title: Cyclosporin A tubular effects contribute to nephrotoxicity: role for Ca2+ and Mg2+ ions.
abstract: BACKGROUND
  Cyclosporin A (CsA) nephrotoxicity has been attributed primarily to renal haemodynamic alterations caused by afferent arteriolar vasoconstriction. However, CsA nephropathy is also characterized by CsA-induced pre-glomerular disturbances and interstitial injury that may occur independently of haemodynamic changes. Given the high lipophilic activity of CsA, we hypothesized that direct tubular injury is likely to contribute to nephrotoxicity.
  
  
  METHODS
  To investigate tubular toxicity of CsA, increasing concentrations of CsA (1, 2.5, 10, 25, 50 and 100 micro g/ml) and its vehicle (cremophor) were added to isolated rat proximal tubules (PT). Cell injury was assessed by lactate dehydrogenase (LDH) release. The role of Ca(2+) ions in tubular toxicity and the effect of calcium channel blockers on CsA toxicity were evaluated by measuring intracellular calcium using the fluorescent dye Fura-2 AM. The role of Mg(2+) ions was assessed using high extracellular Mg(2+) medium (2 mM).
  
  
  RESULTS
  Whereas cremophor alone was not toxic to PT, CsA caused PT injury but only at the highest concentration (100 micro g/ml). After 90 min incubation, LDH was 22.5% in control PT and 41.9% in PT treated with 100 micro g/ml CsA (P < 0.001, n = 11). There was a transient increase in intracellular calcium ([Ca(2+)](i)) after CsA administration. A low calcium medium (100 nM) prevented CsA injury to renal tubules. However, verapamil, but not nifedipine, enhanced cell damage. Only nifedipine completely prevented [Ca(2+)](i) increases following CsA. Finally, a high Mg(2+) medium attenuated CsA-induced injury.
  
  
  CONCLUSIONS
  We found that high CsA concentrations caused Ca(2+)- and Mg(2+)-dependent PT injury. Thus, low extracellular Ca(2+) and high Mg(2+) media attenuated CsA-induced tubular injury. Verapamil, but not nifedipine, enhanced CsA tubular toxicity. Therefore, CsA-induced tubular injury may contribute to CsA nephrotoxicity independently of haemodynamic disturbances.
authors.affiliation: Nephrology Division, University of Sao Paulo School of Medicine, Sao Paulo, Brazil.
authors.forename: Maristela
authors.initials: M
authors.lastname: Carvalho da Costa
authors.forename: Isac
authors.initials: I
authors.lastname: de Castro
authors.forename: Américo L Cuvello
authors.initials: AL
authors.lastname: Neto
authors.forename: Alice T
authors.initials: AT
authors.lastname: Ferreira
authors.forename: Emmanuel A
authors.initials: EA
authors.lastname: Burdmann
authors.forename: Luis
authors.initials: L
authors.lastname: Yu
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002413:Cations, Divalent; D046508:Culture Techniques; D016572:Cyclosporine / Q000009:adverse effects*; D007166:Immunosuppressive Agents / Q000009:adverse effects*; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000473:pathology; D008274:Magnesium / Q000502:physiology*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D014882:Water-Electrolyte Balance / Q000187:drug effects / Q000502:physiology
chemical_list: D002121:Calcium Channel Blockers; D002413:Cations, Divalent; D007166:Immunosuppressive Agents; D016572:Cyclosporine; D008274:Magnesium; D002118:Calcium