Nitrite Activates 5′AMP-Activated Protein Kinase-Endothelial Nitric Oxide Synthase Pathway in Human Glomerular Endothelial Cells

Abstract

Recent studies have shown that orally supplied nitrates, which substantially exist in our daily diets, are reduced into nitrites and become significant sources of nitric oxide (NO) especially in hypoxic tissues. However, physiological significance of nitrites in normal tissues has not been elucidated though our serum concentrations of nitrites reach as high as micromolar levels. We investigated effects of nitrite on endothelial NO synthase (eNOS) using human glomerular endothelial cells to reveal potential glomerular-protective actions of nitrites with its underlying molecular mechanism. Here we demonstrate that nitrite stimulation evokes eNOS activation which is dependent on 5′AMP-activated protein kinase (AMPK) activation in accordance with ATP reduction. Thus, nitrites should facilitate AMPK-eNOS pathway in an energy level-dependent manner in endothelial cells. The activation of AMPK-eNOS signals is suggested to be involved in vascular and renal protective effects of nitrites and nitrates. Nitrites may harbor beneficial effects on metabolic regulations as AMPK activators.Key words nitrite; 5′AMP-activated protein kinase; endothelial nitric oxide synthase; human glomerular endothelial cell (HGEC); nitrate Nitric oxide (NO) is an important signaling molecule involved in many physiological processes. Above all, NO is a dominant vasodilator released from endothelial cells and identified as the nature of endothelium-derived relaxant factor so called, which regulates blood pressures.1) In addition, NO prevents endothelial apoptosis, platelet aggregation and has tissue-protective actions against such proinflammatory and proatherogenic stimulations.2-4) NO is produced from arginine by three distinct isoforms of nitric oxide synthase (NOS). In uninjured endothelial cells, endothelial NOS (eNOS) dominantly catabolizes the NO production. Therefore, appropriate regulation of eNOS activity is quite important to keep vessels and tissues in good conditions. Disruption of endothelial NO synthesis has been reported in such diseases as hypertension, diabetes and hyperlipidemia in accordance. 5-8)The half-life of NO in blood is just in seconds and metabolized into inert nitrate via nitrite. In addition, our daily diets, especially vegetables, ordinarily contain considerable amounts of nitrate and nitrite, and significant concentrations of them distributes throughout our bodies. An analysis using capillary electrophoresis revealed the concentrations of nitrite and nitrate in normal human serum are around 6.6 and 34 µM, respectively. 9)Exogenous NO sources constitute a powerful way to supplement NO when the body cannot generate it enough for normal biological functions. Recent studies have established the notion of nitrate-nitrite-NO pathway (reviewed in 10,11) ). In brief, dietary and salivary glands-secreted nitrate is reduced into nitrite by bacteria in oral cavity. The nitrite is converted into nitrogen oxides including NO in the stomach or other acidic environments. The resultant nitrate in the plasma is taken up and re-secr...

Exercise training modulates adipokine dysregulations in metabolic syndrome

“… 43 The increased adiponectin induces insulin sensitivity in skeletal muscles by binding with adiponectin receptor type 1 and 2, leading to the activation of various signaling pathways such as IRS-1/2, AMPK, and p38 Mitogen-Activated Protein Kinase (p38–MAPK). 44 Also adiponectin alters nitric oxide level and leads to vasoprotective effects via activating AMPK 45 and cyclooxygenase II. 46 Moreover, adiponectin alleviates the inflammatory responses by inhibiting Tumor Necrosis Factor-Alpha (TNF-α), Interleukin-6 (IL-6), Interleukin-10 (IL-10), and Interleukin-1 (IL-1), 42 via Nuclear Factor Kappa-Light-Chain-Enhancer of Activated B Cells (NF-κB), and Protein Kinase A (PKA).…”

Targeted Anti-Cancer Provascular Therapy Using Ultrasound, Microbubbles, and Nitrite to Increase Radiotherapy Efficacy

“…The reason explaining this difference remains to be elucidated. It is possible that nitrite, which is known to be an endogenous NO donor and an endogenous NO production enhancer, is unable to further increase NO beyond a plateau in endogenous NO production in tumoral endothelial cells after UTMC stimulation. It is also possible that tumor vessels treated with UTMC are already close to maximal dilation, in which case adding vasodilating agents could have little or no effect on the blood flow: this effect could be a consequence of the high levels of adenosine in tumor microenvironment, which is known to be a prominent vasodilator. , This could explain the increase in perfusion observed in tumors treated at 750 kPa (1 MHz) + nitrite to a plateau of endogenous NO production or to a maximum dilation, and why there is no difference between the perfusion values of tumors treated with SONOS alone and those treated with SONOS + nitrite (Figure ).…”

“…Furthermore, it was recently shown that UTMC combined with a sodium nitrite coinjection further increased the microvascular blood volume in muscle by 6–8 folds . Since nitrite is a nitric oxide (NO) donor in hypoxic and acidic environments , and can enhance endogenous NO production, we hypothesized that UTMC and nitrite could be synergistic as a spatially targeted provascular therapy in combination with RT in solid tumors. To the best of our knowledge, this effect of increasing perfusion by UTMC has never been validated in the tumor, nor has it been combined with subsequent RT.…”