Skip Navigation


Carcinogenesis Advance Access originally published online on December 13, 2006
Carcinogenesis 2007 28(2):240-245; doi:10.1093/carcin/bgl245
This Article
Right arrow Abstract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow All Versions of this Article:
28/2/240    most recent
bgl245v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrow Search for citing articles in:
ISI Web of Science (5)
Right arrowRequest Permissions
Google Scholar
Right arrow Articles by Le Leu, R. K.
Right arrow Articles by Young, G. P.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Le Leu, R. K.
Right arrow Articles by Young, G. P.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?

© The Author 2006. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Effect of dietary resistant starch and protein on colonic fermentation and intestinal tumourigenesis in rats

Richard K. Le Leu*, Ian L. Brown1, Ying Hu, Tatsuya Morita3, Adrian Esterman2 and Graeme P. Young

Department of Medicine, Flinders University of South Australia Bedford Park, South Australia 5042, Australia
1 National Starch and Chemical Company Bridgewater, NJ 08807, USA
2 School of Nursing and Midwifery, University of South Australia South Australia 5000, Australia
3 Department of Applied Biological Chemistry, Faculty of Agriculture, Shizuoka University Shizuoka 422-8529, Japan

*To whom correspondence should be addressed. Tel: +61 88204 5170; Fax: +61 88204 3943; Email: richard.leleu{at}flinders.edu.au


   Abstract
Top
 Abstract
Introduction
 Materials and methods
 Results
 Discussion
 References
 
Protein as well as starch is fermented in the colon, but the interaction between protein and starch fermentation and the impact on colonic oncogenesis is unknown. High-protein diets increase delivery of protein to the colon and might promote oncogenesis through generation of toxic products. We investigated the interaction of resistant starch (RS) with digestion-resistant potato protein (PP) on colonic fermentation events and their relationship to intestinal tumourigenesis. Male Sprague–Dawley rats were fed an AIN-76A-based diet for 4 weeks and intestinal neoplasms were induced by azoxymethane. Experimental diets included the following: no added RS or PP, 10% high amylose maize starch (source of RS) replacing digestible starch, 15% PP replacing casein and 10% high amylose maize starch + 15% PP. Rats were maintained on diets until killed at 30 weeks. Feeding RS significantly increased short-chain fatty acid (SCFA) levels (P < 0.001) in the caecum and colon. Importantly, butyrate concentration was significantly increased in the distal colon with RS (P < 0.001). Feeding PP increased protein fermentation products, but this effect was reduced by adding RS to the diet. Intestinal neoplasms and colorectal adenocarcinomas were reduced by feeding RS (P < 0.01) regardless of whether PP was fed, whereas PP alone increased the incidence and number of small intestinal neoplasms including the adenocarcinomas (P < 0.01). In conclusion, RS altered the colonic luminal environment by increasing the concentration of SCFAs including butyrate and lowering production of potentially toxic protein fermentation products. These effects of RS not only protected against intestinal tumourigenesis but also ameliorated the tumour-enhancing effects of feeding indigestible protein.

Abbreviations: BCFA, branched-chain fatty acid; CRC, colorectal cancer; HAS, high amylose cornstarch; PP, digestion-resistant potato protein; RS, resistant starch; SCFA, short-chain fatty acid


   Introduction
Top
 Abstract
 Introduction
Materials and methods
 Results
 Discussion
 References
 
Colorectal cancer (CRC) is one of the most commonly diagnosed cancers in affluent countries and is a leading cause of cancer-related mortality in the USA and Australia (1,2). Accumulating evidence from epidemiological and experimental studies suggest that diet is an important environmental factor in the aetiology of CRC. The typical Western diet contains high concentrations of protein including red or processed meat, animal fats, alcohol and refined carbohydrates, all of which are associated with elevated risks of CRC (3,4). On the contrary, there is low consumption of fruits, vegetables, starches and whole grains that have been suggested to be protective against CRC (5–7).

