Is there a relationship between the chromatin status and DNA fragmentation of boar spermatozoa following freezing-thawing?

In this study a radioisotope method, which is based on the quantitative measurements of tritiated-labeled actinomycin D ((3)H-AMD) incorporation into the sperm nuclei ((3)H-AMD incorporation assay), was used to assess the chromatin status of frozen-thawed boar spermatozoa. This study also tested the hypothesis that frozen-thawed spermatozoa with altered chromatin were susceptible to DNA fragmentation measured with the neutral comet assay (NCA). Boar semen was diluted in lactose-hen egg yolk-glycerol extender (L-HEY) or lactose ostrich egg yolk lipoprotein fractions-glycerol extender (L-LPFo), packaged into aluminum tubes or plastic straws and frozen in a controlled programmable freezer. In Experiment 1, the chromatin status and DNA fragmentation were measured in fresh and frozen-thawed spermatozoa from the same ejaculates. There was a significant increase in sperm chromatin destabilization and DNA fragmentation in frozen-thawed semen as compared with fresh semen. The proportions of spermatozoa labeled with (3)H-AMD were concurrent with elevated levels of sperm DNA fragmentation in K-3 extender, without cryoprotective substances, compared with L-HEY or L-LPFo extender. Regression analysis revealed that the results of the (3)H-AMD incorporation assay and NCA for frozen-thawed spermatozoa were correlated. Boars differed significantly in terms of post-thaw sperm DNA damage. In Experiment 2, the susceptibility of sperm chromatin to decondensation was assessed using a low concentration of heparin. Treatment of frozen-thawed spermatozoa with heparin revealed enhanced (3)H-AMD binding, suggesting nuclear chromatin decondensation. The deterioration in post-thaw sperm viability, such as motility, mitochondrial function and plasma membrane integrity, was concurrent with increased chromatin instability and DNA fragmentation. This is the first report to show that freezing-thawing procedure facilitated destabilization in the chromatin structure of boar spermatozoa, resulting in an unstable DNA that was highly susceptible to fragmentation.

Fraser L ，Strzezek J 《THERIOGENOLOGY》

Effect of different procedures of ejaculate collection, extenders and packages on DNA integrity of boar spermatozoa following freezing-thawing.

Whole ejaculate or sperm-rich fraction, collected from four sexually mature boars, was frozen in an extender containing lactose-hen egg yolk with glycerol (lactose-HEY-G) or extender containing lactose, lyophilized lipoprotein fractions isolated from ostrich egg yolk and glycerol (lactose-LPFo-G), and Orvus Es Paste, respectively. The sperm samples were also frozen in a standard boar semen extender (Kortowo-3), without the addition of cryoprotective substances. Sperm DNA integrity was assessed using a modified neutral comet assay. Sperm characteristics such as motility, plasma membrane integrity (SYBR-14/PI), mitochondrial function (rhodamine 123) and acrosome integrity were monitored. Freezing-thawing caused a significant increase (P<0.05) in sperm DNA fragmentation, irrespective of the procedures of ejaculate collection and extender type. Sperm DNA fragmentation was significantly lower (P<0.05) in the whole ejaculate compared with the sperm-rich fraction, indicating that spermatozoa maintained in the whole seminal plasma prior to its removal for freezing-thawing procedure were less vulnerable to cryo-induced DNA fragmentation. Furthermore, spermatozoa frozen in lactose-HEY-G or lactose-LPFo-G extender exhibited lower (P<0.05) DNA fragmentation than those frozen in the absence of cryoprotective substances. The levels of sperm DNA damage, as expressed by comet tail length and tail moment values, were significantly higher (P<0.05) in sperm samples frozen in the absence of cryoprotective substances. The deterioration in post-thaw sperm DNA integrity was concurrent with reduced sperm characteristics. It can be suggested that evaluation of DNA integrity, coupled with different sperm characteristics such as motility, plasma membrane integrity and mitochondrial function, may aid in determining the quality of frozen-thawed boar semen.

Fraser L ，Strzezek J 《ANIMAL REPRODUCTION SCIENCE》

Effects of freezing-thawing on DNA integrity of boar spermatozoa assessed by the neutral comet assay.

