The role of 5-methoxytryptophan in pediatric-onset lupus nephritis: A retrospective cohort study

This clinical study investigates the role of 5-methoxytryptophan (5-MTP) in pediatric systemic lupus erythematosus (SLE), with a particular interest in lupus nephritis (LN). One hundred ten children with SLE were enrolled in the cohort study. Among the patients, seventy-seven (70%) had active LN and thirty-three (30%) were not present with LN during their first visit to the clinic. The diagnoses of LN were biopsy-proven. Serum samples were collected before and after administration of immunosuppressive medications to evaluate 5-MTP levels and regular laboratory data. Data were analyzed longitudinally. Before any treatment started, patients with active LN had significantly higher 5-MTP levels as compared to patients with no LN (1.021 ± 0.709 vs. 0.719 ± 0.606, P = 0.0456). Also, in patient with active LN, 5-MTP level was significant decreased after treatment, compared with the levels before treatment (1.021 ± 0.709 vs. 0.802 ± 0.597, P = 0.0484). Patients who reached complete remission also had significantly higher initial serum 5-MTP levels than that in patients with no remission (1.244 ± 0.784 vs. 0.846 ± 0.556, P = 0.0488). There was an overall reduction in 5-MTP levels after six months of immunosuppressive treatment, regardless of the disease outcome. Subgroup analysis further revealed a significantly higher 5-MTP level during the active stage of LN (1.127 ± 0.149 vs. 0.742 ± 0.092, P = 0.0384). We demonstrated that serum 5-MTP level is positively correlated to the disease activity, prognosis, and remission status of pediatric LN in vivo.