Khat (Catha edulis)-induced apoptosis is inhibited by antagonists of caspase-1 and -8 in human leukaemia cells.
Khat chewing is a widespread habit that has a deep-rooted sociocultural tradition in Africa and the Middle East. The biological effects of khat are inadequately investigated and controversial. For the first time, we show that an organic extract of khat induces a selective type of cell death having all morphological and biochemical features of apoptotic cell death. Khat extract was shown to contain the major alkaloid compounds cathinone and cathine. The compounds alone and in combination also induced apoptosis. Khat-induced apoptosis occurred synchronously in various human cell lines (HL-60, NB4, Jurkat) within 8 h of exposure. It was partially reversed after removal of khat and the effect was dependent on de novo protein synthesis, as demonstrated by cotreatment with cycloheximide. The cell death was blocked by the pan-caspase inhibitor Z-VAD-fmk, and also by submicromolar concentrations of Z-YVAD-fmk and Z-IETD-fmk, inhibitors of caspase-1 and -8, respectively. The 50% inhibition constant (IC(50)) for khat (200 microg ml(-1))-induced apoptosis by Z-VAD-fmk, Z-YVAD-fmk and Z-IETD-fmk was 8 x 10(-7) M as compared to 2 x 10(-8) M and 8 x 10(-8) M, respectively. Western blot analysis showed a specific cleavage of procaspase-3 in apoptotic cells, which was inhibited by Z-VAD-fmk. The cell death by khat was more sensitively induced in leukaemia cell lines than in human peripheral blood leukocytes. It is concluded that khat induces a rather swift and sensitive cell death by apoptosis through mechanisms involving activation of caspase-1, -3 and -8.
Department of Odontology - Oral Pathology and Forensic Odontology, Faculty of Dentistry and Centre for International Health, University of Bergen, Bergen, Norway.
E A O
EA
Dimba
B T
BT
Gjertsen
T
T
Bredholt
K O
KO
Fossan
D E
DE
Costea
G W
GW
Francis
A C
AC
Johannessen
O K
OK
Vintermyr
D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D020170:Caspase 1 / Q000378:metabolism; D053148:Caspase 3; D053181:Caspase 8; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D029754:Catha / Q000737:chemistry*; D045744:Cell Line, Tumor; D003513:Cycloheximide / Q000494:pharmacology; D015853:Cysteine Proteinase Inhibitors; D004789:Enzyme Activation / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D007938:Leukemia / Q000378:metabolism / Q000473:pathology*; D009842:Oligopeptides / Q000494:pharmacology; D010936:Plant Extracts / Q000494:pharmacology*; D011437:Propylamines / Q000737:chemistry; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D000590:Amino Acid Chloromethyl Ketones; D061945:Caspase Inhibitors; D015853:Cysteine Proteinase Inhibitors; D004791:Enzyme Inhibitors; D009842:Oligopeptides; D010936:Plant Extracts; D011437:Propylamines; D011500:Protein Synthesis Inhibitors; C403753:benzyloxycarbonyl-isoleucyl-glutamyl-threonyl-aspartic acid fluoromethyl ketone; C460579:benzyloxycarbonyltyrosyl-valyl-alanyl-aspartic acid fluoromethyl ketone; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D003513:Cycloheximide; C505407:CASP3 protein, human; C505530:CASP8 protein, human; D053148:Caspase 3; D053181:Caspase 8; D020169:Caspases; D020170:Caspase 1