Fluorescent microplate cell assay to measure uptake and metabolism of glucose in normal human lung fibroblasts

3D convolutional neural networks predict cellular metabolic pathway use from fluorescence lifetime decay data

Fluorescence lifetime imaging of the co-enzyme reduced nicotinamide adenine dinucleotide (NADH) offers a label-free approach for detecting cellular metabolic perturbations. However, the relationships between variations in NADH lifetime and metabolic pathway changes are complex, preventing robust interpretation of NADH lifetime data relative to metabolic phenotypes. Here, a three-dimensional convolutional neural network (3D CNN) trained at the cell level with 3D NAD(P)H lifetime decay images (two spatial dimensions and one time dimension) was developed to identify metabolic pathway usage by cancer cells. NADH fluorescence lifetime images of MCF7 breast cancer cells with three isolated metabolic pathways, glycolysis, oxidative phosphorylation, and glutaminolysis were obtained by a multiphoton fluorescence lifetime microscope and then segmented into individual cells as the input data for the classification models. The 3D CNN models achieved over 90% accuracy in identifying cancer cells reliant on glycolysis, oxidative phosphorylation, or glutaminolysis. Furthermore, the model trained with human breast cancer cell data successfully predicted the differences in metabolic phenotypes of macrophages from control and POLG-mutated mice. These results suggest that the integration of autofluorescence lifetime imaging with 3D CNNs enables intracellular spatial patterns of NADH intensity and temporal dynamics of the lifetime decay to discriminate multiple metabolic phenotypes. Furthermore, the use of 3D CNNs to identify metabolic phenotypes from NADH fluorescence lifetime decay images eliminates the need for time- and expertise-demanding exponential decay fitting procedures. In summary, metabolic-prediction CNNs will enable live-cell and in vivo metabolic measurements with single-cell resolution, filling a current gap in metabolic measurement technologies.

Integrin αvβ3 Engagement Regulates Glucose Metabolism and Migration through Focal Adhesion Kinase (FAK) and Protein Arginine Methyltransferase 5 (PRMT5) in Glioblastoma Cells

Metabolic reprogramming promotes glioblastoma cell migration and invasion. Integrin αvβ3 is one of the major integrin family members in glioblastoma multiforme cell surface mediating interactions with extracellular matrix proteins that are important for glioblastoma progression. The role of αvβ3 integrin in regulating metabolic reprogramming and its mechanism of action have not been determined in glioblastoma cells. Integrin αvβ3 engagement with osteopontin promotes glucose uptake and aerobic glycolysis, while inhibiting mitochondrial oxidative phosphorylation. Blocking or downregulation of integrin αvβ3 inhibits glucose uptake and aerobic glycolysis and promotes mitochondrial oxidative phosphorylation, resulting in decreased migration and growth in glioblastoma cells. Pharmacological inhibition of focal adhesion kinase (FAK) or downregulation of protein arginine methyltransferase 5 (PRMT5) blocks metabolic shift toward glycolysis and inhibits glioblastoma cell migration and invasion. These results support that integrin αvβ3 and osteopontin engagement plays an important role in promoting the metabolic shift toward glycolysis and inhibiting mitochondria oxidative phosphorylation in glioblastoma cells. The metabolic shift in cell energy metabolism is coupled to changes in migration, invasion, and growth, which are mediated by downstream FAK and PRMT5 in glioblastoma cells.

Glucose absorption regulation and mechanism of the compounds in Lilium lancifolium Thunb on Caco-2 cells

In this paper, the Caco-2 cell was used to study the glucose absorption regulation and mechanism of kaempferol, caffeic acid and quercetin-3-O-β-D-galactoside in Lilium lancifolium Thunb in vitro. Glucose oxidase-peroxidase (GOD-POD) method was used to measure glucose consumption in supernatant. The fluorescent D-glucose analog (2-NBDG) was used as a tracer probe to study the changes in the fluorescence intensity of 2-NBDG uptake by Caco-2 cells with an inverted fluorescence microscope. Western blotting and quantitative real-time PCR were used to detect the protein expression and mRNA transcription of SGLT1 and GLUT2. The results showed that caffeic acid and quercetin-3-O-β-D-galactoside could significantly promote the absorption of glucose by normal Caco-2 cells compared with the control group (P < 0.001). Both caffeic acid and quercetin-3-O-β-D-galactoside could significantly promote the uptake of glucose tracer 2-NBDG on Caco-2 cells. Caffeic acid and quercetin-3-O-β-D-galactoside could significantly promote SGLT1 and GLUT2 protein expression levels and mRNA transcription (P < 0.001, P < 0.01, P < 0.05). The mechanism might be related to the promotion of SGLT1 and GLUT2 protein expression levels and mRNA transcription.

A novel immobilization fluorescence capillary analysis method and its applications

Fluorescence capillary analysis (FCA) realizes trace-level analysis of micro-volume samples; it is easy to operate, extremely low in analytical cost and can significantly lessen environmental pollution from analytical chemistry waste. FCA has the characteristics of green analytical chemistry and has been applied in clinical, biochemical, pharmaceutical, food safety and other fields. FCA basically involves a micro-volume glass capillary, a capillary holder and an ordinary fluorescence detector. The capillary is not only a container for chemical reaction and detection but also functions as a carrier to immobilize enzymes, gene probes or reagents; it can be used repeatedly or can be disposable. In analysis, the capillary which is modified with functional reagents sucks in a measured liquid for the reaction and is then inserted into the holder within the fluorescent detector for measurement. The immobilized FCA method has been successfully used in the determination of reduced coenzyme I, ethanol in liqueur, lactic acid in dairy products, pyruvic acid and glucose in serum, trace-level sulfated bile acid in urine, the ratio of pyruvic/lactic acid in serum, and pyruvic acid in cells as well as in DNA end-labeling and dyeing methods. Further, FCA can also be extended to capillary arrays to complete multipurpose simultaneous determinations and can be combined with mobile phones as fluorescence detectors for use in mobile health analytical technology. FCA will produce considerable social benefits in medicine, pharmacy, fermentation of food, environmental protection and other fields. Therefore, the relevant contents are presented in this tutorial review.

