Hyaluronan--regulator and initiator of peritoneal inflammation and remodeling

Hyaluronic Acid in Rheumatology

Hyaluronic acid (HA), also known as hyaluronan, is an anionic glycosaminoglycan widely distributed throughout various tissues of the human body. It stands out from other glycosaminoglycans as it lacks sulfation and can attain considerable size: the average human synovial HA molecule weighs about 7 million Dalton (Da), equivalent to roughly 20,000 disaccharide monomers; although some sources report a lower range of 3-4 million Da. In recent years, HA has garnered significant attention in the field of rheumatology due to its involvement in joint lubrication, cartilage maintenance, and modulation of inflammatory and/or immune responses. This review aims to provide a comprehensive overview of HA's involvement in rheumatology, covering its physiology, pharmacology, therapeutic applications, and potential future directions for enhancing patient outcomes. Nevertheless, the use of HA therapy in rheumatology remains controversial with conflicting evidence regarding its efficacy and safety. In conclusion, HA represents a promising therapeutic option to improve joint function and alleviate inflammation and pain.

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.

Sterile Injury Repair and Adhesion Formation at Serosal Surfaces

Most multicellular organisms have a major body cavity containing vital organs. This cavity is lined by a mucosa-like serosal surface and filled with serous fluid which suspends many immune cells. Injuries affecting the major body cavity are potentially life-threatening. Here we summarize evidence that unique damage detection and repair mechanisms have evolved to ensure immediate and swift repair of injuries at serosal surfaces. Furthermore, thousands of patients undergo surgery within the abdominal and thoracic cavities each day. While these surgeries are potentially lifesaving, some patients will suffer complications due to inappropriate scar formation when wound healing at serosal surfaces defects. These scars called adhesions cause profound challenges for health care systems and patients. Therefore, reviewing the mechanisms of wound repair at serosal surfaces is of clinical importance. Serosal surfaces will be introduced with a short embryological and microanatomical perspective followed by a discussion of the mechanisms of damage recognition and initiation of sterile inflammation at serosal surfaces. Distinct immune cells populations are free floating within the coelomic (peritoneal) cavity and contribute towards damage recognition and initiation of wound repair. We will highlight the emerging role of resident cavity GATA6+ macrophages in repairing serosal injuries and compare serosal (mesothelial) injuries with injuries to the blood vessel walls. This allows to draw some parallels such as the critical role of the mesothelium in regulating fibrin deposition and how peritoneal macrophages can aggregate in a platelet-like fashion in response to sterile injury. Then, we discuss how serosal wound healing can go wrong, causing adhesions. The current pathogenetic understanding of and potential future therapeutic avenues against adhesions are discussed.

Use of Mesothelial Cells and Biological Matrices for Tissue Engineering of Simple Epithelium Surrogates

Tissue-engineering technologies have progressed rapidly through last decades resulting in the manufacture of quite complex bioartificial tissues with potential use for human organ and tissue regeneration. The manufacture of avascular monolayered tissues such as simple squamous epithelia was initiated a few decades ago and is attracting increasing interest. Their relative morphostructural simplicity makes of their biomimetization a goal, which is currently accessible. The mesothelium is a simple squamous epithelium in nature and is the monolayered tissue lining the walls of large celomic cavities (peritoneal, pericardial, and pleural) and internal organs housed inside. Interestingly, mesothelial cells can be harvested in clinically relevant numbers from several anatomical sources and not less important, they also display high transdifferentiation capacities and are low immunogenic characteristics, which endow these cells with therapeutic interest. Their combination with a suitable scaffold (biocompatible, degradable, and non-immunogenic) may allow the manufacture of tailored serosal membranes biomimetics with potential spanning a wide range of therapeutic applications, principally for the regeneration of simple squamous-like epithelia such as the visceral and parietal mesothelium vascular endothelium and corneal endothelium among others. Herein, we review recent research progresses in mesothelial cells biology and their clinical sources. We make a particular emphasis on reviewing the different types of biological scaffolds suitable for the manufacture of serosal mesothelial membranes biomimetics. Finally, we also review progresses made in mesothelial cells-based therapeutic applications and propose some possible future directions.

