Hyaluronic acid as a non-invasive biomarker of liver fibrosis

Molecular characterization of a precision-cut rat liver slice model for the evaluation of antifibrotic compounds

Precision-cut liver tissue slice (PCLS) contains all major cell types of the liver parenchyma and preserves the original cell-cell and cell-matrix contacts. It represents a promising ex vivo model to study liver fibrosis and test the antifibrotic effect of experimental compounds in a physiological environment. In this study using RNA sequencing, we demonstrated that various pathways functionally related to fibrotic mechanisms were dysregulated in PCLSs derived from rats subjected to bile duct ligation. The activin receptor-like kinase-5 (Alk5) inhibitor SB525334, nintedanib, and sorafenib each reversed a subset of genes dysregulated in fibrotic PCLSs, and of those genes we identified 608 genes whose expression was reversed by all three compounds. These genes define a molecular signature characterizing many aspects of liver fibrosis pathology and its attenuation in the model. A panel of 12 genes and 4 secreted biomarkers including procollagen I, hyaluronic acid (HA), insulin-like growth factor binding protein 5 (IGFBP5), and WNT1-inducible signaling pathway protein 1 (WISP1) were further validated as efficacy end points for the evaluation of antifibrotic activity of experimental compounds. Finally, we showed that blockade of α_V-integrins with a small molecule inhibitor attenuated the fibrotic phenotype in the model. Overall, our results suggest that the rat fibrotic PCLS model may represent a valuable system for target validation and determining the efficacy of experimental compounds. NEW & NOTEWORTHY We investigated the antifibrotic activity of three compounds, the activin receptor-like kinase-5 (Alk5) inhibitor SB525334, nintedanib, and sorafenib, in a rat fibrotic precision-cut liver tissue slice model using RNA sequencing analysis. A panel of 12 genes and 4 secreted biomarkers including procollagen I, hyaluronic acid (HA), insulin-like growth factor binding protein 5 (IGFBP5), and WNT1-inducible signaling pathway protein 1 (WISP1) were then established as efficacy end points to validate the antifibrotic activity of the α_V-integrin inhibitor CWHM12. This study demonstrated the value of the rat fibrotic PCLS model for the evaluation of antifibrotic drugs.

Serum liver fibrosis markers discriminate significant liver inflammation in chronic hepatitis B patients with normal or near-normal alanine aminotransferase

Chronic liver inflammation caused by chronic hepatitis B virus (CHB) infection leads to liver cirrhosis and hepatocellular carcinoma. Recently, the role of alanine aminotransferase (ALT) as a predictor of liver inflammation has been questioned. The aim of this study was to investigate the utility of noninvasive fibrosis markers including hyaluronic acid (HA), collagen type IV (CIV), N-terminal propeptide of type III procollagen (PIIINP), and laminin (LN) in identifying significant liver inflammation in patients with CHB, especially in patients with normal or near-normal ALT. A total of 242 CHB patients who underwent liver biopsy were enrolled. The serum levels of ALT, aspartate aminotransferase, HA, CIV, PIIINP, and LN were quantified and the relationship between histological staging and serum markers was systematically analyzed. Serum CIV, PIIINP, HA, and LN levels increased significantly along with the increasing severity of liver inflammation. Multivariate analysis showed that CIV and LN were independently associated with significant inflammation. CIV, PIIINP, HA, and LN levels were found to have high diagnostic values for predicting significant inflammation in patients with CHB (area under the curve, AUC = 0.807, 0.795, 0.767, and 0.703, respectively). The combined index for the identification of significant inflammation, including CIV, PIIINP, HA, and LN levels, significantly improved diagnostic performance (AUC = 0.851). Moreover, the combined index also achieved excellent diagnostic accuracy (AUC = 0.861) in patients with CHB with normal or near-normal ALT. In conclusion, the combined index may be a strong indicator for discriminating significant liver inflammation, especially in patients with CHB with normal or near-normal ALT.

Wisteria floribunda agglutinin-positive human Mac-2 binding protein in decompensated cirrhosis

BACKGROUND AND AIM

An assay for Wisteria floribunda agglutinin-positive human Mac-2 binding protein (WFA⁺ -M2BP) has been reported as a useful non-invasive marker for the evaluation of the staging of fibrosis in several chronic liver diseases. However, available data on the effect of WFA⁺ -M2BP level in decompensated cirrhosis patients were limited. It is important that these investigations can validate the diagnostic utility of WFA⁺ -M2BP in the full range of patients with liver cirrhosis.

