Neurocardiac dysregulation and neurogenic arrhythmias in a transgenic mouse model of Huntington's disease.

Huntington's disease (HD) is a heritable neurodegenerative disorder, with heart disease implicated as one major cause of death. While the responsible mechanism remains unknown, autonomic nervous system (ANS) dysfunction may play a role. We studied the cardiac phenotype in R6/1 transgenic mice at early (3 months old) and advanced (7 months old) stages of HD. While exhibiting a modest reduction in cardiomyocyte diameter, R6/1 mice had preserved baseline cardiac function. Conscious ECG telemetry revealed the absence of 24-h variation of heart rate (HR), and higher HR levels than wild-type littermates in young but not older R6/1 mice. Older R6/1 mice had increased plasma level of noradrenaline (NA), which was associated with reduced cardiac NA content. R6/1 mice also had unstable R-R intervals that were reversed following atropine treatment, suggesting parasympathetic nervous activation, and developed brady- and tachyarrhythmias, including paroxysmal atrial fibrillation and sudden death. c-Fos immunohistochemistry revealed greater numbers of active neurons in ANS-regulatory regions of R6/1 brains. Collectively, R6/1 mice exhibit profound ANS-cardiac dysfunction involving both sympathetic and parasympathetic limbs, that may be related to altered central autonomic pathways and lead to cardiac arrhythmias and sudden death.

Novel role of platelets in mediating inflammatory responses and ventricular rupture or remodeling following myocardial infarction.

OBJECTIVE: The goal of this study was to investigate the role of platelets in systemic and cardiac inflammatory responses and the development of postinfarct ventricular complications, as well as the efficacy of antiplatelet interventions. METHODS AND RESULTS: Using a mouse myocardial infarction (MI) model, we determined platelet accumulation and severity of inflammation within the infarcted myocardium by immunohistochemistry and biochemical assays, analyzed peripheral blood platelet-leukocyte conjugation using flow cytometry, and tested antiplatelet interventions, including thienopyridines and platelet depletion. Platelets accumulated within the infarcted region early post-MI and colocalized with inflammatory cells. MI evoked early increase in circulating platelet-leukocyte conjugation mediated by P-selectin/P-selectin glycoprotein ligand-1. Antiplatelet interventions inhibited platelet-leukocyte conjugation in peripheral blood, inflammatory infiltration, content of matrix metalloproteinases or plasminogen activation, and expression of inflammatory mediators in the infarcted myocardium (all P<0.05) and lowered rupture incidence (P<0.01). Clopidogrel therapy alleviated the extent of chronic ventricular dilatation by serial echocardiography. CONCLUSIONS: Platelets play a pivotal role in promoting systemic and cardiac inflammatory responses post-MI. Platelets accumulate within the infarcted myocardium, contributing to regional inflammation, ventricular remodeling, and rupture. Antiplatelet therapy reduces the severity of inflammation and risk of post-MI complications, demonstrating a previously unrecognized protective action.

Hematology and Biochemistry Reference Intervals for American Alligator (Alligator mississippiensis) in South Florida, USA.

We calculated reference intervals for 48 blood parameters from 120 wild American alligators (Alligator mississippiensis) in South Florida, US. Although previously reported by others, this study includes additional parameters not yet reported in wild populations. Most previously reported blood parameter values were similar to ours and fell within our reference intervals.

Hematology and biochemistry reference intervals for American crocodiles (Crocodylus acutus) in South Florida.

The American crocodile (Crocodylus acutus) is considered a vulnerable species by the International Union for Conservation of Nature (IUCN) Red List across its range and classified as locally threatened in several countries. There is a lack of knowledge involving hematological and physiological parameters in American crocodile populations, limiting our understanding of what are considered "normal" blood analyte results for the species and how to link them with health assessments. In this study, we analyzed 40 hematological and biochemical parameters and estimated reference intervals (RIs) for 35 of them based on 436 clinically healthy wild American crocodiles caught in South Florida between 2015 and 2021. Crocodiles were captured across three areas with different levels of human influence [low = Everglades National Park (ENP), medium = Biscayne Bay Estuary (BBE), and high = Turkey Point Nuclear Power Plant (TP)]. There was very strong-to-strong evidence for an effect of where animals were caught on five analytes: basophils %, phosphorus, proportion of (pr) alpha-2 globulins, absolute count (abs) of gamma globulins, and corticosterone, so no reference values were estimated but general statistics are presented and discussed. From the remaining analytes, we found no evidence that sex or size class had an effect on red blood cell (RBC), azurophils and monocytes abs, triglycerides, and albumin abs. However, we did find moderate-to-strong evidence that sex influenced azurophils % and size class influenced white blood cell (WBC), heterophils %, monocytes %, basophils abs, creatine phosphokinase (CPK), potassium, glucose, bile acids, alpha-1 globulin abs, and alpha-2 globulin pr and abs. Finally, there was strong evidence that both sex and size class influenced PCV, lymphocytes % and abs, eosinophils % and abs, aspartate aminotransferase (AST), calcium, sodium, chloride, total protein, albumin/globulin (A/G) ratio, albumin pr, alpha-1 globulin, and beta globulin abs. Intraspecific analysis showed that size is the variable that most influenced analytes explaining up to 29% of the variation, which relates to our findings based on intraindividual analysis. We compared our results with blood parameters reported for conspecifics as well as closely related species and discussed implication of those results for clinical diagnosis and American crocodile conservation.

