Human fibronectin metabolism

EDA Fibronectin Microarchitecture and YAP Translocation During Wound Closure

Fibronectin (Fn) is an extracellular matrix glycoprotein with mechanosensitive structure-function. EDA Fn, a Fn isoform, is not present in adult tissue but is required for tissue repair. Curiously, EDA Fn is linked to both regenerative and fibrotic tissue repair. Given that Fn mechanoregulates cell behavior, Fn EDA organization during wound closure might play a role in mediating these differing responses. One mechanism by which cells sense and respond to their microenvironment is by activating a transcriptional co-activator, Yes-associated protein (YAP). Interestingly, YAP activity is not only required for wound closure, but similarly linked to both regenerative and fibrotic repair. Therefore, this study aims to evaluate how, during normal and fibrotic wound closure, EDA Fn organization might modulate YAP translocation by culturing human dermal fibroblasts on polydimethylsiloxane (PDMS) substrates mimicking normal (soft: 18 kPa) and fibrotic (stiff: 146 kPa) wounded skin. On stiffer substrates mimicking fibrotic wounds, fibroblasts assembled an aligned EDA Fn matrix comprising thinner fibers, suggesting increased microenvironmental tension. To evaluate if cell binding to the EDA domain of Fn was essential to overall matrix organization, fibroblasts were treated with Irigenin, which inhibits binding to the EDA domain within Fn. Blocking adhesion to EDA led to randomly organized EDA Fn matrices with thicker fibers, suggesting reduced microenvironmental tension even during fibrotic wound closure. To evaluate if YAP signaling plays a role in EDA Fn organization, fibroblasts were treated with CA3, which suppresses YAP activity in a dose-dependent manner. Treatment with CA3 also led to randomly organized EDA Fn matrices with thicker fibers, suggesting a potential connected mechanism of reducing tension during fibrotic wound closure. Next, YAP activity was assessed to evaluate the impact of EDA Fn organization. Interestingly, fibroblasts migrating on softer substrates mimicking normal wounds increased YAP activity but on stiffer substrates, decreased YAP activity. When fibroblasts on stiffer substrates were treated with Irigenin or CA3, fibroblasts increased YAP activity. These results suggest there may be disrupted signaling between EDA Fn organization and YAP translocation during fibrotic wound closure that could be restored when reestablishing normal EDA Fn matrix organization to instead drive regenerative wound repair.

Evaluation of EDB Fibronectin in Plasma, Patient-Derived Xenograft Formalin-Fixed Paraffin-Embedded and Fresh Frozen Tumor Tissues Using Immunoaffinity LC-MS/MS

The fibronectin (FN) isoform including the extradomain B (EDB) segment (EDB + FN) is a promising tumor target and is highly expressed in some tumor types, such as breast, head, and neck cancer. To date, mostly immunohistochemistry (IHC) and Western blot have been used for the analysis of EDB + FN. However, complete quantitative measurements of EDB + FN expression in a tumor and circulation are important for the development of anti-EDB therapeutics. To this end, a method using protein enrichment followed by online antipeptide antibody enrichment coupled with a nanoflow LC-MS/MS was developed to quantify EDB + FN in human and cynomolgus plasma, patient-derived xenograft (PDX) tumors, and PDX formalin-fixed paraffin-embedded (FFPE) samples. Mouse plasma EDB + FN was analyzed using a protein immunoaffinity method followed by nanoflow LC-MS/MS. EDB + FN concentrations were 63.1 pmol/g in PDX breast cancer tumor and 49.6 pmol/g in PDX head and neck tumor. Mean plasma concentration was 1.1 nM (pmol/mL, 47.4 ng/mL) in normal healthy humans and 0.35 nM (15.1 ng/mL) in naive cynomolgus. The assay sensitivity was 0.018 nM based on calibration with recombinant human EDB + FN (rhEDB + FN).

Circulating fibronectin contributes to mesangial expansion in a murine model of type 1 diabetes

Fibronectin is ubiquitously expressed in the extracellular matrix, and its accumulation in the glomerular mesangium in diabetic nephropathy is associated with deterioration of renal function in these patients. However, the exact role of fibronectin in the pathogenesis of diabetic nephropathy remains unknown. To clarify this, we administered fluorescent-labeled plasma fibronectin to wild-type mice and found it to accumulate in the mesangium. Using liver-specific conditional-knockout mice to decrease circulating fibronectin, we reduced circulating fibronectin by more than 90%. In streptozotocin-induced diabetes of these knockout mice, the pronounced fall in circulating fibronectin resulted in a decrease in mesangial expansion by 25% and a decline in albuminuria by 30% compared to diabetic control mice. Indeed, the amount of fibronectin in the kidney was reduced, as was the total amount of collagen. In vitro experiments confirmed that matrix accumulation of fibronectin was enhanced by increasing fibronectin only, glucose only, or the combination of both. Thus, circulating fibronectin contributes to mesangial expansion and exacerbation of albuminuria in a murine model of type 1 diabetes.

