A pivotal role of nitric oxide in endothelial cell dysfunction

Influence of endothelial nitric oxide synthase haplotypes on nitric oxide and peroxynitrite productions

The impact of four clinically significant genetic variants of endothelial nitric oxide synthase (eNOS) polymorphisms on the concentrations of nitric oxide [NO] and peroxynitrite [ONOO-] has been given scant consideration. This study utilized a [NO]/[ONOO-] ratio to determine the extent of endothelial dysfunction caused by these variations in the eNOS gene. The single nucleotide polymorphisms (T-786C, C-665T, and Glu298Asp) and a variable number of tandem repeats (intron 4 a/b/c) were genotyped in human umbilical vein endothelial cells (HUVEC), using sanger sequencing and DNA electrophoresis, respectively. Nanosensors were used to determine the maximal [NO] and [ONOO-], while traditional and low-temperature SDS-PAGE were used to evaluate the expression of eNOS and the eNOS dimer-to-monomer ratio, respectively. The study results indicate that the eNOS haplotype H3 (G T/C C 4a/c allele) may have a protective effect against cardiovascular disease (CVD) with the [NO]/[ONOO-] ratio higher than 2. However, the eNOS haplotypes H2 (G T/C C 4a/b) and H5 (T T/C C 4b) increase the susceptibility to CVD with [NO]/[ONOO-] ratio lower than 1. The results suggest that certain eNOS genetic variants may influence susceptibility to cardiovascular disease (CVD) while other variants may have a protective effect.

Rationale and Design of Assessing the Effectiveness of Short-Term Low-Dose Lithium Therapy in Averting Cardiac Surgery-Associated Acute Kidney Injury: A Randomized, Double Blinded, Placebo Controlled Pilot Trial

Background: Burgeoning pre-clinical evidence suggests that therapeutic targeting of glycogen synthase kinase 3β (GSK3β), a convergence point of multiple cellular protective signaling pathways, confers a beneficial effect on acute kidney injury (AKI) in experimental models. However, it remains unknown if GSK3β inhibition likewise mitigates AKI in humans. Cardiac surgery associated acute kidney injury (CSA-AKI) poses a significant challenge for clinicians and currently the only treatment available is general supportive measures. Lithium, an FDA approved mood stabilizer, is the best-known GSK3β inhibitor and has been safely used for over half a century as the first line regimen to treat bipolar affective disorders. This study attempts to examine the effectiveness of short term low dose lithium on CSA-AKI in human patients.

Methods/Design: This is a single center, prospective, randomized, double blinded, placebo controlled pilot study on patients undergoing cardiac surgery with cardiopulmonary bypass. Patients will be randomized to receive a small dose of lithium or placebo treatment for three consecutive days. Renal function will be measured via creatinine as well as novel AKI biomarkers. The primary outcome is incidence of AKI according to Acute Kidney Injury Network (AKIN) criteria, and secondary outcomes include receipt of new dialysis, days on dialysis, days on mechanical ventilation, infections within 1 month of surgery, and death within 90 days of surgery.

Discussion: As a standard selective inhibitor of GSK3β, lithium has been shown to exert a beneficial effect on tissue repair and regeneration upon acute injury in multiple organ systems, including the central nervous system and hematopoietic system. In experimental AKI, lithium at small doses is able to ameliorate AKI and promote kidney repair. Successful completion of this study will help to assess the effectiveness of lithium in CSA-AKI and could potentially pave the way for large-scale randomized trials to thoroughly evaluate the efficacy of this novel regimen for preventing AKI after cardiac surgery.

Trial Registration: This study was registered prospectively on the 17th February 2017 at ClinicalTrials.gov (NCT03056248, https://clinicaltrials.gov/ct2/show/NCT03056248?term=NCT03056248&draw=2&rank=1).

Intraoperative hypotension is a risk factor for postoperative acute kidney injury after femoral neck fracture surgery: a retrospective study

Background

Hip fracture in elderly patients is a serious health concern due to the associated morbidity and mortality. Although acute kidney injury after hip fracture is known to be a significantly poor prognostic factor for morbidity and mortality, the literature regarding the risk factors for acute kidney injury after hip fracture is insufficient. This study aimed to investigate the incidence and associated risk factors for acute kidney injury in patients with femoral neck fracture.

