Motamed Elsayed Mahmoud

Capsaicin pretreatment attenuates LPS-induced hypothermia through TRPV1-independent mechanisms in chicken

It has been demonstrated that chicken TRPV1 (transient receptor potential vanilloid of subtype-1) is insensitive to capsaicin (CAP), and therefore, a chicken model is suitable to analyze the CAP-sensitive TRPV1-independent pathway. We elucidated here the possible involvement of the pathway in hypothermia induced by bacterial endotoxin (lipopolysaccharide, LPS) in chickens. Chicks were pretreated with CAP (10 mg/kg, iv) at 1, 2 and 3 days of age to desensitize them towards the CAP-sensitive pathway. An intravenous injection of LPS in 4-day-old chicks caused progressive hypothermia, ending with collapse and 78% mortality within 12 h after injection. The CAP pretreatment rescued the LPS-induced endotoxin shock and hypothermia in chicks. LPS-induced iNOS expression as well as NO production in liver and lung was suppressed by CAP pretreatment. CAP pretreatment also attenuated hypothermia due to exposure of chicks to cold ambient temperature. These findings suggest that a CAP-sensitive TRPV1-independent pathway may be involved in pathophysiological hypothermic reactions through the mediation of NO in chickens.

Induction of depression-related behaviors by reactivation of chronic Toxoplasma gondii infection in mice.

Although Toxoplasma gondii (T. gondii) infection is relevant to many psychiatric disorders, the fundamental mechanisms of its neurobiological correlation with depression are poorly understood. Here, we show that reactivation of chronic infection by an immunosuppressive regimen caused induction of depressive-like behaviors without obvious sickness symptoms. However, the depression-related behaviors in T. gondii-infected mice, specifically, reduced sucrose preference and increased immobility in the forced-swim test were observed at the reactivation stage, but not in the chronic infection. Interestingly, reactivation of T. gondii was associated with production of interferon-gamma and activation of brain indoleamine 2, 3-dioxygenase, which converts tryptophan to kynurenine and makes it unavailable for serotonin synthesis. Furthermore, serotonin turnover to its major metabolite, 5-hydroxyindoleacetic acid, was also enhanced at the reactivation stage. Thus, enhanced tryptophan catabolic shunt and serotonin turnover may be implicated in development of depressive-like behaviors in mice with reactivated T. gondii.

Mechanisms of interferon‐beta‐induced inhibition of Toxoplasma gondii growth in murine macrophages and embryonic fibroblasts: role of immunity‐related GTPase M1

The apical complex of Toxoplasma gondii enables it to invade virtually all nucleated cells in warm‐blooded animals, including humans, making it a parasite of global importance. Anti‐T. gondii cellular defence mechanisms depend largely on interferon (IFN)‐γ production by immune cells. However, the molecular mechanism of IFN‐β‐mediated defence remains largely unclear. Here, mouse peritoneal macrophages and murine embryonic fibroblasts (MEFs) primed with recombinant IFN‐β and IFN‐γ showed different pathways of activation. Treatment of these cells with IFN‐β or IFN‐γ inhibited T. gondii (type II PLK strain) growth. Priming macrophages with IFN‐β had no effect on inflammatory cytokine expression, inducible nitric oxide synthase or indoleamine 2,3‐dioxygenase, nor did it have an effect on their metabolites, nitric oxide and kynurenine respectively. In contrast, IFN‐γ stimulation was characterized by classical macrophage activation and T. gondii elimination. IFN‐β activation recruited the immunity‐related GTPase M1 (IRGM1) to the parasitophorous vacuole in the macrophages and MEFs. Anti‐toxoplasma activities induced by IFN‐β were significantly reduced after IRGM1 knockdown in murine macrophages and in IRGM1‐deficient MEFs. Thus, this study unravels an alternative pathway of macrophage activation by IFN‐β and provides a mechanistic explanation for the contribution of IRGM1 induced by IFN‐β to the elimination of T. gondii.

Toxoplasma gondii Infection in Mice Impairs Long-Term Fear Memory Consolidation through Dysfunction of the Cortex and Amygdala

ABSTRACT Chronic infection with Toxoplasma gondii becomes established in tissues of the central nervous system, where parasites may directly or indirectly modulate neuronal function. Epidemiological studies have revealed that chronic infection in humans is a risk factor for developing mental diseases. However, the mechanisms underlying parasite-induced neuronal dysfunction in the brain remain unclear. Here, we examined memory associated with conditioned fear in mice and found that T. gondii infection impairs consolidation of conditioned fear memory. To examine the brain pathology induced by T. gondii infection, we analyzed the parasite load and histopathological changes. T. gondii infects all brain areas, yet the cortex exhibits more severe tissue damage than other regions. We measured neurotransmitter levels in the cortex and amygdala because these regions are involved in fear memory expression. The levels of dopamine metabolites but not those of dopamine were increased in the cortex of infected mice compared with those in the cortex of uninfected mice. In contrast, serotonin levels were decreased in the amygdala and norepinephrine levels were decreased in the cortex and amygdala of infected mice. The levels of cortical dopamine metabolites were associated with the time spent freezing in the fear-conditioning test. These results suggest that T. gondii infection affects fear memory through dysfunction of the cortex and amygdala. Our findings provide insight into the mechanisms underlying the neurological changes seen during T. gondii infection.

