20(S)-Protopanaxadiol, a metabolite of ginsenosides, induced cell apoptosis through endoplasmic reticulum stress in human hepatocarcinoma HepG2 cells

Synthesis, biological evaluation and mechanism study based on network pharmacology of amino acids esters of 20(S)-protopanaxadiol as novel anticancer agents

As one of the metabolites of ginseng, 20(S)-protopanaxadiol (PPD) is a compound with dammarane-type tetracyclic triterpene, which performs a wide range of anticancer activities. In this study, PPD was used as a lead. A series of compounds were synthesized respectively with 11 amino acids through esterification and were evaluated for their cytotoxicity against several cancer cell lines. One of the synthetic products (PL) exhibited potent inhibitory effect on Huh-7 cells relative to that of PPD in vitro. Subsequently, the Annexin V-FITC /PI staining assay was used to verify that PL induced apoptosis of Huh-7 cells in a dose-dependent manner. A UPLC-Q/TOF-MS analysis method was established and validated for assessing pharmacokinetic properties after the administration of PPD and PL in rats. The results showed that compared with PPD, T1/2of PL in rats was prolonged, and the peak time was delayed, resulting in broader tissue distribution of the compound in the body. In addition, the targets of PL against several cancers were predicted and analyzed via network pharmacology. Molecular docking simulations demonstrated that PL interacted with the active sites of the above targets. In conclusion, this study provided a theoretical basis for the development and clinical application of anti-tumor activity of PPD.

Structural Characters and Pharmacological Activity of Protopanaxadiol-Type Saponins and Protopanaxatriol-Type Saponins from Ginseng

Ginseng has a long history of drug application in China, which can treat various diseases and achieve significant efficacy. Ginsenosides have always been deemed important ingredients for pharmacological activities. Based on the structural characteristics of steroidal saponins, ginsenosides are mainly divided into protopanaxadiol-type saponins (PDS, mainly including Rb1, Rb2, Rd, Rc, Rh2, CK, and PPD) and protopanaxatriol-type saponins (PTS, mainly including Re, R1, Rg1, Rh1, Rf, and PPT). The structure differences between PDS and PTS result in the differences of pharmacological activities. This paper provides an overview of PDS and PTS, mainly focusing on their chemical profile, pharmacokinetics, hydrolytic metabolism, and pharmacological activities including antioxidant, antifatigue, antiaging, immunodulation, antitumor, cardiovascular protection, neuroprotection, and antidiabetes. It is intended to contribute to an in-depth study of the relationship between PDS and PTS.

Relevance of the endoplasmic reticulum-mitochondria axis in cancer diagnosis and therapy

Dynamic interactions between organelles are responsible for a variety of intercellular functions, and the endoplasmic reticulum (ER)-mitochondrial axis is recognized as a representative interorganelle system. Several studies have confirmed that most proteins in the physically tethered sites between the ER and mitochondria, called mitochondria-associated ER membranes (MAMs), are vital for intracellular physiology. MAM proteins are involved in the regulation of calcium homeostasis, lipid metabolism, and mitochondrial dynamics and are associated with processes related to intracellular stress conditions, such as oxidative stress and unfolded protein responses. Accumulating evidence has shown that, owing to their extensive involvement in cellular homeostasis, alterations in the ER-mitochondrial axis are one of the etiological factors of tumors. An in-depth understanding of MAM proteins and their impact on cell physiology, particularly in cancers, may help elucidate their potential as diagnostic and therapeutic targets for cancers. For example, the modulation of MAM proteins is utilized not only to target diverse intracellular signaling pathways within cancer cells but also to increase the sensitivity of cancer cells to anticancer reagents and regulate immune cell activities. Therefore, the current review summarizes and discusses recent advances in research on the functional roles of MAM proteins and their characteristics in cancers from a diagnostic perspective. Additionally, this review provides insights into diverse therapeutic strategies that target MAM proteins in various cancer types.

Structural Characters and Pharmacological Activity of Protopanaxadiol‐Type Saponins and Protopanaxatriol‐Type Saponins from Ginseng

Ginseng has a long history of drug application in China, which can treat various diseases and achieve significant efficacy. Ginsenosides have always been deemed important ingredients for pharmacological activities. Based on the structural characteristics of steroidal saponins, ginsenosides are mainly divided into protopanaxadiol‐type saponins (PDS, mainly including Rb1, Rb2, Rd, Rc, Rh2, CK, and PPD) and protopanaxatriol‐type saponins (PTS, mainly including Re, R1, Rg1, Rh1, Rf, and PPT). The structure differences between PDS and PTS result in the differences of pharmacological activities. This paper provides an overview of PDS and PTS, mainly focusing on their chemical profile, pharmacokinetics, hydrolytic metabolism, and pharmacological activities including antioxidant, antifatigue, antiaging, immunodulation, antitumor, cardiovascular protection, neuroprotection, and antidiabetes. It is intended to contribute to an in‐depth study of the relationship between PDS and PTS.

Ginsenoside Rb1 Inhibits the Proliferation of Lung Cancer Cells by Inducing the Mitochondrial-mediated Apoptosis Pathway

BACKGROUND

Lung cancer is one of the more common malignant tumors posing a great threat to human life, and it is very urgent to find safe and effective therapeutic drugs. The antitumor effect of ginsenosides has been reported to be a treatment with a strong effect and a high safety profile.

OBJECTIVE

This paper aimed to investigate the inhibitory effect of ginsenoside Rb1 on 95D and NCI-H460 lung cancer cells and its pathway to promote apoptosis.

METHODS

We performed the CCK-8 assay, fluorescence staining assay, flow cytometry, scratch healing assay, and Transwell assay to detect the effects of different concentrations of ginsenoside Rb1 on the antitumor activity of 95D and NCI-H460 cells and Western Blot detected the mechanism of antitumor effect.

RESULTS

Ginsenoside Rb1 treatment significantly increased the inhibition and apoptosis rates of 95D and NCIH460 cells and inhibited the cell cycle transition from S phase to G2/M. Rb1 induces apoptosis by altering the levels of P53, Bax, Cyto-c, Caspase-8, Caspase-3, Cleaved Caspase-3, Bcl-2, MMP-2, and MMP-9 proteins and activating the external apoptotic pathway.

CONCLUSION

Ginsenoside Rb1 inhibits proliferation and migration and induces apoptosis of 95D and NCI-H460 lung cancer cells by regulating the mitochondrial apoptotic pathway to achieve antitumor activity.

