Cysteinyl-leukotriene D4 induced IL-1 beta expression and release in rat vascular smooth muscle cells

Cysteinyl leukotriene receptor 1 mediates LTD4-induced activation of mouse microglial cells in vitro

AIM

To investigate the roles of cysteinyl leukotriene receptors CysLT1R and CysLT2R in leukotriene D4 (LTD4)-induced activation of microglial cells in vitro.

METHODS

Mouse microglial cell line BV2 was transfected with pcDNA3.1(+)-hCysLT1R or pcDNA3.1(+)-hCysLT2R. The expression of relevant mRNAs and proteins in the cells was detected using RT-PCR and Western blotting, respectively. Phagocytosis was determined with flow cytometry analysis. The release of interleukin-1β (IL-1β) from the cells was measured using an ELISA assay.

RESULTS

The expression of CysLT1R or CysLT2R was considerably increased in the transfected BV2 cells, and the receptors were mainly distributed in the plasma membrane and cytosol. Treatment of the cells expressing CysLT1R or CysLT2R with CysLT receptor agonist LTD4 (0.1-100 nmol/L) concentration-dependently enhanced the phagocytosis, and increased mRNA expression and release of IL-1β. Moreover, the responses of hCysLT1R-BV2 cells to LTD4 were significantly larger than those of hCysLT2R-BV2 or WT-BV2 cells. Pretreatment of hCysLT1R-BV2 cells with the selective CysLT1R antagonist montelukast (1 μmol/L) significantly blocked LTD4-induced phagocytosis as well as the mRNA expression and release of IL-1β, whereas the selective CysLT2R antagonist HAMI 3379 (1 μmol/L) had no such effects.

CONCLUSION

CysLT1R mediates LTD4-induced activation of BV2 cells, suggesting that CysLT1R antagonists may exert anti-inflammatory activity in brain diseases.

Oxidative risk for atherothrombotic cardiovascular disease

In the vasculature, reactive oxidant species, including reactive oxygen, nitrogen, or halogenating species, and thiyl, tyrosyl, or protein radicals may oxidatively modify lipids and proteins with deleterious consequences for vascular function. These biologically active free radical and nonradical species may be produced by increased activation of oxidant-generating sources and/or decreased cellular antioxidant capacity. Once formed, these species may engage in reactions to yield more potent oxidants that promote transition of the homeostatic vascular phenotype to a pathobiological state that is permissive for atherothrombogenesis. This dysfunctional vasculature is characterized by lipid peroxidation and aberrant lipid deposition, inflammation, immune cell activation, platelet activation, thrombus formation, and disturbed hemodynamic flow. Each of these pathobiological states is associated with an increase in the vascular burden of free radical species-derived oxidation products and, thereby, implicates increased oxidant stress in the pathogenesis of atherothrombotic vascular disease.

P2X(7) Receptors as a Transducer in the Co-Occurrence of Neurological/Psychiatric and Cardiovascular Disorders: A Hypothesis

Background. Over-stimulation of the purinergic P2X₇ receptor may bring about cellular dysfunction and injury in settings of neurodegeneration, chronic inflammation, as well as in psychiatric and cardiovascular diseases. Here we speculate how P2X₇ receptor over-activation may lead to the co-occurrence of neurological and psychiatric disorders with cardiovascular disorders. Presentation. We hypothesize that proinflammatory cytokines, in particular interleukin-1β, are key players in the pathophysiology of neurological, psychiatric, and cardiovascular diseases. Critically, this premise is based on a role for the P2X₇ receptor in triggering a rise in these cytokines. Given the broad distribution of P2X₇ receptors in nervous, immune, and vascular tissue cells, this receptor is proposed as central in linking the nervous, immune, and cardiovascular systems. Testing. Investigate, retrospectively, whether a bidirectional link can be established between illnesses with a proinflammatory component (e.g., inflammatory and chronic neuropathic pain) and cardiovascular disease, for example, hypertension, and whether patients treated with anti-inflammatory drugs have a lower incidence of disease complications. Positive outcome would indicate a prospective study to evaluate therapeutic efficacy of P2X₇ receptor antagonists. Implications. It should be stressed that sufficient direct evidence does not exist at present supporting our hypothesis. However, a positive outcome would encourage the further development of P2X₇ receptor antagonists and their application to limit the co-occurrence of neurological, psychiatric, and cardiovascular disorders.

