NMDA Receptors Regulate Oxidative Damage in Keratinocytes during Complex Regional Pain Syndrome in HaCaT Cells and Male Rats

Abstract

Complex regional pain syndrome (CRPS), a type of primary chronic pain, occurs following trauma or systemic disease and typically affects the limbs. CRPS-induced pain responses result in vascular, cutaneous, and autonomic nerve alterations, seriously impacting the quality of life of affected individuals. We previously identified the involvement of keratinocyte N-methyl-d-asparagic acid (NMDA) receptor subunit 2 B (NR2B) in both peripheral and central sensitizations in CRPS, although the mechanisms whereby NR2B functions following activation remain unclear. Using an in vivo male rat model of chronic post-ischemia pain (CPIP) and an in vitro oxygen–glucose deprivation/reoxygenation (OGD/R) cell model, we discovered that oxidative injury occurs in rat keratinocytes and HaCaT cells, resulting in reduced cell viability, mitochondrial damage, oxidative damage of nucleotides, and increased apoptosis. In HaCaT cells, OGD/R induced increases in intracellular reactive oxygen species levels and disrupted the balance between oxidation and antioxidation by regulating a series of antioxidant genes. The activation of NMDA receptors via NMDA exacerbated these changes, whereas the inhibition of the NR2B subunit alleviated them. Co-administration of ifenprodil (an NR2B antagonist) and NMDA (an NMDA receptor agonist) during the reoxygenation stage did not result in any significant alterations. Furthermore, intraplantar injection of ifenprodil effectively reversed the altered gene expression that was observed in male CPIP rats, thereby revealing the potential mechanisms underlying the therapeutic effects of peripheral ifenprodil administration in CRPS. Collectively, our findings indicate that keratinocytes undergo oxidative injury in CRPS, with NMDA receptors playing regulatory roles.