Calcium antagonists ameliorate ischemia-induced endothelial cell permeability by inhibiting protein kinase C

Stroke-induced damage on the blood-brain barrier

The blood-brain barrier (BBB) is a functional phenotype exhibited by the neurovascular unit (NVU). It is maintained and regulated by the interaction between cellular and non-cellular matrix components of the NVU. The BBB plays a vital role in maintaining the dynamic stability of the intracerebral microenvironment as a barrier layer at the critical interface between the blood and neural tissues. The large contact area (approximately 20 m2/1.3 kg brain) and short diffusion distance between neurons and capillaries allow endothelial cells to dominate the regulatory role. The NVU is a structural component of the BBB. Individual cells and components of the NVU work together to maintain BBB stability. One of the hallmarks of acute ischemic stroke is the disruption of the BBB, including impaired function of the tight junction and other molecules, as well as increased BBB permeability, leading to brain edema and a range of clinical symptoms. This review summarizes the cellular composition of the BBB and describes the protein composition of the barrier functional junction complex and the mechanisms regulating acute ischemic stroke-induced BBB disruption.

New Insights into the Nephroprotective Potential of Lercanidipine

Kidneys are responsible for many crucial biological processes in the human body, including maintaining the water-electrolyte balance, pH, and blood pressure (BP), along with the elimination of toxins. Despite this, chronic kidney disease (CKD), which affects more and more people, is a disease that develops insidiously without causing any symptoms at first. The main purpose of this article is to summarize the existing literature on lercanidipine, with a particular focus on its nephroprotective properties. Lercanidipine is a third-generation dihydropyridine (DHP) blocker of calcium channels, and as such it possesses unique qualities such as high lipophilicity and high vascular selectivity. Furthermore, it acts by reversibly inhibiting L-type and T-type calcium channels responsible for exerting positive renal effects. It has been shown to reduce tissue inflammation and tubulointerstitial fibrosis, contributing to a decrease in proteinuria. Moreover, it exhibited antioxidative effects and increased expression of molecules responsible for repairing damaged tissues. It also decreased cell proliferation, preventing thickening of the vascular lumen. This article summarizes studies simultaneously comparing the effect of lercanidipine with other antihypertensive drugs. There is still a lack of studies on the medications used in patients with CKD, and an even greater lack of studies on those used in patients with concomitant hypertension. Therefore, further studies on lercanidipine and its potential in hypertensive patients with coexisting CKD are required.

TRPM7 mediates kidney injury, endothelial hyperpermeability and mortality during endotoxemia

Sepsis is the main cause of mortality in patients admitted to intensive care units. During sepsis, endothelial permeability is severely augmented, contributing to renal dysfunction and patient mortality. Ca²⁺ influx and the subsequent increase in intracellular [Ca²⁺]_i in endothelial cells (ECs) are key steps in the establishment of endothelial hyperpermeability. Transient receptor potential melastatin 7 (TRPM7) ion channels are permeable to Ca²⁺ and are expressed in a broad range of cell types and tissues, including ECs and kidneys. However, the role of TRPM7 on endothelial hyperpermeability during sepsis has remained elusive. Therefore, we investigated the participation of TRPM7 in renal vascular hyperpermeability, renal dysfunction, and enhanced mortality induced by endotoxemia. Our results showed that endotoxin increases endothelial hyperpermeability and Ca²⁺ overload through the TLR4/NOX-2/ROS/NF-κB pathway. Moreover, endotoxin exposure was shown to downregulate the expression of VE-cadherin, compromising monolayer integrity and enhancing vascular hyperpermeability. Notably, endotoxin-induced endothelial hyperpermeability was substantially inhibited by pharmacological inhibition and specific suppression of TRPM7 expression. The endotoxin was shown to upregulate the expression of TRPM7 via the TLR4/NOX-2/ROS/NF-κB pathway and induce a TRPM7-dependent EC Ca²⁺ overload. Remarkably, in vivo experiments performed in endotoxemic animals showed that pharmacological inhibition and specific suppression of TRPM7 expression inhibits renal vascular hyperpermeability, prevents kidney dysfunction, and improves survival in endotoxemic animals. Therefore, our results showed that TRPM7 mediates endotoxemia-induced endothelial hyperpermeability, renal dysfunction, and enhanced mortality, revealing a novel molecular target for treating renal vascular hyperpermeability and kidney dysfunction during endotoxemia, sepsis, and other inflammatory diseases.

Lipopolysaccharide impairs permeability of pulmonary microvascular endothelial cells via Connexin40

The endotoxin lipopolysaccharide (LPS)-induced pulmonary endothelial barrier disruption is a key pathogenesis of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). However, the molecular mechanisms underlying LPS-impaired permeability of pulmonary microvascular endothelial cells (PMVECs) are not fully understood. Gap junctions, particularly Connexin40 (Cx40), are necessary for the maintenance of normal vascular function. In this study, we for the first time investigated the role of Cx40 in LPS-impaired permeability of PMVECs and provided potential therapeutic approaches based on mechanistic findings of Cx40 regulation by LPS stimuli. Rat PMVECs were isolated, cultured and identified with cell morphology, specific markers, ultrastructural characteristics and functional tests. Western blot analysis demonstrated that Cx40 is the major connexin highly expressed in PMVECs. Furthermore, by inhibiting Cx40 in a time-dependent manner, LPS impaired gap junction function and induced permeability injury of PMVECs. The key role of Cx40 decline in mediating detrimental effects of LPS was further confirmed in rescue experiments through Cx40 overexpression. Mechanistically, LPS stress on PMVECs inhibited the protein kinase C (PKC) pathway, which may synergize with the inflammatory nuclear factor kappaB (NFκB) signaling activation in suppressing Cx40 expression level and phosphorylation. Moreover, through pharmacological PKC activation or NFκB inhibition, Cx40 activity in PMVECs could be restored, leading to maintained barrier function under LPS stress. Our findings uncover a previously unrecognized role of Cx40 and its regulatory mechanisms in impaired endothelial integrity under endotoxin and inflammation, shedding light on intervention approaches to improve pulmonary endothelial barrier function in ALI and ARDS.

Regulation of pulmonary endothelial barrier function by kinases

The pulmonary endothelium is the target of continuous physiological and pathological stimuli that affect its crucial barrier function. The regulation, defense, and repair of endothelial barrier function require complex biochemical processes. This review examines the role of endothelial phosphorylating enzymes, kinases, a class with profound, interdigitating influences on endothelial permeability and lung function.

Mechanisms underlying capsaicin effects in canine coronary artery: implications for coronary spasm

AIMS

The TRPV1, transient receptor potential vanilloid type 1, agonist capsaicin is considered to be beneficial for cardiovascular health because it dilates coronary arteries through an endothelial-dependent mechanism and may slow atheroma progression. However, recent reports indicate that high doses of capsaicin may constrict coronary arterioles and even provoke myocardial infarction. Thus far, the mechanisms by which TRPV1 activation modulates coronary vascular tone remain poorly understood. This investigation examined whether there is a synergistic interplay between locally acting vasoconstrictive pro-inflammatory hormones (autacoids) and capsaicin effects in the coronary circulation.

