The Natural Metabolite 4-Cresol Improves Glucose Homeostasis and Enhances β-Cell Function

Stimulation of insulin secretion induced by low 4-cresol dose involves the RPS6KA3 signalling pathway

4-cresol (4-methylphenol, p-cresol) is a xenobiotic substance negatively correlated with type 2 diabetes and associated with health improvement in preclinical models of diabetes. We aimed at refining our understanding of the physiological role of this metabolite and identifying potential signalling mechanisms. Functional studies revealed that 4-cresol does not deteriorate insulin sensitivity in human primary adipocytes and exhibits an additive effect to that of insulin on insulin sensitivity in mouse C2C12 myoblasts. Experiments in mouse isolated islets showed that 4-cresol potentiates glucose induced insulin secretion. We demonstrated the absence of off target effects of 4-cresol on a panel of 44 pharmacological compounds. Screening large panels of 241 G protein-coupled receptors (GPCRs) and 468 kinases identified binding of 4-cresol only to TNK1, EIF2AK4 (GCN2) and RPS6KA3 (RSK2), a kinase strongly expressed in human and rat pancreatic islets. Islet expression of RPS6KA3 is reduced in spontaneously diabetic rats chronically treated with 4-cresol and Rps6ka3 deficient mice exhibit reduction in both body weight and fasting glycemia, modest improvement in glycemic control and enhanced insulin release in vivo. Similar to low doses of 4-cresol, incubation of isolated rat islets with low concentrations of the RPS6KA3 inhibitor BIX 02565 stimulates both glucose induced insulin secretion and β-cell proliferation. These results provide further information on the role of low 4-cresol doses in the regulation of insulin secretion.

Metabolomics signature of blood pressure salt sensitivity and its link to cardiovascular disease: A dietary salt-intervention trial

Individuals with a high degree of salt sensitivity (SS) have a greater risk of cardiovascular disease (CVD), but whether SS fosters CVD by influencing metabolomics homeostasis remains unclear. This study aimed to reveal the role of the SS-related metabolomics signature in the development of CVDs, based on the MetaSalt study, which was a dietary salt-intervention trial conducted at four centers in China in 2019. A total of 528 participants were recruited and underwent 3 days of baseline observations, a 10-day low-salt intervention, and a 10-day high-salt intervention. Plasma untargeted metabolomics, lipidomics, and BP measurements were scheduled at each stage. Participants were grouped into extreme SS, moderate SS, and salt-resistant (SR) individuals according to their BP responses to salt. Linear mixed models were used to identify SS-related metabolites and determine the relationship between the SS-related metabolomics signature and arterial stiffness. Mendelian randomization (MR) analyses were applied to establish the causal pathways among the SS-related metabolites, BP, and CVDs. Among the 713 metabolites, 467 were significantly changed after the high-salt intervention. Among them, the changes in 30 metabolites from the low-salt to the high-salt intervention differed among the SS groups. Of the remaining nonsalt-related metabolites, the baseline levels of 11 metabolites were related to SS. These 41 metabolites explained 23% of the variance in SS. Moreover, SS and its metabolomics signature were positively correlated with arterial stiffness. MR analyses demonstrated that the SS-related metabolites may affect CVD risk by altering BP, indicating that the increase in BP was the consequence of the changes in SS-related metabolites rather than the cause. Our study revealed that the metabolomics signature of SS individuals differs from that of SR individuals and that the changes in SS-related metabolites may increase arterial stiffness and foster CVDs. This study provides insight into understanding the biology and targets of SS and its role in CVDs.

Biochemotaxis-Oriented Engineering Bacteria Expressing GLP-1 Enhance Diabetes Therapy by Regulating the Balance of Immune

Glucagon like peptide-1 (GLP-1) is an effective hypoglycemic drug that can repair the pancreas β cells and promote insulin secretion. However, GLP-1 has poor stability and lacks of target ability, which makes it difficult to reach the site of action to exert its efficacy. Here, GLP-1-expressing plasmids are introduced into the Escherichia coli Nissle 1917 (EcN) and a lipid membrane is formed through simple self-assembly on its surface, resulting in an oral delivery system (LEG) capable of resisting the harsh environment of the gastrointestinal tract. The system utilizes the chemotactic properties of probiotics to achieve efficient enrichment at the pancreatic site, and protects islet β cells from destruction by regulating the balance of immune cells. More interestingly, LEG not only continuously produces GLP-1 to restore pancreatic islet β cell function and secrete insulin to control blood sugar levels, but also regulates the intestinal flora and increases the richness and diversity of probiotics. In mice diabetes models, oral administration of LEG only once every other day has good biosafety and compliance, and achieves long-term control of blood glucose. Therefore, this strategy not only provides an oral delivery platform for pancreatic targeting, but also opens up new avenues for reversing diabetes.

