Curcumin modulates DNA methylation in colorectal cancer cells

Back to the future: transgenerational transmission of xenobiotic-induced epigenetic remodeling

Epigenetics, or regulation of gene expression independent of DNA sequence, is the missing link between genotype and phenotype. Epigenetic memory, mediated by histone and DNA modifications, is controlled by a set of specialized enzymes, metabolite availability, and signaling pathways. A mostly unstudied subject is how sub-toxic exposure to several xenobiotics during specific developmental stages can alter the epigenome and contribute to the development of disease phenotypes later in life. Furthermore, it has been shown that exposure to low-dose xenobiotics can also result in further epigenetic remodeling in the germ line and contribute to increase disease risk in the next generation (multigenerational and transgenerational effects). We here offer a perspective on current but still incomplete knowledge of xenobiotic-induced epigenetic alterations, and their possible transgenerational transmission. We also propose several molecular mechanisms by which the epigenetic landscape may be altered by environmental xenobiotics and hypothesize how diet and physical activity may counteract epigenetic alterations.

Curcumin and dimethoxycurcumin induced epigenetic changes in leukemia cells

PURPOSE

Curcumin is an ideal chemopreventive and antitumor agent characterized by poor bioavailability and low stability. The development of synthetic structural analogues like dimethoxycurcumin (DMC) could overcome these drawbacks. In this study we compared the cytotoxicity, metabolism and the epigenetic changes induced by both drugs in leukemia cells.

METHODS

Apoptosis and cell cycle analysis were analyzed by flow cytometry. Real-time PCR was used for gene expression analysis. DNA methylation was analyzed by DNA pyrosequencing. The metabolic stability was determined using human pooled liver microsomes. Chromatin Immunoprecipitation was used to quantify histone methylation.

RESULTS

Clinically relevant concentration of curcumin and DMC were not cytotoxic to leukemia cells and induced G2/M cell cycle arrest. DMC was more metabolically stable than curcumin. Curcumin and DMC were devoid of DNA hypomethylating activity. DMC induced the expression of promoter methylated genes without reversing DNA methylation and increased H3K36me3 mark near the promoter region of hypermethylated genes.

CONCLUSION

DMC is a more stable analogue of curcumin that can induce epigenetic changes not induced by curcumin. DMC induced the expression of promoter methylated genes. The combination of DMC with DNA methyltransferase inhibitors could harness their combined induced epigenetic changes for optimal re-expression of epigenetically silenced genes.

Epigenetic silencing of miR-137 is a frequent event in gastric carcinogenesis

MicroRNAs (miRNA) are involved in posttranscriptional regulation of gene expression and are dysregulated during carcinogenesis. CpG island methylation of miR-137 is a common event in different cancers; however, the role of miR-137 in gastric cancer (GC) remains largely unexplored. In this study we aimed to characterize the epigenetic alterations of miR-137 in gastric carcinogenesis. We analyzed total 295 tissues including paired primary gastric cancer (T-GC) with corresponding adjacent gastric mucosa (N-GC), paired primary colorectal cancer (CRC) tissues with corresponding non-tumorous mucosa, gastric tissues from controls (N), and patients with chronic/atrophic gastritis (CG) with and without Helicobacter pylori infection. Bisulfite pyrosequencing and TaqMan RT-PCR were used to analyze miR-137 methylation and expression, respectively. Survival differences were evaluated using Kaplan-Meier analyses. miR-137 CpG island methylation was more frequent in tumorous compared to non-tumorous conditions and higher in CRC than in GC. In comparison to N-GC, miR 137 methylation level was lower in N and CG tissues, which correlates with Correas cascade. MiR-137 methylation inversely correlates with global LINE-1 methylation and miR-137 expression. miR-137 methylation was higher in intestinal type GC compared to diffuse one, and higher in antrum compared to cardia and corpus, however, miR-137 methylation was associated with worse prognosis in diffuse, but not in intestinal type of GC. The expression in colon was significantly higher compared to any gastric tissues suggesting functional difference. In summary, miR-137 methylation is a frequent event in gastrointestinal cancers which occurs early in stepwise manner during gastric carcinogenesis and inversely correlates with global methylation. © 2015 Wiley Periodicals, Inc.

