Hypoxia-induced modulation of endothelial cell properties: regulation of barrier function and expression of interleukin-6

Hypoxia impairs urothelial barrier function by inhibiting the expression of tight junction proteins in SV-HUC-1 cells

Hypoxia plays an important role in the pathological process of bladder outlet obstruction. Previous research has mostly focused on the dysfunction of bladder smooth muscle cells, which are directly related to bladder contraction. This study delves into the barrier function changes of the urothelial cells under exposure to hypoxia. Results indicated that after a 5-day culture, SV-HUC-1 formed a monolayer and/or bilayer of cell sheets, with tight junction formation, but no asymmetrical unit membrane was observed. qPCR and western blotting revealed the expression of TJ-associated proteins (occludin, claudin1 and ZO-1) was significantly decreased in the hypoxia group in a time-dependent manner. No expression changes were observed in uroplakins. When compared to normoxic groups, immunofluorescent staining revealed a reduction in the expression of TJ-associated proteins in the hypoxia group. Transepithelial electrical resistance (TEER) revealed a statistically significant decrease in resistance in the hypoxia group. Fluorescein isothiocyanate-conjugated dextran assay was inversely proportional to the results of TEER. Taken together, hypoxia down-regulates the expression of TJ-associated proteins and breaks tight junctions, thus impairing the barrier function in human urothelial cells.

Interleukin-6 as surrogate marker for imaging-based hypoxia dynamics in patients with head-and-neck cancers undergoing definitive chemoradiation-results from a prospective pilot trial

Purpose

Intratumoral hypoxia increases resistance of head-and-neck squamous cell carcinoma (HNSCC) to radiotherapy. [¹⁸F]FMISO PET imaging enables noninvasive hypoxia monitoring, though requiring complex logistical efforts. We investigated the role of plasma interleukin-6 (IL-6) as potential surrogate parameter for intratumoral hypoxia in HNSCC using [¹⁸F]FMISO PET/CT as reference.

Methods

Within a prospective trial, serial blood samples of 27 HNSCC patients undergoing definitive chemoradiation were collected to analyze plasma IL-6 levels. Intratumoral hypoxia was assessed in treatment weeks 0, 2, and 5 using [¹⁸F]FMISO PET/CT imaging. The association between PET-based hypoxia and IL-6 was examined using Pearson’s correlation and multiple regression analyses, and the diagnostic power of IL-6 for tumor hypoxia response prediction was determined with receiver-operating characteristic analyses.

Results

Mean IL-6 concentrations were 15.1, 19.6, and 31.0 pg/mL at baseline, week 2 and week 5, respectively. Smoking (p=0.050) and reduced performance status (p=0.011) resulted in higher IL-6 levels, whereas tumor (p=0.427) and nodal stages (p=0.334), tumor localization (p=0.439), and HPV status (p=0.294) had no influence. IL-6 levels strongly correlated with the intratumoral hypoxic subvolume during treatment (baseline: r=0.775, p<0.001; week 2: r=0.553, p=0.007; week 5: r=0.734, p<0.001). IL-6 levels in week 2 were higher in patients with absent early tumor hypoxia response (p=0.016) and predicted early hypoxia response (AUC=0.822, p=0.031). Increased IL-6 levels at week 5 resulted in a trend towards reduced progression-free survival (p=0.078) and overall survival (p=0.013).

Conclusion

Plasma IL-6 is a promising surrogate marker for tumor hypoxia dynamics in HNSCC patients and may facilitate hypoxia-directed personalized radiotherapy concepts.

Trial registration

The prospective trial was registered in the German Clinical Trial Register (DRKS00003830). Registered 20 August 2015

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-021-05602-x.

Novel HIF-1-target gene isthmin1 contributes to hypoxia-induced hyperpermeability of pulmonary microvascular endothelial cells monolayers

Hypoxia-induced pulmonary microvascular endothelial cell (PMVEC) monolayers hyperpermeability is vital for vascular leakage, which participates in vascular diseases, such as acute lung injury (ALI) and high-altitude pulmonary edema (HAPE). We previously observed that PMVEC permeability was markedly elevated in hypoxia when cocultured with primary type II alveolar epithelial cells (AECII) in which isthmin1 (ISM1) was highly upregulated. However, whether the upregulation of ISM1 plays a role in hypoxia-induced PMVEC hyperpermeability is unclear. In this study, we assessed the role of AECII-derived ISM1 in hypoxia-induced PMVEC hyperpermeability with an AECII/PMVEC coculture system and uncovered the underlying mechanism whereby hypoxia stimulates ISM1 gene expression. We found that ISM1 gene expression was upregulated in cultured AECII cells exposed to hypoxia (3% O2) and that AECII-derived ISM1 participated in hypoxia-induced hyperpermeability of PMVEC monolayers, as small interference RNA (siRNA)-mediated knockdown of ISM1 in AECII markedly attenuated the increase in PMVEC permeability in coculture system under hypoxia. In addition, we confirmed that ISM1 was regulated by hypoxia-inducible factor-1α (HIF1α) according to the evidence that silencing of HIF1α inhibited the hypoxia-mediated upregulation of ISM1. Mechanismly, overexpression of HIF1α transcriptionally activated ISM1 gene expression by directly binding to the conserved regulatory elements upstream of the ism1 locus. We identified a novel HIF-1-target gene ISM1, which involves in hyperpermeability of pulmonary microvascular endothelial cell monolayers under hypoxia. Our in vitro cell experiments implied that the upregulated ISM1 derived from alveolar epithelium might be a vital modulator in hypoxia-induced endothelial hyperpermeability and thereby implicates with hypoxic pulmonary-related diseases.

Potential Immunotherapeutic Targets for Hypoxia Due to COVI-Flu

The world is currently embroiled in a pandemic of coronavirus disease 2019 (COVID-19), a respiratory illness caused by the novel betacoronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The severity of COVID-19 disease ranges from asymptomatic to fatal acute respiratory distress syndrome. In few patients, the disease undergoes phenotypic differentiation between 7 and 14 days of acute illness, either resulting in full recovery or symptom escalation. However, the mechanism of such variation is not clear, but the facts suggest that patient's immune status, comorbidities, and the systemic effects of the viral infection (potentially depending on the SARS-CoV-2 strain involved) play a key role. Subsequently, patients with the most severe symptoms tend to have poor outcomes, manifest severe hypoxia, and possess elevated levels of pro-inflammatory cytokines (including IL-1β, IL-6, IFN-γ, and TNF-α) along with elevated levels of the anti-inflammatory cytokine IL-10, marked lymphopenia, and elevated neutrophil-to-lymphocyte ratios. Based on the available evidence, we propose a mechanism wherein SARS-CoV-2 infection induces direct organ damage while also fueling an IL-6-mediated cytokine release syndrome (CRS) and hypoxia, resulting in escalating systemic inflammation, multi-organ damage, and end-organ failure. Elevated IL-6 and hypoxia together predisposes patients to pulmonary hypertension, and the presence of asymptomatic hypoxia in COVID-19 further compounds this problem. Due to the similar downstream mediators, we discuss the potential synergistic effects and systemic ramifications of SARS-CoV-2 and influenza virus during co-infection, a phenomenon we have termed "COVI-Flu." Additionally, the differences between CRS and cytokine storm are highlighted. Finally, novel management approaches, clinical trials, and therapeutic strategies toward both SARS-CoV-2 and COVI-Flu infection are discussed, highlighting host response optimization and systemic inflammation reduction.

Albuminuria in Pediatric Patients With Adenotonsillar Hypertrophy

The relationship between intermittent nocturnal hypoxia and albuminuria in pediatric patients with adenotonsillar hypertrophy was evaluated in this prospective study. Fifty children with grade 3 to 4 adenotonsillar hypertrophy scheduled for adenoidectomy and/or adenotonsillectomy were selected for study group. Fifteen patients with adenotonsillar grade 1 to 2 or adenotonsillectomized subjects in a similar range of sex, age, and body mass index scheduled for other surgeries were selected for control group. All children were monitored using finger pulse oximeter during the night before surgery. At the day of surgery, first morning urine samples were sent to the laboratory for analysis of albuminuria.Albuminuria was determined in 8 (16%) patients in study group and 1 (6.7%) patient in control group. This difference between groups was determined not to be statistically significant (P > 0.05). None of the pulse oximetry parameters was also found to be associated with albuminuria statistically (P > 0.05). However, the adenoid grade was observed to be associated with albuminuria (P = 0.011).This study revealed no relationship between albuminuria and intermittent hypoxia in children, although previous studies have reported that intermittent hypoxia causes albuminuria in adults. On the contrary, the adenoid grade was found to be in association with albuminuria. The reason seems to be unclear because of the lack of studies investigating albuminuria in children with adenotonsillar hypertrophy. However, inflammatory mediators arising from adenoid tissue may cause increase in renal capillary permeability and urine albumin excretion.

