Elevated glucose attenuates agonist- and flow-stimulated endothelial nitric oxide synthase activity in microvascular retinal endothelial cells.

Impaired vasoactive release of opposing vasodilator and vasoconstrictor mediators due to endothelial dysfunction is integral to the pathogenesis of diabetic retinopathy. The aim of this study was to determine the effect of hyperglycemia on the expression of endothelial nitric oxide synthase (eNOS) and the release of nitric oxide (NO) in bovine microvascular retinal endothelial cells (BRECs) under both static (basal and acetylcholine stimulated) and flow (laminar shear stress [10 dynes/cm2 and pulsatile flow 0.3 to 23 dynes/cm2) conditions using a laminar shear apparatus and an in vitro perfused transcapillary culture system. The activity and expression of eNOS, measured by nitrate levels and immunoblot, respectively, were determined following exposure of BRECs to varying concentrations of glucose and mannitol (0 to 25 mM). Under static conditions the expression of eNOS decreased significantly following exposure to increasing concentrations of glucose when compared to osmotic mannitol controls and was accompanied by a significant dose-dependent decrease in nitrate levels in conditioned medium. The acetylcholine stimulated increase in NO release (2.0 +/- 0.3-fold) was significantly reduced by 55% +/- 5% and 65% +/- 4.5% following exposure to 16 and 25 mM glucose, respectively, when compared to osmotic controls. In parallel studies, glucose significantly inhibited both laminar shear stress and pulsatile flow-induced activity when compared to mannitol. We conclude that hyperglycemia impairs agonist- and flow-dependent release of NO in retinal microvascular endothelial cells and may thus contribute to the vascular endothelial dysfunction and impaired autoregulation of diabetic retinopathy.     

切应力通过Pim1/eNOS途径调节人脐静脉内皮细胞NO分泌

目的:探讨层流切应力是否可通过Pim1调节内皮型一氧化氮合酶(eNOS)活性,从而调节血管内皮细胞一氧化氮(NO)分泌。方法:体外原代培养人脐静脉内皮细胞(HUVECs),运用平行平板流动腔系统给HUVECs加载层流切应力(15 dyn/cm^2)。采用Western blot法检测Pim1蛋白表达及eNOS-Ser1177磷酸化水平;硝酸还原酶法检测NO分泌量;利用特异性小干扰RNA(siRNA)转染技术沉默Pim1基因后再检测上述指标的变化。结果:切应力作用HUVECs 15 min,可以显著上调Pim1蛋白表达(P<0.05),同时显著增强eNOS-Ser1177磷酸化水平(P<0.05),伴随HUVECs NO分泌显著增多(P<0.05)。转染siPim1可以抑制切应力诱导的Pim1表达(P<0.05),同时抑制eNOS-Ser1177磷酸化(P<0.05),NO分泌随之显著降低(P<0.05)。结论:流体切应力可能通过Pim1/eNOS途径调节血管内皮细胞NO分泌。     

Endothelial nitric oxide synthase transgenic models of endothelial dysfunction

Endothelial production of nitric oxide is critical to the regulation of vascular responses, including vascular tone and regional blood flow, leukocyte–endothelial interactions, platelet adhesion and aggregation, and vascular smooth muscle cell proliferation. A relative deficiency in the amount of bioavailable vascular NO results in endothelial dysfunction, with conditions that are conducive to the development of atherosclerosis: thrombosis, inflammation, neointimal proliferation, and vasoconstriction. This review focuses on mouse models of endothelial dysfunction caused by direct genetic modification of the endothelial nitric oxide synthase (eNOS) gene. We first describe the cardiovascular phenotypes of eNOS knockout mice, which are a model of total eNOS gene deficiency and thus the ultimate model of endothelial dysfunction. We then describe S1177A and S1177D eNOS mutant mice as mouse models with altered eNOS phosphorylation and therefore varying degrees of endothelial dysfunction. These include transgenic mice that carry the eNOS S1177A and S1177D transgenes, as well as knockin mice in which the endogenous eNOS gene has been mutated to carry the S1177A and S1177D mutations. Together, eNOS knockout mice and eNOS S1177 mutant mice are useful tools to study the effects of total genetic deficiency of eNOS as well as varying degrees of endothelial dysfunction caused by eNOS S1177 phosphorylation.     