METHODS

A multicenter study was conducted at five locations in Japan. A total of 207 patients with liver cirrhosis were enrolled in the present study. To determine whether or not the WFA⁺ -M2BP value was associated with a progression of fibrosis among cirrhosis, this study examined WFA⁺ -M2BP levels between patients with cirrhosis in the decompensated and compensated groups.

RESULTS

The numbers and proportions of compensated and decompensated patients were 113 (54.6%) and 94 (45.4%), respectively. The average WFA⁺ -M2BP levels were 2.22 ± 1.61 in the compensated group and 6.91 ± 5.04 in the decompensated group. Significantly higher WFA⁺ -M2BP levels were observed in the decompensated group than those in the compensated group (P < 0.0001). The respective cut-off index values for decompensated cirrhosis were estimated using receiver-operating characteristic curves for WFA⁺ -M2BP levels. Using a cut-off index value of 3.37 for WFA⁺ -M2BP, predicting decompensated cirrhosis had a sensitivity of 77.8% and a specificity of 86.7%.

CONCLUSIONS

WFA⁺ -M2BP values were higher in patients with decompensated liver cirrhosis.

Clinical significance of decoy receptor 3 upregulation in patients with hepatitis B and liver fibrosis

Decoy receptor 3 (DcR3) is a tumor necrosis factor receptor, which may inhibit apoptosis. The aim of the present study was to investigate the clinical significance of DcR3 upregulation in patients with chronic hepatitis B (CHB) and hepatic fibrosis. A total of 128 patients with a clinical diagnosis of CHB who underwent liver biopsy were included in the present study. The expression levels of DcR3, hyaluronic acid (HA), type III procollagen, type IV collagen (IV-C) and laminin protein were assessed. The diagnostic value of DcR3 in patients with CHB with hepatic fibrosis was determined using receiver operating characteristic (ROC) curve analysis. DcR3 was significantly upregulated in patients with CHB, particularly in patients with active CHB. The expression of DcR3 was significantly increased in patients with CHB with liver fibrosis and liver cirrhosis, compared with patients with CHB without liver fibrosis. The area under the ROC curve for the diagnosis of CHB liver fibrosis based on DcR3 or DcR3 combined with IV-C/HA was 0.807 or 0.869, with a sensitivity and specificity of 76.9 and 77.8% or 84.6 and 81.2%, respectively. DcR3 is a marker for liver fibrosis in patients with hepatitis B infection. The use of DcR3 in combination with IV-C and HA may further increase its diagnostic value for liver fibrosis.

The combination of 5 serum markers compared to FibroScan to predict significant liver fibrosis in patients with chronic hepatitis B virus

BACKGROUND

We evaluated the performance of serum hyaluronan (HA), procollagen type III N-terminal peptide (PIIINP), type IV collagen (IVC), laminin (LN), alanine aminotransferase (ALT), and aspartate aminotransferase (AST), compared to transient elastography (FibroScan) in predicting significant liver fibrosis.

METHODS

We therefore determined 4 serum fibrosis markers, FibroScan and liver biopsy in 70 consecutive adult patients with chronic hepatitis B. According to a modified Scheuer scoring system, significant fibrosis was defined as fibrosis stage ≥S2. We compared serum fibrosis markers to histological staging and FibroScan results using Spearman correlation analysis and area under receiver operating characteristic (ROC) curves (AUROCs).

RESULTS

Of the 212 patients who had the results of FibroScans and four serum fibrosis markers for HBV, 70 had concurrent liver biopsy. Significant liver fibrosis was found in 24/70 patients. The serum levels of HA, PIIINP, IVC, LN, ALT, AST was all positively correlated with fibrosis stage of Liver biopsy. The coefficients with stages were respectively 0.468, 0.392, 0.538, 0.213, 0.350, 0.375. There was a significant difference between mild fibrosis (<S2) and significant fibrosis (≥S2), excluding LN, in the levels of these 5 serum makers (P < .05). AUROC for FibroScans and HA, PIIINP, IVC, LN, ALT, AST to correctly allocate patients to histological fibrosis stage ≥ S2 was 0.866, 0.784, 0.738, 0.827, 0.630, 0.713 and 0.728 respectively. Since LN shows the worst performance of the others. We decided to check the performance of the combination of HA, PIIINP, CIV, ALT, AST, excluding LN, to distinguish fibrosis stages. The index of the histological fibrosis stage ≥ S2, combining the 5 serum markers, significantly improved diagnostic performance (AUROC = 0.861) compared to the use of 5 serum markers alone in all HBV patients.

