Aberrant crypt focus promotion and glucose intolerance: correlation in the rat across diets differing in fat, n-3 fatty acids and energy

Preoperative Serum Triglyceride to High-Density Lipoprotein Cholesterol Ratio Can Predict Prognosis in Non-Small Cell Lung Cancer: A Multicenter Retrospective Cohort Study

Background: Previously, research has reported associations of lipid and lipoprotein imbalances with carcinogenesis and cancer progression, so they have been considered as promising prognostic biomarkers for cancer in recent years. However, the correlation of preoperative serum triglyceride to high-density lipoprotein cholesterol ratio (TG/HDL-C) with non-small cell lung carcinoma (NSCLC) prognosis remains under exploration. Here, the study investigated the prognostic function of TG/HDL-C for NSCLC. Methods: The total combined group of this retrospective study enrolled 479 NSCLC patients from two tertiary referral hospitals, of which 223 patients were defined as the training group (Nanchang) and the remaining 256 were defined as the validation group (Wuhan). The cut-off of preoperative TG/HDL-C was determined through ROC curve in the training group and verified in the validation and combined groups subsequently. With one Cox proportional hazards model and K-M survival curves, a survival analysis was conducted. Results: In the training group, the optimal cut-off of TG/HDL-C was 1.02. Furthermore, the data based on the training group revealed a greater, shorter, overall survival (OS) in patients having a high TG/HDL-C (>1.02) than those having low TG/HDL-C (≤1.02). Meanwhile, in univariate and multivariate analysis, for prognostic OS among NSCLC patients, TG/HDL-C acted as one independent factor. All the results above were confirmed in the validation and combined groups. Conclusion: NSCLC patients with a comparatively low preoperative serum TG/HDL-C level had a correlation with well OS. TG/HDL-C possibly acted as one novel, effective prognostic biomarker for NSCLC patients.

Gender difference in metabolic syndrome and incident colorectal adenoma: A prospective observational study (KCIS No.42)

ABSTRACT

This community-based study aimed to elucidate whether there is a gender difference in the effect of metabolic syndrome (MetS) and its individual components on an elevated risk for incident colorectal adenoma.A prospective cohort study was conducted by enrolling 59,767 subjects aged 40 years or older between 2001 and 2009 in Keelung, Taiwan, to test this hypothesis, excluding those with a prior history of colorectal cancer and those with colorectal cancer diagnosed at the first screening. Cox proportional hazards regression models were used to assess the effect of MetS in terms of a dichotomous classification, each individual component and the number of components for males and females.Colorectal adenoma was present in 2.7% (n = 652) of male participants and 1.1% (n = 403) of female participants. The prevalence rate of MetS was 26.7% and 23.3% for males and females, respectively. The effect of MetS on colorectal adenoma was statistically significant and similar for the 2 genders, with an adjusted hazard ratio (aHR) of 1.33 (95% CI: 1.13-1.58) in males and 1.33 (95% CI: 1.06-1.66) in females after adjustment for confounders. However, MetS led to higher risk of advanced colorectal adenoma in men than in women. Regarding the effect of each component of MetS on colorectal adenoma, abnormal waist circumference and hypertriglyceridemia led to an elevated risk of colorectal adenoma in both genders. A rising risk of colorectal adenoma among females was noted in those with a moderately higher level of glycemia (100-125 mg/dL, aHR = 1.44, 95% CI: 1.12-1.85). Hypertriglyceridemia and high blood pressure were associated with an increased risk of advance colorectal adenoma in males.Both male and female subjects with MetS had a higher risk of colorectal adenoma. The contributions from individual components of MetS varied by gender. These findings suggest that the possible risk reduction of colorectal adenoma through metabolic syndrome-based lifestyle modifications may differ between genders.

