Pathophysiology of sudden cardiac death as demonstrated by molecular pathology of natriuretic peptides in the myocardium

Postmortem biochemistry in deaths from ischemic heart disease

Ischemic heart disease (IHD) is one of the leading causes of morbidity and sudden cardiac death worldwide and is an important public health problem. The presence of ischemia in clinical applications can be detected by ECG, biochemical markers, and radiological methods. Myocardial infarction is also frequently encountered in forensic autopsies. Postmortem diagnosis is determined as a result of histopathological examinations and additional exclusionary examinations (toxicology, microbiology, etc.). However, routine histopathological examinations are insufficient, especially when death occurs in the early period of ischemia. It creates a problem for forensic pathologists and forensic medicine specialists in such cases of sudden cardiac death. Postmortem biochemistry is one of the important and promising disciplines in which forensic applications work in order to diagnose these cases correctly. The issue of whether biomarkers used in the diagnosis of myocardial infarction in clinical studies can be used reliably in postmortem cases has been discussed by forensic medicine researchers for some time. This manuscript aims to review and summarize biomarkers belonging to various categories that have been studied in IHD-related deaths, in biological fluids taken at autopsy, or in animal experiments. Our study shows that the postmortem use of biochemical markers in the diagnosis of IHD yields promising results. However, it should not be forgotten that postmortem biochemistry is different from clinical applications due to its dynamics and that the body causes unpredictable changes in markers in the postmortem process. Therefore, comprehensive studies are needed to evaluate the postmortem stability of these markers in different biological fluids, their significance among various causes of death, and whether they are affected by any variable (Cardiopulmonary resuscitation, Postmortem interval, medications, etc.) before they are routinely applied. It is suggested by the authors that the cut-off values of biomarkers whose significance has been proven by these studies should be determined and that they should be used in this way in routine applications.

Distinguishing Asphyxia from Sudden Cardiac Death as the Cause of Death from the Lung Tissues of Rats and Humans Using Fourier Transform Infrared Spectroscopy

The ability to determine asphyxia as a cause of death is important in forensic practice and helps us to judge whether a case is criminal. However, in some cases where the deceased has underlying heart disease, death by asphyxia cannot be determined by traditional autopsy and morphological observation under a microscope because there are no specific morphological features for either asphyxia or sudden cardiac death (SCD). Here, Fourier transform infrared (FTIR) spectroscopy was employed to distinguish asphyxia from SCD. A total of 40 lung tissues (collected at 0 h and 24 h postmortem) from 20 rats (10 died from asphyxia and 10 died from SCD) and 16 human lung tissues from 16 real cases were used for spectral data acquisition. After data preprocessing, 2675 spectra from rat lung tissues and 1526 spectra from human lung tissues were obtained for subsequent analysis. First, we found that there were biochemical differences in the rat lung tissues between the two causes of death by principal component analysis and partial least-squares discriminant analysis (PLS-DA), which were related to alterations in lipids, proteins, and nucleic acids. In addition, a PLS-DA classification model can be built to distinguish asphyxia from SCD. Second, based on the spectral data obtained from lung tissues allowed to decompose for 24 h, we could still distinguish asphyxia from SCD even when decomposition occurred in animal models. Nine important spectral features that contributed to the discrimination in the animal experiment were selected and further analyzed. Third, 7 of the 9 differential spectral features were also found to be significantly different in human lung tissues from 16 real cases. A support vector machine model was finally built by using the seven variables to distinguish asphyxia from SCD in the human samples. Compared with the linear PLS-DA model, its accuracy was significantly improved to 0.798, and the correct rate of determining the cause of death was 100%. This study shows the application potential of FTIR spectroscopy for exploring the subtle biochemical differences resulting from different death processes and determining the cause of death even after decomposition.

