Energy restriction modulates the development of advanced preneoplastic lesions depending on the level of fat in the diet

Energy Restriction and Colorectal Cancer: A Call for Additional Research

: Colorectal cancer has the second highest cancer-related mortality rate, with an estimated 881,000 deaths worldwide in 2018. The urgent need to reduce the incidence and mortality rate requires innovative strategies to improve prevention, early diagnosis, prognostic biomarkers, and treatment effectiveness. Caloric restriction (CR) is known as the most robust nutritional intervention that extends lifespan and delays the progression of age-related diseases, with remarkable results for cancer protection. Other forms of energy restriction, such as periodic fasting, intermittent fasting, or fasting-mimicking diets, with or without reduction of total calorie intake, recapitulate the effects of chronic CR and confer a wide range of beneficial effects towards health and survival, including anti-cancer properties. In this review, the known molecular, cellular, and organismal effects of energy restriction in oncology will be discussed. Energy-restriction-based strategies implemented in colorectal models and clinical trials will be also revised. While energy restriction constitutes a promising intervention for the prevention and treatment of several malignant neoplasms, further investigations are essential to dissect the interplay between fundamental aspects of energy intake, such as feeding patterns, fasting length, or diet composition, with all of them influencing health and disease or cancer effects. Currently, effectiveness, safety, and practicability of different forms of fasting to fight cancer, particularly colorectal cancer, should still be contemplated with caution.

Caloric restriction reduced 1, 2-dimethylhydrazine-induced aberrant crypt foci and induces the expression of Sirtuins in colonic mucosa of F344 rats

BACKGROUND

Caloric restriction (CR), a lowering of caloric intake without malnutrition, is associated with longevity. CR also decreases incidences of age-related diseases including cancer. The sirtuins (SIRTs) have been implicated as a key mediator for the beneficial effects of CR on longevity. However, the underlying mechanisms by which CR decreases cancer risk have not yet been fully elucidated.

MATERIALS AND METHODS

The present study was conducted to determine whether CR would modify the growth of preneoplastic colonic aberrant crypt foci (ACF). We also analyzed the expression of SIRTs to elucidate the molecular mechanisms of cancer-preventive effects of CR. F344 rats were fed a CR diet (60% of ad libitum diet) or a basal diet ad libitum. Then, the animals were given subcutaneous injection of either 1, 2-dimethylhydrazine (DMH) that enhances cell proliferation of colonic mucosa or saline. All animals were sacrificed at 5 weeks after the beginning of the experiment.

RESULTS

The number of ACF in colonic mucosa was significantly decreased in DMH-treated rats with CR as compared to in those without CR. No ACF was found in DMH-untreated animals with or without CR. Also, we found that CR decreased the cell proliferation of colonic mucosa in DMH-treated rats. The expressions of anti-apoptotic gene, Survivin, and cell cycle progression-associated gene, Cyclin D1, were increased by DMH-treatment. Both of the genes expressions were declined by CR in those of DMH-treated rats. The expressions of all SIRT1-7 mRNAs were significantly increased by CR in DMH-treated rats.

CONCLUSION

As previous studies demonstrated that SIRT1 down-regulates Survivin and Cyclin D1, our findings suggest that at least SIRT1 protect colonic mucosa from formation and development of ACF by increasing apoptosis and reducing excessive cell growth in colon epithelial cells.

Reduction in colon cancer risk by consumption of kava or kava fractions in carcinogen-treated rats

Epidemiological studies suggest that kava reduces colon cancer risk. However, no experimental studies of the chemopreventive properties of kava toward colon cancer have been reported. Further, there are concerns regarding hepatotoxicity of kava. The goal of this study was to determine whether kava consumption reduces markers of colon cancer in an animal model and to study the safety of kava. An ethanolic extract and polar and nonpolar fractions of the kava extract were fed to rats for 12 days prior to, during, and after administration of dimethylhydrazine, a colon-specific carcinogen. After 14 wk, rats fed the nonpolar extract had a significant reduction in precancerous lesions [aberrant crypt (AC) foci (ACF)] as well as large (≥ 4 AC/ACF) sialomucin-only expressing foci, an indicator of greater tumorigenic potential, compared to the control group. Groups fed the ethanolic extract and polar kava fraction trended toward reductions in ACF and large sialomucin-only expressing foci. The combined kava groups had significantly fewer total AC, ACF, large ACF, and large sialomucin-only expressing foci compared to the control group. Histological examination found no hepatic lesions in animals consuming the kava diets, suggesting that kava is safe to consume. Our results support that kava may reduce colon cancer risk.

