Role of NADPH oxidase-mediated generation of reactive oxygen species in the mechanism of apoptosis induced by phenolic acids in HepG2 human hepatoma cells

Although plant-derived phenolic acids have been reported to have anti-cancer activity, the exact mechanism is not completely understood. In this study, we investigated the role for reactive oxygen species (ROS) as a mediator of the apoptosis induced by caffeic acid (CA) and ferulic acid (FA), common phenolic acids in plants, in HepG2 human hepatoma cells. CA and FA reduced cell viability, and induced apoptotic cell death in a dose-dependent manner. In addition, they evoked a dose-related elevation of intracellular ROS. Treatment with various inhibitors of NADPH oxidase (diphenylene iodonium, apocynin, neopterine) significantly blunted both the generation of ROS and the induction of apoptosis induced by CA and FA. These results suggest that ROS generated through activation of NADPH oxidase may play an essential role in the apoptosis induced by CA and FA in HepG2 cells. These results further suggest that CA and FA may be valuable for the therapeutic management of human hepatomas.     

Carnosic acid induces autophagic cell death through inhibition of the Akt/mTOR pathway in human hepatoma cells

The therapeutic goal of cancer treatment is now geared towards triggering tumour‐selective cell death with autophagic cell death being required for the chemotherapy of apoptosis‐resistant cancer. In this study, Carnosic acid (CA), a polyphenolic diterpene isolated from Rosemary (Rosemarinus officinalis), significantly induced autophagic cell death in HepG2 cells. Ca treatment caused the formation of autophagic vacuoles produced an increasing ratio of LC3‐II to LC3‐I in a time‐ and dose‐dependent manner but had no effect on the levels of autophagy‐related protein ATG6 and ATG13 expression. Autophagy inhibitors, 3‐methyladenine (3‐MA), chloroquine and bafilomycin A1, or ATG genes silencing in HepG2 cells significantly inhibited CA‐induced autophagic cell death. The CA treatment decreased the levels of phosphorylated Akt and mTOR without any effects on PI3K or PTEN. Most importantly, overexpression of Akt and knockdown of PTEN attenuated autophagy induction in CA‐treated cells. Taken together, our results indicated that CA induced autophagic cell death through inhibition of the Akt/mTOR pathway in human hepatoma cells. These findings suggest that CA has a great potential for the treatment of hepatoma via autophagic induction. Copyright © 2014 John Wiley & Sons, Ltd.     

Inhibition of autophagy promotes caspase-mediated apoptosis by tunicamycin in HepG2 cells

Tunicamycin (TM) causes accumulation of unfolded protein in endoplasmic reticulum (ER) lumen and introduces from elsewhere ER stress. This study was to assess the apoptosis and autophagy effect induced by TM on HepG2 cells and the role of autophagy in the system. The viability of HepG2 cells was significantly inhibited by TM in a dose-dependent manner detected by MTT assay. Then, the apoptotic morphology change, increasing apoptotic cell rate suggested that apoptosis was induced by TM in a time- and dose-dependent manner. To further determine the involvement of caspase-dependent pathway in TM-induced apoptosis, we discover that the activity of caspase-3/7, 8, 9 and cleavage of PARP markedly increased after TM treatment and the apoptosis was effectively attenuated by using caspase-9 and pan caspase inhibitor. Moreover, provided the rising stained acidic vacuoles and an increased level of LC3II and activation of Beclin1, we concluded that autophagy could be triggered by TM in a time- and dose-dependent manner. In addition, the inhibition of autophagy efficiently promoted TM-induced cell death identified by MTT assay. Meanwhile, the apoptotic cell rate and caspase-3 activation increased significantly after autophagy blockage. In conclusion, we found that TM initiated apoptosis and autophagy both in a time- and dose-dependent manner in HepG2 cells; and inhibition of autophagy may promote TM-induced cell death through enhancing apoptosis.     