The microRNA-7-mediated reduction in EPAC-1 contributes to vascular endothelial permeability and eNOS uncoupling in murine experimental retinopathy

AIMS

To investigate the consequences of oxidative stress and hypoxia on EPAC-1 expression during retinopathy.

METHODS

Oxygen-induced retinopathy was induced in mice and EPAC-1 expression investigated by immunofluorescence. In silico analyses were used to identify a link between EPAC-1 expression and microRNA-7-5p in endothelial cells and confirmed by western blot analyses on cells expressing microRNA-7-5p. In vitro, endothelial cells were either incubated at 2% oxygen or transfected with microRNA-7-5p, and the effects of these treatments on EPAC-1 expression, endothelial hyperpermeability and NO production were assessed. In the Ins2Akita mouse model, levels of EPAC-1 expression as well as microRNA-7-5p were assessed by qPCR. Endothelial nitric oxide synthase was assessed by immunoblotting in the Ins2Akita model.

RESULTS

Hypoxia induces the expression of microRNA-7-5p that translationally inhibits the expression of EPAC-1 in endothelial cells, resulting in hyperpermeability and the loss of eNOS activity. Activation of EPAC-1 by the cAMP analogue 8-pCPT-2'-O-Me-cAMP reduced the sensitivity of EPAC-1 to oxidative stress and restored the endothelial permeability to baseline levels. Additionally, 8-pCPT-2'-O-Me-cAMP rescued eNOS activity and NO production. In mouse models of retinopathy, i.e., oxygen-induced retinopathy and the spontaneous diabetic heterozygous Ins2^Akita mice, EPAC-1 levels are decreased which is associated with an increase in microRNA-7-5p expression and reduced eNOS activity.

CONCLUSION/INTERPRETATION

In retinopathy, EPAC-1 expression is decreased in a microRNA-7-mediated manner, contributing to endothelial dysfunction. Pharmacological activation of remnant EPAC-1 rescues endothelial function. Collectively, these data indicate that EPAC-1 resembles an efficacious and druggable target molecule for the amelioration of (diabetic) retinopathy.

Blast Wave Exposure to the Extremities Causes Endothelial Activation and Damage

Extremity injury is a significant burden to those injured in explosive incidents and local ischaemia can result in poor functionality in salvaged limbs. This study examined whether blast injury to a limb resulted in a change in endothelial phenotype leading to changes to the surrounding tissue.

The hind limbs of terminally anaesthetized rabbits were subjected to one of four blast exposures (high, medium, low, or no blast). Blood samples were analyzed for circulating endothelial cells pre-injury and at 1, 6, and 11 h postinjury as well as analysis for endothelial activation pre-injury and at 1, 6, and 12 h postinjury. Post-mortem tissue (12 h post-injury) was analysed for both protein and mRNA expression and also for histopathology. The high blast group had significantly elevated levels of circulating endothelial cells 6 h postinjury. This group also had significantly elevated tissue mRNA expression of IL-6, E-selectin, TNF-α, HIF-1, thrombomodulin, and PDGF. There was a significant correlation between blast dose and the degree of tissue pathology (hemorrhage, neutrophil infiltrate, and oedema) with the worst scores in the high blast group. This study has demonstrated that blast injury can activate the endothelium and in some cases cause damage that in turn leads to pathological changes in the surrounding tissue. For the casualty injured by an explosion the damaging effects of hemorrhage and shock could be exacerbated by blast injury and vice versa so that even low levels of blast become damaging, all of which could affect tissue functionality and long-term outcomes.

Proteinuria and clinical outcome in CHD patients

INTRODUCTION

CHD patients, especially those with associated hypoxaemia, usually have some level of renal function impairment, even though they are relatively young. The aim of the study was to evaluate those clinical and analytical factors that may contribute to microalbuminuria and determine the association of 24-hour proteinuria with thrombotic events and mortality.

METHODS

A total of 251 CHD patients were studied and demographic characteristics, blood test, and 24-hour urinalysis were analysed.

RESULTS

Of the patients, 221 were non-hypoxaemic, and 30 were hypoxaemic (oxygen saturation of 84.3±5.9%). Of the non-hypoxaemic patients, 30 (13.6%), and of the hypoxaemic patients 9 (30%), showed proteinuria (>0.15 g/24 hours) (p=0.028). Hypoxaemic CHD patients also showed higher haematocrit (%) (50.7 (34.6; 72.1) versus 42.8 (34.6; 48.9), p<0.001), serum creatinine (mg/dl) (1.07±0.2 versus 0.96±1.9, p=0.004), microalbuminuria (mg/dl/24 hours) (1.2 (0.0; 261.5) versus 0.5 (0.0; 4.37), p<0.001), proteinuria (gr/24 hours) (1.0 (0.4; 3.1) versus 0.08 (0.04; 0.52), p=0.043), and N-terminal pro-B-type natriuretic peptide (pg/ml) (417.8 (35.7; 8534.0) versus 44.9 (0.0; 670.5), p<0.001) concentrations than non-hypoxaemic CHD patients. During a median follow-up of 26.0 (16.9; 57.7) months, five patients died - one patient had 24-hour proteinuria and four patients did not (p=0.581) - and three patients had some type of thrombosis - two patients had 24-hour proteinuria and one patient did not (p=0.014). Kaplan-Meier survival analysis showed no significant difference between CHD patients with and without 24-hour proteinuria (p=0.631).

CONCLUSION

CHD patients with proteinuria have significantly more thrombosis and more hypoxaemia than those patients without proteinuria.

[Examination of cytoprotective and anti-inflammatory effect of PACAP-38 on small bowel autotransplantation]

INTRODUCTION

The small intestine is one of the most sensitive organs to ischemia-reperfusion injury during transplantation. Cytoprotective effect of pituitary adenylate cyclase-activating polypeptide (PACAP) is well known. The aim of our study was to measure changes of PACAP-38-like immunoreactivities and cytokine levels in intestinal grafts stored PACAP-38 containing preservation solution.

MATERIAL AND METHODS

Small-bowel autotransplantation was performed on male Wistar rats (n = 56). Grafts were stored in University of Wisconsin (UW) solution at 4 °C for 1 (GI), 3 (GII), and 6 hours (GIII); and in PACAP-38 containing UW solution for 1 (GIV), 3 (GV), and 6 hours (GVI). Reperfusion lasted 3 hours in each group. Intestinal PACAP-38 immunoreactivities were measured by radioimmunoassay. To measure cytokine from tissue homogenates we used rat cytokine array and Luminex Multiplex Immunoassay.

RESULTS

Levels of PACAP-38-like and PACAP-27-like immunoreactivities decreased by preservation time compared to control. This decrease was significant following 6 hours cold storage (p < 0.05). Values remained significantly higher in grafts stored in PACAP-38 containing UW. Expressions of sICAM-1, L-selectin, tissue inhibitor of metalloproteinase-1 were increased in GIII and were decreased in GVI.

CONCLUSION

PACAP-38 increased tissue levels of PACAP-38 and PACAP-27, and decreased cytokine expression. This indicates that PACAP-38 has anti-inflammatory and cytoprotective effects in intestinal autotransplantation model.

