High-fat diet blocks the inhibition of skin carcinogenesis and reductions in protein kinase C by moderate energy restriction

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

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

Obesity and risk of colorectal cancer: a meta-analysis of 31 studies with 70,000 events

BACKGROUND

Colorectal cancer is the second most common cause of death and illness in developed countries. Previous reviews have suggested that obesity may be associated with 30% to 60% greater risk of colorectal cancer, but little consideration was given to the possible effect of publication bias on the reported association.

METHODS

Relevant studies were identified through EMBASE and MEDLINE. Studies were included if they had published quantitative estimates of the association between general obesity [defined here as body mass index (BMI) > or = 30 kg/m(2)] and central obesity (measured using waist circumference) and colorectal cancer. Random-effects meta-analyses were done, involving 70,000 cases of incident colorectal cancer from 31 studies, of which 23 were cohort studies and 8 were case-control studies.

RESULTS

After pooling and correcting for publication bias, the estimated relative risk of colorectal cancer was 1.19 [95% confidence interval (95% CI), 1.11-1.29], comparing obese (BMI > or = 30 kg/m(2)) with normal weight (BMI <25 kg/m(2)) people; and 1.45 (95% CI, 1.31-1.61), comparing those with the highest, to the lowest, level of central obesity. After correcting for publication bias, the risk of colorectal cancer was 1.41 (95% CI, 1.30-1.54) in men compared with 1.08 (95% CI, 0.98-1.18) for women (P(heterogeneity) <0.001). There was evidence of a dose-response relationship between BMI and colorectal cancer: for a 2 kg/m(2) increase in BMI, the risk of colorectal cancer increased by 7% (4-10%). For a 2-cm increase in waist circumference, the risk increased by 4% (2-5%).

CONCLUSIONS

Obesity has a direct and independent relationship with colorectal cancer, although the strength of the association with general obesity is smaller than previously reported.

Protein kinase C (PKC) family in cancer progression

PKC family consist of a number of serine-threonine kinases which are divided into three groups based on their activating factors. PKCs have been linked to carcinogenesis since PKC activators can act as tumor promoters. Furthermore, functional studies have suggested that PKCs play a role in the carcinogenesis and maintenance of malignant phenotype. Potentiation of malignant phenotype may be mediated by activation of selective PKC isoenzymes or through altered isoenzyme expression profile compared to the originating tissue. Activation of PKCalpha and beta isoenzymes have often been linked to malignant phenotype while PKCdelta is thought to mediate anti-cancer effects. This review will focus on the regulation and significance of PKC isoenzymes to cancer progression.

Prevention of mouse skin tumor promotion by dietary energy restriction requires an intact adrenal gland and glucocorticoid supplementation restores inhibition

Our laboratory has demonstrated in the previous studies that dietary energy restriction (DER) inhibited the promotion of skin tumorigenesis and others have found that adrenalectomy may reverse that inhibition. The purpose of the research reported here was to determine if circulating corticosterone (CCS) may be the adrenal hormone responsible for DER prevention of skin carcinogenesis. Female SENCAR mice were initiated with 7,12-dimethylbenzanthracene (DMBA) and promoted with 12-O-tetradecanoylphorbol-13-acetate (TPA) in either sham-operated or adrenalectomized (ADX) mice fed ad libitum (AL) or energy restricted diets. DER was 60% of the AL calorie intake with the removal of energy from fat and carbohydrate. CCS, the main glucocorticoid hormone secreted by the murine adrenal gland, was added to the drinking water of AL/ADX and DER/ADX groups to determine the role of CCS in the DER inhibition of tumor development. In sham-operated groups, DER compared with AL-fed mice experienced significantly decreased papilloma incidence and multiplicity (P < 0.0001). ADX did not alter papilloma incidence or multiplicity in AL-fed mice but ADX partially reversed the inhibition of papilloma multiplicity and incidence in DER mice. CCS supplementation to both DER/ADX and AL/ADX mice resulted in reduced papilloma incidence and multiplicity. In DER/ADX mice, CCS dramatically reduced papilloma rates while in AL/ADX mice CCS reduced the papilloma rates to those seen in the DER sham group. DER significantly reduced carcinoma multiplicity mean counts per effective animal (P < 0.0001) compared with AL-fed groups in sham and ADX/CCS groups. DER/ADX mice lost the carcinoma multiplicity protection seen in sham/DER mice. CCS treatment of ADX mice significantly decreased total carcinoma (in situ and invasive) incidence rates per effective animal (P < 0.0003). ADX followed by CCS treatment in the DER mice resulted in the lowest carcinoma incidence and multiplicity. Thus, DER-inhibition of skin tumorigenesis was mediated at least in part through CCS. However, CCS was more effective in preventing papillomas and carcinomas in DER/ADX mice than in AL/ADX mice, suggesting that other factors may also be involved in the DER prevention of tumor formation.