Biodistribution and pharmacokinetic evaluation of Korean Red Ginseng components using radioisotopes in a rat model

Background

Although many studies have evaluated the efficacy and pharmacokinetics of Korean Red Ginseng (KRG) components (Rg1, Rb1, Rg3, Rd, etc.), few have examined the in vivo pharmacokinetics of the radiolabeled components. This study investigated the pharmacokinetics of ginsenosides and their metabolite compound K (CK), 20(s)-protopanaxadiol (PPD), and 20(s)-protopanaxatriol (PPT) using radioisotopes in rat oral administration.

Methods

Sprague-Dawley rats were dosed orally once with 10 mg/kg of the tritium(3H) radiolabeled samples, and then the blood was collected from the tail vein after 0.25, 0.5, 1, 1.5, 2, 4, 6, 8, 12, 24, 48, 96, and 168 h. Radioactivity in the organs, feces, urine, and carcass was determined using a liquid scintillation counter (LSC) and a bio-imaging analyzer system (BAS).

Results and conclusion

After oral administration, as the ³H-labeled ginsenosides were converted to metabolites, C_max and half-life increased, and T_max decreased. Interestingly, Rb1 and CK showed similar values, and after a single oral administration of components, the cumulative excretion ratio of urine and feces was 88.9%-92.4%. Although most KRG components were excreted within 96-168 h of administration, small amounts of components were detected in almost all tissues and mainly distributed to the liver except for the digestive tract when observed through autoradiography. This study demonstrated that KRG components were distributed to various organs in the rats. Further studies could be conducted to prove the bioavailability and transmission of KRG components to confirm the mechanism of KRG efficacy.

α-Mangostin Induces Apoptosis in Human Osteosarcoma Cells Through ROS-Mediated Endoplasmic Reticulum Stress via the WNT Pathway

α-mangostin has been confirmed to promote the apoptosis of MG-63 cells, but its specific pro-apoptosis mechanism in osteosarcoma (OS) remains further investigation. Here, we demonstrated that α-mangostin restrained the viability of OS cells (143B and Saos-2), but had little effect on the growth of normal human osteoblast. α-mangostin increased OS cell apoptosis by activating the caspase-3/8 cascade. Besides, α-mangostin induced endoplasmic reticulum (ER) stress and restrained the Wnt/β-catenin pathway activity. 4PBA (an ER stress inhibitor) or LiCl (an effective Wnt activator) treatment effectively hindered α-mangostin-induced apoptosis and the caspase-3/8 cascade. Furthermore, we also found that α-mangostin induced ER stress by promoting ROS production. And ER stress-mediated apoptosis caused by ROS accumulation depended on the inactivation of Wnt/β-catenin pathway. In addition, α-mangostin significantly hindered the growth of xenograft tumors, induced the expression of ER stress marker proteins and activation of the caspase-3/8 cascade, and restrained the Wnt/β-catenin signaling in vivo. In short, ROS-mediated ER stress was involved in α-mangostin triggered apoptosis, which might depended on Wnt/β-catenin signaling inactivation.

Inhibitory activities of 20(R, S)-protopanaxatriol against epidermal growth factor receptor tyrosine kinase

As major metabolites of protopanaxatriol-type ginsenosides, 20(R, S)-protopanaxatriol [20(R, S)-PPT] display multiple bioactivities. This work aimed to investigate the inhibitory activities of 20(R, S)-PPT against epidermal growth factor receptor tyrosine kinase and the potential mechanism. 20(R, S)-PPT inhibited the proliferation of HepG2 cells in a dose-dependent manner and blocked cell cycle progression at G1/G0 phase. Then 20(R, S)-PPT were found to influence the protein expressions involved in epidermal growth factor receptor (EGFR)-mitogen-activated protein kinase (MAPK) signaling pathway. Molecular docking suggested that 20(R, S)-PPT could bind to the active sites of all target proteins in EGFR-MAPK pathway. It is worth noting that 20(R, S)-PPT showed stronger binding capacities with EGFR, compared with other proteins. Hence, this work further investigated the binding interactions and binding stabilities between 20(R, S)-PPT and EGFR. Both hydrophobic interactions and hydrogen bonds contributed to the 20(R, S)-PPT-EGFR binding. In addition, the in vitro inhibitory activities of 20(R, S)-PPT against EGFR tyrosine kinase were observed in a homogeneous time-resolved fluorescence assay, with the IC₅₀ values of 24.10 ± 0.17 and 33.19 ± 0.19 μM respectively. Taken together with the above results, both of 20(R)-PPT and 20(S)-PPT might serve as potential EGFR tyrosine kinase inhibitors.

Xanthohumol-Induced Rat Glioma C6 Cells Death by Triggering Mitochondrial Stress

AIM: To investigate the underlying mechanisms of xanthohumol (XN) on the proliferation inhibition and death of C6 glioma cells. METHODS: To determine the effects of XN on C6 cells, cell proliferation and mortality after XN treatment were assessed by SRB assay and trypan blue assay respectively. Apoptotic rates were evaluated by flowcytometry after Annexin V-FITC/PI double staining. The influence of XN on the activity of caspase-3 was determined by Western blot (WB); and nuclear transposition of apoptosis-inducing factor (AIF) was tested by immunocytochemistry and WB. By MitoSOX^TM staining, the mitochondrial ROS were detected. Mitochondrial function was also tested by MTT assay (content of succinic dehydrogenase), flow cytometry (mitochondrial membrane potential (MMP)—JC-1 staining; mitochondrial abundance—mito-Tracker green), immunofluorescence (MMP—JC-1 staining; mitochondrial morphology—mito-Tracker green), WB (mitochondrial fusion-fission protein—OPA1, mfn2, and DRP1; mitophagy-related proteins—Pink1, Parkin, LC3B, and P62), and high-performance liquid chromatography (HPLC) (energy charge). Finally, mitochondrial protein homeostasis of C6 cells after XN treatment with and without LONP1 inhibitor bortezomib was investigated by trypan blue assay (proliferative activity and mortality) and WB (mitochondrial protease LONP1). All cell morphology images were taken by a Leica Microsystems microscope. RESULTS: XN could lead to proliferation inhibition and death of C6 cells in a time- and dose-dependent manner and induce apoptosis of C6 cells through the AIF pathway. After long incubation of XN, mitochondria of C6 cells were seriously impaired, and mitochondria had a diffuse morphology and mitochondrial ROS were increased. The content of succinic dehydrogenase per cell was significantly decreased after XN insults of 24, 48, and 72 h. The energy charge was weakened after XN insult of 24 h. Furthermore, the MMP and mitochondrial abundance were significantly decreased; the protein expression levels of OPA1, mfn2, and DRP1 were down-regulated; and the protein expression levels of Pink1, Parkin, LC3B-II/LC3B-I, and p62 were up-regulated in long XN incubation times (24, 48, and 72 h). XN incubation with bortezomib for 48 h resulted in lower proliferative activity and higher mortality of C6 cells and caused the cell to have visible vacuoles. Moreover, the protein expression levels of LONP1 was up-regulated gradually as XN treatment time increased. CONCLUSION: These data supported that XN could induce AIF pathway apoptosis of the rat glioma C6 cells by affecting the mitochondria.