A colorimetric bioassay for quantitation of both basal and insulin-induced glucose consumption in 3T3-L1 adipose cells

Introduction

The quantitation of glucose consumption in animal cell cultures is mainly based on the use of radiolabeled or fluorescent analogues, resulting in expensive and tedious procedures, requiring special equipment and, sometimes, with potential health and environmental risks.

Objectives

The objective of this work was to evaluate the application of a blood plasma colorimetric assay to quantify glucose consumption in in vitro cultures of adipose cells.

Methods

We worked with 3T3-L1 adipose cells differentiated by 7–8 days, which were exposed to different initial glucose concentrations (5.5, 2.8 and 1.4 mM) for variable times, either in the absence or the presence of 100 nM insulin. Using a commercial colorimetric glucose assay, extracellular glucose was determined, and glucose uptake was calculated as the difference between the initial and final glucose concentration.

Results

The colorimetric assay allowed us to quantify glucose uptake in our cell model, observing a linear response over time (r²≥0.9303) to the different glucose concentrations, both in the basal and insulin-induced condition. The insulin-stimulated glucose consumption was higher than basal consumption at all glucose concentrations evaluated, but significant differences were observed at 120-, 360- and 480-min in glucose 5.5 mM (p ≤ 0.01, n = 5), and 240 min in glucose 1.4 mM (p ≤ 0.01, n = 5). A V_max of 4.1 and 5.9 nmol/ml/min (basal and insulin-induced, respectively) and a K_m of 1.1 mM (same in basal vs insulin-stimulated) were calculated. The bioassay was also useful in a pharmacological context: in glucose 1.4 mM, glucose consumption showed an effect that depended on insulin concentration, with a calculated EC₅₀ of 18.4 ± 1.1 nM.

Conclusions

A simple and low-cost bioassay is proposed to quantify glucose consumption in 3T3-L1 adipose cells.

Development of a deep-red fluorescent glucose-conjugated bioprobe for in vivo tumor targeting

A C1-type d-glucose-conjugated fluorescent probe Glu-1-O-DCSN was synthesized and showed deep-red emission at 685 nm with a Stokes shift of up to 150 nm in DMSO. In in vitro live cell imaging, Glu-1-O-DCSN exhibited similar and competitive uptake behaviours to d-glucose and was selectively located in mitochondria. Furthermore, Glu-1-O-DCSN was successfully employed for in vivo hypermetabolic tumor targeting.

No Cytotoxic and Inflammatory Effects of Empagliflozin and Dapagliflozin on Primary Renal Proximal Tubular Epithelial Cells under Diabetic Conditions In Vitro

Gliflozins are inhibitors of the renal proximal tubular sodium-glucose co-transporter-2 (SGLT-2), that inhibit reabsorption of urinary glucose and they are able to reduce hyperglycemia in patients with type 2 diabetes. A renoprotective function of gliflozins has been proven in diabetic nephropathy, but harmful side effects on the kidney have also been described. In the current project, primary highly purified human renal proximal tubular epithelial cells (PTCs) have been shown to express functional SGLT-2, and were used as an in vitro model to study possible cellular damage induced by two therapeutically used gliflozins: empagliflozin and dapagliflozin. Cell viability, proliferation, and cytotoxicity assays revealed that neither empagliflozin nor dapagliflozin induce effects in PTCs cultured in a hyperglycemic environment, or in co-medication with ramipril or hydro-chloro-thiazide. Oxidative stress was significantly lowered by dapagliflozin but not by empagliflozin. No effect of either inhibitor could be detected on mRNA and protein expression of the pro-inflammatory cytokine interleukin-6 and the renal injury markers KIM-1 and NGAL. In conclusion, empa- and dapagliflozin in therapeutic concentrations were shown to induce no direct cell injury in cultured primary renal PTCs in hyperglycemic conditions.

In vitro anti-diabetic effect of flavonoids and pheophytins from Allophylus cominia Sw. on the glucose uptake assays by HepG2, L6, 3T3-L1 and fat accumulation in 3T3-L1 adipocytes

BACKGROUND AND PURPOSE

Based on ethno-botanical information collected from diabetic patients in Cuba and firstly reported inhibition of PTP1B and DPPIV enzymes activities, Allophylus cominia (A. cominia) was identified as possible source of new drugs that could be used for the treatment of type 2 diabetes mellitus (T2-DM).

EXPERIMENTAL APPROACH

in this study, the activity of the characterised extracts from A. cominia was tested on the glucose uptake using HepG2 and L6 cells, 3T3-L1 fibroblasts and adipocytes as well as their effect on the fat accumulation using 3T3-L1 adipocytes.

KEY RESULTS

on 2-NBDG glucose uptake assay using HepG2 and L6 cells, extracts from A. cominia enhanced insulin activity by increasing glucose uptake. On HepG2 cells Insulin EC₅₀ of 93 ± 21nM decreased to 13 ± 2nM in the presence of the flavonoids mixture from A.cominia. In L6 cells, insulin also produced a concentration-dependent increase with an EC₅₀ of 28.6 ± 0.7nM; EC₅₀ decreased to 0.08 ± 0.02nM and 5 ± 0.9nM in the presence of 100μg/ml of flavonoids and pheophytins mixtures, respectively. In 3T3-L1 fibroblasts, insulin had an EC₅₀ of >1000nM that decreased to 38 ± 4nM in the presence of the flavonoids extract. However, in adipocytes, insulin produced a significant concentration-dependent increase and an EC₅₀ of 30 ± 8nM was a further confirmation of the insulin responsiveness of the adipocytes to the insulin. At 100µg/ml, flavonoids and pheophytins extracts decreased fat accumulation in 3T3-L1 adipocytes by two folds in comparison to the control differentiated cells (p < 0.05). The crude extract of A. cominia did not show any enhancement of 2-NBDG uptake by 3T3-L1 adipocytes in the presence or absence of 100nM insulin. In addition, in fully differentiated adipocytes, both extracts produced significant decrease in lipid droplets in the cells and no lipid accumulation were seen after withdrawal of the extracts from the cell growth medium. However, there was no effect of both extracts on total protein concentration in cells as well as on Glut-4 transporters.

