Monoclonal antibodies to human heart fatty acid-binding protein

Comparative study of high sensitivity troponin T and heart-type fatty acid-binding protein in STEMI patients

AIM AND BACKGROUND

Heart-type fatty acid-binding proteins (H-FABP) which are detected within 2-3 h of acute myocardial infarction are involved in uptake of free fatty acids in the myocardium. Our aim in the present study is to compare window periods of H-FABP to high sensitivity troponin T (hs-Trop T) in acute ST elevation myocardial infarction (STEMI).

METHODS

160 STEMI diagnosed patient's serum samples are analyzed for hs-Trop T and H-FABP. Different window periods of chest pain onset (<3 h, 3-6 h and >6 h) are compared with complications, in-hospital mortality and statistically analyzed.

RESULTS

From 160 patients, 53 (33%) cases are presented in <3 h, 75 (47%) in 3-6, and 32 (20%) after >6 h respectively. Accordingly sensitivity of hs-Trop T was 92%, 94% and 97% while H-FABP was 75%, 88% and 84%, respectively. Overall sensitivity was 94% and 82% respectively. Statistically significant difference between mean hs-Trop T values with respect to window period <3, 3-6 and >6 h was 0.21, 0.35 and 0.80 ng/ml respectively, p value < 0.0001. No significant difference in H-FABP values was observed. Hs-Trop T positively correlated with age (r = 0.153, P = 0.05), window period (r = 0.363, P < 0.0001), TIMI score (r = 0.208, P = 0.008), ejection fraction (r = 0.191, P = 0.008), serum H-FABP (r = 0.229, P = 0.004), and serum hs-CRP (r = 0.326, p < 0.001). There was a statistically significant difference of mean hs-Trop T values with or without in hospital mortality (0.35 vs. 0.85 ng/ml, respectively, p = 0.008). No significant correlation to age, TIMI score, ejection fraction and hs-CRP values for H-FABP was observed.

CONCLUSION

It appears that hs-Trop T is a more sensitive marker than H-FABP in early hours of AMI and higher hs-Trop T predicts increase in-hospital mortality.

Heart type fatty acid binding protein: structure, function and biosensing applications for early detection of myocardial infarction

Heart type fatty acid binding protein (HFABP) as an early marker of cardiac injury holds a promising future with studies indicating surpassing performance as compared to myoglobin. As a plasma marker, this cytoplasmic protein owing to its small size (∼15kDa) and water solubility, appears readily in the blood-stream following cardiomyocyte damage, reaching peak levels within 6h of symptom onset. Low plasma levels of HFABP as compared to tissue levels indicate that minute amounts of the protein when released during myocardial infarction leads to a greater proportional rise. These parameters of kinetic release make it an ideal candidate for rapid assessment of acute myocardial infarction (AMI). The need for development of rapid immunoassays and immunotests so as to use HFABP as an early marker for AMI exclusion is tremendous. In the present review, we outline the various immunoassays and immunosensors developed so far for the detection of HFABP in buffer, plasma or whole blood. The principles behind the detection techniques along with their performance parameters compared to standard ELISA techniques are elucidated.

Highly sensitive recombinant antibodies capable of reliably differentiating heart-type fatty acid binding protein from noncardiac isoforms

During recent times, heart-type fatty acid binding protein (hFABP) has gained increasing credence as a promising cardiac biomarker. This is largely due to its rapid myocardial release and subsequent clearance kinetics, which are superior to those of myoglobin and offer an earlier diagnostic window than the troponins. Realization of its full diagnostic and prognostic potential is dependent on accessibility to robust hFABP-specific assays. Here we describe a rational strategy for generation and screening of hFABP-specific avian-derived recombinant antibodies. These antibodies were confirmed to be exquisitely specific for hFABP, with no cross-reactivity observed in a representative panel of the most homologous non-heart-type FABP isoforms. All of the antibodies tested exhibited single-figure nanomolar affinities, and their analytical potential was demonstrated in a simple inhibition enzyme-linked immunosorbent assay (ELISA) format that returned an impressive limit of quantitation (LOQ) value of 1.9 ng/ml. The cumulative results underline the potential value of these antibodies as enabling reagents for use in a variety of immunodiagnostic configurations.

Heart fatty acid binding protein in the diagnosis of myocardial infarction: where do we stand today?

Heart fatty acid binding protein (hFABP) is a novel small cytosolic protein that is abundant in the heart. It is highly cardiac-specific (i.e. expressed primarily in cardiac tissue), but is also expressed at low concentrations in tissues outside the heart. After myocardial ischemic damage, hFABP can be detected in the blood as early as 1-3 h after onset of chest pain, with peak values reached at 6-8 h and plasma levels returning to normal within 24-30 h. hFABP's clinical diagnostic value is very limited in the presence of renal failure and skeletal muscle diseases as it is completely renally eliminated. In these conditions, the diagnosis of acute myocardial infarction (AMI) may be overestimated. The combination of initial hFABP release after symptom onset, rapid kidney clearance from the circulation and high cardiac specificity suggests great potential for clinical use. Serial measurements of hFABP in the first 24 h after onset of symptoms in AMI patients can: (a) identify patients who are susceptible to reperfusion strategies, (b) detect perioperative AMIs, (c) distinguish patients who reperfuse their infarct-related artery from those who do not, as early as 30 min after starting thrombolytic treatment, (d) detect re-infarction if it occurs within 10 h after symptom onset, and (e) permit an accurate estimation of myocardial infarct size providing important prognosis information.

