Experimental approaches to hyaluronan structure

Thiol-ene clickable hyaluronans: from macro-to nanogels

The fabrication of hyaluronic acid (HA) nanogels using a thiol-ene reaction has been demonstrated. HA was modified with pentenoate groups and then cross-linked with poly(ethylene glycol)-bis(thiol) by exposure to UV light. The cross-linking density and thereby the rigidity of the obtained gels were precisely controlled by the degree of substitution of pentenoate-modified HA. Their swelling properties also depended on cross-linking density. To produce hydrogels at the nanoscale, hyaluronic acid precursors were solely confined inside liposomes before cross-linking and purified after cross-linking. The size of the resulting nanogels followed their swelling properties and was also affected by their cross-linking density. Such bionanogels with tunable mechanical and swelling properties have potential in drug delivery.

Hyaluronic Acid: from biochemical characteristics to its clinical translation in assessment of liver fibrosis

CONTEXT

Hyaluronic acid (HA) is a high molecular weight polysaccharide that is distributed in all bodily tissues and fluids. The liver is the most important organ involved in the synthesis and degradation of HA. Research has shown that liver cell injury can affect serum HA levels. In this review, authors aimed to describe the biochemical and physiological roles of this glycosaminoglycan and its changes in various liver diseases.

EVIDENCE ACQUISITION

Liver fibrosis and in more severe form, cirrhosis are results of an imbalance between fibrogenesis and fibrinolysis. Liver biopsy is the gold standard to assess liver necro inflammatory injuries. This method is invasive and has some major side effects; therefore it is an unfavorable method for both physicians and patients. Now, a wide variety of noninvasive methods have been introduced based on evaluating serum level of different markers. They are safe, readily available, and more favorable. Serum HA levels are used by some researchers to assess stages of liver fibrosis.

RESULTS

There are several scientific studies indicating HA as a biomarker for high score fibrosis and cirrhosis in various liver diseases alone or in algorithm models. It seems from various algorithm models that the use of HA as a major constituent has more diagnostic reliability and accuracy than the use of HA alone.

CONCLUSIONS

Use of HA in an algorithm model, is an extra and valuable tool for assessing liver necro inflammatory injuries- in parallel with liver biopsy- but more comprehensive studies are needed to approve the use of HA as an appropriate clinical tool.

Hyaluronan and synovial joint: function, distribution and healing

Synovial fluid is a viscous solution found in the cavities of synovial joints. The principal role of synovial fluid is to reduce friction between the articular cartilages of synovial joints during movement. The presence of high molar mass hyaluronan (HA) in this fluid gives it the required viscosity for its function as lubricant solution. Inflammation oxidation stress enhances normal degradation of hyaluronan causing several diseases related to joints. This review describes hyaluronan properties and distribution, applications and its function in synovial joints, with short review for using thiol compounds as antioxidants preventing HA degradations under inflammation conditions.

Transient exposure of pulmonary surfactant to hyaluronan promotes structural and compositional transformations into a highly active state

Pulmonary surfactant is a lipid-protein complex that lowers surface tension at the respiratory air-liquid interface, stabilizing the lungs against physical forces tending to collapse alveoli. Dysfunction of surfactant is associated with respiratory pathologies such as acute respiratory distress syndrome or meconium aspiration syndrome where naturally occurring surfactant-inhibitory agents such as serum, meconium, or cholesterol reach the lung. We analyzed the effect of hyaluronan (HA) on the structure and surface behavior of pulmonary surfactant to understand the mechanism for HA-promoted surfactant protection in the presence of inhibitory agents. In particular, we found that HA affects structural properties such as the aggregation state of surfactant membranes and the size, distribution, and order/packing of phase-segregated lipid domains. These effects do not require a direct interaction between surfactant complexes and HA and are accompanied by a compositional reorganization of large surfactant complexes that become enriched with saturated phospholipid species. HA-exposed surfactant reaches very high efficiency in terms of rapid and spontaneous adsorption of surfactant phospholipids at the air-liquid interface and shows significantly improved resistance to inactivation by serum or cholesterol. We propose that physical effects pertaining to the formation of a meshwork of interpenetrating HA polymer chains are responsible for the changes in surfactant structure and composition that enhance surfactant function and, thus, resistance to inactivation. The higher resistance of HA-exposed surfactant to inactivation persists even after removal of the polymer, suggesting that transient exposure of surfactant to polymers like HA could be a promising strategy for the production of more efficient therapeutic surfactant preparations.