Proteotoxic Stress and Cell Death in Cancer Cells

To maintain proteostasis, cells must integrate information and activities that supervise protein synthesis, protein folding, conformational stability, and also protein degradation. Extrinsic and intrinsic conditions can both impact normal proteostasis, causing the appearance of proteotoxic stress. Initially, proteotoxic stress elicits adaptive responses aimed at restoring proteostasis, allowing cells to survive the stress condition. However, if the proteostasis restoration fails, a permanent and sustained proteotoxic stress can be deleterious, and cell death ensues. Many cancer cells convive with high levels of proteotoxic stress, and this condition could be exploited from a therapeutic perspective. Understanding the cell death pathways engaged by proteotoxic stress is instrumental to better hijack the proliferative fate of cancer cells.

(20S)-Protopanaxadiol Ginsenosides Induced Cytotoxicity via Blockade of Autophagic Flux in HGC-27 Cells

(20S)-Protopanaxadiol ginsenosides Rg3, Rh2 and PPD have been demonstrated for their anticancer activity. However, the underlying mechanism of their antitumor activity remains unclear. In the present study, we investigated the role of these three ginsenosides on cell proliferation and death of human gastric cancer cells (HGC-27 cells). The sulforhodamine B (SRB) assay, Western blot analysis, fluorescence microscopy, confocal microscopy, high performance liquid chromatography (HPLC) analysis, flow cytometry, and transmission electron microscopy (TEM) were used to evaluate cell proliferation, apoptosis, and autophagy. The results showed that both Rh2 and PPD were more effective than Rg3 in inhibiting HGC-27 cell proliferation and inducing cytoplasmic vacuolation, while no significant changes in apoptosis were observed. Interestingly, cytoplasmic vacuolation and blockade of autophagy flux were observed after treatment with Rh2 and PPD. Rh2 obviously up-regulated the expression of the LC3II and p62. Furthermore, the increase in lysosomal pH and membrane rupture was observed in Rh2-treated and PPD-treated cells. When HGC-27 cells were pretreated with bafilomycin A1, a specific inhibitor of endosomal acidification, cellular vacuolization was increased, and the cell viability was significantly decreased, which indicated that Rh2-induced lysosome-damage accelerated cell death. Furthermore, data derived from mitochondrial analysis showed that excessive mitochondrial reactive oxygen species (ROS) and dysregulation of mitochondrial energy metabolism were caused by Rh2 and PPD treatment in HGC-27 cells. Taken together, these phenomena indicated that Rh2 and PPD inhibited HCG-27 cells proliferation by inducing mitochondria damage, dysfunction of lysosomes, and blockade of autophagy flux. The number of glycosyl groups at C-3 position could have an important effect on the cytotoxicity of Rg3, Rh2 and PPD.

Natural Products Targeting ER Stress, and the Functional Link to Mitochondria

The endoplasmic reticulum (ER) is a dynamic organelle essential for intracellular homeostasis maintenance, controlling synthesis, the folding of secreted and membrane-bound proteins, and transport of Ca²⁺. During cellular stress, ER dysfunction leads to the activation of unfolded protein response (UPR) due to accumulated misfolded proteins in the ER. This condition is referred as ER stress. Mitochondria and ER form a site of close contact (the mitochondria-associated membrane, MAM) which is a major platform exerting important physiological roles in the regulation of intracellular Ca²⁺ homeostasis, lipid metabolism, mitochondrial fission, autophagosome formation, and apoptosis progression. Natural products have been receiving increasing attention for their ability to interfere with ER stress. Research works have focused on the capacity of these bioactive compounds to induce apoptosis by activating ER stress through the ER stress-mediated mitochondrial apoptotic pathway. In this review we discuss the role of natural products in the signaling communication between ER and mitochondria, focusing on the effects induced by ER stress including Ca²⁺ permeability transition and UPR signaling (protein kinase R-like ER kinase/mitofusin 2).

Dammarane-type leads panaxadiol and protopanaxadiol for drug discovery: Biological activity and structural modification

Based on the definite therapeutic benefits, such as neuroprotective, cardioprotective, anticancer, anti-diabetic and so on, the Panax genus which contains many valuable plants, including ginseng (Panax ginseng C.A. Meyer), notoginseng (Panax notoginseng) and American ginseng (Panax quinquefolius L.), attracts research focus. Actually, the biological and pharmacological effects of the Panax genus are mainly attributed to the abundant ginsenosides. However, the low membrane permeability and the gastrointestinal tract influence seriously limit the absorption and bioavailability of ginsenosides. The acid or base hydrolysates of ginsenosides, 20 (R,S)-panaxadiol and 20 (R,S)-protopanaxadiol showed improved bioavailability and diverse pharmacological activities. Moreover, relative stable skeletons and active hydroxyl group at C-3 position and other reactive sites are suitable for structural modification to improve biological activities. In this review, the pharmacological activities of panaxadiol, protopanaxadiol and their structurally modified derivatives are comprehensively summarized.

