Molecular Imaging of Diffuse Cardiac Fibrosis with a Radiotracer That Targets Proteolyzed Collagen IV.

Purpose To develop an approach for in vivo detection of interstitial cardiac fibrosis using PET with a peptide tracer targeting proteolyzed collagen IV (T-peptide). Materials and Methods T-peptide was conjugated to the copper chelator MeCOSar (chemical name, 5-(8-methyl-3,6,10,13,16,19-hexaaza-bicyclo[6.6.6]icosan-1-ylamino)-5-oxopentanoic acid) and radiolabeled with copper 64 (64Cu). PET/CT scans were acquired following intravenous delivery of 64Cu-T-peptide-MeCOSar (0.25 mg/kg; 18 MBq ± 2.7 [SD]) to male transgenic mice overexpressing ß2-adrenergic receptors with intermediate (7 months of age; n = 4 per group) to severe (10 months of age; n = 11 per group) cardiac fibrosis and their wild-type controls. PET scans were also performed following coadministration of the radiolabeled probe with nonlabeled T-peptide in excess to confirm binding specificity. PET data were analyzed by t tests for static scans and analysis of variance tests (one- or two-way) for dynamic scans. Results PET/CT scans revealed significantly elevated (2.24-4.26-fold; P < .05) 64Cu-T-peptide-MeCOSar binding in the fibrotic hearts of aged transgenic ß2-adrenergic receptor mice across the entire 45-minute acquisition period compared with healthy controls. The cardiac tracer accumulation and presence of diffuse cardiac fibrosis in older animals were confirmed by gamma counting (P < .05) and histologic evaluation, respectively. Coadministration of a nonradiolabeled probe in excess abolished the elevated radiotracer binding in the aged transgenic hearts. Importantly, PET tracer accumulation was also detected in younger (7 months of age) transgenic mice with intermediate cardiac fibrosis, although this was only apparent from 20 minutes following injection (1.6-2.2-fold binding increase; P < .05). Conclusion The T-peptide PET tracer targeting proteolyzed collagen IV provided a sensitive and specific approach of detecting diffuse cardiac fibrosis at varying degrees of severity in a transgenic mouse model. Keywords: Diffuse Cardiac Fibrosis, Molecular Peptide Probe, Molecular Imaging, PET/CT © RSNA, 2024.

PI3K(p110α) as a determinant and gene therapy for atrial enlargement in atrial fibrillation.

Atrial fibrillation (AF) is an irregular heart rhythm, characterised by chaotic atrial activation, which is promoted by remodelling. Once initiated, AF can also propagate the progression of itself in the so-called ''AF begets AF''. Several lines of investigation have shown that signalling molecules, including reactive oxygen species, angiotensin II, and phosphoinositide 3-kinases (PI3Ks), in presence or absence of cardiovascular disease risk factors, stabilise and promote AF maintenance. In particular, reduced cardiac-specific PI3K activity that is not associated with oncology is cardiotoxic and increases susceptibility to AF. Atrial-specific PI3K(p110α) transgene can cause pathological atrial enlargement. Highlighting the crucial importance of the p110α protein in a clinical problem that currently challenges the professional health care practice, in over forty (40) transgenic mouse models of AF (Table1), currently existing, of which some of the models are models of human genetic disorders, including PI3K(p110α) transgenic mouse model, over 70% of them reporting atrial size showed enlarged, greater atrial size. Individuals with minimal to severely dilated atria develop AF more likely. Left atrial diameter and volume stratification are an assessment for follow-up surveillance to detect AF. Gene therapy to reduce atrial size will be associated with a reduction in AF burden. In this overview, PI3K(p110α), a master regulator of organ size, was investigated in atrial enlargement and in physiological determinants that promote AF.

PI3K signalling at the intersection of cardio-oncology networks: cardiac safety in the era of AI.

