Insulin regulation of gluconeogenesis

Oxyberberine Inhibits Hepatic Gluconeogenesis via AMPK-Mediated Suppression of FoxO1 and CRTC2 Signaling Axes

Oxyberberine (OBB), a natural metabolite of berberine, has been shown to exhibit inhibitory effects on gluconeogenesis in our previous work. This work was designed to investigate the potential effects and underlying mechanisms of OBB on hepatic gluconeogenesis. Our work found that OBB significantly inhibited the expressions of glucose 6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK), and decreased the glucose production in palmitic acid-induced HepG2 cells. Then, AMPK/Akt/FoxO1 and AMPK/CRTC2 signaling pathways were confirmed by transcriptomics and network pharmacology analyses. It was shown that AMPK activation may phosphorylate and promote nuclear exclusion of FoxO1 and CRTC2, two key regulators of hepatic gluconeogenesis transcriptional pathways, resulting in the inhibition of gluconeogenesis under OBB administration. Afterwards, AMPK/Akt/FoxO1, AMPK/CRTC2 signaling pathways were evidenced by western blot, immunoprecipitation and confocal immunofluorescence, and the targeted inhibitor (Compound C) and siRNA of AMPK were applied for further mechanism verification. Moreover, it was found that OBB treatment activated AMPK/Akt/FoxO1 and AMPK/CRTC2 signaling pathways to decrease hepatic gluconeogenesis in db/db mice. Similarly, the in vivo inhibitory effects of OBB on gluconeogenesis were also diminished by AMPK inhibition. Our work demonstrated that OBB can inhibit hepatic gluconeogenesis in vitro and in vivo, and its underlying mechanisms were associated with AMPK-mediated suppression of FoxO1 and CRTC2 signaling axes.

"NO" controversy?: A controversial role in insulin signaling of diabetic encephalopathy

Insulin, a critical hormone in the human body, exerts its effects by binding to insulin receptors and regulating various cellular processes. While nitric oxide (NO) plays an important role in insulin secretion and acts as a mediator in the signal transduction pathway between upstream molecules and downstream effectors, holds a significant position in the downstream signal network of insulin. Researches have shown that the insulin-NO system exhibits a dual regulatory effect within the central nervous system, which is crucial in the regulation of diabetic encephalopathy (DE). Understanding this system holds immense practical importance in comprehending the targets of existing drugs and the development of potential therapeutic interventions. This review extensively examines the characterization of insulin, NO, Nitric oxide synthase (NOS), specific NO pathway, their interconnections, and the mechanisms underlying their regulatory effects in DE, providing a reference for new therapeutic targets of DE.

The role of glucose-6-phosphatase activity in glucose homeostasis and its potential for diabetes therapy

Glucose-6-phosphatase catalytic subunit (G6PC)1 and G6PC2 are crucial for glucose metabolism, regulating processes like glycolysis, gluconeogenesis, and glycogenolysis. Despite their structural and functional similarities, G6PC1 and G6PC2 exhibit distinct tissue-specific expression patterns, G6P hydrolysis kinetics, and physiological functions. This review provides a comprehensive overview of their enzymology and distinct roles in glucose homeostasis. We examine how inactivating mutations in G6PC1 lead to glycogen storage disease, and how elevated G6PC1 and G6PC2 expression can affect the incidence of diabetic complications, risk for type 2 diabetes mellitus (T2DM) and various cancers. We also discuss the potential of inhibiting G6PC1 and G6PC2 to protect against complications from elevated blood glucose levels, and highlight drug development efforts targeting G6PC1 and G6PC2, and the therapeutic potential of inhibitors for disease prevention.

Light modulates glucose and lipid homeostasis via the sympathetic nervous system

Light is an important environmental factor for vision, and for diverse physiological and psychological functions. Light can also modulate glucose metabolism. Here, we show that in mice, light is critical for glucose and lipid homeostasis by regulating the sympathetic nervous system, independent of circadian disruption. Light deprivation from birth elicits insulin hypersecretion, glucagon hyposecretion, lower gluconeogenesis, and reduced lipolysis by 6-8 weeks, in male, but not, female mice. These metabolic defects are consistent with blunted sympathetic activity, and indeed, sympathetic responses to a cold stimulus are significantly attenuated in dark-reared mice. Further, long-term dark rearing leads to body weight gain, insulin resistance, and glucose intolerance. Notably, metabolic dysfunction can be partially alleviated by 5 weeks exposure to a regular light-dark cycle. These studies provide insight into circadian-independent mechanisms by which light directly influences whole-body physiology and inform new approaches for understanding metabolic disorders linked to aberrant environmental light conditions.

Patients with chronic liver diseases are at risk for diabetes even before development of cirrhosis

BACKGROUND AND AIMS

The prevalence of insulin resistance (IR) and type 2 diabetes mellitus (T2DM) is higher in patients with cirrhosis, compared to control patients without liver disease. The exact mechanism for this is unknown but could include liver inflammation. In this study we investigate whether cirrhosis is the primum movens of IR or if impaired insulin sensitivity is already present in non-cirrhotic patients with chronic liver diseases.

METHODS

Patients were recruited and divided into three groups: control (CTL), chronic liver disease without cirrhosis (CLD) and cirrhosis (CIR). In patients not taking pharmacological treatment for T2DM, IR was quantified using the homeostasis model assessment of insulin resistance (HOMA-IR). The proportion of patients with T2DM as well as HOMA-IR levels among different disease etiologies were recorded and compared.

RESULTS

532 patients were included in our study. Median glycemia and insulinemia and therefore HOMA-IR values were significantly different between the three cohorts (p-value <0.001): IR levels in CLD subjects lie between those seen in CTL and CIR subjects. The proportion of diabetic patients in the two case categories also differs (p-value = 0.027): one quarter of CLD subjects and one third of CIR patients suffer from T2DM. Finally, HOMA-IR levels vary according to disease etiology (p-value <0.001): metabolic steatosis and chronic viral hepatitis C are at greater risk than alcohol and other disease causes.

CONCLUSION

CLD is already a predisposing factor to T2DM, regardless of the presence of CIR. CIR is a factor which elicits additional increase in insulin levels. Metabolic steatosis and hepatitis C are associated with more severe IR.

NAFLD-associated hepatocellular carcinoma (HCC) - A compelling case for repositioning of existing mTORc1 inhibitors

The increasing prevalence of non-alcoholic fatty liver disease (NAFLD) is a growing concern for the high incidence rate of hepatocellular carcinoma (HCC) globally. The progression of NAFLD to HCC is heterogeneous and non-linear, involving intermediate stages of non-alcoholic steatohepatitis (NASH), liver fibrosis, and cirrhosis. There is a high unmet clinical need for appropriate diagnostic, prognostic, and therapeutic options to tackle this emerging epidemic. Unfortunately, at present, there is no validated marker to identify the risk of developing HCC in patients suffering from NAFLD or NASH. Additionally, the current treatment protocols for HCC don't differentiate between viral infection or NAFLD-specific etiology of the HCC and have a limited success rate. The mammalian target of rapamycin complex 1 (mTORc1) is an important protein involved in many vital cellular processes like lipid metabolism, glucose homeostasis, and inflammation. These cellular processes are highly implicated in NAFLD and its progression to severe liver manifestations. Additionally, hyperactivation of mTORc1 is known to promote cell proliferation, which can contribute to the genesis and progression of tumors. Many mTORc1 inhibitors are being evaluated for different types of cancers under various phases of clinical trials. This paper deliberates on the strong pathological implication of the mTORc1 signaling pathway in NAFLD and its progression to NASH and HCC and advocates for a systematic investigation of known mTORc1 inhibitors in suitable pre-clinical models of HCC having NAFLD/NASH-specific etiology.

The post-translational modification O-GlcNAc is a sensor and regulator of metabolism

Cells must rapidly adapt to changes in nutrient conditions through responsive signalling cascades to maintain homeostasis. One of these adaptive pathways results in the post-translational modification of proteins by O-GlcNAc. O-GlcNAc modifies thousands of nuclear and cytoplasmic proteins in response to nutrient availability through the hexosamine biosynthetic pathway. O-GlcNAc is highly dynamic and can be added and removed from proteins multiple times throughout their life cycle, setting it up to be an ideal regulator of cellular processes in response to metabolic changes. Here, we describe the link between cellular metabolism and O-GlcNAc, and we explore O-GlcNAc's role in regulating cellular processes in response to nutrient levels. Specifically, we discuss the mechanisms of elevated O-GlcNAc levels in contributing to diabetes and cancer, as well as the role of decreased O-GlcNAc levels in neurodegeneration. These studies form a foundational understanding of aberrant O-GlcNAc in human disease and provide an opportunity to further improve disease identification and treatment.

LRP1 facilitates hepatic glycogenesis by improving the insulin signaling pathway in HFD-fed mice

BACKGROUND

LDL receptor-related protein-1 (LRP1) is a cell-surface receptor that functions in diverse physiological pathways. We previously demonstrated that hepatocyte-specific LRP1 deficiency (hLRP1KO) promotes diet-induced insulin resistance and increases hepatic gluconeogenesis in mice. However, it remains unclear whether LRP1 regulates hepatic glycogenesis.

METHODS

Insulin signaling, glycogenic gene expression, and glycogen content were assessed in mice and HepG2 cells. The pcDNA 3.1 plasmid and adeno-associated virus serotype 8 vector (AAV8) were used to overexpress the truncated β-chain (β∆) of LRP1 both in vitro and in vivo.

