Downregulation of EAAT-2 impairs chronic neuropathic pain via increasing of plasma glutamate after herpes zoster infection

Chronic neuropathic pain (CNP) is a debilitating complication of herpes zoster (HZ) with significant impact on quality of life. This study aimed to investigate the association between excitatory amino acid transporter 2 (EAAT-2) expression and plasma glutamate concentrations in HZ patients with CNP. This study was conducted with 102 consecutive patients diagnosed with HZ. Participants were divided into two groups: CNP ( n  = 51) and acute pain (ACP, n  = 51). Pain severity was assessed using the Numerical Rating Scale. Blood samples were collected for genotype analysis, mRNA and protein extraction, and plasma glutamate measurement. EAAT-2 DNA genotyping was analyzed by polymerase chain reaction (PCR); EAAT-2 mRNA expression was analyzed by quantitative real-time PCR; EAAT-2 protein and glutamate levels were analyzed by enzyme-linked immunosorbent assay. The EAAT-2 DNA showed no significant difference in CNP and ACP patients. CNP patients exhibited lower EAAT-2 mRNA and protein levels compared to ACP patients. However, plasma glutamate levels were significantly elevated in the CNP patients. A correlation was observed between EAAT-2 protein concentration and plasma glutamate levels in the CNP group. This study demonstrates EAAT-2 mRNA downregulation, reduced EAAT-2 protein concentration, and elevated plasma glutamate levels play roles in CNP following HZ infection. These findings suggests that EAAT-2 may be a relevant target for further investigation in therapeutic development.