Frankincense (Boswellia serrata) Extract Effects on Growth and Biofilm Formation of Porphyromonas gingivalis, and Its Intracellular Infection in Human Gingival Epithelial Cells.

Frankincense is produced by Boswellia trees, which can be found throughout the Middle East and parts of Africa and Asia. Boswellia serrata extract has been shown to have anti-cancer, anti-inflammatory, and antimicrobial effects. Periodontitis is an oral chronic inflammatory disease that affects nearly half of the US population. We investigated the antimicrobial effects of B. serrata extract on two oral pathogens associated with periodontitis. Using the minimum inhibitory concentration and crystal violet staining methods, we demonstrated that Porphyromonas gingivalis growth and biofilm formation were impaired by treatment with B. serrata extracts. However, the effects on Fusobacterium nucleatum growth and biofilm formation were not significant. Using quantification of colony-forming units and microscopy techniques, we also showed that concentrations of B. serrata that were not toxic for host cells decreased intracellular P. gingivalis infection in human gingival epithelial cells. Our results show antimicrobial activity of a natural product extracted from Boswellia trees (B. serrata) against periodontopathogens. Thus, B. serrata has the potential for preventing and/or treating periodontal diseases. Future studies will identify the molecular components of B. serrata extracts responsible for the beneficial effects.

Non-canonical NLRP3 inflammasome activation and IL-1ß signaling are necessary to L. amazonensis control mediated by P2X7 receptor and leukotriene B4.

Leishmaniasis is a neglected tropical disease affecting millions of individuals worldwide. P2X7 receptor has been linked to the elimination of Leishmania amazonensis. Biological responses evoked by P2X7 receptor activation have been well-documented, including apoptosis, phagocytosis, cytokine release, such as IL-1ß. It was demonstrated that NLRP3 inflammasome activation and IL-1ß signaling participated in resistance against L. amazonensis. Furthermore, our group has shown that L. amazonensis elimination through P2X7 receptor activation depended on leukotriene B4 (LTB4) production and release. Therefore, we investigated whether L. amazonensis elimination by P2X7 receptor and LTB4 involved NLRP3 inflammasome activation and IL-1ß signaling. We showed that macrophages from NLRP3-/-, ASC-/-, Casp-1/11-/-, gp91phox-/- , and IL-1R-/- mice treated with ATP or LTB4 did not decrease parasitic load as was observed in WT mice. When ASC-/- macrophages were treated with exogenous IL-1ß, parasite killing was noted, however, we did not see parasitic load reduction in IL-1R-/- macrophages. Similarly, macrophages from P2X7 receptor-deficient mice treated with IL-1ß also showed decreased parasitic load. In addition, when we infected Casp-11-/- macrophages, neither ATP nor LTB4 were able to reduce parasitic load, and Casp-11-/- mice were more susceptible to L. amazonensis infection than were WT mice. Furthermore, P2X7-/- L. amazonensis-infected mice locally treated with exogenous LTB4 showed resistance to infection, characterized by lower parasite load and smaller lesions compared to untreated P2X7-/- mice. A similar observation was noted when infected P2X7-/- mice were treated with IL-1ß, i.e., lower parasite load and smaller lesions compared to P2X7-/- mice. These data suggested that L. amazonensis elimination mediated by P2X7 receptor and LTB4 was dependent on non-canonical NLRP3 inflammasome activation, ROS production, and IL-1ß signaling.

Disruption of Purinergic Receptor P2X7 Signaling Increases Susceptibility to Cerebral Toxoplasmosis.

Toxoplasmosis is a neglected disease that affects millions of individuals worldwide. Toxoplasma gondii infection is an asymptomatic disease, with lethal cases occurring mostly in HIV patients and organ transplant recipients. Nevertheless, atypical strains of T. gondii in endemic locations cause severe pathology in healthy individuals. Toxoplasmosis has no cure but it can be controlled by the proinflammatory immune response. The purinergic receptor P2X7 (P2X7) is involved in many inflammatory events and has been associated with genes that confer resistance against toxoplasmosis in humans. In vitro studies have reported parasite death after P2X7-receptor activation in various cell types. To understand the contribution of P2X7 during cerebral toxoplasmosis, wild-type and P2rx7 knockout mice were infected orally with T. gondii and their pathologic profiles were analyzed. We found that all P2rx7-/- mice died 8 weeks after infection with an increased number of cysts and fewer inflammatory infiltrates in their brains. The cytokines interleukin-1ß, interleukin-12, tumor necrosis factor-α, and reactive oxygen species were absent or reduced in P2rx7-/- mice. Taken together, these data suggest that the P2X7 receptor promotes inflammatory infiltrates, proinflammatory cytokines, and reactive oxygen species production in the brain, and that P2X7 signaling mediates major events that confer resistance to cerebral toxoplasmosis.

Potential role of P2X7R in esophageal squamous cell carcinoma proliferation.