Deletion of macrophage migration inhibitory factor protects the heart from severe ischemia-reperfusion injury: a predominant role of anti-inflammation.

Inflammation plays an important role in mediating and exacerbating myocardial ischemia-reperfusion (I/R) injury. Macrophage migration inhibitory factor (MIF), a pleiotropic cytokine, facilitates inflammation and modulates metabolism. However, the role of MIF in mediating local inflammation subsequent to ischemic myocardial injury has not been established. We hypothesized that genetic deletion of MIF protects the heart against severe I/R injury by suppressing inflammation and/or modulating energy metabolism. We showed in the mouse I/R model that duration of both ischemia and reperfusion is a determinant for the degree of regional inflammation and tissue damage. Following a prolonged cardiac I/R (60 min/24h) MIF KO mice had a significant reduction in both infarct size (26±3% vs. 45±4%, P<0.05) and cardiomyocyte apoptosis (1.4±0.2% vs. 5.4±0.4%, P<0.05) and preserved contractile function compared with WT. MIF KO mice with I/R had reduced expression of various inflammatory cytokines and mediators (P<0.05), suppressed infiltration of neutrophils (-40%) and macrophages (-33%, both P<0.05), and increased macrophage apoptosis (14.4±1.4% vs. 5.2±0.6%, P<0.05). Expression of toll-like receptor-4 (TLR-4), phosphorylation of c-Jun N-terminal kinase (JNK), and nuclear fraction of NF-κB p65 were also significantly lower in MIF KO hearts with I/R. Further, MIF KO mice exhibited a lower glucose uptake but higher fatty acid oxidation rate than that in WT (both P<0.05). In conclusion, MIF deficiency protected the heart from prolonged/severe I/R injury by suppressing inflammatory responses. We have identified a critical role of MIF in mediating severe I/R injury. Thus, MIF inhibitory therapy may be a novel strategy to protect the heart against severe I/R injury.

Effect of subcutaneous tissue depth on outcomes of kidney transplantation.

Although post-kidney transplant (KT) wound complications are associated with elevated body mass index (BMI), BMI is not an accurate surrogate of obesity. On the other hand, subcutaneous depth (SQD) measurement is a direct marker of truncal obesity. We examined outcomes of differing intraoperative SQD measurements in 113 KT-only recipients over 20 months. Recipients' median age was 51 years; median BMI, 28 kg/m2; and mean SQD, 2.9 cm. Patients were stratified into groups of SQD ≤2.5 cm, >2.5-5 cm, and >5 cm. An SQD of >2.5 to 5 cm correlated with a BMI of 30 kg/m2 (obesity) and an SQD >5 cm correlated with a BMI >35 kg/m2 (severe obesity). Degree of SQD was not associated with more frequent technical complications such as fascial dehiscence, lymphocele formation, renal artery thrombosis/stenosis, urine leak, or ureteral stenosis. However, an SQD >2.5 cm was a risk factor for requiring a wound vacuum-assisted closure device. There was no difference in graft or patient survival among the three SQD groups. Obesity, as measured directly by SQD, was not associated with increased technical complications or poor outcomes after KT. As expected, there was a higher incidence of wound complications in the higher SQD groups requiring intervention.

Pathological hypertrophy reverses ß2-adrenergic receptor-induced angiogenesis in mouse heart.

