Sperm chromatin and DNA integrity, methyltransferase mRNA levels, and global DNA methylation in oligoasthenoteratozoospermia / 대한생식의학회지

OBJECTIVE: To investigate sperm chromatin/DNA integrity, global DNA methylation, and DNMT mRNA transcription in men with oligoasthenoteratozoospermia (OAT) compared with normozoospermic men. METHODS: Semen samples from 32 OAT patients who comprised the case group and 32 normozoospermic men who comprised the control group were isolated and purified using a standard gradient isolation procedure according to World Health Organization criteria. DNMT1, DNMT3A, and DNMT3B transcripts were then compared between groups using real-time quantitative reverse-transcription polymerase chain reaction. Global DNA methylation in sperm was determined by an enzyme-linked immunosorbent assay. Protamine deficiency and the proportion of apoptotic spermatozoa were evaluated using chromomycin A3 (CMA3), aniline blue (AB), and toluidine blue (TB) staining, as well as the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. The p-values < 0.05 were considered to indicate statistical significance. RESULTS: Significantly higher proportions of AB+, TB+, CMA3+, and TUNEL+ spermatozoa, as well as DNMT3A and DNMT3B transcription, were found in the OAT group. Positive correlations were detected between sperm parameters, DNA/chromatin damage, and DNMT3A and DNMT3B transcripts. Global DNA methylation was significantly higher in the OAT patients and had a significant correlation with abnormal results of all sperm chromatin integrity tests, but was not associated with DNMT1, DNMT3A, or DNMT3B expression. CONCLUSION: Oligoasthenoteratozoospermic men showed abnormal sperm parameters, abnormal chromatin/DNA integrity, and a higher global DNA methylation rate, as well as overexpression of DNMT mRNA.

etiologies of sperm DNA abnormalities in male infertility: an assessment and review

The sperm DNA damage may occur in testis, genital ducts, and also after ejaculation. Mechanisms altering chromatin remodeling are abortive apoptosis and oxidative stress resulting from reactive oxygen species. Three classifications of intratesticular, post-testicular, and external factors have been correlated with increased levels of sperm DNA damage which can affect the potential of fertility. Alcohol consumption may not increase the rate of sperm residual histones and protamine deficiency; however, it causes an increase in the percentage of spermatozoa with DNA fragmentation and apoptosis. In a medical problem as spinal cord injury, poor semen parameters and sperm DNA damage were reported. Infection induces reactive oxygen species production, decreases the total antioxidant capacity and sperm DNA fragmentation or antigen production that lead to sperm dysfunctions and DNA fragmentation. While reactive oxygen species generation increases with age, oxidative stress may be responsible for the age-dependent sperm DNA damage. The exposing of reproductive organs in older men to oxidative stress for a long time may produce more DNA-damaged spermatozoa than youngers. Examining the sperm chromatin quality in testicular cancer and Hodgkin's lymphoma patients prior to chemotherapy demonstrated the high incidence of DNA damage and low compaction in spermatozoa at the time of diagnosis. In chemotherapy cycles with genotoxic agents in cancer patients, an increase in sperm DNA damage was shown after treatment. In overall, those factors occurring during the prenatal or the adult life alter the distribution of proteins associated with sperm chromatin induce changes in germ cells which can be detected in infertile patients

Etiologies of sperm oxidative stress

Sperm is particularly susceptible to reactive oxygen species [ROS] during critical phases of spermiogenesis. However, the level of seminal ROS is restricted by seminal antioxidants which have beneficial effects on sperm parameters and developmental potentials. Mitochondria and sperm plasma membrane are two major sites of ROS generation in sperm cells. Besides, leukocytes including polymer phonuclear [PMN] leukocytes and macrophages produce broad category of molecules including oxygen free radicals, non-radical species and reactive nitrogen species. Physiological role of ROS increase the intracellular cAMP which then activate protein kinase in male reproductive system. This indicates that spermatozoa need small amounts of ROS to acquire the ability of nuclear maturation regulation and condensation to fertilize the oocyte. There is a long list of intrinsic and extrinsic factors which can induce oxidative stress to interact with lipids, proteins and DNA molecules. As a result, we have lipid peroxidation, DNA fragmentation, axonemal damage, denaturation of the enzymes, over generation of superoxide in the mitochondria, lower antioxidant activity and finally abnormal spermatogenesis. If oxidative stress is considered as one of the main cause of DNA damage in the germ cells, then there should be good reason for antioxidant therapy in these conditions