Interactive effects of dietary resistant starch and fish oil on short-chain fatty acid production and agonist-induced contractility in ileum of young rats

Triple null mutations in starch synthase SSIIa gene homoeologs lead to high amylose and resistant starch in hexaploid wheat

BACKGROUND

Lack of nutritionally appropriate foods is one of the leading causes of obesity in the US and worldwide. Wheat (Triticum aestivum) provides 20% of the calories consumed daily across the globe. The nutrients in the wheat grain come primarily from the starch composed of amylose and amylopectin. Resistant starch content, which is known to have significant human health benefits, can be increased by modifying starch synthesis pathways. Starch synthase enzyme SSIIa, also known as starch granule protein isoform-1 (SGP-1), is integral to the biosynthesis of the branched and readily digestible glucose polymer amylopectin. The goal of this work was to develop a triple null mutant genotype for SSIIa locus in the elite hard red winter wheat variety 'Jagger' and evaluate the effect of the knock-out mutations on resistant starch content in grains with respect to wild type.

RESULTS

Knock-out mutations in SSIIa in the three genomes of wheat variety 'Jagger' were identified using TILLING. Subsequently, these loss-of function mutations on A, B, and D genomes were combined by crossing to generate a triple knockout mutant genotype Jag-ssiia-∆ABD. The Jag-ssiia-∆ABD had an amylose content of 35.70% compared to 31.15% in Jagger, leading to ~ 118% increase in resistant starch in the Jag-ssiia-∆ABD genotype of Jagger wheat. The single individual genome mutations also had various effects on starch composition.

CONCLUSIONS

Our full null Jag-ssiia-∆ABD mutant showed a significant increase in RS without the shriveled grain phenotype seen in other ssiia knockouts in elite wheat cultivars. Moreover, this study shows the potential for developing nutritionally improved foods in a non-GM approach. Since all the mutants have been developed in an elite wheat cultivar, their adoption in production and supply will be feasible in future.

Effects of Antihypertensive Agents on Intestinal Contractility in the Spontaneously Hypertensive Rat: Angiotensin Receptor System Downregulation by Losartan

Hypertension is an inflammatory condition controlled by the renin angiotensin system and is linked to kidney disease, diabetes mellitus, and recently to dysfunction of the gut. The aim of this study was to determine what effect antihypertensive drug treatments may have on intestinal function of the spontaneously hypertensive rat (SHR). In the first experiment, SHRs were treated with enalapril, hydralazine, or with no treatment as a control. In the second experiment, SHRs were treated with losartan or with no treatment as a control. All drug treatments led to significant lowering of blood pressure after 16 weeks. At termination, intact tissue sections of the ileum and colon were induced to contract ex vivo by KCl; electrical stimulation; and agonists carbachol, angiotensin II, and prostaglandin E2 (PGE2). There were no differences in ileal or colonic contractility due to hydralazine or enalapril compared with no-treatment SHR control. However, for the ileum, the losartan group responded significantly more to KCl and carbachol while responding less to angiotensin II, with no difference for PGE2 compared with the no-treatment SHR control. In contrast, the colon responded similarly to KCl, electrical stimulation, and PGE2 but responded significantly less to angiotensin II. These results demonstrate that the ileum responds differently (with KCl and carbachol as agonists) to the colon after losartan treatment, whereas there is a reduced contractile response in both the ileum and colon following losartan treatment. Although there are few well documented major contraindications for angiotensin receptor blockers, the modulation of gut contractility by losartan may have wider implications for bowel health.

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

BACKGROUND AND AIM

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

RS and other fiber components could influence colorectal health through modulation of stool transit time via effects on muscular contractility.

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.

