Pharmacological approaches and strategies for therapeutic modulation of fibrinogen

Fibrin(ogen) in human disease: both friend and foe

Fibrinogen is an abundant protein synthesized in the liver, present in human blood plasma at concentrations ranging from 1.5-4 g/L in healthy individuals with a normal half-life of 3-5 days. With fibrin, produced by thrombin-mediated cleavage, fibrinogen plays important roles in many physiological processes. Indeed, the formation of a stable blood clot, containing polymerized and cross-linked fibrin, is crucial to prevent blood loss and drive wound healing upon vascular injury. A balance between clotting, notably the conversion of fibrinogen to fibrin, and fibrinolysis, the proteolytic degradation of the fibrin mesh, is essential. Disruption of this equilibrium can cause disease in distinct manners. While some pathological conditions are the consequence of altered levels of fibrinogen, others are related to structural properties of the molecule. The source of fibrinogen expression and the localization of fibrin(ogen) protein also have clinical implications. Low levels of fibrinogen expression have been detected in extra-hepatic tissues, including carcinomas, potentially contributing to disease. Fibrin(ogen) deposits at aberrant sites including the central nervous system or kidney, can also be pathological. In this review, we discuss disorders in which fibrinogen and fibrin are implicated, highlighting mechanisms that may contribute to disease.

Bromelain and cardiovascular risk factors in diabetes: An exploratory randomized, placebo controlled, double blind clinical trial

OBJECTIVE

To assess whether the dietary supplement (bromelain) has the potential to reduce plasma fibrinogen and other cardiovascular disease (CVD) risk factors in patients with diabetes.

METHODS

This randomized placebo controlled, double blind, parallel design, efficacy study was carried out in China and investigated the effect of 12 weeks of bromelain (1,050 mg/day) on plasma fibrinogen. This randomized controlled trial (RCT) recruited 68 Chinese diabetic patients [32 males and 36 females; Han origin, mean age of 61.26 years (standard deviation (SD), 12.62 years)] with at least one CVD risk factor. Patients were randomized into either bromelain or placebo group. While bromelain group received bromelain capsule, the placebo group received placebo capsule which consisted inert ingredient and has no treatment effect. Subjects were required to take 1,050 mg (3×350 mg) of either bromelain or starch-filled placebo capsules, two to be taken (2×350 mg) after breakfast and another (350 mg) after dinner, daily for 12 weeks. Plasma fibrinogen, CVD risk factors and anthropometric indicators were determined at baseline and at 12 weeks.

RESULTS

The change in the fibrinogen level in the bromelain group at the end of the study showed a mean reduction of 0.13 g/L (standard deviation (SD) 0.86g/L) compared with the mean reduction of 0.36 g/L (SD 0.96 g/L) for the placebo group. However, there was no significant difference in the mean change in fibrinogen between the placebo and bromelain groups (mean difference=0.23g/L (SD 0.22 g/L), =0.291). Similarly, the difference in mean change in other CVD risk factors (blood lipids, blood pressure), blood glucose, C-reactive protein and anthropometric measures between the bromelain and placebo groups was also not statistically significant. Statistical differences in fibrinogen between bromelain and placebo groups before the trial despite randomization may have influenced the results of this study.

CONCLUSION

This RCT failed to show a beneficial effect in reducing fibrinogen or influencing other selected CVD risk factors but suggests other avenues for subsequent research on bromelain.

Crosstalk between coagulation and inflammation in mastitis and metritis in dairy cows

Coagulation and inflammation are closely related as part of the mechanisms of host defence during a severe infection. The aim of this study was to investigate the relation between thrombin as a factor in both the coagulative and inflammatory processes and neutrophil secretory function on the basis of lactoferrin (LF), elastase and myeloperoxidase release in the course of mastitis and metritis in cows. Thrombin generation was measured on the basis of hydrolysis of SAR-PRO-ARG-pNA and lactoferrin concentration was estimated by an ELISA method. The greatest thrombin generation was observed in the metritis group (1.18 +/- 0.62 IU). The level of LF was the highest in the group of cows with mastitis (0.74 +/- 0.55 mg/ml) in the first phase of the disease. In the second phase of the diseases the level of serum LF in cows with mastitis diminished to the value of 0.41 +/- 0.16 mg/ml, whereas in cows with metritis the level of LF increased to 0.51 +/- 0.17 mg/ml. This study reveals that the excessive production of thrombin not only causes hypercoagulatory disorders but also exaggerates neutrophil function by the release of some enzymes which may play a destructive role during disseminated intravascular coagulation (DIC). These enzymes also inhibit anticoagulative systems, thus potentially worsening the course of the disease.

