The Broad Spectrum of Responses to Oxidants in Proliferating Cells: A New Paradigm for Oxidative Stress

Abstract

Proliferating mammalian cells exhibit a broad spectrum of responses to oxidative stress, depending on the stress level encountered. Very low levels of hydrogen peroxide, e.g., 3 to 15 microM, or 0.1 to 0.5 micromol/10(7) cells, cause a significant mitogenic response, 25% to 45 % growth stimulation. Greater concentrations of H2O2, 120 to 150 microM, or 2 to 5 micromol/10(7) cells, cause a temporary growth arrest that appears to protect cells from excess energy use and DNA damage. After 4-6 h of temporary growth arrest, many cells will exhibit up to a 40-fold transient adaptive response in which genes for oxidant protection and damage repair are preferentially expressed. After 18 h of H2O2 adaptation (including the 4-6 h of temporary growth arrest) cells exhibit maximal protection against oxidative stress. The H2O2 originally added is metabolized within 30-40 min, and if no more is added the cells will gradually de-adapt, so that by 36 h after the initial H2O2 stimulus they have returned to their original level of H2O2 sensitivity. At H2O2 concentrations of 250 to 400 microM, or 9 to 14 micromol/10(7) cells, mammalian fibroblasts are not able to adapt but instead enter a permanently growth-arrested state in which they appear to perform most normal cell functions but never divide again. This state of permanent growth arrest has often been confused with cell death in toxicity studies relying solely on cell proliferation assays as measures of viability. If the oxidative stress level is further increased to 0.5 to 1.0 mM H2O2, or 15 to 30 micromol/10(7) cells, apoptosis results. This oxidative stress-induced apoptosis involves nuclear condensation, loss of mitochondrial transmembrane potential, degradation/down-regulation of mitochondrial mRNAs and rRNAs, and degradation/laddering of both nuclear and mitochondrial DNA. At very high H2O2 concentrations of 5.0 to 10.0 mM, or 150 to 300 micromol/10(7) cells and above, cell membranes disintegrate, proteins and nucleic acids denature, and necrosis swiftly follows. Cultured cells grown in 20% oxygen are essentially preadapted or preselected to survive under conditions of oxidative stress. If cells are instead grown in 3% oxygen, much closer to physiological cellular levels, they are more sensitive to an oxidative challenge but exhibit far less accumulated oxidant damage. This broad spectrum of cellular responses to oxidant stress, depending on the amount of oxidant applied and the concentration of oxygen in the cell culture system, provides for a new paradigm of cellular oxidative stress responses.

Cellular and molecular mechanisms involved in the neurotoxicity of opioid and psychostimulant drugs

“…Therefore, the effects of chronic exposure to oxidants contrast with the effects of acute exposure. For example, acute exposure to H 2 O 2 induces apoptotic cell death (Benedi et al, 2004;Jang and Surh, 2004), whereas chronic exposure to low concentrations of H 2 O 2 induces cellular resistance to the acute toxicity of this compound (Wiese et al, 1995;Davies, 1999). Acute exposure to H 2 O 2 may then be used as a model of cytotoxicity whereas chronic treatment with a low concentration of H 2 O 2 may be a model of cell adaptation (Jackson et al, 1994).…”

Cell Sorting Experiments Link Persistent Mitochondrial DNA Damage with Loss of Mitochondrial Membrane Potential and Apoptotic Cell Death

“…The responses of cultured cells to H 2 O 2 vary according to cell type and are known to be both time-and, especially, dose-dependent (for review see Ref. 7). For example, low concentrations (3-15 M) of H 2 O 2 were shown to activate a mitogenic response (8), whereas higher doses can have either cytostatic or cytotoxic effects.…”

H2O2 Induces a Transient Multi-phase Cell Cycle Arrest in Mouse Fibroblasts through Modulating Cyclin D and p21Cip1 Expression

“…This also gives the cells extra time to mount an adaptive response to counteract further oxidative damage. Thus, this transient growth arrest is a crucial component of the cellular response to oxidative stress (7,8).…”