Hassan W. Bakos

The effect of paternal diet-induced obesity on sperm function and fertilization in a mouse model.

Although obvious effects of obesity on female reproduction and oocytes are emerging, the effects on male fertility and sperm quality are less clear with studies reporting conflicting results. We hypothesize that male obesity affects sperm function and physiology probably as a result of elevated oxidative stress in spermatozoa and therefore elevated levels of sperm DNA damage and loss of function. Six-week-old C57/Bl6 male mice (n = 36) were randomly allocated to two groups: group 1 (n = 18) received a control diet, whereas group 2 (n = 18) received a high-fat diet (HFD). At the completion of a 9-week period, mice were sacrificed and spermatozoa were obtained. Sperm motility, concentration, intracellular reactive oxygen species (ROS) production and sperm DNA damage were measured. The ability of the sperm to undergo capacitation, acrosome reaction, sperm binding and ability to fertilize an oocyte were also assessed. The percentage of motile spermatozoa was decreased in the HFD group compared with controls (36 ± 2% vs. 44 ± 4%; p < 0.05). Intracellular ROS was elevated (692 ± 83 vs. 409 ± 22 units; p < 0.01) in the HFD group compared with controls. Sperm DNA damage was also increased (1.64 ± 0.6% vs. 0.17 ± 0.06%; p < 0.05) in the HFD group compared with the control group. Furthermore, the percentage of non-capacitated sperm was significantly lower compared with controls (12.34% vs. 21.06%; p < 0.01). The number of sperm bound to each oocyte was significantly lower (41.14 ± 2.5 vs. 58.39 ± 2.4; p < 0.01) in the HFD group compared with that in controls and resulted in significantly lower fertilization rates (25.9% vs. 43.9%; p < 0.01). This report provides evidence that obesity may induce oxidative stress and sperm DNA damage as well as decreased fertilizing ability. This is important as DNA damage in the sperm as a result of oxidative stress has been linked to poor reproductive outcomes.

Paternal body mass index is associated with decreased blastocyst development and reduced live birth rates following assisted reproductive technology

OBJECTIVE To determine the relationship between paternal body mass index (BMI), embryo development and pregnancy, and live birth outcomes after assisted reproductive technology (ART). DESIGN Retrospective analysis of ART cycles. SETTING Major assisted reproduction center. PATIENT(S) Three hundred five couples undergoing ART in a private fertility clinic. INTERVENTION(S) No intervention was undertaken in patients involved in this study. MAIN OUTCOME MEASURE(S) Live birth outcomes and clinical pregnancy rates. RESULT(S) No significant relationship between paternal BMI and early embryo development was found. However, increased paternal BMI was associated with decreased blastocyst development, clinical pregnancy rates and live birth outcomes. CONCLUSION(S) To our knowledge, this is the first report linking increased paternal BMI and clinical pregnancy and live birth rates after ART treatment. Further work to elucidate the mechanisms involved is required.

Impact of obesity on male fertility, sperm function and molecular composition

Male obesity in reproductive-age men has nearly tripled in the past 30 y and coincides with an increase in male infertility worldwide. There is now emerging evidence that male obesity impacts negatively on male reproductive potential not only reducing sperm quality, but in particular altering the physical and molecular structure of germ cells in the testes and ultimately mature sperm. Recent data has shown that male obesity also impairs offspring metabolic and reproductive health suggesting that paternal health cues are transmitted to the next generation with the mediator mostly likely occurring via the sperm. Interestingly the molecular profile of germ cells in the testes and sperm from obese males is altered with changes to epigenetic modifiers. The increasing prevalence of male obesity calls for better public health awareness at the time of conception, with a better understanding of the molecular mechanism involved during spermatogenesis required along with the potential of interventions in reversing these deleterious effects. This review will focus on how male obesity affects fertility and sperm quality with a focus on proposed mechanisms and the potential reversibility of these adverse effects.

Diet-induced paternal obesity in the absence of diabetes diminishes the reproductive health of two subsequent generations of mice

BACKGROUND Obesity and related conditions, notably subfertility, are increasingly prevalent. Paternal influences are known to influence offspring health outcome, but the impact of paternal obesity and subfertility on the reproductive health of subsequent generations has been overlooked. METHODS A high-fat diet (HFD) was used to induce obesity but not diabetes in male C57Bl6 mice, which were subsequently mated to normal-weight females. First-generation offspring were raised on a control diet and their gametes were investigated for signs of subfertility. Second-generation offspring were generated from both first generation sexes and their gametes were similarly assessed. RESULTS We demonstrate a HFD-induced paternal initiation of subfertility in both male and female offspring of two generations of mice. Furthermore, we have shown that diminished reproductive and gamete functions are transmitted through the first generation paternal line to both sexes of the second generation and via the first generation maternal line to second-generation males. Our previous findings that founder male obesity alters the epigenome of sperm, could provide a basis for the developmental programming of subfertility in subsequent generations. CONCLUSIONS This is the first observation of paternal transmission of diminished reproductive health to future generations and could have significant implications for the transgenerational amplification of subfertility observed worldwide in humans.

