"COVID-19/SARS-CoV-2 virus spike protein-related delayed inflammatory reaction to hyaluronic acid dermal fillers: a challenging clinical conundrum in diagnosis and treatment".

We present the first reported cases of delayed inflammatory reactions (DIR) to hyaluronic acid (HA) dermal fillers after exposure to the COVID-19 spike protein. DIR to HA is reported to occur in the different scenarios including: secondary to poor injection technique, following dental cleaning procedures, following bacterial/viral illness, and after vaccination. In this report of 4 cases with distinct clinical histories and presentations: one case occured following a community acquired COVID-19 infection, one case occured in a study subject in the mRNA-1273 clinical phase III trial, one case occurred following the first dose of publically available mRNA-1273 vaccine (Moderna, Cambridge MA), and the last case occurred after the second dose of BNT162b2 vaccine (Pfizer, New York, NY). Injectable HA dermal fillers are prevalent in aesthetic medicine for facial rejuvenation. Structural modifications in the crosslinking of HA fillers have enhanced the products' resistance to enzymatic breakdown and thus increased injected product longevity, however, have also led to a rise in DIR. Previous, DIR to HA dermal fillers can present clinically as edema with symptomatic and inflammatory erythematous papules and nodules. The mechanism of action for the delayed reaction to HA fillers is unknown and is likely to be multifactorial in nature. A potential mechanism of DIR to HA fillers in COVID-19 related cases is binding and blockade of angiotensin 2 converting enzyme receptors (ACE2), which are targeted by the SARS-CoV-2 virus spike protein to gain entry into the cell. Spike protein interaction with dermal ACE2 receptors favors a pro-inflammatory, loco-regional TH1 cascade, promoting a CD8+T cell mediated reaction to incipient granulomas, which previously formed around residual HA particles. Management to suppress the inflammatory response in the native COVID-19 case required high-dose corticosteroids (CS) to suppress inflammatory pathways, with concurrent ACE2 upregulation, along with high-dose intralesional hyaluronidase to dissolve the inciting HA filler. With regards to the two vaccine related cases; in the mRNA-1273 case, a low dose angiotensin converting enzyme inhibitor (ACE-I) was utilized for treatment, to reduce pro-inflammatory Angiotensin II. Whereas, in the BNT162b2 case the filler reaction was suppressed with oral corticosteroids. Regarding final disposition of the cases; the vaccine-related cases returned to baseline appearance within 3 days, whereas the native COVID-19 case continued to have migratory, evanescent, periorbital edema for weeks which ultimately subsided.

Disrupted homeostasis of synovial hyaluronic acid and its associations with synovial mast cell proteases of rheumatoid arthritis patients and collagen-induced arthritis rats.

Hyaluronic acid (HA) is the main component of the extracellular matrix (ECM) of joints, and it is important for a lubricating joint during body movement. Degradation is the main metabolic process of HA in vivo. Hyaluronidases (HAase) were known for HA degradation. The inflammation-induced HA rapid-metabolism can reduce HA viscosity and concentration in joints. Mast cells (MC) containing their specific proteases were found in synovium tissue. It is unclear if MC-proteases could be involved in HA degradation pathways. This study aims to explore the correlations between HA concentration vs mast cell proteases, or matrix metalloproteinase-2/9 (MMP-2/9) and to investigate the association of MC-specific proteases with disrupted synovial HA homeostasis in rheumatoid arthritis (RA) or collagen-induced arthritis rats. The synovial fluid samples from no-RA and RA patients were collected; the collagen-induced arthritis (CIA) rat model was established; HA concentration and the activities of MC-protease and MMP-2/9 in the samples were detected, and the correlations were analyzed. In vitro interaction experiment was carried out by mixing MC-proteases with HA to observe the degradation speed. The HA concentrations in synovial fluids were decreased in RA patients and CIA rats compared with those in no-RA subjects or normal rats respectively. The activities of mast cell proteases in synovial fluids were increased and positively correlated with MMP-9, but negatively correlated with HA concentrations. In vitro study, the addition of MC-chymase and tryptase promoted the speed in HA degradation. MC-proteases may influence HA degradation pathway.

Is hyaluronic acid filler still a potential risk factor for an autoimmune reaction?

