Urinary metabolome identifies signatures of oligozoospermic infertile men

The Role of One-Carbon Metabolism and Methyl Donors in Medically Assisted Reproduction: A Narrative Review of the Literature

One-carbon (1-C) metabolic deficiency impairs homeostasis, driving disease development, including infertility. It is of importance to summarize the current evidence regarding the clinical utility of 1-C metabolism-related biomolecules and methyl donors, namely, folate, betaine, choline, vitamin B12, homocysteine (Hcy), and zinc, as potential biomarkers, dietary supplements, and culture media supplements in the context of medically assisted reproduction (MAR). A narrative review of the literature was conducted in the PubMed/Medline database. Diet, ageing, and the endocrine milieu of individuals affect both 1-C metabolism and fertility status. In vitro fertilization (IVF) techniques, and culture conditions in particular, have a direct impact on 1-C metabolic activity in gametes and embryos. Critical analysis indicated that zinc supplementation in cryopreservation media may be a promising approach to reducing oxidative damage, while female serum homocysteine levels may be employed as a possible biomarker for predicting IVF outcomes. Nonetheless, the level of evidence is low, and future studies are needed to verify these data. One-carbon metabolism-related processes, including redox defense and epigenetic regulation, may be compromised in IVF-derived embryos. The study of 1-C metabolism may lead the way towards improving MAR efficiency and safety and ensuring the lifelong health of MAR infants.

A metabolomic perspective on the mechanisms by which environmental pollutants and lifestyle lead to male infertility

The incidence of male infertility (MI) is rising annually. According to epidemiological studies, environmental pollution (e.g., organic, inorganic, and air pollutants), occupational exposure (e.g., high temperature, organic solvents, and pesticides), and poor lifestyle (e.g., diet, sleep, smoking, alcohol consumption, and exercise) are important non-genetic causative factors of MI. Due to multiple and complex causative factors, the dose-effect relationship, and the uncertainty of pathogenicity, the pathogenesis of MI is far from fully clarified. Recent data show that the pathogenesis of MI can be monitored by the metabolites in serum, seminal plasma, urine, testicular tissue, sperm, and other biological samples. It is considered that these metabolites are closely related to MI phenotypes and can directly reflect the individual pathological and physiological conditions. Therefore, qualitative and quantitative analysis of the metabolome, the related metabolic pathways, and the identification of biomarkers will help to explore the MI-related metabolic problems and provide valuable insights into its pathogenic mechanisms. Here, we summarized new findings in MI metabolomics biomarkers research and their abnormal metabolic pathways triggered by the presented non-genetic risk factors, providing a metabolic landscape of semen and seminal plasma in general MI patients. Then, we compared the similarities and differences in semen and seminal plasma biomarkers between MI patients exposed to environmental and poor lifestyle factors and MI patients in general, and summarized some common biomarkers. We provide a better understanding of the biological underpinnings of MI pathogenesis, which might offer novel diagnostic, prognostic, and precise treatment approaches to MI.

Metabolomics of male infertility

This review explores the use of metabolomics in male infertility. Metabolomics, an evolving omics technology that targets the products of cellular metabolism, is valuable for elucidating underlying pathophysiology of many disorders including male infertility. The identification of reliable biomarkers is essential for accurate diagnosis and for developing precision therapeutics for those afflicted by reproductive dysfunction. Unfortunately, despite significant progress to date, the intricate relationships between these metabolic pathways and male infertility remain elusive. It is clear, however, that additional research is required to more fully characterize the role of metabolomics in this disorder and in the potential development of targeted therapies for precision medicine.

Exploring the internal exposome of seminal plasma with semen quality and live birth: A Pilot Study

Infertility is clinically defined as the inability to achieve pregnancy within 12 months of regular unprotected sexual intercourse and affects 15% of couples worldwide. Therefore, the identification of novel biomarkers that can accurately predict male reproductive health and couples' reproductive success is of major public health significance. The objective of this pilot study is to test whether untargeted metabolomics is capable of discriminating reproductive outcomes and understand associations between the internal exposome of seminal plasma and the reproductive outcomes of semen quality and live birth among ten participants undergoing assisted reproductive technology (ART) in Springfield, MA. We hypothesize that seminal plasma offers a novel biological matrix by which untargeted metabolomics is able to discern male reproductive status and predict reproductive success. The internal exposome data was acquired using UHPLC-HR-MS on randomized seminal plasma samples at UNC at Chapel Hill. Unsupervised and supervised multivariate analyses were used to visualize the differentiation of phenotypic groups classified by men with normal or low semen quality based on World Health Organization guidelines as well as by successful ART: live birth or no live birth. Over 100 exogenous metabolites, including environmentally relevant metabolites, ingested food components, drugs and medications, and metabolites relevant to microbiome-xenobiotic interaction, were identified and annotated from the seminal plasma samples, through matching against the NC HHEAR hub in-house experimental standard library. Pathway enrichment analysis indicated that fatty acid biosynthesis and metabolism, vitamin A metabolism, and histidine metabolism were associated sperm quality; while pathways involving vitamin A metabolism, C21-steroid hormone biosynthesis and metabolism, arachidonic acid metabolism, and Omega-3 fatty acid metabolism distinguished live birth groups. Taken together, these pilot results suggest that seminal plasma is a novel matrix to study the influence of the internal exposome on reproductive health outcomes. Future research aims to increase the sample size to validate these findings.

Environmental metal exposure, seminal plasma metabolome and semen quality: Evidence from Chinese reproductive-aged men

Environmental metal exposure has been associated with decreasing semen quality, but the effects of multiple metal exposure on seminal plasma metabolome remain obscure. In this study, semen and repeated urine samples from 551 volunteers were collected in Wuhan City. Heavy metals and trace elements were measured using inductively coupled plasma mass spectrometer, and seminal plasma metabolomes were acquired using liquid chromatography coupled with high-resolution mass spectrometry. Weighted gene co-expression network analysis showed more than half of the seminal plasma metals were associated with specific metabolite modules, whereas only a few urine metals presented weak associations, indicating that seminal plasma may be an ideal biological sample for male reproductive biomarker discovery and exposure risk assessment. Seminal plasma zinc (Zn) and selenium (Se) concentrations were significantly associated with 22 metabolites (e.g., glycerophospholipids, acyl-carnitines and amino acid derivatives). Among these metabolites, acyl-carnitines were positively associated with semen quality and sperm concentration. Moreover, acyl-carnitines were associated with both Zn and Se exposure, indicating the potential role of carnitine pathway in their toxicity mechanism. Our findings suggest that seminal plasma metabolome connects Zn and Se exposure and sperm concentrations in Chinese men of reproductive age.