FABP3 and FABP10 in Atlantic salmon (Salmo salar L.)--general effects of dietary fatty acid composition and life cycle variations

The increased use of dietary plant oil supplementation combined with high dietary lipid loads challenges the lipid transport systems of cultivated fish species. Fatty acid binding proteins (FABPs) have been thoroughly studied as intracellular fatty acid transporters in vertebrates, but no data have been reported in Atlantic salmon. In the present study, comparative characterizations were performed, and dietary influence of plant oil supplementation on FABP3 and FABP10 expression was studied for several tissues in two separate dietary trials. In trial I, groups (6 fish each) were fed diets for 42 weeks (body mass 142+/-1 to 1463+/-83 g) (mean+/-S.D.), containing graded levels of rapeseed oil substituting for fish oil using a linear regression design. In trial II, groups (3 fish each) were fed 100% fish oil or 100% plant oil for 22 months (0.160+/-0.052 to 2523+/-590 g) (mean+/-S.D.) and sampled at regular intervals. Liver and muscle tissues appeared to express several FABPs possibly linked to different metabolic functions. FABPs mRNA expression did not change with dietary inclusion of 75% rapeseed oil, whereas FABP3 protein expression seemed to be affected by dietary rapeseed oil inclusion. Significant changes in red muscle FABP3 mRNA expression correlate to significant changes in total beta-oxidation capacity during the energy consuming process of smoltification.

Rapid analysis of fatty acid-binding proteins with immunosensors and immunotests for early monitoring of tissue injury

Fatty acid-binding protein (FABP) holds promise for early detection of tissue injury. This small protein (15kD) appears earlier in the blood than large proteins after cell damage. Combined its characteristics of high concentration tissue contents and low normal plasma values provide the possibility of a rapid rise above the respective reference values, and thus an early indication of the appearance of tissue injury. A general review was presented on the current status of different types of FABP for the detection of tissue injury in patients with myocardial injury, brain injury and also in athletes or horses with skeletal muscle injury. To take full advantage of the characteristics of the early marker FABP, rapid analysis is a crucial parameter. In this review, an overview of the development of immunoassay for the quantification of FABP in buffer, plasma or whole blood was outlined. The characteristics of different FABP immunosensors and immunotests were described. The feasibility of these immunoassays to be used in routine clinical practice and in emergency case was also discussed. Nowadays, the improved automated immunoassays (e.g. a microparticle-enhanced turbidimetric immunoassay), less time-consuming bedside immunosensors and immunotests (e.g. a one-step FABP lateral flow immunotest), are the main advance technology in point-of-care testing. With these point-of-care tests, the application of FABP as an early tissue injury marker has a great potential for many clinical purposes.

Fatty acid-binding proteins as plasma markers of tissue injury

BACKGROUND

One of the novel and promising plasma markers for detection of tissue injury is the family of 15 kDa cytoplasmic fatty acid-binding proteins of which various tissue-specific types occur.

AIMS AND OBJECTIVES

The present status of heart-type fatty acid-binding protein (H-FABP) as a diagnostic and prognostic marker for acute and chronic cardiac injury, as well as the preliminary diagnostic use of other types of FABP for detecting injury in other organs, is reviewed.

METHODS

This review is based on an overview of the literature on clinical diagnostics of various forms of organ injury, and uses additional literature on physiological aspects relevant for the interpretation of plasma marker concentrations.

RESULTS

H-FABP not only proves to be an excellent early marker for cardiac injury in acute coronary syndromes, but also allows detection of minor myocardial injury in heart failure and unstable angina. Preliminary results indicate that sensitivity, rule-out power and prognostic value of H-FABP in cardiac injury surpass the performance of the standard early marker myoglobin. The liver only contains liver-type FABP (L-FABP), but co-expression of H-FABP and L-FABP occurs in the kidney. Similarly, intestinal-type FABP (I-FABP) and L-FABP are found in intestines, and brain-type FABP (B-FABP) and H-FABP occur in the brain. Preliminary but promising applications of these proteins have been demonstrated for liver rejection, viability selection of kidneys from non-heart-beating donors (NHBD), inflammatory and ischemic bowel disease, traumatic brain injury and in the prevention of muscle injury in trained athletes.

CONCLUSIONS

Further study of the diagnostic and prognostic use of various FABP types is warranted, but their clinical application will require further commercialization of automated and rapid assays.

