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Method Article
The goal of the thiobarbituric acid reactive substances assay is to assess oxidative stress in biological samples by measuring the production of lipid peroxidation products, primarily malondialdehyde, using visible wavelength spectrophotometry at 532 nm. The method described here can be applied to human serum, cell lysates, and low density lipoproteins.
Despite its limited analytical specificity and ruggedness, the thiobarbituric acid reactive substances (TBARS) assay has been widely used as a generic metric of lipid peroxidation in biological fluids. It is often considered a good indicator of the levels of oxidative stress within a biological sample, provided that the sample has been properly handled and stored. The assay involves the reaction of lipid peroxidation products, primarily malondialdehyde (MDA), with thiobarbituric acid (TBA), which leads to the formation of MDA-TBA2 adducts called TBARS. TBARS yields a red-pink color that can be measured spectrophotometrically at 532 nm. The TBARS assay is performed under acidic conditions (pH = 4) and at 95 °C. Pure MDA is unstable, but these conditions allow the release of MDA from MDA bis(dimethyl acetal), which is used as the analytical standard in this method. The TBARS assay is a straightforward method that can be completed in about 2 h. Preparation of assay reagents are described in detail here. Budget-conscious researchers can use these reagents for multiple experiments at a low cost rather than buying an expensive TBARS assay kit that only permits construction of a single standard curve (and thus can only be used for one experiment). The applicability of this TBARS assay is shown in human serum, low density lipoproteins, and cell lysates. The assay is consistent and reproducible, and limits of detection of 1.1 μM can be reached. Recommendations for the use and interpretation of the spectrophotometric TBARS assay are provided.
Lipid peroxidation is a process in which free radicals, such as reactive oxygen species and reactive nitrogen species, attack carbon-carbon double bonds in lipids, a process that involves the abstraction of a hydrogen from a carbon and insertion of an oxygen molecule. This process leads to a mixture of complex products including, lipid peroxyl radicals, and hydroperoxides as the primary products, as well as malondialdehyde (MDA) and 4-hydroxynonenal as predominant secondary products1.
MDA has been widely used in biomedical research as a marker of lipid peroxidation due to its facile reaction with thiobarbituric acid (TBA). The reaction leads to the formation of MDA-TBA2, a conjugate that absorbs in the visible spectrum at 532 nm and produces a red-pink color2. Other molecules derived from lipid peroxidation besides MDA can also react with TBA and absorb light at 532 nm, contributing to the overall absorption signal that is measured. Similarly, MDA can react with most other major classes of biomolecules, potentially limiting its accessibility for reaction with TBA3,4. As such, this traditional assay is simply considered to measure “thiobarbituric acid reactive substances” or TBARS5.
When correctly applied and interpreted, the TBARS assay is generally considered a good indicator of the overall levels of oxidative stress in a biological sample6. Unfortunately, as documented by Khoubnasabjafari and others, the TBARS assay is often conducted and interpreted in ways that facilitate dubious conclusions3,4,7,8,9,10,11. The causes for this are rooted primarily in sample-related pre-analytical variables and a lack of assay ruggedness that prohibits seemingly minor variations in assay protocol without substantial changes in assay results1,7,12,13.
Preanalytical variables related to biospecimen handling and storage (e.g., blood plasma kept temporarily at -20 °C)14,15 can have a major impact on TBARS assay results16,17; so much so, that TBARS assay results should not be compared across different laboratories unless warranted by explicit interlaboratory analytical validation data. This recommendation is akin to how western blots are commonly used and interpreted. Comparisons of band densities are valid for within-blot and perhaps within-laboratory studies, but comparing band densities between laboratories is generally considered an invalid practice.
Some researchers have suggested that MDA as measured by the TBARS assay simply does not meet the analytical or clinical criteria required of an acceptable biomarker3,9,10,18,19. Indeed, if the assay had not been developed over 50 years ago, it probably would not have gained the widespread use and tacit acceptability that it has today. Although there are other assays with greater analytical sensitivity, specificity, and ruggedness used for determining oxidative stress, TBARS assay based on absorbance at 532 nm remains by far one of the most commonly used assays for the determination of lipid peroxidation20, and thereby assessment of oxidative stress.
The TBARS assay can only be found as an expensive kit (over 400 U.S. dollars), in which the instructions do not provide detailed information on most concentrations of the reagents used. Additionally, the reagents provided can only be used for one experiment, because only one colorimetric standard curve can be made per kit. This can be problematic for researchers who intend to determine levels of oxidation within a few samples at different timepoints, because the same standard curve cannot be used at multiple times. Hence, multiple kits need to be purchased for multiple experiments. Currently, unless an expensive kit is purchased, there is not a detailed protocol available for how to perform a TBARS assay. Some researchers in the past have vaguely described how to perform a TBARS assay21,22, but neither a fully detailed protocol or comprehensive video on how to conduct the TBARS assay without an expensive kit is available in the literature.
Here we report a detailed, analytically validated for-purpose methodology on how to perform a TBARS assay in a simple, reproducible, and inexpensive way. Changes in the lipid peroxidation of human serum, HepG2 lysates, and low density lipoproteins upon treatment with Cu(II) ions are demonstrated as illustrative applications for the TBARS assay. Results demonstrate that this TBARS assay is consistent and reproducible on a day-to-day basis.
