12/15-lipoxygenases mediate toll-like receptor 4-dependent nociplastic pain hypersensitivity in female mice

Chronic nociplastic pain syndromes are characterized by sensitization of peripheral and central nervous systems and exhibit increased incidence in women. However, nonsteroidal anti-inflammatory drugs are ineffective in mitigating nociplastic pain, and current prescription treatments, such as opioids, anticonvulsants, and antidepressants, provide limited therapeutic benefit for these indications. In the current work, we extended previous studies in rats of central Toll-like receptor 4-dependent pain hypersensitivity to male and female C57BL/6N mice, uncovering an unexpected hyperalgesic phenotype in female mice following intrathecal (IT) lipopolysaccharide (LPS). In contrast to previous reports in female C57BL/6J mice, female C57BL/6N mice displayed tactile and cold allodynia, grip force deficits, and a modest increase in locomotor activity in response to IT LPS. Congruent with our previous observations in male rats, LPS released spinal 12/15-lipoxygenase (12/15-LOX) metabolites (12/15-LMs) in female C57BL/6N mice. Likewise, 12/15-LOX enzymes are basally expressed in multiple tissues and cell types relevant to nociceptive transmission. Systemic inhibition of 12/15-LOX in female C57BL/6N mice with selective inhibitors ML355 (targeting 12-LOX-p) or ML351 (targeting 15-LOX-1) completely reversed allodynia and grip force deficits. 12/15-LMs also produce tactile allodynia when administered spinally (IT) or peripherally (paw intraplantar) at a subthreshold dose in a hyperalgesic priming model, similar to others' observations with a subthreshold dose of the cyclooxygenase metabolite prostaglandin E 2 . Collectively, these data suggest that 12/15-LOX enzymes contribute to peripheral and central pain hypersensitivity in rodents, with potential translatability as druggable targets across sexes and species using multiple reflexive and functional outcome measures.