[Show abstract][Hide abstract] ABSTRACT: The endothelium plays a fundamental role in maintaining vascular homeostasis by releasing factors that regulate local blood flow, systemic blood pressure, and the reactivity of leukocytes and platelets. Accordingly, endothelial dysfunction underpins many cardiovascular diseases, including hypertension, myocardial infarction, and stroke. Herein, we evaluated mice with endothelial-specific deletion of Nppc, which encodes C-type natriuretic peptide (CNP), and determined that this mediator is essential for multiple aspects of vascular regulation. Specifically, disruption of CNP leads to endothelial dysfunction, hypertension, atherogenesis, and aneurysm. Moreover, we identified natriuretic peptide receptor-C (NPR-C) as the cognate receptor that primarily underlies CNP-dependent vasoprotective functions and developed small-molecule NPR-C agonists to target this pathway. Administration of NPR-C agonists promotes a vasorelaxation of isolated resistance arteries and a reduction in blood pressure in wild-type animals that is diminished in mice lacking NPR-C. This work provides a mechanistic explanation for genome-wide association studies that have linked the NPR-C (Npr3) locus with hypertension by demonstrating the importance of CNP/NPR-C signaling in preserving vascular homoeostasis. Furthermore, these results suggest that the CNP/NPR-C pathway has potential as a disease-modifying therapeutic target for cardiovascular disorders.
[Show abstract][Hide abstract] ABSTRACT: -Pulmonary hypertension (PH) is a life-threatening disorder characterized by increased pulmonary artery pressure, remodeling of the pulmonary vasculature, and right ventricular failure. Loss of endothelium-derived nitric oxide (NO) and prostacyclin (PGI2) contributes to PH pathogenesis and current therapies are targeted to restore these pathways. Phosphodiesterases (PDEs) are a family of enzymes that break down cGMP and cAMP which underpin the bioactivity of NO and PGI2. The PDE5 inhibitor (PDE5i) sildenafil is licensed for PH, but a role for PDE2 in lung physiology and disease has yet to be established. Herein, we investigated whether PDE2 inhibition modulates pulmonary cyclic nucleotide signaling and ameliorates experimental PH.
[Show abstract][Hide abstract] ABSTRACT: Background and purposeIdiopathic pulmonary fibrosis (IPF) is a progressive fibro-proliferative disorder refractory to current therapy commonly complicated by the development of pulmonary hypertension (PH); the associated morbidity and mortality are substantial. Natriuretic peptides possess vasodilator and anti-fibrotic actions, and pharmacological augmentation of their bioactivity ameliorates renal and myocardial fibrosis. Herein, we investigated whether natriuretic peptides possess an intrinsic cytoprotective function offsetting the development of pulmonary fibrosis and associated PH, and whether therapeutics targeting natriuretic peptide signalling demonstrate efficacy in this life-threatening disorder.Experimental approachPulmonary haemodynamics, right ventricular function, and markers of lung fibrosis were determined in wild type (WT) and natriuretic peptide receptor (NPR)-A knockout (KO) mice exposed to bleomycin (1mg/kg). Human myofibroblast differentiation was studied in vitro.Key resultsExacerbated cardiac, vascular and fibrotic pathology was observed in NPR-A KO animals, compared to WT mice, exposed to bleomycin. Treatment with a drug combination that raised circulating natriuretic peptide levels (ecadotril) and potentiated natriuretic peptide-dependent signalling (sildenafil) reduced indices of disease progression, whether administered prophylactically or to animals with established lung disease; this positive pharmacodynamic effect was diminished in NPR-A KO mice. Atrial natriuretic peptide and sildenafil synergistically reduced transforming growth factor-β-induced human myofibroblast differentiation, a key driver of remodelling in IPF patients.Conclusions and implicationsThese data highlight an endogenous host-defence capacity of natriuretic peptides in lung fibrosis and PH. An ecadotril/sildenafil combination is effective in reversing the pulmonary haemodynamic aberrations and remodelling that characterize the disease, advocating therapeutic manipulation of natriuretic peptide bioactivity in IPF.
