Asymmetric transport of a fluorescent glucose analogue by human erythrocytes

Bioimaging of glucose analogs labeled at the C-1 or C-2 position with a fluorescent dansylamino group

Glucose is the most important energy source in all organisms; however, our understanding of the pathways and mechanisms underlying glucose transportation and localization in living cells is incomplete. Here, we prepared two glucose analogs labeled with a dansylamino group at the C-1 (1-Dansyl) or C-2 (2-Dansyl) position; the dansyl group is a highly fluorescent moiety that is characterized by a large Stokes shift between its excitation and emission wavelengths. We then examined the cytotoxicity of the two glucose analogs in mammalian fibroblast cells and in the ciliated protozoan Tetrahymena thermophila. In both cell types, 2-Dansyl had no negative effects on cell growth. The specificity of cellular uptake of glucose analogs was confirmed using an inhibitor of glucose transporter in NIH3T3 cells. In NIH3T3 cells and T. thermophila, fluorescence microscopy revealed that the glucose analogs localized throughout the cytoplasm, but especially at the periphery of the nucleus. In T. thermophila, we also found that swimming speed was comparable in media containing non-labeled glucose or one of the glucose analogs, which provided more evidence not only that the analogs were not cytotoxic in these cells but also that the analogs had no negative effect on the ciliary motion. Together, the present results suggest that the glucose analogs have low toxicity and will be useful for bioimaging of glucose-related systems.

Recent advances in synthesis of sugar and nucleoside coumarin conjugates and their biological impact

Naturally occurring coumarin and sugar molecules have a diverse range of applications along with superior biocompatibility. Coumarin, a member of the benzopyrone family, exhibits a wide spectrum of medicinal properties, such as anti-coagulant, anti-bacterial, anti-tumor, anti-oxidant, anti-cancer, anti-inflammatory and anti-viral activities. The sugar moiety functions as the central scaffold for the synthesis of complex molecules, attributing to their excellent biocompatibility, well-defined stereochemistry, benign nature and outstanding aqueous solubility. When the coumarin moiety is conjugated with the sugar or nucleoside molecule, the resulting conjugates exhibit significant biological properties. Due to the remarkable growth of such bioconjugates in the field of science over the last decade, owing to their future prospect as a potential bioactive core, an update to this area is very much needed. The present review focusses on the synthesis, characterization and the various therapeutic applications of coumarin conjugates, i.e., sugar and nucleoside coumarin conjugates along with their perspective for future research.

Intestinal tissue-resident T cell activation depends on metabolite availability

The role of tissue-resident memory T cells has come to the forefront, and intestinal intraepithelial lymphocytes (IELs) are abundant. The cells protect the host against invasion and regulate tissue homeostasis and tolerance. Microbial invasion and aberrant IEL activation can contribute to disorders such as inflammatory bowel disease. IELs are kept in a state with limited metabolic activity. We describe the functional analysis of IELs compared with their CD8 circulating counterparts. Although proliferative bursts are similar, IEL metabolism is rapid. Metabolic pathway analysis highlights a tight connection of OXPHOS and glycolysis in IELs and a reliance on pyruvate oxidation. Glucose availability in the local environment can regulate IEL activity, resulting in rapid clearance of an intestinal parasite infection.

The metabolic capacity of many cells is tightly regulated and can adapt to changes in metabolic resources according to environmental changes. Tissue-resident memory (T_RM) CD8⁺ T cells are one of the most abundant T cell populations and offer rapid protection against invading pathogens, especially at the epithelia. T_RM cells metabolically adapt to their tissue niche, such as the intestinal epithelial barrier. In the small intestine, the types of T_RM cells are intraepithelial lymphocytes (IELs), which contain high levels of cytotoxic molecules and express activation markers, suggesting a heightened state of activation. We hypothesize that the tissue environment may determine IEL activity. We show that IEL activation, in line with its semiactive status, is metabolically faster than circulating CD8⁺ T cells. IEL glycolysis and oxidative phosphorylation (OXPHOS) are interdependently regulated and are dependent on rapid access to metabolites from the environment. IELs are restrained by local availability of metabolites, but, especially, glucose levels determine their activity. Importantly, this enables functional control of intestinal T_RM cells by metabolic means within the fragile environment of the intestinal epithelial barrier.

Bioorthogonal Light-Up Fluorescent Probe Enables Wash-Free Real-Time Dynamic Monitoring of Cellular Glucose Uptake

As a significant energy source for living systems, the aberrant cellular glucose uptake is seriously implicated in numerous metabolic diseases. Unfortunately, current shortage of robust tools leaves the limitation to understand its precise biology. Herein we presented a bioorthogonal light-up fluorescent probe consist of two reagents, Glu-HT-Me+AzGlu2, for rapidly responsive (within 25 min), highly specific and sensitive (20-folds enhancement) detection of live-cell glucose uptake based on arylphosphine-induced a-PET effect and Staudinger ligation. Especially, taking the advantage of wash-free characteristic, the probe displayed the real-time dynamic monitoring of cellular glucose uptake. Furthermore, it was successfully capable of not only differentiating cancer cells from normal cells, but also allowing evaluation of anticancer/glycolysis/transport mediated glucose flux. Importantly, it was employed to monitor the fluctuations of glucose uptake in a doxycycline-inducible K-ras^G12 V expression oncogenic cell system, implying its potential as a valuable tool to explore glucose uptake biology.

