Leptin, insulin-like growth factor-1, and insulin-like growth factor-2 are mitogens in ApcMin/+ but not Apc+/+ colonic epithelial cell lines

Effect of Intermittent Fasting, Probiotic-Fermented Camel Milk, and Probiotic-Fermented Camel Milk Incorporating Sukkari Date on Diet-Induced Obesity in Rats

Obesity causes metabolic syndrome disorders that are detrimental to health. The current study examined the effects of intermittent fasting (IF), fermented camel milk (FCM), and fermented camel milk incorporating 10% Sukkari date (FCM-D) on weight loss, blood profile, and antioxidant status in obese rats for 6 weeks. Subsequently, leptin and adiponectin levels and histopathological examination of adipose tissue were carried out. Results showed that IF with FCM or FCM-D decreased body weight by 0.92 and −5.45%, respectively. IF alone lowered non-fasting blood glucose (NFBG) and fasting blood glucose FBG after 6 weeks, whereas adding FCM or FCM-D reduced NFBG after 4 weeks. Intermittently fasting obese rats given FCM or FCM-D had the lowest blood glucose levels (BGL). The hypolipidemic effects of IF, FCM, and FCM-D on obese rats reduced triglycerides (TG), cholesterols (CHO), and their derivatives. FCM-D with IF presented a superior effect on lipid profile. A reduction rate of 40, 37, 66, and 40% for TG, CHO, low-density lipoprotein (LDL-c), and very low-density lipoprotein (VLDL-c), respectively, and an increase in HDL-C by 34% were noticed. Reductions of 40, 37, 66, and 40% for TG, CHO, LDL-c, and VLDL-c, respectively, and a 34% rise in high-density lipoprotein (HDL-C) were noted. Combining IF with FCM or FCM-D lowered the atherogenic index (AI) by 42% and 59%, respectively. Remarkably, treating rats with FCM+IF or FCM-D+IF effectively attenuated leptin and adiponectin levels. Malondialdehyde (MDA) was significantly decreased in a type-dependent manner. Implementing FCM-D or FCM with IF significantly attenuated reduced glutathione (GSH), superoxide dismutase (SOD), MDA, and catalase (CAT) levels. The most efficient treatment was giving FCM-D with IF. Histopathologically, adipocyte lipolysis increases free fatty acids (FFAs) and promotes inflammation. Only IF+FCM-D indicated no histopathological alteration except for a few focal areas of a few inflammatory cell infiltrations in the parenchyma. In conclusion, combining IF and Probiotic-FCM or Probiotic-FCM-D effectively accelerated weight loss, attenuated metabolic markers, and reversed histopathological alterations. Thus, IF combined with Probiotic-FCM or Probiotic-FCM-D is highly recommended for weight loss, strengthening antioxidative status, and preventing health disorders.

Nobiletin and Derivatives: Functional Compounds from Citrus Fruit Peel for Colon Cancer Chemoprevention

The search for effective methods of cancer treatment and prevention has been a continuous effort since the disease was discovered. Recently, there has been increasing interest in exploring plants and fruits for molecules that may have potential as either adjuvants or as chemopreventive agents against cancer. One of the promising compounds under extensive research is nobiletin (NOB), a polymethoxyflavone (PMF) extracted exclusively from citrus peel. Not only does nobiletin itself exhibit anti-cancer properties, but its derivatives are also promising chemopreventive agents; examples of derivatives with anti-cancer activity include 3'-demethylnobiletin (3'-DMN), 4'-demethylnobiletin (4'-DMN), 3',4'-didemethylnobiletin (3',4'-DMN) and 5-demethylnobiletin (5-DMN). In vitro studies have demonstrated differential efficacies and mechanisms of NOB and its derivatives in inhibiting and killing of colon cancer cells. The chemopreventive potential of NOB has also been well demonstrated in several in vivo colon carcinogenesis animal models. NOB and its derivatives target multiple pathways in cancer progression and inhibit several of the hallmark features of colorectal cancer (CRC) pathophysiology, including arresting the cell cycle, inhibiting cell proliferation, inducing apoptosis, preventing tumour formation, reducing inflammatory effects and limiting angiogenesis. However, these substances have low oral bioavailability that limits their clinical utility, hence there have been numerous efforts exploring better drug delivery strategies for NOB and these are part of this review. We also reviewed data related to patents involving NOB to illustrate the extensiveness of each research area and its direction of commercialisation. Furthermore, this review also provides suggested directions for future research to advance NOB as the next promising candidate in CRC chemoprevention.

Polarization of macrophages in the tumor microenvironment is influenced by EGFR signaling within colon cancer cells

Epidermal growth factor receptor (EGFR) is a target of colon cancer therapy, but the effects of this therapy on the tumor microenvironment remain poorly understood. Our in vivo studies showed that cetuximab, an anti-EGFR monoclonal antibody, effectively inhibited AOM/DSS-induced, colitis-associated tumorigenesis, downregulated M2-related markers, and decreased F4/80+/CD206+ macrophage populations. Treatment with conditioned medium of colon cancer cells increased macrophage expression of the M2-related markers arginase-1 (Arg1), CCL17, CCL22, IL-10 and IL-4. By contrast, conditioned medium of EGFR knockout colon cancer cells inhibited expression of these M2-related markers and induced macrophage expression of the M1-related markers inducible nitric oxide synthase (iNOS), IL-12, TNF-α and CCR7. EGFR knockout in colon cancer cells inhibited macrophage-induced promotion of xenograft tumor growth. Moreover, colon cancer-derived insulin-like growth factor-1 (IGF-1) increased Arg1 expression, and treatment with the IGF1R inhibitor AG1024 inhibited that increase. These results suggest that inhibition of EGFR signaling in colon cancer cells modulates cytokine secretion (e.g. IGF-1) and prevents M1-to-M2 macrophage polarization, thereby inhibiting cancer cell growth.

Obesity, Diabetes and Cancer: A Mechanistic Perspective

Nearly 35% of adults and 20% of children in the United States are obese, defined as having a body mass index (BMI) ≥ 30 kg/m². Obesity is an established risk factor for many cancers, and obesity-associated metabolic perturbations often manifest in Type 2 diabetes mellitus and/or the metabolic syndrome. As part of the growth-promoting, proinflammatory microenvironment of the obese and/or diabetic state, crosstalk between macrophages, adipocytes, and epithelial cells occurs via metabolically-regulated hormones, cytokines, and other mediators to enhance cancer risk and/or progression. This review synthesizes the evidence on key biological mechanisms underlying the associations between obesity, diabetes and cancer, with particular emphasis on enhancements in growth factor signaling, inflammation, and vascular integrity processes. These interrelated pathways represent mechanistic targets for disrupting the obesity-diabetes-cancer link, and several diabetes drugs, such as metformin and rosiglitazone, are being intensely studied for repurposing as cancer chemopreventive agents.

Insulin-like growth factors inhibit dendritic cell-mediated anti-tumor immunity through regulating ERK1/2 phosphorylation and p38 dephosphorylation

Insulin-like growth factors (IGFs) can promote tumorigenesis via inhibiting the apoptosis of cancer cells. The relationship between IGFs and dendritic cell (DC)-mediated immunity were investigated. Advanced-stage ovarian carcinoma patients were first evaluated to show higher IGF-1 and IGF-2 concentrations in their ascites than early-stage patients. IGFs could suppress DCs' maturation, antigen presenting abilities, and the ability to activate antigen-specific CD8(+) T cell. IGF-treated DCs also secreted higher concentrations of IL-10 and TNF-α. IGF-treated DCs showed decreased ERK1/2 phosphorylation and reduced p38 dephosphorylation. The percentages of matured DCs in the ascites were significantly lower in the IGF-1 or IGF-2 highly-expressing WF-3 tumor-bearing mice. The IGF1R inhibitor - NVP-AEW541, could block the effects of IGFs to rescue DCs' maturation and to restore DC-mediated antigen-specific immunity through enhancing ERK1/2 phosphorylation and p38 dephosphorylation. IGFs can inhibit DC-mediated anti-tumor immunity through suppressing maturation and function and the IGF1R inhibitor could restore the DC-mediated anti-tumor immunity. Blockade of IGFs could be a potential strategy for cancer immunotherapy.

