Endothelium-derived endothelin-1 reduces cerebral artery sensitivity to nitric oxide by a protein kinase C-independent pathway

Disrupting effects of the emerging contaminant octylmethoxycinnamate (OMC) on human umbilical artery relaxation

Cardiovascular diseases (CVD) represent the number one cause of death worldwide. The vascular endothelium may play a role in the pathophysiology of CVD diseases. Octylmethoxycinnamate (OMC) is a UV-B filter (CAS number: 5466-77-3) widely used worldwide in numerous personal care products, including sunscreens, daily creams, and makeup. This UV-B filter is considered an endocrine disruptor. Therefore, this investigation aimed to evaluate the direct effects of OMC in human umbilical arteries (HUAs) with endothelium and the possible mechanisms involved in the response. The results demonstrated that OMC exerts a rapid (non-genomic) and endothelium-dependent arterial relaxant effect on HUAs previously contracted with serotonin (5-HT) and Histamine (His). On the other hand, when HUAs were contracted with potassium chloride (KCl), the relaxing effect was only observed in HUAs without endothelium, and it appeared to be inhibited in HUAs with endothelium. Thus, the vasorelaxant effect of OMC depends on the endothelium and depends on the contractile agent used, suggesting that OMC may act through different signaling pathways. Furthermore, computational modulation studies, corroborated the binding of OMC to all the proteins under investigation (eNOS, COX-2, ET-1, and TxA2), with higher affinity for COX-2. In summary, the vascular effect of OMC may involve activating different pathways, i.e., acting through the NO pathway, COX pathway, or activating the endothelin-1 pathway.

UV-B filter octylmethoxycinnamate-induced vascular endothelial disruption on rat aorta: In silico and in vitro approach

Throughout human life, an extensive and varied range of emerging environmental contaminants, called endocrine disruptors (EDCs), cause adverse health effects, including in the cardiovascular (CV) system. Cardiovascular diseases (CVD) are worryingly one of the leading causes of all mortality and mobility worldwide. The UV-B filter octylmethoxycinnamate (also designated octinoxate, or ethylhexyl methoxycinnamate (CAS number: 5466-77-3)) is an EDC widely present in all personal care products. However, to date, there are no studies evaluating the OMC-induced effects on vasculature using animal models to improve human cardiovascular health. This work analysed the effects of OMC on rat aorta vasculature and explored the modes of action implicated in these effects. Our results indicated that OMC relaxes the rat aorta by endothelium-dependent mechanisms through the signaling pathways of cyclic nucleotides and by endothelium-independent mechanisms involving inhibition of L-Type voltage-operated Ca²⁺ channels (L-Type VOCC). Overall, OMC toxicity on rat aorta may produce hypotension via vasodilation due to excessive NO release and blockade of L-Type VOCC. Moreover, the OMC-induced endothelial dysfunction may also occur by promoting the endothelial release of endothelin-1. Therefore, our findings demonstrate that exposure to OMC alters the reactivity of the rat aorta and highlight that long-term OMC exposure may increase the risk of human CV diseases.

Frequency selective neuronal modulation triggers spreading depolarizations in the rat endothelin-1 model of stroke

Ischemia is one of the most common causes of acquired brain injury. Central to its noxious sequelae are spreading depolarizations (SDs), waves of persistent depolarizations which start at the location of the flow obstruction and expand outwards leading to excitotoxic damage. The majority of acute stage of stroke studies to date have focused on the phenomenology of SDs and their association with brain damage. In the current work, we investigated the role of peri-injection zone pyramidal neurons in triggering SDs by optogenetic stimulation in an endothelin-1 rat model of focal ischemia. Our concurrent two photon fluorescence microscopy data and local field potential recordings indicated that a ≥ 60% drop in cortical arteriolar red blood cell velocity was associated with SDs at the ET-1 injection site. SDs were also observed in the peri-injection zone, which subsequently exhibited elevated neuronal activity in the low-frequency bands. Critically, SDs were triggered by low- but not high-frequency optogenetic stimulation of peri-injection zone pyramidal neurons. Our findings depict a complex etiology of SDs post focal ischemia and reveal that effects of neuronal modulation exhibit spectral and spatial selectivity.

