P2-09-04: Near Infra Red Quantum Dots as Novel Probes for Sentinel Lymph Node Biopsy

Background: Sentinel Lymph Node Biopsy (SLNB) is a standard procedure in breast cancer surgery. The current tracers for SLNB including the blue dye and radiocolloid, have various limitations like anaphylactic reaction to the dye and exposure of radioactivity to both patients and staff. Quantum dots (QDs) are fluorescent nanoparticles (2-10nm in diameter), with unique photophysical properties like enhanced photostability and size tunable emission wavelengths, that can potentially replace the current tracers for SLNB. QDs emitting in the Near Infra Red (NIR) range of the electromagnetic spectrum can be tracked in deep tissues as biological tissues are transparent to NIR wavelengths (700-2000nm). We have developed Near Infra Red emitting Quantum Dots (NIR QDs) as alternative probes for SLNB and set up a live NIR imaging system to track them in deep tissues.

Materials and Methods: NIR emitting QDs based on CdTeHg were synthesized by a one pot aqueous method and characterized using Transmission Electron Microscopy (TEM), UV-V is*** spectrometry and photoluminescence studies. 100μl of QDs (1mg/ml) were co-injected intradermally with blue dye into the hind legs of rat models (n=4) and compared to controls (n=4) which were injected with blue dye only. The procedure was conducted under inhalational anaesthesia using isofluorane and rats were monitored for hemodynamic instability for a period of 2 hrs after injection. QDs were tracked using a live NIR imaging system including an excitation light of 630nm, emission filter of 850nm and a Hamamatsu Orca 2 UV-Vis-NIR thermoelectrically cooled CCD camera.

Results: NIR QDs had a core diameter of 7nm on TEM and emitted at 860nm upon excitation with a 630nm light source. Within 3 minutes of an intradermal injection QDs entered the lymphatic tracts. The lymphatics converged to the groin and a small surgical incision at this site revealed the underlying sentinel lymph node with minimal dissection. The rats remained hemodynamically stable throughout the duration of the procedure with no significant difference in comparison with the controls.

Conclusion: NIR emitting QDs can be used for accurate localisation of the SLN prior to surgical incision, making this an even more minimally invasive procedure and possibly an office based procedure in the future. The nanosize, surface chemistry and deep tissue visibility of these novel nanoprobes allow relentless possibilities for in vitro and in vivo molecular and cellular imaging. NIR QDs can be conjugated to biomolecules for cancer localisation, detection of micrometastasis and image guided targeted drug delivery of chemotherapeutic agents. Further studies to investigate their in vivo biodistribution are in progress to take this technology one step closer to clinical application.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P2-09-04.

Remote ischaemic preconditioning versus no remote ischaemic preconditioning for vascular and endovascular surgical procedures

BACKGROUND

Despite advances in perioperative care, elective major vascular surgical procedures carry a significant risk of morbidity and mortality. Remote ischaemic preconditioning is initiated by brief, non-lethal periods of ischaemia in a vascular bed different from the one which will be subjected to ischaemic insult during surgery. It has the potential to provide local tissue protection from further prolonged periods of ischaemia.

OBJECTIVES

The aim of this review was to compare the outcomes from vascular and endovascular surgical procedures with and without the use of remote ischaemic preconditioning.

SEARCH METHODS

The Cochrane Peripheral Vascular Diseases Group searched their Specialised Register (June 2011) and CENTRAL (2011, Issue 2). The authors searched MEDLINE via PubMed (July 2011), EMBASE (June 2011), and Science Citation Index Expanded (July 2011).

SELECTION CRITERIA

We considered for inclusion all randomised controlled trials that evaluated the role of remote ischaemic preconditioning in reducing mortality and systemic injury in patients undergoing open vascular or endovascular surgery.