Natriuretic peptides: new challenges — new solutions

Natriuretic peptides (NPs) are one of the most significant biomarkers, the practical use of which increases, and their diagnostic and prognostic value in patients with various chronic noncommunicable diseases is beyond doubt. Since the discovery of these markers, research has been actively carried out to study the biological and pathophysiological roles of NPs in a wide range of diseases, including hypertension and heart failure (HF). These studies showed that A-type and B-type NPs are hormones secreted by the heart in response to pre- or afterload, which prevent high blood pressure and fluid retention. In addition, C-type NPs are produced by the vascular endothelium and act as a local a  mediator with angioprotective properties. Since the NP system is a natural antagonist of the sympathoadrenal and renin-angiotensinaldosterone systems, it is interesting to study novel strategies to use new drug classes for hypertension. These drugs are neprilysin inhibitors, which destroys NPs; their action is to enhance the synthesis of endogenous peptides. Dual angiotensin receptor and neprilysin inhibition is widespread in clinical practice in patients with heart failure with reduced ejection fraction. Neprilysin inhibition has also been shown to be an effective strategy for hypertensive patients. The article discusses the role and value of NP system in  the dia - gnosis of heart failure and blood pressure regulation, and also considers new promising directions for neprilysin inhibition and activation of endogenous NP synthesis.

 

Endoplasmic reticulum stress-related secretory proteins as biomarkers of early myocardial ischemia-induced sudden cardiac deaths

Early myocardial ischemia-induced sudden cardiac deaths (EMI-SCD) remain a great diagnostic challenge for forensic pathologists due to no gross or non-specific histological pathology. The goal of this study was to assess whether three secretory proteins, related with cellular endoplasmic reticulum stress, can be applied in forensic diagnosis of EMI-SCD. These markers included LMAN2, CAPN-1, and VCP and were compared with two clinically used markers (CK-MB and cTnI). A total of 21 EMI-SCD cases with a mean age of 53.0 (± 10.5) years and a mean ischemia interval of < 2.77 (± 2.56) hours were collected. Another 23 cases (mean 44.6 ± 15.0 year old) that died from non-cardiac causes served as control. Enzyme-linked immunosorbent assay (ELISA) was performed to detect target proteins' serum concentrations in the EMI-SCD and control groups. We found that LMAN2, CAPN-1, and VCP were all significantly increased in the EMI-SCD group as compared with control serum, with the fold changes ranging from 1.48 (p = 0.0022, LMAN2), 1.33 (p = 0.041, CAPN-1), to 1.26 (p = 0.021, VCP), respectively. The concentrations of these proteins remained highly stable within 6 h and were not affected by death time, postmortem interval (< 4 h), age, and month at death. Receiver operating characteristic (ROC) curves showed that the areas under the curve (AUC) were 0.8178 (LMAN2), 0.6988 (CAPN-1), and 0.7267 (VCP), all of which were higher than CK-MB (AUC 0.5590) and cTn-I (AUC 0.5911). The diagnostic specificity (all above 60%) was obviously higher than CK-MB (43.48%) and cTnI (34.78%). In conclusion, LMAN-2, CAPN-1, and VCP could be stable serological biomarkers for diagnosis of EMI-SCD cases.

Cardioprotective effects of corilagin on doxorubicin induced cardiotoxicity via P13K/Akt and NF-κB signaling pathways in rats model

Even though doxorubicin (DOX) is a potential chemotherapeutic drug, its usage is restricted due to its ability to induce cardiac damage. In order to prevent this damage, a potent cardioprotective agent should be associated with DOX treatment. Corilagin is a natural polyphenol tannic acid which unveils enormous pharmacological activities predominantly as an antitumor agent. Hence, the current work is designed to study the precise mechanisms of corilagin upon administration in doxorubicin induced cardiotoxicity in experimental rats. DOX treated rats showed diminished level of blood pressures and heart rate, whereas corilagin along with DOX treatment improved the status. Cardiotoxicity enzymes and biomarkers were found to be increased in the serum of DOX induced rats. Upon treatment, corilagin could reduce the cardiotoxicity enzymes and biomarkers in serum. Histopathological examination of cardiac tissue also revealed the anti-toxic effects of corilagin in contrast to DOX. Injection of DOX in rats showed inflammatory cells infiltration, necrosis and fragmented myofibrils. Corilagin treatment reverted the cardiac histology to near normal. Inflammatory mediators and P13K, Akt, and NF-κB were upregulated in DOX administered rats. Corilagin repressed the levels of P13K, Akt, and NF-κB in DOX induced rats. In the present investigations, corilagin improved cardiac function via reducing injury, inflammation and promoting apoptosis thereby suggesting that corilagin would be recommended for DOX-induced cardiotoxicity.