Oral trehalose supplementation improves resistance artery endothelial function in healthy middle-aged and older adults

We hypothesized that supplementation with trehalose, a disaccharide that reverses arterial aging in mice, would improve vascular function in middle-aged and older (MA/O) men and women. Thirty-two healthy adults aged 50-77 years consumed 100 g/day of trehalose (n=15) or maltose (n=17, isocaloric control) for 12 weeks (randomized, double-blind). In subjects with Δbody mass less than 2.3kg (5 lb.), resistance artery endothelial function, assessed by forearm blood flow to brachial artery infusion of acetylcholine (FBFACh), increased ~30% with trehalose (13.3±1.0 vs. 10.5±1.1 AUC, P=0.02), but not maltose (P=0.40). This improvement in FBFACh was abolished when endothelial nitric oxide (NO) production was inhibited. Endothelium-independent dilation, assessed by FBF to sodium nitroprusside (FBFSNP), also increased ~30% with trehalose (155±13 vs. 116±12 AUC, P=0.03) but not maltose (P=0.92). Changes in FBFACh and FBFSNP with trehalose were not significant when subjects with Δbody mass ≥ 2.3kg were included. Trehalose supplementation had no effect on conduit artery endothelial function, large elastic artery stiffness or circulating markers of oxidative stress or inflammation (all P>0.1) independent of changes in body weight. Our findings demonstrate that oral trehalose improves resistance artery (microvascular) function, a major risk factor for cardiovascular diseases, in MA/O adults, possibly through increasing NO bioavailability and smooth muscle sensitivity to NO.

Vascular endothelium - Gatekeeper of vessel health

The vascular endothelium is an interface between the blood stream and the vessel wall. Changes in this single cell layer of the artery wall are believed of primary importance in the pathogenesis of vascular disease/atherosclerosis. The endothelium responds to humoral, neural and especially hemodynamic stimuli and regulates platelet function, inflammatory responses, vascular smooth muscle cell growth and migration, in addition to modulating vascular tone by synthesizing and releasing vasoactive substances. Compromised endothelial function contributes to the pathogenesis of cardiovascular disease; endothelial 'dysfunction' is associated with risk factors, correlates with disease progression, and predicts cardiovascular events. Therapies for atherosclerosis have been developed, therefore, that are directed towards improving endothelial function.

Targeted over-expression of endothelin-1 in astrocytes leads to more severe brain damage and vasospasm after subarachnoid hemorrhage

Background

Endothelin-1 (ET-1) is a potent vasoconstrictor, and astrocytic ET-1 is reported to play a role in the pathogenesis of cerebral ischemic injury and cytotoxic edema. However, it is still unknown whether astrocytic ET-1 also contributes to vasogenic edema and vasospasm during subarachnoid hemorrhage (SAH). In the present study, transgenic mice with astrocytic endothelin-1 over-expression (GET-1 mice) were used to investigate the pathophysiological role of ET-1 in SAH pathogenesis.

Results

The GET-1 mice experienced a higher mortality rate and significantly more severe neurological deficits, blood–brain barrier breakdown and vasogenic edema compared to the non-transgenic (Ntg) mice following SAH. Oral administration of vasopressin V_1a receptor antagonist, SR 49059, significantly reduced the cerebral water content in the GET-1 mice. Furthermore, the GET-1 mice showed significantly more pronounced middle cerebral arterial (MCA) constriction after SAH. Immunocytochemical analysis showed that the calcium-activated potassium channels and the phospho-eNOS were significantly downregulated, whereas PKC-α expression was significantly upregulated in the MCA of the GET-1 mice when compared to Ntg mice after SAH. Administration of ABT-627 (ET_A receptor antagonist) significantly down-regulated PKC-α expression in the MCA of the GET-1 mice following SAH.

Conclusions

The present study suggests that astrocytic ET-1 involves in SAH-induced cerebral injury, edema and vasospasm, through ET_A receptor and PKC-mediated potassium channel dysfunction. Administration of ABT-627 (ET_A receptor antagonist) and SR 49059 (vasopressin V_1a receptor antagonist) resulted in amelioration of edema and vasospasm in mice following SAH. These data provide a strong rationale to investigate SR 49059 and ABT-627 as therapeutic drugs for the treatment of SAH patients.

