Comprehensive metabolic profiles of seminal plasma with different forms of male infertility and their correlation with sperm parameters

Understanding seminal plasma in male infertility: emerging markers and their implications

Infertility affects a significant proportion of the reproductive-aged population, with male-associated factors contributing to over half of the cases. However, current diagnostic tools have limitations, leading to an underestimation of the true prevalence of male infertility. While traditional semen parameters provide some insights, they fail to determine the true fertility potential in a substantial number of instances. Therefore, it is crucial to investigate additional molecular targets responsible for male infertility to improve understanding and identification of such cases. Seminal plasma, the main carrier of molecules derived from male reproductive glands, plays a crucial role in reproduction. Amongst its multifarious functions, it regulates processes such as sperm capacitation, sperm protection and maturation, and even interaction with the egg's zona pellucida. Seminal plasma offers a non-invasive sample for urogenital diagnostics and has shown promise in identifying biomarkers associated with male reproductive disorders. This review aims to provide an updated and comprehensive overview of seminal plasma in the diagnosis of male infertility, exploring its composition, function, methods used for analysis, and the application of emerging markers. Apart from the application, the potential challenges of seminal plasma analysis such as standardisation, marker interpretation and confounding factors have also been addressed. Moreover, we have also explored future avenues for enhancing its utility and its role in improving diagnostic strategies. Through comprehensive exploration of seminal plasma's diagnostic potential, the present analysis seeks to advance the understanding of male infertility and its effective management.

Biomarker-based human and animal sperm phenotyping: the good, the bad and the ugly†

Conventional, brightfield-microscopic semen analysis provides important baseline information about sperm quality of an individual; however, it falls short of identifying subtle subcellular and molecular defects in cohorts of "bad," defective human and animal spermatozoa with seemingly normal phenotypes. To bridge this gap, it is desirable to increase the precision of andrological evaluation in humans and livestock animals by pursuing advanced biomarker-based imaging methods. This review, spiced up with occasional classic movie references but seriously scholastic at the same time, focuses mainly on the biomarkers of altered male germ cell proteostasis resulting in post-testicular carryovers of proteins associated with ubiquitin-proteasome system. Also addressed are sperm redox homeostasis, epididymal sperm maturation, sperm-seminal plasma interactions, and sperm surface glycosylation. Zinc ion homeostasis-associated biomarkers and sperm-borne components, including the elements of neurodegenerative pathways such as Huntington and Alzheimer disease, are discussed. Such spectrum of biomarkers, imaged by highly specific vital fluorescent molecular probes, lectins, and antibodies, reveals both obvious and subtle defects of sperm chromatin, deoxyribonucleic acid, and accessory structures of the sperm head and tail. Introduction of next-generation image-based flow cytometry into research and clinical andrology will soon enable the incorporation of machine and deep learning algorithms with the end point of developing simple, label-free methods for clinical diagnostics and high-throughput phenotyping of spermatozoa in humans and economically important livestock animals.

Metabolites assay offers potential solution to improve the rooster semen cryopreservation

Semen cryopreservation represents a promising technology utilized for preserving high-quality chicken varieties in husbandry practices. However, the efficacy of this methodology is significantly impeded by the diminished quality of sperm. Metabolites, as the end products of metabolic reactions, serve as indicators of biological processes and offer insights into physiological conditions. In this study, we investigaged the sperm quality and alteration in metabolic profiles during the cryopreservation of Longyou Partridge Chicken semen. Following artificial semen collection, four groups of semen samples were established based on four points of the cryopreservation process (Ⅰ, fresh semen; Ⅱ, semen added extender and chilled at 4 °C for 30 min; Ⅲ, semen added cryoprotectants; Ⅳ, semen gradient freezed and stored in liquid nitrogen). Semen cryopreservation has a negative effect on the percentage of sperm in a straight-line trajectory (LIN), has no significant effect on total motile sperms (TM) or the proportion of sperm with typical morphology (NM). Metabolites were identified using LC-MS technique and analyses including Principal Component Analysis (PCA), Orthogonal Partial Least Squares Discriminant Analysis (OPLS-DA), Univariate statistical analysis, and the Kyoto Encyclopedia of Genes and Genomes (KEGG) database were employed to identify metabolites. A total of 2471 metabolites had been identified, with the majority of the list being made up of amino acids and their metabolites as well as benzene and substituted derivatives. Group II exhibits 882 metabolites with significantly elevated abundance relative to Group I, alongside 37 metabolites displaying decreased abundance. In Group III, 836 metabolites demonstrate notably augmented abundance compared to Group II, while 87 metabolites exhibit reduced abundance. Furthermore, Group IV showcases 513 metabolites with markedly heightened abundance in comparison to Group III, and 396 metabolites with decreased abundance. Specific metabolites such as 5-Hydroxylysine, Phosphocholine, and alpha-d-glucose-6-phosphate exhibited a progressive decline during the cryopreservation process, correlating with either dilution and chilling, cryoprotectant addition, or freezing. In conclusion, our investigation systematically examined the changes of seminal metabolome and sperm quality throughout the cryopreservation process of rooster semen.

Cancer risk and male Infertility: Unravelling predictive biomarkers and prognostic indicators

In recent years, there has been a global increase in cases of male infertility. There are about 30 million cases of male infertility worldwide and male reproductive health is showing rapid decline in last few decades. It is now recognized as a potential risk factor for developing certain types of cancer, particularly genitourinary malignancies like testicular and prostate cancer. Male infertility is considered a potential indicator of overall health and an early biomarker for cancer. Cases of unexplained male factor infertility have high levels of oxidative stress and oxidative DNA damage and this induces both denovo germ line mutations and epimutations due to build up of 8-hydroxy 2 deoxygunaosine abase which is highly mutagenic and also induces hypomethylation and genomic instability. Consequently, there is growing evidence to explore the various factors contributing to an increased cancer risk. Currently, the available prognostic and predictive biomarkers associated with semen characteristics and cancer risk are limited but gaining significant attention in clinical research for the diagnosis and treatment of elevated cancer risk in the individual and in offspring. The male germ cell being transcriptionally and translationally inert has a highly truncated repair mechanism and has minimal antioxidants and thus most vulnerable to oxidative injury due to environmental factors and unhealthy lifestyle and social habits. Therefore, advancing our understanding requires a thorough evaluation of the pathophysiologic mechanisms at the DNA, RNA, protein, and metabolite levels to identify key biomarkers that may underlie the pathogenesis of male infertility and associated cancer. Advanced methodologies such as genomics, epigenetics, proteomics, transcriptomics, and metabolomics stand at the forefront of cutting-edge approaches for discovering novel biomarkers, spanning from infertility to associated cancer types. Henceforth, in this review, we aim to assess the role and potential of recently identified predictive and prognostic biomarkers, offering insights into the success of assisted reproductive technologies, causes of azoospermia and idiopathic infertility, the impact of integrated holistic approach and lifestyle modifications, and the monitoring of cancer susceptibility, initiation and progression. Comprehending these biomarkers is crucial for providing comprehensive counselling to infertile men and cancer patients, along with their families.

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.