CONCLUSIONS AND IMPLICATIONS

the pharmacological effects of the extracts from A. cominia observed in experimental diabetic models were shown in this study. A. cominia is potentially a new candidate for the treatment and management of T2-DM.

Attachment and Growth of Fibroblasts on Poly(L-lactide/∊-caprolactone) Scaffolds Prepared in Supercritical CO2 and Modified by Polyethylene Imine Grafting with Ethylene Diamine-Plasma in a Glow-Discharge Apparatus

In this study, a copolymer of L-lactide and ∊-caprolactone (Mn: 73,523, Mw: 127,990 and PI: 1.74) was synthesized by ring-opening polymerization by using stannous octoate as the catalyst. FTIR, 1H-NMR and DSC confirmed the copolymer formation. The copolymer films were prepared and a novel method was developed to produce highly porous sponges for potential use in tissue engineering. Films were subjected to supercritical CO2 at 3300 psi and 70°C to create porous structures for production of possible tissue engineering scaffolds. The pore sizes were in the range of 40–80 mm. The copolymer films were pre-wetted with polyethylene imine (PEI) and then treated with ethylene diamine (EDA)-plasma in glow-discharge apparatus. Gas plasma surface modification of three-dimensional scaffolds fabricated by supercritical carbon dioxide technique was demonstrated to enhance cell adhesion, proliferation, and differentiation over 6 days in culture using L929 fibroblast cell line. Alkaline phosphatase (ALP) activity and glucose uptake in cell culture medium were followed in the cell culture experiments. Fibroblastic cell attachment and growth on the EDA-plasma treated scaffolds were rather low. However, both cell attachment and growth were significantly increased by PEI pre-treatment before EDA-plasma. The changes in ALP activity and glucose uptake also supported the cell growth behavior on these PEI and EDA-plasma treated scaffolds.

IL-15 Activates the Jak3/STAT3 Signaling Pathway to Mediate Glucose Uptake in Skeletal Muscle Cells

Myokines are specialized cytokines that are secreted from skeletal muscle (SKM) in response to metabolic stimuli, such as exercise. Interleukin-15 (IL-15) is a myokine with potential to reduce obesity and increase lean mass through induction of metabolic processes. It has been previously shown that IL-15 acts to increase glucose uptake in SKM cells. However, the downstream signals orchestrating the link between IL-15 signaling and glucose uptake have not been fully explored. Here we employed the mouse SKM C2C12 cell line to examine potential downstream targets of IL-15-induced alterations in glucose uptake. Following differentiation, C2C12 cells were treated overnight with 100 ng/ml of IL-15. Activation of factors associated with glucose metabolism (Akt and AMPK) and known downstream targets of IL-15 (Jak1, Jak3, STAT3, and STAT5) were assessed with IL-15 stimulation. IL-15 stimulated glucose uptake and GLUT4 translocation to the plasma membrane. IL-15 treatment had no effect on phospho-Akt, phospho-Akt substrates, phospho-AMPK, phospho-Jak1, or phospho-STAT5. However, with IL-15, phospho-Jak3 and phospho-STAT3 levels were increased along with increased interaction of Jak3 and STAT3. Additionally, IL-15 induced a translocation of phospho-STAT3 from the cytoplasm to the nucleus. We have evidence that a mediator of glucose uptake, HIF1α, expression was dependent on IL-15 induced STAT3 activation. Finally, upon inhibition of STAT3 the positive effects of IL-15 on glucose uptake and GLUT4 translocation were abolished. Taken together, we provide evidence for a novel signaling pathway for IL-15 acting through Jak3/STAT3 to regulate glucose metabolism.

JQ1 suppresses tumor growth through downregulating LDHA in ovarian cancer

Amplification and overexpression of c-Myc is commonly seen in human ovarian cancers, and this could be a potentially novel therapeutic target for this disease. JQ1, a selective small-molecule BET bromodomain (BRDs) inhibitor, has been found to suppress tumor progression in several cancer cell types. Using ovarian cancer cell lines, a transgenic mouse model, and primary cell cultures from human ovarian cancer tissues, we demonstrated that JQ1 significantly suppressed cellular proliferation and induced cell cycle arrest and apoptosis in ovarian cancer cells and mouse model via targeting c-Myc. In addition, JQ1 had multiple influences on cancer metabolism, particularly in the aerobic glycolysis pathway. JQ1 reduced both the activity and phosphorylation of LDHA, inhibited lactate production, and decreased the energy supply to ovarian cancer cell lines and tumors. Taken together, our findings suggest that JQ1 is an efficacious anti-tumor agent in ovarian cancer that is associated with cell cycle arrest, induction of apoptosis and alterations of metabolism.

Measurement of Glucose Uptake in Cultured Cells

Facilitative glucose uptake transport systems are ubiquitous in animal cells and are responsible for transporting glucose across cell surface membranes. Evaluation of glucose uptake is crucial in the study of numerous diseases and metabolic disorders such as myocardial ischemia, diabetes mellitus, and cancer. Detailed in this unit are laboratory methods for assessing glucose uptake into mammalian cells. The unit is divided into five sections: (1) a brief overview of glucose uptake assays in cultured cells; (2) a method for measuring glucose uptake using radiolabeled 3-O-methylglucose; (3) a method for measuring glucose uptake using radiolabeled 2-deoxyglucose (2DG); (4) a microplate method for measuring 2DG-uptake using an enzymatic, fluorometric assay; and (5) a microplate-based method using a fluorescent analog of 2DG.

