Smoking status modifies the relation between CYP1A1*2C gene polymorphism and idiopathic male infertility: the importance of gene-environment interaction analysis for genetic studies of the disease

Genic-intergenic polymorphisms of CYP1A genes and their clinical impact

The humancytochrome P450 1A (CYP1A) subfamily genes, CYP1A1 and CYP1A2, encoding monooxygenases are critically involved in biotransformation of key endogenous substrates (estradiol, arachidonic acid, cholesterol) and exogenous compounds (smoke constituents, carcinogens, caffeine, therapeutic drugs). This suggests their significant involvement in multiple biological pathways with a primary role of maintaining endogenous homeostasis and xenobiotic detoxification. Large interindividual variability exist in CYP1A gene expression and/or catalytic activity of the enzyme, which is primarily due to the existence of polymorphic alleles which encode them. These polymorphisms (mainly single nucleotide polymorphisms, SNPs) have been extensively studied as susceptibility factors in a spectrum of clinical phenotypes. An in-depth understanding of the effects of polymorphic CYP1A genes on the differential metabolic activity and the resulting biological pathways is needed to explain the clinical implications of CYP1A polymorphisms. The present review is intended to provide an integrated understanding of CYP1A metabolic activity with unique substrate specificity and their involvement in physiological and pathophysiological roles. The article further emphasizes on the impact of widely studied CYP1A1 and CYP1A2 SNPs and their complex interaction with non-genetic factors like smoking and caffeine intake on multiple clinical phenotypes. Finally, we attempted to discuss the alterations in metabolism/physiology concerning the polymorphic CYP1A genes, which may underlie the reported clinical associations. This knowledge may provide insights into the disease pathogenesis, risk stratification, response to therapy and potential drug targets for individuals with certain CYP1A genotypes.

Impact of tobacco smoking in association with H2BFWT, PRM1 and PRM2 genes variants on male infertility

Tobacco's genotoxic components can cause a wide range of gene defects in spermatozoa such as single- or double-strand DNA breaks, cross-links, DNA-adducts, higher frequencies of aneuploidy and chromosomal abnormalities. The aim in this study was to determine the correlation between sperm quality determined by standard parameters, sperm DNA maturity tested by Chromomycin A3 (CMA3) staining, sperm DNA fragmentation tested by TUNEL assay and tobacco smoking in association with the single nucleotides polymorphisms (SNP) of three nuclear protein genes in spermatozoa (H2BFWT, PRM1 and PRM2). In this study, semen samples of 167 male patients were collected and divided into 54 non-smokers and 113 smokers. The target sequences in the extracted sperm DNA were amplified by PCR followed by Sanger sequencing. The results showed the presence of three variants: rs7885967, rs553509 and rs578953 in H2BFWT gene in the study population. Only one variant rs737008 was detected in PRM1 gene, and three variants were detected in the PRM2 gene: rs2070923, rs1646022 and rs424908. No significant association was observed between the concentration, progressive motility, morphology and the occurrence of H2BFWT, PRM1 and PRM2 SNPs. However, sperm parameters were significantly lower in heavy smokers compared to controls (p < 0.01) (sperm count: 46.00 vs. 78.50 mill/ml, progressive motility: 15.00% vs. 22.00%, and morphology 4.00% vs. 5.00%, respectively). Moreover, the heavy smoker individuals exhibited a considerable increase in CMA3 positivity and sDF compared to non-smokers (p < 0.01) (29.50% vs. 20.50% and 24.50% vs. 12.00%, respectively). In conclusion, smoking altered sperm parameters and sperm DNA integrity, but did not show a linkage with genetic variants in H2BFWT, and protamine genes (PRM1 and PRM2).

