Lipid macroamphiphiles (LMAPs) are cell envelope components of bacteria that have been extensively associated with the pathogenesis of disease. It has been reported that these components can also influence the in vivo metabolism of lipids in mammals. For the onset of the skin condition acne vulgaris, in addition to the presence of Propionibacterium acnes on the skin, changes in the composition of skin lipids has been identified as an important etiological factor in the development of the disease. To date, the LMAP of P. acnes has not been purified and, for this reason, the significance of these components remains unclear. In order to study their significance, purification of the LMAP was essential for resolving their structures and diverse biological effects. Following the extraction and consequent purification of lipoteichoic acid (LTA) from S. aureus by hydrophobic interaction chromatography (HIC), a similar method was applied to an extract from P. acnes. The resulting amphiphilic fractions were analysed using SDS-PAGE and found to contain two discrete components. To facilitate the further characterisation, these components were separated on a larger scale by preparative SDS-PAGE and purified from the gel via electro-elution. The purified components were designated LMAP1 (running in the 24-29kDa region) and LMAP2 (running in the 14-20kDa region). Analysis of the LMAP species suggested a lipoglycan structure and revealed evidence for a lipid anchor based on phosphatidylinositol with fatty acids that were comparable to the whole cell fatty acid profile. The polysaccharide moiety of both LMAP1 and LMAP2 contained different relative amounts of mannose, glucose and galactose, and it was these differences that affected the size and hydrophobicity of the two lipoglycan components. Additionally, an amino sugar was detected that was suspected of being a diaminohexuronic acid. This component has been previously identified as a component of the P. acnes cell wall polysaccharide. Consequently, it is proposed that a relationship might exist between these distinctive cell envelope polymers. The effects on lipid metabolism were investigated in an in vitro system using the combined lipoglycan from P. acnes and compared to both LTA and lipopolysaccharide (LPS). All LMAP components investigated inhibited the uptake of fatty acid by hepatocytes. Furthermore, secretion of lipid from hepatocytes was also inhibited following incubation with each of the LMAP components. However, LTA had only a marginal effect in comparison to LPS and lipoglycan. It was also shown that both LPS and lipoglycan had a direct effect on adipocytes by increasing the uptake of fatty acid. Additionally, lipid secretion within these cells was also stimulated, which propounded an increase in fatty acid secretion. This evidence suggested that the lipoglycan of P. acnes can significantly influence the metabolism of lipids by mammalian cells and therefore these lipoglycans might play a crucial role in the pathogenecity of P. acnes and thus in the development of disease.
