A cellular assay for measuring the modulation of glucose production in H4IIE cells

Quantifying the progression of non-alcoholic fatty liver disease in human biomimetic liver microphysiology systems with fluorescent protein biosensors

Metabolic syndrome is a complex disease that involves multiple organ systems including a critical role for the liver. Non-alcoholic fatty liver disease (NAFLD) is a key component of the metabolic syndrome and fatty liver is linked to a range of metabolic dysfunctions that occur in approximately 25% of the population. A panel of experts recently agreed that the acronym, NAFLD, did not properly characterize this heterogeneous disease given the associated metabolic abnormalities such as type 2 diabetes mellitus (T2D), obesity, and hypertension. Therefore, metabolic dysfunction-associated fatty liver disease (MAFLD) has been proposed as the new term to cover the heterogeneity identified in the NAFLD patient population. Although many rodent models of NAFLD/NASH have been developed, they do not recapitulate the full disease spectrum in patients. Therefore, a platform has evolved initially focused on human biomimetic liver microphysiology systems that integrates fluorescent protein biosensors along with other key metrics, the microphysiology systems database, and quantitative systems pharmacology. Quantitative systems pharmacology is being applied to investigate the mechanisms of NAFLD/MAFLD progression to select molecular targets for fluorescent protein biosensors, to integrate computational and experimental methods to predict drugs for repurposing, and to facilitate novel drug development. Fluorescent protein biosensors are critical components of the platform since they enable monitoring of the pathophysiology of disease progression by defining and quantifying the temporal and spatial dynamics of protein functions in the biosensor cells, and serve as minimally invasive biomarkers of the physiological state of the microphysiology system experimental disease models. Here, we summarize the progress in developing human microphysiology system disease models of NAFLD/MAFLD from several laboratories, developing fluorescent protein biosensors to monitor and to measure NAFLD/MAFLD disease progression and implementation of quantitative systems pharmacology with the goal of repurposing drugs and guiding the creation of novel therapeutics.

Small Molecule-Based Enzyme Inhibitors in the Treatment of Primary Hyperoxalurias

Primary hyperoxalurias (PHs) are a group of inherited alterations of the hepatic glyoxylate metabolism. PHs classification based on gene mutations parallel a variety of enzymatic defects, and all involve the harmful accumulation of calcium oxalate crystals that produce systemic damage. These geographically widespread rare diseases have a deep impact in the life quality of the patients. Until recently, treatments were limited to palliative measures and kidney/liver transplants in the most severe forms. Efforts made to develop pharmacological treatments succeeded with the biotechnological agent lumasiran, a siRNA product against glycolate oxidase, which has become the first effective therapy to treat PH1. However, small molecule drugs have classically been preferred since they benefit from experience and have better pharmacological properties. The development of small molecule inhibitors designed against key enzymes of glyoxylate metabolism is on the focus of research. Enzyme inhibitors are successful and widely used in several diseases and their pharmacokinetic advantages are well known. In PHs, effective enzymatic targets have been determined and characterized for drug design and interesting inhibitory activities have been achieved both in vitro and in vivo. This review describes the most recent advances towards the development of small molecule enzyme inhibitors in the treatment of PHs, introducing the multi-target approach as a more effective and safe therapeutic option.

Capacitation increases glucose consumption in murine sperm

Mammalian sperm acquire fertilization capacity in the female reproductive tract in a process known as capacitation. During capacitation, sperm change their motility pattern (i.e., hyperactivation) and become competent to undergo the acrosome reaction. We have recently shown that, in the mouse, sperm capacitation is associated with increased uptake of fluorescently labeled deoxyglucose and with extracellular acidification suggesting enhanced glycolysis. Consistently, in the present work we showed that glucose consumption is enhanced in media that support mouse sperm capacitation suggesting upregulation of glucose metabolic pathways. The increase in glucose consumption was modulated by bicarbonate and blocked by protein kinase A and soluble adenylyl cyclase inhibitors. Moreover, permeable cyclic adenosine monophosphate (cAMP) agonists increase glucose consumption in sperm incubated in conditions that do not support capacitation. Also, the increase in glucose consumption was reduced when sperm were incubated in low calcium conditions. Interestingly, this reduction was not overcome with cAMP agonists. Despite these findings, glucose consumption of sperm from Catsper1 knockout mice was similar to the one from wild type suggesting that other sources of calcium are also relevant. Altogether, these results suggest that cAMP and calcium pathways are involved in the regulation of glycolytic energy pathways during murine sperm capacitation.

