Stimulation of fibrinogen synthesis in cultured rat hepatocytes by fibrinogen degradation product fragment D

Regulation of fibrinogen synthesis

The plasma protein fibrinogen is encoded by 3 structural genes (FGA, FGB, and FGG) that are transcribed to mRNA, spliced, and translated to 3 polypeptide chains (Aα, Bβ, and γ, respectively). These chains are targeted for secretion, decorated with post-translational modifications, and assembled into a hexameric "dimer of trimers" (AαBβγ)2. Fully assembled fibrinogen is secreted into the blood as a 340 kDa glycoprotein. Fibrinogen is one of the most prevalent coagulation proteins in blood, and its expression is induced by inflammatory cytokines, wherein circulating fibrinogen levels may increase up to 3-fold during acute inflammatory events. Abnormal levels of circulating fibrinogen are associated with bleeding and thrombotic disorders, as well as several inflammatory diseases. Notably, therapeutic strategies to modulate fibrinogen levels have shown promise in experimental models of disease. Herein, we review pathways mediating fibrinogen synthesis, from gene expression to secretion. Knowledge of these mechanisms may lead to the identification of biomarkers and new therapeutic targets to modulate fibrinogen in health and disease.

Association of hemostasis and inflammation biomarkers with outcomes in acute coronary syndromes

Plaque rupture triggers a prothrombotic response that is counterbalanced by a fibrinolytic response. d -dimer serves as a marker of both processes. Inflammatory mediators are also released, evidenced with the rise of high-sensitive C reactive protein (hsCRP). Current evidence with these biomarkers has shown conflicting results. Determine an association between d -dimer and hsCRP within hospital and 1-year mortality in patients with acute coronary syndromes. In total, 127 patients were included. In-hospital mortality was 5.7%, and 1-year all-cause and cardiovascular mortality were 14.6 and 9.7%, respectively. The median of admission d -dimer for patients who died during hospital stay was higher than those who survived [4.59 (interquartile ranges (IQR) 1.94-6.05 μg/ml fibrinogen equivalent units (FEU)) vs. 0.56 (IQR 0.31-1.12 μg/ml FEU), P  = 0.001]. At 1-year follow-up, the median of admission d -dimer for patients who died was significantly higher than those who survived: 1.55 (IQR 0.91-5.08 μg/ml FEU) vs. 0.53 (IQR 0.29-0.90 μg/ml FEU), P  < 0.001. Positive d -dimer vs. negative d -dimer at admission analysis evidenced that almost 25% of the positive patients were dead at 1-year follow-up (22.4 vs. 2.4% negative d -dimer, P  = 0.011). Multivariate logistic regression analysis showed that d -dimer has an independent association with 1-year mortality [odds ratio 1.06 (95% confidence interval 1.02-1.10), P  = 0.006]. Positive significative correlations between d -dimer and hsCRP levels ( R  = 0.56, P  < 0.001) were found. High levels of admission d -dimer were strongly associated with in-hospital and 1-year mortality. Significant correlations with hsCRP could explain the inflammatory nature that led to poorer outcomes. d -dimer could be useful in risk stratification in acute coronary syndromes; however, a specific threshold should be defined for this type of patient.

Liver gene regulation of hemostasis-related factors is altered by experimental snake envenomation in mice

