Nitric oxide production increases during Toxoplasma gondii encephalitis in mice

Understanding the mechanisms underlying the disruption of the blood-brain barrier in parasitic infections

Parasites have a significant impact on the neurological, cognitive, and mental well-being of humans, with a global population of over 1 billion individuals affected. The pathogenesis of central nervous system (CNS) injury in parasitic diseases remains limited, and prevention and control of parasitic CNS infections remain significant areas of research. Parasites, encompassing both unicellular and multicellular organisms, have intricate life cycles and possess the ability to infect a diverse range of hosts, including the human population. Parasitic illnesses that impact the central and peripheral nervous systems are a significant contributor to morbidity and mortality in low- to middle-income nations. The precise pathways through which neurotropic parasites infiltrate the CNS by crossing the blood-brain barrier (BBB) and cause neurological harm remain incompletely understood. Investigating brain infections caused by parasites is closely linked to studying neuroinflammation and cerebral impairment. The exact molecular and cellular mechanisms involved in this process remain incomplete, but understanding the exact mechanisms could provide insight into their pathogenesis and potentially reveal novel therapeutic targets. This review paper explores the underlying mechanisms involved in the development of neurological disorders caused by parasites, including parasite-derived elements, host immune responses, and modifications in tight junctions (TJs) proteins.

Type-1 diabetes mellitus down-regulated local cerebral glial fibrillary acidic protein expression in experimental toxoplasmosis

Cerebral toxoplasmosis is an opportunistic infection, occurring mostly in immunosuppressed patients due to the reactivation of latent Toxoplasma cysts. The cerebral comorbidity in diabetic patients tends to intensify the burden of pathogenic infection within the brain. The aim of this work was to study the effect of cerebral toxoplasmosis in experimentally infected hyperglycemic mice, on histopathology and glial fibrillary acidic protein (GFAP) expression, compared to normoglycemic mice at different time intervals. Vasculopathy was exclusively observed in diabetic groups, with features of increased severity during Toxoplasma infection. Gliosis was observed in diabetic groups, while hyperactive astroglial activity was detected in normoglycemic groups, especially at 6 weeks of infection. GFAP expression showed significant up-regulation in normoglycemic mice at 6 weeks of infection (40.03 ± 1.41) afterwards, it decreased to 22.22 ± 3.14 at 12 weeks which was statistically insignificant to the normal level, possibly indicating the successful Toxoplasma stage transformation (to bradyzoite), thereby limiting the infection within the brain. In hyperglycemic infected groups, GFAP was significantly down-regulated, in both acute and chronic phases of infection, most likely indicating failure of stage transformation and infection limitation. This may expose those vulnerable groups to the risk of dissemination, resulting in life-threatening diffuse encephalitis. The current study emphasized the importance of rapid diagnosis of Toxoplasma infection in diabetic subjects, and highlighted the value of using GFAP as a neurological indicator of disease progression in those comorbid cases.

Histopathological, Immunohistochemical and Biochemical Studies of Murine Hepatosplenic Tissues Affected by Chronic Toxoplasmosis

Toxoplasmosis is a serious health problem in humans and animals resulting from obligatory intracellular invasion of reticuloendothelial tissue by Toxoplasma gondii. The profound pathologic effect of toxoplasmosis is confined to nervous tissue, but many other organs, including the liver and spleen, are insulted. Many molecules like caspase-3, CD3, and CD138 are implicated in the tissue immune response in a trial to alleviate hazardous toxoplasmosis impact. This study aimed to investigate the effect of chronic toxoplasmosis on the liver and spleen tissues of mice using biochemical and histopathological techniques and to detect the activity and level of expression of caspase-3, CD3, and CD138 in these tissues using immunohistochemical labeling. Compared with normal control, altered normal histological features accompanied by inflammatory reaction were recorded in hepatosplenic reticuloendothelial tissues in chronically infected mice. The biochemical profile of the liver has been changed in the form of increased liver enzymes, and oxidative stress has been evidenced by elevated nitric oxide (NO) concentration in liver homogenate. The levels of caspase3, CD3, and CD138 were markedly expressed in the liver and spleen of infected mice. Our findings revealed the persistent effect of latent toxoplasmosis on the host's histological architecture, metabolic, and immunological profile, creating a continued challenging host-parasite relationship.