CONCLUSION

The combination of the 5 serum markers and FibroScan performed equally well in predicting significant fibrosis. The combination of the 5 serum markers is a reliable noninvasive method to predict significant liver fibrosis in patients with CHB. So, it provide another choice rather than FibroScan in predicting significant liver fibrosis.

Non-alcoholic fatty liver disease: an update on diagnosis

Background and aim

The non-alcoholic fatty liver disease (NAFLD) and its sub-entity, the non-alcoholic steatohepatitis (NASH) represent a field of a tremendous progress in recent years. Clinicians need to remain updated with new data on pathogenesis and therapy. The present mini review aims to present some new scientific reports on the diagnosis of NAFLD and NASH for clinical practitioners.

Methods

A systematic literature search of the main international databases was performed. We looked for seminal and innovative papers published in main international languages. A narrative review of the topic was consequently written.

Results

This review describes new data on the diagnosis of NAFLD including NASH. Liver punction biopsy remains the gold standard. However many patients and clinicians prefer to use noninvasive methods. We present the serological tests and the imaging methods used to diagnose inflammation and fibrosis occurring in NAFLD and NASH.

Conclusions

NAFLD-NASH are multifaceted entities that have to be diagnosed and treated by skilled and informed practitioners.

Label-free analysis of physiological hyaluronan size distribution with a solid-state nanopore sensor

Hyaluronan (or hyaluronic acid, HA) is a ubiquitous molecule that plays critical roles in numerous physiological functions in vivo, including tissue hydration, inflammation, and joint lubrication. Both the abundance and size distribution of HA in biological fluids are recognized as robust indicators of various pathologies and disease progressions. However, such analyses remain challenging because conventional methods are not sufficiently sensitive, have limited dynamic range, and/or are only semi-quantitative. Here we demonstrate label-free detection and molecular weight discrimination of HA with a solid-state nanopore sensor. We first employ synthetic HA polymers to validate the measurement approach and then use the platform to determine the size distribution of as little as 10 ng of HA extracted directly from synovial fluid in an equine model of osteoarthritis. Our results establish a quantitative method for assessment of a significant molecular biomarker that bridges a gap in the current state of the art.

Inhibition of Systemic Hyaluronan Synthesis Exacerbates Murine Hepatic Carcinogenesis

BACKGROUND/AIM

Hyaluronan (HA) is used as a biomarker of liver fibrosis, which is a key risk factor for the development of hepatocellular carcinoma (HCC). We examined the effects of prolonged pharmacological inhibition of HA synthesis on liver carcinogenesis.

MATERIALS AND METHODS

Liver tumors were induced in mice by administering 0.03% thioacetamide (TAA) in drinking water over a 12-month period. Animals simultaneously received either a diet containing of an inhibitor of HA synthesis [4-methylumbelliferone (4-MU)], or a control diet.

RESULTS

Addition of 4-MU resulted in a significantly higher number of tumors compared to TAA treatment alone. Moreover, addition of 4-MU resulted in a dose-dependent increase in maximum tumor size.

CONCLUSION

While local HA suppression has been shown to have an inhibitory effect on HCC in vitro and in tumor cell implantation experiments, the present results indicate that systemic inhibition of HA synthesis by 4-MU supplementation facilitates hepatic carcinogenesis in vivo.

Pokeweed antiviral protein attenuates liver fibrosis in mice through regulating Wnt/Jnk mediated glucose metabolism

BACKGROUND/AIMS

Pokeweed antiviral protein (PAP) has been reported to downregulate Wnt/Jnk pathway and attenuate liver fibrosis. This study was designed to intensively explore the mechanism of anti-fibrosis effect of PAP.

MATERIALS AND METHODS

Hepatic stellate cell (HSC) activation was induced by high concentration of glucose. Cell viability was detected at different time points after PAP treatment. Meanwhile, hepatic fibrosis models in mice were induced by CCl4 injection. In the end, liver pathology was observed and contents of alanine transaminase, aspartate transaminase, lactic dehydrogenase, hyaluronic acid (HA), and laminin (LN) in serum together with hydroxyproline (Hyp) in liver were measured. The mRNA and protein expressions of HK2, PFKP, PCK1, and FBP1 as well as Jnk expression in HSC-T6 cells and liver tissue were detected by qPCR and western-blot, respectively.

