Uptake of a fluorescent L-glucose derivative 2-NBDLG into three-dimensionally accumulating insulinoma cells in a phloretin-sensitive manner

Synthesis and biological evaluation of mirror isomers of β-(1 → 3)-glucans as immune modulators

β-(1 → 3)-glucan is widely distributed in the cell walls of bacteria, fungi, yeasts and algae. A variety of pharmacological effects of β-(1 → 3)-glucan have been demonstrated, including immune modulation. The enzyme recognition pocket can recognize the chirality of the ligand and often give rise to disparate biological activities. The bioactivity of the mirror-image isomers of natural oligosaccharides is scarcely studied due to the difficulty of acquiring them. In this study, we have successfully completed the total synthesis of the naturally occurring β-ᴅ-(1 → 3)-glucans and their mirror image β-ʟ-(1 → 3)-glucans containing three, four, eight, and twelve monosaccharides for the first time. Subsequently, the immunomodulatory activities of ᴅ- and ʟ-type β-glucans were evaluated to explore their bioactivity and preliminary mechanism of action. The results indicated that mirror-image β-(1 → 3)-glucans exerted bidirectional regulatory effects on M0/M1-type macrophages. The ᴅ-type β-(1 → 3)-glucans have the potential to regulate macrophage polarization through the GPCR and CR3 signalling pathways. In contrast, the ʟ-type β-(1 → 3)-glucans achieved bidirectional regulation of macrophage polarization by influencing cellular metabolism. The findings presented herein provide new evidence for the further investigation of the biological activities of oligosaccharides and their mirror image isomers.

Exploring the Inhibitory Potential of Sodium Alginate Against Digestive Enzymes Linked to Obesity and Type 2 Diabetes

Obesity and type 2 diabetes mellitus (T2DM) are major health concerns worldwide, often managed with treatments that have significant limitations and side effects. This study examines the potential of sodium alginates, extracted from Ecklonia radiata and Sargassum elegans, to inhibit digestive enzymes involved in managing these conditions. We chemically characterized the sodium alginates and confirmed their structural integrity using FTIR, NMR, and TGA. The focus was on evaluating their ability to inhibit key digestive enzymes relevant to T2DM (α-amylase, α-glucosidase, sucrase, maltase) and obesity (pancreatic lipase). Enzyme inhibition assays revealed that these sodium alginates moderately inhibit α-glucosidase, maltase, and lipase by up to 43%, while showing limited effects on sucrase and α-amylase. In addition, the sodium alginates did not affect glucose uptake in human colorectal cells (HCT116), indicating they do not impact cellular glucose absorption. In summary, while the observed enzyme inhibition was moderate, the targeted inhibition of α-glucosidase, maltase, and lipase suggests that sodium alginates could be beneficial for managing postprandial hyperglycemia and lipid absorption in the context of T2DM and obesity.

Development of a selective novel fluorescent substrate for sodium-dependent transporters

AIM

To synthesize, characterize, and validate 6FGA, a fluorescent glucose modified with a Cyanine5.5 at carbon-6 position, for probing the function of sodium-dependent glucose transporters, SGLT1 and SGLT2.

MAIN METHODS

The synthesis of fluorescent glucose analogue was achieved through "click chemistry" of Cyanine5.5-alkyne and 6-azido-6-deoxy-d-glucose. Cell system studies were conducted to characterize the in vivo transport properties.

KEY FINDINGS

Optical analyses revealed that 6FGA displayed similar spectral profiles to Cyanine5.5 in DMSO, allowing for concentration determination, thus supporting its utility in quantitative kinetic studies within biological assays. Uptake studies in cell system SGLT models, LLC-PK1 and HEK293 cells, exhibited concentration and time-dependent behavior, indicating saturation at specific concentrations and durations which are hallmarks of transported-mediated uptake. The results of cytotoxicity assays suggested cell viability at micromolar concentrations, enabling usage in assays for at least 1 h without significant toxicity. The dependence of 6FGA uptake on sodium, the co-transported cation, was demonstrated in LLC-PK1 and HEK293 cells. Fluorescence microscopy confirmed intracellular localization of 6FGA, particularly near the nucleus. Competition studies revealed that glucose tends to weakly reduce 6FGA uptake, although the effect did not achieve statistical significance. Assessments using standard SGLT and GLUT inhibitors highlighted 6FGA's sensitivity for probing SGLT-mediated transport.

SIGNIFICANCE

6FGA is a new fluorescent glucose analog offering advantages over existing probes due to its improved photophysical properties, greater sensitivity, enabling subcellular resolution and efficient tissue penetration in near-infrared imaging. 6FGA presents practicality and cost-effectiveness, making it a promising tool for nonradioactive, microplate-based assays at investigating SGLT-mediated glucose transport mechanisms.