Few studies have addressed gene expression of hemostasis-related factors during acute thrombo-hemorrhagic diseases. Bites by the lanced-headed viper Bothrops jaracaca induce rapid hemostatic disturbances in victims, leading to systemic bleedings, thrombocytopenia and consumption coagulopathy. Although circulating levels of coagulation factors recover rapidly after administration of specific antivenom therapy, it is unclear if B. jararaca venom (BjV) upregulates the mRNA synthesis of hepatic hemostasis-related factors, or if the recovery occurs under basal conditions after the neutralization of venom components by antivenom. Thus, we aimed to investigate if BjV regulates gene expression of important hemostasis-related factors synthetized by the liver. On that account, Swiss mice were injected with saline or BjV (1.6 mg/kg b.w, s.c.), and after 3, 6 and 24 h blood samples and liver fragments were collected to analyze mRNA expression by real-time qPCR. Increased gene expression of fibrinogen chains, haptoglobin and STAT3 was observed during envenomation, particularly at 3 and 6 h. At 24h, mRNA levels of F10 were raised, while those of Serpinc1, Proc and Adamts13 were diminished. Surprisingly, F3 mRNA levels were steadily decreased at 3 h. Gene expression of Thpo, F7, F5 Tfpi, Mug1 was unaltered. mRNA levels of Vwf, P4hb, F8, F2, Plg, and Serpinf2 were minimally altered, but showed important associations with Nfkb1 gene expression. In conclusion, snakebite envenomation upregulates hepatic mRNA synthesis particularly of fibrinogen chains, and acute-phase markers. This response explains the fast recovery of fibrinogen levels after antivenom administration to patients bitten by B. jararaca snakes.

Age, functional status, and racial differences in plasma D-dimer levels in community-dwelling elderly persons

BACKGROUND

Dysregulation of immunologic and coagulation systems is common in elderly persons and is associated with many diseases of aging. Thrombotic events are a major cause of morbidity and mortality in the elderly population. This study assesses whether D-dimer, a marker of fibrinolytic activity, varies systematically by demographic, health, and functional measures, and derives a prediction model for factors related to D-dimer in a sample of community-dwelling elderly persons.

METHODS

D-dimer levels were assessed in a random sample of 1,727 community-dwelling elderly persons from five rural and urban counties in North Carolina in 1992, as part of the Established Populations for the Epidemiologic Studies of the Elderly (Duke University). All subjects were 72 years or older at the time of the blood draw. In addition, all subjects were surveyed yearly by telephone or in person each year from 1986 to 1992 for a variety of health, functional, and social factors. Levels of D-dimer in 1992 were related cross-sectionally to demographics (age, race, education, income, gender, smoking), function (Nagi, Rosow-Breslau, Katz, Older Americans Resources and Services procedures instrumental activities of daily living), life satisfaction and self-rated health, self-reported diseases (heart attack, cancer, stroke, diabetes, and hypertension), and weight change from 1986 to 1992.

RESULTS

D-dimer levels increased with increasing age and functional disability. Among the health variables, only high blood pressure was predictive of D-dimer level. D-dimer levels were dramatically higher in blacks. Blacks were nearly four times more likely to have an extreme value of D-dimer (>600 microg/l) than whites when high D-dimer (yes/no) was analyzed, and blacks had an average level that was nearly 40% higher than whites in analyses of the continuous version of the outcome. This racial effect was not substantively affected in multivariable analyses with demographic and socioeconomic variables controlled. Race, age, functional status, current smoking, high blood pressure, and weight loss were related to level of D-dimer, and race, age, and functional status were related to the presence of a high D-dimer level (in the top 10% of the sample).

CONCLUSIONS

Black, older, and functionally impaired persons had significantly higher levels of D-dimer in this sample of community-dwelling elderly persons. The findings for race were particularly striking and persisted even after controlling for smoking and other factors known to be related to thrombosis and were not mediated by social factors. This result may contribute to our understanding of the increased levels of thrombotic events found in these groups.

Retinoids stimulate fibrinogen production both in vitro (hepatocytes) and in vivo. Induction requires activation of the retinoid X receptor