RESULTS

Compared with high glucose, PAP reduced viability and expressions of HK2, PFKP, α-SMA, and Col1A1, where as enhanced the expressions of PCK1 and FBP1 in HSC-T6 cells (P < 0.05) respectively. PAP attenuated liver pathology, improved liver function, and reduced collagen deposition in liver tissue compared with the model group (P < 0.05) respectively. Moreover, PAP reduced expressions of HK2, PFKP, α-SMA, and Col1A1 where as increased the expression of PCK1 and FBP1 in the liver of mice compared with the model group (P < 0.05) respectively. Most importantly, PAP reduced the phosphorylation of Jnk both in cells and liver tissue compared with the model group (P < 0.05) respectively.

CONCLUSIONS

Our results demonstrated that PAP attenuated liver fibrosis by regulating Wnt/Jnk-mediated glucose metabolism. It provided us a new target for the treatment of liver fibrosis.

Progress in non-invasive detection of liver fibrosis

Liver fibrosis is an important pathological precondition for hepatocellular carcinoma. The degree of hepatic fibrosis is positively correlated with liver cancer. Liver fibrosis is a series of pathological and physiological process related to liver cell necrosis and degeneration after chronic liver injury, which finally leads to extracellular matrix and collagen deposition. The early detection and precise staging of fibrosis and cirrhosis are very important for early diagnosis and timely initiation of appropriate therapeutic regimens. The risk of severe liver fibrosis finally progressing to liver carcinoma is >50%. It is known that biopsy is the gold standard for the diagnosis and staging of liver fibrosis. However, this method has some limitations, such as the potential for pain, sampling variability, and low patient acceptance. Furthermore, the necessity of obtaining a tissue diagnosis of liver fibrosis still remains controversial. An increasing number of reliable non-invasive approaches are now available that are widely applied in clinical practice, mostly in cases of viral hepatitis, resulting in a significantly decreased need for liver biopsy. In fact, the non-invasive detection and evaluation of liver cirrhosis now has good accuracy due to current serum markers, ultrasound imaging, and magnetic resonance imaging quantification techniques. A prominent advantage of the non-invasive detection and assessment of liver fibrosis is that liver fibrosis can be monitored repeatedly and easily in the same patient. Serum biomarkers have the advantages of high applicability (>95%) and good reproducibility. However, their results can be influenced by different patient conditions because none of these markers are liver-specific. The most promising techniques appear to be transient elastography and magnetic resonance elastography because they provide reliable results for the detection of fibrosis in the advanced stages, and future developments promise to increase the reliability and accuracy of the staging of hepatic fibrosis. This article aims to describe the recent progress in the development of non-invasive assessment methods for the staging of liver fibrosis, with a special emphasize on computer-aided quantitative and deep learning methods.

Quantitative proteome analysis of plasma microparticles for the characterization of HCV-induced hepatic cirrhosis and hepatocellular carcinoma

PURPOSE

Hepatocellular carcinoma (HCC) is the most common primary malignant liver tumor and a leading cause of cancer-related deaths worldwide. Cirrhosis induced by hepatitis-C virus (HCV) infection is the most critical risk factor for HCC. However, the mechanism of HCV-induced carcinogenesis is not fully understood. Plasma microparticles (PMP) contribute to numerous physiological and pathological processes and contain proteins whose composition correlates to the respective pathophysiological conditions.

EXPERIMENTAL DESIGN

We analyzed PMP from 22 HCV-induced cirrhosis patients, 16 HCV-positive HCC patients with underlying cirrhosis and 18 healthy controls. PMP were isolated using ultracentrifugation and analyzed via label-free LC-MS/MS.

RESULTS

We identified 840 protein groups and quantified 507 proteins. 159 proteins were found differentially abundant between the three experimental groups. PMP in both disease entities displayed remarkable differences in the proteome composition compared to healthy controls. Conversely, the proteome difference between both diseases was minimal. GO analysis revealed that PMP isolated from both diseases were significantly enriched in proteins involved in complement activation, while endopeptidase activity was downregulated exclusively in HCC patients.

CONCLUSION

This study reports for the first time a quantitative proteome analysis for PMP from patients with HCV-induced cirrhosis and HCC. Data are available via ProteomeXchange with identifier PXD005777.