A modified version of the neutral comet assay was employed to evaluate the effect of the freezing-thawing process on boar-sperm DNA integrity. The sperm-rich fractions were collected from four mature boars and frozen into aluminium tubes and straws after extension in lactose-hen egg yolk-glycerol extender (lactose-HEY-G) or an extender containing lactose, lyophilized lipoprotein fractions extracted from ostrich egg yolk and glycerol (lactose-LPFo-G). The semen samples were also frozen in a standard boar semen extender (Kortowo-3), without the addition of cryoprotective substances. Post-thaw sperm motility and plasma membrane integrity, assessed by SYBR-14/PI and Hoechst 33258 stains, declined (p < or = 0.05) with a corresponding increase (p < or = 0.05) in sperm DNA damage, regardless of the extender type and packaging material. Spermatozoa frozen in lactose-HEY-G or lactose-LPFo-G extender showed lower (p < or = 0.05) DNA damage than those frozen in the absence of cryoprotective substances. The addition of HEY or LPFo to the freezing extender helped reduce the rate of cryo-damage to sperm DNA, which varied among the boars. Inter-boar variations in post-thaw DNA damage were more pronounced in sperm samples frozen in lactose-HEY-G or lactose-LPFo-G extender. The results of this study show that the freezing-thawing process affects the DNA integrity of boar spermatozoa, irrespective of the extender type and packaging material. Furthermore, the use of whole hen egg yolk and ostrich lyophilized lipoprotein fractions in the freezing extender gave similar results regarding sperm DNA integrity. It can be concluded that the neutral comet assay can be used in conjunction with routine sperm parameters for assessment of post-thaw quality of boar semen.

Fraser L ，Strzezek J 《REPRODUCTION IN DOMESTIC ANIMALS》

Comparison of post-thaw DNA integrity of boar spermatozoa assessed with the neutral comet assay and Sperm-Sus Halomax test kit.

In this study, we tested the hypothesis whether the neutral Comet assay (NCA) and the Sperm-Sus-Halomax (SSH) test kit could provide similar measurements of post-thaw DNA fragmentation of boar spermatozoa. Whole ejaculates or sperm-rich fractions of boar semen were frozen in an extender containing lactose, lipoprotein fractions isolated from ostrich egg yolk (LPFo), glycerol (lactose-LPFo-G) or in a standard boar semen extender (K3), without the addition of cryoprotective substances. In all boars, both the NCA and SSH test showed similar levels of post-thaw sperm DNA fragmentation in samples of the same ejaculates, regardless of the ejaculate collection procedure and extender. Yet, the levels of post-thaw sperm DNA damage, detected by the NCA and SSH test, were more accentuated in spermatozoa frozen in the absence of cryoprotective substances. Both the NCA and SSH detected variations among individual boars in terms of post-thaw sperm DNA fragmentation. Agreement between the measurements of the NCA and SSH was confirmed by scatter plots of differences, suggesting that the DNA integrity tests could detect the same sperm populations, which were susceptible to cryo-induced DNA damage. The findings of this study indicate that the NCA and the SSH test are effective in detecting similar levels of sperm DNA fragmentation and reinforce their importance in the assessment of frozen-thawed boar semen quality.

Fraser L ，Parda A ，Filipowicz K ，Strzeżek J ... -  《-》

Dialysis of boar semen prior to freezing-thawing: its effects on post-thaw sperm characteristics.

Low-molecular weight components of the seminal plasma have a detrimental effect on sperm function. The present study was undertaken to evaluate the effect of the removal of low-molecular weight components by dialysis on sperm characteristics prior to and after freezing. Semen, collected from 5 boars, was extended in Kortowo-3 extender (K-3, Poland) and cooled for 3h (control non-dialysis) or dialyzed for 5h in semi-permeable dialysis bags of 12-14kDa molecular weight cut-off prior to freezing. The semen samples were diluted in lactose-hen egg yolk-glycerol extender (lactose-HEY-G) or lactose-lyophilized lipoprotein fractions-glycerol extender (lactose-LPFo-G), packaged into aluminum tubes and frozen in a controlled programmable freezer. Pre-frozen and frozen-thawed spermatozoa were evaluated for motility, plasma membrane (SYBR-14 and propidium iodide) and acrosome integrity, mitochondrial function (Rhodamine 123) and ATP content. The results of the study showed that dialysis significantly improved the sperm characteristics prior to freezing. Dialysis enhanced (P<0.05) post-thaw sperm motility, plasma membrane integrity and mitochondrial function, but had no significant effect (P>0.05) on recovery of spermatozoa with intact acrosomes. Furthermore, dialyzed spermatozoa exhibited higher (P<0.05) ATP content compared with the control after freezing-thawing. Consistent inter-boar variability was detected mainly in dialyzed semen following freezing-thawing. These results indicated that the improvement in sperm quality characteristics prior to freezing and the post-thaw sperm recovery were due to the removal of low-molecular weight components from the seminal plasma. It can be suggested that dialysis is effective in improving the post-thaw quality of boar spermatozoa and has also great practical importance in improving the protocols for cryopreservation of semen. Dialysis may also contribute to a better understanding of different mechanisms underlying cryo-induced damage to boar spermatozoa.

Fraser L ，Dziekońska A ，Strzezek R ，Strzezek J ... -  《THERIOGENOLOGY》