Toxoplasmosis: Targeting neurotransmitter systems in psychiatric disorders

The most common form of the disease caused by Toxoplasma gondii (T. gondii) is latent toxoplasmosis due to the formation of tissue cysts in various organs, such as the brain. Latent toxoplasmosis is probably a risk factor in the development of some neuropsychiatric disorders. Behavioral changes after infection are caused by the host immune response, manipulation by the parasite, central nervous system (CNS) inflammation, as well as changes in hormonal and neuromodulator relationships. The present review focused on the exact mechanisms of T. gondii effect on the alteration of behavior and neurotransmitter levels, their catabolites and metabolites, as well as the interaction between immune responses and this parasite in the etiopathogenesis of psychiatric disorders. The dysfunction of neurotransmitters in the neural transmission is associated with several neuropsychiatric disorders. However, further intensive studies are required to determine the effect of this parasite on altering the level of neurotransmitters and the role of neurotransmitters in the etiology of host behavioral changes.

Effect of spiramycin versus aminoguanidine and their combined use in experimental toxoplasmosis

Toxoplasmosis is one of the widest spread parasitic infections which is caused by Toxoplasma gondii protozoon. Many experimental studies have evaluated the effect of aminoguanidine upon parasitic load and inflammatory process. However, few reports have illustrated the impact of combining aminoguanidine with spiramycin in the treatment of toxoplasmosis. Therefore, our study aimed to explore the possible effects of spiramycin used alone and combined with aminoguanidine against the avirulent (ME49) Toxoplasma gondii strain in experimental toxoplasmosis. Fifty-five Swiss albino mice were included in the study and were divided into five groups: (GI): non-infected control group; (GII): infected untreated control group; (GIII): infected- spiramycin treated group; (GIV): infected-aminoguanidine treated group; (GV): infected and received combination of spiramycin and aminoguanidine. Obtained results exhibited a significant increase in brain cysts numbers in aminoguanidine treated groups compared to infected untreated control groups. Histopathological studies denoted that combination between spiramycin and aminoguanidine improved the pathological features only in liver and heart tissues of the studied groups. Moreover, it was noticed that spiramycin administered alone had no effect on nitric oxide expression, whereas its combination with aminoguanidine had an inhibitory effect on inducible nitric oxide synthase enzyme in brain, liver and heart tissues of different study groups. In conclusion, the combination of spiramycin and aminoguanidine significantly reduced the parasitic burden, yet, it failed to resolve the pathological sequels in brain tissues of Toxoplasma gondii infected mice.

Neurological and Neurobehavioral Disorders Associated with Toxoplasma gondii Infection in Humans

The intracellular parasite Toxoplasma gondii is estimated to infect up to 30% of the world population, leading to lifelong chronic infection of the brain and muscle tissue. Although most latent T. gondii infections in humans have traditionally been considered asymptomatic, studies in rodents suggest phenotypic neurological changes are possible. Consequently, several studies have examined the link between T. gondii infection and diseases such as schizophrenia, epilepsy, depression, bipolar disorder, dysphoria, Alzheimer's disease, Parkinson's disease, and obsessive-compulsive disorder (OCD). To date, there is varying evidence of the relationship of T. gondii to these human neurological or neurobehavioral disorders. A thorough review of T. gondii literature was conducted to highlight and summarize current findings. We found that schizophrenia was most frequently linked to T. gondii infection, while sleep disruption showed no linkage to T. gondii infection, and other conditions having mixed support for a link to T. gondii. However, infection as a cause of human neurobehavioral disease has yet to be firmly established.

Substrate-mediated regulation of the arginine transporter of Toxoplasma gondii

Intracellular parasites, such as the apicomplexan Toxoplasma gondii, are adept at scavenging nutrients from their host. However, there is little understanding of how parasites sense and respond to the changing nutrient environments they encounter during an infection. TgApiAT1, a member of the apicomplexan ApiAT family of amino acid transporters, is the major uptake route for the essential amino acid L-arginine (Arg) in T. gondii. Here, we show that the abundance of TgApiAT1, and hence the rate of uptake of Arg, is regulated by the availability of Arg in the parasite's external environment, increasing in response to decreased [Arg]. Using a luciferase-based 'biosensor' strain of T. gondii, we demonstrate that the expression of TgApiAT1 varies between different organs within the host, indicating that parasites are able to modulate TgApiAT1-dependent uptake of Arg as they encounter different nutrient environments in vivo. Finally, we show that Arg-dependent regulation of TgApiAT1 expression is post-transcriptional, mediated by an upstream open reading frame (uORF) in the TgApiAT1 transcript, and we provide evidence that the peptide encoded by this uORF is critical for mediating regulation. Together, our data reveal the mechanism by which an apicomplexan parasite responds to changes in the availability of a key nutrient.

