Risk factors for aneurysm rupture in patients kept under ultrasound surveillance. UK Small Aneurysm Trial Participants

OBJECTIVE

To investigate risk factors associated with aneurysm rupture using patients randomized into the U.K. Small Aneurysm Trial (n = 1090) or monitored for aneurysm growth in the associated study (n = 1167).

SUMMARY BACKGROUND DATA

The U.K. Small Aneurysm Trial has shown that ultrasound surveillance is a safe management option for patients with small abdominal aortic aneurysms (4.0 to 5.5 cm in diameter), with an annual rupture rate of 1%.

METHODS

In the cohort of 2257 patients (79% male), aged 59 to 77 years, 103 instances of abdominal aortic aneurysm rupture were identified during the 7-year period of follow-up (1991-1998). Almost all patients (98%) had initial aneurysm diameters in the range of 3 to 6 cm, and the majority of ruptures (76%) occurred in patients with aneurysms > or =5 cm in diameter. Kaplan-Meier survival and Cox regression analysis were used to identify baseline risk factors associated with aneurysm rupture.

RESULTS

After 3 years, the annual rate of aneurysm rupture was 2.2% (95% confidence interval 1.7 to 2.8). The risk of rupture was independently and significantly associated with female sex (p < 0.001), larger initial aneurysm diameter (p < 0.001), lower FEV1 (p = 0.004), current smoking (p = 0.01), and higher mean blood pressure (p = 0.01). Age, body mass index, serum cholesterol concentration, and ankle/brachial pressure index were not associated with an increased risk of aneurysm rupture.

CONCLUSIONS

Within this cohort of patients, women had a threefold higher risk of aneurysm rupture than men. Effective control of blood pressure and cessation of smoking are likely to diminish the risk of rupture.

Rapid changes in the coagulant proteins on saphenous vein endothelium in response to arterial flow

Healthy endothelium provides a nonthrombogenic surface. In this study the authors investigated the effect of arterial flow on the saphenous vein endothelial expression of proteins controlling thrombosis. Human saphenous vein segments, freshly excised from patients, were placed in a validated in vitro circuit with flow conditions shown to simulate arterial or venous circulations. In separate experiments, placement of an external polytetrafluoroethylene (PTFE) stent was used to differentiate the effects of pulsatile wall deformation and shear stress, while addition of drugs to the vein perfusate allowed study of the role of ion channels in transducing the response of the vein to arterial flow. Endothelial concentrations of thrombomodulin, nitric oxide synthase, tissue factor, and tissue plasminogen activator were assessed by quantitative immunohistochemistry and Western blotting of endothelial cell lysates, in paired vein samples, in comparison to control proteins. Arterial flow conditions caused a rapid and significant reduction in the endothelial concentration of thrombomodulin: The immunostaining area decreased from 80.1 +/- 7.0 to 48.3 +/- 5.0 and 32.9 +/- 3.0% at 45 and 90 minutes respectively, p = 0.01. These findings were confirmed by Western blotting. The reduction in thrombomodulin concentration was unaffected by eliminating vein wall deformation by placement of an external PTFE stent or by including the K+ channel blocker tetraethylammonium (TEA) in the vein perfusate. In contrast, thrombomodulin concentrations remained high when blockers of stretch-activated cation and calcium channels were included in the vein perfusate. The endothelial concentration of nitric oxide synthase increased after 90 minutes of arterial flow and this change was abolished when TEA was included in the vein perfusate. Arterial flow induced rapid changes in saphenous vein antithrombotic proteins. Different cation channels mediated the flow-induced changes in thrombomodulin and nitric oxide synthase.

Fibrinogen up-regulates the expression of monocyte chemoattractant protein 1 in human saphenous vein endothelial cells

High concentrations of fibrinogen in plasma have been associated with an increased risk of saphenous vein graft pathology. We have investigated the ability of fibrinogen to up-regulate the expression of monocyte chemoattractant protein 1 (MCP-1) in cultured human saphenous vein endothelial cells (HSVEC) isolated from saphenous vein. Increasing concentrations of fibrinogen (0-4 microM) stimulated a 20-fold increase in MCP-1 secretion within 4 h. Incubation of HSVEC with 2 microM fibrinogen for 4 h also caused a 2-fold increase in the MCP-1-to-glyceraldehyde-3-phosphate dehydrogenase mRNA ratio. The fibrinogen-mediated MCP-1 secretion fell to basal levels after preincubation of HSVEC with the complex of fibrinogen fragments D and E but remained unchanged after preincubation of HSVEC with either fibrinogen fragment E, s-ICAM-1 or the pentapeptide GRGDV. In contrast, fibrinogen fragment D acted as a potent inhibitor of fibrinogen-mediated MCP-1 secretion. Labelled fibrinogen fragment D bound to HSVEC with a K(d) of 6.5 microM. These findings indicate that fibrinogen, at physiological concentrations, uses an epitope on the fibrinogen D domain to bind to a receptor on HSVEC to up-regulate MCP-1 expression and secretion. This receptor seems to be distinct from intercellular adhesion molecule 1 and the integrins previously recognized as fibrinogen receptors.

