Of mice and men and women: Sexual dimorphism of the gut microbiome

Gender differences in global antimicrobial resistance

Antimicrobial resistance is one of the leading causes of mortality globally. However, little is known about the distribution of antibiotic resistance genes (ARGs) in human gut metagenomes, collectively referred to as the resistome, across socio-demographic gradients. In particular, limited evidence exists on gender-based differences. We investigated how the resistomes differ between women and men in a global dataset of 14,641 publicly available human gut metagenomes encompassing countries with widely variable economic statuses. We observed a 9% higher total ARG load in women than in men in high-income countries. However, in low- and middle-income countries, the difference between genders was reversed in univariate models, but not significant after adjusting for covariates. Interestingly, the differences in ARG load between genders emerged in adulthood, suggesting resistomes differentiate between genders after childhood. Collectively, our data-driven analyses shed light on global, gendered antibiotic resistance patterns, which may help guide further research and targeted interventions.

Delayed Impact of Ionizing Radiation Depends on Sex: Integrative Metagenomics and Metabolomics Analysis of Rodent Colon Content

There is an escalating need to comprehend the long-term impacts of nuclear radiation exposure since the permeation of ionizing radiation has been frequent in our current societal framework. A system evaluation of the microbes that reside inside a host's colon could meet this knowledge gap since the microbes play major roles in a host's response to stress. Indeed, our past study suggested that these microbes might break their symbiotic association with moribund hosts to form a pro-survival condition exclusive to themselves. In this study, we undertook metagenomics and metabolomics assays regarding the descending colon content (DCC) of adult mice. DCCs were collected 1 month and 6 months after 7 Gy or 7.5 Gy total body irradiation (TBI). The assessment of the metagenomic diversity profile in DCC found a significant sex bias caused by TBI. Six months after 7.5 Gy TBI, decreased Bacteroidetes were replaced by increased Firmicutes in males, and these alterations were reflected in the functional analysis. For instance, a larger number of networks linked to small chain fatty acid (SCFA) synthesis and metabolism were inhibited in males than in females. Additionally, bioenergy networks showed regression dynamics in females at 6 months post-TBI. Increased accumulation of glucose and pyruvate, which are typical precursors of beneficial SCFAs coupled with the activated networks linked to the production of reactive oxygen species, suggest a cross-sex energy-deprived state. Overall, there was a major chronic adverse implication in male mice that supported the previous literature in suggesting females are more radioresistant than males. The sex-biased chronic effects of TBI should be taken into consideration in designing the pertinent therapeutics.

Hallmarks of Cancer Cachexia: Sexual Dimorphism in Related Pathways

Cancer-associated cachexia (CAC), also known as wasting syndrome, is a systemic condition that affects multiple tissues and organs via a variety of metabolic pathways. Systemic inflammation, progressive weight loss, depletion of adipose tissue, and skeletal muscle impairment are some of the hallmark features of cachexia. Despite various studies on the clinical features of CAC, the complexity of the syndrome continues to pose significant challenges in clinical practice, leading to late diagnoses and the absence of a standardised treatment. Men and women respond differently to CAC, which may be prompted by the pre-existing physiologic sex differences. This review presents the sexual dimorphism associated with the hallmark pathways involved in CAC. A comprehensive understanding of sexual dimorphism in these pathways could drive research on cachexia to prioritise the inclusion of more females in related studies in order to achieve personalised sex-based therapeutic approaches and, consequently, enhance treatment efficacy and better patient outcomes.

Dietary Fibre Modulates Body Composition, Blood Glucose, Inflammation, Microbiome, and Metabolome in a Murine Model of Periodontitis