20(S)-protopanaxadiol induces apoptosis in human umbilical vein endothelial cells by activating the PERK-eIF2alpha-ATF4 signaling pathway

20(S)-protopanaxadiol (PPD)-type ginsenosides are generally believed to be the most pharmacologically active components of Panax ginseng. These compounds induce apoptotic cell death in various cancer cells, which suggests that they have anti-cancer activity. Anti-angiogenesis is a promising therapeutic approach for controlling angiogenesis-related diseases such as malignant tumors, age-related macular degeneration, and atherosclerosis. Studies showed that 20(S)-PPD at low concentrations induces endothelial cell growth, but in our present study, we found 20(S)-PPD at high concentrations inhibited cell growth and mediated apoptosis in human umbilical vein endothelial cells (HUVECs). The mechanism by which high concentrations of 20(S)-PPD mediate endothelial cell apoptosis remains elusive. The present current study investigated how 20(S)-PPD induces apoptosis in HUVECs for the first time. We found that caspase-9 and its downstream caspase, caspase-3, were cleaved into their active forms after 20(S)-PPD treatment. Treatment with 20(S)-PPD decreased the level of Bcl-2 expression but did not change the level of Bax expression. 20(S)-PPD induced endoplasmic reticulum stress in HUVECs and stimulated UPR signaling, initiated by protein kinase R-like endoplasmic reticulum kinase (PERK) activation. Total protein expression and ATF4 nuclear import were increased, and CEBP-homologous protein (CHOP) expression increased after treatment with 20(S)-PPD. Furthermore, siRNA-mediated knockdown of PERK or ATF4 inhibited the induction of CHOP expression and 20(s)-PPD-induced apoptosis. Collectively, our findings show that 20(S)-PPD inhibits HUVEC growth by inducing apoptosis and that ATF4 expression activated by the PERK-eIF2α signaling pathway is essential for this process. These findings suggest that high concentrations of 20(S)-PPD could be used to treat angiogenesis-related diseases.

20(s)-Protopanaxadiol (PPD) increases the radiotherapy sensitivity of laryngeal carcinoma

Laryngeal carcinoma (LC) is one of the most prevalent malignant tumors in the head and neck area. Due to its high morbidity and mortality, LC poses a serious threat to human life and health. Even with surgical removal, some patients were not sensitive to radiotherapy or experienced transfer or recurrence. 20(s)-Protopanaxadiol (PPD), a natural product from Panax ginseng, has been reported to have cytotoxic effects against several cancer cell lines. However, whether it can improve the radiation sensitivity and the underlying mechanism of PPD's sensitization effect is still unknown. Herein, from in vitro and in vivo experiments, we found that the combination of PPD and radiation not only significantly inhibited proliferation and induced apoptosis, but also suppressed the tumor growth in mouse models. These findings confirmed the role of PPD in enhancing the sensitivity of radiotherapy. Moreover, our work showed that the expression levels of mTOR and its downstream effectors decreased remarkably after PPD addition when compared to radiation only. This result suggested that PPD's excellent synergistic effects with radiation might be associated with the down-regulation of the mTOR signaling pathway in Hep-2 cells.

"Nano-Ginseng" for Enhanced Cytotoxicity AGAINST Cancer Cells

Panax ginseng has high medicinal and health values. However, the various and complex components of ginseng may interact with each other, thus reducing and even reversing therapeutic effects. In this study, we designed and fabricated a novel "nano-ginseng" with definite ingredients, ginsenoside Rb1/protopanaxadiol nanoparticles (Rb1/PPD NPs), completely based on the protopanaxadiol-type extracts. The optimized nano-formulations demonstrated an appropriate size (~110 nm), high drug loading efficiency (~96.8%) and capacity (~27.9 wt %), long half-time in systemic circulation (nine-fold longer than free PPD), better antitumor effects in vitro and in vivo, higher accumulation at the tumor site and reduced damage to normal tissues. Importantly, this process of "nano-ginseng" production is a simple, scalable, green economy process.

Ginsenoside PPD's Antitumor Effect via Down-Regulation of mTOR Revealed by Super-Resolution Imaging

Derived from Panax ginseng, the natural product 20(S)-Protopanaxadiol (PPD) has been reported for its cytotoxicity against several cancer cell lines. The molecular mechanism is, however, not well understood. Here we show that PPD significantly inhibits proliferation, induces apoptosis and causes G2/M cell cycle arrest in human laryngeal carcinoma cells (Hep-2 cells). PPD also decreases the levels of proteins related to cell proliferation. Moreover, PPD-induced apoptosis is characterized by a dose-dependent down-regulation of Bcl-2 expression and up-regulation of Bax, and is accompanied by the activation of Caspase-3 as well. Further molecular mechanism is revealed by direct stochastic optical reconstruction microscopy (dSTORM)—a novel high-precision localization microscopy which enables effective resolution down to the order of 10 nm. It shows the expression and spatial arrangement of mTOR and its downstream effectors, demonstrating that this ginsenoside exerts its excellent anticancer effects via down-regulation of mTOR signaling pathway in Hep-2 cells. Taken together, our findings elucidate that the antitumor effect of PPD is associated with its regulation of mTOR expression and distribution, which encourages further studies of PPD as a promising therapeutic agent against laryngeal carcinoma.

Anticancer Activities of Protopanaxadiol- and Protopanaxatriol-Type Ginsenosides and Their Metabolites

Recently, most anticancer drugs are derived from natural resources such as marine, microbial, and botanical sources, but the low success rates of chemotherapies and the development of multidrug resistance emphasize the importance of discovering new compounds that are both safe and effective against cancer. Ginseng types, including Asian ginseng, American ginseng, and notoginseng, have been used traditionally to treat various diseases, due to their immunomodulatory, neuroprotective, antioxidative, and antitumor activities. Accumulating reports have shown that ginsenosides, the major active component of ginseng, were helpful for tumor treatment. 20(S)-Protopanaxadiol (PDS) and 20(S)-protopanaxatriol saponins (PTS) are two characteristic types of triterpenoid saponins in ginsenosides. PTS holds capacity to interfere with crucial metabolism, while PDS could affect cell cycle distribution and prodeath signaling. This review aims at providing an overview of PTS and PDS, as well as their metabolites, regarding their different anticancer effects with the proposal that these compounds might be potent additions to the current chemotherapeutic strategy against cancer.

Identification of Human UDP-Glucuronosyltransferase 1A4 as the Major Isozyme Responsible for the Glucuronidation of 20(S)-Protopanaxadiol in Human Liver Microsomes

20(S)-protopanaxadiol (PPD), one of the representative aglycones of ginsenosides, has a broad spectrum of pharmacological activities. Although phase I metabolism has been investigated extensively, information regarding phase II metabolism of this compound remains to be elucidated. Here, a glucuronidated metabolite of PPD in human liver microsomes (HLMs) and rat liver microsomes (RLMs) was unambiguously identified as PPD-3-O-β-d-glucuronide by nuclear magnetic resonance spectroscopy and high resolution mass spectrometry. The chemical inhibition and recombinant human UDP-Glucuronosyltransferase (UGT) isoforms assay showed that the PPD glucuronidation was mainly catalyzed by UGT1A4 in HLM, whereas UGT1A3 showed weak catalytic activity. In conclusion, PPD-3-O-β-d-glucuronide was first identified as the principal glucuronidation metabolite of PPD in HLMs, which was catalyzed by UGT1A4.

