Hepatic glucose uptake, gluconeogenesis and the regulation of glycogen synthesis

PPP1R3C mediates metformin-inhibited hepatic gluconeogenesis

BACKGROUND

Metformin has been widely used to alleviate hyperglycemia in patients with type 2 diabetes mainly via suppressing hepatic gluconeogenesis. However, the underlying mechanism remains incompletely clear. Here, we aimed to explore the role of PPP1R3C in metformin-mediated inhibition of hepatic gluconeogenesis.

METHODS

The differentially expressed genes in primary mouse hepatocytes incubated with 8-Br-cAMP and metformin were analyzed by microarrays. Hepatic glucose production and gluconeogenic gene expressions were detected after adenovirus-mediated overexpression or silence of PPP1R3C in vitro and in vivo. The phosphorylation level and location of transducer of regulated CREB activity 2 (TORC2) were determined by Western blot and immunofluorescence.

RESULTS

Metformin and adenovirus-mediated activation of AMPK suppressed 8-Br-cAMP-stimulated Ppp1r3c mRNA expression in primary mouse hepatocytes. Overexpression of PPP1R3C in primary mouse hepatocytes or the livers of wild-type mice promoted hepatic glucose production and gluconeogenic gene expressions. On the contrary, adenovirus-mediated knockdown of PPP1R3C in primary mouse hepatocytes decreased hepatic gluconeogenesis, with the suppression of cAMP-stimulated gluconeogenic gene expressions and TORC2 dephosphorylation. Notably, Ppp1r3c expression was increased in the liver of db/db mice. After PPP1R3C silence in the livers of wild-type and db/db mice, blood glucose levels and hepatic glucose production were markedly lowered, with decreased expressions of key gluconeogenic enzymes and transcript factors as well as liver glycogen content.

CONCLUSION

Metformin-activated AMPK decreases hepatic PPP1R3C expression, leading to the suppression of hepatic gluconeogenesis through blocking cAMP-stimulated TORC2 dephosphorylation. Hepatic specific silence of PPP1R3C provides a promising therapeutic strategy for type 2 diabetes.

Polarity Protein AF6 Controls Hepatic Glucose Homeostasis and Insulin Sensitivity by Modulating IRS1/AKT Insulin Pathway in an SHP2-Dependent Manner

Insulin resistance is a major contributing factor in the development of metabolic disease. Although numerous functions of the polarity protein AF6 (afadin and MLLT4) have been identified, a direct effect on insulin sensitivity has not been previously described. We show that AF6 is elevated in the liver tissues of dietary and genetic mouse models of diabetes. We generated liver-specific AF6 knockout mice and show that these animals exhibit enhanced insulin sensitivity and liver glycogen storage, whereas overexpression of AF6 in wild-type mice by adenovirus-expressing AF6 led to the opposite phenotype. Similar observations were obtained from in vitro studies. In addition, we discovered that AF6 directly regulates IRS1/AKT kinase-mediated insulin signaling through its interaction with Src homology 2 domain-containing phosphatase 2 (SHP2) and its regulation of SHP2's tyrosine phosphatase activity. Finally, we show that knockdown of hepatic AF6 ameliorates hyperglycemia and insulin resistance in high-fat diet-fed or db/db diabetic mice. These results demonstrate a novel function for hepatic AF6 in the regulation of insulin sensitivity, providing important insights about the metabolic role of AF6.

Tributyltin exposure disturbs hepatic glucose metabolism in male mice

Some previous studies showed that organotin compounds induced diabetes in animal models. The underlying mechanisms should be further revealed. In this study, male KM mice were exposed to tributyltin (TBT) at 0.5, 5 and 50 μg/kg once every three days for 45 days. The TBT-treated mice exhibited an elevation of fasting blood glucose level and glucose intolerance. The fasting serum insulin levels were increased and reached a significant difference in the 50 μg/kg group; the glucagon levels were significantly decreased in all the treatments. Pancreatic β-cell mass was significantly decreased in all the treatments; α-cell mass showed a significant decrease in the 5 and 50 ug/kg groups. The transcription of pancreatic insulin gene (Ins2) showed an up-regulation and reached a significant difference in the 5 and 50 μg/kg groups, which would be responsible for the increased serum insulin levels. The transcription of glucagon gene (Gcg) in the pancreas was significantly down-regulated in the 5 and 50 ug/kg groups. The protein expression of hepatic glucagon receptor was down-regulated, while the expression of glucose-6-phosphatase and phosphoenolpyruvate carboxykinase was up-regulated accompanied by increased hepatic glycogen content. These results indicated that hepatic gluconeogenesis was enhanced during insulin resistance stage caused by TBT exposure, which would exert a potential risk inducing the development of diabetes mellitus.

Role of cadmium and arsenic as endocrine disruptors in the metabolism of carbohydrates: Inserting the association into perspectives

Endocrine disrupting chemicals (EDCs) have widespread environmental distribution originated from both natural and anthropogenic sources. From the last few decades, their contamination has been raised dramatically owing to continuous discharge in sewage and untreated industrial effluents. They have rapidly gained a considerable attention due to their critical role in the development of multiple endocrine-related disorders notably diabetes mellitus (DM). Cadmium and arsenic, among the most hazardous EDCs, are not only widely spread in our environment, but they are also found to be associated with wide range of health hazards. After entering into the human body, they are preferably accumulated in the liver, kidney and pancreas where they exhibit deleterious effects on carbohydrate metabolism pathways notably glycolysis, glucogenesis and gluconeogenesis through the modification and impairment of relevant key enzymes activity. Impairment of hepatic glucose homeostasis plays a crucial role in the pathogenesis of DM. Along with compromised function of pancreas and muscles, diminished liver and kidney functions also contribute considerably to increase the blood glucose level. These metals have potential to bring conformational changes in these enzymes and make them inactive. Additionally, these metals also disturb the hormonal balance, such as insulin, glucocorticoids and catecholamines; by damaging pancreas and adrenal gland, respectively. Moreover, these metals also enhance the production of reactive oxygen species and depress the anti-oxidative defense mechanism with subsequent disruption of multiple organs. In this article, we have briefly highlighted the impact of arsenic and cadmium on the metabolism of carbohydrates and the enzymes that are involved in carbohydrate metabolism and glucose homeostasis.

The proinflammatory effects of chronic excessive exercise

Chronic moderate-intensity exercise is an efficient non-pharmacological strategy to prevent and treat several diseases such as type 2 diabetes mellitus, cardiovascular and chronic obstructive pulmonary diseases, cancers, and Parkinson's disease. On the other hand, improving an athlete's performance requires completing high-intensity and volume exercise sessions. When the delicate balance between high-load exercise sessions and adequate recovery periods is disrupted, excessive training (known as overtraining) can lead to performance decline. The cytokine hypothesis considers that an imbalance involving excessive exercise and inadequate recovery induces musculoskeletal trauma, increasing the production and release of proinflammatory cytokines, mainly interleukin 6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), and interleukin 1beta (IL-1beta), which interact with different organic systems, initiating most of the signs and symptoms linked to performance decrement. This leading article used recent data to discuss the scientific basis of Smith's cytokine theory and highlighted that the adverse effects of excessive exercise go beyond performance decline, proposing a multi-organ approach for this issue. These recent insights will allow coaches and exercise physiologists to develop strategies to avoid chronic excessive exercise-induced adverse outcomes.

