Mitochondrial genome involvement in ischemia/reperfusion-induced adaptive changes in human myocardial cells.

AIM: Following previous studies on the ischemia-induced adaptive changes in human cardiac mitochondria, we examined in the present paper the interaction between nitric oxide-induced (NO) partial inhibition of Cyt. c oxidase (Cyt.OX) and mitochondrial encoded subunit 2 expression. Aim of the study was to investigate specific stages of the biochemical and molecular cascade which takes place in cytoprotective mechanisms of ischemic and reperfused cardiac cell. METHODS: We examined human left ventricle samples obtained from 20 patients undergoing elective valve surgery before aortic cross-clamping, 20+/-2 min (prolonged ischemia), 58+/-5 min after cross-clamping (intermittent ischemia) and 21+/-4 min after reconstitution of coronary blood flow (reperfusion). Cyt.OX activity was determined by spectrophotometric method and adenosine triphosphate (ATP) content using bioluminescent assay. Malondialdehyde (MDA) assumed as reactive oxygen species (ROS) generation marker was determined by high-performance liquid chromatography method. On the same cardiac samples mitochondrial encoded Cyt.OX subunit 2 expression was examined by immunoblot analysis and blu native gel electrophoresis method. Statistical study of obtained data was performed using repeated measures analysis of variance (ANOVA). RESULTS: Prolonged as well intermittent ischemia caused reduction of Cyt.OX activity and ATP, a moderate accumulation of ROS and down-regulation of Cyt.OX subunit 2. When reperfused the cardiomyocytes showed a progressive increase of Cyt.OX activity, ATP pools and Cyt.OX subunit 2 expression. ROS generation was significantly increased by the rapid oxygen re-immission in the cardiac cell. CONCLUSIONS: These data confirm the suggestion that prolonged as well as intermittent ischemia induces activation of cytoprotective mechanisms crucial for cardiac cell survival. Indeed, co-ordinated down-regulation of Cyt.OX activities, ATP pools and mitochondrial encoded Cyt.OX subunit 2 are in favour of an ischemia-activated adaptive mechanism leading to transient and reversible oxidative injury. This observation is confirmed by reduction of apoptosis molecular markers and by complete recovery of mitochondrial oxidative activities in reperfused cardiac tissue.

Signal transduction mechanisms and nitric oxide in hypoxic and ischemic human cardiac ventricular cell.

BACKGROUND: Nitric oxide (NO) plays a well-known role in regulating endocellular adaptive changes to acute hypoxia and ischemia. The reversible inhibition of complex IV of the mitochondrial respiratory chain fulfils a cytoprotective function, whereas the progressive inhibition of complex I and II reveals the onset of irreversible oxidative damage due to persistent NO production in response to prolonged hypoxia and/or ischemia. In hypoxic or ischemic human myocardial cells, death may be caused by apoptosis or necrosis following the activation of the biomolecular signal transduction mechanisms. The activation of MAPK (mitogen-activated protein kinase) followed by ERK (extracellular regulated kinase) and p21waf is necessary in this respect. The myocardial cell is well known for its postmitotic nature and through their activation these kinases aim to repair DNA damaged by oxidative stress in order to guarantee the survival of the cell itself. A direct correlation has been found between the activation of these kinases and NO production. It was decided to carry out this study in hypoxic and ischemic human heart ventricular tissue in order to confirm this connection. METHODS: In 10 patients undergoing cardiac valvular replacement, ventricular samples were collected before aortic clamping, after 15 min of ischemia and after 60 minutes during which the patients received doses of hematic cardioplegic solution at regular intervals. RESULTS: The results show a rapid increase in NO production in response to ischemia followed by a tendency for levels of this element to fall. MAPK, ERK and p21waf activation was parallel to No production, irrespective of the repeated administration of hematic cardioplegic solution. The heart tissue examined 60 minutes after aortic clamping came from a ventricular area subject to preconditioning mechanisms. In view of this, the data obtained must be seen in terms of the close correlation between the mitochondrial action played by NO and the contemporary and consequent activation of unique signal transduction mechanisms. CONCLUSIONS: This may prove important to our understanding of preconditioning mechanisms involving the myocardial and confirms the role played by the said kinases with regard to the survival of hypoxic and ischemic human heart tissue. Although not final, these deductions may be important in clinical and therapeutic terms for the management of critical patients.

The effect of marathon running on carnitine metabolism and on some aspects of muscle mitochondrial activities and antioxidant mechanisms.

Carnitine is an essential co-factor in the catabolism of fats as an energy source. The primary purpose of this study was to investigate the effect of running a marathon on the metabolism of carnitine by endurance-trained athletes, and to evaluate the effect of carnitine administration on the performance of such exercise. The effects of marathon running on mitochondrial enzymes and cellular anti-oxidants were also examined to assess whether the expression of these activities is altered by exercise. Subjects were 10 experienced male marathon runners aged between 19 and 25 years. Running a marathon caused a fall in the plasma content of unesterified carnitine (37%) and an increase in the level of acetylcarnitine present (288%). Loading of the athletes with L-carnitine for 10 days before running a marathon abolished the exercise-induced fall in plasma-free carnitine (P less than 0.05) whilst amplifying the production of acetylcarnitine (P less than 0.05). Carnitine loading of the athletes studied made no detectable improvement in performance of the marathon (P greater than 0.05). Cytochrome oxidase, succinate cytochrome C reductase and superoxide dismutase activities present in skeletal muscle were unaltered by marathon running. However, such exercise caused a large increase in the tissue content of oxidized glutathione (189%) at the expense of reduced glutathione (-18%).