Reinterpreting the best biomarker of oxidative stress: The 8-iso-prostaglandin F2α/prostaglandin F2α ratio shows complex origins of lipid peroxidation biomarkers in animal models

Abstract

Oxidative stress is elevated in numerous environmental exposures and diseases. Millions of dollars have been spent to try to ameliorate this damaging process using anti-oxidant therapies. Currently, the best accepted biomarker of oxidative stress is the lipid oxidation product 8-iso-prostaglandin F2α (8-iso-PGF2α), which has been measured in over a thousand human and animal studies. 8-iso-PGF2α generation has been exclusively attributed to nonenzymatic chemical lipid peroxidation (CLP). However, 8-iso-PGF2α can also be produced enzymatically by prostaglandin-endoperoxide synthases (PGHS) in vivo. When failing to account for PGHS-dependent generation, 8-iso-PGF2α cannot be interpreted as a selective biomarker of oxidative stress. We investigated the formation of 8-iso-PGF2α in rats exposed to carbon tetrachloride (CCl4) or lipopolysaccharide (LPS) using the 8-iso-PGF2α/PGF2α ratio to quantitatively determine the source(s) of 8-iso-PGF2α. Upon exposure to a 120mg/kg dose of CCl4, the contribution of CLP accounted for only 55.6±19.4% of measured 8-iso-PGF2α, whereas in the 1200mg/kg dose, CLP was the predominant source of 8-iso-PGF2α (86.6±8.0% of total). In contrast to CCl4, exposure to 0.5mg/kg LPS was characterized by a significant increase in both the contribution of PGHS (59.5±7.0) and CLP (40.5±14.0%). In conclusion, significant generation of 8-iso-PGF2α occurs through enzymatic as well as chemical lipid peroxidation. The distribution of the contribution is dependent on the exposure agent as well as the dose. The 8-iso-PGF2α/PGF2α ratio accurately determines the source of 8-iso-PGF2α and provides an absolute measure of oxidative stress in vivo.

Classifying oxidative stress by F2-isoprostane levels across human diseases: A meta-analysis

“…Therefore, even if there was an increase in 8-iso-PGF 2α concentration between cases and controls or exposed and unexposed, there is no guarantee that this is due to non-enzymatic peroxidation. A method to separate the contribution of the two pathways has been described [1] and shows that under different conditions the pathway responsible for 8-iso-PGF 2α generation is different [2]. The evidence for the role of an alternate generation pathway voids the conclusion that 8-iso-PGF 2α by itself is a biomarker of oxidative stress.…”

“…Despite this massive amount of research, the importance of increased oxidative damage to pathologies and toxicities is critically debated. This is especially true due to the increasing evidence for potential ambiguity in the specificity of the most popular biomarker of oxidative stress, the F 2 -isoprostane 8-iso-prostaglandin F 2α (8-iso-PGF 2α ) [1], [2].…”

“…However, mounting evidence shows that 8-iso-PGF 2α can be formed not only through oxidative stress but also simultaneously by the prostaglandin endoperoxide synthase enzymes which are induced during inflammation [1], [2]. The problem with the specificity of this biomarker now necessitates additional work to determine the true mechanism by which the increases in the F 2 -isoprostane levels occur.…”

Strategies to decrease oxidative stress biomarker levels in human medical conditions: A meta-analysis on 8-iso-prostaglandin F2α

“…With the historical evidence and recent reinforcement of the complex generation mechanism of F 2 -isoprostanes, especially 8-iso-PGF 2α [25], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44], simple explanations based on historical dogma for the mechanism behind the effect or non-effect of specific strategies should be made with caution. As has been pointed out before [45], [46], [47], in addition to affecting formation by scavenging free radicals, 8-iso-PGF 2α levels can be manipulated by changes in metabolism, excretion rates, substrate availability, redox-environment, and enzymatic activities of prostaglandin H synthase (PGHS).…”

“…Future mechanistic studies will need to be performed to ascertain whether the 8-iso-PGF 2α measured is formed through a chemical or oxidative stress type pathway or whether enzymatic generation is the primary source [43], [44], [60]. This distinction, together with studies on the mechanism of each strategy, will provide the comprehensive evidence needed to fully classify the involvement of oxidative stress across human conditions.…”