DATA COLLECTION AND ANALYSIS

We collected the data on characteristics of the trial, methodological quality, the remote ischaemic preconditioning stimulus used, mortality, morbidity, operating time and hospital stay from each trial. We analysed the data with both the fixed-effect and the random-effects models using RevMan analysis. For each outcome we calculated the risk ratio (RR) or mean difference with 95% confidence interval (CI) based on an intention-to-treat analysis.

MAIN RESULTS

We included four studies with a total of 115 patients randomised to undergo a vascular procedure with remote ischaemic preconditioning and 117 patients randomised to have the procedure without remote ischaemic preconditioning. None of the trials were of low risk of bias. There was no significant difference in mortality between the two groups (RR 1.70, 95% CI 0.51 to 5.72). Similarly, there was no statistically significant difference between the two groups for all other outcomes except reduced risk of myocardial infarction in the remote ischaemic preconditioning group, which was significant by the fixed-effect model (RR 0.31, 95% CI 0.10 to 0.90) but not by the random-effects model (RR 0.34, 95% CI 0.11 to 1.08). This positive effect was from the results of only one trial and was not consistently observed. Furthermore, it was noted that there was an observed trend of high incidence of unplanned critical care admission in the remote ischaemic preconditioning group, although this was not statistically significant (RR 2.15, 95% CI 0.87 to 5.33).

AUTHORS' CONCLUSIONS

Based on current evidence from small pilot trials, there are too few data to be able to say whether remote ischaemic preconditioning has any beneficial or harmful effects. The safety of this technique needs to be confirmed in adequately powered trials. Therefore, further randomised trials on this technique are required.

Adipose-derived stem cells for clinical applications: a review

The use of stem cells derived from adipose tissue as an autologous and self-replenishing source for a variety of differentiated cell phenotypes, provides a great deal of promise for reconstructive surgery. In this article, we review available literature encompassing methods of extraction of pluripotent adipose stem cells (ASCs) from lipoaspirate locations, their storage, options for culture, growth and differentiation, cryopreservation and its effect on stem cell survival and proliferation, and new technologies involving biomaterials and scaffolds. We will conclude by assessing potential avenues for developing this incredibly promising field.

Endothelial Progenitor Cells and Their Potential Clinical Applications in Peripheral Arterial Disease

Endothelial progenitor cells (EPCs) were originally thought to be present only during embryonic development. New evidence suggests that they can persist into adult life, circulate in the peripheral blood and may play an important part in endothelial repair and replacement of dysfunctional endothelium. They may also play a role in the formation of new blood vessels (angiogenesis, vasculogenesis, and arteriogenesis) in ischemic tissues. In addition, EPCs have the potential to endothelialize small-diameter prosthetic vascular bypass grafts and generate a nonthrombogenic surface, thereby increasing the patency rate of these grafts. EPCs may also be used in the clinical assessment of risk of vascular disease. In this review, the authors discuss the potential use of EPCs in the management of peripheral arterial disease (PAD).

Polycystic ovary syndrome, diabetes and cardiovascular disease: risks and risk factors

Polycystic ovary syndrome is one of the most common endocrine disorders in the human, affecting approximately 10% of women of reproductive age. Although originally considered a gynaecological disorder, the syndrome is associated with a wide range of endocrine and metabolic abnormalities, including insulin resistance. Affected women are at an increased risk of developing gestational and non-insulin dependent diabetes and there is an association with cardiovascular risk factors including obesity, hypertension, dyslipidaemia, hyperhomocysteinaemia, increased intima media thickness and impaired vascular elasticity. The effect on cardiovascular mortality is currently unclear. However, in view of the proven links with diabetes and the cardiovascular risk markers, this condition should be considered within the province of physicians as well as gynaecologists.

Increased risk of vascular events in systemic lupus erythematosus: is arterial stiffness a predictor of vascular risk?

