Chemically or surgically induced thyroid dysfunction altered gut microbiota in rat models

Interplay between gut microbiome, host genetic and epigenetic modifications in MASLD and MASLD-related hepatocellular carcinoma

Metabolic dysfunction-associated steatotic liver disease (MASLD) encompasses a wide spectrum of liver injuries, ranging from hepatic steatosis, metabolic dysfunction-associated steatohepatitis (MASH), fibrosis, cirrhosis to MASLD-associated hepatocellular carcinoma (MASLD-HCC). Recent studies have highlighted the bidirectional impacts between host genetics/epigenetics and the gut microbial community. Host genetics influence the composition of gut microbiome, while the gut microbiota and their derived metabolites can induce host epigenetic modifications to affect the development of MASLD. The exploration of the intricate relationship between the gut microbiome and the genetic/epigenetic makeup of the host is anticipated to yield promising avenues for therapeutic interventions targeting MASLD and its associated conditions. In this review, we summarise the effects of gut microbiome, host genetics and epigenetic alterations in MASLD and MASLD-HCC. We further discuss research findings demonstrating the bidirectional impacts between gut microbiome and host genetics/epigenetics, emphasising the significance of this interconnection in MASLD prevention and treatment.

Cross-talk between the gut microbiota and hypothyroidism: a bidirectional two-sample Mendelian randomization study

Background

Multiple observational studies suggest a connection between the composition of the gut microbiota and hypothyroidism. However, it has yet to be determined whether the gut microbiota has a causal effect on hypothyroidism.

Methods

To investigate the connection between the gut microbiota and hypothyroidism, two-sample Mendelian randomization was performed using data from a genome-wide association study meta-analysis (n = 18,430) conducted by the MiBioGen consortium. Summary statistics for hypothyroidism (26,342 cases and 59,827 controls) were obtained using the data from the FinnGen consortium R8 release data. To investigate the causal link between the gut microbiota and hypothyroidism, various methods, including MR-Egger, weighted median, weighted model, simple model, MR-PRESSO, and inverse variance weighted (IVW), were employed. The bacteria that were causally linked to hypothyroidism in forward Mendelian randomization analysis were subjected to reverse Mendelian randomization analysis. Cochran's Q statistics were utilized to gauge the heterogeneity of the instrumental variables.

Results

The results indicated that Akkermansia had a positive impact on hypothyroidism, with an odds ratio of 0.84 (95% CI 0.74-0.95, p = 0.01) based on the inverse variance-weighted estimates. Additionally, Anaerostipes (OR = 1.17, 95% CI 1.01-1.36, p = 0.04), Butyrivibrio (OR = 0.93, 95% CI 0.88-0.99, p = 0.02), Holdemania (OR = 0.89, 95% CI 0.81-0.99, p = 0.03), Intestinimonas (OR = 1.13, 95% CI 1.02-1.26, p = 0.03), Ruminiclostridium5 (OR = 1.19, 95% CI 1.01-1.41, p = 0.04), and Ruminococcaceae UCG-011 (OR = 0.91, 95% CI 0.84-0.99, p = 0.03) were identified. The gut microbiota was not significantly affected by hypothyroidism, as indicated by the results of the reverse MR analysis. There was no significant variation in the instrumental variables or horizontal pleiotropy.

Conclusion

The findings of this study using two-sample Mendelian randomization indicate a causal relationship between Akkermansia and hypothyroidism. Increased Akkermansia inhibits the onset and progression of hypothyroidism. Additional randomized controlled experiments are necessary to elucidate the beneficial impact of probiotics on hypothyroidism and their distinct protective mechanisms.

Intestinal microbiota regulates the gut-thyroid axis: the new dawn of improving Hashimoto thyroiditis

Intestinal microbiota plays an indispensable role in the host's innate immune system, which may be related to the occurrence of many autoimmune diseases. Hashimoto thyroiditis (HT) is one of the most common autoimmune diseases, and there is plenty of evidence indicating that HT may be related to genetics and environmental triggers, but the specific mechanism has not been proven clearly. Significantly, the composition and abundance of intestinal microbiota in patients with HT have an obvious difference. This phenomenon led us to think about whether intestinal microbiota can affect the progress of HT through some mechanisms. By summarizing the potential mechanism of intestinal microflora in regulating Hashimoto thyroiditis, this article explores the possibility of improving HT by regulating intestinal microbiota and summarizes relevant biomarkers as therapeutic targets, which provide new ideas for the clinical diagnosis and treatment of Hashimoto thyroiditis.