Inhibition of prostaglandin E2 synthesis in abdominal aortic aneurysms: implications for smooth muscle cell viability, inflammatory processes, and the expansion of abdominal aortic aneurysms

BACKGROUND

There is no treatment proven to limit the growth of abdominal aortic aneurysms, in which the histological hallmarks include inflammation and medial atrophy, with apoptosis of smooth muscle cells and destruction of elastin.

METHODS AND RESULTS

Aneurysm biopsies were used for explant cultures, the preparation of smooth muscle cell cultures, and isolation of macrophages. Tissue macrophages stained strongly for cyclooxygenase 2. Prostaglandin E2 (PGE2) concentrations in aneurysm tissue homogenates, conditioned medium from explants, and isolated macrophages were 49+/-22 ng/g, 319+/-38 ng/mL, and 22+/-21 ng/mL, respectively. PGE2 inhibited DNA synthesis and proliferation in normal aortic smooth muscle cells (IC50, 23.2+/-3.8 and 23.6+/-4.5 ng/mL, respectively). In smooth muscle cells derived from aneurysmal aorta, PGE2 also caused cell death, with generation of oligonucleosomes. Conditioned medium from the mixed smooth muscle and monocyte cultures derived from explants also had potent growth-inhibitory effects, and fractionation of this medium showed that the growth-inhibitory molecule(s) coeluted with PGE2. In explants, indomethacin 10 micromol/L or mefenamic acid 10 micromol/L abolished PGE2 secretion and significantly reduced IL-1beta and IL-6 secretion. In a separate case-control study, the expansion of abdominal aortic aneurysms was compared in 15 patients taking nonsteroidal anti-inflammatory drugs and 63 control subjects; median growth rates were 1.5 and 3.2 mm/y, respectively, P=0.001.

CONCLUSIONS

The adverse effects of PGE2 on aortic smooth muscle cell viability and cytokine secretion in vitro and the apparent effect of anti-inflammatory drugs to lower aneurysm growth rates suggest that selective inhibition of PGE2 synthesis could be an effective treatment to curtail aneurysm expansion.

The influence of indomethacin on the metabolism and cytokine secretion of human aneurysmal aorta

INTRODUCTION

inflammation and proteolysis are important processes in the development of abdominal aortic aneurysms (AAAs). Prostaglandin E2 (PGE2) (a product of cyclo-oxygenase 2), other inflammatory mediators and proteolytic enzymes are produced in high quantities in the aneurysm wall. We developed an explant culture system for AAA tissue to assess the effects of potential drug therapies.

METHODS

full thickness biopsies of human AAA were established in culture in the presence or absence of indomethacin (a cyclo-oxygenase-2 inhibitor). The conditioned medium was collected at 48 h intervals and analysed for products of collagen breakdown, matrix metalloproteinases, PGE2 and inflammatory cytokines. Explant viability was assessed by histology, glucose consumption, lactate dehydrogenase release and demonstration of protein synthesis in the tissue.

RESULTS

nuclear morphology was maintained for 4 or more days and this, together with biochemical assays, indicated that AAA explants were viable in short-term culture. Indomethacin (10 microM) markedly reduced AAA explant production of prostaglandin E2 from 320 ng/ml to 3.3 ng/ml (p=0.028, n=6). Indomethacin also reduced the release of interleukin-1beta (IL-1beta) (from 166 pg/ml to 9.8 pg/ml, p =0.04, n=5) and interleukin-6 (IL-6) (from 119 ng/ml to 57 ng/ml, p=0.028, n=6), but had no effect on monocyte chemotactic protein 1 or matrix metalloproteinase-9 secretion.

CONCLUSIONS

short-term explants of AAA are a novel method to assess the effects of drugs on aneurysm tissue. Indomethacin reduces the production of PGE2, IL-1beta and IL-6, suggesting that cyclo-oxygenase-2 inhibitors may control the inflammation in the aneurysm wall and potentially limit AAA growth.

Uptake of tetracycline by aortic aneurysm wall and its effect on inflammation and proteolysis

BACKGROUND

Proteolytic degradation of the aortic wall by matrix metalloproteinases (MMPs) is considered important in the pathogenesis of abdominal aortic aneurysms (AAAs). Many of these MMPs are inhibited by tetracycline derivatives, which may have the potential to retard aneurysm growth.

