Regulation of coronary venular barrier function by blood borne inflammatory mediators and pharmacological tools: insights from novel microvascular wall models

We hypothesized that postcapillary venules play a central role in the control of the tightness of the coronary system as a whole, particularly under inflammatory conditions. Sandwich cultures of endothelial cells and pericytes of precapillary arteriolar or postcapillary venular origin from human myocardium as models of the respective vascular walls (sandwich cultures of precapillary arteriolar or postcapillary venular origin) were exposed to thrombin and components of the acutely activatable inflammatory system, and their hydraulic conductivity ( LP) was registered. LP of SC-PAO remained low under all conditions (3.24 ± 0.52·10−8cm·s−1·cmH2O−1). In contrast, in the venular wall model, PGE2, platelet-activating factor (PAF), leukotriene B4 (LTB4), IL-6, and IL-8 induced a prompt, concentration-dependent, up to 10-fold increase in LP with synergistic support when combined. PAF and LTB4 released by metabolically cooperating platelets, and polymorphonuclear leucocytes (PMNs) caused selectively venular endothelial cells to contract and to open their clefts widely. This breakdown of the barrier function was preventable and even reversible within 6–8 h by the presence of 50 μM quercetin glucuronide (QG). LTB4 synthesis was facilitated by biochemical involvement of erythrocytes. Platelets segregated in the arterioles and PMNs in the venules of blood-perfused human myocardium (histological studies on donor hearts refused for heart transplantation). Extrapolating these findings to the coronary microcirculation in vivo would imply that the latter's complex functionality after accumulation of blood borne inflammatory mediators can change rapidly due to selective breakdown of the postcapillary venular barrier. The resulting inflammatory edema and venulo-thrombosis will severely impair myocardial performance. The protection afforded by QG could be of particular relevance in the context of cardiosurgical intervention.

Isolation, bulk cultivation, and characterization of coronary microvascular pericytes: the second most frequent myocardial cell type in vitro

Densely arranged pericytes engird the endothelial tube of all coronary microvessels. Since the experimental access to these abundant cells in situ is difficult, a prerequisite for broader investigation is the availability of sufficient numbers of fully differentiated pericytes in homogenous culture. To reach this goal, we applied strictly standardized cell isolation techniques, optimized culture methods and specific histological staining. Approximately 1,000-fold enriched pericytes were proteolytically detached from highly purified coronary microvascular networks (density gradient centrifugation) of eight mammalian species including human. Addition of species-autologous fetal or neonatal serum (10-20% vol/vol) was a precondition for longer term survival of homogenous pericyte cultures. This ensured optimal growth (doubling time <14 h) and full expression of pericyte-specific markers. In 3-mo, 10(10) pericytes (15 g) could be cultivated from 1 bovine heart. Pericytes could be stored in liquid N(2), recultured, and passaged repeatedly without loss of typical features. In cocultures with EC or vascular smooth muscle cells, pericytes transferred fluorescent calcein to each other and to EC via their antler-like extensions, organized angiogenetic sprouting of vessels, and rapidly activated coagulation factors X and II via tissue factor and prothrombinase. The interconnected pericytes of the coronary system are functionally closely correlated with the vascular endothelium and may play key roles in the adjustment of local blood flow, the regulation of angiogenic processes, and the induction of procoagulatory processes. Their successful bulk cultivation enables direct experimental access under defined in vitro conditions and the isolation of pericyte specific antigens for the production of specific antibodies.

Wall structures of myocardial precapillary arterioles and postcapillary venules reexamined and reconstructed in vitro for studies on barrier functions

