I have some samples that were taken out from the freezer one month ago, unintentionally I used these samples on FRAP assay and surprisingly I obtained similar results than those obtained with perfectly stored samples. Is this possible? What could be happening?
Dear Mayely
Its good, if you are getting same activity. It means storage condition protected your sample from any damage or degradation.
Why you are worry, repetition of results in research is always good. It means your sample is still working and not destroyed by any means in freezer.
Hi Mayley
Do you mean to say that your samples were kept in normal conditions for one month, still they have shown same activity as the perfectly stored ones.
I compared two types of samples: samples stored in good conditions and other samples that were never frozen -they were taken from the subject and remained at room temperature during one month- Specifically these 'damaged' samples are 250 ul plasma in eppendorf tubes inside a box on the desk of my laboratory.
I obtained similar results with both samples, and I'm very surprised since, theoretically it should not happen because antioxidant capacity should be measured in samples stored at -80ºC and light protected, am I right?
Dear Mayely
It is not possible to get similar results in case of plasma sample, you must repeat your test again and again to validate the results. You may also test your sample in some other lab by your colleague.
Hi Mayley
Now this is interesting. I found a file where they say that final containers of plasma protein samples shall have a maximum shelf life of 3 years if they are stored at or below 30 C and 5 years if stored at 5(+-)3 C. I am attaching some files for your use. See page 85 of first attachment.
Also you can see some articles on plasma storage conditions as follows which may help you in final reporting:
Anstall, H. B., Grove-Rasmussen, M. and Shaw, R. S. (1961), Optimal Conditions for Storage of Fresh Frozen Plasma. Transfusion, 1: 87–93. doi: 10.1111/j.1537-2995.1961.tb00018.x
Impact of the storage temperature on human plasma proteomic analysis: implications for the use of human plasma collections in research. Proteomics Clin Appl. 2010 Sep;4(8-9):739-44.
I also want you to double check your results by performing the analysis once again. Might be a third check will be a concrete evidence of the findings. Also take a fresh plasma sample now and keep it at room temperature again as before. Use it after one month and correlate with the present findings. So it will be a double check in terms of sample also. Hope you get something interesting again.
Regards
Many thanks dear Alok!! is useful these information. Additionally, I found that some components such as Flavonoids, uric acid, ascorbic acid, over time may interfere on the FRAP response.
I understand that will always be a baseline although the sample is not perfectly stored. Finally, by small modifications in my protocol, I detected a little more than half of antioxidant capacity in my "damage" samples... this sounds better than when obtained similar values.
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