2,4-dichlorophenol induces ER stress-mediated apoptosis via eIF2α dephosphorylation in vitro

2,4-Dichlorophenol (2,4-DCP) has been widely used to produce herbicides and pharmaceutical intermediates, which exhibits various toxic effects including apoptosis. However, the mechanisms underlying 2,4-DCP-induced apoptosis, especially mediated by endoplasmic reticulum (ER) stress, are still unknown. In the present study, the mouse embryonic fibroblasts (MEFs) were used as an in vitro model system to figure out whether 2,4-DCP could induce ER stress, and further to elucidate the role of ER stress in 2,4-DCP-induced apoptosis. The results showed that 2,4-DCP dramatically caused the decrease of cell viability, the increase of apoptotic cells, the collapse of mitochondrial membrane potential (MMP) and the activation of caspase-3, suggesting that 2,4-DCP did induce apoptosis. Meanwhile, 2,4-DCP acted similarly as ER stress agonist tunicamycin (Tu) to activate all three branches (IRE1α, ATF6 and eIF2α) of ER stress. Furthermore, repression of ER stress or inhibition of eIF2α dephosphorylation significantly alleviated 2,4-DCP-induced apoptosis. Taking these results together, the present study firstly showed that 2,4-DCP induced ER stress-mediated apoptosis via eIF2α dephosphorylation in mammalian cells. These findings will provide new insights into the mechanisms underlying apoptosis after chlorophenols exposure.

Stereoselective suppressive effects of protopanaxadiol epimers on UV-B-induced reactive oxygen species and matrix metalloproteinase-2 in human dermal keratinocytes

This study aimed to assess the skin-related anti-photoaging activities of the 2 epimeric forms of protopanaxadiol (PPD), 20(S)-PPD and 20(R)-PPD, in cultured human keratinocytes (HaCaT cells). The anti-photoaging activity was evaluated by analyzing the levels of reactive oxygen species (ROS) and matrix metalloproteinases (MMPs), as well as cell viability for HaCaT cells under UV-B irradiation. The activities for MMP-2 and -1 in conditioned medium were determined using gelatin zymography, and MMP-2 protein in the conditioned medium was detected using Western blot analysis. 20(S)-PPD, but not 20(R)-PPD, suppressed UV-B-induced ROS elevation. Neither of the epimers, at the concentrations used, exhibited cytotoxicity, irrespective of UV-B irradiation. 20(S)-PPD, but not 20(R)-PPD, exhibited an inhibitory effect on UV-B-induced MMP-2 activity and expression in HaCaT cells. In brief, only 20(S)-PPD, a major metabolic product of PPD-type ginsenosides, inhibits UV-B-induced ROS and MMP-2 elevation, implying its stereospecific anti-photoaging activity on the skin.

Role of the Red Ginseng in Defense against the Environmental Heat Stress in Sprague Dawley Rats

Global temperature change causes heat stress related disorders in humans. A constituent of red ginseng has been known the beneficial effect on the resistance to many diseases. However, the mechanism of red ginseng (RG) against heat stress still remains unclear. To determine the effect of RG on heat stress, we examined the effect of the RG on the gene expression profiles in rats subjected to environmental heat stress. We evaluated the transcripts associated with hepatic lipid accumulation and oxidative stress in rats subjected to heat stress. We also analyzed the reactive oxygen species (ROS) contents. Our results suggested RG inhibited heat stress mediated altering mRNA expressions include HSPA1, DEAF1, HMGCR, and FMO1. We also determined RG attenuated fat accumulation in the liver by altering C/EBPβ expression. RG promoted to repress the heat stress mediated hepatic cell death by inhibiting of Bcl-2 expression in rats subjected to heat stress. Moreover, RG administered group during heat stress dramatically decreased the malondialdehyde (MDA) contents and ROS associated genes compared with the control group. Thus, we suggest that RG might influence inhibitory effect on environmental heat stress induced abnormal conditions in humans.

Production of the dammarene sapogenin (protopanaxadiol) in transgenic tobacco plants and cultured cells by heterologous expression of PgDDS and CYP716A47

KEY MESSAGE

Protopanaxadiol (PPD) is an aglycone of dammarene-type ginsenoside and has high medicinal values. In this work, we reported the PPD production in transgenic tobacco co-overexpressing PgDDS and CYP716A47. PPD is an aglycone of ginsenosides produced by Panax species and has a wide range of pharmacological activities. PPD is synthesized via the hydroxylation of dammarenediol-II (DD) by CYP716A47 enzyme. Here, we established a PPD production system via cell suspension culture of transgenic tobacco co-overexpressing the genes for PgDDS and CYP716A47. The concentration of PPD in transgenic tobacco leaves was 2.3-5.7 µg/g dry weight (DW), depending on the transgenic line. Leaf segments were cultured on medium with various types of hormones to induce callus. Auxin treatment, particularly 2,4-D, strongly enhanced the production of DD (783.8 µg g(-1) DW) and PPD (125.9 µg g(-1) DW). Treatment with 2,4-D enhanced the transcription of the HMG-Co reductase (HMGR) and squalene epoxidase genes. PPD production reached 166.9 and 980.9 µg g(-1) DW in a 250-ml shake flask culture and in 5-l airlift bioreactor culture, respectively.

