Relationship between chromatin ultrastructure and DNA fragmentation in human spermatozoa

Abstract

OBJECTIVE: To explore the relationship between the level of DNA fragmentation and the state of chromatin compaction in a population of severely teratozoospermic patients.DESIGN: Retrospective study.MATERIALS AND METHODS: A population of 77 patients with severe teratozoospermia (Kruger ≤4%) was studied by transmission electron microscopy (TEM) and the TUNEL assay for DNA fragmentation. The degree of chromatin compaction was evaluated on 100 sperm heads by TEM and DNA fragmentation was evaluated under epifluorescence microscopy in 500 sperm heads. Abnormal chromatin compaction was characterized by the percentage of hypodense areas of fibrillar or granular structure. When this percentage was ≤49% the incidence was considered low (Group I), and high when this percentage was ≥50 % (Group II). The presence of different conditions that affect fertility, such as varicocele, infections of the seminal pathway, immunologic factors, etc, was also taken into consideration. Statistical comparisons were performed by analysis of variance followed by Student's t-test.RESULTS: Mean value of DNA fragmentation in Group I was 9.2±6.9% and 15.4±13.3% in Group II (p<0.05). Within Group I, the values of DNA fragmentation in those patients that had conditions affecting spermatogenesis or epididymal sperm transit (10.1±7.5%) were not different from those present in patients without other andrological conditions (7.9±6.2%). When the same differences were compared within group II, the values were statistically different (18.0±14.4% vs. 10.0±8.9%, p<0.05).CONCLUSIONS: In conclusion, higher values of chromatin abnormalities are associated with increased levels of DNA fragmentation. This difference becomes more pronounced in the presence of other conditions that affect sperm quality. These results show that there is an association between high levels of chromatin abnormalities and an increased susceptibility to oxidative stress. OBJECTIVE: To explore the relationship between the level of DNA fragmentation and the state of chromatin compaction in a population of severely teratozoospermic patients. DESIGN: Retrospective study. MATERIALS AND METHODS: A population of 77 patients with severe teratozoospermia (Kruger ≤4%) was studied by transmission electron microscopy (TEM) and the TUNEL assay for DNA fragmentation. The degree of chromatin compaction was evaluated on 100 sperm heads by TEM and DNA fragmentation was evaluated under epifluorescence microscopy in 500 sperm heads. Abnormal chromatin compaction was characterized by the percentage of hypodense areas of fibrillar or granular structure. When this percentage was ≤49% the incidence was considered low (Group I), and high when this percentage was ≥50 % (Group II). The presence of different conditions that affect fertility, such as varicocele, infections of the seminal pathway, immunologic factors, etc, was also taken into consideration. Statistical comparisons were performed by analysis of variance followed by Student's t-test. RESULTS: Mean value of DNA fragmentation in Group I was 9.2±6.9% and 15.4±13.3% in Group II (p<0.05). Within Group I, the values of DNA fragmentation in those patients that had conditions affecting spermatogenesis or epididymal sperm transit (10.1±7.5%) were not different from those present in patients without other andrological conditions (7.9±6.2%). When the same differences were compared within group II, the values were statistically different (18.0±14.4% vs. 10.0±8.9%, p<0.05). CONCLUSIONS: In conclusion, higher values of chromatin abnormalities are associated with increased levels of DNA fragmentation. This difference becomes more pronounced in the presence of other conditions that affect sperm quality. These results show that there is an association between high levels of chromatin abnormalities and an increased susceptibility to oxidative stress.