Dynamics of sperm DNA damage in fresh versus frozen-thawed and gradient processed ejaculates in human donors

The rate of increase of sperm DNA fragmentation (rsDF) in fresh and frozen-thawed and processed sperm samples after a density gradient for sperm selection was analysed after 0, 0.5, 1.5, 4.5, 6, 24, 48 and 72 h of incubation at 37 degrees C, in five donors with proven fertility. The results showed that: (i) sperm DNA fragmentation (sDF) at baseline in fresh samples (14.3 +/- 3.3) was lower than that obtained after freeze-thawing and selection (19.4 +/- 4.1), significant differences; (ii) After 6 h of incubation the mean sDF in fresh samples (24.2 +/- 10.2) was significantly lower than that in frozen-thawed samples (45.3 +/- 7.1); (iii) Subsequently, the rsDF in fresh semen samples was 1.6% per h after 6 h of incubation, while after thawing and selection the rsDF was 4.3% per h; The tendency to increase in sDF showed high R-2 values (R-2 = 0.90) for exponential functions in case of fresh samples, whereas R-2 values for linear functions were higher after sperm selection (R-2 = 0.97). These results indicate that differences in sperm DNA fragmentation dynamics before and after storage are an important issue that must be considered for storage of sperm to be used for artificial reproduction techniques.