P18 (SRS35/TgSAG4) Plays a Role in the Invasion and Virulence of Toxoplasma gondii

Toxoplasmosis is a prevalent parasitic disease caused by Toxoplasma gondii (T. gondii). Under the control of the host immune system, T. gondii persists as latent bradyzoite cysts. Immunosuppression leads to their reactivation, a potentially life-threatening condition. Interferon-gamma (IFN-γ) controls the different stages of toxoplasmosis. Here, we addressed the role of the parasite surface antigen P18, belonging to the Surface-Antigen 1 (SAG-1) Related Sequence (SRS) family, in a cyst-forming strain. Deletion of P18 gene (KO P18) impaired the invasion of parasites in macrophages and IFN-γ-mediated activation of macrophages further reduced the invasion capacity of this KO, as compared to WT strain. Mice infected by KO P18, showed a marked decrease in virulence during acute toxoplasmosis. This was consequent to less parasitemia, accompanied by a substantial recruitment of dendritic cells, macrophages and natural killer cells (NK). Furthermore, KO P18 resulted in a higher number of bradyzoite cysts, and a stronger inflammatory response. A prolonged survival of mice was observed upon immunosuppression of KO P18 infected BALB/c mice or upon oral infection of Severe Combined Immunodeficiency (SCID) mice, with intact macrophages and natural killer (NK) cells. In stark contrast, oral infection of NSG (NOD/Shi-scid/IL-2Rγnull) mice, defective in macrophages and NK cells, with KO P18, was as lethal as that of the control strain showing that the conversion from bradyzoites to tachyzoites is intact and, suggesting a role of P18 in the response to host IFN-γ. Collectively, these data demonstrate a role for P18 surface antigen in the invasion of macrophages and in the virulence of the parasite, during acute and chronic toxoplasmosis.

Oxidative Stress as a Possible Target in the Treatment of Toxoplasmosis: Perspectives and Ambiguities

Toxoplasma gondii is an apicomplexan parasite causing toxoplasmosis, a common disease, which is most typically asymptomatic. However, toxoplasmosis can be severe and even fatal in immunocompromised patients and fetuses. Available treatment options are limited, so there is a strong impetus to develop novel therapeutics. This review focuses on the role of oxidative stress in the pathophysiology and treatment of T. gondii infection. Chemical compounds that modify redox status can reduce the parasite viability and thus be potential anti-Toxoplasma drugs. On the other hand, oxidative stress caused by the activation of the inflammatory response may have some deleterious consequences in host cells. In this respect, the potential use of natural antioxidants is worth considering, including melatonin and some vitamins, as possible novel anti-Toxoplasma therapeutics. Results of in vitro and animal studies are promising. However, supplementation with some antioxidants was found to promote the increase in parasitemia, and the disease was then characterized by a milder course. Undoubtedly, research in this area may have a significant impact on the future prospects of toxoplasmosis therapy.

Histone deacetylase SIR2 in Toxoplasma gondii modulates functions of murine macrophages in vitro and protects mice against acute toxoplasmosis in vivo

Silent information regulator 2 (SIR2) in histone deacetylase (HDAC) is particularly conserved and widely expressed in all eukaryotic cells. HDAC is a crucial post-translational modification protein regulating gene expression. In the present study, a Toxoplasma gondii (T. gondii) silent information regulator 2 (TgSIR2) gene in HDAC was cloned and the modulation effects of recombinant TgSIR2 (rTgSIR2) on murine Ana-1 macrophages were characterized in vitro. The results indicated that rTgSIR2 had a good capacity to eliminate T. gondii by promoting proliferation, apoptosis, and phagocytosis, and modulating the secretion of nitric oxide (NO), pro-inflammatory cytokines, and anti-inflammatory cytokines. In in vivo experiments, animals were immunized with recombinant TgSIR2, followed by a lethal dose of T. gondii RH strain challenge 14 days after the second immunization. As compared to the blank and control group, the animals immunized with rTgSIR2 could generate specific humoral responses, as demonstrated by the significantly high titers of total IgG and subclasses IgG1 and IgG2a. Significant increases of IFN-γ, IL-4, and IL-10 were seen, while no significant changes were detected in IL-17. The percentage of CD4⁺ and CD8⁺ T lymphocytes in animals immunized with rTgSIR2 significantly increased. A significantly long survival time was also observed in animals vaccinated with rTgSIR2 14 days after the last immunization. All these results clearly indicate that rTgSIR2 played an essential role in modulating host macrophages and offered the potential to develop a therapeutic strategy against T. gondii.

