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Adhesion and migration of leukocytes into the surrounding tissue are crucial steps in inflammation, immunity and atherogenesis. Expression of cell adhesion molecules by endothelial cells plays a role in these processes. Propionate is a naturally occurring short chain fatty acid produced by bacterial fermentation of dietary fibre. High intake of dietary fibre has been associated with an improved bowel function and with a reduced risk of cardiovascular disease. However, the molecular mechanisms responsible for these effects remain unknown. In this study, the effects of propionate on the expression of endothelial leukocyte adhesion molecules by cytokine-stimulated human umbilical vein endothelial cells (HUVEC) were investigated. Pretreatment of HUVEC with propionate significantly inhibited the tumor necrosis factor-alpha (TNF-)-induced expression of vascular cell adhesion molecule-1 (VCAM-1) and intracellular adhesion molecule-1 (ICAM-1) in a time- and dose-dependent manner. At 10 mM, propionate also inhibited the interleukin-1 (IL-1)-mediated VCAM-1 and ICAM-1 expression, with the latter effect being more pronounced, as well as decreased the TNF--induced VCAM-1 and ICAM-1 mRNA expression in a similar manner. The decrease in VCAM-1 and ICAM-1 expression was associated with a reduction of adherence of monocytes and lymphocytes to the cytokine-stimulated HUVEC. In addition, propionate significantly inhibited the TNF--induced activation of nuclear factor-kappa B (NF-B) and significantly increased the expression of peroxisome proliferator-activated receptor alpha (PPAR) in HUVEC. These results demonstrate that propionate may have antiinflammatory and possibly antiatherogenic properties. Our findings warrant further investigation into the therapeutic effects of propionate on a number of pathological events involving leukocyte recruitment.
Stroke-induced inflammatory reaction leads to the accumulation of leukocytes in the brain ischaemic region, where they exert a detrimental effect - promotion and extension of cerebral damage. Intracerebral infiltration of peripheral blood leukocytes requires prior endothelial-leukocyte interactions that are mediated by such cell surface proteins as adhesion molecules. Among adhesion molecules, it is the immunoglobulin gene superfamily (IgSF) that is responsible for strong attachment and transendothelial migration of leukocytes. The principal members of IgSF are: intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and platelet endothelial cell adhesion molecule-1 (PECAM-1). In this review the following issues were described and discussed: an increased expression of ICAM-1 and VCAM-1 in ischaemic brain as well as a detection of their soluble(s) forms in sera of stroke victims. The presented data suggest the involvement of both ICAM-1 and VCAM-1 in the sequence and timing of the infiltration of leukocytes into the brain ischaemic zone after stroke. They have also revealed changes in serum concentrations of sICAM-1 and sVCAM-1 that are characteristic for stroke. Recently, increase in sPECAM-1 levels in serum and cerebrospinal fluid (CSF) has been shown within 24 h of the onset of stroke, having indirectly suggested involvement of the molecule in the inflammatory events during the early phase of stroke.
The aim of this study was to determine whether Desulfovibrio desulfuricans-derived LPS stimulate the release of IL-6 and IL-8 from ECs and the expression of their adhesion molecules at the transcriptional level. Confluent monolayers of HUVEC were incubated in the absence or presence of 20 μg/ml and 60 μg/ml LPSs derived from the DdT and DdA bacterial strains. Also, the simultaneous stimulation of cells with LPSs and IL-1β was evaluated. The levels of cytokines released were measured using ELISA. LPS-activated HUVEC increased the secretion of both IL-6 and IL-8, which was not LPS dose dependent. The expression of E-selectin and VCAM-1 was assessed by TR-PCR. The transcripts were detectable at all the concentrations (20, 40, 60 μg/ml) of LPSs used. These results suggest that D. desulfuricans LPS may activate immune functions in endothelial cells and influence the inflammatory response during bacteremia caused by these bacteria.
Platelet-leukocyte interactions represent an important determinant of the inflammatory response. Although mechanisms of platelet-neutrophil adhesion were studied extensively, little is known on the mechanisms of platelet-eosinophil interactions. The aim of the present study was to analyze the involvement of adhesion molecules and lipid mediators in platelet-eosinophil adhesion as compared to platelet-neutrophil adhesion. For that purpose human platelets, eosinophils and neutrophils were isolated and platelet-eosinophil and platelet-neutrophil adhesion induced by thrombin (30 mU/ml), LPS (0.01 µg/ml) and fMLP (1 µM) was quantified using the "rosettes" assay. The involvement of adhesion molecules such as selectin P, glycoprotein IIb/IIIa (GPIIb/IIIa) and lipid mediators such as of thromboxane A2 (TXA2), platelet activating factor (PAF) and cysteinyl leukotrienes (cysLTs) were studied using monoclonal antibodies and pharmacological inhibitors, respectively. Thrombin (30 mU/ml), LPS (0.01 µg/ml) and fMLP (1 µM) each of them induced platelet-eosinophil adhesion that was even more pronounced as compared with platelet-neutrophil adhesion induced by the same stimulus. Anti-CD62P antibody (1 µg/ml) and anti-GP IIb/IIIa antibody (abciximab - 3 µg/ml) strongly inhibited platelet-eosinophil as well as platelet-neutrophil adhesion. Aspirin inhibited platelet-eosinophil adhesion, while MK 886 - a FLAP inhibitor (10 µM), or WEB 2170 - a PAF receptor antagonist (100 µM) were less active. On the other hand aspirin, MK 886 and WEB 2170 all three of them inhibited platelet-neutrophil adhesion. In summary, platelets adhered avidly to eosinophils both after activation of platelets by thrombin, eosinophils by fMLP or simultaneous activation of platelets and eosinophils by LPS. Similarly to platelet-neutrophil interaction adhesion of platelets to eosinophils involved not only adhesion molecules (selectin P, GPIIb/IIIa), but also lipid mediators such as TXA2. The involvement of PAF and cysteinyl leukotrienes in platelet-eosinophil adhesion was less pronounced as compared to platelet-neutrophil adhesion.
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