Purinergic transmission in blood vessels

Extracellular nucleotides in smooth muscle contraction

Extracellular nucleotides and nucleosides are crucial signalling molecules, eliciting diverse biological responses in almost all organs and tissues. These molecules exert their effects by activating specific nucleotide receptors, which are finely regulated by ectonucleotidases that break down their ligands. In this comprehensive review, we aim to elucidate the relevance of extracellular nucleotides as signalling molecules in the context of smooth muscle contraction, considering the modulatory influence of ectonucleotidases on this intricate process. Specifically, we provide a detailed examination of the involvement of extracellular nucleotides in the contraction of non-vascular smooth muscles, including those found in the urinary bladder, the airways, the reproductive system, and the gastrointestinal tract. Furthermore, we present a broader overview of the role of extracellular nucleotides in vascular smooth muscle contraction.

Migraine signaling pathways: purine metabolites that regulate migraine and predispose migraineurs to headache

Migraine is a debilitating disorder that afflicts over 1 billion people worldwide, involving attacks that result in a throbbing and pulsating headache. Migraine is thought to be a neurovascular event associated with vasoconstriction, vasodilation, and neuronal activation. Understanding signaling in migraine pathology is central to the development of therapeutics for migraine prophylaxis and for mitigation of migraine in the prodrome phase before pain sets in. The fact that both vasoactivity and neural sensitization are involved in migraine indicates that agonists which promote these phenomena may very well be involved in migraine pathology. One such group of agonists is the purines, in particular, adenosine phosphates and their metabolites. This manuscript explores what is known about the relationship between these metabolites and migraine pathology and explores the potential for such relationships through their known signaling pathways. Reported receptor involvement in vasoaction and nociception.

Current therapeutic targets and multifaceted physiological impacts of caffeine

Caffeine, which shares consubstantial structural similarity with purine adenosine, has been demonstrated as a nonselective adenosine receptor antagonist for eliciting most of the biological functions at physiologically relevant dosages. Accumulating evidence supports caffeine's beneficial effects against different disorders, such as total cardiovascular diseases and type 2 diabetes. Conversely, paradoxical effects are also linked to caffeine ingestion in humans including hypertension-hypotension and tachycardia-bradycardia. These observations suggest the association of caffeine action with its ingested concentration and/or concurrent interaction with preferential molecular targets to direct explicit events in the human body. Thus, a coherent analysis of the functional targets of caffeine, relevant to normal physiology, and disease pathophysiology, is required to understand the pharmacology of caffeine. This review provides a broad overview of the experimentally validated targets of caffeine, particularly those of therapeutic interest, and the impacts of caffeine on organ-specific physiology and pathophysiology. Overall, the available empirical and epidemiological evidence supports the dose-dependent functional activities of caffeine and advocates for further studies to get insights into the caffeine-induced changes under specific conditions, such as asthma, DNA repair, and cancer, in view of its therapeutic applications.

Differential effects of purines and prostaglandins on hypoxia induced dilatation of porcine retinal vessels at different branching level ex vivo

The metabolic pathways leading from hypoxia to retinal vasodilatation can involve effects of both purines and prostaglandins, but the effects of these compounds at different vascular branching levels are unknown. The purpose of the present study was to investigate differential effects of purines and prostaglandins in hypoxia-induced dilatation of retinal arterioles, precapillary arterioles and capillaries ex vivo. Porcine hemiretinas were mounted in a tissue chamber while monitoring temperature, pH, and oxygen tension. The effect of hypoxia on the diameter of larger arterioles, precapillary arterioles and capillaries was studied in the presence of the ecto-nucleotidase inhibitor AOPCP, the nonselective P2 purinoreceptor antagonist PPADS, the A2B adenosine receptor antagonist MRS 1754, the A3 adenosine receptor antagonist MRS 1523, the EP1 receptor antagonist SC-19220, the EP2 receptor antagonist PF-04418948, the EP3 receptor antagonist L-798,106, the EP4 receptor antagonist L-161-982, the prostaglandin synthesis inhibitor ibuprofen, and ibuprofen combined with AOPCP or ATP. Hypoxia-induced dilatation in arterioles was reduced by the A2B adenosine receptor antagonist (p < 0.01) and increased by the EP2 and the EP3 receptor antagonists (p < 0.01 for both comparisons). In precapillary arterioles the dilatation was reduced by the EP2 receptor antagonist (p < 0.04) and increased by the EP1 receptor antagonist (p < 0.03), whereas in capillaries the dilatation was increased by both the A3 adenosine receptor antagonist (p < 0.01), by ibuprofen in combination with the unspecific ecto-nucleotidase inhibitor AOPCP (p = 0.04) and by the prostaglandin EP3 receptor antagonist. Hypoxia-induced dilatation of retinal vessels is influenced by adenosine A2B and A3 receptors, and by the prostaglandin EP1, EP2 and EP3 receptors. The effects mediated by these receptors differ at different branching levels of the resistance vessels.

Markers of arterial stiffness and urinary metabolomics in young adults with early cardiovascular risk: the African-PREDICT study

INTRODUCTION

Increased exposure to risk factors in the young and healthy contributes to arterial changes, which may be accompanied by an altered metabolism.

OBJECTIVES

To increase our understanding of early metabolic alterations and how they associate with markers of arterial stiffness, we profiled urinary metabolites in young adults with cardiovascular disease (CVD) risk factor(s) and in a control group without CVD risk factors.

METHODS

We included healthy black and white women and men (N = 1202), aged 20-30 years with a detailed CVD risk factor profile, reflecting obesity, physical inactivity, smoking, excessive alcohol intake, masked hypertension, hyperglycemia, dyslipidemia and low socio-economic status, forming the CVD risk group (N = 1036) and the control group (N = 166). Markers of arterial stiffness, central systolic blood pressure (BP) and pulse wave velocity were measured. A targeted metabolomics approach was followed by measuring amino acids and acylcarnitines using a liquid chromatography-tandem mass spectrometry method.

RESULTS

In the CVD risk group, central systolic BP (adjusted for age, sex, ethnicity) was negatively associated with histidine, arginine, asparagine, serine, glutamine, dimethylglycine, threonine, GABA, proline, methionine, pyroglutamic acid, aspartic acid, glutamic acid, branched chain amino acids (BCAAs) and butyrylcarnitine (all P ≤ 0.048). In the same group, pulse wave velocity (adjusted for age, sex, ethnicity, mean arterial pressure) was negatively associated with histidine, lysine, threonine, 2-aminoadipic acid, BCAAs and aromatic amino acids (AAAs) (all P ≤ 0.044). In the control group, central systolic BP was negatively associated with pyroglutamic acid, glutamic acid and dodecanoylcarnitine (all P ≤ 0.033).

CONCLUSION

In a group with increased CVD risk, markers of arterial stiffness were negatively associated with metabolites related to AAA and BCAA as well as energy metabolism and oxidative stress. Our findings may suggest that metabolic adaptations may be at play in response to increased CVD risk to maintain cardiovascular integrity.

Prostaglandin D2 Controls Local Blood Flow and Sleep-Promoting Neurons in the VLPO via Astrocyte-Derived Adenosine

Prostaglandin D₂ (PGD₂) is one of the most potent endogenous sleep-promoting molecules. However, the cellular and molecular mechanisms of the PGD₂-induced activation of sleep-promoting neurons in the ventrolateral preoptic nucleus (VLPO), the major nonrapid eye movement (NREM)-sleep center, still remains unclear. We here show that PGD₂ receptors (DP₁) are not only expressed in the leptomeninges but also in astrocytes from the VLPO. We further demonstrate, by performing real-time measurements of extracellular adenosine using purine enzymatic biosensors in the VLPO, that PGD₂ application causes a 40% increase in adenosine level, via an astroglial release. Measurements of vasodilatory responses and electrophysiological recordings finally reveal that, in response to PGD₂ application, adenosine release induces an A_2AR-mediated dilatation of blood vessels and activation of VLPO sleep-promoting neurons. Altogether, our results unravel the PGD₂ signaling pathway in the VLPO, controlling local blood flow and sleep-promoting neurons, via astrocyte-derived adenosine.

