Lipid composition of the normal human brain: gray matter, white matter, and myelin

Gray matter, white matter, and myelin were isolated from the frontal lobes of humans aged 10 months, 6 yr, 9 yr, and 55 yr and the lipid compositions of each were determined. Myelin had a much higher lipid content (78–81% of the dry weight) than white matter (49–66%) or gray matter (36–40%). Myelin contained much higher molar percentages of cerebroside and cerebroside sulfate, slightly higher molar percentages of cholesterol, and lower molar percentages of ethanolamine glycerophosphatides and choline glycerophosphatides than gray matter. The molar percentages of serine glycerophosphatides and sphingomyelin were about the same in each tissue.The aldehyde content of glycerophosphatides, expressed as molar percentage of the total lipoidal residues in each lipid, were as follows: ethanolamine glycerophosphatides from myelin 40–50%; ethanolamine glycerophosphatides from gray matter 21–27%; serine glycerophosphatides from myelin 21–36%; serine glycerophosphatides from gray matter 0.3–3.8%. Choline glycerophosphatides from either tissue contained only traces of aldehydes.The extra-myelin portion of white matter had a lipid composition that was very similar to that of myelin, but quite different from that of gray matter.Assuming a molecular weight of 28,000 for myelin protein(s), it was calculated that for each protein molecule in human myelin there are 186 lipid molecules, 111 of which are polar lipids and 75 of which consist of cholesterol. The over-all molar ratios of the polar lipids are phosphatidal ethanolamine:serine glycerophosphatides:choline glycerophosphatides:sphingomyelin:cerebroside:cerebroside sulfate:ceramide:uncharacterized lipids 25:9:20:9:29:7:3:9. It was calculated that the molar ratio of protein amino acids to polar lipids in human myelin is 2.38 to 1.