Oxygen free radical damage of isolated cardiomyocytes: comparative protective effect of radical scavengers and calcium antagonists

Measuring and regulating oxygen levels in microphysiological systems: design, material, and sensor considerations

As microfabrication techniques and tissue engineering methods improve, microphysiological systems (MPS) are being engineered that recapitulate complex physiological and pathophysiological states to supplement and challenge traditional animal models. Although MPS provide unique microenvironments that transcend common 2D cell culture, without proper regulation of oxygen content, MPS often fail to provide the biomimetic environment necessary to activate and investigate fundamental pathways of cellular metabolism and sub-cellular level. Oxygen exists in the human body in various concentrations and partial pressures; moreover, it fluctuates dramatically depending on fasting, exercise, and sleep patterns. Regulating oxygen content inside MPS necessitates a sensitive biological sensor to quantify oxygen content in real-time. Measuring oxygen in a microdevice is a non-trivial requirement for studies focused on understanding how oxygen impacts cellular processes, including angiogenesis and tumorigenesis. Quantifying oxygen inside a microdevice can be achieved via an array of technologies, with each method having benefits and limitations in terms of sensitivity, limits of detection, and invasiveness that must be considered and optimized. This article will review oxygen physiology in organ systems and offer comparisons of organ-specific MPS that do and do not consider oxygen microenvironments. Materials used in microphysiological models will also be analyzed in terms of their ability to control oxygen. Finally, oxygen sensor technologies are critically compared and evaluated for use in MPS.

Biologically active constituents of the secretome of human W8B2+ cardiac stem cells

The benefits of adult stem cells for repair of the heart have been attributed to the repertoire of salutary paracrine activities they appear to exert. We previously isolated human W8B2⁺ cardiac stem cells (CSCs) and found they powerfully influence cardiomyocytes and endothelial cells to collectively promote cardiac repair and regeneration. Here, the complexity of the W8B2⁺ CSC secretomes was characterised and examined in more detail. Using ion exchange chromatography to separate soluble proteins based on their net surface charge, the secreted factors responsible for the pro-survival activity of W8B2⁺ CSCs were found within the low and medium cation fractions. In addition to the soluble proteins, extracellular vesicles generated from W8B2⁺ CSCs not only exhibited pro-survival and pro-angiogenic activities, but also promoted proliferation of neonatal cardiomyocytes. These extracellular vesicles contain a cargo of proteins, mRNA and primary microRNA precursors that are enriched in exosomes and are capable of modulating collectively many of the cellular pathways involved in protein metabolism, cell growth, as well as cellular responses to stress and organisation of the extracellular matrix. Thus the W8B2⁺ CSC secretome contains a multitude of bioactive paracrine factors we have now characterised, that might well be harnessed for therapeutic application for cardiac repair and regeneration.

Synthesis and study of new paramagnetic and diamagnetic verapamil derivatives

New derivatives of verapamil (1) modified with nitroxides and their precursors were synthesized and screened for reactive oxygen species (ROS)-scavenging activities. The basic structure was modified by changing the nitrile group to an amide or the methyl substituent on tertiary nitrogen with nitroxides and their reduced forms (hydroxylamine and secondary amines). Among the new verapamil derivatives compound 16B [Mohan, I. K.; Kahn, M.; Wisel, S.; Selvendiran, K.; Sridhar, A.; Carnes, C.A.; Bognár, B.; Kálai, T.; Hideg, K.; Kuppusamy, P. Am. J. Physiol. Heart Circ. Physiol.2009, 296, 140], modified with hydroxylamine salt of 2,2,6,6-tetramethyl-1,2,3,6-tetrahydropyridine-1-yloxyl proved to be the best ROS scavenger in vitro and protected HSMC and CHO cells against H(2)O(2) induced damage.

Potential role and mechanisms of subcellular remodeling in cardiac dysfunction due to ischemic heart disease

Several studies have revealed varying degrees of changes in sarcoplasmic reticular and myofibrillar activities, protein content, gene expression and intracellular Ca-handling during cardiac dysfunction due to ischemia-reperfusion (I/R); however, relatively little is known about the sarcolemmal and mitochondrial alterations, as well as their mechanisms in the I/R hearts. Because I/R is associated with oxidative stress and intracellular Ca-overload, it has been indicated that changes in subcellular activities, protein content and gene expression due to I/R are related to both oxidative stress and Ca-overload. Intracellular Ca-overload appears to induce changes in subcellular activities, protein contents and gene expression (subcellular remodeling) by activation of proteases and phospholipases, as well as by affecting the genetic apparatus, whereas oxidative stress is considered to cause oxidation of functional groups of different subcellular proteins in addition to modifying the genetic machinery. Ischemic preconditioning, which is known to depress the development of both intracellular Ca-overload and oxidative stress due to I/R, was observed to attenuate the I/R-induced subcellular remodeling and improve cardiac performance. It is suggested that a combination therapy with antioxidants and interventions, which reduce the development of intracellular Ca-overload, may improve cardiac function by preventing or attenuating the occurrence of subcellular remodeling due to ischemic heart disease. It is proposed that defects in the activities of subcellular organelles may serve as underlying mechanisms for I/R-induced cardiac dysfunction under acute conditions, whereas subcellular remodeling due to alterations in gene expression may explain the impaired cardiac performance under chronic conditions of I/R.