British Journal of Pharmacology 03/2014; · 5.07 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: There is an increasing need to understand the leukocytes and soluble mediators that drive acute inflammation and bring about its resolution in humans. We therefore carried out an extensive characterisation of the cantharidin skin blister model in healthy male volunteers. A novel fluorescence staining protocol was designed and implemented, which facilitated the identification of cell populations by flow cytometry. We observed that at the onset phase, 24 h after blister formation, the predominant cells were CD16hi/CD66b+ PMNs followed by HLA-DR+/CD14+ monocytes/macrophages, CD11c+ and CD141+ dendritic cells as well as Siglec-8+ eosinophils. CD3+ T cells, CD19+ B cells and CD56+ NK cells were also present, but in comparatively fewer numbers. During resolution, 72 h following blister induction, numbers of PMNs declined whilst the numbers of monocyte/macrophages remain unchanged, though they upregulated expression of CD16 and CD163. In contrast, the overall numbers of dendritic cells and Siglec-8+ eosinophils increased. Post hoc analysis of these data revealed that of the inflammatory cytokines measured, TNF-α but not IL-1β or IL-8 correlated with increased PMN numbers at the onset. Volunteers with the greatest PMN infiltration at onset displayed the fastest clearance rates for these cells at resolution. Collectively, these data provide insight into the cells that occupy acute resolving blister in humans, the soluble mediators that may control their influx as well as the phenotype of mononuclear phagocytes that predominate the resolution phase. Further use of this model will improve our understanding of the evolution and resolution of inflammation in humans, how defects in these over-lapping pathways may contribute to the variability in disease longevity/chronicity, and lends itself to the screen of putative anti-inflammatory or pro-resolution therapies.
PLoS ONE 01/2014; 9(3):e89375. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To evaluate the comparative efficacy (50% reduction in seizure frequency) and tolerability (premature withdrawal due to adverse events) of antiepileptic drugs (AEDs) for refractory epilepsy. METHODS: We searched Cochrane Central Register of Controlled Trials (Cochrane Library 2009, issue 2) including Epilepsy Group's specialised register; MEDLINE (1950 to March 2009); EMBASE (1980 to March 2009); and Current Contents Connect (1998 to March 2009) to conduct a systematic review of published studies, developed a treatment network and undertook a network meta-analysis. RESULTS: Forty-two eligible trials with 6346 patients and 12 interventions, including placebo, contributed to the analysis. Only two direct drug comparator trials were identified, the remaining 40 trials being placebo-controlled. Conventional random-effects meta-analysis indicated all drugs were superior in efficacy to placebo (overall odds ratio [OR] 3.78 [95% CI 3.14 to 4.55]) but did not permit firm distinction between drugs on the basis of the efficacy or tolerability. A Bayesian network meta-analysis prioritised oxcarbazepine, topiramate and pregabalin on the basis of short-term efficacy. However, sodium valproate, levetiracetam, gabapentin and vigabatrin were prioritised on the basis of short-term efficacy and tolerability, with the caveat that vigabatrin is recognised as being associated with serious visual disturbance with chronic use. CONCLUSION: Of the wide range of AEDs licensed for the treatment of refractory epilepsy, sodium valproate, levetiracetam, and gabapentin demonstrated the best balance of efficacy and tolerability. Until regulators mandate greater use of active-comparator trials with longer term follow-up, network meta-analysis provides the only available means to quantify these clinically important parameters.
