Sperm DNA Fragmentation:

Effect of cigarettes smoking on embryo development through its effect on Sperm DNA Fragmentation-A Systematic Review

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Abstract

Background: The negative deleterious effects of cigarette smoking are widely known, especially the relationship its influence on semen quality and sperm DNA fragmentation. Male cigarette smoking was highlighted and hypothesized to not only affect cause DNA fragmentation, but also affect the early embryo development. To summarize various literature studies, a systematic review of relevant observational studies was conducted to determine the relationship between cigarette smoking amongst men and DNA fragmentation and the ultimate influence on embryo development.

Methods: A systematic search of observational literature on the subject was performed on Google Scholar. All papers relevant observational papers reporting on the association of cigarette smoking with sperm DNA fragmentation and embryo development were included. The retrieval of pertinent reports was done and subsequently the systematic search of reference lists in order to help in the identification of studies qualifying for inclusion.

Results: Of the 14 studies, 4 papers were retrieved reporting observational findings that cigarette smoking causes adverse DNA damage which is evidentially associated with poor embryo development. However, the remaining studies had no information implying any existent relationship between cigarette smoking, DNA damage and embryo development.

Conclusions: The literature asserts that cigarette smoking through sperm DNA fragmentation affects early embryonic development. Well-designed research literatures with evidence-based, pre-defined criterial for subject selection, definition of cigarette smoking and its contents are essential in achieving consistent evidences on the effect of smoking on DNA fragmentation and ultimately, embryo development.

Keywords: DNA fragmentation, Cigarette smoking, Blastocyst development

Introduction

This systematic review seeks to determine the relationship between cigarette smoking amongst men and DNA fragmentation and the ultimate influence on embryo development. Substantial evidence-based assertions from human studies reveal that cigarette smoke comprises of harmful carcinogens and mutagens, which may gradually ensue in the induction of nuclear damage od spermatozoa DNA, defective Semen quality, compromising chances of healthy embryo development.

The harmful substances include nicotine, alkaloids, hydoxycotinine, nitrosamines and cotinine. Research suggests that the substances produce overly reactive oxygen (O2) species (ROS). Observational evidences assert the effect of the ROS on the reproductive cycle as they affect the integrity of sperm nucleus DNA through multiple base modifications, abnormal packing of the chromatins and abnormal DNA strand breaks. The structure of the sperm DNA keeps nuclear chromatins compact and highly stable; conversely, pro-mutagenic change is caused by DNA damage which in severe degrees affect the germ line quality, preventing embryo development. Studies reveal high levels of negative association between multiple reproductive indices such as the rate of fertilization, embryo cleavage, implantation and the degree of DNA fragmentation or damage. Furthermore, researchers established recently that severe damage to spermatozoa DNA may be consequential to recurrent spontaneous abortion.

Methods

Research Strategy and selection criteria

The systematic review was conducted on studies detailing the eeffect of cigarettes smoking on embryo development through its effect on Sperm DNA Fragmentation. The analysis complied to the PRISMA criteria in reporting results. We conducted research using Google Scholar database from the beginning of January using the following key words: "DNA fragmentation", Cigarettes, Blastocyst development. Only full studies published in the English language were included in the search. 14 additional observational studies were included from my personal journal collection. Two investigators were actively engaged in conducting an independent review of the literature to establish any discrepancies and eligibility. Notably, discrepancies were resolved accordingly in a group discussion.

Eligibility and Data Extraction

Studies that evaluated the relationship between cigarette smoking by the male partner, the damage to Spermatozoa DNA through nuclear DNA fragmentation and the negative effects in embryo development were selected. Patient selection, male inclusion and exclusion criteria, Sperm DNA assay types, the relationship between sperm DNA damage results as a result of cigarette smoking and embryo development test results were recorded. Embryo development was referred to as "cleavage rate" in some instances.2 Information on DNA fragmentation as a result of cigarette smoking was collected1 was collected from the sources. Detailed information related to cigarette smoking, spermatozoa DNA fragmentation and embryo development was recorded was collected from a number of studies 4 while one source3detailed test results revealing that cigarette smoking indeed causes oxidation, but does not necessarily result in poor quality of sperms through DNA fragmentation.

-571500-22860000PRISMA 2009 Flow Diagram

274320056121300018859505955030Studies included in quantitative synthesis (meta-analysis)(n = 6)

00Studies included in quantitative synthesis (meta-analysis)(n = 6)

18859504926330Studies included in qualitative synthesis(n = 6)

00Studies included in qualitative synthesis(n = 6)

42291003897630Full-text articles excluded, with reasons(n = 10 )

00Full-text articles excluded, with reasons(n = 10 )

3600450424053000274320045834300018859503897630Full-text articles assessed for eligibility(n = 16 )

00Full-text articles assessed for eligibility(n = 16 )

357822532689800042291002983230Records excluded(n = 68 )

00Records excluded(n = 68 )

19081752983230Records screened(n = 84)

00Records screened(n = 84)

