Disturbed Ca2+-signaling by chloroacetaldehyde: a possible cause for chronic ifosfamide nephrotoxicity.
BACKGROUND
Renal damage following chemotherapy with ifosfamide is attributed to the metabolic activation of the drug and the generation of chloroacetaldehyde (CAA). Little is known about the mechanism by which CAA impairs renal function. In this study the effect of CAA on intracellular Ca(2+) homeostasis in human renal proximal tubule cells (RPTEC) in primary culture was investigated.


METHODS
Intracellular Ca(2+) was measured using the Ca(2+)-sensitive dye fura-2. Cell viability was determined by protein content and cell number. Oncotic and apoptotic cell death was assayed using trypan blue exclusion, caspase-3 activity, and 4',6-diamino-2-phenylindole (DAPI) staining.


RESULTS
CAA (1.5 to 150 micromol/L) induced sustained elevations of intracellular free calcium ([Ca(2+)](i)) from 75 +/- 3 nmol/L to maximal 151 +/- 6 nmol/L. This effect was dependent on extracellular Ca(2+), but not Ca(2+) entry. The rise in [Ca(2+)](i) mediated by CAA could be attributed to inhibition of Na(+)-dependent extrusion of intracellular Ca(2+), indicating an inhibitory action of CAA on Na(+)/Ca(2+) exchange. Modulation of protein kinase A (PKA), but not protein kinase C (PKC) blunted the effect of CAA. Thus, CAA seems to inhibit Na(+)/Ca(2+) exchange by interaction with cyclic adenosine monophosphate (cAMP)-PKA-signaling. A 48-hour exposure to 15 micromol/L CAA significantly reduced cell number and protein content of RPTEC by induction of necrosis. This effect of 15 micromol/L CAA could be overcome by coadministration of the intracellular Ca(2+) chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTA-AM).


CONCLUSIONS
First, CAA inhibits the Na+/Ca2+-exchanger. Second, this effect is dependent on PKA. Third, CAA induces necrotic rather than apoptotic cell death. Finally, disturbed Ca(2+) homeostasis via Na(+)/Ca(2+) exchange contributes to the nephrotoxic action of CAA in RPTEC.
Benesic
Andreas
A
Department of Physiology, University of Wuerzburg, Germany. andreas.benesic@mail.uni-wuerzburg.de
Schwerdt
Gerald
G
Mildenberger
Sigrid
S
Freudinger
Ruth
R
Gordjani
Nader
N
Gekle
Michael
M
D000079:Acetaldehyde / Q000031:analogs & derivatives* / Q000378:metabolism; D018906:Antineoplastic Agents, Alkylating / Q000633:toxicity*; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D027682:Cation Transport Proteins / Q000378:metabolism; D002460:Cell Line; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D006706:Homeostasis / Q000187:drug effects; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007069:Ifosfamide / Q000633:toxicity*; D007674:Kidney Diseases / Q000139:chemically induced* / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D053499:Plasma Membrane Calcium-Transporting ATPases; D012333:RNA, Messenger / Q000032:analysis; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D012964:Sodium / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000235:genetics / Q000378:metabolism
D018906:Antineoplastic Agents, Alkylating; D027682:Cation Transport Proteins; D012333:RNA, Messenger; D019831:Sodium-Calcium Exchanger; D012964:Sodium; C004656:chloroacetaldehyde; D053499:Plasma Membrane Calcium-Transporting ATPases; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D000079:Acetaldehyde; D002118:Calcium; D007069:Ifosfamide