Sodium butyrate induces human colon carcinoma HT-29 cell apoptosis through a mitochondrial pathway

Cytotoxic Potential of Betulinic Acid Fatty Esters and Their Liposomal Formulations: Targeting Breast, Colon, and Lung Cancer Cell Lines

Betulinic acid is a lupane-type pentacyclic triterpene mostly found in birch bark and thoroughly explored for its wide range of pharmacological activities. Despite its impressive biological potential, its low bioavailability has challenged many researchers to develop different formulations for achieving better in vitro and in vivo effects. We previously reported the synthesis of fatty acid esters of betulinic acid using butyric, stearic, and palmitic acids (But-BA, St-BA, and Pal-BA) and included them in surfaced-modified liposomes (But-BA-Lip, St-BA-Lip, Pal-BA-Lip). In the current study, we evaluated the cytotoxic effects of both fatty acid esters and their respective liposomal formulations against MCF-7, HT-29, and NCI-H460 cell line. The cytotoxic assessment of BA derivatives revealed that both the fatty esters and their liposomal formulations acted as cytotoxic agents in a dose- and time-dependent manner. But-BA-Lip exerted stronger cytotoxic effects than the parent compound, BA and its liposomal formulation, and even stronger effects than 5-FU against HT-29 cells (IC50 of 30.57 μM) and NCI-H460 cells (IC50 of 30.74 μM). BA's fatty esters and their respective liposomal formulations facilitated apoptosis in cancer cells by inducing nuclear morphological changes and increasing caspase-3/-7 activity. The HET-CAM assay proved that none of the tested compounds induced any irritative effect, suggesting that they can be used safely for local applications.

The Crucial Roles of Diet, Microbiota, and Postbiotics in Colorectal Cancer

PURPOSE OF REVIEW

Colorectal cancer is the second deadliest cancer in the world, and its prevalence has been increasing alarmingly in recent years. After researchers discovered the existence of dysbiosis in colorectal cancer, they considered the use of probiotics in the treatment of colorectal cancer. However, for various reasons, including the low safety profile of probiotics in susceptible and immunocompromised patient5s, and the risk of developing antibiotic resistance, researchers have shifted their focus to non-living cells, their components, and metabolites. This review aims to comprehensively evaluate the literature on the effects of diet, microbiota, and postbiotics on colorectal cancer and the future of postbiotics.

RECENT FINDINGS

The link between diet, gut microbiota, and colorectal cancer has been established primarily as a relationship rather than a cause-effect relationship. The gut microbiota can convert gastrointestinal tract and dietary factors into either onco-metabolites or tumor suppressor metabolites. There is serious dysbiosis in the microbiota in colorectal cancer. Postbiotics appear to be promising agents in the prevention and treatment of colorectal cancer. It has been shown that various postbiotics can selectively induce apoptosis in CRC, inhibit cell proliferation, growth, invasion, and migration, modulate the immune system, suppress carcinogenic signaling pathways, maintain intestinal epithelial integrity, and have a synergistic effect with chemotherapy drugs. However, it is also reported that some postbiotics are ineffective and may be risky in terms of safety profile in some patients. Many issues need to be researched about postbiotics. Large-scale, randomized, double-blind clinical studies are needed.

Designing function-specific minimal microbiomes from large microbial communities

Microorganisms exist in large communities of diverse species, exhibiting various functionalities. The mammalian gut microbiome, for instance, has the functionality of digesting dietary fibre and producing different short-chain fatty acids. Not all microbes present in a community contribute to a given functionality; it is possible to find a minimal microbiome, which is a subset of the large microbiome, that is capable of performing the functionality while maintaining other community properties such as growth rate and metabolite production. Such a minimal microbiome will also contain keystone species for SCFA production in that community. In this work, we present a systematic constraint-based approach to identify a minimal microbiome from a large community for a user-proposed function. We employ a top-down approach with sequential deletion followed by solving a mixed-integer linear programming problem with the objective of minimising the L1-norm of the membership vector. Notably, we consider quantitative measures of community growth rate and metabolite production rates. We demonstrate the utility of our algorithm by identifying the minimal microbiomes corresponding to three model communities of the gut, and discuss their validity based on the presence of the keystone species in the community. Our approach is generic, flexible and finds application in studying a variety of microbial communities. The algorithm is available from https://github.com/RamanLab/minMicrobiome .

Role of dietary fiber and lifestyle modification in gut health and sleep quality

Dietary fiber has an immense role in the gut microbiome by modulating juvenile growth, immune system maturation, glucose, and lipid metabolism. Lifestyle changes might disrupt gut microbiota symbiosis, leading to various chronic diseases with underlying inflammatory conditions, obesity, and its associated pathologies. An interventional study of 16 weeks examined the impact of psyllium husk fiber with and without lifestyle modification on gut health and sleep quality in people with central obesity (men = 60 and women = 60), those aged from 40 to 60 years, those having WC ≥ 90 cm (men) and WC ≥ 80 cm (women), and no history of any chronic disease or regular medication. The participants were subgrouped into three intervention groups, namely, the psyllium husk fiber (PSH) group, the lifestyle modification (LSM) group, and the LSM&PSH group and control group with equal gender bifurcation (men = 15 and women = 15). A 24-h dietary recall, gastrointestinal tract (GIT) symptoms, and sleep quality analysis data were collected on validated questionnaires. The analyses of variance and covariance were used for baseline and post-intervention, respectively. Student's t-test was applied for pre- and post-intervention changes on the variable of interest. The intervention effect on GIT health was highly significant (P < 0.001). The mean GIT scores of the LSM, PSH, and LSM&PSH groups were 2.99 ± 0.14, 2.49 ± 0.14, and 2.71 ± 0.14, respectively, compared to the mean GIT scores of the control group. No significant (P = 0.205) effect of either intervention was observed on sleep quality. The study concluded that psyllium husk fiber significantly improved the GIT symptoms, while no significant effect of the intervention was observed on sleep quality analysis.

