Increased leukotriene B4 plasma concentration in type 2 diabetes individuals with cardiovascular autonomic neuropathy.

BACKGROUND AND AIM: A low-grade inflammation is associated with cardiac autonomic neuropathy (CAN) and increased concentration of leukotriene B4 (LTB4) was found in individuals with type 1 diabetes and definitive CAN. This cross-sectional study evaluated plasma concentration of LTB4 and of other inflammatory mediators, namely, tumor necrosis factor (TNF), interleukin (IL)1B, and IL10 in individuals with type 2 diabetes (T2D) and different degrees of CAN, and correlated these inflammatory mediators with the degree of glycemic control and with a surrogate marker of insulin resistance. METHODS: TNF, IL1B, IL10 and LTB4 plasma concentrations were measured in 129 T2D subjects (62% women with [median] age of 63 years, disease duration of 8 years and HbA1c of 7.3%) with or without CAN. The Lipid accumulation product index was used as a surrogate marker of insulin resistance. RESULTS: LTB4 concentration was significantly higher in those presenting incipient CAN (69.7 ± 16.6 pg mL-1) and definitive CAN (71.5 ± 15.7 pg mL-1) versus those without CAN (57.0 ± 13.9 pg mL-1). The groups without CAN and with incipient CAN were pooled (group without definitive CAN) and compared to those with definitive CAN. LTB4 concentration was higher in the latter group, as well as TNF concentration, while IL10 concentration was lower in this group. After adjustment for confounding variables, only LTB4 concentration remained significantly different between the groups with and without definitive CAN. Plasma concentration of LTB4 did not correlate with the degree of glycemic control. After sorting the participants by sex, a borderline weak correlation was found between LTB4 and the Lipid accumulation product index in women. CONCLUSION: In the T2D setting, circulating LTB4 concentration seems to be associated with cardiovascular dysautonomia.

Leukotriene Involvement in the Insulin Receptor Pathway and Macrophage Profiles in Muscles from Type 1 Diabetic Mice.

Type 1 diabetes (T1D) is a metabolic disease associated with systemic low-grade inflammation and macrophage reprogramming. There is evidence that this inflammation depends on the increased systemic levels of leukotriene (LT) B4 found in T1D mice, which shifts macrophages towards the proinflammatory (M1) phenotype. Although T1D can be corrected by insulin administration, over time T1D patients can develop insulin resistance that hinders glycemic control. Here, we sought to investigate the role of leukotrienes (LTs) in a metabolically active tissue such as muscle, focusing on the insulin signaling pathway and muscle-associated macrophage profiles. Type 1 diabetes was induced in the 129/SvE mouse strain by streptozotocin (STZ) in mice deficient in the enzyme responsible for LT synthesis (5LO-/-) and the LT-sufficient wild type (WT). The response to insulin was evaluated by the insulin tolerance test (ITT), insulin concentration by ELISA, and Akt phosphorylation by western blotting. The gene expression levels of the insulin receptor and macrophage markers Stat1, MCP-1, Ym1, Arg1, and IL-6 were evaluated by qPCR, and that of IL-10 by ELISA. We observed that after administration of a single dose of insulin to diabetic mice, the reduction in glycemia was more pronounced in 5LO-/- than in WT mice. When muscle homogenates were analyzed, diabetic 5LO-/- mice showed a higher expression of the insulin receptor gene and higher Akt phosphorylation. Moreover, in muscle homogenates from diabetic 5LO-/- mice, the expression of anti-inflammatory macrophage markers Ym1, Arg1, and IL-10 was increased, and the relative expression of the proinflammatory cytokine IL-6 was reduced compared with WT diabetic mice. These results suggest that LTs have an impact on the insulin receptor signaling pathway and modulate the inflammatory profile of muscle-resident macrophages from T1D mice.

Platelet activating factor receptor antagonists improve the efficacy of experimental chemo- and radiotherapy.

