Proinflammatory actions of thromboxane receptors to enhance cellular immune responses

Platelet interaction and performance of antibacterial bioinspired nanostructures passivated with human plasma

The ever-increasing ageing of the world population is demanding superior orthopedic devices. Issues such as implant infection, poor osseointegration, or chronic inflammation remain problematic to the lifespan and long-term efficacy of implants. Fabrication of materials with bioinspired nanostructures is one emerging antibacterial strategy to prevent implant infection, however their interactions with blood components, and whether they retain their bactericidal properties in an environment displaying a complex protein corona, remains largely unexplored. In the present study, titanium alloy, commercially pure and plasma-sprayed titania were hydrothermally etched, passivated with human native plasma to develop a protein corona, and then incubated with either Staphylococcus aureus, Pseudomonas aeruginosa or human platelets. Surface analysis was first used to characterize the topography, chemical composition or crystallinity of each material. Fluorescence staining and SEM were performed to evaluate the nanostructure bactericidal properties, as well as to study platelet attachment and morphology. Composition of platelet supernatant was studied using ELISA and flow cytometry. Overall, our study showed that the bioinspired nanostructured surfaces displayed both impressive antibacterial properties in a complex environment, and a superior blood biocompatibility profile in terms of platelet activation (particularly for titanium alloy). Additionally, the amount of pro-inflammatory cytokines released by platelets was found to be no different to that found in native plasma (background levels) and, in some cases, presented a more pro-healing profile with an increased secretion of factors such as TGF-β, PDGF-BB or BMP-2. The nanostructured surfaces performed equally, or better, than hydroxyapatite-coated titanium which is one of the current gold standards in orthopedics. Although further in vivo studies are required to validate these results, such bioinspired nanostructured surfaces certainly show promise to be safely applied to medical device surfaces used in orthopedics and other areas.

Aerosolized Harmful Algal Bloom Toxin Microcystin-LR Induces Type 1/Type 17 Inflammation of Murine Airways

Harmful algal blooms are increasing globally and pose serious health concerns releasing cyanotoxins. Microcystin-LR (MC-LR), one of the most frequently produced cyanotoxins, has recently been detected in aerosols generated by the normal motions of affected bodies of water. MC-LR aerosol exposure has been linked to a pro-inflammatory influence on the airways of mice; however, little is understood about the underlying mechanism or the potential consequences. This study aimed to investigate the pro-inflammatory effects of aerosolized MC-LR on murine airways. C57BL/6 and BALB/c mice were exposed to MC-LR aerosols, as these strains are predisposed to type 1/type 17 and type 2 immune responses, respectively. Exposure to MC-LR induced granulocytic inflammation in C57BL/6 but not BALB/c mice, as observed by increased expression of cytokines MIP-1α, CXCL1, CCL2, and GM-CSF compared with their respective vehicle controls. Furthermore, the upregulation of interleukins IL-17A and IL-12 is consistent with Th1- and Th17-driven type 1/type 17 inflammation. Histological analysis confirmed inflammation in the C57BL/6 lungs, with elevated neutrophils and macrophages in the bronchoalveolar lavage fluid and increased pro-inflammatory and pro-resolving oxidized lipids. In contrast, BALB/c mice showed no significant airway inflammation. These results highlight the ability of aerosolized MC-LR to trigger harmful airway inflammation, requiring further research, particularly into populations with predispositions to type 1/type 17 inflammation.

Acetylsalicylic acid inhibition of the lipoxygenase pathway: Implications for HIV prevention

BACKGROUND

1.5 million new HIV infections occurred in 2021, suggesting new prevention methods are needed. Inflammation increases the risk for HIV acquisition by attracting HIV target cells to the female genital tract (FGT). In a pilot study, acetylsalicylic acid (ASA/Aspirin) decreased the proportion of FGT HIV target cells by 35 %. However, the mechanism remains unknown.

METHODS

Women from Nairobi, Kenya took low-dose ASA (81 mg) daily for 6-weeks. Free oxylipins in the plasma were quantified by high-performance liquid chromatography-tandem mass spectroscopy.

RESULTS

Oxylipins from 9 fatty acid substrates were detected, with more than one analyte from 4 substrates reduced post-ASA. Summary analysis found ASA downregulated cyclooxygenase and lipoxygenase but not cytochrome P450 activity with a lower n-6/n-3 oxylipin profile, reflecting reduced inflammation post-ASA.

CONCLUSIONS

Inflammation is associated with increased lipoxygenase activity and HIV risk. Our data suggests ASA reduces inflammation through downregulation of oxylipins. Understanding how ASA reduces inflammation may lead to novel HIV prevention approaches.

Blocking Thromboxane-Prostanoid Receptor Signaling Attenuates Lipopolysaccharide- and Stearic Acid-Induced Inflammatory Response in Human PBMCs

Inflammation is implicated in the etiology of obesity-related diseases. Thromboxane-prostanoid receptor (TPR) is known to play a role in mediating an inflammatory response in a variety of cells. Gut-derived lipopolysaccharide (LPS), a TLR4 agonist, is elevated in obesity. Moreover, free fatty acids (FFAs) are important mediators of obesity-related inflammation. However, the role and mechanisms by which TPR regulates the inflammatory response in human immune cells remain unclear. We sought to determine the link between TPR and obesity and the role/mechanisms by which TPR alters LPS- or stearic acid (SA)-induced inflammatory responses in PBMCs. Cells were pre-treated with agents blocking TPR signaling, followed by treatment with LPS or stearic acid (SA). Our findings showed that TPR mRNA levels are higher in PBMCs from individuals with obesity. Blockade of TPR as well as ROCK, which acts downstream of TPR, attenuated LPS- and/or SA-induced pro-inflammatory responses. On the other hand, TPR activation using its agonist enhanced the pro-inflammatory effects of LPS and/or SA. Of note, the TPR agonist by itself elicits an inflammatory response, which was attenuated by blocking TPR or ROCK. Our data suggest that TPR plays a key role in promoting an inflammatory response in human PBMCs, and this effect is mediated via TLR4 and/or ROCK signaling.

TXA2 attenuates allergic lung inflammation through regulation of Th2, Th9, and Treg differentiation

In lung, thromboxane A2 (TXA2) activates the TP receptor to induce proinflammatory and bronchoconstrictor effects. Thus, TP receptor antagonists and TXA2 synthase inhibitors have been tested as potential asthma therapeutics in humans. Th9 cells play key roles in asthma and regulate the lung immune response to allergens. Herein, we found that TXA2 reduces Th9 cell differentiation during allergic lung inflammation. Th9 cells were decreased approximately 2-fold and airway hyperresponsiveness was attenuated in lungs of allergic mice treated with TXA2. Naive CD4+ T cell differentiation to Th9 cells and IL-9 production were inhibited dose-dependently by TXA2 in vitro. TP receptor-deficient mice had an approximately 2-fold increase in numbers of Th9 cells in lungs in vivo after OVA exposure compared with wild-type mice. Naive CD4+ T cells from TP-deficient mice exhibited increased Th9 cell differentiation and IL-9 production in vitro compared with CD4+ T cells from wild-type mice. TXA2 also suppressed Th2 and enhanced Treg differentiation both in vitro and in vivo. Thus, in contrast to its acute, proinflammatory effects, TXA2 also has longer-lasting immunosuppressive effects that attenuate the Th9 differentiation that drives asthma progression. These findings may explain the paradoxical failure of anti-thromboxane therapies in the treatment of asthma.

