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Ribas-Maynou J, Novo S, Salas-Huetos A, Rovira S, Antich M, Yeste M. Condensation and protamination of sperm chromatin affect ICSI outcomes when gametes from healthy individuals are used. Hum Reprod 2023; 38:371-386. [PMID: 36539233 DOI: 10.1093/humrep/deac261] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Revised: 11/29/2022] [Indexed: 12/24/2022] Open
Abstract
STUDY QUESTION Do defects in sperm chromatin protamination and condensation have an impact on ICSI outcomes? SUMMARY ANSWER Sperm protamination is related to fertilization rates in healthy donors, and the in vitro capacity of sperm to condense their chromatin is linked to blastocyst rates, both associations being more apparent in women <33 years of age. WHAT IS KNOWN ALREADY Previous data on how sperm chromatin damage affects ICSI outcomes are inconsistent. Revealing which sperm factors influence embryo development is necessary to understand the male contribution to ICSI success and to develop novel sperm selection techniques or male-based treatments. Sperm chromatin is mainly condensed in protamines, which are cross-linked through disulphide bridges. This study aimed to determine whether sperm protamination and the integrity of disulphide bonds (condensation) are related to embryo development after ICSI. STUDY DESIGN, SIZE, DURATION The design was a retrospective study with a blind analysis of sperm chromatin. Gametes were divided into two groups: double donation (DD) cohort and single donation (SD) cohort. Samples from 45 semen donors used in 55 ICSI cycles with oocyte donors (age range 19-33 years), generating 491 embryos, were included in the DD cohort. The SD cohort consisted of samples from 34 semen donors used in 41 ICSI cycles with oocytes from healthy females (single-parent families or lesbian couples, age range 20-44 years), generating a total of 378 embryos. PARTICIPANTS/MATERIALS, SETTINGS, METHODS Donor sperm samples from DD and SD cohorts were used for standard ICSI, and embryo development was observed by time-lapse imaging. The incidence of thiol reduction (dibromobimane, DBB) and the degree of chromatin protamination (chromomycin A3, CMA3, indicating non-protaminated regions) in sperm were determined by flow cytometry at 0 and 4 h post-thawing. MAIN RESULTS AND THE ROLE OF CHANCE Percentages ± standard deviation of CMA3 were 21.08 ± 9.09 and 35.01 ± 14.68 at 0 and 4 h post-thawing, respectively, in the DD cohort and 22.57 ± 9.48 and 35.79 ± 12.58, at 0 and 4 h post-thawing, respectively, in the SD cohort. Percentages of DBB+ were 16.57 ± 11.10 and 10.51 ± 8.40 at 0 and 4 h post-thawing (P < 0.0001), respectively, in the DD cohort and 17.98 ± 10.19 and 12.72 ± 8.76 at 0 and 4 h post-thawing (P < 0.0001), respectively, in the SD cohort. Female age correlated with fertilization rates, and the relation between sperm chromatin and embryo development was determined through multiple linear regression. While CMA3 was associated with fertilization rates, with no influence of female age, in the DD cohort (β1 = -1.036, P < 0.001 for CMA3; β2 = 0.667, P = 0.304 for female age), this was not observed in the SD cohort, where female age had a significant effect, masking the effects of CMA3 (β1 = -0.066, P = 0.804 for CMA3; β 2 = -1.451, P = 0.003 for female age). The in vitro capacity of sperm to condense their chromatin after 4 h of incubation was associated with blastocyst rates, independent of female age (DD cohort: β1 = -0.238, P = 0.008 for %DBB+ variation; β2 = 0.404, P = 0.638 for female age; SD cohort: β1 = -0.278, P = 0.010 for %DBB+ variation; β2 = -0.292, P = 0.594 for female age). The in vitro capacity of sperm to condense their chromatin was also related to the time required for the embryo to reach blastocyst stage in the DD cohort (P = 0.007). Finally, multiple logistic regression showed that both chromatin protamination and condensation, together with the age of the oocyte donors and the embryo recipients, had an impact on pregnancy achievement (P < 0.01) and on live birth rates (P < 0.01). LIMITATIONS, REASONS FOR CAUTION The main limitation was the restrictive selection of couples, which led to a relatively small sample size and could influence the observed outcomes. For this reason, and to reduce Type I error, the level of significance was