Short-chain fatty acids and thyroid hormone interact in regulating enterocyte gene transcription

How gut microbiota may impact ocular surface homeostasis and related disorders

Changes in the bacterial flora in the gut, also described as gut microbiota, are readily acknowledged to be associated with several systemic diseases, especially those with an inflammatory, neuronal, psychological or hormonal factor involved in the pathogenesis and/or the perception of the disease. Maintaining ocular surface homeostasis is also based on all these four factors, and there is accumulating evidence in the literature on the relationship between gut microbiota and ocular surface diseases. The mechanisms involved are mostly interconnected due to the interaction of central and peripheral neuronal networks, inflammatory effectors and the hormonal system. A better understanding of the influence of the gut microbiota on the maintenance of ocular surface homeostasis, and on the onset or persistence of ocular surface disorders could bring new insights and help elucidate the epidemiology and pathology of ocular surface dynamics in health and disease. Revealing the exact nature of these associations could be of paramount importance for developing a holistic approach using highly promising new therapeutic strategies targeting ocular surface diseases.

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.

Gut Microbiome and the Role of Metabolites in the Study of Graves’ Disease

Graves’ disease (GD) is an autoimmune thyroid disease (AITD), which is one of the most common organ-specific autoimmune disorders with an increasing prevalence worldwide. But the etiology of GD is still unclear. A growing number of studies show correlations between gut microbiota and GD. The dysbiosis of gut microbiota may be the reason for the development of GD by modulating the immune system. Metabolites act as mediators or modulators between gut microbiota and thyroid. The purpose of this review is to summarize the correlations between gut microbiota, microbial metabolites and GD. Challenges in the future study are also discussed. The combination of microbiome and metabolome may provide new insight for the study and put forward the diagnosis, treatment, prevention of GD in the future.

The impact of the gut microbiota on the reproductive and metabolic endocrine system

As the gut microbiota exerts various effects on the intestinal milieu which influences distant organs and pathways, it is considered to be a full-fledged endocrine organ. The microbiota plays a major role in the reproductive endocrine system throughout a woman's lifetime by interacting with estrogen, androgens, insulin, and other hormones. Imbalance of the gut microbiota composition can lead to several diseases and conditions, such as pregnancy complications, adverse pregnancy outcomes, polycystic ovary syndrome (PCOS), endometriosis, and cancer; however, research on the mechanisms is limited. More effort should be concentrated on exploring the potential causes and underlying the mechanisms of microbiota-hormone-mediated disease, and providing novel therapeutic and preventive strategies.As the gut microbiota exerts various effects on the intestinal milieu which influences distant organs and pathways, it is considered to be a full-fledged endocrine organ. The microbiota plays a major role in the reproductive endocrine system throughout a woman's lifetime by interacting with estrogen, androgens, insulin, and other hormones. Imbalance of the gut microbiota composition can lead to several diseases and conditions, such as pregnancy complications, adverse pregnancy outcomes, polycystic ovary syndrome (PCOS), endometriosis, and cancer; however, research on the mechanisms is limited. More effort should be concentrated on exploring the potential causes and underlying the mechanisms of microbiota-hormone-mediated disease, and providing novel therapeutic and preventive strategies.

Dietary Alaska Pollock Protein Attenuates the Experimental Colitis Induced by Dextran Sulfate Sodium via Regulation of Gut Microbiota and Its Metabolites in Mice

Protein derived from fish has not only nutritional properties but also health-promoting properties. Few studies have examined the effect of dietary Alaska pollock protein (APP) on the anticolitis effect reported to be associated with metabolic syndrome (MetS). This study investigated the effect of APP intake on colitis symptoms, gut microbiota, and its metabolites in the experimental colitis mouse model induced by dextran sulfate sodium (DSS). Male C57BL/6J mice were divided into three groups: (1) DSS-untreated mice fed an American Institute of Nutrition (AIN) 93G diet (protein source is casein), (2) DSS-treated mice fed an AIN93G diet, and (3) DSS-treated mice fed an APP diet. After the mice were fed the diets for 21 days, experimental colitis was induced by three cycles of 2% DSS administration for 5 days followed by washouts over the course of 5 days. APP-reduced body weight loss increased the disease activity index, and elevated spleen weight and alleviated colon length shortening and colonic tissue damage. Furthermore, APP altered the structure and composition of the microbiota and short-chain fatty acids in feces. Since APP intake alleviates experimental colitis induced by DSS administration through alterations in the gut microbiota and its metabolites, we deduced that APP would inhibit MetS progression via colitis suppression.