Resistant starch (RS) is a component of dietary starch that is not absorbed in the small intestine of healthy individuals and thus reaches the colon undigested, similar to dietary fibre. RS can be classified into four main types, of which the first three may occur in a typical human diet (8). RS1 includes physically entrapped starch within whole plant cells and food matrices (e.g. coarsely milled grain). RS2 consists of native starch granules that are highly resistant to digestion by {alpha}-amylases (e.g. green banana, high amylose maize starch). RS3 comprises retrograded starches, formed when starchy foods are cooked and cooled. RS4 comprises chemically modified starches (e.g. esterified starches) where the modification interferes with the amylolytic activity of digestive enzymes (RS4 are used in the food industry). RS is a potential source of fermentable substrate for anaerobic bacteria resulting in the production of gases (CO2, CH4, and H2) and short-chain fatty acids (SCFAs) (9). The SCFA butyrate has generated the most interest as it may be protective against CRC (10,11). Butyrate is the primary energy source for colonic epithelium (12), and it also inhibits the growth of cancer cells in vitro and forces a more normal differentiated phenotype (10). In addition, it is a potent pro-apoptotic agent (13) that might aid removal of cells with damaged DNA. Colonic production of butyrate by fermentation is associated with reduced tumour mass in an animal model, provided that fermentation is active in the distal colon (14). Consumption of a high-RS diet has been shown to increase fermentation products (particularly butyrate) and this has been suggested as a means of protection in South African blacks (15). Furthermore, population studies suggest that CRC risk can be lowered by increased RS consumption possibly through increased butyrate production (7). Fermentation may be important in prevention of CRC via other effects including altering gut microbiota toward a more beneficial composition microflora (16,17).

Previous studies in our laboratory have shown that RS can facilitate the acute apoptotic response to a genotoxic carcinogen in the rat colon (18). RS might regulate mutational load in the colon and eliminate DNA-damaged cells that might otherwise progress to malignancy, thereby exerting a protective effect at the early stages in the onset of cancer (19). RS was also shown to influence fermentation parameters such as lowering pH, increasing SCFA production including butyrate, while also stimulating desirable bacteria within the colon (20). RS may also protect through broader mechanisms associated with fibre such as faecal bulking, decreased transit time and altered pH (9). All these effects might mediate protection.

Protein and amino acids also pass into the colon where they are available for bacterial fermentation. Around 13 g of protein material may enter the colon each day (21,22). Dietary sources make up at least 50% of this protein material; however, the amount may vary due to protein intake and the physical form of the food (21,23). Other sources of protein in the colon include bacterial secretions such as enzymes, sloughed-off epithelial cells, bacterial lysis products and mucins (22). Evidence from ileostomy studies suggests that it is the amount of protein in the diet rather than its source that determines the amount reaching the colon (23). Protein fermentation products that may be produced in the colon include branched-chain fatty acids (BCFAs) (isobutyric and isovaleric acids) (24) and potentially toxic substances such as ammonia, amines, N-nitroso compounds, phenols, thiols and indoles (25). Production of the latter are increased after supplementary dietary protein in humans (26,27). Experimental evidence is accumulating from animal models and in vitro data, which shows that dietary proteins can influence cancer expression (28,29). Recently, animal studies have shown that increased dietary protein consumption can cause increased colonic DNA damage, as measured by the comet assay, and thinning of the colonic mucus barrier, whereas with inclusion of RS into the diet, these damaging effects are attenuated (30,31). Furthermore, SCFA production, particularly butyrate, may be enhanced if indigestible carbohydrates like RS are combined with dietary protein sources like rice, soy or potato (32).

This study was designed to investigate the interaction of RS2 and/or undigested dietary protein on colonic luminal environment and relationship of this to intestinal cancer formation in Sprague–Dawley rats. Potato protein was chosen as the dietary protein source because of its indigestibility so as to ensure that more protein reaches the colon. In addition, we determined the effects of these diets on bacterial ß-glucuronidase activity. ß-Glucuronidase is an enzyme that is believed to be largely responsible for hydrolysis of glucuronide conjugates in the intestine and is thought to play an important role in the generation of toxic and carcinogenic substances (33).


   Materials and methods
Top
 Abstract
 Introduction
 Materials and methods
Results
 Discussion
 References
 
Animals and diets
A total of 120 male Sprague–Dawley rats, 5 weeks of age, were obtained from the Animal Resource Centre, Perth, Western Australia. Animals were divided randomly into four experimental groups and housed three per plastic cage in an animal holding room under controlled conditions of 22 ± 2°C (SD), 80 ± 10% humidity and 12 h light–dark cycle. Animals were given free access to water and weighed weekly throughout the study.

