NO is recognized as a vital molecule involved in many physiological and pathological processes. NO is naturally produced by the body's immune system to provide a first line of defense against invading pathogens. It is a powerful molecule with a short half-life of a few seconds in the blood, enabling it to be cleared rapidly from the body. NO has been shown to play a critical role in the function of several body systems. For example, as vasodilator of smooth muscles, NO enhances blood flow and circulation. In addition, NO is involved in regulation of a wound healing and immune responses to infection. The pharmacology, toxicity and other data for NO in humans is generally well known, and its use has been approved by the FDA in a number of therapeutic applications, mainly as a vasodilator.
NO has multiple immunoregulatory and antimicrobial functions that are likely to be of relevance to inhaled NO therapy. In vitro studies suggest that NO possesses anti-microbial activity against common bacteria, gram positive and gram negative, as well as mycobacteria, fungi, yeast, parasites and helminthes. It has the potential to eliminate multi-drug resistant strains of the above. Anti-viral activity covers respiratory viruses such as influenza, corona viruses, RSV and others. In healthy humans, NO has been shown to stimulate muccocilary clearance, and low levels of nasal NO correlate with impaired muccociliary function in the human upper airway. Unlike other inhaled drugs, NO is also a smooth muscle relaxant and avoids the concomitant bronchial constriction often associated with inhaled antibiotics and muccolytics. In addition to treating CF infections, this suggests that NO may be useful in directly treating the mucus caused by CF, which is the principal manifestation of the disease.