Fibrin as a factor in atherogenesis

Assessing cardiovascular disease: looking beyond cholesterol

PURPOSE OF REVIEW

The low-density lipoprotein (LDL)-cholesterol level is a weak predictor of developing cardiovascular (CV) disease and can only explain a small proportion of CV risk. It is not used to determine CV risk on either the atherosclerotic cardiovascular disease (ASCVD) calculator in the United States, or the Qrisk3 in the UK.A study in JAMA in 2022 suggested that ' the absolute benefits of statins are modest and may not be strongly mediated through the degree of LDL reduction '. Perhaps it is time to look beyond cholesterol to a different causal model - the 'thrombogenic' model of ASCVD.

RECENT FINDINGS

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) pandemic demonstrated that infectious agents damage the endothelium and the glycocalyx - the glycoprotein layer protecting underlying endothelial cells. There are numerous other conditions leading to this kind of damage, which can trigger thrombus formation, causing strokes and myocardial infarctions.Although these are acute events, they highlight a mechanism for the development of ASCVD which centres on endothelial damage and thrombus formation as both the primary causal mechanism for acute events, and the driver behind progression towards atherosclerotic plaque development.

SUMMARY

The cholesterol hypothesis, that a raised LDL is directly causal for ASCVD, does not adequately explain cardiovascular risk in individuals, or populations. An alternative 'thrombogenic' hypothesis is proposed as a more valid causal model.

Inflammation and necrosis syndrome is associated with alterations in blood and metabolism in pigs

BACKGROUND

Swine inflammation and necrosis syndrome (SINS) can lead to significant clinical alterations at tail, ears, claws and other parts of the body in suckling piglets, weaners and fatteners. Clinical findings are associated with vasculitis, intima proliferation and thrombosis. The syndrome can be found in newborns, indicating a primarily endogenous aetiology. It has been hypothesized that SINS is triggered by gut-derived microbial-associated molecular patterns, causing derangements in liver metabolism and activity of peripheral white blood cells involving inflammation and blood haemostasis. In order to characterize these metabolic derangements of SINS for the first time, red and white blood counts, parameters of blood haemostasis, serum metabolites and acute phase proteins in the serum were analysed in 360 piglets, weaners and fatteners, each with significantly different SINS scores.

RESULTS

SINS scores and haematological/clinical chemical parameters were significantly associated (P < 0.05), especially in weaners and fatteners. Higher degrees of clinical SINS were associated with increased numbers of monocytes and neutrophils. Blood coagulation was altered in weaners and a thrombocytopenia was found in fatteners. Additionally, acute phase proteins, especially C-reactive protein and fibrinogen were increased in serum. Serum metabolites and serum liver enzymes were slightly altered. Aspartate transaminase levels overall exceeded physiological limit and increased in parallel with SINS scores in fatteners.

CONCLUSION

Clinical inflammation and necrosis at tail, ears, claws and other parts of the body were significantly associated with haematology and serum clinical chemistry, especially in weaners and fatteners. The involvement of inflammatory cells, blood coagulation, acute phase proteins and certain serum metabolites support the inflammatory-necrotising character of the syndrome and provide starting points for further studies to decipher its exact pathogenesis. The low to moderate variations seem less suitable for diagnostic use.

Age-dependent messenger RNA expression of toll-like receptor 4 and intercellular adhesion molecule-1 in peripheral blood mononuclear cells

BACKGROUND

Inflammation plays an important role in the ageing process in which monocytes/macrophages are important players. Intercellular adhesion molecule-1 (ICAM-1), tumour necrosis factor-α (TNF-α) and Toll-like receptor 4 (TLR4) are well-known inflammatory markers. This study aimed to investigate the relationship between age and the expression and correlation of ICAM-1, TNF-α and TLR4 mRNA in peripheral blood mononuclear cells (PBMCs).

METHODS

A total of 239 participants were recruited in a medical centre in Taiwan. The mRNA isolated from the PBMCs was used to determine the levels of ICAM-1, TNF-α and TLR4 mRNAs with real-time polymerase chain reaction (PCR). The propensity-matched analysis was also applied for subgroup analysis.

RESULTS

When compared 189 older adults (≧65 years) to 50 younger adults (<65 years), the ICAM-1, TNF-α and TLR4 mRNA levels in PBMCs were significantly higher in older adults (2.00 ± 0.72 vs 0.87 ± 0.34 for ICAM-1, 2.32 ± 0.69 vs 1.15 ± 0.44 for TNF-α and 1.56 ± 0.47 vs 1.05 ± 0.51 for TLR4, and all P < .0001). Also, both age and TLR4 were independent factors affecting mononuclear cell ICAM-1 in the multiple linear regression analysis (P < .0001).

CONCLUSION

The mRNA levels of ICAM-1 and TLR4 in PBMCs are higher in older adults than those in younger adults. TLR4 is an independent factor affecting ICAM-1 expression in PBMCs, especially in older adults. This may suggest that ICAM-1 and TLR4 in PBMCs are potential biomarkers and their relationship may shed some light on the ageing process.

Chronic Inflammation in Peritoneal Dialysis: The Search for the Holy Grail?

Mortality and morbidity in chronic kidney disease (CKD) patients are unacceptably high. The annual mortality rate due to cardiovascular disease (CVD) is approximately 9%, which, for the middle-aged person, is at least 10- to 20-fold higher than for the general population. Classic risk factors for CVD are highly prevalent in CKD patients, but they cannot fully account for the excessive rate of CVD in this population. Instead, it has become increasingly clear that nontraditional risk factors, such as systemic inflammation, may play a key role in the development of atherosclerosis. It is well established that inflammatory markers are very powerful predictors of high CVD morbidity and mortality not only in the general population, but particularly in CKD patients. Signs of a sustained low-grade inflammation, such as increased levels of C-reactive protein (CRP), are present in the majority of stage 5 CKD patients, even in patients in clinically stable condition, and they are also commonly observed after the initiation of dialysis therapy. Dialysis therapy — hemodialysis as well as peritoneal dialysis (PD) — may itself contribute to systemic inflammation. Local intraperitoneal inflammation can also occur in patients treated with PD. These local effects may result in a low-grade inflammation, caused by the bioincompatibility of conventional glucose-based dialysis fluids, to intense inflammation associated with peritonitis. Given these circumstances, it is reasonable to hypothesize that strategies aiming to reduce inflammation are potentially important and novel, and could serve to reduce CVD, thereby lowering morbidity and mortality in patients with CKD. In this review we provide information supporting the hypothesis that systemic inflammation is tightly linked to the most common complications of CKD patients, in particular those on PD, and that local inflammation in PD may contribute to various related complications. The aims of this review are to discuss the reasons that make inflammation an attractive target for intervention in CKD, the particular aspects of the inflammation–CVD axis during PD treatment that are likely involved, and possible means for the detection and management of chronic inflammation in PD patients.

Coexistence of High Fibrinogen and Low High-density Lipoprotein Cholesterol Levels Predicts Recurrent Cerebral Venous Thrombosis

BACKGROUND

Cerebral venous thrombosis (CVT) may lead to serious neurological disorders; however, little is known about the risk factors for recurrent CVT. Our aim was to determine the association between elevated fibrinogen and decreased high-density lipoprotein cholesterol (HDL-C) levels with recurrent CVT.

METHODS

This retrospective cohort study included participants if they had a first episode of objectively defined CVT and were admitted to Xuan Wu Hospital, Capital Medical University from August 2005 to September 2009. Demographic and clinical variables were collected, as well as laboratory parameters, including plasma fibrinogen and HDL-C. Patients with CVT were followed for recurrent symptomatic CVT. Follow-up was through the end of September 2010. Potential predictors of recurrence were analyzed using Cox survival analysis.

RESULTS

At the end of the follow-up, 95 patients were eligible for the study. Twelve of 95 patients (12.6%) had recurred CVT. The median time of recurrence was 7 months (range: 1-39 months). Eight of these 12 (66.7%) experienced recurrence within the first 12 months after their initial CVT. The recurrence rate of CVT was 2.76 per 100 patient-years. Multivariate Cox regression analysis demonstrated that the coexistence of high fibrinogen (>4.00 g/L) and low HDL-C (<1.08 mmol/L) levels at baseline was the only independent predictor for recurrent CVT (hazard ratio: 4.69; 95% confidence interval: 1.10-20.11; P < 0.05). Of the twelve patients with recurrent CVT in our study, 7 (58.3%) had high fibrinogen plus low HDL-C levels. All 7 of these patients took warfarin for 3-12 months, and 6 of 7 had recurrent CVT after the discontinuation of anticoagulant treatment.