Lipoxin and glycation in SREBP signaling: Insight into diabetic cardiomyopathy and associated lipotoxicity

Diabetes and cardiovascular diseases are the leading cause of morbidity and mortality worldwide. Diabetes increases cardiovascular risk through hyperglycemia and atherosclerosis. Chronic hyperglycemia accelerates glycation reaction, which forms advanced glycation end products (AGEs). Additionally, hyperglycemia with enhanced levels of cholesterol, native and oxidized low-density lipoproteins, free fatty acids, and oxidative stress induces lipotoxicity. Accelerated glycation and disturbed lipid metabolism are characteristic features of diabetic heart failure. SREBP signaling plays a significant role in lipid and glucose homeostasis. AGEs increase lipotoxicity in diabetic cardiomyopathy by inhibiting SREBP signaling. While anti-inflammatory lipid mediators, lipoxins resolve inflammation caused by lipotoxicity by upregulating the PPARγ expression and regulating CD36. PPARγ connects the bridge between glycation and lipoxin in SREBP signaling. A summary of treatment modalities against diabetic cardiomyopathy is given in brief. This review indicates the novel therapeutic approach in the crosstalk between glycation and lipoxin in SREBP signaling.

Characterization of prostanoids response to Bordetella pertussis antigen BscF and Tdap in LPS-challenged monocytes

Prostanoids are potent inflammatory mediators that play a regulatory role in the innate immune activation of the adaptive immune response to determine the duration of protection against infection. We aim to quantify the modulation of prostanoids profiles in lipopolysaccharide (LPS)-stimulated THP-1 cells treated with the novel pertussis antigen BscF. We compared the effect with pertussis antigens present in the current Tdap vaccine to understand the immunomodulatory effect that might contribute to the diminished Tdap vaccine effectiveness. The inflammatory challenge with LPS induced a robust elevation of most prostanoid family members compared to the control treatment. Treatment with BscF and Tdap significantly reduced the LPS-stimulated elevation of prostaglandins (PGs) D2, E2, and F2α, as well as thromboxane (TX) A2 levels. An opposite trend was observed for PGI2, as both antigens accelerated the LPS-stimulated upregulation. Further, we quantified cyclooxygenases (COXs) that catalyze the biosynthesis of prostanoids and found that both antigens significantly reduced LPS-stimulated COX-1 and COX-2, demonstrating that the waning of acellular pertussis vaccines' protective immunity may be due to other downstream enzymes not related to COXs. Our present study validates the potential role of BscF as an adjuvant, resulting in the next-generation pertussis vaccine discovery.

Prostaglandin regulation of type 2 inflammation: From basic biology to therapeutic interventions

Type 2 immunity is critical for the protective and repair responses that mediate resistance to parasitic helminth infection. This immune response also drives aberrant inflammation during atopic diseases. Prostaglandins are a class of critical lipid mediators that are released during type 2 inflammation and are integral in controlling the initiation, activation, maintenance, effector functions, and resolution of Type 2 inflammation. In this review, we explore the roles of the different prostaglandin family members and the receptors they bind to during allergen‐ and helminth‐induced Type 2 inflammation and the mechanism through which prostaglandins promote or suppress Type 2 inflammation. Furthermore, we discuss the potential role of prostaglandins produced by helminth parasites in the regulation of host–pathogen interactions, and how prostaglandins may regulate the inverse relationship between helminth infection and allergy. Finally, we discuss opportunities to capitalize on our understanding of prostaglandin pathways to develop new therapeutic options for humans experiencing Type 2 inflammatory disorders that have a significant prostaglandin‐driven component including allergic rhinitis and asthma.

Arachidonic Acid Derivatives and Neuroinflammation

Neuroinflammation is characterized by dysregulated inflammatory responses localized within the brain and spinal cord. Neuroinflammation plays a pivotal role in the onset of several neurodegenerative disorders and is considered a typical feature of these disorders. Microglia perform primary immune surveillance and macrophage-like activities within the central nervous system. Activated microglia are predominant players in the central nervous system response to damage related to stroke, trauma, and infection. Moreover, microglial activation per se leads to a proinflammatory response and oxidative stress. During the release of cytokines and chemokines, cyclooxygenases and phospholipase A2 are stimulated. Elevated levels of these compounds play a significant role in immune cell recruitment into the brain. Cyclic phospholipase A2 plays a fundamental role in the production of prostaglandins by releasing arachidonic acid. In turn, arachidonic acid is biotransformed through different routes into several mediators that are endowed with pivotal roles in the regulation of inflammatory processes. Some experimental models of neuroinflammation exhibit an increase in cyclic phospholipase A2, leukotrienes, and prostaglandins such as prostaglandin E2, prostaglandin D2, or prostacyclin. However, findings on the role of the prostacyclin receptors have revealed that their signalling suppresses Th2-mediated inflammatory responses. In addition, other in vitro evidence suggests that prostaglandin E2 may inhibit the production of some inflammatory cytokines, attenuating inflammatory events such as mast cell degranulation or inflammatory leukotriene production. Based on these conflicting experimental data, the role of arachidonic acid derivatives in neuroinflammation remains a challenging issue.

The antiplatelet agent revacept prevents the increase of systemic thromboxane A2 biosynthesis and neointima hyperplasia

Neointima hyperplasia is a crucial component of restenosis after coronary angioplasty. We have hypothesized that enhanced generation of platelet-derived thromboxane (TX)A₂ in response to vascular damage plays a critical role in neointimal hyperplasia and that antiplatelet agents may mitigate it. In cocultures of human platelets and coronary artery smooth muscle cells (CASMC), we found that platelets induced morphologic changes and enhanced the migration of CASMC. The exposure of platelets to Aspirin [an inhibitor of cyclooxygenase (COX)-1] reduced the generation of TXA₂ and prevented the morphological and functional changes induced by platelets in CASMC. Platelet-derived TXA₂ induced COX-2 and enhanced prostaglandin (PG)E₂ biosynthesis in CASMC, a known mechanism promoting neointimal hyperplasia. COX-2 induction was prevented by different antiplatelet agents, i.e., Aspirin, the TP antagonist SQ29,548, or Revacept (a dimeric soluble GPVI-Fc fusion protein). The administration of the novel antiplatelet agent Revacept to C57BL/6 mice, beginning three days before femoral artery denudation, and continuing up to seven days after injury, prevented the increase of the systemic biosynthesis di TXA₂ and reduced femoral artery intima-to-media area and the levels of markers of cell proliferation and macrophage infiltration. Revacept might serve as a therapeutic agent for percutaneous coronary angioplasty and stent implantation.

Inflammation, Lipid (Per)oxidation, and Redox Regulation

Significance: Inflammation increases during the aging process. It is linked to mitochondrial dysfunction and increased reactive oxygen species (ROS) production. Mitochondrial macromolecules are critical targets of oxidative damage; they contribute to respiratory uncoupling with increased ROS production, redox stress, and a cycle of senescence, cytokine production, and impaired oxidative phosphorylation. Targeting the formation or accumulation of oxidized biomolecules, particularly oxidized lipids, in immune cells and mitochondria could be beneficial for age-related inflammation and comorbidities. Recent Advances: Inflammation is central to age-related decline in health and exhibits a complex relationship with mitochondrial redox state and metabolic function. Improvements in mass spectrometric methods have led to the identification of families of oxidized phospholipids (OxPLs), cholesterols, and fatty acids that increase during inflammation and which modulate nuclear factor erythroid 2-related factor 2 (Nrf2), peroxisome proliferator-activated receptor gamma (PPARγ), activator protein 1 (AP1), and NF-κB redox-sensitive transcription factor activity. Critical Issues: The kinetic and spatial resolution of the modified lipidome has profound and sometimes opposing effects on inflammation, promoting initiation at high concentration and resolution at low concentration of OxPLs. Future Directions: There is an emerging opportunity to prevent or delay age-related inflammation and vascular comorbidity through a resolving (oxy)lipidome that is dependent on improving mitochondrial quality control and restoring redox homeostasis.