Potential Role of ROS in Butyrate- and Dietary Fiber-Mediated Growth Inhibition and Modulation of Cell Cycle-, Apoptosis- and Antioxidant-Relevant Proteins in LT97 Colon Adenoma and HT29 Colon Carcinoma Cells

The aim of the present study was to examine whether reactive oxygen species (ROS) contribute to chemopreventive effects of fermentation supernatants (FS) of different dietary fibers (Synergy1^®, oat-, barley-, yeast β-glucan, Curdlan) and butyrate as a fermentation metabolite. LT97 and HT29 cells were treated with butyrate and FS alone or with N-acetyl-cysteine (NAC) and their impact on ROS formation, cell growth, and protein expression (Cyclin D2, p21, PARP, Bid, GPx2) was investigated. Butyrate and FS significantly decreased cell growth. ROS levels were significantly increased, particularly in LT97 cells, while co-treatment with NAC decreased ROS formation and growth inhibitory effects in both cell lines. After treatment with butyrate and FS, Cyclin D2 expression was reduced in LT97 cells and p21 expression was increased in both cell lines. Levels of full-length PARP and Bid were decreased, while levels of cleaved PARP were enhanced. GPx2 expression was significantly reduced by fiber FS in HT29 cells. A notable effect of NAC on butyrate- and FS-modulated protein expression was observed exclusively for PARP and Bid in HT29 cells. From the present results, a contribution of ROS to growth inhibitory and apoptotic effects of butyrate and FS on LT97 and HT29 cells cannot be excluded.

Changes in Gut Microbiome upon Orchiectomy and Testosterone Administration in AOM/DSS-Induced Colon Cancer Mouse Model

PURPOSE

Sex hormones are known to affect the gut microbiota. Previously, we reported that endogenous and exogenous testosterone are associated with colorectal cancer (CRC) development and submucosal invasion. In the present study, we investigated whether the gut microbiota is affected by orchiectomy (ORX) and testosterone propionate (TP) administration using an azoxymethane/dextran sulfate sodium (AOM/DSS)-induced CRC mouse model.

MATERIALS AND METHODS

Gut microbiota was evaluated by means of 16S rRNA gene sequencing of stool DNA extracted from feces that were obtained at 13 weeks after AOM injection (from 22-week-old animals) and stored in a gas-generating pouch.

RESULTS

The increase in microbial diversity (Chao1 and Phylogenetic Diversity index) and Firmicutes/Bacteroidetes (F/B) ratio upon AOM/DSS treatment in ORX mice was significantly decreased by TP supplementation. The ratio of commensal bacteria to opportunistic pathogens was lower in the TP-administered females and ORX mice than in the AOM/DSS group. Opportunistic pathogens (Mucispirillum schaedleri or Akkermansia muciniphila) were identified only in the TP group. In addition, microbial diversity and F/B ratio were higher in male controls than in female and ORX controls. Flintibacter butyricus, Ruminococcus bromii, and Romboutsia timonensis showed similar changes in the male control group as those in the female and ORX controls.

CONCLUSION

In conclusion, testosterone determines the dysbiosis of gut microbiota, which suggests that it plays a role in the sex-related differences in colorectal carcinogenesis.

Dietary Fibre Intervention for Gut Microbiota, Sleep, and Mental Health in Adults with Irritable Bowel Syndrome: A Scoping Review

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder affecting 4-5% of the global population. This disorder is associated with gut microbiota, diet, sleep, and mental health. This scoping review therefore aims to map existing research that has administrated fibre-related dietary intervention to IBS individuals and reported outcomes on at least two of the three following themes: gut microbiota, sleep, and mental health. Five digital databases were searched to identify and select papers as per the inclusion and exclusion criteria. Five articles were included in the assessment, where none reported on all three themes or the combination of gut microbiota and sleep. Two studies identified alterations in gut microbiota and mental health with fibre supplementation. The other three studies reported on mental health and sleep outcomes using subjective questionnaires. IBS-related research lacks system biology-type studies targeting gut microbiota, sleep, and mental health in patients undergoing diet intervention. Further IBS research is required to explore how human gut microbiota functions (such as short-chain fatty acids) in sleep and mental health, following the implementation of dietary pattern alteration or component supplementation. Additionally, the application of objective sleep assessments is required in order to detect sleep change with more accuracy and less bias.

Chemopreventive effects of raw and roasted oat flakes after in vitro fermentation with human faecal microbiota

The aim of the present study was to analyse chemopreventive effects of oat flakes under consideration of processing. Thin and thick flakes were roasted and subjected to an in vitro digestion and fermentation. Fermentation supernatants (FS) were characterised and chemopreventive effects were analysed in LT97 colon adenoma cells. Compared to the fermentation control, pH values were decreased (from pH 6.3 to pH 5.0) and concentrations of SCFA, in particular butyrate, were increased in oat FS (2.6-fold, on average). Ammonia levels were not altered. Oat FS significantly decreased cell growth time- and dose-dependently. Caspase 3 activity was significantly increased (9.7-fold, on average). Oat FS slightly increased the mRNA expression of CAT (2.0-fold), SOD2 (1.7-fold) and GSTP1 (2.8-fold), on average, while GPX1 mRNA (0.3-fold) was decreased. The results indicate a chemopreventive potential of in vitro digested oat flakes regarding colon cancer development mediated mostly by growth inhibition and apoptosis, unaffected by roasting.

Dietary Emulsifier Sodium Stearoyl Lactylate Alters Gut Microbiota in vitro and Inhibits Bacterial Butyrate Producers

Dietary emulsifiers are widely used in industrially processed foods, although the effects of these food additives on human gut microbiota are not well studied. Here, we investigated the effects of five different emulsifiers [glycerol monoacetate, glycerol monostearate, glycerol monooleate, propylene glycol monostearate, and sodium stearoyl lactylate (SSL)] on fecal microbiota in vitro. We found that 0.025% (w/v) of SSL reduced the relative abundance of the bacterial class Clostridia and others. The relative abundance of the families Clostridiaceae, Lachnospiraceae, and Ruminococcaceae was substantially reduced whereas that of Bacteroidaceae and Enterobacteriaceae was increased. Given the marked impact of SSL on Clostridia, we used genome reconstruction to predict community-wide production of short-chain fatty acids, which were experimentally assessed by GC-MS analysis. SSL significantly reduced concentrations of butyrate, and increased concentrations of propionate compared to control cultures. The presence of SSL increased lipopolysaccharide, LPS and flagellin in cultured communities, thereby enhancing the proinflammatory potential of SSL-selected bacterial communities.