Microbiome Metabolites and Thyroid Dysfunction

Thyroid diseases are common conditions that have a negative impact on the health of all populations. The literature sheds light on the differences in the composition of the intestinal microbiota in patients suffering from thyroid diseases compared to healthy individuals. The microbiome affects the proper functioning of the thyroid gland, and the existence of the gut–thyroid axis is discussed in the context of both thyroid diseases and intestinal dysbiosis. The purpose of this review is to describe associations between the microbiome and its metabolites and thyroid dysfunction. We try to explain the role of the microbiome in the metabolism of thyroid hormones and the impact of thyroid autoimmune diseases. In addition, we raise issues related to the influence of bacterial metabolites, such as short-chain fatty acids or secondary bile acids, in the functioning of the thyroid gland. Last but not least, we explored the interactions between the gut microbiota and therapeutics and supplements typically administered to patients with thyroid diseases.

Human gut bacteria as potent class I histone deacetylase inhibitors in vitro through production of butyric acid and valeric acid

Overexpression of histone deacetylase (HDAC) isoforms has been implicated in a variety of disease pathologies, from cancer and colitis to cardiovascular disease and neurodegeneration, thus HDAC inhibitors have a long history as therapeutic targets. The gut microbiota can influence HDAC activity via microbial-derived metabolites. While HDAC inhibition (HDI) by gut commensals has long been attributed to the short chain fatty acid (SCFA) butyrate, the potent metabolic reservoir provided by the gut microbiota and its role in host physiology warrants further investigation in a variety of diseases. Cell-free supernatants (CFS) of 79 phylogenetically diverse gut commensals isolated from healthy human donors were screened for their SCFA profile and their total HDAC inhibitory properties. The three most potent HDAC inhibiting strains were further evaluated and subjected to additional analysis of specific class I and class II HDAC inhibition. All three HDAC inhibitors are butyrate producing strains, and one of these also produced substantial levels of valeric acid and hexanoic acid. Valeric acid was identified as a potential contributor to the HDAC inhibitory effects. This bacterial strain, Megasphaera massiliensis MRx0029, was added to a model microbial consortium to assess its metabolic activity in interaction with a complex community. M. massiliensis MRx0029 successfully established in the consortium and enhanced the total and specific HDAC inhibitory function by increasing the capacity of the community to produce butyrate and valeric acid. We here show that single bacterial strains from the human gut microbiota have potential as novel HDI therapeutics for disease areas involving host epigenetic aberrations.

The microbiota and autoimmunity: Their role in thyroid autoimmune diseases

Since the 1970s, the role of infectious diseases in the pathogenesis of Graves' disease (GD) has been an object of intensive research. The last decade has witnessed many studies on Yersinia enterocolitica, Helicobacter pylori and other bacterial organisms and their potential impact on GD. Retrospective, prospective and molecular binding studies have been performed with contrary outcomes. Until now it is not clear whether bacterial infections can trigger autoimmune thyroid disease. Common risk factors for GD (gender, smoking, stress, and pregnancy) reveal profound changes in the bacterial communities of the gut compared to that of healthy controls but a pathogenetic link between GD and dysbiosis has not yet been fully elucidated. Conventional bacterial culture, in vitro models, next generation and high-throughput DNA sequencing are applicable methods to assess the impact of bacteria in disease onset and development. Further studies on the involvement of bacteria in GD are needed and may contribute to the understanding of pathogenetic processes. This review will examine available evidence on the subject.

Enhanced production of recombinant proteins by a small molecule protein synthesis enhancer in combination with an antioxidant in recombinant Chinese hamster ovary cells

The improvement in the production of recombinant proteins has been linked in a number of small molecules such as carboxylic acids to the inhibition of histone deacetylase, leading to increased transcription of genes. However, carboxylic acids such as pentanoic acid and butanoic acid have been shown to promote an apoptotic response in Chinese hamster ovary (CHO) cell culture. Supplementation of cultures with antioxidants has shown the ability to reduce the apoptotic response of carboxylic acid supplementation, leading to increased therapeutic protein production. In this study, we showed that pentanoic acid reduced the number of cells entering early apoptosis relative to butanoic acid by 15.4%. Additionally, supplementation of butanoic acid- and pentanoic acid-treated cultures with N-acetyl cysteine (NAC) reduced the population of cells entering early apoptosis by 5.3 and 10.0%, respectively, while increasing productivity by 19.5% in the presence of pentanoic acid and NAC. Conversely, a decrease of 5.7% in production was observed in response to combined butanoic acid and N-acetyl cysteine treatment. The results presented herein provide evidence that a culture supplementation method is critical for optimization of biopharmaceutical manufacturing processes.

