Effect of in vitro ischemic or hypoxic treatment on mitochondrial electron transfer activity in rat brain slices assessed by gas-tissue autoradiography using

Aging: Impact Upon Local Cerebral Oxygenation and Blood Flow With Acute Isovolemic Hemodilution

Data from the neurosurgical critical care arena demonstrate a correlation between cerebral oxygenation, survival, and cognitive function. Transfusion may increase and hemodilution decrease cerebral oxygenation. Both acute and chronic anemia have been associated with cognitive dysfunction. Aggressive blood conservation protocols have been instituted across all age groups without conclusive evidence for their impact upon outcome. Aged subjects are at the greatest risk of cognitive sequelae after major surgery associated with significant blood loss. We hypothesize that cerebral physiologic changes associated with "normal" aging may compromise cerebral oxygenation in the presence of severe anemia.Fischer 344 rats, the NIH National Institute of Aging normal aging rat model, underwent a stepwise isovolemic hemodilution protocol. Age groups (Age Grp) studied were as follows: Age Grp-A (3 months), n=14; Age Grp-B (9 to 12 months), n=14; and Age Grp-C (24 months), n=14. Brain oxygen tension (PBrO2), laser Doppler flow, and mean arterial pressure were measured. Final hemoglobin averaged 6.1+/-0.9 g/dL. PBrO2 levels decreased from a baseline of 18.1+/-4.1 to 17.5+/-6.8 mm Hg (P=0.49), and laser Doppler flow increased by 18+/-20% (P<0.0001) after hemodilution. Employing repeated measures multiple regression, Age Grp (P=0.30) was not a significant controlling covariate of PBrO2 in response to isovolemic hemodilution. PBrO2 levels were actually higher in Age Grp-C animals at all time points of the hemodilution protocol, although this was not statistically significant. Aged animals were also fully capable of mounting a robust local cerebral hyperemic response to the anemic challenge that was not separable from the response of younger animals.

Intracerebral Hemorrhage-Induced Brain Injury Is Aggravated in Senescence-Accelerated Prone Mice

Background and Purpose— In cerebral stroke, the overall mortality rate of older individuals is higher than that of younger individuals. We therefore investigated aging-related changes in brain tissue damage and immune response in response to intracerebral hemorrhage (ICH) in mice.

Methods— ICH was induced by microinjecting autologous whole blood (5 μL) into the striatum of 4- or 14-month-old senescence-accelerated prone (SAMP8) mice or senescence-accelerated resistant (SAMR1) mice.

Results— In all groups, neurological deficits occurred within 6 hours and gradually improved after the first day, but improvement was most delayed in 14-month-old SAMP8 mice. Isolectin B4-positive and amoeboid microglia/macrophages were abundantly distributed around and inside the hemorrhagic lesions in 14-month-old SAMP8 mice. In contrast, myeloperoxidase-immunoreactive neutrophils and reactive astrocytes with intensified glial fibrillary acidic protein–stained processes and swollen cytoplasm did not differ in number or distribution between SAMP8 and SAMR1 mice. Regardless of their age, the immunoreactivity of Mn-SOD, a major antioxidant enzyme in mitochondria, was much weaker in SAMP8 than in SAMR1 mice. The expression of inducible nitric oxide, however, was higher in old SAMP8 mice than in the other experimental groups.

Conclusions— These results suggest that activated microglia/monocytes may aggravate intracerebral hemorrhagic damage in old SAMP8 mice. Further studies on the exact role of activated microglia/monocytes and the altered activities of antioxidant enzymes in old SAMP8 mice may provide useful information for ICH-induced brain injury in relation with aging.

