1 SCIENTIFIC REPORTS | (2019) 9:8922 | https://doi.org/10.1038/s41598-019-45529-w www.nature.com/scientificreports On the molecular and cellular efects of omeprazole to further support its efectiveness as an antigiardial drug Gabriel López-Velázquez 1 , Cynthia Fernández-Lainez 2 , José Ignacio de la Mora-de la Mora 1 , Daniela Caudillo de la Portilla 1 , Rafael Reynoso-Robles 3 , Angélica González-Maciel 3 , Cecilia Ridaura 4 , Itzhel García-Torres 1 , Pedro Gutiérrez-Castrellón 5 , Alfonso Olivos-García 6 , Luis Antonio Flores-López 1,7 & Sergio Enríquez-Flores 1 Research on Giardia lamblia has accumulated large information about its molecular cell biology and infection biology. However, giardiasis is still one of the commonest parasitic diarrheal diseases afecting humans. Additionally, an alarming increase in cases refractory to conventional treatment has been reported in low prevalence settings. Consequently, eforts directed toward supporting the efcient use of alternative drugs, and the study of their molecular targets appears promising. Repurposing of proton pump inhibitors is efective in vitro against the parasite and the toxic activity is associated with the inhibition of the G. lamblia triosephosphate isomerase (GlTIM) via the formation of covalent adducts with cysteine residue at position 222. Herein, we evaluate the efectiveness of omeprazole in vitro and in situ on GlTIM mutants lacking the most superfcial cysteines. We studied the infuence on the glycolysis of Giardia trophozoites treated with omeprazole and characterized, for the frst time, the morphological efect caused by this drug on the parasite. Our results support the efectiveness of omeprazole against GlTIM despite of the possibility to mutate the druggable amino acid targets as an adaptive response. Also, we further characterized the efect of omeprazole on trophozoites and discuss the possible mechanism involved in its antigiardial efect. Giardiasis is caused by Giardia lamblia, which is one of the most common infectious protozoans on the globe and is responsible for diarrheal disease and chronic postinfectious illnesses such as irritable bowel syndrome 1 . Te clinical impact of giardiasis seems to be stronger in the frst 3 years of life and in undernourished or immu- nodefcient individuals 2,3 . Tis parasitic disease continues to be the major cause of nonviral or bacterial diarrhea in humans and other vertebrates 4–6 . Its prokaryotic‐like anaerobic metabolism renders it selectively sensitive to certain bacterial drugs, especially nitroimidazoles, which are activated to form toxic radicals. Nevertheless, the drugs used to treat giardiasis have associated side efects, and drug resistance has been demonstrated or induced in vitro 7,8 . Te ability of Giardia cysts to persist in the environment, including in the presence of disinfectants 9,10 , and the existence of lethal strains with the potential to infect humans 11,12 is strikingly important in the context of bioter- rorism. Altogether, the features of giardiasis highlight the importance of this disease as a public health problem and have led to a search for novel experimental strategies and evaluation of alternative treatment regimens. 1 Grupo de Investigación en Biomoléculas y Salud Infantil, Laboratorio de EIMyT, Instituto Nacional de Pediatría, Ciudad de México, 04530, Mexico. 2 Laboratorio de Errores Innatos del Metabolismo y Tamiz, Instituto Nacional de Pediatría, Ciudad de México, 04530, Mexico. 3 Laboratorio de Morfología Celular y Tisular, Instituto Nacional de Pediatría, Ciudad de México, 04530, Mexico. 4 Departamento de Patología, Instituto Nacional de Pediatría, Ciudad de México, 04530, Mexico. 5 Hospital General Dr. Manuel Gea González, Ciudad de México, 14080, Mexico. 6 Unidad de Investigación en Medicina Experimental, Facultad de Medicina, Universidad Nacional Autónoma de México y Hospital General, Ciudad de México, 04510, Mexico. 7 CONACYT-Instituto Nacional de Pediatría, Secretaría de Salud, Ciudad de México, 04530, Mexico. Correspondence and requests for materials should be addressed to G.L.-V. (email: glv_1999@ciencias.unam.mx) or S.E.-F. (email: sergioenriquez@ciencias.unam.mx) Received: 7 February 2019 Accepted: 5 June 2019 Published: xx xx xxxx OPEN