Energy metabolism of rat colonocytes changes during the tumorigenic process and is dependent on diet and carcinogen

Traditional Processed Meat Products Re-designed Towards Inulin-rich Functional Foods Reduce Polyps in Two Colorectal Cancer Animal Models

Inulin-rich foods exert a prebiotic effect, as this polysaccharide is able to enhance beneficial colon microbiota populations, giving rise to the in situ production of short-chain fatty acids (SCFAs) such as propionic and butyric acids. These SCFAs are potent preventive agents against colorectal cancer due to their histone deacetylases inhibitory properties, which induce apoptosis in tumor colonocytes. As colorectal cancer is the fourth most common neoplasia in Europe with 28.2 new cases per 100,000 inhabitants, a cost-effective preventive strategy has been tested in this work by redesigning common porcine meat products (chorizo sausages and cooked ham) consumed by a substantial proportion of the population towards potential colorectal cancer preventive functional foods. In order to test the preventive effect of these inulin-rich meat products against colorectal cancer, an animal model (Rattus norvegicus F344) was used, involving two doses of azoxymethane (10 mg/kg) and two treatments with dextran sodium sulfate (DSS) during a 20-week assay period. Control feed, control sausages, functional sausages (15.7% inulin), control cooked ham and functional cooked ham (10% inulin) were used to feed the corresponding animal cohorts. Then, the animals were sacrificed and their digestive tract tissues were analyzed. The results showed a statistically significant 49% reduction in the number of colon polyps in the functional meat products cohorts with respect to the control meat products animals, as well as an increase in the cecum weight (an indicator of a diet rich in prebiotic fiber), a 51.8% increase in colon propionate production, a 39.1% increase in colon butyrate concentrations, and a reduction in the number of hyperplastic Peyer's patches. Metagenomics studies also demonstrated colon microbiota differences, revealing a significant increase in Bacteroidetes populations in the functional meat products (mainly due to an increase in Bacteroidaceae and Prevotellaceae families, which include prominent propionate producers), together with a reduction in Firmicutes (especially due to lower Lachnospiraceae populations). However, functional meat products showed a remarkable increase in the anti-inflammatory and fiber-fermentative Blautia genus, which belongs to this Lachnospiraceae family. The functional meat products cohorts also presented a reduction in important pro-inflammatory bacterial populations, such as those of the genus Desulfovibrio and Bilophila. These results were corroborated in a genetic animal model of CRC (F344/NSlc-Apc1588/kyo) that produced similar results. Therefore, processed meat products can be redesigned towards functional prebiotic foods of interest as a cost-effective dietary strategy for preventing colorectal cancer in human populations.

Transcriptome and DNA Methylome Analysis in a Mouse Model of Diet-Induced Obesity Predicts Increased Risk of Colorectal Cancer

Colorectal cancer (CRC) tends to occur at older age; however, CRC incidence rates have been rising sharply among young age groups. The increasing prevalence of obesity is recognized as a major risk, yet the mechanistic underpinnings remain poorly understood. Using a diet-induced obesity mouse model, we identified obesity-associated molecular changes in the colonic epithelium of young and aged mice, and we further investigated whether the changes were reversed after weight loss. Transcriptome analysis indicated that obesity-related colonic cellular metabolic switch favoring long-chain fatty acid oxidation happened in young mice, while obesity-associated downregulation of negative feedback regulators of pro-proliferative signaling pathways occurred in older mice. Strikingly, colonic DNA methylome was pre-programmed by obesity at young age, priming for a tumor-prone gene signature after aging. Furthermore, obesity-related changes were substantially preserved after short-term weight loss, but they were largely reversed after long-term weight loss. We provided mechanistic insights into increased CRC risk in obesity.