Antagonism of the Thromboxane-Prostanoid Receptor as a Potential Therapy for Cardiomyopathy of Muscular Dystrophy

Background Muscular dystrophy (MD) causes a progressive cardiomyopathy characterized by diffuse fibrosis, arrhythmia, heart failure, and early death. Activation of the thromboxane-prostanoid receptor (TPr) increases calcium transients in cardiomyocytes and is proarrhythmic and profibrotic. We hypothesized that TPr activation contributes to the cardiac phenotype of MD, and that TPr antagonism would improve cardiac fibrosis and function in preclinical models of MD. Methods and Results Three different mouse models of MD (mdx/utrn double knockout, second generation mdx/mTR double knockout, and delta-sarcoglycan knockout) were given normal drinking water or water containing 25 mg/kg per day of the TPr antagonist ifetroban, beginning at weaning. After 6 months (10 weeks for mdx/utrn double knockout), mice were evaluated for cardiac and skeletal muscle function before euthanization. There was a 100% survival rate of ifetroban-treated mice to the predetermined end point, compared with 60%, 43%, and 90% for mdx/utrn double knockout, mdx/mTR double knockout, and delta-sarcoglycan knockout mice, respectively. TPr antagonism improved cardiac output in mdx/utrn double knockout and mdx/mTR mice, and normalized fractional shortening, ejection fraction, and other parameters in delta-sarcoglycan knockout mice. Cardiac fibrosis in delta-sarcoglycan knockout was reduced with TPr antagonism, which also normalized cardiac expression of claudin-5 and neuronal nitric oxide synthase proteins and multiple signature genes of Duchenne MD. Conclusions TPr antagonism reduced cardiomyopathy and spontaneous death in mouse models of Duchenne and limb-girdle MD. Based on these studies, ifetroban and other TPr antagonists could be novel therapeutics for treatment of the cardiac phenotype in patients with MD.

Multi-target-directed-ligands acting as enzyme inhibitors and receptor ligands

In this review, we present the latest advances in the field of multi-target-directed ligand (MTDL) design for the treatment of various complex pathologies of multifactorial origin. In particular, latest findings in the field of MTDL design targeting both an enzyme and a receptor are presented for different diseases such as Alzheimer's disease (AD), depression, addiction, glaucoma, non-alcoholic steatohepatitis and pain and inflammation. The ethology of the diseases is briefly described, with special emphasis on how the MTDL can evolve into novel therapies that replace the classic pharmacological dogma "one target one disease". Considering the current needs for therapy adherence improvement, it is exposed as from the medicinal chemistry, different molecular scaffolds are studied. With the use of structure activity relationship studies and molecular optimization, new hybrid molecules are generated with improved biological properties acting at two biologically very distinct targets.

Differential expression of the TPα and TPβ isoforms of the human T Prostanoid receptor during chronic inflammation of the prostate: Role for FOXP1 in the transcriptional regulation of TPβ during monocyte-macrophage differentiation

Inflammation is linked to prostate cancer (PCa) and to other diseases of the prostate. The prostanoid thromboxane (TX)A₂ is a pro-inflammatory mediator implicated in several prostatic diseases, including PCa. TXA₂ signals through the TPα and TPβ isoforms of the T Prostanoid receptor (TP) which exhibit several functional differences and transcriptionally regulated by distinct promoters Prm1 and Prm3, respectively, within the TBXA2R gene. This study examined the expression of TPα and TPβ in inflammatory infiltrates within human prostate tissue. Strikingly, TPβ expression was detected in 94% of infiltrates, including in B- and T-lymphocytes and macrophages. In contrast, TPα was more variably expressed and, where present, expression was mainly confined to macrophages. To gain molecular insight into these findings, expression of TPα and TPβ was evaluated as a function of monocyte-to-macrophage differentiation in THP-1 cells. Expression of both TPα and TPβ was upregulated following phorbol-12-myristate-13-acetate (PMA)-induced differentiation of monocytic THP-1 to their macrophage lineage. Furthermore, FOXP1, an essential transcriptional regulator down-regulated during monocyte-to-macrophage differentiation, was identified as a key trans-acting factor regulating TPβ expression through Prm3 in THP-1 cells. Knockdown of FOXP1 increased TPβ, but not TPα, expression in THP-1 cells, while genetic reporter and chromatin immunoprecipitation (ChIP) analyses established that FOXP1 exerts its repressive effect on TPβ through binding to four cis-elements within Prm3. Collectively, FOXP1 functions as a transcriptional repressor of TPβ in monocytes. This repression is lifted in differentiated macrophages, allowing for upregulation of TPβ expression and possibly accounting for the prominent expression of TPβ in prostate tissue-resident macrophages.

Platelet-Specific Deletion of Cyclooxygenase-1 Ameliorates Dextran Sulfate Sodium-Induced Colitis in Mice

Inflammatory bowel disease (IBD) is associated with an increased risk for thromboembolism, platelet activation, and abnormalities in platelet number and size. In colitis, platelets can extravasate into the colonic interstitium. We generated a mouse with a specific deletion of cyclooxygenase (COX)-1 in megakaryocytes/platelets [(COX-1 conditional knockout (cKO)] to clarify the role of platelet activation in the development of inflammation and fibrosis in dextran sodium sulfate (DSS)-induced colitis. The disease activity index was assessed, and colonic specimens were evaluated for histologic features of epithelial barrier damage, inflammation, and fibrosis. Cocultures of platelets and myofibroblasts were performed. We found that the specific deletion of COX-1 in platelets, which recapitulated the human pharmacodynamics of low-dose aspirin, that is, suppression of platelet thromboxane (TX)A₂ production associated with substantial sparing of the systemic production of prostacyclin, resulted in milder symptoms of colitis, in the acute phase, and almost complete recovery from the disease after DSS withdrawal. Reduced colonic accumulation of macrophages and myofibroblasts and collagen deposition was found. Platelet-derived TXA₂ enhanced the ability of myofibroblasts to proliferate and migrate in vitro, and these effects were prevented by platelet COX-1 inhibition or antagonism of the TXA₂ receptor. Our findings allow a significant advance in the knowledge of the role of platelet-derived TXA₂ in the development of colitis and fibrosis in response to intestinal damage and provide the rationale to investigate the potential efficacy of the antiplatelet agent low-dose aspirin in limiting the inflammatory response and fibrosis associated with IBD. SIGNIFICANCE STATEMENT: Inflammatory bowel disease (IBD) is characterized by the development of a chronic inflammatory response, which can lead to intestinal fibrosis for which currently there is no medical treatment. Through the generation of a mouse with specific deletion of cyclooxygenase-1 in megakaryocytes/platelets, which recapitulates the human pharmacodynamics of low-dose aspirin, we demonstrate the important role of platelet-derived thromboxane A₂ in the development of experimental colitis and fibrosis, thus providing the rationale to investigate the potential efficacy of low-dose aspirin in limiting the inflammation and tissue damage associated with IBD.