Patients with systemic lupus erythematosus (SLE) have an increased vascular morbidity and mortality. Several established vascular risk factors are more prevalent in this population but cannot fully explain the reported excess atherosclerotic burden. Emerging vascular risk factors may also contribute to the increased vascular risk in these patients although the evidence is limited and often conflicting. SLE-specific risk factors also play a role in the pathogenesis of atherosclerosis.Given the multifactorial aetiology of vascular disease in SLE, an integrated index of risk could be useful in the management of these patients. Arterial stiffness possibly represents such an index and accumulating data suggest an increased prevalence of arterial stiffness in SLE. Many factors play a role in the loss of arterial elasticity in this population, including both emerging and established vascular risk factors. Arterial stiffness may emerge as a useful index for risk stratification in SLE and has the potential to guide therapeutic decisions in these patients.

Topical haemostatic agents

BACKGROUND

A variety of local haemostatic agents is now available to stop troublesome bleeding. These agents are indicated for use during surgical interventions where conventional methods of haemostasis are not applicable because of the site of surgery or the degree of bleeding.

METHOD

A literature search using the PubMed and ISI Web of Knowledge databases identified relevant studies on topical haemostatic agents. Manufacturers' recommendations were also sought through commercial websites.

RESULTS AND CONCLUSION

A significant body of evidence now exists to support the use of topical haemostatic agents in a wide variety of clinical situations. The advantages and disadvantages of many of these agents are highlighted.

Assessment of the potential of progenitor stem cells extracted from human peripheral blood for seeding a novel vascular graft material

OBJECTIVE

A novel nanocomposite has recently been developed based on polyhedral oligomeric silsesquioxane attached by direct reaction onto a urethane segment, as a potential vascular graft material; its trade name is UCL-Nano. The UCL-Nano has been demonstrated to have similar viscoelastic properties to the walls of a natural artery, to be resistant to degradation and to be able to sustain endothelial cell seeding. Human peripheral blood contains both circulating endothelial cells and endothelial progenitor cells, which may be suitable for conduit seeding. The aim of this study was to develop a system with the potential to deliver an endothelial cell-seeded bypass graft in a realistic time frame.

MATERIALS AND METHODS

Endothelial progenitor cells and circulating endothelial cells were isolated from human peripheral blood and were characterized by fluorescent-activated cell sorting, reverse transcriptase-polymerase chain reaction and immunohistochemistry. Isolated cells were seeded on nanocomposite and were maintained in culture for 35 days.

RESULTS

The UCL-Nano was successfully seeded with cells and a confluent cell layer was achieved after 14-day culture. Cells remained viable and confluent on the nanocomposite for 35 days.

CONCLUSION

In conclusion, these results suggest that this process has potential both for a realistic and achievable two-stage seeding process for vascular bypass grafts and for the potential development of a device, with the aim of achieving in situ seeding once implanted.

Regional differences in the expression of nitric oxide synthase and specific receptors in the vascular tissues of control and diabetic rabbits: a pilot study

BACKGROUND

Atherosclerosis can influence the expression of endothelial nitric oxide synthase (eNOS) as well as endothelin-1 (ET-1) and 5-hydroxytryptamine (5HT; serotonin) receptors. Diabetes has an effect on the onset, severity and pattern of atherosclerosis with a predilection for more distal arteries. We aimed to identify regional differences in the distribution of eNOS activity, ET-1 and 5HT receptors in vascular tissues obtained from control and diabetic rabbits.

MATERIALS AND METHODS

The mid abdominal aorta, right renal and right femoral arteries were harvested from 12 adult rabbits (6 months old, 3-3.9 kg); 8 controls and 4 diabetic (induced using alloxan 7 months previously). Samples were stored in liquid nitrogen for Western immunoblotting for eNOS as well as ET-1 and 5HT receptors.

RESULTS

Significant differences were found in the distribution of eNOS, ET-1 and 5HT between the aorta, renal and femoral arteries in the controls. The number of ET-1 receptors was significantly higher (aorta; p=0.016, renal; p=0.004, femoral; p=0.05,) whereas, the expression of eNOS was significantly lower (aorta; p =0.004, renal; p =0.004, femoral; p =0.008) when comparing arteries from normal rabbits with these from diabetics ones. The number of 5HT receptors was higher in arteries from diabetic rabbits but this was not statistically significantly.