Treatment with insulin analog X10 and IGF-1 increases growth of colon cancer allografts

Obesity and type 2 diabetes are associated with an increased risk for development of certain forms of cancer, including colon cancer. The publication of highly controversial epidemiological studies in 2009 raised the possibility that use of the insulin analog glargine increases this risk further. However, it is not clear how mitogenic effects of insulin and insulin analogs measured in vitro correlate with tumor growth-promoting effects in vivo. The aim of this study was to examine possible growth-promoting effects of native human insulin, insulin X10 and IGF-1, which are considered positive controls in vitro, in a short-term animal model of an obesity- and diabetes-relevant cancer. We characterized insulin and IGF-1 receptor expression and the response to treatment with insulin, X10 and IGF-1 in the murine colon cancer cell line (MC38 cells) in vitro and in vivo. Furthermore, we examined pharmacokinetics and pharmacodynamics and monitored growth of MC38 cell allografts in mice with diet-induced obesity treated with human insulin, X10 and IGF-1. Treatment with X10 and IGF-1 significantly increased growth of MC38 cell allografts in mice with diet-induced obesity and we can therefore conclude that supra-pharmacological doses of the insulin analog X10, which is super-mitogenic in vitro and increased the incidence of mammary tumors in female rats in a 12-month toxicity study, also increase growth of tumor allografts in a short-term animal model.

The metabolic and mitogenic properties of basal insulin analogues

CONTEXT

Retrospective, observational studies have reported an association between diabetes treatment with insulin and a higher incidence of cancer.

OBJECTIVE

Overview the literature for in vitro and in vivo studies of the metabolic and mitogenic properties of basal insulin analogues and assess the implications for clinical use.

METHODS

Relevant studies were identified through PubMed and congress abstract database searches; data on metabolic and mitogenic signalling in relation to insulin treatment of diabetes are included in this review.

RESULTS

The balance of evidence shows that although some analogues have demonstrated mitogenic potency in some in vitro studies in cancer cell lines, these findings do not translate to the in vivo setting in animals or to the clinical setting in humans.

CONCLUSIONS

The current consensus is that there is no clinical or in vivo evidence to indicate that any commercially available insulin analogue has carcinogenic effects. Large-scale, prospective clinical and observational studies will further establish any potential link.

Chemopreventive effects of RXR-selective rexinoid bexarotene on intestinal neoplasia of Apc(Min/+) mice

Retinoid X receptor (RXR) has been implicated in several neoplastic diseases. Previously, we have shown that RXR-α is downregulated in human and rodent colonic tumors, suggesting a potential target for colon cancer prevention (http://www.cancer.org/Cancer/ColonandRectumCancer/DetailedGuide/colorectal-cancer-key-statistics). Experiments were designed to assess the chemopreventive efficacy of the selective RXR agonist bexarotene for the suppression of intestinal tumorigenesis in Apc(Min/+) mice. Before the efficacy studies, we determined that the maximal tolerated dose in C57BL/6J mice was less than 400 ppm. For the efficacy study, 6-week-old male and female C57BL/6J-Apc(Min/+) mice (nine mice per group) were fed diets containing 0, 30, and 60 ppm of bexarotene or 200 ppm of bexarotene for 80 days before intestinal tumors were evaluated. Dietary administration of 30 and 60 ppm of bexarotene suppressed the intestinal polyp formation by 38% (P < .015) and 60% (P < .0001) in males, respectively, and by 8.5% and 37% (P < .007) in females, respectively. Also, significant inhibition (50%-100%) of colonic tumor formation was observed in both male and female mice with bexarotene treatment. Administration of 200 ppm of bexarotene showed significant suppression of tumor formation (66%, P < .0001); however, it had significant toxicity. Intestinal tumors of bexarotene-fed mice showed significantly reduced expression of proliferating cell nuclear antigen (60%, P < .0001), cyclin D1, and cyclooxygenase 2 and increased RXR-α messenger RNA and uptake of oleate (34%, P < .01). Also, bexarotene-fed mice showed dose-dependent suppression of serum triglycerides (25%-72%, P < .0001) and inflammatory cytokines.

Type 2 diabetes and cancer: what is the connection?

Epidemiological studies have demonstrated an association between type 2 diabetes and cancer. Type 2 diabetes is characterized by insulin resistance and hyperinsulinemia. Hyperinsulinemia may lead to cancer through insulin's effect on its cognate receptor and the insulin-like growth factor system. The effects of insulin and insulin-like growth factor I on cancer development and progression have been demonstrated in animal and human studies. Type 2 diabetes has been positively associated with cancers of the breast, colon, and pancreas. An inverse relationship has been observed between type 2 diabetes and prostate cancer, and this may be due to lower testosterone levels in men with type 2 diabetes. Medications used to treat type 2 diabetes may affect cancer cells directly or indirectly by affecting serum insulin levels. Hyperinsulinemia may be an important risk factor for cancer as well as a target for cancer therapy.