Design, synthesis, and evaluation of positron emission tomography/fluorescence dual imaging probes for targeting facilitated glucose transporter 1 (GLUT1)

Increased energy metabolism followed by enhanced glucose consumption is a hallmark of cancer. Most cancer cells show overexpression of facilitated hexose transporter GLUT1, including breast cancer. GLUT1 is the main transporter for 2-deoxy-2-[¹⁸F]fluoro-d-glucose (2-[¹⁸F]FDG), the gold standard of positron emission tomography (PET) imaging in oncology. The present study's goal was to develop novel glucose-based dual imaging probes for their use in tandem PET and fluorescence (Fl) imaging. A glucosamine scaffold tagged with a fluorophore and an ¹⁸F-label should confer selectivity to GLUT1. Out of five different compounds, 2-deoxy-2-((7-sulfonylfluoro-2,1,3-benzoxadiazol-4-yl)amino)-d-glucose (2-FBDG) possessed favorable fluorescent properties and a similar potency as 2-deoxy-2-((7-nitro-2,1,3-benzoxadiazol-4-yl)amino)-d-glucose (2-NBDG) in competing for GLUT1 transport against 2-[¹⁸F]FDG in breast cancer cells. Radiolabeling with ¹⁸F was achieved through the synthesis of prosthetic group 7-fluoro-2,1,3-benzoxadiazole-4-sulfonyl [¹⁸F]fluoride ([¹⁸F]FBDF) followed by the reaction with glucosamine. The radiotracer was finally analyzed in vivo in a breast cancer xenograft model and compared to 2-[¹⁸F]FDG. Despite favourable in vitro fluorescence imaging properties, 2-[¹⁸F]FBDG was found to lack metabolic stability in vivo, resulting in radiodefluorination. Glucose-based 2-[¹⁸F]FBDG represents a novel dual-probe for GLUT1 imaging using FI and PET with the potential for further structural optimization for improved metabolic stability in vivo.

Approaches to Study Gap Junctional Coupling

Astrocytes and oligodendrocytes are main players in the brain to ensure ion and neurotransmitter homeostasis, metabolic supply, and fast action potential propagation in axons. These functions are fostered by the formation of large syncytia in which mainly astrocytes and oligodendrocytes are directly coupled. Panglial networks constitute on connexin-based gap junctions in the membranes of neighboring cells that allow the passage of ions, metabolites, and currents. However, these networks are not uniform but exhibit a brain region-dependent heterogeneous connectivity influencing electrical communication and intercellular ion spread. Here, we describe different approaches to analyze gap junctional communication in acute tissue slices that can be implemented easily in most electrophysiology and imaging laboratories. These approaches include paired recordings, determination of syncytial isopotentiality, tracer coupling followed by analysis of network topography, and wide field imaging of ion sensitive dyes. These approaches are capable to reveal cellular heterogeneity causing electrical isolation of functional circuits, reduced ion-transfer between different cell types, and anisotropy of tracer coupling. With a selective or combinatory use of these methods, the results will shed light on cellular properties of glial cells and their contribution to neuronal function.

Antidiabetic potential of gallic acid from Emblica officinalis: Improved glucose transporters and insulin sensitivity through PPAR-γ and Akt signaling

BACKGROUND

Nature has gifted a variety of vital phytochemicals having potential therapeutic application against various ailments. Emblica officinalis (E. officinalis), an ancient plant, has long been used as a remedy for diabetes and cardiovascular complications, and presence of abundant amount of gallic acid could be accountable for its medicinal potential.

PURPOSE

The study was aimed to determine the in-vivo and in-vitro anti-diabetic potential of gallic acid and fruit juice of E. officinalis. Molecular mechanism of gallic acid as well as fruit juice of E. officinalis for anti-diabetic potential has also been revealed.

EXPERIMENTAL STUDY DESIGN

Anti-diabetic potential of E. officinalis and gallic acid was evaluated in 3T3-L1 preadipocytes and various animal models like db/db mice and fructose administered rats. PPAR-γ expression and glucose translocation were observed using western blot and PCR techniques.

RESULTS

Treatment of E. officinalis fruit juice and gallic acid facilitated their glucose homeostasis; improved insulin sensitivity; reduced obesity; abridged elevated blood pressure and declined cholesterol level, and also induced adipogenesis in 3T3-L1 adipocytes. Mechanistically, treatment increased expression of PPAR-γ through activation of C/EBPs and simultaneously increased Glut4 translocation in 3T3-L1 adipocytes. Moreover, gallic acid treatment increased insulin sensitivity through activation of Akt rather than AMPK signaling pathway while fruit juice of E. officinalis showed dual activation, Akt and AMPK as well.

CONCLUSION

These findings reveal the role of gallic acid in E. officinalis mediated antidiabetic potential, and delineate the upregulation of pAkt, PPAR-γ and Glut4 in gallic acid mediated antidiabetic activity, thus providing potential therapy for diabetes and related disorders.

L-Glucose: Another Path to Cancer Cells

Cancerous tumors comprise cells showing metabolic heterogeneity. Among numerous efforts to understand this property, little attention has been paid to the possibility that cancer cells take up and utilize otherwise unusable substrates as fuel. Here we discuss this issue by focusing on l-glucose, the mirror image isomer of naturally occurring d-glucose; l-glucose is an unmetabolizable sugar except in some bacteria. By combining relatively small fluorophores with l-glucose, we generated fluorescence-emitting l-glucose tracers (fLGs). To our surprise, 2-NBDLG, one of these fLGs, which we thought to be merely a control substrate for the fluorescent d-glucose tracer 2-NBDG, was specifically taken up into tumor cell aggregates (spheroids) that exhibited nuclear heterogeneity, a major cytological feature of malignancy in cancer diagnosis. Changes in mitochondrial activity were also associated with the spheroids taking up fLG. To better understand these phenomena, we review here the Warburg effect as well as key studies regarding glucose uptake. We also discuss tumor heterogeneity involving aberrant uptake of glucose and mitochondrial changes based on the data obtained by fLG. We then consider the use of fLGs as novel markers for visualization and characterization of malignant tumor 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.

Improving cellular uptake of therapeutic entities through interaction with components of cell membrane

Efficient cellular delivery of biologically active molecules is one of the key factors that affect the discovery and development of novel drugs. The plasma membrane is the first barrier that prevents direct translocation of chemic entities, and thus obstructs their efficient intracellular delivery. Generally, hydrophilic small molecule drugs are poor permeability that reduce bioavailability and thus limit the clinic application. The cellular uptake of macromolecules and drug carriers is very inefficient without external assistance. Therefore, it is desirable to develop potent delivery systems for achieving effective intracellular delivery of chemic entities. Apart from of the types of delivery strategies, the composition of the cell membrane is critical for delivery efficiency due to the fact that cellular uptake is affected by the interaction between the chemical entity and the plasma membrane. In this review, we aimed to develop a profound understanding of the interactions between delivery systems and components of the plasma membrane. For the purpose, we attempt to present a broad overview of what delivery systems can be used to enhance the intracellular delivery of poorly permeable chemic entities, and how various delivery strategies are applied according to the components of plasma membrane.

