Local cerebral glucose utilization in chronic middle cerebral artery occlusion in the cat

Imaging of a clinically relevant stroke model: glucose hypermetabolism revisited

BACKGROUND AND PURPOSE

Ischemic stroke has been shown to cause hypermetabolism of glucose in the ischemic penumbra. Experimental and clinical data indicate that infarct-related systemic hyperglycemia is a potential therapeutic target in acute stroke. However, clinical studies aiming for glucose control in acute stroke have neither improved functional outcome nor reduced mortality. Thus, further studies on glucose metabolism in the ischemic brain are warranted.

METHODS

We used a rat model of stroke that preserves collateral flow. The animals were analyzed by [2-(18)F]-2-fluoro-2-deoxy-d-glucose positron emission tomography or magnetic resonance imaging during 90-minute occlusion of the middle cerebral artery and during 60 minutes after reperfusion. Results were correlated to magnetic resonance imaging of cerebral blood flow, diffusion of water, lactate formation, and histological data on cell death and blood-brain barrier breakdown.

RESULTS

We detected an increased [2-(18)F]-2-fluoro-2-deoxy-d-glucose uptake within ischemic regions succumbing to infarction and in the peri-infarct region. Magnetic resonance imaging revealed impairment of blood flow to ischemic levels in the infarct and a reduction of cerebral blood flow in the peri-infarct region. Magnetic resonance spectroscopy revealed lactate in the ischemic region and absence of lactate in the peri-infarct region. Immunohistochemical analyses revealed apoptosis and blood-brain barrier breakdown within the infarct.

CONCLUSIONS

The increased uptake of [2-(18)F]-2-fluoro-2-deoxy-d-glucose in cerebral ischemia most likely reflects hypermetabolism of glucose meeting increased energy needs of ischemic and hypoperfused brain tissue, and it occurs under both anaerobic and aerobic conditions measured by local lactate production. Infarct-related systemic hyperglycemia could serve to facilitate glucose supply to the ischemic brain. Glycemic control by insulin treatment could negatively influence this mechanism.

14 C-deoxyglucose imaging overestimates myocardial viability in subacute infarction of rats

Clinical studies using 18F-fluorodeoxyglucose suggest that this tracer may overestimate myocardial viability. This study aimed to elucidate whether 2-deoxyglucose accurately indicates myocardial viability at the early phase of myocardial infarction. Autoradiography with 14C-deoxyglucose was performed in fasting rats whose left coronary artery was occluded for 60 min and then reperfused. 14C-deoxyglucose was injected 30 min after the reperfusion (acute; n=10) or 1 week later (subacute; n=9). Infarction and risk areas were identified by triphenyl tetrazolium chloride or haematoxylin-eosin staining and methylene blue, respectively. Immuno-histochemical staining using anti-glucose transporter 1 and 4 antibodies was performed. At the acute stage, the uptake of deoxyglucose was consistent with the grade of anti-glucose transporter 4 expression. At the subacute stage, the uptake of deoxyglucose in poorly viable myocardium (543.4+/-343.7%: normalized with the uptake at the right ventricle) as well as in the viable one (335.2+/-149.8%) in the risk area was significantly greater than that in the remote area (116.4+/-94.9%, P<0.01). Anti-glucose transporter 1 was expressed in the poorly viable area where inflammatory cells infiltrated. It is concluded that deoxyglucose uptake by inflammatory cells which express anti-glucose transporter 1 causes overestimation of myocardial viability at subacute stage.

Application of PET-MRI registration techniques to cat brain imaging

In positron emission tomography (PET) studies of diseased animals, it is very useful to have accurate anatomical information as a reference. In human studies, anatomical information is usually obtained from magnetic resonance imaging (MRI) of the subject with retrospective registration of the subject's PET image to the MRI. A number of PET-MRI registration techniques are used for this purpose. However, the utility of these methods has not been tested for animals image registration. This paper studies the feasibility of applying two currently used human brain PET-MRI registration techniques to cat brain images.

METHODS

Three cats were anesthetized with isoflurane gas, and PET images were acquired with H(2)(15)O, benzodiazepine receptor ligand 11C-flumazemil (FMZ), dopamine receptor ligand 11C-nemonapride (NEM) and fluorodeoxy glucose (18F-FDG). The four PET scans were acquired consecutively within the same day while the cat remained fixed in the scanner. We also obtained T1-weighted and T2-weighted MRI of the cats in a 4.7 T unit. The PET images were registered to MRI using two human brain registration techniques: a semi-automatic method (SAM), which is a two-step method based on the extraction of the midsagittal plane, and an automatic method (AMIR) method that minimizes PET pixel variance within spatially connected segments determined by MRI.

RESULTS

T2-weighted MRI provided better structural information than T1 MRI. FMZ did, while FDG or H(2)O PET images did not, provide a structural outline of the brain. The FMZ PET image was registered to MRI satisfactorily using SAM. The striatum visualized in nemonapride PET image re-sliced with the same parameters matched the striatum identified in T2-weighted MRI. Registration by AMIR was successful by inspection for FMZ, FDG or H(2)O PET images in only one of the three cats. The registration error of SAM was estimated to be less than 2 mm or 2 degrees.

CONCLUSION

A satisfactory registration of FMZ-PET to T2-weighted MRI of the cat brain was obtained by a two-step manual registration technique. This will enhance the usefulness of PET in the field of cerebral pathophysiology.

