Structure-dependent activity of glycyrrhetinic acid derivatives as peroxisome proliferator-activated receptor {gamma} agonists in colon cancer cells

Potential of Glycyrrhiza in the prevention of colitis-associated colon cancer

ETHNOPHARMACOLOGICAL RELEVANCE

Glycyrrhiza, a legume native to the Mediterranean region, has a long history of ethnomedicinal use in China. Due to its antiviral, antibacterial, anti-inflammatory, antioxidant, antitumor, anti-ulcer, and hepatoprotective properties, Glycyrrhiza is widely utilized in the treatment of gastrointestinal disorders.

THE AIM OF THE REVIEW

The specific mechanisms of the main active constituents of glycyrrhiza in the treatment of inflammatory bowel disease, precancerous lesions and colorectal cancer at all stages of the colitis-associated colon cancer "Inflammation-Dysplasia-Cancer" sequence, as well as its pharmacokinetics, toxicology, formulation improvements, and application studies, are reviewed to provide new insights and perspectives on glycyrrhiza as a dietary supplement to treat and prevent colitis-associated colon cancer.

MATERIALS AND METHODS

Information on Glycyrrhiza was retrieved from electronic databases, including PubMed and Web of Science.

RESULTS

Glycyrrhiza is a well-established medicinal plant with significant potential for applications in both the food and pharmaceutical industries. Over 400 active constituents have been identified in Glycyrrhiza, including terpenoids, flavonoids, isoflavones, coumarins, and polyphenols. Numerous studies have demonstrated that Glycyrrhiza and its active compounds can inhibit the "Inflammation-Dysplasia-Cancer" progression of colitis-associated colon cancer by mitigating inflammatory bowel disease, reducing the number of intestinal precancerous lesions, and counteracting colorectal cancer. Furthermore, derivatives and nanocarriers are crucial for the effective treatment of colitis-associated colon cancer using Glycyrrhiza and its active constituents.

CONCLUSION

In conclusion, Glycyrrhiza is a plant with both medicinal and nutritional value, making it a potential food ingredient and dietary supplement for the treatment of colitis-associated colon cancer.

Neuroprotective Effects of Glycyrrhiza glabra Total Extract and Isolated Compounds

Glycyrrhiza glabra L. is a plant commonly utilized in herbal medicine and stands out as one of the more extensively researched medicinal plants globally. It has been documented with respect to several pharmacological activities, notably, neuroprotective effects, among others. However, the neuroprotective activity of pure phenolic compounds has not been reported yet. The chromatographic of a methanolic extract yielded twenty-two compounds, viz.: naringenin 4'-O-glucoside (1), 3',4',7-trihydroxyflavanone (butin) (2), liquiritin (3), liquiritin apioside (4), abyssinone (5), glabrol (6), isoliquiritin (7), neoisoliquiritin (8), isoliquiritin apioside (9), licuraside (10). 3'[O], 4'-(2,2-dimethylpyrano)-3,7-dihydroxyflavanone (11), glabrocoumarin (12), glabrene (13), isomedicarpin (14), 7-hydroxy-4'-methoxyflavone (formononetin) (15), ononin (16), glycyroside (17), (3S)-7,4'-dihydroxy-2'-methoxyisoflavan (18), glabridin (19), neoliquiritin (20), 3,11-dioxooleana-1,12-dien-29-oic acid (21), and 3-oxo-18β-glycyrrhetinic acid (22). The results of the neuroprotection evaluation showed that G. glabra total extract (TE) and compounds 1, 7, 11, 16, and 20 protected SH-SY5Y cells by inhibiting the depletion of ATP and elevated caspase 3/7 activities induced by MPP+. Indeed, this study reports for the first time the structure and activity of compound 11 and the neuroprotective activity of some phenolic constituents from G. glabra.

Natural compounds targeting nuclear receptors for effective cancer therapy

Human nuclear receptors (NRs) are a family of forty-eight transcription factors that modulate gene expression both spatially and temporally. Numerous biochemical, physiological, and pathological processes including cell survival, proliferation, differentiation, metabolism, immune modulation, development, reproduction, and aging are extensively orchestrated by different NRs. The involvement of dysregulated NRs and NR-mediated signaling pathways in driving cancer cell hallmarks has been thoroughly investigated. Targeting NRs has been one of the major focuses of drug development strategies for cancer interventions. Interestingly, rapid progress in molecular biology and drug screening reveals that the naturally occurring compounds are promising modern oncology drugs which are free of potentially inevitable repercussions that are associated with synthetic compounds. Therefore, the purpose of this review is to draw our attention to the potential therapeutic effects of various classes of natural compounds that target NRs such as phytochemicals, dietary components, venom constituents, royal jelly-derived compounds, and microbial derivatives in the establishment of novel and safe medications for cancer treatment. This review also emphasizes molecular mechanisms and signaling pathways that are leveraged to promote the anti-cancer effects of these natural compounds. We have also critically reviewed and assessed the advantages and limitations of current preclinical and clinical studies on this subject for cancer prophylaxis. This might subsequently pave the way for new paradigms in the discovery of drugs that target specific cancer types.

Krüppel-like Factors 4 and 5 in Colorectal Tumorigenesis

Krüppel-like factors (KLFs) are transcription factors regulating various biological processes such as proliferation, differentiation, migration, invasion, and homeostasis. Importantly, they participate in disease development and progression. KLFs are expressed in multiple tissues, and their role is tissue- and context-dependent. KLF4 and KLF5 are two fascinating members of this family that regulate crucial stages of cellular identity from embryogenesis through differentiation and, finally, during tumorigenesis. They maintain homeostasis of various tissues and regulate inflammation, response to injury, regeneration, and development and progression of multiple cancers such as colorectal, breast, ovarian, pancreatic, lung, and prostate, to name a few. Recent studies broaden our understanding of their function and demonstrate their opposing roles in regulating gene expression, cellular function, and tumorigenesis. This review will focus on the roles KLF4 and KLF5 play in colorectal cancer. Understanding the context-dependent functions of KLF4 and KLF5 and the mechanisms through which they exert their effects will be extremely helpful in developing targeted cancer therapy.