Metabolomics profiling of haloperidol and validation of thromboxane-related signaling in the early development of zebrafish

Haloperidol is a common butyrophenone-derivative antipsychotic drug that is used clinically to treat schizophrenia and to control Tourette disorder. Haloperidol has been shown to be an embryonic toxicant and to cause a variety of adverse effects that affect human embryonic development. However, the pathway impaired by haloperidol during the developmental stages remains unclear. To elucidate the innate toxicological pathway of haloperidol, we investigated the lethality of haloperidol during the embryonic development of zebrafish. We observed that haloperidol caused serious morphological changes, with an LD₅₀ of 9.7 x 10^-6 ± 2.4 x 10^-6 μg/L. Next, we established a systematic approach to perform metabolite profiling in embryonic zebrafish with various concentrations of haloperidol and analyzed the metabolites using ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF MS). A total of 304 metabolites were identified and 86 metabolites were chosen to predict potential pathways. Among the metabolites, we found through prediction that numerous metabolomics-biological pathways are associated with haloperidol, including peroxisome-proliferator-activated receptor (ppar), thromboxane, and mTOR signaling. Quantitative real time-qPCR was then used to validate the gene expression potentially associated with the thromboxane, which is a metabolic product of arachidonic acid and considered to be important for cell proliferation and the inflammatory response. To sum up, analysis of metabolites in the zebrafish model provides a system for mining biomarkers that reflect biological significance and highlight the therapeutic potency in humans. In addition, it may show potential for application to other pharmaceuticals to identify their various activities and clarify functional mechanisms in the future.

Dissecting the Genomic Architecture of Resistance to Eimeria maxima Parasitism in the Chicken

Coccidiosis in poultry, caused by protozoan parasites of the genus Eimeria, is an intestinal disease with substantial economic impact. With the use of anticoccidial drugs under public and political pressure, and the comparatively higher cost of live-attenuated vaccines, an attractive complementary strategy for control is to breed chickens with increased resistance to Eimeria parasitism. Prior infection with Eimeria maxima leads to complete immunity against challenge with homologous strains, but only partial resistance to challenge with antigenically diverse heterologous strains. We investigate the genetic architecture of avian resistance to E. maxima primary infection and heterologous strain secondary challenge using White Leghorn populations of derived inbred lines, C.B12 and 15I, known to differ in susceptibility to the parasite. An intercross population was infected with E. maxima Houghton (H) strain, followed 3 weeks later by E. maxima Weybridge (W) strain challenge, while a backcross population received a single E. maxima W infection. The phenotypes measured were parasite replication (counting fecal oocyst output or qPCR for parasite numbers in intestinal tissue), intestinal lesion score (gross pathology, scale 0-4), and for the backcross only, serum interleukin-10 (IL-10) levels. Birds were genotyped using a high density genome-wide DNA array (600K, Affymetrix). Genome-wide association study located associations on chromosomes 1, 2, 3, and 5 following primary infection in the backcross population, and a suggestive association on chromosome 1 following heterologous E. maxima W challenge in the intercross population. This mapped several megabases away from the quantitative trait locus (QTL) linked to the backcross primary W strain infection, suggesting different underlying mechanisms for the primary- and heterologous secondary- responses. Underlying pathways for those genes located in the respective QTL for resistance to primary infection and protection against heterologous challenge were related mainly to immune response, with IL-10 signaling in the backcross primary infection being the most significant. Additionally, the identified markers associated with IL-10 levels exhibited significant additive genetic variance. We suggest this is a phenotype of interest to the outcome of challenge, being scalable in live birds and negating the requirement for single-bird cages, fecal oocyst counts, or slaughter for sampling (qPCR).

Expression of the TPα and TPβ isoforms of the thromboxane prostanoid receptor (TP) in prostate cancer: clinical significance and diagnostic potential

The prostanoid thromboxane (TX) A₂ plays a central role in haemostasis and is increasingly implicated in cancer progression. TXA₂ signals through two T Prostanoid receptor (TP) isoforms termed TPα and TPβ, with both encoded by the TBXA2R gene. Despite exhibiting several functional and regulatory differences, the role of the individual TP isoforms in neoplastic diseases is largely unknown.

This study evaluated expression of the TPα and TPβ isoforms in tumour microarrays of the benign prostate and different pathological (Gleason) grades of prostate cancer (PCa). Expression of TPβ was significantly increased in PCa relative to benign tissue and strongly correlated with increasing Gleason grade. Furthermore, higher TPβ expression was associated with increased risk of biochemical recurrence (BCR) and significantly shorter disease-free survival time in patients post-surgery. While TPα was more variably expressed than TPβ in PCa, increased/high TPα expression within the tumour also trended toward increased BCR and shorter disease-free survival time. Comparative genomic CpG DNA methylation analysis revealed substantial differences in the extent of methylation of the promoter regions of the TBXA2R that specifically regulate expression of TPα and TPβ, respectively, both in benign prostate and in clinically-derived tissue representative of precursor lesions and progressive stages of PCa. Collectively, TPα and TPβ expression is differentially regulated both in the benign and tumourigenic prostate, and coincides with clinical pathology and altered CpG methylation of the TBXA2R gene. Analysis of TPβ, or a combination of TPα/TPβ, expression levels may have significant clinical potential as a diagnostic biomarker and predictor of PCa disease recurrence.

CD4+ T cells in atherosclerosis: Regulation by platelets

Atherosclerosis is an inflammatory and thrombotic disease, in which both CD4+ T cells and platelets play important roles throughout all stages of atherogenesis. CD4+ T cells are the most abundant T cells present in atherosclerotic lesions. They are primarily seen as type 1 T helper (Th1) cells, while the other CD4+ T cell subsets Th2, Th17, and regulatory T (Treg) cells are also found in the lesions with lower frequencies. CD4+ T effector cells release various cytokines, which exert paracrine or autocrine effects among different CD4+ T cell subsets and other lesional cells and subsequently modulate inflammatory processes in the lesions. Platelets are instrumental in thrombosis and haemostasis, but also play important regulatory roles in immune response, inflammation, and angiogenesis. The present review summarises the current knowledge and/or understanding on how platelets regulate recruitment, activation, differentiation, and cytokine production of different CD4+ T cell subsets, as well as impacts of the platelet-CD4+ T cell interactions on atherogenesis. The research perspectives of platelet-CD4+ T cell interaction in atherosclerosis are also discussed.

Prostaglandin E2 produced following infection with Theiler's virus promotes the pathogenesis of demyelinating disease

Infection of various cells with Theiler’s murine encephalomyelitis virus (TMEV) activates the TLR- and melanoma differentiation-associated gene 5 (MDA5)-dependent pathways, resulting in the production of IL-1β via the activation of caspase-1 upon assembly of the node-like receptor protein 3 (NLRP3) inflammasome. The role of IL-1β in the pathogenesis of TMEV-induced demyelinating disease was previously investigated. However, the signaling effects of prostaglandin E2 (PGE₂) downstream of the NLRP3 inflammasome on the immune responses to viral determinants and the pathogenesis of demyelinating disease are unknown. In this study, we investigated the levels of intermediate molecules leading to PGE₂ signaling and the effects of blocking PGE₂ signaling on the immune response to TMEV infection, viral persistence and the development of demyelinating disease. We demonstrate here that TMEV infection activates the NLRP3 inflammasome and PGE₂ signaling much more vigorously in dendritic cells (DCs) and CD11b⁺ cells from susceptible SJL mice than in cells from resistant B6 mice. Inhibition of virus-induced PGE₂ signaling using AH23848 resulted in decreased pathogenesis of demyelinating disease and viral loads in the central nervous system (CNS). In addition, AH23848 treatment caused the elevation of protective early IFN-γ-producing CD4⁺ and CD8⁺ T cell responses. Because the levels of IFN-β were lower in AH23848-treated mice but the level of IL-6 was similar, over-production of pathogenic IFN-β was modulated and the generation of IFN-γ-producing T cell responses was enhanced by the inhibition of PGE₂ signaling. These results strongly suggest that excessive activation of the NLRP3 inflammasome and downstream PGE₂ signaling contribute to the pathogenesis of TMEV-induced demyelinating disease.

