Abstract P2005: Antioxidant Resveratrol Attenuates Cardiac Fibrosis and Reduces Matrix Metalloproteinase-2 Activity in Heart Failure Rats

Increased reactive oxygen species activate matrix metalloproteinases (MMP) playing a critical role in cardiovascular remodeling after myocardial infarction (MI). We evaluated the antioxidant effect of resveratrol (RESV) on cardiac remodeling and MMP-2 activity in heart failure (HF) rats. Wistar rats were divided into the following groups: Control; Control+RESV; HF; HF+RESV (10mg/kg/day, p.o., 4 wk). The MI was elicited by ligation of the coronary artery. After four weeks, the animals were anesthetized to evaluate the cardiac function and to collect the hearts and blood samples. Heart weight/body weight (HW/BW, mg/g) ratio and the infarct size were calculated. Histological assessment of the left ventricle was carried out with hematoxylin/eosin, and fibrosis was quantified with Masson trichrome-staining. Cardiac and plasma MMP-2 activities were determined by gel zymography. The oxidative stress was assessed measuring the thiobarbituric acid reactive substances (TBARS) from plasma. HF and HF+RESV showed similar infarct size. The HW/BW ratio increased (3.7±0.2 vs 3.8±0.2 vs 3.0±0.05). RESV improved the maximal slope of the systolic increment of left ventricular pressure in HF animals (9004±1120 vs 5849±595 vs 7181±533 mmHg/s) and reduced the end diastolic pressure (4±1 vs 18±4 vs 7±1 mmHg). HF increased TBARS, whereas RESV produced an antioxidant effect in HF+RESV group (11.2±0.9 vs 21.7±3 vs 8.2±1.4 μmol/L). HF augmented cardiac fibrosis (30,8±1,3 vs 8,8±0,5%) and myocyte hypertrophy (12,2±0,7 vs 8,8±0,3μm). RESV reduced collagen deposition in HF hearts (22,7±1,9%), but did not reduce the myocyte hypertrophy (11,7±0,6 μm). Cardiac and plasma MMP-2 activity were higher in HF animals (plasma: 1344±39 vs. 1164±47; heart: 536±54 vs. 262±18). RESV decreased plasma MMP-2 activity in control (992±27) and HF animals (1200±49) and reduced cardiac MMP-2 activity only in HF+RESV group (426±42). In conclusion, the antioxidant effect of RESV improved cardiac function and fibrosis and reduced MMP-2 levels in the heart and plasma from HF rats.

Antioxidant and antihypertensive responses to oral nitrite involves activation of the Nrf2 pathway

Impaired redox balance contributes to the cardiovascular alterations of hypertension and activation of nuclear factor erythroid 2-related factor 2 (Nrf2) pathway may counteract these alterations. While nitrite recycles back to NO and exerts antioxidant and antihypertensive effects, the mechanisms involved in these responses are not fully understood. We hypothesized that nitrite treatment of two-kidney, one-clip (2K1C) hypertensive rats activates the Nrf2 pathway, promotes the transcription of antioxidant genes, and improves the vascular redox imbalance and dysfunction in this model. Two doses of oral nitrite were studied: 15 mg/kg and the sub-antihypertensive dose of 1 mg/kg. Nitrite 15 mg/kg (but not 1 mg/kg) decreased blood pressure and increased circulating plasma nitrite and nitrate. Both doses blunted hypertension-induced increases in mesenteric artery reactive oxygen species concentrations assessed by DHE technique and restored the impaired mesenteric artery responses to acetylcholine. While 2K1C hypertension decreased nuclear Nrf2 accumulation, both doses of nitrite increased nuclear Nrf2 accumulation and mRNA expression of Nrf2-regulated genes including superoxide dismutase-1 (SOD1), catalase (CAT), glutathione peroxidase (GPX), thioredoxin-1(TRDX-1) and -2 (TRDX-2). To further confirm nitrite-mediated antioxidant effects, we measured vascular SOD and GPX activity and we found that nitrite at 1 or 15 mg/kg increased the activity of both enzymes (P < 0.05). These results suggest that activation of the Nrf2 pathway promotes antioxidant effects of nitrite, which may improve the vascular dysfunction in hypertension, even when nitrite is given at a sub-antihypertensive dose. These findings may have many clinical implications, particularly in the therapy of hypertension and other cardiovascular diseases.

