Low-amylose Maize Starch Research Articles

Dietary butyrylated high-amylose starch reduces azoxymethane-induced colonic O6-methylguanine adducts in rats as measured by immunohistochemistry and high-pressure liquid chromatography

O6-methyl guanine (O6MeG) adducts are major toxic, promutagenic, and procarcinogenic adducts involved in colorectal carcinogenesis. Resistant starch and its colonic metabolite butyrate are known to protect against oncogenesis in the colon. In this study, we hypothesized that a dietary intervention that specifically delivers butyrate to the large bowel (notably butyrylated high-amylose maize starch [HAMSB]) would reduce colonic levels of O6MeG in rats shortly after exposure to the deoxyribonucleic acid (DNA) alkylating agent azoxymethane (AOM) when compared with a low-amylose maize starch (LAMS). A further objective was to validate an immunohistochemistry (IHC) method for quantifying O6MeG against a high-performance liquid chromatography method using fluorescence and diode array detection. Rats were fed either LAMS or HAMSB diets for 4 weeks followed by a single injection of AOM or saline and killed 6 hours later. After AOM exposure, both IHC and high-performance liquid chromatography method using fluorescence and diode array detection measured a substantially increased quantity of DNA adducts in the colon (P<.001). Both techniques demonstrated equally that consumption of HAMSB provided a protective effect by reducing colonic adduct load compared with the LAMS diet (P<.05). In addition, IHC allowed visualization of the O6MeG distribution, where adduct load was reduced in the lower third of the crypt compartment in HAMSB-fed rats (P=.036). The apoptotic response to AOM was higher in the HAMSB-fed rats (P=.002). In conclusion, the reduction in O6MeG levels and enhancement of the apoptotic response to DNA damage in the colonic epithelium through consumption of HAMSB provide mechanistic insights into how HAMSB protects against colorectal tumorigenesis.

Resistant starch alters colonic contractility and expression of related genes in rats fed a Western diet.

Dietary fiber shortens gut transit time, but data on the effects of fiber components (including resistant starch, RS) on intestinal contractility are limited. We have examined RS effects in male Sprague-Dawley rats fed either a high-amylose maize starch (HAMS) or a wholemeal made from high-amylose wheat (HAW) on ileal and colonic contractility ex vivo and expression of genes associated with smooth muscle contractility. Rats were fed diets containing 19 % fat, 20 % protein, and either low-amylose maize starch (LAMS), HAMS, wholemeal low-amylose wheat (LAW) or HAW for 11 week. Isolated ileal and proximal colonic sections were induced to contract electrically, or by receptor-independent (KCl) or receptor-dependent agents. Colonic gene expression was assessed using an Affymetrix microarray. Ileal contractility was unaffected by treatment. Maximal proximal colonic contractility induced electrically or by angiotensin II or carbachol was lower for rats fed HAMS and LAW relative to those fed LAMS (P < 0.05). The colonic expression of genes, including cholinergic receptors (Chrm2, Chrm3), serotonin receptors (Htr5a, Htr7), a protease-activated receptor (F2r), a prokineticin receptor (Prokr1), prokineticin (Prok1), and nitric oxide synthase 2 (Nos2), was altered by dietary HAMS relative to LAMS (P < 0.05). HAW did not significantly affect these genes or colonic contractility relative to effects of LAMS. RS and other fiber components could influence colorectal health through modulation of stool transit time via effects on muscular contractility.

Resistant Starches Protect against Colonic DNA Damage and Alter Microbiota and Gene Expression in Rats Fed a Western Diet1–3

Resistant starch (RS), fed as high amylose maize starch (HAMS) or butyrylated HAMS (HAMSB), opposes dietary protein-induced colonocyte DNA damage in rats. In this study, rats were fed Western-type diets moderate in fat (19%) and protein (20%) containing digestible starches [low amylose maize starch (LAMS) or low amylose whole wheat (LAW)] or RS [HAMS, HAMSB, or a whole high amylose wheat (HAW) generated by RNA interference] for 11 wk (n = 10/group). A control diet included 7% fat, 13% protein, and LAMS. Colonocyte DNA single-strand breaks (SSB) were significantly higher (by 70%) in rats fed the Western diet containing LAMS relative to controls. Dietary HAW, HAMS, and HAMSB opposed this effect while raising digesta levels of SCFA and lowering ammonia and phenol levels. SSB correlated inversely with total large bowel SCFA, including colonic butyrate concentration (R2 = 0.40; P = 0.009), and positively with colonic ammonia concentration (R2 = 0.40; P = 0.014). Analysis of gut microbiota populations using a phylogenetic microarray revealed profiles that fell into 3 distinct groups: control and LAMS; HAMS and HAMSB; and LAW and HAW. The expression of colonic genes associated with the maintenance of genomic integrity (notably Mdm2, Top1, Msh3, Ung, Rere, Cebpa, Gmnn, and Parg) was altered and varied with RS source. HAW is as effective as HAMS and HAMSB in opposing diet-induced colonic DNA damage in rats, but their effects on the large bowel microbiota and colonocyte gene expression differ, possibly due to the presence of other fiber components in HAW.

