Comparison of dialysis,thin layer and silicic acid column chromatography for prostaglandin isolation from biological material

Chemical and biochemical methods assaying the total content of neutral lipids during some conventional procedures for purification and isolation of prostaglandins from biological fluids revealed all fractions to be contaminated with fatty acids, cholesterol, cholesterol esters, tri-, di- and/or mono-glycerides. It was demonstrated that it was not possible to make pure prostaglandin fractions by simple dialysis. On the basis of these findings a new preparative schedule involving either dialysis or column chromatography on silicic acid, combined with preparative thin layer chromatography, made it possible to isolate substantially pure PGE₂ from a synthetic biological system involving arachidonic acid as a precursor and the microsomal synthesizing system from sheep vesicular glands. Sheep vesicular glands have been used for biosynthesis of prostaglandins (PG) (1). For the study of the metabolism of various prostaglandins, labeled PGE₁ has been prepared from 8, 11, 14-eicosatrienoic acid labeled at various positions (2). Recently a method employing arachidonic acid and sheep vesicular glands for the formation of PGE₂ has been patented. The method claims a high purity (98%) with quick recovery of PGE₂ from the incubation mixture. The essential feature of the method is the use of a dialysis step which is said to be superior to the time-consuming chromatographic procedures (3). In our recent studies on the metabolism of essential fatty acids, we have found it impossible to prepare chemically pure prostaglandins by the above mentioned methods, since cholesterol, cholesterol esters, fatty acids and glycerides were found to contaminate the final products. The present paper therefore gives some data on these contaminants, and on this basis a new approach to the isolation of chemically pure prostaglandin (PGE₂) has been developed.