Search

A previous cytochemical study revealed that chromatin alterations could be induced in frozen-thawed human sperm. In order to evaluate the biological consequences of such chromatin alterations, we evaluated the relationship between these chromatin alterations and the drastic decrease or loss of sperm fertilizing ability after freeze-thawing. Using acridine orange staining and Feulgen-DNA quantitative microspectrophotometry, the nuclear variables of sperm were compared using samples which had either recovered, or lost their fertilizing ability after freezing-thawing during artificial inseminations, despite good post-thaw motility. There was a clear decrease in Feulgen-DNA content and nuclear surface values in sperm which exhibited a loss of fertilizing ability. Thus freeze-thawing may alter the DNA/nuclear protein relationships and impair the fertilizing ability of human sperm.

In vitro capacitation of human spermatozoa is commonly evaluated by the progressive motility percent. However its effects on sperm chromatin have hardly been studied. Our aim was to determine the extent to which in vitro capacitation with two treatments (B2 or human follicular fluid) alters the chromatin of human spermatozoa, by using two analytical methods, acridine orange staining and Feulgen-DNA cytophotometric measures. Ejaculates were obtained from 23 men participating in our in vitro fertilization program, and several measurements were made on the same ejaculate for each subject. No alteration was observed for the percent of native DNA after capacitation in B2, but spermatozoa incubation during the same time in human follicular fluid was followed by a significant decrease of the percent of native DNA (P less than 0.01). Feulgen-DNA content significantly increased after capacitation in either B2 or follicular fluid (P less than 0.05, P less than 0.001 respectively), and so did sperm nuclear surface area (P less than 0.001). In this study we observed a negative correlation between Feulgen-DNA content and fertilization rate (P less than 0.02). Moreover, the greater effects on Feulgen-DNA content were observed in men with abnormal sperm, whose spontaneous percent of native DNA was lower (P less than 0.05) and Feulgen-DNA content higher (P less than 0.05) than in men with normal sperm. These results indicate that capacitation in B2 as well as in human follicular fluid may alter the chromatin stability of human spermatozoa. Such results suggest a partial decondensation state of human spermatozoa during in vitro capacitation. However, beyond some level of decondensation, the fertilizing ability could be altered.

Freezing-thawing effects on the nuclei of porcine and human spermatozoa were studied by determining native DNA percentage from fluorescence after acridine orange (AO) staining and by analyzing chromatin structure by a quantitative microspectrophotometric study of Feulgen-DNA complexes before and after freezing. The study of boar spermatozoa revealed no alteration in native DNA percentage after freezing. However, native DNA percentage decreased significantly in human spermatozoa. Feulgen-DNA content and sperm nuclear surface area decreased in both species after freezing. These results prompted us to hypothesize an overcondensation of sperm chromatin after freezing-thawing. This overcondensation may be related to the lower conception rates obtained with human and porcine semen after cryostorage via defective decondensation.

Cryopreservation and freezing-thawing effects on the fertilizing ability of human spermatozoa commonly are evaluated by post-thaw motility. Various studies have depicted the ultrastructural changes caused by freezing-thawing, yet the chromatin alterations have been studied very limitedly. Our aim was to determine the extent to which freezing-thawing alters the chromatin of human spermatozoa, using two analytical methods: acridine orange staining and Feulgen-DNA cytophotometric studies. Both methods revealed a dramatic effect of freezing-thawing on sperm chromatin: the native DNA content decreased as did the Feulgen-DNA content, and sperm surface area was reduced. These results indicate an effect on DNA, diminished accessibility for Feulgen, and a decrease in nuclear surface area and prompt us to hypothesize a relationship between an "overcondensation" state for sperm chromatin after freezing-thawing and a lower conception rate for human semen after cryostorage.