set at P ≤ 0.01. On the other hand, the use of cryopreserved samples could also be a limitation. WIDER IMPLICATIONS OF THE FINDINGS This research demonstrated that protamination and condensation of sperm chromatin are related to embryo development after ICSI, but female age could be a confounding factor when oocytes from older females are used. STUDY FUNDING/COMPETING INTEREST(S) This work was supported by the European Union's Horizon 2020 Research and Innovation scheme under the Marie Skłodowska-Curie grant agreement No 801342 (Tecniospring INDUSTRY; TECSPR-19-1-0003); La Marató de TV3 Foundation (214/857-202039); the Ministry of Science and Innovation, Spain (IJC2019-039615-I); the Catalan Agency for Management of University and Research Grants, Regional Government of Catalonia, Spain (2017-SGR-1229); and the Catalan Institution for Research and Advanced Studies, Spain (ICREA). The authors declare no competing interests. TRIAL REGISTRATION NUMBER N/A.
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Affiliation(s)
- Jordi Ribas-Maynou
- Unit of Cell Biology, Department of Biology, Faculty of Sciences, University of Girona, Girona, Spain.,Biotechnology of Animal and Human Reproduction (TechnoSperm), Institute of Food and Agricultural Technology, University of Girona, Girona, Spain
| | - Sergi Novo
- Fertilab-Institut Catala de Fertilitat SL, Barcelona, Spain.,Fertibank, Barcelona, Spain
| | - Albert Salas-Huetos
- Unit of Cell Biology, Department of Biology, Faculty of Sciences, University of Girona, Girona, Spain.,Biotechnology of Animal and Human Reproduction (TechnoSperm), Institute of Food and Agricultural Technology, University of Girona, Girona, Spain.,Department of Nutrition, Harvard T.H. Chan School of Public Health, Boston, MA, USA
| | - Sergi Rovira
- Fertilab-Institut Catala de Fertilitat SL, Barcelona, Spain.,Fertibank, Barcelona, Spain
| | - Marta Antich
- Fertilab-Institut Catala de Fertilitat SL, Barcelona, Spain.,Fertibank, Barcelona, Spain
| | - Marc Yeste
- Unit of Cell Biology, Department of Biology, Faculty of Sciences, University of Girona, Girona, Spain.,Biotechnology of Animal and Human Reproduction (TechnoSperm), Institute of Food and Agricultural Technology, University of Girona, Girona, Spain.,Catalan Institution for Research and Advanced Studies (ICREA), Barcelona, Spain
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Extend the Survival of Human Sperm In Vitro in Non-Freezing Conditions: Damage Mechanisms, Preservation Technologies, and Clinical Applications. Cells 2022; 11:cells11182845. [PMID: 36139420 PMCID: PMC9496714 DOI: 10.3390/cells11182845] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2022] [Revised: 09/05/2022] [Accepted: 09/08/2022] [Indexed: 11/17/2022] Open
Abstract
Preservation of human spermatozoa in vitro at normothermia or hypothermia maintaining their functions and fertility for several days plays a significant role in reproductive biology and medicine. However, it is well known that human spermatozoa left in vitro deteriorate over time irreversibly as the consequence of various stresses such as the change of osmolarity, energy deficiency, and oxidative damage, leading to substantial limitations including the need for semen examinations, fertility preservation, and assisted reproductive technology. These problems may be addressed with the aid of non-freezing storage techniques. The main and most effective preservation strategies are the partial or total replacement of seminal plasma with culture medium, named as extenders, and temperature-induced metabolic restriction. Semen extenders consist of buffers, osmolytes, and antioxidants, etc. to protect spermatozoa against the above-mentioned adverse factors. Extended preservation of human spermatozoa in vitro has a negative effect on sperm parameters, whereas its effect on ART outcomes remains inconsistent. The storage duration, temperature, and pre-treatment of semen should be determined according to the aims of preservation. Advanced techniques such as nanotechnology and omics have been introduced and show great potential in the lifespan extension of human sperm. It is certain that more patients will benefit from it in the near future. This review provided an overview of the current knowledge and prospects of prolonged non-freezing storage of human sperm in vitro.