The barrier functions of myocardial precapillary arteriolar and postcapillary venular walls (PCA or PCV, respectively) are of considerable scientific and clinical interest (regulation of blood flow and recruitment of immune defense). Using enzyme histochemistry combined with confocal microscopy, we reexamined the cell architecture of human PCA and PVC and reconstructed appropriate in vitro models for studies of their barrier functions. Contrary to current opinion, the PCA endothelial tube is encompassed not by smooth muscle cells but rather by a concentric layer of pericytes cocooned in a thick, microparticle-containing extracellular matrix (ECM) that contributes substantially to the tightness of the arteriolar wall. This core tube extends upstream into the larger arterioles, there additionally enwrapped by smooth muscle. PCV consist of an inner layer of large, contractile endothelial cells encompassed by a fragile, wide-meshed pericyte network with a weakly developed ECM. Pure pericyte and endothelial cell preparations were isolated from PCA and PCV and grown in sandwich cultures. These in vitro models of the PCA and PCV walls exhibited typical histological and functional features. In both plasma-like (PLM) and serum-containing (SCM) media, the PCA model (including ECM) maintained its low hydraulic conductivity (L(P) = 3.24 ± 0.52·10(-8)cm·s(-1)·cmH(2)O(-1)) and a high selectivity index for transmural passage of albumin (SI(Alb) = 0.95 ± 0.02). In contrast, L(P) and SI(Alb) in the PCV model (almost no ECM) were 2.55 ± 0.32·10(-7)cm·s(-1)·cmH(2)O(-1) and 0.88 ± 0.03, respectively, in PLM, and 1.39 ± 0.10·10(-6)cm·s(-1)·cmH(2)O(-1) and 0.49 ± 0.04 in SCM. With the use of these models, systematic, detailed studies on the regulation of microvascular barrier properties now appear to be feasible.

Early and mid term mortality after coronary artery bypass grafting in women depends on the surgical protocol: retrospective analysis of 3441 on- and off-pump coronary artery bypass grafting procedures

Background

Since 2002 MI and stroke, not cancer, are leading causes of death in women. We studied 30-days and 1 year mortality of 3441 patients undergoing coronary artery bypass grafting (CABG) operations in our institution performed either conventionally or off pump (OPCAB). Our objective was to investigate the gender-related mortality in both groups.

Patients and Methods

Between 2004 and 2008, 3441 patients (733 women, 2708 men) underwent CABG. 252 women and 854 men were operated using OPCAB, 481 women and 1854 men using extracorporeal circulation (ECC). Medical data was prospectively entered and retrospectively reviewed. 30-days and one year mortality rates were analyzed with Kaplan-Meier estimates and Cox proportional hazards models. Linear and logistic regression models were used to test gender differences.

Results

a) 30-day mortality using ECC: 5.2% in women vs. 2.5% in men (p = 0.001). One year ECC mortality: 8.7% in women vs. 4.8% in men (p = 0.0008). b) OPCAB: 30-days and 1 year mortality in women measured 1.7%. Mortality in men was 2.1% after 30 days and 3.7% after one year c) gender specific mortality: 30 days mortality in women was 1.7% using OPCAB and 5.2% using ECC (p = 0.002), one year mortality in women was 1.7% using OPCAB vs. 8.7% using ECC (p = 0.0004). In men, 30-days mortality in OPCAB was 2.1%, one year mortality was 3.7%; using ECC early and late mortality was 2.5% and 4.8%.

Conclusions

Female gender is a strong independent predictor and risk factor of increased early and midterm postoperative mortality rates when ECC is used. OPCAB significantly reduces early and midterm postoperative mortality in women and may therefore be proposed as the preferred revascularization technique in female patients.

Search for optimized conditions for sealing and storage of bypass vessels: influence of preservation solution and filling pressure on the degree of endothelialization

The aim of the present study was to develop methods for the rapid assessment of intimal quality of coronary bypass segments of venous origin, and to prevent endothelial damage by improved intraoperative handling of graft segments. Particular attention was paid to the influence of the composition of the preservation solution and the intravasal filling pressure on the degree of endothelialization. Intrava-sal exposure to Alcian blue at pH<3 resulted in highly specific staining of intimal regions with functionally or structurally damaged endothelium. Standardization of preparation, staining and image acquisition of the intimal surface of graft remnants and subsequent computer-aided planimetry of these images made it possible for the first time to perform rapid serial investigations for quality control of bypass grafts. Using saline as the rinsing and intraoperative storage medium resulted in the loss of more than 50% of the endothelium at intravasal pressures of 0-100 mmHg. Increasing the pressure resulted eventually in complete de-endothelialization. In contrast, grafts incubated in a customized plasma derivative tolerated pressures of up to 200 mmHg with no significant endothelial loss; and even after exposure to 1,000 mmHg (10 times the average mean arterial pressure!) more than 70% of the endothelium were intact and vital. These findings imply strongly that the quality of aortocoronary bypass grafts of venous origin can be improved substantially by the use of a plasma derivative solution for intraoperative preservation and by monitoring and controlling the intravasal pressures reached during sealing and storage.

