Mitochondria-cytochrome C-caspase-9 cascade mediates isorhamnetin-induced apoptosis.
Isorhamnetin is a flavanoid present in plants of the Polygonaceae family and is also an immediate metabolite of quercetin in mammals. Since the plasma level of isorhamnetin is maintained longer than quercetin, isorhamnetin may be a key metabolite to mediate the anti-tumor effect of quercetin. In the present study, we investigated the apoptotic mechanism of isorhamnetin in Lewis lung cancer (LLC) cells in vitro and established its in vivo anti-cancer efficacy. In cell culture, isorhamnetin significantly increased DNA fragmentation, and TUNEL positive apoptotic bodies and sub-G(1) apoptotic population in time- and dose-dependent manners. Western blot analyses revealed increased cleavage of caspase-3, and caspase-9 and PARP and increased cytosolic cytochrome C in isorhamnetin-treated cells. These events were accompanied by a reduced mitochondrial potential. Apoptosis was blocked by a general caspase inhibitor or the specific inhibitor of caspase-3 or -9. These in vitro results support mitochondria-dependent caspase activation to mediate isorhamnetin-induced apoptosis. Furthermore, an animal study revealed for the first time that isorhamnetin given by i.p. injection at a dose that is at least one order of magnitude lower than quercetin significantly suppressed the weights of tumors excised from LLC bearing mice. The in vivo anti-tumor efficacy was accompanied by increased TUNEL-positive and cleaved-caspase-3-positive tumor cells. Our data therefore support isorhamnetin as an active anti-cancer metabolite of quercetin in part through caspase-mediated apoptosis.
Lee
Hyo-Jung
HJ
Cancer Preventive Material Development Research Center, College of Oriental Medicine, Kyunghee University, 1 Hoegi-dong, Dongdaemun-gu, Seoul 131-701, Republic of Korea.
Lee
Hyo-Jeong
HJ
Lee
Eun-Ok
EO
Ko
Seong-Gyu
SG
Bae
Hyun-Soo
HS
Kim
Cheol-Ho
CH
Ahn
Kyoo-Seok
KS
Lu
Junxuan
J
Kim
Sung-Hoon
SH
D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000008:administration & dosage / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D018827:Carcinoma, Lewis Lung / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D053453:Caspase 9 / Q000378:metabolism*; D061945:Caspase Inhibitors; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D045304:Cytochromes c / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005260:Female; D044948:Flavonols / Q000008:administration & dosage / Q000494:pharmacology*; D007274:Injections, Intraperitoneal; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D008928:Mitochondria / Q000187:drug effects* / Q000201:enzymology / Q000473:pathology; D011794:Quercetin / Q000031:analogs & derivatives; D013997:Time Factors
D000972:Antineoplastic Agents, Phytogenic; D061945:Caspase Inhibitors; D015853:Cysteine Proteinase Inhibitors; D044948:Flavonols; C047368:3-methylquercetin; D045304:Cytochromes c; D011794:Quercetin; C506434:Casp9 protein, mouse; D053453:Caspase 9