Dietary nitrate reduces blood pressure and cerebral artery velocity fluctuations and improves cerebral autoregulation in transient ischemic attack patients

Cerebrovascular carbon dioxide reactivity is intact in chronic kidney disease

Chronic kidney disease (CKD) is characterized by an elevated risk for cerebrovascular disease including stroke. One mechanism that may contribute to this heightened risk is an impairment in cerebrovascular carbon dioxide reactivity (CVR). We compared CVR between CKD patients stages III-IV and controls (CON) without CKD but matched for hypertension and diabetes status. CVR was measured via 5% CO2 inhalation followed by voluntary hyperventilation in 14 CKD and 11 CON participants while mean arterial pressure, end-tidal carbon dioxide, and middle cerebral artery blood velocity (MCAv) were measured continuously. CVR was quantified as the linear relationship between etCO2 and MCAv. We observed no difference in CVR between groups. Hypercapnic CVR: CKD = 1.2 ± 0.9 cm/s/mm Hg, CON = 1.3 ± 0.8 cm/s/mm Hg, hypocapnic CVR: CKD = 1.3 ± 0.9 cm/s/mm Hg, CON = 1.5 ± 0.7 cm/s/mm Hg, integrated CVR: CKD = 1.5 ± 1.1 cm/s/mm Hg, CON = 1.7 ± 0.8 cm/s/mm Hg, p ≥ 0.48. Unexpectedly, CVR was inversely related to estimated glomerular filtration rate in CKD (R2 = 0.37, p = 0.02). We report that CVR remains intact in CKD and is inversely related to eGFR. These findings suggest that other mechanisms beyond CVR contribute to the elevated stroke risk observed in CKD.

Does dietary nitrate boost the effects of caloric restriction on brain health? Potential physiological mechanisms and implications for future research

Dementia is a highly prevalent and costly disease characterised by deterioration of cognitive and physical capacity due to changes in brain function and structure. Given the absence of effective treatment options for dementia, dietary and other lifestyle approaches have been advocated as potential strategies to reduce the burden of this condition. Maintaining an optimal nutritional status is vital for the preservation of brain function and structure. Several studies have recognised the significant role of nutritional factors to protect and enhance metabolic, cerebrovascular, and neurocognitive functions. Caloric restriction (CR) positively impacts on brain function via a modulation of mitochondrial efficiency, endothelial function, neuro-inflammatory, antioxidant and autophagy responses. Dietary nitrate, which serves as a substrate for the ubiquitous gasotransmitter nitric oxide (NO), has been identified as a promising nutritional intervention that could have an important role in improving vascular and metabolic brain regulation by affecting oxidative metabolism, ROS production, and endothelial and neuronal integrity. Only one study has recently tested the combined effects of both interventions and showed preliminary, positive outcomes cognitive function. This paper explores the potential synergistic effects of a nutritional strategy based on the co-administration of CR and a high-nitrate diet as a potential and more effective (than either intervention alone) strategy to protect brain health and reduce dementia risk.

Acute beetroot juice consumption does not alter cerebral autoregulation or cardiovagal baroreflex sensitivity during lower-body negative pressure in healthy adults

Introduction

Beetroot juice (BRJ) improves peripheral endothelial function and vascular compliance, likely due to increased nitric oxide bioavailability. It is unknown if BRJ alters cerebrovascular function and cardiovagal baroreflex control in healthy individuals.

Purpose

We tested the hypotheses that BRJ consumption improves cerebral autoregulation (CA) and cardiovagal baroreflex sensitivity (cBRS) during lower-body negative pressure (LBNP).

Methods

Thirteen healthy adults (age: 26 ± 4 years; 5 women) performed oscillatory (O-LBNP) and static LBNP (S-LBNP) before (PRE) and 3 h after consuming 500 mL of BRJ (POST). Participants inhaled 3% CO2 (21% O2, 76% N2) during a 5 min baseline and throughout LBNP to attenuate reductions in end-tidal CO2 tension (PETCO2). O-LBNP was conducted at ∼0.02 Hz for six cycles (-70 mmHg), followed by a 3-min recovery before S-LBNP (-40 mmHg) for 7 min. Beat-to-beat middle cerebral artery blood velocity (MCAv) (transcranial Doppler) and blood pressure were continuously recorded. CA was assessed using transfer function analysis to calculate coherence, gain, and phase in the very-low-frequency (VLF; 0.020-0.070 Hz) and low-frequency bands (LF; 0.07-0.20 Hz). cBRS was calculated using the sequence method. Comparisons between POST vs. PRE are reported as mean ± SD.

Results

During O-LBNP, coherence VLF was greater at POST (0.55 ± 0.06 vs. 0.46 ± 0.08; P < 0.01), but phase VLF (P = 0.17) and gain VLF (P = 0.69) were not different. Coherence LF and phase LF were not different, but gain LF was lower at POST (1.03 ± 0.20 vs. 1.12 ± 0.30 cm/s/mmHg; P = 0.05). During S-LBNP, CA was not different in the VLF or LF bands (all P > 0.10). Up-cBRS and Down-cBRS were not different during both LBNP protocols.

Conclusion

These preliminary data indicate that CA and cBRS during LBNP in healthy, young adults is largely unaffected by an acute bolus of BRJ.

