The effect of sodium nitrite infusion on renal function, brachial and central blood pressure during enzyme inhibition by allopurinol, enalapril or acetazolamide in healthy subjects: a randomized, double-blinded, placebo-controlled, crossover study

Orally administered sodium nitrite prevents the increased α-1 adrenergic vasoconstriction induced by hypertension and promotes the S-nitrosylation of calcium/calmodulin-dependent protein kinase II

The unsatisfactory rates of adequate blood pressure control among patients receiving antihypertensive treatment calls for new therapeutic strategies to treat hypertension. Several studies have shown that oral sodium nitrite exerts significant antihypertensive effects, but the mechanisms underlying these effects remain unclear. While these mechanisms may involve nitrite-derived S-nitrosothiols, their implication in important alterations associated with hypertension, such as aberrant α1-adrenergic vasoconstriction, has not yet been investigated. Here, we examined the effects of oral nitrite treatment on vascular responses to the α1-adrenergic agonist phenylephrine in two-kidney, one clip (2K1C) hypertensive rats and investigated the potential underlying mechanisms. Our results show that treatment with oral sodium nitrite decreases blood pressure and prevents the increased α1-adrenergic vasoconstriction in 2K1C hypertensive rats. Interestingly, we found that these effects require vascular protein S-nitrosylation, and to investigate the specific S-nitrosylated proteins we performed an unbiased nitrosoproteomic analysis of vascular smooth muscle cells (VSMCs) treated with the nitrosylating compound S-nitrosoglutathione (GSNO). This analysis revealed that GSNO markedly increases the nitrosylation of calcium/calmodulin-dependent protein kinase II γ (CaMKIIγ), a multifunctional protein that mediates the α1-adrenergic receptor signaling. This result was associated with reduced α1-adrenergic receptor-mediated CaMKIIγ activity in VSMCs. We further tested the relevance of these findings in vivo and found that treatment with oral nitrite increases CaMKIIγ S-nitrosylation and blunts the increased CaMKIIγ activity induced by phenylephrine in rat aortas. Collectively, these results are consistent with the idea that oral sodium nitrite treatment increases vascular protein S-nitrosylation, including CaMKIIγ as a target, which may ultimately prevent the increased α1-adrenergic vasoconstriction induced by hypertension. These mechanisms may help to explain the antihypertensive effects of oral nitrite and hold potential implications in the therapy of hypertension and other cardiovascular diseases associated with abnormal α1-adrenergic vasoconstriction.

The effect of orally administered nitrate on renal function and blood pressure in a randomized, placebo-controlled, crossover study in healthy subjects

BACKGROUND

Several studies have shown inorganic nitrate/nitrite to reduce blood pressure in both healthy subjects and hypertensive patients. An effect presumably caused through bioconversion to nitric oxide. However, studies on inorganic nitrate/nitrite have shown inconsistent results on renal functions such as GFR and sodium excretion. The current study investigated whether orally administered nitrate would decrease blood pressure and increase GFR and urinary sodium excretion.

METHODS

In a randomized, placebo-controlled, double-blinded, crossover study, 18 healthy subjects received a daily dose of 24 mmol potassium nitrate and placebo (potassium chloride) during 4 days in a randomized order. Subjects also ingested a standardized diet and completed a 24-h urine collection. GFR was determined by the constant infusion technique and during GFR measurement, brachial blood pressure (BP) and central blood pressure (cBP), heart rate, and arterial stiffness were measured every half hour using the Mobil-O-Graph®. Blood samples was analyzed for nitrate, nitrite, cGMP, vasoactive hormones and electrolytes. Urine was analyzed for nitrate, nitrite, cGMP, electrolytes, ENaC_γ, NCC, CrCl, C_H2O and UO.

RESULTS

No differences in GFR, blood pressure or sodium excretion were found between the treatments with potassium nitrate and placebo. However, both nitrate and nitrite levels in plasma and urine were significantly increased by potassium nitrate intake and the 24-h urinary excretion of sodium and potassium were stable, showing adherence to the standardized diet and the study medication.