Class I phosphoinositide 3-kinases (PI3Ks) are a family of lipid kinases. They are super elevated in many human cancer types and exert their main cellular functions by activating Akt to trigger an array of distinct responses, affecting metabolism and cell polarity. The signal equally plays important roles in cardiovascular pathophysiology. PI3K is required for cardiogenesis and regulation of cardiac structure and function. Overexpression of PI3K governs the development of cardiac pressure overload adaptation and compensatory hypertrophy. Therefore, inhibition of PI3K shortens life span, enhances cardiac dysfunction and pathological hypertrophy. The inverse inhibition effect, however, desirably destroys many cancer cells by blocking several aspects of the tumorigenesis phenotype. Given the contrasting effects in cardio-oncology; the best therapeutic strategy to target PI3K in cancer, while maintaining or rather increasing cardiac safety is under intense investigational scrutiny. To improve our molecular understanding towards identifying cardiac safety signalling of PI3K and/or better therapeutic strategy for cancer treatment, this article reviews PI3K signalling in cardio-oncology. PI3K signalling at the interface of metabolism, inflammation and immunity, and autonomic innervation networks were examined. Examples were then given of cardiovascular drugs that target the networks, being repurposed for cancer treatment. This was followed by an intersection scheme of the networks that can be functionalised with machine learning for safety and risk prediction, diagnoses, and defining new novel encouraging leads and targets for clinical translation. This will hopefully overcome the challenges of the one-signalling-one-health-outcome alliance, and expand our knowledge of the totality of PI3K signalling in cardio-oncology.

Assessment of the epi-pericardial fibrotic substrate by collagen-targeted probes.

The identification of the fibrotic arrhythmogenic substrate as a means of improving the diagnosis and prediction of atrial fibrillation has been a focus of research for many years. The relationship between the degree of atrial fibrosis as a major component of atrial cardiomyopathy and the recurrence of arrhythmia after AF ablation can correlate. While the focus in identification and characterisation of this substrate has been centred on the atrial wall and the evaluation of atrial scar and extracellular matrix (ECM) expansion by late gadolinium-enhancement (LGE) on cardiac magnetic resonance imaging (CMRI), LGE cannot visualise diffuse fibrosis and diffuse extravasation of gadolinium. The atrial pericardium is a fine avascular fibrous membranous sac that encloses the atrial wall, which can undergo remodelling leading to atrial disease and AF. Nevertheless, little attention has been given to the detection of its fibrocalcification, impact on arrhythmogenesis and, most importantly, on the potential prothrombotic role of epi-pericardial remodelling in generation of emboli. We have recently reported that tracers against collagen I and IV can provide a direct assessment of the ECM, and thus can estimate fibrotic burden with high sensitivity. Here, we show the ability of these optical tracers to identify epi-pericardial fibrosis, as well as to demonstrate subtle interstitial fibrosis of the atrial wall in a mouse model of beta-2-adrenergic receptor (ß2-AR) cardiac overexpression.

Molecular imaging of atrial myopathy: Towards early AF detection and non-invasive disease management.

Atrial fibrillation (AF) is a common arrhythmia that can lead to stroke. The diseased muscle tissue of the atria develops atrial fibrosis, inflammation, thrombosis and subsequent strokes, resulting in significant morbidity and mortality. Current diagnostic and evaluation paradigms for clinical AF focus on identifying functional and morphological abnormalities of the left atria by echocardiography. Notably, the development of atrial substrate that marks AF likely occurs for years before the manifestation of AF onset, meaning that the functional and morphometrical aberrations are end-stage features, representing a stable state of an already-compromised tissue. There is no existing 'gold standard' measure to identify the early atrial muscle disease and characterization of the atrial substrate is inadequate. In fact, sub-clinical identification of atrial myopathy is not undertaken in clinical practice because there is no robust screening method. Development of molecular imaging probes for detection of atrial muscle disease might enable early detection and staging of AF, ultimately leading to improved treatment outcome. In this review, we discuss possible molecular imaging targets that may enable early diagnosis of cardiovascular disease, with focus on novel insights, challenges and opportunities for sub-clinical imaging of atrial myopathy and AF.