Tumor-Targeting NHC-Au(I) Complex Induces Immunogenic Cell Death in Hepatocellular Carcinoma

Immunogenic cell death (ICD) is a promising direction of cancer immunotherapy in hepatocellular carcinoma (HCC). A series of novel NHC-Au(I) complexes derived from 4,5-diarylimidazole, containing glycyrrhetinic acid (GA) as an efficient targeting ligand for HCC, were herein designed and synthesized. Among these, complex 4C exhibited excellent effectiveness for tumor targeting and antitumor activity, which induced the occurrence of ICD in HCC cells. Additionally, 4C can effectively inhibit TrxR enzyme activity, increase reactive oxygen species (ROS) expression, lead to redox homeostasis disorder, mediate mitochondrial dysfunction and endoplasmic reticulum stress (ERS), and cause the characteristic discharge of damage-associated molecular patterns (DAMPs) in HCC cells. More importantly, 4C showed a great ICD-inducing effect in a vaccination mouse model and activated antitumor immunity in a tumor-bearing C57BL/6 mouse model, which is consistent with the in vitro results. In conclusion, we found the potential of Au(I) complex with HCC-targeted capability for effective tumor immunotherapy.

Nanocarrier-Based Tumor-Targeting Drug Delivery Systems for Hepatocellular Carcinoma Treatments: Enhanced Therapeutic Efficacy and Reduced Drug Toxicity

Hepatocellular carcinoma (HCC), due to the lack of efficient diagnostic methods and short of available treatments, becomes the third main cause of cancer deaths. Novel treatments for HCCs are thus in great need. The fast-growing area of drug delivery provides intriguing possibility to design nanocarriers with unique properties. The nanocarriers performanced as drug deliver vehicles enable the design of diverse drug delivery systems, which could serve multiple purposes, including improved bioavailability, controlled or triggered release and targeted delivery, leading to enhanced drug efficacy and lowered drug toxicity. This paper provides an overview on the types of delivery vehicles, functions of drug nanocarriers and types of ligand-based targeting systems and highlights the advances made towards better HCC treatments.

Glycyrrhetinic acid induces oxidative/nitrative stress and drives ferroptosis through activating NADPH oxidases and iNOS, and depriving glutathione in triple-negative breast cancer cells

Reactive oxygen species (ROS)/reactive nitrogen species (RNS)-mediated ferroptosis becomes a novel effective target for anti-cancer treatment. In the present study, we tested the hypothesis that 18-β-glycyrrhetinic acid (GA), an active compound from medicinal herbal Licorice, could induce the production of ROS/RNS, increase lipid peroxidation and trigger ferroptosis in MDA-MB-231 triple negative breast cancer cells. To confirm the GA's anti-cancer effects, we detected cell viability, apoptosis and ferroptosis in the MDA-MB-231 cells. To explore the effects of GA on inducing ferroptosis, we measured mitochrondrial morphology, ROS/RNS production, lipid peroxidation, ferrous ion, glutathione (GSH), System Xc^-, GPX4, glutathione peroxidases (GPX), NADPH oxidase and iNOS in the MDA-MB-231 cells. The major discoveries are included as below: (1) GA treatment selectively decreased cell viability and induced ferroptosis companied with the increased lipid peroxidation and ferrous ion in the MDA-MB-231 triple negative breast cancer cells. Iron chelator deferoxamine mesylate (DFO) and ferroptosis inhibitor Ferrostatin-1 abolished the effects of GA. (2) GA treatment up-regulated the expression and activity of NADPH oxidase and iNOS, and increased ROS/RNS productions (O₂^•-, ^•OH, NO and ONOO^-) in the MDA-MB-231 cells; (3) GA down-regulated the expression of SLC7A11 of System X_c^-, decreased glutathione (GSH) level and inhibited GPX activity. Taken together, GA could promote the productions of ROS and RNS via activating NADPH oxidases and iNOS, and decreasing GSH and GPX activity, subsequently aggravating lipid peroxidation and triggering ferroptosis in triple-negative breast cancer cells.

Calorimetric Evaluation of Glycyrrhetic Acid (GA)- and Stearyl Glycyrrhetinate (SG)-Loaded Solid Lipid Nanoparticle Interactions with a Model Biomembrane

Glycyrrhetic acid (GA) and stearyl glycyrrhetinate (SG) are two interesting compounds from Glycyrrhiza glabra, showing numerous biological properties widely applied in the pharmaceutical and cosmetic fields. Despite these appreciable benefits, their potential therapeutic properties are strongly compromised due to unfavourable physical-chemical features. The strategy exploited in the present work was to develop solid lipid nanoparticles (SLNs) as carrier systems for GA and SG delivery. Both formulations loaded with GA and SG (GA-SLNs and SG-SLNs, respectively) were prepared by the high shear homogenization coupled to ultrasound (HSH-US) method, and we obtained good technological parameters. DSC was used to evaluate their thermotropic behaviour and ability to act as carriers for GA and SG. The study was conducted by means of a biomembrane model (multilamellar vesicles; MLVs) that simulated the interaction of the carriers with the cellular membrane. Unloaded and loaded SLNs were incubated with the biomembranes, and their interactions were evaluated over time through variations in their calorimetric curves. The results of these studies indicated that GA and SG interact differently with MLVs and SLNs; the interactions of SG-SLNs and GA-SLNs with the biomembrane model showed different variations of the MLVs calorimetric curve and suggest the potential use of SLNs as delivery systems for GA.