Bioluminescent-based imaging and quantification of glucose uptake in vivo

Glucose is a major source of energy for most living organisms, and its aberrant uptake is linked to many pathological conditions. However, our understanding of disease-associated glucose flux is limited owing to the lack of robust tools. To date, positron-emission tomography imaging remains the gold standard for measuring glucose uptake, and no optical tools exist for non-invasive longitudinal imaging of this important metabolite in in vivo settings. Here, we report the development of a bioluminescent glucose-uptake probe for real-time, non-invasive longitudinal imaging of glucose absorption both in vitro and in vivo. In addition, we demonstrate that the sensitivity of our method is comparable with that of commonly used 18F-FDG-positron-emission-tomography tracers and validate the bioluminescent glucose-uptake probe as a tool for the identification of new glucose transport inhibitors. The new imaging reagent enables a wide range of applications in the fields of metabolism and drug development.

Aberrant Uptake of a Fluorescent L-Glucose Analogue (fLG) into Tumor Cells Expressing Malignant Phenotypes

Glucose, one of the most fundamental sugar elements, has either D- or L-conformation. Of these, most cells preferentially take up D-glucose as an essential energy/carbon source. Such stereoselective uptake of glucose has been explored by fluorophore-bearing D- and L-glucose analogues. 2-[N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose (2-NBDG), the most widely used fluorescent D-glucose analogue, was abundantly taken up into living Escherichia coli cells, whereas no detectable uptake was obtained for 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-L-glucose (2-NBDLG), the antipode of 2-NBDG developed as a fluorescent L-glucose analogue (fLG). Interestingly, we found three-dimensionally accumulating tumor cell aggregates taking up 2-NBDLG when they expressed nuclear heterogeneity, one of the major cytological criteria for cells suspected of high-grade malignancy in clinical diagnosis. 2-NBDLG uptake was not detected in aggregates consisting of homogeneous cells and was specifically abolished by phloretin, a broad-spectrum inhibitor against transporters/channels. Preliminary studies have suggested that a combined use of 2-NBDLG, which emits green fluorescence, with 13-[4-[(2-deoxy-D-glucopyranose-2-yl)aminosulfonyl]-2-sulfonatophenyl]-4,5-trimethylene-7,8-trimethylene-1,2,3,4,6,9,10,11-octahydro-4-aza-6-oxa-8-azoniapentacene (2-TRLG), a membrane-impermeable fLG bearing a large red fluorophore, is effective for discriminating malignant tumor from benign cells both in living biopsy specimens endoscopically dissected from patients with early-stage gastric cancer and in ascites fluid of patients with gynecological cancers. Confocal endomicroscopic imaging of a carcinogen-induced cancer in bile duct of hamsters indicated that the fLG uptake pattern well correlated with pathological diagnosis for carcinoma. Safety tests according to Good Laboratory Practice regulations have been successfully completed so far. fLGs are unique fluorescent glucose analogues for identifying and characterizing living cancer cells based on derangements in their transport function.

In-vivo topical mucosal delivery of a fluorescent deoxy-glucose delineates neoplasia from normal in a preclinical model of oral epithelial neoplasia

Metabolic imaging of oral cavity mucosal surfaces could benefit early detection of oral squamous cell carcinoma (OSCC) and oral epithelial dysplasia (OED). Fluorescent deoxy-glucose agents provide contrast for glucose metabolism similar to ¹⁸FDG-PET imaging and allow use of optical imaging, which provides high resolution and lower potential cost. However, in-vivo topical mucosal delivery of fluorescent deoxy-glucose agents without injection or tissue resection has not been shown. We introduce in-vivo optical imaging of neoplasia following mucosal delivery of 2-deoxy-2-[(7-nitro-2,1,3-benzoxadiazol-4-yl)amino]-D-glucose (2-NBDG) in an OSCC/OED hamster model and demonstrate uptake into epithelium across the mucosal surface without injection or disrupting the epithelium. 2-NBDG fluorescence intensity following 30-minutes topical application was 6-fold and 4-fold higher in OSCC and OED, respectively, compared to normal mucosa. Receiver operator characteristic analysis show 83% sensitivity and 73% specificity for detection of neoplasia vs benign (normal and inflammation). Faster 2-NBDG fluorescence temporal decay in neoplasia indicated higher uptake and glucose metabolic rate than normal mucosa. Mucosal delivery of 2-NBDG by topical application to the in-vivo oral surface is feasible and delineates neoplasia from normal mucosa, providing in-vivo noninvasive molecular imaging of dysregulated glucose metabolism, which could benefit preclinical studies of carcinogenesis or be developed for use in early detection.

Current technical approaches to brain energy metabolism

Neuroscience is a technology-driven discipline and brain energy metabolism is no exception. Once satisfied with mapping metabolic pathways at organ level, we are now looking to learn what it is exactly that metabolic enzymes and transporters do and when, where do they reside, how are they regulated, and how do they relate to the specific functions of neurons, glial cells, and their subcellular domains and organelles, in different areas of the brain. Moreover, we aim to quantify the fluxes of metabolites within and between cells. Energy metabolism is not just a necessity for proper cell function and viability but plays specific roles in higher brain functions such as memory processing and behavior, whose mechanisms need to be understood at all hierarchical levels, from isolated proteins to whole subjects, in both health and disease. To this aim, the field takes advantage of diverse disciplines including anatomy, histology, physiology, biochemistry, bioenergetics, cellular biology, molecular biology, developmental biology, neurology, and mathematical modeling. This article presents a well-referenced synopsis of the technical side of brain energy metabolism research. Detail and jargon are avoided whenever possible and emphasis is given to comparative strengths, limitations, and weaknesses, information that is often not available in regular articles.

