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. 2015 Jun:83:245-51.
doi: 10.1016/j.freeradbiomed.2015.03.004. Epub 2015 Mar 12.

Reinterpreting the best biomarker of oxidative stress: The 8-iso-PGF(2α)/PGF(2α) ratio distinguishes chemical from enzymatic lipid peroxidation

Thomas J van 't Erve  1 , Fred B Lih  2 , Maria B Kadiiska  3 , Leesa J Deterding  2 , Thomas E Eling  4 , Ronald P Mason  3
Affiliations

Reinterpreting the best biomarker of oxidative stress: The 8-iso-PGF(2α)/PGF(2α) ratio distinguishes chemical from enzymatic lipid peroxidation

Thomas J van 't Erve et al. Free Radic Biol Med. 2015 Jun.

Abstract

The biomarker 8-iso-prostaglandin F2α (8-iso-PGF2α) is regarded as the gold standard for detection of excessive chemical lipid peroxidation in humans. However, biosynthesis of 8-iso-PGF2α via enzymatic lipid peroxidation by prostaglandin-endoperoxide synthases (PGHSs), which are significantly induced in inflammation, could lead to incorrect biomarker interpretation. To resolve the ambiguity with this biomarker, the ratio of 8-iso-PGF2α to prostaglandin F2α (PGF2α) is established as a quantitative measure to distinguish enzymatic from chemical lipid peroxidation in vitro, in animal models, and in humans. Using this method, we find that chemical lipid peroxidation contributes only 3% to the total 8-iso-PGF2α in the plasma of rats. In contrast, the 8-iso-PGF2α levels in plasma of human males are generated >99% by chemical lipid peroxidation. This establishes the potential for an alternate pathway of biomarker synthesis, and draws into question the source of increases in 8-iso-PGF2α seen in many human diseases. In conclusion, increases in 8-iso-PGF2α do not necessarily reflect increases in oxidative stress; therefore, past studies using 8-iso-PGF2α as a marker of oxidative stress may have been misinterpreted. The 8-iso-PGF2α/PGF2α ratio can be used to distinguish biomarker synthesis pathways and thus confirm the potential change in oxidative stress in the myriad of disease and chemical exposures known to induce 8-iso-PGF2α.

Keywords: Biomarkers; F(2)-isoprostanes; Inflammation; Lipid peroxidation; Oxidative stress.

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Figures

Fig. 1
Fig. 1. PGHS-2 produces 8-iso-PGF2α at a ratio of 0.004 in relation to PGF2α; this ratio is constant regardless of enzyme activity
A: The absolute amounts of 8-iso-PGF2α and PGF2α increase linearly with induction of PGHS-2 activity. B: The ratio between the two products does not change significantly. C: The absolute amounts of 8-iso-PGF2α and PGF2α are decreased with inhibition of PGHS-2 enzyme activity by meclofenamic acid (66 and 75% inhibition for PGF2α and 8-iso-PGF2α, respectively). D: The 8-iso-PGF2α / PGF2α ratio is not altered significantly from control with inhibition of PGHS-2 enzyme activity with meclofenamic acid. E: The absolute amounts of 8-iso-PGF2α and PGF2α are decreased with inhibition of PGHS-2 enzyme activity by indomethacin (72% inhibition for both PGF2α and 8-iso-PGF2α). F: The ratio between PGF2α and 8-iso-PGF2α is not altered significantly with inhibition of PGHS-2 enzyme activity with indomethacin.
Fig. 2
Fig. 2. The ratio of 8-iso-PGF2α to PGF2α is a highly sensitive and selective measure of increased chemical lipid peroxidation
A: Arachidonic acid incubated with the water-soluble free radical generator AAPH produces near equal amounts of 8-iso-PGF2α and PGF2α. B: A mathematical simulation of the 8-iso-PGF2α / PGF2α ratio when chemical lipid peroxidation (CLP) is varied relative to the prostaglandin-endoperoxide synthases (PGHS-1 & PGHS-2). The expression of PGHS-2 is varied in three distinct ratios with respect to PGHS-1 to simulate the effect of enzyme induction on the 8-iso-PGF2α / PGF2α ratio. The equation of this model (Equation 2) can be used to determine the relative contributions of both pathways to the measured 8-iso-PGF2α levels.
Fig 3
Fig 3. 8-iso-PGF2α is mainly a product of enzymatic lipid peroxidation in male fisher 344 rats and mostly of chemical lipid peroxidation in healthy human males
A: 8-iso-PGF2α and PGF2α were measured in the plasma of 4 untreated rats, and the ratio between the two compounds calculated (Ratiorat plasma = 0.06 ± 0.02; mean ± SE). B: Using Equation 2, at baseline, the source of the measured 8-iso-PGF2α in rat plasma is mainly from PGHS (96.7 ± 1.5 % of total); 3.3 ± 1.5 % comes from chemical lipid peroxidation (CLP). C: 8-iso-PGF2α and PGF2α were measured in the plasma of 4 healthy nonsmoking human males. The levels for each individual are reported as mean ± SE. D: The ratio between 8-iso-PGF2α and PGF2α in human plasma is 0.88 ± 0.26 (mean ± SE). E: Using Equation 2, at baseline, the source of the measured 8-iso-PGF2α in human plasma is mainly from CLP (99.5 ± 0.5 % of total); 0.5 ± 0.5 % comes from PGHSs.
Scheme 1
Scheme 1
The peroxidation of arachidonic acid with the chemical structures of intermediates and products integral to this study.
See this image and copyright information in PMC

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