Molecular mass dependence of hyaluronan detection by sandwich ELISA-like assay and membrane blotting using biotinylated hyaluronan binding protein

Hyaluronan (HA) is widely detected in biological samples and its concentration is most commonly determined by the use of a labeled specific HA binding protein (aggrecan G1-IGD-G2, HABP), employing membrane blotting and sandwich enzyme-linked immunosorbent assay (ELISA)-like methods. However, the detected signal intensity or the quantified value obtained by using these surface-based methods is related to the molecular mass (M) of HA, especially for HA in the low M range below ~150 kDa. At the same mass or mass concentration, higher M HA gives a higher signal than lower M HA. We have experimentally determined the quantitative relationship between the M of HA (in the range 20-150 kDa) and the relative signal intensity in comparison with a standard HA, in a sandwich ELISA-like assay. An M-dependent signal correction factor (SCF) was calculated and used to correct the signal intensity, so that the corrected concentration value would more accurately reflect the true HA concentration in solution. The SCF for polydisperse low M HA was also calculated and compared with experimental results. When the molecular mass distribution of an HA sample is determined by a method such as gel electrophoresis, then its appropriately averaged SCF can be calculated and used to correct the signal in sandwich ELISA to obtain a more accurate concentration estimation. The correction method works for HA with M between ~150 and 20 kDa, but lower M HA is too poorly detected for useful analysis. The physical basis of the M-dependent detection is proposed to be the increase in detector-accessible fraction of each surface-bound molecule as M increases.

Applications and emerging trends of hyaluronic acid in tissue engineering, as a dermal filler and in osteoarthritis treatment

Hyaluronic acid (HA) is a naturally occurring biodegradable polymer with a variety of applications in medicine, including scaffolding for tissue engineering, dermatological fillers and viscosupplementation for osteoarthritis treatment. HA is available in most connective tissues in body fluids such as synovial fluid and the vitreous humor of the eye. HA is responsible for several structural properties of tissues as a component of extracellular matrix and is involved in cellular signaling. Degradation of HA is a stepwise process that can occur via enzymatic or non-enzymatic reactions. A reduction in HA mass or molecular weight via degradation or slowing of synthesis affects physical and chemical properties such as tissue volume, viscosity and elasticity. This review addresses the distribution, turnover and tissue-specific properties of HA. This information is used as the context for considering recent products and strategies for modifying the viscoelastic properties of HA in tissue engineering, as a dermal filler and in osteoarthritis treatment.

A decrease in moisture absorption-retention capacity of N-deacetylation of hyaluronic acid

The linear non-sulfated glycosaminoglycan, hyaluronic acid (HA), is widely distributed throughout connective, epithelial and neural tissues etc., and is of great importance in tissue hydration, lubrication and cellular function. Along with the age growth, HA will lose its acetyl groups under action of HA N-deacetylase in vivo. However, the biological consequence of this physiological process remains largely unknown. Herein two highly N-deacetylated HAs, dHA-6 and dHA-10 were generated via the NH2NH2-HIO3 procedure. Their molecular weights were estimated to be 24 and 16 kDa by high performance gel-permeation chromatography (HPGPC), and the N-deacetylation degrees were 79.4 % and 93 % respectively, as determined by (1)H nuclear magnetic resonance (NMR). The study on moisture-absorption (Ra) and -retention (Rh) abilities demonstrated that the Ra values of dHAs under conditions of 81 % or 43 % relative humidity, as well as the Rh values of dHAs under dry condition or 43 % relative humidity, were significantly smaller than that of their respective re-N-acetylated products. The decline of moisture-absorption and -retention capacity after HA N-deacetylation were consistent with the appearance of unsolvated amides remained in the N-deacetylated products, as indicated by circular dichroism (CD) spectroscopy. Our findings implied that HA N-deacetylation, in addition to the decrease of HA contents in the elderly persons, might account for manifestations of naturally aged skin, such as laxity, sagging, and wrinkling.

Detailed characterization of hyaluronan using aqueous size exclusion chromatography with triple detection and multiangle light scattering detection

Hyaluronan (HA) has attracted great interest and attention from ophthalmic surgical and eye care companies owing to its unique properties. A more complete understanding of HA biopolymers has, therefore, become increasingly critical as thorough characterization of raw materials helps promote product quality and process control. Often, such detailed information requires the use of a combination of analytical techniques. In this study, we compared size exclusion chromatography (SEC) with online multiangle light scattering (SEC-MALS) and SEC with triple detection (SEC-TD) experiments for HA analysis. Three lots of commercially available eye drop grade HA were characterized by SEC-MALS and SEC-TD. The absolute molecular weight averages, molecular weight distribution, radius of gyration, and solution conformation of the three HA lots were determined and compared by the two techniques. In addition, the intrinsic viscosity and intrinsic viscosity distribution were measured by SEC-TD.

