Article

Screening of new chemopreventive compounds from Digitalis purpurea

Authors:
If you want to read the PDF, try requesting it from the authors.

Abstract

Chemopreventive agents induce a battery of genes whose protein products can protect cells from chemical-induced carcinogenesis. In this study, we isolated four different glycosides (1 acteoside; 2 purpureaside A; 3 calceolarioside B; and 4, plantainoside D) from the leaves of Digitalis purpurea and studied their abilities to induce glutathione S-transferase (GST) and their protective efficiencies against aflatoxin B1-induced cytotoxicity in H4IIE cells. Of these four glycosides, acteoside significantly inhibited the cytotoxicity induced by aflatoxin B1 (AFB1) and also selectively increased GSTalpha protein levels. Reporter gene analysis using an antioxidant response element (ARE) containing construct and subcellular fractionation assays, revealed that GSTalpha induction by acteoside might be associated with Nrf2/ARE activation. The results suggest that acteoside possesses a potent hepatoprotective effect against AFB1 and that it can be applied as a potential chemopreventive agent.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Plantamajoside is also found in several other species from the Plantaginaceae family; two Digitalis species: D. purpurea Oh et al., 2005;Lee et al., 2006a) and D. lanata (Kirmizibekmez et al., 2009). It is also found in Hemiphragma heterophyllum (Calis et al., 1991;Ma et al., 1995), Lagotis stolonifera (Calis et al., 1991), Picrorhiza scrophulariiflora (Zou et al., 2007(Zou et al., , 2008, Rehmannia glutinosa (Shoyama et al., 1986, in two Veronica species: V. beccabunga (Jensen et al., 2011) and V. fuhsii (Ozipek et al., 1999) and in Wulfeniopsis amherstiana (Jensen et al., 2009), Wulfenia baldaccii (Taskova et al., 2005) (see Table 1). ...
... Cytotoxic activity was measured using S9 Cell fraction (Koo et al., 2009), or cell line A549 (human lung carcinoma), HL-60 (human promyelocytic leukemia) and P388 (murine leukemia) . The activity against flatoxin B1-induced cytotoxicity in H4IIE cells (Lee et al., 2006a) was also determined. Enzyme inhibitory activity was determined using cAMP phosphodiesterase from beef heart and 5-lipooxygenase from RBL-1 cells (Deyama et al., 2006;Nishibe, 1994Nishibe, , 2002Skari et al., 1999). ...
... Enzyme inhibitory activity was determined using cAMP phosphodiesterase from beef heart and 5-lipooxygenase from RBL-1 cells (Deyama et al., 2006;Nishibe, 1994Nishibe, , 2002Skari et al., 1999). Genotoxicity was determined using the chromosomal aberration test (Koo et al., 2009), induction of glutathione S-transferase (GST) (Lee et al., 2006a), inhibitory activity against edema was demonstrated using arachidonic acid-induced mouse ear oedema (Deyama et al., 2006;Nishibe, 1994Nishibe, , 2002 and cAMP phosphodiesterase was used to demonstrate enzyme activity (Ravn et al., 1990;Jimé nez and Riguera, 1994) and enzyme inhibitory effects were further investigated on 5-lipoxygenase (Ravn et al., 1990) and enzymatic lipid peroxidation (Skari et al., 1999). The pathogenesis of diabetes was measured by testing glycation inhibitory activity (Choi et al., 2008), and prevention of diabetic complications (Won et al., 2007). ...
Article
Plantamajoside is a bioactive caffeic acid derivative, a dihydroxyphenethyl glucoside in the group of polyphenolic compounds. It is one of the principal caffeic acid glycoside in the Plantago Digitalis, Hemiphragma, Lagotis, Picrorhiza, Rehmannia, Veronica, Wulfeniopsis and Wulfenia genera within the Plantaginaceae family. This compound is also present in the genera Aeschynanthus and Chirita of the Gesneriaceae family and the genus Boschniakia of the Orobanchaceae family. Plantamajoside is present in the greatest concentrations in roots of young plants, but it is also found in seeds, flower stalks, stems, leaves, in vivo cultivated plant cells and transgenic root cultures. Plantamajoside is used as a biomarker in chemotaxonomical studies, and is a compound with numerous biological applications and considerable pharmacological potential. It is a protective agent against ultra-violet light in plants and acts as antioxidant agent with very low toxicity. In addition, plantamajoside can also be industrially synthesized. This review aims to give an overview of plantamajoside in various plantago species as well as its potential as a biomarker and as a new drug compound.