Simvastatin may induce insulin resistance through a novel fatty acid mediated cholesterol independent mechanism

Statins are a class of oral drugs that are widely used for treatment of hypercholesterolemia. Recent clinical data suggest that chronic use of these drugs increases the frequency of new onset diabetes. Studies to define the risks of statin-induced diabetes and its underlying mechanisms are clearly necessary. We explored the possible mechanism of statin induced insulin resistance using a well-established cell based model and simvastatin as a prototype statin. Our data show that simvastatin induces insulin resistance in a cholesterol biosynthesis inhibition independent fashion but does so by a fatty acid mediated effect on insulin signaling pathway. These data may help design strategies for prevention of statin induced insulin resistance and diabetes in patients with hypercholesterolemia.

Macrophage embedded fibrin gels: an in vitro platform for assessing inflammation effects on implantable glucose sensors

The erroneous and unpredictable behavior of percutaneous glucose sensors just days following implantation has limited their clinical utility for diabetes management. Recent research has implicated the presence of adherent inflammatory cells as the key mitigating factor limiting sensor functionality in this period of days post-implantation. Here we present a novel in vitro platform to mimic the cell-embedded provisional matrix that forms adjacent to the sensor immediately after implantation for the focused investigation of the effects of early stage tissue response on sensor function. This biomimetic surrogate is formed by imbibing fibrin-based gels with physiological densities of inflammatory RAW 264.7 macrophages. When surrounding functional sensors, macrophage-embedded fibrin gels contribute to sensor signal declines that are similar in both shape and magnitude to those observed in previous whole blood and small animal studies. Signal decline in the presence of gels is both metabolically-mediated and sensitive to cell type and activation. Computational modeling of the experimental setup is also presented to validate the design by showing that the cellular glucose uptake parameters necessary to achieve such experimental declines align well with literature values. Together, these data suggest this in vitro provisional matrix surrogate may serve as an effective screening tool for testing the biocompatibility of future glucose sensor designs.

Okadaic acid: more than a diarrheic toxin

Okadaic acid (OA) is one of the most frequent and worldwide distributed marine toxins. It is easily accumulated by shellfish, mainly bivalve mollusks and fish, and, subsequently, can be consumed by humans causing alimentary intoxications. OA is the main representative diarrheic shellfish poisoning (DSP) toxin and its ingestion induces gastrointestinal symptoms, although it is not considered lethal. At the molecular level, OA is a specific inhibitor of several types of serine/threonine protein phosphatases and a tumor promoter in animal carcinogenesis experiments. In the last few decades, the potential toxic effects of OA, beyond its role as a DSP toxin, have been investigated in a number of studies. Alterations in DNA and cellular components, as well as effects on immune and nervous system, and even on embryonic development, have been increasingly reported. In this manuscript, results from all these studies are compiled and reviewed to clarify the role of this toxin not only as a DSP inductor but also as cause of alterations at the cellular and molecular levels, and to highlight the relevance of biomonitoring its effects on human health. Despite further investigations are required to elucidate OA mechanisms of action, toxicokinetics, and harmful effects, there are enough evidences illustrating its toxicity, not related to DSP induction, and, consequently, supporting a revision of the current regulation on OA levels in food.

Increased T cell glucose uptake reflects acute rejection in lung grafts

Although T cells are required for acute lung rejection, other graft-infiltrating cells such as neutrophils accumulate in allografts and are also high glucose utilizers. Positron emission tomography (PET) with the glucose probe [(18)F]fluorodeoxyglucose ([(18)F]FDG) has been employed to image solid organ acute rejection, but the sources of glucose utilization remain undefined. Using a mouse model of orthotopic lung transplantation, we analyzed glucose probe uptake in the grafts of syngeneic and allogeneic recipients with or without immunosuppression treatment. Pulmonary microPET scans demonstrated significantly higher [(18)F]FDG uptake in rejecting allografts when compared to transplanted lungs of either immunosuppressed or syngeneic recipients. [(18)F]FDG uptake was also markedly attenuated following T cell depletion therapy in lung recipients with ongoing acute rejection. Flow cytometric analysis using the fluorescent deoxyglucose analog 2-NBDG revealed that T cells, and in particular CD8(+) T cells, were the largest glucose utilizers in acutely rejecting lung grafts followed by neutrophils and antigen-presenting cells. These data indicate that imaging modalities tailored toward assessing T cell metabolism may be useful in identifying acute rejection in lung recipients.

Glucose metabolism down-regulates the uptake of 6-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-2-deoxyglucose (6-NBDG) mediated by glucose transporter 1 isoform (GLUT1): theory and simulations using the symmetric four-state carrier model

The non-metabolizable fluorescent glucose analogue 6-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-2-deoxyglucose (6-NBDG) is increasingly used to study cellular transport of glucose. Intracellular accumulation of exogenously applied 6-NBDG is assumed to reflect concurrent gradient-driven glucose uptake by glucose transporters (GLUTs). Here, theoretical considerations are provided that put this assumption into question. In particular, depending on the microscopic parameters of the carrier proteins, theory proves that changes in glucose transport can be accompanied by opposite changes in flow of 6-NBDG. Simulations were carried out applying the symmetric four-state carrier model on the GLUT1 isoform, which is the only isoform whose kinetic parameters are presently available. Results show that cellular 6-NBDG uptake decreases with increasing rate of glucose utilization under core-model conditions, supported by literature, namely where the transporter is assumed to work in regime of slow reorientation of the free-carrier compared with the ligand-carrier complex. To observe an increase of 6-NBDG uptake with increasing rate of glucose utilization, and thus interpret 6-NBDG increase as surrogate of glucose uptake, the transporter must be assumed to operate in regime of slow ligand-carrier binding, a condition that is currently not supported by literature. Our findings suggest that the interpretation of data obtained with NBDG derivatives is presently ambiguous and should be cautious because the underlying transport kinetics are not adequately established.

