Proteolysis is a confounding factor in the interpretation of faecal calprotectin

Abstract

AbstractCalprotectin is a 36 kDa calcium and zinc binding protein. An increased level of calprotectin points towards inflammatory bowel disease. However, the biomarker calprotectin shows 14 potential cleavages sites for trypsin. Next to trypsin, also the presence of its inhibitor αAn in vitro model was created. As calprotectin source, leukocytes were isolated and subsequently lysed (1% Triton X-100) and diluted in faecal matrix. Trypsin digestion was carried out by adding trypsin. Incubation occurred for 24 h or 48 h (37 °C). To study the influence of αIn vitro experiments enabled monitoring of the faecal calprotectin digestion, leading to loss of immunoreactivity. Trypsin activity was a potential confounder in the interpretation of calprotectin, in particular for proximal lesions, where exposure of calprotectin to trypsin is prolonged. Relative calprotectin loss was proportional to the amount of trypsin. Decrease of calprotectin was more pronounced after 48 h of incubation in comparison to 24 h of incubation. Analogue experiments also showed stable calprotectin values after adding αTransit time, trypsin activity and addition of blood as a source of α