The diets were modified forms of the AIN-76a standard for purified diets for rats and mice (34). Each group of animals was fed an experimental diet based on the control diet. The control diet contained 200 g casein, 461.5 g cornstarch, 109.5 g sugar and 180 g sunflower oil/kg of diet. Choline, methionine, minerals and vitamins were added as described previously (20). The experimental diets varied in protein type and density between treatment groups. The first group ‘control’ consumed a diet containing no added fibre or RS. The second group ‘RS’ had a diet that contained 100 g/kg raw high amylose cornstarch (HAS). The third group ‘digestion-resistant potato protein’ (PP) had a diet that contained potato protein 150 g/kg diet. The fourth group’s diet ‘PP + RS’ contained 150 g/kg potato protein and 100 g/kg raw HAS. High amylose cornstarch (Hi-maize® 958), an RS2, was used as the source of RS and was supplied by the National Starch and Chemical Company, Bridgewater, NJ. High amylose cornstarch was added to the diets so as to displace an equal amount of digestible cornstarch. Potato protein was supplied by Hokuren Co. (Hokkaido, Japan) and was prepared from potato juice by steam coagulation at pH 5.0–5.5 as described previously (32). The chemical and amino acid compositions of this protein have been reported previously (35). The protein content of the potato protein isolate was 60.7% (as is basis) as measured by the Kjeldahl's method using 6.25 as the conversion factor. The true digestibility of potato protein was determined by the method of Njaa (36) under isonitrogenous condition in rats by using the following equation: true digestibility = [nitrogen intake – (faecal nitrogen excretion – faecal nitogen excretion in the protein-free diet)]/nitrogen intake x 100 and was found to be 84.0 ± 0.7% (SD) and was significantly lower compared with casein 95.0 ± 0.3% (SD). The potato protein was added to the PP diets at the expense of an equal amount of casein.

Experimental procedure
After 4 weeks on experimental diets, each rat received s.c. injections of azoxymethane (15 mg/kg body wt) (Sigma Chemical Co., St Louis, MO) once weekly for 2 weeks and then maintained on their dietary regimen until killed at 30 weeks. The rats in each group were weighed once weekly. In the fourth week of the experiment, 15 rats from each treatment group were placed in metabolic cages to measure faecal output, food intake and collect urine. Fresh faecal samples were collected from each rat and diluted in three volumes of internal standard solution (heptanoic acid, 1.68 mmol/l) and stored at –20°C for later analysis of SCFA concentrations on the last 3 days of the experimental period by gently handling the rats until they produced a faecal sample.

As scheduled, all rats were killed by CO2 asphyxiation. After laparotomy, the entire stomach, small intestine and large intestine were resected. They were opened longitudinally and the caecal and colonic contents were collected for SCFA measurements. Distal and proximal colonic contents and caecal digesta were collected and diluted in three volumes of internal standard solution (heptanoic acid, 1.68 mmol/l) and stored at –20°C for later analysis of SCFA concentrations. The distal portion was collected from the lower one-third of colon whereas the proximal portion was taken from ‘herringbone’ area. The small intestine and colon were examined for intestinal tumours, and the location and number of tumours were assessed with a dissection microscope (magnification x20) and recorded.

The Flinders University of South Australia Animals Welfare Committee approved all experimental procedures. The Committee operates in accordance with the Australian Code of Practice for the Care and Use of Animals for Scientific Purposes.

Intestinal tumours
Using a light microscope (magnification x40), the small intestine and colon were scored for tumour number and location by an independent observer who was unaware of dietary treatment as described previously (37). Tumours were removed and embedded in paraffin (5 µm) for histopathological analysis. All tumours were examined histologically and evaluated by an independent observer based on the criteria of Pozharisski (38). Adenoma was characterized by expansion of the mucosa layer, reduction in goblet cell number, cellular dysplasia and moderate loss of mucosal architecture by glandular growth and lack of invasion through the basement membrane. Adenocarcinoma was identified from the following characteristics: typical cytological change, prominent cellular atypia, loss of cell polarity, marked distortion of glandular architecture and invasion (38).

SCFA analysis
SCFA including acetate, propionate and butyrate, as well as BCFA isobutyrate, isovaleric and valeric acids, were determined in the caecal, colon contents and faeces of rats as described previously (20).

Phenol/p-cresol analysis
Phenol and p-cresol in urine were determined by previously described methods (39).

ß-Glucuronidase
ß-Glucuronidase in caecal content was assayed according to the method of Goldin et al. (40) as modified by Jenab et al. (41) but with 0.3 mol trichloroacetic acid/l excluded in the final step, before phenolphthalein colour development and spectrophotometric assay. The results are expressed as phenolphthalein released (mg) per caecal content (g) per hour.

Statistical analysis
Data are presented as the mean ± SEM for each treatment group. The effect of RS and protein on tumour data and fermentation outcomes were analyzed by creating dummy variables for RS, PP and their interaction, and entering them into an appropriate generalized linear model. If the interaction term was not statistically significant (P ≤ 0.05), the regression model was rerun omitting the interaction effect to assess the significance of the two main factors. A Gaussian generalized linear model was used for continuous data, Poisson for neoplasm counts and log binomial for incidence. The incidence of rats with tumours was chosen over multiplicity (number of tumours per rat) because the goal in present study is protection against cancer formation. The statistical package Stata 8 was used for all analyses.


   Results
Top
 Abstract
 Introduction
 Materials and methods
 Results
Discussion
 References
 
Body weights, food intake and faecal output
Table I summarizes weight gain, food intake and faecal output. The PP group gained less weight (g/30 weeks) over the duration of the study (P = 0.001). Daily food intake tended to be lower with PP (P = 0.002). Faecal output was increased by feeding RS and PP (P < 0.001).