RESULTS

On a normal chow diet, hLRP1KO mice exhibited impaired insulin signaling and decreased glycogen content. Moreover, LRP1 expression in HepG2 cells was significantly repressed by palmitate in a dose- and time-dependent manner. Both LRP1 knockdown and palmitate treatment led to reduced phosphorylation of Akt and GSK3β, increased levels of phosphorylated glycogen synthase (GYS), and diminished glycogen synthesis in insulin-stimulated HepG2 cells, which was restored by exogenous expression of the β∆-chain. By contrast, AAV8-mediated hepatic β∆-chain overexpression significantly improved the insulin signaling pathway, thus activating glycogenesis and enhancing glycogen storage in the livers of high-fat diet (HFD)-fed mice.

CONCLUSION

Our data revealed that LRP1, especially its β-chain, facilitates hepatic glycogenesis by improving the insulin signaling pathway, suggesting a new therapeutic strategy for hepatic insulin resistance-related diseases.

Time and dose selective glucose metabolism for glucose homeostasis and energy conversion in the liver

Hepatic glucose metabolism serves dual purposes: maintaining glucose homeostasis and converting glucose into energy sources; however, the underlying mechanisms are unclear. We quantitatively measured liver metabolites, gene expression, and phosphorylated insulin signaling molecules in mice orally administered varying doses of glucose, and constructed a transomic network. Rapid phosphorylation of insulin signaling molecules in response to glucose intake was observed, in contrast to the more gradual changes in gene expression. Glycolytic and gluconeogenic metabolites and expression of genes involved in glucose metabolism including glucose-6-phosphate, G6pc, and Pck1, demonstrated high glucose dose sensitivity. Whereas, glucokinase expression and glycogen accumulation showed low glucose dose sensitivity. During the early phase after glucose intake, metabolic flux was geared towards glucose homeostasis regardless of the glucose dose but shifted towards energy conversion during the late phase at higher glucose doses. Our research provides a comprehensive view of time- and dose-dependent selective glucose metabolism.

Di (2-ethyl hexyl) phthalate and its metabolite-induced metabolic syndrome: a review of molecular mechanisms

OBJECTIVES

Metabolic disorders, as multifactorial disorders, are induced by genetic susceptibility and exposure to environmental chemicals. Di (2-ethyl hexyl) phthalate (DEHP), a ubiquitous plasticizer, is well known as an endocrine-disrupting chemical in living organisms. In recent decades, researchers have focused on the potential of DEHP and its main metabolite (Mono (2-ethylhexyl) phthalate) (MEHP) to induce metabolic disorders. In the present review, we aimed to summarize studies regarding DEHP and MEHP-induced Metabolic syndrome (MetS) as well as address the involved mechanisms.

METHODS

A search has been carried out in Google Scholar, PubMed, Scopus, and Web of Science databases using appropriate keywords including 'Metabolic syndrome' or 'Metabolic disorder' or 'Obesity' or 'Hyperglycemia' or 'Hyperlipidemia' or 'Hypertension' or 'Non-alcoholic fatty liver disease' and 'DEHP' or 'Di (2-ethyl hexyl) phthalate' or 'Bis(2-ethylhexyl) phthalate' or 'MEHP' or 'Mono (2-ethylhexyl) phthalate'. Studies were chosen based on inclusion and exclusion criteria. Inclusion criteria are in vitro, in vivo, epidemiological studies, and English-written studies. Exclusion criteria are lack of access to the full text of studies, editorial articles, review articles, and conference articles.

RESULTS

Animal studies indicate that DEHP and MEHP disrupt insulin hemostasis, increase glucose content, and induce hyperlipidemia and hypertension as well as obesity, which could lead to type 2 diabetes mellitus (T2DM) and cardiovascular disease (CVD). DEHP and its metabolite induce such effects directly through influence on nuclear receptors such as peroxisome proliferator-activated receptors (PPARs) or indirectly through reactive oxygen species (ROS) production. Both events led to the disruption of several molecular signaling pathways and subsequently metabolic syndrome (MetS). Furthermore, epidemiological studies showed that there was a correlation between DEHP metabolites levels and obesity, hyperglycemia, and hypertension.

CONCLUSIONS

According to studies, DEHP and its main metabolite have the potential to induce MetS by involving various molecular mechanisms. Epidemiological studies concerning the association of DEHP and MetS in humans are not sufficient. Therefore, more studies are needed in this regard.

The fate of pyruvate dictates cell growth by modulating cellular redox potential

Pyruvate occupies a central node in carbohydrate metabolism such that how it is produced and consumed can optimize a cell for energy production or biosynthetic capacity. This has been primarily studied in proliferating cells, but observations from the post-mitotic Drosophila fat body led us to hypothesize that pyruvate fate might dictate the rapid cell growth observed in this organ during development. Indeed, we demonstrate that augmented mitochondrial pyruvate import prevented cell growth in fat body cells in vivo as well as in cultured mammalian hepatocytes and human hepatocyte-derived cells in vitro. This effect on cell size was caused by an increase in the NADH/NAD+ ratio, which rewired metabolism toward gluconeogenesis and suppressed the biomass-supporting glycolytic pathway. Amino acid synthesis was decreased, and the resulting loss of protein synthesis prevented cell growth. Surprisingly, this all occurred in the face of activated pro-growth signaling pathways, including mTORC1, Myc, and PI3K/Akt. These observations highlight the evolutionarily conserved role of pyruvate metabolism in setting the balance between energy extraction and biomass production in specialized post-mitotic cells.

Gluconeogenesis unraveled: A proteomic Odyssey with machine learning

The metabolic pathway known as gluconeogenesis, which produces glucose from non-carbohydrate substrates, is essential for maintaining balanced blood sugar levels while fasting. It's extremely important to anticipate gluconeogenesis rates accurately to recognize metabolic disorders and create efficient treatment strategies. The implementation of deep learning and machine learning methods to forecast complex biological processes has been gaining popularity in recent years. The recognition of both the regulation of the pathway and possible therapeutic applications of proteins depends on accurate identification associated with their gluconeogenesis patterns. This article analyzes the uses of machine learning and deep learning models, to predict gluconeogenesis efficiency. The study also discusses the challenges that come with restricted data availability and model interpretability, as well as possible applications in personalized healthcare, metabolic disease treatment, and the discovery of drugs. The predictor utilizes statistics moments on the structures of gluconeogenesis and their enzymes, while Random Forest is utilized as a classifier to ensure the accuracy of this model in identifying the best outcomes. The method was validated utilizing the independent test, self-consistency, 10k fold cross-validations, and jackknife test which achieved 92.33 %, 91.87%, 87.88%, and 87.02%. An accurate prediction of gluconeogenesis has significant implications for understanding metabolic disorders and developing targeted therapies. This study contributes to the rising field of predictive biology by mixing algorithms for deep learning, and machine learning, with metabolic pathways.

Carthamus tinctorius L. (Safflower) Flower Extract Attenuates Hepatic Injury and Steatosis in a Rat Model of Type 2 Diabetes Mellitus via Nrf2-Dependent Hypoglycemic, Antioxidant, and Hypolipidemic Effects

This study aimed to examine the hepatic and anti-steatotic protective effects of methanolic extract from Carthamus tinctorius (safflower) flowers (SFFE), using a rat model of type 2 diabetes mellitus (T2DM), and to examine the molecular mechanisms underlying these effects. Adult male Wistar rats were used for this study. First, T2DM was induced in some rats by feeding them a high-fat diet (HFD) for 4 weeks, followed by a single dose of streptozotocin (STZ) (35 mg/kg, i.p.). Experimental groups included the following five groups (n = 8 in each): control, control + SFFE, T2DM, T2DM + SFFE, and T2DM + SFFE + brusatol (an Nrf2 inhibitor, 2 mg/kg, i.p.). SFFE was administered at a concentration of 300 mg/kg, and all experiments concluded after 8 weeks. Treatments with SFFE significantly reduced fasting blood glucose levels, free fatty acids (FFAs), cholesterol, triglycerides, and low-density lipoprotein cholesterol in both the control and T2DM rats, but they failed to reduce fasting insulin levels in these groups. SFFE treatments also improved the liver structure and reduced hepatocyte vacuolization and hepatic levels of triglycerides and cholesterol in T2DM rats, in addition to increasing the hepatic mRNA levels of keap1 and the cytoplasmic levels and nuclear activities of Nrf2 in both the control and T2DM rats. SFFE also stimulated the expression levels of PPARα and CPT-1 but reduced the malondialdehyde (MDA), mRNA levels of SREBP1, fatty acid synthase, and acetyl CoA carboxylase in both the control and T2DM rats; meanwhile, it reduced hepatic mRNA and the nuclear activities of NF-κB and increased levels of glutathione, superoxide dismutase, and heme oxygenase-1 in the livers of both groups of treated rats. Furthermore, SFFE suppressed the levels of caspase-3, Bax, tumor necrosis factor-α, and interleukin-6 in the T2DM rats. Treatment with brusatol prevented all of these effects of SFFE. In conclusion, SFFE suppresses liver damage and hepatic steatosis in T2DM through Nrf2-dependent hypoglycemic, antioxidant, anti-inflammatory, and hypolipidemic effects.