Obesity and cancer: at the crossroads of cellular metabolism and proliferation

Obesity is associated with an increased risk of cancer. The mechanisms underlying this association include but are not limited to increased systemic inflammation, an anabolic hormonal milieu, and adipocyte-cancer crosstalk, aberrant stimuli that conspire to promote neoplastic transformation. Cellular proliferation is uncoupled from nutrient availability in malignant cells, promoting tumor progression. Elucidation of the mechanisms underlying the obesity-cancer connection will lead to the development of novel metabolism-based agents for cancer prevention and treatment.

Epidemiological transition of colorectal cancer in developing countries: Environmental factors, molecular pathways, and opportunities for prevention

Colorectal cancer (CRC) is one of the leading causes of cancer and cancer-related mortality worldwide. The disease has been traditionally a major health problem in industrial countries, however the CRC rates are increasing in the developing countries that are undergoing economic growth. Several environmental risk factors, mainly changes in diet and life style, have been suggested to underlie the rise of CRC in these populations. Diet and lifestyle impinge on nuclear receptors, on the intestinal microbiota and on crucial molecular pathways that are implicated in intestinal carcinogenesis. In this respect, the epidemiological transition in several regions of the world offers a unique opportunity to better understand CRC carcinogenesis by studying the disease phenotypes and their environmental and molecular associations in different populations. The data from these studies may have important implications for the global prevention and treatment of CRC.

Effects of calorie restriction and diet-induced obesity on murine colon carcinogenesis, growth and inflammatory factors, and microRNA expression

Obesity is an established colon cancer risk factor, while preventing or reversing obesity via a calorie restriction (CR) diet regimen decreases colon cancer risk. Unfortunately, the biological mechanisms underlying these associations are poorly understood, hampering development of mechanism-based approaches for preventing obesity-related colon cancer. We tested the hypotheses that diet-induced obesity (DIO) would increase (and CR would decrease) colon tumorigenesis in the mouse azoxymethane (AOM) model. In addition, we established that changes in inflammatory cytokines, growth factors, and microRNAs are associated with these energy balance-colon cancer links, and thus represent mechanism-based targets for colon cancer prevention. Mice were injected with AOM once a week for 5 weeks and randomized to: 1) control diet; 2) 30% CR diet; or 3) DIO diet. Mice were euthanized at week 5 (n = 12/group), 10 (n = 12/group), and 20 (n = 20/group) after the last AOM injection. Colon tumors were counted, and cytokines, insulin-like growth factor 1 (IGF-1), IGF binding protein 3 (IGFBP-3), adipokines, proliferation, apoptosis, and expression of microRNAs (miRs) were measured. The DIO diet regimen induced an obese phenotype (∼36% body fat), while CR induced a lean phenotype (∼14% body fat); controls were intermediate (∼26% body fat). Relative to controls, DIO increased (and CR decreased) the number of colon tumors (p = 0.01), cytokines (p<0.001), IGF-1 (p = 0.01), and proliferation (p<0.001). DIO decreased (and CR increased) IGFBP-3 and apoptosis (p<0.001). miRs including mir-425, mir-196, mir-155, mir-150, mir-351, mir-16, let-7, mir34, and mir-138 were differentially expressed between the dietary groups. We conclude that the enhancing effects of DIO and suppressive effects of CR on colon carcinogenesis are associated with alterations in several biological pathways, including inflammation, IGF-1, and microRNAs.

Obesity, energy balance, and cancer: a mechanistic perspective

Nearly 36 % of adults and 20 % of children in the USA are obese, defined as a body mass index (BMI) ≥30 kg/m(2). Obesity, which is accompanied by metabolic dysregulation often manifesting in the metabolic syndrome, is an established risk factor for many cancers. Within the growth-promoting, proinflammatory environment of the obese state, cross talk between macrophages, adipocytes, and epithelial cells occurs via obesity-associated hormones, cytokines, and other mediators that may enhance cancer risk and/or progression. This chapter synthesizes the evidence on key biological mechanisms underlying the obesity-cancer link, with particular emphasis on obesity-associated enhancements in growth factor signaling, inflammation, and vascular integrity processes, as well as obesity-dependent microenvironmental perturbations, including the epithelial-to-mesenchymal transition. These interrelated pathways represent possible mechanistic targets for disrupting the obesity-cancer link.

Reduction of intestinal polyp formation in min mice fed a high-fat diet with aloe vera gel extract

Aloe vera gel supercritical CO2 extract (AVGE) has been shown to contain five phytosterols, reduce visceral fat accumulation, and influence the metabolism of glucose and lipids in animal model experiments. Recent epidemiologic studies have shown that obesity is an established risk factor for several cancers including colorectal cancer. Therefore, we examined the effects of AVGE on intestinal polyp formation in Apc-deficient Min mice fed a high-fat diet. Male Min mice were divided into normal diet (ND), high fat diet (HFD), low dose AVGE (HFD+LAVGE) and high dose AVGE (HFD+HAVGE) groups. The ND group received AIN-93G diet and the latter 3 groups were given modified high-fat AIN-93G diet (HFD) for 7 weeks. AVGE was suspended in 0.5% carboxymethyl cellulose (CMC) and administered orally to mice in HFD+LAVGE and HFD+HAVGE groups every day (except on Sunday) for 7 weeks at a dose of 3.75 and 12.5 mg/kg body weight, respectively. ND and HFD groups received 0.5% CMC alone. Between weeks 4 and 7, body weights in the HFD and HFD+LAVGE groups were reduced more than those in the ND group. However, body weights were not reduced in the HFD+HAVGE group. Mice were sacrificed at the end of the experiment and their intestines were scored for polyps. No significant differences were observed in either the incidence and multiplicity of intestinal polyps (≥0.5 mm in a diameter) among the three groups fed HFD. However, when intestinal polyps were categorized by their size into 0.5-1.4, 1.5-2.4, or ≥2.5 mm, the incidence and multiplicity of large polyps (≥2.5 mm) in the intestine in the HFD+HAVGE group were significantly lower than those in the HFD group. We measured plasma lipid (triglycerides and total cholesterol) and adipocytokine [interleukin-6 and high molecular weight (HMW) adiponectin] levels as possible indicators of mechanisms of inhibition. The results showed that HMW adiponectin levels in the HFD group were significantly lower than those in the ND group. However, the levels in the HFD+HAVGE group were significantly higher than those in the HFD group. These results indicate that HAVGE reduced large-sized intestinal polyps and ameliorated reduction in plasma HMW adiponectin levels in Min mice fed HFD.

Diabetes and cancer: two diseases with obesity as a common risk factor

There is a growing body of evidence to support a connection between diabetes (predominantly type 2), obesity and cancer. Multiple meta-analyses of epidemiological data show that people with diabetes are at increased risk of developing many different types of cancers, along with an increased risk of cancer mortality. Several pathophysiological mechanisms for this relationship have been postulated, including insulin resistance and hyperinsulinaemia, enhanced inflammatory processes, dysregulation of sex hormone production and hyperglycaemia. In addition to these potential mechanisms, a number of common risk factors, including obesity, may be behind the association between diabetes and cancer. Indeed, obesity is associated with an increased risk of cancer and diabetes. Abdominal adiposity has been shown to play a role in creating a systemic pro-inflammatory environment, which could result in the development of both diabetes and cancer. Here, we examine the relationship between diabetes, obesity and cancer, and investigate the potential underlying causes of increased cancer risk in individuals with diabetes. Current treatment recommendations for reducing the overall disease burden are also explored and possible areas for future research are considered.

Mechanisms of obesity-induced gastrointestinal neoplasia

Obesity is among the fastest growing diseases worldwide; treatment is inadequate, and associated disorders, including gastrointestinal cancers, have high morbidity and mortality. An increased understanding of the mechanisms of obesity-induced carcinogenesis is required to develop methods to prevent or treat these cancers. In this report, we review the mechanisms of obesity-associated colorectal, esophageal, gastric, and pancreatic cancers and potential treatment strategies.

Adipokines and obesity are associated with colorectal polyps in adult males: a cross-sectional study

BACKGROUND

Obesity increases the risk of colon cancer. It is also known that most colorectal cancers develop from adenomatous polyps. However, the effects of obesity and adipokines on colonic polyp formation are unknown.