Methods

A total of 248 patients who underwent an operation for femoral neck fracture between January 2011 and January 2015 were retrospectively analyzed. Acute kidney injury was defined according to the Kidney Disease: Improving Global Outcomes guidelines.

Results

The incidence of acute kidney injury was 17.7% (n = 44). Risk factors for acute kidney injury included diabetes mellitus, pre-existing renal disease, preoperative blood urea nitrogen (BUN), preoperative estimated glomerular filtration rate (eGFR), preoperative haemoglobin (Hb) level, type of operation, postoperative creatinine level and intraoperative hypotension (P <  0.05). After controlling for confounding variables, intraoperative hypotension was only the independent risk factor for acute kidney injury (P = 0.012).

Conclusions

Acute kidney injury was found to occur frequently after surgery for femur neck fracture. Surgeons should be aware of acute kidney injury when planning the management of patients with femoral neck fracture and consider that the duration of intraoperative hypotension is a risk factor for acute kidney injury.

Desflurane inhibits endothelium-dependent vasodilation more than sevoflurane with inhibition of endothelial nitric oxide synthase by different mechanisms

The effects of desflurane on endothelium-dependent vasodilation remain uncertain, whereas sevoflurane is known to inhibit it. Endothelium-dependent vasodilation is mainly mediated by endothelial nitric oxide synthase. The effects of desflurane on endothelium-dependent vasodilation were compared with those of sevoflurane, and inhibition mechanisms, including phosphorylation of endothelial nitric oxide synthase and the calcium pathway, were evaluated for the two anesthetics. We hypothesized that desflurane would inhibit endothelium-dependent vasodilation in a concentration-dependent manner more than sevoflurane, with inhibition of a calcium pathway. Isolated rat aortic rings were randomly assigned to treatment with desflurane or sevoflurane for measurements of the vasodilation ratio. To determine NO production with desflurane and sevoflurane, an in vitro assay was performed with cultured bovine aortic endothelial cells. These cells were also used for measurement of intracellular calcium or Western blotting. For endothelium-dependent vasodilation, the ratio of vasodilation was more significantly inhibited by 11.4% desflurane than by 4.8% sevoflurane. Inhibition did not between 5.7% desflurane and 2.4% sevoflurane. No inhibitory effect of desflurane or sevoflurane was observed in endothelium-denuded aorta. Desflurane inhibited nitric oxide production caused by stimulation of bradykinin significantly more than sevoflurane. Desflurane had a greater suppressive effect on the bradykinin-induced increase in intracellular calcium concentration than did sevoflurane. Sevoflurane, but not desflurane, inhibited phosphorylation of the serine 1177 residue by bradykinin stimulation. Desflurane inhibited endothelium-dependent vasodilation more than sevoflurane through inhibition of a calcium pathway. Sevoflurane inhibited endothelium-dependent vasodilation by inhibition of phosphorylation of the serine 1177 residue of endothelial nitric oxide synthase.

Major comorbid disease processes associated with increased incidence of acute kidney injury

Acute kidney injury (AKI) is commonly seen amongst critically ill and hospitalized patients. Individuals with certain co-morbid diseases have an increased risk of developing AKI. Thus, recognizing the co-morbidities that predispose patients to AKI is important in AKI prevention and treatment. Some of the most common co-morbid disease processes that increase the risk of AKI are diabetes, cancer, cardiac surgery and human immunodeficiency virus (HIV) acquired immune deficiency syndrome (AIDS). This review article identifies the increased risk of acquiring AKI with given co-morbid diseases. Furthermore, the pathophysiological mechanisms underlying AKI in relation to co-morbid diseases are discussed to understand how the risk of acquiring AKI is increased. This paper reviews the effects of various co-morbid diseases including: Diabetes, cancer, cardiovascular disease and HIV AIDS, which all exhibit a significant increased risk of developing AKI. Amongst these co-morbid diseases, inflammation, the use of nephrotoxic agents, and hypoperfusion to the kidneys have been shown to be major pathological processes that predisposes individuals to AKI. The pathogenesis of kidney injury is complex, however, effective treatment of the co-morbid disease processes may reduce its risk. Therefore, improved management of co-morbid diseases may prevent some of the underlying pathology that contributes to the increased risk of developing AKI.

