The role of the male partner and sperm health in infertility, pregnancy loss, and the health of the offspring has been mostly unknown and presumed insignificant. The primary focus on improving in vitro fertilization (IVF) outcomes has been on oocyte quality, embryo culture, and uterine receptivity. Infertility testing for the male partner has historically been a screening semen analysis to check for sperm concentration, motility, and morphology primarily. Additional testing for the male partner typically is only performed if the semen analysis is severely abnormal, such as complete azoospermia. The clinical utility and availability of Sperm DNA fragmentation (SDF) testing has become more widely recognized in recent years. The incidence and implications of SDF has increased the popularity of testing. SDF has been shown to be more prevalent in men with certain lifestyle factors, such as smoking, but it is also prevalent in men with advanced paternal age, varicoceles and oligospermia.1–7. However, men with completely normal semen profiles can also have high SDF with no other factors.8,9 SDF testing currently is not routinely run as part of the screening infertility testing but is generally used for specific clinical scenarios such as repeat pregnancy loss and cycles.10 Unfortunately, these scenarios often follow adverse painful and emotionally difficult situations. Performing SDF assays, which are often covered by insurance, are affordable, and can be done from the patient’s home, could potentially save couples from adverse outcomes, emotional distress, and money spent on treatments with low chances of success. Elevated SDF has been shown to be associated with poor outcomes with natural conception and IUI. Not only does the chance of success decrease drastically, but the risk of pregnancy loss also increases. By choosing to move forward with IVF, the couple can save money, time, and the stress and heartache of unsuccessful treatments or miscarriage. SDF has been shown to decrease the success of IVF treatments as well. SDF is correlated with poor fertilization, poor embryo development, poor embryo quality, slower embryo morphokinetics, poor implantation rates, and increased pregnancy loss.11–18 The physician, based on the SDF results, may decide to look for possible causes and treat the male partner before treating the couple. However, due to the complexity of SDF, the cause is often unknown. Instead, the treatment plan may change, increasing the couples’ chance for a successful outcome.
There are different assays available that measure SDF through different methods. The one used in this study, Sperm DNA Fragmentation Assay (SDFA™, the acridine orange and flow cytometry as described in the SCSA© method, ReproSource), also is comprised of other useful components with clinical significance. These are Oxidative Stress Adducts (OSA™) and High DNA Stainability (HDS). The OSA is measured by a quantification of peroxidation of the lipids in the sperm membrane caused by oxidative stress. Some levels of oxidative stress are needed for normal sperm function, such as in the compaction of histones to protamine. However, abnormal levels of oxidative stress cannot only alter the sperm membrane and morphology, it can cause functional issues with the acrosome, and it can also disrupt the compaction of histones resulting in a high level of histone retention.19 HDS is a measurement of the percentage of cells with high levels of protamines.20 This may be indicative of immature sperm that have not completed the final stages of spermiogenesis and thus also may be aneuploid or have altered sperm function. Studies have found correlations between histone retention, oxidative stress, and men with infertility. The components of the SDFA measure the overall health of the sperm and are a powerful predictive tool for fertility treatment outcomes and should be routinely used as part of the diagnosis before the onset of treatment.
Reactive oxygen species (ROS) have been a significant focus when looking for the cause of SDF both in vivo and in vitro. The presence of ROS, both in the laboratory, induced by or in the body, and generally in the epididymis, causes DNA damage as well as functional damage to the sperm.21–24 ROS, such as oxygen, hydrogen peroxide, hydroxyl radicals, hypochlorous acid and nitric oxide, are highly reactive molecules with short half-lives.1,2,25,26 One of the greatest sources of ROS, particularly in men with infertility, is the immature sperm that fail to undergo apoptosis and give off high levels of ROS.25,27 Other endogenous sources of ROS are mitochondrial respiration and the by-products of different enzymatic systems such as NADPH oxidase.28 ROS can indirectly cause sperm damage by activating sperm endonucleases and caspases, which are highly efficient at initiating sperm DNA damage.1–3,28
Many of the ROS that cause SDF are from exogenous sources such as chemotherapy, radiation, ultraviolet lights, cigarette smoking, daily alcohol consumption, drugs such as acetaminophen or antidepressants, air pollution, chemicals in products that we consume, and many sources yet to be determined.1–3,29−31 Studies have shown that the cytotoxic effects of cancer treatments will affect the level of SDF before and after treatment and can lead to decreased fertility and even complete azoospermia. Certain factors such as age, smoking, and obesity have been strongly correlated with elevated SDF. The mechanisms of how these occur can be a combination of increased ROS and apoptosis to heat stress and other mechanisms that are still unknown.1–3,26 Alcohol consumption also has been shown to have deleterious effects on sperm parameters though much is still unknown about SDF.32–34 In a meta-analysis by Ricci et al. in 2016, it was concluded that alcohol’s effects on sperm parameters were dependent on the frequency of consumption, and there were significant correlations with daily alcohol consumption and SDF, whereas occasional intake had no correlation with SDF.32 SDF levels can change rapidly based on the health and lifestyle factors even with the length of time between ejaculations. The abstinence period, longer than the recommended 2–5 days, will increase SDF as sperm in the epididymis are exposed to ROS.1–3
In addition to these lifestyle factors and exposures, the way the sperm is handled in the IVF laboratory can also greatly increase SDF. In 2013, Rougier et al. determined that SDF levels significantly decreased after processing over gradient, but the SDF index would increase to abnormal levels after two hours of incubation or 1.5 hours of exposure to polyvinylpyrrolidone (PVP).35 In 2010, Jackson et al. found that timing and temperature, though not cryopreservation methods, in the laboratory had great effects on inducing further SDF.36 These different sources and causes of oxidative stress make it clear why SDF is so prevalent and an area that merits more investigation. Microfluidic technology uses the sperm’s motility to propel it through a series of micro channels to ideally select out the best of the cohort based on its own moment and morphology simulating the female reproductive tract’s natural ability to sort sperm. Cho et al. (2003) showed motility and morphology near 100% following the use of microfluidic technology. However, this technology has not been widely adopted for clinical use. More recent development of a macro-microfluidic chamber that contains a polycarbonate filter of different pore diameters act as barriers which only allow sperm with adequate motility and morphology to pass. Recent publications have shown that the sperm sorted through this device have nearly undetectable DNA fragmentation with significant improvements over the neat semen sample as well as gradient processed.38,39 The commercially available device used in these studies has the potential to change the methods of sperm processing by making a device accessible, affordable and easy to use in the laboratory. The device also eliminates the use of centrifugation, which is beneficial to eliminating a step known to introduce reactive oxygen species, but could also eliminate the need for the expensive equipment. More clinical studies that show the effects on improving IVF outcomes, particularly in men with high SDF, are needed.