Effect of caloric intake on Western-style diet-induced intestinal tumors in a mouse model for hereditary colon cancer

Increased caloric intake has been associated with increased risk for cancer of the large intestine. We studied caloric intake effect on tumor formation in Apc1638( N/+ ) mice, a preclinical model for human familial adenomatous polyposis. Mice were fed a controlled AIN-76A diet or a new Western-style diet (NWD). Intestinal tumor development was evaluated after 6 mo of feeding 1) AIN-76A diet (fed ad libitum) vs. AIN-76A (caloric intake reduced 30%); 2) NWD (fed ad libitum) vs. NWD (caloric intake reduced 30%); and 3) AIN-76A (fed ad libitum) vs. NWD (paired-fed with NWD providing equal caloric intakes to AIN-76A). Intestinal tumor incidences were 78-100% with intergroup variation P > 0.05; however, tumor multiplicity responded differently to dietary treatment: 1) Tumor multiplicity was unchanged after AIN-76A (caloric intake reduced 30% vs. mice fed AIN-76A ad libitum); 2) tumor multiplicity was unchanged after NWD (caloric intake reduced 30% vs. NWD ad libitum); and 3) tumor multiplicity increased 130% after NWD was paired-fed with the same caloric intake as mice fed AIN-76A ad libitum (P < 0.05). Body weights showed no association with tumor development. Findings indicated modified nutrients in NWD were mainly responsible for increased tumors in mice fed NWD vs. AIN-76A in this preclinical mouse model for human FAP.

Prevention of colon carcinogenesis by apple juice in vivo: impact of juice constituents and obesity

It is estimated that 75-85% of all chronic diseases are linked to lifestyle-related and environmental factors. The development of colon cancer is positively associated with obesity and inversely associated with the intake of dietary fibre, fruit and vegetable. Apple juice is the most widely consumed fruit beverage in Germany. It contains a specific spectrum of polyphenols and other components that may reduce the risk of colon cancer. Epidemiologic studies suggest an inverse correlation between apple consumption and colon cancer risk, although the mechanisms for these observations are not clear. The present review summarizes the preventive potential of apple juices and different apple constituents on biomarkers related to colon carcinogenesis with special focus on the in vivo evidence and the cancer promoting condition of obesity. However, under the cancer promoting condition of obesity, apple juice did not show cancer-preventive bioactivity. In our experiments a cancer-preventive bioactivity of apple juice is lacking in rats under the cancer-promoting condition of obesity. To further investigate, whether this lack of efficacy observed in obese rats might be representative for obese individuals human intervention studies on high risk groups such as obese or diabetic individuals are of interest and will be conducted.

Insulin resistance and hyperinsulinaemia in the development and progression of cancer

Experimental, epidemiological and clinical evidence implicates insulin resistance and its accompanying hyperinsulinaemia in the development of cancer, but the relative importance of these disturbances in cancer remains unclear. There are, however, theoretical mechanisms by which hyperinsulinaemia could amplify such growth-promoting effects as insulin may have, as well as the growth-promoting effects of other, more potent, growth factors. Hyperinsulinaemia may also induce other changes, particularly in the IGF (insulin-like growth factor) system, that could promote cell proliferation and survival. Several factors can independently modify both cancer risk and insulin resistance, including subclinical inflammation and obesity. The possibility that some of the effects of hyperinsulinaemia might then augment pro-carcinogenic changes associated with disturbances in these factors emphasizes how, rather than being a single causative factor, insulin resistance may be most usefully viewed as one strand in a network of interacting disturbances that promote the development and progression of cancer.

Obesity-related promotion of aberrant crypt foci in DMH-treated obese Zucker rats correlates with dyslipidemia rather than hyperinsulinemia

BACKGROUND

Obesity and energy restriction modulate the development of precancerous aberrant crypt foci (ACF) in animal models of colon cancer.

AIM

Investigation of the major obesity-associated determinants for ACF-development and underlying mechanisms leading to ACF-modulation, such as changes in DNA damage or colonocytes hyperproliferation.

METHODS

Lean and obese Zucker rats fed ad libitum (a.l.) or obese pair fed (p.f.) were induced with 1,2-dimethylhydrazine (DMH) for colon cancer. Multiple regression analyses were performed to identify major metabolic factors correlated with ACF number and size (aberrant crypts/ACF). DNA damage is analyzed by the comet-assay, epithelial proliferation by immunohistochemistry.

RESULTS

Aberrant crypt foci number was significantly elevated in Zucker obese a.l. (205.7+/-65.4 vs. lean 9.5+/-6.3, P<0.05) and is reduced by pair feeding in Zucker obese rats (81.4+/-28.5 vs. obese a.l., P<0.05). Compared to lean the ACF size was higher in Zucker obese a.l. (2.1+/-0.3 vs. lean 1.3+/-0.2., P<0.05) but is not reduced by pair feeding (1.7+/-0.2; P>0.05). While ACF number and size were modulated by genotype and/or pair feeding the DMH-induced DNA damage and hyperproliferation in colonocytes did not differ significantly between groups. Regression analysis showed that plasma parameters associated with lipid-metabolism (triglycerides, cholesterol, malondialdehyde) significantly correlated with the ACF number and size while parameters linked to carbohydrate-metabolism (glucose, insulin) were weaker determinants.

CONCLUSION

Obesity or pair feeding-associated modulation of ACF correlate with parameters related to lipid-metabolism but is not accompanied by changes in DNA damage and proliferation.