Impaired acetylcholine-induced cutaneous vasodilation in young smokers: roles of nitric oxide and prostanoids

Cigarette smoking attenuates acetylcholine (ACh)-induced cutaneous vasodilation in humans, but the underlying mechanisms are unknown. We tested the hypothesis that smokers have impaired nitric oxide (NO)- and cyclooxygenase (COX)-dependent cutaneous vasodilation to ACh infusion. Twelve young smokers, who have smoked more than 5.2 ± 0.7 yr with an average daily consumption of 11.4 ± 1.2 cigarettes, and 12 nonsmokers were tested. Age, body mass index, and resting mean arterial pressure were similar between the groups. Cutaneous vascular conductance (CVC) was evaluated as laser-Doppler flux divided by mean arterial pressure, normalized to maximal CVC (local heating to 43.0°C plus sodium nitroprusside administration). We evaluated the increase in CVC from baseline to peak (CVCΔpeak) and area under the curve of CVC (CVCAUC) during a bolus infusion (1 min) of 137.5 μM ACh at four intradermal microdialysis sites: 1) Ringer (control), 2) 10 mM N(G)-nitro-l-arginine methyl ester (l-NAME; NO synthase inhibitor), 3) 10 mM ketorolac (COX inhibitor), and 4) combination of l-NAME + ketorolac. CVCΔpeak and CVCAUC at the Ringer site in nonsmokers were greater than in smokers (CVCΔpeak, 42.9 ± 5.1 vs. 22.3 ± 3.5%max, P < 0.05; and CVCAUC, 8,085 ± 1,055 vs. 3,145 ± 539%max·s, P < 0.05). In nonsmokers, CVCΔpeak and CVCAUC at the l-NAME site were lower than the Ringer site (CVCΔpeak, 29.5 ± 6.2%max, P < 0.05; and CVCAUC, 5,377 ± 1,109%max·s, P < 0.05), but in smokers, there were no differences between the Ringer and l-NAME sites (CVCΔpeak, 16.8 ± 4.3%max, P = 0.11; and CVCAUC, 2,679 ± 785%max·s, P = 0.30). CVCΔpeak and CVCAUC were reduced with ketorolac in nonsmokers (CVCΔpeak, 13.3 ± 3.6%max, P < 0.05; and CVCAUC, 1,967 ± 527%max·s, P < 0.05) and smokers (CVCΔpeak, 7.8 ± 1.8%max, P < 0.05; and CVCAUC, 1,246 ± 305%max·s, P < 0.05) and at the combination site in nonsmokers (CVCΔpeak, 15.9 ± 3.1%max, P < 0.05; and CVCAUC, 2,660 ± 512%max·s, P < 0.05) and smokers (CVCΔpeak, 11.5 ± 2.6%max, P < 0.05; and CVCAUC, 1,693 ± 409%max·s, P < 0.05), but the magnitudes were greater in nonsmokers (P < 0.05). These results suggest that impaired ACh-induced skin vasodilation in young smokers is related to diminished NO- and COX-dependent vasodilation.

Autonomic cerebral vascular response to sildenafil in diabetic patient

BACKGROUND

Erectile dysfunction is a common problem in type 2 diabetic patients who are at higher risk of cerebrovascular events, and it's recorded with sildenafil, a drug which is primarily used for erectile dysfunction.

OBJECTIVES

We tested the hypothesis whether or not sildenafil modulates cerebrovascular reactivity (CVR) in patients with type 2 diabetes mellitus.

METHODS

A total of 35 male participants were enrolled; eighteen with type 2 diabetes mellitus matched with seventeen normal individuals. Transcranial Doppler Ultrasonographic examination (TCD) was performed for all participants to insonate the middle cerebral artery (MCA) through a trans-temporal window. CVR was assessed by using breath holding (BH)-hyperventilation (HV) test, before and after oral 50 mg sildenafil; recordings were analyzed by using SPSS program version 12.

RESULTS

In normal individuals, sildenafil did not result in statistically significant change in breath holding index (BHI) from 0.91 ± 0.11 to 0.81 ± 0.09 and full range of vasodilatation (FVD) from (59.4% ± 6.3%) to (53.7% ± 4.9%). In diabetic patients, giving sildenafil resulted in significant increase in BHI (from 0.74 ± 0.14 to 1.03 ± 0.14) and FVD (from 60.2% ± 4.96% to 74% ± 4.8%), (p < 0.05).