Khdc3 Regulates Metabolism Across Generations in a DNA-Independent Manner

Genetic variants can alter the profile of heritable molecules such as small RNAs in sperm and oocytes, and in this manner ancestral genetic variants can have a significant effect on offspring phenotypes even if they are not themselves inherited. Here we show that wild type female mice descended from ancestors with a mutation in the mammalian germ cell gene Khdc3 have hepatic metabolic defects that persist over multiple generations. We find that genetically wild type females descended from Khdc3 mutants have transcriptional dysregulation of critical hepatic metabolic genes, which persist over multiple generations and pass through both female and male lineages. This was associated with dysregulation of hepatically-metabolized molecules in the blood of these wild type mice with mutational ancestry. The oocytes of Khdc3-null females, as well as their wild type descendants, had dysregulation of multiple small RNAs, suggesting that these epigenetic changes in the gametes transmit the phenotype between generations. Our results demonstrate that ancestral mutation in Khdc3 can produce transgenerational inherited phenotypes, potentially indefinitely.

Evaluation of elevated plasma fatty acids as relevant factors for adult-onset asthma: The Nagahama Study

BACKGROUND

Obesity and increased body mass index (BMI) are the known risk factors for adult-onset asthma. Serum free fatty acid (FFA) and other blood lipid levels are generally elevated in patients with obesity and may be involved in the onset of asthma. However, it remains largely unknown. This study aimed to elucidate the relationship between plasma fatty acids and new-onset asthma.

METHODS

This community-based Nagahama Study in Japan enrolled 9804 residents. We conducted self-reporting questionnaires, lung function tests, and blood tests at baseline and 5 years later as follow-up. At the follow-up, plasma fatty acids were measured using gas chromatography-mass spectrometry. Body composition analysis was also measured at the follow-up. The associations between fatty acids and new-onset asthma were evaluated using a multifaceted approach, including targeted partial least squares discriminant analysis (PLS-DA).

RESULTS

In PLS-DA for new-onset asthma, palmitoleic acid was identified as the fatty acid most associated with asthma onset. In the multivariable analysis, higher levels of FFA, palmitoleic acid, or oleic acid were significantly associated with new-onset asthma, independent of other confounding factors. The high body fat percentage itself was not the relevant factor, but showed a positive interaction with plasma palmitoleic acid for new-onset asthma. When stratified by gender, the impacts of higher levels of FFA or palmitoleic acid on new-onset asthma remained significant in females, but not in males.

CONCLUSIONS

Elevated levels of plasma fatty acids, particularly palmitoleic acid, may be a relevant factor for new-onset asthma.

p-Cresol Sulfate Is a Sensitive Urinary Marker of Fecal Microbiota Transplantation and Antibiotics Treatments in Human Patients and Mouse Models

Fecal microbiota transplantation (FMT) has emerged as a highly effective therapy for recurrent Clostridioides difficile infection (rCDI) and also a potential therapy for other diseases associated with dysbiotic gut microbiota. Monitoring metabolic changes in biofluids and excreta is a noninvasive approach to identify the biomarkers of microbial recolonization and to understand the metabolic influences of FMT on the host. In this study, the pre-FMT and post FMT urine samples from 11 rCDI patients were compared through metabolomic analyses for FMT-induced metabolic changes. The results showed that p-cresol sulfate in urine, a microbial metabolite of tyrosine, was rapidly elevated by FMT and much more responsive than other microbial metabolites of aromatic amino acids (AAAs). Because patients were treated with vancomycin prior to FMT, the influence of vancomycin on the microbial metabolism of AAAs was examined in a mouse feeding trial, in which the decreases in p-cresol sulfate, phenylacetylglycine, and indoxyl sulfate in urine were accompanied with significant increases in their AAA precursors in feces. The inhibitory effects of antibiotics and the recovering effects of FMT on the microbial metabolism of AAAs were further validated in a mouse model of FMT. Overall, urinary p-cresol sulfate may function as a sensitive and convenient therapeutic indicator on the effectiveness of antibiotics and FMT for the desired manipulation of gut microbiota in human patients.

A phenome-wide association study (PheWAS) to identify the health impacts of 4-cresol sulfate in the Nagahama Study

Gut-microbiota derived metabolites are important regulators of host biology and metabolism. To understand the impacts of the microbial metabolite 4-cresol sulfate (4-CS) on four chronic diseases [type 2 diabetes mellitus, metabolic syndrome (MetS), non-alcoholic fatty liver disease, and chronic kidney disease (CKD)], we conducted association analyses of plasma 4-CS quantified by liquid chromatography coupled to mass spectrometry (LC-MS) in 3641 participants of the Nagahama study. Our results validated the elevation of 4-CS in CKD and identified a reducing trend in MetS. To delineate the holistic effects of 4-CS, we performed a phenome-wide association analysis (PheWAS) with 937 intermediate biological and behavioral traits. We detected associations between 4-CS and 39 phenotypes related to blood pressure regulation, hepatic and renal functions, hematology, sleep quality, intraocular pressure, ion regulation, ketone and fatty acid metabolisms, disease history and dietary habits. Among them, 19 PheWAS significant traits, including fatty acids and 14 blood pressure indices, were correlated with MetS, suggesting that 4-CS is a potential biomarker for MetS. Consistent associations of this gut microbial-derived metabolite on multiple endophenotypes underlying distinct etiopathogenesis support its role in the overall host health, with prospects of probiotic-based therapeutic solutions in chronic diseases.

