Background: Nitric oxide (NO) is involved in numerous physiologic and phathophysiologic processes. Recently, further investigators have focused on serum NO determination. In our previous study, we validated a simple, cheap and rapid method for serum NO determination based on the Greiss reaction. Deproteinization is a necessary step for this reaction, thus, the present study was designed to assess different deproteinization methods for serum NO determination. Materials and methods: Ten common protein precipitating chemicals including methanol, ethanol, zinc sulfate, methanol/diethyl ether, acetonitrile, TCA, PCA, sodium tangstate, ammonium sulfate and filter were used for deproteinization of 42 human sera, while results were compared to filter separation as a reference. Serum NO levels were determined in 60 sera of adult human. Results: Data showed that correlation coefficient of precipitating agents: methanol, ethanol, zinc sulfate, methanol-diethylether, acetonitrile, TCA, PCA, sodium tangstate, ammonium sulfate against filter separation method were 0.84, 0.92, 0.91, 0.79, 0.88, 0.85, 0.93, 0.53, and 0.78, respectively (p<0.001). Methanol, ethanol and methanol/diethylether caused overestimation, while TCA, PCA, sodium tangstate, and ammonium sulfate caused underestimation of serum NO results. Serum NO level had normal distribution with mean ±SE of 33±1.3 μmol/L. Conclusion: Although different chemical protein precipitants are used for serum NO determination, our study revealed that zinc sulfate is the best choice for this purpose.

Keywords: Nitric oxide, Deproteinization, Greiss reaction, Serum

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