Collagen-Targeted Peptides for Molecular Imaging of Diffuse Cardiac Fibrosis.

Background Cardiac fibrosis is the excessive deposition of extracellular matrix in the heart, triggered by a cardiac insult, aging, genetics, or environmental factors. Molecular imaging of the cardiac extracellular matrix with targeted probes could improve diagnosis and treatment of heart disease. However, although this technology has been used to demonstrate focal scarring arising from myocardial infarction, its capacity to demonstrate extracellular matrix expansion and diffuse cardiac fibrosis has not been assessed. Methods and Results Here, we report the use of collagen-targeted peptides labeled with near-infrared fluorophores for the detection of diffuse cardiac fibrosis in the ß2-AR (ß-2-adrenergic receptor) overexpressing mouse model and in ischemic human hearts. Two approaches were evaluated, the first based on a T peptide that binds matrix metalloproteinase-2-proteolyzed collagen IV, and the second on the cyclic peptide EP-3533, which targets collagen I. The systemic and cardiac uptakes of both peptides (intravenously administered) were quantified ex vivo by near-infrared imaging of whole organs, tissue sections, and heart lysates. The peptide accumulation profiles corresponded to an immunohistochemically-validated increase in collagen types I and IV in hearts of transgenic mice versus littermate controls. The T peptide could encouragingly demonstrate both the intermediate (7 months old) and severe (11 months old) cardiomyopathic phenotypes. Co-immunostainings of fluorescent peptides and collagens, as well as reduced collagen binding of a control peptide, confirmed the collagen specificity of the tracers. Qualitative analysis of heart samples from patients with ischemic cardiomyopathy compared with nondiseased donors supported the collagen-enhancement capabilities of these peptides also in the clinical settings. Conclusions Together, these observations demonstrate the feasibility and translation potential of molecular imaging with collagen-binding peptides for noninvasive imaging of diffuse cardiac fibrosis.

Pathophysiology and therapeutic relevance of PI3K(p110α) protein in atrial fibrillation: A non-interventional molecular therapy strategy.

Genetically modified animal studies have revealed specific expression patterns and unequivocal roles of class I PI3K isoenzymes. PI3K(p110α), a catalytic subunit of class I PI3Ks is ubiquitously expressed and is well characterised in the cardiovascular system. Given that genetic inhibition of PI3K(p110α) causes lethal phenotype embryonically, the catalytic subunit is critically important in housekeeping and biological processes. A growing number of studies underpin crucial roles of PI3K(p110α) in cell survival, proliferation, hypertrophy and arrhythmogenesis. While the studies provide great insights, the precise mechanisms involved in PI3K(p110α) hypofunction and atrial fibrillation (AF) are not fully known. AF is a well recognised clinical problem with significant management limitations. In this translational review, we attempted a narration of PI3K(p110α) hypofunction in the molecular basis of AF pathophysiology. We sought to cautiously highlight the relevance of this molecule in the therapeutic approaches for AF management per se (i.e without conditions associate with cell proliferation, like cancer), and in mitigating effects of clinical risk factors in atrial substrate formation leading to AF progression. We also considered PI3K(p110α) in AF gene association, with the aim of identifying mechanistic links between the ever increasingly well-defined genetic loci (regions and genes) and AF. Such mechanisms will aid in identifying new drug targets for arrhythmogenic substrate and AF.

Electrical and structural remodeling contribute to atrial fibrillation in type 2 diabetic db/db mice.

