The unique reactivity of EKODE lipid peroxidation products allows in vivo detection of inflammation

Lipid peroxidation is a complex biochemical process associated with oxidative stress, and its products play crucial roles in cellular signaling and the pathophysiology of many diseases. Among the diverse array of lipid peroxidation (LPO) products, epoxyketooctadecenoic acids (EKODEs) have emerged as intriguing molecules with potential impacts on inflammatory diseases. EKODEs arise from linoleic acid reacting with reactive oxygen and nitrogen species present during inflammation. A hallmark of many LPO products is an electrophilic chemical functionality that can react with different biological nucleophiles to form adducts that impact a broad swath of physiologic processes. Here, we present the identification of reactivity patterns exhibited by the EKODE class of LPO products that arise due to the unique chemistry of the EKODE electrophiles, namely α, β-unsaturated epoxyketones of variable regiochemistry. Our initial investigations with models of the EKODE reactive core showed that surrogates of lysine did not react, and histidine nucleophiles formed reversible Michael adducts. However, when models of cysteine nucleophiles were tested, a unique reactivity profile emerged where rapid Michael addition was followed by slow rearrangement and epoxide opening at an unpredicted electrophilic site, affording what we postulated to be an advanced lipoxidation end product (ALE). After confirming the EKODE reactivity in model systems, we produced polyclonal antibodies of a stable epitope of the EKODE-based ALE and used these antibodies to investigate an approach for in vivo monitoring of inflammatory disease progression.