Anomalous Behavior of Hyaluronan Crosslinking Due to the Presence of Excess Phospholipids in the Articular Cartilage System of Osteoarthritis

Atomic-Resolution Experimental Structural Biology and Molecular Dynamics Simulations of Hyaluronan and Its Complexes

This review summarizes the atomic-resolution structural biology of hyaluronan and its complexes available in the Protein Data Bank, as well as published studies of atomic-resolution explicit-solvent molecular dynamics simulations on these and other hyaluronan and hyaluronan-containing systems. Advances in accurate molecular mechanics force fields, simulation methods and software, and computer hardware have supported a recent flourish in such simulations, such that the simulation publications now outnumber the structural biology publications by an order of magnitude. In addition to supplementing the experimental structural biology with computed dynamic and thermodynamic information, the molecular dynamics studies provide a wealth of atomic-resolution information on hyaluronan-containing systems for which there is no atomic-resolution structural biology either available or possible. Examples of these summarized in this review include hyaluronan pairing with other hyaluronan molecules and glycosaminoglycans, with ions, with proteins and peptides, with lipids, and with drugs and drug-like molecules. Despite limitations imposed by present-day computing resources on system size and simulation timescale, atomic-resolution explicit-solvent molecular dynamics simulations have been able to contribute significant insight into hyaluronan's flexibility and capacity for intra- and intermolecular non-covalent interactions.

Hyaluronic acid-entecavir conjugates-core/lipid-shell nanohybrids for efficient macrophage uptake and hepatotropic prospects

Drug covalently bound to polymers had formed, lately, platforms with great promise in drug delivery. These drug polymer conjugates (DPC) boosted drug loading and controlled medicine release with targeting ability. Herein, the ability of entecavir (E) conjugated to hyaluronic acid (HA) forming the core of vitamin E coated lipid nanohybrids (EE-HA LPH), to target Kupffer cells and hepatocyte had been proved. The drug was associated to HA with efficiency of 93.48 ± 3.14 % and nanohybrids loading of 22.02 ± 2.3 %. DiI labelled lipidic nanohybrids improved the macrophage uptake in J774 cells with a 21 day hepatocytes retention post intramuscular injection. Finally, in vivo biocompatibility and safety with respect to body weight, organs indices and histopathological alterations were demonstrated. Coating with vitamin E and conjugation of E to HA (a CD44 ligand), could give grounds for prospective application for vectored nano-platform in hepatitis B.

Effect of Loading on the Adhesion and Frictional Characteristics of Top Layer Articular Cartilage Nanoscale Contact: A Molecular Dynamics Study

Articular cartilage is a water-lubricated naturally occurring biological interface imparting unique mechanical and ultralow frictional properties in bone joints. Although the material of cartilage, synovial fluid composition, and their lubricating modes and properties have been extensively investigated at various scales experimentally, there is still a lack of understanding of load bearing, adhesion, and friction mechanisms of the cartilage-cartilage interface from an atomistic perspective under heavy loads. In this study, the effect of loading on adhesion and frictional behavior in articular cartilage is investigated with a proposed atomistic model for top layer cartilage-cartilage contact in unhydrated conditions using molecular dynamics (MD) simulations. Pull-off tests reveal that cohesive interactions occur at the interface due to formation of heavily interpenetrated atomistic sites leading to stretching and localized pulling of fragments during sliding. Sliding tests show that friction is load- and direction-dependent with the coefficient of friction (COF) obtained in the range of 0.20-0.75 at the interface for sliding in parallel and perpendicular directions to the collagen axis. These values are in good agreement with earlier nanoscale experimental results reported for the top layer cartilage-cartilage interface. The COF reduces with an increase in load and tends to be higher for the parallel sliding case than for the perpendicular case owing to the presence of the constant number of H-bonds. Overall, this work contributes toward understanding sliding in unhydrated biointerfaces, which is the precursor of wear, and provides insights into implant research.

Hydrogen and Water Bonding between Glycosaminoglycans and Phospholipids in the Synovial Fluid: Molecular Dynamics Study

Synovial fluid is a lubricant of the synovial joint that shows remarkable tribological properties. These properties originate in the synergy between its components, with two of its major components, glycosaminoglycans (GAGs) and phospholipids (PLs), playing a major role in boundary and mixed lubrication regimes. All-atom molecular dynamic simulations were performed to investigate the way these components bond. Hyaluronic acid (HA) and chondroitin sulphate (CS) bonding with three types of lipids was tested. The results show that both glycosaminoglycans bind lipids at a similar rate, except for 1,2-d-ipalmitoyl-sn-glycero-3-phosphoethanolamine lipids, which bind to chondroitin at a much higher rate than to hyaluronan. The results suggest that different synovial fluid lipids may play a different role when binding to both hyaluronan and chondroitin sulphate. The presented results may help in understanding a process of lubrication of articular cartilage at a nanoscale level.