Involvement of host defense mechanisms against Toxoplasma gondii infection in anhedonic and despair-like behaviors in mice

ABSTRACT Toxoplasma gondii is a pathogen relevant to psychiatric disorders. We recently showed that reactivation of chronic T. gondii infection induced depression-like behaviors in mice. Furthermore, it has been hypothesized that depression-like behaviors are mediated via a host defense mechanism against invading pathogens; proximate mechanisms of this behavioral hypothesis remain unclear. In the present study, we investigate the contribution of indoleamine 2,3-dioxygenase (IDO), inflammation, and interferon gamma (IFN-γ) to anhedonic and despair-related behaviors in T. gondii-infected mice by using sucrose preference and forced-swim tests, respectively. First, we confirmed that BALB/c mice exhibited both sickness and depression-like behaviors during acute infection. Treatment of infected wild-type mice with minocycline (anti-inflammatory drug) abated sickness and anhedonic and despair-like behaviors, whereas in T. gondii-infected mice, treatment normalized kynurenine/tryptophan (Kyn/Trp) ratios in both plasma and brain tissue. Additionally, T. gondii infection failed to induce anhedonic and despair-like behaviors or increase the Kyn/Trp ratio in immunocompromised (IFN-γ−/−) mice, whereas sickness behavior was observed in both immunocompetent and IFN-γ−/− mice following infection. Furthermore, treatment with 1-methyl tryptophan (an IDO inhibitor) did not affect locomotor activity, attenuated clinical scores and anhedonic and despair-like behaviors, and resulted in normal Kyn/Trp ratios in T. gondii-infected wild-type mice. Although low levels of serotonin and dopamine were observed in the brain during acute and chronic infections, anhedonic and despair-like behaviors were not detected in the chronic stage of infection. Collectively, our results demonstrated that immune enhancement in response to infection with T. gondii resulted in IFN-γ production, IDO activation, and inflammation associated with anhedonic and despair-like behaviors.

Capsaicin inhibits IFN-γ-induced MHC class II expression by suppressing transcription of class II transactivator gene in murine peritoneal macrophages

Major histocompatibility complex (MHC) class II molecules play crucial roles in adaptive immune response and antigen presentation. Owing to enlargement of capsaicins availability as an anti-inflammatory agent in medical therapeutics, we investigated the new effects of capsaicin that are related to adaptive immune response in terms of MHC class II expression in murine primary cultured macrophages. Capsaicin (0.1-10microM) reduced the expression of MHC class II mRNA levels in cultured peritoneal macrophages upon treatment with interferon (IFN)-gamma (100units/ml). In agreement with this, treatment of the cells with capsaicin also inhibited MHC class II transactivator (CIITA) mRNA expression induced by IFN-gamma in a dose-dependent manner. In contrast, production of nitric oxide, which has the ability to reduce MHC class II expression, was not enhanced but rather suppressed by capsaicin treatment in IFN-gamma-stimulated macrophages. These findings suggest that capsaicin suppresses expression of MHC class II via downregulation of CIITA transcription but not through the mediation of nitric oxide production by macrophages. These new immunopharmacological roles of capsaicin in specific transcription regulation of genes involved in antigen presentation of macrophages could be useful for the treatment of adaptive immune-mediated disorders.

Immunization with Toxoplasma gondii peroxiredoxin 1 induces protective immunity against toxoplasmosis in mice.

To develop a vaccine against Toxoplasma gondii, a vaccine antigen with immune-stimulating activity is required. In the present study, we investigated the immunogenicity and prophylactic potential of T. gondii peroxiredoxin 1 (TgPrx1). The TgPrx1 was detected in the ascitic fluid of mice 6 days postinfection, while specific antibody levels were low in the sera of chronically infected mice. Treatment of murine peritoneal macrophages with recombinant TgPrx1 triggered IL-12p40 and IL-6 production, but not IL-10 production. In response to TgPrx1, activation of NF-kB and IL-6 production were confirmed in mouse macrophage cell line (RAW 264.7). These results suggest the immune-stimulating potentials of TgPrx1. Immunization of mice with recombinant TgPrx1 stimulated specific antibody production (IgG1 and IgG2c). Moreover, spleen cell proliferation and interferon-gamma production significantly increased in the TgPrx1- sensitized cells from mice immunized with the same antigen. Immunization with TgPrx1 also increased mouse survival and decreased cerebral parasite burden against lethal T. gondii infection. Thus, our results suggest that TgPrx1 efficiently induces humoral and cellular immune responses and is useful as a new vaccine antigen against toxoplasmosis.