Current Perspectives on Epigenetic Modifications by Dietary Chemopreventive and Herbal Phytochemicals

Studies during the last two decades have revealed the involvement of epigenetic modifications in the development of human cancer. It is now recognized that the interplay of DNA methylation, post-translational histone modification, and non-coding RNAs can interact with genetic defects to drive tumorigenesis. The early onset, reversibility, and dynamic nature of such epigenetic modifications enable them to be developed as promising cancer biomarkers and preventive/therapeutic targets. In addition to the recent approval of several epigenetic therapies in the treatment of human cancer, emerging studies have indicated that dietary phytochemicals might exert cancer chemopreventive effects by targeting epigenetic mechanisms. In this review, we will present the current understanding of the epigenetic alterations in carcinogenesis and highlight the potential of targeting these mechanisms to treat/prevent cancer. The latest findings, published in the past three years regarding the effects of dietary phytochemicals in modulating epigenetic mechanisms will also be discussed.

"Curcumin, the King of Spices": Epigenetic Regulatory Mechanisms in the Prevention of Cancer, Neurological, and Inflammatory Diseases

Curcumin (diferuloylmethane), a polyphenolic compound, is a component of Curcuma longa, commonly known as turmeric. It is a well-known anti-inflammatory, anti-oxidative, and anti-lipidemic agent and has recently been shown to modulate several diseases via epigenetic regulation. Many recent studies have demonstrated the role of epigenetic inactivation of pivotal genes that regulate human pathologies, such as neurocognitive disorders, inflammation, obesity, and cancers. Epigenetic changes involve changes in DNA methylation, histone modifications, or altered microRNA expression patterns which are known to be interconnected and play a key role in tumor progression and failure of conventional chemotherapy. The majority of epigenetic changes are influenced by lifestyle and diets. In this regard, dietary phytochemicals as dietary supplements have emerged as a promising source that are able to reverse these epigenetic alterations, to actively regulate gene expression and molecular targets that are known to promote tumorigenesis, and also to prevent age-related diseases through epigenetic modifications. There have been several studies which reported the role of curcumin as an epigenetic regulator in neurological disorders, inflammation, and in diabetes apart from cancers. The epigenetic regulatory roles of curcumin include (1) inhibition of DNA methyltransferases (DNMTs), which has been well defined from the recent studies on its function as a DNA hypomethylating agent; (2) regulation of histone modifications via regulation of histone acetyltransferases (HATs) and histone deacetylases (HDACs); and (3) regulation of micro RNAs (miRNA). This review summarizes the current knowledge on the effect of curcumin in the treatment and/or prevention of inflammation, neurodegenerative diseases, and cancers by regulating histone deacetylases, histone acetyltransferases, and DNA methyltransferases.

Curcumin inhibits anchorage-independent growth of HT29 human colon cancer cells by targeting epigenetic restoration of the tumor suppressor gene DLEC1

Colorectal cancer remains the most prevalent malignancy in humans. The impact of epigenetic alterations on the development of this complex disease is now being recognized. The dynamic and reversible nature of epigenetic modifications makes them a promising target in colorectal cancer chemoprevention and treatment. Curcumin (CUR), the major component in Curcuma longa, has been shown as a potent chemopreventive phytochemical that modulates various signaling pathways. Deleted in lung and esophageal cancer 1 (DLEC1) is a tumor suppressor gene with reduced transcriptional activity and promoter hypermethylation in various cancers, including colorectal cancer. In the present study, we aimed to investigate the inhibitory role of DLEC1 in anchorage-independent growth of the human colorectal adenocarcinoma HT29 cells and epigenetic regulation by CUR. Specifically, we found that CUR treatment inhibited colony formation of HT29 cells, whereas stable knockdown of DLEC1 using lentiviral short hairpin RNA vector increased cell proliferation and colony formation. Knockdown of DLEC1 in HT29 cells attenuated the ability of CUR to inhibit anchorage-independent growth. Methylation-specific polymerase chain reaction (MSP), bisulfite genomic sequencing, and methylated DNA immunoprecipitation revealed that CUR decreased CpG methylation of the DLEC1 promoter in HT29 cells after 5 days of treatment, corresponding to increased mRNA expression of DLEC1. Furthermore, CUR decreased the protein expression of DNA methyltransferases and subtypes of histone deacetylases (HDAC4, 5, 6, and 8). Taken together, our results suggest that the inhibitory effect of CUR on anchorage-independent growth of HT29 cells could, at least in part, involve the epigenetic demethylation and up-regulation of DLEC1.