Anti-diabetic effects of Centratherum anthelminticum seeds methanolic fraction on pancreatic cells, β-TC6 and its alleviating role in type 2 diabetic rats

ETHNOPHARMACOLOGICAL RELEVANCE

Seeds of Centratherum anthelminticum (Asteraceae) have been popularly used in Ayurvedic medicine to treat diabetes and skin disorders. Folk medicine from Rayalaseema (Andhra Pradesh, India) reported wide spread usage in diabetes.

AIM OF THE STUDY

To investigate the hypoglycemic properties and mechanism of the methanolic fraction of C. anthelminticum seeds (CAMFs) on mouse β-TC6 pancreatic cell line and streptozotocin (STZ)-induced diabetic rat models.

MATERIALS AND METHODS

We investigated the crude methanolic fraction of C. anthelminticum seeds (CAMFs) on β-TC6 cell line and confirmed its effects on type 1 and type 2 diabetic rats to understand its mechanism in managing diabetes mellitus. CAMFs were initially tested on β-TC6 cells for cytotoxicity, 2-NBDG glucose uptake, insulin secretion and glucose transporter (GLUT-1, 2 and 4) protein expression. Furthermore, streptozotocin (STZ)-induced type 1 diabetic and STZ-nicotinamide-induced type 2 diabetic rats were intraperitoneally (i.p) injected or administered orally with CAMFs daily for 28 days. The effect of CAMFs on blood glucose and insulin levels was subsequently evaluated.

RESULTS

In cell line studies, CAMFs showed non-cytotoxic effect on β-TC6 cell proliferation compared to untreated control cells at 50 μg/ml. CAMFs increased glucose uptake and insulin secretion dose-dependently by up-regulating GLUT-2 and GLUT-4 expression in these cells. Further in vivo studies on streptozotocin induced diabetic rat models revealed that CAMFs significantly reduced hyperglycemia by augmenting insulin secretion in type 2 diabetic rats. However, CAMFs displayed less significant effects on type 1 diabetic rats.

CONCLUSIONS

CAMFs demonstrated anti-diabetic potential on β-TC6 cells and type 2 diabetic rat model, plausibly through enhancing glucose uptake and insulin secretion.

Optimized mixture of hops rho iso-alpha acids-rich extract and acacia proanthocyanidins-rich extract reduces insulin resistance in 3T3-L1 adipocytes and improves glucose and insulin control in db/db mice

Rho iso-alpha acids-rich extract (RIAA) from Humulus lupulus (hops) and proanthocyanidins-rich extracts (PAC) from Acacia nilotica exert anti-inflammatory and anti-diabetic activity in vitro and in vivo. We hypothesized that a combination of these two extracts would exert enhanced effects in vitro on inflammatory markers and insulin signaling, and on nonfasting glucose and insulin in db/db mice. Over 49 tested combinations, RIAA:PAC at 5:1 (6.25 µg/mL) exhibited the greatest reductions in TNFα-stimulated lipolysis and IL-6 release in 3T3-L1 adipocytes, comparable to 5 µg/mL troglitazone. Pretreatment of 3T3-L1 adipocytes with this combination (5 µg/mL) also led to a 3-fold increase in insulin-stimulated glucose uptake that was comparable to 5 µg/mL pioglitazone or 901 µg/mL aspirin. Finally, db/db mice fed with RIAA:PAC at 5:1 (100 mg/kg) for 7 days resulted in 22% decrease in nonfasting glucose and 19% decrease in insulin that was comparable to 0.5 mg/kg rosiglitazone and better than 100 mg/kg metformin. RIAA:PAC mixture may have the potential to be an alternative when conventional therapy is undesirable or ineffective, and future research exploring its long-term clinical application is warranted.

Alterations in metabolism-related genes induced in SHSY5Y cells by okadaic acid exposure

Okadaic acid (OA) is a widely distributed marine toxin produced by several phytoplanktonic species and responsible for diarrheic shellfish poisoning in humans. At the molecular level OA is a specific inhibitor of several types of serine/threonine protein phosphatases. Due to this enzymic inhibition, OA was reported to induce numerous alterations in relevant cellular physiological processes, including several metabolic pathways such as glucose uptake, lipolysis and glycolysis, heme metabolism, and glycogen and protein synthesis. In order to further understand the underlying mechanisms involved in OA-induced effects on cellular metabolism, the expression levels of six genes related to different catabolic and anabolic metabolism-related processes were analyzed by real-time polymerase chain reaction. Specifically, the expression patterns of GAPDH, TOMM5, SLC25A4, COII, QARS, and RGS5 genes were determined in SHSY5Y human neuroblastoma cells exposed to OA for 3, 24, or 48 h. All these genes showed alterations in their expression levels after at least one of the OA treatments tested. These alterations provide a basis to understand the mechanisms underlying the previously described OA-induced effects on different metabolic processes, mainly regarding glucose and mitochondrial metabolism. However, other OA-induced affected genes can not be ruled out, and further studies are required to more comprehensively characterize in the mechanisms of OA-induced interaction on cell metabolism.

A fluorescence method for measurement of glucose transport in kidney cells

BACKGROUND

Diabetes may alter renal glucose reabsorption by sodium (Na(+))-dependent glucose transporters (SGLTs). Radiolabeled substrates are commonly used for in vitro measurements of SGLT activity in kidney cells. We optimized a method to measure glucose uptake using a fluorescent substrate, 2-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-2-deoxyglucose (2-NBDG).