Nitrite treatment downregulates vascular MMP-2 activity and inhibits vascular remodeling in hypertension independently of its antihypertensive effects

Hypertension is associated with cardiovascular remodeling. Given that impaired redox state activates matrix metalloproteinase (MMP)- 2 and promotes vascular remodeling, we hypothesized that nitrite treatment at a non-antihypertensive dose exerts antioxidant effects and attenuates both MMP-2 activation and vascular remodeling of hypertension. We examined the effects of oral sodium nitrite at antihypertensive (15 mg/kg) or non-antihypertensive (1 mg/kg) daily dose in hypertensive rats (two kidney, one clip; 2K1C model). Sham-operated and 2K1C hypertensive rats received vehicle or nitrite by gavage for four weeks. Systolic blood pressure decreased only in hypertensive rats treated with nitrite 15 mg/Kg/day. Both low and high nitrite doses decreased 2K1C-induced vascular remodeling assessed by measuring aortic cross-sectional area, media/lumen ratio, and number of vascular smooth muscle cells/aortic length. Both low and high nitrite doses decreased 2K1C-induced vascular oxidative stress assessed in situ with the fluorescent dye DHE and with the lucigenin chemiluminescence assay. Vascular MMP-2 expression and activity were assessed by gel zymography, Western blot, and in situ zymography increased with hypertension. While MMP-2 levels did not change in response to both doses of nitrite, both doses completely prevented hypertension-induced increases in vascular MMP activity. Moreover, incubation of aortas from hypertensive rats with nitrite at 1-20 μmol/L reduced gelatinolytic activity by 20-30%. This effect was fully inhibited by the xanthine oxidase (XOR) inhibitor febuxostat, suggesting XOR-mediated generation of nitric oxide (NO) from nitrite as a mechanism explaining the responses to nitrite. In vitro incubation of aortic extracts with nitrite 20 μmol/L did not affect MMP-2 activity. These results show that nitrite reverses the vascular structural alterations of hypertension, independently of anti-hypertensive effects. This response is mediated, at least in part, by XOR and is attributable to antioxidant effects of nitrite blunting vascular MMP-2 activation. Our findings suggest nitrite therapy to reverse structural alterations of hypertension.

Nitrite exerts antioxidant effects, inhibits the mTOR pathway and reverses hypertension-induced cardiac hypertrophy

Cardiac hypertrophy is a common consequence of chronic hypertension and leads to heart failure and premature death. The anion nitrite is now considered as a bioactive molecule able to exert beneficial cardiovascular effects. Previous results showed that nitrite attenuates hypertension-induced increases in reactive oxygen species (ROS) production in the vasculature. Whether antioxidant effects induced by nitrite block critical signaling pathways involved in cardiac hypertrophy induced by hypertension has not been determined yet. The Akt/mTOR signaling pathway is responsible to activate protein synthesis during cardiac remodeling and is activated by increased ROS production, which is commonly found in hypertension. Here, we investigated the effects of nitrite treatment on cardiac remodeling and activation of this hypertrophic signaling pathway in 2 kidney-1 clip (2K1C) hypertension. Sham and 2K1C rats were treated with oral nitrite at 1 or 15 mg/kg for four weeks. Nitrite treatment (15 mg/kg) reduced systolic blood pressure and decreased ROS production in the heart tissue from hypertensive rats. This nitrite dose also blunted hypertension-induced activation of mTOR pathway and cardiac hypertrophy. While the lower nitrite dose (1 mg/kg) did not affect blood pressure, it exerted antioxidant effects and tended to attenuate mTOR pathway activation and cardiac hypertrophy induced by hypertension. Our findings provide strong evidence that nitrite treatment decreases cardiac remodeling induced by hypertension as a result of its antioxidant effects and downregulation of mTOR signaling pathway. This study may help to establish nitrite as an effective therapy in hypertension-induced cardiac hypertrophic remodeling.