Insulin receptors in the kidneys in health and disease

Insulin is an important hormone that affects various metabolic processes, including kidney function. Impairment in insulin’s action leads to insulin resistance in the target tissue. Besides defects in post-receptor insulin signaling, impairment at the receptor level could significantly affect insulin sensitivity of the target tissue. The kidney is a known target of insulin; however, whether the kidney develops “insulin resistance” is debatable. Regulation of the insulin receptor (IR) expression and its function is very well studied in major metabolic tissues like liver, skeletal muscles, and adipose tissue. The physiological relevance of IRs in the kidney has recently begun to be clarified. The credit goes to studies that showed a wide distribution of IR throughout the nephron segments and their reduced expression in the insulin resistance state. Moreover, altered renal and systemic metabolism observed in mice with targeted deletion of the IR from various epithelial cells of the kidney has strengthened this proposition. In this review, we recapitulate the crucial findings from literature that have expanded our knowledge regarding the significance of the renal IR in normal- and insulin-resistance states.

Molecular pathways of nonalcoholic fatty liver disease development and progression

Nonalcoholic fatty liver disease (NAFLD) is a main hepatic manifestation of metabolic syndrome. It represents a wide spectrum of histopathological abnormalities ranging from simple steatosis to nonalcoholic steatohepatitis (NASH) with or without fibrosis and, eventually, cirrhosis and hepatocellular carcinoma. While hepatic simple steatosis seems to be a rather benign manifestation of hepatic triglyceride accumulation, the buildup of highly toxic free fatty acids associated with insulin resistance-induced massive free fatty acid mobilization from adipose tissue and the increased de novo hepatic fatty acid synthesis from glucose acts as the "first hit" for NAFLD development. NAFLD progression seems to involve the occurrence of "parallel, multiple-hit" injuries, such as oxidative stress-induced mitochondrial dysfunction, endoplasmic reticulum stress, endotoxin-induced, TLR4-dependent release of inflammatory cytokines, and iron overload, among many others. These deleterious factors are responsible for the triggering of a number of signaling cascades leading to inflammation, cell death, and fibrosis, the hallmarks of NASH. This review is aimed at integrating the overwhelming progress made in the characterization of the physiopathological mechanisms of NAFLD at a molecular level, to better understand the factor influencing the initiation and progression of the disease.

Contribution of Non-canonical Cortisol Actions in the Early Modulation of Glucose Metabolism of Gilthead Sea Bream (Sparus aurata)

Teleost fish are exposed to diverse stressors in farming and wildlife conditions during their lifespan. Cortisol is the main glucocorticoid hormone involved in the regulation of their metabolic acclimation under physiological stressful conditions. In this context, increased plasma cortisol is associated with energy substrate mobilization from metabolic tissues, such as liver and skeletal muscle, to rapidly obtain energy and cope with stress. The metabolic actions of cortisol have primarily been attributed to its genomic/classic action mechanism involving the interaction with intracellular receptors, and regulation of stress-responsive genes. However, cortisol can also interact with membrane components to activate rapid signaling pathways. In this work, using the teleost fish gilthead sea bream (Sparus aurata) as a model, we evaluated the effects of membrane-initiated cortisol actions on the early modulation of glucose metabolism. For this purpose, S. aurata juveniles were intraperitoneally administrated with cortisol and with its membrane impermeable analog, cortisol-BSA. After 1 and 6 h of each treatment, plasma cortisol levels were measured, together with glucose, glycogen and lactate in plasma, liver and skeletal muscle. Transcript levels of corticosteroids receptors (gr1, gr2, and mr) and key gluconeogenesis (g6pc and pepck)- and glycolysis (pgam1 and aldo) related genes in the liver were also measured. Cortisol and cortisol-BSA administration increased plasma cortisol levels in S. aurata 1 h after administration. Plasma glucose levels enhanced 6 h after each treatment. Hepatic glycogen content decreased in the liver at 1 h of both cortisol and cortisol-BSA administration, while increased at 6 h due to cortisol but not in response to cortisol-BSA. Expression of gr1, g6pc, pgam1, and aldo were preferentially increased by cortisol-BSA in the liver. Taking all these results in consideration, we suggest that non-canonical cortisol mechanisms contribute to the regulation of the early glucose metabolism responses to stress in S. aurata.

Inhibition of SphK2 Stimulated Hepatic Gluconeogenesis Associated with Dephosphorylation and Deacetylation of STAT3

BACKGROUND

Sphingosine kinase (SphK) is considered as a potential target for developing novel therapeutics of cancer and other diseases including diabetes. As the major SphK isoform in the liver, much less is known the role of SphK2 involved in regulating hepatic glucose metabolism.

METHOD

In this study, RNA interference, real time RT-PCR, western blot and immunoprecipitation method was used to investigate the regulation of SphK2 in hepatic glucose metabolism.

RESULTS

Both siRNA and SphK2 inhibitor ABC294640 stimulated expression of gluconeogenetic gene PEPCK and G6Pase but not enzymes of hepatic glycogenolysis, glycolysis and glycogen synthesis. Inhibition of SphK2 also prevented insulin repressed PEPCK and G6Pase expression as well as glucose production levels. Furtherly, inhibition of SphK2 inactivated STAT3 by decreasing both phosphorylation on Tyr705 and acetylation on lysine residue, and led to stimulation of PEPCK and G6Pase expression. Inhibition of SphK2 also prevented IL-6 dependent activation of STAT3 and suppression of PEPCK and G6pase expression both in vitro and in vivo.

CONCLUSION

Our study suggests that SphK2 participates in hepatic glucose metabolism related to activation of STAT3.

Involvement of AMPK activation in the inhibition of hepatic gluconeogenesis by Ficus carica leaf extract in diabetic mice and HepG2 cells

The aim of this study was to explore the possible mechanisms of Ficus carica leaf (FCL) extract in suppressing hepatic gluconeogenesis in diabetic mice. Diabetic mice (streptozotocin-induced) received 1 g/kg of FCL extract twice a day for 6 weeks. Fasting blood glucose levels were measured and a 2-h oral glucose tolerance test was conducted. AMP-activated protein kinase (AMPK), phosphoenolpyruvate carboxykinase (PEPCK), glucose-6-phosphatase (G6Pase), and peroxisome proliferator activated receptor-γ coactivator-1α (PGC-1α) expression was examined. HepG2 hepatocytes were treated with FCL extract and an AMPK inhibitor (compound C) or agonist (AICAR), and PEPCK, G6pase, PGC-1α, AMPK, forkhead transcription factor O1 (FOXO1), and hepatic nuclear factor 4α (HNF4α) expression was determined. The results showed that FCL extract inhibited the expression of PEPCK and G6Pase in the liver of diabetic mice and HepG2 hepatocytes. FCL extract activated AMPK and decreased PGC-1α, HNF4α, and FOXO1 expression. The AMPK inhibitor attenuated those effects through inhibiting gluconeogenesis, while the AMPK agonist partially enhanced gluconeogenesis. In conclusion, FCL extract inhibits hepatic gluconeogenesis via activation of AMPK and down-regulation of gluconeogenic enzymes.