Prediction of semen analysis parameters improvement after varicocelectomy using 1 H NMR-based metabonomics assays

BACKGROUND

Varicocele is the most common correctable cause of male infertility, however, predicting varicocelectomy outcomes is difficult. "Omics" techniques have been increasingly used to develop new diagnostic and prognostics tools for several male infertility causes, and could be applied to study varicocele.

OBJECTIVES

To create metabolomics models capable of segregating men who improved semen analysis (SA) parameters or achieved natural pregnancy after microsurgical varicocelectomy (MV) from those who did not, using Hydrogen-1 nuclear magnetic resonance (¹ H NMR) spectra of seminal plasma of pre-operative samples.

MATERIAL AND METHODS

We recruited 29 infertile men with palpable varicocele. ¹ H NMR spectra of seminal plasma were obtained from pre-operative samples and used to create metabonomics models. Improvement was defined as an increase in the total motile progressive sperm count (TMC) of the post-operative SA when compared to the baseline, and pregnancy was assessed during 24 months after MV.

RESULTS

Using Linear Discriminant Analysis (LDA), we created a model that discriminated the men who improved SA from those who did not with accuracy of 93.1%. Another model segregated men who achieved natural pregnancy from men who did not. We identified 7 metabolites that were important for group segregation: caprylate, isoleucine, N-acetyltyrosine, carnitine, N-acetylcarnitine, creatine and threonine.

DISCUSSION

We described the use of metabonomics model to predict with high accuracy the outcomes of MV in infertile men with varicocele. The most important metabolites for groups segregation are involved in energy metabolism and oxidative stress response, highlighting the pivotal role of these mechanisms in the pathophysiology of varicocele.

CONCLUSIONS

¹ H NMR spectroscopy of seminal plasma can be used in conjunction with multivariate statistical tools to create metabonomics models useful segregate men with varicocele based on the reproductive outcomes of MV. These models may help counseling infertile men with varicocele regarding their prognosis after surgery. This article is protected by copyright. All rights reserved.

Effect of environmental temperature on semen quality and seminal plasma metabolites of Mediterranean buffalo bulls

High-quality semen with high viability is critical to improving the in-vitro fertilization efficiency. This study aimed to understand the effect of ambient temperature and humidity on semen quality and seminal plasma biochemical parameters of Mediterranean buffalo in March and July. The metabolites of seminal plasma in two seasons were detected using the UPLC-MS/MS method. The results showed that temperature and humidity index (THI) in March were 66.86 ± 2.98, and 82.94 ± 3.52 in July. Compared with in March, breath frequency, rectal temperature, and heat shock protein 70 expressions of seminal plasma were significantly increased in July (p < 0.05), motility of sperm was dramatically reduced, and sperm deformity rate was significantly increased (p < 0.05). Fructose, acid phosphatase and α-glucosidase in seminal plasma were significantly increased (p < 0.05) in July, while testosterone level was significantly reduced (p < 0.05). Six different metabolites were found in the two groups, which involved in three metabolic pathways, the tricarboxylic acid cycle, glycerophospholipid, glyoxylic acid and dicarboxylic acid. The above results indicate that the increased ambient temperature has obvious side effects on the semen quality of Mediterranean buffalo, and the compromised quality is associated with the change of metabolites related to male hormone secretion, energy metabolism and fatty acid oxidation.

K. M, Karthikkeyan G, Prasad TSK, Modi PK, Datta TK, Ramesha K, Manimaran A, Jeyakumar S. Deep Metabolomic Profiling Reveals Alterations in Fatty Acid Synthesis and Ketone Body Degradations in Spermatozoa and Seminal Plasma of Astheno-Oligozoospermic Bulls

Male fertility is extremely important in dairy animals because semen from a single bull is used to inseminate several thousand females. Asthenozoospermia (reduced sperm motility) and oligozoospermia (reduced sperm concentration) are the two important reasons cited for idiopathic infertility in crossbred bulls; however, the etiology remains elusive. In this study, using a non-targeted liquid chromatography with tandem mass spectrometry-based approach, we carried out a deep metabolomic analysis of spermatozoa and seminal plasma derived from normozoospermic and astheno-oligozoospermic bulls. Using bioinformatics tools, alterations in metabolites and metabolic pathways between normozoospermia and astheno-oligozoospermia were elucidated. A total of 299 and 167 metabolites in spermatozoa and 183 and 147 metabolites in seminal plasma were detected in astheno-oligozoospermic and normozoospermic bulls, respectively. Among the mapped metabolites, 75 sperm metabolites were common to both the groups, whereas 166 and 50 sperm metabolites were unique to astheno-oligozoospermic and normozoospermic bulls, respectively. Similarly, 86 metabolites were common to both the groups, whereas 45 and 37 seminal plasma metabolites were unique to astheno-oligozoospermic and normozoospermic bulls, respectively. Among the differentially expressed metabolites, 62 sperm metabolites and 56 seminal plasma metabolites were significantly dysregulated in astheno-oligozoospermic bulls. In spermatozoa, selenocysteine, deoxyuridine triphosphate, and nitroprusside showed significant enrichment in astheno-oligozoospermic bulls. In seminal plasma, malonic acid, 5-diphosphoinositol pentakisphosphate, D-cysteine, and nicotinamide adenine dinucleotide phosphate were significantly upregulated, whereas tetradecanoyl-CoA was significantly downregulated in the astheno-oligozoospermia. Spermatozoa from astheno-oligozoospermic bulls showed alterations in the metabolism of fatty acid and fatty acid elongation in mitochondria pathways, whereas seminal plasma from astheno-oligozoospermic bulls showed alterations in synthesis and degradation of ketone bodies, pyruvate metabolism, and inositol phosphate metabolism pathways. The present study revealed vital information related to semen metabolomic differences between astheno-oligozoospermic and normospermic crossbred breeding bulls. It is inferred that fatty acid synthesis and ketone body degradations are altered in the spermatozoa and seminal plasma of astheno-oligozoospermic crossbred bulls. These results open up new avenues for further research, and current findings can be applied for the modulation of identified pathways to restore sperm motility and concentration in astheno-oligozoospermic bulls.