Ameliorative potential of Lavandula stoechas in metabolic syndrome via multitarget interactions

ETHNOPHARMACOLOGICAL IMPORTANCE

Decoction and infusion prepared from aerial parts of Lavandula stoechas L. (L. stoechas) have been traditionally used as remedy against several components of metabolic syndrome (MetS) and associated disorders including type II diabetes and cardiovascular diseases by Anatolian people.

AIM OF THE STUDY

The aim is to elucidate the potential ameliorative effects of L. stoechas aqueous extracts on insulin resistance and inflammation models through multitarget in vitro approaches and also to elucidate mechanism of action by analyzing transcriptional and metabolic responses.

MATERIALS AND METHODS

An aqueous extract was prepared and fractionated to give rise to ethyl acetate (EE) and butanol (BE) extracts. The anti-insulin resistance effects of BE and EE were evaluated on palmitate induced insulin resistance model of H4IIE, C2C12 and 3T3L1 cells by using several metabolic parameters. Specifically, whole genome transcriptome analysis was performed by using microarray over 55.000 genes in control, insulin resistant and EE (25 µg/mL) treated insulin resistant H4IIE cells. Anti-inflammatory effects of both extracts were analyzed in LPS-stimulated RAW264.7 macrophages.

RESULTS

Both EE and BE at low doses (25-50 µg/mL) significantly decreased hepatic gluconeogenesis in H4IIE cell line by suppressing the expression of PEPCK and G6Pase. In C2C12 myotubes, both extracts increased the insulin stimulated glucose uptake more effectively than metformin. Both extracts decreased the isoproterenol induced lipolysis in 3T3L1 cell line. Moreover, they also effectively increased the expression of lipoprotein lipase protein level in insulin resistant myotubes at low doses. EE increased the protein level of PPARγ and stimulated the activation AKT in insulin resistant H4IIE and C2C12 cell lines. The results obtained from biochemical assays, mRNA/protein studies and whole genome transcriptome analyses were found to be complementary and provided support for the hypothesis that EE might be biologically active against insulin resistance and act through the inhibition of liver gluconeogenesis and AKT activation. Besides, LPS induced inflammation in RAW264.7 macrophages was mainly inhibited by EE through suppression of iNOS/NO signaling, IL1β and COX-2 genes. HPLC-TOF/MS analysis of EE of L. stoechas mainly resulted in caffeic acid, apigenin, luteolin, rosmarinic acid and its methyl ester, 4-hydroxybenzoic acid, vanillic acid, ferrulic acid and salicylic acid.

CONCLUSION

Data suggest that EE of L. stoechas contains phytochemicals that can be effective in the treatment/prevention of insulin resistance and inflammation. These results validate the traditional use of L. stoechas in Anatolia against several metabolic disorders including metabolic syndrome.

Pioglitazone inhibits mitochondrial pyruvate metabolism and glucose production in hepatocytes

Pioglitazone is used globally for the treatment of type 2 diabetes mellitus (T2DM) and is one of the most effective therapies for improving glucose homeostasis and insulin resistance in T2DM patients. However, its mechanism of action in the tissues and pathways that regulate glucose metabolism are incompletely defined. Here we investigated the direct effects of pioglitazone on hepatocellular pyruvate metabolism and the dependency of these observations on the purported regulators of mitochondrial pyruvate transport, MPC1 and MPC2. In cultured H4IIE hepatocytes, pioglitazone inhibited [2-¹⁴ C]-pyruvate oxidation and pyruvate-driven oxygen consumption and, in mitochondria isolated from both hepatocytes and human skeletal muscle, pioglitazone selectively and dose-dependently inhibited pyruvate-driven ATP synthesis. Pioglitazone also suppressed hepatocellular glucose production (HGP), without influencing the mRNA expression of key HGP regulatory genes. Targeted siRNA silencing of MPC1 and 2 caused a modest inhibition of pyruvate oxidation and pyruvate-driven ATP synthesis, but did not alter pyruvate-driven HGP and, importantly, it did not influence the actions of pioglitazone on either pathway. In summary, these findings outline a novel mode of action of pioglitazone relevant to the pathogenesis of T2DM and suggest that targeting pyruvate metabolism may lead to the development of effective new T2DM therapies.

