The lubrication effect of hyaluronic acid and chondroitin sulfate on the natural temporomandibular cartilage under torsional fretting wear

Lubricants for osteoarthritis treatment: From natural to bioinspired and alternative strategies

Osteoarthritis is the most common degenerative and highly prevalent joint disease, characterized by progressive loss and destruction of articular cartilage. The damaged cartilage surface has an increased friction, which causes patients to suffer from serious pain. Restoring the lubrication ability of the joint is central to the treatment of osteoarthritis, a key topic in medical research. A variety of lubricants have been designed to reduce friction in joints and promote cartilage tissue repair to alleviate the symptoms of osteoarthritis. Herein, we review the recent progress of lubricants from the three perspectives of natural, bioinspired, and alternative strategies for osteoarthritis treatment, as well as the structural characterization and lubrication properties of such lubricants. Specifically, natural lubricants include glycosaminoglycans, lubricin and lipids in joints, bioinspired lubricants include scaffolds mimicking hyaluronic acid or lubricin, and alternative lubricants include modified lubricants based on hyaluronic acid, lipids, nanoparticles, and peptides. We also discuss the current challenges and long-term perspectives for further research in this area.

Characterization of Synovial Fluid Components: Albumin-Chondroitin Sulfate Interactions Seen through Molecular Dynamics

The friction coefficient of articular cartilage (AC) is very low. A method of producing tailor-made materials with even similar lubrication properties is still a challenge. The physicochemical reasons for such excellent lubrication properties of AC are still not fully explained; however, a crucial factor seems to be synergy between synovial fluid (SF) components. As a stepping stone to being able to produce innovative materials characterized by a very low friction coefficient, we studied the interactions between two important components of SF: human serum albumin (HSA) and chondroitin sulfate (CS). The molecular dynamics method, preceded by docking, is used in the study. Interactions of HSA with two types of CS (IV and VI), with the addition of three types of ions often found in physiological solutions: Ca2+, Na+, and Mg2+, are compared. It was found that there were differences in the energy of binding values and interaction maps between CS-4 and CS-6 complexes. HSA:CS-4 complexes were bound stronger than in the case of HSA:CS-6 because more interactions were formed across all types of interactions except one-the only difference was for ionic bridges, which were more often found in HSA:CS-6 complexes. RMSD and RMSF indicated that complexes HSA:CS-4 behave much more stably than HSA:CS-6. The type of ions added to the solution was also very important and changed the interaction map. However, the biggest difference was caused by the addition of Ca2+ ions which were prone to form ionic bridges.

Clinical effectiveness and safety of intra-articular injection of HYALGO in the management of knee osteoarthritis symptoms: A multicenter prospective study

BACKGROUND

The reduced concentration of hyaluronic acid in the synovial fluid, leading to impairment of joint function and painful symptomatology during knee osteoarthritis (OA), can be restored by using injectable formulations of hyaluronic acid (HA) and chondroitin sulfate (CS), variable for relative composition, HA/CS molecular modifications, and injection protocols. The present study aims to assess the safety and performance of the intra-articular (IA) viscosupplementing agent HYALGO, a formulation combining 40 mg/mL HA (>1700 kDa) and 40 mg/mL CS, in the treatment of patients suffering from knee OA.

METHODS

74 patients affected by knee lesions classified as grade II and III according to Kellgren and Lawrence classification were prospectively recruited and treated with three HYALGO injections (2 mL) given one week apart. Visual analogue scale (VAS) pain changes were monitored at each injection and over-time at 6, 14, and 26 weeks of follow-up. Secondary endpoints were: Western Ontario McMaster University Osteoarthritis index (WOMAC), Patient's Global Assessment (PGA) score, Clinical Observer Global Assessment (COGA) score, Outcome Measures in Rheumatology Committee (OMERACT) and Osteoarthritis Research Society International (OARSI) responders rates. Patients were also assessed for changes in their ultrasound joint scores according to the criteria of the OMERACT US Task Force Group.

RESULTS

Pain reduction was statistically significant starting from the first IA injection. Mean pain reduction from baseline to week 26 was -90.6%. At 26 weeks, WOMAC Pain was reduced by -62.7%, WOMAC Stiffness by -47.2%, WOMAC Physical Function by -54.1%; Total WOMAC by -53.8%. The VAS PGA change from baseline was -48.0 [mm] and VAS COGA -41.0 [mm]. Responders at week 26 were 78.4%. Ultrasound parameters (joint effusion, synovial thickness, and popliteal cysts) improved or remained stable from baseline to week 6.

CONCLUSIONS

Three injections of HYALGO were safe and effective to manage symptomatic knee OA, with a beneficial effect that increased progressively over time, peaking 6 months after injection.

Biotribology of Synovial Cartilage: A New Method for Visualization of Lubricating Film and Simultaneous Measurement of the Friction Coefficient

A healthy natural synovial joint is very important for painless active movement of the natural musculoskeletal system. The right functioning of natural synovial joints ensures well lubricated contact surfaces with a very low friction coefficient and wear of cartilage tissue. The present paper deals with a new method for visualization of lubricating film with simultaneous measurements of the friction coefficient. This can contribute to better understanding of lubricating film formation in a natural synovial joint. A newly developed device, a reciprocating tribometer, is used to allow for simultaneous measurement of friction forces with contact visualization by fluorescence microscopy. The software allowing for snaps processing and subsequent evaluation of fluorescence records is developed. The evaluation software and the follow-up evaluation procedure are also described. The experiments with cartilage samples and model synovial fluid are carried out, and the new software is applied to provide their evaluation. The primary results explaining a connection between lubrication and friction are presented. The results show a more significant impact of albumin proteins on the lubrication process, whereas its clusters create a more stable lubrication layer. A decreasing trend of protein cluster count, which corresponds to a decrease in the thickness of the lubrication film, is found in all experiments. The results highlight a deeper connection between the cartilage friction and the lubrication film formation, which allows for better understanding of the cartilage lubrication mechanism.