Preclinical Research on a Mixture of Red Ginseng and Licorice Extracts in the Treatment and Prevention of Obesity

The anti-obesity effects of RL (a 3:1 mixture of Panax ginseng saponin fractions and Glycyrrhiza glabra L. extracts) on 3T3-L1 adipocytes and C57BL/6J obese mice were evaluated at different concentrations. We investigated the anti-obesity effects of RL through lipid accumulation inhibition rate, serum lipid composition analysis, adipose tissue size, adipogenic transcription factors and AMPK pathway. RL inhibited the lipid accumulation of 3T3-L1 adipocytes in a dose-dependent manner at concentrations of 50–200 μg/mL without cytotoxicity (50–400 μg/mL). Oral administration of RL at the highest concentration (400 mg/kg/day) did not cause significant liver toxicity in high-fat diet-induced obese mice. RL stimulated adiponectin secretion in a dose-dependent manner and primarily mediates the AMPK pathway to inhibit triglyceride synthesis and attenuate adipocyte hypertrophy. RL significantly reduced weight in obese mice, but none of the body weight, adipose tissue weight, serum triglyceride level, and AMPK pathway activation degree showed any difference between dosing concentrations of 200 and 400 mg/kg/day. Therefore, 200 mg/kg/day of RL is the optimal preclinical concentration, which can be a reference concentration for conversion into a human clinical trial dose.

Synthesis and antitumor effects of novel 18β-glycyrrhetinic acid derivatives featuring an exocyclic α,β-unsaturated carbonyl moiety in ring A

A series of novel 18β-glycyrrhetinic acid (GA) derivatives featuring an exocyclic α,β-unsaturated carbonyl moiety in ring A were synthesized and evaluated for their antitumor activities. Compounds 5c and 5l showed stronger cytotoxicity than other compounds and reported GA analogue CDODA-Me (methyl 2-cyano-3,11-dioxo-18β-olean-1,12-dien-30-oate). 5c and 5l induced apoptosis in cancer cells accompanying with c-Flip reduction and Noxa induction, associated with decreased HDAC3 expression and increased acetylation of H3. 5l displayed better stability properties than 5c and CDODA-Me in microsomes and plasma, 5l also showed favorable pharmacokinetic profiles and inhibited tumor growth in mice. Compound 5l represents a new type of GA derivatives with improved antitumor activity.

Deep insights into the response of human cervical carcinoma cells to a new cyano enone-bearing triterpenoid soloxolone methyl: a transcriptome analysis

Semisynthetic triterpenoids, bearing cyano enone functionality in ring A, are considered now as novel promising anti-tumor agents. However, despite the large-scale studies, their effects on cervical carcinoma cells and, moreover, mechanisms underlying cell death activation by such compounds in this cell type have not been fully elucidated. In this work, we attempted to reconstitute the key pathways and master regulators involved in the response of human cervical carcinoma KB-3-1 cells to the novel glycyrrhetinic acid derivative soloxolone methyl (SM) by a transcriptomic approach. Functional annotation of differentially expressed genes, analysis of their cis^- regulatory sequences and protein-protein interaction network clearly indicated that stress of endoplasmic reticulum (ER) is the central event triggered by SM in the cells. A range of key ER stress sensors and transcription factor AP-1 were identified as upstream transcriptional regulators, controlling the response of the cells to SM. Additionally, by using Gene Expression Omnibus data, we showed the ability of SM to modulate the expression of key genes involved in regulation of the high proliferative rate of cervical carcinoma cells. Further Connectivity Map analysis revealed similarity of SM's effects with known ER stress inducers thapsigargin and geldanamycin, targeting SERCA and Grp94, respectively. According to the molecular docking study, SM could snugly fit into the active sites of these proteins in the positions very close to that of both inhibitors. Taken together, our findings provide a basis for the better understanding of the intracellular processes in tumor cells switched on in response to cyano enone-bearing triterpenoids.

Modification, Antitumor Activity, and Targeted PPARγ Study of 18β-Glycyrrhetinic Acid, an Important Active Ingredient of Licorice

Licorice is a traditional Chinese medicine, which is often used as sweetener and cosmetic ingredients in food and pharmaceutical industries. Among them, glycyrrhetic acid is one of the most important agents. Studies have shown that glycyrrhetic acid exhibited antitumor activities as PPARγ agonist. However, the limited number of PPARγ glycyrrhetinic agonists and their high toxicity greatly limit the design based on the structure. Therefore, clarifying the binding mode between PPARγ and small molecules, we focused on the introduction of a natural active piperazine skeleton in the position of glycyrrhetinic acid C-3. According to the Combination Principle and the Structure-Based Drug Design, 19 glycyrrhetic acid derivatives were designed and synthesized as potential PPARγ agonists. Compounds 4c and 4q were screened as high-efficiency and low-toxicity lead compounds.

Preparation and characterization of norcantharidin liposomes modified with stearyl glycyrrhetinate

In the current study, norcantharidin (NCTD)-loaded liposomes (LIPs) modified with stearyl glycyrrhetinate (SG; SG-NCTD-LIP) were prepared by the ethanol injection method. To increase the drug encapsulation efficiency (EE), the formulation of NCTD-LIP was optimized by single factor test and orthogonal design. The release of NCTD in vitro from SG-NCTD-LIP was evaluated by equilibrium dialysis. The cytotoxicity of SG-NCTD-LIP in HepG2 was investigated by MTT assay. The results revealed that the EE of liposomes was ~27.80%, the average SG-NCTD-LIP was 87.5 nm, the in vitro NCTD release from SG-NCTD-LIP was delayed compared with NCTD in solution and the drug-release kinetic followed a first-order model. MTT assays revealed increased cytotoxicity activity against HepG2 cells for SG-NCTD-LIP compared with free NCTD. In conclusion, SG-NCTD-LIP prepared in the present study may be a promising liposomal drug delivery system for anticancer drugs in liver-targeting therapy.