High throughput cell-based assay for identification of glycolate oxidase inhibitors as a potential treatment for Primary Hyperoxaluria Type 1

Glycolate oxidase (GO) and alanine:glyoxylate aminotransferase (AGT) are both involved in the peroxisomal glyoxylate pathway. Deficiency in AGT function causes the accumulation of intracellular oxalate and the primary hyperoxaluria type 1 (PH1). AGT enhancers or GO inhibitors may restore the abnormal peroxisomal glyoxylate pathway in PH1 patients. With stably transformed cells which mimic the glyoxylate metabolic pathway, we developed an indirect glycolate cytotoxicity assay in a 1,536-well plate format for high throughput screening. This assay can be used to identify compounds that reduce indirect glycolate-induced cytotoxicity by either enhancing AGT activity or inhibiting GO. A pilot screen of 4,096 known compounds identified two membrane permeable GO inhibitors: dichromate salt and colistimethate. We also developed a GO enzyme assay using the hydrogen peroxide-Amplex red reporter system. The IC₅₀ values of potassium dichromate, sodium dichromate, and colistimethate sodium were 0.096, 0.108, and 2.3 μM in the GO enzyme assay, respectively. Further enzyme kinetic study revealed that both types of compounds inhibit GO activity by the mixed linear inhibition. Our results demonstrate that the cell-based assay and GO enzyme assay developed in this study are useful for further screening of large compound libraries for drug development to treat PH1.

The mechanisms of genome-wide target gene regulation by TCF7L2 in liver cells

In the liver Wnt-signaling contributes to the metabolic fate of hepatocytes, but the precise role of the TCF7L2 in this process is unknown. We employed a temporal RNA-Seq approach to examine gene expression 3–96 h following Tcf7l2 silencing in rat hepatoma cells, and combined this with ChIP-Seq to investigate mechanisms of target gene regulation by TCF7L2. Silencing Tcf7l2 led to a time-dependent appearance of 406 differentially expressed genes (DEGs), including key regulators of cellular growth and differentiation, and amino acid, lipid and glucose metabolism. Direct regulation of 149 DEGs was suggested by strong proximal TCF7L2 binding (peak proximity score > 10) and early mRNA expression changes (≤18 h). Indirect gene regulation by TCF7L2 likely occurred via alternate transcription factors, including Hnf4a, Foxo1, Cited2, Myc and Lef1, which were differentially expressed following Tcf7l2 knock-down. Tcf7l2-silencing enhanced the expression and chromatin occupancy of HNF4α, and co-siRNA experiments revealed that HNF4α was required for the regulation of a subset of metabolic genes by TCF7L2, particularly those involved in lipid and amino-acid metabolism. Our findings suggest TCF7L2 is an important regulator of the hepatic phenotype, and highlight novel mechanisms of gene regulation by TCF7L2 that involve interplay between multiple hepatic transcriptional pathways.

Diacylglycerol kinase θ couples farnesoid X receptor-dependent bile acid signalling to Akt activation and glucose homoeostasis in hepatocytes

DGKs (diacylglycerol kinases) catalyse the conversion of diacylglycerol into PA (phosphatidic acid), a positive modulator of mTOR (mammalian target of rapamycin). We have found that chenodeoxycholic acid and the synthetic FXR (farnesoid X receptor) ligand GW4064 induce the mRNA and protein expression of DGKθ in the HepG2 cell line and in primary human hepatocytes. Reporter gene studies using 1.5 kB of the DGKθ promoter fused to the luciferase gene revealed that bile acids increase DGKθ transcriptional activity. Mutation of putative FXR-binding sites attenuated the ability of GW4046 to increase DGKθ luciferase activity. Consistent with this finding, ChIP (chromatin immunoprecipitation) assays demonstrated that bile acid signalling increased the recruitment of FXR to the DGKθ promoter. Furthermore, GW4064 evoked a time-dependent increase in the cellular concentration of PA. We also found that GW4064 and PA promote the phosphorylation of mTOR, Akt and FoxO1 (forkhead box O1), and that silencing DGKθ expression significantly abrogated the ability of GW4046 to promote the phosphorylation of these PA-regulated targets. DGKθ was also required for bile-acid-dependent decreased glucose production. Taken together, our results establish DGKθ as a key mediator of bile-acid-stimulated modulation of mTORC2 (mTOR complex 2), the Akt pathway and glucose homoeostasis.