Growth hormone, the insulin-like growth factor axis, insulin and cancer risk

Growth hormone (GH), insulin-like growth factor (IGF)-I and insulin have potent growth-promoting and anabolic actions. Their potential involvement in tumor promotion and progression has been of concern for several decades. The evidence that GH, IGF-I and insulin can promote and contribute to cancer progression comes from various sources, including transgenic and knockout mouse models and animal and human cell lines derived from cancers. Assessments of the GH-IGF axis in healthy individuals followed up to assess cancer incidence provide direct evidence of this risk; raised IGF-I levels in blood are associated with a slightly increased risk of some cancers. Studies of human diseases characterized by excess growth factor secretion or treated with growth factors have produced reassuring data, with no notable increases in de novo cancers in children treated with GH. Although follow-up for the vast majority of these children does not yet extend beyond young adulthood, a slight increase in cancers in those with long-standing excess GH secretion (as seen in patients with acromegaly) and no overall increase in cancer with insulin treatment, have been observed. Nevertheless, long-term surveillance for cancer incidence in all populations exposed to increased levels of GH is vitally important.

Insulin resistance-related biomarker clustering and subclinical inflammation as predictors of cancer mortality during 21.5 years of follow-up

OBJECTIVES

Risk of cancer is increased in conditions associated with insulin resistance, but this could be secondary to subclinical inflammation. We evaluated whether insulinemia, indices of insulin resistance or a validated insulin resistance-related biomarker cluster, could predict cancer mortality independently of subclinical inflammation.

METHODS

Fasting insulin and glucose concentrations and insulin-related metabolic variables were recorded in 1,016 white males, of whom 718 also had an oral glucose tolerance test (OGTT). Baseline measurements included the following: fasting insulin and the derived insulin resistance index, HOMA-IR; OGTT insulin and the derived insulin resistance index, Matsuda-IS; the factor score for a validated insulin resistance-related biomarker cluster; white blood cell count; erythrocyte sedimentation rate; and serum albumin and globulin concentrations.

RESULTS

There were 105 deaths from cancer during the 21.5-year mean follow-up. Insulin concentrations and insulin resistance were not predictive. Insulin resistance-related biomarker clustering predicted cancer mortality (hazard ratio 1.65, 95% CI 1.26-2.17, p < 0.001). Subclinical inflammation markers were also predictive, but the insulin resistance-related biomarker cluster predicted cancer mortality independently of these and was particularly associated with death from colorectal cancer.

CONCLUSIONS

Despite insulin concentrations or derived indices of insulin resistance failing to predict cancer mortality, insulin resistance-related biomarker clustering was highly predictive and predicted independently of simple measures of subclinical inflammation.

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.

Development of aberrant crypt foci in the colons of ob/ob and db/db mice: evidence that leptin is not a promoter

Leptin is elevated in obesity and has been suggested to increase the risk of colorectal cancer (CRC), although the evidence is conflicting. The objective of this study was to compare the susceptibility to colon carcinogenesis of db/db mice that have highly elevated circulating leptin and leptin-deficient ob/ob mice, both of which are obese. Seven-week-old male ob/ob, db/db, and WT mice received 4 weekly i.p. injections of 5 mg/kg azoxymethane (AOM) and were killed 14 wk later for the analysis of putative preneoplastic aberrant crypt foci (ACF). There were no differences in ACF number or multiplicity between ob/ob and db/db mice. Leptin has been shown to induce CYP2E1, the main enzyme that activates AOM, but we observed no differences in hepatic CYP2E1 activity or colonic CYP2E1 protein levels between ob/ob and db/db mice. We also induced ACF with 2 oral doses 3 d apart of 30 mg/kg methylnitrosourea (MNU), a direct-acting carcinogen. There were no differences in ACF number or multiplicity between the two groups of obese animals 5 wk following the last dose of MNU. The colonic mucosa of db/db mice expressed significantly lower mRNA levels of ObRa, the predominant short form of the leptin receptor, compared to ob/ob mice, and following i.p. injection with 1 mg/kg recombinant mouse leptin, exhibited significantly reduced p44/42 pMAPK compared to saline-treated controls. These results show that ObRa is functionally active in the colons of db/db mice. We conclude that leptin does not play a significant role in ACF development.

