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Acute Blood Pressure Lowering, Vasoprotective, and Antiplatelet Properties of Dietary Nitrate via Bioconversion to Nitrite

Diets rich in fruits and vegetables reduce blood pressure (BP) and the risk of adverse cardiovascular events. However, the mechanisms of this effect have not been elucidated. Certain vegetables possess a high nitrate content, and we hypothesized that this might represent a source of vasoprotective nitric oxide via bioactivation. In healthy volunteers, approximately 3 hours after ingestion of a dietary nitrate load (beetroot juice 500 mL), BP was substantially reduced (&Dgr;max −10.4/8 mm Hg); an effect that correlated with peak increases in plasma nitrite concentration. The dietary nitrate load also prevented endothelial dysfunction induced by an acute ischemic insult in the human forearm and significantly attenuated ex vivo platelet aggregation in response to collagen and ADP. Interruption of the enterosalivary conversion of nitrate to nitrite (facilitated by bacterial anaerobes situated on the surface of the tongue) prevented the rise in plasma nitrite, blocked the decrease in BP, and abolished the inhibitory effects on platelet aggregation, confirming that these vasoprotective effects were attributable to the activity of nitrite converted from the ingested nitrate. These findings suggest that dietary nitrate underlies the beneficial effects of a vegetable-rich diet and highlights the potential of a “natural” low cost approach for the treatment of cardiovascular disease.

Inorganic Nitrate Supplementation Lowers Blood Pressure in Humans. Role for Nitrite-Derived NO

Ingestion of dietary (inorganic) nitrate elevates circulating and tissue levels of nitrite via bioconversion in the entero-salivary circulation. In addition, nitrite is a potent vasodilator in humans, an effect thought to underlie the blood pressure–lowering effects of dietary nitrate (in the form of beetroot juice) ingestion. Whether inorganic nitrate underlies these effects and whether the effects of either naturally occurring dietary nitrate or inorganic nitrate supplementation are dose dependent remain uncertain. Using a randomized crossover study design, we show that nitrate supplementation (KNO3 capsules: 4 versus 12 mmol [n=6] or 24 mmol of KNO3 (1488 mg of nitrate) versus 24 mmol of KCl [n=20]) or vegetable intake (250 mL of beetroot juice [5.5 mmol nitrate] versus 250 mL of water [n=9]) causes dose-dependent elevation in plasma nitrite concentration and elevation of cGMP concentration with a consequent decrease in blood pressure in healthy volunteers. In addition, post hoc analysis demonstrates a sex difference in sensitivity to nitrate supplementation dependent on resting baseline blood pressure and plasma nitrite concentration, whereby blood pressure is decreased in male volunteers, with higher baseline blood pressure and lower plasma nitrite concentration but not in female volunteers. Our findings demonstrate dose-dependent decreases in blood pressure and vasoprotection after inorganic nitrate ingestion in the form of either supplementation or by dietary elevation. In addition, our post hoc analyses intimate sex differences in nitrate processing involving the entero-salivary circulation that are likely to be major contributing factors to the lower blood pressures and the vasoprotective phenotype of premenopausal women.

Postconditioning protects against human endothelial ischaemia–reperfusion injury via subtype-specific KATP channel activation and is mimicked by inhibition of the mitochondrial permeability transition pore

AIMS Intermittent early reperfusion (ischaemic postconditioning; PostC) reduces ischaemia-reperfusion (IR) injury. Using an in vivo model of endothelial IR injury in humans, we sought to determine the role of K(ATP) channels in PostC and whether inhibition of the mitochondrial permeability transition pore (mPTP) at the onset of reperfusion protected against endothelial IR injury. METHODS AND RESULTS Endothelial function (EF) in healthy volunteers was assessed using vascular ultrasound to measure the percentage increase in the diameter of the brachial artery in response to reactive hyperaemia [flow-mediated dilatation (FMD)]. In resistance vessels, venous occlusion plethysmography was used to measure the dilator response to acetylcholine (ACh) [area under ACh dose-response curve (ACh AUC)]. Measurements were made before and after IR injury. Ischaemic postconditioning consisted of three 10 s cycles of alternating ischaemia and reperfusion in the first minute of reperfusion. Oral glibenclamide and glimepiride were used to determine the role of K(ATP) channel subtypes in PostC. Intra-arterial cyclosporine was used to determine the role of mPTP in endothelial IR injury. Ischaemia-reperfusion reduced EF in the brachial artery (FMD 7.1 ± 0.9% pre-IR, 2.8 ± 0.4% post-IR; P < 0.001) and resistance vessels [ACh AUC (×10(4)) 2.1 ± 0.4 pre-IR, 1.5 ± 0.2 post-IR; P < 0.05]. Ischaemic postconditioning preserved EF in the brachial artery [FMD 6.8 ± 0.9% (P < 0.001 vs. post-IR)] and resistance vessels [ACh AUC (×10(4)) 1.9 ± 0.2 (P < 0.001 vs. post-IR)]. Protection by PostC was abolished by glibenclamide in the brachial artery [FMD 3.3 ± 0.2% (P < 0.001 vs. post-IR + PostC)] and in resistance vessels [ACh AUC (×10(4)) 1.1 ± 0.2 (P < 0.001 vs. post-IR + PostC)], whereas glimepiride had no effect. Cyclosporine preserved EF after IR injury in the resistance vessels [ACh AUC (×10(4)) 1.4 ± 0.2 post-IR vs. 2.2 ± 0.3 post-IR + cyclosporine; P < 0.05]. CONCLUSION Protection by PostC against endothelial IR injury in humans depends on K(ATP) channel activation and is mimicked by inhibition of the mPTP at reperfusion.

