Biomembranal Myristoyl-Phosphatidylcholine as a Potential Target of the Cell Injury Activity of Vitamin D Decomposition Products in Eukaryotic Cells.

Background: Vitamin D decomposition products target a myristic acid sidechain of the predominant glycerophospholipid constructed in the biomembranes of Helicobacter pylori, causing gastric cancer in humans, and disrupt the membrane structure, followed by bacteriolysis. No earlier studies, however, elucidate whether vitamin D decomposition products interact with the glycerophospholipids that construct the eukaryotic biomembranes and confer whatever cell disorders.

Methods: A gastric cancer cell line, MKN45, and a non-cancer cell line, Vero, were used in this study. Cell injury activities of vitamin D decomposition products (VDP1 and VD2-1) and a VDP1 derivative (VD3-7) were examined by the 3-(4,5-di-methylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Identification of a glycerophospholipid was performed by ¹H-nuclear magnetic resonance (NMR). Fatty acid composition and glycerophospholipid molecular species were analyzed by gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/mass spectrometry (LC/MS), respectively. Structure collapse-induction activity of VDP1, VD2-1 and VD3-7 to glycerophospholipid vesicles was examined using the pigment-containing lamellar vesicles.

Results: MKN45 cells exhibited higher susceptibility to the cell injury activity of VDP1 and VD2-1 than Vero cells. In the analysis of biomembrane lipids, the glycerophospholipid phosphatidylcholine (PC) molecular species turned out to conspicuously differ between MKN45 cells and Vero cells. Contents of myristoyl-PC were higher in MKN45 cells than in Vero cells, while contents of oleoyl-PC were higher in Vero cells than in MKN45 cells. Meanwhile, the contents of palmitoyl- and palmitoleoyl-PC were almost equal between these cells. We next examined the structure collapse-induction activity of VDP1, VD2-1 and VD3-7 on the lamellar vesicles prepared with dimyristoyl-PC, dipalmitoyl-PC and dioleoyl-PC. The vitamin D decomposition products and a VDP1 derivative induced the structural collapse of dimyristoyl- and dipalmitoyl-PC lamellar vesicles but almost no structural collapse of dioleoyl-PC lamellar vesicles. These results suggest that the contents of myristoyl-PC in biomembranes are associated with the susceptibility of eukaryotic cells to the cell injury activity of VDP1, VD2-1 and VD3-7. In addition, no VD3-7 affected the viability of Vero cells and selectively decreased the viability of MKN45 cells.

Conclusions: In the future, we will expect to be capable of developing novel antitumor agents targeting the myristic acid sidechain of biomembranal PC using a vitamin D decomposition product as the fundamental structure.