CONCLUSIONS

Concomitant high fibrinogen and low HDL-C levels may be associated with recurrence of CVT. The effect of potential risk factors related to atherothrombosis on recurrent CVT should be closely monitored.

Impaired fibrinolysis is associated with the severity of aortic stenosis in humans

BACKGROUND

A role of fibrinolysis in the pathogenesis of aortic valve stenosis (AS) is unknown, although fibrinolytic proteins have been detected in aortic stenotic valves.

OBJECTIVE

To investigate whether impaired fibrinolysis could be associated with AS.

METHODS AND RESULTS

We studied 74 patients with AS (43 male, 31 female, aged 62.7 ± 10.7 years) without documented atherosclerotic valvular disease scheduled for isolated valve replacement and 68 controls. The plasma fibrin clot lysis time (CLT) in the presence of tissue factor (TF) and tissue plasminogen activator (tPA), along with plasma plasminogen activator inhibitor-1 (PAI-1) were determined. Valvular expression of fibrin and PAI-1 together with macrophages and mast cells (MC) was evaluated by immunostaining. Patients with AS compared with controls were characterized by a prolonged CLT (median, 110 [54-153] vs. 92.5 [58-115] min, P = 0.0007) and increased plasma PAI-1 (78.6 [35.5-149] vs. 38.5 [18-61] ng mL(-1) , P < 0.0001). CLT was correlated with maximal (r = 0.43, P = 0.0002) and mean (r = 0.38, P = 0.001) transvalvular pressure gradients, and aortic valve area (r = -0.59, P < 0.0001). In AS patients, the CLT was positively correlated with the valve leaflet thickness (r = 0.67, P = 0.003), the degree of valve calcification (r = 0.65, P < 0.00001), valvular fibrin (r = 0.54, P = 0.007) and PAI-1 expression (r = 0.48, P = 0.007). Double-immunostaining revealed colocalization of valvular PAI-1 with MC (87 ± 17% cells) and macrophages (48 ± 11% cells) within stenotic valves.

CONCLUSIONS

Hypofibrinolysis might be a marker of severe AS and be implicated in AS progression.

Increased expression of heparanase in symptomatic carotid atherosclerosis

OBJECTIVE

Proliferation of smooth muscle cells (SMCs) can stabilize atherosclerotic lesions but the molecular mechanisms that regulate this process in humans are largely unknown. We have previously shown that heparan sulfate proteoglycans (HSPGs), such as perlecan, regulate SMC growth in animal models by modulating heparin-binding mitogens. Since perlecan is expressed at low levels in human atherosclerosis, we speculated that the effect of heparan sulfate (HS) in human disease was rather influenced by HS degradation and investigated the expression of heparanase (HPSE) in human carotid endarterectomies.

METHODS AND RESULTS

Gene expression analysis from 127 endarterectomies in the BiKE database revealed increased expression of HPSE in carotid plaques compared with normal arteries, and a further elevation in symptomatic lesions. Increased HPSE protein expression in symptomatic plaque tissue was verified by tissue microarrays. HPSE mRNA levels correlated positively with expression of inflammatory markers IL-18, RANTES and IL-1β, and also T-cell co-stimulatory molecules, such as B7.2, CD28, LFA-1 and 4-1BB. Previously reported single nucleotide polymorphisms within HPSE were associated with differential mRNA expression in plaques. Immunohistochemistry revealed that inflammatory cells were major producers of HPSE in plaque tissue. HPSE immunoreactivity was also observed in SMCs adjacent to the necrotic core and was co-localized to deposits of fibrin.

CONCLUSIONS

This study demonstrates increased expression of HPSE in human atherosclerosis associated with inflammation, coagulation and plaque instability. Since HS can regulate SMC proliferation and influence plaque stability, the findings suggest that HPSE degradation of HS take part in the regulation of SMC function in human atherosclerosis.

The role of fibrinolytic genes and proteins in the development of allograft vascular disease

BACKGROUND

We have previously shown that lack of plasminogen activator inhibitor-1 (PAI-1) expression in donor tissue greatly increases intimal proliferation (IP) after allogeneic transplantation. We sought to determine the relative role of PAI-1 and other fibrinolytic proteins in the development of IP.

METHODS

We used an abdominal aortic transplant model in mice to investigate IP in 3 groups of 6 recipients. In the isograft group, CBA/J strain mice were donors and recipients, donors for allograft group were C57BL/6J mice, and for the allograft/knockout group, C57BL/6J PAI-1 knockout mice. All groups received weekly injections of anti-CD8/CD4 monoclonal antibodies. IP was calculated at 50 days, and sections were analyzed for fibrinolytic proteins, messenger RNA (mRNA) and PAI-1 activity using immunohistochemistry (IHC), in situ hybridization (ISH), reverse transcription-polymerase chain reaction (RT-PCR), and Western blot analysis.

RESULTS

Significantly more IP developed in the allograft/knockout group vs the isograft (p < 0.001) and the allograft groups (p = 0.003). There was marked intimal expression of tissue plasminogen activator (tPA), urokinase PA (uPA), and uPA receptor (uPAR) proteins and mRNA in the allograft and allograft/knockout groups vs the isograft group. Allografts also showed significant intimal staining for PAI-1 protein and mRNA. RT-PCR demonstrated a stepwise increase in profibrinolytic protein mRNA from isograft to allograft to allograft/knockout groups, particularly uPA (p = 0.02) and uPAR (p = 0.016). Western blot data showed complementary findings. PAI-1 activity was persistently present in isograft and allograft animals, only. Intimas in allograft and allograft/knockout groups were primarily smooth muscle cells.

CONCLUSIONS

PAI-1 reduces IP by limiting smooth muscle cell activity, with little change in matrix composition likely by modulating profibrinolytic protein expression.

Enhancement of fibrinolysis by inhibiting enzymatic cleavage of precursor α2-antiplasmin

BACKGROUND AND OBJECTIVE

Resistance of thrombi to plasmin digestion depends primarily on the amount of α(2)-antiplasmin (α(2)AP) incorporated within fibrin. Circulating prolyl-specific serine proteinase, antiplasmin-cleaving enzyme (APCE), a homologue of fibroblast activation protein (FAP), cleaves precursor Met-α(2)AP between -Pro12-Asn13- to yield Asn-α(2)AP, which is crosslinked to fibrin approximately 13× more rapidly than Met-α(2)AP and confers resistance to plasmin. We reasoned that an APCE inhibitor might decrease conversion of Met-α(2)AP to Asn-α(2)AP and thereby enhance endogenous fibrinolysis.

METHODS AND RESULTS

We designed and synthesized several APCE inhibitors and assessed each vs. plasma dipeptidyl peptidase IV (DPPIV) and prolyl oligopeptidase (POP), which have amino acid sequence similarity with APCE. Acetyl-Arg-(8-amino-3,6-dioxaoctanoic acid)-D-Ala-L-boroPro selectively inhibited APCE vs. DPPIV, with an apparent K(i) of 5.7 nm vs. 6.1 μm, indicating that an approximately 1000-fold greater inhibitor concentration is required for DPPIV than for APCE. An apparent K(i) of 7.4 nm was found for POP inhibition, which is similar to 5.7 nm for APCE; however, the potential problem of overlapping FAP/APCE and POP inhibition was negated by our finding that normal human plasma lacks POP activity. The inhibitor construct caused a dose-dependent decrease of APCE-mediated Met-α(2)AP cleavage, which ultimately shortened plasminogen activator-induced plasma clot lysis times. Incubation of the inhibitor with human plasma for 22 h did not lessen its APCE inhibitory activity, with its IC(50) value in plasma remaining comparable to that in phosphate buffer.

CONCLUSION

These data establish that inhibition of APCE might represent a therapeutic approach for enhancing thrombolytic activity.

Early Atherosclerosis Exhibits an Enhanced Procoagulant State

Background— Thrombin generation in vivo may be important in regulating atherosclerotic progression. In the present study, we examined for the first time the activity and presence of relevant coagulation proteins in relation to the progression of atherosclerosis.

