Cysteinyl leukotrienes and their receptors: Bridging inflammation and colorectal cancer

Long-standing inflammation has emerged as a hallmark of neoplastic transformation of epithelial cells and may be a limiting factor of successful conventional tumor therapies.A complex milieu composed of distinct stromal and immune cells,soluble factors and inflammatory mediators plays a crucial role in supporting and promoting various types of cancers.An augmented inflammatory response can predispose a patient to colorectal cancer(CRC).Common risk factors associated with CRC development include diet and lifestyle,altered intestinal microbiota and commensals,and chronic inflammatory bowel diseases.Cysteinyl leukotrienes are potent inflammatory metabolites synthesized from arachidonic acid and have a broad range of functions involved in the etiology of various pathologies.This review discusses the important role of cysteinyl leukotriene signaling in linking inflammation and CRC.

The effects of 5-lipoxygenase inhibitor and cysteinyl leukotriene receptor 1 antagonist on 1-methyl-4-phenylpyridine-induced neurotoxicity

OBJECTIVE Previously we demonstrated the neuroprotective effect of 5-lipoxygenase(5-LOX)inhibitor as well as cysteinyl leukotriene receptor 1(Cys LT1)antagoniston rotenone-induced microglial activation and neuronal death.In this study,we determined the effects of 5-LOX inhibitor zileuton and Cys LT1 antagonist montelukast on neurotoxicity induced by 1-methyl-4-phenylpyridine(MPP+)in an in vitro model of Parkinson disease(PD).METHODS The neurotoxicity of MPP+,a neurotoxin relevant to PD,on the PC12 cells was measured by MTT assay,lactate dehydrogenase(LDH)release and double fluorescence staining with Hoechst/propidiumiodide(PI).The protective effects of 5-LOX inhibitor zileuton and Cys LT1 antagonist montelukast were investigated by the above methods.RESULTS We found that exposure of PC12 cells to MPP+led to a reduced cell viability and an increased level of LDH in a concentration-dependent manner.Pretreatment with zileuton and montelukast significantly attenuated viability loss and LDH release in MPP+-treated PC12 cells.Furthermore,MPP+increasednecrotic cell death in PC12 cells.Administration of montelukast significantly decreased MPP+-induced cell necrosis in PC12 cells.CONCLUSION The 5-LOX inhibitor zileuton and Cys LT1 antagonist montelukast have a neuroprotective effects on MPP+-induced neurotoxicity in PC12 cells.The 5-LOX inhibitor and Cys LT1 antagonist might raise a possibility as potential therapeutic agent for PD and other inflammation-related the central nervous system disorders.

Involvement of cysteinyl leukotriene signaling in microglial morphological changes and CASP1 expression in vitro

OBJECTIVE We have recently reported that cysteinyl leukotriene(Cys LT) signaling plays an important role in microglial interleukin(IL)-1β secretion and subsequent neurotoxicity.The present study aimed to examine microglial morphological changes and the upstream molecular underlying IL^(-1)β production in Cys LT receptor agonist leukotriene D4(LTD4)-treated BV2 microglia in vitro.METHODS Twenty-four hours after murine microglial BV2 cells were stimulated with LTD4(1-100 nmol·L^(-1)),the cell proliferation and morphology were observed.The expression level of cysteinyl aspartate-specific protease 1(CASP1) protein was measured by Western blotin BV2 cells.In addition,BV2 cells were pretreated with or without CysLT1 receptor antagonist montelukast for 1 h and the effects of monte-lukaston LTD4-stimulated microglial activation and CASP1 expression were evaluated.RESULTS The number of BV2 cells had an increasing tendency after 24 h treatment with LTD4,but no significant differences were observed between the control and LTD4-treated cells(P>0.05).Under basal and resting conditions,BV2 microglial cells displayed a ramified morphology.However,LTD4 at 100 nmool·L^(-1) drove microglial morphological changes from a ramified towards an amoeboid shape.The expression of CASP1 protein was significantly upregulated in 100 nmool·L^(-1) LTD4-treated BV2 microglia(P<0.01).Furthermore,pretreatment with CysLT1 receptor antagonist montelukast prevented cell morphological changes and suppressed the increased CASP1 expression in LTD4-treated BV2 cells(P<0.05).CONCLUSION Cys LT receptor agonist LTD4 induces morphological changes and CASP1 expressionin BV2 microglia,which can be inhibited by CysLT1 antagonist.These results suggest the involvement of Cys LT signaling in microglial morphological changes and CASP1 expression.

