gms | German Medical Science

Objectives: Based on several studies a reduction of SF viscosity has been associated with synovial joint pathologies. A major cause of pathological joint degeneration is Osteoarthritis. A change in synovial hyaluronan MW and concentration, could be linked to a higher risk of OA progression. While the rheological properties of synovial fluid are well studied at bulk. In contrast to this its molecular organization and how this is linked to osteoarthritis is poorly understood. We analyzed synovial fluids of patients without joint damage, advanced osteoarthritis and TEP.

Methods: Multipleparticle-tracking microrheologyanalysis suggests that HA forms a dynamic network in SF. By analyzing the diffusion of fluorescent beads, multipleparticle-tracking microrheology allows to study the organisation of the SF at microscopic scale, but it does not allow the specific observation of endogenous SF components. For thus single molecule microscopy is able to probe the properties of a single component in a complex biological environment by selective labeling. Next to selectivity, single molecule microscopy provides a high spatial and temporal resolution. By using this method it was confirmed that HA molecules form random coil structures in buffer solution. Here we measured the diffusion of fluorescent hyaluronan (fl-HA) and compared it to the diffusion of fluorescent dextran as inert tracer in human synovial fluid.

Results and Conclusion: In contrast to fl-Dextran fl-HA showed a significantly slower diffusion in the control group (2.2 µm²/s) compared to patient with progressed OA (5.1 µm²/s) or TEP (4.5µm²/s). While the diffusion coefficients of all three groups show a large overlap (Fig 1.), plotting the fl-HA over the fl-Dextran diffusion coefficient the OST and TEP group are clearly distinguishable from the control group. The diffusion coefficient of fl-HA and Dextran shows a linear relationship with a high correlation coefficient in the control and TEP group (0.88 vs. 0.9). By just increasing the overall viscosity of the fluid, the ratio of the diffusion coefficients of fl-HA and fl-Dextran should stay the same. The slope of the linear regression analysis in the TEP-group (1.2+/- 0.2) is in good concurrence with ratio of the diffusion coefficients of fl-HA and fl-Dextran in buffer (1.3+/- 0.1). In contrast to this the slope of fl-HA over fl-Dextran is reduced to 0.4+/-0.1 in the control group.

This shows that fl-HA undergo specific intermolecular interactions within the synovial fluid environment. Furthermore this interaction is reduced in patients with joint damage.

Aside from a decreased SF viscosity in OA, major changes of the synovial fluid molecular organization occur in OA. The decreased capability to form a dynamic network which includes HA in the synovial fluid seems to be at least a major indicator of progressive joint damage. Thus, single molecule microscopy is a useful method for probing the organization of human synovial fluid and to examine its changes in disease states like osteoarthritis.