Esophageal cancer is an aggressive tumor and is the sixth leading cause of cancer death worldwide. ATP is well known to regulate cancer progression in a variety of models by different mechanisms, including P2X7R activation. This study aimed to evaluate the role of P2X7R in esophageal squamous cell carcinoma (ESCC) proliferation. Our results show that treatment with high ATP concentrations induced a decrease in cell number, cell viability, number of polyclonal colonies, and reduced migration of ESCC. The treatment with the selective P2X7R antagonist A740003 or siRNA for P2X7 reverted this effect in the KYSE450 cell line. In addition, results showed that P2X7R is highly expressed, at mRNA and protein levels, in KYSE450 lineage. Additionally, KYSE450, KYSE30, and OE21 cells express P2X3R, P2X4R, P2X5R, P2X6R, and P2X7R genes. P2X1R is expressed by KYSE30 and KYSE450, and only KYSE450 expresses the P2X2R gene. Furthermore, esophageal cancer cell line KYSE450 presented higher expression of E-NTPDases 1 and 2 and of Ecto-5'-NT/CD73 when compared to normal cells. This cell line also exhibits ATPase, ADPase, and AMPase activity, although in different levels, and the co-treatment of apyrase was able to revert the antiproliferative effects of ATP. Moreover, results showed high immunostaining for P2X7R in biopsies of patients with esophageal carcinoma, indicating the involvement of this receptor in the growth of this type of cancer. The results suggest that P2X7R may be a potential pharmacological target to treat ESCC and can lead us to further investigate the effect of this receptor in cancer cell progression.

P2X7 Receptor Modulation of the Gut Microbiota and the Inflammasome Determines the Severity of Toxoplasma gondii-Induced Ileitis.

In mice, oral Toxoplasma gondii infection induces severe ileitis. The aim of the present study was to investigate the impact of the P2X7 receptor (P2X7) on the inflammatory response to T. gondii-induced ileitis. Cysts of the ME49 strain of T. gondii were used to induce ileitis. The infected mice were euthanized on day 8 and ileal tissue and peripheral blood were collected for histopathological and immunohistochemical analyses. Ileal contractility, inflammatory mediators, inflammasome activation, quantitative PCR analysis of gene expression, and fecal microbiota were assessed using appropriate techniques, respectively. The infected P2X7-/- mice had greater disease severity, parasitic burden, liver damage, and intestinal contractility than the infected wild-type (WT) mice. Infection increased serum IL-6 and IFN-γ and tissue caspase-1 but not NLRP3 in P2X7-/- mice compared to WT mice. Bacteroidaceae, Rikenellaceae, and Rhodospirillales increased while Muribaculaceae and Lactobacillaceae decreased in the infected WT and P2X7-/- mice. Bacteroidia and Tannerellaceae increased in the P2X7-/- mice with ileitis. By contrast, Clostridiales and Mollicutes were absent in the P2X7-/- mice but increased in the WT mice. P2X7 protects mice against T. gondii infection by activating the inflammasome and regulating the local and systemic immune responses. Specific gut bacterial populations modulated by P2X7 determine disease severity.

The Complexity of Purinergic Signaling During Toxoplasma Infection.

Toxoplasmosis is a neglected disease caused by infection by the protozoan Toxoplasma gondii. One-third of the global population is expected to be by infected T. gondii. In Europe and North America, most infections do not induce disease, except in the context of immunosuppression. However, in endemic regions such Central and South America, infections induce severe ocular and potentially lethal disease, even in immunocompetent individuals. The immune response against T. gondii infection involves components of innate immunity even in the chronic phase of the disease, including dangerous signal molecules such as extracellular nucleotides. Purinergic signaling pathways include ionotropic and metabotropic receptors activated by extracellular nucleotides that are divided into P2X, P2Y, and A1 receptor families. The activation of purinergic signaling impacts biological systems by modulating immune responses to intracellular pathogens such as T. gondii. Ten years ago, purinergic signaling in the T. gondii infection was reported for the first time. In this review, we update and summarize the main findings regarding the role of purinergic signaling in T. gondii infection; these include in vitro findings: the microbicidal effect of P2Y and P2X7 activation phagocytic cells and parasite control by P2X7 activation in non-phagocytic cells; and in vivo findings: the promotion of early pro-inflammatory events that protect the host in acute and chronic models.

The P2X7 Receptor Mediates Toxoplasma gondii Control in Macrophages through Canonical NLRP3 Inflammasome Activation and Reactive Oxygen Species Production.