METHODS

To determine if BMI, waist circumference or adipokines are associated with colon polyps in males, 126 asymptomatic men (48-65 yr) were recruited at time of colonoscopy, and anthropometric measures as well as blood were collected. Odds ratios were determined using polytomous logistic regression for polyp number (0 or ≥3) and polyp type (no polyp, hyperplastic polyp, tubular adenoma).

RESULTS

41% of the men in our study were obese (BMI ≥30). The odds of an obese individual having ≥3 polyps was 6.5 (CI: 1.3-33.0) times greater than those of a lean (BMI<25) individual. Additionally, relative to lean individuals, obese individuals were 7.8 (CI: 2.0-30.8) times more likely to have a tubular adenoma than no polyp. As BMI category increased, participants were 2.9 (CI: 1.5-5.4) times more likely to have a tubular adenoma than no polyps. Serum leptin, IP-10 and TNF-α were significantly associated with tubular adenoma presence. Serum leptin and IP-10 were significantly associated with increased likelihood of ≥3 polyps, and TNF-α showed a trend (p = 0.09).

CONCLUSIONS

Obese men are more likely to have at least three polyps and adenomas. This cross-sectional study provides evidence that colonoscopy should be recommended for obese, white males.

Mechanistic targets and phytochemical strategies for breaking the obesity-cancer link

The prevalence of obesity, an established risk and progression factor for many cancers, has increased dramatically in many countries over the past three decades. Worldwide, an estimated 600 million adults are currently obese. Thus, a better understanding of the mechanistic links between obesity and cancer is urgently needed to identify intervention targets and strategies to offset the procancer effects of obesity. This review synthesizes the evidence on key biological mechanisms underlying the obesity-cancer association, with particular emphasis on obesity-associated enhancements in growth factor signaling, inflammation, and perturbations in the tumor microenvironment. These interrelated pathways and processes that are aberrantly regulated in obese individuals represent mechanism-based targets for disrupting the obesity-cancer link using phytochemicals.

Calorie restriction and cancer prevention: a mechanistic perspective

Calorie restriction (CR) is one of the most potent broadly acting dietary interventions for inducing weight loss and for inhibiting cancer in experimental models. Translation of the mechanistic lessons learned from research on CR to cancer prevention strategies in human beings is important given the high prevalence of excess energy intake, obesity, and metabolic syndrome in many parts of the world and the established links between obesity-associated metabolic perturbations and increased risk or progression of many types of cancer. This review synthesizes findings on the biological mechanisms underlying many of the anticancer effects of CR, with emphasis on the impact of CR on growth factor signaling pathways, inflammation, cellular and systemic energy homeostasis pathways, vascular perturbations, and the tumor microenvironment. These CR-responsive pathways and processes represent targets for translating CR research into effective cancer prevention strategies in human beings.

Curcumin and docosahexaenoic acid block insulin-induced colon carcinoma cell proliferation

Diets high in fish and curcumin are associated with a decreased risk of CRC. Insulin resistance and obesity are associated with increased CRC risk and higher reoccurrence rates. We utilized cell culture to determine if dietary compounds could reduce insulin-induced cell proliferation comparing the response in normal and metastatic colon epithelial cells. We treated model normal murine colon epithelial cells (YAMC) and adenocarcinoma cells (MC38) with docosahexaenoic acid (DHA) or curcumin alone and then co-treatments of the diet-derived compound and insulin were combined. Cell proliferation was stimulated with insulin (1 ug/mL) to model insulin resistance in obesity. Despite the presence of insulin, proliferation was reduced in the MC38 cells treated with 10 μM curcumin (p<0.001) and 50 μM DHA (p<0.001). Insulin stimulated MAPK and MEK phosphorylation was inhibited by DHA and curcumin in MC38 cancer cells. Here we show that curcumin and DHA can block insulin-induced colon cancer cell proliferation in vitro via a MEK mediated mechanism.

Obesity, metabolic dysregulation, and cancer: a growing concern and an inflammatory (and microenvironmental) issue

Obesity is an established risk and progression factor for many cancers. In the United States more than one-third of adults, and nearly one in five children, are currently obese. Thus, a better understanding of the mechanistic links between obesity and cancer is urgently needed to identify intervention targets and strategies to offset the procancer effects of obesity. This review synthesizes the evidence on key biological mechanisms underlying the obesity–cancer association, with particular emphasis on obesity-associated enhancements in growth factor signaling, inflammation, and perturbations in the tumor microenvironment. These interrelated pathways and processes represent mechanistic targets for disrupting the obesity–cancer link.

The Australian fruit Illawarra plum (Podocarpus elatus Endl., Podocarpaceae) inhibits telomerase, increases histone deacetylase activity and decreases proliferation of colon cancer cells

Fruit antioxidants have many health benefits including prevention of cancer development. The native Australian bush fruit Illawarra plum (Podocarpus elatus Endl., Podocarpaceae) has a high content of anthocyanin-rich phenolics, with an antioxidant capacity at levels higher than most fruits. In the present study the molecular mechanisms of the anti-proliferative activity of Illawarra plum on colorectal cancer cells were investigated. Non-tumorigenic young adult mouse colonic (YAMC) cells and tumorigenic human colonic (HT-29) cells were treated with a polyphenolic-rich Illawarra plum extract (0-1000 microg/ml). Illawarra plum had anti-proliferative properties in only the cancer cells, with growth suppressed in a dose- and time-dependent manner. Treatment of HT-29 cells with Illawarra plum extract (500 mg/ml; 24 h) was also associated with a 2-fold increase in apoptosis, and a cell cycle delay in the S phase (P < 0.01). Assessment of biomarkers for DNA damage revealed that plum treatment caused a 93% down-regulation of telomerase activity (P < 0.001) and a decrease in telomere length (up to 75%; P < 0.01). Treatment with Illawarra plum extract also induced morphological alterations to HT-29 cells that were suggestive of induction of autophagy, as the formation of cytoplasmic vacuoles was observed in many cells. This could be induced by the increased (6-fold) histone deacetylase (HDAC) activity (P < 0.001) and the trend for increased expression of the class III HDAC sirtuin 1. The present study has shown that Illawarra plum extract is able to reduce the proliferation of colon cancer cells by altering the cell cycle, increasing apoptosis and possibly inducing autophagy. The active ingredients in Illawarra plum may provide an alternative chemoprevention strategy to conventional chemotherapy.

Growth signals, inflammation, and vascular perturbations: mechanistic links between obesity, metabolic syndrome, and cancer

Nearly 35% of adults and 20% of children in the United States are obese, defined as a body mass index ≥ 30 kg/m(2). Obesity, which is accompanied by metabolic dysregulation often manifesting in the metabolic syndrome, is an established risk factor for many cancers. Within the growth-promoting, proinflammatory environment of the obese state, cross talk between macrophages, adipocytes, and epithelial cells occurs via obesity-associated hormones, cytokines, and other mediators that may enhance cancer risk and progression. This review synthesizes the evidence on key biological mechanisms underlying the obesity-cancer link, with particular emphasis on obesity-associated enhancements in growth factor signaling, inflammation, and vascular integrity processes. These interrelated pathways represent possible mechanistic targets for disrupting the obesity-cancer link.