Site specific delivery of microencapsulated fish oil to the gastrointestinal tract of the rat

The aim of this study was to design food grade matrices to deliver microencapsulated fish oil to the large bowel of the rat where the potential exists to retard inflammation and cancer development. Digestion in simulated gastric fluid and intestinal fluid demonstrated that only 4-6% of oil was released from the following dried emulsion formulations: 50% fish oil encapsulated in heated casein-glucose-dried glucose syrup (1:1:1) (Cas-Glu-DGS-50); 25% fish oil in casein-modified resistant starch (Hylon VII) (1:1) (Cas-Hylon-25); or 25% fish oil in Cas-Glu-Hylon (1:1:1) (Cas-Glu-Hylon-25). A short-term gavage study (0-12 h) with fish oil and Cas-Glu-DGS-50 demonstrated the appearance of fish oil long chain (LC) n-3 polyunsaturated fatty acids (PUFA) into the plasma indicating specific small intestinal absorption with little LC n-3 PUFA reaching the large bowel. In a 2-week-long term, daily gavage study, the bioavailability of fish oil and fish oil in Cas-Glu-DGS-50 or Cas-Hylon-25 demonstrated that fish oil and Cas-Glu-DGS-50 LC n-3 PUFA were incorporated into the tissue of the small intestine and colon, whereas Cas-Hylon-25 was resistant to degradation in the small intestine. The use of modified Hylon VII for targeted colonic delivery was confirmed in the final short-term gavage study (0-14 h) using Cas-Glu-Hylon-25 with [(14)C]-trilinolenin as a marker incorporated into the microcapsules, where up to 60% of the labeled oil reached the large bowel. Depending on the microencapsulating matrix employed, fish oil can be delivered selectively to the small intestine or to a high degree to the large bowel.

Interactive and individual effects of dietary non-digestible carbohydrates and oils on DNA damage, SCFA and bacteria in the large bowel of rats

Dietary non-digestible carbohydrates (NDC) play an important role in large-bowel health and one form of NDC, resistant starch (RS), can promote low levels of DNA damage and other markers of colonic health. The objective of the present study was to determine whether the ability of dietary RS or other NDC to influence colonic health, particularly DNA damage, is dependent on the type of dietary oil. We compared the effects of diets containing 10 % of NDC from cellulose, wheat bran, high-amylose maize starch (HAS, a rich source of RS type 2) or a retrograded HAS (RHAS, a rich source of RS type 3) on DNA damage, SCFA production and bacterial changes in the large bowel of rats. Each carbohydrate source was combined with 10 % fish oil (FO) or Sunola oil (SO; rich in oleic acid). There was a significant interaction between NDC and oil treatments on single-strand DNA breaks in colonocytes isolated from the colon. The damage in rats consuming RHAS was greater for FO consumption than for SO consumption. There was a significant interaction between NDC and oils on caecum weights and treatment effects of NDC and oils were observed for the weights and lengths of other gut tissues. Significant differences were found in colonic SCFA pools and caecal numbers of lactobacilli, bifidobacteria, Escherichia coli and Bacteroides fragilis with the various NDC and oil treatments. The present results demonstrate that the effects of NDC and oils, particularly on colonic DNA damage, can depend on how they are combined within the diet.

Dietary fish oil dose-response effects on ileal phospholipid fatty acids and contractility

We have reported that dietary fish oil (FO) leads to the incorporation of long-chain n-3 PUFA into the gut tissue of small animal models, affecting contractility, particularly of rat ileum. This study examined the FO dose response for the incorporation of n-3 PUFA into ileal tissue and how this correlated with in vitro contractility. Groups of ten to twelve 13-wk-old Wistar-Kyoto rats were fed 0, 1, 2.5, and 5% FO-supplemented diets balanced with sunflower seed oil for 4 wk, after which ileal total phospholipid FA were determined and in vitro contractility assessed. For the total phospholipid fraction, increasing the dietary FO levels led to a significant increase first evident at 1% FO, with a stepwise, nonsaturating six-fold increase in n-3 PUFA as EPA (20:5n-3), DPA (docosapentaenoic acid, 22:5n-3), and DHA, but mainly as DHA (22:6n-3), replacing the n-6 PUFA linoleic acid (18:2n-6) and arachidonic acid (20:4n-6) over the dosage range. There was no difference in KCl-induced depolarization-driven contractility. However, a significant increase in receptor-dependent maximal contractility occurred at 1% FO for carbachol and at 2.5% FO for prostaglandin E2, with a concomitant increase in sensitivity for prostaglandin E2 at 2.5 and 5% FO. These results demonstrate that significant increases in ileal membrane n-3 PUFA occurred at relatively low doses of dietary FO, with differential receptor-dependent increases in contractility observed for muscarinic and prostanoid agonists.