Indolepropionic Acid, a Gut Bacteria-Produced Tryptophan Metabolite and the Risk of Type 2 Diabetes and Non-Alcoholic Fatty Liver Disease

Preventive role of Pastinaca sativa in mitigating metabolic dysfunction-associated steatotic liver disease via modulation of metabolic endotoxemia

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a leading global liver disorder. Parsnip (Pastinaca sativa), rich in dietary fiber and medicinal properties, has shown health benefits, but its effects on MASLD are largely unexplored. This study evaluated the prebiotic and anti-MASLD effects of parsnip root water-soluble extract (PRE) in a mouse model. Mice fed a high-fat diet with 50 or 100 mg/kg PRE for eight weeks showed reduced fat accumulation, improved serum metabolic profiles, and decreased liver injury markers. PRE also lowered hepatic lipogenic protein levels induced by the high-fat diet. Additionally, PRE enhanced gut health by reducing endotoxins, improving intestinal permeability, and upregulating tight junction proteins. These results indicate that PRE can improve gut health, prevent MASLD, and support its potential as a dietary supplement to enhance metabolic health.

The mechanism of action of indole-3-propionic acid on bone metabolism

Indole-3-propionic acid (IPA), a metabolite produced by gut microbiota through tryptophan metabolism, has recently been identified as playing a pivotal role in bone metabolism. IPA promotes osteoblast differentiation by upregulating mitochondrial transcription factor A (Tfam), contributing to increased bone density and supporting bone repair. Simultaneously, it inhibits the formation and activity of osteoclasts, reducing bone resorption, possibly through modulation of the nuclear factor-κB (NF-κB) pathway and downregulation of osteoclast-associated factors, thereby maintaining bone structural integrity. Additionally, IPA provides indirect protection to bone health by regulating host immune responses and inflammation via activation of receptors such as the Aryl hydrocarbon Receptor (AhR) and the Pregnane X Receptor (PXR). This review summarizes the roles and signaling pathways of IPA in bone metabolism and its impact on various bone metabolic disorders. Furthermore, we discuss the therapeutic potential and limitations of IPA in treating bone metabolic diseases, aiming to offer novel strategies for clinical management.

The moderating effect of dietary fiber intake on the association between sleep pattern and liver fibrosis in metabolic dysfunction-associated steatotic liver disease: a study from NHANES

BACKGROUND

Insufficient nocturnal sleep was associated with a higher risk of fibrosis in patients with metabolic dysfunction-associated steatotic liver disease (MASLD). Dietary fiber intake may improve the stimulate the secretion of sleep cytokines, inhibit the inflammatory pathway, contribute to regulating sleep disorders and alleviate liver fibrosis. The associations of dietary fiber intake, sleep patterns, with liver fibrosis remain unclear. The study aimed to explore the associations between dietary fiber, sleep, and liver fibrosis, as well as the moderating effect of dietary fiber intake between sleep patterns and liver fibrosis in MASLD patients.

METHODS

Using data from the National Health and Nutrition Examination Survey (NHANES) database spanning from 2017 to 2020, a cross-sectional study included participants with MASLD was performed to assess the relationship between sleep patterns, dietary fiber intake, and liver fibrosis. Weighted univariate and multivariate logistic regression models were used to examine the linear connection between sleep pattern, dietary fiber intake, and liver fibrosis. Restricted cubic spline (RCS) method was also performed to describe the nonlinear relationship. A two-part linear regression model was also used to estimate threshold effects. The moderating effect of dietary fiber intake was further investigated in different subgroups. All results were presented as odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

Totally, 1343 MASLD patients were included for final analysis. Among them, 207 (15.41%) have liver fibrosis. Dietary fiber intake did not correlate significantly with sleep pattern in patients with MASLD (Spearman's r = -0.028, P = 0.1678). Poor sleep pattern was related to higher odds of liver fibrosis (OR = 3.23, 95%CI: 1.05-9.90), while dietary fiber intake ≥ 15 gm/day was associated with lower liver fibrosis risk (OR = 0.51, 95%CI: 0.32-0.83). On the association between sleep pattern and liver fibrosis stratified by dietary fiber intake revealed that poor sleep patterns (OR = 15.13, 95%CI: 4.40-52.01) remained associated with increased liver fibrosis risk among individuals with dietary fiber intake < 15 gm/day. No connection was observed between poor sleep patterns and liver fibrosis in MASLD patients with higher dietary fiber intake, with moderate dietary fiber supplementation beneficial in mitigating poor sleep patterns associated with liver fibrosis. The similar findings were also found in patients aged < 50 years old, ≥ 50 years old, females, those with and without CVD groups, hypertension, and dyslipidemia. Particularly, dietary fiber intake also moderates the relationship between sleep patterns and liver fibrosis in the F4 stage (OR = 13.26, 95%CI: 4.08-43.11).

CONCLUSION

Dietary fiber intake affects the relationship between sleep patterns and liver fibrosis in MASLD patients.

