Nonpunya et al. Chinese Medicine 2014, 9:12 http://www.cmjournal.org/content/9/1/12 RESEARCH Open Access Cratoxylum formosum (Jack) Dyer ssp. pruniflorum (Kurz) Gogel. (Hóng yá mù) extract induces apoptosis in human hepatocellular carcinoma HepG2 cells through caspase-dependent pathways Apiyada Nonpunya1, Natthida Weerapreeyakul2,3* and Sahapat Barusrux2,4,5 Abstract Background: Cratoxylum formosum (Jack) Dyer ssp. pruniflorum (Kurz) Gogel. (Hóng yá mù) (CF) has been used for treatment of fever, cough, and peptic ulcer. Previously, a 50% ethanol-water extract from twigs of CF was shown highly selective in cytotoxicity against cancer cells. This study aims to investigate the molecular mechanisms underlying the apoptosis-inducing effect of CF. Methods: The cytotoxicity of CF was evaluated in the human hepatocellular carcinoma (HCC) HepG2 cell line in comparison with a non-cancerous African green monkey kidney epithelial cell line (Vero) by a neutral red assay. The apoptosis induction mechanisms were investigated through nuclear morphological changes, DNA fragmentation, mitochondrial membrane potential alterations, and caspase enzyme activities. Results: CF selectively induced HepG2 cell death compared with non-cancerous Vero cells. A 1.5-fold higher apoptotic effect compared with melphalan was induced by 120 μg/mL of the 50% ethanol-water extract of CF. The apoptotic cell death in HepG2 cells occurred via extrinsic and intrinsic caspase-dependent pathways in dose- and time-dependent manners by significantly increasing the activities of caspase 3/7, 8, and 9, decreasing the mitochondrial membrane potential, and causing apoptotic body formation and DNA fragmentation. Conclusions: CF extract induced a caspase-dependent apoptosis in HepG2 cells. Background strategy for both primary and secondary HCC prevention Hepatocellular carcinoma (HCC) is the fifth leading cancer of HCC by phytochemicals or non-nutritive plant com- worldwide and the third cause of cancer death [1] with a pounds. The development and research of new anticancer poor prognosis owing to the ineffectiveness of therapy [2]. agents has decreased HCC-associated mortality [2]. The treatment options for HCC patients, such as surgical Some anti-cancer agents induced apoptosis of cancer resection and liver transplantation [2], are only appropriate cells [3]. Apoptotic cancer cells are characterized by mor- for the early stages of tumor development. A second pri- phological changes, including chromatin condensation, mary site can be caused by a malignant clone even if the membrane blebbing, and apoptotic body formation, first cancer site has been diagnosed and resected [1]. Che- which are related to DNA fragmentation observed as a moprevention is considered to be another important ladder on gel electrophoresis [2]. Apoptosis comprises two major pathways, the intrinsic and extrinsic pathways * Correspondence: [email protected] [4]. The caspase enzymes are proteases playing an im- 2Center for Research and Development of Herbal Health Products portant role in the classification of apoptosis. Several (CRD-HHP), Khon Kaen University, Khon Kaen 40002, Thailand studies have screened potential compounds that can trig- 3Faculty of Pharmaceutical Sciences, Khon Kaen University, Khon Kaen 40002, Thailand ger apoptosis via measurement of caspase activity [5-7]. Full list of author information is available at the end of the article © 2014 Nonpunya et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Nonpunya et al. Chinese Medicine 2014, 9:12 Page 2 of 9 http://www.cmjournal.org/content/9/1/12 Table 1 Cytotoxicity and selectivity index of 50% ethanol-water extract of CF on HepG2 cells compared with Vero cells c Sample Part IC50 ±SD(μg/mL) Selectivity index (SI) used HepG2 Vero Cratoxylum formosum (Jack) Dyer ssp. pruniflorum (Kurz) Gogel. Twig 55.9 ± 10.6 Inactiveb 8.9 Melphalana 37.7 ± 9.8 59.9 ± 3.2 1.6 Data expressed as the mean ± SD of three determinations. aStandard anticancer drug. b IC50 > 500 μg/mL is considered inactive. cSI referred to Selectivity Index, when SI value > 3 indicates high selectivity. Currently, anticancer drugs such as cisplatin, paclitaxel, and human oral cancer KB cells [13]. The cytotoxic ef- adriamycin, and melphalan have been reported to eradi- fect of the CF extract was selectively high against human cate cancer via the induction of apoptosis [5,7-9]. leukemia cancer cells (U937) compared with normal Cratoxylum formosum (Jack) Dyer ssp. pruniflorum cells (Vero). Our group previously reported the apop- (Kurz) Gogel. (CF) (Hóng yá mù or commonly known as totic effect of CF on U937 cells, based on observations “Kuding Tea” in Southwest mainland China [10] and of DNA laddering and nuclear morphological changes “Tiew kon” in Thailand [11]) is widely found in South- [8]. This study aims to investigate the molecular mecha- east Asia [12] and belongs to