Platelet activating factor is a lipid mediator of inflammation, and in recent decades, it has emerged as an important factor in tumor outcomes. Platelet activating factor acts by specific binding to its receptor, which is present in both tumor cells and cells that infiltrate tumors. Pro-tumorigenic effects of platelet activating factor receptor in tumors includes promotion of tumor cell proliferation, production of survival signals, migration of vascular cells and formation of new vessels and stimulation of dendritic cells and macrophages suppressor phenotype. In experimental models, blocking of platelet activating factor receptor reduced tumor growth and increased animal survival. During chemotherapy and radiotherapy, tumor cells that survive treatment undergo accelerated proliferation, a phenomenon known as tumor cell repopulation. Work from our group and others showed that these treatments induce overproduction of platelet activating factor-like molecules and increase expression of its receptor in tumor cells. In this scenario, antagonists of platelet activating factor markedly reduced tumor repopulation. Here, we note that combining chemo- and radiotherapy with platelet activating factor antagonists could be a promising strategy for cancer treatment.

Impaired wound healing in type 1 diabetes is dependent on 5-lipoxygenase products.

Type 1 diabetes is associated with systemic low grade inflammation (LGI). We have previously shown that LGI in diabetic mice depends on systemic circulation of leukotriene (LTB4) which potentiates the toll-like/IL1ß receptors response in macrophages. Impaired wound healing is an important co-morbidity in diabetes, and macrophages play a key role in this process. Here, we investigated the role of leukotrienes on monocytes and macrophages phenotype and in the impaired wound healing in diabetic mice. Type 1 diabetes was induced with streptozotocin in 129SvE wild-type (WT) and leukotrienes-deficient 5LO-/- (5-lipoxygenase knockout) mice. In diabetics, the systemic levels of LTB4, TNF-α, IL-6, IL-10, IL-12 and IFNγ were increased as well as the frequency of pro-inflammatory monocytes (CD11b+Ly6ChighLy6G-) compared to healthy mice. In diabetic 5LO-/- mice, these parameters were similar to those in healthy mice. Resident peritoneal macrophages from diabetic WT mice showed a classically activated M1-like phenotype (high Nos2, Stat and Il12 expression, and nitrite levels). Macrophages from diabetic 5LO-/- mice presented alternatively activated M2-macrophages markers (high Arg1 and Chi3l3 expression and arginase activity) and when stimulated with IL4, enhanced phosphorylated-STAT6. Cutaneous wound healing in diabetic WT mice was impaired, which correlated with the decreased frequency of M2-macrophages (CD45+F4/80+CD206+) in the lesions. In diabetic 5LO-/- mice, the frequency of M2-macrophages in the wound was similar to that in healthy mice, suggesting that the impaired healing of diabetic mice depends on 5LO products. The inhibition of leukotrienes or antagonism of its receptors could be a therapeutic alternative for diabetic patients with impaired healing.

Isolation, synthesis and bioactivity studies of phomactin terpenoids.

Studies of secondary metabolites (natural products) that cover their isolation, chemical synthesis and bioactivity investigation present myriad opportunities for discovery. For example, the isolation of novel secondary metabolites can inspire advances in chemical synthesis strategies to achieve their practical preparation for biological evaluation. In the process, chemical synthesis can also provide unambiguous structural characterization of the natural products. Although the isolation, chemical synthesis and bioactivity studies of natural products are mutually beneficial, they are often conducted independently. Here, we demonstrate the benefits of a collaborative study of the phomactins, diterpenoid fungal metabolites that serve as antagonists of the platelet activating factor receptor. Our isolation of novel phomactins has spurred the development of a bioinspired, unified approach that achieves the total syntheses of six congeners. We also demonstrate in vitro the beneficial effects of several phomactins in suppressing the rate of repopulation of tumour cells following gamma radiation therapy.

Nuclear PTEN enhances the maturation of a microRNA regulon to limit MyD88-dependent susceptibility to sepsis.

