Vitamin D and cancer.

The role of vitamin D in the prevention of chronic diseases including cancer, has received a great deal of attention during the past few decades. The term "Cancer" represents multiple disease states with varying biological complexities. The strongest link between vitamin D and cancer is provided by ecological and studies like observational, in preclinical models. It is apparent that vitamin D exerts diverse biological responses in a tissue specific manner. Moreover, several human factors could affect bioactivity of vitamin D. The mechanism(s) underlying vitamin D initiated anti-carcinogenic effects are diverse and includes changes at the muti-system levels. The oncogenic environment could easily corrupt the traditional role of vitamin D or could ensure resistance to vitamin D mediated responses. Several researchers have identified gaps in our knowledge pertaining to the role of vitamin D in cancer. Further areas are identified to solidify the role of vitamin D in cancer control strategies.

The emerging role of phosphorus in human health.

Phosphorus, an essential nutrient, performs vital functions in skeletal and non-skeletal tissues and is pivotal for energy production. The last two decades of research on the physiological importance of phosphorus have provided several novel insights about its dynamic nature as a nutrient performing functions as a phosphate ion. Phosphorous also acts as a signaling molecule and induces complex physiological responses. It is recognized that phosphorus homeostasis is critical for health. The intake of phosphorus by the general population world-wide is almost double the amount required to maintain health. This increase is attributed to the incorporation of phosphate containing food additives in processed foods purchased by consumers. Research findings assessed the impact of excessive phosphorus intake on cells' and organs' responses, and highlighted the potential pathogenic consequences. Research also identified a new class of bioactive phosphates composed of polymers of phosphate molecules varying in chain length. These polymers are involved in metabolic responses including hemostasis, brain and bone health, via complex mechanism(s) with positive or negative health effects, depending on their chain length. It is amazing, that phosphorus, a simple element, is capable of exerting multiple and powerful effects. The role of phosphorus and its polymers in the renal and cardiovascular system as well as on brain health appear to be important and promising future research directions.

The Emerging Role of Vitamin B6 in Inflammation and Carcinogenesis.

Vitamin B6 serves as a coenzyme catalyzing more than 150 enzymes regulating metabolism and synthesis of proteins, carbohydrates, lipids, heme, and important bioactive metabolites. For several years vitamin B6 and its vitamers (B6) were recognized as antioxidant and antiinflammatory and in modulating immunity and gene expression. During the last 10 years, there were growing reports implicating B6 in inflammation and inflammation-related chronic illnesses including cancer. It is unclear if the deficiency of B6 or additional intake of B6, above the current requirement, should be the focus. Whether the current recommended daily intake for B6 is adequate should be revisited, since B6 is important to human health beyond its role as a coenzyme and its status is affected by many factors including but not limited to age, obesity, and inflammation associated with chronic illnesses. A link between inflammation B6 status and carcinogenesis is not yet completely understood. B6-mediated synthesis of H2S, a gasotransmitter, and taurine in health and disease, especially in maintaining mitochondrial integrity and biogenesis and inflammation, remains an important area to be explored. Recent developments in the molecular role of B6 and its direct interaction with inflammasomes, and nuclear receptor corepressor and coactivator, receptor-interacting protein 140, provide a strong impetus to further explore the multifaceted role of B6 in carcinogenesis and human health.

Fermentable Carbohydrates Differentially Affect Colon Tumor Formation in Azoxymethane-Induced Male Fischer 344 Rats.

