Seung Joon Baek

Molecular Targets of Dietary Polyphenols with Anti-inflammatory Properties

There is persuasive epidemiological and experimental evidence that dietary polyphenols have anti-inflammatory activity. Aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) have long been used to combat inflammation. Recently, cyclooxygenase (COX) inhibitors have been developed and recommended for treatment of rheumatoid arthritis (RA) and osteoarthritis (OA). However, two COX inhibitors have been withdrawn from the market due to unexpected side effects. Because conventional therapeutic and surgical approaches have not been able to fully control the incidence and outcome of many inflammatory diseases, there is an urgent need to find safer compounds and to develop mechanism-based approaches for the management of these diseases. Polyphenols are found in many dietary plant products, including fruits, vegetables, beverages, herbs, and spices. Several of these compounds have been found to inhibit the inflammation process as well as tumorigenesis in experimental animals; they can also exhibit potent biological properties. In addition, epidemiological studies have indicated that populations who consume foods rich in specific polyphenols have lower incidences of inflammatory disease. This paper provides an overview of the research approaches that can be used to unravel the biology and health effects of polyphenols. Polyphenols have diverse biological effects, however, this review will focus on some of the pivotal molecular targets that directly affect the inflammation process.

Enhanced dispersibility and bioactivity of curcumin by encapsulation in casein nanocapsules.

In this work, a novel encapsulation method was studied by spray-drying a warm aqueous ethanol solution with codissolved sodium caseinate (NaCas) and lipophilic food components, using curcumin as a model compound. The encapsulation caused the loss of crystallinity of curcumin. After hydration of spray-dried powder and centrifugation, 137 μg/mL curcumin was dispersed in the transparent dispersion, which was 4 decades higher than its water solubility. Dynamic light scattering and atomic force microscopy results showed that curcumin-loaded casein nanoparticles were bigger than those of NaCas processed at encapsulation conditions but were smaller than those of the native NaCas. The increased nanoparticle dimension, together with fluorescence and FTIR spectroscopy results, suggested that curcumin was entrapped in the nanoparticle core through hydrophobic interactions. The curcumin encapsulated in casein nanoparticles had higher biological activity, as assessed by antioxidant and cell proliferation assays, than pristine curcumin, likely due to the improved dispersibility. This simple approach may be applied to encapsulate various lipophilic bioactive compounds.

Induction of cell growth arrest by atmospheric non-thermal plasma in colorectal cancer cells

Plasma is generated by ionizing neutral gas molecules, resulting in a mixture of energy particles, including electrons and ions. Recent progress in the understanding of non-thermal atmospheric plasma has led to applications in biomedicine. However, the exact molecular mechanisms involved in plasma-induced cell growth arrest are unclear. In this study, we investigated the feasibility of non-thermal atmospheric plasma treatment for cancer therapy and examined the mechanism by which plasma induces anti-proliferative properties and cell death in human colorectal cancer cells. Non-thermal atmospheric plasma induced cell growth arrest and induced apoptosis. In addition, plasma reduced cell migration and invasion activities. As a result, we found that plasma treatment to the cells increases β-catenin phosphorylation, suggesting that β-catenin degradation plays a role at least in part in plasma-induced anti-proliferative activity. Therefore, non-thermal atmospheric plasma constitutes a new biologic tool with the potential for therapeutic applications that modulate cell signaling and function.

Multiple mechanisms are involved in 6-gingerol-induced cell growth arrest and apoptosis in human colorectal cancer cells

6‐Gingerol, a natural product of ginger, has been known to possess anti‐tumorigenic and pro‐apoptotic activities. However, the mechanisms by which it prevents cancer are not well understood in human colorectal cancer. Cyclin D1 is a proto‐oncogene that is overexpressed in many cancers and plays a role in cell proliferation through activation by β‐catenin signaling. Nonsteroidal anti‐inflammatory drug (NSAID)‐activated gene‐1 (NAG‐1) is a cytokine associated with pro‐apoptotic and anti‐tumorigenic properties. In the present study, we examined whether 6‐gingerol influences cyclin D1 and NAG‐1 expression and determined the mechanisms by which 6‐gingerol affects the growth of human colorectal cancer cells in vitro. 6‐Gingerol treatment suppressed cell proliferation and induced apoptosis and G1 cell cycle arrest. Subsequently, 6‐gingerol suppressed cyclin D1 expression and induced NAG‐1 expression. Cyclin D1 suppression was related to inhibition of β‐catenin translocation and cyclin D1 proteolysis. Furthermore, experiments using inhibitors and siRNA transfection confirm the involvement of the PKCε and glycogen synthase kinase (GSK)‐3β pathways in 6‐gingerol‐induced NAG‐1 expression. The results suggest that 6‐gingerol stimulates apoptosis through upregulation of NAG‐1 and G1 cell cycle arrest through downregulation of cyclin D1. Multiple mechanisms appear to be involved in 6‐gingerol action, including protein degradation as well as β‐catenin, PKCε, and GSK‐3β pathways.

