The nephrotoxin ochratoxin A induces apoptosis in cultured human proximal tubule cells.
To test the apoptotic potential of the nephrotoxic mycotoxin ochratoxin A (OTA), we exposed human proximal tubule-derived cells (IHKE cells) for various times to OTA concentrations close to those occurring during dietary exposure (from 2 to 100 nmol/L) and investigated caspase 3 activation, chromatin condensation, and DNA fragmentation. OTA induced a time- and concentration-dependent activation of caspase 3: concentrations as low as 5 nmol/L OTA caused a slight but significant increase in caspase 3 activity after 7 days of OTA exposure. Exposure to 10 nmol/L OTA for 72 or 24 h led to a significantly increased activity of caspase 3 in human proximal tubule-derived cells. Radical scavengers such as N-acetylcysteine had no effect on OTA-induced caspase 3 activation. Chelation of intracellular calcium with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis (acetoxymethylester) (BAPTA-AM) also showed no effect. Exposure to 30 nmol/L or more OTA led to DNA fragmentation and chromatin condensation in IHKE cells. Cultured renal epithelial MDCK-C7 and MDCK-C11 or OK cells also showed increased caspase 3 activity after OTA exposure. We conclude that exposure to low OTA concentrations can lead to direct or indirect caspase 3 activation and subsequently to apoptosis in cultured human proximal tubule cells and in other renal epithelial cell lines of different origins.
Schwerdt
G
G
Physiologisches Institut, Universität Würzburg, Germany. gerald.schwerdt@mail.uni-wuerzburg.de
Freudinger
R
R
Mildenberger
S
S
Silbernagl
S
S
Gekle
M
M
D000111:Acetylcysteine / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D002118:Calcium / Q000378:metabolism; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002461:Cell Line, Transformed; D002843:Chromatin / Q000187:drug effects; D004789:Enzyme Activation; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D009183:Mycotoxins / Q000633:toxicity*; D009793:Ochratoxins / Q000633:toxicity*
D002843:Chromatin; D009183:Mycotoxins; D009793:Ochratoxins; C025589:ochratoxin A; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D002118:Calcium; D000111:Acetylcysteine