Soluble mediators and the interaction of drugs in IBD.

The chronic idiopathic bowel diseases (IBD) - Crohn's disease and ulcerative colitis - are considered to be the result of an unrestrained inflammatory reaction. Although an explanation for the etiopathogenesis has still not emerged, the explosion of information on the inflammatory process is expected to yield a multitude of drugs targeted at particular elements of the inflammatory process. The final common pathway of immune activation in IBD is the local influx of monocytes, macrophages and polymorphonuclear neutrophils (PMNs). The processes which account for the recruitment of these cells include cytokine generation, complement activation and eicosanoid biosynthesis. Once the influx of PMNs and macrophages occurs, an increased production of platelet-activating factor (PAF) and leukotrienes (LTs), in particular LTB(4), results in the secondary amplification of the inflammatory response, which provides the clinical manifestations of IBD. Other important soluble mediators of inflammation include complement-derived and chemotactic peptides, specific adhesion molecules, neuropeptides and reactive metabolites of oxygen and nitrogen. Current established therapies, such as glucocorticoids and 5-aminosalicylic acid (5-ASA), inhibit raised concentrations of these interdependent soluble mediators of inflammation, which may amplify one another or have parallel effects. Future medical options for treatment of IBD aim at removing perpetuating antigens or inhibiting the entry of inflammatory cells by manipulating adhesion molecules, by blocking the proinflammatory molecules, or by preserving endogenous suppressive molecules or correcting genetic defects. However, it remains to be defined whether targeting multiinflammatory actions or a single key pivotal process is the better therapeutic strategy and whether subgroups of IBD with different clinical courses will require different treatment approaches.