A requirement for septins and the autophagy receptor p62 in the proliferation of intracellular Shigella

Shigella flexneri, a Gram-negative enteroinvasive pathogen, causes inflammatory destruction of the human intestinal epithelium. During infection of epithelial cells, Shigella escape from the phagosome to the cytosol, where they reroute host cell glycolysis to obtain nutrients for proliferation. Septins, a poorly understood component of the cytoskeleton, can entrap cytosolic Shigella targeted to autophagy in cage-like structures to restrict bacterial proliferation. Although bacterial entrapment by septin caging has been the subject of intense investigation, the role of septins and the autophagy machinery in the proliferation of noncaged Shigella is mostly unknown. Here, we found that intracellular Shigella fail to efficiently proliferate in SEPT2-, SEPT7-, or p62/SQSTM1-depleted cells. Consistent with a failure to proliferate, single cell analysis of bacteria not entrapped in septin cages showed that the number of metabolically active Shigella in septin- or p62-depleted cells is reduced. Targeted metabolomic analysis revealed that host cell glycolysis is dysregulated in septin-depleted cells, suggesting a key role for septins in modulation of glycolysis. Together, these results suggest that septins and the autophagy machinery may regulate metabolic pathways that promote the proliferation of intracellular Shigella not entrapped in septin cages.

Gum odina: an emerging gut modulating approach in colorectal cancer prevention

This study is focused on Gum Odina (GO), a reported prebiotic in our earlier work, and its impact on colorectal cancer (CRC).

Genome-wide analysis of the rat colon reveals proximal-distal differences in histone modifications and proto-oncogene expression

Since disease susceptibility of the intestine exhibits an anatomical bias, we propose that the chromatin landscape, especially the site-specific epigenetic differences in histone modification patterns throughout the colonic longitudinal axis, contributes to the differential incidence of site-specific pathology. To test this hypothesis, we assessed the chromatin structure associated with gene expression profiles in the rat proximal and distal colon by globally correlating chromatin immunoprecipitation next-generation sequencing analysis (ChIP-Seq) with mRNA transcription (RNA-Seq) data. Crypts were isolated from the proximal and distal colonic regions from rats maintained on a semipurified diet, and mRNA gene expression profiles were generated by RNA-Seq. The remaining isolated crypts were formaldehyde-cross-linked and chromatin immunoprecipitated with antibodies against H3K4me3, H3K9me3, and RNA polymerase II. Globally, RNA-Seq results indicate that 9,866 genes were actively expressed, of which 540 genes were differentially expressed between the proximal and distal colon. Gene ontology analysis indicates that crypt location significantly affected both chromatin and transcriptional regulation of genes involved in enterocyte movement, lipid metabolism, lymphatic development, and immune cell trafficking. Gene function analysis indicates that the PI3-kinase signaling pathway was regulated in a site-specific manner, e.g., proto-oncogenes, JUN, FOS, and ATF, were upregulated in the distal colon. Middle and long noncoding RNAs (lncRNAs) were also detected in the colon, including select lncRNAs formerly only detected in the rat nervous system. In summary, distinct combinatorial patterns of histone modifications exist in the proximal versus distal colon. These site-specific differences may explain the differential effects of chemoprotective agents on cell transformation in the ascending (proximal) and descending (distal) colon.

Studies on the chemopreventive effect of carnitine on tumorigenesis in vivo, using two experimental murine models of colon cancer

Carnitine is known for its essential role in intermediary metabolism. In vitro studies suggest that its antioxidant and anti-inflammatory properties are potentially beneficial toward cancer prevention. This study tested effects of carnitine on the development of colon cancer in vivo using 2 murine models: azoxymethane (AOM) treatment as a model of carcinogen-induced colon cancer and a genetically induced model using Apc (Min/+) mice. AOM and Apc (Min/+) mice divided into dietary groups varying in lipid content, with or without carnitine supplementation (0.08%). AOM-exposed mice on a high butterfat diet had significantly increased aberrant crypts (ACF) (9.3 ± 0.88 vs. 6.3 ± 0.65), and macroscopic tumors (3.8 ± 0.95 vs. 2.0 ± 0.25) compared to mice on a control diet. In AOM mice fed the high butterfat diet, carnitine supplementation inhibited ACF (4.9 ± 0.7 vs. 9.3 ± 0.88, P < 0.001), crypt multiciplicity (1.6 ± 0.08 vs. 1.92 ± 0.1, P < 0.01) and tumors (1.5 ± 0.38 vs. 3.8 ± 0.95, P < 0.001). Carnitine supplementation resulted in significantly increased tissue carnitine and acylcarnitine levels. Carnitine inhibited the development of precancerous lesions and macroscopic colonic tumors in AOM-treated mice. However, carnitine did not exert protective effects on intestinal tumors in Apc (Min/+) mice.

