A Novel Competitive ELISA for Both Free and Protein-Bound Nitrotyrosine

Rapid and sensitive determination of protein-nitrotyrosine by ELISA: Application to human plasma

3-Nitrotyrosine (3NT) is known as an important indicator of nitrosative stress and has been linked to various diseases. Our aim was to develop an indirect ELISA (enzyme-linked immunosorbent assay) method suitable for the detection of protein-bound 3NT in clinical plasma and serum samples. Nitrated protein standards and reduced protein standards were prepared. Limit of detection was determined for standards; recovery and reproducibility were determined for human plasma samples. The limit of detection for this method is 1.82±0.56 pmol/mg protein. Mean recovery of standards was 95%. 3NT concentration in plasma samples of obese and normal weight subjects was determined to be between 2 pmol/mg and 19 pmol/mg. No time-consuming sample preparation or expensive laboratory equipment is required, and applied antibodies are commercially available. Sensitivity, rapid analysis time, possibilities of high throughput applications and small sample volumes make this ELISA attractive for use in clinical laboratories.

Protective effects of flavonoids against oxidative stress induced by simulated microgravity in SH-SY5Y cells

Many lines of evidence suggest that microgravity results in increased oxidative stress in the nervous system. In order to protect neuronal cells from oxidative damage induced by microgravity, we selected some flavonoids that might prevent oxidative stress because of their antioxidant activities. Among the 20 flavonoids we examined, we found that isorhamnetin and luteolin had the best protective effects against H(2)O(2) or SIN-1-induced cytotoxicity in SH-SY5Y cells. Using a clinostat to simulate microgravity, we found that isorhamnetin and luteolin treatment protected SH-SY5Y cells by preventing microgravity-induced increases in reactive oxygen species (ROS), nitric oxide (NO) and 3-nitrotyrosine (3-NT) levels, and a decrease in antioxidant power (AP). Moreover, isorhamnetin and luteolin treatment downregulated the expression of inducible nitric oxide synthase (iNOS), and oxidative stress was significantly inhibited by an iNOS inhibitor in SH-SY5Y cells exposed to simulated microgravity (SMG). These results indicate that isorhamnetin and luteolin could protect against microgravity-induced oxidative stress in neuroblastoma SH-SY5Y cells by inhibiting the ROS-NO pathway. These two flavonoids may have potential for preventing oxidative stress induced by space flight or microgravity.

p38MAPK and ERK promote nitric oxide production in cultured human retinal pigmented epithelial cells induced by high concentration glucose

Increased nitric oxide (NO) has been correlated with diabetic retinopathy. In this study we investigated the cell injury, production of NO in retinal pigment epithelial (RPE) cells exposed to increased glucose concentration, and its molecular mechanism involved. Cultured human RPE cells (ARPE-19) were exposed for 4 days with normal blood glucose concentration (5.5mM D-glucose), followed by exposure to either normal (5.5mM) or high (33 mM) concentrations of D-glucose for 48 h. To determine the cytotoxicity of high glucose, cell viability, ROS production and SOD activity were measured, respectively. The end product of NO (nitrite and nitrate) was determined by a colorimetric assay and nitrotyrosine levels were quantified by a competitive ELISA. The expression of iNOS and the activation of p38MAPK, ERK and JNK were analyzed by Western blot. Treatment of RPE cells with high glucose-induced a significant increased of iNOS, accompanied by an increase in cell damage, NO and nitrotyrosine levels. High glucose caused activation of p38MAPK and ERK, inhibition for p38MAPK and ERK abrogated the high glucose-induced increase in iNOS, cell injury and levels of NO and nitrotyrosine. High glucose causes increased cell damage and NO generation in RPE cells by a process of iNOS expression that requires the activation of p38MAPK and ERK.

Effects of quercetin on hyper-proliferation of gastric mucosal cells in rats treated with chronic oral ethanol through the reactive oxygen species-nitric oxide pathway

AIM: To investigate the effect of quercetin (3,3’,4’,5,7-pentahydroxy flavone), a major flavonoid in human diet, on hyper-proliferation of gastric mucosal cells in rats treated with chronic oral ethanol.

METHODS: Forty male Sprague-Dawley rats, weighing 200-250 g, were randomly divided into control group (tap water ad libitum), ethanol treatment group (6 mL/L ethanol), quercetin treatment group (intragastric gavage with 100 mg/kg of quercetin per day), and ethanol plus quercetin treatment group (quercetin and 6 mL/L ethanol). Expression levels of proliferating cell nuclear antigen (PCNA) and Cyclin D1 were detected by Western blot to assay gastric mucosal cell proliferation in rats. To demonstrate the influence of quercetin on the production of extra-cellular reactive oxygen species/nitrogen species (ROS/RNS) in rats, changes in levels of thiobarbituric acid reactive substance (TBARS), protein carbonyl, nitrite and nitrate (NOx) and nitrotyrosine (NT) were determined. The activity of inducible nitric oxide synthase (NOS) including iNOS and nNOS was also detected by Western blot.