Type 2 diabetes mellitus as risk factor for colorectal cancer

Colorectal cancer occurs more frequently in patients with type 2 diabetes mellitus. The hyperinsulinemia-hypothesis suggests that elevated levels of insulin and free IGF-1 promote proliferation of colon cells and lead to a survival benefit of transformed cells, ultimately resulting in colorectal cancer. In patients with type 2 diabetes mellitus, epidemiological studies show an increased risk for colorectal cancer and an even higher risk if patients are treated with sulphonylureas or insulin. Moreover, tumour progression at hyperinsulinemia is more rapid and tumour-associated mortality is increased. Colorectal cancer can be avoided by screening. Recommendations for colorectal cancer screening should employ the recent epidemiologic evidence. All patients with type 2 diabetes mellitus should be recommended to undergo colonoscopy before starting insulin therapy, and screening intervals should not exceed 5 years. For this concept, a review of the evidence is presented, and a screening algorithm for colorectal cancer in patients with type 2 diabetes mellitus is proposed.

A specific inducible nitric oxide synthase inhibitor, ONO-1714 attenuates inflammation-related large bowel carcinogenesis in male Apc(Min/+) mice

It is generally assumed that inflammation influences carcinogenesis. We previously reported that dextran sodium sulfate (DSS) strongly enhances colon carcinogenesis in the Apc(Min/+) mice and the over-expression of inducible nitric oxide synthase (iNOS) contributes to this enhancement. In the current study, we investigated the effect of a selective iNOS inhibitor, ONO-1714 on colitis-related colon carcinogenesis in the Apc(Min/+) mouse treated with DSS. Male C57BL/6J Apc(Min/+) and Apc(+/+) mice were exposed to 1% DSS in their drinking water for 7 days. ONO-1714 was given to the mice at a dose level of 50 or 100 ppm in diet for 5 weeks (during the administration of DSS). The tumor inhibitory effects by ONO-1714 were assessed at week 5 by counting the incidence and multiplicity of colonic neoplasms. Additionally, we assessed serum lipid levels and colonic mRNA expression for cyclooxygenase (COX)-2, iNOS, tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta. Feeding with ONO-1714 significantly inhibited the occurrence of colonic adenocarcinoma in a dose-dependent manner in the Apc(Min/+) mice. In addition, the treatment with ONO-1714 significantly lowered the serum triglyceride levels and mRNA expression levels of COX-2, TNFalpha and IL-1beta of colonic mucosa in the DSS-treated Apc(Min/+) mice. Neither ONO-1714 nor DSS affected the colonic pathology in the Apc(+/+) mice. Our findings may suggest that ONO-1714 could therefore serve as an effective agent for suppression of colitis-related colon cancer development in the Apc(Min/+) mice.

Association of metabolic syndrome with proximal and synchronous colorectal neoplasm

BACKGROUND & AIMS

Metabolic syndrome and its associated morbidities have become a major public health problem in both developed and developing countries. Insulin resistance, the core mechanism of metabolic syndrome, has been associated with the development of colorectal neoplasm, but the interrelation between metabolic syndrome and colon cancer is rarely addressed. Our study aimed to determine whether metabolic syndrome is associated with the risk and clinical presentation of colorectal neoplasia.

METHODS

Consecutive 4277 ethnic Chinese who received complete total colonoscopy and thorough health checkups were enrolled. Both National Cholesterol Education Program's Adult Treatment Panel III and modified Asian criteria were used for defining metabolic syndrome. Logistic regression modeling was used to elucidate the association between colorectal neoplasia and metabolic syndrome. The impact of metabolic syndrome on distribution and number of colorectal neoplasia was also assessed.

RESULTS

Of all those enrolled, 27.1% of men and 18.9% of women met the criteria of metabolic syndrome, and 9.8% had colorectal neoplasia. Metabolic syndrome was associated with odds ratio (OR) of 1.35 (95% confidence interval [CI], 1.05-1.73) for colorectal neoplasia. OR was 0.96 (95% CI, 0.67-1.38) for distal lesions, 1.62 (95% CI, 1.14-2.30) for proximal lesions, 2.15 (95% CI, 1.40-3.31) for synchronous lesions, and 2.30 (95% CI, 1.42-3.72) for synchronous lesions located at both sides of colon.

CONCLUSIONS

Subjects with metabolic syndrome have a higher risk of colon neoplasia at the proximal colon and synchronous lesions at both sides of the colon. These findings will help future colon cancer screening and prevention in patients with metabolic syndrome.