BACKGROUND: Rejuvenation of the skin with hyaluronic acid (HA) filler is considered to be one of the most favourable procedures in the field of aesthetics. Nevertheless, some adverse effects still occur though infrequently, and are associated with its use. Previous research has suggested that HA filler may stimulate antibodies. Consequently, an investigation of the immune interactions associated with use of HA filler is an important area for investigation. OBJECTIVES: The aim of this research is to investigate whether HA filler influences the initiation of an autoimmune reaction in healthy women who had received HA filler by screening for autoantibodies in the blood. Results will be compared with agematched apparently healthy control women who did not receive the filler. METHODS: Serum samples were obtained from 44 females who had received HA filler and 44 females who had not as a control group. The enzyme-linked immunosorbent assay (ELISA) technique was utilised to measure serum concentrations of anti- Thyroglobulin (Tg), anti -thyroid peroxidase (TPO), rheumatoid factor (RF), anti-nuclear antibody (ANA) and anticentromeres. RESULTS: The number of women who tested positive for the measured autoantibodies was not statistically significant (p=0.803) between those who had received HA filler (n=10/44, 25%) and the control group (n=11/44, 22.7%). CONCLUSION: Based on our result HA filler procedures do not induce an autoimmune reaction in women who received HA filler compared to controls. And consequently, HA filler procedures are relatively safe, and these results contradict the findings of other non-controlled works.

Hyaluronan molecular weight: Effects on dissolution time of dissolving microneedles in the skin and on immunogenicity of antigen.

Biomaterials used as matrix for dissolving micro needles (dMNs) may affect the manufacturing process as well as the potency of the active pharmaceutical ingredient, e.g. the immunogenicity of incorporated vaccine antigens. The aim of this study was to investigate the effect of the molecular weight of hyaluronan, a polymer widely used in the fabrication of dMNs, ranging in molecular weight from 4.8 kDa to 1.8 MDa, on the dissolution of microneedles in the skin in time as well as the antibody response in mice and T-cell activation in vitro. Hyaluronan molecular weight (HA-MWs) did not affect antibody responses (when lower than 150 kDa) nor CD4+ T-cell responses against model antigen ovalbumin. However, the HA-MWs had an effect on the fabrication of dMNs. The 1.8 MDa HA was not suitable for the fabrication of dMNs. Similarly, the 4.8 kDa HA generated dMN arrays less robust compared to the other HA-MWs requiring optimization of the drying conditions. Finally, higher HA-MWs led to longer application time of dMN arrays for a complete dissolution of microneedles into the skin. Specifically, we identified 20 kDa HA as the optimal HA-MW for the fabrication of dMNs as with this MW the dMNs are robust and dissolve fast in the skin without affecting immunogenicity.

Hyaluronan Fragmentation During Inflammatory Pathologies: A Signal that Empowers Tissue Damage.

The mechanisms that modulate the response to tissue injury are not fully understood. Abnormalities in the repair response are associated with a variety of chronic disease states characterized by inflammation, followed subsequently by excessive ECM deposition. As cell-matrix interactions are able to regulate cellular homeostasis, modification of ECM integrity appears to be an unspecific factor in promoting the onset and progression of inflammatory diseases. Evidence is emerging to show that endogenous ECM molecules supply signals to damage tissues and cells in order to promote further ECM degradation and inflammation progression. Several investigations have been confirmed that HA fragments of different molecular sizes exhibit different biological effects and responses. In fact, the increased deposition of HA into the ECM is a strong hallmark of inflammation processes. In the context of inflammatory pathologies, highly polymerized HA is broken down into small components, which are able to exacerbate the inflammatory response by inducing the release of various detrimental mediators such as reactive oxygen species, cytokines, chemokines and destructive enzymes and by facilitating the recruitment of leukocytes. However, strategies involving the modulation of the HA fragment with specific receptors on cell surface could represent different promising effects for therapeutic scope. This review will focus on the inflammation action of small HA fragments in recent years obtained by in vivo reports.

Hyaluronic Acid-Antibody Fragment Bioconjugates for Extended Ocular Pharmacokinetics.

