BACKGROUND:Semipermeability to fluid transport is one of the principal attributes of a tissue like articular cartilage. Consequently, this characteristic can be exploited in attempts to understand the functional roles of the biological layer of Surface Active Phospholipids (SAPL) which form on its surfaces. A previous study, relevant to peritoneal SAPL was carried out in which hypertonic glucose solution was dialysed against physiological saline through SAPL membrane and concluded that SAPL possessed semipermeability. Our analysis extends this previous study by dialysing hypertonic and hypotonic saline solutions against physiological saline via SAPL membranes which is more relevant to the articular joint environment.MATERIAL/METHODS:Membranes were produced from either synthetic or bovine cartilage SAPL and used to carry out tests involving the dialysis of hypotonic and hypertonic sodium chloride solutions against physiological saline, using an Ussing chamber to hold both the membranes and dialysis fluids.RESULTS:The dialysis produced osmotic pressures which are commensurate with our experimental constraints, but strongly indicated that it is indeed possible to generate osmotic pressures using SAPL membranes, indicating the semipermeability of this lipid structure.CONCLUSIONS:It is widely accepted that the collagen-proteoglycan membrane provides the semipermeability of articular cartilage despite the low levels of osmotic pressure recorded in our experiments, our results demonstrate that SAPL aggregation can constitute a semipermeable layer with a strong capability to contribute to the semipermeablity of the collagen-proteoglycan system especially on the surface of the tissue. Consequently its deficiency, as seen in osteoarthritis could lead/contribute to cartilage dysfunction.

Background The identity of the vital active ingredient within synovial fluid (SF)-to which we owe the near frictionless performance of diarthrodial joints-has been the quest of researchers for many years. Initially, hyaluronic acid (HA) was thought to be the lubricant, but it has been shown not to possess the load-bearing ability required within the physiological joint. The glycoprotein fraction of synovial fluid (lubricin) has been shown to have the same lubricating ability as synovial fluid. All or part of this is thought to be due to the surfaceactive phospholipids (SAPLs) present in lubricin. We characterized the SAPLs adsorbed on the surface of retrieved prostheses which have been implicated as the boundary lubricant.Material and methods Rinsing fluids collected from the bearing surfaces of 40 prostheses removed from hip and knee revision operations were analyzed using high-performance liquid chromatography (HPLC).Results SAPLs were detected on all retrieved implants. During the study, 8 different species of phosphatidylcholines were identified. We also determined the relative concentration of each species, which suggested that the unsaturated SAPL species predominate.Interpretation It is of value to know the identity of the lubricating constituents of SF, not only for the future development of artificial joints, but also in developing cures for several disease processes in which lubrication plays a role.

Background Evidence has strongly indicated that surface-active phospholipid (SAPL), or surfactant, lines the surface of cartilage and serves as a lubricating agent. Previous clinical study showed that a saturated phosphatidylcholine (SPC), dipalmitoyl-phosphatidylcholine (DPPC), was effective in the treatment of osteoarthritis, however recent studies suggested that the dominant SAPL species at some sites outside the lung are not SPC, rather, are unsaturated phosphatidylcholine (USPC). Some of these USPC have been proven to be good boundary lubricants by our previous study, implicating their possible important physiological roles in joint if their existence can be confirmed. So far, no study has been conducted to identify the whole molecule species of different phosphatidylcholine (PC) classes on the surface of cartilage. In this study we identified the dominant PC molecule species on the surface of cartilage. We also confirmed that some of these PC species possess a property of semipermeability. Methods HPLC was used to analyse the PC profile of bovine cartilage samples and comparisons of DPPC and USPC were carried out through semipermeability tests. Results It was confirmed that USPC are the dominant SAPL species on the surface of cartilage. In particular, they are Dilinoleoyl-phosphatidylcholine (DLPC), Palmitoyl-linoleoyl-phosphatidylcholine, (PLPC), Palmitoyl-oleoyl-phosphatidylcholine (POPC) and Stearoyl-linoleoyl-phosphatidylcholine (SLPC). The relative content of DPPC (a SPC) was only 8%. Two USPC, PLPC and POPC, were capable of generating osmotic pressure that is equivalent to that by DPPC. Conclusion The results from the current study confirm vigorously that USPC is the endogenous species inside the joint as against DPPC thereby confirming once again that USPC, and not SPC, characterizes the PC species distribution at non-lung sites of the body. USPC not only has better anti-friction and lubrication properties than DPPC, they also possess a level of semipermeability that is equivalent to DPPC. We therefore hypothesize that USPC can constitute a possible addition or alternative to the current commercially available viscosupplementation products for the prevention and treatment of osteoarthritis in the future.

Background: It has been confirmed that surface‐active phospholipid (SAPL), or surfactant, lines the surface of peritoneum and serves as a release and lubricating agent. The most important component in SAPL is phosphatidylcholine. A previous animal study showed that a saturated phosphatidylcholine, dipalmitoyl‐phosphatidylcholine, reduced the formation of surgical adhesion. Latest studies have indicated that the dominant SAPL species at some sites outside the lung are not saturated phosphatidylcholine but, rather, are unsaturated phosphatidylcholineMethods: High performance liquid chromatography was used to analyse the phosphatidylcholine profile of dialysate samples obtained from peritoneal dialysis patients. Friction tests were performed on dipalmitoyl‐phosphatidylcholine and selected unsaturated phosphatidylcholine.Results: It was discovered that unsaturated phosphatidylcholine was the dominant SAPL species inside the peritoneal cavity. They are palmitoyl‐linoleoyl‐phosphatidylcholine, palmitoyl‐oleoylphosphatidylcholine and stearoylarachidonoylphosphatidylcholine. Most interestingly, there was no dipalmitoyl‐phosphatidylcholine detected from these dialysate samples. The coefficients of static and dynamic friction from palmitoyllinoleoyl‐phosphatidylcholine and palmitoyloleoyl‐phosphatidylcholine were measured and found to be lower than that of dipalmitoyl‐phosphatidylcholine.Conclusion: The results from the current study reveal that unsaturated phosphatidylcholine is the endogenous species inside the peritoneal cavity. This discovery offers further evidence that the dominant SAPL species at non‐lung sites are unsaturated phosphatidylcholine, not saturated phosphatidylcholine, strongly indicating the difference between phosphatidylcholine species distribution at lung and non‐lung sites. Unsaturated phosphatidylcholine has better anti‐friction and lubrication properties than dipalmitoyl‐phosphatidylcholine. Unsaturated phosphatidylcholine‐based SAPL pharmaceutical products should be developed and evaluated.

The type and relative importance of saturated and unsaturated phospholipid components of surfactant within the epithelial lining fluid (ELF) of the inner and outer surfaces of the lung is not known.