Exploring the role of gut microbiome in male reproduction

Causal relationships between gut microbiota and male reproductive inflammation and infertility: Insights from Mendelian randomization

The study observed interactions between gut microbiota and male reproductive health, noting that the causal relationships were previously unclear. It aimed to explore the potential cause-and-effect relationship between gut bacteria and male reproductive problems such as inflammation, infertility, and sperm functionality, using a two-sample Mendelian randomization method to examine these connections. The analysis found that certain bacterial genera, such as Erysipelatoclostridium (0.71 [0.55-0.92]), Parasutterella (0.74 [0.57-0.96]), Ruminococcaceae UCG-009 (0.77 [0.60-0.98]), and Slackia (0.69 [0.49-0.96]), showed protective effects against prostatitis. In contrast, other genera like Faecalibacterium (1.59 [1.08-2.34]), Lachnospiraceae UCG004 (1.64 [1.15-2.34]), Odoribacter (1.68 [1.01-2.81]), Paraprevotella (1.28 [1.03-1.60]), and Sutterella (1.58 [1.13-2.19]) were detrimental. Additionally, causal relationships were identified between 2 genera and orchitis and epididymitis, 3 genera and male infertility, and 5 genera and abnormal spermatozoa. Further analysis of sperm-related proteins revealed causal associations between specific bacterial genera and proteins such as SPACA3, SPACA7, SPAG11A, SPAG11B, SPATA9, SPATA20, and ZPBP4. The results remained robust after sensitivity analysis and reverse Mendelian randomization analysis. The study concluded that specific bacterial genera have causal roles in reproductive inflammation, infertility, and sperm-associated proteins. This provides a novel strategy for the early diagnosis and identification of therapeutic targets in reproductive inflammation and infertility.

Protective effects of Bifidobacterium longum subsp. longum BL21 against cyclophosphamide-induced reproductive dysfunction in zebrafish

This study aimed to investigate the effects of probiotic Bifidobacterium longum subsp. longum BL21 on reproductive health in zebrafish (Danio rerio), focusing on hormonal modulation, sperm vitality, and overall reproductive function improvement. Adult male zebrafish of the wild-type AB strain were divided into four groups: control (CTL), model control with cyclophosphamide-induced oligospermia (CS), probiotic-treated (BL21), and a positive control treated with clomiphene citrate (CC). All groups, except CTL, were exposed to cyclophosphamide from day 1 to day 9 to induce reproductive dysfunction, with subsequent monitoring until day 16. Key metrics assessed included body and testicular weight, sperm vitality, male courtship behavior, hormone levels, sperm DNA fragmentation, and gene expression of PCNA, NANOG, ZBTB16, mTOR, DDX4, CYP26A1, and ALDH1A2. In this study, BL21 demonstrated significant therapeutic potential in treating reproductive dysfunction in zebrafish. Metabolomic analysis revealed that BL21 influenced crucial pathways, notably upregulating mTOR signaling and isoflavone biosynthesis, while downregulating the TCA cycle and pyruvate metabolism, suggesting a broad biochemical impact. The probiotic treatment notably improved testicular weight (p < 0.01) and sperm count and vitality (p < 0.001) compared to the cyclophosphamide-induced model control, underscoring its efficacy in enhancing reproductive parameters. Additionally, BL21 intervention led to a marked increase in chasing behavior and sex hormone levels, surpassing those of the positive control. The treatment also significantly reduced sperm DNA fragmentation (p < 0.001) and increased the expression of genes crucial for spermatogenesis and testicular function (p < 0.05), confirming its potential to restore reproductive health at multiple biological levels. These results highlight the promise of BL21 as a multi-faceted agent for improving reproductive health, warranting further investigation in clinical settings. Probiotic BL21 enhances reproductive parameters in zebrafish by modulating hormone levels, improving sperm quality, and positively affecting reproductive behavior. These findings suggest potential therapeutic applications of probiotics in managing reproductive health issues.

Chronic exposure to liquid crystal monomer EBCN at environmentally relevant concentrations induces testicular dysfunction via the gut-testis axis

4-Cyano-4'-ethoxybiphenyl (EBCN) is a representative cyano liquid crystal monomer (LCM). While prior studies have documented the widespread occurrence of LCMs in diverse environmental and biological samples, research on their reproductive effects in vivo remains limited. This study employed 35-day and 70-day exposure models in mice to assess the short-term and long-term effects of environmentally relevant concentrations of EBCN on testicular health. Our findings indicate that EBCN exposure, irrespective of duration, had minimal impact on body weight, testis weight, and testicular organ coefficient. However, it induced dose-dependent reductions in seminiferous tubule area, sperm count, accompanied by decreases in Leydig cells and spermatogenic cells, along with disruptions in sex hormone levels. Moreover, EBCN exposure led to the upregulation of inflammatory factors in serum, partially attributable to the activation of necroptosis-related pathways. Additionally, 16S rRNA sequencing and metabolomic analysis revealed a decline in gut microbiome diversity and a decrease in anti-inflammatory metabolites, specifically L-carnosine, in the intestine, potentially contributing to the observed testicular toxicity. Supplementation with exogenous L-carnosine mitigated EBCN-induced testicular dysfunction by inhibiting the expression of necroptosis-related genes. In conclusion, our study suggests that prolonged EBCN exposure at environmentally relevant concentrations adversely impacts testicular function via the gut-testis axis.

Microbiota-derived β carotene is required for strobilation of Aurelia aurita by impacting host retinoic acid signaling

The strobilation process, an asexual reproduction mechanism in Aurelia aurita, transitions from the sessile polyp to the pelagic medusa stage. This study explored the essential role of the microbiome in strobilation, particularly through bacterial beta carotene's impact on the host's retinoic acid signaling pathway. Experiments demonstrated that native polyps undergo normal strobilation while sterile polyps exhibit morphological defects. Supplementing sterile polyps with provitamin A beta carotene or the vitamin A metabolite 9-cis retinoic acid (RA) remedied these defects, underscoring their crucial role in strobilation. Transcriptional analysis revealed that beta carotene and 9-cis RA restored expression of strobilation genes in sterile polyps to native levels. Inhibition of key enzymes in the RA pathway disrupted strobilation, further confirming its importance. The expression of bacterial β-carotenoid synthesis genes in the native microbiome, contrasted with tremendously reduced expression in antibiotic-treated polyps, emphasizes the microbiome's pivotal role in beta carotene provision, facilitating A. aurita's strobilation through RA signaling.

Effects of semen inflammation on embryo implantation, placentation, pregnancy outcomes and offspring health

This review explores the critical role of semen inflammation in sperm quality, embryo implantation, placentation, and its broader implications on reproductive health. Chronic inflammation of the male genital tract has been increasingly recognized as a significant factor contributing to infertility. This inflammation not only impairs semen quality but also disrupts the intricate immune cross-talk between the male and female genital tracts, which is essential for successful implantation, placentation and pregnancy. The review synthesizes existing research on the mechanisms by which inflammatory mediators in semen influence the female immune environment, leading to altered uterine receptivity, placental formation, and embryo implantation. Furthermore, the impact of these disruptions on the health and development of the offspring is discussed, highlighting the transgenerational effects of male genital tract inflammation. Through an examination of both animal models and human studies, this review underscores the need for a deeper understanding of the immune interactions in reproductive biology and the potential for novel therapeutic interventions aimed at mitigating the adverse outcomes associated with semen inflammation.

The role of probiotics in the regulation of expression of genes supporting antioxidant status and functionality of mouse testes in LPS-induced inflammatory processes

Systemic lipopolysaccharide (LPS)-induced inflammation has a significant impact on various organs, including the male reproductive system. In this study, we have demonstrated that LPS-induced inflammation causes oxidative stress in mouse testes, reduces expression of genes encoding the catalytic subunit of glutamate-cysteine ligase (Gclc) and superoxide dismutase 2 (Sod2). Inflammation suppressed transcription of genes involved in differentiation and metabolic regulation of testicular cells and sperm maturation: in the LPS group, the expression of the Amh, Lepr, Eif2b4 genes was approximately 3 times lower compared to the control group. The intake of probiotic microorganisms caused a decrease in the intensity of lipid peroxidation, which was manifested in a decrease in the level of conjugated dienes (CD) compared to the LPS group, contributed to maintaining the level of expression of genes supporting the antioxidant status, as well as genes supporting the functionality of the mouse testes. The data obtained suggest that probiotics may be considered as potential tools for maintaining male reproductive function under conditions of inflammatory processes.

