Surface‐active phospholipid: a Pandora’s box of clinical applications. Part II. Barrier and lubricating properties

Abstract

In Part I, it was described how their configuration renders phospholipid molecules surface active and capable of acting at interfaces in addition to the liquid-air interface to which conventional theory has hitherto confined the study of 'surfactant' in the lung. Surface-active phospholipid (SAPL) appears no different to comparable surfactants studied in the physical sciences for the highly desirable properties that their adsorption (reversible binding) can impart to solid surfaces. In Part II, these properties are considered in sites where there is no air. Highly desirable properties include boundary lubrication (lubricity), release (antistick) and the ability of the strongly adsorbed and strongly cohesive SAPL linings to act as barriers against abrasion, corrosion and, possibly, against invasion by microorganisms. As the 'sealant', it could be the true barrier rather than the cells providing its mechanical support. Evidence is reviewed for SAPL providing the gastric mucosal barrier to acid in the stomach and preventing the digestion of Helicobacter pylori until that barrier is broken by bile in the duodenum, where H. pylori cause ulcers. The concept that SAPL provides effortless sliding of many tissues, including pleura, pericardium and peritoneum is reviewed. Particular attention is paid to the load-bearing joints, where a deficiency has been associated with osteoarthritis. The ability of the same SAPL lining to perform multiple roles is discussed in relation to the peritoneum, where it could provide the lubricant/release agent preventing surgical adhesions, while imparting semipermeability to 'the membrane' vital for peritoneal dialysis. In each site, the prophylactic use of exogenous SAPL is discussed for its potential clinical applications.

Synergies in lubrication

“…51 These are important findings considering that phospholipids are present in the synovial fluid at concentrations 6 of 0.1-0.2 mg mL À1 and multilayers of phospholipids have been reported to exist on the cartilage surface. 52 Thus, naturally, phospholipids have been implied as important biolubricants 52 even though other studies stress the importance of biomacromolecules for the superior lubrication of synovial joints with phospholipids providing less benefits. 6 Based on the data above it is clear that the hydration lubrication mechanism can provide superior lubrication up to high loads on flat surfaces.…”

Synovial joint lubrication — does nature teach more effective engineering lubrication strategies?

“…Thus, the fluid film provides lubrication wherever it can support the load but, with physiological velocities being so low by engineering criteria, SAPL would appear to play a major role as a boundary lubricant, especially in load bearing joints [5,20,21] although this theory is challenged by other researchers [22]. The capability of SAPL to act as a boundary lubricant was first recognised in the thoraic cavity, in which frictionless sliding of the lungs is needed to reduce the work of breathing [23]. Researchers have speculated that SAPL is the boundary lubricant found wherever tissues need to slide over each other, also acting as an antistick agent [23].…”

“…The capability of SAPL to act as a boundary lubricant was first recognised in the thoraic cavity, in which frictionless sliding of the lungs is needed to reduce the work of breathing [23]. Researchers have speculated that SAPL is the boundary lubricant found wherever tissues need to slide over each other, also acting as an antistick agent [23].…”

Lecithin as a Therapeutic Agent in Ulcerative Colitis

“…It facilitates the gas exchange and prohibits the entrance of microbes [9]. In the intestine, the PC-containing structures are referred to as ‘surfactant-like particles' and prevent invasion of the commensal flora of the colon [9]. In a healthy gut, there are 1 trillion bacteria per gram of stool which live in harmony with the organism.…”

“…In the lung, the PC layer covering the inside of the alveoli and bronchioli is defined as ‘surfactant'. It facilitates the gas exchange and prohibits the entrance of microbes [9]. In the intestine, the PC-containing structures are referred to as ‘surfactant-like particles' and prevent invasion of the commensal flora of the colon [9].…”