The role of intestinal inflammation on the gut-liver axis

The gut and the liver are anatomically related by portal circulation, and their functional unit realizes the gut-liver axis (GLA) with the integrity of intestinal barrier crucial for the maintenance of liver homeostasis. The GLA connects the liver with the intestine via bile acid metabolism. Bile acids (BAs) are amphipathic steroid acids, synthesized from cholesterol in the liver, that regulate lipid, glucose and energy metabolism. Moreover, a specific role of BAs as immunomodulators is emerging. The regulatory functions of BAs are predominantly mediated by the bile receptors, such as the nuclear receptors farnesoid-X-receptor (FXR) and pregnane-X-receptor (PXR) as well as the membrane G-protein-coupled-receptor TGR5. Recent findings suggest that the occurrence of gut inflammation, featured by altered epithelial and vascular permeability that causes the major translocation of bacterial antigens, may affect the healthy liver as well as worsen the severity of liver diseases, in particular of the non-alcholic fatty liver disease (NAFLD) and its progressive form, the non- alcoholic steatohepatitis (NASH). Aims: Accordingly, the whole purpose of this project is to assess the impact of gut inflammation on liver health and disease For this purpose, in a first part of the thesis we aimed to: 1.Investigate in vitro and in vivo the possibility that gut inflammation affects the healthy liver by altering BA receptors FXR, PXR and TGR5 and increasing the production of inflammatory and oxidative stress molecules; 2.analyze ex vivo the expression pattern of BA receptors and the apical sodium- dependent bile acid transporter (ASBT) in the inflamed colonic tissues of a group of pediatric patients with inflammatory bowel disease (IBD) and age-matched controls. In a second part of the thesis, we aimed to: 1. develop an animal model of hepatic steatosis, displaying the disease both in its early (NAFLD) and late (NASH) phase, in which an important intestinal inflammation was also induced; 2. use this model to assess that gut inflammation significantly contributes to the progression of the liver disease (from NAFLD to NASH) by altering BA receptor expression and increasing inflammatory (IL-6, TNF, NLRP3, TLR4, MCP-1, HMGB1) as well as fibrotic (TGF-, -SMA) mediator expression; 3. evaluate the potential of the anti-inflammatory molecule, the dipotassium glycyrrhizate (DPG), to improve the liver disease by reducing gut inflammation. Results: Results and conclusions of the first part of experimentation are reported in the original paper published in Journal of Pediatric Gastroenterology and Nutrition (Negroni A, Fiaschini N, Palone F, Vitali R, Colantoni E, Laudadio I, Oliva S, Aloi M, Cucchiara S, Stronati L. “Intestinal inflammation alters the expression of hepatic bile acid receptors causing liver impairment” J Pediatr Gastroenterol Nutr. 2020 Aug;71(2):189-196) that has been attached to the thesis. Results of the second part of experimentation are fully described in the thesis. We have developed an animal model with intestinal inflammation and liver steatosis/steatohepatitis by treating C57BL/6J mice with dextran sodium sulphate (DSS) to induce colitis and high fat diet (HFD) with high glucose/fructose for different times to induce NAFLD/NASH. Mice with NAFLD/NASH without colitis served as control group. A further group of NAFLD/NASH-DSS-mice were also treated with DPG. Results show that gut inflammation, assessed by the release of the alarmin HMGB1 in the stools, and consequent altered intestinal epithelial and vascular permeability, confirmed by a reduced expression of the tight junction protein zonulin-1 (ZO-1) and an increased level of the endothelial cell-specific protein plasmalemma vesicle-associated protein 1 (PV1), correlate with altered BAs receptor expression (TGR5 and PXR), increase of inflammatory marker expression (IL-6, TNF, NLRP3, TLR4, MCP-1, HMGB1) and inflammatory infiltrate in the steatotic liver of NASH-DSS mice. Moreover, the latter showed a significant rise of collagen fiber deposition and increased fibrotic marker (- SMA and TGF-) expression as compared to DSS-mice. The administration of DPG to DSS- NASH mice significantly reduced these effects. Conclusions: These data confirm our hypothesis that the presence of gut inflammation causes liver injury and accelerates fibrosis in a steatotic liver, contributing to the progression of NAFLD towards NASH. We also suggest that reducing gut inflammation by using DPG could represent an interesting novel strategy for the management of the hepatic disease

Towards a Material-by-Design Approach to Electrospun Scaffolds for Tissue Engineering Based on Statistical Design of Experiments (DOE)