RNA-Seq transcriptome profiling of Nile rat livers reveals novel insights on the anti-diabetic mechanisms of Water-Soluble Palm Fruit Extract

Water-Soluble Palm Fruit Extract (WSPFE) has been shown to confer anti-diabetic effects in the Nile rat (NR) (Arvicanthis niloticus). Liquid and powder WSPFE both deterred diabetes onset in NRs fed a high-carbohydrate (hiCHO) diet, but the liquid form provided better protection. In this study, NRs were fed either a hiCHO diet or the same diet added with liquid or powder WSPFE. Following feeding of the diets for 8 weeks, random blood glucose levels were measured to categorize NRs as either diabetes-resistant or diabetes-susceptible, based on a cut-off value of 75 mg/dL. Livers were then obtained for Illumina HiSeq 4000 paired end RNA-sequencing (RNA-Seq) and the data were mapped to the reference genome. Consistent with physiological and biochemical parameters, the gene expression data obtained indicated that WSPFE was associated with protection against diabetes. Among hepatic genes upregulated by WSPFE versus controls, were genes related to insulin-like growth factor binding protein, leptin receptor, and processes of hepatic metabolism maintenance, while those downregulated were related to antigen binding, immunoglobulin receptor, inflammation- and cancer-related processes. WSPFE supplementation thus helped inhibit diabetes progression in NRs by increasing insulin sensitivity and reducing both the inflammatory effects of a hiCHO diet and the related DNA-damage compensatory mechanisms contributing to liver disease progression. In addition, the genetic permissiveness of susceptible NRs to develop diabetes was potentially associated with dysregulated compensatory mechanisms involving insulin signaling and oxidative stress over time. Further studies on other NR organs associated with diabetes and its complications are warranted.

Review on mechanisms of hypoglycemic effects of compounds from highland barley and potential applications

The rising prevalence of metabolic diseases, such as diabetes and obesity, presents a significant global health challenge. Dietary interventions, with their minimal side effects, hold great promise as effective strategies for blood sugar management. Highland barley (HB) boasts a comprehensive and unique nutritional composition, characterized by high protein, high fiber, high vitamins, low fat, low sugar, and diverse bioactive components. These attributes make it a promising candidate for alleviating high blood sugar. This review explores the mechanisms underlying the glucose-lowering properties of HB, emphasizing its nutritional profile and bioactive constituents. Additionally, it examines the impact of common HB processing techniques on its nutrient composition and highlights its applications in food products. By advancing the understanding of HB's value and mechanisms in diabetes prevention, this review aims to facilitate the development of HB-based foods suitable for diabetic patients.

Exploring maternal and developmental toxicity of perfluoroalkyl ether acids PFO4DA and PFO5DoA using hepatic transcriptomics and serum metabolomics

Production of per- and polyfluoroalkyl substances (PFAS) has shifted from long-chain perfluoroalkyl acids to short-chain compounds and those with ether bonds in the carbon chain. Next-generation perfluoroalkylether PFAS include HFPO-DA ("GenX chemicals"), Nafion Byproducts, and the PFOx homologous series that includes perfluoro-3,5,7,9-butaoxadecanoic acid (PFO4DA) and perfluoro-3,5,7,9,11-pentaoxadodecanoic acid (PFO5DoA). PFO4DA and PFO5DoA have been detected in serum and/or tissues from humans and wildlife proximal to contamination point sources. However, toxicity data are extremely limited, with no in vivo developmental toxicology data. To address these data gaps, pregnant Sprague-Dawley rats were exposed via oral gavage to vehicle, PFO4DA, or PFO5DoA across a series of doses (0.1 to 62.5 mg/kg/day) from gestation day (GD) 18-22. Hepatic transcriptomics were assayed in dams and fetuses, and serum metabolomics in dams. These data were overlaid with serum PFO4DA and PFO5DoA concentrations to perform dose-response modeling. Both dams and fetuses exhibited dose-responsive disruption of hepatic gene expression in response to PFO4DA or PFO5DoA, with fetal expression disrupted at lower doses than dams. Several differentially expressed genes were upregulated by every dose of PFO5DoA in both maternal and fetal samples, including genes encoding enzymes that hydrolyze acyl-coA to free fatty acids. Maternal serum metabolomics revealed PFO4DA exposure did not induce significant changes at any tested dose, whereas PFO5DoA exposure resulted in dose-dependent differential metabolite abundance for 149 unique metabolites. Multi-omics pathway analyses of integrated maternal liver transcriptomics and serum metabolomics revealed significant convergent changes as low as 3 mg/kg/d PFO4DA and 0.3 mg/kg/d PFO5DoA exposure. Overall, transcriptomic and metabolomic effects of PFO4DA and PFO5DoA appear consistent with other carboxylic acid PFAS, with primary changes related to lipid metabolism, bile acids, cholesterol, and cellular stress. Importantly, PFO5DoA exposure more potently induced changes in maternal and fetal hepatic gene expression and maternal circulating metabolites, despite high structural similarity. Further, we report in vitro PPARα and PPARγ receptor activation for both compounds as putative molecular mechanisms. This work demonstrates the potential developmental toxicity of alternative moiety perfluoroethers and highlights the developing liver as particularly vulnerable to transcriptomic disruption. Synopsis: Developmental exposure to fluoroether carboxylic acids PFO4DA and PFO5DoA result in differential impacts on hepatic transcriptome in dams and offspring and circulating metabolome in dams, with PFO5DoA exhibiting higher potency than PFO4DA.