Background: Dietary fibre plays a crucial role in metabolic regulation, inflammation, and microbiome composition. However, its impact on systemic and oral health, particularly in periodontitis, remains unclear. This study investigated the effects of high- and low-fibre diets on body composition, glycaemic control, inflammation, microbiome, and metabolome in a murine model of experimental periodontitis. Methods: Thirty-six male C57BL/6 mice were randomised to a high-fibre (40% fibre) or low-fibre (5% fibre) diet for eight weeks. Body weight, fat mass, lean mass, fasting blood glucose, serum inflammatory markers, alveolar bone loss, and root length were assessed. Oral and faecal microbiome composition was analysed using 16S rRNA sequencing. Metabolomic and short-chain fatty acid (SCFA) profiling was conducted using liquid chromatography-mass spectrometry (LC-MS). Results: Mice on the high-fibre diet exhibited significantly lower body weight (p < 0.0001), fat mass (p = 0.0007), and lean mass (p < 0.0001) compared to the low-fibre group. Fasting blood glucose levels were significantly lower in the high-fibre group (p = 0.0013). TNF-α and IFN-γ levels were significantly elevated in the low-fibre group (p < 0.0001), suggesting a heightened pro-inflammatory state. While alveolar bone loss and root length did not differ significantly, microbiome analysis revealed distinct bacterial compositions (PERMANOVA, p < 0.05), with fibre-fermenting taxa enriched in high-fibre-fed mice. Metabolomic analysis identified 19 significantly altered metabolites, indicating dietary adaptations. Conclusions: A high-fibre diet improves glycaemic control, reduces systemic inflammation, and alters microbial and metabolic profiles in experimental periodontitis. These findings highlight dietary fibre's role in modulating metabolic and inflammatory pathways relevant to periodontal and systemic diseases.

Salt-Responsive Gut Microbiota Induces Sex-Specific Blood Pressure Changes

BACKGROUND

Tryptophan metabolism is important in blood pressure regulation. The tryptophan-indole pathway is exclusively mediated by the gut microbiota. ACE2 (angiotensin-converting enzyme 2) participates in tryptophan absorption, and a lack of ACE2 leads to changes in the gut microbiota. The gut microbiota has been recognized as a regulator of blood pressure. Furthermore, there is ample evidence for sex differences in the gut microbiota. However, it is unclear whether such sex differences impact blood pressure differentially through the tryptophan-indole pathway.

METHODS

To study the sex-specific mechanisms of gut microbiota-mediated tryptophan-indole pathway in hypertension, we generated a novel rat model with Clustered Regularly Interspaced Short Palindromic Repeats/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats-associated protein 9)-targeted deletion of Ace2 in the Dahl salt-sensitive rat. Cecal microbiota transfers from donors of both sexes to female S recipients were performed. Also, Dahl salt-sensitive rats of both sexes were orally gavaged with indole to investigate blood pressure response.

RESULTS

The female gut microbiota and its tryptophan-indole pathway exhibited greater buffering capacity when exposed to tryptophan, due to Ace2 deficiency, and salt. In contrast, the male gut microbiota and its tryptophan-indole pathway were more vulnerable. Female rats with male cecal microbiota responded to salt with a higher blood pressure increase compared with those with female cecal microbiota. Indole, a tryptophan-derived metabolite produced by gut bacteria, increased blood pressure in male but not in female rats. Moreover, salt altered host-mediated tryptophan metabolism, characterized by reduced serum serotonin of both sexes and higher levels of kynurenine derivatives in the females.

CONCLUSIONS

We uncovered a novel sex-specific mechanism in the gut microbiota-mediated tryptophan-indole pathway in blood pressure regulation. Salt tipped the tryptophan metabolism between the host and gut microbiota in a sex-dependent manner. Our study provides evidence for a novel concept that gut microbiota and its metabolism play sex-specific roles in the development of salt-sensitive hypertension.

Gut microbes, diet, and genetics as drivers of metabolic liver disease: a narrative review outlining implications for precision medicine

Metabolic dysfunction-associated steatotic liver disease (MASLD) is rapidly increasing in prevalence, impacting over a third of the global population. The advanced form of MASLD, Metabolic dysfunction-associated steatohepatitis (MASH), is on track to become the number one indication for liver transplant. FDA-approved pharmacological agents are limited for MASH, despite over 400 ongoing clinical trials, with only a single drug (resmetirom) currently on the market. This is likely due to the heterogeneous nature of disease pathophysiology, which involves interactions between highly individualized genetic and environmental factors. To apply precision medicine approaches that overcome interpersonal variability, in-depth insights into interactions between genetics, nutrition, and the gut microbiome are needed, given that each have emerged as dynamic contributors to MASLD and MASH pathogenesis. Here, we discuss the associations and molecular underpinnings of several of these factors individually and outline their interactions in the context of both patient-based studies and preclinical animal model systems. Finally, we highlight gaps in knowledge that will require further investigation to aid in successfully implementing precision medicine to prevent and alleviate MASLD and MASH.