Decreased systemic IGF-1 in response to calorie restriction modulates murine tumor cell growth, nuclear factor-κB activation, and inflammation-related gene expression

Calorie restriction (CR) prevents obesity and has potent anticancer effects associated with altered hormones and cytokines. We tested the hypothesis that CR inhibits MC38 mouse colon tumor cell growth through modulation of hormone-stimulated nuclear factor (NF)-κB activation and protumorigenic gene expression. Female C57BL/6 mice were randomized (n = 30/group) to receive control diet or 30% CR diet. At 20 wk, 15 mice/group were killed for body composition analysis. At 21 wk, serum was obtained for hormone analysis. At 22 wk, mice were injected with MC38 cells; tumor growth was monitored for 24 d. Gene expression in excised tumors and MC38 cells was analyzed using real-time RT-PCR. In vitro MC38 NF-κB activation (by p65 ELISA and immunofluorescence) were measured in response to varying IGF-1 concentrations (1-400 ng/mL). Relative to controls, CR mice had decreased tumor volume, body weight, body fat, serum IGF-1, serum leptin, and serum insulin, and increased serum adiponectin (P < 0.05, each). Tumors from CR mice, versus controls, had downregulated inflammation- and/or cancer-related gene expression, including interleukin (IL)-6, IL-1β, tumor necrosis factor-α, cyclooxygenase-2, chemokine (C-C motif) ligand-2, S100A9, and F4/80, and upregulated 15-hydroxyprostaglandin dehydrogenase expression. In MC38 cells in vitro, IGF-1 increased NF-κB activation and NF-κB downstream gene expression (P < 0.05, each). We conclude that CR, in association with reduced systemic IGF-1, modulates MC38 tumor growth, NF-κB activation, and inflammation-related gene expression. Thus, IGF-1 and/or NF-κB inhibition may pharmacologically mimic the anticancer effects of CR to break the obesity-colon cancer link.

High-fat diet alters gene expression in the liver and colon: links to increased development of aberrant crypt foci

BACKGROUND

Obesity is associated with an increased risk of colon cancer. High-fat diets that lead to obesity may be a contributing factor, but the mechanisms are unknown.

AIMS

This study examines susceptibility to azoxymethane (AOM)-induced precancerous lesions in mice in response to consumption of either a low or a high-fat diet and associated molecular changes in the liver and colon.

METHODS

Gene markers of xenobiotic metabolism, leptin-regulated inflammatory cytokines and proliferation were assessed in liver and colon in response to high-fat feeding to determine links with increased sensitivity to AOM.

RESULTS

High-fat feeding increased development of AOM-induced precancerous lesions and was associated with increased CYP2E1 gene expression in the liver, but not the colon. Leptin receptors and the colon stem cell marker (Lgr5) were down-regulated in the proximal colon, with a corresponding up-regulation of the inflammatory cytokine (IL6) in response to high-fat feeding. Notably in the distal colon, where aberrant crypt foci develop in response to AOM, the proliferative stem cell marker, Lgr5, was significantly up-regulated with high-fat feeding.

CONCLUSIONS

The current study provides evidence that high-fat diets can alter regulation of molecular markers of xenobiotic metabolism that may expose the colon to carcinogens, in parallel with activation of β-catenin-regulated targets regulating colon epithelial cells. High-fat diets associated with obesity may alter multiple molecular factors that act synergistically to increase the risk of colon cancer associated with obesity.

Dietary energy balance modulation of epithelial carcinogenesis: a role for IGF-1 receptor signaling and crosstalk

Obesity affects more than one third of the U.S. population and is associated with increased risk and/or disease severity for several chronic diseases, including cancer. In contrast, calorie restriction (CR) consistently inhibits cancer across species and cancer types. Differential effects on globally active circulatory proteins, particularly insulin-like growth factor-1 (IGF-1), provide a plausible mechanistic explanation for the energy balance-cancer link. Diet-induced changes in circulating IGF-1 modulate IGF-1R/EGFR activation and downstream signaling to Akt and mTOR. These dietary energy balance effects on signaling ultimately modulate the levels and/or activity of cell cycle regulatory proteins, regulating proliferation, and modulating susceptibility to tumor development. Selective targeting of mTORC1 potently inhibits tumorigenesis in several model systems producing CR mimetic effects. Targeting this and other pathways modulated by dietary energy balance may lead to the development of strategies for cancer chemoprevention and for reversing the effects of obesity on cancer development and progression.

Diet-induced weight loss reduces colorectal inflammation: implications for colorectal carcinogenesis

BACKGROUND

Epidemiologic data have shown that obesity independently increases colorectal cancer (CRC) risk, but the mechanisms are poorly understood. Obesity is an inflammatory state, and chronic colonic inflammation induces CRC.

OBJECTIVE

We conducted this proof-of-principle study to seek evidence of obesity-associated colorectal inflammation and to evaluate effects of diet-induced weight loss.

DESIGN

We measured inflammatory cytokines, gene arrays, and macrophage infiltration in rectosigmoid mucosal biopsies of 10 obese premenopausal women [mean ± SD body mass index (in kg/m(2)): 35 ± 3.5] before and after weight loss induced by a very-low-calorie diet.

RESULTS

Subjects lost a mean (±SD) of 10.1 ± 1% of their initial weight. Weight loss significantly reduced fasting blood glucose, total cholesterol, triglycerides, LDL, tumor necrosis factor-α (TNF-α), and interleukin (IL)-8 concentrations (P < 0.05). After weight loss, rectosigmoid biopsies showed a 25-57% reduction in TNF-α, IL-1β, IL-8, and monocyte chemotactic protein 1 concentrations (P < 0.05). T cell and macrophage counts decreased by 28% and 42%, respectively (P < 0.05). Gene arrays showed dramatic down-regulation of proinflammatory cytokine and chemokine pathways, prostaglandin metabolism, and the transcription factors STAT3 (signal transducer and activator of transcription 3) and nuclear transcription factor κB. Weight loss reduced expression of FOS and JUN genes and down-regulated oxidative stress pathways and the transcription factors ATF (activating transcription factor) and CREB (cyclic AMP response element-binding).

CONCLUSIONS

Our data show that diet-induced weight loss in obese individuals reduces colorectal inflammation and greatly modulates inflammatory and cancer-related gene pathways. These data imply that obesity is accompanied by inflammation in the colorectal mucosa and that diet-induced weight loss reduces this inflammatory state and may thereby lower CRC risk.

Energy balance modulates colon tumor growth: Interactive roles of insulin and estrogen

Obesity increases colorectal cancer (CRC) risk and progression. However, the impact of obesity on CRC in women is dependent on ovarian hormone status. The purpose of this study was to determine the interactive roles of obesity and ovarian hormones on serum markers of inflammation, cell signaling, and transplanted colon tumor growth. Female C57BL/6 mice (6 wk) were either ovariectomized (OVX) or ovaries left intact (nonovariectomized, NOVX) and randomized to receive a (1) control, (2) 30% calorie-restricted (CR), or (3) diet-induced obese (DIO) diet regimen for 20 wk to induce differing levels of adiposity. Serum was collected and inflammatory and metabolic markers were measured using an antibody array (62 proteins) and ELISAs. Mice were subcutaneously injected with syngeneic MC38 colon cancer cells after 20 wk and sacrificed 4 wk later. CR mice had the smallest tumors irrespective of hormone status, whereas the largest tumors were observed in DIO-OVX mice. Glucose tolerance was impaired in OVX mice, being most severe in the DIO-OVX group. Cytokine arrays suggested that in CR animals, inhibition of tumor growth paralleled insulin sensitivity and associated changes in leptin, adiponectin, and IGF-BPs. Conversely, in DIO-OVX animals, tumor growth was associated with insulin and leptin resistance as well as higher levels of pro-inflammatory proteins. In vitro, leptin and adiponectin had no effect, whereas insulin induced MC38 cell proliferation and MAPK activation. Co-treatment with estrogen blocked the stimulatory effects of insulin. Thus, our in vitro and in vivo data indicate female reproductive hormones have a modulating effect on obesity-induced insulin resistance and inflammation, which may directly or indirectly influence CRC progression.

Metabolic surgery and cancer: protective effects of bariatric procedures

The worldwide epidemic of obesity and the global incidence of cancer are both increasing. There is now epidemiological evidence to support a correlation between obesity, weight gain, and some cancers. Metabolic or bariatric surgery can provide sustained weight loss and reduced obesity-related mortality. These procedures can also improve the metabolic profile to decrease cardiovascular risk and resolve diabetes in morbidly obese patients. The operations offer several physiological steps, the so-called BRAVE effects: 1) bile flow alteration, 2) reduction of gastric size, 3) anatomical gut rearrangement and altered flow of nutrients, 4) vagal manipulation and 5) enteric gut hormone modulation. Metabolic operations are also associated with a significant reduction of cancer incidence and mortality. The cancer-protective role of metabolic surgery is strongest for female obesity-related tumors; however, the underlying mechanisms may involve both weight-dependent and weight-independent effects. These include the improvement of insulin resistance with attenuation of the metabolic syndrome as well as decreased oxidative stress and inflammation in addition to the beneficial modulation of sex steroids, gut hormones, cellular energetics, immune system, and adipokines. Elucidating the precise metabolic mechanisms of cancer prevention by metabolic surgery can increase our understanding of how obesity, diabetes, and metabolic syndrome are associated with cancer. It may also offer novel treatment strategies in the management of tumor generation and growth.