Calorie restriction and life-extending mutation downregulate miR-34a to facilitate lipid metabolism in the liver

Ames dwarf mice (df/df) display delayed aging relative to their normal (N) siblings, living approximately 40-60 % longer. As such, investigating the mechanisms that enable these organisms to have extended lifespan is useful for the development of interventions to slow aging and deter age-related disease. Nonalcoholic fatty liver disease (NAFLD) is a condition that is characterized by the accumulation of excess adipose tissue in the liver. Previous studies highlight the potential of calorie restriction (CR) in promoting longevity, but little is known about its effects on the biomolecular processes that govern NAFLD. In this study, we examined the role of 6-month CR on genes regulating lipid metabolism in the livers of long-living df/df mice and their N littermates. Importantly, our findings showed significant downregulation of miR-34a-5p in N-CR mice and df/df mice regardless of dietary regimen. Alongside, our RT-PCR results indicated that downregulation of miR-34a-5p is correlated with the expression of metabolism-associated mRNAs involved in modulating the processes of de novo lipogenesis (DNL), fatty acid oxidation (FAO), very-low density lipoprotein transport (VLDL-T), and reverse cholesterol transport (RCT). To further verify the role of miR-34a-5p in regulating metabolic processes, we transfected the human liver cancer (HepG2) cell line with miR-34a mimic, and studied its effect on direct targets Sirt1, Ampk, and Ppara as well as downstream lipid transport regulating genes. Our findings suggest that CR and df/df life extending mutation are robust drivers of the miR-34a-5p signaling pathway and prevent the pathogenesis of age-related diseases by improving overall lipid homeostasis.

Tankyrase1/2 inhibitor XAV-939 reverts EMT and suggests that PARylation partially regulates aerobic activities in human hepatocytes and HepG2 cells

The maintenance of a highly functional metabolic epithelium in vitro is challenging. Metabolic impairments in primary human hepatocytes (PHHs) over time is primarily due to epithelial-to-mesenchymal transitioning (EMT). The immature hepatoma cell line HepG2 was used as an in vitro model to explore strategies for enhancing the hepatic phenotype. The phenotypic characterization includes measuring the urea cycle, lipid storage, tricarboxylic acid-related metabolites, reactive oxygen species, endoplasmic reticulum calcium efflux, mitochondrial membrane potentials, oxygen consumptions rate, and CYP450 biotransformation capacity. Expression studies were performed with transcriptomics, co-immunoprecipitation and proteomics. CRISPR/Cas9 was also employed to genetically engineer HepG2 cells. After confirming that PHHs develop an EMT phenotype, expression of tankyrase1/2 was found to increase over time. EMT was reverted when blocking tankyrases1/2-dependent poly-ADP-ribosylation (PARylation) activity, by biochemical and genetic perturbation. Wnt/β-catenin inhibitor XAV-939 blocks tankyrase1/2 and treatment elevated several oxygen-consuming reactions (electron-transport chain, OXHPOS, CYP450 mono-oxidase activity, phase I/II xenobiotic biotransformation, and prandial turnover), suggesting that cell metabolism was enhanced. Glutathione-dependent redox homeostasis was also significantly improved in the XAV-939 condition. Oxygen consumption rate and proteomics experiments in tankyrase1/2 double knockout HepG2 cells then uncovered PARylation as master regulator of aerobic-dependent cell respiration. Furthermore, novel tankyrase1/2-dependent PARylation targets, including mitochondrial DLST, and OGDH, were revealed. This work exposed a new mechanistic framework by linking PARylation to respiration and metabolism, thereby broadening the current understanding that underlies these vital processes. XAV-939 poses an immediate and straightforward strategy to improve aerobic activities, and metabolism, in (immature) cell cultures.

A transcriptional regulatory mechanism of genes in the tricarboxylic acid cycle in the heart

The tricarboxylic acid (TCA) cycle plays a crucial role in mitochondrial ATP production in the healthy heart. However, in heart failure, the TCA cycle becomes dysregulated. Understanding the mechanism by which TCA cycle genes are transcribed in the healthy heart is an important prerequisite to understanding how these genes become dysregulated in the failing heart. PPARγ coactivator 1α (PGC-1α) is a transcriptional coactivator that broadly induces genes involved in mitochondrial ATP production. PGC-1α potentiates its effects through the coactivation of coupled transcription factors, such as estrogen-related receptor (ERR), nuclear respiratory factor 1 (Nrf1), GA-binding protein-a (Gabpa), and Yin Yang 1 (YY1). We hypothesized that PGC-1α plays an essential role in the transcription of TCA cycle genes. Thus, utilizing localization peaks of PGC-1α to TCA cycle gene promoters would allow the identification of coupled transcription factors. PGC-1α potentiated the transcription of 13 out of 14 TCA cycle genes, partly through ERR, Nrf1, Gabpa, and YY1. ChIP-sequencing showed PGC-1α localization peaks in TCA cycle gene promoters. Transcription factors with binding elements that were found proximal to PGC-1α peak localization were generally essential for the transcription of the gene. These transcription factor binding elements were well conserved between mice and humans. Among the four transcription factors, ERR and Gabpa played a major role in potentiating transcription when compared to Nrf1 and YY1. These transcription factor-dependent PGC-1α recruitment was verified with Idh3a, Idh3g, and Sdha promoters with DNA binding assay. Taken together, this study clarifies the mechanism by which TCA cycle genes are transcribed, which could be useful in understanding how those genes are dysregulated in pathological conditions.

Lipid Metabolism in Relation to Carbohydrate Metabolism

Carbohydrates and lipids integrate into a complex metabolic network that is essential to maintain homeostasis. In insects, as in most metazoans, dietary carbohydrates are taken up as monosaccharides whose excess is toxic, even at relatively low concentrations. To cope with this toxicity, monosaccharides are stored either as glycogen or neutral lipids, the latter constituting a quasi-unlimited energy store. Breakdown of these stores in response to energy demand depends on insect species and on several physiological parameters. In this chapter, we review the multiple metabolic pathways and strategies linking carbohydrates and lipids that insects utilize to respond to nutrient availability, food scarcity or physiological activities.

Optimization of an in situ liver perfusion method to evaluate hepatic function of juvenile American alligators (Alligator mississippiensis)

American alligators (Alligator mississippiensis) are a sentinel species whose health is representative of environmental quality. However, their susceptibility to various natural or anthropogenic stressors is yet to be comprehensively studied. Understanding hepatic function in such assessments is essential as the liver is the central organ in the metabolic physiology of an organism, and therefore influences its adaptive capability. In this study, a novel liver perfusion system was developed to study the hepatic physiology of juvenile alligators. First, a cannulation procedure was developed for an in situ liver perfusion preparation. Second, an optimal flow rate of 0.5 ml/min/g liver was determined based on the oxygen content in the effluent perfusate. Third, the efficacy of the liver preparation was tested by perfusing the liver with normoxic or hypoxic Tyrode's buffer while various biomarkers of hepatic function were monitored in the effluent perfusate. Our results showed that in the normoxic perfusion, the aspartate transferase (AST) and lactate/pyruvate ratio in the perfusate remained stable and within an acceptable physiological range for 6 h. In contrast, hypoxia exposure significantly increased the lactate/pyruvate ratio in the perfusate after 2 h, indicating an induction of anaerobic metabolism. These results suggest that the perfused liver remained viable during the perfusion period and exhibited the expected physiological response under hypoxia exposure. The liver perfusion system developed in this study provides an experimental framework with which to study the basic hepatic physiology of alligators and elucidate the effects of environmental or anthropogenic stressors on the metabolic physiology of this sentinel species.

The multi-tissue gene expression and physiological responses of water deprived Peromyscus eremicus

The harsh and dry conditions of desert environments have resulted in genomic adaptations, allowing for desert organisms to withstand prolonged drought, extreme temperatures, and limited food resources. Here, we present a comprehensive exploration of gene expression across five tissues (kidney, liver, lung, gastrointestinal tract, and hypothalamus) and 19 phenotypic measurements to explore the whole-organism physiological and genomic response to water deprivation in the desert-adapted cactus mouse (Peromyscus eremicus). The findings encompass the identification of differentially expressed genes and correlative analysis between phenotypes and gene expression patterns across multiple tissues. Specifically, we found robust activation of the vasopressin renin-angiotensin-aldosterone system (RAAS) pathways, whose primary function is to manage water and solute balance. Animals reduced food intake during water deprivation, and upregulation of PCK1 highlights the adaptive response to reduced oral intake via its actions aimed at maintained serum glucose levels. Even with such responses to maintain water balance, hemoconcentration still occurred, prompting a protective downregulation of genes responsible for the production of clotting factors while simultaneously enhancing angiogenesis which is thought to maintain tissue perfusion. In this study, we elucidate the complex mechanisms involved in water balance in the desert-adapted cactus mouse, P. eremicus. By prioritizing a comprehensive analysis of whole-organism physiology and multi-tissue gene expression in a simulated desert environment, we describe the complex response of regulatory processes.

Mechanisms of Non-alcoholic Fatty Liver Disease and Beneficial Effects of Semaglutide: A Review

Non-alcoholic fatty liver disease stands as the predominant cause of chronic liver disease, with its prevalence and morbidity expected to escalate significantly, leading to substantial healthcare costs and diminished health-related quality of life. It comprises a range of disease manifestations that commence with basic steatosis, involving the accumulation of lipids in hepatocytes, a distinctive histological feature. If left untreated, it often advances to non-alcoholic steatohepatitis, marked by inflammatory and/or fibrotic hepatic changes, leading to the eventual development of non-alcoholic fatty liver disease-related cirrhosis and hepatocellular carcinoma. Because of the liver's vital role in body metabolism, non-alcoholic fatty liver disease is considered both a consequence and a contributor to the metabolic abnormalities observed in the metabolic syndrome. As of date, there are no authorized pharmacological agents for non-alcoholic fatty liver disease or non-alcoholic steatohepatitis. Semaglutide, with its glycemic and weight loss advantages, could potentially offer benefits for individuals with non-alcoholic fatty liver disease. This review aims to investigate the impact of semaglutide on non-alcoholic fatty liver disease.

