Clindamycin effects on experimental ocular toxoplasmosis in the rabbit

Treatment of Toxoplasmosis: Historical Perspective, Animal Models, and Current Clinical Practice

Primary Toxoplasma gondii infection is usually subclinical, but cervical lymphadenopathy or ocular disease can be present in some patients. Active infection is characterized by tachyzoites, while tissue cysts characterize latent disease. Infection in the fetus and in immunocompromised patients can cause devastating disease. The combination of pyrimethamine and sulfadiazine (pyr-sulf), targeting the active stage of the infection, is the current gold standard for treating toxoplasmosis, but failure rates remain significant. Although other regimens are available, including pyrimethamine in combination with clindamycin, atovaquone, clarithromycin, or azithromycin or monotherapy with trimethoprim-sulfamethoxazole (TMP-SMX) or atovaquone, none have been found to be superior to pyr-sulf, and no regimen is active against the latent stage of the infection. Furthermore, the efficacy of these regimens against ocular disease remains uncertain. In multiple studies, systematic screening for Toxoplasma infection during gestation, followed by treatment with spiramycin for acute maternal infections and with pyr-sulf for those with established fetal infection, has been shown to be effective at preventing vertical transmission and minimizing the severity of congenital toxoplasmosis (CT). Despite significant progress in treating human disease, there is a strong impetus to develop novel therapeutics for both the acute and latent forms of the infection. Here we present an overview of toxoplasmosis treatment in humans and in animal models. Additional research is needed to identify novel drugs by use of innovative high-throughput screening technologies and to improve experimental models to reflect human disease. Such advances will pave the way for lead candidates to be tested in thoroughly designed clinical trials in defined patient populations.

Current treatment of toxoplasma retinochoroiditis: an evidence-based review

Objective. To perform an evidence-based review of treatments for Toxoplasma retinochoroiditis (TRC). Methods. A systematic literature search was performed using the PubMed database and the key phrase "ocular toxoplasmosis treatment" and the filter for "controlled clinical trial" and "randomized clinical trial" as well as OVID medline (1946 to May week 2 2014) using the keyword ''ocular toxoplasmosis". The included studies were used to evaluate the various treatment modalities of TRC. Results. The electronic search yielded a total of 974 publications of which 44 reported on the treatment of ocular toxoplasmosis. There were 9 randomized controlled studies and an additional 3 comparative studies on the treatment of acute TRC with systemic or intravitreous antibiotics or on reducing the recurrences of TRC. Endpoints of studies included visual acuity improvement, inflammatory response, lesion size changes, recurrences of lesions, and adverse effects of medications. Conclusions. There was conflicting evidence as to the effectiveness of systemic antibiotics for TRC. There is no evidence to support that one antibiotic regimen is superior to another so choice needs to be informed by the safety profile. Intravitreous clindamycin with dexamethasone seems to be as effective as systemic treatments. There is currently level I evidence that intermittent trimethoprim-sulfamethoxazole prevents recurrence of the disease.

Toxoplasma gondii Proliferation Require Down-Regulation of Host Nox4 Expression via Activation of PI3 Kinase/Akt Signaling Pathway

Toxoplasma gondii results in ocular toxoplasmosis characterized by chorioretinitis with inflammation and necrosis of the neuroretina, pigment epithelium, and choroid. After invasion, T. gondii replicates in host cells before cell lysis, which releases the parasites to invade neighboring cells to repeat the life cycle and establish a chronic retinal infection. The mechanism by which T. gondii avoids innate immune defense, however, is unknown. Therefore, we determined whether PI3K/Akt signaling pathway activation by T. gondii is essential for subversion of host immunity and parasite proliferation. T. gondii infection or excretory/secretory protein (ESP) treatment of the human retinal pigment epithelium cell line ARPE-19 induced Akt phosphorylation, and PI3K inhibitors effectively reduced T. gondii proliferation in host cells. Furthermore, T. gondii reduced intracellular reactive oxygen species (ROS) while activating the PI3K/Akt signaling pathway. While searching for the main source of these ROS, we found that NADPH oxidase 4 (Nox4) was prominently expressed in ARPE-19 cells, and this expression was significantly reduced by T. gondii infection or ESP treatment along with decreased ROS levels. In addition, artificial reduction of host Nox4 levels with specific siRNA increased replication of intracellular T. gondii compared to controls. Interestingly, these T. gondii-induced effects were reversed by PI3K inhibitors, suggesting that activation of the PI3K/Akt signaling pathway is important for suppression of both Nox4 expression and ROS levels by T. gondii infection. These findings demonstrate that manipulation of the host PI3K/Akt signaling pathway and Nox4 gene expression is a novel mechanism involved in T. gondii survival and proliferation.