View this table:
[in this window]
[in a new window]

  		Table I Effect of RS and potato protein on weight gain, feed intake and faecal output in ratsa,b

 
Effect of the diets on colonic carbohydrate fermentation
Table II summarizes the SCFA concentrations in the caecum, proximal and distal colonic contents and faeces of rats fed the different experimental diets.


View this table:
[in this window]
[in a new window]

  		Table II Effects of RS and potato protein on caecal, proximal and distal colon and faecal SCFA concentrations (µmol/g) in ratsa,b

 
The SCFA concentrations in the caecum were approximately twice those of the faeces. Caecal total SCFA (P < 0.001) and acetate concentration (P = 0.001) were elevated with RS. RS and indigestible dietary protein showed an interactive effect (RS x PP, P = 0.001) on caecal propionate and butyrate, with the highest butyrate concentration achieved when combining RS with PP (i.e. PP + RS).

The SCFA concentrations in the proximal colonic content were slightly lower than that in the caecum and displayed similar relative differences to those within the caecum.

In the distal colon, RS significantly elevated total acetate and butyrate concentrations (P < 0.001). An interaction effect (RS x PP) was observed on propionate concentration in the distal colon (P = 0.029).

In the faeces, both total SCFA (P = 0.001) and butyrate (P = 0.002) concentrations were significantly elevated by RS supplementation. Interactions between RS and PP were observed for both acetate (P = 0.024) and propionate (P = 0.01) concentrations in the faeces.

Effect of diets on protein fermentation products
BCFA concentrations were consistently higher with indigestible protein than with other diets (Table III). An interaction between RS and PP (RS x PP) was observed with caecal BCFA (P = 0.049). Proximal BCFAs were significantly lower with RS (P < 0.001) and significantly higher with PP (P < 0.001). Distal (P = 0.004) and faecal (P = 0.014) BCFAs were elevated with PP.


View this table:
[in this window]
[in a new window]

  		Table III Faecal BCFA concentrations (µmol/g) and urinary phenols (µg/ml) in rats fed RS and potato proteina,b

 
Indigestible protein (PP) significantly increased the concentration of urinary p-cresol (P < 0.001) whereas RS had the opposite effect (P < 0.001). An interaction between PP and RS was observed for urinary phenol, with the RS interacting with the PP to lower the concentration (P < 0.001).

Effect of diets on caecal ß-glucuronidase activity
In the caecum, ß-glucuronidase activity was significantly reduced with RS (P < 0.001) (Figure 1).


Figure 1
View larger version (8K):
[in this window]
[in a new window]
[Download PowerPoint slide]
  		Fig. 1 Effect of resistant starch (RS) and digestion-resistant potato protein (PP) on caecal ß-glucuronidase activity in rats.

 
Colonic neoplasms.
The effects of diet on incidence (number of rats with neoplasms) and the number and type of azoxymethane-induced neoplasms in the colon are shown in Table IV. RS protected against adenocarcinoma formation by reducing the incidence of rats affected whether or not PP was present in the diet (P = 0.038). PP alone was not protective. A similar trend that did not reach significance was seen for the effect of RS on total number of adenocarcinomas.


View this table:
[in this window]
[in a new window]

  		Table IV Effect of RS and potato protein on measures of azoxymethane-induced colonic neoplasmsa,b

 
Intestinal neoplasms.
The effects of diet on incidence (number of rats with neoplasms) and the number and type of azoxymethane-induced neoplasms in the small intestine and small intestine combined with colon are shown in Table V. RS feeding significantly lowered both the incidence and numbers of total neoplasms (P = 0.01) and of adenocarcinomas (P = 0.008) in the small intestine. In contrast, PP feeding promoted the incidence of total neoplasms (P = 0.004) and adenocarcinoma incidence (P = 0.003) in the small intestine.


View this table:
[in this window]
[in a new window]

  		Table V Effect of RS and potato protein on measures of azoxymethane-induced intestinal neoplasms in ratsa,b

 
When the neoplasms of both the small intestine and colon were combined, RS protected against overall adenocarcinoma incidence (P = 0.002) and total number of intestinal adenocarcinomas (P = 0.001).


   Discussion
Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
References
 
Our results have demonstrated that there are many interactions between starch and protein that have major effects on luminal environment with also significant implications for oncogenesis.

RS supplementation altered the luminal environment throughout the large bowel and in faeces. SCFA concentrations in the caecum and colon were all elevated with RS feeding. RS feeding also lowered the production of potentially harmful by-products of protein fermentation such as phenols and cresols. Furthermore, the activity of bacterial ß-glucuronidase was diminished. ß-Glucuronidase is an enzyme that is believed to be largely responsible for hydrolysis of glucuronide conjugates in the intestine and is thought to play an important role in the generation of toxic and carcinogenic substances (33). These effects might also contribute to protection.