... Boron (B), chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), arsenic (As) and lead (Pb), in various plant parts of Digitalis purpurea at pre and post flowering stages were determined. The concentration of most of the minerals was higher at the post-flowering than that of the preflowering stage (Lee 2006). ...
Chapter
Full-text available
Digitalis purpurea L. is an important medicinal plant belonging to the family Scrophulariaceae is an important source of secondary metabolites. The most important is digitoxin an extremely poisonous and cumulative drug that is insoluble in water. It is used in the treatment of cardiovascular disease, internal haemorrhage, inflammatory diseases, delirium tremens, epilepsy, acute mania and various other diseases with real or supposed benefits. Digitalis is a drug that has been used for centuries to treat heart disease. The other uses of digitalis include asthma, epilepsy, tuberculosis, constipation, headache, spasm, wounds, and burns, causing vomiting and other conditions.
... Boron (B), chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), arsenic (As) and lead (Pb), in various plant parts of Digitalis purpurea at pre and post flowering stages were determined. The concentration of most of the minerals was higher at the post-flowering than that of the preflowering stage (Lee 2006). ...
Chapter
Full-text available
This chapter focuses on doubling the farmer's income by practicing protected cultivation techniques specialized in vegetable cultivation
... The neuroprotective action of cardiac glycoside neriifolin was evaluated on in ischemic stroke. Neriifolin provided significant neuroprotection in a neonatal model of hypoxia/ischemia and in a middle cerebral artery occlusion model of transient focal ischemia (146) . ...
Article
Full-text available
In this study, online databases including Web Science, PubMed, Scopus and Science Direct, were searched for papers studied the hepatoprotective effects of medicinal plants against carbon tetrachloride, D-galactosamine (D-GalN), D-galactosamine (D-GalN)/ lipopolysaccharide (LPS), N, N-dimethylformamide (DMF), oxytetracyclin thioacetamide (TAA), nitrosodiethylamine, paracetamol, rifampin, INH, aflatoxins, iron-overload and oxidative stress induced hepatotoxicity and against hepatic cancer induced chemically.
... paracetamol-induced liver damage in rats roots extract, 100 and 200mg/kg bw. [144][145][146][147] Acteoside significantly inhibited the cytotoxicity induced by aflatoxin B1 (AFB1) and also selectively increased GSTalpha protein levels. Reporter gene analysis using an antioxidant response element (ARE) containing construct and subcellular fractionation assays, revealed that GST alpha induction by acteoside might be associated with Nrf2/ARE activation to induce glutathione S-transferase (GST) and their protective efficiencies against aflatoxin B1-induced cytotoxicity Four different glycosides (acteoside, purpureaside A, calceolarioside B and plantainoside D) ...
Article
Full-text available
The liver plays a central role in transforming and clearing chemicals and is susceptible to the toxicity from these agents. Drug-induced hepatic injury is the most common reason cited for withdrawal of an approved drug. Many medicinal plants showed hepatoprotective activity. The current review will discuss the medicinal plants possessed hepatoprotective effects.
... µg/g. The concentration of most of the minerals was higher at post flowering than that of pre flowering stage [49]. ...
Article
Full-text available
Digitalis lanata and Digitalis purpurea of the family Plantaginaceae were grown in Iraq. Digitalis lanata and Digitalis purpurea contains cardiac glycosides, volatile oil, fatty matter, starch, gum and sugars. They possessed cardiovascular, cytotoxic, antidiabetic, antioxidant, insecticidal, immunological, hepato, neuro and cardioprotective effects. This review highlights the chemical constituents and pharmacological effects of Digitalis lanata and Digitalis purpurea.
... hongyao and other similar plants [5][6][7][8][9]. Preliminary pharmacological studies have demonstrated that PD showed strong angiotensin-converting enzyme inhibitive effects, radical scavenging activity and antioxidant effects [10][11][12][13][14]. Significant inhibitory activity of angiotensin-converting enzyme (ACE) of PD was confirmed by monitoring in vitro the transformation of a hippuryl-histidyl-leucine (HHL) substrate into the product hippuric acid (HA). ...