Sex-Specific Mechanisms of Fluoride-Induced Gonadal Injury: A Multi-Omics Investigation into Reproductive Toxicity and Gut Microbiota Disruption

Fluoride, a common agricultural additive used to enhance plant resilience and pest control, poses toxicity risks when exposure surpasses safe thresholds, affecting ecosystems and human health. While its reproductive toxicity is recognized, the sex-specific and cross-generational effects remain underexplored. To address this gap, we employed an integrative approach combining transcriptomics (next-generation sequencing (NGS)), bioinformatic network analysis, gut microbiota sequencing, and in vivo functional assays. ICR mice (F0 generation), both male and female, were exposed to fluoride (100 mg/L in drinking water) for 35 days, continuing through gestation and offspring weaning. Our transcriptomic analysis revealed significant upregulation of autophagy (via the PI3K-AKT-mTOR pathway) and oxidative stress-induced mitochondrial dysfunction in gonadal tissue, with more pronounced effects observed in males. Further integrated analyses of transcriptomic and metabolomic data, supported by in vivo experiments, highlighted oxidative stress, mitochondrial dysfunction, and PI3K-AKT-mTOR pathway activation with stronger effects in males. The principal component analysis confirmed sex-specific transcriptome alterations, with males showing more substantial disruption. Additionally, 16S rRNA sequencing identified significant gut dysbiosis, particularly in males, with an increased Firmicutes/Bacteroidetes ratio and higher abundances of Oscillospirales and Anaerovoracaceae. Moreover, our study identified significant correlations between specific gut microbiota (e.g., Firmicutes, Proteobacteria) and autophagy, oxidative stress, and mitochondrial dysfunction pathways, with notable sex-dependent differences. These findings suggest that gut microbiota may play a critical role in modulating fluoride-induced reproductive toxicity, particularly through their effects on oxidative stress and cellular homeostasis. The breakdown of the gut barrier and elevated serum/gonadal lipopolysaccharide (LPS) levels in fluoride-treated mice further established a link between gut dysbiosis and fluoride-induced reproductive toxicity. These findings underscore the importance of considering sex differences in xenobiotic-induced reproductive and developmental toxicity.

Acupuncture mediates the "gut-testis axis" to improve asthenozoospermia

Background

Asthenozoospermia is a common cause of male infertility. Studies have shown that sperm quality and motility are affected by the gut-testis axis that can regulate testicular metabolism and function through the gut microbiota and its metabolites. Acupuncture is an important modality of complementary and alternative medicine. It can improve sperm motility, but it remains unclear whether acupuncture can enhance sperm vitality by influencing the gut-testis axis.

Methods

In this study, sperm quality, testicular pathology, and serum hormone levels were assessed using a cyclophosphamide-induced mouse model. Real-time PCR, a western blot analysis, and immunofluorescence techniques were used to assess the effects of acupuncture on the gut barrier and blood-testis barrier functions. In addition, gut microbiome and metabolomics were used to study the impact of acupuncture on the gut microbiota structure, serum, and testicular metabolites in asthenozoospermic mice. Further validation was obtained by performing a fecal microbiota transplantation (FMT).

Results

Acupuncture improved the sperm quality; ameliorated testicular pathology; increased serum testosterone (T), follicle-stimulating hormone (FSH), and luteinizing hormone (LH) levels; and repaired gut and blood-testis barrier damage in asthenozoospermic mice. The abundances of Bacteroidota, Firmicutes, Faecalibaculum, and Dubosiella were associated with sperm motility, as shown by a gut microbiome analysis. Serum metabolomics revealed that differentially expressed metabolites (DEMs), such as cytosine and N-oleyl-leucine, were closely related to sperm motility. Testicular metabolomics analysis revealed DEMs, such as 5-fluorouridine and 1-acetylimidazole, were also associated with sperm motility. Furthermore, reproductive function improvements in asthenozoospermic mice through acupuncture were achieved via an FMT.

Conclusion

Acupuncture may alleviate asthenozoospermia symptoms by modulating the gut-testis axis and repairing the gut-testis barrier.

Ammonia and hydrogen sulfide - new insights into gut microbiota and male infertility through meta-analysis

Background

Ammonia (NH3) and hydrogen sulfide (H2S) are produced during digestion in the human gut, yet the impact of these internally generated gases on male reproduction have received limited attention in scientific research.

Methods

We systematically reviewed 935 scientific publications, spanning from 1947 to 2023, focusing on external or internal NH3 and/or H2S, male infertility, and gut microbiota. Meta-analysis was conducted to evaluate the summary relative risk (RR) and 95% confidence intervals (CIs) of combined studies.

Results

Our findings revealed that the internal NH3 and/or H2S were negatively related to the Lactobacillus, which is beneficial to male fertility, whereas NH3 and H2S were positively related to Bacteroides, which showed negative effects on male fertility. The meta-analysis comparing Lactobacillus and Bacteroides levels with NH3 showed statistically significant results (p<0.001).

Conclusions

The meta-analysis is the first to confirm these facts and explored the potential existence of a gut microbiota-inner gases-male fertility axis in the human gut.

Selenium-Enriched Aspergillus oryzae A02 Enhances Testicular Antioxidant Capacity in Mice by Regulating Intestinal Microbiota and Serum Metabolite

Selenium (Se) is a trace element that is essential for health. Organic Se created by Se-enriched microorganisms has the characteristics of low toxicity, high bioavailability, and regulation of physiological functions. Here, the regulatory effect of Se-enriched Aspergillus oryzae A02 on the reproductive function of male mice and its potential molecular mechanism was studied. Specifically, twenty-four male mice were randomly divided into a control group and a Se-enriched A. oryzae A02 (Nano-Se) (daily gavage of 0.5 mg/kg, dissolved in saline) for an 8-week experiment. The results showed that Nano-Se intervention did not affect body weight and testicular index, but increased sperm concentration and seminiferous epithelium height in experimental mice, indicating that Nano-Se has the potential to improve the reproductive performance of male mice. Mechanistically, Nano-Se intervention increased the levels of antioxidant-related indicators catalase (CAT) and glutathione peroxidase (GSH-Px) in mouse serum, and increased the relative mRNA expression of GSH-Px, heme oxygenase-1 (HO-1), and NADPH quinine oxidoreductase-1 (NQO-1) in testicular tissues. We identified 9,10,13-trihydroxyoctadecenoic acids (TriHOMEs), stearidonic acid and selenomethionine linked with alpha-linolenic acid metabolism, selenocompound metabolism, folate biosynthesis, ubiquinone, and other terpenoid-quinone biosynthesis and biosynthesis of cofactors. In addition, Nano-Se did not influence the fecal bacterial alpha and beta diversity (P > 0.05), but increased the abundance of the Actinobacteriota and Proteobacteria phyla and the Staphylococcus and Corynebacterium genera, and lowered the abundance of the Bacteroidota phylum and the Lactobacillus and norank_f_Muribaculaceae genera. Nano-Se is considered a novel and promising nutritional regulator to improve reproductive function.

Variations in gut microbiota composition and reproductive hormone levels between laying and broody Muscovy ducks

High broodiness in Muscovy ducks impedes animal husbandry growth. The interaction between endocrine hormones and gut microbiota has been proven to play a crucial role in reproductive performance, and whether it can regulate the broody behavior of Muscovy ducks requires further research. Nine laying ducks (Laying group) and nine broody ducks (Broodiness group) were selected. Corresponding serum, ileum, and cecum chyme were collected for further research. The results showed that, compared to the laying group, the serum concentration of prolactin decreased, while the levels of Mullerian inhibiting substance, follicle-stimulating hormone, and follistatin increased in the broodiness group (P < 0.05). 16S rDNA sequencing showed that, the broodiness group exhibited lower abundance levels of Rothia, Streptococcus, and Lactobacillus, whereas the abundance of Turicibacter, Aliicoccus, and Facklamia was higher in the ileum compared to the laying group (P < 0.05). In the cecum, the broodiness group exhibits a significant reduction in the abundance of Butyricicoccus and unclassified_f_Rikenellaceae, while the abundance of Christensenellaceae_R-7_group, Ruminococcus_torques_group, Parabacteroides, norank_f_Oscillospiraceae, Cloacibacillus, Sellimonas, Shuttleworthia, norank_f_UCG-010, unclassified_f_Lachnospiraceae, Oscillospira, Synergistes, Family_XIII_AD3011_group and Eubacterium_nodatum_group is higher compared to the laying group. A Spearman correlation analysis reveals that both in the ileum and cecum, serum hormones exhibit significant correlations with the top 20 abundant intestinal microbial genera. Among these, serum follistatin has most entries of significant correlations with the detected microbial genera (P < 0.05). In conclusion, the broody behavior of Muscovy ducks can be modulated by the interaction between hormones and gut microbiota. Notably, the relationship between Follistatin and the composition of gut microbiota, specifically Firmicutes, is the most prominent.