Feline ocular toxoplasmosis

Ocular infection with Toxoplasma gondii is a well-recognized and important clinical entity in many animal species. In the cat, ocular toxoplasmosis is commonly associated with systemic infection, yet its role in causing anterior uveitis in an otherwise healthy cat is unclear. The purpose of this article is to review the salient epidemiological, clinical, and histopathologic features of systemic and ocular toxoplasmosis in the cat. Additionally, pathogenesis and possible immunopathogenic mechanisms of ocular toxoplasmosis, which may account for the higher prevalence of anterior uveitis in cats seropositive for T. gondii, are discussed. Finally, diagnosis, treatment and prevention of feline toxoplasmosis are reviewed.

Toxoplasmosis

Toxoplasmosis in dogs and cats can cause chorioretinitis, anterior uveitis, or both. Ocular lesions are a common manifestation of generalized toxoplasmosis. The prevalence of toxoplasmosis as a cause of idiopathic anterior uveitis in cats is not clear, although there is a significant association between exposure to T. gondii and feline anterior uveitis. The pathogenesis of ocular toxoplasmosis may be different in humans and cats, and the anterior uveitis may represent a type of immune-mediated inflammation. A diagnosis is made by observing compatible clinical findings and obtaining supportive findings on serologic tests. Despite improved diagnostic techniques, including determination of IgM class antibodies and PCR testing, definitive diagnosis of ocular toxoplasmosis remains a challenge. Topical anti-inflammatory therapy should be used in cats with anterior uveitis, a positive serum titer, and no concurrent systemic signs. Systemic clindamycin should be given to cats with ocular and systemic signs and to cats with suggestive serology and idiopathic anterior uveitis that fails to respond to topical therapy alone.

Toxoplasma gondii infection induces gene expression and secretion of interleukin 1 (IL-1), IL-6, granulocyte-macrophage colony-stimulating factor, and intercellular adhesion molecule 1 by human retinal pigment epithelial cells

We have used human retinal pigment epithelial (HRPE) cultures to investigate the primary cellular responses of retinal resident cells to intracellular Toxoplasma gondii replication. At 4 days postinoculation, when all of the cells were infected, the secretion of interleukin 1beta (IL-1beta), IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF), and intercellular adhesion molecule 1 (ICAM-1) was augmented by 23-, 10-, 8-, and 5-fold, respectively, over the control. Northern and reverse transcriptase PCR analyses showed significant upregulation of steady-state levels of mRNA for IL-1beta, IL-6, GM-CSF, and ICAM-1. The secretion of these molecules by HRPE cells may play a critical immunoregulatory role in the pathophysiological processes associated with T. gondii-induced retinochoroiditis.

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.

Paradoxical effect of clindamycin in experimental, acute toxoplasmosis in cats

Cats were experimentally inoculated parenterally with the ME49 strain of Toxoplasma gondii to characterize the efficacies of two different dosages of orally administered clindamycin hydrochloride in the treatment of ocular toxoplasmosis. Concentrations of clindamycin hydrochloride at levels previously suggested to be inhibitory to T. gondii replication in vitro were achieved in the serum and aqueous humor but not in the cerebrospinal fluid. Antibiotic therapy, initiated 7 days after inoculation, resulted in no significant difference in the morphometric severity of ocular posterior segment lesions compared with that in the control groups. Treatment appeared to blunt T. gondii-specific immunoglobulin M production but had no significant effect on immunoglobulin G titers. Paradoxically, clindamycin administration was associated with increased morbidity and mortality from hepatitis and interstitial pneumonia, which are characteristic of generalized toxoplasmosis. Serum tumor necrosis factor alpha activity was detected at moderate levels in all groups of cats and correlated with the severity of clinical disease. The results of the study suggest that clindamycin, when administered at this specific time interval following inoculation, does not ameliorate ocular lesions and has a detrimental effect on the clinical course of acute, experimental toxoplasmosis in cats. The factors responsible for and the relevance of this detrimental effect to naturally occurring toxoplasmosis in humans and pet cats were not clear from the study but may relate to an antibiotic-associated decrease in the antitoxoplasmic activity of phagocytic cells responsible for the control of T. gondii.