A continuous displacement immunoassay for human heart-type fatty acid-binding protein in plasma

Human heart-type fatty acid-binding protein (FABP) is suggested as an early plasma marker of acute myocardial infarction (AMI), and several studies have proved that, for early diagnosis of AMI, FABP performs better than myoglobin, which is a more often used early marker protein. Because serial measurement of biochemical markers in plasma is now universally accepted as an important determinant in AMI diagnosis, a rapid and continuous measuring method for FABP would be desirable. The aim of the present study was to develop an immunoassay based on the principle of displacement and using a column for rapid and continuous measurement of FABP in plasma. Glass columns filled with Sepharose-bound FABP were loaded with a horseradish peroxidase (HRP)-labeled antibody (Ab) and equilibrated with human plasma. After reaching a stable baseline, human plasma spiked with FABP or plasma from AMI patients was added. The Ab-HRP complex dissociated due to the presence of FABP in the plasma and was subsequently quantified. For plasma from AMI patients (n=5), the Ab-HRP level thus measured correlated with the corresponding plasma FABP concentration (R=0.96). The results of this study show the feasibility of a sensor for continuous monitoring of FABP in plasma.

Lipid-binding proteins and lipoprotein lipase activity in human skeletal muscle: influence of physical activity and gender

The protein and mRNA levels of several muscle lipid-binding proteins and the activity and mRNA level of muscle lipoprotein lipase (mLPL) were investigated in healthy, nonobese, nontrained (NT), moderately trained, and endurance-trained (ET) women and men. FAT/CD36 protein level was 49% higher ( P < 0.05) in women than in men, irrespective of training status, whereas FAT/CD36 mRNA was only higher ( P < 0.05) in women than in men in NT subjects (85%). Plasma membrane-bound fatty acid binding protein (FABPpm) content was higher in ET men compared with all other groups, whereas training status did not affect FABPpmcontent in women. FABPpmmRNA was higher ( P < 0.05) in NT women than in ET women and NT men. mLPL activity was not different between gender, but mLPL mRNA was 160% higher ( P < 0.001) in women than in men. mLPL activity was 48% higher ( P < 0.05) in ET than in NT subjects, irrespective of gender, in accordance with 49% higher ( P < 0.05) mLPL mRNA in ET than in NT subjects. A 90-min exercise bout induced an increase ( P < 0.05) in FAT/CD36 mRNA (∼25%) and FABPpmmRNA (∼15%) levels in all groups. The present study demonstrated that, in the NT state, women had higher muscle mRNA levels of several proteins related to muscle lipid metabolism compared with men. In the ET state, only the gender difference in mLPL mRNA persisted. FAT/CD36 protein in muscle was higher in women than in men, irrespective of training status. These findings may help explain gender differences in lipid metabolism and, furthermore, suggest that the balance between gene transcription, translation, and possibly breakdown of several proteins in muscle lipid metabolism depend on gender.

Regulation of plasma long-chain fatty acid oxidation in relation to uptake in human skeletal muscle during exercise

In the present study, we investigated possible sites of regulation of long-chain fatty acid (LCFA) oxidation in contracting human skeletal muscle. Leg plasma LCFA kinetics were determined in eight healthy men during bicycling (60 min, 65% peak oxygen uptake) with either high (H-FOX) or low (L-FOX) leg fat oxidation (H-FOX: 1,098 +/- 140; L-FOX: 494 +/- 84 micromol FA/min, P < 0.001), which was achieved by manipulating preexercise muscle glycogen (H-FOX: 197 +/- 21; L-FOX: 504 +/- 25 mmol/kg dry wt, P < 0.001). Several blood metabolites and hormones were kept nearly similar between trials by allocating a preexercise meal and infusing glucose intravenously during exercise. During exercise, leg plasma LCFA fractional extraction was identical between trials (H-FOX: 17.8 +/- 1.6; L-FOX: 18.2 +/- 1.8%, not significant), suggesting similar LCFA transport capacity in muscle. On the contrary, leg plasma LCFA oxidation was 99% higher in H-FOX than in L-FOX (421 +/- 47 vs. 212 +/- 37 micromol/min, P < 0.001). Probably due to the slightly higher (P < 0.01) plasma LCFA concentration in H-FOX than in L-FOX, leg plasma LCFA uptake was nonsignificantly (P = 0.17) higher (25%) in H-FOX than in L-FOX, yet the fraction of plasma LCFA uptake oxidized was 61% higher (P < 0.05) in H-FOX than in L-FOX. Accordingly, the muscle content of several lipid-binding proteins did not differ significantly between trials, although fatty acid translocase/CD36 and caveolin-1 were elevated (P < 0.05) by the high-intensity exercise and dietary manipulation allocated on the day before the experimental trial. The present data suggest that, in contracting human skeletal muscle with different fat oxidation rates achieved by manipulating preexercise glycogen content, transsarcolemmal transport is not limiting plasma LCFA oxidation. Rather, the latter seems to be limited by intracellular regulatory mechanisms.

