toxoplasmosis. Outbred Swiss mice acutely infected with tachyzoites of the virulent RH strain were treated for 10 days from day +1 postinfection. The efficacy of each regimen was assessed in terms of survival rates and sequential titration of parasites in blood, brain, and lungs by using a tissue culture method. Administration of azithromycin at 300, 150, or 75 mg/kg of body weight per day resulted in prolonged survival relative to that of untreated controls; sequential examination of parasite burden showed early eradiaction of Toxoplasma gondii from the lungs, whereas dissemination to the brain was not prevented. A remarkable synergistic effect was observed when azithromycin (150 mg/kg/day) was administered in combination with pyrimethamine or sulfadiazine at noncurative dosages, i.e., 12.5 and 200 mg/kg/day, respectively. In mice treated with azithromycin plus sulfadiazine and azithromycin plus pyrimethamine, parasite burdens in blood and organs, relapses after cessation of therapy, and mortality were all markedly reduced relative to mice treated with any of the agents alone. These results show that azithromycin, which is remarkably active on pulmonary Toxoplasma infection, significantly potentiates the curative effect of sulfadiazine or pyrimethamine.

Pyrimethamine concentrations in serum during treatment of acute murine experimental toxoplasmosis.

Central nervous system toxoplasmosis is a major opportunistic infection in patients with acquired immunodeficiency syndrome. The standard therapy for this infection is pyrimethamine (PYR) and sulfonamides. To assess in vivo if PYR alone could adequately treat toxoplasmosis, a murine model of acute toxoplasmosis was used. The CD1 strain of mice was infected intraperitoneally with 10(4) parasites of the RH strain of Toxoplasma gondii. Pyrimethamine was administered in mouse chow at concentrations of 0, 0.03125, 0.0625, 0.125, 0.25, or 1.0 mg of PYR/g of food, which provides the following daily PYR dosages: 0, 6.25, 12.5, 25, 50, and 200 mg/kg/day. No sulfonamides were administered. Serum PYR levels proved more accurate than mg of PYR/g of food in predicting survival. Mice with serum PYR levels greater than or equal to 500 ng/ml (2 microM) survived and had no parasites present on peritoneal lavage. Mice with serum PYR levels less than 100 ng/ml (0.4 microM) had a 100% mortality rate and the average parasite count was 3 x 10(7) organisms in the lavage fluid. At a PYR level of 370 ng/ml, six of 11 mice survived and the lavage fluid contained 2.5 x 10(5) organisms. Previously, using 3H-uracil in an in vitro assay, PYR at a concentration of 500 ng/ml was shown to be as effective in inhibiting Toxoplasma growth as the combination of PYR (100 ng/ml) and sulfonamides 25 micrograms/ml). These data suggest the potential usefulness of PYR for monotherapy of toxoplasmosis and are consistent with previously described in vitro assays.

Anti-Toxoplasma effects of dapsone alone and combined with pyrimethamine

The efficacy of dapsone alone or combined with pyrimethamine against Toxoplasma gondii was investigated experimentally. For in vitro studies, a sensitive immunoassay was used for assessment of Toxoplasma growth in tissue cultures; dapsone was found to have a significant inhibitory effect at a concentration of 0.5 micrograms/ml in the cultures, and the 50% inhibitory concentration was estimated to be 0.55 micrograms/ml. When pyrimethamine and dapsone were combined, an important synergistic effect which was associated with morphological alterations of the parasites was observed. In vivo studies were performed in a murine model of acute toxoplasmosis in which a tissue culture method was used to estimate the parasite burden in the blood, lungs, and brains of infected mice. Dapsone alone, which was administered at 100 mg/kg/day for 10 days from day 1 after infection, was unable to prevent parasite dissemination and only delayed the time to death of treated mice compared with the time of death of untreated controls. When dapsone and pyrimethamine (18.5 mg/kg/day) were administered in combination from day 4 after infection, parasites were cleared from blood and organs within 6 days, but relapses were observed 15 days after the cessation of therapy. When treatment was started at day 1 after infection, 100% of mice survived and relapses were not observed, suggesting a good efficacy of this combination for preventive therapy.

Activity of gamma interferon in combination with pyrimethamine or clindamycin in treatment of murine toxoplasmosis

The activity of recombinant gamma interferon (rIFN-gamma) in combination with either pyrimethamine or clindamycin was examined in a murine model of acute toxoplasmosis. Mice received either pyrimethamine or clindamycin alone or in combination with rIFN-gamma. Significantly increased survival and/or time to death was observed in animals treated with pyrimethamine or clindamycin in combination with rIFN-gamma compared to those that received treatment with any of the agents alone.

Activity of A-56268 (TE-031), a new macrolide, against Toxoplasma gondii in mice.

The activity of A-56268 (TE-031), a new macrolide, was tested in a murine model of acute toxoplasmosis. All control animals died in 8 +/- 1 days, while all mice treated with nine daily doses of A-56268 at 300 mg/kg, administered by gavage, survived. Moreover, 41.6% of the surviving mice were free from cerebral infection with Toxoplasma gondii, as assessed by brain subpassage. A-56268 is active against T. gondii in vivo, but further studies are needed to determine its usefulness in the treatment of human toxoplasmosis.