Sprouty2 expression controls endothelial monolayer integrity and quiescence

Vascular integrity is fundamental to the formation of mature blood vessels and depends on a functional, quiescent endothelial monolayer. However, how endothelial cells enter and maintain quiescence in the presence of angiogenic factors is still poorly understood. Here we identify the fibroblast growth factor (FGF) antagonist Sprouty2 (Spry2) as a key player in mediating endothelial quiescence and barrier integrity in mouse aortic endothelial cells (MAECs): Spry2 knockout MAECs show spindle-like shapes and are incapable of forming a functional, impermeable endothelial monolayer in the presence of FGF2. Whereas dense wild type cells exhibit contact inhibition and stop to proliferate, Spry2 knockout MAECs remain responsive to FGF2 and continue to proliferate even at high cell densities. Importantly, the anti-proliferative effect of Spry2 is absent in sparsely plated cells. This cell density-dependent Spry2 function correlates with highly increased Spry2 expression in confluent wild type MAECs. Spry2 protein expression is barely detectable in single cells but steadily increases in cells growing to high cell densities, with hypoxia being one contributing factor. At confluence, Spry2 expression correlates with intact cell-cell contacts, whereas disruption of cell-cell contacts by EGTA, TNFα and thrombin decreases Spry2 protein expression. In confluent cells, high Spry2 levels correlate with decreased extracellular signal-regulated kinase 1/2 (Erk1/2) phosphorylation. In contrast, dense Spry2 knockout MAECs exhibit enhanced signaling by Erk1/2. Moreover, inhibiting Erk1/2 activity in Spry2 knockout cells restores wild type cobblestone monolayer morphology. This study thus reveals a novel Spry2 function, which mediates endothelial contact inhibition and barrier integrity.

Changes of PACAP immunoreactivities and cytokine levels after PACAP-38 containing intestinal preservation and autotransplantation

Small bowel is one of the most sensitive organs to ischemia-reperfusion injury, which is a significant problem during transplantation. Pituitary adenylate cyclase-activating polypeptide (PACAP) has cytoprotective effect in ischemic injuries of various tissues. The aim of our study was to measure changes of PACAP-38 and PACAP-27 immunoreactivities and cytokine levels in intestinal grafts stored in PACAP-38-containing preservation solution. Small bowel autotransplantation was performed on male Wistar rats. Grafts were stored in University of Wisconsin (UW) solution at 4 °C for 1 h (group (G)I), for 3 h (GII), and for 6 h (GIII) and in PACAP-38-containing UW solution for 1 h (GIV), for 3 h (GV), and for 6 h (GVI). After preservation, performing vessel anastomosis reperfusion began, which lasted 3 h in each group. Tissue biopsies were collected after laparotomy (control) and at the end of the reperfusion periods. Intestinal PACAP-38 and PACAP-27 immunoreactivities were measured by radioimmunoassay. To measure cytokines from tissue homogenates, we used rat cytokine array and Luminex Multiplex Immunoassay. Levels of PACAP-38 and PACAP-27 immunoreactivity decreased after 1 and 3 h preservation compared to control levels. This decrease was significant following 6 h cold storage (p < 0.05). Values remained significantly higher in grafts stored in PACAP-38-containing UW. Cytokine array revealed that expression of the soluble intercellular adhesion molecule-1 (CD54) and L-selectin (CD62L/LECAM-1) was increased in GIII. Both 6 h cold storage in PACAP-38-containing UW solution and 3 h reperfusion caused strong reduction in these cytokines activation in GVI. RANTES (CCL5) levels were increased in all groups. Strong activation of the tissue inhibitor of metalloproteinase-1 was in GIII. However, PACAP-38-containing cold storage could decrease its activation in GVI. Furthermore, strong activation of the tissue inhibitor of metalloproteinase-1 was detected in 6 h preserved grafts without PACAP-38 (GIII). PACAP-38-containing cold storage could decrease its activation in GVI. Our present study showed that PACAP-38 and PACAP-27 immunoreactivities decreased in a time-dependent manner during intestinal cold preservation, which could be ameliorated by administration of exogenous PACAP-38 to the preservation solution. Moreover, PACAP-38 could attenuate tissue cold ischemic injury-induced changes in cytokine expression.

Cilostazol Reduces the Risk of Hemorrhagic Infarction After Administration of Tissue-Type Plasminogen Activator in a Murine Stroke Model

Background and Purpose—

Prior use of antiplatelet agents improves stroke outcome in patients undergoing thrombolytic therapy as shown by reduced arterial reocclusion, although the risk of cerebral hemorrhage can be increased.

Methods—

The effect of cilostazol, an antiplatelet drug that improves endothelial function through upregulation of intracellular cAMP, on cerebral hemorrhage after thrombolytic therapy was investigated using a highly reproducible transient ischemia model.

Results—

Treatment with cilostazol for 7 days before ischemia significantly suppressed the risk and severity of cerebral hemorrhage after injection of tissue-type plasminogen activator, although treatment with aspirin had no such protective effect compared with nontreated mice. Immunohistological analysis revealed that treatment with cilostazol suppressed disruption of the microvasculature in the ischemic area associated with reduced matrix metalloproteinase-9 activity.

Conclusions—

Our results suggest that patients treated with cilostazol before onset of stroke could have a lower risk of cerebral hemorrhage after thrombolytic therapy and might also have a longer therapeutic time window for thrombolysis. Furthermore, the risk of cerebral hemorrhage can be significantly altered by prestroke therapies, and analysis of the effects of multiple drugs on tissue-type plasminogen activator-induced cerebral hemorrhage in animal models is essential for the extending safe and effective thrombolytic therapy to a wider group of patients.

Interplay of hypoxia and A2B adenosine receptors in tissue protection

That adenosine signaling can elicit adaptive tissue responses during conditions of limited oxygen availability (hypoxia) is a long-suspected notion that recently gained general acceptance from genetic and pharmacologic studies of the adenosine signaling pathway. As hypoxia and inflammation share an interdependent relationship, these studies have demonstrated that adenosine signaling events can be targeted to dampen hypoxia-induced inflammation. Here, we build on the hypothesis that particularly the A(2B) adenosine receptor (ADORA(2B)) plays a central role in tissue adaptation to hypoxia. In fact, the ADORA(2B) requires higher adenosine concentrations than any of the other adenosine receptors. However, during conditions of hypoxia or ischemia, the hypoxia-elicited rise in extracellular adenosine is sufficient to activate the ADORA(2B). Moreover, several studies have demonstrated very robust induction of the ADORA(2B) elicited by transcriptional mechanisms involving hypoxia-dependent signaling pathways and the transcription factor "hypoxia-induced factor" 1. In the present chapter, genetic and pharmacologic evidence is presented to support our hypothesis of a tissue protective role of ADORA(2B) signaling during hypoxic conditions, including hypoxia-elicited vascular leakage, organ ischemia, or acute lung injury. All these disease models are characterized by hypoxia-elicited tissue inflammation. As such, the ADORA(2B) has emerged as a therapeutic target for dampening hypoxia-induced inflammation and tissue adaptation to limited oxygen availability.

Microalbuminuria and hypoxemia in patients with chronic obstructive pulmonary disease

RATIONALE

Microalbuminuria (MAB), a marker of endovascular dysfunction, is a predictor of cardiovascular events and all-cause mortality in the general population. There is evidence of vascular dysfunction in patients with chronic obstructive pulmonary disease (COPD).

OBJECTIVES

To assess the prevalence and relationship of MAB with clinical and physiological parameters in stable patients with COPD.

METHODS

We measured urinary albumin rate (urinary albumin to creatinine ratio: UACR), smoking history, arterial blood pressure, gas exchange, body mass index, lung function, BODE index (body mass index, airflow obstruction, dyspnea, exercise performance), and comorbidity index in 129 patients with stable COPD and 51 smokers with normal spirometry without known cardiovascular disease. MAB levels were compared between groups. A multivariate analysis was performed to determine the best determinants of MAB levels.

MEASUREMENTS AND MAIN RESULTS

MAB was higher in patients with COPD than in control smokers (8 [5th-95th percentile (P₅₋₉₅), 2.9-113] vs. 4.2 [P₅₋₉₅, 1.8-22.7] mg/g, P < 0.001]). The difference remained significant even after using the standard pathologic threshold (MAB, 30-299 mg/g in women and 20-299 mg/g in men; 24% in patients with COPD vs. 6% in control smokers; P = 0.005). In patients with COPD, there was a negative correlation between Pa(O₂) and MAB (r = -0.40, P < 0.001). Using multivariate analysis, MAB was only associated with the Pa(O₂) (relative risk, 0.934; 95% confidence interval, 0.880-0.992; P < 0.001) and with the systolic arterial blood pressure (relative risk, 1.034; 95% confidence interval, 1.011-1.057; P = 0.003).

CONCLUSIONS

MAB is frequent in patients with COPD and is associated with hypoxemia independent of other cardiovascular risk factors. Further studies are necessary to investigate whether MAB could be an early simple biomarker of cardiovascular compromise in patients with COPD.

