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

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.

Displacement immunoassay for the detection of ochratoxin A using ochratoxin B modified glass beads

We report here the development of a new assay for the detection of ochratoxin A (OTA) based on the use of its dechlorinated analogue, ochratoxin B (OTB), in a displacement immunoassay. OTB was immobilised on controlled-pore glass beads followed by the binding of anti-OTA antibody, with anti-IgG antibody peroxidase conjugate used as a label. In this manner, an original bio-sensing material was obtained. Upon incubation of this material with OTA, the toxin competes with OTB for the binding sites of the anti-OTA antibodies and releases the antibody-tagged peroxidase complex into the solution. Compared to classic competitive immunoassays, this newly developed displacement immunoassay presents a similar detection limit and assay time. Moreover, the detection, based on the activity of the horseradish peroxidase, is performed for the first time in situ using wine samples.

Diagnostic accuracy of a bedside qualitative immunochromatographic test for acute myocardial infarction

OBJECTIVE

To evaluate the diagnostic efficacy of a bedside immunochromatographic test (CardioDetect) that identifies human heart-type fatty acid-binding protein in whole blood.

METHODS

Sixty-four patients with chest pain had CardioDetect test performed together with serial determination of serum troponin I (TnI) and creatine kinase (CK). CardioDetect results were interpreted twice, 24 hours apart, by 3 independent observers who were blinded to patients' clinical and laboratory data. Acute myocardial infarction was diagnosed by a physician blinded to the results of the CardioDetect test. Sensitivity, specificity, positive and negative predictive values, diagnostic accuracy, and receiver operating characteristic curves were determined for all tests at 4 predefined times. Intraobserver and interobserver reliabilities were determined.

RESULTS

At less than 4 hours after chest pain, CardioDetect had a sensitivity and specificity of 62.5% and 100% compared with 50% and 80% for TnI and 37.5% and 80% for CK, respectively. At more than 4 hours but 12 hours or less in duration, the sensitivity of CardioDetect and TnI was 100%, whereas that of CK was 85.7%. Intraobserver agreement and interobserver reliability were high for CardioDetect (kappa >0.80 [P < .0001] and intraclass correlation coefficient, >0.90, respectively).

CONCLUSION

CardioDetect was a reliable point-of-care test for the early diagnosis (<12 hours) of acute myocardial infarction in the ED.

Unbound Free Fatty Acids and Heart-Type Fatty Acid–Binding Protein: Diagnostic Assays and Clinical Applications

Background: A biomarker that reliably detects myocardial ischemia in the absence of necrosis would be useful for initial identification of unstable angina patients and for differentiating patients with chest pain of an etiology other than coronary ischemia, and could provide clinical utility complementary to that of cardiac troponins, the established markers of necrosis. Unbound free fatty acids (FFAu) and their intracellular binding protein, heart-type fatty acid–binding protein (H-FABP), have been suggested to have clinical utility as indicators of cardiac ischemia and necrosis, respectively.

Methods: We examined results of clinical assessments of FFAu and H-FABP as biomarkers of cardiac ischemia and necrosis. Data published on FFAu and H-FABP over the past 30 years were used as the basis for this review.

Results: Although little clinical work has been done on FFAu since the initial reports, recent studies documented an association between increased serum FFAs and ventricular dysrhythmias and death in patients with acute myocardial infarction (AMI). Recent data suggest that serum FFAu concentrations increase well before markers of cardiac necrosis and are sensitive indicators of ischemia in AMI. H-FABP is abundant in cardiac muscle and is presumed to be involved in myocardial lipid homeostasis. Similar to myoglobin, plasma H-FABP increases within 3 h after AMI and returns to reference values within 12–24 h.

Conclusions: FFAu may have a potential role in identifying patients with cardiac ischemia. H-FABP is useful for detecting cardiac injury in acute coronary syndromes and predicting recurrent cardiac events in acute coronary syndromes and in congestive heart failure patients. Assays are available for both markers that could facilitate further clinical investigations to assess their possible roles as markers of cardiac ischemia and/or necrosis.

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.

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.