BACKGROUND: The role of fermentation compared with the source or type of the fermentable material in colon tumorigenesis remains an issue in refining the definition of dietary fiber (DF). OBJECTIVE: The aim of this study was to investigate the fermentation and source-specific effects of various carbohydrates in a medium-term colon tumorigenesis model. METHODS: Six-week-old male Fischer 344 rats were randomly allocated into 6 groups (n = 36/group) to receive either AIN-93G (control) or diets containing fructooligosaccharides, wheat bran (WB), oat bran (OB), polydextrose, or high-amylose maize starch (HAMS), each adjusted to contain a total DF concentration of 7% (wt:wt) and have a fermentability of 3% (wt:wt). After 2 wk, 24 rats/group received 2 subcutaneous doses of azoxymethane (at 15 mg/kg body weight) 1 wk apart while 12 rats/group were injected with a saline vehicle; all rats were maintained on the assigned diets for 24 wk postinjection and then killed. Colon tumor outcomes and pathology together with cecal short-chain fatty acid composition were assessed. RESULTS: No tumors were found in saline-injected rats, and all subsequent analyses were restricted to azoxymethane-injected rats. Colon tumor incidence was significantly lower in the polydextrose (21%) and WB (13%) groups than in the control group (63%; P < 0.05) but not different from the fructooligosaccharide (58%), HAMS (46%), and OB (33%) groups. In comparison to the control group (8 proximal/31 total tumors), fermentable materials reduced the number of tumors (P < 0.05) originating in the proximal colon: HAMS (5/15), polydextrose (2/7), OB (2/9), fructooligosaccharides (1/21), and WB (1/3). The mean ± SEM number of tumors/tumor-bearing rats was significantly lower in the WB (1.00 ± 0.00), OB (1.13 ± 0.13), and HAMS (1.36 ± 0.15) groups than in the control group (2.07 ± 0.27; P < 0.02); other groups did not differ. The mean ± SEM tumor burden/diet group was lower in the WB (1.2 ± 0.7 mm2), polydextrose (6.7 ± 3.2 mm2), and OB (7.0 ± 3.0 mm2) groups than in the control (21.4 ± 5.9 mm2) and fructooligosaccharide (22.1 ± 7.1 mm2; P < 0.05) groups but not significantly different from the HAMS group (15.1 ± 6.1 mm2). Total cecal SCFA concentrations did not differ among diet groups (overall mean ± SEM: 81 ± 4 µmol/g wet weight). CONCLUSION: The rate and extent of fermentation of the carbohydrate material as well as the characteristics of the material in the lumen of the lower gastrointestinal tract all appear to have an important role in tumor outcomes in the azoxymethane-induced rat colon tumorigenesis assay.

Differential expression of TNF-α signaling molecules and ERK1 in distal and proximal colonic tumors associated with obesity.

Distal and proximal colon cancers have been recognized as two different disease types in human population. The environmental factors involved in the pathogenesis of the proximal and distal tumors also differ. The main objective of this study was to determine if obesity-augmented colonic tumors differ from each other if they are located in different regions of the colonic axis. Zucker obese rats were injected with azoxymethane (AOM) 10 mg/kg body weight/week for 2 weeks. The tumors appeared within 20 weeks. The highest proportion of the tumors was in the distal colon, and the number declined towards the splenic flexure. A number of proteins previously reported to be altered in tumor tissue were assessed in the present study in tumors appearing in proximal and distal regions. Distal colonic tumors had higher TNF-α R2, NF-κB, and IκBα levels than tumors of proximal origin. In contrast, IKKß was decreased in the proximal tumors. Insulin receptor and insulin-like growth factor-1R were higher in distal tumors. The mitogen-activated protein kinase (ERK2) levels were similar in the tumor groups; however, the ERK1 was significantly higher in the distal tumor than in the proximal tumor. Our findings suggest that colon tumors induced by AOM in different colonic regions are different from each other with respect to differential expression of proteins and support the concept that these disease states could respond differently to tumor-promoting and inhibitory conditions. Moreover, these findings support the concept that cancer preventive or therapeutic agents need to be evaluated for their effectiveness on proximal as well as on distal tumors.

Elevated expression of tumor necrosis factor-alpha signaling molecules in colonic tumors of Zucker obese (fa/fa) rats.