CONCLUSION

Sildenafil significantly improves CVR in type 2 diabetic patients but not in normal subjects.

Endothelium-derived endothelin-1

One year after the revelation by Dr. Furchgott in 1980 that the endothelium was obligatory for acetylcholine to relax isolated arteries, it was clearly shown that the endothelium could also promote contraction. In 1988, Dr. Yanagisawa's group identified endothelin-1 (ET-1) as the first endothelium-derived contracting factor. The circulating levels of this short (21-amino acid) peptide were quickly determined in humans, and it was reported that, in most cardiovascular diseases, circulating levels of ET-1 were increased, and ET-1 was then tagged as "a bad guy." The discovery of two receptor subtypes in 1990, ET(A) and ET(B), permitted optimization of the first dual ET-1 receptor antagonist in 1993 by Dr. Clozel's team, who entered clinical development with bosentan, which was offered to patients with pulmonary arterial hypertension in 2001. The revelation of Dr. Furchgott opened a Pandora's box with ET-1 as one of the actors. In this brief review, we will discuss the physiological and pathophysiological role of endothelium-derived ET-1 focusing on the regulation of the vascular tone, and as much as possible in humans. The coronary bed will be used as a running example in this review because it is the most susceptible to endothelial dysfunction, but references to the cerebral and renal circulation will also be made. Many of the cardiovascular complications associated with aging and cardiovascular risk factors are initially attributable, at least in part, to endothelial dysfunction, particularly dysregulation of the vascular function associated with an imbalance in the close interdependence of nitric oxide and ET-1.

Endotoxin has acute and chronic effects on the cerebral circulation of fetal sheep

We studied the impact of endotoxemia on cerebral blood flow (CBF), cerebral vascular resistance (CVR), and cerebral oxygen transport (O2 transport) in fetal sheep. We hypothesized that endotoxemia impairs CBF regulation and O2 transport, exposing the brain to hypoxic-ischemic injury. Responses to lipopolysaccharide (LPS; 1 μg/kg iv on 3 consecutive days, n = 9) or normal saline ( n = 5) were studied. Of LPS-treated fetuses, five survived and four died; in surviving fetuses, transient cerebral vasoconstriction at 0.5 h (ΔCVR approximately +50%) was followed by vasodilatation maximal at 5–6 h (ΔCVR approximately −50%) when CBF had increased (approximately +60%) despite reduced ABP (approximately −20%). Decreased CVR and increased CBF persisted 24 h post-LPS and the two subsequent LPS infusions. Cerebral O2 transport was sustained, although arterial O2 saturation was reduced ( P < 0.05). Histological evidence of neuronal injury was found in all surviving LPS-treated fetuses; one experienced grade IV intracranial hemorrhage. Bradykinin-induced cerebral vasodilatation (ΔCVR approximately −20%, P < 0.05) was abolished after LPS. Fetuses that died post-LPS ( n = 4) differed from survivors in three respects: CVR did not fall, CBF did not rise, and O2 transport fell progressively. In conclusion, endotoxin disrupts the cerebral circulation in two phases: 1) acute vasoconstriction (1 h) and 2) prolonged vasodilatation despite impaired endothelial dilatation (24 h). In surviving fetuses, LPS causes brain injury despite cerebral O2 transport being maintained by elevated cerebral perfusion; thus sustained O2 transport does not prevent brain injury in endotoxemia. In contrast, cerebral hypoperfusion and reduced O2 transport occur in fetuses destined to die, emphasizing the importance of sustaining O2 transport for survival.

