Electrospray ionization mass spectrometric analyses of phospholipids from INS-1 insulinoma cells: comparison to pancreatic islets and effects of fatty acid supplementation on phospholipid composition and insulin secretion

Insulin secretion by pancreatic islet beta-cells is impaired in diabetes me llitus, and normal beta-cells are enriched in phospholipids with arachidona te as sn-2 substituent. Such molecules may play structural roles in exocyto tic membrane fusion or serve as substrates for phospholipases activated by insulin secretagogues. INS-1 insulinoma cells respond to secretagogues and permit the study of effects of culture with free fatty acids on phospholipi d composition and secretion. INS-1 cell glycerophosphocholine (GPC) and gly cerophosphoethanolamine (GPE) lipids are demonstrated here by electrospray ionization mass spectrometry to contain a lower fraction of molecules with arachidonate and a higher fraction with oleate as sn-2 substituent than nat ive islets, Palmitic acid supplementation induces little change in these IN S-1 cell lipids, but supplementation with linoleate or arachidonate induces a large rise in the fraction of INS-1 cell GPC species with polyunsaturate d sn-2 substituents and a fall in oleate-containing species to yield a GPC profile similar to native islets. The fraction of GPE lipids comprised of p lasmenylethanolamine species with polyunsaturated sn-2 substituents in earl y-passage INS-1 cells is similar to that of islets, but declines on serial passage. Such molecules might participate in exocytotic membrane fusion, an d late-passage INS-1 cells have reduced insulin secretory responses. Arachi donate supplementation induces a rise in the fraction of INS-1 cell GPE lip ids with polyunsaturated sn-2 substituents and partially restores responses to insulin secretagogues by late-passage INS-1 cells, but does not further amplify secretion by early-passage cells. Effects of extracellular free fa tty acids on beta-cell phospholipid composition and secretory responses cou ld be involved in changes in beta-cell function during the period of hyper- free fatty acidemia that precedes diabetes mellitus. (C) 2000 Elsevier Scie nce B.V. All rights reserved.