Arecoline-induced pro-fibrotic proteins in LLC-PK1 cells are dependent on c-Jun N-terminal kinase

Areca nut (AN) chewing is associated with chronic kidney disease (CKD). However, the molecular mechanisms of AN-induced CKD are not known. Thus, we studied the effects of arecoline, a major alkaloid of AN, on proximal tubule (LLC-PK1) cells in terms of cytotoxicity, fibrosis, transforming growth factor-β (TGF-β) and c-Jun N-terminal kinase (JNK). We found that arecoline dose (0.1-0.5mM) and time (24-72h)-dependently induced cytotoxicity without causing cell death. Arecoline (0.25 mM) also time-dependently (24-72h) increased fibronectin and plasminogen activator inhibitor-1 (PAI1) protein expressions. Arecoline (0.25 mM) time-dependently (24-72h) increased TGF-β gene transcriptional activity and supernatant levels of active TGF-β1. Moreover, arecoline (0.25 mM) activated JNK while SP600125 (a JNK inhibitor) attenuated arecoline-induced TGF-β gene transcriptional activity. SP600125, but not SB431542 (a TGF-β receptor type I kinase inhibitor), attenuated arecoline-induced fibronectin and PAI1 protein expressions. Finally, tubulointerstitial fibrosis occurred and renal cortical expressions of fibronectin and PAI1 proteins increased in arecoline-fed mice at 24 weeks. We concluded that arecoline induced tubulointerstitial fibrosis in mice while arecoline-induced TGF-β and pro-fibrotic proteins (fibronectin, PAI1) are dependent on JNK in LLC-PK1 cells.

The neovasculature homing motif NGR: more than meets the eye

A growing body of evidence suggests that peptides containing the Asn-Gly-Arg (NGR) motif can selectively recognize tumor neovasculature and can be used, therefore, for ligand-directed targeted delivery of various drugs and particles to tumors or to other tissues with an angiogenesis component. The neovasculature binding properties of these peptides rely on the interaction with an endothelium-associated form of aminopeptidase N (CD13), an enzyme that has been implicated in angiogenesis and tumor growth. Recent studies have shown that NGR can rapidly convert to isoaspartate-glycine-arginine (isoDGR) by asparagine deamidation, generating alpha(v)beta(3) ligands capable of affecting endothelial cell functions and tumor growth. This review focuses on structural and functional properties of the NGR motif and its application in drug development for angiogenesis-dependent diseases. Furthermore, we discuss the time-dependent transition of NGR to isoDGR in natural proteins, such as fibronectins, and its potential role of as a "molecular timer" for generating new binding sites for integrins impli-cated in angiogenesis.

Spontaneous formation of L-isoaspartate and gain of function in fibronectin

Isoaspartate formation in extracellular matrix proteins, by aspartate isomerization or asparagine deamidation, is generally viewed as a degradation reaction occurring in vivo during tissue aging. For instance, non-enzymatic isoaspartate formation at RGD-integrin binding sites causes loss of cell adhesion sites, which in turn can be enzymatically "repaired" to RGD by protein-l-isoAsp-O-methyltransferase. We show here that isoaspartate formation is also a mechanism for extracellular matrix activation. In particular, we show that deamidation of Asn263 at the Asn-Gly-Arg (NGR) site in fibronectin N-terminal region generates an alpha(v)beta3-integrin binding site containing the L-isoDGR sequence, which is enzymatically "deactivated" to DGR by protein-L-isoAsp-O-methyltransferase. Furthermore, rapid NGR-to-isoDGR sequence transition in fibronectin fragments generates alpha(v)beta3 antagonists (named "isonectins") that competitively bind RGD binding sites and inhibit endothelial cell adhesion, proliferation, and tumor growth. Time-dependent generation of isoDGR may represent a sort of molecular clock for activating latent integrin binding sites in proteins.

Effect of plasma fibronectin on the incisional wound healing in rats

BACKGROUND

Abdominal wall repair after celiotomy is important because insufficient incisional wound strength results in wound failures such as fascial dehiscence and herniation. Plasma fibronectin (pFn) has been shown to play an important role in wound healing. The purpose of this study was to investigate whether pFn improves incisional wound healing in a rat skin incision and celiotomy model.