METHODS

Uptake buffers for 2-NBDG were the same as for (14)C-labeled α-methyl-d-glucopyranoside ([(14)C]AMG). Cell lysis buffer was optimized for fluorescence of 2-NBDG and Hoechst DNA stain. Uptake was performed on cultures of primary mouse kidney cells (PMKCs), the LLC-PK(1) proximal tubule cell line, or COS-7 cells transiently overexpressing mouse SGLT1 or SGLT2 by incubating cells at 37°C in buffer containing 50-200 μM 2-NBDG. Microscopy was performed to visualize uptake in intact cells, while a fluorescence microplate reader was used to measure intracellular concentration of 2-NBDG ([2-NBDG](i)) in cell homogenates.

RESULTS

Fluorescent cells were observed in cultures of PMKCs and LLC-PK(1) cells exposed to 2-NBDG in the presence or absence of Na(+). In LLC-PK(1) cells, 2-NBDG transport in the presence of Na(+) had a maximum rate of 0.05 nmol/min/μg of DNA. In these cells, Na(+)-independent uptake of 2-NBDG was blocked with the GLUT inhibitor, cytochalasin B. The Na(+)-dependent uptake of 2-NBDG decreased in response to co-exposure to the SGLT substrate, AMG, and it could be blocked with the SGLT inhibitor, phlorizin. Immunocytochemistry showed overexpression of SGLT1 and SGLT2 in COS-7 cells, in which, in the presence of Na(+), [2-NBDG](i) was fivefold higher than in controls.

CONCLUSION

Glucose transport in cultured kidney cells can be measured with the fluorescence method described in this study.

Disruption of the actin cytoskeleton induces fluorescent glucose accumulation on the rat hepatocytes Clone 9

BACKGROUND

Glucose transport and metabolism are highly specialized in hepatocytes. Actin cytoskeleton is fundamental to the maintenance of their morphology as well as to ensure their functionality. Here we study the effect of the actin disrupting natural compounds cytochalasin B and latrunculin A on the glucose metabolism of the Clone 9 rat hepatocytes once the glucose molecule is inside them and the effects of two hormones which main function is regulating the glucose metabolism on the actin cytoskeleton of Clone 9 cells.

METHODS

F-actin was labeled by using Oregon Green 514 ® phalloidin and glucose inside cells was monitored with the fluorescent D-glucose derivative; 2-NBDG. Observations and measurements were carried out by using a confocal microscope.

RESULTS

Nor insulin neither glucagon was able to induce any significant effect in the quantity of F-actin present on Clone 9 cells. But insulin triggers a strong reorganization on the pattern of distribution of F-actin. However, the actin cytoskeleton disruption induced by CB and more efficiently by Lat A caused accumulation of 2-NBDG in cells.

CONCLUSION

These results state that disruption of the actin cytoskeleton induces fluorescent glucose accumulation on the rat hepatocytes Clone 9 suggesting that actin disrupting agents cause a blockage in the glycolytic pathway of Clone 9 hepatocytes.

A CD36-dependent pathway enhances macrophage and adipose tissue inflammation and impairs insulin signalling

Aims

Obesity and hyperlipidaemia are associated with insulin resistance (IR); however, the mechanisms responsible remain incompletely understood. Pro-atherogenic hyperlipidaemic states are characterized by inflammation, oxidant stress, and pathophysiologic oxidized lipids, including ligands for the scavenger receptor CD36. Here we tested the hypothesis that the absence of CD36 protects mice from IR associated with diet-induced obesity and hyperlipidaemia.

Methods and results

Adipose tissue from CD36^−/− mice demonstrated a less inflammatory phenotype and improved insulin signalling in vivo and at the level of the adipocyte and macrophage. The pathophysiologic ligand oxidized low-density lipoprotein (oxLDL) activated c-Jun N-terminal kinase (JNK) and disrupted insulin signalling in both adipocytes and macrophages in a CD36-dependent manner. Macrophages isolated from CD36^−/− mice after high-fat diet feeding elicited less JNK activation and inhibition of insulin signalling in adipocytes after co-culture compared with wild-type macrophages.

Conclusion

These data suggest that a CD36-dependent inflammatory paracrine loop between adipocytes and macrophages facilitates chronic inflammation and contributes to IR common in obesity and dyslipidaemia.

Novel use of fluorescent glucose analogues to identify a new class of triazine-based insulin mimetics possessing useful secondary effects

There is an urgent need to discover new compounds that effectively treat diabetes by mimicking the action of insulin (insulin mimetics). Traditional approaches to studying anti-diabetic agents in cells are inconvenient for screening chemical libraries to identify insulin mimetics. 2-(N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-2-deoxyglucose (2-NBDG) and 6-NBDG are fluorescent analogues of glucose that could be employed in screening. However, there are no published data about the use of these analogues to identify new insulin mimetics. We have developed a screening system based on 6-NBDG using 3T3-L1 adipocytes in a 96-well culture plate format. 6-NBDG was found to produce a larger signal than 2-NBDG in this screening system. 6-NBDG uptake in 3T3-L1 adipocytes was sensitive to insulin, known insulin mimetics, inhibitors of glucose transport and insulin-sensitizing compounds. To validate our screening system, a chemical library of 576 tagged, triazine-based small molecules was screened. The screening results were identical to that obtained from a commercial enzyme-based glucose assay. Two inducers of glucose uptake were shown to be non-cytotoxic and confirmed as insulin mimetic compounds by their inhibition of epinephrine-stimulated free fatty acid release from adipocytes. These novel insulin mimetics functioned at a markedly lower concentration than two widely studied insulin mimetics, zinc(ii) complexes and vanadium compounds, and also showed novel, beneficial effects on endothelial cell function (a key determinant of secondary complications in diabetes). The discovery of new insulin mimetics using 6-NBDG validates the use of this probe in the development of large-scale, cell-based screening systems based on the uptake of fluorescent-tagged glucose analogues. This research should aid the development of novel strategies to discover new drugs and drug targets for combating the increasing prevalence of diabetes.

