Biochemical and immunological characterization of human opsonic alpha2SB glycoprotein: its identity with cold-insoluble globulin

Phagocytosis of Bioactive Microspheres

The influence of several proteins on the uptake of microspheres was investigated using mouse peritoneal macrophages. Thioglycollate-stimulated macrophages were cultivated for 3 h with protein-grafted and protein-coated cellulose microspheres smaller than 2 μm in the presence and the absence of serum. Bovine serum albumin reduced the phagocytosis of microspheres, while y-globulin, human fibronectin, bovine tuftsin, and gelatin enhanced the phagocytosis. This trend was not influenced substantially by the presence of serum and the mode of surface binding of the proteins; that is, covalent grafting or physical adsorption (coating). However, in the case of gelatin binding, phagocytosis was greatly enhanced by the presence of serum as compared with the other proteins.

Does Fibronectin Reduce Mortality in Sepsis? A Meta-Analysis

We examine the effect of fibronectin administration on mortality in sepsis. An English language literature search using MEDLINE, EMBASE, SCISEARCH, and compu terized databases of unpublished research in addition to bibliographic review was performed, and duplicate independent review of 41 articles by two observers identified six relevant randomized clinical trials. Study quality and descriptive information concerning the pop ulation, intervention, and outcome measurements were assessed. Three of six trials demonstrated favorable mor tality trends, but none reached statistical significance. Results of the 282 patients in all six trials yield a com mon odds ratio of 0.97 and a 95% confidence interval of 0.58 to 1.61. These results do not show a statistically significant effect favoring treatment, but neither do they exclude a clinically important benefit. The benefit of fibronectin in decreasing mortality in sepsis is not sup ported by these studies. However, methodological heterogeneity and the possibility of a Type II error, as well as our understanding of the role of fibronectin in the pathophysiology of sepsis, do not allow for a firm negative conclusion regarding the therapeutic efficacy of fibronectin in sepsis. A large, rigorously designed trial should be considered once investigators can reach a consensus regarding current methodological and patho physiological controversies.

Implications for collagen binding from the crystallographic structure of fibronectin 6FnI1-2FnII7FnI

Collagen and fibronectin (FN) are two abundant and essential components of the vertebrate extracellular matrix; they interact directly with cellular receptors and affect cell adhesion and migration. Past studies identified a FN fragment comprising six modules, ⁶FnI^1–2FnII^7–9FnI, and termed the gelatin binding domain (GBD) as responsible for collagen interaction. Recently, we showed that the GBD binds tightly to a specific site within type I collagen and determined the structure of domains ^8–9FnI in complex with a peptide from that site. Here, we present the crystallographic structure of domains ⁶FnI^1–2FnII⁷FnI, which form a compact, globular unit through interdomain interactions. Analysis of NMR titrations with single-stranded collagen peptides reveals a dominant collagen interaction surface on domains ²FnII and ⁷FnI; a similar surface appears involved in interactions with triple-helical peptides. Models of the complete GBD, based on the new structure and the ^8–9FnI·collagen complex show a continuous putative collagen binding surface. We explore the implications of this model using long collagen peptides and discuss our findings in the context of FN interactions with collagen fibrils.

Fibronectin and atherosclerosis

Fibronectin is a polymorphic glycoprotein of plasma, other body fluids and connective tissue, and it occurs in an insoluble and a soluble form. Insoluble fibronectin is found associated with basement membranes and in loose connective tissue matrix as well as in the pericellular matrix formed around cultured adherent cells, such as endothelial, fibroblastic and smooth muscle cells. In these positions fibronectin apparently functions as a substrate for cell attachment and as a scaffold for cell migration and movement. Soluble fibronectin, present e.g. in the circulation (300 micronm/ml) exhibits some important interations with other proteins. It is covalently cross-linked to fibrin during thrombus formation and binds to collagen. Fibronectin is released from platelets during their aggregation and soluble fibronectin potentiates the action of plasminogen activator. We have detected fibronectin in the sub-endothelium, in the matrix of smooth muscle cells of the media and in the adventitia of arteries. By using immunohistological techniques we have further found that fibronectin is prominent in atherosclerotic lesions of the intima, especially in developing fibrous plaques. Fibronectin was also prominent in experimentally induced atherosclerotic lesions. These findings suggest that fibronectin is an indicator of connective tissue formation in atherosclerotic processes and that the protein can have a role in their pathogenesis.

Changes in the distribution pattern of gelatin-binding protein of 28 kDa (adiponectin) in myocardial remodelling after ischaemic injury

AIMS

Gelatin-binding protein of 28 kDa (GBP28) is a collagen-like plasma protein having a binding capacity with collagens. We investigated GBP28 role on myocardial remodelling as well as the diagnostic significance of GBP28 immunostaining in myocardial infarction.

METHODS AND RESULTS

Myocardial tissues obtained from 47 autopsied hearts with infarction were immunostained with antibodies against GBP28, fibronectin, type III and IV collagens, and prolyl 4-hydroxylase. GBP28 was distributed in interstitium of infarcted lesions at an early stage. GBP28 was linearly found both along the border with vital myocardium and at the periphery of surviving cardiomyocyte around the lesion at granulative stage. However, it was not observed in the scar. GBP28 distribution patterns were similar to those of fibronectin in infarcted lesions and those of type IV collagen at the periphery of cardiomyocyte. Type III collagen was not recognized in the early-stage lesion but increased along with scar maturation. Prolyl 4-hydroxylase was found in surviving cardiomyocytes around the lesion during all stages and in interstitial cells appeared in granulation tissue.