Purinergic signaling in myocardial ischemia-reperfusion injury

Purines and their derivatives, extensively distributed in the body, act as a class of extracellular signaling molecules via a rich array of receptors, also known as purinoceptors (P1, P2X, and P2Y). They mediate multiple intracellular signal transduction pathways and participate in various physiological and pathological cell behaviors. Since the function in myocardial ischemia-reperfusion injury (MIRI), this review summarized the involvement of purinergic signal transduction in diversified pathological processes, including energy metabolism disorder, oxidative stress injury, calcium overload, inflammatory immune response, platelet aggregation, coronary vascular dysfunction, and cell necrosis and apoptosis. Moreover, increasing evidence suggests that purinergic signaling also mediates the prevention and treatment of MIRI, such as ischemic conditioning, pharmacological intervention, and some other therapies. In conclusion, this review exhibited that purinergic signaling mediates the complex processes of MIRI which shows its promising application and prospecting in the future.

Effects of physical exercise on the functionality of human nucleotidases: A systematic review

Nucleotidases contribute to the regulation of inflammation, coagulation, and cardiovascular activity. Exercise promotes biological adaptations, but its effects on nucleotidase activities and expression are unclear. The objective of this study was to review systematically the effects of exercise on nucleotidase functionality in healthy and unhealthy subjects. The MEDLINE, EMBASE, Cochrane Library, and Web of Science databases were searched to identify, randomized clinical trials, non-randomized clinical trials, uncontrolled clinical trials, quasi-experimental, pre-, and post-interventional studies that evaluated the effects of exercise on nucleotidases in humans, and was not limited by language and date. Two independent reviewers performed the study selection, data extraction, and assessment of risk of bias. Of the 203 articles identified, 12 were included in this review. Eight studies reported that acute exercise, in healthy and unhealthy subjects, elevated the activities or expression of nucleotidases. Four studies evaluated the effects of chronic training on nucleotidase activities in the platelets and lymphocytes of patients with metabolic syndrome, chronic kidney disease, and hypertension and found a decrease in nucleotidase activities in these conditions. Acute and chronic exercise was able to modify the blood plasma and serum levels of nucleotides and nucleosides. Our results suggest that short- and long-term exercise modulate nucleotidase functionality. As such, purinergic signaling may represent a novel molecular adaptation in inflammatory, thrombotic, and vascular responses to exercise.

The purinergic signalling and inflammation in the pathogenesis and progression of diabetes: key factors and therapeutic targets

Type 2 diabetes mellitus (T2DM) is an important chronic disease around the world, and according to the World Health Organization, it is the 9th principal cause of global death. This pathology is characterized by high levels of circulating glucose as a result of insulin resistance, and it is well stated that inflammation related to obesity is directly associated with the development of the disease. The purinergic signalling is involved in both pancreatic destruction, which impairs insulin secretion, and the cytokine production that favors insulin resistance in T2DM. In this review, the purinergic signalling aspects will be discussed, showing the impact of the enzymes, nucleotides, nucleosides, and receptors of this system and the cytokines that result in inflammation, in the development and progression of T2DM, besides, pointing the purinergic receptors as a possible therapeutic approach.

Changes in P2Y6 receptor-mediated vasoreactivity following focal and global ischemia

Ischemia, both in the form of focal thromboembolic stroke and following subarachnoid hemorrhage (SAH), causes upregulation of vasoconstrictive receptor systems within the cerebral vasculature. Descriptions regarding changes in purinergic signaling following ischemia are lacking, especially when the importance of purinergic signaling in regulating vascular tone is taken into consideration. This prompted us to evaluate changes in P2Y₆ -mediated vasomotor reactivity in two different stroke models in rat. We used wire myography to measure changes in cerebral vasoreactivity to the P2Y₆ agonist UDP-β-S following either experimental SAH or transient middle cerebral artery occlusion. Changes in receptor localization or receptor expression were evaluated using immunohistochemistry and quantitative flow cytometry. Transient middle cerebral artery occlusion caused an increase in Emax when compared to sham (233.6 [206.1-258.5]% vs. 161.1 [147.1-242.6]%, p = 0.0365). No such change was seen following SAH. Both stroke models were associated with increased levels of P2Y₆ receptor expression in the vascular smooth muscle cells (90.94 [86.99-99.15]% and 93.79 [89.96-96.39]% vs. 80.31 [70.80-80.86]%, p = 0.021) and p = 0.039 respectively. There was no change in receptor localization in either of the stroke models. Based on these findings, we conclude that focal ischemic stroke increases vascular sensitivity to UDP-β-S by upregulating P2Y₆ receptors on vascular smooth muscle cells while experimental SAH did not induce changes in vasoreactivity in spite of increased P2Y₆ receptor expression.

A map of metabolic phenotypes in patients with myalgic encephalomyelitis/chronic fatigue syndrome

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating disease usually presenting after infection. Emerging evidence supports that energy metabolism is affected in ME/CFS, but a unifying metabolic phenotype has not been firmly established. We performed global metabolomics, lipidomics, and hormone measurements, and we used exploratory data analyses to compare serum from 83 patients with ME/CFS and 35 healthy controls. Some changes were common in the patient group, and these were compatible with effects of elevated energy strain and altered utilization of fatty acids and amino acids as catabolic fuels. In addition, a set of heterogeneous effects reflected specific changes in 3 subsets of patients, and 2 of these expressed characteristic contexts of deregulated energy metabolism. The biological relevance of these metabolic phenotypes (metabotypes) was supported by clinical data and independent blood analyses. In summary, we report a map of common and context-dependent metabolic changes in ME/CFS, and some of them presented possible associations with clinical patient profiles. We suggest that elevated energy strain may result from exertion-triggered tissue hypoxia and lead to systemic metabolic adaptation and compensation. Through various mechanisms, such metabolic dysfunction represents a likely mediator of key symptoms in ME/CFS and possibly a target for supportive intervention.

Effects of Dual Purinoceptor-dependent Approach on Release of Vascular Endothelial Growth Factor From Human Microvascular Endothelial Cell (HMEC-1) and Endothelial Cell Condition

In the recent years, the awareness of the role purinergic signaling plays as a therapeutic target has increased considerably. The purinoceptor allows the action of extracellular nucleotides (P2 receptors) and intermediary products of their metabolism, such as adenosine (P1 receptors), regulating pivotal processes occurring in the cardiovascular system. This study focuses on a dual purinoreceptor-dependent approach, based on the activation of adenosine P1 receptors with the simultaneous inhibition of P2Y12 receptors that can be used as novel platelet inhibitors in antithrombotic therapy. Endothelial cells are directly exposed to the drugs circulating in the bloodstream. That is why effects of our concept on human microvascular endothelial cells (HMEC-1) were examined in in vitro studies, such as enzyme-linked immunosorbent assay and scratch assays. In response to adenosine receptor agonists, levels of secreted vascular endothelial growth factor varied. Two of them, 5'-N-ethylcarboxamidoadenosine and MRE0094 remarkably increased vascular endothelial growth factor release. The elevated levels were reduced when used together with the P2Y12 receptor antagonist. Also, rates of wound closure in a scratch assay were significantly reduced in these cases. The results suggest that the proposed treatment does not impair endothelial cell condition. In addition, it is suggested as a collateral benefit, namely solving the problem of excessive activation of endothelial cells during antiplatelet therapy.