BACKGROUND: Atrial fibrillation (AF) is highly prevalent in diabetes mellitus (DM), yet the basis for this finding is poorly understood. Type 2 DM may be associated with unique patterns of atrial electrical and structural remodeling; however, this has not been investigated in detail. OBJECTIVE: The purpose of this study was to investigate AF susceptibility and atrial electrical and structural remodeling in type 2 diabetic db/db mice. METHODS: AF susceptibility and atrial function were assessed in male and female db/db mice and age-matched wildtype littermates. Electrophysiological studies were conducted in vivo using intracardiac electrophysiology and programmed stimulation. Atrial electrophysiology was also investigated in isolated atrial preparations using high-resolution optical mapping and in isolated atrial myocytes using patch-clamping. Molecular biology studies were performed using quantitative polymerase chain reaction and western blotting. Atrial fibrosis was assessed using histology. RESULTS: db/db mice were highly susceptible to AF in association with reduced atrial conduction velocity, action potential duration prolongation, and increased heterogeneity in repolarization in left and right atria. In db/db mice, atrial K+ currents, including the transient outward current (Ito) and the ultrarapid delayed rectifier current (IKur), were reduced. The reduction in Ito occurred in association with reductions in Kcnd2 mRNA expression and KV4.2 protein levels. The reduction in IKur was not related to gene or protein expression changes. Interstitial atrial fibrosis was increased in db/db mice. CONCLUSION: Our study demonstrates that increased susceptibility to AF in db/db mice occurs in association with impaired electrical conduction as well as electrical and structural remodeling of the atria.

Aberrant cardiac metabolism leads to cardiac arrhythmia.

Diabetes, obesity and increased body mass index are associated with changes in metabolism that lead to an inadequate reservoir or use of ATP in the heart and susceptibility to arrhythmia. Lack of availability of ATP and abnormal levels of metabolic end products can cause gene reprogramming and electrical remodelling that make myfibers susceptible to arrhythmia. Understanding the metabolic aberrations that lead to arrhythmia require better understanding of cardiac metabolism. Here, I discuss metabolic genes, enzymes and reducing equivalents and functional aspects of metabolic-induced arrhythmia with a special focus on atrial induced arrhythmia. It appears that normalisation of altered Kv1.5 channel, an oxygen sensing ion channel and fulfillment of oxygen demand by myocardium might offer a new strategy for preventing alterations of repolarisation that cause arrhythmia.

Loss of insulin signaling may contribute to atrial fibrillation and atrial electrical remodeling in type 1 diabetes.

Atrial fibrillation (AF) is prevalent in diabetes mellitus (DM); however, the basis for this is unknown. This study investigated AF susceptibility and atrial electrophysiology in type 1 diabetic Akita mice using in vivo intracardiac electrophysiology, high-resolution optical mapping in atrial preparations, and patch clamping in isolated atrial myocytes. qPCR and western blotting were used to assess ion channel expression. Akita mice were highly susceptible to AF in association with increased P-wave duration and slowed atrial conduction velocity. In a second model of type 1 DM, mice treated with streptozotocin (STZ) showed a similar increase in susceptibility to AF. Chronic insulin treatment reduced susceptibility and duration of AF and shortened P-wave duration in Akita mice. Atrial action potential (AP) morphology was altered in Akita mice due to a reduction in upstroke velocity and increases in AP duration. In Akita mice, atrial Na+ current (INa) and repolarizing K+ current (IK) carried by voltage gated K+ (Kv1.5) channels were reduced. The reduction in INa occurred in association with reduced expression of SCN5a and voltage gated Na+ (NaV1.5) channels as well as a shift in INa activation kinetics. Insulin potently and selectively increased INa in Akita mice without affecting IK Chronic insulin treatment increased INa in association with increased expression of NaV1.5. Acute insulin also increased INa, although to a smaller extent, due to enhanced insulin signaling via phosphatidylinositol 3,4,5-triphosphate (PIP3). Our study reveals a critical, selective role for insulin in regulating atrial INa, which impacts susceptibility to AF in type 1 DM.

TRP Channels Mediated Pathological Ca2+-Handling and Spontaneous Ectopy.

