Cyclic Mechanical Loading Enhances Transport of Antibodies Into Articular Cartilage

Abstract

The goal of this study was to characterize antibody penetration through cartilage tissue under mechanical loading. Mechanical stimulation aids in the penetration of some proteins, but this effect has not characterized molecules such as antibodies (>100 kDa), which may hold some clinical value for treating osteoarthritis (OA). For each experiment, fresh articular cartilage plugs were obtained and exposed to fluorescently labeled antibodies while under cyclic mechanical load in unconfined compression for several hours. Penetration of these antibodies was quantified using confocal microscopy, and finite element (FE) simulations were conducted to predict fluid flow patterns within loaded samples. Transport enhancement followed a linear trend with strain amplitude (0.25-5%) and a nonlinear trend with frequency (0.25-2.60 Hz), with maximum enhancement found to be at 5% cyclic strain and 1 Hz, respectively. Regions of highest enhancement of transport within the tissue were associated with the regions of highest interstitial fluid velocity, as predicted from finite-element simulations. Overall, cyclic compression-enhanced antibody transport by twofold to threefold. To our knowledge, this is the first study to test how mechanical stimulation affects the diffusion of antibodies in cartilage and suggest further study into other important factors regarding macromolecular transport.

Biomimetic proteoglycans diffuse throughout articular cartilage and localize within the pericellular matrix

“…The diffusion coefficients for BPGs into articular cartilage are similar to what others have found for large molecule diffusion in cartilage. Leddy and Guilak (Leddy & Guilak, ) measured the diffusion of 500 kDa dextran into cartilage to be ~5 μm 2 /s and DiDomenico et al (DiDomenico, Xiang Wang, & Bonassar, ) measured the diffusion of a 150 kDa antibody into cartilage range from 2.8 to 6 μm 2 /s. Using avidin, Bajpayee et al (Bajpayee et al, ) found a diffusion coefficient of 38 μm 2 /s which is closer to the diffusion coefficients for the earlier time points of BPGs where there is a higher driving force similar to the higher potential that a positively charged molecule, like avidin, would experience when diffusing through a negatively charged cartilage matrix.…”

Biomimetic proteoglycans can molecularly engineer early osteoarthritic cartilage in vivo

“…A number of studies have investigated the diffusion of molecules into the articular cartilage ECM as treatments or drug delivery vehicles . Work done by other groups demonstrated diffusion of a positively charged molecule (66 kDa avidin ex vivo and in vivo) a large neutral molecule (500 kDa dextran ex vivo), and antibodies (150 kDa goat‐anti‐mouse antibodies ex vivo) into articular cartilage. The study involving dextran showed the diffusion coefficient of 500 kDa dextran to be greater in the superficial zone and reduced deeper into the cartilage, whereas the diffusion coefficients for 40 and 70 kDa dextran followed an opposite trend with the diffusion coefficient being the lowest at the surface.…”

How can 50 years of solute transport data in articular cartilage inform the design of arthritis therapeutics?

“…Other methods, such as solute desorption techniques 18,21,23,24,30,40e43 or diffusion cells 20,22,23,25,43e46 , rely on quantifying a volume of solute that diffuses through a sample over a given time, often using fluorescent or radioactive labels. Additionally, there are methods that track local fluorescence of a labeled solute within cartilage, such as fluorescence recovery after photobleaching (FRAP) 32,47 , and fluorescence gradient techniques 28,29,32,46e48 .…”

“…The diffusivity and convection coefficient quantify the diffusive speed of the molecule and the ratio of solute convective velocity to interstitial fluid velocity, respectively. These metrics can be measured as an average for the entire tissue, or measured locally 32 . Overall, there are many potential solutions to Eq.…”

“…Consequently, dextrans were used to investigate how transport was affected by large changes in hydrodynamic size or molecular weight (MW) (3 kDae500 kDa) 28e30 . Despite their therapeutic potential, transport of large antibodies (25 kDae200 kDa) has only recently been comprehensively examined 15,31,32 . Ultimately, the diversity of molecules studied for transport in cartilage is remarkable, and there are dozens of studies that have contributed to the knowledge in this field.…”