Lactate in the brain: from metabolic end-product to signalling molecule

Lactate in the brain has long been associated with ischaemia; however, more recent evidence shows that it can be found there under physiological conditions. In the brain, lactate is formed predominantly in astrocytes from glucose or glycogen in response to neuronal activity signals. Thus, neurons and astrocytes show tight metabolic coupling. Lactate is transferred from astrocytes to neurons to match the neuronal energetic needs, and to provide signals that modulate neuronal functions, including excitability, plasticity and memory consolidation. In addition, lactate affects several homeostatic functions. Overall, lactate ensures adequate energy supply, modulates neuronal excitability levels and regulates adaptive functions in order to set the 'homeostatic tone' of the nervous system.

MicroRNA regulation and analytical methods in cancer cell metabolism

The reprogramming of glucose metabolism from oxidative to glycolytic metabolism, known as the Warburg effect, is an anomalous characteristic of cancer cell metabolism. Recent studies have revealed a subset of microRNAs (miRNAs) that play critical roles in regulating the reprogramming of glucose metabolism in cancer cells. These miRNAs regulate cellular glucose metabolism by directly targeting multiple metabolic genes, including those encoding key glycolytic enzymes. In the first part of this review, we summarized the recent knowledge of miRNA regulation in the reprogramming of glucose metabolism in cancer cells and discussed the potential utilization of the key miRNA regulators as metabolic targets for developing new antitumor agents. Then, we summarized recent advances in methods and techniques for studying miRNA regulation in cancer cell metabolism.

Red Blood Cells for Glucose-Responsive Insulin Delivery

Glucose-responsive delivery of insulin mimicking the function of pancreatic β-cells to achieve meticulous control of blood glucose (BG) would revolutionize diabetes care. Here the authors report the development of a new glucose-responsive insulin delivery system based on the potential interaction between the glucose derivative-modified insulin (Glc-Insulin) and glucose transporters on erythrocytes (or red blood cells, RBCs) membrane. After being conjugated with the glucosamine, insulin can efficiently bind to RBC membranes. The binding is reversible in the setting of hyperglycemia, resulting in fast release of insulin and subsequent drop of BG level in vivo. The delivery vehicle can be further simplified utilizing injectable polymeric nanocarriers coated with RBC membrane and loaded with Glc-Insulin. The described work is the first demonstration of utilizing RBC membrane to achieve smart insulin delivery with fast responsiveness.

Novel glycoconjugated squaraine dyes for selective optical imaging of cancer cells

Glycoconjugated squaraine dyes for selective internalisation in cancer cell lines are reported. The cancer cell selectivity was achieved through the “Warburg effect”.

Chemical Approach to Positional Isomers of Glucose-Platinum Conjugates Reveals Specific Cancer Targeting through Glucose-Transporter-Mediated Uptake in Vitro and in Vivo

Glycoconjugation is a promising strategy for specific targeting of cancer. In this study, we investigated the effect of d-glucose substitution position on the biological activity of glucose-platinum conjugates (Glc-Pts). We synthesized and characterized all possible positional isomers (C1α, C1β, C2, C3, C4, and C6) of a Glc-Pt. The synthetic routes presented here could, in principle, be extended to prepare glucose conjugates with different active ingredients, other than platinum. The biological activities of the compounds were evaluated both in vitro and in vivo. We discovered that varying the position of substitution of d-glucose alters not only the cellular uptake and cytotoxicity profile but also the GLUT1 specificity of resulting glycoconjugates, where GLUT1 is glucose transporter 1. The C1α- and C2-substituted Glc-Pts (1α and 2) accumulate in cancer cells most efficiently compared to the others, whereas the C3-Glc-Pt (3) is taken up least efficiently. Compounds 1α and 2 are more potent compared to 3 in DU145 cells. The α- and β-anomers of the C1-Glc-Pt also differ significantly in their cellular uptake and activity profiles. No significant differences in uptake of the Glc-Pts were observed in non-cancerous RWPE2 cells. The GLUT1 specificity of the Glc-Pts was evaluated by determining the cellular uptake in the absence and in the presence of the GLUT1 inhibitor cytochalasin B, and by comparing their anticancer activity in DU145 cells and a GLUT1 knockdown cell line. The results reveal that C2-substituted Glc-Pt 2 has the highest GLUT1-specific internalization, which also reflects the best cancer-targeting ability. In a syngeneic breast cancer mouse model overexpressing GLUT1, compound 2 showed antitumor efficacy and selective uptake in tumors with no observable toxicity. This study thus reveals the synthesis of all positional isomers of d-glucose substitution for platinum warheads with detailed glycotargeting characterization in cancer.

Glucose Absorption by the Bacillary Band of Trichuris muris

Background

A common characteristic of Trichuris spp. infections in humans and animals is the variable but low efficacy of single-dose benzimidazoles currently used in mass drug administration programmes against human trichuriasis. The bacillary band, a specialised morphological structure of Trichuris spp., as well as the unique partly intracellular habitat of adult Trichuris spp. may affect drug absorption and perhaps contribute to the low drug accumulation in the worm. However, the exact function of the bacillary band is still unknown.

Methodology

We studied the dependency of adult Trichuris muris on glucose and/or amino acids for survival in vitro and the absorptive function of the bacillary band. The viability of the worms was evaluated using a motility scale from 0 to 3, and the colorimetric assay Alamar Blue was utilised to measure the metabolic activity. The absorptive function of the bacillary band in living worms was explored using a fluorescent glucose analogue (6-NBDG) and confocal microscopy.

To study the absorptive function of the bacillary band in relation to 6-NBDG, the oral uptake was minimised or excluded by sealing the oral cavity with glue and agarose.

Principal Findings

Glucose had a positive effect on both the motility (p < 0.001) and metabolic activity (p < 0.001) of T. muris in vitro, whereas this was not the case for amino acids. The 6-NBDG was observed in the pores of the bacillary band and within the stichocytes of the living worms, independent of oral sealing.