The in vitro effects of retinoids on fibrinogen synthesis were investigated in HepG2 cells and primary human hepatocytes. In vivo effects were studied in the rat. In HepG2 cells, maximal stimulation (twofold) of fibrinogen secretion was obtained when cells were incubated in the presence of 1 mumol/L all-trans retinoic acid (T-RA) for 24 hours. A comparable increase was observed for both de novo fibrinogen synthesis and fibrinogen beta chain mRNA level. In primary cultures of human hepatocytes, treatment with 1 mumol/L T-RA for 72 hours also gave a twofold increase in fibrinogen production. Furthermore, rats treated for 6 days with 100 mg.kg-1.d-1 T-RA presented increased fibrinogen plasma levels (110%). A selective retinoic X receptor (RXR) agonist, 4-[1-3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydro-2-naphthyl)-ethenyl]benzoi c acid (3-methyl TTNEB), as well as 9-cis retinoic acid, a natural RXR ligand, mimicked the effects of T-RA on fibrinogen synthesis in vitro at lower concentrations. In contrast, a selective retinoic A receptor alpha (RAR alpha) agonist was a poor activator. The ED50 of the different retinoids on fibrinogen secretion by HepG2 cells was 25 nmol/L for T-RA, 4 nmol/L for 9-cis retinoic acid, 11 nmol/L for the synthetic RXR agonist, and > 500 nmol/L for the RAR alpha agonist. However, incubation of HepG2 cells with RXR agonist together with RAR alpha agonist resulted in a further increase in fibrinogen production. The secretion of two other acute-phase proteins, alpha-antichymotrypsin and caeruloplasmin, was also stimulated by retinoids in HepG2 cells but by a different regulatory mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of factor XIa-alpha 1-antitrypsin in plasma, a contact phase-activated coagulation factor-inhibitor complex, in patients with coronary artery disease

Excess activated factor XI (FXIa) in plasma indicates increased activation during the contact phase of blood coagulation. To investigate the relationship between such elevations and coronary atherosclerosis, we examined FXIa values in patients with coronary artery disease (CAD) by an enzyme-linked immunosorbent assay method that we developed that detects FXIa in plasma samples as an FXIa-alpha 1-antitrypsin complex (FXIa-alpha 1AT). The presence and extent of CAD were documented by coronary angiography and assessed by a recently developed scoring system for semiquantitative estimation of coronary atherosclerosis. Plasma FXIa-alpha 1AT levels were significantly increased in patients with angiographically proven CAD (13.9 +/- 3.0 micrograms/L, n = 42) compared with age-matched, healthy control subjects (11.9 +/- 1.7 micrograms/L, n = 20) as well as patients with angiographically normal coronary arteries (12.0 +/- 2.3 micrograms/L, n = 25). Moreover, in the total patient population, the FXIa-alpha 1AT level was related to the number of significant coronary artery stenoses as well as to the total coronary score. FXIa-alpha 1AT showed a positive correlation with thrombin-antithrombin III complex, fibrinogen, and Lp(a) and an inverse correlation with apo A-I, as determined by multi-variate analysis. Our studies provide evidence that increased activation of the contact pathway occurs in patients with CAD and is related to the severity of the disease. Although it is unknown whether this abnormality is the cause or the result of the vascular lesion, it may be important for progression of the underlying atherosclerosis or for propagation of the atherosclerotic process itself.

Enhancement of interleukin-6 production by fibrinogen degradation product D in human peripheral monocytes and perfused murine liver

The effect of fibrinogen degradation products D and E (FDP-D, FDP-E) on IL-6 production in perfused mouse livers and peripheral monocytes is studied. Similarly to bacterial endotoxin FDP-D is highly potent to augment the IL-6 production measured in perfused mouse livers, while FDP-E is not stimulatory. FDP-D but not FDP-E is able to stimulate the in vitro IL-6 production of human peripheral monocytes, as well. Plasmin alone is almost ineffective on IL-6 production both in perfused livers and monocytes. Our findings suggest a direct positive feedback circuit, among fibrinogen, FDP and IL-6.

Pretreatment fibrinogen levels are associated with response to chemotherapy in patients with small cell carcinoma of the lung: Department of Veterans Affairs Cooperative Study 188

Small cell carcinoma of the lung (SCCL) responds commonly to combination chemotherapy but resistance to therapy follows. Prior reports have suggested that a relationship may exist between plasma fibrinogen levels and response to therapy in SCCL. This study was designed to determine the possible predictive value of the fibrinogen level for tumor response (chemoresistance) in SCCL. Pretreatment fibrinogen levels were correlated with outcome and response to therapy in a cohort of 119 previously untreated patients with SCCL who were admitted to VA Cooperative Study 188. Higher pretreatment fibrinogen levels at diagnosis correlated significantly with more advanced stage of disease at entry (P < 0.001) and with reduced overall survival (P = 0.030). In addition, higher pretreatment fibrinogen levels were correlated significantly with a reduced likelihood of achieving subsequent disease regression with combination chemotherapy (P = 0.005). Because several clinical trials have shown that anticoagulant therapy improves tumor response rates and survival of SCCL, we postulate that tumor cell thrombin generation not only promotes SCCL growth but may also be primarily responsible for both increased fibrinogen levels and for resistance to chemotherapy. These findings provide incentive for studies of thrombin effects on the development of multidrug resistance, and for new clinical trials of more potent and specific inhibitors of thrombin that may further improve tumor response and survival in SCCL.