Toxoplasma gondii (T. gondii) is the protozoan parasite that causes toxoplasmosis, a potentially fatal disease to immunocompromised patients, and which affects approximately 30% of the world's population. Previously, we showed that purinergic signaling via the P2X7 receptor contributes to T. gondii elimination in macrophages, through reactive oxygen species (ROS) production and lysosome fusion with the parasitophorous vacuole. Moreover, we demonstrated that P2X7 receptor activation promotes the production of anti-parasitic pro-inflammatory cytokines during early T. gondii infection in vivo. However, the cascade of signaling events that leads to parasite elimination via P2X7 receptor activation remained to be elucidated. Here, we investigated the cellular pathways involved in T. gondii elimination triggered by P2X7 receptor signaling, during early infection in macrophages. We focused on the potential role of the inflammasome, a protein complex that can be co-activated by the P2X7 receptor, and which is involved in the host immune defense against T. gondii infection. Using peritoneal and bone marrow-derived macrophages from knockout mice deficient for inflammasome components (NLRP3-/-, Caspase-1/11-/-, Caspase-11-/-), we show that the control of T. gondii infection via P2X7 receptor activation by extracellular ATP (eATP) depends on the canonical inflammasome effector caspase-1, but not on caspase-11 (a non-canonical inflammasome effector). Parasite elimination via P2X7 receptor and inflammasome activation was also dependent on ROS generation and pannexin-1 channel. Treatment with eATP increased IL-1ß secretion from infected macrophages, and this effect was dependent on the canonical NLRP3 inflammasome. Finally, treatment with recombinant IL-1ß promoted parasite elimination via mitochondrial ROS generation (as assessed using Mito-TEMPO). Together, our results support a model where P2X7 receptor activation by eATP inhibits T. gondii growth in macrophages by triggering NADPH-oxidase-dependent ROS production, and also by activating a canonical NLRP3 inflammasome, which increases IL-1ß production (via caspase-1 activity), leading to mitochondrial ROS generation.

P2X7 Receptor Signaling Contributes to Sepsis-Associated Brain Dysfunction.

Sepsis results in unfettered inflammation, tissue damage, and multiple organ failure. Diffuse brain dysfunction and neurological manifestations secondary to sepsis are termed sepsis-associated encephalopathy (SAE). Extracellular nucleotides, proinflammatory cytokines, and oxidative stress reactions are associated with delirium and brain injury, and might be linked to the pathophysiology of SAE. P2X7 receptor activation by extracellular ATP leads to maturation and release of IL-1ß by immune cells, which stimulates the production of oxygen reactive species. Hence, we sought to investigate the role of purinergic signaling by P2X7 in a model of sepsis. We also determined how this process is regulated by the ectonucleotidase CD39, a scavenger of extracellular nucleotides. Wild type (WT), P2X7 receptor (P2X7-/-), or CD39 (CD39-/-) deficient mice underwent sham laparotomy or CLP induced by ligation and puncture of the cecum. We noted that genetic deletion of P2X7 receptor decreased markers of oxidative stress in murine brains 24 h after sepsis induction. The pharmacological inhibition or genetic ablation of the P2X7 receptor attenuated the IL-1ß and IL-6 production in the brain from septic mice. Furthermore, our results suggest a crucial role for the enzyme CD39 in limiting P2X7 receptor proinflammatory responses since CD39-/- septic mice exhibited higher levels of IL-1ß in the brain. We have also demonstrated that P2X7 receptor blockade diminished STAT3 activation in cerebral cortex and hippocampus from septic mice, indicating association of ATP-P2X7-STAT3 signaling axis in SAE during sepsis. Our findings suggest that P2X7 receptor might serve as a suitable therapeutic target to ameliorate brain damage in sepsis.

Pyrimidinergic Receptor Activation Controls Toxoplasma gondii Infection in Macrophages.

Infection by the protozoan parasite Toxoplasma gondii is highly prevalent worldwide and may have serious clinical manifestations in immunocompromised patients. T. gondii is an obligate intracellular parasite that infects almost any cell type in mammalian hosts, including immune cells. The immune cells express purinergic P2 receptors in their membrane--subdivided into P2Y and P2X subfamilies--whose activation is important for infection control. Here, we examined the effect of treatment with UTP and UDP in mouse peritoneal macrophages infected with T. gondii tachyzoites. Treatment with these nucleotides reduced parasitic load by 90%, but did not increase the levels of the inflammatory mediators NO and ROS, nor did it modulate host cell death by apoptosis or necrosis. On the other hand, UTP and UDP treatments induced early egress of tachyzoites from infected macrophages, in a Ca2+-dependent manner, as shown by scanning electron microscopy analysis, and videomicroscopy. In subsequent infections, prematurely egressed parasites had reduced infectivity, and could neither replicate nor inhibit the fusion of lysosomes to the parasitophorous vacuole. The use of selective agonists and antagonists of the receptor subtypes P2Y2 and P2Y4 and P2Y6 showed that premature parasite egress may be mediated by the activation of these receptor subtypes. Our results suggest that the activity of P2Y host cell receptors controls T. gondii infection in macrophages, highlighting the importance of pyrimidinergic signaling for innate immune system response against infection. Finally the P2Y receptors should be considered as new target for the development of drugs against T. gondii infection.