Brain- and Heart-Type Fatty Acid-Binding Proteins in the Brain: Tissue Distribution and Clinical Utility

Background: Detection of brain injury by serum markers is not a standard procedure in clinical practice, although several proteins, such as S100B, neuron-specific enolase (NSE), myelin basic protein, and glial fibrillary acidic protein, show promising results. We investigated the tissue distribution of brain- and heart-type fatty acid-binding proteins (B-FABP and H-FABP) in segments of the human brain and the potential of either protein to serve as plasma marker for diagnosis of brain injury.

Methods: B-FABP and H-FABP were measured immunochemically in autopsy samples of the brain (n = 6) and in serum samples from (a) patients with mild traumatic brain injury (MTBI; n = 130) and (b) depressed patients undergoing bilateral electroconvulsive therapy (ECT; n = 14). The protein markers S100B and NSE were measured for comparison. Reference values of B-FABP and H-FABP were established in healthy individuals (n = 92).

Results: The frontal, temporal, and occipital lobes, the striatum, the pons, and the cerebellum had different tissue concentrations of B-FABP and of H-FABP. B-FABP ranged from 0.8 μg/g wet weight in striatum tissue to 3.1 μg/g in frontal lobe. H-FABP was markedly higher, ranging from 16.2 μg/g wet weight in cerebellum tissue to 39.5 μg/g in pons. No B-FABP was detected in serum from healthy donors. H-FABP serum reference value was 6 μg/L. In the MTBI study, serum B-FABP was increased in 68% and H-FABP in 70% of patients compared with S100B (increased in 45%) and NSE (increased in 51% of patients). In ECT, serum B-FABP was increased in 6% of all samples (2 of 14 patients), whereas H-FABP was above its upper reference limit (6 μg/L) in 17% of all samples (8 of 14 patients), and S100B was above its upper reference limit (0.3 μg/L) in 0.4% of all samples.

Conclusions: B-FABP and H-FABP patterns differ among brain tissues, with the highest concentrations in the frontal lobe and pons, respectively. However, in each part of the brain, the H-FABP concentration was at least 10 times higher than that of B-FABP. Patient studies indicate that B-FABP and H-FABP are more sensitive markers for minor brain injury than the currently used markers S100B and NSE.

Do we need additional markers of myocyte necrosis: the potential value of heart fatty-acid-binding protein

Heart fatty-acid-binding protein (FABP) is a small cytosolic protein that is abundant in the heart and has low concentrations in the blood and in tissues outside the heart. It appears in the blood as early as 1.5 h after onset of symptoms of infarction, peaks around 6 h and returns to baseline values in 24 h. These features of H-FABP make it an excellent potential candidate for the detection of acute myocardial infarction (AMI). We review the strengths and weaknesses of H-FABP as a clinically applicable marker of myocyte necrosis in the context of acute coronary syndromes.

Fatty Acid Binding Protein as a Serum Marker for the Early Diagnosis of Stroke

No biological marker is currently available for the routine diagnosis of stroke. The aim of this pilot study was to determine whether heart-fatty acid binding protein (H-FABP) could be used as a valid diagnostic biomarker for stroke, as compared with neuron-specific enolase (NSE) and S100B proteins. Using two-dimensional gel electrophoresis separation of cerebrospinal fluid proteins and mass spectrometry techniques, FABP was found elevated in the cerebrospinal fluid of deceased patients, used as a model of massive brain damage. Because H-FABP, a FABP form present in many organs, is also localized in the brain, an enzyme-linked immunosorbant assay was developed to detect H-FABP in stroke versus control plasma samples. However, H-FABP being also a marker of acute myocardial infarction (AMI), troponin-I and creatine kinase-MB levels were assayed at the same time in order to exclude any concomitant heart damage. NSE and S100B levels were assayed simultaneously. These assays were assessed in serial plasma samples from 22 control patients with no AMI or stroke, 20 patients with AMI but no stroke, and 22 patients with an acute stroke but no AMI. Twenty-two out of the 22 control patients and 15 out of the 22 stroke patients were correctly classified, figures much better than those obtained with NSE or S100B, in the same study's population. H-FABP appears to be a valid serum biomarker for the early diagnosis of stroke. Further studies on large cohorts of patients are warranted.

Development of a displacement immunoassay for human heart-type fatty acid-binding protein in plasma: the basic conditions

To risk-stratify patients with chest pain who are admitted to emergency rooms and for whom initial evaluation is not conclusive, the use of cardiac markers has become a standard procedure. A recently introduced early plasma marker for acute myocardial infarction (AMI) is the 14.5-kDa cytoplasmic heart-type fatty acid-binding protein (FABP). To fully exploit its early release from injured myocardium, a rapid method for repeated measurements or continuous monitoring of FABP in plasma is desirable. Such an on-line method could be an immunosensor based on displacement. The aim of the present study was to further investigate the principles underlying the displacement assay of FABP, both in buffer and in plasma. Batches of sepharose-bound FABP were loaded with an antibody-horseradish peroxidase (HRP) conjugate (anti-FABP). Continuous measurement of FABP was mimicked by repeated addition of FABP containing solutions followed by several washing steps. In the presence of free FABP the antibody-HRP complex dissociated and was subsequently quantified. Significant displacement in the presence of free FABP was observed in both buffer and human plasma. Anti-FABP could be intermittently displaced in the same batch, for at least 9 h, and the displacement was concentration-dependent. These results show the feasibility of a sensor based on the displacement principle to be used for the diagnosis of AMI in emergency medicine.