Acute Kidney Injury in Cardiac Surgery and Cardiac Intensive Care

Acute kidney injury (AKI) is a serious postoperative complication following cardiac surgery. Despite the incidence of AKI requiring temporary renal replacement therapy being low, it is nonetheless associated with high morbidity and mortality. Therefore, preventing AKI associated with cardiac surgery can dramatically improve outcomes in these patients. The pathogenesis of AKI is multifactorial and many attempts to prevent or treat renal injury have been met with limited success. In this article, we will discuss the incidence and risk factors for cardiac surgery associated AKI, including the pathophysiology, potential biomarkers of injury, and treatment modalities.

Role of phosphatase activity of soluble epoxide hydrolase in regulating simvastatin-activated endothelial nitric oxide synthase

Soluble epoxide hydrolase (sEH) has C-terminal epoxide hydrolase and N-terminal lipid phosphatase activity. Its hydrolase activity is associated with endothelial nitric oxide synthase (eNOS) dysfunction. However, little is known about the role of sEH phosphatase in regulating eNOS activity. Simvastatin, a clinical lipid-lowering drug, also has a pleiotropic effect on eNOS activation. However, whether sEH phosphatase is involved in simvastatin-activated eNOS activity remains elusive. We investigated the role of sEH phosphatase activity in simvastatin-mediated activation of eNOS in endothelial cells (ECs). Simvastain increased the phosphatase activity of sEH, which was diminished by pharmacological inhibitors of sEH phosphatase. In addition, pharmacological inhibition of sEH phosphatase or overexpressing the inactive phosphatase domain of sEH enhanced simvastatin-induced NO bioavailability, tube formation and phosphorylation of eNOS, Akt, and AMP-activated protein kinase (AMPK). In contrast, overexpressing the phosphatase domain of sEH limited the simvastatin-increased NO biosynthesis and eNOS phosphorylation at Ser1179. Simvastatin evoked epidermal growth factor receptor–c-Src–increased Tyr phosphorylation of sEH and formation of an sEH–Akt–AMPK–eNOS complex, which was abolished by the c-Src kinase inhibitor PP1 or c-Src dominant-negative mutant K298M. These findings suggest that sEH phosphatase activity negatively regulates simvastatin-activated eNOS by impeding the Akt–AMPK–eNOS signaling cascade.

AKI associated with cardiac surgery

Approximately 18% of patients undergoing cardiac surgery experience AKI (on the basis of modern standardized definitions of AKI), and approximately 2%-6% will require hemodialysis. The development of AKI after cardiac surgery portends poor short- and long-term prognoses, with those developing RIFLE failure or AKI Network stage III having an almost 2-fold increase in the risk of death. AKI is caused by a variety of factors, including nephrotoxins, hypoxia, mechanical trauma, inflammation, cardiopulmonary bypass, and hemodynamic instability, and it may be affected by the clinician's choice of fluids and vasoactive agents as well as the transfusion strategy used. The risk of AKI may be ameliorated by avoidance of nephrotoxins, achievement of adequate glucose control preoperatively, and use of goal-directed therapy hemodynamic strategies. Remote ischemic preconditioning is an exciting future strategy, but more work is needed before widespread implementation. Unfortunately, there are no pharmacologic agents known to reduce the risk of AKI or treat established AKI.

Glutamine supplementation alleviates vasculopathy and corrects metabolic profile in an in vivo model of endothelial cell dysfunction

Endothelial Cell Dysfunction (ECD) is a recognized harbinger of a host of chronic cardiovascular diseases. Using a mouse model of ECD triggered by treatment with L-Nω-methylarginine (L-NMMA), we previously demonstrated that renal microvasculature displays a perturbed protein profile, including diminished expression of two key enzymes of the Krebs cycle associated with a Warburg-type suppression of mitochondrial metabolism. We hypothesized that supplementation with L-glutamine (GLN), that can enter the Krebs cycle downstream this enzymatic bottleneck, would normalize vascular function and alleviate mitochondrial dysfunction. To test this hypothesis, mice with chronic L-NMMA-induced ECD were co-treated with GLN at different concentrations for 2 months. Results confirmed that L-NMMA led to a defect in acetylcholine-induced relaxation of aortic rings that was dose-dependently prevented by GLN. In caveolin-1 transgenic mice characterized by eNOS inactivation, L-NMMA further impaired vasorelaxation which was partially rescued by GLN co-treatment. Pro-inflammatory profile induced by L-NMMA was blunted in mice co-treated with GLN. Using an LC/MS platform for metabolite profiling, we sought to identify metabolic perturbations associated with ECD and offset by GLN supplementation. 3453 plasma molecules could be detected with 100% frequency in mice from at least one treatment group. Among these, 37 were found to be differentially expressed in a 4-way comparison of control vs. LNMMA both with and without GLN. One of such molecules, hippuric acid, an “uremic toxin” was found to be elevated in our non-uremic mice receiving L-NMMA, but normalized by treatment with GLN. Ex vivo analysis of hippuric acid effects on vasomotion demonstrated that it significantly reduced acetylcholine-induced vasorelaxation of vascular rings. In conclusion, functional and metabolic profiling of animals with early ECD revealed macrovasculopathy and that supplementation GLN is capable of improving vascular function. Metabolomic analyses reveal elevation of hippuric acid, which may further exacerbate vasculopathy even before the development of uremia.