Study on chemopreventive effects of raw and roasted β-glucan-rich waxy winter barley using an in vitro human colon digestion model

Fermentation supernatants of barley flakes exhibit chemopreventive effects in LT97 colon adenoma cells without impact of roasting.

Fructooligosaccharides and wheat bran fed at similar fermentation levels differentially affect the expression of genes involved in transport, signaling, apoptosis, cell proliferation, and oncogenesis in the colon epithelia of healthy Fischer 344 rats

The influence of the source of fermentable material (FM) on the luminal concentrations of their end products and its effects on colon cell metabolism and disease susceptibility is not well characterized. We hypothesized that total fermentation but not the source (type) of FM would be the main factor in determining cellular /molecular outcomes in the healthy colon epithelia. The main aim of this study was to elucidate the role of two different sources of FM, fructooligosaccharides (FOS) and wheat bran (WB), on the expression of genes involved in short chain fatty acid (SCFA) transport, G-protein signaling, apoptosis, cell proliferation and oncogenesis in colon epithelia of healthy rats. Male Fischer 344 rats (n = 10/group) were fed AIN-93G control (0% FM) or experimental diets containing WB (~1%, 2%, or 5% FM) or FOS (~2%, 5%, or 8% FM). Rats were killed after 6 weeks and the colon mucosa was assessed for the expression of target genes using real-time quantitative polymerase chain reaction. By comparison to the control, dose-related changes of mRNA levels were found in rats fed FOS-based diets, including: (a) upregulation of three SCFA transporters (Smct2, Mct1 and Mct4) but downregulation of Mct2, (b) upregulation of Gpr109a and downregulation of Gpr120, Gpr43, Gprc5a, Rgs2 and Rgs16, (c) upregulation of apoptosis-related genes including Bcl2, Bcl2-like 1, Bak1, Caspase 3, Caspase 8 and Caspase 9, (d) downregulation of the oncogenes and metastasis genes Ros1, Fos, Cd44, Fn1 and Plau, and (e) downregulation of several genes involved in cellular proliferation including Hbegf, Hoxb13, Cgref1, Wfdc1, Tgm3, Fgf7, Nov and Lumican. In contrast, rats fed WB-based diets resulted in dose-related upregulation of mRNA levels of Smct2, Rgs16, Gprc5a, Gpr109a, Bcl2-like 1, Caspase 8, and Fos. Additionally, different gene expression responses were observed in rats fed FOS and WB at 2% and 5% FM. Over all, these gene changes elicited by FOS and WB were independent of the expression of the tumor suppressor Tp53. These results suggest that fermentation alone is not the sole determinant of gene responses in the healthy rat colon.

Dynamics of Human Gut Microbiota and Short-Chain Fatty Acids in Response to Dietary Interventions with Three Fermentable Fibers

Production of short-chain fatty acids (SCFAs), especially butyrate, in the gut microbiome is required for optimal health but is frequently limited by the lack of fermentable fiber in the diet. We attempted to increase butyrate production by supplementing the diets of 174 healthy young adults for 2 weeks with resistant starch from potatoes (RPS), resistant starch from maize (RMS), inulin from chicory root, or an accessible corn starch control. RPS resulted in the greatest increase in total SCFAs, including butyrate. Although the majority of microbiomes responded to RPS with increases in the relative abundance of bifidobacteria, those that responded with an increase in Ruminococcus bromii or Clostridium chartatabidum were more likely to yield higher butyrate concentrations, especially when their microbiota were replete with populations of the butyrate-producing species Eubacterium rectale RMS and inulin induced different changes in fecal communities, but they did not generate significant increases in fecal butyrate levels.IMPORTANCE These results reveal that not all fermentable fibers are equally capable of stimulating SCFA production, and they highlight the importance of the composition of an individual's microbiota in determining whether or not they respond to a specific dietary supplement. In particular, R. bromii or C. chartatabidum may be required for enhanced butyrate production in response to RS. Bifidobacteria, though proficient at degrading RS and inulin, may not contribute to the butyrogenic effect of those fermentable fibers in the short term.

New insights into the roles and regulation of SphK2 as a therapeutic target in cancer chemoresistance

Chemoresistance is a complicated process developed by most cancers and accounts for the majority of relapse and metastasis in cancer. The main mechanisms of chemoresistance phenotype include increased expression and/or activated drug efflux pumps, altered DNA repair, altered metabolism of therapeutics as well as impaired apoptotic signaling pathways. Aberrant sphingolipid signaling has also recently received considerable attention in chemoresistance. Sphingolipid metabolites regulate main biological processes such as apoptosis, cell survival, proliferation, and differentiation. Two sphingosine kinases, SphK1 and SphK2, convert sphingosine to sphingosine-1-phosphate, an antiapoptotic bioactive lipid mediator. Numerous evidence has revealed the involvement of activated SphK1 in tumorigenesis and resistance, however, contradictory results have been found for the role of SphK2 in these functions. In some studies, overexpression of SphK2 suppressed cell growth and induced apoptosis. In contrast, some others have shown cell proliferation and tumor promotion effect for SphK2. Our understanding of the role of SphK2 in cancer does not have a sufficient integrity. The main focus of this review will be on the re-evaluation of the role of SphK2 in cell death and chemoresistance in light of our new understanding of molecular targeted therapy. We will also highlight the connections between SphK2 and the DNA damage response. Finally, we will provide our insight into the regulatory mechanisms of SphKs by two main categories, micro and long, noncoding RNAs as the novel players of cancer chemoresistance.