Conclusions/Significance

Trichuris muris is dependent on glucose for viability in vitro, and the bacillary band has an absorptive function in relation to 6-NBDG, which accumulates within the stichocytes. The absorptive function of the bacillary band calls for an exploration of its possible role in the uptake of anthelmintics, and as a potential anthelmintic target relevant for future drug development.

The human whipworm, Trichuris trichiura is prevalent in many tropical and subtropical countries and is believed to infect more than 460 million people worldwide. Treatment with single-dose albendazole or mebendazole is the current control strategy for human trichuriasis. This strategy, however, has a poor-to-mediocre treatment effect. The reason for the low treatment efficacy has been assessed in various ways, including genetic analysis, and both in vitro and in vivo pharmacological studies. However, these studies have not been conclusive and did not evaluate whether the biology of Trichuris spp. may have an impact on the inadequate treatment efficacy. To assess a possible reason for this, we here explore the absorptive function of a specialised structure, named the bacillary band. We found that glucose was absorbed by the band and accumulated within the worm independent of oral ingestion, and we speculate that anthelmintics may enter the worm by the same route. If this is the case, this new insight may be used to optimise drug formulations of current and/or future anthelmintic drugs in the treatment of human trichuriasis.

Hyperglycemia-induced metabolic compensation inhibits metformin sensitivity in ovarian cancer

Increasing interest in repurposing the diabetic medication metformin for cancer treatment has raised important questions about the translation of promising preclinical findings to therapeutic efficacy, especially in non-diabetic patients. A significant limitation of the findings to date is the use of supraphysiologic metformin doses and hyperglycemic conditions in vitro. Our goals were to determine the impact of hyperglycemia on metformin response and to address the applicability of metformin as a cancer therapeutic in non-diabetic patients. In normoglycemic conditions, lower concentrations of metformin were required to inhibit cell viability, while metformin treatment in hyperglycemic conditions resulted in increased glucose uptake and glycolytic flux, contributing to cell survival. Mechanistically, maintenance of c-Myc expression under conditions of hyperglycemia or via gene amplification facilitated metabolic escape from the effects of metformin. In vivo, treatment of an ovarian cancer mouse model with metformin resulted in greater tumor weight reduction in normoglycemic vs. hyperglycemic mice, with increased c-Myc expression observed in metformin-treated hyperglycemic mice. These findings indicate that hyperglycemia inhibits the anti-cancer effects of metformin in vitro and in vivo. Furthermore, our results suggest that metformin may elicit stronger responses in normoglycemic vs. hyperglycemic patients, highlighting the need for prospective clinical testing in patients without diabetes.

A Simple Flow Cytometric Method to Measure Glucose Uptake and Glucose Transporter Expression for Monocyte Subpopulations in Whole Blood

Monocytes are innate immune cells that can be activated by pathogens and inflammation associated with certain chronic inflammatory diseases. Activation of monocytes induces effector functions and a concomitant shift from oxidative to glycolytic metabolism that is accompanied by increased glucose transporter expression. This increased glycolytic metabolism is also observed for trained immunity of monocytes, a form of innate immunological memory. Although in vitro protocols examining glucose transporter expression and glucose uptake by monocytes have been described, none have been examined by multi-parametric flow cytometry in whole blood. We describe a multi-parametric flow cytometric protocol for the measurement of fluorescent glucose analog 2-NBDG uptake in whole blood by total monocytes and the classical (CD14(++)CD16(-)), intermediate (CD14(++)CD16(+)) and non-classical (CD14(+)CD16(++)) monocyte subpopulations. This method can be used to examine glucose transporter expression and glucose uptake for total monocytes and monocyte subpopulations during homeostasis and inflammatory disease, and can be easily modified to examine glucose uptake for other leukocytes and leukocyte subpopulations within blood.

A high-content screening platform with fluorescent chemical probes for the discovery of first-in-class therapeutics

Phenotypic screening has emerged as a promising approach to discover novel first-in-class therapeutic agents. Rapid advances in phenotypic screening systems facilitate a high-throughput unbiased evaluation of compound libraries. However, limited sets of phenotypic changes are utilized in high-content screening, which require extensive genetic engineering. Therefore, it is critical to develop new chemical probes that can reflect phenotypic changes in any type of cells, especially primary cells, tissues, and organisms. Herein, we introduce our continuous efforts in the development of fluorescent bioprobes and their application to phenotypic screening. In addition, we emphasize the importance of the phenotype-based approach in conjunction with target identification at an early stage of research to accelerate the discovery of therapeutics with new modes of action.

Syntheses of D-Glucose Derivatives Emitting Blue Fluorescence through Pd-Catalyzed C-N Coupling

Green fluorescence-emitting D-glucose derivatives such as 2-NBDG have been effectively used to monitor D-glucose uptake through glucose transporters GLUTs at the single cell level. By contrast, GLUT-permeable D-glucose derivatives emitting blue fluorescence have been long awaited. A glucose tracer, 2-deoxy-2-(2-oxo-2H-chromen-7-yl)amino-D-glucose (CDG) (1), together with related compounds have been synthesized by Pd-catalyzed C-N coupling. Of these, CDG (1) is a promising blue fluorescence-emitting candidate molecule that may enter into mammalian cells through GLUTs.

A Potent Glucose-Platinum Conjugate Exploits Glucose Transporters and Preferentially Accumulates in Cancer Cells

Three rationally designed glucose-platinum conjugates (Glc-Pts) were synthesized and their biological activities evaluated. The Glc-Pts, 1-3, exhibit high levels of cytotoxicity toward a panel of cancer cells. The subcellular target and cellular uptake mechanism of the Glc-Pts were elucidated. For uptake into cells, Glc-Pt 1 exploits both glucose and organic cation transporters, both widely overexpressed in cancer. Compound 1 preferentially accumulates in and annihilates cancer, compared to normal epithelial, cells in vitro.

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.