CONCLUSION

We found no decrease in blood pressure or increase in GFR and sodium excretion of 24 mmol potassium nitrate capsules as compared to placebo after 4 days of treatment. Healthy subjects may be able to compensate the effects of nitrate supplementation during steady state conditions. Future research should focus on long-term studies on the difference in response between healthy subjects and patients with cardiac or renal disease.

Technetium-99m-MAG3 and technetium-99m-DTPA: Renal clearance measured by the constant infusion technique - Old news?

BACKGROUND

Accurate, precise and straightforward methods for measuring glomerular filtration rate (GFR) and/or renal plasma flow (RPF) are still in demand today. The time-consuming constant infusion technique (CIT) is the gold standard and preferred for research, whereas the simple, but less precise, single injection technique (SIT) is used in clinical settings. This study investigated the use of ^99m Tc-DTPA and ^99m Tc-MAG₃ by CIT as a measure of renal function. We developed and evaluated a model to balance the primer dose and infusion rate in an attempt to obtain plasma steady state as quickly as possible.

METHODS

14 healthy subjects received ^99m Tc-DTPA and 6 hypertensive patients received ^99m Tc-MAG₃ in a standardized protocol. All participants had an eGFR above 60 ml/min and none had fluid retention. An intravenous primer injection of the relevant tracer was followed by a sustained infusion over 4.5 h with the same radiopharmaceutical. Blood and urine samples were collected at fixed intervals.

RESULTS

^99m Tc-DTPA clearance reached steady state after 210 min (plasma clearance 78 ± 18 ml/min, urine clearance 110 ± 28 ml/min), whereas ^99m Tc-MAG₃  clearance achieved steady state after 150 min (plasma clearance 212 ± 56 ml/min, urine clearance 233 ± 59 ml/min).

CONCLUSION

Constant infusion technique with fixed primer and infusion rate using ^99m Tc-MAG₃ is feasible for research purposes. The longer time for reaching plasma steady state using ^99m Tc-DTPA makes CIT with this tracer less optimal. If the primer/sustained balance can be optimized, for example using a priori SIT information, ^99m Tc-DTPA as tracer for CIT may also be feasible.

Protective Effect of Red Okra (Abelmoschus esculentus (L.) Moench) Pods against Sodium Nitrite-Induced Liver Injury in Mice

Vegetables, drinking water, and preserved meats may contain sodium nitrite (NaNO₂), which causes liver disease by inducing oxidative stress. Phytochemicals are highly recommended as an alternative to synthetic drugs and affordable medicines to treat liver disease because they have fewer or no side effects. Therefore, this study aims to determine the antioxidant and hepatoprotective potential of red okra fruit ethanol extract against NaNO₂-induced liver damage. Thirty-six male mice were separated into six groups. The normal control group (WA) was given distilled water only, and the NaNO₂ (SN) group was given only 50 mg/kg BW NaNO₂. The other four groups (P1, P2, P3, and P4) were given NaNO₂ and red okra ethanol extract at doses of 25, 50, 75, and 100 mg/kg BW, respectively. Gavage was administered orally for 21 consecutive days. Commercial kits define all biochemical parameters according to the manufacturer's instructions. Liver tissue staining followed standard protocols using hematoxylin and eosin. The study revealed that NaNO₂ induction causes oxidative stress and damages the liver. The activity of antioxidant enzymes (superoxide dismutase and catalase) significantly increased in the groups treated (P2-P4) with ethanol extract of red okra (p < 0.05). Besides, the oxidants (malondialdehyde, F2-isoprostanes, and nitric oxide) in the liver homogenate significantly decreased in the P4 group, which were given red okra ethanol extract (p < 0.05). Likewise, red okra pods decreased significantly for the serum biochemical parameters of liver damage (aspartate aminotransferase, alkaline phosphatase, and alanine aminotransferase) in the P3 and P4 groups (p < 0.05). Then, it led to a restoration of the histological structure compared to exposed mice (SN), as the pathological scores decreased significantly in the P3 and P4 groups (p < 0.05), as well as the number of the necrotic and swollen liver cells was reduced. Hepatocytes returned to normal. The results showed that the ethanol extract of red okra fruit could be helpful as an affordable medicine. It is an antioxidant and hepatoprotective agent to protect the liver from damage caused by NaNO₂.