Expression and regulation of endothelial nitric oxide synthase by vascular endothelial growth factor in ECV 304 cells

Nitric oxide (NO) seems to play a pivotal role in the vascular endothelial growth factor (VEGF)-induced endothelial cell proliferation. This study was designed to investigate the role and intracellular signal pathway of endothelial nitric oxide synthase (eNOS) activation induced by VEGF. ECV 304 cells were treated with VEGF(165) and then cell proliferation, eNOS protein and mRNA expression levels were analyzed to elucidate the functional role of eNOS in cell proliferation induced by VEGF. After exposure of cells to VEGF(165), eNOS activity and cell growth were increased by approximately two-fold in the VEGF(165) -treated cells compared to the untreated cells. In addition, VEGF stimulated eNOS expression at both the mRNA and protein levels in a dose-dependent manner. Phosphatidylinositol-3 kinase (PI-3K) inhibitors were used to assess PI-3K involvement in eNOS regulation. LY294002 was found to attenuate VEGF-stimulated eNOS expression. Wortmannin was not as effective as LY294002, but the reduction effect was detectable. Cells activated by VEGF showed increased ERK1/2 levels. Moreover, the VEGF-induced eNOS expression was reduced by the PD98059, MAPK pathway inhibitor. This suggests that eNOS expression might be regulated by PI-3K and the ERK1/2 signaling pathway. In conclusion, VEGF(165) induces ECV 304 cell proliferation via the NO produced by eNOS. In addition, eNOS may be regulated by the PI-3K or mitogen-activated protein kinase pathway.     

当归、川芎、红花、人参萃取液对离体培养牛血管内皮细胞一氧化氮合酶的影响

目的：研究以当归、川芎、红花、人参为主要成份的CO2超临界萃取液对低切应力条件下培养的内皮细胞一氧化氮合酶(eNOS)表达的影响；探讨该萃取液改善血管功能、防止动脉粥样硬化的机理。方法：采用Westem blot印迹免疫检测，研究该萃取液对低切应力环境下体外培养的牛血管内皮细胞eNOS表达的影响。结果：低切应力水平下，内皮细胞eNOS表达降低，给予0.5％萃取液1ml(以萃取原液为100％)，eNOS的表达明显增加，并接近在高切应力水平下内皮细胞eNOS的正常表达水平。结论：当归、川芎、红花、人参萃取液可上调低切应力环境下内皮细胞eNOS的表达。     

Nitric oxide protects mast cells from activation-induced cell death: the role of the phosphatidylinositol-3 kinase-Akt-endothelial nitric oxide synthase pathway

NO is known to suppress mast cell activation, but the role of NO in mast cell survival is unclear. Ligation of the high-affinity receptor for IgE (FcepsilonRI) resulted in NO production in mast cells within minutes. This NO production was largely dependent on NO synthase (NOS) activity and extracellular Ca(2+). The NO production required an aggregation of FcepsilonRI and was accompanied by increased phosphorylation of endothelial NOS (eNOS) at Ser1177 and Akt at Ser473. The phosphorylation of eNOS and Akt and the production of NO were abolished by the PI-3K inhibitor wortmannin. Although thapsigargin (TG) induced NO production as well, this response occurred with a considerable lag time (>10 min) and was independent of FcepsilonRI aggregation and PI-3K and NOS activity. Mast cells underwent apoptosis in response to TG but not upon FcepsilonRI ligation. However, when the NOS-dependent NO production was blocked, FcepsilonRI ligation caused sizable apoptosis, substantial mitochondrial cytochrome c release, caspase-3/7 activation, and collapse of the mitochondrial membrane potential, all of which were inhibited by the caspase-3 inhibitor z-Asp-Glu-Val-Asp-fluoromethylketone. The data suggest that the NO produced by the PI-3K-Akt-eNOS pathway is involved in protecting mast cells from cell death.     