METHODS

Rats underwent a linear skin incision in the dorsal plane or a full-thickness incisional wound (celiotomy) in the abdominal wall. The same operative procedures were performed on rats whose pFn levels were reduced by antirat pFn serum. The wounds were sutured, and purified human pFn or albumin was given intravenously.

RESULTS

After the celiotomy, pFn levels decreased immediately and reached a minimum at 3 h after incision. A single injection of pFn (10 mg/kg) significantly increased the breaking strength of the skin and the bursting pressure of the abdominal wall. The amount of hydroxyproline in the skin incisional wound with pFn was significantly greater than with an injection of albumin as control. In rats with pFn levels decreased by antirat pFn serum, a single administration of pFn significantly increased the breaking strength of the skin and the bursting pressure of the abdominal wall compared to a control injection of albumin.

CONCLUSIONS

It is important for wound healing to maintain sufficiently high levels of pFn. A single intravenous injection of pFn after celiotomy may be useful in the prevention of fascial dehiscence and herniation.

Protective effect of fibronectin for endotoxin-induced liver injury after partial hepatectomy in rats1

BACKGROUND

Endotoxemia may occur after hepatectomy and become the cause of post-operative death. Fibronectins (Fns) are involved in a number of biological processes, such as cellular adhesion, motility, differentiation, apoptosis, hemostasis, wound healing, and ischemic injury. Studies were performed to determine whether Fn influences the survival rate of rats subjected to endotoxin-induced liver injury after partial hepatectomy.

MATERIALS AND METHODS

Lipopolysaccharide (LPS) was administered intravenously to male Sprague-Dawley rats within 48 h of 70% hepatectomy. Before LPS administration, plasma Fn or bovine serum albumin was given intravenously.

RESULTS

The survival rate of the Fn-treated group was markedly improved compared with that of the controls. Fn prevented increases in the concentrations of serum enzymes and total bilirubin related to liver injury. The levels of inflammatory cytokines, including tumor necrosis factor-alpha, interleukin-1beta, and cytokine-induced neutrophil chemoattractant, in serum and liver tissue, also were significantly lower in the Fn-treated group than in the control group. Furthermore, the degree of apoptosis and necrosis in remnant liver was significantly decreased in the Fn-treated rats compared with the controls.

CONCLUSIONS

These results indicate that Fn prevents endotoxin-induced liver injury after partial hepatectomy, at least in part through the inhibition of production of inflammatory cytokines, necrosis and apoptosis in the remaining liver.

The effects of acute and chronic protein depletion and accretion on plasma concentrations of insulin-like growth factor-1, fibronectin and total protein for ruminants nourished by intragastric infusion of nutrients

The relationships of N input or protein status and the concentrations of serum insulin-like growth factor-1 (IGF-1), plasma fibronectin (FN) and total protein (TP) were examined in three experiments with steers and sheep nourished by intragastric infusion of nutrients. In Expt 1, three steers (340 kg live weight) were infused with three levels of volatile fatty acids (0, 300 and 600 kJ/kg metabolic weight (W0.75) per d) and six levels of casein (0, 200, 400, 650, 1500 and 2500 mg N/kg W0.75 per d). Each N treatment was imposed for 5 d. In Expts 2 and 3, five groups of sheep (about 35 kg live weight) were infused with casein at 500 mg N/kg W0.75 per d for 2 weeks followed by 1500, 500 or 50 mg N/kg W0.75 per d in Expt 2, and in Expt 3, with 100 mg N/kg W0.75 per d for 6 weeks or 10 mg N/kg W0.75 per d for 4 weeks. Non-protein energy was maintained constant at 500 kJ/kg W0.75 per d throughout. Daily N balance and total body N content at the end were measured, and protein status was defined as a percentage of cumulative N accretion or depletion in relation to the total body N content at maintenance. It was found that IGF-1 and FN responded rapidly and substantially to altered N input, and that when daily N input was maintained constantly at sub-maintenance, their continuous declines were related closely to progressive protein depletion in the sheep. Plasma TP concentration was independent of N input when N input was altered acutely in the steers, but declined significantly and gradually with severe, chronic body protein depletion in the sheep. Plasma content of TP in the sheep however reduced acutely with a reduction in N input. Plasma volume fell substantially over the first 2 weeks of protein depletion, compensating for the declines in TP content and maintaining TP concentration plateau. The possible implications of the changes in TP concentration and content (concentration x volume) to body protein loss in sheep are discussed.