Gut microbiota and gut-derived metabolites are altered and associated with dietary intake in women with polycystic ovary syndrome

BACKGROUND

Disturbances in the gut microbiota may act as mechanisms influencing the interplay between dietary factors and metabolic disorders. Studies have demonstrated that these alterations are associated with the diagnosis of polycystic ovary syndrome (PCOS). Within this context, we aimed to investigate associations between gut microbiota, gut-derived metabolites (short-chain fatty acids [SCFAs] and indole-3-propionic acid [IPA]), and dietary intake in women with PCOS.

METHODS

We conducted a cross-sectional study of 24 women with PCOS, previously recruited for two studies at our research center, compared with 14 age-matched healthy controls. The mean (SD) age of all 38 participants was 33.3 (7.5) years, and the mean (SD) body mass index was 29.5 (4.8) kg/m2. Primary outcomes included gut microbiota analysis by sequencing the V4 region of the 16 S rRNA gene, serum IPA levels measured by liquid chromatography/triple-quadrupole mass spectrometry (LC-QqQ-MS), and fecal and plasma SCFA levels measured by LC-MS/MS.

RESULTS

Gut microbiota diversity, composition, and metabolic pathways differed between the PCOS and control groups. A higher abundance of two operational taxonomic units specializing in complex carbohydrate metabolism was observed in healthy control women. The PCOS group exhibited a less favorable dietary intake than the control group, and a significant correlation was observed between gut microbiota composition and dietary glycemic load in PCOS (r = 0.314, P = 0.03 in Mantel test). Multivariable-adjusted linear regression models indicated that lower levels of IPA and higher circulating levels of two SCFAs (acetic acid and propionic acid) were independently associated with the diagnosis of PCOS.

CONCLUSIONS

Our data support the differentiation between women with PCOS and healthy controls based on gut microbiota analysis. Furthermore, changes in gut bacteria and their metabolites could be, at least in part, the biological mechanism by which a low glycemic load diet may potentially improve PCOS-related reproductive and cardiometabolic outcomes.

Targeting the Gut Microbiota for Prevention and Management of Type 2 Diabetes

Type 2 diabetes (T2D) is a chronic metabolic disorder with a heterogeneous etiology encompassing societal and behavioral risk factors in addition to genetic and environmental susceptibility. The cardiovascular consequences of diabetes account for more than two-thirds of mortality among people with T2D. Not only does T2D shorten life expectancy, but it also lowers quality of life and is associated with extremely high health expenditures since diabetic complications raise both direct and indirect healthcare costs. An increasing body of research indicates a connection between T2D and gut microbial traits, as numerous alterations in the intestinal microorganisms have been noted in pre-diabetic and diabetic individuals. These include pro-inflammatory bacterial patterns, increased intestinal permeability, endotoxemia, and hyperglycemia-favoring conditions, such as the alteration of glucagon-like peptide-1 (GLP-1) secretion. Restoring microbial homeostasis can be very beneficial for preventing and co-treating T2D and improving antidiabetic therapy outcomes. This review summarizes the characteristics of a "diabetic" microbiota and the metabolites produced by microbial species that can worsen or ameliorate T2D risk and progression, suggesting gut microbiota-targeted strategies to restore eubiosis and regulate blood glucose. Nutritional supplementation, diet, and physical exercise are known to play important roles in T2D, and here their effects on the gut microbiota are discussed, suggesting non-pharmacological approaches that can greatly help in diabetes management and highlighting the importance of tailoring treatments to individual needs.

Multi-omics insights into anti-colitis benefits of the synbiotic and postbiotic derived from wheat bran arabinoxylan and Limosilactobacillus reuteri

Exploring nutritional therapies that manipulate tryptophan metabolism to activate AhR signaling represents a promising approach for mitigating chronic colitis. Arabinoxylan is a bioactive constituent abundant in wheat bran. Here, we comprehensively investigated anti-colitis potentials of wheat bran arabinoxylan (WBAX), its synbiotic and postbiotic derived from WBAX and Limosilactobacillus reuteri WX-94 (i.e., a probiotic strain exhibiting tryptophan metabolic activity). WBAX fueled L. reuteri and promoted microbial conversion of tryptophan to AhR ligands during in vitro fermentation in the culture medium and in the fecal microbiota from type 2 diabetes. The WBAX postbiotic outperformed WBAX and its synbiotic in augmenting efficacy of tryptophan in restoring DSS-disturbed serum immune markers, colonic tight junction proteins and gene profiles involved in amino acid metabolism and FoxO signaling. The WBAX postbiotic remodeled gut microbiota and superiorly enhanced AhR ligands (i.e., indole metabolites and bile acids), alongside with elevation in colonic AhR and IL-22. Associations between genera and metabolites modified by the postbiotic and colitis in human were verified and strong binding capacities between metabolites and colitis-related targets were demonstrated by molecular docking. Our study advances the novel perspective of WBAX in manipulating tryptophan metabolism and anti-colitis potentials of WBAX postbiotic via promoting gut microbiota-dependent AhR signaling.