血流生理脉动切应力与内皮细胞一氧化氮产生的关系

目的研究生理脉动切应力对血管内皮细胞一氧化氮产生的影响.材料与方法利用本室已建立的平行板模拟血流循环装置,在模拟生理脉动切应力(19.29,56.25dynes/cm2)分别作用于培养人脐静脉内皮细胞0,1,2,4,6,10,24h后,用一氧化氮微量测定法测定循环液中一氧化氮的含量.结果在两组模拟生理脉动切应力的作用下,于2h时一氧化氮释放出现一峰值,之后逐渐下降,并且内皮细胞释放一氧化氮的量随切应力的增大而增加.结论生理脉动切应力对血管内皮细胞一氧化氮的产生具有调节作用,可能对血管动脉粥样硬化的形成与发展中,临床手术前后发生的血管痉挛与血栓形成等增多有重要影响.     

Alterations in the activity and expression of endothelial NO synthase in aged human endothelial cells

This study was to investigate factors underlying the age-related decrease in NO production in vascular endothelial cells. The age-related changes in NO production, the activity and expression level of eNOS, and eNOS binding proteins, were studied in HUVECs.NO production in HUVECs significantly decreased in an age-dependent manner. The potentiation of NO production by l-Arg was significantly suppressed by L-NIO (eNOS-specific inhibitor) in young HUVECs and was suppressed by 1400W (iNOS-specific inhibitor) in aged HUVECs. The aged HUVECs had lower eNOS protein levels than young cells. eNOS phosphorylation at Ser-1177 (active) decreased gradually from PDL 23 through 40, and eNOS phosphorylation at Thr-495 (inactive) increased in aged cells. Changes of intracellular eNOS binding proteins, such as caveolin-1, pAkt, and Hsp90, as well as interaction between eNOS and eNOS binding proteins, indicated decreasing enzyme activity in aged HUVECs.Aging might decrease the activity as well as expression level of eNOS in HUVECs. And the decrease in eNOS activity probably implicated to the alterations in the regulatory binding proteins. For further study, it needs to be confirmed that the age-related change in the intracellular distribution of eNOS and the relative contribution of eNOS and iNOS on vascular dysfunction in aged endothelial cells.     

Cigarette smoke-induced alterations in endothelial nitric oxide synthase phosphorylation: role of protein kinase C.

Endothelial nitric oxide synthase (eNOS) is regulated by phosphorylation of Ser(1177) and Thr(495), which affects NO bioavailability. Cigarette smoke disturbs the eNOS-cGMP-NO pathway and causes decreased NO production. Here the authors investigated the acute effects of cigarette smoke on eNOS phosphorylation, focusing on protein kinases (PKs). Endothelial cell culture was concentration- and time-dependently treated first with cigarette smoke buffer (CSB), then with reduced glutathione (GSH) or various PK inhibitors (H-89, LY-294002, Ro-318425, and ruboxistaurin). eNOS, phospho-Ser(1177)-eNOS, phospho-Thr(495)-eNOS, Akt(PKB), and phospho-Akt protein levels were determined by Western blot. CSB increased the phosphorylation of eNOS at Ser(1177) and more at Thr(495) in a concentration- and time-dependent manner (p < .01, p < .05 versus control, respectively) and resulted in the dissociation of the active dimeric form of eNOS (p < .05). GSH decreased the phosphorylation of eNOS at both sites (p < .05 versus CSB without GSH) and prevented the decrease of dimer eNOS level. CSB treatment also decreased the level of phospho-Ser(473)-Akt (p < .05 versus control). Inhibition of PKA by H-89 did not affect CSB-induced phosphorylation, whereas the PKB inhibitor LY-294002 enhanced it at Ser(1117). The PKC blockers Ro-318425 and ruboxistaurin augmented the CSB-induced phosphorylation at Ser(1177) but decreased phosphorylation at Thr(495) (p < .05 versus CSB). Cigarette smoke causes a disruption of the enzymatically active eNOS dimers and shifts the eNOS phosphorylation to an inhibitory state. Both effects might lead to reduced NO bioavailability. The shift of the eNOS phosphorylation pattern to an inhibitory state seems to be independent of the PKA and phosphoinositol 3-kinase (PI3-K)/Akt pathways, whereas PKC appears to play a key role.     

