Biochemical Titration of Glycogen In vitro

Summary

We describe here an accurate, reproducible and convenient biochemical method for titration of glycogen in vitro. This technique uses the Abcam Glycogen assay kit and is based on successive hydrolysis of glycogen to glucose and glucose titration by fluorescence.

Abstract

Glycogen is the main energetic polymer of glucose in vertebrate animals and plays a crucial role in whole body metabolism as well as in cellular metabolism. Many methods to detect glycogen already exist but only a few are quantitative. We describe here a method using the Abcam Glycogen assay kit, which is based on specific degradation of glycogen to glucose by glucoamylase. Glucose is then specifically oxidized to a product that reacts with the OxiRed probe to produce fluorescence. Titration is accurate, sensitive and can be achieved on cell extracts or tissue sections. However, in contrast to other techniques, it does not give information about the distribution of glycogen in the cell. As an example of this technique, we describe here the titration of glycogen in two cell lines, Chinese hamster lung fibroblast CCL39 and human colon carcinoma LS174, incubated in normoxia (21% O₂) versus hypoxia (1% O₂). We hypothesized that hypoxia is a signal that prepares cells to synthesize and store glycogen in order to survive¹.

Introduction

Glycogen is a multibranched polymer of glucose residues, which is present in the cytoplasm of many cell types. It is one of the main forms of energy storage in cells and plays an important role in glucose metabolism. Most mammalian cells are able to produce and store glycogen, which can be rapidly degraded into glucose to promote glycolysis and ATP production during metabolic stress. Hepatocytes produce massive amounts of glycogen to regulate the blood sugar level thereby providing a continuous supply of glucose to the body. In contrast, the concentration of glycogen in other cells (muscles, red blood cells, etc.) is relatively low. However, locally, the....

Protocol

Biochemical Titration of Glycogen

1. Cell Lysis

1. Seed cells at a concentration of 0.5-2 x 10⁶ per 100 mm diameter dish.
2. Treatment: incubate cells 24, 48, or 72 hr in low oxygen concentration (hypoxia) in a Bug-Box anaerobic work station (Ruskinn Technology Biotrace International Plc, Bridgend, UK) set at 1% or 0.1% O₂, 94% or 94.9% N₂, and 5% CO₂. In parallel, incubate cells in normoxia (21% O₂, 5% CO₂). Change medium (25 mM glucose-containing medium) every 24 hr to minimize variations in the glucose concentration during the time of experiment.
3. Af....

Results

A low level of oxygen (hypoxia) in tumors signals to tumor cells the need to store energy to handle subsequent nutrient depletion, so as to survive. As glycogen is the main energetic polymer of glucose in mammalian cells, we studied the regulation of glycogen storage in hypoxia. The calculation and standardization of the concentration of glycogen in cell lysates must be performed on the raw data of fluorescence as shown in Tables 1, 2, and 3. The biochemical assay for gl.......

Discussion

Biochemical titration of glycogen in vitro allows an accurate quantification of cells glycogen content. Comparing to some other techniques (PAS, immunofluorescence with a glycogen antibody, etc.), this titration is very specific, sensitive and reproducible. Moreover, the method is convenient since it requires no radioactivity but a fluorescence spectrometer. However, this technique is purely quantitative and does not provide information about glycogen distribution in the cell.

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
REAGENTS
DMEM	Invitrogen	31966.047
Glycogen Assay Kit	Abcam	ab65620
PBS
EQUIPMENT
Fluorescence Spectrometer	PerkinElmer	LS 50B