Changes in seminal plasma microecological dynamics and the mechanistic impact of core metabolite hexadecanamide in asthenozoospermia patients

Asthenozoospermia (AZS) is a prevalent contributor to male infertility, characterized by a substantial decline in sperm motility. In recent years, large-scale studies have explored the interplay between the male reproductive system's microecology and its implications for reproductive health. Nevertheless, the direct association between seminal microecology and male infertility pathogenesis remains inconclusive. This study used 16S rDNA sequencing and multi-omics analysis to conduct a comprehensive investigation of the seminal microbial community and metabolites in AZS patients. Patients were categorized into four distinct groups: Normal, mild AZS (AZS-I), moderate AZS (AZS-II), and severe AZS (AZS-III). Microbiome differential abundance analysis revealed significant differences in microbial composition and metabolite profiles within the seminal plasma of these groups. Subsequently, patients were classified into a control group (Normal and AZS-I) and an AZS group (AZS-II and AZS-III). Correlation and cross-reference analyses identified distinct microbial genera and metabolites. Notably, the AZS group exhibited a reduced abundance of bacterial genera such as Pseudomonas, Serratia, and Methylobacterium-Methylorubrum in seminal plasma, positively correlating with core differential metabolite (hexadecanamide). Conversely, the AZS group displayed an increased abundance of bacterial genera such as Uruburuella, Vibrio, and Pseudoalteromonas, with a negative correlation with core differential metabolite (hexadecanamide). In vitro and in vivo experiments validated that hexadecanamide significantly enhanced sperm motility. Using predictive metabolite-targeting gene analysis and single-cell transcriptome sequencing, we profiled the gene expression of candidate target genes PAOX and CA2. Protein immunoblotting techniques validated the upregulation protein levels of PAOX and CA2 in sperm samples after hexadecanamide treatment, enhancing sperm motility. In conclusion, this study uncovered a significant correlation between six microbial genera in seminal plasma and the content of the metabolite hexadecanamide, which is related to AZS. Hexadecanamide notably enhances sperm motility, suggesting its potential integration into clinical strategies for managing AZS, providing a foundational framework for diagnostic and therapeutic advancements.

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.

Quantitative Analysis of the Human Semen Phosphorometabolome by 31P-NMR

Phosphorus-containing metabolites occupy a prominent position in cell pathways. The phosphorometabolomic approach in human sperm samples will deliver valuable information as new male fertility biomarkers could emerge. This study analyzed, by 31P-NMR, seminal plasma and whole semen from asthenozoospermic and normozoospermic samples (71% vs. 27% and 45% vs. 17%, total and progressive sperm motility, respectively), and also ejaculates from healthy donors. At least 16 phosphorus-containing metabolites involved in central energy metabolism and phospholipid, nucleotide, and nicotinamide metabolic pathways were assigned and different abundances between the samples with distinct sperm quality was detected. Specifically, higher levels of phosphocholine, glucose-1-phosphate, and to a lesser degree, acetyl phosphate were found in the asthenozoospermic seminal plasma. Notably, the phosphorometabolites implicated in lipid metabolism were highlighted in the seminal plasma, while those associated with carbohydrate metabolism were more abundant in the spermatozoa. Higher levels of phosphocholine, glucose-1-phosphate, and acetyl phosphate in the seminal plasma with poor quality suggest their crucial role in supporting sperm motility through energy metabolic pathways. In the seminal plasma, phosphorometabolites related to lipid metabolism were prominent; however, spermatozoa metabolism is more dependent on carbohydrate-related energy pathways. Understanding the presence and function of sperm phosphorylated metabolites will enhance our knowledge of the metabolic profile of healthy human sperm, improving assessment and differential diagnosis.

Exposure to PM2.5, seminal plasma metabolome, and semen quality among Chinese adult men: Association and potential mediation analyses

Exposure to ambient fine particulate matter (PM2.5) has been linked to a decline in semen quality, but the underlying mechanisms for this association remain unclear. We aimed to examine whether specific metabolites act as mediators in the association between PM2.5 exposure and changes in semen quality. We conducted untargeted metabolomics analysis using LC-MS/MS platforms to identified seminal plasma metabolites associated with various semen quality parameters among 200 Chinese adult men. Additionally, we performed mediation analyses to examine the effects of the seminal plasma metabolites on the association between PM2.5 exposure and semen quality. We identified 140 differential metabolites between the normal and abnormal semen groups, involving two metabolic pathways: Alanine, aspartate and glutamate metabolism, and Aminoacyl-tRNA biosynthesis. We additionally identified 7 specific seminal plasma metabolites that were associated with discrepant metabolic networks related to semen quality. The mediation analysis revealed that D-Aspartate might play a mediating role in the adverse effects of ambient PM2.5 exposure on both total and progressive motility during spermatogenesis period (70-90 days before ejaculation), with a proportion of mediation up to 16% and 17%, respectively. Exposure to PM2.5 was associated with alterations in D-Aspartate levels, which might partially mediate the association between PM2.5 and reduced sperm motility.

Critical Factors in Sample Collection and Preparation for Clinical Metabolomics of Underexplored Biological Specimens

This review article compiles critical pre-analytical factors for sample collection and extraction of eight uncommon or underexplored biological specimens (human breast milk, ocular fluids, sebum, seminal plasma, sweat, hair, saliva, and cerebrospinal fluid) under the perspective of clinical metabolomics. These samples are interesting for metabolomics studies as they reflect the status of living organisms and can be applied for diagnostic purposes and biomarker discovery. Pre-collection and collection procedures are critical, requiring protocols to be standardized to avoid contamination and bias. Such procedures must consider cleaning the collection area, sample stimulation, diet, and food and drug intake, among other factors that impact the lack of homogeneity of the sample group. Precipitation of proteins and removal of salts and cell debris are the most used sample preparation procedures. This review intends to provide a global view of the practical aspects that most impact results, serving as a starting point for the designing of metabolomic experiments.

Comparison of the metabolite profile of donkey and horse seminal plasma and its relationship with sperm viability and motility

Previous research revealed that several seminal plasma (SP) metabolites are related to sperm functionality, fertility, and preservation. While it is understood that variations between species exist, whether the SP metabolome differs between donkeys and horses has not been previously investigated. The aim of this work, therefore, was to characterize and compare donkey and horse SP metabolites using nuclear magnetic resonance (NMR) spectroscopy, and relate them to sperm viability and motility. For this purpose, ejaculates from 18 different donkeys and 18 different horses were collected and separated into two aliquots: one for harvesting the SP by centrifugation and obtaining the metabolic profile through NMR, and the other for evaluating sperm viability and motility. Based on total motility and sperm viability, samples were classified as with good (GQ) or poor (PQ) quality. The metabolomic profile of donkey and horse SP revealed the presence of 28 metabolites, which coincided in the two species. Yet, differences between horses and donkeys were observed in the concentration of 18 of these 28 metabolites, as well as between ejaculates classified as GQ or PQ and in the relationship of metabolites with sperm motility and viability. These findings suggest that sperm from donkeys and horses differ in their metabolism and energetic requirements, and that the concentration of specific SP metabolites may be related to sperm functionality. Further research should shed light on the metabolic needs of donkey and horse sperm, and evaluate how the knowledge collected from the contribution of these metabolites can help improve semen preservation in the two species.

