HQNO is a NADH oxidase inhibitor.
The NADPH oxidase, a membrane-bound enzyme complex facing the extracellular space, can be found in the plasma membrane and in the membranes of phagosomes used by neutrophil white blood cells to engulf microorganisms. Isoforms are designated NOX1, NOX2, NOX3, as well as NOX4.
In vitro: Previous study found that HQNO could inhibit the Na+-dependent NADH oxidase but had very limited effect on the NA+-independent activity of mutant membranes. Moreover, the NADH:quinone oxidoreductase was observed to be the Na+-dependent HQNO-sensitive site of the NADH oxidase. In addition, HQNO was found to be able to cause a strong inhibition of the Na+ pump with limited effect on the overall H+ extrusion by respiration in the wild type cells. The inhibition of the Na+ pump by HQNO could be overcome by oxidized but not reduced TMPD. The electron flow NADH to oxygen appeared to bypass the HQNO-sensitive site and energize the Na+ pump in the presence of oxidised TMPD [1].
In vivo: Up to now, there is no animal in vivo data reported.
Clinical trial: So far, no clinical study has been conducted.
Reference:
[1] Tokuda, H. , and Unemoto, T. Na+ is translocated at NADH:quinone oxidoreductase segment in the respiratory chain of Vibrio alginolyticus. The Journal of Biological Chemisty 259(12), 7785-7790 (1984).