A new Optical device for the assessment of Mitochondrial Function using NADH Fluorescence in-vivo
Why to Evaluate Mitochondrial Function?
Most of the ATP produced in the cells is synthesized by the mitochondria under aerobic conditions. The efficacy of ATP production is almost 20:1 when oxygen is available. Therefore, monitoring of mitochondrial function will provide direct information on the energy balance in the tissue. The MitoViewer is the ultimate device that enables the monitoring of mitochondrial function, in experimental animals, in vivo.
Why to measure Mitochondrial NADH?
Three enzymes of the respiratory chain are candidate for the evaluation of the oxidative phosphorylation process. Monitoring of Flavoproteins or Cytochrome aa3 redox state is not possible in blood perfused organs under in-vivo conditions due to various artifacts. Therefore NADH fluorescence signal is the best one to evaluate mitochondrial function in vivo.
Principle of NADH monitoring
The tissue is excited by UV light (366 nm) passed via optical fiber to the monitoring site. Mitochondrial NADH (and not NAD+) absorbs the UV light and emits fluorescent light peaking at 450nm. The emitted light from the tissue at 450 nm (Fluorescence signal) and 366 nm (the Reflectance signal) is transferred to the fluorometer via other optical fibers. The changes in the reflected light are correlated to tissue blood volume and also serve to correct the NADH signal for hemodynamic artifacts. The reflected light and the NADH relative levels are displayed continuously in real time.
MitoViewer Main Features:
Typical responses of the mitochondrial function measured by the MitoViewer
Responses to Anoxia (100% nitrogen)
Typical responses of the brain to complete oxygen depletion by exposing the rat to 100% nitrogen. As can be seen, the Fluorescence signal (blue) is elevated due to inhibition of the respiratory chain activity while the Krebs cycle continues to produce NADH. The Reflected light signal (green) is decreasing, as expected under this condition, due to the elevation in blood volume in the monitored tissue. The corrected NADH signal (black) shows a symmetrical increase and decrease during the anoxic cycle.
Effects of an increase in energy consumption by the tissue
It was induced by exposure of the brain to Cortical Spreading Depression (by high level of potassium). In the normoxic brain the oxygen supply is not limited, and accordingly the Fluorescence signal (blue) and the NADH (red) decreased due to the oxidation of NADH. Under this condition the ATP turnover was dramatically increased and the extra oxygen supply was provided by an increase in microcirculatory blood flow. The same response was recorded in the kidney under mannitol infusion.
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