Vibrational Imaging of Glucose Uptake Activity in Live Cells and Tissues by Stimulated Raman Scattering

Glucose is a ubiquitous energy source for most living organisms. Its uptake activity closely reflects cellular metabolic demand in various physiopathological conditions. Extensive efforts have been made to specifically image glucose uptake, such as with positron emission tomography, magnetic resonance imaging, and fluorescence microscopy, but all have limitations. A new platform to visualize glucose uptake activity in live cells and tissues is presented that involves performing stimulated Raman scattering on a novel glucose analogue labeled with a small alkyne moiety. Cancer cells with differing metabolic activities can be distinguished. Heterogeneous uptake patterns are observed with clear cell-cell variations in tumor xenograft tissues, neuronal culture, and mouse brain tissues. By offering the distinct advantage of optical resolution but without the undesirable influence of fluorophores, this method will facilitate the study of energy demands of living systems with subcellular resolution.

Determination of Glucose Utilization Rates in Cultured Astrocytes and Neurons with [14C]deoxyglucose: Progress, Pitfalls, and Discovery of Intracellular Glucose Compartmentation

2-Deoxy-D-[¹⁴C]glucose ([¹⁴C]DG) is commonly used to determine local glucose utilization rates (CMR_glc) in living brain and to estimate CMR_glc in cultured brain cells as rates of [¹⁴C]DG phosphorylation. Phosphorylation rates of [¹⁴C]DG and its metabolizable fluorescent analog, 2-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-2-deoxyglucose (2-NBDG), however, do not take into account differences in the kinetics of transport and metabolism of [¹⁴C]DG or 2-NBDG and glucose in neuronal and astrocytic cells in cultures or in single cells in brain tissue, and conclusions drawn from these data may, therefore, not be correct. As a first step toward the goal of quantitative determination of CMR_glc in astrocytes and neurons in cultures, the steady-state intracellular-to-extracellular concentration ratios (distribution spaces) for glucose and [¹⁴C]DG were determined in cultured striatal neurons and astrocytes as functions of extracellular glucose concentration. Unexpectedly, the glucose distribution spaces rose during extreme hypoglycemia, exceeding 1.0 in astrocytes, whereas the [¹⁴C]DG distribution space fell at the lowest glucose levels. Calculated CMR_glc was greatly overestimated in hypoglycemic and normoglycemic cells because the intracellular glucose concentrations were too high. Determination of the distribution space for [¹⁴C]glucose revealed compartmentation of intracellular glucose in astrocytes, and probably, also in neurons. A smaller metabolic pool is readily accessible to hexokinase and communicates with extracellular glucose, whereas the larger pool is sequestered from hexokinase activity. A new experimental approach using double-labeled assays with DG and glucose is suggested to avoid the limitations imposed by glucose compartmentation on metabolic assays.

High Temporal Resolution Detection of Patient-Specific Glucose Uptake from Human ex Vivo Adipose Tissue On-Chip

Human tissue in vitro models on-chip are highly desirable to dissect the complexity of a physio-pathological in vivo response because of their advantages compared to traditional static culture systems in terms of high control of microenvironmental conditions, including accurate perturbations and high temporal resolution analyses of medium outflow. Human adipose tissue (hAT) is a key player in metabolic disorders, such as Type 2 Diabetes Mellitus (T2DM). It is involved in the overall energy homeostasis not only as passive energy storage but also as an important metabolic regulator. Here, we aim at developing a large scale microfluidic platform for generating high temporal resolution of glucose uptake profiles, and consequently insulin sensitivity, under physio-pathological stimulations in ex vivo adipose tissues from nondiabetic and T2DM individuals. A multiscale mathematical model that integrates fluid dynamics and an intracellular insulin signaling pathway description was used for assisting microfluidic design in order to maximize measurement accuracy of tissue metabolic activity in response to perturbations. An automated microfluidic injection system was included on-chip for performing precise dynamic biochemical stimulations. The temporal evolution of culture conditions could be monitored for days, before and after perturbation, measuring glucose concentration in the outflow with high temporal resolution. As a proof of concept for detection of insulin resistance, we measured insulin-dependent glucose uptake by hAT from nondiabetic and T2DM subjects, mimicking the postprandial response. The system presented thus represents an important tool in dissecting the role of single tissues, such as hAT, in the complex interwoven picture of metabolic diseases.

Fiber-optic system for dual-modality imaging of glucose probes 18F-FDG and 6-NBDG in atherosclerotic plaques

Background

Atherosclerosis is a progressive inflammatory condition that underlies coronary artery disease (CAD)–the leading cause of death in the United States. Thus, the ultimate goal of this research is to advance our understanding of human CAD by improving the characterization of metabolically active vulnerable plaques within the coronary arteries using a novel catheter-based imaging system. The aims of this study include (1) developing a novel fiber-optic imaging system with a scintillator to detect both ¹⁸F and fluorescent glucose probes, and (2) validating the system on ex vivo murine plaques.

Methods

A novel design implements a flexible fiber-optic catheter consisting of both a radio-luminescence and a fluorescence imaging system to detect radionuclide ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) and the fluorescent analog 6-(N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-6-Deoxyglucose (6-NBDG), respectively. Murine macrophage-rich atherosclerotic carotid plaques were imaged ex vivo after intravenous delivery of ¹⁸F-FDG or 6-NBDG. Confirmatory optical imaging by IVIS-200 and autoradiography were also performed.

Results

Our fiber-optic imaging system successfully visualized both ¹⁸F-FDG and 6-NBDG probes in atherosclerotic plaques. For ¹⁸F-FDG, the ligated left carotid arteries (LCs) exhibited 4.9-fold higher radioluminescence signal intensity compared to the non-ligated right carotid arteries (RCs) (2.6×10⁴±1.4×10³ vs. 5.4×10³±1.3×10³ A.U., P = 0.008). Similarly, for 6-NBDG, the ligated LCs emitted 4.3-fold brighter fluorescent signals than the control RCs (1.6×10²±2.7×10¹ vs. 3.8×10¹±5.9 A.U., P = 0.002). The higher uptake of both ¹⁸F-FDG and 6-NBDG in ligated LCs were confirmed with the IVIS-200 system. Autoradiography further verified the higher uptake of ¹⁸F-FDG by the LCs.