ERK regulates strain-induced migration and proliferation from different subcellular locations

Repetitive deformation like that engendered by peristalsis or villous motility stimulates intestinal epithelial proliferation on collagenous substrates and motility across fibronectin, each requiring ERK. We hypothesized that ERK acts differently at different intracellular sites. We stably transfected Caco-2 cells with ERK decoy expression vectors that permit ERK activation but interfere with its downstream signaling. Targeting sequences constrained the decoy inside or outside the nucleus. We assayed proliferation by cell counting and migration by circular wound closure with or without 10% repetitive deformation at 10 cycles/min. Confocal microscopy confirmed localization of the fusion proteins. Inhibition of phosphorylation of cytoplasmic RSK or nuclear Elk confirmed functionality. Both the nuclear-localized and cytosolic-localized ERK decoys prevented deformation-induced proliferation on collagen. Deformation-induced migration on fibronectin was prevented by constraining the decoy in the nucleus but not in the cytosol. Like the nuclear-localized ERK decoy, a Sef-overexpressing adenovirus that sequesters ERK in the cytoplasm also blocked the motogenic and mitogenic effects of strain. Inhibiting RSK or reducing Elk ablated both the mitogenic and motogenic effects of strain. RSK isoform reduction revealed isoform specificity. These results suggest that ERK must translocate to the nucleus to stimulate cell motility while ERK must act in both the cytosol and the nucleus to stimulate proliferation in response to strain. Selectively targeting ERK within different subcellular compartments may modulate or replace physical force effects on the intestinal mucosa to maintain the intestinal mucosal barrier in settings when peristalsis or villous motility are altered and fibronectin is deposited into injured tissue.

Energy balance, host-related factors, and cancer progression

Obesity is associated with an increased risk and worsened prognosis for many types of cancer, but the mechanisms underlying the obesity-cancer progression link are poorly understood. Several energy balance-related host factors are known to influence tumor progression and/or treatment responsiveness after cancer develops, and these have been implicated as key contributors to the complex effects of obesity on cancer outcome. These host factors include leptin, adiponectin, steroid hormones, reactive oxygen species associated with inflammation, insulin, insulin-like growth factor-1, and sirtuins. Each of these host factors is considered in this article in the context of energy balance and cancer progression. In addition, future research directions in this field are discussed, including the importance of study designs addressing energy balance across the life course, the development and application of highly relevant animal models, potential roles of cancer stem cells in the response to energy balance modulation, and emerging pharmacologic approaches that target energy balance-related pathways.

Adipokine regulation of colon cancer: adiponectin attenuates interleukin-6-induced colon carcinoma cell proliferation via STAT-3

Obesity results in increased circulating levels of specific adipokines, which are associated with colon cancer risk. The disease state is associated with increased leptin, insulin, IGF-1, and IL-6. Conversely, adiponectin levels are decreased in obese individuals. Previously, we demonstrated adipokine-enhanced cell proliferation in preneoplastic, but not normal, colon epithelial cells, demonstrating a differential effect of adipokines on colon cancer progression in vitro. Using a model of late stage carcinoma cancer cell, namely murine MC-38 colon carcinoma cells, we compared the effect of obesity-associated adipokines (leptin, insulin, IGF-1, and IL-6) on MC-38 cell proliferation and determined whether adiponectin (full length or globular) could modulate adipokine-induced cell proliferation. We show that insulin and IL-6, but not leptin and IGF-1, induce proliferation in MC-38 cells. Adiponectin treatment of MC-38 cells did not inhibit insulin-induced cell proliferation but did inhibit IL-6-induced cell proliferation by decreasing STAT-3 phosphorylation and activation. Nitric oxide (NO) production was increased in MC-38 cells treated with IL-6; co-treatment with adiponectin blocked IL-6-induced iNOS and subsequent NO production. These data are compared to previously reported findings from our laboratory using the YAMC (model normal colon epithelial cells) and IMCE (model preneoplastic) cells. The cell lines are utilized to construct a model summarizing the hormonal consequences of obesity and the impact on the differential regulation of colon epithelial cells along the continuum to carcinoma. These data, taken together, highlight mechanisms involved in obesity-associated cancers and may lead to potential-targeted therapies.

Obesity promotes melanoma tumor growth: role of leptin

Epidemiological studies suggest that obesity increases the risk of developing several cancers, including melanoma. Obesity increases the expression of angiogenic factors, such as leptin, that may contribute to tumor growth. However, a direct cause and effect relationship between obesity and tumor growth has not been clearly established and the role of leptin in accelerating tumor growth is unclear. Our objective in the present study was to examine the rate of melanoma tumor growth in lean and obese mice with leptin deficiency or high levels of plasma leptin. We injected 1 x 10(6) B16F10 melanoma cells subcutaneously into lean wild type (WT), obese melanocortin receptor 4 knockout (MC4R(-/-)), which have high leptin levels, obese leptin-deficient (ob(-/-)), pair fed lean ob(-/-), and lean ob(+/-) mice. Mean body weights were 29.7 +/- 0.3 g (WT), 46.3 +/- 1.9 g (MC4R(-/-)), 63.7 +/- 0.9 g (ob(-/-)), 30.5 +/- 1.0 g (pair fed ob(-/-)) and 31.6 +/- 1.7 g (ob(+/-)). Tumors were much larger in the obese leptin deficient ob(-/-) (5.1 +/- 0.9 g) and obese MC4R(-/-) (5.1 +/- 0.7 g) than in lean WT (1.9 +/- 0.3 g) and ob(+/-) (2.8 +/- 0.7 g) mice. Prevention of obesity by pair feeding ob(-/-) mice dramatically reduced tumor weight (0.95 +/- 0.2 g) to a level that was significantly lower than in WT mice of the same weight. Tumor VEGF levels were the highest in the obese mouse tumors (p < 0.05), regardless of the host leptin levels. Except for the lean ob(+/-), MC4R(-/-) and ob(-/-) melanomas had the highest VEGF receptor 1 and VEGF receptor 2 protein expression (p < 0.01 and p < 0.05), respectively. These results indicate that obesity markedly increases melanoma tumor growth rate by mechanisms that may involve upregulation of VEGF pathways. Although tumor growth does not require host leptin, melanoma tumor growth may be accelerated by leptin.

Adipocytokines as new promising markers of colorectal tumors: adiponectin for colorectal adenoma, and resistin and visfatin for colorectal cancer

Adipocytokines are adipocyte-secreted hormones associated with some malignancies such as colorectal, breast, and prostate cancer. We hypothesized that changes in the levels of adipocytokines may indicate the carcinogenesis and progression of colorectal cancer and adenoma, and investigated the association of the blood levels of several adipocytokines through a case-control study. Blood levels of adiponectin, leptin, resistin, visfatin, and C-peptide at diagnosis were measured in 115 colorectal cancer patients and 115 age-, sex-, and body mass index-matched controls. The same analysis was performed in 72 colorectal adenoma patients and 72 controls. Logistic regression models were used for estimating odds ratios and 95% confidence intervals, and one-way anova was performed to determine the prevalence of each variable between two or more groups. Resistin and visfatin levels in cancer patients were significantly higher than those of controls on multivariate analysis (P = 0.03 and P < 0.01, respectively). Stage progression significantly correlated with resistin and visfatin levels (P < 0.01 for both). The adiponectin level in adenoma patients was significantly lower than that of controls on multivariate analysis (P = 0.04). Its level was inversely correlated with the number of adenoma (P = 0.02), but not correlated with the size of adenoma. Resistin and visfatin may be good biomarkers of colorectal malignant potential and stage progression. Adiponectin level may be a good biomarker of colorectal adenoma.