Mesothelial cells in tissue repair and fibrosis

Mesothelial cells are fundamental to the maintenance of serosal integrity and homeostasis and play a critical role in normal serosal repair following injury. However, when normal repair mechanisms breakdown, mesothelial cells take on a profibrotic role, secreting inflammatory, and profibrotic mediators, differentiating and migrating into the injured tissues where they contribute to fibrogenesis. The development of new molecular and cell tracking techniques has made it possible to examine the origin of fibrotic cells within damaged tissues and to elucidate the roles they play in inflammation and fibrosis. In addition to secreting proinflammatory mediators and contributing to both coagulation and fibrinolysis, mesothelial cells undergo mesothelial-to-mesenchymal transition, a process analogous to epithelial-to-mesenchymal transition, and become fibrogenic cells. Fibrogenic mesothelial cells have now been identified in tissues where they have not previously been thought to occur, such as within the parenchyma of the fibrotic lung. These findings show a direct role for mesothelial cells in fibrogenesis and open therapeutic strategies to prevent or reverse the fibrotic process.

Cancer cell glycocalyx mediates mechanotransduction and flow-regulated invasion

Mammalian cells are covered by a surface proteoglycan (glycocalyx) layer, and it is known that blood vessel-lining endothelial cells use the glycocalyx to sense and transduce the shearing forces of blood flow into intracellular signals. Tumor cells in vivo are exposed to forces from interstitial fluid flow that may affect metastatic potential but are not reproduced by most in vitro cell motility assays. We hypothesized that glycocalyx-mediated mechanotransduction of interstitial flow shear stress is an un-recognized factor that can significantly enhance metastatic cell motility and play a role in augmentation of invasion. Involvement of MMP levels, cell adhesion molecules (CD44, α3 integrin), and glycocalyx components (heparan sulfate and hyaluronan) was investigated in a cell/collagen gel suspension model designed to mimic the interstitial flow microenvironment. Physiological levels of flow upregulated MMP levels and enhanced the motility of metastatic cells. Blocking the flow-enhanced expression of MMP activity or adhesion molecules (CD44 and integrins) resulted in blocking the flow-enhanced migratory activity. The presence of a glycocalyx-like layer was verified around tumor cells, and the degradation of this layer by hyaluronidase and heparinase blocked the flow-regulated invasion. This study shows for the first time that interstitial flow enhancement of metastatic cell motility can be mediated by the cell surface glycocalyx - a potential target for therapeutics.

Impact of intraperitoneal pressure of a CO2 pneumoperitoneum on the surgical peritoneal environment

BACKGROUND

Animal experiments have suggested that a high intraperitoneal pressure (IPP) might adversely affect the surgical peritoneal environment. The present experimental study investigates the impact of IPP of a CO(2) pneumoperitoneum on human peritoneum.

METHODS

Patients undergoing laparoscopic surgery were subjected to either low (8 mmHg) or standard (12 mmHg) IPP. Normal peritoneum was collected from the parietal wall at the beginning of surgery and every 60 min thereafter. Expression levels of 168 genes that encode extracellular matrix proteins, adhesion molecules or inflammatory cytokine signaling molecules were measured in peritoneal tissues using real-time polymerase chain reaction (PCR)-based assay panels. Human peritoneal mesothelial cells (HPMCs) and human peritoneal fibroblasts (HPFBs) were incubated in a CO(2) insufflation chamber for 1 h at 12 or 8 mmHg. Hyaluronan (HA) synthesis and mRNA expression levels of hyaluronic acid synthases (HAS) and hyaluronidases (Hyal) in HPMCs and HPFBs were measured at 0, 4, 8, 12, 24 and 48 h after CO(2) gas exposure by ELISA and real-time PCR, respectively.

RESULTS

Expression levels of connective tissue growth factor (CTGF), matrix metalloproteinase-9, E-selectin, chemokine (C-X-C motif) ligand 2 (CXCL-2), Hyal-1 and Hyal-2 were significantly higher and those of HAS-1, HAS-3, thrombospondin-2 (TSP-2) and interleukin-10 were significantly lower in the 12 mmHg group compared with the 8 mmHg group. HA synthesis was significantly lower in the 12 mmHg group compared with the 8 mmHg group in HPMCs and HPFBs throughout the time course.