Is there an estrogenic component in the metabolic syndrome?

One of the major upcoming concerns leading to health related problems in the industrialized societies is the metabolic syndrome which is characterized by central obesity, hypertension, raised fasting glucose and triglyceride levels. The focus of this review is on a potential estrogenic linkage between the metabolic mechanisms involved into the development of this disease cluster and specific estrogen related regulatory pattern. The candidate molecules for this link are insulin and insulin-like growthfactor, C-reactive protein, peroxisome-proliferation-activatingreceptorgamma, and leptin which all seem to interact with each other and show a responsiveness to changing estrogen levels. From this perspective they might also represent target molecules for a phytochemical intervention with phytoestrogens.

Hyperinsulinemia, but not other factors associated with insulin resistance, acutely enhances colorectal epithelial proliferation in vivo

The similarity in risk factors for insulin resistance and colorectal cancer (CRC) led to the hypothesis that markers of insulin resistance, such as elevated circulating levels of insulin, glucose, fatty acids, and triglycerides, are energy sources and growth factors in the development of CRC. The objective was thus to examine the individual and combined effects of these circulating factors on colorectal epithelial proliferation in vivo. Rats were fasted overnight, randomized to six groups, infused iv with insulin, glucose, and/or Intralipid for 10 h, and assessed for 5-bromo-2-deoxyuridine labeling of replicating DNA in colorectal epithelial cells. Intravenous infusion of insulin, during a 10-h euglycemic clamp, increased colorectal epithelial proliferation in a dose-dependent manner. The addition of hyperglycemia to hyperinsulinemia did not further increase proliferation. Intralipid infusion alone did not affect proliferation; however, the combination of insulin, glucose, and Intralipid infusion resulted in greater hyperinsulinemia than the infusion of insulin alone and further increased proliferation. Insulin infusion during a 10-h euglycemic clamp decreased total IGF-I levels and did not affect insulin sensitivity. These results provide evidence for an acute role of insulin, at levels observed in insulin resistance, in the proliferation of colorectal epithelial cells in vivo.

Hypertriglyceridemia is positively correlated with the development of colorectal tubular adenoma in Japanese men

AIM: To determine the real association between serum lipid levels and colonic polyp formation.

METHODS: We performed a large scale retrospective study to analyze the correlation between the incidence of colorectal adenoma or carcinoma and the fasting serum levels of total cholesterol (TC) and triglycerides (TG) in patients who underwent total colonoscopy for screening for colon cancer.

RESULTS: Both levels were significantly elevated in patients with adenomas as compared with patients without any neoplastic lesion (TC 207.6 ± 29.5 vs 199.5±34.3, n= 4883, P< 0.001; TG 135.0 ± 82.2 vs 108.7±71.5, n= 4874, P< 0.001). The difference was significant in patients with tubular adenoma but not in those with villous or serrated adenoma. Multiple logistic regression analysis including age and sex revealed that TG was an independent correlation factor in male (P < 0.01), but not in female patients. The level of TG in patients with invasive carcinoma did not show a significant elevation from that in patients with adenoma. These findings suggest that hypertriglyceridemia is an independent risk factor for colonic adenoma in men.

CONCLUSION: Although a high level of serum triglyceride does not appear to be mechanically involved in the development of carcinoma, reduction of serum TG and intensive surveillance with total colonoscopy may have benefit in men with hypertriglyceridemia.

A pilot randomised controlled trial to reduce colorectal cancer risk markers associated with B-vitamin deficiency, insulin resistance and colonic inflammation

Colorectal cancer risk is associated with biochemical markers for B-vitamin deficiency, insulin resistance and colonic inflammation, suggesting that these three conditions are each involved in colon carcinogenesis. We expected that dietary supplements of folic acid, n-3 fatty acids and calcium would reduce the markers and thus possibly cancer risk. We therefore randomised 98 participants, with previous colonic polyps or intramucosal carcinomas, to a combined treatment of supplementary folic acid, fish oil and calcium carbonate, or placebos for 28 days. Blood and faecal samples were obtained prior to and at the conclusion of the intervention and analysed for plasma folate, homocysteine, insulin, free fatty acids, triglycerides and faecal calprotectin. In addition, plasma vitamin B12, thiamin, glucose and C-reactive protein were assessed. Our supplemental strategy modestly affected some of the biomarkers associated with folate metabolism and insulin resistance, but had no effect on those associated with colonic inflammation. This pilot study demonstrates the feasibility and practicality of clinical trials aimed at reducing diet-related biochemical risk markers for colon cancer. We suggest that long-term intervention studies with tumour-related end points should be undertaken when the intervention agents used are found effective in short-term biochemical risk marker trials.