The effect of molecular weight on hyaluronan's cartilage boundary lubricating ability--alone and in combination with proteoglycan 4

OBJECTIVES

(1) assess the molecular weight dependence of hyaluronan's (HA) cartilage boundary lubricating ability, alone and in combination with proteoglycan 4 (PRG4), at physiological concentrations; (2) determine if HA and PRG4 interact in solution via electrophoretic mobility shift assay (EMSA).

METHODS

The cartilage boundary lubricating ability of a broad range of MW HA (20 kDa, 132 kDa, 780 kDa, 1.5 MDa, and 5 MDa) at 3.33 mg/ml, both alone and in combination with PRG4 at 450 μg/ml, was assessed using a previously described cartilage-on-cartilage friction test. Static, μ(static, Neq), and kinetic, <μ(kinetic, Neq)>, were calculated. An EMSA was conducted with PRG4 and monodisperse 150 kDa and 1,000 kDa HA.

RESULTS

Friction coefficients were reduced by HA, in a MW-dependent manner. Values of <μ(kinetic, Neq)> in 20 kDa HA, 0.098 (0.089, 0.108), were significantly greater compared to both 780 kDa, 0.080 (0.072, 0.088), and 5 MDa, 0.079 (0.070, 0.089). Linear regression showed a significant correlation between both μ(static, Neq) and <μ(kinetic, Neq)>, and log HA MW. Friction coefficients were also reduced by PRG4, and with subsequent addition of HA; however the synergistic effect was not dependent on HA MW. Values of <μ(kinetic, Neq)> in PRG4, 0.080 (0.047, 0.113), were significantly greater than values of PRG4+various MW HA (similar in value, averaging 0.040 (0.033, 0.047)). EMSA indicated that migration of 150 kDa and 1,000 kDa HA was retarded when combined with PRG4 at high PRG4:HA ratios.

CONCLUSIONS

These results suggest alterations in HA MW could significantly affect synovial fluid's cartilage boundary lubricating ability, yet this diminishment in function could be circumvented by physiological levels of PRG4 forming a complex, potentially in solution, with HA.

Polypeptide grafted hyaluronan: A self-assembling comb-branched polymer constructed from biological components

Rheological evidence is provided demonstrating that covalent grafting of monodisperse isotactic poly(L-leucine) branches onto linear hyaluronan (HA) polysaccharide chains yields comb-branched HA chains that self-assemble into long-lived physical networks in aqueous solutions driven by hydrophobic interactions between poly(L-leucine) chains. This is in stark contrast to native (unmodified) HA solutions which exhibit no tendency to form long-lived physical networks.

Solid-state NMR spectroscopy provides atomic-level insights into the dehydration of cartilage

An atomic-level insight into the functioning of articular cartilage would be useful to develop prevention strategies and therapies for joint diseases such as osteoarthritis. However, the composition and structure of cartilage and their relationship to its unique mechanical properties are quite complex and pose tremendous challenges to most biophysical techniques. In this study, we present an investigation of the structure and dynamics of polymeric molecules of articular cartilage using time-resolved solid-state NMR spectroscopy during dehydration. Full-thickness cartilage explants were used in magic-angle spinning experiments to monitor the structural changes of rigid and mobile carbons. Our results reveal that the dehydration reduced the mobility of collagen amino acid residues and carbon sugar ring structures in glycosaminoglycans but had no effect on the trans-Xaa-Pro conformation. Equally interestingly, our results demonstrate that the dehydration effects are reversible, and the molecular structure and mobility are restored upon rehydration.

Size determination of hyaluronan using a gas-phase electrophoretic mobility molecular analysis

Hyaluronan (HA) is a linear non-sulfated polysaccharide mainly found in the extracellular matrix. The size of HA can vary from a few disaccharides up to at least 25,000 units, reaching molecular weights of 10 10(3) kDa. HA has many biological functions, and both its size and tissue concentration play an important role in many physiological and pathological processes. It is relatively easy to determine the HA concentration using enzyme-linked binding protein assays, but the molecular weight of HA has so far been shown to be a more challenging task to measure. Here, we present a method for size determination of HA using gas-phase electrophoretic mobility molecular analysis (GEMMA), which utilizes the electrophoretic mobility of molecules in air to estimate the molecular weight of the analyte. We show that this method gives reliable molecular weight estimations of HA in the range of 30-2400 kDa, which covers almost its whole biological range. The average measuring time for one GEMMA spectrum is between 5 and 10 min using only 6 pg of HA. In addition, the peak area in a GEMMA spectrum can be used to estimate the HA concentration in the sample. The high sensitivity and small sample volumes make GEMMA an excellent tool for both size determinations and estimation of concentration of samples with low HA concentration, as is the case for HA extracted from small tissue samples.

