Technique Monitors Oxidative Stress

Brent D. Johnson

Julio F. Turrens and his colleagues at the University of South Alabama in Mobile are exposing liposomes, amino acids and proteins such as bovine serum albumin to different peroxides to identify the wavelengths that are associated with oxidative stress. The experiments may enable the development of a noninvasive method to quantify oxidative stress and may lead to possible treatments.

There is a constant, steady state between oxidants and antioxidants in living organisms. Conditions such as reperfusion injury, inflammation and hyperoxia cause oxidative stress, resulting in the production of powerful oxidants. These reactions are oxygen-dependent, yielding reactive species that start chain reactions.

As oxidative stress continues, it produces electronically excited intermediates that are responsible for the spontaneous emission that can be used to estimate the magnitude of different pathological scenarios. Using a photon counter, it is possible to record these changes in the emitted light.

In recent work, the scientists employed a CDM30 photon counter from Electron Tubes Inc. of Rockaway, N.J., equipped with an S20 photomultiplier to measure the weak visible emissions from the samples. Interference filters with a 50-nm bandwidth and 45 percent transmittance were positioned between the samples and the photomultiplier, and the setup offered responses of approximately 100 counts per second. The spectral response from the oxidation of liposomes, bovine serum albumin and various amino acids was in the 450- to 600-nm range. Although the chemiluminescence also yields infrared emissions, photomultipliers display lower sensitivity in that region, so the researchers focused on visible wavelengths.

Having identified the primary wavelengths in the visible, they are now investigating the amplification of these signals. Under normal conditions, when tissues are perfused with blood in vivo, the background signal appears to be caused by the production of peroxynitrite resulting from nitric oxide and superoxide from the endothelial cells.

The amount of light is almost negligible -- very close to the level of background noise -- but still measurable. Turrens believes that the researchers should be able to characterize peak wavelengths during the oxidation of particular chemicals.