Electrospinning bears great potential for the manufacturing of scaffolds for tissue engineering, consisting of a porous mesh of ultrafine fibers that effectively mimic the extracellular matrix (ECM) and aid in directing stem cell fate. However, for engineering purposes, there is a need to develop material-by-design approaches based on predictive models. In this methodological study, a rational methodology based on statistical design of experiments (DOE) is discussed in detail, yielding heuristic models that capture the linkage between process parameters (Xs) of the electrospinning and scaffold properties (Ys). Five scaffolds made of polycaprolactone are produced according to a 22-factorial combinatorial scheme where two Xs, i.e., flow rate and applied voltage, are varied between two given levels plus a center point. The scaffolds were characterized to measure a set of properties (Ys), i.e., fiber diameter distribution, porosity, wettability, Young’s modulus, and cell adhesion on murine myoblast C1C12 cells. Simple engineering DOE models were obtained for all Ys. Each Y, for example, the biological response, can be used as a driver for the design process, using the process-property model of interest for accurate interpolation within the design domain, enabling a material-by-design strategy and speeding up the product development cycle. The implications are also illustrated in the context of the design of multilayer scaffolds with microstructural gradients and controlled properties of each layer. The possibility of obtaining statistical models correlating between diverse output properties of the scaffolds is highlighted. Noteworthy, the featured DOE approach can be potentially merged with artificial intelligence tools to manage complexity and it is applicable to several fields including 3D printing

Design and Manufacturing of Antibacterial Electrospun Polysulfone Membranes Functionalized by Ag Nanocoating via Magnetron Sputtering

Antibacterial properties of engineered materials are important in the transition to a circular economy and societal security, as they are central to many key industrial areas, such as health, food, and water treatment/reclaiming. Nanocoating and electrospinning are two versatile, simple, and low-cost technologies that can be combined into new advanced manufacturing approaches to achieve controlled production of innovative micro- and nano-structured non-woven membranes with antifouling and antibacterial properties. The present study investigates a rational approach to design and manufacture electrospun membranes of polysulfone (PSU) with mechanical properties optimized via combinatorial testing from factorial design of experiments (DOE) and endowed with antimicrobial silver (Ag) nanocoating. Despite the very low amount of Ag deposited as a conformal percolating nanocoating web on the polymer fibers, the antimicrobial resistance assessed against the Gram-negative bacteria E. coli proved to be extremely effective, almost completely inhibiting the microbial proliferation with respect to the reference uncoated PSU membrane. The results are relevant, for example, to improve antifouling behavior in ultrafiltration and reverse osmosis in water treatment

Electrospun PCL Filtration Membranes Enhanced with an Electrosprayed Lignin Coating to Control Wettability and Anti-Bacterial Properties

This study reports on the two-step manufacturing process of a filtration media obtained by first electrospinning a layer of polycaprolactone (PCL) non-woven fibers onto a paper filter backing and subsequently coating it by electrospraying with a second layer made of pure acidolysis lignin. The manufacturing of pure lignin coatings by solution electrospraying represents a novel development that requires fine control of the underlying electrodynamic processing. The effect of increasing deposition time on the lignin coating was investigated for electrospray time from 2.5 min to 120 min. Microstructural and physical characterization included SEM, surface roughness analysis, porosity tests, permeability tests by a Gurley densometer, ATR-FTIR analysis, and contact angle measurements vs. both water and oil. The results indicate that, from a functional viewpoint, such a natural coating endowed the membrane with an amphiphilic behavior that enabled modulating the nature of the bare PCL non-woven substrate. Accordingly, the intrinsic hydrophobic behavior of bare PCL electrospun fibers could be reduced, with a marked decrease already for a thin coating of less than 50 nm. Instead, the wettability of PCL vs. apolar liquids was altered in a less predictable manner, i.e., producing an initial increase of the oil contact angles (OCA) for thin lignin coating, followed by a steady decrease in OCA for higher densities of deposited lignin. To highlight the effect of the lignin type on the results, two grades of oak (AL-OA) of the Quercus cerris L. species and eucalyptus (AL-EU) of the Eucalyptus camaldulensis Dehnh species were compared throughout the investigation. All grades of lignin yielded coatings with measurable antibacterial properties, which were investigated against Staphylococcus aureus and Escherichia coli, yielding superior results for AL-EU. Remarkably, the lignin coatings did not change overall porosity but smoothed the surface roughness and allowed modulating air permeability, which is relevant for filtration applications. The findings are relevant for applications of this abundant biopolymer not only for filtration but also in biotechnology, health, packaging, and circular economy applications in general, where the reuse of such natural byproducts also brings a fundamental demanufacturing advantage

Colonic inflammation accelerates the progression of liver disease: A protective role of dipotassium glycyrrhizate