Interactions between Gut Microbiota and Natural Bioactive Polysaccharides in Metabolic Diseases: Review

The gut microbiota constitutes a complex ecosystem, comprising trillions of microbes that have co-evolved with their host over hundreds of millions of years. Over the past decade, a growing body of knowledge has underscored the intricate connections among diet, gut microbiota, and human health. Bioactive polysaccharides (BPs) from natural sources like medicinal plants, seaweeds, and fungi have diverse biological functions including antioxidant, immunoregulatory, and metabolic activities. Their effects are closely tied to the gut microbiota, which metabolizes BPs into health-influencing compounds. Understanding how BPs and gut microbiota interact is critical for harnessing their potential health benefits. This review provides an overview of the human gut microbiota, focusing on its role in metabolic diseases like obesity, type II diabetes mellitus, non-alcoholic fatty liver disease, and cardiovascular diseases. It explores the basic characteristics of several BPs and their impact on gut microbiota. Given their significance for human health, we summarize the biological functions of these BPs, particularly in terms of immunoregulatory activities, blood sugar, and hypolipidemic effect, thus providing a valuable reference for understanding the potential benefits of natural BPs in treating metabolic diseases. These properties make BPs promising agents for preventing and treating metabolic diseases. The comprehensive understanding of the mechanisms by which BPs exert their effects through gut microbiota opens new avenues for developing targeted therapies to improve metabolic health.

Association between whole-grain consumption, tryptophan metabolism and psychological distress: a secondary analysis of a randomised controlled trial

This study aimed to investigate whether psychological distress, whole-grain consumption and tryptophan metabolism are associated with participants undergoing weight management intervention. Seventy-nine women and men (mean age 49·7 (sd 9·0) years; BMI 34·2(sd 2·5) kg/m2) participated in a 7-week weight-loss (WL) period and in a 24-week weight maintenance (WM) intervention period. Whole-grain consumption was measured using 4 d food diaries. Psychological distress was assessed with the General Health Questionnaire-12 (GHQ), and participants were divided into three GHQ groups based on the GHQ scores before WL. Tryptophan metabolites were determined from the participants' fasting plasma using liquid chromatography-MS. GHQ scores were not associated with the whole-grain consumption. A positive association was observed between the whole-grain consumption and indole propionic acid (IPA) during the WM (P = 0·033). Serotonin levels were higher after the WL in the lowest GHQ tertile (P = 0·033), while the level at the end of the WM was higher compared with other timepoints in the highest GHQ tertile (P = 0·015 and P = 0·001). This difference between groups was not statistically significant. Furthermore, levels of several tryptophan metabolites changed within the groups during the study. Tryptophan metabolism changed during the study in the whole study group, independently from the level of psychological distress. The association between whole-grain consumption and IPA is possibly explained by the effects of dietary fibre on gut microbiota. This broadens the understanding of the pathways behind the health benefits associated with the intake of whole grains.

Soybean oil-based HFD induces gut dysbiosis that leads to steatosis, hepatic inflammation and insulin resistance in mice

High-fat diets (HFDs) shape the gut microbiome and promote obesity, inflammation, and liver steatosis. Fish and soybean are part of a healthy diet; however, the impact of these fats, in the absence of sucrose, on gut microbial dysbiosis and its association with liver steatosis remains unclear. Here, we investigated the effect of sucrose-free soybean oil-and fish oil-based high fat diets (HFDs) (SF-Soy-HFD and SF-Fish-HFD, respectively) on gut dysbiosis, obesity, steatosis, hepatic inflammation, and insulin resistance. C57BL/6 mice were fed these HFDs for 24 weeks. Both diets had comparable effects on liver and total body weights. But 16S-rRNA sequencing of the gut content revealed induction of gut dysbiosis at different taxonomic levels. The microbial communities were clearly separated, showing differential dysbiosis between the two HFDs. Compared with the SF-Fish-HFD control group, the SF-Soy-HFD group had an increased abundance of Bacteroidetes, Firmicutes, and Deferribacteres, but a lower abundance of Verrucomicrobia. The Clostridia/Bacteroidia (C/B) ratio was higher in the SF-Soy-HFD group (3.11) than in the SF-Fish-HFD group (2.5). Conversely, the Verrucomicrobiacae/S24_7 (also known as Muribaculaceae family) ratio was lower in the SF-Soy-HFD group (0.02) than that in the SF-Fish-HFD group (0.75). The SF-Soy-HFD group had a positive association with S24_7, Clostridiales, Allobaculum, Coriobacteriaceae, Adlercreutzia, Christensenellaceae, Lactococcus, and Oscillospira, but was related to a lower abundance of Akkermansia, which maintains gut barrier integrity. The gut microbiota in the SF-Soy-HFD group had predicted associations with host genes related to fatty liver and inflammatory pathways. Mice fed the SF-Soy-HFD developed liver steatosis and showed increased transcript levels of genes associated with de novo lipogenesis (Acaca, Fasn, Scd1, Elovl6) and cholesterol synthesis (Hmgcr) pathways compared to those in the SF-Fish-HFD-group. No differences were observed in the expression of fat uptake genes (Cd36 and Fabp1). The expression of the fat efflux gene (Mttp) was reduced in the SF-Soy-HFD group. Moreover, hepatic inflammation markers (Tnfa and Il1b) were notably expressed in SF-Soy-HFD-fed mice. In conclusion, SF-Soy-HFD feeding induced gut dysbiosis in mice, leading to steatosis, hepatic inflammation, and impaired glucose homeostasis.

