Toxicity profiling of phenazopyridine in zebrafish: An emerging pharmaceutical contaminant in the environment

Phenazopyridine is an azo dye analgesic routinely used in the management of urinary tract infections. An overdose of this pharmaceutical agent causes methemoglobinemia and renal failure across all age groups. There is limited knowledge regarding the implications of early phenazopyridine exposure, whether via medicinal use or inadvertent contact, or its toxicity in specific organs in living organisms. Moreover, 40-50 % of this drug gets eliminated in its native form and hence it contributes to the pharmaceutical burden in the environment. In this study, we used zebrafish, a versatile model system for assessing drug-induced toxicity, to investigate the effects of phenazopyridine exposure on embryonic development and hematopoiesis. Zebrafish embryos exposed to sublethal doses showed distinct toxicological manifestations including cardiotoxicity, delayed hatching, and absence of swim bladder, which are indicative of developmental anomalies associated with the phenazopyridine exposure. Phenazopyridine-exposed embryos also had a significant reduction in blood cell population and defective vascularization, indicating an effect on hematopoiesis. Investigation of molecular mechanisms in the treated embryos revealed elevated ROS signals and downregulation of key genes involved in host's antioxidant response, suggesting the induction of oxidative stress upon phenazopyridine exposure. While the results of this study clearly demonstrate the developmental toxicity associated with phenazopyridine exposure in living systems, the use of zebrafish, which is an aquatic organism, also highlights the long-term implications of this pharmaceutical contaminant on the life forms in the aquatic environment, given that this medication is a frequently used over-the-counter analgesic.