Microvascular in vivo assessment of reperfusion injury: significance of prostaglandin E1 and I2 in postischemic “no-reflow” and “reflow-paradox”

Breast cancer metastasis progression as revealed by intravital videomicroscopy

Metastasis is the spread of cells from a primary tumor to a distant site, where they arrest and grow to form a secondary tumor. Conventional metastasis models have focused primarily on analysis of end point tumor formation following inoculation with tumor cells. This approach can be used to measure the metastatic potential of cell lines, the morphology of metastases and their vasculature and the overall effectiveness of treatment strategies. However, it cannot, reveal the dynamics of metastatic progression, tumor cell interactions with host tissues or the characteristics of blood flow within the tumor microvasculature. Intravital videomicroscopy has been developed to visualize and quantify the movement of tumor cells and their interactions with host tissues as they travel through metastatic pathways within the body and arrest at secondary sites. Intravital videomicroscopy can also be used to quantify the morphology and functional capacity of tumor microvasculature, as well as the timing and dynamic effects of drugs targeted to disrupt tumor vasculaturization. With the development of new fluorescent probes and reporter genes, intravital videomicroscopy has the potential to provide evidence of the timing and location of metabolic processes within the metastatic cascade that may serve as specific targets for the treatment of breast cancer.

The PRAISE study: a prospective, multi-center, randomized, double blinded, placebo-controlled study for the evaluation of iloprost in the early postoperative period after liver transplantation (ISRCTN12622749)

Background

Liver graft dysfunction can deteriorate to complete organ failure and increases perioperative morbidity and mortality after liver transplantation. Therapeutic strategies reducing the rate of graft dysfunction are of current clinical relevance. One approach is the systemic application of prostaglandins, which were demonstrated to be beneficial in reducing ischemia-reperfusion injury. Preliminary data indicate a positive effect of prostacyclin analogue iloprost on allograft viability after liver transplantation. The objective of the study is to evaluate the impact of iloprost in a multi-center trial.

Methods/Design

A prospective, double-blinded, randomized, placebo-controlled multicenter study in a total of 365 liver transplant recipients was designed to assess the effect of intravenous iloprost after liver transplantation. Primary endpoint will be the primary graft dysfunction characterized as presentation of one or more of the following criteria: ALAT or ASAT level > 2000 IU/ml within the first 7 postoperative days, bilirubine ≥ 10 mg/dl on postoperative day 7; INR ≥ 1.6 on postoperative day 7 or initial non-function. Secondary endpoints are parameters of post-transplant morbidity, like rates of infections, biliary complications, need of clotting factors or renal replacement therapy and the graft and patient survival.

Discussion

A well-established treatment concept to avoid graft dysfunction after liver transplantation does not exist at the moment. If the data of this research project confirm prior findings, iloprost would improve the general outcome after liver transplantation.

Trial Registration

German Clinical Trials Register: DRKS00003514. Current Controlled Trials Register: ISRCTN12622749.

Molecular mechanisms regulating the vascular prostacyclin pathways and their adaptation during pregnancy and in the newborn

Prostacyclin (PGI(2)) is a member of the prostanoid group of eicosanoids that regulate homeostasis, hemostasis, smooth muscle function and inflammation. Prostanoids are derived from arachidonic acid by the sequential actions of phospholipase A(2), cyclooxygenase (COX), and specific prostaglandin (PG) synthases. There are two major COX enzymes, COX1 and COX2, that differ in structure, tissue distribution, subcellular localization, and function. COX1 is largely constitutively expressed, whereas COX2 is induced at sites of inflammation and vascular injury. PGI(2) is produced by endothelial cells and influences many cardiovascular processes. PGI(2) acts mainly on the prostacyclin (IP) receptor, but because of receptor homology, PGI(2) analogs such as iloprost may act on other prostanoid receptors with variable affinities. PGI(2)/IP interaction stimulates G protein-coupled increase in cAMP and protein kinase A, resulting in decreased [Ca(2+)](i), and could also cause inhibition of Rho kinase, leading to vascular smooth muscle relaxation. In addition, PGI(2) intracrine signaling may target nuclear peroxisome proliferator-activated receptors and regulate gene transcription. PGI(2) counteracts the vasoconstrictor and platelet aggregation effects of thromboxane A(2) (TXA(2)), and both prostanoids create an important balance in cardiovascular homeostasis. The PGI(2)/TXA(2) balance is particularly critical in the regulation of maternal and fetal vascular function during pregnancy and in the newborn. A decrease in PGI(2)/TXA(2) ratio in the maternal, fetal, and neonatal circulation may contribute to preeclampsia, intrauterine growth restriction, and persistent pulmonary hypertension of the newborn (PPHN), respectively. On the other hand, increased PGI(2) activity may contribute to patent ductus arteriosus (PDA) and intraventricular hemorrhage in premature newborns. These observations have raised interest in the use of COX inhibitors and PGI(2) analogs in the management of pregnancy-associated and neonatal vascular disorders. The use of aspirin to decrease TXA(2) synthesis has shown little benefit in preeclampsia, whereas indomethacin and ibuprofen are used effectively to close PDA in the premature newborn. PGI(2) analogs have been used effectively in primary pulmonary hypertension in adults and have shown promise in PPHN. Careful examination of PGI(2) metabolism and the complex interplay with other prostanoids will help design specific modulators of the PGI(2)-dependent pathways for the management of pregnancy-related and neonatal vascular disorders.

