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      Physiological role for nitrate-reducing oral bacteria in blood pressure control

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          Abstract

          Circulating nitrate (NO 3 ), derived from dietary sources or endogenous nitric oxide production, is extracted from blood by the salivary glands, accumulates in saliva, and is then reduced to nitrite (NO 2 ) by the oral microflora. This process has historically been viewed as harmful, because nitrite can promote formation of potentially carcinogenic N-nitrosamines. More recent research, however, suggests that nitrite can also serve as a precursor for systemic generation of vasodilatory nitric oxide, and exogenous administration of nitrate reduces blood pressure in humans. However, whether oral nitrate-reducing bacteria participate in “setting” blood pressure is unknown. We investigated whether suppression of the oral microflora affects systemic nitrite levels and hence blood pressure in healthy individuals. We measured blood pressure (clinic, home, and 24-h ambulatory) in 19 healthy volunteers during an initial 7-day control period followed by a 7-day treatment period with a chlorhexidine-based antiseptic mouthwash. Oral nitrate-reducing capacity and nitrite levels were measured after each study period. Antiseptic mouthwash treatment reduced oral nitrite production by 90% ( p < 0.001) and plasma nitrite levels by 25% ( p = 0.001) compared to the control period. Systolic and diastolic blood pressure increased by 2–3 .5 mm Hg, increases correlated to a decrease in circulating nitrite concentrations ( r 2 = 0.56, p = 0.002). The blood pressure effect appeared within 1 day of disruption of the oral microflora and was sustained during the 7-day mouthwash intervention. These results suggest that the recycling of endogenous nitrate by oral bacteria plays an important role in determination of plasma nitrite levels and thereby in the physiological control of blood pressure.

          Highlights

          ► Antiseptic mouthwash use abrogates oral bacterial conversion of nitrate to nitrite. ► Interruption of the enterosalivary circulation reduces plasma nitrite levels. ► The reduction in plasma nitrite levels is associated with elevations in blood pressure. ► The results indicate the importance of oral nitrate-reducing bacteria in blood pressure control. ► Our findings intimate adverse effects of mouthwash by disturbing NO/nitrite homeostasis.

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          Author and article information

          Contributors
          Journal
          Free Radic Biol Med
          Free Radic. Biol. Med
          Free Radical Biology & Medicine
          Elsevier Science
          0891-5849
          1873-4596
          1 February 2013
          February 2013
          : 55
          : C
          : 93-100
          Affiliations
          [a ]Centre for Clinical Pharmacology, William Harvey Research Institute, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, London EC1M 6BQ, UK
          [b ]Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden
          Author notes
          [* ]Corresponding author. Fax: +44 207 882 3408. a.ahluwalia@ 123456qmul.ac.uk
          Article
          FRB11385
          10.1016/j.freeradbiomed.2012.11.013
          3605573
          23183324
          © 2013 Elsevier Inc.

          This document may be redistributed and reused, subject to certain conditions.

          Categories
          Original Contribution

          Molecular biology

          blood pressure, nitric oxide, nitrite, nitrate, bacteria, free radicals

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