Calories and carcinogenesis: lessons learned from 30 years of calorie restriction research

Calorie restriction (CR) is arguably the most potent, broadly acting dietary regimen for suppressing the carcinogenesis process, and many of the key studies in this field have been published in Carcinogenesis. Translation of the knowledge gained from CR research in animal models to cancer prevention strategies in humans is urgently needed given the worldwide obesity epidemic and the established link between obesity and increased risk of many cancers. This review synthesizes the evidence on key biological mechanisms underlying many of the beneficial effects of CR, with particular emphasis on the impact of CR on growth factor signaling pathways and inflammatory processes and on the emerging development of pharmacological mimetics of CR. These approaches will facilitate the translation of CR research into effective strategies for cancer prevention in humans.

Dietary flavonoids suppress azoxymethane-induced colonic preneoplastic lesions in male C57BL/KsJ-db/db mice

Obesity is known to be a risk factor for colon carcinogenesis. Although there are several reports on the chemopreventive abilities of dietary flavonoids in chemically induced colon carcinogenesis, those have not been addressed in an obesity-associated carcinogenesis model. In the present study, the effects of 3 flavonoids (chrysin, quercetin and nobiletin) on modulation of the occurrence of putative preneoplastic lesions, aberrant crypt foci (ACF), and beta-catenin-accumulated crypts (BCACs) in the development of colon cancer were determined in male db/db mice with obesity and diabetic phenotypes. Male db/db mice were given 3 weekly intraperitoneal injections of azoxymethane (AOM) to induce the ACF and BCAC. Each flavonoid (100ppm), given in the diet throughout the experimental period, significantly reduced the numbers of ACF by 68-91% and BCAC by 64-71%, as well as proliferation activity in the lesions. Clinical chemistry results revealed that the serum levels of leptin and insulin in mice treated with AOM were greater than those in the untreated group. Interestingly, the most pronounced suppression of development of preneoplastic lesions and their proliferation were observed in the quercetin-fed group, in which the serum leptin level was lowered. Furthermore, quercetin-feeding decreased leptin mRNA expression and secretion in differentiated 3T3-L1 mouse adipocytes. These results suggest that the present dietary flavonoids are able to suppress the early phase of colon carcinogenesis in obese mice, partly through inhibition of proliferation activity caused by serum growth factors. Furthermore, they indicate that certain flavonoids may be useful for prevention of colon carcinogenesis in obese humans.

Physical activity, obesity and risk for esophageal adenocarcinoma

Over the past three decades, an increasing incidence of esophageal adenocarcinoma (EADC) has been reported throughout North America and Europe at a rate exceeding that of any other human solid tumor. Recent studies have clearly implicated chronic gastroesophageal reflux disease and several lifestyle risk factors, including tobacco consumption, diet and obesity, to be associated with increased risk of EADC. Although physical inactivity is now recognized as a risk factor for several chronic diseases including cancer, only a very limited number of studies have specifically evaluated the association between physical activity and esophageal malignancy. Furthermore, the precise biological mechanisms underlying the association between physical activity, obesity and cancer risk remain unclear. Since successful promotion of healthy body weight and exercise may substantially reduce the future incidence of cancer in the population, the purpose of this review is to explore current evidence linking physical activity, obesity and risk of malignancy – specifically EADC.

Adiponectin suppresses tumorigenesis in Apc(Min)(/+) mice

Recent reports have shown that adiponectin has a suppressive effect on various types of malignancy. In order to clarify the role of adiponectin in colorectal carcinogenesis, we examined the effect of exogenous administration of adiponectin on intestinal polyp formation in C57BL/6J-Apc(Min)(/+) mice, which possess a point mutation in the Apc gene. And we found that adiponectin treatment significantly decreased the number of adenomatous polyps, especially polyps larger than 2mm in diameter, in the small intestine. Two major receptors for adiponectin, AdipoR1 and AdipoR2, were expressed in adenomatous polyps, and their expression levels were not altered by adiponectin injection. In conclusion, adiponectin suppresses the growth of intestinal adenomas in the Apc(Min)(/+) mice. Increasing the adiponectin level may be a new strategy for the prevention of colorectal cancer at an early step of carcinogenesis.

Novel mechanism for obesity-induced colon cancer progression

Adipose tissue secretes factors linked to colon cancer risk including leptin. A hallmark of cancer is sustained angiogenesis. While leptin promotes angiogenesis in adipose tissue, it is unknown whether leptin can induce epithelial cells to produce factors that may drive angiogenesis, vascular development and therefore cancer progression. The purpose of this study was to compare the effects of leptin-stimulated colon epithelial cells differing in adenomatous polyposis coli (Apc) genotype (gatekeeper tumor suppressor gene for colon cancer) on angiogenesis. We employed novel colonic epithelial cell lines derived from the Immorto mouse [young adult mouse colon (YAMC)] and the Immorto-Min mouse [Immorto-Min colonic epithelial cell (IMCE)], which carries the Apc Min mutation, to study the effects of leptin-stimulated colon epithelial cells on angiogenesis. We utilized ex vivo rat mesenteric capillary bioassay and human umbilical vein endothelial cell (HUVEC) models to study angiogenesis. IMCE cells stimulated with leptin produced significantly more vascular endothelial growth factor (VEGF) than YAMC (268 +/- 18 versus 124 +/- 8 pg/ml; P < 0.01) cells. Leptin treatment induced dose-dependent increases in VEGF only in IMCE cells. Conditioned media from leptin (50 ng/ml)-treated IMCE cells induced significant capillary formation compared with control, which was blocked by the addition of a neutralizing antibody against VEGF. Conditioned media from leptin-treated IMCE cells also induced HUVEC cell proliferation, chemotaxis, upregulation of adhesion proteins and cell-signaling activation resulting in nuclear factor kappa B nuclear translocation and DNA binding due to VEGF. This is the first study demonstrating that leptin can induce preneoplastic colon epithelial cells to orchestrate VEGF-driven angiogenesis and vascular development, thus providing a specific mechanism and potential target for obesity-associated cancer.

Citrus compounds inhibit inflammation- and obesity-related colon carcinogenesis in mice

Dietary polyphenols are important potential chemopreventive natural agents. Other agents, such as citrus compounds, are also candidates for cancer chemopreventives. They act on multiple key elements in signal transduction pathways related to cellular proliferation, differentiation, apoptosis, inflammation, and obesity. This short review article provides our findings of preclinical studies on potential chemopreventive activities of dietary citrus compounds, auraptene, collinin, and citrus unshiu segment membrane (CUSM), using clitis- and obesity-related colon tumorigenesis models. Dietary feeding with auraptene and collinin at dose levels of 0.01% and 0.05% significantly lowered the incidence (50-60% reduction) and multiplicity (67-80% reduction) of colonic adenocarcinomas induced by azoxymetahene [AOM, single intraperitoneal injection of 10 mg/kg body weight (bw)] and dextran sodium sulfate (1% in drinking water). Anti-inflammatory potency of aurapene and collinin may contribute to the effects. Administration with CUSM at 3 doses in diet significantly inhibited development of aberrant crypts foci induced by 5 weekly subcutaneous injections of AOM (15 mg/kg bw) in male db/db mice: 53% inhibition by 0.02% CUSM, 54% inhibition by 0.1% CUSM, and 59% inhibition by 0.5% CUSM. CUSM treatment also decreased serum level of triglycerides. Our findings suggest that certain citrus materials are capable of inhibiting clitis- and obesity-related colon carcinogenesis.