Hyperfructosemia in sleep disordered breathing: metabolome analysis of Nagahama study

Sleep disordered breathing (SDB), mainly obstructive sleep apnea (OSA), constitutes a major health problem due to the large number of patients. Intermittent hypoxia caused by SDB induces alterations in metabolic function. Nevertheless, metabolites characteristic for SDB are largely unknown. In this study, we performed gas chromatography-mass spectrometry-based targeted metabolome analysis using data from The Nagahama Study (n = 6373). SDB-related metabolites were defined based on their variable importance score in orthogonal partial least squares discriminant analysis and fold changes in normalized peak-intensity levels between moderate-severe SDB patients and participants without SDB. We identified 20 metabolites as SDB-related, and interestingly, these metabolites were frequently included in pathways related to fructose. Multivariate analysis revealed that moderate-severe SDB was a significant factor for increased plasma fructose levels (β = 0.210, P = 0.006, generalized linear model) even after the adjustment of confounding factors. We further investigated changes in plasma fructose levels after continuous positive airway pressure (CPAP) treatment using samples from patients with OSA (n = 60) diagnosed by polysomnography at Kyoto University Hospital, and found that patients with marked hypoxemia exhibited prominent hyperfructosemia and their plasma fructose levels lowered after CPAP treatment. These data suggest that hyperfructosemia is the abnormality characteristic to SDB, which can be reduced by CPAP treatment.

Are gut dysbiosis, barrier disruption, and endotoxemia related to adipose tissue dysfunction in metabolic disorders? Overview of the mechanisms involved

Recently, compelling evidence points to dysbiosis and disruption of the epithelial intestinal barrier as major players in the pathophysiology of metabolic disorders, such as obesity. Upon the intestinal barrier disruption, components from bacterial metabolism and bacteria itself can reach peripheral tissues through circulation. This has been associated with the low-grade inflammation that characterizes obesity and other metabolic diseases. While circulating bacterial DNA has been postulated as a common feature of obesity and even type 2 diabetes, almost no focus has been given to the existence and effects of bacteria in peripheral tissues, namely the adipose tissue. As a symbiont population, it is expected that gut microbiota modulate the immunometabolism of the host, thus influencing energy balance mechanisms and inflammation. Gut inflammatory signals cause direct deleterious inflammatory responses in adipose tissue and may also affect key gut neuroendocrine mechanisms governing nutrient sensing and energy balance, like incretins and ghrelin, which play a role in the gut-brain-adipose tissue axis. Thus, it is of major importance to disclose how gut microbiota and derived signals modulate neuroendocrine and inflammatory pathways, which contribute to the dysfunction of adipose tissue and to the metabolic sequelae of obesity and related disorders. This review summarizes the current knowledge regarding these topics and identifies new perspectives in this field of research, highlighting new pathways toward the reduction of the inflammatory burden of metabolic diseases.

Short-chain fatty acids, secondary bile acids and indoles: gut microbial metabolites with effects on enteroendocrine cell function and their potential as therapies for metabolic disease

The gastrointestinal tract hosts the largest ecosystem of microorganisms in the body. The metabolism of ingested nutrients by gut bacteria produces novel chemical mediators that can influence chemosensory cells lining the gastrointestinal tract. Specifically, hormone-releasing enteroendocrine cells which express a host of receptors activated by these bacterial metabolites. This review will focus on the activation mechanisms of glucagon-like peptide-1 releasing enteroendocrine cells by the three main bacterial metabolites produced in the gut: short-chain fatty acids, secondary bile acids and indoles. Given the importance of enteroendocrine cells in regulating glucose homeostasis and food intake, we will also discuss therapies based on these bacterial metabolites used in the treatment of metabolic diseases such as diabetes and obesity. Elucidating the mechanisms gut bacteria can influence cellular function in the host will advance our understanding of this fundamental symbiotic relationship and unlock the potential of harnessing these pathways to improve human health.

Microbial metabolite p-cresol inhibits gut hormone expression and regulates small intestinal transit in mice

p-cresol is a metabolite produced by microbial metabolism of aromatic amino acid tyrosine. p-cresol and its conjugated forms, p-cresyl sulfate and p-cresyl glucuronide, are uremic toxins that correlate positively with chronic kidney disease and diabetes pathogenesis. However, how p-cresol affects gut hormones is unclear. Here, we expose immortalized GLUTag cells to increasing concentrations of p-cresol and found that p-cresol inhibited Gcg expression and reduced glucagon-like peptide-1 (GLP-1) secretion in vitro. In mice, administration of p-cresol in the drinking water for 2 weeks reduced the transcript levels of Gcg and other gut hormones in the colon; however, it did not affect either fasting or glucose-induced plasma GLP-1 levels. Furthermore, it did not affect glucose tolerance but promoted faster small intestinal transit in mice. Overall, our data suggest that microbial metabolite p-cresol suppresses transcript levels of gut hormones and regulates small intestinal transit in mice.