Molecular Dambusters: What Is Behind Hyperpermeability in Bradykinin-Mediated Angioedema?

In the last few decades, a substantial body of evidence underlined the pivotal role of bradykinin in certain types of angioedema. The formation and breakdown of bradykinin has been studied thoroughly; however, numerous questions remained open regarding the triggering, course, and termination of angioedema attacks. Recently, it became clear that vascular endothelial cells have an integrative role in the regulation of vessel permeability. Apart from bradykinin, a great number of factors of different origin, structure, and mechanism of action are capable of modifying the integrity of vascular endothelium, and thus, may participate in the regulation of angioedema formation. Our aim in this review is to describe the most important permeability factors and the molecular mechanisms how they act on endothelial cells. Based on endothelial cell function, we also attempt to explain some of the challenging findings regarding bradykinin-mediated angioedema, where the function of bradykinin itself cannot account for the pathophysiology. By deciphering the complex scenario of vascular permeability regulation and edema formation, we may gain better scientific tools to be able to predict and treat not only bradykinin-mediated but other types of angioedema as well.

Mapping immune variation and var gene switching in naive hosts infected with Plasmodium falciparum

Falciparum malaria is clinically heterogeneous and the relative contribution of parasite and host in shaping disease severity remains unclear. We explored the interaction between inflammation and parasite variant surface antigen (VSA) expression, asking whether this relationship underpins the variation observed in controlled human malaria infection (CHMI). We uncovered marked heterogeneity in the host response to blood challenge; some volunteers remained quiescent, others triggered interferon-stimulated inflammation and some showed transcriptional evidence of myeloid cell suppression. Significantly, only inflammatory volunteers experienced hallmark symptoms of malaria. When we tracked temporal changes in parasite VSA expression to ask whether variants associated with severe disease rapidly expand in naive hosts, we found no transcriptional evidence to support this hypothesis. These data indicate that parasite variants that dominate severe malaria do not have an intrinsic growth or survival advantage; instead, they presumably rely upon infection-induced changes in their within-host environment for selection.

Brain endothelial cell TRPA1 channels initiate neurovascular coupling

Cerebral blood flow is dynamically regulated by neurovascular coupling to meet the dynamic metabolic demands of the brain. We hypothesized that TRPA1 channels in capillary endothelial cells are stimulated by neuronal activity and instigate a propagating retrograde signal that dilates upstream parenchymal arterioles to initiate functional hyperemia. We find that activation of TRPA1 in capillary beds and post-arteriole transitional segments with mural cell coverage initiates retrograde signals that dilate upstream arterioles. These signals exhibit a unique mode of biphasic propagation. Slow, short-range intercellular Ca²⁺ signals in the capillary network are converted to rapid electrical signals in transitional segments that propagate to and dilate upstream arterioles. We further demonstrate that TRPA1 is necessary for functional hyperemia and neurovascular coupling within the somatosensory cortex of mice in vivo. These data establish endothelial cell TRPA1 channels as neuronal activity sensors that initiate microvascular vasodilatory responses to redirect blood to regions of metabolic demand.

Diabetes and hypertension: Pivotal involvement of purinergic signaling

Diabetes mellitus (DM) and hypertension are highly prevalent worldwide health problems and frequently associated with severe clinical complications, such as diabetic cardiomyopathy, nephropathy, retinopathy, neuropathy, stroke, and cardiac arrhythmia, among others. Despite all existing research results and reasonable speculations, knowledge about the role of purinergic system in individuals with DM and hypertension remains restricted. Purinergic signaling accounts for a complex network of receptors and extracellular enzymes responsible for the recognition and degradation of extracellular nucleotides and adenosine. The main components of this system that will be presented in this review are: P1 and P2 receptors and the enzymatic cascade composed by CD39 (NTPDase; with ATP and ADP as a substrate), CD73 (5′-nucleotidase; with AMP as a substrate), and adenosine deaminase (ADA; with adenosine as a substrate). The purinergic system has recently emerged as a central player in several physiopathological conditions, particularly those linked to inflammatory responses such as diabetes and hypertension. Therefore, the present review focuses on changes in both purinergic P1 and P2 receptor expression as well as the activities of CD39, CD73, and ADA in diabetes and hypertension conditions. It can be postulated that the manipulation of the purinergic axis at different levels can prevent or exacerbate the insurgency and evolution of diabetes and hypertension working as a compensatory mechanism.

Purinergic Regulation of Endothelial Barrier Function

Increased vascular permeability is a hallmark of several cardiovascular anomalies, including ischaemia/reperfusion injury and inflammation. During both ischaemia/reperfusion and inflammation, massive amounts of various nucleotides, particularly adenosine 5'-triphosphate (ATP) and adenosine, are released that can induce a plethora of signalling pathways via activation of several purinergic receptors and may affect endothelial barrier properties. The nature of the effects on endothelial barrier function may depend on the prevalence and type of purinergic receptors activated in a particular tissue. In this review, we discuss the influence of the activation of various purinergic receptors and downstream signalling pathways on vascular permeability during pathological conditions.

Blood-Brain Barrier Disruption: A Common Driver of Central Nervous System Diseases

The brain is endowed with a unique cellular composition and organization, embedded within a vascular network and isolated from the circulating blood by a specialized frontier, the so-called blood-brain barrier (BBB), which is necessary for its proper function. Recent reports have shown that increments in the permeability of the blood vessels facilitates the entry of toxic components and immune cells to the brain parenchyma and alters the phenotype of the supporting astrocytes. All of these might contribute to the progression of different pathologies such as brain cancers or neurodegenerative diseases. Although it is well known that BBB breakdown occurs due to pericyte malfunctioning or to the lack of stability of the blood vessels, its participation in the diverse neural diseases needs further elucidation. This review summarizes what it is known about BBB structure and function and how its instability might trigger or promote neuronal degeneration and glioma progression, with a special focus on the role of pericytes as key modulators of the vasculature. Moreover, we will discuss some recent reports that highlights the participation of the BBB alterations in glioma growth. This pan-disease analysis might shed some light into these otherwise untreatable diseases and help to design better therapeutic approaches.

Adenosine metabolism in the vascular system

The concept of extracellular purinergic signaling was first proposed by Geoffrey Burnstock in the early 1970s. Since then, extracellular ATP and its metabolites ADP and adenosine have attracted an enormous amount of attention in terms of their involvement in a wide range of immunomodulatory, thromboregulatory, angiogenic, vasoactive and other pathophysiological activities in different organs and tissues, including the vascular system. In addition to significant progress in understanding the properties of nucleotide- and adenosine-selective receptors, recent studies have begun to uncover the complexity of regulatory mechanisms governing the duration and magnitude of the purinergic signaling cascade. This knowledge has led to the development of new paradigms in understanding the entire purinome by taking into account the multitude of signaling and metabolic pathways involved in biological effects of ATP and adenosine and compartmentalization of the adenosine system. Along with the "canonical route" of ATP breakdown to adenosine via sequential ecto-nucleoside triphosphate diphosphohydrolase-1 (NTPDase1/CD39) and ecto-5'-nucleotidase/CD73 activities, it has now become clear that purine metabolism is the result of concerted effort between ATP release, its metabolism through redundant nucleotide-inactivating and counteracting ATP-regenerating ectoenzymatic pathways, as well as cellular nucleoside uptake and phosphorylation of adenosine to ATP through complex phosphotransfer reactions. In this review I provide an overview of key enzymes involved in adenosine metabolic network, with special emphasis on the emerging roles of purine-converting ectoenzymes as novel targets for cancer and vascular therapies.