Butyrate enhances mitochondrial function during oxidative stress in cell lines from boys with autism

Butyrate (BT) is a ubiquitous short-chain fatty acid (SCFA) principally derived from the enteric microbiome. BT positively modulates mitochondrial function, including enhancing oxidative phosphorylation and beta-oxidation and has been proposed as a neuroprotectant. BT and other SCFAs have also been associated with autism spectrum disorders (ASD), a condition associated with mitochondrial dysfunction. We have developed a lymphoblastoid cell line (LCL) model of ASD, with a subset of LCLs demonstrating mitochondrial dysfunction (AD-A) and another subset of LCLs demonstrating normal mitochondrial function (AD-N). Given the positive modulation of BT on mitochondrial function, we hypothesized that BT would have a preferential positive effect on AD-A LCLs. To this end, we measured mitochondrial function in ASD and age-matched control (CNT) LCLs, all derived from boys, following 24 and 48 h exposure to BT (0, 0.1, 0.5, and 1 mM) both with and without an in vitro increase in reactive oxygen species (ROS). We also examined the expression of key genes involved in cellular and mitochondrial response to stress. In CNT LCLs, respiratory parameters linked to adenosine triphosphate (ATP) production were attenuated by 1 mM BT. In contrast, BT significantly increased respiratory parameters linked to ATP production in AD-A LCLs but not in AD-N LCLs. In the context of ROS exposure, BT increased respiratory parameters linked to ATP production for all groups. BT was found to modulate individual LCL mitochondrial respiration to a common set-point, with this set-point slightly higher for the AD-A LCLs as compared to the other groups. The highest concentration of BT (1 mM) increased the expression of genes involved in mitochondrial fission (PINK1, DRP1, FIS1) and physiological stress (UCP2, mTOR, HIF1α, PGC1α) as well as genes thought to be linked to cognition and behavior (CREB1, CamKinase II). These data show that the enteric microbiome-derived SCFA BT modulates mitochondrial activity, with this modulation dependent on concentration, microenvironment redox state, and the underlying mitochondrial function of the cell. In general, these data suggest that BT can enhance mitochondrial function in the context of physiological stress and/or mitochondrial dysfunction, and may be an important metabolite that can help rescue energy metabolism during disease states. Thus, insight into this metabolic modulator may have wide applications for both health and disease since BT has been implicated in a wide variety of conditions including ASD. However, future clinical studies in humans are needed to help define the practical implications of these physiological findings.

Chemopreventive Potential of Raw and Roasted Pistachios Regarding Colon Carcinogenesis

Pistachios are rich in health-promoting bioactive compounds such as B vitamins, γ-tocopherol, polyphenols and dietary fiber, which could contribute to the reduction of colon cancer risk in terms of chemoprevention (Fischer, S.; Glei, M. Health-Potential of Nuts. Ernaehrungs Umsch. Int. 2013, 60, 206-215.). Since pistachios are often consumed roasted, the present study aims at investigating the influence of different roasting conditions (RC) on potential chemopreventive effects of pistachios in colon adenoma cells such as growth and apoptosis, genotoxic- and anti-genotoxic effects and modulation of gene expression of detoxifying enzymes (CAT, SOD2, GPx1, and GSTP1). Fermentation supernatants (FS) were obtained from raw and roasted (RC1 = 141 °C/25 min, RC2 = 160 °C/15 min and RC3 = 185 °C/21 min) pistachios after in vitro fermentation. FS of pistachios significantly reduced LT97 cell growth in a time- and dose-dependent manner. Compared to the blank control, pistachio FS (2.5%) led to a significant average reduction of H₂O₂-induced DNA damage (1.5-fold). Levels of CAT mRNA were significantly increased (1.3-fold, on average for 5% FS). Pistachio FS (5%) significantly increased the number of early apoptotic cells (up to 2.1-fold) and levels of caspase-3 activities (up to 6.9-fold). The present results confirm a chemopreventive potential of pistachios, which is mediated by growth inhibition, induction of apoptosis and anti-genotoxic effects, as well as induction of CAT. These effects remain mostly unaffected by roasting.

Polo-like kinase 1 expression is suppressed by CCAAT/enhancer-binding protein α to mediate colon carcinoma cell differentiation and apoptosis

BACKGROUND

Human polo-like kinase 1 (PLK1), a highly conserved serine/threonine kinase is a key player in several essential cell-cycle events. PLK1 is considered an oncogene and its overexpression often correlates with poor prognosis of cancers, including colorectal cancer (CRC). However, regulation of PLK1 expression in colorectal cells was never studied earlier and it is currently unknown if PLK1 regulates differentiation and apoptosis of CRC.

METHODS

PLK1 expression was analyzed by real-time PCR and western blotting. Transcriptional regulation was studied by reporter assay, gene knock-down, EMSA and ChIP.

RESULTS

PLK1 expression was down-regulated during butyrate-induced differentiation of HT-29 and other CRC cells. Also, PLK1 down-regulation mediated the role of butyrate in CRC differentiation and apoptosis. We report here a novel transcriptional regulation of PLK1 by butyrate. Transcription factors CCAAT/enhancer-binding protein α (C/EBPα) and Oct-1 share an overlapping binding site over the PLK1 promoter. Elevated levels of C/EBPα by butyrate treatment of CRC cells competed out the activator protein Oct-1 from binding to the PLK1 promoter and sequestered it. Binding of C/EBPα was associated with increased deacetylation near the transcription start site (TSS) of the PLK1 promoter, which abrogated transcription through reduced recruitment of RNA polymerase II. We also found a synergistic role between the synthetic PLK1-inhibitor SBE13 and butyrate on the apoptosis of CRC cells.

CONCLUSION

This study offered a novel p53-independent regulation of PLK1 during CRC differentiation and apoptosis.

GENERAL SIGNIFICANCE

Down-regulation of PLK1 is one of the mechanisms underlying the anti-cancer role of dietary fibre-derived butyrate in CRC.

