Clinical aspects of sperm DNA fragmentation detection and male infertility

Over the past 25 years, various methods have been developed to measure sperm DNA strand breaks in situ. Currently, there are four major tests of sperm DNA fragmentation, including the Comet, Tunel, sperm chromatin structure assay (SCSA) and the acridine orange test (AOT). The Comet assay is a light microscope technique where the sperm cells are mixed with melted agarose and then placed on a glass slide. The cells are lysed and then subjected to horizontal electrophoresis. The Tunel assay, another light microscope technique, transfers labeled nucleotide to the 3′OH group of a broken DNA strand with the use of terminal deoxynucleotidyl transferase. The fluorescence intensity of each scored sperm is determined as a “yes” or “no” for sperm on a light microscope slide or by channels of fluorescent intensity in a flow cytometer. The light microscope-based AOT, uses the metachromatic properties of acridine orange to stain sperm cells. The SCSA treats sperm with low pH to denature DNA at the sites of DNA strand breaks, followed by acridine orange (AO) staining of green for native DNA and red for denatured DNA as measured by flow cytometry (FCM) as well as % sperm with high DNA stainability (HDS: immature sperm with intact DNA related to decreased fertilization rates). The SCSA method has defined a 27–30% DNA fragmentation index (DFI) as the point in which a man is placed into a statistical category of taking a longer time to in vivo pregnancy, intra uterine insemination (IUI) and more routine in vitro fertilization (IVF) cycles or no pregnancy. Current data suggest that intracytoplasmic sperm injection (ICSI) may help overcome the diminished pregnancy prognosis with high DFI over the other ART or natural methods.