Oxidative status and anti-oxidant enzyme activity during calcium paradox in the rat isolated heart

Heterotopic rat heart transplantation: severe loss of glutathione in 8-hour ischemic hearts

BACKGROUND

Tissue damage caused by reactive oxygen species (ROS) formed during ischemia/reperfusion seems to be an important risk factor in the failure of transplanted hearts. Although endogenous anti-oxidants protect the myocardium against free radical attack under physiologic conditions, their capacity may become limited during severe oxidative stress. Thus, we investigated the effect of 8-hour cold ischemia on the myocardial anti-oxidative defense system in a heterotopic rat heart transplantation model.

METHODS

Lewis rat hearts were subjected to 30 or 480 minutes of 4 degrees C cold ischemia in Bretschneider cardioplegic solution with or without transplantation and reperfusion (30 or 240 minutes) into F344 recipients. Activity levels of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and glutathione S-transferase (GST), and concentrations of glutathione (GSH), glutathione disulfide (GSSG) and lipid hydroperoxides (LOOH) were analyzed in heart homogenates. For histology, cross-sections of the ventricles were stained with hematoxylin-eosin.

RESULTS

Except for GST, enzyme activities and GSSG concentration increased and the glutathione redox ratio (GSH/GSH + 2GSSG) significantly decreased in 480-minute ischemic hearts compared with those with 30-minute ischemia. Reperfusion dramatically decreased both GSH and GSSG and increased LOOH formation but without severe histopathologic findings in the transplants. Applying a tree-structured classifier technique, GSH and LOOH were identified as significant features indicative of transplantation-induced oxidative stress.

CONCLUSIONS

In the present study severe loss of glutathione and formation of LOOH indicated transplantation-induced oxidative stress in the rat heart; therefore, alterations of these parameters may hint at relevant deficits in the myocardial anti-oxidative defense and may also predict subsequent tissue damage.

Role of reactive oxygen species in ischemic preconditioning of subcellular organelles in the heart

Ischemic preconditioning (IPC) is an endogenous adaptive mechanism and is manifested by early and delayed phases of cardioprotection. Brief episodes of ischemia-reperfusion during IPC cause some subtle functional and structural alterations in sarcolemma, mitochondria, sarcoplasmic reticulum, myofibrils, glycocalyx, as well as nucleus, which render these subcellular organelles resistant to subsequent sustained ischemia-reperfusion insult. These changes occur in functional groups of various receptors, cation transporters, cation channels, and contractile and other proteins, and may explain the initial effects of IPC. On the other hand, induction of various transcriptional factors occurs to alter gene expression and structural changes in subcellular organelles and may be responsible for the delayed effects of IPC. Reactive oxygen species (ROS), which are formed during the IPC period, may cause these changes directly and indirectly and act as a trigger of IPC-induced cardioprotection. As ROS may be one of the several triggers proposed for IPC, this discussion is focused on the current knowledge of both ROS-dependent and ROS-independent mechanisms of IPC. Furthermore, some events, which are related to functional preservation of subcellular organelles, are described for a better understanding of the IPC phenomenon.