Apoptotic activity is increased in brain cortex infarct after hypothermic circulatory arrest in a porcine model

Glutamate excitotoxicity mediates neuronal apoptosis after hypothermic circulatory arrest

BACKGROUND

Prolonged hypothermic circulatory arrest results in neuronal cell death and neurologic injury. We have previously shown that hypothermic circulatory arrest causes both neuronal apoptosis and necrosis in a canine model. Inhibition of neuronal nitric oxide synthase reduced neuronal apoptosis, while glutamate receptor antagonism reduced necrosis in our model. This study was undertaken to determine whether glutamate receptor antagonism reduces nitric oxide formation and neuronal apoptosis after hypothermic circulatory arrest.

METHODS

Sixteen hound dogs underwent 2 hours of circulatory arrest at 18 degrees C and were sacrificed after 8 hours. Group 1 (n = 8) was treated with MK-801, 0.75 mg/kg intravenously prior to arrest followed by 75 microg/kg/hour infusion. Group 2 dogs (n = 8) received vehicle only. Intracerebral levels of excitatory amino acids and citrulline, an equal coproduct of nitric oxide, were measured. Apoptosis, identified by hematoxylin and eosin staining and confirmed by electron microscopy, was blindly scored from 0 (normal) to 100 (severe injury), while nick-end labeling demonstrated DNA fragmentation.

RESULTS

Dogs in groups 1 and 2 had similar intracerebral levels of glutamate. However, MK-801 significantly reduced intracerebral glycine and citrulline levels compared with hypothermic circulatory arrest controls. The MK-801 significantly inhibited apoptosis (7.92 +/- 7.85 vs 62.08 +/- 6.28, group 1 vs group 2, p < 0.001).

CONCLUSIONS

Our results showed that glutamate receptor antagonism significantly reduced nitric oxide formation and neuronal apoptosis. We provide evidence that glutamate excitotoxicity mediates neuronal apoptosis in addition to necrosis after hypothermic circulatory arrest. Clinical glutamate receptor antagonists may have therapeutic benefits in ameliorating both types of neurologic injury after hypothermic circulatory arrest.

Cobalt Chloride Pretreatment Attenuates Myocardial Apoptosis After Hypothermic Circulatory Arrest

BACKGROUND

Deep hypothermic circulatory arrest (DHCA) causes myocyte injury as a consequence of ischemia and reperfusion. Previous studies have shown that hypoxia or hypoxia-mimetic agents (cobalt chloride [CoCl2] or deferoxamine [DFX]) limit myocyte necrosis by upregulating the transcription factor hypoxia-inducible factor. However, it remains unknown whether these agents attenuate myocardial apoptosis after DHCA. This study tested the hypotheses (1) that hypoxia, DFX, or CoCl2 preconditioning attenuates myocardial apoptosis during DHCA; and (2) that the protective mechanism involves the altered expression of apoptosis regulatory proteins pAkt (antiapoptotic), Bcl-2 (antiapoptotic), and Bax (proapoptotic).

METHODS

Anesthetized neonatal piglets were randomly assigned to four groups (n = 6 in a group): control (NaCl injection); hypoxia (pO2 of 30 to 40 mm Hg for 3 hours); DFX injection; or CoCl2 injection. Twenty-four hours later, the animals underwent cardiopulmonary bypass (CPB) and 110 minutes of DHCA. One week after CPB, percentage of apoptotic myocytes (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling [TUNEL] assay) and expression of the pAKT, Bcl-2, and Bax were assessed by Western blot.

RESULTS

Although preconditioning with hypoxia and DFX failed to show a protective benefit, CoCl2 pretreatment significantly attenuated myocardial apoptosis (9.3% +/- 4.1%) versus controls (33.8% +/- 9.7%, p = 0.042). That was associated with increased myocardial pAkt expression (0.19 +/- 0.006 in CoCl2 versus 0.12 +/- 0.008 in control, p < 0.001). The expression of Bcl-2 was also significantly higher in the CoCl2 group (0.15 +/- 0.02) versus control (0.11 +/- 0.01, p = 0.007), whereas Bax expression was lower (0.34 +/- 0.04 versus 0.54 +/- 0.03 for control, p < 0.001).

CONCLUSIONS

Preconditioning with CoCl2 before prolonged DHCA in neonatal piglets attenuates myocardial apoptosis by mechanisms involving phosphorylation of Akt, upregulation of the antiapoptotic protein Bcl-2, and decreased expression of the proapoptotic protein Bax.