A High Level of Intestinal Alkaline Phosphatase Is Protective Against Type 2 Diabetes Mellitus Irrespective of Obesity

Mice deficient in intestinal alkaline phosphatase (IAP) develop type 2 diabetes mellitus (T2DM). We hypothesized that a high level of IAP might be protective against T2DM in humans. We determined IAP levels in the stools of 202 diabetic patients and 445 healthy non-diabetic control people. We found that compared to controls, T2DM patients have approx. 50% less IAP (mean +/- SEM: 67.4 +/- 3.2 vs 35.3 +/- 2.5 U/g stool, respectively; p < 0.000001) indicating a protective role of IAP against T2DM. Multiple logistic regression analyses showed an independent association between the IAP level and diabetes status. With each 25 U/g decrease in stool IAP, there is a 35% increased risk of diabetes. The study revealed that obese people with high IAP (approx. 65 U/g stool) do not develop T2DM. Approx. 65% of the healthy population have < 65.0 U/g stool IAP, and predictably, these people might have 'the incipient metabolic syndrome', including 'incipient diabetes', and might develop T2DM and other metabolic disorders in the near future. In conclusion, high IAP levels appear to be protective against diabetes irrespective of obesity, and a 'temporal IAP profile' might be a valuable tool for predicting 'the incipient metabolic syndrome', including 'incipient diabetes'.

The intestinal epithelial cell differentiation marker intestinal alkaline phosphatase (ALPi) is selectively induced by histone deacetylase inhibitors (HDACi) in colon cancer cells in a Kruppel-like factor 5 (KLF5)-dependent manner

The histone deacetylase inhibitor (HDACi) sodium butyrate promotes differentiation of colon cancer cells as evidenced by induced expression and enzyme activity of the differentiation marker intestinal alkaline phosphatase (ALPi). Screening of a panel of 33 colon cancer cell lines identified cell lines sensitive (42%) and resistant (58%) to butyrate induction of ALP activity. This differential sensitivity was similarly evident following treatment with the structurally distinct HDACi, MS-275. Resistant cell lines were significantly enriched for those harboring the CpG island methylator phenotype (p = 0.036, Chi square test), and resistant cell lines harbored methylation of the ALPi promoter, particularly of a CpG site within a critical KLF/Sp regulatory element required for butyrate induction of ALPi promoter activity. However, butyrate induction of an exogenous ALPi promoter-reporter paralleled up-regulation of endogenous ALPi expression across the cell lines, suggesting the presence or absence of a key transcriptional regulator is the major determinant of ALPi induction. Through microarray profiling of sensitive and resistant cell lines, we identified KLF5 to be both basally more highly expressed as well as preferentially induced by butyrate in sensitive cell lines. KLF5 overexpression induced ALPi promoter-reporter activity in resistant cell lines, KLF5 knockdown attenuated butyrate induction of ALPi expression in sensitive lines, and butyrate selectively enhanced KLF5 binding to the ALPi promoter in sensitive cells. These findings demonstrate that butyrate induction of the cell differentiation marker ALPi is mediated through KLF5 and identifies subsets of colon cancer cell lines responsive and refractory to this effect.

