Reversible and irreversible damage in reoxygenated 'ischemic' ventricular myocytes in culture

Elucidating the role of hypoxia/reoxygenation in hippocampus-dependent memory impairment: do SK channels play role?

Professionals and mountaineers often face the problem of reperfusion injury due to re-oxygenation, upon their return to sea-level after sojourn at high altitude. Small conductance calcium-activated potassium channels (SK channels) have a role in regulating hippocampal synaptic plasticity. However, the role of SK channels under hypoxia-reoxygenation (H/R) is unknown. The present study hypothesized that SK channels play a significant role in H/R induced cognitive dysfunction. Sprague-Dawley rats were exposed to simulated HH (25,000 ft) continuously for 7 days followed by reoxygenation periods 3, 6, 24, 48, 72 and 120 h. It was observed that H/R exposure caused impairment in spatial memory as indicated by increased latency (p < 0.001) and pathlength (p < 0.001). The SK1 channel expression increased upon HH exposure (102.89 ± 7.055), which abrogated upon reoxygenation. HH exposure results in an increase in SK2 (CA3, 297.67 ± 6.69) and SK3 (CA1, 246 ± 5.13) channels which continued to increase gradually upon reoxygenation. The number of pyknotic cells (24 ± 2.03) (p < 0.01) and the expression of caspase-3 increased with HH exposure, which continued in the reoxygenation group (177.795 ± 1.264). Similar pattern was observed in lipid peroxidation (p < 0.001), LDH activity (p < 0.001) and ROS production (p < 0.001). A positive correlation of memory, cell death and oxidative stress indicates that H/R exposure increases oxidative stress coupled with SK channel expression, which may play a role in H/R-induced cognitive decline and neurodegeneration.

Relation of serum lactate dehydrogenase to coronary artery disease

Serum lactate dehydrogenase (LDH) is known pathologic marker for a diversity of diseases, including myocardial ischemia. Strenuous and enduring physical activity can transiently induce a greater total LDH level, still within its normal range. To date, however, it has not been determined whether normal-range LDH might be inversely associated with coronary artery disease (CAD) in the low-cardiovascular-risk, physically active, adult population. We conducted a retrospective cohort analysis. A total of 5,519 healthy adults aged 34 to 86 years were followed up for a mean period of 4.2 years. The cohort incidence of CAD was 6.1% (338 cases) from 2001 to 2009. In the present cohort, greater mean LDH levels were significantly associated with a greater number of years, days/week, and minutes/week of leisure time activity (p = 0.02, p = 0.04, and p = 0.01, respectively). These associations were externally validated successfully by analysis of all 5,064 healthy participants aged ≥40 years with normal-range LDH from the 2007 to 2010 National Health and Nutrition Examination Surveys combined. For instance, the mean LDH level was significantly greater in those engaged in 6 to 7 versus 1 to 5 days/wk of vigorous-intensity work activity (138.0 ± 20.7 IU/L vs 133.3 ± 21.7 IU/L, respectively, p = 0.007). In our cohort, the hazard ratio for CAD according to the normal total serum LDH tertiles, adjusted for multiple risk and protective CAD factors in a Cox proportional hazards model, was 0.70 (95% confidence interval 0.54 to 0.92) in the greater versus lower tertile (p for trend = 0.01). In conclusion, we suggest that increased normal-range total serum LDH is associated with reduced short-term risk of CAD outcome in this low-risk, physically active population.

Paradoxical Toxicity of Cardioplegic Compounds on Ischemic Cardiomyocyte Using Optimal Design Strategy

BACKGROUND

The aim of this study was to evaluate the effects of major components of cardioplegic solutions on myocardial tissue submitted to prolonged cold ischemia.

METHODS

Our methodology was based on the simultaneous testing in the same series of experiments of many compounds (19 in number), which were included in the composition of 20 established solutions. All the experiments were performed by a matricial-predefined protocol that allows the evaluation of the protective or toxic effects of each of these 19 compounds. Pig hearts were removed and left ventricular myocardiums were cut into 320 pieces. For each solution tested, 8 pieces of myocardial tissue were incubated at 4 degrees C for 24 hours and 8 other pieces were incubated for 72 hours. At the end of incubation period, tissue injury was assessed by measuring the leakage of myocardial enzymes(glutamic-oxaloacetic transaminase, lactate dehydrogenase, creatine phosphokinase) into the incubation medium. Initially, the effects of each solution were evaluated, and then a mathematical analysis was performed and the effects of each compound deduced.

RESULTS

After the 24-hour incubation period, pyruvate (5 mmol/liter), polyethylene glycol (5 mmol/liter), Ala-Gln (20 mmol/liter), and reduced glutathione (3 mmol/liter) showed toxic effects, whereas ethanol (1%) and calcium chloride (2 mmol/liter) seemed to be protective. After 72 hours' incubation, similar data were obtained; dextran 70 (0.57 mmol/liter) was also found to be deleterious.

CONCLUSIONS

The results revealed surprising myocardial toxicity (enzymatic release) from components included in cardioplegic solutions. Some components would induce metabolic activation during prolonged hypothermic ischemia, which may be inappropriated and which may perhaps exacerbate damages by increasing membrane ruptures. This concept confirms eventual discrepant effects of preservative compounds on cardiomyocyte membrane during deep hypothermia, according to the metabolic state of the cell.

Metallothionein-overexpressing neonatal mouse cardiomyocytes are resistant to H2O2 toxicity

To study cellular and molecular events of cardiac protection by metallothionein (MT) from oxidative injury, a primary neonatal cardiomyocyte culture was established from a specific cardiac MT-overexpressing transgenic mouse model. Ventricular cardiomyocytes were isolated from 1- to 3-day-old neonatal mice and cultured in an Eagle's minimum essential medium supplemented with 20% fetal bovine serum under an atmosphere of 5% CO2-95% air at 37 degreesC. Forty-eight hours after plating was completed, the purity of such cultures was 95% myocytes, assessed by an immunocytochemical assay. Over 80% of the cardiomyocytes beat spontaneously on the first day of culture and synchronously in a confluent monolayer after the sixth day of culture. Cellular MT concentrations in the transgenic cardiomyocytes before culturing and on the sixth day postculturing were about seven- and twofold higher than nontransgenic controls, respectively. However, there were no significant differences in cell morphology, glutathione content, and antioxidant enzymatic activities between these two types of cardiomyocytes. When these cells were challenged by H2O2, the transgenic cardiomyocytes displayed a significant resistance to the toxic effect of this oxidant, as measured by cell viability, lactate dehydrogenase leakage, and morphological alterations. In addition, the transgenic cells were highly protected from H2O2-induced lipid peroxidation. These observations demonstrate that MT protects the cultured cardiomyocytes from H2O2 toxicity by preventing its interaction with macromolecules such as lipids, and this cultured primary neonatal mouse cardiomyocyte system provides a valuable tool to directly study cellular and molecular events of MT in cardiac protection against oxidative injury.