Zucker obese rats are highly sensitive to colon cancer and possess a plethora of metabolic abnormalities including elevated levels of cytokine tumor necrosis factor-alpha (TNF-alpha). The main objective of this study was to determine if physiologically elevated TNF-alpha affects colonic tumor phenotype with regard to an altered TNF-alpha signaling pathway. Zucker obese (fa/fa, homozygous recessive for dysfunctional leptin receptors), Zucker lean (Fa/fa, Fa/Fa) and Sprague-Dawley (SD) rats were injected twice with azoxymethane (10 mg/kg) over 2 weeks. After 30 weeks, the animals were terminated and physiological and tumor parameters were assessed. Obese rats had notably higher body and organ weights as well as plasma TNF-alpha, insulin and leptin levels than lean or SD animals. A 100% tumor incidence and significantly higher tumor size, multiplicity and burden were found in obese rats compared to the lean group that had 47.8% tumor incidence. The SD group had the lowest tumor incidence (20.0%). Tumors from obese animals had higher protein levels of TNF-alpha, TNF-alpha-receptor-2 (TNFR2), nuclear transcription factor-kappaB (NF-kappaB) and IkappaB-kinasebeta (IKKbeta) compared to lean animals. In both obese and lean groups, expression levels of these proteins were higher in tumors than in surrounding, normal-appearing colonic mucosae. These findings support an important role for TNF-alpha signaling in tumorigenesis and demonstrate that tumors growing in an obese state had significantly different expression levels of TNFR2 and NF-kappaB, proteins known to play a critical role in growth and survival, than those growing in the lean state. It is concluded that the physiological state of the host intricately affects tumor phenotype.

Inhibition of colon carcinogenesis by post-initiation induction of NQO1 in Sprague-Dawley rats.

Inducers of phase II detoxifying enzymes have been studied as chemopreventive agents for a variety of cancers. Phase II detoxifying enzymes may play a significant role in preventing carcinogen-induced colon cancer at the initiation and post-initiation stage, but the contribution of NAD(P) H:quinone oxidoreductase 1 (NQO1) to this effect remains unclear. Using the carcinogen-induced colon cancer Sprague-Dawley rat model, we previously showed that oltipraz selectively induces NQO1 in the colons of these rats without inducing other phase II detoxifying enzymes. We demonstrated that selective induction of NQO1 in the rat colon prior to treatment with a carcinogen significantly inhibited the formation of aberrant crypt foci (ACF). Using the same rat model, we found that rats fed oltipraz containing diet following treatment with the colon carcinogen, azoxymethane (AOM), had 60% fewer ACF after 12 weeks compared with rats fed a control diet. In addition, rats fed oltipraz containing diet after AOM treatment developed 40% fewer colon adenomas and fewer colon tumors than rats fed a control diet. There was also a 60% increase in the percentage of apoptotic cells in ACF from oltipraz fed rats compared with ACF from control fed rats. Together, these results suggest that NQO1 can contribute to inhibition of colon carcinogenesis at the post-initiation stage. A possible mechanism for this effect may be that induction of NQO1 increases apoptosis in carcinogen initiated colonic epithelial cells that prevents these cells from progressing to a neoplastic state. Thus, NQO1 may be an important target for chemoprevention of colon cancer.

Soy isoflavones modulate azoxymethane-induced rat colon carcinogenesis exposed pre- and postnatally and inhibit growth of DLD-1 human colon adenocarcinoma cells by increasing the expression of estrogen receptor-beta.

We studied the effects of lifetime exposure to dietary soy isoflavones in an azoxymethane (AOM)-induced rat colon cancer model. Male pups born to Sprague-Dawley rats exposed (including during pregnancy and lactation) to soy isoflavones at either no (0 mg = control), low (40 mg), or high (1000 mg) doses/kg diet were weaned and continued receiving their respective parental diets until the end of the study. Weaned rats received 2 subcutaneous injections (15 mg/kg body weight) of AOM 1 wk apart. After 26 wk, rats were killed and the coordinates of colon aberrant crypt foci (ACF) and tumors were determined. Expression of estrogen receptor (ER)-beta was assessed in rat colon tumors and in DLD-1 human colon adenocarcinoma cells exposed to soy isoflavones. Compared with the control, soy isoflavones did not affect incidences or multiplicities of colon ACF or tumors. Low-dose soy isoflavones decreased tumor burden and size compared with the control (P < 0.05). Expression of ERbeta increased in colon tumors of soy isoflavone-treated groups compared with the control. Soy isoflavones dose-dependently arrested the growth of DLD-1 cells and at subcytotoxic levels increased the expression of ERbeta. Our results suggest that pre- and postnatal exposure to dietary soy isoflavones suppresses the growth of colon tumors in male rats. The overexpression of ERbeta in both rat colon tumors and DLD-1 cells caused by soy isoflavones suggests that ERbeta is a critical mediator in mitigating its cancer-preventive effects.

