Norepinephrine-induced cardiac hypertrophy and fibrosis are not due to mast cell degranulation

Mast cells: a novel therapeutic avenue for cardiovascular diseases?

Mast cells are tissue-resident immune cells strategically located in different compartments of the normal human heart (the myocardium, pericardium, aortic valve, and close to nerves) as well as in atherosclerotic plaques. Cardiac mast cells produce a broad spectrum of vasoactive and proinflammatory mediators, which have potential roles in inflammation, angiogenesis, lymphangiogenesis, tissue remodelling, and fibrosis. Mast cells release preformed mediators (e.g. histamine, tryptase, and chymase) and de novo synthesized mediators (e.g. cysteinyl leukotriene C4 and prostaglandin D2), as well as cytokines and chemokines, which can activate different resident immune cells (e.g. macrophages) and structural cells (e.g. fibroblasts and endothelial cells) in the human heart and aorta. The transcriptional profiles of various mast cell populations highlight their potential heterogeneity and distinct gene and proteome expression. Mast cell plasticity and heterogeneity enable these cells the potential for performing different, even opposite, functions in response to changing tissue contexts. Human cardiac mast cells display significant differences compared with mast cells isolated from other organs. These characteristics make cardiac mast cells intriguing, given their dichotomous potential roles of inducing or protecting against cardiovascular diseases. Identification of cardiac mast cell subpopulations represents a prerequisite for understanding their potential multifaceted roles in health and disease. Several new drugs specifically targeting human mast cell activation are under development or in clinical trials. Mast cells and/or their subpopulations can potentially represent novel therapeutic targets for cardiovascular disorders.

Innate Immunity Effector Cells as Inflammatory Drivers of Cardiac Fibrosis

Despite relevant advances made in therapies for cardiovascular diseases (CVDs), they still represent the first cause of death worldwide. Cardiac fibrosis and excessive extracellular matrix (ECM) remodeling are common end-organ features in diseased hearts, leading to tissue stiffness, impaired myocardial functional, and progression to heart failure. Although fibrosis has been largely recognized to accompany and complicate various CVDs, events and mechanisms driving and governing fibrosis are still not entirely elucidated, and clinical interventions targeting cardiac fibrosis are not yet available. Immune cell types, both from innate and adaptive immunity, are involved not just in the classical response to pathogens, but they take an active part in "sterile" inflammation, in response to ischemia and other forms of injury. In this context, different cell types infiltrate the injured heart and release distinct pro-inflammatory cytokines that initiate the fibrotic response by triggering myofibroblast activation. The complex interplay between immune cells, fibroblasts, and other non-immune/host-derived cells is now considered as the major driving force of cardiac fibrosis. Here, we review and discuss the contribution of inflammatory cells of innate immunity, including neutrophils, macrophages, natural killer cells, eosinophils and mast cells, in modulating the myocardial microenvironment, by orchestrating the fibrogenic process in response to tissue injury. A better understanding of the time frame, sequences of events during immune cells infiltration, and their action in the injured inflammatory heart environment, may provide a rationale to design new and more efficacious therapeutic interventions to reduce cardiac fibrosis.

Mast Cells in Cardiac Fibrosis: New Insights Suggest Opportunities for Intervention

Mast cells (MC) are innate immune cells present in virtually all body tissues with key roles in allergic disease and host defense. MCs recognize damage-associated molecular patterns (DAMPs) through expression of multiple receptors including Toll-like receptors and the IL-33 receptor ST2. MCs can be activated to degranulate and release pre-formed mediators, to synthesize and secrete cytokines and chemokines without degranulation, and/or to produce lipid mediators. MC numbers are generally increased at sites of fibrosis. They are potent, resident, effector cells producing mediators that regulate the fibrotic process. The nature of the secretory products produced by MCs depend on micro-environmental signals and can be both pro- and anti-fibrotic. MCs have been repeatedly implicated in the pathogenesis of cardiac fibrosis and in angiogenic responses in hypoxic tissues, but these findings are controversial. Several rodent studies have indicated a protective role for MCs. MC-deficient mice have been reported to have poorer outcomes after coronary artery ligation and increased cardiac function upon MC reconstitution. In contrast, MCs have also been implicated as key drivers of fibrosis. MC stabilization during a hypertensive rat model and an atrial fibrillation mouse model rescued associated fibrosis. Discrepancies in the literature could be related to problems with mouse models of MC deficiency. To further complicate the issue, mice generally have a much lower density of MCs in their cardiac tissue than humans, and as such comparing MC deficient and MC containing mouse models is not necessarily reflective of the role of MCs in human disease. In this review, we will evaluate the literature regarding the role of MCs in cardiac fibrosis with an emphasis on what is known about MC biology, in this context. MCs have been well-studied in allergic disease and multiple pharmacological tools are available to regulate their function. We will identify potential opportunities to manipulate human MC function and the impact of their mediators with a view to preventing or reducing harmful fibrosis. Important therapeutic opportunities could arise from increased understanding of the impact of such potent, resident immune cells, with the ability to profoundly alter long term fibrotic processes.