Conclusions

This novel fiber-optic imaging system was sensitive to both radionuclide and fluorescent glucose probes taken up by murine atherosclerotic plaques. In addition, 6-NBDG is a promising novel fluorescent probe for detecting macrophage-rich atherosclerotic plaques.

Determination of glucose flux in live myoblasts by microfluidic nanosensing and mathematical modeling

Quantitative dissection of dynamic glucose handling processes in live myoblasts without use of glucose analogs and radioactive hexoses.

Exploiting the mechanism of cellular glucose uptake to develop an image-based high-throughput screening system in living cells

Biophysical understanding of cellular glucose uptake led us to the development of an image-based high-throughput screening system by using a fluorescent glucose bioprobe, GB2. The accuracy, robustness, and practicality of our image-based HTS system were demonstrated through the pilot screening and the subsequent in vitro confirmation.

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.

Novel method to differentiate 3T3 L1 cells in vitro to produce highly sensitive adipocytes for a GLUT4 mediated glucose uptake using fluorescent glucose analog

Adipocytes play a vital role in glucose metabolism. 3T3 L1 pre adipocytes after differentiation to adipocytes serve as excellent in vitro models and are useful tools in understanding the glucose metabolism. The traditional approaches adopted in pre adipocyte differentiation are lengthy exercises involving the usage of IBMX and Dexamethasone. Any effort to shorten the time of differentiation and quality expression of functional differentiation in 3T3 L1 cells in terms of enhanced Insulin sensitivity has an advantage in the drug discovery process. Thus, there is a need to develop a new effective method of differentiating the pre adipocytes to adipocytes and to use such methods for developing efficacious therapeutic molecules. We observed that a combination of Dexamethasone and Troglitazone generated differentiated adipocytes over fewer days as compared to the combination of IBMX and Dexamethasone which constitutes the standard protocol followed in our laboratory. The experiments conducted to compare the quality of differentiation yielded by various differentiating agents indicated that the lipid droplet accumulation increased by 112 % and the GLUT4 mediated glucose uptake by 137 % in cells differentiated with Troglitazone and Dexamethasone than in cells differentiated traditionally. The comparative studies conducted for evaluating efficient measurable glucose uptake by GOPOD assay, radioactive (3)H-2-deoxy-D-glucose assay and by non-radioactive 6-NBDG (fluorescent analog of glucose) indicated that the non-radioactive method using 6-NBDG showed a higher signal to noise ratio than the conventional indirect glucose uptake method (GOPOD assay) and the radioactive (3)H-2-deoxy-D-glucose uptake method. Differentiated 3T3 L1 cells when triggered with 2.5 ng/mL of Insulin showed 3.3 fold more glucose uptake in non-radioactive method over the radioactive (3)H-2-deoxy-D-glucose uptake method. The results of this study have suggested that a combination of Dexamethasone and Troglitazone for 3T3 L1 cell differentiation helps in better quality differentiation over a short period of time with increased sensitivity to Insulin. The application of these findings for developing new methods of screening novel Insulin mimetics and for evaluating the immunological responses has been discussed.

A nonradioisotope chemiluminescent assay for evaluation of 2-deoxyglucose uptake in 3T3-L1 adipocytes. Effect of various carbonyls species on insulin action

We have developed a rapid nonradioisotope chemiluminescent assay adapted to high-throughput screening experiments, to evaluate glucose uptake activity in cultured cells. For chemiluminescence quantification of 2-deoxyglucose, we used a luminol oxidation reaction after an enzymatic dephosphorylation of 2-deoxyglucose-6-phosphate. All reactions were performed at 37 °C by consecutive addition of reagents, and the assay is able to quantify 2DG in picomole per well. To confirm the reliability of this method, we have evaluated the dose-effect of insulin, GLUT4 inhibitors and insulin-sensitizing agent on 2DG uptake into 3T3-L1 cells. The results obtained with the assay for 2DG uptake in vitro in the absence or presence of insulin stimulation, were similar to those obtained by the previous radioisotopic and enzymatic methods. We have also used this assay to evaluate the effect of various reactive carbonyl and oxygen species on insulin-stimulated 2DG-uptake into adipocytes. All reactive carbonyl species tested decreased insulin-stimulated glucose uptake in a time- and dose-dependent manner without affecting basal glucose uptake in 3T3-L1 cells. 4-hydroxynonenal was found to be the most potent in the impairment of glucose uptake. This new enzymatic chemiluminescent assay is rapid and useful for measurement of 2DG uptake in insulin-responsive in cultured cells.

Fueling and imaging brain activation

Metabolic signals are used for imaging and spectroscopic studies of brain function and disease and to elucidate the cellular basis of neuroenergetics. The major fuel for activated neurons and the models for neuron–astrocyte interactions have been controversial because discordant results are obtained in different experimental systems, some of which do not correspond to adult brain. In rats, the infrastructure to support the high energetic demands of adult brain is acquired during postnatal development and matures after weaning. The brain's capacity to supply and metabolize glucose and oxygen exceeds demand over a wide range of rates, and the hyperaemic response to functional activation is rapid. Oxidative metabolism provides most ATP, but glycolysis is frequently preferentially up-regulated during activation. Underestimation of glucose utilization rates with labelled glucose arises from increased lactate production, lactate diffusion via transporters and astrocytic gap junctions, and lactate release to blood and perivascular drainage. Increased pentose shunt pathway flux also causes label loss from C1 of glucose. Glucose analogues are used to assay cellular activities, but interpretation of results is uncertain due to insufficient characterization of transport and phosphorylation kinetics. Brain activation in subjects with low blood-lactate levels causes a brain-to-blood lactate gradient, with rapid lactate release. In contrast, lactate flooding of brain during physical activity or infusion provides an opportunistic, supplemental fuel. Available evidence indicates that lactate shuttling coupled to its local oxidation during activation is a small fraction of glucose oxidation. Developmental, experimental, and physiological context is critical for interpretation of metabolic studies in terms of theoretical models.