氯唑沙腙对抗HepG2肿瘤细胞的作用研究

目的研究氯唑沙腙(chlorzoxazone)对HepG2细胞存活和凋亡的影响。方法采用MTT法检测氯唑沙腙对体外培养的HepG2细胞存活率的影响,通过检测LDH释放观察氯唑沙腙对HepG2细胞的致坏死作用,通过TUNEL法评价细胞凋亡率,透射镜评价细胞的超微结构。结果氯唑沙腙在50～500μmol.L-1浓度范围内对HepG2细胞的存活率均有抑制作用,呈明显的剂量依赖效应关系。荧光显微镜和透射电镜下可见典型的肿瘤细胞凋亡改变。氯唑沙腙在100、200、300及500μmol.L-1浓度下作用48h均可诱导HepG2细胞凋亡,具有明显的剂量效应关系。氯唑沙腙100、200、300及500μmol.L-14种浓度分别作用于HepG2细胞24、48及72h,发现以上各种浓度在48h即可诱导细胞凋亡,作用时间越长,凋亡率越高,有明显的时间效应关系。结论氯唑沙腙能够抑制HepG2细胞存活和诱导细胞凋亡。     

The course of uncarinic acid E-induced apoptosis of HepG2 cells from damage to DNA and p53 activation to mitochondrial release of cytochrome c

Uncarinic acid E, an active component isolated from Gelsemium elegans BENTH, has been reported to exhibit antitumor effects, but little is known about its molecular mechanisms of action. In this study, the growth-inhibitory activity of uncarinic acid E for HepG2 cells is in time- and dose-dependent manner. HepG2 cells treated with uncarinic acid E exhibited several typical characteristics of apoptosis through photomicroscopical observation, DNA agarose gel electrophoresis. The inhibitory effect of uncarinic acid E on HepG2 cells was partially reversed by the inhibitors of pan-caspase, caspase-3 and caspase-6. The protein expression ratio of Bcl-xL/Bax and Bcl-2/Bax was down-regulated and uncarinic acid E-induced apoptosis involves the initial phase mediated by the balance among Bcl-xL, Bcl-2 and Bax proteins, resulting in cytochrome c release from the mitochondria. Uncarinic acid E significantly increased the expression of p53 proteins indicates that p53 plays a pivotal role in the initiation phase of uncarinic acid E-induced HepG2 cell apoptosis. The phoshatidylinositol 3-kinase (PI3-K) family inhibitor wortmanin and the MEK inhibitor (PD98059) rescued the viability loss induced by uncarinic acid E through the expression of p53. Taken together, uncarinic acid E induces apoptosis in HepG2 cells via accumulation of p53, alters the Bax/Bcl-2 ratio, and activates caspases, resulting in cytochrome c release from the mitochondria.     

Furazolidone induces apoptosis through activating reactive oxygen species-dependent mitochondrial signaling pathway and suppressing PI3K/Akt signaling pathway in HepG2 cells

Furazolidone (FZD), a synthetic nitrofuran with a broad spectrum of antimicrobial activities, has been shown to be genotoxic and potentially carcinogenic in several types of cells. However, the proper molecular mechanisms of FZD toxicity remain unclear. This study was aimed to explore the effect of FZD on apoptosis in HepG2 cells and uncover signaling pathway underlying the cytotoxicity of FZD. The results showed that FZD induced apoptosis in HepG2 cells in a dose-dependent manner characterized by nuclei morphology changes, cell membrane phosphatidylserine translocation, poly (ADP-ribose) polymerase (PARP) cleavage and a cascade activation of caspase-9 and -3. FZD could enhance reactive oxygen species (ROS) generation, up-regulate Bax/Bcl-2 ratio, disrupt mitochondrial membrane potential (MMP) and subsequently cause cytochrome c release. Both ROS scavenger (N-acetyl cysteine, NAC) and caspase inhibitors suppressed FZD-induced apoptosis. Furthermore, NAC attenuated FZD-induced ROS generation and mitochondrial dysfunction. Meanwhile, FZD treatment inhibited both the activation and expression of Akt, and PI3K/Akt inhibitor LY294002 promoted FZD-induced apoptosis. On the contrary, PI3K/Akt activator insulin-like growth factor-1 (IGF-1) attenuated lethality of FZD in HepG2 cells. In conclusion, it is first demonstrated that FZD-induced apoptosis in HepG2 cells might be mediated through ROS-dependent mitochondrial signaling pathway and involves PI3K/Akt signaling.     