CONCLUSION

The "regional" distribution of eNOS activity as well as ET-1 and 5HT receptors in control rabbits varies significantly according to the vessel assessed. Further studies are needed to evaluate the effect of blocking these receptors (e.g. on the risk of re-stenosis). Regional receptor differences may explain why diabetes is linked with a predilection for atherosclerosis (and possibly calcification) in distal arteries.

Increased apoptosis and decreased proliferation of colorectal cancer cells using insulin-like growth factor binding protein-4 gene delivered locally by gene transfer

OBJECTIVE

Insulin-like growth factor (IGF)-I induces proliferation of transformed cells. Its binding proteins (IGFBP) are involved in local regulation of IGF. This study assessed the effects of overexpression of IGFBP-4 on the development of cancer in vivo.

METHOD

Nude mice were subcutaneously inoculated with HT-29 colorectal cancer cells (3 x 10(6)). When the tumour became visible (1 week after inoculation), animals received either 150 microg of mammalian expression vector containing IGFBP-4 cDNA or vector alone (n = 6 each) by peritumoural injection. Tumour size was measured during the growth. After 3 weeks of IGFBP-4 induction, animals were killed and tumour tissue samples were collected for examining the level of IGFBP-4 expression. Tumour mitotic activities were determined by counting numbers of mitotic cells on the tissue section. Apoptosis was investigated by terminal deoxynucleotidyl transferase-mediated dUDP nick end labelling assay.

RESULTS

Following IGFBP-4 treatment, tumour showed large necrotic areas, significantly increased numbers of apoptotic cells (36.67 +/- 7.36 vs 7.07 +/- 1.91, P < 0.01 vs control), decreased cells undergoing mitosis (2.31 +/- 0.32 vs 3.61 +/- 0.27, P < 0.01 vs control) and higher expression of IGFBP-4 (P < 0.05 vs control).

CONCLUSION

IGFBP-4 gene transfer increased apoptosis and decreased mitosis, but tumour volume was not significantly altered possibly due to cellular debris filling the centre of tumours.

The role of established and emerging risk factors in peripheral vascular graft occlusion

Several studies have evaluated the association between established as well as emerging vascular risk factors with peripheral graft occlusion. There is evidence for a link between the risk for graft occlusion and total serum cholesterol, low-density lipoprotein cholesterol and triglyceride levels. The overall effect of smoking shows a 2.35-fold increase in risk of graft failure. Studies involving diabetic patients undergoing peripheral bypass may have failed to detect higher occlusion rates, possibly due to increased morbidity and mortality as well as higher amputation rates even if the graft is patent. Both antiplatelet agents and anticoagulation seem to be effective in the prevention of graft occlusion. Unconvincing data have been published with regards to the effect of hypertension on graft patency. Emerging factors such as fibrinogen, lipoprotein (a), C-reactive protein and homocysteine levels should also be considered when assessing the risk of graft occlusion. More research is needed to prevent graft occlusion due to the obvious clinical relevance, quality of life and cost issues.

Remote ischaemic preconditioning of the hind limb reduces experimental liver warm ischaemia-reperfusion injury

BACKGROUND

Direct ischaemic preconditioning of the liver reduces ischaemia-reperfusion injury (IRI). Remote ischaemic preconditioning (RIPC) of a limb has been shown to reduce IRI to the heart. This study determined the effect of brief remote ischaemia to the limb in reducing early liver warm IRI.

METHODS

Twenty-eight male rabbits were allocated to four groups: sham operated, RIPC alone, IRI alone, and RIPC plus IRI. RIPC was induced in the leg with a tourniquet, before liver IRI, by three alternate cycles of 10 min ischaemia followed by 10 min reperfusion. Liver IRI was produced by total inflow occlusion for 25 min. Markers of liver injury and systemic and hepatic haemodynamics were measured for 2 h after reperfusion.

