Delayed-release rapamycin halts progression of left ventricular hypertrophy in subclinical feline hypertrophic cardiomyopathy: results of the RAPACAT trial

Immunosenescence and Inflammaging in Dogs and Cats: A Narrative Review

A consistent and important feature of biological aging is the change in the types and functions of cells comprising the immune system. Across various mammalian species, this change follows consistent patterns, including diminished protective capacity, leading to increased vulnerability to infectious disease, and increased low-grade chronic inflammation, raising the risk of numerous aging-associated diseases. Although these patterns are well characterized in rodents and humans, there is less evidence available in companion animal species. The most recent review of the literature evaluating aging changes in the immune system in dogs and cats was published in 2010. The purpose of this narrative review is to summarize the currently available information concerning immune system aging in these species and to review what is known about the clinical consequences of this process and about potential strategies for mitigation.

Evolving FATE: A New Lens on the Pathogenesis and Management of Feline Cardiogenic Arterial Thromboembolism

Feline cardiogenic arterial thromboembolism (FATE) remains one of the most devastating complications of feline cardiomyopathies, with high mortality and recurrence rates. Despite its clinical importance, significant knowledge gaps persist in our understanding of FATE's pathogenesis and optimal management strategies. Our review aims to address these gaps by providing a comprehensive overview of the current understanding of FATE, including disease mechanisms, risk factors, emerging diagnostics, and preventative strategies. Importantly, we identify key areas such as immunothrombosis, procoagulant platelets, platelet heterogeneity, and altered fibrinolysis where future research may yield novel biomarkers and therapeutic targets to improve outcomes in affected feline patients.

Proteomic Analysis of Valsartan for Attenuating Disease Evolution in Early Sarcomeric Hypertrophic Cardiomyopathy (VANISH) Clinical Trial

BACKGROUND

In hypertrophic cardiomyopathy (HCM), the mechanisms through which pathogenic sarcomere variants (G+) lead to left ventricular hypertrophy (LVH) are not understood.

METHODS

VANISH (Valsartan for Attenuating Disease Evolution in Early Sarcomeric Hypertrophic Cardiomyopathy) was a multicenter, double-blind, placebo-controlled randomized trial testing valsartan's ability to attenuate phenotypic progression in early sarcomeric (G+LVH+) and subclinical HCM (G+LVH-). The outcome was a composite Z score reflecting cardiac remodeling from baseline to year 2 (end of study). Baseline and year 2 blood samples were used to quantify 276 proteins using a proximity extension assay (Olink, Sweden). We explored relative differences in protein abundance between early and subclinical HCM at baseline. In addition, we compared proteomic changes between baseline and year 2 in subclinical HCM participants who experienced phenotypic conversion to early HCM (converters) versus nonconverters; early HCM participants receiving valsartan versus placebo; and in association with changes in Z score. Comparisons were made using t test/Mann-Whitney U test, linear mixed models, and generalized linear models, correcting for multiple testing.

RESULTS

Circulating proteins were analyzed in 192 participants (32 subclinical and 160 early HCM [81 allocated to valsartan]). NT-proBNP (N-terminal pro-B-type natriuretic peptide) differentiated early from subclinical HCM and tracked with phenotypic progression in early HCM (1-unit worsening in Z score associated with a 27% increase in NT-proBNP [95% CI, 17-37%]). Some extracellular matrix remodeling proteins showed higher abundance (tissue-type plasminogen activator) in early compared with subclinical HCM or tracked with disease progression (decorin) in early HCM. Growth factors had higher relative abundance in early HCM (fibroblast growth factor-21). While no individual protein was able to distinguish converters from nonconverters, multiprotein the panels lipocalin 2, lectin-like oxidized low-density lipoprotein receptor 1, and either NT-proBNP or interleukin-17 receptor A, could distinguish these groups.

CONCLUSIONS

NT-proBNP was the most robust protein to track progression. Studying pathways involving growth factors and extracellular matrix remodeling may yield additional insights into mechanisms behind disease progression.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique identifier: NCT01912534.

Clinical-Diagnostic and Therapeutic Advances in Feline Hypertrophic Cardiomyopathy

A comprehensive literature review was conducted to summarise existing evidence and the latest therapeutic advancements in feline HCM. The disease phenotype is characterised by the development of concentric hypertrophy, which is variable but often asymmetric, primarily affecting the left ventricle. The HCM is marked by diastolic dysfunction, resulting in a reduced intracavitary internal diameter due to the disordered alignment of cardiomyocytes and excessive collagen deposition, which thickens the myocardial tissue and impairs relaxation. There is strong evidence supporting the role of genetic mutations in sarcomeric genes in the development of HCM. Clinical signs vary but are frequently associated with congestive heart failure (CHF) and ATE. Diagnosis is based on a combination of clinical evaluation, laboratory tests, and imaging studies, although certain aspects of the disease remain insufficiently understood and require further research. Therapeutic management focuses on controlling clinical signs, slowing disease progression, and improving both quality of life and life expectancy. However, ongoing studies are essential to refine diagnostic strategies and explore novel treatment options for better disease management.