Regular exercise modulates cardiac mast cell activation in ovariectomized rats

It is well accepted that regular exercise is a significant factor in the prevention of cardiac dysfunction; however, the cardioprotective mechanism is as yet not well defined. We have examined whether regular exercise can modulate the activity of cardiac mast cells (CMC) after deprivation of female sex hormones, as well as the density and percentage degranulation of mast cells, in ventricular tissue of ovariectomized (OVX) rats after an 11-week running program. A significant increase in CMC density with a greater percentage degranulation was induced after ovarian sex hormone deprivation. Increased CMC density was prevented by estrogen supplements, but not by regular training. To the contrary, increased CMC degranulation in the OVX rat heart was attenuated by exercise training, but not by estrogen supplement. These findings indicate a significant correlation between the degree of CMC degranulation and myocyte cross-section area. However, no change in the expression of inflammatory mediators, including chymase, interleukin-6, and interleukin-10, was detected. Taken together, these results clearly indicate one of the cardioprotective mechanisms of regular aerobic exercise is the modulation of CMC activation.

Metformin Inhibits Isoproterenol-induced Cardiac Hypertrophy in Mice

The present study examined whether metformin treatment prevents isoporterenol-induced cardiac hypertrophy in mice. Chronic subcutaneous infusion of isoproterenol (15 mg/kg/24 h) for 1 week using an osmotic minipump induced cardiac hypertrophy measured by the heart-to-body weight ratio and left ventricular posterior wall thickness. Cardiac hypertrophy was accompanied with increased interleukin-6 (IL-6), transforming growth factor (TGF)-β, atrial natriuretic peptide (ANP), collagen I and III, and matrix metallopeptidase 2 (MMP-2). Coinfusion of metformin (150 mg/kg/24 h) with isoproterenol partially inhibited cardiac hypertrophy that was followed by reduced IL-6, TGF-β, ANP, collagen I and III, and MMP-2. Chronic subcutaneous infusion of metformin did not increase AMP-activated protein kinase (AMPK) activity in heart, although acute intraperitoneal injection of metformin (10 mg/kg) increased AMPK activity. Isoproterenol increased nitrotyrosine levels and mRNA expression of antioxidant enzyme glutathione peroxidase and metformin treatment normalized these changes. These results suggest that metformin inhibits cardiac hypertrophy through attenuating oxidative stress.

Collagen-related biomarkers in severe sepsis: a big stretch?

Biomedical scientists are aggressively investigating biomarkers of disease and injury. The rationale for identifying biomarkers during pathological states, such as severe sepsis, is to improve clinical prognostication and stratify therapeutic interventions for optimal recovery. An added benefit of biomarker studies is knowledge genesis on pathophysiological mechanisms, critical information that provides a basis for hypothesis-driven research. Unfortunately, biomarkers rarely alter our clinical approach in severe sepsis as they are often non-specific, lack adequate sensitivity and/or are difficult to measure and interpret accurately. Given the complexity and heterogeneity of severe sepsis, and the unique genetically derived susceptibilities of individuals, it is highly unlikely that one or even a handful of biomarkers will provide adequate biomedical information for clinical guidance. Thus, biomarkers will ultimately alter clinical decision making only once a panel of promising biomarkers is identified, maximizing sensitivity and specificity, and then adequately scrutinized with quantitative scoring methods over large populations of patients.