Comparison of intestinal warm ischemic injury in PACAP knockout and wild-type mice

Pituitary adenylate cyclase-activating polypeptide (PACAP) is present in the gastrointestinal tract and plays a central role in the intestinal physiology, mainly in the secretion and motility. The aim of our study was to compare the ischemic injury in wild-type and PACAP-38 knockout mice following warm mesenteric small bowel ischemia. Warm ischemia groups were designed with occlusion of superior mesenteric artery for 1, 3, and 6 h in wild-type (n = 10 in each group) and PACAP-38 knockout (n = 10 in each group) mice. Small bowel biopsies were collected after laparotomy (control) and at the end of the ischemia periods. To determine oxidative stress parameters, malondialdehyde (MDA), reduced glutathione (GSH), and superoxide dismutase (SOD) were measured. Tissue damage was analyzed by qualitative and quantitative methods on hematoxylin/eosin-stained sections. In PACAP-38 knockout animals, tissue MDA increased significantly after 3 and 6 h ischemia (133.97 ± 6,2; 141.86 ± 5,8) compared to sham-operated (100.92 ± 3,6) and compared to wild-type results (112.8 ± 2,1; 118.4 ± 1.03 μmol/g, p < 0.05). Meanwhile, tissue concentration of GSH and activity of SOD decreased significantly in knockout mice compared to wild-type form (GSH, 795.97 ± 10.4; 665.1 ± 8,8 vs. 893.23 ± μmol/g; SOD, 94.4 ± 1.4; 81.2 ± 3.9 vs. 208.09 ± 3,7 IU/g). Qualitative and quantitative histological results showed destruction of the mucous, submucous layers, and crypts in knockout mice compared to wild-type tissues. These processes correlated with the warm ischemia periods. Our present results propose an important protective effect of endogenous PACAP-38 against intestinal warm ischemia, which provides basis for further investigation to elucidate the mechanism of this protective effect.

The dynamics of fibroblast-myocyte-capillary interactions in the heart

In the heart, electrical, mechanical, and chemical signals create an environment essential for normal cellular responses to developmental and pathologic cues. Communication between fibroblasts, myocytes, and endothelial cells, as well as the extracellular matrix, are critical to fluctuations in heart composition and function during normal development and pathology. Recent evidence suggests that cytokines play a role in cell-cell signaling in the heart. Indeed, we find that interactions between myocytes and cardiac fibroblasts results in increased interleukin-6 and tumor necrosis factor-alpha secretion. We also used confocal and transmission electron microscopy to observe close relationships and possible direct communication between these cells in vivo. Our results highlight the importance of direct cell-cell communication in the heart, and indicate that interactions between fibroblasts, myocytes, and capillary endothelium results in differential cytokine expression. Studying these cell-cell interactions has many implications for the process of cardiac remodeling and overall heart function during development and cardiopathology.

Impact of interleukin-6 on hypoxia-induced pulmonary hypertension and lung inflammation in mice

Background

Inflammation may contribute to the pathogenesis of various forms of pulmonary hypertension (PH). Recent studies in patients with idiopathic PH or PH associated with underlying diseases suggest a role for interleukin-6 (IL-6).

Methods

To determine whether endogenous IL-6 contributes to mediate hypoxic PH and lung inflammation, we studied IL-6-deficient (IL-6^-/-) and wild-type (IL-6^+/+) mice exposed to hypoxia for 2 weeks.

Results

Right ventricular systolic pressure, right ventricle hypertrophy, and the number and media thickness of muscular pulmonary vessels were decreased in IL-6^-/- mice compared to wild-type controls after 2 weeks' hypoxia, although the pressure response to acute hypoxia was similar in IL-6^+/+ and IL-6^-/- mice. Hypoxia exposure of IL-6^+/+ mice led to marked increases in IL-6 mRNA and protein levels within the first week, with positive IL-6 immunostaining in the pulmonary vessel walls. Lung IL-6 receptor and gp 130 (the IL-6 signal transducer) mRNA levels increased after 1 and 2 weeks' hypoxia. In vitro studies of cultured human pulmonary-artery smooth-muscle-cells (PA-SMCs) and microvascular endothelial cells revealed prominent synthesis of IL-6 by PA-SMCs, with further stimulation by hypoxia. IL-6 also markedly stimulated PA-SMC migration without affecting proliferation. Hypoxic IL-6^-/- mice showed less inflammatory cell recruitment in the lungs, compared to hypoxic wild-type mice, as assessed by lung protein levels and immunostaining for the specific macrophage marker F4/80, with no difference in lung expression of adhesion molecules or cytokines.

Conclusion

These data suggest that IL-6 may be actively involved in hypoxia-induced lung inflammation and pulmonary vascular remodeling in mice.

ET-Kyoto solution plus dibutyryl cyclic adenosine monophosphate is superior to University of Wisconsin solution in rat liver preservation

ET-Kyoto solution (ET-K) is an extracellular-type organ preservation solution containing the cytoprotective disaccharide, trehalose. A previous study reported the supplement of dibutyryl cyclic adenosine monophosphate (db-cAMP) in conventional ET-K to attenuate lung ischemia-reperfusion injury. In this study, the efficacy of this modified ET-K for liver preservation was investigated by comparison with University of Wisconsin solution (UW). ET-K was supplemented with db-cAMP (2 mmol/L). Lewis rats were randomly assigned to two groups, and liver grafts were flushed and stored at 40C for 24 h with ET-K or UW before syngeneic liver transplantation. The graft function and histological changes at 4 h posttransplant as well as 7-day survival were evaluated. Recipient rat survival rate was significantly higher in the ET-K group than in the UW group. Preservation in ET-K resulted in a significant reduction in serum parenchymal transaminase level and promotion of bile production in comparison with UW. The serum hyaluronic acid level, an indicator of sinusoidal endothelial cell injury, was significantly lower after ET-K preservation than that in UW. Histologically, at 4 h after transplantation, the liver grafts preserved in UW solution demonstrated a greater degree of injury than those in ET-K, which appeared to be apoptosis, rather than necrosis. The continuity of the sinusoidal lining was better preserved in ET-K than in UW. In conclusion, ET-K supplemented with db-cAMP is superior to UW in rat liver preservation. This modified ET-K might therefore be a novel candidate for the procurement and preservation of multiple organs.

Influence of PACAP on oxidative stress and tissue injury following small-bowel autotransplantation

Tissue injury caused by cold preservation and reperfusion remains an unsolved problem during small-bowel transplantation. Pituitary adenylate cyclase-activating polypeptide (PACAP) is present and plays a central role in the intestinal physiology. This study investigated effect of PACAP-38 on the oxidative stress and tissue damage in autotransplanted intestine. Sham-operated, ischemia/reperfusion, and autotransplanted groups were established in Wistar rats. In ischemia/reperfusion groups, 1 h (group A), 2 h (group B), and 3 h (group C) ischemia followed by 3 h of reperfusion was applied. In autotransplanted groups, total orthotopic intestinal autotransplantation was performed. Grafts were preserved in University of Wisconsin (UW) solution and in UW containing 30 microg PACAP-38 for 1, 2, 3, and 6 h. Reperfusion lasted 3 h in all groups. Endogenous PACAP-38 concentration was measured by radioimmunoassay. To determine oxidative stress parameters, malondialdehyde, reduced glutathione, and superoxide dismutase were measured in tissue samples. Tissue damage was analyzed by qualitative and quantitative methods on hematoxylin/eosin-stained sections. Concentration of endogenous PACAP-38 significantly decreased in groups B and C compared to sham-operated group. Preservation solution containing PACAP-38 ameliorated bowel tissue oxidative injury induced by cold ischemia and reperfusion. Histological results showed that preservation caused destruction of the mucous, submucous, and muscular layers, which were further deteriorated by the end of reperfusion. In contrast, PACAP-38 significantly protected the intestinal structure. Ischemia/reperfusion decreased the endogenous PACAP-38 concentration in the intestinal tissue. Administration of PACAP-38 mitigated the oxidative injury and histological lesions in small-bowel autotransplantation model.