Intramammary infusion of leptin decreases proliferation of mammary epithelial cells in prepubertal heifers

High energy intake and excessive body fatness impair mammogenesis in prepubertal ruminants. High energy intake and excessive fatness also increase serum leptin. Our objective was to determine if an infusion of leptin decreases proliferation of mammary epithelial cells of prepubertal heifers in vivo. Ovine leptin at 100 microg/ quarter per d with or without 10 microg of insulin-like growth factor (IGF)-I was infused via the teat canal into mammary glands of prepubertal dairy heifers; contralateral quarters were used as controls. After 7 d of treatment, bromodeoxyuridine was infused intravenously and heifers were slaughtered approximately 2 h later. Tissue from 3 regions of the mammary parenchyma was collected and immunostained for bromodeoxyuridine (BrdU), proliferating cell nuclear antigen (Ki-67), and caspase-3. Leptin decreased the number of mammary epithelial cells in the S-phase of the cell cycle by 48% in IGF-I-treated quarters and by 19% in saline-treated quarters. Leptin did not alter the number of mammary epithelial cells within the cell cycle, as indicated by Ki-67 labeling. Caspase-3 immunostaining within the mammary parenchyma was very low in these heifers, but leptin significantly increased labeling in saline-treated quarters. Leptin enhanced SOCS-3 expression in IGF-I-treated quarters but did not alter SOCS-1 or SOCS-5 expression. We conclude that a high concentration of leptin in the bovine mammary gland reduces proliferation of mammary epithelial cells. The reduced proliferation is accompanied by an increase in SOCS-3 expression, suggesting a possible mechanism for leptin inhibition of IGF-I action. Whether leptin might be a physiological regulator of mammogenesis remains to be determined.

C/EBPbeta regulates body composition, energy balance-related hormones and tumor growth

The prevalence of obesity, an established epidemiologic risk factor for many chronic diseases including cancer, has been steadily increasing in the US over several decades. The mechanisms used to regulate energy balance and adiposity and the relationship of these factors to cancer are not completely understood. Here we have used knockout mice to examine the roles of the transcription factors CCAAT/enhancer-binding protein (C/EBP) beta and C/EBPdelta in regulating body composition and systemic levels of hormones such as insulin-like growth factor-1 (IGF-1), leptin and insulin that mediate energy balance. Dual-energy X-ray absorptiometry showed that C/EBPbeta, either directly or indirectly, modulated body weight, fat content and bone density in both males and females, while the effect of C/EBPdelta was minor and only affected adiposity and body weight in female animals. Levels of IGF-1, leptin and insulin in the serum were decreased in both male and female C/EBPbeta(-/-) mice, and C/EBPbeta was associated with their promoters in vivo. Moreover, colon adenocarcinoma cells displayed reduced tumorigenic potential when transplanted into C/EBPbeta-deficient animals, especially males. Thus, C/EBPbeta contributes to endocrine expression of IGF-1, leptin and insulin, which modulate energy balance and can contribute to cancer progression by creating a favorable environment for tumor cell proliferation and survival.

Strain-induced proliferation requires the phosphatidylinositol 3-kinase/AKT/glycogen synthase kinase pathway

The intestinal epithelium is repetitively deformed by shear, peristalsis, and villous motility. Such repetitive deformation stimulates the proliferation of intestinal epithelial cells on collagen or laminin substrates via ERK, but the upstream mediators of this effect are poorly understood. We hypothesized that the phosphatidylinositol 3-kinase (PI3K)/AKT cascade mediates this mitogenic effect. PI3K, AKT, and glycogen synthase kinase-3beta (GSK-3beta) were phosphorylated by 10 cycles/min strain at an average 10% deformation, and pharmacologic blockade of these molecules or reduction by small interfering RNA (siRNA) prevented the mitogenic effect of strain in Caco-2 or IEC-6 intestinal epithelial cells. Strain MAPK activation required PI3K but not AKT. AKT isoform-specific siRNA transfection demonstrated that AKT2 but not AKT1 is required for GSK-3beta phosphorylation and the strain mitogenic effect. Furthermore, overexpression of AKT1 or an AKT chimera including the PH domain and hinge region of AKT2 and the catalytic domain and C-tail of AKT1 prevented strain activation of GSK-3beta, but overexpression of AKT2 or a chimera including the PH domain and hinge region of AKT1 and the catalytic domain and C-tail of AKT2 did not. These data delineate a role for PI3K, AKT2, and GSK-3beta in the mitogenic effect of strain. PI3K is required for both ERK and AKT2 activation, whereas AKT2 is sequentially required for GSK-3beta. Furthermore, AKT2 specificity requires its catalytic domain and tail region. Manipulating this pathway may prevent mucosal atrophy and maintain the mucosal barrier in conditions such as ileus, sepsis, and prolonged fasting when peristalsis and villous motility are decreased and the mucosal barrier fails.

Leptin promotes motility and invasiveness in human colon cancer cells by activating multiple signal-transduction pathways

Leptin serum levels are about 5 times higher in obese people than in normal individuals. We aimed at investigating the signaling pathways induced by leptin in the human colonic cell lines LS174T and HM7. Both cells expressed the leptin transmembrane Ob-receptor. Leptin activated the mitogen-activated protein kinase pathway, induced invasion of colonic cells and concomitantly increased the formation of lamellipodial structures. A direct and novel dose- and time-dependent activation of RhoA, Cdc42 and Rac1 by leptin is demonstrated in these aggressive colon cancer cells. The activation of the Rho family of GTPases was amenable to specific inhibition: Wortmannin inhibited leptin-induced Rac1 and Cdc42 activation but did not affect RhoA activation, and inhibited the formation of leptin-induced lamellipodia and cell invasion. The Rac1 inhibitor NSC23766 inhibited only leptin-induced Rac1 activation and concomitantly, lamellipodium formation and cell invasion. The Src kinase inhibitor II (SrcKI-II) exerted a positive effect on RhoA activation, inhibited tyrosine phosphorylation of p190RhoGAP and inhibited leptin-induced Cdc42 activation and leptin-induced lamellopodium formation and cell invasion. The specific JAK2 inhibitor AG490 exerted a positive effect on Rac1 and Cdc42 activation by leptin and concomitantly inhibited RhoA activation. AG490 did not inhibit leptin-induced lamellopodium formation or cell invasion. Our findings clearly indicate that leptin activates PI3K and Src kinase pathways in the metastatic colon cancer cells LS174T and HM7. These signaling pathways induce the activation of Rac1 and Cdc42, lamellopodium formation and concomitantly enhanced cell invasion, but leptin activation of RhoA is not associated with enhanced cell locomotion and invasion. Understanding in-depth the pathways involved in leptin-associated enhanced cell locomotion and invasion may contribute with the design of novel therapeutics to treat obesity-associated advanced colorectal cancer.

Unbiased screening for transcriptional targets of ZKSCAN3 identifies integrin beta 4 and vascular endothelial growth factor as downstream targets

We previously described the novel zinc finger protein ZKSCAN3 as a new "driver" of colon cancer progression. To investigate the underlying mechanism and because the predicted structural features (tandem zinc fingers) are often present in transcription factors, we hypothesized that ZKSCAN3 regulates the expression of a gene(s) favoring tumor progression. We employed unbiased screening to identify a DNA binding motif and candidate downstream genes. Cyclic amplification and selection of targets using a random oligonucleotide library and ZKSCAN3 protein identified KRDGGG as the DNA recognition motif. In expression profiling, 204 genes were induced 2-29-fold, and 76 genes reduced 2-5-fold by ZKSCAN3. To enrich for direct targets, we eliminated genes under-represented (<3) for the ZKSCAN3 binding motif (identified by CAST-ing) in 2 kilobases of regulatory sequence. Up-regulated putative downstream targets included genes contributing to growth (c-Met-related tyrosine kinase (MST1R), MEK2; the guanine nucleotide exchanger RasGRP2, insulin-like growth factor-2, integrin beta 4), cell migration (MST1R), angiogenesis (vascular endothelial growth factor), and proteolysis (MMP26; cathepsin D; PRSS3 (protease serine 3)). We pursued integrin beta 4 (induced up to 6-fold) as a candidate target because it promotes breast cancer tumorigenicity and stimulates phosphatidyl 3-kinase implicated in colorectal cancer progression. ZKSCAN3 overexpression/silencing modulated integrin beta 4 expression, confirming the array analysis. Moreover, ZKSCAN3 bound to the integrin beta 4 promoter in vitro and in vivo, and the integrin beta 4-derived ZKSCAN3 motif fused upstream of a tk-Luc reporter conferred ZKSCAN3 sensitivity. Integrin beta 4 knockdown by short hairpin RNA countered ZKSCAN3-augmented anchorage-independent colony formation. We also demonstrate vascular endothelial growth factor as a direct ZKSCAN3 target. Thus, ZKSCAN3 regulates the expression of several genes favoring tumor progression including integrin beta 4.