METHODS AND RESULTS

Experiments were performed in canine conduit coronary artery rings and isolated smooth muscle cells (CASMCs). Isometric tension measurements revealed that 1-10 μM capsaicin alone did not affect resting tension of coronary artery rings. In contrast, in endothelium-intact rings pre-contracted with a Gq/11-coupled FP/TP (prostaglandin F/thromboxane) receptor agonist, prostaglandin F2α (PGF2α; 10 μM), capsaicin first induced transient dilation that was followed by sustained contraction. In endothelium-denuded rings pre-contracted with PGF2α or thromboxane analogue U46619 (1 μM, a TP receptor agonist), capsaicin induced only sustained contraction. Blockers of the TP receptor or TRPV1 significantly inhibited capsaicin effects, but these were still observed in the presence of 50 μM nifedipine and 70 mM KCl. Capsaicin also potentiated 20 mM KCl-induced contractions. Fluorescence imaging experiments in CASMCs revealed that the Gq/11-phospholipase C (PLC)-protein kinase C (PKC) and Ca(2+)-PLC-PKC pathways are likely involved in sensitizing CASMC TRPV1 channels.

CONCLUSION

Capsaicin alone does not cause contractions in conduit canine coronary artery; however, pre-treatment with pro-inflammatory prostaglandin-thromboxane agonists may unmask capsaicin's vasoconstrictive potential.

Reactive oxygen species in inflammation and tissue injury

Abstract Reactive oxygen species (ROS) are key signaling molecules that play an important role in the progression of inflammatory disorders. An enhanced ROS generation by polymorphonuclear neutrophils (PMNs) at the site of inflammation causes endothelial dysfunction and tissue injury. The vascular endothelium plays an important role in passage of macromolecules and inflammatory cells from the blood to tissue. Under the inflammatory conditions, oxidative stress produced by PMNs leads to the opening of inter-endothelial junctions and promotes the migration of inflammatory cells across the endothelial barrier. The migrated inflammatory cells not only help in the clearance of pathogens and foreign particles but also lead to tissue injury. The current review compiles the past and current research in the area of inflammation with particular emphasis on oxidative stress-mediated signaling mechanisms that are involved in inflammation and tissue injury.

Sirolimus-FKBP12.6 impairs endothelial barrier function through protein kinase C-α activation and disruption of the p120-vascular endothelial cadherin interaction

OBJECTIVE

Sirolimus (SRL) is an immunosuppressant drug used to prevent rejection in organ transplantation and neointimal hyperplasia when delivered from drug-eluting stents. Major side effects of SRL include edema and local collection of intimal lipid deposits at drug-eluting stent sites, suggesting that SRL impairs endothelial barrier function (EBF). The aim of this study was to address the role of SRL on impaired EBF and the potential mechanisms involved.

APPROACH AND RESULTS

Cultured human aortic endothelial cells (HAECs) and intact human and mouse endothelium was examined to determine the effect of SRL, which binds FKBP12.6 to inhibit the mammalian target of rapamycin, on EBF. EBF, measured by transendothelial electrical resistance, was impaired in HAECs when treated with SRL or small interfering RNA for FKBP12.6 and reversed when pretreated with ryanodine, a stabilizer of ryanodine receptor 2 intracellular calcium release channels. Intracellular calcium increased in HAECs treated with SRL and normalized with ryanodine pretreatment. SRL-treated HAECs demonstrated increases in protein kinase C-α phosphorylation, a calcium sensitive serine/threonine kinase important in vascular endothelial (VE) cadherin barrier function through its interaction with p120-catenin (p120). Immunostaining of HAECs, human coronary and mouse aortic endothelium treated with SRL showed disruption of p120-VE cadherin interaction treated with SRL. SRL impairment of HAEC EBF was reduced with protein kinase C-α small interfering RNA. Mice treated with SRL demonstrated increased vascular permeability by Evans blue albumin extravasation in the lungs, heart, and aorta.

CONCLUSIONS

SRL-FKBP12.6 impairs EBF by activation of protein kinase C-α and downstream disruption of the p120-VE cadherin interaction in vascular endothelium. These data suggest this mechanism may be an important contributor of SRL side effects related to impaired EBF.

N-n-butyl haloperidol iodide ameliorates cardiomyocytes hypoxia/reoxygenation injury by extracellular calcium-dependent and -independent mechanisms

N-n-butyl haloperidol iodide (F2) has been shown to antagonize myocardial ischemia/reperfusion injury by blocking calcium channels. This study explores the biological functions of ERK pathway in cardiomyocytes hypoxia/reoxygenation injury and clarifies the mechanisms by which F2 ameliorates cardiomyocytes hypoxia/reoxygenation injury through the extracellular-calcium-dependent and -independent ERK1/2-related pathways. In extracellularcalcium-containing hypoxia/reoxygenation cardiomyocytes, PKCα and ERK1/2 were activated, Egr-1 protein level and cTnI leakage increased, and cell viability decreased. The ERK1/2 inhibitors suppressed extracellular-calcium-containing-hypoxia/reoxygenation-induced Egr-1 overexpression and cardiomyocytes injury. PKCα inhibitor downregulated extracellularcalcium-containing-hypoxia/reoxygenation-induced increase in p-ERK1/2 and Egr-1 expression. F2 downregulated hypoxia/reoxygenation-induced elevation of p-PKCα, p-ERK1/2, and Egr-1 expression and inhibited cardiomyocytes damage. The ERK1/2 and PKCα activators antagonized F2's effects. In extracellular-calcium-free-hypoxia/reoxygenation cardiomyocytes, ERK1/2 was activated, LDH and cTnI leakage increased, and cell viability decreased. F2 and ERK1/2 inhibitors antagonized extracellular-calcium-free-hypoxia/reoxygenation-induced ERK1/2 activation and suppressed cardiomyocytes damage. The ERK1/2 activator antagonized F2's above effects. F2 had no effect on cardiomyocyte cAMP content or PKA and Egr-1 expression. Altogether, ERK activation in extracellular-calcium-containing and extracellular-calcium-free hypoxia/reoxygenation leads to cardiomyocytes damage. F2 may ameliorate cardiomyocytes hypoxia/reoxygenation injury by regulating the extracellular-calcium-dependent PKCα/ERK1/2/Egr-1 pathway and through the extracellular-calcium-independent ERK1/2 activation independently of the cAMP/PKA pathway or Egr-1 overexpression.

Pinacidil pretreatment improves vascular reactivity after shock through PKCα and PKCε in rats

We investigated the beneficial effect of pinacidil pretreatment on vascular reactivity, calcium sensitivity, and animal survival after hemorrhagic shock, its relationship to protein kinase Cα (PKCα), protein kinase Cε (PKCε), and adenosine. Using hemorrhagic shock rats, the protective effects of different extents of pinacidil pretreatment on vascular reactivity and in which the roles of PKCα, PKCε, and adenosine were observed. Pinacidil pretreatment significantly improved shock-induced decrease of vascular reactivity of superior mesenteric artery, which was antagonized by the PKCα antagonist Gö-6976 (5 × 10 mole/L) and PKCε pseudosubstrate inhibitory peptide (1 × 10 mole/L). Pinacidil pretreatment induced the translocation of PKCα and PKCε from the cytoplasm to the membrane. This translocation of PKCα and PKCε was eliminated by adenosine A1 receptor antagonist DPCPX (1 × 10 mole/L). As compared with simple fluid resuscitation, combination with pinacidil pretreatment significantly improved the vascular reactivity and survival rate of hemorrhagic-shocked rats. These results suggested that pinacidil pretreatment could induce good protective effects on vascular reactivity and calcium sensitivity after hemorrhagic shock mainly through the activation of PKCα and PKCε via adenosine A1 receptor, and this protective effect made an important contribution to the overall outcome of shock therapy.