Administration of recombinant human IL11 after supralethal radiation exposure promotes survival in mice: interactive effect with thrombopoietin

In the present study, we evaluated the therapeutic potential of recombinant human IL11 in lethally irradiated C57BL6/J mice exposed to gamma rays. IL11 administered for 5 consecutive days beginning 2 h after total-body irradiation with 8 or 9 Gy 60Co gamma rays resulted in a significant increase in 30-day survival. When IL11 was administered, only a slight improvement in the hematopoietic status (both blood cell counts and progenitor cells) was observed after an 8-Gy exposure, and no improvement in hematopoietic reconstitution was observed after 9 Gy total-body irradiation. The enhancement of fibrinogen in the plasma of irradiated animals suggested the importance of infections in the death of animals. IL11 was able to limit the increase in fibrinogen levels. However, prevention of bacterial infections by antibiotic treatment, although it delayed death, was ineffective in promoting survival either in placebo-treated and IL11-treated mice. IL11 was administered along with thrombopoietin (TPO) or bone marrow transplantation to limit the hematopoietic syndrome, in addition to antibiotic treatment. When IL11 was combined with TPO, a potent stimulator of hematopoiesis, the survival of animals which had been irradiated with 10 Gy 137Cs gamma rays was increased significantly compared to those treated with IL11 or TPO alone. Furthermore, an interactive effect of TPO and IL11 on hematopoietic reconstitution was observed. Similarly, IL11 in combination with bone marrow transplantation enhanced survival after 15 Gy 137Cs gamma rays. These data suggest that the effect of IL11 on the hematopoietic system is only moderate when it is used alone in supralethally irradiated mice but that the effect is improved in the presence of a hematopoietic growth factor or bone marrow transplantation.

Effects of diet, drugs, and genes on plasma fibrinogen levels

Plasma levels of fibrinogen have been identified as independent risk predictors of cardiovascular disease. This has greatly increased interest in the regulation of plasma fibrinogen levels. Many demographic and environmental factors are known to affect fibrinogen levels, such as diet, use of several drugs, age, smoking, body mass, gender, physical exercise, race, and season. Additionally, it is also known that genetic factors determine the fibrinogen levels, and also that they determine the response of fibrinogen levels to environmental factors. Estimates, based on twin studies, suggest that 30-50% of the plasma fibrinogen level is genetically determined. The effect of dietary components on plasma fibrinogen levels is modest. Several components have been identified as factors that influence fibrinogen levels. Among those are fish oil, other lipids, and fibers. Dietary components that were expected to have an effect on fibrinogen, but for which no association was observed are black and green tea. Several drugs are known to influence fibrinogen levels, the most studied of which are platelet aggregation inhibiting drugs, such as ticlopidine, and the lipid lowering fibric acid derivatives (fibrates). Both types of drugs decreased the plasma fibrinogen level by about 10%, and bezafibrate lowers fibrinogen even more in patients with diabetes. No clear effect was observed for the HMG-CoA reductase inhibitors (statins). In the Bezalip study, fibrinogen levels decreased in patients treated with bezafibrate, but this had no clear effect on the risk of cardiovascular disease. This suggests that several mechanisms influence the fibrinogen level and that these mechanisms may contribute differently to cardiovascular disease. Several variations in the fibrinogen genes have been described and especially variations in the promoter region of the fibrinogen beta-gene are interesting, because the synthesis of the fibrinogen B beta chain is considered to be the rate limiting step in the fibrinogen biosynthesis. In many studies the fibrinogen beta-gene polymorphisms (-455G/A, -148C/T, and BclI) are found to be associated with the plasma levels of fibrinogen. However, they are not associated with the risk of cardiovascular events, although in several studies an association with the severity and progression of atherosclerosis has been reported. It has also been observed frequently that the fibrinogen beta-gene promoter polymorphisms are associated with the response of fibrinogen levels to environmental factors, such as exercise and trauma. In conclusion, plasma fibrinogen levels are regulated by an interesting and complex interplay between environmental and genetic factors.