Translational approaches to addressing complex genetic pathways in colorectal cancer

Colorectal cancer (CRC) is among the most prevalent cancers worldwide and represents a major public health challenge in the developed world. From the perspective of translational investigation, scientists have enormous opportunity to elucidate the molecular genetic mechanisms that contribute to CRC pathogenesis because most cancers develop from adenomatous precursor lesions. The process of adenoma growth and transformation is accompanied by cumulative mutations in dominant genetic pathways that confer a growth advantage. Although this developmental process permits interrogation of informative pathways before the development of cancer, only a few adenomas progress to CRC. Accordingly, a major challenge for clinical translational investigators is to identify the molecular signatures that indicate increased likelihood for adenoma progression. By corollary, these molecular signatures include mutations in high penetrance alleles, which include the Adenomatous Polyposis Coli (APC) gene as well as other alleles in the Wnt/beta-catenin signaling pathway that specify increased genetic susceptibility to CRC. Interactions between these high penetrance alleles and other modifier genes as well as with environmental factors are of particular importance to understand the complex network of events that lead to CRC. This brief review will highlight 3 areas where important questions concerning genetic and environmental risk factors have fueled translational investigation into possible pathways that lead to CRC.

Insulin resistance and its contribution to colon carcinogenesis

The insulin resistance-colon cancer hypothesis, stating that insulin resistance may be associated with the development of colorectal cancer, represents a significant advance in colon cancer, as it emphasizes the potential for this cancer to become a modifiable disease. The fact that the incidence of insulin resistance has been increasing in the United States and much of the rest of the Western world where colon cancer remains the second leading cause of cancer death makes the exploration of the interrelationship of these conditions a subject of high priority. Here, we review the salient features of insulin resistance, defined as impaired biological response to the action of insulin. Recent epidemiological studies, evaluating potential associations between colon cancer risk and diabetes mellitus, dietary intake and metabolic factors, and IGF levels in several clinical settings, provide strong support of the insulin resistance-colon cancer hypothesis (without establishing causality). Mechanistically, insulin resistance has been associated with hyperinsulinemia, increased levels of growth factors including IGF-1, and alterations in NF-kappaB and peroxisome proliferator-activated receptor signaling, which may promote colon cancer through their effects on colonocyte kinetics. It is a reasonable expectation that in the not too distant future, critical interventions to the already mapped molecular sequence of events, which link two apparently disparate entities, combined with lifestyle changes could abrogate the development of colon cancer.

Steady state levels of transforming growth factor-beta1 and -beta2 mRNA and protein expression are elevated in colonic tumors in vivo irrespective of dietary lipids intervention

Colonic tumors of human origin produce abundant transforming growth factor (TGF)-beta suggesting that TGF-beta is critical to their growth. Dietary lipids regulate a number of growth factors including TGF-beta. Whether elevated TGF-beta levels are consistently expressed in colonic tumors irrespective of the environmental milieu in an in vivo model is not known and forms the main objective of the present study. Male F344 rats were injected with azoxymethane, 10 weeks later, rats bearing preneoplastic lesions were fed a low fat (5% corn oil) diet and 3 high fat (5% corn oil with 18% corn oil, fish oil or beef tallow) diets for 16 weeks. Colonic tumors and mucosae were processed and assessed for TGF-beta status. TGF-beta1 and -beta2 mRNA levels were upregulated in colonic tumors more than in mucosae of all diet groups. Dietary lipids modulated TGF-beta mRNA in both tumors and mucosae, high corn and fish oil diets upregulated TGF-beta1 significantly more than the low fat corn oil or high fat beef tallow diets. Immunohistochemical assessments of tissues with different biological features revealed that TGF-beta1 and -beta2 were elevated in tumors and in selected microscopic preneoplastic lesions compared to normal mucosae. This is the first in vivo study, documenting that developing colonic tumors acquire upregulated TGF-beta phenotype even in the presence of lipid environments capable of differentially regulating TGF-beta in normal mucosae. Elevated expression of TGF-beta in a selected subset of microscopic preneoplastic lesions suggests that TGF-beta plays an important role on both early and late stages of colon carcinogenesis.

The significance of aberrant crypt foci in understanding the pathogenesis of colon cancer

Animal models provide a unique opportunity to study the biology of the disease process, and to test hypotheses linking environmental factors in the etiology and prevention of colon cancer. The concept of cancer prevention is to retard, regress or eliminate precancerous lesions. To actuate this concept, it is important to identify and enumerate preneoplastic lesions of various growth dimensions. The study of the precancerous stages in the colon is possible by the identification of aberrant crypt foci (ACF) in rodent colons treated with a carcinogen. The growth, morphological and molecular features of ACF support the contention that ACF are putative preneoplastic lesions. The ACF system is used extensively to identify modulators of colon carcinogenesis. Among the various endpoints being used in cancer research, ACF are the only endpoints which provides a quantitative approach to assess the disease process and the underlying cellular and molecular events as affected by cancer preventive or promoting agents. Many dietary components have been classified as tumor promoters or inhibitors based on their ability to change the tumor outcome. Whether they affect the growth of very early or advanced preneoplastic lesions is not known and can be explored by using ACF system. This information will provide a better understanding of cancer pathogenesis and will lead to the development of different cancer preventive strategies for high-risk individuals and the general population.