Time course of fractional gluconeogenesis after meat ingestion in healthy adults: a D2O study

In the postprandial state, glucose homeostasis is challenged by macronutrient intake, including proteins that trigger insulin secretion and provide glucose precursors. However, little is known about the postprandial response of gluconeogenesis to a protein meal. We aimed to quantify the evolution of fractional gluconeogenesis after a meat meal. Thirteen healthy subjects received oral doses of D₂O. After fasting overnight, they ingested a steak (120 g). Glycemia, insulinemia, and ²H enrichments in glucose and plasma water were measured for 8 h after the meal. Fractional gluconeogenesis was assessed using the average method. Glucose was stable for 5 h and then decreased. There was a slight increase of insulin 1 h after the meal. ²H enrichment in the carbon 5 position of glucose (C5) increased after 2 h, whereas it decreased in plasma water. Consequently, fractional gluconeogenesis increased from 68.2 ± 7.2% before the meal to 75.5 ± 5.8% 8 h after the meal, the latter corresponding to 22 h without a glucose supply. These values are consistent with the exhaustion of glycogen stores after 24 h but represent the highest among values in the literature. The impact of methodological conditions is discussed.

miR‑338‑3p mediates gluconeogenesis via targeting of PP4R1 in hepatocytes

Hyperglycaemia is a characteristic of type 2 diabetes. In hepatocytes, impaired insulin sensitivity leads to increased gluconeogenesis and decreased glycogenesis. MicroRNA (miR)‑338‑3p is associated with tumour necrosis factor (TNF)‑α‑induced suppression of hepatic glycogenesis via regulation of protein phosphatase 4 regulatory subunit 1 (PP4R1). However, the effect of miR‑338‑3p on gluconeogenesis in hepatocytes remains unknown. In a previous study, it was demonstrated that miR‑338‑3p is downregulated in the livers of mice and in mouse HEPA1‑6 hepatocytes following treatment with TNF‑α. In the present study, the effect of miR‑338‑3p on TNF‑α‑induced gluconeogenesis in hepatocytes was investigated. The levels of phosphorylated‑FOXO1/FOXO1, phosphoenolpyruvate carboxykinase (PEPCK), peroxisome proliferator‑activated receptor γ coactivator (PGC‑1α) and glucose‑6‑phosphatase (G6Pase) were measured by western blotting. The mRNA levels of PEPCK, PGC‑1α and G6Pase were determined by quantitative polymerase chain reaction. Pyruvate tolerance testing was used to determine the gluconeogenesis of mouse livers. The results demonstrated that treatment with TNF‑α resulted in increased levels of gluconeogenesis in the livers of mice and decreased miR‑338‑3p expression levels in HEPA1‑6 cells. Overexpression of miR‑338‑3p reversed TNF‑α‑induced glucose production via enhancement of phosphorylated forkhead box O1 levels and downregulation of the expression levels of genes associated with gluconeogenesis, including peroxisome proliferator‑activated receptor γ coactivator‑1α, phosphoenolpyruvate carboxykinase and glucose‑6‑phosphatase. However, inhibition of miR‑338‑3p expression was revealed to enhance gluconeogenesis in the livers of mice and in HEPA1‑6 cells. Furthermore, downregulation of PP4R1 was revealed to attenuate the effect on glucose production following treatment with miR‑338‑3p inhibitors. In conclusion, the results of the present study revealed that miR‑338‑3p may be involved in TNF‑α‑mediated gluconeogenesis via targeting of PP4R1 in hepatocytes.

Tributyltin reduces the levels of serum adiponectin and activity of AKT and induces metabolic syndrome in male mice

Tributyltin (TBT), a proven environmental obesogen, functions as a nanomolar agonist of the peroxisome proliferator activated receptor-γ (PPARγ). However, the adverse effects of TBT on metabolism are incompletely understood. In this study, male ICR mice were administered TBT (5 and 50 μg·kg^-1 ) by an intraperitoneal injection once every 3 days for 30 days from 28 days of age and bred for another 30 days after the last administration of TBT. We analyzed the effects of these exposures on the fat depot weights, serum lipid profile, serum leptin and adiponectin, hepatic lipid accumulation, and activity of AKT in the liver and skeletal muscle isolated from mice 8 mins after receiving an insulin injection. Pubertal exposure to TBTCl resulted in a higher body weight, increased epididymal and liver fat accumulation, hyperlipidemia, an elevated low-density lipoprotein/high-density lipoprotein ratio, serum adiponectin deficiency, worse glucose tolerance, and lower insulin-dependent AKT phosphorylation in the liver and muscle in mice. These results showed that TBT exposure induced peripheral insulin resistance and metabolic syndrome in mice.

p300/CBP as a Key Nutritional Sensor for Hepatic Energy Homeostasis and Liver Fibrosis

The overwhelming frequency of metabolic diseases such as obesity and diabetes are closely related to liver diseases, which might share common pathogenic signaling processes. These metabolic disorders in the presence of inflammatory response seem to be triggered by and to reside in the liver, which is the central metabolic organ that plays primary roles in regulating lipid and glucose homeostasis upon alterations of metabolic conditions. Recently, abundant emerging researches suggested that p300 and CREB binding protein (CBP) are crucial regulators of energy homeostasis and liver fibrosis through both their acetyltransferase activities and transcriptional coactivators. Plenty of recent findings demonstrated the potential roles of p300/CBP in mammalian metabolic homeostasis in response to nutrients. This review is focused on the different targets and functions of p300/CBP in physiological and pathological processes, including lipogenesis, lipid export, gluconeogenesis, and liver fibrosis, also provided some nutrients as the regulator of p300/CBP for nutritional therapeutic approaches to treat liver diseases.

Sirt2 facilitates hepatic glucose uptake by deacetylating glucokinase regulatory protein

Impaired hepatic glucose uptake (HGU) causes postprandial hyperglycemia in type 2 diabetes. Here, we show that diminished hepatic Sirt2 activity impairs HGU in obese diabetic mice. Hepatic Sirt2 overexpression increases HGU in high-fat diet (HFD)-fed obese diabetic mice and mitigates their impaired glucose tolerance. Hepatic Sirt2 knockdown in non-diabetic mice reduces HGU and causes impaired glucose tolerance. Sirt2 promotes glucose-dependent HGU by deacetylating K126 of glucokinase regulatory protein (GKRP). Glucokinase and GKRP glucose-dependent dissociation is necessary for HGU but is inhibited in hepatocytes derived from obese diabetic mice, depleted of Sirt2 or transfected with GKRP acetylation-mimicking mutants. GKRP deacetylation-mimicking mutants dissociate from glucokinase in a glucose concentration-dependent manner in obese diabetic mouse-derived hepatocytes and increase HGU and glucose tolerance in HFD-induced or db/db obese diabetic mice. We demonstrate that Sirt2-dependent GKRP deacetylation improves impaired HGU and suggest that it may be a therapeutic target for type 2 diabetes.

During diabetes, postprandial hyperglycemia is caused by impaired glucose uptake. Here, Watanabe and colleagues show that impaired hepatic glucose uptake during obesity is caused by a reduction in Sirt2 activity, which promotes glucokinase regulatory protein acetylation and its dissociation from glucokinase.