Analytical aspects of meet-in-metabolite analysis for molecular pathway reconstitution from exposure to adverse outcome

To explore the etiology of diseases is one of the major goals in epidemiological study. Meet-in-metabolite analysis reconstitutes biomonitoring-based adverse outcome (AO) pathways from environmental exposure to a disease, in which the chemical exposome-related metabolism responses are transmitted to incur the AO-related metabolism phenotypes. However, the ongoing data-dependent acquisition of non-targeted biomonitoring by high-resolution mass spectrometry (HRMS) is biased against the low abundance molecules, which forms the major of molecular internal exposome, i.e., the totality of trace levels of environmental pollutants and/or their metabolites in human samples. The recent development of data-independent acquisition protocols for HRMS screening has opened new opportunities to enhance unbiased measurement of the extremely low abundance molecules, which can encompass a wide range of analytes and has been applied in metabolomics, DNA, and protein adductomics. In addition, computational MS for small molecules is urgently required for the top-down exposome databases. Although a holistic analysis of the exposome and endogenous metabolites is plausible, multiple and flexible strategies, instead of "putting one thing above all" are proposed.

Assessment of Blood Plasma Free-amino Acid Levels in Infertile Men

BACKGROUND/AIM

The objective of this study was to investigate the significance of the blood levels of free amino acids (AAs) in infertile men.

PATIENTS AND METHODS

Ninety-three men who underwent examinations for infertility were included. The concentrations of 20 AAs were measured and compared in four groups (normospermia, obstructive azoospermia, oligozoospermia, non-obstructive azoospermia) based on semen analysis and clinical parameters.

RESULTS

When the 93 men were divided into normospermia, obstructive azoospermia, oligozoospermia, and non-obstructive azoospermia groups, no significant differences were found in the concentrations of the 20 AAs between them. We then compared 49 men diagnosed with normozoospermia or oligozoospermia according to the median sperm motility and morphology abnormalities rates (30% and 20%, respectively). Men with low motility rates had significantly lower levels of tryptophan and alanine, and men with high abnormal morphology rates had significantly lower levels of aspartate and glutamate.

CONCLUSION

AAs are probably involved in the pathogenesis of male infertility, particularly oligozoospermia.

Cardiorespiratory Effects of Indoor Ozone Exposure Associated with Changes in Metabolic Profiles among Children: A Repeated-Measure Panel Study

Ozone is one of the major gaseous pollutants associated with short-term adverse cardiopulmonary effects, even at concentrations below the current indoor air quality limits. However, the underlying biological mechanisms of cardiorespiratory changes with exposure to ozone remain unclear. To further explore molecular linkages between indoor ozone exposure and relevant cardiorespiratory effects, a repeated-measure panel study including 46 schoolchildren was conducted and real-time exposure measurements including ozone were performed inside classrooms every weekday during the study period. Repeated health measurements and urine sample collection were conducted in each participant. Ultra-high-performance liquid chromatography/tandem mass spectrometry and meet-in-metabolite approach were used in metabolomics analysis. Methods including mixed-effect models were adopted to identify metabolites associated with ozone exposure or health indices. Nine metabolites were found to be associated with ozone after mixed-effect model analysis, which are mainly involved in amino acid and bile acid metabolism. Boys may have a greater decrease in bile acid and RNA related metabolites. Four of the nine ozone-related metabolites were also associated with cardiorespiratory function indices. Furthermore, 26.67% of the positive association between ozone and heart rate was mediated by cholestane-3,7,12,25-tetrol-3-glucuronide. Exposure to ozone below the current indoor standards was associated with the deteriorated cardiovascular function by disturbing bile acid and endogenous nitric oxide-related oxidation and inflammation, and associated with the exacerbated airway inflammation by reducing GPx-related anti-oxidation. The results provide metabolic evidence of the cardiorespiratory effects of indoor ozone exposure. Indoor ozone pollution should be controlled further, and more attention should be paid to preventing its adverse health effects, especially in children.

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Indoor O₃ exposure far below the indoor air quality limits disturbed amino acid and bile acid metabolism of children

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Exposure to indoor O₃ at low concentrations was associated with the deteriorated HRV, BP by affecting bile acid- and endogenous NO-related oxidation and inflammation

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Exposure to indoor O₃ at low concentrations was associated with the aggravated airway inflammation by reducing GPx-related anti-oxidation

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The cardiorespiratory effects of low-level ozone exposure indoors in children require additional attention

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Indoor ozone pollution should be controlled further and the current indoor ozone standards should be revised

Meet-in-metabolite analysis: A novel strategy to identify connections between arsenic exposure and male infertility

BACKGROUND

Despite a trend in the use of systems epidemiology to fill the knowledge gap between risk-factor exposure and adverse outcomes in the OMICS data, such as the metabolome, seriously hindrances need to be overcome for identifying molecular connections.

OBJECTIVES

Using male infertility phenotypes and arsenic exposure, we aimed to identify intermediate biomarkers that reflect both arsenic exposure and male infertility with a meet-in-metabolite analysis (MIMA).