Genetic influences on human blood metabolites in the Japanese population

An increase in ethnic diversity in genetic studies has the potential to provide unprecedented insights into how genetic variations influence human phenotypes. In this study, we conducted a quantitative trait locus (QTL) analysis of 121 metabolites measured using gas chromatography-mass spectrometry with plasma samples from 4,888 Japanese individuals. We found 60 metabolite-gene associations, of which 13 have not been previously reported. Meta-analyses with another Japanese and a European study identified six and two additional unreported loci, respectively. Genetic variants influencing metabolite levels were more enriched in protein-coding regions than in the regulatory regions while being associated with the risk of various diseases. Finally, we identified a signature of strong negative selection for uric acid ( S ˆ  = -1.53, p = 6.2 × 10^-18). Our study expanded the knowledge of genetic influences on human blood metabolites, providing valuable insights into their physiological, pathological, and selective properties.

Regeneration of Pancreatic β-Cells for Diabetes Therapeutics by Natural DYRK1A Inhibitors

The pathogenesis of diabetes mellitus is characterized by insulin resistance and islet β-cell dysfunction. Up to now, the focus of diabetes treatment has been to control blood glucose to prevent diabetic complications. There is an urgent need to develop a therapeutic approach to restore the mass and function of β-cells. Although exogenous islet cell transplantation has been used to help patients control blood glucose, it is costly and has very narrow application scenario. So far, small molecules have been reported to stimulate β-cell proliferation and expand β-cell mass, increasing insulin secretion. Dual-specificity tyrosine-regulated kinase 1A (DYRK1A) inhibitors can induce human β-cell proliferation in vitro and in vivo, and show great potential in the field of diabetes therapeutics. From this perspective, we elaborated on the mechanism by which DYRK1A inhibitors regulate the proliferation of pancreatic β-cells, and summarized several effective natural DYRK1A inhibitors, hoping to provide clues for subsequent structural optimization and drug development in the future.

In vivo drug discovery for increasing incretin-expressing cells identifies DYRK inhibitors that reinforce the enteroendocrine system

Analogs of the incretin hormones Gip and Glp-1 are used to treat type 2 diabetes and obesity. Findings in experimental models suggest that manipulating several hormones simultaneously may be more effective. To identify small molecules that increase the number of incretin-expressing cells, we established a high-throughput in vivo chemical screen by using the gip promoter to drive the expression of luciferase in zebrafish. All hits increased the numbers of neurogenin 3-expressing enteroendocrine progenitors, Gip-expressing K-cells, and Glp-1-expressing L-cells. One of the hits, a dual-specificity tyrosine phosphorylation-regulated kinase (DYRK) inhibitor, additionally decreased glucose levels in both larval and juvenile fish. Knock-down experiments indicated that nfatc4, a downstream mediator of DYRKs, regulates incretin+ cell number in zebrafish, and that Dyrk1b regulates Glp-1 expression in an enteroendocrine cell line. DYRK inhibition also increased the number of incretin-expressing cells in diabetic mice, suggesting a conserved reinforcement of the enteroendocrine system, with possible implications for diabetes.

Gut microbiota-derived metabolites as key actors in type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is one of the most risk factors threatening human health. Although genetic and environmental factors contribute to the development of T2DM, gut microbiota has also been found to be involved. Gut microbiota-derived metabolites are a key factor in host-microbe crosstalk, and have been revealed to play a central role in the physiology and physiopathology of T2DM. In this review, we provide a timely and comprehensive summary of the microbial metabolites that are protective or causative for T2DM, including some amino acids-derived metabolites, short-chain fatty acids, trimethylamine N-oxide, and bile acids. The mechanisms by which metabolites affect T2DM have been elaborated. Knowing more about these processes will increase our understanding of the causal relationship between gut microbiota and T2DM. Moreover, some frontier therapies that target gut microbes and their metabolites to improve T2DM, including dietary intervention, fecal microbiota transplantation, probiotics, prebiotics or synbiotics intervention, and drugging microbial metabolism, have been critically discussed. This review may provide novel insights for the development of targeted and personalized treatments for T2DM based on gut microbial metabolites. More high-quality clinical trials are needed to accelerate the clinical translation of gut-targeted therapies for T2DM.

Role of the Gut Microbiome in Beta Cell and Adipose Tissue Crosstalk: A Review

In the last decades, obesity has reached epidemic proportions worldwide. Obesity is a chronic disease associated with a wide range of comorbidities, including insulin resistance and type 2 diabetes mellitus (T2D), which results in significant burden of disease and major consequences on health care systems. Of note, intricate interactions, including different signaling pathways, are necessary for the establishment and progression of these two closely related conditions. Altered cell-to-cell communication among the different players implicated in this equation leads to the perpetuation of a vicious circle associated with an increased risk for the development of obesity-related complications, such as T2D, which in turn contributes to the development of cardiovascular disease. In this regard, the dialogue between the adipocyte and pancreatic beta cells has been extensively studied, although some connections are yet to be fully elucidated. In this review, we explore the potential pathological mechanisms linking adipocyte dysfunction and pancreatic beta cell impairment/insulin resistance. In addition, we evaluate the role of emerging actors, such as the gut microbiome, in this complex crosstalk.

