Table 1.
Characteristics of the human donors, tissue collection, and sample analyzes.
Figure 1.
Structure of conventional phospholipids and plasmalogens.
Conventional phospholipids such as phosphatidyl-choline and phosphatidyl-etanolamine contain ester bonds in order to link R1 and R2 acyl- moieties at the sn-1 and sn-2 positions of glycerol, respectively. As for ethanolamine- and choline- plasmalogens, they have a vinyl ether bond at the sn-1 position of the glycerol backbone to link alkenyl- moieties and an ester bond at the sn-2 position to link acyl- residues.
Table 2.
Fatty acid composition of total phospholipids purified from erythrocytes, retinas and optic nerves from human donors evaluated by gas chromatography (% of total fatty acids).
Figure 2.
Selected significant associations between erythrocyte and retinal or optic nerve lipids after gas chromatographic analyses.
Erythrocyte arachidonic acid (C20:4n-6) was positively associated with retinal C20:4n-6 (rSpearman = 0.833, P<0.01) and optic nerve C20:4n-6 (rSpearman = 0.828, P = 0.04). Erythrocyte docosahexaenoic acid (C22:6n-3, DHA) was negatively associated with retinal DHA (rSpearman = −0.733, P = 0.02) whereas no significant association emerged between erythrocyte and optic nerve levels of plasmalogens (evaluated by dimethylacetals, DMA).
Table 3.
Statistically significant associations between erythrocyte and optic nerve or retinal phospholipid fatty acid compositions evaluated by gas chromatography.
Figure 3.
LC-ESI-MS normal-phase chromatogram of the lipid extract from human retina.
The retention times of phosphatidyl-ethanolamine (PE), phosphatidyl-inositol (PI), phosphatidyl-serine (PS), phosphatidyl-choline (PC), sphingomyelin (SM), and lyso-phosphatidyl-choline (LPC) classes were of 7–8.5 min, 11–12 min, 12–14 min, 15.5–22 min, and 23–27.5 min, respectively. The mass spectrometer was operated under full scan in the negative ion mode from 0 to 15 min and in the positive ion mode from 15 min to 40 min.
Figure 4.
Positive-ion HPLC-ESI-MS Mass spectra of total phosphatidyl-choline fraction collected from human neural retina.
A.) optic nerve (B.) and red blood cells (C.), by scanning for precursors at m/z 184 amu in the positive mode. Positive-ion HPLC-ESI-MS Mass spectra of total PE fraction collected from human neural retina D.), optic nerve (E.) and red blood cells (F.), using neutral loss scan at 141 amu in the positive mode.
Figure 5.
Erythrocyte PC16:0/20:4 as a possible marker of a pool of retinal VLC-PUFA.
A): In the retina, VLC-PUFA accounted for about 25% of retinal PC species esterified to DHA, themself representing 11% of retinal total PC and PlsC. B): PC34:6/22:6, PC36:6/22:6, and PC36:5/22:6 were the longest and the most unsaturated VLC-PUFA in the retina. These three species accounted for 22.7% of total retinal VLC-PUFA. C) This pool of retinal VLC-PUFA was negatively associated with erythrocyte PC16:0/20:4 (rSpearman = −0.783, P = 0.01). Abbreviations of individual PC species are as follows: position on the glycerol backbone as shown as sn-1/sn-2 of the fatty alcohol radicals (abbreviated as number of carbons: number of double bonds).
Table 4.
Statistically significant associations between erythrocyte and retinal individual choline-phospholipid concentrations evaluated by liquid chromatography coupled with tandem mass spectrometry.
Table 5.
Statistically significant associations between erythrocyte and optic nerve individual choline-phospholipid concentrations evaluated by liquid chromatography coupled with tandem mass spectrometry.
Figure 6.
Identification of circulating indexes of retinal PE esterified to DHA.
A) PE with DHA accounted for 63% of total retinal PE species. Within these entities, two different pools of molecules were of concern as they represented 79% and 89% of the total PE with 22:6. B) PlsE18:0/20:4 in erythrocytes was negatively associated to the first group represented by PE18:0/22:6+PE18:1/22:6+PE20:3/22:6 (rSpearman = −1.000, P<0.001). C) The second fraction of retinal PE with 22:6 represented by PE16:0/22:6+PE18:0/22:6+PE18:1/22:6 was positively associated to PE18:0/22:4 (black circles, rSpearman = 0.950, P = 0.04) and PE18:0/20:4+PE18:0/22:5 (open circles, rSpearman = −0.995, P = 0.01) in erythrocytes. Abbreviations of individual PE species are as follows: position on the glycerol backbone as shown as sn-1/sn-2 of the fatty alcohol radicals (abbreviated as number of carbons: number of double bonds).
Table 6.
Statistically significant associations between erythrocyte and retinal individual ethanolamine-phospholipid concentrations evaluated by liquid chromatography coupled with tandem mass spectrometry.
Figure 7.
PlsE16:0/22:6 and PlsE16:0/22:4 as indexes of a pool of optic nerve PlsE.
A) PlsE18:0/22:5, PlsE16:0/20:3, PlsE16:0/20:4, PlsE18:0/20:4, and PlsE16:0/22:4 represented 19% of optic nerve PlsE. B) This group of optic nerve PlsE was negatively associated to PlsE16:0/22:6 and PlsE16:0/22:4 in erythrocytes (rSpearman = −0.988, P<0.001). Abbreviations of individual PlsE species are as follows: position on the glycerol backbone as shown as sn-1/sn-2 of the fatty alcohol radicals (abbreviated as number of carbons: number of double bonds).
Table 7.
Statistically significant associations between erythrocyte and optic nerve individual ethanolamine-phospholipid concentrations evaluated by liquid chromatography coupled with tandem mass spectrometry.