Postpartum levels of 8-iso-prostaglandin F2α in plasma and milk phospholipid fractions as biomarker of oxidative stress in first-lactating dairy cows

• 8-iso-PGF2α as biomarker of oxidative stress in dairy cows.
• Higher 8-iso-PGF2α concentrations in heifers compared to cows.
• 8-iso-PGF2α is detectable from milk phospholipids.
• Milk 8-iso-PGF2α levels correlates with plasma concentrations.
• 8-iso-PGF2α concentrations did not correlate with milk yield.

F2-isoprostanes such as 8-iso-prostaglandin F2 (8-iso-PGF2α) are formed by free radical-catalyzed mechanisms from membrane phospholipids and from low density lipoproteins through peroxidation of arachidonic acid. Esterified 8-iso-PGF2α is cleaved by phospholipases, circulates in blood and is excreted as putatively harmful oxidatively modified lipid via the kidney into urine. In this study we demonstrate that 8-iso-PGF2α concentrations in plasma samples from heifers are higher (p < 0.005) compared to those from first-lactating dairy cows at 71 days postpartum. Furthermore, plasma 8-iso-PGF2α concentrations vary with ovarian activity and differ in response to luteolytic initiation as well as activation of the hypothalamic–pituitary–gonadal axis between heifers and first-lactating cows. Sustainable concentrations of 8-iso-PGF2α (50–150 pg/ml) are detectable in the phospholipid fraction of milk, suggesting milk as an additional excretion route for 8-isoprostanes. Plasma levels largely paralleled levels in milk (p < 0.001). Plasma phospholipid 8-iso-PGF2α concentrations in cyclic cows decreased (p < 0.05) from day 38 to day 71 postpartum, whereas milk phospholipid 8-iso-PGF2α rather increased (p < 0.05). Cyclic cows tend to have higher 8-isoprostane levels compared to acyclic animals. In contrast to lipohydroperoxides, concentration of 8-iso-PGF2α were not correlated with milk yield (p > 0.05). Our data indicate 8-iso-PGF2α may be a novel biomarker of oxidative stress in dairy cow, which is detectable in blood as well as in milk.