Background: The incidence of non-alcoholic fatty liver disease (NAFLD) and its more severe and progressive form, non-alcoholic steatohepatitis (NASH) is increasing worldwide. Gut inflammation seems to concur to the pathogenesis of NASH. No drugs are currently approved for NASH treatment. Aims: To investigate if inflamed gut directly contributes to the progression of NASH through gut epithelial and vascular barrier impairment and to evaluate the efficacy of dipotassium glycyrrhizate (DPG) to improve the liver disease. Methods: A NASH model was set up by feeding mice, for 8 and 13 weeks, with high fat diet with high fructose and glucose (HFD-FG) supplemented periodically with dextran sulfate sodium (DSS) in drinking water. A group was also treated with DPG by gavage. Histological, immunohistochemical and molecular analysis were performed. Results: DSS-induced colitis increased steatosis, inflammatory (IL-6, TNFα, NLRP3, MCP-1) as well as fibrotic (TGF-β, α-SMA) mediator expression in HFD-FG mice. Beneficial effect of DPG was associated with restoration of intestinal epithelial and vascular barriers, evaluated respectively by ZO-1 and PV-1 expression, that are known to limit bacterial translocation. Conclusion: Colonic inflammation strongly contributes to the progression of NASH, likely by favouring bacterial translocation. DPG treatment could represent a novel strategy to reduce liver injury

Intestinal Inflammation Alters the Expression of Hepatic Bile Acid Receptors Causing Liver Impairment

The gut-liver axis has been recently investigated in depth in relation to intestinal and hepatic diseases. Key actors are bile acid (BA) receptors, as farnesoid-X-receptor (FXR), pregnane-X-receptor (PXR) and G-protein-coupled-receptor (TGR5), that control a broad range of metabolic processes as well as inflammation and fibrosis.The present study aims to investigate the impact of intestinal inflammation on liver health with a focus on FXR, PXR and TGR5 expression. The strategy to improve liver health by reducing gut inflammation is also considered. Modulation of BA receptors in the inflamed colonic tissues of Inflammatory Bowel Disease (IBD) pediatric patients is analyzed

Liver Steatosis and Steatohepatitis Alter Bile Acid Receptors in Brain and Induce Neuroinflammation: A Contribution of Circulating Bile Acids and Blood-Brain Barrier

A tight relationship between gut-liver diseases and brain functions has recently emerged. Bile acid (BA) receptors, bacterial-derived molecules and the blood-brain barrier (BBB) play key roles in this association. This study was aimed to evaluate how non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) impact the BA receptors Farnesoid X receptor (FXR) and Takeda G-protein coupled receptor 5 (TGR5) expression in the brain and to correlate these effects with circulating BAs composition, BBB integrity and neuroinflammation. A mouse model of NAFLD was set up by a high-fat and sugar diet, and NASH was induced with the supplementation of dextran-sulfate-sodium (DSS) in drinking water. FXR, TGR5 and ionized calcium-binding adaptor molecule 1 (Iba-1) expression in the brain was detected by immunohistochemistry, while Zonula occludens (ZO)-1, Occludin and Plasmalemmal Vesicle Associated Protein-1 (PV-1) were analyzed by immunofluorescence. Biochemical analyses investigated serum BA composition, lipopolysaccharide-binding protein (LBP) and S100β protein (S100β) levels. Results showed a down-regulation of FXR in NASH and an up-regulation of TGR5 and Iba-1 in the cortex and hippocampus in both treated groups as compared to the control group. The BA composition was altered in the serum of both treated groups, and LBP and S100β were significantly augmented in NASH. ZO-1 and Occludin were attenuated in the brain capillary endothelial cells of both treated groups versus the control group. We demonstrated that NAFLD and NASH provoke different grades of brain dysfunction, which are characterized by the altered expression of BA receptors, FXR and TGR5, and activation of microglia. These effects are somewhat promoted by a modification of circulating BAs composition and by an increase in LBP that concur to damage BBB, thus favoring neuroinflammation

Innovative Multilayer Electrospun Patches for the Slow Release of Natural Oily Extracts as Dressings to Boost Wound Healing

Electrospinning is an advanced manufacturing strategy used to create innovative medical devices from continuous nanoscale fibers that is endowed with tunable biological, chemical, and physical properties. Innovative medical patches manufactured entirely by electrospinning are discussed in this paper, using a specific plant-derived formulation “1 Primary Wound Dressing©” (1-PWD) as an active pharmaceutical ingredient (API). 1-PWD is composed of neem oil (Azadirachta indica A. Juss.) and the oily extracts of Hypericum perforatum (L.) flowers, according to the formulation patented by the ENEA of proven therapeutic efficacy as wound dressings. The goal of this work is to encapsulate this API and demonstrate that its slow release from an engineered electrospun patch can increase the therapeutic efficacy for wound healing. The prototyped patch is a three-layer core–shell membrane, with a core made of fibers from a 1-PWD-PEO blend, enveloped within two external layers made of medical-grade polycaprolactone (PCL), ensuring mechanical strength and integrity during manipulation. The system was characterized via electron microscopy (SEM) and chemical and contact angle tests. The encapsulation, release, and efficacy of the API were confirmed by FTIR and LC-HRMS and were validated via in vitro toxicology and scratch assays