Targeted Amino Acids Profiling of Human Seminal Plasma from Teratozoospermia Patients Using LC-MS/MS

Identifying the metabolome of human seminal plasma (HSP) is a new research area to screen putative biomarkers of infertility. This case-control study was performed on HSP specimens of 15 infertile patients with teratozoospermia (defined as normal sperm morphology < 4%) and 12 confirmed fertile normozoospermic men as the control group to investigate the seminal metabolic signature and whether there are differences in the metabolome between two groups. HSPs were subjected to LC-MS-MS analysis. MetaboAnalyst5.0 software was utilized for statistical analysis. Different univariate and multivariate analyses were used, including T-tests, fold change analysis, random forest (RF), and metabolite set enrichment analysis (MSEA). Teratozoospermic samples contained seventeen significantly different amino acids. Upregulated metabolites include glutamine, asparagine, and glycylproline, whereas downregulated metabolites include cysteine, γ-aminobutyric acid, histidine, hydroxylysine, hydroxyproline, glycine, proline, methionine, ornithine, tryptophan, aspartic acid, argininosuccinic acid, α-aminoadipic acid, and β-aminoisobutyric acid. RF algorithm defined a set of 15 metabolites that constitute the significant features of teratozoospermia. In particular, increased glutamine, asparagine, and decreased cysteine, tryptophan, glycine, and valine were strong predictors of teratozoospemia. The most affected metabolic pathways in teratozoospermic men are the aminoacyl-tRNA, arginine, valine-leucine, and isoleucine biosynthesis. Altered metabolites detected in teratozoospermia were responsible for various roles in sperm functions that classified into four subgroups as follows: related metabolites to antioxidant function, energy production, sperm function, and spermatogenesis. The altered amino acid metabolome identified in this study may be related to the etiology of teratozoospermia, and may provide novel insight into potential biomarkers of male infertility for therapeutic targets.

Metabolomics profiling of seminal plasma in obesity-induced asthenozoospermia

BACKGROUND

Asthenozoospermia is one of the essential causes of male infertility, and its incidence is significantly higher in obese men. Due to its complex etiology and unknown pathomechanism, the diagnosis and treatment of obesity-induced asthenozoospermia is a prevalent problem in reproductive medicine.

OBJECTIVE

This study aims to explore major differential metabolites and metabolic pathways in seminal plasma and pathological mechanisms for obesity-induced asthenozoospermia.

MATERIALS AND METHODS

We performed non-target metabolomic studies on the seminal plasma of healthy men with normal semen parameters (HN group, n = 20), obese men with normal semen parameters (ON group, n = 20), and men with obesity-induced asthenozoospermia (OA group, n = 20) based on gas chromatography-mass spectrometry. Metabolic profilings and related pathway analyses were conducted to discriminate differential metabolites and metabolic pathways.

RESULTS

A total of 20 differential metabolites including fructose, succinic acid, aconitic acid, methylmaleic acid, glucopyranose, serine, valine, leucine, phenylalanine, glycine, glutamic acid, alanine, proline and threonine were identified in HN group and ON group; 24 differential metabolites including glucose, fructose, pyruvic acid, citric acid, succinic acid, aconitic acid, glucopyranose, glutamic acid, valine, leucine, glycine, phenylalanine, lysine, citrulline, proline and alanine were produced in OA group and ON group; and 28 differential metabolites including glucose, fructose, citric acid, succinic acid, glucopyranose, valine, glycine, serine, leucine, phenylalanine, alanine, threonine, proline, glutamic acid, citrulline, lysine and tyrosine were produced in OA group and HN group. In addition, abnormal energy metabolism including carbohydrate metabolism (TCA cycle, glycolysis/gluconeogenesis, and pyruvate metabolism) and amino acid metabolism (phenylalanine, tyrosine, and tryptophan biosynthesis, D-glutamine and D-glutamate metabolism; phenylalanine metabolism, etc.) were found in ON group and OA group.

CONCLUSION

Obesity could affect the metabolite composition in seminal plasma and abnormal energy metabolism in seminal plasma mainly including carbohydrate metabolism and amino acid metabolism were closely related to obesity-induced asthenozoospermia.

Seminal plasma untargeted metabolomic and lipidomic profiling for the identification of a novel panel of biomarkers and therapeutic targets related to male infertility

Male infertility occurs approximately in about 50% of all infertility cases and represents a serious concern worldwide. Traditional semen analysis alone is insufficient to diagnose male infertility. Over the past two decades, advances in omics technologies have led to the widespread application of metabolomics profiling as a valuable diagnostic tool for various diseases and disorders. Seminal plasma represents a rich and easily accessible source of metabolites surrounding spermatozoa, a milieu that provides several indispensable nutrients to sustain sperm motility and fertilization. Changes of metabolic profiles in seminal plasma reflect male reproductive tract disorders. Here, we performed seminal plasma metabolomics and lipidomics profiling to identify a new pattern of biomarkers of male infertility. Seminal plasma samples from unfertile subjects (n = 31) and fertile controls (n = 19) were analyzed using an untargeted metabolomics/lipidomics integrated approach, based on Ultra-High-Pressure Liquid Chromatography-tandem Mass Spectrometry. Partial Least Squares-Discriminant Analysis showed a distinct separation between healthy fertile men and infertile subjects. Among the 15 selected candidate biomarkers based on Variable Importance in Projection scores, phosphatidylethanolamine (PE) (18:1; 18:1) resulted with the highest score. In total, 40 molecular species showed statistically significant variations between fertile and infertile men. Heat-map and volcano plot analysis indicated that acylcarnitines, phosphatidylserine (PS) (40:2) and lactate were decreased, while PE (18:1; 18:1), Phosphatidic acid (PA) (O-19:2; 18:1), Lysophosphatidylethanolamine (LPE) (O-16:1) and Phosphatidylcholine (PC) (O-16:2; 18:1)-CH3 were increased in the infertile group. The present study is the first one to analyze the metabolomics/lipidomics dysregulation in seminal plasma between fertile and infertile individuals regardless of sub-infertility condition. Association of several metabolites/lipids dysregulation with male infertility reinforced data of previous studies performed with different approaches. In particular, we confirmed significantly decreased levels of PS and carnitines in infertile patients as well as the positive correlation with sperm motility and morphology. If validated on a larger prospective cohort, the metabolite biomarkers of infertility in seminal plasma we identified in the present study might inform novel strategies for diagnosis and interventions to overcome male infertility.

Comprehensive metabolomics profiling of seminal plasma in asthenozoospermia caused by different etiologies

BACKGROUND

Asthenozoospermia (AZS) is a disease characterized by decreased sperm motility induced by multiple etiologies, and the pathological mechanisms of various AZS are unclear. We simultaneously analyzed the metabolic profiling of four representative AZS to provide new insights into the etiologies of AZS.

METHOD

Seminal plasma samples were collected from healthy control (HC; n = 30) and four AZS induced by varicocele (VA, n = 30), obesity (OA, n = 22), reproductive system infections (RA; n = 17) and idiopathic (IA, n = 30), respectively, and were analyzed using gas chromatography-mass spectrometry. Disturbed metabolites and metabolic pathways were compared between AZS and HC, as well as IA and the other three AZS.

RESULTS

A total of 40 different metabolites were identified in the seminal plasma of AZS and HC, of which lactic acid, fructose, citric acid, glutamine and pyruvic acid metabolic abnormalities associated with all the AZS groups, while each AZS group had unique metabolic changes. RA was significantly separated from the other three AZS, and metabolites such as cholesterol, octadecanoic acid and serine mainly contributed to the separation.

CONCLUSION

The comprehensive metabolomic analysis and comparison of four various AZS provided evidence and clues for the mechanism mining, which will benefit future etiology, diagnosis and treatment of AZS.

