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 mellitus, and normal beta-cells are enriched in phospholipids with arachidonate as sn-2 substituent. Such molecules may play structural roles in exocytotic 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 phospholipid composition and secretion. INS-1 cell glycerophosphocholine (GPC) and glycerophosphoethanolamine (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 native islets. Palmitic acid supplementation induces little change in these INS-1 cell lipids, but supplementation with linoleate or arachidonate induces a large rise in the fraction of INS-1 cell GPC species with polyunsaturated 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 plasmenylethanolamine species with polyunsaturated sn-2 substituents in early-passage INS-1 cells is similar to that of islets, but declines on serial passage. Such molecules might participate in exocytotic membrane fusion, and late-passage INS-1 cells have reduced insulin secretory responses. Arachidonate supplementation induces a rise in the fraction of INS-1 cell GPE lipids 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 fatty acids on beta-cell phospholipid composition and secretory responses could be involved in changes in beta-cell function during the period of hyper-free fatty acidemia that precedes diabetes mellitus.
Ramanadham
S
S
Medicine Department Mass Spectrometry Facility, Division of Endocrinology, Diabetes, and Metabolism, Washington University School of Medicine, St. Louis, MO 63110, USA. sramanad@im.wustl.edu
Hsu
F
F
Zhang
S
S
Bohrer
A
A
Ma
Z
Z
Turk
J
J
D000818:Animals; D005227:Fatty Acids / Q000494:pharmacology*; D007328:Insulin / Q000032:analysis*; D007340:Insulinoma; D007515:Islets of Langerhans / Q000737:chemistry* / Q000378:metabolism; D013058:Mass Spectrometry / Q000379:methods; D010190:Pancreatic Neoplasms; D010743:Phospholipids / Q000737:chemistry*; D051381:Rats; D014407:Tumor Cells, Cultured
D005227:Fatty Acids; D007328:Insulin; D010743:Phospholipids