Platelets in Pulmonary Immune Responses and Inflammatory Lung Diseases

Platelets are essential for physiological hemostasis and are central in pathological thrombosis. These are their traditional and best known activities in health and disease. In addition, however, platelets have specializations that broaden their functional repertoire considerably. These functional capabilities, some of which are recently discovered, include the ability to sense and respond to infectious and immune signals and to act as inflammatory effector cells. Human platelets and platelets from mice and other experimental animals can link the innate and adaptive limbs of the immune system and act across the immune continuum, often also linking immune and hemostatic functions. Traditional and newly recognized facets of the biology of platelets are relevant to defensive, physiological immune responses of the lungs and to inflammatory lung diseases. The emerging view of platelets as blood cells that are much more diverse and versatile than previously thought further predicts that additional features of the biology of platelets and of megakaryocytes, the precursors of platelets, will be discovered and that some of these will also influence pulmonary immune defenses and inflammatory injury.

Thromboxane synthase deficiency improves insulin action and attenuates adipose tissue fibrosis

Thromboxane A2, an arachidonic acid-derived eicosanoid generated by thromboxane synthase (TBXAS), plays critical roles in hemostasis and inflammation. However, the contribution of thromboxane A2 to obesity-linked metabolic dysfunction remains incompletely understood. Here, we used in vitro and mouse models to better define the role of TBXAS in metabolic homeostasis. We found that adipose expression of Tbxas and thromboxane A2 receptor (Tbxa2r) was significantly upregulated in genetic and dietary mouse models of obesity and diabetes. Expression of Tbxas and Tbxa2r was detected in adipose stromal cells, including macrophages. Furthermore, stimulation of macrophages with interferon-γ or resistin factors known to be upregulated in obesity induced Tbxas and Tbxa2r expression. Mice lacking Tbxas had similar weight gain, food intake, and energy expenditure. However, loss of Tbxas markedly enhanced insulin sensitivity in mice fed a low-fat diet. Improvement in glucose homeostasis was correlated with the upregulated expression of multiple secreted metabolic regulators (Ctrp3, Ctrp9, and Ctrp12) in the visceral fat depot. Following a challenge with a high-fat diet, Tbxas deficiency led to attenuated adipose tissue fibrosis and reduced circulating IL-6 levels without adipose tissue macrophages being affected; however, these changes were not sufficient to improve whole body insulin action. Together, our results highlight a novel, diet-dependent role for thromboxane A2 in modulating peripheral tissue insulin sensitivity and adipose tissue fibrosis.

Glucocorticoids sensitize rat placental inflammatory responses via inhibiting lipoxin A4 biosynthesis

Inflammation dysregulation in placenta is implicated in the pathogenesis of numerous pregnancy complications. Glucocorticoids (GCs), universally considered anti-inflammatory, can also exert proinflammatory actions under some conditions, whereas whether and how GCs promote placental inflammation have not been intensively investigated. In this paper we report the opposing regulation of rat placental inflammation by synthetic GC dexamethasone (Dex). When Dex was subcutaneously injected 1 h after we administered an intraperitoneal lipopolysaccharide (LPS) challenge, neutrophil infiltration and proinflammatory Il1b, Il6, and Tnfa expression in rat placenta were significantly reduced. In contrast, Dex pretreatment for 24 h potentiated rat placental proinflammatory response to LPS and delayed inflammation resolution, which involved MAPKs and NF-kappaB activation. Mechanically, Dex pretreatment promoted 5-lipoxygenase (ALOX5) activation and increased leukotriene B4 production, whereas it inhibited the anti-inflammatory and proresolving lipid mediator lipoxin A4 (LXA4) biosynthesis in rat placenta via downregulating ALOX15 and ALOX15B expression. Moreover, LXA4 supplementation dampened Dex-potentiated placental inflammation and suppressed Dex-mediated ALOX5 activation in vivo and in vitro. Taken together, these findings suggest that GCs exposure could promote placental inflammation initiation and delay resolution via disrupting LXA4 biosynthesis.

Polyunsaturated Fatty Acid-derived lipid mediators and T cell function

Fatty acids are involved in T cell biology both as nutrients important for energy production as well as signaling molecules. In particular, polyunsaturated fatty acids are known to exhibit a range of immunomodulatory properties that progress through T cell mediated events, although the molecular mechanisms of these actions have not yet been fully elucidated. Some of these immune activities are linked to polyunsaturated fatty acid-induced alteration of the composition of cellular membranes and the consequent changes in signaling pathways linked to membrane raft-associated proteins. However, significant aspects of the polyunsaturated fatty acid bioactivities are mediated through their transformation to specific lipid mediators, products of cyclooxygenase, lipoxygenase, or cytochrome P450 enzymatic reactions. Resulting bioactive metabolites including prostaglandins, leukotrienes, and endocannabinoids are produced by and/or act upon T leukocytes through cell surface receptors and have been shown to alter T cell activation and differentiation, proliferation, cytokine production, motility, and homing events. Detailed appreciation of the mode of action of these lipids presents opportunities for the design and development of therapeutic strategies aimed at regulating T cell function.

Comparison of supplementation of n-3 fatty acids from fish and flax oil on cytokine gene expression and growth of milk-fed Holstein calves

The ability to reduce incidence of disease in calves and improve early vaccination strategies is of particular interest for dairy producers. The n-3 fatty acids have been reported to reduce inflammatory diseases in humans but limited research has been done in calves. The objective of this study was to compare supplementation of n-3 fatty acids from fish and flax oil on gene expression of whole blood cells and growth of milk-fed Holstein calves. Forty-eight Holstein bull calves from a commercial dairy were randomly assigned to 1 of 3 diets beginning at 4d old: (1) control milk replacer (MR) with all pork fat, (2) MR with 2% flax oil, and (3) MR with 2% fish oil. All MR were 17% fat, 27% crude protein on a dry matter (DM) basis, with all protein from whey sources. Calves were each fed 654g DM of MR daily for the first 25d and then 327g/d for d26, 27, and 28. On d28, calves were challenged with a Pasteurella vaccine and the temperature response to the vaccine was recorded. Milk and feed intake and fecal scores were recorded daily, and body weight and hip width were recorded weekly. Blood was collected from all calves on d25. One tube of collected blood was incubated with endotoxin (lipopolysaccharide; LPS) for 2h and frozen with a second tube of control blood. Quantitative real-time PCR was used to assess the effects of LPS stimulation on cytokine gene expression. During the 28 d, calves supplemented with flax oil had a greater growth rate and feed efficiency than calves fed fish oil (0.52±0.02 vs. 0.48±0.02g of gain:g of feed). Fish oil tended to decrease LPS stimulation of tumor necrosis factor-α expression. Flax oil, but not fish oil, decreased the expression of IL-4 and tended to decrease expression of osteopontin and IL-8. Flax oil tended to reduce the increase in rectal temperature in response to a Pasteurella vaccine. In conclusion, our data support the idea that supplementation with n-3 fatty acids affects cytokine gene expression.

Proinflammatory and immunoregulatory roles of eicosanoids in T cells

Eicosanoids are inflammatory mediators primarily generated by hydrolysis of membrane phospholipids by phospholipase A2 to ω-3 and ω-6 C20 fatty acids that next are converted to leukotrienes (LTs), prostaglandins (PGs), prostacyclins (PCs), and thromboxanes (TXAs). The rate-limiting and tightly regulated lipoxygenases control synthesis of LTs while the equally well-controlled cyclooxygenases 1 and 2 generate prostanoids, including PGs, PCs, and TXAs. While many of the classical signs of inflammation such as redness, swelling, pain, and heat are caused by eicosanoid species with vasoactive, pyretic, and pain-inducing effects locally, some eicosanoids also regulate T cell functions. Here, we will review eicosanoid production in T cell subsets and the inflammatory and immunoregulatory functions of LTs, PGs, PCs, and TXAs in T cells.

