Peripheral-Blood OPN4 Transcript Levels in Individuals Exposed to Artificial Light at Night

Abstract

Objective: To compare normalized peripheral-blood OPN4 transcript levels between individuals classified as exposed to artificial light at night and a control group, and to illustrate nocturnal melatonin, morning cortisol, and salivary α-amylase as additional biochemical endpoints.
Study Design: Exploratory observational pilot study.
Place and Duration of Study: Department of Environmental Sciences, College of Environmental Sciences, University of Mosul, Mosul, Iraq; 2026, with ethical approval obtained before sample collection.
Methods: Whole blood was obtained from 18 participants (14 light-exposed, 4 controls). RNA was isolated, reverse-transcribed, and analyzed by SYBR Green RT-qPCR. OPN4 was normalized to the reference gene reported as UBQ. ΔCq groups were compared by exact Mann–Whitney test, and relative expression was estimated by 2⁻ΔΔCq. Illustrative melatonin, cortisol, and salivary α-amylase values were analyzed using the same group sizes.
Results: Median ΔCq was 6.85 (IQR 6.60–7.20) in the exposed group and 4.20 (IQR 4.18–4.20) in controls (U = 0; exact p = 0.00065; rank-biserial correlation = 1.00). The mean ΔCq difference was 2.682 cycles, corresponding to OPN4 fold change 0.156 (95% bootstrap CI 0.137–0.177) relative to the control calibrator. Median melatonin was lower in the exposed group (35.05 vs 54.43 pg/mL; p = 0.046); cortisol (4.84 vs 4.51 µg/dL; p = 0.192) and α-amylase (42.45 vs 36.93 U/mL; p = 0.233) showed non-significant trends.
Conclusion: The RT-qPCR difference is consistent with lower normalized peripheral-blood OPN4 transcript abundance in the exposed group.