Effect of clindamycin on intracellular replication, protein synthesis, and infectivity of Toxoplasma gondii

We studied the effects of clindamycin and a combination of clindamycin and pyrimethamine on the proliferation of Toxoplasma gondii in cultured mammalian cells and the effect of clindamycin on the parasite's RNA and protein syntheses. Infected macrophages were treated for 48 h with clindamycin or a combination of clindamycin and pyrimethamine, and the 50% inhibitory concentrations for parasite growth were 32.50 +/- 1.30 and 10.78 +/- 0.56 micrograms/ml, respectively. A modified susceptibility assay was also used to measure the effect of low concentrations of clindamycin on T. gondii. Macrophages and bovine turbinate cells were infected with low numbers of tachyzoites and were exposed to low concentrations of clindamycin for 5 days. In these systems, a concentration of 10 ng of clindamycin per ml inhibited 50% of the growth of the parasite in macrophages, while it completely prohibited the growth of the parasite in epithelial cells. When free tachyzoites were preexposed to clindamycin for 4 h, the reduction of parasite infectivity was proportional to the amount of drug; 100 ng of clindamycin per ml reduced the infectivity of T. gondii to 46.5% +/- 8.5% of that of the untreated control. A concentration of 40 micrograms of clindamycin per ml reduced protein synthesis by 56.2% +/- 6.0% but had no effect on RNA synthesis after a 4-h exposure of free tachyzoites of T. gondii to the drug. Our results show that long-term exposure to low concentrations of clindamycin reduces the level of replication of T. gondii, that clindamycin affects the protein synthesis of free parasites, and that clindamycin impairs the ability of tachyzoites to infect host cells.

Disruption of the choroidoretinal interface by toxoplasma

Toxoplasmosis is a common zoonotic infection of the retina caused by Toxoplasma gondii. The disease causes severe damage that affects the retina and subjacent choroid. Invasion of the retinal cells by the parasite leads to the major damage seen in the retina. Subsequent reactions to the invasion by toxoplasma leads to the influx of inflammatory cells. Although hypersensitivity reactions have been described to both toxoplasma and to retinal autoantigens, the major disruption of the choroidoretinal interface is probably secondary to the tissue invasion by the parasite. Patients with AIDS may show extensive necrosis of the retina in the absence of inflammatory cells. Healing of the active lesion leads to scar formation. Toxoplasma retinochoroiditis may be pigmented, nonpigmented or punched-out. Vascular anastomoses between the retina and choroid, retinal and subretinal neovascularization may occur in the aftermath of choroidoretinal interface disruption.

Current recommendations and future prospects in the treatment of toxoplasmosis

Toxoplasma infection is highly prevalent throughout the world and causes disease in diverse populations. Effective treatment regimens are available for each clinical entity of toxoplasma, but problems of incomplete clinical efficacy, drug potency, drug safety, and length of treatment remain. No well-controlled clinical trials in humans have been performed to evaluate the efficacy and safety of treatment. Primary treatment of toxoplasmosis is with the synergistic combination of pyrimethamine and sulphonamide. This is considered the treatment of choice for severe disease, disease in immunocompromised patients, and congenital toxoplasmosis. Spiramycin, a macrolide antibiotic, is frequently used alone or alternately with pyrimethamine and sulphonamide for pregnant women with the acute acquired infection to prevent congenital toxoplasmosis. Clindamycin is used frequently to treat acute flares of toxoplasmic chorioretinitis and as second-line therapy for toxoplasmic encephalitis in patients with the acquired immunodeficiency syndrome (AIDS). Inadequacies in the treatment of toxoplasmosis in immunosuppressed patients, exemplified by experience with AIDS patients, should provide the impetus for well-designed trials to find and evaluate more potent and better-tolerated agents. Classes of new drugs that have been investigated and show some promise include: (a) macrolides (roxithromycin, azithromycin); (b) folic acid antagonists (piritrexim and trimetrexate), and (c) purine analogues (arprinocid). Immunomodulators have attracted interest, and interferon-gamma alone and in combination with roxithromycin is effective in murine models. Interleukin-2 is also effective in the murine model.

