The chemopreventive activity of butyrate-containing structured lipids in experimental rat hepatocarcinogenesis

The Role of Gut Microbiome-Derived Short-Chain Fatty Acid Butyrate in Hepatobiliary Diseases

The short-chain fatty acid butyrate, produced from fermentable carbohydrates by gut microbiota in the colon, has multiple beneficial effects on human health. At the intestinal level, butyrate regulates metabolism, helps in the transepithelial transport of fluids, inhibits inflammation, and induces the epithelial defense barrier. The liver receives a large amount of short-chain fatty acids via the blood flowing from the gut via the portal vein. Butyrate helps prevent nonalcoholic fatty liver disease, nonalcoholic steatohepatitis, inflammation, cancer, and liver injuries. It ameliorates metabolic diseases, including insulin resistance and obesity, and plays a direct role in preventing fatty liver diseases. Butyrate has different mechanisms of action, including strong regulatory effects on the expression of many genes by inhibiting the histone deacetylases and modulating cellular metabolism. The present review highlights the wide range of beneficial therapeutic and unfavorable adverse effects of butyrate, with a high potential for clinically important uses in several liver diseases.

Food-Borne Chemical Carcinogens and the Evidence for Human Cancer Risk

Commonly consumed foods and beverages can contain chemicals with reported carcinogenic activity in rodent models. Moreover, exposures to some of these substances have been associated with increased cancer risks in humans. Food-borne carcinogens span a range of chemical classes and can arise from natural or anthropogenic sources, as well as form endogenously. Important considerations include the mechanism(s) of action (MoA), their relevance to human biology, and the level of exposure in diet. The MoAs of carcinogens have been classified as either DNA-reactive (genotoxic), involving covalent reaction with nuclear DNA, or epigenetic, involving molecular and cellular effects other than DNA reactivity. Carcinogens are generally present in food at low levels, resulting in low daily intakes, although there are some exceptions. Carcinogens of the DNA-reactive type produce effects at lower dosages than epigenetic carcinogens. Several food-related DNA-reactive carcinogens, including aflatoxins, aristolochic acid, benzene, benzo[a]pyrene and ethylene oxide, are recognized by the International Agency for Research on Cancer (IARC) as causes of human cancer. Of the epigenetic type, the only carcinogen considered to be associated with increased cancer in humans, although not from low-level food exposure, is dioxin (TCDD). Thus, DNA-reactive carcinogens in food represent a much greater risk than epigenetic carcinogens.

Butyrate-containing structured lipids act on HDAC4, HDAC6, DNA damage and telomerase activity during promotion of experimental hepatocarcinogenesis

Hepatocellular carcinoma (HCC) presents with a high treatment resistance and poor prognosis. Early diagnosis and preventive approaches such as chemoprevention are essential for the HCC control. Therefore, we evaluated the chemopreventive effects of butyrate-containing structured lipids (STLs) administered during the promotion stage of hepatocarcinogenesis in rats submitted to the 'resistant hepatocyte' (RH) model. Administration of butyrate-containing STLs inhibited the incidence and mean number of visible hepatic nodules per rat and reduced the number and area of glutathione S-transferase placental form-positive (GST-P+) preneoplastic focal lesions in the livers. This was accompanied by the induction of apoptosis and an increased level of hepatic butyric acid. Treatment with butyrate-containing STLs resulted in increased histone H3 lysine 9 (H3K9) acetylation, reduction of total histone deacetylase (HDAC) activity, and lower levels of HDAC4 and HDAC6 proteins. The chemopreventive effect of butyrate-containing STLs was also associated with the increased nuclear compartmentalization of p53 protein and reduced expression of the Bcl-2 protein. In addition, rats treated with butyrate-containing STLs showed decreased DNA damage and telomerase activity in the livers. These results demonstrate that the suppressive activity of butyrate-containing STLs is associated with inhibition of elevated during hepatocarcinogenesis chromatin-modifying proteins HDAC4 and HDAC6, subcellular redistribution of the p53 protein, and decreased DNA damage and telomerase activity.

Butyrate-containing structured lipids inhibit RAC1 and epithelial-to-mesenchymal transition markers: a chemopreventive mechanism against hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is one of the most aggressive human cancers. The rising incidence of HCC worldwide and its resistance to pharmacotherapy indicate that the prevention of HCC development may be the most impactful strategy to improve HCC-related morbidity and mortality. Among the broad range of chemopreventive agents, the use of dietary and nutritional agents is an attractive and promising approach; however, a better understanding of the mechanisms of their potential cancer suppressive action is needed to justify their use. In the present study, we investigated the underlying molecular pathways associated with the previously observed suppressive effect of butyrate-containing structured lipids (STLs) against liver carcinogenesis using a rat "resistant hepatocyte" model of hepatocarcinogenesis that resembles the development of HCC in humans. Using whole transcriptome analysis, we demonstrate that the HCC suppressive effect of butyrate-containing STLs is associated with the inhibition of the cell migration, cytoskeleton organization, and epithelial-to-mesenchymal transition (EMT), mediated by the reduced levels of RACGAP1 and RAC1 proteins. Mechanistically, the inhibition of the Racgap1 and Rac1 oncogenes is associated with cytosine DNA and histone H3K27 promoter methylation. Inhibition of the RACGAP1/RAC1 oncogenic signaling pathways and EMT may be a valuable approach for liver cancer prevention.