齐墩果酸诱导人肝癌HepG2细胞凋亡及其作用机制研究

目的探讨齐墩果酸对人肝癌HepG2细胞增殖的抑制作用和诱导凋亡作用,并考察其作用机制。方法采用MTT法检测齐墩果酸对HepG2细胞增殖的影响,吖啶橙/溴化乙锭(AO/EB)双重染色法进行细胞形态学观察,流式细胞仪检测细胞凋亡、活性氧(ROS)水平和线粒体膜电位(MMP)的变化。结果随着齐墩果酸浓度的升高,抑制率显著增加,呈现明显的时间与剂量相关性;齐墩果酸在25.0、50.0、100.0μmol/L作用12 h时,细胞形态学发生改变,细胞的总凋亡率随着齐墩果酸浓度的增加而升高,细胞中ROS水平随着齐墩果酸浓度的增加而升高,细胞内的MMP水平随着齐墩果酸浓度的增加而降低。结论齐墩果酸通过调节ROS和MMP体外抑制人肝癌HepG2细胞的增殖和诱导其凋亡     

Mono-2-ethylhexyl phthalate induced loss of mitochondrial membrane potential and activation of Caspase3 in HepG2 cells

L02 and HepG2 cells were exposed to mono-(2-ethylhexyl) phthalate (MEHP) at concentrations of 6.25-100μM. After 48h treatment, MEHP decreased HepG2 cell viability in a concentration-dependent manner and L02 cell viability in the 50 and 100μM groups (p<0.01). Furthermore, at 24 and 48h after treatment, MEHP decreased the glutathione levels of HepG2 cells in all treatment groups and in the ΔΨ(m) in L02 and HepG2 cells with MEHP≥25μM (p<0.05 or p<0.01). At 24h after treatment, MEHP induced activation of caspase3 in all treated HepG2 and L02 cells (p<0.05 or p<0.01) except the 100μM MEHP treatment group. The increase in the Bax to Bcl-2 ratio suggests that Bcl-2 family involved in the control of MEHP-induced apoptosis in these two cell types. The data suggest that MEHP could induce apoptosis of HepG2 cells through mitochondria- and caspase3-dependent pathways.     

Molecular mechanisms of adenosine-induced apoptosis in human HepG2 cells

AIM: To investigate effects of adenosine on cell proliferation and apoptosis in human HepG2 cells. METHODS: HepG2 cells were incubated in the presence of adenosine (0.1-5 mmol/L) for 12-48 h, and the effect of adenosine on cell proliferation was evaluated by using 3-(4,5-dimethyl-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. Hoechst 33342 fluorescent staining, dUTP-fluorescein isothiocyanate (FITC) fluorescence and flow cytometric analysis techniques were used to observe cell apoptosis. The effects of adenosine receptor (A1, A2a, A3 and nonspecific receptor) antagonists (8-cpt, DMPX, MRS1191, and theophylline) and an adenosine transporter protein inhibitor (dipyridamole) on adenosine-induced cell apoptosis were observed. Mitochondrial membrane potential was analyzed using DePsipher fluorescent staining, and caspase activity was detected using a Fluorometric assay kit and a fluorescence microplate reader. RESULTS: Adenosine significantly reduced cell viability in a dose- and time-dependent manner. The cytotoxicity of adenosine was related to the induction of cell apoptosis. Four adenosine receptor antagonists had no effect on cell apoptosis. However, dipyridamole significantly reduced the percentage of adenosine-induced apoptotic cells from 27.3% to 7.1% (P<0.05). At 48 h after treatment, 3 mmol/L adenosine increased caspase-3 activity 3.5-fold; dipyridamole markedly decreased caspase-3 activity 1.6-fold, and decreased apoptotic cell numbers. When HepG2 cells were treated with 3 mmol/L adenosine, mitochondrial membrane potential and the activity of caspase-8 or -9 remained unchanged. CONCLUSION: Our results suggest that adenosine-induced apoptosis in HepG2 cells is related to intracellular events rather than cell surface receptors, and that a caspase-3 cascade activation is required, which is not mediated via a mitochondrial pathway.     