Pericytes in the macrovascular intima: possible physiological and pathogenetic impact

The frequently observed de-endothelialization of venous coronary bypass grafts prepared using standard methods exposes subendothelial prothrombotic cells to blood components, thus endangering patients by inducing acute thromboembolic infarction or long-term proliferative stenosis. Our aim was to gain deeper histological and physiological insight into these relations. An intricate network of subendothelial cells, characterized by histological features specific for true pericytes, was detected even in healthy vessels and forms, coupled to the luminal endothelium, a second leaflet of the macrovascular intima. These cells, and particularly those in the venous intima, express enormous concentrations of tissue factor and can recruit additional amounts of up to the 25-fold concentration within 1 h during preincubation with serum (intimal pericytes of venous origin activate 30.71 +/- 4.07 pmol coagulation factor x.min(-1).10(-6) cells; n = 15). Moreover, decoupled from the endothelium, they proliferate rapidly (generation time, 15 +/- 2.1 h, n = 8). Central regions of atherosclerotic plaques, as well as of those of restenosed areas of coronary vein grafts, consist almost completely of these cells. In stark contrast with the prothrombogenicity of the intimal pericytes, intact luminal endothelium recruits high concentrations of thrombomodulin (CD 141) specifically within its intercellular junctions, activates Protein C rapidly (42 +/- 5.1 pmol/min.10(6) venous endothelial cells at thrombin saturation; n = 15), can thus actively prevent coagulatory processes, and never expresses histologically detectable and functionally active tissue factor. Given this strongly prothrombotic potential of the intimal pericytes and their overshooting growth behavior in endothelium-denuded vascular regions, they may play important roles in the development of atherosclerosis, thrombosis, and saphenous vein graft disease.

Heart-lung transplantation in patients with pulmonary atresia and ventricular septal defect

OBJECTIVE

Heart-lung transplantation for patients with pulmonary atresia and ventricular septal defect is challenging. The aim of the study was to present a single-center experience with heart-lung transplantation in this difficult group of patients.

METHODS

A retrospective review identified 9 patients aged 4.1 to 45.6 years (median, 25.4 years) with pulmonary atresia and ventricular septal defect who underwent heart-lung transplantation. Four (44.4%) patients had previous heart operations: 3 of them had palliative procedures (systemic-to-pulmonary shunts), and 1 had multistage correction. A standard transplantation method was used, with the exception of 1 patient with heterotaxy syndrome who underwent a modified operation. Major aortopulmonary collateral arteries were controlled by using various techniques.

RESULTS

Follow-up ranged between 2 days and 12.6 years (median, 1.2 years). The hospital mortality rate was 22.2% (n = 2). In the late postoperative period, 3 patients died. The survival curve was similar to that of patients with other diagnoses undergoing heart-lung transplantation. The median length of intensive care unit stay was 58 days (range, 22-82 days), and the median length of hospital stay was 83 days (range, 35-136 days). The most common early complication was bleeding requiring re-exploration. In all cases the bleeding was proved to be from collateral vessels.

CONCLUSIONS

Heart-lung transplantation in patients with pulmonary atresia and ventricular septal defect requires carefully planned and meticulously performed surgical intervention. This management should be taken into consideration as a future option if the specific anatomy is uncorrectable in early childhood, and the palliative procedures should be avoided.

Extensive deendothelialization and thrombogenicity in routinely prepared vein grafts for coronary bypass operations: facts and remedy

