Hi everyone! I would be grateful if any of you could give me some idea about the stability of nitric oxide (NO) in frozen human serum sample. We have frozen human serum since last several years, can we still detect NO level in the sample? Kindly share your knowledge on this and please try to link the related reference(s) with the answer. Thank you!
I have used the Griess assay kits before on frozen endothelial cell lysates stored at -80 and I have been able to obtain results sensitive to about 10 picomoles according to standard dilution controls. I rarely stored my lysates for longer than two weeks, so I am unsure about long-term storage. I always thawed on ice and used immediately once thawed. The instructions for the kit suggest serum NO should also be stable stored at -80, but you will always have some loss of sample due to a freeze thaw cycle. You could try a fresh serum sample as a positive control to see if your frozen samples still hold enough stable NO upon storage/thaw. Your best bet is to call the tech support of the kits or regents you're interested in using for acquiring NO measurements and discuss at length with a tech specialist. Abcam had a decent kit for me (http://www.abcam.com/nitric-oxide-assay-kit-colorimetric-ab65328.html?productWallTab=Abreviews), references are at the website.
Hi, actually in serum what you measure is not nitric oxide but some of its degradation products i.e. nitrate and nitrite. In blood nitrite is unstable and reacts rapidly with hemoglobin forming nitrate. Thus what you measure with most of commercial kits is nitrate. Nitrate represents about 99% of the so called "NO" you detect with common commercial kits included Cayman's one, it is stable in biological fluids and obviously in serum. The only problem is represented by the fact that only a percentage of nitrate derives from NO being diet the main font of it. For example spinach and broad-leaved vegetables contain large quantities of nitrate. In any case you can also follow this simple procedure which is essentially based on Griess's reagent like Cayman's one. In this paper we describe also common interference and pitfalls which can influence the results using this of the method.
Article Nitrite and Nitrate Measurement by Griess Reagent in Human P...
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