The impact of GLP-1 signalling on the energy metabolism of pancreatic islet β-cells and extrapancreatic tissues

Glucagon-like peptide-1 signalling impacts glucose homeostasis and appetite thereby indirectly affecting substrate availability at the whole-body level. The incretin canonically produces an insulinotropic effect, thereby lowering blood glucose levels by promoting the uptake and inhibiting the production of the sugar by peripheral tissues. Likewise, GLP-1 signalling within the central nervous system reduces the appetite and food intake, whereas its gastric effect delays the absorption of nutrients, thus improving glycaemic control and reducing the risk of postprandial hyperglycaemia. We review the molecular aspects of the GLP-1 signalling, focusing on its impact on intracellular energy metabolism. Whilst the incretin exerts its effects predominantly via a Gs receptor, which decodes the incretin signal into the elevation of intracellular cAMP levels, the downstream signalling cascades within the cell, acting on fast and slow timescales, resulting in an enhancement or an attenuation of glucose catabolism, respectively.

Disabled-2, a versatile tissue matrix multifunctional scaffold protein with multifaceted signaling: Unveiling its potential in the cancer battle

A multifunctional scaffold protein termed Disabled-2 (Dab2) has recently gained attention in the scientific community and has emerged as a promising candidate in the realm of cancer research. Dab2 protein is involved in a variety of signaling pathways, due to which its significance in the pathogenesis of several carcinomas has drawn considerable attention. Dab2 is essential for controlling the advancement of cancer because it engages in essential signaling pathways such as the Wnt/β-catenin, epidermal growth factor receptor (EGFR), and transforming growth factor-beta (TGF-β) pathways. Dab2 can also repress epithelial-mesenchymal transition (EMT) which is involved in tumor progression with metastatic expansion and adds another layer of significance to its possible impact on cancer spread. Furthermore, the role of Dab2 in processes such as cell growth, differentiation, apoptosis, invasion, and metastasis has been explored in certain investigative studies suggesting its significance. The present review examines the role of Dab2 in the pathogenesis of various cancer subtypes including breast cancer, ovarian cancer, gastric cancer, prostate cancer, and bladder urothelial carcinoma and also sheds some light on its potential to act as a therapeutic target and a prognostic marker in the treatment of various carcinomas. By deciphering this protein's diverse signaling, we hope to provide useful insights that may pave the way for novel therapeutic techniques and tailored treatment approaches in cancer management. Preclinical and clinical trial data on the impact of Dab2 regulation in cancer have also been included, allowing us to delineate role of Dab2 in tumor suppressor function, as well as its correlation with disease stage classification and potential therapy options. However, we observed that there is very scarce data in the form of studies on the evaluation of Dab2 role and treatment function in carcinomas, and further research into this matter could prove beneficial in the generation of novel therapeutic agents for patient-centric and tailored therapy, as well as early prognosis of carcinomas.

Porphyra haitanensis glycoprotein regulates glucose homeostasis: targeting the liver

In this study, we investigated the effects of glycoprotein (PG)-mediated regulation of Porphyra haitanensis on liver glucose metabolism in hyperglycemic mouse models, and sought to establish the underlying mechanism, as determined by the changes in liver gene expression and metabolic profiles. The results showed that 30-300 mg kg-1 PG upregulated the expression of the liver genes Ins1, Ins2, Insr, Gys2, Gpi1, Gck, and downregulated the expression of G6pc, G6pc2, and G6pc3, in a concentration-dependent manner. 300 mg kg-1 PG downregulated the concentrations of glucose-related metabolites in the liver, but upregulated lactic acid, 2-aminoacetic acid, and glucose-1-phosphate concentrations. It was assumed that PG regulated liver glucose metabolism by enriching insulin secretion, glycolysis/gluconeogenesis, and the AMPK signaling pathway, and promoting insulin secretion, glycogen synthesis, and glycolysis. Our findings supported the development of P. haitanensis and its glycoproteins as novel natural antidiabetic compounds that regulated blood glucose homeostasis.

Insights into the Cardioprotective Effects of Pyridoxine Treatment in Diabetic Rats: A Study on Cardiac Oxidative Stress, Cardiometabolic Status, and Cardiovascular Biomarkers

The aims of this study were to examine the effects of pyridoxine administration on the activities of cardiac antioxidant stress enzymes superoxide dismutase (SOD) and catalase (CAT) and enzyme indicators of cardiometabolic status, lactate and malate dehydrogenase (LDH, MDH), as well as LDH and MDH isoforms' distribution in the cardiac tissue of healthy and diabetic Wistar male rats. Experimental animals were divided into five groups: C1-control (0.9% sodium chloride-NaCl-1 mL/kg, intraperitoneally (i.p.), 1 day); C2-second control (0.9% NaCl 1 mL/kg, i.p., 28 days); DM-diabetes mellitus (streptozotocin 100 mg/kg in 0.9% NaCl, i.p., 1 day); P-pyridoxine (7 mg/kg, i.p., 28 days); and DM + P-diabetes mellitus and pyridoxine (streptozotocin 100 mg/kg, i.p., 1 day and pyridoxine 7 mg/kg, i.p., 28 days). Pyridoxine treatment reduced CAT and MDH activity in diabetic rats. In diabetic rats, the administration of pyridoxine increased LDH1 and decreased LDH4 isoform activities, as well as decreased peroxisomal MDH and increased mitochondrial MDH activities. Our findings highlight the positive effects of pyridoxine administration on the complex interplay between oxidative stress, antioxidant enzymes, and metabolic changes in diabetic cardiomyopathy.

Comprehensive review on glucose 6 phosphate dehydrogenase: A critical immunometabolic and redox switch in insects

Mounting an active immune response is energy intensive and demands the reallocation of nutrients to maintain the body's resistance and tolerance against infections. Central to this metabolic adaptation is Glucose-6-phosphate dehydrogenase (G6PDH), a housekeeping enzyme involve in pentose phosphate pathway (PPP). PPP play an essential role in generating ribose, which is critical for nicotinamide adenine dinucleotide phosphate (NADPH). It is vital for physiological and cellular processes such as generating nucleotides, fatty acids and reducing oxidative stress. The G6PDH is extremely conserved enzyme across species in PP shunt. The deficiency of enzymes leads to serious consequences on organism, particularly on adaptation and development. Acute deficiency can lead to impaired cell development, halted embryonic growth, reduce sensitivity to insulin, hypertension and increase inflammation. Historically, research focusing on G6PDH and PPP have primarily targeted diseases on mammalian. However, our review has investigated the unique functions of the G6PDH enzyme in insects and greatly improved mechanistic understanding of its operations. This review explore how G6PDH in insects plays a crucial role in managing the redox balance and immune related metabolism. This study aims to investigate the enzyme's role in different metabolic adaptations.

Multifaceted physiological and therapeutical impact of curcumin on hormone-related endocrine dysfunctions: A comprehensive review

Over the past five decades, Curcumin (Cur), derived from turmeric (Curcuma longa), has gained considerable attention for its potential therapeutic applications. Synthesizing insights from clinical trials conducted over the last 25 years, this review delves into diseases where Cur has demonstrated promise, offering a nuanced understanding of its pharmacokinetics, safety, and effectiveness. Focusing on specific examples, the impact of Cur on various human diseases is explored. Endocrine glands and associated signaling pathways are highlighted, elucidating how Cur influences cellular signaling. The article underscores molecular mechanisms such as hormone level alteration, receptor interaction, cytokine and adipokine expression inhibition, antioxidant enzyme activity, and modulation of transcription factors. Cur showcases diverse protective mechanisms against inflammation and oxidative damage by suppressing antiapoptotic genes and impeding tumor promotion. This comprehensive overview emphasizes the potential of Cur as a natural agent for countering aging and degenerative diseases, calling for further dedicated research in this realm.

Hepatic glucagon action: beyond glucose mobilization

Glucagon's ability to promote hepatic glucose production has been known for over a century, with initial observations touting this hormone as a diabetogenic agent. However, glucagon receptor agonism [when balanced with an incretin, including glucagon-like peptide 1 (GLP-1) to dampen glucose excursions] is now being developed as a promising therapeutic target in the treatment of metabolic diseases, like metabolic dysfunction-associated steatotic disease/metabolic dysfunction-associated steatohepatitis (MASLD/MASH), and may also have benefit for obesity and chronic kidney disease. Conventionally regarded as the opposing tag-team partner of the anabolic mediator insulin, glucagon is gradually emerging as more than just a "catabolic hormone." Glucagon action on glucose homeostasis within the liver has been well characterized. However, growing evidence, in part thanks to new and sensitive "omics" technologies, has implicated glucagon as more than just a "glucose liberator." Elucidation of glucagon's capacity to increase fatty acid oxidation while attenuating endogenous lipid synthesis speaks to the dichotomous nature of the hormone. Furthermore, glucagon action is not limited to just glucose homeostasis and lipid metabolism, as traditionally reported. Glucagon plays key regulatory roles in hepatic amino acid and ketone body metabolism, as well as mitochondrial turnover and function, indicating broader glucagon signaling consequences for metabolic homeostasis mediated by the liver. Here we examine the broadening role of glucagon signaling within the hepatocyte and question the current dogma, to appreciate glucagon as more than just that "catabolic hormone."