ANG II inhibits insulin-mediated production of PI 3,4,5-trisphosphates via a Ca2+-dependent but PKC-independent pathway in the cardiomyocytes

Insulin resistance (IR) is a condition where different organs are refractory to insulin stimulation of glucose uptake. ANG II has been suggested to be involved in the development of IR in the heart. The precise mechanism by which this occurs is still unknown. Here we have used dynamic fluorescent imaging techniques to show that ANG II inhibits insulin production of phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P3] in cardiac myocytes. Fluorophore (Venus)-conjugated cAMP-dependent protein kinase-pleckstrin homology domain, which specifically binds to PI(3,4,5)P3, was transfected in neonatal rat cardiac myocytes. Insulin induced a robust increase in the fluorescence intensity at the cell surface, which was diminished by application of ANG II. The inhibitory action of ANG II was antagonized by RNH-6270 (an angiotensin type 1 receptor antagonist) but not by PD-122370 (an angiotensin type 2 receptor antagonist). BAPTA-AM (Ca2+ chelator) largely attenuated the ANG II effect, whereas K-252b (PKC inhibitor) did not. Furthermore, an elevation of intracellular Ca2+ induced by ionomycin mimicked the ANG II effect. Therefore, it is suggested that ANG II antagonizes insulin-mediated production of PI(3,4,5)P3 via a Ca2+-dependent but PKC-independent pathway in cardiac myocytes.

Controlled microscale diffusion gradients in quiescent extracellular fluid

Microchannels offer a means of establishing concentration gradients of soluble factors over micron length scales representative of those in tissues. Here, we report the development of a microfluidic channel system wherein a hydrogel has been patterned to generate temporally and spatially stable concentration gradients of multiple solutes in quiescent extracellular fluid. The fluorophore Alexa Fluor 488 and a fluorescent glucose analog are used as probes to illustrate the generation of stable, reproducible, and linear probe concentration gradients. A method is described for estimating the diffusivity and hydrogel permeability of a solute from in situ imaging data. Concentration gradients are also generated in the presence of a mouse insulinoma cell line to demonstrate the compatibility of the system with living cells. The net transport and metabolism rate of the glucose analog is found to be heterogeneous and independent of the applied extracellular gradient. This system may be suitable for the study of cell response to various extracellular gradients of soluble factors.

The methyl ester of okadaic acid is more potent than okadaic acid in disrupting the actin cytoskeleton and metabolism of primary cultured hepatocytes

BACKGROUND AND PURPOSE

Okadaic acid (OA) and microcystins (MCs) are structurally different toxins with the same mechanism of action, inhibition of serine/threonine protein phosphatases (PPs). Methyl okadaate (MeOk), a methyl ester derivative of OA, was considered almost inactive due to its weak inhibition of PP1 and PP2A. Here, we have investigated the activity and potency of MeOk in hepatic cells in comparison with that of OA and MCs.

EXPERIMENTAL APPROACH

We tested the effects of MeOK, OA and microcystin-leucine and arginine (MC-LR) on the metabolic rate, the actin cytoskeleton and glucose uptake in a rat hepatocyte cell line (Clone 9) and in primary cultured rat hepatocytes. PP2A was assayed to compare OA and MeOk activity.

KEY RESULTS

MeOk disrupted the actin cytoskeleton and depressed the metabolic rate of both types of rat hepatocytes, being six-fold less potent than OA in Clone 9 cells but nearly six-fold more potent in primary cultured hepatocytes. However, unlike OA, MeOk did not change glucose uptake in these cells, suggesting a weak inhibition of PP2A, as confirmed in direct assays of PP2A activity.

CONCLUSIONS AND IMPLICATIONS

Although MeOk was originally described as a weakly bioactive molecule, it clearly depressed the metabolic rate and disrupted the cytoskeleton in primary and immortalized rat hepatocytes. Furthermore, MeOk affected primary hepatocytes at much lower concentrations than those affecting immortalized cells. These effects were unrelated to PP2A inhibition. Our results suggest the risk to public health from MeOk in foodstuffs should be re-evaluated.

Apolipoprotein E4 domain interaction induces endoplasmic reticulum stress and impairs astrocyte function

Domain interaction, a structural property of apolipoprotein E4 (apoE4), is predicted to contribute to the association of apoE4 with Alzheimer disease. Arg-61 apoE mice, a gene-targeted mouse model specific for domain interaction, have lower brain apoE levels and synaptic, functional, and cognitive deficits. We hypothesized that domain interaction elicits an endoplasmic reticulum (ER) stress in astrocytes and an unfolded protein response that targets Arg-61 apoE for degradation. Primary Arg-61 apoE astrocytes had less intracellular apoE than wild-type astrocytes, and unfolded protein response markers OASIS (old astrocyte specifically induced substance), ATF4, and XBP-1 and downstream effectors were up-regulated. ER stress appears to cause global astrocyte dysfunction as glucose uptake was decreased in Arg-61 apoE astrocytes, and astrocyte-conditioned medium promoted neurite outgrowth less efficiently than wild-type medium in Neuro-2a cell cultures. We showed age-dependent up-regulation of brain OASIS levels and processing in Arg-61 apoE mice. ER stress and astrocyte dysfunction represent a new paradigm underlying the association of apoE4 with neurodegeneration.

"Fluorescent glycogen" formation with sensibility for in vivo and in vitro detection

There are presently many methods of detecting complex carbohydrates, and particularly glycogen. However most of them require radioisotopes or destruction of the tissue and hydrolysis of glycogen to glucose. Here we present a new method based on the incorporation of 2-NBDG (2-{N-[7-nitrobenz-2-oxa-1, 3-diazol 4-yl] amino}-2-deoxyglucose), a D-glucose fluorescent derivative, into glycogen. Two kinds of approaches were carried out by using Clone 9 rat hepatocytes as a cellular model; (1) Incubation of cell lysates with 2-NBDG, carbohydrate precipitation in filters and measurement of fluorescence in a microplate reader (2) Incubation of living hepatocytes with 2-NBDG and recording of fluorescence images by confocal microscopy. 2-NBDG labeled glycogen in both approaches. We confirmed this fact by comparison to the labeling obtained with a specific monoclonal anti-glycogen antibody. Also drugs that trigger glycogen synthesis or degradation induced an increase or decrease of fluorescence, respectively. This is a simple but efficient method of detecting glycogen with 2-NBDG. It could be used to record changes in glycogen stores in living cells and cell-free systems and opens the prospect of understanding the role of this important energy reserve under various physiological and pathophysiological conditions.

