Tracking biochemical changes correlated with ultra-weak photon emission using metabolomics

•UPE proved linked with biochemical changes in biological systems.•UPE data correlates with metabolic profile of amino acids and nucleosides.•UPE kinetics likely to provide important biological information.

Ultra-weak photon emission (UPE) is light emitted spontaneously by biological systems without the use of specific luminescent complexes. UPE is emitted in the near-UV/UV-Vis/near-IR spectra during oxidative metabolic reactions; however, the specific pathways involved in UPE remain poorly understood. Here, we used HL-60 cells, a human promyelocytic cell line that is often used to study respiratory burst, as a model system to measure UPE kinetics together with metabolic changes. HL-60 cells were differentiated into neutrophil-like cells by culturing in all-trans-retinoic acid for 7 days. We then used a targeted metabolomics approach with capillary electrophoresis-mass spectrometry to profile intracellular metabolites in HL-60 cells and to investigate the biochemical changes based on the measured UPE profile. Our analysis revealed that the levels of specific metabolites, including putrescine, creatine, β-alanine, methionine, hydroxyproline, serine, and S-adenosylmethionine, were significantly altered in HL-60 cells after inducing respiratory burst. A comparison with recorded UPE data revealed that the changes in putrescine, glutathione, sarcosine, creatine, β-alanine, methionine, and hydroxyproline levels were inversely correlated with the change in UPE intensity. These results suggest that these metabolic pathways, particular the methionine pathway, may play a role in the observed changes in UPE in HL-60 cells and therefore demonstrate the potential for using UPE to monitor metabolic changes.