The key roles of thyroid hormone in mitochondrial regulation, at interface of human health and disease

Mitochondria are highly plastic and dynamic organelles long known as the powerhouse of cellular bioenergetics, but also endowed with a critical role in stress responses and homeostasis maintenance, supporting and integrating activities across multifaced cellular processes. As a such, mitochondria dysfunctions are leading causes of a wide range of diseases and pathologies. Thyroid hormones (THs) are endocrine regulators of cellular metabolism, regulating intracellular nutrients fueling of sugars, amino acids and fatty acids. For instance, THs regulate the balance between the anabolism and catabolism of all the macro-molecules, influencing energy homeostasis during different nutritional conditions. Noteworthy, not only most of the TH-dependent metabolic modulations act via the mitochondria, but also THs have been proved to regulate the mitochondrial biosynthesis, dynamics and function. The significance of such an interplay is different in the context of specific tissues and strongly impacts on cellular homeostasis. Thus, a comprehensive understanding of THs-dependent mitochondrial functions and dynamics is required to develop more precise strategies for targeting mitochondrial function. Herein, we describe the mechanisms of TH-dependent metabolic regulation with a focus on mitochondrial action, in different tissue contexts, thus providing new insights for targeted modulation of mitochondrial dynamics.

Oleic Acid and Succinic Acid: A Potent Nutritional Supplement in Improving Hepatic Glycaemic Control in Type 2 Diabetic Sprague-Dawley Rats

Nutritional supplements are gaining traction for their effects in mitigating the impacts of various health conditions. In particular, many supplements are being proposed to reduce the impacts of type 2 diabetes (T2D), a metabolic condition that has reached global epidemic proportions. Recently, a supplement of oleic acid (OA) and succinic acid (SA; 1 : 1, w/w) was reported to improve glycaemic control in type 2 diabetic (T2D) Sprague-Dawley (S-D) rats through ameliorating insulin release and sensitivity. Here, we investigate the effects of the supplement (OA and SA) on hepatic and pancreatic function in T2D S-D rats. Eighteen (18) S-D rats were rendered diabetic and were divided into three equal groups: diabetic control, diabetic treatment, and diabetic glibenclamide. Another 12 S-D rats were obtained and served as the normal groups. The animals were treated daily with the vehicle, OA and SA (800 mg/kg body weight (bw); 1 : 1), or glibenclamide (10 mg/kg bw) which served as the positive control. The findings indicated that treatment with the supplement resulted in a 35.69 ± 4.22% reduction (p=0.006) in blood glucose levels (BGL). Analysis of hepatic enzymes depicted that the nutritional supplement reduced the activity of the gluconeogenesis enzyme, glucose-6-phosphatase (G6P) while improved the activity of catabolic enzymes such as glucose-6-phosphate dehydrogenase (G6PD) and pyruvate kinase (PK). Furthermore, the supplement attenuated oxidative stress through restoration of catalase (CAT) and superoxide dismutase (SOD), while reducing malondialdehyde (MDA) levels. Finally, the supplement showed no liver or kidney toxicity and improved the size and number of pancreatic islets of Langerhans, indicating its potential application in treating T2D. The study highlighted that a supplement of the two organic acids may be beneficial in reducing the rate of pathogenesis of type 2 diabetes. Therefore, it may offer therapeutic value as a dietary or nutritional supplement in the approach against diabetes and its complications.

Adaptive Effects of Endocrine Hormones on Metabolism of Macronutrients during Fasting and Starvation: A Scoping Review

Food deprivation can occur for different reasons. Fasting (<24 h duration) occurs to meet religious or well-being goals. Starvation (>1-day duration) occurs when there is intentional (hunger strike or treatment of a medical condition) or unintentional (anorexia nervosa, drought, epidemic famine, war, or natural disaster) food deprivation. A scoping review was undertaken using the PubMed database to explore 1805 abstracts and review 88 eligible full-text articles to explore the adaptive relationships that emerge between cortisol, insulin, glucagon, and thyroid hormones on the metabolic pathways of macronutrients in humans during fasting and starvation. The collected data indicate that fasting and starvation prime the human body to increase cortisol levels and decrease the insulin/glucagon ratio and triiodothyronine (T3) levels. During fasting, increased levels of cortisol and a decreased insulin/glucagon ratio enhance glycogenolysis and reduce the peripheral uptake of glucose and glycogenesis, whereas decreased T3 levels potentially reduce glycogenolysis. During starvation, increased levels of cortisol and a decreased insulin/glucagon ratio enhance lipolysis, proteolysis, fatty acid and amino acid oxidation, ketogenesis, and ureagenesis, and decreased T3 levels reduce thermogenesis. We present a potential crosstalk between T3 and the above hormones, including between T3 and leptin, to extend their adaptive roles in the metabolism of endogenous macronutrients during food deprivation.

Disable 2, A Versatile Tissue Matrix Multifunctional Scaffold Protein with Multifaceted Signaling: Unveiling Role in Breast Cancer for Therapeutic Revolution

The Disabled-2 (DAB2) protein, found in 80-90% of various tumors, including breast cancer, has been identified as a potential tumor suppressor protein. On the contrary, some hypothesis suggests that DAB2 is associated with the modulation of the Ras/MAPK pathway by endocytosing the Grb/Sos1 signaling complex, which produces oncogenes and chemoresistance to anticancer drugs, leading to increased tumor growth and metastasis. DAB2 has multiple functions in several disorders and is typically under-regulated in several cancers, making it a potential target for treatment of cancer therapy. The primary function of DAB2 is the modulation of transforming growth factor- β (TGF-β) mediated endocytosis, which is involved in several mechanisms of cancer development, including tumor suppression through promoting apoptosis and suppressing cell proliferation. In this review, we will discuss in detail the mechanisms through which DAB2 leads to breast cancer and various advancements in employing DAB2 in the treatment of breast cancer. Additionally, we outlined its role in other diseases. We propose that upregulating DAB2 could be a novel approach to the therapeutics of breast cancer.

Increased hepatic gluconeogenesis and type 2 diabetes mellitus

Abnormally increased hepatic gluconeogenesis is a significant contributor to hyperglycemia in the fasting state in patients with type 2 diabetes mellitus (T2DM) due to insulin resistance. Metformin, the most prescribed drug for the treatment of T2DM, is believed to exert its effect mainly by reducing hepatic gluconeogenesis. Here, we discuss how increased hepatic gluconeogenesis contributes to T2DM and we review newly revealed mechanisms underlying the attenuation of gluconeogenesis by metformin. In addition, we analyze the recent findings on new determinants involved in the regulation of gluconeogenesis, which might ultimately lead to the identification of novel and targeted treatment strategies for T2DM.

Unveiling the chemical profiling and remarkable modulation of carbohydrate metabolism by costus root, Dolomiaea costus (Falc.) in streptozotocin (STZ)-induced diabetic rats

ETHNOPHARMACOLOGICAL RELEVANCE

Dolomiaea costus (Falc.), formerly Saussurea costus (Falc.) Lipsch., an ayurvedic medicinal plant, has long been recognized and utilized in diverse indigenous systems of medicine for its multifaceted therapeutic properties, including anti-inflammatory, carminative, expectorant, antiarthritic, antiseptic, aphrodisiac, anodyne, and antidiabetic effects.

AIM OF THE STUDY

The potential and underlying mechanisms of D. costus root as an antidiabetic agent were investigated in this study. Additionally, the quantification of phenolic and flavonoid compounds, which dominate the extracts, was of particular interest in order to elucidate their contribution to the observed effects.

MATERIALS AND METHODS

High-performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS) was employed to analyze the chemical constituents in D. costus root aqueous extract (DCA) and D. costus root ethanolic extract (DCE). Furthermore, the inhibitory potentials of DCE and its respective fractions as well as DCA against α-amylase, α-glucosidase, and lipase enzymes were assessed. Subsequently, the efficacy of DCA and DCE extracts was evaluated using an established streptozotocin (STZ)-induced diabetic animal model; this involved administering the extracts at doses of 200 and 400 mg/kg bwt. and comparing them with a positive control (glibenclamide (Glib.) at 0.6 mg/kg bwt.). After induction of diabetes (except for negative control), all animals received the treatments orally for 21 days consecutively, followed by the collection of rat serum to assess various parameters including, glycemic and lipid profiles, liver and kidney functions, antioxidant activity, glycolysis, and gluconeogenesis pathways.

RESULTS

The results of HPLC-ESI-MS/MS revealed that isochlorogenic acid A (8393.64 μg/g) and chlorogenic acid (6532.65 μg/g) were the predominant compounds in DCE and DCA, respectively. Both extracts exhibited notable antidiabetic properties, as evidenced by their ability to regulate blood glycemic and lipid profiles (glucose, insulin, HBA1C; HDL, TC, TGs), liver enzymes (ALT, ALP, AST), kidney function (urea, creatinine, uric acid), oxidative stress biomarkers (MDA), antioxidant enzymes (CAT, GSH, SOD), as well as glycolysis (glucokinase) and gluconeogenesis (G-6-P, FBP1) pathways.

CONCLUSIONS

Furthermore, the administration of D. costus extracts significantly mitigated STZ-induced diabetic hyperglycemia. These results can be attributed, at least partially, to the presence of several polyphenolic compounds with potent antioxidant and anti-inflammatory activities.

MicroRNA-721 regulates gluconeogenesis via KDM2A-mediated epigenetic modulation in diet-induced insulin resistance in C57BL/6J mice

BACKGROUND

Aberrant gluconeogenesis is considered among primary drivers of hyperglycemia under insulin resistant conditions, with multiple studies pointing towards epigenetic dysregulation. Here we examine the role of miR-721 and effect of epigenetic modulator laccaic acid on the regulation of gluconeogenesis under high fat diet induced insulin resistance.

