Role of ceramide in TNF-alpha-induced impairment of endothelium-dependent vasorelaxation in coronary arteries

The role of perirenal adipose tissue deposition in chronic kidney disease progression: Mechanisms and therapeutic implications

Chronic kidney disease (CKD) represents a significant and escalating global health challenge, with morbidity and mortality rates rising steadily. Evidence increasingly implicates perirenal adipose tissue (PRAT) deposition as a contributing factor in the pathogenesis of CKD. This review explores how PRAT deposition may exert deleterious effects on renal structure and function. The anatomical proximity of PRAT to the kidneys not only potentially causes mechanical compression but also leads to the dysregulated secretion of adipokines and inflammatory mediators, such as adiponectin, leptin, visfatin, tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and exosomes. Additionally, PRAT deposition may contribute to renal lipotoxicity through elevated levels of free fatty acids (FFA), triglycerides (TAG), diacylglycerol (DAG), and ceramides (Cer). PRAT deposition is also linked to the hyperactivation of the renin-angiotensin-aldosterone system (RAAS), which further exacerbates CKD progression. Recognizing PRAT deposition as an independent risk factor for CKD underscores the potential of targeting PRAT as a novel strategy for the prevention and management of CKD. This review further discusses interventions that could include measuring PRAT thickness to establish a baseline, managing metabolic risk factors that promote its deposition, and inhibiting key PRAT-induced signaling pathways.

Differences in endothelial function between patients with Type 1 and Type 2 diabetes: effects of red blood cells and arginase

The mechanisms underlying endothelial dysfunction in Type 1 and Type 2 diabetes (T1DM and T2DM) are unresolved. The red blood cells (RBCs) with increased arginase activity induce endothelial dysfunction in T2DM, but the implications of RBCs and the role of arginase inhibition in T1DM are unexplored. We aimed to investigate the differences in endothelial function in patients with T1DM and T2DM, with focus on RBCs and arginase. Thirteen patients with T1DM and twenty-six patients with T2DM, matched for HbA1c and sex were included. In vivo endothelium-dependent and -independent vasodilation (EDV and EIDV) were assessed by venous occlusion plethysmography before and after administration of an arginase inhibitor. RBCs were co-incubated with rat aortic segments for 18h followed by evaluation of endothelium-dependent (EDR) and -independent relaxation (EIDR) in isolated organ chambers. In vivo EDV, but not EIDV, was significantly impaired in patients with T2DM compared with patients with T1DM. Arginase inhibition resulted in improved EDV only in T2DM. RBCs from patients with T2DM induced impaired EDR but not EIDR in isolated aortic segments, whereas RBCs from patients with T1DM did not affect EDR nor EIDR. The present study demonstrates markedly impaired EDV in patients with T2DM in comparison with T1DM. In addition, it highlights the divergent roles of RBCs and arginase in mediating endothelial dysfunction in T1DM and T2DM. While endothelial dysfunction is mediated via RBCs and arginase in T2DM, these phenomena are not prominent in T1DM thereby indicating distinct differences in underlying mechanisms.

Characteristics of Inflammatory and Normal Endothelial Exosomes on Endothelial Function and the Development of Hypertension

Endothelial dysfunction is associated with the development of hypertension. We hypothesize that inflammatory and normal endothelial exosomes play their roles by mediating endothelial function, and they induce endothelial angiogenesis through different signaling pathways. Endothelial cell-derived exosomes were isolated from the human umbilical vein endothelial cells (HUVECs) treated with (TExo) or without (CExo) tumor necrosis factor (TNF)-α. We monitored dermal microcirculation profiles in spontaneously hypertensive rats (SHRs) and WKY rats using a laser Doppler imager and a laser Doppler perfusion and temperature monitor. Tube formation, levels of angiogenesis-related proteins in HUVEC-conditioned media, and reactive oxygen species (ROS) levels were assessed following TNF-α, CExo, or TExo treatments. Western blot analysis was conducted to examine signaling proteins associated with inflammation and ROS. The results showed increased blood perfusion and the mean amplitude of endothelial oscillator in SHRs following CExo administration. TNF-α, CExo, and TExo treatments promoted endothelial tube formation and elevated levels of angiogenic factors and ROS. TExo significantly increased phosphorylation levels of STAT3, p38, and level of NF-κB, while decreasing phosphorylation levels of JNK and Erk (P < 0.01 or P < 0.05). CExo significantly increased STAT3 phosphorylation and reduced JNK and Erk phosphorylation (all P < 0.01). In conclusion, TNF-α and TExo induce inflammatory and pathological angiogenesis via the NF-κB pathway, while CExo exhibits a physiologically pro-angiogenic effect on endothelial cells. Increased ROS, interplaying with inflammatory signals, contribute to exosome-mediated alterations of endothelial function, thereby playing a role in the development of hypertension.

Effects of intrarenal pelvic infusion of tumour necrosis factor-α and interleukin 1-β on reno-renal reflexes in anaesthetised rats

OBJECTIVE

Reno-renal reflexes are disturbed in cardiovascular and hypertensive conditions when elevated levels of pro-inflammatory mediators/cytokines are present within the kidney. We hypothesised that exogenously administered inflammatory cytokines tumour necrosis factor alpha (TNF-α) and interleukin (IL)-1β modulate the renal sympatho-excitatory response to chemical stimulation of renal pelvic sensory nerves.

METHODS

In anaesthetised rats, intrarenal pelvic infusions of vehicle [0.9% sodium chloride (NaCl)], TNF-α (500 and 1000 ng/kg) and IL-1β (1000 ng/kg) were maintained for 30 min before chemical activation of renal pelvic sensory receptors was performed using randomized intrarenal pelvic infusions of hypertonic NaCl, potassium chloride (KCl), bradykinin, adenosine and capsaicin.

RESULTS

The increase in renal sympathetic nerve activity (RSNA) in response to intrarenal pelvic hypertonic NaCl was enhanced during intrapelvic TNF-α (1000 ng/kg) and IL-1β infusions by almost 800% above vehicle with minimal changes in mean arterial pressure (MAP) and heart rate (HR). Similarly, the RSNA response to intrarenal pelvic adenosine in the presence of TNF-α (500 ng/kg), but not IL-1β, was almost 200% above vehicle but neither MAP nor HR were changed. There was a blunted sympatho-excitatory response to intrapelvic bradykinin in the presence of TNF-α (1000 ng/kg), but not IL-1β, by almost 80% below vehicle, again without effect on either MAP or HR.

CONCLUSION

The renal sympatho-excitatory response to renal pelvic chemoreceptor stimulation is modulated by exogenous TNF-α and IL-1β. This suggests that inflammatory mediators within the kidney can play a significant role in modulating the renal afferent nerve-mediated sympatho-excitatory response.

Mechanisms and clinical implications of endothelium-dependent vasomotor dysfunction in coronary microvasculature

Coronary microvascular disease (CMD), which affects the arterioles and capillary endothelium that regulate myocardial perfusion, is an increasingly recognized source of morbidity and mortality, particularly in the setting of metabolic syndrome. The coronary endothelium plays a pivotal role in maintaining homeostasis, though factors such as diabetes, hypertension, hyperlipidemia, and obesity can contribute to endothelial injury and consequently arteriolar vasomotor dysfunction. These disturbances in the coronary microvasculature clinically manifest as diminished coronary flow reserve, which is a known independent risk factor for cardiac death, even in the absence of macrovascular atherosclerotic disease. Therefore, a growing body of literature has examined the molecular mechanisms by which coronary microvascular injury occurs at the level of the endothelium and the consequences on arteriolar vasomotor responses. This review will begin with an overview of normal coronary microvascular physiology, modalities of measuring coronary microvascular function, and clinical implications of CMD. These introductory topics will be followed by a discussion of recent advances in the understanding of the mechanisms by which inflammation, oxidative stress, insulin resistance, hyperlipidemia, hypertension, shear stress, endothelial cell senescence, and tissue ischemia dysregulate coronary endothelial homeostasis and arteriolar vasomotor function.

Phytochemical Contents and Pharmacological Potential of Parkia speciosa Hassk. for Diabetic Vasculopathy: A Review

Diabetes mellitus (DM) is a metabolic disorder characterized by hyperglycemia and is considered a major health problem in the world. It is associated with endothelial dysfunction which causes progressive vascular damage. DM is a known risk factor for atherosclerosis and cardiovascular complications such as peripheral artery disease, coronary artery disease, and stroke. Medicinal plants may act as an alternative resource or adjunctive treatment option in the treatment of diabetes and its cardiovascular complications. Parkia speciosa (Fabaceae) is a plant found abundantly in the Southeast Asian region. Its seeds, with or without pods, and roots have long been used as a traditional medicine in this region to treat hypertension and diabetes. Studies have shown its numerous beneficial pharmacological properties. Extracts of P. speciosa, particularly from its seeds and empty pods, show the presence of polyphenols. They also exhibit potent antioxidant, hypoglycemic, anti-inflammatory, and antihypertensive properties. Its hypoglycemic properties are reported to be associated with the presence of β-sitosterol, stigmasterol, and stigmat-4-en-3-one. The current review aimed to provide an overview of the current status of P. speciosa, its pharmacological potential, and its phytochemical content in attenuating diabetic vasculopathy. Glycemic status, oxidative stress, inflammation, and hyperlipidemia are known to play pivotal roles in the initiation and severity of diabetic cardiovascular diseases; thus, targeting these factors might be beneficial for preventing and/or treating diabetic vasculopathy.