A Prospective Study of Plasma C-Peptide and Colorectal Cancer Risk in Men

BACKGROUND

Colorectal cancer and type 2 diabetes share many risk factors, and hyperinsulinemia appears to be associated with an increased risk of colorectal cancer. We used the concentration of plasma C-peptide (an indicator of insulin production) to determine whether insulin and insulin resistance are associated with the risk of developing colorectal cancer.

METHODS

We conducted a nested case-control study in the Physicians' Health Study. Plasma samples were collected from 14 916 cancer-free men from August 1982 through December 1984. Plasma C-peptide concentration, measured with an enzyme-linked immunosorbent assay, was available for 176 case patients who developed incident colorectal cancer through December 31, 1995, and 294 age- and smoking status-matched control subjects. Information on four other insulin resistance-related factors at baseline was obtained. We used conditional logistic regression models to investigate associations. All statistical tests were two-sided.

RESULTS

Plasma C-peptide concentration was positively associated with age, body mass index (BMI), and number of insulin resistance-related factors, and it was inversely associated with fasting time before the blood draw, alcohol consumption, and vigorous exercise. An increased concentration of plasma C-peptide was statistically significantly associated with an increased risk of colorectal cancer (relative risk [RR] for the highest versus lowest quintile of plasma C-peptide = 2.7, 95% confidence interval [CI] = 1.2 to 6.2; P(trend) =.047), after adjusting for age, smoking status, fasting, BMI, alcohol consumption, vigorous exercise, and aspirin assignment in the Physicians' Health Study. The association became even stronger when the analysis was further adjusted for factors related to insulin resistance other than insulin levels (RR for the highest versus lowest quintile = 3.4, 95% CI = 1.4 to 8.3; P(trend) =.02) or when data from case patients who were diagnosed during the first 5 years of follow-up were excluded (RR for the highest versus the lowest quintile = 3.4, 95% CI = 1.3 to 8.8; P(trend) =.03). Adjusting for plasma levels of insulin-like growth factor I (IGF-I) and its binding protein 3 (IGFBP-3) did not materially change the results. There was no apparent modification of risk by BMI, insulin resistance-related factors, or vigorous exercise.

CONCLUSION

Elevated insulin production, as reflected by elevated concentrations of plasma C-peptide, may predict the risk of developing colorectal cancer, independently of BMI, factors related to insulin resistance, or levels of IGF-I and IGFBP-3.

Insulin and cancer

Obesity has recently been linked to mortality from the majority of cancers. The insulin/insulin-like growth factor (IGF) system may partly explain this effect. The metabolic syndrome, associated with hyperinsulinemia, may modulate this effect. Recent evidence supports the role of insulin and IGF-1 as important growth factors, acting through the tyrosine kinase growth factor cascade in enhancing tumor cell proliferation. In addition, the metabolic syndrome associated with a chronic inflammatory state and accompanying cytokine abnormalities may also contribute to tumor progression. Growing links between insulin and the etiology as well as prognosis in colon, prostate, pancreatic, and, particularly, breast cancer are reviewed. Of particular concern is the evidence that elevated IGF-1 may interfere with cancer therapy, adversely affecting prognosis. The role of insulin is of concern because of the increasing levels of obesity and the associated metabolic syndrome. Weight gain, through typical Western diet; limited levels of activity; and, more recently, stress-related changes in neuroendocrine function may lead to insulin resistance and hyperinsulinemia. The opportunity for a multidisciplinary approach involving nutrition, exercise, and stress reduction in an integrative setting may be crucial to limiting the insulin-resistant state and improving cancer outcomes.

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.