Fibrinogen promotes neutrophil activation and delays apoptosis

The acute phase of the inflammatory response involves an increase in the concentrations of different plasma proteins that include fibrinogen (Fbg) and multiple proinflammatory mediators. In parallel, neutrophil activation is thought to play a crucial role in several inflammatory conditions, and it has been recently demonstrated that Fbg specifically binds to the alpha-subunit of CD11b/CD18 on neutrophil surface. Although several reports have shown that CD11b engagement modulates neutrophil responses, the effect of human Fbg (hFbg), one of CD11b physiologic ligands, has not been exhaustively investigated. We have now shown that incubation of purified neutrophils with hFbg induces a transient and rapid elevation of free intracellular Ca2+. This early intracellular signal is accompanied by changes in the expression of neutrophil activation markers, including enhancement of CD11b and CD66b, and down-regulation of FcgammaRIII. In addition, we have evaluated the effect of hFbg on two functional events related to expression and resolution of inflammation: cytotoxic capacity and rate of neutrophil apoptosis. We have found that activation of neutrophils by hFbg resulted in both enhancement of phagocytosis and Ab-dependent cellular cytotoxicity, and delay of apoptosis. We conclude that during inflammatory processes, soluble Fbg could influence neutrophil responses, increasing and prolonging their functional capacity.

Single administration of thrombopoietin to lethally irradiated mice prevents infectious and thrombotic events leading to mortality

A sufficiently high dose of thrombopoietin to overcome initial c-mpl-mediated clearance stimulates hematopoietic reconstitution following myelosuppressive treatment. We studied the efficacy of thrombopoietin on survival after supralethal total body irradiation (9 Gy) of C57BL6/J mice and the occurrence of infectious and thrombotic complications in comparison with a bone marrow graft or prophylactic antibiotic treatment. Administration of 0.3 microg thrombopoietin, 2 hours after irradiation, protected 62% of the mice as opposed to no survival in placebo controls. A graft with a supraoptimal number of syngeneic bone marrow cells (10(6) cells) fully prevented mortality, whereas antibiotic treatment was ineffective. Blood cell recovery was observed in the thrombopoietin-treated mice but not in the placebo or antibiotic-treated group. Bone marrow and spleen cellularity as well as colony-forming unit granulocyte-macrophage and burst-forming unit erythroid were considerably increased in thrombopoietin-treated mice relative to controls. Histologic examination at day 11 revealed numerous petechiae and vascular obstructions within the brain microvasculature of placebo-treated mice, which was correlated with hypercoagulation and hypofibrinolysis. Thrombopoietin treatment prevented coagulation/fibrinolysis disorder and vascular thrombosis. High fibrinogen levels were related to bacterial infections in 67% of placebo-treated mice and predicted mortality, whereas the majority of the thrombopoietin-treated mice did not show high fibrinogen levels and endotoxin was not detectable in plasma. We conclude that thrombopoietin administration prevents mortality in mice subjected to 9-Gy total body irradiation both by interfering in the cascade leading to thrombotic complications and by amelioration of neutrophil and platelet recovery and thus protects against infections and hemorrhages.

Alteration of the fibrinogen molecule and its phosphorylation state in myocardial infarction patients undergoing thrombolytic treatment

Fibrinogen was purified by protamine-agarose chromatography from plasma from three patients after their submission to hospital due to acute myocardial infarction. The total amount of phosphate bound to fibrinogen and the concentration of fibrinogen was determined in samples withdrawn immediately after submission and after thrombolytic treatment. Streptokinase treatment almost totally removed circulating fibrinogen while recombinant tissue plasminogen activator spared much of it. In patients treated with streptokinase, the new circulating fibrinogen was homogeneous according to the single alpha-band seen after sodium dodecyl sulphate polyacrylamide gel electrophoresis analysis under reducing conditions, whereas fibrinogen from the recombinant tissue plasminogen activator-treated patient as well as healthy controls exhibited two alpha-bands in the 66-kDa region. The molar ratios of phosphate to fibrinogen of healthy controls and commercial fibrinogen were 0.82 (+/-0.04) and 0. 87 (+/-0.05), respectively. For two streptokinase-treated patients the degree of phosphorylation increased threefold from a normal range of 0.97 (+/-0.11) and 0.67 (+/-0.09) mol/mol fibrinogen before treatment to 3.33 (+/-0.32) and 1.86 (+/-0.17) mol/mol in newly formed fibrinogen on day 1. Recombinant tissue plasminogen activator treatment led to a smaller increase in phosphorylation, from 1.14 (+/-0.13) pretreatment to 1.65 (+/-0.11) after treatment on day 1. In conclusion we show in this report that after streptokinase treatment of patients with acute myocardial infarction, the new Aalpha-chain of fibrinogen was a homogeneous single 66-kDa band on sodium dodecyl sulphate polyacrylamide gel electrophoresis under reducing conditions and that the degree of phosphorylation of plasma fibrinogen was elevated, approaching the theoretical limit of 4 mol phosphate/mol fibrinogen.

