Effect of pentoxifylline on the intrinsic swimming forces of human sperm assessed by optical tweezers

It is still controversial whether in vitro exposure of sperm to pentoxifyll ine increases sperm motility and force, which is defined as the product of velocity by beat frequency of the tail. Laser optical tweezers have been su ccessfully used in the past to evaluate sperm force in basal conditions. Th e aim of this prospective study was to determine whether exposure of human sperm to pentoxifylline has any effect on sperm intrinsic forces. Twelve he althy subjects undergoing routine semen analysis were enrolled in the study . Ten exhibited normal semen parameters, 2 exhibited asthenozoospermia. Eac h semen specimen was washed and, after swim-up, resuspended in human tubal fluid (HTF) and divided into 2 aliquots. One aliquot was incubated with pen toxifylline for 30 minutes (final concentration = 3.6 mM); the second aliqu ot, without pentoxifylline, served as a control. After 30 minutes the pento xifylline-treated aliquot was divided into 2 portions, 1 of which was washe d to remove the pentoxifylline, the other was left in prolonged coincubatio n with the chemical. The main outcome was the measurement of sperm intrinsi c force in milliwatts (mW), which was assessed by means of a noninvasive in frared laser optical trap created by a continuous wave, 1064-nm Nd:YAG lase r beam directed in an inverted microscope. Exposure of sperm to pentoxifyll ine consistently increased sperm relative escape force from the laser optic al trap. The increase ranged from 33% to 154% over baseline force compared with controls. The average absolute increase in sperm force rose from 37 mW to 79 mW (P < .05). Specimens with sperm having an initial low relative es cape force gained the highest relative increase. The effect of pentoxifylli ne on sperm force, already apparent after 5 minutes, reached a peak at 30 m inutes and persisted for up to 3 hours in sperm that were left in coincubat ion and in those on which the pentoxifylline had been washed off. In conclu sion, pentoxifylline significantly increases sperm intrinsic relative force in normozoospermic and asthenozoospermic samples. This experiment confirms that optical tweezers can provide an accurate determination of sperm force in in vitro conditions. Clinical data must now establish whether a documen ted increase in sperm force is an important parameter for assessing sperm f ertilizing capacity.