RESULTS

Reanalysis of miRNA profiling data of high-fat diet-induced insulin-resistant mice model, GEO dataset (GSE94799) revealed a significant upregulation of miR-721, which was further validated in invivo insulin resistance in mice and invitro insulin resistance in Hepa 1-6 cells. Interestingly, miR-721 mimic increased glucose production in Hepa 1-6 cells via activation of FOXO1 regulated gluconeogenic program. Concomitantly, inhibition of miR-721 reduced glucose production in palmitate induced insulin resistant Hepa 1-6 cells by blunting the FOXO1 induced gluconeogenesis. Intriguingly, at epigenetic level, enrichment of the transcriptional activation mark H3K36me2 got decreased around the FOXO1 promoter. Additionally, identifying targets of miR-721 using miRDB.org showed H3K36me2 demethylase KDM2A as a potential target. Notably, miR-721 inhibitor enhanced KDM2A expression which correlated with H3K36me2 enrichment around FOXO1 promoter and the downstream activation of the gluconeogenic pathway. Furthermore, inhibition of miR-721 in high-fat diet-induced insulin-resistant mice resulted in restoration of KDM2A levels, concomitantly reducing FOXO1, PCK1, and G6PC expression, attenuating gluconeogenesis, hyperglycemia, and improving glucose tolerance. Interestingly, the epigenetic modulator laccaic acid also reduced the hepatic miR-721 expression and improved KDM2A expression, supporting our earlier report that laccaic acid attenuates insulin resistance by reducing gluconeogenesis.

CONCLUSION

Our study unveils the role of miR-721 in regulating gluconeogenesis through KDM2A and FOXO1 under insulin resistance, pointing towards significant clinical and therapeutic implications for metabolic disorders. Moreover, the promising impact of laccaic acid highlights its potential as a valuable intervention in managing insulin resistance-associated metabolic diseases.

From classical dualistic antagonism to hormone synergy: potential of overlapping action of glucagon, insulin and GLP-1 for the treatment of diabesity

The increasing prevalence of 'diabesity', a combination of type 2 diabetes and obesity, poses a significant global health challenge. Unhealthy lifestyle factors, including poor diet, sedentary behaviour, and high stress levels, combined with genetic and epigenetic factors, contribute to the diabesity epidemic. Diabesity leads to various significant complications such as cardiovascular diseases, stroke, and certain cancers. Incretin-based therapies, such as GLP-1 receptor agonists and dual hormone therapies, have shown promising results in improving glycaemic control and inducing weight loss. However, these therapies also come with certain disadvantages, including potential withdrawal effects. This review aims to provide insights into the cross-interactions of insulin, glucagon, and GLP-1, revealing the complex hormonal dynamics during fasting and postprandial states, impacting glucose homeostasis, energy expenditure, and other metabolic functions. Understanding these hormonal interactions may offer novel hypotheses in the development of 'anti-diabesity' treatment strategies. The article also explores the question of the antagonism of insulin and glucagon, providing insights into the potential synergy and hormonal overlaps between these hormones.

Sterol Regulatory Element Binding Protein 1: A Mediator for High-Fat Diet-Induced Hepatic Gluconeogenesis and Glucose Intolerance in Fish

BACKGROUND

Sterol regulatory element binding protein (SREBP) 1 is considered to be a crucial regulator for lipid synthesis in vertebrates. However, whether SREBP1 could regulate hepatic gluconeogenesis under high-fat diet (HFD) condition is still unknown, and the underlying mechanism is also unclear.

OBJECTIVES

This study aimed to determine gluconeogenesis-related gene and protein expressions in response to HFD in large yellow croaker and explore the role and mechanism of SREBP1 in regulating the related transcription and signaling.

METHODS

Croakers (mean weight, 15.61 ± 0.10 g) were fed with diets containing 12% crude lipid [control diet (ND)] or 18% crude lipid (HFD) for 10 weeks. The glucose tolerance, insulin tolerance, hepatic gluconeogenesis-related genes, and proteins expressions were determined. To explore the role of SREBP1 in HFD-induced gluconeogenesis, SREBP1 was inhibited by pharmacologic inhibitor (fatostatin) or genetic knockdown in croaker hepatocytes under palmitic acid (PA) condition. To explore the underlying mechanism, luciferase reporter and chromatin immunoprecipitation assays were conducted in HEK293T cells. Data were analyzed using analysis of variance or Student t test.

RESULTS

Compared with ND, HFD increased the mRNA expressions of gluconeogenesis genes (2.40-fold to 2.60-fold) (P < 0.05) and reduced protein kinase B (AKT) phosphorylation levels (0.28-fold to 0.34-fold) (P < 0.05) in croakers. However, inhibition of SREBP1 by fatostatin addition or SREBP1 knockdown reduced the mRNA expressions of gluconeogenesis genes (P < 0.05) and increased AKT phosphorylation levels (P < 0.05) in hepatocytes, compared with that by PA treatment. Moreover, fatostatin addition or SREBP1 knockdown also increased the mRNA expressions of irs1 (P < 0.05) and reduced serine phosphorylation of IRS1 (P < 0.05). Furthermore, SREBP1 inhibited IRS1 transcriptions by binding to its promoter and induced IRS1 serine phosphorylation by activating diacylglycerol-protein kinase Cε signaling.

CONCLUSIONS

This study reveals the role of SREBP1 in hepatic gluconeogenesis under HFD condition in croakers, which may provide a potential strategy for improving HFD-induced glucose intolerance.

Tyrosine-phosphorylated DNER sensitizes insulin signaling in hepatic gluconeogenesis by inducing proteasomal degradation of TRB3

OBJECTIVE

Hepatic insulin resistance, which leads to increased hepatic gluconeogenesis, is a major contributor to fasting hyperglycemia in type 2 diabetes mellitus (T2DM). However, the mechanism of impaired insulin-dependent suppression of hepatic gluconeogenesis remains elusive. Delta/Notch-like epidermal growth factor (EGF)-related receptor (DNER), firstly described as a neuron-specific Notch ligand, has been recently identified as a susceptibility gene for T2DM through genome-wide association studies. We herein investigated whether DNER regulates hepatic gluconeogenesis and whether this is mediated by enhanced insulin signaling.

METHODS

The association between DNER, tribbles homolog 3 (TRB3) and Akt signaling was evaluated in C57BL/6J, ob/ob and db/db mice by western blot analysis. DNER loss-of-function and gain-of-function in hepatic gluconeogenesis were analyzed by western blot analysis, quantitative real-time PCR, glucose uptake and output assay in AML-12 cells and partially validated in primary mouse hepatocytes. Hepatic DNER knockdown mice were generated by tail vein injection of adenovirus to confirm the effects of DNER in vivo. The interaction between DNER and TRB3 was investigated by rescue experiments, cycloheximide chase analysis, co-immunoprecipitation and immunofluorescence. The potential insulin-stimulated phosphorylation sites of DNER were determined by co-immunoprecipitation, LC-MS/MS analysis and site-specific mutagenesis.

RESULTS

Here we show that DNER enhanced hepatic insulin signaling in gluconeogenesis by inhibiting TRB3, an endogenous Akt inhibitor, through the ubiquitin-proteasome degradation pathway. In AML-12 hepatocytes, insulin-stimulated activation of Akt and suppression of gluconeogenesis are attenuated by DNER knockdown, but potentiated by DNER over-expression. In C57BL/6J mice, hepatic DNER knockdown is accompanied by impaired glucose and pyruvate tolerance. Furthermore, the in vitro effects of DNER knockdown or over-expression on both Akt activity and hepatic gluconeogenesis can be rescued by TRB3 knockdown or over-expression, respectively. In response to insulin stimulation, DNER interacted directly with insulin receptor and was phosphorylated at Tyr677. This site-specific phosphorylation is essential for DNER to upregulate Akt activity and then downregulate G6Pase and PEPCK expression, by interacting with TRB3 directly and inducing TRB3 proteasome-dependent degradation.

CONCLUSIONS

Taken together, the crosstalk between insulin-Akt and DNER-TRB3 pathways represents a previously unrecognized mechanism by which insulin regulates hepatic gluconeogenesis.

Characterization of palmitic acid toxicity induced insulin resistance in HepG2 cells

BACKGROUND

An etiology of palmitic acid (PA) induced insulin resistance (IR) is complex for which two mechanisms are proposed namely ROS induced JNK activation and lipid induced protein kinase-C (PKCε) activation. However, whether these mechanisms act alone or in consortium is not clear.

METHODS AND RESULTS

In this study, we have characterized PA induced IR in liver cells. These cells were treated with different concentrations of PA for either 8 or 16 h. Insulin responsiveness of cells treated with PA for 8 h was found to be same as that of control. However, cells treated with PA for 16 h, showed increased glucose output both in the presence and in absence of insulin only at higher concentrations, indicating development of IR. In these, both JNK and PKCε were activated in response to increased ROS and lipid accumulation, respectively. Activated JNK and PKCε phosphorylated IRS1 at Ser-307 resulting in inhibition of AKT which in turn inactivated GSK3β, leading to reduced glycogen synthase activity. Inhibition of AKT also reduced insulin suppression of hepatic gluconeogenesis by activating Forkhead box protein O1 (FOXO1) and increased expression of the gluconeogenic enzymes and their transcription factors.

CONCLUSION

Thus, our data clearly demonstrate that both these mechanisms work simultaneously and more importantly, identified a threshold of HepG2 cells, which when crossed led to the pathological state of IR in response to PA.

