Allergic rhinitis (AR) is a common chronic inflammatory condition of the nasal mucosa driven by IgE-mediated hypersensitivity, yet reliable biomarkers of systemic immune activity and oxidative stress remain limited despite involvement of Th2 cytokines, eosinophils, and macrophages. Neopterin (NPT) is a macrophage-derived marker of interferon-γ–induced immune activation and oxidative imbalance, but current plasma detection methods are expensive, or lack sufficient sensitivity for routine clinical use. Herein, a validated fluorescence-based method was developed for determination of plasma NPT using o-phthaldehyde derivatization in the presence of 2-mercaptoethanol under mildly alkaline conditions. The reaction formed a stable isoindole derivative with strong fluorescence (λₑx = 335 nm, λₑm = 455 nm), increasing the quantum yield from 0. 24 for native NPT to 0. 65 for the NPT–OPA product. The method showed linearity from 1 to 20 ng/mL (r² = 0. 9996), with a detection limit of 0. 22 ng/mL and a quantification limit of 0. 66 ng/mL. Accuracy ranged from 99. 0% to 100. 8%, and precision remained below 1. 0%. No interference appeared from biopterin, folic acid, riboflavin, or xanthopterin, each contributing less than 5% of the NPT signal. Plasma NPT was measured in 26 AR patients and 26 healthy controls. AR patients showed elevated NPT concentrations (2. 9 ± 0. 7 ng/mL) compared to controls (1. 5 ± 0. 3 ng/mL, p < 0. 001). NPT levels correlated with symptom severity (r = 0. 44, p = 0. 015) and eosinophil counts (r = 0. 41, p = 0. 022), indicating an association between immune activation and disease intensity. The fluorescence-based method provides a sensitive, selective, and rapid approach for plasma NPT quantification and supports NPT as a potential biomarker of immune activation and oxidative stress in AR.
Alqahtani et al. (Wed,) studied this question.