Blockade of cholesterol absorption by ezetimibe reveals a complex homeostatic network in enterocytes

Enterocyte cholesterol homeostasis reflects aggregated rates of sterol synthesis, efflux, and uptake from plasma and gut lumen. Cholesterol synthesis and LDL uptake are coordinately regulated by sterol regulatory element-binding proteins (SREBP), whereas sterol efflux is regulated by liver X receptors (LXR). How these processes are coordinately regulated in enterocytes, the site of cholesterol absorption, is not well understood. Here, we treat mice with ezetimibe to investigate the effect of blocking cholesterol absorption on intestinal SREBPs, LXRs, and their effectors. Ezetimibe increased nuclear SREBP-2 8-fold. HMG-CoA reductase (HMGR) and LDL receptor (LDLR) mRNA levels increased less than 3-fold, whereas their protein levels increased 30- and 10-fold, respectively. Expression of inducible degrader of LDLR (IDOL), an LXR-regulated gene that degrades LDLRs, was reduced 50% by ezetimibe. Coadministration of ezetimibe with the LXR agonist T0901317 abolished the reduction in IDOL and prevented the increase in LDLR protein. Ezetimibe-stimulated LDLR expression was independent of proprotein convertase subtilisin/kexin type 9 (PSCK9), a protein that degrades LDLRs. To maintain cholesterol homeostasis in the face of ezetimibe, enterocytes boost LDL uptake by increasing LDLR number, and they boost sterol synthesis by increasing HMGR and other cholesterologenic genes. These studies reveal a hitherto undescribed homeostatic network in enterocytes triggered by blockade of cholesterol absorption.

Butyrate utilization by the colonic mucosa in inflammatory bowel diseases: a transport deficiency

The short-chain fatty acid butyrate, which is mainly produced in the lumen of the large intestine by the fermentation of dietary fibers, plays a major role in the physiology of the colonic mucosa. It is also the major energy source for the colonocyte. Numerous studies have reported that butyrate metabolism is impaired in intestinal inflamed mucosa of patients with inflammatory bowel disease (IBD). The data of butyrate oxidation in normal and inflamed colonic tissues depend on several factors, such as the methodology or the models used or the intensity of inflammation. The putative mechanisms involved in butyrate oxidation impairment may include a defect in beta oxidation, luminal compounds interfering with butyrate metabolism, changes in luminal butyrate concentrations or pH, and a defect in butyrate transport. Recent data show that butyrate deficiency results from the reduction of butyrate uptake by the inflamed mucosa through downregulation of the monocarboxylate transporter MCT1. The concomitant induction of the glucose transporter GLUT1 suggests that inflammation could induce a metabolic switch from butyrate to glucose oxidation. Butyrate transport deficiency is expected to have clinical consequences. Particularly, the reduction of the intracellular availability of butyrate in colonocytes may decrease its protective effects toward cancer in IBD patients.

Synergy between docosahexaenoic acid and butyrate elicits p53-independent apoptosis via mitochondrial Ca(2+) accumulation in colonocytes

Butyrate, a short-chain fatty acid fiber fermentation product, induces colonocyte apoptosis in part via a Fas-mediated (extrinsic) pathway. In previous studies, we demonstrated that docosahexaenoic acid (DHA, 22:6(Delta4,7,10,13,16,19)) enhances the effect of butyrate by increasing mitochondrial lipid oxidation and mitochondrial Ca(2+)-dependent apoptosis in the colon. In this study, we further examined the mechanism of DHA-butyrate synergism in 1) human colon tumor (HCT-116 isogenic p53+/+ vs. p53-/-) cells and 2) primary cultures of rat colonic crypts. Herein, we show that DHA and butyrate promote apoptosis by enhancing mitochondrial Ca(2+) accumulation in both isogenic cell lines. Ca(2+) accumulation and apoptosis were inhibited by blockade of mitochondrial uniporter-mediated Ca(2+) uptake. In addition, Mito-Q, a mitochondria-targeted antioxidant, also blocked apoptosis induced by DHA and butyrate. In complementary experiments, rats were fed diets supplemented with either corn oil (control, contains no DHA) or fish oil (contains DHA). Colonic crypts were isolated and incubated with or without butyrate, after which the mitochondria-to-cytosol Ca(2+) ratio and crypt viability were measured. No significant difference (P > 0.05) in basal mitochondrial Ca(2+) levels was observed between fish oil- or corn oil-fed animals. In contrast, when fish oil was the dietary lipid source, crypts incubated with butyrate exhibited a significant increase (3.6-fold, P < 0.001) in mitochondrial Ca(2+) compared with corn oil plus butyrate treatment. On the basis of these data, we propose that the combination of DHA and butyrate compared with butyrate alone further enhances colonocyte apoptosis by inducing a p53-independent, oxidation-sensitive, mitochondrial Ca(2+) -dependent (intrinsic) pathway.