The Expression of BNP, ET-1, and TGF-β1 in Myocardium of Rats with Ventricular Arrhythmias

Ventricular arrhythmia (VA) is a major component of sudden cardiac death (SCD). To investigate the expression of brain natriuretic peptide (BNP), endothelin-1 (ET-1), and transforming growth factor-beta 1 (TGF-β1) during VA, we established a rat model of VA induced by BaCl₂ solution through a microinjector pump. PD142893 (ET-1 receptor blocker) and SB431542 (TGF-β1 receptor type I blocker) were used to explore the effect of ET-1 and TGF-β1 on BNP expression in the myocardium after VA. BNP, ET-1, and TGF-β1 in rat myocardium were assayed by western blot and immunohistochemical staining for proteins, and real-time quantitative polymerase chain reaction for mRNAs. We found increased expression of BNP and ET-1 in rat myocardium that was associated with the duration of VA. However, TGF-β1 protein expression remained unchanged. Such early increases in BNP and ET-1 may be attributed to fatal arrhythmias associated with SCD, suggesting these may be novel biomarkers of this disease. After intraperitoneal injection of PD142893 and SB431542, respectively, BNP was downregulated in the myocardium of the left ventricle; however, this was abrogated by co-application of the two inhibitors. These results suggested that both ET-1 and TGF-β1, by specifically binding to their receptors, might be involved in the myocardial synthesis of BNP during VA in vivo.

BNP and NT-proBNP as Diagnostic Biomarkers for Cardiac Dysfunction in Both Clinical and Forensic Medicine

Currently, brain natriuretic peptide (BNP) and N-terminal proBNP (NT-proBNP) are widely used as diagnostic biomarkers for heart failure (HF) and cardiac dysfunction in clinical medicine. They are also used as postmortem biomarkers reflecting cardiac function of the deceased before death in forensic medicine. Several previous studies have reviewed BNP and NT-proBNP in clinical medicine, however, few articles have reviewed their application in forensic medicine. The present article reviews the biological features, the research and application status, and the future research prospects of BNP and NT-proBNP in both clinical medicine and forensic medicine, thereby providing valuable assistance for clinicians and forensic pathologists.

Identification of Pulmonary Edema in Forensic Autopsy Cases of Sudden Cardiac Death Using Fourier Transform Infrared Microspectroscopy: A Pilot Study

Many studies have proven the usefulness of biofluid-based infrared spectroscopy in the clinical domain for diagnosis and monitoring the progression of diseases. Here we present a state-of-the-art study in the forensic field that employed Fourier transform infrared microspectroscopy for postmortem diagnosis of sudden cardiac death (SCD) by in situ biochemical investigation of alveolar edema fluid in lung tissue sections. The results of amide-related spectral absorbance analysis demonstrated that the pulmonary edema fluid of the SCD group was richer in protein components than that of the neurologic catastrophe (NC) and lethal multiple injuries (LMI) groups. The complementary results of unsupervised principle component analysis (PCA) and genetic algorithm-guided partial least-squares discriminant analysis (GA-PLS-DA) further indicated different global spectral band patterns of pulmonary edema fluids between these three groups. Ultimately, a random forest (RF) classification model for postmortem diagnosis of SCD was built and achieved good sensitivity and specificity scores of 97.3% and 95.5%, respectively. Classification predictions of unknown pulmonary edema fluid collected from 16 cases were also performed by the model, resulting in 100% correct discrimination. This pilot study demonstrates that FTIR microspectroscopy in combination with chemometrics has the potential to be an effective aid for postmortem diagnosis of SCD.