Cardiac surgery-associated acute kidney injury

Cardiac surgery-associated acute kidney injury (AKI) is a major health problem that is extremely common and has a significant effect on cardiac surgical outcomes. AKI occurs in nearly 30 % of patients undergoing cardiac surgery, with about 1-2 % of these ultimately requiring dialysis. The development of AKI predicts a significant increase in morbidity and mortality independent of other risk factors. The pathogenetic mechanisms associated with cardiac surgery-associated AKI include several biochemical pathways, of which the most important are hemodynamic, inflammatory and nephrotoxic factors. Risk factors for AKI have been identified in several models, and these facilitate physicians to prognosticate and develop a strategy for tackling patients predisposed to developing renal dysfunction. Effective therapy of the condition is still suboptimal, and hence the accent has always been on risk factor modification. Thus, strategies for reducing preoperative anemia, perioperative blood transfusions and surgical re-explorations may be effective in attenuating the incidence and severity of this complication.

Sildenafil potentiates bone morphogenetic protein signaling in pulmonary arterial smooth muscle cells and in experimental pulmonary hypertension

OBJECTIVE

Mutations in the bone morphogenetic protein type II receptor (BMPR-II) are responsible for the majority of cases of heritable pulmonary arterial hypertension (PAH), and BMPR-II deficiency contributes to idiopathic and experimental forms of PAH. Sildenafil, a potent type-5 nucleotide-dependent phosphodiesterase inhibitor, is an established treatment for PAH, but whether sildenafil affects bone morphogenetic protein (BMP) signaling in the pulmonary circulation remains unknown.

METHODS AND RESULTS

Studies were undertaken in human pulmonary arterial smooth muscle cells (PASMCs) and in vivo in the monocrotaline rat model of PAH. In PASMCs, sildenafil enhanced BMP4-induced phosphorylation of Smad1/5, Smad nuclear localization, and Inhibitor of DNA binding protein 1 gene and protein expression. This effect was mimicked by 8-bromo-cyclic GMP. Pharmacological inhibition or small interfering RNA knockdown of cyclic GMP-dependent protein kinase I inhibited the effect of sildenafil on BMP signaling. In functional studies, we observed that sildenafil potentiated the antiproliferative effects of BMP4 on PASMC proliferation. Furthermore, sildenafil restored the antiproliferative response to BMP4 in PASMCs harboring mutations in BMPR-II. In the monocrotaline rat model of PAH, which is characterized by BMPR-II deficiency, sildenafil prevented the development of pulmonary hypertension and vascular remodeling, and partly restored Smad1/5 phosphorylation and Inhibitor of DNA binding protein 1 gene expression in vivo in monocrotaline exposed rat lungs.

CONCLUSIONS

Sildenafil enhances canonical BMP signaling via cyclic GMP and cyclic GMP-dependent protein kinase I in vitro and in vivo, and partly restores deficient BMP signaling in BMPR-II mutant PASMCs. Our findings demonstrate a novel mechanism of action of sildenafil in the treatment of PAH and suggest that targeting BMP signaling may be beneficial in this disease.