Energy imbalance and prostate cancer

In this review, the emerging evidence that excessive energy intake relative to energy expenditure increases the risk of prostate cancer is discussed. The adverse effects of energy imbalance can be inferred from an experimental study demonstrating reduced prostate tumor growth, lower circulating concentrations of insulin-like growth factor-I and decreased expression of vascular endothelial growth factor with energy restriction in transplantable tumor models. The effects of energy restriction on factors mediating greater proliferation relative to apoptosis and angiogenesis suggest that energy imbalance may act late in the carcinogenic pathway. Energy intake also has been evaluated in relation to prostate cancer risk in 23 analytic epidemiologic studies. Among studies reporting effect estimates, 8 of 14 case-control studies support a direct association [top versus bottom quantile, OR(summary) = 1.3; 95% confidence interval (CI), 1.1-1.4], but none of four cohort studies do (RR(summary) = 1.0; 95% CI, 0.8-1.2). The four case-control studies that evaluated advanced disease suggest a higher risk with higher energy intake (OR(summary) = 1.6; 95% CI, 1.2-2.0). However, none of these studies considered the balance of energy intake with body size and physical activity, the major determinants of variability in energy demand. Numerous research questions remain to be addressed, including, Which biological pathways are adversely affected by energy imbalance? Does energy imbalance act early or late in prostate carcinogenesis? What is the optimal energy balance for minimizing risk of clinically important prostate cancer? Evidence is beginning to show that energy intake in excess of expenditure may affect prostate carcinogenesis and, in particular, risk of advanced disease.

A protective role of dietary vitamin D3 in rat colon carcinogenesis

The aim of the present work was to gain insight into a putative anticancer effect of dietary vitamin D3 (cholecalciferol) in a rat model of colon carcinogenesis. Male rats were assigned to three different dietary groups. The dietary regimens were based on a standard murine-defined diet (AIN-76A) or a stress diet containing 20% fat, reduced Ca2+ concentration, a high phosphorus-to-Ca2+ ratio, and either low or high vitamin D3 content. Colorectal cancer was induced by administration of the procarcinogen 1,2-dimethylhydrazine (DMH). Blood Ca2+, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], and 25-hydroxyvitamin D3 [25(OH)D3] levels were measured in DMH-treated rats and in respective weight- and age-matched dietary control groups. Colonic epithelial proliferation was assessed by determining thymidine kinase (TK) activity, bromodeoxyuridine (BrdUrd) incorporation into crypt cell DNA, and the mean labeling index along the colonic crypt continuum. Maintenance of rats on the stress diet either unmodified or supplemented with vitamin D3 in the absence of carcinogen treatment provoked a time-dependent rise in colonic TK activity and hyperproliferation of colonic epithelium. DMH treatment of rats maintained on the standard diet caused a marked increase in the proliferative indexes of colonic epithelium and in expansion of the crypt proliferative compartment. TK activity and the crypt mitotic zone were significantly augmented in the animal group fed the stress diet. Supplementary vitamin D3 abrogated the stress diet-enhanced colonic responses to the carcinogenic insult. Colon tumor multiplicity was fourfold higher in animals fed the stress diet than in animals maintained on a standard diet. The marked rise in colonic tumor multiplicity and adenocarcinoma incidence in rats fed the stress diet was obliterated by supplemental dietary vitamin D3. Cumulatively, the present results indicate that dietary vitamin D3 impedes the neoplastic process in murine large intestine and strengthen the view that inappropriate changes in dietary components and micronutrients are contributory determinants of colorectal cancer.

Insulin, insulin-like growth factors and colon cancer: a review of the evidence

Insulin and insulin-like growth factor (IGF) axes are major determinants of proliferation and apoptosis and thus may influence carcinogenesis. In various animal models, modulation of insulin and IGF-1 levels through various means, including direct infusion, energy excess or restriction, genetically induced obesity, dietary quality including fatty acid and sucrose content, inhibition of normal insulin secretion and pharmacologic inhibition of IGF-1, influences colonic carcinogenesis. Human evidence also associates high levels of insulin and IGF-1 with increased risk of colon cancer. Clinical conditions associated with high levels of insulin (noninsulin-dependent diabetes mellitus and hypertriglyceridemia) and IGF-1 (acromegaly) are related to increased risk of colon cancer, and increased circulating concentrations of insulin and IGF-1 are related to a higher risk of colonic neoplasia. Determinants and markers of hyperinsulinemia (physical inactivity, high body mass index, central adiposity) and high IGF-1 levels (tall stature) are also related to higher risk. Many studies indicate that dietary patterns that stimulate insulin resistance or secretion, including high consumption of sucrose, various sources of starch, a high glycemic index and high saturated fatty acid intake, are associated with a higher risk of colon cancer. Although additional environmental and genetic factors affect colon cancer, the incidence of this malignancy was invariably low before the technological advances that rendered sedentary lifestyles and obesity common, and increased availability of highly processed carbohydrates and saturated fatty acids. Efforts to counter these patterns are likely to have the most potential to reduce colon cancer incidence, as well as cardiovascular disease and diabetes mellitus.