Diet dependent impact of benzoate on diabetes and obesity in mice

The gut microbiota contributes to mammalian host biology by supplying metabolites from nutrients and pro-inflammatory molecules. We have recently shown that urinary hippurate is associated with reduced risk of obesity, increased gut microbiome diversity and gene richness, and functional modules for microbial production of its precursor benzoate. Obese mice infused with hippurate exhibit profound alterations of glucose homeostasis. Here, we tested the biological effects of chronic administration of benzoate on cardiometabolic phenotypes in lean and obese mice. Benzoate induced glucose intolerance, enhanced insulin secretion, increased adiposity and stimulated liver inflammation in lean mice fed control diet. In contrast, in condition of obesity and diabetes induced by high fat diet feeding, benzoate infusion resulted in reduction of glucose intolerance, stimulation of both glucose-induced insulin secretion and β-cell proliferation, and reduction of liver triglyceride and collagen accumulation. These results combined with those previously obtained in mice treated with hippurate underline the importance of the benzoate-hippurate pathway in cardiometabolic diseases and pave the way to diagnostic and therapeutic solutions.

Human and preclinical studies of the host-gut microbiome co-metabolite hippurate as a marker and mediator of metabolic health

OBJECTIVE

Gut microbial products are involved in regulation of host metabolism. In human and experimental studies, we explored the potential role of hippurate, a hepatic phase 2 conjugation product of microbial benzoate, as a marker and mediator of metabolic health.

DESIGN

In 271 middle-aged non-diabetic Danish individuals, who were stratified on habitual dietary intake, we applied ¹H-nuclear magnetic resonance (NMR) spectroscopy of urine samples and shotgun-sequencing-based metagenomics of the gut microbiome to explore links between the urine level of hippurate, measures of the gut microbiome, dietary fat and markers of metabolic health. In mechanistic experiments with chronic subcutaneous infusion of hippurate to high-fat-diet-fed obese mice, we tested for causality between hippurate and metabolic phenotypes.

RESULTS

In the human study, we showed that urine hippurate positively associates with microbial gene richness and functional modules for microbial benzoate biosynthetic pathways, one of which is less prevalent in the Bacteroides 2 enterotype compared with Ruminococcaceae or Prevotella enterotypes. Through dietary stratification, we identify a subset of study participants consuming a diet rich in saturated fat in which urine hippurate concentration, independently of gene richness, accounts for links with metabolic health. In the high-fat-fed mice experiments, we demonstrate causality through chronic infusion of hippurate (20 nmol/day) resulting in improved glucose tolerance and enhanced insulin secretion.

CONCLUSION

Our human and experimental studies show that a high urine hippurate concentration is a general marker of metabolic health, and in the context of obesity induced by high-fat diets, hippurate contributes to metabolic improvements, highlighting its potential as a mediator of metabolic health.

Molecular Aspects of Lifestyle and Environmental Effects in Patients With Diabetes: JACC Focus Seminar

Diabetes is characterized as an integrated condition of dysregulated metabolism across multiple tissues, with well-established consequences on the cardiovascular system. Recent advances in precision phenotyping in biofluids and tissues in large human observational and interventional studies have afforded a unique opportunity to translate seminal findings in models and cellular systems to patients at risk for diabetes and its complications. Specifically, techniques to assay metabolites, proteins, and transcripts, alongside more recent assessment of the gut microbiome, underscore the complexity of diabetes in patients, suggesting avenues for precision phenotyping of risk, response to intervention, and potentially novel therapies. In addition, the influence of external factors and inputs (eg, activity, diet, medical therapies) on each domain of molecular characterization has gained prominence toward better understanding their role in prevention. Here, the authors provide a broad overview of the role of several of these molecular domains in human translational investigation in diabetes.

Impacts of lipid-related metabolites, adiposity, and genetic background on blood eosinophil counts: the Nagahama study

Blood eosinophil count is a useful measure in asthma or COPD management. Recent epidemiological studies revealed that body mass index (BMI) is positively associated with eosinophil counts. However, few studies focused on the role of adiposity and fatty acid-related metabolites on eosinophil counts, including the effect of genetic polymorphism. In this community-based study involving 8265 participants (30-74 year old) from Nagahama city, we investigated the relationship between eosinophil counts and serum levels of fatty acid-related metabolites. The role of MDC1, a gene that is related to eosinophil counts in our previous study and encodes a protein that is thought to be involved in the repair of deoxyribonucleic acid damage, was also examined taking into account its interaction with adiposity. Serum levels of linoleic acid (LA) and β-hydroxybutyric acid (BHB) were negatively associated with eosinophil counts after adjustment with various confounders; however, there were positive interactions between serum LA and BMI and between serum BHB and BMI/body fat percentages in terms of eosinophil counts. In never-smokers, there was positive interaction for eosinophil counts between the CC genotype of MDC1 rs4713354 and BMI/body fat percentages. In conclusion, both serum LA and BHB have negative impacts on eosinophil counts, while adiposity shows robust positive effects on eosinophil counts, partly via genetic background in never-smokers.

