Permeability of hyaluronic acid solutions. The effects of matrix concentration, calcium, and pH

Molecular weight-dependent hyaluronic acid permeability and tight junction modulation in human buccal TR146 cell monolayers

The oral route is considered an attractive method for drug delivery, as it avoids the hepatic and intestinal first-pass metabolism processes. Hyaluronic acid (HA) beneficial effects to the human body include anti-aging and wound healing but its effects on oral barrier integrity and mechanical function have not yet been investigated. In this study, we analyzed oral barrier integrity and the paracellular pathway of HA transportation in TR146 cell monolayers during and after permeation and using low molecular weight HA (LMW-HA, <100 kDa) and high molecular weight HA (HMW-HA, >500 kDa). Cytotoxicity assays in TR146 cells revealed that neither LMW-HA or HMW-HA altered cell viability at concentrations <0.5 % during 24 h of treatment. HA-treated TR146 cell monolayers showed enhanced oral barrier integrity and reduced apparent permeability of fluorescein. Moreover, HA significantly increased tight junction (TJ)-related genes expression, including ZO-2, marvelD3, cingulin, claudin-1, claudin-3, and claudin-4 expression. Overall, the results of the present study indicate that HA can permeate across the oral barrier and enhance oral barrier function via the upregulated expression of TJ-related genes.

Effect of calcium ions and pH on the morphology and mechanical properties of hyaluronan brushes

Hyaluronan (HA) is a linear, regular polysaccharide that plays as a chief structural and functional component in peri- and extracellular matrices, thus contributing significantly to many basic cellular processes. To understand more comprehensively the response of the supramolecular organization of HA polymers to changes in their aqueous environment, we study the effects of Ca2+ concentration and pH on the morphology and rigidity of films of end-grafted HA polymers on planar supports (HA brushes), as a well-defined in vitro model system of HA-rich matrices, by reflection interference contrast microscopy and quartz crystal microbalance. The thickness and softness of HA brushes decrease significantly with Ca2+ concentration but do not change with pH, within the physiological ranges of these parameters. The effect of Ca2+ on HA brush thickness is virtually identical to the effect of Na+ at 10-fold higher concentrations. Moreover, the thickness and softness of HA brushes decrease appreciably upon HA protonation at pH less than 6. Effects of pH and calcium ions are fully reversible over large parameter ranges. These findings are relevant for understanding the supramolecular organization and dynamics of HA-rich matrices in biological systems and will also benefit the rational design of synthetic HA-rich materials with tailored properties.

Preparation of a hyaluronic acid hydrogel through polyion complex formation using cationic polylactide-based microspheres as a biodegradable cross-linking agent

A novel hyaluronic acid (HA)-based hydrogel was prepared through polyion complex (PIC) formation between cationic polylactide (PLA)-based microspheres (MS+) and hyaluronic acid (HA-) as an anionic polyelectrolyte. The MS+ and HA formed a biodegradable PIC hydrogel (HA-/MS+) when mixed in aqueous media. The swelling behavior and mechanical properties of the PIC hydrogel could be controlled by changing the charge ratio between HA- and MS+. In addition, the HA-/MS+ PIC hydrogel resulted in a lower inflammatory response compared with a collagen hydrogel in vivo.

The control of intracellular pH in cultured avian chondrocytes

1. Mechanical loading of cartilaginous tissue generates an increase in the concentration of cations in the extracellular matrix. This includes a decrease of the extracellular pH (pHo), which is known to affect the intracellular pH (pHi), thereby modifying the intracellular metabolism. Thus, the regulation of pHi is essential for the physiological function of cartilage. The fluorescent pH-sensitive dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester (BCECF AM) was employed in order to assess the mechanisms responsible for control of the pHi in an embryonic avian chondrocyte cell suspension. 2. Steady-state pHi in the absence of physiological HCO3- was 7.15 +/- 0.01 pH units as compared to a pHi of 6.94 +/- 0.02 pH units in its presence (P < 0.01). The intrinsic buffering power of chondrocytes (beta i) was 38.9 mM/pH unit and the total buffering capacity (beta T) was 65.8 mM/pH unit. 3. Cells maintained in a Hepes-buffered solution were exposed to an intracellular acid load by the NH4+ prepulse technique (20 mM NH4Cl). The initial rate of pHi recovery was 0.106 pH units/min (n = 18). Amiloride (0.33 mM), an inhibitor of the Na(+)-H+ exchanger, or replacement of external sodium [Na+]o with choline induced a 60% inhibition of the recovery rate, indicating a predominant involvement of this antiporter in the response to intracellular acidification. 4. H(+)-ATPase inhibitors (oligomycin 20 micrograms/ml; N,N;-dicyclohexylcarbodiimide (DCC), 0.5 mM; N-ethylmaleimide (NEM), 0.25 mM) and iodomycin (2 mM), a metabolic cell suppressor, reduced acid extrusion by 25% as measured by the NH4Cl prepulse in Hepes-bathed cells. 5. Chondrocytes transferred from a Hepes-buffered solution to a 5% CO2-25 mM HCO3- medium (HCO3- solution) underwent a pHi decrease of approximately 0.20 pH units, followed by a regulatory alkalinizing response of 0.118 pH units/min. The Na(+)-H+ exchanger was responsible for only 15% of this alkalinization (amiloride, 0.33 mM), in contrast to its primary role in HCO(3-)-free solution. 6. The activity of a Na(+)-dependent Cl(-)-HCO3- exchanger in physiological HCO3- solution was estimated by addition of the inhibitors 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulphonic acid (SITS; 0.5 mM) or diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS; 100 microM) and by the suspensions of chondrocytes in a Na(+)-free solution. Acidification performed under these conditions resulted in a 45% inhibition of the recovery rate as compared to control rates.(ABSTRACT TRUNCATED AT 400 WORDS)