CONCLUSIONS

A low IPP (8 mmHg) may be better than the standard IPP (12 mmHg) to minimize the adverse impact on the surgical peritoneal environment during a CO(2) pneumoperitoneum.

Pathophysiology of the peritoneal membrane during peritoneal dialysis: the role of hyaluronan

During peritoneal dialysis (PD), constant exposure of mesothelial cells to bioincompatible PD solutions results in the denudation of the mesothelial monolayer and impairment of mesothelial cell function. Hyaluronan, a major component of extracellular matrices, is synthesized by mesothelial cells and contributes to remesothelialization, maintenance of cell phenotype, and tissue remodeling and provides structural support to the peritoneal membrane. Chronic peritoneal inflammation is observed in long-term PD patients and is associated with increased hyaluronan synthesis. During inflammation, depolymerization of hyaluronan may occur with the generation of hyaluronan fragments. In contrast to native hyaluronan which offers a protective role to the peritoneum, hyaluronan fragments exacerbate inflammatory and fibrotic processes and therefore assist in the destruction of the tissue. This paper will discuss the contribution of mesothelial cells to peritoneal membrane alterations that are induced by PD and the putative role of hyaluronan in these processes.

The Use of Topical Hyaluronic Acid and Silver Sulfadiazine (Altergen®) in Patients Undergoing Two-Stage Anterior Urethroplasty with Oral Mucosal Graft

This investigative pilot study was conducted with the objective of evaluating the therapeutic effect of a cream containing hyaluronic acid (HA) and silver-sulfadiazine (Altergen®, IBSA Farmaceutici Italia, S.r.l.) in adult patients undergoing two-stage urethroplasty using an oral mucosal graft for anterior urethral strictures due to failed hypospadias repair. We used a cream (Altergen®) containing the following active ingredients: 100 g HA, 0.20 mg sodium salt, and 1 g silver-sulfadiazine. During the period of January 2009 - May 2010, 40 patients, mean age 24 years, who had undergone hypospadias surgery during childhood were enrolled in the study, according to some inclusion and exclusion criteria (age >18 years, with the absence of diabetes, neurovascular disease, lichen sclerosus or other dermatological lesions). All 40 patients had navicularis or penile urethral strictures and underwent two-stage urethroplasty using an oral mucosa graft. Post-operatively, 20 patients (50%) were treated with a cream containing HA and silver-sulfadiazine (Altergen®) and 20 patients (50%) were treated using a standard topical treatment (iodopovidone 10% gel). All patients underwent a follow-up at 6, 15, 30, 60 and 120 days after surgery. Out of the 20 patients treated with the HA and silver-sulfadiazine-containing cream (Altergen®), 18 (90%) showed good and complete healing of the graft implant 30 days after surgery. Of the 20 patients not treated with the HA and silver-sulfadiazine-contaning cream (Altergen®), 13 (65%) showed good and complete healing of the graft implant 30 days after surgery. These results were constant in all follow-ups in both patient groups. In patients who underwent a navicularis or penile two-stage oral mucosal graft urethroplasty, the use of a HA and silver-sulfadiazine-containing cream was associated with a higher success rate of the graft implant and a lower incidence of post-surgical complications compared to the controls.

Low molecular weight hyaluronic acid effects on murine macrophage nitric oxide production

Hyaluronic acid (HA) is increasingly used for a number of medical device applications. Since the chemical structure of HA is identical no matter its bacterial or animal origin, it should be the ideal biomaterial. However, short term transient inflammatory reactions are common, while rare long-term adverse events may correlate with subclinical chronic inflammation. Concern has been raised that low molecular weight components or degradation fragments from implanted HA may directly stimulate inflammatory reactions. This study examined a panel of HA molecular weights from the unitary disaccharide up to 1.7 x 10(6) Dalton lengths, in which endotoxin was assayed at a very low level (less than 0.03 EU/mg). The murine cell line RAW 264.7, rat splenocytes, and rat adherent differentiated primary macrophages were assayed for nitric oxide production under a variety of inflammatory conditions plus or minus HA. Under the highest inflammatory states, nitric oxide production was mildly suppressed by HMW-HA while slightly augmented by LMW-HA at mg/mL concentrations. However, at micromolar concentrations fragments below 5000 Daltons, thought to have drug-like qualities, were without effect. These data support the hypothesis that if endotoxin is reduced to an extremely low level, LMW-HA may not directly provoke normal tissue macrophage-mediated inflammatory reactions.