Methods and Results— Both early and stable advanced atherosclerotic lesions were collected pairwise from each individual (n=27) during autopsy. Tissue homogenates were prepared from both total plaques and isolated plaque layers, in which the activity of factors (F) II, X, and XII and tissue factor was determined. Microarray analysis was implemented to elucidate local messenger RNA synthesis of coagulation proteins. Part of each specimen was paraffin embedded, and histological sections were immunohistochemically stained for multiple coagulation markers with the use of commercial antibodies. Data are expressed as median (interquartile range [IQR]). Tissue factor, FII, FX, and FXII activities were significantly higher in early atherosclerotic lesions than in stable advanced atherosclerotic lesions. Endogenous thrombin potential and thrombin-antithrombin complex values consolidated a procoagulant profile of early atherosclerotic lesions (endogenous thrombin potential, 1240 nmol/L · min [IQR, 1173 to 1311]; thrombin-antithrombin complex, 1045 ng/mg [IQR, 842.6 to 1376]) versus stable advanced atherosclerotic lesions (endogenous thrombin potential, 782 nmol/L · min [IQR, 0 to 1151]; thrombin-antithrombin complex, 718.4 ng/mg [IQR, 508.6 to 1151]). Tissue factor, FVII, and FX colocalized with macrophages and smooth muscle cells. In addition, multiple procoagulant and anticoagulant proteases were immunohistochemically mapped to various locations throughout the atherosclerotic vessel wall in both early and advanced atherosclerotic stages.

Conclusions— This study shows an enhanced procoagulant state of early-stage atherosclerotic plaques compared with advanced-stage plaques, which may provide novel insights into the role of coagulation during atherosclerotic plaque progression.

The effect of a single nucleotide polymorphism on human alpha 2-antiplasmin activity

The primary inhibitor of plasmin, alpha(2)-antiplasmin (alpha(2)AP), is secreted by the liver into plasma with Met as the amino-terminus. During circulation, Met-alpha(2)AP is cleaved by antiplasmin-cleaving enzyme (APCE), yielding Asn-alpha(2)AP, which is crosslinked into fibrin approximately 13 times faster than Met-alpha(2)AP. The Met-alpha(2)AP gene codes for either Arg or Trp as the sixth amino acid, with both polymorphic forms found in human plasma samples. We determined the Arg6Trp genotype frequency in a healthy population and its effects on Met-alpha(2)AP cleavage and fibrinolysis. Genotype frequencies were RR 62.5%, RW 34.0%, and WW 3.5%. The polymorphism related to the percentage of Met-alpha(2)AP in plasma was WW (56.4%), RW (40.6%), and RR (23.6%). WW plasma tended to have shorter lysis times than RR and RW plasmas. APCE cleaved purified Met-alpha(2)AP(Arg6) approximately 8-fold faster than Met-alpha(2)AP(Trp6), which is reflected in Asn-alpha(2)AP/Met-alpha(2)AP ratios with time in RR, RW, and WW plasmas. Removal of APCE from plasma abrogated cleavage of Met-alpha(2)AP. We conclude that the Arg6Trp polymorphism is functionally significant, as it clearly affects conversion of Met-alpha(2)AP to Asn-alpha(2)AP, and thereby, the rate of alpha(2)AP incorporation into fibrin. Therefore, the Arg6Trp polymorphism may play a significant role in governing the long-term deposition/removal of intravascular fibrin.

New risk factors for atherosclerosis in hypertension: focus on the prothrombotic state and lipoprotein(a)

Although adequate control of blood pressure is of basic importance in cardiovascular prevention in hypertensive patients, correction of additional risk factors is an integral part of their management. In addition to classical risk factors, epidemiological research has identified a number of other conditions that might significantly contribute to cardiovascular risk in the general population and might achieve specific relevance in patients with high blood pressure. In fact, more than 20% of patients with premature cardiovascular events do not have any of the traditional risk factors and, although effective intervention on blood pressure and additional risk factors has significantly reduced cardiovascular morbidity and mortality, the contribution to stroke, coronary artery disease and renal failure is still unacceptably high. Evaluation of new risk factors may further expand our capacity to predict atherothrombotic events when these factors are included along with the traditional ones in the assessment of global cardiovascular risk in hypertensive patients. Because it could be anticipated that the role of these novel factors will become increasingly evident in the future, researchers with an interest in hypertension and physicians dealing with problems related to cardiovascular prevention should give them appropriate consideration. This review summarizes the basic biology and clinical evidence of two emerging risk factors that are reciprocally related and contribute to the development and progression of organ damage in hypertension: the prothrombotic state and lipoprotein(a).

Possible Protective Role for C-Reactive Protein in Atherogenesis

Background— Previous work indicated that enzymatically remodeled LDL (E-LDL) might activate complement in atherosclerotic lesions via a C-reactive protein (CRP)–dependent and CRP-independent pathway. We sought to substantiate this contention and determine whether both pathways drive the sequence to completion.

Methods and Results— E-LDL was prepared by sequential treatment of LDL with a protease and cholesteryl esterase. Trypsin, proteinase K, cathepsin H, or plasmin was used with similar results. Functional tests were used to assess total complement hemolytic activity, and immunoassays were used to demonstrate C3 cleavage and to quantify C3a, C4a, C5a, and C5b-9. E-LDL preparations activated complement to completion, independent of CRP, when present above a threshold concentration (100 to 200 μg/mL in 5% serum). Below the threshold, all E-LDL preparations activated complement in dependence of CRP, but the pathway then halted before the terminal sequence. Native LDL and oxidized LDL did not activate complement under any circumstances tested. Immunohistological analyses corroborated the concept that CRP-dependent complement activation inefficiently generates C5b-9.

Conclusions— Binding of CRP to E-LDL is the first trigger for complement activation in the atherosclerotic lesion, but the terminal sequence is thereby spared. This putatively protective function of CRP is overrun at higher E-LDL concentrations, so that potentially harmful C5b-9 complexes are generated.

Increased fibrin polymerization rate in patients with primary antiphospholipid syndrome and systemic lupus erythematosus

The main event in blood coagulation is the thrombincatalyzed conversion of fibrinogen into fibrin. This singular transformation of a soluble protein into an insoluble polymeric network occurs with faultless precision. Abnormalities of fibrin polymerization can lead to hemorragic and thrombotic disorders. Increased fibrinogen plasma concentration (Fg) and fibrin polymerization rate (FPR) could be additional risk factors associated with atherothrombosis in antiphospholipid syndrome (APS) and in systemic lupus erythematosus (SLE). Our objective was to investigate Fg and FPR in consecutive patients with APS and SLE. Thirty-nine patients and 31 age- and gender-matched healthy controls were studied. Sixteen patients had primary APS, 13 patients had SLE, and 10 patients had SLE plus APS. The mean of the FPR was significantly increased (0.2799 +/- 0.091) in patients with APS plus SLE as compared with the control group (0.2052 +/- 0.055) (p < 0.05). Fg was higher in APS plus SLE (3.15 g/L +/- 0.43) and in primary APS (3.03 g/L +/- 0.29) than in controls (2.87 g/L +/- 0.49). Our results demonstrated an increased FPR in patients with APS plus SLE. This phenomenon could be an additional risk factor for thrombosis in these autoimmune diseases.

Endothelial dysfunction in peripheral arterial disease is related to increase in plasma markers of inflammation and severity of peripheral circulatory impairment but not to classic risk factors and atherosclerotic burden

OBJECTIVE

We undertook this study to evaluate in patients with peripheral arterial disease (PAD) the relationship of endothelial dysfunction, which is directly related to progression and clinical complications of atherosclerosis, with variables including classic risk factors, inflammation, severity of peripheral circulatory impairment, and atherosclerotic burden.

METHODS

This cross-sectional study included outpatients seen in an academic angiologic unit. Eighty-eight consecutive patients with PAD (ankle/brachial index [ABI] < 0.90) were studied. The control group consisted of 30 age-matched and sex-matched healthy subjects. Main outcome measures were endothelial function in the form of brachial artery flow-mediated dilation (FMD), plasma levels of C-reactive protein (CRP) and fibrinogen, severity of PAD according to ABI, and atherosclerotic burden, ie, atherosclerosis in one leg or in two or more other sites.