Although RS had a favourable effect on the luminal environment, feeding the indigestible potato protein showed that increased colonic protein might create effects that could be detrimental. Results showed that incorporation of indigestible protein significantly increased markers of protein fermentation evident by higher BCFAs in the caecum and colon and elevated levels of the putrefactive catabolites phenol and p-cresol. These putrefactive protein catabolites have been postulated to have negative influences on gut health (26). It is possible that the increased production of the putrefactive catabolites may be an indirect effect of dietary proteins effect on the activity of undesirable bacteria populations (such as sulphate-reducing bacteria, Escherichia coli, Clostridia and Bacteroides). The typical Western diet of humans contains high concentrations of protein with ~13 g of protein being able to escape digestion and enter the colon on a daily basis (22). Increased delivery of protein to the colon results in greater amino acid fermentation with production of potentially toxic substances such as ammonia, amines, N-nitroso compounds, phenols, thiols and indoles (25). We chose potato protein in the current study because it has a lower digestibility than that of casein and so serves to test what happens when extra protein escapes digestion in the small intestine and reaches the colon (32).

As a diet, protein and carbohydrate are consumed together. In the present study, we have shown that the carbohydrate RS can modulate the fermentation effects of dietary protein. It has been shown previously that indigestible potato protein promotes caecal butyrate production (32), an effect that may be explained by the indigestible protein altering the ratio of carbohydrate:nitrogen in the colon, thereby further sustaining fermentation. It was suggested from this study that indigestible proteins have an important physiologic role through interaction with RS in providing butyrate to colonic tissues. However, in the present study, although a significant interaction between RS and indigestible potato protein was seen in the caecum with increased caecal butyrate levels, this effect was not sustained through the colon. Any perceived benefit of enhanced caecal butyrate levels may be counteracted by increased production of potentially toxic fermentation substances throughout the gastrointestinal tract. The fermentation of protein by the colonic microflora was substantially modified by the supplementation of RS, as evidenced by a decrease in the concentration of putrefactive compounds and BCFA. This phenomenon has been observed previously in animal studies (30) as well as human intervention studies (42,43). Previous studies by Toden et al. (30) also demonstrated that RS may attenuate colonic DNA damage induced by consumption of a high dietary protein diet.

In parallel with its effects on starch and protein fermentation, RS feeding protected against intestinal tumourigenesis, including the development of colonic adenocarcinoma. This suggests that a favourable shift in the luminal environment achieved through RS feeding contributes to protection against intestinal tumourigenesis. In the distal colon, which is the site where tumours predominate (44), butyrate concentration was markedly increased with the RS supplementation. Butyrate is thought probably to promote colonic health and protect against CRC. Colonic production of butyrate by fermentation has previously been associated with reduced tumour mass provided that fermentation is active in distal colon (14) and is often hypothesized as a protective factor against CRC (7,45). Previous studies from our laboratory have shown that fermentable substrates such as RS or wheat bran can increase apoptosis in response to a genotoxic carcinogen, and furthermore, this appears to be dependant on the concentration of butyrate (18,46). Increased apoptosis during initiation events might enhance the elimination of mutated cells that might otherwise progress to malignancy (19). Such an effect might be a mechanism by which RS acts to protect against CRC. Other factors such as a decrease in harmful protein catabolites (phenols and cresols) and bacterial enzymes may also contribute to RS protective effects. Several studies have shown that carcinogen-induced tumour incidence is associated with a modification of bacterial ß-glucuronidase activity. An increase in bacterial ß-glucuronidase activity is often associated with a higher tumour risk (47) whereas a decrease in ß-glucuronidase activity has been associated with a reduction in tumour incidence (48).

The effect of RS supplementation in previous animal studies on tumourigenesis is limited and conflicting (49–53) and is summarized in Young et al. (49). More recently, hydrothermally treated RS3 protected against dimethylhydrazine-induced colon carcinogenesis (54). There are several explanations for the varying results between the reported studies as follows: the different carcinogen protocols (dose and duration), differences in starch type, feeding regimens and the comparative control diet. Some of these will alter luminal conditions known to have a major influence on colonic oncogenesis (9,55). RS can be classified into four main types based upon structural considerations and bacterial degradation (8), each with different characteristics and different fermentation patterns (56) that may lead to different effects on luminal environment. As a consequence, different types of RS should not be considered equivalent.