Protective effect of photodegradation product of nifedipine against tumor necrosis factor alpha-induced oxidative stress in human glomerular endothelial cells

Recently, increasing evidence suggests that the antihypertensive drug nifedipine acts as a protective agent for endothelial cells, and that the activity is unrelated to its calcium channel blocking. Nitrosonifedipine (NO-NIF) is metabolically and photochemically produced from nifedipine, and NO-NIF has been recognized as a contaminant of nifedipine because it has no antihypertensive effect. Treatment of tumor necrosis factor-α (TNF-α) suppressed the cell viability and facilitated the expression of Inter-Cellular Adhesion Molecule 1(ICAM-1) in human glomerular endothelial cells (HGECs) though, pretreatment of NO-NIF significantly recovered the TNF-α-induced cell damage to the same extent as Trolox-C did, and suppressed the ICAM-1 expression in a concentration dependent manner. In addition, NO-NIF inhibited the cell toxicity induced by cumene hydroperoxide, which hampers the integrity of cell membrane through oxidative stress, as effective as Trolox-c. These data suggest that NO-NIF is a candidate for a new class of antioxidative drug that protect cells against oxidative stress in glomerular endothelial cells.

N-n-Butyl haloperidol iodide protects against hypoxia/reoxygenation-induced cardiomyocyte injury by modulating protein kinase C activity

N-n-Butyl haloperidol iodide (F2), a novel compound derived from haloperidol, protects against the damaging effects of ischemia/reperfusion (I/R) injury in vitro and in vivo. We tested whether the myocardial protection of F2 on cardiomyocyte hypoxia/reoxygenation (H/R) injury is mediated by modulating protein kinase C (PKC) activity in primary cultured cardiomyocytes. Primary cultures of ventricular cardiomyocytes underwent 2-h hypoxia and 30-min reoxygenation. Total PKC activity was measured, and the translocation pattern of PKCalpha, betaII, delta and epsilon isoforms was assessed by fractionated western blot analysis. We investigated the association of PKC isoform translocation and H/R-induced injury in the presence and absence of the specific inhibitors and activator. Measurements included cell damage evaluated by creatine kinase (CK) release, and apoptosis measured by annexin V-FITC assay. In primary cultured cardiomyocytes exposed to H/R, PKCalpha, delta and epsilon were translocated, with no change in PKCbetaII activity. Total PKC activity, CK release and apoptosis were increased after H/R. Treatment with the conventional PKC inhibitor Go6976 reduced early growth response-1 (Egr-1) protein expression and attenuated apoptosis. The PKCepsilon inhibitor peptide epsilonV1-2 increased H/R injury without influencing Egr-1 expression. Pretreatment with F2 inhibited translocation of PKCalpha, increased translocation of PKCepsilon, and relieved the CK release and apoptosis. The protection of F2 was blocked in part by the conventional PKC activator thymeleatoxin (TXA) and epsilonV1-2 peptide. F2 significantly alleviated H/R-induced injury, which might be attributed to the combined benefits of inhibiting PKCalpha and activating PKCepsilon.

Drug discovery for overcoming chronic kidney disease (CKD): development of drugs on endothelial cell protection for overcoming CKD

Chronic kidney disease (CKD) is becoming a major public health problem worldwide. It is important to protect endothelial function in CKD treatment because injury of the endothelium is a critical event for the generation and progression of CKD. Recently, clinical studies showed that nifedipine, an antihypertensive drug, acts as a protective agent of endothelial cells (ECs). Nifedipine is reported to partially decompose to a nitrosonifedipine that has high reactivity against lipid-derived radicals in vitro. However, it is still unclear whether nitrosonifedipine is a biologically active agent against endothelial injury. We observed that nitrosonifedipine was converted to radical form by reaction with cultured ECs. The cumene hydroperoxide mediated cytotoxity was reduced by nitrosonifedipine in cultured human glomerular ECs (HGECs). Also nitrosonifedipine suppressed the expression of TNF-alpha-induced intercellular cell adhesion molecule-1 in HGECs. Chronic administration of N(omega)-nitro-L-arginine methyl ester (L-NAME) caused systemic arterial hypertension, endothelial injury, and renal dysfunction. In L-NAME-induced hypertensive rats, nitrosonifedipine treatment improved not only the acetylcholine-induced vasodilation of the aortic rings, but also renal dysfunction such as increasing the levels of serum creatinine and urinary protein excretion. Our preliminary data suggest that nitrosonifedipine is a new and useful drug for the treatment of CKD involving ameliorating effects on EC disorder.

Blood-brain barrier tight junction permeability and ischemic stroke

The blood-brain barrier (BBB) is formed by the endothelial cells of cerebral microvessels, providing a dynamic interface between the peripheral circulation and the central nervous system. The tight junctions (TJs) between the endothelial cells serve to restrict blood-borne substances from entering the brain. Under ischemic stroke conditions decreased BBB TJ integrity results in increased paracellular permeability, directly contributing to cerebral vasogenic edema, hemorrhagic transformation, and increased mortality. This loss of TJ integrity occurs in a phasic manner, which is contingent on several interdependent mechanisms (ionic dysregulation, inflammation, oxidative and nitrosative stress, enzymatic activity, and angiogenesis). Understanding the inter-relation of these mechanisms is critical for the development of new therapies. This review focuses on those aspects of ischemic stroke impacting BBB TJ integrity and the principle regulatory pathways, respective to the phases of paracellular permeability.

Counter regulatory effects of PKCbetaII and PKCdelta on coronary endothelial permeability

OBJECTIVE

The aim of this study was to examine the endothelial distribution and activity of selected PKC isoforms in coronary vessels with respect to their functional impact on endothelial permeability under the experimental conditions relevant to diabetes.

METHODS AND RESULTS

En face immunohistochemistry demonstrated a significant increase of PKC(betaII) and decrease of PKCdelta expression in coronary arterial endothelium of Zucker diabetic rats. To test whether changes in PKC expression alter endothelial barrier properties, we measured the transcellular electric resistance in human coronary microvascular endothelial monolayers and found that either PKC(betaII) overexpression or PKCdelta inhibition disrupted the cell-cell adhesive barrier. Three-dimensional fluorescence microscopy revealed that hyperpermeability was caused by altered PKC activity in association with distinct translocation of PKC(betaII) to the cell-cell junction and PKCdelta localization to the cytosol. Further analyses in fractionated endothelial lysates confirmed the differential redistribution of these isozymes. Additionally, FRET analysis of PKC subcellular dynamics demonstrated a high PKC(betaII) activity at the cell surface and junction, whereas PKCdelta activity is concentrated in intracellular membrane organelles.

CONCLUSIONS

Taken together, these data suggest that PKC(betaII) and PKCdelta counter-regulate coronary endothelial barrier properties by targeting distinctive subcellular sites. Imbalanced PKC(betaII)/PKCdelta expression and activity may contribute to endothelial hyperpermeability and coronary dysfunction in diabetes.

Sustained pharmacological inhibition of deltaPKC protects against hypertensive encephalopathy through prevention of blood-brain barrier breakdown in rats

Hypertensive encephalopathy is a potentially fatal condition associated with cerebral edema and the breakdown of the blood-brain barrier (BBB). The molecular pathways leading to this condition, however, are unknown. We determined the role of deltaPKC, which is thought to regulate microvascular permeability, in the development of hypertensive encephalopathy using deltaV1-1 - a selective peptide inhibitor of deltaPKC. As a model of hypertensive encephalopathy, Dahl salt-sensitive rats were fed an 8% high-salt diet from 6 weeks of age and then were infused s.c. with saline, control TAT peptide, or deltaV1-1 using osmotic minipumps. The mortality rate and the behavioral symptoms of hypertensive encephalopathy decreased significantly in the deltaV1-1-treated group relative to the control-treated group, and BBB permeability was reduced by more than 60%. Treatment with deltaV1-1 was also associated with decreased deltaPKC accumulation in capillary endothelial cells and in the endfeet of capillary astrocytes, which suggests decreased microvasculature disruption. Treatment with deltaV1-1 prevented hypertension-induced tight junction disruption associated with BBB breakdown, which suggests that deltaPKC may specifically act to dysregulate tight junction components. Together, these results suggest that deltaPKC plays a role in the development of hypertension-induced encephalopathy and may be a therapeutic target for the prevention of BBB disruption.