Differential expression of B-type natriuretic peptide between left and right ventricles, with particular regard to sudden cardiac death

The aim of the present study was to investigate the differential expression of B-type natriuretic peptide (BNP) between the left and right ventricle (RV) in sudden cardiac death (SCD). A total of 26 forensic autopsy cases of sudden death (survival time <30 min, postmortem interval <48 h or frozen within 6 h following death) in the present institute were examined. The cases consisted of acute ischemic heart disease (AIHD, n=15) with/without apparent myocardial necrosis as a sign of infarction (acute myocardial infarction, n=6; ischemic heart disease, IHD, n=9), and arrhythmogenic right ventricular cardiomyopathy (ARVC/D, n=5), in addition to traffic accidents and high falls without any pre existing heart disease as control (C, total n=6). BNP was investigated in all cases by the colloidal gold method, hematoxylin-eosin staining, immunohistochemistry (IHC) and the molecular pathological method. The IHC results demonstrated that a positive BNP immunostaining was detected in all groups; however, there was no difference between different causes of death. Pericardial N-terminal (NT)-proBNP concentration was significantly increased in deaths resulting from AIHD and ARVC/D compared with control group. The relative quantification of BNP mRNA demonstrated that relative expression levels of BNP mRNA were significantly increased in the left ventricle (LV) in the AIHD group, and in the RV of the ARVC/D group. The relative quantification difference and ratio of BNP mRNA between LV and RV demonstrated a significantly greater value in the AIHD group compared with control group. BNP mRNA in myocardium and NT-proBNP concentration in pericardial fluid were elevated in SCD patients, and left ventricular dysfunction predominated in AIHD patients, whereas right ventricular dysfunction predominated in ARVC/D patients. The results of the present study suggest the possible use of molecular pathology of BNP for the determination of terminal cardiac function in SCD and analysis of its fatal mechanism in forensic practice.

The Expression of B-Type Natriuretic Peptide After CaCl2-Induced Arrhythmias in Rats

To investigate the patterns of B-type natriuretic peptide (BNP) expression after arrhythmia, BNP was assessed at different time points (0 minute, 10 minutes, 30 minutes, 1 hour, 3 hours, and 6 hours) in CaCl2-induced arrhythmia in rats through various methods such as immunohistochemistry, Western blotting, quantitative real-time polymerase chain reaction, and enzyme-linked immunosorbent assay. Immunohistochemistry results showed that the expression of BNP in the endocardium was higher than that in the epicardium in rats undergoing sustained arrhythmias. The BNP-to-GAPDH (glyceraldehyde-3-phosphate dehydrogenase) ratios determined by Western blotting analysis revealed no change at 0 minute but increased at 10 minutes and reached the first peak (0.48 [0.03]) at 30 minutes. After a brief decline, the second peak was observed at 6 hours (0.54 [0.03]). Similar patterns of BNP messenger RNA expression were also observed by quantitative real-time polymerase chain reaction. The plasma BNP concentrations did not change after initial bouts of cardiac arrhythmias but significantly increased 30 minutes after CaCl2 injections. The results demonstrate that arrhythmia causes an elevation of BNP in the myocardium and blood, and BNP messenger RNA increases in initial arrhythmia while its protein in myocardium and plasma does not; however, both of them were elevated after sustained arrhythmia. Such an elevated BNP expression, which is directly related to the severity and duration of the arrhythmias, may suggest the existence of fatal arrhythmia in sudden cardiac death.

