The orphan receptor APJ and its recently identified endogenous ligand, apelin, exhibit high levels of mRNA expression in the heart. However, the functional importance of apelin in the cardiovascular system is not known. In isolated perfused rat hearts, infusion of apelin (0.01 to 10 nmol/L) induced a dose-dependent positive inotropic effect (EC ₅₀ : 33.1±1.5 pmol/L). Moreover, preload-induced increase in dP/dt _max was significantly augmented ( P <0.05) in the presence of apelin. Inhibition of phospholipase C (PLC) with U-73122 and suppression of protein kinase C (PKC) with staurosporine and GF-109203X markedly attenuated the apelin-induced inotropic effect ( P <0.001). In addition, zoniporide, a selective inhibitor of Na ⁺ -H ⁺ exchange (NHE) isoform-1, and KB-R7943, a potent inhibitor of the reverse mode Na ⁺ -Ca ²⁺ exchange (NCX), significantly suppressed the response to apelin ( P <0.001). Perforated patch-clamp recordings showed that apelin did not modulate L-type Ca ²⁺ current or voltage-activated K ⁺ currents in isolated adult rat ventricular myocytes. Apelin mRNA was markedly downregulated in cultured neonatal rat ventricular myocytes subjected to mechanical stretch and in vivo in two models of chronic ventricular pressure overload. The present study provides the first evidence for the physiological significance of apelin in the heart. Our results show that apelin is one of the most potent endogenous positive inotropic substances yet identified and that the inotropic response to apelin may involve activation of PLC, PKC, and sarcolemmal NHE and NCX.

Objective Cardiac mast cells participate in myocardial dysfunction, but the mechanisms are presently unknown. Design By examining spontaneously hypertensive rats (SHRs) during their entire lifespan, we attempted to define the role of mast cells in the induction of cardiac hypertrophy and transition to heart failure. Methods and results By contrast to normotensive littermates, hearts of newborn SHRs already contained mast cells. In the prehypertensive (2-week-old) SHRs, the increased expression of c-kit and soluble stem cell factor correlated with an increased number of cardiac mast cells. The mast cells contained tumour necrosis factor-α which, together with nuclear factor kappa-B (NF-κB) and interleukin (IL)-6, was significantly induced in the prehypertensive SHRs. Stimulation of cardiac mast cells with compound 48/80 in an ex-vivo Langendorff heart perfusion system resulted in increased expression of nuclear factor Kappa-B (NF-κB) (four-fold) and IL-6 (nine-fold) mRNA in the left ventricles of adult rat hearts. In the presence of an inhibitor of mast cell degranulation, disodium cromoglycate, the induced expression of NF-κB and IL-6 was inhibited. In the late hypertensive stage, the hearts of SHRs with advanced cardiac hypertrophy (12-month-old) and heart failure (20-month-old) had significantly increased levels of transforming growth factor (TGF)-β₁ and basic fibroblast growth factor (bFGF), and displayed increased myocardial fibrosis. Activated mast cells were a major source of TGF-β₁ and bFGF, and localized to areas of myocardial fibrosis. Conclusions By synthesizing and secreting prohypertrophic cytokines and profibrotic growth factors, cardiac mast cells participate in the induction of cardiac hypertrophy and cardiac fibrosis, which are the key steps in the transition to heart failure.

Cardiac hypertrophy in response to pressure overload is initially beneficial but eventually leads to heart failure, a major cause of morbidity and mortality in the Western countries. Although abnormalities in left ventricular (LV) diastolic filling are early features associated with pressure overload-induced LV hypertrophy, the molecular mechanisms regulating transition to diastolic heart failure are poorly understood. We analyzed global changes in gene expression in 12-, 16-, and 20-month-old spontaneously hypertensive rats (SHR) and their age-matched controls, Wistar Kyoto rats, using DNA microarrays. In SHR, a progressive LV hypertrophy was associated with increased expression of hypertrophy-associated genes including contractile protein and natriuretic peptide genes. Echocardiography indicated that 16-month-old SHR had features of diastolic dysfunction leading to diastolic failure at age 20 months without significant changes in LV systolic function. Comparison analysis revealed that the extracellular matrix genes strikingly dominated the list of altered genes after transition to the heart failure, whereas there was no major shift in gene expression patterns involved in calcium homeostasis and neurohumoral activation, as well as myofilament contractile and cytoskeletal proteins. The microarray analysis also revealed differential gene expression of several novel factors, such as thrombospondin-4 and matrix Gla protein, as well as unknown expressed sequence tags. Our data show that transition from LV hypertrophy to diastolic hypertensive heart failure is almost exclusively associated with progressive remodeling of the extracellular matrix and provide new insights into the pathogenesis of hypertrophy by suggesting existence of novel regulators of LV remodeling.