Indole-3-propionic acid regulates lateral root development by targeting auxin signaling in Arabidopsis

Indole-3-propionic acid (IPA) is known to be a microbe-derived compound with a similar structure to the phytohormone auxin (indole-3-acetic acid, IAA). Previous studies reported that IPA exhibited auxin-like bioactivities in plants. However, the underlying molecular mechanism is not totally understood. Here, we revealed that IPA modulated lateral root (LR) development via auxin signaling in the model plant Arabidopsis thaliana. Genetic analysis indicated that deficiency of the TIR1/AFB-Aux/IAA-ARF auxin signaling pathway abolished the effects of IPA on regulating LR development. Further biochemical, transcriptomic profiling and cell biological analyses revealed that IPA directly bound to the TIR1/AFB-Aux/IAA coreceptor complex and thus activated downstream gene expression. Therefore, our work revealed that IPA is a potential signaling molecule that modulates plant growth and development by targeting the TIR1/AFB-Aux/IAA-mediated auxin signaling pathway, providing potential insights into root growth regulation in plants.

Distinct Plasma Metabolomic and Gut Microbiome Profiles after Gestational Diabetes Mellitus Diet Treatment: Implications for Personalized Dietary Interventions

Gestational diabetes mellitus (GDM) triggers alterations in the maternal microbiome. Alongside metabolic shifts, microbial products may impact clinical factors and influence pregnancy outcomes. We investigated maternal microbiome-metabolomic changes, including over 600 metabolites from a subset of the "Choosing Healthy Options in Carbohydrate Energy" (CHOICE) study. Women diagnosed with GDM were randomized to a diet higher in complex carbohydrates (CHOICE, n = 18, 60% complex carbohydrate/25% fat/15% protein) or a conventional GDM diet (CONV, n = 16, 40% carbohydrate/45% fat/15% protein). All meals were provided. Diets were eucaloric, and fiber content was similar. CHOICE was associated with increases in trimethylamine N-oxide, indoxyl sulfate, and several triglycerides, while CONV was associated with hippuric acid, betaine, and indole propionic acid, suggestive of a healthier metabolome. Conversely, the microbiome of CHOICE participants was enriched with carbohydrate metabolizing genes and beneficial taxa such as Bifidobacterium adolescentis, while CONV was associated with inflammatory pathways including antimicrobial resistance and lipopolysaccharide biosynthesis. We also identified latent metabolic groups not associated with diet: a metabolome associated with less of a decrease in fasting glucose, and another associated with relatively higher fasting triglycerides. Our results suggest that GDM diets produce specific microbial and metabolic responses during pregnancy, while host factors also play a role in triglycerides and glucose metabolism.

The Tryptophan Metabolite Indole-3-Propionic Acid Raises Kynurenic Acid Levels in the Rat Brain In Vivo

Alterations in the composition of the gut microbiota may be causally associated with several brain diseases. Indole-3-propionic acid (IPrA) is a tryptophan-derived metabolite, which is produced by intestinal commensal microbes, rapidly enters the circulation, and crosses the blood-brain barrier. IPrA has neuroprotective properties, which have been attributed to its antioxidant and bioenergetic effects. Here, we evaluate an alternative and/or complementary mechanism, linking IPrA to kynurenic acid (KYNA), another neuroprotective tryptophan metabolite. Adult Sprague-Dawley rats received an oral dose of IPrA (200 mg/kg), and both IPrA and KYNA were measured in plasma and frontal cortex 90 minutes, 6 or 24 hours later. IPrA and KYNA levels increased after 90 minutes and 6 hours (brain IPrA: ~56- and ~7-fold; brain KYNA: ~4- and ~3-fold, respectively). In vivo microdialysis, performed in the medial prefrontal cortex and in the striatum, revealed increased KYNA levels (~2.5-fold) following the administration of IPrA (200 mg/kg, p.o), but IPrA failed to affect extracellular KYNA when applied locally. Finally, treatment with 100 or 350 mg IPrA, provided daily to the animals in the chow for a week, resulted in several-fold increases of IPrA and KYNA levels in both plasma and brain. These results suggest that exogenously supplied IPrA may provide a novel strategy to affect the function of KYNA in the mammalian brain.

The influence of indole propionic acid on molecular markers of steroidogenesis, ER stress, and apoptosis in rat granulosa cells exposed to high glucose conditions

Hyperglycemia is known as one of the main causes of infertility in human societies. Indole propionic acid (IPA) is produced by intestinal microbiota and has antioxidant and anti-inflammatory properties. This study aims to investigate the effects of IPA on molecular indices of steroidogenesis, ER stress, and apoptosis induced by high glucose (HG) in granulosa cells. Primary GCs, isolated from ovarian follicles of Rats were cultured in 5 mM (control) and 30 mM (HG) of glucose and in the presence of 10 and 20 µM of IPA for 24 h. The cell viability was assessed by MTT. The gene expression of P450SCC, 3βHSD, CYP19A, BAX, BCL2, and STAR was evaluated by Real-Time PCR. Protein expression of ATF6, PERK, GRP78, and CHOP determined by western blot. Progesterone, estradiol, IL-1β, and TNF-α were measured by ELISA. HG decreased the viability, and expression of P450SCC, 3βHSD, CYP19A, BCL2, STAR, and increased BAX. 10 and 20 µM of IPA increased cell viability, expression of P450SCC, 3βHSD, CYP19A, BCL2 and STAR and decreased BAX compared to the HG group. The expression of ATF6, PERK, GRP78, and CHOP proteins increased by HG and IPA decreased the expression of these proteins compared to the HG group. Also, HG decreased progesterone and estradiol levels and increased IL-1β and TNF-α. IPA significantly increased progesterone and estradiol and decreased IL-1β and TNF-α compared to the HG group. IPA can improve the side effects of HG in GCs of rats, as responsible cells for fertility, by improving steroidogenesis, regulation of ER-stress pathway, suppression of inflammation, and apoptosis.