Eicosanoid profile in cultured human pulmonary artery smooth muscle cells treated with IL-1 beta and TNF alpha

Interleukin-1beta (IL-1beta) and tumor necrosis factor (TNF alpha) induce prostanoid biosynthesis in vascular smooth muscle cells by promoting cyclooxygenase (COX) expression, but little is known about the biosynthesis of lipoxygenase (LPO) metabolites. We investigated the effects of human recombinant IL-1beta and TNF alpha on the production of arachidonic acid (AA) metabolites by high-performance liquid chromatography (HPLC). After being labelled with 3H-AA, cultured human pulmonary artery smooth muscle cells (HPASMC) were incubated with or without IL-1beta (200 U/ml) and TNF alpha (500 U/ml). The arachidonic acid metabolites released from HPASMC were then analysed by HPLC. In control HPASMC, 6-keto-PGF1alpha and PGE2 were the principal metabolites of the COX pathway, while 5-HETE, LTC4 and D4 were the main products of the LPO pathway. HPASMC treated with 200 U/ml of IL-1beta and 500 U/ml of TNF alpha produced more COX metabolites such as 6-keto-PGF1alpha, thromboxane B2, PGF2alpha and PGE2 than control cells. Significant increases in the production of LPO derivatives such as LTB4, C4, D4, and 15-HETE were also found in IL-1beta-treated HPASMC. Although the release of LPO products tended to increase in TNF alpha-treated cells, no significant change was noted. Many AA metabolites including LTB4 are responsible for the inflammatory process in vivo. AA metabolites produced by pulmonary artery smooth muscle cells might play important roles in cytokine-mediated acute lung injury and inflammation.

Suppression of cytokine synthesis, integrin expression and chronic inflammation by inhibitors of cytosolic phospholipase A2

To define the isoform of phospholipases A2 active in inflammation we evaluated the effects of low-molecular-weight inhibitors of secretory and cytosolic phospholipases A2. We found that inhibitors of cytosolic phospholipase A2 had therapeutic efficacy in an in vivo model of chronic inflammation (rat adjuvant arthritis), whereas inhibitors of secretory phospholipase A2 had no beneficial effect. In vitro, inhibitors of cytosolic phospholipase A2 diminished surface expression of Mac-1 (CD11b/CD18) beta2-integrin on calcium ionophore-stimulated human blood granulocytes and suppressed synthesis of interleukin-1beta in lipopolysaccharide-stimulated human blood monocytes and U937 cells by reducing mRNA levels. Lipid mediators promote Mac-1 exocytosis and transcription of interleukin-1beta, which further enhances cytosolic phospholipase A2 activity and expression. Thus, superinduction of cytosolic phospholipase A2 may establish a positive feedback loop, converting acute inflammation into chronic inflammation. Consequently, inhibitors of cytosolic phospholipase A2 may prevent inflammation in vivo by interfering with cellular activation and infiltration. We conclude that cytosolic phospholipase A2 but not secretory phospholipase A2 is the predominant enzyme in inflammatory signalling.

Differentiated properties and proliferation of arterial smooth muscle cells in culture

The smooth muscle cell is the sole cell type normally found in the media of mammalian arteries. In the adult, it is a terminally differentiated cell that expresses cytoskeletal marker proteins like smooth muscle alpha-actin and smooth muscle myosin heavy chains, and contracts in response to chemical and mechanical stimuli. However, it is able to revert to a proliferative and secretory active state equivalent to that seen during vasculogenesis in the fetus, and this is a prerequisite for the involvement of the smooth muscle cell in the formation of atherosclerotic and restenotic lesions. A similar transition from a contractile to a synthetic phenotype occurs when smooth muscle cells are established in culture. Accordingly, an in vitro system has been used extensively to study the regulation of differentiated properties and proliferation of these cells. During the first few days after seeding, the cells are reorganized structurally with a loss of myofilaments and formation of a widespread endoplasmic reticulum and a prominent Golgi complex. In parallel, they lose their contractility and instead become competent to divide in response to a large variety of mitogens, including platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF). After entering the cell cycle, they start to produce these and other mitogens on their own, and continue to replicate in the absence of exogenous stimuli for a restricted number of generations. Furthermore, they start to secrete extracellular matrix components such as collagen, elastin, and proteoglycans. The mechanisms that control this change in morphology and function of the smooth muscle cells are still poorly understood. Adhesive proteins such as fibronectin and laminin apparently have an important role in determining the basic phenotypic state of the cells and exert their effects via integrin receptors. The proliferative and secretory activities of the cells are influenced by a multitude of growth factors, cytokines, and other molecules. Although much work remains before an integrated view of this regulatory machinery can be achieved, there is no doubt that the cell culture technique has contributed substantially to our knowledge of smooth muscle differentiation and growth. At the same time, it has been crucial in exploring the role of these cells in vascular disease and developing new therapeutic strategies to cope with major causes of human death and disability.