Influence of roasting on the chemopreventive potential of in vitro fermented almonds in LT97 colon adenoma cells

The consumption of almonds may contribute to the prevention of colon cancer due to their unique composition of health promoting compounds. Since almonds are often consumed roasted, the impact of different roasting (R) conditions (R1 = 139.2 °C/25 min, R2 = 161.5 °C/20 min and R3 = 170.8 °C/15 min) on chemopreventive effects of in vitro-fermented almonds was analysed in LT97 colon adenoma cells. Fermentation supernatants (FS) of raw and roasted almonds had no genotoxic effects. FS obtained from raw or mildly roasted almonds (R1) significantly increased mRNA levels of CAT (4.6-fold), SOD2 (5.6-fold) and GSTP1 (3.9-fold) but not of GPx1. FS of almonds significantly reduced the growth of LT97 cells in a time- and dose-dependent manner. Treatment with 5% almonds FS increased the number of early apoptotic cells (17.4%, on average) and caspase-3 activity (4.9-fold, on average). The results indicate a chemopreventive potential of in vitro-fermented almonds which is largely independent of the roasting process.

Butyrate induces apoptosis by activating PDC and inhibiting complex I through SIRT3 inactivation

The underlying anticancer effects of butyrate, an end-product of the intestinal microbial fermentation of dietary fiber, remain elusive. Here, we report that butyrate promotes cancer cell apoptosis by acting as a SIRT3 inhibitor. Butyrate inhibits SIRT3 both in cultured cells and in vitro. Butyrate-induced PDHA1 hyperacetylation relieves the inhibitory phosphorylation of PDHA1 at serine 293, thereby activating an influx of glycolytic intermediates into the tricarboxylic acid (TCA) cycle and reversing the Warburg effect. Meanwhile, butyrate-induced hyperacetylation inactivates complex I of the electron transfer chain and prevents the utilization of TCA cycle intermediates. These metabolic stresses promote apoptosis in hyperglycolytic cancer cells, such as HCT116p53-/- cells. SIRT3 deacetylates both PDHA1 and complex I. Genetic ablation of Sirt3 in mouse hepatocytes abrogated the ability of butyrate to induce apoptosis. Our results identify a butyrate-mediated anti-tumor mechanism and indicate that the combined activation of PDC and inhibition of complex I is a novel tumor treatment strategy.

Suppression of Spleen Tyrosine Kinase (Syk) by Histone Deacetylation Promotes, Whereas BAY61-3606, a Synthetic Syk Inhibitor Abrogates Colonocyte Apoptosis by ERK Activation

Spleen tyrosine kinase (Syk), a non-receptor tyrosine kinase, regulates tumor progression, either negatively or positively, depending on the tissue lineage. Information about the role of Syk in colorectal cancers (CRC) is limited, and conflicting reports have been published. We studied Syk expression and its role in differentiation and apoptosis of the colonocytes. Here, we reported for the first time that expression of two transcript variants of Syk is suppressed in colonocytes during butyrate-induced differentiation, which mediates apoptosis of HT-29 cells. Despite being a known HDAC inhibitor, butyrate deacetylates histone3/4 around the transcription start site (TSS) of Syk. Histone deacetylation precludes the binding of RNA Polymerase II to the promoter and inhibits transcription. Since butyrate is a colonic metabolite derived from undigested fibers, our study offers a plausible explanation of the underlying mechanisms of the protective role of butyrate as well as the dietary fibers against CRC through the regulation of Syk. We also report that combined use of butyrate and highly specific Syk inhibitor BAY61-3606 does not enhance differentiation and apoptosis of colonocytes. Instead, BAY completely abolishes butyrate-induced differentiation and apoptosis in a Syk- and ERK1/2-dependent manner. While butyrate dephosphorylates ERK1/2 in HT-29 cells, BAY re-phosphorylates it, leading to its activation. This study describes a novel mechanism of butyrate action in CRC and explores the role of Syk in butyrate-induced differentiation and apoptosis. In addition, our study highlights those commercial small molecule inhibitors, although attractive drug candidates should be used with concern because of their frequent off-target effects. J. Cell. Biochem. 118: 191-203, 2017. © 2016 Wiley Periodicals, Inc.

Effect of knockdown or overexpression of heat shock transcription factor 2 on apoptosis and migration of human colonic epithelial cells

AIM: To explore the role of heat shock transcription factor 2 (HSF2) in cell apoptosis and migration in human colonic epithelial cell line HT-29 by means of interference and overexpression.

METHODS: Apoptosis of HT-29 cells was induced by incubation with sodium butyrate (SB) for different durations. Cytotoxicity was estimated by MTT assay, and the cell cycle and apoptosis were observed by flow cytometry to choose the optimal time and concentration of SB. HT-29 cells were then transfected with HSF2 siRNA or a lentiviral vector (Ubi-MCS-3FLAG-SV40-EGFP). The overexpression or knockdown of HSF2 was detected by Leica DMIRB and Western blot. After transfection, cell migration ability was measured by wound healing assay and Transwell assay. Apoptosis of HT-29 cells was induced with SB after transfection, cell proliferation was studied by MTT assay, and cell cycle and apoptosis were observed by flow cytometry.

RESULTS: Compared with the negative control (NC) group, SB at 2.5, 5.0, or 10 mmol/L could significantly cause growth inhibition after 48 h of incubation (P < 0.01), and the effect was time- and dose-dependent. The apoptosis rate was significantly higher in the SB treated groups (1.25, 2.5, 5.0, or 10 mmol/L for 48 h) than in the NC group (51.588% ± 5.110%, 77.732% ± 2.746%, 90.115% ± 1.438%, 94.247% ± 1.243% vs 0.548% ± 0.113%, P < 0.01). When the SB concentration was>2.5 mmol/L, the apoptosis rate increased significantly (P < 0.01). When treated with 1.25 mmol/L SB for 48 h, the percentage of cells in G₀/G₁ phase cell did not show a significant difference compared with the NC group; when the concentration was > 2.5 mmol/L (5.0 or 10.0 mmol/L), SB could induce G₁/G₀ arrest (P < 0.01). After lentiviral transfection, a large number of HT-29 cells with green fluorescence was observed by Leica DMIRB (transfection efficiency>80%). Lentiviral transfection of siRNA could effectively inhibit expression of HSF2, while lentiviral transfection of Ubi-MCS-3FLAG-SV40-EGFP induced overexpression of HSF2. HSF2 overexpression significantly increased cell proliferation and migration compared with the empty vector treated group (P < 0.05), while HSF2 knockdown significantly inhibited the proliferation and migration of HT-29 cells compared with the negative siRNA group (P < 0.05). HSF2 overexpression or knockdown had no significant impact on cell cycle distribution. HSF2 overexpression significantly decreased cell apoptosis rate (P < 0.05), while HSF2 knockdown significantly increased cell apoptosis rate (P < 0.05).