Sepsis-induced organ damage is caused by systemic inflammatory response syndrome (SIRS), which results in substantial comorbidities. Therefore, it is of medical importance to identify molecular brakes that can be exploited to dampen inflammation and prevent the development of SIRS. We investigated the role of phosphatase and tensin homolog (PTEN) in suppressing SIRS, increasing microbial clearance, and preventing lung damage. Septic patients and mice with sepsis exhibited increased PTEN expression in leukocytes. Myeloid-specific Pten deletion in an animal model of sepsis increased bacterial loads and cytokine production, which depended on enhanced myeloid differentiation primary response gene 88 (MyD88) abundance and resulted in mortality. PTEN-mediated induction of the microRNAs (miRNAs) miR125b and miR203b reduced the abundance of MyD88. Loss- and gain-of-function assays demonstrated that PTEN induced miRNA production by associating with and facilitating the nuclear localization of Drosha-Dgcr8, part of the miRNA-processing complex. Reconstitution of PTEN-deficient mouse embryonic fibroblasts with a mutant form of PTEN that does not localize to the nucleus resulted in retention of Drosha-Dgcr8 in the cytoplasm and impaired production of mature miRNAs. Thus, we identified a regulatory pathway involving nuclear PTEN-mediated miRNA generation that limits the production of MyD88 and thereby limits sepsis-associated mortality.

Platelet-Activating Factor Receptor Ligands Protect Tumor Cells from Radiation-Induced Cell Death.

Irradiation generates oxidized phospholipids that activate platelet-activating factor receptor (PAFR) associated with pro-tumorigenic effects. Here, we investigated the involvement of PAFR in tumor cell survival after irradiation. Cervical cancer samples presented higher levels of PAF-receptor gene (PTAFR) when compared with normal cervical tissue. In cervical cancer patients submitted to radiotherapy (RT), the expression of PTAFR was significantly increased. Cervical cancer-derived cell lines (C33, SiHa, and HeLa) and squamous carcinoma cell lines (SCC90 and SCC78) express higher levels of PAFR mRNA and protein than immortalized keratinocytes. Gamma radiation increased PAFR expression and induced PAFR ligands and prostaglandin E2 (PGE2) in these tumor cells. The blocking of PAFR with the antagonist CV3938 before irradiation inhibited PGE2 and increased tumor cells death. Similarly, human carcinoma cells transfected with PAFR (KBP) were more resistant to radiation compared to those lacking the receptor (KBM). PGE2 production by irradiated KBP cells was also inhibited by CV3988. These results show that irradiation of carcinoma cells generates PAFR ligands that protect tumor cells from death and suggests that the combination of RT with a PAFR antagonist could be a promising strategy for cancer treatment.

Platelet activating factor receptor antagonists improve the efficacy of experimental chemo- and radiotherapy

Platelet activating factor is a lipid mediator of inflammation, and in recent decades, it has emerged as an important factor in tumor outcomes. Platelet activating factor acts by specific binding to its receptor, which is present in both tumor cells and cells that infiltrate tumors. Pro-tumorigenic effects of platelet activating factor receptor in tumors includes promotion of tumor cell proliferation, production of survival signals, migration of vascular cells and formation of new vessels and stimulation of dendritic cells and macrophages suppressor phenotype. In experimental models, blocking of platelet activating factor receptor reduced tumor growth and increased animal survival. During chemotherapy and radiotherapy, tumor cells that survive treatment undergo accelerated proliferation, a phenomenon known as tumor cell repopulation. Work from our group and others showed that these treatments induce overproduction of platelet activating factor-like molecules and increase expression of its receptor in tumor cells. In this scenario, antagonists of platelet activating factor markedly reduced tumor repopulation. Here, we note that combining chemo- and radiotherapy with platelet activating factor antagonists could be a promising strategy for cancer treatment.

Imbalance between HDAC and HAT activities drives aberrant STAT1/MyD88 expression in macrophages from type 1 diabetic mice.