Impact of stable PGI₂ analog iloprost on early graft viability after liver transplantation: a pilot study

BACKGROUND

Ischemia/reperfusion injury after liver transplantation (LT) may be associated with primary graft dysfunction (PDF) or non-function. Prostaglandins were demonstrated to be beneficial in reducing ischemic injury by improving microcirculation and protecting endothelial cells. The aim of this study was to analyze the effect of the continuously administered prostaglandin I(2) analog iloprost on allograft function after LT.

METHODS

Eighty patients were prospectively randomized and assigned to two groups. Patients in the treatment group received iloprost for seven d after transplantation, and those in the control group did not. The primary end point was graft dysfunction.

RESULTS

The incidence of PDF was 20% (n = 8) in the control group and 5% (n = 2) in the treatment group, respectively (p = 0.087). Four patients in the control group underwent re-transplantation for initial non-function (INF). There was no evidence for INF in the treatment group. Iloprost was associated with improved allograft function. Clinical course and outcome were comparable.

CONCLUSIONS

We suggest iloprost to be beneficial for early post-transplant liver function. If the rate of PDF can be significantly reduced with this treatment concept, it should be analyzed in a larger number of patients (ISRCTN95672167).

Dynamics of angiogenesis during wound healing: a coupled in vivo and in silico study

OBJECTIVE

The most critical determinant of restoration of tissue structure during wound healing is the re-establishment of a functional vasculature, which largely occurs via angiogenesis, specifically endothelial sprouting from the pre-existing vasculature.

MATERIALS AND METHODS

We used confocal microscopy to capture sequential images of perfused vascular segments within the injured panniculus carnosus muscle in the mouse dorsal skin-fold window chamber to quantify a range of microcirculatory parameters during the first nine days of healing. This data was used to inform a mathematical model of sequential growth of the vascular plexus. The modeling framework mirrored the experimental circular wound domain and incorporated capillary sprouting and endothelial cell (EC) sensing of vascular endothelial growth factor gradients.

RESULTS

Wound areas, vessel densities and vessel junction densities obtained from the corresponding virtual wound were in excellent agreement both temporally and spatially with data measured during the in vivo healing process. Moreover, by perturbing the proliferative ability of ECs in the mathematical model, this leads to a severe reduction in vascular growth and poor healing. Quantitative measures from this second set of simulations were found to correlate extremely well with experimental data obtained from animals treated with an agent that targets endothelial proliferation (TNP-470).

CONCLUSION

Our direct combination and comparison of in vivo longitudinal analysis (over time in the same animal) and mathematical modeling employed in this study establishes a useful new paradigm. The virtual wound created in this study can be used to investigate a wide range of experimental hypotheses associated with wound healing, including disorders characterized by aberrant angiogenesis (e.g., diabetic models) and the effects of vascular enhancing/disrupting agents or therapeutic interventions such as hyperbaric oxygen.

