A new approach to reduce the level of reactive oxygen species (ROS) in human semen by using N-acetyl-L-cysteine (NAC) was evaluated. Semen samples were incubated with or without NAC (1.0 mgml-') at room temperature. The chemiluminescent signal of the oxidation of lumi-no1 was detected by means of an MTP reader after 0, 20, 40, 60 and 120 min, respectively, using 200 pM luminol. In addition, the dose-dependent action of NAC (0.1, 1.0 and 5.0 mg ml-') and the influence of NAC on functional sperm parameters (motility and acrosome reaction) were studied.ROS levels decreased significantly after 20 min incubation with NAC. This reduction was greater in the high ROS group (>30000 counts/107 viable sperm at t = 0) than in the low ROS group (<30000). In addition, a marked dosedependence of NAC was observed. Concerning sperm function, total sperm motility improved after incubation with NAC, but no significant change was observed with respect to the acrosome reaction.NAC (at concentrations of 1 .O mg ml-') significantly reduced ROS in human semen and showed the possibility of improving impaired sperm function. After further testing NAC might be useful for the treatment of male infertility patients.

Summary. Many studies have examined the impact of genital tract infections on male fertility; however, the effect of bacteriospermia on sperm quality is still controversial. Bacterial infections are more frequently found in semen samples from asymptomatic infertile patients than in those from fertile men. Bacteriospermia is also a common problem of male partners from couples undergoing IVF. Therefore, the effects of microorganisms on human sperm acrosome reaction of oocytes have been studied in vitro and in vivo. Incubation of spermatozoa with Escherichia coli or Mycoplasma hominis in vitro resulted in reduced sperm motility and inducibility of acrosome reaction (ΔAR) after exposure to calcium ionophore A23187. To show possible effects of E. coli and mycoplasma species on sperm functions in vivo, data from 488 patients were evaluated, in whose ejaculates microbiological examinations and determinations of acrosome reaction after exposure to low temperature had been performed. U. urealyticum and E. coli were found in semen samples from 52 and 31 men, respectively. M. hominis was only present in a minor number of samples and was not included in this study. Semen concentrations of E. coli and U. urealyticum ranged between 500–100000 cfu x ml−1 and 100–80000 cfu x ml−1. No correlation was found between ΔAR and concentration of bacteria (Spearman rank correlation coefficient, E. coli: r‐0.081, P = 0.6644; U. urealyticum: r = ‐0.081, P = 0.5698). In 69% of cases with U. urealyticum infection and reduced inducibility of acrosome reaction, this sperm function was normal after antibiotic therapy. However, improvement of acrosomal function may only be due to intra‐individual variations of acrosome reaction. While E. coli and mycoplasma species affect sperm functions in vitro, the present data and a review of the literature fail to demonstrate similar effects in vivo.

It is now widely accepted that the higher levels of reactive oxygen species (ROS) produced by damaged or deficient spermatozoa are associated with a loss of motility and a decreased capacity for sperm-oocyte fusion. Furthermore, earlier studies show, under physiological conditions, that some ROS may be involved in capacitation and hyperactivation of human spermatozoa. We measured ROS levels, acrosome reaction (AR) and acrosin activity (AA) in semen samples from suspected subfertile men to reveal the influence of ROS on AR and AA of human spermatozoa. Semen samples were obtained from 60 patients. Samples with > or = 1 x 10(6) leukocytes/mL were excluded from the study. ROS production was determined using a chemiluminescence technique. AR was determined using a triple stain technique. The percentage of acrosome-reacted spermatozoa after low temperature induction of the AR (test value), and the inducibility of AR (= the difference between the test value and the control), were calculated. The AA was analysed by determining the proteolytic potential of spermatozoa on gelatin plates. The mean halo diameter and percentage of halo formation in each sample were measured as AA parameters. Scatter plots of ROS levels and AR parameters showed that the percentage of acrosome reacted spermatozoa and AR inducibility were better in samples with low rather than high ROS levels. On the other hand, there were no apparent similarities between ROS and the AA parameters. Therefore, the percentage of acrosome-reacted spermatozoa and AR inducibility were significantly higher in the low than in the high ROS group (p = 0.028, p = 0.0001, respectively). In addition, there was no significant difference in AA parameters between groups. These findings suggest that lower ROS in semen may have a role in AR but excessive ROS may exert a negative influence on AR, while ROS in semen has no relationship to AA.