Fibroblast apoptosis precedes cardiomyocyte mass reduction during left ventricular remodeling in hypertensive rats treated with amlodipine

BACKGROUND

A transient induction of apoptosis accompanies the normalization of left ventricular mass index in spontaneously hypertensive rats (SHR) treated with dihydropyridine calcium-channel blockers. However, the cell type undergoing apoptosis in this model and the temporal correlation with onset cardiac remodeling remain undefined.

METHODS AND RESULTS

SHR were treated either with vehicle or amlodipine (20 mg/kg per day) for 4, 7, 10, 14 or 28 days. Amlodipine stably reduced systolic blood pressure by day 2 (-26 +/- 2%) and stably reduced the left ventricular concentration of atrial natriuretic peptide (ANP) mRNA by approximately 50% as early as day 4, suggesting the early reduction of cardiomyocyte stress. Left ventricular mass index was significantly reduced by day 7 (-4.6 +/- 1.5%), in coordination with reduced DNA content (-23 +/- 2%) and non-cardiomyocyte number (-17 +/- 4%). However, the cardiomyocyte cross-sectional area was reduced only starting from day 14. Caspase-3 cleavage was significantly increased at day 7 only. Ultimately, amlodipine for 28 days induced a slight increase in capillary density without affecting total cardiomyocyte number, while reducing the total number of non-cardiomyocytes down to levels seen in untreated normotensive Wistar-Kyoto rats. Bax to Bcl-2 protein ratios were increased from day 7 to day 28. In situ double labeling by the terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) method (apoptosis) combined with rhodamine-labeled lectin binding (endothelial cell marker) revealed a significant increase (> 3-fold) in TUNEL-positive, lectin-negative non-cardiomyocytes in the interstitium between days 7 and 14.

CONCLUSIONS

Left ventricular remodeling induced by amlodipine in SHR involves selective deletion of excess fibroblasts via apoptosis prior to cardiomyocyte mass reduction, but after attenuation of ANP gene expression.

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.

Cellular and molecular mechanisms of tissue protection by lipophilic calcium channel blockers

Long-acting third-generation dihydropyridine calcium channel blockers (CCBs) improve endothelial dysfunction and prevent cardiovascular events in humans, but their cellular and molecular mechanisms of tissue protection are not elucidated in detail. We assessed organ (renal) protection by the highly lipophilic CCB lercanidipine in a double-transgenic rat (dTGR) model with overexpression of human renin and angiotensinogen genes. We randomly treated dTGR with lercanidipine (2.5 mg/kg/day; n=20) or vehicle (n=20) for 3 wk. Furthermore, we explored the influence of lercanidipine on protein kinase C (PKC) signaling in vivo and in vitro using endothelial and vascular smooth muscle cell cultures. Cumulative mortality was 60% in untreated dTGR, whereas none of the lercanidipine-treated animals died (P<0.001). We found significantly less albuminuria and improved renal function in lercanidipine-treated dTGR (both P<0.05). Lercanidipine treatment also significantly (P<0.05) reduced blood levels of the endogenous NOS inhibitor asymmetric dimethylarginine. On histological examination, we observed significantly less tissue inflammation and fibrosis in lercanidipine-treated animals (both P<0.05). Lercanidipine significantly inhibited angiotensin (ANG) I-mediated PKC-alpha and -delta activation in vivo and in vitro, partly due to reduced intracellular calcium flux. As a result, lercanidipine improved endothelial cell permeability in vitro. Lercanidipine prevents tissue injury and improves survival in a model of progressive organ damage. These effects may result, at least in part, from inhibition of tissue inflammation as well as improved NO bioavailability. Modulation of PKC activity may be an important underlying intracellular mechanism.

Regulation of skin microvasculature angiogenesis, cell migration, and permeability by a specific inhibitor of PKCalpha

Activation of protein kinase C (PKC) induces phenotypic changes in the morphology of microvascular endothelial cells that affect major functions of the microvasculature. These functions include the first stages of sprouting in angiogenesis, cell migration following wounding, and vascular permeability. The specific isoform(s) of PKC responsible for each of these changes has not been previously identified. In this study, we used two inflammatory agents, IL-1beta and phorbol myristic acetate, to activate PKC isozymes and specific inhibitors of PKCalpha (Gö6976) and PKCbeta (hispidin) to distinguish how each of these isoform(s) controls angiogenesis, wound healing, and permeability. In all cases, only inhibition of PKCalpha inhibited each of these functions when compared to the inhibition of PKCbeta. Additional analysis of the mechanism of action of Gö6976 (RT-PCR, Western blots, and immunohistochemistry) of the changes in the phosphorylated and nonphosphorylated forms of PKCalpha in the cell membrane and cytoplasm confirmed the specificity of PKCalpha inhibition by Gö6976. These studies therefore indicate a specific and a regulatory role of the PKCalpha isoform in three major endothelial cell functions that are important in the maintenance of microvascular homeostasis.

Endothelial antioxidant actions of dihydropyridines and angiotensin converting enzyme inhibitors

Dihydropyridines and angiotensin converting enzyme inhibitor effects on superoxide and nitric oxide (NO) were compared in high glucose (20 mM, 24 h)-treated human Ea.hy 926 endothelial cells. High glucose stimulated superoxide both extracellularly (lucigenin chemiluminescence, cytochrome c reduction) and intracellularly (dihydrorhodamine 123 fluorescence). The dihydropyridines amlodipine, nisoldipine, BayK 8644 or the angiotensin converting enzyme inhibitors captopril and enalaprilat attenuated extra- and intracellular superoxide formation; nifedipine blocked extracellular increases only, ramiprilat was without antioxidant effect. Dihydropyridines and captopril also prevented NADPH-driven superoxide release. Antioxidant actions were blunted by a bradykinin B(2) receptor antagonist or an inhibitor of p38 mitogen activated protein kinase (MAPK), and were accompanied by improved NO release (amperometric sensor). p38MAPK inhibition prevented the NO-sparing actions of dihydropyridines but not angiotensin converting enzyme inhibitors. Thus, dihydropyridines and angiotensin converting enzyme inhibitors limit high glucose-induced superoxide formation and improve NO bioavailability in human endothelial cells, in part via bradykinin and p38MAPK.

