Prednisolone Targets Claudins in Mouse Brain Blood Vessels.

Endothelial cells in brain capillaries are crucial for the function of the blood-brain barrier (BBB), and members of the tight junction protein family of claudins are regarded to be primarily responsible for barrier properties. Thus, the analysis of bioactive substances that can affect the BBB's permeability is of great importance and may be useful for the development of new therapeutic strategies for brain pathologies. In our study, we tested the hypothesis that the application of the glucocorticoid prednisolone affects the murine blood-brain barrier in vivo. Isolated brain tissue of control and prednisolone-injected mice was examined by employing immunoblotting and confocal laser scanning immunofluorescence microscopy, and the physiological and behavioral effects were analyzed. The control tissue samples revealed the expression of barrier-forming tight junction proteins claudin-1, -3, and -5 and of the paracellular cation and water-channel-forming protein claudin-2. Prednisolone administration for 7 days at doses of 70 mg/kg caused physiological and behavioral effects and downregulated claudin-1 and -3 and the channel-forming claudin-2 without altering their localization in cerebral blood vessels. Changes in the expression of these claudins might have effects on the ionic and acid-base balance in brain tissue, suggesting the relevance of our findings for therapeutic options in disorders such as cerebral edema and psychiatric failure.

SARS-CoV-2-Induced Pathology-Relevance to COVID-19 Pathophysiology.

In spite of intensive studies of different aspects of a new coronavirus infection, many issues still remain unclear. In a screening analysis of histopathology in l200 lethal cases, authors succeeded in performing a wide spectrum of immune histochemical reactions (CD2, CD 3, CD 4, CD 5, CD 7, CD 8, CD14, CD 20, CD 31, CD 34, CD 56, CD 57, CD 68, CD 163, collagen 1,3, spike protein SARS-CoV-2, caspase-3, MLCM; ACE2 receptor, occludin, and claudin-1 and -3) and electron microscopy. The results of the histological and IHC studies of deceased people with varying degrees of severity of coronavirus infection confirmed the ability of these pathogens to cause cytoproliferative changes, primarily in epithelial and endothelial cells. Lesions of various organs are possible, while the reasons for significant differences in organotropy remain unclear. Severe respiratory failure in COVID-19 in humans is associated with a very peculiar viral pneumonia. In the pathogenesis of COVID-19, the most important role is played by lesions of the microcirculatory bed, the genesis of which requires further study, but direct viral damage is most likely. Endothelial damage can be associated with both thrombosis in vessels of various calibers, leading to characteristic complications, and the development of DIC syndrome with maximal kidney damage. Such lesions can be the basis of clinically diagnosed septic shock, while usually there are no morphological data in favor of classical sepsis caused by bacteria or fungi. A massive infiltration of the lung tissue and other organs, mainly by T lymphocytes, including those with suppressor properties, makes it necessary to conduct a differential diagnosis between the morphological manifestation of the protective cellular immune response and direct viral lesions but does not exclude the hypothesis of an immunopathological component of pathogenesis. In many of the deceased, even in the absence of clear clinical symptoms, a variety of extrapulmonary lesions were also detected. The mechanism of their development probably has a complex nature: direct lesions associated with the generalization of viral infection and vascular disorders associated with endothelial damage and having an autoimmune nature. Many aspects of the pathogenesis of coronavirus infection require further comprehensive study.

Cholera toxin perturbs the paracellular barrier in the small intestinal epithelium of rats by affecting claudin-2 and tricellulin.

Cholera toxin is commonly known to induce chloride secretion of the intestine. In recent years, effects on epithelial barrier function have been reported, indicating synergistic co-regulation of transporters and tight junction proteins. Our current study focused on the analysis of cholera toxin effects on transepithelial resistance and on tight junction proteins, the latter known as structural correlates of barrier function. Ligated segments of the rat jejunum were injected with buffered solution containing cholera toxin (1 µg/ml) and incubated for 4 h. Subsequently, selfsame tissue specimens were mounted in Ussing chambers, and cholera toxin (1 µg/ml) was added on the apical side. Transepithelial resistance and permeability of sodium fluorescein (376 Da) were analyzed. Subsequently, tissues were removed, expression and localization of claudins were analyzed, and morphological studies were performed employing transmission electron microscopy and confocal laser scanning microscopy. Cholera toxin induced a marked decrease in transepithelial resistance in the rat jejunal epithelium and an increase in paracellular permeability for sodium fluorescein. Immunoblotting of tight junction proteins revealed an increase in claudin-2 signals, which was verified by confocal laser scanning immunofluorescence microscopy, and a decrease in tricellulin, whereas other tight junction proteins remained unchanged. Transmission electron microscopy showed a reduction in the number of microvilli after incubation with cholera toxin. Moreover, cholera toxin led to a widening of the intercellular space between enterocytes. In accordance with the commonly known prosecretory effect of cholera toxin, our study revealed a complementary effect on small intestinal barrier function and integrity, which might constitute a pathomechanism with high relevance for prevention and therapeutic approaches.