AIMS: To investigate the hypothesis that alteration in histone acetylation/deacetylation triggers aberrant STAT1/MyD88 expression in macrophages from diabetics. Increased STAT1/MyD88 expression is correlated with sterile inflammation in type 1 diabetic (T1D) mice. METHODS: To induce diabetes, we injected low-doses of streptozotocin in C57BL/6 mice. Peritoneal or bone marrow-differentiated macrophages were cultured in 5mM (low) or 25mM (high glucose). ChIP analysis of macrophages from nondiabetic or diabetic mice was performed to determine acetylation of lysine 9 in histone H3 in MyD88 and STAT1 promoter regions. Macrophages from diabetic mice were treated with the histone acetyltransferase inhibitor anacardic acid (AA), followed by determination of mRNA expression by qPCR. RESULTS: Increased STAT1 and MyD88 expression in macrophages from diabetic but not naive mice cultured in low glucose persisted for up to 6days. Macrophages from diabetic mice exhibited increased activity of histone acetyltransferases (HAT) and decreased histone deacetylases (HDAC) activity. We detected increased H3K9Ac binding to Stat1/Myd88 promoters in macrophages from T1D mice and AA in vitro treatment reduced STAT1 and MyD88 mRNA expression. CONCLUSIONS/INTERPRETATION: These results indicate that histone acetylation drives elevated Stat1/Myd88 expression in macrophages from diabetic mice, and this mechanism may be involved in sterile inflammation and diabetes comorbidities.

Modulation of Tumor-Associated Macrophages (TAM) Phenotype by Platelet-Activating Factor (PAF) Receptor.

Platelet-activating factor (PAF) plays an important role in the pathogenesis of several types of tumors. The biological effects of PAF are mediated by the PAF receptor (PAFR), which can be expressed by tumor cells and host cells that infiltrate the tumor microenvironment. In the present study, we investigated the role of PAFR expressed by leukocytes that infiltrate two types of tumors, one that expresses PAFR (TC-1 carcinoma) and another that does not express the receptor (B16F10 melanoma) implanted in mice that express the receptor or not (PAFR KO). It was found that both tumors grew significantly less in PAFR KO than in wild-type (WT) mice. Analysis of the leukocyte infiltration shown in PAFR KO increased the frequency of neutrophils (Gr1+) and of CD8+ lymphocytes in B16F10 tumors and of CD4+ lymphocytes in TC-1 tumors. PAFR KO also had a higher frequency of M1-like (CD11c+) and lower M2-like (CD206+) macrophages infiltrated in both tumors. This was confirmed in macrophages isolated from the tumors that showed higher iNOS, lower arginase activity, and lower IL10 expression in PAFR KO tumors than WT mice. These data suggest that in the tumor microenvironment, endogenous PAF-like activity molecules bind PAFR in macrophages which acquire an M2-like profile and this promotes tumor growth.

PAFR activation of NF-κB p65 or p105 precursor dictates pro- and anti-inflammatory responses during TLR activation in murine macrophages.

Platelet-activating factor receptor (PAFR) is a G protein-coupled receptor (GPCR) implicated in many diseases. Toll-like receptors (TLRs) play a critical role in shaping innate and adaptive immune responses. In this study, we investigated whether PAFR signaling changes the macrophages responsiveness to agonists of TLR2 (Pam3Cys), TLR4 (LPS), and TLR3 agonist Poly(I:C). Exogenous PAF inhibited the production of pro-inflammatory cytokines (IL-12p40, IL-6, and TNF-α) and increased anti-inflammatory IL-10 in macrophages challenged with Pam3Cys and LPS, but not with Poly (I:C). PAF did not affect mRNA expression of MyD88, suggesting that PAF acts downstream the adaptor. PAF inhibited LPS-induced phosphorylation of NF-κB p65 and increased NF-κB p105 phosphorylation, which is processed in the proteasome to generate p50 subunit. The PAF potentiation of IL-10 production was dependent on proteasome processing but independent of NF-κB transactivation domain. Inhibition of p50 abolished the PAF-induced IL-10 production. These findings indicate that the impaired transcriptional activity of the p65 subunit and the enhanced p105 phosphorylation induced by PAF are responsible for down regulation of pro-inflammatory cytokines and up regulation of IL-10, respectively, in LPS-challenged macrophages. Together, our data unveil a heretofore unrecognized role for PAFR in modulating activation of NF-κB in macrophages.