Association between gut microbiota and male infertility: a two-sample Mendelian randomization study

Previous research has confirmed the significant association between gut microbiota (GM) and male infertility (MI), but the causality between them remains unclear. This study aims to investigate the causal relationship between GM and MI using Mendelian randomization (MR) and provide supplementary information for the optimization of future randomized controlled trials (RCTs). Instrumental variables for 211 GM taxa were obtained from genome-wide association studies (GWAS), and inverse variance weighted (IVW) method was used as the main analysis method for two-sample MR analysis to assess the impact of GM on the risk of MI. Four methods were used to test for horizontal pleiotropy and heterogeneity of MR results to ensure the reliability of the MR findings. A total of 50 single-nucleotide polymorphisms (SNPs) closely related to GM were included, and ultimately identified 1 family and 4 general are causally associated with MI. Among them, Anaerotruncus (OR = 1.96, 95% CI 1.31-3.40, P = 0.016) is significantly associated with increased MI risk. Furthermore, we used four MR methods to evaluate the causality, and the results supported these findings. The leave-one-out analysis showed stable results with no instrumental variables exerting strong influence on the results. The causal direction indicated a positive effect, and the effects of heterogeneity and horizontal pleiotropy on the estimation of causal effect were minimized. We confirmed a causal relationship between GM taxa and MI, providing new insights into the mechanisms underlying GM-mediated MI.

Causal Link between Gut Microbiota and Infertility: A Two-sample Bidirectional Mendelian Randomization Study

OBJECTIVE

To investigate the associations of the gut microbiota with reproductive system diseases, including female infertility, male infertility, polycystic ovary syndrome (PCOS), primary ovarian failure, endometriosis, uterine fibroids, uterine polyps, sexual dysfunction, orchitis, and epididymitis.

METHODS

A two-sample bidirectional Mendelian randomization (MR) analysis was performed to evaluate the potential causal relationship between the composition of gut microbiota and infertility, along with associated diseases.

RESULTS

Sixteen strong causal associations between gut microbes and reproductive system diseases were identified. Sixty-one causal associations between gut microbes and reproductive system diseases were determined. The genus Eubacterium hallii was a protective factor against premature ovarian failure and a pathogenic factor of endometriosis. The genus Erysipelatoclostridium was the pathogenic factor of many diseases, such as PCOS, endometriosis, epididymitis, and orchitis. The genus Intestinibacter is a pathogenic factor of male infertility and sexual dysfunction. The family Clostridiaceae 1 was a protective factor against uterine polyps and a pathogenic factor of orchitis and epididymitis. The results of reverse causal association analysis revealed that endometriosis, orchitis, and epididymitis all led to a decrease in the abundance of bifidobacteria and that female infertility-related diseases had a greater impact on gut microbes than male infertility-related diseases did.

CONCLUSIONS

The findings from the MR analysis indicate that there is a bidirectional causal relationship between the gut microbiota and infertility as well as associated ailments. Compared with ovarian diseases, uterine diseases are more likely to lead to changes in women's gut microbiota. The findings of this research offer valuable perspectives on the mechanism and clinical investigation of reproductive system diseases caused by microorganisms.

Causal effects of gut microbiota on the risk of erectile dysfunction: a Mendelian randomization study

Erectile dysfunction ranks among the prevalent sexual disorders in men. Several studies have indicated a potential link between gut microbiota and erectile dysfunction. To validate this potential association, we were to screen statistical data from genome-wide association studies of gut microbiota and erectile dysfunction. p values of less than 1 × 10-5 were set as the threshold for screening instrumental variables that were strongly associated with gut microbiota. At the same time, in order to obtain more convincing findings, we further excluded instrumental variables with possible chain imbalance, instrumental variables with the presence of palindromes, instrumental variables with F-statistics less than 10, and instrumental variables associated with risk factors for erectile dysfunction. Five methods including inverse-variance weighted method, weighted median method, weighted mode, Mendelian randomization egger method and Mendelian randomization pleiotropy residual sum and outlier test were then used to analyse the 2591 instrumental variables obtained from the screening. We identified correlations between six gut microbiota and the risk of erectile dysfunction. The genus Ruminococcaceae UCG-013 exhibited an inverse association with the risk of developing erectile dysfunction (0.79 (0.65-0.97), P = 0.0214). Conversely, the genus Tyzzerella3 (1.13 (1.02-1.26), P = 0.0225), genus Erysipelotrichaceae UCG-003 (1.18 (1.01-1.38), P = 0.0412), genus LachnospiraceaeNC2004group (1.19 (1.03-1.37), P = 0.0191), genus Oscillibacter (1.23 (1.08-1.41), P = 0.0022), and family Lachnospiraceae (1.26 (1.05-1.52), P = 0.0123) demonstrated positive associations with an increased risk of erectile dysfunction. These sensitivity analyses of the gut microbiota were consistent. This study demonstrated a possible causal relationship between gut microbiota and erectile dysfunction risk through Mendelian randomization analysis, providing new potential possibilities for the prevention and treatment of erectile dysfunction.

Exploring the hypothetical links between environmental pollutants, diet, and the gut-testis axis: The potential role of microbes in male reproductive health

The gut system, commonly referred to as one of the principal organs of the human "superorganism," is a home to trillions of bacteria and serves an essential physiological function in male reproductive failures or infertility. The interaction of the endocrine-immune system and the microbiome facilitates reproduction as a multi-network system. Some recent studies that link gut microbiota to male infertility are questionable. Is the gut-testis axis (GTA) real, and does it affect male infertility? As a result, this review emphasizes the interconnected links between gut health and male reproductive function via changes in gut microbiota. However, a variety of harmful (endocrine disruptors, heavy metals, pollutants, and antibiotics) and favorable (a healthy diet, supplements, and phytoconstituents) elements promote microbiota by causing dysbiosis and symbiosis, respectively, which eventually modify the activities of male reproductive organs and their hormones. The findings of preclinical and clinical studies on the direct and indirect effects of microbiota changes on testicular functions have revealed a viable strategy for exploring the GTA-axis. Although the GTA axis is poorly understood, it may have potential ties to reproductive issues that can be used for therapeutic purposes in the future.

The Equilibrium of Bacterial Microecosystem: Probiotics, Pathogenic Bacteria, and Natural Antimicrobial Substances in Semen

Semen is a complex fluid that contains spermatozoa and also functions as a dynamic bacterial microecosystem, comprising probiotics, pathogenic bacteria, and natural antimicrobial substances. Probiotic bacteria, such as Lactobacillus and Bifidobacterium, along with pathogenic bacteria like Pseudomonas aeruginosa and Escherichia coli, play significant roles in semen preservation and reproductive health. Studies have explored the impact of pathogenic bacteria on sperm quality, providing insights into the bacterial populations in mammalian semen and their influence on sperm function. These reviews highlight the delicate balance between beneficial and harmful bacteria, alongside the role of natural antimicrobial substances that help maintain this equilibrium. Moreover, we discuss the presence and roles of antimicrobial substances in semen, such as lysozyme, secretory leukocyte peptidase inhibitors, lactoferrin, and antimicrobial peptides, as well as emerging antibacterial substances like amyloid proteins. Understanding the interactions among probiotics, pathogens, and antimicrobial agents is crucial for elucidating semen preservation and fertility mechanisms. Additionally, the potential for adding probiotic bacteria with recombinant antibacterial properties presents a promising avenue for the development of new semen extenders. This review offers updated insights to understand the equilibrium of the bacterial microecosystem in semen and points toward innovative approaches for improving semen preservation.

The elusive male microbiome: revealing the link between the genital microbiota and fertility. Critical review and future perspectives

There is a growing focus on understanding the role of the male microbiome in fertility issues. Although research on the bacterial communities within the male reproductive system is in its initial phases, recent discoveries highlight notable variations in the microbiome's composition and abundance across distinct anatomical regions like the skin, foreskin, urethra, and coronary sulcus. To assess the relationship between male genitourinary microbiome and reproduction, we queried various databases, including MEDLINE (available via PubMed), SCOPUS, and Web of Science to obtain evidence-based data. The literature search was conducted using the following terms "gut/intestines microbiome," "genitourinary system microbiome," "microbiome and female/male infertility," "external genital tract microbiome," "internal genital tract microbiome," and "semen microbiome." Fifty-one relevant papers were analyzed, and eleven were strictly semen quality or male fertility related. The male microbiome, especially in the accessory glands like the prostate, seminal vesicles, and bulbourethral glands, has garnered significant interest because of its potential link to male fertility and reproduction. Studies have also found differences in bacterial diversity present in the testicular tissue of normozoospermic men compared to azoospermic suggesting a possible role of bacterial dysbiosis and reproduction. Correlation between the bacterial taxa in the genital microbiota of sexual partners has also been found, and sexual activity can influence the composition of the urogenital microbiota. Exploring the microbial world within the male reproductive system and its influence on fertility opens doors to developing ways to prevent, diagnose, and treat infertility. The present work emphasizes the importance of using consistent methods, conducting long-term studies, and deepening our understanding of how the reproductive tract microbiome works. This helps make research comparable, pinpoint potential interventions, and smoothly apply microbiome insights to real-world clinical practices.