Prostanoids as regulators of innate and adaptive immunity

Potent, oxygenated lipid molecules called prostanoids regulate a wide variety of physiological responses and pathological processes. Prostanoids are produced by various cell types and act on target cells through specific G protein-coupled receptors. Although prostanoids have historically been considered acute inflammation mediators, studies using specific receptor knockout mice indicate that prostanoids, in fact, regulate various aspects of both innate and adaptive immunity. Each prostanoid, depending on which receptor it acts on, exerts specific effects on immune cells such as macrophages, dendritic cells, and T and B lymphocytes, often in concert with microbial ligands and cytokines, to affect the strength, quality, and duration of immune responses. Prostanoids are also relevant to immunopathology, from inflammation to autoimmunity and cancer. Here, we review the role of prostanoids in regulating immunity, their involvement in immunopathology, and areas of insight that may lead to new therapeutic opportunities.

Aspirin and immune system

The time-tested gradual exploration of aspirin's diverse pharmacological properties has made it the most reliable therapeutic agent worldwide. In addition to its well-argued anti-inflammatory effects, many new and exciting data have emerged regarding the role of aspirin in cells of the immune system and certain immunopathological states. For instance, aspirin induces tolerogenic activity in dendritic cells and determines the fate of naive T cells to regulatory phenotypes, which suggests its immunoregulatory potential in relevance to immune tolerance. It also displays some intriguing traits to modulate the innate and adaptive immune responses. In this article, the immunomodulatory relation of aspirin to different immune cells, such as neutrophils, macrophages, dendritic cells (DCs), natural killer (NK) cells, and the T and B lymphocytes has been highlighted. Moreover, the clinical prospects of aspirin in terms of autoimmunity, allograft rejection and immune tolerance have also been outlined.

Thromboxane receptor signaling is required for fibronectin-induced matrix metalloproteinase 9 production by human and murine macrophages and is attenuated by the Arhgef1 molecule

During an inflammatory response, resident and newly recruited tissue macrophages adhere to extracellular matrix and cell-bound integrin ligands. This interaction induces the expression of pro-inflammatory mediators that include matrix metalloproteinases (MMPs). Arhgef1 is an intracellular signaling molecule expressed by myeloid cells that normally attenuates murine macrophage MMP production in vivo and in vitro after cell culture on the extracellular matrix protein, fibronectin. In this study, we have extended the characterization of this fibronectin-induced Arhgef1-regulated signaling pathway in both human and murine myeloid cells. Our results show that MMP9 production by fibronectin-stimulated monocytes and macrophages depends on autocrine thromboxane receptor signaling and that under normal conditions, this signaling pathway is attenuated by Arhgef1. Finally, we show that the expression of ARHGEF1 by human peripheral blood monocytes varies between individuals and inversely correlates with fibronectin-mediated MMP9 production.

International Union of Basic and Clinical Pharmacology. LXXXIII: classification of prostanoid receptors, updating 15 years of progress

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=58). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP(2) receptor, also termed CRTH2, has little structural resemblance to DP(1) and other receptors described in the original prostanoid receptor classification. DP(2) receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A(2) heterodimeric receptors for 8-epi-prostaglandin E(2), wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

Platelets contribute to allograft rejection through glutamate receptor signaling

Platelets recruit leukocytes and mediate interactions between leukocytes and endothelial cells. Platelets have been long described as markers of transplant rejection, but the contribution of platelets to transplant rejection has not been critically examined. We demonstrate in this study that following T cell initiation of allograft rejection, platelets contribute to T cell recruitment and increased plasma inflammatory mediators and accelerate T cell-meditated skin graft rejection. Prior work from our laboratory has shown that platelets secrete glutamate when activated, which then induces platelet thromboxane production by signaling through platelet-expressed ionotropic glutamate receptors. Glutamate receptor antagonists therefore represent, to our knowledge, novel inhibitors of platelet-accelerated inflammation. We have found that plasma glutamate is increased in mice that receive skin grafts and that mice treated with glutamate receptor antagonists have improved graft survival and decreased plasma thromboxane, platelet factor 4 (CXCL4), and IFN-γ. Taken together, our work now demonstrates that subsequent to T cell initiation of skin graft rejection, platelets contribute to further T cell recruitment and that by blunting glutamate-mediated platelet activation, graft survival is improved.

Thromboxane prostanoid receptor stimulation induces shedding of the transmembrane chemokine CX3CL1 yet enhances CX3CL1-dependent leukocyte adhesion

In atherosclerosis, chemokines recruit circulating mononuclear leukocytes to the vascular wall. A key factor is CX3CL1, a chemokine with soluble and transmembrane species that acts as both a chemoattractant and an adhesion molecule. Thromboxane A2 and its receptor, TP, are also critical to atherogenesis by promoting vascular inflammation and consequent leukocyte recruitment. We examined the effects of TP stimulation on processing and function of CX3CL1, using CX3CL1-expressing human ECV-304 cells and primary human vascular endothelial cells. TP agonists promoted rapid shedding of cell surface CX3CL1, which was inhibited by pharmacological inhibitors or specific small interfering RNA targeting tumor necrosis factor-α-converting enzyme (TACE). Because it reduced cell surface CX3CL1, we predicted that TP stimulation would inhibit adhesion of leukocytes expressing the CX3CL1 cognate receptor but, paradoxically, saw enhanced adhesion. We questioned whether the enhanced ability of the remaining membrane-associated CX3CL1 to bind targets was caused by changes in its lateral mobility. Using fluorescence recovery after photobleaching, we found that plasmalemmal CX3CL1 was initially tethered but ultimately mobilized by TP agonists. TP stimulation provoked clustering of transmembrane CX3CL1 at sites of contact with adherent leukocytes. These data demonstrate that TP stimulation induces two distinct effects: a rapid cleavage of surface CX3CL1, thereby releasing the soluble chemoattractant, plus mobilization of the remaining transmembrane CX3CL1 to enhance the avidity of interactions with adherent leukocytes. The dual effect of TP allows CX3CL1 to recruit leukocytes to sites of vascular inflammation while enhancing their adhesion once recruited.

Pharmacokinetic-pharmacodynamic modelling of the analgesic effects of lumiracoxib, a selective inhibitor of cyclooxygenase-2, in rats

BACKGROUND AND PURPOSE

This study establishes a pharmacokinetic/pharmacodynamic (PK/PD) model to describe the time course and in vivo mechanisms of action of the antinociceptive effects of lumiracoxib, evaluated by the thermal hyperalgesia test in rats.

EXPERIMENTAL APPROACH

Female Wistar fasted rats were injected s.c. with saline or carrageenan in the right hind paw, followed by either 0, 1, 3, 10 or 30 mg*kg(-1) of oral lumiracoxib at the time of carrageenan injection (experiment I), or 0, 10 or 30 mg*kg(-1) oral lumiracoxib at 4 h after carrageenan injection (experiment II). Antihyperalgesic responses were measured as latency time (LT) to a thermal stimulus. PK/PD modelling of the antinociceptive response was performed using the population approach with NONMEM VI.

