title: Maleic Acid--but Not Structurally Related Methylmalonic Acid--Interrupts Energy Metabolism by Impaired Calcium Homeostasis.
abstract: Maleic acid (MA) has been shown to induce Fanconi syndrome via disturbance of renal energy homeostasis, though the underlying pathomechanism is still under debate. Our study aimed to examine the pathomechanism underlying maleic acid-induced nephrotoxicity. Methylmalonic acid (MMA) is structurally similar to MA and accumulates in patients affected with methymalonic aciduria, a defect in the degradation of branched-chain amino acids, odd-chain fatty acids and cholesterol, which is associated with the development of tubulointerstitial nephritis resulting in chronic renal failure. We therefore used MMA application as a control experiment in our study and stressed hPTECs with MA and MMA to further validate the specificity of our findings. MMA did not show any toxic effects on proximal tubule cells, whereas maleic acid induced concentration-dependent and time-dependent cell death shown by increased lactate dehydrogenase release as well as ethidium homodimer and calcein acetoxymethyl ester staining. The toxic effect of MA was blocked by administration of single amino acids, in particular L-alanine and L-glutamate. MA application further resulted in severe impairment of cellular energy homeostasis on the level of glycolysis, respiratory chain, and citric acid cycle resulting in ATP depletion. As underlying mechanism we could identify disturbance of calcium homeostasis. MA toxicity was critically dependent on calcium levels in culture medium and blocked by the extra- and intracellular calcium chelators EGTA and BAPTA-AM respectively. Moreover, MA-induced cell death was associated with activation of calcium-dependent calpain proteases. In summary, our study shows a comprehensive pathomechanistic concept for MA-induced dysfunction and damage of human proximal tubule cells.
authors.affiliation: Department of General Pediatrics, Division of Inborn Metabolic Diseases, University Children's Hospital, Heidelberg, Germany.
authors.forename: Ali Tunç
authors.initials: AT
authors.lastname: Tuncel
authors.affiliation: Department of General Pediatrics, Division of Inborn Metabolic Diseases, University Children's Hospital, Heidelberg, Germany.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Ruppert
authors.affiliation: Department of General Pediatrics, Division of Inborn Metabolic Diseases, University Children's Hospital, Heidelberg, Germany.
authors.forename: Bei-Tzu
authors.initials: BT
authors.lastname: Wang
authors.affiliation: Department of General Pediatrics, Division of Inborn Metabolic Diseases, University Children's Hospital, Heidelberg, Germany.
authors.forename: Jürgen Günther
authors.initials: JG
authors.lastname: Okun
authors.affiliation: Department of General Pediatrics, Division of Inborn Metabolic Diseases, University Children's Hospital, Heidelberg, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Kölker
authors.affiliation: Department of General Pediatrics, Division of Inborn Metabolic Diseases, University Children's Hospital, Heidelberg, Germany.
authors.forename: Marina Alexandra
authors.initials: MA
authors.lastname: Morath
authors.affiliation: Department of General Pediatrics, Division of Inborn Metabolic Diseases, University Children's Hospital, Heidelberg, Germany.
authors.forename: Sven Wolfgang
authors.initials: SW
authors.lastname: Sauer
mesh_terms: D002118:Calcium / Q000378:metabolism* / Q000502:physiology; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004734:Energy Metabolism / Q000187:drug effects*; D006706:Homeostasis / Q000187:drug effects*; D006801:Humans; D007676:Kidney Failure, Chronic / Q000139:chemically induced; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008298:Maleates / Q000494:pharmacology*; D008764:Methylmalonic Acid / Q000494:pharmacology*; D010101:Oxygen Consumption / Q000187:drug effects; D013329:Structure-Activity Relationship
chemical_list: D008298:Maleates; D008764:Methylmalonic Acid; C030272:maleic acid; D007770:L-Lactate Dehydrogenase; D002118:Calcium