Treatment of ocular diseases associated with neovascularization currently requires frequent intravitreal injections of antivascular endothelial growth factor (anti-VEGF) therapies. Reducing the required frequency of anti-VEGF injections and associated clinical visits may improve patient adherence to the prescribed treatment regimen and improve outcomes. Herein, we explore conjugation of rabbit and fragment antibodies (Fab) to the biopolymer hyaluronic acid (HA) as a half-life modifying strategy, and assess the impact on Fab biophysical properties and vitreal pharmacokinetics. HA-Fab conjugates of three distinct molecular weights and hydrodynamic radii (RH) were assessed for in vivo pharmacokinetic performance relative to unconjugated Fab after intravitreal injection in rabbits. Covalent conjugation to HA did not significantly alter the thermal stability or secondary or tertiary structure, or diminish the potency of the Fab, thereby preserving its pharmacological properties. Conjugation to HA did significantly slow the in vivo clearance of Fab from the rabbit vitreous in an RH-dependent manner. Compared to free Fab (observed vitreal half-life of 2.8 days), HA-Fab conjugates cleared with observed half-lives of 7.6, 10.2, and 18.3 days for 40 kDa, 200 kDa, and 600 kDa HA conjugates, respectively. This work elucidates a possible strategy for long-acting delivery of proteins intended for the treatment of chronic posterior ocular diseases.

High and Low Molecular Weight Hyaluronic Acid Differentially Influences Oxylipins Synthesis in Course of Neuroinflammation.

Hyaluronic acid (HA), a major glycosaminoglycan of the extracellular matrix, has cell signaling functions that are dependent on its molecular weight. Anti-inflammatory effects for high-molecular-weight (HMW) HA and pro-inflammatory effects for low-molecular-weight (LMW) HA effects were found for various myeloid cells, including microglia. Astrocytes are cells of ectodermal origin that play a pivotal role in brain inflammation, but the link between HA with different molecular weights and an inflammatory response in these cells is not clear. We tested the effects of LMW and HMW HA in rat primary astrocytes, stimulated with Poly:IC (PIC, TLR3 agonist) and lipopolysaccharide (LPS, TLR4 agonist). Oxylipin profiles were measured by the UPLC-MS/MS analysis and metabolites HDoHEs (from docosahexaenoic acid), -HETEs, prostaglandins (from arachidonic acid), DiHOMEs and HODEs (from linoleic acid) were detected. Both, HMW and LMW HA downregulated the cyclooxygenase-mediated polyunsaturated fatty acids metabolism, LMW also reduced lipoxygenase-mediated fatty acid metabolism. Taken together, the data show that both LMW and HMW (i) influence themselves on cytokines (TNFα, IL-6, IL-10), enzymes iNOS, COX-2, and oxylipin levels in extracellular medium of cultured astrocytes, (ii) induced cellular adaptations in long-term applications, (iii) modulate TLR4- and TLR3-signaling pathways. The effects of HMW and LMW HA are predominantly revealed in TLR4- and TLR3- mediated responses, respectively.

LL-37 alone and in combination with IL17A enhances proinflammatory cytokine expression in parallel with hyaluronan metabolism in human synovial sarcoma cell line SW982-A step toward understanding the development of inflammatory arthritis.

LL-37 is the only human cathelicidin-family host defense peptide and has been reported to interact with invading pathogens causing inflammation at various body sites. Recent studies showed high levels of LL-37 in the synovial-lining membrane of patients with rheumatoid arthritis, a common type of inflammatory arthritis. The present study aims to investigate the role of LL-37 on mechanisms associated with pathogenesis of inflammatory arthritis. The effects of LL-37 on the expression of proinflammatory cytokines, hyaluronan (HA) metabolism-related genes, cell death-related pathways, and cell invasion were investigated in SW982, a human synovial sarcoma cell line. Time-course measurements of proinflammatory cytokines and mediators showed that LL-37 significantly induced IL6 and IL17A mRNA levels at early time points (3-6 hr). HA-metabolism-related genes (i.e., HA synthase 2 (HAS2), HAS3, hyaluronidase 1 (HYAL1), HYAL2, and CD44) were co-expressed in parallel. In combination, LL-37 and IL17A significantly enhanced PTGS2, TNF, and HAS3 gene expression concomitantly with the elevation of their respective products, PGE2, TNF, and HA. Cell invasion rates and FN1 gene expression were also significantly enhanced. However, LL-37 alone or combined with IL17A did not affect cell mortality or cell cycle. Treatment of SW982 cells with both LL-37 and IL17A significantly enhanced IKK and p65 phosphorylation. These findings suggest that the chronic production of a high level of LL-37 may synchronize with its downstream proinflammatory cytokines, especially IL17A, contributing to the co-operative enhancement of pathogenesis mechanisms of inflammatory arthritis, such as high production of proinflammatory cytokines and mediators together with the activation of HA-metabolism-associated genes and cell invasion.