Single-molecule imaging of hyaluronan in human synovial fluid

Human synovial fluid contains a high concentration of hyaluronan, a high molecular weight glycosaminoglycan that provides viscoelasticity and contributes to joint lubrication. In osteoarthritis synovial fluid, the concentration and molecular weight of hyaluronan decrease, thus impairing shock absorption and lubrication. Consistently, substitution of hyaluronan (viscosupplementation) is a widely used treatment for osteoarthritis. So far, the organization and dynamics of hyaluronan in native human synovial fluid and its action mechanism in viscosupplementation are poorly characterized at the molecular level. Here, we introduce highly sensitive single molecule microscopy to analyze the conformation and interactions of fluorescently labeled hyaluronan molecules in native human synovial fluid. Our findings are consistent with a random coil conformation of hyaluronan in human synovial fluid, and point to specific interactions of hyaluronan molecules with the synovial fluid matrix. Furthermore, single molecule microscopy is capable of detecting the breakdown of the synovial fluid matrix in osteoarthritis. Thus, single molecule microscopy is a useful new method to probe the structure of human synovial fluid and its changes in disease states like osteoarthritis.

Biocompatible blood pool MRI contrast agents based on hyaluronan

Biocompatible gadolinium blood pool contrast agents based on a biopolymer, hyaluronan, were investigated for magnetic resonance angiography application. Hyaluronan, a non-sulfated linear glucosaminoglycan composed of 2000-25,000 repeating disaccharide subunits of D-glucuronic acid and N-acetylglucosamine with molecular weight up to 20 MDa, is a major component of the extracellular matrix. Two gadolinium contrast agents based on 16 and 74 kDa hyaluronan were synthesized, both with R(1) relaxivity around 5 mM(-1)  s(-1) per gadolinium at 9.4 T at 25°C. These two hyaluronan based agents show significant enhancement of the vasculature for an extended period of time. Initial excretion was primarily through the renal system. Later uptake was observed in the stomach and lower gastrointestinal tract. Macromolecular hyaluronan-based gadolinium agents have a high clinical translation potential as hyaluronan is already approved by FDA for a variety of medical applications.

A mechanism to explain physiological lubrication

A new mechanism of physiological lubrication is proposed to explain how low-viscosity synovial fluid prevents articular surfaces from contacting and wearing. The new mechanism is based on the hypothesis that the hyaluronic acid chains in synovial fluid bind to the cartilage surfaces through electrostatic charges, with the phospholipid layer on an articular surface supplying the necessary attractive charges. The stationary hyaluronic acid network causes a large hydrodynamic resistance to outward flow from the gap. To determine the effectiveness of the network in preventing contact, squeeze-film flow between two incompressible, permeable disks is analyzed when a constant load is suddenly applied, and the solvent--synovial fluid minus the hyaluronic acid--escapes through the network and through the permeable disks. The analysis yields the approximate time for the gap distance to decrease to asperity size. For realistic physiological parameters, the time for the surfaces to contact is a minimum of several minutes and likely much longer. The role of albumin in the synovial fluid is included because the large protein molecules are trapped by the small openings in the hyaluronic acid network, which increases the flow resistance of the network and thereby delays contact of the surfaces.

Polypeptide grafted hyaluronan: synthesis and characterization

Poly(l-leucine) grafted hyaluronan (HA-g-PLeu) has been synthesized via a Michael addition reaction between primary amine terminated poly(l-leucine) and acrylate-functionalized HA (TBAHA-acrylate). The precursor hyaluronan was first functionalized with acrylate groups by reaction with acryloyl chloride in the presence of triethylamine in N,N-dimethylformamide. (1)H NMR analysis of the resulting product indicated that an increase in the concentration of acryloylchoride with respect to hydroxyl groups on HA has only a moderate effect on functionalization efficiency, f. A precise control of stoichiometry was not achieved, which could be attributed to partial solubility of intermolecular aggregates and the hygroscopic nature of HA. Michael addition at high [PLeu-NH(2)]/[acrylate](TBAHA) ratios gave a molar grafting ratio of only 0.20 with respect to the repeat unit of HA, indicating grafting limitation due to insolubility of the grafted HA-g-PLeu. Soluble HA-g-PLeu graft copolymers were obtained for low grafting ratios (<0.039) with <8.6% by mass of PLeu and were characterized thoroughly using light scattering, (1)H NMR, FT-IR, and AFM techniques. Light scattering experiments showed a strong hydrophobic interaction between PLeu chains, resulting in aggregates with segregated nongrafted HA segments. This yields local networks of aggregates, as demonstrated by atomic force microscopy. Circular dichroism spectroscopy showed a β-sheet conformation for aggregates of poly(l-leucine).