Antioxidant and nitric oxide-sparing actions of dihydropyridines and ACE inhibitors differ in human endothelial cells

The effects of dihydropyridine Ca2+ channel blockers (DHP) and ACE inhibitors on superoxide formation and nitric oxide (NO) bioavailability were compared in human EA.Hy926 endothelial cells (EC). EC were stimulated 4 h with angiotensin II (Ang II, 10 nM) +/- study drugs. Specific superoxide formation was measured by lucigenin-enhanced chemiluminescence, reduction of cytochrome c and rhodamine-123 fluorescence. Free NO release was determined with an amperometric NO sensor. NADPH oxidase subunits expression was examined with Western Blot. In untreated EC the intracellular superoxide is -64.3 +/- 6.0% decreased compared to Ang II stimulated EC. Elevated extracellular superoxide formation was on a -43.0 +/- 1.7% lower level in untreated EC. The DHP Ca2+-channel agonist BayK8644 and ACE inhibitors captopril and ramiprilat led extracellular superoxide concentration to control level. Enalaprilat blocked extracellular superoxide, the DHP amlodipine and nisoldipine prevented intracellular increases only (n = 8-9, p < 0.05). Icatibant (HOE 140), a kinin-B2 receptor antagonist, attenuated antioxidant actions of all tested agents except of nisoldipine. Ang II-induced superoxide was elevated by the phorbolester PMA and blocked by the protein kinase C (PKC) inhibitor chelerythrine. Suppression of substance P-evoked NO release by Ang II (>70%, n = 6) was reversed by the PKC inhibitor chelerythrine, the DHP amlodipine and nisoldipine and the ACE inhibitor ramiprilat. Further, Ang II reduces Nox-4 expression by 34.5 +/- 4.9. Nox-2 expression was not regulated. DHP and ACE inhibitors exert different antioxidant effects in human EC stimulated with Ang II, but both improve NO bioavailability via bradykinin and modulation of redox-regulating enzymes.

Catheter-mediated subselective intracoronary gene delivery to the rabbit heart: introduction of a novel method

BACKGROUND

Recent studies suggest that gene therapy using replication-deficient adenoviruses will benefit treatment of cardiovascular diseases including heart failure. A persistent hurdle is the effective and reproducible delivery of a transgene to the myocardium with minimal iatrogenic morbidity. In this study, we sought to design a relatively non-invasive percutaneous gene delivery system that would maximize cardiac transgene expression and minimize mortality after intracoronary adenovirus injection.

METHODS

Adult rabbits received a left circumflex coronary artery (LCx) infusion of 5x10(11) total viral particles of an adenovirus containing the marker transgene beta-galactosidase (Adeno-betaGal) via either a continuous infusion method utilizing an oxygenated, normothermic, physiologic pH Krebs solution driven by a Langendorff apparatus (n=12) or a timed bolus and set concentration at a constant infusion rate to the LCx (n=12). Six rabbits underwent global transgene delivery via an invasive method involving intraventricular delivery and aortic root cross-clamping. The efficacy of transgene expression via these three distinct delivery methods was determined in the left ventricle at 5 days by histological staining and colorimetric quantification assay.

RESULTS

While the open-chest, aortic cross-clamping method provides the highest level of gene expression throughout the heart, the morbidity of this procedure is clinically prohibitive. Percutaneous LCx delivery of Adeno-betaGal using the Langendorff apparatus was associated with the lowest morbidity and mortality while still supporting significant myocardial gene expression.

CONCLUSIONS

Percutaneous delivery of an adenovirus solution using a continuous infusion of oxygenated Krebs solution via a Langendorff apparatus appears to be a gene delivery modality offering the best compromise of gene expression and clinical utility to maximize any potential therapeutic outcome.

Nifedipine-induced vascular endothelial growth factor secretion from coronary smooth muscle cells promotes endothelial tube formation via the kinase insert domain-containing receptor/fetal liver kinase-1/NO pathway

Endothelial cells (ECs) are the critical cellular element responsible for postnatal angiogenesis. Since the calcium channel blocker (CCB) nifedipine indirectly upregulates endothelial superoxide dismutase expression by stimulating the production of vascular endothelial growth factor (VEGF) from smooth muscle cells (SMCs), we examined whether nifedipine would induce human coronary artery endothelial cell (HCEC) tube formation via an increase in VEGF production from human coronary artery SMCs (HCSMCs) in an in vitro model. Nifedipine stimulated VEGF production from HCSMCs, and this stimulation was abolished by protein kinase C (PKC) inhibitors and a bradykinin B2 receptor antagonist. In addition, supernatant derived from nifedipine-treated HCSMCs induced HCEC tube formation. This tube formation was inhibited by pretreatment with a specific inhibitor of kinase insert domain-containing receptor/fetal liver kinase-1 (KDR/Flk-1) tyrosine kinase and an inhibitor of nitric oxide (NO) synthase. In conclusion, nifedipine increases VEGF secretion through PKC activation via the B2 receptor. The VEGF secretion directly induces HCEC tube formation via the KDR/Flk-1/NO pathway. CCBs may thus have novel beneficial effects in improving coronary microvascular blood flow in addition to their main effect of reducing blood pressure.

Nifedipine protects against overproduction of superoxide anion by monocytes from patients with systemic sclerosis

We have reported previously that dihydropyridine-type calcium-channel antagonists (DTCCA) such as nifedipine decrease plasma markers of oxidative stress damage in systemic sclerosis (SSc). To clarify the cellular basis of these beneficial effects, we investigated the effects in vivo and in vitro of nifedipine on superoxide anion (O₂^•-) production by peripheral blood monocytes. We compared 10 healthy controls with 12 patients with SSc, first after interruption of treatment with DTCCA and second after 2 weeks of treatment with nifedipine (60 mg/day). O₂^•- production by monocytes stimulated with phorbol myristate acetate (PMA) was quantified by the cytochrome c reduction method. We also investigated the effects in vitro of DTCCA on O₂^•- production and protein phosphorylation in healthy monocytes and on protein kinase C (PKC) activity using recombinant PKC. After DTCCA had been washed out, monocytes from patients with SSc produced more O₂^•- than those from controls. Nifedipine treatment considerably decreased O₂^•- production by PMA-stimulated monocytes. Treatment of healthy monocytes with nifedipine in vitro inhibited PMA-induced O₂^•- production and protein phosphorylation in a dose-dependent manner. Finally, nifedipine strongly inhibited the activity of recombinant PKC in vitro. Thus, the oxidative stress damage observed in SSc is consistent with O₂^•- overproduction by primed monocytes. This was decreased by nifedipine treatment both in vivo and in vitro. This beneficial property of nifedipine seems to be mediated by its cellular action and by the inhibition of PKC activity. This supports the hypothesis that this drug could be useful for the treatment of diseases associated with oxidative stress.

Reduction of high glucose and phorbol-myristate-acetate-induced endothelial cell permeability by protein kinase C inhibitors LY379196 and hypocrellin A

Endothelial barrier dysfunction plays a pivotal role in the pathogenesis of diabetic vascular complications. Although recent studies have established a link between protein kinase C (PKC) pathway and hyperglycaemic-induced vascular permeability, it is unclear which PKC isoforms involve increased endothelial cell permeability. In the present study, we investigated whether high glucose induced endothelial hyperpermeability via distinct PKC isoforms in human umbilical vein endothelial cells (HUVECs) and whether increased endothelial permeability could be substantially reversed by PKC inhibitors LY379196 and hypocrellin A (HA). High glucose (20 mM) and phorbol-myristate-acetate (PMA)-induced endothelial hyperpermeability was almost abolished by 150 nM HA and partially reduced by 30 nM PKC beta inhibitor (LY379196). LY379196 and HA inhibited the membrane fraction of PKC activity in a dose-dependent manner. Western blot analysis revealed high-glucose-induced overexpression of PKC alpha and PKC beta2 in the membrane fraction of HUVECs. LY379196 (30 and 150 nM) selectively inhibited PKC beta2 with no significant effect on PKC alpha expression. HA (150 nM) significantly reduced PKC alpha expression with no inhibitory effect on PKC beta2. At higher concentrations (300 nM), both LY379196 and HA were no longer selective for PKC beta or alpha, respectively. This study showed that both PKC alpha and beta2 contributed to endothelial hyperpermeability. Since reduction of endothelial hyperpermeability was greater with inhibition of PKC alpha rather than PKC beta2, we conclude that PKC alpha may be a major isoform involved in endothelial permeability in HUVECs, and that PKC alpha-mediated endothelial permeability was significantly reversed by the PKC inhibitor HA.

