Efficacy of potential chemopreventive agents on rat colon aberrant crypt formation and progression

In vitro synergistic effect of farnesol and human gingival cells againstCandida albicans

Farnesol prevents the germination of yeast cells into mycelia, a fact that may be useful in eliminating C. albicans pathogenicity. Given the clinical potential of farnesol, its impact on C. albicans and host cells merited further investigation. We thus studied the effect of farnesol on C. albicans growth and filamentation and on gingival epithelial cells and fibroblasts and the synergistic effect of both gingival cells and farnesol on C. albicans filamentation. Repeated additions of farnesol reduced the growth of C. albicans. Farnesol was also effective at reducing C. albicans germ tube formation. While farnesol inhibited germ tube formation under the conditions tested, it was most effective at inhibiting C. albicans filamentation when added to the culture medium at the same time as the serum. Farnesol also had an effect on gingival cells. In a serum-free medium, farnesol reduced fibroblast adhesion and proliferation, promoted epithelial cell differentiation and reduced proliferation up to 48 h post-treatment. These effects were not seen in the presence of serum. When C. albicans, farnesol and gingival cells were present in the same culture, significantly greater inhibition of the yeast-to-hyphal transition was observed than germ tube inhibition in cultures containing only C. albicans and farnesol, suggesting a synergistic effect between the gingival cells and farnesol in inhibiting the transition. Overall, the data suggest that farnesol is effective against C. albicans and may have an effect on host cells at certain concentrations.

Retinol inhibits the growth of all-trans-retinoic acid-sensitive and all-trans-retinoic acid-resistant colon cancer cells through a retinoic acid receptor-independent mechanism

Retinol (vitamin A) is thought to exert its effects through the actions of its metabolite, all-trans-retinoic acid (ATRA), on gene transcription mediated by retinoic acid receptors (RAR) and retinoic acid response elements (RARE). However, retinoic acid resistance limits the chemotherapeutic potential of ATRA. We examined the ability of retinol to inhibit the growth of ATRA-sensitive (HCT-15) and ATRA-resistant (HCT-116, SW620, and WiDR) human colon cancer cell lines. Retinol inhibited cell growth in a dose-responsive manner. Retinol was not metabolized to ATRA or any bioactive retinoid in two of the cell lines examined. HCT-116 and WiDR cells converted a small amount of retinol to ATRA; however, this amount of ATRA was unable to inhibit cell growth. To show that retinol was not inducing RARE-mediated transcription, each cell line was transfected with pRARE-chloramphenicol acetyltransferase (CAT) and treated with ATRA and retinol. Although treatment with ATRA increased CAT activity 5-fold in ATRA-sensitive cells, retinol treatment did not increase CAT activity in any cell line examined. To show that growth inhibition due to retinol was ATRA, RAR, and RARE independent, a pan-RAR antagonist was used to block RAR signaling. Retinol-induced growth inhibition was not alleviated by the RAR antagonist in any cell line, but the antagonist alleviated ATRA-induced growth inhibition of HCT-15 cells. Retinol did not induce apoptosis, differentiation or necrosis, but affected cell cycle progression. Our data show that retinol acts through a novel, RAR-independent mechanism to inhibit colon cancer cell growth.

Dietary whey protein lowers serum C-peptide concentration and duodenal SREBP-1c mRNA abundance, and reduces occurrence of duodenal tumors and colon aberrant crypt foci in azoxymethane-treated male rats

We evaluated partially hydrolyzed whey protein (WPH) for inhibitory effects on the development of colon aberrant crypt foci (ACF) and intestinal tumors in azoxymethane (AOM)-treated rats. Pregnant Sprague-Dawley rats and their progeny were fed AIN-93G diets containing casein (CAS, control diet) or WPH as the sole protein source. Colons and small intestines from the male progeny were obtained at 6, 12, 20 and 23 weeks after AOM treatment. At 6 and 23 weeks, post-AOM, WPH-fed rats had fewer ACF than did CAS-fed rats. Intestinal tumors were most frequent at 23 weeks, post-AOM. At this time point, differences in colon tumor incidence with diet were not observed; however, WPH-fed rats had fewer tumors in the small intestine (7.6% vs. 26% incidence, P=.004). Partially hydrolized whey protein suppressed circulating C-peptide concentration (a stable indicator of steady-state insulin secretion) at all four time points relative to the corresponding CAS-fed animals. The relative mRNA abundance for the insulin-responsive, transcription factor gene, SREBP-1c, was reduced by WPH in the duodenum but not colon. Results indicate potential physiological linkages of dietary protein type with circulating C-peptide (and by inference insulin), local expression of SREBP-1c gene and propensity for small intestine tumorigenesis.