Dynamics of hyaluronan aqueous solutions as assessed by fast field cycling NMR relaxometry

Fast field cycling (FFC) NMR relaxometry has been used to study the conformational properties of aqueous solutions of hyaluronan (HYA) at three concentrations in the range 10 to 25 mg mL(-1). Results revealed that, irrespective of the solution concentration, three different hydration layers surround hyaluronan. The inner layer consists of water molecules strongly retained in the proximity of the HYA surface. Because of their strong interactions with HYA, water molecules in this inner hydration layer are subject to very slow dynamics and have the largest correlation times. The other two hydration layers are made of water molecules which are located progressively further from the HYA surface. As a result, decreasing correlation times caused by faster molecular motion were measured. The NMRD profiles obtained by FFC-NMR relaxometry also showed peaks attributable to (1)H-(14)N quadrupole interactions. Changes in intensity and position of the quadrupolar peaks in the NMRD profiles suggested that with increasing concentration the amido group is progressively involved in the formation of weak and transient intramolecular water bridging adjacent hyaluronan chains. In this work, FFC-NMR was used for the first time to obtain deeper insight into HYA-water interactions and proved itself a powerful and promising tool in hyaluronan chemistry.

Ions in hyaluronic acid solutions

Hyaluronic acid (HA) is an anionic biopolymer that is almost ubiquitous in biological tissues. An attempt is made to determine the dominant features that account for both its abundance and its multifunctional role, and which set it apart from other types of biopolymers. A combination of osmotic and scattering techniques is employed to quantify its dynamic and static properties in near-physiological solution conditions, where it is exposed both to mono- and divalent counterions. An equation of state is derived for the osmotic pressure Pi in the semidilute concentration region, in terms of two variables, the polymer concentration c and the ionic strength J of the added salt, according to which Pi=1.4x10(3)c(9/4)/J(3/4) kPa, where c and J are expressed in mole. Over the physiological ion concentration range, the effect of the sodium chloride and calcium chloride on the osmotic properties of HA solutions is fully accounted for by their contributions to the ionic strength. The absence of precipitation, even at high CaCl(2) concentrations, distinguishes this molecule from other biopolymers such as DNA. Dynamic light scattering measurements reveal that the collective diffusion coefficient in HA solutions exceeds that in aqueous solutions of typical neutral polymers by a factor of approximately 5. This property ensures rapid adjustment to, and recovery from, stress applied to HA-containing tissue. Small angle x-ray scattering measurements confirm the absence of appreciable structural reorganization over the observed length scale range 10-1000 A, as a result of calcium-sodium ion exchange. The scattered intensity in the transfer momentum range q>0.03 A(-1) varies as 1/q, indicating that the HA chain segments in semidilute solutions are linear over an extended concentration range. The osmotic compression modulus c partial differential Pi/partial differential c, a high value of which is a prerequisite in structural biopolymers, is several times greater than in typical neutral polymer solutions.

Structural behavior of highly concentrated hyaluronan

When investigated under high concentration conditions, hyaluronan (HA) solutions in physiological saline are shown to generate stable superstructures. An abrupt change in the rheological properties observed on increasing the temperature suggests the breaking of certain cooperative bonds. The thermal disruption of the HA superstructure is accompanied by a sharp transition from a long- to a restricted-connectivity water structuring, which is interpreted as a concurrent transition from a stable to a temporary polymer network. The intermolecular associations are considered to be originated by hydrophobic interactions between the nonpolar groups of the polymer backbones.

Ultrastructure of ulvan: a polysaccharide from green seaweeds

Ultrastructural analysis of the gel forming green seaweed sulfated polysaccharide ulvan revealed a spherical-based morphology (10-18 nm diameter) more or less aggregated in aqueous solution. At pH 13 in TBAOH (tetrabutyl ammonium hydroxyde) or NaOH, ulvan formed an open gel-like structure or a continuous film by fusion or coalescence of bead-like structures, while in acidic pH conditions, ulvan appeared as dispersed beads. Low concentrations of sodium chloride, copper or boric acid induced the formation of aggregates. These results highlight the hydrophobic and aggregative behavior of ulvan that are discussed in regard to the peculiar gel formation and the low intrinsic viscosity of the polysaccharide in aqueous solution. (c) 2009 Wiley Periodicals, Inc. Biopolymers 91: 652-664, 2009.This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com.