Dual-Specificity, Tyrosine Phosphorylation-Regulated Kinases (DYRKs) and cdc2-Like Kinases (CLKs) in Human Disease, an Overview

Dual-specificity tyrosine phosphorylation-regulated kinases (DYRK1A, 1B, 2-4) and cdc2-like kinases (CLK1-4) belong to the CMGC group of serine/threonine kinases. These protein kinases are involved in multiple cellular functions, including intracellular signaling, mRNA splicing, chromatin transcription, DNA damage repair, cell survival, cell cycle control, differentiation, homocysteine/methionine/folate regulation, body temperature regulation, endocytosis, neuronal development, synaptic plasticity, etc. Abnormal expression and/or activity of some of these kinases, DYRK1A in particular, is seen in many human nervous system diseases, such as cognitive deficits associated with Down syndrome, Alzheimer's disease and related diseases, tauopathies, dementia, Pick's disease, Parkinson's disease and other neurodegenerative diseases, Phelan-McDermid syndrome, autism, and CDKL5 deficiency disorder. DYRKs and CLKs are also involved in diabetes, abnormal folate/methionine metabolism, osteoarthritis, several solid cancers (glioblastoma, breast, and pancreatic cancers) and leukemias (acute lymphoblastic leukemia, acute megakaryoblastic leukemia), viral infections (influenza, HIV-1, HCMV, HCV, CMV, HPV), as well as infections caused by unicellular parasites (Leishmania, Trypanosoma, Plasmodium). This variety of pathological implications calls for (1) a better understanding of the regulations and substrates of DYRKs and CLKs and (2) the development of potent and selective inhibitors of these kinases and their evaluation as therapeutic drugs. This article briefly reviews the current knowledge about DYRK/CLK kinases and their implications in human disease.

Roles of Gut Microbial Metabolites in Diabetic Kidney Disease

Diabetes is a highly prevalent metabolic disease that has emerged as a global challenge due to its increasing prevalence and lack of sustainable treatment. Diabetic kidney disease (DKD), which is one of the most frequent and severe microvascular complications of diabetes, is difficult to treat with contemporary glucose-lowering medications. The gut microbiota plays an important role in human health and disease, and its metabolites have both beneficial and harmful effects on vital physiological processes. In this review, we summarize the current findings regarding the role of gut microbial metabolites in the development and progression of DKD, which will help us better understand the possible mechanisms of DKD and explore potential therapeutic approaches for DKD.

Multi-compartment metabolomics and metagenomics reveal major hepatic and intestinal disturbances in cancer cachectic mice

BACKGROUND

Cancer cachexia is a multifactorial syndrome characterized by multiple metabolic dysfunctions. Besides the muscle, other organs such as the liver and the gut microbiota may also contribute to this syndrome. Indeed, the gut microbiota, an important regulator of the host metabolism, is altered in the C26 preclinical model of cancer cachexia. Interventions targeting the gut microbiota have shown benefits, but mechanisms underlying the host-microbiota crosstalk in this context are still poorly understood.

METHODS

To explore this crosstalk, we combined proton nuclear magnetic resonance (¹ H-NMR) metabolomics in multiple compartments with 16S rDNA sequencing. These analyses were complemented by molecular and biochemical analyses, as well as hepatic transcriptomics.

RESULTS

¹ H-NMR revealed major changes between control (CT) and cachectic (C26) mice in the four analysed compartments (i.e. caecal content, portal vein, liver, and vena cava). More specifically, glucose metabolism pathways in the C26 model were altered with a reduction in glycolysis and gluconeogenesis and an activation of the hexosamine pathway, arguing against the existence of a Cori cycle in this model. In parallel, amino acid uptake by the liver, with an up to four-fold accumulation of nine amino acids (q-value <0.05), was mainly used for acute phase response proteins synthesis rather than to fuel the tricarboxylic acid cycle and gluconeogenesis. We also identified a 35% reduction in hepatic carnitine levels (q-value <0.05) and a lower activation of the phosphatidylcholine pathway as potential contributors to the hepatic steatosis present in this model. Our work also reveals a reduction of different beneficial intestinal bacterial activities in cancer cachexia. We found decreased levels of two short-chain fatty acids, acetate and butyrate (72% and 88% reduction in C26 caecal content; q-value <0.001), and a reduction in aromatic amino acid metabolites, which may contribute to the altered intestinal homeostasis in these mice. A member of the Ruminococcaceae family (ASV 2) was identified as the main bacterium responsible for the drop in butyrate. Finally, we report a two-fold intestinal transit acceleration (P-value <0.001) as a key factor shaping the gut microbiota composition and activity in cancer cachexia, which together lead to a faecal loss of proteins and amino acids.

CONCLUSIONS

Our work highlights new metabolic pathways potentially involved in cancer cachexia and further supports the interest of exploring the gut microbiota composition and activity, as well as intestinal transit, in cancer patients with and without cachexia.