RESULTS

At 2 h, IRI alone was associated with increased serum levels of aminotransferases, and reduced mean arterial blood pressure, hepatic blood flow and peripheral oxygen saturation. There was significant improvement in these variables in animals that had RIPC before liver IRI, and hepatic venous nitrate/nitrite levels were also significantly higher.

CONCLUSION

In this experimental model RIPC appeared to reduce liver IRI.

Nanocomposite Containing Bioactive Peptides Promote Endothelialisation by Circulating Progenitor Cells: An In vitro Evaluation

OBJECTIVE

The formation of an endothelial cell layer on the luminal surface of cardiovascular devices, especially bypass grafts, is an important attribute in order to improve their patency. Endothelial progenitor cells (EPCs) have a potential role in the endothelialisation of bypass grafts. We hypothesised that a novel approach to improve endothelialisation of bypass grafts by EPCs would be the creation on the graft lumen of a microenvironment that supports EPC adhesion and differentiation.

METHODS

A new generation of nanocomposite based on silsesquioxane in the form of polyhedral oligomeric silsesquioxane (POSS) nanocages which incorporate bioactive peptides (RGD) was made into sheets. Peripheral blood mononuclear cells (PBMCs) containing EPCs isolated from six consenting young, healthy, adult volunteers were then plated both on (1) sheets of the nanocomposite with the bioactive peptide, (2) sheets of the nanocomposite without the bioactive peptide, (3) culture dishes as control and then cultured in presence of vascular endothelial growth factor (VEGF). Confirmation of endothelial and EPCs markers was carried out using fluorescence-activated cell sorter (FACS) analysis, reverse transcription polymerase chain reaction (RT-PCR) and immunostaining.

RESULTS

One to two percent of PBMCs expressed CD34 as determined by FACS analysis. Cells were demonstrated to express mRNA for the EPC markers CD34, platelet-endothelial cell adhesion molecule-1 (CD31), CD133 and vascular endothelial growth factor receptor-2(FlK-1/KDR). Endothelial cell-colony forming units were formed between day 5 and day 7 after plating. Colonies were confirmed to be endothelial like cells by immunostaining. There were significantly greater numbers of EPC colonies on the bioactive nanocomposites as compared to the nanocomposite alone and the uncoated dishes.

CONCLUSION

We report a new nanocomposite based biomaterial that has been demonstrated, in vitro, to promote endothelialisation from PBMCs containing EPCs.

Tissue engineering of blood vessels

BACKGROUND

Tissue engineering techniques have been employed successfully in the management of wounds, burns and cartilage repair. Current prosthetic alternatives to autologous vascular bypass grafts remain poor in terms of patency and infection risk. Growing biological blood vessels has been proposed as an alternative.

METHODS

This review is based on a literature search using Medline, PubMed, ISIS and CAS of original articles and reviews, and unpublished material and abstracts.

RESULTS AND CONCLUSIONS

Complete incorporation into host tissues and the maintenance of a viable and self-renewing endothelial layer are the fundamental goals to be achieved when developing a tissue-engineered blood vessel. Sourcing of cells and modulating their interaction with extracellular matrix and supporting scaffold have been the focus of intense research. Although the use of tissue-engineered blood vessels in humans is so far limited, advances in our knowledge of stem cell precursors and the development of new biomaterials should enable this technology to reach routine clinical practice within a decade.

The mechanical properties of infrainguinal vascular bypass grafts: their role in influencing patency

When autologous vein is unavailable, prosthetic graft materials, particularly expanded polytetrafluoroethylene are used for peripheral arterial revascularisation. Poor long term patency of prosthetic materials is due to distal anastomotic intimal hyperplasia. Intimal hyperplasia is directly linked to shear stress abnormalities at the vessel wall. Compliance and calibre mismatch between native vessel and graft, as well as anastomotic line stress concentration contribute towards unnatural wall shear stress. High porosity reduces graft compliance by causing fibrovascular infiltration, whereas low porosity discourages the development of an endothelial lining and hence effective antithrombogenicity. Therefore, consideration of mechanical properties is necessary in graft development. Current research into synthetic vascular grafts concentrates on simulating the mechanical properties of native arteries and tissue engineering aims to construct a new biological arterial conduit.