Glycycoumarin exerts anti-liver cancer activity by directly targeting T-LAK cell-originated protein kinase

Glycycoumarin (GCM) is a major bioactive coumarin compound isolated from licorice and the anti-cancer activity of GCM has not been scientifically addressed. In the present study, we have tested the anti-liver cancer activity of GCM using both in vitro and in vivo models and found for the first time that GCM possesses a potent activity against liver cancer evidenced by cell growth inhibition and apoptosis induction in vitro and tumor reduction in vivo. Mechanistically, GCM was able to bind to and inactivate oncogenic kinase T-LAK cell-originated protein kinase (TOPK), which in turn led to activation of p53 pathway. Our findings supported GCM as a novel active compound that contributed to the anti-cancer activity of licorice and TOPK could be an effective target for hepatocellular carcinoma (HCC) treatment.

Surface Engineering of Nanoparticles for Targeted Delivery to Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-associated deaths worldwide. There is a lack of efficient therapy for HCC; the only available first-line systemic drug, sorafenib, can merely improve the average survival by two months. Among the efforts to develop an efficient therapy for HCC, nanomedicine has drawn the most attention, owing to its unique features such as high drug-loading capacity, intrinsic anticancer activities, integrated diagnostic and therapeutic functionalities, and easy surface engineering with targeting ligands. Despite its tremendous advantages, no nanomedicine can be effective unless it successfully targets the tumor site, which is a challenging task. In this review, the features of HCC are described, and the physiological hurdles that prevent nanoparticles from targeting HCC are discussed. Then, the surface physicochemical factors of nanoparticles that can influence targeting efficiency are discussed. Finally, a thorough description of the physiological barriers that nanomedicine must conquer before uptake by HCC cells if possible is provided, as well as the surface engineering approaches to nanomedicine to achieve targeted delivery to HCC cells. The physiological hurdles and corresponding solutions summarized in this review provide a general guide for the rational design of HCC targeting nanomedicine systems.

An Overview of Structurally Modified Glycyrrhetinic Acid Derivatives as Antitumor Agents

Glycyrrhetinic Acid (GA), a triterpenoid aglycone component of the natural product glycyrrhizinic acid, was found to possess remarkable anti-proliferative and apoptosis-inducing activity in various cancer cell lines. Though GA was not as active as other triterpenes, such as betulinic acid and oleanolic acid, it could trigger apoptosis in tumor cells and it can be obtained easily and cheaply, which has stimulated scientific interest in using GA as a scaffold to synthesize new antitumor agents. The structural modifications of GA reported in recent decades can be divided into four groups, which include structural modifications on ring-A, ring-C, ring-E and multiple ring modifications. The lack of a comprehensive and recent review on this topic prompted us to gather more new information. This overview is dedicated to summarizing and updating the structural modification of GA to improve its antitumor activity published between 2005 and 2016. We reviewed a total of 210 GA derivatives that we encountered and compiled the most active GA derivatives along with their activity profile in different series. Furthermore, the structure activity relationships of these derivatives are briefly discussed. The included information is expected to be of benefit to further studies of structural modifications of GA to enhance its antitumor activity.

SP and KLF Transcription Factors in Digestive Physiology and Diseases

Specificity proteins (SPs) and Krüppel-like factors (KLFs) belong to the family of transcription factors that contain conserved zinc finger domains involved in binding to target DNA sequences. Many of these proteins are expressed in different tissues and have distinct tissue-specific activities and functions. Studies have shown that SPs and KLFs regulate not only physiological processes such as growth, development, differentiation, proliferation, and embryogenesis, but pathogenesis of many diseases, including cancer and inflammatory disorders. Consistently, these proteins have been shown to regulate normal functions and pathobiology in the digestive system. We review recent findings on the tissue- and organ-specific functions of SPs and KLFs in the digestive system including the oral cavity, esophagus, stomach, small and large intestines, pancreas, and liver. We provide a list of agents under development to target these proteins.

Ligand-based targeted therapy: a novel strategy for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common primary liver cancer with high morbidity and mortality worldwide. Chemotherapy is recommended to patients with intermediate or advanced stage cancer. However, the conventional chemotherapy yields low desired response rates due to multidrug resistance, fast clearance rate, nonspecific delivery, severe side effects, low drug concentration in cancer cells, and so on. Nanoparticle-mediated targeted drug delivery system can surmount the aforementioned obstacles through enhanced permeability and retention effect and active targeting as a novel approach of therapeutics for HCC in recent years. The active targeting is triggered by ligands on the delivery system, which recognize with and internalize into hepatoma cells with high specificity and efficiency. This review focuses on the latest targeted delivery systems for HCC and summarizes the ligands that can enhance the capacity of active targeting, to provide some insight into future research in nanomedicine for HCC.