Effect of Probiotics on Sperm Quality in the Adult Mouse

The administration of probiotics for the treatment of different diseases has gained interest in recent years. However, few studies have evaluated their effects on reproductive traits. The objective of this study was to examine the effect of two mixtures of probiotics, a commercial probiotic (Vivomixx®) and a mix of Lacticaseibacillus rhamnosus GG and Faecalibacterium duncaniae A2-165, on sperm quality in a mouse model. Adult male mice (8 months old) were used for two experimental and one control groups (n = 5 each). The probiotics or physiological serum (control) was administered orally, twice a week, during 5 weeks. Sperm were collected from the cauda epididymis, and their total number, motility, kinematics, morphology, and acrosome integrity were assessed in recently collected samples and after a 60-min in vitro incubation. Results showed a higher percentage of normal sperm in both experimental groups, with fewer head abnormalities than in the control. Differences were found among groups in the morphometry of sperm heads, being more elongated in mice treated with probiotics. Sperm from probiotic-treated mice showed similar total motility when compared to the controls, although the proportion of progressively moving sperm and their vigor of motility were lower. Sperm swimming descriptors were measured with a CASA system. Velocity parameters were similar among groups whereas linearity was higher in mice treated with the commercial probiotic. These results suggest that the administration of probiotics may increase the proportion of sperm with normal morphology and lead to modifications in sperm head shape that may enhance sperm swimming. Studies using a longer administration period would be useful in further characterizing the effect of these probiotic mixtures on sperm quality and fertilization capacity.

The potential influence and intervention measures of gut microbiota on sperm: it is time to focus on testis-gut microbiota axis

As the global male infertility rate continues to rise, there is an urgent imperative to investigate the underlying causes of sustained deterioration in sperm quality. The gut microbiota emerges as a pivotal factor in host health regulation, with mounting evidence highlighting its dual influence on semen. This review underscores the interplay between the Testis-Gut microbiota axis and its consequential effects on sperm. Potential mechanisms driving the dual impact of gut microbiota on sperm encompass immune modulation, inflammatory responses mediated by endotoxins, oxidative stress, antioxidant defenses, gut microbiota-derived metabolites, epigenetic modifications, regulatory sex hormone signaling. Interventions such as probiotics, prebiotics, synbiotics, fecal microbiota transplantation, and Traditional natural herbal extracts are hypothesized to rectify dysbiosis, offering avenues to modulate gut microbiota and enhance Spermatogenesis and motility. Future investigations should delve into elucidating the mechanisms and foundational principles governing the interaction between gut microbiota and sperm within the Testis-Gut microbiota Axis. Understanding and modulating the Testis-Gut microbiota Axis may yield novel therapeutic strategies to enhance male fertility and combat the global decline in sperm quality.

The Association between the Gut Microbiota and Erectile Dysfunction

PURPOSE

Explore the causal relationship between the gut microbiota and erectile dysfunction (ED) at phylum, class, order, family, and genus levels, and identify specific pathogenic bacteria that may be associated with the onset and progression of ED.

MATERIALS AND METHODS

The genetic variation data of 196 human gut microbiota incorporated in our study came from the human gut microbiome Genome Wide Association Studies (GWAS) dataset released by the MiBioGen Consortium. The GWAS statistics for ED were extracted from one study by Bovijn et al., which included 223,805 participants of European ancestry, of whom 6,175 were diagnosed with ED. Subsequently, Mendelian randomization (MR) analysis was carried out to explore whether a causal relationship exists between the gut microbiota and ED. Additionally, bidirectional MR analysis was performed to examine the directionality of the causal relationship.

RESULTS

Through MR analysis, we found that family Lachnospiraceae (odds ratio [OR]: 1.27, 95% confidence interval [CI]: 1.05-1.52, p=0.01) and its subclass genus LachnospiraceaeNC2004 group (OR: 1.17, 95% CI: 1.01-1.37, p=0.04) are associated with a higher risk of ED. In addition, genus Oscillibacter (OR: 1.17, 95% CI: 1.02-1.35, p=0.03), genus Senegalimassilia (OR: 1.32, 95% CI: 1.06-1.64, p=0.01) and genus Tyzzerella3 (OR: 1.14, 95% CI: 1.02-1.27, p=0.02) also increase the risk of ED. In contrast, the inverse variance weighted estimate of genus RuminococcaceaeUCG013 (OR: 0.77, 95% CI: 0.61-0.96, p=0.02) suggests that it has a protective effect against the occurrence of ED.

CONCLUSIONS

This study preliminarily identified 6 bacterial taxa that may have a causal relationship with ED, including family Lachnospiraceae, genus Lachnospiraceae NC2004 group, Oscillibacter, Senegalimassilia, Tyzzerella 3 and Ruminococcaceae UCG013. These identified important bacterial taxa may serve as candidates for microbiome intervention in future ED clinical trials.

Multiple omics integration analysis reveals the regulatory effect of chitosan oligosaccharide on testicular development

Infertility is a global health problem affecting millions of people of reproductive age worldwide, with approximately half caused by males. Chitosan oligosaccharide (COS) has strong antioxidant capacity, but its impact on the male reproductive system has not been effectively evaluated. To address this, we integrated RNA-seq, serum metabolomics and intestinal 16 S rDNA analysis to conduct a comprehensive investigation on the male reproductive system. The results showed that COS has potential targets for the treatment of oligospermia, which can promote the expression of meiotic proteins DDX4, DAZL and SYCP1, benefit germ cell proliferation and testicular development, enhance antioxidant capacity, and increase the expression of testicular steroid proteins STAR and CYP11A1. At the same time, COS can activate PI3K-Akt signaling pathway in testis and TM3 cells. Microbiome and metabolomics analysis suggested that COS alters gut microbial community composition and cooperates with serum metabolites to regulate spermatogenesis. Therefore, COS promotes male reproduction by regulating intestinal microorganisms and serum metabolism, activating PI3K-Akt signaling pathway, improving testicular antioxidant capacity and steroid regulation.

Differential gene expression and gut microbiota composition in low-altitude and high-altitude goats

Previous studies have presented evidence suggesting that altitude exerts detrimental effects on reproductive processes, yet the underlying mechanism remains elusive. Our study employed two distinct goat breeds inhabiting low and high altitudes, and conducted a comparative analysis of mRNA profiles in testis tissues and the composition of gut microbiota. The results revealed a reduced testis size in high-altitude goats. RNA-seq analysis identified the presence of 214 differentially expressed genes (DEGs) in the testis. These DEGs resulted in a weakened immunosuppressive effect, ultimately impairing spermatogenesis in high-altitude goats. Additionally, 16S rDNA amplicon sequencing recognized statistically significant variations in the abundance of the genera Treponema, unidentified_Oscillospiraceae, Desulfovibrio, Butyricicoccus, Dorea, Parabacteroides between the two groups. The collective evidence demonstrated the gut and testis played a synergistic role in causing decreased fertility at high altitudes. Our research provides a theoretical basis for future investigations into the reproductive fitness of male goats.

Contribution of the seminal microbiome to paternal programming

The field of Developmental Origins of Health and Disease has primarily focused on maternal programming of offspring health. However, emerging evidence suggests that paternal factors, including the seminal microbiome, could potentially play important roles in shaping the developmental trajectory and long-term offspring health outcomes. Historically, the microbes present in the semen were regarded as inherently pathogenic agents. However, this dogma has recently been challenged by the discovery of a diverse commensal microbial community within the semen of healthy males. In addition, recent studies suggest that the transmission of semen-associated microbes into the female reproductive tract during mating has potentials to not only influence female fertility and embryo development but could also contribute to paternal programming in the offspring. In this review, we summarize the current knowledge on the seminal microbiota in both humans and animals followed by discussing their potential involvement in paternal programming of offspring health. We also propose and discuss potential mechanisms through which paternal influences are transmitted to offspring via the seminal microbiome. Overall, this review provides insights into the seminal microbiome-based paternal programing, which will expand our understanding of the potential paternal programming mechanisms which are currently focused primarily on the epigenetic modifications, oxidative stresses, and cytokines.

Bidirectional Mendelian randomization to explore the causal relationships between the gut microbiota and male reproductive diseases

Gut bacteria might play an important role in male reproductive disorders, such as male infertility and sperm abnormalities; however, their causal role is unclear. Herein, Mendelian randomization (MR)-Egger, weighted median, inverse variance weighting, Simple mode, and Weighted mode were used to test the causal relationship between gut microbes and male reproductive diseases. The MR results were validated using various metrics. The MR results were also consolidated using reverse causality speculation, conducted using two-way MR analysis and Steiger filtering. Biological function was analysed using enrichment analyses. The results suggested that eight intestinal microflorae were causally associated with male infertility. The Eubacterium oxidoreducens group was associated with an increased risk of male infertility, while the family Bacteroidaceae was negatively associated with male reproductive diseases. Eight intestinal microflorae were causally associated with abnormal spermatozoa. The family Streptococcaceae was associated with a high risk of abnormal spermatozoa, whereas the family Porphyromonadaceae was associated with a low risk of abnormal spermatozoa. No pleiotropy was observed, this study identified a high correlation between the gut flora and the likelihood of male reproductive diseases. Future research will attempt to advance microbial-focused treatments for such diseases.