Nitric oxide counters the inhibitory effects of uremic toxin indoxyl sulfate on endothelial cells by governing ERK MAP kinase and myosin light chain activation

Uremic toxins such as indoxyl sulfate (IS) accumulate at a high level in end stage renal disease (ESRD) and can exhibit significant systemic endothelial toxicity leading to accelerated cardiovascular events. The precise molecular mechanisms by which IS causes endothelial dysfunction are unknown. We tested the hypothesis that IS negatively influences properties of endothelial cells, such as migration and tube formation, by depleting nitric oxide (NO) bioavailability, and that an NO donor can reverse these inhibitory effects. IS inhibited human umbilical vein endothelial cell (HUVEC) migration and formation of tubes on matrigel. Mechanistically, IS inhibited VEGF-induced NO release from HUVECs. An NO donor, SNAP, reversed IS-mediated inhibition of HUVEC migration as well as tube-formation. IS inhibited ERK 1/2 MAP kinase activity in a dose-dependent manner, but this was preserved by SNAP. Inhibition of ERK 1/2 with a pharmacological inhibitor (U0126) decreased HUVEC migration and tube formation; these effects too were prevented by SNAP. Further, IS stimulated activation of myosin light chain (MLC), potentially stimulating endothelial contractility, while SNAP decreased MLC activation. Thus, we conclude that the negative effects of IS on endothelial cells are prevented, to a major extent, by NO, via its divergent actions on ERK MAP kinase and MLC.

Indolent course of tubulointerstitial disease in a mouse model of subpressor, low-dose nitric oxide synthase inhibition

Deficiency of nitric oxide (NO) represents a consistent manifestation of endothelial dysfunction (ECD), and the accumulation of asymmetric dimethylarginine occurs early in renal disease. Here, we confirmed in vitro and in vivo the previous finding that a fragment of collagen XVIII, endostatin, was upregulated by chronic inhibition of NO production and sought to support a hypothesis that primary ECD contributes to nephrosclerosis in the absence of other profibrotic factors. To emulate more closely the indolent course of ECD, the study was expanded to an in vivo model with N(G)-monomethyl-L-arginine (L-NMMA; mimics effects of asymmetric dimethylarginine) administered to mice in the drinking water at subpressor doses of 0.3 and 0.8 mg/ml for 3-6 mo. This resulted in subtle but significant morphological alterations detected in kidneys of mice chronically treated with L-NMMA: 1) consistent perivascular expansion of interstitial matrix components at the inner stripe of the outer medulla and 2) collagen XVIII/endostatin abundance. Ultrastructural abnormalities were detected in L-NMMA-treated mice: 1) increased activity of the interstitial fibroblasts; 2) occasional detachment of endothelial cells from the basement membrane; 3) splitting of the vascular basement membrane; 4) focal fibrosis; and 5) accumulation of lipofuscin by interstitial fibroblasts. Preembedding labeling of microvasculature with anti-CD31 antibodies showed infiltrating leukocytes and agglomerating platelets attaching to the visibly intact or denuded capillaries. Collectively, the data indicate that the mouse model of subpressor chronic administration of L-NMMA is not a robust one (endothelial pathology visible only ultrastructurally), and yet it closely resembles the natural progression of endothelial dysfunction, microvascular abnormalities, and associated tubulointerstitial scarring.

Platelet-derived exosomes induce endothelial cell apoptosis through peroxynitrite generation: experimental evidence for a novel mechanism of septic vascular dysfunction

Introduction

Several studies link hematological dysfunction to severity of sepsis. Previously we showed that platelet-derived microparticles from septic patients induce vascular cell apoptosis through the NADPH oxidase-dependent release of superoxide. We sought to further characterize the microparticle-dependent vascular injury pathway.

Methods

During septic shock there is increased generation of thrombin, TNF-α and nitric oxide (NO). Human platelets were exposed for 1 hour to the NO donor diethylamine-NONOate (0.5 μM), lipopolysaccharide (LPS; 100 ng/ml), TNF-α (40 ng/ml), or thrombin (5 IU/ml). Microparticles were recovered through filtration and ultracentrifugation and analyzed by electron microscopy, flow cytometry or Western blotting for protein identification. Redox activity was characterized by lucigenin (5 μM) or coelenterazine (5 μM) luminescence and by 4,5-diaminofluorescein (10 mM) and 2',7'-dichlorofluorescein (10 mM) fluorescence. Endothelial cell apoptosis was detected by phosphatidylserine exposure and by measurement of caspase-3 activity with an enzyme-linked immunoassay.