Fibrinogen fractions in the third trimester of pregnancy and in puerperium

The concentration of fibrinogen, its fractions, and the concentration of C-reactive protein were determined in 45 healthy pregnant women before and after vaginal (27) or caesarean section 18 delivery. The control group consisted of 33 blood donors. In pregnancy, increased concentration of total fibrinogen and its fractions and a normal concentration of C-reactive protein were noted. Three days after vaginal delivery the concentration of total and high molecular weight fibrinogen fraction decreased slightly and the ratio of high to low molecular weight fibrinogen increased. After caesarean section both total and high molecular weight fibrinogen and the ratio of high to low molecular weight fibrinogen increased. The C-reactive protein concentration increased after either type of delivery. The degree of augmentation, however, was ten times as strong after caesarean section. In all women at the end of puerperium the concentrations of the compounds studied returned to normal values. The results suggest that the mechanisms leading to the increase of fibrinogen during pregnancy and after delivery are different. The increase of all fibrinogen fractions in pregnancy may depend first of all on hormones, whereas the increased proportion of high molecular weight to low molecular weight fibrinogen after delivery depends on the acute phase reaction. The degree of this reaction depends on the type of delivery.

Fibrates Suppress Fibrinogen Gene Expression in Rodents Via Activation of the Peroxisome Proliferator-Activated Receptor-

Plasma fibrinogen levels have been identified as an important risk factor for cardiovascular diseases. Among the few compounds known to lower circulating fibrinogen levels in humans are certain fibrates. We have studied the regulation of fibrinogen gene expression by fibrates in rodents. Treatment of adult male rats with fenofibrate (0.5% [wt/wt] in the diet) for 7 days decreased hepatic A-, Bβ-, and γ-chain mRNA levels to 52% ± 7%, 46% ± 8%, and 81% ± 19% of control values, respectively. In parallel, plasma fibrinogen concentrations were decreased to 63% ± 7% of controls. The suppression of fibrinogen expression was dose-dependent and was already evident after 1 day at the highest dose of fenofibrate tested (0.5% [wt/wt]). Nuclear run-on experiments showed that the decrease in fibrinogen expression after fenofibrate occurred at the transcriptional level, as exemplified for the gene for the A-chain. Other fibrates tested showed similar effects on fibrinogen expression and transcription. The effect of fibrates is specific for peroxisome proliferator-activated receptor- (PPAR) because a high-affinity ligand for PPARγ, the thiazolidinedione BRL 49653, lowered triglyceride levels, but was unable to suppress fibrinogen expression. Direct evidence for the involvement of PPAR in the suppression of fibrinogen by fibrates was obtained using PPAR-null (−/−) mice. Compared with (+/+) mice, plasma fibrinogen levels in (−/−) mice were significantly higher (3.20 ± 0.48 v 2.67 ± 0.42 g/L). Also, hepatic fibrinogen A-chain mRNA levels were 25% ± 11% higher in the (−/−) mice. On treatment with 0.2% (wt/wt) fenofibrate, a significant decrease in plasma fibrinogen to 77% ± 10% of control levels and in hepatic fibrinogen A-chain mRNA levels to 65% ± 12% of control levels was seen in (+/+) mice, but not in (−/−) mice. These studies show that PPAR regulates basal levels of plasma fibrinogen and establish that fibrate-suppressed expression of fibrinogen in rodents is mediated through PPAR.