Macrophage Membrane Coated Manganese Dioxide Nanoparticles Loaded with Rapamycin Alleviate Intestinal Ischemia-Reperfusion Injury by Reducing Oxidative Stress and Enhancing Autophagy

Background

Intestinal ischemia-reperfusion (I/R) injury is a common and severe clinical issue. With high morbidity and mortality, it burdens patients and the healthcare system. Despite the efforts in medical research, current treatment options are unsatisfactory, urging novel therapeutic strategies. Oxidative stress and dysregulated autophagy play pivotal roles in the pathogenesis of I/R injury, damaging intestinal tissues and disrupting normal functions. The aim of this study is to fabricate macrophage membrane-coated manganese dioxide nanospheres loaded with rapamycin [Ma@(MnO₂+RAPA)] for alleviating intestinal I/R injury.

Methods

We engineered honeycomb MnO2 nanospheres coated with a macrophage membrane to act as a drug delivery system, encapsulating RAPA. In vitro OGD/R model in IEC-6 cells and in vivo mouse I/R injury models were used. Targeting ability was evaluated through in-vivo imaging system. Effects on cell viability, reactive oxygen species (ROS) levels, oxygen generation, inflammatory factors, apoptosis, autophagy, and biocompatibility were detected by methods such as MTT assay, fluorescence microscopy, ELISA kit, TUNEL assay, Western blotting and histological analysis.

Results

In this study, Ma@(MnO₂+RAPA) efficiently deliver RAPA to damaged tissues and exhibited good ROS-responsive release. Our data showed that Ma@(MnO₂+RAPA) reduced ROS, increased O₂, inhibited inflammation, and promoted autophagy while reducing apoptosis in IEC-6 cells. In a mouse I/R model, Ma@(MnO₂+RAPA) significantly reduced Chiu's score, improved tight conjunction proteins, decreased apoptosis, reduced levels of inflammatory cytokines and oxidative stress. RAPA released from the Ma@(MnO₂+RAPA), enhanced the expression of autophagy-regulated proteins p62, Beclin-1, and LC3II. The biocompatibility and safety of Ma@(MnO₂+RAPA) were confirmed through histological analysis and biochemical detection in mice.

Conclusion

Our results demonstrated that Ma@(MnO₂+RAPA) alleviated intestinal I/R injury by reducing oxidative stress, promoting autophagy, and inhibiting inflammation. This study offers a potential therapeutic strategy for the treatment of intestinal ischemia-reperfusion injury.

Test of Rapamycin in Aging Dogs (TRIAD): study design and rationale for a prospective, parallel-group, double-masked, randomized, placebo-controlled, multicenter trial of rapamycin in healthy middle-aged dogs from the Dog Aging Project

Companion dogs are a powerful model for aging research given their morphologic and genetic variability, risk for age-related disease, and habitation of the human environment. In addition, the shorter life expectancy of dogs compared to human beings provides a unique opportunity for an accelerated timeline to test interventions that might extend healthy lifespan. The Test of Rapamycin In Aging Dogs (TRIAD) randomized clinical trial is a parallel-group, double-masked, randomized, placebo-controlled, multicenter trial that will test the ability of rapamycin to prolong lifespan and improve several healthspan metrics in healthy, middle-aged dogs recruited from Dog Aging Project participants. Here, we describe the rationale, design, and goals of the TRIAD randomized clinical trial, the first rigorous test of a pharmacologic intervention against biological aging with lifespan and healthspan metrics as endpoints to be performed outside of the laboratory in any species.

Involvement of TGF-β, mTOR, and inflammatory mediators in aging alterations during myxomatous mitral valve disease in a canine model

Inflammaging, a state of chronic low-grade inflammation associated with aging, has been linked to the development and progression of various disorders. Cellular senescence, a state of irreversible growth arrest, is another characteristic of aging that contributes to the pathogenesis of cardiovascular pathology. Senescent cells accumulate in tissues over time and secrete many inflammatory mediators, further exacerbating the inflammatory environment. This senescence-associated secretory phenotype can promote tissue dysfunction and remodeling, ultimately leading to the development of age-related cardiovascular pathologies, such as mitral valve myxomatous degeneration. The species-specific form of canine myxomatous mitral valve disease (MMVD) provides a unique opportunity to investigate the early causes of induction of ECM remodeling in mitral valve leaflets in the human form of MMVD. Studies have shown that in both humans and dogs, the microenvironment of the altered leaflets is inflammatory. More recently, the focus has been on the mechanisms leading to the transformation of resting VICs (qVICs) to myofibroblast-like VICs (aVICs). Cells affected by stress fall into a state of cell cycle arrest and become senescent cells. aVICs, under the influence of TGF-β signaling pathways and the mTOR complex, enhance ECM alteration and accumulation of systemic inflammation. This review aims to create a fresh new view of the complex interaction between aging, inflammation, immunosenescence, and MMVD in a canine model, as the domestic dog is a promising model of human aging and age-related diseases.