The underlying causes, treatment options of gut microbiota and food habits in type 2 diabetes mellitus: a narrative review

Type 2 diabetes mellitus is a long-lasting endocrine disorder characterized by persistent hyperglycaemia, which is often triggered by an entire or relative inadequacy of insulin production or insulin resistance. As a result of resistance to insulin (IR) and an overall lack of insulin in the body, type 2 diabetes mellitus (T2DM) is a metabolic illness that is characterized by hyperglycaemia. Notably, the occurrence of vascular complications of diabetes and the advancement of IR in T2DM are accompanied by dysbiosis of the gut microbiota. Due to the difficulties in managing the disease and the dangers of multiple accompanying complications, diabetes is a chronic, progressive immune-mediated condition that plays a significant clinical and health burden on patients. The frequency and incidence of diabetes among young people have been rising worldwide. The relationship between the gut microbiota composition and the physio-pathological characteristics of T2DM proposes a novel way to monitor the condition and enhance the effectiveness of therapies. Our knowledge of the microbiota of the gut and how it affects health and illness has changed over the last 20 years. Species of the genus Eubacterium, which make up a significant portion of the core animal gut microbiome, are some of the recently discovered 'generation' of possibly helpful bacteria. In this article, we have focused on pathogenesis and therapeutic approaches towards T2DM, with a special reference to gut bacteria from ancient times to the present day.

Alteration of Plasma Indoles in Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is one of the most common endocrinopathies in reproductive-aged women. The occurrence of PCOS was reported to be associated with the alteration of gut microbiota. Microbiota-derived indoles may possibly play a key role in glycemic control. The purpose of this work is to reveal the alteration of plasma indoles in PCOS patients and to investigate the correlation between indoles levels and glucose metabolism. Sixty-five patients with PCOS and twenty-eight age-matched women were enrolled in this work. The concentrations of plasma indoles, including indoxyl sulfate (IS), indole-3-acetic acid (IAA), indole-3-propionate (IPA), indole (IND), and 3-methylindole (3-MI), were measured by HPLC with the fluorescence detection. The plasma levels of IS, IAA, and IND were significantly elevated in patients with PCOS compared to those in the control group (p < 0.05). Furthermore, the plasma levels of IS, IAA, and IND were positively correlated with fasting glucose, fasting insulin, and the homeostatic model of insulin resistance index (HOMA-IR) (p < 0.05). Besides, the 3-MI level in the plasma was positively correlated with the fasting glucose level, whereas plasma levels of IS, IAA, IND, and 3-MI were negatively correlated with glucagon-like peptide 1 (p < 0.05). Moreover, IS and IND were considered to be risk factors for PCOS after age, BMI, T, LH, and HOMA-IR adjustment. The area under the receiver-operating characteristic curve of the combined index of five indoles was 0.867 for PCOS diagnosis. Additionally, plasma indoles altered in PCOS, which was closely associated with the glucose metabolism.

Dysrupted microbial tryptophan metabolism associates with SARS-CoV-2 acute inflammatory responses and long COVID

Protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and risk of long COVID has been associated with the depletion or over-abundance of specific taxa within the gut microbiome. However, the microbial mechanisms mediating these effects are not yet known. We hypothesized that altered microbial production of tryptophan and its downstream derivatives might contribute to inappropriate immune responses to viral infection. In patients hospitalized with COVID-19 (n = 172), serum levels of tryptophan and indole-3-propionate (IPA) negatively correlated with serum levels of many proinflammatory mediators (including C-reactive protein and Serum amyloid A), while C-glycosyltryptophan (C-Trp), indole-3-lactic acid (ILA) and indole-3-acetic acid (IAA) levels were positively correlated with levels of acute phase proteins, proinflammatory cytokines, alarmins and chemokines. A similar pattern was observed in long COVID patients (n = 20) where tryptophan and IPA were negatively associated with a large number of serum cytokines, while C-Trp and IAA were positively associated with circulating cytokine levels. Metagenomic analysis of the fecal microbiota showed the relative abundance of genes encoding the microbial enzymes required for tryptophan production (e.g. anthranilate synthase) and microbial tryptophan metabolism was significantly lower in patients hospitalized with COVID-19 (n = 380) compared to healthy controls (n = 270). Microbial tryptophan metabolites reduced innate cell proinflammatory responses to cytosolic DNA sensor Stimulator of interferon genes (STING), toll-like receptor (TLR)-3 and TLR-4 stimulation in vitro, while IL-10 secretion was enhanced. Microbial tryptophan metabolites also modified ex vivo human lymphocyte responses by limiting the production of TH1 and TH17 associated cytokines, while enhancing secretion of IL-22. These data suggest that lower levels of tryptophan production and tryptophan metabolism by gut microbes may increase the risk of severe and chronic outcomes to SARS-CoV-2 infection due to impaired innate and adaptive responses to infection. Screening patients for lower-level microbiome capacity for tryptophan metabolism may help identify at-risk individuals.