Glycyrrhetinic Acid Mediated Drug Delivery Carriers for Hepatocellular Carcinoma Therapy

Glycyrrhetinic acid (GA), the main hydrolysate of glycyrrhizic acid extracted from the root of licorice, has been used in hepatocellular carcinoma (HCC) therapy. Particularly, GA as a ligand in HCC therapy has been widely explored in different drug delivery systems, including liposomes, micelles, and nanoparticles. There is considerable interest worldwide with respect to the development of GA-modified drug delivery systems due to the extensive presence of GA receptors on the surface of hepatocyte. Up until now, much work has been focused on developing GA-modified drug delivery systems which bear good liver- or hepatocyte-targeted efficiency both in vitro and in vivo. Owing to its contribution in overcoming the limitations of low lipophilicity and poor bioavailability as well as its ability to promote receptor-mediated endocytosis, GA-modified drug delivery systems play an important role in enhancing liver-targeting efficacy and thus are focused on the treatment of HCC. Moreover, since GA-modified delivery systems present more favorable pharmacokinetic properties and hepatocyte-targeting effects, they may be a promising formulation for GA in the treatment of HCC. In this review, we will give an overview of GA-modified novel drug delivery systems, paying attention to their efficacy in treating HCC and discussing their mechanism and the treatment effects.

The licorice pentacyclic triterpenoid component 18β-glycyrrhetinic acid enhances the activity of antibiotics against strains of methicillin-resistant Staphylococcus aureus

This study aimed to identify compounds that enhance the activity of current antibiotics against multidrug-resistant bacteria. Screening of a 350+ compound proprietary small molecules library revealed that the Glycyrrhiza glabra (licorice)-derived triterpenoid 18β-glycyrrhetinic acid (18β-GA) potentiated the antibacterial activity of certain antibiotics against Staphylococcus aureus. Here, we evaluated the ability of pentacyclic triterpenoids to potentiate the activity of antibiotics against strains of methicillin-resistant S. aureus (MRSA). Checkerboard assays were used to assess the minimum inhibitory concentration (MIC) of tobramycin and ten pentacyclic triterpenoids against S. aureus. The effect of 18β-GA on the MIC of different antibiotics against MRSA was also determined in an in vitro airway MRSA infection model. 18β-GA enhanced the bactericidal activity of the aminoglycosides tobramycin, gentamicin and amikacin, and of polymyxin B against two MRSA strains, reducing the MIC of these antibiotics 32-64-fold [fractional inhibitory concentration index (FICI) of 0.12-0.13]. Other β-amyrin triterpenoids and α-amyrin triterpenoids did not exert such synergistic effects. 18β-GA did not enhance the activity of antibiotics from other structural classes against the MRSA strains. In an air-exposed airway epithelial cell culture, 18β-GA enhanced the bactericidal activity of tobramycin and polymyxin B against the MRSA strain. These data demonstrate the potential of 18β-GA to synergise with certain types of antibiotics to eliminate strains of MRSA.

Glycyrrhiza glabra

Liquorice foliage

Synthesis and biological activity of novel deoxycholic acid derivatives

We report the synthesis and biological activity of new semi-synthetic derivatives of naturally occurring deoxycholic acid (DCA) bearing 2-cyano-3-oxo-1-ene, 3-oxo-1(2)-ene or 3-oxo-4(5)-ene moieties in ring A and 12-oxo or 12-oxo-9(11)-ene moieties in ring C. Bioassays using murine macrophage-like cells and tumour cells show that the presence of the 9(11)-double bond associated with the increased polarity of ring A or with isoxazole ring joined to ring A, improves the ability of the compounds to inhibit cancer cell growth.

Luteolin potentiates the sensitivity of colorectal cancer cell lines to oxaliplatin through the PPARγ/OCTN2 pathway

Oxaliplatin is a chemotherapeutic agent used in the treatment of colorectal cancers. However, the mechanism controlling the cellular uptake and efflux of oxaliplatin is not completely understood. Organic cation/carnitine transporter 2 (OCTN2) is a member of the solute carrier superfamily and is a determinant of oxaliplatin uptake. OCTN2 is regulated by peroxisome proliferator-activated receptor γ (PPARγ) binding to the PPAR-response element within the first intron. Luteolin is a naturally occurring flavonoid and an agonist of PPARγ. Thus, we hypothesize that luteolin-mediated OCTN2 expression and activity potentiate the sensitivity of cancer cells to oxaliplatin. In this study, luteolin increased mRNA and protein expression of OCTN2 in a time-dependent and dose-dependent manner in colorectal cancer SW480 cells. This induction was attenuated by PPARγ antagonist GW9662 as well as by PPARγ knockdown, suggesting that the induction by luteolin is dependent on PPARγ. In uptake studies, luteolin increased the binding affinity of OCTN2 toward oxaliplatin and enhanced intracellular concentration of oxaliplatin. This finding is likely because of the increase of PDZ domain containing 1 (PDZK1) and PDZ domain containing 3 (PDZK2), which are known to facilitate the expression of OCTN2 on the cell surface and/or enhance transporter activity. Moreover, cell viability and cell apoptosis assays showed that luteolin increased oxaliplatin uptake and intracellular accumulation through OCTN2. Thus, our study showed that luteolin increased the sensitivity of colorectal cancer SW480 cells to oxaliplatin, likely through the PPARγ/OCTN2 pathway.

Potential drug interactions associated with glycyrrhizin and glycyrrhetinic acid

Glycyrrhizin (GZ), the main active component of licorice, is a widely used therapeutic in the clinic. Depending on the disease, the treatment may involve a long course of high dose GZ. Another component of licorice, glycyrrhetinic acid (GA), is the main active metabolite of GZ and is thought to be responsible for the majority of the pharmacological properties of GZ. Therefore, GZ and GA are both used for therapeutic purposes. In addition, GZ and GA are also widely used to sweeten and flavor foods. Due to this widespread, multifaceted use of these substances, potential drug interactions with GZ and GA have recently gained attention. Along these lines, this review covers the known effects of GZ and GA on drug-metabolizing enzymes and efflux transporters. We conclude that both GZ and GA may have an effect on the activity of CYPs. For example, GZ may induce CYP3A activity through activation of PXR. Also, GZ and GA may affect glucuronidation in rats and humans. Furthermore, 18β-GA is a potent inhibitor of P-gp, while GZ and GA are inhibitors of MRP1, MRP2 and BCRP. The pharmacokinetics and pharmacodynamics of many medications may be altered when used concurrently with GZ or GA, which is also covered in this review. Overall, GZ, GA or related products should be taken with caution when taken with additional medications due to the possible drug interactions.