A nanoparticulate drug-delivery system for 20(S)-protopanaxadiol: formulation, characterization, increased oral bioavailability and anti-tumor efficacy

As with many other hydrophobic anticancer agents, 20(S)-protopanaxadiol (PPD) has a very low oral bioavailability. In this study, a precipitation-combined ultrasonication technique was used to prepare PPD nanosuspensions. The mean particle size of the nanosuspensions was approximately 222 ± 12 nm, the drug payload achieved 50% after lyophilization and the maximum PPD concentration can reach 100 mg/ml, which is over 30 000 times the solubility of PPD in aqueous solution (3 μg/ml). After oral administration, the C_max and AUC_last values of PPD nanosuspensions were approximately 3.66-fold and 3.48-fold as those of PPD coarse suspensions, respectively. In contrast to the free drug solution, PPD nanosuspensions showed higher in vitro anti-tumor activity against HepG-2 cells (an IC₅₀ value of 1.40 versus 5.83 μg/ml at 24 h, p < 0.01). The in vivo study in H22-tumor-bearing mice demonstrated that PPD nanosuspensions showed good anti-tumor efficacy with an inhibition rate of 79.47% at 100 mg/kg, while 50 mg/kg of cyclophosphamide was displayed as positive control, and the inhibition rate was 87.81%. Considering the highest drug payload, oral bioavailability reported so far, significant anti-tumor efficacy and excellent safety of encapsulated drugs, PPD nanosuspensions could be used in potential effective strategies for anticancer therapy; further investigation is ongoing.

Ampelopsin-induced autophagy protects breast cancer cells from apoptosis through Akt-mTOR pathway via endoplasmic reticulum stress

Our previous study has shown that ampelopsin (AMP), a flavonol mainly found in Ampelopsis grossedentata, could induce cell death in human breast cancer cells via reactive oxygen species generation and endoplasmic reticulum (ER) stress pathway. Here, we examined whether autophagy is activated in AMP-treated breast cancer cells and, if so, sought to find the exact role and underlying molecular profile of autophagy in AMP-induced cell death. Our results showed that AMP treatment activated autophagy in MDA-MB-231 and MCF-7 breast cancer cells, as evidenced by the accumulation of autophagosomes, an increase of microtubule-associated protein 1 light chain 3 beta-2 (LC3B-II) and the conversion of LC3B-I to LC3B-II, the degradation of the selective autophagic target p62/SQSTM1, and the formation of green fluorescent protein (GFP)-LC3 puncta. Blockage of autophagy augmented AMP-induced cell death, suggesting that autophagy has cytoprotective effects. Meanwhile, AMP treatment suppressed Akt-mammalian target of rapamycin (mTOR) pathway as evidenced by dose- and time-dependent decrease of the phosphorylation of Akt, mTOR and ribosomal protein S6 kinase (p70S6K), whereas Akt activator insulin-like growth factor-1 (IGF-1) pretreatment partially restored Akt-mTOR pathway inhibited by AMP and decreased AMP-inuduced autophagy, signifying that AMP activated autophagy via inhibition of the Akt-mTOR pathway. Additionally, blocking ER stress not only reduced autophagy induction, but also alleviated inhibition of the Akt-mTOR pathway induced by AMP, suggesting that activation of ER stress was involved in induction of autophagy and inhibition of the Akt-mTOR pathway. Taken together, these findings indicate that AMP induces protective autophagy in human breast cancer cells through Akt-mTOR pathway via ER stress.

Metabolic profiles of 20(S)-protopanaxadiol in rats after oral administration using ultra-performance liquid chromatography/quadrupole time-of-flight tandem mass spectrometry

RATIONALE

20(S)-Protopanaxadiol (PPD), a dammarane-type triterpenoid sapogenin, acts as the pharmacophore of ginsenosides which are considered as the principal bioactive components in Chinese ginseng. To fully understand the mechanism of action of PPD, it is important to study its metabolic profiles in vivo.

METHODS

Plasma, urine, fece and bile were collected after administration of PPD formulated in 0.5% aqueous Tween-80 to rats (150 mg/kg). Samples were analyzed by using a sensitive and reliable method based on ultra-performance liquid chromatography/quadrupole time-of-flight tandem mass spectrometry (UPLC/Q-TOF-MS/MS) in both positive and negative ion mode. The chemical structures of metabolites were elucidated by comparing the retention time, accurate molecular mass, and fragmentation patterns of analytes with those of PPD.

RESULTS

In total 29 metabolites, including 10 new metabolites (M20-M29), were tentatively identified and characterized. Among them, two metabolites (M3 and M4) were unambiguously identified by matching their retention times and fragmentation patterns with their standards. Principal metabolites, namely, 20, 24-oxide metabolites (M3 and M4), 26/27-carboxylic acid derivatives (M22 and M23) and a glucuronidated product (M28), were found in the rat plasma.

CONCLUSIONS

The results showed that phase I metabolites are monooxygenation, dioxygenation and oxidative dehydrogenation metabolites, and phase II metabolic pathways were demonstrated to be cysteine conjugation and glucuronidation. The newly identified metabolites are useful to understand the mechanism of elimination of PPD and, in turn, its effectiveness and toxicity.

Endoplasmic reticulum stress-mediated activation of p38 MAPK, Caspase-2 and Caspase-8 leads to abrin-induced apoptosis

Abrin from Abrus precatorius plant is a potent protein synthesis inhibitor and induces apoptosis in cells. However, the relationship between inhibition of protein synthesis and apoptosis is not well understood. Inhibition of protein synthesis by abrin can lead to accumulation of unfolded protein in the endoplasmic reticulum causing ER stress. The observation of phosphorylation of eukaryotic initiation factor 2α and upregulation of CHOP (CAAT/enhancer binding protein (C/EBP) homologous protein), important players involved in ER stress signaling by abrin, suggested activation of ER stress in the cells. ER stress is also known to induce apoptosis via stress kinases such as p38 MAPK and JNK. Activation of both the pathways was observed upon abrin treatment and found to be upstream of the activation of caspases. Moreover, abrin-induced apoptosis was found to be dependent on p38 MAPK but not JNK. We also observed that abrin induced the activation of caspase-2 and caspase-8 and triggered Bid cleavage leading to mitochondrial membrane potential loss and thus connecting the signaling events from ER stress to mitochondrial death machinery.