Review: Hyperglycaemia and the vascular glycocalyx: the key to microalbuminuria and cardiovascular disease in diabetes mellitus?

The vascular glycocalyx is a gel layer between endothelium and the blood, 0.5 µm thick. Evidence is presented from published studies to indicate that hyperglycaemia causes damage to the vascular glycocalyx. This damage results in microalbuminuria, excess fluid transfer to the interstitium, reduction in nitric oxide (NO) production by arterial endothelium, and leukocyte and platelet adhesion to endothelium leading to atherothrombosis. The lack of NO production proceeds from the fact that glycocalyx is the mechanotransducer transmitting the signal for increased shear stress between blood and arterial wall, and this function is inhibited by hyperglycaemia. When hyperinsulinaemia is also present, the problem is compounded by general arterial dilatation leading to low shear rates throughout the arterial tree. These findings explain the predisposition to atherothrombosis in the pre-diabetic condition of insulin resistance/metabolic syndrome/obesity and diabetes mellitus. It is proposed that greater efforts than ever are required to detect occult insulin resistance, to treat such patients and diabetics with ever more strict blood glucose control while minimising insulin levels, and to carry out further research into how glycocalyx structure and function can be preserved.

Biocompatibility and Tolerability of a Purely Bicarbonate-Buffered Peritoneal Dialysis Solution

Background

Novel peritoneal dialysis solutions are characterized by a minimal content of glucose degradation products and a neutral pH. Many studies have shown the biocompatibility of neutral lactate-buffered solutions; however, until now, the effect of purely bicarbonate-buffered solutions has not been intensively studied in vivo.

Methods

This study was an open label, prospective, crossover multicenter trial to investigate the biocompatibility of a purely bicarbonate-buffered solution (bicPDF) by measuring biocompatibility parameters such as cancer antigen 125 (CA125) in peritoneal effluent. 55 patients were enrolled in the study. After a 2-week run-in phase, 53 patients could be randomized into 2 groups, starting with either standard lactate-buffered peritoneal dialysis fluid (SPDF) for 12 weeks (phase 1) and then switching to bicPDF for 12 weeks (phase 2), or vice versa. Overnight peritoneal effluents were collected at baseline and at the end of phases 1 and 2 and were tested for CA125, hyaluronic acid, vascular endothelial growth factor (VEGF), tumor necrosis factor-alpha (TNF-α), interleukin 6 (IL-6), interferon gamma (IFNγ), and transforming growth factor-beta1 (TGF-β1). Total ultrafiltration and residual renal function were also assessed. At the end of the study, pain during fluid exchange and dwell was evaluated using special questionnaires.

Results

34 patients completed the study; 27 of them provided data for analysis of the biocompatibility parameters. CA125 levels in overnight effluent were significantly higher with bicPDF (61.9 ± 33.2 U/L) than with SPDF (18.6 ± 18.2 U/L, p < 0.001). Hyaluronic acid levels were significantly lower after the use of bicPDF (185.0 ± 119.6 ng/mL) than after SPDF (257.4 ± 174.0 ng/mL, p = 0.013). Both TNF-α and TGF-β1 showed higher levels with the use of bicPDF than with SPDF. No differences were observed for IL-6, VEGF, or IFNγ levels. We observed an improvement in the glomerular filtration rate with the use of bicPDF but no differences were observed for total fluid loss. Pain scores could be analyzed in 23 patients: there was no difference between the solutions.

Conclusions

The use of a purely bicarbonate-buffered low-glucose degradation product solution significantly changes most of the peritoneal effluent markers measured, suggesting an improvement in peritoneal membrane integrity. Additionally, it seems to have a positive effect on residual renal function.