Impact of maternal high-fat diet on offspring gut microbiota during short-term high-fat diet exposure in mice

Alterations in the gut microbiome have been linked to obesity, with maternal high-fat diet (HF) playing a role in shaping offspring microbiome composition. However, the sex-specific responses to maternal HF diet and the impact of subsequent dietary challenges remain unclear. This study investigated the effects of maternal HF diet on offspring gut microbiota structure and predicted functional profile in response to short-term postnatal HF diet exposure with a focus on sex-specific responses. Female and male offspring of maternal control (C) diet or maternal HF diet were weaned onto C diet or HF diet. Offspring were euthanized at 13 weeks of age and cecal contents were collected for bacterial taxonomic profiling. Maternal HF diet reduced α-diversity, notably in male offspring weaned onto HF diet. Sex-specific differences were observed in the gut microbial composition and predicted functional potential. Furthermore, the influence of maternal diet on bacterial community structure and functional potential varied depending on postnatal diet. Maternal HF diet led to increased relative abundance of Corynebacterium in female offspring and decreased abundance of Akkermansia and Roseburia in male offspring. These findings underscore the sexually dimorphic nature of maternal HF diet effects on gut microbiota composition and function, with implications for developmental programming and metabolic health.

Microbiome Taxonomic and Functional Differences in C3H/HeJ Mice Fed a Long-Term High-Fat Diet with Beef Protein ± Ammonium Hydroxide Supplementation

Studies have suggested that alkalinized foods may reduce the effects of the acidogenic Western diet in promoting obesity, metabolic syndrome, type 2 diabetes, cancer, and coronary heart disease. Indeed, a recent study in mice fed a high-fat diet containing dietary beef supplemented with ammonium hydroxide showed improvement in a suite of metabolic outcomes. However, the effects of dietary protein ammonium supplementation on the microbiome remain unknown. In this study, the effects of ammonium supplementation on beef protein towards microbiome taxa and function in a high-fat diet were analyzed. Fecal microbiomes were characterized using a shotgun metagenomic approach for 16-month-old male and female mice after long-term diet treatments. The results for ammoniated diets showed that several bacteria known to be associated with health benefits increased significantly, including Romboutsia, Oscillospiraceae, and Lactococcus cremoris. The beneficial mucin-degrader Akkermansia was especially abundant, with a high prevalence (~86%) in females. Concurrently, the phyla Actinomycetota (Actinobacteria) and Bacteroidota (Bacteroidetes) were significantly reduced. While sex was a confounding factor affecting microbiome responses to ammonium supplementation in dietary protein, it is worth noting that several putatively beneficial microbiome functions increased with ammonium supplementation, such as glycine betaine transport, xenobiotic detoxification, enhanced defense, and others. Conversely, many disease-associated microbiome functions reduced. Importantly, modifying protein pH alone via ammonium supplementation induced beneficial microbiota changes. Taken together, these results suggest that ammonium-supplemented proteins may mediate some negative microbiome-associated effects of high-fat/Western diets.

Baseline gut microbiome and metabolites are correlated with alcohol consumption in a zonisamide clinical trial of heavy drinking alcoholic civilians

Development and severity of alcohol use disorder (AUD) has been linked to variations in gut microbiota and their associated metabolites in both animal and human studies. However, the involvement of the gut microbiome in alcohol consumption of individuals with AUD undergoing treatment remains unclear. To address this, stool samples (n=48) were collected at screening (baseline) and trial completion from a single site of a multi-site double-blind, placebo-controlled trial of Zonisamide in individuals with AUD. Alcohol consumption, gamma-glutamyl transferase (GGT), and phosphatidylethanol (PEth)levels were measured both at baseline and endpoint of 16-week trial period. Fecal microbiome was analyzed via 16S rRNA sequencing and metabolome via untargeted LC-MS. Both sex (p = 0.003) and psychotropic medication usage (p = 0.025) are associated with baseline microbiome composition. The relative abundance of 12 genera at baseline was correlated with percent drinking reduction, baseline and endpoint alcohol consumption, and changes in GGT and PeTH over the course of treatment (p.adj < 0.05). Overall microbiome community structure at baseline differed between high and low responders (67-100% and 0-33% drinking reduction, respectively; p = 0.03). A positive relationship between baseline fecal GABA levels and percent drinking reduction (R=0.43, p < 0.05) was identified by microbiome function prediction and confirmed by ELISA and metabolomics. Predicted microbiome function and metabolomics analysis have found that tryptophan metabolic pathways are over-represented in low responders. These findings highlight importance of baseline microbiome and metabolites in alcohol consumption in AUD patients undergoing zonisamide treatment.

