Review Article | Published:

The nitrate–nitrite–nitric oxide pathway in physiology and therapeutics

Nature Reviews Drug Discovery volume 7, pages 156167 (2008) | Download Citation



The inorganic anions nitrate (NO3) and nitrite (NO2) were previously thought to be inert end products of endogenous nitric oxide (NO) metabolism. However, recent studies show that these supposedly inert anions can be recycled in vivo to form NO, representing an important alternative source of NO to the classical l-arginine–NO-synthase pathway, in particular in hypoxic states. This Review discusses the emerging important biological functions of the nitrate–nitrite–NO pathway, and highlights studies that implicate the therapeutic potential of nitrate and nitrite in conditions such as myocardial infarction, stroke, systemic and pulmonary hypertension, and gastric ulceration.

Key points

  • The inorganic anions nitrite (NO2) and nitrate (NO3) are usually viewed as inert end products of nitric oxide (NO) metabolism or unwanted residues in the food chain.

  • Recent studies show that nitrate and nitrite are physiologically recycled in blood and tissue to form NO and other bioactive nitrogen oxides. Thus, they should be viewed as storage pools for NO-like bioactivity, thereby complementing the NO synthase-dependent pathway.

  • There are two major sources of nitrate and nitrite: the endogenous l-arginine/NO-synthase pathway and the diet. Vegetables are particularly rich in nitrate.

  • The bioactivation of nitrate from dietary or endogenous sources requires its initial reduction to nitrite, and this conversion is mainly carried out by commensal bacteria inhabiting the gastrointestinal tract.

  • There are numerous pathways in the body for the further reduction of nitrite to bioactive NO, involving haemoglobin, myoglobin, xanthine oxidoreductase, ascorbate, polyphenols and protons.

  • The generation of NO by all these pathways is greatly enhanced during hypoxia and acidosis, thereby ensuring NO production in situations for which the oxygen-dependent NO-synthase enzyme activities are compromised.

  • Nitrite reduction to NO during physiological and pathological hypoxia appear to contribute to physiological hypoxic signalling, vasodilation, modulation of cellular respiration and the cellular response to ischaemic stress.

  • An expanding number of studies suggest a therapeutic potential for nitrate and nitrite in diseases such as myocardial infarction, stroke, systemic and pulmonary hypertension, and gastric ulceration.

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We wish to thank J. Moffett, librarian of the Needham Research Institute, University of Cambridge, UK, for providing the image used in figure 1a, and G. K. Hansson for valuable comments on the manuscript. We have received support from the European Community's Sixth Framework programme (Eicosanox, LSMH-CT-2004-005033), the Swedish Heart and Lung Foundation, The Swedish Research Council, Torsten and Ragnar Söderbergs Foundation, Vinnova (CIDaT), and Stockholm County Council (ALF).

Author information


  1. Department of Physiology and Pharmacology, Karolinska Institute, SE-171 77 Stockholm, Sweden.

    • Jon O. Lundberg
  2. Section of Anesthesiology and Intensive Care, Department of Physiology and Pharmacology, Karolinska Institute, SE-171 77 Stockholm.

    • Eddie Weitzberg
  3. Pulmonary and Vascular Medicine Branch, National Heart, Lung, and Blood Institute, National Institutes of Heath, Bethesda, Maryland 20892, USA.

    • Mark T. Gladwin
  4. Critical Care Medicine Department, Clinical Center, National Institutes of Health, Bethesda.

    • Mark T. Gladwin


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Competing interests

M.G. is named as a co-inventor on a patent application by the NIH for the use of nitrite salts for cardiovascular disease. J.L. and E.W. have filed a patent application for the use of nitrite in the treatment of catheter-associated infections.


Xanthine oxidoreductase

An enzyme involved in purine metabolism that catalyses the oxidation of hypoxanthine to xanthine and the further oxidation of xanthine to uric acid.


A form of hormonal signalling in which a cell secretes a chemical messenger that binds to receptors on the same cell, leading to changes in the cell.


A form of cell signalling in which the target cell is close to (para = alongside of or next to) the signal-releasing cell.


A form of cell signalling in which chemical mediators are released directly into local blood vessels and travel to distant organ's to regulate the target organs function.

Hypoxic vasodilation

A physiological phenomenon in which blood vessels dilate in response to low oxygen levels.


A form of the oxygen-carrying protein haemoglobin in which the iron in the haem group is in the Fe3+ state, not the Fe2+ of normal haemoglobin. Methaemoglobin is unable to carry oxygen.

Facultative anaerobic bacteria

A bacterium, that makes ATP by aerobic respiration if oxygen is present but is also capable of switching to anaerobic respiration.

Electron acceptor

A chemical entity that accepts electrons transferred to it from another compound. It is an oxidizing agent that, by virtue of it accepting electrons, is itself reduced in the process.

cyclic GMP

A cyclic nucleotide derived from guanosine triphosphate (GTP) that acts as a second messenger, much like cyclic AMP.


Allosteric regulation is the regulation of an enzyme or protein by binding an effector molecule at a site other than the protein's active site.

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An electron transport chain associates energy-rich electron donors (for example, NADH) and mediates the biochemical reactions that produce ATP, which is the energy currency of life.

Reactive oxygen species

(ROS). Include oxygen ions, free radicals and peroxides that are both inorganic and organic. They are generally highly reactive owing to the presence of unpaired valence shell electrons. ROS form as a natural by-product of the normal metabolism of oxygen and have important roles in cell signalling. However, during times of environmental stress ROS levels can increase dramatically, which can result in significant damage to cell structures.

Organic nitrates

Drugs used principally in the treatment of angina pectoris and acting mainly by dilating the blood vessels by the formation of nitric oxide.


The conversion of thiol groups (-SH), including cysteine residues in proteins, to form S-nitrosothiols. S-Nitrosation has been suggested to be a mechanism for dynamic, post-translational regulation of proteins. In addition, S-nitrosothiols can act as donors of nitric oxide.


A phenomenon in which a brief exposure to ischaemia renders the heart or another organ more tolerant to a subsequent sustained ischaemic insult.

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