Platelet hyaluronidase-2 regulates the early stages of inflammatory disease in colitis.

Platelets are specialized cells essential for hemostasis that also function as crucial effectors capable of mediating inflammatory and immune responses. These sentinels continually survey their environment and discriminate between homeostatic and danger signals such as modified components of the extracellular matrix. The glycosaminoglycan hyaluronan (HA) is a major extracellular matrix component that coats the vascular lumen and, under normal conditions, restricts access of inflammatory cells. In response to tissue damage, the endothelial HA matrix enhances leukocyte recruitment and regulates the early stages of the inflammatory response. We have shown that platelets can degrade HA from the surface of activated endothelial cells via the enzyme hyaluronidase-2 (HYAL2) and that HYAL2 is deficient in platelets isolated from patients with inflammatory bowel disease (IBD). Platelets are known to be involved in the pathogenesis of several chronic disease states, including IBD, but they have been largely overlooked in the context of intestinal inflammation. We therefore wanted to define the mechanism by which platelet HYAL2 regulates the inflammatory response during colitis. In this study, we provide evidence that HA catabolism is disrupted in human intestinal microvascular endothelial cells isolated from patients with IBD. Furthermore, mice deficient in HYAL2 are more susceptible to an acute model of colitis, and this increased susceptibility is abrogated by transfusion of HYAL2-competent platelets. Finally, we show that platelets, via HYAL2-dependent degradation of endothelial HA, regulate the early stages of inflammation in colitis by limiting leukocyte extravasation.

Emerging evidence for the essential role of hyaluronan in cutaneous biology.

Hyaluronan (HA), a linear non-sulfated glycosaminoglycan, participates in a variety of biological processes in the skin, such as cell-matrix interactions and activation of chemokines/cytokines, enzymes, and growth factors. In these activation events, HA acts as a damage-associated molecular pattern (DAMP). This review discusses the progress in functional research on HA, and its associated factors, in several aspects of cutaneous biology; e.g., immunity and wound repair.

Chemical Modification of the N-Acetyl Moieties of Hyaluronic Acid from Streptococcus equi for Studies in Cytokine Production.

Partial N-deacetylation and certain N-reacylations of low-molecular-weight hyaluronic acid (hyaluronan) abate its proinflammatory properties in mammalian systems. Here, we describe the treatment of bacterial hyaluronic acid by hydrazine or NaOH to yield smaller partially deacetylated polymers. These N-deacetylated polymers can be reacylated with acyl anhydrides to yield substituted hyaluronic acid derivatives of equivalent size and equimolar N-acyl substitutions.

Delayed-Onset Nodules to Differentially Crosslinked Hyaluronic Acids: Comparative Incidence and Risk Assessment.

BACKGROUND: Robust and long-term data on true incidence of delayed-onset nodules and immune tolerance of hyaluronic acid (HA) fillers are lacking. OBJECTIVE: To characterize the incidence of delayed nodules in Vycross (VYC) HA fillers compared with previously reported FDA and non-FDA data of all HA fillers. METHODS AND MATERIALS: The incidence of delayed nodules in all patients who had received VYC fillers in a 12-month period was assessed through a retrospective chart review. Nodule incidence for currently approved nonanimal-stabilized hyaluronic acid (NASHA) fillers was assessed using the FDA Summary of Safety and Effectiveness Data. RESULTS: Overall, 1,029 patients received 1,250 VYC filler treatments. Five patients developed delayed nodules to VOB, with an incidence of 1.0% per patient and 0.8% per syringe. No nodules were observed in patients who received VLR or VOL. All nodules were treated successfully using a combination of intralesional triamcinolone and hyaluronidase. Compared with other currently approved NASHA fillers, VOB is associated with a higher incidence of nodule formation. CONCLUSION: The introduction of VYC HAs has introduced a new variable that may be changing the immune tolerance of these substances, resulting in a higher incidence of delayed nodules than previously expected.

Chitosan Acetylation Degree Influences the Physical Properties of Polysaccharide Nanoparticles: Implication for the Innate Immune Cells Response.