METHODS

Urinary arsenic levels and metabolome were measured by using inductively coupled plasma-mass spectrometry (ICP-MS) and HPLC-quadrupole time-of-flight mass spectrometry (HPLC-QTOF-MS), respectively. To identify arsenic-related metabolic markers (A-MIMA), the intermediate markers were profiled by orthogonal projections to latent structures (OPLS-DA). To detect infertility-related metabolic markers (I-MIMA), the intermediate markers were investigated by weighted gene co-expression network analysis. The key node markers, related to both A-MIMA and I-MIMA, were determined by O2PLS and defined as MIMA markers. Finally, network analysis was used to construct the MIMA-related metabolic network.

RESULTS

Twelve markers each were defined through the significant associations with arsenic exposure (A-MIMA) and/or infertility (I-MIMA), respectively. Seven of them, including acetyl-N-formyl-5-methoxykynurenamine, carnitine, estrone, 2-oxo-4-methylthiobutanoic acid, malonic acid, valine, and LysoPC (10:0), were defined through the associations with both arsenic exposure and male infertility (MIMA markers). These intermediate markers were involved majorly in oxidative stress, one-carbon metabolism, steroid hormone homeostasis, and lipid metabolism pathways. The core correlation network analysis further highlighted that testosterone is a vital link between the effect of arsenic and male infertility.

CONCLUSIONS

From arsenic exposure to male infertility, the arsenic methylation that coupled one-carbon metabolism disruption with oxidation stress may have extended its effect to fatty acid oxidation and steroidogenesis dysfunction. Testosterone is at the hub between arsenic exposure and male infertility modules and, along with the related metabolic pathways, may service as a potential surrogate marker in risk assessment for male dysfunction due to arsenic exposure.

Association of the serum metabolomic profile by nuclear magnetic resonance spectroscopy with sperm parameters: a cross-sectional study of 325 men

OBJECTIVE

To determine whether 155 circulating metabolic measures relevant to lifestyle and metabolic health are associated with sperm parameters, as measured by concentration, motility, and total motile sperm count (TMSC).

STUDY DESIGN

Cross sectional.

SETTING

University hospital.

PATIENT(S)

Three hundred twenty-five men prospectively recruited between April 1, 2017 and March 31, 2019.

INTERVENTION(S)

Detailed demographic, lifestyle, fertility, medical history, and semen analysis with quantification of nonfasting serum lipids, lipoprotein subclasses, and low-molecular weight metabolites (including amino acids, glycolysis, and inflammatory markers) by nuclear magnetic resonance (NMR) spectroscopy.

MAIN OUTCOME MEASURE(S)

Association of serum metabolic profiles with sperm parameters.

RESULT(S)

The age of the participants was mean 37.2 years, with a median sperm concentration of 35 million/mL and median motility of 53%. Of these men, 76% had a TMSC >15 million, 10% had 5-15 million, and 14% had <5 million. In both univariate and confounder adjusted analyses, an extensive range of lipids and lipoproteins, glycolysis-related metabolites, amino acids, ketone bodies, creatinine, or albumin showed no strong statistically significant association with sperm concentration, motility, or the odds of having a reduced or low TMSC. Higher levels of glycolysis metabolites and ketone bodies were associated with an increased odds of TMSC <15 million compared with ≥15 million (odds ratios of ∼1.2-1.3), and several lipids/lipoprotein concentrations appeared to protect against very low TMSC (<5 million compared with ≥5 million) with odds ratios of ∼0.8 or greater.

CONCLUSION(S)

Several metabolites exhibited potentially clinically relevant strength of association with the odds of a low TMSC and warrant replication.

Proteomics and metabolomics - Current and future perspectives in clinical andrology

Proteomics and metabolomics are emerging as promising tools to investigate the molecular mechanisms associated with male infertility. Proteins and metabolites play a pivotal role in regulating the molecular pathways associated with physiological functions of spermatozoa. Semen analysis, physical examination and laboratory work up cannot identify the etiology of infertility in 30%-40% of cases, which are classified as idiopathic. Therefore, the application of proteomics and metabolomics in the field of andrology will aid to overcome the limitations of the standard semen analysis. Understanding the molecular pathways associated with male infertility will help in planning ad hoc treatments, contributing to the clinical management of infertile patients. In this review, proteomics and metabolomics studies on spermatozoa and seminal plasma are discussed with a focus on molecular biomarkers associated with male infertility-related conditions.

Metabolomic characterization of semen from asthenozoospermic patients using ultra-high-performance liquid chromatography-tandem quadrupole time-of-flight mass spectrometry

Asthenozoospermia (AS) is a common factor of male infertility, and its pathogenesis remains unclear. The purpose of this study was to investigate the differential seminal plasma metabolic pattern in asthenozoospermic men and to identify potential biomarkers in relation to spermatogenic dysfunction using sensitive ultra‐high‐performance liquid chromatography–tandem quadruple time‐of‐flight MS (UHPLC–Q‐TOF/MS). The samples of seminal plasma from patients with AS (n = 20) and healthy controls (n = 20) were checked and differentiated by UHPLC–Q‐TOF/MS. Compared with the control group, the AS group showed a total of nine significantly different metabolites, including increases in creatinine, uric acid, N⁶‐methyladenosine (m⁶A), uridine, and taurine and decreases in carnitine, nicotinamide, N‐acetylputrescine and l‐palmitoylcarnitine. By analyzing the correlation among these metabolites and clinical computer‐assisted semen analysis reports, we found that m⁶A is significantly correlated with not only the four decreased metabolites but also with sperm count, motility, and curvilinear velocity. Furthermore, nicotinamide was shown to correlate with other identified metabolites, indicating its important role in the metabolic pathway of AS. Current results implied that sensitive untargeted seminal plasma metabolomics could identify distinct metabolic patterns of AS and would help clinicians by offering novel cues for discovering the pathogenesis of male infertility.