Tissue-specific attenuation of endogenous DNA I-compounds in rats by carcinogen azoxymethane: possible role of dietary fish oil in colon cancer prevention

I-compounds are bulky covalent DNA modifications that are derived from metabolic intermediates of nutrients. Some I-compounds may play protective roles against cancer, aging, and degenerative diseases. Many carcinogens and tumor promoters significantly reduce I-compound levels gradually during carcinogenesis. Colon cancer is the second leading cause of cancer death in the United States, whereas cancer of the small intestine is relatively rare. Here we have studied levels of I-compounds in DNA of colon and duodenum of male Sprague-Dawley rats treated with azoxymethane. The effects of dietary lipids (fish oil or corn oil) on colon and duodenal DNA I-compounds were also investigated. Rats fed a diet containing fish oil or corn oil were treated with 15 mg/kg azoxymethane. Animals were terminated 0, 6, 9, 12, or 24 hours after injection. I-compound levels were analyzed by the nuclease P1-enhanced (32)P-postlabeling assay. Rats treated with azoxymethane displayed lower levels of I-compounds in colon DNA compared with control groups (0 hour). However, I-compound levels in duodenal DNA were not diminished after azoxymethane treatment. Animals fed a fish oil diet showed higher levels of I-compounds in colonic DNA compared with corn oil groups (mean adduct levels for fish and corn oil groups were 13.35 and 10.69 in 10(9) nucleotides, respectively, P = 0.034). Taken together, these results support claims that fish oil, which contains a high level of omega-3 polyunsaturated fatty acids, may have potent chemopreventive effects on carcinogen-induced colon cancer. The fact that duodenal I-compounds were not diminished by azoxymethane treatment may have been due to the existence of tissue-specific factors protecting against carcinogenesis. In conclusion, our observations show that endogenous DNA adducts may serve not only as sensitive biomarkers in carcinogenesis and cancer prevention studies, but are also helpful to further our understanding of the chemopreventive properties of omega-3 fatty acids and mechanisms of carcinogenesis.

An increase in reactive oxygen species by dietary fish oil coupled with the attenuation of antioxidant defenses by dietary pectin enhances rat colonocyte apoptosis

We showed previously that the dietary combination of fish oil, rich in (n-3) fatty acids, and the fermentable fiber pectin enhances colonocyte apoptosis in a rat model of experimentally induced colon cancer. In this study, we propose that the mechanism by which this dietary combination heightens apoptosis is via modulation of the colonocyte redox environment. Male Sprague-Dawley rats (n = 60) were fed 1 of 2 fats (corn oil or fish oil) and 1 of 2 fibers (cellulose or pectin) for 2 wk before determination of reactive oxygen species (ROS), oxidative DNA damage, antioxidant enzyme activity [superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx)] and apoptosis in isolated colonocytes. Fish oil enhanced ROS, whereas the combination of fish oil and pectin suppressed SOD and CAT and enhanced the SOD/CAT ratio compared with a corn oil and cellulose diet. Despite this modulation to a seemingly prooxidant environment, oxidative DNA damage was inversely related to ROS in the fish oil and pectin diet, and apoptosis was enhanced relative to other diets. Furthermore, apoptosis increased exponentially as ROS increased. These results suggest that the enhancement of apoptosis associated with fish oil and pectin feeding may be due to a modulation of the redox environment that promotes ROS-mediated apoptosis.