Visualizing sweetness: increasingly diverse applications for fluorescent-tagged glucose bioprobes and their recent structural modifications

Glucose homeostasis is a fundamental aspect of life and its dysregulation is associated with important diseases, such as cancer and diabetes. Traditionally, glucose radioisotopes have been used to monitor glucose utilization in biological systems. Fluorescent-tagged glucose analogues were initially developed in the 1980s, but it is only in the past decade that their use as a glucose sensor has increased significantly. These analogues were developed for monitoring glucose uptake in blood cells, but their recent applications include tracking glucose uptake by tumor cells and imaging brain cell metabolism. This review outlines the development of fluorescent-tagged glucose analogues, describes their recent structural modifications and discusses their increasingly diverse biological applications.

Response to 'comment on recent modeling studies of astrocyte-neuron metabolic interactions': much ado about nothing

For many years, a tenet of cerebral metabolism held that glucose was the obligate energy substrate of the mammalian brain and that neuronal oxidative metabolism represented the majority of this glucose utilization. In 1994, Pellerin and Magistretti formulated the astrocyte-neuron lactate shuttle (ANLS) hypothesis, in which astrocytes, not neurons, metabolized glucose, with subsequent transport of the glycolytically derived lactate to fuel the energy needs of the neuron during neurotransmission. By considering the concentrations and kinetic characteristics of the nutrient transporter proteins, Simpson et al later supported the opposite view, in which lactate flows from neurons to astrocytes, thus leading to the neuron-astrocyte lactate shuttle (NALS). Most recently, a commentary was published in this journal attempting to discredit the NALS. This challenge has stimulated the present response in which we detail the inaccuracies of the commentary and further model several different possibilities. Although our simulations continue to support the predominance of neuronal glucose utilization during activation and neuronal to astrocytic lactate flow, the most important result is that, regardless of the direction of the flow, the overall contribution of lactate to cerebral glucose metabolism is found to be so small as to make this ongoing debate 'much ado about nothing'.

Syntheses of 2-NBDG analogues for monitoring stereoselective uptake of D-glucose

2-NBDG is a widely used fluorescent tracer for monitoring d-glucose uptake into single living cells. However, 2-NBDG alone is not sufficient for monitoring the net stereoselective uptake of d-glucose, unless its possible non-stereoselective uptake is properly evaluated. l-Glucose derivatives, which emit fluorescence distinct from that of 2-NBDG, should provide valuable information on the stereoselective uptake, when used with 2-NBDG in combination. In the present study, we synthesized Texas Red (sulforhodamine 101 acid)-coupled and [2-(benz-2-oxa-1,3-diazol-4-yl)amino]-coupled 2-deoxy-D-glucose, referred to as [2-TRG] and [2-BDG], respectively. These derivatives showed emission wavelength longer and shorter than that of 2-NBDG, respectively. 2-TRLG, an antipode of 2-TRG, proved to be an effective tracer for evaluating the extent of non-stereoselective uptake of 2-NBDG when used simultaneously with 2-NBDG. On the other hand, 2-BDG exhibited very weak fluorescence, but the application of a novel cross coupling in the presence of a benzoxadiazole group may be useful for the future development of effective glucose tracers.

Predominant enhancement of glucose uptake in astrocytes versus neurons during activation of the somatosensory cortex

Glucose is the primary energetic substrate of the brain, and measurements of its metabolism are the basis of major functional cerebral imaging methods. Contrary to the general view that neurons are fueled solely by glucose in proportion to their energetic needs, recent in vitro and ex vivo analyses suggest that glucose preferentially feeds astrocytes. However, the cellular fate of glucose in the intact brain has not yet been directly observed. We have used a real-time method for measuring glucose uptake in astrocytes and neurons in vivo in male rats by imaging the trafficking of the nonmetabolizable glucose analog 6-deoxy-N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-aminoglucose (6-NBDG) using two-photon microscopy. During resting conditions we found that astrocytes and neurons both take up 6-NBDG at the same rate in the barrel cortex of the rat. However, during intense neuronal activity triggered by whisker stimulation, astrocytes rapidly accelerated their uptake, whereas neuronal uptake remained almost unchanged. After the stimulation period, astrocytes returned to their preactivation rates of uptake paralleling the neuronal rate of uptake. These observations suggest that glucose is taken up primarily by astrocytes, supporting the view that functional imaging experiments based on glucose analogs extraction may predominantly reflect the metabolic activity of the astrocytic network.

Confocal laser scanning microscopy (CLSM) based evidence for cell permeation by mono-4-(N-6-deoxy-6-amino-β-cyclodextrin)-7-nitrobenzofuran (NBD-β-CyD)

Beta-cyclodextrin (β-CyD), amantadine and glucose were fluorescently tagged with 4-chloro-7-nitrobenz-2-oxa-1,3-diazole (NBD chloride) to afford NBD-β-CyD, NBD-amantadine and NBD-glucose, respectively. NBD-β-CyD/amantadine and β-CyD/NBD-amantadine inclusion complexes were prepared. Fluorescence emission maxima (λ(max) 544nm) and relative fluorescence intensities for NBD-β-CyD and NBD-β-CyD/amantadine were virtually identical, precluding the use of emission spectrum shifts for distinguishing free NBD-β-CyD from the complex. Intracellular accumulation of NBD-β-CyD was studied in HepG2 and SK-MEL-24 cells using confocal laser scanning microscopy (CLSM). No major differences were observed between uptake of NBD-β-CyD and NBD-β-CyD/amantadine. Serum proteins did not perturb uptake, whereas temperature-dependent uptake, indicative of cell entry via diffusion, was observed. Intracellular distribution favoured mitochondria, with less fluorescent material present in cytoplasm and none in cell nuclei. No experimental evidence of NBD-β-CyD breakdown to NBD-glucose was found upon chromatographic analysis of incubation mixtures, providing additional evidence of intact NBD-β-CyD entry into these cells. Endocytosis and/or cholesterol-independent membrane modulation are discussed as possible mechanisms for the transmembrane passage of NBD-β-CyD.

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.