Farnesol and geraniol chemopreventive activities during the initial phases of hepatocarcinogenesis involve similar actions on cell proliferation and DNA damage, but distinct actions on apoptosis, plasma cholesterol and HMGCoA reductase

Chemopreventive activities of farnesol (FOH) and geraniol (GOH) were evaluated during the initial phases of hepatocarcinogenesis. Rats received during eight consecutive weeks 25 mg/100 g body weight FOH (FOH group) or GOH (GOH group), or only corn oil (CO group, controls). Incidence (%) and mean number of visible hepatocyte nodules/animal were inhibited in FOH group (13% and 4 +/- 1; P < 0.05), but not in GOH group (42% and 18 +/- 17, P > 0.05), compared to CO group (100% and 42 +/- 17). Mean area (mm2) and % liver section area occupied by total hepatic placental glutathione S-transferase positive preneoplastic lesions (PNLs) were reduced in FOH group (0.09 +/- 0.06; 2.8 +/- 1.3; P < 0.05) compared to CO group (0.18 +/- 0.12; 10.0 +/- 2.8), while in GOH group only the mean area of these PNL was reduced (0.11 +/- 0.09; P < 0.05), but not the % liver section area occupied by them (5.1 +/- 1.1; P > 0.05). Compared to CO group, FOH and GOH groups showed reduced (P < 0.05) PNL cell proliferation and DNA damage, but only GOH group showed increased PNL apoptosis (P < 0.05). FOH group, but not GOH group, presented reduced (P < 0.05) total plasma cholesterol levels and increased (P < 0.05) hepatic levels of 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase mRNA, compared to CO group. No differences (P > 0.05) were observed between CO, FOH and GOH regarding hepatic levels of farnesoid X activated receptor (FXR) protein. Results indicate that FOH and GOH could represent promising chemopreventive agents against hepatocarcinogenesis. Inhibition of cell proliferation and DNA damage relate to both isoprenoids' anticarcinogenic actions while induction of apoptosis specifically relates to GOH protective actions. Inhibition of HMGCoA reductase activity could be associated with FOH, but not GOH anticarcinogenic actions. FXR does not seem to be involved in the isoprenoids' chemopreventive activities.

Ferulic acid stabilizes a solution of vitamins C and E and doubles its photoprotection of skin

Ferulic acid is a potent ubiquitous plant antioxidant. Its incorporation into a topical solution of 15%l-ascorbic acid and 1%alpha-tocopherol improved chemical stability of the vitamins (C+E) and doubled photoprotection to solar-simulated irradiation of skin from 4-fold to approximately 8-fold as measured by both erythema and sunburn cell formation. Inhibition of apoptosis was associated with reduced induction of caspase-3 and caspase-7. This antioxidant formulation efficiently reduced thymine dimer formation. This combination of pure natural low molecular weight antioxidants provides meaningful synergistic protection against oxidative stress in skin and should be useful for protection against photoaging and skin cancer.

Characterization of the Oxidase Activity in Mammalian Catalase

Catalase is a highly conserved heme-containing antioxidant enzyme known for its ability to degrade hydrogen peroxide into water and oxygen. In low concentrations of hydrogen peroxide, the enzyme also exhibits peroxidase activity. We report that mammalian catalase also possesses oxidase activity. This activity, which is detected in purified catalases, cell lysates, and intact cells, requires oxygen and utilizes electron donor substrates in the absence of hydrogen peroxide or any added cofactors. Using purified bovine catalase and 10-acetyl-3,7-dihydroxyphenoxazine as the substrate, the oxidase activity was found to be temperature-dependent and displays a pH optimum of 7-9. The Km for the substrate is 2.4 x 10(-4) m, and Vmax is 4.7 x 10(-5) m/s. Endogenous substrates, including the tryptophan precursor indole, the neurotransmitter precursor beta-phenylethylamine, and a variety of peroxidase and laccase substrates, as well as carcinogenic benzidines, were found to be oxidized by catalase or to inhibit this activity. Several dietary plant micronutrients that inhibit carcinogenesis, including indole-3-carbinol, indole-3-carboxaldehyde, ferulic acid, vanillic acid, and epigallocatechin-3-gallate, were effective inhibitors of the activity of catalase oxidase. Difference spectroscopy revealed that catalase oxidase/substrate interactions involve the heme-iron; the resulting spectra show time-dependent decreases in the ferric heme of the enzyme with corresponding increases in the formation of an oxyferryl intermediate, potentially reflecting a compound II-like intermediate. These data suggest a mechanism of oxidase activity involving the formation of an oxygen-bound, substrate-facilitated reductive intermediate. Our results describe a novel function for catalase potentially important in metabolism of endogenous substrates and in the action of carcinogens and chemopreventative agents.

Pretreatment of acetylsalicylic acid promotes tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis by down-regulating BCL-2 gene expression

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been shown to be selective in the induction of apoptosis in cancer cells with minimal toxicity to normal tissues. However, not all cancers are sensitive to TRAIL-mediated apoptosis. Thus, TRAIL-resistant cancer cells must be sensitized first to become responsive to TRAIL. In this study, we observed that pretreatment by acetylsalicylic acid (ASA) augmented TRAIL-induced apoptotic death in human prostate adenocarcinoma LNCaP and human colorectal carcinoma CX-1 cells. Western blot analysis showed that pretreatment of ASA followed by TRAIL treatment activated caspases (8, 9, and 3) and cleaved poly(ADP-ribose) polymerase, the hallmark feature of apoptosis. Most interestingly, at least 12 h of pretreatment with ASA was prerequisite for promoting TRAIL-induced apoptosis and was related to down-regulation of BCL-2. Biochemical analysis revealed that ASA inhibited NF-kappaB activity, which is known to regulate BCL-2 gene expression, by dephosphorylating IkappaB-alpha and inhibiting IKKbeta activity but not by affecting the HER-2/neu phosphatidylinositol 3-kinase-Akt signal pathway. Overexpression of BCL-2 suppressed the promotive effect of ASA on TRAIL-induced apoptosis and changes in mitochondrial membrane potential. Taken together, our studies suggested that ASA-promoted TRAIL cytotoxicity is mediated through down-regulating BCL-2 and by decreasing mitochondrial membrane potential.