Current innovations in nutraceuticals and functional foods for intervention of non-alcoholic fatty liver disease

As innovations in global agricultural production and food trading systems lead to major dietary shifts, high morbidity rates from non-alcoholic fatty liver disease (NAFLD), accompanied by elevated risk of lipid metabolism-related complications, has emerged as a growing problem worldwide. Treatment and prevention of NAFLD and chronic liver disease depends on the availability of safe, effective, and diverse therapeutic agents, the development of which is urgently needed. Supported by a growing body of evidence, considerable attention is now focused on interventional approaches that combines nutraceuticals and functional foods. In this review, we summarize the pathological progression of NAFLD and discuss the beneficial effects of nutraceuticals and the active ingredients in functional foods. We also describe the underlying mechanisms of these compounds in the intervention of NAFLD, including their effects on regulation of lipid homeostasis, activation of signaling pathways, and their role in gut microbial community dynamics and the gut-liver axis. In order to identify novel targets for treatment of lipid metabolism-related diseases, this work broadly explores the molecular mechanism linking nutraceuticals and functional foods, host physiology, and gut microbiota. Additionally, the limitations in existing knowledge and promising research areas for development of active interventions and treatments against NAFLD are discussed.

The role of bacterial metabolites derived from aromatic amino acids in non-alcoholic fatty liver disease

The review deals with the role of aromatic amino acids and their microbial metabolites in the development and progression of non-alcoholic fatty liver disease (NAFLD). Pathological changes typical for NAFLD, as well as abnormal composition and/or functional activity of gut microbiota, results in abnormal aromatic amino acid metabolism. The authors discuss the potential of these amino acids and their bacterial metabolites to produce both negative and positive impact on the main steps of NAFLD pathophysiology, such as lipogenesis and inflammation, as well as on the liver functions through regulation of the intestinal barrier and microbiota-gut-liver axis signaling. The review gives detailed description of the mechanism of biological activity of tryptophan and its derivatives (indole, tryptamine, indole-lactic, indole-propyonic, indole-acetic acids, and indole-3-aldehyde) through the activation of aryl hydrocarbon receptor (AhR), preventing the development of liver steatosis. Bacteria-produced phenyl-alanine metabolites could promote liver steatosis (phenyl acetic and phenyl lactic acids) or, on the contrary, could reduce liver inflammation and increase insulin sensitivity (phenyl propionic acid). Tyramine, para-cumarate, 4-hydroxyphenylacetic acids, being by-products of bacterial catabolism of tyrosine, can prevent NAFLD, whereas para-cresol and phenol accelerate the progression of NAFLD by damaging the barrier properties of intestinal epithelium. Abnormalities in bacterial catabolism of tyrosine, leading to its excess, stimulate fatty acid synthesis and promote lipid infiltration of the liver. The authors emphasize a close interplay between bacterial metabolism of aromatic amino acids by gut microbiota and the functioning of the human body. They hypothesize that microbial metabolites of aromatic amino acids may represent not only therapeutic targets or non-invasive biomarkers, but also serve as bioactive agents for NAFLD treatment and prevention.

Mendelian Randomization Study on Amino Acid Metabolism Suggests Tyrosine as Causal Trait for Type 2 Diabetes

Circulating levels of branched-chain amino acids, glycine, or aromatic amino acids have been associated with risk of type 2 diabetes. However, whether those associations reflect causal relationships or are rather driven by early processes of disease development is unclear. We selected diabetes-related amino acid ratios based on metabolic network structures and investigated causal effects of these ratios and single amino acids on the risk of type 2 diabetes in two-sample Mendelian randomization studies. Selection of genetic instruments for amino acid traits relied on genome-wide association studies in a representative sub-cohort (up to 2265 participants) of the European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam Study and public data from genome-wide association studies on single amino acids. For the selected instruments, outcome associations were drawn from the DIAGRAM (DIAbetes Genetics Replication And Meta-analysis, 74,124 cases and 824,006 controls) consortium. Mendelian randomization results indicate an inverse association for a per standard deviation increase in ln-transformed tyrosine/methionine ratio with type 2 diabetes (OR = 0.87 (0.81-0.93)). Multivariable Mendelian randomization revealed inverse association for higher log10-transformed tyrosine levels with type 2 diabetes (OR = 0.19 (0.04-0.88)), independent of other amino acids. Tyrosine might be a causal trait for type 2 diabetes independent of other diabetes-associated amino acids.

Intestinal microbial metabolites in human metabolism and type 2 diabetes

Humans with the metabolic syndrome and type 2 diabetes have an altered gut microbiome. Emerging evidence indicates that it is not only the microorganisms and their structural components, but also their metabolites that influences the host and contributes to the development of the metabolic syndrome and type 2 diabetes. Here, we discuss some of the mechanisms underlying how microbial metabolites are recognised by the host or are further processed endogenously in the context of type 2 diabetes. We discuss the possibility that gut-derived microbial metabolites fuel the development of the metabolic syndrome and type 2 diabetes. Graphical abstract.