High-fat diet induced obesity promotes inflammation, oxidative stress, and hepatotoxicity in female FVB/N mice

Although obesity and subsequent liver injury are increasingly prevalent in women, female mouse models have generally shown resistance to high-fat diet (HFD)-induced obesity. We evaluated control and HFD-fed male and female FVB/N mice, a strain well-suited to transgenic analyses, for phenotypic, histological, and molecular markers related to control of glucose, lipids, and inflammation in serum, liver, and perigonadal white adipose tissues. Unlike many mouse models, HFD-fed FVB/N females gained more perigonadal and mesenteric fat mass and overall body weight than their male counterparts, with increased hepatic expression of lipogenic PPARγ target genes (Cd36, Fsp27, and Fsp27β), oxidative stress genes and protein (Nqo1 and CYP2E1), inflammatory gene (Mip-2), and the pro-fibrotic gene Pai-1, along with increases in malondialdehyde and serum ALT levels. Further, inherent to females (independently of HFD), hepatic antioxidant heme oxygenase-1 (HMOX1, HO-1) protein levels were reduced compared to their male counterparts. In contrast, males may have been relatively protected from HFD-induced oxidative stress and liver injury by elevated mRNA and protein levels of hepatic antioxidants BHMT and Gpx2, increased fatty acid oxidation genes in liver and adipocytes (Pparδ), despite disorganized and inflamed adipocytes. Thus, female FVB/N mice offer a valuable preclinical, genetically malleable model that recapitulates many of the features of diet-induced obesity and liver damage observed in human females.

Estimating the effect of lipid-lowering agents on novel subtypes of adult-onset diabetes

AIMS

The aims of the present study were to assess the effects of lipid-lowering drugs [HMG-CoA reductase inhibitors, proprotein convertase subtilisin/kexin type 9 inhibitors, and Niemann-Pick C1-Like 1 (NPC1L1) inhibitors] on novel subtypes of adult-onset diabetes through a Mendelian randomisation study.

MATERIALS AND METHODS

We first inferred causal associations between lipid-related traits [including high-density lipoprotein cholesterol, low-density lipoprotein cholesterol (LDL-C), triglycerides (TG), apolipoproteins A-I, and apolipoproteins B] and novel subtypes of adult-onset diabetes. The expression quantitative trait loci of drug target genes for three classes of lipid-lowering drugs, as well as genetic variants within or nearby drug target genes associated with LDL-C, were then utilised as proxies for the exposure of lipid-lowering drugs. Mendelian randomisation analysis was performed using summary data from genome-wide association studies of LDL-C, severe autoimmune diabetes, severe insulin-deficient diabetes (SIDD), severe insulin-resistant diabetes (SIRD), mild obesity-related diabetes (MOD), and mild age-related diabetes.

RESULTS

There was an association between HMGCR-mediated LDL-C and the risk of SIRD [odds ratio (OR) = 0.305, 95% confidence interval (CI) = 0.129-0.723; p = 0.007], and there was an association of PCSK9-mediated LDL-C with the risk of SIDD (OR = 0.253, 95% CI = 0.120-0.532; p < 0.001) and MOD (OR = 0.345, 95% CI = 0.171-0.696; p = 0.003). Moreover, NPC1L1-mediated LDL-C (OR = 0.109, 95% CI = 0.019-0.613; p = 0.012) and the increased expression of NPC1L1 gene in blood (OR = 0.727, 95% CI = 0.541-0.977; p = 0.034) both showed a significant association with SIRD. These results were further confirmed by sensitivity analyses.

CONCLUSIONS

In summary, the different lipid-lowering medications have a specific effect on the increased risk of different novel subtypes of adult-onset diabetes.

Zinc deficiency affects insulin secretion and alters insulin-regulated metabolic signaling in rats

BACKGROUND

The essential trace element zinc is important in stabilizing pancreatic insulin secretion. Zinc not only influences the synthesis of insulin but also affects its activity. Insulin not only exerts a hypoglycemic effect but also regulates glucose and lipid metabolisms in insulin target organs. In this study, we aimed to determine changes to pancreatic β cells and insulin secretion induced by different zinc concentrations and to evaluate the effect of zinc deficiency on glucose intolerance, insulin resistance, and insulin target organs via changing insulin levels.

METHODS

We set up two experimental trials. In the first trial, male Sprague Dawley (SD) rats were divided into three groups. Group one (ZnC) received a standard diet, group two (ZnF) was given a zinc-free diet, and group three (ZnFC) was initially fed a zinc-free diet followed by a reversion to the standard diet. After sacrifice, we observed changes in blood parameters, including insulin, and examined alterations in pancreatic tissue using immunostaining, with focus on the localization of pancreatic β-cells. In the second trial, male SD rats were split into two groups, with one receiving a standard diet and the other a zinc-free diet. Oral glucose tolerance and insulin tolerance tests were then performed. After sacrifice, we evaluated changes in lipid and glucose metabolism within insulin target organs using quantitative polymerase chain reaction.

RESULTS

In the first trial, blood insulin levels and the area of insulin-positive staining in pancreatic β-cells decreased in the ZnF compared to the ZnC group. The ZnFC group did not show recovery in either blood insulin levels or the area of insulin-positive staining in pancreatic β-cells. In the second trial, no differences were observed in glucose tolerance or insulin resistance between the ZnC and ZnF groups. However, changes in the expression of insulin target genes were noted in the liver and adipose tissue in the ZnF group.

CONCLUSION

We reveal that dietary zinc concentrations not only affect the concentration of insulin in the blood but also impact the localization of pancreatic β-cells involved in insulin production. Furthermore, our results suggest that changes in blood insulin levels, induced by different zinc concentrations, could cause metabolic alterations in insulin target organs such as the liver and adipose tissue. This study sheds more light on the role of zinc in insulin-regulated metabolic diseases.

High Starch Induces Hematological Variations, Metabolic Changes, Oxidative Stress, Inflammatory Responses, and Histopathological Lesions in Largemouth Bass (Micropterus salmoides)

This study evaluated effects of high starch (20%) on hematological variations, glucose and lipid metabolism, antioxidant ability, inflammatory responses, and histopathological lesions in largemouth bass. Results showed hepatic crude lipid and triacylglycerol (TAG) contents were notably increased in fish fed high starch. High starch could increase counts of neutrophils, lymphocytes, monocytes, eosinophils, and basophils and serum contents of TAG, TBA, BUN, and LEP (p < 0.05). There were increasing trends in levels of GLUT2, glycolysis, gluconeogenesis, and LDH in fish fed high starch through the AKT/PI3K signal pathway. Meanwhile, high starch not only triggered TAG and cholesterol synthesis, but mediated cholesterol accumulation by reducing ABCG5, ABCG8, and NPC1L1. Significant increases in lipid droplets and vacuolization were also shown in hepatocytes of D3-D7 groups fed high starch. In addition, high starch could decrease levels of mitochondrial Trx2, TrxR2, and Prx3, while increasing ROS contents. Moreover, high starch could notably increase amounts of inflammatory factors (IL-1β, TNF-α, etc.) by activating NLRP3 inflammasome key molecules (GSDME, caspase 1, etc.). In conclusion, high starch could not only induce metabolic disorders via gluconeogenesis and accumulation of glycogen, TAG, and cholesterol, but could disturb redox homeostasis and cause inflammatory responses by activating the NLRP3 inflammasome in largemouth bass.

Assessing the predictive value of insulin resistance indices for metabolic syndrome risk in type 2 diabetes mellitus patients

Limited research has explored the effectiveness of insulin resistance (IR) in forecasting metabolic syndrome (MetS) risk, especially within the Iranian population afflicted with type 2 diabetes mellitus (T2DM). The present investigation aimed to assess the efficacy of IR indices in predicting the risk of MetS among T2DM patients. Convenient sampling was utilized to select four hundred subjects with T2DM. Metabolic factors and IR indices, including the Waist Circumference-Triglyceride Index (WTI), Triglyceride and Glucose Index (TyG index), the product of TyG index and abdominal obesity indices, and the Metabolic Score for Insulin Resistance (METS-IR), were evaluated. Logistic regression, coupled with modeling, was employed to explore the risk of MetS. The predictive performance of the indices for MetS stratified by sex was evaluated via receiver operating characteristic (ROC) curve analysis and estimation of the area under the curve (AUC) values. The TyG-Waist Circumference (TyG-WC) index exhibited the largest AUCs in both males (0.91) and females (0.93), while the TyG-Body Mass Index (TyG-BMI) demonstrated the smallest AUCs (0.77 in males and 0.74 in females). All indices significantly predicted the risk of MetS in all subjects before and after adjustment (p < 0.001 for all). The TyG-WC index demonstrated the highest odds ratios for MetS (8.06, 95% CI 5.41-12.00). In conclusion, all IR indices assessed in this study effectively predicted the risk of MetS among Iranian patients with T2DM, with the TyG-WC index emerging as the most robust predictor across both genders.

Genetic and Epigenetic Associations with Post-Transplant Diabetes Mellitus

Post-transplant diabetes mellitus (PTDM) is a common complication of solid organ transplantation. PTDM prevalence varies due to different diabetes definitions. Consensus guidelines for the diagnosis of PTDM have been published based on random blood glucose levels, glycated hemoglobin (HbA1c), and oral glucose tolerance test (OGTT). The task of diagnosing PTDM continues to pose challenges, given the potential for diabetes to manifest at different time points after transplantation, thus demanding constant clinical vigilance and repeated testing. Interpreting HbA1c levels can be challenging after renal transplantation. Pre-transplant risk factors for PTDM include obesity, sedentary lifestyle, family history of diabetes, ethnicity (e.g., African-Caribbean or South Asian ancestry), and genetic risk factors. Risk factors for PTDM include immunosuppressive drugs, weight gain, hepatitis C, and cytomegalovirus infection. There is also emerging evidence that genetic and epigenetic variation in the organ transplant recipient may influence the risk of developing PTDM. This review outlines many known risk factors for PTDM and details some of the pathways, genetic variants, and epigenetic features associated with PTDM. Improved understanding of established and emerging risk factors may help identify people at risk of developing PTDM and may reduce the risk of developing PTDM or improve the management of this complication of organ transplantation.