Butyrate Inhibits Indices of Colorectal Carcinogenesis via Enhancing α-Ketoglutarate-Dependent DNA Demethylation of Mismatch Repair Genes

SCOPE

Butyrate, the fermentation end product of gut microbiota in the colon, is known for its antitumor effects, but the mechanisms remained to be defined. α-ketoglutarate (α-KG) mediates DNA demethylation and aberrant epigenetic modifications are associated with carcinogenesis. The objectives of this study are to evaluate the effects of butyrate on α-KG mediated epigenetic modification in colorectal adenocarcinoma HT-29 and Caco-2 cells.

METHODS AND RESULTS

Butyrate suppressed proliferation, potentiated differentiation, and induced apoptosis in both HT-29 and Caco-2 cells, associated with enhanced expression of isocitrate dehydrogenase 1 (IDH1) and pyruvate dehydrogenase. Furthermore, butyrate upregulated acetyl-CoA and α-KG, concomitant with enhanced histone acetylation and DNA demethylation in the promoter of DNA mismatch repair (MMR) gene. Knocking down IDH1 abolished the positive effects of butyrate on CRC apoptosis and MMR protein expression, in conjunction with reduced α-KG content. Importantly, α-KG supplementation recovered the beneficial effects of butyrate in IDH1-deficient cells.

CONCLUSION

In summary, butyrate inhibits indices of colorectal carcinogenesis in an α-KG-dependent manner.

Effects of monobutyrin and tributyrin on liver lipid profile, caecal microbiota composition and SCFA in high-fat diet-fed rats

Butyric acid has been shown to have suppressive effects on inflammation and diseases related to the intestinal tract. The aim of the present study was to investigate whether supplementation of two glycerol esters, monobutyrin (MB) and tributyrin (TB), would reach the hindgut of rats, thus having an effect on the caecal profile of SCFA, microbiota composition and some risk markers associated with chronic inflammation. For this purpose, rats were fed high-fat diets after adding MB (1 and 5 g/kg) and TB (5 g/kg) to a diet without any supplementation (high-fat control; HFC). A low-fat (LF) diet was also included. In the liver, total cholesterol concentrations, LDL-cholesterol concentrations, LDL:HDL ratio, and succinic acid concentrations were reduced in rats given the MB and TB (5 g/kg) diets, compared with the group fed the HFC diet. These effects were more pronounced in MB than TB groups as also expressed by down-regulation of the gene Cyp8b1. The composition of the caecal microbiota in rats fed MB and TB was separated from the group fed the HFC diet, and also the LF diet, as evidenced by the absence of the phylum TM7 and reduced abundance of the genera Dorea (similar to LF-fed rats) and rc4-4. Notably, the caecal abundance of Mucispirillum was markedly increased in the MB group compared with the HFC group. The results suggest that dietary supplementation of MB and TB can be used to counteract disturbances associated with a HFC diet, by altering the gut microbiota, and decreasing liver lipids and succinic acid concentrations.

Improvement of the BALB/c-3T3 cell transformation assay: a tool for investigating cancer mechanisms and therapies

The identification of cancer preventive or therapeutic substances as well as carcinogenic risk assessment of chemicals is nowadays mostly dependent on animal studies. In vitro cell transformation assays mimic different stages of the in vivo neoplastic process and represent an excellent alternative to study carcinogenesis and therapeutic options. In the BALB/c-3T3 two-stage transformation assay cells are chemically transformed by treatment with MCA and TPA, along with the final Giemsa staining of morphological aberrant foci. In addition to the standard method we can show, that it is possible to apply other chemicals in parallel to identify potential preventive or therapeutic substances during the transformation process. Furthermore, we successfully combined the BALB/c cell transformation assay with several endpoint applications for protein analysis (immunoblot, subcellular fractionation and immunofluorescence) or energy parameter measurements (glucose and oxygen consumption) to elucidate cancer mechanisms in more detail. In our opinion the BALB/c cell transformation assay proves to be an excellent model to investigate alterations in key proteins or energy parameters during the different stages of transformation as well as therapeutic substances and their mode of action.

Synthesis of structured triacylglycerols enriched in n-3 fatty acids by immobilized microbial lipase

The search for new biocatalysts has aroused great interest due to the variety of micro-organisms and their role as enzyme producers. Native lipases from Aspergillus niger and Rhizopus javanicus were used to enrich the n-3 long-chain polyunsaturated fatty acids content in the triacylglycerols of soybean oil by acidolysis with free fatty acids from sardine oil in solvent-free media. For the immobilization process, the best lipase/support ratios were 1:3 (w/w) for Aspergillus niger lipase and 1:5 (w/w) for Rhizopus javanicus lipase using Amberlite MB-1. Both lipases maintained constant activity for 6 months at 4°C. Reaction time, sardine-free fatty acids:soybean oil mole ratio and initial water content of the lipase were investigated to determine their effects on n-3 long-chain polyunsaturated fatty acids incorporation into soybean oil. Structured triacylglycerols with 11.7 and 7.2% of eicosapentaenoic acid+docosahexaenoic acid were obtained using Aspergillus niger lipase and Rhizopus javanicus lipase, decreasing the n-6/n-3 fatty acids ratio of soybean oil (11:1 to 3.5:1 and 4.7:1, respectively). The best reaction conditions were: initial water content of lipase of 0.86% (w/w), sardine-free faty acids:soybean oil mole ratio of 3:1 and reaction time of 36h, at 40°C. The significant factors for the acidolysis reaction were the sardine-free fatty acids:soybean oil mole ratio and reaction time. The characterization of structured triacylglycerols was obtained using easy ambient sonic-spray ionization mass spectrometry. The enzymatic reaction led to the formation of many structured triacylglycerols containing eicosapentaenoic acid, docosahexaenoic acid or both polyunsaturated fatty acids.