Increased delivery of protein to the colon promoted intestinal tumourigenesis, although the effect was obvious in small intestine and not colon. Consumption of high protein diets in rats has previously been shown to increase the genetic damage in the colon as measured by the comet assay (30). Why indigestible protein promotes tumourigenesis in small intestine but not colon in the present study is not entirely clear and needs more investigation. Although harmful fermentative products are produced in the colon, they might act systemically on small intestine thereby increasing tumourigenesis. When RS was combined with indigestible protein, no enhancement of small intestinal tumourigenesis was observed and this might be due to the local effect of higher concentrations of butyrate, as indigestible protein promotes fermentation of carbohydrate to butyrate. Enhanced colonic production of butyrate raises not only the portal level of butyrate but also the arterial level (57), suggesting that butyrate potentially may have effects on cells not in direct proximity to the gut (58). Certainly, RS decreased protein fermentation products and decreased the promotional effect of indigestible protein on intestinal tumourigenesis.

Changes in the luminal environment in response to delivery of starch and/or protein to the colon are sizeable and complex—they also correlate with risk for cancer. RS favourably influences the colonic luminal environment through enhanced butyrate production and reduction in harmful bacterial enzymes and products of protein fermentation. These conditions are associated with reduced risk of tumourigenesis in the colon and small intestine. Increased protein delivery to the colon increases the accumulation of potentially harmful by-products of aromatic amino acids. This set of conditions is associated with increased intestinal tumourigenesis but adding RS reduces such accumulation and protects against protein-enhanced tumourigenesis.


   Acknowledgments
 
The authors wish to thank Olga Pennino and Damien Belobrajdic for technical assistance.

Conflict of Interest Statement: Richard K.Le Leu and Graeme P.Young are currently conducting research sponsored by the National Starch and Chemical Company. No other authors have declared any conflict of interest.