Differential effects of rapamycin in anti-GBM glomerulonephritis

The immunosuppressive mammalian target of rapamycin inhibitor rapamycin is widely used in solid-organ transplantation, but the effect of rapamycin on kidney disease is controversial. This study evaluated the effect of rapamycin in the autologous phase of anti-glomerular basement membrane (anti-GBM) glomerulonephritis. Disease was induced by preimmunizing the animals with rabbit IgG 5 d before administration of rabbit anti-mouse GBM antiserum. When rapamycin was started on the day of immunization (group 1), mice were protected from glomerulonephritis, suggested by a dramatic decrease in albuminuria, influx of inflammatory cells, and Th1-cytokine expression in the kidneys. Activation of T cells and production of autologous mouse anti-rabbit IgG were also significantly reduced in rapamycin-treated animals. In contrast, when rapamycin was started 14 d after immunization (group 2), mice had a significant increase in albuminuria and renal infiltration of inflammatory cells compared with vehicle-treated animals, and there were no differences in T and B cell responses. A significant decrease in vascular endothelial growth factor-A and an increase in IL-6 were detected in kidneys of these rapamycin-treated mice. In conclusion, rapamycin has the potential to significantly reduce the B and T cell responses and thereby protect from glomerulonephritis when administered early in disease. Once disease is established, however, rapamycin seems to worsen glomerulonephritis by disturbing the endothelial cell/vascular endothelial growth factor system in the kidney.

Evaluation of bone-derived and marrow-derived vascular endothelial cells by microarray analysis

This study focused on the differential expression levels of proteins that may exist between bone-derived and marrow-derived vascular endothelial cells (BVEC and MVEC). The vascular cells were isolated from trabecular bone regions and central marrow cavity regions of mouse long bones. Cells were cultured for 1 week to expand the population then separated from non-vascular cells using biotinylated isolectin B4, streptavidin-coated metallic microbeads, and a magnetic column. After an additional week of culture time, RNA was isolated from both cell types and compared using microarray analysis. RT-PCR was used to confirm and relatively quantitate the RNA messages. The bone-derived cells expressed more aldehyde dehydrogenase 3A1 (ALDH3A1), Secreted Modular Calcium-2 (SMOC-2), CCAAT enhancer binding protein (C/EBP-beta), matrix metalloproteinase 13 (MMP-13), and annexin 8 (ANX8) than the marrow-derived cells. Spalpha and matrix GLA-protein (MGP) were produced in greater abundance by the marrow-derived cells. This study reveals that there are profound and unique differences between the vasculature of the metaphysis as compared to that of the central marrow cavity. The unique array of proteins expressed by the bone-derived endothelial cells may support growth of tumors from cancer cells that frequently metastasize and lodge in the trabecular bone regions.

Role of pulmonary adenosine during hypoxia: extracellular generation, signaling and metabolism by surface adenosine deaminase/CD26

Numerous parallels exist between limited oxygen availability (hypoxia) and acute inflammation. The lungs in particular are prone to acute inflammation during hypoxia, resulting in pulmonary edema, vascular leakage and neutrophil infiltration. The innate response elicited by hypoxia is associated with increased extracellular adenosine effects. Although studies on acute pulmonary hypoxia show a protective role of extracellular adenosine by attenuating pulmonary edema and excessive inflammation, chronic elevation of pulmonary adenosine may be detrimental. Adenosine deaminase (ADA)-deficient mice, for example, develop signs of chronic pulmonary injury in association with highly elevated levels of adenosine. Thus, the authors hypothesized the existence of hypoxia-elicited clearance mechanisms to offset deleterious influences of chronically elevated adenosine. Such studies indicated a second response to hypoxia characterized by pulmonary induction of ADA and CD26. In fact, hypoxia-inducible ADA is enzymatically active and tethered on the outside of the membrane via CD26 to form a complex capable of degrading extracellular adenosine to inosine. This paper reviews metabolic and transcriptional changes of extracellular adenosine generation, signaling and degradation during acute and prolonged pulmonary hypoxia.

Role of the endothelium in pulmonary arterial hypertension

Pulmonary hypertension represents a significant disease burden in both the developed and developing worlds. Certain forms of pulmonary hypertension are more common in some countries than others but people of all races, all ages and both sexes are affected. Treatment options are limited and expensive. The development of new therapies will be determined by improved understanding of endothelial cell biology.

Role of alveolar epithelial sodium transport in high altitude pulmonary edema (HAPE)

Alveolar edema results from an imbalance between fluid filtration into the alveolar space and removal by reabsorption. Hypoxia increases filtration by raising pulmonary capillary pressure and increasing endothelial and epithelial permeability allowing fluid and blood cells to access the alveoli. Active Na-reabsorption drives the fluid reabsorption from the alveolar space, but hypoxia inhibits reabsorption by inhibition of epithelial Na-channels (ENaC) and Na/K-ATPase. A (genetically determined) low activity of alveolar reabsorption in normoxia and further inhibition by hypoxia might cause HAPE-susceptibility, since at some point the depressed reabsorption may not keep pace with increased filtration. Na-reabsorption might even prove totally inefficient in the presence of large leaks of the alveolar barrier. Alveolar Na-reabsorption has not been measured in HAPE. Nasal epithelial Na-transport has been used as surrogate marker based on similarities in subunit expression of ENaC in nasal, airway, and alveolar epithelium. At high altitude cold, dryness, and nasal infections affect the nasal potential making any extrapolation to processes at the alveolar epithelium unreliable. The variability in nasal Na- and Cl-transport reduces the usefulness of nasal potentials to diagnose HAPE-susceptibility.

Microvascular endothelial cells sustain preadipocyte viability under hypoxic conditions

Obesity, soft tissue wound healing, adipose tissue engineering, lipomas, and other physiological and pathophysiological conditions necessitate a clear understanding of the interactions between adipocytes and endothelial cells. Adipogenesis and angiogenesis are intimately integrated, despite not being in direct apposition with one another. However, underlying mechanisms have not been elucidated. In this study, the interactions of preadipocytes (PAs) and microvascular endothelial cells are investigated under varying defined O2 conditions, using a coculture system. Results clearly demonstrate that endothelial cells release a soluble factor that sustains PAs viability under hypoxic conditions. Vascular endothelial cell growth factor is not the potential soluble factor (data not shown).

Perinatal changes in pulmonary vascular endothelial function

The pulmonary endothelium plays a crucial role in lung development and function during the perinatal period. Its 2 most important functions at this time are to help reduce pulmonary vascular resistance (PVR) in order to permit the entire cardiac output to pass through the lungs for the first time and to facilitate the clearance of lung fluid. In response to changes in environmental factors such as oxygen tension, blood flow, circulating cytokines, and growth factors, the endothelium synthesizes and/or extracts many vasoactive mediators such as endothelin-1 (ET-1), norepinephrine, angiotensin 1, thromboxane, prostacyclin (PGI(2)), and the endothelial-derived relaxing factor nitric oxide (NO). The endothelium acts as a transducer conveying information about environmental changes to the underlying smooth muscle cells (SMCs), which helps regulate their reactivity and pulmonary vascular tone. The endothelial layer also acts as a barrier, regulating the exchange of fluids and nutrients between blood components and the surrounding tissues. The purpose of this review is to demonstrate the importance of structural and functional changes in the pulmonary endothelium during the perinatal period and explain their role in the regulation of the pulmonary circulation in health and disease. We also highlight signalling pathways of some of the most important endothelium-derived factors and indicate potential targets for pharmacological intervention.

Mechanisms of endothelial dysfunction in obesity

Obesity is a chronic disease, whose incidence is alarmingly growing, affecting not only adults but also children and adolescents. It is associated with severe metabolic abnormalities and increased cardiovascular morbidity and mortality. Adipose tissue secretes a great number of hormones and cytokines that not only regulate substrate metabolism but may deeply and negatively influence endothelial physiology, a condition which may lead to the formation of the atherosclerotic plaque. In this review, the physiology of the endothelium is summarised and the mechanisms by which obesity, through the secretory products of adipose tissue, influences endothelial function are explained. A short description of methodological approaches to diagnose endothelial dysfunction is presented. The possible pathogenetic links between obesity and cardiovascular disease, mediated by oxidative stress, inflammation and endothelial dysfunction are described as well.

Garlic supplementation increases peripheral blood flow: a role for interleukin-6?