Intestinal alkaline phosphatase gene expression is activated by ZBP-89

Intestinal alkaline phosphatase (IAP) is an enterocyte differentiation marker that functions to limit fat absorption. Zinc finger binding protein-89 (ZBP-89) is a Kruppel-type transcription factor that appears to promote a differentiated phenotype in the intestinal epithelium. The purpose of this study was to investigate the regulation of IAP gene expression by ZBP-89. RT-PCR, quantitative real-time RT-PCR, Western blot analyses, and reporter assays were used to determine the regulation of IAP by ZBP-89 in HT-29 and Caco-2 colon cancer cells. ZBP-89 knockdown was achieved by specific short interfering (si)RNA. EMSA and chromatin immunoprecipitation (ChIP) were performed to examine the binding of ZBP-89 to the IAP promoter. The results of RT-PCR, quantitative real-time PCR, and Western blot analyses showed that ZBP-89 was expressed at low levels in Caco-2 and HT-29 cells, whereas IAP was minimally expressed and absent in these cells, respectively. Transfection with ZBP-89 expression plamid increased IAP mRNA and protein levels in both cell lines, whereas knockdown of endogenous ZBP-89 by siRNA reduced basal levels of IAP gene expression in Caco-2 cells. IAP-luciferase reporter assays, EMSA, and ChIP established that ZBP-89 activated the IAP gene through a response element (ZBP-89 response element: 5'-CCTCCTCCC-3') located between -1018 and -1010 bp upstream of the AUG start codon. We conclude that ZBP-89 is a direct transcriptional activator of the enterocyte differentiation marker IAP. These findings are consistent with the role that this transcription factor is thought to play as a tumor suppressor and suggests its possible function in the physiology of fat absorption.

Bile acids regulate the ontogenic expression of ileal bile acid binding protein in the rat via the farnesoid X receptor

BACKGROUND & AIMS

In the rat, an increase in ileal bile acid binding protein (IBABP) expression occurs during the third postnatal week. In vitro studies suggest that bile acids (BAs) increase IBABP transcription by activating the BA receptor, farnesoid X receptor (FXR). Thus, we investigated the role of BAs on the ontogenic expression of IBABP and whether FXR may mediate these effects.

METHODS

Suckling rats were gavage-fed taurocholate for 3 days or were allowed to develop normally. Ileums were collected for Northern and Western blot analyses. Electrophoretic mobility shift assays for functional FXR were performed using nuclear extracts from ileums of both adult and developing rats.

RESULTS

Taurocholate gavage significantly elevated IBABP messenger RNA and protein levels in suckling animals. Gelshift assays using adult ileal nuclear extracts incubated with a radiolabeled consensus inverted repeat-1 oligonucleotide (response element for FXR) revealed a high-molecular weight DNA/protein complex. Cold competition and supershift assays showed that this complex is sequence specific and confirmed that FXR is a component of the complex. Gelshift assays with nuclear extracts from rat ileum at different ages revealed absence of the DNA/protein complex in the second postnatal week when there is lack of IBABP expression and presence of these complexes at later ages when there is normally high expression. Western blot analyses showed FXR and its heterodimer partner, retinoid X receptor alpha, protein levels are low in the ileum during the suckling period and increase during the third postnatal week.

CONCLUSIONS

BAs play a role in the normal developmental expression of IBABP through FXR activation, and decreased functional FXR in ileal nuclei during the suckling period may account, in part, for the lack of IBABP expression at this time.

Molecular and cellular biology of small-bowel mucosa

Study of the molecular and cellular biology of the small-intestinal mucosa is providing insights into the remarkable properties of this unique tissue. With its structured pattern of cell proliferation, differentiation, and apoptosis, and its ability to adapt following exposure to luminal nutrients or injury from surgery or pathogens, it functions in a regulated but responsive manner. We review recent publications on factors affecting development, gene expression, cell turnover, and adaptation.

Mechanism(s) of butyrate transport in Caco-2 cells: role of monocarboxylate transporter 1

The short-chain fatty acid butyrate was readily taken up by Caco-2 cells. Transport exhibited saturation kinetics, was enhanced by low extracellular pH, and was Na(+) independent. Butyrate uptake was unaffected by DIDS; however, alpha-cyano-4-hydroxycinnamate and the butyrate analogs propionate and L-lactate significantly inhibited uptake. These results suggest that butyrate transport by Caco-2 cells is mediated by a transporter belonging to the monocarboxylate transporter family. We identified five isoforms of this transporter, MCT1, MCT3, MCT4, MCT5, and MCT6, in Caco-2 cells by PCR, and MCT1 was found to be the most abundant isoform by RNase protection assay. Transient transfection of MCT1, in the antisense orientation, resulted in significant inhibition of butyrate uptake. The cells fully recovered from this inhibition by 5 days after transfection. In conclusion, our data showed that the MCT1 transporter may play a major role in the transport of butyrate into Caco-2 cells.