Differences in Surfactant Lipids Collected from Pleural and Pulmonary Lining Fluids

Factors influencing airway smooth muscle tone: a comprehensive review with a special emphasis on pulmonary surfactant

A thin film of pulmonary surfactant lines the surface of the airways and alveoli, where it lowers the surface tension in the peripheral lungs, preventing collapse of the bronchioles and alveoli and reducing the work of breathing. It also possesses a barrier function for maintaining the blood-gas interface of the lungs and plays an important role in innate immunity. The surfactant film covers the epithelium lining both large and small airways, forming the first line of defense between toxic airborne particles/pathogens and the lungs. Furthermore, surfactant has been shown to relax airway smooth muscle (ASM) after exposure to ASM agonists, suggesting a more subtle function. Whether surfactant masks irritant sensory receptors or interacts with one of them is not known. The relaxant effect of surfactant on ASM is absent in bronchial tissues denuded of an epithelial layer. Blocking of prostanoid synthesis inhibits the relaxant function of surfactant, indicating that prostanoids might be involved. Another possibility for surfactant to be active, namely through ATP-dependent potassium channels and the cAMP-regulated epithelial chloride channels [cystic fibrosis transmembrane conductance regulators (CFTRs)], was tested but could not be confirmed. Hence, this review discusses the mechanisms of known and potential relaxant effects of pulmonary surfactant on ASM. This review summarizes what is known about the role of surfactant in smooth muscle physiology and explores the scientific questions and studies needed to fully understand how surfactant helps maintain the delicate balance between relaxant and constrictor needs.

Successful Treatment With Daptomycin of MRSA Empyema Complicated by Right-Sided Loculated Pleural Effusion Refractory to Vancomycin

Empyema is a serious complication of pneumonia and has been reported to have a mortality rate of 8.7%. For methicillin-resistant Staphylococcus aureus (MRSA) empyema, treatment includes drainage and specific antibiotics such as vancomycin and linezolid. Strikingly, there are increasing incidences of empyema refractory to vancomycin and linezolid. Despite being inactivated in the lung parenchyma by pulmonary surfactant, daptomycin can penetrate the pleural space and may be better at treating MRSA empyema than vancomycin and linezolid. Some case reports have shown that daptomycin has been used to successfully treat MRSA empyema refractory to linezolid and vancomycin-resistant enterococcus (VRE) empyema. Here, we present a 26-year-old male with a past medical history of intravenous (IV) drug use, newly diagnosed HIV, HCV, and multifocal pneumonia complicated by a left-sided MRSA empyema that partially resolved with vancomycin and drainage. However, he subsequently developed a right-sided loculated pleural effusion. After the patient was switched to daptomycin with continued drainage, the right and left pleural effusions improved significantly. Once medically stable, he was discharged to a rehabilitation facility for further recovery. Our case report demonstrates that daptomycin could be considered as an effective treatment for MRSA empyema, particularly when refractory to vancomycin.

Lubricating recovery of damaged pleural mesothelium: effect of time and of phosphatidylcholines

Effect of time and phosphatidylcholines (PCs) on lubrication of damaged mesothelium has been investigated. Marked increase in coefficient of kinetic friction (μ) of pleural specimens after mesothelial blotting and rewetting decreased by 23.4±3.5%, 41.8±3.8%, and 40.5±2.7% after 30min, 1h, and 2h. Hence, damaged mesothelium is able to partially reset lubricating molecules on its surface. Increase in μ of post-blotting Ringer 2h after addition of unsaturated PCs (3mg/ml) decreased a little more than after 2h Ringer. Effects of unsaturated and saturated PCs were similar, contrary to expectation raised by their different percentage in pleural and alveolar lavage. Effect of PCs did not increase at 6mg/ml, and was nil at 0.4mg/ml. Increase of μ after short phospholipase treatment decreased by 45.9±2.0% after 2h Ringer, and a little more after addition of unsaturated or saturated PCs. Hence, PCs, as other phospholipids, have a small effect, likely because of difficulty in resetting their relationships with main lubricating molecules.

Pleural mesothelium lubrication after phospholipase treatment

Coefficient of kinetic friction (μ) of rabbit pleural mesothelium increased after short treatment of specimens with phospholipase C. This increase was removed by addition of a solution with hyaluronan or sialomucin, as previously shown in post-blotting Ringer or after short pronase treatment. After phospholipase μ decreased with increase in sliding velocity, but at highest velocity it was still greater than control; this difference was removed by addition of hyaluronan or sialomucin, as in post-blotting Ringer or after short pronase treatment. Hyaluronan placed on specimen before phospholipase treatment reduced increase in μ by protecting phospholipids from enzyme, as shown by others for alveolar and synovial phospholipids. Samples of parietal pleura stained with silver nitrate showed that mesothelial cells were not disrupted by short phospholipase treatment. Instead, they were disrupted if this treatment was preceded by a short pronase treatment; but even after this disruption addition of hyaluronan or sialomucin brought μ back to control.

Unsaturated phosphatidylcholines lining on the surface of cartilage and its possible physiological roles

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.

Boundary lubrication of joints: characterization of surface-active phospholipids found on retrieved implants

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 surface-active 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.