The matricellular protein TSP1 promotes human and mouse endothelial cell senescence through CD47 and Nox1

Senescent cells withdraw from the cell cycle and do not proliferate. The prevalence of senescent compared to normally functioning parenchymal cells increases with age, impairing tissue and organ homeostasis. A contentious principle governing this process has been the redox theory of aging. We linked matricellular protein thrombospondin 1 (TSP1) and its receptor CD47 to the activation of NADPH oxidase 1 (Nox1), but not of the other closely related Nox isoforms, and associated oxidative stress, and to senescence in human cells and aged tissue. In human endothelial cells, TSP1 promoted senescence and attenuated cell cycle progression and proliferation. At the molecular level, TSP1 increased Nox1-dependent generation of reactive oxygen species (ROS), leading to the increased abundance of the transcription factor p53. p53 mediated a DNA damage response that led to senescence through Rb and p21^cip, both of which inhibit cell cycle progression. Nox1 inhibition blocked the ability of TSP1 to increase p53 nuclear localization and p21^cip abundance and its ability to promote senescence. Mice lacking TSP1 showed decreases in ROS production, p21^cip expression, p53 activity, and aging-induced senescence. Conversely, lung tissue from aging humans displayed increases in the abundance of vascular TSP1, Nox1, p53, and p21^cip Finally, genetic ablation or pharmacological blockade of Nox1 in human endothelial cells attenuated TSP1-mediated ROS generation, restored cell cycle progression, and protected against senescence. Together, our results provide insights into the functional interplay between TSP1 and Nox1 in the regulation of endothelial senescence and suggest potential targets for controlling the aging process at the molecular level.

Oral nitrite circumvents antiseptic mouthwash-induced disruption of enterosalivary circuit of nitrate and promotes nitrosation and blood pressure lowering effect

The nitric oxide (NO^•) metabolites nitrite and nitrate exert antihypertensive effects by mechanisms that involve gastric formation of S-nitrosothiols. However, while the use of antiseptic mouthwash (AM) is known to attenuate the responses to nitrate by disrupting its enterosalivary cycle, there is little information about whether AM attenuates the effects of orally administered nitrite. We hypothesized that the antihypertensive effects of orally administered nitrite would not be prevented by AM because, in contrast to oral nitrate, oral nitrite could promote S-nitrosothiols formation in the stomach without intereference by AM. Chronic effects of oral nitrite or nitrate were studied in two-kidney, one-clip (2K1C) hypertensive rats (and normotensive controls) treated with AM (or vehicle) once/day. We found that orally administered nitrite exerts antihypertensive effects that were not affected by AM. This finding contrasts with lack of antihypertensive responses to oral nitrate in 2K1C hypertensive rats treated with AM. Nitrite and nitrate treatments increased plasma nitrites, nitrates, and S-nitrosothiols concentrations. However, while treatment with AM attenuated the increases in plasma nitrite concentrations after both nitrite and nitrate treatments, AM attenuated the increases in S-nitrosothiols in nitrate-treated rats, but not in nitrite-treated rats. Moreover, AM attenuated vascular S-nitrosylation (detected by the SNO-RAC method) after nitrate, but not after nitrite treatment. Significant correlations were found between the hypotensive responses and S-nitrosothiols, and vascular S-nitrosylation levels. These results show for the first time that oral nitrite exerts antihypertensive effects notwithstanding the fact that antiseptic mouthwash disrupts the enterosalivary circulation of nitrate. Our results support a major role for S-nitrosothiols formation resulting in vascular S-nitrosylation as a key mechanism for the antihypertensive effects of both oral nitrite and nitrate.

Gastric S-nitrosothiol formation drives the antihypertensive effects of oral sodium nitrite and nitrate in a rat model of renovascular hypertension

Many effects of nitrite and nitrate are attributed to increased circulating concentrations of nitrite, ultimately converted into nitric oxide (NO(•)) in the circulation or in tissues by mechanisms associated with nitrite reductase activity. However, nitrite generates NO(•) , nitrous anhydride, and other nitrosating species at low pH, and these reactions promote S-nitrosothiol formation when nitrites are in the stomach. We hypothesized that the antihypertensive effects of orally administered nitrite or nitrate involve the formation of S-nitrosothiols, and that those effects depend on gastric pH. The chronic effects of oral nitrite or nitrate were studied in two-kidney, one-clip (2K1C) hypertensive rats treated with omeprazole (or vehicle). Oral nitrite lowered blood pressure and increased plasma S-nitrosothiol concentrations independently of circulating nitrite levels. Increasing gastric pH with omeprazole did not affect the increases in plasma nitrite and nitrate levels found after treatment with nitrite. However, treatment with omeprazole severely attenuated the increases in plasma S-nitrosothiol concentrations and completely blunted the antihypertensive effects of nitrite. Confirming these findings, very similar results were found with oral nitrate. To further confirm the role of gastric S-nitrosothiol formation, we studied the effects of oral nitrite in hypertensive rats treated with the glutathione synthase inhibitor buthionine sulfoximine (BSO) to induce partial thiol depletion. BSO treatment attenuated the increases in S-nitrosothiol concentrations and antihypertensive effects of oral nitrite. These data show that gastric S-nitrosothiol formation drives the antihypertensive effects of oral nitrite or nitrate and has major implications, particularly to patients taking proton pump inhibitors.