Cardiac hypertrophy in neonatal nephrectomized rats: the role of the sympathetic nervous system

Cardiac hypertrophy is frequently encountered in patients with renal failure and represents an independent risk factor for cardiovascular morbidity and mortality. The pathogenesis of cardiac hypertrophy is related to multiple factors, including excess adrenergic activity. This study investigated how renal injury in the early stages of life affects the adrenergic system and thereby potentially influences cardiac growth. Biomarkers of cardiac hypertrophy were used to assess adrenergic function. Newborn male Sprague-Dawley rats were allocated to three groups of five rats each: 5/6 nephrectomy (Nx), pair-fed controls (PF), and sham-operated (SH). Nx animals had significantly higher plasma urea nitrogen, serum creatinine, and mean arterial blood pressure. The heart-weight/body-weight ratio of the Nx cohort was higher than SH and PF (p < 0.001) groups. Plasma norepinephrine (NE) of Nx animals was almost twofold higher than SH and PF (p < 0.01) animals. Compared with SH and PF, Nx animals had higher alpha1A-receptor protein expression, lower cardiac beta1- and beta2-receptor protein expression (p < 0.05), but higher G-protein-coupled receptor kinase-2 (GRK2) expression (p < 0.05). Norepinephrine transporter protein (NET) and renalase protein expression in cardiac tissue from Nx pups were significantly lower than SH and PF. Our data suggest that early age Nx animals have increased circulating catecholamines due to decreased NE metabolism. Enhancement of cardiac GRK2 and NE can contribute to cardiac hypertrophy seen in Nx animals. Furthermore, AKT (activated via alpha1A receptors), as well as increased alpha1A receptors and their agonist NE, might contribute to the observed hypertrophy.

Myocardial Matrix Remodeling and the Matrix Metalloproteinases: Influence on Cardiac Form and Function

It is now becoming apparent that dynamic changes occur within the interstitium that directly contribute to adverse myocardial remodeling following myocardial infarction (MI), with hypertensive heart disease and with intrinsic myocardial disease such as cardiomyopathy. Furthermore, a family of matrix proteases, the matrix metalloproteinases (MMPs) and the tissue inhibitors of MMPs (TIMPs), has been recognized to play an important role in matrix remodeling in these cardiac disease states. The purpose of this review is fivefold: 1) to examine and redefine the myocardial matrix as a critical and dynamic entity with respect to the remodeling process encountered with MI, hypertension, or cardiomyopathic disease; 2) present the remarkable progress that has been made with respect to MMP/TIMP biology and how it relates to myocardial matrix remodeling; 3) to evaluate critical translational/clinical studies that have provided a cause-effect relationship between alterations in MMP/TIMP regulation and myocardial matrix remodeling; 4) to provide a critical review and analysis of current diagnostic, prognostic, and pharmacological approaches that utilized our basic understanding of MMP/TIMPs in the context of cardiac disease; and 5) most importantly, to dispel the historical belief that the myocardial matrix is a passive structure and supplant this belief that the regulation of matrix protease pathways such as the MMPs and TIMPs will likely yield a new avenue of diagnostic and therapeutic strategies for myocardial remodeling and the progression to heart failure.

Characterization of myocardial hypertrophy in prehypertensive spontaneously hypertensive rats: interaction between adrenergic and nitrosative pathways

OBJECTIVE AND METHODS

Left ventricular hypertrophy in human and experimental hypertension is not always associated with pressure overload but seems to precede an increase in blood pressure. In this study, performed in male 5-week-old prehypertensive spontaneously hypertensive rats (SHR; n = 65) and age-matched Wistar-Kyoto rats (n = 56), the relationship between myocardial structure and activation of the adrenergic and nitric oxide systems was evaluated.

RESULTS

Body weight, blood pressure and heart rate were similar in both groups. A higher left ventricle/body weight ratio was found in SHR, as a result of greater mononuclear (+47%) and binuclear (+43%) myocyte volumes, without changes in interstitial collagen. Both adrenergic and nitric oxide pathways were activated in SHR, as expressed by higher myocardial norepinephrine content, tyrosine hydroxylase activity, myocardial nitric oxide synthase 3 expression and protein nitration, indicating greater peroxynitrite (ONOO) generation from nitric oxide and superoxide. No difference was measured in nitric oxide synthase 1 expression, whereas nitric oxide synthase 2 was undetectable. A positive correlation between myocardial tyrosine hydroxylase activity and protein nitration was observed in SHR (r = 0.328; P < 0.01). Early treatment with a superoxide dismutase mimetic, 4-hydroxy-2,2,6,6-tetramethyl piperidinoxyl, from the third to the fifth week of age, reduced ONOO generation, protein nitration and sympathetic activation in SHR without changes in myocardial structure.