Effect of short-term dietary intake of bovine lactoferrin on intestinal lymphocyte apoptosis in healthy mice.

OBJECTIVE: The objective of this study was to describe the effects of short-term dietary exposure of bovine lactoferrin (Lf) on intestinal lymphocyte apoptosis and expression of tumor necrosis factor-alpha (TNF-alpha) in healthy mice. METHODS: Female C57BL/6 mice were randomly assigned to three treatment groups: 0% Lf (n = 16), 0.2% Lf (n = 16), and 2.0% Lf (n = 15). Bovine Lf was administered orally, as part of the diet, for 4 consecutive days. Intestinal lymphocytes (ILs) were isolated and analyzed for percentages of CD4, CD8, apoptotic CD4, and apoptotic CD8 cells using flow cytometry. Pro- (caspase-3) and anti- (Bcl-2) apoptotic protein expressions and TNF-alpha expression in ILs were determined by Western blotting. RESULTS: There were significant increases in the percentages of CD4 (P = 0.02) and apoptotic CD4 (P = 0.02) ILs in bovine Lf-fed compared with control mice. Percentages of CD8 and apoptotic CD8 cells and expression of caspase-3 and Bcl-2 in ILs did not differ significantly by diet group. In contrast, the expression of TNF-alpha was significantly lower in Lf-fed versus control mice (P = 0.01). CONCLUSION: Short-term dietary Lf decreased TNF-alpha expression in ILs and increased apoptosis of CD4 ILs in healthy mice.

Diosgenin, a naturally occurring steroid [corrected] saponin suppresses 3-hydroxy-3-methylglutaryl CoA reductase expression and induces apoptosis in HCT-116 human colon carcinoma cells.

A growing body of experimental evidence suggests the therapeutic potential of diosgenin, a steroid [corrected] saponin against several cancers. However, precise molecular and cellular mechanisms underlying the modes of action of this compound against colon cancer remain only partially understood. In this study, we investigated if the anticancer mechanism of diosgenin in HCT-116 human colon carcinoma cells involves modulation in the expression of 3-hydroxy-3-methylglutaryl Co-enzyme A (HMG-CoA) reductase, the rate-limiting enzyme of the cholesterol biosynthetic pathway. Diosgenin treatment resulted in a dose-dependent decrease in the viability and growth of HCT-116 cells. The IC(50) cytotoxic dose of diosgenin in HCT-116 was approximately 35 microM after 24h, while concentrations of approximately 32 microM or greater decreased the percent viable cells by 50%. Higher doses of diosgenin (30-40 microM) effectively inhibited recovery of cells for up to 24h post-treatments. At sub-cytotoxic doses, diosgenin induced a dose-dependent increase in apoptotic demise. In part, the apoptotic mechanism was through the cleavage of the 116 kDa poly (ADP-ribose) polymerase protein to the 85kDa fragment. The expression of HMG-CoA reductase at both mRNA and protein levels was significantly lowered by increasing concentrations of diosgenin. This was accompanied by a concomitant dose-dependent decrease in the expression of p21 ras and beta-catenin. In conclusion, our data demonstrates that the food saponin, diosgenin is a potent inhibitor of HCT-116 human colon carcinoma cells by growth inhibition and induction of apoptosis. Importantly, our result identifies that the growth suppressive or apoptotic activity of diosgenin may involve cholesterol homeostasis.

A NAD(P)H:quinone oxidoreductase 1 polymorphism is a risk factor for human colon cancer.