There is considerable epidemiological and clinical evidence that regular garlic supplementation reduces cardiovascular risk. In this study, we have investigated the hypothesis that dietary garlic supplementation increases tissue blood flow and this is mediated by the vasodilatory actions of interleukin-6 (IL-6). Venous occlusion plethysmography was used to measure resting calf blood flow before and after oral administration of 600 mg of garlic tablets once daily for 7 days in 13 young healthy female volunteers (treatment group) and 13 female controls matched for age and body mass index (BMI). Blood samples were obtained at the time of plethysmography to measure plasma levels of IL-6, nitrate, nitrite and c-GMP. In the treatment group, calf blood flow increased significantly from 3.01 (2.56 to 3.3) ml min(-1) 100 mL(-1) of tissue before garlic to 3.46 (3.0 to 4.03) ml min(-1) 100 mL(-1) of tissue after 7 days of garlic (P = 0.001). Plasma IL-6 concentrations increased significantly from 54.6 (32.3 to 151.6) mcg/mL before to 151 (135.75 to 422.3) mcg/mL after 7 days of garlic (P = 0.02). However, there was no significant change in the plasma levels of nitrate, nitrite and c-GMP after the garlic (P = 0.4, 0.9 and 0.65 respectively). In the control group, resting calf blood flow and plasma levels of IL-6, nitrite, nitrate and c-GMP remained unchanged after 7 days (P = 0.62, 0.92, 0.28 and 0.35 respectively). Calf blood flow showed a non-linear correlation with plasma IL-6 levels after garlic supplementation (r = 0.86, p = <0.001) but not before. There was no significant relationship between blood flow and plasma nitrate, nitrite and c-GMP in either groups and between blood flow and IL-6 in the control group. These data suggest that garlic supplementation increases resting tissue blood flow and this may be mediated by IL-6.

Effects of calycosin on the impairment of barrier function induced by hypoxia in human umbilical vein endothelial cells

The purpose of the present study was to examine the effects of calycosin, an isoflavonoid isolated from Astragali Radix, on the impairment of barrier function induced by hypoxia in cultured human umbilical vein endothelial cells. Hypoxia induced an increase in endothelial cell monolayer permeability, indicating endothelial cell barrier impairment. Endothelial barrier dysfunction induced by hypoxia was accompanied by decreases in cytosolic ATP concentration and cAMP level, the development of actin stress fibers and intercellular gap formation, suggesting that the decreases in cytosolic ATP and cAMP levels and rearrangements of F-actin could be associated with an increase in permeability of endothelial monolayers. Application of calycosin inhibited the hypoxia-induced increase in endothelial permeability in a dose-dependent fashion, which is compatible with inhibition of lactate dehydrogenase release, decrease of the fall in ATP and cAMP contents, and improvement of F-actin rearrangements. These findings indicate that calycosin protected endothelial cells from hypoxia-induced barrier impairment by increasing intracellular energetic sources and promoting regeneration of the cAMP level, as well as improving cytoskeleton remodeling.

Carbon monoxide promotes hypoxic pulmonary vascular remodeling

CO is a biologically active gas that produces cellular effects by multiple mechanisms. Because cellular binding of CO by heme proteins is increased in hypoxia, we tested the hypothesis that CO interferes with hypoxic pulmonary vascular remodeling in vivo. Rats were exposed to inspired CO (50 parts/million) at sea level or 18,000 ft of altitude [hypobaric hypoxia (HH)], and changes in vessel morphometry and pulmonary pressure-flow relationships were compared with controls. Vascular cell single strand DNA (ssDNA) and proliferating cell nuclear antigen (PCNA) were assessed, and changes in gene and protein expression of smooth muscle alpha-actin (sm-alpha-actin), beta-actin, and heme oxygenase-1 (HO-1) were evaluated by Western analysis, RT-PCR, and immunohistochemistry. After 21 days of HH, vascular pressure at constant flow and vessel wall thickness increased and lumen diameter of small arteries decreased significantly. The presence of CO, however, further increased both pulmonary vascular resistance (PVR) and the number of small muscular vessels compared with HH alone. CO + HH also increased vascular PCNA and nuclear ssDNA expression compared with hypoxia, suggesting accelerated cell turnover. CO in hypoxia downregulated sm-alpha-actin and strongly upregulated beta-actin. CO also increased lung HO activity and HO-1 mRNA and protein expression in small pulmonary arteries during hypoxia. These data indicate an overall propensity of CO in HH to promote vascular remodeling and increase PVR in vivo.

Role of mitochondrial oxidant generation in endothelial cell responses to hypoxia

Endothelial cells increase their secretion of the cytokine interleukin-6 (IL-6) during hypoxia, which then acts in an autocrine fashion to increase the permeability of cell monolayers. These responses are attenuated by antioxidants, suggesting that reactive oxygen species (ROS) participate in signaling in hypoxic endothelium. We tested whether mitochondria are responsible for these ROS in human umbilical vein endothelial cells exposed to hypoxia. Oxidation of the probe 2', 7'-dichlorodihydrofluorescein to fluorescent dichlorofluorescein or the probe dihydroethidium was used to assess oxidant signaling, whereas permeability was assessed by using transendothelial electrical resistance. Hypoxia elicited increases in dichlorofluorescein and dihydroethidium fluorescence that were abrogated by the mitochondrial electron transport (ET) inhibitors rotenone (2 micromol/L) and diphenyleneiodonium (5 micromol/L). The same ET inhibitors also attenuated hypoxia-induced increases in nuclear factor-kappaB (NF-kappaB) activation, although they did not abrogate NF-kappaB activation in response to endotoxin (lipopolysaccharide). ET inhibition also abolished the hypoxia-induced increases in IL-6 mRNA expression, hypoxia-stimulated IL-6 secretion into the media, and the hypoxia-induced increases in transendothelial electrical resistance of human umbilical vein endothelial cell monolayers. By contrast, the above responses to hypoxia were not significantly affected by treatment with the NAD(P)H oxidase inhibitor apocynin (30 micromol/L), the xanthine oxidase inhibitor allopurinol (100 micromol/L), or the NO synthase inhibitor N-nitro-L-arginine (100 micromol/L). We conclude that ROS signals originating from the mitochondrial ET chain trigger the increase in NF-kappaB activation, the transcriptional activation of IL-6, the secretion of IL-6 into the cell culture media, and the increases in endothelial permeability observed during hypoxia.

The enhancement of endogenous cAMP with pituitary adenylate cyclase-activating polypeptide protects rat kidney against ischemia through the modulation of inflammatory response

BACKGROUND

Cyclic nucleotide analogue administration improves ischemia-reperfusion damage in several organs. The neuropeptide pituitary adenylate cyclase-activating polypeptide, PACAP-38, is a potent stimulus to enhance cellular cAMP levels. This study tested the protective effect of enhancing endogenous cAMP levels by PACAP-38 in a model of warm renal ischemia.

METHODS

Sprague-Dawley rats underwent 40 min of bilateral warm renal ischemia. PACAP-38 continuous infusion began either before ischemia or at 6 hr or 18 hr after ischemia. A mini-osmotic pump infused PACAP-38 throughout 7 days of follow-up. Groups were constructed with sham, ischemic control, and dibutyryl cAMP treated animals, and four PACAP-38 treatment groups, using 16 pmol/hr or 160 pmol/hr of the compound, or delaying its administration by 6 hr or 18 hr after ischemia. Renal function was assessed by means of serum creatinine levels on days 1, 2, 3, and 7 after ischemia. Conventional histology was performed on day 7. Renal myeloperoxidase (MPO) activity, infiltrating CD45+ cells, plasma and tissue cAMP, and serum IL-6 were measured.

RESULTS

Continuous administration of the high concentration of PACAP-38 ameliorated renal function and morphologic abnormalities induced by warm ischemia. Treatment with dibutyryl cAMP produced morphologic protection but only partial functional effect on the ischemic kidney. A 6-hour delay in the administration of the compound after ischemia offered similar protective effect, whereas an 18-hr delay did not. The neuropeptide clearly increased circulating cAMP after ischemia but not cAMP in renal tissue. PACAP-38 increased circulating IL-6, and minimized renal inflammatory cell infiltration induced by ischemia-reperfusion injury, as evidenced by a reduction of MPO activity and the number of CD45+ cells in ischemic renal tissue.

CONCLUSIONS

Enhancement of endogenous circulating cAMP with PACAP-38 modulates postischemic inflammatory response and strongly protects from ischemic acute renal failure, even when administration is delayed for 6 hr after injury.