Simultaneous dynamic glucose-enhanced (DGE) MRI and fiber photometry measurements of glucose in the healthy mouse brain

Glucose is the main energy source in the brain and its regulated uptake and utilization are important biomarkers of pathological brain function. Glucose Chemical Exchange Saturation Transfer (GlucoCEST) and its time-resolved version Dynamic Glucose-Enhanced MRI (DGE) are promising approaches to monitor glucose and detect tumors, since they are radioactivity-free, do not require ¹³C labeling and are is easily translatable to the clinics. The main principle of DGE is clear. However, what remains to be established is to which extent the signal reflects vascular, extracellular or intracellular glucose. To elucidate the compartmental contributions to the DGE signal, we coupled it with FRET-based fiber photometry of genetically encoded sensors, a technique that combines quantitative glucose readout with cellular specificity. The glucose sensor FLIIP was used with fiber photometry to measure astrocytic and neuronal glucose changes upon injection of D-glucose, 3OMG and L-glucose, in the anaesthetized murine brain. By correlating the kinetic profiles of the techniques, we demonstrate the presence of a vascular contribution to the signal, especially at early time points after injection. Furthermore, we show that, in the case of the commonly used contrast agent 3OMG, the DGE signal actually anticorrelates with the glucose concentration in neurons and astrocytes.

Tumour enzyme affinity mediated peptide molecular crowding for targeted disruption of hyperactivated glucose uptake

An unconventional environment-responsive molecular crowding via specific binding between small molecule peptide inhibitor derivatives and an overexpressed tumour enzyme has been developed. Assemblies of such short peptides selectively localize on tumour surfaces and exhibited unique functions in disrupting hyperactivated glucose uptake, providing novel insights towards strategic tumour treatment.

Multimodal molecular imaging evaluation for early diagnosis and prognosis of cholangiocarcinoma

Cholangiocarcinoma (CCA) is an aggressive and lethal malignancy with limited therapeutic options. Despite recent advances in diagnostic imaging for CCA, the early diagnosis of CCA and evaluation of tumor invasion into the bile duct and its surrounding tissues remain challenging. Most patients with CCA are diagnosed at an advanced stage, at which treatment options are limited. Molecular imaging is a promising diagnostic method for noninvasive imaging of biological events at the cellular and molecular level in vivo. Molecular imaging plays a key role in the early diagnosis, staging, and treatment-related evaluation and management of cancer. This review will describe different methods for molecular imaging of CCA, including nuclear medicine, magnetic resonance imaging, optical imaging, and multimodal imaging. The main challenges and future directions in this field are also discussed.

Uptake of fluorescent D- and L-glucose analogues, 2-NBDG and 2-NBDLG, into human osteosarcoma U2OS cells in a phloretin-inhibitable manner

Mammalian cells take in d-glucose as an essential fuel as well as a carbon source. In contrast, l-glucose, the mirror image isomer of d-glucose, has been considered merely as a non-transportable/non-metabolizable control for d-glucose. We have shown that 2-[N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose (2-NBDG), a d-glucose analogue combining a fluorophore NBD at the C-2 position, is useful as a tracer for monitoring d-glucose uptake through glucose transporters (GLUTs) into mammalian cells. To more precisely evaluate the stereoselectivity of 2-NBDG uptake, we developed an l-glucose analogue 2-NBDLG, the mirror-image isomer of 2-NBDG. Interestingly, 2-NBDLG was taken up into mouse insulinoma MIN6 cells showing nuclear heterogeneity, a cytological feature of malignancy, while remaining MIN6 cells only exhibited a trace amount of 2-NBDLG uptake. The 2-NBDLG uptake into MIN6 cells was abolished by phloretin, but persisted under blockade of major mammalian glucose transporters. Unfortunately, however, no such uptake could be detected in other tumor cell lines. Here we demonstrate that human osteosarcoma U2OS cells take in 2-NBDLG in a phloretin-inhibitable manner. The uptake of 2-NBDG, and not that of 2-NBDLG, into U2OS cells was significantly inhibited by cytochalasin B, a potent GLUT inhibitor. Phloretin, but neither phlorizin, an inhibitor of sodium-glucose cotransporter (SGLT), nor a large amount of d/l-glucose, blocked the 2-NBDLG uptake. These results suggest that a phloretin-inhibitable, non-GLUT/non-SGLT, possibly non-transporter-mediated yet unidentified mechanism participates in the uptake of the fluorescent l-glucose analogue in two very different tumor cells, the mouse insulinoma and the human osteosarcoma cells.