Uptake of a fluorescent deoxyglucose analog (2-NBDG) in tumor cells

PURPOSE

A new fluorescent analog of D -glucose was recently developed by [Yoshioka K, Takahashi H, Homma T, Sato M, Ki Bong O, Nemoto Y, Matsuoka H (1996) A novel fluorescent derivative of glucose applicable to the assessment of glucose uptake activity of Escherichia coli. Biochim Biophys Acta 1289:5-9] and shown to be transported into normal cells. The purpose of this preliminary study was to assess the use of this fluorescent 2-deoxyglucose analog, 2-[N-(7-nitrobenz-2-oxa-1,3-diaxol-4-yl)amino]-2-deoxyglucose (2-NBDG), as a sensitive probe for monitoring glucose uptake into malignant tumor cells.

PROCEDURES

MCF-7 breast cancer epithelial cells were grown and plated on coverslips for analysis of 2-NBDG uptake via fluorescence imaging microscopy.

RESULTS

Steady-state fluorescence analysis of 2-NBDG uptake displayed rapid uptake for the first one to five minutes, then slowed, reaching an apparent maximum uptake near 20-30 minutes. Addition of 5 mM D -glucose to the media markedly reduced 2-NBDG uptake. Uptake of 2-NBDG in nonmalignant epithelial cells (M-1 epithelial cells) was slow, averaging less than 20% of that observed for tumorigenic cells, the MCF-7 breast cancer cells and the HepG2 liver cancer cell line.

CONCLUSIONS

The preliminary data clearly demonstrate a rapid uptake of 2-NBDG into tumor cells that can be monitored by fluorescence imaging analysis. The uptake displays saturation and competition with D -glucose, all properties expected for 2-NBDG uptake and retention in cancer cells. Additional studies, including comparisons among other malignant cell lines and control cells, will be needed to fully characterize the kinetic properties of 2-NBDG uptake and the potential use of this 2-DG analog as a probe for glucose uptake in malignant cells.

Glucose uptake in enterocytes: a test for molecular targets of okadaic acid

The main diarrheic shellfish poisoning (DSP) toxin is okadaic acid (OA). Although OA is a protein phosphatase 1 and 2A inhibitor less is known about the involvement of the toxin in diarrhea. The initial statement was that OA, by altering the phosphorylation state of proteins, might modify glucose uptake and consequently ionic and water reabsorption across the small intestine. This report presents studies of glucose transport in isolated rabbit enterocytes by using a fluorescent derivative of D-glucose. The dye allowed examining the relation between the toxic effect of OA and cellular mechanisms involved in glucose transport. The central findings are: (i) OA potentiates decrease on glucose uptake due to protein kinase A (PKA) inhibitors such as H89; and (ii) the increase of sugar uptake induced by the protein kinase C (PKC) inhibitor chelerythrine is enhanced by OA. Importance of this work is justified by the need to determine molecular targets of diarrheic toxins in intestinal cells.

Modulation of glucose uptake in glial and neuronal cell lines by selected neurological drugs

Glucose is the main energy source of brain cells. The transport of glucose across the cell membrane is the first step of its utilization. Any modification in glucose uptake capacity may cause deleterious effects on neural cell functions. In the present study, 3-O-methyl-D-glucose (3-OMG) uptake and its modulation by selected neurological drugs (amitriptyline, selegiline, carbamazepine and phenytoin) were studied in differentiated (with retinoic acid and 12-O-tetradecanoyl phorbol 13-acetate) and undifferentiated neuroblastoma SH-SY5Y and astrocytoma U-373 MG cell lines, using tracer methods. The expression of glucose transporters was studied by immunocytochemistry. SH-SY5Y and U-373 MG cells showed differences both in their glucose uptake properties and in the modulation of glucose uptake by the drugs, which might reflect different specialization of neuronal and glial cells in vivo. While selegiline and amitriptyline had a minor and variable effect on 3-OMG uptake in all cell cultures, the anticonvulsants carbamazepine and phenytoin increased 3-OMG uptake in U-373 MG cells, but decreased that in SH-SY5Y cells. Differentiated SH-SY5Y cells were more sensitive to the effects of the anticonvulsants than undifferentiated SH-SY5Y cells. The results suggest that, the cell lines are promising neural models for the evaluation of drug side effects due to disturbances in glucose uptake.

BHK cell attachment and growth on EDA-plasma-modified poly(L-lactide/epsilon-caprolactone) biodegradable films

In this study, attachment and growth of Baby Hamster Kidney (BHK) cells on ethylene diamine (EDA)-plasma-treated poly(L-lactide/epsilon-caprolactone) biodegradable copolymer films were investigated. The co-polymer (Mw: 58000; Mn: 35000 and PI 1.60) was synthesised by ring-opening polymerization of the respective dimers with using stannous octoate as the catalyst. The final ratio of L-lactide to epsilon-caprolactone obtained by 1H-NMR was 87:13. The co-polymer films were treated with the EDA-plasma in a glow-discharge apparatus. The BHK-30 cell line was cultured on plain and EDA-plasma-treated films and their pre-wetted forms (with ethanol and/or cell culture medium before use). Cell attachment and growth were followed. Alkaline phosphatase (ALP) activity and glucose uptake in cell culture medium were also investigated. There was no attachment in the first 12 h. Glow-discharge treatment increased significantly the attachment and growth. Pre-wetting with ethanol and cell culture medium was also increase significantly both the attachment and growth.