Dihydroartemisinin induces apoptosis in human leukemia cells HL60 via downregulation of transferrin receptor expression

Dihydroartemisinin (DHA), a water-soluble active metabolite of artemisinin derivatives, is the safest and most effective antimalarial analog of artemisinin. In the present investigation, we assessed the apoptotic effect of DHA on leukemia HL60 cells and its regulation of transferrin receptor (TfR). Cell growth inhibition was assessed by Trypan blue exclusive staining; the expression of caspase-3, Bcl-2, and Bax in HL60 cells was evaluated by Western blotting; DHA-induced apoptosis was determined by AO/EB double staining, DNA fragmentation assay, and flow cytometric analysis; the expression of TfR in HL60 cells was examined by real-time PCR assays, Western blotting, and flow cytometric analysis. DHA could specifically reduce the mRNA and protein expression of TfR in HL60 cells, and the flow cytometric analysis presented the unity tendency that the TfR content decreased progressively in a dose-dependent manner. Consequently, DHA exhibited high anticancer activity in HL60 cells; MTT assay and growth inhibition assay showed that DHA could specifically inhibit the growth of HL60 cells in a dose-dependent (0.25-8 micromol/l) and time-dependent (12-72 h) manner. DHA-induced DNA fragmentation also induced the activation of caspase-3 and influenced the expression of Bcl-2 and Bax. Taken together, these data from our study show that DHA can induce HL60 cell apoptosis via the effect of downregulation TfR expression resulting in an induction of apoptosis through the mitochondrial pathway, and it might be a potential antileukemia strategy for leukemia therapy.     

冬凌草甲素上调人肝癌HepG2细胞 PTEN基因表达与诱导凋亡作用

［摘要］目的研究冬凌草甲素诱导人肝细胞癌HepG2细胞凋亡及与PTEN基因表达的关系。方法四甲基偶氮唑蓝（MTT）比色法测定冬凌草甲素诱导HepG2细胞的增长抑制；流式细胞术分析DNA倍体测定细胞凋亡；琼脂糖凝胶电泳观察DNA碎片；逆转录 聚合酶链式反应（RT PCR）半定量分析冬凌草甲素诱导人肝细胞癌HepG2细胞后PTEN mRNA的表达情况。结果MTT比色法测得冬凌草甲素对HepG2细胞增殖具有明显抑制作用，并随冬凌草甲素浓度的升高及作用时间的延长而增强；流式细胞术分析HepG2细胞经冬凌草甲素诱导后，细胞凋亡率随作用时间延长而增加；DNA电泳呈梯状条带。RT PCR测得PTEN基因mRNA的表达随细胞凋亡增加而逐渐增高。 结论冬凌草甲素能够明显抑制HepG2细胞增殖，并诱导肝癌细胞凋亡， 其作用途径可能与上调PTEN mRNA表达有关。     

白藜芦醇烟酸酯抑制人肝癌细胞HepG2增殖并诱导细胞的凋亡

目的：观察白藜芦醇的修饰物白藜芦醇烟酸酯（ResT）对人肝癌细胞HepG2生长增殖的影响及诱导凋亡的作用。方法：用不同浓度的ResT处理HepG2细胞，MTT法检测ResT对HepG2细胞生长增殖的抑制作用；应用Hochest荧光染色法观察凋亡细胞的发生；流式细胞术（FCM）检测分析细胞周期和细胞凋亡率；比色法测定Caspase-3酶活性。结果：ResT抑制HepG2细胞的增殖并呈现一定的量效和时效关系，HepG2细胞与ResT作用后出现典型的凋亡细胞形态改变，FCM分析显示大部分细胞阻滞于G1期，S期细胞比例降低。且药物作用组出现凋亡峰。药物作用12、24、48h后，细胞的凋亡率分别为8．7％、21．1％、和32.7％。显示ResT诱导的细胞凋亡作用随时间的延长而增加，同时Caspase-3酶活性显著增强。结论：ResT可抑制人肝癌细胞HepG2的生长增殖，其作用机制之一可能与阻滞细胞于G1期及诱导细胞凋亡有关。     