The endocytic hyaluronan receptor in rat liver sinusoidal endothelial cells is Ca(+2)-independent and distinct from a Ca(+2)-dependent hyaluronan binding activity

Isolated and cultured rat liver sinusoidal endothelial cells (LECs) retain the ability to specifically bind 125I-hyaluronan (HA) and internalize it using a coated pit pathway [Biochem J, 257:875-884, 1989]. Here we have determined the effect of Ca+2 on the binding and endocytosis of HA by LECs. 125I-HA binding to intact LECs at 4 degrees C occurred both in the absence (10 mM EGTA) or the presence of physiologic concentrations of Ca+2 (1.8 mM). However, the specific binding of 125I-HA to LECs increased linearly with increasing Ca+2 concentrations. After permeabilization with the nonionic detergent digitonin, the Ca(+2)-independent HA binding activity increased approximately 743%, while the Ca(+2)-dependent binding activity was enhanced only approximately 46%. Therefore, the Ca(+2)-dependent HA binding activity appears not to be intracellular, whereas the Ca(+2)-independent HA receptor is found both inside LECs and on the cell surface. When LECs were allowed to endocytose 125I-HA at 37 degrees C in 10 mM EGTA or in 1.8 mM Ca+2, no differences were seen in the extent or rate of endocytosis. When LECs were allowed to endocytose 125I-HA in the presence of 10 mM Ca+2, the amount of cell-associated radioactivity increased approximately 20-50-fold. However, this additional cell-associated 125I-HA was not sensitive to hyperosmolarity and was removed by washing the cells in 10 mM EGTA at 4 degrees C. Therefore, the Ca(+2)-dependent cell-associated 125I-HA had accumulated on the cell surface and had not been internalized. From these studies we conclude that LECs have at least two types of specific HA binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium destabilizes and causes conformational changes in hyaluronic acid

The physical properties of proteoglycans found in the extracellular matrix influence the behavior of resident macromolecules, micro-ions, and cells. The forces stabilizing structured regions of hyaluronic acid (HA), a major component of extracellular matrix, were measured. The free energy of stability associated with structured regions within human HA was determined by potentiometric titration. A plot of free energy versus temperature demonstrated that the secondary structure was most stable at 25 degrees C and was destabilized at temperatures near 50 degrees C. In the presence of 5 mM CaCl2, the free energy of stability of the structured regions was reduced by 30 cal/mole. Classical light scattering and viscosity measurements confirmed the impact of calcium on HA. CaCl2 (5 mM) reduced the radius of gyration of HA. Above concentrations of 3 mM calcium, the viscosity of 0.1% HA solutions was reduced sharply. The ability of cells to secrete calcium, combined with the exquisite sensitivity of HA to calcium, may permit cell-mediated modification of the extracellular matrix and thus may facilitate cell motility.

A hypothesis on the pathogenesis of rheumatoid and other non-specific synovitides based on a combination of observations often overlooked

In early synovitides the tissue inflammatory cell reaction is often weak and sometimes absent, many alterations being consistent with nonvasculitic exudation (I). Increased permeability to protein may require little, if any, endothelial damage. In rheumatoid arthritis (RA) increased transfer of fluid and protein from vessels is not restricted to joints, suggesting that exudation is more liable to induce inflammation in joints than in other tissues of ambulant individuals (II). At least 17 vascular, rheological and other "primary" mechanisms may contribute to the formation of exudates; combinations of only a few of these may be required to produce joint effusions. Some mechanisms may explain why inflammation in RA favours joints (III). Joint effusions increase intra-articular hydrostatic pressure, contributing to synovial hypoxia, glycolysis and acidosis, which may be important "secondary" mechanisms in synovial inflammation (IV). Only a few of the "primary" mechanisms are strictly local ones, and RA may predominantly be a systemic disease dependent on combinations of minor aberrations in metabolic, endocrine and other functions (V). The combination of contributing mechanisms is not necessarily the same in two patients fulfilling the criteria for RA, and patients with clinically different types of synovitis may share pathogenetic mechanisms (VI).

Ultrastructure of a hyaluronic acid matrix

Freeze-etch replicas of a hylauronic acid matrix were visualized by electron microscopy. In water a coarse branching fibrillar network of hyaluronic acid aggregates was seen. The high solvent permeability of this matrix suggests that the spaces observed are relatively devoid of unaggregated polymer. Addition of calcium disordered the matrix, resulting in a more dispersed felt of polymer.