Natural joints: Boundary lubrication and antiphospholipid syndrome (APS).

The paper shows that osteoporosis (OA) changes the SF content and the lipid profile substantially. To estimate the implication of the lipid environment in case the articular cartilage (AC) changes, we measured friction coefficient normal samples, with early and late stages of (OA). During joint inflammation and osteoarthritis, enzymatically activated ß2-Glycoprotein I is transformed into antibody conformation. Our hypothesis about cartilage degradation of PL bilayers by antibodies (ß2-Glycoprotein I) is considering antiphospholipid syndrome (APS), which was not discussed in the literature before. Deactivated PL molecule has no ability to form bilayers, lamellar phases, and liposomes. The phospholipid content in synovial fluid (SF) during joint inflammation, osteoarthritis, and rheumatoid arthritis is significantly higher (2-3 times) above the normal concentration of PL, and has a poor boundary-lubricating ability is deactivated.

Articular cartilage. Strong adsorption and cohesion of phospholipids with the quaternary ammonium cations providing satisfactory lubrication of natural joints.

Much evidence supports the hypothesis that surface-active phospholipid (SAPL) molecules on articular cartilage (AC) adsorbed to negatively-charged proteoglycan matrix form phospholipid (membrane), are negatively charged surface (-PO4-) and hydrophilic. In Hills cartilage model (1984) phospholipids adsorbed to cartilage surface act as boundary lubricants making the surface extremely hydrophobic. Hydrophobic surface of AC has gained no support in all experimental facts presented in this paper and the current literature showing that AC is amphoteric and hydrophilic with the negatively charged surface (-PO4-). The interfacial energy of the model membrane of spherical lipid bilayers evident from phosphatidylcholine "bell-shaped curve" has amphoteric character and lowest energy in lubrication at a pH 7.4 ± 1 of the natural joint.

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.