CONCLUSION

In prehypertensive SHR, left ventricular hypertrophy is associated with adrenergic and nitrosative imbalance. Early superoxide dismutase mimetic treatment in SHR effectively reduces higher myocardial ONOO generation, sympathetic activation, and heart rate without affecting the development of myocardial hypertrophy.

Cardiac function in hearts isolated from a rat model deficient in mast cells

Several studies have examined the role of mast cells in the myocardial response to injury such as that caused by hypertension and ischemia-reperfusion. However, little is known about the influence of mast cells on normal myocardial structure and function. The present experiments examined cardiac function in Langendorff-perfused hearts isolated from 6- and 9-mo-old male mast cell-deficient ( Ws/ Ws) and mast cell-competent rats. A fluid-filled balloon catheter was used to measure left ventricular diastolic and systolic function at increasing preload volumes. At 6 mo of age, mast cell-deficient rats showed a slight cardiac hypertrophy (as monitored by heart weight and heart weight-to-body weight ratio) but no significant change in maximum observed systolic or diastolic function. In contrast, at 9 mo of age, the mast cell-deficient group showed no signs of hypertrophy but displayed a diastolic dysfunction characterized by decreased compliance without a significant decline in maximum observed basal −dP/d tmax. There were no significant differences in maximum observed values for measures of systolic function (developed pressure and +dP/d tmax). In summary, the results of this study in adult rats suggest that mast cells influence cardiac function in the absence of injury and that observed differences between mast cell-competent and -deficient animals vary with age. Thus it is important to consider these “physiological” actions and resulting changes in function when studying effects of insult in mast cell-deficient models.

Antiglaucoma eye drop pulses--increased interleukin-6 secretion by Tenon's capsule fibroblast cultures

PURPOSE

Long-term antiglaucoma eye drop therapy prior to trabeculectomy is a risk factor for surgical failure resulting from Tenon's capsule fibrosis at the fistula site. The study tested the hypothesis that secretion of the proinflammatory cytokine interleukin (IL)-6 by wounded Tenon's capsule-fibroblasts is elevated by prior long-term antiglaucoma eye drop treatment.

METHODS

Fibroblast cultures were established from Tenon's capsule biopsies during trabeculectomy. Twice daily and for four and a half days, confluent secondary (2-4 passages) cultures were treated (30 minutes at 37 degrees C) with the following drugs (diluted at 1:400-1:100): 0.2% brimonidine-tartrate (Alphagan), 2.0% dorzolamide-HCl (Trusopt), 0.5% timolol-maleate (Timoptic), 2.0% dorzolamide-HCl/0.5% timolol-maleate (Cosopt), 2 and 4% pilocarpine-HCl (Akarpine and Pilocar), 0.005% latanoprost (Xalatan), placebos for Trusopt and Timoptic, and 0.01% benzalkonium chloride. Subsequently, cultures were wounded by removing cells grown on half of each culture dishes along with the medium and conditioned for 20 hours in serum-free growth medium, which was then collected for ELISA for IL-6 (and TNF-alpha and IL-1 beta). Cultures were grown for four additional days to show the maintenance of culture sterility.

RESULTS

Latanoprost, pilocarpine-HCl, and timolol-maleate increased IL-6 levels in the conditioned medium in a dilution factor-dependent manner (P < 0.05, ANOVA). IL-6 concentrations were increased most significantly by latanoprost and were (pg/ml; mean +/- SEM; N = 3 cultures) 186 +/- 37, 187 +/- 33, 295 +/- 46 and 336 +/- 76 in cultures treated at 1:400, 1:250, 1:150, and 1:100 dilutions, respectively, whereas those of six control cultures averaged 80 +/- 9. Benzalkonium chloride, brimonidine-tartrate, dorzolamide-HCl, Cosopt placebo, Timoptic placebo, and dorzolamide-HCl/timolol-maleate did not significantly elevate IL-6 concentrations. IL-1 beta and TNF-alpha were not detected in the medium of control cultures and those treated with pilocarpine (1:200).

CONCLUSIONS

The present study demonstrated for the first time that the level of IL-6 secretion by wounded Tenon's capsule fibroblast cell cultures was increased by repeat pulsing of these cultures with some, but not all, antiglaucoma eye drops prior to wounding.