The Role of MSC Therapy in Attenuating the Damaging Effects of the Cytokine Storm Induced by COVID-19 on the Heart and Cardiovascular System

The global pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes coronavirus disease 2019 (COVID-19) has led to 47 m infected cases and 1. 2 m (2.6%) deaths. A hallmark of more severe cases of SARS-CoV-2 in patients with acute respiratory distress syndrome (ARDS) appears to be a virally-induced over-activation or unregulated response of the immune system, termed a "cytokine storm," featuring elevated levels of pro-inflammatory cytokines such as IL-2, IL-6, IL-7, IL-22, CXCL10, and TNFα. Whilst the lungs are the primary site of infection for SARS-CoV-2, in more severe cases its effects can be detected in multiple organ systems. Indeed, many COVID-19 positive patients develop cardiovascular complications, such as myocardial injury, myocarditis, cardiac arrhythmia, and thromboembolism, which are associated with higher mortality. Drug and cell therapies targeting immunosuppression have been suggested to help combat the cytokine storm. In particular, mesenchymal stromal cells (MSCs), owing to their powerful immunomodulatory ability, have shown promise in early clinical studies to avoid, prevent or attenuate the cytokine storm. In this review, we will discuss the mechanistic underpinnings of the cytokine storm on the cardiovascular system, and how MSCs potentially attenuate the damage caused by the cytokine storm induced by COVID-19. We will also address how MSC transplantation could alleviate the long-term complications seen in some COVID-19 patients, such as improving tissue repair and regeneration.

Dietary Fatty Acid Saturation Modulates Sphingosine-1-Phosphate-Mediated Vascular Function

Sphingolipids, modified by dietary fatty acids, are integral components of plasma membrane and caveolae that are also vasoactive compounds. We hypothesized that dietary fatty acid saturation affects vasoconstriction to sphingosine-1-phosphate (S1P) through caveolar regulation of rho kinase. Wild type (WT) and caveolin-1-deficient (cav-1 KO) mice which lack vascular caveolae were fed a low-fat diet (LF), 60% high-saturated fat diet (lard, HF), or 60% fat diet with equal amounts of lard and n-3 polyunsaturated menhaden oil (MO). Weight gain of WT on HF and MO diets was similar while markedly blunted in cav-1 KO. Neither high-fat diet affected the expression of cav-1, rho, or rho kinase in arteries from WT. In cav-1 KO, MO increased the vascular expression of rho but had no effect on rho kinase. HF had no effect on rho or rho kinase expression in cav-1 KO. S1P produced a concentration-dependent constriction of gracilis arteries from WT on LF that was reduced with HF and restored to normal with MO. Constriction to S1P was reduced in cav-1 KO and no longer affected by a high-saturated fat diet. Inhibition of rho kinase which reduced constriction to PE independent of diet in arteries from WT and cav-1 KO only reduced constriction to S1P in arteries from WT fed MO. The data suggest that dietary fatty acids modify vascular responses to S1P by a caveolar-dependent mechanism which is enhanced by dietary n-3 polyunsaturated fats.

Oxidative stress and reactive oxygen species in endothelial dysfunction associated with cardiovascular and metabolic diseases

Reactive oxygen species (ROS) are reactive intermediates of molecular oxygen that act as important second messengers within the cells; however, an imbalance between generation of reactive ROS and antioxidant defense systems represents the primary cause of endothelial dysfunction, leading to vascular damage in both metabolic and atherosclerotic diseases. Endothelial activation is the first alteration observed, and is characterized by an abnormal pro-inflammatory and pro-thrombotic phenotype of the endothelial cells lining the lumen of blood vessels. This ultimately leads to reduced nitric oxide (NO) bioavailability, impairment of the vascular tone and other endothelial phenotypic changes collectively termed endothelial dysfunction(s). This review will focus on the main mechanisms involved in the onset of endothelial dysfunction, with particular focus on inflammation and aberrant ROS production and on their relationship with classical and non-classical cardiovascular risk factors, such as hypertension, metabolic disorders, and aging. Furthermore, new mediators of vascular damage, such as microRNAs, will be discussed. Understanding mechanisms underlying the development of endothelial dysfunction is an important base of knowledge to prevent vascular damage in metabolic and cardiovascular diseases.

Epicardial Fat: Physiological, Pathological, and Therapeutic Implications

Epicardial fat is closely related to blood supply vessels, both anatomically and functionally, which is why any change in this adipose tissue's behavior is considered a potential risk factor for cardiovascular disease development. When proinflammatory adipokines are released from the epicardial fat, this can lead to a decrease in insulin sensitivity, low adiponectin production, and an increased proliferation of vascular smooth muscle cells. These adipokines move from one compartment to another by either transcellular passing or diffusion, thus having the ability to regulate cardiac muscle activity, a phenomenon called vasocrine regulation. The participation of these adipokines generates a state of persistent vasoconstriction, increased stiffness, and weakening of the coronary wall, consequently contributing to the formation of atherosclerotic plaques. Therefore, epicardial adipose tissue thickening should be considered a risk factor in the development of cardiovascular disease, a potential therapeutic target for cardiovascular pathology and a molecular point of contact for "endocrine-cardiology."

Coronary endothelial dysfunction induced by nucleotide oligomerization domain-like receptor protein with pyrin domain containing 3 inflammasome activation during hypercholesterolemia: beyond inflammation

AIMS

This study hypothesized that activation of endothelial nucleotide oligomerization domain-like receptor protein with pyrin domain containing 3 (Nlrp3) inflammasomes directly produces endothelial dysfunction during hypercholesterolemia, which is distinct from its canonical roles in inflammation.

RESULTS

Acute hypercholesterolemia in mice was induced by intraperitoneal administration of poloxamer 407 (0.5 g/kg) for 24 h. Endothelial dysfunction was assessed by evaluating endothelium-dependent vasodilation in isolated, perfused, and pressurized coronary arteries in response to bradykinin (10(-10)-10(-6) M) and acetylcholine (10(-9)-10(-5) M). Impaired endothelium-dependent vasodilation was observed in Nlrp3(+/+) mice with acute hypercholesterolemia, which was markedly ameliorated in Nlrp3(-/-) mice. Treatment of mice with inhibitors for caspase-1 or high mobility group box 1 (HMGB1) significantly restored endothelium-dependent vasodilation in Nlrp3(+/+) mice with acute hypercholesterolemia. Confocal microscopic analysis demonstrated that hypercholesterolemia markedly increased caspase-1 activity and HMGB1 expression in coronary arterial endothelium of Nlrp3(+/+) mice, which was absent in Nlrp3-deficient mice. Further, recombinant HMGB1 directly induced endothelial dysfunction in normal Nlrp3(+/+) coronary arteries. In vitro, Nlrp3 inflammasome formation and its activity were instigated in cultured endothelial cells by cholesterol crystal, a danger factor associated with hypercholesterolemia. Moreover, cholesterol crystals directly induced endothelial dysfunction in coronary arteries from Nlrp3(+/+) mice, which was attenuated in Nlrp3(-/-) arteries. Such cholesterol crystal-induced impairment was associated with enhanced superoxide production, downregulation of endothelial nitric oxide synthase activity, and pyroptosis.

INNOVATION AND CONCLUSION

Our data provide the first evidence that activation of endothelial Nlrp3 inflammasome directly impairs endothelial function beyond its canonical inflammatory actions. This novel non-canonical action of Nlrp3 inflammasomes may initiate or exacerbate vascular injury during hypercholesterolemia.

Perivascular adipose tissue inhibits endothelial function of rat aortas via caveolin-1

Perivascular adipose tissue (PVAT)-derived factors have been proposed to play an important role in the pathogenesis of atherosclerosis. Caveolin-1 (Cav-1), occupying the calcium/calmodulin binding site of endothelial NO synthase (eNOS) and then inhibiting nitric oxide (NO) production, is also involved in the development of atherosclerosis. Thus, we investigated whether PVAT regulated vascular tone via Cav-1 and/or endothelial NO pathways. Isometric tension studies were carried out in isolated thoracic aortas from Wistar rats in the presence and absence of PVAT. Concentration-response curves of phenylephrine, acetylcholine, and sodium nitroprusside were illustrated to examine the vascular reactivity and endothelial function. The protein expressions of eNOS and Cav-1 were also examined in aortic homogenates. Our results demonstrated that PVAT significantly enhanced vasoconstriction and inhibited vasodilatation via endothelium-dependent mechanism. The aortic NO production was diminished after PVAT treatment, whereas protein expression and activity of eNOS were not significantly affected. In addition, Cav-1 protein expression was significantly increased in aortas with PVAT transfer. Furthermore, a caveolae depleter methyl-β-cyclodextrin abolished the effect of PVAT on the enhancement of vasoconstriction, and reversed the impairment of aortic NO production. In conclusion, unknown factor(s) released from PVAT may inhibit endothelial NO production and induce vasocontraction via an increase of Cav-1 protein expression.

The effect of tumour necrosis factor-α and insulin on equine digital blood vessel function in vitro

OBJECTIVE AND DESIGN

Insulin and inflammatory cytokines may be involved in equine laminitis, which might be associated with digital vascular dysfunction. This study determined the effects of TNF-α and insulin on the endothelial-dependent relaxant responses of equine digital blood vessels and on equine digital vein endothelial cell (EDVEC) cGMP production.

MATERIAL

Isolated rings of equine digital arteries (EDAs) and veins (EDVs) were obtained and EDVECs were cultured from horses euthanized at an abattoir.

METHODS

The effect of incubation with TNF-α (10 ng/ml) and/or insulin (1,000 μIU/ml) for 1.5 h or overnight under hyperoxic and hypoxic conditions on carbachol (endothelium-dependent) induced relaxation was assessed. The time course and concentration dependency of the effect of TNF-α and the effect of insulin (1,000 μIU/ml) on EDVEC cGMP production was determined.

RESULTS

Incubation of EDAs overnight with TNF-α under hypoxic conditions resulted in endothelial-dependent vascular dysfunction. EDVs produced a more variable response. TNF-α increased EDVEC cGMP formation in a time- and concentration-dependent manner. Insulin had no significant effects.

CONCLUSIONS

There is a mismatch between the results obtained from isolated vessel rings and cultured endothelial cells suggesting TNF-α may reduce the biological effect of NO by reducing its bioavailability rather than its formation, leading to endothelial cell dysregulation.

Gene deletion of protein tyrosine phosphatase 1B protects against sepsis-induced cardiovascular dysfunction and mortality

OBJECTIVE

Cardiovascular dysfunction is a major cause of mortality in patients with sepsis. Recently, we showed that gene deletion or pharmacological inhibition of protein tyrosine phosphatase 1B (PTP1B) improves endothelial dysfunction and reduces the severity of experimental heart failure. However, the cardiovascular effect of PTP1B invalidation in sepsis is unknown. Thus, we explored the beneficial therapeutic effect of PTP1B gene deletion on lipopolysaccharide (LPS)-induced cardiovascular dysfunction, inflammation, and mortality.

APPROACH AND RESULTS

PTP1B(-/-) or wild-type mice received LPS (15 mg/kg) or vehicle followed by subcutaneous fluid resuscitation (saline, 30 mL/kg). α-1-dependent constriction and endothelium-dependent dilatation, assessed on isolated perfused mesenteric arteries, were impaired 8 hours after LPS and significantly improved in PTP1B(-/-) mice. This was associated with reduced vascular expression of interleukin1-β, intercellular adhesion molecule-1, vascular cell adhesion molecule-1, cyclooxygenase-2, and inducible nitric oxide synthase mRNA. PTP1B gene deletion also limited LPS-induced cardiac dysfunction assessed by echocardiography, left ventricular pressure-volume curves, and in isolated perfused hearts. PTP1B(-/-) mice also displayed reduced LPS-induced cardiac expression of tumor necrosis factor-α, interleukin1-β, intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and Gp91phox, as well as of several markers of cellular infiltration. PTP1B deficiency also reduced cardiac P38 and extracellular signal-regulated protein kinase 1 and 2 phosphorylation and increased phospholamban phosphorylation. Finally, PTP1B(-/-) mice displayed a markedly reduced LPS-induced mortality, an effect also observed using a pharmacological PTP1B inhibitor. PTP1B deletion also improved survival in a cecal ligation puncture model of sepsis.

CONCLUSIONS

PTP1B gene deletion protects against septic shock-induced cardiovascular dysfunction and mortality, and this may be the result of the profound reduction of cardiovascular inflammation. PTP1B is an attractive target for the treatment of sepsis.

Vasomotor regulation of coronary microcirculation by oxidative stress: role of arginase

Overproduction of reactive oxygen species, i.e., oxidative stress, is associated with the activation of redox signaling pathways linking to inflammatory insults and cardiovascular diseases by impairing endothelial function and consequently blood flow dysregulation due to microvascular dysfunction. This review focuses on the regulation of vasomotor function in the coronary microcirculation by endothelial nitric oxide (NO) during oxidative stress and inflammation related to the activation of L-arginine consuming enzyme arginase. Superoxide produced in the vascular wall compromises vasomotor function by not only scavenging endothelium-derived NO but also inhibiting prostacyclin synthesis due to formation of peroxynitrite. The upregulation of arginase contributes to the deficiency of endothelial NO and microvascular dysfunction in various vascular diseases by initiating or following oxidative stress and inflammation. Hydrogen peroxide, a diffusible and stable oxidizing agent, exerts vasodilator function and plays important roles in the physiological regulation of coronary blood flow. In occlusive coronary ischemia, the release of hydrogen peroxide from the microvasculature helps to restore vasomotor function of coronary collateral microvessels with exercise training. However, excessive production and prolonged exposure of microvessels to hydrogen peroxide impairs NO-mediated endothelial function by reducing L-arginine availability through hydroxyl radical-dependent upregulation of arginase. The redox signaling can be a double-edged sword in the microcirculation, which helps tissue survival in one way by improving vasomotor regulation and elicits oxidative stress and tissue injury in the other way by causing vascular dysfunction. The impact of vascular arginase on the development of vasomotor dysfunction associated with angiotensin II receptor activation, hypertension, ischemia-reperfusion, hypercholesterolemia, and inflammatory insults is discussed.

Hypertension in metabolic syndrome: vascular pathophysiology

METABOLIC SYNDROME IS A CLUSTER OF METABOLIC AND CARDIOVASCULAR SYMPTOMS: insulin resistance (IR), obesity, dyslipemia. Hypertension and vascular disorders are central to this syndrome. After a brief historical review, we discuss the role of sympathetic tone. Subsequently, we examine the link between endothelial dysfunction and IR. NO is involved in the insulin-elicited capillary vasodilatation. The insulin-signaling pathways causing NO release are different to the classical. There is a vasodilatory pathway with activation of NO synthase through Akt, and a vasoconstrictor pathway that involves the release of endothelin-1 via MAPK. IR is associated with an imbalance between both pathways in favour of the vasoconstrictor one. We also consider the link between hypertension and IR: the insulin hypothesis of hypertension. Next we discuss the importance of perivascular adipose tissue and the role of adipokines that possess vasoactive properties. Finally, animal models used in the study of vascular function of metabolic syndrome are reviewed. In particular, the Zucker fatty rat and the spontaneously hypertensive obese rat (SHROB). This one suffers macro- and microvascular malfunction due to a failure in the NO system and an abnormally high release of vasoconstrictor prostaglandins, all this alleviated with glitazones used for metabolic syndrome therapy.

TRAIL death receptor 4 signaling via lysosome fusion and membrane raft clustering in coronary arterial endothelial cells: evidence from ASM knockout mice

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its receptor, death receptor 4 (DR4), have been implicated in the development of endothelial dysfunction and atherosclerosis. However, the signaling mechanism mediating DR4 activation leading to endothelial injury remains unclear. We recently demonstrated that ceramide production via hydrolysis of membrane sphingomyelin by acid sphingomyelinase (ASM) results in membrane raft (MR) clustering and the formation of important redox signaling platforms, which play a crucial role in amplifying redox signaling in endothelial cells leading to endothelial dysfunction. The present study aims to investigate whether TRAIL triggers MR clustering via lysosome fusion and ASM activation, thereby conducting transmembrane redox signaling and changing endothelial function. Using confocal microscopy, we found that TRAIL induced MR clustering and co-localized with DR4 in coronary arterial endothelial cells (CAECs) isolated from wild-type (Smpd1 (+/+)) mice. Furthermore, TRAIL triggered ASM translocation, ceramide production, and NADPH oxidase aggregation in MR clusters in Smpd1 ( +/+ ) CAECs, whereas these observations were not found in Smpd1 (-/-) CAECs. Moreover, ASM deficiency reduced TRAIL-induced O(2) (-[Symbol: see text]) production in CAECs and abolished TRAIL-induced impairment on endothelium-dependent vasodilation in small resistance arteries. By measuring fluorescence resonance energy transfer, we found that Lamp-1 (lysosome membrane marker protein) and ganglioside G(M1) (MR marker) were trafficking together in Smpd1 (+/+) CAECs, which was absent in Smpd1 (-/-) CAECs. Consistently, fluorescence imaging of living cells with specific lysosome probes demonstrated that TRAIL-induced lysosome fusion with membrane was also absent in Smpd1 (-/-) CAECs. Taken together, these results suggest that ASM is essential for TRAIL-induced lysosomal trafficking, membrane fusion and formation of MR redox signaling platforms, which may play an important role in DR4-mediated redox signaling in CAECs and consequently endothelial dysfunction.

Hyperresponsiveness of mice deficient in plasma-secreted sphingomyelinase reveals its pivotal role in early phase of host response

Plasma secretion of acid sphingomyelinase is a hallmark of cellular stress response resulting in the formation of membrane embedded ceramide-enriched lipid rafts and the reorganization of receptor complexes. Consistently, decompartmentalization of ceramide formation from inert sphingomyelin has been associated with signaling events and regulation of the cellular phenotype. Herein, we addressed the question of whether the secretion of acid sphingomyelinase is involved in host response during sepsis. We found an exaggerated clinical course in mice genetically deficient in acid sphingomyelinase characterized by an increased bacterial burden, an increased phagocytotic activity, and a more pronounced cytokine storm. Moreover, on a functional level, leukocyte-endothelial interaction was found diminished in sphingomyelinase-deficient animals corresponding to a distinct leukocytes’ phenotype with respect to rolling and sticking as well as expression of cellular surface proteins. We conclude that hydrolysis of membrane-embedded sphingomyelin, triggered by circulating sphingomyelinase, plays a pivotal role in the first line of defense against invading microorganisms. This function might be essential during the early phase of infection leading to an adaptive response of remote cells and tissues.

TNF-α impairs endothelial function in adipose tissue resistance arteries of mice with diet-induced obesity

We tested the hypothesis that high fat (HF) feeding results in endothelial dysfunction in resistance arteries of epididymal white adipose tissue (eWAT) and is mediated by adipose tissue inflammation. When compared with normal chow (NC)-fed mice (n = 17), HF-fed male B6D2F1 mice were glucose intolerant and insulin resistant as assessed by glucose tolerance test (area under the curve; HF, 18,174 ± 1,889 vs. NC, 15,814 ± 666 mg·dl(-1)·min(-1); P < 0.05) and the homeostatic model assessment (HF, 64.1 ± 4.3 vs. NC, 85.7 ± 6.4; P = 0.05). HF diet-induced metabolic dysfunction was concomitant with a proinflammatory eWAT phenotype characterized by greater macrophage infiltration (HF, 3.9 ± 0.8 vs. NC, 0.8 ± 0.4%; P = 0.01) and TNF-α (HF, 22.6 ± 4.3 vs. NC, 11.4 ± 2.5 pg/dl; P < 0.05) and was associated with resistance artery dysfunction, evidenced by impaired endothelium-dependent dilation (EDD) (maximal dilation; HF, 49.2 ± 10.7 vs. NC, 92.4 ± 1.4%; P < 0.01). Inhibition of nitric oxide (NO) synthase by N(ω)-nitro-L-arginine methyl ester (L-NAME) reduced dilation in NC (28.9 ± 6.3%; P < 0.01)- and tended to reduce dilation in HF (29.8 ± 9.9%; P = 0.07)-fed mice, eliminating the differences in eWAT artery EDD between NC- and HF-fed mice, indicative of reduced NO bioavailability in eWAT resistance arteries after HF feeding. In vitro treatment of excised eWAT arteries with recombinant TNF-α (rTNF) impaired EDD (P < 0.01) in NC (59.7 ± 10.9%)- but not HF (59.0 ± 9.3%)-fed mice. L-NAME reduced EDD in rTNF-treated arteries from both NC (21.9 ± 6.4%)- and HF (29.1 ± 9.2%)-fed mice (both P < 0.01). In vitro treatment of arteries with a neutralizing antibody against TNF-α (abTNF) improved EDD in HF (88.2 ± 4.6%; P = 0.05)-fed mice but was without effect on maximal dilation in NC (89.0 ± 5.1%)-fed mice. L-NAME reduced EDD in abTNF-treated arteries from both NC (25.4 ± 7.5%)- and HF (27.1 ± 16.8%)-fed mice (both P < 0.01). These results demonstrate that inflammation in the visceral adipose tissue resulting from diet-induced obesity impairs endothelial function and NO bioavailability in the associated resistance arteries. This dysfunction may have important implications for adipose tissue blood flow and appropriate tissue function.

Vasodilator signals from perivascular adipose tissue

Visceral fat has been linked to metabolic disturbances and increased risk for cardiovascular disease and type 2 diabetes. Recent studies propose a paracrine role for periadventitial adipose tissue in the control of arterial vascular tone. This regulation depends on the anatomical integrity of the vessels and involves a transferable mediator(s) (adipokine) released from either periadventitial adipocytes or perivascular adipose tissue. Although a number of adipokines with vasoactive properties have been identified, a still unidentified adipocyte-derived relaxing factor (ADRF) plays a major role in the periadventitial vasoregulation of visceral arteries, such as the aorta and mesenteric arteries. ADRF is released by visceral periadventitial adipocytes and primarily produces endothelium-independent vasorelaxation by opening voltage-dependent (K(v) ) K(+) channels in the plasma membrane of smooth muscle cells. At least in part, KCNQ (K(v) 7) channels could represent the subtype of K(v) channels involved. Glibenclamide-sensitive K(ATP) channels are not involved or play a minor role. The 'third gas', namely H(2) S, could represent ADRF. Alterations in the paracrine control of arterial tone by visceral periadventitial adipose tissue have been found in animal models of hypertension and metabolic disease. ADRF, or perhaps its putative targets, might represent exciting new targets for the development of drugs for treatment of cardiovascular and metabolic disorders.

LINKED ARTICLES

This article is part of a themed section on Fat and Vascular Responsiveness. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-3.

Inhibition of ceramide synthesis reverses endothelial dysfunction and atherosclerosis in streptozotocin-induced diabetic rats

OBJECTIVES

To explore the effect of myriocin on EDVD and atherosclerosis in diabetic rats.

METHODS

Rats were fed with a high-fat/high-sucrose/high-cholesterol diet (20% sucrose, 10% animal oil, 1.0% bile salt and 2.5% cholesterol) (hereinafter defined as diabetic groups) or Purina Rodent Chow (NC group), the former was intervened with low dose streptozotocin (30 mg/kg) after feeding 1 month to make diabetic model. The NC group was intervened with citrate buffer and the diabetic rats were intervened with myriocin (0.3 mg/kg Qod) (MTD group) or just solvent (DC group) for 14 weeks. The EDVD, thickness of fatty deposition under endothelium, ceramide, PI3K/PKB/eNOS, NO and other vital parameters were measured after the rats sacrificed.

RESULTS

In DC group, the ceramide contents in serum and aorta increased, the EDVD was impaired, the fatty deposition under endothelium increased, and the phosphorylation of PI3K/PKB/eNOS and NO release decreased all compared with the NC group (P<0.05). Compared with the DC group, the ceramide contents in MTD group decreased, the EDVD ameliorated, the fatty deposition diminished, and PI3K/PKB/eNOS phosphorylation and NO release (P<0.05) increased.

CONCLUSIONS

After treated with myriocin, the EDVD in diabetic rats has been improved by increasing PI3K/PKB/eNOS phosphorylation and NO release, and meanwhile the atherosclerosis has reversed.

Regulation of vascular tone by adipocytes

Recent studies have shown that adipose tissue is an active endocrine and paracrine organ secreting several mediators called adipokines. Adipokines include hormones, inflammatory cytokines and other proteins. In obesity, adipose tissue becomes dysfunctional, resulting in an overproduction of proinflammatory adipokines and a lower production of anti-inflammatory adipokines. The pathological accumulation of dysfunctional adipose tissue that characterizes obesity is a major risk factor for many other diseases, including type 2 diabetes, cardiovascular disease and hypertension. Multiple physiological roles have been assigned to adipokines, including the regulation of vascular tone. For example, the unidentified adipocyte-derived relaxing factor (ADRF) released from adipose tissue has been shown to relax arteries. Besides ADRF, other adipokines such as adiponectin, omentin and visfatin are vasorelaxants. On the other hand, angiotensin II and resistin are vasoconstrictors released by adipocytes. Reactive oxygen species, leptin, tumour necrosis factor α, interleukin-6 and apelin share both vasorelaxing and constricting properties. Dysregulated synthesis of the vasoactive and proinflammatory adipokines may underlie the compromised vascular reactivity in obesity and obesity-related disorders.

Membrane raft redox signalosomes in endothelial cells

Membrane rafts (MRs) are specialized microdomains in the cell membrane with an altered lipid composition. Upon various stimulations, MRs can be clustered to aggregate or recruit NADPH oxidase sub-units and related proteins to form MR redox signalosomes in the membrane of cells like vascular endothelial cells (ECs). Multiple protein complexes, like MR redox signalosomes, are now considered to play a crucial role in the regulation of cell function and in the development of different cell dysfunctions. To form such redox signalosomes, ceramide will be generated from the hydrolysis of sphingomyelin by lysosomal acid sphingomyelinase that has been translocated via lysosome fusion to the MR area. In this brief review, current information is provided to help understand the occurrence and function of MR redox signalosomes. This may increase enthusiasm of the scientific community for further studies on the molecular mechanisms and the functional significance of forming such MR redox signalosomes.

Membrane raft-lysosome redox signalling platforms in coronary endothelial dysfunction induced by adipokine visfatin

AIMS

The adipokine visfatin, produced during obesity, has been reported to participate in the development of cardiovascular disease associated with metabolic syndrome. The present study was designed to test a hypothesis that visfatin causes coronary endothelial dysfunction through lysosome trafficking and fusion to cell membranes, membrane raft (MR) clustering, and formation of redox signalosomes.

