Choose Your Nitric Oxide Tests Carefully

The moral of a new study about inaccuracies in nitric oxide measurements is choose your assay wisely. Because of NO’s role in controlling multiple biological processes, scientists are interested in NO-releasing molecules as possible therapeutics. But they need a way to accurately measure the NO released. Mark H. Schoenfisch and coworkers at the University of North Carolina, Chapel Hill, compared the performance of three methods commonly used to measure NO: the Griess assay, which measures NO as nitrite; chemiluminescence; and electrochemical sensors (Anal. Chem., DOI: 10.1021/ac303787p). The team measured NO released from a small-molecule donor in various sample types, including biological fluids, cell-culture media, and bacterial broth. The Griess assay was the least accurate of the three tests. Chemiluminescence worked only in media that don’t foam when purged with N₂ gas, ruling out protein-rich samples. The electrochemical sensor worked in all sample types, but the measured concentrations were significantly lower than the expected values. The electrochemical sampling deviations might not matter if they accurately reflect NO scavenging, the researchers note. Their results suggest that the right NO-monitoring method depends on the medium used and the questions being asked.