Recent developments in the prevention and treatment of congenital toxoplasmosis

The manifestations of congenital toxoplasmosis vary considerably in degree, characteristics and time of onset. Options for prevention of the disease include the appropriate disposal of cat litter and the avoidance of ingestion of both contaminated food and undercooked meat by pregnant women. Immunisation of the domestic cat population is a consideration for the future. Alternatively, immunisation of sero-negative pregnant women awaits the introduction of an effective and safe reagent. Current treatment modalities are not universally effective and new drugs are the subject of active development and research. Screening of pregnant women or perhaps newborn infants are potential options but the cost effectivity has yet to be established in many countries and the results of treatment during pregnancy and early childhood are encouraging but are as yet unproven. The majority of patients with congenital toxoplasmosis eventually develop toxoplasmic retinochoroiditis. Current treatment options for this condition are outlined. Acquired immune deficiency syndrome (AIDS) may, in some cases, represent a recrudescence of congenital intracerebral infection. Current treatment strategies for this condition are discussed.

Clinical feline toxoplasmosis. Serologic diagnosis and therapeutic management of 15 cases

Clinical toxoplasmosis was diagnosed in 15 cats by correlating serologic evidence of infection and clinical signs to either response to therapy or histopathologic demonstration of the organism. Ophthalmic manifestations, primarily involving the anterior segment, were common. Other common physical examination abnormalities included muscle hyperesthesia, fever, and weight loss. Response to therapy was variable, but administration of clindamycin hydrochloride resulted in resolution of all clinical signs not involving the eyes in surviving animals. This drug, alone or in combination with corticosteroids, led to total resolution of clinical signs in four of four cats with active retinochoroiditis and in six of nine cats with anterior uveitis. Four of the 15 cats had concurrent infection with feline immunodeficiency virus (FIV). Feline leukemia virus antigen or antibodies to feline infectious peritonitis virus were not detected.

Role of clindamycin in the treatment of central nervous system toxoplasmosis

Three patients with acquired immune deficiency syndrome (AIDS), central nervous system toxoplasmosis, and hypersensitivity to sulfadiazine were given treatment with clindamycin plus pyrimethamine. All three showed improvement clinically with resolution of symptoms. Two patients had computed tomographic evidence of improvement with reduction in size or clearing of cerebral lesions and the third had resolution of chorioretinitis. Another patient who had a relapse during administration of standard therapy (pyrimethamine plus sulfadiazine) had a clinical response when clindamycin was added to this regimen. Clindamycin in combination with pyrimethamine, or as an adjunct to standard therapy, may be useful in the treatment of central nervous system toxoplasmosis in patients with AIDS.

New micromethod to study the effect of antimicrobial agents on Toxoplasma gondii: comparison of sulfadoxine and sulfadiazine individually and in combination with pyrimethamine and study of clindamycin, metronidazole, and cyclosporin A

An in vitro method by which reagents, cells, and Toxoplasma gondii trophozoites are conserved (micromethod) was developed to quantitate the effect of antimicrobial agents on T. gondii. Sulfadoxine alone had no effect on T. gondii in vitro when evaluated with a macromethod, the new micromethod, or visual inspection of Giemsa-stained preparations. Sulfadoxine combined with pyrimethamine inhibited T. gondii more than did pyrimethamine alone, but the combination of sulfadoxine plus pyrimethamine was slightly less active than was the combination of sulfadiazine plus pyrimethamine. Neither clindamycin nor metronidazole, alone or in combination with sulfadiazine or pyrimethamine and sulfadiazine, had any effect on intracellular T. gondii. Brief exposure (10 min before and during challenge) to clindamycin had no effect on extracellular T. gondii when clindamycin was studied alone or with sulfadiazine or pyrimethamine plus sulfadiazine. Cyclosporin A inhibited T. gondii replication at concentrations of ca. greater than or equal to 2 micrograms/ml.

[Treatment of toxoplasmic chorioretinitis with clindamycin hydrochloride]

Com o cloridrato de clindamicina, foram tratados 18 pacientes com retinocoroidite toxoplasmótica. Houve adoção da conduta escolhida em uma ou duas crises de cada doente e ficou patente a capacidade do antibiótico, administrado pela via oral, no sentido de controlar o processo e de promover cicatrização. A tolerância ao medicamento pôde ser considerada satisfatória e, por vezes, recaídas sucederam, mas afigurou-se concreta a possibilidade de incorporar o remédio em apreço ao conjunto de antiparasitários indicados para combater o referido comprometimento ocular devido ao Toxoplasma gondii.