METHODS AND RESULTS

By using confocal microscopy, it was found that visfatin, but not adiponectin, stimulated NADPH oxidase (NOX) subunits, gp91(phox) aggregation in MR clusters and p47(phox) translocation to these MR clusters in bovine coronary arterial endothelial cells (CAECs), leading to activation of NOX with a 2.5-fold increase in O(2)(·-) production. A signalling lipid, ceramide, was found to be enriched in such membrane MR-NOX complexes of CAECs. Lysosomal fluorescent dye (FM1-43) quenching and de-quenching revealed that visfatin induced the fusion of lysosomes to cell membranes and incorporation of acid sphingomyelinase and its product, ceramide, in such MR-NOX signalling platforms. Functionally, visfatin significantly attenuated endothelium-dependent vasodilation in small coronary arteries (by 80%), which was blocked by lysosomal function inhibitor and MR disruptors.

CONCLUSION

These results suggest that lysosome-associated molecular trafficking and consequent ceramide accumulation in cell membrane may mediate the assembly of NOX subunits and their activation in response to adipokine visfatin in CAECs, thereby producing endothelial dysfunction in coronary circulation.

Interleukin-10 inhibits the in vivo and in vitro adverse effects of TNF-alpha on the endothelium of murine aorta

TNF-α is a proinflammatory cytokine and is an important mediator of maternal endothelial dysfunction leading to preeclampsia. In this study, we tested whether IL-10 protects against TNF-α-induced endothelial dysfunction in murine aorta. In in vitro experiments, aortic rings of C57BL/6 female mice were incubated in Dulbecco's modified Eagle's medium in the presence of either vehicle (distilled H(2)O), TNF-α (4 nmol/l), or recombinant mouse IL-10 (300 ng/ml) or in the presence of both TNF-α and IL-10 for 22 h at 37°C. In in vivo experiments C57BL6/IL-10 knockout female mice were treated with saline or TNF-α (220 ng·kg(-1)·day(-1)) for 14 days. Aortic rings were isolated from in vitro and in vivo experiments and mounted in a wire myograph (Danish Myotech) and stretched to a tension of 5 mN. Endothelium-dependent relaxation was assessed by constructing cumulative concentration-response curves to acetylcholine (ACh, 0.001-10 μmol/l) during phenylephrine (10 μmol/l)-induced contraction. As a result, overnight exposure of aortic rings to TNF-α resulted in significant blunted maximal relaxing responses (E(max)) to ACh compared with untreated rings (22 ± 4 vs. 82 ± 3%, respectively). IL-10 knockout mice treated with TNF-α showed significant impairment in ACh responses (E(max)) compared with C57BL/6 mice treated with TNF-α (51 ± 3 vs. 72 ± 3%, respectively). Western blot analysis showed that endothelial nitric oxide synthase (eNOS) expression was reduced by TNF-α in in vitro and in vivo experiments, whereas IL-10 restored the eNOS expression. In conclusion, the anti-inflammatory cytokine IL-10 prevents impairment in endothelium-dependent vasorelaxation caused by TNF-α by protecting eNOS expression.

Alterations in ceramide concentration and pH determine the release of reactive oxygen species by Cftr-deficient macrophages on infection

We recently demonstrated that the accumulation of ceramide in Cftr-deficient epithelial cells is important for the pathophysiology of CF. However, the role of ceramide in other lung cells, particularly lung macrophages, requires definition. In this study, we report that ceramide is accumulated in Cftr-deficient lung macrophages. Alveolar macrophages contain a vesicle population, which is stained with LysoSensor probes but not by tetramethylrhodamine dextran. These vesicles, presumably secretory lysosomes, exhibit a higher pH in Cftr-deficient macrophages than the corresponding vesicles in lung macrophages isolated from wild-type (WT) mice. Alkalinization of these vesicles in Cftr-deficient macrophages correlates with a failure of the macrophages to respond to infection with various Pseudomonas aeruginosa strains by acutely activating acid sphingomyelinase, releasing ceramide, forming ceramide-enriched membrane platforms that serve to cluster gp91(phox), and, most importantly, releasing reactive oxygen species (ROS). In contrast, these events occur rapidly in WT lung macrophages postinfection. Inhibiting ROS in WT macrophages prevents the killing of P. aeruginosa. These findings provide evidence for a novel pH-controlled pathway from acid sphingomyelinase activation via ceramide and clustering of gp91(phox) to the release of ROS in lung macrophages.

Activation of membrane NADPH oxidase associated with lysosome-targeted acid sphingomyelinase in coronary endothelial cells

This study explored the mechanism mediating the aggregation of membrane NADPH oxidase (NOX) subunits and subsequent activation of this enzyme in bovine coronary arterial endothelial cells (CAECs). With confocal microscopy, we found that FasL stimulated lipid rafts (LRs) clustering with NOX subunit aggregation and acid sphingomyelinase (ASM) gathering, which was blocked by the siRNA of sortilin, an intracellular protein responsible for the binding and targeting of ASM to lysosomes. Correspondingly, FasL-induced O(2)(.-) production through NOX in LRs fractions was abolished by sortilin siRNA. Further, with flow-cytometry and fluorescence resonance energy transfer (FRET) analysis, we surprisingly demonstrated that after FasL stimulation, sortilin was exposed to cell membranes from lysosomes together with Lamp-1 and ASM, and these lysosomal components were aggregated and form a signaling complex in cell membranes. With co-immunoprecipitation, lysosomal sortilin and ASM were found to interact more strongly when CAECs were stimulated by FasL. Functionally, inhibition of either sortilin expression, lysosome function, LRs clustering, or NOX activity significantly attenuated FasL-induced decrease in nitric oxide (NO) levels. It is concluded that lysosome-targeted ASM, through sortilin, is able to traffic to and expose to cell-membrane surface, which may lead to LRs clustering and NOX activation in CAECs.

Direct relationship between levels of TNF-alpha expression and endothelial dysfunction in reperfusion injury

We previously found that myocardial ischemia/reperfusion (I/R) initiates expression of tumor necrosis factor-alpha (TNF) leading to coronary endothelial dysfunction. However, it is not clear whether there is a direct relationship between levels of TNF expression and endothelial dysfunction in reperfusion injury. We studied levels of TNF expression by using different transgenic animals expressing varying amounts of TNF in I/R. We crossed TNF overexpression (TNF(++/++)) with TNF knockout (TNF(-/-)) mice; thus we have a heterozygote population of mice with the expression of TNF "in between" the TNF(-/-) and TNF(++/++) mice. Mouse hearts were subjected to 30 min of global ischemia followed by 90 min of reperfusion and their vasoactivity before and after I/R was examined in wild type (WT), TNF(-/-), TNF(++/++) and TNF heterozygote (TNF(-/++), cross between TNF(-/-) and TNF(++/++)) mice. In heterozygote TNF(-/++) mice with intermediate cardiac-specific expression of TNF, acetylcholine-induced or flow-induced endothelial-dependent vasodilation following I/R was between TNF(++/++) and TNF(-/-) following I/R. Neutralizing antibodies to TNF administered immediately before the onset of reperfusion-preserved endothelial-dependent dilation following I/R in WT, TNF(-/++) and TNF(++/++) mice. In WT, TNF(-/++) and TNF(++/++) mice, I/R-induced endothelial dysfunction was progressively lessened by administration of free-radical scavenger TEMPOL immediately before initiating reperfusion. During I/R, production of superoxide (O(2) (.-)) was greatest in TNF(++/++) mice as compared to WT, TNF(-/++) and TNF(-/-) mice. Following I/R, arginase mRNA expression was elevated in the WT, substantially elevated in the TNF(-/++) and TNF(++/++) mice and not affected in the TNF(-/-) mice. These results suggest that the level of TNF expression determines arginase expression in endothelial cells during myocardial I/R, which is one of the mechanisms by which TNF compromises coronary endothelial function in reperfusion injury.

Upregulation of TNF-alpha and Receptors Contribute to Endothelial Dysfunction in Zucker Diabetic Rats

Diabetes mellitus is a major risk factor to impair endothelial function and induce cardiovascular diseases. TNF-alpha (TNF) is expressed during a variety of inflammatory conditions. We hypothesized that impairment in coronary endothelial function in type 2 diabetes is due to the overexpression of TNF and TNF receptors (TNFRs). Endothelium-dependent (acetylcholine, ACh) and -independent vasodilation (sodium nitroprusside, SNP) of isolated, pressurized (60 cmH(2)O) coronary arteries (50-100 μm) from lean control and Zucker diabetic fatty (ZDF, the model of type 2 diabetes) rats were determined. In lean rats, SNP and ACh induced dose-dependent vasodilation, but dilation to only ACh was blocked by the NOS inhibitor N(G)-monomethyl-L-arginine (L-NMMA, 10 μM). In ZDF rats, dilation to ACh was blunted compared to lean rats, but SNP-induced dilation was comparable. Neutralizing antibodies to TNF, or blockade of NAD(P)H and xanthine oxidase, partially restored endothelium-dependent, NO-mediated vasodilation in isolated coronary arteries in ZDF rats, but anti-TNF did not alter endothelium-dependent vasodilation in lean rats. The mRNA expression of TNF receptor 1 (TNFR1, but not TNFR2) significantly increased in coronary arteries in ZDF rats. Protein expression of TNF and N-Tyr (ONOO(-)) were higher in coronary arteries in ZDF than those in lean rats. Production of H(2)O(2), NAD(P)H oxidase and xanthine oxidase activity were all higher in ZDF rats than those in lean controls; anti-TNF reduces the production of H(2)O(2), N-Tyr expression, NAD(P)H oxidase and xanthine oxidase activity in ZDF rats. These results demonstrate the endothelial dysfunction occurring in type 2 diabetes is the result of effects of the inflammatory cytokine TNF that activates NAD(P)H oxidase and xanthine oxidase; and perhaps acts mainly through the overexpression of TNFR1.

TRPV4-mediated endothelial Ca2+ influx and vasodilation in response to shear stress

The transient receptor potential vallinoid type 4 (TRPV4) channel has been implicated in the endothelial shear response and flow-mediated dilation, although the precise functions of this channel remain poorly understood. In the present study, we investigated the role of TRPV4 in shear stress-induced endothelial Ca(2+) entry and the potential link between this signaling response and relaxation of small resistance arteries. Using immunohistochemical analysis and RT-PCR, we detected strong expression of TRPV4 protein and mRNA in the endothelium in situ and endothelial cells freshly isolated from mouse small mesenteric arteries. The selective TRPV4 agonist GSK1016790A increased endothelial Ca(2+) and induced potent relaxation of small mesenteric arteries from wild-type (WT) but not TRPV4(-/-) mice. Luminal flow elicited endothelium-dependent relaxations that involved both nitric oxide and EDHFs. Both nitric oxide and EDHF components of flow-mediated relaxation were markedly reduced in TRPV4(-/-) mice compared with WT controls. Using a fura-2/Mn(2+) quenching assay, shear was observed to produce rapid Ca(2+) influx in endothelial cells, which was markedly inhibited by the TRPV4 channel blocker ruthenium red and TRPV4-specific short interfering RNA. Flow elicited a similar TRPV4-mediated Ca(2+) entry in HEK-293 cells transfected with TRPV4 channels but not in nontransfected cells. Collectively, these data indicate that TRPV4 may be a potential candidate of mechanosensitive channels in endothelial cells through which the shear stimulus is transduced into Ca(2+) signaling, leading to the release of endothelial relaxing factors and flow-mediated dilation of small resistance arteries.

Transient receptor potential vanilloid type 4-deficient mice exhibit impaired endothelium-dependent relaxation induced by acetylcholine in vitro and in vivo

Agonist-induced Ca2+ entry is important for the synthesis and release of vasoactive factors in endothelial cells. The transient receptor potential vanilloid type 4 (TRPV4) channel, a Ca2+-permeant cation channel, is expressed in endothelial cells and involved in the regulation of vascular tone. Here we investigated the role of TRPV4 channels in acetylcholine-induced vasodilation in vitro and in vivo using the TRPV4 knockout mouse model. The expression of TRPV4 mRNA and protein was detected in both conduit and resistance arteries from wild-type mice. In small mesenteric arteries from wild-type mice, the TRPV4 activator 4alpha-phorbol-12,13-didecanoate increased endothelial [Ca2+]i in situ, which was reversed by the TRPV4 blocker ruthenium red. In wild-type animals, acetylcholine dilated small mesenteric arteries that involved both NO and endothelium-derived hyperpolarizing factors. In TRPV4-deficient mice, the NO component of the relaxation was attenuated and the endothelium-derived hyperpolarizing factor component was largely eliminated. Compared with their wild-type littermates, TRPV4-deficient mice demonstrated a blunted endothelial Ca2+ response to acetylcholine in mesenteric arteries and reduced NO release in carotid arteries. Acetylcholine (5 mg/kg, IV) decreased blood pressure by 37.0+/-6.2 mm Hg in wild-type animals but only 16.6+/-2.7 mm Hg in knockout mice. We conclude that acetylcholine-induced endothelium-dependent vasodilation is reduced both in vitro and in vivo in TRPV4 knockout mice. These findings may provide novel insight into mechanisms of Ca2+ entry evoked by chemical agonists in endothelial cells.

Sphingomyelinases: their regulation and roles in cardiovascular pathophysiology

Sphingomyelinases (SMases) hydrolyse sphingomyelin, releasing ceramide and creating a cascade of bioactive lipids. These lipids include sphingosine and sphingosine-1-phosphate, all of which have a specific signalling capacity. Sphingomyelinase activation occurs in different cardiovascular system cell types, namely cardiac myocytes, endothelial and vascular smooth muscle cells, mediating cell proliferation, cell death, and contraction of cardiac and vascular myocytes. Three main types of SMases contribute to cardiovascular physiology: the lysosomal and secreted acidic SMases (L- and S-ASMases, respectively) and the membrane neutral SMase (NSMase). These three enzymes have common activators, including ischaemia/reperfusion stress and proinflammatory cytokines, but they differ in their enzymatic properties and subcellular locations that determine the final effect of enzyme activation. This review focuses on the recent advances in the understanding of ASMase and NSMase pathways and their specific contribution to cardiovascular pathophysiology. Current knowledge indicates that the inhibitors of the different SMase types are potential tools for the treatment of cardiovascular diseases. Acid SMase inhibitors could be tools against post-ischaemia reperfusion injury and in the treatment of atherosclerosis. Neutral SMase inhibitors could be tools for the treatment of atherosclerosis, heart failure, and age-related decline in vasomotion. However, the design of bioavailable and more specific SMase-type inhibitors remains a challenge.

Lipid raft-redox signaling platforms in plasma membrane

Membrane lipid rafts (LRs) have been demonstrated to be importantly involved in transmembrane signaling in a variety of mammalian cells. Many receptors can be aggregated within the LR clusters to form signaling platforms. Currently, LRs were reported to be clustered to aggregate, recruit, and assemble NADPH oxidase subunits and related proteins in various cells in response to various stimuli, forming redox signaling platforms. These LR signaling platforms may play important roles in the regulation of cellular activity and cell function, and also in the development of cell dysfunction or injury associated with various pathological stimuli. This LRs clustering-mediated mechanism is considered to take a center stage in redox signaling associated with death receptors. In this chapter, some basic methods and procedures for characterization of LR-redox signaling platforms formation and for determination of the function of these signaling platforms are described in detail, which include identification of LR-redox signaling platforms in cell membrane by using fluorescent or confocal microscopy of LR-redox signaling platforms and fluorescent resonance energy transfer analysis, isolation of LR-redox signaling platforms by flotation of detergent-resistant membranes, and function measurement of LR-redox signaling platforms by electron spin resonance spectroscopy. It is expected that information provided here will help readers to design necessary experiments in their studies on LR signaling platforms and redox regulation of cell function.

Maturation-induces endothelial dysfunction via vascular inflammation in diabetic mice

We hypothesized that maturation-induced vascular inflammation produces endothelial dysfunction in type II diabetes and TNFalpha plays a key role in triggering inflammation in the development of diabetes. In control (Db/db) mice aged 6, 12, 18 and 24 weeks, sodium nitroprusside (SNP) and acetylcholine (ACh) induced dose-dependent vasodilation, and dilation to ACh was blocked by the NO synthase inhibitor N (G)-monomethyl-L: -arginine. In type II diabetic (db/db) mice at age of 12, 18 and 24 weeks, ACh or flow-induced dilation was blunted compared to Db/db; endothelial function is normal at 6 weeks of age in db/db Vs. control mice, but SNP produced comparable dilation at age of 6, 12, 18 and 24 weeks. Decrements in endothelial function in db/db mice progressively increased from 6-12 to 18-24 weeks. Administration of neutralizing antibodies to TNFalpha ameliorated endothelial dysfunction in db/db mice aged 12, 18 and 24 weeks. The effect was most prominent in the younger animals. Plasma concentration, expression of TNFalpha and TNFalpha receptor 1 (TNFR1) were elevated in coronary arterioles, even at the age of 6 weeks before the development of diabetes in db/db mice compared to control mice. Superoxide production was lower in Db/db mice compared to db/db mice and increments in superoxide production in db/db mice progressively increased from 6-12 to 18-24 weeks. NAD(P)H oxidase inhibitor apocynin attenuated superoxide production in db/db mice at 12 weeks of age, mitochondria respiratory chain inhibitor rotenone attenuated superoxide production at 24 weeks in db/db and Db/db mice, but the combination of apocynin and rotenone reduced superoxide production at 18 weeks for db/db and Db/db mice. The expression of TNFalpha and its receptors increase progressively with maturation in concert with the development of diabetes. Incremental increases in TNFalpha/TNFR1 expression induces activation and production of superoxide via NAD(P)H oxidase and/or mitochondria respiratory chain, leading to endothelial dysfunction progressing to the development of type II diabetes.

The role of inflammatory cytokines in endothelial dysfunction

Clinical and experimental data support a link between endothelial dysfunction and inflammation. Inflammatory cytokines are important protagonists in formation of atherosclerotic plaque, eliciting effects throughout the atherosclerotic vessel. Importantly, the development of atherosclerotic lesions, regardless of the risk factor, e.g., diabetes, hypertension, obesity, is characterized by disruption in normal function of the endothelial cells. Endothelial cells, which line the internal lumen of the vasculature, are part of a complex system that regulates vasodilation and vasoconstriction, growth of vascular smooth muscle cells, inflammation, and hemostasis, maintaining a proper blood supply to tissues and regulating inflammation and coagulation. Current concepts suggest that the earliest event in atherogenesis is endothelial dysfunction, manifested by deficiencies in the production of nitric oxide (NO) and prostacyclin. The focus of this review is to summarize recent evidence showing the effects of inflammation on vascular dysfunction in ischemic-heart disease, which may prompt new directions for targeting inflammation in future therapies.

Adiponectin protects against angiotensin II or tumor necrosis factor alpha-induced endothelial cell monolayer hyperpermeability: role of cAMP/PKA signaling

OBJECTIVE

Angiotensin II (Ang II) and tumor necrosis factor (TNF)-alpha levels increase endothelial permeability, and we hypothesized that adiponectin suppressed these responses in a cAMP-dependent manner.

METHODS AND RESULTS

The effect of adiponectin on transendothelial electric resistance (TEER) and diffusion of albumin through human umbilical vein and bovine aortic endothelial cell monolayers induced by Ang II (100 nmol/L) or TNF-alpha (5 ng/mL) was measured. Treatment with the globular domain of adiponectin (3 mug/mL) for 16 hours abrogated the adverse TEER effect of TNF-alpha (-35 versus -12 Omega/cm(2) at 45 minutes, P<0.05) and Ang II (-25 versus -5 Omega/cm(2) at 45 minutes, P<0.01) and partially suppressed the increased diffusion of albumin with Ang II (40% versus 10% change, P<0.05) or TNF-alpha (40% versus 20% change, P<0.05). Full-length adiponectin also suppressed Ang II-induced monolayer hyperpermeability. Adiponectin treatment also suppressed Ang II-induced increased actin stress fiber development, intercellular gap formation, and beta-tubulin disassembly. Adiponectin increased cAMP levels, and its effects were abrogated by inhibition of adenylyl cyclase or cAMP-dependent protein kinase signaling.

CONCLUSIONS

Adiponectin protects the endothelial monolayer from Ang II or TNF-alpha-induced hyperpermeability by modulating microtubule and cytoskeleton stability via a cAMP/ PKA signaling cascade.

Local production of O2- by NAD(P)H oxidase in the sarcoplasmic reticulum of coronary arterial myocytes: cADPR-mediated Ca2+ regulation

The present study was designed to determine whether the sarcoplasmic reticulum (SR) could locally produce superoxide (O2-) via NAD(P)H oxidase (NOX) in coronary arterial myocytes (CAMs) and to address whether cADPR-RyR/Ca2+ signaling pathway regulates this local O2- production from the SR. Using confocal microscopic imaging analysis in intact single CAMs, a cell-permeable indicator CM-H2DCFDA for dynamic changes in intracellular ROS (in green color) and a highly selective ER-Tracker Red dye for tracking of the SR were found co-localized. A quantitative analysis based on the intensity of different spectra demonstrated a local O2- production derived from the SR. M(1)-receptor agonist, oxotremorine (Oxo) and a Ca2+ ionophore, A23187, time-dependently increased this O2- production colocalized with the SR. NOX inhibitors, diphenylene iodonium (DPI) and apocynin (Apo), or superoxide dismutase (SOD) and catalase, and Nox4 (a major intracellular NOX subunit) siRNA all substantially blocked this local production of O2-, demonstrating an involvement of NOX. This SR-derived O2- production was also abolished by the inhibitors of cyclic ADP-ribose (cADPR)-mediated Ca2+ signaling, such as nicotinamide (Nicot, 6 mM), ryanodine (Rya, 50 muM) or 8-Br-cADPR (30 microM). However, IP3 antagonist, 2-APB (50 microM) had no effect. In CAMs transfected with siRNA of ADP-ribosyl cyclase or RyR, this SR O2- production was attenuated. Electron spin resonance (ESR) spectromic assay in purified SR also demonstrated the production of O2- that was dependent on NOX activity and Ca2+ concentrations. These results provide direct evidence that O2- could be locally produced via NOX on the SR and that this local O2- producing system is controlled by cADPR-RyR/Ca2+ signaling pathway.

Lipid second messengers and cell signaling in vascular wall

Agonists of cellular receptors, such as receptor tyrosine kinases, G protein-coupled receptors, cytokine receptors, etc., activate phospholipases (C(gamma), C(beta), A(2), D), sphingomyelinase, and phosphatidylinositol-3-kinase. This produces active lipid metabolites, some of which are second messengers: inositol trisphosphate, diacylglycerides, ceramide, and phosphatidylinositol 3,4,5-trisphosphate. These universal mechanisms are involved in signal transduction to maintain blood vessel functions: regulation of vasodilation and vasoconstriction, mechanical stress resistance, and anticoagulant properties of the vessel lumen surface. Different signaling pathways realized through lipid second messengers interact to one another and modulate intracellular events. In early stages of atherogenesis, namely, accumulation of low density lipoproteins in the vascular wall, cascades of pro-atherogenic signal transduction are triggered through lipid second messengers. This leads to atherosclerosis, the general immuno-inflammatory disease of the vascular system.

Lipid raft redox signaling platforms in endothelial dysfunction

In response to various stimuli, membrane lipid rafts (LRs) are clustered to aggregate or recruit NADPH oxidase subunits and related proteins in vascular endothelial cells (ECs), forming redox signaling platforms. These LR signaling platforms may play important roles in the normal regulation of endothelial function and in the development of endothelial dysfunction or injury under pathological conditions. This LR-mediated mechanism now takes center stage in cell signaling for the regulation of many cellular activities or cell function such as ECs redox signaling, phagosomal activity of phagocytes, and cell apopotosis of lymphocytes. This brief review summarizes current evidence that relates to the formation of LR redox signaling platforms and their features in ECs, the functional significance of these signaling platforms in mediating death receptor activation-induced endothelial dysfunction, and the mechanisms initiating or promoting the formation of these platforms. It is expected that information provided here will help readers to understand this new signaling mechanism and perhaps extend the LR signaling platform concept to other research areas related to death receptors, redox signaling, endothelial biology, and cell/molecular biology of the cardiovascular system.

Contribution of lysosomal vesicles to the formation of lipid raft redox signaling platforms in endothelial cells

We have demonstrated that the formation of lipid raft (LR)-redox signaling platforms membrane is associated with activation of acid sphingomyelinase (ASMase) in coronary arterial endothelial cells (CAECs). Given that the trafficking of lysosomal vesicles might play an essential role in ASMase activation, the present study tested whether lysosomal vesicles contribute to the formation of LR redox signaling platforms. By confocal microscopy, we found that Fas ligand (FasL) induced the formation of LR clusters in the plasma membrane of CAECs, accompanied by aggregation of NAD(P)H oxidase subunits, gp91phox and p47phox, and ROS production. When the cells were pretreated with two structurally different lysosomal vesicle function inhibitors, bafilomycin A1 (Baf) and glycyl-L-phenylalanine-beta-naphthylamide (GPN), the FasL-induced LRs clustering was substantially blocked, and corresponding ROS production significantly decreased. By confocal microscopic observations in living CAECs by using LysoTracker, a colocalization of LRs and lysosomal vesicles was found around the cell membrane, which was abolished by Baf or GPN. Functionally, FasL-induced inhibition of endothelium-dependent vasorelaxation was also reduced by both inhibitors of lysosome function. These results suggest that lysosomal vesicles importantly contribute to the formation of LR-redox signaling platforms and thereby participate in the oxidative injury of endothelial function during activation of death receptor-Fas in coronary arteries.

Effect of ceramide N-acyl chain and polar headgroup structure on the properties of ordered lipid domains (lipid rafts)

Ceramides are sphingolipids that greatly stabilize ordered membrane domains (lipid rafts), and displace cholesterol from them. Ceramide-rich rafts have been implicated in diverse biological processes. Because ceramide analogues have been useful for probing the biological function of ceramide, and may have biomedical applications, it is important to characterize how ceramide structure affects membrane properties, including lipid raft stability and composition. In this report, fluorescence quenching assays were used to evaluate the effect of analogues of ceramide with different N-acyl chains or different sphingoid backbones on raft stability and sterol content. The effect of replacing 18 mol% of sphingomyelin (SM) with ceramide in vesicles composed of a 1:1 (mol:mol) mixture of SM and dioleoylphosphatidylcholine (DOPC), with or without 25 mol% sterol, was examined. In the absence of sterol, the thermal stability of the SM-rich ordered domains increased with ceramide N-acyl chain length in the order C2:0 approximately C6:0 approximately C8:0<no ceramide<C12:0<C16:0. In vesicles containing 25 mol% cholesterol (1:1:0.66 sphingolipid:DOPC:cholesterol), the dependence of raft stability on ceramide N-acyl chain length increased in the order C8:0 approximately C6:0<C2:0<C12:0 approximately no ceramide<C16:0. We also studied the stability of lipid rafts in the presence of N-lauroyl- and N-palmitoylsphingosine analogues containing altered structures in or near the polar portion of the sphingoid base. In almost all cases, the analogues stabilized rafts to about the same degree as a normal ceramide containing the same acyl chain. The only exception was N-palmitoyl-4D-ribophytosphingosine, which was very strongly raft-stabilizing. We conclude that variations in sphingoid base structure induce only insignificant changes in raft properties. N-Lauroyl and N-palmitoylsphingosine and their analogues displaced sterol from rafts to a significant degree. Both C12:0 and C16:0 analogues of ceramide may be good mimics of natural ceramide, and useful for cellular studies in which maintenance of the normal physical properties of ceramide are important.