CONCLUSION: HSF2 might be a protective factor for epithelial cell apoptosis. HSF2 achieves the effects of cell protection possibly through the cell cycle regulation.

Butyrylated starch affects colorectal cancer markers beneficially and dose-dependently in genotoxin-treated rats

Population studies suggest that greater dietary fiber intake may lower colorectal cancer (CRC) risk, possibly through the colonic bacterial fermentative production of butyrate. Butyrylated starch delivers butyrate to the colon of humans with potential to reduce CRC risk but high doses may exacerbate risk through promoting epithelial proliferation. Here we report the effects of increasing dietary butyrylated high amylose maize starch (HAMSB) on azoxymethane (AOM) induced distal colonic DNA damage, cell proliferation, mucus layer thickness and apoptosis in rats. Five groups of 15 rats were fed AIN-93G based diets containing 0–40% HAMSB for 4 weeks then injected with (AOM) and killed 6 hours later. Large bowel total SCFA, acetate and butyrate pools and hepatic portal venous plasma total SCFA, acetate and butyrate concentrations were higher with greater HAMSB intake. Distal colonic epithelial apoptotic index and colonic mucus thickness increased, while DNA single strand breaks decreased dose-dependently with greater HAMSB intake. Colonocyte proliferation rates were unaffected by diet. These data suggest that increasing large bowel butyrate may reduce the risk of CRC in a dose dependent manner by enhancing apoptotic surveillance in the colonic epithelium for damaged cells without promoting the risk of tumorigenesis through increased cell proliferation.

Mitochondrial-mediated apoptosis pathway in alveolar epithelial cells exposed to the metals in combustion-generated particulate matter

Previously a significant mitochondrial impairment was identified in alveolar epithelial cells exposed to metals adsorbed to combustion-generated particulate matter (PM). Due to the critical role of mitochondria in apoptosis, the aim of this study was to investigate the pro-apoptotic potential of metals present in oil fly ash (OFA). A549 cells were exposed to water-soluble components of an OFA sample, containing vanadium [V(IV)], iron [Fe(III)], and nickel [Ni(II)] (68.8, 110.4, and 18 μM, respectively). Experiments were also performed using individual metal solutions. Apoptosis was detected and the mitochondrial role was assessed by a caspase-9 inhibitor (Z-LEHD-FMK). To determine whether the presence of impaired mitochondria in unexposed daughter cells increased apoptosis, an in vitro model was developed that allowed determination of effects until the third cell generation. To specifically examine the toxicity of vanadium (V), that characterize the airborne pollutant examined in this study, p53involvement and metabolic impairment through changes in HIF-1α and Glut-1 expression were determined. OFA and individual metal solutions produced significant apoptosis in the progeny of exposed cells, triggering the intrinsic apoptosis pathway. In apoptosis induced by poorly genotoxic metal V, p53 did not play a significant role. However, V exposure increased nuclear translocation of HIF-1α and expression of the Glut-1 receptor, indicating metabolic impairment due to metal-induced mitochondrial dysfunction. Overall, these results improve our knowledge of the pathogenic role that airborne metals and in particular V exerted in respiratory epithelium.

Combining small molecules for cell reprogramming through an interatomic analysis

The knowledge available about the application and generation of induced pluripotent stem cells (iPSC) has grown since their discovery, and new techniques to enhance the reprogramming process have been described. Among the new approaches to induce iPSC that have gained great attention is the use of small molecules for reprogramming. The application of small molecules, unlike genetic manipulation, provides for control of the reprogramming process through the shifting of concentrations and the combination of different molecules. However, different researchers have reported the use of "reprogramming cocktails" with variable results and drug combinations. Thus, the proper combination of small molecules for successful and enhanced reprogramming is a matter for discussion. However, testing all potential drug combinations in different cell lineages is very costly and time-consuming. Therefore, in this article, we discuss the use of already employed molecules for iPSC generation, followed by the application of systems chemo-biology tools to create different data sets of protein-protein (PPI) and chemical-protein (CPI) interaction networks based on the knowledge of already used and new reprogramming cocktail combinations. We further analyzed the biological processes associated with PPI-CPI networks and provided new potential protein targets to be inhibited or expressed for stem cell reprogramming. In addition, we applied a new interference analysis to prospective targets that could negatively affect the classical pluripotency-associated factors (SOX2, NANOG, KLF4 and OCT4) and thus potentially improve reprogramming protocols.

Selenium-binding protein 1 is associated with the degree of colorectal cancer differentiation and is regulated by histone modification

The aim of the present study was to examine the regulation of selenium binding protein 1 (SELENBP1) expression in colorectal cancer (CRC). Samples of cancer tissue and adjacent normal mucosa were collected from 83 CRC patients, and analyzed for SELENBP1 expression by 2D-DIGE, immunoblotting, RT-PCR and immunostaining. Expression levels of SELENBP1, carcinoembryonic antigen (CEA) and alkaline phosphatase (AKP) were determined in cultures of human colon cancer cell lines (SW480, SW620 and HT29) folllowing treatment with i) sodium butyrate (NaB, 2 mM), a differentiation inducer; ii) Trichostatin A (TSA, 0.3 µM), a histone deacetylase inhibitor; or iii) 5'-aza-2'-deoxycytidine (5-Aza-dC, 5 µM), a DNA methylation inhibitor. SELENBP1 expression was found to be downregulated (2.54-fold) in the CRC samples as determined by 2D-DIGE and confirmed by immunoblotting and RT-PCR. SELENBP1 expression was correlated with the degree of differentiation, but not with TNM stage or lymph node metastasis, and was higher in benign polyps (1.97±0.57) than in CRC tissues (0.96±0.59). In the CRC cell lines, NaB treatment led to the upregulation of SELENBP1, CEA and AKP when compared with the untreated cells (2.24- to 4.82-fold). SELENBP1 was also upregulated in cells treated with TSA alone (1.25- to 3.64-fold), or in combination with 5-Aza-dC (1.32- to 4.13-fold). In CRC, the downregulated SELENBP1 expression was reactivated by inducing differentiation. Therefore, SELENBP1 is a potential pharmacological target for individualized CRC treatment.