METHODS

Patients undergoing elective repair of an AAA (n = 5) received an intravenous bolus of tetracycline (500 mg) on induction of anaesthesia and levels of tetracycline in serum, aneurysm wall and mural thrombus were assessed by microbiological assay. In a separate series of patients (n = 7) aneurysm biopsies were placed into explant culture (with and without tetracyline) and the accumulation of protein, hydroxyproline, MMP-9, interleukin (IL) 6 and monocyte chemoattractant protein (MCP) 1 in the medium was assessed by colorimetric assay or immunoassay.

RESULTS

At aortic cross-clamping the median concentration of tetracycline was 8.3 microg/ml in serum, 2.9 microg per g tissue in aortic wall and zero in mural thrombus. Tetracycline inhibited, in a concentration-dependent manner, both MMP-9 and MCP-1 secretion (P = 0.022 and P = 0.018 respectively), but did not alter hydroxyproline or IL-6 secretion. At the highest concentration of tetracycline (100 microg/ml) median MMP-9 secretion was reduced from 27 to 5 ng/ml (P = 0.007) and median MCP-1 secretion was reduced from 50 to 10 ng/ml (P = 0.008).

CONCLUSION

Tetracycline rapidly penetrates the aortic wall, but the concentration achieved may be insufficient to alter collagen turnover through limitation of MMP production or activity.

Vascular surgical society of great britain and ireland: non-steroidal anti-inflammatory drugs to treat abdominal aortic aneurysm

BACKGROUND: Prostaglandin E2 (PGE2) and inflammatory cytokine levels are raised in the wall of abdominal aortic aneurysms (AAAs) and inflammatory processes appear to contribute to aneurysm expansion. The effect of PGE2 on aortic smooth muscle cells (SMCs) and the influence of indomethacin on AAA growth and production of inflammatory mediators were investigated. METHODS: Proliferation and apoptosis of aortic SMCs cultured with PGE2 were assessed by 5-bromo-2'-deoxyuridine uptake and oligonucleosome enzyme-linked immunosorbent assay. Full-thickness AAA explant cultures were used to measure the secretion of PGE2, interleukin (IL) 1beta and IL-6 in the presence and absence of indomethacin. In a case-control study, the effect of non-steroidal anti-inflammatory drugs (NSAIDs), including indomethacin, on AAA growth was examined. RESULTS: PGE2 suppressed proliferation (IC50 6 ng ml-1) and increased apoptosis of aneurysm SMCs. Indomethacin diminished secretion of PGE2, IL-1beta and IL-6 by AAA explants (see Table below). The median AAA growth rate of 19 patients taking NSAIDs was 1.8 (range 0-11.2) mm per year compared with 3.2 (0.4-10.9) mm per year in 59 patients (matched for age, sex, smoking and initial AAA diameter) not taking these drugs (P = 0.004). CONCLUSION: PGE2 is produced in the AAA wall in concentrations that are detrimental to SMCs. Indomethacin reduces PGE2, IL-1beta and IL-6 synthesis in aneurysm tissue and NSAIDs appear to reduce AAA growth. These drugs warrant further consideration for the treatment of AAA.

Vascular surgical society of great britain and ireland: uptake of tetracycline in aortic aneurysms: influence on inflammation and proteolysis

BACKGROUND: Derivatives of tetracycline (TC), through their inhibition of matrix metalloproteinases (MMPs), have been suggested as potential medical therapy to limit growth of abdominal aortic aneurysms (AAAs), but penetration of the aortic wall in vivo has not been demonstrated. The uptake and concentration of TC in aneurysm wall, and its effect on MMP and cytokine production, were investigated. METHODS: Patients undergoing elective AAA repair (n = 5) were given a single bolus of intravenous TC 500 mg on induction of anaesthesia. The TC concentrations achieved in serum, aneurysm wall and mural thrombus were determined using a microbiological assay. In separate patients, not given TC, AAA biopsy explants were established and the effect of TC (0, 10 and 100 &mgr;g ml-1) on hydroxyproline, MMP-9 and cytokine (MCP-1 and interleukin (IL) 6) secretion were investigated using colorimetric assays and immunoassays. RESULTS: At the time of aortic cross-clamping median TC concentration was 9 (range 5-12) &mgr;g ml-1 in serum, 2.7 (1.3-9. 6) &mgr;g g-1 in AAA wall and nil in mural thrombus (see Table ). CONCLUSION: TC rapidly penetrates AAA wall in vivo and inhibits MMP-9 and MCP-1 release by AAA explants. This suggests that TCs have the potential to limit aneurysm growth.

Arterial flow conditions downregulate thrombomodulin on saphenous vein endothelium

BACKGROUND

The antithrombogenic properties of venous endothelium may be attenuated when vein is implanted in the arterial circulation. Such changes may facilitate thrombosis, which is the final common pathway for saphenous vein arterial bypass graft occlusion.