Inflammatory ascites formation induced by macromolecules in mice and rats

Different macromolecules were administered intraperitoneally to stimulate formation of protein-rich ascitic fluid in rodents. Stimulatory effect of plant lectins depended on the attachment to cell surface carbohydrates, Canavalia ensiformis (ConA) lectin was used in the majority of experiments. The time course of ConA-induced ascites was divided into an early (up to 4 h) and a late (from 6 h on) phase, with a transitional period between the two. Water and protein accumulation showed parallel time courses: volume of the ascitic fluid peaked at around 3 h, and fibrin threads appeared after 6 h. Viscosity of the ascitic fluid and its supernatant increased with time, reaching maximal fibrinogen concentration at around 16 h. Peritoneal permeability, followed by pleural and pericardial effusions, was elicited only by lectins that form soluble complexes with serum glycoproteins, whereas the effect of serum-precipitating lectins was restricted to the peritoneum. Macromolecules with serial positive charges (e.g., polylysine or polyethyleneimine) enhanced peritoneal permeability by ionic interactions with cell surface molecules. Viscosity of the polycation-induced ascitic fluid did not tend to increase with time and corresponded to the early phase of the ConA-induced ascites. Polyglutamate, a polyanionic macromolecule, inhibited the effect of polycations, but not that of ConA. The most efficient stimulatory macromolecules appear to induce ascites by noncovalent cross-linking of cell surface glycoproteins or glycosaminoglycans or both. A similar mechanism may operate in the maintenance of basal secretion to prevent eventual desiccation. Noncovalent cross-linking appears to be a common denominator of both basal and enhanced permeability.

Intrinsic Cells: Mesothelial Cells — Central Players in Regulating Inflammation and Resolution

Background

Preservation of the structural and functional integrity of the peritoneum is essential to maintain the dialytic efficacy of the peritoneal membrane. Although much improvement has been made to peritoneal dialysis (PD) fluids, they remain bioincompatible, and together with peritonitis, they continue to induce peritoneal inflammation and fibrosis.

Method

This article reviews the putative factors that mediate mesothelial cell inflammation during PD, and the mechanisms by which mesothelial cells attempt to regulate and resolve peritoneal inflammation.

Results

The mesothelium is the first line of defense to foreign particles and chemicals in the peritoneal cavity. Constant exposure of the mesothelium to the bioincompatible constituents of PD solutions results in denudation of the mesothelium and loss of the peritoneal cavity's protective layer. Detached mesothelial cells in PD solutions have the capacity to replenish the mesothelial layer through their ability to migrate and attach to areas of denudation. Mesothelial cells synthesize a plethora of growth factors, matrix proteins, and proteoglycans that aid in the reparative process and regulate the formation of chemotactic gradients that are essential for infiltration of leukocytes to sites of injury.

Conclusions

Far from being bystanders in peritoneal function, mesothelial cells have been shown to play a dynamic role in peritoneal homeostasis and immunoregulation. Studies have highlighted the potential use of mesothelial cells in gene therapy and cell transplantation, both of which may provide novel therapeutic strategies for the preservation of the peritoneum during PD.

Pericellular hyaluronan coat visualized in live cells with a fluorescent probe is scaffolded by plasma membrane protrusions

Many cell types wear up to 20-mum-wide hyaluronidase-sensitive surface coats, detected by exclusion of sedimenting particles like fixed erythrocytes. The structure of the coat is enigmatic, being apparently too thick to be accounted by random coils or even extended chains of just hyaluronan attached to cell surface. We have shown that hyaluronan synthesis enforced by green fluorescent protein-hyaluronan synthase transfection creates microvillous protrusions. The idea that the plasma membrane protrusions rather than hyaluronan alone is responsible for the exclusion space was studied with a fluorescent probe for hyaluronan and a dye with membrane affinity, applied to live cell cultures. Mesothelial and smooth muscle cells, fibroblasts, and chondrocytes, all known for their endogenously active hyaluronan synthesis, showed hyaluronan-coated plasma membrane protrusions, barely visible in phase contrast microscopy. Treatment with hyaluronidase and inhibition of hyaluronan synthesis caused retraction of the protrusions unless they were attached to substratum. Hyaluronan and the exclusion space were reduced, but did not disappear, by purified hyaluronan hexasaccharides that compete with hyaluronan attached to CD44. The results suggest that slender plasma membrane protrusions are an inherent feature of hyaluronan coats, form their scaffold, and largely result from ongoing hyaluronan synthesis in their plasma membrane. This manuscript contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials.