IL-4/STAT6 axis observed to reverse proliferative defect in SCA3 patient-derived neural progenitor cells

Spinocerebellar ataxia 3 (SCA3) is an incurable, neurodegenerative genetic disorder that leads to progressive cerebellar ataxia and other parkinsonian-like pathologies because of loss of cerebellar neurons. The role of an expanded polyglutamine aggregate on neural progenitor cells is unknown. Here, we show that SCA3 patient-specific induced neural progenitor cells (iNPCs) exhibit proliferative defects. Moreover, SCA3 iNPCs have reduced autophagic expression compared to control. Furthermore, although SCA3 iNPCs continue to proliferate, they do not survive subsequent passages compared to control iNPCs, indicating the likelihood that SCA3 iNPCs undergo rapid senescence. Exposure to interleukin-4 (IL-4), a type 2 cytokine produced by immune cells, resulted in an observed increase in expression of autophagic programs and a reduction in the proliferation defect observed in SCA3 iNPCs. Our results indicate a previously unobserved role of SCA3 disease ontology on the neural stem cell pool and a potential therapeutic strategy using IL-4 to ameliorate or delay disease pathology in the SCA3 neural progenitor cell population.

Type 2 cytokines promote angiogenesis in ischemic muscle via endothelial IL-4Rα signaling

Peripheral arterial disease (PAD) is one of the leading causes of cardiovascular morbidity and mortality worldwide, yet current trials on therapeutic angiogenesis remain suboptimal. Type 2 immunity is critical for post-ischemic regeneration, but its regulatory role in revascularization is poorly characterized. Here, we show that type 2 cytokines, interleukin-4 (IL-4) and interleukin-13 (IL-13), are the key mediators in post-ischemic angiogenesis. IL-4/IL-13-deficient mice exhibit impaired reperfusion and muscle repair in an experimental model of PAD. We find that deletion of IL-4Rα in the endothelial compartment, rather than the myeloid compartment, leads to remarkable impairment in revascularization. Mechanistically, IL-4/IL-13 promote endothelial cell proliferation, migration, and tube formation via IL-4Rα/STAT6 signaling. Furthermore, attenuated IL-4/IL-13 expression is associated with the angiogenesis deficit in the setting of diabetic PAD, while IL-4/IL-13 treatment rescues this defective regeneration. Our findings reveal the therapeutic potential of type 2 cytokines in treating patients with muscle ischemia.

Association between immune checkpoint inhibitors and myocardial infarction in Asians: A population-based self-controlled case series

BACKGROUND

While immune checkpoint inhibitors (ICIs) are associated with elevated cardiovascular risks, evidence of any association between ICIs and myocardial infarction (MI) was scarce, especially in Asians.

METHODS

Using prospectively collected population-based data, this self-controlled case series included patients prescribed an ICI between 1/1/2014 and 31/12/2020 in Hong Kong who had MI within January 1, 2013 to December 31, 2021. Incidence rate ratios (IRRs) for MI during and after ICI exposure were estimated, compared to the year before ICI initiation.

RESULTS

Of 3684 identified ICI users, 24 had MI during the study period. MI incidence increased significantly in the first 90 days of exposure (IRR 3.59 [95% confidence interval: 1.31-9.83], p = 0.013), but not days 91-180 (p = 0.148) or ≥181 (p = 0.591) of exposure, nor postexposure (p = 0.923). Sensitivity analyses excluding patients with MI-related death and incorporating extended exposure periods produced consistent results separately.

CONCLUSIONS

ICIs were associated with increased MI incidence in Asian Chinese patients during the first 90 days of use, but not later.

Nonlinear analysis of beat-to-beat variability of action potential time series data identifies dynamic re-entrant substrates in a hypokalaemic mouse model of acquired long QT syndrome

Background

Previous studies have quantified repolarization variability using time-domain, frequency-domain and nonlinear analysis in mouse hearts. Here, we investigated the relationship between these parameters and ventricular arrhythmogenicity in a hypokalaemia model of acquired long QT syndrome.

Methods

Left ventricular monophasic action potentials (MAPs) were recorded during right ventricular regular 8 Hz pacing during normokalaemia (5.2 mM [K+]), hypokalaemia modeling LQTS (3 mM [K+]) or hypokalaemia with 0.1 mM heptanol in Langendorff-perfused mouse hearts.

Results

During normokalaemia, mean APD was 33.5 ± 3.7 ms. Standard deviation (SD) of APDs was 0.63 ± 0.33 ms, coefficient of variation was 1.9 ± 1.0% and the root mean square (RMS) of successive differences in APDs was 0.3 ± 0.1 ms. Low- and high-frequency peaks were 0.6 ± 0.5 and 2.3 ± 0.7 Hz, respectively, with percentage powers of 38 ± 22 and 61 ± 23%. Poincaré plots of APDn+1 against APDn revealed ellipsoid morphologies with SD along the line-of-identity (SD2) to SD perpendicular to the line-of-identity (SD1) ratio of 4.6 ± 1.1. Approximate and sample entropy were 0.49 ± 0.12 and 0.64 ± 0.29, respectively. Detrended fluctuation analysis revealed short- and long-term fluctuation slopes of 1.62 ± 0.27 and 0.60 ± 0.18, respectively. Hypokalaemia provoked ventricular tachycardia in six of seven hearts, prolonged APDs (51.2 ± 7.9 ms), decreased SD2/SD1 ratio (3.1 ± 1.0), increased approximate and sample entropy (0.68 ± 0.08 and 1.02 ± 0.33) and decreased short-term fluctuation slope (1.23 ± 0.20) (ANOVA, P < 0.05). Heptanol prevented VT in all hearts studied without further altering the above repolarization parameters observed during hypokalaemia.

Conclusion

Reduced SD2/SD1, increased entropy and decreased short-term fluctuation slope may reflect arrhythmic risk in hypokalaemia. Heptanol exerts anti-arrhythmic effects without affecting repolarization variability.

Physiological concentration of protocatechuic acid directly protects vascular endothelial function against inflammation in diabetes through Akt/eNOS pathway

Background

Cardiovascular diseases (CVDs) have been the major cause of mortality in type 2 diabetes. However, new approaches are still warranted since current diabetic medications, which focus mainly on glycemic control, do not effectively lower cardiovascular mortality rate in diabetic patients. Protocatechuic acid (PCA) is a phenolic acid widely distributed in garlic, onion, cauliflower and other plant-based foods. Given the anti-oxidative effects of PCA in vitro, we hypothesized that PCA would also have direct beneficial effects on endothelial function in addition to the systemic effects on vascular health demonstrated by previous studies.

Methods and results

Since IL-1β is the major pathological contributor to endothelial dysfunction in diabetes, the anti-inflammatory effects of PCA specific on endothelial cells were further verified by the use of IL-1β-induced inflammation model. Direct incubation of db/db mouse aortas with physiological concentration of PCA significantly ameliorated endothelium-dependent relaxation impairment, as well as reactive oxygen species overproduction mediated by diabetes. In addition to the well-studied anti-oxidative activity, PCA demonstrated strong anti-inflammatory effects by suppressing the pro-inflammatory cytokines MCP1, VCAM1 and ICAM1, as well as increasing the phosphorylation of eNOS and Akt in the inflammatory endothelial cell model induced by the key player in diabetic endothelial dysfunction IL-1β. Upon blocking of Akt phosphorylation, p-eNOS/eNOS remained low and the inhibition of pro-inflammatory cytokines by PCA ceased.

Conclusion

PCA exerts protection on vascular endothelial function against inflammation through Akt/eNOS pathway, suggesting daily acquisition of PCA may be encouraged for diabetic patients.

Association between visit-to-visit lipid variability and incident cancer: a population-based cohort study

Dyslipidaemia is associated with increased cancer risk. However, the prognostic value of visit-to-visit lipid variability (VVLV) is unexplored in this regard. To investigate the associations between VVLV and the risk of incident cancer, we conducted a retrospective cohort study on adult patients attending a family medicine clinic in Hong Kong during 2000-2003, excluding those with <3 tests for low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), triglycerides, and total cholesterol (TC) each, those with prior cancer diagnosis, and those with <1 year of follow-up. Visit-to-visit LDL-C, HDL-C, TC, and triglycerides variabilities were measured by the coefficient of variation (CV). Patients were followed up until 31^st December 2019 for the primary outcome of incident cancer. Altogether, 69,186 patients were included (26,679 males (38.6%); mean age 60±13 years; mean follow-up 16±3 years); 7958 patients (11.5%) had incident cancer. Higher variability of LDL-C, HDL-C, TC, and TG was associated with higher risk of incident cancer. Patients in the third tercile of the CV of LDL-C (adjusted hazard ratio (aHR) against first tercile 1.06 [1.00, 1.12], p=0.049), HDL-C (aHR 1.37 [1.29, 1.44], p<0.001), TC (aHR 1.10 [1.04, 1.17], p=0.001), and TG (aHR 1.11 [1.06, 1.18], p<0.001) had the highest risks of incident cancer. Among these, only HDL-C variability remained associated with the risk of incident cancer in users of statins/fibrates. To conclude, higher VVLV was associated with significantly higher long-term risks of incident cancer. VVLV may be a clinically useful tool for cancer risk stratification.

Cardiovascular outcomes and hospitalizations in Asian patients receiving immune checkpoint inhibitors: a population-based study

Immune checkpoint inhibitors (ICI) have known associations with cardiotoxicity. However, a representative quantification of the adverse cardiovascular events and cardiovascular attendances amongst Asian users of ICI has been lacking. This retrospective cohort study identified all ICI users in Hong Kong, China, between 2013-2021. All patients were followed up until the end of 2021 for the primary outcome of major adverse cardiovascular event (MACE; a composite of cardiovascular mortality, myocardial infarction, heart failure, and stroke). Patients with prior diagnosis of any component of MACE were excluded from all MACE analyses. In total, 4324 patients were analysed (2905 (67.2%) males; median age 63.5 years old (interquartile range 55.4-70.7 years old); median follow-up 1.0 year (interquartile range 0.4-2.3 years)), of whom 153 were excluded from MACE analyses due to prior events. MACE occurred in 116 (2.8%) with an incidence rate (IR) of 1.7 [95% confidence interval: 1.4, 2.0] events per 100 patient-years; IR was higher within the first year of follow-up (2.9 [2.3, 3.5] events per 100 patient-years). Cardiovascular hospitalization(s) occurred in 188 (4.4%) with 254 episodes (0.5% of all episodes) and 1555 days of hospitalization (1.3% of all hospitalized days), for whom the IR of cardiovascular hospitalization was 5.6 [4.6, 6.9] episodes per 100 person-years with 52.9 [39.8, 70.3] days' stay per 100 person-years. Amongst Asian users of ICI, MACE was uncommon, and a small proportion of hospitalizations was cardiovascular in nature. Most MACE and cardiovascular hospitalizations occurred during the first year after initiating ICI.

Type 2 innate immunity drives distinct neonatal immune profile conducive for heart regeneration

Aims: Neonatal immunity is functionally immature and skewed towards a T_H2-driven, anti-inflammatory profile. This neonatal immunotolerance is partly driven by the type 2 cytokines: interleukin-4 (IL-4) and interleukin-13 (IL-13). Studies on neonatal cardiac regeneration reveal the beneficial role of an anti-inflammatory response in restoring cardiac function after injury. However, the role of an imbalanced immune repertoire observed in neonates on tissue regeneration is poorly understood; specifically, whether IL-4 and IL-13 actively modulate neonatal immunity during cardiac injury.

Methods and results: Neonatal mice lacking IL-4 and IL-13 (DKOs) examined at 2 days after birth exhibited reduced anti-inflammatory immune populations with basal cardiac immune populations like adult mice. Examination of neonates lacking IL-4 and IL-13 at 2 days post cardiac ischemic injury, induced on the second day after birth, showed impaired cardiac function compared to their control counterparts. Treatment with either IL-4 or IL-13 cytokine during injury restored both cardiac function and immune population profiles in knockout mice. Examination of IL-4/IL-13 downstream pathways revealed the role of STAT6 in mediating the regenerative response in neonatal hearts. As IL-4/IL-13 drives polarization of alternatively activated macrophages, we also examined the role of IL-4/IL-13 signaling within the myeloid compartment during neonatal cardiac regeneration. Injury of IL-4Rα myeloid specific knockout neonates 2 days after birth revealed that loss of IL-4/IL-13 signaling in macrophages alone was sufficient to impair cardiac regeneration.

Conclusions: Our results confirm that the T_H2 cytokines: IL-4 and IL-13, which skews neonatal immunity to a T_H2 profile, are necessary for maintaining and mediating an anti-inflammatory response in the neonatal heart, in part through the activation of alternatively activated macrophages, thereby permitting a niche conducive for regeneration.

Crocodile blood supplementation protects vascular function in diabetic mice

Abstract

Cardiovascular disease is a major cause of mortality in diabetic patients due to the heightened oxidative stress and pro-inflammatory state in vascular tissues. Effective approaches targeting cardiovascular health for diabetic patients are urgently needed. Crocodile blood, an emerging dietary supplement, was suggested to have anti-oxidative and anti-inflammatory effects in vitro, which have yet to be proven in animal models. This study thereby aimed to evaluate whether crocodile blood can protect vascular function in diabetic mice against oxidation and inflammation. Diabetic db/db mice and their counterparts db/m+ mice were treated daily with crocodile blood soluble fraction (CBSF) or vehicle via oral gavage for 4 weeks before their aortae were harvested for endothelium-dependent relaxation (EDR) quantification using wire myograph, which is a well-established functional study for vascular function indication. Organ culture experiments culturing mouse aortae from C57BL/6 J mice with or without IL-1β and CBSF were done to evaluate the direct effect of CBSF on endothelial function. Reactive oxygen species (ROS) levels in mouse aortae were assessed by dihydroethidium (DHE) staining with inflammatory markers in endothelial cells quantified by quantitative polymerase chain reaction (qPCR). CBSF significantly improved deteriorated EDR in db/db diabetic mice through both diet supplementation and direct culture, with suppression of ROS level in mouse aortae. CBSF also maintained EDR and reduced ROS levels in mouse aortae against the presence of pro-inflammatory IL-1β. Under the pro-inflammatory state induced by IL-1β, gene expressions of inflammatory cytokines were downregulated, while the protective transcripts UCP2 and SIRT6 were upregulated in endothelial cells. Our study suggests a novel beneficial effect of crocodile blood on vascular function in diabetic mice and that supplementation of diet with crocodile blood may act as a complementary approach to protect against vascular diseases through anti-oxidation and anti-inflammation in diabetic patients.

Graphical abstract

Potential of crocodile blood as a medication and dietary supplement: A systemic review

Crocodile blood has long been used as a traditional medicine in many Asian countries to treat diseases such as asthma, allergies, and many others. Yet, only recently has the safety and effectiveness of using crocodile blood as a medicine been examined using modern scientific methods; with both conserved and novel active components identified from crocodile blood. Further in vitro and in vivo investigations found that crocodile blood can have a wide range of beneficial effects, including antimicrobial, antiviral, anti-oxidative, anti-inflammatory, antitumour effects, anti-anaemia, and enhancement of wound healing. A systematic research of literature published in English-language journals up to April 2020 was conducted in PubMed, Google Scholar, and Web of Science. Based on the biological and chemical knowledge of crocodile immunity and crocodile blood, this article aims to: provide a critical review on the proposed properties of crocodile blood, identify the knowledge gap and offer some insights for future investigations regarding the use of crocodile blood as a medication or dietary supplement.

Butyrate protects endothelial function through PPARδ/miR-181b signaling

Reports of the beneficial roles of butyrate in cardiovascular diseases, such as atherosclerosis and ischemic stroke, are becoming increasingly abundant. However, the mechanisms of its bioactivities remain largely unknown. In this study, we explored the effects of butyrate on endothelial dysfunction and its potential underlying mechanism. In our study, ApoE^-/- mice were fed with high-fat diet (HFD) for ten weeks to produce atherosclerosis models and concurrently treated with or without sodium butyrate daily. Thoracic aortas were subsequently isolated from C57BL/6 wild-type (WT), PPARδ^-/-, endothelial-specific PPARδ wild-type (EC-specific PPARδ WT) and endothelial-specific PPARδ knockout (EC-specific PPARδ KO) mice were stimulated with interleukin (IL)-1β with or without butyrate ex vivo. Our results demonstrated that butyrate treatment rescued the impaired endothelium-dependent relaxations (EDRs) in thoracic aortas of HFD-fed ApoE^-/- mice. Butyrate also rescued impaired EDRs in IL-1β-treated thoracic aorta ring ex vivo. Global and endothelial-specific knockout of PPARδ eliminated the protective effects of butyrate against IL-1β-induced impairment to EDRs. Butyrate abolished IL-1β-induced reactive oxygen species (ROS) production in endothelial cells while the inhibitory effect was incapacitated by genetic deletion of PPARδ or pharmacological inhibition of PPARδ. IL-1β increased NADPH oxidase 2 (NOX2) mRNA and protein expressions in endothelial cells, which were prevented by butyrate treatment, and the effects of butyrate were blunted following pharmacological inhibition of PPARδ. Importantly, butyrate treatment upregulated the miR-181b expression in atherosclerotic aortas and IL-1β-treated endothelial cells. Moreover, transfection of endothelial cells with miR-181b inhibitor abolished the suppressive effects of butyrate on NOX2 expressions and ROS generation in endothelial cells. To conclude, butyrate prevents endothelial dysfunction in atherosclerosis by reducing endothelial NOX2 expression and ROS production via the PPARδ/miR-181b pathway.

Abstract 486: Type 2 Cytokines Are Required for the Resolution of Injury in Neonatal Hearts Following Ischemic Injury

Background: Type 2 signals such as interleukin-4 (IL-4) and interleukin-13 (IL-13) have been canonically defined as skewing naïve T-cells to Th2 cells and upregulating anti-inflammatory immune programs following injury. As opposed to adults, the immature immune system of the neonate basally prefers a Th2 versus a Th1 profile to maintain fetomaternal tolerance during development.

Hypothesis: Due to the required activation of type 2 immunity for proper resolution of injury coupled with the inherent Th2 immune profile of the neonate, we hypothesized that IL-4 and IL-13 play an indispensable role in the proper resolution of injury in the neonatal heart niche by fostering an anti-inflammatory response conducive for niche remodeling and growth factor release.

Methods and Results: Neonatal Balb/C and IL-4 -/- /IL-13 -/- (DKO) immune populations and overall heart regenerative capacity after left anterior descending (LAD) coronary artery ligation were profiled using flow cytometry and transthoracic echocardiography. DKO mice had significantly reduced CD4/CD8 ratios and suppression of CD206 + alternatively activated macrophages whilst increasing the population of pro-inflammatory Ly6c Hi monocytes. WT Balb/C mice had high CD4/CD8 ratios and actively reduced Ly6c Hi populations, preferring Ly6c Mid populations and anti-inflammatory CD206 + alternatively-activated macrophages. Furthermore, echocardiography demonstrated a reduction in both EF and FS in DKO mice following LAD ligation compared to control mice, which had complete restoration of EF and FS.

Summary: Our results confirmed that both IL-4 and IL-13 are required for mediating a Th2/M2 immune response following LAD ligation in the neonate, thereby permitting a niche that is conducive for regeneration. Future studies are needed to determine whether application of IL-4 and IL-13 in adult mice with myocardial infarction can similarly promote cardiac regeneration.

Chronic black tea extract consumption improves endothelial function in ovariectomized rats

Purpose

Menopause escalates the risk of cardiovascular diseases in women. There is an unmet need for better treatment strategy for estrogen-deficiency-related cardiovascular complications. Here we investigated the impact of chronic black tea extract (BT) consumption on cardiovascular function and lipid metabolism using a rat model of estrogen deficiency.

Methods

Female Sprague–Dawley rats were ovariectomized (OVX) and treated with BT (15 mg/kg/day, 4 weeks; active ingredients: theaflavins) or estrogen (E2) treatment for 4 weeks. Serum was collected for measuring cholesterol, triacylglycerol and estradiol levels. Changes in vascular reactivity were examined. The protein levels of NADPH oxidases were assessed by Western blotting. Reactive oxygen species (ROS) level was measured using dihydroethidium fluorescence imaging. The concentrations of cGMP were measured using ELISA kit.

Results

Aortic rings from control, BT-treated and E2-treated OVX rats exhibited a greater increase in Phe-induced contraction after inhibition of NO synthase compared with those from OVX rats. ACh-induced endothelium-dependent relaxations were augmented in aortae and renal arteries in BT/E2-treated OVX rats than in OVX rats. BT/E2 treatment improved flow-mediated dilatation in small mesenteric resistance arteries of OVX rats. BT/E2 treatment restored the eNOS phosphorylation level and reversed the up-regulation of NADPH oxidases and ROS overproduction in OVX rat aortae. ACh-stimulated cGMP production was significantly elevated in the aortae from BT- and E2-treated rats compared with those from OVX rats. BT/E2 treatment reduced circulating levels of total cholesterol.

Conclusions

The present study reveals the novel benefits of chronic BT consumption to reverse endothelial dysfunction and favorably modifying cholesterol profile in a rat model of estrogen deficiency and provides insights into developing BT as beneficial dietary supplements for postmenopausal women.

Regulation of multiple transcription factors by reactive oxygen species and effects of pro-inflammatory cytokines released during myocardial infarction on cardiac differentiation of embryonic stem cells

BACKGROUND

The mechanism of how reactive oxygen species (ROS) regulate cardiac differentiation in the long-run is unclear and the effect of pro-inflammatory cytokines secreted during myocardial infarction on the cardiac differentiation of embryonic stem cells (ESCs) is unknown. The aims of this study were 1) to investigate the effect of ROS on cardiac differentiation and the regulations of transcription factors in ESC differentiation cultures and 2) to investigate the effect of pro-inflammatory cytokines on the expression of cardiac structural genes and whether this effect is mediated through ROS signaling.

METHODS

ESCs were differentiated using hanging drop method. Degree of cardiac differentiation was determined by the appearance of beating embryoid bodies (EBs) and by the expression of cardiac genes using real-time PCR and Western blot. Intracellular ROS level was examined by confocal imaging.

RESULTS

H2O2-treated EBs were found to have enhanced cardiac differentiation in the long run as reflected by, firstly, an earlier appearance of beating EBs, and secondly, an upregulation in cardiac structural protein expression at both mRNA and protein levels. Also, ROS upregulated the expression of several cardiac-related transcription factors, and increased the post-translationally-activated transcription factors SRF and AP-1. IL-1β, IL-10, IL-18 and TNF-α upregulated the expression of cardiac structural proteins and increased the ROS level in differentiating EBs. In addition, ROS scavenger reversed the cardiogenic effect of IL-10 and IL-18.

CONCLUSIONS

These results demonstrated that ROS enhance cardiac differentiation of ESCs through upregulating the expression and activity of multiple cardiac-related transcription factors. IL-1β, IL-10, IL-18 and TNF-α enhance cardiac differentiation and ROS may serve as the messenger in cardiogenic signaling from these cytokines.

Oxidative stress-dependent cyclooxygenase-2-derived prostaglandin f(2α) impairs endothelial function in renovascular hypertensive rats

Abstract Aims: The role of endothelium-derived contracting factors (EDCFs) in regulating renovascular function is yet to be elucidated in renovascular hypertension (RH). The current study investigated whether oxidative stress-dependent cyclooxygenase (COX)-2-derived prostaglandin F(2α) (PGF(2α)) impairs endothelial function in renal arteries of renovascular hypertensive rats (RHR).

RESULTS

Renal hypertension was induced in rats by renal artery stenosis of both kidneys using the 2-kidney 2-clip model. Acute treatment with reactive oxygen species (ROS) scavengers, COX-2 inhibitors, and thromboxane-prostanoid receptor antagonists, but not COX-1 inhibitors, improved endothelium-dependent relaxations and eliminated endothelium-dependent contractions in RHR renal arteries. Five weeks of treatment with celecoxib or tempol reduced blood pressure, increased renal blood flow, and restored endothelial function in RHRs. Increased ROS production in RHR arteries was inhibited by ROS scavengers, but unaffected by COX-2 inhibitors; whereas increased PGF(2α) release was reduced by both ROS scavengers and COX-2 inhibitors. ROS also induced COX-2-dependent contraction in RHR renal arteries, which was accompanied by the release of COX-2-derived PGF(2α). Further, chronic tempol treatment reduced COX-2 and BMP4 upregulation, p38MAPK phosphorylation, and the nitrotyrosine level in RHR renal arteries.

CONCLUSION

These findings demonstrate the functional importance of oxidative stress, which serves as an initiator of increased COX-2 activity, and that COX-2-derived PGF(2α) plays an important role in mediating endothelial dysfunction in RH.

INNOVATION

The current study, thus, suggests that drugs targeting oxidative stress-dependent COX-2-derived PGF(2α) may be useful in the prevention and management of RH. Antioxid. Redox Signal. 16, 363-373.

Catalysis-based inhibitors of the calcium signaling function of CD38

CD38 is a signaling enzyme responsible for catalyzing the synthesis of cyclic ADP ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate; both are universal Ca(2+) messenger molecules. Ablation of the CD38 gene in mice causes multiple physiological defects, including impaired oxytocin release, that result in altered social behavior. A series of catalysis-based inhibitors of CD38 were designed and synthesized, starting with arabinosyl-2'-fluoro-2'-deoxynicotinamide mononucleotide. Structure-function relationships were analyzed to assess the structural determinants important for inhibiting the NADase activity of CD38. X-ray crystallography was used to reveal the covalent intermediates that were formed with the catalytic residue, Glu226. Metabolically stable analogues that were resistant to inactivation by phosphatase and esterase were synthesized and shown to be effective in inhibiting intracellular cADPR production in human HL-60 cells during induction of differentiation by retinoic acid. The inhibition was species-independent, and the analogues were similarly effective in blocking the cyclization reaction of CD38 in rat ventricular tissue extracts, as well as inhibiting the α-agonist-induced constriction in rat mesentery arteries. These compounds thus represent the first generally applicable and catalysis-based inhibitors of the Ca(2+) signaling function of CD38.

Raloxifene improves vascular reactivity in pressurized septal coronary arteries of ovariectomized hamsters fed cholesterol diet

Although vascular effects of selective estrogen receptor modulators (SERMs) have been extensively examined in conduit arteries, whether SERMs could favorably modulate myogenic response in resistance arteries is unknown. The impact of raloxifene therapy and cholesterol diet on myogenic constriction during estrogen deficiency is unresolved. This study investigated changes in vascular reactivity and myogenic responses in female ovariectomized (Ovx) hamsters fed high-cholesterol diet (HCD) with and without chronic treatment of raloxifene. Functional studies were performed on hamster septal coronary arteries cannulated in a pressure myograph. Acetylcholine (ACh)-induced dilatation was reduced in arteries from cholesterol-fed Ovx hamsters, but not in those from cholesterol-fed hamsters, while pressure-induced myogenic constriction was unaffected. Chronic treatment with raloxifene restored ACh-induced dilatation in cholesterol-fed Ovx hamsters. U46619-induced constriction was increased in arteries from cholesterol-fed Ovx hamsters but not from cholesterol-fed control hamsters, which was normalized by chronic raloxifene treatment. The pressure-diameter relationship is presented as normalized diameter versus intraluminal pressure, while the effect of ACh or U46619 is expressed as percentage of tone at 80 mm Hg. Two-way analysis of variance (ANOVA) followed by Bonferroni post-tests were used for statistical evaluation among different treatment groups. P<0.05 was taken as statistically significant. The present results show that chronic treatment with raloxifene could benefit myogenically active coronary arteries by (i) restoring ACh-induced dilatation and (ii) reducing U46619-induced constriction without affecting pressure-induced myogenic responses in cholesterol-fed hamsters during estrogen deficiency. If such benefit can be observed in humans, raloxifene and other SERMs may be useful to preserve endothelial function and curtail vascular hypersensitivity in resistance coronary arteries in post-menopausal women with hypercholesterolemia or hyperlipidemia, a lipid condition implicated in the pathogenesis of myocardial infarction.

Inhibition of renin-angiotensin system reverses endothelial dysfunction and oxidative stress in estrogen deficient rats

Background

Estrogen deficiency increases the cardiovascular risks in postmenopausal women. Inhibition of the renin-angiotensin system (RAS) and associated oxidative stress confers a cardiovascular protection, but the role of RAS in estrogen deficiency-related vascular dysfunction is unclear. The present study investigates whether the up-regulation of RAS and associated oxidative stress contributes to the development of endothelial dysfunction during estrogen deficiency in ovariectomized (OVX) rats.

Methodology/Principal Findings

Adult female rats were ovariectomized with and without chronic treatment with valsartan and enalapril. Isometric force measurement was performed in isolated aortae. The expression of RAS components was determined by immunohistochemistry and Western blotting method while ROS accumulation in the vascular wall was evaluated by dihydroethidium fluorescence. Ovariectomy increased the expression of angiotensin-converting enzyme (ACE), angiotensin II type 1 receptor (AT₁R), NAD(P)H oxidase, and nitrotyrosine in the rat aorta. An over-production of angiotensin II and ROS was accompanied by decreased phosphorylation of eNOS at Ser¹¹⁷⁷ in OVX rat aortae. These pathophysiological changes were closely coupled with increased oxidative stress and decreased nitric oxide bioavailability, culminating in markedly impaired endothelium-dependent relaxations. Furthermore, endothelial dysfunction and increased oxidative stress in aortae of OVX rats were inhibited or reversed by chronic RAS inhibition with enalapril or valsartan.

Conclusions/Significance

The novel findings highlight a significant therapeutic benefit of RAS blockade in the treatment of endothelial dysfunction-related vascular complications in postmenopausal states.

Design, synthesis and biological characterization of novel inhibitors of CD38

Human CD38 is a novel multi-functional protein that acts not only as an antigen for B-lymphocyte activation, but also as an enzyme catalyzing the synthesis of a Ca(2+) messenger molecule, cyclic ADP-ribose, from NAD(+). It is well established that this novel Ca(2+) signaling enzyme is responsible for regulating a wide range of physiological functions. Based on the crystal structure of the CD38/NAD(+) complex, we synthesized a series of simplified N-substituted nicotinamide derivatives (Compound 1-14). A number of these compounds exhibited moderate inhibition of the NAD(+) utilizing activity of CD38, with Compound 4 showing the highest potency. The crystal structure of CD38/Compound 4 complex and computer simulation of Compound 7 docking to CD38 show a significant role of the nicotinamide moiety and the distal aromatic group of the compounds for substrate recognition by the active site of CD38. Biologically, we showed that both Compounds 4 and 7 effectively relaxed the agonist-induced contraction of muscle preparations from rats and guinea pigs. This study is a rational design of inhibitors for CD38 that exhibit important physiological effects, and can serve as a model for future drug development.

Therapeutically relevant concentrations of raloxifene dilate pressurized rat resistance arteries via calcium-dependent endothelial nitric oxide synthase activation

OBJECTIVE

Selective estrogen receptor modulators (SERMs) inhibit constriction of mammalian conduit arteries. However, it is unknown whether SERMs at therapeutically achievable concentrations could reduce vascular tone in resistance arteries. The present study aimed to examine roles of Ca(2+) influx in endothelium and endothelial nitric oxide synthase (eNOS) activation in dilatations induced by raloxifene, a second-generation SERM in myogenically active arteries.

METHODS AND RESULTS

Small mesenteric arteries from Sprague-Dawley rats were isolated and mounted in a pressure myograph for measurement of changes in vessel diameter. [Ca(2+)](i) images on native endothelial cells of intact arteries were determined by the fluorescence imaging technique, and phosphorylation of eNOS was assayed by Western blotting. Raloxifene (0.3 to 10 nmol/L) produced dilatations on established steady myogenic constriction. Female rat arteries dilated significantly more in response to raloxifene than male arteries. Raloxifene-induced dilatations of female arteries were blunted by N(G)-nitro-l-arginine methyl ester but unaffected by 1400W, charybdotoxin plus apamin, wortmannin, or LY294002. Raloxifene (3 nmol/L) triggered rises in endothelial cell [Ca(2+)](i) and increased eNOS phosphorylation at Ser1177. Both effects were greater in arteries from female rats than in arteries from male rats. Increases in endothelial cell [Ca(2+)](i) and in eNOS phosphorylation were prevented by removal of extracellular Ca(2+) ions. Finally, ICI 182,780 did not affect the raloxifene-stimulated rise in endothelial cell [Ca(2+)](i), eNOS phosphorylation, and vasodilatations. Chronic raloxifene treatment reduced myogenic constriction in arteries from female but not male rats.

CONCLUSION

Raloxifene at therapeutically relevant concentrations inhibits myogenic constriction by an NO-dependent mechanism that causally involves the elevated [Ca(2+)](i) in endothelial cells and subsequent eNOS activation. Raloxifene dilates resistance arteries more effectively in female rats, indicating its significant gender-related action on endothelial cells in microcirculation.

Prostanoid TP receptor-mediated impairment of cyclic AMP-dependent vasorelaxation is reversed by phosphodiesterase inhibitors

Activation of the thromboxane prostanoid (TP) receptor produces potent vasoconstriction, which contributes to the increased vascular tone and blood pressure. The present study was designed to examine the hypothesis that stimulation of prostanoid TP receptors impairs endothelium-independent relaxations to cyclic AMP-elevating agents via increasing the activity of phosphodiesterases (PDEs). Rat carotid arteries without endothelium were isolated and suspended in myograph for the measurement of changes in isometric tension; the tissue content of cyclic AMP was assayed by enzyme immunoassay kit; and prostanoid TP receptor was detected in vascular wall by immunohistochemistry and Western blot. In phenylephrine-contracted rings without endothelium, relaxations induced by isoprenaline (receptor-mediated) and forskolin (receptor-independent) were markedly reduced by the presence of a prostanoid TP receptor agonist, U46619; the attenuated relaxations were prevented by acute treatment with S18886, the selective prostanoid TP receptor antagonist, but not by protein kinase C inhibitors. The reduced relaxations were partially restored by IBMX (non-selective PDE inhibitor), cilostazol (PDE3 inhibitor), rolipram (PDE4 inhibitor) or by Y27632 (Rho kinase inhibitor), but not by T0156 (PDE5 inhibitor). U46619 diminished isoprenaline- or forskolin-stimulated rise in cyclic AMP and this effect was inhibited by cilostazol, rolipram or Y27632. The present results suggest that activation of prostanoid TP receptors impairs cyclic AMP-dependent vasorelaxations partly via PDE- and RhoA/Rho kinase-dependent mechanisms. Inhibitors of PDEs and Rho kinase may be useful in the treatment of cardiovascular complications.

Thromboxane prostanoid receptor activation impairs endothelial nitric oxide-dependent vasorelaxations: the role of Rho kinase

Activation of thromboxane prostanoid (TP) receptors causes potent vasoconstriction, which contributes to increased vascular tone and blood pressure. The present study examined the hypothesis that stimulation of TP receptor impaired endothelial nitric oxide-mediated vasorelaxation via a Rho kinase-dependent mechanism. The common carotid arteries of Sprague-Dawley rats were isolated and suspended in myograph for measurement of changes in isometric tension. The production of nitric oxide in primary cultured aortic endothelial cells was assayed with an imaging technique and phosphorylated levels of endothelial NOS were determined by Western blot analysis. 9,11-dideoxy-11alpha,9alpha-epoxy-methanoprostaglandin F(2alpha) (U46619) inhibited isoprenaline-induced relaxations in rings with or without endothelium. Treatment with Rho kinase inhibitors, Y27632 (2 microM) or HA 1077 (10 microM) prevented the effect of U46619 only in rings with endothelium while protein kinase C inhibitors were without effect. Rho kinase inhibitors did not affect isoprenaline-induced relaxations in endothelium-intact rings treated with L-NAME or 1H-[1,2,4]oxadizolo[4,3-a]quinoxalin-1-one (ODQ). Isoprenaline stimulated rises in nitric oxide (NO) production in cultured rat endothelial cells. The increased NO production was inhibited by U46619 (100 nM) and this effect was prevented by treatment with Y27632 but unaffected by the absence of extracellular calcium ions. U46619 attenuated isoprenaline-stimulated phosphorylation of eNOS, which was sensitive to inhibition by Y27632 and HA 1077. U46619-mediated effects were abolished by TP receptor antagonist, S18886 and the TP receptor was present in endothelial cells. The present results demonstrate that Rho kinase activation is likely to be the primary mechanism that underlies the U46619-stimulated TP-receptor-mediated inhibition of endothelial NO production and subsequent endothelium-dependent relaxations to isoprenaline.

Protopanaxadiol and protopanaxatriol bind to glucocorticoid and oestrogen receptors in endothelial cells

BACKGROUND AND PURPOSE

Ginsenosides are used widely for medicinal purposes, but the mechanisms of their action are still unclear, although there is some evidence that these effects are mediated by nuclear receptors. Here we examined whether two metabolites of ginsenoside, protopanaxadiol (g-PPD) and protopanaxatriol (g-PPT), could modulate endothelial cell functions through the glucocorticoid receptor (GR) and oestrogen receptor (ER). EXPERIMENT APPROACHES: The effects of g-PPD and g-PPT on intracellular calcium ion concentration ([Ca(2+)](i)) and nitric oxide (NO) production in human umbilical vein endothelial cells (HUVECs) were measured using Fura-2-acetoxymethyl ester, 4-amino-5-methylamino-2',7'-difluorofluorescein and Griess reagent. Effects on expression of GR and ER isoforms in HUVECs were determined using reverse transcriptase-/real-time PCR and immunocytochemistry. Phosphorylation of endothelial NO synthase (eNOS) was assessed by Western blotting.

RESULTS

Ginsenoside protopanaxadiol and g-PPT increased [Ca(2+)](i), eNOS phosphorylation and NO production in HUVECs, which were inhibited by the GR antagonist, RU486, the ER antagonist, ICI 182,780 and siRNA targeting GR or ERbeta. The NO production was Ca(2+)-dependent and the [Ca(2+)](i) elevation in HUVECs resulted from both intracellular Ca(2+) release and extracellular Ca(2+) influx.

CONCLUSIONS AND IMPLICATIONS

Ginsenoside protopanaxadiol and g-PPT were functional ligands for both GR and ERbeta, through which these ginsenoside metabolites exerted rapid, non-genomic effects on endothelial cells.

Role of cyclic nucleotides in the control of cytosolic Ca2+ levels in vascular endothelial cells

1. Endothelial cells have a key role in the cardiovascular system. Most endothelial cell functions depend on changes in cytosolic Ca(2+) concentrations ([Ca(2+)](i)) to some extent and Ca2+ signalling acts to link external stimuli with the synthesis and release of regulatory factors in endothelial cells. The [Ca(2+)](i) is maintained by a well-balanced Ca(2+) flux across the endoplasmic reticulum and plasma membrane. 2. Cyclic nucleotides, such as cAMP and cGMP, are very important second messengers. The cyclic nucleotides can affect [Ca(2+)](i) directly or indirectly (via the actions of protein kinase (PK) A or PKG-mediated phosphorylation) by regulating Ca(2+) mobilization and Ca(2+) influx. Fine-tuning of [Ca(2+)](i) is also fundamental to protect endothelial cells against damaged caused by the excessive accumulation of Ca(2+). 3. Therapeutic agents that control cAMP and cGMP levels have been used to treat various cardiovascular diseases. 4. The aim of the present review is to discuss: (i) the functions of endothelial cells; (ii) the importance of [Ca(2+)](i) in endothelial cells; (iii) the impact of excessive [Ca(2+)](i) in endothelial cells; and (iv) the balanced control of [Ca(2+)](i) in endothelial cells via involvement of cyclic nucleotides (cAMP and cGMP) and their general effectors.

Inhibition of anti-IgE mediated human mast cell activation by NO donors is dependent on their NO release kinetics

BACKGROUND AND PURPOSE

Although the mast cell is a source of nitric oxide (NO), the effect of NO on human mast cells has not been defined. This study investigated if exogenous NO could affect human mast cell activation.

EXPERIMENTAL APPROACH

Effects of different NO donors on immunoglobulin E (IgE)-dependent activation of human-cultured mast cells (HCMC) derived from precursors in buffy coat were investigated by measuring histamine release. Intracellular NO in HCMC was monitored with confocal microscopy using the fluorescent NO indicator 4-amino-5-methylamino-2', 7'-difluorofluorescein.

KEY RESULTS

Diethylamine NONOate (DEA/NO) and MAHMA NONOate (NOC-9), both have rapid NO release rates, only inhibited anti-IgE-induced histamine release when added to HCMC at the time of activation. NO donors with slower NO release kinetics were ineffective even after 30 min incubation. Confocal microscopy revealed that the effectiveness of NO donors was dependent on the availability of adequate NO inside HCMC during activation. The inhibitory action of DEA/NO was diminished by the NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl but potentiated by the anti-oxidant, N-acetylcysteine (NAC). Furthermore, co-incubation with NAC allowed previously ineffective NO donors to suppress HCMC activation and thus suggested that NAC could increase the availability of NO from NO donors.

CONCLUSIONS AND IMPLICATIONS

Our results demonstrated that NO was able to modulate human mast cell activation but only when enough NO was present at the time of cell activation. Our findings explain the controversy over the effectiveness of NO on mast cell degranulation and supports the possibility that NO donors could be beneficial for treating allergic inflammation.