Assessment of plasma fibronectin in malnourished Nigerian children

BACKGROUND

Severe malnutrition is associated with septic infections. The concentrations of fibronectin, albumin, and transferrin in plasma were measured in three groups of children with protein-energy malnutrition, aged 1-3 years, each group comprising 20 children. The aim of which was to test whether plasma fibronectin, being an opsonic protein, was reduced in such children, and if it was a useful index for assessing the severity of malnutrition.

METHODS

The concentrations of fibronectin, albumin, and transferrin in plasma were studied by enzyme immunoassay/ immunoblotting, spectrophotometry and immunoturbidimetry respectively.

RESULTS

All values were significantly lower in the patients with malnutrition than in the age- and sex-matched well-nourished Nigerian reference children. Within the malnourished group, the fibronectin value was evenly reduced in all subgroups. Albumin and transferrin values were lowest in the patients with kwashiorkor, highest in the marasmic patients, and intermediate in the patients with marasmic kwashiorkor; the values correlated mutually in individual cases as well, but not with the fibronectin levels. Neither plasma fibronectin fragmentation nor tissue fibronectin was detected in any patient with malnutrition or in the reference subjects.

CONCLUSIONS

The reduced plasma fibronectin values in these patients may be due to reduced synthesis by the liver, as evidenced by the equally reduced albumin and transferrin concentrations and/or to the multiple infections characteristic of the patients.

Clinical evaluation of plasma fibronectin level as a biomarker of preeclampsia

OBJECTIVE

To evaluate the clinical feasibility of plasma fibronectin as a biomarker and predictor for preeclampsia.

METHODS

A total of 13 patients who had severe preeclampsia in prior pregnancies were enrolled for longitudinal study, and the profiles of plasma fibronectin were observed throughout their pregnancies. In cross-sectional study, the correlation between plasma fibronectin within a week before delivery and the grade of preeclampsia were analyzed in 96 pregnant women including tangible preeclampsia.

RESULTS

In the longitudinal study, 5 patients developed severe preeclampsia, in whom plasma fibronectin was elevated over the normal range 2-9 weeks before the onset of preeclampsia. In the cross-sectional study, plasma fibronectin levels elevated significantly corresponding with the severity of preeclampsia, and the abnormal elevation of fibronectin reflected the existence of preeclampsia with satisfactory sensitivity and specificity.

CONCLUSION

Increased plasma fibronectin levels may be a highly sensitive and specific diagnostic indicator for preeclampsia.

Problems and priorities for controlling opportunistic pathogens with new antimicrobial strategies; an overview of current literature

An International Study Group on New Antimicrobial Strategies (ISGNAS) has been formed in response to the recognition that development of microbial resistance to antibiotics is becoming a serious, world-wide problem. The group met in 1993 for the first time to discuss the feasibility of developing rational alternatives to the use of antibiotics and prepared, as a result, a comprehensive overview of normal (physiological) mechanisms involved in the control of potentially pathogenic (oppotunistic) microorganisms. One objective of ISGNAS is to understand the conditions which allow opportunistic microbes present among the symbionts to cause an infection. There is a need for more coherent information concerning the habitat, growth requirements and host and pathogen properties which allow opportunistic pathogens to cause life-threatening infections. In particular, information is urgently being sought to understand the complexity of the interactions between the vast number of microbial species, and the interactions between the microbes and their host. Another goal is to inspire and enable basic and clinical research that will lead to the development of new therapies for regulating colonization, translocation and infection by opportunistic micro-organisms in patients during periods of decreased resistance. With a sufficient amount of knowledge of how healthy individuals keep opportunistic micro-organisms under control, it may become feasible for physicians to maintain host resistance and inter-microbial factors involved in the containment of opportunistic microbes. Therapies aimed at boostering natural resistance mechanisms will be of critical importance to individuals whose resistance has been compromised as a result of another clinical condition.

Assessment of the fibrogenetic activity in chronic pancreatitis. The role of circulating levels of extracellular matrix components

Determination of circulating levels of extracellular matrix components has been proposed as a reliable method to assess the activity of fibrogenetic processes. Therefore, we aimed to analyze circulating levels of laminin, fibronectin, and procollagen III peptide (PIIIP) in patients with chronic pancreatitis (CP) and to correlate them with the morphological and functional stage, and duration of the disease. Thirty patients with CP and 18 healthy controls were studied. Serum PIIIP concentrations (RIA), but not fibronectin (RID) and laminin (RIA), were abnormally high in 8 patients with CP. No correlation was found between circulating levels of extracellular matrix components and both functional and morphological stage and duration of CP. Nevertheless, patients with elevated serum PIIIP levels tend to have a more advanced CP (morphological and functional changes) than those with normal levels after a similar duration of the disease. We hypothesize that whereas functional and morphological findings reflect the cumulative effect of chronic inflammation on the pancreas, serum PIIIP concentrations would reflect the activity of the fibrogenetic process within the gland at the time of sampling. The results shown in the present study may be considered a starting point for longitudinal studies that examine the relationship between serum PIIIP or other markers for fibrogenetic activity and evolution of CP.