Overweight, obesity, and cancer risk

Over the past few decades the proportion of people with excess body weight has been increasing in both developed and less developed countries. About 50% of men and 35% of women in Europe are currently estimated to be overweight or obese. In addition to an increase in the risk of cardiovascular disease and type II diabetes, the evidence summarised here shows that excess body weight is directly associated with risk of cancer at several organ sites, including colon, breast (in postmenopausal women), endometrium, oesophagus, and kidney. In part, these associations with cancer risk may be explained by alterations in the metabolism of endogenous hormones-including sex steroids, insulin, and insulin-like growth factors-which can lead to distortion of the normal balance between cell proliferation, differentiation, and apoptosis. Avoidance of weight gain thus seems to be an important factor for cancer prevention.

Fat intake and risk of squamous cell carcinoma of the skin

The varied effects of different classes of dietary fatty acids on carcinogenesis suggest that fatty acid composition is an important determining factor in tumor development. In the present study, we investigated the association between dietary n-3 and n-6 fatty acid intake and risk of squamous cell carcinoma of the skin (SCC). Data were taken from a population-based case-control study of skin SCC in Southeastern Arizona. Our data show a consistent tendency for a lower risk of SCC with higher intakes of n-3 fatty acids [p (for trend) = 0.055]. The adjusted odds ratios for increasing levels of n-3 fatty acids were 0.85 [95% confidence interval (CI) = 0.56-1.27] and 0.71 (95% CI = 0.49-1.00) compared with the lower level as the referent. For the ratio of n-3 to n-6 fatty acids, the odds ratios in successively higher levels were 0.88 (95% CI = 0.59-1.32) and 0.74 (95% CI = 0.51-1.05), suggesting a tendency toward decreased risk of SCC with increased intake of diets with high ratio of n-3 to n-6 fatty acid. More studies are clearly needed to elucidate the function of dietary fatty acids so that recommendations can be made to alter the human diet for cancer prevention, particularly in light of the increasing incidence of SCC of the skin.

The influence of maternal diet on breast cancer risk among female offspring

The induction of breast cancer is a long process, containing a series of biological events that drive a normal mammary cell towards malignant growth. However, it is not known when the initiation of breast cancer occurs. One hypothesis is that a high estrogenic environment during the perinatal period increases subsequent breast cancer risk. There are many sources of extragonadal estrogens, particularly in the diet. The purpose of this paper is to review the evidence that a high maternal intake of dietary fats increases serum estrogens during pregnancy and increases breast cancer risk in daughters. Our animal studies show that a high maternal consumption of corn oil consisting mainly of linoleic acid (omega-6 polyunsaturated fatty acid, PUFA), increases both circulating estradiol (E2) levels during pregnancy and the risk of developing carcinogen-induced mammary tumors among the female rat offspring. A similar increase in breast cancer risk occurs in female offspring exposed to injections of E2 through their pregnant mother. Our data suggest that the mechanisms by which an early exposure to dietary fat and/or estrogens increases breast cancer risk is related to reduced differentiation of the mammary epithelial tree and increased number of mammary epithelial cell structures that are known to the sites of neoplastic transformation. These findings may reflect our data of the reduced estrogen receptor protein levels and protein kinase C activity in the developing mammary glands of female rats exposed to a high-fat diet in utero. In summary, a high dietary linoleic acid intake can elevate pregnancy estrogen levels and this, possibly by altering mammary gland morphology and expression of fat- and/or estrogen-regulated genes, can increase breast cancer risk in the offspring. If true for women, breast cancer prevention in daughters may include modulating the mother's pregnancy intake of some dietary fats.