Cyclooxygenase-2–Derived Prostaglandin F 2α Mediates Endothelium-Dependent Contractions in the Aortae of Hamsters With Increased Impact During Aging

Hypertension and vascular dysfunction result in the increased release of endothelium-derived contracting factors (EDCFs), whose identity is poorly defined. We tested the hypothesis that endothelial cyclooxygenase (COX)-2 can generate EDCFs and identified the possible EDCF candidate. Changes in isometric tension of aortae of young and aged hamsters were recorded on myograph. Real-time changes in intracellular calcium concentrations ([Ca 2+ ] i ) in native aortic endothelial cells were measured by imaging. Endothelium-dependent contractions were triggered by acetylcholine (ACh) after inhibition of nitric oxide production and they were abolished by COX-2 but not COX-1 inhibitors or by thromboxane–prostanoid receptor antagonists. 2-Aminoethoxydiphenyl borate (cation channel blocker) eliminated endothelium-dependent contractions and ACh-stimulated rises in endothelial cell [Ca 2+ ] i . RT-PCR and Western blotting showed COX-2 expression mainly in the endothelium. Enzyme immunoassay and high-performance liquid chromatography-coupled mass spectrometry showed release of prostaglandin (PG)F 2α and prostacyclin (PGI 2 ) increased by ACh; only PGF 2α caused contraction at relevant concentrations. COX-2 expression, ACh-stimulated contractions, and vascular sensitivity to PGF 2α were augmented in aortae from aged hamsters. Human renal arteries also showed thromboxane–prostanoid receptor–mediated ACh- or PGF 2α -induced contractions and COX-2–dependent release of PGF 2α . The present study demonstrates that PGF 2α , derived from COX-2, which is localized primarily in the endothelium, is the most likely EDCF underlying endothelium-dependent, thromboxane–prostanoid receptor–mediated contractions to ACh in hamster aortae. These contractions involved increases in endothelial cell [Ca 2+ ] i . The results support a critical role of COX-2 in endothelium-dependent contractions in this species with an increased importance during aging and, possibly, a similar relevance in humans.

Raloxifene protects endothelial cell function against oxidative stress

BACKGROUND AND PURPOSE

Maintaining a delicate balance between the generation of nitric oxide (NO) and removal of reactive oxygen species (ROS) within the vascular wall is crucial to the physiological regulation of vascular tone. Increased production of ROS reduces the effect and/or bioavailability of NO, leading to an impaired endothelial function. This study tested the hypothesis that raloxifene, a selective oestrogen receptor modulator, can prevent endothelial dysfunction under oxidative stress.

EXPERIMENTAL APPROACH

Changes in isometric tension were measured in rat aortic rings. The content of cyclic GMP in aortic tissue was determined by radioimmunoassay. Phosphorylation of endothelial NOS (eNOS) and Akt was assayed by Western blot analysis.

KEY RESULTS

In rings with endothelium, ACh-induced relaxations were attenuated by a ROS-generating reaction (hypoxanthine plus xanthine oxidase, HXXO). The impaired relaxations were ameliorated by acute treatment with raloxifene. HXXO suppressed the ACh-stimulated increase in cyclic GMP levels; this effect was antagonized by raloxifene. The improved endothelial function by raloxifene was abolished by ICI 182,780, and by wortmannin or LY294002. Raloxifene also protected endothelial cell function against H2O2. Raloxifene increased the phosphorylation of eNOS at Ser-1177 and Akt at Ser-473; this effect was blocked by ICI 182,780. Finally, raloxifene was not directly involved in scavenging ROS, and neither inhibited the activity of xanthine oxidase nor stimulated that of superoxide dismutase.

CONCLUSION AND IMPLICATIONS

Raloxifene is effective against oxidative stress-induced endothelial dysfunction in vitro through an ICI 182,780-sensitive mechanism that involves the increased phosphorylation and activity of Akt and eNOS in rat aortae.

Prevention of nitroglycerin tolerance in vitro by T0156, a selective phosphodiesterase type 5 inhibitor

The efficacy of nitroglycerin as a vasodilator is limited by tolerance, which develops shortly after treatment begins. The present study aims to examine whether T0156, a newly developed potent and selective inhibitor of phosphodiesterase type 5 (PDE5), could attenuate the tolerance to nitroglycerin on rat aortas. Rat aortic rings were suspended in organ bath for the measurement of changes in isometric tension and nitrate tolerance was acutely induced by preceding exposure for 90 min to 30 microM nitroglycerin. Concentration-response curves to nitroglycerin were obtained on aortic rings pre-contracted with phenylephrine. Pre-exposure of rings with or without endothelium to nitroglycerin reduced the relaxations to nitroglycerin. The tissue levels of cyclic GMP were measured by enzyme immunoassay kit. Treatment with T0156 inhibited and prevented the reduced relaxation and cyclic GMP levels in response to nitroglycerin in tolerant rings. In contrast, nitroglycerin-induced tolerance was unaffected by cilostazol (PDE3 inhibitor) and rolipram (PDE4 inhibitor). Finally, incubation of aortic rings with thromboxane prostanoid receptor antagonist, cyclooxygenase inhibitor, or endothelin ET(A) receptor antagonist did not inhibit the development of tolerance. The present results suggest that nitroglycerin tolerance may involve an increased activity of PDE5 but not PDE3 or PDE4 isoforms in vascular smooth muscle cells since T0156 prevents the development of tolerance. Thromboxane A(2), cyclooxygenase (COX)-dependent prostaglandins and endothelin 1 play little role in the acute induction of nitroglycerin tolerance.

Store-operated calcium entry in vascular smooth muscle

In non-excitable cells, activation of G-protein-coupled phospholipase C (PLC)-linked receptors causes the release of Ca(2+) from intracellular stores, which is followed by transmembrane Ca(2+) entry. This Ca(2+) entry underlies a small and sustained phase of the cellular [Ca(2+)](i) increases and is important for several cellular functions including gene expression, secretion and cell proliferation. This form of transmembrane Ca(2+) entry is supported by agonist-activated Ca(2+)-permeable ion channels that are activated by store depletion and is referred to as store-operated Ca(2+) entry (SOCE) and represents a major pathway for agonist-induced Ca(2+) entry. In excitable cells such as smooth muscle cells, Ca(2+) entry mechanisms responsible for sustained cellular activation are normally considered to be mediated via either voltage-operated or receptor-operated Ca(2+) channels. Although SOCE occurs following agonist activation of smooth muscle, this was thought to be more important in replenishing Ca(2+) stores rather than acting as a source of activator Ca(2+) for the contractile process. This review summarizes our current knowledge of SOCE as a regulator of vascular smooth muscle tone and discusses its possible role in the cardiovascular function and disease. We propose a possible hypothesis for its activation and suggest that SOCE may represent a novel target for pharmacological therapeutic intervention.

Raloxifene, tamoxifen and vascular tone

1. Oestrogen deficiency causes progressive reduction in endothelial function. Despite the benefits of hormone-replacement therapy (HRT) evident in earlier epidemiological studies, recent randomized trials of HRT for the prevention of heart disease found no overall benefit. Instead, HRT users had higher incidences of stroke and heart attack. Most women discontinue HRT because of its many side-effects and/or the increased risk of breast and uterine cancer. This has contributed to the development of selective oestrogen receptor modulators (SERMs), such as tamoxifen and raloxifene, as alternative oestrogenic agents. 2. A SERM is a molecule that binds with high affinity to oestrogen receptors but has tissue-specific effects distinct from oestrogen, acting as an oestrogen agonist in some tissues and as an antagonist in others. Clinical and animal studies suggest multiple cardiovascular effects of SERMs. For example, raloxifene lowers serum levels of cholesterol and homocysteine, attenuates oxidation of low-density lipoprotein, inhibits endothelial-leucocyte interaction, improves endothelial function and reduces vascular smooth muscle tone. 3. Available evidence suggests that raloxifene and tamoxifen are capable of acting directly on both endothelial cells and the underlying vascular smooth muscle cells and cause a multitude of favourable modifications of the vascular wall, which jointly contribute to improved local blood flow. The outcome of the Raloxifene Use for the Heart (RUTH) trial will determine whether raloxifene, currently approved for the treatment of post-menopausal osteoporosis, could substitute for HRT in alleviating cardiovascular symptoms in post-menopausal women.