Dietary supplement of isohumulones inhibits the formation of aberrant crypt foci with a concomitant decrease in prostaglandin E2 level in rat colon

Male Fischer 344 rats were subcutaneously injected with azoxymethane (AOM) twice weekly at a dose of 15 mg/kg and were fed with freeze-dried (FD) samples of beer brewed without hops (non-hops beer), beer with hops at 4 times the amount of regular lager beer (x 4-hops beer), and isomerized hop extract (IHE) for the whole experimental period (I/PI) or for the post-initiation period (PI) only. Feeding FD beer samples at a dose of 1% significantly decreased the number of aberrant cryp foci (ACF) in the PI protocol over five weeks.x4-hops beer showed stronger inhibitory effects on the development of the numbers of aberrant crypts per focus and large ACF with four or more crypts than non-hops beer. Feeding IHE to rats at a dose of 0.01% or 0.05% in either the I/PI or PI experiment significantly reduced the numbers of ACF. Prostaglandin E2 (PGE2) levels in colonic mucosa of AOM-treated rats were significantly reduced by feeding of IHE. PGE2 production induced by lipopolysaccharide/interferon-gamma (LPS/IFN-gamma) in RAW264.7 cells was also reduced by treatment with IHE and isohumulone in a dose-dependent manner. These observations suggest that isohumulones show chemopreventive effects on ACF formation in rat colon by inhibiting the production of PGE2.

Risk factors for colorectal cancer in relation to number and size of aberrant crypt foci in humans

Several characteristics of aberrant crypt foci (ACF) suggest that they are precursors of colorectal cancer, but the factors that promote or inhibit their growth are largely unknown. We conducted a pilot study to explore whether factors associated with risk of colorectal cancer are also associated with number or size of rectal ACF. Thirty-two U.S. veterans, ages 50 to 80 years, were recruited to undergo magnifying chromoendoscopy for imaging of rectal ACF and colonoscopy for identification of polyps or cancer. Participants completed a questionnaire on cigarette smoking, use of nonsteroidal anti-inflammatory drugs (NSAIDs), and family history of colorectal cancer. Fisher's exact test was used to assess the statistical significance of associations between colorectal cancer risk factors and characteristics of ACF. Cochran-Mantel-Haenszel statistics and polytomous regression were used to test the significance of associations adjusted for age. Participants with a history of adenoma had more ACF than those without (age-adjusted P = 0.02), but the numbers in the two groups overlapped markedly. Older participants had more (P = 0.06) and larger (P = 0.009) ACF than younger participants. No associations were identified between either ACF number or size and cigarette smoking, use of NSAIDs, or family history of colorectal cancer. These findings suggest that persons with adenomas have somewhat more rectal ACF than persons without, and that older age is a risk factor for ACF growth. Future research should be directed toward developing techniques to identify ACF that are likely to progress to cancer and the modifiable factors that promote or inhibit such progression.

Histamine receptor antagonists and incident colorectal adenomas

BACKGROUND

Prior studies suggest that histamines may modulate the development of colorectal neoplasia.

AIM

To assess whether histamine receptor antagonist use was associated with adenoma formation.

METHODS

Patients (n = 2366) were drawn from three adenoma chemoprevention trials. All underwent baseline colonoscopy with removal of adenoma(s) and were deemed free of remaining lesions; they were followed with surveillance colonoscopy. Medication use was assessed by questionnaire. Adjusted risk ratios for adenoma formation related to histamine receptor antagonist use (histamine H1 and H2 receptor, H1RA and H2RA) were determined using log linear models.

RESULTS

In pooled analyses, H1RA exposure was not associated with subsequent adenoma risk (RR = 1.10; 95% CI 0.97-1.25) or multiple adenoma formation (RR = 0.85; 95% CI 0.67-1.07). H2RA use also was not associated with adenoma (RR = 0.90; 95% CI 0.77-1.06), or multiple adenoma (RR = 0.77; 95% CI 0.57-1.04) in the pooled analyses, but H2RA users in the first trial had a decreased risk of adenoma (RR = 0.70; 95% CI 0.48-1.03) and multiple adenoma (RR = 0.31; 95% CI 0.12-0.79).

CONCLUSION

H2RA use was associated with reduced risk for adenoma in one trial, but not in the pooled analyses. Further study would be warranted before undertaking randomized trials of H2RAs for adenoma chemoprevention.

Folate and its preventive potential in colorectal carcinogenesis

Based on a 15-year old hypothesis, it is believed that an adequate ingestion of folate vitamins decreases, whereas a nutritional depletion of folate increases the risk of colorectal cancer. The present article reviews the efforts to provide biochemical and epidemiological evidence for folate as a chemopreventive agent against colorectal carcinogenesis. BIOLOGICAL EVIDENCE: Tetrahydrofolates govern the intracellular one-carbon metabolism and account for proper DNA biosynthesis and macromolecular modification. Numerous experimental studies traced different molecular pathways and tried to link folate depletion with DNA instability and/or mutagenesis. However, none of the proposed underlying molecular mechanisms appear clearly defined. EPIDEMIOLOGICAL EVIDENCE: Numerous case-control and prospective studies have been conducted on folate and colorectal cancer, which all together miss a clinical bottom line. The recommendation of folate intake to prevent colorectal cancer is therefore not evidence-based.