Changes in serum fibronectin levels at delivery in pregnant women and their fetuses with idiopathic fetal growth retardation

We determined maternal and neonatal umbilical artery serum concentrations of fibronectin (Fn) in 15 pregnant women with idiopathic IUGR (Intrauterine growth retardation) and 17 normal pregnant women at the time of delivery, by use of a rate nephelometric procedure. The results showed that the maternal serum levels of Fn in pregnant women with idiopathic IUGR were significantly higher than those in normal pregnant women at the time of delivery (P < 0.01), but umbilical artery serum concentrations in the two groups were not significantly different (P > 0.05), suggesting that the significant increase in maternal serum levels of Fn appeared to be related to uteroplacental vascular endothelial cell lesion, formation of microthrombi and deficiency of placental perfusion.

Identification and characterization of opsonic fibronectin in synovial fluids of patients with active rheumatoid arthritis

A cofactor that selectively opsonizes particulate activators of the human alternative complement pathway and enhances their phagocytosis by human monocytes was identified in synovial fluids of patients with rheumatoid arthritis. The active material was present in fluids treated with protease inhibitors, was heat stable, and was unaffected by incubation with hyaluronidase. Chromatographic isolation of synovial fluid fibronectin by gelatin affinity and by immunoaffinity on antifibronectin monoclonal antibody BD4 yielded similar quantities of protein for each of 3 fluids. Synovial fluid proteins with the BD4 fibronectin epitope accounted for essentially all of the phagocytosis-enhancing activity and expressed this activity by opsonizing target activators. Additional chromatographic analyses of synovial fluid fibronectin with the BD4 epitope were carried out using Sepharose-bearing gelatin and 4 additional antifibronectin monoclonal antibodies. The opsonic materials were characterized as having 2 distinct fibronectin epitopes, which always mapped from the cell adhesive domain to the carboxyl-terminus of plasma fibronectin, but only rarely contained the gelatin binding domain.

Isotopic determination of fibronectin synthesis in humans

Fibronectin is an opsonic protein that, among other functions, activates the reticuloendothelial system. Accurate measurement of its rate of synthesis is necessary to more fully understand its physiological role in normal and pathological conditions. We have determined the rate of fibronectin synthesis in three normal volunteers using a primed-constant infusion of 15N-glycine and 1,2-13C-leucine, and measuring the incorporation of the isotopes into the protein over 5 days of infusion. In nine additional subjects, the fractional synthetic rate (FSR) of fibronectin was calculated during a 24-hour infusion using urinary hippurate and plasma alpha-ketoisocaproic acid enrichment to represent the precursors for incorporation of labeled glycine and leucine, respectively, into fibronectin. The FSR using glycine and leucine was 1.56 +/- 0.14 and 1.29 +/- 0.04 (%/h), respectively, in the 5-day infusion study, and 1.56 +/- 0.10 versus 1.83 +/- 0.09 (%/h), respectively, in the 24-hour study. The results of the 5-day infusion of 15N-glycine justify the use of urinary hippurate to reflect the precursor enrichment for the determination of the FSR of fibronectin during a shorter (less than 24 hour) infusion period.

Follow-up of the serum levels of extracellular matrix components in acute and chronic pancreatitis

Time-dependent serum concentrations of extracellular matrix proteins were studied in 32 patients with pancreatitis in order to find potential markers of the reparative response during the disease. Patients were subdivided by clinical and biochemical criteria: severe acute pancreatitis (n = 10), moderate acute pancreatitis (n = 17), and acute attack of chronic pancreatitis (n = 5). Serum and plasma samples were collected on days 1-7, 10, 14, and 21 for measurements of the aminoterminal propeptide of type III procollagen (PIIINP), hyaluronic acid, laminin, fibronectin, and routine clinical-chemical parameters. During an acute attack of chronic pancreatitis all parameters were within the reference range. In moderate acute pancreatitis concentrations of PIIINP, laminin, and hyaluronic acid fluctuated around the upper reference limit, but declined to mid-normal levels at day 21. In severe acute pancreatitis all three parameters increased. In patients who died as a consequence of sepsis and multi-organ failure the increase in PIIINP, laminin and hyaluronic acid was much more pronounced and paralleled by a decrease in plasma concentrations of fibronectin. In conclusion, this study revealed a relation between the severity of acute pancreatitis and the increase in serum concentrations of extracellular matrix components, especially PIIINP.