RESULTS

Compared with patients with FMD greater than 6.2% (ie, 5th percentile of FMD in control subjects), patients with FMD less than 6.2% had a similar prevalence of classic risk factors but higher median levels of CRP (1.6 vs 6.0 mg/L; P <.01) and fibrinogen (200 vs 374 mg/dL; P <.01). The two inflammatory markers were negatively correlated with FMD (P <.01). ABI was higher in patients with FMD greater than 6.2% than in those with worse endothelial function (0.72 +/- 0.15 vs 0.62 +/- 16; P <.01); there was no difference with respect to atherosclerotic burden. Multivariate analysis showed that the association of CRP, fibrinogen, and ABI with FMD less than 6.2% was unrelated to classic risk factors. In a second model, which included CRP, fibrinogen, and ABI, all three variables were independently related to FMD less than 6.2%.

CONCLUSION

Inflammation and severity of circulatory impairment are implicated in the pathophysiology of dysfunctional endothelium in PAD.

Donor PAI-1 expression inhibits the intimal response of early allograft vascular disease

BACKGROUND

The development of allograft vascular disease (AVD) may be related to altered expression of the fibrinolytic system. We determined the extent to which plasminogen activator inhibitor type 1 (PAI-1) expression in donor tissue influences intimal proliferation (IP) in a mouse model of AVD.

METHODS

We utilized an end-to-end abdominal aortic transplant model in mice to investigate the development of IP in 3 groups of 6 recipients. Group A (negative control) utilized C57BL/6J strain mice as both donors and recipients. In Groups B (positive control) and C, C57BL/6J mice were vessel donors and CBA/J mice were recipients. Both groups received intraperitoneal anti-CD4 and anti-CD8 monoclonal antibodies (250 microg/week for 5 weeks). Group C recipients, however, were transplanted with vessels from C57BL/6J PAI-1 knockout mice. Animals were killed at 50 days. Transplanted aortas were removed and intimal areas calculated using morphometric analysis.

RESULTS

Group A (mean intimal area 6421 +/- 8507 microm(2)) demonstrated very little IP in comparison to the other groups. IP was significantly higher in Group B (mean intimal area 56357 +/- 35629 microm(2)) than Group A (p = 0.008). Group C (mean intimal area 288195 +/- 123279 microm(2)) demonstrated significantly more intimal proliferation than either Groups A or B (vs B, p = 0.003; vs A, p < 0.001). The significance of these results is maintained if intimal thickness is measured as a stand-alone reference for the intimal response.

CONCLUSIONS

Lack of PAI-1 expression in donor tissue greatly exaggerates the extent of IP after allogeneic transplantation and suggests that PAI-1 is important in limiting the early phase of AVD.

[Fibrinogen as a risk factor in ischemic heart disease]

<zakljucak> Mesto fibrinogena u razvoju ateroskleroze i arterijske tromboze je verovatno znacajno jer on ucestvuje i u procesu nastanka i rasta plaka modulise hemoreoloske osobine krvi, a cini i osnovu koaguluma tokom procesa tromboze. Koncentracija fibrinogena u krvi je dobar nezavisan prognosticki parametar za razvoj akutnog infarkta miokarda, kako kod zdravih odraslih osoba, tako i kod koronarnih bolesnika. Nivo fibrinogena u krvi je delimicno genetski determinisan, ali i brojni faktori spoljasnje sredine uticu na njegov nivo. Vrlo je bitan odnos izmedju fibrinogena i nekih drugih vaznih faktora rizika. Fibrinogen i holesterol imaju izgleda sinergisticki ucinak na razvoj akutnog koronarnog sindroma. Moguce je da je fibrinogen jedna od najznacajnijih spona izmedju pusenja i koronarne bolesti. Veoma je mali broj lekova koji se mogu dugorocno primenjivati i smanjiti nivo fibrinogena u krvi, tako da za sada ne postoje klinicke studije o vrednosti ovakve terapije u lecenju i prevenciji akutnih koronarnih sindroma. Shodno tome sve dok se ne dokaze da se smanjenjem nivoa fibrinogena u krvi smanjuje rizik za ispoljavanje koronarne bolesti, njegova uloga kao faktora rizika ostaje nedovoljno definisana.

Anticardiolipin antibody titre and plasma homocysteine level independently predict intima media thickness of carotid arteries in subjects with idiopathic antiphospholipid antibodies

This study evaluated whether IgG anticardiolipin antibody (aCL) titre and traditional risk factors for atherosclerosis bore any relationship to the intima media thickness (IMT) of carotid arteries of patients with idiopathic antiphospholipid antibodies (aPL). IMT was assessed by high-resolution sonography at the common carotid, carotid bifurcation and internal carotid in 42 (13 male, 29 female, mean age 31+/-10 years) aPL subjects, 29 with primary thrombotic antiphospholipid syndrome and 13 with persistence of aPL in the absence of any underlying disorder. In the same subjects the following were measured: plasma fibrinogen (FNG), von Willebrand factor (vWF), plasminogen activator inhibitor (PAI), homocysteine (HC), total cholesterol (CHO), triglycerides (TG), high density and low density lipoprotein (HDL and LDL), platelet numbers and aCL of IgG and IgM isotype. IMT of the internal carotid was greater in males than females (0.48+/-0.03 vs 0.39+/-0.01 mm, P=0.02). IMT of the carotid bifurcation was greater in thrombotic than nonthrombotic subjects (0.50+/-0.02 vs 0.42+/-0.02 mm, P=0.04). By simple regression, IMT of the common carotids correlated with age (P< 0.0001) IgG aCL titre (P=0.001), FNG (P=0.006), LDL (0.01), CHO (0.02) and PAI (P=0.02). IMT of the carotid bifurcation correlated with age (P=0.002), IgG aCL titre (P=0.0002), FNG (P=0.0001), HC (P=0.009), CHO (P=0.02), vWF (P=0.01) and number of thrombotic events (P=0.03). IMT of the internal carotids correlated with age (P=0.002), IgG aCL titre (P=0.0001), FNG (P=0.0008), PAI (P=0.002) and HC (P=0.01). By stepwise multiple regression analysis, IgG aCL titre independently predicted IMT at all carotid segments examined (P always <0.005). In addition, plasma FNG and HC also resulted independent predictors of IMT at the carotid bifurcation (P=0.001 and P<0.0001, respectively) and internal carotid (P=0.03 and P<0.0001, respectively). These data strongly support an atherogenic role for IgG aCL in patients with aPL. Measurement of plasma HC and FNG may help define aPL subjects at higher vascular risk who may require lowering of HC and FNG by vitamin and/or pharmacologic intervention.

Inflammation in end-stage renal disease: sources, consequences, and therapy

Cardiovascular disease (CVD) remains the main cause of morbidity and mortality in patients with end-stage renal disease (ESRD). Although traditional risk factors are common in ESRD patients, they alone may not be sufficient to account for the high prevalence of CVD in this condition. Recent evidence demonstrates that chronic inflammation, a nontraditional risk factor which is commonly observed in ESRD patients, may cause malnutrition and progressive atherosclerotic CVD by several pathogenetic mechanisms. The causes of inflammation in ESRD are multifactorial and, while it may reflect underlying CVD, an acute-phase reaction may also be a direct cause of vascular injury by several pathogenetic mechanisms. Available data suggest that proinflammatory cytokines play a central role in the genesis of both malnutrition and CVD in ESRD. Thus it could be speculated that suppression of the vicious cycle of malnutrition, inflammation, and atherosclerosis (MIA syndrome) would improve survival in dialysis patients. Recent evidence has demonstrated strong associations between inflammation and both increased oxidative stress and endothelial dysfunction in ESRD patients. As there is not yet any recognized, or even proposed, treatment for ESRD patients with chronic inflammation, it would be of obvious interest to study the long-term effect of various anti-inflammatory treatment strategies on the nutritional and cardiovascular status as well as outcome in these patients.