Nonsteroidal anti‐inflammatory drug‐activated gene (NAG‐1) is induced by genistein through the expression of p53 in colorectal cancer cells

Genistein is an isoflavenoid found in soy that has anti‐tumorigenic activities. Treatment of colorectal carcinoma HCT‐116 cells with 50 μM genistein results in a 50% reduction in cell proliferation and a 6‐fold increase in apoptosis. Genistein induces nonsteroidal anti‐inflammatory drug‐activated gene 1 (NAG‐1), a protein with antitumorigenic activities, in a time‐ and concentration‐dependent manner in HCT‐116 cells. In addition, p53 and p21 are induced in HCT‐116 cells. The induction of p53 (3 hr) precedes the induction of NAG‐1 (12 hr), suggesting that genistein‐induced NAG‐1 expression is mediated by p53. In contrast, NAG‐1 is not induced by genistein in the p53‐negative colorectal carcinoma cell line HCT‐15. Luciferase reporter constructs of the NAG‐1 promoter containing 2 p53 sites showed that the p53 sites within the NAG‐1 promoter are critical to genistein‐induced NAG‐1 expression in p53‐positive U2OS cells. The expression of p53 was critical for NAG‐1 promoter activity since no promoter activity was observed with genistein treatment in HCT‐15 cells. However, genistein‐induced promoter activity was restored in HCT‐15 cells by transfection with wild‐type p53. Together our data suggest a relationship between genistein, p53 and NAG‐1 forming a novel pathway responsible for the antitumorigenic activity of genistein.

Effects of atmospheric nonthermal plasma on invasion of colorectal cancer cells

The effect that the gas content and plasma power of atmospheric, nonthermal plasma has on the invasion activity in colorectal cancer cells has been studied. Helium and helium plus oxygen plasmas were induced through a nozzle and operated with an ac power of less than 10 kV which exhibited a length of 2.5 cm and a diameter of 3-4 mm in ambient air. Treatment of cancer cells with the plasma jet resulted in a decrease in cell migrationinvasion with higher plasma intensity and the addition of oxygen to the He flow gas.

Autonomous Bioluminescent Expression of the Bacterial Luciferase Gene Cassette (lux) in a Mammalian Cell Line

Background The bacterial luciferase (lux) gene cassette consists of five genes (luxCDABE) whose protein products synergistically generate bioluminescent light signals exclusive of supplementary substrate additions or exogenous manipulations. Historically expressible only in prokaryotes, the lux operon was re-synthesized through a process of multi-bicistronic, codon-optimization to demonstrate for the first time self-directed bioluminescence emission in a mammalian HEK293 cell line in vitro and in vivo. Methodology/Principal Findings Autonomous in vitro light production was shown to be 12-fold greater than the observable background associated with untransfected control cells. The availability of reduced riboflavin phosphate (FMNH2) was identified as the limiting bioluminescence substrate in the mammalian cell environment even after the addition of a constitutively expressed flavin reductase gene (frp) from Vibrio harveyi. FMNH2 supplementation led to a 151-fold increase in bioluminescence in cells expressing mammalian codon-optimized luxCDE and frp genes. When injected subcutaneously into nude mice, in vivo optical imaging permitted near instantaneous light detection that persisted independently for the 60 min length of the assay with negligible background. Conclusions/Significance The speed, longevity, and self-sufficiency of lux expression in the mammalian cellular environment provides a viable and powerful alternative for real-time target visualization not currently offered by existing bioluminescent and fluorescent imaging technologies.

