The Circadian Rhythm of Intracellular Protoporphyrin IX Accumulation Through Heme Synthesis Pathway in Bladder Urothelial Cancer Cells Exposed to 5-Aminolevulinic Acid

Abstract

Background/Objectives: The standard recommendation for patients with non-muscle invasive bladder cancer is 5-aminolevulinic acid-mediated photodynamic diagnosis. The intensity of the fluorescence caused by the intracellular accumulation of protoporphyrin IX (PPIX) varies among tumors and patients. This study investigated the circadian rhythm of intracellular PPIX accumulation in bladder urothelial cancer cells exposed to 5-aminolevulinic acid. Methods: The expression of two clock genes, PER2 and BMAL1, and their impact on intracellular PPIX accumulation were evaluated in two bladder cancer cell lines, UM-UC-3 and J82, and mouse xenograft models. We evaluated the enzymes involved in the heme synthesis pathway that potentially affect the circadian rhythm of intracellular PPIX accumulation. The red fluorescence intensity of the images captured during photodynamic diagnosis-assisted transurethral resection of bladder tumors was quantified and compared among the four groups according to surgery start time: 9 a.m.–11 a.m., 11 a.m.–1 p.m., 1–3 p.m., and 3–5 p.m. Results: We observed the circadian rhythm of intracellular PPIX accumulation, which was potentially regulated by the clock genes PER2 and BMAL1. Two enzymes involved in the heme synthesis pathway, coproporphyrinogen oxidase and ferrochelatase, exhibit a circadian rhythm. The fluorescence intensity started gradually increasing at 12 p.m., and the highest level was observed in patients who underwent surgery between 3 and 5 p.m. Conclusions: Our findings suggest that it may be possible to optimize the timing of the photodynamic diagnosis in photodynamic diagnosis-assisted transurethral resection of bladder cancer based on the circadian rhythm to improve tumor detection and treatment outcomes.