Nutritional metabolomics: Recent developments and future needs

Metabolomics has rapidly been adopted as one of the key methods in nutrition research. This review focuses on the recent developments and updates in the field, including the analytical methodologies that encompass improved instrument sensitivity, sampling techniques and data integration (multiomics). Metabolomics has advanced the discovery and validation of dietary biomarkers and their implementation in health research. Metabolomics has come to play an important role in the understanding of the role of small molecules resulting from the diet-microbiota interactions when gut microbiota research has shifted towards improving the understanding of the activity and functionality of gut microbiota rather than composition alone. Currently, metabolomics plays an emerging role in precision nutrition and the recent developments therein are discussed.

The role of intestinal microbes on intestinal barrier function and host immunity from a metabolite perspective

The gut is colonized by many commensal microorganisms, and the diversity and metabolic patterns of microorganisms profoundly influence the intestinal health. These microbial imbalances can lead to disorders such as inflammatory bowel disease (IBD). Microorganisms produce byproducts that act as signaling molecules, triggering the immune system in the gut mucosa and controlling inflammation. For example, metabolites like short-chain fatty acids (SCFA) and secondary bile acids can release inflammatory-mediated signals by binding to specific receptors. These metabolites indirectly affect host health and intestinal immunity by interacting with the intestinal epithelial and mucosal immune cells. Moreover, Tryptophan-derived metabolites also play a role in governing the immune response by binding to aromatic hydrocarbon receptors (AHR) located on the intestinal mucosa, enhancing the intestinal epithelial barrier. Dietary-derived indoles, which are synthetic precursors of AHR ligands, work together with SCFA and secondary bile acids to reduce stress on the intestinal epithelium and regulate inflammation. This review highlights the interaction between gut microbial metabolites and the intestinal immune system, as well as the crosstalk of dietary fiber intake in improving the host microbial metabolism and its beneficial effects on the organism.

A Metabolite Perspective on the Involvement of the Gut Microbiota in Type 2 Diabetes

Type 2 diabetes (T2D) is a commonly diagnosed condition that has been extensively studied. The composition and activity of gut microbes, as well as the metabolites they produce (such as short-chain fatty acids, lipopolysaccharides, trimethylamine N-oxide, and bile acids) can significantly impact diabetes development. Treatment options, including medication, can enhance the gut microbiome and its metabolites, and even reverse intestinal epithelial dysfunction. Both animal and human studies have demonstrated the role of microbiota metabolites in influencing diabetes, as well as their complex chemical interactions with signaling molecules. This article focuses on the importance of microbiota metabolites in type 2 diabetes and provides an overview of various pharmacological and dietary components that can serve as therapeutic tools for reducing the risk of developing diabetes. A deeper understanding of the link between gut microbial metabolites and T2D will enhance our knowledge of the disease and may offer new treatment approaches. Although many animal studies have investigated the palliative and attenuating effects of gut microbial metabolites on T2D, few have established a complete cure. Therefore, conducting more systematic studies in the future is necessary.

Abnormal tryptophan catabolism in diabetes mellitus and its complications: Opportunities and challenges

In recent years, the incidence rate of diabetes mellitus (DM), including type 1 diabetes mellitus(T1DM), type 2 diabetes mellitus(T2DM), and gestational diabetes mellitus (GDM), has increased year by year and has become a major global health problem. DM can lead to serious complications of macrovascular and microvascular. Tryptophan (Trp) is an essential amino acid for the human body. Trp is metabolized in the body through the indole pathway, kynurenine (Kyn) pathway and serotonin (5-HT) pathway, and is regulated by intestinal microorganisms to varying degrees. These three metabolic pathways have extensive regulatory effects on the immune, endocrine, neural, and energy metabolism systems of the body, and are related to the physiological and pathological processes of various diseases. The key enzymes and metabolites in the Trp metabolic pathway are also deeply involved in the pathogenesis of DM, playing an important role in pancreatic function, insulin resistance (IR), intestinal barrier, and angiogenesis. In DM and its complications, there is a disruption of Trp metabolic balance. Several therapy approaches for DM and complications have been proven to modify tryptophan metabolism. The metabolism of Trp is becoming a new area of focus for DM prevention and care. This paper reviews the impact of the three metabolic pathways of Trp on the pathogenesis of DM and the alterations in Trp metabolism in these diseases, expecting to provide entry points for the treatment of DM and its complications.

Plasma metabolomic profiles of plant-based dietary indices reveal potential pathways for metabolic syndrome associations

BACKGROUND AND AIMS

Plant-based dietary patterns have been associated with improved health outcomes. This study aims to describe the metabolomic fingerprints of plant-based diet indices (PDI) and examine their association with metabolic syndrome (MetS) and its components in a Danish population.

METHODS

The MAX study comprised 676 participants (55% women, aged 18-67 y) from Copenhagen. Sociodemographic and dietary data were collected using questionnaires and three 24-h dietary recalls over one year (at baseline, and at 6 and 12 months). Mean dietary intakes were computed, as well as overall PDI, healthful (hPDI) and unhealthful (uPDI) scores, according to food groups for each plant-based index. Clinical variables were also collected at the same time points in a health examination that included complete blood tests. MetS was defined according to the International Diabetes Federation criteria. Plasma metabolites were measured using a targeted metabolomics approach. Metabolites associated with PDI were selected using random forest models and their relationships with PDIs and MetS were analyzed using generalized linear mixed models.