CONCLUSION

GBP28 plays a role as a scaffold of newly formed collagen in myocardial remodelling after ischaemic injury, and GBP28 immunostaining may assist in a diagnosis of healing stage.

Lung matrix incorporation of plasma fibronectin reduces vascular permeability in postsurgical bacteremia

Plasma fibronectin (pFN) can incorporate into the lung extracellular matrix (ECM) as well as enhance hepatic cell phagocytic removal of bloodborne microparticulate debris that can contribute to lung vascular injury. Treatment of human pFN (hFN) with N-ethylmaleimide (NEM) blocks its ECM incorporation but not its ability to augment phagocytosis. Using hFN purified from fresh human plasma cryoprecipitate, we compared the effect of NEM-treated hFN versus normal hFN on lung transvascular protein clearance (TVPC) in postoperative bacteremic sheep to determine whether the ability of hFN to attenuate the increase in lung endothelial permeability required its ECM incorporation. Sheep with lung lymph fistulas were infused with a sublethal dose of Pseudomonas aeruginosa (5 x 10(8)) 48 h after surgery. In the first study, sheep received either FN-rich human cryoprecipitate, FN-deficient cryoprecipitate, FN purified from cryoprecipitate (hFN), FN-deficient cryoprecipitate reconstituted with purified hFN, or the sterile saline diluent. In the second study, sheep received either 200 mg of purified hFN (group I), 200 mg of NEM-treated hFN (group II), or the saline diluent (group III). In the first study, the increase in TVPC after bacterial challenge was attenuated by FN-rich cryoprecipitate, hFN, or reconstituted FN-deficient cryoprecipitate (P < 0.05) but not by saline and FN-deficient cryoprecipitate. In the second study, TVPC increased by 2 h (P < 0.05) and peaked over 4-8 h (P < 0.05) at 380-420% above baseline in postoperative bacteremic sheep given the diluent (group III). In contrast, intravenous infusion of hFN, but not of NEM-treated hFN, significantly (P < 0.05) attenuated this increase of lung protein clearance. Thus the ability for the intravenously infused purified pFN to attenuate the increase in lung endothelial protein permeability in sheep during postsurgical bacteremia appears to require its ECM incorporation into the interstitial ECM of the lung.

Lung matrix deposition of normal and alkylated plasma fibronectin: response to postsurgical sepsis

Plasma fibronectin (Fn) can both enhance phagocytic clearance of microparticulate debris by macrophages as well as incorporate it into the lung extracellular matrix (ECM). The goal of this study was to document that N-ethylmaleimide (NEM)-treated human plasma Fn (HFn) would lose its ability to incorporate into the lung ECM in vivo even though it would retain its ability to stimulate test particle phagocytosis and bind to fibrin. Using dual-label immunofluorescence, we compared the lung deposition of purified normal HFn and NEM-alkylated HFn (NEM-HFn) after their intravenous injection into postoperative nonbacteremic and bacteremic sheep in relationship to the localization of endogenous sheep Fn. Two days after a sterile surgical thoracotomy, sheep were infused with either 5 x 10(8) Pseudomonas aeruginosa (postsurgical bacteremic model) or the diluent (nonbacteremic model). They also received a bolus 100-mg injection (5 min) of either HFn or NEM-HFn. Analysis of serial lung biopsies harvested at 2-h intervals demonstrated little deposition of NEM-HFn compared with HFn in the lung interstitial matrix of postoperative nonbacteremic sheep. In contrast, enhanced deposition of both HFn and NEM-HFn was observed in the lungs of postoperative bacteremic sheep. However, in the lungs of bacteremic sheep, HFn displayed a diffuse fibrillar deposition pattern in the lung characteristic of ECM incorporation, whereas the enhanced NEM-HFn deposition, especially in the interstitial ECM region of the lung, was primarily focal and punctate, with very little fibrillar incorporation. Immunofluorescent analysis with antibodies specific to fibrinogen, Fn, and lung macrophage surface antigens coupled with immunoperoxidase staining for HFn antigen revealed that the punctate fluorescence pattern was due to both the binding of HFn to fibrin and its colocalization with inflammatory cells. Thus treatment of plasma Fn with low concentrations of NEM will limit its normal in vivo fibrillar incorporation into the interstitial ECM region of the lung.