Reducing the weight of cancer: mechanistic targets for breaking the obesity-carcinogenesis link

The prevalence of obesity, an established epidemiologic risk factor for many cancers, has risen steadily for the past several decades in the US. The increasing rates of obesity among children are especially alarming and suggest continuing increases in the rates of obesity-related cancers for many years to come. Unfortunately, the mechanisms underlying the association between obesity and cancer are not well understood. In particular, the effects on the carcinogenesis process and mechanistic targets of interventions that modulate energy balance, such as reduced-calorie diets and physical activity, have not been well characterized. The purpose of this review is to provide a strong foundation for the translation of mechanism-based research in this area by describing key animal and human studies of energy balance modulations involving diet or physical activity and by focusing on the interrelated pathways affected by alterations in energy balance. Particular attention is placed on signaling through the insulin and insulin-like growth factor-1 receptors, including components of the Akt and mammalian target of rapamycin (mTOR) signaling pathways downstream of these growth factor receptors. These pathways have emerged as potential targets for disrupting the obesity-cancer link. The ultimate goal of this work is to provide the missing mechanistic information necessary to identify targets for the prevention and control of cancers related to or caused by excess body weight.

Adiponectin blocks multiple signaling cascades associated with leptin-induced cell proliferation in Apc Min/+ colon epithelial cells

We previously demonstrated that leptin, an adipose-derived hormone, induces cell proliferation in a model of preneoplastic (IMCE (Apc(Min/+)), but not normal (YAMC (Apc(+/+)), colon epithelial cells by inducing autocrine IL-6 production and trans-IL-6 signaling. Low serum adiponectin is associated with colon, prostate and breast cancer. Adiponectin is secreted by white adipose tissue; the levels of adiponectin in the blood decrease as body mass index (and leptin) increases. In our study, we tested whether murine recombinant globular adiponectin (gArcp30) could modulate leptin-induced cell proliferation, autocrine IL-6 production, trans-IL-6 signaling and other leptin-induced cell signaling events previously observed in IMCE cells but not YAMC cells. Under serum-free conditions, adiponectin (1 mug/ml) inhibited leptin-induced autocrine IL-6 production, soluble IL-6 receptor shedding, trans-IL-6 signaling and subsequent STAT3 phosphorylation in IMCE cells. Adiponectin inhibited leptin-induced cell proliferation in the IMCE cells and this inhibition was associated with I kappa B-alpha phosphorylation, I kappa B-alpha degradation and decreased NF-kappaB p65 DNA activation and binding. These data indicate that adiponectin acts on preneoplastic colon epithelial cells to regulate cell growth via 2 distinct pathways inhibiting leptin-induced NF-kappaB-dependent autocrine IL-6 production and trans-IL-6 signaling. We hypothesize that adiponectin may be an important regulator of colon epithelial cell homeostasis by linking the observed reduced risk for cancer in populations with high serum adiponectin concentrations to specific mechanisms of cell number homeostasis in a model of preneoplastic colon epithelial cells. These data may have broad implications for diet and lifestyle strategies for the prevention and treatment of obesity-associated cancers.

Associations between obesity and changes in adult BMI over time and colon cancer risk

Obesity has been associated with increased colon cancer risk in epidemiological studies; however, the specific time periods during which obesity may be most relevant as well as how changes in adult body size over time affect colon cancer risk have not been well explored. We evaluated potential associations between BMI in each age decade(20s, 30s, 40s, 50s, and 2 years before study recruitment ("recruitment period")) and in BMI changes over timeand colon cancer risk in a population-based case-control study comprising 438 cases and 491 controls. We found that obese (BMI>or=30.0 kg/m2) compared to normal (BMI>or=18.5 to <25.0 kg/m2) body size at the recruitment period was associated with increased colon cancer risk (odds ratio (OR)=1.54; 95% confidence interval (CI)=1.03-2.31; P=0.03). No associations were observed for obese body size in the other age decades. An increased risk was found for changes in BMI between the 30s decade and the recruitment period of 5-10 kg/m2 (OR=1.54; 95%CI=1.02-2.34; P=0.04) and >10 kg/m2 (OR=2.40; 95% CI=1.23-4.66; P=0.01) (P trend=0.01). Stratification by gender revealed that BMI changes>10 kg/m2 increased risk in women but not men. Similar results were found for BMI changes between the 20s decade and the recruitment period but effect sizes were smaller. Our results provide additional support to obesity's role in colon cancer and suggest large body size increases exceeding 10 kg/m2 may potentially be more important after age 30, particularly among women; however, prospective studies with sex hormone, growth factor, and pro-inflammatory biomarkers are needed to provide insights to the underlying biological mechanism(s).

Reduced susceptibility of muscle-specific insulin receptor knockout mice to colon carcinogenesis

Insulin resistance is a risk factor for colon cancer, but it is not clear which of its metabolic sequelae are involved. The objective of this study was to determine whether increased adiposity and elevated circulating lipids commonly seen in insulin resistance promote colon carcinogenesis independent of changes in insulin. We made use of muscle-specific insulin receptor knockout (MIRKO) mice that exhibit elevated serum triglycerides (TG), free fatty acids (FFA), and fat mass but have similar body weights, circulating glucose, and insulin and insulin sensitivity to their wild-type littermates used as controls. Seven-week-old male MIRKO mice and controls received four weekly intraperitoneal injections of either 5 mg/kg azoxymethane (AOM) to induce aberrant crypt foci (ACF) or 10 mg/kg AOM to induce tumors and were killed at 24 or 40 wk of age, respectively. The MIRKO mice displayed hyperinsulinemia at 7 wk of age and reduced insulin sensitivity at 16 wk of age compared with controls. The previously reported MIRKO phenotype developed between 16 and 24 wk of age. By 40 wk of age, however, MIRKO mice were again insulin resistant. ACF development did not differ between MIRKO mice and controls, but MIRKO mice developed significantly fewer colon tumors. Our results suggest that circulating TG and FFA are not promoters of colon tumor development. Indeed, we show that the cumulative effects of the metabolic changes that occur with knockout of the insulin receptor in muscle are associated with reduced susceptibility to colon tumorigenesis.

Microarray analysis reveals that leptin induces autocrine/paracrine cascades to promote survival and proliferation of colon epithelial cells in an Apc genotype-dependent fashion

The imbalance in systemic mediators of inflammation, such as leptin, is thought to be involved in obesity-associated cancers. In addition, systemic endocrine signals can influence the local autocrine/paracrine factors produced within this microenvironment to influence epithelial cell fate. We previously demonstrated that leptin preferentially promotes the survival and proliferation of colon epithelial cells possessing an Apc mutation (IMCE) but not model normal cells (YAMC). Therefore, the purpose of this study was to identify leptin-induced functional gene family changes which characterize the response of colon epithelial cells possessing an Apc mutation but not normal cells. Consistent with our knowledge of colon carcinogenesis, genes regulating the Wnt/beta-catenin-mediated pathway including Mdm2, Pik3r1, and Rb1 were upregulated by leptin. Importantly, leptin induced IGF-mediated pathway gene expression changes and their protein products in IMCE cells. In the IMCE cells IGFBP-6, IGF-1, and Crim1 expression was upregulated, while IGFBP-2, IGFBP-3, IGFBP-4, IGFBP-5, and Nov expression was downregulated by leptin treatment. These data establish a biologically plausible mechanistic link between the elevated levels of growth factors and the increased risk of colon cancer associated with obesity.

The obesity-cancer link: lessons learned from a fatless mouse

Current dogma suggests that the positive correlation between obesity and cancer is driven by white adipose tissue that accompanies obesity, possibly through excess secretion of adipokines. Recent studies in fatless A-Zip/F1 mice, which have undetectable adipokine levels but display accelerated tumor formation, suggest that adipokines are not required for the enhanced tumor development. The A-Zip/F-1 mice are also diabetic and display elevated circulating levels of other factors frequently associated with obesity (insulin, insulin-like growth factor-1, and proinflammatory cytokines) and activation of several signaling pathways associated with carcinogenesis. In view of this information, the risk factors underlying the obesity-cancer link need to be revisited. We postulate that the pathways associated with insulin resistance and inflammation, rather than adipocyte-derived factors, may represent key prevention and therapeutic targets for disrupting the obesity-cancer link.