Butyrate delivered by butyrylated starch increases distal colonic epithelial apoptosis in carcinogen-treated rats

Animal studies show that increasing large bowel butyrate concentration through ingestion of butyrylated or resistant starches opposes carcinogen-induced tumorigenesis, which is consistent with population data linking greater fiber consumption with lowered colorectal cancer (CRC) risk. Butyrate has been shown to regulate the apoptotic response to DNA damage. This study examined the impact of increasing large bowel butyrate concentration by dietary butyrylated starch on the colonic epithelium of rats treated with the genotoxic carcinogen azoxymethane (AOM). Four groups of 10 male rats were fed AIN-93G based-diets containing either low amylose maize starch (LAMS), LAMS with 3% tributyrin, 10% high amylose maize starch (HAMS) or 10% butyrylated HAMS (HAMSB). HAMS and HAMSB starches were cooked by heating in water. After 4 weeks, rats were injected once with AOM and killed 6 h later. Rates of apoptosis and proliferation were measured in colonic epithelium. Short-chain fatty acid concentrations in large bowel digesta and hepatic portal venous plasma were higher in HAMSB than all other groups. Apoptotic rates in the distal colon were increased by HAMSB and correlated with luminal butyrate concentrations but cellular proliferation rates were unaffected by diet. The increase in apoptosis was most marked in the base and proliferative zone of the crypt. Regulation of luminal butyrate using HAMSB increases the rates of apoptotic deletion of DNA-damaged colonocytes. We propose this pro-apoptotic function of butyrate plays a major role reducing tumour formation in the AOM-treated rat and that these data support a potential protective role of butyrate in CRC.

Dietary resistant and butyrylated starches have different effects on the faecal bacterial flora of azoxymethane-treated rats

Epidemiological studies have suggested that dietary fibre lowers the risk of colorectal cancer, which may be due to increased butyrate production from colonic fermentation of a type of fibre, resistant starch (RS). The present study investigated the effects of dietary RS and butyrylated RS on the faecal microbiota of rats treated with azoxymethane. A total of four groups of nine rats were fed diets containing either standard maize starch (low-amylose maize starch (LAMS), low RS), LAMS with 3 % tributyrin (LAMST), cooked 10 % high-amylose maize starch (HAMS, high RS) or cooked 10 % butyrylated HAMS (HAMSB). Faecal samples were examined by denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA gene fragments. Multivariate analysis demonstrated no differences between faecal microbiota before treatment but revealed differences in DGGE patterns between diet groups, with the exception of the two low-RS groups (LAMS and LAMST). Subsequent analysis identified eleven DGGE bands contributing significantly to the differentiation between diets. These phylotypes belonged to Clostridiales (five), Lactobacillus (one) and Bacteroidetes (five) lineages. Rats fed HAMS had increased concentration of propionate in their distal colonic digesta and developed faecal populations containing Ruminococcus bromii-like bacteria. HAMSB increased propionate and butyrate concentrations in distal colonic digesta and was associated with the appearance of two non-butyrate-producing bacteria, Lactobacillus gasseri and Parabacteroides distasonis. In conclusion, supplementation with specific dietary RS leads to changes in faecal microbiota profiles that may be associated with improved bowel health.

Butyrylated starch increases large bowel butyrate levels and lowers colonic smooth muscle contractility in rats

The short-chain fatty acids acetate, propionate, and butyrate are produced by colonic bacterial fermentation of carbohydrates. Butyrate is important in the regulation of the colonocyte cell cycle and gut motility and may also reduce the risk of large bowel cancer. We have shown that dietary butyrylated starch can deliver butyrate to the large bowel in a sustained manner. We hypothesized that ingestion of butyrylated starch increases large bowel butyrate levels and decreases colonic contractility. Groups of male Sprague-Dawley rats (n = 8) were fed AIN-93G-based diet containing a highly digestible low-amylose maize starch (LAMS) control or 5% or 10% butyrylated LAMS (LAMSB) for 10 days. We found that cecal but not colonic tissue weight as well as cecal and distal colonic digesta weights and fecal output were higher in LAMSB fed rats. Butyrylated LAMS lowered digesta pH throughout the large bowel. Cecal, proximal, and distal colonic butyrate pools and portal venous butyrate concentrations were higher in rats fed LAMSB. Electrically stimulated and receptor-dependent carbachol and prostaglandin E(2)-induced isotonic contractions were lower in isolated intact sections of proximal colon (P < .05) but not the terminal ileum after 10% LAMSB ingestion. These results demonstrated that elevation of butyrate levels in the large bowel of the rat correlated with reduction of contractile activity of the colonic musculature, which may assist in the reabsorption of water and minerals.