Comprehensive Proteomics Profiling Identifies Circulating Biomarkers to Distinguish Hypertrophic Cardiomyopathy From Other Cardiomyopathies With Left Ventricular Hypertrophy

BACKGROUND

Distinguishing hypertrophic cardiomyopathy (HCM) from other cardiomyopathies with left ventricular hypertrophy (LVH), such as hypertensive LVH, transthyretin amyloid cardiomyopathy, and aortic stenosis, is sometimes challenging. Using plasma proteomics profiling, we aimed to identify circulating biomarkers and dysregulated signaling pathways specific to HCM.

METHODS

In this multicenter case-control study, plasma proteomics profiling was performed in cases with HCM and controls with hypertensive LVH, transthyretin amyloid cardiomyopathy, and aortic stenosis. Two-thirds of patients enrolled earlier in each disease group were defined as the training set and the remaining one-third as the test set. Protein concentrations in HCM were compared with those in hypertensive LVH (comparison 1), transthyretin amyloid cardiomyopathy (comparison 2), and aortic stenosis (comparison 3). Candidate proteins that meet the following 2 criteria were selected: (1) higher abundance in HCM throughout all 3 comparisons or lower abundance in HCM throughout all 3 comparisons with univariable P<0.05 and |log2(fold change)| >0.5 in both the training and test sets and (2) independently associated with HCM with multivariable P<0.05 after adjusting for clinical parameters significantly different between HCM and controls. Using the selected candidate proteins, a logistic regression model to distinguish HCM from controls was developed in the training set and applied to the test set. Finally, pathway analysis was performed in each comparison using proteins with different abundance.

RESULTS

Overall, 4979 proteins in 1415 patients (HCM, n=879; hypertensive LVH, n=331; transthyretin amyloid cardiomyopathy, n=169; aortic stenosis, n=36) were analyzed. Of those, 5 proteins were selected as candidate proteins. The logistic regression model with these 5 proteins had an area under the receiver operating characteristic curve of 0.86 (95% CI, 0.82-0.89) in the test set. The MAPK (mitogen-activated protein kinase) and HIF-1 (hypoxia-inducible factor 1) pathways were dysregulated in HCM throughout the 3 comparisons.

CONCLUSIONS

This study identified circulating biomarkers that distinguish HCM from other cardiomyopathies with LVH independently from confounders and revealed signaling pathways associated with HCM.

Multi-Omic, Histopathologic, and Clinicopathologic Effects of Once-Weekly Oral Rapamycin in a Naturally Occurring Feline Model of Hypertrophic Cardiomyopathy: A Pilot Study

Hypertrophic cardiomyopathy (HCM) remains the single most common cardiomyopathy in cats, with a staggering prevalence as high as 15%. To date, little to no direct therapeutical intervention for HCM exists for veterinary patients. A previous study aimed to evaluate the effects of delayed-release (DR) rapamycin dosing in a client-owned population of subclinical, non-obstructive, HCM-affected cats and reported that the drug was well tolerated and resulted in beneficial LV remodeling. However, the precise effects of rapamycin in the hypertrophied myocardium remain unknown. Using a feline research colony with naturally occurring hereditary HCM (n = 9), we embarked on the first-ever pilot study to examine the tissue-, urine-, and plasma-level proteomic and tissue-level transcriptomic effects of an intermittent low dose (0.15 mg/kg) and high dose (0.30 mg/kg) of DR oral rapamycin once weekly. Rapamycin remained safe and well tolerated in cats receiving both doses for eight weeks. Following repeated weekly dosing, transcriptomic differences between the low- and high-dose groups support dose-responsive suppressive effects on myocardial hypertrophy and stimulatory effects on autophagy. Differences in the myocardial proteome between treated and control cats suggest potential anti-coagulant/-thrombotic, cellular remodeling, and metabolic effects of the drug. The results of this study closely recapitulate what is observed in the human literature, and the use of rapamycin in the clinical setting as the first therapeutic agent with disease-modifying effects on HCM remains promising. The results of this study establish the need for future validation efforts that investigate the fine-scale relationship between rapamycin treatment and the most compelling gene expression and protein abundance differences reported here.