Enhanced expressions and activations of leukotriene C4synthesis enzymes in D-galactosamine/lipopolysaccharide-induced rat fulminant hepatic failure model

AIM： To investigate the expression and activity of leukotriene C4 （LTC4） synthesis enzymes and their underlying relationship with cysteinyl leukotriene （cys-LT） generation in a rat fulminant hepatic failure （FHF） model induced by D-galactosamine/lipopolysaccharide （D-GaIN/ LPS）. METHODS： Rats were treated with D-GaIN （300 mg/kg） plus LPS （0.1 mg/kg） for 1, 3, 6, and 12 h. Enzyme immunoassay was used to determine the hepatic cys-LT content. Reverse transcription-polymerase chain reaction （RT-PCR）, Western blot or immunohistochemical assay were employed to assess the expression or location of LTC4 synthesis enzymes, which belong to membrane associated proteins in eicosanoid and glutathione （MAPEG） metabolism superfamily. Activity of LTC4 synthesis enzymes was evaluated by determination of the products of LTA4 after incubation with liver microsomes using high performance liquid chromatography （HPLC）. RESULTS： Livers were injured after treatment with D-GaIN/LPS, accompanied by cys-LT accumulation at the prophase of liver injury. Both LTC4 synthase （LTC4S） and microsomal glutathione-S-transferase （mGST） 2 were expressed in the rat liver, while the latter was specifically located in hepatocytes. Their mRNA and protein expressions were up-regulated at an earlier phase after treatment with D-GaIN/LPS. Meantime, a higher activity of LTC4 synthesis enzymes was detected, although theactivity of LTC4S played the main role in this case. CONCLUSION： The expression and activity of both LTC4S and mGST2 are up regulated in a rat FHF model, which are, at least, partly responsible for cys-LT hepatic accumulation.

Aggravated inflammation and increased expression of cysteinyl leuko-triene receptors in the brain after focal cerebral ischemia in AQP4-deficient mice

Objective Aquaporin-4 （AQP4）, the main water channel protein in the brain, plays a critical role in water homeostasis and brain edema. Here, we investigated its role in the inflammatory responses after focal cerebral ischemia. Methods In AQP4-knockout （KO） and wild-type mice, focal cerebral ischemia was induced by 30 rain of middle cerebral arterial occlusion （MCAO）. Ischemic neuronal injury and cellular inflammatory responses, as well as the expression and localization of cysteinyl leukotriene CysLT2 and CysLT~ receptors, were determined at 24 and 72 h after MCAO. Results AQP4-KO mice showed more neuronal loss, more severe microglial activation and neutrophil infiltration, but less astrocyte proliferation in the brain after MCAO than wild-type mice. In addition, the protein levels of both CysLT1 and CysLT2 receptors were up-regulated in the ischemic brain, and the up-regulation was more pronounced in AQP4-KO mice. The CysLT1 and CysLT2 receptors were primarily localized in neurons, microglia and neutrophils; those localized in microglia and neutrophils were enhanced in AQP4-KO mice. Conclusion AQP4 may play an inhibitory role in postischemic inflammation.

Pathogenesis of NSAID-induced reactions in aspirin-exacerbated respiratory disease

It is well-established that following ingestion of aspirin or any other inhibitor of cyclooxygenase-1, patients with Samter’s disease, or aspirin-exacerbated respiratory disease (AERD) develop the sudden onset of worsening respiratory clinical symptoms, which usually in-volves nasal congestion, rhinorrhea, wheezing and bronchospasm. Gastrointestinal distress, nausea, a pruritic rash and angioedema can also occasionally develop. However, the underlying pathologic mechanism that drives these clinical reactions remains elusive. Pretreatment with medications that inhibit the leukotriene pathway decreases the severity of clinical reactions, which points to the involvement of cysteinyl leukotrienes (cysLTs) in the pathogenesis of these aspirin-induced reactions. Furthermore, studies of aspirin challenges in carefully-phenotyped patients with AERD have confirmed that both proinflammatory lipid mediators, predominantly cysLTs and prostaglandin (PG) D 2, and the influx of effector cells to the respiratory tissue, contribute to symptom development during aspirin-induced reactions. Mast cells, which have been identified as the major cellular source of cysLTs and PGD 2, are likely to be major participants in the acute reactions, and are an attractive target for future pharmacotherapies in AERD. Although several recent studies support the role of platelets as inflammatory effector cells and as a source of cysLT overproduction in AERD, it is not yet clear whether platelet activation plays a direct role in the development of the aspirin-induced reactions. To further our understanding of the pathogenesis of aspirin-induced reactions in AERD, and to broaden the pharmacotherapeutic options available to these patients, additional investigations with targeted clinical trials will be required.