Incorporation of circulating fibronectin into various tissues during sepsis: colocalization with endogenous tissue fibronectin

We studied the plasma clearance and tissue incorporation of intravenously infused purified human plasma fibronectin into various tissues during a period of acute lung vascular injury induced by lethal postoperative bacteremia in sheep. Lung, liver, spleen, and heart tissue were examined for both endogenous sheep tissue fibronectin as well as the experimentally infused human fibronectin using dual-label immunofluorescence. Awake sheep (n = 4) received a postoperative iv infusion of 5 x 10(9) live Pseudomonas over a 60-min infusion interval. Bacterial challenge was started 2 hr after starting the iv fibronectin infusion of purified human plasma fibronectin (100 mg iv bolus; 4 hr iv at 100 mg/hr). Human fibronectin displayed a biphasic rate of clearance from the plasma with entrance into lymph. Human fibronectin readily incorporated in all tissues studied, including the lung which was the focus of vascular injury. Analysis of tissue sections by dual-label immunofluorescence indicated that the exogenous human fibronectin colocalized with the endogenous sheep fibronectin. Thus, the plasma fibronectin concentration may influence the lung vascular barrier due to its incorporation into the tissue pool of fibronectin. Moreover, the plasma may serve as a reservoir for soluble fibronectin which can enter and colocalize with the insoluble tissue pool of fibronectin in various tissues.

Leukocyte elastase-independent proteolysis of gelatin-bound fibronectin by inflammatory macrophages

Fragmentation of lung matrix fibronectin by proteases released from activated phagocytic cells has been implicated in lung vascular injury. We examined whether denatured collagen (gelatin)-bound fibronectin can be degraded by peritoneal exudate mononuclear phagocytes harvested from rats 96 h after intraperitoneal casein injection. Microtiter plates were pretreated with gelatin and then supplemented with purified 125I rat plasma fibronectin, which readily bound to the gelatin. Stimulated inflammatory exudate cells were added and proteolysis of the bound fibronectin was studied by the release of [125I]fibronectin fragments into the media. Following 2 h of incubation, peritoneal exudate mononuclear macrophages stimulated with opsonized zymosan released three times more radiolabeled fibronectin into the medium as compared to background controls, and 1.5 times more radiolabeled fibronectin as compared to cells not stimulated with zymosan. Western blot analysis and autoradiography confirmed the presence of fragments of fibronectin in the culture medium. Some of these fragments were clearly derived from the radiolabeled matrix, but others that were not labeled were potentially released directly from the added stimulated macrophages. The release of radiolabeled fibronectin was inhibited by N-p-tosyl-L-lysine chloromethyl ketone (TLCK), a trypsin specific inhibitor, but not by methoxysuccinyl-alanine-alanine-proline-valine-chloromethyl-ketone (AAPVCK), a leukocyte elastase-specific inhibitor. These results suggest that fibronectin bound to denatured collagen is susceptible to leukocyte elastase-independent enzymatic degradation by stimulated inflammatory exudate mononuclear phagocytic cells. Such proteolysis may mimic a pathological process associated with lung vascular injury during the sequestration of activated macrophages in the lung microcirculation and interstitium.

A study on content and distribution of plasma and tissue fibronectin in rats using ELISA and immunofluorescence

The content of plasma fibronectin and tissue extractable fibronectin in normal rats was measured with rocket immunoelectrophoresis and ELISA in the present study. The difference in tissue fibronectin distribution in various organs and the correlation between distribution and content of fibronectin have been studied. We suggest that tissue fibronectin may be a complex component. The change in plasma fibronectin reflects a dynamic balance existing between the tissue fibronectin pool and plasma fibronectin pool in normal rats. Plasma fibronectin and tissue fibronectin concentrations are not static, and they can only be maintained in a relatively stable state in normal rats.

Response of fibronectin to liver regeneration after hepatectomy

The relationship between plasma fibronectin concentration and the regenerative process in liver remnants after hepatectomy was studied in 12 patients and in male Sprague-Dawley rats with and without cirrhosis. Plasma fibronectin levels were reduced immediately after hepatectomy in humans and rats. Patients and rats without cirrhosis displayed preoperative fibronectin levels within 1 mo and 1 wk, respectively, but low fibronectin levels persisted longer in those with cirrhosis. Plasma fibronectin levels correlated well with the degree of hepatic regeneration in the patients with cirrhosis (r = 0.4227; p less than 0.05) and without cirrhosis (r = 0.8148; p less than 0.001), and also with the percentage of change in liver weight during regeneration in the rat with thioacetamide-induced cirrhosis (r = 0.4905; p less than 0.01) or in the rat without cirrhosis (r = 0.6422; p less than 0.001). These results suggest that plasma fibronectin is a useful marker for the detection of regenerating liver.

Plasma fibronectin concentrations in blood products

Plasma fibronectin is an important opsonic protein of the mononuclear phagocyte system (MPS). In this study, plasma fibronectin concentrations were measured in stored and fresh whole blood, fresh frozen plasma and AGH cryoprecipitate. Stored whole blood had the lowest concentrations (151 +/- 50 mg/l). The concentrations in fresh whole blood plasma (227 +/- 66 mg/l) and fresh frozen plasma (224 +/- 78 mg/l) were similar but significantly higher than in stored whole blood (p less than 0.05). In contrast, AHG cryoprecipitate had the highest fibronectin concentrations (3249 +/- 502 mg/l) (p less than 0.001). In correcting fibronectin deficiency the best results can thus be expected from an infusion of cryoprecipitate, but fresh whole blood and fresh frozen plasma may also increase depressed fibronectin levels.