Protection against hypoxia-induced blood-brain barrier disruption: changes in intracellular calcium

Tissue damage after stroke is partly due to disruption of the blood-brain barrier (BBB). Little is known about the role of calcium in modulating BBB disruption. We investigated the effect of hypoxic and aglycemic stress on BBB function and intracellular calcium levels. Bovine brain microvessel endothelial cells were treated with A-23187 to increase intracellular calcium without hypoxia or treated with a calcium chelator (BAPTA) or calcium channel blockers (nifedipine or SKF-96365) and 6 h of hypoxia. A-23187 alone did not increase paracellular permeability. Hypoxia increased intracellular calcium, and hypoxia or hypoxia-aglycemia increased paracellular permeability. Treatment with nifedipine and SKF-96365 increased intracellular calcium under normoglycemic conditions, instead of blocking calcium influx, and was protective against hypoxia-induced BBB disruption under normoglycemia. Protection by nifedipine and SKF-96365 was not due to antioxidant properties of these compounds. These data indicate that increased intracellular calcium alone is not enough to disrupt the BBB. However, increased intracellular calcium after drug treatment and hypoxia suggests a potential mechanism for these drugs in BBB protection; nifedipine and SKF-96365 plus hypoxic stress may trigger calcium-mediated signaling cascades, altering BBB integrity.

The metabolic inhibitor antimycin A can disrupt cell-to-cell communication by an ATP- and Ca(2+)-independent mechanism

In cardiac myocytes of new-born rats, the degree of intercellular communication through gap junctional channels closely depends on the metabolic state of the cells. In contrast, in stably transfected HeLa cells expressing rat cardiac connexin43 (Cx43, the main channel-forming protein present in ventricular myocytes), a major part of junctional communication persisted in ATP-depleted conditions, in the presence of a metabolic inhibitor (KCN) or of a broad spectrum inhibitor of protein kinases (H7). However, another metabolic inhibitor, antimycin A, which like cyanide inhibits electron transfer in the respiratory chain, totally interrupted cell-to-cell communication between Cx43-HeLa cells, even in whole-cell conditions, when ATP (5 mM) was present. Antimycin A caused a modest increase in cytosolic calcium concentration; however, junctional uncoupling still occurred when this rise was prevented. Conditions of ischemic insult (e.g. ischemia or chemical hypoxia) frequently cause the activation of protein kinases, particularly of Src and MAP kinases, and such activations are known to markedly disrupt gap junctional communication. Antimycin-induced junctional uncoupling occurred even in the presence of inhibitors of these kinases. Antimycin A appears able to cause junctional uncoupling either through the ATP depletion it induces as a metabolic poison or via a direct action on gap junction constituents.

Ischemic preconditioning prevents ischemia-induced beta-adrenergic receptor sequestration

Preconditioning enables endogenous protection to repeated myocardial ischemia. However, the effect of preconditioning on beta1 adrenergic receptor (AR) signal remains controversial. We have recently developed receptor assay system using whole cells, in which overexpressed cell surface beta ARs can be readily quantitated without disrupting the cell. Using this technique, we examined the effects of chemical/metabolic ischemia on the beta1 AR sequestration and adenylyl cyclase activity. Isoproterenol treatment, but not forskolin treatment, of HEK293T cells overexpressing beta1 ARs led to a rapid decrease (within 2 hours) in the number of the cell surface receptor, which was negated in the presence of concanavalin A. Similarly, treatment of cells with potassium cyanide and 2-deoxy-D-glucose (chemical/metabolic ischemia) induced similar receptor sequestration. When isoproterenol was superimposed on chemical/metabolic ischemia, the degree of sequestration became greater. However, when cells were pre-exposed to potassium cyanide on the preceding day (chemical preconditioning), the sequestration induced by either isoproterenol or chemical/metabolic ischemia was attenuated. Adenylyl cyclase catalytic activity as assessed by stimulation with forskolin was decreased by chemical/metabolic ischemia but fully recovered after 24 hours, suggesting that chemical/metabolic ischemia treatment did not alter cell viability. Putting together, chemical/metabolic ischemia induced beta1 AR sequestration in a similar manner to isoproterenol. In addition, preconditioning prevented the beta1 AR sequestration induced by both isoproterenol and chemical/metabolic ischemia. Pre-conditioning may play a role in preserving the cell surface beta ARs by inhibiting the sequestration that is usually induced by an ischemic event or beta adrenergic stimulation.

Targets for pharmacological intervention of endothelial hyperpermeability and barrier function

Many diseases share the common feature of vascular leakage, and endothelial barrier dysfunction is often the underlying cause. The subsequent stages of endothelial barrier dysfunction contribute to endothelial hyperpermeability. Vasoactive agents induce loss of junctional integrity, a process that involves actin-myosin interaction. Subsequently, the interaction of leukocytes amplifies leakage by the leukocyte-derived mediators. The processes mainly occur at the postcapillary venules. The whole microvascular bed, including the capillaries, becomes involved in vascular leakage by the induction of angiogenesis. Plasma leakage results from gaps between endothelial cells as well as by the induction of transcellular transport pathways. Several mechanisms can improve endothelial barrier function, depending on the tissue affected and the cause of hyperpermeability. They include blockade of specific receptors and elevation of cyclic AMP (cAMP) by agents such as beta(2)-adrenergic agents. However, current therapies based on these principles often fail. Recent research has identified several new promising targets for pharmacological therapy. Endogenous compounds were also found with barrier-improving characteristics. Important insights were obtained in the different pathways involved in barrier dysfunction. Such insights regard the regulation of endothelial contraction and endothelial junction integrity: inhibitors of RhoA activation and Rho kinase represent a potentially valuable group of agents with endothelial hyperpermeability reducing properties, and strategies to target vascular endothelial growth factor (VEGF)-mediated edema are under current investigation. In clinical practice, not only tools to improve an impaired endothelial barrier function are necessary. Sometimes, a controlled, temporal, and local increase in permeability can also be desired, for example, with the aim to enhance drug delivery. Therefore, vessel leakiness is also being exploited to enable tissue access of liposomes, viral vectors, and other therapeutic agents that do not readily cross healthy endothelium. This review discusses strategies for targeting signaling molecules in therapies for diseases involving altered endothelial permeability.

Protein kinase signaling in the modulation of microvascular permeability

The permeability of exchange microvessels is regulated through complex interactions between signaling molecules and structural proteins in the endothelium. Endothelial barrier integrity is maintained by adhesive interactions occurring at the cell-cell and cell-matrix contacts via junctional proteins and focal adhesion complexes that are anchored to the cytoskeleton. Cyclic AMP (cAMP) and cAMP-dependent kinase counteract with the nitric oxide (NO)-cyclic GMP (cGMP) pathway to protect the basal barrier function. Upon stimulation by physical stress, growth factors, or inflammatory agents, endothelial cells undergo a series of intracellular signaling reactions involving activation of protein kinase C (PKC), protein kinase G (PKG), mitogen-activated protein kinases (MAPK), and/or protein tyrosine kinases. The phosphorylation cascades trigger biochemical and conformational changes in the barrier structure and ultimately lead to an opening of the paracellular pathway. In particular, myosin light chain kinase (MLCK) activation and subsequent myosin light chain (MLC) phosphorylation in endothelial cells directly result in cell contraction and shape changes. The phosphorylation of beta-catenin may cause disorganization of adherens junctions or dissociation of vascular endothelial (VE)-cadherin-catenin complex from its cytoskeletal anchor, leading to loose or opened intercellular junctions. Additionally, focal adhesion kinase (FAK) phosphorylation-coupled focal adhesion assembly and redistribution provide an anchorage support for the conformational changes occurring in the cells and at the cell junctions. The Src family tyrosine kinases may serve as common signals that coordinate these molecular events to facilitate the paracellular transport of macromolecules. The critical roles of protein kinases in endothelial hyperpermeability implicate the therapeutic significance of protein kinase inhibitors in the prevention and treatment of diseases and injuries that are associated with microvascular barrier dysfunction.