The zebrafish retinol dehydrogenase, rdh1l, is essential for intestinal development and is regulated by the tumor suppressor adenomatous polyposis coli

Retinoic acid (RA) is a potent signaling molecule that plays important roles in multiple and diverse developmental processes. The contribution of retinoic acid to promoting the development and differentiation of the vertebrate intestine and the factors that regulate RA production in the gut remain poorly defined. Herein, we report that the novel retinol dehydrogenase, rdh1l, is required for proper gut development and differentiation. rdh1l is expressed ubiquitously during early development but becomes restricted to the gut by 3 days postfertilization. Knockdown of rdh1l results in a robust RA-deficient phenotype including lack of intestinal differentiation, which can be rescued by the addition of exogenous retinoic acid. We report that adenomatous polyposis coli (APC) mutant zebrafish harbor an RA-deficient phenotype including aberrant intestinal differentiation and that these mutants can be rescued by treatment with retinoic acid or injection of rdh1l mRNA. Further, we have found that although APC mutants are deficient in rdh1l expression, they harbor increased expression of raldh2 suggesting the control of RA production by APC is via retinol dehydrogenase activity. These results provide genetic evidence that retinoic acid is required for vertebrate gut development and that the tumor suppressor APC controls the production of RA in the gut by regulating the expression of the retinol dehydrogenase, rdh1l.

Modulation of hepatic and renal drug metabolizing enzyme activities in rats by subchronic administration of farnesol

Farnesol demonstrates antitumor activity in several animal models for human cancer and was being considered for development as a cancer chemopreventive agent. This study was performed to characterize the effects of minimally toxic doses of farnesol on the activity of phase I and II drug metabolizing enzymes. CD((R)) rats (20/sex/group) received daily gavage exposure to farnesol doses of 0, 500, or 1000 mg/kg/day for 28 days; 10 rats/sex/group were necropsied at the termination of farnesol exposure; remaining animals were necropsied after a 28-day recovery period. No deaths occurred during the study, and farnesol had no significant effects on body weight, food consumption, clinical signs, or hematology/coagulation parameters. Modest but statistically significant alterations in several clinical chemistry parameters were observed at the termination of farnesol exposure; all clinical pathology effects were reversed during the recovery period. At the termination of dosing, the activities of CYP1A, CYP2A1-3, CYP2B1/2, CYP2C11/12, CYP2E1, CYP3A1/2, CYP4A1-3, CYP19, glutathione reductase, NADPH/quinone oxidoreductase and UDP-glucuronosyltransferase were significantly increased in the livers of farnesol-treated rats; farnesol also increased the activity of glutathione S-transferase in the kidney. The effects of farnesol on hepatic and renal enzymes were reversed during the recovery period. At the end of the dosing period, increases in absolute and relative liver and kidney weights were seen in farnesol-treated rats. These increases may be secondary to induction of drug metabolizing enzymes, since organ weight increases were not associated with histopathologic alterations and were reversed upon discontinuation of farnesol exposure. Administration of farnesol at doses of up to 1000 mg/kg/day induced reversible increases in the activities of several hepatic and renal drug metabolizing enzymes in rats, while inducing only minimal toxicity. It is concluded that non-toxic or minimally toxic doses of farnesol could alter the metabolism, efficacy, and/or toxicity of drugs with which it is co-administered.

Multiple signaling pathways converge on beta-catenin in thyroid cancer

The beta-catenin pathway has been conclusively demonstrated to regulate differentiation and patterning in multiple model systems. In thyroid cancer, alterations are often seen in proteins that regulate beta-catenin, including those of the RAS, PI3K/AKT, and peroxisome proliferation activated receptor-gamma (PPARgamma) pathways, and evidence from the literature suggests that beta-catenin may play a direct role in the dedifferentiation commonly observed in late-stage disease. RET/PTC rearrangements are frequent in thyroid cancer and appear to be exclusive from mutational events in RAS and BRAF. Activation of AKT by phosphatidylinositide-3 kinase (PI3K), a RAS effector, results in GSK3beta phosphorylation and deactivation and subsequent beta-catenin upregulation in thyroid cancer. Activating mutations in beta-catenin, which have been demonstrated in late-stage thyroid tumors, correlate with beta-catenin nuclear localization and poor prognosis. We hypothesize that activation of the RAS, PI3K/AKT, and PPARgamma pathways ultimately impinges upon beta-catenin. We further propose that if mutations in BRAF, RAS, and RET/PTC rearrangements are mutually exclusive in certain thyroid tumors or tumor types, as has already been shown for papillary thyroid cancer, then these interconnected pathways may cooperate in the initiation and promotion of the disease. We believe that clinical benefit for thyroid cancer patients could be derived from disrupting the middle or distal pathway effectors of these pathways, such as AKT or beta-catenin.