Effect of prostaglandin E1 on TNF-induced vascular inflammation in human umbilical vein endothelial cells

Prostaglandin E1 (PGE1) is a member of the prostaglandins and has a variety of cardiovascular protective effects. Increasing attention has been paid to the anti-inflammation activity of PGE1, but little direct evidence has been found. We investigated the effects of PGE1 on cell adhesion and inflammation and the mechanisms responsible for this activity in tumor necrosis factor (TNF)-treated human umbilical vein endothelial cells. Results demonstrated that pretreatment with PGE1 decreased the adhesion between vascular endothelial cells and monocytes, reduced the expression of vascular cell adhesion molecule-1, intercellular adhesion molecule-1, and E-selectin in vascular endothelial cells. In addition, PGE1 suppressed TNF-induced NF-kappaB activation and production of reactive oxygen species. We concluded that PGE1 suppressed the vascular inflammatory process, which might be closely related to the inhibition of reactive oxygen species and NF-kappaB activation in human umbilical vein endothelial cells.

Reoxygenation attenuates the adhesion of neutrophils to microvascular endothelial cells

In humans, the pathophysiological inflammation response subsequent to hypoxia and reoxygenation often leads to systemic inflammation and multiorgan failure. We applied a newly developed static interaction model using human polymorphonuclear neutrophils and microvascular endothelial cells to clarify the role of hypoxia and hypoxia/reoxygenation in vitro. Human dermal microvascular endothelial cell cultures (n = 7) were exposed to hypoxia and different reoxygenation periods and the adherence rate of neutrophils to the endothelial cells as well as to the protein matrix on the culture slide surface were determined by quantitative microscopy. Hypoxia clearly triggered neutrophil adhesion to human dermal microvascular endothelial cells whereas additional reoxygenation significantly decreased neutrophil adhesion. These in vitro findings suggest that systemic inflammation caused by increased neutrophil adherence to the microvascular endothelium is already initiated by hypoxia rather than by subsequent reoxygenation.

Protective effects of prostaglandin E1 on human umbilical vein endothelial cell injury induced by hydrogen peroxide

AIM

To investigate the protective effects of prostaglandin E(1) (PGE(1)) against H(2)O(2)-induced oxidative damage on human umbilical vein endothelial cells (HUVECs).

METHODS

HUVECs were pretreated with PGE(1) (0.25, 0.50, and 1.00 micromol/L) for 24 h and exposed to H(2)O(2) (200 micromol/L) for 12 h, and cell viability was measured by the MTT assay. LDH, NO, SOD, GSH-Px, MDA, ROS, and apoptotic percentage were determined. eNOS expression was measured by Western blotting and real-time PCR.

RESULTS

PGE(1) (0.25-1.00 micromol/L) was able to markedly restore the viability of HUVECs under oxidative stress, and scavenged intracellular reactive oxygen species induced by H(2)O(2). PGE(1) also suppressed the production of lipid peroxides, such as MDA, restored the activities of endogenous antioxidants including SOD and GSH-Px, and inhibited cell apoptosis. In addition, PGE(1) significantly increased NO content, eNOS protein, and mRNA expression.

CONCLUSION

PGE(1) effectively protected endothelial cells against oxidative stress induced by H(2)O(2), an activity that might depend on the up-regulation of NO expression.

Platelets arachidonic acid metabolism in patients with essential hypertension

Arachidonic acid's (AA) metabolites, eicosanoids, exert a tremendous influence on circulatory and vascular homeostasis, and in humans are generated by many organs and cell types. In this study we wanted to verify whether platelets AA metabolism play a significant role in pathogenesis of essential hypertension (EH). Participants were divided into the study (EH) and the control group. Plasma and urine concentrations of isoprostanes (8-iPF(2alpha)-III) and thromboxane B(2) (TxB(2)) were determined using the ELISA method. The levels of 5- and 12-hydroxyeicosatetraenoic (HETE) acids, generated by platelets, were analysed using RP-HPLC. In a suspension of not stimulated and AA-stimulated platelets TxB(2) level was statistically lower in the study than in the control group (p < 0.0001 and 0.001 respectively). The concentration of 12-HETE was significantly elevated in EH patients compared to the control group; however, only in the non-stimulated conditions (p < 0.05). Plasma and urine F2-isoprostanes levels were significantly higher in hypertensive individuals than in the control group (p < 0.00002 and p < 0.01 respectively). Moreover, EH patients excreted more TxB(2) in urine than normotensive individuals (p < 0.05). Our results highlight the mutual connections between the platelets AA metabolism and indicate its possible role in the pathogenesis of arterial hypertension. Moreover, we hypothesize that platelets AA metabolism may exert a pro-atherosclerotic effect. Finally, we suggest the use of (5-HETE+12-HETE)/TxB(2) parameter in further studies.

