Structural transformation of the pancreatic duct system in patients with chronic pancreatitis
Background. Chronic pancreatitis (CP) is characterized by a number of specific changes in the structure and function of the pancreas, including atrophy of functional tissue, fibrosis and ductal degeneration, a decrease in the number of islets. Despite a large number of possible etiological factors, the main pathophysiological mechanisms of CP development have much in common. Thus, with the preservation of secretory activity under obstruction of the ducts and their compensatory expansion, pancreatic secret infiltrates the surrounding tissue with the formation of edema, followed by intrapancreatic activation of digestive enzymes, in particular trypsinogen, which initiates proteolytic necrobiosis of the pancreocytes. The duct cells make up to 30 % of the human pancreas, compared to 1–2 % of endocrine cells. One of the first signs of CP is the abnormal increase in the number of ductal branches. It has also been shown that in the ducts of CP patients, the number of cells containing insulin increases, as well as cells that contain other endocrine and exocrine markers. Modeling chronic, acute and complicated pancreatitis in rats also confirmed that epithelial cells are involved in the regulation of extracellular matrix of the pancreas. Materials and methods. Comprehensive histopathological and immunohistochemical (IHC) study was performed in the laboratory of histological and immunohistochemical diagnosis of the university hospital of Zaporizhia State Medical University on postoperative
material of 40 patients with CP aged 28 to 74 years, who were operated at the clinic of surgery and minimally invasive technologies of Zaporizhia State Medical University. Immunohistochemical examination was carried out according to standard procedures using a mouse monoclonal antibody Alpha Smooth Muscle Actin (Clone 1A4) against the a-isoform of smooth muscle actin (a-SMA) and Desmin (Clone D33) against desmin (DAKO, USA), monoclonal rabbit antibody against collagen I (Clone RAH C11) anti-collagen type 1 (Imtek, RF) and rabbit polyclonal antibodies against fibronectin (DAKO, USA). Quantitative determination of the intensity and the relative area of the markers’ stromal expression was reproduced using the program for medical digital image processing ImageJ v.1.48, embedded plugin Colour Deconvolution analysis circuit and coloring H DAB (hematoxylin + DAB) for determining the area occupied by immunopositive structure in immunohistochemical preparations and optical (densitometric) intensity of immunostaining by patented procedure. Results. Pathohistological study of biopsies with a specific staining of collagen (by Van Gieson and Masson’s trichrome) showed that fibrotic changes in all the patients with CP were characterized by a combination of pronounced perilobular fibrosis, which covered all lobules, widespread intralobular fibrosis, and significant periductal fibrosis near large, sharply defined narrowed and cystically dilated ducts. There was also a pronounced expansion of interlobular fibrosis, a noticeable thickening of intralobular connective tissue strands directed deep into the lobules and connective tissue strands that surrounded some acini, as well as a significant tortuosity and widening of the ducts with retention cysts. In most cases, the deformation of the ductal system was one of the most significant structural changes. Thus, 87.5 % of cases were characterized by the unevenly narrowed and cystic-altered interlobular ducts, pronounced concentric fibrosis, protein plugs and concrements observed in the ducts. In 7.5 % of the cases, in the main pancreatic duct, foci of the epithelium atrophy were present, which alternated with foci of papillary intraepithelial hyperplasia, identified as pancreatic intraepithelial neoplasia. The parenchyma of the pancreas was thus constituted small, atrophic acini, surrounded by dense fibrous strands, with an increased number of gaping ducts of different diameters. Also, in 17.5 % of cases, phenomena of acinar-ductal metaplasia were observed. In the centers of the acinar-ductal metaplasia zones, the transformation of some acinar cells into ductal cells was determined with the formation of small duct-like structures, the so-called tubular complexes, which, according to the literature, are the primary focus of acinar tissue regeneration. In particular, a large number of activated a-SMA + pancreatic stellate cells (PSC) is detected in the zones of fibrosis. The pattern of expression of this marker is characterized by pronounced a-SMA-immunopositive staining of both PSC and their processes, and, in part, of the fibrillar component. Primary statistical processing of morphometry data revealed a direct relationship between the expression of a-SMA and the area of collagen I type, but this relationship was not significant (r = +0.321, p > 0.05). In order to further objectify the statistical studies, we isolated a group of cases characterized by low a-SMA expression (n = 9). A further study using medical statistics methods showed that the average area of type I collagen and the intensity of its expression in this group was significantly lower than in the other biopsy specimens (p < 0.05). In contrast, desmin expression was identified both in connective tissue, which was characterized by a lower intensity of immunostaining, in acinar tissue and in the epithelium of the pancreatic ducts. The pattern of its expression in fibrosis zones in CP was similar to that of a-SMA, but in 27.5 % of cases, the intensity of staining was below the threshold for determination by morphometric methods. We isolated a group of cases characterized by high expression of fibronectin (n = 9). A further study using medical statistics showed that the average area of type I collagen and the intensity of its expression in this group was significantly higher than in the other biopsy specimens (p < 0.05). Thus, IHC study of the material obtained from patients with CP showed that a large number of activated PSC expressing a-SMA and desmin are concentrated in the pancreatic ductal zones. Also, in these zones, a significant accumulation of fibronectin was found, which is synthesized in excess by activated PSC. The pattern of IHC staining of type I collagen in the zones of severe pancreatic fibrosis is characterized by a weak and moderate intensity with a average level of its expression. Conclusions. A characteristic morphological picture of the CP development is a combination of fibrosis with deformation of the ductal system due to periductal fibrosis with the expansion of interlobular fibrosis, thickening of intralobular connective tissue strands, as well as considerable tortuosity and widening of the ducts with retention cysts. Significant structural reorganization of the pancreatic duct system in patients with CP was observed in 87.5 % of cases, in 17.5 % of cases, the picture was supplemented by phenomena of acinar-ductal metaplasia with the transformation of acinar cells into ductal cells and the formation of small duct-like structures, the so-called tubular complexes. In 7.5 % of cases, in the main pancreatic duct, foci of atrophy of the epithelium were identified, which alternated with foci of papillary intraepithelial epithelial hyperplasia (PanIN). The development of pancreatic fibrosis in CP is facilitated by the accumulation of a-SMA+ activated pancreatic stellate cells synthesizing an excess of components of the extra-cellular matrix, in particular type I collagen. The mean area of type I collagen and the intensity of its expression were significantly lower with reduced a-SMA expression (p < 0.05), and significantly higher in cases of pronounced fibronectin expression (p < 0.05).
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