The objective of this study was to gain deeper insight into the early reasons for saphenous vein graft disease and to find a practical approach to obviate it. Intraoperative storage of freshly explanted venous grafts (45 min, 20 degrees C; n=25 in each case) in saline, saline + 5% albumin, or HTK-solution and also in heparinized autologous blood was poorly tolerated by the endothelium. Large endothelial areas (mostly >75% of total surface) were detached already during brief non-pulsatile flushing just before the transplantation. Contact of deendothelialized areas in graft remnants with defined mixtures of coagulation factors or blood (n=11-17) caused rapid coagulatory processes via expression of tissue factor and assembly of prothrombinase in the subendothelium. Attached platelets and leukocytes accelerated the procoagulatory processes further, and endothelium-dependent anticoagulatory activities were significantly abolished. During pulsatile arterial flow, the resulting blood clots exacerbated the damage of the intima markedly, because they were flushed away tearing off further endothelium. In contrast, storage of venous grafts in a plasma preparation freed from isoagglutinins and coagulation factors preserved the endothelium, which resisted arterial flow and revealed anticoagulatory activity in the presence of antithrombin III and/or protein C. We conclude that gentle preparation and preservation of the vascular endothelium with a suitable storage solution during bypass surgery is a decisive first step to obviate saphenous vein graft disease.

Fibrin glue in coronary artery bypass grafting operations: casting out the Devil with Beelzebub?

OBJECTIVE

Fibrin sealants are frequently used in aortocoronary bypass operations. Although they are considered to be clinically safe, we performed a retrospective analysis of our data to examine the possible side effects of Tissucol fibrin sealant, namely the acute thrombosis of grafts and native coronary arteries resulting in severe myocardial damage and patient deaths.

METHODS

The data of 2716 patients (2001 male, 715 female) who received an aortocoronary bypass operation from November 1995 to December 1999 were studied retrospectively. Two groups (group 1: received Tissucol, group 2: no sealant used) were compared with respect to an a priori selected set of demographic and clinical variables and with respect to their effect on the outcome using bivariate tabulation. Multiple exploratory assessments of factors possibly related to fatal outcome were done by multiple logistic regression.

RESULTS

Nine hundred ninety patients (group 1) received Tissucol, 1726 patients (group 2) did not receive it. Mean patient age was 64+/-9.1 years. Group 1 had a higher risk of death (7.8% vs 2.8%, p<0.001). The peak values of creatine kinase >500 and creatine kinase-myocardial band >50 were higher in group 1 than in group 2, p<0.001. Adjusted odds ratios for the risk of fatal outcome were: 2.01 for the use of Tissucol, 2.71 for patient age >70 years, 2.02 for aortic cross clamp time >90 min, 3.95 for postoperative ventricular fibrillation, 6.35 for postoperative cardiopulmonary resuscitation, 4.55 for postoperative aortocoronary reoperation.

CONCLUSION

In our analysis an increased risk of myocardial injury or even death was found in coronary artery bypass grafting patients when Tissucol fibrin sealant was used intraoperatively.

Continuous graft perfusion: optimizing the quality of saphenous vein grafts

BACKGROUND

Healthy unaltered vascular endothelium in graft material is a prerequisite for a successful CABG operation. Damage done to the endothelium during vein harvest is responsible for an early graft occlusion rate of 20% in the first year after operation. Minimally invasive vein harvesting is regarded to minimize the damage done to the Endothelium. We compared minimally invasive vein harvesting with conventional vein harvesting and studied the influence of a continuous perfusion of the veins with patient autologous blood on their endothelial integrity.

METHODS

80 patients were randomly split into 4 groups: Group 1: Conventional vein harvest and storage of the vein in a crystalloid solution before usage. Group 2: Endoscopic vein harvest and storage in cristallloid solution. Group 3: Conventional harvest under continuous perfusion of the vein with 100 ml blood via the heart lung machine. Group 4: Endoscopic vein harvest under continuous perfusion. Immediately prior to the first peripheral anastomosis a sample was taken from each graft and evaluated by scanning electron microscopy. The endothelial integrity was rated in 5 categories (from "completely confluent endothelium" (1) to "no endothelium" (5)).

RESULTS

Group 1: 2.7+/-1.13 Group 2: 2.2+/-1.06 Group 3: 1.6+/-0.68 Group 4: 1.6+/-0.69

CONCLUSION

In regard to the endothelial integrity endoscopic vein harvesting is superior to conventional vein harvest. If the grafts are harvested while continuously perfused with blood there is no more difference between the groups. Considering the well known additional benefits such as reduction in wound healing disorders endoscopic vein harvesting appears to be the preferable technique.