Article
Full-text available
Plantainoside D (PD) is a potential anti-hypertensive active ingredient newly isolated from the dried plants of Chirita longgangensis var. hongyao. A sensitive and specific LC-ESI-MS/MS method was first developed and validated for the analysis of PD in rat plasma using genistein as the internal standard (IS). The plasma samples were pretreated with methanol-acetonitrile (50:50, v/v) to precipitate protein, and then chromatographed on a reverse-phase Agilent Zorbax XDB C18 column (50 mm × 2.1 mm, 3.5 μm). Gradient elution was utilized, with a mobile phase consisting of water and acetonitrile both containing 0.1% formic acid, and the flow rate was set at 0.50 mL/min. The analytes were monitored by tandem-mass spectrometry with negative electrospray ionization. The precursor/product transitions (m/z) in the negative ion mode were 639.2 → 160.9 Thomson (Th) and 268.9 → 158.9 Thomson (Th) for PD and IS, respectively. Linearity was achieved in the 0.10-200 ng/mL range, with a lower limit of quantification of 0.10 ng/mL. The precision and accuracy for both intra- and inter-day determination of the analyte were all within ±15%. The present method has been applied for pharmacokinetic study of PD after oral and intravenous administration in rats. The oral absolute bioavailability (F) of PD in rats was estimated to be 1.12% ± 0.46% with an elimination half-life (t1/2) value of 1.63 ± 0.19 h, suggesting its poor absorption and/or strong metabolism in vivo.
Article
Digitalis trojana Ivan, a member of Digitalis genus, has highly bioactive properties due to efficient phenolics. These compounds have shown to convert into each other in a limited time. Seasonal fluctuations of this plant leaves have been studied during the summer season using the high performance liquid chromatography–tandem mass spectrometry. Caffeic acid in June (2.48 mg/g extract), p-coumaric acid in August (6.69 mg/g extract) and trans-ferulic acid in July (4.85 mg/g extract) were the main compounds in the non-hydrolysed extracts. These compounds were heavily found in the hydrolysed extracts in August (14.63, 18.29 and 5.70 mg/g extracts, respectively). In addition, analysed flavonoids were found to be highest in July. Total phenolic contents were measured spectrophotometrically by using Folin-Ciocalteu’s phenol reagent. The spectrophotometrically results were lowest (e.g. 43.50 mg GAE/g extract) in July while those of the hydrolysed extracts were highest (e.g. 167.19 mg GAE/g extract) in June.
Article
Full-text available
In the absence of an effective therapy against Hepatocellular Carcinoma (HCC), chemoprevention remains an important strategy to circumvent morbidity and mortality. Here, we examined chemopreventive potential of Acteoside (ACT), a plant derived phenylethanoid glycoside against an environmental and dietary carcinogen, diethylnitrosamine (DEN)-induced rat hepatocarcinogenesis. ACT treatment (0.1 and 0.3% supplemented with diet) started 2 weeks before DEN challenge and continued for 18 weeks thereafter, showed a remarkable chemopreventive activity. ACT treatment resulted in reduced HCC nodules. Histopathology showed progressive tissue damage, necrosis (5 weeks), hepatocytic injury (10 weeks), anisonucleosis with presence of prominent nucleoli, sinusidal dilations, and lymphomono nuclear inflammation (18 weeks). Biochemical analysis showed hepatocytic injury (raised ALT, p < 0.001), inflammation [IL-6, IFN-γ (p < 0.05), and TNF-α (p < 0.001)], apoptosis [elevated Caspase-3 (p < 0.001)]. ACT at 0.1 and 0.3% ameliorated DEN-induced pre-hepatocarcinogenic manifestations. Mechanistic studies of ACT chemoprevention was elucidated using Hep3B cells with an aim to develop an in vitro DEN-induced toxicity model. Hep3B was found to be a reliable and more sensitive towards DEN toxicity compared to HepG2 and HuH7 cells. ACT prevented DEN-induced cytotoxicity (p < 0.001), DNA damage, and genotoxicity (micronuclei test, DNA ladder test, Hoechst staining, cell cycle analysis). ACT significantly (p < 0.001) scavenged DEN-induced reactive oxygen species (ROS) levels and prevented mitochondrial membrane potential (MMP) loss. Immunoblotting showed ACT treatment reversed DEN-induced NF-κB, Bax, Cytochrome C, Bcl-2, and Stat-3 levels. We conclude that chemoprotective effect of ACT is mediated by STAT-3 dependent regulation of oxidative stress and apoptosis and ACT has potential to be developed as a chemopreventive agent. © 2016 Wiley Periodicals, Inc. Environ Toxicol, 2016.