ß-adrenergic activation and angiogenesis are pivotal for myocardial function but the link between both events remains unclear. The aim of this study was to explore the cardiac angiogenesis profile in a mouse model with cardiomyocyte-restricted overexpression of ß2-adrenoceptors (ß2-TG), and the effect of cardiac pressure overload. ß2-TG mice had heightened cardiac angiogenesis, which was essential for maintenance of the hypercontractile phenotype seen in this model. Relative to controls, cardiomyocytes of ß2-TGs showed upregulated expression of vascular endothelial growth factor (VEGF), heightened phosphorylation of cAMP-responsive-element-binding protein (CREB), and increased recruitment of phospho-CREB, CREB-binding protein (CBP), and p300 to the VEGF promoter. However, when hearts were subjected to pressure overload by transverse aortic constriction (TAC), angiogenic signaling in ß2-TGs was inhibited within 1 week after TAC. ß2-TG hearts, but not controls, exposed to pressure overload for 1-2 weeks showed significant increases from baseline in phosphorylation of Ca(2+)/calmodulin-dependent kinase II (CaMKIIδ) and protein expression of p53, reduction in CREB phosphorylation, and reduced abundance of phospho-CREB, p300 and CBP recruited to the CREB-responsive element (CRE) site of VEGF promoter. These changes were associated with reduction in both VEGF expression and capillary density. While non-TG mice with TAC developed compensatory hypertrophy, (2-TGs exhibited exaggerated hypertrophic growth at week-1 post-TAC, followed by LV dilatation and reduced fractional shortening measured by serial echocardiography. In conclusion, angiogenesis was enhanced by the cardiomyocyte (2AR/CREB/VEGF signaling pathway. Pressure overload rapidly inhibited this signaling, likely as a consequence of activated CaMKII and p53, leading to impaired angiogenesis and functional decompensation.

Chronic activation of the low affinity site of ß1-adrenoceptors stimulates haemodynamics but exacerbates pressure-overload cardiac remodelling.

BACKGROUND AND PURPOSE: The ß1-adrenoceptor has at least two binding sites, high and low affinity sites (ß1H and ß1L, respectively), which mediate cardiostimulation. While ß1H-adrenoceptor can be blocked by all clinically used ß-blockers, ß1L-adrenoceptor is relatively resistant to blockade. Thus, chronic ß1L-adrenoceptor activation may mediate persistent cardiostimulation, despite the concurrent blockade of ß1H-adrenoceptors. Hence, it is important to determine the potential significance of ß1L-adrenoceptors in vivo, particularly in pathological situations. EXPERIMENTAL APPROACH: C57Bl/6 male mice were used. Chronic (4 or 8 weeks) ß1L-adrenoceptor activation was achieved by treatment, via osmotic mini pumps, with (-)-CGP12177 (10 mg·kg(-1)·day(-1)). Cardiac function was assessed by echocardiography and micromanometry. KEY RESULTS: (-)-CGP12177 treatment of healthy mice increased heart rate and left ventricular (LV) contractility. (-)-CGP12177 treatment of mice subjected to transverse aorta constriction (TAC), during weeks 4-8 or 4-12 after TAC, led to a positive inotropic effect and exacerbated fibrogenic signalling while cardiac hypertrophy tended to be more severe. (-)-CGP12177 treatment of mice with TAC also exacerbated the myocardial expression of hypertrophic, fibrogenic and inflammatory genes compared to untreated TAC mice. Washout of (-)-CGP12177 revealed a more pronounced cardiac dysfunction after 12 weeks of TAC. CONCLUSIONS AND IMPLICATIONS: ß1L-adrenoceptor activation provides functional support to the heart, in both normal and pathological (pressure overload) situations. Sustained ß1L-adrenoceptor activation in the diseased heart exacerbates LV remodelling and therefore may promote disease progression from compensatory hypertrophy to heart failure.

Standardizing a simpler, more sensitive and accurate tail bleeding assay in mice.

AIM: To optimize the experimental protocols for a simple, sensitive and accurate bleeding assay. METHODS: Bleeding assay was performed in mice by tail tip amputation, immersing the tail in saline at 37 °C, continuously monitoring bleeding patterns and measuring bleeding volume from changes in the body weight. Sensitivity and extent of variation of bleeding time and bleeding volume were compared in mice treated with the P2Y receptor inhibitor prasugrel at various doses or in mice deficient of FcRγ, a signaling protein of the glycoprotein VI receptor. RESULTS: We described details of the bleeding assay with the aim of standardizing this commonly used assay. The bleeding assay detailed here was simple to operate and permitted continuous monitoring of bleeding pattern and detection of re-bleeding. We also reported a simple and accurate way of quantifying bleeding volume from changes in the body weight, which correlated well with chemical assay of hemoglobin levels (r (2) = 0.990, P < 0.0001). We determined by tail bleeding assay the dose-effect relation of the anti-platelet drug prasugrel from 0.015 to 5 mg/kg. Our results showed that the correlation of bleeding time and volume was unsatisfactory and that compared with the bleeding time, bleeding volume was more sensitive in detecting a partial inhibition of platelet's haemostatic activity (P < 0.01). Similarly, in mice with genetic disruption of FcRγ as a signaling molecule of P-selectin glycoprotein ligand-1 leading to platelet dysfunction, both increased bleeding volume and repeated bleeding pattern defined the phenotype of the knockout mice better than that of a prolonged bleeding time. CONCLUSION: Determination of bleeding pattern and bleeding volume, in addition to bleeding time, improved the sensitivity and accuracy of this assay, particularly when platelet function is partially inhibited.