Clinical potential of microbiota in thyroid cancer therapy

Thyroid cancer is one of the most common tumors of the endocrine system because of its rapid and steady increase in incidence and prevalence. In recent years, a growing number of studies have identified a key role for the gut, thyroid tissue and oral microbiota in the regulation of metabolism and the immune system. A growing body of evidence has conclusively demonstrated that the microbiota influences tumor formation, prevention, diagnosis, and treatment. We provide extensive information in which oral, gut, and thyroid microbiota have an effect on thyroid cancer development in this review. In addition, we thoroughly discuss the various microbiota species, their potential functions, and the underlying mechanisms for thyroid cancer. The microbiome offers a unique opportunity to improve the effectiveness of immunotherapy and radioiodine therapy thyroid cancer by maintaining the right type of microbiota, and holds great promise for improving clinical outcomes and quality of life for thyroid cancer patients.

Association analysis of gut microbiota-metabolites-neuroendocrine changes in male rats acute exposure to simulated altitude of 5500 m

Hyperactivation of hypothalamic-pituitary-adrenal (HPA) axis and hypothalamic-pituitary-thyroid (HPT) axis were found in acute high altitude challenge, but the role of gut microbiota and metabolites is unknown. We utilized adult male Sprague-Dawley rats at a simulated altitude of 5500 m for 3 days in a hypobaric-hypoxic chamber. ELISA and metabolomic analyses of serum and 16S rRNA and metabolomic analyses of fecal samples were then performed. Compared with the normoxic group, serum corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH), corticosterone (CORT), and thyroxine (tT₄) were increased in the hypoxia group, whereas thyrotropin-releasing hormone (TRH) was decreased. Bacteroides, Lactobacillus, Parabacteroides, Butyricimonas, SMB53, Akkermansia, Phascolarctobacterium, and Aerococcus were enriched in hypoxia group, whereas [Prevotella], Prevotella, Kaistobacter, Salinibacterium, and Vogesella were enriched in normoxic group. Metabolomic analysis indicated that acute hypoxia significantly affected fecal and serum lipid metabolism. In addition, we found five fecal metabolites may mediate the cross-talk between TRH, tT₄, and CORT with [Prevotella], Kaistobacter, Parabacteroides, and Aerococcus, and 6 serum metabolites may mediate the effect of TRH and tT₄ on [Prevotella] and Kaistobacter by causal mediation analysis. In conclusion, this study provides new evidence that key metabolites mediate the cross-talk between gut microbiota with HPA and HPT axis under acute hypobaric hypoxia challenge.

Yijung-tang improves thermogenesis and reduces inflammation associated with gut microbiota in hypothyroid rats

Currently, considerable attention is focused on exploring the potential relationship between herbal medicine (HM) and the gut microbiome in terms of thermoregulation, which is an important aspect of human health, in modern system biology. However, our knowledge of the mechanisms of HM in thermoregulation is inadequate. Here, we demonstrate that the canonical herbal formula, Yijung-tang (YJT), protects against hypothermia, hyperinflammation, and intestinal microbiota dysbiosis in PTU-induced hypothyroid rats. Notably, these properties were associated with alterations in the gut microbiota and signaling crosstalk between the thermoregulatory and inflammatory mediators in the small intestine and brown adipose tissue (BAT). In contrast to the conventional drug L-thyroxine for curing hypothyroidism, YJT has an efficacy for attenuating systematic inflammatory responses, related with depression in intestinal TLR4 and Nod2/Pglyrp1 signaling pathways. Our findings suggest that YJT could promote BAT thermogenesis and prevent systemic inflammation in PTU-induced hypothyroid rats, which was associated with its prebiotic effect on modulating of the gut microbiota and gene expression with relevance in the enteroendocrine function and innate immune systems. These findings may strengthen the rationale of the microbiota-gut-BAT axis for a paradigm shift to enable holobiont-centric medicine.