Article
Protecting cells or tissues from damage by many exogenous or endogenous carcinogens is the effective way for cancer chemoprevention. This protection could be achieved by the induction of phase II metabolic enzymes which were mediated mainly by nuclear factor E2-related factor 2/ antioxidant responsive element (Nrf2/ARE) pathway. It is suggested that some natural compounds, which exist chemopreventive effects, can activate Nrf2/ARE to mediate expression of phase II metabolic enzymes. This review is focused on natural compounds as potential cancer preventive agents via the pathway mentioned above.
Article
In this study, we examined the antiwrinkle effects of Plantago asiatica seed (PAS) on UV-induced human dermal fibroblasts (HDFs) and hairless mice models to determine if an anti-inflammatory agent could also be developed as an antiaging treatment. Acute UV irradiation induced matrix metallproteinase (MMP)-1 protein expression levels, but this was suppressed by PAS in HDFs. Next, we investigated the effect of PAS on UV-induced skin changes in hairless mice. Chronic UV exposure of the dorsal skin increased skin thickness and induced wrinkle formation. PAS significantly suppressed UV-induced morphologic skin changes. In addition, MMP-1 expression was dramatically attenuated by treatment with plantainoside D which was purely isolated from PAS, indicating that this is the principle compound inhibiting MMP-1 expression in HDFs. Taken together, our data suggest that PAS can prevent the harmful effects of UV that lead to skin aging.
Article
The new phenylethanoid glycosides, purpureaside D (Ia) and purpureaside E (Ib), are isolated together with two known phenylethanoid glycosides.
Article
Acteoside is one kind of phenylethanoid glycoside, which has shown a lot of biological activities. This article reviewed the study progress of acteoside, such as distribution, preparation, identification, and bioactivities.
Article
Full-text available
Recent research has shown the anticancer effects of digitalis compounds suggesting their possible use in medical oncology. Four extracts obtained from the leaves of Digitalis purpurea subsp. heywoodii have been assessed for cytotoxic activity against three human cancer cell lines, using the SRB assay. All of them showed high cytotoxicity, producing IC50 values in the 0.78 - 15 microg/mL range with the methanolic extract being the most active, in non toxic concentrations. Steroid glycosides (gitoxigenin derivatives) were detected in this methanolic extract. Gitoxigenin and gitoxin were evaluated in the SRB assay using the three human cancer cell lines, showing IC50 values in the 0.13 - 2.8 microM range, with the renal adenocarcinoma cancer cell line (TK-10) being the most sensitive one. Morphological apoptosis evaluation of the methanolic extract and both compounds on the TK-10 cell line showed that their cytotoxicity was mediated by an apoptotic effect. Finally, possible mechanisms involved in apoptosis induction by digitalis compounds are discussed.
Article
Expression of phase II detoxifying genes is regulated by NF-E2–related factor 2 (Nrf2)-mediated antioxidant response element (ARE) activation. We showed previously that phosphatidylinositol 3 (PI3)-kinase plays an essential role in ARE-mediated rGSTA2 induction by oxidative stress. In view of the fact that the signaling pathway of PI3-kinase controls microfilaments and translocation of actin-associated proteins, the current study was designed to investigate the PI3-kinase–mediated nuclear translocation of Nrf2 and the interaction of Nrf2 with actin.tert-Butylhydroquinone (t-BHQ) caused Nrf2 to translocate into the nucleus in H4IIE cells, which was prevented by pretreatment of the cells with PI3-kinase inhibitors (wortmannin/LY294002). t-BHQ relocalized Nrf2 in concert with changes in actin microfilament architecture, as visualized by superposition of immunochemically stained Nrf2 and fluorescent phalloidin-stained actin. Furthermore, t-BHQ increased the level of nuclear actin, coimmunoprecipitated with Nrf2, which returned to that of control by pretreatment of the cells with PI3-kinase inhibitors. Cytochalasin B, an actin disruptor, alone stimulated actin-mediated nuclear translocation of Nrf2 and induced rGSTA2. In contrast, phalloidin, an agent that prevents actin filaments from depolymerization, inhibited Nrf2 translocation and rGSTA2 induction by t-BHQ. Subcellular fractionation and immunoblot analyses allowed us to detect both 57- and 100-kDa Nrf2. Immunoblot and immunoprecipitation assays showed that the 100-kDa protein comprised both Nrf2 and actin. The present study demonstrates that the PI3-kinase signaling pathway regulates rearrangement of actin microfilaments in response to oxidative stress and that depolymerization of actin causes a complex of Nrf2 bound with actin to translocate into nucleus.