Cryopreservation Induces Acetylation of Metabolism-Related Proteins in Boar Sperm

Cryodamage affects the normal physiological functions and survivability of boar sperm during cryopreservation. Lysine acetylation is thought to be an important regulatory mechanism in sperm functions. However, little is known about protein acetylation and its effects on cryotolerance or cryodamage in boar sperm. In this study, the characterization and protein acetylation dynamics of boar sperm during cryopreservation were determined using liquid chromatography-mass spectrometry (LC-MS). A total of 1440 proteins were identified out of 4705 modified proteins, and 2764 quantifiable sites were elucidated. Among the differentially modified sites, 1252 were found to be upregulated compared to 172 downregulated sites in fresh and frozen sperms. Gene ontology indicated that these differentially modified proteins are involved in metabolic processes and catalytic and antioxidant activities, which are involved in pyruvate metabolism, phosphorylation and lysine degradation. In addition, the present study demonstrated that the mRNA and protein expressions of SIRT5, IDH2, MDH2 and LDHC, associated with sperm quality parameters, are downregulated after cryopreservation. In conclusion, cryopreservation induces the acetylation and deacetylation of energy metabolism-related proteins, which may contribute to the post-thawed boar sperm quality parameters.

Low-polarity untargeted metabolomic profiling as a tool to gain insight into seminal fluid

INTRODUCTION

A decrease in sperm cell count has been observed along the last several decades, especially in the most developed regions of the world. The use of metabolomics to study the composition of the seminal fluid is a promising approach to gain access to the molecular mechanisms underlying this fact.

OBJECTIVES

In the present work, we aimed at relating metabolomic profiles of young healthy men to their semen quality parameters obtained from conventional microscopic analysis.

METHODS

An untargeted metabolomics approach focusing on low- to mid-polarity compounds was used to analyze a subset of seminal fluid samples from a cohort of over 2700 young healthy men.

RESULTS

Our results show that a broad metabolic profiling comprising several families of compounds (including acyl-carnitines, steroids, and other lipids) can contribute to effectively distinguish samples provided by individuals exhibiting low or high absolute sperm counts.

CONCLUSION

A number of metabolites involved in sexual development and function, signaling, and energy metabolism were highlighted as being distinctive of samples coming from either group, proving untargeted metabolomics as a promising tool to better understand the pathophysiological processes responsible for male fertility impairment.

Relevance of PUFA-derived metabolites in seminal plasma to male infertility

Aim

This study aims to investigate the biological effects of polyunsaturated fatty acid (PUFA)-derived metabolites in seminal plasma on male fertility and to evaluate the potential of PUFA as a biomarker for normozoospermic male infertility.

Methods

From September 2011 to April 2012, We collected semen samples from 564 men aged 18 to 50 years old (mean=32.28 years old)ch., residing in the Sandu County, Guizhou Province, China. The donors included 376 men with normozoospermia (fertile: n=267; infertile: n=109) and 188 men with oligoasthenozoospermia (fertile: n=121; infertile: n=67). The samples thus obtained were then analyzed by liquid chromatography-mass spectrometry (LC-MS) to detect the levels of PUFA-derived metabolites in April 2013. Data were analyzed from December 1, 2020, to May 15, 2022.

Results

Our analysis of propensity score-matched cohorts revealed that the concentrations of 9/26 and 7/26 metabolites differed significantly between fertile and infertile men with normozoospermia and oligoasthenozoospermia, respectively (FDR < 0.05). In men with normozoospermia, higher levels of 7(R)-MaR1 (HR: 0.4 (95% CI [0.24, 0.64]) and 11,12-DHET (0.36 (95% CI [0.21, 0.58]) were significantly associated with a decreased risk of infertility, while higher levels of 17(S)-HDHA (HR: 2.32 (95% CI [1.44, 3.79]), LXA5 (HR: 8.38 (95% CI [4.81, 15.24]), 15d-PGJ2 (HR: 1.71 (95% CI [1.06, 2.76]), and PGJ2 (HR: 2.28 (95% CI [1.42, 3.7]) correlated with an increased risk of infertility. Our ROC model using the differentially expressed metabolites showed the value of the area under the curve to be 0.744.

Conclusion

The PUFA-derived metabolites 7(R)-MaR1, 11,12-DHET, 17(S)-HDHA, LXA5, and PGJ2 might be considered as potential diagnostic biomarkers of infertility in normozoospermic men.

Ram sperm cryopreservation disrupts metabolism of unsaturated fatty acids

In ram sperm, metabolites are important components of the plasma membrane, energy metabolism cycle, and precursors for other membrane lipids, and they may have important roles in maintaining plasma membrane integrity, energy metabolism, and regulation of cryotolerance. In this study, the ejaculates from 6 Dorper rams were pooled and sperm were systematically investigated by metabolomics at various steps of cryopreservation (37 °C, fresh [F]; from 37 to 4 °C, cooling [C]; and from 4 to -196 to 37 °C, frozen-thawed [FT]) to identify differential metabolites (DM). There were 310 metabolites identified, of which 86 were considered DMs. Regarding the DMs, there were 23 (0 up and 23 down), 25 (12 up and 13 down), and 38 (7 up and 31 down) identified during cooling (C vs F), freezing (FT vs C), and cryopreservation (FT vs F), respectively. Furthermore, some key polyunsaturated fatty acids (FAs), particularly, linoleic acid (LA), docosahexaenoic acid (DHA), and arachidonic acid (AA) were down-regulated during cooling and cryopreservation. Significant DMs were enriched in several metabolic pathways including biosynthesis of unsaturated FAs, LA metabolism, mammalian target of rapamycin (mTOR), forkhead box transcription factors (FoxO), adenosine monophosphate-activated protein kinase (AMPK), phosphatidylinositol 3-kinase/protein kinase B (PI3K-Akt) signaling pathways, regulation of lipolysis in adipocytes, and FA biosynthesis. This was apparently the first report to compare metabolomics profiles of ram sperm during cryopreservation and provided new knowledge to improve this process.

Sperm physiology and in vitro fertilising ability rely on basal metabolic activity: insights from the pig model

Whether basal metabolic activity in sperm has any influence on their fertilising capacity has not been explored. Using the pig as a model, the present study investigated the relationship of energetic metabolism with sperm quality and function (assessed through computer-assisted sperm analysis and flow cytometry), and fertility (in vitro fertilisation (IVF) outcomes). In semen samples from 16 boars, levels of metabolites related to glycolysis, ketogenesis and Krebs cycle were determined through a targeted metabolomics approach using liquid chromatography-tandem mass spectrometry. High-quality sperm are associated to greater levels of glycolysis-derived metabolites, and oocyte fertilisation and embryo development are conditioned by the sperm metabolic status. Interestingly, glycolysis appears to be the preferred catabolic pathway of the sperm giving rise to greater percentages of embryos at day 6. In conclusion, this study shows that the basal metabolic activity of sperm influences their function, even beyond fertilisation.

Comprehensive analysis of microRNA and metabolic profiles in bovine seminal plasma of different semen quality

Background

Seminal plasma plays a pivotal role in modulating sperm viability and function. However, the underlying mechanisms have not been fully elucidated.

Method

In this study, the bull semen production records of core breeding farms and bull stations in the past 10 years were analyzed.