Reduced cyclic stretch,endothelial dysfunction,and oxidative stress: an ex vivo model

BackgroundThe objective of this study was to investigate whether reduction of cyclic circumferential stretch will impair endothelial function and elevate basal levels of oxidative stress, both known risk factors linked to cardiovascular disease.MethodsEx vivo and in vitro models were used to perfuse porcine carotid arteries and porcine endothelial cells, respectively, for 24 h. In both cases, one group was allowed to stretch naturally when exposed to a pulse shear stress (6±3 dynes/cm²) combined with a pulse pressure of 80±10 mmHg, yielding a physiological cyclic stretch of 4–5%. This group was compared to a reduced stretch group, achieved by wrapping the arterial segment with a silicon band or by seeding the endothelial cells inside less compliant tubes, decreasing cyclic stretch to 1%.ResultsThe experimentally reduced compliance caused a significant decrease in bradykinin-dependent vascular relaxation. Reduced compliance significantly decreased the phosphorylation of serine 1177 (Ser1177) on eNOS, suggesting the activity of eNOS was decreased. Overall production of reactive oxygen species was increased by reducing compliance, as visualized with DHE. Finally, p22-phox and p47-phox, key players in the superoxide-generating NAD(P)H oxidase, were also up-regulated by reduced compliance.ConclusionsThese findings point out how reduced arterial compliance increases the risk of arterial disease by creating a less functional endothelium, interrupting the eNOS activation pathway, and increasing the vascular levels of oxidative stress.     

Phosphorylation and activation of the endothelial nitric oxide synthase by fluid shear stress

Fluid shear stress activates the endothelial nitric oxide (NO) synthase (eNOS) by a mechanism which does not require an increase in the intracellular concentration of free Ca2+ ([Ca2+]i), and is sensitive to several kinase inhibitors. Although phosphorylation of eNOS has been suggested to regulate enzyme activity, the mechanism of eNOS activation is still unclear. Here we demonstrate that fluid shear stress elicits the phosphorylation of eNOS on tyrosine and serine residues. Inhibition of phosphatidylinositol 3-kinase (PI3K), using wortmannin or a dominant negative mutant of its downstream target, Akt (protein kinase B), prevented the maintained serine phosphorylation and activation of eNOS. Enhancing eNOS phosphorylation by inhibiting serine/threonine phosphatases, increased eNOS activity by approximately twofold, as assessed by the accumulation of intracellular cyclic GMP, without increasing the intracellular concentration of free Ca2+. These data suggest that shear stress activates a pathway involving PI3K and the serine/threonine kinase Akt, which phosphorylates eNOS. This phosphorylation directly increases eNOS activity at resting [Ca2+]i, thus rendering the shear stress-induced activation of eNOS apparently Ca2+-independent.     

Activation of endothelial nitric oxide synthase following spinal cord injury in mice

Endothelial nitric oxide synthase (eNOS) plays a neuroprotective role after cerebral ischemia through the production of NO, which enhances cerebral blood flow. However, precise details regarding activation of eNOS after spinal cord injury (SCI) largely remain to be elucidated. In the present study we investigated chronological alteration and cellular location of eNOS and phosphorylated (p)-eNOS at Ser(1177) following SCI in mice. Western blot analysis showed eNOS to be significantly phosphorylated at Ser(1177) from 1 to 2 days after mild SCI, with gradual decrease thereafter. Immunohistochemistry revealed the p-eNOS to be mainly expressed in the endothelial cells of microvessels within gray matter under these conditions. These findings suggest that mild SCI activates eNOS in the subacute stage, which increases spinal cord blood flow and may be involved in protective and repair responses.     

非诺贝特上调血管内皮细胞一氧化氮合酶的表达

目的:观察PPARα激动剂非诺贝特对牛主动脉(BAECs)内皮细胞一氧化氮合酶(eNOS)活性和表达的影响。方法:制备5-9代BAECs,加入不同浓度的非诺贝特(0, 5, 10, 50, 100 μmol/L)后,用NOS Assay Kit测定eNOS活性,RT-PCR法检测eNOS mRNA表达,Western blot分析检测eNOS蛋白质表达。结果: 非诺贝特以浓度和时间依赖的方式增加eNOS活性,非诺贝特浓度10 μmol/L以上时,明显增加eNOS活性。50μmol/L非诺贝特处理48 h时eNOS活性最大(为对照组的2.32±0.47倍,P<0.01)。非诺贝特处理1 h和12 h不增加eNOS活性。RT-PCR分析表明,非诺贝特浓度大于5 μmol/L以上时,明显增加eNOS mRNA水平,在非诺贝特浓度为50 μmol/L时作用最大,为对照组的2.08±0.33倍(P<0.01)。此作用在6 h时出现,持续到48 h。Western blot显示,非诺贝特处理48 h,eNOS蛋白表达明显增加,在浓度为10,50 和100 μmol/L时,eNOS蛋白表达分别为对照组的1.80±0.45, 2.70±0.42 和 2.20±0.32 倍,均P<0.01。在非诺贝特处理12 h后出现,持续到48 h。结论:PPARα激动剂非诺贝特增加BAECs eNOS基因表达,提高eNOS活性及增加蛋白表达。     