Diabetes Affects the A1 Adenosine Receptor-Dependent Action of Diadenosine Tetraphosphate (Ap4A) on Cortical and Medullary Renal Blood Flow

Diabetes through adenosine A1 receptor (A1R) and P2 receptors (P2Rs) may lead to disturbances in renal microvasculature. We investigated the renal microvascular response to Ap4A, an agonist of P2Rs, in streptozotocin-induced diabetic rats. Using laser Doppler flowmetry, renal blood perfusion (RBP) was measured during infusion of Ap4A alone or in the presence of A1R antagonist, either DPCPX (8-cyclopentyl-1,3-dipropylxanthine) or 8-cyclopentyltheophylline (CPT). Ap4A induced a biphasic response in RBP: a phase of rapid decrease was followed by a rapid increase, which was transient in diabetic rats but extended for 30 min in nondiabetic rats. Phase of decreased RBP was not affected by DPCPX or CPT in either group. Early and extended increases in RBP were prevented by DPCPX and CPT in nondiabetic rats, while in diabetic rats, the early increase in RBP was not affected by these antagonists. A1R mRNA and protein levels were increased in isolated glomeruli of diabetic rats, but no changes were detected in P2Y1R and P2Y2R mRNA. Presence of unblocked A1R is a prerequisite for the P2R-mediated relaxing effect of Ap4A in nondiabetic conditions, but influence of A1R on P2R-mediated renal vasorelaxation is abolished under diabetic conditions.

Adenosine and ATPγS protect against bacterial pneumonia-induced acute lung injury

Lipopolysaccharide (LPS), a component of the outer membrane of gram-negative bacteria, disrupts the alveolar-capillary barrier, triggering pulmonary vascular leak thus inducing acute lung injury (ALI). Extracellular purines, adenosine and ATP, protected against ALI induced by purified LPS. In this study, we investigated whether these purines can impact vascular injury in more clinically-relevant E.coli (non-sterile LPS) murine ALI model. Mice were inoculated with live E. coli intratracheally (i.t.) with or without adenosine or a non-hydrolyzable ATP analog, adenosine 5'-(γ-thio)-triphosphate (ATPγS) added intravenously (i.v.). After 24 h of E. coli treatment, we found that injections of either adenosine or ATPγS 15 min prior or adenosine 3 h after E.coli insult significantly attenuated the E.coli-mediated increase in inflammatory responses. Furthermore, adenosine prevented weight loss, tachycardia, and compromised lung function in E. coli-exposed mice. Accordingly, treatment with adenosine or ATPγS increased oxygen saturation and reduced histopathological signs of lung injury in mice exposed to E. coli. Lastly, lung-targeting gene delivery of adenosine or ATPγS downstream effector, myosin phosphatase, significantly attenuated the E. coli-induced compromise of lung function. Collectively, our study has demonstrated that adenosine or ATPγS mitigates E. coli-induced ALI in mice and may be useful as an adjuvant therapy in future pre-clinical studies.

Functional implications of vascular endothelium in regulation of endothelial nitric oxide synthesis to control blood pressure and cardiac functions

The endothelium is the innermost vascular lining performing significant roles all over the human body while maintaining the blood pressure at physiological levels. Malfunction of endothelium is thus recognized as a biomarker linked with many vascular diseases including but not limited to atherosclerosis, hypertension and thrombosis. Alternatively, prevention of endothelial malfunctioning or regulating the functions of its associated physiological partners like endothelial nitric oxide synthase can prevent the associated vascular disorders which account for the highest death toll worldwide. While many anti-hypertensive drugs are available commercially, a comprehensive description of the key physiological roles of the endothelium and its regulation by endothelial nitric oxide synthase or vice versa is the need of the hour to understand its contribution in vascular homeostasis. This, in turn, will help in designing new therapeutics targeting endothelial nitric oxide synthase or its interacting partners present in the cellular pool. This review describes the central role of vascular endothelium in the regulation of endothelial nitric oxide synthase while outlining the emerging drug targets present in the vasculature with potential to treat vascular disorders including hypertension.

Purinergic Dysfunction in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a life‐threatening disease characterized by increased pulmonary arterial pressure and pulmonary vascular resistance, which result in an increase in afterload imposed onto the right ventricle, leading to right heart failure. Current therapies are incapable of reversing the disease progression. Thus, the identification of novel and potential therapeutic targets is urgently needed. An alteration of nucleotide‐ and nucleoside‐activated purinergic signaling has been proposed as a potential contributor in the pathogenesis of PAH. Adenosine‐mediated purinergic 1 receptor activation, particularly A_2AR activation, reduces pulmonary vascular resistance and attenuates pulmonary vascular remodeling and right ventricle hypertrophy, thereby exerting a protective effect. Conversely, A_2BR activation induces pulmonary vascular remodeling, and is therefore deleterious. ATP‐mediated P2X₇R activation and ADP‐mediated activation of P2Y₁R and P2Y₁₂R play a role in pulmonary vascular tone, vascular remodeling, and inflammation in PAH. Recent studies have revealed a role of ectonucleotidase nucleoside triphosphate diphosphohydrolase, that degrades ATP/ADP, in regulation of pulmonary vascular remodeling. Interestingly, existing evidence that adenosine activates erythrocyte A_2BR signaling, counteracting hypoxia‐induced pulmonary injury, and that ATP release is impaired in erythrocyte in PAH implies erythrocyte dysfunction as an important trigger to affect purinergic signaling for pathogenesis of PAH. The present review focuses on current knowledge on alteration of nucleot(s)ide‐mediated purinergic signaling as a potential disease mechanism underlying the development of PAH.

Nitrergic perivascular innervation in health and diseases: Focus on vascular tone regulation

For a long time, the vascular tone was considered to be regulated exclusively by tonic innervation of vasoconstrictor adrenergic nerves. However, accumulating experimental evidence has revealed the existence of nerves mediating vasodilatation, including perivascular nitrergic nerves (PNN), in a wide variety of mammalian species. Functioning of nitrergic vasodilator nerves is evidenced in several territories, including cerebral, mesenteric, pulmonary, renal, penile, uterine and cutaneous arteries. Nitric oxide (NO) is the main neurogenic vasodilator in cerebral arteries and acts as a counter-regulatory mechanism for adrenergic vasoconstriction in other vascular territories. In the penis, NO relaxes the vascular and cavernous smooth muscles leading to penile erection. Furthermore, when interacting with other perivascular nerves, NO can act as a neuromodulator. PNN dysfunction is involved in the genesis and maintenance of vascular disorders associated with arterial and portal hypertension, diabetes, ageing, obesity, cirrhosis and hormonal changes. For example defective nitrergic function contributes to enhanced sympathetic neurotransmission, vasoconstriction and blood pressure in some animal models of hypertension. In diabetic animals and humans, dysfunctional nitrergic neurotransmission in the corpus cavernosum is associated with erectile dysfunction. However, in some vascular beds of hypertensive and diabetic animals, an increased PNN function has been described as a compensatory mechanism to the increased vascular resistance. The present review summarizes current understanding on the role of PNN in control of vascular tone, its alterations under different conditions and the associated mechanisms. The knowledge of these changes can serve to better understand the mechanisms involved in these disorders and help in planning new treatments.

Simultaneous quantification of 8 nucleotides and adenosine in cells and their medium using UHPLC-HRMS

Purinergic signalling is involved in physiological processes, particularly during ischemia-reperfusion injuries for which it has a protective effect. The purpose of this work was to develop a method for simultaneous quantification of eight nucleotides and adenosine in biological matrices by liquid chromatography coupled with high-resolution mass spectrometry. A method was developed that was sufficiently robust to quantify the targeted analytes in 20 min with good sensitivity. Analysis of extracellular media from cultured endothelial cells detected the release of nucleotides and adenosine during 2 h of hypoxia. The quantification of cylic adenosine monophosphate (cAMP) allowed to establish a dose-response curve after receptor stimulation. Therefore, our method allows us to study the involvement of nucleotides in various processes in both the intracellular and extracellular compartment.

