Peroxynitrite induced oxidative modification of low density lipoprotein

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Interaction of peroxynitrite with carotenoids and tocopherols within low density lipoprotein

AbstractPeroxynitrite is a powerful oxidising and nitrating agent generated in vivo by the combination of nitric oxide and superoxide. Previous studies have shown that on exposure to peroxynitrite, low density lipoprotein (LDL) is modified resulting in both a time- and concentration-dependent change to lipid and protein components. The present investigation highlights the reaction between carotenoids and tocopherols, present within the lipophilic phase of LDL, and peroxynitrite at varying concentrations. It was observed that the carotenoids were consumed by a significantly greater proportion than that of the tocopherols with lycopene (87.2±11%) being more reactive than β-carotene (68.2±5.8%) when exposed to peroxynitrite (50 μM) for 1 min. Among the tocopherols, α-tocopherol (54.9±20.2%) was more extensively depleted than γ-tocopherol (14.7±1.09%) at peroxynitrite concentration of 500 μM. It was also observed that peroxynitrite, unlike copper ions, does not lead to significant peroxidation of LDL as determined by the formation of conjugated dienes and thiobarbituric acid-reactive substances

Health assessment of converter transformer pressboard insulation based on FDS and digital image processing

The stable operation of the converter transformer is an essential task for power system operation reliability and security. Nowadays, Frequency domain spectroscopy (FDS) technology is prominently utilized for assessing oil-impregnated pressboard insulation. The present study examines the effect of the pressboard insulation material as a function of frequency and elevated temperature. The experimental analysis on oil-impregnated pressboard insulation is carried out at temperatures from 30 °C to 130 °C with an incremental rise of 20 °C intervals with frequency variation from 1 Hz to 10 MHz. The frequency-dependent permittivity, conductivity and loss tangent angle studies also confirm the deterioration of oil-impregnated pressboard insulation. The surface morphological changes inside the pressboard insulation are recorded with the help of scanning electron microscopy (SEM). The synergistic effect generated on pressboard insulation is examined by fiber width changeand image processing approach by randomly selecting the average of three local areas of SEM image. A canny operator is selected to extract the exact boundaries of images and more change is recorded in the edge detection count after 90 °C.The porosity and pore size distribution can be increased with elevated temperatures. A single-phase, 315 MVA valve side star winding with 60 discs of single-phase converter transformers model is developed in MATLAB Simulink. An impulse of 100 kV, 1.2/50μsec is applied across the star winding to identify the pressboard insulation degradation derived from FDS data with the help of mathematical morphology and wavelet transform technique. The energy of the wavelet coefficient on the neutral current capture during the impulse test adds a significant contribution to analyzing pressboard insulation degradation. The results presented are in good agreement with the published work

The effect of dietary nitrate on salivary, plasma, and urinary nitrate metabolism in humans

Dietary nitrate is metabolized to nitrite by bacterial flora on the posterior surface of the tongue leading to increased salivary nitrite concentrations. In the acidic environment of the stomach, nitrite forms nitrous acid, a potent nitrating/nitrosating agent. The aim of this study was to examine the pharmacokinetics of dietary nitrate in relation to the formation of salivary, plasma, and urinary nitrite and nitrate in healthy subjects. A secondary aim was to determine whether dietary nitrate increases the formation of protein-bound 3-nitrotyrosine in plasma, and if dietary nitrate improves platelet function. The pharmacokinetic profile of urinary nitrate excretion indicates total clearance of consumed nitrate in a 24 h period. While urinary, salivary, and plasma nitrate concentrations increased between 4- and 7-fold, a significant increase in nitrite was only detected in saliva (7-fold). High dietary nitrate consumption does not cause a significant acute change in plasma concentrations of 3-nitrotyrosine or in platelet function

Nitration of endogenous para-hydroxyphenylacetic acid and the metabolism of nitrotyrosine

Reactive nitrogen species, such as peroxynitrite, can nitrate tyrosine in proteins to form nitrotyrosine. Nitrotyrosine is metabolized to 3-nitro-4-hydroxyphenylacetic acid (NHPA), which is excreted in the urine. This has led to the notion that measurement of urinary NHPA may provide a time-integrated index of nitrotyrosine formation in vivo. However, it is not known whether NHPA is derived exclusively from metabolism of nitrotyrosine, or whether it can be formed by nitration of circulating para -hydroxyphenylacetic acid (PHPA), a metabolite of tyrosine. In the present study, we have developed a gas chromatography MS assay for NHPA and PHPA to determine whether or not NHPA can be formed directly by nitration of PHPA. Following the injection of nitrotyrosine, 0.5+/-0.16% of injected dose was recovered unchanged as nitrotyrosine, and 4.3+/-0.2% as NHPA in the urine. To determine whether or not NHPA could be formed by the nitration of PHPA, deuterium-labelled PHPA ([(2)H(6)]PHPA) was injected, and the formation of deuterated NHPA ([(2)H(5)]NHPA) was measured. Of the infused [(2)H(6)]PHPA, 78+/-2% was recovered in the urine unchanged, and approx. 0.23% was recovered as [(2)H(5)]NHPA. Since the plasma concentration of PHPA is markedly higher than free nitrotyrosine (approx. 400-fold), the nitration of high-circulating endogenous PHPA to form NHPA becomes very significant and accounts for the majority of NHPA excreted in urine. This is the first study to demonstrate that NHPA can be formed by nitration of PHPA in vivo, and that this is the major route for its formation