Hydrogen peroxide generated by xanthine/xanthine oxidase system represses the proliferation of colorectal cancer cell line Caco-2

The twin character of reactive oxygen species is substantiated by a growing body of evidence that reactive oxygen species within cells act as inducers and accelerators of the oncogenic phenotype of cancer cells, while reactive oxygen species can also induce cancer cell death and can therefore function as anti-tumorigenic species. The aim of this study was to assess a possible influence of xanthine/xanthine oxidase on the proliferation of colorectal cancer cell line Caco-2. xanthine/xanthine oxidase (2.5 µM/0.25 mU/ml–25 µM/2.5 mU/ml) dose-dependently inhibited the proliferation of Caco-2 cells. Experiments utilizing reactive oxygen species scavengers (superoxide dismutase, catalase and mannitol) and exogenous hydrogen peroxide revealed a major role of hydrogen peroxide in the xanthine/xanthine oxidase effect. Investigations utilizing annexin V-fluorescein/PI assay using flow cytometry, and the lactate dehydrogenase extracellular release assay indicated that hydrogen peroxide induced necrosis, but not apoptosis, in Caco-2 cells. These results suggest that hydrogen peroxide generated by xanthine/xanthine oxidase has the potential to suppress colorectal cancer cell proliferation.

Modulators affecting the immune dialogue between human immune and colon cancer cells

The link between chronic inflammation and colorectal cancer has been well established. The events proceeding along tumorigenesis are complicated and involve cells activated at the cancer microenvironment, tumor infiltrating polymorphonuclears, immune cells including lymphocyte subtypes and peripheral blood mononuclear cells (PBMC), as well as tumor-associated macrophages. The immune cells generate inflammatory cytokines, several of them playing a crucial role in tumorigenesis. Additional factors, such as gene expression regulated by cytokines, assembling of tumor growth- and transforming factors, accelerated angiogenesis, delayed apoptosis, contribute all to initiation, development and migration of tumor cells. Oxygen radical species originating from the inflammatory area promote cell mutation and cancer proliferation. Tumor cells may over-express pro-inflammatory mediators that in turn activate immune cells for inflammatory cytokines production. Consequently, an immune dialogue emerges between immune and cancer cells orchestrated through a number of activated molecular pathways. Cytokines, encompassing migration inhibitory factor, transforming growth factor beta 1, tumor necrosis factor-α, Interleukin (IL)-6, IL-10, IL-12, IL-17, IL-23 have been reported to be involved in human cancer development. Some cytokines, namely IL-5, IL-6, IL-10, IL-22 and growth factors promote tumor development and metastasis, and inhibit apoptosis via activation of signal transducer activator transcription-3 transcription factor. Colon cancer environment comprises mesenchymal, endothelial and immune cells. Assessment of the interaction between components in the tumor environment and malignant cells requires a reconsideration of a few topics elucidating the role of chronic inflammation in carcinogenesis, the function of the immune cells expressed by inflammatory cytokine production, the immunomodulation of cancer cells and the existence of a cross-talk between immune and malignant cells leading to a balance in cytokine production. It is conceivable that the prevalence of anti-inflammatory cytokine production by PBMC in the affected colonic mucosa will contribute to the delay, or even to halt down malignant expansion. Targeting the interplay between immune and cancer cells by mediators capable to alter cytokine secretion toward increased anti-inflammatory cytokine release by PBMC and tumor associated macrophages, may serve as an additional strategy for treatment of malignant diseases. This review will focus on the inflammatory events preceding tumorigenesis in general, and on a number of modulators capable to affect colon cancer cell-induced production of inflammatory cytokines by PBMC through alteration of the immune cross-talk between PBMC and cancer cells.

Strawberry and human health: effects beyond antioxidant activity

The usefulness of a diet rich in vegetables and fruits on human health has been widely recognized: a high intake of antioxidant and bioactive compounds may in fact play a crucial role in the prevention of several diseases, such as cancer, cardiovascular, neurodegenerative, and other chronic pathologies. The strawberry (Fragaria × ananassa Duch.) possesses a remarkable nutritional composition in terms of micronutrients, such as minerals, vitamin C, and folates, and non-nutrient elements, such as phenolic compounds, that are essential for human health. Although strawberry phenolics are known mainly for their anti-inflammatory and antioxidant actions, recent studies have demonstrated that their biological activities also spread to other pathways involved in cellular metabolism and cellular survival. This paper has the main objective of reviewing current information about the potential mechanisms involved in the effects elicited by strawberry polyphenols on human health, devoting special attention to the latest findings.