the family of Guttiferae. nisms underlying the apoptosis-inducing effect. Five other Cratoxylum species were found in Thailand and Southwest China, namely Cratoxylum arborescens, Materials and methods Cratoxylum cochinchinense, Cratoxylum maingayi, Cra- Reagents and chemicals toxylum sumatranum ssp. neriifolium, and Cratoxylum The organic solvents used for extraction were of analytical formosum (Jack) Dyer [13]. grade and obtained from Fisher Scientific (Loughborough, CF has been used in Chinese medicine for treatment UK) and Labscan (Bangkok, Thailand). The reagents used of fever, cough, stomach ache, flatulence, diarrhea, food in the cell assays were of molecular biological grade. Dul- poisoning, internal bleeding, and peptic ulcer [10,13]. It becco’s modified Eagle’s medium (DMEM), fetal bovine has also been used as a diuretic and for its tonic effects serum (FBS), penicillin, and streptomycin were purchased [10]. CF produces various secondary metabolites includ- from GIBCO® (Invitrogen Corporation, Carlsbad, CA, ing xanthones, anthraquinones [10,14], triterpenoids, fla- USA). Standard reagents, melphalan, and 4′,6-diamidino- vonoids [13-16], and phenolic compounds [6]. These 2-phenylindole (DAPI) were obtained from Sigma-Aldrich compounds are widely found in plants and some of Inc. (St. Louis, MO, USA). Dimethylsulfoxide (DMSO) them have been shown to exert cytotoxic effects toward was purchased from United States Biological (Salem, MA, some cancer cell lines and other biological activities such USA). The reagents for cytotoxicity testing included neu- as antibacterial effects and antimicrobial effects [10]. tral red (NR) and sodium bicarbonate (NaHCO3). We Fractions obtained from dichloromethane crude ex- used a FlexiGene DNA Kit (Qiagen GmbH, Germany), tract of CF roots was reported to exhibit anticancer ac- isopropyl alcohol biotechnology grade (Bio Basic Inc., tivity against MCF-7 human breast cancer cells, human USA), and methanol analytical grade (BDH, England). cervical cancer HeLa cells, colon cancer HT-29 cells, Agarose molecular grade was purchased from Bio-Rad (Hercules, CA, USA). We purchased a 100 bp + 1.5 kb DNA ladder stained with loading dye from SibEnzyme Ltd. (Russia). Caspase-Glo® 3/7, 8, and 9 Assay Kits were purchased from Promega (Madison, WI, USA). We ob- tained 3,3′-dihexyloxacarbocyanine iodide (DiOC6) from Sigma-Aldrich Inc. Pure concentrated hydrogen peroxide (35%, v/v) was purchased from Qrec Co. Ltd. (New Zealand). Cell culture An African green monkey kidney cell line (Vero) at pas- sage 26 and a human HCC cell line (HepG2) at passage 40 were maintained in DMEM supplemented with 10% FBS and 1% (w/v) penicillin/streptomycin. All cells were Figure 1 The HepG2 viability profile after treated with cultured at 37°C in a humidified atmosphere containing melphalan or CF for 24 h (n = 3). 5% CO2. Nonpunya et al. Chinese Medicine 2014, 9:12 Page 3 of 9 http://www.cmjournal.org/content/9/1/12 (A)Melphalan treated HepG2 cells (B)C. formosum treated HepG2 cells (C)Control HepG2 cells (untreated) (41.6±2.1%) (62.2±4.5%) (0%) Figure 2 Nuclei morphological changes and percentage of apoptotic cells in HepG2 cells (A) after treatment with 80 μg/mL of melphalan, (B) 120 μg/mL of CF, and (C) in the control or untreated HepG2 cells. Apoptotic bodies are indicated by white arrows. Pictures captured using an inverted fluorescent microscope at 40 × objective magnification. Plant material and extraction selective cancer cell line cytotoxicity [9]. The SI of the Twigs of CF were collected in 2008 from the northeastern test compound was compared with the IC50 for the Vero region of Thailand. The plants were visually authenticated cells divided by the IC50 for the HepG2 cells. according to taxonomy [17] and voucher specimens (TT- OC-SK-862) were deposited at the Medicinal Herbarium Apoptosis induction assay of the Faculty of Pharmaceutical Sciences, Khon Kaen Uni- DAPI staining assay versity, Thailand. Briefly, 1 kg of dried plants was cut and Cells (1 × 106 cells/well) were treated with CF extract macerated with 6 L of 50% ethanol and water for 7 days. and the melphalan for 24 h at 2 × IC , and the morpho- The solvent was filtered, distilled in vacuo by a rotary 50 logical changes of the induced apoptotic cells were de- evaporator below 40°C, and freeze-dried, yielding a 3.78% termined by DAPI staining. The concentrations of CF (w/w) crude extract. The crude extract was stored at 4°C extract and melphalan used in the following apoptosis in an airtight container. The stock solution of CF extract experiments were 120 and 80 μg/mL, respectively. The was freshly prepared and dissolved in 100% DMSO, and cells were fixed in pure methanol at 4°C for 10 min, and the concentration of DMSO in all experiments was re- then stained with DAPI (1 μg/mL) at room temperature stricted to ≤ 1% to maintain the cytotoxicity at < 10%.