Classification of oxidative stress based on its intensity

Abstract

In living organisms production of reactive oxygen species (ROS) is counterbalanced by their elimination and/or prevention of formation which in concert can typically maintain a steady-state (stationary) ROS level. However, this balance may be disturbed and lead to elevated ROS levels called oxidative stress. To our best knowledge, there is no broadly acceptable system of classification of oxidative stress based on its intensity due to which proposed here system may be helpful for interpretation of experimental data. Oxidative stress field is the hot topic in biology and, to date, many details related to ROS-induced damage to cellular components, ROS-based signaling, cellular responses and adaptation have been disclosed. However, it is common situation when researchers experience substantial difficulties in the correct interpretation of oxidative stress development especially when there is a need to characterize its intensity. Careful selection of specific biomarkers (ROS-modified targets) and some system may be helpful here. A classification of oxidative stress based on its intensity is proposed here. According to this classification there are four zones of function in the relationship between "Dose/concentration of inducer" and the measured "Endpoint": I - basal oxidative stress (BOS); II - low intensity oxidative stress (LOS); III - intermediate intensity oxidative stress (IOS); IV - high intensity oxidative stress (HOS). The proposed classification will be helpful to describe experimental data where oxidative stress is induced and systematize it based on its intensity, but further studies will be in need to clear discriminate between stress of different intensity.

Keywords: free radicals; reactive nitrogen species; reactive oxygen species; system response.

Figure 1. Reduction of molecular oxygen via four- and one-electron schemes

Figure 2. Equation 1

Figure 3. Equation 2

Figure 4. Equation 3

Figure 5. Equation 4

Figure 6. Equation 5

Figure 7. Equation 6

Figure 8. Equation 7

Figure 9. Equation 8

Figure 10. Equation 9

Figure 11. Figure 2: The dynamics of levels of reactive oxygen species in biological systems. The basic steady-state (stationary) level of reactive oxygen species fluctuates over a certain range under normal conditions. However, under stress ROS levels may increase beyond the normal range resulting in acute or chronic oxidative stress. Under some conditions, ROS levels may not return to their initial range and stabilize at a new quasi-stationary level.

Figure 12. Figure 3: Relationships between the dose of an inducer of oxidative stress and commonly used endpoint (end parameter) parameters that may be measured. Zone I - no observable effects are registered due to very low intensity oxidative stress (basal intensity oxidative stress - BOS); zone II - low intensity (mild) oxidative stress (LOS) with a slightly enhanced level of oxidatively modified molecules and enhanced activity of antioxidant enzymes in response to oxidative stress; zone III - intermediate intensity oxidative stress (IOS); and zone IV - high intensity (strong) oxidative stress (HOS). Curve 1 - ROS-induced ROS-sensitive function (ROSISP), curve 2 - level of oxidatively modified components. Abbreviations: NOE - no observable effect point; ZEP - zero equivalent point - the level of components of interest corresponds to the initial (basic) level in the absence of inducers of oxidative stress.