British Journal of Clinical Pharmacology 01/2013; · 3.58 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Pulmonary hypertension (PH) is a debilitating disease with a dismal prognosis. Recent advances in therapy (e.g. prostacyclin analogues, endothelin receptor antagonists and phosphodiesterase 5 inhibitors), whilst significantly improving survival, simply delay the inexorable progression of the disease. An array of endogenous vasoconstrictors and vasodilators coordinates to maintain pulmonary vascular homeostasis and morphological integrity, and an imbalance in the expression and function of these mediators precipitates PH and related lung diseases. The vasodilator peptides, including natriuretic peptides, vasoactive intestinal peptide, calcitonin gene-related peptide and adrenomedullin, trigger the production of cyclic nucleotides (e.g. cGMP and cAMP) in many pulmonary cell types, which in tandem exert a multifaceted protection against the pathogenesis of PH, encompassing vasodilatation, inhibition of vascular smooth muscle proliferation, anti-inflammatory and anti-fibrotic effects and salutary actions on the right ventricle. This coordinated beneficial activity underpins a contemporary perception that to advance treatment of PH it is necessary to offset multiple disease mechanisms (i.e. the pulmonary vasoconstriction, pulmonary vascular remodelling, right ventricular dysfunction). Thus, there is considerable potential for harnessing the favourable activity of peptide mediators to offer a novel, efficacious therapeutic approach in PH.
Handbook of experimental pharmacology 01/2013; 218:477-511.
[Show abstract][Hide abstract] ABSTRACT: Mechanistic studies may be defined as ‘an experiment, using an intervention in healthy subjects or patients, to better understand human biology and/or disease’. Such studies provide useful physiological insights into clinical conditions in humans and expand our knowledge of physiology in health and disease. Well-planned mechanistic studies are therefore a vital step in progressing drug discovery in humans. It is important in such studies that the rights and safety of research participants are preserved, while at the same time not allowing lengthy and complex approval procedures to stifle and potentially prohibit this type of research.
[Show abstract][Hide abstract] ABSTRACT: Pulmonary hypertension (PH) is a multifactorial disease characterized by increased pulmonary vascular resistance and right ventricular failure; morbidity and mortality remain unacceptably high. Loss of nitric oxide (NO) bioactivity is thought to contribute to the pathogenesis of PH, and agents that augment pulmonary NO signaling are clinically effective in the disease. Inorganic nitrate (NO(3)(-)) and nitrite (NO(2)(-)) elicit a reduction in systemic blood pressure in healthy individuals; this effect is underpinned by endogenous and sequential reduction to NO. Herein, we determined whether dietary nitrate and nitrite might be preferentially reduced to NO by the hypoxia associated with PH, and thereby offer a convenient, inexpensive method of supplementing NO functionality to reduce disease severity.
Dietary nitrate reduced the right ventricular pressure and hypertrophy, and pulmonary vascular remodeling in wild-type mice exposed to 3 weeks of hypoxia; this beneficial activity was mirrored largely by dietary nitrite. The cytoprotective effects of dietary nitrate were associated with increased plasma and lung concentrations of nitrite and cGMP. The beneficial effects of dietary nitrate and nitrite were reduced in mice lacking endothelial NO synthase or treated with the xanthine oxidoreductase inhibitor allopurinol.
These data demonstrate that dietary nitrate, and to a lesser extent dietary nitrite, elicit pulmonary dilatation, prevent pulmonary vascular remodeling, and reduce the right ventricular hypertrophy characteristic of PH. This favorable pharmacodynamic profile depends on endothelial NO synthase and xanthine oxidoreductase -catalyzed reduction of nitrite to NO. Exploitation of this mechanism (ie, dietary nitrate/nitrite supplementation) represents a viable, orally active therapy for PH.
[Show abstract][Hide abstract] ABSTRACT: Ischemia-reperfusion injury is a composite of damage accumulated during reduced perfusion of an organ or tissue and the additional insult sustained during reperfusion. Such injury occurs in a wide variety of clinically important syndromes, such as ischemic heart disease and stroke, which are responsible for a high degree of morbidity and mortality worldwide. Basic research has identified a number of interventions that stimulate innate resistance of tissues to ischemia-reperfusion injury. Here, we summarise the experimental and clinical trial data underpinning one of these "conditioning" strategies, the phenomenon of remote ischemic preconditioning.
Cardiology research and practice. 01/2012; 2012:620681.
