HPLC Measurement of the DNA Oxidation Biomarker, 8-oxo-7,8-dihydro-2’-deoxyguanosine, in Cultured Cells and Animal Tissues

Summary

The goal of this protocol is the detection of the DNA oxidation marker, 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dGuo) by HPLC-ED, in DNA from cultured cells or animal tissues.

Abstract

Oxidative stress is associated with many physiological and pathological processes, as well as xenobiotic metabolism, leading to the oxidation of biomacromolecules, including DNA. Therefore, efficient detection of DNA oxidation is important for a variety of research disciplines, including medicine and toxicology. A common biomarker of oxidatively damaged DNA is 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dGuo; often erroneously referred to as 8-hydroxy-2'-deoxyguanosine (8-OH-dGuo or 8-oxo-dG)). Several protocols for 8-oxo-dGuo measurement by high pressure liquid chromatography with electrochemical detection (HPLC-ED) have been described. However, these were mainly applied to purified DNA treated with pro-oxidants. In addition, due to methodological differences between laboratories, mainly due to differences in analytical equipment, the adoption of published methods for detection of 8-oxo-dGuo by HPLC-ED requires careful optimization by each laboratory. A comprehensive protocol, describing such an optimization process, is lacking. Here, a detailed protocol is described for the detection of 8-oxo-dGuo by HPLC-ED, in DNA from cultured cells or animal tissues. It illustrates how DNA sample preparation can be easily and rapidly optimized to minimize undesirable DNA oxidation that can occur during sample preparation. This protocol shows how to detect 8-oxo-dGuo in cultured human alveolar adenocarcinoma cells (i.e., A549 cells) treated with the oxidizing agent KBrO₃, and from the spleen of mice exposed to the polycyclic aromatic hydrocarbon dibenzo(def,p)chrysene (DBC, formerly known as dibenzo(a,l)pyrene, DalP). Overall, this work illustrates how an HPLC-ED methodology can be readily optimized for the detection of 8-oxo-dGuo in biological samples.

Introduction

Reactive oxygen species (ROS), whose steady-state levels can increase during many pathological conditions and xenotoxic metabolism, contribute to an increased frequency of oxidative DNA damage. Among several possible nucleobases oxidation products, oxidative DNA damage can readily be measured using the stable marker 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dGuo), which is one of the oxidized forms of 2’-deoxyguanosine (dGuo)¹. 8-oxo-dGuo is the most abundant DNA lesion² and, therefore, has been studied to greater detail as a DNA oxidation biomarker despite the existence of multiple DNA oxidation products ³. In humans, this ....

Protocol

Ensure that all animal husbandry, housing, handling and experimentation adhere to local rules and regulations and that experimentation protocols are approved prior to commencing any study. For the described experiments, animal care, handling, and treatment were approved by the Health Canada Animal Care Committee. See the “Reagents table” for the suppliers’ information.

1. Collecting Biological Samples

1. Cells or Animal Tissues
   1. Grow human alveolar adenocarcinoma A549 cells in F12-K media containing 10% fetal bovine serum, 100 units/ml of penicillin and 100 µg/ml of streptomycin.
   2. Seed ce....

Results

dGuo was observed to have a retention time of 4.7 min whereas 8-oxo-dGuo had a retention time of approximately 6.4 min (Figure 2A and B). There is about 1,000-fold difference in the peak heights between the two analytes, as seen in Figure 2C. Voltammograms for 8-oxo-dGuo and dGuo were obtained by running standards at a working potential in the range of +0.2 to +1.1 V. The optimum working potential for 8-oxo-dGuo was determined to be +0.5 V, and +0.9 V for dGuo (F.......

Discussion

Although 8-oxo-dGuo has been reported as a useful biomarker of DNA oxidation, its reliable quantification can pose a challenge. Although several published methods exist, there is a need for a comprehensive, descriptive overview of protocol to permit researchers to deploy the method in their laboratories. Here we present a detailed overview of an HPLC-based protocol that will permit new users to establish an effective method for 8-oxo-dGuo detection and quantification.

Three major methods that .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
8-oxo-dGuo standard	Cayman Chemical Company	89320	Inappropriately referred to as "8-hydroxy-2'-deoxy Guanosine"; see Fig. 1 and text for details.
Alkaline phosphatase	Sigma-Aldrich	P5931	From E. coli
Chelex 100	Sigma-Aldrich	C7901	Chelates heavy metals
Desferoxamine mesylate	Sigma-Aldrich	D9533
dGuo standard	Sigma-Aldrich	D7145
Dibasic sodium phosphate	Sigma-Aldrich	S9390
DNA from salmon sperm	Sigma-Aldrich	D1626	Sodium salt
DNase I	Sigma-Aldrich	D4527	TypeII, from bovine pancreas
DNAzol	Invitrogen	10503-27
Ethylenediaminetetraacetic acid disodium salt dihydrate (EDTA)	Sigma-Aldrich	E4884	The compound would not completely dissolve until solution pH is adjusted to 8.0 (e.g. with NaOH)
F12-K media	ATCC	30-2004
Foetal bovine serum	ATCC	30-2020
Guard column	Chromatographic Specialties	YBA 99S03 0204GC	Protects colum from contamination; may also lead to pressure build-up
Magnesium chloride	Sigma-Aldrich	M8266
Monobasic sodium phosphate	Sigma-Aldrich	S9638
Penicillin-Streptomycin	Invitrogen	15140-122
Phosphate buffered saline	Invitrogen	15190-250
Phosphodiesterase I enzyme	Sigma-Aldrich	P3243	Type II from Crotalus adamaneus venom
Teflon homogenizer	Thomas Scientific	7724T-1 or 7724T-5 for 1 or 5 mL, respectively	Volume (holding capacity) depends on the amount of sample to be processed.
Trypsin	Invitrogen	15050-065
YMC-BASIC column with bonded spherical silica	Chromatographic Specialties	YBA 99S03 1546WT