Colon cancer is one of the most common cancers in North America and generally develops from colonic epithelial cells following initiation by carcinogens. We have shown that the phase II detoxifying enzyme, NAD(P)H:quinone oxidoreductase 1 (NQO1) contributes to the inhibition of carcinogen-induced colon cancer in rats at both the initiation and postinitiation stages. An inactivating polymorphism at base 609 of the NQO1 gene, (609)C (NQO1 *1) --> (609)T (NQO1 *2), occurs at high frequency in the human population. Thus, we carried out a case-control study to determine if this polymorphism is associated with an increased risk of developing colon cancer. A total of 298 patients with colon cancer and 349 healthy controls matched for age, gender, and ethnic origin were enrolled in the study. There was an increased incidence of the NQO1 *2/*2 genotype in patients with colon cancer, with a gender and age-adjusted odds ratio of 2.68 (95% confidence intervals, 1.14-6.28). However, the incidence of the NQO1 *1/*2 genotype was not increased in patients with colon cancer compared with controls. When the patient and control groups were stratified by tobacco and alcohol use, the incidences of the NQO1 *2/*2 genotype were increased in patients with colon cancer for tobacco and alcohol users and nonusers, suggesting that there is no interaction between the NQO1 base 609 polymorphism and tobacco or alcohol use. These results strongly suggest that NQO1 plays a significant role in preventing the development of colon cancer, and individuals with an NQO1 *2/*2 genotype are at an increased risk of developing this disease.

Obese state leads to elevated levels of TGF-beta and COX isoforms in platelets of Zucker rats.

Platelets are rich sources of growth factors and enzymes that are implicated in a number of diseases including obesity, atherosclerosis, heart disease, syndrome X, liver and kidney diseases and certain types of cancers. In this research we investigated, if platelets in Zucker obese rats differ from their lean counterparts with respect to the levels of TGF-beta and COX isoforms, implicated in the pathogenesis of chronic diseases. In addition, we investigated if energy intake of the animals affects the platelet physiology. Platelets were isolated from obese and lean rats bearing preneoplastic lesions in their colon. Prior to platelet isolation these rats were fed either ad libitum (Ob or Ln) or energy restricted (Ob-ER or Ln-ER) diets for 8 weeks (n = 8/group). The levels of TGF-beta1/-beta2 and COX-1/-2 proteins in platelets were analyzed by Western blot. The platelets of the Ob rats had significantly higher levels of TGF-beta1, COX-1/-2 (p < 0.001) than did the platelets of the Ln rats and were not affected by moderate energy restriction. There were no significant differences in the protein expression of platelet TGF-beta2 among any of the groups. These results demonstrate that cytokines and candidates playing a role in the pathogenesis of chronic diseases, such as TGF-beta1 and COX-1/-2, are over-expressed in platelets of Zucker obese rats by comparison to their lean counterparts. These findings also demonstrate that the genotype of the animals exerts a significant effect on the biochemical composition of the platelets and could contribute to the pathogenesis of colon cancer and other metabolic abnormalities associated with obesity.

Elevated insulin receptor protein expression in experimentally induced colonic tumors.

Insulin is associated with augmented colon carcinogenesis in vivo, but the mechanism(s) of growth promotion is not known. This study investigates the expression profile of a key component of the insulin signaling pathway, the insulin receptor (IR), in colonic tumors in comparison to normal colonic mucosa and the effects of dietary lipids. Male F344 rats harboring preneoplastic lesions were randomly allocated to three high fat diet groups: beef tallow (HFB), corn oil (HFC), fish oil (HFF) or a low fat corn oil (LFC) diet for 16 weeks. Colonic tumors and mucosae were analyzed for IR protein by Western blot and immunohistochemical analyses. IR mRNA expression was also analyzed by semi-quantitative RT-PCR. Western blot analysis demonstrated that IR protein level was significantly greater (P < or =0.001) in tumors than in normal-appearing mucosae in each diet group, and varied (P < or =0.001) among the tumors in the order HFF>LFC>HFB>HFC. Immunohistochemical assessment of the tumors as compared to the normal mucosa confirmed the elevated expression of IR protein in the tumor cells compared to normal mucosae. Immunoreactivity was noted in the nuclear compartment. In normal colonic mucosae, IR protein levels were lower (P < or =0.001) in the saturated fat diet group (HFB) than the three unsaturated fat diet groups (LFC, HFC and HFF). IR mRNA transcript levels did not differ between colonic tumors and mucosae, and no significant diet effect was observed. These results demonstrate that steady state levels of IR are elevated in colonic tumors above that of normal mucosae in vivo irrespective of the dietary lipid environment. However, the IR mRNA transcript levels did not reflect any significant diet effect and remained relatively steady between the tumor and normal mucosa, indicating altered post transcriptional regulation of IR in tumor tissues compared to normal mucosae.