Gnidilatimonoein from<Emphasis Type="Italic">Daphne mucronata</Emphasis> induces differentiation and apoptosis in leukemia cell lines

Gnidilatimonoein is a new diterpene ester, recently isolated from the leaves of Daphne macronata with potent anti-tumoral and anti-metastastic activities (Yazdanparast et al., 2004). Promyeloblastic (KG1), promyelocytic (NB4) and promonocytic (U937) cells were cultured in the presence of various concentrations of the drug (0.5-3.0 microM) for 3 days. Herein, we report that gnidilatimonoein induces differentiation and apoptosis in KG1, NB4 and U937 cells. The drug inhibited growth and proliferation of KG1, NB4 and U937 cells with IC50 values of 1.5, 1.5 and 1.0 microM, respectively, after 72 h of treatment. Cell viability was also decreased by 18%, 20% and 23%, respectively, after 72 h treatment with the drug. NBT reducing assay revealed that the inhibition of proliferation is associated with differentiation especially toward monocytes-like morphology. Indeed, the drug at 0.5-1.5 microM induced differentiation by 5-50% in the cells. Acridine orange/ethidium bromide (AO/EtBr) double staining and DNA fragmentation assays revealed that apoptosis occurred after differentiation of the cells. Based on the present data, it seems that the new compound is a good candidate for further evaluation as an effective chemotherapeutic agent acting through induction of differentiation and apoptosis.     

3-O-(3-甲氧基肉桂酰)-甘草次酸酯对HepG2细胞体外抑制作用研究

目的探讨3-O-(3-甲氧基肉桂酰)-甘草次酸酯对Hep G2细胞体外抑制作用及其作用机制。方法采用MTT法考察药物对肝癌细胞Hep G2、宫颈癌细胞He La、结肠癌细胞HT-29、心肌细胞H9C2、犬肾上皮细胞MDCK和血管内皮细胞HY926的细胞毒性,利用细胞染色法观察不同浓度3-O-(3-甲氧基肉桂酰)-甘草次酸酯对Hep G2细胞形态的影响,流式细胞术评价该化合物诱导Hep G2细胞的凋亡。结果 3-O-(3-甲氧基肉桂酰)-甘草次酸酯具有较好的抑制Hep G2细胞增殖活性作用,其半数有效抑制浓度(IC50)为8.28μmol/L,明显强于甘草次酸的活性(IC5050μmol/L)。3-O-(3-甲氧基肉桂酰)-甘草次酸酯及其合成原料甘草次酸、3-甲氧基肉桂酸对非肿瘤细胞MDCK、HY926、H9C2细胞毒性较弱(IC5024μmol/L)。3-O-(3-甲氧基肉桂酰)-甘草次酸酯浓度在12.5μmol/L时,对MDCK、HY926、H9C2细胞抑制率分别为17.05%、16.08%、4.66%,与对Hep G2细胞的抑制效果相比差异明显。不同浓度3-O-(3-甲氧基肉桂酰)-甘草次酸酯对Hep G2细胞Giemsa染色、H33342染色的细胞形态有明显差异。随着3-O-(3-甲氧基肉桂酰)-甘草次酸酯浓度的升高,早期凋亡率逐渐增加,而晚期凋亡率无明显变化,提示3-O-(3-甲氧基肉桂酰)-甘草次酸酯可以有效地诱导细胞早期凋亡,并呈现一定的量效关系。结论 3-O-(3-甲氧基肉桂酰)-甘草次酸酯具有良好的抗肿瘤作用,对Hep G2细胞抑制效果最好,对非癌细胞MDCK、HY926、H9C2没有明显抑制效果,该作用主要通过诱导Hep G2细胞凋亡,且呈现一定的量效关系。     

Effects of glycolic acid on the induction of apoptosis via caspase-3 activation in human leukemia cell line (HL-60).