Abstract 096: Sequential Activation of Nox1 and Gremlin1 Leads to Endothelial Proliferation in Human Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a rapidly degenerating and devastating disease of increased pulmonary vessel resistance leading to eventual right heart failure. Until now, palliative modalities have targeted the reduction of vascular tone with little success. Recent studies have delved into the mechanisms regulating increased pulmonary vascular resistance: aberrant vascular remodeling and occlusion. However, little is known of the molecular mechanisms responsible for endothelial proliferation, a root cause of PAH-associated vascular remodeling. We provide the first evidence to our knowledge of an upregulation of NADPH oxidase 1 (Nox1) at the transcript and protein (2.1±0.62 -fold, P < 0.05) level in resistance vessels from PAH vs. non-PAH subjects. This coincided with an increase in bone morphogenetic protein (BMP) antagonist Gremlin1 protein expression (2.3±0.47 [[Unable to Display Character: &#8211;]]fold vs. non-PAH, P < 0.05) and reactive oxygen species (ROS) production (iodonium-inhibitable hydrogen peroxide production: 0.69±0.06 vs. 0.43±0.032 nmol/min/mg protein for PAH vs. non-PAH, respectively, P < 0.05). In vitro studies in human pulmonary artery endothelial cells (HPAEC) demonstrate that hypoxia (24 hr, 1 % O 2 ) drives Nox1 subunit expression (Nox1 protein: 1.4±0.075-fold vs. normoxia, P < 0.05), assembly and oxidase activity (superoxide production, nmol/min/mg protein: 14.0±1.9 vs. 6.00±0.94 for normoxia, P < 0.01) leading to elevation in sonic hedgehog (SHH; 1.5±0.011 fold, P < 0.05) and Gremlin1 (1.90±0.32-fold, P < 0.01) expression. Nox1 gene-silencing in hypoxia-exposed HPAEC abrogated this cascade. Moreover, hypoxia-induced endothelial cell proliferation (1.18±0.038-fold vs. normoxia, P < 0.05) was attenuated with loss of either Nox1 or Gremlin1. Finally, incubation of normoxic HPAEC with conditioned media from hypoxia-exposed HPAEC resulted in increased proliferation, which was abrogated by Nox1 suppression of donor cells. Together these data support a Nox1-Gremlin1 signaling axis in pulmonary vascular endothelium that is likely to contribute to pathophysiological endothelial proliferation and the progression of pulmonary hypertension. The findings also support targeting of Nox1 as a viable therapeutic option to combat PAH.

Abstract 123: Age-Related Endothelial Senescence is Driven by Thrombospondin-1-Activated NADPH Oxidase Nox1

Organismal aging represents an independent risk factor underlying many vascular diseases, including systemic and pulmonary hypertension, and atherosclerosis. While the mechanisms driving aging are largely elusive, a steady persistent increase in tissue oxidative stress has been associated with senescence. Previously we showed TSP1 elicits NADPH oxidase (Nox)-dependent vascular smooth muscle cell oxidative stress. However mechanisms by which TSP1 affects endothelial redox biology are unknown. Here, we tested the hypothesis that TSP1 induces endothelial oxidative stress-linked senescence in aging. Using rapid autopsy disease-free human pulmonary (PA) artery, we identified a significant positive correlation between age, protein levels of TSP1, Nox1 and the cell-cycle repressor p21cip (p<0.05). Age also positively associated with increased Amplex Red-detected PA hydrogen peroxide levels (p<0.05). Moreover, treatment of human PA endothelial cells (HPAEC) with TSP1 (2.2nM; 24h) increased expression (~1.9 fold; p<0.05) and activation of Nox1 (~1.7 fold; p<0.05) compared to control, as assessed by Western blot and SOD-inhibitable cytochrome c reduction. Western blotting and immunofluorescence showed a TSP1-mediated increase in p53 activation, indicative of the DNA damage response. Moreover, TSP1 significantly increased HPAEC senescence in a p53/p21cip/Rb-dependent manner, as assessed by immunofluorescent detection of subcellular localization and senescence-associated β-galactosidase staining. To explore this pathway in vivo, middle-aged (8-10 month) wild-type and TSP1-null mice were utilized. In the TSP1-null, reduced lung senescence, oxidative stress, Nox1 levels and p21cip expression were observed compared to wild-type supporting findings in human samples and cell experiments. Finally, prophylactic treatment with specific Nox1 inhibitor NoxA1ds (10μM) attenuated TSP1-induced HPAEC ROS, p53 activation, p21cip expression and senescence. Taken together, our results provide molecular insight into the functional interplay between TSP1 and Nox1 in the regulation of endothelial senescence, with implications for molecular control of the aging process.

