Molecular cloning, sequencing and expression analysis of a fatty acid transport gene in rat heart induced by ischemic preconditioning and oxidative stress

Mechanisms of the beneficial actions of ischemic preconditioning on subcellular remodeling in ischemic-reperfused heart

Cardiac function is compromised by oxidative stress which occurs upon exposing the heart to ischemia reperfusion (I/R) for a prolonged period. The reactive oxygen species (ROS) that are generated during I/R incur extensive damage to the myocardium and result in subcellular organelle remodeling. The cardiac nucleus, glycocalyx, myofilaments, sarcoplasmic reticulum, sarcolemma, and mitochondria are affected by ROS during I/R injury. On the other hand, brief periods of ischemia followed by reperfusion, or ischemic preconditioning (IPC), have been shown to be cardioprotective against oxidative stress by attenuating the cellular damage and alterations of subcellular organelles caused by subsequent I/R injury. Endogenous defense mechanisms, such as antioxidant enzymes and heat shock proteins, are activated by IPC and thus prevent damage caused by oxidative stress. Although these cardioprotective effects of IPC against I/R injury are considered to be a consequence of changes in the redox state of cardiomyocytes, IPC is considered to promote the production of NO which may protect subcellular organelles from the deleterious actions of oxidative stress. The article is intended to focus on the I/R-induced oxidative damage to subcellular organelles and to highlight the cardioprotective effects of IPC. In addition, the actions of various endogenous cardioprotective interventions are discussed to illustrate that changes in the redox state due to IPC are cardioprotective against I/R injury to the heart.

Role of oxidants in the signaling pathway of preconditioning

This review focuses on the possible role of reactive oxygen species in the pathogenesis of this phenomenon. Evidence in support of a role of oxidants in preconditioning has come from the observation that administration of oxygen radical scavengers during the reperfusion period following the initial "preconditioning" ischemia could prevent the phenomenon. In addition, a brief exposure to a low, nontoxic dose of oxygen radicals may reproduce the beneficial effects of ischemic preconditioning, thus suggesting that radicals can directly trigger the preconditioning pathway. To explain the effects of oxidants in this setting, it has been suggested that reperfusion after the initial, "preconditioning" ischemic episode results in the generation of relatively low amounts of oxygen radicals, which are insufficient to determine cell necrosis, but nevertheless could modify cellular activities that have been implicated as mediators of the preconditioning phenomenon. Recent evidence suggests that low levels of oxidants may have a modulatory role on several cell functions. Possible mechanisms of oxidant-mediated protection might be protein kinase C and other kinases, ATP-dependent potassium channels, or changes in sulfhydryl group redox state, while an effect on adenosine metabolism, or the induction of myocardial stunning presumably does not contribute to oxidant-mediated preconditioning. Finally, de novo protein synthesis and gene expression, and increased antioxidant defenses might be involved in the late phase of preconditioning. In summary, available data strongly suggest that oxygen radicals might be possible mediators of preconditioning. However, further investigation is required to clearly elucidate their exact role and mechanisms of action.

The ischemic heart--experimental models

Results obtained by experimental studies of the ischemic heart have been of tremendous importance for the understanding of physiology, biochemistry and lately also the molecular genetics of the heart. Experimental models in use for the study of the ischemic heart involve studies on the integrated organism, experiments with isolated hearts or multicellular preparation, and also studies of cells isolated from the heart. Regional ischemia in the anaesthetized animal has been a standard model. Knowledge about infarct size limitation as well as heart function in acute and chronic ischemia has been obtained based on experiments in a wide variety of species. The isolated perfused heart has been subjected to extensive use. As a result, the understanding of intracellular processes is constantly developing. Cell models and transgenic-mice models represent promising additions. Each model and each species has certain advantages and disadvantages. Variability in susceptibility towards ischemia and reperfusion is also present. The consequences of ischemia can be described as contractile dysfunction and stunning, arrhythmia and infarction each representing different endpoints of injury. The experimental model is also heavily dependent on the endpoint that is chosen for the study. Results obtained in one experimental model can, therefore, not be generalized into universal conclusions about the ischemic heart. With respect to the human and the disease caused by myocardial ischemia, fragments of knowledge put together from different types of experimental models create the background for successful design of potential treatment.

Metabolism of the lipid peroxidation product, 4-hydroxy-trans-2-nonenal, in isolated perfused rat heart

The metabolism of 4-hydroxy-trans-2-nonenal (HNE), an alpha, beta-unsaturated aldehyde generated during lipid peroxidation, was studied in isolated perfused rat hearts. High performance liquid chromatography separation of radioactive metabolites recovered from [3H]HNE-treated hearts revealed four major peaks. Based on the retention times of synthesized standards, peak I, which accounted for 20% radioactivity administered to the heart, was identified to be due to glutathione conjugates of HNE. Peaks II and III, containing 2 and 37% radioactivity, were assigned to 1, 4-dihydroxy-2-nonene (DHN) and 4-hydroxy-2-nonenoic acid, respectively. Peak IV was due to unmetabolized HNE. The electrospray ionization mass spectrum of peak I revealed two prominent metabolites with m/z values corresponding to [M + H]+ of HNE and DHN conjugates with glutathione. The presence of 4-hydroxy-2-nonenoic acid in peak III was substantiated using gas chromatography-chemical ionization mass spectroscopy. When exposed to sorbinil, an inhibitor of aldose reductase, no GS-DHN was recovered in the coronary effluent, and treatment with cyanamide, an inhibitor of aldehyde dehydrogenase, attenuated 4-hydroxy-2-nonenoic acid formation. These results show that the major metabolic transformations of HNE in rat heart involve conjugation with glutathione and oxidation to 4-hydroxy-2-nonenoic acid. Further metabolism of the GS-HNE conjugate involves aldose reductase-mediated reduction, a reaction catalyzed in vitro by homogenous cardiac aldose reductase.