Apoptosis is a particular process that leads to the programmed cell death, and it has been a potentially therapeutic target of cancer. In this study, we evaluated the possible apoptotic effects of glycolic acid on human leukemia cell line (HL-60) in vitro. The morphological changes, cell viability, apoptosis induction, and caspase-3 activity were measured by phase microscopy, flow cytometry, and Western blot analysis. Morphological changes including shrinkage of cells were clearly demonstrated in HL-60 cells treated with increasing concentrations of glycolic acid. Cell viability was significantly affected by glycolic acid treatment in a dose- and time-dependent manner. In comparison to the control group, glycolic acid treatment had a profound effect in the induction of apoptosis by flow cytometric assays. In the cell cycle analysis, glycolic acid caused the increased percentage of cells in G2/M phase and the decreased expression of the cyclin A and cyclin B1, suggesting the induction of G2/M arrest of cell cycle by glycolic acid. Moreover, glycolic acid treatment promoted caspase-9 and -3 activity in a dose-dependent manner, but caspse-8 activity was not affected during the same process. Glycolic acid co-administrated with broad-spectrum caspase inhibitor, z-VAD-fmk, caspase-3 activity was blunted and apoptosis was also markedly blocked in HL-60 cells. In conclusion, glycolic acid-induced apoptosis in HL-60 cells may be through the activation of caspase-3. Future studies focusing on cell signaling and biological significance of glycolic acid-induced apoptosis would lead to exploring the mechanisms of chemotherapeutic potency of glycolic acid in human cancers.     

环孢素A诱导人胃癌MGC80-3细胞凋亡以及对P糖蛋白表达的影响

目的研究环孢素A(cyclosporin A,CsA)诱导人胃癌MGC80-3细胞的凋亡作用以及对P-糖蛋白(P-glycoprotein,P-gp)表达的影响,探讨细胞凋亡与P-gp表达的关系。方法四甲基偶氮唑蓝(MTT)比色法检测不同浓度CsA处理24、48、72h对MGC80-3细胞增殖的抑制作用,吖啶橙/溴化乙啶(acridine orange/ethidium bromide,AO/EB)染色和An-nexin-V-FITC/PI双染分别于荧光显微镜和流式细胞仪(flowcytometry,FCM)分析CsA处理48 h后凋亡细胞形态的改变并计算细胞凋亡率,Western blot法检测MGC803细胞P-gp的表达。结果 CsA对人胃癌MGC80-3细胞增殖有抑制作用,在0～25.0μmol·L-1浓度范围和24～72 h时间范围内CsA对胃癌MGC80-3细胞增殖抑制作用与药物浓度和作用时间呈现明显依赖关系。AO/EB染色和Annexin V-FITC/PI双染FCM检测显示CsA处理MGC80-3细胞48 h后通过荧光显微镜观察可见细胞出现形态不规则、核染色质固缩等细胞凋亡形态学的改变,提高CsA作用剂量,导致细胞凋亡率增加,与control组相比差异具有统计学意义(P<0.05或P<0.01)。Western blot表明CsA下调了MGC80-3细胞P-gp的表达,蛋白表达量呈现浓度依赖性降低(P<0.05或P<0.01)。结论 CsA能诱导人胃癌MGC80-3细胞凋亡和下调P-gp的表达,其诱导细胞凋亡作用可能与P-gp的表达相关。     

Ca2+ influx mediates apoptosis induced by 4-aminopyridine, a K+ channel blocker, in HepG2 human hepatoblastoma cells

Apoptosis appears to be implicated in the pathogenesis and therapeutic applications of cancer. In this study we investigated the induction of apoptosis by 4-aminopyridine (4-AP), a K(+) channel blocker, and its mechanism in HepG2 human hepatoblastoma cells. 4-AP reduced cell viability and induced DNA fragmentation, a hallmark of apoptosis, in a dose-dependent manner. In addition, 4-AP induced a sustained increase in intracellular Ca(2+) concentration, which was completely inhibited by the extracellular Ca(2+) chelation with EGTA. 4-AP also induced Mn(2+) influx, indicating that the 4-AP-induced increased intracellular Ca(2+) levels were due to activation of Ca(2+) influx pathway. 4-AP also depolarized membrane potential that was measured by using di-O-C(5)(3), a voltage-sensitive fluorescent dye. 4-AP-induced Ca(2+) influx was significantly inhibited not by voltage-operative Ca(2+) channel blockers (nifedipine or verapamil), but by flufenamic acid (FA), a known nonselective cation channel blocker. Quantitative analysis of apoptosis by the flow cytometry revealed that treatment with either FA or BAPTA, an intracellular Ca(2+) chelator, significantly inhibited the 4-AP-induced apoptosis. Taken together, these results suggest that the observed 4-AP-induced apoptosis in the HepG2 cells may result from Ca(2+) influx through the activation of voltage-sensitive Ca(2+)-permeable non-selective cation channels. These results further suggest that membrane potential change by modulation of K(+) channel activity may be involved in the mechanism of apoptosis in human hepatoma cells.     