Facilitation of molecular motion to develop turn-on photoacoustic bioprobe for detecting nitric oxide in encephalitis

Nitric oxide (NO) is an important signaling molecule overexpressed in many diseases, thus the development of NO-activatable probes is of vital significance for monitoring related diseases. However, sensitive photoacoustic (PA) probes for detecting NO-associated complicated diseases (e.g., encephalitis), have yet to be developed. Herein, we report a NO-activated PA probe for in vivo detection of encephalitis by tuning the molecular geometry and energy transformation processes. A strong donor-acceptor structure with increased conjugation can be obtained after NO treatment, along with the active intramolecular motion, significantly boosting "turn-on" near-infrared PA property. The molecular probe exhibits high specificity and sensitivity towards NO over interfering reactive species. The probe is capable of detecting and differentiating encephalitis in different severities with high spatiotemporal resolution. This work will inspire more insights into the development of high-performing activatable PA probes for advanced diagnosis by making full use of intramolecular motion and energy transformation processes.

Role of Melatonin in the Synchronization of Asexual Forms in the Parasite Plasmodium falciparum

The indoleamine compound melatonin has been extensively studied in the regulation of the circadian rhythm in nearly all vertebrates. The effects of melatonin have also been studied in Protozoan parasites, especially in the synchronization of the human malaria parasite Plasmodium falciparum via a complex downstream signalling pathway. Melatonin activates protein kinase A (PfPKA) and requires the activation of protein kinase 7 (PfPK7), PLC-IP₃, and a subset of genes from the ubiquitin-proteasome system. In other parasites, such as Trypanosoma cruzi and Toxoplasma gondii, melatonin increases inflammatory components, thus amplifying the protective response of the host’s immune system and affecting parasite load. The development of melatonin-related indole compounds exhibiting antiparasitic properties clearly suggests this new and effective approach as an alternative treatment. Therefore, it is critical to understand how melatonin confers stimulatory functions in host–parasite biology.

Disruption of the Blood-Brain Barrier During Neuroinflammatory and Neuroinfectious Diseases

As the organ of highest metabolic demand, utilizing over 25% of total body glucose utilization via an enormous vasculature with one capillary every 73 μm, the brain evolves a barrier at the capillary and postcapillary venules to prevent toxicity during serum fluctuations in metabolites and hormones, to limit brain swelling during inflammation, and to prevent pathogen invasion. Understanding of neuroprotective barriers has since evolved to incorporate the neurovascular unit (NVU), the blood-cerebrospinal fluid (CSF) barrier, and the presence of CNS lymphatics that allow leukocyte egress. Identification of the cellular and molecular participants in BBB function at the NVU has allowed detailed analyses of mechanisms that contribute to BBB dysfunction in various disease states, which include both autoimmune and infectious etiologies. This chapter will introduce some of the cellular and molecular components that promote barrier function but may be manipulated by inflammatory mediators or pathogens during neuroinflammation or neuroinfectious diseases.

Toxoplasma gondii Modulates the Host Cell Responses: An Overview of Apoptosis Pathways

Infection with Toxoplasma gondii has a major implication in public health. Toxoplasma gondii is an obligate intracellular protozoan parasite that can infect all nucleated cells belonging to a wide range of host species. One of the particularities of this parasite is its invasion and persistence in host cells of immunocompetent people. This infection is usually asymptomatic. In immunocompromised patients, the infection is severe and symptomatic. The mechanisms by which T. gondii persists are poorly studied in humans. In mouse models, many aspects of the interaction between the parasite and the host cells are being studied. Apoptosis is one of these mechanisms that could be modulated by Toxoplasma to persist in host cells. Indeed, Toxoplasma has often been implicated in the regulation of apoptosis and viability mechanisms in both human and murine infection models. Several of these studies centered on the regulation of apoptosis pathways have revealed interference of this parasite with host cell immunity, cell signalling, and invasion mechanisms. This review provides an overview of recent studies concerning the effect of Toxoplasma on different apoptotic pathways in infected host cells.