Article
The effects of dietary administration of ethoxyquin (EQ) on aflatoxin B1 (AFB1) metabolism, DNA adduct formation and removal, and hepatic tumorigenesis were examined in male Fischer rats. Rats were fed a semipurified diet containing 0.4% EQ for 1 wk, gavaged with 250 micrograms of AFB1 per kg 5 times a wk during the next 2 wk, and, finally, restored to the control diet 1 wk after cessation of dosing. At 4 mo, focal areas of hepatocellular alteration were identified and quantitated by staining sections of liver for gamma-glutamyl transpeptidase. Treatment with EQ reduced by greater than 95% both area and volume of liver occupied by gamma-glutamyl transpeptidase-positive foci. Utilizing the same multiple dosing protocol, patterns of covalent modifications of DNA by AFB1 were determined. EQ produced a dramatic reduction in the binding of AFB1 to hepatic DNA: 18-fold initially and 3-fold at the end of the dosing period. Although binding was detectable at 3 and 4 mo postdosing, no effect of EQ was observed, suggesting that these persistent adducts are not of primary relevance to AFB1 carcinogenesis. Analysis of nucleic acid bases by high-performance liquid chromatography revealed no qualitative differences in adduct species between treatment groups. The inhibitory effect of EQ on AFB1 binding to DNA and tumorigenesis appears related to induction of detoxication enzymes. Rats fed 0.4% EQ for 7 days showed a 5-fold increase in hepatic cytosolic glutathione S-transferase (GST)-specific activities. Multiple molecular forms of GST were induced, and concomitant elevations in messenger RNA levels coding for the synthesis of GST subunits were observed. Correspondingly, biliary elimination of AFB1-glutathione conjugate was increased 4.5-fold in animals on the EQ diet during the first 2 h following p.o. administration of 250 micrograms of AFB1 per kg. Thus, induction by EQ of enzymes important to AFB1 detoxication, such as GST, can lead to enhanced carcinogen elimination, as well as reductions of AFB1-DNA adduct formation and subsequent expression of preneoplastic lesions, and, ultimately, neoplasia.
Article
Diallyl sulfide (DAS) is a principal thioether of garlic (Allium sativum) accounting, in part, for the flavor and fragrance of this herb. Previous studies have shown that DAS is a potent inhibitor of experimentally induced colon cancer in mice. Metabolic studies of other garlic-derived substances suggested that DAS could prevent tumorigenicity of other hepatic activated carcinogens. The present study was designed to determine whether DAS could inhibit the DNA-damaging and tumorigenic effects of N-nitrosomethylbenzylamine in rat esophagus. A dose of 200 mg/kg of DAS given p.o. 3 h prior to N-nitrosomethylbenzylamine administration was found to inhibit the carcinogen-induced nuclear toxicity by 64% to 56% at the two doses (3 and 5 mg/kg) of NMBA tested. These results suggested that the compound was potentially anticarcinogenic. In the carcinogenicity experiment it was found that DAS totally inhibited tumor formation in rats treated with a carcinogenic dose of NMBA (100% inhibition of papilloma and squamous cell carcinoma incidence, P less than 0.0001). Additionally DAS was found to substantially reduce hepatic microsomal metabolism of the carcinogen. These data demonstrate that DAS is unique in its anticarcinogenic activity. It strongly suppresses the tumorigenic effects of potent, metabolically activated monoalkylating carcinogens in the gastrointestinal tract.