Results

Size, morphology, high exposure of the tetraspanins CD9, CD63, and CD81, together with low phosphatidylserine, showed that platelets exposed to NONOate and LPS, but not to TNF-α or thrombin, generate microparticles similar to those recovered from septic patients, and characterize them as exosomes. Luminescence and fluorescence studies, and the use of specific inhibitors, revealed concomitant superoxide and NO generation. Western blots showed the presence of NO synthase II (but not isoforms I or III) and of the NADPH oxidase subunits p22^phox, protein disulfide isomerase and Nox. Endothelial cells exposed to the exosomes underwent apoptosis and caspase-3 activation, which were inhibited by NO synthase inhibitors or by a superoxide dismutase mimetic and totally blocked by urate (1 mM), suggesting a role for the peroxynitrite radical. None of these redox properties and proapoptotic effects was evident in microparticles recovered from platelets exposed to thrombin or TNF-α.

Conclusion

We showed that, in sepsis, NO and bacterial elements are responsible for type-specific platelet-derived exosome generation. Those exosomes have an active role in vascular signaling as redox-active particles that can induce endothelial cell caspase-3 activation and apoptosis by generating superoxide, NO and peroxynitrite. Thus, exosomes must be considered for further developments in understanding and treating vascular dysfunction in sepsis.

TRP channels in endothelial function and dysfunction

Endothelial cells produce various factors that regulate vascular tone, vascular permeability, angiogenesis, and inflammatory responses. The dysfunction of endothelial cells is believed to be the major culprit in various cardiovascular diseases, including hypertension, atherosclerosis, heart and renal failure, coronary syndrome, thrombosis, and diabetes. Endothelial cells express multiple transient receptor potential (TRP) channel isoforms, the activity of which serves to modulate cytosolic Ca(2+) levels ([Ca(2+)](i)) and regulate membrane potential, both of which affect various physiological processes. The malfunction and dysregulation of TRP channels is associated with endothelial dysfunction, which is reflected by decreased nitric oxide (NO) bioavailability, inappropriate regulation of vascular smooth muscle tonicity, endothelial barrier dysfunction, increased oxidative damage, impaired anti-thrombogenic properties, and perturbed angiogenic competence. Evidence suggests that dysregulation of TRPC4 and -C1 results in vascular endothelial barrier dysfunction; malfunction of TRPP1 and -P2 impairs endothelial NO synthase; the reduced expression or activity of TRPC4 and -V1 impairs agonist-induced vascular relaxation; the decreased activity of TRPV4 reduces flow-induced vascular responses; and the activity of TRPC3 and -C4 is associated with oxidative stress-induced endothelial damage. In this review, we present a comprehensive summary of the literature on the role of TRP channels in endothelial cells, with an emphasis on endothelial dysfunction.

Acute kidney injury associated with cardiac surgery

Acute renal failure (ARF) occurs in up to 30% of patients who undergo cardiac surgery, with dialysis being required in approximately 1% of all patients. The development of ARF is associated with substantial morbidity and mortality independent of all other factors. The pathogenesis of ARF involves multiple pathways. Hemodynamic, inflammatory, and nephrotoxic factors are involved and overlap each other in leading to kidney injury. Clinical studies have identified risk factors for ARF that can be used to determine effectively the risk for ARF in patients who undergo bypass surgery. These high-risk patients then can be targeted for renal protective strategies. Thus far, no single strategy has demonstrated conclusively its ability to prevent renal injury after bypass surgery. Several compounds such as atrial natriuretic peptide and N-acetylcysteine have shown promise, but large-scale trials are needed.

Pathophysiology of ischaemic acute renal failure

This chapter summarizes the pathophysiology of ischaemic acute renal failure from both the experimental and clinical points of view. Traditionally, the abrupt fall in glomerular filtration rate (GFR) is thought to be due to an interplay of haemodynamic and tubular abnormalities. The intrarenal haemodynamic alterations include renal vasoconstriction, leukocyte-endothelium interactions and loss of blood flow and GFR autoregulation. During recent years it has become evident that pronounced outer medulary ischaemia makes an important contribution. In severe and prolonged ischaemia, the tubular epithelial cells can undergo either sublethal or lethal cell damage. Cell death occurs by necrosis and apoptosis. The different mechanisms of post-ischaemic cell damage are discussed. The post-ischaemic kidney also shows a dramatic capacity for recovery. During this recovery phase some of the damaged cells undergo de-differentiation--which is an important step in regeneration of the tubular epithelium. Recent evidence points to the possibility that infiltration of the kidney with bone-marrow-derived stem cells contributes to the repair process. The molecular mechanisms and the effect of growth factors are summarized.

