No abstract

Pulmonary fibrosis is characterized by excessive accumulation of connective tissue, along with activated extracellular matrix (ECM)‐producing cells, myofibroblasts. The pathological mechanisms are not well known, however serotonin (5‐HT) and 5‐HT class 2 (5‐HT 2) receptors have been associated with fibrosis. The aim of the present study was to investigate the role of 5‐HT 2B receptors in fibrosis, using small molecular 5‐HT 2B receptor antagonists EXT5 and EXT9, with slightly different receptor affinity. Myofibroblast differentiation [production of alpha‐smooth muscle actin (α‐SMA)] and ECM synthesis were quantified in vitro, and the effects of the receptor antagonists were evaluated. Pulmonary fibrosis was also modeled in mice by subcutaneous bleomycin administrations (under light isoflurane anesthesia), and the effects of receptor antagonists on tissue density, collagen‐producing cells, myofibroblasts and decorin expression were investigated. In addition, cytokine expression was analyzed in serum. Lung fibroblasts displayed an increased α‐SMA (P < 0.05) and total proteoglycan production (P < 0.01) when cultured with TGF‐β1 together with 5‐HT, which were significantly reduced with both receptor antagonists. Following treatment with EXT5 or EXT9, tissue density, expression of decorin, number of collagen‐producing cells, and myofibroblasts were significantly decreased in vivo compared to bleomycin‐treated mice. Receptor antagonization also significantly reduced systemic levels of TNF‐α and IL‐1β, indicating a role in systemic inflammation. In conclusion, 5‐HT 2B receptor antagonists have potential to prevent myofibroblast differentiation, in vitro and in vivo, with subsequent effect on matrix deposition. The attenuating effects of 5‐HT 2B receptor antagonists on fibrotic tissue remodeling suggest these receptors as novel targets for the treatment of pulmonary fibrosis.

Intestinal macromolecular transmission in young rats of 10, 14, 18, 22 and 30 days of age was measured as the blood serum levels of markers 6 h after oral feeding of a solution containing bovine IgG (BIgG), bovine serum albumin (BSA) and fluorescein-isothiocyanate-labeled dextran 70,000 (FITC-D), either alone (controls) or with soybean trypsin inhibitor (SBTI) or swine colostrum trypsin inhibitor (SCTI). In the 10- and 14-day-old rats, transmission of all three macromolecular markers was high, with a preference for IgG. Transmission was greatly reduced by the age of 18 days and totally arrested for the protein markers at 22 days, with a low transmission of FITC-D remaining at 30 days of age. Addition of either of the two protease inhibitors significantly elevated the transmission of the protein markers in the rats aged 10, 14 and 18 days, while the transmission of the protease-independent marker FITC-D was unaffected. From 14 days of age, the rats have a functioning intestinal proteolysis, since only small amounts of marker proteins were left in the gut lumen 6 h after feeding, and since the addition of protease inhibitors resulted in increased amounts of undegraded proteins intraluminally. The results indicate that the increase of intraluminal proteolytic activity during development and the presence of protease inhibitors in the food are of importance for the intestinal transmission of undegraded proteins in the young rat. The Fc receptor for IgG in the enterocyte is not sufficient to maintain an optimal transmission of IgG, since the intraluminal proteolytic activity also appears to be of importance.

The mucosal activities of cathepsin B and D were assayed in the small intestine of newborn pigs and of pigs 24 h, 6 days and 4–8 weeks old, respectively. Before sacrificing these animals, the intestinal capacity to internalise and further transmit macromolecules into the blood serum was evaluated by feeding a marker solution containing bovine IgG, bovine serum albumin and fluorescein-isothiocyanate-conjugated dextran 70,000 (FITC-dextran). No significant differences in the activities of cathepsin B or D were observed in the mucosa from the various age groups of pigs. The transmission of the marker macromolecules into the blood was higher in the newborn pigs than in older postclosure animals, all of which only had low or undetectable serum marker concentrations. No apparent difference in the uptake of the markers into the intestinal epithelium could be detected between that of the newborn, preclosure pigs and pigs 24 h old. Both groups showed a similar pattern of mucosal fluorescence, indicating that there had been a high uptake of all markers into the epithelium. In the 6-day-old pigs, epithelial uptake was only visible in the distal small intestine, whereas no uptake at all could be found in the animals 4–8 weeks of age. The results suggest that intestinal closure in the pig, i.e. the dramatic decrease in the transfer of macromolecules from the intestinal epithelium into the blood at about 24 h of age, is not due to a decrease in the endocytotic ability of the enterocytes, nor to a higher degradation rate within these cells. More probably, closure may be the result of a decreased transfer of the internalised macromolecules into the blood.

Transient waves of different mediators appear during the course of the arthritis. This indicates the presence of active downregulatory mechanisms. Here the model could differ from human rheumatoid arthritis.