Calcium antagonist clevidipine reduces myocardial reperfusion injury by a mechanism related to bradykinin and nitric oxide

Certain calcium antagonists, in addition to their classic actions, can increase blood flow during ischemia via bradykinin- and nitric oxide (NO)-dependent mechanisms and protect the ischemic myocardium against reperfusion injury by enhancing NO bioavailability. The current study aimed to investigate the possible involvement of bradykinin and NO in the cardioprotective action of the short-acting calcium antagonist clevidipine during late ischemia and reperfusion. Anesthetized pigs were subjected to 45-min ligation of the left anterior descending coronary artery (LAD) followed by 4 h of reperfusion. Four groups were given vehicle, clevidipine, clevidipine in combination with the bradykinin B2 receptor antagonist HOE 140 or clevidipine in combination with HOE 140 and the NO donor S-nitroso-N-acetyl-D,L-penicillamine (SNAP) into the LAD during the last 10 min of ischemia and the first 5 min of reperfusion. There were no significant differences in hemodynamics among the groups before ischemia or during ischemia-reperfusion. The infarct size (IS) was 87% +/- 2% of the area at risk in the vehicle group. Clevidipine reduced the IS to 60% +/- 3% (p < 0.001 vs vehicle). When clevidipine was administered together with HOE 140, the protective effect of clevidipine was abolished (IS, 80% +/- 3%; p < 0.001 vs clevidipine), whereas addition of SNAP restored cardioprotection (IS, 62% +/- 5%; p < 0.001 vs vehicle). The increase in LAD blood flow by endothelium-dependent dilator substance P was significantly larger in the clevidipine group than in the other groups. The results suggest that the cardioprotective effect of clevidipine during late ischemia and early reperfusion is mediated via bradykinin- and NO-related mechanisms.

Nifedipine prevents apoptosis of endothelial cells induced by oxidized low-density lipoproteins

Calcium channel blockade has been shown to inhibit experimental atherosclerosis, and early clinical trials suggest that it also reduces atherosclerosis in humans. However, the mechanisms underlying the direct protective effect of calcium channel blockade on endothelial cell injury are not fully understood. The apoptosis of endothelial cells induced by oxidized low-density lipoproteins (oxLDL) may provide a mechanistic clue to the "response-to-injury" hypothesis of atherogenesis. Here we report that the calcium channel blocker, nifedipine, prevents the apoptosis of human umbilical venous endothelial cells (HUVECs) induced by oxLDL via downregulation of the endothelial receptor for oxidized LDL (LOX-1) and inhibition of CPP32-like protease activity. The incubation of HUVEC with oxLDL increased LOX-1 mRNA levels and CPP32-like protease activity, and induced apoptosis. Preincubation of HUVEC with nifedipine before incubation with oxLDL significantly suppressed the increase in LOX-1 mRNA levels and CPP32-like protease activity, preventing apoptosis in a dose-dependent manner. These results suggest that nifedipine blocks the suicide pathway leading to the apoptosis of endothelial cells by decreasing LOX-1 mRNA levels and CPP32-like protease activity. Thus, nifedipine seems to play a protective role against the "response-to-injury" hypothesis of atherogenesis.

Cilnidipine is a novel slow-acting blocker of vascular L-type calcium channels that does not target protein kinase C

Cilnidipine is a novel dihydropyridine (DHP) antagonist. However, its pharmacological effects on vascular DHP-sensitive L-type channels and protein kinase C (PKC)-mediated arterial contraction is incompletely understood. To address this issue, we studied the effects of cilnidipine on multi-subunit, C-class L-type Ca2+ channels in rat aortic A7r5 cells, as well as on Ca2+ channel (L-type) alpha1C-b and (T-type) alpha1G subunits in the Xenopus oocyte expression system. Cilnidipine dose- and time-dependently inhibited Ba2+ currents in A7r5 cells, with half-maximal inhibitions (IC50) at 10 nmol/l after 10 min. Unlike classical pharmacological Ca2+ channel blockers, cilnidipine's block of Ca2+ currents did not reach steady-state levels within 10 min, indicating steady-state half-maximal inhibition of native, multi-subunit L-type channels at < 10 nmol/l. In contrast, smooth muscle alpha1Cb currents were blocked by cilnidipine at much higher doses (steady-state IC50, 20 micromol/l) whereas alpha1G currents were not inhibited by cilnidipine (30 micromol/l). Cilnidipine dose-dependently inhibited depolarization- and Ca2+-induced contractions of rat aortic rings, with an IC50 of 10 nmol/l at 10 min. However, the onset of the effects was very slow, with approximately 71% inhibition by 3 nmol/l cilnidipine after 90 min exposure to cilnidipine. In contrast, cilnidipine did not inhibit phorbol 12-myristate-13-acetate (100 nmol/l)-mediated contractions. We conclude that cilnidipine represents an extremely slow-acting DHP that targets multi-subunit L-type channels, but not PKC in arterial smooth muscle. Because cilnidipine is less potent in cells expressing the pore-forming alpha1C-b subunit, the data further suggest that this unique slow-acting mechanism of cilnidipine is mediated by a complex interaction of cilnidipine with alpha1C-b and accessory channel subunits.

Parathyroid hormone effects on signaling pathways in endothelial cells vary with peptide concentration

We have previously reported that parathyroid hormone (PTH) has specific effects on a human umbilical vein endothelial cell line. Further studies were performed to characterize the signaling cascades initiated by PTH. We report that PTH induced the appearance of voltage sensitive calcium channels. Furthermore, PTH increased ceramide but not diacylglycerol content. Since elevations in [Ca(2+)](i) and phospholipid turnover are signals for the activation of protein kinase C (PKC), the cells were screened for PKC isoforms. PTH induced a redistribution of the PKCepsilon to the particulate fractions of cell homogenates. In summary, PTH induced PKC translocation through a calcium-phospholipid pathway in an endothelial cell line.

In vivo myocardial gene transfer: optimization and evaluation of intracoronary gene delivery in vivo

Clinical reports suggest that intracoronary delivery of adenoviruses encoding angiogenic growth factors, or their transactivators, has a therapeutic benefit. However there has not been a systematic assessment of the transfection efficiency of this technique in vivo. In rabbits we investigated the efficiency of myocardial gene transfer following intracoronary infusion of 1 x 10(-10) -1 x 10(12) p.f.u. of adenovirus in combination with interventions to enhance transfection. In five standard short axis sections, we were barely able to detect reporter gene expression following unmodified intracoronary infusion. Efficiency was not enhanced by the exclusion of blood and the increase of intracoronary dwell time through occlusive engagement of the left coronary ostium enabled by oxygenated perfluorocarbon emulsion as viral diluent. Of the interventions and pretreatments designed to increase vascular permeability, VEGF, calcium-free viral diluent and adenosine, only the latter tended to increase efficiency. However an intervention designed to increase the myocardial transcapillary gradient, by increasing venular pressure with pulmonary artery occlusion and arteriolar pressure with occlusion of the aorta above the coronary ostia, increased transfection efficiency by two orders of magnitude. Unfortunately the clinical utility of this technique may be limited by accompanying cardiac dilation and marked elevations in intracardiac pressure.