Increased arterial stiffness in HIV-infected children: risk factors and antiretroviral therapy

BACKGROUND Recent evidence suggests that both the HIV virus and antiretroviral therapy (ART) are associated with premature atherosclerosis in adults. Increased arterial stiffness as assessed by pulse wave velocity (PWV) has been associated with adverse cardiovascular outcome in adults. The relationship between HIV infection and treatment and arterial stiffness has not been evaluated in children. METHODS We studied 83 HIV-infected children with a mean +/-sd age of 11.0 +/-3.1 years and 59 controls aged 12.2 +/-2.8 years. Among the HIV-infected children, 48 were receiving ART (23 including a protease inhibitor). Arterial stiffness was assessed non-invasively by carotid-radial PWV. Disease severity was defined according to the CDC classification. RESULTS PWV was significantly increased in HIV-infected children compared with controls (P<0.05). A significant association between age and PWV was noted in HIV-infected children but not in controls. HIV-infected children receiving ART had significantly increased total cholesterol levels and PWV compared with non-treated children (P<0.001 and P<0.05, respectively). CDC stage was greater in ART-treated compared with non-treated HIV-infected children (P<0.001). No differences in other cardiovascular risk factors were noted in the two groups. After multivariable analysis, ART, systolic blood pressure, disease severity and total cholesterol remained independent predictors of PWV. CONCLUSIONS HIV-infected children have increased arterial stiffness compared with healthy children. These changes were more pronounced with increasing age in HIV-infected children particularly in those who were receiving ART.

Reciprocal regulation of human soluble and particulate guanylate cyclases in vivo

We demonstrated previously that reciprocal regulation of soluble (sGC) and particulate (pGC) guanylate cyclases by NO and natriuretic peptides coordinates cyclic cGMP‐mediated vasodilatation in vitro. Herein, we investigated whether such an interaction contributes to vascular homeostasis in mice and humans in vivo.

Comparison of two automatic methods for the assessment of brachial artery flow-mediated dilation.

Objectives Brachial artery flow-mediated dilation (FMD) is associated with risk factors providing information on cardiovascular prognosis. Despite the large effort to standardize the methodology, the FMD examination is still characterized by problems of reproducibility and reliability that can be partially overcome with the use of automatic systems. We developed real-time software for the assessment of brachial FMD (FMD Studio, Institute of Clinical Physiology, Pisa, Italy) from ultrasound images. The aim of this study is to compare our system with another automatic method (Brachial Analyzer, MIA LLC, IA, USA) which is currently considered as a reference method in FMD assessment. Methods The agreement between systems was assessed as follows. Protocol 1: Mean baseline (Basal), maximal (Max) brachial artery diameter after forearm ischemia and FMD, calculated as maximal percentage diameter increase, have been evaluated in 60 recorded FMD sequences. Protocol 2: Values of diameter and FMD have been evaluated in 618 frames extracted from 12 sequences. Results All biases are negligible and standard deviations of the differences are satisfactory (protocol 1: −0.27 ± 0.59%; protocol 2: −0.26 ± 0.61%) for FMD measurements. Analysis times were reduced (−33%) when FMD Studio is used. Rejected examinations due to the poor quality were 2% with the FMD Studio and 5% with the Brachial Analyzer. Conclusions In conclusion, the compared systems show a optimal grade of agreement and they can be used interchangeably. Thus, the use of a system characterized by real-time functionalities could represent a referral method for assessing endothelial function in clinical trials.

Endothelial response to childhood infection: The role of mannose-binding lectin (MBL)

OBJECTIVE To assess the influence of mannose-binding lectin (MBL) genotype on endothelial function in the presence and absence of infection in childhood. METHODS We studied 2176 children aged 10 years drawn from the Avon Longitudinal Study of Parents and Children. Endothelial function was assessed by flow mediated dilatation (FMD). Exon 1 and promoter polymorphisms in the MBL gene were determined by heteroduplexing procedures. Children were classified as AA (wild type) AO (heterozygotes) and OO (homozygotes). RESULTS During the vascular assessment, 544 children presented with current or recent (<2 weeks) infection (INF). FMD was reduced in the INF group compared to controls (10% reduction in FMD, p<0.001). MBL genotype was not associated with FMD in controls, although a relationship with the degree of impairment during INF was observed (8.0%, 7.6% and 26.6% lower FMD compared to controls for groups AA, AO, OO respectively, p<0.05). After multivariate analysis, OO was associated with reduced FMD in the INF group (odds ratio 2.95 [1.33, 6.52], p<0.001). CONCLUSION Homozygosity for MBL variant alleles is associated with greater impairment in FMD during infection in childhood. This suggests a gene-environment interaction operating in early life that may have relevance for the initiation and progression of atherosclerosis.