Evidence from both clinical and preclinical studies indicates that females experience a faster progression to drug addiction and more severe addiction-related health effects compared with males. Estradiol (E2) plays a critical role in these sex differences. Recently, we demonstrated that E2 significantly exacerbates adverse health effects, such as respiratory distress and weight loss, in ovariectomized (OVX) female rats during withdrawal from extended-access fentanyl self-administration. To uncover the mechanisms behind E2-enhanced toxicity, we investigated proteomic changes in the plasma of fentanyl-withdrawn OVX rats under both E2 and non-E2 presentation conditions.Plasma samples were collected following extended-access fentanyl self-administration during protracted withdrawal, when adverse health effects were most pronounced. Using liquid chromatography coupled with electrospray ionization tandem mass spectrometry (LC-ESI MS/MS) we conducted proteomic analysis in OVX rats comparing the effect of fentanyl withdrawal, with or without E2, to drug-naïve control rats.We found a significant effect of fentanyl withdrawal on plasma proteomes within OVX rats. Fentanyl withdrawal was associated with a significant change in 15 plasma proteins including B-factor, properdin (Cfb), apolipoprotein E (ApoE), complement 4, precursor (C4), C-reactive protein (Crp), zinc-alpha-2-glycoprotein precursor (Azgp1), and serine peptidase inhibitor 3L (Serinpa3l). The addition of E2 was associated with enhanced proteomic changes. Bioinformatic gene ontology enrichment analysis indicates that fentanyl withdrawal can disrupt the expression of proteins associated with immunity, lipid transport, and components of the extracellular matrix. We identify protein changes in plasma that may contribute to adverse health outcomes in females, with and without E2, during fentanyl withdrawal. These findings support the development of targeted strategies addressing health risks during opioid use disorder in women.
© 2025 The Author(s). Journal of Neuroendocrinology published by John Wiley & Sons Ltd on behalf of British Society for Neuroendocrinology.