Basic mechanisms and clinical implications of peritoneal fibrosis

We have stressed the role of certain growth factors and cytokines in peritoneal fibrosis, including TGFbeta, TIMP-1, and inflammatory cytokines, especially IL-1beta. Recent research highlights the myofibroblast-like transformation of mesothelial cells as a central initiating event in peritoneal fibrosis. The induction, survival, and apoptosis of the myofibroblast cell population likely dictate the nature of the fibrogenic response. The accumulation of collagen occurs in a nondegradative environment, and collagenases and their inhibitors have a role in the maintenance of fibrosis. Fibrosis appears to be a ubiquitous response of peritoneal tissues to the damaging effects of uremia, bioincompatible dialysate, recurrent infection, and inflammation. Recent research has focused on the induction of angiogenesis, as this appears to correlate with increased solute transport and peritoneal membrane ultrafiltration failure. Fibrosis may play an integral part in peritoneal membrane dysfunction in several aspects. Angiogenesis may be induced as part of the fibrotic response, as many key fibrogenic cytokines are also strongly angiogenic. Fibrotic tissue may support and preserve angiogenesis. Changes in the interstitium may have a direct effect on the hydrodynamic properties of the peritoneum and may directly influence fluid movement. In its most extreme form, fibrosis manifests as the rare but devastating EPS. Peritoneal biopsy studies have identified a high prevalence of peritoneal fibrosis in PD patients. Research into peritoneal fibrosis will be enhanced by new animal models where the role of various cytokines and growth factors, cellular processes, and matrix interactions can be studied. With these models, the role of fibrosis in alteration of peritoneal membrane function can be better assessed. Clinical trials to assess the role of prevention of peritoneal injury using biocompatible solutions and treatments targeted directly at peritoneal fibrosis will be important, but challenging to design and carry out.