Curcumin inhibits the AKT/NF-κB signaling via CpG demethylation of the promoter and restoration of NEP in the N2a cell line

Curcumin (CUR), a non-toxic polyphenol from Curcuma longa, has been investigated as a potential therapy with anti-inflammatory and anti-oxidative effects for Alzheimer's disease (AD), which depicts features of chronic inflammatory environment resulting in cellular death. However, it remains largely unknown whether the anti-inflammatory effect of CUR in AD is associated with its property of CpG demethylation, which is another function of CUR with the most research interest during recent years. Neprilysin (NEP, EP24.11), a zinc-dependent metallopeptidase expressed relatively low in the brain, is emerging as a potent inhibitor of AKT/Protein Kinase B. In addition, hypermethylated promoter of NEP has been reported to be associated with decreases in NEP expression. In the present study, using bisulfite-sequencing PCR (BSP) assay, we showed that the CpG sites in NEP gene were hypermethylated both in wild-type mouse neuroblastoma N2a cells (N2a/wt) and N2a cells stably expressing human Swedish mutant amyloid precursor protein (APP) (N2a/APPswe) associated with familial early onset AD. CUR treatment induced restoration of NEP gene via CpG demethylation. This CUR-mediated upregulation of NEP expression was also concomitant with the inhibition of AKT, subsequent suppression of nuclear transcription factor-κB (NF-κB) and its downstream pro-inflammatory targets including COX-2, iNOS in N2a/APPswe cells. This study represents the first evidence on a link between CpG demethylation effect on NEP and anti-inflammation ability of CUR that may provide a novel mechanistic insight into the anti-inflammatory actions of CUR as well as new basis for using CUR as a therapeutic intervention for AD.

EGCG inhibits the growth and tumorigenicity of nasopharyngeal tumor-initiating cells through attenuation of STAT3 activation

A subset of cancer cells, termed cancer stem cells (CSCs) or tumor-initiating cells (TICs) could initiate tumors and are responsible for tumor recurrence and chemotherapeutic resistance. In this study, we enriched TICs in nasopharyngeal carcinoma (NPC) by the spheres formation and characterized the stem-like signatures such as self-renewal, proliferation, chemoresistance and tumorigenicity. By this method, we investigated that epigallocathechin gallate (EGCG), the major polyphenol in green tea could target TICs and potently inhibit sphere formation, eliminate the stem-like properties and enhance chemosensitivity in NPC through attenuation of STAT3 activation, which could be important in regulating the stemness expression in NPC. Our results demonstrated that STAT3 pathway plays an important role in mediating tumor-initiating capacities in NPC and suggest that inactivation of STAT3 with EGCG may represent a potential preventive and therapeutic approach for NPC.

Potential therapeutic efficacy of curcumin in liver cancer

PURPOSE

Liver cancer, one of the most common cancers in China, is reported to feature relatively high morbidity and mortality. Curcumin (Cum) is considered as a drug possessing anti-angiogenic, anti-inflammation and anti-oxidation effect. Previous research has demonstrated antitumor effects in a series of cancers.

MATERIALS AND METHODS

In this study the in vitro cytotoxicity of Cum was measured by MTT assay and pro-apoptotic effects were assessed by DAPI staining and measurement of caspase-3 activity. In vivo anti-hepatoma efficacy of Cum was assessed with HepG2 xenografts.

RESULTS

It is found that Cum dose-dependently inhibited cell growth in HepG2 cells with activation of apoptosis. Moreover, Cum delayed the growth of liver cancer in a dose-dependent manner in nude mice.

CONCLUSIONS

Cum might be a promising phytomedicine in cancer therapy and further efforts are needed to explore this therapeutic strategy.

Monochloramine suppresses the proliferation of colorectal cancer cell line Caco-2 by both apoptosis and G2/M cell cycle arrest

The aim of this study was to assess a possible role of monochloramine (NH2 Cl), one of the reactive chlorine species, which induce oxidative stress, on the proliferation of colorectal cancer cell line Caco-2. At concentrations ranging from 10 to 200 μM, NH2 Cl (14-61% inhibition), but not hypochlorous acid, dose-dependently inhibited the cell viability of Caco-2 cells. Experiments utilizing methionine (a scavenger of NH2 Cl), taurine-chloramine and glutamine-chloramine revealed that only NH2 Cl affects the cancer cell proliferation among reactive chlorine species, with a relative specificity. Furthermore, flow-cytometry experiments showed that the anti-proliferative effect of NH2 Cl is partially attributable to both apoptosis and G2/M cell cycle arrest. These results suggest that NH2 Cl has the potential to suppress colorectal cancer cell proliferation.