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.

Effect of administration of fibronectin or aprotinin on liver regeneration after experimental hepatectomy

Following 70% hepatectomy, male Sprague-Dawley strain rats were given purified human plasma fibronectin and/or aprotinin intraperitoneally after hepatectomy and were divided into 4 groups: Group FA (40 mg/kg of FN and 25,000 KIU/kg of aprotinin), Group F (40 mg/kg of fibronectin), Group A (25,000 KIU/kg of aprotinin), and Group C which served as a control. The liver regeneration rate 72 hours after hepatectomy in Groups FA and F, and the plasma FN levels at 24 and 72 hours following hepatectomy in groups with FN, were significantly higher than that of the control group. The incorporation of 3H-thymidine into DNA and the phagocytic index of the reticuloendothelial system at 24 hours in Groups FA and F, and the mitotic index at 72 hours after hepatectomy in Group FA were significantly increased as compared to the control. But the supplementation of 20 mg/kg of indomethacin to the 4 groups resulted in significant suppression of 3H-thymidine uptake 24 hours after hepatectomy. Moreover, plasma fibronectin levels in rats correlated well with the phagocytic index and DNA synthesis 24 hours following partial hepatectomy. These results suggest that fibronectin may act as an activator of the reticuloendothelial system, related to prostaglandins, in the process of liver regeneration.

Plasma fibronectin synthesis in normal and injured humans as determined by stable isotope incorporation

In humans, plasma fibronectin decreases early after operative injury, burn, or trauma, followed by a rapid restoration with a secondary decline typically observed if such patients become septic. We determined the rate of plasma fibronectin and plasma fibrinogen synthesis in normal subjects and injured patients using a stable isotope incorporation technique with [15N]glycine. During a constant 14-h infusion of [15N]glycine, the enrichment of [15N]glycine in both the free plasma glycine precursor pool as well as the urinary hippurate pool was determined; the latter used as an estimate of intracellular hepatic precursor enrichment. [15N]Glycine enrichment in both plasma fibronectin and fibrinogen was also quantified. The synthesis rate (Js/V) expressed in micrograms per milliliter of plasma per hour and the fractional synthesis rate (FSR) expressed as percentage of the plasma pool produced per day were determined. In normal subjects, the FSR for plasma fibronectin using 15N enrichment into urinary hippurate was 35.35 +/- 1.46%/d, whereas the Js/V was 4.45 +/- 0.19 micrograms/ml plasma per h. In normal subjects, the FSR for plasma fibronectin using 15N enrichment into free plasma glycine was 14.73 +/- 0.63%/d, whereas the Js/V was 1.98 +/- 0.09 micrograms/ml plasma per h. Early (2-3 d) after burn injury, fibronectin synthesis was increased (Js/V = 5.74 +/- 0.36; P less than 0.05), whereas later after injury, fibronectin synthesis began to decline (Js/V = 3.52 +/- 0.24; P less than 0.05) based on 15N enrichment of urinary hippurate. In contrast, the Js/V and FSR of plasma fibrinogen, a well-documented acute-phase plasma protein, revealed a sustained elevation (P less than 0.05) after injury in both the trauma and burn patients. Thus, plasma fibronectin synthesis is elevated early postinjury, which may contribute to the rapid restoration of its blood level. However, once fibronectin levels have normalized, the synthesis of plasma fibronectin appears to decline.

Predictive value of increased plasma levels of fibronectin in gestational hypertension