Gut Microbial Community and Host Thermoregulation in Small Mammals

The endotherms, particularly the small mammals living in the polar region and temperate zone, are faced with extreme challenges for maintaining stable core body temperatures in harsh cold winter. The non-hibernating small mammals increase metabolic rate including obligatory thermogenesis (basal/resting metabolic rate, BMR/RMR) and regulatory thermogenesis (mainly nonshivering thermogenesis, NST, in brown adipose tissue and skeletal muscle) to maintain thermal homeostasis in cold conditions. A substantial amount of evidence indicates that the symbiotic gut microbiota are sensitive to air temperature, and play an important function in cold-induced thermoregulation, via bacterial metabolites and byproducts such as short-chain fatty acids and secondary bile acids. Cold signal is sensed by specific thermosensitive transient receptor potential channels (thermo-TRPs), and then norepinephrine (NE) is released from sympathetic nervous system (SNS) and thyroid hormones also increase to induce NST. Meanwhile, these neurotransmitters and hormones can regulate the diversity and compositions of the gut microbiota. Therefore, cold-induced NST is controlled by both Thermo-TRPs—SNS—gut microbiota axis and thyroid—gut microbiota axis. Besides physiological thermoregulation, small mammals also rely on behavioral regulation, such as huddling and coprophagy, to maintain energy and thermal homeostasis, and the gut microbial community is involved in these processes. The present review summarized the recent progress in the gut microbiota and host physiological and behavioral thermoregulation in small mammals for better understanding the evolution and adaption of holobionts (host and symbiotic microorganism). The coevolution of host-microorganism symbionts promotes individual survival, population maintenance, and species coexistence in the ecosystems with complicated, variable environments.

The Role of the Microbiota in Graves' Disease and Graves' Orbitopathy

Graves' disease (GD) is a clinical syndrome with an enlarged and overactive thyroid gland, an accelerated heart rate, Graves' orbitopathy (GO), and pretibial myxedema (PTM). GO is the most common extrathyroidal complication of GD. GD/GO has a significant negative impact on the quality of life. GD is the most common systemic autoimmune disorder, mediated by autoantibodies to the thyroid-stimulating hormone receptor (TSHR). It is generally accepted that GD/GO results from complex interactions between genetic and environmental factors that lead to the loss of immune tolerance to thyroid antigens. However, the exact mechanism is still elusive. Systematic investigations into GD/GO animal models and clinical patients have provided important new insight into these disorders during the past 4 years. These studies suggested that gut microbiota may play an essential role in the pathogenesis of GD/GO. Antibiotic vancomycin can reduce disease severity, but fecal material transfer (FMT) from GD/GO patients exaggerates the disease in GD/GO mouse models. There are significant differences in microbiota composition between GD/GO patients and healthy controls. Lactobacillus, Prevotella, and Veillonella often increase in GD patients. The commonly used therapeutic agents for GD/GO can also affect the gut microbiota. Antigenic mimicry and the imbalance of T helper 17 cells (Th17)/regulatory T cells (Tregs) are the primary mechanisms proposed for dysbiosis in GD/GO. Interventions including antibiotics, probiotics, and diet modification that modulate the gut microbiota have been actively investigated in preclinical models and, to some extent, in clinical settings, such as probiotics (Bifidobacterium longum) and selenium supplements. Future studies will reveal molecular pathways linking gut and thyroid functions and how they impact orbital autoimmunity. Microbiota-targeting therapeutics will likely be an essential strategy in managing GD/GO in the coming years.

Characteristics of the Intestinal Flora of TPOAb-Positive Women With Subclinical Hypothyroidism in the Second Trimester of Pregnancy: A Single-Center Prospective Cohort Study

Pregnant women are at high risk of developing subclinical hypothyroidism (SCH), and anti-thyroid peroxidase antibody (TPOAb) positivity can further inhibit thyroxine synthesis. Emerging evidence indicates that intestinal flora can modulate metabolic and immune homeostasis. The characteristics of intestinal flora of TPOAb-positive women with SCH in their second trimester of pregnancy have not been reported. This single-center prospective observational cohort study investigated gut microbial composition and metabolic function using sequencing of the 16S rRNA gene in fecal samples from 75 TPOAb-positive women with SCH and 90 TPOAb-negative women with SCH during their second trimester of pregnancy. Women were treated with no levothyroxine (LT₄), low-dose LT₄ (≤50ug/d), or high-dose LT₄ (>50ug/d). Taxonomic analysis showed Firmicutes and Bacteroidetes were the dominant phyla, followed by Actinobacteria and Proteobacteria. Faecalibacterium, Bacteroides, Prevotella 9, Bifidobacterium, Subdoligranulum, Lachnospira, and Megamonas were the predominant genera. The intestinal flora of TPOAb-positive women with SCH who received no LT₄ was characterized by bacterial amplicon sequence variants (ASVs)/operational taxonomic units (OTUs) enriched in the genus Subdoligranulum. The intestinal flora of TPOAb-positive women with SCH who received low-dose or high-dose LT₄ were characterized by bacterial ASVs/OTUs depleted of the species Ruminococcus sp._or Bacteroides massiliensis, respectively. A total of 19 metabolic functions of intestinal flora, mainly involving lipid and amino acid metabolism, discriminated TPOAb-positive and TPOAb-negative women with SCH. Our study suggests that there are differences in the composition and metabolic function of intestinal flora of TPOAb-positive and TPOAb-negative women with SCH treated with different doses of LT₄ in the second trimester of pregnancy. The findings provide insight into intestinal flora as novel targets for the treatment of TPOAb-positive women with SCH during pregnancy.