Article
Oltipraz [5-(2-pyrazinyl)-4-methyl-1,2-dithiole-3-thione] protects against chemical carcinogenesis in several animal models and is currently under evaluation as a possible chemopreventive agent in humans. Ideally, clinical chemopreventive interventions use dosing regimens that maximize efficacy while minimizing toxicity. Toward this end, the chemopreventive efficacy achieved by administration of intermittent doses of oltipraz was evaluated in rats. F344 rats were treated with oltipraz (0.5 mmol/kg, p.o.) once weekly, twice weekly, or daily over a 5-week period. After the first week, all rats were gavaged with 20 micrograms/kg of aflatoxin B1 for 28 consecutive days. Livers were analyzed 2 months after the last aflatoxin B1 dose, and the volume of liver occupied by glutathione S-transferase (GST)-P positive foci, a presumptive marker of neoplasia, was observed to be decreased > 95%, > 97%, or > 99% in livers of rats receiving once-, twice-weekly or daily oltipraz treatments, respectively. The chemopreventive actions of oltipraz have been associated with increases in the levels of phase 2 detoxifying enzymes, such as the glutathione S-transferase isozymes. Accordingly, GST conjugation activity measured with 1-chloro-2,4-dinitrobenzene as substrate increased 1.5-, 1.8-, or 2.4-fold for the once-weekly, twice-weekly or daily treatments, respectively, throughout a 7-day period. Quantitative HPLC analyses of GST subunits 24 h after 2 or 7 daily administrations of oltipraz showed that the levels of subunits Yb1, Yp, Yc2, and Ya2 were increased with maximum elevations of 5.6-, 11.1-, 6.4-, and 10.4-fold, respectively. In comparison, levels of subunits Yb2 and Yc1 were modestly elevated 1.8- to 2.6-fold, respectively, whereas subunit Ya1 was not induced. Remarkably, the levels of subunit Yp and Ya2 remained elevated approximately 2.3-fold 7 days after a single dose of oltipraz. In contrast, the levels of subunits Yb1 and Yc2 diminished to approximate control levels within 7 days after a single dose of oltipraz. GST mRNA levels for Ya, Yb, and Yp were measured by Northern blot analysis and were found to be elevated maximally to 13.7-, 13.5-, and 3.9-fold, respectively, after two daily oltipraz doses. Interestingly, GST Ya and Yb mRNA diminished to constitutive levels after 7 daily doses of oltipraz, with no corresponding decreases in GST subunit or activity levels. The levels of GST Ya and Yb mRNA decreased to constitutive levels within 4 days after a single oltipraz administration, whereas GST Yp mRNA levels remained elevated throughout the 7-day follow-up period.(ABSTRACT TRUNCATED AT 400 WORDS)
Article
The role of reactive oxygen species (ROS) in AFB1-induced cell injury was investigated using cultured rat hepatocytes. Malonaldehyde (MDA) generation and lactate dehydrogenase (LDH) release were determined as indices of lipid peroxidation and cell injury, respectively. Exposure to AFB1 for up to 72 h resulted in significantly elevated levels of LDH being released into the medium as well as the MDA generation in cultured hepatocytes. These effects were dose-dependent, indicating that AFB1 was capable of inducing oxidative damages in the cell. Further, MDA generation and LDH release were effectively inhibited by the addition of the following: (1) superoxide dismutase (500 units/ml), (2) catalase (1500 units/ml), (3) 10 mM desferrioxamine (a specific iron chelator), or (4) 260 mM dimethyl sulfoxide (a hydroxyl radical scavenger). These evidences therefore suggest that ROS, such as superoxide radicals, hydroxyl radicals and hydrogen peroxides, are involved in AFB1-induced cell injury in cultured rat hepatocytes.
Article
Detoxication enzymes protect cells from a wide variety of xenobiotics and endogenous toxins. Current data suggest that the balance between the Phase I carcinogen-activating enzymes and the Phase II detoxifying enzymes is critical to determining an individual's risk for cancer. Human deficiencies in Phase II enzyme activity, specifically glutathione-S-transferase (GST), have been identified and associated with increased risk for colon cancer. The increased frequency of the GST M1 null genotype among individuals with primarily smoking-related cancers has been documented. Induction of Phase II enzymes by naturally occurring or synthetic agents represents a promising strategy for cancer prevention. Both the required characteristics of potential chemopreventive agents and the role of the antioxidant response element in the monofunctional induction of Phase II enzymes have been discussed. The synthetic dithiolthione oltipraz induces a battery of Phase II enzymes and inhibits chemically induced tumors in a variety of target organs. Its ability to induce Phase II enzymes in human colon tissue and blood lymphocytes has been reported. Other promising inducers with chemopreventive activity include the isothiocyanates and polyphenols. These data collectively support the future development of Phase II enzyme inducers as clinical chemopreventive agents.