The sequential change of local cerebral blood flow and local cerebral glucose metabolism after focal cerebral ischaemia and reperfusion in rat and the effect of MK-801 on local cerebral glucose metabolism

In order to investigate the time course change of local cerebral blood flow (1CBF) and local cerebral glucose metabolism (ICGM) and the effect of MK-801 (dizocilpine), an NMDA receptor antagonist on glucose metabolism in a middle cerebral artery occlusion-reperfusion model, 14C-Iodo-antipyrine and 14C-Deoxyglucose autoradiographic method have been used. The 1CBF was reduced to 0-10% of the control level in the ischaemic core and to 12-40% in the ischaemic penumbra between 60 and 120 min after the onset of the ischaemia. In the ischaemic core, the marked hyperfusion appeared at 15 min and maintained about 30 to 45 min following reperfusion. In the ischaemic penumbra, the hyperfusion during reperfusion was not found. Hypermetabolism occurred at 30 min and reached to the peak at 60 min after the middle cerebral artery (MCA) occlusion both in the ischaemic core and in the penumbra. The shift from hyper- to hypometabolism was observed during the ischaemia. The reperfusion following 2 hours of MCA occlusion facilitated the decrease of cerebral glucose metabolism in the ischaemic region. The pretreatment of MK-801 (0.4 mg/kg) inhibited both increased glucose metabolism during the ischaemia and decreased glucose metabolism during the reperfusion. The effect of limiting decreased glucose metabolism during the reperfusion by MK-801 was remarkable in the ischaemic penumbra. These findings support the hypothesis that excitation-induced hypermetabolism play a major role in the ischaemic insult following focal cerebral vascular occlusion.

Functional cerebral activity during regeneration from entorhinal lesions in the rat

The consequences of an unilateral electrolytic entorhinal lesion on the functional activity in all major anatomically defined brain regions were evaluated in the rat. The 14C-2 deoxyglucose method served as a tool to quantify alterations of local cerebral glucose utilization (LCGU) ipsilateral and contralateral to the lesion at 4 days, 2 weeks, or 3 months after stereotaxic surgery. Apart from a few minor increases in the contralateral hemisphere, the predominant pattern consisted of reductions in the range of 10-40% in the ipsilateral hemisphere. Ipsilaterally, in extrahippocampal areas, LCGU had regained control levels at 2 weeks postlesion in contrast to hippocampal regions, where reductions were more pronounced than in other brain areas and partially persisted for up to 3 months. Interestingly, the termination zones of entorhinal fibers in the dentate gyrus did not regain control levels within 3 months. We conclude from the data that functional recovery of denervated primary target areas does not occur within 3 months after entorhinal lesions and that altered functional activity may be found beyond the primary target areas predominantly during the acute recovery period after the lesion. The data suggest that sprouting fibers do not reestablish a fully functional neuronal network during the recovery period.

Lactate production by human monocytes/macrophages determined by proton MR spectroscopy

Elevated brain lactate has been observed by in vivo proton MRS in different pathological situations. The origin of this lactate remains controversial. The possibility that it was produced by the metabolism of phagocytic cells has been proposed. To investigate this hypothesis, the authors have employed high-resolution proton MRS to monitor changes in glucose, lactate, and other metabolites in the medium used to culture human monocyte-derived macrophages in vitro. Results show that the differentiation of human monocytes/macrophages in the presence of physiological stimulating factors (M-CSF or GM-CSF) was associated with an increase in lactate production and glucose utilization. The present results are consistent with the hypothesis that lactate detected by proton MRS in vivo may be produced by the metabolism of macrophages when infiltrates of these cells are present. The possible extrapolation of the authors' finding to the in vivo situation and its relevance are discussed.

Postischemic neuronal damage causes astroglial activation and increase in local cerebral glucose utilization of rat hippocampus

The purpose of the present study was to determine the consequences of postischemic neuronal damage on CMRglc. Forebrain ischemia of 10 min duration was induced in male Wistar rats. The extent of neuronal damage and the numbers of immunocytochemically detected astrocytes in the hippocampal CA1 subfield as well as CMRglc were determined 2, 5, 7, and 14 days after ischemia. CBF was additionally measured 7 days postischemia. CMRglc was decreased in cortical and thalamic structures up to 5 days postischemia, and was normalized again on day 7 after ischemia. In the hippocampal areas, CMRglc was decreased only on day 2 after ischemia, was normalized after 5 days, and increased in the stratum oriens and pyramidale of the CA1 subfield from postischemic day 7 onward. Neuronal damage was clearly demonstrable 5 days after ischemia and further increased up to day 7. The number of GFAP-reactive astrocytes increased markedly at day 7 postischemia. It is assumed that the activation of astrocytes is induced by neuronal damage, and that the astroglial metabolism is responsible for the increase in CMRglc of the CA1 subfield 7 days after ischemia. The decrease in CBF of the CA1 subfield 7 days after ischemia could be caused by a reduced density of perfused capillaries.

Glucose utilization in rat hippocampus after long-term recovery from ischemia

The influence on hippocampal glucose utilization of a transient 10-min forebrain ischemia was quantified in male Wistar rats after 2 and 3 weeks as well as after 3 months by application of the [14C]2-deoxyglucose technique. Ischemia was induced by occlusion of the carotid arteries and simultaneous lowering of the blood pressure to 40 mm Hg. For identification of the hippocampal architecture, sections were stained for perikarya (cresyl violet) and for acetylcholinesterase. The hippocampal regions clearly showed different responses to the ischemic insult. The necrotic pyramidal cells being almost completely removed, significant increases in glucose utilization occurred in most layers of the CA1 sector at 2 and 3 weeks post ischemia, while widespread reductions prevailed in all other sectors and the dentate gyrus. At 3 months after the ischemic insult, glucose utilization was reduced in all hippocampal structures including the CA1 region. The increases in glucose utilization in the CA1 sector are suggested to indicate long-lasting presynaptic hyperexcitation, while the widespread reductions in glucose utilization demonstrate that neuronal activity is also altered in hippocampal areas that do not show major histological damage.