TEMPOL enhances the antihypertensive effects of sodium nitrite by mechanisms facilitating nitrite-derived gastric nitric oxide formation

Orally administered nitrite exerts antihypertensive effects associated with increased gastric nitric oxide (NO) formation. While reducing agents facilitate NO formation from nitrite, no previous study has examined whether antioxidants with reducing properties improve the antihypertensive responses to orally administered nitrite. We hypothesized that TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl) could enhance the hypotensive effects of nitrite in hypertensive rats by exerting antioxidant effects (and enhancing NO bioavailability) and by promoting gastric nitrite-derived NO generation. The hypotensive effects of intravenous and oral sodium nitrite were assessed in unanesthetized freely moving rats with L-NAME (N(ω)-nitro-L-arginine methyl ester; 100mg/kg; po)-induced hypertension treated with TEMPOL (18mg/kg; po) or vehicle. While TEMPOL exerted antioxidant effects in hypertensive rats, as revealed by lower plasma 8-isoprostane and vascular reactive oxygen species levels, this antioxidant did not affect the hypotensive responses to intravenous nitrite. Conversely, TEMPOL enhanced the dose-dependent hypotensive responses to orally administered nitrite, and this effect was associated with higher increases in plasma nitrite and lower increases in plasma nitrate concentrations. In vitro experiments using electrochemical and chemiluminescence NO detection under variable pH conditions showed that TEMPOL enhanced nitrite-derived NO formation, especially at low pH (2.0 to 4.0). TEMPOL signal evaluated by electron paramagnetic resonance decreased when nitrite was reduced to NO under acidic conditions. Consistent with these findings, increasing gastric pH with omeprazole (30mg/kg; po) attenuated the hypotensive responses to nitrite and blunted the enhancement in plasma nitrite concentrations and hypotensive effects induced by TEMPOL. Nitrite-derived NO formation in vivo was confirmed by using the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (C-PTIO), which blunted the responses to oral nitrite. Our results showed that TEMPOL promotes nitrite reduction to NO in the stomach and enhanced plasma nitrite concentrations and the hypotensive effects of oral sodium nitrite through mechanisms critically dependent on gastric pH. Interestingly, the effects of TEMPOL on nitrite-mediated hypotension cannot be explained by increased NO formation in the stomach alone, but rather appear more directly related to increased plasma nitrite levels and reduced nitrate levels during TEMPOL treatment. This may relate to enhanced nitrite uptake or reduced nitrate formation from NO or nitrite.

Abstract 297: Chronic Antihypertensive Effects of Sodium Nitrite in L-name-induced Hypertension in Rats

Dietary nitrite and nitrate have been recently implicated as an important source of nitric oxide with antihypertensive effects. We have previously shown acute antihypertensive effects exerted by a single oral dose of sodium nitrite (NaNO 2 ) in renovascular hypertension. However, the possible chronic antihypertensive effects of NaNO 2 have not been examined yet. We evaluated the effects of NaNO 2 on L-NAME (Nω-Nitro-L-arginine methyl ester)-induced hypertension in Wistar rats.

METHODS: Rats received vehicle (tap water) or L-NAME (1g/L) in their drinking water. After two weeks of treatment, the rats received NaNO 2 (15 mg/kg/day by gavage) or vehicle for 4 weeks. Systolic blood pressure (SBP) was evaluated by pletismography weekly. Plasma levels of nitrate and nitrite were assessed by Griess reaction and ozone-based chemiluminescence, respectively. Dihydroethidium (DHE) was used in aortic sections to evaluate reactive oxygen species (ROS) production by fluorescence microscopy.