Pentoxifylline reduces coronary leukocyte accumulation early in reperfusion after cold ischemia

BACKGROUND

Ischemia/reperfusion injury can complicate recovery in cardiac operations. Ischemia induces endothelial dysfunction, which may contribute to leukocyte accumulation during reperfusion. Leukocyte-mediated injury may then occur. Using intravital microscopy we previously reported increased leukocyte retention in coronary capillaries and venules during early reperfusion during warm ischemia/reperfusion. In this study we investigated whether cold cardioplegic protection would limit leukocyte sequestration in coronary microvessels early in reperfusion. Pentoxifylline (PTX) has antiinflammatory effects and may limit endothelial dysfunction during ischemia/reperfusion. The effect of cardioplegia modification with PTX was also examined.

METHODS

Isolated rat hearts were subjected to 90 minutes of 4 degrees C ischemia after arrest with cardioplegia. Hearts were reperfused with diluted whole blood containing fluorescent-labeled leukocytes. Leukocyte retention in coronary microvessels was observed with intravital microscopy. Three groups were studied, nonischemic control, cold ischemia, and PTX-modified cold ischemia.

RESULTS

In coronary capillaries, leukocyte trapping was nearly doubled in unmodified cold ischemia versus control. PTX modification significantly reduced leukocyte accumulation. In coronary venules, greater leukocyte adhesion was observed in unmodified cold ischemia compared to nonischemic controls. PTX modification significantly reduced leukocyte adhesion.

CONCLUSIONS

Cold cardioplegia did not prevent leukocyte retention in the coronary microcirculation early in reperfusion. PTX modification of cardioplegia significantly reduced leukocyte sequestration in coronary capillaries and venules. Preserving endothelial function during ischemia may limit leukocyte accumulation and ischemia/reperfusion injury after cardiac operation.

Neutrophil-epithelial crosstalk at the intestinal lumenal surface mediated by reciprocal secretion of adenosine and IL-6

Adenosine is formed in the intestinal lumen during active inflammation from neutrophil-derived 5' AMP. Using intestinal epithelial cell line T84, we studied the effect of adenosine on the secretion of IL-6, a proinflammatory cytokine involved in neutrophil degranulation and lymphocyte differentiation. Stimulation of T84 monolayers with either apical or basolateral adenosine induces A2b receptor-mediated increase in IL-6 secretion, which is polarized to the apical (luminal) compartment. In addition, Salmonella typhimurium, TNF-alpha, and forskolin, known inducers of IL-6 secretion in intestinal epithelial cells, also stimulate IL-6 secretion into the apical compartment. We show that IL6 promoter induction by adenosine occurs through cAMP-mediated activation of nuclear cAMP-responsive element-binding protein (CREB). We also show that IL-6 released in the luminal (apical) compartment achieves a sufficient concentration to activate neutrophils (from which the adenosine signal originates), since such IL-6 is found to induce an intracellular [Ca(++)] flux in neutrophils. We conclude that adenosine released in the intestinal lumen during active inflammation may induce IL-6 secretion, which is mediated by cAMP/CREB activation and occurs in an apically polarized fashion. This would allow sequential activation of neutrophil degranulation in the lumen -- a flow of events that would, in an epithelium-dependent fashion, enhance microbicidal activity of neutrophils as they arrive in the intestinal lumen.

Endothelial cell responses to hypoxia: initiation of a cascade of cellular interactions

The origin of several vascular pathologies involves sudden or recurrent oxygen deficiency. In this review, we examine what the biochemical and molecular responses of the endothelial cells to the lack of oxygen are and how these responses may account for the features observed in pathological situations, mainly by modifications of cell-cell interactions. Two major responses of the endothelial cells have been observed depending on the degree and duration of the oxygen deficiency. Firstly, acute hypoxia rapidly activates the endothelial cells to release inflammatory mediators and growth factors. These inflammatory mediators are able to recruit and promote the adherence of neutrophils to the endothelium where they become activated. The synthesis of platelet-activating factor plays a key role in this adherence process. Secondly, longer periods of hypoxia increase the expression of specific genes such as those encoding some cytokines as well as for the growth factors platelet-derived growth factor and vascular endothelial growth factor. The transcriptional induction of these genes is mediated through the activation of several transcription factors, the most important one being hypoxia inducible factor-1. The link between our knowledge of the signalling cascade of the cellular and molecular events initiated by hypoxia and their involvement in several vascular pathological situations, varicose veins, tumor angiogenesis and pulmonary hypertension is discussed briefly.

Hypoxic signal transduction in critical illness

Derangements in tissue perfusion occur during critical illness, and the resulting deficit in oxygen delivery may play an important role in the pathogenesis of hemorrhagic and septic shock. Cells and organisms have developed a variety of adaptive strategies to maintain adequate energy production to maintain normal cellular function under hypoxic conditions. Recent studies from our laboratory suggest that certain proinflammatory cytokines, which are likely to be elaborated during or after shock, can interfere with the ability of cells to adapt to hypoxia, and thereby contribute to the development of organ system dysfunction.

High altitude increases circulating interleukin-6, interleukin-1 receptor antagonist and C-reactive protein

Hypoxic pulmonary vasoconstriction is associated with but may not be sufficient for the development of high-altitude pulmonary oedema (HAPO). Hypoxia is known to induce an inflammatory response in immune cells and endothelial cells. It has been speculated that hypoxia-induced inflammatory cytokines at high altitude may contribute to the development of HAPO by causing capillary leakage in the lung. We were interested if such an inflammatory response, possibly involved in a later development of HAPO, is detectable at high altitude in individuals without HAPO. We examined the plasma levels of interleukin 6 (IL-6), interleukin 1 receptor antagonist (IL-1ra) and C-reactive protein (CRP) in two independent studies: study A, Jungfraujoch, Switzerland, three overnight stays at 3458 m, n=12; study B: Capanna Regina Margherita, Italy, 3 overnight stays at 3647 m and one overnight stay at 4559 m, n=10. In both studies, probands showed symptoms of acute mountain sickness but no signs of HAPO. At the Jungfraujoch, IL-6 increased from 0.1+/-0.03 pg/ml to 2. 0+/-0.5 pg/ml (day 2, P=0.03), IL-1ra from 101+/-21 to 284+/-73 pg/ml (day 2, P=0.01), and CRP from 1.0+/-0.4 to 5.8+/-1.5 micrograms/ml (day 4, P=0.01). At the Capanna Margherita, IL-6 increased from 0. 5+/-0.2 pg/ml to 2.0+/-0.8 pg/ml (P=0.02), IL-1ra from 118+/-25 to 213+/-28 pg/ml (P=0.02), and CRP from 0.4+/-0.03 to 3.5+/-1.1 micrograms/ml (P=0.03). IL-8 was below the detection limit of the ELISA (<25 pg/ml) in both studies. The increase of IL-6 and IL-1ra in response to high altitude was delayed and preceded the increase of CRP. We conclude that: (1) circulating IL-6, IL-1ra and CRP are upregulated in response to hypobaric hypoxic conditions at high altitude, and (2) the moderate systemic increase of these inflammatory markers may reflect considerable local inflammation. The existence and the kinetics of high altitude-induced cytokines found in this study support the hypothesis that inflammation is involved in the development of HAPO.

Adaptive responses of the endothelium to stress

It is now established that endothelial cells acquire several functional properties in response to a diverse array of extracellular stimuli. This expression of an altered phenotype is referred to as endothelial cell activation, and it includes several activities that promote inflammation and coagulation. While it is recognized that endothelial cell activation has a principal role in host defense, recent studies also demonstrate that endothelial cells are capable of complex molecular responses that protect the endothelium against various forms of stress including heat shock, hypoxia, oxidative stress, shock, ischemia-reperfusion injury, toxins, wounds, and mechanical stress. In this review, we examine endothelial cell genotypic and phenotypic responses to stress. Also, we highlight important cellular stress responses that, although not yet demonstrated directly in endothelial cells, likely exist as part of the repertoire of stress responses in endothelium. A detailed understanding of the molecular mechanisms mediating the adaptive responses of endothelial cells to stress should facilitate the development of novel therapeutics to aid in the management of diverse surgical diseases and their complications.