Farnesol is glucuronidated in human liver, kidney and intestine in vitro, and is a novel substrate for UGT2B7 and UGT1A1

Farnesol is an isoprenoid found in many aromatic plants and is also produced in humans, where it acts on numerous nuclear receptors and has received considerable attention due to its apparent anticancer properties. Although farnesol has been studied for over 30 years, its metabolism has not been well characterized. Recently, farnesol was shown to be metabolized by cytochromes P450 in rabbit; however, neither farnesol hydroxylation nor glucuronidation in humans have been reported to date. In the present paper, we show for the first time that farnesol is metabolized to farnesyl glucuronide, hydroxyfarnesol and hydroxyfarnesyl glucuronide by human tissue microsomes, and we identify the specific human UGTs (uridine diphosphoglucuronosyltransferases) involved. Farnesol metabolism was examined by a sensitive LC (liquid chromatography)-MS/MS method. Results indicate that farnesol is a good substrate for glucuronidation in human liver, kidney and intestine microsomes (values in nmol/min per mg). Initial analysis using expressed human UGTs indicated that UGTs 1A1 and 2B7 were primarily responsible for glucuronidation in vitro, with significantly lower activity for all the other UGTs tested (UGTs 1A3, 1A4, 1A6, 1A9 and 2B4). Kinetic analysis and inhibition experiments indicate that, in liver microsomes, UGT1A1 is primarily responsible for farnesol glucuronidation; however, in intestine microsomes, UGT2B7 is probably the major isoform involved, with a very-low-micromolar K(m). We also show the first direct evidence that farnesol can be metabolized to hydroxyfarnesol by human liver microsomes and that hydroxyfarnesol is metabolized further to hydroxyfarnesyl glucuronide. Thus glucuronidation may modulate the physiological and/or pharmacological properties of this potent signalling molecule.

In vivo measurement of DNA synthesis rates of colon epithelial cells in carcinogenesis

We describe here a highly sensitive technique for measuring DNA synthesis rates of colon epithelial cells in vivo. Male SD rats were given (2)H(2)O (heavy water). Colon epithelial cells were isolated, DNA was extracted, hydrolyzed to deoxyribonucleosides, and the deuterium enrichment of the deoxyribose moiety was determined by gas chromatographic/mass spectrometry. Turnover time of colon crypts and the time for migration of cells from basal to top fraction of the crypts were measured. These data were consistent with cell cycle analysis and bromodeoxyuridine labeling. By giving different concentrations of a promoter, dose-dependent increases in DNA synthesis rates were detected, demonstrating the sensitivity of the method. Administration of a carcinogen increased DNA synthesis rates cell proliferation in all fractions of the crypt. In conclusion, DNA synthesis rates of colon epithelial cells can be measured directly in vivo using stable-isotope labeling. Potential applications in humans include use as a biomarker for cancer chemoprevention studies.

Targeting epigenetic regulatory mechanisms in cancer chemoprevention

Dysregulation of the epigenome plays a fundamental role in tumour development. Epigenetic events are a major mechanism for inactivating tumour suppressor and DNA repair genes and occur ubiquitously during the early stages of tumour development. Unlike genes inactivated by mutation, genes silenced epigenetically are intact and potentially responsive to reactivation by small molecules. This review discusses the potential for restoring epigenetic balance as a means to prevent cancer.

Squalene does not exhibit a chemopreventive activity and increases plasma cholesterol in a Wistar rat hepatocarcinogenesis model

The eventual chemopreventive effect of squalene (SQ), a triterpene present in olive oil, was evaluated when administered to Wistar rats during a period comprising the initiation and selection/promotion of the "resistant hepatocyte" (RH) model of hepatocarcinogenesis. During 8 consecutive wk, animals received by gavage SQ (100 or 150 mg/100 g body weight) dissolved in corn oil (CO) daily. Animals treated with only CO and submitted to the RH model were used as controls. Treatments with SQ did not result in inhibition of macroscopically visible hepatocyte nodules (P > 0.05) or of hepatic placental glutathione S-transferase- positive preneoplastic lesions (PNL; P > 0.05). Hepatic cell proliferation and apoptosis indexes were not different (P > 0.05) among the different experimental groups, both regarding PNL and surrounding normal tissue areas. There were no significant differences (P > 0.05) among comets presented by rats treated with the two SQ doses or with CO. On the other hand, SQ increased total plasma cholesterol levels when administered at both doses (P < 0.05). This indicates that the isoprenoid was absorbed. Thus, SQ did not present chemopreventive activity during hepatocarcinogenesis and had a hypercholesterolemic effect, suggesting caution when considering its use in chemoprevention of cancer.

Bile acids as carcinogens in human gastrointestinal cancers

Bile acids were first proposed to be carcinogens in 1939 and 1940. On the basis of later work with rodent models, bile acids came to be regarded as cancer promoters rather than carcinogens. However, considerable indirect evidence, obtained more recently, supports the view that bile acids are carcinogens in humans. At least 15 reports, from 1980 through 2003, indicate that bile acids cause DNA damage. The mechanism is probably indirect, involving induction of oxidative stress and production of reactive oxygen species that then damage DNA. Repeated DNA damage likely increases the mutation rate, including the mutation rate of tumor suppressor genes and oncogenes. Additional reports, from 1994 through 2002, indicate that bile acids, at the increased concentrations accompanying a high fat diet, induce frequent apoptosis. Those cells within the exposed population with reduced apoptosis capability tend to survive and selectively proliferate. That bile acids cause DNA damage and may select for apoptosis-resistant cells (both leading to increased mutation), indicates that bile acids are likely carcinogens. In humans, an increased incidence of cancer of the laryngopharyngeal tract, esophagus, stomach, pancreas, the small intestine (near the Ampulla of Vater) and the colon are associated with high levels of bile acids. The much larger number of cell generations in the colonic (and, likely, other gastrointestinal) epithelia of humans compared to rodents may allow time for induction and selection of mutations leading to cancer in humans, although not in rodents.