Pro-oxidant environment of the colon compared to the small intestine may contribute to greater cancer susceptibility

The colon and small intestine have inherent differences (e.g. redox status) that may explain the variation in cancer occurrence at these two sites. This study examined basal and induced (oxidative challenge) reactive oxygen species (ROS) generation, antioxidant enzyme activity and oxidative DNA damage. Basal ROS and antioxidant enzyme activities in the colon were greater than in the small intestine. During oxidative stress, 8-oxo-deoxyguanosine (8-oxodG) DNA adducts in the colon exceeded levels in the small intestine concomitant with increased ROS. Thus the colon responds to oxidative stress less effectively than the small intestine, possibly contributing to increased cancer incidence at this site.

Microbial degradation products influence colon cancer risk: the butyrate controversy

All dietary fiber, by definition, escapes digestion in the small intestine and thus arrives relatively intact in the large intestine. Its fate in the large intestine depends upon the type of fiber and the colonic microflora. Highly fermentable fibers result in short chain fatty acids including butyrate, which is thought by some to be protective against colon cancer. However, not all studies support a chemopreventive effect for butyrate and the lack of agreement (particularly between in vivo and in vitro studies) on butyrate and colon cancer has been termed the "butyrate paradox." There are a number of reasons for this discrepant effect including differences between the in vitro and in vivo environments, the timing of butyrate administration, the amount of butyrate administered, the source of butyrate (usually dietary fiber) as a potential confounder, and an interaction with dietary fat. Collectively, the studies suggest that the chemopreventive benefits of butyrate depend in part on amount, time of exposure with respect to the tumorigenic process, and the type of fat in the diet.

Dietary n-3 PUFA alter colonocyte mitochondrial membrane composition and function

There is experimental evidence that dietary fish oil, which contains the n-3 fatty acid family, i.e., EPA and DHA, protects against colon tumor development, in part by increasing apoptosis. Since mitochondria can act as central executioners of apoptosis, we hypothesized that EPA and DHA incorporation into colonocyte mitochondrial membranes, owing to their high degree of unsaturation, would enhance susceptibility to damage by reactive oxygen species (ROS) generated via oxidative phosphorylation. This, in turn, would compromise mitochondrial function, thereby initiating apoptosis. To test this hypothesis, colonic crypts were isolated from rats fed either fish oil, purified n-3 fatty acid ethyl esters, or corn oil (control). Dietary lipid source had no effect on colonic mitochondrial phospholipid class mole percentages, although incorporation of EPA and DHA was associated with a reduction in n-6 fatty acids known to enhance colon tumor development, i.e., linoleic acid LNA) and its metabolic product, arachidonic acid (ARA). Select compositional changes in major phospholipid pools were correlated to alterations in mitochondrial function as assessed by confocal microscopy. The mol% sum of LNA plus ARA in cardiolipin was inversely correlated with ROS (P = 0.024). Ethanolamine glycerophospholipid ARA (P = 0.046) and choline glycerophospholipid LNA (P = 0.033) levels were positively correlated to mitochondrial membrane potential. In contrast, ethanolamine glycerophospholipid EPA (P = 0.042) and DHA (P = 0.024) levels were negatively correlated to mitochondrial membrane potential. Additionally, EPA and DHA levels in choline glycerophospholipids (P = 0.026) were positively correlated with caspase 3 activity. These data provide evidence in vivo indicating that dietary EPA and DHA induce compositional changes in colonic mitochondrial membrane phospholipids that facilitate apoptosis.

Substrate utilization by intestinal mucosal tissue strips from patients with inflammatory bowel disease

A primary metabolic disorder may be present in the colonic mucosa of patients with ulcerative colitis. Preserving the epithelium in situ, we evaluated the metabolism of the colonic mucosa of control patients and patients with ulcerative colitis and Crohn's disease. Colonic mucosal strips (approximately 500 mg) were incubated with partially 14C-labeled acetate (C2), butyrate (C4), hexanoate (C6), octanoate (C8), and glucose, and the production of CO2 and ketone bodies was quantitated. Metabolism by small intestinal mucosal strips was also evaluated. Compared with controls, no decrease in either CO2 or ketone body production by colonic strips from patients with either ulcerative colitis or Crohn's disease was observed for any substrate. The CO2 production from each of the C2-C8 fatty acids was the same for colonic and small intestinal strips, whereas CO2 production from glucose was higher in small intestinal strips than in colonic strips. The production of ketone bodies was low in small intestinal strips. A primary metabolic disorder in the colonic mucosa of patients with inflammatory bowel disease was not found.