Glucocorticoid mediation of dietary energy restriction inhibition of mouse skin carcinogenesis

Dietary energy restriction (DER) inhibits carcinogenesis in numerous animal models. DER is a potent and reproducible inhibitor of two-stage mouse skin carcinogenesis when administered during the promotion phase. Previous research demonstrated that adrenalectomy abolished cancer prevention by food restriction. Several lines of evidence suggest that glucocorticoid elevation in the DER mouse mediates the prevention of skin cancer. Our research tested the hypothesis that elevated glucocorticoid hormone activates the glucocorticoid receptor (GR) and that this activated receptor interferes with the activator protein-1 (AP-1) transcription factor. Induction of AP-1 by the phorbol ester tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) is essential to tumor promotion. We have been unable to demonstrate elevated activated GR in the epidermis of the DER mouse, perhaps because only indirect strategies have been possible with the use of epidermis from DER mice. However, DER blocked the induction of AP-1 and c-jun, a constituent protein of AP-1, in the epidermis of mice. Current studies are focused on the inhibition of signaling down the MAP-1/Raf-1 kinase pathway that leads to induction of constituent proteins of AP-1, including c-Jun. Although several pathways lead to the induction of AP-1 transcriptional activity, the MAP-1/Raf-1 pathway can be activated by protein kinase C (PKC); previous studies from our laboratory demonstrated an inhibition of PKC activity and a reduction in selected isoforms of PKC in the epidermis of the DER mouse. Our current working hypothesis is that elevated glucocorticoid hormone in the DER mouse reduces the amount and activity of PKC isoforms important in the activation of MAP-1/Raf-1 kinase pathway. We propose that this results in attenuation in the induction of the AP-1 transcription factor by TPA. Because AP-1 induction by TPA is obligatory for mouse skin promotion, we propose this as an essential component of the mechanism of DER prevention of mouse skin carcinogenesis.

Mechanisms by which high maternal fat intake during pregnancy increases breast cancer risk in female rodent offspring

Emerging evidence indicates that a high in utero estrogenic environment increases breast cancer risk in women. We have proposed that a maternal intake of a high-fat diet is a source for high pregnancy estrogen levels and increases breast cancer risk among female offspring. In this review, the role of dietary fat in breast cancer, particularly during fetal life, is discussed. In addition, we provide possible mechanisms of action of the effects of a high-fat diet on the breast. These mechanisms include protein kinase C, estrogens and estrogen receptor, and alterations in mammary parenchymal structures.

Dietary fat and risk of chronic disease: mechanistic insights from experimental studies

The primary nutritionally linked diseases are coronary heart disease, stroke and cancers of the stomach, colon, pancreas, prostate, breast, ovary, and endometrium. Dietary fats operate through a promoting mechanism. An S-shaped dose-response curve with a threshold has been demonstrated in models of breast and colon cancer in which the standard Western fat intake of 40% of energy yields a high level of promotion, and reduction of fat to 10% to 20% of energy (the traditional Japanese fat intake) has a low promoting action. In models of breast and colon cancer, saturated fats such as beef fat or lard, and monounsaturated oils, such as olive oil, display only a weak promoting effect, with the incidence of induced tumors being similar at intake levels of 40% and 10% of energy. On the other hand, the n-6-polyunsaturated oils display a strong promoting effect. Such findings may have a parallel in the low but definitely increasing slope of postmenopausal breast cancer incidence in the past 30 years as the American public decreased saturated fat intake to avoid heart disease and increased use of the n-6-polyunsaturated oils. Mechanisms underlying the cancer-promoting effect in the colon stem from increased hepatic production of bile acids, which are transferred to the intestinal tract via the bile. Ingestion of 40% fat calories yields higher concentrations of bile acids in the colon than lower levels of dietary fat ingestion. Cancer in the mammary gland is promoted through higher concentrations of fats and phospholipids in the gland as well as increased levels of estrogen secondary to production by the ovary and other endocrine tissues that, in turn, affect the generation of pituitary hormones such as prolactin and growth hormone. The n-3-fats, as found in fish and fish oils, have a pronounced inhibitory effect in models of colon and breast cancer, presumably through their shifting of prostaglandin metabolism to the generation of prostaglandins, which lower cell proliferation potential and, thus, decrease promotional effects. The role of dietary fat as a promoter can be modified by other nutritional components. Finally, one of the best pieces of evidence for an enhancing effect of many dietary fats in the nutritionally linked cancers is the current increase in the incidence of these diseases in Japan as the nutritional habits of people in that country become more Westernized.