PAFR in adipose tissue macrophages is associated with anti-inflammatory phenotype and metabolic homoeostasis.

Metabolic dysfunction is associated with adipose tissue inflammation and macrophage infiltration. PAFR (platelet-activating factor receptor) is expressed in several cell types and binds to PAF (platelet-activating factor) and oxidized phospholipids. Engagement of PAFR in macrophages drives them towards the anti-inflammatory phenotype. In the present study, we investigated whether genetic deficiency of PAFR affects the phenotype of ATMs (adipose tissue macrophages) and its effect on glucose and insulin metabolism. PARFKO (PAFR-knockout) and WT (wild-type) mice were fed on an SD (standard diet) or an HFD (high-fat diet). Glucose and insulin tolerance tests were performed by blood monitoring. ATMs were evaluated by FACS for phenotypic markers. Gene and protein expression was investigated by real-time reverse transcription-quantitative PCR and Western blotting respectively. Results showed that the epididymal adipose tissue of PAFRKO mice had increased gene expression of Ccr7, Nos2, Il6 and Il12, associated with pro-inflammatory mediators, and reduced expression of the anti-inflammatory Il10. Moreover, the adipose tissue of PAFRKO mice presented more pro-inflammatory macrophages, characterized by an increased frequency of F4/80(+)CD11c(+) cells. Blood monocytes of PAFRKO mice also exhibited a pro-inflammatory phenotype (increased frequency of Ly6C(+) cells) and PAFR ligands were detected in the serum of both PAFRKO and WT mice. Regarding metabolic parameters, compared with WT, PAFRKO mice had: (i) higher weight gain and serum glucose concentration levels; (ii) decreased insulin-stimulated glucose disappearance; (iii) insulin resistance in the liver; (iv) increased expression of Ldlr in the liver. In mice fed on an HFD, some of these changes were potentiated, particularly in the liver. Thus it seems that endogenous ligands of PAFR are responsible for maintaining the anti-inflammatory profile of blood monocytes and ATMs under physiological conditions. In the absence of PAFR signalling, monocytes and macrophages acquire a pro-inflammatory phenotype, resulting in adipose tissue inflammation and metabolic dysfunction.

Lipoxin Inhibits Fungal Uptake by Macrophages and Reduces the Severity of Acute Pulmonary Infection Caused by Paracoccidioides brasiliensis.

Cysteinyl leukotrienes (CysLTs) and lipoxins (LXs) are lipid mediators that control inflammation, with the former inducing and the latter inhibiting this process. Because the role played by these mediators in paracoccidioidomycosis was not investigated, we aimed to characterize the role of CysLT in the pulmonary infection developed by resistant (A/J) and susceptible (B10.A) mice. 48 h after infection, elevated levels of pulmonary LTC4 and LXA4 were produced by both mouse strains, but higher levels were found in the lungs of susceptible mice. Blocking the CysLTs receptor by MTL reduced fungal loads in B10.A, but not in A/J mice. In susceptible mice, MLT treatment led to reduced influx of PMN leukocytes, increased recruitment of monocytes, predominant synthesis of anti-inflammatory cytokines, and augmented expression of 5- and 15-lipoxygenase mRNA, suggesting a prevalent LXA4 activity. In agreement, MTL-treated macrophages showed reduced fungal burdens associated with decreased ingestion of fungal cells. Furthermore, the addition of exogenous LX reduced, and the specific blockade of the LX receptor increased the fungal loads of B10.A macrophages. This study showed for the first time that inhibition of CysLTs signaling results in less severe pulmonary paracoccidioidomycosis that occurs in parallel with elevated LX activity and reduced infection of macrophages.

Leukotriene B4-mediated sterile inflammation promotes susceptibility to sepsis in a mouse model of type 1 diabetes.

Type 1 diabetes mellitus (T1DM) is associated with chronic systemic inflammation and enhanced susceptibility to systemic bacterial infection (sepsis). We hypothesized that low insulin concentrations in T1DM trigger the enzyme 5-lipoxygenase (5-LO) to produce the lipid mediator leukotriene B4 (LTB4), which triggers systemic inflammation that may increase susceptibility to polymicrobial sepsis. Consistent with chronic inflammation, peritoneal macrophages from two mouse models of T1DM had greater abundance of the adaptor MyD88 (myeloid differentiation factor 88) and its direct transcriptional effector STAT-1 (signal transducer and activator of transcription 1) than macrophages from nondiabetic mice. Expression of Alox5, which encodes 5-LO, and the concentration of the proinflammatory cytokine interleukin-1ß (IL-1ß) were also increased in peritoneal macrophages and serum from T1DM mice. Insulin treatment reduced LTB4 concentrations in the circulation and Myd88 and Stat1 expression in the macrophages from T1DM mice. T1DM mice treated with a 5-LO inhibitor had reduced Myd88 mRNA in macrophages and increased abundance of IL-1 receptor antagonist and reduced production of IL-ß in the circulation. T1DM mice lacking 5-LO or the receptor for LTB4 also produced less proinflammatory cytokines. Compared to wild-type or untreated diabetic mice, T1DM mice lacking the receptor for LTB4 or treated with a 5-LO inhibitor survived polymicrobial sepsis, had reduced production of proinflammatory cytokines, and had decreased bacterial counts. These results uncover a role for LTB4 in promoting sterile inflammation in diabetes and the enhanced susceptibility to sepsis in T1DM.

Characterization of the inflammatory response during Ehrlich ascitic tumor development.

INTRODUCTION: Ehrlich tumor is a mammary adenocarcinoma with aggressive behavior. Inoculated in mice peritoneal cavity, the Ehrlich tumor grows in ascitic form (EAT). Since inflammation modulates tumor progression we further investigated the inflammatory response during EAT growth. METHODS: Balb/C mice were intraperitoneal inoculated with 5×10(5) Ehrlich cells and after every 2days, blood samples were collected for hemoglobin, hematocrit, platelets and leukocytes counts. The ascitic fluid was collected for protein concentration and cell count. Phenotype analysis of the peritoneal cells was made by FACS, prostaglandin E2 (PGE2) and cytokines by ELISA, nitric oxide (NO) by nitrate conversion protocol, and cyclooxygenase-1 (COX1), COX2 and inducible nitric oxide synthase (iNOS) by immunoblotting. RESULTS: Following EAT inoculation into the peritoneal cavity there was a rapid increase in ascitis volume and protein concentration. The cell number in ascitis remained stable until day 8 (lag phase) followed by a sharp increase. As tumor progressed, blood leukocytes increased and erythrocyte decreased. Phenotypic analysis showed that during the lag phase the percentage of F4/80(+) cells remained similar to control levels and around 7% of this population was also positive for the GR1 marker. These double-positive cells (probably inflammatory monocytes) markedly increased at day 6. The percentage of F4/80-GR1(+)cells (probably neutrophils) was low and did not significantly vary during tumor progression. CD4(+) and CD8(+) cells were not detected in the time points analyzed. iNOS and COX1 expression increased after day 2 reaching peak levels on day 10. COX2 enzyme expression did not change significantly over time. Sustained increase in PGE2 and NO levels was observed. IL-10 and MCP-1 peaked at day 14 and IL-1ß increased progressively till day 10. IFN-γ levels were low till day 10, increasing progressively after that. DISCUSSION: These data extended the characterization of the inflammatory response during Ehrlich ascitis tumor growth, further validating it as a useful model for antitumor drugs screening.

