Our prior work demonstrates that adult prenatal alcohol exposed (PAE) rats with minimal nerve injury develop allodynia (pathological light touch sensitivity) in concert with aberrant peripheral-spinal glial and immune activation. Nerve-injured PAE rats display heightened proinflammatory cytokine production (IL-1β, TNF-α, CCL2) typically produced following activation of innate immune receptors, TLR4 and Nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasomes. This suggests that PAE-related adaptations prime peripheral macrophages and central nervous system (CNS) glia to over-respond to subtle challenges through exaggerated TLR4 and NLRP3 inflammasome reactivity. Interestingly, morphine, a standard opioid pain therapeutic, binds the μ-opioid receptor and also glial TLR4 leading to NLRP3 inflammasome activation. Therefore, we hypothesized that PAE primes immune cell reactivity through augmented TLR4 activation and downstream NLRP3-mediated proinflammatory cytokine release, which is exacerbated by exposure to morphine treatment. Thus, we predicted morphine paradoxically exacerbates allodynia following an adult-onset peripheral nerve injury only in PAE offspring. We confirm PAE is a risk factor for developing allodynia in mice with minor injury. Results show that following minor nerve injury, morphine treatment (10 mg/kg, 5 subsequent days) significantly prolongs allodynia in PAE mice, while Sac control mice spontaneously resolve sooner. Moreover, selectively blocking NLRP3 inflammasome activity using the inhibitor, MCC950 (i.v. 10 mg/kg) reversed the morphine-prolongation of allodynia observed in PAE mice. In vitro studies were designed to examine the TLR4-NLRP3-dependent enhanced reactivity of PAE immune cells to typical immune stimuli with/without morphine treatment. Data show morphine further enhances NLRP3 inflammasome activity, as measured by flow cytometric detection of intracellular levels of active Caspase-1 and IL-1β release (by ELISA) from PAE leukocytes. Together, these data provide evidence that PAE exaggerates morphine-induced immune activation via the TLR4-NLRP3 pathway and may be predictive of adverse responses to opioids as pain therapeutics for individuals with FASD.
Noor, Shahani; Melody S. Sun; Chaselyn D. Ruffaner-Hanson; Monique V. Nysus; Diane C. Jimenez; Fernando F. Valenzuela; and Erin D. Milligan. "Prenatal alcohol exposure enhances morphine-mediated toll like receptor (tlr)-4 actions and paradoxically prolongs nerve injury-induced pathological pain." (2021). https://digitalrepository.unm.edu/hsc-bbhrd/23