Toxicity to the Male Reproductive System after Exposure to Polystyrene Nanoplastics: A Macrogenomic and Metabolomic Analysis

Nanoplastics (NPs) cause serious contamination of drinking water and potential damage to human health. This study aimed to investigate the effects of NPs with different particle sizes and concentrations on the reproductive function of male mice. In this study, free drinking water exposure was used to expose male BALB/C mice to PS-NPs (20 nm, 200 nm, and 1000 nm) at 0.1 mg/L, 1 mg/L, and 5 mg/L for 4 months. The male reproductive function of the mice was assessed after NPs exposure, and fecal and blood samples were collected for macrogenomics and metabolomics. The results showed that PS-NPs resulted in mice with reduced testicular organ coefficients, decreased sperm quality, altered testicular tissue structure, disturbed sex hormone levels, and abnormal levels of inflammatory factors and oxidative stress. Furthermore, this study found that NP exposure affected the alteration of gut communities and metabolic pathways related to male reproduction, such as Clostridium and glutathione metabolism. Importantly, we found an effect of NP particle size on reproductive function. In the future, more attention should be paid to the smaller particle sizes of NPs.

Effects of polycyclic aromatic hydrocarbons on the gut-testis axis

Polycyclic aromatic hydrocarbons (PAHs) are a large group of organic compounds which are comprised of two or more fused benzene rings. As a typical environmental pollutant, PAHs are widely distributed in water, soil, atmosphere and food. Despite extensive researches on the mechanisms of health damage caused by PAHs, especially their carcinogenic and mutagenic toxicity, there is still a lack of comprehensive summarization and synthesis regarding the mechanisms of PAHs on the gut-testis axis, which represents an intricate interplay between the gastrointestinal and reproductive systems. Thus, this review primarily focuses on the potential forms of interaction between PAHs and the gut microbiota and summarizes their adverse outcomes that may lead to gut microbiota dysbiosis, then compiles the possible mechanistic pathways on dysbiosis of the gut microbiota impairing the male reproductive function, in order to provide valuable insights for future research and guide further exploration into the intricate mechanisms underlying the impact of gut microbiota dysbiosis caused by PAHs on male reproductive function.

Gut bacterial composition shows sex-specific shifts during breeding season in ex situ managed black-footed ferrets

The gut microbiome of mammals engages in a dynamic relationship with the body and contributes to numerous physiological processes integral to overall health. Understanding the factors shaping animal-associated bacterial communities is therefore paramount to the maintenance and management in ex situ wildlife populations. Here, we characterized the gut microbiome of 48 endangered black-footed ferrets (Mustela nigripes) housed at Smithsonian's National Zoo and Conservation Biology Institute (Front Royal, Virginia, USA). We collected longitudinal fecal samples from males and females across two distinct reproductive seasons to consider the role of host sex and reproductive physiology in shaping bacterial communities, as measured using 16S rRNA amplicon sequencing. Within each sex, gut microbial composition differed between breeding and non-breeding seasons, with five bacterial taxa emerging as differentially abundant. Between sexes, female and male microbiomes were similar during non-breeding season but significantly different during breeding season, which may result from sex-specific physiological changes associated with breeding. Finally, we found low overall diversity consistent with other mammalian carnivores alongside high relative abundances of potentially pathogenic microbes such as Clostridium, Escherichia, Paeniclostridium, and (to a lesser degree) Enterococcus-all of which have been associated with gastrointestinal or reproductive distress in mammalian hosts, including black-footed ferrets. We recommend further study of these microbes and possible therapeutic interventions to promote more balanced microbial communities. These results have important implications for ex situ management practices that can improve the gut microbial health and long-term viability of black-footed ferrets.

Gut-Derived Exosomes Mediate the Microbiota Dysbiosis-Induced Spermatogenesis Impairment by Targeting Meioc in Mice

Diseases like obesity and intestinal inflammation diseases are accompanied by dysbiosis of the gut microbiota (DSGM), which leads to various complications, including systemic metabolic disorders. DSGM reportedly impairs the fertility of male mice; however, the regulatory mechanism is unclear. Exosomes are molecular mediators of intercellular communication, but the regulation of spermatogenesis by non-reproductive tissue-originated exosomes remains unknown. The present study shows that DSGM altered the miRNA expression profile of mouse circulating exosomes and impaired spermatogenesis. Moreover, the single-cell sequencing results indicate that circulating exosomes from mice with DSGM impaired spermatogenesis, while circulating exosomes from wild mice improved spermatogenesis by promoting meiosis. Further study demonstrates that DSGM leads to abnormal upregulation of miR-211-5p in gut-derived circulating exosomes, which inhibited the expression of meiosis-specific with coiled-coil domain (Meioc) in the testes and impaired spermatogenesis by disturbing meiosis process. In summary, this study defines the important role of gut-derived exosomes in connecting the "gut-testis" axis.

Future in the past: paternal reprogramming of offspring phenotype and the epigenetic mechanisms

That certain preconceptual paternal exposures reprogram the developmental phenotypic plasticity in future generation(s) has conceptualized the "paternal programming of offspring health" hypothesis. This transgenerational effect is transmitted primarily through sperm epigenetic mechanisms-DNA methylation, non-coding RNAs (ncRNAs) and associated RNA modifications, and histone modifications-and potentially through non-sperm-specific mechanisms-seminal plasma and circulating factors-that create 'imprinted' memory of ancestral information. The epigenetic landscape in sperm is highly responsive to environmental cues, due to, in part, the soma-to-germline communication mediated by epididymosomes. While human epidemiological studies and experimental animal studies have provided solid evidences in support of transgenerational epigenetic inheritance, how ancestral information is memorized as epigenetic codes for germline transmission is poorly understood. Particular elusive is what the downstream effector pathways that decode those epigenetic codes into persistent phenotypes. In this review, we discuss the paternal reprogramming of offspring phenotype and the possible underlying epigenetic mechanisms. Cracking these epigenetic mechanisms will lead to a better appreciation of "Paternal Origins of Health and Disease" and guide innovation of intervention algorithms to achieve 'healthier' outcomes in future generations. All this will revolutionize our understanding of human disease etiology.

Multiomics Reveals the Microbiota and Metabolites Associated with Sperm Quality in Rongchang Boars

In this study, we investigated the correlation between the composition and function of the gut microbiota and the semen quality of Rongchang boars. Significant differences in gut microbial composition between boars with high (group H) and low (group L) semen utilization rates were identified through 16S rRNA gene sequencing, with 18 differential microbes observed at the genus level. Boars with lower semen utilization rates exhibited a higher relative abundance of Treponema, suggesting its potential role in reducing semen quality. Conversely, boars with higher semen utilization rates showed increased relative abundances of Terrisporobacter, Turicibacter, Stenotrophomonas, Clostridium sensu stricto 3, and Bifidobacterium, with Stenotrophomonas and Clostridium sensu stricto 3 showing a significant positive correlation with semen utilization rates. The metabolomic analyses revealed higher levels of gluconolactone, D-ribose, and 4-pyridoxic acid in the H group, with 4 pyridoxic acid and D-ribose showing a significant positive correlation with Terrisporobacter and Clostridium sensu stricto 3, respectively. In contrast, the L group showed elevated levels of D-erythrose-4-phosphate, which correlated negatively with Bifidobacterium and Clostridium sensu stricto 3. These differential metabolites were enriched in the pentose phosphate pathway, vitamin B6 metabolism, and antifolate resistance, potentially influencing semen quality. These findings provide new insights into the complex interplay between the gut microbiota and boar reproductive health and may offer important information for the discovery of disease biomarkers and reproductive health management.

Heat stress-induced dysbiosis of the gut microbiota impairs spermatogenesis by regulating secondary bile acid metabolism in the gut

Heat stress (HS) poses a substantial challenge to livestock. Studies have demonstrated that HS reduces fertility and leads to gut microbiota dysbiosis in bulls. However, the impact of the gut microbiota on fertility in bulls during HS is still unclear. Our research revealed that HS exposure decreased semen quality in bulls, and fecal microbiota transplantation (FMT) from heat-stressed bulls to recipient mice resulted in a significant decrease in number of testicular germ cells and epididymal sperm. Untargeted metabolomics methodology and 16S rDNA sequencing conjoint analysis revealed that Akkermansia muciniphila (A. muciniphila) seemed to be a key bacterial regulator of spermatogenesis after HS exposure. Moreover, the research indicated that A. muciniphila regulated secondary bile acid metabolism by promoting the colonization of bile salt hydrolase (BSH)-metabolizing bacteria, leading to increase of retinol absorption in the host gut and subsequently elevation of testicular retinoic acid level, thereby improving spermatogenesis. This study sheds light on the relationship between HS-induced microbiota dysbiosis and spermatogenesis, offering a potential therapeutic approach for addressing bull spermatogenic dysfunction triggered by HS exposure.