In vivo absorption of medium-chain fatty acids by the rat colon exceeds that of short-chain fatty acids

BACKGROUND AND AIMS

Short-chain fatty acids (SCFAs) are main fuels of the colonic epithelium, and are avidly absorbed by the colon of animal and man. The current knowledge on colonic metabolism and absorption of medium-chain fatty acids (MCFAs) is limited. In some clinical situations, colonic absorption of high-energy substances could compensate for reduced absorptive capacity because of a shortened or malfunctioning small bowel. We evaluated and compared colonic absorption and metabolism of MCFAs (octanoate, decanoate, and dodecanoate), SCFAs (acetate and butyrate), and long-chain fatty acids (LCFAs) (oleate).

METHODS

Rats were surgically operated on to cannulate a 7-cm segment of proximal colon, isolate the vasculature, and cannulate the right colic vein draining this segment. The lumen was perfused with (14)C-labeled substrates for 100 minutes. Right colic vein blood was analyzed for total (14)C, (14)CO(2), and metabolites by scintillation counting and high-performance liquid chromatography.

RESULTS

The transport from the colonic lumen to mesenteric blood of substrate carbon from MCFAs exceeded by 2-13-fold that of SCFAs and LCFAs. The CO(2) production from the oxidation of MCFAs was as high as or higher than that from SCFAs. CO(2) produced from the LCFA, oleate, was lower than from SCFAs or MCFAs. In addition to CO(2), ketone bodies were major metabolites of SCFAs and MCFAs. Ketogenesis from butyrate and the MCFAs was significantly higher than from acetate and oleate. A substantial proportion (50%-90%) of all substrates was absorbed without being metabolized.

CONCLUSIONS

The colonic epithelium serves to absorb and partially metabolize MCFAs. For patients with a compromised small-bowel function, colonic absorption of MCFAs could represent an important way of receiving calories.

Utilization of short-chain fatty acids by colonic mucosal tissue strips. A new method of assessing colonic mucosal metabolism

BACKGROUND

Previous metabolic studies of the colonic mucosa have been done using isolated cells or small biopsy specimens.

METHODS

A new method for assessing the utilization of short-chain fatty acids in human colonic mucosal tissue strips considerably larger than routine samples was evaluated and compared with the method of isolated colonocytes. Human colonic mucosal strips and isolated human and rat colonocytes were incubated with acetate (C2), butyrate (C4), and hexanoate (C6), and oxidation rates obtained by quantifying the production of CO2.

RESULTS

The wet weight of strips was highly correlated with the production of CO2, and intersample coefficient of variance was <10%. The production of CO2 from the oxidation of C2, C4, and C6 was in the order of C2 > C4 > C6 for both strips and isolated human and rat colonocytes. The production of adenosine triphosphate (ATP) in strips and isolated human and rat colonocytes was in the order of C2 < or = C4 < or = C6. The Km value for the oxidation of butyrate to CO2 in strips (1.8 mmol/l) was several times higher than previously reported for isolated human and rat colonocytes (0.1-0.3 mmol/l).

CONCLUSIONS

This new method is highly reproducible and able to assess the metabolic activity of the colonic mucosa. The high Km value of butyrate oxidation in mucosal strips seems to reflect the in vivo Km value of colonocytes and shows the importance of a preserved anatomic structure in metabolic studies of the colonic epithelium. The low Km value for isolated colonocytes probably reflects the intracellular ability to oxidize butyrate. We propose that both isolated colonocytes and mucosal strips be used in studies of colonic mucosal metabolism. This method is relevant in disease states of the colon in which a disagreement prevails as to the ability to oxidize butyrate by colonocytes, such as in ulcerative colitis.