Seminal Fluid Metabolomic Markers of Oligozoospermic Infertility in Humans

Infertility affects 12–15% of couples worldwide, and male factors are the cause of nearly half of all cases. Studying seminal fluid composition could lead to additional diagnostic accuracy and a better understanding of the pathophysiology of male factor infertility. Metabolomics offers a new opportunity to evaluate biomarkers and better understand pathological mechanisms. The aim of the study was to identify new markers or therapeutic targets to improve outcomes in male factor or idiopathic infertility patients. Semen samples were obtained from 29 men with a normal spermogram test, and from 18 oligozoospermic men. Samples were processed and analyzed by Nuclear Magnetic Resonance spectroscopy and, subsequently, multivariate and univariate statistical analyses. Receiving Operator Curves (ROC) and Spearman correlations were also performed. An Orthogonal Partial Least Square Discriminant Analysis supervised multivariate model was devised to compare the groups. The levels of fructose, myo-inositol, aspartate and choline were altered. Moreover, Spearman Correlation associated fructose, aspartate and myo-inositol with the total amount of spermatozoa, total motile spermatozoa, % of immotility and % of “in situ” spermatozoic motility respectively. NMR-based metabolomics allowed the identification of a specific metabolic fingerprint of the seminal fluids of patients affected by oligozoospermia.

Seminal plasma metabolites mediate the associations of multiple environmental pollutants with semen quality in Chinese men

Environmental exposure to arsenic, phthalate esters (PAEs) and perfluorinated compounds (PFCs) has been associated with human semen quality. However, the epidemiological "black-box" of these associations remains poorly uncovered. In this study, based on the association analysis between arsenic, PAE and PFC exposure and semen quality parameters (i.e., semen volume, sperm concentration, sperm count, progressive motility, total motility and normal morphology) in a Chinese male population, we explored the seminal plasma metabolic signatures that may mediate the exposure-outcome relations by using the meet-in-metabolite-analysis (MIMA) approach. As a result, a negative association was found between DMA and sperm concentration, whereas MEHP and PFHxS were positively associated with sperm count and concentration, respectively. Metabolomics analysis revealed that sixteen and twenty-two seminal plasma metabolites were related to sperm concentration and count, respectively, and they are mainly involved in fatty acid, lipid and amino acid metabolism. Moreover, it was further indicated that eicosatetraenoate, carnitines and DHA may impact the inverse association between DMA and sperm concentration, while eicosatetraenoate, carnitines, DHA, PGB2 and tocotrienol are possible mediators of the positive association between PFHxS and sperm concentration. As these metabolic biomarkers are relevant to antioxidation and fatty acid β-oxidation, we suggest that redox balance and energy generation shifts in seminal plasma are involved in the association of human semen quality with environmental DMA and PFHxS exposure.

Seminal plasma metabolome in relation to semen quality and urinary phthalate metabolites among Chinese adult men

BACKGROUND

A growing body of evidence has found links between endocrine disruptor phthalates and male reproductive disorders, but the mechanisms underlying these relationships are poorly known. Seminal plasma metabolomes may mediate associations of phthalate exposure with impaired semen quality.

OBJECTIVE

To identify seminal plasma metabolomes associated with poor semen quality and evaluate their associations with urinary phthalate metabolites among 660 Chinese adult men.

METHOD

The seminal plasma metabolic profiles were acquired using an untargeted approach based on liquid chromatography-high resolution mass spectrometry. We explored the differences in seminal plasma metabolites between participants with poor and good semen quality and evaluated cross-sectional associations between discriminatory metabolic biomarkers and urinary phthalate metabolites.

RESULTS

Differences between poor and good semen quality groups were observed in relation to 25 seminal plasma metabolites, mostly related to the metabolism of polyunsaturated fatty acids (PUFA) and acylcarnitine (all p < 0.05). After adjusting for various confounders and multiple tests, metabolites were all significantly associated with one or more individual sperm quality parameters (motility, concentration, total count, and morphology) (all p < 0.05). Among identified metabolic biomarkers, seminal plasma L-palmitoylcarnitine, linoelaidyl carnitine, and oleic acid were inversely associated with urinary mono-(2-ethylhexyl) phthalate (MEHP), and seminal plasma L-acetylcarnitine was inversely associated with the proportion of di-(2-ethylhexyl)-phthalate metabolites (DEHP) excreted as MEHP in urine (%MEHP) (all p < 0.05). Mediation analysis revealed that oleic acid and L-acetylcarnitine mediated significant proportions (6.7% and 17%, respectively) of the positive associations between urinary DEHP metabolites and the percentage of spermatozoa with an abnormal head.

CONCLUSIONS

Elevated urinary phthalate metabolites may impact semen quality by causing metabolic disorders of seminal plasma PUFAs and acylcarnitine. These pathways warrant further investigation.

Characterizing semen abnormality male infertility using non-targeted blood plasma metabolomics

Semen abnormality (SA) male infertility has become a worldwide reproductive health problem. The invasive tests (e.g., testicular biopsy) and labor-intensive methods of semen collection severely inhibit diagnosis of male infertility. In addition, the pathogenesis and biological interpretation of male infertility are still obscure. In this report, a total of 84 semen abnormality (SA) patients, diagnosed as teratozoospermia (TE, n = 21), asthenozoospermia (AS, n = 23), oligozoospermia (OL, n = 20), azoospermia (AZ, n = 20), and age-matched healthy controls (HC, n = 29) were analyzed by GC-MS for discrimination analysis and discovery of potential biomarkers. Twenty-three biomarkers were obtained by multivariate statistical method (partial least squares-discriminant analysis, PLS-DA) and univariate statistical method (analysis of variance, ANOVA) with comparisons of TE versus HC, AS versus HC, OL versus HC and AZ versus HC. Based on those biomarkers, the most relevant pathways were mainly associated with the metabolism of carbohydrates, amino acids, and lipids. The principal metabolic alternations in SA male infertility included increased levels of energy-related metabolisms, such as tricarboxylic acid cycle, pyruvate metabolism, glyoxylate and dicarboxylate metabolism, glycine, serine, threonine metabolism and saturated fatty acid metabolism. Furthermore, increased levels of glutathione metabolism were related to oxidative stress. Finally, decreased levels of arginine and proline metabolism and inositol phosphate metabolism were observed. In conclusion, blood plasma metabolomics is powerful for characterizing metabolic disturbances in SA male infertility. From metabolic pathway analysis, energy production, oxidation stress and the released enzyme during spermatogenesis take the primary responsibilities for SA male infertility.