Sodium butyrate induces DRP1-mediated mitochondrial fusion and apoptosis in human colorectal cancer cells

Sodium butyrate (NaBt) is the byproduct of anaerobic microbial fermentation inside the gastro-intestinal tract that could reach up to 20mM, and has been shown to inhibit the growth of various cancers. Herein, we evaluated its effect on mitochondrial fusion and associated induction of apoptosis in colorectal cancer cells (CRC). NaBt treatment at physiological (1-5mM) concentrations for 12 and 24h decreased the cell viability and induced G2-M phase cell cycle arrest in HCT116 (12h) and SW480 human CRC cells. This cell cycle arrest was associated with mitochondria-mediated apoptosis accompanied by a decrease in survivin and Bcl-2 expression, and generation of reactive oxygen species (ROS). Furthermore, NaBt treatment resulted in a significant decrease in the mitochondrial mass which is an indicator of mitochondrial fusion. Level of dynamin-related protein 1 (DRP1), a key regulator of mitochondrial fission and fusion where its up-regulation correlates with fission, was found to be decreased in CRC cells. Further, at early treatment time, DRP1 down-regulation was noticed in mitochondria which later became drastically reduced in both mitochondria as well as cytosol. DRP1 is activated by cyclin B1-CDK1 complex by its ser616 phosphorylation in which both cyclin B1-CDK1 complex and phospho-DRP1 (ser616) were strongly reduced by NaBt treatment. DRP1 was observed to be regulated by apoptosis as pan-caspase inhibitor showing rescue from NaBt-induced apoptosis also caused the reversal of DRP1 to the normal level as in control proliferating cells. Together, these findings suggest that NaBt can modulate mitochondrial fission and fusion by regulating the level of DRP1 and induce cell cycle arrest and apoptosis in human CRC cells.

Colorectal carcinogenesis: a cellular response to sustained risk environment

The current models for colorectal cancer (CRC) are essentially linear in nature with a sequential progression from adenoma through to carcinoma. However, these views of CRC development do not explain the full body of published knowledge and tend to discount environmental influences. This paper proposes that CRC is a cellular response to prolonged exposure to cytotoxic agents (e.g., free ammonia) as key events within a sustained high-risk colonic luminal environment. This environment is low in substrate for the colonocytes (short chain fatty acids, SCFA) and consequently of higher pH with higher levels of free ammonia and decreased mucosal oxygen supply as a result of lower visceral blood flow. All of these lead to greater and prolonged exposure of the colonic epithelium to a cytotoxic agent with diminished aerobic energy availability. Normal colonocytes faced with this unfavourable environment can transform into CRC cells for survival through epigenetic reprogramming to express genes which increase mobility to allow migration and proliferation. Recent data with high protein diets confirm that genetic damage can be increased, consistent with greater CRC risk. However, this damage can be reversed by increasing SCFA supply by feeding fermentable fibre as resistant starch or arabinoxylan. High protein, low carbohydrate diets have been shown to alter the colonic environment with lower butyrate levels and apparently greater mucosal exposure to ammonia, consistent with our hypothesis. Evidence is drawn from in vivo and in vitro genomic and biochemical studies to frame experiments to test this proposition.

Sodium butyrate restores ASC expression and induces apoptosis in LS174T cells

Sodium butyrate (NaBu) is a short-chain fatty acid (SCFA), which has been proposed as a potential anticancer agent. Apoptosis-associated speck-like protein (ASC) is a pro-apoptotic signaling factor that is subjected to epigenetic silencing in human cancers. Modulation by the aberrant methylation of CpG islands of ASC is a well-characterized epigenetic mechanism, and the methylation-induced silencing of ASC has been observed in several types of tumors. NaBu induces cell cycle arrest, markers of cell differentiation and apoptosis in colon cancer. NaBu promotes transcriptional activation by relaxing the DNA conformation and displays anti-proliferative and differentiating activity in a wide variety of cancers. Thus, we used NaBu to investigate the relationship between the status of cell proliferation and the re-expression of ASC in colon carcinoma LS174T cells. Our experiments determined ASC re-expression at the protein level using western blotting. In addition, we used reverse transcription-polymerase chain reaction to detect the expression levels of ASC mRNA and an MTT assay to detect the inhibitory rate of cell growth. The apoptosis rate was also detected for further validation of the re-expression of ASC. The results showed that ASC re-expression was significantly increased in the LS174 cells following NaBu treatment in a time- and dose-dependent manner. The expression of ASC also induced the apoptosis of LS174T cells. These results suggest that NaBu plays a role in the reactivation of ASC expression and that the latter promotes the apoptosis of LS174T cells.

A review of the potential mechanisms for the lowering of colorectal oncogenesis by butyrate

Colorectal cancer (CRC) is a leading cause of preventable cancer deaths worldwide, with dietary factors being recognised as key risk modifiers. Foods containing dietary fibre are protective to a degree that the World Cancer Research Fund classifies the evidence supporting their consumption as ‘convincing’. The mechanisms by which fibre components protect against CRC remain poorly understood, especially their interactions with the gut microbiome. Fibre is a composite of indigestible plant polysaccharides and it is emerging that fermentable fibres, including resistant starch (RS), are particularly important. RS fermentation induces SCFA production, in particular, relatively high butyrate levels, and in vitro studies have shown that this acid has strong anti-tumorigenic properties. Butyrate inhibits proliferation and induces apoptosis of CRC cell lines at physiological concentrations. These effects are attributed to butyrate's ability to alter gene transcription by inhibiting histone deacetylase activity. However, the more recent discovery of G-protein coupled receptors that bind butyrate and other SCFA and data obtained from proteomic and genomic experiments suggest that alternative pathways are involved. Here, we review the mechanisms involved in butyrate-induced apoptosis in CRC cells and, additionally, the potential role this SCFA may play in mediating key processes in tumorigenesis including genomic instability, inflammation and cell energy metabolism. This discussion may help to inform the development of strategies to lower CRC risk at the individual and population levels.