Geranylgeraniol and β-ionone inhibit hepatic preneoplastic lesions, cell proliferation, total plasma cholesterol and DNA damage during the initial phases of hepatocarcinogenesis, but only the former inhibits NF-κB activation

Chemopreventive activities of the isoprenoids geranylgeraniol (GGO) and beta-ionone (BI) were evaluated during initial phases of hepatocarcinogenesis. Rats received 8 or 16 mg/100 g body wt GGO (GGO8 and GGO16 groups) or BI (BI8 and BI16 groups), or only corn oil (CO group, controls) daily for 7 weeks. Incidence (%) and the mean number of visible hepatocyte nodules/animal were inhibited in the GGO8 (64% and 21 +/- 40), GGO16 (33% and 3 +/- 5), BI8 (50% and 13 +/- 34) and BI16 (42% and 9 +/- 19) groups compared with the CO group (100% and 34 +/- 51) (P < 0.05, except for the GGO8 group). Number/cm(2) liver section, mean area (mm(2)) and % liver section area occupied by persistent hepatic placental glutathione S-transferase positive preneoplastic lesions (PNL) were reduced in the GGO8 (11 +/- 9; 0.26 +/- 0.35; 2.7 +/- 3.0), GGO16 (6 +/- 6; 0.18 +/- 0.16; 0.9 +/- 0.9), BI8 (9 +/- 5; 0.13 +/- 0.20; 1.1 +/- 1.2) and BI16 (8 +/- 6; 0.08 +/- 0.09; 0.6 +/- 0.4) groups compared with the CO group (26 +/- 18; 0.29 +/- 0.34; 7.0 +/- 5.5) (P < 0.05). GGO16 and BI16 groups showed smaller visible hepatocyte nodules, reduced PNL cell proliferation and total plasma cholesterol levels compared with the CO group (P < 0.05), but did not show any differences (P > 0.05) in PNL apoptosis. DNA damage expressed as comet length (microm) was reduced in the GGO8 (96.7 +/- 1.5), GGO16 (94.2 +/- 1.5), BI8 (97.1 +/- 1.1) and BI16 (95.1 +/- 1.5) groups compared with the CO group (102.1 +/- 1.7) (P < 0.05). In comparison with normal animals, the CO group animals showed increased (P < 0.05) nuclear levels of nuclear factor kappa B (NF-kappaB) p65 subunit in hepatic cells, which were decreased (P < 0.05) in the GGO16 group animals. Anticarcinogenic actions of these isoprenoids seem to follow a dose-response relationship. Results indicate that GGO and BI could be represented as promising chemopreventive agents against hepatocarcinogenesis. Inhibition of cell proliferation and DNA damage seems to be important for the anticarcinogenic actions of isoprenoids, while the inhibition of NF-kappaB activation seems to be specifically related to GGO actions.

Myh deficiency enhances intestinal tumorigenesis in multiple intestinal neoplasia (ApcMin/+) mice

Monoallelic APC and biallelic MYH (homolog of Escherichia coli mutY) germ-line mutations are independently associated with a strong predisposition to colorectal adenomas and carcinoma in humans. Whereas mice heterozygous for mutant Apc develop intestinal tumors, mice homozygous for mutant Myh do not show increased tumor susceptibility. We analyzed the phenotype of Apc(Min/+)/Myh(-/-) mice and found that they developed significantly more adenomas in the small intestine than did Apc(Min/+)/Myh(+/+) or Apc(Min/+)/Myh(+/-) mice (median 231 versus 151 versus 152). In the large bowel, Apc(Min/+)/Myh(-/-) mice showed significant increases in the number of aberrant crypt foci. In addition, Apc(Min/+)/Myh(-/-) mice developed an increased number of mammary tumors. Molecular analyses suggested that at least 19% of intestinal tumors from Apc(Min/+)/Myh(-/-) mice had acquired intragenic Apc mutations rather than allelic loss. Consistent with a defect in base excision repair, three intragenic Apc mutations in polyps without allelic loss from Apc(Min/+)/Myh(-/-) mice were shown to be G:C to T:A transversions which resulted in termination codons; no such mutations were found in polyps from Apc(Min/+)/Myh(+/+) or Apc(Min/+)/Myh(+/-) mice. Tumors from Apc(Min/+)/Myh(+/-) mice harbored neither somatic mutations nor allelic loss at Myh. Thus, homozygous, but not heterozygous, Myh deficiency enhanced intestinal tumorigenesis in Apc(Min/+) mice. The excess small-bowel adenomas in Apc(Min/+)/Myh(-/-) mice, therefore, appear to be a model of MYH-associated polyposis in humans.