Alteration of purinergic signaling in diabetes: Focus on vascular function

Diabetes is an important risk factor for the development of cardiovascular disease including atherosclerosis and ischemic heart disease. Vascular complications including macro- and micro-vascular dysfunction are the leading causes of morbidity and mortality in diabetes. Disease mechanisms at present are unclear and no ideal therapies are available, which urgently calls for the identification of novel therapeutic targets/agents. An altered nucleotide- and nucleoside-mediated purinergic signaling has been implicated to cause diabetes-associated vascular dysfunction in major organs. Alteration of both purinergic P1 and P2 receptor sensitivity rather than the changes in receptor expression accounts for vascular dysfunction in diabetes. Activation of P2X₇ receptors plays a crucial role in diabetes-induced retinal microvascular dysfunction. Recent findings have revealed that both ecto-nucleotidase CD39, a key enzyme hydrolyzing ATP, and CD73, an enzyme regulating adenosine turnover, are involved in the renal vascular injury in diabetes. Interestingly, erythrocyte dysfunction in diabetes by decreasing ATP release in response to physiological stimuli may serve as an important trigger to induce vascular dysfunction. Nucleot(s)ide-mediated purinergic activation also exerts long-term actions including inflammatory and atherogenic effects in hyperglycemic and diabetic conditions. This review highlights the current knowledge regarding the altered nucleot(s)ide-mediated purinergic signaling as an important disease mechanism for the diabetes-associated vascular complications. Better understanding the role of key receptor-mediated signaling in diabetes will provide more insights into their potential as targets for the treatment.

Purinergic Signaling During Hyperglycemia in Vascular Smooth Muscle Cells

The activation of purinergic receptors by nucleotides and/or nucleosides plays an important role in the control of vascular function, including modulation of vascular smooth muscle excitability, and vascular reactivity. Accordingly, purinergic receptor actions, acting as either ion channels (P2X) or G protein-coupled receptors (GCPRs) (P1, P2Y), target diverse downstream effectors, and substrates to regulate vascular smooth muscle function and vascular reactivity. Both vasorelaxant and vasoconstrictive effects have been shown to be mediated by different purinergic receptors in a vascular bed- and species-specific manner. Purinergic signaling has been shown to play a key role in altering vascular smooth muscle excitability and vascular reactivity following acute and short-term elevations in extracellular glucose (e.g., hyperglycemia). Moreover, there is evidence that vascular smooth muscle excitability and vascular reactivity is severely impaired during diabetes and that this is mediated, at least in part, by activation of purinergic receptors. Thus, purinergic receptors present themselves as important candidates mediating vascular reactivity in hyperglycemia, with potentially important clinical and therapeutic potential. In this review, we provide a narrative summarizing our current understanding of the expression, function, and signaling of purinergic receptors specifically in vascular smooth muscle cells and discuss their role in vascular complications following hyperglycemia and diabetes.

Discovery and Characterization of the Potent and Selective P2X4 Inhibitor N-[4-(3-Chlorophenoxy)-3-sulfamoylphenyl]-2-phenylacetamide (BAY-1797) and Structure-Guided Amelioration of Its CYP3A4 Induction Profile

The P2X4 receptor is a ligand-gated ion channel that is expressed on a variety of cell types, especially those involved in inflammatory and immune processes. High-throughput screening led to a new class of P2X4 inhibitors with substantial CYP 3A4 induction in human hepatocytes. A structure-guided optimization with respect to decreased pregnane X receptor (PXR) binding was started. It was found that the introduction of larger and more polar substituents on the ether linker led to less PXR binding while maintaining the P2X4 inhibitory potency. This translated into significantly reduced CYP 3A4 induction for compounds 71 and 73. Unfortunately, the in vivo pharmacokinetic (PK) profiles of these compounds were insufficient for the desired profile in humans. However, BAY-1797 (10) was identified and characterized as a potent and selective P2X4 antagonist. This compound is suitable for in vivo studies in rodents, and the anti-inflammatory and anti-nociceptive effects of BAY-1797 were demonstrated in a mouse complete Freund's adjuvant (CFA) inflammatory pain model.

Role of opioid receptors in modulation of P2X receptor-mediated cardiac sympathoexcitatory reflex response

Myocardial ischemia evokes powerful reflex responses through activation of vagal and sympathetic afferents in the heart through the release of ischemic metabolites. We have demonstrated that extracellular ATP stimulates cardiac sympathetic afferents through P2 receptor-mediated mechanism, and that opioid peptides suppress these afferents' activity. However, the roles of both P2 receptor and endogenous opioids in cardiac sympathoexcitatory reflex (CSR) responses remain unclear. We therefore hypothesized that activation of cardiac P2 receptor evokes CSR responses by stimulating cardiac sympathetic afferents and these CSR responses are modulated by endogenous opioids. We observed that intrapericardial injection of α,β-methylene ATP (α,β-meATP, P2X receptor agonist), but not ADP (P2Y receptor agonist), caused a graded increase in mean arterial pressure in rats with sinoaortic denervation and vagotomy. This effect of α,β-meATP was abolished by blockade of cardiac neural transmission with intrapericardial procaine treatment and eliminated by intrapericardial A-317491, a selective P2X_2/3 and P2X₃ receptor antagonist. Intrapericardial α,β-meATP also evoked CSR response in vagus-intact rats. Furthermore, the P2X receptor-mediated CSR responses were enhanced by intrapericardial naloxone, a specific opioid receptor antagonist. These data suggest that stimulation of cardiac P2X_2/3 and P2X₃, but not P2Y receptors, powerfully evokes CSR responses through activation of cardiac spinal afferents, and that endogenous opioids suppress the P2X receptor-mediated CSR responses.

Perivascular Adipose Tissue: the Sixth Man of the Cardiovascular System

Perivascular adipose tissue (PVAT) refers to the local aggregate of adipose tissue surrounding the vascular tree, exhibiting phenotypes from white to brown and beige adipocytes. Although PVAT has long been regarded as simply a structural unit providing mechanical support to vasculature, it is now gaining reputation as an integral endocrine/paracrine component, in addition to the well-established modulator endothelium, in regulating vascular tone. Since the discovery of anti-contractile effect of PVAT in 1991, the use of multiple rodent models of reduced amounts of PVAT has revealed its regulatory role in vascular remodeling and cardiovascular implications, including atherosclerosis. PVAT does not only release PVAT-derived relaxing factors (PVRFs) to activate multiple subsets of endothelial and vascular smooth muscle potassium channels and anti-inflammatory signals in the vasculature, but it does also provide an interface for neuron-adipocyte interactions in the vascular wall to regulate arterial vascular tone. In this review, we outline our current understanding towards PVAT and attempt to provide hints about future studies that can sharpen the therapeutic potential of PVAT against cardiovascular diseases and their complications.

Molecular pathways linking adipose innervation to insulin action in obesity and diabetes mellitus

Adipose tissue comprises adipocytes and many other cell types that engage in dynamic crosstalk in a highly innervated and vascularized tissue matrix. Although adipose tissue has been studied for decades, it has been appreciated only in the past 5 years that extensive arborization of nerve fibres has a dominant role in regulating the function of adipose tissue. This Review summarizes the latest literature, which suggests that adipocytes signal to local sensory nerve fibres in response to perturbations in lipolysis and lipogenesis. Such adipocyte signalling to the central nervous system causes sympathetic output to distant adipose depots and potentially other metabolic tissues to regulate systemic glucose homeostasis. Paracrine factors identified in the past few years that mediate such adipocyte-neuron crosstalk are also reviewed. Similarly, immune cells and endothelial cells within adipose tissue communicate with local nerve fibres to modulate neurotransmitter tone, blood flow, adipocyte differentiation and energy expenditure, including adipose browning to produce heat. This understudied field of neurometabolism related to adipose tissue biology has great potential to reveal new mechanistic insights and potential therapeutic strategies for obesity and type 2 diabetes mellitus.

