High-performance liquid chromatography of water-soluble choline metabolites

We have developed a new method for the separation of [3H]choline metabolites by high-performance liquid chromatography. Using this method it is possible to separate, in one step, all of the known major water-soluble choline metabolites present in crude acid extracts of cells that have been incubated with [3H]choline, with baseline or near-baseline resolution. We use a gradient HPLC system with a normal-phase silica column as the stationary phase, and a linear gradient of increasing polarity and ionic strength as the mobile phase. The mobile phase is composed of two buffers: Buffer A, containing acetonitrile/water/ethyl alcohol/acetic acid/0.83 M sodium acetate (800/127/68/2/3), and buffer B (400/400/68/53/79), pH 3.6. A linear gradient from 0 to 100% buffer B, with a slope of 5%/min, is started 15 min after injection. At a flow rate of 2.7 ml/min and column temperature of 45 degrees C, typical retention times for the following compounds are (in min): betaine, 10; acetylcholine, 18; choline, 22; glycerophosphocholine, 26; CDP-choline, 31; and phosphorylcholine, 40. This procedure has been applied in tracer studies of choline metabolism utilizing the neuronal NG108-15 cell line and rat hippocampal slices as model systems. While the compounds labeled in the NG108-15 cells were primarily phosphorylcholine and glycerophosphocholine, reflecting high rates of phospholipid turnover, in the hippocampal slices choline and acetylcholine were the major labeled species. Identification of individual peaks was confirmed by comparing the elution profiles of untreated cell extracts with extracts that had been treated with hydrolyzing enzymes of differing specificities. This HPLC method may be useful in studies of acetylcholine and phosphatidylcholine metabolism, and of the possible interrelationships of these compounds in cholinergic cells.