Proteolytic enzymes in inflammatory bowel disease

Corneal myofibroblasts and fibrosis

Myofibroblasts are alpha-smooth muscle actin (SMA)+ cells that have a critical role in the corneal stromal response to infections, injuries, and surgeries, and which produce corneal scarring fibrosis when they develop in excess. These contractile and opaque cells-produce large amounts of disordered extracellular matrix (ECM)-and develop from keratocyte-derived corneal fibroblasts or bone marrow-derived fibrocytes, and possibly other cell types, in response to TGFβ1, TGFβ2 and PDGF from the epithelium, tears, endothelium, and other stromal cells. Recent proteomic analyses have revealed that the myofibroblasts that develop from different progenitors aren't interchangeable, but have major differences in protein expression and functions. Absence or defective regeneration of the epithelial basement membrane (EBM) and/or Descemet's basement membrane (DBM) results in development and persistence of myofibroblasts in the corneal stroma. The functions of myofibroblasts in the cornea include production of volume-additive ECM, tissue contraction, production of various growth factors, cytokines and chemokines that regulate stromal cells, including other myofibroblasts, production of collagenases and metalloproteinases involved in tissue remodeling, and the expression of toll-like receptors that likely have critical roles in the clearance of bacteria and viruses causing corneal infections.

Spontaneous and cytokine induced expression and activity of matrix metalloproteinases in human colonic epithelium

Matrix metalloproteinases (MMPs) have been implicated in tissue damage associated with inflammatory bowel disease (IBD).As the role of the intestinal epithelium in this process is unknown, we determined MMP expression and enzyme activity in human colonic epithelial cells (CEC). MMP mRNA expression was assessed by reverse transcription-polymerase chain reaction in HT-29 and DLD-1 cells and in CEC isolated from biopsies from IBD and control patients. Total MMP activity in the cells was measured by a functional assay, based on degradation of a fluorescent synthetic peptide containing the specific bond for MMP cleavage. HT-29 and DLD-1 expressed several MMPs and levels of MMP-3, -10 and -13 mRNA expression were increased significantly by tumour necrosis factor (TNF)-alpha exposure. Transcripts of MMP-1, -3, -7, -9, -10 and -12 were detected in CECs and all, except MMP12, at significantly increased levels in cells from inflamed IBD mucosa. MMP-2 and -8 mRNA were expressed inconsistently and MMP-11, -13 and -14 mRNA undetectable. Proteolytic MMP activity was detected in CEC supernatants and the level was increased significantly in inflamed IBD epithelium. The enzyme activity was inhibited strongly by a specific MMP inhibitor (GM 6001). A significant TNF-alpha-mediated increase in MMP enzyme activity was also detected in HT-29 cells in vitro. In conclusion, the expression of several MMPs as well as the level of functional MMPactivity is increased in CEC from patients with active IBD. The results suggest that MMPs released by the intestinal epithelium may be involved in the pathogenesis of IBD by promoting local mucosal damage.

Pathophysiology of diverticular disease

There is substantial evidence that colonic diverticulosis is related to civilization, industrialization and a "Western" lifestyle and diet, being described as "a disease of Western civilization". Its increased incidence during the 20th century and the morbidity and mortality associated with complications, demand that this condition should receive greater attention in terms of aetiology, prevention and management. It is generally believed that low dietary fibre and ageing are the two main pathogenic factors involved in this disease. Physiological studies have also demonstrated that there is a higher intraluminal pressure in the large bowel with diverticula. This chapter provides the evidence currently available for the pathophysiology of colonic diverticulosis and discusses its aetiological factors, including low dietary fibre, ageing and intraluminal pressure as well as extracelluar matrix such as collagen and elastin. The difference between the left-sided diverticulosis commonly seen in Caucasians and the right-sided predominantly observed in Asians is also presented.