Endogenous methyl palmitate modulates nicotinic receptor-mediated transmission in the superior cervical ganglion

Nitric oxide (NO) is identified as the endothelium-derived relaxing factor and a neurotransmitter with a superfusion bioassay cascade technique. By using a similar technique with rat superior cervical ganglion (SCG) as donor tissue and rabbit endothelium-denuded aortic ring as detector tissue, we report here that a vasodilator, which is more potent than NO, is released in the SCG upon field electrical stimulation (FES) or addition of nicotine. Release of this vasodilator was enhanced by arginine analogs, including N(omega)-nitro-l-arginine (a NO synthase inhibitor), suggesting that it is not NO. Analysis by gas chromatography/mass spectrometry identified 2 saturated fatty acids, palmitic acid methyl ester (PAME) and stearic acid methyl ester (SAME), being released from the SCG upon FES in the presence of arginine analogs. Exogenous PAME but not SAME induced significant aortic dilation (EC(50) = 0.19 nM), indicating that PAME is the potent vasodilator. Release of PAME and SAME was significantly diminished in chronically decentralized SCG but not denervated SCG, suggesting the preganglionic origin. Furthermore, release of both fatty acids was calcium- and myosin light chain kinase-dependent, suggesting that both were released from axoplasmic vesicular stores. Electrophysiological studies further demonstrated that PAME but not SAME inhibited nicotine-induced inward currents in cultured SCG and the alpha7-nicotinic acetylcholine receptor-expressing Xenopus oocytes. Endogenous PAME appears to play a role in modulation of the autonomic ganglionic transmission and to complement the vasodilator effect of NO.

Brimonidine evokes heterogeneous vasomotor response of retinal arterioles: diminished nitric oxide-mediated vasodilation when size goes small

Brimonidine, an α2-adrenergic receptor (AR) agonist, has been employed in the treatment of glaucoma due to its beneficial effects on intraocular pressure reduction and neuroprotection. In addition, some studies have implicated that brimonidine might influence ocular blood flow; however, its effect on the retinal microcirculation has not been documented. Herein, we examined the vasomotor action of brimonidine on different branching orders of retinal arterioles in vitro and determined the contribution of the α2-AR subtype and the role of endothelium-derived nitric oxide (NO) in this vasomotor response. First- and second-order retinal arterioles of pigs were isolated, cannulated, and pressurized for functional studies. Videomicroscopic techniques were employed to record diameter changes in response to brimonidine. RT-PCR was performed for detection of α-AR and endothelial NO synthase (eNOS) mRNA in retinal arterioles. All first-order arterioles (82 ± 2 μm ID) dilated dose dependently to brimonidine (0.1 nM to 10 μM) with 10% dilation at the highest concentration. Second-order arterioles (50 ± 1 μm ID) responded heterogeneously with either dilation or constriction. The incidence and magnitude of vasoconstriction were increased with increasing brimonidine concentration. Administration of the NO synthase inhibitor NG-nitro-l-arginine methyl ester abolished the brimonidine-induced vasodilation in first- and second-order arterioles. Regardless of vessel size, vasomotor responses (i.e., vasodilation and vasoconstriction) of retinal arterioles were sensitive to the α2-AR antagonist rauwolscine. Consistent with the functional data, α2A-AR and eNOS mRNAs were detected in retinal arterioles. Collectively, our data demonstrate that brimonidine at clinical doses evokes a consistent NO-dependent vasodilation in first-order retinal arterioles but a heterogeneous response in second-order arterioles. These vasomotor responses are mediated by the activation of α2-AR. It appears that brimonidine, depending on the concentration and vessel size, may alter local retinal blood flow.

Chronically elevated endothelin levels reduce pulmonary vascular reactivity to nitric oxide

Although local tissue activation of the endothelin (ET) system contributes to the development of pulmonary hypertension, the impact of isolated chronic plasma hyperendothelinemia on the pulmonary circulation is unknown.

METHODS

Mini-osmotic pumps were implanted in rats to deliver ET-1 during 7 or 28 days. After in vivo hemodynamics, the lungs were isolated to derive pressure-flow relations. Small pulmonary arteries ( approximately 250 microm) were mounted on an isometric myograph to study their reactivity.

RESULTS

Plasma ET-1 approximately doubled (p < 0.05) after 7 and 28 days. Lung tissue ET-1 level increased fourfold after 7 days (p < 0.001) but was no longer significantly elevated after 28 days. Right ventricular systolic pressure was unaffected. The pulmonary pressure-flow relation shifted upward with a steeper slope (p < 0.05) at 7 days, but not after 28 days. Maximum dilatations to both acetylcholine (p < 0.01) and sodium nitroprusside (p < 0.001) were greatly reduced by approximately 50% after 28 days and were normalized by the addition of the nitric oxide synthase inhibitor L-NNA and the antioxidant N-acetyl-L-cysteine, respectively.