Rationale:: The extracellular matrix (ECM) is a major determinant of the structural integrity and functional properties of the myocardium in common pathological conditions, and changes in vasculature contribute to cardiac dysfunction. Collagen (Col) XV is preferentially expressed in the ECM of cardiac muscle and microvessels. Objective:: We aimed to characterize the ECM, cardiovascular function and responses to elevated cardiovascular load in mice lacking Col XV ( Col15a1 ^−/− ) to define its functional role in the vasculature and in age- and hypertension-associated myocardial remodeling. Methods and Results:: Cardiac structure and vasculature were analyzed by light and electron microscopy. Cardiac function, intraarterial blood pressure, microhemodynamics, and gene expression profiles were studied using echocardiography, telemetry, intravital microscopy, and PCR, respectively. Experimental hypertension was induced with angiotensin II or with a nitric oxide synthesis inhibitor. Under basal conditions, lack of Col XV resulted in increased permeability and impaired microvascular hemodynamics, distinct early-onset and age-dependent defects in heart structure and function, a poorly organized fibrillar collagen matrix with marked interstitial deposition of nonfibrillar protein aggregates, increased tissue stiffness, and irregularly organized cardiomyocytes. In response to experimental hypertension, Col15a1 gene expression was increased in the left ventricle of wild-type mice, and mRNA expression of natriuretic peptides (ANP and BNP) and ECM modeling were abnormal in Col15a1 ^−/− mice. Conclusions:: Col XV is necessary for ECM organization in the heart, and for the structure and functions of microvessels. Col XV deficiency leads to a complex cardiac phenotype and predisposes the subject to pathological responses under cardiac stress.

Plastic is a widely utilized material and polyethylene is one of the most used plastic types. Microplastics are plastic particles (size <5 mm) which are primarily a micro-size range or results from degeneration of larger plastic pieces in the environment. Drinking water and food are two main human exposure sources for microplastics and consequently effects of microplastics in gastrointestinal tract are considered important. Still, only little is known how microplastics and plastic associated chemicals affect the human health. The aim of our study was to evaluate the ability of micro-sized polyethylene to cause harmful effects in human intestinal cells. Raw ultra-high molecular-weight polyethylene (size 5-60 μm) was used. In addition, polyethylene particles were extracted with ethanol to determine the effect of extraction process on toxicity of the particles. In the experiments, human colorectal adenocarcinoma Caco-2 and HT-29 cells were exposed to polyethylene (0.25-1.0 mg/ml) or extracts for 48 h. After exposure, cell viability and cytotoxicity were assessed with MTT and lactate dehydrogenase assay. Reactive oxygen species (ROS) production was measured with dichlorofluorescin diacetate and cytoplasmic production of superoxide with dihydroethidium and mitochondrial superoxide production with MitoSOX. The 48-h exposure to polyethylene decreased dose-dependently cell viability and increased oxidative stress, especially mitochondrial superoxide production, in both cell lines. Effects on ROS or cytosolic superoxide production were not observed. Also, exposure to extracts decreased cell viability and increased oxidative stress in cell cultures, but there were differences between cell lines. These effects were most probably caused by the remaining particles rather than the compounds released from the plastic during the extraction. In conclusion, our study shows that micro-sized polyethylene and ethanol-extracted polyethylene in high concentrations decreased cell viability and increased oxidative stress responses in intestinal cells. These results contribute to the existing evidence on potential adverse human health effects of microplastics.