Insulin resistance and environmental pollutants: experimental evidence and future perspectives

BACKGROUND

The metabolic disruptor hypothesis postulates that environmental pollutants may be risk factors for metabolic diseases. Because insulin resistance is involved in most metabolic diseases and current health care prevention programs predominantly target insulin resistance or risk factors thereof, a critical analysis of the role of pollutants in insulin resistance might be important for future management of metabolic diseases.

OBJECTIVES

We aimed to critically review the available information linking pollutant exposure to insulin resistance and to open the discussion on future perspectives for metabolic disruptor identification and prioritization strategies.

METHODS

We searched PubMed and Web of Science for experimental studies reporting on linkages between environmental pollutants and insulin resistance and identified a total of 23 studies as the prime literature.

DISCUSSION

Recent studies specifically designed to investigate the effect of pollutants on insulin sensitivity show a potential causation of insulin resistance. Based on these studies, a summary of viable test systems and end points can be composed, allowing insight into what is missing and what is needed to create a standardized insulin resistance toxicity testing strategy.

CONCLUSIONS

It is clear that current research predominantly relies on top-down identification of insulin resistance-inducing metabolic disruptors and that the development of dedicated in vitro or ex vivo screens to allow animal sparing and time- and cost-effective bottom-up screening is a major future research need.

Newly developed glycogen synthase kinase-3 (GSK-3) inhibitors protect neuronal cells death in amyloid-beta induced cell model and in a transgenic mouse model of Alzheimer's disease

Glycogen synthase kinase-3 (GSK-3) is emerging as a prominent therapeutic target of Alzheimer's disease (AD). A number of studies have been undertaken to develop GSK-3 inhibitors for clinical use. We report two novel GSK-3 inhibitors (C-7a and C-7b) showing good activity and pharmacokinetic (PK) profiles. IC50 of new GSK-3 inhibitors were in the range of 120-130 nM, and they effectively reduced the Aβ-oligomers induced neuronal toxicity. Also, new GSK-3 inhibitors decreased the phosphorylated tau at pThr231, pSer396, pThr181, and pSer202, and inhibited the GSK-3 activity against Aβ-oligomers induced neuronal cell toxicity. In B6;129-Psen1(tm1Mpm) Tg(APPSwe, tauP301L)1Lfa/Mmjax model of AD, oral administration of C-7a (20 mg/kg, 50 mg/kg) showed increased total arm entries and spontaneous alteration of Y-maze which was regarded as short-term memory. In particular, 50 mg/kg C-7a treated mice significantly decreased the level of phosphorylated tau (Ser396) in brain hippocampus. We suggest that new GSK-3 inhibitor (C-7a) is potential candidates for the treatment of AD.

In Vitro and in Vivo Anti-Diabetic Effects of Anthocyanins from Maqui Berry (Aristotelia chilensis)

We used a murine model of type II diabetes, which reproduces the major features of the human disease, and a number of cellular models to study the antidiabetic effect of ANC, a standardised anthocyanin-rich formulation from maqui berry (Aristotelia chilensis). We also isolated delphinidin 3-sambubioside-5-glucoside (D3S5G), a characteristic anthocyanin from maqui berry, and studied its antidiabetic properties. We observed that oral administration of ANC improved fasting blood glucose levels and glucose tolerance in hyperglycaemic obese C57BL/6J mice fed a high fat diet. In H4IIE rat liver cells, ANC decreased glucose production and enhanced the insulin-stimulated down regulation of the gluconeogenic enzyme, glucose-6-phosphatase. In L6 myotubes ANC treatment increased both insulin and non-insulin mediated glucose uptake. As with the ACN, oral administration of pure D3S5G dose-dependently decreased fasting blood glucose levels in obese C57BL/6J mice, and decreased glucose production in rat liver cells. D3S5G also increased glucose uptake in L6 myotubes and is at least partially responsible for ANC's anti-diabetic properties.