Using a high-resolution mass spectrometry-based metabolomics strategy for comprehensively screening and identifying biomarkers of phthalate exposure: Method development and application

Di-(2-propylheptyl) phthalate (DPHP) is an alternative plasticizer that can replace other phthalates currently being scrutinized, and its use and production volumes are increasing. This study aimed to develop a high-resolution mass spectrometry (HRMS)-based metabolomics strategy to comprehensively screen urinary biomarkers of DPHP exposure and filter out potentially useful DPHP exposure markers for human exposure assessments. This strategy included three stages: screening of biomarkers, verification of dose-response relationships in laboratory animals, and application in human subjects. The multivariate data analysis method known as orthogonal partial least-squares discriminant analysis (OPLS-DA) was used to screen and find meaningful signals in an MS dataset generated from urine samples collected from DPHP-administered rats. Thirty-six MS signals were verified as exposure marker candidates by assessing dose-response relationships in an animal feeding study. A biotransformation product of DPHP, mono-(2-propyl-7-dihydroxy-heptyl) phthalate, was suggested as a DPHP exposure marker for general human exposure assessments after the human application study and chemical structure identification. Three previously oxidized DPHP biotransformation products might be suitable for human exposure assessments in high-level exposure groups but not in the general population due to their low sensitivity.

Plasma metabolic profiling analysis of Strychnos nux-vomica Linn. and Tripterygium wilfordii Hook F-induced renal toxicity using metabolomics coupled with UPLC/Q-TOF-MS

Both Strychnos nux-vomica Linn. (SNV) and Tripterygium wilfordii Hook F (TwHF) have received extensive attention due to their excellent clinical efficacies. However, clinical applications of SNV and TwHF have been limited by their narrow therapeutic windows and severe kidney toxicities. In this paper, based on ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF-MS), endogenous metabolites after administration of SNV and TwHF extracts were detected, and biomarkers were screened successfully. Additionally, the levels of Cr and BUN in serum and pathological findings of kidneys were detected and observed. Finally, both biochemical and pathological tests of the SNV group and TwHF group indicated that kidney damage had occurred. After comparison with the normal saline group, 15 nephrotoxic biomarkers were selected from the SNV group, and 17 nephrotoxic biomarkers were selected from the TwHF group. The experimental results showed that there are some differences in the mechanisms of nephrotoxicity induced by SNV and TwHF, which are significant for revealing the mechanisms of renal injury of different medicines.

Tests for comparison of multiple endpoints with application to omics data

In biomedical research, multiple endpoints are commonly analyzed in "omics" fields like genomics, proteomics and metabolomics. Traditional methods designed for low-dimensional data either perform poorly or are not applicable when analyzing high-dimensional data whose dimension is generally similar to, or even much larger than, the number of subjects. The complex biochemical interplay between hundreds (or thousands) of endpoints is reflected by complex dependence relations. The aim of the paper is to propose tests that are very suitable for analyzing omics data because they do not require the normality assumption, are powerful also for small sample sizes, in the presence of complex dependence relations among endpoints, and when the number of endpoints is much larger than the number of subjects. Unbiasedness and consistency of the tests are proved and their size and power are assessed numerically. It is shown that the proposed approach based on the nonparametric combination of dependent interpoint distance tests is very effective. Applications to genomics and metabolomics are discussed.

Impaired sperm function in infertile men relies on the membrane sterol pattern

Membrane cholesterol removal appears a key step for the gain of fertility potential during sperm maturation. However, the membrane sterol pattern in sperm cells from infertile patients, with impaired sperm parameters, has been poorly investigated. To elucidate a causative link between sperm membrane composition in male fertility, here we have investigated the levels of cholesterol and its oxidized derivatives 7β-hydroxycholesterol and 7-keto-cholesterol in sixteen infertile patients with oligo-asthenozoospermia and 16 normozoospermic (N) fertile subjects. Furthermore, ten of 16 N fertile subjects agreed to receive a defined testicular thermal challenge by adhering to a programme of sauna sessions for 1 month. Semen samples were obtained from each of the participants, and sperm parameters were assessed according to the World Health Organization criteria. Sperm levels of cholesterol, 7β-hydroxycholesterol and 7-keto-cholesterol were quantified by ultra-pressure liquid chromatography mass spectrometry. The results showed that oligo-asthenozoospermia patients had a huge amount of cholesterol content compared with fertile subjects (12.40 ± 6.05 μg/10⁶ cells vs. 0.45 ± 0.28 μg/10⁶ cells, p < 0.001, N and oligo-asthenozoospermia, respectively). Also, oxidized derivatives were significantly higher in oligo-asthenozoospermia patients (7β-hydroxycholesterol: 1.96 ± 1.03 ng/10⁶ cells vs. 0.075 ± 0.05 ng/10⁶ cells, p < 0.001 and 7-keto-cholesterol: 1.11 ± 0.72 ng/10⁶ cells vs. 0.005 ± 0.003 ng/10⁶ cells, p < 0.001). Moreover, sauna exposure, in parallel with a progressive worsening of sperm motility parameters, was associated with a reversible increase in sperm cholesterol after the third and fourth week of treatment, whilst 7β-hydroxycholesterol and 7-keto-cholesterol levels showed an earlier enhancement starting from the second week. Our data show for the first time in humans a strong difference in the cholesterol and its oxidized derivatives of infertile and fertile subjects. These findings suggest a strict biochemical link relating testis function, sperm membrane status and male fertility potential.