Increased paracellular permeability of tumor-adjacent areas in 1,2-dimethylhydrazine-induced colon carcinogenesis in rats.

OBJECTIVE: The morphology and functions of the proximal and distal large intestine are not the same. The incidence of colorectal cancer in these regions is also different, as tumors more often appear in the descending colon than in the ascending colon. Inflammatory bowel disease and colorectal cancer can increase transepithelial permeability, which is a sign of reduced intestinal barrier function. However, there is not enough evidence to establish a connection between the difference in colorectal cancer incidence in the proximal and distal colon and intestinal permeability or the effects of carcinogenesis on the barrier properties in various areas of the colon. The aim of the study was to assess the permeability of different segments of the large intestine according to a developed mapping methodology in healthy rats and rats with 1,2-dimethylhydrazine (DMH)-induced colon adenocarcinoma. METHODS: The short circuit current, the transepithelial electrical resistance and the paracellular permeability to fluorescein of large intestine wall of male Wistar rats were examined in the Ussing chambers. The optical density of the solution from the serosa side to assess the concentration of the diffused fluorescein from mucosa to serosa was analyzed by spectrophotometry. The morphometric and histological studies were performed by optical microscopy. RESULTS: Rats with DMH-induced colon adenocarcinomas showed elevated transepithelial electrical resistance in the areas of neoplasm development. In contrast, there was no change in the electrophysiological properties of tumor adjacent areas, however, the paracellular permeability of these areas to fluorescein was increased compared to the control rats and was characterized by sharply reduced barrier function. CONCLUSIONS: The barrier properties of the colon vary depending on tumor location. The tumors were less permeable than the intact intestinal wall and probably have a negative influence on tumor-adjacent tissues by disrupting their barrier function.

Comparative analysis of theophylline and cholera toxin in rat colon reveals an induction of sealing tight junction proteins.

Claudin tight junction proteins have been identified to primarily determine intestinal epithelial barrier properties. While functional contribution of single claudins has been characterized in detail, information on the interplay with secretory mechanisms in native intestinal epithelium is scarce. Therefore, effects of cholera toxin and theophylline on rat colon were analyzed, including detection of sealing claudins. Tissue specimens were stripped off submucosal tissue layers and mounted in Ussing chambers, and short-circuit current (ISC) and transepithelial resistance (TER) were recorded. In parallel, expression and localization of claudins was analyzed and histological studies were performed employing hematoxylin-eosin staining and light and electron microscopy. Theophylline induced a strong increase of ISC in colon tissue specimens. In parallel, a decrease of TER was observed. In contrast, cholera toxin did not induce a significant increase of ISC, whereas an increase of TER was detected after 120 min. Western blots of membrane fractions revealed an increase of claudin-3 and -4 after incubation with cholera toxin, and theophylline induced an increase of claudin-4. In accordance, confocal laser-scanning microscopy exhibited increased signals of claudin-3 and -4 after incubation with cholera toxin, and increased signals of claudin-4 after incubation with theophylline, within tight junction complexes. Morphological analyses revealed no general changes of tight junction complexes, but intercellular spaces were markedly widened after incubation with cholera toxin and theophylline. We conclude that cholera toxin and theophylline have different effects on sealing tight junction proteins in native colon preparations, which may synergistically contribute to transport functions, in vitro.

Altered expression of tight junction proteins in mammary epithelium after discontinued suckling in mice.

Milk production is modulated by the paracellular barrier function of tight junction (TJ) proteins located in the mammary epithelium. The aim of our study was the molecular analysis of TJs in native lactating murine mammary gland epithelium as this process may strongly challenge epithelial barrier properties and regulation. Mammary gland tissue specimens from lactating control mice and animals after a 20-h interruption of suckling were prepared; histological analyses were performed by light and electron microscopy; and expression of TJ proteins was detected by PCR, Western blotting, immunofluorescent staining, and confocal laser scanning microscopy. Discontinuation of suckling resulted in a substantial accumulation of milk in mammary glands, an increase of alveolar size, and a flattening of epithelial cells without effects on inflammatory indicators. In control tissues, PCR and Western blots showed signals for occludin, and claudin-1, -2, -3, -4, -5, -7, -8, -15, and -16. After a 20-h accumulation of milk, expression of two sealing TJ proteins, claudin-1 and -3, was markedly increased, whereas two TJ proteins involved in cation transport, claudin-2 and -16, were reduced. Real-time PCR validated increased transcripts of claudin-1 and claudin-3. During extension of mammary glands in the process of lactation, claudin-1 and -3 are markedly induced and claudin-2 and -16 are decreased. Volume and composition of milk might be strongly dependent on this counter-regulation of sealing claudins with permeability-mediating claudins, indicating a physiological process of a tightening of TJs against a back-leak of solutes and ions from the alveolar lumen.