The effects of parathyroid hormone fragments on bone formation and their lack of effects on the initiation of colon carcinogenesis in rats as indicated by preneoplastic aberrant crypt formation.

The parathyroid hormone (PTH) and some of its fragments and analogs stimulate bone growth in various animal models and humans and one of them (hPTH-(1-34)) has been approved by the USFDA for treating osteoporosis. However, there are reports that PTH can stimulate the PI-3 kinase/mitogen-activated protein kinases-mediated proliferation of rat enterocytes and that primary hyperparathyroidism in humans is associated with an increased incidence of colon cancer. Here we have investigated the ability of two PTH fragments, hPTH-(1-34)NH(2) and [Leu(27)]cyclo(Glu(22)-Lys(26))hPTH-(1-31)NH(2) to initiate colon carcinogenesis or increase the initiatory activity of the widely used colon carcinogen azoxymethane (AOM). The initiation of colon carcinogenesis by AOM was indicated by the very early appearance of aberrant crypt foci. While both PTH peptides strongly stimulated femoral bone formation, they did not cause the appearance of ACFs or affect the number or the distribution along the colon of AOM-induced ACFs. Nor did AOM affect the PTHs' ability to stimulate bone formation. Thus, a relatively short PTH treatment that is long enough to strongly stimulate bone formation does not initiate colon carcinogenesis in rats.

Energy restriction reduces the number of advanced aberrant crypt foci and attenuates the expression of colonic transforming growth factor beta and cyclooxygenase isoforms in Zucker obese (fa/fa) rats.

Several epidemiological studies have supported the concept that high energy intake, obesity, and/or hyperinsulinemia are risk factors for colon cancer. Previously, it was shown that Zucker obese rats are more sensitive to chemically induced colon cancer than their lean counterparts. The present study investigated whether moderate (20-25%) dietary energy restriction (ER) would attenuate colon carcinogenesis in the Zucker obese rat model. Six-week-old Zucker obese (fa/fa) rats and lean (Fa/Fa) rats received s.c. injections of azoxymethane at a dose of 10 mg/kg body weight once weekly for 2 weeks. A week later, obese rats (n = 16) were assigned to an ER diet (Ob-ER group), based on a low-fat AIN-93G semisynthetic diet. The remaining obese and lean rats (n = 16 rats/group) were fed the low-fat diet ad libitum (Ob group and Ln group, respectively). All rats were euthanized after 8 weeks, and their colons were assessed for aberrant crypt foci (ACF; n = 8/group) or for the expression of transforming growth factor (TGF)-beta and cyclooxygenase (COX) isoforms at the protein and mRNA transcript levels (n = 8/group). Ob rats had a higher number of advanced ACF (crypt multiplicity >or=7) than Ln rats. Dietary ER significantly reduced the appearance of advanced ACF in Ob-ER rats without significantly affecting the blood insulin level or body weights. TGF-beta and COX isoforms were differentially expressed in the colonic mucosae of Ob and Ln rats. Dietary ER significantly reduced TGF-beta1/beta2 and COX-1/2 protein expression in obese rats. This study is the first to demonstrate that moderate ER attenuated TGF-beta and COX protein expression and the carcinogenic process in Zucker obese rats. These findings provide insights leading to the proposal that the mechanism(s) underlying the early events of colon carcinogenesis in Zucker obese rats may extend beyond the role of excessive body weight and hyperinsulinemia per se.

Induction of NAD(P)H quinone: oxidoreductase1 inhibits carcinogen-induced aberrant crypt foci in colons of Sprague-Dawley rats.

