International Journal of Molecular Sciences Review Aristolochic Acid-Induced Nephrotoxicity: Molecular Mechanisms and Potential Protective Approaches Etienne Empweb Anger, Feng Yu and Ji Li * Department of Clinical Pharmacy, School of Basic Medical Sciences and Clinical Pharmacy, China Pharmaceutical University, Nanjing 211198, China; [email protected] (E.E.A.); [email protected] (F.Y.) * Correspondence: [email protected]; Tel.: +86-139-5188-1242 Received: 25 November 2019; Accepted: 5 February 2020; Published: 10 February 2020 Abstract: Aristolochic acid (AA) is a generic term that describes a group of structurally related compounds found in the Aristolochiaceae plants family. These plants have been used for decades to treat various diseases. However, the consumption of products derived from plants containing AA has been associated with the development of nephropathy and carcinoma, mainly the upper urothelial carcinoma (UUC). AA has been identified as the causative agent of these pathologies. Several studies on mechanisms of action of AA nephrotoxicity have been conducted, but the comprehensive mechanisms of AA-induced nephrotoxicity and carcinogenesis have not yet fully been elucidated, and therapeutic measures are therefore limited. This review aimed to summarize the molecular mechanisms underlying AA-induced nephrotoxicity with an emphasis on its enzymatic bioactivation, and to discuss some agents and their modes of action to reduce AA nephrotoxicity. By addressing these two aspects, including mechanisms of action of AA nephrotoxicity and protective approaches against the latter, and especially by covering the whole range of these protective agents, this review provides an overview on AA nephrotoxicity. It also reports new knowledge on mechanisms of AA-mediated nephrotoxicity recently published in the literature and provides suggestions for future studies. Keywords: aristolochic acid; aristolochic acid nephrotoxicity; DNA adducts formation; upper urothelial carcinoma; potential protective mechanisms 1. Introduction Remedies prepared from Aristolochiaceae plants containing aristolochic acid (AA) under various pharmaceutical formulations, including pills, powder, granules, pellets, infusions, and capsules [1,2], have been used for decades throughout the world to treat diverse diseases, including hepatitis, urinary tract infection, vaginitis, upper respiratory tract infection, eczema, dysmenorrhea, arthralgia, hypertension, bronchitis, pneumonia, heart failure, and edema [3–5]. However, plants or botanical-derived products containing AA were reported to be nephrotoxic, mutagenic, and carcinogenic to humans [3,6]. The first observation of unusual renal disease which consisted of rapidly progressive tubulointerstitial nephritis was made in Belgium in the 1990s among young female patients [7]. The etiology of this renal disease was quickly associated with consumption of body weight-loss pills containing a Chinese herb, Gang Fang Ji [5,8,9]. In this slimming regimen, Stephania tetrandra (Han Fang Ji) had been mistakenly substituted by Aristolochia fangchi (Gang Fang Ji) [4,10]. This pathology was initially known as Chinese herb nephropathy (CHN) because of the origin (China) of the slimming pills. After identifying AA as the causative agent of this pathology [11,12], CHN was then appropriately termed aristolochic acid nephropathy (AAN) [13,14]. A similar situation in some southeastern regions of Europe previously identified as Balkan endemic nephropathy (BEN), was later described to be the result of AA consumption too [15,16]. Int. J. Mol. Sci. 2020, 21, 1157; doi:10.3390/ijms21031157 www.mdpi.com/journal/ijms Int. J. Mol. Sci. 2020, 21, 1157 2 of 20 Int. J. Mol. Sci. 2020, 21, x FOR PEER REVIEW 2 of 20 AristolochicAristolochic acid (AA) is a genericgeneric termterm thatthat refersrefers toto aa structurallystructurally relatedrelated groupgroup ofof nitrophenanthrenenitrophenanthrene carboxyliccarboxylic acidsacids derivedderived fromfrom plantsplants ofof thethe AristolochiaceaeAristolochiaceae familyfamily thatthat includesincludes severalseveral species.species. Plant species belonging to Aristolochia and Asarum genera are the most reportedreported toto containcontain AAAA [[3,16].3,16]. Aristolochic acid I (AAI) and AristolochicAristolochic acidacid IIII (AAII),(AAII), twotwo compoundscompounds thatthat areare structurallystructurally didifferentfferent onlyonly byby thethe presencepresence ofof thethe O-methoxyO-methoxy groupgroup atat thethe 8-position8-position forfor AAIAAI andand thethe absenceabsence ofof thisthis O-methoxyO-methoxy group at the 8-position for AAII (Figure1 1)) are are considered considered to to be be the the most most abundantabundant andand activeactive componentscomponents ofof AAAA [[17].17]. FigureFigure 1.1. FormulaFormula ofof the the most most abundant abundant and and active active of Aristolochicof Aristolochic acids acids compounds: compounds: Aristolochic Aristolochic acid Iacid and I Aristolochicand Aristolochic acid II.acid II. TheThe InternationalInternational AgencyAgency for for Research Research on on Cancer Cancer (IARC) (IARC) classified classified AA AA as as carcinogenic carcinogenic group group I to I humans,to humans, acting acting by aby genotoxic a genotoxic mechanism mechanism [18]. [18]. Thus, Thus, the the use use of plants of plants or remedies or remedies containing containing AA hasAA beenhas been banned banned in several in several countries countries [19–21]. [19–21]. However, Ho duewever, to the due worldwide to the worldwide distribution distribution of Aristolochia of plantAristolochia species plant and species the great and use the of great herbal use medicines of herbal medi in somecines regions, in some individuals regions, individuals are still exposed are still toexposed AA [16 to,22 AA,23 ].[16,22,23]. In this context, In this researchcontext, rese to understandarch to understand the molecular the molecular mechanisms mechanisms of AA-induced of AA- nephrotoxicityinduced nephrotoxicity might allow might for allow finding for out finding efficient out protectiveefficient protective mechanisms mechanisms or eventually, or eventually, to provide to aprovide model ofa studymodel for of investigating study for drug-inducedinvestigating organdrug-induced toxicity. Indeed, organ sincetoxicity. the identificationIndeed, since of AAthe asidentification the causative of agentAA as of the CHN causative [11,12], agent several of CHN studies [11,12], using several animal modelsstudies andusing cultured animal cellmodels systems and havecultured been cell conducted. systems have However, been theconducted. comprehensive However, cellular the comprehensive and molecular cellular action mechanismsand molecular of AA-inducedaction mechanisms nephrotoxicity of AA-induced have not yetnephrotoxicity been fully elucidated have not and yet AAN been treatment fully elucidated is therefore and limited. AAN treatmentSeveral is therefore studieshave limited. reviewed and summarized the mechanisms reported to be involved in AASeveral pathogenesis, studies have but reviewed only few and have summarized covered the the mechanisms whole range reported of protective to be involved or potential in AA protectivepathogenesis, mechanisms but only against few have AA-induced covered nephrotoxicity.the whole range In thisof protective review, we or discuss potential the molecularprotective mechanismsmechanisms ofagainst action underlyingAA-induced AA-induced nephrotoxicity. nephrotoxicity, In this while review, emphasizing we discuss the role the of enzymaticmolecular biotransformationmechanisms of action of AA, underlying which result AA-induced in potentiating nephrotoxicity, its carcinogenic while and emphasizing nephrotoxic the eff ects,role asof reportedenzymatic in biotransformation recent studies. Finally, of AA, we addresswhich result the protective in potentiating strategies its andcarcinogenic give a summary and nephrotoxic of agents andeffects, their as potential reported protectivein recent studies. mechanisms Finally, against we address AA nephrotoxicity the protectivein stra vitrotegiesand andin vivo give, asa summary found in theof agents literature. and their potential protective mechanisms against AA nephrotoxicity in vitro and in vivo, as found in the literature. 2. Enzymatic Metabolization of AA Leading to the Formation of DNA Adducts and Induction of Tp53 Mutations 2. Enzymatic Metabolization of AA Leading to the Formation of DNA Adducts and Induction of Tp53Studies Mutations in rodents have indicated that after oral administration of AA, the drug is absorbed from the gastrointestinal tract into the blood stream and then distributed throughout the body, as evidenced Studies in rodents have indicated that after oral administration of AA, the drug is absorbed from by the presence of DNA adducts detected in several rodent organs, including stomach, intestine, the gastrointestinal tract into the blood stream and then distributed throughout the body, as liver, spleen, lung, and kidney [17,19,24]. It has been suggested that AA is metabolized by oxidation evidenced by the presence of DNA adducts detected in several rodent organs, including stomach, (mainly AAI) and reduction pathways [25,26]. The reduction, primarily the nitroreduction of AAI intestine, liver, spleen, lung, and kidney [17,19,24]. It has been suggested that AA is metabolized by and AAII leads respectively to N-hydroxyaristolactam I and N-hydroxyaritololactam II, which are oxidation (mainly AAI) and reduction pathways