Smoking and Its Consequences on Male and Female Reproductive Health

Smoking contributes to the death of around one in 10 adults worldwide. Specifically, cigarettes are known to contain around 4000 toxins and chemicals that are hazardous in nature. The negative effects of smoking on human health and interest in smoking-related diseases have a long history. Among these concerns are the harmful effects of smoking on reproductive health. Thirteen percent of female infertility is due to smoking. Female smoking can lead to gamete mutagenesis, early loss of reproductive function, and thus advance the time to menopause. It has been also associated with ectopic pregnancy and spontaneous abortion. Even when it comes to assisted reproductive technologies cycles, smokers require more cycles, almost double the number of cycles needed to conceive as non-smokers. Male smoking is shown to be correlated with poorer semen parameters and sperm DNA fragmentation. Not only active smokers but also passive smokers, when excessively exposed to smoking, can have reproductive problems comparable to those seen in smokers. In this book chapter, we will approach the effect of tobacco, especially tobacco smoking, on male and female reproductive health. This aims to take a preventive approach to infertility by discouraging smoking and helping to eliminate exposure to tobacco smoke in both women and men.

Genetic variations as molecular diagnostic factors for idiopathic male infertility: current knowledge and future perspectives

INTRODUCTION

Infertility is a major health problem, worldwide, which affects 10-15% of couples. About half a percent of infertility cases are related to male-related factors. Male infertility is a complex disease that is the result of various insults as lifestyle issues, genetics, and epigenetic factors. Idiopathic infertility is responsible for 30% of total cases. The genetic factors responsible for male infertility include chromosomal abnormalities, deletions of chromosome Y, and mutations and genetic variations of key genes.

AREAS COVERED

In this review article, we aim to narrate performed studies on polymorphisms of essential genes involved in male infertility including folate metabolizing genes, oxidative stress-related genes, inflammation, and cellular pathways related to spermatogenesis. Moreover, possible pathophysiologic mechanisms responsible for genetic polymorphisms are discussed.

EXPERT OPINION

Analysis and assessment of these genetic variations could help in screening, diagnosis, and treatment of idiopathic male infertility.

Association between CYP1A1 rs4646903 T > C genetic variations and male infertility risk: A meta-analysis

BACKGROUND

Number of studies have been performed to investigate the relationship between the CYP1A1 rs4646903 polymorphism and male infertility risk, but the sample size was small and the results were conflicting. A meta-analysis was performed to assess these associations.

METHODS

A systematic search was conducted to identify all relevant studies from Medline, Web of science, Embase, China biology medical literature database (CBM), China National Knowledge Infrastructure (CNKI), WanFang and Weipu (VIP) databases up to June 30, 2018. The odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to assess the strength of associations. All of the statistical analyses were conducted using Revman 5.3 and Stata 14.0.

RESULTS

Ten studies involved 3028 cases and 3258 controls. Overall, significant association was observed between the CYP1A1 rs4646903 polymorphism and male infertility (C vs T: OR = 1.42, 95%CI = 1.14-1.76; CC vs TT: OR = 2.13, 95%CI = 1.36-3.34; CC vs CT+TT: OR = 1.96, 95%CI = 1.30-2.95; CC+CT vs TT: OR = 1.51, 95%CI = 1.16-1.97). In subgroup analysis by ethnic group, a statistically significant association was observed in Asians (C vs T: OR = 1.59, 95%CI = 1.22-2.08), but not in Non-Asians (C vs T: OR = 1.01, 95%CI = 0.79-1.30). Additionally, none of the individual studies significantly affected the association between CYP1A1 rs4646903 polymorphism and male infertility, according to sensitivity analysis.

CONCLUSION

Our meta-analysis supports that the CYP1A1 rs4646903 polymorphism might contribute to individual susceptibility to male infertility in Asians.

Environmental PAH exposure and male idiopathic infertility: a review on early life exposures and adult diagnosis

The male reproductive system is acutely and uniquely sensitive to a variety of toxicities, including those induced by environmental pollutants throughout the lifespan. Early life hormonal and morphological development results in several especially sensitive critical windows of toxicity risk associated with lifelong decreased reproductive health and fitness. Male factor infertility can account for over 40% of infertility in couples seeking treatment, and 44% of infertile men are diagnosed with idiopathic male infertility. Human environmental exposures are poorly understood due to limited available data. The latency between maternal and in utero exposure and a diagnosis in adulthood complicates the correlation between environmental exposures and infertility. The results from this review include recommendations for more and region specific monitoring of polycyclic aromatic hydrocarbon (PAH) exposure, longitudinal and clinical cohort considerations of exposure normalization, gene-environment interactions, in utero exposure studies, and controlled mechanistic animal experiments. Additionally, it is recommended that detailed semen analysis and male fertility data be included as endpoints in environmental exposure cohort studies due to the sensitivity of the male reproductive system to environmental pollutants, including PAHs.

