Allopurinol and 5-aminosalicylic acid influence thiopurine-induced hepatotoxicity in vitro.
BACKGROUND
The use of thiopurines is frequently accompanied by hepatotoxicity. Studies on hepatocyte cultures showed a time- and dose-dependent increase of thiopurine toxicity. 5-Aminosalicylic acid (5-ASA) and allopurinol can influence thiopurine metabolism; however, it is unknown whether this affects in vitro cytotoxicity.


METHODS
Human hepatoma cells (Huh7, HepG2 and HepaRG) were incubated with increasing concentrations of thiopurines, 5-ASA or allopurinol. Water-soluble tetrazolium salt-1 (WST-1) cytotoxicity assays were used to calculate cell survival curves and half maximal inhibitory concentrations (IC50). Combination experiments with thiopurines with a fixed dose of 200 μM 5-ASA or 100 μM allopurinol were conducted in HepaRG cells. Caspase-3/7 activation was evaluated, and single cell electrophoresis analysis was performed.


RESULTS
A time- and dose-related cytotoxic effect was seen with azathioprine (AZA) in all hepatoma cells, whereas Huh7 and HepG2 cells did not show toxicity to 6-mercaptopurine (6-MP). HepaRG cells expressed the highest levels of drug metabolising enzymes, and therefore, combination experiments were conducted in HepaRG cells. Addition of a non-toxic dose of allopurinol resulted in a twofold to threefold increased cytotoxicity of all thiopurines, which seemed to be mediated by apoptosis/DNA damage.


CONCLUSIONS
The addition of allopurinol to thiopurines leads to a two-threefold increased cytotoxicity in HepaRG cells.
Department of Gastroenterology, Radboud University Nijmegen Medical Center, 455, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands, mark.broekman@radboudumc.nl.
Mark M T J
MM
Broekman
Hennie M J
HM
Roelofs
Dennis R
DR
Wong
Mariska
M
Kerstholt
Alex
A
Leijten
Frank
F
Hoentjen
Wilbert H M
WH
Peters
Geert J A
GJ
Wanten
Dirk J
DJ
de Jong
D000493:Allopurinol / Q000494:pharmacology*; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology; D000963:Antimetabolites / Q000494:pharmacology; D001379:Azathioprine / Q000494:pharmacology*; D045744:Cell Line, Tumor; D022781:Hepatocytes / Q000187:drug effects*; D006801:Humans; D015122:Mercaptopurine / Q000494:pharmacology*; D019804:Mesalamine / Q000494:pharmacology*
D000894:Anti-Inflammatory Agents, Non-Steroidal; D000963:Antimetabolites; D019804:Mesalamine; D000493:Allopurinol; D015122:Mercaptopurine; D001379:Azathioprine