Metabolic profiling putatively identifies plasma biomarkers of male infertility using UPLC-ESI-IT-TOFMS

Male infertility has become a global health problem. Currently, the diagnosis of male infertility depends on the results of semen quality or requires invasive surgical intervention. The process is complex and time-consuming. Metabolomics is an emerging platform with unique advantages in disease diagnosis and pathological mechanism research. In this study, ultra-performance liquid chromatography-electrospray ionization-ion trap-time of flight mass spectrometry (UPLC-ESI-IT-TOFMS) combined with chemometrics methods was used to discover potential biomarkers of male infertility based on non-targeted plasma metabolomics. Plasma samples from healthy controls (HC, n = 43) and various types of infertile patients, i.e., patients having oligozoospermia (OS, n = 36), asthenospermia (AS, n = 56) and erectile dysfunction (ED, n = 45) were analyzed by UPLC-ESI-IT-TOFMS. Principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) were performed. The results of OPLS-DA showed that HCs could be discriminated from infertile patients including OS (R² = 0.903, Q² = 0.617, AUC = 0.992), AS (R² = 0.985, Q² = 0.658, AUC = 0.999) or ED (R² = 0.942, Q² = 0.500, AUC = 0.998). Some potential biomarkers were successfully discovered by variable selection methods and variable important in the projection (VIP) in combination with the T-test. Statistical significance was set at p < 0.05; the Benjamini–Hochberg false discovery rate was used to reduce type 1 errors resulting from multiple comparisons. The identified biomarkers were associated with energy consumption, hormone regulation and antioxidant defenses in spermatogenesis. To elucidate the pathophysiology of male infertility, relative metabolic pathways were studied. It was found that male infertility is closely related to disturbed phospholipid metabolism, amino acid metabolism, steroid hormone biosynthesis metabolism, metabolism of fatty acids and products of carnitine acylation, and purine and pyrimidine metabolisms. Plasma metabolomics provides a novel strategy for the diagnosis of male infertility and offers a new insight to study pathogenesis mechanism.

Ultra-performance liquid chromatography-electrospray ionization-ion trap-time of flight mass spectrometry combined with chemometrics methods was used to discover potential biomarkers of male infertility based on untargeted plasma metabolomics.

Plasma metabolic profiling analysis of Cortex Periplocae-induced cardiotoxicity based on UPLC/Q-TOF-MS

Cortex Periplocae is a well-known form of traditional medicine with its unique cardiotonic action, anti-tumor activity and immune regulation effect. However, improper use of Cortex Periplocae often leads to cardiac toxicity, which in the most severe cases can even be life-threatening. Biochemical tests and histopathological examinations are primary methods for clinical trials. However, such approaches are time-consuming, lack specificity and have low sensitivity, which can easily lead to negative results in studies. Therefore, a more scientific and systematic evaluation of Cortex Periplocae cardiotoxicity is particularly important. In this study, we established a method that combines metabonomics with trend analysis of a gavage concentration series to find cardiac toxicity biomarkers of Cortex Periplocae. We created rat cardiotoxicity models, in which the toxicity was caused by Cortex Periplocae. We collected data from rat plasma samples based on metabonomics using ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF-MS). Multiple statistical analyses, such as principal component analysis (PCA) and partial least squares-discriminant analysis (PLS-DA), were used to examine metabolite profile changes in plasma samples to screen potential cardiotoxicity biomarkers and metabolic pathways. Compared with the control group, after 7 days administration, the pathological sections showed cardiac toxicity. Moreover, some metabolites in the body changed significantly. Receiver operating characteristic curve (ROC) analysis showed that there are 11 metabolites related with cardiac toxicity, which play a role in “phenylalanine, tyrosine and tryptophan biosynthesis”; “phenylalanine metabolism”; “valine, leucine and isoleucine biosynthesis”; “glycerophospholipid metabolism” as well as “pantothenate and CoA biosynthesis”. These metabolites can better explain the cardiotoxicity mechanism of Cortex Periplocae and provide a scientific and systematic method to evaluate the cardiotoxicity of Cortex Periplocae.

The experimental design flow for screening the cardiotoxicity biomarkers induced by Cortex Periplocae.

Phthalate metabolites related to infertile biomarkers and infertility in Chinese men

Although in vitro and in vivo laboratory studies have demonstrated androgen and anti-androgen effects on male reproduction from phthalate exposures, human studies still remain inconsistent. Therefore, a case-control study (n = 289) was conducted to evaluate the associations between phthalate exposures, male infertility risks, and changes in metabolomic biomarkers. Regional participants consisted of fertile (n = 150) and infertile (n = 139) males were recruited from Nanjing Medical University' affiliated hospitals. Seven urinary phthalate metabolites were measured using HPLC-MS/MS. Associations between levels of phthalate metabolites, infertility risks, and infertility-related biomarkers were statistically evaluated. MEHHP, one of the most abundant DEHP oxidative metabolites was significantly lower in cases than in controls (p = 0.039). When using the 1st quartile range as a reference, although statistically insignificant for odds ratios (ORs) of the 2nd, 3rd, and 4th quartiles (OR (95% CI) = 1.50 (0.34-6.48), 0.70 (0.14-3.52) and 0.42 (0.09-2.00), respectively), the MEHHP dose-dependent trend of infertility risk expressed as OR decreased significantly (p = 0.034). More interestingly, most of the phthalate metabolites, including MEHHP, were either positively associated with fertile prevention metabolic biomarkers or negatively associated with fertile hazard ones. Phthalate metabolism, along with their activated infertility-related biomarkers, may contribute to a decreased risk of male infertility at the subjects' ongoing exposure levels. Our results may be illustrated by the low-dose related androgen effect of phthalates and can improve our understanding of the controversial epidemiological results on this issue.

Seminal plasma metabolomics approach for the diagnosis of unexplained male infertility

We used a gas chromatography-mass spectrometry (GC-MS) based metabolomics approach to obtain the metabolic profiling of unexplained male infertility (UMI), and identified seminal plasma biomarkers associated with UMI by a two-stage population study. A robust OPLS-DA model based on these identified metabolites was able to distinguish 82% of the UMI patients from health controls with a specificity of 92%. In this model, 44 metabolites were found differentially expressed in UMI subjects compared with health controls. By pathway enrichment analysis, we identified several major changed metabolic pathways related to UMI. Our findings provide new perspective for the diagnosis of UMI.