Protective effect of caffeic acid phenethyl ester on tert-butyl hydroperoxide-induced oxidative hepatotoxicity and DNA damage

Increased oxidative stress and associated high levels of free radical generation have been described to occur during the pathogeneses of various diseases in animal models. In the present work, we investigated the protective effects of the phenethyl ester of caffeic acid (CAPE), an active component of honeybee propolis, on tert-butyl hydroperoxide (t-BHP)-induced hepatotoxicity in a cultured HepG2 cell line and in rat liver. CAPE was found to significantly reduce t-BHP-induced oxidative injury in HepG2 cells, as determined by cell cytotoxicity, and lipid peroxidation and reactive oxygen species (ROS) levels in a dose-dependent manner. Furthermore, CAPE protected HepG2 cells against t-BHP-induced oxidative DNA damage, as determined by the Comet assay. Consistently, CAPE reduced hydroxyl radical-induced 2-deoxy-d-ribose degradation by ferric ion-nitrilotriacetic acid and H2O2, and also removed the superoxide anion generated by a xanthine/xanthine oxidase system. Our in vivo study showed that pretreatment with CAPE prior to the administration of t-BHP significantly and dose-dependently prevented increases in the serum levels of hepatic enzyme markers (alanine aminotransferase and aspartate aminotransferase) and reduced lipid peroxidation in rat liver. Moreover, histopathological evaluation of livers consistently revealed that CAPE reduced liver lesion induction by t-BHP. Taken together, these results suggest that the protective effects of CAPE against t-BHP-induced hepatotoxicity may, at least in part, be due to its ability to scavenge ROS and protect DNA from oxidative stress-induced damage.     

Mechanism of apoptosis induced by diazoxide,a K<Superscript>+</Superscript> channel opener,in HepG2 Human hepatoma cells

The effect of diazoxide, a K+ channel opener, on apoptotic cell death was investigated in HepG2 human hepatoblastoma cells. Diazoxide induced apoptosis in a dose-dependent manner and this was evaluated by flow cytometric assays of annexin-V binding and hypodiploid nuclei stained with propidium iodide. Diazoxide did not alter intracellular K+ concentration, and various inhibitors of K+ channels had no influence on the diazoxide-induced apoptosis; this implies that K+ channels activated by diazoxide may be absent in the HepG2 cells. However, diazoxide induced a rapid and sustained increase in intracellular Ca(2+) concentration, and this was completely inhibited by the extracellular Ca(2+) chelation with EGTA, but not by blockers of intracellular Ca(2+) release (dantrolene and TMB-8). This result indicated that the diazoxide-induced increase of intracellular Ca(2+) might be due to the activation of a Ca(2+) influx pathway. Diazoxide-induced Ca(2+) influx was not significantly inhibited by either voltage-operative Ca(2+) channel blockers (nifedipine or verapamil), or by inhibitors of Na+, Ca(2+)-exchanger (bepridil and benzamil), but it was inhibited by flufenamic acid (FA), a Ca(2+)-permeable nonselective cation channel blocker. A quantitative analysis of apoptosis by flow cytometry revealed that a treatment with either FA or BAPTA, an intracellular Ca(2+) chelator, significantly inhibited the diazoxide-induced apoptosis. Taken together, these results suggest that the observed diazoxide-induced apoptosis in the HepG2 cells may result from a Ca(2+) influx through the activation of Ca(2+)-permeable non-selective cation channels. These results are very significant, and they lead us to further suggest that diazoxide may be valuable for the therapeutic intervention of human hepatomas.