The gut microbiota contributes to methamphetamine-induced reproductive toxicity in male mice

Methamphetamine (METH) is a psychostimulant drug belonging to the amphetamine-type stimulant class, known to exert male reproductive toxicity. Recent studies suggest that METH can disrupt the gut microbiota. Furthermore, the gut-testis axis concept has gained attention due to the potential link between gut microbiome dysfunction and reproductive health. Nonetheless, the role of the gut microbiota in mediating the impact of METH on male reproductive toxicity remains unclear. In this study, we employed a mouse model exposed to escalating doses of METH to assess sperm quality, testicular pathology, and reproductive hormone levels. The fecal microbiota transplantation method was employed to investigate the effect of gut microbiota on male reproductive toxicity. Transcriptomic, metabolomic, and microbiological analyses were conducted to explore the damage mechanism to the male reproductive system caused by METH. We found that METH exposure led to hormonal disorders, decreased sperm quality, and changes in the gut microbiota and testicular metabolome in mice. Testicular RNA sequencing revealed enrichment of several Gene Ontology terms associated with reproductive processes, as well as PI3K-Akt signaling pathways. FMT conveyed similar reproductive damage from METH-treated mice to healthy recipient mice. The aforementioned findings suggest that the gut microbiota plays a substantial role in facilitating the reproductive toxicity caused by METH, thereby highlighting a prospective avenue for therapeutic intervention in the context of METH-induced infertility.

Testis–Gut-Reproduction Axis: The Key to Reproductive Health

Reproductive health is an important issue for humanity. In the context of the increasing incidence rate of male infertility, it is essential to find the factors that affect male reproductive health. Gastrointestinal health is closely related to reproductive health. Gastrointestinal hormones (GIH) and gut microbiota (GM), as important material foundations for gastrointestinal function, can promote or inhibit testicular reproductive function, including spermatogenesis, sperm maturation, androgen synthesis, and even broader male diseases such as sexual function, prostate cancer, etc. On the contrary, the functional health of the testes is also of great significance for the stability of gastrointestinal function. This review mainly discusses the important regulatory effects of GIH and GM on male reproductive function.

Gut microbiota is involved in male reproductive function: a review

Globally, ~8%-12% of couples confront infertility issues, male-related issues being accountable for 50%. This review focuses on the influence of gut microbiota and their metabolites on the male reproductive system from five perspectives: sperm quality, testicular structure, sex hormones, sexual behavior, and probiotic supplementation. To improve sperm quality, gut microbiota can secrete metabolites by themselves or regulate host metabolites. Endotoxemia is a key factor in testicular structure damage that causes orchitis and disrupts the blood-testis barrier (BTB). In addition, the gut microbiota can regulate sex hormone levels by participating in the synthesis of sex hormone-related enzymes directly and participating in the enterohepatic circulation of sex hormones, and affect the hypothalamic-pituitary-testis (HPT) axis. They can also activate areas of the brain that control sexual arousal and behavior through metabolites. Probiotic supplementation can improve male reproductive function. Therefore, the gut microbiota may affect male reproductive function and behavior; however, further research is needed to better understand the mechanisms underlying microbiota-mediated male infertility.

Genetically proxied intestinal microbiota and risk of erectile dysfunction

BACKGROUND

The interaction between intestinal microbiota and erectile dysfunction (ED) is less investigated. This study was performed to explore the association between intestinal microbiota and ED.

METHODS

In this two-sample Mendelian randomization (MR) study, genetic variants of gut microbiota were obtained from MiBioGen consortium containing 18,340 individuals. Six methods including inverse variance weighting (IVW), MR-Egger, weighted median, maximum likelihood, MR robust adjusted profile score, and MR pleiotropy residual sum and outlier were used to investigate the causal links between intestinal microbiota and ED. Furthermore, reverse MR analysis was performed to exclude the causal impact of ED on gut microbiota.

RESULTS

As revealed by the IVW estimator, the risks of ED were raised by genetically proxied Lachnospiraceae (OR: 1.27), Lachnospiraceae NC2004 group (OR: 1.17), Oscillibacter (OR: 1.20), Senegalimassilia (OR: 1.32) (All P < 0.05) and Tyzzerella-3 (OR: 1.14, P < 0.05). It was observed that Ruminococcaceae UCG013 exerted protective effect against ED (OR: 0.77, P < 0.05). These results were consistent with other estimators in sensitivity analyses. In reverse MR analyses, genetic liability to ED did not alter the abundances of Lachnospiraceae, Lachnospiraceae NC2004 group, Oscillibacter, Senegalimassilia, Tyzzerella-3, and Ruminococcaceae UCG013 (All P > 0.05). No heterogeneity and pleiotropy were detected by Cochran's Q-test, MR-Egger, and global test (All P > 0.05).

CONCLUSIONS

This study provided novel evidence that genetically proxied Lachnospiraceae, Lachnospiraceae NC2004 group, Oscillibacter, Senegalimassilia, Tyzzerella-3, and Ruminococcaceae UCG013 had potentially causal effects on ED. Further studies are needed to clarify the biological mechanisms linking intestinal microbiota to ED.

Inflammatory cytokines may mediate the causal relationship between gut microbiota and male infertility: a bidirectional, mediating, multivariate Mendelian randomization study

Introduction

Studies have shown that the gut microbiota is associated with male infertility (MI). However, their causal relationship and potential mediators need more evidence to prove. We aimed to investigate the causal relationship between the gut microbiome and MI and the potential mediating role of inflammatory cytokines from a genetic perspective through a Mendelian randomization approach.

Methods

This study used data from genome-wide association studies of gut microbes (Mibiogen, n = 18, 340), inflammatory cytokines (NFBC1966, FYPCRS, FINRISK 1997 and 2002, n=13, 365), and male infertility (Finngen, n=120, 706) to perform two-way Mendelian randomization (MR), mediated MR, and multivariate MR(MVMR) analyses. In this study, the inverse variance weighting method was used as the primary analysis method, and other methods were used as supplementary analysis methods.

Results

In the present study, two gut microbes and two inflammatory cytokines were found to have a potential causal relationship with MI. Of the two gut microorganisms causally associated with male infertility, Anaerotruncus increased the risk of male infertility (odds ratio = 1.81, 95% confidence interval = 1.18-2.77, P = 0.0062), and Bacteroides decreased the risk of male infertility (odds ratio = 0.57, 95% confidence interval = 0.33-0.96, P = 0.0363). In addition, of the two inflammatory cytokines identified, hepatocyte growth factor(HGF) reduced the risk of male infertility (odds ratio = 0.50, 95% confidence interval = 0.35-0.71, P = 0.0001), Monocyte chemotactic protein 3 (MCP-3) increased the risk of male infertility (odds ratio = 1.28, 95% confidence interval = 1.03-1.61, P = 0.0039). Mediated MR analysis showed that HGF mediated the causal effect of Bacteroides on MI (mediated percentage 38.9%). Multivariate MR analyses suggest that HGF may be one of the pathways through which Bacteroides affects MI, with other unexplored pathways.

Conclusion

The present study suggests a causal relationship between specific gut microbiota, inflammatory cytokines, and MI. In addition, HGF may mediate the relationship between Bacteroides and MI.

The buzz within: the role of the gut microbiome in honeybee social behavior

Gut symbionts influence the physiology and behavior of their host, but the extent to which these effects scale to social behaviors is an emerging area of research. The use of the western honeybee (Apis mellifera) as a model enables researchers to investigate the gut microbiome and behavior at several levels of social organization. Insight into gut microbial effects at the societal level is critical for our understanding of how involved microbial symbionts are in host biology. In this Commentary, we discuss recent findings in honeybee gut microbiome research and synthesize these with knowledge of the physiology and behavior of other model organisms to hypothesize how host-microbe interactions at the individual level could shape societal dynamics and evolution.

Comparison of the gut microbiome composition between men with erectile dysfunction and a matched cohort: a pilot study

BACKGROUND

To-date there have been minimal studies to investigate an association between the gut microbiome and erectile dysfunction. There have been many inflammatory diseases linked to gut microbiome dysbiosis; such as cardiovascular disease and metabolic syndrome. These same inflammatory diseases have been heavily linked to erectile dysfunction. Given the correlations between both conditions and cardiovascular disease and the metabolic syndrome, we believe that it is worthwhile to investigate a link between the two.

OBJECTIVE

To investigate the potential association between the gut microbiome and erectile dysfunction.

METHODS

Stool samples were collected from 28 participants with erectile dysfunction and 32 age-matched controls. Metatranscriptome sequencing was used to analyze the samples.

RESULTS

No significant differences were found in the gut microbiome characteristics, including Kyoto Encyclopedia of Genes and Genomes richness (p = 0.117), Kyoto Encyclopedia of Genes and Genomes diversity (p = 0.323), species richness (p = 0.364), and species diversity (p = 0.300), between the erectile dysfunction and control groups.

DISCUSSION

The association of gut microbiome dysbiosis and pro-inflammatory conditions has been well studied and further literature continues to add to this evidence. Our main limitation for this study was our small-sample size due to recruitment issues. We believe that a study with a larger population size may find an association between the gut microbiome and erectile dysfunction.

CONCLUSIONS

The results of this study do not support a significant association between the gut microbiome and erectile dysfunction. Further research is needed to fully understand the relationship between these two conditions.