Hypoxia induces cell-specific changes in gene expression in vascular wall cells: implications for pulmonary hypertension

Mammals respond to reduced oxygen concentrations (hypoxia) in many different ways at the systemic, local, cellular and molecular levels. Within the pulmonary circulation, exposure to chronic hypoxia has been demonstrated to illicit increases in pulmonary artery pressure as well as dramatic structural changes in both large and small vessels. It has become increasingly clear that the response to hypoxia in vivo is differentially regulated at the level of specific cell types within the vessel wall. For instance, in large pulmonary blood vessels there is now convincing evidence to suggest that the medial layer is made up of many different subpopulations of smooth muscle cells. In response to hypoxia there are remarkable differences in the proliferative and matrix producing responses of these cells to the hypoxic environment. Some cell populations proliferate and increase matrix protein synthesis, while in other cell populations no apparent change in the proliferative or differentiation state of the cell takes place. In more peripheral vessels, the predominant proliferative changes in response to hypoxia in the pulmonary circulation occur in the adventitial layer rather than in the medial layer. Here again, specific increases in proliferation and matrix protein synthesis take place. Accumulating evidence suggests that the unique responses exhibited by specific cell types of hypoxia in vivo can be modeled in vitro. We have isolated, in culture, specific medial cell populations which demonstrate significant increases in proliferation in response to hypoxia, and others which exhibit no change or, in fact, a decrease in proliferation under hypoxic conditions. We have also isolated and cloned several unique populations of adventitial fibroblasts. There is good evidence that only certain fibroblast populations are capable of responding to hypoxia with an increase in proliferation. We have begun to elucidate the signaling pathways which are activated in those cell populations that exhibit proliferative responses to hypoxia. We show that hypoxia, in the absence of serum or mitogens, specifically activates select members of the protein kinase C isozyme family, as well as members of the mitogen-activated protein kinase (MAPK) family of proteins. This selective activation appears to take place in response to hypoxia only in those cells exhibiting a proliferative response, and antagonists of this pathway inhibit the response. Thus, there appear to be cells within each organ that demonstrate unique responses to hypoxia. A better understanding of why these cells exist and how they specifically transduce hypoxia-mediated signals will lead to a better understanding of how the changes in the pulmonary circulation take place under conditions of chronic hypoxia.

Brain endothelial cell production of a neuroprotective cytokine, interleukin-6, in response to noxious stimuli

Brain endothelial cells (BECs), specialized cells of the blood-brain barrier (BBB), are ideally positioned to monitor and respond to events in the periphery. The present study examined their potential role in transducing immune signals to the brain and in responding to noxious stimuli. BECs were isolated from rhesus monkeys at 3 age points (fetal/neonatal, adult, and very old animals). Cells were then challenged in vitro with either an immune stimulus (interleukin-1 beta (IL-1 beta), or lipopolysaccharide (LPS)) or an oxidative challenge (hypoxia). BECs released interleukin-6 (IL-6), which is known to have neurotrophic and neuroprotective functions. Furthermore, higher amounts of IL-6 were released in both baseline and stimulated conditions by BECs derived from aged animals. This research indicates a pathway whereby immune signals may be communicated to the CNS and has revealed one way that the BBB may protect neuronal survival under challenge conditions.

Downregulation of protein kinase cdelta activity enhances endothelial cell adaptation to hypoxia

BACKGROUND

Although protein kinase C (PKC) has been implicated in ischemic cell death, the role of individual PKC isoenzymes in the response of endothelial cells (ECs) to hypoxia is unknown.

METHODS AND RESULTS

To test the effect of hypoxia on the activity of individual PKC isoenzymes, human ECs were exposed to 95% N(2) with 5% CO(2) for 24 hours. This severe hypoxia reduced PKCdelta specific activity in both human umbilical vein ECs (HUVECs) and a HUVEC-derived EC line (ECVs) significantly (80.5+/-5.7% and 55.5+/-8. 6% of normoxia controls, respectively); the activities of PKCalpha and PKCepsilon were unchanged. The protein levels of PKCalpha, PKCdelta, and PKCepsilon were unchanged by hypoxia. To determine whether PKCdelta downregulation by hypoxia was linked to EC function, ECVs in which PKCdelta was stably overexpressed (PKCdelta-ECs) were exposed to hypoxia. A significant increase in cell death was observed in PKCdelta-ECs compared with controls (5.8+/-0.6% versus 2. 3+/-0.4% at 24 hours, 13.2+/-1.2% versus 4.1+/-0.4% at 48 hours, P<0. 05) during hypoxia. Neither the DNA laddering assay nor TUNEL staining revealed an increase in apoptosis of PKCdelta-ECs exposed to hypoxia, suggesting a hypoxia-induced increase in nonapoptotic cell death of PKCdelta-ECs. Inhibition of NO synthase with N(G)-monomethyl-L-arginine (L-NMMA) affected neither the decline in PKCdelta activity nor the EC death induced by hypoxia.

CONCLUSIONS

PKCdelta activity is decreased by hypoxia by a mechanism that does not involve NO synthase; this downregulation appears to enhance EC survival during hypoxia by decreasing nonapoptotic cell death.

Effect of exercise on cytokines and growth mediators in prepubertal children

Many of the anabolic effects of exercise are mediated through insulin-like growth factor-I (IGF-I), but in adolescents, brief exercise training leads to reductions, rather than the expected increase, in circulating IGF-I. Certain cytokines--interleukin-(IL) 1beta (IL-1beta), IL-6 (IL-6), and tumor necrosis factor-alpha--are increased by exercise in adults and are known to inhibit IGF-I. To test the hypothesis that these cytokines might play a role in the adaptation to exercise, we measured the acute effects of exercise on selected cytokines and growth factors in 17 healthy 8- to 11-y-old children (4 females). Designed to mimic patterns and intensity of exercise found in the real lives of American children, the exercise protocol consisted of a 1.5-h soccer practice (of which about 40 min constituted of vigorous exercise). Pre- and postexercise urine and saliva samples were obtained in all subjects and both blood and urine in nine subjects. The exercise led to significant increases in circulating tumor necrosis factor-alpha (18 +/- 7%, p < 0.05) and IL-6 (125 +/- 35%, p < 0.01) as well as a significant increase in the antiinflammatory cytokine IL-1 receptor antagonist (33 +/- 10%, p < 0.01). Urine levels of IL-6 were also substantially increased by exercise (440 +/- 137%, p < 0.0001). Circulating levels of IGF-I were reduced to a small but significant degree (-6.4 +/- 3.2%, p < 0.05), although IGF-binding protein-1 (known to inhibit IGF-I) was substantially increased (156 +/- 40%, p < 0.001). Cytokines are systemically increased after relatively brief exercise in healthy children. This increase may alter critical anabolic agents such as IGF-I and its binding proteins.

Cyclic-3',5'-nucleotide phosphodiesterase isozymes in cell biology and pathophysiology of the kidney

Investigations of recent years revealed that isozymes of cyclic-3', 5'-nucleotide phosphodiesterase (PDE) are a critically important component of the cyclic-3',5'-adenosine monophosphate (cAMP) protein kinase A (PKA) signaling pathway. The superfamily of cyclic-3', 5'-phosphodiesterase (PDE) isozymes consists of at least nine gene families (types): PDE1 to PDE9. Some PDE families are very diverse and consist of several subtypes and numerous PDE isoform-splice variants. PDE isozymes differ in molecular structure, catalytic properties, intracellular regulation and location, and sensitivity to selective inhibitors, as well as differential expression in various cell types. A number of type-specific "second-generation" PDE inhibitors have been developed. Current evidence indicates that PDE isozymes play a role in several pathobiologic processes in kidney cells. In rat mesangial cells, PDE3 and PDE4 compartmentalize cAMP signaling to the PDE3-linked cAMP-PKA pathway that modulates mitogenesis and PDE4-linked cAMP-PKA pathway that modulates generation of reactive oxygen species. Administration of selective PDE isozyme inhibitors in vivo suppresses proteinuria and pathologic changes in experimental anti-Thy-1.1 mesangial proliferative glomerulonephritis in rats. Increased activity of PDE5 (and perhaps also PDE9) in glomeruli and in cells of collecting ducts in sodium-retaining states, such as nephrotic syndrome, accounts for renal resistance to atriopeptin; diminished ability to excrete sodium can be corrected by administration of the selective PDE5 inhibitor zaprinast. Anomalously high PDE4 activity in collecting ducts is a basis of unresponsiveness to vasopressin in mice with hereditary nephrogenic diabetes insipidus. Apparently, PDE isozymes apparently also play an important role in the pathogenesis of acute renal failure of different origins. Administration of PDE isozyme-selective inhibitors suppresses some components of immune responses to allograft transplant and improves preservation and survival of transplanted organ. PDE isozymes are a target for action of numerous novel selective PDE inhibitors, which are key components in the design of novel "signal transduction" pharmacotherapies of kidney diseases.