Hepatoprotective Effects of Nonpolar Extracts from Inflorescences of Thistles Cirsium vulgare and Cirsium ehrenbergii on Acute Liver Damage in Rat

BACKGROUND

Drugs for the treatment of liver diseases are scarce and not effective enough. Some species of the genus Cirsium possess hepatoprotective activity. There are no studies on the hepatoprotective effects of nonpolar extracts from inflorescences of thistles Cirsium vulgare and Cirsium ehrenbergii, and there are few reports on their chemical composition.

OBJECTIVE

The aim is to obtain the hexane extract from inflorescences of both thistles and to identify preliminarily their main chemical component, and to evaluate the hepatoprotective properties of the extracts.

MATERIALS AND METHODS

Hexane extracts were obtained using a Soxhlet apparatus. The chemical composition was analyzed using infrared spectra and gas chromatography-mass spectrometry. Two doses (250 and 500 mg/kg, p.o.) of both extracts were administered to assess their hepatoprotective effect on acute carbon tetrachloride (TC)-induced liver damage in rats using biochemical markers of necrosis, cholestasis, functionality, oxidative stress, and histological analysis.

RESULTS

Extracts were shown to have a very similar chemical profile. Their major constituent seems to be lupeol acetate. The two doses of both extracts demonstrated comparable hepatoprotective properties because they significantly diminished all the liver injury indicators (P < 0.05) and were corroborated using histopathology.

CONCLUSION

This is the first study on the hepatoprotective effects of nonpolar extracts from inflorescences of thistles C. vulgare and C. ehrenbergii. Hexane extracts administration totally prevented the acute TC-induced liver damage. The preliminary chemical analysis strongly suggests the lupeol acetate as their major constituent. Lupeol and its derivatives have been previously reported as antiinflammatory and hepatoprotective agents.

SUMMARY

Hexane extracts of both thistles kept normal liver functionality and glycogen store in carbon tetrachloride-induced acute liver damageHexane extracts of both thistles showed anti-necrotic and anti-cholestatic effects, also diminished the lipid peroxidation and nitric oxide levels on the carbon tetrachloride-induced acute liver damageThe two doses of hexane extracts administered (250 and 500 mg/kg) prevented the liver injury in a very similar extentBoth nonpolar extracts are chemically very similar and their main compound seems to be lupeol acetate. Abbreviations used: TC: Carbon tetrachloride; FT-IR: Fourier transform Infrared spectroscopy; GC-MS: Gas chromatography - Mass spectrometry; V: Vehicle; E: Extract; Ecv: Extract of Cirsium vulgare; Ece: Extract of Cirsium ehrenbergii; AP: Alkaline phosphatase; GGTP: γ-Glutamyl transpeptidase; ALT: Alanine aminotransferase; DB: Direct bilirubin; TB: Total bilirubin; LP: Lipid peroxidation; MDA: Malondialdehyde; NO: Nitric oxide; TNF-α: Tumor necrosis factor-α.

Current trends in small molecule discovery targeting key cellular signaling events towards the combined management of diabetes and obesity

Non-insulin dependent diabetes mellitus, also known as Type 2 diabetes is a polygenic disorder leading to abnormalities in the carbohydrate and lipid metabolism. The major contributors in the pathophysiology of type 2 diabetes (T2D) include resistance to insulin action, β cell dysfunction, an abnormality in glucose metabolism and storage, visceral obesity and to some extent inflammation and oxidative stress. Insulin resistance, along with a defect in insulin secretion by the pancreatic β cells is instrumental towards progression to hyperglycemia. Increased incidence of obesity is also a major contributing factor in the escalating rates of type 2 diabetes. Drug discovery efforts are therefore crucially dependent on identifying individual molecular targets and validating their relevance to human disease. The current review discusses bioactive compounds from medicinal plants offering enhanced therapeutic potential for the combined patho-physiology of diabetes and obesity. We have demonstrated that 3β-taraxerol a pentacyclic triterpenoid (14-taraxeren-3-ol) isolated from the ethyl acetate extract of Mangifera indica, chlorogenic acid isolated from the methanol extract of Cichorium intybus, methyl tetracosanoate from the methanol extract of Costus pictus and vitalboside A derived from methanolic extract of Syzygium cumini exhibited significant effects on insulin stimulated glucose uptake causing insulin sensitizing effects on 3T3L1 adipocytes (an in vitro model mimicking adipocytes). Whereas, (3β)-stigmast-5-en-3-ol isolated from Adathoda vasica and Aloe emodin isolated from Cassia fistula showed significant insulin mimetic effects favoring glucose uptake in L6 myotubes (an in vitro model mimicking skeletal muscle cells). These extracts and molecules showed glucose uptake through activation of PI3K, an important insulin signaling intermediate. Interestingly, cinnamic acid isolated from the hydro-alcohol extract of Cinnamomum cassia was found to activate glucose transport in L6 myotubes through the involvement of GLUT4 via the PI3K-independent pathway. However, the activation of glucose storage was effective in the presence of 3β-taraxerol and aloe emodin though inhibition of GSK3β activity. Therefore, the mechanism of improvement of glucose and lipid metabolism exhibited by the small molecules isolated from our lab is discussed. However, Obesity is a major risk factor for type-2 diabetes leading to destruction of insulin receptors causing insulin resistance. Identification of compounds with dual activity (anti-diabetic and antiadipogenic activity) is of current interest. The protein tyrosine phosphatase 1B (PTP1B) is an important negative regulator of the insulin and leptin-signaling pathway is of significance in target definition and discovery.

FBP1 expression is associated with basal-like breast carcinoma

The present study aimed to investigate the value of liver fructose 1,6-bisphophatase (FBP1) and hypoxia-inducible factor-1α (HIF-1α) in the molecular subtyping of breast carcinoma. Tissue obtained from 60 surgical specimens from patients with breast carcinoma underwent immunohistochemical staining for cytokeratin 5/6, HIF-1α and FBP1. The variation in the expression levels of these markers and clinicopathological factors were compared between molecular subtypes. In addition, disease-free survival was compared between basal-like and luminal breast carcinoma, according to differing expression levels of HIF-1α and FBP1. The results revealed that HIF-1α expression was detectable in 20/60 (33.3%) of the breast carcinoma cases, and was positively associated with lymph node metastasis (P=0.007). HIF-1α-positive patients exhibited a shorter disease-free survival, compared with HIF-1α-negative patients with invasive breast cancer. The expression levels of FBP1 were positive in 33/60 tumor tissues (55%; P<0.001), and FBP1 expression was associated with nuclear grade (P=0.017) and tumor stage (P=0.012). In breast carcinoma, HIF-1α expression levels were significantly negatively correlated with FBP1 levels (r=-0.711; P<0.001). Cox regression analysis identified FBP1 and tumor size as independent prognostic factors. Therefore, the present study demonstrated that patients with basal-like breast carcinoma exhibited lower levels of FBP1 expression in tumor tissues, compared with patients with luminal type breast cancer, and that low or absent expression levels of FBP1 may be associated with reduced disease-free survival.

c-MYC-Making Liver Sick: Role of c-MYC in Hepatic Cell Function, Homeostasis and Disease

Over 35 years ago, c-MYC, a highly pleiotropic transcription factor that regulates hepatic cell function, was identified. In recent years, a considerable increment in the number of publications has significantly shifted the way that the c-MYC function is perceived. Overexpression of c-MYC alters a wide range of roles including cell proliferation, growth, metabolism, DNA replication, cell cycle progression, cell adhesion and differentiation. The purpose of this review is to broaden the understanding of the general functions of c-MYC, to focus on c-MYC-driven pathogenesis in the liver, explain its mode of action under basal conditions and during disease, and discuss efforts to target c-MYC as a plausible therapy for liver disease.

