In-Vivo Measurement of Cytochrome Using NIRS During Acute Focal Cerebral Ischaemia and Reperfusion in Rats

Abstract

Objectives: Near-infrared spectroscopy (NIRS) based technology allows in-vivo monitoring of focal tissue cytochrome aa₃ (cytochrome-c-oxidase). The aim of this study was to assess early cell alteration during acute focal cerebral ischaemia and reperfusion.

Methods: Focal cerebral ischaemia was induced in 12 rats using an endovascular occlusion technique of the middle cerebral artery (MCA). Occlusion time was 60 minutes followed by reperfusion for another 60 minutes. Monitoring of oxygen saturation (SO₂) and oxidized cytochrome complex (oxid. Cytaa₃) was performed by NIRS via a parietal burr hole before (baseline), during occlusion and reperfusion. Twenty-four hours after MCA occlusion (MCAO) infarction was confirmed by TTC staining.

Results: In all animals SO₂ and oxid. Cytaa₃ immediately decreased to zero during occlusion indicating complete ischaemia. According to the results of NIRS measurements during reperfusion animals were subdivided into two groups. All animals of group A demonstrated identical or even higher levels of SO₂ and oxid. Cytaa₃ compared to baseline. On the contrary, both parameters in group B remained at a distinct lower level compared to baseline (p < 0.05). Average reperfusion/baseline ratios for SO₂ and oxid. Cytaa₃ were 0.8 (± 0.4) and 0.4 (± 0.2), respectively. The results of TTC-staining were distributed to the above mentioned two groups as follows: group A, only lesions in the basal ganglia or little cortical infarction (n = 8); group B, lesions in the basal ganglia and cortical area (n =4 ).

Conclusions: After 1 hour MCAO a subgroup of animals with associated cortical infarction was identified, whose oxid. Cytaa₃ values did not reach baseline values during reperfusion indicating early intracellular disturbance.

Zusammenfassung:

Fragestellung: Die Nahe-Infrarot-Spektroskopie (NIRS) ermöglicht eine In-vivo-Messung von Cytochrom aa₃ (Cytochrom-c-oxidase) im Gewebe. Ziel dieser experimentellen Studie war es, frühe Zellschädigungen während akuter fokaler zerebraler Ischämie und Reperfusion zu erfassen.

Methode: Bei 12 Ratten wurde eine fokale zerebrale Ischämie mittels endovaskulärer Okklusion der A. cerebri media (MCA) induziert. Die Verschlusszeit betrug 60 Minuten, gefolgt von einer Reperfusionsphase über weitere 60 Minuten. Über ein parietales Bohrloch wurde sowohl die Sauerstoffsättigung (SO₂) als auch der oxidierte Anteil des Cytochromkomplexes (oxid. Cytaa₃) mittels NIRS vor (baseline), während und nach Gefäßverschluss gemessen. 24 Stunden nach MCA-Verschluss (MCAO) wurde das Ausmaß des Hirninfarktes mittels TTC-Färbung bestimmt.

Ergebnisse: Während MCAO erreichten SO₂ und oxid. Cytaa₃ bei allen Tieren sofort Nullwerte. Die Tiere wurden in der weiteren Auswertung anhand der NIRS-Messungen in der Reperfusionsphase in zwei Untergruppen eingeteilt. Alle Tiere der Gruppe A zeigten identische oder sogar höhere SO₂- und oxid. Cytaa₃-Werte verglichen mit der baseline. Andererseits erreichten beide Parameter in der Gruppe B während der Reperfusion signifikant niedrigere Werte (p < 0,05). Die durchschnittliche Reperfusion/baseline ratio für SO₂ und oxid. Cytaa₃ der Gruppe B betrugen lediglich 0,8 (± 0,4) und 0,4 (± 0,2). Die TTC-Färbung ergab folgende Resultate bezogen auf beide Gruppen: Gruppe A, nur Infarkte der Stammganglien oder kleiner kortikaler Infarkt (n = 8); Gruppe B, Infarkte der Stammganglien und des Kortex (n = 4).

Schlussfolgerung: Nach 1 Stunde MCAO konnte eine Subgruppe von Tieren mit assoziierten kortikalen Hirninfarkten identifiziert werden. Dabei erreichte das oxid. Cytaa₃ als Ausdruck früher intrazellulärer Störung nicht die Ausgangswerte (baseline).

Key words:

Cytochrome aa₃ - MCA occlusion - NIRS - oxygen saturation - reperfusion

Schlüsselwörter:

Cytochrom aa₃ - MCA-Okklusion - NIRS - O₂-Sättigung - Reperfusion

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