Pharmacological sodium nitrate supplementation has been reported to reduce the O2 cost of submaximal exercise in humans. In this study, we hypothesized that dietary supplementation with inorganic n...

/pdf/dietary-nitrate-supplementation-reduces-the-o2-cost-of-low-x1v5si1jxj.pdf

Dietary nitrate supplementation reduces the O2 cost of low-intensity exercise and enhances tolerance to high-intensity exercise in humans

Dietary inorganic nitrate improves mitochondrial efficiency in humans.

Inorganic nitrate and nitrite from endogenous or dietary sources are metabolized in vivo to nitric oxide (NO) and other bioactive nitrogen oxides. The nitrate-nitrite-NO pathway is emerging as an important mediator of blood flow regulation, cell signaling, energetics and tissue responses to hypoxia. The latest advances in our understanding of the biochemistry, physiology and therapeutics of nitrate, nitrite and NO were discussed during a recent 2-day meeting at the Nobel Forum, Karolinska Institutet in Stockholm.

/pdf/nitrate-and-nitrite-in-biology-nutrition-and-therapeutics-3mmdlvmbva.pdf

Nitrate and nitrite in biology, nutrition and therapeutics

Most reactive oxygen species (ROS) are generated in cells by the mitochondrial respiratory chain. Mitochondrial ROS production is modulated largely by the rate of electron flow through respiratory chain complexes. Recently, it has become clear that under hypoxic conditions, the mitochondrial respiratory chain also produces nitric oxide (NO), which can generate other reactive nitrogen species (RNS). Although excess ROS and RNS can lead to oxidative and nitrosative stress, moderate to low levels of both function in cellular signaling pathways. Especially important are the roles of these mitochondrially generated free radicals in hypoxic signaling pathways, which have important implications for cancer, inflammation and a variety of other diseases.

https://www.cell.com/trends/endocrinology-metabolism/pdf/S1043-2760(09)00088-5.pdf

Mitochondrial generation of free radicals and hypoxic signaling

Nitric oxide (NO) is a key signalling molecule in the cardiovascular, immune and central nervous systems, and crucial steps in the regulation of NO bioavailability in health and disease are well characterized. Although early approaches to therapeutically modulate NO bioavailability failed in clinical trials, an enhanced understanding of fundamental subcellular signalling has enabled a range of novel therapeutic approaches to be identified. These include the identification of: new pathways for enhancing NO synthase activity; ways to amplify the nitrate-nitrite-NO pathway; novel classes of NO-donating drugs; drugs that limit NO metabolism through effects on reactive oxygen species; and ways to modulate downstream phosphodiesterases and soluble guanylyl cyclases. In this Review, we discuss these latest developments, with a focus on cardiovascular disease.

Strategies to increase nitric oxide signalling in cardiovascular disease

In this review we consider the effects of endogenous and pharmacological levels of nitrite under conditions of hypoxia. In humans, the nitrite anion has long been considered as metastable intermediate in the oxidation of nitric oxide radicals to the stable metabolite nitrate. This oxidation cascade was thought to be irreversible under physiological conditions. However, a growing body of experimental observations attests that the presence of endogenous nitrite regulates a number of signaling events along the physiological and pathophysiological oxygen gradient. Hypoxic signaling events include vasodilation, modulation of mitochondrial respiration, and cytoprotection following ischemic insult. These phenomena are attributed to the reduction of nitrite anions to nitric oxide if local oxygen levels in tissues decrease. Recent research identified a growing list of enzymatic and nonenzymatic pathways for this endogenous reduction of nitrite. Additional direct signaling events not involving free nitric oxide are proposed. We here discuss the mechanisms and properties of these various pathways and the role played by the local concentration of free oxygen in the affected tissue.

/pdf/nitrite-as-regulator-of-hypoxic-signaling-in-mammalian-5dc70ahb8i.pdf

Nitrite as regulator of hypoxic signaling in mammalian physiology

In autoimmune Type 1 diabetes (T1D), islet-infiltrating leukocytes synthesize noxious free radicals to collectively mediate b-cell lysis and enhance diabetogenic T cell responses as a pro-inflammatory third signal. We recently demonstrated a crucial role for NADPH oxidase (NOX)-dependent superoxide in T1D, as NOX-deficient Non-obese diabetic (NOD. Ncf1 m1J ) mice were highly resistant to autoimmune diabetes due to an enhanced alternatively-activated M2 macrophage phenotype, diminished pro-inflammatory cytokine and Type I interferon synthesis upon Toll-like receptor stimulation, dampened Th1 cytokine responses, and blunted CD8 T cell cytotoxicity. To further define the synergy between free radicals and T1D, we employed a 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) immuno-spin trapping technique to identify the generation of free radicals upon T cell activation and infection with Coxsackie B4 (CB4) virus, a putative diabetogenic enterovirus and hypothesized that NOD. Ncf1 m1J immune cells would exhibit severe reductions in DMPO adducts. In the absence of superoxide, NOD. Ncf1 m1J macrophages and CD4 T cells exhibited a significant decrease in DMPO adducts upon CB4 infection and autoantigen stimulation, respectively, in contrast to wild type cells. Future studies will utilize this technique to visualize the interface between free radicals and immune cells during spontaneous T1D progression and determine if immuno-spin trapping can be used as a biomarker during spontaneous T1D progression.

Ron Mason

Papers

Nitrite as regulator of hypoxic signaling in mammalian physiology

Immuno-spin trapping to detect immune-derived free radicals in type 1 diabetes (TECH2P.903)