Uridine adenosine tetraphosphate and purinergic signaling in cardiovascular system: An update

Uridine adenosine tetraphosphate (Up4A), biosynthesized by activation of vascular endothelial growth factor receptor (VEGFR) 2, was initially identified as a potent endothelium-derived vasoconstrictor in perfused rat kidney. Subsequently, the effect of Up4A on vascular tone regulation was intensively investigated in arteries isolated from different vascular beds in rodents including rat pulmonary arteries, aortas, mesenteric and renal arteries as well as mouse aortas, in which Up4A produces vascular contraction. In contrast, Up4A produces vascular relaxation in porcine coronary small arteries and rat aortas. Intravenous infusion of Up4A into conscious rats or mice decreases blood pressure, and intravenous bolus injection of Up4A into anesthetized mice increases coronary blood flow, indicating an overall vasodilator influence in vivo. Although Up4A is the first dinucleotide described that contains both purine and pyrimidine moieties, its cardiovascular effects are exerted mainly through activation of purinergic receptors. These effects not only encompass regulation of vascular tone, but also endothelial angiogenesis, smooth muscle cell proliferation and migration, and vascular calcification. Furthermore, this review discusses a potential role for Up4A in cardiovascular pathophysiology, as plasma levels of Up4A are elevated in juvenile hypertensive patients and Up4A-mediated vascular purinergic signaling changes in cardiovascular disease such as hypertension, diabetes, atherosclerosis and myocardial infarction. Better understanding the vascular effect of the novel dinucleotide Up4A and the purinergic signaling mechanisms mediating its effects will enhance its potential as target for treatment of cardiovascular disease.

Changes in aortic reactivity associated with the loss of equilibrative nucleoside transporter 1 (ENT1) in mice

Slc29a1 encodes for equilibrative nucleoside transporter subtype 1 (ENT1), the primary mechanism of adenosine transfer across cell membranes. Previous studies showed that tissues isolated from Slc29a1-null mice are relatively resistant to injury caused by vascular ischemia-reperfusion. To determine if there are similar changes in the microvasculature, and investigate underlying mechanism, we examined aortas isolated from wildtype and Slc29a1-null mice. Aorta macrostructure and gene expression were examined histologically and by qPCR, respectively. Wire myography was used to assess the contractile properties of isolated thoracic aortic rings and their response to adenosine under both normoxic and hypoxic conditions. In vivo haemodynamic parameters were assessed using the tail-cuff method. Slc29a1-null mice had significantly (P<0.05) increased plasma adenosine (2.75-fold) and lower blood pressure (~15% ↓) than wild-type mice. Aortas from Slc29a1-null mice were stiffer with a smaller circumference (11% ↓), and had an enhanced contractile response to KCl and receptor-mediated stimuli. Blockade of ENT1 with nitrobenzylthioinosine significantly enhanced (by ~3.5-fold) the response of aorta from wild-type mice to phenylephrine, but had minimal effect on aortas from Slc29a1-null mice. Adenosine enhanced phenylephrine-mediated constriction in the wild-type tissue under both normoxic (11.7-fold) and hypoxic (3.6-fold) conditions, but had no effect on the Slc29a1-null aortic aorta. In conclusion, aortas from Slc29a1-null mice respond to hypoxic insult in a manner comparable to wild-type tissues that have been pharmacologically preconditioned with adenosine. These data also support a role for ENT1 in the regulation of the protective effects of adenosine on contractile function in elastic conduit arteries such as thoracic aorta.

The clinical toxicology of caffeine: A review and case study

Caffeine is a widely recognized psychostimulant compound with a long history of consumption by humans. While it has received a significant amount of attention there is still much to be learned with respect to its toxicology in humans, especially in cases of overdose. A review of the history of consumption and the clinical toxicology of caffeine including clinical features, pharmacokinetics, toxicokinetics, a thorough examination of mechanism of action and management/treatment strategies are undertaken. While higher (i.e., several grams) quantities of caffeine are known to cause toxicity and potentially lethality, cases of mainly younger individuals who have experienced severe side effects and death despite consuming doses not otherwise known to cause such harm is troubling and deserves further study. An attempted case reconstruction is performed in an effort to shed light on this issue with a focus on the pharmacokinetics and pharmacodynamics of caffeine.

Origin and Consequences of Necroinflammation

When cells undergo necrotic cell death in either physiological or pathophysiological settings in vivo, they release highly immunogenic intracellular molecules and organelles into the interstitium and thereby represent the strongest known trigger of the immune system. With our increasing understanding of necrosis as a regulated and genetically determined process (RN, regulated necrosis), necrosis and necroinflammation can be pharmacologically prevented. This review discusses our current knowledge about signaling pathways of necrotic cell death as the origin of necroinflammation. Multiple pathways of RN such as necroptosis, ferroptosis, and pyroptosis have been evolutionary conserved most likely because of their differences in immunogenicity. As the consequence of necrosis, however, all necrotic cells release damage associated molecular patterns (DAMPs) that have been extensively investigated over the last two decades. Analysis of necroinflammation allows characterizing specific signatures for each particular pathway of cell death. While all RN-pathways share the release of DAMPs in general, most of them actively regulate the immune system by the additional expression and/or maturation of either pro- or anti-inflammatory cytokines/chemokines. In addition, DAMPs have been demonstrated to modulate the process of regeneration. For the purpose of better understanding of necroinflammation, we introduce a novel classification of DAMPs in this review to help detect the relative contribution of each RN-pathway to certain physiological and pathophysiological conditions.

ATP-Gated P2X Receptor Channels: Molecular Insights into Functional Roles

In the nervous system, ATP is co-stored in vesicles with classical transmitters and released in a regulated manner. ATP from the intracellular compartment can also exit the cell through hemichannels and following shear stress or membrane damage. In the past 30 years, the action of ATP as an extracellular transmitter at cell-surface receptors has evolved from somewhat of a novelty that was treated with skepticism to purinergic transmission being accepted as having widespread important functional roles mediated by ATP-gated ionotropic P2X receptors (P2XRs). This review focuses on work published in the last five years and provides an overview of ( a) structural studies, ( b) the molecular basis of channel properties and regulation of P2XRs, and ( c) the physiological and pathophysiological roles of ATP acting at defined P2XR subtypes.

Lack of tone in mouse small mesenteric arteries leads to outward remodeling, which can be prevented by prolonged agonist-induced vasoconstriction

Inward remodeling of resistance vessels is an independent risk factor for cardiovascular events. Thus far, the remodeling process remains incompletely elucidated, but the activation level of the vascular smooth muscle cell appears to play a central role. Accordingly, previous data have suggested that an antagonistic and supposedly beneficial response, outward remodeling, may follow prolonged vasodilatation. The present study aimed to determine whether 1) outward remodeling follows 3 days of vessel culture without tone, 2) a similar response can be elicited in a much shorter 4-h timeframe, and, finally, 3) whether a 4-h response can be prevented or reversed by the presence of vasoconstrictors in the medium. Cannulated mouse small mesenteric arteries were organocultured for 3 days in the absence of tone, leading to outward remodeling that continued throughout the culture period. In more acute experiments in which cannulated small mesenteric arteries were maintained in physiological saline without tone for 4 h, we detected a similar outward remodeling that proceeded at a rate several times faster. In the 4-h experimental setting, continuous vasoconstriction to ~50% tone by abluminal application of UTP or norepinephrine + neuropeptide Y prevented outward remodeling but did not cause inward remodeling. Computational modeling was used to simulate and interpret these findings and to derive time constants of the remodeling processes. It is suggested that depriving resistance arteries of activation will lead to eutrophic outward remodeling, which can be prevented by vascular smooth muscle cell activation induced by prolonged vasoconstrictor exposure. NEW & NOTEWORTHY We have established an effective 4-h method for studying outward remodeling in pressurized mouse resistance vessels ex vivo and have determined conditions that block the remodeling response. This allows for investigating the subtle but clinically highly relevant phenomenon of outward remodeling while avoiding both laborious 3-day organoid culture of cannulated vessels and in vivo experiments lasting several weeks.

