| Introduction:Myocardial infarction (myocardial infarction, MI) is necrosis of the myocardium as a result of severe ischaemia. MI is extremely common, accounting for 10-15% of all deaths and about 60% of sudden unexpected deaths. Therefore, as an important disease of the cardiovascular system, MI is a worldwide health risks and burdens.According to the interval, MI can be divided into acute myocardial infarction (acute myocardial infarction, AMI) and old myocardial infarction (old myocardial infarction, OMI). AMI is often manifested in the lytic necrosis of cadiocytes. Cadiocytes displays swelling, and myofibrils are widely dissolved, disappeared, or only the nuclear and the membrane left, the cadiocyte looks like an empty sheath. Finally, the nucleus is dismissed and the frame is disrupted. Due to the poor regeneration capacity, the most common repair is scar formation, which necrotic tissue completely replaced by collagen fibers, fibers arranged irregularly. Old scar is dense, and the collagen fibers can occur hyaline degeneration, or calcium calm, which are the main pathological changes of OMI. At the hispathological level, MI leads to acute inflammation, and necrotic tissue is gradually replaced by scar, the process continued for about 6-8 weeks.The processes of diseases are from normal tissues to small lesions, and then typical lesions. Not only the diagnosis of early stage of AMI by pathological change is difficult, but also the complex pathological changes of OMI and AMI increase the difficulty to distinguish effectively. In practice, both in macro-observation of macro-samples and microscopic observation of sections, due to the complicated pathologic changes, it is difficult to accurately identify and distinguish the histopathological minimal changes only relying on subjective experiences. Therefore it is useful to find a convenient, sensitive and reproducible method to fit for the needs of forensic pathology.Fourier transform infrared spectroscopy (FTIR) technology emerged in 80's of 20th century. It is an effective technology to determine the moleculer composition and structure. The advantages include simple analysis process, low noise, high light quantity, high precision of wave number, wide measuring range, low cost and nondestructive test. It is widely used in chemical, metallurgy, mining, petroleum, pharmaceuticals, forensic science and other areas. For the solid, liquid or gas samples, the purity of a single component and multi-component mixture of materials can be measured using by FTIR techniques. FTIR can be used for qualitative analysis and quantitative analysis of samples. In addition, the advantage of simple sample-preparation and no staining significantly reduces measurement time. Based on samples reservation and re-identify of the samples, non-destructive and repeatable characteristics made the FTIR particularly important.After absorbsorption of infrared light, the organic molecules will produce molecular vibration for transition. Due to the diversity of vibrational forms, vibrational directions and vibrational amplitudes of organic molecules, the transition displays variously. The different structures of the compounds showed absorption bands with different wavelength, which is IR. FTIR is the IR applied mathematic Fourier's transform. For polyatomic organical, the same type of chemical bond vibrations have similar frequencies, some vibration derive from the whold molecule, and some from the vibration of partial chemical bonds or functional groups. Based on characteristic absorption peak of infrared absorption generated by different modes of motion, FTIR determines the characteristics of chemical structure or molecular functional group.Cell is composed of cell membrane, cytoplasm and nucleus. Its main chemical compositions are protein, lipid, glycogen and nucleic acid. The contents, configurations and conformations of these components are different in different cells. In the course of many diseases, these components change, which could be shown by difference infrared spectra. The diagnosis of cancer, COPD, Alzheimer's disease and other diseases are studied by FTIR. Foreign scholars have differentiated the old myocardial infarction and acute myocardial infarction used MRI'in vivo, but no reports was seen on study of molecular characteristics of myocardial infarction by FTIR and mapping technology in national and international region.Our study breaked through the traditional thinking on molecular characteristics, detected the technology molecular characteristics of myocardial infarction applied by FTIR pioneeringly, eliminated the impact of the changes after death, and detected the relationship of protein, glycogen, nucleic acids and lipid changes of old myocardial infarction and acute myocardial infarction. The mapping technology allowed chemical images directly reflecting the distribution of major elements and changes, and established a-good correspondence with histopathologic changes, and extended the areas of "infrared pathology". The present study is the innovation with cross-application of chemical technology and forensic science.Objective:The present study focused on forensic identification of myocardial infarction, and the distinction of acute myocardial infarction and old myocardial infarction. The present study detected the molecular characteristics of old myocardial infarction and acute myocardial