Results

We found that the semen of 5-year-old bulls collected for the first time is of the best quality (p &lt; 0.05). Despite the bull semen collected under the above conditions, low-quality sperm is still obtained from part of bulls due to individual differences. Interestingly, seminal plasma from normal semen is capable of improving low-quality semen motility. To identify the potential key factors in seminal plasma, the differences in miRNA and metabolite profiles between normal and low-quality seminal plasma were analyzed. We found that 59 miRNAs were differently expressed, including 38 up-regulated and 21 down-regulated miRNAs. Three hundred and ninety-one and 327 significantly different metabolites were identified from the positive and negative ion models, respectively. These multiple miRNAs and metabolites collectively contribute to the motility of sperm, subsequently, affect semen quality.

Discussion

Together, these results not only revealed the critical factors of seminal plasma improving sperm quality but also provided potential miRNA- or metabolite-based biomarkers to identify the high semen quality.

Study on comparative analysis of differential metabolites in Guanzhong dairy goat semen before and after freezing

In order to explore the differential metabolites between fresh and frozen-thawed semen of Guanzhong dairy goats, semen samples were collected by artificial vagina method, and divided into fresh and frozen-thawed semen groups, with six replicates in each group. Liquid Chromatography-mass spectrometry (LC-MS) technology was used to detect semen metabolites in both groups. The metabolites were analyzed and identified by the combination of multidimensional statistical analysis, namely principal component analysis (PCA), partial least squares discriminant analysis (PLS-DA), orthogonal partial least squares discriminant analysis (OPLS-DA) and univariate statistical analysis, Differential metabolites were identified according to One-step Solution for Identification of Small Molecules in Metabolomics Studies (OSI/SMMS) combined with Human Metabolome Database (HMDB), Lipidmaps and Metlin and the metabolic pathways of different metabolites were enriched and analyzed by Kyoto Encyclopedia of Genes and Genomes (KEGG) database. The results showed that a total of 53 differential metabolites were detected in fresh and frozen-thawed semen groups, of which 10 metabolites were significantly up-regulated (P < 0.05) and 43 were significantly down-regulated (P < 0.05). Most of the metabolites belonged to lipids and lipid-like molecules, organic acids and their derivatives, organic oxygen compounds, etc. According to the functional enrichment analysis of the top twenty differential metabolites in the KEGG database, significant changes occurred in linoleic acid metabolism pathway out of total eleven pathways observed. These differential metabolites can be used as metabolic markers of sperm cryo-injury in dairy goats.

A new perspective on semen quality of aged male: The characteristics of metabolomics and proteomics

Background

Semen quality is negatively correlated with male age and is mainly quantified by a routine semen analysis, which is descriptive and inconclusive. Sperm proteins or semen metabolites are used as the intermediate or end-products, reflecting changes in semen quality, and hold much promise as a new biomarker to predict fertility in advanced-aged males.

Objectives

In this study, we sought to assess whether the semen metabolome and proteome of aged males can affect semen quality and serve as biomarkers for predicting semen quality.

Materials and methods

We retrospectively analyzed 12825 males that underwent semen routine analysis to understand the age-dependent changes in sperm quality. To identify the difference between aged and young adults, metabolomics (n=60) analyses of semen and proteomics (n=12) analyses of sperm were conducted. Finally, integrated machine learning of metabolomics was conducted to screen biomarkers to identify aging semen.

Results

We discovered that male age was positively correlated with sperm concentration as well as DNA fragmentation index(DFI), and negatively with progressive motile sperm count, total sperm count, sperm volume and progressive sperm motility. The differential metabolites were significantly enriched in various metabolic pathways, and four of these differential metabolites (Pipamperone, 2,2-Bis(hydroxymethyl)-2,2',2''-nitrilotriethanol, Arg-Pro and Triethyl phosphate) were utilized to establish a biomarker panel to identify aging semen. Proteomic analysis showed that differential proteins were significantly enriched in protein digestion and absorption and some energy-related pathways. An integrated analysis of the metabolome and proteome identified differential energy metabolism and oxidative stress-related proteins, which could explain the decreased motility and the increased DFI of aging sperm.

Discussion and conclusion

We provide compelling evidence that the changes in semen metabolome and sperm proteome are related to the decline of semen quality in aged males. Moreover, a biomarker panel based on four metabolites was established to identify aging semen.

A Metabolomic Profile of Seminal Fluid in Extremely Severe Oligozoopermia Suggesting an Epididymal Involvement

Male infertility has increased in the last decade. Pathophysiologic mechanisms behind extreme oligospermia (EO) are not yet fully understood. In new “omics” approaches, metabolomic can offer new information and help elucidate these mechanisms. We performed a metabolomics study of the seminal fluid (SF) in order to understand the mechanisms implicated in EO. We realized a targeted quantitative analysis using high performance liquid chromatography and mass spectrometry to compare the SF metabolomic profile of 19 men with EO with that of 22 men with a history of vasectomy (V) and 20 men with normal semen parameters (C). A total of 114 metabolites were identified. We obtained a multivariate OPLS-DA model discriminating the three groups. Signatures show significantly higher levels of amino acids and polyamines in C group. The sum of polyunsaturated fatty acids and free carnitine progressively decrease between the three groups (C > EO > V) and sphingomyelins are significantly lower in V group. Our signature characterizing EO includes metabolites already linked to infertility in previous studies. The similarities between the signatures of the EO and V groups are clear evidence of epididymal dysfunction in the case of testicular damage. This study shows the complexity of the metabolomic dysfunction occurring in the SF of EO men and underlines the importance of metabolomics in understanding male infertility.

An integrated overview on the regulation of sperm metabolism (glycolysis-Krebs cycle-oxidative phosphorylation)

An overview of the sperm metabolism is presented; using the stallion as a model we review glycolysis, Krebs Cycle and oxidative phosphorylation, paying special attention to the interactions among them. In addition, metabolism implies a series of coordinated oxidation-reduction reactions and in the course of these reactions reactive oxygen species (ROS) and reactive oxoaldehydes are produced ; the electron transport chain (ETC) in the mitochondria is the main source of the anion superoxide and hydrogen peroxide, while glycolysis produces 2-oxoaldehydes such as methylglyoxal as byproducts; due to the adjacent carbonyl groups are strong electrophiles (steal electrons oxidizing other compounds). Sophisticated mechanisms exist to maintain redox homeostasis, because ROS under controlled production also have important regulatory functions in the spermatozoa. The interactions between metabolism and production of reactive oxygen species are essential for proper sperm function, and deregulation of these processes rapidly leads to sperm malfunction and finally death. Lastly, we briefly describe two techniques that will expand our knowledge on sperm metabolism in the coming decades, metabolic flow cytometry and the use of the "omics" technologies, proteomics and metabolomics, specifically the micro and nano proteomics/metabolomics. A better understanding of the metabolism of the spermatozoa will lead to big improvements in sperm technologies and the diagnosis and treatment of male factor infertility.

Metabolomics of Human Semen: A Review of Different Analytical Methods to Unravel Biomarkers for Male Fertility Disorders

Background: Human life without sperm is not possible. Therefore, it is alarming that the fertilizing ability of human spermatozoa is continuously decreasing. The reasons for that are widely unknown, but there is hope that metabolomics-based investigations may be able to contribute to overcoming this problem. This review summarizes the attempts made so far. Methods: We will discuss liquid chromatography–mass spectrometry (LC-MS), gas chromatography (GC), infrared (IR) and Raman as well as nuclear magnetic resonance (NMR) spectroscopy. Almost all available studies apply one of these methods. Results: Depending on the methodology used, different compounds can be detected, which is (in combination with sophisticated methods of bioinformatics) helpful to estimate the state of the sperm. Often, but not in all cases, there is a correlation with clinical parameters such as the sperm mobility. Conclusions: LC-MS detects the highest number of metabolites and can be considered as the method of choice. Unfortunately, the reproducibility of some studies is poor, and, thus, further improvements of the study designs are needed to overcome this problem. Additionally, a stronger focus on the biochemical consequences of the altered metabolite concentrations is also required.