   References
Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 

  1. Parkin D.M., et al. (2005) Global cancer statistics, 2002. CA Cancer J. Clin 55:74–108.[Abstract/Free Full Text]
  2. Jemal A., et al. (2005) Cancer statistics, 2005. CA Cancer J. Clin 55:10–30.[Abstract/Free Full Text]
  3. Chao A., et al. (2005) Meat consumption and risk of colorectal cancer. JAMA 293:172–182.[Abstract/Free Full Text]
  4. World Cancer Research Fund. (1997) Food, Nutrition and the Prevention of Cancer: A Global Perspective. (American Institute for Cancer Research, Washington, DC).
  5. Levi F., et al. (1999) Food groups and colorectal cancer risk. Br. J. Cancer 79:1283–1287.[CrossRef][ISI][Medline]
  6. Young G.P., et al. (2002) Preventing cancer: dietary lifestyle or clinical intervention? Asia Pac. J. Clin. Nutr. 11:suppl. 3, S618–S631.
  7. Cassidy A., et al. (1994) Starch intake and colorectal cancer risk: an international comparison. Br. J. Cancer 69:937–942.[ISI][Medline]
  8. Englyst H.N., et al. (1992) Classification and measurement of nutritionally important starch fractions. Eur. J. Clin. Nutr. 46:suppl. 2, S33–S50.
  9. Topping D.L., et al. (2001) Short-chain fatty acids and human colonic function: roles of resistant starch and nonstarch polysaccharides. Physiol. Rev. 81:1031–1064.[Abstract/Free Full Text]
  10. Whitehead R.H., et al. (1986) Effects of short chain fatty acids on a new human colon carcinoma cell line (LIM1215). Gut 27:1457–1463.[Abstract/Free Full Text]
  11. In Young G.P. (Ed.), et al. Butyrate and the Human Cancer Cell (1995) (Cambridge University Press, Cambridge, UK).
  12. Roediger W.E. (1982) Utilization of nutrients by isolated epithelial cells of the rat colon. Gastroenterology 83:424–429.[ISI][Medline]
  13. Medina V., et al. (1997) Induction of caspase-3 protease activity and apoptosis by butyrate and trichostatin A (inhibitors of histone deacetylase): dependence on protein synthesis and synergy with a mitochondrial/cytochrome c-dependent pathway. Cancer Res. 57:3697–3707.[Abstract/Free Full Text]
  14. McIntyre A., et al. (1993) Butyrate production from dietary fibre and protection against large bowel cancer in a rat model. Gut 34:386–391.[Abstract/Free Full Text]
  15. Ahmed R., et al. (2000) Fermentation of dietary starch in humans. Am. J. Gastroenterol. 95:1017–1020.[CrossRef][ISI][Medline]
  16. McGarr S.E., et al. (2005) Diet, anaerobic bacterial metabolism, and colon cancer: a review of the literature. J. Clin. Gastroenterol. 39:98–109.[ISI][Medline]
  17. Guarner F., et al. (2003) Gut flora in health and disease. Lancet 361:512–519.[CrossRef][ISI][Medline]
  18. Le Leu R.K., et al. (2003) Effect of resistant starch on genotoxin-induced apoptosis, colonic epithelium, and lumenal contents in rats. Carcinogenesis 24:1347–1352.[Abstract/Free Full Text]
  19. Young G.P., et al. (2005) Dietary fibre and colorectal cancer: a model for environment—gene interactions. Mol. Nutr. Food Res. 49:571–584.[CrossRef][ISI][Medline]
  20. Le Leu R.K., et al. (2005) A synbiotic combination of resistant starch and Bifidobacterium lactis facilitates apoptotic deletion of carcinogen-damaged cells in rat colon. J. Nutr. 135:996–1001.[Abstract/Free Full Text]
  21. Chacko A., et al. (1988) Nitrogen losses from the human small bowel: obligatory losses and the effect of physical form of food. Gut 29:809–815.[Abstract/Free Full Text]
  22. Cummings J.H., et al. (1997) Role of intestinal bacteria in nutrient metabolism. J. Parenter. Enteral Nutr. 21:357–365.[Abstract]
  23. Silvester K.R., et al. (1995) Does digestibility of meat protein help explain large bowel cancer risk? Nutr. Cancer 24:279–288.[ISI][Medline]
  24. Nordgaard I., et al. (1995) Small intestinal malabsorption and colonic fermentation of resistant starch and resistant peptides to short-chain fatty acids. Nutrition 11:129–137.[ISI][Medline]
  25. Cummings J.H., et al. (1979) The effect of meat protein and dietary fiber on colonic function and metabolism. II. Bacterial metabolites in feces and urine. Am. J. Clin. Nutr. 32:2094–2101.[Free Full Text]
  26. Geypens B., et al. (1997) Influence of dietary protein supplements on the formation of bacterial metabolites in the colon. Gut 41:70–76.[Abstract/Free Full Text]
  27. Hughes R., et al. (2001) Dose-dependent effect of dietary meat on endogenous colonic N-nitrosation. Carcinogenesis 22:199–202.[Abstract/Free Full Text]
  28. Visek W.J. (1986) Dietary protein and experimental carcinogenesis. Adv. Exp. Med. Biol. 206:163–186.[Medline]
  29. McIntosh G.H., et al. (2001) The influence of dietary proteins on colon cancer risk. Nutr. Res. 21:1053–1066.[CrossRef][ISI][Medline]
  30. Toden S., et al. (2005) Resistant starch attenuates colonic DNA damage induced by higher dietary protein in rats. Nutr. Cancer 51:45–51.[CrossRef][ISI][Medline]
  31. Toden S., et al. (2006) Resistant starch prevents colonic DNA damage induced by high dietary cooked red meat or casein in rats. Cancer Biol. Ther. 5:267–272.[ISI][Medline]
  32. Morita T., et al. (1998) Resistant proteins alter cecal short-chain fatty acid profiles in rats fed high amylose cornstarch. J. Nutr. 128:1156–1164.[Abstract/Free Full Text]
  33. Kulkarni N., et al. (1994) Inhibitory effect of Bifidobacterium longum cultures on the azoxymethane-induced aberrant crypt foci formation and fecal bacterial beta-glucuronidase. Proc. Soc. Exp. Biol. Med. 207:278–283.[Abstract]
  34. AIN. (1977) Report of the American Institute of Nurtition ad hoc Committee on Standards for Nutritional Studies. J. Nutr. 107:1340–1348.[Free Full Text]