Ampelopsin induces cell growth inhibition and apoptosis in breast cancer cells through ROS generation and endoplasmic reticulum stress pathway

Ampelopsin (AMP), a major bioactive constituent of Ampelopsis grossedentata, exerts a number of biological effects. In this study, we investigated its anti-cancer activity in human breast cancer cell lines, and explored the underlying mechanism of this action. Our results showed that treatment with AMP dose-dependently inhibited cell viability and induced apoptosis in MCF-7 and MDA-MB-231 breast cancer cells without cytotoxicity in human normal breast epithelial cells MCF-10A. Meanwhile, AMP dose- dependently triggered reactive oxygen species (ROS) generation in both breast cancer cells. The ROS scavenger N-acetyl-L-cysteine (NAC) strongly attenuated AMP-induced ROS production, along with cell growth inhibition and apoptosis. Furthermore, AMP was observed to activate endoplasmic reticulum (ER) stress, as evidenced by the up-regulation of ER stress-related proteins, including GRP78, p-PERK, p-elF2α, cleaved ATF6α and CHOP, while knockdown of ATF6α or PERK markedly down-regulated AMP-induced CHOP expression. Blocking ER stress using 4-phenylbutyric acid not only down-regulated AMP-induced GRP78 and CHOP expression, but also significantly decreased AMP-induced cell growth inhibition and apoptosis, whereas ER stress inducer thapsigargin played opposing effects. Additionally, NAC inhibited AMP-induced ER stress by down-regulating GRP78 and CHOP expression. Conversely, blocking ER stress using CHOP siRNA decreased AMP-induced ROS production and cell apoptosis. Taken together, these results demonstrate that AMP has anti-tumor effects against breast cancer cells through ROS generation and ER stress pathway, which therefore provide experimental evidences for developing AMP as a new therapeutic drug for breast cancer.

20S-dihydroprotopanaxadiol, a ginsenoside derivative, boosts innate immune responses of monocytes and macrophages

20S-dihydroprotopanaxadiol (2H-PPD) is a derivative of protopanaxadiol, a glycone of ginsenosides prepared from Panax ginseng. Although ginsenosides and acidic polysaccharides are known to be major active ingredients in ginseng, the immunopharmacological activities of their metabolites and derivatives have not been fully explored. In this study, we aimed to elucidate the regulatory action of 2H-PPD on the function of monocytes and macrophages in innate immune responses. 2H-PPD was able to boost the phagocytic uptake of fluorescein isothiocyanate-dextran in macrophages and enhance the generation of radicals (reactive oxygen species) in sodium nitroprusside-treated RAW264.7 cells. The surface levels of the costimulatory molecules such as CD80 and CD86 were also increased during 2H-PPD treatment. In addition, this compound boosted U937 cellcell aggregation induced by CD29 and CD43 antibodies, but not by cell-extracellular matrix (fibronectin) adhesion. Similarly, the surface levels of CD29 and CD43 were increased by 2H-PPD exposure. Therefore, our results strongly suggest that 2H-PPD has the pharmacological capability to upregulate the functional role of macrophages/monocytes in innate immunity.

Ginseng saponin metabolite 20(S)-protopanaxadiol inhibits tumor growth by targeting multiple cancer signaling pathways

Plant-derived active constituents and their semi-synthetic or synthetic analogs have served as major sources of anticancer drugs. 20(S)-protopanaxadiol (PPD) is a metabolite of ginseng saponin of both American ginseng (Panax quinquefolius L.) and Asian ginseng (Panax ginseng C.A. Meyer). We previously demonstrated that ginsenoside Rg3, a glucoside precursor of PPD, exhibits anti-proliferative effects on HCT116 cells and reduces tumor size in a xenograft model. Our subsequent study indicated that PPD has more potent antitumor activity than that of Rg3 in vitro although the mechanism underlying the anticancer activity of PPD remains to be defined. Here, we investigated the mechanism underlying the anticancer activity of PPD in human cancer cells in vitro and in vivo. PPD was shown to inhibit growth and induce cell cycle arrest in HCT116 cells. The in vivo studies indicate that PPD inhibits xenograft tumor growth in athymic nude mice bearing HCT116 cells. The xenograft tumor size was significantly reduced when the animals were treated with PPD (30 mg/kg body weight) for 3 weeks. When the expression of previously identified Rg3 targets, A kinase (PRKA) anchor protein 8 (AKAP8L) and phosphatidylinositol transfer protein α (PITPNA), was analyzed, PPD was shown to inhibit the expression of PITPNA while upregulating AKAP8L expression in HCT116 cells. Pathway-specific reporter assays indicated that PPD effectively suppressed the NF-κB, JNK and MAPK/ERK signaling pathways. Taken together, our results suggest that the anticancer activity of PPD in colon cancer cells may be mediated through targeting NF-κB, JNK and MAPK/ERK signaling pathways, although the detailed mechanisms underlying the anticancer mode of PPD action need to be fully elucidated.

Characterization of metabolites of 20(S)-protopanaxadiol in rats using ultra-performance liquid chromatography/quadrupole-time-of-flight mass spectrometry

In this study, ultra-performance liquid chromatography (UPLC)/quadrupole-time-of-flight mass spectrometry (QTOF-MS) was applied to the rapid analysis of 20(S)-protopanaxadiol (PPD) metabolites in rats after oral administration, enabling the structural characterization of 23 metabolites in plasma, bile, urine, and feces. 16 of these, including M1-M5, M9, and M11-M15, have not been previously reported. The results also indicated that demethylation, dehydration, dehydrogenation, oxidation, deoxidation, and glucuronidation were the major metabolic reactions of PPD in vivo. This study provides important information about the metabolism of PPD which will be helpful for fully understanding its mechanism of action. Furthermore, structural modification of PPD in vivo may aid in obtaining new chemical derivatives for pharmacological screening.

Lithium adduct as precursor ion for sensitive and rapid quantification of 20 (S)-protopanaxadiol in rat plasma by liquid chromatography/quadrupole linear ion trap mass spectrometry and application to rat pharmacokinetic study

A novel, rapid and sensitive liquid chromatography/quadrupole linear ion trap mass spectrometry [LC-ESI-(QqLIT)MS/MS] method was developed and validated for the quantification of protopanaxadiol (PPD) in rat plasma. Oleanolic acid (OA) was used as internal standard (IS). A simple protein precipitation based on acetonitrile (ACN) was employed. Chromatographic separation was performed on a Sepax GP-C18 column (50 × 2.1 mm, 5 μM) with a mobile phase consisting of ACN-water and 1.5 μM formic acid and 25 mM lithium acetate (90 : 10, v/v) at a flow rate of 0.4 ml/min for 3.0 min. Multiple-reaction-monitoring mode was performed using lithium adduct ion as precursor ion of m/z 467.5/449.4 and 455.6/407.4 for the drug and IS, respectively. Calibration curve was recovered over a concentration range of 0.5-100 ng/ml with a correlation coefficient >0.99. The limit of detection was 0.2 ng/ml in rat plasma for PPD. The results of the intraday and interday precision and accuracy studies were well within the acceptable limits. The validated method was successfully applied to investigate the pharmacokinetic study of PPD after intravenous and gavage administration to rat.