Nitrous anhydrase activity of carbonic anhydrase II: cysteine is required for nitric oxide (NO) dependent phosphorylation of VASP in human platelets

The carbonic anhydrase (CA) family does not only catalyse the reversible hydration of CO₂ to bicarbonate, but it also possesses esterase and phosphatase activity. Recently, bovine CA II and human CA II have been reported to convert inorganic nitrite (O=N-O⁻) to nitric oxide (NO) and nitrous anhydride (N₂O₃). Given the ability of NO to mediate vasodilation and inhibit platelet aggregation, this CA II activity would represent a bioactivation of nitrite. There are contradictory reports in the literature and the physiological role of CA II nitrite bioactivation is still disputed. Here, we provide new experimental data in support of the nitrous anhydrase activity of CA II and the key role L-cysteine in the bioactivation of nitrite by CA II. Using washed human platelets and by measuring VASP phosphorylation we provide evidence that exogenous nitrite (10 µM) is bioactivated to NO in a manner strongly depending on L-cysteine (100 and 200 µM). The process is not inhibitable by acetazolamide, a potent CA inhibitor. The contradictory results of recently published studies in this area are thoroughly discussed.

Side effects of acetazolamide: a systematic review and meta-analysis assessing overall risk and dose dependence

Introduction

Acetazolamide (AZM) is used for various conditions (eg, altitude sickness, sleep apnoea, glaucoma), but therapy is often limited by its side effect profile. Our objective was to estimate the risk of commonly reported side effects based on meta-analyses. We hypothesised that these risks are dose-dependent.

Methods

We queried MEDLINE/EMBASE (Medical Literature Analysis and Retrieval System Online/Excerpta Medica dataBASE) up until 04/10/2019, including any randomised placebo-controlled trial in which adults received oral AZM versus placebo reporting side effects. Eligibility assessment was performed by two independent reviewers. Data were abstracted by one reviewer who verified key entries at a second time point. For side effects reported by >3 studies a pooled effect estimate was calculated, and heterogeneity assessed via I²; for outcomes reported by >5 studies effect modification by total daily dose (EMbyTDD; <400 mg/d, 400–600 mg/d, >600 mg/d) was assessed via meta-regression. For pre-specified, primary outcomes (paraesthesias, taste disturbances, polyuria and fatigue) additional subgroup analyses were performed using demographics, intervention details, laboratory changes and risk of bias.

Results

We included 42 studies in the meta-analyses (N_subjects=1274/1211 in AZM/placebo groups). AZM increased the risk of all primary outcomes (p<0.01, I² ≤16% and low-to-moderate quality of evidence for all)—the numbers needed to harm (95% CI; n_Studies) for each were: paraesthesias 2.3 (95% CI 2 to 2.7; n=39), dysgeusia 18 (95% CI 10 to 38, n=22), polyuria 17 (95% CI 9 to 49; n=22), fatigue 11 (95% CI 6 to 24; n=14). The risk for paraesthesias (beta=1.8 (95% CI 1.1 to 2.9); P_EMbyTDD=0.01) and dysgeusia (beta=3.1 (95% CI 1.2 to 8.2); P_EMbyTDD=0.02) increased with higher AZM doses; the risk of fatigue also increased with higher dose but non-significantly (beta=2.6 (95% CI 0.7 to 9.4); P_EMbyTDD=0.14).

Discussion

This comprehensive meta-analysis of low-to-moderate quality evidence defines risk of common AZM side effects and corroborates dose dependence of some side effects. These results may inform clinical decision making and support efforts to establish the lowest effective dose of AZM for various conditions.