Phase II detoxifying enzymes like NAD(P)H (quinone acceptor)oxidoreductase1 (NQO1), glutathione S-transferases (GST), and UDP-glucuronyltransferases (UGT) may play an important role in preventing carcinogen-induced cancers. Inducers of these enzymes have been shown to inhibit carcinogen-induced colon tumors in rat and mouse models. However, it has not been clearly demonstrated that NQO1 contributes to this effect. We examined the effect of NQO1 inducers on colon carcinogenesis using an aberrant crypt foci (ACF) rat model. Sprague-Dawley rats were fed control diet or diet containing 400 ppm dimethyl fumarate or 200 ppm oltipraz for 7 days, and Phase II enzymes in rat colon and liver were measured. Dimethyl fumarate significantly increased NQO1 and GST activities in colon and liver but did not increase UGT activities in these tissues. In contrast, oltipraz significantly increased NQO1 activities in colon and liver and produced a small increase in GST activity in the liver but did not increase GST activity in the colon or UGT activities in the liver or colon. Sprague Dawley rats were fed control diet or diet containing 200 ppm oltipraz and then treated with the carcinogens azoxymethane or methyl nitrosourea. Both carcinogens produced ACF in all of the rat colons, but rats fed oltipraz diet had significantly fewer ACF than those fed control diet. This protective effect was reversed in rats treated with the NQO1 inhibitor, dicoumarol. However, treatment with oltipraz did not alter the distribution of crypt multiplicities in the ACF. These studies demonstrated that induction of NQO1 plays a significant role in inhibiting initiation of carcinogen-induced ACF in Sprague-Dawley rats. This provides the first direct evidence that NQO1 may play a role in preventing colon cancer. The study also found that oltipraz added to the diet of Sprague-Dawley rats selectively increased NQO1 activity in colon mucosa with no increase in GST and UGT activities in these tissues. Thus, this model will be useful for further investigating the role of NQO1 in prevention of colon cancer.

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

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

Differential modulation of transforming growth factor-betas and cyclooxygenases in the platelet lysates of male F344 rats by dietary lipids and piroxicam.

Platelets are implicated in the pathogenesis of various chronic diseases including cancer. The main objective of the present study was to determine if dietary fish oil and piroxicam, known modulators of colon tumorigenesis, effect transforming growth factor (TGF)-betas and cyclooxygenase (COX) isozymes in the platelets of colon tumor-bearing male F344 rats. TGF-betas and COXs are important in the development of chronic illnesses including colon cancer. Animals harboring preneoplastic colonic lesions were randomly allocated to a low fat diet (5% by weight--low corn oil, LFC) and three high fat diets (23% by weight--high corn oil, HFC; high corn oil containing 150-ppm piroxicam, HFC+P; and high fish oil, HFF) for 16 weeks. TGF-beta1, TGF-beta2, COX-1 and COX-2 protein levels were assessed in the platelets by Western blot analysis. Active TGF-beta1 (12.5 kDa) level was significantly lower in the platelets of the HFC+P group (p < 0.001), whereas precursor TGF-beta1 (39 kDa) level was significantly lower in the platelets of the HFF group (p < 0.001). The anti-rabbit TGF-beta2 polyclonal antibody did not detect the 13-kDa active TGF-beta2 protein in the platelets. However a 29-kDa protein, potentially a precursor of TGF-beta2, was detected in the platelets of all the groups and was significantly lower in the HFC+P and HFF groups than in LFC and HFC (p < 0.001). COX-1 level was significantly lower in the HFF group than the other three groups (p < 0.001). COX-2 protein was detected in the platelets of all diet groups. Piroxicam in the presence of high corn oil (HFC+P) significantly lowered the level of COX-2 (p < 0.001), without having any effect on COX-1 level. These findings conclusively show that LFC and HFC differ from HFF and HFC+P, and piroxicam differs from fish oil, in regulating the levels of TGF-betas and COX in the platelets. This supports the conjecture that the levels of bioactive constituents of the platelets are profoundly modulated by dietary lipids, which in turn could influence the pathogenesis of chronic illnesses.