Just a clarification that lipid peroxides and aldehydes are NOT free radicals, neither possess an unpaired electron. On the flip side, non-specific assays when properly controlled can be effectively used as first step screening tools.

Dear Alaaeldin A. Hamza, Thanks for adding some new information to the discussion. I do agree that TBARS is very popular among researchers however it has low specificity in measuring and monitoring free radical activity. There are other alternative and novel biomarkers available for measuring the free radical activity in biological samples. IsoP is one such marker. We must also look other aspects such as feasibility and validity of the assay apart from affordability.

TBARS are thiobarbituric acid( TBA)  reactive substances. They are  different types of aldehydes.  due to the presence of  reactive oxygen species in the cells  lipid peroxidation occurs.  Intermediates of lipid peroxidation will ultimately converted to different types of aldehydes ex formaldehydes, acetaldehydes etc.  Malondialdehyde is the end product. So malondialdehyde is the commonly accepted biomarker of lipid peroxidation  TBA is the reagent used to  determine the amount of aldehydes or the products of lipid peroxidation. All types of  aldehydes are reactive with TBA. It is aldol condensation reaction. After the reaction with  different aldehydes with TBA, TBA-aldehyde adducts gives different coloured compounds.  It is not an free radical assay  it is a test for estimation of lipid peroxidation with its end products you can check out my publication: Ultra sensitive detection of malondialdehyde with surface enhanced Raman spectroscopy.http://download.springer.com/static/pdf/566/art%253A10.1007%252Fs00216-010-4225-3.pdf?auth66=1406078746_ae8cf38aeae9ec1b11c9493e35db32d6&ext=.pdf 

Measurement of MDA free of TBARs are not very relevant in plasma or tissues because MDA is also generated by cyclooxygenase. My preference is to assess the lipid peroxydatiion by measuring hydroxy-alkenals. The main advantage is that you can discriminate which polyunsaturated fatty acid series is peroxidized. In fact, 4-hydroxy-nonenal refects the n-6 polyunsaturated fatty acid peroxidation while the  4-hydroxy-hexenal reflects the peroxidation of n-3 polyunsaturated  fatty acids.

The Answer from Dr Guichardant is very interesting. I would add that I personnaly like the lipid hydroperoxide assay kit from Cayman chemical. Comparable kits are probably available from other manufacturer as well. Lipid hydroperoxide (LPO) are unstable intermediate products of lipid oxidation. They are very complementary to 4-hydroxynonenal and 4-hydroxyhexenal in that they are not specific to a certain class of fatty acid. In fact, they are neither specific to phospholipid oxidation as they also include oxidation of fatty acid chains of cholesterol.

They are aslo complementary regarding the time frame of production and elimination. LPO are of short term duration; natural antioxidant defenses are effective in reducing these (moslty) membrane bound peroxides. Measurements of LPO must be made rapidely after the oxidative insult to a tissue otherwise, they may be undetectables. LPO assay has good specificity. This is because the first step consist in lipid extraction that eliminates most of the possible interfering substances.

Hence, they are reliable markers that are very complementary to specific lipoxidation end products (aldehydes). The downside is that this assay requires handling organic solvant in fume hoods, and also a nitrogen tank to degas chloroform. Hence it requires the practicionner to be familiar with organic solvant handling and general lipid analysis care.

"Circulating levels of these compounds may not truly reflect FR activity".

Yes.

Is it possible to assume that the research results  COMPLETELY! reflect reality?

I agree with Dr. Hamza, TBARs assay is nonspecific.

The TBA-RS did not quantify lipid peroxides, but rather the end products of reactions such as aldehydes or as previously mentionned isoprostanes or phytoprostanes depending on the dietary lipids. Additionnaly, when TBA-RS were analyzed by HPLC paired for example with a fluorimeter, it was posssible to quantify specifically MDA.

Isoprostanes and 4-hydroxy nonenal

TBARS are thiobarbituric acid( TBA) reactive substances. They are different types of aldehydes. due to the presence of reactive oxygen species in the cells lipid peroxidation occurs. Intermediates of lipid peroxidation will ultimately converted to different types of aldehydes ex formaldehydes, acetaldehydes etc. Malondialdehyde is the end product. So malondialdehyde is the commonly accepted biomarker of lipid peroxidation TBA is the reagent used to determine the amount of aldehydes or the products of lipid peroxidation. All types of aldehydes are reactive with TBA. It is aldol condensation reaction. After the reaction with different aldehydes with TBA, TBA-aldehyde adducts gives different coloured compounds. It is not an free radical assay it is a test for estimation of lipid peroxidation with its end products you can check out my publication: Ultra sensitive detection of malondialdehyde with surface enhanced Raman spectroscopy.http://download.springer.com/static/pdf/566/art%253A10.1007%252Fs00216-010-4225-3.pdf?auth66=1406078746_ae8cf38aeae9ec1b11c9493e35db32d6&ext=.pdf

It is interesting note by Dr Alaaeldin A. Hamza, on the current issue and debate as to the ideal assay for measuring in vivo free radical activity.  IsoP seems to have a great promise. More research work need to be focused on the non invasive methods for measuring the in vivo free radical activity. At least it should be feasible for an average research worker to conduct the assay in any lab.

TBARS are not lipid peroxides, but they are aldehydes such as MDA generated by the ROS induced degradation of polyunsaturated fatty acids .

TBARS assay is not specific.

Thanks Anca Dinischiotu, for the response. It is true that TBARS assay is non specific and it is now obsolete. It is not advisable to use this assay for measurement of true FR activity in future research work.