Optimum Doses and Forms of Selenium Maintaining Reproductive Health via Regulating Homeostasis of Gut Microbiota and Testicular Redox, Inflammation, Cell Proliferation, and Apoptosis in Roosters

BACKGROUND

There is a U-shaped relationship between dietary selenium (Se) ingestion and optimal sperm quality.

OBJECTIVES

This study aimed to investigate the optimal dietary dose and forms of Se for sperm quality of breeder roosters and the relevant mechanisms.

METHODS

In experiment 1, 18-wk-old Jingbai laying breeder roosters were fed a Se-deficient base diet (BD, 0.06 mg Se/kg), or the BD + 0.1, 0.2, 0.3, 0.4, 0.5, or 1.0 mg Se/kg for 9 wk. In experiment 2, the roosters were fed the BD or the BD + sodium selenite (SeNa), seleno-yeast (SeY), or Se-nanoparticles (SeNPs) at 0.2 mg Se/kg for 9 wk.

RESULTS

In experiment 1, added dietary 0.2 and 0.3 mg Se/kg led to higher sperm motility and lower sperm mortality than the other groups at weeks 5, 7, and/or 9. Furthermore, added dietary 0.2-0.4 mg Se/kg produced better testicular histology and/or lower testicular 8-hydroxy-deoxyguanosine than the other groups. Moreover, integrated testicular transcriptomic and cecal microbiomic analysis revealed that inflammation, cell proliferation, and apoptosis-related genes and bacteria were dysregulated by Se deficiency or excess. In experiment 2, compared with SeNa, SeNPs slightly increased sperm motility throughout the experiment, whereas SeNPs slightly reduced sperm mortality compared with SeY at week 9. Both SeY and SeNPs decreased malondialdehyde in the serum than those of SeNa, and SeNPs led to higher glutathione peroxidase (GPX) and thioredoxin reductase activities and GPX1 and B-cell lymphoma 2 protein concentrations in the testis compared with SeY and SeNa.

CONCLUSIONS

The optimal dietary Se dose for reproductive health of breeder roosters is 0.25-0.35 mg Se/kg, and SeNPs displayed better effects on reproductive health than SeNa and SeY in laying breeder roosters. The optimal doses and forms of Se maintain reproductive health of roosters associated with regulation intestinal microbiota homeostasis and/or testicular redox balance, inflammation, cell proliferation, and apoptosis.

Characteristics of gut microbiota in patients with asthenozoospermia: a Chinese pilot study

BACKGROUND

Identification of intestinal flora composition is significant for exploring the cause and pathogenic mechanisms of the gut-testis axis and clarifying the relationship between microbiota and infertility. Our study aimed to examine the alternation in gut microbiota composition and identify potential microbes associated with development of Asthenozoospermia (AS).

METHOD

A total of 580 males were recruited in the outpatient department of Tianjin Medical University General Hospital between September 2021 and March 2023. Sperm parameters were analyzed according to the WHO laboratory manual. The 16 S rRNA gene high-throughput sequencing was performed to detect the gut microbiota composition in fecal samples. LEfSe analysis was used to screen key microbiota. PICRUSt2 software was utilized to predict relevant pathways.

RESULTS

After rigorous screening, 60 isolated AS patients (AS group) and 48 healthy men (NC group) were enrolled. No significant differences were observed in demographic characteristics (p > 0.05), semen volume (p = 0.718), sperm concentration (p = 0.109), or total sperm count (p = 0.200). Sperm total motility and progressive motility were significantly decreased in the AS group (p < 0.001). AS patients had significantly lower alpha diversity indices (Chao1, observed OTUs, and PD Whole-tree; p < 0.05). The beta-diversity of gut microbiota in AS patients significantly differed from NC men (PCoA analysis, p = 0.001). Firmicutes, Bacteroidota, Proteobacteria, and Actinobacteria were the primary phyla, with the dominant genera including Bacteroides, Prevotella, and Blautia. Eleven key genera such as Escherichia_Shigella and Prevotellaceae_UCG_001 were identified by LEfSe analysis. Most of these genera were negatively correlated with sperm mobility. Eighty-eight KEGG pathways, including steroid biosynthesis and meiosis, were significantly enriched between the two groups.

CONCLUSIONS

It appears that gut microbiota composition in AS patients significantly differed from that in healthy men, and the development of AS might be associated with intestinal flora dysbiosis.

Gut microbiota composition may be an indicator of erectile dysfunction

Erectile Dysfunction (ED) is considered a physical and mental illness. A variety of potential associations between gut microbiota and health or disease have been found. By comparing the gut microbiota of healthy controls and ED patients, our study investigated the relationship between ED and gut microbiota. The results revealed that the ED group exhibited a significantly higher relative abundance of Bacteroides, Fusobacterium, Lachnoclostridium, Escherichia-Shigella and Megamonas, while showing a significantly lower relative abundance of Bifidobacterium compared to the control group. The dysbiosis of gut microbiota played a role in the onset and progression of ED by influencing the gut barrier, cardiovascular system and mental health, which provided a novel perspective on understanding the pathophysiology of ED. What is more, we had identified several key gut microbiota. By combining 16S rRNA sequencing with machine learning techniques, we were able to uncover the significant value and impact of gut microbiota in the early detection of ED.

Exploring the potential relationships among obstructive sleep apnea, erectile dysfunction, and gut microbiota: a narrative review

INTRODUCTION

Poor sleep quality is closely associated with comorbidities affecting a multitude of organ systems. Among the sleep disorders in the population, there has recently been an increase in the prevalence of obstructive sleep apnea (OSA), which has particularly affected men. The intermittent hypoxia and sleep fragmentation associated with OSA can result in the manifestation or aggravation of a number of pathophysiologic conditions, including the impairment of reproductive function in men and women. In this context, erectile dysfunction (ED) is of particular concern. Other consequences of OSA are changes in the gastrointestinal microbiota, with the resultant dysbiosis having potentially harmful consequences that promote downstream exacerbation of various comorbidities.

OBJECTIVES

This narrative review aims to explore the potential relationships among ED, gut microbiota, and OSA.

METHODS

A search of the relevant literature was performed in the PubMed, Embase, Medline, and Web of Science databases.

RESULTS

Sleep is important for regulating the body's functions, and sleep deprivation can negatively affect health. OSA can damage organic functions, including reproductive function, and can lead to ED. Restoring the microbiota and improving sleep can help to improve sexual function or reverse ED and enhance other associated conditions mediated through the gut-brain axis relationship. Probiotics and prebiotics can be used as supportive strategies in the prevention and treatment of OSA, as they help to reduce systemic inflammation and improve intestinal barrier function.

CONCLUSION

A good diet, a healthy lifestyle, and proper bowel function are essential in controlling depression and several other pathologies. Modulating the gut microbiota through probiotics and prebiotics can provide a viable strategy for developing new therapeutic options in treating many conditions. A better understanding of these a priori unrelated phenomena would foster our understanding of the effects of OSA on human fertility and how changes in gut microbiota may play a role.

Heat Stress Impairs Male Reproductive System with Potential Disruption of Retinol Metabolism and Microbial Balance in the Testis of Mice

BACKGROUND

Heat stress (HS) has a harmful impact on the male reproductive system, primarily by reducing the sperm quality. The testicular microenvironment plays an important role in sperm quality.

OBJECTIVES

This study aimed to explore the underlying mechanism by which HS impairs the male reproductive system through the testicular microenvironment.

METHODS

Ten-week-old male mice (n = 8 mice/group) were maintained at a normal temperature (25°C, control) or subjected to HS (38°C for 2 h each day, HS) for 2 wk. The epididymides and testes were collected at week 2 to determine sperm quality, histopathology, retinol concentration, the expression of retinol metabolism-related genes, and the testicular microbiome. The testicular microbiome profiles were analyzed using biostatistics and bioinformatics; other data were analyzed using a 2-sided Student's t test.

RESULTS

Compared with the control, HS reduced (P < 0.05) sperm count (42.4%) and motility (97.7%) and disrupted the integrity of the blood-testis barrier. Testicular microbial profiling analysis revealed that HS increased the abundance of the genera Asticcacaulis, Enhydrobacter, and Stenotrophomonas (P < 0.05) and decreased the abundance of the genera Enterococcus and Pleomorphomonas (P < 0.05). Notably, the abundance of Asticcacaulis spp. showed a significant negative correlation with sperm count (P < 0.001) and sperm motility (P < 0.001). Moreover, Asticcacaulis spp. correlated significantly with most blood differential metabolites, particularly retinol (P < 0.05). Compared with the control, HS increased serum retinol concentrations (25.3%) but decreased the testis retinol concentration by 23.7%. Meanwhile, HS downregulated (P < 0.05) the expression of 2 genes (STRA6 and RDH10) and a protein (RDH10) involved in retinol metabolism by 27.3%-36.6% in the testis compared with the control.

CONCLUSIONS

HS reduced sperm quality, mainly because of an imbalance in the testicular microenvironment potentially caused by an increase in Asticcacaulis spp. and disturbed retinol metabolism. These findings may offer new strategies for improving male reproductive capacity under HS.

