Deterioration of spermatozoal plasma membrane is associated with an increase of sperm lyso-phosphatidylcholines

Spermatozoa with plasma membranes that lost their asymmetry or permeability for larger molecules can be identified by binding of annexin V to membrane phosphatidylserine ( PS). Paramagnetic annexin-V-conjugated microbeads (AN-MB) can be used to eliminate these spermatozoa by magnetic activated cell sorting ( MACS). Semen samples of six healthy volunteers with normal spermiogram parameters were divided into two sperm fractions by MACS as a function of bound AN-MB, and their individual lipid compositions were examined by matrix-assisted laser desorption and ionisation time-of-flight mass spectrometry (MALDI-TOF MS). As a model system, liposomes composed of phosphatidylcholines ( PC) from egg yolk were digested by phospholipase A2 (PLA2). The MALDI-TOF mass spectra of organic extracts of both sperm subpopulations differed significantly. The ratio between lyso-phosphatidylcholine LPC 16 : 0 and PC 16 : 0/22 : 6 was approximately 2.5-4.7-fold higher (median 2.9) in the sperm group binding AN-MB than in spermatozoa with intact membrane unable to bind AN-MB. The ratio between LPC 22 : 6 and PC 16 : 0/22 : 6 was also enhanced in the spermatozoa with impaired membrane structure ( factor in the range: 1.9-3.9; median 2.6). These alterations corresponded to the effects of PLA2 on artificial phospholipids. It is concluded that spermatozoa with deteriorated membrane and exposed PS are characterized by an increased lyso-phosphatidylcholine content that is likely generated by phospholipases.