Use of biocarrier beads and flow cytometry for single-cell studies of fibronectin gene regulation in dibutyryl cyclic AMP reverse transformed CHO-K1 cells

The protease sensitivity of a number of cell surface or cytoskeletal components and the relationship of these to the substratum in attached cells has prevented the quantitative measurement of their expression by flow cytometry. Using traditional cell sorting techniques, cells must be treated with a protease to detach them from a substrate in order to produce a single-cell suspension. Unfortunately, proteolytic treatment alters or destroys a number of cellular proteins. Fibronectin either on the cell surface or as part of the substratum laid down by the cell is particularly sensitive to proteases, preventing its quantitative study by flow cytometry. To circumvent these problems and produce a single cell suspension necessary for flow cytometric analysis, CHO-K1, a Chinese hamster ovary cell line, were grown in suspension on specially-treated 25 microns biocarrier beads. The CHO-K1 cell line is composed of transformed epithelial-like cells that have lost the fibronectin deposit around their cell membranes. To restore the typical fibroblastic deposit of fibronectin, the cells attached to beads were induced by dibutyryl cAMP to undergo a reverse transformation reaction to restore fibroblastic morphology and the typical fibroblastic deposite of fibronectin on the cell surface and substratum. The cells attached to beads were then immunofluorescently labeled for the protease-sensitive, extracellular matrix component, fibronectin, and examined on a flow cytometer. Cell surface fibronectin heterogeneity was then examined on a cell-by-cell basis as a function of cell cycle using Hoechst 33342 dye that binds to AT base pairs of cellular DNA. Dual laser measurement and multiparameter list mode data analysis were used to study the relationship between cell surface fibronectin of biocarrier bead attached cells and cell cycle.

Concentrations of fibronectin in the sera and crevicular fluid in various stages of periodontal disease

While fibronectin (FN) has previously been demonstrated to be present in gingival crevicular fluid (GCF), its quality and quantity has not been reported. Since this information is relevant for ongoing studies on the use of FN for gingival reattachment, we performed these measurements and compared plasma levels in healthy subjects, patients with gingivitis and periodontitis, and in patients undergoing maintenance therapy. Plasma and GCF samples were obtained from 4 sites in each subject using a Periotron to permit quantification of samples. FN concentrations were determined in a microELISA using hyperimmune anti-FN antibody. Purified FN served as a reference for quantification. The functional activity of each sample was assessed by examining the natural affinity of FN for gelatin. Subjects with gingivitis and those in maintenance had significantly depressed levels of plasma fibronectin. While little fibronectin could be detected in the GCF of healthy sites regardless of patient category, examination of the most diseased sites in each group revealed that the concentration of FN in the GCF was highest in health and reduced when there was gingival inflammation. In no case was GCF FN found to be biologically active.

Fibronectin decrease in liver cirrhosis is related to spleen size

We found a significantly lower plasma fibronectin concentration in cirrhotic patients than in controls, a significant inverse relationship between fibronectin and spleen size, but no correlation between fibronectin and hepatic blood flow, prothrombin time, or serum albumin. We suggest that the increased degradation in the enlarged spleen is more relevant than the decreased synthesis in reducing plasma fibronectin levels during liver cirrhosis with portal hypertension.

Progressive loss of fibronectin-mediated opsonic activity in plasma cryoprecipitate with storage. Role of fibronectin fragmentation

Septic injured patients often manifest a deficiency of plasma fibronectin. Several studies have shown improvements in organ function in such patients following infusion of fibronectin-rich plasma cryoprecipitate, while other studies found no improvement. One explanation for these differences may be the use of plasma cryoprecipitate which has been stored for various time intervals prior to its use as a source of fibronectin. This investigation tested the hypothesis that the opsonic activity of fibronectin in cryoprecipitate may decline with increased storage duration. Using a bioassay of opsonic activity, we evaluated human plasma cryoprecipitate that was stored at either -20 or -80 degrees C for various intervals (2 weeks to 12 months) after its preparation from fresh donor plasma. Our findings demonstrated that the opsonic activity of fibronectin in cryoprecipitate declined with increasing time of storage. Significant loss (p less than 0.05) of opsonic activity was first evident after 2 months of storage. Storage at -80 degrees C did not prevent this decline in opsonic activity as compared to storage at -20 degrees C. Immunoblot analysis revealed extensive fragmentation of the dimeric fibronectin (440 kdaltons) and the presence of lower molecular weight fragments in 4- to 12-month-old plasma cryoprecipitate. Therefore, plasma cryoprecipitate of varying ages (storage time) when used as a source of fibronectin for replacement therapy to support phagocytic function in septic injured patients may result in different fibronectin-mediated responses. The decline in activity may be due, in part, to fragmentation of the fibronectin molecule.

Plasma fibronectin in normolipidaemic and hyperlipidaemic uraemic patients treated with haemodialysis

Plasma fibronectin (PF) concentrations, were investigated in normolipidaemic and hyperlipidaemic (type IV) patients with chronic renal failure treated with hemodialysis (n = 29) and in controls (n = 34). Mean PF was significantly reduced in both subsets of dialysed patients. Among the hemodialysed patients the presence of hyperlipidaemia did not modify PF levels, which resulted, on the contrary, significantly higher in hyperlipidaemic controls as compared with the normolipidaemic group. In controls, according to a multivariate analysis model, PF was directly related with age and inversely with HDL-cholesterol. In the hemodialysed patients total cholesterol was the unique significant PF related variate, being this group, therefore, characterized by the lack of any inverse relation between PF and HDL-cholesterol. Finally, no PF modifications were observed in hemodialyzed patients affected by arterial hypertension or clinically evident atherosclerotic lesions.