Article
The naturally occurring organosulfur compounds (OSCs) diallyl sulfide (DAS), diallyl disulfide (DADS), dipropyl sulfide (DPS), and dipropyl disulfide (DPDS) were studied with respect to their effects on hepatic, intestinal, renal, and pulmonary phase II drug metabolizing enzymes, i.e., glutathione S-transferase (GST), microsomal epoxide hydrolase (mEH), quinone reductase (QR), and UDP-glucuronosyltransferase (UGT). OSCs were administered po to male SPF Wistar rats. In addition to assays of total enzyme activity, the ability of OSCs to modify the levels of mEH and rGSTA1/A2, A3/A5, M1, M2, and P1 was assessed by Western blotting. Remarkably, DADS significantly increased all Phase II enzyme activities, except the pulmonary mEH. It was noteworthy that only DADS induced QR activity. DAS, DPS, and DPDS induced mEH, GST, and UGT activities in the liver. Interestingly, DAS, DPS, and DPDS significantly decreased renal GST activity. In the same manner, DAS, DPS, and DPDS decreased rGSTA1/A2 and A3/A5 levels in the kidney. Conversely, all OSCs were able to induce GST of alpha and mu classes in the liver. In the intestine, DADS and DAS increased rGSTA1/A2, M2, and P1, while rGSTA3/A5 and M2 were only increased by DADS. In addition, DADS induced rGSTP1 dramatically in the four tissues analyzed. DADS also increased the mEH levels in the liver, intestine, and kidney, while DAS and DPS moderately induced mEH level in the liver. This study brings additional insights into the effects of OSCs on Phase II enzymes and suggests that DADS could be a promising chemopreventive agent considering its pleiotropic capacity of induction.
Article
The protective adaptive response to electrophiles and reactive oxygen species is mediated by enhanced expression of phase II detoxifying genes, including glutathione S-transferases, through activation of antioxidant response element (ARE). The current study was designed to investigate the role of phosphatidylinositol 3-kinase (PI3-kinase)-Akt and mitogen-activated protein (MAP) kinase signaling pathways in the induction of rGSTA2 by tert-butylhydroquinone (t-BHQ). Nuclear ARE complex was activated 1 to 6 h after treatment of H4IIE cells with t-BHQ. The rGSTA2 mRNA level was elevated 6 to 24 h after t-BHQ treatment, which led to the enzyme induction. Activities of PI3-kinase and Akt were increased 10 min through 6 h after t-BHQ treatment, whereas wortmannin or LY294002, PI3-kinase inhibitors, completely abolished ARE binding activity and increases in rGSTA2 mRNA and protein. Extracellular signal-regulated kinase (ERK), p38 MAP kinase, and c-Jun N-terminal kinase (JNK) were all activated by t-BHQ. Treatment with PD98059, an ERK inhibitor, however, increased rGSTA2 mRNA and further enhanced t-BHQ-induced expression of rGSTA2. Neither SB203580 nor overexpression of JNK1 dominant negative mutant altered t-BHQ-inducible rGSTA2 expression. These results demonstrated that t-BHQ activated PI3-kinase and Akt, which was responsible for ARE-mediated rGSTA2 induction, and that ERK might negatively regulate rGSTA2 expression, whereas activation of p38 MAP kinase or of JNK by t-BHQ was not associated with the enzyme induction.
