Endothelial cell interactions with neutrophils : studies of adhesion and effects of lipoxygenase metabolites and antirheumatic drugs

Abstract

Inflammation is a process of vital importance in the defence and elimination of microorganisms as well as in the repair of the damaged tissue. However, inadequate or excessive inflammation leads to inflammatory diseases such as rheumatoid arthritis. Neutrophil polyntorphonuclear granulocytes (PMN) are important participators in inflammatory reactions. Endothelial cells (EC) are crucial for the regulation of inflammatory responses by their capacity to modulate their expression of adhesion molecules as well as activating molecules.

Mechanisms of adhesion of PMN to human umbilical vein endothelial cells (HUVEC) were studied in vitro with emphasis on effects of leukotrienes, lipoxins, cytokines and antirheumatic agents. Lipoxin A4 (LXA4), but not LXB4, induced an increase in HUVEC binding of PMN. The kinetic of the adhesive response was intermediate to that of rapid (e.g. LTB4) and slow acting agonists (e.g. IL-1ß). The LXA4 response was partially blocked by the PAF-receptor antagonist WEB-2086, indicating the involvement of PAF in the activation process. The LXA4 induced adhesive response was resistant to pertussis toxin (PT), indicating that the activation process was independent of PT-sensitive G-proteins. Pre-treatment of EC with LXA4 prior to stimulation with LT134 reduced the adhesive responses conferred by LTB4. Thus, LXA4 seems not to be a pro- or anti-inflammatory agent but an inflammatory modulator.

The peptido-leukotrienes C4 (LTC4) and LTD4 are potent inflammatory mediators involved in the pathophysiology of e.g. bronchial asthma. LTD4 induced rapid rises of intracellular Ca2+ in HUVEC as well as PMN, LTC4 only in HUVEC. LTC4 and LTD4, in contrast to LTB4, did not affect the adhesive responses of HUVEC or PMN. The intracellular release of Ca2+ was blocked by the peptido-leukotriene blocker SKF 104,353, indicating the presence and involvement of specific receptors on HUVEC as well as on PMN. Peroxisome proliferator-activating receptors (PPAR) are nuclear receptors that regulates transcription of e.g. enzymes involved in lipid metabolism but also involved in the regulation of inflammatory responses. PPAR[alpha] is expressed in EC. However, treatment of HUVEC with the PPAR[alpha] agonist WY 14,643 had no influence on adhesive interactions between HUVEC and PMN, indicating that the modulating capacity of PPAR is conferred at other steps than the adhesive interactions.

Gold sodium thiornalat (GSTM) and auranofin (AF) interfered with adhesive interactions between PMN and HUVEC induced by IL-1ß. Likewise, GSTM reduced endothelial expression of E-selectin, AF interfered with expression of E- selectin as well as of ICAM-1. Prednisolone interfered with adhesive as well as cytotoxic interactions between PMN and HUVEC, by multiple effects on the PMN as well as on the HUVEC, including a hampering effect on cytokine induced E-selectin expression. Thus, adhesive interactions between EC and PMN (as well as other classes of leukocytes) are of pivotal importance in inflammatory reactions. Agents interfering with these interactions will offer more potent and selective treatments of inflammatory disorders.