Definition of fibronectin-mediated uptake of gelatinized latex by liver slices and macrophages

These studies show that both liver slices and macrophages carried out fibronectin concentration-dependent uptake of 125I-labeled gelatin-coated latex (test latex). Lack of phagocytosis of test latex by liver slices was shown directly by electron microscopy and indirectly by trypsin treatment, which caused the release of all test latex taken up in response to fibronectin. Inhibitors of phagocytosis did not alter this uptake. On the other hand, trypsin released only a portion of test latex from macrophages. Inhibitors of phagocytosis did not effect the released radioactive particles from macrophages but greatly reduced the trypsin-resistant radioactivity, taken as representing phagocytized particles. Opsonization of test latex with fibronectin did not require heparin but its association with liver slices occurred only in the presence of heparin. Macrophages, however, readily bound and internalized the opsonized test latex and heparin only potentiated these reactions. Gelatin competed with test latex for fibronectin for opsonization, but did not inhibit binding and phagocytosis of fibronectin-test latex complexes. Finally, soluble fibronectin-gelatin complexes did not compete for binding and phagocytosis of fibronectin-test latex complexes. Thus, fibronectin concentrated on the surface of latex is preferred for interaction with the fibronectin receptor of macrophages. Gelatin, however, was not essential for this reaction, because fibronectin directly coupled to latex was also readily taken up.

Fibronectin and cryoprecipitation

Fourteen patients with essential mixed cryoglobulinemia were studied. The relevance of fibronectin (FN) in cryoprecipitation seems to be of relative importance since only two thirds of the cryoprecipitates have a higher cryocrit level when FN is present. On the other hand, the other samples show a lower precipitating activity after plasma heating at 60 degrees C. This reduction may reflect either a structural FN modification by heating or the denaturation of other cryoprecipitating molecules. It is possible, even if not necessary, that at least in vitro FN plays a role in the cryoprecipitate formation.

Reversal of opsonic deficiency in surgical, trauma, and burn patients by infusion of purified human plasma fibronectin. Correlation with experimental observations

Plasma fibronectin deficiency has been documented in critically ill surgical, trauma, and burn patients. Human plasma fibronectin was isolated by gelatin-Sepharose affinity chromatography and evaluated with respect to its opsonic activity following pasteurization, its in vivo clearance kinetics, and its short-term influence on cardiovascular hemodynamics in postoperative septic sheep. Six patients with low plasma fibronectin levels were also evaluated with respect to temporal changes of immunoreactive fibronectin and opsonic activity following infusion of fibronectin at a dose calculated to elevate the plasma fibronectin level to 400 micrograms/ml. With utilization of three different in vitro radioisotopic phagocytic assays, i.e., liver slice assay, peritoneal macrophage monolayer assay, and Kupffer cell monolayer assay, retention of opsonic activity by fibronectin following pasteurization was documented. The normal biphasic kinetics associated with plasma clearance of fibronectin were also not altered by pasteurization. In postoperative septic sheep with hemodynamic instability, intravenous infusion of 500 mg of purified human fibronectin initiated no abnormal hemodynamic response. Indeed, as compared with placebo, the infusion of fibronectin into the postoperative septic sheep resulted in a more stable systemic vascular resistance and pulmonary vascular resistance with a higher arterial pressure. It also elevated immunoreactive fibronectin levels (p less than 0.05) and increased opsonic activity (p less than 0.05). Surgical, trauma, and burn patients (ages 18 to 80 years) with low plasma fibronectin levels (160 to 236 micrograms/ml) manifested no disturbance in cardiovascular, respiratory, or hematologic parameters following fibronectin infusion (590 to 988 mg per patient), but did display an early increase of opsonic activity. This standardized, pasteurized, and opsonically active preparation of purified human plasma fibronectin (5.0 mg/ml after reconstitution) has utility for future randomized clinical trials in injured patients with sepsis.

Fibronectin: applications to clinical medicine

In summary, the role of fibronectin in clinical medicine is not yet certain. Correlation of sepsis and organ failure with decreased fibronectin levels is still to some degree questionable; controlled clinical trials are urgently needed. The risk of hepatitis, AIDS, and other transfusion-transmitted diseases must be balanced by data substantiating the clinical efficacy of fibronectin therapy. To date, no results from controlled trials using purified fibronectin have been reported. Final judgement must be reserved pending results of appropriate human studies. It is likely, however, that even if fibronectin is proven to be clinically useful, the patient population which will achieve some benefit from its use will be restricted to septic and/or critically ill patients. As noted by Mosher and Grossman however, physicians treating such patients would likely welcome any new and effective therapeutic intervention.