CONCLUSION

Chronic hyperendothelinemia reduces the pulmonary vasodilator reserve in response to nitric oxide. Correction by an antioxidant and L-NNA suggests that this relates to increased production of reactive oxygen species, which may have clinical relevance for conditions associated with chronic increase of ET. Further studies are required to determine if, in the long term, this could contribute to the development of pulmonary hypertension.

Influence of morphine and naloxone on endothelin and its receptors in newborn piglet brain vascular endothelial cells: clinical implications in neonatal care

The present study examines the hypothesis that morphine exposure alters newborn brain vascular endothelial cell production of endothelin (ET)-1, as well as the mRNA expression of its receptors. Newborn piglet vascular endothelial cells were treated with morphine (100 ng/mL media), naloxone (100 ng/mL media), or drug-free media (control) for 6, 24, 48, and 96 h. Media was analyzed for ET-1 and big ET-1 levels and the cells were assessed for ETA and ETB receptor mRNA expression. Morphine exposure progressively increased ET-1 production from 6 to 96 h with concurrent reductions in big ET-1 levels starting at 24 h to almost undetectable levels by 96 h. Whereas ETA receptor mRNA expression increased 2-fold at 6 h and 4-fold at 96 h, ETB receptor mRNA expression remained unchanged. Naloxone exposure caused significant decreases in ET-1 levels, whereas an opposite effect was noted in big ET-1 levels, which increased from 6 through 96 h. Naloxone caused a progressive decrease in ETA receptor mRNA expression at 6 h through 96 h and a 2-fold increase in ETB receptor mRNA expression at 48 and 96 h. Increased ET-1 and its receptors in response to morphine may suggest altered cerebrovascular perfusion and brain metabolism in the immature piglet brain.

Hyper-reactivity of cerebral arteries from ovariectomized rats: therapeutic benefit of tamoxifen

1. An increased incidence of systemic hypertension has been documented in postmenopausal women and identified as an independent risk factor in the development of cerebrovascular stroke. The present study examined whether cerebrovascular reactivity was increased in the hypertensive ovariectomized rat, and explored the potential therapeutic benefit of the partial estrogen receptor agonist tamoxifen. 2. Female Sprague-Dawley rats were subjected to bilateral ovariectomy (OVX, n=16) or a sham operation (n=8). At 6-week postsurgery, rats were anesthetized to assess ventricular contractility and blood pressure. In a second series of experiments, OVX rats (n=8) were given tamoxifen starting 3 weeks postsurgery, and continued for 3 weeks. At the end of each protocol, the middle cerebral artery was harvested and rings were mounted in wire-myographs to measure isometric tension. 3. Systolic arterial pressure (SAP) was significantly increased (P<0.05) in the OVX rat (174+/-8 mmHg), as compared to sham (135+/-6 mmHg). The resting tension of isolated cerebral arteries from OVX rats (186+/-15 mg) was significantly elevated (P<0.05), as compared to sham (129+/-9 mg). Phenylephrine treatment did not elicit a constriction of cerebral arteries isolated from sham rats, whereas a potent response (P<0.05) was observed in OVX rats. Nitric oxide (NO) synthase inhibition with L-NNA led to a limited contraction in sham rats (8+/-3% of Emax), whereas a significant (P<0.05) increase was observed in OVX rats (34+/-12% of Emax). Lastly, vascular sensitivity (pD2) to sodium nitroprusside was significantly increased (P<0.05) in OVX rats, as compared to sham. 4. Tamoxifen therapy normalized the resting tension of isolated cerebral arteries from OVX rats, abrogated phenylephrine-mediated contraction, and modestly reduced SAP. By contrast, tamoxifen treatment of OVX rats did not attenuate L-NNA-mediated contractile response of cerebral arteries. 5. These data demonstrate that the cerebral artery isolated from the OVX rat was associated with an exaggerated vasoconstrictor response to phenylephrine, and altered NO-dependent vascular reactivity. The administration of tamoxifen to OVX rats normalized cerebral artery reactivity to phenylephrine. These findings provide the impetus to examine the potential therapeutic benefit of the partial estrogen receptor agonist tamoxifen to reduce the incidence of cerebrovascular stroke in postmenopausal women.