C1q/TNF-related protein-12 (CTRP12), a novel adipokine that improves insulin sensitivity and glycemic control in mouse models of obesity and diabetes

Despite the prevalence of insulin resistance and type 2 diabetes mellitus, their underlying mechanisms remain incompletely understood. Many secreted endocrine factors and the intertissue cross-talk they mediate are known to be dysregulated in type 2 diabetes mellitus. Here, we describe CTRP12, a novel adipokine with anti-diabetic actions. The mRNA and circulating levels of CTRP12 were decreased in a mouse model of obesity, but its expression in adipocytes was increased by the anti-diabetic drug rosiglitazone. A modest rise in circulating levels of CTRP12 by recombinant protein administration was sufficient to lower blood glucose in wild-type, leptin-deficient ob/ob, and diet-induced obese mice. A short term elevation of serum CTRP12 by adenovirus-mediated expression improved glucose tolerance and insulin sensitivity, normalized hyperglycemia and hyperinsulinemia, and lowered postprandial insulin resistance in obese and diabetic mice. CTRP12 improves insulin sensitivity in part by enhancing insulin signaling in the liver and adipose tissue. Further, CTRP12 also acts in an insulin-independent manner; in cultured hepatocytes and adipocytes, CTRP12 directly activated the PI3K-Akt signaling pathway to suppress gluconeogenesis and promote glucose uptake, respectively. Collectively, these data establish CTRP12 as a novel metabolic regulator linking adipose tissue to whole body glucose homeostasis through insulin-dependent and independent mechanisms.

Chromatin occupancy of transcription factor 7-like 2 (TCF7L2) and its role in hepatic glucose metabolism

AIMS/HYPOTHESIS

The mechanisms by which transcription factor 7-like 2 (TCF7L2) regulates the pathways that are important in the pathogenesis of type 2 diabetes are unknown. We therefore examined the role of TCF7L2 in hepatic glucose production (HGP) in vitro and characterised the whole-genome chromatin occupancy of TCF7L2 in hepatocytes.

METHODS

We investigated the effect of TCF7L2 silencing and overexpression on HGP from gluconeogenic precursors and used chromatin-immunoprecipitation (ChIP) combined with massively parallel DNA sequencing (ChIP-Seq) to investigate the DNA binding patterns of TCF7L2 across the whole genome.

RESULTS

Silencing of TCF7L2 induced a marked increase in basal HGP, which was accompanied by significant increases in the expression of the gluconeogenic genes Fbp1, Pck1 and G6pc. Overexpression of Tcf7l2 reversed this phenotype and significantly reduced HGP. TCF7L2 silencing did not affect the half-maximal inhibitory concentration of insulin or metformin, but HGP remained elevated in TCF7L2-silenced cells due to the increased baseline HGP. Using ChIP-Seq, we detected 2,119 binding events across the genome. Pathway analysis demonstrated that diabetes genes were significantly over-represented in the dataset. Our results indicate that TCF7L2 binds directly to multiple genes that are important in regulation of glucose metabolism in the liver, including Pck1, Fbp1, Irs1, Irs2, Akt2, Adipor1, Pdk4 and Cpt1a.

CONCLUSIONS/INTERPRETATION

TCF7L2 is an important regulator of HGP in vitro and binds directly to genes that are important in pathways of glucose metabolism in the liver. These data highlight the possibility that TCF7L2 may affect fasting and postprandial hyperglycaemia in carriers of at-risk TCF7L2 genetic polymorphisms.

Screening and evaluation of new inhibitors of hepatic glucose production

In the course of our screening program for inhibitors of hepatic glucose production in rat hepatoma H4IIE-C3 cells, which were used as model liver cells, five naphtoquinone derivatives-javanicin, solaniol, 9-O-methylfusarubin, 5,10-dihydroxy-1,7-dimethoxy-3-methyl-1H-naphtho[2,3-c]pyran-6,9-dione, 9-O-methylbostrycoidin-and vanillin were selected from our natural product library. These naphtoquinone derivatives inhibited hepatic glucose production at IC(50) values of 3.8-29 microM, but showed cytotoxicity against hepatic cells after incubation for 48 h. However, vanillin showed an IC(50) value of 32 microM without exhibiting cytotoxicity at 50 microM. Therefore, we examined 12 vanillin derivatives to investigate their inhibitory activities against glucose production. Among these analogs, 4-hydro-3-methoxyacetophenone and 5-nitrosalicylaldehyde exhibited stronger inhibition than the other compounds at IC(50) values of 25 and 24 microM, respectively, with no cytotoxicity at a concentration of 50 microM. Hence, 4-hydro-3-methoxyacetophenone and 5-nitrosalicylaldehyde may be useful as a lead compound of anti-type 2 diabetic drugs.