Calcium Sensing Receptor in Human Colon Carcinoma: Interaction with Ca2+ and 1,25-Dihydroxyvitamin D3

Recent studies show that the human parathyroid calcium sensing receptor (CaSR) is expressed in human colon epithelium and functions to regulate epithelial proliferation and differentiation. In this study, we show that the cells of the colon crypt acquire CaSR expression as they differentiate and migrate towards the apex of the crypt. CaSR expression was weak in colon carcinomas with a more-differentiated histologic pattern, whereas CaSR expression was undetectable in less-differentiated tumors. We found that Ca2+ and/or 1,25(OH)2D3 stimulated CaSR promoter activity and CaSR protein expression in the human colon carcinoma CBS cells, which possessed a functional CaSR. Both agents concomitantly induced a series of changes in the CBS cells that influence proliferation and differentiation, but cellular responses to the two agents were not identical. Ca2+ strongly induced E-cadherin expression and inhibited the expression of the nuclear transcription factor, TCF4. 1,25(OH)2D3 was weaker in its effect on E-cadherin and was not able to inhibit TCF4 expression. 1,25(OH)2D3 was as strong or stronger than Ca2+ in its induction of the cyclin-dependent kinase inhibitors, P21 and p27. It is concluded that CaSR may function in the colon to regulate epithelial differentiation and that loss of CaSR expression may be associated with abnormal differentiation and/or malignant progression. Extracellular Ca2+ and 1,25(OH)2D3 are potential candidates involved in regulating CaSR expression in the colon and the chemopreventive actions of Ca2+ and 1,25(OH)2D3 in colon cancer may be mediated, in part, through the CaSR.

Flat Dysplastic Aberrant Crypt Foci Are Related to Tumorigenesis in the Colon of Azoxymethane-Treated Rat

We evaluated the role of aberrant crypt foci (ACF) as biomarkers of colon cancer by studying the sequential development (6-28 weeks) from early lesion to tumor in the colon of azoxymethane-exposed F344 rats (15 mg/kg bw × 2). Surface examination of unsectioned methylene blue–stained colon preparations, transilluminated in the inverse light microscope, revealed two types of early lesions: classic elevated ACF and small flat lesions, which we denoted flat ACF and which were characterized by bright blue staining, compressed crypt openings, and crypts not elevated above the surrounding mucosa. At a later stage, the crypts surrounding large flat ACF became enlarged, a change that slightly raised the structure; principally, large flat ACF and nascent tumors displayed the same surface morphology. Furthermore, flat ACF with 18.6 ± 10.6 crypt/focus and tumors showed a uniform picture of severe dysplasia with frequent presence of Paneth cells, compressed crypts, cytoplasmic/nuclear overexpression of β-catenin, and nuclear overexpression of cyclin D1. In contrast, classic elevated ACF with 5.3 ± 2.5 crypts/focus did not display such changes: they showed mainly hyperplasia, mild or moderate dysplasia but never severe dysplasia. Along the time course, the number of flat ACF + tumors, including microscopic and macroscopic, was virtually constant, ∼2.5 lesions/rat. The number of classic elevated ACF was initially ∼180 lesions/rat and terminally ∼80 lesions/rat. Flat ACF grew significantly faster than classic elevated ACF. In conclusion, our data indicate a continuous developmental growth from small flat dysplastic ACF to the stage of a tumor. In contrast, classic elevated ACF do not seem to be as closely related to tumorigenesis.

Correlation of in vitro chemopreventive efficacy data from the human epidermal cell assay with animal efficacy data and clinical trial plasma levels

The human epidermal cell (HEC) assay, which uses carcinogen exposed normal skin keratinocytes to screen for cancer prevention efficacy, was used to screen possible preventive agents. The endpoints measured were inhibition of carcinogen-induced growth and induction of involucrin, an early marker of differentiation. Sixteen of twenty agents (apigenin, apomine, budesonide, N-(2-carboxyphenyl)retinamide, ellagic acid, ibuprofen, indomethacin, melatonin, (-)-2-oxo-4-thiazolidine carboxylic acid, polyphenon E, resveratrol, beta-sitosterol, sulfasalazine, vitamin E acetate, and zileuton) were positive in at least one of the two assay endpoints. Four agents (4-methoxyphenol, naringenin, palmitoylcarnitine chloride, and silymarin) were negative in the assay. Nine of the sixteen agents were positive for both endpoints. Agents that showed the greatest response included: ellagic acid > budesonide, ibuprofen > apigenin, and quinicrine dihydrochloride. Fifty-eight of sixty-five agents that have been evaluated in the HEC assay have also been evaluated in one or more rodent bioassays for cancer prevention and several are in clinical trials for cancer prevention. The assay has an overall predictive accuracy of approximately 91.4% for efficacy in rodent cancer prevention irrespective of the species used, the tissue model, or the carcinogen used. Comparison of the efficacious concentrations in vitro to plasma levels in clinical trials show that concentrations that produced efficacy in the HEC assay were achieved in clinical studies for 31 of 33 agents for which plasma levels and/or C(max) levels were available. For two agents, 9-cis-retinoic acid (RA) and dehydroepiandrosterone (DHEA), the plasma levels greatly exceeded the highest concentration (HC) found to have efficacy in vitro. Thus, the HEC assay has an excellent predictive potential for animal efficacy and is responsive at clinically achievable concentrations.