The Testicular Protection Effect of Thiamine Pyrophosphate Against Cisplatin-treated Male Rats

Infertility is a worldwide problem affecting both genders, it can be defined as the inability of the adult males to make a fertile woman pregnant after one year of regular intercourse. Cisplatin considers one of the most potent antineoplastic drugs that is extensively   used, alone or in combination with other antitumor agents, to manage solid and germ cell cancer. The major drawback in cisplatin treatment is its damaging consequence on various body tissue, including the testis, liver, renal and others. One of its pronounced adverse effects is testicular injury, which may proceed to end with infertility. Thiamine pyrophosphate is the active form of thiamine which has an important role in the oxidative phosphorylation pathway. It acts as a co-factor and energy source for many cellular enzymes, also it utilizes by pentose-phosphate shut that elevates NADPH and improves antioxidants level. This study aimed to evaluate the effect of thiamine pyrophosphate on sperm parameters and gonadotropic hormones (luteal and follicle-stimulating hormone) of male rats exposed to a single dose of cisplatin. Twenty-eight albino male rats were randomly grouped into four groups. Control group: received normal saline, Cisplatin group: received normal saline and cisplatin, TPP50 group: received thiamine pyrophosphate (50mg/kg) with cisplatin, and TPP100 group: as third group (TPP50) but thiamine pyrophosphate dose was 100 mg/kg. Semen samples used to measure the sperms viability and morphology, while serum samples were gathered to measure the levels of gonadotropic hormones (FSH and LH). This study revealed that rat’s testicular function was notably deteriorated by cisplatin administration, represented by a reduction in sperm parameters (viability and normal morphology), and serum gonadotropic hormones (FSH and LH). In this work, thiamine pyrophosphate was act as a protective agent that ameliorates rat’s testicular damage induced by cisplatin in a dose-dependent manner. The suggested mechanism may attribute to its antioxidant and anti-apoptotic action

Omics and Male Infertility: Highlighting the Application of Transcriptomic Data

Male infertility is a multifaceted disorder affecting approximately 50% of male partners in infertile couples. Over the years, male infertility has been diagnosed mainly through semen analysis, hormone evaluations, medical records and physical examinations, which of course are fundamental, but yet inefficient, because 30% of male infertility cases remain idiopathic. This dilemmatic status of the unknown needs to be addressed with more sophisticated and result-driven technologies and/or techniques. Genetic alterations have been linked with male infertility, thereby unveiling the practicality of investigating this disorder from the “omics” perspective. Omics aims at analyzing the structure and functions of a whole constituent of a given biological function at different levels, including the molecular gene level (genomics), transcript level (transcriptomics), protein level (proteomics) and metabolites level (metabolomics). In the current study, an overview of the four branches of omics and their roles in male infertility are briefly discussed; the potential usefulness of assessing transcriptomic data to understand this pathology is also elucidated. After assessing the publicly obtainable transcriptomic data for datasets on male infertility, a total of 1385 datasets were retrieved, of which 10 datasets met the inclusion criteria and were used for further analysis. These datasets were classified into groups according to the disease or cause of male infertility. The groups include non-obstructive azoospermia (NOA), obstructive azoospermia (OA), non-obstructive and obstructive azoospermia (NOA and OA), spermatogenic dysfunction, sperm dysfunction, and Y chromosome microdeletion. Findings revealed that 8 genes (LDHC, PDHA2, TNP1, TNP2, ODF1, ODF2, SPINK2, PCDHB3) were commonly differentially expressed between all disease groups. Likewise, 56 genes were common between NOA versus NOA and OA (ADAD1, BANF2, BCL2L14, C12orf50, C20orf173, C22orf23, C6orf99, C9orf131, C9orf24, CABS1, CAPZA3, CCDC187, CCDC54, CDKN3, CEP170, CFAP206, CRISP2, CT83, CXorf65, FAM209A, FAM71F1, FAM81B, GALNTL5, GTSF1, H1FNT, HEMGN, HMGB4, KIF2B, LDHC, LOC441601, LYZL2, ODF1, ODF2, PCDHB3, PDHA2, PGK2, PIH1D2, PLCZ1, PROCA1, RIMBP3, ROPN1L, SHCBP1L, SMCP, SPATA16, SPATA19, SPINK2, TEX33, TKTL2, TMCO2, TMCO5A, TNP1, TNP2, TSPAN16, TSSK1B, TTLL2, UBQLN3). These genes, particularly the above-mentioned 8 genes, are involved in diverse biological processes such as germ cell development, spermatid development, spermatid differentiation, regulation of proteolysis, spermatogenesis and metabolic processes. Owing to the stage-specific expression of these genes, any mal-expression can ultimately lead to male infertility. Therefore, currently available data on all branches of omics relating to male fertility can be used to identify biomarkers for diagnosing male infertility, which can potentially help in unravelling some idiopathic cases.

OUP accepted manuscript

STUDY QUESTION

Are taurine and its transporter TAUT associated with spermiogenesis and early embryo development?

SUMMARY ANSWER

Morphologically abnormal spermatozoa increased after local functional interference by intratesticular injection, and taurine depletion significantly reduced the normal embryo numbers in vivo and blastocyst formation rate in vitro.

WHAT IS KNOWN ALREADY

Taurine is one of the most abundant amino acids in the male reproductive system and it has been demonstrated that taurine can efficiently improve spermatogenic function in rat models of testicular injury. However, limited information is known about the role of taurine and its transporter TAUT in spermatogenesis and early embryo development.

STUDY DESIGN, SIZE, DURATION

Clinical characteristics from 110 couples who have experienced recurrent pregnancy loss (RPL) were collected from December 2014 to March 2018. According to whether a fetal heartbeat was seen in the previous pregnancy under ultrasonic monitoring, patients with RPL were divided into two groups: an RPL without heartbeat (pregnancy with no fetal heartbeat, ROH) group, and an RPL with heartbeat (one or more pregnancies with fetal heartbeat, RWH) group. Semen samples (21 ROH and 20 RWH) were finally used for metabolomic analysis. Furthermore, semen samples were obtained from 30 patients with teratozoospermia (normal sperm morphology <4%) seeking evaluation for infertility and 25 age-matched control subjects with normal semen quality for western blotting. Animal experiments were performed in CD-1/ICR mice.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Metabolomics was performed to determine the metabolic changes between the ROH and RWH groups. Sperm proteins from patients with teratozoospermia and healthy controls were extracted for detecting TAUT expression using western blot analysis. Immunofluorescence was used to characterize the localization of TAUT in the testis and ejaculated spermatozoa. Functional analysis in mice was performed by intratesticular injection of siRNAs or antagonist (β-alanine) and 5% β-alanine was provided in drinking water to 3-week-old male mice for 5 weeks with the aim of depleting taurine. Murine epididymal spermatozoa were stained with hematoxylin and eosin for morphological assessment. IVF and mating tests were performed in mice for assessing fertility.