274320035547300027432002526030003886200149733000160020014973300013569951954530Records after duplicates removed(n = 16)

00Records after duplicates removed(n = 16)

2914650811530Additional records identified through other sources(n = 14)

00Additional records identified through other sources(n = 14)

342900811530Records identified through database searching(n = 70)

00Records identified through database searching(n = 70)

-926993302906Identification

00Identification

-931039235315Screening

00Screening

-926993158997Eligibility

00Eligibility

-918901256596Included

00Included

Results

Studies Selected

Overall, a total of 84 studies were retrieved, 14 from personal journal collections and 70 from the Google Scholar database. However, a review of the abstracts, respective titles and introductory content indicated that the 68 were not directly relevant to the subject. From the remaining 16 citations, full articles were obtained. Following an explorative review of the 16 research papers, 5 as they did not mention DNA fragmentation or cigarette smoking. Of the remaining 11, 1 study was excluded for reporting on sperm DNA quality in relation to Intrauterine Insemination without any mention of the other key words of the study while 4 were omitted for relating paternal influence (Invitro fertilization) with poor embryo development following intracytoplasmic sperm injection (ICSI). The remaining 6 research studies reported findings of observational studies revealing relational factors between cigarette smoking, sperm DNA damage and embryo development.

Study Characteristics

The 6 eligible research studies, 1 reported on the effect of cigarette smoking on DNA fragmentation and sperm quality, A questionnaire was employed in the assessment of smoking intoxication and measured using CO-Tester.

Study Design

2 were prospective studies, 1 cohort, 2 cross-sectional and 2 retrospective studies.

Test results

Findings suggest deleterious effects on the nuclear quality of the spermatozoa for cigarette smokers. DNA fragmentation, therefore can be considered as an independent parameter that has strategic, diagnostic and prognostic value in infertility treatments. In addition, cigarette smoking, High DNA stainability and DFI (DNA fragmentation) were also tested.

DNA Fragmentation

Findings from results investigating the relationship between cigarette smoking and sperm DNA fragmentation were not uniform. Spaniark et al analyzed sperm samples and revealed that the rate of DNA fragmentation ranged between 5.1% to 69.2% and the mean value was 28.8%.3 There was a significant difference between non-smokers and smokers in the fragmentation of their DNA spermatozoa (p,0.001). Generally, it is evident that the consumption of tobacco results in increased rates of aneuploidy for specific chromosomes, their susceptibility to nondisjunction caused by smoking at some point in male meiosis varies among various chromosome pairs.1

Fig 2: Effects of smoke on DNA fragmentation

High DNA Stainability (HDS)

% of cells exhibiting immature chromatin, hence high levels of HDS was found to be significantly higher amongst non-fertile cigarette smokers.

Cigarette smoking

Drawing from the results, evidences revealing the positive association of the percentage of HDS, DFI and significant sperm DNA fragmentation was found. Cigarette smoking showed positive, reliable and significant correlation with the percentage of DFI. In essence, it was clearly outlined that cigarette smoking shows negative association with sperms with a normal morphology (p<0.001).

Embryo Development

Of the 6 eligible studies, 1 reported on the correlation between damaged DNA through Sperm DNA fragmentation and embryo development. 6 The study reported significant positive association between embryo quality, sperm DNA damage and poor embryo development and damage to DNA fragmentation.

Sperm morphology

Over time, sperm morphology and motility has been employed in the evaluation of male fertility potential. One study conducted heterogeneity causes in two subgroup analyses.3 Sperm morphology was examined and mean as per the criteria of WHO in both controls and patients ranged from 21.2% to 72.0% and 8.4% and 30.8% respectively. The study concluded that Varicocele affects sperm morphology negatively hence influencing the degree of damage to the sperm DNA and ultimately embryo development.

Outcome measures

The study's primary outcome measures were specified as sperm DNA fragmentation (% DFI), sperm morphology (% normal forms), and sperms with high rates of HDS (% high DNA sustainability). The parameters are frequently employed in clinical settings as laboratory measures for the investigations on varicocele. The description of results is presented as mean +_S.D. While some literatures provided required data on all outcomes, others covered one or two outcome measures. For each study, we assessed the following characteristics: Semen analysis methods, control type, Study design.

Summary of Findings Table

People: Fertile non-smokers, infertile non-smokers, infertile smokers

Methodology: Prospective cohort, retrospective and cross-sectional studies

Comparison: Fertility status and smoking of cigarettes

Outcomes Impacts Number of

subjects Certainty of the evidence

(GRADE)*

DNA fragmentation [Calogero et al., Soares & Melo, Zini et al., Elshal et al. Spaniak et al.,] DNA fragmentation (DFI) is a result of abnormal sperm morphology, sperm motility evidenced in HDS in close consideration of the vital roles the parameters play in embryo development, cigarette smoke affects DNA chromatin integrity. 5 Low

Cigarette smoking [Calogero et al., Spaniak et al., Soares & Melo] Cigarettes smoking has negative impacts on sperm DNA chromatin integrity. 3

Moderate

High DNA Stainability...