Demonstration of hyperaccumulation of [18F]2-fluoro-2-deoxy-D-glucose under oxygen deprivation in living brain slices using bioradiography

To clarify the mechanism of hyperaccumulation of glucose in acute brain ischemia by PET, changes of glucose metabolism and mitochondrial electron transfer function were examined in living brain slices in vitro during control, hypoxic, and anoxic conditions by positron autoradiography using [(18)F]2-fluoro-2-deoxy-D-glucose ([(18)F]FDG) and [(15)O]oxygen. [(15)O]Oxygen fixation reflecting mitochondrial electron transfer function was reduced and [(18)F]FDG uptake reflecting glucose metabolism was increased in proportion to the strength of oxygen deprivation during anoxia and hypoxia. Mitochondrial electron transfer function decreased with no regional differences, whereas the glucose metabolism was the most enhanced in the hippocampus and thalamus. The enhanced glucose metabolism was associated with an increased glutamate efflux after hypoxia and anoxia. Glucose metabolism was also increased by the addition of glutamate and was attenuated by the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 in the hippocampus and thalamus. The hyperaccumulation of glucose in acute brain ischemia was demonstrated in living brain slices using bioradiography with reduced mitochondrial electron transfer. The activation of NMDA receptors by glutamate during acute brain ischemia might be responsible for hyperutilization of glucose in the hippocampus and thalamus.

Glutathione monoethyl ester provides neuroprotection in a rat model of stroke

Oxidative stress plays an important role in the development of tissue damage following transient focal cerebral ischaemia. Glutathione is a central component in the antioxidant defence of cells. We have previously shown a close association between mitochondrial glutathione loss and cell death following middle cerebral artery (MCA) occlusion. Glutathione monoethyl ester increases cellular glutathione and is particularly effective in increasing the mitochondrial pool. In the present investigation, we infused glutathione monoethyl ester into the third ventricle during 2 h of MCA occlusion and 48 h of reperfusion. Infarct size was reduced from 46% of the total ischaemic hemisphere in saline-treated animals to 16% following ester treatment. Thus, glutathione monoethyl ester provides neuroprotection following transient focal cerebral ischaemia.

In vitro hypoxia and excitotoxicity in human brain induce calcineurin-Bcl-2 interactions

Although pathogenesis of neuronal ischemia is incompletely understood, evidence indicates apoptotic neuronal death after ischemia. Bcl-2, an anti-apoptotic and neuroprotective protein, interacts with calcineurin in non-neuronal tissues. Activation of calcineurin, which is abundant in the brain, may play a role in apoptosis. Using co-immunoprecipitation experiments in biopsy-derived, fresh human cortical and hippocampal slices, we examined possible interactions between calcineurin and Bcl-2. Calcineuin-Bcl-2 interactions increased after exposure in vitro to excitotoxic agents and conditions of hypoxia/aglycia. This interaction may shuttle calcineurin to substrates such as the inositol-1,4,5-tris-phosphate receptor because under these experimental conditions interactions between calcineurin and inositol-1,4,5-tris-phosphate receptor also increased. A specific calcineurin inhibitor, FK-520, attenuated insult-induced increases in calcineurin-Bcl-2 interactions and augmented caspase-3 like activity. These data suggest that Bcl-2 modulates neuroprotective effects of calcineurin and that calcineurin inhibitors increase ischemic neuronal damage.

Development of a transportable incubator for autoradiographic experiments with positron emitter-labeled tracers in living brain tissues

For autoradiography using positron emitter-labeled tracers in living human brain tissues, samples have to be transported to a positron emission tomography (PET) facility. We have developed a transportable apparatus in which slices are incubated in Krebs-Ringer medium with 95% O(2)/5% CO(2) at 34 degrees C. The incubator comprises a polystyrene foam container, inner chamber, heater, thermostat and battery. The container is sealed and oxygen gas is supplied through a filter (pore size 0.2 microm). The gas is evacuated from the container through the filter, to avoid bacterial contamination. Slices (330 microm) of rat brain were arranged on the nylon net of the inner chamber, and lightly fixed in place by covering them with a fine nylon net stretched over a stainless steel ring. The incubation was carried out at a temperature of 34 degrees C maintained by a heater and thermostat, and the medium was bubbled with 95% O(2)/5% CO(2) from a portable gas cylinder. The temperature of the medium in the container was well controlled (34.0+/-0.5 degrees C) for up to 200 min with no positional differences. In the dynamic autoradiographic experiment, the rate of uptake of [(18)F]2-fluoro-2-deoxy-D-glucose (FDG) in sections preincubated for 45 min in the transportable apparatus was no different from that in the sections kept in the usual incubating apparatus. This apparatus may enable autoradiography using positron emitter-labeled tracers in living human brain tissues.