Association of serum levels of laminin, type IV collagen, procollagen III N-terminal peptide, and hyaluronic acid with the progression of interstitial lung disease

Noninvasive and convenient tests to assess pulmonary fibrosis and disease progression in interstitial lung diseases (ILDs) are currently unavailable. The extracellular matrix molecules, laminin (LN), type IV collagen (IVC), procollagen III N-terminal peptide (PIIINP), and hyaluronic acid (HA) are involved in ILD development and progression. This study aims to investigate the association of disease progression and serum levels of LN, IVC, PIIINP, and HA in patients with ILD. This retrospective study included 323 patients (162 cases of idiopathic pulmonary fibrosis [IPF] and 161 cases of connective tissue diseases ILD [CTD-ILD]) treated in Shanghai Pulmonary Hospital between January 2013 and January 2015 and 160 healthy controls. Serum LN, IVC, PIIINP, and HA were analyzed by radioimmunoassay. Data of the percentage of forced vital capacity in the prediction value (FVC%pred), the percentage of diffusing capacity of the lung for carbon monoxide in the prediction value (DLCO%pred), high resolution computed tomography (HRCT) score, and patient mortality were collected. Serum LN, IVC, PIIINP, and HA were significantly increased in the patients with IPF or CTD-ILD compared with the healthy controls (all P < .05) and were further elevated in the acute exacerbation cases (all P < .05). Serum LN, IVC, PIIINP, and HA positively correlated with HRCT score and negatively correlated with FVC%pred and DLCO%pred significantly in the patients (all P < .05). The survived patients had significantly lower serum LN, IVC, PIIINP, and HA than the dead patients (all P < .05). Serum levels of LN, IVC, PIIINP, and HA may reflect ILD progression and may be indicators for the severity of ILDs.

Serum Wisteria Floribunda Agglutinin-Positive Mac-2 Binding Protein Could Not Always Predict Early Cirrhosis in Non-Viral Liver Diseases

Background: Wisteria floribunda agglutinin-positive human Mac-2-binding protein (WFA(+)-M2BP) is a novel non-invasive marker of liver fibrosis. The goal of the study was to investigate whether the novel serum biomarker WFA(+)-M2BP or other non-invasive markers are useful for the prediction of liver fibrosis in patients with nonalcoholic steatohepatitis (NASH), autoimmune hepatitis (AIH), and primary biliary cholangitis (PBC). Methods: We examined a significant correlation between serum WFA(+)-M2BP levels and histological staging of fibrosis in several chronic liver diseases, such as NASH, AIH, and PBC. Results: WFA(+)-M2BP could not predict hepatic fibrosis in these patients. We also showed that the level of platelet counts is a useful predictor of hepatic fibrosis progression in patients with NASH, AIH, and PBC. There was a significant correlation between staging of fibrosis and grading of activity in the liver in all groups except for AIH patients. Conclusion: Platelet counts can predict hepatic fibrosis in patients with NASH, AIH, or PBC. Clinicians should pay attention to the grading of liver activity in the use of WFA(+)-M2BP.

Gas6 as a putative noninvasive biomarker of hepatic fibrosis

AIM

To evaluate serum growth arrest-specific gene 6 (Gas6) concentration as a biomarker of liver fibrosis progression.

MATERIALS & METHODS

One hundred and thirteen consecutive patients affected by chronic liver disease underwent transient elastography, Gas6 measurement and, if clinically indicated, liver biopsy.

RESULTS

Gas6 concentration was directly correlated to liver stiffness (r = 0.67; p < 0.0001) and was significantly higher in patients with advanced fibrosis (Ishak 4-5; p < 0.001). A plasma concentration <30 ng/ml Gas6 ruled out fibrosis with 84% sensitivity and 56% specificity, while values >42 ng/ml identified severe fibrosis with a sensitivity of 64% and a specificity of 95%; the diagnostic accuracy was comparable to that of transient elastography.

CONCLUSION

Gas6 is a novel biomarker of liver fibrosis, with a potential clinical and pathophysiological relevance.