Fermented foods: Harnessing their potential to modulate the microbiota-gut-brain axis for mental health

Over the past two decades, whole food supplementation strategies have been leveraged to target mental health. In addition, there has been increasing attention on the ability of gut microbes, so called psychobiotics, to positively impact behaviour though the microbiota-gut-brain axis. Fermented foods offer themselves as a combined whole food microbiota modulating intervention. Indeed, they contain potentially beneficial microbes, microbial metabolites and other bioactives, which are being harnessed to target the microbiota-gut-brain axis for positive benefits. This review highlights the diverse nature of fermented foods in terms of the raw materials used and type of fermentation employed, and summarises their potential to shape composition of the gut microbiota, the gut to brain communication pathways including the immune system and, ultimately, modulate the microbiota-gut-brain axis. Throughout, we identify knowledge gaps and challenges faced in designing human studies for investigating the mental health-promoting potential of individual fermented foods or components thereof. Importantly, we also suggest solutions that can advance understanding of the therapeutic merit of fermented foods to modulate the microbiota-gut-brain axis.

Sex shapes gut-microbiota-brain communication and disease

Research into the microbiota-gut-brain axis (MGBA) has entered a golden age, raising the hope that therapeutics acting on it may offer breakthroughs in the treatment of many illnesses. However, most of this work overlooks a fundamental, yet understudied, biological variable: sex. Sex differences exist at every level of the MGBA. Sex steroids shape the structure of the gut microbiota, and these microbes in turn regulate levels of bioactive sex steroids. These hormones and microbes act on gut sensory enteroendocrine cells, which modulate downstream activity in the enteric nervous system, vagus nerve, and brain. We examine recent advances in this field, and discuss the scientific and moral imperative to include females in biomedical research, using autism spectrum disorder (ASD) as an example.

The effect of host admixture on wild house mouse gut microbiota is weak when accounting for spatial autocorrelation

The question of how interactions between the gut microbiome and vertebrate hosts contribute to host adaptation and speciation is one of the major problems in current evolutionary research. Using bacteriome and mycobiome metabarcoding, we examined how these two components of the gut microbiota vary with the degree of host admixture in secondary contact between two house mouse subspecies (Mus musculus musculus and M. m. domesticus). We used a large data set collected at two replicates of the hybrid zone and model-based statistical analyses to ensure the robustness of our results. Assuming that the microbiota of wild hosts suffers from spatial autocorrelation, we directly compared the results of statistical models that were spatially naive with those that accounted for spatial autocorrelation. We showed that neglecting spatial autocorrelation can strongly affect the results and lead to misleading conclusions. The spatial analyses showed little difference between subspecies, both in microbiome composition and in individual bacterial lineages. Similarly, the degree of admixture had minimal effects on the gut bacteriome and mycobiome and was caused by changes in a few microbial lineages that correspond to the common symbionts of free-living house mice. In contrast to previous studies, these data do not support the hypothesis that the microbiota plays an important role in host reproductive isolation in this particular model system.

Effects of Dietary Methionine Restriction on Cognition in Mice

Dietary restriction of the essential amino acid, methionine, has been shown to induce unique metabolic protection. The peripheral benefits of methionine restriction (MR) are well established and include improvements in metabolic, energy, inflammatory, and lifespan parameters in preclinical models. These benefits all occur despite MR increasing energy intake, making MR an attractive dietary intervention for the prevention or reversal of many metabolic and chronic conditions. New and emerging evidence suggests that MR also benefits the brain and promotes cognitive health. Despite widespread interest in MR over the past few decades, many findings are limited in scope, and gaps remain in our understanding of its comprehensive effects on the brain and cognition. This review details the current literature investigating the impact of MR on cognition in various mouse models, highlights some of the key mechanisms responsible for its cognitive benefits, and identifies gaps that should be addressed in MR research moving forward. Overall findings indicate that in animal models, MR is associated with protection against obesity-, age-, and Alzheimer's disease-induced impairments in learning and memory that depend on different brain regions, including the prefrontal cortex, amygdala, and hippocampus. These benefits are likely mediated by increases in fibroblast growth factor 21, alterations in methionine metabolism pathways, reductions in neuroinflammation and central oxidative stress, and potentially alterations in the gut microbiome, mitochondrial function, and synaptic plasticity.