[Show abstract][Hide abstract] ABSTRACT: The UK National Health Service (NHS) currently spends in excess of £250 million per annum on angiotensin II receptor blockers (ARBs) for the treatment of hypertension and heart failure; with candesartan currently dominating the market. With the recent introduction of generic losartan, we set out to directly compare the branded market leader to its now cheaper alternative. The primary objectives were to compare the blood pressure (BP) lowering efficacy and cardiovascular outcomes of candesartan and losartan in the treatment of essential hypertension and chronic heart failure, respectively. The secondary objective was to model their comparative incremental cost-effectiveness in a UK NHS setting. The Cochrane Central Register of Controlled Trials (Cochrane Library 2009, issue 2), which contains the Hypertension and Heart Group's specialist register, Medline (1950-February 2010), and Embase (1980-February 2010) were included in the search strategy. Selection criteria were randomised studies of candesartan versus losartan in adults (> 18 years). The main outcome measures were as follows: Hypertension: mean change from baseline in trough (24 h postdose) systolic and diastolic BP. Heart failure: composite of cardiovascular death and hospital admission for management of heart failure. Two reviewers applied inclusion criteria, assessed trial quality, and extracted data. Eight (three of which met inclusion criteria) and zero trials compared candesartan directly with losartan in the treatment of hypertension and heart failure, respectively. A between-treatment difference of -1.96 mmHg [95% confidence interval (CI) -2.40 to -1.51] for trough diastolic BP and -3.00 mmHg (95% CI -3.79 to -2.22) for trough systolic BP in favour of candesartan was observed. Based on this differential, a 10-year Markov model estimates the cost per quality-adjusted life-year gained to exceed £40,000 for using candesartan in place of generic losartan. Candesartan reduces BP to a slightly greater extent when compared with losartan, however, such difference is unlikely to be cost-effective based on current acquisition costs, perceived NHS affordability thresholds and use of combination regimens. We could find no robust evidence supporting the superiority of candesartan over losartan in the treatment of heart failure. We therefore recommend using generic losartan as the ARB of choice which could save the UK NHS approximately £200 million per annum in drug costs.
International Journal of Clinical Practice 03/2011; 65(3):253-63. · 2.43 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ischemic preconditioning (IPC) is a mechanism protecting tissues from injury during ischemia and reperfusion. Remote IPC (RIPC) can be elicited by applying brief periods of ischemia to tissues with ischemic tolerance, thus protecting vital organs more susceptible to ischemic damage. Using a porcine model, we determined whether RIPC of the limb is protective against brain injury caused by hypothermic circulatory arrest (HCA).
Twelve piglets were randomized to control and RIPC groups. RIPC was induced in advance of cardiopulmonary bypass by 4 cycles of 5 minutes of ischemia of the hind limb. All animals underwent cardiopulmonary bypass followed by 60 minutes of HCA at 18°C. Brain metabolism and electroencephalographic activity were monitored for 8 hours after HCA. Assessment of neurological status was performed for a week postoperatively. Finally, brain tissue was harvested for histopathological analysis. Study groups were balanced for baseline and intraoperative parameters. Brain lactate concentration was significantly lower (P<0.0001, ANOVA) and recovery of electroencephalographic activity faster (P<0.05, ANOVA) in the RIPC group. RIPC had a beneficial effect on neurological function during the 7-day follow-up (behavioral score; P<0.0001 versus control, ANOVA). Histopathological analysis demonstrated a significant reduction in cerebral injury in RIPC animals (injury score; mean [interquartile range]: control 5.8 [3.8 to 7.5] versus RIPC 1.5 [0.5 to 2.5], P<0.001, t test).
These data demonstrate that RIPC protects the brain against HCA-induced injury, resulting in accelerated recovery of neurological function. RIPC might be neuroprotective in patients undergoing surgery with HCA and improve long-term outcomes. Clinical trials to test this hypothesis are warranted.
[Show abstract][Hide abstract] ABSTRACT: 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.
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].
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.