Endotoxin free hyaluronan and hyaluronan fragments do not stimulate TNF-α, interleukin-12 or upregulate co-stimulatory molecules in dendritic cells or macrophages

The extracellular matrix glycosaminoglycan, hyaluronan, has been described as a regulator of tissue inflammation, with hyaluronan fragments reported to stimulate innate immune cells. High molecular mass hyaluronan is normally present in tissues, but upon inflammation lower molecular mass fragments are generated. It is unclear if these hyaluronan fragments induce an inflammatory response or are a consequence of inflammation. In this study, mouse bone marrow derived macrophages and dendritic cells (DCs) were stimulated with various sizes of hyaluronan from different sources, fragmented hyaluronan, hyaluronidases and heavy chain modified-hyaluronan (HA-HC). Key pro-inflammatory molecules, tumour necrosis factor alpha, interleukin-1 beta, interleukin-12, CCL3, and the co-stimulatory molecules, CD40 and CD86 were measured. Only human umbilical cord hyaluronan, bovine testes and Streptomyces hyaluronlyticus hyaluronidase stimulated macrophages and DCs, however, these reagents were found to be contaminated with endotoxin, which was not fully removed by polymyxin B treatment. In contrast, pharmaceutical grade hyaluronan and hyaluronan fragments failed to stimulate in vitro-derived or ex vivo macrophages and DCs, and did not induce leukocyte recruitment after intratracheal instillation into mouse lungs. Hence, endotoxin-free pharmaceutical grade hyaluronan does not stimulate macrophages and DCs in our inflammatory models. These results emphasize the importance of ensuring hyaluronan preparations are endotoxin free.

New Concepts on Pathogenesis and Diagnosis of Liver Fibrosis; A Review Article

Liver fibrosis is a potentially reversible response to hepatic insults, triggered by different chronic diseases most importantly viral hepatitis, alcoholic, and nonalcoholic fatty liver disease. In the course of the chronic liver disease, hepatic fibrogenesis may develop, which is attributed to various types of cells, molecules, and pathways. Activated hepatic stellate cell (HSC), the primary source of extracellular matrix (ECM), is fundamental in pathophysiology of fibrogenesis, and thus is the most attractable target for reversing liver fibrosis. Although, liver biopsy has long been considered as the gold standard for diagnosis and staging of hepatic fibrosis, assessing progression and regression by biopsy is hampered by its limitations. We provide recent views on noninvasive approaches including serum biomarkers and radiologic techniques.

Cardiovascular Risk and Serum Hyaluronic Acid: A Preliminary Study in a Healthy Population of Low/Intermediate Risk

BACKGROUND

Hyaluronic acid (HA) has been found to be an important trigger of atherosclerosis. In this study, we investigate the possible association of serum HA with cardiovascular disease risk in a population of low/intermediate risk for cardiovascular events.

METHODS

We enrolled 200 subjects with low/intermediate risk for developing cardiovascular disease. High specific C-reactive protein (hsCRP) was used as an indicator of preclinical atherosclerosis. The Framingham score was used to calculate the cardiovascular risk.

RESULTS

Participants with dyslipidemia had significantly higher levels of serum HA than those without dyslipidemia (t-test, P = 0.05), higher levels of hsCRP (Kruskal-Wallis test, P = 0.04), and higher cardiovascular risk according to the Framingham score (Kruskal-Wallis test, P = 0.05). Serum HA concentration correlated significantly with the Framingham score for risk for coronary heart disease over the next 10 years (Spearman r = 0.152, P = 0.02). Diabetic volunteers had significantly higher HA than those without diabetes (t-test, P = 0.02). Participants with metabolic syndrome had higher serum HA levels and higher hsCRP (Kruskal-Wallis test, P = 0.01) compared to volunteers without metabolic syndrome (t-test, P = 0.03).

CONCLUSIONS

Serum HA should be explored as an early marker of atheromatosis and cardiovascular risk.

Hyaluronan as a therapeutic target in human diseases

Accumulation and turnover of extracellular matrix is a hallmark of tissue injury, repair and remodeling in human diseases. Hyaluronan is a major component of the extracellular matrix and plays an important role in regulating tissue injury and repair, and controlling disease outcomes. The function of hyaluronan depends on its size, location, and interactions with binding partners. While fragmented hyaluronan stimulates the expression of an array of genes by a variety of cell types regulating inflammatory responses and tissue repair, cell surface hyaluronan provides protection against tissue damage from the environment and promotes regeneration and repair. The interactions of hyaluronan and its binding proteins participate in the pathogenesis of many human diseases. Thus, targeting hyaluronan and its interactions with cells and proteins may provide new approaches to developing therapeutics for inflammatory and fibrosing diseases. This review focuses on the role of hyaluronan in biological and pathological processes, and as a potential therapeutic target in human diseases.