Rapid increase in endothelial nitric oxide production by bradykinin is mediated by protein kinase A signaling pathway

Bradykinin (BK) acutely increases endothelial nitric oxide (NO) production by activating endothelial NO synthase (eNOS), and this increase is in part correlated with enhanced phosphorylation/dephosphorylation of eNOS by several protein kinases and phosphatases. However, the signaling mechanisms producing this increase are still controversial. In an attempt to delineate the acute effect of BK on endothelial NO production, confluent bovine aortic endothelial cells were incubated with BK, and NO production was measured by NO-specific chemiluminescence. Significant increase in NO levels was detected as early as 1 min after BK treatment, with concomitant increase in the phosphorylation of Ser(1179) (bovine sequence) site of eNOS (eNOS-Ser(1179)). This acute effect of BK on both increases was blocked only by treatment of protein kinase A inhibitor H-89, but not by the inhibitors of calmodulin-dependent kinase II and protein kinase B, suggesting that the rapid increase in NO production by BK is mediated by the PKA-dependent phosphorylation of eNOS-Ser(1179).

In vivo and in vitro models demonstrate a role for caveolin-1 in the pathogenesis of ischaemic acute renal failure

Caveolae and their proteins, the caveolins, transport macromolecules; compartmentalize signalling molecules; and are involved in various repair processes. There is little information regarding their role in the pathogenesis of significant renal syndromes such as acute renal failure (ARF). In this study, an in vivo rat model of 30 min bilateral renal ischaemia followed by reperfusion times from 4 h to 1 week was used to map the temporal and spatial association between caveolin-1 and tubular epithelial damage (desquamation, apoptosis, necrosis). An in vitro model of ischaemic ARF was also studied, where cultured renal tubular epithelial cells or arterial endothelial cells were subjected to injury initiators modelled on ischaemia-reperfusion (hypoxia, serum deprivation, free radical damage or hypoxia-hyperoxia). Expression of caveolin proteins was investigated using immunohistochemistry, immunoelectron microscopy, and immunoblots of whole cell, membrane or cytosol protein extracts. In vivo, healthy kidney had abundant caveolin-1 in vascular endothelial cells and also some expression in membrane surfaces of distal tubular epithelium. In the kidneys of ARF animals, punctate cytoplasmic localization of caveolin-1 was identified, with high intensity expression in injured proximal tubules that were losing basement membrane adhesion or were apoptotic, 24 h to 4 days after ischaemia-reperfusion. Western immunoblots indicated a marked increase in caveolin-1 expression in the cortex where some proximal tubular injury was located. In vitro, the main treatment-induced change in both cell types was translocation of caveolin-1 from the original plasma membrane site into membrane-associated sites in the cytoplasm. Overall, expression levels did not alter for whole cell extracts and the protein remained membrane-bound, as indicated by cell fractionation analyses. Caveolin-1 was also found to localize intensely within apoptotic cells. The results are indicative of a role for caveolin-1 in ARF-induced renal injury. Whether it functions for cell repair or death remains to be elucidated.

Endothelial cell activation by endotoxin involves superoxide/NO-mediated nitration of prostacyclin synthase and thromboxane receptor stimulation

In bovine coronary artery segments, peroxynitrite inhibits prostacyclin (PGI2) synthase by tyrosine nitration. Using this pharmacological model, we show that a 1 h exposure of bovine coronary artery segments to endotoxin (lipopolysaccharide [LPS]) inhibits the relaxation phase following angiotensin II (Ang II) stimulation and causes a vasospasm that can be suppressed by a thromboxane A2 (TxA2) receptor blocker. In parallel, PGI2 synthesis decreases in favor of prostaglandin E2 formation. Immunoprecipitation and costaining with an anti-nitrotyrosine antibody identified PGI2 synthase as the main nitrated protein in the endothelium. All effects of LPS could be prevented in the presence of the nitric oxide (NO) synthase inhibitor Nomega-mono-methyl-L-arginine and polyethylene-glycolated Cu/Zn- superoxide dismutase. Thus, the early phase of endothelial cell activation in bovine coronary arteries by inflammatory agents proceeds by a protein synthesis-independent priming process for a source of superoxide that we tentatively attribute to xanthine oxidase. Upon receptor activation, Ang II stimulates NO and superoxide production, resulting in a peroxynitrite-mediated nitration and inhibition of PGI2 synthase. The remaining 15-hydroxy-prostaglandin 9,11-endoperoxide (PGH2) first activates the TxA2/PGH2 receptor and then is converted to prostaglandin E2 (PGE2) by smooth muscle cells. PGE2 together with a lack of NO and PGI2 is known to promote the adhesion of white blood cells and their immigration to the inflammatory locus.