Mechanisms linking diet and colorectal cancer: the possible role of insulin resistance

Diet is clearly implicated in the origin of colorectal cancer, with risk factors for the disease including reduced consumption of vegetables, fiber, and starch and increased consumption of red meat and animal fat. Several hypotheses have been developed to explain these associations. Most recently, McKeown-Eyssen and Giovannucci noted the similarity of the risk factors for colorectal cancer and those for insulin resistance and suggested that insulin resistance leads to colorectal cancer through the growth-promoting effect of elevated levels of insulin, glucose, or triglycerides. We briefly review the evidence from observational, epidemiological, and experimental animal studies linking diet with insulin resistance and colorectal cancer. The evidence suggests that diets high in energy and saturated fat and with high glycemic index carbohydrate and low levels of fiber and n-3 fatty acids lead to insulin resistance with hyperinsulinemia, hyperglycemia, and hypertriglyceridemia. We then consider how insulin, the related insulin-like growth factors, triglycerides, and nonesterified fatty acids could lead to increased growth of colon cancer precursor lesions and the development of colorectal cancer. Finally, we consider the implications of this scheme on possible future research directions, including studies of satiety and clinical tests of the importance of insulin resistance in the colon carcinogenesis process.

The relation of type 2 diabetes and cancer

Increasing evidence indicates that individuals with type 2 diabetes (diabetes) are at elevated risk for several common human malignancies, including cancers of the colon, breast, endometrium, pancreas, and liver. In particular, the consistent positive results reported by prospective investigations make it unlikely that methodologic issues, occult tumors, or chance results could explain the findings. Since diabetes and impaired fasting glucose together affect >25% of Americans above age 50, even a moderate etiologic association (e.g., relative risk = 1.5) would explain >10% of involved malignancies. Laboratory studies have suggested biologically plausible mechanisms. Insulin, for example, is typically at high levels during the development and early stages of diabetes. Activation of the insulin receptor by its ligand, or cross-activation of the insulin-like growth factor-I receptor, has been shown to be mitogenic and promote tumorigenesis in various model systems. A "unifying concept," in fact, holds that hyperinsulinemia may underlie the cancer associations of several additional risk factors, including high waist circumference, visceral fat, waist-to-hip ratio, body mass index, sedentary lifestyle, and energy intake. In this review, we assess current evidence regarding the relation of type 2 diabetes with cancer, and evaluate the findings in terms of well-accepted criteria for establishing causality.

Glycemic index, nutrient density, and promotion of aberrant crypt foci in rat colon

We speculated that a diet with a high glycemic index (GI) or a diet with a low nutrient density (nutrient-to-calorie ratio) would enhance colon carcinogenesis, presumably via increased insulin resistance. Forty-eight Sprague-Dawley (SD) rats received an azoxymethane injection (20 mg/kg) and were randomized into five groups given an AIN-76 diet containing 1) 65% starch by weight, 2) 65% glucose (GI = 100), 3) 65% fructose (GI = 23), 4) 82% starch, or 5) 39% oil and 39% sucrose. The nutrient density of Diets 4 and 5 was one-half that of Diets 1-3. Promotion was assessed by the multiplicity (number of crypts) of aberrant crypt foci (ACF), an early marker of colon carcinogenesis. Insulin resistance was estimated by the FIRI index (blood insulin x blood glucose), by plasma triglycerides, and by visceral fat. To confirm the results in another rat strain, the experiment was duplicated in 48 Fischer (F344) rats. Results show that 1) the ACF multiplicity was not different in glucose- and fructose-fed rats (p > 0.7): diets with contrasting GI had the same effect on ACF growth; 2) diets of low nutrient density increased visceral fat (p < 0.05) but reduced the ACF size in F344 rats (p < 0.001, no reduction in SD rats); and 3) indirect insulin resistance markers (FIRI index, blood triglycerides, and visceral fat) did not correlate with ACF multiplicity. These results do not support the hypothesis that diets with a high GI or low nutrient density or diets that increase some indirect insulin resistance markers can promote colon carcinogenesis in F344 or SD rats.