Mild hypothermia mitigates post-ischemic neuronal death following focal cerebral ischemia in rat brain: immunohistochemical study of Fas, caspase-3 and TUNEL

Systemic hypothermia, but not regional gut hypothermia, improves survival from prolonged hemorrhagic shock in rats

BACKGROUND

Extracorporeal blood perfusion of the gut or enterectomy can improve survival during hemorrhagic shock (HS), suggesting that the gut may be of primary importance in resuscitation. We hypothesized that cooling the gut alone could improve survival in a rat HS model and avoid potential deleterious effects of systemic hypothermia.

METHODS

Thirty-two Sprague-Dawley rats were anesthetized with halothane. The gut (small intestine, cecum, and colon) was exteriorized. The right atrial (T ), rectal, and gut (T ) intraluminal temperatures were monitored. HS was induced by withdrawal of 2 mL of blood per 100 g body weight over 10 minutes. Mean arterial pressure was then maintained at 35 to 40 mm Hg to HS 90 min. From HS 20 min to resuscitation time 1 h, rats were randomized into four groups (n = 8 each): normothermia (T and T approximately 38.0 degrees C), gut-25 degrees C (T approximately 38 degrees C, T approximately 25 degrees C, induced by rinsing the gut with cooled saline), gut-33 degrees C (T approximately 38 degrees C, T approximately 33 degrees C), and systemic hypothermia (T approximately 33 degrees C, T approximately 25 degrees C). At HS 90 min, shed blood and Ringer's solution were infused to restore normotension. Survival, metabolism, and tissue damage were observed to 72 hours.

RESULTS

Blood pressure was not different between groups. Compared with the normothermia group, the systemic hypothermia group had lower base deficit and lactate, and needed less fluid during resuscitation for normotension (p < 0.05), but these values were not different in the gut hypothermia groups. In addition, there were no significant improvements in tissue protection induced by regional gut hypothermia, whereas the systemic hypothermia group had lower plasma potassium, lower ornithine carbamoyltransferase (marker of liver injury), and higher glucose levels after HS (all p < 0.05). All rats in the systemic hypothermia group survived to 72 hours, whereas there was only one survivor in the normothermia group, two in the gut-33 degrees C group, and none in the gut-25 degrees C group (all p < 0.05 vs. systemic hypothermia).

CONCLUSION

Cooling the gut alone does not improve acute survival from HS, suggesting that early deaths are not secondary to gut ischemia. Mild systemic hypothermia allowed 100% survival from prolonged HS.

Effects of mild and moderate hypothermia on apoptosis in neuronal PC12 cells

BACKGROUND

There is still a possibility that mild hypothermic therapy may be useful as a neuroprotective tool during the intraoperative period, although the mechanism of cerebral protection by mild hypothermia is not well understood. We hypothesized that mild hypothermia may be protective against cerebral ischaemia by inhibiting post-ischaemia apoptosis. In this study, we used serum-deprived PC12 cells as the neuronal apoptotic model and examined the direct effects of mild and moderate hypothermia.

METHODS

Apoptosis was induced by depriving the cell culture medium of serum, which is one of the most representative methods to induce apoptosis, but not necrosis, in PC12 cells. Effects of mild (35 and 33 degrees C) and moderate (31 and 29 degrees C) hypothermia on apoptosis were evaluated. Cytotoxicity (lactate dehydrogenase leakage) and the percentage of apoptotic cells (calculated by flow cytometry with propidium iodide) were evaluated 4 days after induction of apoptosis. As a control, cells without induction of apoptosis were incubated under the same conditions as the apoptosis group.

RESULTS

Without induction at 37 degrees C, cytotoxicity and the percentage of apoptotic cells were over 60 and 90%, respectively. At each temperature examined below 35 degrees C, significant decreases in cytotoxicity and the percentage of apoptotic cells were observed. Mean cytotoxicity at 31 and 29 degrees C was 50.2 (SD 4.2)% and 47.9 (4.4)%, respectively. The percentage of apoptotic cells at 31 and 29 degrees C was 42.5 (7.4)% and 36.5 (7.3)%, respectively. In the control group, cytotoxicity and the percentage of apoptotic cells were significantly higher at 29 degrees C than at 37 degrees C.

CONCLUSIONS

Mild and moderate hypothermia (29-35 degrees C) inhibited apoptosis, although hypothermia below 30 degrees C may induce apoptosis in intact cells.