Butyrate interferes with the differentiation and function of human monocyte-derived dendritic cells

Dendritic cells (DCs) are specialized antigen-presenting cells that are uniquely capable of either inducing immune responses or maintaining a state of self-tolerance, depending on their stage of maturation. In the present study, we describe a way to interfere with DCs maturation. The compound butyrate can affect the differentiation of DCs generated from human monocytes and can inhibit T cell proliferation. We demonstrate that butyrate substantially down-regulates the expression of CD80, CD83, and MHC class II molecules; increases endocytic capability; reduces allostimulatory abilities; promote interleukin-10 (IL-10) production; and inhibits interleukin-12 (IL-12) and interferon-γ (IFN-γ) production. These results demonstrate a specific immune suppression property of butyrate and supports further investigation for butyrate as a new immunotherapeutic agent.

Small-molecule chromatin-modifying agents: therapeutic applications

Suberoylanilide hydroxamic acid (vorinostat) was the first of the histone deacetylase inhibitors (HDACi) to be entered as therapy for the treatment of cutaneous T-cell lymphoma. Since then, a number of HDACi belonging to the short-chain fatty acid, hydroxamate, cyclic peptide or benzamide classes have been investigated in Phase II or III clinical trials (alone or in combination) for the treatment of many kinds of tumors. In addition, HDACi can be useful in antimalarial and antifungal therapies, and can reactivate HIV-1 expression in latent cellular reservoirs, thus suggesting that they could be used in combination with highly active antiretroviral therapy. Moreover, they have also proved their efficacy in neurodegenerative diseases, such as Huntington's disease, Parkinson's disease and Friedreich's ataxia. In particular, a new series of bis-anilides demonstrating a peculiar mechanism of action displayed highly beneficial effects against Huntington's disease and Friedreich's ataxia. In addition, a number of sirtuin inhibitors demonstrated antiproliferative effects in cell assays as well as in mouse tumor models, thus suggesting a role of such compounds in therapy against cancer. Furthermore, the SIRT2-selective AGK-2 has been reported to have protective effects against Parkinson's disease, and resveratrol and other sirtuin activators can be useful for the treatment of Alzheimer's disease.

Effect of butyrate on aromatase cytochrome P450 levels in HT29, DLD-1 and LoVo colon cancer cells

Epidemiological studies suggest that colonic production of butyrate and estrogen may be involved in human susceptibility to colorectal cancer (CRC). Estrone (E1) can be produced by the aromatase pathway during the conversion of androstenedione (A) to E1. Therefore, we studied the effect of sodium butyrate (NaBu) on the CYP19A1 transcript and protein levels and on the conversion of A to E1 in HT29, DLD-1 and LoVo CRC cells. We found that NaBu significantly downregulated CYP19A1 transcript and protein levels, a phenomenon that was associated with reduced conversion of A to E1 in HT29, DLD-1 and LoVo cells. Our studies demonstrated that, although butyrate exhibited a protective role in CRC development, this compound may reduce aromatase activity and the production of E1 in colon cancer cells.

Butyrate induces expression of 17β-hydroxysteroid dehydrogenase type 1 in HT29 and SW707 colorectal cancer cells

Epidemiological studies have revealed that butyrate and 17β-estradiol (E2) may decrease the incidence of colorectal cancer (CRC). In peripheral tissue, E2 can be produced locally by 17β-hydroxysteroid dehydrogenase 1 (HSD17B1) estrone (E1) reduction. Using quantitative real-time polymerase chain reaction and western blotting analysis, we found that sodium butyrate significantly upregulates HSD17B1 long and short transcripts and protein levels in HT29 and SW707 CRC cells. Chromatin immunoprecipitation analysis showed that upregulation of these transcript levels correlated with an increase in binding of Polymerase II to proximal and distal promoters of HSD17B1. Moreover, we observed that upregulation of HSD17B1 protein levels was associated with increased conversion of E1 to E2 in HT29 and SW707 CRC cells. Since sodium butyrate increases the conversion of E1 to E2, our findings may support the validity of butyrate in the prophylaxis of CRC incidence.

The protective role of 5-HMF against hypoxic injury

In an attempt to find new types of anti-hypoxic agents from herbs, we identified 5-hydroxymethyl-2-furfural (5-HMF) as a natural agent that fulfills the criterion. 5-HMF, the final product of carbohydrate metabolism, has favorable biological effects such as anti-oxidant activity and inhibiting sickling of red blood cells. The role of 5-HMF in hypoxia, however, is not yet. Our pilot results showed that pretreatment with 5-HMF markedly increased both the survival time and the survival rate of mice under hypoxic stress. The present study was aimed to further investigate the protective role of 5-HMF and the underlying mechanisms in hypoxic injury using ECV304 cells as an in vitro model. ECV304 cells pretreated with or without 5-HMF for 1 h were exposed to hypoxic condition (0.3% O(2)) for 24 h and then cell apoptosis, necrosis, the changes of mitochondrial membrane potential (MMP) and the expressions of phosphorylation- extracellular signal-regulated kinase (p-ERK) were investigated. Pretreatment with 5-HMF markedly attenuated hypoxia-induced cell necrosis and apoptosis at late stage (p < 0.01). Furthermore, pretreatment with 5-HMF rescued both the decline of the MMP and the increase of p-ERK protein under hypoxia. In a word, these results indicated that 5-HMF had protective effects against hypoxic injury in ECV304 cells, and its effects on MMP and p-ERK may be involved in the mechanism.