Blood pressure, proteinuria, and plasma fibronectin and plasminogen activator inhibitor-1 levels were measured in 120 apparently healthy normotensive primigravid women during the first, second, and third trimesters of pregnancy and 2 days post partum. Thirty-two women developed hypertension (diastolic blood pressure greater than or equal to 90 mm Hg) that in 17 women was associated with proteinuria (greater than 0.3 gm/day). Fibronectin levels were 83% +/- 22% of normal (mean +/- SD) during the first trimester and 75% +/- 20% at term in the healthy women but increased from 94% +/- 36% to 187% +/- 36% in the women who developed gestational hypertension (with or without proteinuria) (p less than 0.0001). Plasminogen activator inhibitor-1 levels increased from 26 +/- 19 ng/ml to 110 +/- 86 ng/ml in healthy women and from 32 +/- 35 ng/ml to 290 +/- 90 ng/ml in hypertensive women (p less than 0.001). Increased levels of fibronectin at 25 to 36 weeks of pregnancy (greater than or equal to mean + 2 SD of the healthy women, or greater than 140%) were found in 31 of the 32 women with gestational hypertension with or without proteinuria and in 5 of the 88 healthy women (sensitivity 96%, specificity 94%). Fibronectin levels increased 3.6 +/- 1.9 weeks earlier than the onset of hypertension and/or proteinuria. Increased levels of plasminogen activator inhibitor-1 at 25 to 32 weeks (greater than or equal to 280 ng/ml) were found in 16 of the 32 women who developed gestational hypertension with or without proteinuria and in 4 of the 88 healthy women (sensitivity 50%, specificity 95%). We conclude that increased fibronectin levels are the best predictor of gestational hypertension with or without proteinuria and that its level in plasma increases several weeks before the development of hypertension.

Fibronectin is related to prealbumin in plasma of decompensated cirrhotics

In a group of 23 patients with advanced liver cirrhosis we have found a statistically significant positive correlation (r = 0.746; p less than 0.0001) between fibronectin and prealbumin levels measured in plasma by immunonephelometric methods and found significantly lower than in healthy controls (p less than 0.001). On the contrary, no correlation of fibronectin neither to albumin nor to the presence of an enlarged spleen was observed. Since the sensitivity of prealbumin as an index of liver function is believed to be higher than that of albumin, our results support the view that the decreased fibronectin in advanced cirrhotics is mainly due to their liver failure, an enlarged spleen playing only a minor role.

Evidence for the presence of a free N-terminal fibronectin 30-kDa domain in human plasma by quantitative determination with an indirect immunosorbent assay

The free N-terminal 30-kDa domain of the fibronectin subunit chains had previously been shown to mediate binding of soluble fibrin to phagocytic cells. In order to demonstrate whether the fragment is available in plasma in a suitable concentration, an indirect immunoassay procedure for its quantitative evaluation was developed. The free form of the 30-kDa domain was separated from fibronectin and the bulk of the plasma proteins by two-step affinity chromatography on gelatin- and heparin-Sepharose. In the eluate of the heparin-Sepharose the 30-kDa fragment was determined by its capacity to inhibit the immune reaction between a specific antiserum and the 30-kDa fragment immobilized on microtiter wells. The procedure offered reproductibility comparable with other immunoassays (coefficient of variation 4.0 to 8.0%); the lowest amount of detectable 30-kDa fragment was 0.1 microgram/ml. In human plasma this method detected for the first time ca. 5 micrograms/ml 30-kDa fragment. This concentration is in the range required for binding of fibrin to cells.

Metabolism of plasma fibronectin in rabbits with experimental hyperthyroidism and hypothyroidism

We previously reported that the concentration of plasma fibronectin (pFN) is increased in patients with hyperthyroidism and decreased in those with hypothyroidism. In this work, labeled pFN was given intravenously to euthyroid, hyperthyroid, and hypothyroid rabbits to examine its metabolism in states of thyroid dysfunction. In euthyroid rabbits, the serum concentration of thyroxine (T4) was 2.94 +/- 0.59 micrograms/dL, and that of pFN was 24.2 +/- 1.2 mg/dL. With 125I-FN as tracer, the half life was estimated as 72.8 +/- 2.6 hours, the fractional catabolic rate (FCR) as 2.08 +/- 0.07%/h, the rate of synthesis (SR) as 3.84 +/- 0.20 mg/kg/day and j1/j2 (the ratio of the exchange coefficients between intravascular and extravascular compartments) of pFN as 0.295 +/- 0.051. With 3H-FN as tracer, these values were not significantly different. In hyperthyroid rabbits, obtained by treatment with I-thyroxine, the serum T4 concentration was increased to 5.73 +/- 1.58 micrograms/dL and the pFN concentration to 29.6 +/- 2.2 mg/dL. In these animals, the half life of pFN was shortened to 59.8 +/- 1.0 hour, the FCR was slightly increased to 3.07 +/- 0.52%/h and the SR was greatly increased to 7.13 +/- 1.17 mg/kg/d. In hypothyroid rabbits, obtained by treatment with methylthiouracil, the serum T4 and pFN levels were reduced to 1.50 +/- 0.36 micrograms/dL and to 20.7 +/- 1.7 mg/dL, respectively, the FCR and SR were also decreased to 1.39 +/- 0.04%/h and 2.26 +/- 0.14 mg/kg/d, respectively. The values of j1/j2 did not significantly change during this work.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of partial hepatectomy on plasma fibronectin concentrations in the rat