Plasma fibronectin concentrations in mucocutaneous lymph node syndrome

Plasma fibronectin concentrations were measured in 41 patients suffering from mucocutaneous lymph node syndrome (MCLS, Kawasaki disease). Plasma fibronectin concentrations were decreased significantly in the early days of the disease, but increased gradually and reached significantly high concentrations by the fourth week of the disease. In nine of the 41 patients, coronary involvement was found by echocardiographic examination. These patients showed significantly lower plasma fibronectin concentrations in the first and second weeks of the disease than those without coronary involvement. As the underlying pathology of MCLS is known to be vasculitis, the lower plasma fibronectin concentrations might be partly the result of injury inflicted upon the endothelial cells, which are thought to be the major site of synthesis of circulating plasma fibronectin concentrations.

The effect of proteolytic degradation of plasma fibronectin on the responses of functional and immunometric assays for intact fibronectin

Numerous studies have been made into the nature and importance of altered levels of plasma fibronectin seen in a range of clinical disorders. However, fibronectin is highly sensitive to the proteolytic degradation which may accompany some of these conditions. The influence of such degradation on the assays used is frequently unknown. We have investigated the effects of controlled protease degradation on the responses of an electroimmuno and a functional assay, using purified fibronectin. Tryptic digestion influenced the assays more than thrombin, in relation to the degree of breakdown. Both enzymes reduced the functional (gelatin-binding) activity whilst tryptic cleavage increased the apparent concentration by electroimmunoassay. The findings demonstrate that certain assays may be inappropriate for those clinical conditions where levels of intact fibronectin are of most interest. It is also necessary, then, to determine the degree of fibronectin breakdown when measuring pathological levels.

Plasma fibronectin metabolism during hemorrhagic shock and starvation

In this report we characterize the response of the plasma protein fibronectin to hemorrhagic shock and starvation, conditions associated with decreased function of mononuclear phagocyte system (MPS). Rats were starved for 3 days, then half of the animals were subjected to fixed-volume hemorrhagic shock by removing an estimated 35% of their blood volumes for 20 min. After volume replacement, animals were injected iv with [14C]valine. At time points up to 10 hr after hemorrhage, plasma fibronectin concentrations and fibronectin synthesis were quantitated. In additional rats treated identically, fibronectin clearance was assessed by measuring the disappearance of 125I-fibronectin from the plasma. When compared to control animals, either starvation or hemorrhagic shock produced similar perturbations in plasma fibronectin metabolism; fibronectin concentrations were reduced from 241.3 +/- 34.6 micrograms/ml (mean +/- SEM) (controls) to 123 +/- 32.6 micrograms/ml (starvation) or 150.0 +/- 13.0 micrograms/ml (hemorrhage). Plasma [14C]fibronectin specific radioactivities, indicative of fibronectin synthesis, were also significantly reduced. Hemorrhagic shock in rats that previously had been starved did not depress fibronectin concentrations or synthesis to a greater extent than starvation alone. The rates of 125I-fibronectin clearance were increased in starvation and hemorrhagic shock (t1/2 = 233.0 +/- 13.0 min, controls; 174.6 +/- 10.7 min, starvation; 167.4 +/- 13.6 min, hemorrhage). In contrast to changes observed in fibronectin metabolism, total plasma protein concentrations were not significantly altered in any experimental groups. Furthermore, total plasma protein synthesis increased in rats subjected to either starvation or hemorrhagic shock, but decreased in starved rats that were subsequently shocked.(ABSTRACT TRUNCATED AT 250 WORDS)

Fibrinmonomer binding to macrophages mediated by fibrin-binding fibronectin fragments

Binding of 125-I-fibrinmonomer to peritoneal macrophages was investigated in dependence of plasma fibronectin and of its thrombin- or plasmin-derived fragments. Plasma fibronectin failed to enhance cell binding of 125-I-fibrinmonomer. In contrast, 30kD-fragments derived from the N-termini of the fibronectin subunits improved binding considerably. The association with the cell surface was completely inhibited by EDTA, 2-5 mM putrescine and to about 40 per cent by 0.1 mM dansylcadaverine suggesting that a transamidase-catalyzed cross-linking reaction was involved. Thrombin-derived 200kD-remnants of the fibronectin subunit chains failed to mediate cell binding of 125-I-fibrinmonomer provided they had been deprived of residual thrombin activity. Otherwise they were active and their activity was inhibited by the thrombin inhibitor hirudin. Plasmin-derived 200 kD-fragments were inactive as well.

Enzyme-linked immunosorbent assay to quantify fibronectin

Fibronectin, a multifunctional soluble glycoprotein, is found in soluble form in blood and other body fluids. Fibronectin binds to biological substrata--collagen, gelatin, etc.--and to nonbiological substrata as well. An interesting finding was that fibronectin bound to polystyrene plastic quickly and tightly and further treatment of plastic with denaturing agents did not remove or denature it once it was adsorbed. Through the use of this property, a three-step noncompetitive enzyme-linked immunosorbent assay has been developed to quantify soluble fibronectin in biological samples. The following parameters were studied: selective attachment of fibronectin to polystyrene; interference caused by increasing amounts of external protein; and linear response and limit of sensitivity. The procedure has been applied to measure fibronectin from different animal sources.