  35. Morita T., et al. (1997) Cholesterol-lowering effects of soybean, potato and rice proteins depend on their low methionine contents in rats fed a cholesterol-free purified diet. J. Nutr. 127:470–477.[Abstract/Free Full Text]
  36. Njaa L.R. (1959) A shortened version of the Mitchell method for determination of the biological value of protein; growth rate as a source of error. Br. J. Nutr. 13:137–142.[CrossRef][ISI][Medline]
  37. Hu Y., et al. (2005) Absence of acute apoptotic response to genotoxic carcinogens in p53-deficient mice is associated with increased susceptibility to azoxymethane-induced colon tumours. Int. J. Cancer 115:561–567.[CrossRef][ISI][Medline]
  38. Pozharisski K.M. (1990) Pathology of tumours in laboratory animals. Tumours of the rat. Tumours of the intestines. IARC Sci. Publ. 99:159–198.
  39. Murray K.E., et al. (1988) Determination of simple phenols in faeces and urine by high-performance liquid chromatography. J. Chromatogr. 431:143–149.[ISI][Medline]
  40. Goldin B.R., et al. (1976) The relationship between diet and rat fecal bacterial enzymes implicated in colon cancer. J. Natl Cancer Inst. 57:371–375.[ISI][Medline]
  41. Jenab M., et al. (1996) The influence of flaxseed and lignans on colon carcinogenesis and beta-glucuronidase activity. Carcinogenesis 17:1343–1348.[Abstract/Free Full Text]
  42. Birkett A., et al. (1996) Resistant starch lowers fecal concentrations of ammonia and phenols in humans. Am. J. Clin. Nutr. 63:766–772.[Abstract/Free Full Text]
  43. Muir J.G., et al. (2004) Combining wheat bran with resistant starch has more beneficial effects on fecal indexes than does wheat bran alone. Am. J. Clin. Nutr. 79:1020–1028.[Abstract/Free Full Text]
  44. Bufill J.A. (1990) Colorectal cancer: evidence for distinct genetic categories based on proximal or distal tumor location. Ann. Intern. Med. 113:779–788.[ISI][Medline]
  45. Stephen A.M., et al. (1980) Mechanism of action of dietary fibre in the human colon. Nature 284:283–284.[CrossRef][Medline]
  46. Hu Y., et al. (2002) The colonic response to genotoxic carcinogens in the rat: regulation by dietary fibre. Carcinogenesis 23:1131–1137.[Abstract/Free Full Text]
  47. Reddy B.S., et al. (1974) Colon carcinogenesis in germ-free rats with 1, 2-dimethylhydrazine and N-methyl-n'-nitro-N-nitrosoguanidine. Cancer Res. 34:2368–2372.[Abstract/Free Full Text]
  48. Goldin B.R., et al. (1980) Effect of Lactobacillus acidophilus dietary supplements on 1, 2-dimethylhydrazine dihydrochloride-induced intestinal cancer in rats. J. Natl Cancer Inst. 64:263–265.[ISI][Medline]
  49. Young G.P., et al. (2004) Resistant starch and colorectal neoplasia. J. AOAC Int. 87:775–786.[ISI][Medline]
  50. Sakamoto J., et al. (1996) Comparison of resistant starch with cellulose diet on 1, 2-dimethylhydrazine-induced colonic carcinogenesis in rats. Gastroenterology 110:116–120.[CrossRef][ISI][Medline]
  51. Young G.P., et al. (1996) Wheat bran suppresses potato starch–potentiated colorectal tumorigenesis at the aberrant crypt stage in a rat model. Gastroenterology 110:508–514.[CrossRef][ISI][Medline]
  52. Pierre F., et al. (1997) Short-chain fructo-oligosaccharides reduce the occurrence of colon tumors and develop gut-associated lymphoid tissue in Min mice. Cancer Res. 57:225–228.[Abstract/Free Full Text]
  53. Williamson S.L., et al. (1999) Intestinal tumorigenesis in the Apc1638N mouse treated with aspirin and resistant starch for up to 5 months. Carcinogenesis 20:805–810.[Abstract/Free Full Text]
  54. Bauer-Marinovic M., et al. (2006) Dietary resistant starch type 3 prevents tumor induction by 1, 2-dimethylhydrazine and alters proliferation, apoptosis and dedifferentiation in rat colon. Carcinogenesis 27:1849–1859.[Abstract/Free Full Text]
  55. Andoh A., et al. (2003) Role of dietary fiber and short-chain fatty acids in the colon. Curr. Pharm. Des. 9:347–358.[CrossRef][ISI][Medline]
  56. Champ M.M. (2004) Physiological aspects of resistant starch and in vivo measurements. J. AOAC Int. 87:749–755.[ISI][Medline]
  57. Bach Knudsen K.E., et al. (2005) Rye bread enhances the production and plasma concentration of butyrate but not the plasma concentrations of glucose and insulin in pigs. J. Nutr. 135:1696–1704.[Abstract/Free Full Text]
  58. Smith J.G., et al. (1998) Butyric acid from the diet: actions at the level of gene expression. Crit. Rev. Food Sci. Nutr. 38:259–297.[CrossRef][ISI][Medline]
Received August 14, 2006; revised November 21, 2006; accepted November 27, 2006.


Add to CiteULike CiteULike   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us    What's this?


This article has been cited by other articles:


Home page
 CarcinogenesisHome page
S. Toden, A. R. Bird, D. L. Topping, and M. A. Conlon
High red meat diets induce greater numbers of colonic DNA double-strand breaks than white meat in rats: attenuation by high-amylose maize starch
Carcinogenesis, November 1, 2007; 28(11): 2355 - 2362.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow All Versions of this Article:
28/2/240    most recent
bgl245v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrow Search for citing articles in:
ISI Web of Science (5)
Right arrowRequest Permissions
Google Scholar
Right arrow Articles by Le Leu, R. K.
Right arrow Articles by Young, G. P.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Le Leu, R. K.
Right arrow Articles by Young, G. P.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?