Increased liver fat and glycogen stores after consumption of high versus low glycaemic index food: A randomized crossover study

AIM

To investigate the acute and longer-term effects of low (LGI) versus high glycaemic index (HGI) diets on hepatic fat and glycogen accumulation and related blood measures in healthy volunteers.

METHODS

Eight healthy men (age 20.1 ± 0.4 years, body mass index 23.0 ± 0.9 kg/m² ) attended a test day before and after a 7-day macronutrient- and energy-matched HGI or LGI diet, followed by a minimum 4-week wash-out period, and then returned to repeat the intervention with the alternative diet. During test days, participants consumed either an HGI or an LGI test meal corresponding to their diet week, and liver fat [ ¹ H magnetic resonance spectroscopy (MRS)], glycogen ( ¹³ C MRS) and gastric content volume (MRI) were measured. Blood samples were obtained regularly throughout the test day to assess plasma glucose and insulin levels.

RESULTS

Plasma glucose and insulin peak values and area under the curve were significantly greater after the HGI test meal compared with the LGI test meal, as expected. Hepatic glycogen concentrations increased more after the HGI test meal ( P < .05) and peak levels were significantly greater after 7 days of HGI dietary intervention compared with those at the beginning of the intervention ( P < .05). Liver fat fractions increased significantly after the HGI dietary intervention compared with the LGI dietary intervention (two-way repeated-measures analysis of variance P ≤ .05).

CONCLUSIONS

Compared with an LGI diet, a 1-week HGI diet increased hepatic fat and glycogen stores. This may have important clinical relevance for dietary interventions in the prevention and management of non-alcoholic fatty liver disease.

Recurrent nightly ketosis after prolonged exercise in type 1 diabetes - the need for glycogen replacement strategies. Case report and review of literature

Exercise in diabetes patients has many benefits but also several risks, of which hypoglycemia is most often discussed. We present a case with recurrent keto-acidosis post-exercise, in which we hypothesize that glycogen replacement strategies were insufficient. Our experience in this case and review of the literature emphasize the importance of discussing glycogen replacement strategies with your diabetic athletes.

Combined pharmacological activation of AMPK and PPARδ potentiates the effects of exercise in trained mice

The combined activation of the cellular energy sensor AMP‐activated protein kinase (AMPK) and the nuclear transcription factor peroxisome proliferator‐activated receptor delta (PPARδ) has been demonstrated to improve endurance and muscle function by mimicking the effects of exercise training. However, their combined pharmacological activation with exercise training has not been explored. Balb/c mice were trained on a treadmill and administered both the AMPK activator AICAR and the PPARδ agonist GW0742 for 4 weeks. AICAR treatment potentiated endurance, but the combination of AICAR and GW0742 further potentiated endurance and increased all running parameters significantly relative to exercised and nonexercised groups (138–179% and 355% increase in running time, respectively). Despite the lack of change in basal whole‐body metabolism, a significant shift to fat as the main energy source with a decline in carbohydrate utilization was observed upon indirect calorimetry analysis at the period near exhaustion. Increased energy substrates before exercise, and elevated muscle nonesterified fatty acids (NEFA) and elevated muscle glycogen at exhaustion were observed together with increased PDK4 mRNA expression. Citrate synthase activity was elevated in AICAR‐treated groups, while PGC‐1α protein level tended to be increased in GW0742‐treated groups. At exhaustion, Pgc1a was robustly upregulated together with Pdk4, Cd36, and Lpl in the muscle. A robust upregulation of Pgc1a and a downregulation in Chrebp were observed in the liver. Our data show that combined pharmacological activation of AMPK and PPARδ potentiates endurance in trained mice by transcriptional changes in muscle and liver, increased available energy substrates, delayed hypoglycemia through glycogen sparing accompanied by increased NEFA availability, and improved substrate shift from carbohydrate to fat.

Targeting hepatic glucose metabolism in the treatment of type 2 diabetes

Type 2 diabetes mellitus is characterized by the dysregulation of glucose homeostasis, resulting in hyperglycaemia. Although current diabetes treatments have exhibited some success in lowering blood glucose levels, their effect is not always sustained and their use may be associated with undesirable side effects, such as hypoglycaemia. Novel antidiabetic drugs, which may be used in combination with existing therapies, are therefore needed. The potential of specifically targeting the liver to normalize blood glucose levels has not been fully exploited. Here, we review the molecular mechanisms controlling hepatic gluconeogenesis and glycogen storage, and assess the prospect of therapeutically targeting associated pathways to treat type 2 diabetes.

Reduced Insulin Receptor Expression Enhances Proximal Tubule Gluconeogenesis

Reduced insulin receptor protein levels have been reported in the kidney cortex from diabetic humans and animals. We recently reported that, targeted deletion of insulin receptor (IR) from proximal tubules (PT) resulted in hyperglycemia in non-obese mice. To elucidate the mechanism, we examined human proximal tubule cells (hPTC) and C57BL/6 mice fed with high-fat diet (HFD, 60% fat for 20 weeks). Immunoblotting revealed a significantly lower protein level of IR in HFD compare to normal chow diet (NCD). Furthermore, a blunted rise in p-AKT³⁰⁸ levels in the kidney cortex of HFD mice was observed in response to acute insulin (0.75 IU/kg body weight, i.p) relative to NCD n = 8/group, P < 0.05). Moreover, we found significantly higher transcript levels of phosphoenolpyruvate carboxykinase (PEPCK, a key gluconeogenic enzyme) in the kidney cortex from HFD, relative to mice on NCD. The higher level of PEPCK in HFD was confirmed by immunoblotting. However, no significant differences were observed in cortical glucose-6-phosphatase (G6Pase) or fructose-1,6, bisphosphosphatase (FBPase) enzyme transcript levels. Furthermore, we demonstrated insulin inhibited glucose production in hPTC treated with cyclic AMP and dexamethasone (cAMP/DEXA) to stimulate gluconeogenesis. Transcript levels of the gluconeogenic enzyme PEPCK were significantly increased in cAMP/DEXA-stimulated hPTC cells (n = 3, P < 0.05), and insulin attenuated this upregulation Furthermore, the effect of insulin on cAMP/DEXA-induced gluconeogenesis and PEPCK induction was significantly attenuated in IR (siRNA) silenced hPTC (n = 3, P < 0.05). Overall the above data indicate a direct role for IR expression as a determinant of PT-gluconeogenesis. Thus reduced insulin signaling of the proximal tubule may contribute to hyperglycemia in the metabolic syndrome via elevated gluconeogenesis. J. Cell. Biochem. 118: 276-285, 2017. © 2016 Wiley Periodicals, Inc.