Tumor necrosis factor-alpha induces endothelial dysfunction in Lepr(db) mice

BACKGROUND

We hypothesized that the inflammatory cytokine tumor necrosis factor-alpha (TNF) produces endothelial dysfunction in type 2 diabetes.

METHODS AND RESULTS

In m Lepr(db) control mice, sodium nitroprusside and acetylcholine induced dose-dependent vasodilation, and dilation to acetylcholine was blocked by the NO synthase inhibitor N(G)-monomethyl-L-arginine. In type 2 diabetic (Lepr(db)) mice, acetylcholine- or flow-induced dilation was blunted compared with m Lepr(db), but sodium nitroprusside produced comparable dilation. In Lepr(db) mice null for TNF (db(TNF-)/db(TNF-)), dilation to acetylcholine or flow was greater than in diabetic Lepr(db) mice and comparable to that in controls. Plasma concentration of TNF was significantly increased in Lepr(db) versus m Lepr(db) mice. Real-time polymerase chain reaction and Western blotting showed that mRNA and protein expression of TNF and nuclear factor-kappaB were higher in Lepr(db) mice than in controls. Administration of anti-TNF or soluble receptor of advanced glycation end products attenuated nuclear factor-kappaB and TNF expression in the Lepr(db) mice. Immunostaining results show that TNF in mouse heart is localized predominantly in vascular smooth muscle cells rather than in endothelial cells and macrophages. Superoxide generation was elevated in vessels from Lepr(db) mice versus controls. Administration of the superoxide scavenger TEMPOL, NAD(P)H oxidase inhibitor (apocynin), or anti-TNF restored endothelium-dependent dilation in Lepr(db) mice. NAD(P)H oxidase activity, protein expression of nitrotyrosine, and hydrogen peroxide production were increased in Lepr(db) mice (compared with controls), but these variables were restored to control levels by anti-TNF.

CONCLUSIONS

Advanced glycation end products/receptor of advanced glycation end products and nuclear factor-kappaB signaling play pivotal roles in TNF expression through an increase in circulating and/or local vascular TNF production in the Lepr(db) mouse with type 2 diabetes. Increases in TNF expression induce activation of NAD(P)H oxidase and production of reactive oxidative species, leading to endothelial dysfunction in type 2 diabetes.

Sphingolipid Metabolism in Systemic Inflammation

The inflammatory response - induced and regulated by a variety of mediators such as cytokines, prostaglandins, and reactive oxygen species (ROS) - is the localized host’s response of the tissue to injury, irritation, or infection. In a very similar and stereotyped sequence, the mediators are thought to induce an acute phase response orchestrated by an array of substances produced locally or near the source or origin of the inflammatory response. Despite its basically protective function, the response can become inappropriate in intensity or duration damaging host tissues or interfering with normal metabolism. Thus, inflammation is the cause and/or consequence of a diversity of diseases and plays a major role in the development of remote organ failure. Better knowledge of the underlying mechanisms of these processes is, therefore, a fundamental pre-requisite fostering the molecular understanding of novel therapeutic targets or diagnostic variables.

Sphingolipid Metabolism in Systemic Inflammation

The inflammatory response — induced and regulated by a variety of mediators such as cytokines, prostaglandins, and reactive oxygen species (ROS) — is the localized host’s response of the tissue to injury, irritation, or infection. In a very similar and stereotyped sequence, the mediators are thought to induce an acute phase response orchestrated by an array of substances produced locally or near the source or origin of the inflammatory response. Despite its basically protective function, the response can become inappropriate in intensity or duration damaging host tissues or interfering with normal metabolism. Thus, inflammation is the cause and/or consequence of a diversity of diseases and plays a major role in the development of remote organ failure. Better knowledge of the underlying mechanisms of these processes is, therefore, a fundamental pre-requisite fostering the molecular understanding of novel therapeutic targets or diagnostic variables.

Recent advances in the immunobiology of ceramide

Ceramide, a sphingosine-based lipid molecule, has emerged as a key regulator of a wide spectrum of biological processes such as cellular differentiation, proliferation, apoptosis and senescence. Sphingomyelinase-dependent hydrolysis of sphingomyelin and de novo synthesis involving the coordinated action of serinepalmitoyl transferase and ceramide synthase are the two major pathways involved in ceramide synthesis. Clustering of plasma membrane rafts into ceramide-enriched platforms serves as an important transmembrane signaling mechanism for cell surface receptors. Ceramides have been implicated in apoptosis, stress signaling cascades as well as ion channels. There is accumulating evidence that targeted manipulation of ceramide metabolism pathway has immense therapeutic potential and may eventually prove to be a boon in the design of novel strategies and development of innovative treatments for diverse conditions including cardiovascular diseases, cancer and Alzheimer's disease. As yet uncharacterized natural ceramide analogs and novel inhibitors of ceramide metabolism might prove to have potent effects in the drugs. In this review, we discuss significant advances that continue to provide intriguing insights into the complex cellular and molecular mechanisms underlying ceramide-mediated signaling cascades.

Autocrine/paracrine pattern of superoxide production through NAD(P)H oxidase in coronary arterial myocytes

The present study tested the hypothesis that membrane-bound NAD(P)H oxidase in coronary arterial myocytes (CAMs) is capable of producing superoxide (O(2)(*-)) toward extracellular space to exert an autocrine- or paracrine-like action in these cells. Using a high-speed wavelength-switching fluorescent microscopic imaging technique, we simultaneously monitored the binding of dihydroethidium-oxidizing product to exogenous salmon testes DNA trapped outside CAMs and to nuclear DNA as indicators of extra- and intracellular O(2)(*-) production. It was found that a muscarinic agonist oxotremorine (OXO; 80 microM) increased O(2)(*-) levels more rapidly outside than inside CAMs. In the presence of superoxide dismutase (500 U/ml) plus catalase (400 U/ml) and NAD(P)H oxidase inhibitor diphenylene iodonium (50 microM) or apocynin (100 microM), these increases in extra- and intracellular O(2)(*-) levels were substantially abolished or attenuated. The O(2)(*-) increase outside CAMs was also confirmed by detecting oxidation of nitro blue tetrazolium and confocal microscopic localization of Matrigel-trapped OxyBURST H(2)HFF Green BSA staining around these cells. By electron spin resonance spectrometry, the extracellular accumulation of O(2)(*-) was demonstrated as a superoxide dismutase-sensitive component outside CAMs. Furthermore, RNA interference of NAD(P)H oxidase subunits Nox1 or p47 markedly blocked OXO-induced increases in both extra- and intracellular O(2)(*-) levels, whereas small inhibitory RNA of Nox4 only attenuated intracellular O(2)(*-) accumulation. These results suggest that Nox1 represents a major NAD(P)H oxidase isoform responsible for extracellular O(2)(*-) production. This rapid extracellular production of O(2)(*-) seems to be unique to OXO-induced M(1)-receptor activation, since ANG II-induced intra- and extracellular O(2)(*-) increases in parallel. It is concluded that the outward production of O(2)(*-) via NAD(P)H oxidase in CAMs may represent an important producing pattern for its autocrine or paracrine actions.

Upregulation of arginase by H2O2 impairs endothelium-dependent nitric oxide-mediated dilation of coronary arterioles

OBJECTIVE

Overproduction of reactive oxygen species such as hydrogen peroxide (H2O2) has been implicated in various cardiovascular diseases. However, mechanism(s) underlying coronary vascular dysfunction induced by H2O2 is unclear. We studied the effect of H2O2 on dilation of coronary arterioles to endothelium-dependent and endothelium-independent agonists.

METHODS AND RESULTS

Porcine coronary arterioles were isolated and pressurized without flow for in vitro study. All vessels developed basal tone and dilated dose-dependently to activators of nitric oxide (NO) synthase (adenosine and ionomycin), cyclooxygenase (arachidonic acid), and cytochrome P450 monooxygenase (bradykinin). Intraluminal incubation of vessels with H2O2 (100 micromol/L, 60 minutes) did not alter basal tone but inhibited vasodilations to adenosine and ionomycin in a manner similar as that by NO synthase inhibitor L-NAME. H2O2 affected neither endothelium-dependent responses to arachidonic acid and bradykinin nor endothelium-independent dilation to sodium nitroprusside. The inhibited adenosine response was not reversed by removal of H2O2 but was restored by excess L-arginine. Inhibition of L-arginine consuming enzyme arginase by alpha-difluoromethylornithine or N(omega)-hydroxy-nor-L-arginine also restored vasodilation. Administering deferoxamine, an inhibitor of hydroxyl radical production, prevented the H2O2-induced impairment of vasodilation to adenosine. Western blot and reverse-transcription polymerase chain reaction results indicated that arginase I was upregulated after treating vessels with H2O2.

CONCLUSIONS

H2O2 specifically impairs endothelium-dependent NO-mediated dilation of coronary microvessels by reducing L-arginine availability through upregulation of arginase. The formation of hydroxyl radicals from H2O2 may contribute to this process.