Results: while NaNO 2 treatment induced no changes on SBP in vehicle-treated rats (p>0.05), this treatment significantly reduced SBP in L-NAME-treated rats (192±2 mmHg in L-NAME + vehicle group versus 164±2 mmHg in L-NAME + nitrite group; P<0.05). At the end of treatment, we found lower plasma nitrite levels in L-NAME rats compared with normotensive controls (148±14 nM versus 445±97; P<0.05). NaNO 2 treatment increased plasma nitrite levels in both normotensive controls and in L-NAME-treated rats (P<0.05). While no significant changes were found in plasma nitrate levels in L-NAME-treated rats when compared with controls (903±157 nM versus 995±145; p>0.05), NaNO 2 treatment induced significant increases in plasma nitrate levels in both normotensive and hypertensive rats (191±13 nM and 199±17 respectively; p<0.05 when compared to the controls). When compared to the control groups, higher ROS levels were found in the aortic rings from L-NAME treated rats (4091±249 A.U. versus 5709±598 A.U.; p<0.05) but treatment did not affect this increase (p>0.05).

Conclusion: Our results show for the first time that NaNO 2 has relevant chronic antihypertensive effects in L-NAME hypertension. However, was unable to reverse the oxidative stress associated with L-NAME-induced hypertension.

Abstract 189: Omeprazole Decreases Chronic Antihypertensive Effects of Sodium Nitrite

Introduction: Recent studies showed that sodium nitrite decreases blood pressure (BP) in two kidney, one clip (2K1C) hypertension, probably as a result of nitrite being converted into nitric oxide in the acid environment of the stomach. This study aimed at examining whether increasing gastric pH with omeprazol reduces the chronic antihypertensive effects of nitrite.

Methods: 2K1C hypertensive and sham operated control rats were treated with omeprazole (10mg/Kg; i.p.) or vehicle and sodium nitrite (15mg/Kg; gavage) or saline for two weeks. Systolic BP (SBP) was measured by tail pletismografy weekly. Circulating nitrite levels were measured by chemiluminesce and gastric pH was measured with an electrode. The results were analyzed by two-way ANOVA. The results are show as mean ± standard deviation.

Results: 2K1C rats were hypertensive two weeks after surgery (SBP=180±17 mmHg). After 4 weeks of treatment, nitrite exerted antihypertensive effects in rats treated with vehicle (SBP=161±23 mmHg versus 200±29 mmHg, respectively, in the 2K1C+nitrite and in the 2K1C+saline groups; P<0.05). However, nitrite exerted no antihypertensive effects in 2K1C rats treated with omeprazole (SBP=200±34 mmHg; P>0.05 versus 2K1C+saline group). We found no significant differences among the sham operated groups. Similar increases in plasma nitrite concentrations were found when animals treated with nitrite and omeprazol were compared with those treated with nitrite and vehicle (8.5±4.1 versus 5.2±3.6 μM, respectively; P>0.05). Omeprazole increased gastric pH in all animals treated with this drug (P<0.05).

Conclusion Treatment with omeprazole blunts the chronic antihypertensive effects of sodium nitrite in 2K1C rats. However, this effect is probably not associated with significant differences in plasma nitrite concentrations.

Increase in gastric pH reduces hypotensive effect of oral sodium nitrite in rats

The new pathway nitrate-nitrite-nitric oxide (NO) has emerged as a physiological alternative to the classical enzymatic pathway for NO formation from l-arginine. Nitrate is converted to nitrite by commensal bacteria in the oral cavity and the nitrite formed is then swallowed and reduced to NO under the acidic conditions of the stomach. In this study, we tested the hypothesis that increases in gastric pH caused by omeprazole could decrease the hypotensive effect of oral sodium nitrite. We assessed the effects of omeprazole treatment on the acute hypotensive effects produced by sodium nitrite in normotensive and L-NAME-hypertensive free-moving rats. In addition, we assessed the changes in gastric pH and plasma levels of nitrite, NO(x) (nitrate+nitrite), and S-nitrosothiols caused by treatments. We found that the increases in gastric pH induced by omeprazole significantly reduced the hypotensive effects of sodium nitrite in both normotensive and L-NAME-hypertensive rats. This effect of omeprazole was associated with no significant differences in plasma nitrite, NO(x), or S-nitrosothiol levels. Our results suggest that part of the hypotensive effects of oral sodium nitrite may be due to its conversion to NO in the acidified environment of the stomach. The increase in gastric pH induced by treatment with omeprazole blunts part of the beneficial cardiovascular effects of dietary nitrate and nitrite.