Constitutive and regulated secretion of secretory leukocyte proteinase inhibitor by human intestinal epithelial cells

BACKGROUND & AIMS

Epithelial cells participate in immune regulation and mucosal integrity by generating a range of biologically active mediators. In the intestine, little is known about the potential endogenous anti-inflammatory molecules. Secretory leukocyte proteinase inhibitor (SLPI) is a major serine proteinase inhibitor, a potent antibiotic, and thus a potential anti-inflammatory molecule, although it is not known if it is secreted by intestinal epithelial cells.

METHODS

We show, by reverse-transcription polymerase chain reaction, the presence of SLPI messenger RNA in human model intestinal epithelial cell lines (Caco2-BBE, T84, and HT29-Cl.19A) and human jejunum and colon biopsy specimens. The polymerase chain reaction product was cloned and sequenced and is identical to that of SLPI isolated previously from the human parotid gland.

RESULTS

As analyzed by enzyme-linked immunosorbent assay, the constitutive secretion of SLPI occurs in a markedly polarized manner toward the apical surface and is enhanced by inflammatory mediators including tumor necrosis factor alpha and interleukin 1beta (approximately 3.5-fold increase over control value). SLPI release is also stimulated by activation of protein kinase C isoenzymes, but not by activation of adenosine 3',5'-cyclic monophosphate- or Ca(2+)-regulated signaling molecules. SLPI protein is detectable in intestinal lavage fluids collected from normal adult humans. Recombinant SLPI attenuates digestive enzyme (trypsin)- or leukocyte proteinase (elastase)-induced permeability alteration of a model epithelia in a dose-dependent manner. Moreover, SLPI exhibits an antibacterial activity against at least one major intestinal pathogen, Salmonella typhimurium. In contrast, SLPI does not influence epithelial barrier integrity as assessed by transepithelial conductance measurements or electrogenic ion transport.

CONCLUSIONS

These results establish that human intestinal epithelium expresses and apically secretes SLPI, a molecule that may significantly contribute to the protection against attack from inflammatory cells and digestive enzymes, as well as against microbial infection.

Therapy of inflammatory bowel disease

In the last decade, substantial gains have been made in the treatment of inflammatory bowel disease (IBD). Refinements in drug formulation have provided the ability to target distinct sites of delivery, enhancing the safety and efficacy of older agents. Immunosuppressive agents beyond corticosteroids have assumed a routine part in the care of patients with IBD. Moreover, as the century closes, we stand at the threshold of unprecedented advances in knowledge of the pathogenesis of ulcerative colitis and Crohn's disease. Simultaneous progress in biotechnology has fostered the development of new agents that strategically target pivotal processes in disease pathogenesis. This review covers agents currently used in the treatment of IBD and seeks to provide an overview of emerging therapies.

Novel therapies for inflammatory bowel disease

Looking back at successes and failures in newer approaches to treating IBD, it is tempting--although still difficult--to draw conclusions about pathogenesis. When a therapy proves effective, do clinicians truly know how it works? Even with a therapy as specific as anti-TNF antibody, it is not clear if the benefit is attributable to simple binding and clearance of TNF-alpha or to binding on the cell surface and subsequent deletion of the activated macrophage. When a drug appears to be less effective than preclinical models suggest, can failures in effectiveness from delivery or dosing be differentiated? The disappointing results of clinical trials with IL-10--so at odds with the prediction of benefit from animal models--bring into question the validity of those models as well as the soundness of design of the clinical trials on which efficacy of IL-10 is judged. The variability of response even to the most narrowly targeted agents suggests that these diseases are far more heterogeneous in humans than in their murine counterparts. Clinicians are only just beginning to recognize subclinical markers of response, and it may soon be possible to predict response on the basis of genetic composition. For the moment, however, the field of pharmacogenetics is embryonic. Challenges in developing new therapeutic strategies include not only identifying novel agents, but also improving the definitions of clinical endpoints and defining efficacy at the biologic level. Only through considered evaluation of clinical evidence may clinicians determine which therapies should remain novelties and which should become an accepted part of the armamentarium.