A new principle for rapid immunoassay of proteins based on in situ precipitate-enhanced ellipsometry

A new technique is presented that allows measurement of protein concentrations in the picomolar range with an assay time of only 10-20 min. The method is an enzyme-linked immunosorbent assay (ELISA), but uses in-situ ellipsometric measurement of a precipitating enzyme product instead of the usual colorimetric detection of accumulating enzyme product in solution. Quantitative validation was obtained by use of annexin V, a protein with high binding affinity for phosphatidylserine-containing phospholipid membranes, resulting in a transport-limited adsorption rate. This property was exploited to obtain a range of low surface concentrations of annexin V by timed exposures of phospholipid bilayers to known concentrations of annexin V. Using polyvinylchloride (PVC)-coated and silanized silicon slides, various versions of this technique were used for the rapid assay of fatty acid-binding protein (FABP), a recently introduced early marker for acute myocardial infarction with a normal plasma concentration below 1 nmol/l, interleukin 6 (IL-6), a cytokine with normal plasma concentrations below 1 pmol/l, and again, annexin V. A possible future application of the method in the development of a one-step ELISA is discussed.

Fatty acid binding protein in heart and skeletal muscles of the migratory barnacle goose throughout development

The long-distance migratory flights of birds are predominantly fueled by the oxidation of fatty acids, which are sourced primarily from extracellular adipose stores. These fatty acids have to be transported, via the circulatory system, to the mitochondria of the active muscles. An important facilitator of fatty acid transport within the cytoplasm of muscle cells is fatty acid binding protein (FABP), which serves as an intracellular carrier of long-chain fatty acids. In mammals, the muscular FABP content is related to the fatty acid oxidation capacity of the tissue. The aim of this study was to measure FABP in samples taken from the cardiac, pectoralis, and semimembranosus muscles of a long-distance avian migrant, the barnacle goose (Branta leucopsis), at various stages of development. Western blot analysis identified a single goose muscle protein of 15 kDa that was able to bind fatty acids and showed a 66% cross-reactivity with antibodies against human heart-type FABP. Captive goslings showed no significant changes in FABP content of either the heart (62.6 +/- 10.6 microgram/g wet wt) or the semimembranosus muscle (8.4 +/- 1.9 microgram/g wet wt) during development. However, in both peripheral and deep sites within the pectoralis muscle, FABP content of samples taken from captive goslings were approximately 10-fold higher throughout development and reached values of 30-40 microgram/g wet wt in fledging goslings at 7 wk of age. A further twofold higher value was seen in wild but not in captive goslings immediately before migration (12 wk of age). Similarly, FABP content was significantly higher in pectoralis samples taken from wild adults (94.3 +/- 3.6 microgram/g wet wt) compared with those from captive adults (60.5 +/- 3.6 micro/g wet wt). These results suggest that the experience of flight activity may be of critical importance in achieving maximal expression of FABP in the pectoralis muscles of postfledging and mature geese immediately before migration.

On-line flow displacement immunoassay for fatty acid-binding protein

In standard displacement flow immunoassays the analyte in the sample creates an active dissociation of labelled antigens (or antigen homologues) from an antigen binding site of an immobilized antibody, after which the labelled substance is measured downstream. Such systems have been described for molecules up to 1 kDa. In this study, we demonstrate displacement in a flow system for the detection of a small protein, cytoplasmic heart-type fatty acid-binding protein (15 kDa), a plasma marker for myocardial injury. The displacement system uses an inverse set-up: enzyme labelled monoclonal antibodies are associated to immobilized antigen, and are displaced by analyte in the sample. The system permits detection of both physiological (2-12 microg l(-1)) and pathological concentrations (12-2000 microg l(-1)) of fatty acid-binding protein in an on-line flow system.

Kinetic analysis of immunointeractions with covalently immobilized fatty acid-binding protein using a grating coupler sensor

Application of a grating coupler sensor (GCS) to the real time investigation of the interaction kinetics of covalently immobilized recombinant bovine heart-type fatty acid-binding protein (H-FABP) and corresponding antibody is described. The immobilization of the antigen is performed by activating the matrix hydroxyl groups with p-toluenesulfonyl chloride (TSC) and afterwards coupling the protein by reaction with its nucleophilic aminogroups. Covalent coupling via TSC permits reproducible measurements of immunointeractions on the same grating coupler sensor chip and complete regeneration after each binding cycle with glycine-hydrochloride. We demonstrate the analysis of binding data obtained on a GCS by linearization as well as direct curve fitting using the integrated rate equation for the determination of apparent rate and affinity constants. With both analysis methods we studied H-FABP/monoclonal anti-H-FABP-antibody interactions and obtained an average apparent association rate constant ka = 4.2 X 10(3) M(-1) s(-1) a dissociation rate constant of kd=1.3 X 10(-4) s(-1) and an equilibrium constant of KD=3 X 10(-8) M.

