More than 60 current clinical trials are using molecules called F2-isoprostanes (F2-IsoPs) as biomarkers of endogenous oxidative injury. Previous studies have shown that F2-IsoPs are increased in multiple oxidative stress-related diseases, including cardiovascular disease, neurodegeneration, diabetes, certain types of cancer and COVID-19.
A recent study published in Redox Biology demonstrates that factors other than oxidative stress, however, can modify F2-IsoP levels. Ginger Milne, PhD, research professor of Medicine in the Division of Clinical Pharmacology, and colleagues found that two abundantly produced F2-IsoPs are rapidly metabolized by enzymes called UGTs. This study suggests that changes in UGT expression and availability can change concentrations of metabolized and unmetabolized F2-IsoPs.
“Quantifying unmetabolized F2-IsoPs is commonly used in both experimental and clinical research as a measure of oxidative stress, but this may result in a biased, inaccurate assessment of true F2-IsoP production,” Milne said.
F2-IsoPs were discovered more than 30 years ago by the late Jackson Roberts II, MD, and Jason Morrow, MD, in the Division of Clinical Pharmacology. F2-IsoPs are biologically active molecules that are formed when free radicals — highly reactive molecules typically derived from oxygen — attack lipids in cell membranes. Studies have shown that F2-IsoPs are formed in a dose- and time-dependent manner in response to a potent inducer of oxidative stress, establishing them as biomarkers of endogenous oxidative injury in human disease.
In the current study, Milne and her colleagues used liquid chromatography-mass spectrometry to analyze the metabolism of two related F2-IsoPs by human liver microsomes. They identified the major metabolites as glucuronide conjugates. UGTs catalyze the addition of glucuronic acid to F2-IsoPs to form these conjugates.
The researchers found that F2-IsoP glucuronides, but not unmetabolized F2-IsoPs, were reduced in people taking a fish oil supplement. The fatty acids found in fish oil have previously been shown to alter the addition of glucuronic acid to other endogenously formed small molecules such as estrogen.
“There are numerous medications and foods that can influence the activity of UGTs, and UGT expression is altered in many diseases, which could impact the concentration of metabolized and unmetabolized F2-IsoPs,” Milne said. “It will be important to further characterize the metabolism of these biologically active molecules and to develop chemical standards for quantifying these metabolites.”
The Eicosanoid Core Lab, which Milne directs, was established by Roberts and Morrow as a central location for the measurement of oxidized lipid mediators, such as F2-IsoPs, and is the premier location in the world for the measurement of these biomarkers, she said.
In collaboration with researchers at Children’s Hospital Los Angeles and Boston Children’s Hospital, the lab measured F2-IsoPs for a recent study examining the impact of stress from adversity (psychological, physical or sexual abuse, parental violence, exposure to substance abuse, mentally ill or imprisoned household members) on cognitive development. The study found that high levels of F2-IsoPs, measured in the plasma of mothers and the urine of infants at age 2 months, correlated with lower cognitive development scores at age 12 months.
“This is the first study of its kind to identify a biological marker that reflects the effect of toxic stress on infant brain development,” Milne said. “These findings demonstrate the potential of F2-IsoPs to be used as biomarkers for the early detection and/or prevention of cognitive deficiencies. In future studies, it will be of great interest to investigate the effects of adversity on F2-IsoP metabolism.”
Milne is the first and corresponding author of the Redox Biology report. VUMC co-authors include Marina Nogueira, PhD, Benlian Gao, PhD, Stephanie Sanchez, Warda Amin, Sarah Thomas, Harvey Murff, MD, MPH, and Gong Yang, MD, MPH. The research was supported by the National Institutes of Health (grants P30DK020593, R01CA237895) and the Cayman Biomedical Research Institute.