Autologous endothelialized vein allograft: a solution in the search for small-caliber grafts in coronary artery bypass graft operations

BACKGROUND

Early graft failure after the use of less satisfactory autologous grafts (30% of all vein grafts) is caused primarily by the following problems: (1) suitable autologous transplants are limited; (2) biotechnology has not yet been able to produce reliable graft substitutes that are legally and ethically approved; and (3) current prosthetic materials are prothrombotic. To overcome these problems, we developed an easily accessible, quality-controlled graft.

METHODS AND RESULTS

Human autologous venous endothelial cells (HAVECs) were isolated from short segments of peripheral veins unsuitable for bypass grafting. After mechanical deendothelialization of cryopreserved allograft veins (CAVs) and precoating with recipient autologous serum, these homologous cells were seeded by use of a rotating device. Growth of a confluent HAVEC layer within 1 week in a special incubator was observed. After histological and mechanical tests, 12 patients received 15 grafts in total. Bypass operation was followed by clinical and angiographic follow-up. Production period was 22+/-8 days. HAVEC-coated CAVs showed normal connective tissue wall structure and a tight endothelial monolayer (burst pressure >2000 mm Hg). To date, 12 CABG patients lacking suitable autologous graft material have been treated. One patient died of a cause unrelated to the grafts, which were found morphologically normal and patent during autopsy. Of 15 grafts, 2 were occluded at the first angiographic follow-up. The oldest graft has now been in place for approximately 3 years. Immune suppression was not administered.

CONCLUSIONS

At present, autologous endothelialized CAVs present good alternative small-caliber grafts for patients lacking suitable autologous vessels.

An inward rectifier and a voltage-dependent K+ current in single, cultured pericytes from bovine heart

OBJECTIVE

The purpose of this study was to describe passive electrical properties and major membrane currents in coronary pericytes.

METHODS

78 single, cultured bovine pericytes were studied with the patch-clamp technique in the whole-cell mode.

RESULTS

The membrane potential of the cells was -48.9+/-9.6 mV (mean+/-S.D.) with 5 mM and -23.2+/-2.2 mV with 60 mM extracellular K+. The membrane capacitance was 150.2+/-123.2 pF. The current-voltage relation of the pericytes was dominated by an inward current at hyperpolarized potentials and an outward current at depolarized potentials. Increasing extracellular K+ from 5 to 60 mM led to an increase of the inward current and to a shift of this current to more depolarized potentials. The inward current was very sensitive to extracellular barium (50 microM). The maximum slope conductance of the cells at hyperpolarized potentials was 2.9+/-2.8 nS. Inward rectification of whole-cell currents was steep (slope factor = 6.8 mV). With elevated external K+ the outward current reversed near the potassium equilibrium potential. Onset of the outward current was sigmoid and inactivation of this current was monoexponential, slow (time constant = 12.8 s) and incomplete. Voltage-dependence of outward current steady-state activation was steep (slope factor = 4.6 mV). The outward current was very sensitive to 4-aminopyridine (dissociation constant = 0.1 mM). The maximum slope conductance at depolarized potentials was 16.6+/-15.6 nS.

CONCLUSION

We report for the first time, patch-clamp recordings from coronary pericytes. An inward rectifier and a voltage-dependent K+ current were identified and characterized. Regulation of these currents may influence coronary blood flow.

The harmonic scalpel: optimizing the quality of mammary artery bypass grafts

BACKGROUND

The damage done to the endothelium during the preparation of a graft used in an aortocoronary procedure is a risk factor for early graft failure. We compared the effect on the endothelium of the mammary arteries when the harvest was done either by the harmonic scalpel (HS) or the high-frequency electrocauter (HF).

METHODS

Twenty-four mammary arteries were harvested and divided into two groups depending on the use of the HS or the HF. The endothelial damage was analyzed with a scanning electron microscope. The groups were compared in regard to the size of the internal mammary artery (IMA) pedicle.

RESULTS

The endothelial damage of the IMAs taken down with the HS was significantly less than when taken down with the HF if the IMA pedicle size was less than 0.5 cm.

CONCLUSIONS

The HS has a positive effect on the endothelial preservation, especially when the preparation is done closely to the IMA. The HS is profitable in minimally invasive procedures, particularly when it is difficult to keep a wide enough distance from the IMA.