IDO, COX and iNOS have an important role in the proliferation of Neospora caninum in neuron/glia co-cultures

Central nervous system (CNS) is the main site for encystment of Neospora caninum in different animal species. In this tissue, glial cells (astrocytes and microglia) modulate responses to aggression in order to preserve homeostasis and neuronal function. Previous data showed that when primary cultures of glial cells are infected with N. caninum, they develop gliosis and the immune response is characterized by the release of TNF and IL-10, followed by the control of parasite proliferation. In order to elucidate this control, three enzymatic systems involved in parasite-versus-host interactions were observed on a model of neuron/glia co/cultures obtained from rat brains. Indoleamine 2,3-dioxygenase (IDO), induced nitric oxide synthase (iNOS) responsible for the catabolism of tryptophan and arginine, respectively, and cycloxigenase (COX) were studied comparing their modulation by respective inhibitors with the number of tachyzoites or the immune response measured by the release of IL-10 and TNF. Cells were treated with the inhibitors of iNOS (1.5 mM L-NAME), IDO (1 mM 1-methyl tryptophan), COX-1 (1 μM indomethacin) and COX-2 (1 μM nimesulide) before infection with tachyzoites of N. caninum (1:1 cell: parasite). After 72 h of infection, immunocytochemistry showed astrogliosis and a significant increase in the number and length of neurites, compared with uninfected co-cultures, while an increase of IL-10 and TNF was verified. N. caninum did not change iNOS activity, but the inhibition of the basal levels of this enzyme stimulated parasite proliferation. Additionally, a significant increase of about 40% was verified in the IDO activity, whose inhibition caused 1.2-fold increase in parasitic growth. For COX-2 activity, infection of cultures stimulated a significant increase in release of PGE₂ and its inhibition by nimesulide allowed the parasitic growth. These data indicate that iNOS, IDO and COX-2 control the proliferation of N. caninum in this in vitro model. On the other hand, the release of IL-10 by glia besides modulating the inflammation also allow the continuity of parasitism.

Toxoplasmosis: A pathway to neuropsychiatric disorders

Toxoplasma gondii is an obligate intracellular parasite that resides, in a latent form, in the human central nervous system. Infection with Toxoplasma drastically alters the behaviour of rodents and is associated with the incidence of specific neuropsychiatric conditions in humans. But the question remains: how does this pervasive human pathogen alter behaviour of the mammalian host? This fundamental question is receiving increasing attention as it has far reaching public health implications for a parasite that is very common in human populations. Our current understanding centres on neuronal changes that are elicited directly by this intracellular parasite versus indirect changes that occur due to activation of the immune system within the CNS, or a combination of both. In this review, we explore the interactions between Toxoplasma and its host, the proposed mechanisms and consequences on neuronal function and mental health, and discuss Toxoplasma infection as a public health issue.

Could Araucaria heterophylla resin extract be used as a new treatment for toxoplasmosis?

Toxoplasmosis is a worldwide parasitic disease responsible for serious health problems to human. The currently available drugs used for toxoplasmosis treatment showed a limited efficacy and cause serious host toxicity. The in vitro screening for toxoplasmicidal activity of Araucaria heterophylla resin (AHR) extract and its major component 13-epi-cupressic acid (CUP) showed that both AHR (EC₅₀ = 3.90) and CUP (EC₅₀ = 3.69) have high toxoplasmicidal activity in comparison with standard cotrimoxazole (EC₅₀ = 4.28). The antiprotozoal effects of AHR and CUP were investigated against acute and chronic toxoplasmosis using mice models. Two groups of Swiss albino mice were infected by RH Toxoplasma strain intraperitoneally and by Me49 strain orally. Both groups were treated with AHR and CUP in different doses. Their effects were evaluated by survival rate, peritoneal, spleen and liver parasite burdens, brain cyst burden, NO serum level and histopathological lesions. The ultrastructural changes of tachyzoites of acutely infected mice were studied using scanning electron microscopy (SEM). There is an evidence of toxoplasmicidal activity of AHR and CUP in acute and chronic experimental toxoplasmosis. In the acute model, mice treated with AHR and CUP showed prolonged survival rates, a significant decrease in the parasite density in peritoneal lavage and pathological insult in both liver and spleen compared with that of untreated ones. SEM results denote evident morphological alterations of treated tachyzoites. In chronic experimental toxoplasmosis, AHR and CUP treated groups could significantly reduce brain cyst burden by 96.05% and 98.02% respectively. This study indicates that AHR and CUP showed potent toxoplasmicidal activities experimentally and could be used as a potential natural nontoxic agent for treatment of toxoplasmosis.