Early assessment of exercise induced skeletal muscle injury using plasma fatty acid binding protein

OBJECTIVE

To test whether fatty acid binding protein (FABP) is a useful plasma marker for the early detection of exercise induced skeletal muscle injury in healthy subjects.

METHODS

Plasma concentrations of FABP and myoglobin (Mb) were measured in six healthy physical education teacher trainees after 20 minutes of downhill running (16% incline; mean lactate 4 mmol/l; 70% (VO2MAX). Creatine kinase (CK) was measured for comparison.

RESULTS

Significant increases were found in plasma FABP (mean peak level 50 micrograms/l), Mb (823 micrograms/l), and CK (491 U/l). Mb and FABP concentrations were already significantly elevated (p < 0.05) at 30 minutes, but CK not until two hours after exercise. Whereas Mb and FABP decreased to normal levels within 24 hours, CK activity remained elevated until 48 hours. The Mb to FABP ratio in plasma after exercise induced muscle injury was 15.0 (1.3) (mean (SEM)) (range 7.4-31.1), which is within the range of ratios calculated for skeletal muscle tissue contents of Mb and FABP, but different from the reported plasma ratio after myocardial injury (4-6).

CONCLUSIONS

After eccentric exercise induced muscle injury, plasma FABP and Mb increase and decrease more rapidly than CK, indicating that both FABP and Mb are more useful than CK for the early detection of such injuries and the monitoring of injury during repeated exercise bouts. In addition, the Mb to FABP ratio in the plasma identifies the type of muscle injured.

Recombinant human heart-type fatty acid-binding protein as standard in immunochemical assays

Cytoplasmic heart-type fatty acid-binding protein has recently gained much attention in clinical diagnosis as a very early marker of acute myocardial infarction. Immunoassays have been developed for determination of this protein in plasma and urine samples. In the present study it is shown that those types of fatty acid-binding proteins which are abundant in tissues other than heart and muscle do not interfere with immunochemical determination of heart-type fatty acid-binding protein. To provide sufficient protein of consistent quality as standard in these immunoassays, human heart-type fatty acid-binding protein was cloned, expressed in Escherichia coli and purified to homogeneity. For quantitation of the recombinant protein its extinction coefficient was determined. Comparison of the recombinant and tissue-derived proteins by a variety of methods revealed both proteins to show similar kinetic as well as equilibrium constants with respect to two monoclonal antibodies currently applied in immunochemical detection of heart-type fatty acid-binding protein. Both preparations were indistiguishable in sandwich-ELISA and immunosensor measurements. A high stability of the recombinant protein was proven by ELISA measurements during storage and several freeze and thaw cycles. Thus, recombinant and tissue-derived heart-type fatty acid-binding proteins are immunochemically equivalent. The recombinant human heart-type fatty acid-binding protein is now available as standard for immunoassays.

Fatty acid-binding protein and the early detection of acute myocardial infarction

Fatty acid-binding protein (FABP) is a newly introduced plasma marker of acute myocardial infarction (AMI). The plasma kinetics of FABP (15 kD) closely resemble those of myoglobin (18 kD) in that elevated plasma concentrations are found within 3 h after AMI and return to normal generally within 12 to 24 h. This makes both myoglobin and FABP useful biochemical markers for the early assessment or exclusion of AMI. The myocardial tissue content of FABP (0.5 mg/g) is about five-fold lower than that of myoglobin (2.5 mg/g), but the reference plasma concentration of FABP (ca. 2 microg/l) is about 15-fold lower than that of myoglobin (ca. 32 microg/l), together suggesting a superior performance of FABP for the early detection of AMI. Indeed, in a study including blood samples from 83 patients with confirmed AMI, taken immediately upon admission to the hospital (< 6 h after AMI), the diagnostic sensitivity was significantly greater for FABP (78%, confidence interval 67-87%) than for myoglobin (53%, CI 40-64%) (P < 0.05). In addition, the differences in contents of myoglobin and FABP in heart and skeletal muscles and their simultaneous release upon muscle injury allow the plasma ratio of myoglobin/FABP to be applied for discrimination of myocardial (ratio 4-5) from skeletal muscle injury (ratio 20-70). Rapid and sensitive immunochemical assay systems for FABP in plasma are now being developed and soon will enable the introduction of this marker in clinical practice.

