Molecular species of lecithins in human gallbladder bile

Using a precise high performance liquid chromatography (HPLC) technique, we identified the molecular species of lecithins in gallbladder biles from patients with cholesterol gallstones (n = 29), pigment gallstones (n = 9), morbid obesity (n = 5), and "controls" (n = 10). The major lecithin species identified in all groups, in descending rank order as represented by the fatty acids in the sn-1 and sn-2 positions, were 16:0-18:2, 16:0-18:1, 16:0-20:4, 18:0-18:2, and 18:1-18:2. Lecithin species were found to be more numerous and in substantially different proportions than reported by previous investigators. No significant differences were found between any biliary lecithin species in the cholesterol and pigment stone groups. However, compared with controls, both cholesterol and pigment stone patients had smaller proportions of 16:0-20:4, the principal arachidonyl lecithin species. Using the HPLC elution sequence for quantifying the hydrophilic-hydrophobic balance, we developed a Hydrophobic Index for lecithin species in each bile based upon the principles proposed by D. M. Heuman for bile salt species. Hydrophobic indices of bile salts and lecithin were positively correlated (r = 0.48, R2 = 0.23, P = 0.0002) suggesting that more hydrophobic bile salts were associated with biliary secretion of more hydrophobic lecithins. The most hydrophobic major lecithin species, 18:0-18:2, was present in greater proportions in biles with cholesterol monohydrate crystals in their sediments and in those with cholesterol saturation indices greater than one. This work provides rigorous separation, identification, and quantitation of the lecithin species in human gallbladder bile from a large cohort of patients but, apart from a more hydrophobic bile salt pattern coupling more hydrophobic lecithins, we fail to identify any relationships of biomedical importance between lecithin species and other major biliary constituents.