MAIN RESULTS AND THE ROLE OF CHANCE

Metabolomic analysis demonstrated that the taurine content was lower in spermatozoa but higher in seminal plasma from the ROH than the RWH group. TAUT expression was lower in spermatozoa from patients with teratozoospermia than controls. Immunofluorescence showed that TAUT was localized to the manchette in mouse elongated spermatids functional analysis showed that morphologically abnormal spermatozoa increased after interference, and this defect increased after supplementation with 5% β-alanine but was improved by 5% taurine supplementation. Supplementation with 5% β-alanine significantly reduced the normal embryo number in the mouse uterus as well as blastocyst formation rate in vitro.

LARGE SCALE DATA

N/A

LIMITATIONS, REASONS FOR CAUTION

The sample size was low and larger cohorts are needed to confirm the positive effect of taurine on human sperm quality. A comprehensive safety examination should be performed to evaluate whether taurine is a possible treatment for teratozoospermia. Furthermore, the specific molecular mechanism of TAUT involvement in spermiogenesis remains to be clarified.

WIDER IMPLICATIONS OF THE FINDINGS

The study provides new insights into the role of taurine and its transporter TAUT in male reproduction and embryo development. The results also indicate that TAUT is a promising molecular candidate for the assessment of sperm quality, which may contribute to the diagnosis and treatment for teratozoospermia.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by grants from the National Natural Science Foundation of China (no. 81774075, 31900605, 81971451), Jiangsu Science and Technology Program Grant (BK20190654) and Maternal and child health scientific research of Jiangsu Province (F202121). The authors declare no competing financial interests.

Identification and Structure Prediction of Human Septin-4 as a Biomarker for Diagnosis of Asthenozoospermic Infertile Patients-Critical Finding Toward Personalized Medicine

Semen parameters are been found as a key factor to evaluate the count and morphology in the given semen sample. The deep knowledge of male infertility will unravel with semen parameters correlated with molecular and biochemical parameters. The current research study is to identify the motility associated protein and its structure through the in-silico approach. Semen samples were collected and initial analysis including semen parameters was analyzed by using the World Health Organization protocol. Semen biochemical parameters, namely, seminal plasma protein concentration, fructose content, and glucosidase content were calculated and evaluated for correlation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) were carried out for identification of Septin-4 presence in the semen sample. Mascot search was done for protein conformation and in-silico characterization of Septin-4 by structural modeling in Iterative Threading Assembly Refinement (I-TASSER). Twenty-five nanoseconds molecular dynamics (MD) simulations results showed the stable nature of Septin-4 in the dynamic system. Overall, our results showed the presence of motility-associated protein in normospermia and control samples and not in the case of asthenospermia and oligoasthenospermia. Molecular techniques characterized the presence of Septin-4 and as a novel biomarker for infertility diagnosis.

Metabolomic fingerprinting of pig seminal plasma identifies in vivo fertility biomarkers

Background

Metabolomic approaches, which include the study of low molecular weight molecules, are an emerging -omics technology useful for identification of biomarkers. In this field, nuclear magnetic resonance (NMR) spectroscopy has already been used to uncover (in) fertility biomarkers in the seminal plasma (SP) of several mammalian species. However, NMR studies profiling the porcine SP metabolome to uncover in vivo fertility biomarkers are yet to be carried out. Thus, this study aimed to evaluate the putative relationship between SP-metabolites and in vivo fertility outcomes. To this end, 24 entire ejaculates (three ejaculates per boar) were collected from artificial insemination (AI)-boars throughout a year (one ejaculate every 4 months). Immediately after collection, ejaculates were centrifuged to obtain SP-samples, which were stored for subsequent metabolomic analysis by NMR spectroscopy. Fertility outcomes from 1525 inseminations were recorded over a year, including farrowing rate, litter size, stillbirths per litter and the duration of pregnancy.

Results

A total of 24 metabolites were identified and quantified in all SP-samples. Receiver operating characteristic (ROC) curve analysis showed that lactate levels in SP had discriminative capacity for farrowing rate (area under the curve [AUC] = 0.764) while carnitine (AUC = 0.847), hypotaurine (AUC = 0.819), sn-glycero-3-phosphocholine (AUC = 0.833), glutamate (AUC = 0.799) and glucose (AUC = 0.750) showed it for litter size. Similarly, citrate (AUC = 0.743), creatine (AUC = 0.812), phenylalanine (AUC = 0.750), tyrosine (AUC = 0.753) and malonate (AUC = 0.868) levels had discriminative capacity for stillbirths per litter; and malonate (AUC = 0.767) and fumarate (AUC = 0.868) levels for gestation length.

Conclusions

The assessment of selected SP-metabolites in ejaculates through NMR spectroscopy could be considered as a promising non-invasive tool to predict in vivo fertility outcomes in pigs. Moreover, supplementing AI-doses with specific metabolites should also be envisaged as a way to improve their fertility potential.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-021-00636-5.

Metabolomic signature of spermatozoa established during holding time is responsible for differences in boar sperm freezability

Holding at room temperature is the first step in most boar semen cryopreservation protocols. It is well accepted that a holding time (HT) of 24 h increases sperm cryotolerance. However, the effect of HT on ejaculates with different freezability is not entirely clear. The aim of this study was to understand how HT influences spermatic and seminal plasma metabolite profiles of boar ejaculates and how these possible changes affect freezability. Twenty-seven ejaculates were collected and extended to 1:1 (v: v) with BTS and split into two aliquots. The first aliquot was cryopreserved without holding time (0 h), and the second was held at 17°C for 24 h before cryopreservation. Spermatozoa and seminal plasma were collected by centrifugation at two times, before HT (0 h) and after HT (24 h), and subsequently frozen until metabolite extraction and UPLC-MS analysis. After thawing, the semen samples were evaluated for kinetics, membrane integrity, mitochondrial potential, membrane lipid peroxidation, and fluidity. The ejaculates were then allocated into two phenotypes (good ejaculate freezers [GEF] and poor ejaculate freezers [PEF]) based on the percent reduction in sperm quality (%RSQ) as determined by the difference in total motility and membrane integrity between raw and post-thaw samples cryopreserved after 24 h of HT. The metabolic profile of the seminal plasma did not seem to influence ejaculate freezability, but that of the spermatozoa were markedly different between GEF and PEF. We identified a number of metabolic markers in the sperm cells (including inosine, hypoxanthine, creatine, ADP, niacinamide, spermine, and 2-methylbutyrylcarnitine) that were directly related to the improvement of ejaculate freezability during HT; these were components of metabolic pathways associated with energy production. Furthermore, PEF showed an up-regulation in the arginine and proline as well as the glutathione metabolism pathways. These findings help to better understand the effect of holding time on boar sperm freezability and propose prospective metabolic markers that may predict freezability; this has implications in both basic and applied sciences.

Effect of bacterial infection on sperm quality and DNA fragmentation in subfertile men with Leukocytospermia

Background

Although bacterial infections have been recognized as a possible cause of male infertility, the effect of bacterial infections on sperm quality and sperm DNA fragmentation remains controversial. The current study aimed to investigate the prevalence rate of bacterial infection in subfertile men and its effect on semen quality. Seminal fluid was collected from 172 male members of infertile couples attending the andrology infertility center and a group of 35 fertile subjects as a control. Sperm parameters and DNA fragmentation were evaluated based on the type of bacteria in all ejaculates.