An immunosensor based on disposable electrodes for rapid estimation of fatty acid-binding protein, an early marker of myocardial infarction

An immunosensor was developed that allows the rapid estimation of fatty acid-binding protein (FABP) in neat plasma samples. FABP is released into the blood following myocardial infarction and elevated levels are found already 3 h after onset of symptoms. The sensor is based on screen-printed graphite working and Ag/AgCl reference electrodes and an immunosandwich procedure for the quantification of FABP. The capture antibodies are bound to the electrode surface by adsorption and will trap FABP from the plasma sample. The sandwich is then completed by a second monoclonal antibody conjugated with alkaline phosphatase. The enzyme converts p-aminophenylphosphate to p-aminophenol, which is detected amperometrically at +350 mV. The high binding capacity and very short response time of the working electrode allow within 20 min the quantification of FABP in the measuring range 10-350 ng/ml, covering the pathological range of FABP release into the circulation. Measurements of plasma samples from a patient with acute myocardial infarction show an excellent correlation of the results obtained with the biosensor and those obtained with the respective reference ELISA. Owing to the long stability of the electrodes with immobilized capture antibody (> 3 months) a quick application without the need of labour-intensive electrode preparation is possible.

Serum concentrations of myoglobin vs human heart-type cytoplasmic fatty acid-binding protein in early detection of acute myocardial infarction

We compared the diagnostic utility of serum concentrations of human heart-type cytoplasmic fatty acid-binding protein (H-FABPc), myoglobin, and their ratio for the early diagnosis of acute myocardial infarction (AMI) in 104 healthy volunteers and 165 patients at admission within 6 h of the onset of chest pain. The ROC curves of the H-FABPc [0.946, 95% confidence interval (CI) = 0.913–0.979] and myoglobin (0.895, 95% CI = 0.846–0.944) between patients with AMI and healthy volunteers were significantly greater than the area under the ratio of myoglobin to H-FABPc (0.823, 95% CI = 0.765–0.881). In 165 patients, the sensitivity (81.8%, 95% CI = 74.2–89.4%), specificity (86.4%, 95% CI = 78.1–94.6%), and predictive accuracy (83.6%, 95% CI = 78.0–89.3%) of H-FABPc &gt;12 μg/L in diagnosing AMI were significantly higher than those of myoglobin, and were similar to those of the combination of H-FABPc &gt;12 μg/L and the ratio ≤14. We conclude that H-FABPc is a more sensitive and specific marker than myoglobin for the early diagnosis of AMI, and that their ratio cannot give a clear advantage over the measurement of H-FABPc alone.

Early detection of successful coronary reperfusion based on serum concentration of human heart-type cytoplasmic fatty acid-binding protein

Both human heart-type cytoplasmic fatty acid-binding protein (H-FABPc) and myoglobin are low molecular weight proteins that are abundant in the cytoplasm of myocardial cells. Unlike myoglobin, H-FABPc content in the skeletal muscle is less than in cardiac muscle. To investigate the usefulness of the serum concentration of H-FABPc in the early detection of successful coronary reperfusion, we measured serum concentrations of H-FABPc and myoglobin in 45 patients with acute myocardial infarction treated with intracoronary thrombolysis or direct percutaneous transluminal coronary angioplasty. Coronary angiography was performed every 5 min for reperfusion therapy to identify the onset of reperfusion. Reperfusion, defined as a TIMI grade 2 or 3, was achieved within 60 min of the initiation of reperfusion therapy in 30 patients (the reperfused group), but was not achieved in 15 patients (the non-reperfused group). Blood samples were obtained before initiation of treatment and 15, 30 and 60 min after initiation of treatment in the non-reperfused group. In the reperfused group, samples were obtained before reperfusion and 15, 30 and 60 min after reperfusion. The H-FABPc ratio (the ratio of value after to value before the initiation of treatment or reperfusion) increased sharply after the onset of reperfusion, peaking at 41 +/- 18 min, and decreased rapidly thereafter. The predictive accuracy of an H-FABPc ratio of > 1.8 for the detection of reperfusion within 60 min of the initiation of treatment was 93% at 15 min after reperfusion, 98% at 30 min, and 100% at 60 min. Similar rates of predictive accuracy were observed for a myoglobin ratio > 2.4. The H-FABPc ratio detected successful reperfusion as early as 15 min after the onset of reperfusion and was highly accurate in detecting reperfusion within 60 min of the onset of reperfusion. The predictive accuracy of the H-FABPc ratio was similar to that of the myoglobin ratio for the early detection of successful coronary reperfusion.

One-step enzyme-linked immunosorbent assay (ELISA) for plasma fatty acid-binding protein

To allow a more rapid determination of heart-type fatty acid-binding protein (FABP) concentration in plasma a direct non-competitive (sandwich-type) ELISA was developed which uses high-affinity monoclonal antibodies to FABP. Total performance time of the one-step immunoassay is 45 min. The standard curve was linear between 0.2-6 micrograms/L, and the within-run and between-run coefficients of variations were below 6 and 11%, respectively. The serum FABP concentration measured in 79 healthy individuals was 1.6 (0.8) [mean (SD), range 0.3-5.0] micrograms/L. The assay can be used for rapid plasma or serum FABP measurement in the early diagnosis of acute myocardial infarction.