Modulation of oxidative neurometabolism in ischemia/reperfusion by nitrite

Nitrite has been viewed essentially as an inert metabolic endpoint of nitric oxide (^•NO). However, under certain conditions, nitrite can be a source of ^•NO. In the brain, this alternative source of ^•NO production independent of nitric oxide synthase activity may be particularly relevant in ischemia/reperfusion (I/R), where low oxygen availability limits enzymatic production of ^•NO. Notably, in vivo concentration of nitrite can be easily increased with diet, through the ingestion of nitrate-rich foods, opening the window for a therapeutic intervention based on diet. Considering the modulation of mitochondrial respiration by ^•NO, we have hypothesized that the protective action of nitrite in I/R may also result from modulation of mitochondrial function. We used high-resolution respirometry to evaluate the effects of nitrite in two in vitro models of I/R. In both cases, an increase in oxygen flux was observed following reoxygenation, a phenomenon that has been coined "oxidative burst". The amplitude of this "oxidative burst" was decreased by nitrite in a concentration-dependent manner. Additionally, a pilot in vivo study in which animals received a nitrate-rich diet as a strategy to increase circulating and tissue levels of nitrite also revealed that the "oxidative burst" was decreased in the nitrate-treated animals. These results may provide mechanistic support to the observation of a protective effect of nitrite in situations of brain ischemia.

Dietary nitrate and brain health. Too much ado about nothing or a solution for dementia prevention?

Dementia is a significant public health priority with approximately 55 million cases worldwide, and this number is predicted to quadruple by 2050. Adherence to a healthy diet and achieving optimal nutritional status are vital strategies to improve brain health. The importance of this area of research has been consolidated into the new term ‘nutritional psychiatry’. Dietary nitrate, closely associated with the intake of fruits and vegetables, is a compound that is increased in dietary patterns such as the Mediterranean and MIND diets and has protective effects on cognition and brain health. Nitrate is characterised by a complex metabolism and is the precursor of the nitrate–nitrite–nitric oxide (NO) pathway contributing to systemic NO generation. A higher intake of dietary nitrate has been linked to protective effects on vascular outcomes including blood pressure and endothelial function. However, the current evidence supporting the protective effects of dietary nitrate on brain health is less convincing. This article aims to provide a critical appraisal of the current evidence for dietary nitrate supplementation for improving brain health and provide suggestions for future research.

Nitrate Metabolism and Ischemic Cerebrovascular Disease: A Narrative Review

Inorganic and organic nitrates are present in vivo and in vitro. Inorganic nitrate is considered a pool of nitric oxide (NO), but it can be converted into nitrite and NO through various mechanisms. It plays an important role in the regulation of complex physiological and biochemical reactions, such as anti-inflammatory processes and the inhibition of platelet aggregation, which are closely related to the pathology and treatment of cerebrovascular disease. Ischemic cerebrovascular disease is characterized by high incidence, recurrence, and disability rates. Nitrate, nitrite, and NO were recently found to be involved in cerebrovascular disease. In this review, we describe the relationship between cerebrovascular disease and nitrate metabolism to provide a basis for further advances in laboratory and clinical medicine.

Integrative cerebral blood flow regulation in ischemic stroke

Optimizing cerebral perfusion is key to rescuing salvageable ischemic brain tissue. Despite being an important determinant of cerebral perfusion, there are no effective guidelines for blood pressure (BP) management in acute stroke. The control of cerebral blood flow (CBF) involves a myriad of complex pathways which are largely unaccounted for in stroke management. Due to its unique anatomy and physiology, the cerebrovascular circulation is often treated as a stand-alone system rather than an integral component of the cardiovascular system. In order to optimize the strategies for BP management in acute ischemic stroke, a critical reappraisal of the mechanisms involved in CBF control is needed. In this review, we highlight the important role of collateral circulation and re-examine the pathophysiology of CBF control, namely the determinants of cerebral perfusion pressure gradient and resistance, in the context of stroke. Finally, we summarize the state of our knowledge regarding cardiovascular and cerebrovascular interaction and explore some potential avenues for future research in ischemic stroke.

Effect of drug interventions on cerebral hemodynamics in ischemic stroke patients

The ischemic penumbra is sensitive to alterations in cerebral perfusion. A myriad of drugs are used in acute ischemic stroke (AIS) management, yet their impact on cerebral hemodynamics is poorly understood. As part of the Cerebral Autoregulation Network led INFOMATAS project (Identifying New Targets for Management and Therapy in Acute Stroke), this paper reviews some of the most common drugs a patient with AIS will come across and their potential influence on cerebral hemodynamics with a particular focus being on cerebral autoregulation (CA). We first discuss how compounds that promote clot lysis and prevent clot formation could potentially impact cerebral hemodynamics, before focusing on how the different classes of antihypertensive drugs can influence cerebral hemodynamics. We discuss the different properties of each drug and their potential impact on cerebral perfusion and CA. With emerging interest in CA status of AIS patients, either during or soon after treatment when timely reperfusion and salvageable tissue is at its most critical, the properties of these pharmacological agents may be relevant for modelling cerebral perfusion accuracy and for setting individualised treatment strategies.