Salivary Nitric Oxide Test Strips – why they do not indicate efficacy of PBM therapy

“there is no justification for the use of salivary nitrite strips as a marker for NO”

There is increasing medical and research interest in Nitric Oxide (NO) bioavailability in relation to its ability to affect a number of functions, including cardiovascular (Ignarro, L.J., 2002; Klinger, J. et al., 2017; Lunberg et al, 2009), cellular and immune (Olekhonovitch et al., 2004) and neurophysiological (Paul et al., 2011), and with this, interest in developing a diagnostic marker. Since saliva collection is low-cost, non-invasive and relatively straightforward (Nunes et al., 2015), there has been a concomitant development of NO saliva test strips, the assumption being that measurements using these products are indicative of circulatory NO.

Therapeutics increasing circulatory NO has increased focus on the use of such strips as surrogate assessment. The impact of increased dietary nitrate intake, e.g. from green vegetables and beetroot juice, on NO bioavailability has been investigated on blood pressure (Webb, A. et al., 2008), NO-dependent exercise performance (Nyakayiru J. et al, 2017; Larsen et al., 2006; Webb et al., 2008) and also on oral health (Hohensinn et al, 2016). Most ingested nitrate is taken up by salivary glands from the circulation, concentrated in saliva and reduced to nitrite by oral bacteria, with a resultant 1000-fold increase in nitrite concentration in saliva in comparison with plasma (Pereira, C. et al, 2013). Ingested nitrate is therefore reflected in salivary nitrite.

NO is at the centre of the mechanistic action of Photobiomodulation Therapy (PBMT), across multiple disease areas. PBMT in red and near-infrared ranges causes NO to be released from cytochrome c oxidase, the terminal electron acceptor in the mitochondrial electron transfer chain (refs to add from Res Laser here). It is not surprising then that in the PBMT arena, as in nutritional studies, we see an increased focus on assessment of salivary NO metabolites with the aim of assessing increased endogenous NO after PBMT.

Importantly, it has only been very recently that research has investigated validity of salivary nitrite strips against standard laboratory measures of NO metabolites: nitrites and nitrates, in both saliva and serum, with serum measures as the gold standard for clinical assays. Plasma nitrite levels are indicative of NO bioavailability, but research does not show plasma nitrite to correlate with salivary nitrite levels. There is also great individual variation in the response of salivary nitrite to dietary nitrate (Clodfelter et al., 2015). Salivary nitrite is also increased in smokers (Preethi, S. et al., 2016) and is reduced with the use of mouth washes, such as Odol or Listerene (Kapil, V. et al., 2013).

There is no justification therefore for the use of salivary nitrite strips as a marker for NO bioavailability (Shapiro, D., 2015; Modi A. et al., 2017) and therapeutic products claiming to lead to increase NO bioavailability as assessed with such strips should be viewed with caution.

Dr Pat Burton, PhD

Ignarro, L. J. (2002). Nitric Oxide as a unique signalling molecule in the vascular system: a historical overview. J. Physiol & Pharmacol 53 (4): 503 – 514
Klinger, J. R. et al. (2017). The nitric Oxide Pathway in Pulmonary Vascular Disease. Am J Cardiol 120; S71 – S79
Lundberg, J. O. (2009). Nitrate and nitrite in biology, nutrition and therapeutics. Nat Chem Biol. 5 (12): 865 – 869
Olekhonovitch, R. et al. (2011). Collective nitric oxide production provides tissue-wide immunity during Leishmania. J. Clin. Invest. 124 (4): 1711 – 1722
Paul, V. et al. (2011). Involvement of nitric Oxide in learning and memory processes. P 471 – 478.
Nunes, L.A. et al. (2015). Clinical and diagnostic utility of saliva as a non-invasive diagnostic fluid: a systematic review. Biochemia Medica 25 (2); 177 -92.
Nyakayiru J. et al. (2017). Beetroot Juice Supplementation Improves High-Intensity Intermittent Type Exercise Performance in Trained Soccer Players. Nutrients 9: 314. Doi:10.3390/nu9030314
Larsen et al. (2006). Effects of dietary nitrate on blood pressure in healthy volunteers. N Engl J Med 28, 355 (26): 2792 – 3
Webb et al. (2008). Acute blood pressure lowering, vasoprotective, and antiplatelet properties of dietary nitrate via bioconversion to nitrite. Hypertens. 51 (3): 784 – 90
Hohensinn, B. et al. (2016). Sustaining elevated levels of nitrite in the oral cavity through consumption of nitrate-rich beetroot juice in young healthy adults reduces salivary pH. Nitric Oxide 60: 10 – 15
Pereira, C. et al. (2013). The redox interplay between nitrite and nitric oxide: From the gut to the brain. Redox Biology 1 276 – 284
Clodfelter et al. (2015). The Relationship between Plasma and Salivary NOx. Nitric Oxide 47: 85 – 90
Preethi, S. et al. (2016). Evaluation of Salivary Nitric Oxide Levels in Smokers, Tobacco Chewers and Patients with Oral Lichenoid Reactions. J Clin Diag Res. 10 (1): ZC63 – ZC 66
Kapil, V. et al. (2013). Physiological role for nitrate-reducing oral bacteria in blood pressure control. Free Radic Biol Med. 55: 93 – 100
Shapiro, D. (2015). Pitfalls in measuring NO bioavailability using NOx. Nitric Oxide 44: 1- 2
Modi, A. et al. (2017). Validation of two point-of-care tests against standard lab measures of NO in saliva and in serum. Nitric oxide 64: 16 – 21