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

OBJECTIVE

It has been shown that apoptosis contributes to neuronal cell death after ischemia, and we evaluated the degree of apoptotic activity occurring in brain cortex of pigs after hypothermic circulatory arrest (HCA).

DESIGN

Thirty-one pigs underwent 75 min of HCA at 20 degrees C. Histological examination of the brain was performed, and slides of brain cortex were evaluated for apoptotic activity by the TUNEL method.

RESULTS

Ten animals died during the first postoperative day and 21 survived until the seventh postoperative day. Brain cortex infarcts were found in animals that survived 7 days and these were included in this study. The median histopathological score among animals that died on the first postoperative day was 3.0 (range, 2-4), whereas it was 4.0 (range, 2-4) among survivors (p = 0.019). The apoptotic index was particularly high in the area of the infarct, whereas only a few TUNEL-stained cells were observed in noninfarcted areas. The apoptotic index was nil in all pigs that died in the first postoperative period, whereas it was 2.0 (range, 0-6) among the animals that survived until the seventh postoperative day (p < 0.0001).

CONCLUSION

The apoptotic index was significantly increased in brain cortex infarcts of animals that survived 7 days after HCA, whereas only a few apoptotic cells were observed in noninfarcted areas of these animals as well as in animals that died on the first postoperative day. Further studies are required to elucidate the timing of development of brain infarction after HCA and whether neuroprotective strategies targeting the apoptotic process may mitigate brain damage.

Hypothermic protection of the ischemic heart via alterations in apoptotic pathways as assessed by gene array analysis

Hypothermia improves resistance to ischemia in the cardioplegia-arrested heart. This adaptive process produces changes in specific signaling pathways for mitochondrial proteins and heat-shock response. To further test for hypothermic modulation of other signaling pathways such as apoptosis, we used various molecular techniques, including cDNA arrays. Isolated rabbit hearts were perfused and exposed to ischemic cardioplegic arrest for 2 h at 34 degrees C [ischemic group (I); n = 13] or at 30 degrees C before and during ischemia [hypothermic group (H); n = 12]. Developed pressure, the maximum first derivative of left ventricular pressure, oxygen consumption, and pressure-rate product (P < 0.05) recovery were superior in H compared with in I during reperfusion. mRNA expression for the mitochondrial proteins, adenine translocase and the beta-subunit of F1-ATPase, was preserved by hypothermia. cDNA arrays revealed that ischemia altered expression of 13 genes. Hypothermia modified this response to ischemia for eight genes, six related to apoptosis. A marked, near fivefold increase in transformation-related protein 53 in I was virtually abrogated in H. Hypothermia also increased expression for the anti-apoptotic Bcl-2 homologue Bcl-x relative to I but decreased expression for the proapoptotic Bcl-2 homologue bak. These data imply that hypothermia modifies signaling pathways for apoptosis and suggest possible mechanisms for hypothermia-induced myocardial protection.

Moderate hypothermia in severe head injuries: the present and the future

The use of therapeutic moderate hypothermia for treating severe traumatic brain injury has been reported for more than 50 years. However, the most intense investigation of this treatment has occurred during the last 10 to 15 years. Virtually all preclinical studies have documented a robust treatment effect, not only in terms of reduced excitotoxicity and cerebral acidosis, but also in terms of histologic preservation and improved behavioral outcomes. Several single-center and small multicenter clinical trials conducted during the last decade also demonstrated benefit of early and late therapeutic hypothermia. However, a multicenter trial reported in February 2001 that included nearly 400 patients found no notable differences in neurologic outcomes in matched patients with head injuries who were treated with 48 hours of therapeutic moderate hypothermia compared with those kept at normal temperature. Findings from this study did suggest that rapid rewarming of patients with head injuries may be deleterious. A subgroup of young patients (less than 45 years of age) who were kept normovolemic showed a trend toward improved outcomes when treated with hypothermia. Current investigations, particularly in the preclinical arena, are focusing on combination therapy. To date, however, the addition of fibroblast growth factor, cyclosporine, or interleukin (IL)-10 to therapeutic moderate hypothermia has not been found to provide greater benefit than either therapy when used alone. Future investigations are aimed at further identifying the physiologic mechanisms responsible for secondary brain injury and ways in which other novel combination therapies may be expected to improve outcomes.