Levels of haemostatic factors, arteriosclerosis and cardiovascular disease

Plasma levels of haemostasis factors (HFs) such as fibrinogen, tissue-type plasminogen activator (t-PA), plasminogen activator inhibitor-1 (PAI-1) and D-dimer may be markers of arteriosclerosis for the following reasons: There seems to be no difference in levels of HFs between patients with longstanding stable angina and those with an isolated myocardial infarction. HF levels are generally positively associated with subclinical arteriosclerosis as determined by ankle-arm index and carotid ultrasonography in asymptomatic individuals. Levels of most HFs are positively associated with inflammation, which is an essential part of the initiation and progression of the disease. A rough classification is assigned to the associations found in under (2) and (3). Fibrinogen is strongly associated with subclinical arteriosclerosis and with inflammation; Factor VII is not, while an intermediate group is formed by, for instance, von Willebrand Factor (vWF), Factor VIII (F VIII), t-PA, PAI-1, and D-dimer. Also, the associations of HFs with cardiovascular events follow a similar pattern. Fibrinogen is a strong and consistent risk factor in several studies, Factor VII is not, and a similar intermediate group as mentioned under (2) and (3) exists. It suggests that the risk of cardiovascular events in relation to HF levels is explained by their identity as markers of arteriosclerosis. A causal association between HF levels and the disease is not proven. Out of the HF, the markers of coagulation such as thrombin-antithrombin complex and of fibrinolysis such as D-dimer are more likely to act causally. Increased levels indicate that they are markers of arteriosclerosis, but in addition, they may reflect a low-grade, continuous formation and subsequent lysis of fibrin in the disease. As the latter reflects an increased tendency to thrombosis, a causal association of levels of markers of coagulation and fibrinolysis with arteriosclerosis, although not yet proven, seems likely.

Role of D and E domains in the migration of vascular smooth muscle cells into fibrin gels

The structure of fibrin plays an important role in the organization of thrombi, the development of atherosclerosis, and restenosis after PTCA. In this study, we examined the mechanisms of the migration of vascular smooth muscle cells (SMCs) into fibrin gels, using an in vitro assay system. Cultured SMCs from bovine fetal aortic media migrated into fibrin gels prepared with thrombin, which cleaves both fibrinopeptides A and B from fibrinogen, without other chemotactic stimuli. Both desA fibrin gels prepared with batroxobin, which cleaves only fibrinopeptide A, and desB fibrin gels prepared with Agkistrodon contortrix thrombin-like enzyme (ACTE), which cleaves only fibrinopeptide B, similarly induced the migration of SMCs compared to fibrin gels prepared with thrombin. These results suggest that the cleavage of fibrinopeptides is not necessary, but rather that the three-dimensional structure of the gel may be important for the migration of SMCs. Furthermore, gels prepared with protamine sulfate, which forms fibrin-like gels non-enzymatically, similarly induced the migration of SMCs compared to the gels prepared with thrombin. Both anti-fibrin(ogen) fragment D and anti-fibrin(ogen) E antibodies inhibited the migration of SMCs into fibrin gels, suggesting that both the D and E domains of fibrin(ogen) are involved in the migration of SMCs into fibrin gels. The addition of GRGDS, a synthetic RGD-containing peptide, but not that of GRGES, a control peptide, partially inhibited the migration of SMCs into fibrin gels, suggesting that the migration of SMCs into fibrin gels is at least in part dependent on the RGD-containing region of the alpha chain. The migration of SMCs into fibrin gels was also inhibited by a monoclonal antibody for integrin alpha v beta 3 and alpha 5 beta 1, indicating that migration is dependent on these integrins. Furthermore, both fibrin(ogen) fragments D and E inhibited the migration of SMCs into fibrin gels, suggesting that these fragments, generated during fibrino(geno)lysis, may be relevant in the regulation of SMC migration into fibrin gels.

Monocytic cell adhesion to intact and plasmin-modified fibrinogen: possible involvement of Mac-1 (CD11b/CD18) and ICAM-1 (CD54)

beta(2)-integrin Mac-1 and immunoglobulin-like ICAM-1 adhesion molecules are expressed by monocytes and both known to bind fibrinogen and its degradation products. Here, we investigated whether fibrinogen cleavage with plasmin modulates the adherence of monocytic cells and what types of adhesion molecules are involved. Using several cell types, characterized by different patterns of Mac-1 and ICAM-1 expression, and monoclonal antibodies against beta(2)-integrins and ICAM-1 we demonstrate, that fibrinogen cleavage evokes gradual decrease in beta(2)-integrin-dependent cell adhesion. Furthermore, generation of the early degradation products, fragments X and Y, by minimum cleavage of fibrinogen stimulates cell adhesion, mediated by ICAM-1.

Characterization of crosslinking sites in fibrinogen for plasminogen activator inhibitor 2 (PAI-2)

PAI-2 is a serpin that can be crosslinked to fibrin(ogen) via the Gln-Gln-Ile-Gln sequence (residues 83-86). We have characterized the lysine residues in fibrinogen to which PAI-2 is crosslinked by tissue transglutaminase and factor XIIIa. There was no competition with the crosslinking of alpha 2-antiplasmin, another inhibitor of fibrinolysis, which was specific for Lys 303 in the A alpha chain. PAI-2 was crosslinked to several lysine residues, all in the A alpha chain, 148, 176, 183, 230, 413, and 457, but not to Lys 303. The contrast with alpha 2-antiplasmin was clear from studies with truncated fibrinogens and competition by peptides. This was confirmed and extended by mass spectrometry of peptides after protease digestion of crosslinked products, which identified the lysine residues to which the inhibitors were crosslinked. PAI-2 remained active after cross-linking and inhibited fibrin breakdown, even by two-chain t-PA. Thus, a second inhibitor of fibrinolysis, in addition to alpha 2-antiplasmin, is crosslinked to fibrin and protects it from lysis.

Antioxidant susceptibility of pathogenic pathways in subjects with antiphospholipid antibodies: a pilot study

The pathogenesis of antiphospholipid antibody (aPL) related thrombosis is multifactorial and includes, amongst others, enhanced coagulation activation measured as prothrombin fragment 1 + 2 (F1 + 2), elevated plasma levels of von Willebrand factor (vWF), plasminogen activator inhibitor (PAI) and endothelin-1 (ET-1) as well as heightened thromboxane generation and lipid peroxidation. To evaluate the antioxidant susceptibility of some of the above pathways, probucol (500 mg/d orally, a cholesterol lowering agent bearing antioxidant properties) was administered for a three week period to 14 subjects with aPL and to seven healthy controls. At baseline aPL participants showed higher plasma levels of vWF (P = 0.006), ET-1 (P = 0.0002) and enhanced urinary excretion of 11-dehydro-thromboxane-B2 (TXB2) (P = 0.0004), F2-isoprostanes (marker of lipid peroxidation) (P = 0.02) and albumin (P = 0.04) than controls. In the aPL group baseline IgG anticardiolipin (aCL) titre positively related with urinary TXB2 (r2 = 0.43, P = 0.01) and inversely with urinary NOx (r2 = -0.6, P = 0.005) whereas urinary NOx and TXB2 were negatively correlated (r2 = -0.42, P = 0.01). After the treatment period significant decreases from baseline values were noted for PAI (P = 0.01), ET-1 (P = 0.006), TXB2 (P = 0.02), F2-isoprostanes (P = 0.01) and albuminuria (P = 0.01) in aPL participants but not in controls. These pilot data support oxidative sensitive mechanisms and a potential role for antioxidant treatment in the pathogenesis of aPL induced vasculopathy.

Increased plasma fibrinogen level and future risk of coronary artery disease after repair of abdominal aortic aneurysm

BACKGROUND

Cardiovascular disease such as coronary artery disease is a major cause of late death after repair of abdominal aortic aneurysm (AAA). But risk factors are not well known. So, we investigated the incidence of cardiovascular events after surgery and examined the prognostic factors.

STUDY DESIGN

We retrospectively reviewed 270 patients who underwent elective surgery for AAA from 1985 to 1995. Kaplan-Meier survival analysis was used to estimate survival rates and the probability of coronary, cerebrovascular, and cardiovascular events. The risk factors for each endpoint were investigated using multivariate analysis.