Identification of potential serum biomarkers associated with HbA1c levels in Indian type 2 diabetic subjects using NMR-based metabolomics

BACKGROUND

The prevalence of type 2 diabetes mellitus (T2DM), a progressive metabolic disorder characterized by chronic hyperglycemia and the development of insulin resistance, has increased globally, with worrying statistics coming from children, adolescents, and young adults from developing countries like India. Here, we investigated unique circulating metabolic signatures associated with prediabetes and T2DM in an Indian cohort using NMR-based metabolomics.

MATERIALS AND METHODS

The study subjects included healthy volunteers (N = 101), prediabetic subjects (N = 75), and T2DM patients (N = 108). Serum metabolic profiling was performed using 1H NMR spectroscopy and major perturbed metabolites were identified by multivariate analysis and receiver operating characteristic (ROC) modules.

RESULTS

Of the 36 aqueous abundant metabolites, 24 showed a statistically significant difference between healthy volunteers, prediabetics, and established T2DM subjects. On performing multivariate ROC curve analysis with 5 commonly dysregulated metabolites (namely, glucose, pyroglutamate, o-phosphocholine, serine, and methionine) in prediabetes and T2DM, AUC values obtained were 0.96 (95 % confidence interval (CI) = 0.93, 0.98) for T2DM; and 0.88 (95 % CI = 0.81, 0.93) for prediabetic subjects, respectively.

CONCLUSION

We propose that the identified metabolite panel can be used in the future as a biomarker for clinical diagnosis, patient surveillance, and for predicting individuals at risk for developing diabetes.

Characterization of diseased primary human hepatocytes in an all-human cell-based triculture system

Liver diseases, including NAFLD, are a growing worldwide health concern. Currently, there is a lack of suitable in vitro models that sustain basic primary human hepatocyte (PHH) morphology and functionality while supporting presentation of disease-associated phenotypic characteristics such as lipid accumulation and inflammasome activation. In TruVivo, an all-human triculture system (hTCS), basic metabolic functions were characterized in PHHs isolated from normal or diseased livers during two-weeks of culture. Decreases in albumin and urea levels and CYP3A4 activity were seen in diseased-origin PHHs compared to normal PHHs along with higher CYP2E1 expression. Positive expression of the macrophage markers CD68 and CD163 were seen in the diseased PHH preparations. Elevated levels of the pro-inflammatory cytokines IL-6 and MCP-1 and the fibrotic markers CK-18 and TGF-β were also measured. Gene expression of FASN, PCK1, and G6PC in the diseased PHHs was decreased compared to the normal PHHs. Further characterization revealed differences in lipogenesis and accumulation of intracellular lipids in normal and diseased PHHs when cultured with oleic acid and high glucose. TruVivo represents a promising new platform to study lipogenic mechanisms in normal and diseased populations due to the preservation of phenotypic differences over a prolonged culture period.

3,4',5-Trimethoxy-trans-stilbene ameliorates hepatic insulin resistance and oxidative stress in diabetic obese mice through insulin and Nrf2 signaling pathways

Resveratrol has profound benefits against diabetes. However, whether its methylated derivative 3,4',5-trimethoxy-trans-stilbene (3,4',5-TMS) also plays a protective role in glucose metabolism is not characterized. We aimed to study the anti-diabetic effects of 3,4',5-TMS in vitro and in vivo. Insulin-resistant HepG2 cells (IR-HepG2) were induced by high glucose plus dexamethasone whilst six-week-old male C57BL/6J mice received a 60 kcal% fat diet for 14 weeks to establish an obese diabetic model. 3,4',5-TMS did not reduce the cell viability of IR-HepG2 cells at concentrations of 0.5 and 1 μM, which enhanced the capability of glycogen synthesis and glucose consumption in IR-HepG2 cells. Four-week oral administration of 3,4',5-TMS at 10 mg kg-1 day-1 ameliorated insulin sensitivity and glucose tolerance of diet-induced obese (DIO) mice. 3,4',5-TMS activated the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway by inhibiting phosphorylation of insulin receptor substrate (IRS)-1 at Ser307 and increasing the protein levels of IRS-1 and IRS-2 to restore the insulin signaling pathway in diabetes. 3,4',5-TMS also upregulated the phosphorylation of glycogen synthase kinase 3 beta (GSK3β) at Ser9. 3,4',5-TMS suppressed oxidative stress by increasing the protein levels of nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1) and NAD(P)H : quinone oxidoreductase 1 (NQO1) and antioxidant enzyme activity. In summary, 3,4',5-TMS alleviated hepatic insulin resistance in vitro and in vivo, by the activation of the insulin signaling pathway, accomplished by the suppression of oxidative stress.

NAD metabolic therapy in metabolic dysfunction-associated steatotic liver disease: Possible roles of gut microbiota

Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly named non-alcoholic fatty liver disease (NAFLD), is induced by alterations of hepatic metabolism. As a critical metabolites function regulator, nicotinamide adenine dinucleotide (NAD) nowadays has been validated to be effective in the treatment of diet-induced murine model of MASLD. Additionally, gut microbiota has been reported to have the potential to prevent MASLD by dietary NAD precursors metabolizing together with mammals. However, the underlying mechanism remains unclear. In this review, we hypothesized that NAD enhancing mitochondrial activity might reshape a specific microbiota signature, and improve MASLD progression demonstrated by fecal microbiota transplantation. Here, this review especially focused on the mechanism of Microbiota-Gut-Liver Axis together with NAD metabolism for the MASLD progress. Notably, we found significant changes in Prevotella associated with NAD in a gut microbiome signature of certain MASLD patients. With the recent researches, we also inferred that Prevotella can not only regulate the level of NAD pool by boosting the carbon metabolism, but also play a vital part in regulating the branched-chain amino acid (BCAA)-related fatty acid metabolism pathway. Altogether, our results support the notion that the gut microbiota contribute to the dietary NAD precursors metabolism in MASLD development and the dietary NAD precursors together with certain gut microbiota may be a preventive or therapeutic strategy in MASLD management.

Renal Cortical Glucose Uptake Is Decreased in Insulin Resistance and Correlates Inversely With Serum Free-fatty Acids

CONTEXT

Studies on human renal metabolism are scanty. Nowadays, functional imaging allows the characterization of renal metabolism in a noninvasive manner. We have recently demonstrated that fluorodeoxyglucose F18 (18F FDG) positron emission tomography can be used to analyze renal glucose uptake (GU) rates, and that the renal cortex is an insulin-sensitive tissue.

OBJECTIVE

To confirm that renal GU is decreased in people with obesity and to test whether circulating metabolites are related to renal GU.

DESIGN, SETTING AND PARTICIPANTS

Eighteen people with obesity and 18 nonobese controls were studied with [18F]FDG positron emission tomography during insulin clamp. Renal scans were obtained ∼60 minutes after [18F]FDG injection. Renal GU was measured using fractional uptake rate and after correcting for residual intratubular [18F]FDG. Circulating metabolites were measured using high-throughput proton nuclear magnetic resonance metabolomics.

RESULTS

Cortical GU was higher in healthy nonobese controls compared with people with obesity (4.7 [3.4-5.6] vs 3.1 [2.2-4.3], P = .004, respectively), and it associated positively with the degree of insulin sensitivity (M value) (r = 0.42, P = .01). Moreover, cortical GU was inversely associated with circulating β-OH-butyrate (r = -0.58, P = .009), acetoacetate (r = -0.48, P = .008), citrate (r = -0.44, P = .01), and free fatty acids (r = -0.68, P < .0001), even when accounting for the M value. On the contrary, medullary GU was not associated with any clinical parameters.

CONCLUSION

These data confirm differences in renal cortical GU between people with obesity and healthy nonobese controls. Moreover, the negative correlations between renal cortex GU and free fatty acids, ketone bodies, and citrate are suggestive of substrate competition in the renal cortex.

Impacts of glutamate, an exercise-responsive metabolite on insulin signaling

AIMS

Disruption of the insulin signaling pathway leads to insulin resistance (IR). IR is characterized by impaired glucose and lipid metabolism. Elevated levels of circulating glutamate are correlated with metabolic indicators and may potentially predict the onset of metabolic diseases. Glutamate receptor antagonists have significantly enhanced insulin sensitivity, and improved glucose and lipid metabolism. Exercise is a well-known strategy to combat IR. The aims of our narrative review are to summarize preclinical and clinical findings to show the correlations between circulating glutamate levels, IR and metabolic diseases, discuss the causal role of excessive glutamate in IR and metabolic disturbance, and present an overview of the exercise-induced alteration in circulating glutamate levels.

MATERIALS AND METHODS

A literature search was conducted to identify studies on glutamate, insulin signaling, and exercise in the PubMed database. The search covered articles published from December 1955 to January 2024, using the search terms of "glutamate", "glutamic acid", "insulin signaling", "insulin resistance", "insulin sensitivity", "exercise", and "physical activity".

KEY FINDINGS

Elevated levels of circulating glutamate are correlated with IR. Excessive glutamate can potentially hinder the insulin signaling pathway through various mechanisms, including the activation of ectopic lipid accumulation, inflammation, and endoplasmic reticulum stress. Glutamate can also modify mitochondrial function through Ca2+ and induce purine degradation mediated by AMP deaminase 2. Exercise has the potential to decrease circulating levels of glutamate, which can be attributed to accelerated glutamate catabolism and enhanced glutamate uptake.

SIGNIFICANCE

Glutamate may act as a mediator in the exercise-induced improvement of insulin sensitivity.