The role of red ginseng in men's reproductive health: a literature review

BACKGROUND

Red ginseng (RG) is a traditional herb commonly used in China, Korea, and other East Asian countries. Recently, it has demonstrated a better clinical value in men's reproductive health (MRH). The present review aimed to examine the effects of RG treatment on MRH.

RESULTS

Overall, 42 articles related to RG application in MRH were reviewed, of which 31 were animal experiments and 11 were clinical studies. Furthermore, this review analyzed the use of RG in some male reproductive diseases in clinical trials and determined the associated mechanisms of action. The mechanism of action of RG in MRH may be related to oxidative stress, regulation of sex hormones and spermatogenesis-related proteins, and anti-inflammation.

CONCLUSIONS

The application of RG for the treatment of male infertility, erectile dysfunction, and prostate diseases has the potential to contribute to MRH.

Microbial Dysbiosis and Male Infertility: Understanding the Impact and Exploring Therapeutic Interventions

The human microbiota in the genital tract is pivotal for maintaining fertility, but its disruption can lead to male infertility. This study examines the relationship between microbial dysbiosis and male infertility, underscoring the promise of precision medicine in this field. Through a comprehensive review, this research indicates microbial signatures associated with male infertility, such as altered bacterial diversity, the dominance of pathogenic species, and imbalances in the genital microbiome. Key mechanisms linking microbial dysbiosis to infertility include inflammation, oxidative stress, and sperm structural deterioration. Emerging strategies like targeted antimicrobial therapies, probiotics, prebiotics, and fecal microbiota transplantation have shown potential in adjusting the genital microbiota to enhance male fertility. Notably, the application of precision medicine, which customizes treatments based on individual microbial profiles and specific causes of infertility, emerges as a promising approach to enhance treatment outcomes. Ultimately, microbial dysbiosis is intricately linked to male infertility, and embracing personalized treatment strategies rooted in precision medicine principles could be the way forward in addressing infertility associated with microbial factors.

Inonotus obliquus polysaccharide are linear molecules that alter the abundance and composition of intestinal microbiota in Sprague Dawley rats

Introduction

The macromolecular polysaccharide Inonotus obliquus polysaccharide (IOP) is composed of various monosaccharides, and it could modulate the composition and diversity of intestinal flora. However, its impact on the intestinal flora in rats of different genders remains unclear. Therefore, this study aims to investigate the structural changes of IOP and its effects on the intestinal flora after administration in male and female rats.

Methods

In this study, the molecular weight and purity of IOP were analyzed by high-performance gel permeation chromatography (HPGPC) and phenol sulfuric acid method, and NMR was used to confirm the chemical structure of IOP. Sex hormone [testosterone (T) and estradiol (E2)] levels and intestinal microbial changes were detected by enzyme-linked immunosorbent assay (ELISA) and 16S rRNA, respectively, after gavage of IOP (100 mg/kg) in male and female Sprague Dawley (SD) rats.

Results

HPGPC analysis showed that the average molecular weight (Mw) of IOP was 4,828  Da, and the total sugar content of the purified IOP was 96.2%, indicating that the polysaccharide is of high purity. NMR revealed that IOP is a linear macromolecule with an α-D-type glucose backbone. The results of ELISA and 16S rRNA showed that the IOP increased the abundance of beneficial bacteria, such as Clostridia_UCG-014 and Prevotellaceae_NK3B31, and reduced that of harmful bacteria, such as Colidextribacter and Desulfobacterota in the intestine of both male and female rats, and IOP changed the levels of sex hormones in male and female rats. Further analyses revealed that the increase in alpha diversity was higher in male than female rats. α diversity and β diversity revealed a significant difference in the composition of cecal microbiota between male and female rats in the control group, but IOP intake reduced this difference. Meanwhile, α analysis revealed a change in the composition of bacterial flora was more stable in male than female rats.

Conclusions

This study enhances our comprehension of the IOP structure and elucidates the alterations in intestinal flora following IOP administration in rats of varying genders. Nonetheless, further investigation is warranted to explore the specific underlying reasons for these discrepancies.

Male infertility risk and gut microbiota: a Mendelian randomization study

Background

In recent decades, the decline of male sperm quality has become a worldwide phenomenon, with sperm quality of critical importance for the ability to conceive naturally. Recent studies suggest that male fertility function is closely linked to the gut microbiota, however, the cause-and-effect association between the gut microbiota and male infertility risk is currently unclear.

Methods

We performed one two-sample Mendelian randomization (MR) study, which uses summary data on human gut microbiota from the MiBioGen consortium as factors of exposure. FinnGen Consortium R8 data was used to obtain GWAS data for male infertility. To evaluate cause-and-effect associations linking gut microbiota and male infertility risk with multiple Mendelian randomization methods, we included inverse variance weighted (IVW), MR-Egger, and Maximum Likelihood (ML) Ratio. The heterogeneity of instrumental variables was evaluated through Cochran's Q, Rucker's Q, and leave-one-out analysis methods.

Results

We found a positive association between Allisonella, Anaerotruncus, Barnesiella, Intestinibacter, and Lactococcus with male infertility risk according to the MR analysis results. Bacteroides Romboutsia, Ruminococcaceae (NK4A2140group), and Ruminococcaceae (UCG011) play a protective function in male infertility pathogenesis.

Conclusion

It was found that gut microbiota and infertility are causally related in this study. In subsequent studies, there is a need to build a larger and more comprehensive GWAS database on male infertility, which will reveal the underlying mechanisms for gut microbiota and male infertility. There is a need for randomized controlled trials for validating the protective effect of the associated gut microbiota against male infertility risk, and for exploring the associated mechanisms.

Genetically predicted the causal relationship between gut microbiota and infertility: bidirectional Mendelian randomization analysis in the framework of predictive, preventive, and personalized medicine

Objective

Several studies have reported the association between gut microbiota and infertility; however, the causal association between them remains unclear. This study aimed to explore the causal relationship between gut microbiota and infertility and evaluate how specific gut microbiota can support early monitoring and prevention of infertility in the context of predictive, preventive, and personalized medicine (PPPM/3PM).

Methods

The gut microbiota GWAS data included 18,340 individuals. Female infertility (6481 cases and 68,969 controls) and male infertility data (680 cases and 72,799 controls) were obtained from the FinnGen consortium. The inverse variance weighting (IVW), MR-Egger, weighted median (WM), Cochran Q tests, MR-PRESSO, and leave-one-out were used as a supplement to Mendelian randomization (MR) results and sensitivity analysis.

Results

The results of MR analysis indicated a significant causal association between Eubacterium oxidoreducens (OR = 2.048, P = 0.008), Lactococcus (OR = 1.445, P = 0.042), Eubacterium ventriosum (OR = 0.436, P = 0.018), Eubacterium rectale (OR = 0.306, P = 0.002), and Ruminococcaceae NK4A214 (OR = 0.537, P = 0.045) and male infertility. Genetically predicted Eubacterium ventriosum (OR = 0.809, P = 0.018), Holdemania (OR = 0.836, P = 0.037), Lactococcus (OR = 0.867, P = 0.020), Ruminococcaceae NK4A214 (OR = 0.830, P < 0.050), Ruminococcus torques (OR = 0.739, P = 0.022), and Faecalibacterium (OR = 1.311, P = 0.007) were associated with female infertility. Sensitivity analysis did not detect heterogeneity and pleiotropy (P > 0.05).

Conclusions

Our results provided evidence for the causal relationship between some gut microbiota and male and female infertility. These findings might be valuable in providing personalized treatment options for preventing infertility and improving reproductive function by monitoring and regulating the gut microbiota of infertility patients in the context of PPPM. Moreover, detecting the abundance of microbiota in feces can support preventive and personalized strategies, which may benefit more infertility patients.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13167-023-00332-6.

Seasonal Variation in Gut Microbiota of the Wild Daurian Ground Squirrel (Spermophilus dauricus): Metagenomic Insights into Seasonal Breeding

The Spermophilus dauricus, the wild Daurian ground squirrel, is known to exhibit seasonal breeding behavior. Although the importance of gut microbiota in animal digestion, metabolism, and immunity is well-established, the correlation between gut microbiota and seasonal breeding in this species remains inadequately explored. In the present study, using metagenomic sequencing technology, the compositions and functions of the gut microbiota of wild Daurian ground squirrels in different breeding seasons were explored. The dominant gut microbial phyla were Firmicutes and Bacteroidetes. The Firmicutes were predominant in the breeding season, whereas Bacteroidetes were predominant in the non-breeding season. At the genus level, Lactobacillus accumulated during the breeding season, whereas Odoribacter and Alistipes increased during the non-breeding season. GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genome) annotations indicated that genes in gut samples were highly associated with metabolic functions. The differential expression gene analysis showed that genes related to the phosphotransferase system, cysteine, and methionine metabolism were highly expressed during the breeding season, whereas the non-breeding season upregulated genes were enriched in starch and sucrose metabolism and bacterial chemotaxis pathways. In conclusion, this study could provide a reference for investigating gut microbiota in seasonal breeding animals and offer new insight into gut microbial function.