Nitric oxide signalling in kidney regulation and cardiometabolic health

The prevalence of cardiovascular and metabolic disease coupled with kidney dysfunction is increasing worldwide. This triad of disorders is associated with considerable morbidity and mortality as well as a substantial economic burden. Further understanding of the underlying pathophysiological mechanisms is important to develop novel preventive or therapeutic approaches. Among the proposed mechanisms, compromised nitric oxide (NO) bioactivity associated with oxidative stress is considered to be important. NO is a short-lived diatomic signalling molecule that exerts numerous effects on the kidneys, heart and vasculature as well as on peripheral metabolically active organs. The enzymatic L-arginine-dependent NO synthase (NOS) pathway is classically viewed as the main source of endogenous NO formation. However, the function of the NOS system is often compromised in various pathologies including kidney, cardiovascular and metabolic diseases. An alternative pathway, the nitrate-nitrite-NO pathway, enables endogenous or dietary-derived inorganic nitrate and nitrite to be recycled via serial reduction to form bioactive nitrogen species, including NO, independent of the NOS system. Signalling via these nitrogen species is linked with cGMP-dependent and independent mechanisms. Novel approaches to restoring NO homeostasis during NOS deficiency and oxidative stress have potential therapeutic applications in kidney, cardiovascular and metabolic disorders.

Oral nitrite treatment increases S-nitrosylation of vascular protein kinase C and attenuates the responses to angiotensin II

Nitrate and nitrite supplement deficient endogenous nitric oxide (NO) formation. While these anions may generate NO, recent studies have shown that circulating nitrite levels do not necessarily correlate with the antihypertensive effect of oral nitrite administration and that formation of nitrosylated species (RXNO) in the stomach is critically involved in this effect. This study examined the possibility that RXNO formed in the stomach after oral nitrite administration promotes target protein nitrosylation in the vasculature, inhibits vasoconstriction and the hypertensive responses to angiotensin II. Our results show that oral nitrite treatment enhances circulating RXNO concentrations (measured by ozone-based chemiluminescence methods), increases aortic protein kinase C (PKC) nitrosylation (measured by resin-assisted capture SNO-RAC method), and reduces both angiotensin II-induced vasoconstriction (isolated aortic ring preparation) and hypertensive (in vivo invasive blood pressure measurements) effects implicating PKC nitrosylation as a key mechanism for the responses to oral nitrite. Treatment of rats with the nitrosylating compound S-nitrosoglutathione (GSNO) resulted in the same effects described for oral nitrite. Moreover, partial depletion of thiols with buthionine sulfoximine prevented PKC nitrosylation and the blood pressure effects of oral nitrite. Further confirming a role for PKC nitrosylation, preincubation of aortas with GSNO attenuated the responses to both angiotensin II and to a direct PKC activator, and this effect was attenuated by ascorbate (reverses GSNO-induced nitrosylation). GSNO-induced nitrosylation also inhibited the increases in Ca2+ mobilization in angiotensin II-stimulated HEK293T cells expressing angiotensin type 1 receptor. Together, these results are consistent with the idea that PKC nitrosylation in the vasculature may underlie oral nitrite treatment-induced reduction in the vascular and hypertensive responses to angiotensin II.

•

Oral nitrite treatment exerts antihypertensive effects.

•

The mechanisms explaining such effects are not entirely known.

•

Oral nitrite treatment increases circulating concentrations of nitrosylating species.

•

Vascular PKC nitrosylation attenuates the vascular responses to angiotensin II.

The nitric oxide dependence of cutaneous microvascular function to independent and combined hypoxic cold exposure

When separated from local cooling, whole body cooling elicited cutaneous reflex vasoconstriction via mechanisms independent of nitric oxide removal. Hypoxia elicited cutaneous vasodilatation via mechanisms mediated primarily by nitric oxide synthase, rather than xanthine oxidase-mediated nitrite reduction. Cold-induced vasoconstriction was blunted by the opposing effect of hypoxic vasodilatation, whereas the underpinning mechanisms did not interrelate in the absence of local cooling. Full vasoconstriction was restored with nitric oxide synthase inhibition.

"Removal of nitrate and nitrite by hemodialysis in end-stage renal disease and by sustained low-efficiency dialysis in acute kidney injury"

BACKGROUND & PURPOSE

It is well established that end-stage renal disease (ESRD) is associated with increased cardiovascular morbidity and mortality both in the adult and pediatric population. Although the underlying molecular mechanisms are poorly understood, compromised nitric oxide (NO) bioactivity has been suggested as a contributing factor. With this in mind, we investigated the effects of hemodialysis on NO homeostasis and bioactivity in blood.

