Nitric oxide release: part III. Measurement and reporting

Abstract

Nitric oxide's expansive physiological and regulatory roles have driven the development of therapies for human disease that would benefit from exogenous NO administration. Already a number of therapies utilizing gaseous NO or NO donors capable of storing and delivering NO have been proposed and designed to exploit NO's influence on the cardiovascular system, cancer biology, the immune response, and wound healing. As described in Nitric oxide release: Part I. Macromolecular scaffolds and Part II. Therapeutic applications, the preparation of new NO-release strategies/formulations and the study of their therapeutic utility are increasing rapidly. However, comparison of such studies remains difficult due to the diversity of scaffolds, NO measurement strategies, and reporting methods employed across disciplines. This tutorial review highlights useful analytical techniques for the detection and measurement of NO. We also stress the importance of reporting NO delivery characteristics to allow appropriate comparison of NO between studies as a function of material and intended application.

Figure 1

The reaction of nitrite (NO₂⁻) with Griess assay reagents forms an azo dye that is easily detected spectrophotometrically to extrapolate NO concentrations released from the sample.

Figure 2

The detection of NO using chemiluminescence involves the reaction of NO with ozone (O₃) to form NO₂*. Upon relaxation to NO₂, a photon is emitted, which is then detected and is proportional to the concentration of NO released from the sample.

Figure 3

Electrochemical detection of NO can be achieved through the oxidation or reduction of NO.

Figure 4

Graphical representation of (A) total NO release from a surface including designations for total NO release ([NO]_T) and half life of NO release (t_1/2) and (B) instantaneous NO release from a surface with maximum NO flux ([NO]_max) and the time to [NO]_max (t[NO]_max) indicated.