Metformin improves hepatic IRS2/PI3K/Akt signaling in insulin-resistant rats of NASH and cirrhosis

Nonalcoholic fatty liver disease and cirrhosis are strongly associated with insulin resistance and glucose intolerance. To date, the influence of metformin on glycogen synthesis in the liver is controversial. Limited studies have evaluated the effect of metformin on hepatic insulin signaling pathway in vivo In this study, an insulin-resistant rat model of nonalcoholic steatohepatitis and cirrhosis was developed by high-fat and high-sucrose diet feeding in combination with subcutaneous injection of carbon tetrachloride. Liver tissues of the model rats were featured with severe steatosis and cirrhosis, accompanied by impaired liver function and antioxidant capacity. The glucose tolerance was impaired, and the index of insulin resistance was increased significantly compared with the control. The content of hepatic glycogen was dramatically decreased. The expression of insulin receptor β (IRβ); phosphorylations of IRβ, insulin receptor substrate 2 (IRS2), and Akt; and activities of phosphatidylinositol 3-kinase (PI3K) and glycogen synthase (GS) in the liver were significantly decreased, whereas the activities of glycogen synthase kinase 3α (GSK3α) and glycogen phosphorylase a (GPa) were increased. Metformin treatment remarkably improved liver function, alleviated lipid peroxidation and histological damages of the liver, and ameliorated glucose intolerance and insulin resistance. Metfromin also significantly upregulated the expression of IRβ; increased the phosphorylations of IRβ, IRS2, and Akt; increased the activities of PI3K and GS; and decreased GSK3α and GPa activities. In conclusion, our study suggests that metformin upregulates IRβ expression and the downstream IRS2/PI3K/Akt signaling transduction, therefore, to increase hepatic glycogen storage and improve insulin resistance. These actions may be attributed to the improved liver histological alterations by metformin.

Nutritional regulation of the anabolic fate of amino acids within the liver in mammals: concepts arising from in vivo studies

At the crossroad between nutrient supply and requirements, the liver plays a central role in partitioning nitrogenous nutrients among tissues. The present review examines the utilisation of amino acids (AA) within the liver in various physiopathological states in mammals and how the fates of AA are regulated. AA uptake by the liver is generally driven by the net portal appearance of AA. This coordination is lost when demands by peripheral tissues is important (rapid growth or lactation), or when certain metabolic pathways within the liver become a priority (synthesis of acute-phase proteins). Data obtained in various species have shown that oxidation of AA and export protein synthesis usually responds to nutrient supply. Gluconeogenesis from AA is less dependent on hepatic delivery and the nature of nutrients supplied, and hormones like insulin are involved in the regulatory processes. Gluconeogenesis is regulated by nutritional factors very differently between mammals (glucose absorbed from the diet is important in single-stomached animals, while in carnivores, glucose from endogenous origin is key). The underlying mechanisms explaining how the liver adapts its AA utilisation to the body requirements are complex. The highly adaptable hepatic metabolism must be capable to deal with the various nutritional/physiological challenges that mammals have to face to maintain homeostasis. Whereas the liver responds generally to nutritional parameters in various physiological states occurring throughout life, other complex signalling pathways at systemic and tissue level (hormones, cytokines, nutrients, etc.) are involved additionally in specific physiological/nutritional states to prioritise certain metabolic pathways (pathological states or when nutritional requirements are uncovered).

A Polysaccharide from Ganoderma atrum Improves Liver Function in Type 2 Diabetic Rats via Antioxidant Action and Short-Chain Fatty Acids Excretion

The present study was to evaluate the beneficial effect of polysaccharide isolated from Ganoderma atrum (PSG-1) on liver function in type 2 diabetic rats. Results showed that PSG-1 decreased the activities of serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT), while increasing hepatic glycogen levels. PSG-1 also exerted strong antioxidant activities, together with upregulated mRNA expression of peroxisome proliferator-activated receptor-γ (PPAR-γ), glucose transporter-4 (GLUT4), phosphoinositide 3-kinase (PI3K), and phosphorylated-Akt (p-Akt) in the liver of diabetic rats. Moreover, the concentrations of short-chain fatty acids (SCFA) were significantly higher in the liver, serum, and faeces of diabetic rats after treating with PSG-1 for 4 weeks. These results suggest that the improvement of PSG-1 on liver function in type 2 diabetic rats may be due to its antioxidant effects, SCFA excretion in the colon from PSG-1, and regulation of hepatic glucose uptake by inducing GLUT4 translocation through PI3K/Akt signaling pathways.

Influence of plasma macronutrient levels on hepatic metabolism: role of regulatory networks in homeostasis and disease states

Multilevel regulations by metabolic, signaling and transcription pathways form a complex network that works to provide robust metabolic regulation in the liver. This analysis indicates that dietary perturbations in these networks can lead to insulin resistance.

Thermo-responsive polymer aided spheroid culture in cryogel based platform for high throughput drug screening

A versatile and widely applicable cryogel-based high throughput platform for spheroid culture in the presence of a thermo-responsive polymer and drug screening.

da Silva AS. Downhill Running-Based Overtraining Protocol Improves Hepatic Insulin Signaling Pathway without Concomitant Decrease of Inflammatory Proteins

The purpose of this study was to verify the effects of overtraining (OT) on insulin, inflammatory and gluconeogenesis signaling pathways in the livers of mice. Rodents were divided into control (CT), overtrained by downhill running (OTR/down), overtrained by uphill running (OTR/up) and overtrained by running without inclination (OTR). Rotarod, incremental load, exhaustive and grip force tests were used to evaluate performance. Thirty-six hours after a grip force test, the livers were extracted for subsequent protein analyses. The phosphorylation of insulin receptor beta (pIRbeta), glycogen synthase kinase 3 beta (pGSK3beta) and forkhead box O1 (pFoxo1) increased in OTR/down versus CT. pGSK3beta was higher in OTR/up versus CT, and pFoxo1 was higher in OTR/up and OTR versus CT. Phosphorylation of protein kinase B (pAkt) and insulin receptor substrate 1 (pIRS–1) were higher in OTR/up versus CT and OTR/down. The phosphorylation of IκB kinase alpha and beta (pIKKalpha/beta) was higher in all OT protocols versus CT, and the phosphorylation of stress-activated protein kinases/Jun amino-terminal kinases (pSAPK-JNK) was higher in OTR/down versus CT. Protein levels of peroxisome proliferator-activated receptor-gamma coactivator 1alpha (PGC-1alpha) and hepatocyte nuclear factor 4alpha (HNF-4alpha) were higher in OTR versus CT. In summary, OTR/down improved the major proteins of insulin signaling pathway but up-regulated TRB3, an Akt inhibitor, and its association with Akt.