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Torra-Massana M, Quintana-Vehí A, Barragán M, Bellido R, Rodríguez A, Vassena R. How long can the sperm wait? Effect of incubation time on ICSI outcomes. Mol Reprod Dev 2022; 89:133-145. [PMID: 35195315 DOI: 10.1002/mrd.23561] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2021] [Revised: 12/03/2021] [Accepted: 01/10/2022] [Indexed: 11/11/2022]
Abstract
In sperm processing for IVF/ICSI incubation times differ considerably both between and within assisted reproduction facilities. There is no established consensus on the optimal sperm incubation timings to maximize pregnancy rates, and the few studies addressing this association rely on manual and operator-dependent methods for time recording. The present retrospective cohort study includes 1169 ICSI cycles using fresh semen processed by swim-up. An operator-independent, radiofrequency-based system was used to record sperm incubation times: from sample collection to swim-up (T1, 0.35 ± 0.26); from swim-up to ICSI (T2, 3.30 ± 2.2); and total time from sample collection to ICSI (T, 3.66 ± 2.26). In oocyte donation cycles, we observed a significant negative effect of T1 on fertilization rate (FR; generalized linear modelling regression, coeff. -0.20, p = 0.001); however, after analysing all times by deciles and by adjusted logistic regression, none of the time intervals had a significant effect on pregnancy (biochemical, clinical, and ongoing) and live birth (LB) rates (p > 0.05 for all outcomes). In cycles using the patient's oocytes, we observed a negative effect of T2 (ordinal regression, coeff. -0.25, p = 0.011) and T (-0.33, p = 0.005) on the mean morphological score of the embryo cohort. In these cycles, a trend associating longer values of T with higher LB rates was identified (OR = 1.47, p = 0.050), although this difference is likely not clinically significant. In conclusion, while longer sperm incubation in vitro may impact slightly both FRs and embryo morphology after ICSI, no adverse effects were detected on the reproductive outcomes.
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Ranéa C, Pariz JR, Drevet JR, Hallak J. Sperm motility in asthenozoospermic semen samples can be improved by incubation in a continuous single culture medium (CSCM®). Syst Biol Reprod Med 2022; 68:25-35. [PMID: 35100915 DOI: 10.1080/19396368.2021.2004623] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
Standard protocols for clinical in vitro fertilization (IVF) laboratories recommend incubating semen at 37°C in 5% CO2 without strictly specifying which medium should be used or for how long. This study aimed to test the most common different incubation media used in Latin American andrology and micromanipulation laboratories and verify which, if any, is the most appropriate medium to improve asthenozoospermic semen samples' motility in the infertile male population. Ejaculates (136) collected from asthenozoospermic men were divided into two cohorts with similar characteristics (cohort 1; n = 28 and cohort 2; n = 108). Cohort 1 was used to evaluate the optimal incubation time with regard to unprepared asthenozoospermic sample sperm motility. After defining an optimal incubation period of 2 h, cohort 2 was used to evaluate which of the four media commonly used in IVF clinics (continuous single culture medium = CSCM®; SpermRinse medium = SR®; in vitro fertilization medium = G-IVF® and human tubal fluid medium = HTF®) was preferred for semen samples from asthenozoospermic patients. Overall, it was determined that a 2-h incubation in CSCM® medium led to the highest asthenozoospermic sperm motility. Thus, this simple, cost-effective, easily reproducible protocol could prove extremely useful for andrology laboratories working with IVF clinics dealing with asthenozoospermic semen specimens. This is particularly relevant since the incidence of the latter is on the rise as semen quality decreases around the globe.Abbreviations: ANOVA: Analysis of variance; ARTs: Assisted reproductive techniques; BWW: Biggers, Whitten, and Whittingham; CO2: Carbon dioxide; CPM: counted per minute; CSCM: Continuous Single Culture Medium; DAB: 3.3'- diaminobenzidine; DFI: DNA Fragmentation Index; DMSO: Dimethyl sulfoxide; G-IVF: In Vitro Fertilization Medium; GSH: Glutathione; GPx: glutathione peroxidase; HDS: High DNA Stainability; HSA: Human Serum Albumin; HTF: Human Tubal Fluid; HYP: Hyperactivity; ICSI: Intracytoplasmic sperm injection; IUI: Intrauterine insemination; IVF: in vitro fertilization; LIN: Linearity; ROS: Reactive Oxygen Species-level; SC: Sperm concentration; SCA: Sperm Computer Analysis; SCSA: Sperm Chromatin Structural Assay; SR: SpermRinse medium; SSS: Synthetic Serum Substitute; STR: Straightness; SOD: superoxide dismutase; TNE: Tris-Borate-EDTA; TSC: Total sperm count; VAP: Mean velocity; VCL: Curvilinear velocity; VSL: Linear velocity; WHO: World Health Organization; WOB: Wobble; spz: spermatozoa; AO: antioxidant.
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Affiliation(s)
- Caroline Ranéa
- Androscience, Science and Innovation Center in Andrology and High-Complex Clinical and Andrology Laboratory, São Paulo, Brazil.,Division of Urology, Department of Surgery, Hospital Das Clinicas, University of Sao Paulo Medical School, São Paulo, Brazil
| | - Juliana Risso Pariz
- Androscience, Science and Innovation Center in Andrology and High-Complex Clinical and Andrology Laboratory, São Paulo, Brazil.,Division of Urology, Department of Surgery, Hospital Das Clinicas, University of Sao Paulo Medical School, São Paulo, Brazil.,Department of Pathology, Reproductive Toxicology Unit, University of São Paulo Medical School, São Paulo, Brazil.,Institute for Advanced Studies, University of Sao Paulo, Sao Paulo, Brazil
| | - Joël R Drevet
- Université Clermont Auvergne, GReD Institute, Faculty of Medicine, Clermont-Ferrand, France
| | - Jorge Hallak
- Androscience, Science and Innovation Center in Andrology and High-Complex Clinical and Andrology Laboratory, São Paulo, Brazil.,Division of Urology, Department of Surgery, Hospital Das Clinicas, University of Sao Paulo Medical School, São Paulo, Brazil.,Department of Pathology, Reproductive Toxicology Unit, University of São Paulo Medical School, São Paulo, Brazil.,Institute for Advanced Studies, University of Sao Paulo, Sao Paulo, Brazil
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Karimi Zarchi M, Maleki B, Dehghani Ashkezari M, Motamed Zadeh L, Agha-Rahimi A. The Effects of In Vitro Incubation of Asthenoteratozoospermic Semen after Density Gradient Centrifugation at Room Temperature and 37° C on Sperm Parameters, Chromatin Quality and DNA Fragmentation in a Short Time Period. J Reprod Infertil 2020; 21:275-282. [PMID: 33209744 PMCID: PMC7648867 DOI: 10.18502/jri.v21i4.4332] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Background: Sperm quality is an important factor in assisted reproductive technology (ART) that affects the success rate of infertile couples treatment. In vitro incubation of sperm can influence its parameters and DNA integrity. The present study focused on the effect of different incubation temperatures sperm parameters on asthenoteratozoospermia semen prepared with density gradient centrifugation at different times. Methods: Twenty-seven samples were collected and prepared. Then, the suspension was divided into two parts. One part was incubated at room temperature (RT), and another was incubated at 37°C. Immediately and after 2 hr (2H) and 4 hr (4H), spermatozoa were evaluated regarding motility, viability, morphology, sperm protamine deficiency, chromatin and DNA fragmentation. Statistical analysis was performed using paired t-test and repeated measures. The p<0.05 was considered statistically significant. Results: Our results showed that following 2 and 4 hr of incubation at RT, sperm progressive motility and viability decreased significantly. Sperm DNA fragmentation increased significantly following 2 and 4 hr of incubation at RT and 37°C. The Trend analysis confirmed that there were no significant differences between sperm parameters and DNA fragmentation after different times at RT and 37°C. Conclusion: Incubation of sperm at RT in comparison to 37°C didn’t preserve sperm parameters and DNA efficiently. Therefore, IVF, ICSI and IUI procedure should be performed in the soonest possible time after sperm preparation.