Therapeutic concentrations of raloxifene augment nitric oxide-dependent coronary artery dilatation in vitro

BACKGROUND AND PURPOSE

Raloxifene improves cardiovascular function. This study examines the hypothesis that therapeutic concentrations of raloxifene augment endothelium-dependent relaxation via up-regulation of eNOS expression and activity in porcine coronary arteries.

EXPERIMENTAL APPROACH

Isometric tension was measured in rings from isolated arteries. Intracellular Ca(2+) concentrations ([Ca(2+)](i)) in arterial endothelial cells were detected by Ca(2+) fluorescence imaging. Phosphorylation of eNOS at Ser-1177 was assayed by Western blot analysis.

KEY RESULTS

In arterial rings pre-contracted with 9,11-dideoxy-11alpha,9alpha-epoxy-methano-prostaglandin F(2alpha) (U46619), treatment with raloxifene (1-3 nM) augmented bradykinin- or substance P-induced relaxation and this effect was antagonized by ICI 182,780, an estrogen receptor antagonist. The enhanced relaxation was abolished in rings treated with inhibitors of nitric oxide/cyclic GMP-dependent dilation, N(G)-nitro-L-arginine methyl ester (L-NAME) plus 1H-[1,2,4]oxadizolo[4,3-a]quinoxalin-1-one (ODQ). In contrast, effects of raloxifene were unaffected after inhibition of endothelium-derived hyperpolarizing factors by charybdotoxin plus apamin. Raloxifene (3 nM) did not influence endothelium-independent relaxation to sodium nitroprusside. 17beta-Estradiol (3-10 nM) also enhanced bradykinin-induced relaxation, which was inhibited by ICI 182,780. Treatment with raloxifene (3 nM) did not affect bradykinin-stimulated rise in endothelial cell [Ca(2+)](i). Raloxifene, 17beta-estradiol, and bradykinin increased eNOS phosphorylation at Ser-1177 and ICI 182,780 prevented effects of raloxifene or 17beta-estradiol but not that of bradykinin. Raloxifene had neither additive nor antagonistic effects on 17beta-estradiol-induced eNOS phosphorylation.

CONCLUSIONS AND IMPLICATIONS

Raloxifene in therapeutically relevant concentrations augmented endothelial function in porcine coronary arteries in vitro through ICI 182,780-sensitive mechanisms that were associated with increased phosphorylation of eNOS but independent of changes in endothelial cell [Ca(2+)](i).

Non-genomic effects of ginsenoside-Re in endothelial cells via glucocorticoid receptor

We demonstrated that ginsenoside-Re (Re), a pharmacological active component of ginseng, is a functional ligand of glucocorticoid receptor (GR) using competitive ligand-binding assay (IC(50)=156.6 nM; K(d)=49.7 nM) and reporter gene assay. Treatment with Re (1 microM) raises intracellular Ca(2+) ([Ca(2+)](i)) and nitric oxide (NO) levels in human umbilical vein endothelial cells as measured using fura-2 and 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate, respectively. Western blot analysis shows that Re increased phosphorylation of endothelial nitric oxide synthase. These effects were abolished by GR antagonist RU486, siRNA targeting GR, non-selective cation channel blocker 2-aminoethyldiphenylborate, or in the absence of extracellular Ca(2+), indicating Re is indeed an agonistic ligand for the GR and the activated GR induces rapid Ca(2+) influx and NO production in endothelial cells.

Calcium and reactive oxygen species increase in endothelial cells in response to releasers of endothelium-derived contracting factor

BACKGROUND AND PURPOSE

Experiments were designed to assess whether or not the intracellular concentration of calcium and reactive oxygen species (ROS) increase in endothelial cells of the rat thoracic aorta in response to releasers of endothelium-derived contracting factor (EDCF) and if so, whether or not a difference exists between spontaneously hypertensive (SHR) and normotensive (WKY) rats.

EXPERIMENTAL APPROACH

Calcium and ROS were measured by confocal microscopy, using Fura-red in combination with Fluo-4 and dichlorodihydrofluorescein diacetate, respectively.

KEY RESULTS

Acetylcholine caused a rapid increase in cytosolic calcium concentration in endothelial cells of both SHR and WKY, which was significantly more pronounced in aortae of the former strain. This rise of calcium was not affected by indomethacin (an inhibitor of cyclooxygenase) or Tiron plus diethyldithiocarbamate acid (DETCA) (membrane permeable antioxidants). In the presence of a nitric oxide synthase blocker, acetylcholine also caused a rapid increase in ROS in endothelial cells of SHR but not in those of WKY. The burst of ROS was prevented by indomethacin or Tiron plus DETCA.

CONCLUSIONS AND IMPLICATIONS

These experiments show that endothelial cells of SHR are more prone to calcium and ROS overload upon stimulation with acetylcholine. The abnormal accumulation of calcium is a prerequisite to initiate the release of EDCF and can be mimicked using the calcium ionophore A23187. The sequence of events occurring during endothelium-dependent contractions firstly requires the accumulation of calcium, which then activates cyclooxygenase and produces ROS along with EDCF that in turn stimulates TP-receptors, resulting in EDCF-mediated contractions.

Cilnidipine, a slow-acting Ca2+ channel blocker, induces relaxation in porcine coronary artery: role of endothelial nitric oxide and [Ca2+]i

Cilnidipine is a dual blocker of L-type voltage-gated Ca(2+) channels in vascular smooth muscle and N-type Ca(2+) channels in sympathetic nerve terminals that supply blood vessels. However, the clinical benefits of cilnidipine and underlying mechanisms are incompletely understood. This study was designed to compare the time course of relaxant responses to cilnidipine and nifedipine, and to examine the role of endothelial NO and [Ca(2+)](i) in the vasorelaxation. Porcine left circumflex coronary arteries were isolated and isometric tension was measured with Grass force transducers. Endothelial [Ca(2+)](i) in intact arteries was determined by a calcium fluorescence imaging technique. The free radical scavenging capacity was also assayed. Cilnidipine and nifedipine induced concentration-dependent relaxations in high KCl-precontracted artery rings, while the former-induced relaxation was slower as compared to the latter. Treatment with L-NAME or ODQ reduced relaxations to cilnidipine or nifedipine to the same extent as in rings without endothelium. Indomethacin or omega-conotoxin had no effects. L-Arginine antagonized the effect of L-NAME on cilnidipine-induced relaxations. Cilnidipine did not affect sodium nitroprusside-induced relaxation in rings with and without endothelium. Cilnidipine and nifedipine caused extracellular Ca(2+)-dependent increases in endothelial [Ca(2+)](i) in intact arteries and cilnidipine's action had a slower onset, similar to that of cilnidipine-induced relaxation. Neither cilnidipine nor nifedipine exhibited a free radical scavenging property. The present results demonstrate that cilnidipine can produce endothelium-dependent relaxation in porcine coronary arteries in vitro in addition to blocking Ca(2+) channels. Like short-acting nifedipine, cilnidipine-dependent relaxation, albeit to a slower onset, is partly mediated by endothelial NO but not by prostacyclin. The increased release or bioavailability of NO may causally result from elevated endothelial [Ca(2+)](i) in arteries. The Ca(2+) channel-independent effect suggests the usefulness of cilnidipine in the treatment of cardiovascular diseases associated with diminished NO release, such as atherosclerosis.

Endothelium-independent relaxation to raloxifene in porcine coronary artery

Although the vascular action of raloxifene has been studied in several vascular beds, the underlying mechanisms are still incompletely understood. The role of endothelium in raloxifene-induced vascular responses was controversial. The present study was designed to examine endothelium-independent effects of raloxifene in isolated porcine left circumflex coronary arteries. Arterial rings were suspended in organ baths and changes in isometric tension were measured. The large-conductance Ca2+-activated K+(BK(Ca)) currents were recorded using a whole-cell patch-clamp technique. Treatment with raloxifene (1-10 micromol/l) reduced the contractions to 9,11-dideoxy-11alpha,9alpha-epoxy-methanoprostaglandin F2alpha (U46619), serotonin (5-HT), endothelin-1 in normal Krebs solution and to CaCl2 in a Ca2+-free, high K+-containing solution. In endothelin-1-contracted rings, raloxifene (0.3 to 50 micromol/l) caused relaxations which were comparable in rings with and without endothelium. The raloxifene-induced relaxation was reduced by putative K+ channel blockers, iberiotoxin and tetraethyl ammonium chloride (TEA+) in rings with and without endothelium, or by elevated extracellular K+ ions (30 mmol/l K+ and 60 mmol/l K+). 13-methyl-7-[9-(4,4,5,5,5-pentafluoropentylsulfinyl)nonyl]-7,8,9,11,12,13,14,15,16, 17-decahydro-6H-cyclopenta[a] phenanthrene-3,17-diol (ICI 182,780) did not affect raloxifene-induced relaxation. Raloxifene enhanced the outward BK(Ca) currents, which were sensitive to inhibition by iberiotoxin. In summary, the present study shows that raloxifene acutely relaxes porcine coronary arteries via an endothelium-independent mechanism without involving the ICI 182,780-sensitive estrogen receptors. Raloxifene mainly acts on the vascular smooth muscle cells to induce vasorelaxation by the inhibition of Ca2+ channels and the activation of BK(Ca) channels. The former mechanism appears to play a more significant role.