切应力对培养人脐静脉内皮细胞形态的影响

用可模拟生理及超生理切应力的平行板模拟循环流动装置进行实验，发现模拟生理脉动切应力及超生理脉动切应力均可使培养人脐静脉内皮细胞沿液体流动方向伸长。采用计算机半自动图像分析系统半定量处理，进一步发现内皮细胞伸长程度与切应力大小及作用时间呈正相关、并且，模拟超生理切应力对内皮细胞形态的影响较生理脉动切应力大。     

Src kinase mediates angiotensin II-dependent increase in pulmonary endothelial nitric oxide synthase

We have previously demonstrated that angiotensin II (Ang II) stimulates nitric oxide (NO) production in bovine pulmonary artery endothelial cells (BPAECs) by increasing NO synthase (NOS) expression via the type 2 receptor. The purpose of this study was to identify the Ang II-dependent signaling pathway that mediates this increase in endothelial NOS (eNOS). The Ang II-dependent increase in eNOS expression is prevented when BPAECs are pretreated with the tyrosine kinase inhibitors, herbimycin A and 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-D]pyrimidine, which also blocked Ang II-dependent mitogen-activated protein kinase (MAPK) kinase/extracellular-regulated protein kinase (MEK)-1 and MAPK phosphorylation, suggesting that Src is upstream of MAPK in this pathway. Transfection of BPAECs with an Src dominant negative mutant cDNA prevented the Ang II-dependent Src activation and increase in eNOS protein expression. PD98059, a MEK-1 inhibitor, prevented the Ang II-dependent phosphorylation of extracellular-regulated protein kinases 1 and 2 and increase in eNOS expression. Neither AG1478, an epidermal growth factor receptor kinase inhibitor, nor AG1295, a platelet derived growth factor receptor kinase inhibitor, had any effect on Ang II-stimulated Src activity, MAPK activation, or eNOS expression. Pertussis toxin prevented the Ang II-dependent increase in Src activity, MAPK activation, and eNOS expression. These data suggest that Ang II stimulates Src tyrosine kinase via a pertussis toxin-sensitive pathway, which in turn activates the MAPK pathway, resulting in increased eNOS protein expression in BPAECs.     

AngⅡ/AT_1R通路通过激活人脐静脉内皮细胞PP2A导致eNOS Ser1177磷酸化水平下调

目的:初步探讨血管紧张素Ⅱ(angiotensinⅡ,AngⅡ)/血管紧张素Ⅱ1型受体(angiotensinⅡtype1 receptor,AT_1R)通路是否通过激活人脐静脉内皮细胞蛋白磷酸酶2A(protein phosphatase 2A,PP2A)导致内皮型一氧化氮合酶(eNOS)Ser1177磷酸化水平下调。方法:将人脐静脉内皮细胞随机分为正常对照(control)组、AngⅡ处理组、单纯坎地沙坦(candesartan,CAN;AT_1R特异性阻断剂)组和CAN预处理+AngⅡ组。用Western blot方法检测各组eNOS总蛋白表达、eNOS Ser1177磷酸化水平、PP2Ac蛋白表达、PP2Ac-Tyr307磷酸化水平和PP2A内源性抑制蛋白I_2~(PP2A)表达水平。采用化学比色法检测各组细胞培养基中的NO含量。结果:与control组相比,AngⅡ处理后eNOS Ser1177磷酸化水平及细胞培养基中的NO含量降低(P0.05);与同一浓度AngⅡ组相比,CAN预处理可增加eNOS Ser1177磷酸化水平及细胞培养基中的NO含量(P0.05);各组间eNOS蛋白表达差异无统计学显著性。与control组比较,AngⅡ处理后PP2Ac Tyr307磷酸化水平和I_2~(PP2A)表达降低(P0.05);与同一浓度AngⅡ组相比,CAN预处理可增加PP2Ac Tyr307磷酸化水平和I_2~(PP2A)表达(P0.05);各组间PP2Ac蛋白表达差异无统计学显著性。结论:AngⅡ可通过AT_1R通路导致人脐静脉内皮细胞eNOS Ser1177磷酸化水平下调,NO合成减少,这一效应可能与AngⅡ/AT_1R通路降低PP2Ac Tyr307磷酸化水平和I_2~(PP2A)表达水平、导致PP2A活性增强有关。特异性AT_1R阻断剂CAN预处理可通过增加PP2Ac Tyr307磷酸化水平和I_2~(PP2A)表达水平而降低PP2A活性,最终上调eNOS Ser1177磷酸化水平,恢复eNOS活性。     