A new level of regulation in gluconeogenesis: metabolic state modulates the intracellular localization of aldolase B and its interaction with liver fructose-1,6-bisphosphatase

Understanding how glucose metabolism is finely regulated at molecular and cellular levels in the liver is critical for knowing its relationship to related pathologies, such as diabetes. In order to gain insight into the regulation of glucose metabolism, we studied the liver-expressed isoforms aldolase B and fructose-1,6-bisphosphatase-1 (FBPase-1), key enzymes in gluconeogenesis, analysing their cellular localization in hepatocytes under different metabolic conditions and their protein-protein interaction in vitro and in vivo. We observed that glucose, insulin, glucagon and adrenaline differentially modulate the intracellular distribution of aldolase B and FBPase-1. Interestingly, the in vitro protein-protein interaction analysis between aldolase B and FBPase-1 showed a specific and regulable interaction between them, whereas aldolase A (muscle isozyme) and FBPase-1 showed no interaction. The affinity of the aldolase B and FBPase-1 complex was modulated by intermediate metabolites, but only in the presence of K(+). We observed a decreased association constant in the presence of adenosine monophosphate, fructose-2,6-bisphosphate, fructose-6-phosphate and inhibitory concentrations of fructose-1,6-bisphosphate. Conversely, the association constant of the complex increased in the presence of dihydroxyacetone phosphate (DHAP) and non-inhibitory concentrations of fructose-1,6-bisphosphate. Notably, in vivo FRET studies confirmed the interaction between aldolase B and FBPase-1. Also, the co-expression of aldolase B and FBPase-1 in cultured cells suggested that FBPase-1 guides the cellular localization of aldolase B. Our results provide further evidence that metabolic conditions modulate aldolase B and FBPase-1 activity at the cellular level through the regulation of their interaction, suggesting that their association confers a catalytic advantage for both enzymes.

Perfluorooctanoic acid exposure for 28 days affects glucose homeostasis and induces insulin hypersensitivity in mice

Perfluoroalkyl acids (PFAAs) are widely used in many applications due to their unique physical and chemical characteristics. Because of the increasing prevalence of metabolic syndromes, including obesity, dyslipidemia and insulin resistance, concern has arisen about the roles of environmental pollutants in such diseases. Earlier epidemiologic studies showed a potential association between perfluorooctanoic acid (PFOA) and glucose metabolism, but how PFOA influences glucose homeostasis is still unknown. Here, we report on the modulation of the phosphatidylinositol 3-kinase-serine/threonine protein kinase (PI3K-AKT) signaling pathway in the livers of mice after 28 d of exposure to PFOA. Compared with normal mice, PFOA exposure significantly decreased the expression of the phosphatase and tensin homologue (PTEN) protein and affected the PI3K-AKT signaling pathway in the liver. Tolerance tests further indicated that PFOA exposure induced higher insulin sensitivity and glucose tolerance in mice. Biochemical analysis revealed that PFOA exposure reduced hepatic glycogen synthesis, which might be attributed to gluconeogenesis inhibition. The levels of several circulating proteins were altered after PFOA exposure, including proteins potentially related to diabetes and liver disease. Our results suggest that PFOA affected glucose metabolism and induced insulin hypersensitivity in mice.

CD38-mediated Ca(2+) signaling contributes to glucagon-induced hepatic gluconeogenesis

CD38 is a multifunctional enzyme for the synthesis of Ca²⁺ second messengers. Glucagon promotes hepatic glucose production through Ca²⁺ signaling in the fasting condition. In this study, we investigated the role of CD38 in the glucagon signaling of hepatocytes. Here, we show that glucagon induces cyclic ADP-ribose (cADPR) production and sustained Ca²⁺ increases via CD38 in hepatocytes. 8-Br-cADPR, an antagonistic cADPR analog, completely blocked glucagon-induced Ca²⁺ increases and phosphorylation of cAMP response element-binding protein (CREB). Moreover, glucagon-induced sustained Ca²⁺ signals and translocation of CREB-regulated transcription coactivator 2 to the nucleus were absent and glucagon-induced glucose production and expression of glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (Pck1) are remarkably reduced in hepatocytes from CD38^−/− mice. Furthermore, in the fasting condition, CD38^−/− mice have decreased blood glucose and hepatic expression of G6Pase and Pck1 compared to wild type mice. Our data suggest that CD38/cADPR-mediated Ca²⁺ signals play a key role in glucagon-induced gluconeogenesis in hepatocytes, and that the signal pathway has significant clinical implications in metabolic diseases, including type 2 diabetes.

Hepatic Phosphoserine Aminotransferase 1 Regulates Insulin Sensitivity in Mice via Tribbles Homolog 3

Phosphoserine aminotransferase 1 (PSAT1) is an enzyme participating in serine synthesis. A role of PSAT1 in the regulation of insulin sensitivity, however, is unknown. In this study, we showed that hepatic PSAT1 expression and liver serine levels are reduced in genetically engineered leptin receptor-deficient (db/db) mice and high-fat diet (HFD)-induced diabetic mice. Additionally, overexpression of PSAT1 by adenovirus expressing PSAT1 improved insulin signaling and insulin sensitivity in vitro and in vivo under normal conditions. Opposite effects were observed when PSAT1 was knocked down by adenovirus expressing small hairpin RNA specific for PSAT1 (Ad-shPSAT1). Importantly, overexpression of PSAT1 also significantly ameliorated insulin resistance in diabetic mice. In addition, PSAT1 inhibited the expression of hepatic tribbles homolog 3 (TRB3) in vitro and in vivo, and adenoviruses expressing small hairpin RNA against TRB3-mediated inhibition of TRB3 reversed the attenuated insulin sensitivity in Ad-shPSAT1 mice. Interestingly, we found that serine mediates PSAT1 regulation of TRB3 expression and insulin signaling in vitro. These results identify a novel function for hepatic PSAT1 in regulating insulin sensitivity and provide important insights in targeting PSAT1 for treating insulin resistance and type 2 diabetes. Our results also suggest that nonessential amino acid serine may play an important role in regulating insulin sensitivity.

Progressive Impairment of Lactate-based Gluconeogenesis in the Huntington's Disease Mouse Model R6/2

Huntington’s disease (HD) is a neurodegenerative illness, where selective neuronal loss in the brain caused by expression of mutant huntingtin protein leads to motor dysfunction and cognitive decline in addition to peripheral metabolic changes. In this study we confirm our previous observation of impairment of lactate-based hepatic gluconeogenesis in the transgenic HD mouse model R6/2 and determine that the defect manifests very early and progresses in severity with disease development, indicating a potential to explore this defect in a biomarker context. Moreover, R6/2 animals displayed lower blood glucose levels during prolonged fasting compared to wild type animals.

In vivo Magnetic Resonance Spectroscopy of cerebral glycogen metabolism in animals and humans

Glycogen serves as an important energy reservoir in the human body. Despite the abundance of glycogen in the liver and skeletal muscles, its concentration in the brain is relatively low, hence its significance has been questioned. A major challenge in studying brain glycogen metabolism has been the lack of availability of non-invasive techniques for quantification of brain glycogen in vivo. Invasive methods for brain glycogen quantification such as post mortem extraction following high energy microwave irradiation are not applicable in the human brain. With the advent of (13)C Magnetic Resonance Spectroscopy (MRS), it has been possible to measure brain glycogen concentrations and turnover in physiological conditions, as well as under the influence of stressors such as hypoglycemia and visual stimulation. This review presents an overview of the principles of the (13)C MRS methodology and its applications in both animals and humans to further our understanding of glycogen metabolism under normal physiological and pathophysiological conditions such as hypoglycemia unawareness.