Article
Expression of phase II detoxifying genes is regulated by NF-E2-related factor 2 (Nrf2)-mediated antioxidant response element (ARE) activation. We showed previously that phosphatidylinositol 3 (PI3)-kinase plays an essential role in ARE-mediated rGSTA2 induction by oxidative stress. In view of the fact that the signaling pathway of PI3-kinase controls microfilaments and translocation of actin-associated proteins, the current study was designed to investigate the PI3-kinase-mediated nuclear translocation of Nrf2 and the interaction of Nrf2 with actin. tert-Butylhydroquinone (t-BHQ) caused Nrf2 to translocate into the nucleus in H4IIE cells, which was prevented by pretreatment of the cells with PI3-kinase inhibitors (wortmannin/LY294002). t-BHQ relocalized Nrf2 in concert with changes in actin microfilament architecture, as visualized by superposition of immunochemically stained Nrf2 and fluorescent phalloidin-stained actin. Furthermore, t-BHQ increased the level of nuclear actin, coimmunoprecipitated with Nrf2, which returned to that of control by pretreatment of the cells with PI3-kinase inhibitors. Cytochalasin B, an actin disruptor, alone stimulated actin-mediated nuclear translocation of Nrf2 and induced rGSTA2. In contrast, phalloidin, an agent that prevents actin filaments from depolymerization, inhibited Nrf2 translocation and rGSTA2 induction by t-BHQ. Subcellular fractionation and immunoblot analyses allowed us to detect both 57- and 100-kDa Nrf2. Immunoblot and immunoprecipitation assays showed that the 100-kDa protein comprised both Nrf2 and actin. The present study demonstrates that the PI3-kinase signaling pathway regulates rearrangement of actin microfilaments in response to oxidative stress and that depolymerization of actin causes a complex of Nrf2 bound with actin to translocate into nucleus.
Article
This study investigated the protective effects of acteoside, a phenylethanoid glycoside, on the carbon tetrachloride-induced hepatotoxicity as well as the possible mechanisms involved in this protection in mice. Pretreatment with acteoside prior to the administration of carbon tetrachloride significantly prevented the increased serum enzymatic activities of alanine and aspartate aminotransferase in a dose-dependent manner. In addition, pretreatment with acteoside significantly prevented the increase in hepatic malondialdehyde formation and the depletion of the reduced glutathione content in the liver of carbon tetrachloride-intoxicated mice. Carbon tetrachloride-induced hepatotoxicity was also essentially prevented, as indicated by a liver histopathologic study. The effects of acteoside on cytochrome P450 (P450) 2E1, the major isozyme involved in carbon tetrachloride bioactivation were also investigated. Treatment of the mice with acteoside resulted in a significant decrease in the P450 2E1-dependent pnitrophenol and aniline hydroxylation in a dose-dependent manner. Consistent with these observations, the P450 2El protein levels were also lower. Acteoside exhibited anti-oxidant effects on FeCl2-ascorbate induced lipid peroxidation in a mouse liver homogenate, and on superoxide radical scavenging activity. These results suggest that the protective effects of acteoside against the carbon tetrachloride-induced hepatotoxicity possibly involve mechanisms related to its ability to block the P450-mediated carbon tetrachloride bioactivation and free radical scavenging effects.
Article
Hepatocellular carcinoma is one of the most common cancers worldwide. Infection with hepatitis B virus and exposure to aflatoxins in the diet act synergistically to amplify risk. From a public health perspective, hepatitis virus vaccination programs and efforts to both reduce aflatoxin exposures and to attenuate the toxicological consequences of unavoidable exposures should have major impacts on the global incidence of this disease. Experimentally, aflatoxin-induced hepatocarcinogenesis can be inhibited by over a score of different chemopreventive agents with multiple mechanisms of action. One agent, oltipraz, is a potent inducer of phase 2 enzymes involved in the detoxication of carcinogens including aflatoxin. A second agent, chlorophyllin, impedes the bioavailability of carcinogens by forming molecular complexes and enhances their elimination in the fecal stream. This review highlights the findings of recent randomized clinical trials with oltipraz and chlorophyllin conducted in individuals exposed to dietary aflatoxins and at high risk for development of liver cancer. Both chemopreventive agents modulated levels of aflatoxin biomarkers in the study participants in manners consonant with protection. Although pharmacological approaches establish proof of principle and help identify key molecular targets for interventions, food-based approaches that also use these molecular targets may be the most practical for widespread application in high-risk populations.
Classics of Cardiology
  • F A Willius
  • T E Keys
Willius FA, Keys TE (1941) Classics of Cardiology. New York, NY: Dover Publications Inc. 1: 231-252.