Intestinal Absorption and Tissue Distribution of Aza-Sugars from Mulberry Leaves and Evaluation of Their Transport by Sugar Transporters

Mulberry leaves are rich in aza-sugars, particularly 1-deoxynojirimycin (DNJ), fagomine, and 2-O-α-d-galactopyranosyl-1-deoxynojirimycin (GAL-DNJ), which have antidiabetes and antiobesity properties. To help us understand the mechanisms of action of aza-sugars, pharmacokinetic studies are necessary. Therefore, in this study, we evaluated and compared the absorption and organ distribution of these aza-sugars in rats. Following oral intake, DNJ exhibited the highest plasma concentration followed by fagomine and GAL-DNJ. Meanwhile, similar amounts of DNJ and fagomine were present in organs, while GAL-DNJ was hardly detected, suggesting the diversity in absorption and distribution characteristics of these aza-sugars. We then investigated the role of the sodium-glucose cotransporter and the glucose transporter (GLUT) in the transport of aza-sugars and found that both are involved in DNJ transport, while transport of fagomine is solely facilitated by the GLUT. These findings provide insight into the bioavailability and bioactive mechanisms of these aza-sugars.

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.

A new perspective of probe development for imaging pancreatic beta cell in vivo

Beta cells assume a fundamental role in maintaining blood glucose homeostasis through the secretion of insulin, which is contingent on both beta cell mass and function, in response to elevated blood glucose levels or secretagogues. For this reason, evaluating beta cell mass and function, as well as scrutinizing how they change over time in a diabetic state, are essential prerequisites in elucidating diabetes pathophysiology. Current clinical methods to measure human beta cell mass and/or function are largely lacking, indirect and sub-optimal, highlighting the continued need for noninvasive in vivo beta cell imaging technologies such as optical imaging techniques. While numerous probes have been developed and evaluated for their specificity to beta cells, most of them are more suited to visualize beta cell mass rather than function. In this review, we highlight the distinction between beta cell mass and function, and the importance of developing more probes to measure beta cell function. Additionally, we also explore various existing probes that can be employed to measure beta cell mass and function in vivo, as well as the caveats in probe development for in vivo beta cell imaging.

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.

Multicolor GLUT5-permeable fluorescent probes for fructose transport analysis

The specificity of carbohydrate transporters towards their substrates poses a significant challenge for the development of molecular probes to monitor sugar uptake in cells for biochemical and biomedical applications. Herein we report a new set of coumarin-based fluorescent sugar conjugates applicable for the analysis of fructose uptake due to their free passage through the fructose-specific transporter GLUT5. The reported probes cover a broad range of the fluorescence spectrum providing essential tools for the evaluation of fructose transport capacity in live cells.

Unknown biological effects of L-glucose, ALA, and PUFA

Key substrates including glucose, amino acids, and fatty acids play core roles in nutrient metabolism. In this review, we describe phenomena observed when key substrates are applied to cells. We focused on three promising substrates: L-glucose derivatives, 5-aminolevulinic acid, and polyunsaturated fatty acid. Since they are assumed to give a specific reaction when they are transported into cells or metabolized in cells, they are expected to be applied in a clinical setting. We provide the latest knowledge regarding their behaviors and effects on cells.

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.

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.

Imaging hamster model of bile duct cancer in vivo using fluorescent L-glucose derivatives

Extrahepatic bile duct cancer (cholangiocarcinoma) has a poor prognosis. Since surgical resection is the only way to prolong the patient’s life, it is of critical importance to correctly determine the extent of lesions. However, conventional pre-operative assessments have insufficient spatial resolution for determining the surgical margin. A fluorescent contrast agent might provide a more precise measure to identify anomalies in biliary surface, when combined with probe-based confocal laser endomicroscopy (pCLE). We have previously shown that 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-l-glucose (2-NBDLG), a fluorescent derivative of l-glucose (fLG), is specifically taken up into spheroids consisting of cells showing heterogeneous nuclear-cytoplasm ratio, a feature of malignant cells in clinical settings. In addition, a combined use of 2-TRLG, a membrane-impermeable fLG, with 2-NBDLG visualized membrane integrity as well. We therefore explored in the present study the availability of the fLGs in vivo as a contrast agent for pCLE by using a hamster model of cholangiocarcinoma. Extrahepatic cholangiocarcinoma developed in mid common duct in ~20 % of the animals subjected to cholecystoduodenostomy with the ligation at the distal end of the common duct followed by injection of a carcinogen N-nitrosobis(2-oxopropyl)amine. After infusing bile duct with a solution containing 2-NBDLG and 2-TRLG, the lumen was surgically exposed and examined by pCLE. Fluorescence pattern characterized by bright spots and dark clumps was detected in the areas diagnosed with cholangiocarcinoma in later histopathology, whereas no such pattern was detected in control animals. These findings may form a basis for elucidating a potential availability of fLGs in imaging cholangiocarcinoma by pCLE.