The influence of controlled limb reperfusion with PGE1 on reperfusion injury after prolonged ischemia

BACKGROUND

Controlled reperfusion of ischemic limbs has been found to be protective in limiting ischemia-reperfusion injury. We aimed to analyze local hemodynamic effects of prostaglandin E1 (PGE1) administrated during controlled reperfusion in an in vivo setting.

MATERIAL AND METHODS

Twenty-four pigs underwent exposure of the infrarenal aorta and iliac vessels. Pigs were observed for 7.5 h without limb ischemia (group I). In the others, limb ischemia was produced by clamping the aorta for 6 h. Reperfusion was conducted in uncontrolled (group II), controlled (group III), and controlled fashion with addition of PGE1 (group IV) for the initial 30 min. We evaluated regional blood flow in the left common iliac artery, cardiac output, systemic vascular resistance, oxygen and glucose consumption, muscle adenosine triphosphate (ATP), and potassium levels in iliac vein.

RESULTS

Benefits after reperfusion were observed in group IV compared with group III regarding regional blood flow at 60 min (P < 0.01) and 90 min (P < 0.01), glucose consumption at 30 min, (P < 0.05) and potassium regulation at 30 (P < 0.05) and 90 min (P < 0.05).

CONCLUSION

The addition of PGE1 to controlled reperfusion further reduces local hemodynamic effects of ischemia-reperfusion injury compared with standard controlled and uncontrolled reperfusion in an animal model.

Perioperative iloprost and endothelial progenitor cells in uremic patients with severe limb ischemia undergoing peripheral revascularization

The incidence of severe limb ischemia (SLI) is high among haemodialysis (HD) patients. Limb rescue rate after surgical revascularization is relatively poor compared with patients with normal renal function. Prostanoids are an interesting category as adjuvants to revascularization. New vessel growth develops not exclusively by proliferation of endothelial cells in vascular extremities but also by cells mobilized from the bone marrow (HSC), transformed into endothelial progenitor cells (EPC) contributing to both re-endothelialization and neovascularization. Basal number of HSC and EPC is significantly reduced in HD patients and correlated with a subsequent defective neovascularization. The aim of this study was to evaluate the effects of perioperative treatment with iloprost in uremic patients with acute ischemia of lower limbs, undergoing surgical revascularization, on endothelial progenitor cells, hypothesizing a possible biological mechanism induced by the prostanoids. A search was also made for vascular remodeling processes through the analysis of the concentrations of soluble adhesion molecules (i-CAM, v-CAM, e-selectin), biochemical markers of endothelial activation. Thirty HD patients with SLI undergoing peripheral revascularization were enrolled (15 were treated with iloprost and 15 with a placebo). Iloprost was administered as an intra-arterial bolus of 3000 ng over 1 to 3 min immediately after revascularization and in the same affected artery. Serum samples were taken before revascularization (T0), at 6 (T6) and 24 h (T24) after infusion to measure sICAM-1, sE-selectin, and sVCAM-1, and for quantification of HSC and EPC. Progenitors were identified by specific surface markers CD34+, CD133+ and VEGFR2+. Count was conducted using PROCOUNT performed in a TRUCOUNT tube and with a FACSort flow cytometer. Before revascularization, all patients showed a decreased number of HSC and EPC. After 6 h, HSC augmented significantly compared with T0 in both groups. The iloprost group attained a significant increase compared with the placebo group. HSC levels reduced drastically at T24. EPC augmented significantly compared with basal level after 24 h. In the iloprost group, the increase was considerable compared with the placebo group. A close negative correlation, assessed by Pearson coefficient (r), was found between HSC and EPC at T24 in the iloprost group (R = 0.82 P < 0.01). Adhesion molecules had increased levels at T6 and T24 in both groups. Moreover, a close positive correlation, assessed by Pearson coefficient, was found between EPC and adhesion molecules in both groups but the iloprost group maintained a better statistical association. Revascularization stimulated HSC and EPC release from bone marrow but at a different time: HSC increased suddenly at 6 h and diminished to a minimal amount at T24, conversely, EPC increased significantly only at T24. Iloprost treatment was able to amplify this mechanism validating recent findings (North TE et al., [31]). Adhesion molecules as markers of endothelial activation and vascular development confirmed this tendency.