RESULTS

A two-compartment model described the plasma disposition. A first-order model, including lag time and decreased relative bioavailability as a function of the dose, described the absorption process. The response model was: LT=LT(0)/(1 +MED). LT(0) is the baseline response, and MED represents the level of inflammatory mediators. The time course of MED was assumed to be equivalent to the predicted profile of COX-2 activity and was modelled according to an indirect response model with a time variant synthesis rate. Drug effects were described as a reversible inhibition of the COX-2 activity. The in vivo estimate of the dissociation equilibrium constant of the COX-2-lumiracoxib complex was 0.24 microg*mL(-1).

CONCLUSIONS

The model developed appropriately described the time course of pharmacological responses to lumiracoxib, in terms of its mechanism of action and pharmacokinetics.

Glomerular type 1 angiotensin receptors augment kidney injury and inflammation in murine autoimmune nephritis

Studies in humans and animal models indicate a key contribution of angiotensin II to the pathogenesis of glomerular diseases. To examine the role of type 1 angiotensin (AT1) receptors in glomerular inflammation associated with autoimmune disease, we generated MRL-Faslpr/lpr (lpr) mice lacking the major murine type 1 angiotensin receptor (AT1A); lpr mice develop a generalized autoimmune disease with glomerulonephritis that resembles SLE. Surprisingly, AT1A deficiency was not protective against disease but instead substantially accelerated mortality, proteinuria, and kidney pathology. Increased disease severity was not a direct effect of immune cells, since transplantation of AT1A-deficient bone marrow did not affect survival. Moreover, autoimmune injury in extrarenal tissues, including skin, heart, and joints, was unaffected by AT1A deficiency. In murine systems, there is a second type 1 angiotensin receptor isoform, AT1B, and its expression is especially prominent in the renal glomerulus within podocytes. Further, expression of renin was enhanced in kidneys of AT1A-deficient lpr mice, and they showed evidence of exaggerated AT1B receptor activation, including substantially increased podocyte injury and expression of inflammatory mediators. Administration of losartan, which blocks all type 1 angiotensin receptors, reduced markers of kidney disease, including proteinuria, glomerular pathology, and cytokine mRNA expression. Since AT1A-deficient lpr mice had low blood pressure, these findings suggest that activation of type 1 angiotensin receptors in the glomerulus is sufficient to accelerate renal injury and inflammation in the absence of hypertension.

Dynamics of thromboxane level changes during early phase of allograft reperfusion

BACKGROUND

Thromboxane (Tx) is a metabolite of arachidonic acid, which exerts a significant influence on kidney homeostasis, and may be involved in the pathogenesis of allograft rejection. The aim of this study was to: examine the dynamics of TxB2 changes during early phase of kidney allograft reperfusion, and analyze whether the observed changes in the concentrations and direction of TxB2 changes, are associated with post-transplant graft function.

METHODS

Sixty-nine transplant recipients were divided into early, slow and delayed graft function group. Blood samples were collected directly before and during first the five minutes of allograft reperfusion. TxB2 concentrations were measured using ELISA. Creatinine and GFR levels were measured on the first, fifth, and 10th post-transplant day.

RESULTS

The results demonstrated that during reperfusion significant differences in TxB2 concentrations occur in all groups. Moreover, significant differences in the concentrations, as well as in the dynamics of TxB2 changes between patients with immediate graft function, and individuals with allograft activation problems, were noticed. These differences were associated with post-transplant graft function.

CONCLUSIONS

Human renal transplantations are accompanied by changes in TxB2 concentrations, and the dynamics of TxB2 changes is associated with early post-transplant graft function. Our results also highlight TxB2 as a potential pre-transplant marker of post-transplant allograft function.

Platelets an inflammatory force in transplantation

Platelet interactions with dendritic cells, T cells and B cells have been best studied in vasculitis and atherosclerosis, but similar mechanisms may contribute to acute and chronic vascular lesions in transplants. In acute inflammation, platelets adhere to vessels and release mediators that increase endothelial cell activation and leukocyte recruitment. Adherent platelets can also augment antibody and cellular immune responses. Activated platelets recruit T cells and initiate a feedback loop. In this loop, platelets secrete chemokines to recruit T cells, and then activated T cells stimulate platelets through CD40-CD154 interactions to secrete more chemokines thereby recruiting more T cells. The interaction of platelets and T cells is enhanced by P-selectin/PSGL-1 stimulation. Both helper and cytotoxic T cells are stimulated by platelets. Antibody production that is stimulated through increased helper T-cell function can activate complement. This sets up another activation loop because platelets express receptors for antibodies and complement. In addition to inflammation, platelets stimulate repair by releasing growth factors and chemokines to recruit circulating vascular progenitor cells. These repair mechanisms could promote the replacement of donor parenchmal cells with recipient cells and contribute to vascuplopathy. This review discusses the interplay of platelets and the immune system in relation to transplantation.

Antagonism of thromboxane receptors by diclofenac and lumiracoxib

BACKGROUND AND PURPOSE

Non-steroidal anti-inflammatory drugs (NSAIDs) are analgesic and anti-inflammatory by virtue of inhibition of the cyclooxygenase (COX) reaction that initiates biosynthesis of prostaglandins. Findings in a pulmonary pharmacology project gave rise to the hypothesis that certain members of the NSAID class might also be antagonists of the thromboxane (TP) receptor.

EXPERIMENTAL APPROACH

Functional responses due to activation of the TP receptor were studied in isolated airway and vascular smooth muscle preparations from guinea pigs and rats as well as in human platelets. Receptor binding and activation of the TP receptor was studied in HEK293 cells.

KEY RESULTS

Diclofenac concentration-dependently and selectively inhibited the contraction responses to TP receptor agonists such as prostaglandin D2 and U-46619 in the tested smooth muscle preparations and the aggregation of human platelets. The competitive antagonism of the TP receptor was confirmed by binding studies and at the level of signal transduction. The selective COX-2 inhibitor lumiracoxib shared this activity profile, whereas a number of standard NSAIDs and other selective COX-2 inhibitors did not.

CONCLUSIONS AND IMPLICATIONS

Diclofenac and lumiracoxib, in addition to being COX unselective and highly COX-2 selective inhibitors, respectively, displayed a previously unknown pharmacological activity, namely TP receptor antagonism. Development of COX-2 selective inhibitors with dual activity as potent TP antagonists may lead to coxibs with improved cardiovascular safety, as the TP receptor mediates cardiovascular effects of thromboxane A2 and isoprostanes.

Requirements for T lymphocyte migration in explanted lymph nodes

Although the requirements for T lymphocyte homing to lymph nodes (LNs) are well studied, much less is known about the requirements for T lymphocyte locomotion within LNs. Imaging of murine T lymphocyte migration in explanted LNs using two-photon laser-scanning fluorescence microscopy provides an opportunity to systematically study these requirements. We have developed a closed system for imaging an intact LN with controlled temperature, oxygenation, and perfusion rate. Naive T lymphocyte locomotion in the deep paracortex of the LN required a perfusion rate of >13 microm/s and a partial pressure of O(2) (pO(2)) of >7.4%. Naive T lymphocyte locomotion in the subcapsular region was 38% slower and had higher turning angles and arrest coefficients than naive T lymphocytes in the deep paracortex. T lymphocyte activation decreased the requirement for pO(2), but also decreased the speed of locomotion in the deep paracortex. Although CCR7(-/-) naive T cells displayed a small reduction in locomotion, systemic treatment with pertussis toxin reduced naive T lymphocyte speed by 59%, indicating a contribution of Galpha(i)-mediated signaling, but involvement of other G protein-coupled receptors besides CCR7. Receptor knockouts or pharmacological inhibition in the adenosine, PG/lipoxygenase, lysophosphatidylcholine, and sphingosine-1-phosphate pathways did not individually alter naive T cell migration. These data implicate pO(2), tissue architecture, and G-protein coupled receptor signaling in regulation of naive T lymphocyte migration in explanted LNs.