METHODS AND RESULTS

Using human saphenous vein in a validated ex vivo flow circuit, we investigated (1) the possibility that arterial flow conditions (mean pressure, 100 mm Hg, 90 cpm, approximately 200 mL/min) alter the concentration of proteins involved in regulating thrombosis at the vessel wall and (2) the influence of ion channel blockade on such effects. Concentrations of thrombomodulin and tissue factor were quantified by Western blotting (ratio of von Willebrand factor staining) and immunohistochemistry (as a percentage of CD31-staining area). Thrombomodulin concentrations after 90 minutes of venous and arterial flow conditions were quantified by immunostaining (68.9+/-4.8% and 41.0+/-3.0% CD31, respectively; P<0.01) and by Western blotting (1.35+/-0.20 and 0. 15+/-0.03 ratio of von Willebrand factor, respectively; P<0.01). The ability of endothelial cells to generate activated protein C also decreased from 62+/-14 to 19+/-10 ng. min-1. 1000 cells-1 (P=0.01). The significant reduction in thrombomodulin was attenuated if calcium was removed from the perfusate but not by external vein stenting. Inclusion in the vein perfusate of drugs that reduce calcium entry (including Gd3+, to block stretch-activated ion channels, and nifedipine) abolished the reduction in thrombomodulin concentration observed after arterial flow conditions. In freshly excised vein, negligible concentrations of tissue factor were detected on the endothelium and concentrations did not increase after 90 minutes of arterial flow conditions, although the inclusion of nifedipine caused the immunostaining to increase from 3.0+/-0.4% to 8.5+/-0.7% CD31 (P<0.02).

CONCLUSIONS

In saphenous vein endothelium exposed to arterial flow conditions, there is rapid downregulation of thrombomodulin, sufficient to limit protein C activation, by a calcium-dependent mechanism.

Does nibbling or grazing protect the peripheral arteries from atherosclerosis?

BACKGROUND

It has been suggested that frequent food intake is metabolically advantageous. We investigated whether meal frequency was associated with the development of peripheral arterial disease among smokers.

DESIGN

Hospital-based case-control study of smokers, recruited from outpatient clinics and inpatient wards at two London teaching hospitals.

METHODS

Two-hundred and ninety-one smokers, newly referred with peripheral arterial disease (cases) and 828 age- and sex-matched smokers without smoking-related disorders and with negative Rose questionnaire responses for intermittent claudication (controls) were recruited. All cases and controls completed a validated questionnaire concerning dietary habits. Odds ratios for peripheral arterial disease in association with several dietary variables were calculated, after adjustment for confounding variables.

RESULTS

After adjustment for age, sex, pack-years of smoking, diabetes, hypertension and body mass index, the odds ratio for peripheral arterial disease among those smokers eating between meals (grazing) compared with those who did not, was 0.54 (95% confidence interval 0.42-0.83; P < 0.001). Among cases and controls, grazing was also associated with significantly lower plasma cholesterol concentrations (median 5.67 mmol/l in grazers compared with 6.08 mmol/l in non-grazers; P < 0.001) in those with apparently similar overall fat intakes. Neither plasma lipoprotein (a) nor fibrinogen concentrations varied with meal frequency.

CONCLUSIONS

In smokers, grazing was associated with a reduced risk of developing symptomatic peripheral atherosclerosis. This is the first study to demonstrate the apparent benefits of grazing on a cardiovascular end-point.

Outcome of femoropopliteal angioplasty

OBJECTIVE

To assess prospectively the outcome of femoropopliteal angioplasty and investigate prognostic indicators of success.

BACKGROUND

Percutaneous transluminal angioplasty is commonly used to treat symptomatic femoropopliteal stenoses or occlusions, but the durability of the procedure is uncertain.

METHODS

Seventy-four consecutive patients treated by femoropopliteal angioplasty for intermittent claudication (43), rest pain (4), and tissue loss (27) were followed by assessment of symptoms, ankle-brachial pressure index (ABPI) to measure hemodynamic outcome, and duplex monitoring of velocity gradient at the angioplasty site to identify restenosis at 1 day and 3, 6, 9, and 12 months. Univariate comparisons, life table analysis, and backward stepwise regression were used to investigate factors predicting the symptomatic and hemodynamic outcome and restenosis.

RESULTS

Technical success was obtained in 67 patients (91%); failure occurred in 7 patients. At 1 year, a successful symptomatic outcome was achieved in 35 patients (51%), hemodynamic success was achieved in 41 patients (58%), and restenosis developed in 39%. ABPI at 24 hours after angioplasty was the most significant variable predicting a symptomatic outcome, hemodynamic outcome, and restenosis at 12 months. Life table analysis demonstrated that in 24% of patients with a 24-hour ABPI > or =0.9, restenosis developed by 12 months, compared with 64% of patients with a 24-hour ABPI <0.9.