The anticancer effects of resveratrol – Modulation of transcription factors

Resveratrol (3, 4′, 5-trihydroxystilbene), a naturally occurring phytoalexin readily available in the diet, is reported to possess both chemopreventive and chemotherapeutic activities in several cancers. However, despite the identification of numerous molecular targets, the underlying mechanisms involved in the anticancer activities of resveratrol are not completely understood. Resveratrol is postulated to function as a potential signaling pathway modulator and, as such, is demonstrated to affect a multitude of signal transduction pathways associated with tumorigenesis and/or carcinogenesis; it is likely that this collective activity, rather than just a single effect, may play an important role in the anticancer properties of resveratrol. Since transcription factors control the expression of many genes, the elucidation of molecular targets of resveratrol involved in transcriptional regulation is necessary to better understand how this dietary phytochemical affects chemopreventive and chemotherapeutic processes. As a result, investigators have increasingly searched for and examined possible targets of resveratrol. In this review, we summarize the current knowledge on molecular targets, specifically transcription factors, that contribute to the observed anticancer effects of resveratrol related to 1) inhibition of carcinogenic activation and induction of carcinogen detoxification, 2) induction of growth arrest and apoptosis, and 3) suppression of proinflammatory signaling pathways related to cancer progression.

Activating Transcription Factor 3 and Early Growth Response 1 Are the Novel Targets of LY294002 in a Phosphatidylinositol 3-Kinase–Independent Pathway

LY294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor, has been widely used to study the function of PI3K in cellular responses. Based on its inhibitory effect on PI3K, LY294002 has been shown to exert antitumorigenic effect in vivo and in vitro. Here, we report that LY294002 alters early growth response 1 (EGR-1) phosphorylation and subsequently enhances activating transcription factor 3 (ATF3) expression independently of PI3K inhibition. This pathway may be, in part, responsible for the antitumorigenic effect of LY294002 in human colorectal cancer cells. ATF3 expression was increased by LY294002, followed by the induction of apoptosis in several colorectal cancer cell lines. This is consistent with results showing that the down-regulation of the ATF3 gene by small interfering RNA suppressed LY294002-induced apoptosis in HCT-116 cells. On the other hand, ATF3 expression was not affected by another PI3K inhibitor, wortmannin, as well as phosphatase and tensin homologue or dominant-negative Akt overexpression. We also found that LY294002 increases ATF3 promoter activity and the transactivation is partly mediated by a GC-rich sequence located in the promoter. EGR-1 binds to the ATF3 promoter as assessed by gel shift assay. Furthermore, phosphorylated EGR-1 was highly increased in LY294002-treated cells, indicating that EGR-1 phosphorylation induced by LY294002 may facilitate ATF3 transactivation. Our data suggest that EGR-1 acts as a mediator in LY294002-induced ATF3 expression via a PI3K-independent pathway. ATF3 and EGR-1 may provide a novel explanation for the antitumorigenic properties of LY294002 in human colorectal cancer cells.

A novel peroxisome proliferator–activated receptor γ ligand, MCC-555, induces apoptosis via posttranscriptional regulation of NAG-1 in colorectal cancer cells

Apoptosis and/or differentiation induction caused by the peroxisome proliferator–activated receptor γ (PPARγ) ligand is a promising approach to cancer therapy. The thiazolidinedione derivative MCC-555 has an apoptotic activity in human colorectal cancer cells, accompanied by up-regulation of a proapoptotic nonsteroidal anti-inflammatory drug–activated gene (NAG-1) in a PPARγ-independent manner. Treatment with MCC-555 resulted in the induction of NAG-1 expression and apoptosis in HCT-116 cells. Down-regulation of NAG-1 by small interfering RNA suppressed MCC-555-induced apoptosis. MCC-555 was found to affect NAG-1 mRNA stability. To further define the underlying mechanism of RNA stability affected by MCC-555, we cloned the 3′-untranslated region (3′UTR) of human NAG-1 mRNA, which contains four copies of an AU-rich element (ARE), downstream from the luciferase gene. The reporter activity was reduced to ∼70% by inserting the 3′UTR. In addition, deletion of ARE sequences in the 3′UTR or MCC-555 treatment substantially restored activity. This effect of MCC-555 on the ARE-mediated mRNA degradation was inhibited by extracellular signal–regulated kinase (ERK) pathway inhibitors. Subsequently, rapid phosphorylation of ERK1/2 by MCC-555 treatment was detected. Moreover, ERK small interfering RNA suppressed MCC-555-induced NAG-1 expression. These results suggest that ARE sequences in the 3′UTR of the NAG-1 gene contribute to mRNA degradation and ERK1/2 phosphorylation is responsible for the stabilization of NAG-1 mRNA. These findings may provide a novel explanation for the antitumorigenic and/or proapoptotic action of MCC-555 in human colorectal cancer and the ability of pharmacologic approaches to be used against diseases caused by alterations of RNA stability. [Mol Cancer Ther 2006;5(5):1352–61]