Use of mitochondrial inhibitors to demonstrate that cytochrome oxidase near-infrared spectroscopy can measure mitochondrial dysfunction noninvasivelyin the brain

The use of near-infrared spectroscopy to measure noninvasively changes in t he redox state of cerebral cytochrome oxidase in vivo is controversial. We therefore tested these measurements using a multiwavelength detector in the neonatal pig brain. Exchange transfusion with perfluorocarbons revealed th at the spectrum of cytochrome oxidase in the near-infrared was identical in the neonatal pig, the adult rat, and in the purified enzyme. Under normoxi c conditions, the neonatal pig brain contained 15 mu mol/L deoxyhemoglobin, 29 mu mol/L oxyhemoglobin, and 1.2 mu mol/L oxidized cytochrome oxidase. T he mitochondrial inhibitor cyanide was used to determine whether redox chan ges in cytochrome oxidase could be detected in the presence of the larger c erebral hemoglobin concentration. Addition of cyanide induced full reductio n of cytochrome oxidase in both blooded and bloodless animals. In the blood ed animals, subsequent anoxia caused large changes in hemoglobin oxygenatio n and concentration but did not affect the cytochrome oxidase near-infrared signal. Simultaneous blood oxygenation level-dependent magnetic resonance imaging measurements showed a good correlation with near-infrared measureme nts of deoxyhemoglobin concentration. Possible interference in the near-inf rared measurements from light scattering changes was discounted by simultan eous measurements of the optical pathlength using the cerebral water absorb ance as a standard chromophore. We conclude that, under these conditions, n ear-infrared spectroscopy can accurately measure changes in the cerebral cy tochrome oxidase redox state.