RESULTS

The overall survival rate was 87.3% at 3 years, 76.4% at 5 years, and 52.3% at 10 years. Current cigarette use, renal insufficiency, advanced age (> or = 70 years old), and higher plasma fibrinogen level (> or = 300 mg/dL) were significant factors influencing survival. The probability of a coronary event was 4.9% at 3 years, 7.1% at 5 years, and 20.7% at 10 years. Plasma fibrinogen level and cerebrovascular disease were significant prognostic factors for coronary events. The probability of a cerebrovascular event was 5.3% at 3 years, 7.6% at 5 years, and 18.0% at 10 years. No significant prognostic factors for cerebrovascular events existed. The probability of a cardiovascular event was 10.3% at 3 years, 14.9% at 5 years, and 33.6% at 10 years. Plasma fibrinogen level was a significant risk factor for cardiovascular events. But the presence of coronary artery disease did not affect survival or the incidence of coronary, cerebrovascular, or cardiovascular events.

CONCLUSIONS

Plasma fibrinogen level is an independent risk factor of future coronary events after surgery for AAA, and the increased risk of coronary artery events contributes to the impaired survival. Patients with higher plasma fibrinogen level need careful surveillance for cardiovascular disease after surgery.

Cardiovascular disease in diabetes mellitus type 2: a potential role for novel cardiovascular risk factors

A major consequence of diabetes mellitus type 2 is the accelerated development of atherosclerosis. Assessment of conventional risk factors such as plasma lipids, lipoproteins and hypertension only partly account for the excessive risk of developing cardiovascular disease in this population. Increasing evidence has emerged suggesting that conditions associated with diabetes mellitus type 2, such as insulin resistance, hyperinsulinemia and hyperglycemia, may also play a significant role in regulating 'novel' cardiovascular risk factors. These factors and their potential roles in the development of atherosclerosis and cardiovascular events are discussed in this review.

Effect of gemfibrozil on peripheral atherosclerosis and platelet activation in a pig model of hyperlipidemia

BACKGROUND

Gemfibrozil has been shown to have beneficial effects in the primary and secondary prevention of atherosclerosis. However, a platelet pro-activating effect induced by the drug has been reported.

MATERIAL AND METHODS

We analysed the effect of hyperlipidemia and its treatment with gemfibrozil on platelet-fibrinogen binding and the development of early fibrinogen-rich vascular lesions in a porcine model of atherosclerosis. Polyclonal antibodies were raised against purified pig fibrinogen and intact platelets. Two groups of animals were fed a cholesterol/saturated fat-enriched diet for 50 days; one group was treated with gemfibrozil and the other with placebo.

RESULTS

The hyperlipidemic diet induced a significant increase in total cholesterol; this was prevented by gemfibrozil (P<0.05). The increase in platelet-fibrinogen binding induced by hypercholesterolemia was mildly reduced in the gemfibrozil treated animals. Histological analysis of aortic vascular wall (abdominal aorta at the iliac bifurcation) from hyperlipidemic animals showed early lesions with fibrinogen infiltration; the lesions were reduced in the fibrate-treated animals.

CONCLUSIONS

Gemfibrozil delayed the development of peripheral atherosclerotic plaque, normalised the impaired lipid profile induced by the hyperlipidemic diet and did not show a functionally detectable platelet pro-activating effect able to increase platelet-fibrinogen binding.

C-reactive protein in the arterial intima: role of C-reactive protein receptor-dependent monocyte recruitment in atherogenesis

Infiltration of monocytes into the arterial wall is an early cellular event in atherogenesis. Recent evidence shows that C-reactive protein (CRP) is deposited in the arterial intima at sites of atherogenesis. In this study, we demonstrate that CRP deposition precedes the appearance of monocytes in early atherosclerotic lesions. CRP is chemotactic for freshly isolated human blood monocytes. A specific CRP receptor is demonstrated on monocytes in vitro as well as in vivo, and blockage of the receptor by use of a monoclonal anti-receptor antibody completely abolishes CRP-induced chemotaxis. CRP may play a major role in the recruitment of monocytes during atherogenesis.

Experimental thrombosis I: relation with fibrinogen and other haemostatic parameters

Epidemiological studies have shown that the haemostatic parameters Fibrinogen (Fg), Factor VII (F VII), Factor VIII (F VIII), von Willebrand factor (vWF), Tissue Plasminogen Activator (t-PA), Plasminogen Activator Inhibitors (PAI) are risk factors/markers of ischemic cardiovascular disease. Ferritin (sFER) and Leukocytosis have also been implicated. In the present study we have followed the levels of fibrinogen, von Willebrand factor and thrombomodulin in relation to lipids, iron and the appearance of atherosclerotic lesions in New Zealand rabbits fed with a cholesterol enriched diet for a two-month period compared with a group of control rabbits. Hematocrit and white blood cell count (WBC) were measured in parallel. In hyperchlesterolemic rabbits the levels of fibrinogen and von Willebrand factor increased progressively, showing a positive correlation with the increasing cholesterol levels. There was an increase in soluble thrombomodulin beginning at the eighth week of study. In addition, these animals showed gross intimal atherosclerotic lesions in the whole extension of their aortas. Immunohistochemical studies showed the presence of fibrin(ogen) related antigen throughout the arterial wall and in the central portions of the atheromas. In the control group there was no formation of atherosclerotic plaques and all haemostatic, haematological and biochemical parameters were within the normal range. WBC and sFER levels were unaffected in both groups. Our results show that increased levels of fibrinogen and von Willebrand factor, known coronary risk factors, are strongly associated with the formation of atherosclerotic plaques in rabbits. The plaques contain a considerable amount of fibrinogen related antigen.

Simvastatin attenuates vascular hypercoagulability in cardiac transplant recipients

BACKGROUND

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors have been shown to reduce cardiac allograft failure and to lower the incidence of transplant coronary artery disease. These effects result from as yet unknown mechanisms not clearly attributable to lipid lowering. We here report that low-dose simvastatin treatment inhibits excessive expression of monocyte tissue factor (TF) and reduces the persistent hypercoagulability state seen in cardiac transplant recipients.

METHODS

Fifteen consecutive heart transplant recipients receiving standard oral immunosuppression were newly assigned to a 10 mg daily simvastatin therapy. Levels of TF activity in both unstimulated and lipopolysaccharide-stimulated peripheral blood mononuclear cells drawn from transplant recipients before and under simvastatin therapy were evaluated by one-stage clotting assay.

RESULTS

Monocyte TF activity was found to be significantly increased in cardiac transplant recipients when compared with healthy controls. Excessive monocyte procoagulant activity was reduced in cardiac transplant recipients during simvastatin treatment. This effect occurred independently of the reduction of serum low-density lipoprotein cholesterol. As demonstrated by reverse transcriptase-polymerase chain reaction, monocyte TF reduction by simvastatin, observed in 13 of the 15 transplant recipients investigated, could be ascribed to an inhibition of monocyte TF gene transcription. The reduction of monocyte TF activity during treatment with simvastatin paralleled with the normalization of elevated levels of thrombin-antithrombin complex, prothrombin fragment F1+2, and D-dimer, which are markers of thrombin and fibrin formation indicating coagulation activation after cardiac transplantation.

CONCLUSION

Inhibition of monocyte TF expression and attenuation of the persistent hypercoagulable state observed in cardiac transplant recipients during treatment with simvastatin may represent an important mechanism by which HMG-CoA reductase inhibitors protect against the development of transplant coronary artery disease.