Red rice koji extract alleviates hyperglycemia by increasing glucose uptake and glucose transporter type 4 levels in skeletal muscle in two diabetic mouse models

Background

Red rice koji (RRK), prepared by growing Monascus species on steamed rice, has been reported to lower blood glucose levels in diabetic animal models. However, the action mechanism is not yet completely understood.

Objective

The objective of this study was to examine the mechanism underlying the hypoglycemic action of RRK extract in two diabetic animal models: the insulin-deficiency mice, where the insulin deficiency was induced by streptozotocin (STZ), and insulin-resistance mice, where the insulin resistance was induced by a high-fat diet (HFD).

Design

Low (12.5 mg/kg body weight [BW]) and high (50.0 mg/kg BW) doses of RRK extract were orally administered to the mice for 10 successive days (0.25 mL/day/mouse). The protein expression levels of glucose transporter type 4 (GLUT4) in the skeletal muscle and glucose transporter type 2 (GLUT2) in the liver were measured. Blood glucose (BG) levels of STZ-treated mice in insulin tolerance test (ITT) and BG and insulin levels of HFD-fed mice in intraperitoneal glucose tolerance test (IPGTT) were investigated.

Results

In the STZ-treated mice, oral administration of RRK extract lowered BG levels and food intake but increased plasma 1,5-anhydroglucitol level. Moreover, the RRK extract lowered the BG levels of STZ-treated mice as measured by ITT. In the HFD-fed mice, we confirmed that the orally administered RRK extract lowered the BG and the homeostasis model assessment index for insulin resistance. Furthermore, the RRK extract lowered the BG and insulin levels of HFD-fed mice in IPGTT. Regarding the protein levels of GLUT, the orally administered RRK extract increased the GLUT4 level in the skeletal muscle; however, the RRK extract did not alter the GLUT2 level in the liver of either the STZ-treated or the HFD-fed mice.

Discussion

Our study demonstrates that RRK extract can improve impaired glucose tolerance in mouse models of diabetes by enhancing GLUT4 expression in skeletal muscle.

Conclusion

These results suggest that RRK extract could potentially be a functional food for the treatment of diabetes mellitus.

Implication of the Gut Microbiota in Metabolic Inflammation Associated with Nutritional Disorders and Obesity

SCOPE

More than a decade ago, the concept of "metabolic endotoxemia" is elaborated on the fact that some bacterial components, classified as microbial associated membrane pathogens (MAMPs) can pass through the gut barrier and create a systemic low tone inflammation.

METHODS AND RESULTS

The translocation of lipopolysaccharides and its contribution to systemic inflammation are largely studied in murine models of obesity, allowing to unravel the molecular pathways involved in the process. Many different pathological contexts evoke the loss of gut barrier as an event contributing to inflammation and thereby driving metabolic and behavioral alterations.

CONCLUSION

This review describes the role of nutrition as a modulator of metabolic regulation and focuses on the contribution of the gut microbiota in the process of the production of a large diversity of bioactive metabolites. The two first sections of the review will be dedicated to the impact of nutritional disorders on both the gut microbiota composition and on metabolic inflammation. The last and more prominent section will describe the role of different nutrient-derived gut metabolites on the gut barrier integrity, metabolic inflammation, and peripheral tissue alterations during obesity or associated complications.

Plasma Metabolites Related to Peripheral and Hepatic Insulin Sensitivity Are Not Directly Linked to Gut Microbiota Composition

Plasma metabolites affect a range of metabolic functions in humans, including insulin sensitivity (IS). A subset of these plasma metabolites is modified by the gut microbiota. To identify potential microbial–metabolite pathways involved in IS, we investigated the link between plasma metabolites, gut microbiota composition, and IS, using the gold-standard for peripheral and hepatic IS measurement in a group of participants with metabolic syndrome (MetSyn). In a cross-sectional study with 115 MetSyn participants, fasting plasma samples were collected for untargeted metabolomics analysis and fecal samples for 16S rRNA gene amplicon sequencing. A two-step hyperinsulinemic euglycemic clamp was performed to assess peripheral and hepatic IS. Collected data were integrated and potential interdependence between metabolites, gut microbiota, and IS was analyzed using machine learning prediction models. Plasma metabolites explained 13.2% and 16.7% of variance in peripheral and hepatic IS, respectively. Fecal microbiota composition explained 4.2% of variance in peripheral IS and was not related to hepatic IS. Although metabolites could partially explain the variances in IS, the top metabolites related to peripheral and hepatic IS did not significantly correlate with gut microbiota composition (both on taxonomical level and alpha-diversity). However, all plasma metabolites could explain 18.5% of the variance in microbial alpha-diversity (Shannon); the top 20 metabolites could even explain 44.5% of gut microbial alpha-diversity. In conclusion, plasma metabolites could partially explain the variance in peripheral and hepatic IS; however, these metabolites were not directly linked to the gut microbiota composition, underscoring the intricate relation between plasma metabolites, the gut microbiota, and IS in MetSyn