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Erythropoietic protoporphyria (EPP) is an inherited disease caused by loss-of-function mutations of ferrochelatase, an enzyme in the heme biosynthesis pathway that converts protoporphyrin IX (PPIX) into heme. PPIX accumulation in patients with EPP leads to phototoxicity and hepatotoxicity, and there is no cure. Here, we demonstrated that the PPIX efflux transporter ABCG2 (also called BCRP) determines EPP-associated phototoxicity and hepatotoxicity. We found that ABCG2 deficiency decreases PPIX distribution to the skin and therefore prevents EPP-associated phototoxicity. We also found that ABCG2 deficiency protects against EPP-associated hepatotoxicity by modulating PPIX distribution, metabolism, and excretion. In summary, our work has uncovered an essential role of ABCG2 in the pathophysiology of EPP, which suggests the potential for novel strategies in the development of therapy for EPP.

Idelalisib (ILB) is a selective phosphatidylinositol-3-kinase delta inhibitor approved for the treatment of hematological malignancies. However, ILB frequently causes hepatotoxicity, and the exact mechanism remains unclear. The current study profiled the metabolites of ILB in mouse liver, urine, and feces. The major metabolites found in the liver were oxidized metabolite GS-563117 (M1) and ILB-glutathione (GSH) adduct (M2). These metabolic pathways were confirmed by analysis of urine and feces from mice treated with ILB. Identification of ILB-GSH adduct (M2) suggests the formation of reactive metabolites of ILB. We also found that M1 can produce reactive metabolites and form M1-GSH adducts. The GSH-conjugates identified in mouse liver were also found in the incubations of ILB and M1 with human liver microsomes. Furthermore, we illustrated that CYP3A4 and 2C9 are the key enzymes contributing to the bioactivation pathway of ILB and M1. In summary, our work revealed that both ILB and its major metabolite M1 can undergo bioactivation to produce reactive metabolites in the liver. Further studies are required to determine whether these metabolic pathways contribute to ILB hepatotoxicity.

Introduction Among the infectious diseases, tuberculosis (TB) remains the second cause of death after HIV. TB treatment requires the combination of multiple drugs including the rifamycin class. However, rifamycins are activators of human pregnane X receptor (PXR), a transcription factor that regulates drug metabolism, drug resistance, energy metabolism, and immune response. Rifamycin-mediated PXR activation may affect the outcome of TB therapy. Areas covered This review describes the role of PXR in modulating metabolism, efficacy, toxicity, and resistance to anti-TB drugs; as well as polymorphisms of PXR that potentially affect TB susceptibility. Expert opinion The wide range of PXR functions aside mediating drug metabolism and toxicity in TB therapy is underappreciated and thus understudied. Further studies are needed to determine the overall impact of PXR activation on the outcome of TB therapy.