In Vivo PET Imaging of Adenosine 2A Receptors in Neuroinflammatory and Neurodegenerative Disease

Adenosine receptors are G-protein coupled P1 purinergic receptors that are broadly expressed in the peripheral immune system, vasculature, and the central nervous system (CNS). Within the immune system, adenosine 2A (A_2A) receptor-mediated signaling exerts a suppressive effect on ongoing inflammation. In healthy CNS, A_2A receptors are expressed mainly within the neurons of the basal ganglia. Alterations in A_2A receptor function and expression have been noted in movement disorders, and in Parkinson's disease pharmacological A_2A receptor antagonism leads to diminished motor symptoms. Although A_2A receptors are expressed only at a low level in the healthy CNS outside striatum, pathological challenge or inflammation has been shown to lead to upregulation of A_2A receptors in extrastriatal CNS tissue, and this has been successfully quantitated using in vivo positron emission tomography (PET) imaging and A_2A receptor-binding radioligands. Several radioligands for PET imaging of A_2A receptors have been developed in recent years, and A_2A receptor-targeting PET imaging may thus provide a potential additional tool to evaluate various aspects of neuroinflammation in vivo. This review article provides a brief overview of A_2A receptors in healthy brain and in a selection of most important neurological diseases and describes the recent advances in A_2A receptor-targeting PET imaging studies.

Developing a Wireless, High Precision and Processing Speed Pulse Monitoring Headset Using Photoplethysmography

In this paper, thorough improvement of pulse monitoring and analysis equipment with a headset structure is presented. In order to study the most suitable infrared wavelength for the acquisition of the pulse wave at the earlobe, Monte Carlo simulation was adapted. Both high frequency noise and baseline drift, generated in the signal acquisition process, are considered. To further optimize the system design and improve accuracy, for the sensor's dimensional drift, the corresponding compensation was carried on in the software. This paper introduced nonlinear quantization, especially in terms of very weak pulse signal, in the time domain analysis process. A quick extraction method named table look-up combing with interpolation was utilized to obtain frequency domain information whose processing speed can be increased by about 30 times compared with fast Fourier transformation setting the sampling point as 300. The results demonstrated the sensor's excellent performance in pulse signal acquisition whose maximum residual is less than 0.004 mV. The test on a random sample of 300 people indicates that the system had high correlation with reference, validating the system accuracy is extremely high. Overall, this paper provides a practical pulse monitoring and analysis system with high precision and processing speed that can be widely applied in the field of health management or medical measurement.

Pannexins Are Potential New Players in the Regulation of Cerebral Homeostasis during Sleep-Wake Cycle

During brain homeostasis, both neurons and astroglia release ATP that is rapidly converted to adenosine in the extracellular space. Pannexin-1 (Panx1) hemichannels represent a major conduit of non-vesicular ATP release from brain cells. Previous studies have shown that Panx1^−/− mice possess severe disruption of the sleep-wake cycle. Here, we review experimental data supporting the involvement of pannexins (Panx) in the coordination of fundamental sleep-associated brain processes, such as neuronal activity and regulation of cerebrovascular tone. Panx1 hemichannels are likely implicated in the regulation of the sleep-wake cycle via an indirect effect of released ATP on adenosine receptors and through interaction with other somnogens, such as IL-1β, TNFα and prostaglandin D2. In addition to the recently established role of Panx1 in the regulation of endothelium-dependent arterial dilation, similar signaling pathways are the major cellular component of neurovascular coupling. The new discovered role of Panx in sleep regulation may have broad implications in coordinating neuronal activity and homeostatic housekeeping processes during the sleep-wake cycle.

Cerebral blood flow regulation and neurovascular dysfunction in Alzheimer disease

Cerebral blood flow (CBF) regulation is essential for normal brain function. The mammalian brain has evolved a unique mechanism for CBF control known as neurovascular coupling. This mechanism ensures a rapid increase in the rate of CBF and oxygen delivery to activated brain structures. The neurovascular unit is composed of astrocytes, mural vascular smooth muscle cells and pericytes, and endothelia, and regulates neurovascular coupling. This Review article examines the cellular and molecular mechanisms within the neurovascular unit that contribute to CBF control, and neurovascular dysfunction in neurodegenerative disorders such as Alzheimer disease.

Nerve-perivascular fat communication as a potential influence on the performance of blood vessels used as coronary artery bypass grafts

Perivascular fat, the cushion of adipose tissue surrounding blood vessels, possesses dilator, anti-contractile and constrictor actions. The majority of these effects have been demonstrated in vitro and may depend on the vessel and/or the experimental method or species used. In general, the relaxant effect of perivascular adipose tissue is local and may be either endothelium-dependent or endothelium-independent. However, nerve stimulation studies show that, in general, perivascular adipose tissue (PVAT) has an anti-contractile vascular effect likely to involve an action of the autonomic vascular nerves. Apart from a direct effect of perivascular fat-derived factors on bypass conduits, an interaction with a number of neurotransmitters and other agents may play an important role in graft performance. Although the vascular effects of PVAT are now well-established there is a lack of information regarding the role and/or involvement of peripheral nerves including autonomic nerves. For example, are perivascular adipocytes innervated and does PVAT affect neuronal control of vessels used as grafts? To date there is a paucity of electrophysiological studies into nerve-perivascular fat control. This review provides an overview of the vascular actions of PVAT, focussing on its potential relevance on blood vessels used as bypass grafts. In particular, the anatomical relationship between the perivascular nerves and fat are considered and the role of the perivascular-nerve/fat axis in the performance of bypass grafts is also discussed.

Purinergic Signaling in the Cardiovascular System

There is nervous control of the heart by ATP as a cotransmitter in sympathetic, parasympathetic, and sensory-motor nerves, as well as in intracardiac neurons. Centers in the brain control heart activities and vagal cardiovascular reflexes involve purines. Adenine nucleotides and nucleosides act on purinoceptors on cardiomyocytes, AV and SA nodes, cardiac fibroblasts, and coronary blood vessels. Vascular tone is controlled by a dual mechanism. ATP, released from perivascular sympathetic nerves, causes vasoconstriction largely via P2X1 receptors. Endothelial cells release ATP in response to changes in blood flow (via shear stress) or hypoxia, to act on P2 receptors on endothelial cells to produce nitric oxide, endothelium-derived hyperpolarizing factor, or prostaglandins to cause vasodilation. ATP is also released from sensory-motor nerves during antidromic reflex activity, to produce relaxation of some blood vessels. Purinergic signaling is involved in the physiology of erythrocytes, platelets, and leukocytes. ATP is released from erythrocytes and platelets, and purinoceptors and ectonucleotidases are expressed by these cells. P1, P2Y₁, P2Y₁₂, and P2X1 receptors are expressed on platelets, which mediate platelet aggregation and shape change. Long-term (trophic) actions of purine and pyrimidine nucleosides and nucleotides promote migration and proliferation of vascular smooth muscle and endothelial cells via P1 and P2Y receptors during angiogenesis, vessel remodeling during restenosis after angioplasty and atherosclerosis. The involvement of purinergic signaling in cardiovascular pathophysiology and its therapeutic potential are discussed, including heart failure, infarction, arrhythmias, syncope, cardiomyopathy, angina, heart transplantation and coronary bypass grafts, coronary artery disease, diabetic cardiomyopathy, hypertension, ischemia, thrombosis, diabetes mellitus, and migraine.

