BIOCHEMISTRY AND PHARMACOLOGY OF THE LIPID MEDIATORS OF INFLAMMATION

The mediators of inflammation include substances with varied chemical natures (fatty acids, phospholipids, peptides and biogenic amines) which act as modulators of the inflammatory process. Our laboratory focuses on various aspects of the biochemistry and pharmacology of lipids mediators of inflammation which are derived from arachidonic acid, that is: leukotrienes, prostaglandins, thromboxanes, and the platelet-activating factor (Paf).

Our main research area focuses on the regulatory mechanisms of the biosynthesis of leukotrienes and Paf. Leukotrienes and Paf are synthesized by cells which are involved in the inflammatory process. These cells include neutrophils, monocytes, macrophages, eosinophils, basophils, mast cells and B lymphocytes. These cells do not normally produce leukotrienes or Paf (or very little); the synthesis of leukotrienes and Paf occurs only when cells are stimulated by proinflammatory factors such as chemotactic agents, inflammatory cytokines and bacteria. The enzymes involved in the synthesis of leukotrienes have been identified recently (in particular 5-lipoxygenase, and the 5-lipoxygenase activating protein or phospholipase A) and are currently being studied using molecular tools (cDNAs, antibodies, recombinant proteins, specific inhibitors, etc.).

The observation of the modulatory effects of some cytokines on phagocyte functions was an important step towards understanding the regulation of the inflammatory process. In one of our projects, we are currently investigating by which mechanism(s) these cytokines, in particular the tumor necrosis factor a and the granulocyte macrophage-colony stimulating factor, enhance leukotriene and Paf synthesis in human neutrophils. We are also investigating how these cytokines control the expression of proteins involved in the synthesis of leukotrienes and Paf, as well as the putative effects of these cytokines on the activation of these enzymes (phosphorilation, translocation). In addition, we have recently observed that adenosine is a strong natural inhibitor of leukotriene synthesis and of other cellular functions in human neutrophils. Currently, we are investigating the underlying mechanism(s) involved in this inhibitory effects of leukotrienes synthesis. These studies will lead to a better understanding of the inflammatory reaction as it occurs in host defense, as well as in inflammatory and allergic diseases.

The mode of action of antiinflammatory agents constitutes another important aspect of our research. One of our studies examines the mode of action of methotrexate, a potent antiinflammatory drug used in the treatment of inflammatory diseases, specifically rheumatoid arthritis. We are currently investigating the hypothesis that the antiinflammatory action of methotrexate may be linked to its ability to increase the concentration of adenosine (a natural antiinflammatory agent) at sites of inflammation.

Finally, we are pursuing the development of novel physicochemical assay methods for the mediators of inflammation. Our laboratory has extensive expertise in chromatography (HPLC) and mass spectrometry. It is equipped with a modern mass spectrometer with an electrospray ion source. Such an instrument allows the direct analysis of samples in solutions without requiring solute extraction or chemical modification. The lack of more efficient, more sensitive and more selective assay methods is still a limiting factor in the progress of biomedical research.

These projects are supported by the Medical Research Council of Canada and the Arthritis Society of Canada.

Marleau S, Fortin C, Poubelle PE, Borgeat P (1993) In vivo desensitization to leukotriene B4 (LTB4) in the rabbit: inhibition of LTB4-induced neutropenia during intravenous infusion of LTB4. J Immunol 150: 206-213.

Surette ME, Palmantier R, Gosselin J, Borgeat P (1993) Lipopolysaccharides prime whole human blood and isolated neutrophils for the increased synthesis of 5-lipoxygenase products by enhancing arachidonic acid availability: involvement of the CD14 antigen. J Exp Med 178: 1347-1355.

Surette ME, Odeimat A, Palmantier R, Marleau S, Poubelle PE, Borgeat P (1994) Reverse phase HPLC analysis of arachidonic acid metabolites in plasma after stimulation of whole blood ex vivo. Anal Biochem 216: 392-400.

Gosselin J, Borgeat P (1997) Epstein-Barr virus modulates 5-lipoxygenase product synthesis in human peripheral blood mononuclear cells. Blood 89: 2122-2130.