The Neurotropic Parasite Toxoplasma gondii Induces Sustained Neuroinflammation with Microvascular Dysfunction in Infected Mice

Toxoplasmosis is one of the leading parasitic diseases worldwide. Some data suggest that chronic acquired toxoplasmosis could be linked to behavioral alterations in humans. The parasite infects neurons, forming immunologically silent cysts. Cerebral microcirculation homeostasis is determinant to brain functions, and pathologic states can alter capillarity or blood perfusion, leading to neurodegeneration and cognitive deficits. Albino mice were infected with Toxoplasma gondii (ME49 strain) and analyzed after 10, 40, and 180 days. Infected mice presented decreased cerebral blood flow at 10 and 40 days post infection (dpi), which were restored at 180 dpi, as shown by laser speckle contrast imaging. Intravital microscopy demonstrated that infection led to significant capillary rarefaction, accompanied by neuroinflammation, with microglial activation and increased numbers of rolling and adherent leukocytes to the wall of cerebral capillaries. Acetylcholine-induced vasodilation was altered at all time points, and blood brain barrier permeability was evident in infected animals at 40 dpi. Infection reduced angiogenesis, with a decreased number of isolectin B4-stained blood vessels and a decrease in length and branching of laminin-stained capillaries. Sulfadiazine reduced parasite load and partially repaired microvascular damages. We conclude that T. gondii latent infection causes a harmful insult in the brain, promoting neuroinflammation and microcirculatory dysfunction in the brain, with decreased angiogenesis and can contribute to a neurodegenerative process.

The Investigation of the Cox-2 Selective Inhibitor Parecoxib Effects in Spinal Cord Injury in Rat

Aim: Today, spinal cord injury (SCI) can be rehabilitated but cannot be treated adequately. This experimental study was conducted to investigate possible beneficial effects of methylprednisolone and parecoxib in treatment of SCI. Materials and methods: Forty-eight male Wistar albino rats were assigned into CONTROL, acute (MP-A, PX-A, and PXMP-A), and subacute (MP-S, PX-S, and PXMP-S) stage groups. Then, to induce SCI, a temporary aneurysm clip was applied to the spinal cord following T7-8 laminectomy, except in the CONTROL group. Four hours later parecoxib, methylprednisolone, or their combination was administered to rats intraperitoneally except CONTROL, SHAM-A, and SHAM-S groups. Rats in the acute stage group were sacrificed 72 h later, and whereas rats in the subacute stage were sacrificed 7 days later for histopathological and biochemical investigation and for gene-expression analyses. Results: Parecoxib and methylprednisolone and their combination could not improve histopathological grades in any stage. They also could not decrease malondialdehyde or caspase-3, myeloperoxidase levels in any stage. Parecoxib and methylprednisolone could decrease the TNF-α gene expression in subacute stage. Methylprednisolone could increase TGF-1β gene-expression level in acute stage. Conclusion: Neither of the experimental drugs, either alone or in combination, did not show any beneficial effects in SCI model in rats.

Immunocompetent host develops mild intestinal inflammation in acute infection with Toxoplasma gondii

Toxoplasma gondii (T. gondii) is the causative agent of toxoplasmosis, common zoonosis among vertebrates and high incidence worldwide. During the infection, the parasite needs to transpose the intestinal barrier to spread throughout the body, which may be a trigger for an inflammatory reaction. This work evaluated the inflammatory alterations of early T. gondii infection in peripheral blood cells, in the mesenteric microcirculation, and small intestinal tissue by measurement of MPO (myeloperoxidase) activity and NO (nitric oxide) level in rats. Animals were randomly assigned into control group (CG) that received saline orally and groups infected with 5,000 oocysts for 6 (G6), 12 (G12), 24 (G24), 48 (G48) and 72 hours (G72). Blood samples were collected for total and differential leukocyte count. Intravital microscopy was performed in the mesentery to evaluate rolling and adhesion of leukocytes. After euthanasia, 0.5cm of the duodenum, jejunum and ileum were collected for the determination of MPO activity, NO level and PCR to identify the parasite DNA and also the mesentery were collected to perform immunohistochemistry on frozen sections to quantify adhesion molecules ICAM-1, PECAM-1 and P-Selectin. The parasite DNA was identified in all infected groups and there was an increase in leukocytes in the peripheral blood and in expression of ICAM-1 and PECAM-1 in G6 and G12, however, the expression of P-selectin was reduced in G12. Leukocytes are in rolling process during the first 12 hours and they are adhered at 24 hours post-infection. The activity of MPO increased in the duodenum at 12 hours, and NO increased in the jejunum in G72 and ileum in G24, G48 and G72. Our study demonstrated that T. gondii initiates the infection precociously (at 6 hours) leading to a systemic activation of innate immune response resulting in mild inflammation in a less susceptible experimental model.

