Endogenously produced hyaluronan contributes to the regulation of peritoneal adhesion development.

Peritoneal adhesions are postsurgical fibrotic complications connected to peritoneal inflammation. The exact mechanism of development is unknown; however, an important role is attributed to activated mesothelial cells (MCs) overproducing macromolecules of extracellular matrix (ECM), including hyaluronic acid (HA). It was suggested that endogenously-produced HA contributes to the regulation of different fibrosis-related pathologies. However, little is known about the role of altered HA production in peritoneal fibrosis. We focused on the consequences of the increased turnover of HA in the murine model of peritoneal adhesions. Changes of HA metabolism were observed in early phases of peritoneal adhesion development in vivo. To study the mechanism, human MCs MeT-5A and murine MCs isolated from the peritoneum of healthy mice were pro-fibrotically activated by transforming growth factor ß (TGFß), and the production of HA was attenuated by two modulators of carbohydrate metabolism, 4-methylumbelliferone (4-MU) and 2-deoxyglucose (2-DG). The attenuation of HA production was mediated by upregulation of HAS2 and downregulation of HYAL2 and connected to the lower expression of pro-fibrotic markers, including fibronectin and α-smooth muscle actin (αSMA). Moreover, the inclination of MCs to form fibrotic clusters was also downregulated, particularly in 2-DG-treated cells. The effects of 2-DG, but not 4-MU, were connected to changes in cellular metabolism. Importantly, the inhibition of AKT phosphorylation was observed after the use of both HA production inhibitors. In summary, we identified endogenous HA as an important regulator of peritoneal fibrosis, not just a passive player during this pathological process.

An in vitro model that mimics the foreign body response in the peritoneum: Study of the bioadhesive properties of HA-based materials.

A cascade of reactions known as the foreign body response (FBR) follows the implantation of biomaterials leading to the formation of a fibrotic capsule around the implant and subsequent health complications. The severity of the FBR is driven mostly by the physicochemical characteristics of implanted material, the method and place of implantation, and the degree of immune system activation. Here we present an in vitro model for assessing new materials with respect to their potential to induce a FBR in the peritoneum. The model is based on evaluating protein sorption and cell adhesion on the implanted material. We tested our model on the free-standing films prepared from hyaluronan derivatives with different hydrophobicity, swelling ratio, and rate of solubilization. The proteomic analysis of films incubated in the mouse peritoneum showed that the presence of fibrinogen was driving the cell adhesion. Neither the film surface hydrophobicity/hydrophilicity nor the quantity of adsorbed proteins were decisive for the induction of the long-term cell adhesion leading to the FBR, while the dissolution rate of the material proved to be a crucial factor. Our model thus helps determine the probability of a FBR to materials implanted in the peritoneum while limiting the need for in vivo animal testing.

Pseurotin D inhibits delayed type IV hypersensitivity response.

Pseurotins, secondary metabolites of fungi, represent a group of bioactive natural products with newly recognized biological activities, including the modulation of specific immune response. However, the type of immune response affected by pseurotins and the mechanistic details underlying these effects are still not understood. Thus, the aim of the current study was to examine the effects of pseurotin D on delayed-type IV hypersensitivity (DTH) reaction induced by chicken ovalbumin in vivo and to examine the effects of pseurotin D on major types of leukocytes responsible for DTH development in vitro. Pseurotin D significantly decreased paw swelling, the major symptom of DTH, as well as the DTH-related production of pro-inflammatory cytokine IL-1ß, IL-4, IL-6, IFN-γ and anti-inflammatory cytokine IL-10 in paws tissue, spleen enlargement, and DTH-related changes in leukocyte counts in peripheral blood. In vitro, pseurotin D mediated a decrease in the proliferation and differentiation of both Th1 and Th2 cells, as was concluded on the basis of the inhibition of the gene expressions of Gata3 and Tbx21 and the production of effector cytokines IFN-γ and IL-13 in vitro. Further, pseurotin D significantly inhibited the activation and differentiation of B cells, as was documented by the significant inhibition of B cell proliferation, CD138 expression, and IgE production. In conclusion, the results show the potential of pseurotin D to inhibit DTH reaction, this phenomenon involving the inhibition of the activation and differentiation of both T cells and B cells.

Endogenously-Produced Hyaluronan and Its Potential to Regulate the Development of Peritoneal Adhesions.

Formation of peritoneal adhesions (PA) is one of the major complications following intra-abdominal surgery. It is primarily caused by activation of the mesothelial layer and underlying tissues in the peritoneal membrane resulting in the transition of mesothelial cells (MCs) and fibroblasts to a pro-fibrotic phenotype. Pro-fibrotic transition of MCs-mesothelial-to-mesenchymal transition (MMT), and fibroblasts activation to myofibroblasts are interconnected to changes in cellular metabolism and culminate in the deposition of extracellular matrix (ECM) in the form of fibrotic tissue between injured sides in the abdominal cavity. However, ECM is not only a mechanical scaffold of the newly synthetized tissue but reciprocally affects fibrosis development. Hyaluronan (HA), an important component of ECM, is a non-sulfated glycosaminoglycan consisting of N-acetyl-D-glucosamine (GlcNAc) and D-glucuronic acid (GlcUA) that can affect the majority of processes involved in PA formation. This review considers the role of endogenously produced HA in the context of different fibrosis-related pathologies and its overlap in the development of PA.