Purinergic P2Y6 receptors: A new therapeutic target of age-dependent hypertension

Aging has a remarkable effect on cardiovascular homeostasis and it is known as the major non-modifiable risk factor in the development of hypertension. Medications targeting sympathetic nerve system and/or renin-angiotensin-aldosterone system are widely accepted as a powerful therapeutic strategy to improve hypertension, although the control rates remain unsatisfactory especially in the elder patients with hypertension. Purinergic receptors, activated by adenine, uridine nucleotides and nucleotide sugars, play pivotal roles in many biological processes, including platelet aggregation, neurotransmission and hormone release, and regulation of cardiovascular contractility. Since clopidogrel, a selective inhibitor of G protein-coupled purinergic P2Y₁₂ receptor (P2Y₁₂R), achieved clinical success as an anti-platelet drug, P2YRs has been attracted more attention as new therapeutic targets of cardiovascular diseases. We have revealed that UDP-responsive P2Y₆R promoted angiotensin type 1 receptor (AT1R)-stimulated vascular remodeling in mice, in an age-dependent manner. Moreover, the age-related formation of heterodimer between AT1R and P2Y₆R was disrupted by MRS2578, a P2Y₆R-selective inhibitor. These findings suggest that P2Y₆R is a therapeutic target to prevent age-related hypertension.

The effect of purinergic signaling via the P2Y11 receptor on vascular function in a rat model of acute inflammation

There is a growing body of evidence pointing to the role of purinergic signaling in the development and progression of various conditions that have inflammation as a common pathogenetic denominator. The aim of the present study was to assess the involvement of P₂Y₁₁ purinergic receptors in the regulation of vascular function in aortic segments obtained using an experimental model of acute inflammation, the lipopolysaccharide (LPS, 8 mg/kg, i.p)-treated rats. Twelve hours after LPS administration, thoracic aortas were isolated and used for studies of vascular reactivity in the organ bath and for the measurement of reactive oxygen species (ROS) generation, respectively. LPS treatment significantly increased contractility to phenylephrine and attenuated the endothelium-dependent relaxation of the vascular segments in response to acetylcholine; an increased production of hydrogen peroxide (H₂O₂) was also recorded. The P₂Y₁₁ activator, NF_546, decreased the LPS-induced aortic H₂O₂ release and partially normalized the vasomotor function, namely reduced contractility and improved relaxation. The effect was abolished by co-treatment with the P₂Y₁₁ inhibitor, NF_340, and also after endothelium denudation. Importantly, NF₅₄₆ did not elicit an antioxidant effect by acting as a H₂O₂ scavenger, suggesting that the beneficial outcome of this treatment on the vasculature is the consequence of P₂Y₁₁ stimulation. In conclusion, purinergic P₂Y₁₁ receptors stimulation improves vascular function and mitigates oxidative stress in the setting of acute systemic inflammation, revealing salutary effects and therapeutic potential in pathologies associated with endothelial dysfunction.

A Comparative Study of Vasorelaxant Effects of ATP, ADP, and Adenosine on the Superior Mesenteric Artery of SHR

We investigated superior mesenteric arteries from spontaneously hypertensive rats (SHR) to determine the relaxation responses induced by ATP, ADP, and adenosine and the relationship between the relaxant effects of these compounds and nitric oxide (NO) or cyclooxygenase (COX)-derived prostanoids. In rat superior mesenteric artery, relaxation induced by ATP and ADP but not by adenosine was completely eliminated by endothelial denudation. In the superior mesenteric arteries isolated from SHR [vs. age-matched control Wistar Kyoto rats (WKY)], a) ATP- and ADP-induced relaxations were weaker, whereas adenosine-induced relaxation was similar in both groups, b) ATP- and ADP-induced relaxations were substantially and partly reduced by N(G)-nitro-L-arginine [a NO synthase (NOS) inhibitor], respectively, c) indomethacin, an inhibitor of COX, increased ATP- and ADP-induced relaxations, d) ADP-induced relaxation was weaker under combined inhibition by NOS and COX, and e) adenosine-induced relaxation was not altered by treatment with these inhibitors. These data indicate that levels of responsiveness to these nucleotides/adenosine vary in the superior mesenteric arteries from SHR and WKY and are differentially modulated by NO and COX-derived prostanoids.

Neurovascular mechanisms underlying augmented cold-induced reflex cutaneous vasoconstriction in human hypertension

KEY POINTS

In hypertensive adults (HTN), cardiovascular risk increases disproportionately during environmental cold exposure. Despite ample evidence of dysregulated sympathetic control of the peripheral vasculature in hypertension, no studies have examined integrated neurovascular function during cold stress in HTN. The findings of the present study show that whole-body cold stress elicits greater increases in sympathetic outflow directed to the cutaneous vasculature and, correspondingly, greater reductions in skin blood flow in HTN. We further demonstrate an important role for non-adrenergic sympathetic co-transmitters in mediating the vasoconstrictor response to cold stress in hypertension. In the context of thermoregulation and the maintenance of core temperature, sympathetically-mediated control of the cutaneous vasculature is not only preserved, but also exaggerated in hypertension. Given the increasing prevalence of hypertension, clarifying the mechanistic underpinnings of hypertension-induced alterations in neurovascular function during cold exposure is clinically relevant.

ABSTRACT

Despite ample evidence of dysregulated sympathetic control of the peripheral vasculature in hypertension, no studies have examined integrated neurovascular function during cold stress in hypertensive adults (HTN). We hypothesized that (i) whole-body cooling would elicit greater cutaneous vasoconstriction and greater increases in skin sympathetic nervous system activity (SSNA) in HTN (n = 14; 56 ± 2 years) compared to age-matched normotensive adults (NTN; n = 14; 55 ± 2 years) and (ii) augmented reflex vasoconstriction in HTN would be mediated by an increase in cutaneous vascular adrenergic sensitivity and a greater contribution of non-adrenergic sympathetic co-transmitters. SSNA (peroneal microneurography) and red cell flux (laser Doppler flowmetry; dorsum of foot) were measured during whole-body cooling (water-perfused suit). Sympathetic adrenergic- and non-adrenergic-dependent contributions to reflex cutaneous vasoconstriction and vascular adrenergic sensitivity were assessed pharmacologically using intradermal microdialysis. Cooling elicited greater increases in SSNA (NTN: +64 ± 13%_baseline  vs. HTN: +194 ± 26%_baseline ; P < 0.01) and greater reductions in skin blood flow (NTN: -16 ± 2%_baseline  vs. HTN: -28 ± 3%_baseline ; P < 0.01) in HTN compared to NTN, reflecting an increased response range for sympathetic reflex control of cutaneous vasoconstriction in HTN. Norepinephrine dose-response curves showed no HTN-related difference in cutaneous adrenergic sensitivity (logEC₅₀ ; NTN: -7.4 ± 0.3 log M vs. HTN: -7.5 ± 0.3 log M; P = 0.84); however, non-adrenergic sympathetic co-transmitters mediated a significant portion of the vasoconstrictor response to cold stress in HTN. Collectively, these findings indicate that hypertension increases the peripheral cutaneous vasoconstrictor response to cold via greater increases in skin sympathetic outflow coupled with an increased reliance on non-adrenergic neurotransmitters.