CYP1A1 3801T>C polymorphism implicated in altered xenobiotic metabolism is not associated with variations in sperm production and function as measured by total motile sperm and fertilization rates with intracytoplasmic sperm injection

OBJECTIVE

To evaluate the cytochrome P450 3801T>C polymorphism's frequency in relation to semen production, as determined by semen analysis parameters, and sperm function, as determined by fertilization rates with intracytoplasmic sperm injection (ICSI).

DESIGN

Case-control study.

SETTING

Academic-affiliated private practice.

PATIENT(S)

This study included patients undergoing IVF from 2004 to 2014 grouped into categories based on semen analysis parameters performed at a single andrology laboratory. Cases were patients with total motile sperm (TMS) counts of ≤20 × 10(6). Frequency-matched controls were selected with TMS of >20 × 10(6).

INTERVENTION(S)

The 3801T>C polymorphism was identified using DNA from serum samples with real-time quantitative polymerase chain reaction.

MAIN OUTCOME MEASURE(S)

CYP1A1 3801T>C polymorphism frequency in TMS groups and distribution in fertilization rate outcomes with ICSI.

RESULT(S)

A total of 460 cases were identified with ≤20 × 10(6) TMS, and 489 age-matched controls with >20 × 10(6) TMS were selected across the study time frame. For those with <5 × 10(6) vs. >20 × 10(6) TMS there was no difference when comparing heterozygous (odds ratio [OR] 0.96; 95% confidence interval [CI] 0.66-1.40) or homozygous mutant (OR 1.33; 95% CI 0.52-3.20) with the wild-type patients. Additionally, no difference was seen when analyzing subgroups <5 × 10(6), 5-20 × 10(6), and >20 × 10(6) TMS in a similar fashion. Receiver operating characteristic (ROC) curve analysis did not find a significant TMS count based on presence of the polymorphism (area under the ROC curve = 0.51). There were 460 patients who underwent IVF/ICSI, and fertilization rates did not differ with presence of the polymorphism (area under the ROC curve = 0.50).

CONCLUSION(S)

Allele frequency of the 3801T>C polymorphism does not correlate with semen production as determined by TMS counts or sperm function as determined by fertilization rates with ICSI. The use of neither semen analysis parameters nor fertilization rates with ICSI helps identify CYP1A1 polymorphism carriers.

Smoking and Male Infertility: An Evidence-Based Review

Many studies have reported that the contents of cigarette smoke negatively affect sperm parameters, seminal plasma, and various other fertility factors. Nevertheless, the actual effect of smoking on male fertility is not clear. The effect of smoking on semen parameters is based on the well-established biological finding that smoking increases the presence of reactive oxygen species, thereby resulting in oxidative stress (OS). OS has devastating effects on sperm parameters, such as viability and morphology, and impairs sperm function, hence reducing male fertility. However, not all studies have come to the same conclusions. This review sheds light upon the arguable association between smoking and male fertility and also assesses the impact of non-smoking routes of tobacco consumption on male infertility. It also highlights the evidence that links smoking with male infertility, including newly emerging genetic and epigenetic data, and discusses the clinical implications thereof.

