Associations between central and peripheral measures of phospholipid breakdown revealed by cerebral 31-phosphorus magnetic resonance spectroscopy andfatty acid composition of erythrocyte membranes

1. Abnormal neuronal membrane phospholipid metabolism is increasingly recog nized as being of central importance to a number of neuropsychiatric disord ers. Currently, two important indices of membrane phospholipid metabolism t end to be measured: the ratio of the areas of the phosphomonoester (PME) an d phosphodiester (PDE) peaks from in vivo cerebral phosphorus magnetic reso nance spectroscopy (P-31 MRS) studies; and erythrocyte membrane fatty acid concentrations. Thus far, there have been no studies comparing these two in dices to ascertain the extent to which they agree. 2. The authors measured these indices in nine normal adults. Spectral local ization was achieved using four-dimensional chemical shift imaging methods and erythrocyte membrane fatty acid concentrations (from blood samples take n at the time of scanning) were measured using gas liquid chromatography. 3. Levels of PDE (an index of phospholipid catabolism), measured using cere bral 31P MRS, were significantly correlated with reduced concentrations of the highly unsaturated fatty acids docosahexacnoic acid (DHA) (r = -0.68, p < 0.05) and eicosapentacnoic acid (EPA) (r = -0.78, p < 0.02). No signific ant correlations were found between peripheral concentrations of any highly unsaturated fatty acids and PME levels, nor between their essential fatty acid precursors and either PDE or PME levels. Other 31-phosphorus metabolit es also showed no significant correlations with the blood fatty acid measur es. 4. The correlations between central measures of PDE and peripheral measures of DHA and EPA provide validation of cerebral P-31 MRS as a non-invasive t echnique for the study of membrane phospholipid metabolism in vivo.