On the interaction of hyaluronic acid with synovial fluid lipid membranes

All-atom molecular dynamics simulations have been used to investigate the adsorption of low molecular weight hyaluronic acid to lipid membranes. We have determined the interactions that govern the adsorption of three different molecular weight hyaluronic acid molecules (0.4, 3.8 & 15.2 kDa) to lipid bilayers that are representative of the surface-active phospholipid bilayers found in synovial joints. We have found that both direct hydrogen bonds and water-mediated interactions with the lipid headgroups play a key role in the binding of hyaluronic acid to the lipid bilayer. The water-mediated interactions become increasingly important in stabilising the adsorbed hyaluronic acid molecules as the molecular weight of hyaluronic acid increases. We also observe a redistribution of ions around bound hyaluronic acid molecules and the associated lipid headgroups, and that the degree of redistribution increases with the molecular weight of hyaluronic acid. By comparing this behaviour to that observed in simulations of the charge-neutral polysaccharide dextran (MW ∼ 15 kDa), we show that this charge redistribution leads to an increased alignment of the lipid headgroups with the membrane normal, and therefore to more direct and water-mediated interactions between hyaluronic acid and the lipid membrane. These findings provide a detailed understanding of the general structure of hyaluronic acid-lipid complexes that have recently been presented experimentally, as well as a potential mechanism for their enhanced tribological properties.

Physical crosslinking of hyaluronic acid in the presence of phospholipids in an aqueous nano-environment

Hyaluronic acid and phospholipids are two components in the synovial joint cavity that contribute to joint lubrication synergistically. Molecular dynamics simulations were performed and hydrogen bonds in hyaluronic acid were analyzed to identify specific sites that are responsible for its physical cross-linking. Two molecular masses of hyaluronic acid, 10 kDa and 160 kDa, were considered. We use molecular dynamics simulations and the small world network approach to investigate dynamic couplings using a distance map applied to oxygen atoms in a chain of hyaluronic acid in the presence of phospholipids and water. The distance characterizing the coupling can be defined in various ways to bring out the most evident differences between various scenarios of the polymer chain conformation We show herein a physical distance understood as H-bond length and classes of these distances which are defined in a coarse-grained picture of the molecule. Simulation results indicate that addition of phospholipids has little influence on hyaluronic acid crosslinking. However, longer chains and addition of lipids promote appreciably long lasting (resilient) networks that may be of importance in biological systems. Specific sites for hydrogen bonding of phospholipids to hyaluronic acid have also been identified.

Capstan-like mechanism in hyaluronan-phospholipid systems

Functionality of articular cartilage results from complex interactions between its molecular components. Among many biomolecules, two are of prime importance for lubrication: hyaluronic acid (HA) and phospholipids (PL). The purpose of this study is to discuss a mechanism of interaction between these two components and how their synergies contribute to nanobiolubrication of articular cartilage. Preliminary molecular dynamics simulations have been performed to investigate these interactions by adopting a capstan-like mechanism of action. By applying a constant pulling force to both ends of a HA molecule, wrapped around a PL micelle, we viewed the rotation of the PL micelle. The simulations were performed upon two physicochemical constraints: force- and solvent-dependency. The results show the efficiency of rotation from intermolecular bond creation and annihilation. We found a direct relation between the available surface of the micelle and the magnitude of the force, which varies significantly through the unwinding. The movement of the attached molecules is characterized by a slide-to-roll relation, which is affected by the viscosity of the surrounding medium. As a consequence, two solvents were studied for specific force conditions and the molecular dynamics simulation exhibited double the slide-to-roll coefficient for the viscous solvent as compared to its low-viscosity limit.

Hyaluronan-Chondroitin Sulfate Anomalous Crosslinking Due to Temperature Changes

Glycosaminoglycans are a wide class of biopolymers showing great lubricating properties due to their structure and high affinity to water. Two of them, hyaluronic acid and chondroitin sulfate, play an important role in articular cartilage lubrication. In this work, we present results of the all-atom molecular dynamics simulations of both molecules placed in water-based solution. To mimic changes of the physiological conditions, especially temperature, of the synovial fluid in joints under successive load (e.g., walking, jogging, jumping), simulations have been performed at different physiological temperatures in the range of 300 to 320 Kelvin (normal intra-articular temperature is 305 K). The stability of the biopolymeric network at equilibrium (isothermal and isobaric) conditions has been studied. To understand the process of physical crosslinking, the dynamics of intra- and intermolecular hydrogen bonds forming and breaking have been studied. The results show that following addition of chondroitin sulfate, hyaluronan creates more intermolecular hydrogen bonds than when in homogeneous solution. The presence of chondroitin in a hyaluronan network is beneficial as it may increase its stability. Presented data show hyaluronic acid and chondroitin sulfate as viscosity modifiers related to their crosslinking properties in different physicochemical conditions.

The Anomalies of Hyaluronan Structures in Presence of Surface Active Phospholipids-Molecular Mass Dependence

Interactions between hyaluronan (A-) and phospholipids play a key role in many systems in the human body. One example is the articular cartilage system, where the synergistic effect of such interactions supports nanoscale lubrication. A molecular dynamics simulation has been performed to understand the process of formation of hydrogen bonds inside the hyaluronan network, both in the presence and absence of phospholipids. Additionally, the effect of the molecular mass of (A-) was analyzed. The main finding of this work is a robust demonstration of the optimal parameters (H-bond energy, molecular mass) influencing the facilitated lubrication mechanism of the articular cartilage system. Simulation results show that the presence of phospholipids has the greatest influence on hyaluronan at low molecular mass. We also show the specific sites of H-bonding between chains. Simulation results can help to understand how hyaluronan and phospholipids interact at several levels of articular cartilage system functioning.