The aim of the present contribution is twofold as it reports (i) on the role played by chitosan acetylation degree for the stability of nanoparticles (NPs) formed with hyaluronan and (ii) on the effect of the interaction of such NPs with immune cells. Chitosans with similar viscosity-average molecular weight, [Formula: see text], (i.e., 200 000) and different fractions of acetylated units ( FA) together with low-molecular-weight hyaluronan were chosen for developing a select library of formulations via electrostatic complex coacervation. The resulting NPs were analyzed in terms of size, polydispersity, surface charge, and stability in physiological-mimicked media by dynamic light scattering. Only medium acetylated chitosan ( FA = 0.16) guaranteed the stability of NPs. To explore the effect of NPs interaction with immune cells, the release of proinflammatory cytokines and the reactive oxygen species production by human macrophages and neutrophils, respectively, were evaluated. Strikingly, a structure-function relationship emerged, showing that NPs made of chitosans with FA = 0.02, 0.25, 0.46, and 0.63 manifested a proinflammatory activity, linked to the instability of the system. Conversely, NPs made of chitosan with FA = 0.16 neither modified the functional response of macrophages nor that of neutrophils. Of note, such NPs were found to possess additional properties potentially advantageous in applications such as delivery of therapeutics to target inflamed sites: (i) they are devoid of cytotoxic effects, (ii) they avoid engulfment during the early stage of interaction with macrophages, and (iii) they are muco-adhesive, thereby providing for site-specificity and long-residence effects.

Capsular Polysaccharide of Group A Streptococcus.

Most clinical isolates of Streptococcus pyogenes elaborate a capsular polysaccharide, which is composed of hyaluronic acid, a high-molecular-mass polymer of alternating residues of N-acetyl glucosamine and glucuronic acid. Certain strains, particularly those of the M18 serotype, produce abundant amounts of capsule, resulting in formation of large, wet-appearing, translucent or "mucoid" colonies on solid media, whereas strains of M-types 4 and 22 produce none. Studies of acapsular mutant strains have provided evidence that the capsule enhances virulence in animal models of infection, an effect attributable, at least in part, to resistance to complement-mediated opsonophagocytic killing by leukocytes. The presence of the hyaluronic acid capsule may mask adhesins on the bacterial cell wall. However, the capsule itself can mediate bacterial attachment to host cells by binding to the hyaluronic-acid binding protein, CD44. Furthermore, binding of the S. pyogenes capsule to CD44 on host epithelial cells can trigger signaling events that disrupt cell-cell junctions and facilitate bacterial invasion into deep tissues. This article summarizes the biochemistry, genetics, regulation, and role in pathogenesis of this important virulence determinant.

Design of peptide mimetics to block pro-inflammatory functions of HA fragments.

Hyaluronan is a simple extracellular matrix polysaccharide that actively regulates inflammation in tissue repair and disease processes. The native HA polymer, which is large (>500 kDa), contributes to the maintenance of homeostasis. In remodeling and diseased tissues, polymer size is strikingly polydisperse, ranging from <10 kDa to >500 kDa. In a diseased or stressed tissue context, both smaller HA fragments and high molecular weight HA polymers can acquire pro-inflammatory functions, which result in the activation of multiple receptors, triggering pro-inflammatory signaling to diverse stimuli. Peptide mimics that bind and scavenge HA fragments have been developed, which show efficacy in animal models of inflammation. These studies indicate both that HA fragments are key to driving inflammation and that scavenging these is a viable therapeutic approach to blunting inflammation in disease processes. This mini-review summarizes the peptide-based methods that have been reported to date for blocking HA signaling events as an anti-inflammatory therapeutic approach.

The hyaluronic acid-rich node and duct system is a structure organized for innate immunity and mediates the local inflammation.

The Hyaluronic Acid-rich Node and Duct System (HAR-NDS or NDS), Primo Vascular System (PVS) or Bonghan System (BHS), is thought to be a third circulatory system independent of the blood and lymphatic systems and a structure of connected nodes and ducts. Although it seems to be part of the immune system as it is enriched with cells of innate immunity, little is known about its immunological roles. We performed cellular profiling and secretome analysis of NDS in a steady state and under TLR2- or TLR4-mediated local inflammation, and found that the NDS is pre-dominantly enriched with the myeloid cells, selectively attracts the inflammatory macrophages and neutrophils, has a flexible structure just like the lymph node, and is structured with the fibroblastic reticular cells and reticular network. NDS dominantly harbored the myeloid cells in both steady and activated status, and secreted various types of inflammatory cytokines by proinflammatory stimuli. These results suggest that NDS is the lymphoid structure for the innate immunity and plays an intermediary role in the innate immune cell-mediated local inflammation.