Biochemical markers of myocardial injury during cardiac operations

The evaluation of myocardial damage in relation to cardiac operation from a clinical and a research perspective is of great importance, particularly for the evaluation of different cardioprotective strategies. Although measurements of serum biochemical markers have often been used, their value has been limited by their lack of sensitivity and specificity in the presence of skeletal muscle damage. A newer range of markers are now available that may reliably indicate both perioperative myocardial infarction, as well as more subtle degrees of subclinical myocyte injury. In this review, the application of biochemical markers for clinical and research purposes during cardiac operation is considered.

Progress in myocardial damage detection: new biochemical markers for clinicians

New clinical requirements for triaging chest pain patients challenge the abilities of the current cardiac markers. Serial measurements of myoglobin, creatine kinase (CK) isoenzyme MB (CKMB) mass, or CK isoforms in emergency rooms help to rapidly rule out acute myocardial infarction (AMI). However, within the first 3 to 4 h from chest pain onset, their sensitivities are too low to contribute significantly to AMI diagnosis during this period. CKMB and lactate dehydrogenase (LDH) isoenzyme 1 are not heart-specific, which hampers reliable diagnosis in patients with concomitant skeletal muscle damage. By contrast, the regulatory proteins troponin I and troponin T are expressed in three different isoforms: one for slow-twitch skeletal muscle fibers, one for fast-twitch skeletal muscle fibers, and one for cardiac muscle (cTnI, cTnT); cardiac-specific cTnI and cTnT assays are already available for routine use. cTnT and cTnI are the most promising markers for risk stratification in patients with unstable angina pectoris. Recent reports on increased cTnT in patients with renal failure or myopathy without evidence of myocardial injury and undetectable cTnI suggest that cTnT could be reexpressed similar to CKMB and LDH-1 in chronically damaged human skeletal muscle. Therefore, cTnI is probably the most heart-specific marker. Among the recently proposed new markers for early AMI diagnosis: glycogen phosphorylase isoenzyme BB (GPBB), fatty acid binding protein, phosphoglyceric acid mutase isoenzyme MB, enolase isoenzyme alpha beta, S100a0, and annexin V, GPBB is the most promising because it increases as early as 1 to 4 h from chest pain onset and its early release appears to be essentially dependent on ischemic myocardial injury.

One-step purification of rat heart-type fatty acid-binding protein expressed in Escherichia coli

Heart-type fatty acid-binding protein (H-FABP) is a member of a family of 14-15 kDa lipid binding proteins which are believed to enhance intracellular transport of lipids by facilitating their cytoplasmic diffusion. To obtain sufficient amounts of protein for in vitro studies, we expressed rat H-FABP in Escherichia coli and compared its biochemical properties with the protein isolated from rat heart. An effective method was developed to purify recombinant rat H-FABP from cell lysates in a single step using anion-exchange chromatography. This method also proved to be applicable for purifying heterologously expressed human H-FABP. Recombinant rat H-FABP, which made up approximately 25% of the soluble proteins in E. coli, was obtained in a yield of 30-40 mg/l culture. Characterization showed that recombinant rat H-FABP was indistinguishable from the protein isolated from rat heart regarding molecular mass and oleic acid binding. Some heterogeneity upon isoelectric focusing was observed, presumably due to differences in N-terminal processing of the proteins. In conclusion, a method is presented for efficient high-yield production of recombinant rat H-FABP.

Discrimination between myocardial and skeletal muscle injury by assessment of the plasma ratio of myoglobin over fatty acid-binding protein

BACKGROUND

Myoglobin and fatty acid-binding protein (FABP) each are useful as early biochemical markers of muscle injury. We studied whether the ratio of myoglobin over FABP in plasma can be used to distinguish myocardial from skeletal muscle injury.

METHODS AND RESULTS

Myoglobin and FABP were assayed immunochemically in tissue samples of human heart and skeletal muscle and in serial plasma samples from 22 patients with acute myocardial infarction (AMI), from 9 patients undergoing aortic surgery (causing injury of skeletal muscles), and from 10 patients undergoing cardiac surgery. In human heart tissue, the myoglobin/FABP ratio was 4.5 and in skeletal muscles varied from 21 to 73. After AMI, the plasma concentrations of both proteins were elevated between approximately 1 and 15 to 20 hours after the onset of symptoms. In this period, the myoglobin/FABP ratio was constant both in subgroups of patients receiving and those not receiving thrombolytics and amounted to 5.3 +/- 1.2 (SD). In serum from aortic surgery patients, both proteins were elevated between 6 and 24 hours after surgery; the myoglobin/FABP ratio was 45 +/- 22 (SD), which is significantly different from plasma values in AMI patients (P < .001). In patients with cardiac surgery, the ratio increased from 11.3 +/- 4.7 to 32.1 +/- 13.6 (SD) during 24 hours after surgery, indicating more rapid release of protein from injured myocardium than from skeletal muscles.

CONCLUSIONS

The ratio of the concentrations of myoglobin over FABP in plasma from patients with muscle injury reflects the ratio found in the affected tissue. Since this ratio is different between heart (4.5) and skeletal muscle (20 to 70), its assessment in plasma allows the discrimination between myocardial and skeletal muscle injury in humans.