Da West

MR image-guided investigation of regional signal transducers and activators of transcription-1 activation in a rat model of focal cerebral ischemia

BACKGROUND AND PURPOSE STAT-1 is a member of a family of proteins called signal transducers and activators of transcription (STATs), and recent studies have shown its involvement in the induction of apoptosis. There is limited information on the role of STAT-1 following stroke. In this study we use MRI measurements of cerebral perfusion and bioenergetic status to target measurements of regional STAT-1 activity. METHODS Rats were subjected to 60 or 90 min of middle cerebral artery occlusion with and without reperfusion. MRI maps of the apparent diffusion coefficient of water and cerebral blood flow were acquired throughout the study. After the ischemia or reperfusion period, the brain was excised and samples were analyzed by Western blots using anti-phospho-STAT1 and anti-Fas antibodies. Regions were selected for analysis according to their MRI characteristics. RESULTS Transcriptional factor STAT-1 was enhanced in the lesion core and, to a lesser extent, in the lesion periphery, following ischemia and reperfusion. This level of activity was greater than for ischemia alone. Western blots demonstrated STAT-1 phosphorylation on tyrosine 701 and not serine 727 after ischemia and 3 h of reperfusion. Enhanced expression of the apoptotic death receptor Fas was confirmed after ischemia followed by reperfusion. CONCLUSIONS This study demonstrates that focal ischemia of the rat brain can induce STAT-1 activation, particularly following a period of reperfusion. The activation occurs not only in the lesion core, but also in the lesion periphery, as identified using MRI. STAT-1 may play an important role in the induction of cell death following stroke.

416 Cerebral Alanine Increases During the Evolution of Secondary Energy Failure Following Transient Hypoxia-Ischaemia in Newborn Brain

Background: Alanine (Ala), a nonessential amino acid, is present in normal brain at a concentration of ∼0.5 mmol/kg. During acute hypoxia-ischaemia (HI) Ala increases due to decreased flux of pyruvate through the Krebs cycle and the activity of alanine transaminase (AAT). Brain Ala increases in proportion to the severity of HI and may be detected using proton (1H) magnetic resonance spectroscopy (MRS).Aim: To investigate relationships between the severity of secondary (delayed) energy failure (SEF) and late brain Ala metabolite ratios following transient cerebral HI in the newborn piglet.Design/Methods: Seven newborn piglets (<24 hrs old) were studied under general anaesthesia (isoflurane & morphine) before, during and for up to 48 hours following transient HI (reversible bilateral carotid occlusion and 12% FiO2 for 45 min). Whole-brain pulse-acquire phosphorus (31P; repetition time (TR) 10 s) and localised 1H (PRESS, thalamic, echo time 270 ms, TR 5 s) MRS data were acquired serially before, during (31P only), and following HI. Spectra were analysed using AMARES (31P) and LCModel (1H).Results: In two piglets SEF was not observed. In the remaining 5 SEF ranged between mild and severe as quantified by delayed reductions in [phosphocreatine]/[inorganic phosphate] ([PCr]/[Pi]) and [nucleotide triphosphate]/[exchangeable high-energy phosphate pool] ([NTP]/[EPP]) and increases in lactate/total creatine (Lac/Cr).Ala was only detected in the 5 SEF piglets. During SEF evolution we observed progressively increasing thalamic Ala/Cr and Lac/Cr. When the final measurements were compared both Lac/Cr and Ala/Cr separately showed inverse linear correlations with [NTP]/[EPP] and [PCr]/[Pi] (all p<0.05) (Figure 1).Figure 1No Caption Available.Conclusions: Both Ala/Cr and Lac/Cr increased concomitant with the development and proportional to the severity of SEF. These observations are consistent with decreased pyruvate flux through the Krebs cycle and increased flux through lactate-dehydrogenase and AAT during the evolution of SEF leading to concomitant accumulation of Lac and Ala respectively.