CONCLUSION

Only half of the patients treated by femoropopliteal angioplasty had symptomatic improvement at 1 year, raising concern about the cost-benefit ratio of this procedure. Restoration of ABPI to >0.9 predicted a favorable outcome.

Molecular and cellular changes in vein grafts: influence of pulsatile stretch

Adaptation of saphenous vein, with its intrinsic myogenic tone, from the low-pressure, minimally pulsatile flow of the venous system to the pulsatile flow of the arterial circulation is a minor miracle. Changes in gene expression caused by the pulsatile circumferential deformation (cyclic strain) initiate changes in gene expression, which lead to both vein graft adaptation and pathology. Removal of circumferential deformation by external stenting attenuates the early changes in gene expression and the later development of intimal hyperplasia. Pathways for the transduction of cyclic strain into cellular events have been elucidated in cultured vascular cells. The important second messengers include calcium and reactive oxygen species.

Human saphenous vein endothelial cells express a tetrodotoxin-resistant, voltage-gated sodium current

Whole-cell patch-clamp electrophysiological investigation of endothelial cells cultured from human saphenous vein (HSVECs) has identified a voltage-gated Na+ current with a mean peak magnitude of -595 +/- 49 pA (n = 75). This current was inhibited by tetrodotoxin (TTX) in a concentration-dependent manner, with an IC50 value of 4.7 microM, suggesting that it was of the TTX-resistant subtype. An antibody directed against the highly conserved intracellular linker region between domains III and IV of known Na+ channel alpha-subunits was able to retard current inactivation when applied intracellularly. This antibody identified a 245-kDa protein from membrane lysates on Western blotting and positively immunolabeled both cultured HSVECs and intact venous endothelium. HSVECs were also shown by reverse transcription-polymerase chain reaction to contain transcripts of the hH1 sodium channel gene. The expression of Na+ channels by HSVECs was shown using electrophysiology and cell-based enzyme-linked immunosorbent assay to be dependent on the concentration and source of human serum. Together, these results suggest that TTX-resistant Na+ channels of the hH1 isoform are expressed in human saphenous vein endothelium and that the presence of these channels is controlled by a serum factor.

Vascular damage from smoking: disease mechanisms at the arterial wall

The products of tobacco combustion are absorbed into the systemic circulation. Absorbed nicotine stimulates the release of catecholamines, whilst other products (perhaps including nicotine) injure the arterial endothelium and promote atherogenesis. Free radicals and aromatic compounds diminish the endothelial synthesis of nitric oxide, causing impaired endothelium-dependent relaxation of arteries, the earliest clinical sign of endothelial dysfunction. Smoking alters the shear forces and rheology at the endothelial surface and these changes enhance the effects of products of tobacco combustion to upregulate leucocyte adhesion molecules on the endothelial surface. The increased oxidation of low density lipoprotein (LDL) in smokers has synergistic effects to promote monocyte adhesion and monocyte migration into the subintimal space. Continued stimulation of intimal cells by oxidized LDL leads to the development of atherosclerosis. Many of these effects are ameliorated by high concentrations of vitamin C. Smoking also potentiates thrombosis at the dysfunctional endothelium by increasing the concentration of plasma fibrinogen and altering the activity of platelets. All these proatherogenic effects of smoking to injure the endothelium also are observed, albeit to lesser extent, in passive smokers.

The effects of potassium channel openers on saphenous vein exposed to arterial flow

OBJECTIVES

To assess the sensitivity of saphenous vein to potassium channel opening drugs (KCOs).

METHODS

Saphenous vein, harvested at bypass surgery or high ligation for correction of varicose veins, was exposed to an in vitro flow circuit and vasomotor responses assessed by organ bath pharmacology.

OUTCOME MEASURES

Effective drug concentrations for 50% reduction in vein ring tension (IC50).

RESULTS

Vein rings pre-contracted with phenylephrine showed a concentration-dependent relaxation to all the KCOs tested with a potency ranking of HOE 234 > cromakalim > pinacidil > diazoxide. The relaxation to cromakalim was endothelium-independent and was inhibited by glibenclamide (an ATP-sensitive K+ channel blocker). The sensitivity of vein rings to cromakalim increased after exposure to arterial flow conditions for 90 minutes (IC50 before 1.7 +/- 0.25 microM and after 0.25 +/- 0.08 microM, p > 0.001). This effect was not evident after 90 min of venous flow conditions, 2.19 +/- 0.49 microM. When the workload on vein, exposed to arterial flow conditions, was reduced mechanically by external stenting with PTFE the increased sensitivity to cromakalim was abolished.