METHODS & RESULTS

Plasma and dialysate samples were obtained before and after hemodialysis sessions from adults (n = 33) and pediatric patients (n = 10) with ESRD on chronic renal replacement therapy, and from critically ill adults with acute kidney injury (n = 12) at their first sustained low-efficiency dialysis session. Levels of nitrate, nitrite, cyclic guanosine monophosphate (cGMP) and amino acids relevant for NO homeostasis were analyzed. We consistently found that nitrate and cGMP levels in plasma were significantly reduced after hemodialysis, whereas post-dialysis nitrite and amino acids coupled to NO synthase activity (i.e., arginine and citrulline) were only significantly reduced in adults with ESRD. The amount of excreted nitrate and nitrite during dialysis were similar to daily endogenous levels that would be expected from endothelial NO synthase activity.

CONCLUSIONS

Our results show that hemodialysis significantly reduces circulating levels of nitrate and cGMP, indicating that this medical procedure may impair NO synthesis and potentially NO signaling pathways.

Central blood pressure for the management of hypertension: Is it a practical clinical tool in current practice?

Since noninvasive central blood pressure (BP) measuring devices are readily available, central BP has gained growing attention regarding its clinical application in the management of hypertension. The disagreement between central and peripheral BP has long been recognized. Some previous studies showed that noninvasive central BP may be better than the conventional brachial BP in association with target organ damages and long-term cardiovascular outcomes. Recent studies further suggest that the central BP strategy for confirming a diagnosis of hypertension may be more cost-effective than the conventional strategy, and guidance of hypertension management with central BP may result in less use of medications to achieve BP control. Despite the use of central BP being promising, more randomized controlled studies comparing central BP-guided therapeutic strategies with conventional care for cardiovascular events reduction are required because noninvasive central and brachial BP measures are conveniently available. In this brief review, the rationale supporting the utility of central BP in clinical practice and relating challenges are summarized.

Post-exercise hypotension and skeletal muscle oxygenation is regulated by nitrate-reducing activity of oral bacteria

Post-exercise hypotension (PEH) is a common physiological phenomenon leading to lower blood pressure after acute exercise, but it is not fully understood how this intriguing response occurs. This study investigated whether the nitrate-reducing activity of oral bacteria is a key mechanism to trigger PEH. Following a randomized, double blind and crossover design, twenty-three healthy individuals (15 males/8 females) completed two treadmill trials at moderate intensity. After exercise, participants rinsed their mouth with antibacterial mouthwash to inhibit the activity of oral bacteria or a placebo mouthwash. Blood pressure was measured before, 1h and 2 h after exercise. The microvascular response to a reactive hyperaemia test, as well as blood and salivary samples were taken before and 2 h after exercise to analyse nitrate and nitrite concentrations and the oral microbiome. As expected, systolic blood pressure (SBP) was lower (1 h: -5.2 ± 1.0 mmHg; P < 0.001); 2 h: -3.8 ± 1.1 mmHg, P = 0.005) after exercise compared to baseline in the placebo condition. This was accompanied by an increase of circulatory nitrite 2 h after exercise (2h: 100 ± 13 nM) compared to baseline (59 ± 9 nM; P = 0.013). Additionally, an increase in the peak of the tissue oxygenation index (TOI) during the reactive hyperaemia response was observed after exercise (86.1 ± 0.6%) compared to baseline levels (84.8 ± 0.5%; P = 0.010) in the placebo condition. On the other hand, the SBP-lowering effect of exercise was attenuated by 61% at 1 h in the recovery period, and it was fully attenuated 2 h after exercise with antibacterial mouthwash. This was associated with a lack of changes in circulatory nitrite (P > 0.05), and impaired microvascular response (peak TOI baseline: 85.1 ± 3.1%; peak TOI post-exercise: 84.6 ± 3.2%; P > 0.05). Diversity of oral bacteria did not change after exercise in any treatment. These findings show that nitrite synthesis by oral commensal bacteria is a key mechanism to induce the vascular response to exercise over the first period of recovery thereby promoting lower blood pressure and greater muscle oxygenation.