Extracellular Glucose Depletion as an Indirect Measure of Glucose Uptake in Cells and Tissues Ex Vivo

Summary

Extracellular depletion of fluorescently labeled glucose correlates with glucose uptake and could be used for high-throughput screening of glucose uptake in excised organs and cell cultures.

Abstract

The ongoing worldwide epidemic of diabetes increases the demand for the identification of environmental, nutritional, endocrine, genetic, and epigenetic factors affecting glucose uptake. The measurement of intracellular fluorescence is a widely used method to test the uptake of fluorescently-labeled glucose (FD-glucose) in cells in vitro, or for imaging glucose-consuming tissues in vivo. This assay assesses glucose uptake at a chosen time point. The intracellular analysis assumes that the metabolism of FD-glucose is slower than that of endogenous glucose, which participates in catabolic and anabolic reactions and signaling. However, dynamic glucose metabolism also alters uptake mechanisms, which would require kinetic measurements of glucose uptake in response to different factors. This article describes a method for measuring extracellular FD-glucose depletion and validates its correlation with intracellular FD-glucose uptake in cells and tissues ex vivo. Extracellular glucose depletion may be potentially applicable for high-throughput kinetic and dose-dependent studies, as well as identifying compounds with glycemic activity and their tissue-specific effects.

Introduction

The demand for measuring glucose uptake rises together with the critical need to address an epidemic increase in a multitude of diseases dependent on glucose metabolism. Underlying mechanisms of degenerative metabolic diseases, neurological and cognitive disorders¹, inflammatory² and infectious diseases³, cancer^4,5, as well as aging⁶, depend on glucose metabolism for energy and its storage, anabolic processes, protein, and gene modification, signaling, regulation of genes, and nucleic acids synthesis and replication....

Protocol

Animal studies were approved by the Institutional Animal Care and Use Committee of The Ohio State University (OSU, protocol 2007A0262-R4).

NOTE: All procedures must be done in a class II biosafety cabinet with the blower on and the lights off.

1. Preparation of materials

NOTE: All materials are listed in the Table of Materials.

1. Prepare Medium 1, centrifugation Medium 2, and storage and working solutions of fluorescent 2-deoxy-2-[(7-nitro-2,1,3-benzoxadiazol-4-yl) amino]-D-glucose (2-NBDG or FD-glucose) according to Table 1 ....

Results

Intracellular intake and extracellular glucose depletion were measured in 3T3-L1 preadipocytes, in response to different concentrations of FD-glucose (Figure 2) with and without insulin stimulation. Figure 2A demonstrates a dose-dependent increase in the intracellular uptake of FD-glucose, which was significantly increased in the presence of insulin. The concomitant decrease in extracellular FD-glucose in the same cells is shown in

Discussion

The direct comparison of extracellular FD-glucose depletion with normalized intracellular glucose uptake in cells culture showed a high correlation, suggesting that extracellular glucose depletion could be a surrogate measurement for glucose uptake assessment. The measurement of extracellular FD-glucose can use a broad range of FD glucose concentrations, also 0.5-2.5 μg FD-glucose/mL appear to provide the optimal range. Extracellular FD-glucose does not require normalization to cell number or protein concentrations .......

Materials

Name	Company	Catalog Number	Comments
3T3-L1 mouse fibroblasts	ATCC	CL-173	Cell line
96-well plates	Falcon	353227	Plastic ware
B6.V-Lepob/J male mice	Jackson Laboratory	stock number 000632	Mice
BioTek Synergy H1 modular multimode microplate reader (Fisher Scientific, US)	Fisher Scientific, US	B-SHT	Device
Bovine serum	Gibco/ThermoFisher	161790-060	Cell culture
Calf serum	Gibco/ThermoFisher	26010-066	Cell culture
Cell incubator	Forma	Series II Water Jacket	Device
Diet (mouse/rat diet, irradiated)	Envigo	Teklad LM-485	Diet
Dimethylsulfoxide (DMSO)	Sigma LifeScience	D2650-100mL	Reagent
Dulbecco's Modified Eagle Medium	Gibco/ThermoFisher	11965-092	Cell culture
Ethanol	Sigma Aldrich	E7023-500mL	Reagent
Fluorescent 2-deoxy-2-[(7-nitro-2,1,3-benzoxadiazol-4-yl) amino]-D-glucose)	Sigma	72987-1MG	Assay
Glucose-free and phenol red-free DMEM	Gibco/ThermoFisher	A14430-01	Cell culture
Human insulin 10 mg/mL	MilliporeSigma, Cat N 91077C	Cat N 91077C	Reagent
Isoflurane, 5%	Henry Schein	NDC 11695-6776-2	Anestaetic
Penicillin/streptomycin (P/S)	Gibco/ThermoFisher	15140-122	Cell culture
Phosphate buffered solution	Sigma-Aldrich	DA537-500 mL	Cell culture
Pierce bicinchoninic acid (BCA) protein assay	ThermoFisher	Cat N23225	Assay
Radioimmunoprecipitation assay lysis buffer	Santa Cruz Biotechnology	sc-24948	Assay
Trypsin-EDTA (0.05%)	Gibco/ThermoFisher	25300-054	Cell culture