Adaptive cellular stress pathways as therapeutic targets of dietary phytochemicals: focus on the nervous system

During the past 5 decades, it has been widely promulgated that the chemicals in plants that are good for health act as direct scavengers of free radicals. Here we review evidence that favors a different hypothesis for the health benefits of plant consumption, namely, that some phytochemicals exert disease-preventive and therapeutic actions by engaging one or more adaptive cellular response pathways in cells. The evolutionary basis for the latter mechanism is grounded in the fact that plants produce natural antifeedant/noxious chemicals that discourage insects and other organisms from eating them. However, in the amounts typically consumed by humans, the phytochemicals activate one or more conserved adaptive cellular stress response pathways and thereby enhance the ability of cells to resist injury and disease. Examplesof such pathways include those involving the transcription factors nuclear factor erythroid 2-related factor 2, nuclear factor-κB, hypoxia-inducible factor 1α, peroxisome proliferator-activated receptor γ, and forkhead box subgroup O, as well as the production and action of trophic factors and hormones. Translational research to develop interventions that target these pathways may lead to new classes of therapeutic agents that act by stimulating adaptive stress response pathways to bolster endogenous defenses against tissue injury and disease. Because neurons are particularly sensitive to potentially noxious phytochemicals, we focus on the nervous system but also include findings from other cell types in which actions of phytochemicals on specific signal transduction pathways have been more thoroughly studied.

3-(2,6-Dichloro-benzyloxy)-11-oxo-olean-12-ene-29-oic acid, a semisynthetic derivative of glycyrrhetic acid: synthesis, antiproliferative, apoptotic and anti-angiogenesis activity

The synthesis and biological evaluation of the semisynthetic analogs of glycyrrhetic acid are described.

Novel Inhibitory Effects of Glycyrrhizic Acid on the Accumulation of Advanced Glycation End Product and Its Receptor Expression

Beneficial effects of glycyrrhizic acid (GA), a bioactive extract of licorice root, in the prevention of metabolic syndrome have been consistently reported while advanced glycation end products (AGE) and receptor for advanced glycation end product (RAGE) are the leading factors in the development of diabetes mellitus. The aim of this study was to investigate the effects of GA on the AGE-RAGE axis using high-fat/high-sucrose (HF/HS) diet-induced metabolic syndrome rat models. Twenty four male Sprague-Dawley rats were randomly assigned into three groups for 4 weeks: (1) Group A, normal diet with standard rat chow; (2) Group B, HF/HS diet; (3) Group C, HF/HS diet and oral administration of 100 mg/kg GA per day. The results showed that HF/HS diet elevated the fasting blood glucose level and insulin resistance index which was prevented by GA supplementation. GA treatment significantly lowered the circulating AGE independent of its glucose-lowering effect. HF/HS diet also triggered RAGE upregulation in the abdominal muscles while GA administration downregulated RAGE expression in the abdominal muscles, aorta and subcutaneous adipose tissues. In conclusion, HF/HS diet could cause glucose intolerance, insulin resistance and upregulation of RAGE expression while GA ameliorated the metabolic dysregulation besides exhibiting inhibitory effects on the AGE-RAGE axis.

Oleanolic acid derivatives induce apoptosis in human leukemia K562 cell involved in inhibition of both Akt1 translocation and pAkt1 expression

Oleanolic acid (OA) derivatives exhibit numerous pleiotropic effects in many cancers. The present study aimed to investigate the molecular mechanisms of 5'-amino-oleana-2,12-dieno[3,2-d]pyrimidin-28-oic acid (compound 4) and oleana-2,12-dieno[2,3-d]isoxazol-28-oic acid (compound 5) inducing apoptosis in human leukemia K562 cell. We investigated the effects of the compounds on K562 cell growth, apoptosis and cell cycle. The compounds showed strong inhibitory effects on K562 cell viability in a dose-dependent manner determined by the 3-(4,5-dimethylthiazoyl)-2,5-diphenyltetrazolium bromide assay and significantly increased chromatin condensation and apoptotic bodies in K562 cells. Flow cytometry assay suggested that the compounds induced inhibition of K562 cell proliferation associated with G1 phase arrest. In addition, the compounds inhibited Akt1 recruiting to membrane in CHO cells which express Akt1-EGFP constitutively and down-regulated the expression of pAkt1 in K562 cell. These results suggested that the compounds can efficiently inhibit proliferation and induce apoptosis perhaps involved in inactivation of Akt1. The OA derivatives may be potential chemotherapeutic agents for the treatment of human cancer.

Glycyrrhizinate reduces portal hypertension in isolated perfused rat livers with chronic hepatitis

AIM: To investigate the effects of diammonium glycyrrhizinate (Gly) on portal hypertension (PHT) in isolated portal perfused rat liver (IPPRL) with carbon tetrachloride (CCl₄)-induced chronic hepatitis.

METHODS: PHT model was replicated with CCl₄ in rats for 84 d. Model was identified by measuring the ascetic amounts, hepatic function, portal pressure in vivo, splenic index, and pathological alterations. Inducible nitric oxide synthase (iNOS) in liver was assessed by immunohistochemistry. IPPRLs were performed at d₀, d₂₈, d₅₆, and d₈₄. After phenylephrine-induced constriction, Gly was geometrically used to reduce PHT. Gly action was expressed as median effective concentration (EC₅₀) and area under the curve (AUC). Underlying mechanism was exploited by linear correlation between AUC values of Gly and existed iNOS in portal triads.