Decreased Mrp2-dependent bile flow in the post-warm ischemic rat liver

BACKGROUND

The link between microcirculatory disturbance and hepatocellular dysfunction remains unknown. The present study was designed to examine the key event of warm ischemia reperfusion (WIR) injury with subsequent cholestasis.

METHODS

A left lobar 70% ischemia and reperfusion rat model was used in this study. The portal vein and hepatic artery to the left lateral lobe of the liver were subjected to 20 min of warm ischemia followed by 60 min of reperfusion to collect bile and to measure its constituents.

RESULTS

The hepatocellular injury was increased significantly in livers exposed to WIR, as judged by serum alanine aminotransferase. This event coincided with decreased bile production and biliary concentration of glutathione (GSH), suggesting impaired bile salts-independent bile flow, while biliary phospholipids and bile salts were not decreased. Additionally, hepatic adenosine triphosphate and GSH were not decreased after WIR. Since the biliary GSH, which is a major driving force for bile salts-independent bile flow, is excreted from hepatocytes into the bile via multidrug resistance protein 2 (Mrp2), we examined whether intracellular localization of Mrp2 occurred. Immunohistochemical analyses revealed hepatocellular Mrp2 was retrieved from bile canalicular membrane into the pericanalicular cytoplasm in the post-warm ischemic livers. Microcirculatory disturbance in livers exposed to 20 min of warm ischemia improved to levels comparable to controls.

CONCLUSION

Mrp2 internalization, observed in this study, may play an important determinant of cholestasis in the post-warm ischemic livers.

The use of diagnostic frequency continuous ultrasound to improve microcirculatory function after ischemia-reperfusion injury

OBJECTIVE

Damage to the circulatory system resulting from ischemia-reperfusion injury (I/R injury) occurs during heart attacks and hemorrhagic shock. The authors report a method for mitigating microcirculatory injury, using diagnostic frequency continuous-mode ultrasound and how effects are influenced by nitric oxide production impairment.

METHODS

Five groups of hamsters were studied using the dorsal skin fold window chamber: (1) I/R; (2) I/R + ultrasound during ischemia; (3) I/R + ultrasound after ischemia; (4) I/R + N(omega)-nitro-L-arginine methyl ester (L-NAME); and (5) I/R + L-NAME + ultrasound. Functional capillary density (FCD) and microvascular diameter, flow velocity, and flow were monitored. During the exposures 2.49 MHz continuous ultrasound was used.

RESULTS

Significant improvements in animals exposed to ultrasound after ischemia were found at 24 h of reperfusion in FCD, arteriolar diameter, and arteriolar and venular flow velocity and flow. Animals exposed to ultrasound during ischemia showed significantly improved FCD. L-NAME treatment reduced the improvement of microvascular function, compared to animals exposed after ischemia.

CONCLUSIONS

The use of continuous-mode diagnostic frequency ultrasound is beneficial in preventing long-term ischemia-reperfusion effects in the microcirculation as shown by the return of microvascular parameters to baseline values, an effect not attained in the absence of ultrasound treatment. The effects may be in part due to the production of nitric oxide consequent to locally induced shear stress effects by ultrasound exposure.

In vivo observation of leukocyte-endothelium interaction in ischemia reperfusion injury with the dorsal window chamber and the effects of pentoxifylline on reperfusion injury

OBJECTIVE

Ischemia reperfusion injury can cause failure in microsurgical operations. Interaction between leukocytes and endothelium is recognized as an integral step in ischemia reperfusion injury. Pentoxifylline is a methylxanthine derivative that has pharmacological properties that can be beneficial in ischemia reperfusion injury. The aim of this study was to investigate the in vivo effect of pentoxifylline on leukocyte-endothelium interaction in ischemia reperfusion injury.