infarction by FTIR and mapping technology. The aim was to find the changes of protein, lipid, glycogen and nucleic acid changes and the relationships reflected by infrared spectra, and explore its relationship with the corresponding of histopathology changes and the chemical images.Material and Method:Meterial and machines:The heart samples of old myocardial infarction and acute myocardial infarction of autospy cases in our departmet from 1999 to 2008.Nicolet 6700 FTIR, Thermo Fisher Scientific, USA;Nicolet continuum microscope, Thermo Fisher Scientific, USA;Nicolet iN10 FTIR, Thermo Fisher Scientific, USA;OMNIC workstation 8.0, Thermo Fisher Scientific, USA;Dotslide virtural micro-imaging systerm 2.1, Olympus, Japan;Spin-drier, AP-280X, Microm, Germany;Embedding machine, STP-120, Microm, Germany;Microtome, HM-340E, Microm, Germany;Expanding machine, ZPJ-1, tianli aviation machinery electrical company, China;Toasting machine, KPJ-1, tianli aviation machinery electrical company, China.Methods:Detection by FTIR and micro-spectroscopy methodSamples were conventionally made wax block, and cross-section of 6μm. One section was mounted on a glass slide, conventionally stained with H&E. The section was scanned by Dotslide the virtual imaging system at resolutions of 40, and identified as the control group and experimental group according to pathological changes of myocardial infarction lesion. Another section was mounted on a special infrared reflective slide, only routinely done with deparaffinageing and dehydration, without any staining processing, and dried for FTIR.The research was applied by combined Nicolet 6700 FTIR, Nicolet continuum infrared microscope (objective×15, eyepiece×10) and OMNIC workstation 8.0. the present research was in reflection mode, and cooled by liquid nitrogen, at room temperature 24℃. The infrared range was 4000 cm-1 to 650 cm-1. The parameters were setted that covered area was 25μm×25μm, with the resolution of 4cm-1, scanning time of 32 times. The background of each sample was scanned first and the spectra were saved. According to the virtual imaging of HE stained section, the control group and experimental group were setted. Randomly chosen ten test points from each group, the collected infrared spectra were saved and processed by OMNIC 8.0 workstations. Automatic baseline correction and auto-smoothing were performed by OMNIC software. Wave number and peak intensity of the protein, carbohydrate and lipid and nucleic acid bands'and the peak height ratio of some characteristic bands were analysed. The molecular characteristics were used to interpret the instinct of old myocardial infarction and acute myocardial infarction, and to establish the corresponding relations of histopathology and infrared spectra.Detection by FTIR and mapping techologyThe sections were treated the same as the research above-mentioned. The research was performed by combined Nicolet iN10 FTIR, Nicolet continuum micro-spectroscopy and OMNIC workstation 8.0. The parameters were setted that covered area was 100μm×100μm, with the resolution of 16cm-1, scanning time of 1 time. Other parameters were the same as the research mentioned above. The chemical image was collected for the whole section. The chemical image was treated with auto-baseline correction and auto-smothing to establish the corresponding relations of histopathology and the chemical image.Stastatical analysis and image processingThe data were statistically by SPSS 13.0 for one-way AVON analysis, with the mean±standard deviation, the P<0.05 was considered as statistical significance.Result:In old myocardial infarction region, all the amide bands displayed the same trend, what were the wave number diaplayed blue shift and the intensity increasing. The antisymmetry and symmetry of CH3 and CH2 displayed intensity increasing. The antisymmetry of PO2 displayed blue shift and the intensity decreasing, but the symmetry of the bond had no wave number shift. The C-O bond of glycogen displayed intensity decreasing. The ratio of I1652/I1634,I1650/I1550 showed heighten, the ratio of I1550/I3300,I1160/I1080 showed the opposite, and the ratio of I2920/I2960 showed no difference.In acute myocardial infarction region, all the amide bands displayed the same trend, what were the wave number diaplayed intensity decreasing. Except the antisymmetry CH3 bond displayed red shift, all the other stretching vibration of CH3 and CH2 displayed no shift and intensity decreasing. The symmetry of PO2 displayed red shift and the intensity decreasing, but the antisymmetry of the bond had no wave number shift. The C-O bond of glycogen displayed intensity decreasing. The ratio of I1652/I1634showed lower, the ratio of I1650/I1550 showed the opposite, and the ratio of I1550/I3300,I1160/I1080,I2920/I2960 showed no difference.Conclusion:The molecular characteristics of old myocardial infarction and acute myocardial infarction were revealed by FTIR and mapping technology. The old myocardial infarction and acute myocardial infarction were distinguished according to infrared pathology. It intuitively and sensitively established the corresponding relationship of histopathology and Chemical images. Combined with infrared spectroscopy, the chemical image could initially distinguish the pathological changes of old myocardial infarction and acute myocardial infarction.
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