Expression, localization, and activity of tissue factor pathway inhibitor in normal and atherosclerotic human vessels

Tissue factor (TF) pathway inhibitor (TFPI) is the major downregulator of the procoagulant activity of the TF-factor VIIa (FVIIa) complex (TF. FVII). The active TF present in the atherosclerotic vessel wall is proposed to be responsible for the major complication of primary atherosclerosis, namely, acute thrombosis after plaque rupture, but our knowledge of the sites of TFPI expression in relation to TF remains fragmentary. The aim of this study was to investigate the expression, localization, and activity of TFPI and its relation to the activity and distribution of TF in the normal and atherosclerotic vessel wall. We applied a novel approach in which serial cross sections of human vascular segments were used to perform a complete set of assays: immunolabeling for TFPI and/or TF, in situ hybridization for the expression of TFPI mRNA, ELISA for the determination of TFPI antigen, and functional assay for the activity of TFPI and TF. In healthy vessels, TFPI protein and mRNA are present in luminal and microvascular endothelial cells (ECs) and in the medial smooth muscle cells (SMCs). In atherosclerotic vessels, TFPI protein and mRNA frequently colocalized with TF in ECs overlying the plaque and in microvessels, as well as in the medial and neointimal SMCs, and in macrophages and T cells in areas surrounding the necrotic core. At the ultrastructural level, immunogold electron microscopy confirmed the localization of TFPI in ECs, macrophages/foam cells, and SMCs. In ECs and SMCs, the gold particles decorated the plasmalemma proper and the caveolae. ELISA on cross sections revealed that atherosclerotic tissues contain more TFPI than do the healthy vessels. TFPI was functionally active against TF. FVIIa-induced coagulation, and its activity was higher in those tissues that display less TF. The largest amount of TFPI and TF were detected in complicated arterial plaques. By immunofluorescence, TFPI colocalized with platelet- and fibrin-rich areas within the organized thrombi. Atherosclerotic vessel sections promote activation of factor X, which is dependent on the presence of TF and enhanced by preincubation of the sections with anti-TFPI IgG. Taken altogether, our results suggest that TFPI is largely expressed in the normal vessel wall and enhanced in the atherosclerotic vessel, in a manner suggesting a significant role of TFPI in the regulation of TF activity.

The clinical manipulation of angiogenesis: pathology, side-effects, surprises, and opportunities with novel human therapies

The first phase of angiogenesis research has provided knowledge of the basic pathobiology of angiogenesis and its manipulation in models, mouse, and man. The first line of therapeutic substances has been devised and is now in clinical trials. New lessons are being learned from clinical observations. Unexpected side-effects are being noted, particularly affecting the nervous system. Other side-effects may be anticipated from a sound knowledge of clinical pathology and recognition of the commonality of angiogenesis to multiple disease mechanisms, but these may be tolerable or avoidable. Angiogenesis researchers await further feedback and ideas from the clinic to stimulate the next phase of basic and applied research.

Integrin alphavbeta3-RGDS interaction mediates fibrin-induced morphological changes of glomerular endothelial cells

BACKGROUND

In our previous studies, we found that intraglomerular deposition of fibrin and its metabolites was related to glomerular sclerosis and reduced renal function. It has been reported that both overlying and underlying fibrin may induce specific morphological changes of cultured endothelial cells from large blood vessels. The dependency of these morphological changes on the integrin alphavbeta3-arginyl-glycyl-aspartyl-serine (RGDS) interaction is still controversial. We hypothesized that glomerular endothelial cells (GECs) stimulated by fibrin might undergo morphological changes through an integrin alphavbeta3-RGDS interaction. Methods. In vitro studies were performed to examine the growing status of GECs stimulated by overlying and underlying fibrin gels in the presence or absence of the following: 50 microg/ml anti-alphavbeta3 integrin monoclonal antibody 23C6 or nonimmune mouse IgG, 1 mg/ml synthetic RGDS or arginyl-glycyl-glycyl-serine (RGGS) peptide, 10 mg/ml sodium heparin, 100 microg/ml cycloheximide, and 10 microM actinomycin D. Fast protein liquid chromatography (FPLC)-purified fibrinogen and the third to fifth passages of human GECs were also used in this study.

RESULTS

GECs developed capillary tube structure after 60 hours of culturing on fibrin gels, and GECs cultured on gelatin-coated plates displayed a monolayer of cobblestone-like cells in the presence or absence of 23C6 and synthetic RGDS peptide. Fibrin-induced capillary tube formation was promoted by 23C6 and inhibited by RGDS peptide, cycloheximide, and actinomycin D. Disorganization of the GEC monolayer was induced by overlying fibrin, but was not induced by overlying agarose gels and glass cover slips or culturing in fibrinogen, 0.05 NIH U/ml thrombin, fibrin supernatants, as well as in fibrin degradation products. Disorganization of GEC monolayer can be induced by both des-AA-fibrin and des-AABB-fibrin and was unaffected by heparin. Furthermore, both 23C6 and synthetic RGDS peptide prevented disorganization of GECs induced by overlying fibrin, whereas nonimmune mouse IgG, synthetic RGGS peptide, cycloheximide, and actinomycin D had no similar effect.

CONCLUSIONS

GECs cultured on fibrin gels may develop capillary structure spontaneously, and GECs covered by fibrin gels may undergo disorganization. Our data suggest that these GEC morphological changes are mediated by an integrin alphavbeta3-RGDS interaction.

Fibrin Fragment Induction of Plasminogen Activator Inhibitor Transcription Is Mediated by Activator Protein-1 Through a Highly Conserved Element

Plasminogen activator inhibitor type-1 (PAI-1), a serine protease inhibitor, affects the processes of fibrinolysis, wound healing, and vascular remodeling. We have demonstrated that PAI-1 transcription is induced by D dimer, a plasmin proteolytic fragment of fibrin, supporting its role in negative feedback on peri-cellular proteolysis. The focus of this study was to define the mechanism of D dimer’s effects on PAI-1 transcription. D dimer increased the binding activity of the transcription factor activator protein-1 components c-fos/junD and c-fos mRNA levels in a time- and concentration-dependent manner to a greater extent than fibrinogen. Both basal and D dimer-induced PAI-1 transcriptional activity were entirely dependent on elements within the −161 to −48 bp region of the PAI-1 gene in fibroblasts. Mutations within the AP-1–like element (−59 to −52 bp) in the PAI-1 gene affected D dimer-induced transcriptional activity, c-fos/junD DNA binding, and basal and c-fos inducible PAI-1 transcriptional activity. Furthermore, expression of either wild-type or mutant c-fos proteins augmented or diminished the response of the PAI-1 promoter (−161 to +26 bp) to D dimer, respectively. D dimer-induced binding of c-fos/junD to the highly conserved and unique AP-1 like element in the PAI-1 gene provides a mechanism whereby specific fibrin fragments control fibrin persistence at sites of inflammation, fibrosis, and neoplasia.

Fibrin Fragment Induction of Plasminogen Activator Inhibitor Transcription Is Mediated by Activator Protein-1 Through a Highly Conserved Element

Plasminogen activator inhibitor type-1 (PAI-1), a serine protease inhibitor, affects the processes of fibrinolysis, wound healing, and vascular remodeling. We have demonstrated that PAI-1 transcription is induced by D dimer, a plasmin proteolytic fragment of fibrin, supporting its role in negative feedback on peri-cellular proteolysis. The focus of this study was to define the mechanism of D dimer’s effects on PAI-1 transcription. D dimer increased the binding activity of the transcription factor activator protein-1 components c-fos/junD and c-fos mRNA levels in a time- and concentration-dependent manner to a greater extent than fibrinogen. Both basal and D dimer-induced PAI-1 transcriptional activity were entirely dependent on elements within the −161 to −48 bp region of the PAI-1 gene in fibroblasts. Mutations within the AP-1–like element (−59 to −52 bp) in the PAI-1 gene affected D dimer-induced transcriptional activity, c-fos/junD DNA binding, and basal and c-fos inducible PAI-1 transcriptional activity. Furthermore, expression of either wild-type or mutant c-fos proteins augmented or diminished the response of the PAI-1 promoter (−161 to +26 bp) to D dimer, respectively. D dimer-induced binding of c-fos/junD to the highly conserved and unique AP-1 like element in the PAI-1 gene provides a mechanism whereby specific fibrin fragments control fibrin persistence at sites of inflammation, fibrosis, and neoplasia.

Potential new cardiovascular risk factors: left ventricular hypertrophy, homocysteine, lipoprotein(a), triglycerides, oxidative stress, and fibrinogen

The 1996 Bethesda Conference acknowledged left ventricular hypertrophy, hyperhomocysteinemia, lipoprotein(a) excess, hypertriglyceridemia, oxidative stress, and hyperfibrinogenemia as possible new cardiac risk factors. This review summarizes the current literature that supports these conditions as cardiac risk factors. Left ventricular hypertrophy is an independent risk factor for vascular disease. Improvement or progression of left ventricular hypertrophy influences subsequent cardiovascular complications. Clinical trials are under way to assess the potential benefit of decreasing homocysteine levels. The role of lipoprotein(a) excess in vascular disease is controversial. The atherogenic potential of lipoprotein(a) seems to be neutralized by effective reduction of low-density lipoprotein cholesterol levels. Increasing evidence supports an independent role of hypertriglyceridemia in cardiovascular disease and a possible clinical benefit from decreasing triglyceride levels. Among antioxidant micronutrients, supplementation with vitamin E has been shown to be beneficial in primary and secondary prevention studies. Data supporting the use of other antioxidants are much weaker. Preliminary evidence suggests that reducing fibrinogen levels in patients with high baseline levels and coronary disease may be beneficial. Despite the potential relation between new risk factors and cardiovascular disease, routine clinical application of these conditions as cardiovascular risk factors would be premature. Evidence is needed that these conditions extend prognostic ability beyond conventional risk factors and that modification of these conditions can reduce the risk for cardiovascular events.