Rats were subjected to 60% partial hepatectomy. In the immediate postoperative period, there was a small decline in plasma fibronectin concentrations, which was normalized already 12 h post-operatively. Metabolic labelling of fibronectin with 35S-methionine showed that the rate of incorporation of label was unchanged after partial hepatectomy. However, when the abdominal viscera were excluded from the circulation, no incorporation of label was found. These results show that the rate of fibronectin biosynthesis has the rapid regulation characteristics of an acute phase reactant. Peripheral tissues do not contribute significantly to the plasma fibronectin concentration. Intra- or retro-peritoneal viscera, most likely the liver, are responsible for the synthesis of rat plasma fibronectin.

Measurement of connective tissue parameters in serum for diagnosis and follow-up of liver fibrosis

Hepatic fibrogenesis, i.e. activated synthesis and excessive intercellular deposition of connective tissue molecules (collagens, adhesive glycoproteins, proteoglycans) occurs in chronic alcoholic and viral liver injury and, less frequently, in some other conditions. The process may be monitored biochemically by the radioimmunoassay of some connective tissue molecules or their fragments and by the measurement of the activity of certain enzymes in serum. Currently, the radioimmunoassay of the aminoterminal propeptide of type III procollagen in serum reflects best the activity of liver fibrogenesis. The serum level of laminin, a high molecular weight basement membrane glycoprotein, was found to be correlated with an elevated portal venous pressure.

Fibronectin during thyroid hormone replacement therapy

Hemostasis may be affected by thyroid function in various ways. We studied plasma concentration of Fibronectin in 13 untreated patients after total thyroidectomy due to thyroid carcinoma. Fibronectin levels were significantly decreased compared to an equal numbered group of healthy volunteers (p 0.0005). The same patients were studied again after an oral thyroid replacement of 200 micrograms L-thyroxine/d over at least six weeks. Fibronectin had increased significantly, compared to untreated patients and controls resp. Furthermore, a significant positive correlation was found between plasma concentrations of Fibronectin and total T4 (r = 0.92; y = 6.617 + 0.52x). In contrast Factor V activity was low in untreated patients but normal during high dose replacement therapy. No correlation was found between Factor V and thyroid hormone concentrations. We discuss the relation between fibronectin plasma levels and thyroid hormones.

Functional analysis of plasma fibronectin with special consideration of binding interferences

So far, soluble fibronectin has been quantitated mostly by immunological techniques. In this investigation we show that an immunological assay provides reliable results only with intact fibronectin. Fibronectin fragments resulting from proteolysis give rise to falsely raised values. We present four functional tests based on the sandwich (ELISA) technique on microtitre plates. These quantify fibronectin on the basis of its binding capacity to collagen, heparin, fibrin and carboxy-group-modified IgG with high sensitivity, specificity and precision. Analysis of the bioactivity spectrum of intact fibronectin is not disturbed by fibronectin fragments. Furthermore we demonstrate interferences, in particular between heparin and collagen in their mutual binding to fibronectin. This provides new indications of a "substrate activation" of fibronectin.

Fibronectin is synthesized as an acute phase reactant in rat hepatocytes

Elevated concentrations of fibronectin were found in plasma of rats under different acute phase conditions. Untreated animals showed a plasma fibronectin concentration of 150 +/- 50 mg/l, which increased to 412 +/- 59 mg/l 24 h after subcutaneous injection of turpentine. The time course of the changes in plasma fibronectin concentration showed a peak at 24 h and a decline to normal concentrations 72 h after turpentine treatment. Additional stimulation by dexamethasone resulted in plasma fibronectin concentrations of 661 +/- 49 mg/l. No or only slight elevations of fibronectin concentrations were observed after treatment with adrenaline, thyroxine and triiodothyronine as compared with saline-injected animals. The common identity of plasma fibronectin in controls, turpentine and turpentine-dexamethasone-treated animals was shown by slab gel electrophoresis under nonreducing conditions, followed by western blot and immunofluorescence staining. One dimensional immunoelectrophoresis performed with polyclonal antibodies to human fibronectin cross-reacting with rat fibronectin (shown by Ouchterlony gel diffusion) revealed identical precipitation lines for the plasma of control and acute phase animals. Hepatocytes of turpentine-pretreated rats show a threefold increase of [14C]valine incorporation into total protein and a fourfold increase of immunoreactive radioactively labeled fibronectin in the culture medium, compared with control hepatocyte cultures. These results point to the role of hepatocytes in the synthesis of plasma fibronectin, which behaves in rats as an acute phase reactant.