VEGF expression in hypoxia and hyperglycemia: reciprocal effect on branching angiogenesis in epithelial-endothelial co-cultures

Vascular endothelial growth factor (VEGF), an angiogenic factor for endothelial cells, is produced by glomerular and tubular epithelia. Using immunoelectron microscopy, VEGF expression by podocytes (GEC) and the proximal tubular epithelium of rat kidney was confirmed. To elucidate the mechanisms of VEGF production and its physiologic consequences, studies were performed in cultured GEC and proximal tubular epithelial cells (RPTEC). Both GEC and RPTEC expressed VEGF-120 and 164 mRNA, as detected by quantitative RT-PCR. Hypoxia resulted in an increase in mRNA abundance, more robust in RPTEC than in GEC, and an increase in VEGF expression by 1.9- and 1.6-fold, respectively. 30 mM D-glucose, but not 30 mM L-glucose, resulted in the elevation of VEGF mRNA in RPTEC, but not in GEC, although both cell types showed a comparable modest increase in VEGF expression. Combined treatment (hypoxia and 30 mM D-glucose) resulted in an increase of VEGF mRNA only in RPTEC; however, an enhanced protein expression was detectable in both cell types. To investigate the role of VEGF in branching angiogenesis, "sandwich" co-cultures were applied with endothelial cells and capillary tube formation was compared under the above conditions. Both RPTEC and GEC induced VEGF-dependent capillary tube formation by co-cultured endothelial cells and in both cell types hypoxia further augmented angiogenesis. In contrast, 30 mM D-glucose suppressed angiogenesis in co-cultures with both cell types despite increased mRNA for VEGF receptors 1 and 2. This study shows (1) that VEGF produced by GEC and RPTEC is necessary for branching angiogenesis and (2) that hypoxic environment stimulates VEGF production by both epithelial cell types and augments branching angiogenesis, whereas (3) hyperglycemic microenvironment, although also stimulatory for VEGF production, fails to augment angiogenesis.

The pathophysiology of erectile dysfunction related to endothelial dysfunction and mediators of vascular function

The incidence of erectile dysfunction increases with diabetes, hypertension, hypercholesterolaemia, cardiovascular disease and renal failure. All these conditions are associated with endothelial dysfunction. This review addresses the pathophysiology of erectile dysfunction with a special focus on new insights into nitric oxide (NO)-mediated pathways, oxidative stress and parallels to endothelial dysfunction. NO appears to be the key mediator promoting endothelium-derived vasodilation and penile erection. The possibility is discussed that elevated plasma concentrations of asymmetrical dimethylarginine (ADMA), an endogenous NO synthase inhibitor, may provide an additional pathomechanism for various forms of erectile dysfunction associated with cardiovascular risk factors and disease. Likewise, the role of endothelium-derived factors mediating NO-independent pathways is evaluated.

Endothelial nitric oxide production during in vitro simulation of external limb compression

External pneumatic compression (EPC) is effective in preventing deep vein thrombosis (DVT) and is thought to alter endothelial thromboresistant properties. We investigated the effect of EPC on changes in nitric oxide (NO), a critical mediator in the regulation of vasomotor and platelet function. An in vitro cell culture system was developed to simulate flow and vessel collapse conditions under EPC. Human umbilical vein endothelial cells were cultured and subjected to tube compression (C), pulsatile flow (F), or a combination of the two (FC). NO production and endothelial nitric oxide synthase (eNOS) mRNA expression were measured. The data demonstrate that in the F and FC groups, there is a rapid release of NO followed by a sustained increase. NO production levels in the F and FC groups were almost identical, whereas the C group produced the same low amount of NO as the control group. Conditions F and FC also upregulate eNOS mRNA expression by a factor of 2.08 +/- 0.25 and 2.11 +/- 0.21, respectively, at 6 h. Experiments with different modes of EPC show that NO production and eNOS mRNA expression respond to different time cycles of compression. These results implicate enhanced NO release as a potentially important factor in the prevention of DVT.