Production and characterization of interferon from endothelial cells

The capacity of cultured bovine aortic, capillary, and corneal endothelial cells as well as of human umbilical cord endothelial cells to produce interferon (IFN) was investigated. The endothelial cells of the two species produced significant amounts of IFN in response to various viruses and poly (I) poly (C). The IFN produced by human umbilical cord endothelial cells was a mixture of alpha- and beta-IFN, as determined by neutralization with antibodies directed against these two types of IFNs as well as by measuring the antiviral activity on heterologous cells. Bovine endothelial cells also produced a mixture of at least two IFN subspecies, one of them labile at pH 2 and active on human cells and the other stable at pH 2 and inactive on human cells.

Plasma fibronectin in various hemopathic diseases

Plasma fibronectin was determined by laser nephelometric immunoassay in two populations: (a) healthy subjects separated into three age groups (16-29 yr, 30-50 yr and over 50 yr) and, (b) patients with various hemopathic diseases without any infection or any therapy. Results showed that fibronectin levels in a healthy population were strongly influenced by age. An increase of human plasma fibronectin was shown to occur with age. Results in hemopathic patients were expressed in terms of percentage of mean deviations as compared to normal mean values for the corresponding age range. We found that plasma fibronectin was significantly decreased in acute myeloblastic leukemia, especially in transfused patients, polycythemia vera, osteomyelofibrosis. Waldenström disease, benign dysproteinemia, refractory anemia and stage IV non-Hodgkin malignant lymphoma. Plasma fibronectin-decreased levels appear to be of prognostic value in the evolution of malignant hemopathic diseases.

Plasma fibronectin is initially decreased during septicemia

Plasma fibronectin (PFN) levels were measured by radioimmunoassay in 24 normals and serially in 24 septic patients without underlying major trauma. All patients responded promptly to antibiotic therapy and none developed signs of shock or disseminated intravascular coagulation (DIC). After an initial decrease in PFN registered in most of the septic patients, the levels were normalized within 2 weeks of antibiotic treatment. The mean nadir levels of PFN were decreased (p less than 0.001) both in patients with gram-negative and gram-positive etiologies compared to the control group. Furthermore, the mean PFN value of the gram-positive group was lower (p less than 0.05) than that of the gram-negative group. It is concluded that a transient depletion of PFN is a constant finding in septic patients with a favourable outcome and that a single low PFN level alone does not justify fibronectin replacement therapy nor does it indicate a poor prognosis.

The effects of malnutrition on serum fibronectin and reticuloendothelial function

A rat model was used to investigate the effects of starvation and protein depletion on serum fibronectin levels and reticuloendothelial function. Serum fibronectin levels decreased significantly following both test diets. The uptake of opsonin-independent test agents was minimally affected by starvation and protein depletion. Clearance of gelatinized colloidal carbon, which is dependent on circulating opsonins, was significantly reduced in the malnourished animals. This clearance defect was corrected by incubation of colloidal carbon with normal serum. These data suggest that reticuloendothelial dysfunction secondary to malnutrition is primarily mediated by a deficiency of circulating opsonins.

Modulation of the metastatic activity of melanoma cells by laminin and fibronectin

Metastatic mouse melanoma cells have a high affinity for the basement membrane and the ability to degrade it; these properties may allow tumor cells to invade the membrane and disseminate. In this study it was found that the metastatic potential of mouse melanoma cells varied when the cells were exposed in culture to fibronectin or laminin. After removal of fibronectin or exposure to laminin, the cells had an increased affinity for basement membrane collagen, were more invasive of basement membranes in vitro, and produced more lung colonies in vivo. These changes are correlated with and may be due to an increase in the laminin-binding capacity of the tumor cell surface.

[Fibronectin]

Fibronectin is a dimeric glycoprotein with a molecular weight of 440,000. It is a soluble constituent of plasma and other body fluids and a fibrillar matrix protein of connective tissue. The two components are structurally similar and convertible. The possibility of multiple molecular interactions gives rise to a variety of biological functions. The regulation of cell growth and the reduced shedding of fibronectin from malignant cells raises the question as to whether fibronectin is valid as a tumour marker. In wound healing and chronic inflammation fibronectin serves as a scaffold for the formation of collagen. As opsonic protein it maintains reticuloendothelial function. Especially in shock, fibronectin may become the limiting factor of unspecific host defence mechanisms. The value of a substitution therapy will be discussed.

Determination of activated plasma fibronectin using radioactive labelled collagen I

The plasma concentration of biological active fibronectin was assayed by a protein binding assay using 125I-collagen I as ligand and heparin as activator. The standard curve is linear for a fibronectin range of 1.1-11 pmol (0.5-5.0 micrograms) and the coefficient of variation was less than 10%. The active or activable fibronectin was compared to the immunoreactive fibronectin in plasma from patients with various bacterial diseases. Similar concentrations were detected by the two assays suggesting that all the circulating fibronectin was functionally active. The assay was also applied to determine the structure-function relationship of heparin and heparansulphate in activation of fibronectin. Low-sulphated heparansulphate from umbilical cords and heparin-activated fibronectin but the effect was uncorrelated to anticoagulation activity. Only a small fraction of the heparin was actually capable of activating fibronectin. It is concluded that the assay is very convenient to detect biological active fibronectin and to elucidate the structure-function relationship of heparin and heparansulphate in activating fibronectin.