CONCLUSIONS

Saphenous vein has ATP-sensitive K+ channels responsive to KCOs. The increased sensitivity to cromakalim, induced by arterial flow conditions, may represent an endogenous protective mechanism limiting ischaemic damage resulting from the higher workload imposed on grafted vein.

Unrestricted usage of immunoglobulin heavy chain genes in B cells infiltrating the wall of atherosclerotic abdominal aortic aneurysms

The aim of this study was to provide evidence for the hypothesis that the B cell rich infiltrate concentrated in the adventitia of atherosclerotic abdominal aortic aneurysms is an autoimmune response to specific tissue antigens. Detailed histological examination of biopsies from 26 atherosclerotic abdominal aortic aneurysms showed in the adventitia, the presence of lymphoid follicles in 7/26 (27%) and of plasma cells in all cases. DNA prepared from the outer aneurysm wall (n = 25) was amplified using the polymerase chain reaction to investigate the repertoire of the immunoglobulin heavy chain (VH) genes used. Amplification of the VDJ region of VH, using both framework 2 and 3 primers, revealed unrestricted usage of the VH gene in 24/25 cases. The only case where restricted usage of the VH genes was observed, might have been attributable to severe virally-induced tissue inflammation. These results indicate that, in the vast majority of atherosclerotic abdominal aortic aneurysms, the B cell rich adventitial infiltrates are not an autoimmune response to a limited repertoire of tissue antigens.

An association between arterial pulse pressure and variation in the fibrillin-1 gene

OBJECTIVE

To investigate whether variation in the fibrillin-1 gene was associated with blood pressure in healthy middle aged men, as had been observed in patients with abdominal aortic aneurysm.

DESIGN, SETTING, AND PATIENTS

Middle aged men (n = 245), aged 50 to 61 years, were recruited from one of the nine general practices participating in the second Northwick Park heart study. Blood samples were obtained for the preparation of genomic DNA and analysis of plasma variables.

MAIN OUTCOME MEASURES

Systolic, diastolic, and pulse pressures; fibrillin-1 genotype characterised with a four allele variable tandem nucleotide repeat polymorphism in intron 28.

RESULTS

In healthy middle aged men only three common genotypes were observed: 2-2 (frequency 54.1%), 2-3 (16%) and 2-4 (15%). The mean arterial systolic (and pulse) pressure varied according to fibrillin-1 genotype: 2-4 genotype, 126-3 (47.6) mm Hg; 2-2 genotype, 131.0 (51.3) mm Hg; and 2-3 genotype, 135.5 (54.2) mm Hg. The median pulse pressure was 50 mm Hg. Distribution of men around the median pulse pressure, according to genotype, showed a significant trend for patients of 2-4 genotype to have the lowest pulse pressures, those of 2-2 genotype to have intermediate pressures, and those of 2-3 genotype to have the highest pulse pressures (p = 0.003 for healthy men).

CONCLUSIONS

There appears to be a significant association between fibrillin-1 genotype and arterial pulse pressure in men aged 50 to 61 years.

Dilatation of saphenous vein grafts by nitric oxide

OBJECTIVES

To investigate firstly whether flow-dependent vasodilation is maintained in vein grafts, and secondly whether nitric oxide donors dilate vein grafts to improve the flow through graft stenoses.

DESIGN, MATERIALS AND METHODS

The vasodilatation of mature patent vein grafts, in response to reactive hyperaemia and glyceryl trinitrate (GTN), was assessed by the change in external diameter using duplex ultrasonography. The severity (ratio of proximal systolic velocity, V1, to peak systolic velocity at the stenosis, V2, of vein graft stenoses was determined by duplex ultrasonography before and after 24 h of local application of GTN patches.

RESULTS

In post-occlusion hyperaemia the diameter of patent distal vein grafts (n = 7) increased to a maximum of 112 +/- 1.9% of resting diameter after 2 min, p = 0.026. The diameter increased further to 117 +/- 2.5% of the resting value 5 min after oral GTN (n = 5), p = 0.007. The velocity ratio, V2/V1, through graft stenoses (n = 6) decreased by 20 +/- 5% after application of GTN patches, principally as a result of reduction in V2, mean difference 0.8, p = 0.15. The changes in response to GTN were more evident for proximal than distal vein graft stenoses.

CONCLUSION

Flow-induced vasodilatation responses, which have been attributed to the endothelial release of nitric oxide, are maintained in patent vein grafts: the grafts dilate even further in response to GTN. The application of GTN patches close to a vein graft stenoses appears to reduce the velocity ratio through vein graft stenoses. GTN patches might be used to reduce the risk of graft occlusion when there is a delay between the detection and the treatment of haemodynamically significant graft stenoses.

