Heart Fatty Acid Binding Protein As A Marker For Postmortem Diagnosis Of Acute Myocardial Infarction

Acute myocardial infarction (AMI) is a common cause for sudden and unexpected death. However, it is difficult to detect the myocardial changes in medico-legal practice with traditional macroscopic examination or routine histological stains when the sudden death occurs in the hyper-acute phase of infarction (<3h). Although many markers and various methods have been introduced for postmortem detection or exclusion of AMI, up to date, there is neither a marker nor a method in routine medico-legal use can solve this problem satisfactorily.Heart-type fatty acid binding protein (H-FABP) is a low molecular weight protein (14~15kDa) with special tissue distribution, which is abundant in the cytoplasm of myocardial cells. It may play an important role in the uptake and oxygenation of long-chain fatty acids in cardiac myocyte. As myocardial cell membrane damaged by ischemia, H-FABP leaks to the extracellular space and enters the blood circulation very easily and quickly due to its small size and water soluble. It has been demonstrated that H-FABP is more sensitive and specific than myoglobin (Mb) for clinical detection of AMI within 12 hours after the onset of symptoms by quantifying its plasma concentration, because its molecule is smaller than that of Mb (18kDa) and it presents mainly in cardiomyocyte. So it is proposed as an early indicator of AMI by World Health Organization recently.1. Immuniohistochemical study on H-FABP as a marker for postmortem diagnosis ofAMI1.1 Animal model of AMIAnimal model of AMI was produced by ligating its left anterior descending coronary artery (LAD). Briefly, 54 Wistar rats weighting 250-350g of either sex, were randomly distributed into 6 study groups and three control groups. They were anesthetized with 10% chloral hydrate and artificially ventilated with animal ventilator. After opening the skin andthe left 4th intercostal space, LAD was ligated at its proximal. Successful ligation was confirmed by visual inspection for pallor of the involved myocardium and ST segment elevation >0.1mv on electrocardiogram (ECG). Sham-operated control group rats underwent the same surgical protocol as the study group except LAD ligation. The study group rats were killed at 15min, 30min, Ih, 2h, 4h, 8h after ligation and the control rats killed at Ih after operation. Then all hearts were dissected and fixed in 10% formalin in PBS over 24h. The tissue blocks were taken transversely through the center of the infarcted area and embedded in paraffin according to routine histological procedures. 1.2 Immunohistochemical staining for H-FABP and MbThe streptavidin-peroxidase conjugated method (S-P) was used for immunohistochemical staining of H-FABP and Mb. In normal control group, cytoplasm of all cardiomyocytes were stained homogeneous brown (positive for H-FABP and Mb), after counterstaining with hematoxylin, the nuclei stained light blue. No positive expression of H-FABP or Mb was found in interstitial tissue or other cell component. In study groups, the depletion of H-FABP from cardiomyocytes in infarcted areas at varying post-infarction intervals exhibited a nearly identical pattern with that of Mb as described before. Briefly, partial depletion occurred in a few disseminated cells in the subendocardial layer and papillary muscles in 15min group. In 30min group, diminished or absent immunostaining cells appeared, but still located in subendocardial layer and papillary muscles. Patchy depletion happened in Ih group and extended to the middle myocardium in 2h group. By 4h after ligation, completely depletion involving almost all myocardium which was distinct from normal cell started and then the depletion area increased with the prolongation of infarcted time.The comparison and statistical analysis between the depletion areas of H-FABP and Mb in various ischemic time group show: the depletion area of both H-FABP and Mb in every study group is significant different from that in their relative control group; there is no significant difference between the depletion area of H-FABP and Mb in 15min,...