Lercanidipine: a novel lipophilic dihydropyridine calcium antagonist with long duration of action and high vascular selectivity

Lercanidipine is a new 1,4-dihydropyridine derivative with potent, long-lasting and vascular-selective calcium entry blocking activity. Animal models of hypertension have shown lercanidipine to be potent, with a slow rate of onset and long lasting action and to have minimal or no effects on cardiac contractility. There was no evidence of tolerance after repeated oral treatment, and no effects were found on the autonomic nervous, central nervous, gastrointestinal or respiratory systems at antihypertensive doses. In man, lercanidipine is well absorbed after oral administration, with peak plasma levels occurring approximately 1.5 - 3 h after dosing. The drug is subject to extensive hepatic first pass metabolism with an elimination half-life of 2 - 5 h. With a more sensitive method, a mean terminal elimination half-life of 8 - 10 h was defined. Despite this short plasma half-life the drug has a long duration of action, most likely due to the high lipophilicity of lercanidipine and its partitioning in to the lipid bilayer of cell membranes, followed by diffusion to the receptor binding site. The efficacy of lercanidipine has been established in extensive clinical trials with comparison to both placebo and standard well-established antihypertensive therapies. These trials confirmed the efficacy of lercanidipine and its long duration of action which renders it suitable for once daily administration. Tolerability was good in all studies: the adverse event profile was comparable to that of placebo at lower doses, with a low incidence of palpitations and ankle oedema. Lercanidipine is a recently introduced example of a lipophilic and vasoselective dihydropyridine calcium antagonist which is an effective antihypertensive drug with a slow onset and long duration of action; it is associated neither with reflex tachycardia nor cardio-depressant activity.

Regional differences of superoxide dismutase activity enhance the superoxide–induced electrical heterogeneity in rabbit hearts

During myocardial ischemia and the subsequent reperfusion, free radicals are important intermediates of the cellular damage and rhythm disturbances. We examined the effects of superoxide radicals or hydrogen peroxide (H(2)O(2)) on the action potentials in isolated rabbit Purkinje fibers, atrial muscle and ventricular muscle. Reactive oxygen species (ROS) donors such as adriamycin, xanthine/xanthine oxidase and menadione induced prolongation of APD(90) in Purkinje fibers. Menadione (30 microM), the most specific superoxide radical donor, prolonged the action potential duration at 90% repolarization (APD(90)) by 17% in Purkinje fibers, whereas it shortened the APD by 57% in ventricular muscle, and it did not affect the atrial APD. All these menadione-induced effects were completely blocked by 2,2,6,6-tetramethyl- 1-peperadinyloxy, a superoxide radical scavenger. Superoxide dismutase (SOD) activity was lowest in Purkinje fibers, it was moderate in atrial muscle and highest in ventricular muscle. H(2)O(2) shortened the APDs of all three cardiac tissues in a concentration-dependent manner. These results suggest that the different electrical responses to O(2) ([Symbol: see text]-) in different cardiac regions may result from the regional differences in the SOD activity, thereby enhancing the regional electrical heterogeneity.

Role of oxidative stress in cardiovascular diseases

OBJECTIVES

In view of the critical role of intracellular Ca2 overload in the genesis of myocyte dysfunction and the ability of reactive oxygen species (ROS) to induce the intracellular Ca2+-overload, this article is concerned with analysis of the existing literature with respect to the role of oxidative stress in different types of cardiovascular diseases.

OBSERVATIONS

Oxidative stress in cardiac and vascular myocytes describes the injury caused to cells resulting from increased formation of ROS and/or decreased antioxidant reserve. The increase in the generation of ROS seems to be due to impaired mitochondrial reduction of molecular oxygen, secretion of ROS by white blood cells, endothelial dysfunction, auto-oxidation of catecholamines, as well as exposure to radiation or air pollution. On the other hand, depression in the antioxidant reserve, which serves as a defense mechanism in cardiac and vascular myocytes, appears to be due to the exhaustion and/or changes in gene expression. The deleterious effects of ROS are mainly due to abilities of ROS to produce changes in subcellular organelles, and induce intracellular Ca2+-overload. Although the cause-effect relationship of oxidative stress with any of the cardiovascular diseases still remains to be established, increased formation of ROS indicating the presence of oxidative stress has been observed in a wide variety of experimental and clinical conditions. Furthermore, antioxidant therapy has been shown to exert beneficial effects in hypertension, atherosclerosis, ischemic heart disease, cardiomyopathies and congestive heart failure.

CONCLUSIONS

The existing evidence support the view that oxidative stress may play a crucial role in cardiac and vascular abnormalities in different types of cardiovascular diseases and that the antioxidant therapy may prove beneficial in combating these problems.

Lipid peroxidation, antioxidative enzyme activities, and cytosolic free calcium levels in rat hippocampus-derived cells exposed to free radicals

To elucidate mechanisms of free radical-induced neuronal cell death, lipid peroxidation measured as thiobarbituric acid-reactive substances (TBARS), three antioxidative enzyme activities (superoxide dismutase, glutathione peroxidase, and catalse), and cytosolic free Ca2+ (Ca2+i) were examined in rat hippocampus-derived cells (HV16-4) exposed to free radicals generated by a hypoxanthine-xanthine oxidase system. The viability of cells decreased with an increase in numbers of free radical positive cells in a dose-dependent manner of xanthine oxidase. The protein-bound TBARS did not change, whereas free TBARS increased at 135% of initial value. No remarkable change was observed in three antioxidative enzyme activities. On the other hand, Ca2+i increased after exposure followed by cell death. Furthermore, the addition of Co2+, a nonspecific Ca2+ channel blocker, delayed the increase of Ca2+i and subsequent cell death. These findings suggested that the influx of Ca2+ played a crucial role for HV16-4 cell death induced by free radicals.