Ischaemic preconditioning improves microvascular perfusion and oxygenation following reperfusion injury of the intestine

BACKGROUND

Ischaemia-reperfusion (IR) injury of the intestine occurs commonly during abdominal surgery. Ischaemic preconditioning (IPC) provides a way of protecting the organ from damage inflicted by IR. This study was designed to evaluate the beneficial effect of IPC, focusing on the intestinal microcirculation and oxygenation in intestinal IR injury.

METHODS

Rats were allocated to three groups. Animals in the IR and IPC groups underwent 30 min of intestinal ischaemia followed by 2 h of reperfusion. In the IPC group this was preceded by 10 min of ischaemia and 10 min of reperfusion. Animals in the third group underwent laparotomy but no vascular occlusion. Intestinal microvascular perfusion, oxygenation and portal venous blood flow (PVF) were monitored continuously. At the end of the reperfusion period, blood samples were obtained for measurement of lactate dehydrogenase (LDH) and biopsies of ileum for histological evaluation.

RESULTS

: IPC improved intestinal microvascular perfusion and tissue oxygenation significantly at the end of the reperfusion period (P < 0.001). PVF improved significantly in the IPC compared with the IR group (P = 0.005). The serum LDH concentration was significantly lower in the IPC than the IR group (mean(s.e.m.) 667.1(86.8) versus 1973.8(306.5) U/l; P < 0.001) Histological examination showed that ileal mucosa was significantly less injured in the IPC group.

CONCLUSIONS

This study demonstrated that IPC improves intestinal microvascular perfusion and oxygenation.

Microvascular dysfunction in women with polycystic ovary syndrome

BACKGROUND

Polycystic ovary syndrome (PCOS) is associated with multiple cardiovascular risk factors and an increased prevalence of arterial dysfunction. However, microvascular dysfunction in PCOS has not been assessed.

METHODS

Subjects comprised 12 women with PCOS and 12 age-matched controls with normal ovaries. Microvascular function was assessed by observing forearm skin microvascular erythrocyte flux responses, to cumulative iontophoretic doses of 1% (w/v) acetylcholine (ACh) and 1% (w/v) sodium nitroprusside (SNP), using laser Doppler imaging.

RESULTS

Basal microvascular perfusion was comparable in PCOS and controls. The increase in skin microvascular perfusion in response to ACh was however generally blunted in PCOS women (P = 0.018). Peak ACh-induced erythrocyte flux was also less (p < 0.04) in PCOS women (125.1 +/- 21.7, i.e. 5.3-fold basal flux) than in controls (200.8 +/- 28.5, i.e. 8.3-fold basal flux). Analysis of covariance indicated this effect was unrelated to differences in body mass index or serum testosterone but serum insulin may be a weak confounder. No differences were noted between the PCOS and control groups in their response to SNP.

CONCLUSION

Despite its limited sample size studied, this is the first demonstration that women with PCOS exhibit microvascular endothelial dysfunction, indicated by an inhibited vasodilatory response to ACh.

A comparison of bile composition from heart-beating and non-heart-beating rabbit organ donors during normothermic extracorporeal liver perfusion: experimental evaluation using proton magnetic resonance spectroscopy

BACKGROUND

Organs retrieved from marginal and non-heart-beating donors (NHBDs) have sustained variable degrees of preretrieval damage that result in an increased incidence of complications. Normothermic extracorporeal liver perfusion (NELP) provides an opportunity to evaluate and resuscitate such organs. The aim of this study was to identify markers of ischemic injury in bile during perfusion of livers from heart-beating donors (HBDs) and NHBDs.