Diet and exercise in an obese mouse fed a high-fat diet improve metabolic health and reverse perturbed sperm function.

Male obesity is associated with reduced sperm motility and morphology and increased sperm DNA damage and oxidative stress; however, the reversibility of these phenotypes has never been studied. Therefore, the aim of this study was to assess the reversibility of obesity and its associated sperm physiology and function in mice in response to weight loss through diet and exercise. C57BL6 male mice (n = 40) were fed either a control diet (CD; 6% fat) or a high-fat diet (HFD; 21% fat) for 10 wk before allocation to either diet and/or swimming exercise interventions for 8 wk. Diet alone reduced adiposity (1.6-fold) and serum cholesterol levels (1.7-fold, P < 0.05), while exercise alone did not alter these, but exercise plus diet also improved glucose tolerance (1.3-fold, P < 0.05). Diet and/or exercise improved sperm motility (1.2-fold) and morphology (1.1-fold, P < 0.05), and reduced sperm DNA damage (1.5-fold), reactive oxygen species (1.1-fold), and mitochondrial membrane potential (1.2-fold, P < 0.05) and increased sperm binding (1.4-fold) (P < 0.05). Sperm parameters were highly correlated with measures of glycemia, insulin action, and serum cholesterol (all P < 0.05) regardless of adiposity or intervention, suggesting a link between systemic metabolic status and sperm function. This is the first study to show that the abnormal sperm physiology resulting from obesity can be reversed through diet and exercise, even in the presence of ongoing obesity, suggesting that diet and lifestyle interventions could be a combined approach to target subfertility in overweight and obese men.

Paternal diet-induced obesity impairs embryo development and implantation in the mouse

OBJECTIVE To use a rodent model of male diet-induced obesity (DIO) to examine resultant preimplantation embryo development and implantation rate, as well as fetal and placental growth. DESIGN Experimental animal study. SETTING University research facilities. ANIMAL(S) C57BL/6 male and CBAxC57BL/6 female mice. INTERVENTION(S) Male mice were fed a standard rodent chow (lean) or a high-fat diet (obese) for up to 13 weeks. After mating, zygotes were collected and cultured to the blastocyst stage, then assessed or transferred into recipient females. MAIN OUTCOME MEASURE(S) Embryo morphology and cell number were assessed and pregnancy outcomes determined at postmortem day 18. RESULT(S) Embryos from obese males had reduced cleavage and decreased development to blastocyst stage during culture relative to control males. Blastocysts from obese males implanted at a reduced rate, and the proportion of fetuses that developed was significantly decreased, although fetal and placental weight did not differ between groups. CONCLUSION(S) This study demonstrates that paternal obesity impairs preimplantation embryo development and implantation but does not influence gross fetal or placental morphology. It highlights the important contribution that paternal health and lifestyle choices have for achieving a viable pregnancy.

Paternal obesity negatively affects male fertility and assisted reproduction outcomes: a systematic review and meta-analysis

This systematic review investigated the effect of paternal obesity on reproductive potential. Databases searched were Pubmed, Ovid, Web of Science, Scopus, Cinahl and Embase. Papers were critically appraised by two reviewers, and data were extracted using a standardized tool. Outcomes were: likelihood of infertility, embryo development, clinical pregnancy, live birth, pregnancy viability, infant development, sperm; concentration, morphology, motility, volume, DNA fragmentation, chromatin condensation, mitochondrial membrane potential (MMP), and seminal plasma factors. Thirty papers were included, with a total participant number of 115,158. Obese men were more likely to experience infertility (OR = 1.66, 95% CI 1.53-1.79), their rate of live birth per cycle of assisted reproduction technology (ART) was reduced (OR = 0.65, 95% CI 0.44-0.97) and they had a 10% absolute risk increase of pregnancy non-viability. Additionally, obese men had an increased percentage of sperm with low MMP, DNA fragmentation, and abnormal morphology. Clinically significant differences were not found for conventional semen parameters. From these findings it can be concluded that male obesity is associated with reduced reproductive potential. Furthermore, it may be informative to incorporate DNA fragmentation analysis and MMP assessment into semen testing, especially for obese men whose results suggest they should have normal fertility.