Joint effect of glutathione S-transferase genotypes and cigarette smoking on idiopathic male infertility

Inconsistent results of association studies investigated the role of glutathione S-transferase genes in idiopathic male infertility may be explained by ethnical differences in gene-gene and gene-environment interactions. In this study, we investigated a joint contribution of GSTM1, GSTT1 and GSTP1 gene polymorphisms and cigarette smoking to the risk of idiopathic infertility in Russian men. DNA samples from 203 infertile and 227 fertile men were genotyped by a multiplex polymerase chain reaction (GSTM1 and GSTT1 deletions) and PCR-restriction fragment length polymorphism (GSTP1 I105V) methods. The GSTP1 genotype 105IV was associated with increased risk of male infertility (OR = 1.50 95% CI 1.02-2.20 P = 0.04). Genotype combinations GSTP1 105II/GSTT1 del (G1), GSTM1 del/GSTT1 del (G2) and GSTM1 + /GSTT1 del (G3) were associated with decreased risk of male infertility (P ≤ 0.003), whereas a genotype combination GSTP1 105IV/GSTT1 + (G4) was associated with increased disease risk (P = 0.001). The genotype combinations G3 and G4 showed a significant association with infertility in smokers; however, nonsmokers carriers did show the disease risk. In conclusion, GSTM1, GSTT1 and GSTP1 genes are collectively involved in the development of idiopathic male infertility and their phenotypic effects on the disease risk are potentiated by cigarette smoking.

Synergism between the N-acetyltransferase 2 gene and oxidant exposure increases the risk of idiopathic male infertility

N-acetyltransferase (NAT2) is a phase-II xenobiotic-metabolizing enzyme participating in the detoxification of toxic arylamines, aromatic amines and hydrazines. The present study was designed to investigate whether two common single-nucleotide polymorphisms (SNP) of the NAT2 gene (481C>T, rs1799929; 590G>A, rs1799930) are associated with susceptibility to idiopathic male infertility and to assess if the risk is modified by oxidant and antioxidant exposures. A total 430 DNA samples (203 infertile patients and 227 fertile men) were genotyped for the polymorphisms by PCR and restriction fragment length polymorphism. No association was found between the NAT2 polymorphisms and idiopathic male infertility. However, gene-environment interaction analysis revealed that a low-acetylation genotype, 590GA, was significantly associated with increased disease risk in men who had environmental risk factors such as cigarette smoking (OR 1.71, 95% CI 1.02-2.87, P = 0.042), alcohol abuse (OR 2.14, 95% CI 1.08-4.27, P = 0.029) and low fruit/vegetable intake (OR 1.68, 95% CI 1.01-2.79, P = 0.04). This pilot study found, as far as is known for the first time, that the polymorphism 590G>A of NAT2 is a novel genetic marker for susceptibility to idiopathic male infertility, but the risk is potentiated by exposure to various environmental oxidants.

Association between 3801T>C polymorphism of CYP1A1 and idiopathic male infertility risk: a systematic review and meta-analysis

BACKGROUND

Epidemiological studies have evaluated the association between 3801T>C polymorphism of CYP1A1 gene and the risk for idiopathic male infertility, but the results are inconclusive. We aimed to derive a more precise estimation of the relationship by conducting a meta-analysis of case-control studies.

METHODS

This study conformed to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. PubMed, Embase and CNKI databases were searched through November 2013 to identify relevant studies. Pooled odds ratios with 95% confidence intervals were used to assess the strength of the association between CYP1A1 3801T>C polymorphism and idiopathic male infertility risk. Q-test was performed to evaluate between-study heterogeneity and publication bias was appraised using funnel plots. Sensitivity analyses were conducted to evaluate the robustness of meta-analysis findings.

RESULTS

Six studies involving 1,060 cases and 1,225 controls were included in this meta-analysis. Overall, significant associations between 3801T>C polymorphism and idiopathic male infertility risk were observed in allelic comparison (OR = 1.36, 95% CI: 1.01-1.83), homozygous model (OR = 2.18, 95% CI: 1.15-4.12), and recessive model (OR = 1.86, 95% CI: 1.09-3.20), with robust findings according to sensitivity analyses. However, subgroup analyses did not further identify the susceptibility to idiopathic male infertility in all comparisons. Funnel plot inspections did not reveal evidence of publication bias.

CONCLUSIONS

The current meta-analysis provides evidence of a significant association between CYP1A1 3801T>C polymorphism and idiopathic male infertility risk. Considering the limitation inherited from the eligible studies, further confirmation in large-scale and well-designed studies is needed.