Circadian rhythms, the molecular clock, and skeletal muscle

Circadian rhythms are the approximate 24-h biological cycles that function to prepare an organism for daily environmental changes. They are driven by the molecular clock, a transcriptional:translational feedback mechanism that in mammals involves the core clock genes Bmal1, Clock, Per1/2, and Cry1/2. The molecular clock is present in virtually all cells of an organism. The central clock in the suprachiasmatic nucleus (SCN) has been well studied, but the clocks in the peripheral tissues, such as heart and skeletal muscle, have just begun to be investigated. Skeletal muscle is one of the largest organs in the body, comprising approximately 45% of total body mass. More than 2300 genes in skeletal muscle are expressed in a circadian pattern, and these genes participate in a wide range of functions, including myogenesis, transcription, and metabolism. The circadian rhythms of skeletal muscle can be entrained both indirectly through light input to the SCN and directly through time of feeding and activity. It is critical for the skeletal muscle molecular clock not only to be entrained to the environment but also to be in synchrony with rhythms of other tissues. When circadian rhythms are disrupted, the observed effects on skeletal muscle include fiber-type shifts, altered sarcomeric structure, reduced mitochondrial respiration, and impaired muscle function. Furthermore, there are detrimental effects on metabolic health, including impaired glucose tolerance and insulin sensitivity, which skeletal muscle likely contributes to considering it is a key metabolic tissue. These data indicate a critical role for skeletal muscle circadian rhythms for both muscle and systems health. Future research is needed to determine the mechanisms of molecular clock function in skeletal muscle, identify the means by which skeletal muscle entrainment occurs, and provide a stringent comparison of circadian gene expression across the diverse tissue system of skeletal muscle.

Virtual Systems Pharmacology (ViSP) software for simulation from mechanistic systems-level models

Multiple software programs are available for designing and running large scale system-level pharmacology models used in the drug development process. Depending on the problem, scientists may be forced to use several modeling tools that could increase model development time, IT costs and so on. Therefore, it is desirable to have a single platform that allows setting up and running large-scale simulations for the models that have been developed with different modeling tools. We developed a workflow and a software platform in which a model file is compiled into a self-contained executable that is no longer dependent on the software that was used to create the model. At the same time the full model specifics is preserved by presenting all model parameters as input parameters for the executable. This platform was implemented as a model agnostic, therapeutic area agnostic and web-based application with a database back-end that can be used to configure, manage and execute large-scale simulations for multiple models by multiple users. The user interface is designed to be easily configurable to reflect the specifics of the model and the user's particular needs and the back-end database has been implemented to store and manage all aspects of the systems, such as Models, Virtual Patients, User Interface Settings, and Results. The platform can be adapted and deployed on an existing cluster or cloud computing environment. Its use was demonstrated with a metabolic disease systems pharmacology model that simulates the effects of two antidiabetic drugs, metformin and fasiglifam, in type 2 diabetes mellitus patients.

Alpha-lipoic acid attenuates insulin resistance and improves glucose metabolism in high fat diet-fed mice

AIM

To investigate whether alpha-lipoic acid (ALA) could attenuate the insulin resistance and metabolic disorders in high fat diet-fed mice.

METHODS

Male mice were fed a high fat diet (HFD) plus ALA (100 and 200 mg·kg(-1)·d(-1)) or HFD plus a positive control drug metformin (300 mg·kg(-1)·d(-1)) for 24 weeks. During the treatments, the relevant physiological and metabolic parameters of the mice were measured. After the mice were euthanized, blood samples and livers were collected. The expression of proteins and genes related to glucose metabolism in livers were analyzed by immunoblotting and real time-PCR.

RESULTS

HFD induced non-alcoholic fatty liver disease (NAFLD) and abnormal physiological and metabolic parameters in the mice, which were dose-dependently attenuated by ALA. ALA also significantly reduced HFD-induced hyperglycemia and insulin resistance in HFD-fed mice. Furthermore, ALA significantly upregulated the glycolytic enzymes GCK, HK-1 and PK, and the glycogen synthesis enzyme GS, and downregulated the gluconeogenic enzymes PEPCK and G6Pase, thus decreased glucose production, and promoted glycogen synthesis and glucose utilization in livers. Moreover, ALA markedly increased PKB/Akt and GSK3β phosphorylation, and nuclear carbohydrate response element binding protein (ChREBP) expression in livers. Metformin produced similar effects as ALA in HFD-fed mice.

CONCLUSION

ALA is able to sustain glucose homeostasis and prevent the development of NAFLD in HFD-fed mice.

Anti-phosphoenolpyruvate carboxykinase 2 antibody in patients with autoimmune hepatitis

AIM

To identify a novel autoantibody specific to autoimmune hepatitis (AIH) and to evaluate its clinical significance.

METHODS

Non-nuclear component protein extracted from normal human liver cell CyrohNHpes cultures that reacted with sera from AIH patients on a western blot was identified as an antigenic protein and subjected to N-terminal amino acid analysis to identify phosphoenolpyruvate carboxykinase 2 (PCK2). Enzyme-linked immunoassay (ELISA) for anti-PCK2 antibody was conducted on sera samples from patients with AIH (n = 42), primary biliary cirrhosis (PBC; n = 48), non-alcoholic steatohepatitis (NASH, n = 41), chronic hepatitis C (CHC, n = 20), drug-induced liver injury (DILI, n = 10), systemic lupus erythematosus (SLE, n = 16) and on sera samples from healthy volunteers (n = 30). Clinical findings were compared for AIH patients testing positive and negative for anti-PCK2 antibody.

RESULTS

ELISA findings showed that mean anti-PCK2 antibody titer in sera from AIH patients was significantly higher than in PBC, NASH, CHC, DILI and SLE patients, as well as in healthy volunteers. Anti-PCK2 antibody was present in 50.0% (21/42) of AIH, 14.6% (7/48) of PBC, 4.9% (2/41) of NASH, and 10.0% (2/20) of CHC patients, 0% (0/10) of DILI, 12.5% (2/16) of SLE and in 3.3% (1/30) of healthy volunteers. The sensitivity, specificity and accuracy of using the detection of anti-PCK2 antibody in diagnosing AIH were 50.0%, 91.5% and 83.1%, respectively. None of the AIH patients positive for anti-PCK2 antibody showed characteristic clinical features.

CONCLUSION

Although further investigations into the clinical usefulness are necessary, anti-PCK2 may have potential as a diagnostic marker for AIH.

A model integration approach linking signalling and gene-regulatory logic with kinetic metabolic models

Systems biology has to increasingly cope with large- and multi-scale biological systems. Many successful in silico representations and simulations of various cellular modules proved mathematical modelling to be an important tool in gaining a solid understanding of biological phenomena. However, models spanning different functional layers (e.g. metabolism, signalling and gene regulation) are still scarce. Consequently, model integration methods capable of fusing different types of biological networks and various model formalisms become a key methodology to increase the scope of cellular processes covered by mathematical models. Here we propose a new integration approach to couple logical models of signalling or/and gene-regulatory networks with kinetic models of metabolic processes. The procedure ends up with an integrated dynamic model of both layers relying on differential equations. The feasibility of the approach is shown in an illustrative case study integrating a kinetic model of central metabolic pathways in hepatocytes with a Boolean logical network depicting the hormonally induced signal transduction and gene regulation events involved. In silico simulations demonstrate the integrated model to qualitatively describe the physiological switch-like behaviour of hepatocytes in response to nutritionally regulated changes in extracellular glucagon and insulin levels. A simulated failure mode scenario addressing insulin resistance furthermore illustrates the pharmacological potential of a model covering interactions between signalling, gene regulation and metabolism.