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Affiliation(s)
- Motahareh Karimi Zarchi
- Department of Biology, Medical Biotechnology Research Center, Ashkezar Branch, Islamic Azad University, Yazd, Iran
| | - Behnam Maleki
- Research and Clinical Center for Infertility, Yazd Reproductive Sciences Institute, Shahid Sadoughi University of Medical Sciences, Yazd, Iran
| | - Mahmood Dehghani Ashkezari
- Department of Biology, Medical Biotechnology Research Center, Ashkezar Branch, Islamic Azad University, Yazd, Iran
| | - Leila Motamed Zadeh
- Research and Clinical Center for Infertility, Yazd Reproductive Sciences Institute, Shahid Sadoughi University of Medical Sciences, Yazd, Iran
| | - Azam Agha-Rahimi
- Research and Clinical Center for Infertility, Yazd Reproductive Sciences Institute, Shahid Sadoughi University of Medical Sciences, Yazd, Iran
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Agarwal A, Majzoub A, Baskaran S, Panner Selvam MK, Cho CL, Henkel R, Finelli R, Leisegang K, Sengupta P, Barbarosie C, Parekh N, Alves MG, Ko E, Arafa M, Tadros N, Ramasamy R, Kavoussi P, Ambar R, Kuchakulla M, Robert KA, Iovine C, Durairajanayagam D, Jindal S, Shah R. Sperm DNA Fragmentation: A New Guideline for Clinicians. World J Mens Health 2020; 38:412-471. [PMID: 32777871 PMCID: PMC7502318 DOI: 10.5534/wjmh.200128] [Citation(s) in RCA: 120] [Impact Index Per Article: 30.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2020] [Revised: 07/13/2020] [Accepted: 07/13/2020] [Indexed: 12/13/2022] Open
Abstract
Sperm DNA integrity is crucial for fertilization and development of healthy offspring. The spermatozoon undergoes extensive molecular remodeling of its nucleus during later phases of spermatogenesis, which imparts compaction and protects the genetic content. Testicular (defective maturation and abortive apoptosis) and post-testicular (oxidative stress) mechanisms are implicated in the etiology of sperm DNA fragmentation (SDF), which affects both natural and assisted reproduction. Several clinical and environmental factors are known to negatively impact sperm DNA integrity. An increasing number of reports emphasizes the direct relationship between sperm DNA damage and male infertility. Currently, several assays are available to assess sperm DNA damage, however, routine assessment of SDF in clinical practice is not recommended by professional organizations. This article provides an overview of SDF types, origin and comparative analysis of various SDF assays while primarily focusing on the clinical indications of SDF testing. Importantly, we report four clinical cases where SDF testing had played a significant role in improving fertility outcome. In light of these clinical case reports and recent scientific evidence, this review provides expert recommendations on SDF testing and examines the advantages and drawbacks of the clinical utility of SDF testing using Strength-Weaknesses-Opportunities-Threats (SWOT) analysis.