The renin-angiotensin system in essential hypertension: associations with cardiovascular risk

The importance of the renin-angiotensin system (RAS) in blood pressure regulation is well established. High RAS activity has also been implicated in connection with elevated cardiovascular risk in patients with essential hypertension. Data from epidemiological studies have related high plasma renin levels in essential hypertensive patients to cardiovascular complications. However, whether renin itself is a risk factor of cardiovascular events or just acts as a marker for other risk factors still remains to be elucidated. Several possible mechanisms that could be responsible for the association between elevated RAS activity and cardiovascular risk are reviewed. The concept of high RAS activity being a cardiovascular risk factor is strongly supported by results from large clinical studies showing the beneficial effects of angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers in congestive heart failure and hypertension. Knowing more about the exact mechanisms of the association between high RAS activity and cardiovascular complications would enable us to profile the treatment of high blood pressure more specifically to improve outcome in individuals or groups of patients.

Measuring plasma fibrinogen to predict stroke and myocardial infarction: an update

Plasma fibrinogen is a major determinant of platelet aggregation and blood viscosity. The decrease in plasma fibrinogen by bezafibrate is associated with a decrease in the risk of reinfarctions. To strengthen the predictive value of plasma fibrinogen with respect to cardiovascular risk, we performed a meta-analysis of studies conducted between 1984 and 1998. Emphasis has been put on the relationship between high levels of plasma fibrinogen and fatal and/or nonfatal cardiovascular events in both the general population and in patients with previous cardiovascular events. Twenty-two studies (13 prospective, 5 cross-sectional, and 4 case-control) addressing the association between fibrinogen plasma concentrations and cardiovascular disease were analyzed. The overall estimate of risk of cardiovascular event in subjects with plasma fibrinogen levels in the higher tertile, was twice as high as that of subjects in the lower one (odds ratio, 1.99; 95% confidence interval, 1.85 to 2.13). High plasma fibrinogen levels were associated with an increased risk of cardiovascular disease in healthy as much as in high-risk individuals. A metaregression showed no confounding effects attributable to selected characteristics of retrieved studies. A subgroup analysis (study design, follow up, mean fibrinogen levels, percentage of smokers, and mean age) allowed us to conclude that fibrinogen is an independent risk factor for cardiovascular disease; that it interacts with major determinants of myocardial and cerebrovascular ischemia; and that, in secondary prevention studies, it enhances by 8% the prediction of future events by established risk factors. Thus, fibrinogen measurements should be encouraged to refine the overall risk profiles of individuals and to better tailor preventive interventions.

The clinical manipulation of angiogenesis: pathology, side-effects, surprises, and opportunities with novel human therapies

The first phase of angiogenesis research has provided knowledge of the basic pathobiology of angiogenesis and its manipulation in models, mouse, and man. The first line of therapeutic substances has been devised and is now in clinical trials. New lessons are being learned from clinical observations. Unexpected side-effects are being noted, particularly affecting the nervous system. Other side-effects may be anticipated from a sound knowledge of clinical pathology and recognition of the commonality of angiogenesis to multiple disease mechanisms, but these may be tolerable or avoidable. Angiogenesis researchers await further feedback and ideas from the clinic to stimulate the next phase of basic and applied research.

In situ detection of tissue factor within the coronary intima in rat cardiac allograft vasculopathy

Cardiac allograft vasculopathy is a major cause of morbidity and mortality of cardiac transplant recipients. The underlying cause of this disease remains unclear. Histological studies have implicated accelerated hemostasis and intravascular fibrin deposition in its pathogenesis. In the present study a defined model of this disease in the rat was used to elucidate the implication of tissue factor in the production of the hypercoagulable state observed in cardiac allograft vessels. Tissue factor protein and mRNA expression were studied in rat heart allografts developing allograft vasculopathy resembling human disease. Immunohistochemistry demonstrated tissue-factor-positive cells present in the allograft coronary intima and adventitia. Significant staining for tissue factor was detected in the endothelium lining coronary lesions in cardiac allografts and in interstitial mononuclear cells, respectively. Both transplant coronary endothelial cells and mononuclear cells contained tissue factor mRNA as indicated by oligo-cell reverse transcription polymerase chain reaction after laser-assisted cell picking. In contrast, tissue factor mRNA and protein were not or negligibly detectable within the coronary intima of nontransplanted control hearts. Thus, the present study clearly demonstrates that aberrant tissue factor expression occurs within the coronary intima after cardiac transplantation. Tissue factor, activating downstream coagulation mechanisms, may account for the intravascular clotting abnormalities observed in cardiac allografts and may represent a key factor in transplant atherogenesis.

The role of tissue factor in the pathogenesis of thrombosis and atherosclerosis

TF is a major regulator of coagulation and hemostasis. High levels of TF antigen and activity are detected in atherosclerotic lesions, particularly in the advanced lesions. When the plaques are ruptured or eroded, exposure of cellular and extracellular TF to circulating blood play a pivotal role in mediating fibrin-rich thrombus formation leading to acute coronary syndromes. On the other hand, activation of blood coagulation and deficiency of coagulation inhibitors, without endothelial cell denudation, are considered to be an important factor of thrombogenesis in the microcirculation. The imbalance between TF and TFPI seems to be important in promoting fibrin thrombus formation in the lung of endotoxin induced DIC condition.

Effect of crosslinking by factor XIIIa on the migration of vascular smooth muscle cells into fibrin gels

We evaluated the migration of vascular smooth muscle cells into crosslinked fibrin gels, using an in vitro assay system. Vascular smooth muscle cells from bovine fetal aorta migrated into non-crosslinked and crosslinked fibrin gels and showed a characteristic elongated spindle-shaped appearance with long cytoplasmic processes. The cells displayed two-fold increase in migration into crosslinked fibrin gels compared to non-crosslinked gels, suggesting the importance of fibrin crosslinking by factor XIIIa on its three-dimensional structure for the migration of smooth muscle cells.

Regulation of the uPAR/uPA system expressed on monocytes by the deactivating cytokines, IL-4, IL-10 and IL-13: consequences on cell adhesion to vitronectin and fibrinogen

Urokinase (uPA) and its receptor (uPAR) have been proposed to be involved in monocyte migration by inducing degradation of matrix proteins. In addition, uPAR is also implicated in cell adhesion to the vascular wall. The adhesive function of uPAR depends on a direct interaction with vitronectin which is increased by uPA and by modification of cell surface integrin (such as CD11b-CD18) when associated to uPAR. In this study we analysed the role of three deactivating cytokines, IL-4, IL-10 and IL-13, on the surface expression of uPA, uPAR and CD11b by monocytes and their consequences on monocyte adhesion to immobilized fibrinogen and vitronectin. IL-10 induced a decrease in uPA and CD11b after 18 h incubation and a delayed decrease in uPAR which was only significant after 48 h incubation. These results may explain the decrease in monocyte adhesion, which was observed after an 18 h incubation with IL-10, on immobilized vitronectin and fibrinogen. In contrast, IL-4 and IL-13 induced a decrease in uPAR after 18 h and a significant increase in uPA both in the cell lysates and at the cell surface, as well as an increase in cell surface associated CD11b. These cytokines did not modify cell adhesiveness to vitronectin or fibrinogen despite the increase in CD11b-CD18. This could be due to the decrease in uPAR because CD11b-CD18/uPAR forms a cell adhesion complex. In addition, the increase in uPA induced by IL-4 could counterbalance the direct interaction of uPAR with vitronectin. The increase in uPA suggests that IL-4 and IL-13 could induce plaque fissuring by monocytes, whereas IL-10 may induce protection against matrix protein degradation by decreasing uPA.