Decreased mRNA levels of cardiac Cx43 and ZO1 in sudden cardiac death related to coronary atherosclerosis: a pilot study

Sudden cardiac death (SCD) is the most frequent cause of sudden unexplained death in forensic practice. The most common cause of SCD is coronary artery disease related to coronary atherosclerosis. Previous study suggested the possible application of connexin 43 (Cx43) and zonula occludens-1 (ZO1) immunostaining in the early diagnosis of myocardial ischemia. However, there appears to be insufficient data with regard to their mRNA levels. The present study investigated the cardiac mRNA levels of Cx43 and ZO1, using forensic autopsy materials consisting of 41 control cases without any disease or structural abnormality of the heart (group 1), 32 deaths due to acute ischemic heart disease related to coronary atherosclerosis without apparent myocardial necrosis (group 2), and 29 traumatic deaths with coronary atherosclerosis (group 3). Ten candidate reference genes were evaluated in the left ventricles of 10 forensic autopsy cases. EEF1A1, PPIA, TPT1, and RPL13A were identified as the most stable reference genes. Using these validated reference genes, mRNA levels of Cx43 and ZO1 were examined in the bilateral ventricles and atria of the heart. Relative mRNA quantification demonstrated decreased calibrated normalized relative quantity (CNRQ) values of Cx43 and ZO1 in bilateral ventricles of group 2. When using one conventional reference gene (GAPDH or ACTB) for normalization, nearly no difference was detected among the three groups. These findings indicate that ventricular gap junction remodeling may be a key contributor to rhythm disturbances. Analysis of cardiac Cx43 and ZO1 using real-time PCR is useful in diagnosis of SCD, and validation of reference genes is crucial.

Postmortem mRNA expression patterns in left ventricular myocardial tissues and their implications for forensic diagnosis of sudden cardiac death

Sudden cardiac death (SCD), which is primarily caused by lethal heart disorders resulting in structural and arrhythmogenic abnormalities, is one of the prevalent modes of death in most developed countries. Myocardial ischemia, mainly due to coronary artery disease, is the most common type of heart disease leading to SCD. However, postmortem diagnosis of SCD is frequently complicated by obscure histological evidence. Here, we show that certain mRNA species, namely those encoding hemoglobin A1/2 and B (Hba1/2 and Hbb, respectively) as well as pyruvate dehydrogenase kinase 4 (Pdk4), exhibit distinct postmortem expression patterns in the left ventricular free wall of SCD subjects when compared with their expression patterns in the corresponding tissues from control subjects with non-cardiac causes of death. Hba1/2 and Hbb mRNA expression levels were higher in ischemic SCD cases with acute myocardial infarction or ischemic heart disease without recent infarction, and even in cardiac death subjects without apparent pathological signs of heart injuries, than control subjects. By contrast, Pdk4 mRNA was expressed at lower levels in SCD subjects. In conclusion, we found that altered myocardial Hba1/2, Hbb, and Pdk4 mRNA expression patterns can be employed as molecular signatures of fatal cardiac dysfunction to forensically implicate SCD as the primary cause of death.

Forensic molecular pathology: its impacts on routine work, education and training

The major role of forensic pathology is the investigation of human death in relevance to social risk management to determine the cause and process of death, especially in violent and unexpected sudden deaths, which involve social and medicolegal issues of ultimate, personal and public concerns. In addition to the identification of victims and biological materials, forensic molecular pathology contributes to general explanation of the human death process and assessment of individual death on the basis of biological molecular evidence, visualizing dynamic functional changes involved in the dying process that cannot be detected by morphology (pathophysiological or molecular biological vital reactions); the genetic background (genomics), dynamics of gene expression (up-/down-regulation: transcriptomics) and vital phenomena, involving activated biological mediators and degenerative products (proteomics) as well as metabolic deterioration (metabolomics), are detected by DNA analysis, relative quantification of mRNA transcripts using real-time reverse transcription-PCR (RT-PCR), and immunohisto-/immunocytochemistry combined with biochemistry, respectively. Thus, forensic molecular pathology involves the application of omic medical sciences to investigate the genetic basis, and cause and process of death at the biological molecular level in the context of forensic pathology, that is, 'advanced molecular autopsy'. These procedures can be incorporated into routine death investigations as well as guidance, education and training programs in forensic pathology for 'dynamic assessment of the cause and process of death' on the basis of autopsy and laboratory data. Postmortem human data can also contribute to understanding patients' critical conditions in clinical management.