Ion channel biology offers great opportunity in identifying and learning about cardiac pathophysiology mechanisms. The discovery of transient receptor potential (TRP) channels is an add-on to the opportunity. Interacting with numerous signaling pathways, being activated multimodally, and having prescribed signatures underlining acute hemodynamic control and cardiac remodeling, TRP channels regulate cardiac pathophysiology. Impaired Ca2+-handling cause contractile abnormality. Modulation of intracellular Ca2+ concentration ([Ca2+]i) is a major part of Ca2+-handling processes in cardiac pathophysiology. TRP channels including TRPM4 regulate [Ca2+]i, Ca2+-handling and cardiac contractility. The channels modulate flux of divalent cations, such as Ca2+ during Ca2+-handling and cardiac contractility. Seminal works implicate TRPM4 and TRPC families in intracellular Ca2+ homeostasis. Defective Ca2+-homeostasis through TRP channels interaction with Ca2+-dependent regulatory proteins such as sodium calcium exchanger (NCX) results in abnormal Ca2+ handling, contractile dysfunction and in spontaneous ectopy. This review provides insight into TRP channels mediated pathological Ca2+-handling and spontaneous ectopy.

Necessity to evaluate PI3K/Akt signalling pathway in proarrhythmia.

The incidence of QT prolongation and torsades de pointes is on the rise due to the use of cardiovascular and non-cardiovascular drugs. Robust efforts have been made and are still ongoing to understand the underlying mechanisms that can enhance or prevent the development of drug-induced proarrhythmia. A caveat in the use of antiarrhythmic drugs is the ability to obtain safe action potential prolongation therapeutic effects, through IKr blockade. This remains as yet completely unachievable, as blockers of the potassium channel have not provided complete safe measures. Because of this, efforts at understanding the mechanisms of proarrhythmia have continued. PI3K/Akt signalling pathway appears to possess some potential advantage in this regard because cardiomyocytes intracellular dialysis with phosphatidylinositol (3,4,5)-trisphosphate (PIP3) normalises ion channel alterations and eliminates proarrhythmic features. However, there is a conundrum. Increased activities of PIP3 signalling can enhance cell proliferation and survival, and reduced activities of PIP3 signalling can lead to proarrhythmia. PI3K inhibitors used in cancer treatment have been found to cause proarrhythmia, and represent a potential avenue for the research and evaluation of potential effectiveness of a battery of antiarrhythmic and cancer drugs that are either currently in use or in development. Despite this knowledge, limited information is available on PI3K/Akt signalling and arrhythmogenesis. This highlights the need to search for new ways to improve testing of antiarrhythmic drugs and increase our understanding in PI3K/Akt signalling and arrhythmogenesis.

A New Perspective of Lysosomal Cation Channel-Dependent Homeostasis in Alzheimer's Disease.

Studies have reported typically biophysical lysosomal cation channels including TPCs. Their plausible biological roles are being elucidated by pharmacological, genetic and conventional patch clamp procedures. The best characterized so far among these channels is the ML1 isoform of TRP. The reported TRPs and TPCs are bypass for cation fluxes and are strategic for homeostasis of ionic milieu of the acidic organelles they confine to. Ca(2+) homeostasis and adequate acidic pHL are critically influential for the regulation of a plethora of biological functions these intracellular cation channels perform. In lysosomal ion channel biology, we review: ML1 and TPC2 in Ca(2+) signaling, ML1 and TPC2 in pH(L) regulation. Using Aß42 and tau proteins found along clathrin endolysosomal internalization pathway (Fig. 3), we proffer a mechanism of abnormal pH(L) and ML1/TPC2-dependent cation homeostasis in AD.

Infection, inflammation and prostate carcinogenesis.

Several reports have shown that the incidence of prostate cancer is on the increase and that more men would be diagnosed of prostate cancer in the next decades. Many approaches are being applied towards reducing the cases of prostate cancer, especially in the very rich countries. However, these have not been effective due to the poor current understanding of the pathophysiology of prostate carcinogenesis. The current work presents a review of how chronic infection and inflammation may contribute to prostate carcinogenesis.