RESULTS: PHT model was confirmed with ascites, splenomegaly, serum biomarkers of hepatic injury, and elevated portal pressure. Pathological findings had shown normal hepatic structure at d₀, degenerations at d₂₈, fibrosis at d₅₆, cirrhosis at d₈₄ in PHT rats. Pseudo lobule ratios decreased and collagen ratios increased progressively along with PHT development. Gly does dose-dependently reduce PHT in IPPRLs with CCl₄-induced chronic hepatitis. Gly potencies were increased gradually along with PHT development, characterized with its EC₅₀ at 2.80 × 10^-10, 3.03 × 10^-11, 3.77 × 10^-11 and 4.65×10^-11 mol/L at d₀, d₂₈, d₅₆ and d₈₄, respectively. Existed iNOS was located at hepatocyte at d₀, stellate cells at d₂₈, stellate cells and macrophages at d_56, and macrophages in portal triads at d₈₄. Macrophages infiltrated more into portal triads and expressed more iNOS along with PHT development. AUC values of Gly were positively correlated with existed iNOS levels in portal triads.

CONCLUSION: Gly reduces indirectly PHT in IPPRL with CCl₄-induced chronic hepatitis. The underlying mechanisms may relate to rescue NO bioavailability from macrophage-derived peroxynitrite in portal triads.

Discovery of a potential anti-inflammatory agent: 3-oxo-29-noroleana-1,9(11),12-trien-2,20-dicarbonitrile

Fifteen novel derivatives of glycyrrhetinic acid (GA) were synthesized and evaluated for anti-inflammatory activities. It was found that the introduction of 1-en-3-one and 9(11),12-diene and 2,20-dinitrile functionalities into the scaffold of GA led to the discovery of potent compound 19 for inhibition of LPS-induced NO production. Furthermore, 19 effectively inhibited the protein and mRNA expression of inducible NO synthase (iNOS) and the mRNA expression of TNF-α, IL-6, and IL-1β in LPS-stimulated RAW 264.7 macrophages. Mechanistically, 19 exerted inhibitory effects on the activation of the three main MAPKs and phosphorylation and degradation of IκB-α, as well as the ratio of nuclear/cytosolic content of p65. Importantly, 19 significantly decreased the mortality rate in the mouse model of LPS-induced sepsis shock. It is noteworthy that inhibitory effect of 19 on NO production was not blocked by the glucocorticoid receptor antagonist mifepristone, indicating that it does not act through the glucocorticoid receptor.

Characterization of PPAR dual ligand MCC-555 in AOM-induced colorectal tumorigenesis

Colorectal cancer (CRC) is one of the most commonly diagnosed cancers. Peroxisome proliferator-activated receptor γ (PPARγ) agonists represent a potentially important family of chemopreventive/therapeutic compounds for cancer treatment by affecting cell proliferation, differentiation, and apoptosis. Dual ligands for PPARα and PPARγ, such as netoglitazone (MCC-555), have been developed to improve treatment of metabolic syndromes, including hyperglycemia and hyperlipidemia. Interestingly, these dual ligands also possess anti-proliferative activities against a variety of cancer cell lines with a greater potency than conventional PPARγ specific ligands. In this study, chemopreventive properties of MCC-555 in colorectal tumorigenesis were evaluated using azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) in A/J mice. We found that MCC-555 suppressed AOM-induced ACF in A/J mice, compared to the control group. Administration of MCC-555 resulted in decreased mitoses and increased apoptotic cells in the colon. Furthermore, expression of tumor suppressor protein MUC2 was increased in MCC-555 treated mice. Our data clearly suggest that MCC-555 has an effect on the early events of colon carcinogenesis, thus providing evidence that MCC-555 could be a potential preventive compound for CRC.

Licorice abuse: time to send a warning message

Licorice extract has always been recognized as a sweetener and a thirst quencher. Its nutritive value is overrated by many who consume significant amounts and are prone to complications. Glycyrrhetic acid, the active metabolite in licorice, inhibits the enzyme 11-ß-hydroxysteroid dehydrogenase enzyme type 2 with a resultant cortisol-induced mineralocorticoid effect and the tendency towards the elevation of sodium and reduction of potassium levels. This aldosterone-like action is the fundamental basis for understanding its health benefits and the wide spectrum of adverse effects. Herein, we present a comprehensive review of licorice along with the reported complications related to excess intake. Despite its apparent use in a few clinical scenarios, the daily consumption of licorice is never justified because its benefits are minor compared to the adverse outcomes of chronic consumption. The review highlights the importance of investigating the dietary habits and herbal remedies which are being used worldwide on cultural and habitual bases rather than reliable scientific evidence. Licorice is a US Food and Drug Administration (FDA) approved food supplement used in many products without precise regulations to prevent toxicity. Increased awareness among the public is required through TV commercials, newspapers, internet sites, magazines and product labels regarding the upper limit of ingestion and health hazards associated with excess intake. We hope that this review will serve as a warning message that should be transmitted from physicians to patients to avoid excessive licorice intake as well as a message to the FDA to start regulating the use of this substance.

18β-Glycyrrhetinic acid preferentially blocks late Na current generated by ΔKPQ Nav1.5 channels

AIM

To compare the effects of two stereoisomeric forms of glycyrrhetinic acid on different components of Na(+) current, HERG and Kv1.5 channel currents.

METHODS

Wild-type (WT) and long QT syndrome type 3 (LQT-3) mutant ΔKPQ Nav1.5 channels, as well as HERG and Kv1.5 channels were expressed in Xenopus oocytes. In addition, isolated human atrial myocytes were used. Two-microelectrode voltage-clamp technique was used to record the voltage-activated currents.

