Lipid analysis of human spermatozoa and seminal plasma by MALDI-TOF mass spectrometry and NMR spectroscopy - effects of freezing and thawing

Abstract

In the present study, the applicability of proton NMR spectroscopy and matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS) to the analysis of the lipid composition of human spermatozoa and seminal fluids as well as changes after cryopreservation of human spermatozoa was investigated. Whereas NMR spectra primarily indicated a high content of double bonds within the spermatozoa but no marked differences upon cryopreservation, MS detected intense peaks which could be assigned to phosphatidylcholines containing one docosahexaenoic and one palmitic or stearic acid residue (m/z=806 and 834). In contrast, the seminal plasma contained more saturated fatty acids and especially more sphingomyelin (SM). A freezing/thawing cycle markedly influences the lipid composition of spermatozoa. There was a diminution of phosphatidylcholines (16:0, 22:6 and 18:0, 22:6) and SM (16:0) and the appearance of lysophosphatidylcholines (16:0 and 18:0) and ceramide (16:0). These data demonstrate the release or activation of both phospholipase A(2) and sphingomyelinase in human spermatozoa due to the freezing/thawing cycle. These results were finally confirmed by experiments on the action of phospholipases on lipids containing docosahexaenoic acid.