The formulation and delivery of curcumin with solid lipid nanoparticles for the treatment of on non-small cell lung cancer both in vitro and in vivo

Curcumin was determined to have anticancer potency on several kinds of carcinoma. However, its medical application was limited because of its poor bioavailability, unsatisfying dispersity and rapid metabolism in vivo. In this study, curcumin was delivered by solid lipid nanoparticles (SLN) for lung cancer treatment. The physiochemical characters of SLN-curcumin were detected by HPLC, TEM, Zeta potential analysis and FTIR, and the anticancer efficiency on lung cancer was determined both in vitro and in vivo. SLN-curcumin was synthesized by sol-gel method with the size ranged from 20 to 80 nm. After being loaded in SLN, the IC50 of SLN-curcumin on A549 cells was 4 μM, only 1/20 of plain drug. The plasmid concentration of curcumin was highly increased in mice via i.p. after loaded with SLN. Furthermore, SLN-curcumin enhanced the targeting of curcumin to lung and tumor, which finally increased the inhibition efficiency of curcumin from 19.5% to 69.3%. The Flow Cytometry (FCM) analysis and immuno staining confirmed that the inhibition effect mostly came from apoptosis, but not necrosis. The tumor targeting and profound tumor inhibition effect of SLN-curcumin indicated its medical application on lung cancer treatment, and also provided a novel method for new anticancer agents' development.

Photoactivaed curcumin inhibits cell growth and promotes apoptosis in human gastric cancer cell line MGC-803

AIM: To investigate the effect of photoactivated curcumin on cell growth and apoptosis in human gastric cancer cell line MGC-803 and to analyze its intracellular distribution.

METHODS: After MGC-803 cells were treated with 5.0 μmol/L of photoactivated curcumin for different durations (12, 24 and 48 h), cell growth was assessed by MTT assay; apoptosis was determined by flow cytometry; nuclear morphological changes were detected by fluorescence microscopy; and the distribution of intracellular curcumin was examined by confocal laser microscopy.

RESULTS: The reduced rates of cell growth were 35.53% ± 3.52%, 40.17% ± 2.01% and 44.93% ± 3.61% in MGC-803 cells treated with photoactivation curcumin for 12, 24 and 48 h, and the apoptosis rates were 20.32% ± 3.07%, 22.46% ± 1.51% and 26.58% ± 2.67%. Compared to the control group, the reduced rates of cell growth were significantly lower and apoptosis rates were significantly higher in the photoactivation curcumin group at all time points (all P < 0.05). Obvious apoptotic bodies were observed after treatment with photoactivated curcumin for 48 hours. Photoactivated curcumin was mainly distributed in the cell membrane and nuclear membrane. Scattered distribution of photoactivated curcumin was noted in other subcellular structures.

CONCLUSION: Photoactivated curcumin can inhibit growth and promote apoptosis of gastric cancer cells in a time-dependent manner. Photoactivated curcumin is mainly located in the plasma membrane and nuclear membrane and sporadically in other subcellular structures.

Epigenetics and colorectal cancer pathogenesis

Colorectal cancer (CRC) develops through a multistage process that results from the progressive accumulation of genetic mutations, and frequently as a result of mutations in the Wnt signaling pathway. However, it has become evident over the past two decades that epigenetic alterations of the chromatin, particularly the chromatin components in the promoter regions of tumor suppressors and oncogenes, play key roles in CRC pathogenesis. Epigenetic regulation is organized at multiple levels, involving primarily DNA methylation and selective histone modifications in cancer cells. Assessment of the CRC epigenome has revealed that virtually all CRCs have aberrantly methylated genes and that the average CRC methylome has thousands of abnormally methylated genes. Although relatively less is known about the patterns of specific histone modifications in CRC, selective histone modifications and resultant chromatin conformation have been shown to act, in concert with DNA methylation, to regulate gene expression to mediate CRC pathogenesis. Moreover, it is now clear that not only DNA methylation but also histone modifications are reversible processes. The increased understanding of epigenetic regulation of gene expression in the context of CRC pathogenesis has led to development of epigenetic biomarkers for CRC diagnosis and epigenetic drugs for CRC therapy.

Genome-wide screening for understanding the role of DNA methylation in colorectal cancer

DNA methylation analysis methods have undergone an impressive revolution over the past 15 years. Regarding colorectal cancer (CRC), the localization and distribution of several differently methylated genes have been determined by genome-wide DNA methylation assays. These genes do not just influence the pathogenesis of CRC, but can be used further as diagnostic or prognostic markers. Moreover, the identified four DNA methylation-based subgroups of CRC have important clinical and therapeutic merit. Since genome-wide DNA methylation analyzes result in a large amount of data, there is a need for complex bioinformatic and pathway analysis. Future challenges in epigenetic alterations of CRC include the demand for comprehensive identification and experimental validation of gene abnormalities. By introduction of genome-wide DNA methylation profiling into clinical practice not only the patients' risk stratification but development of targeted therapies will also be possible.