METHODS

Intravital fluorescent microscopy was used to observe leukocyte-endothelium interaction in a "dorsal window chamber" model. Twenty-eight postcapillary veins were analyzed in group 1, and twenty-two in group 2. Group 1 received 25 mg/kg pentoxifylline 20 min before reperfusion. Group 2 received an equivalent volume of 0.9% saline at the same time. The period of ischemia was 4 h.

RESULTS

Quantification of leukocyte 'sticking' and 'rolling' was done before ischemia and at 30, 60, and 120 min after reperfusion. Offline video analysis was used for evaluating the results. Statistical evaluation showed that pentoxifylline significantly attenuated leukocyte 'sticking' and 'rolling' in postcapillary venules. It was also effective in preventing 'no-reflow' when compared with the control group.

CONCLUSION

These results indicate pentoxifylline diminishes leukocyte-endothelium interaction, and may have a therapeutic role in preventing ischemia reperfusion injury in microsurgical operations.

Metabolism of eicosanoids and their action on renal function during ischaemia and reperfusion: the effect of alprostadil

Eicosanoids, active metabolites of arachidonic acid (AA), play an important role in the regulation of renal haemodynamics and glomerular filtration. Our study verified the hypothesis on the positive action of exogenously administered PGE(1) on renal function during an operation with temporary ischaemia of the lower half of the body. Also the effect of alprostadil (prostaglandin E(1) analogue) administered during the operation of an abdominal aorta aneurysm on the postoperative systemic metabolism of AA and the glomerular filtration rate (GFR) was investigated. The study included 42 patients with a diagnosed abdominal aorta aneurysm who have been qualified for the operation of implantation of the aortic prosthesis. The patients were randomly assigned to two groups: the study group (I) receiving alprostadil and the control group (II) without alprostadil. The levels of hydroxyeicosatetraenoic acids (15-HETE, 12-HETE, 5-HETE) were determined by RP-HPLC and the level of thromboxane B(2) (TxB(2)) was determined by ELISA in the plasma of the blood drawn from vena cava superior immediately before aortic clamping (A) and 5 min after aortic declamping (B). The administration of PGE(1) affects the metabolism of 15-HETE in a manner dependent on the baseline value of GFR but does not significantly change the postoperative renal function. The metabolism of 15-HETE is affected by the baseline value of GFR1 and a longer period of ischaemia is correlated with lower concentrations of 5-HETE during reperfusion. The results of our studies indicate that TxB(2) influences the postoperative function of kidneys.

The ILAILL study: iloprost as adjuvant to surgery for acute ischemia of lower limbs: a randomized, placebo-controlled, double-blind study by the italian society for vascular and endovascular surgery

SUMMARY BACKGROUND DATA

High rate of complications has been reported following revascularization for acute limb ischemia (ALI). No adjuvant pharmacologic treatment, apart from anticoagulation and standard perioperative care, has been shown clinically effective.

OBJECTIVE

Aim of this study was to evaluate the effects of the prostacyclin analog iloprost as adjuvant to surgery for ALI.

METHODS

A total of 300 patients were randomly assigned to receive perioperative iloprost (intra-arterial, intraoperative bolus of 3000 ng, plus intravenous infusion of 0.5-2.0 ng/kg/min for 6 hours/day for 4-7 days following surgery), or placebo. The primary endpoint was the combined incidence of death and amputation at 3-month follow-up. Secondary endpoints were the incidence of each single major complication, total event rate, symptomatology, and tolerability.

RESULTS

The combined incidence of death and amputation was 19.9% in the placebo and 14.1% in the iloprost group (relative risk, 1.56; 95% confidence interval, 0.89-2.75, P = 0.12, Cox regression analysis). A statistically significant lower mortality (4.7%) was reported in patients receiving iloprost, compared with controls (10.6%; relative risk, 2.61; 95% confidence interval, 1.07-6.37, P = 0.03). The overall incidence of fatal plus major cardiovascular events was 33.1% and 22.8% in placebo and iloprost groups, respectively (relative risk, 1.61; 95% confidence interval, 1.04-2.49, P = 0.03). No serious adverse reactions occurred after iloprost administration, nor differences in the incidence of bleeding or hypotension between treatment groups.

CONCLUSIONS

Although at lower levels than previously reported, our results confirm the severity of ALI. Iloprost as adjuvant to surgery significantly reduced mortality and overall major event rate. Further data are needed to support this finding, and to face a still open medical issue.