RESULTS

Superfusion of 18β-glycyrrhetinic acid (18β-GA, 1-100 μmol/L) blocked both the peak current (I(Na,P)) and late current (I(Na,L)) generated by WT and ΔKPQ Nav1.5 channels in a concentration-dependent manner, while 18α-glycyrrhetinic acid (18α-GA) at the same concentrations had no effects. 18β-GA preferentially blocked I(Na,L) (IC(50)=37.2 ± 14.4 μmol/L) to I(Na,P) (IC(50)=100.4 ± 11.2 μmol/L) generated by ΔKPQ Nav1.5 channels. In human atrial myocytes, 18β-GA (30 μmol/L) inhibited 47% of I(Na,P) and 87% of I(Na,L) induced by Anemonia sulcata toxin (ATX-II, 30 nmol/L). Superfusion of 18β-GA (100 μmol/L) had no effects on HERG and Kv1.5 channel currents.

CONCLUSION

18β-GA preferentially blocked the late Na current without affecting HERG and Kv1.5 channels.

Targeted inhibition of tumor proliferation, survival, and metastasis by pentacyclic triterpenoids: potential role in prevention and therapy of cancer

Over the last two decades, extensive research on plant-based medicinal compounds has revealed exciting and important pharmacological properties and activities of triterpenoids. Fruits, vegetables, cereals, pulses, herbs and medicinal plants are all considered to be biological sources of these triterpenoids, which have attracted great attention especially for their potent anti-inflammatory and anti-cancer activities. Published reports in the past have described the molecular mechanism(s) underlying the various biological activities of triterpenoids which range from inhibition of acute and chronic inflammation, inhibition of tumor cell proliferation, induction of apoptosis, suppression of angiogenesis and metastasis. However systematic analysis of various pharmacological properties of these important classes of compounds has not been done. In this review, we describe in detail the pre-clinical chemopreventive and therapeutic properties of selected triterpenoids that inhibit multiple intracellular signaling molecules and transcription factors involved in the initiation, progression and promotion of various cancers. Molecular targets modulated by these triterpenoids comprise, cytokines, chemokines, reactive oxygen intermediates, oncogenes, inflammatory enzymes such as COX-2, 5-LOX and MMPs, anti-apoptotic proteins, transcription factors such as NF-κB, STAT3, AP-1, CREB, and Nrf2 (nuclear factor erythroid 2-related factor) that regulate tumor cell proliferation, transformation, survival, invasion, angiogenesis, metastasis, chemoresistance and radioresistance. Finally, this review also analyzes the potential role of novel synthetic triterpenoids identified recently which mimic natural triterpenoids in physical and chemical properties and are moving rapidly from bench to bedside research.

Induction of apoptosis with mitochondrial membrane depolarization by a glycyrrhetinic acid derivative in human leukemia K562 cells

Glycyrrhetinic acid (GA) is the active compound in Glycyrrhizae radix, a famous traditional Chinese medicine. Recently the anticancer activity of GA became the focus of scientific interest and many GA derivatives were developed as anti-tumor lead compounds. We previously reported that AEGA, a GA derivative, has proliferation inhibition and apoptosis-inducing activity in various human tumor cells. The present study was undertaken to further investigate the molecular mechanisms involved in AEGA-induced apoptosis in human leukemia K562 cells. AEGA can inhibit the growth of K562 cells in dose- and time-dependent manners determined by the MTT assay. Induction of apoptosis was evidenced by morphological changes and biochemical markers such as cell shrinkage, chromatin condensation and DNA ladder formation. Further mechanistic analysis revealed that AEGA induced apoptosis through the collapse of mitochondrial membrane potential, the accumulation of the cytosolic cytochrome c and the activation of caspase-9 and caspase-3. The apoptosis induction by AEGA was associated with the alteration in the ratio of Bcl-2/Bax protein expression. These results suggest that AEGA may induce apoptosis through a mitochondria-mediated pathway, and might have the therapeutic value against hematological malignancies.

Cancer and diet: How are they related?

Extensive research in the past decade has revealed cancer to be a multigenic disease caused by perturbation of multiple cell signalling pathways and dysregulation of numerous gene products, all of which have been linked to inflammation. It is also becoming evident that various lifestyle factors, such as tobacco and alcohol use, diet, environmental pollution, radiation and infections, can cause chronic inflammation and lead to tumourigenesis. Chronic diseases caused by ongoing inflammation therefore require chronic, not acute, treatment. Nutraceuticals, compounds derived from fruits, vegetables, spices and cereals, can be used chronically. This study discusses the molecular targets of some nutraceuticals that happen to be markers of chronic inflammation and how they can prevent or treat cancer. These naturally-occurring agents in the diet have great potential as anti-cancer drugs, thus proving Hippocrates, who proclaimed 25 centuries ago, 'Let food be thy medicine and medicine be thy food'.

PPARgamma: The Portrait of a Target Ally to Cancer Chemopreventive Agents

Peroxisome proliferator-activated receptor-gamma (PPARγ), one of three ligand-activated transcription factors named PPAR, has been identified as a molecular target for cancer chemopreventive agents. PPARγ was initially understood as a regulator of adipocyte differentiation and glucose homeostasis while later on, it became evident that it is also involved in cell differentiation, apoptosis, and angiogenesis, biological processes which are deregulated in cancer. It is now established that PPARγ ligands can induce cell differentiation and yield early antineoplastic effects in several tumor types. Moreover, several bioactive natural products with cancer protecting potential are shown to operate through activation of PPARγ. Overall, PPARγ appears to be a prevalent target ally to cancer chemopreventive agents and therefore pursuing research in this area is of great relevance.