Improving Metabolic Health in Obese Male Mice via Diet and Exercise Restores Embryo Development and Fetal Growth

Paternal obesity is now clearly associated with or causal of impaired embryo and fetal development and reduced pregnancy rates in humans and rodents. This appears to be a result of reduced blastocyst potential. Whether these adverse embryo and fetal outcomes can be ameliorated by interventions to reduce paternal obesity has not been established. Here, male mice fed a high fat diet (HFD) to induce obesity were used, to determine if early embryo and fetal development is improved by interventions of diet (CD) and/or exercise to reduce adiposity and improve metabolism. Exercise and to a lesser extent CD in obese males improved embryo development rates, with increased cell to cell contacts in the compacting embryo measured by E-cadherin in exercise interventions and subsequently, increased blastocyst trophectoderm (TE), inner cell mass (ICM) and epiblast cell numbers. Implantation rates and fetal development from resulting blastocysts were also improved by exercise in obese males. Additionally, all interventions to obese males increased fetal weight, with CD alone and exercise alone, also increasing fetal crown-rump length. Measures of embryo and fetal development correlated with paternal measures of glycaemia, insulin action and serum lipids regardless of paternal adiposity or intervention, suggesting a link between paternal metabolic health and subsequent embryo and fetal development. This is the first study to show that improvements to metabolic health of obese males through diet and exercise can improve embryo and fetal development, suggesting such interventions are likely to improve offspring health.

Obese father's metabolic state, adiposity, and reproductive capacity indicate son's reproductive health

OBJECTIVE To determine whether dietary and exercise regimes in obese males can provide a novel intervention window for improving the reproductive health of the next generation. DESIGN Experimental animal study. SETTING University research facilities. ANIMAL(S) C57BL6 male and female mice. INTERVENTION(S) Mice were fed a control diet (6% fat) or high-fat diet (21% fat) for 9 weeks. After the initial feeding, high-fat-diet males were allocated to diet and/or exercise interventions for a further 9 weeks. After intervention males were mated with females fed standard chow (4% fat) before and during pregnancy. MAIN OUTCOME MEASURE(S) F1 sperm motility, count, morphology, capacitation, mitochondrial function, and sperm binding and weight of reproductive organs. RESULT(S) Our primary finding was that diet intervention alone in founders improved offspring sperm motility and mitochondrial markers of sperm health (decreased reactive oxygen species and mitochondrial membrane potential), ultimately improving sperm binding. Sperm binding and capacitation was also improved in F1 males born to a combined diet and exercise intervention in founders. Founder sperm parameters and metabolic measures as a response to diet and/or exercise (i.e., lipid/glucose homeostasis, sperm count and morphology) correlated with offsprings sperm function, independent of founder treatment. This implicates paternal metabolic and reproductive status in predicting male offsprings reproductive function. CONCLUSION(S) This is the first study to show that improvements to both metabolic (lipids, glucose and insulin sensitivity) and reproductive function (sperm motility and morphology) in obese fathers via diet and exercise interventions can improve subsequent reproductive health in offspring.

The density of human semen and the validation of weight as an indicator of volume: a multicentre study

A multi-centre study was undertaken to: a/ determine the density of human semen, and b/ assess the validity of measuring semen volume either volumetrically or gravimetrically. Semen samples from four clinical categories (azoospermia following vasectomy, azoospermia without vasectomy, oligozoospermia (<20x10(6)/ml) and normozoospermia (>/=20x10(6)/ml)) had similar densities (one-way ANOVA: F(3,180)=1.25, not significant), being close to 1.0 g/ml when taken to one decimal place. Measurement of semen volume was then made with either a graduated pipette or by weighing and assuming a density of 1 g/ml. A comparison of the two methods gave an excellent correlation, with a gradient of 1.0571 and a coefficient of determination (R(2)) of 0.98 (p<0.0001). However, it was noted that the aspiration of the ejaculate in to a graduated pipette underestimated the volume by approximately 0.2 ml, but in an inconsistent manner making the use of a set correction factor inappropriate. The estimation of volume to one decimal place by weighing the collection container before and after ejaculation, assuming a density of 1 g/ml, would seem to be a viable alternative although the density of a small number of samples may deviate from this assumption. Whilst the relatively small underestimation of volume with a pipette is unlikely to have clinical significance, the known reporting of inaccurate results by a laboratory is contrary to the philosophy and key principles of quality management.