Measurement of the time between biosynthesis and surface excretion of sebaceous lipids in the horse.

This study investigates the time interval between the production and secretion of sebum, a type of skin lipid, in horses. It involves tracking this process using radiolabelled molecules, finding evidence for intervening stages in lipid biosynthesis, and indicating that fatty acids remain in certain cell components between these stages.

Experimental Method

• The researchers studied the timing of sebum biosynthesis and excretion to the skin surface in a horse. This was done by injecting a radiolabelled compound, [1-14C]acetate, into the skin and periodically collecting surface lipids.
• The presence of radioactivity in different lipid categories, namely equolides (ring-shaped lactones with large number of carbons) and cholesteryl esters, was assessed using thin-layer chromatography and autoradiography. These techniques help separate and visualize radioactively labelled compounds.
• The team also broke down the monounsaturated equolides by oxidation and analyzed the resulting fragments.

Key Findings

• The peak of radioactivity in equolides and cholesteryl esters was detected 15-21 and 10-16 days post-injection, respectively. This suggests the time taken for these lipids to be synthesized and secreted.
• The course of radioactivity of equolide oxidation fragments differed according to the type. This indicates that different types of equolides are produced through different pathways.

Interpretation and Conclusion

• The researchers interpret their observations as evidence that the biosynthesis of a large proportion of equolides involves stages, in which de novo (or, ‘from the beginning’) fatty acid synthesis does not directly lead to fatty acid chain elongation. This is contrary to a previous assumption that these two processes occur consecutively in lipid synthesis.
• They propose that phospholipids in sebaceous cells serve as an intermediate storage area where fatty acids stay between these biosynthetic steps. Phospholipids are a major component of all cell membranes, and this hypothesis suggests a specific role for them in the complex process of lipid (sebum) biosynthesis in horses.