Development of an in vitro model to study the response of saphenous vein endothelium to pulsatile arterial flow and circumferential deformation

OBJECTIVES

To develop an in vitro model of human saphenous vein bypass to facilitate study of the early adaptive responses of venous endothelium to arterial flow conditions. DESIGN MATERIAL AND METHODS: Segments of human saphenous vein (with or without external polytetrafluoroethylene (PTFE) stents to limit circumferential and radial deformation) were mounted in a bypass circuit and subjected to pulsatile flow with oxygenated Krebs solution to simulate arterial or venous flow conditions for a period of 90 min. The viability of the vein was assessed by the tissue ATP concentration and vasomotor responses to phenylephrine, sodium nitroprusside and bradykinin (endothelium-dependent). Immunohistochemistry was used to assess both endothelial preservation (CD31) and the expression of proteins involved in leukocyte adhesion: E-selectin, P-selectin and ICAM-1. Freshly excised veins were used as controls.

RESULTS

The concentration of ATP was 320 +/- 11 nmol/g in freshly excised vein (n = 8) and following exposure to the arterial flow circuit increased to 566 +/- 60 nmol/g (n = 8, paired t-test, p = 0.003) in unstented veins and to 421 +/- 49 nmol/g (n = 8, paired t-test, p = 0.002) in externally stented veins (with PTFE). Both endothelium-dependent and sodium nitroprusside-induced vasodilatation responses were preserved after veins were exposed to the arterial flow circuit, but the sensitivity to phenylephrine was increased: EC50 decreasing from 9 microM, p = 0.008. There was a 5-10% decrease in staining area for CD31 after veins, stented or unstented, were exposed to the arterial flow circuit. However, after exposure to the arterial flow circuit, the staining area ratio for ICAM-1/CD31, which remained unchanged in externally stented veins, increased two-fold in unstented veins, p > 0.01: there were no changes in the staining area ratio P-selectin/CD31 and no staining for E-selectin was observed.

CONCLUSION

Vasomotor responses and tissue ATP concentration indicate that the viability of saphenous vein can be maintained for up to 90 min in an ex vivo flow circuit and the CD31 staining indicated endothelial preservation. This opens up the possibility of investigating the early changes in saphenous vein endothelium following exposure to arterial pressure, as at bypass surgery. First results suggest that there is rapid upregulation of the leukocyte adhesion molecule ICAM-1, which can be prevented by limiting the circumferential deformation of the vein with an external PTFE stent.

Circumferential deformation and shear stress induce differential responses in saphenous vein endothelium exposed to arterial flow

Adaptation of saphenous vein to the hemodynamic stresses of the arterial circulation is critical to the maturation of vein bypass grafts. We have investigated early adaptive responses of venous endothelium by placing excised human saphenous vein in a bypass circuit with either venous or arterial flow conditions, using external stenting to resolve the effects of longitudinal (shear) from circumferential stress. Endothelial protein concentrations were assessed by immunostaining area (ratio of protein/CD31) and Western blotting of endothelial cell lysates (staining ratio protein/vWf). In both unstented and stented veins nitric oxide synthase increased after 90 min of arterial flow: twofold increase of immunostaining area (P = 0.001), four- to fivefold increase by Western blotting (P = 0.02), and increased A23187mediated maximum endothelium-dependent relaxation of vein rings (P = 0.01). In unstented veins, ICAM-1 concentration was increased after 45 min of arterial flow: twofold increase by immunostaining (P = 0.001) and Western blotting (P = 0.038), with maximum fibrinogen-mediated endothelium-dependent relaxation increasing from 55.9+/-4.9 to 97+/-2.1% (P = 0.01). In contrast, in unstented veins there was a threefold decrease of VCAM-1 and no change in P-selectin after arterial flow for 45 and 90 min, respectively. However, no changes in ICAM-1 and VCAM-1 were observed in stented veins. The flow-induced alterations in nitric oxide synthase, ICAM-1, and VCAM-1 were abolished when 3 mM tetraethylammonium ion (K+ channel blocker) was included in the vein perfusate. The very rapid changes in ICAM-1 and VCAM-1 expression are a response to circumferential stress, whereas the slower upregulation of nitric oxide synthase is a response to longitudinal (shear) stress. Similar changes could influence the adhesiveness of endothelium in newly implanted saphenous vein bypass grafts.

Risk factors associated with the development of peripheral arterial disease in smokers: a case-control study

PURPOSE AND METHOD

A hospital based case-control study was designed to investigate what aspects of smoking and what co-factors of smoking are associated with the development of peripheral arterial disease (PAD). Cases were 291 smokers, newly referred with PAD, and controls were 828 age and sex matched smokers without PAD.