Human serum specimens were obtained from consenting volunteers under IRB approval and according to the principles expressed in the Declaration of Helsinki. Specimens were coded and de-identified before transfer to the analytical laboratory.
1. Sample preparation
2. Reagent preparation
CAUTION: Thiobarbituric acid causes skin and eye irritation and maybe harmful by inhalation or skin absorption. Acetic acid can damage internal organs if inhaled. Prepare all acid solutions in a fume hood.
3. Malondialdehyde bis(dimethyl acetal) standard sample preparation
NOTE: Malondialdehyde (MDA) is unstable and not commercially available. However, there are different chemical forms of MDA that are commercially available, such as MDA tetrabutylammonium salt, MDA bis(dimethyl acetal), and MDA bis(diethyl acetal). Of these three chemical forms, MDA bis(dimethyl acetal) is used here, because a majority of studies use this same standard21,22. If choosing to use the other two chemical forms of MDA, prior validation of their suitability should be carried out.
4. TBARS assay
NOTE: Once the TBARS assay is started, it should be finished without stopping.
Under acidic conditions (pH = 4) and at 95 °C, malondialdehyde (MDA) bis(dimethyl acetal) yields MDA23. MDA and closely related chemical congeners react with two molecules of thiobarbituric acid (TBA) to produce compounds called thiobarbituric acid reactive substances (TBARS), which give a red-pink color and have an absorbance λmax at 532 nm (Figure 1, Figure 2). Using MDA bis (dimethyl acetal) as the standard, standa...
Despite its limitations1,3,4,7,8,9,10,12,13,14,15,19 and a lack of suitability for comparison between laboratories, t...
The authors have no competing financial interests or other conflicts of interest to disclose.
The research reported here was supported in part by the National Cancer Institute of the National Institutes of Health under award no. R33 CA217702 and the Initiative for Maximizing Student Development (IMSD) program. The content is solely the responsibility of the authors and does not necessarily represent the official view of the National Institutes of Health.
Name | Company | Catalog Number | Comments |
1x Sterile PBS pH 7.4 1 L | VWR, PA | 101642--262 | cell lysis reagent |
50 mL self-standing centrifuge tube | Corning, NY | CLS430897 | General material |
96 well plate, Non-Treated, clear, with lid, Non-sterile | Thermo Fisher Scientific, MA | 280895 | To measure absorbance |
Amicon Ultra-0.5 100 kD centrifugal spin filter device | Fisher Scientific, NH | UFC510024 | LDL purification |
Caps for glass tubes | Thermo Fisher Scientific, MA | 14-930-15D | for TBARS assay |
Copper II Chloride | SIGMA, MO | 222011-250G | to induce oxidation |
Culture tubes, Disposable, with Screw-Cap Finish, Borosilicate Glass (13 x 100 mm) | VWR, PA | 53283-800 | for TBARS assay |
Eagle's Minimum Essential Medium (EMEM) | ATCC, VA | HB-8065 | HepG2 cell media |
Eppendorf Safe-Lock Tubes, 1.5 mL | eppendorf, NY | 22363204 | General material |
Eppendorf Safe-Lock Tubes, 2.0 mL | Genesee Sceitific, CA | 22363352 | General material |
Fetal Bovine Serum US Source | Omega Scientific, CA | FB-11 | for cell culture |
Glacial Acetic Acid | SIGMA, MO | 27225-1L-R | TBARS Reagent |
Halt Protease Inhibitor Cocktail (100x) | Thermo Scientific, MA | 87786 | cell lysis reagent |
HEPES | SIGMA, MO | H3375-250G | LDL solvent |
HepG2 Cells | ATCC, VA | HB-8065 | Biological matrix prototype |
Hydrocloric acid (HCl) | Fisher Scientific, NH | A144-212 | cell lysis reagent |
Legend Micro 17 Centrifuge | Thermo Scientific, MA | 75002431 | General material |
Low Density Lipoprotein, Human Plasma | Athens Research & Technology, GA | 12-16-120412 | Biological matrix prototype |
Magnetic Stir Bars, Octagon 6-Assortment | VWR, PA | 58948-025 | General material |
Malondialdehyde bis (dimethyl acetal) | SIGMA, MO | 8207560250 | TBARS Standard |
Multiskan Go Microplate Spectrophotometer | Fisher Scientific, NH | 51119200 | To measure absorbance |
NP-40 | EMD Millipore Corp, MA | 492016-100ML | cell lysis reagent |
Sodium Chloride | SIGMA, MO | S7653-1KG | cell lysis reagent |
Sodium dodecyl sulfate (SDS) | SIGMA, MO | 436143-100G | TBARS Reagent |
Sodium hydroxide | SIGMA, MO | 367176-2.5KG | TBARS Reagent |
SpeedVac Concentrator | Thermo Scientific, MA | SC250EXP | For concentrating cell lysates |
T-75 Flask, Tissue Culture Treated, 250 mL, w/filter cap | USA Scientific, FL | 658175 | cell culture |
Thiobarbituric Acid | SIGMA, MO | T5500-100G | TBARS Reagent |
TRIS base | Fluka, GA | 93362 | cell lysis reagent |
Trypsin (1x) | VWR, PA | 16777-166 | To detach HepG2 cells |
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