Age and functional correlations of markers of coagulation and inflammation in the elderly: functional implications of elevated crosslinked fibrin degradation products (D-dimers)

OBJECTIVE

To measure markers of inflammation in a cohort of young and old subjects and relate these findings to the functional level of the individuals.

DESIGN

For the pilot study, blood samples were obtained from 18 young (age 20-35 years) and 18 old (age 68-83 years) subjects. The main study population included community-dwelling subjects between the ages of 70 and 79. The group consisted of 282 subjects with minimal physical limitations, 17 subjects from the middle third, and 16 from the lower third of physical function rankings.

METHODS

Plasma markers were measured by ELISA techniques, and certain biochemical values were obtained through routine clinical tests performed by a commercial laboratory.

RESULTS

D-Dimers were higher for physically impaired subjects in all groups, but most prominently among black females, who also had significantly higher D-Dimer levels in every functional group. To inquire whether higher D-Dimers were associated with markers of inflammation, we also examined the macrophage metabolite, neopterin, the neutrophil product, elastase complexed to antitrypsin (E/a), and the albumin globulin ratio (A/G ratio). No differences were found in neopterin or E/a levels on the basis of gender, race, or functional status. The A/G ratio was significantly lower in functionally impaired subjects.

CONCLUSION

These preliminary findings demonstrate racial/ethnic and gender differences in D-Dimers in a population of community-dwelling elderly, and suggest that factors influencing hemostasis may be particularly relevant to physical functional status in black women. A sample containing more subjects with lower physical function will be needed to establish the relationship between inflammation, altered hemostasis, and physical function decline.

Fibrin degradation product D-dimer induces the synthesis and release of biologically active IL-1 beta, IL-6 and plasminogen activator inhibitors from monocytes in vitro

Disseminated intravascular coagulation, characterized by circulating fibrin(ogen) degradation products (FDP), is associated with both acute and chronic inflammatory conditions. Since the association of FDP with monocytes could influence the release of cytokines and other regulatory proteins with significant clinical ramifications, we have studied cytokine synthesis and release following the interaction of D-dimer (DD), a terminal degradation product of fibrin, with human monocytes in vitro. Adherent peripheral blood monocytes were incubated with purified DD for 24 and 48 h and secreted or cell-associated IL-1 beta and IL-6 antigen levels and activity determined. DD (50 micrograms/ml) boosted the secretion of IL-1 beta antigen from median control levels of 659 pg/ml to 2704 pg/ml and that of IL-6 antigen from 806 pg/ml to > 3000 pg/ml at 48 h (P < 0.05). Similar increases in extracellular biologically active IL-1 and IL-6 were observed. Although DD increased cell associated IL-1 beta antigen levels from median values of 188 to 1600 pg/106 cells and IL-6 antigen from 660 to 2215 pg/106 cells (P < 0.05), cell-associated IL-1 functional activity decreased from control levels of 98 inhibitor units/ml to 65 units/ml for cells exposed to DD. Secreted plasminogen activator inhibitor (PAI) bioactivity and PAI type 2 antigen levels were significantly increased following exposure of monocytes to DD. This may explain the decreased cell associated IL-1 activity observed in our study as PAI are known to inhibit biologically active membrane bound IL-1. Our finding that DD enhances monocyte release of biologically active cytokines suggests the presence of positive feedback pathways for fibrinogen synthesis by hepatocytes. Furthermore, the association of monocytes with DD may potentiate localized coagulation processes by subsequent alterations in pericellular proteolysis.