Beyond classic concepts in thyroid homeostasis: Immune system and microbiota

It has long been known that thyroid hormones have implications for multiple physiological processes and can lead to serious illness when there is an imbalance in its metabolism. The connections between thyroid hormone metabolism and the immune system have been extensively described, as they can participate in inflammation, autoimmunity, or cancer progression. In addition, changes in the normal intestinal microbiota involve the activation of the immune system while triggering different pathophysiological disorders. Recent studies have linked the microbiota and certain bacterial fragments or metabolites to the regulation of thyroid hormones and the general response in the endocrine system. Even if the biology and function of the thyroid gland has attracted more attention due to its pathophysiological importance, there are essential mechanisms and issues related to it that are related to the interplay between the intestinal microbiota and the immune system and must be further investigated. Here we summarize additional information to uncover these relationships, the knowledge of which would help establish new personalized medical strategies.

Cecal microbial transplantation attenuates hyperthyroid-induced thermogenesis in Mongolian gerbils

Endothermic mammals have a high energy cost to maintain a stable and high body temperature (T_b , around 37°C). Thyroid hormones are a major regulator for energy metabolism and T_b . The gut microbiota is involved in modulating host energy metabolism. However, whether the interaction between the gut microbiota and thyroid hormones is involved in metabolic and thermal regulations is unclear. We hypothesized that thyroid hormones via an interaction with gut microbiota orchestrate host thermogenesis and T_b . l-thyroxine-induced hyperthyroid Mongolian gerbils (Meriones unguiculatus) increased resting metabolic rate (RMR) and T_b , whereas Methimazole-induced hypothyroid animals decreased RMR. Both hypothyroid and hyperthyroid animals differed significantly in faecal bacterial community. Hyperthyroidism increased the relative abundance of pathogenic bacteria, such as Helicobacter and Rikenella, and decreased abundance of beneficial bacteria Butyricimonas and Parabacteroides, accompanied by reduced total bile acids and short-chain fatty acids. Furthermore, the hyperthyroid gerbils transplanted with the microbiota from control donors increased type 2 deiodinase (DIO2) expression in the liver and showed a greater rate of decline of both serum T3 and T4 levels and, consequently, a more rapid recovery of normal RMR and T_b . These findings indicate that thyroid hormones regulate thermogenesis depending on gut microbiota and colonization with normal microbiota by caecal microbial transplantation attenuates hyperthyroid-induced thermogenesis. This work reveals the functional consequences of the gut microbiota-thyroid axis in controlling host metabolic physiology and T_b in endotherms.

The Composition of Gut Microbiota in Patients Bearing Hashimoto's Thyroiditis with Euthyroidism and Hypothyroidism

AIMS

Hashimoto's thyroiditis (HT), a type of autoimmune disease, occurs due to genetic predisposition and environmental factors. It is well known that thyroid function may affect the gut microbiota. However, the composition of gut microbiota in HT patients with different thyroid function status has been less highlighted. Therefore, we focused on the alterations in the composition of gut microbiota in HT patients with euthyroidism and hypothyroidism.

METHODS

We performed a cross-sectional study, including 45 HT patients with euthyroidism, 18 HT patients with hypothyroidism, and 34 healthy controls. Fecal samples were collected, and microbiota was examined by using 16S RNA ribosomal RNA gene sequencing. Then, we analyzed the possible pathways in relation to the enriched bacteria by linear discriminant analysis (LDA) effect size (LEfSe).

RESULTS

Compared with the controls, bacterial richness and diversity were significantly lower in patients with HT, especially in hypothyroidism. Moreover, Lachnospiraceae_incertae_sedis, Lactonifactor, Alistipes, and Subdoligranulum were more enriched in HT patients with euthyroidism, while Phascolarctobacterium was more abundant in those with hypothyroidism. Further analysis suggested that Phascolarctobacterium was negatively related to several pathways, including environmental information processing and metabolism.

CONCLUSION

In summary, our study demonstrated the altered composition of gut microbiota in HT patients with different thyroid function status. Moreover, Phascolarctobacterium may be involved in the development of HT.