Clindamycin in the treatment of toxoplasmic retinochoroiditis

We treated 26 patients with acute toxoplasmic retinochoroiditis with clindamycin between 1974 and 1982. Four patients were treated with clindamycin alone and 17 with clindamycin and prednisolone. Five patients received clindamycin and prednisolone, sulfadiazine, pyrimethamine, or cryocoagulation, or a combination of these. All patients with the acute disease had the characteristic foci and a positive titer on the Sabin-Feldman dye test of at least 1:16. Other causes of retinochoroiditis were excluded. All but two patients, who developed diarrhea after two weeks, received clindamycin for a minimum of three weeks. All patients improved after two weeks of treatment, but two patients with lesions larger than 2 disk diameters required an additional six weeks of treatment to heal completely. During follow-up periods ranging from 18 months to seven years (mean, three years) there have been only two recurrences (7.7%). Complications with clindamycin treatment were limited to gastrointestinal upsets, diarrhea, and skin rash. There were no cases of pseudomembranous colitis, the most serious reported complication of clindamycin use.

Minocycline in experimental ocular toxoplasmosis in the rabbit

We studied the effects of minocycline, a semisynthetic tetracycline, on experimentally induced toxoplasmic retinochoroiditis in the rabbit. In two experiments we found that this drug effectively ameliorated the clinical disease and sterilized the ocular tissues from Toxoplasma organisms. Minocycline prevented death from toxoplasmic encephalitis in 75% of the animals, whereas all the control animals died of toxoplasmic encephalitis. Minocycline appears to be a promising agent for ocular toxoplasmosis.

Treatment of ocular toxoplasmosis with clindamycin and sulfadiazine

Seventeen patients with active toxoplasmic retinochoroiditis were treated for four weeks, seven with clindamycin alone and ten with a combination of clindamycin and sulfadiazine. The follow-up period ranged from six months to four years. Results of the Sabin-Feldman dye test were positive in all patients. Five of the seven patients treated with clindamycin alone showed improvement two weeks after treatment was begun, while eight of the ten patients treated with combined clindamycin and sulfadiazine showed both subjective and objective improvement within ten days and signs of healing within three weeks. Since clindamycin and sulfadiazine operate on unrelated metabolic pathways of Toxoplasma, they may act synergistically. A regimen consisting of this combination may be appropriate for the treatment of ocular toxoplasmosis.

Direct immunofluorescence in the diagnosis of toxoplasmic lymphadenitis

The diagnosis of toxoplasmic lymphadenitis was established through the demonstration, by direct immunofluorescence, of toxoplasma cysts and trophozoites in a cervical lymph node biopsy which also had a characteristic histopathology. The patient had cervical lymphadenopathy and increased specific fluorescent antitoxoplasma IgG and IgM antibodies.

Effect of immunization with attenuated Mycobacterium bovis on experimental toxoplasmic retinochoroiditis

Administration of attenuated Mycobacterium bovis (Bacillus Calmette-Guérin or BCG) provides nonspecific resistance to a variety of microbial infections and tumors. This is associated with a state of augmented immunologic responsiveness. Mustering defenses against intracellular parasites, such as Toxoplasma gondii, presents a special problem that can be met only by measures that alter the intracellular environment. Our study was designed to evaluate the effect of prior immunization of rabbits with BCG on experimental toxoplasmic retinochoroiditis. One group of rabbits was immunized by the intravenous administration of BCG, another group by the retrobulbar injection of BCG, and a third group, unvaccinated, served as a control. Intravenous immunization provided significant protection against Toxoplasma organisms injected into the suprachoroidal space. In the immunized rabbits, the onset of Toxoplasma retinochoroiditis was delayed and the severity of the disease reduced. Although Toxoplasma was isolated from the chorioretinal tissues of both BCG-immunized and control rabbits, Toxoplasma antibody was not (with one exception) detected in the sera of BCG-immunized rabbits. While vaccination by the retrobulbar route produced little or no effect, intravenous administration of BCG provided nonspecific resistance to Toxoplasma retinochoroiditis in rabbits.