Hyaluronan-based dissolving microneedles with high antigen content for intradermal vaccination: Formulation, physicochemical characterization and immunogenicity assessment.

The purpose of this study was to optimize the manufacturing of dissolving microneedles (dMNs) and to increase the antigen loading in dMNs to investigate the effect on their physicochemical properties. To achieve this, a novel single-array wells polydimethylsiloxane mold was designed, minimizing antigen wastage during fabrication and achieving homogeneous antigen distribution among the dMN arrays. Using this mold, hyaluronan (HA)-based dMNs were fabricated and tested for maximal ovalbumin (OVA) content. dMNs could be fabricated with an OVA:HA ratio as high as 1:1 (w/w), without compromising their properties such as shape and penetration into the ex vivo human skin, even after storage at high humidity and temperature. High antigen loading did not induce protein aggregation during dMN fabrication as demonstrated by complementary analytical methods. However, the dissolution rate in ex vivo human skin decreased with increasing antigen loading. About 2.7 µg OVA could be delivered in mice by using a single array with an OVA:HA ratio of 1:3 (w/w). Intradermal vaccination with dMNs induced an immune response similar as subcutaneous injection and faster than after hollow microneedle injection. In conclusion, results suggest that (i) the polydimethylsiloxane mold design has an impact on the manufacturing of dMNs, (ii) the increase in antigen loading in dMNs affects the microneedle dissolution and (iii) dMNs are a valid alternative for vaccine administration over conventional injection.

Hyaluronan and Its Interactions With Immune Cells in the Healthy and Inflamed Lung.

Hyaluronan is a hygroscopic glycosaminoglycan that contributes to both extracellular and pericellular matrices. While the production of hyaluronan is essential for mammalian development, less is known about its interaction and function with immune cells. Here we review what is known about hyaluronan in the lung and how it impacts immune cells, both at homeostasis and during lung inflammation and fibrosis. In the healthy lung, alveolar macrophages provide the first line of defense and play important roles in immunosurveillance and lipid surfactant homeostasis. Alveolar macrophages are surrounded by a coat of hyaluronan that is bound by CD44, a major hyaluronan receptor on immune cells, and this interaction contributes to their survival and the maintenance of normal alveolar macrophage numbers. Alveolar macrophages are conditioned by the alveolar environment to be immunosuppressive, and can phagocytose particulates without alerting an immune response. However, during acute lung infection or injury, an inflammatory immune response is triggered. Hyaluronan levels in the lung are rapidly increased and peak with maximum leukocyte infiltration, suggesting a role for hyaluronan in facilitating leukocyte access to the injury site. Hyaluronan can also be bound by hyaladherins (hyaluronan binding proteins), which create a provisional matrix to facilitate tissue repair. During the subsequent remodeling process hyaluronan concentrations decline and levels return to baseline as homeostasis is restored. In chronic lung diseases, the inflammatory and/or repair phases persist, leading to sustained high levels of hyaluronan, accumulation of associated immune cells and an inability to resolve the inflammatory response.

Protection of the endothelial glycocalyx by antithrombin in an endotoxin-induced rat model of sepsis.

INTRODUCTION: Injury and loss of the endothelial glycocalyx occur during the early phase of sepsis. We previously showed that antithrombin has a protective effect on this structure in vitro. Here, we investigated the possible protective effects of antithrombin in an animal model of sepsis. METHODS: Wistar rats were injected with endotoxin, and circulating levels of syndecan-1, hyaluronan, albumin, lactate and other biomarkers were measured in an antithrombin-treated group and an untreated control group (n = 6 in each group). Intravital microscopy was used to observe leukocyte adhesion, microcirculation, and syndecan-1 staining. RESULTS: The circulating levels of syndecan-1 and hyaluronan were significantly reduced in the antithrombin-treated group, compared with the untreated controls. Lactate levels and albumin reduction were significantly attenuated in the antithrombin-treated group. Intravital microscopic observation revealed that both leukocyte adhesion and blood flow were better maintained in the treatment group. The syndecan-1 lining was disrupted after endotoxin treatment, and this derangement was attenuated by treatment with antithrombin. CONCLUSION: Antithrombin effectively maintained microcirculation and vascular integrity by protecting the glycocalyx in a rat sepsis model.