Sepsis-induced lung inflammation is modulated by insulin.

BACKGROUND: We have previously shown that diabetic rats are more susceptible to sepsis, but that the Acute lung injury (ALI) secondary to sepsis is less intense than in non-diabetics. In the present study, we further investigated the ALI-secondary to sepsis in diabetic rats and the effect of insulin treatment. METHODS: Diabetes was induced in male Wistar rats by alloxan and sepsis by cecal ligation and puncture surgery (CLP). Some diabetic rats were given neutral protamine Hagedorn (NPH) insulin (4 IU, s.c.) 2 h before CLP. Six h later, the lungs were examined for edema, cell infiltration and prostaglandin-E2 (PGE2) levels in the bronchoalveolar lavage (BAL). RESULTS: The results confirmed that leukocyte infiltration and edema were milder in diabetic rats with sepsis. After insulin treatment, the lung inflammation in diabetics increased to levels comparable to the non-diabetics. The BAL concentration of PGE2 was also lower in diabetics with sepsis, and increased after insulin treatment. Sepsis was followed by early fibroblast activation in the lung parenchyma, evaluated by increased transforming growth factor (TGF)-ß and smooth muscle actin (α-SMA) expression, as well as an elevated number of cells with myofibroblasts morphology. These events were significantly lower in diabetic rats and increased after insulin treatment. CONCLUSION: The results show that insulin modulates the early phase of inflammation and myofibroblast differentiation in diabetic rats.

Essential role of leukotriene B4 on Leishmania (Viannia) braziliensis killing by human macrophages.

Although Leishmania (Viannia) braziliensis is the most prevalent species that cause American tegumentary leishmaniasis (ATL), the immune response against this parasite has been poorly investigated. Upon activation, macrophages produce a series of pro-inflammatory molecules, including the lipid mediator leukotriene B4 (LTB4). LTB4 has been shown to enhance several macrophage functions, but its role in human macrophages is less known. Here, we investigated the role of LTB4 on human monocyte-derived macrophages infected with human isolate of L. (V.) braziliensis (IMG3). It was found that human macrophages produce LTB4 upon infection with Leishmania, which by autocrine or paracrine activation of its high affinity receptor BLT1, potentiates macrophage leishmanicidal activity. This LTB4 effect is mediated by increased secretion of reactive oxygen species (ROS). Moreover, Leishmania infection decreased the expression of BLT1, leading to the speculation that this could represent a parasite escape mechanism to establish a chronic inflammatory infection. Therefore, our data suggest that LTB4 could be used in therapeutic strategies to control Leishmania infection.

PAF receptor and tumor growth.

The receptor for the lipid mediator PAF (PAFR) is a G-protein coupled receptor expressed in several cell types. Besides PAF, a series of oxidized phospholipids can also bind to PAFR. Dying cells also express PAFR-ligands and, in both situations, scavenger receptors are involved as well. There is evidence that the scavenger receptor CD36 and PAFR associate in the macrophages membrane and signal in conjunction to induce a regulatory phenotype. In the tumor microenvironment, apoptotic cells are abundant due to hypoxia, and PAF-like phospholipids are generated. Engagement of PAFR expressed by tumor macrophages and dendritic cells induces a regulatory/tolerogenic phenotype and subverts the innate and adaptive immune response to the tumor. During cancer therapies, PAFR-ligands can be generated, further aggravating the immune suppression. Moreover, some tumor cells express PAFR and its activation by PAFR-ligands generated during chemotherapy induce anti-apoptotic factors, which protect the tumor cells from death induced by these treatments. It is proposed that PAFR antagonists, administered in combination with chemotherapy, may represent a promising strategy for cancer treatment.