Effects of amlodipine and lacidipine on cardiac remodelling and renin production in salt-loaded stroke-prone hypertensive rats

1. Calcium channel blockers (CCBs) are anti-hypertensive drugs that are usually considered to act mainly as vasodilators. We investigated the relation between the reduction of blood pressure evoked by two long-acting CCBs and their protective effect against cardiac and renal damage in salt-loaded stroke-prone spontaneously hypertensive rats (SHRSP). 2. SHRSP were exposed to high dietary salt intake (1% NaCl in drinking solution) from 8 to 14 weeks of age, with or without amlodipine or lacidipine at three dosage regimens producing similar effects on blood pressure. 3. The lowest dosages of both drugs had non-significant effects on blood pressure but inhibited the paradoxical increases in plasma renin activity (PRA) and in renin mRNA in kidney that were found in salt-loaded SHRSP. The lowest dosage of lacidipine (but not of amlodipine) restored the physiological downregulation of renin production by high salt and reduced left ventricular hypertrophy and mRNA levels of atrial natriuretic factor and transforming growth factor-beta1. 4. The intermediate dosages reduced blood pressure and PRA in a comparable manner, but cardiac hypertrophy was more reduced by lacidipine than by amlodipine. 5. Although the highest doses exhibited a further action on blood pressure, they had no additional effect on cardiac hypertrophy, and they increased PRA and kidney levels of renin mRNA even more than in the absence of drug treatment. 6. We conclude that reduction of blood pressure is not the sole mechanism involved in the prevention of cardiac remodelling by CCBs, and that protection against kidney damage and excessive renin production by low and intermediate dosages of these drugs contributes to their beneficial cardiovascular effects.

Nephrotoxicants Induce Endothelin Release and Signaling in Renal Proximal Tubules: Effect on Drug Efflux

We previously used killifish proximal tubules, fluorescent substrates, and confocal microscopy to demonstrate that transport mediated by the multidrug resistance protein (Mrp2) and by P-glycoprotein was reduced by nanomolar concentrations of endothelin-1 (ET), acting through a basolateral B-type ET receptor and protein kinase C (PKC). Here we show that representatives of two classes of nephrotoxicants decrease transport by activating the endothelin-PKC signaling pathway. Exposing tubules to radiocontrast agents (iohexol, diatrizoate) or aminoglycoside antibiotics (gentamicin, amikacin) reduced Mrp2-mediated fluorescein methotrexate (FL-MTX) transport from cell to tubular lumen. Pretreating the tubules with an ET(B)-receptor antagonist or with PKC-selective inhibitors abolished these effects. The nephrotoxicants activated signaling by inducing release of ET from the tubules, because adding of an antibody against ET to the medium abolished the effects. Elevating medium Ca(2+) also reduced FL-MTX transport; this reduction was abolished when tubules were pretreated with an ET antibody, an ET(B)-receptor antagonist, PKC-selective inhibitors, or the Ca(2+) channel blocker, nifedipine. None of these drugs by themselves affected FL-MTX transport. Importantly, nifedipine also blocked the ET(B)-receptor/PKC-dependent reduction in FL-MTX transport caused by gentamicin and diatrizoate. These results for two classes of structurally unrelated nephrotoxicants suggest that Ca(2+)-dependent ET release and subsequent action through an autocrine mechanism may be an early response to tubular injury.

Effects of cyanide and deoxyglucose on Ca2+ signalling in macrovascular endothelial cells

1. We have studied the effects of the metabolic inhibitors cyanide (CN) and deoxyglucose (DG) on the intracellular Ca2+ concentration ([Ca2+]i) in macrovascular endothelial cells derived from human umbilical vein (EA cells). 2. CN- and DG increased [Ca2-]i in non-voltage clamped cells. This effect was dependent on extracellular Ca2+ concentration and membrane potential, indicating that CN- induced a Ca2+ entry. 3. During expose to CN- and/or DG, EA cells depolarise. This depolarisation is sometimes preceded by a small, but transient hyperpolarisation due to activation of a big - conductance K+ channels, BKCa, present in EA cells. However, in approximately 90% of the cells tested, the CN- and/or DG induced elevation of [Ca2+]i was insufficient to activate BKCa. 4. CN- and/or DG enhanced BKCa currents preactivated by an elevation of [Ca2+]i via cell dialysis with 0.5 and 1 microM, respectively. Thus, metabolic inhibition sensitises BKCa. 5. The CN- induced depolarisation of EA cells occurs by activating a current that reversed at positive membrane potentials. Substituting extracellular cations abolished the inward component of this current by NMDG, indicating that CN- activated a non-selective cation channel, NSC. This current was reduced by extracellular Ca2+ and Mg2'+ but is partially carried by Ca2+. 6. It is concluded that CN elevates [Ca2+]i by activating Ca2+ permeable NSC channels. The properties of these channels are similar to those of the recently described trp3 channels expressed in endothelium.

Effects of extracellular calcium and potassium on the sodium pump of rat adrenal glomerulosa cells

Because the activity of the sodium pump (Na-K-ATPase) influences the secretion of aldosterone, we determined how extracellular potassium (K(o)) and calcium affect sodium pump activity in rat adrenal glomerulosa cells. Sodium pump activity was measured as ouabain-sensitive (86)Rb uptake in freshly dispersed cells containing 20 mM sodium as measured with sodium-binding benzofluran isophthalate. Increasing K(o) from 4 to 10 mM in the presence of 1.8 mM extracellular calcium (Ca(o)) stimulated sodium pump activity up to 165% and increased intracellular free calcium as measured with fura 2. Increasing K(o) from 4 to 10 mM in the absence of Ca(o) stimulated the sodium pump approximately 30% and did not increase intracellular free calcium concentration ([Ca(2+)](i)). In some experiments, addition of 1.8 mM Ca(o) in the presence of 4 mM K(o) increased [Ca(2+)](i) above the levels observed in the absence of Ca(o) and stimulated the sodium pump up to 100%. Ca-dependent stimulation of the sodium pump by K(o) and Ca(o) was inhibited by isradipine (10 microM), a blocker of L- and T-type calcium channels, by compound 48/80 (40 microg/ml) and calmidizolium (10 microM), which inhibits calmodulin (CaM), and by KN-62 (10 microM), which blocks some forms of Ca/CaM kinase II (CaMKII). Staurosporine (1 microM), which effectively blocks most forms of protein kinase C, had no effect. In the presence of A-23187, a calcium ionophore, the addition of 0.1 mM Ca(o) increased [Ca(2+)](i) to the level observed in the presence of 10 mM K(o) and 1.8 mM Ca(o) and stimulated the sodium pump 100%. Ca-dependent stimulation by A-23187 and 0.1 mM Ca(o) was not reduced by isradipine but was blocked by KN-62. Thus, under the conditions that K(o) stimulates aldosterone secretion, it stimulates the sodium pump by two mechanisms: direct binding to the pump and by increasing calcium influx, which is dependent on Ca(o). The resulting increase in [Ca(2+)](i) may stimulate the sodium pump by activating CaM and/or CaMKII.