RESULTS

Reported recent tobacco usage was similar in cases and controls but total tobacco exposure was associated with the risk of PAD-adjusted odds ratios (ORs) increasing with tertile of pack-years smoked to reach 1.63 (95% CI, 1.11-2.39; P = 0.011), for the highest tertile ( > 48 pack-years) compared with smokers in the lowest tertile (< 31 pack-years). Cases reported smoking significantly lower tar and nicotine yield cigarettes than controls, but tended to inhale more deeply, and had significantly higher plasma concentrations of cotinine. ORs for PAD were significantly and independently increased by systolic blood pressure > 160 mmHg (8.1 (5.2 13.0); P < 0.0001), history of hypertension (2.4 (1.5-3.2); P = 0.0003) and apolipoprotein B > 0.9 g/l(3.8 (2.3-7.6); P = 0.008).

CONCLUSIONS

Increased total exposure to tobacco and the ability to smoke tobacco in a way which maximises nicotine yield are associated with increased risk of smokers developing PAD. There is no evidence that smoking low tar cigarettes reduces this risk, whereas both hypertension (particularly systolic) and high levels of apolipoprotein B, increase this risk.

The influence of diabetes on the vasomotor responses of saphenous vein and the development of infra-inguinal vein graft stenosis

There has been a prejudice that diabetes modulates the function of saphenous vein in a manner that predisposes to bypass graft failure, although most of the evidence accrues from animal studies. We have investigated the effect of diabetes on the vasodilator responses and ultrastructure of saphenous vein harvested from patients undergoing infrainguinal bypass surgery for limb salvage and the development of stenoses within the vein grafts. Of 55 consecutive patients undergoing vein bypass surgery for critical ischemia, 16 (29%) were diabetic: diabetes was not a risk factor for graft stenosis, which occurred in 17 of 56 (30%) grafts. Endothelium-dependent relaxation by nitric oxide pathways stimulated after receptor activation (bradykinin and thrombin) was not different in vein rings from diabetic (n = 12) and nondiabetic patients (n = 12). Prostarioid-mediated vasorelaxation was absent in vein rings from diabetic patients, and the production of 6-keto prostaglandin F(1alpha) (PGF(1alpha)) from diabetic vein was only 66 +/- 27 pg x cm-2 x min-1 compared with 112 +/- 20 pg x cm-2 x min-1 from control vein (P = 0.011). Fibrinogen-mediated vasorelaxation, normally inhibited by K+ channel blockers, was negligible in vein from diabetic patients. No ultrastructural differences were observed between the endothelium of saphenous vein harvested from diabetic and nondiabetic patients. However, diabetes was associated significantly with the presence of spiraled collagen in media. The maintenance of receptor-activated stimulation of nitric oxide pathways and the damping of the response to fibrinogen in saphenous vein endothelium may provide, in part, for the good prognosis of vein graft surgery in diabetic patients: diabetes is not a risk factor for early (12 months) infrainguinal vein graft stenosis.

Influence of hypercholesterolemia and adventitial inflammation on the development of aortic aneurysm in rabbits

Abdominal aortic aneurysms are characterized by intimal atherosclerosis, disruption and attenuation of the elastic media, and a variable adventitial inflammatory infiltrate. We have developed an animal model of this disorder to evaluate the contribution of hypercholesterolemia, medial injury, and adventitial inflammation to aneurysmal dilatation. To accomplish this, we used periaortic application of calcium chloride, which induced both medial injury with calcification and endothelial injury. Ultrasonography was used to demonstrate the dilatation and thickening of the aortic wall. Over the first 3 weeks after periaortic application of 0.25 mol/L CaCl2, the external aortic diameter increased from 3.5 +/- 0.5 to 4.2 +/- 0.8 mm, but the ID remained unchanged. This apparent wall thickening was accompanied by vascular remodeling, and biochemical changes included approximately 50% reduction in tissue hydroxyproline concentration and increased activity of gelatinases (matrix metalloproteinase [MMP]-2 and MMP-9). Independently, cholesterol feeding to induce hypercholesterolemia or the concomitant periaortic application of thioglycollate had little effect on the histological, biochemical, or diameter changes. Together, hypercholesterolemia and thioglycollate were associated with rapid aortic dilatation in CaCl2, treated animals but not controls: after 3 weeks, the ID and OD had doubled, the OD increasing from 3.5 +/- 0.4 to 7.1 +/- 0.4 mm, P = .005. The remarkable feature that accompanied this dilatation was the infiltration of cells, mostly foamy macrophages, into the adventitia, with a further reduction in hydroxyproline concentration. Adventitial inflammation may provide the critical stimulus to dilatation of an aorta with preexisting intimal and medial injury.