Imbalanced synthesis of cyclooxygenase-derived thromboxane A2 and prostacyclin compromises vasomotor function of the thoracic aorta in Marfan syndrome

BACKGROUND AND PURPOSE

Thoracic aortic dissection is a life-threatening complication of Marfan syndrome, a connective tissue disorder caused by mutations in the gene encoding fibrillin-1. We have demonstrated that nitric oxide-mediated endothelial-dependent relaxation is impaired in the thoracic aorta in Marfan syndrome. In the present study, we determined whether the cyclooxygenase (COX)-pathway is involved in the compromised aortic vasomotor function.

EXPERIMENTAL APPROACH

Thoracic aortae from mice at 3, 6 and 9 months of age, heterozygous for the Fbn1 allele encoding a cysteine substitution (Fbn1 (C1039G/+), 'Marfan', n=35), were compared with those from age-matched controls (n=35).

KEY RESULTS

Isometric force measurement revealed that preincubation with indomethacin, a non-specific COX inhibitor, but not valeryl salicylate, a specific COX-1 inhibitor, improved the phenylephrine-induced contractions (at 6 months, EC(50) and E(max) were increased 4.5-fold and by 45%, respectively) in Marfan aortae. Sensitivity to acetylcholine-induced relaxation was improved 10-fold. Blockade of the thromboxane-endoperoxide receptor by SQ-29548 did not affect phenylephrine-mediated contractions in Marfan aortae, although they did respond to the thromboxane analogue, U46619. From 6 months on, phenylephrine-induced secretion of prostacyclin and thromboxane A(2) in Marfan aortae was 200% and 40%, respectively, of those in controls. Reduced COX-1 expression was detected in Marfan aortae at 3 and 9 months, whilst COX-2 expression was increased from 3 months on.

CONCLUSIONS AND IMPLICATIONS

The compromised vasomotor function in Marfan thoracic aortae is associated with an imbalanced synthesis of thromboxane A(2) and prostacyclin resulting from the differential protein expression of COX-1 and COX-2.

Thromboxane A2 is a key regulator of pathogenesis during Trypanosoma cruzi infection

Chagas' disease is caused by infection with the parasite Trypanosoma cruzi. We report that infected, but not uninfected, human endothelial cells (ECs) released thromboxane A(2) (TXA(2)). Physical chromatography and liquid chromatography-tandem mass spectrometry revealed that TXA(2) is the predominant eicosanoid present in all life stages of T. cruzi. Parasite-derived TXA(2) accounts for up to 90% of the circulating levels of TXA(2) in infected wild-type mice, and perturbs host physiology. Mice in which the gene for the TXA(2) receptor (TP) has been deleted, exhibited higher mortality and more severe cardiac pathology and parasitism (fourfold) than WT mice after infection. Conversely, deletion of the TXA(2) synthase gene had no effect on survival or disease severity. TP expression on somatic cells, but not cells involved in either acquired or innate immunity, was the primary determinant of disease progression. The higher intracellular parasitism observed in TP-null ECs was ablated upon restoration of TP expression. We conclude that the host response to parasite-derived TXA(2) in T. cruzi infection is possibly an important determinant of mortality and parasitism. A deeper understanding of the role of TXA(2) may result in novel therapeutic targets for a disease with limited treatment options.

Eicosanoids and the vascular endothelium

Cyclooxygenase (COX) enzymes catalyse the biotransformation of arachidonic acid to prostaglandins which subserve important functions in cardiovascular homeostasis. Prostacyclin (PGI2) and prostaglandin (PG)E2, dominant products of COX activityin macro- and microvascular endothelial cells, respectively, in vitro, modulate the interaction of blood cells with the vasculature and contribute to the regulation of blood pressure. COXs are the target for inhibition by nonsteroidal anti-inflammatory drugs (NSAIDs--which include those selective for COX-2) and for aspirin. Modulation of the interaction between COX products of the vasculature and platelets underlies both the cardioprotection afforded by aspirin and the cardiovascular hazard which characterises specific inhibitors of COX-2.

Role of thromboxane A2 in the induction of apoptosis of immature thymocytes by lipopolysaccharide

Lipopolysaccharide (LPS) causes apoptotic deletion of CD4(+) CD8(+) thymocytes, a phenomenon that has been linked to immune dysfunction and poor survival during sepsis. Given the abundance of thromboxane-prostanoid (TP) receptors in CD4(+) CD8(+) thymocytes and in vitro evidence that thromboxane A(2) (TXA(2)) causes apoptosis of these cells, we tested whether enhanced generation of TXA(2) plays a role in LPS-induced thymocyte apoptosis. Mice injected with 50 micro LPS intraperitoneally displayed a marked increase in generation of TXA(2) and prostaglandin E(2) in the thymus as well as apoptotic deletion of CD4(+) CD8(+) thymocytes. Administration of indomethacin or rofecoxib inhibited prostanoid synthesis but did not affect thymocyte death. In contrast, thymocyte apoptosis in response to LPS was significantly attenuated in TP-deficient mice. These studies indicate that TXA(2) mediates a portion of apoptotic thymocyte death caused by LPS. The absence of an effect of global inhibition of prostanoid synthesis suggests a complex role for prostanoids in this model.

Prostanoids modulate inflammation and alloimmune responses during graft rejection

Acute rejection of a transplanted organ is characterized by intense inflammation within the graft. Yet, for many years transplant researchers have overlooked the role of classic mediators of inflammation such as prostaglandins and thromboxane (prostanoids) in alloimmune responses. It has been demonstrated that local production of prostanoids within the allograft is increased during an episode of acute rejection and that these molecules are able to interfere with graft function by modulating vascular tone, capillary permeability, and platelet aggregation. Experimental data also suggest that prostanoids may participate in alloimmune responses by directly modulating T lymphocyte and antigen-presenting cell function. In the present paper, we provide a brief overview of the alloimmune response, of prostanoid biology, and discuss the available evidence for the role of prostaglandin E2 and thromboxane A2 in graft rejection.

Oxidative stress and nitric oxide deficiency in the kidney: a critical link to hypertension?

There is growing evidence that oxidative stress contributes to hypertension. Oxidative stress can precede the development of hypertension. In almost all models of hypertension, there is oxidative stress that, if corrected, lowers BP, whereas creation of oxidative stress in normal animals can cause hypertension. There is overexpression of the p22(phox) and Nox-1 components of NADPH oxidase and reduced expression of extracellular superoxide dismutase (EC-SOD) in the kidneys of ANG II-infused rodents, whereas there is overexpression of p47(phox) and gp91(phox) and reduced expression of intracellular SOD with salt loading. Several mechanisms have been identified that can make oxidative stress self-sustaining. Reactive oxygen species (ROS) can enhance afferent arteriolar tone and reactivity both indirectly via potentiation of tubuloglomerular feedback and directly by microvascular mechanisms that diminish endothelium-derived relaxation factor/nitric oxide responses, generate a cyclooxygenase-2-dependent endothelial-derived contracting factor that activates thromboxane-prostanoid receptors, and enhance vascular smooth muscle cells reactivity. ROS can diminish the efficiency with which the kidney uses O(2) for Na(+) transport and thereby diminish the P(O(2)) within the kidney cortex. This may place a break on further ROS generation yet could further enhance vasculopathy and hypertension. There is a tight relationship between oxidative stress in the kidney and the development and maintenance of hypertension.