PI3K/Akt/eNOS信号通路在葛根素抑制ox-LDL诱导的血管内皮细胞组织因子表达中的作用

目的:探讨磷脂酰肌醇3-激酶/蛋白激酶B/内皮型一氧化氮合酶(PI3K/Akt/eNOS)信号通路在葛根素(puerarin)抑制氧化型低密度脂蛋白(oxidized low-density lipoprotein,ox-LDL)诱导的血管内皮细胞组织因子(tissue factor,TF)表达中的作用。方法:实时荧光定量PCR检测TF的mRNA表达,Western blot检测TF和Akt的蛋白表达,硝酸盐还原酶法检测一氧化氮(nitric oxide,NO)含量。结果:与对照组相比,ox-LDL孵育内皮细胞后,内皮细胞TF的mRNA和蛋白表达升高,Akt蛋白磷酸化水平降低,细胞内NO产生减少;而葛根素预孵育内皮细胞1 h后,再用ox-LDL孵育,内皮细胞TF mRNA和蛋白表达下降,Akt蛋白磷酸化升高,细胞内NO产生增多;PI3K抑制剂LY294002和葛根素共同预孵育内皮细胞1 h后,再用ox-LDL孵育,内皮细胞TF的mRNA和蛋白表达升高,Akt蛋白磷酸化降低,细胞内NO产生减少;eNOS抑制剂NG-硝基-L-精氨酸甲酯(L-NAME)和葛根素共同预孵育内皮细胞,也明显阻断葛根素对ox-LDL诱导的内皮细胞TF mRNA和蛋白表达、细胞Akt蛋白磷酸化和细胞内NO产生的作用。结论:葛根素可通过上调PI3K/Akt/eNOS信号通路抑制ox-LDL诱导的人脐静脉内皮细胞TF mRNA和蛋白表达。     

Arrest of B16 melanoma cells in the mouse pulmonary microcirculation induces endothelial nitric oxide synthase-dependent nitric oxide release that is cytotoxic to the tumor cells

Metastatic cancer cells seed the lung via blood vessels. Because endothelial cells generate nitric oxide (NO) in response to shear stress, we postulated that the arrest of cancer cells in the pulmonary microcirculation causes the release of NO in the lung. After intravenous injection of B16F1 melanoma cells, pulmonary NO increased sevenfold throughout 20 minutes and approached basal levels by 4 hours. NO induction was blocked by N(G)-nitro-L-arginine methyl ester (L-NAME) and was not observed in endothelial nitric oxide synthase (eNOS)-deficient mice. NO production, visualized ex vivo with the fluorescent NO probe diaminofluorescein diacetate, increased rapidly at the site of tumor cell arrest, and continued to increase throughout 20 minutes. Arrested tumor cells underwent apoptosis with apoptotic counts more than threefold over baseline at 8 and 48 hours. Neither the NO signals nor increased apoptosis were seen in eNOS knockout mice or mice pretreated with L-NAME. At 48 hours, 83% of the arrested cells had cleared from the lungs of wild-type mice but only approximately 55% of the cells cleared from eNOS-deficient or L-NAME pretreated mice. eNOS knockout and L-NAME-treated mice had twofold to fivefold more metastases than wild-type mice, measured by the number of surface nodules or by histomorphometry. We conclude that tumor cell arrest in the pulmonary microcirculation induces eNOS-dependent NO release by the endothelium adjacent to the arrested tumor cells and that NO is one factor that causes tumor cell apoptosis, clearance from the lung, and inhibition of metastasis.