First description of enhanced expression of glia maturation factor-beta in experimental toxoplasmic encephalitis

Objective We previously showed that Toxoplasma gondii infection induces severe neuropathology in the form of oxidative stress, high nitric oxide production, glial activation, and apoptosis. This study examined the association between glia maturation factor-beta (GMF-β) expression, activated astrocytes/microglia, and neuropathology in toxoplasmic encephalitis (TE). Methods Mouse brain GMF expression was examined by immunohistochemistry on days 10 and 30 post- T. gondii infection. Results Neuropathology of infected mice was associated with increased GMF expression in reactive glial cells and neurons compared with healthy controls. Specific up-regulation of GMF-β expression in glial cells was associated with increased gliosis in TE. Conclusions GMF up-regulation in glial cells causes neuronal destruction, suggesting a TE pathological pathway involving GMF-mediated brain cell cytotoxicity. GMF-β may therefore be a good biomarker for disease risk assessment and to estimate host neuropathy after exposure to T. gondii, as well as providing a new therapeutic target. This is the first study to demonstrate the expression of GMF-β in reactive glial cells and its association with neuropathology in TE.

The potential use of melatonin to treat protozoan parasitic infections: A review

Melatonin (N-acetyl-5-methoxytryptamine) is a circadian hormone produced in vertebrates by the pineal gland and other organs. Melatonin is believed to influence immune cells leading to modulation of the proliferative response of stimulated lymphocytes as well as cytokine production. Due to the antioxidant and immunomodulatory effects of melatonin, it is suggested that this molecule could be a therapeutic alternative agent to fight bacterial, viral, and parasitic infections by a variety of mechanisms. Herein, we review the effects of melatonin on the cell biology of protozoan parasites and host's immune response. In toxoplasmosis, African trypanosomiasis and Chagas' disease, melatonin enhances host's immune response against the parasite via regulating the secretion of inflammatory mediators. In amoebiasis, melatonin reduces the amoebic lesions as well as increasing the leukophagocytosis and the number of dead amoebae. In giardiasis, serum melatonin levels are elevated in these patients; this suggests a positive correlation between the level of melatonin and phagocytic activity in the G. duodenalis infected patients, possibly related to melatonin's immunomodulatory effect. In leishmaniasis, melatonin arrests parasite replication accompanied by releasing mitochondrial Ca²⁺ into the cytosol, increasing the level of mitochondrial nitrites as well as reducing superoxide dismutase (SOD) activity. In malaria, melatonin synchronizes the Plasmodium cell cycle via modulating cAMP-PKA and IP3-Ca²⁺ pathways. Thus, simultaneous administration of melatonin agonists or giving pharmacological doses of melatonin may be considered a novel approach for treatment of malarial infection.

Toxoplasmosis accelerates acquisition of epilepsy in rats undergoing chemical kindling

Epilepsy is one of the most common neurologic disorders worldwide with no distinguishable cause in 60% of patients. One-third of the world population has been infected with Toxoplasma gondii. This intracellular parasite has high tropism for excitable cells including neurons. We assessed impact of acute and chronic T. gondii infection on epileptogenesis in pentylenetetrazole (PTZ) kindling model in male rats. T. gondii cysts were administered to rats by intraperitoneal (i.p.) injection. The presence of T. gondii cysts in the brain of rats was verified by hematoxylin-eosin staining. One and eight weeks after cysts injection, as acute and chronic phases of infection, PTZ (30mg/kg, i.p.) was injected to the rats every other day until manifestation of generalized seizures. Histologic findings confirmed cerebral toxoplasmosis in rats. The rats with acute or chronic Toxoplasma infection became kindled by lower number of PTZ injections (14.8±1 and 13.6±1 injections, respectively) compared to corresponding uninfected rats (18.7±1 and 16.9±1 injections, p<0.05). Toxoplasma infection increased the rate of kindling in rats. The chronically-infected rats achieved focal and also generalized seizures earlier than the rats with acute infection. Toxoplasmosis might be considered as a risk factor for acquisition of epilepsy.