Antihypertensive and antioxidant effects of a single daily dose of sodium nitrite in a model of renovascular hypertension

Dietary nitrite and nitrate have been reported as alternative sources of nitric oxide (NO). In this regard, we reported previously that sodium nitrite added to drinking water was able to exert antihypertensive effects in an experimental model of hypertension in a dose-dependent manner. Taking into consideration that nitrite is continuously converted to nitrate in the bloodstream, here we expanded our previous report and evaluate whether a single daily dose of sodium nitrite could exert antihypertensive effects in 2 kidney-1 clip (2K1C) hypertensive rats. Sham-operated and 2K1C rats were treated with vehicle or sodium nitrite (15 mg/kg/day) for 4 weeks. We evaluated the effects induced by sodium nitrite treatment on systolic blood pressure (SBP) and NO markers such as plasma nitrite, nitrite + nitrate (NOx), cGMP, and blood levels of nitrosyl-hemoglobin. In addition, we also evaluated effects of nitrite on oxidative stress and antioxidant enzymes. Dihydroethidium (DHE) was used to evaluate aortic reactive oxygen species (ROS) production by fluorescence microscopy, and plasma levels of thiobarbituric acid-reactive species (TBARS) were measured in plasma samples from all experimental groups. Red blood cell superoxide dismutase (SOD) and catalase activity were evaluated with commercial kits. Sodium nitrite treatment reduced SBP in 2K1C rats (P < 0.05). We found lower plasma nitrite and NOx levels in 2K1C rats compared with normotensive controls (both P < 0.05). Nitrite treatment restored the lower levels of nitrite and NOx. While no change was found in the blood levels of nitrosyl-hemoglobin (P > 0.05), nitrite treatment increased the plasma levels of cGMP in 2K1C rats (P < 0.05). Higher plasma TBARS levels and aortic ROS levels were found in hypertensive rats compared with controls (P < 0.05), and nitrite blunted these alterations. Lower SOD and catalase activities were found in 2K1C hypertensive rats compared with controls (both P < 0.05). Nitrite treatment restored SOD activity (P < 0.05), whereas catalase was not affected. These data suggest that even a single daily oral dose of sodium nitrite is able to lower SBP and exert antioxidant effects in renovascular hypertension.

Sodium nitrite downregulates vascular NADPH oxidase and exerts antihypertensive effects in hypertension

Dietary nitrite and nitrate are important sources of nitric oxide (NO). However, the use of nitrite as an antihypertensive drug may be limited by increased oxidative stress associated with hypertension. We evaluated the antihypertensive effects of sodium nitrite given in drinking water for 4 weeks in two-kidney one-clip (2K1C) hypertensive rats and the effects induced by nitrite on NO bioavailability and oxidative stress. We found that, even under the increased oxidative stress conditions present in 2K1C hypertension, nitrite reduced systolic blood pressure in a dose-dependent manner. Whereas treatment with nitrite did not significantly change plasma nitrite concentrations in 2K1C rats, it increased plasma nitrate levels significantly. Surprisingly, nitrite treatment exerted antioxidant effects in both hypertensive and sham-normotensive control rats. A series of in vitro experiments was carried out to show that the antioxidant effects induced by nitrite do not involve direct antioxidant effects or xanthine oxidase activity inhibition. Conversely, nitrite decreased vascular NADPH oxidase activity. Taken together, our results show for the first time that nitrite has antihypertensive effects in 2K1C hypertensive rats, which may be due to its antioxidant properties resulting from vascular NADPH oxidase activity inhibition.