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Affiliation(s)
- Ashok Agarwal
- American Center for Reproductive Medicine, Cleveland Clinic, Cleveland, OH, USA.
| | - Ahmad Majzoub
- Department of Urology, Hamad Medical Corporation, Doha, Qatar
- Department of Urology, Weill Cornell Medicine - Qatar, Doha, Qatar
| | - Saradha Baskaran
- American Center for Reproductive Medicine, Cleveland Clinic, Cleveland, OH, USA
| | | | - Chak Lam Cho
- Department of Surgery, Union Hospital, Hong Kong
- S. H. Ho Urology Centre, Department of Surgery, The Chinese University of Hong Kong, Hong Kong
| | - Ralf Henkel
- Department of Metabolism, Digestion and Reproduction, Imperial College London, London, UK
- Department of Medical Bioscience, University of the Western Cape, Bellville, South Africa
| | - Renata Finelli
- American Center for Reproductive Medicine, Cleveland Clinic, Cleveland, OH, USA
| | - Kristian Leisegang
- School of Natural Medicine, Faculty of Community and Health Sciences, University of the Western Cape, Bellville, South Africa
| | - Pallav Sengupta
- Department of Physiology, Faculty of Medicine, Bioscience and Nursing, MAHSA University, Jenjarom, Malaysia
| | - Catalina Barbarosie
- Department of Genetics, Faculty of Biology, University of Bucharest, Bucharest, Romania
| | - Neel Parekh
- Department of Urology, Cleveland Clinic Foundation, Cleveland, OH, USA
| | - Marco G Alves
- Department of Microscopy, Laboratory of Cell Biology & Unit for Multidisciplinary Research in Biomedicine (UMIB), Institute of Biomedical Sciences Abel Salazar (ICBAS), University of Porto, Porto, Portugal
| | - Edmund Ko
- Department of Urology, Loma Linda University, Loma Linda, CA, USA
| | - Mohamed Arafa
- Department of Urology, Hamad Medical Corporation, Doha, Qatar
- Andrology Department, Cairo University, Giza, Egypt
| | - Nicholas Tadros
- Division of Urology, Southern Illinois University School of Medicine, Springfield, IL, USA
| | | | - Parviz Kavoussi
- Austin Fertility & Reproductive Medicine/Westlake IVF, Austin, TX, USA
| | - Rafael Ambar
- Urology Department of Centro Universitario em Saude do ABC, Santo André, Brazil
| | | | - Kathy Amy Robert
- American Center for Reproductive Medicine, Cleveland Clinic, Cleveland, OH, USA
| | - Concetta Iovine
- Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, University of Campania "Luigi Vanvitelli", Caserta, Italy
| | | | - Sunil Jindal
- Department of Andrology and Reproductive Medicine, Jindal Hospital, Meerut, India
| | - Rupin Shah
- Department of Urology, Lilavati Hospital and Research Centre, Mumbai, India
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Dynamic assessment of human sperm DNA damage II: the effect of sperm concentration adjustment during processing. J Assist Reprod Genet 2019; 36:799-807. [PMID: 30805848 DOI: 10.1007/s10815-019-01423-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2018] [Accepted: 02/14/2019] [Indexed: 10/27/2022] Open
Abstract
PURPOSE To evaluate the effect of sperm concentration adjustment in human ejaculates on the sperm DNA quality and longevity. METHODS Semen samples were obtained from 30 donors with a normal spermiogram. Following centrifugation, the sperm pellet was resuspended in PBS, and the sperm concentration adjusted to 200, 100, 50, 25, 12, and 6 × 106/mL. Each set of samples was incubated at 37 °C for 24 h, and the sperm DNA damage was assessed using the chromatin-dispersion test following 0 h, 2 h, 6 h, and 24 h of incubation. RESULTS Sperm DNA fragmentation (SDF) did not differ between the selected experimental conditions at T0; however, Kaplan-Meier estimates for survival showed significant differences with respect to the dilution and time (all P values were smaller than .001). DNA fragmentation in semen samples adjusted to 200 × 106/mL was approximately 3.3 times higher when compared to samples containing 25 × 106/mL and 3.9 higher in comparison with samples adjusted to 12 × 106/mL following 2 h of in vitro incubation. Although there was evidence of individual variation in SDF during the incubation period, the general finding was that lower sperm concentrations resulted in a slower rate of DNA fragmentation. CONCLUSIONS Incubation of spermatozoa for ART purposes should be done following a concentration adjustment below 25 × 106/mL in order to avoid a higher susceptibility of the sperm DNA molecule towards fragmentation.
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