Supplementation with postbiotic from Bifidobacterium Breve BB091109 improves inflammatory status and endocrine function in healthy females: a randomized, double-blind, placebo-controlled, parallel-groups study

This study evaluated the effects of dietary supplementation with a postbiotic extract of Bifidobacterium breve BB091109 on pro-inflammatory cytokines levels and markers of endocrine function. A prospective, double-blind, placebo-controlled, randomized, single-centered, parallel study was conducted on a group of 40-55-year-old females. The study included 30 healthy females, divided into two groups: a supplement (n = 20) and a placebo (n = 10) groups. Blood and saliva samples were collected at baseline (wk0), after 4 weeks (wk 4) and 12 weeks (12wk) of daily supplementation (500 mg), and 4 weeks (wk 16) after termination of supplementation. The levels of fasting CRP, IL-6, IL-10, TNF-α, IFN-γ, DHEA, estradiol, estriol, progesterone, cortisol and human growth hormone were analysed. The results revealed a significant effect of the 90-day supplementation with B. breve postbiotic extract on changes in CRP, IL-6 levels, DHEA, estradiol and estriol. In conclusion, the supplementation with the B. breve postbiotic extract improved endocrine function in females over 40 years old and induced protective changes in inflammatory markers. These findings highlight the potential health benefits of this supplementation in promoting hormonal balance and reducing inflammation in this population.

Microbial glutamate metabolism predicts intravenous cocaine self-administration in diversity outbred mice

The gut microbiome is thought to play a critical role in the onset and development of psychiatric disorders, including depression and substance use disorder (SUD). To test the hypothesis that the microbiome affects addiction predisposing behaviors and cocaine intravenous self-administration (IVSA) and to identify specific microbes involved in the relationship, we performed 16S rRNA gene sequencing on feces from 228 diversity outbred mice. Twelve open field measures, two light-dark assay measures, one hole board and novelty place preference measure significantly differed between mice that acquired cocaine IVSA (ACQ) and those that failed to acquire IVSA (FACQ). We found that ACQ mice are more active and exploratory and display decreased fear than FACQ mice. The microbial abundances that differentiated ACQ from FACQ mice were an increased abundance of Barnesiella, Ruminococcus, and Robinsoniella and decreased Clostridium IV in ACQ mice. There was a sex-specific correlation between ACQ and microbial abundance, a reduced Lactobacillus abundance in ACQ male mice, and a decreased Blautia abundance in female ACQ mice. The abundance of Robinsoniella was correlated, and Clostridium IV inversely correlated with the number of doses of cocaine self-administered during acquisition. Functional analysis of the microbiome composition of a subset of mice suggested that gut-brain modules encoding glutamate metabolism genes are associated with the propensity to self-administer cocaine. These findings establish associations between the microbiome composition and glutamate metabolic potential and the ability to acquire cocaine IVSA thus indicating the potential translational impact of targeting the gut microbiome or microbial metabolites for treatment of SUD. This article is part of the Special Issue on "Microbiome & the Brain: Mechanisms & Maladies".

Sex bias in lymphocytes: Implications for autoimmune diseases

Autoimmune diseases are characterized by a significant sex dimorphism, with women showing increased susceptibility to disease. This is, at least in part, due to sex-dependent differences in the immune system that are influenced by the complex interplay between sex hormones and sex chromosomes, with contribution from sociological factors, diet and gut microbiota. Sex differences are evident in the number and function of lymphocyte populations. Women mount a stronger pro-inflammatory response than males, with increased lymphocyte proliferation, activation and pro-inflammatory cytokine production, whereas men display expanded regulatory cell subsets. Ageing alters the immune landscape of men and women in differing ways, resulting in changes in autoimmune disease susceptibility. Here we review the current literature on sex differences in lymphocyte function, the factors that influence this, and the implications for autoimmune disease. We propose that improved understanding of sex bias in lymphocyte function can provide sex-specific tailoring of treatment strategies for better management of autoimmune diseases.