Serum Metabolomic Profiling Identifies Characterization of Non-Obstructive Azoospermic Men

Male infertility is considered a common health problem, and non-obstructive azoospermia with unclear pathogenesis is one of the most challenging tasks for clinicians. The objective of this study was to investigate the differential serum metabolic pattern in non-obstructive azoospermic men and to determine potential biomarkers related to spermatogenic dysfunction. Serum samples from patients with non-obstructive azoospermia (n = 22) and healthy controls (n = 31) were examined using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Serum metabolomic profiling could differentiate non-obstructive azoospermic patients from healthy control subjects. A total of 24 metabolites were screened and identified as potential markers, many of which are involved in energy production, oxidative stress and cell apoptosis in spermatogenesis. Moreover, the results showed that various metabolic pathways, including d-glutamine and d-glutamate metabolism, taurine and hypotaurine metabolism, pyruvate metabolism, the citrate cycle and alanine, aspartate and glutamate metabolism, were disrupted in patients with non-obstructive azoospermia. Our results indicated that the serum metabolic disorders may contribute to the etiology of non-obstructive azoospermia. This study suggested that serum metabolomics could identify unique metabolic patterns of non-obstructive azoospermia and provide novel insights into the pathogenesis underlying male infertility.

A simulation based method for assessing the statistical significance of logistic regression models after common variable selection procedures

Classification models can demonstrate apparent prediction accuracy even when there is no underlying relationship between the predictors and the response. Variable selection procedures can lead to false positive variable selections and overestimation of true model performance. A simulation study was conducted using logistic regression with forward stepwise, best subsets, and LASSO variable selection methods with varying total sample sizes (20, 50, 100, 200) and numbers of random noise predictor variables (3, 5, 10, 15, 20, 50). Using our critical values can help reduce needless follow-up on variables having no true association with the outcome.

Plasma metabolic profiling analysis of cyclophosphamide-induced cardiotoxicity using metabolomics coupled with UPLC/Q-TOF-MS and ROC curve

Cyclophosphamide (CY) is a commonly-used nitrogen mustard alkylating agent, but its clinical application is severely limited by its cardiotoxicity. Since the development of metabolomics, the change of metabolite profiles caused by cyclophosphamide has been studied by metabolomics and has gained much attention. In this study, we analyzed rat plasma samples collected one, three and five days after cyclophosphamide administration using ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC/Q-TOF-MS). Multiple statistical analyses, such as principal component analysis (PCA) and partial least squares - discriminant analysis (PLS-DA), were used to examine metabolite profile changes in plasma samples in order to screen for potential cardiotoxicity biomarkers and metabolic pathways. Levels of a dozen of metabolites changed significantly in plasma from the CY-treated group after one, three, and five days compared with the control group treated with normal saline (NS). Receiver operator characteristic (ROC) curve analysis suggested that the total 16 metabolites play important roles in different times of CY-induced cardiotoxicity respectively. Our results suggest that these metabolites in linoleic acid metabolism and glycerol phospholipid metabolism may be related to CY-induced cardiotoxicity. These metabolites could act as sensitive biomarkers for CY-induced cardiotoxicity and be useful for investigating toxic mechanisms. They may also lay a foundation for clinical use of cyclophosphamide.

Gene-gene and gene-environment interactions on risk of male infertility: Focus on the metabolites

Infertility affects about 17% couples, and males contribute to half of the cases. Compared with independent effects of genetic and environmental factors, interactions between them help in the understanding of the susceptibility to male infertility. Thus, we genotyped 25 polymorphisms, measured 16 urinary chemical concentrations and explored interactions between gene-gene and gene-environment in 1039 Han Chinese using metabolomic analysis. We first observed that GSTT1 might interact with GSTM1 (Pinter=6.33×10(-8)). Furthermore, an interaction between GSTM1 and 4-n-octylphenol (4-n-OP) was identified (Pinter=7.00×10(-3)), as well as a 2-order interaction among GSTT1, GSTM1 and 4-n-OP (Pinter=0.04). Subjects with GSTT1-present and GSTM1-null genotypes were susceptible to male infertility when exposed to 4-n-OP (OR=14.05, 95% CI=4.78-60.20, P=2.34×10(-5)). Most metabolites identified were involved in the tricarboxylic acid cycle. In conclusion, it is a novel study of the interaction on male infertility from the aspect of metabolomics.

A potential tool for diagnosis of male infertility: Plasma metabolomics based on GC-MS

Male infertility has become an important public health problem worldwide. Nowadays the diagnosis of male infertility frequently depends on the results of semen quality or requires more invasive surgical intervention. Therefore, it is necessary to develop a novel approach for early diagnosis of male infertility. According to the presence or absence of normal sexual function, the male infertility is classified into two phenotypes, erectile dysfunction (ED) and semen abnormalities (SA). The aim of this study was to investigate the GC-MS plasma profiles of infertile male having erectile dysfunction (ED) and having semen abnormalities (SA) and discover the potential biomarkers. The plasma samples from healthy controls (HC) (n=61) and infertility patients with ED (n=26) or with SA (n=44) were analyzed by gas chromatography-mass spectrometry (GC-MS) for discrimination and screening potential biomarkers. The partial least squares-discriminant analysis (PLS-DA) was performed on GC-MS dataset. The results showed that HC could be discriminated from infertile cases having SA (AUC=86.96%, sensitivity=78.69%, specificity=84.09%, accuracy=80.95%) and infertile cases having ED (AUC=94.33%, sensitivity=80.33%, specificity=100%, accuracy=87.36%). Some potential biomarkers were successfully discovered by two commonly used variable selection methods, variable importance on projection (VIP) and original coefficients of PLS-DA (β). 1,5-Anhydro-sorbitol and α-hydroxyisovaleric acid were identified as the potential biomarkers for distinguishing HC from the male infertility patients. Meanwhile, lactate, glutamate and cholesterol were the found to be the important variables to distinguish between patients with erectile dysfunction from those with semen abnormalities. The plasma metabolomics may be developed as a novel approach for fast, noninvasive, and acceptable diagnosis and characterization of male infertility.

A short review of applications of liquid chromatography mass spectrometry based metabolomics techniques to the analysis of human urine

Mass spectrometry based metabolomics profiling.