METHODS

Livers were retrieved from New Zealand white rabbits. The HBD group (n=4) had no in situ warm ischemia before retrieval and the NHBD group (n=4), 45 minutes of in situ warm ischemia before liver retrieval. After 40 minutes of postretrieval cold ischemia, all livers were dual vessel reperfused, normothermically with oxygenated buffer solution supplemented with rabbit red blood cells, for 6 hours. Bile was collected and examined with 1HMRS.

RESULTS

Perfusion bile from HBD group showed an increased concentration of bile acids, lactate, glucose, and phosphatidylcholine, but a decreased concentration of acetate as compared to retrieval bile. This trend was further enhanced in NHBD group. The mean +/- SD (in micromol/L) were bile acids (10.48 +/- 2.8 vs 26.05 +/- 12.1 vs 44.5 +/- 44.5), lactate (10.66 +/- 4.5 vs 14.66 +/- 5.2 vs 13.22 +/- 1.8), glucose (5.37 +/- 2 vs 21.2 +/- 5.0 vs 29.09 +/- 15.3), phosphatidylcholine (0.21 +/- 0.02 vs 5.57 +/- 1.7 vs 6.42 +/- 0.3), and acetate (1.8 +/- 0.5 vs 0.39 +/- 0.1 vs 0.38 +/- 0.09) for retrieval bile, HBD perfusion bile, and NHBD perfusion bile, respectively. One animal from each group did not produce any bile during perfusion.

CONCLUSIONS

1HMRS of biliary constituents revealed differences with the type of ischemia. These indices may be potential markers of the extent of warm ischemic injury and the functional activity of an extracorporeally perfused liver.

A model to study total hepatic ischemia-reperfusion injury

BACKGROUND

Most experimental animal models for studying hepatic ischemia-reperfusion injury (IRI) involve partial or segmental ischemia of the liver or a portocaval shunt procedure to avoid mesenteric congestion. However, these do not reflect the global ischemia that occurs during liver transplantation. A rabbit model of total hepatic ischemia without a portocaval shunt is described.

METHODS

Twenty male New Zealand white rabbits (3.5 +/- 0.3 kg) were allocated to four groups: group 1 (n = 5), sham-operated; group 2 (n = 5), 20-minute total hepatic ischemia; group 3 (n = 5), 25-minute total hepatic ischemia; and group 4 (n = 5), 30-minute total hepatic ischemia. Total hepatic ischemia was induced by occluding the portal inflow vessels (portal vein and artery) with an atraumatic vascular loop and were measurements taken for 2 hours during reperfusion.

RESULTS

A total hepatic ischemia of 30 minutes caused severe liver injury resulting in cardiac arrest at 2 hours of reperfusion in all five animals due to metabolic acidosis. Twenty minutes of total ischemia was tolerated and did not produce significant liver injury. Twenty-five minutes of total ischemia was tolerated but at 2 hours of reperfusion, resulted in significant liver injury (68 +/- 41, 283.0 +/- 20.5, and 835.2 +/- 52.7 U/L) compared with the sham-operated group (serum ALT, 25.4 +/- 2.7; serum AST, 47.4 +/- 3.0; serum LDH, 307.6 +/- 44.4 U/L; P < .003).

CONCLUSIONS

Rabbits can tolerate 25 minutes of total hepatic ischemia without a portosystemic shunt. This 25-minute ischemia model simulates operative conditions during liver transplantation and will be valuable in studies modulating IRI.

A review of methods currently used for assessment of in vivo endothelial function

An intact vascular endothelium is critical to the maintenance of normal arterial tone and coagulation status. Endothelial injury leading to dysfunction is thought to be a precursor to most if not all vascular disease, and has been implicated as a critical event in atherosclerosis. At present there are several methods available for detection of in vivo endothelial function, and the aim of this study was to critically review these methods. Five distinct methods were identified and studied in detail. These methods are diverse and each assesses a different vascular bed. Importantly there is no uniformity among investigators over choice of method and protocol, making it difficult to compare in vivo enothelial dysfunction between groups. These issues need to be addressed in large scale comparative analyses so that investigators can agree a common approach to endothelial function assessment.