RESULTS

The mean prevalence of MetS was 10.8%. High, compared to low, hPDI and uPDI scores were associated with a lower and higher odd of MetS, respectively [odds ratio (95%CI); hPDI: 0.56 (0.43-0.74); uPDI: 1.61 (1.26-2.05)]. Out of 411 quantified plasma metabolites, machine-learning metabolomics fingerprinting revealed 13 metabolites, including food and food-related microbial metabolites, like hypaphorine, indolepropionic acid and lignan-derived enterolactones. These metabolites were associated with all PDIs and were inversely correlated with MetS components (p < 0.05). Furthermore, they had an explainable contribution of 12% and 14% for the association between hPDI or uPDI, respectively, and MetS only among participants with overweight/obesity.

CONCLUSIONS

Metabolites associated with PDIs were inversely associated with MetS and its components, and may partially explain the effects of plant-based diets on cardiometabolic risk factors.

Towards Individually Tailored Diets in Prevention and Treatment of Diabetes?

Type 2 diabetes (T2D) is a heterogenous disease regarding its phenotype and genotype [...].

Determination of Indolepropionic Acid and Related Indoles in Plasma, Plasma Ultrafiltrate, and Saliva

The microbial metabolite indolepropionic acid (IPA) and related indolic metabolites, including indolecarboxylic acid (ICA), indolelactic acid (ILA), indoleacetic acid (IAA), indolebutyric acid (IBA), indoxylsulfate (ISO4), and indole, were determined in human plasma, plasma ultrafiltrate (UF), and saliva. The compounds were separated on a 150 × 3 mm column of 3 μm Hypersil C18 eluted with a mobile phase of 80% pH 5 0.01 M sodium acetate containing 1.0 g/L of tert-butylammonium chloride/20% acetonitrile and then detected fluorometrically. Levels of IPA in human plasma UF and of ILA in saliva are reported for the first time. The determination of IPA in plasma UF enables the first report of free plasma IPA, the presumed physiologically active pool of this important microbial metabolite of tryptophan. Plasma and salivary ICA and IBA were not detected, consistent with the absence of any prior reported values. Observed levels or limits of detection for other indolic metabolites usefully supplement limited prior reports.

Natural Product Skatole Ameliorates Lipotoxicity-Induced Multiple Hepatic Damage under Hyperlipidemic Conditions in Hepatocytes

Skatole (3-methylindole, 3MI) is a natural-origin compound derived from plants, insects, and microbial metabolites in human intestines. Skatole has an anti-lipid peroxidation effect and is a biomarker for several diseases. However, its effect on hepatocyte lipid metabolism and lipotoxicity has not been elucidated. Hepatic lipotoxicity is induced by excess saturated free fatty acids in hyperlipidemia, which directly damages the hepatocytes. Lipotoxicity is involved in several metabolic diseases and hepatocytes, particularly affecting nonalcoholic fatty liver disease (NAFLD) progression. NAFLD is caused by the accumulation of fat by excessive free fatty acids (FFAs) in the blood and is accompanied by hepatic damage, such as endoplasmic reticulum (ER) stress, abnormal glucose and insulin metabolism, oxidative stress, and lipoapoptosis with lipid accumulation. Hepatic lipotoxicity causes multiple hepatic damages in NAFLD and has a directly effect on the progression from NAFLD to nonalcoholic steatohepatitis (NASH). This study confirmed that the natural compound skatole improves various damages to hepatocytes caused by lipotoxicity in hyperlipidemic conditions. To induce lipotoxicity, we exposed HepG2, SNU-449, and Huh7 cells to palmitic acid, a saturated fatty acid, and confirmed the protective effect of skatole. Skatole inhibited fat accumulation in the hepatocytes, reduced ER and oxidative stress, and recovered insulin resistance and glucose uptake. Importantly, skatole reduced lipoapoptosis by regulating caspase activity. In conclusion, skatole ameliorated multiple types of hepatocyte damage induced by lipotoxicity in the presence of excess free fatty acids.

Extensive Summary of the Important Roles of Indole Propionic Acid, a Gut Microbial Metabolite in Host Health and Disease

Increasing evidence suggests that metabolites produced by the gut microbiota play a crucial role in host-microbe interactions. Dietary tryptophan ingested by the host enters the gut, where indole-like metabolites such as indole propionic acid (IPA) are produced under deamination by commensal bacteria. Here, we summarize the IPA-producing bacteria, dietary patterns on IPA content, and functional roles of IPA in various diseases. IPA can not only stimulate the expression of tight junction (TJ) proteins to enhance gut barrier function and inhibit the penetration of toxic factors, but also modulate the immune system to exert anti-inflammatory and antioxidant effects to synergistically regulate body physiology. Moreover, IPA can act on target organs through blood circulation to form the gut-organ axis, which helps maintain systemic homeostasis. IPA shows great potential for the diagnosis and treatment of various clinical diseases, such as NAFLD, Alzheimer's disease, and breast cancer. However, the therapeutic effect of IPA depends on dose, target organ, or time. In future studies, further work should be performed to explore the effects and mechanisms of IPA on host health and disease to further improve the existing treatment program.