Seroepidemiological study of Toxoplasma gondii infection in a population of Iranian epileptic patients

Epilepsy is one of the most common neurologic disorders. Underlying cause of epilepsy is unknown in 60 % of the patients. Toxoplasma gondii is an intracellular parasite which is capable of forming tissue cysts in brain of chronically infected hosts including humans. Some epidemiological studies suggested an association between toxoplasmosis and acquisition of epilepsy. In this study we determined seroprevalence of latent Toxoplasma infection in a population of Iranian epileptic patients. Participants were classified in three groups as Iranian epileptic patients (IEP, n = 414), non-epileptic patients who had other neurologic disorders (NEP, n = 150), and healthy people without any neurologic disorders (HP, n = 63). The presence of anti-Toxoplasma IgG antibodies and IgG titer in the sera were determined by ELISA method. Anti-T. gondii IgG seroprevalence obtained 35.3 %, 34.7 % and 38.1 % in IEP, NEP and HP, respectively. The seroprevalence rate was not significantly different among the three groups (P = 0.88). Anti-T. gondii IgG titer was 55.7 ± 78, 52.4 ± 74 and 69.7 ± 92 IU/ml in IEP, NEP and HP, respectively. There was not any statistically significant difference in the antibody titer between the study groups (P = 0.32). The rate of T. gondii infection in epileptic patients was not higher than non-epileptic patients and healthy people in the Iranian population.

Contribution of dopamine neurotransmission in proconvulsant effect of Toxoplasma gondii infection in male mice

Epilepsy is one of the most common neurologic disorders worldwide with no distinguishable cause in 60% of patients. One-third of world's population is infected with Toxoplasma gondii (T. gondii). This intracellular parasite has high tendency to excitable cells including neurons. We assessed seizure susceptibility and involvement of dopaminergic system in male mice with acute and chronic T. gondii infection. Mice were infected by intraperitoneal injection of T. gondii cysts. Acute and chronic stages of infection were determined by quantification of SAG1/BAG1 transcripts and level of repetitive REP-529 sequence in the brain of mice by real-time PCR. Threshold of clonic seizures was measured by tail vein infusion of pentylenetetrazole. The infected mice were pretreated with D1 and D2 dopamine receptor antagonists, and seizure threshold was measured. Moreover, seizure threshold was determined after treatment of toxoplasmosis by sulfamethoxazole and trimethoprim. SAG1 level reached the maximum at week 2 after infection and then declined. The maximum level of BAG1 was observed at the week 3 and preserved till the week 8. REP-529 was detected at first week after infection, reached maximum at the week 3 and kept at this level till the eighth week. Threshold of seizures significantly decreased in both acute and chronic phases of infection. D1 and D2 receptors antagonists inhibited proconvulsant effect of toxoplasmosis. Chemotherapy inhibited parasite growth and multiplication, and returned seizure susceptibility to the level of non-infected mice. Dopaminergic neurotransmission participates in proconvulsant effect of T. gondii. The effect of parasite is eliminated by antibiotic therapy. © 2017 Wiley Periodicals, Inc.

Role of oxidative stress in the pathophysiology of Toxoplasma gondii infection

Oxidative stress (OS) plays an essential role in the pathogenesis of common neurodegenerative diseases. We have previously shown that Toxoplasma gondii (T. gondii) induces high nitric oxide (NO) production, glial activation, and apoptosis that altogether cause severe neuropathology in toxoplasma encephalitis (TE). The objective of this study was to investigate the cytotoxic effect of OS and to identify a correlation between the causes of T. gondii induced neuropathology. Expression levels of glutathione reductase (GR), Cu/Zn superoxide dismutase (SOD1), neuron specific enolase (NSE), and 8-hydroxy-2'-deoxyguanosine (8-OHdG) were investigated. Results of the study revealed that the levels of GR (P <0.005) and NSE (P <0.001) expression in the brain tissue markedly increased while SOD1 activity decreased (P <0.001) in the infected group compared to the non-infected group. In addition, intense staining for 8-OHdG (P <0.05) was observed both in the nucleus and the cytoplasm of neurons and glial cells that underwent OS. These results were reasonable to suggest that T. gondii-mediated OS might play a pivotal role and a different type of role in the mechanism of neurodegeneration/neuropathology in the process of TE. The results also clearly indicated that increased levels of NO and apoptosis might contribute to OS-related pathogenesis of TE. As a result, OS and expression of NSE might give an idea of the disease progress and may have a critical diagnostic significance for patients with T. gondii infection.