RESULTS: Compared to control animals, cell proliferation in the gastric mucosa of animals subjected to ethanol treatment for 7 days was significant increased (increased to 290% for PCNA density P < 0.05, increased to 150 for Cyclin D1 density P < 0.05 and 21.6 ± 0.8 vs 42.3 ± 0.7 for PCNA positive cells per view field), accompanied by an increase in ROS generation (1.298 ± 0.135 &mgr;mol vs 1.772 ± 0.078 &mgr;mol for TBARS P < 0.05; 4.36 ± 0.39 mmol vs 7.48 ± 0.40 mmol for carbonyl contents P < 0.05) and decrease in NO generation (11.334 ± 0.467 &mgr;mol vs 7.978 ± 0.334 &mgr;mol P < 0.01 for NOx; 8.986 ± 1.351 &mgr;mol vs 6.854 ± 0.460 &mgr;mol for nitrotyrosine P < 0.01) and nNOS activity (decreased to 43% P < 0.05). This function was abolished by the co-administration of quercetin.

CONCLUSION: The antioxidant action of quercetin relies, in part, on its ability to stimulate nNOS and enhance production of NO that would interact with endogenously produced reactive oxygen to inhibit hyper-proliferation of gastric mucosal cells in rats treated with chronic oral ethanol.

Measurement and significance of 3-nitrotyrosine in systemic lupus erythematosus

Nitration of free and protein associated tyrosine represents, in vivo, a mechanism that can severely compromise the cell function. The detection of 3-nitrotyrosine (3-NT) in pathological tissues is suggestive of the occurrence of nitrating pathways and has been identified as a marker of inflammation and a stable end product of increased reactive nitrogen intermediate production. Protein nitration occurs in many disease conditions including systemic lupus erythematosus (SLE). In this study we show that the level of both free and protein bound 3-NT, which is produced by reactive nitrogen species (RNS)-dependent oxidative damage, is elevated in patients with SLE and that there is a possible role of RNS-modified epitopes in the aetiology of the disease. Commercially available poly L-tyrosine was exposed to nitrating species, inducing nitration in tyrosine residues. Immunoglobulin-G (IgG) purified on Protein-A-Sepharose matrix from 24 SLE patients was studied for their recognition of native and nitrated poly L-tyrosine by direct binding and competition enzyme-linked immunosorbent assay (ELISA). The formation of immune complex between SLE IgG and nitrated poly L-tyrosine was visualized by gel retardation assay. Free 3-NT in patients' sera was detected and quantitated by high performance liquid chromatography whereas protein-bound 3-NT was analysed by Western blotting and the concentration was calculated by sandwich ELISA. The concentration of free 3-NT was found to be 1.4 +/- 0.09 microm whereas the concentration of protein bound 3-NT was 96.52 +/- 21.12 microm nitrated bovine serum albumin equivalents/mg protein, which was significantly higher when compared with healthy controls. Elevated level of 3-NT was observed in SLE patients using two different techniques, when compared with healthy subjects confirms the overproduction of RNS in the pathogenesis of human SLE.

Protein nitration increased by simulated weightlessness and decreased by melatonin and quercetin in PC12 cells

A variety of experiments suggest that space flight is associated with an increase in oxidative stress in organism. To explore the effects of oxidative stress on neuronal cells during microgravity, we used rat pheochromocytoma (PC12) cells as a neuronal cell model, cultured in a clinostat, which could simulate microgravity, to investigate the effects of reactive nitrogen species on protein nitration in PC12 cells during clinorotation. The effects of melatonin and quercetin on protein nitration in PC12 cells were also assayed to evaluate the possible protective role of melatonin or quercetin as an antioxidant. The results of immunological staining showed that after the 3 days' clinorotation the protein expressions of neuronal nitric oxide synthase and inducible nitric oxide synthesis were up-regulated. Our data also reflected that the concentrations of nitric oxide and nitrotyrosine were significantly increased after clinorotation, and they were reduced markedly in cells that were treated with 50 micromol/L melatonin or 0.5 micromol/L quercetin during simulated microgravity, when compared to those of control cells. These results suggest that clinorotation-induced weightlessness increases oxidative stress responses in PC12 cells, and melatonin or quercetin was shown to protect PC12 cells from oxidative damage during simulated weightlessness.