Fibrates Suppress Fibrinogen Gene Expression in Rodents Via Activation of the Peroxisome Proliferator-Activated Receptor-

Plasma fibrinogen levels have been identified as an important risk factor for cardiovascular diseases. Among the few compounds known to lower circulating fibrinogen levels in humans are certain fibrates. We have studied the regulation of fibrinogen gene expression by fibrates in rodents. Treatment of adult male rats with fenofibrate (0.5% [wt/wt] in the diet) for 7 days decreased hepatic A-, Bβ-, and γ-chain mRNA levels to 52% ± 7%, 46% ± 8%, and 81% ± 19% of control values, respectively. In parallel, plasma fibrinogen concentrations were decreased to 63% ± 7% of controls. The suppression of fibrinogen expression was dose-dependent and was already evident after 1 day at the highest dose of fenofibrate tested (0.5% [wt/wt]). Nuclear run-on experiments showed that the decrease in fibrinogen expression after fenofibrate occurred at the transcriptional level, as exemplified for the gene for the A-chain. Other fibrates tested showed similar effects on fibrinogen expression and transcription. The effect of fibrates is specific for peroxisome proliferator-activated receptor- (PPAR) because a high-affinity ligand for PPARγ, the thiazolidinedione BRL 49653, lowered triglyceride levels, but was unable to suppress fibrinogen expression. Direct evidence for the involvement of PPAR in the suppression of fibrinogen by fibrates was obtained using PPAR-null (−/−) mice. Compared with (+/+) mice, plasma fibrinogen levels in (−/−) mice were significantly higher (3.20 ± 0.48 v 2.67 ± 0.42 g/L). Also, hepatic fibrinogen A-chain mRNA levels were 25% ± 11% higher in the (−/−) mice. On treatment with 0.2% (wt/wt) fenofibrate, a significant decrease in plasma fibrinogen to 77% ± 10% of control levels and in hepatic fibrinogen A-chain mRNA levels to 65% ± 12% of control levels was seen in (+/+) mice, but not in (−/−) mice. These studies show that PPAR regulates basal levels of plasma fibrinogen and establish that fibrate-suppressed expression of fibrinogen in rodents is mediated through PPAR.

Prostaglandin-independent stimulation of interleukin-6 production by fibrinogen degradation product D in perfused murine liver

Bacterial endotoxin (LPS) and fibrinogen degradation product D (FDP-D) are both potent stimulators of interleukin-6 (IL-6) production in liver, however, there are differences in their metabolic effects. The aim of the present study was to compare the role of prostaglandins in the enhancement of IL-6 production by LPS or FDP-D in perfused mouse livers. Indomethacin inhibited the effect of LPS significantly but was ineffective in the case of FDP-D. Accordingly, production of prostaglandins D2 and E2 was not elevated following the addition of FDP-D, while their formation was increased several fold by LPS. At the same time interleukin-1 (IL-1) production in perfused liver rose markedly upon the addition of FDP-D. It is suggested that prostaglandins are not involved in the effects of FDP-D on the liver. The stimulatory effect of FDP-P on IL-6 production might be the consequence of elevated IL-1 levels.

Postoperative plasma interleukin-6 in patients with renal cancer correlates with C-reactive protein but not with total fibrinogen or with high molecular weight fibrinogen fraction

The concentration of fibrinogen (Fb) and its fractions, the levels of interleukin-6 (I1-6), C-reactive protein (CRP), and immunoglobulin G (IgG) were determined in 38 patients operated on because of renal cancer. The increased Fb and I1-6 concentrations were found in approximately one-half of the patients with malignancy. The relations among the high molecular weight (HMW) and two low molecular weight (LMW and LMW') fibrinogen fractions in these patients before surgery did not differ from the corresponding relations in normal subjects. The levels of all (except IgG) compounds studied increased after surgery and the peak of I1-6 was observed on the first postoperative day but that of CRP on the third day. The concentrations of total Fb and of its HMW fraction were the highest also on the third postoperative day and this was in contrast with the decline of low molecular weight fractions at the same time. These variations of estimated variables can be regarded as being relevant to the acute phase response. We have noted a correlation between the maximal concentrations of I1-6 and CRP, but not between the corresponding concentrations of Il-6 and total Fb or HMW Fb; this may suggest that the concentration of Fb is also under the control of a factor other than I1-6.