Results

From the 172 patients investigated for infertility, 60 (34.88%) patients had a positive culture for pathogenic bacteria of different species. Leukocytospermia was significantly higher in infected samples in comparison with non-infected samples (p < 0.05). Sperm concentration and motility and morphology were significantly lower in infected than non-infected samples. Moreover, sperm DNA fragmentation was significantly higher in infected than non-infected samples. Besides, our results showed that sperm DNA fragmentation was correlated significantly with leukocytospermia (R: 0.22, p < 0.01).

Conclusion

The present study suggested that bacterial infection significantly correlated with leukocytospermia could impair male fertility potential through decreasing sperm motility, morphology, and DNA integrity.

Metabolite Profiling of Pig Seminal Plasma Identifies Potential Biomarkers for Sperm Resilience to Liquid Preservation

Metabolomic approaches allow the study of downstream gene expression events since metabolites are considered as the products of cell signaling pathways. For this reason, many studies in humans have already been conducted to determine the influence of the metabolites present in seminal plasma (SP) on sperm physiology, and to identify putative biomarkers. However, in livestock species, these relationships are yet to be uncovered. Thus, the present study aimed to explore: (i) if concentrations of metabolites in pig SP are related to sperm quality and functionality, and (ii) if they could predict the sperm resilience to liquid storage at 17°C. To this end, 28 ejaculates were individually collected and split into three aliquots: one was used for SP analysis through nuclear magnetic resonance (NMR) spectroscopy; another served for the evaluation of sperm concentration and morphology; and the last one was utilized to determine sperm functionality parameters using computer-assisted sperm analysis (CASA) and flow cytometry after 0 h and 72 h of liquid-storage at 17°C. NMR analysis allowed the identification and quantification of 23 metabolites present in pig SP which, except for fumarate, were not observed to follow a breed-dependent behavior. Moreover, specific relationships between metabolites and sperm variables were identified: (i) glutamate, methanol, trimethylamine N-oxide, carnitine, and isoleucine were seen to be related to some sperm quality and functionality parameters evaluated immediately after semen collection; (ii) leucine, hypotaurine, carnitine and isoleucine were found to be associated to the sperm ability to withstand liquid storage; and (iii) Bayesian multiple regression models allowed the identification of metabolite patterns for specific sperm parameters at both 0 h and 72 h. The identification of these relationships opens up the possibility of further investigating these metabolites as potential sperm functional biomarkers.

A literature survey of all volatiles from healthy human breath and bodily fluids: the human volatilome

This paper comprises an updated version of the 2014 review which reported 1846 volatile organic compounds (VOCs) identified from healthy humans. In total over 900 additional VOCs have been reported since the 2014 review and the VOCs from semen have been added. The numbers of VOCs found in breath and the other bodily fluids are: blood 379, breath 1488, faeces 443, milk 290, saliva 549, semen 196, skin 623 and urine 444. Compounds were assigned CAS registry numbers and named according to a common convention where possible. The compounds have been included in a single table with the source reference(s) for each VOC, an update on our 2014 paper. VOCs have also been grouped into tables according to their chemical class or functionality to permit easy comparison. Careful use of the database is needed, as a number of the identified VOCs only have level 2-putative assignment, and only a small fraction of the reported VOCs have been validated by standards. Some clear differences are observed, for instance, a lack of esters in urine with a high number in faeces and breath. However, the lack of compounds from matrices such a semen and milk compared to breath for example could be due to the techniques used or reflect the intensity of effort e.g. there are few publications on VOCs from milk and semen compared to a large number for breath. The large number of volatiles reported from skin is partly due to the methodologies used, e.g. by collecting skin sebum (with dissolved VOCs and semi VOCs) onto glass beads or cotton pads and then heating to a high temperature to desorb VOCs. All compounds have been included as reported (unless there was a clear discrepancy between name and chemical structure), but there may be some mistaken assignations arising from the original publications, particularly for isomers. It is the authors' intention that this work will not only be a useful database of VOCs listed in the literature but will stimulate further study of VOCs from healthy individuals; for example more work is required to confirm the identification of these VOCs adhering to the principles outlined in the metabolomics standards initiative. Establishing a list of volatiles emanating from healthy individuals and increased understanding of VOC metabolic pathways is an important step for differentiating between diseases using VOCs.

Metabolomic signature of the seminal plasma in men with severe oligoasthenospermia

BACKGROUND

Male factor is incriminated in approximately 50% of cases of infertility. The metabolomic approach has recently been used in the assessment of sperm quality and male fertility.

MATERIALS AND METHODS

We analyzed the metabolomic signatures of the seminal plasma in 20 men with severe oligoasthenospermia (prewash total motile sperm count < 5.10⁶ ) (SOA) and compared it to 20 men with normal semen parameters, with a standardized approach of targeted and quantitative metabolomics using high-performance liquid chromatography, coupled with tandem mass spectrometry, and the Biocrates Absolute IDQ p180 kit.

RESULTS

Among the 188 metabolites analyzed, 110 were accurately measured in the seminal plasma. A robust model discriminating the two populations (Q_2(cum) = 55.2%) was obtained by OPLS-DA (orthogonal partial least-squares discriminant analysis), based on the drop in concentrations of 37 metabolites with a VIP (variable important for projection) greater than 1. Overall, in men with SOA, there was a significant decrease in: 17 phosphatidylcholines and four sphingomyelins; acylcarnitines, with free L-carnitine being the most discriminating metabolite; polyunsaturated fatty acids; six amino acids (glutamate, aspartate, methionine, tryptophan, proline, and alanine); and four biogenic amines (spermine, spermidine, serotonin, and alpha-aminoadipate).

DISCUSSION

Our signature includes several metabolic changes with different impacts on the sperm quality: a change in phospholipid composition and the saturation of their fatty acids that is potentially linked to the deterioration of sperm membranes; a carnitine deficiency that can negatively impact the energy production via fatty acid oxidation and oxidative phosphorylation; and a decreased level of amino acids and biogenic amines that can lead to dysregulated metabolic and signaling pathways.

CONCLUSION

We provide a global overview of the metabolic defects contributing to the structural and functional alteration of spermatozoa in severe oligoasthenospermia. These findings offer new insights into the pathophysiology of male factor infertility that could help to develop future specific treatments.

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.

1H Nuclear Magnetic Resonance of Pig Seminal Plasma Reveals Intra-Ejaculate Variation in Metabolites

In pigs, ejaculate is expelled in fractions, mainly the sperm-rich fraction (SRF) and the post-SRF (PSRF), which differ in both sperm content and origin. In addition, intra-ejaculate variability between fractions in terms of sperm reproductive characteristics has been previously reported, the highest sperm quality being observed in the first 10 mL of the SRF (SRF-P1). As seminal plasma (SP) composition has been purported to influence sperm physiology, the aim of this study was to profile pig SP metabolite composition and to find putative differences between the ejaculate portions (SRF-P1, the rest of SRF [SRF-P2], PSRF) and entire ejaculate (EE). To this end, ejaculates (n = 8, one per boar) were collected in fractions and SP was analyzed using 1H Nuclear Magnetic Resonance spectroscopy. We identified 19 metabolites present in all ejaculate portions and the EE, and reported correlations between the metabolites. Additionally, and for the first time in mammals, we found intra-ejaculate variability in the SP metabolites, observing different relative abundances in choline, glycerophosphocholine and glycine. Regarding their influence in sperm physiology, we hypothesize that these metabolites may explain the specific reproductive characteristics of each ejaculate portion. Finally, the reported SP metabolites could serve as a first steppingstone in the study of quality, functionality, and fertility biomarkers.