Enhanced oral absorption of 20(S)-protopanaxadiol by self-assembled liquid crystalline nanoparticles containing piperine: in vitro and in vivo studies

Background

20(S)-protopanaxadiol (PPD), similar to several other anticancer agents, has low oral absorption and is extensively metabolized. These factors limit the use of PPD for treatment of human diseases.

Methods

In this study, we used cubic nanoparticles containing piperine to improve the oral bioavailability of PPD and to enhance its absorption and inhibit its metabolism. Cubic nanoparticles loaded with PPD and piperine were prepared by fragmentation of glyceryl monoolein (GMO)/poloxamer 407 bulk cubic gel and verified using transmission electron microscopy and differential scanning calorimetry. We evaluated the in vitro release of PPD from these nanoparticles and its absorption across the Caco-2 cell monolayer model, and subsequently, we examined the bioavailability and metabolism of PPD and its nanoparticles in vivo.

Results

The in vitro release of PPD from these nanoparticles was less than 5% at 12 hours. PPD-cubosome and PPD-cubosome loaded with piperine (molar ratio PPD/piperine, 1:3) increased the apical to basolateral permeability values of PPD across the Caco-2 cell monolayer from 53% to 64%, respectively. In addition, the results of a pharmacokinetic study in rats showed that the relative bioavailabilities of PPD-cubosome [area under concentration–time curve (AUC)_0–∞] and PPD-cubosome containing piperine (AUC_0–∞) compared to that of raw PPD (AUC_0–∞) were 166% and 248%, respectively.

Conclusion

The increased bioavailability of PPD-cubosome loaded with piperine is due to an increase in absorption and inhibition of metabolism of PPD by cubic nanoparticles containing piperine rather than because of improved release of PPD. The cubic nanoparticles containing piperine may be a promising oral carrier for anticancer drugs with poor oral absorption and that undergo extensive metabolism by cytochrome P450.

Alkylphenols from the roots of Ardisia brevicaulis induce G1 arrest and apoptosis through endoplasmic reticulum stress pathway in human non-small-cell lung cancer cells

From the roots of Ardisia brevicaulis DIELS, two new alkylphenol derivatives, named ardisiphenol E (2) and F (3), have been isolated together with a known alkylphenol, ardisiphenol D (1). The structures of 1-3 were elucidated by chemical and spectroscopic techniques. Compounds 1 and 2 exhibited strong cytotoxicities on two human non-small-cell lung cancer cell lines (H1299 and A549). We found that compounds 1 and 2 upregulated mRNA and protein expressions of endoplasmic reticulum (ER) stress markers including C/EBP homologous protein (CHOP), binding immunoglobulin protein (Bip) and inositol-requiring enzyme 1 (IRE1) indicating 1 and 2 are novel natural ER stress inducers. Treatments with 1 and 5 µM of 1 or 2 triggered G1 arrest in H1299 and A549 cells with concomitant downregulation of ubiquitin fusion degradation protein 1 (Ufd1) and S-phase kinase-associated protein 2 (Skp2) proteins and the accumulation of p27, the key axes of ER stress-mediated G1 arrest. Compounds 1 and 2 also induced apoptosis at high concentrations (10, 20 µM) which was shown to be coupled with the upregulation of CHOP and Bim, the activation of caspase-9, caspase-3 and poly(ADP-ribose) polymerase (PARP) cleavage. These results indicate that compounds 1 and 2 induce ER stress that subsequently causes G1 arrest and apoptosis in human non-small-cell lung cancer cells and they may have potential anticancer effects.

Gambogic acid as a non-competitive inhibitor of ATP-binding cassette transporter B1 reverses the multidrug resistance of human epithelial cancers by promoting ATP-binding cassette transporter B1 protein degradation

Gambogic acid (GA) is known for its anti-cancer activity in a phase II clinical trial. However, the detailed molecular mechanisms of its anti-multidrug resistance remain unclear. The present study was designed to study the relationship between GA and multidrug-resistant protein ATP-binding cassette transporter B1 (ABCB1). GA dose dependently inhibited ABCB1 activity levels in the in vitro Pgp-Glo assay system and increased the cellular accumulation of ABCB1 substrate adriamycin. Although GA had no significant influence on ABCB1 mRNA in the real-time PCR assay, Western blot detection indicated the compound reduced ABCB1 protein levels. Further study showed the proteasome inhibitor MG-132 reversed the GA-decreased ABCB1 level and prolonged half-life of ABCB1. It was also found that GA coordinated with other anti-cancer drugs (such as adriamycin, docetaxel, verapamil and protopanaxadiol) to enhance cellular cytotoxicity on human epithelial cancer cell lines with higher ABCB1 expression levels. These data suggest that GA functions as a non-competitive inhibitor of ABCB1 by directly inhibiting and reducing its expression levels by promoting protein degradation through post-translational proteasome pathway. The results of this study will aid in the understanding of the synergistic effects of combining GA with other drugs as a new anti-multidrug-resistant agent.

Crosstalk between endoplasmic reticulum stress and oxidative stress in apoptosis induced by α-tocopheryl succinate in human gastric carcinoma cells

α-Tocopheryl succinate (α-TOS) has been shown to be a potent apoptosis inducer and growth inhibitor in a variety of cancer cells. Our previous studies showed the important role of endoplasmic reticulum (ER) stress and reactive oxygen species (ROS) generation in the apoptosis induced by α-TOS. However, the relationship of oxidative stress with ER stress is still controversial. The objective of the present study was to investigate the interplay between the two stress responses induced by α-TOS in SGC-7901 human gastric cancer cells. In response to α-TOS, cytological changes typical of apoptosis, induction of glucose-regulated protein 78 (GRP78) and CCAAT/enhancer-binding protein (C/EBP) homologous protein transcription factor (CHOP), and activation of caspase-4 were observed. And the antioxidant N-acetyl-l-cysteine inhibited induction of both GRP78 and CHOP by α-TOS transcriptionally and translationally. Furthermore, knocking down CHOP by RNA interference decreased ROS generation, increased glutathione level and induced glutathione peroxidase mRNA expression in α-TOS-treated cells, whereas catalase and superoxide dismutases mRNA expression were not altered. The results imply that α-TOS induces ER stress response through ROS production, while CHOP perturbs the redox state of SGC-7901 cells treated with α-TOS.