European Heart Journal 02/2011; 32(10):1266-74. · 14.10 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Pulmonary hypertension (PH) is a debilitating disease with a poor prognosis. Therapeutic options remain limited despite the introduction of prostacyclin analogues, endothelin receptor antagonists and phosphodiesterase 5 inhibitors within the last 15 years; these interventions address predominantly the endothelial and vascular dysfunctionS associated with the condition, but simply delay progression of the disease rather than offer a cure. In an attempt to improve efficacy, emerging approaches have focused on targeting the pro-proliferative phenotype that underpins the pulmonary vascular remodelling in the lung and contributes to the impaired circulation and right heart failure. Many novel targets have been investigated and validated in animal models of PH, including modulation of guanylate cyclases, phosphodiesterases, tyrosine kinases, Rho kinase, bone morphogenetic proteins signalling, 5-HT, peroxisome proliferator activator receptors and ion channels. In addition, there is hope that combinations of such treatments, harnessing and optimizing vasodilator and anti-proliferative properties, will provide a further, possibly synergistic, increase in efficacy; therapies directed at the right heart may also offer an additional benefit. This overview highlights current therapeutic options, promising new therapies, and provides the rationale for a combination approach to treat the disease.
British Journal of Pharmacology 12/2010; 163(1):125-40. · 5.07 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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 (KNO(3) capsules: 4 versus 12 mmol [n=6] or 24 mmol of KNO(3) (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.
[Show abstract][Hide abstract] ABSTRACT: Reactive oxygen species have been implicated in the pathogenesis of ischemia/reperfusion (IR) injury. Recent studies suggest that NADPH oxidase may be a source of ROS during IR. Using an in vivo model of endothelial IR injury in the arm, we compared the response to IR in healthy volunteers with that in patients with chronic granulomatous disease. These patients have a molecular lesion in a subunit of NADPH oxidase that renders the enzyme inactive.
Flow-mediated dilatation was used to assess endothelial function in patients with X-linked (NOX2) or autosomal (p47) chronic granulomatous disease. IR injury was induced by 20 minutes of upper limb ischemia followed by reperfusion. Flow-mediated dilatation was determined before IR and after 20 minutes of reperfusion. The response to IR in chronic granulomatous disease patients was compared with that in age- and sex-matched healthy control subjects. Flow-mediated dilatation was expressed as mean and compared statistically with mixed linear models. IR caused a significant reduction in flow-mediated dilatation in control subjects (-5.1%; 95% confidence interval, 6.3 to 3.%; P<0.001; n=11). IR had no effect on endothelial function in NOX2-chronic granulomatous disease patients (-0.9; 95% confidence interval, -2.1 to 0.3; P=0.12; n=11). Similarly, IR-induced reduction in flow-mediated dilatation was not observed in p47-chronic granulomatous disease patients (-1.5%; 95% confidence interval, -3.1 to 0.2; P=0.08; n=6) in contrast to healthy control subjects (-6.5%; 95% confidence interval, -8.2 to -4.9%; P<0.001; n=6).
These data indicate, for the first time in humans in vivo, that reactive oxygen species produced by NADPH oxidase are determinants of endothelial function after IR injury in humans. These findings have implications for the design of strategies to limit clinical IR injury.
[Show abstract][Hide abstract] ABSTRACT: A recent communication from the United States Food and Drug Administration highlighted a possible increased risk of stroke associated with use of the relatively new inhaled anticholinergic drug, tiotropium bromide. Using the United Kingdom General Practice Research Database, we set out to assess the risk of stroke in individuals exposed to inhaled tiotropium bromide and two other inhaled treatments for airways disease.
We used the self-controlled case-series that reduces confounding and minimizes the potential for biases in the quantification of risk estimates.
Of 1043 people with a diagnosis of incident stroke who had had at least one prescription for tiotropium bromide, 980 satisfied inclusion criteria. The age-adjusted incidence rate ratio for all-cause stoke in individuals exposed to tiotropium bromide (n = 980), ipratropium bromide (n = 4181) and fluticasone propionate/salmeterol xinafoate (n = 1000) was 1.1 [95% confidence interval (CI) 0.9, 1.3], 0.8 (95% CI 0.7, 0.9) and 1.0 (95% CI 0.9, 1.2), respectively.
We found no evidence of an increased risk of all-cause stroke for individuals exposed to commonly prescribed inhaled treatments for chronic obstructive pulmonary disease.
British Journal of Clinical Pharmacology 11/2009; 68(5):731-6. · 3.58 Impact Factor