The relationship between blood and serum lead levels in peripartum women and their respective umbilical cords

Foetal exposure to lead (Pb) during pregnancy is a major problem. However, no previous study has examined whether Pb concentrations in blood (Pb-B) and in serum (Pb-S) from pregnant women correlate with Pb-B and Pb-S in the foetuses. This hypothesis was tested in the present study. We measured Pb-B and Pb-S in 120 healthy pregnant women (more than 38 weeks of gestation) and their respective umbilical cord samples. The analyses were carried out with an inductively coupled plasma mass spectrometer. We found higher Pb-B levels in the women compared with their respective umbilical cord samples (1.736 ± 0.090 μg/dL and 1.194 ± 0.062 μg/dL, respectively; p < 0.05). In parallel, we found higher Pb-S levels in the women compared with their respective umbilical cord samples (0.042 ± 0.003 μg/dL and 0.032 ± 0.003 μg/dL, respectively; p < 0.05). However, similar %Pb-S/Pb-B ratios were found in the women compared with their respective umbilical cord samples (2.414 ± 0.210% and 2.740 ± 0.219%, respectively; p > 0.05). Interestingly, we found positive correlations between Pb-B in the umbilical cords and Pb-B in the respective pregnant women (rs = 0.5714; p < 0.0001), and between Pb-S in the umbilical cords and Pb-S in the respective pregnant women (rs = 0.3902; p < 0.0001) as well as between %Pb-B/Pb-S in the umbilical cords and %Pb-B/Pb-S in the respective pregnant women (rs = 0.3767; p < 0.0001). These results indicate that the assessment of Pb-B and Pb-S in pregnant women provides relevant indexes of foetal exposure to Pb. Moreover, the similar %Pb-S/Pb-B in pregnant women and in the umbilical cords shows that the foetuses are directly exposed to the rapidly exchangeable Pb fraction found in their mothers.

Vitamin D receptor haplotypes affect lead levels during pregnancy

Pregnant women are particularly susceptible to toxic effects associated with lead (Pb) exposure. Pb accumulates in bone tissue and is rapidly mobilized from bones during pregnancy, thus resulting in fetal contamination. While vitamin D receptor (VDR) polymorphisms modify bone mineralization and affect Pb biomarkers including blood (Pb-B) and serum (Pb-S) Pb concentrations, and %Pb-S/Pb-B ratio, the effects of these polymorphisms on Pb levels in pregnant women are unknown. This study aimed at examining the effects of three (FokI, BsmI and ApaI) VDR polymorphisms (and VDR haplotypes) on Pb levels in pregnant women. Pb-B and Pb-S were determined by inductively coupled plasma mass spectrometry in samples from 256 healthy pregnant women and their respective umbilical cords. Genotypes for the VDR polymorphisms were determined by PCR and restriction fragment length digestion. While the three VDR polymorphisms had no significant effects on Pb-B, Pb-S or %Pb-S/Pb-B ratio, the haplotype combining the f, a, and b alleles for the FokI, ApaI and BsmI polymorphisms, respectively, was associated with significantly lower Pb-S and %Pb-S/Pb-B (P<0.05). However, maternal VDR haplotypes had no effects on Pb levels in the umbilical cords. To our knowledge, this is the first study showing that a combination of genetic polymorphisms (haplotype) commonly found in the VDR gene affects Pb-S and %Pb-S/Pb-B ratios in pregnant women. These findings may have major implications for Pb toxicity because they may help to predict the existence of a group of subjects that is genetically less prone to Pb toxicity during pregnancy.

Should we measure serum or plasma lead concentrations?

PROJECT

Serum samples may not be appropriate to assess lead (Pb) concentrations because they may contain artificially higher Pb concentrations compared with those measured in plasma samples. Here, we compared Pb concentrations in serum versus heparin plasma separated from blood collected with or without vacuum. We have also examined the effects of sample standing time on Pb concentrations measured in serum, heparin plasma, and EDTA plasma.

PROCEDURE

We studied plasma and serum samples from twelve healthy subjects. Blood samples were collected via venous drainage phlebotomy with and without vacuum into trace metal free tubes containing no anticoagulants (serum), or lithium heparin, or EDTA (to obtain plasma). Variable sample standing times (0, 5, and 30 min) prior to centrifugation were allowed. Plasma and serum Pb and iron concentrations were determined by inductively coupled plasma mass spectrometry. Plasma and serum cell-free hemoglobin concentrations were measured.

RESULTS

Pb concentrations in serum and in heparin plasma from blood samples collected with or without vacuum were similar and not associated with significant changes in iron or hemoglobin concentrations. The sample standing time (up to 30 min) did not affect Pb concentrations in serum or in heparin plasma, which were approximately 50% lower than those found in EDTA plasma.

CONCLUSIONS

Serum or heparin plasma separated from blood samples collected via venous phlebotomy with or without vacuum are appropriate medium to assess Pb concentrations, independently of the sample standing time.