Tamoxifen dilates porcine coronary arteries: roles for nitric oxide and ouabain-sensitive mechanisms

BACKGROUND AND PURPOSE

Experiments were designed to determine the mechanism of the relaxation induced by tamoxifen in porcine coronary arteries at the tissue, cellular and molecular levels.

EXPERIMENTAL APPROACH

Porcine left circumflex coronary arteries were isolated and isometric tension was measured. [Ca2+]i in native endothelial cells of intact arteries was determined by a calcium fluorescence imaging technique and eNOS ser1177 phosphorylation was assayed by Western blotting.

KEY RESULTS

Tamoxifen induced an endothelium-dependent relaxation that was antagonized by ICI 182,780 and abolished by NG-nitro-L-arginine methyl ester (L-NAME) or 1H-[1,2,4]oxadizolo[4,3-a]quinoxalin-1-one (ODQ). L-Arginine reversed the effect of L-NAME while indomethacin was without effect. Tamoxifen-induced relaxation was attenuated by charybdotoxin (CTX) plus apamin, ouabain or by incubation in a K+ -free solution. Moreover, tamoxifen triggered extracellular Ca2+ -dependent increases in endothelial [Ca2+]i and this effect was abolished by ICI 182,780. Endothelium-independent relaxation to sodium nitroprusside was also inhibited by ouabain or in a K+ -free solution. Furthermore, tamoxifen increased endothelial nitric oxide synthase (eNOS) phosphorylation at Ser-1177 and ICI 182,780 prevented this effect.

CONCLUSIONS AND IMPLICATIONS

The present results suggest that tamoxifen mainly induces endothelium-dependent relaxation and that endothelial nitric oxide (NO) is the primary mediator of this effect. NO-dependent responses may result from elevated [Ca2+]i in endothelial cells; an effect abolished by ICI 182,780. NO activates Na+/K+ -ATPase in vascular smooth muscle, leading to relaxation. These results suggest that tamoxifen is able to modulate eNOS phosphorylation directly.

Endothelial mediators of the acetylcholine-induced relaxation of the rat femoral artery

This study examined endothelium-derived mediators of acetylcholine-induced relaxation in male rat femoral arteries. Arterial rings were suspended in a myograph for the measurement of isometric force. The generation of hydrogen peroxide (H2O2) in endothelial cells was detected using the fluorescent probe, 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate acetyl ester. N(G)-nitro-L-arginine methyl ester (L-NAME, NOS inhibitor) and 1H-[1,2,4]oxadiazolo[4,2-alpha]quinoxalin-1-one (ODQ, guanylate cyclase inhibitor) alone or in combination with indomethacin (cycloxygenase inhibitor) diminished acetylcholine-induced endothelium-dependent relaxation to a similar extent. A small relaxation to acetylcholine in 60 mM KCl-constricted rings was abolished by L-NAME. Acetylcholine-induced relaxation was reduced by charybdotoxin plus apamin (intermediate- and small-conductance Ca2+-activated K+ channel blockers, respectively) or by 30 mM KCl. Both ouabain (Na+/K+ ATPase inhibitor) and BaCl2 (K(IR) channel blocker) also inhibited the relaxation albeit to a lesser degree. In the presence of L-NAME, ODQ plus indomethacin, charybdotoxin plus apamin or ouabain plus BaCl2 produced further inhibition. Catalase attenuated acetylcholine-induced relaxations and this attenuation was prevented by 3-amino-1,2,4-triazole (catalase inhibitor). Catalase did not affect acetylcholine-induced relaxations in rings treated with L-NAME or ODQ. Acetylcholine increased the dichlorofluorescein fluorescence intensity in native endothelial cells and this effect was abolished by catalase and by L-NAME. Exogenous H2O2 caused endothelium-independent relaxation that was slightly inhibited by iberiotoxin, ODQ or significantly reduced by elevated KCl, and abolished by catalase. The present results indicate that in addition to nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF, sensitive to charybdotoxin plus apamin, ouabain, and BaCl2), the endothelium of rat femoral artery can release H2O2 in response to acetylcholine, which was sensitive to L-NAME. Thus, the eNOS-dependent H2O2 is likely to be the third mediator of acetylcholine-mediated relaxations in rat femoral arteries.

Reactive oxygen species in vascular wall

Reactive oxygen species (ROS) contribute to the pathogenesis of cardiovascular diseases including hypertension, atherosclerosis, cardiac hypertrophy, heart failure and diabetes mellitus. Oxidative stress is resulted from excessive generation of ROS that outstrips the antioxidant system. Various agonists, pathological conditions and therapeutic interventions lead to modulated expression and function of oxidant and antioxidant enzymes, including NAD(P)H oxidase, endothelial nitric oxide synthase, xanthine oxidase, myeloperoxidase, superoxide dismutases, catalase and glutathione peroxidase. ROS formed in vascular wall target a wide range of signaling molecules and cellular pathways in both endothelium and vascular smooth muscle, such as transcription factors, protein tyrosine phosphatase, protein tyrosine kinase, mitogen-activated protein kinase, Ca(2+)-transporting system and protein modification. ROS also have distinct physiological and pathophysiological impacts on vascular cells. ROS contribute to vascular dysfunction and remodeling through oxidative damage by (1) reducing the bioavailability of NO, (2) impairing endothelium-dependent vasodilatation and endothelial cell growth, (3) causing apoptosis or anoikis, (4) stimulating endothelial cell migration, and (5) activating adhesion molecules and inflammatory reaction, leading to endothelial dysfunction, an initial episode progressing toward hypertension and atherosclerosis. Cellular events underlying these processes involve changes in vascular smooth muscle cell growth, apoptosis/anoikis, cell migration, inflammation, and vasoconstriction. The present communication focuses on the biology of ROS signaling in vascular cells, discusses how oxidative stress contributes to vascular damage, and the therapeutic strategies/biotic factors that can prevent or treat ROS-associated cardiovascular disorders.

Raloxifene relaxes rat intrarenal arteries by inhibiting Ca2+ influx

Raloxifene may confer vascular benefits without causing estrogen-related side effects. However, its action on renal vascular circulation is unknown. This study aimed to examine the sex difference and roles of the endothelium and Ca2+ channels in rat renovascular relaxation to raloxifene. On isolated intralobar renal artery rings mounted in a myograph and contracted by U-46619, concentration-relaxation curves were constructed for raloxifene and contractions to CaCl2 were studied. Changes in intracellular Ca2+ concentration levels ([Ca2+]i) of vascular smooth muscle (VSM) were measured by fura 2 fluorescence. Raloxifene or 17β-estradiol was equally effective in relaxing renal arteries from both sexes, with raloxifene being more potent than 17β-estradiol. Endothelial denudation did not affect raloxifene- or 17β-estradiol-induced relaxation. NG-nitro-l-arginine methyl ester, charybdotoxin plus apamin, indomethacin, or ICI-182, 780 did not modify the effect of raloxifene. Raloxifene caused similar relaxations in rings contracted by U-46619 and high K+. Nifedipine attenuated the potency of raloxifene. Raloxifene reduced CaCl2-induced contractions. K+ (80 mM) stimulated an increase in VSM [Ca2+]i, and raloxifene attenuated this effect. Raloxifene-induced reduction of contraction and increase in VSM [Ca2+]i were insensitive to ICI-182, 780. In summary, raloxifene causes relaxation in rat renal arteries; this effect is independent of a functional endothelium and is not mediated by ICI 182, 780-sensitive estrogen receptors. Raloxifene inhibited both contractions and VSM [Ca2+]i in response to CaCl2, indicating that raloxifene relaxes rat renal arteries primarily through inhibiting Ca2+ influx via Ca2+ channels. There is little sex difference in raloxifene-induced relaxation.