Effect of acute plasma fibronectin depletion on tissue fibronectin levels: analysis by a new fluorescent immunoassay

Plasma fibronectin modulates reticuloendothelial (RE) phagocytosis of cellular and tissue debris, fibrin microaggregates, and gelatin-coated particulates. An antigenically related, but more insoluble form of fibronectin is found in various tissues and suspected to play a role in vascular permeability, cell adhesion, and wound healing. The current study developed a fluorescent immunoassay which could be utilized for the quantification of tissue fibronectin following its extraction from tissues. Additionally, the changes in tissue fibronectin induced by the intravenous injection of gelatin-coated colloids in rats (300-350 g), which acutely depletes the plasma fibronectin level, were also investigated. Injection of gelatinized RE test lipid emulsion (50 mg/100 g) depleted the plasma fibronectin at 2 hr (80-85% depletion) followed by rebound restoration within 24 hr as quantified by either electroimmunoassay or fluorescent immunoassay. RES system clearance of the test particles from the blood resulted in an acute elevation in fibronectin extractable from the liver with a normalization by 48 hr. In contrast, assay of tissue fibronectin following a single extraction revealed a decrease in lung extractable fibronectin within 2 hr following RE blockade which persisted for 24-48 hr. Extractable fibronectin in spleen and renal tissue was unaltered by RE blockade. This microfluorescent immunoassay may provide a sensitive method to quantify fibronectin in small aliquots of tissue. Increased hepatic fibronectin most likely reflects interiorization of plasma fibronectin during Kupffer cell clearance of the test particles. Decreased lung extractable fibronectin may alter lung vascular sensitivity to a subsequent septic and/or intravascular coagulation stress. Thus, similar to the labile nature of plasma fibronectin, the concentration of fibronectin in various tissues, can undergo dynamic alterations.

Modifications of fibronectin in age-related diseases: diabetes and cancer

Fibronectin is present in tissues and also in body fluids (plasma). Both forms were studied in normal controls, diabetics and cancer patients; both of these diseases show an age-dependent increasing trend. Age-dependent variations were shown to occur for both forms of fibronectin. Plasma fibronectin increases exponentially with age in a normal population. This increase is strongly attenuated or absent in diabetics and in mammary cancer patients. On the contrary, tissue fibronectin increases in diabetic skin. In mammary cancer fibronectin disappears from the tumor cell membranes but increases in the peritumoral stroma. The above modifications may be attributed to increased protease activity in tumour tissue and also to the possibility of an increased retention of plasma fibronectin in diabetic skin and peritumoral stroma, both tissues exhibiting a modification of intercellular matrix biosynthesis which does involve the increased production of retention sites of fibronectin. An increased local synthesis in both tissues may also occur. The above results are confronted with those reported by other authors and support the contention that plasma and tissue fibronectins undergo age-dependent modifications which may be seriously perturbed in diabetes and cancer.

Separation of macrophages from mouse peritoneal exudate cells with substrata coated with chemically modified collagens

A cell-separation technique was designed on the basis of specific interaction between macrophages and chemically modified collagens in the presence of serum. When unseparated mouse peritoneal exudate cells containing approximately 50% macrophages and 50% lymphocytes were incubated in dishes coated with unmodified and chemically modified collagens, only macrophages adhered more rapidly and in greater numbers to succinylated and methylated collagen than to unmodified collagen. The adherent macrophages could be easily detached from the substrata by divalent cation chelating agents. The purity and recovery of macrophages separated by this method were approximately 92-94% and 41-48%, respectively.

Phagocytosis of hepatocyte mitochondria by rat Kupffer cells in vitro

Kupffer cells in primary culture bind and endocytose rapidly added rat liver mitochondria. Using phase contrast microscopy various stages of the uptake and digestion of these organelles were documented. Activities of mitochondrial enzymes within the Kupffer cells increased during the early phase of phagocytosis; they later declined, reaching the endogenous level of the Kupffer cell mitochondria after 3 to 4 h. The uptake was enhanced in the presence of heparin or rat serum, while iodoacetate, cytochalasin B or anti-fibronectin antisera were inhibitory. The transient presence of enzymatically active hepatocyte mitochondria renders Kupffer cells capable of producing urea. This mechanism partially explains earlier observations of urea formation in non-parenchymal rat liver cells.

Fibronectin and factor VIII-related antigen in liver cirrhosis and acute liver failure

The liver is involved in the turnover of fibronectin in two different ways: hepatic synthesis contributes substantially to the plasma fibronectin pool, while Kupffer-cells, performing an important role of the reticuloendothelial system, remove fibronectin opsonized material from the circulation. In 45 patients with histologically confirmed liver cirrhosis and six patients with acute liver failure due to intoxication we determined fibronectin concentration in plasma by electroimmunoassay and additionally measured factor VIII-related antigen, which is a large glycoprotein not synthesized in the liver. Fibronectin levels in plasma were decreased in liver cirrhosis. This decrease was correlated with the extent of porto-caval collateral circulation. Very low levels were found in patients with acute liver failure. Factor VIII-related antigen levels were greatly increased as a function of the hepatic insufficiency. Between both parameters there was a significant inverse correlation. It is concluded that the simultaneous determination of both proteins provides reliable information about the remaining liver function.