Changes in starch physical characteristics following digestion of foods in the human small intestine

Factors controlling the concentration of resistant starch (RS) in foods are of considerable interest on account of the potential for this type of fibre to deliver health benefits to consumers. The present study was aimed at establishing changes in starch granule morphology as a result of human small-intestinal digestion. Volunteers with ileostomy consumed six selected foods: breakfast cereal (muesli), white bread, oven-baked French fries, canned mixed beans and a custard containing either a low-amylose maize starch (LAMS) or a high-amylose maize starch (HAMS). Analysis showed that digesta total RS (as a fraction of ingested starch) was: muesli, 8.9 %; bread, 4.8 %; fries, 4.2 %; bean mix, 35.9 %; LAMS custard, 4.0 %; HAMS custard, 29.1 %. Chromatographic analysis showed that undigested food contained three major starch fractions. These had average molecular weights (MW) of 43,500 kDa, 420 kDa and 8.5 kDa and were rich in amylopectin, higher-MW amylose and low-MW amylose, respectively. The low-MW amylose fraction became enriched preferentially in the stomal effluent while the medium-MW starch fraction showed the greatest loss. Fourier transform IR spectroscopy showed that absorbance at 1022 per cm decreased after digestion while the absorbance band at 1047 per cm became greater. Such changes have been suggested to indicate shifts from less ordered to more ordered granule structures. Further analysis of amylose composition by scanning iodine spectra indicated that the MW of amylose in ileal digesta was lower than that of undigested amylose. It appears that high-MW amylose is preferentially digested and that MW, rather than amylose content alone, is associated with resistance of starch to digestion in the upper gut of humans.

Comparative Effects of a High-Amylose Starch and a Fructooligosaccharide on Fecal Bifidobacteria Numbers and Short-Chain Fatty Acids in Pigs Fed Bifidobacterium animalis

Pigs were fed a freeze-dried probiotic (Bifidobacterium animalis CSCC 1941) plus a high-amylose maize starch (HAMS) and a fructooligosaccharide (FOS) separately or together. Fecal output and total and individual major short-chain fatty acid (SCFA) concentrations and excretion were higher and pH was lower with HAMS than with FOS relative to when they were fed a low-amylose maize starch (LAMS; control). Fecal bifidobacteria numbers and total excretion were equally higher during feeding of FOS or HAMS and highest with HAMS + FOS. When probiotic supplementation was stopped, bifidobacteria numbers declined rapidly when they were fed LAMS, more slowly with FOS or HAMS, and were maintained with HAMS + FOS. The data confirm that both HAMS and FOS are prebiotics and suggest that they act through different mechanisms and that they are most effective in combination. However only HAMS raises fecal SCFA.

Excretion of starch and esterified short-chain fatty acids by ileostomy subjects after the ingestion of acylated starches

Background: Short-chain fatty acids (SCFAs) have a role in maintaining bowel health and can assist in the prevention and treatment of colonic disease. The ability of acylated starches to deliver SCFAs to the large bowel has been shown in animal studies but has not been established in humans.Objective: The aim was to determine whether cooked, highly acylated starches were resistant to small intestinal digestion in ileostomy volunteers.Design: Volunteers consumed single doses of custards containing 20 g cooked acetylated, propionylated, or butyrylated high-amylose maize starches (HAMSA, HAMSP, and HAMSB, respectively) on each collection day. The amounts of starch and of esterified SCFAs ingested and subsequently excreted in the stoma effluent were measured. Custards containing unacylated high-amylose maize starch (Hylon VII, HAMS) and low-amylose maize starch (3401C, LAMS) were consumed as controls.Results: Between 73% and 76% of the esterified SCFAs survived small intestinal digestion, which showed the potential of acylated starches to deliver specific SCFAs to the large bowel. The resistance of starches to small intestinal digestion as measured by ileal excretion was significantly greater for HAMSA, HAMSP, HAMSB, and HAMS than for LAMS (P < 0.001). The concentration of acetate in stoma digesta was higher than expected in all groups; this additional acid may have been derived from endogenous sources.Conclusions: Acylated starches are a potentially effective method of delivering significant quantities of specific SCFAs to the colon in humans. These products have potential application in the treatment and prevention of bowel disorders amenable to modulation by SCFAs.