Modification of N‐Acetyltransferases and Glutathione S‐Transferases by Coffee Components: Possible Relevance for Cancer Risk

Enzymes of xenobiotic metabolism are involved in the activation and detoxification of carcinogens and can play a pivotal role in the susceptibility of individuals toward chemically induced cancer. Differences in such susceptibility are often related to genetically predetermined enzyme polymorphisms but may also be caused by enzyme induction or inhibition through environmental factors or in the frame of chemopreventive intervention. In this context, coffee consumption, as an important lifestyle factor, has been under thorough investigation. Whereas the data on a potential procarcinogenic effect in some organs remained inconclusive, epidemiology has clearly revealed coffee drinkers to be at a lower risk of developing cancers of the colon and the liver and possibly of several other organs. The underlying mechanisms of such chemoprotection, modifications of xenobiotic metabolism in particular, were further investigated in rodent and in vitro models, as a result of which several individual chemoprotectants out of the >1000 constituents of coffee were identified as well as some strongly metabolized individual carcinogens against which they specifically protected. This chapter discusses the chemoprotective effects of several coffee components and whole coffee in association with modifications of the usually protective glutathione-S-transferase (GST) and the more ambivalent N-acetyltransferase (NAT). A key role is played by kahweol and cafestol (K/C), two diterpenic constituents of the unfiltered beverage that were found to reduce mutagenesis/tumorigenesis by strongly metabolized compounds, such as 2-amino-1-methyl-6-phenylimidazo-[4,5-b]pyridine, 7,12-dimethylbenz[a]anthracene, and aflatoxin B(1), and to cause various modifications of xenobiotic metabolism that were overwhelmingly beneficial, including induction of GST and inhibition of NAT. Other coffee components such as polyphenols and K/C-free coffee are also capable of increasing GST and partially of inhibiting NAT, although to a somewhat lesser extent.

The effect of lycopene on cell growth and oxidative DNA damage of Hep3B human hepatoma cells

Lycopene, the predominant carotenoid in tomatoes and tomato-based foods, is reported to protect against various cancers, especially prostate cancer. We investigated the effect of lycopene on DNA damage and cell growth inhibition in the Hep3B human hepatoma cell line. Lycopene was analyzed by HPLC, and cell proliferation was determined by 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) assay. A final lycopene concentration of 0.1-50 microM was added to cells plated in 96-well plates. After a 24-hr incubation, cell viability was measured as absorbance at 570 nm after the MTT assay. The effects of lycopene on cell cycle progression were investigated with flow cytometry. Lycopene induced G0/G1 arrest and S phase block. Oxidative DNA damage was determined by the Comet (single-cell gel electrophoresis) assay. Lycopene inhibited cell growth in a dose-dependent manner. Cell growth was inhibited 20% at 0.2 microM lycopene and 40% at 50 microM lycopene after a 24-hr incubation. In the Comet assay, lycopene-treated cells showed less DNA damage than did placebo-treated cells. The inhibition of Hep3B cell growth in this study demonstrates the antitumor properties of lycopene.

Vitamin A prevents high fat diet-induced ACF development and modifies the pattern of expression of peroxisome proliferator and retinoic acid receptor m-RNA

Some dietary compounds, among them fats, are modulators of colon cancer risk. This study reports the modulating effects of n-6, with or without vitamin A, on promotion of colon preneoplasic lesions induced by 1,2-dimethylhydrazine (DMH) and on the expression of nuclear receptors (PPARgamma, RXRalpha, and RARbeta). One group of male Fisher rats was fed a basic diet (5% safflower oil) and two groups were fed a high-fat diet (HFD, 25% safflower oil). Of these, one was supplemented with 200 IU vitamin A for 5 mo. The safflower oil contained polyunsaturated fatty acids, mainly linoleic acid (73%). The data showed an increasing effect of safflower oil-enriched diet on aberrant crypt foci occurrence and multiplicity. This effect was impaired by vitamin A supplementation. In addition, an HFD-related up-regulation of PPARgamma and a concomitant down-regulation of RARbeta mRNA expression were observed with or without chemical initiation and were prevented by vitamin A. Moreover, when treated with DMH, HFD rats exhibited a dramatically decreased expression of RXRalpha mRNA (-49%). It was hypothesized that HFD, leading to hyperexpression of PPARgamma, would produce an alteration of retinoic acid signaling and, in this way, create a background modulating colon cancer risk.

beta-catenin-mediated signaling: a molecular target for early chemopreventive intervention

Dysregulation of Wnt signaling appears to be a critical event in the formation of intestinal tumors and some other cancers. Accumulating data from preclinical studies strongly suggest that targeted disruption of beta-catenin-mediated TCF signaling is a promising strategy for early chemopreventive intervention, particularly with respect to intestinal tumorigenesis. While the search for potent inhibitors is just getting underway, the ability of several synthetic and naturally occurring agents to decrease the transcriptional activity of a luciferase reporter plasmid under the control of TCF-4 regulatory elements (pTOPFLASH) has been demonstrated already. Additional enthusiasm for this approach is provided by data from several groups, which indicate that sulindac, sulindac sulfone and indomethacin can modulate the subcellular localization of beta-catenin in vivo, resulting in either decreased nuclear compartmentalization or enhanced localization of beta-catenin to the plasma membrane. Although the mechanism by which agents disrupt beta-catenin-mediated TCF signaling remains to be elucidated, possibilities include: (1) physical inhibition of the beta-catenin/TCF complex formation, (2) upregulation of the ubiquitin-mediated proteosomal degradation of beta-catenin, (3) accelerated nuclear export of beta-catenin and (4) enhanced sequestration of beta-catenin by E-cadherin. The common role of beta-catenin in both Wnt signaling and cell adhesion provides a unique opportunity to develop chemopreventive therapies that both prevent the development of cancer and delay tumor progression.

Ferulic acid is quickly absorbed from rat stomach as the free form and then conjugated mainly in liver

Ferulic acid (FA) is one of the most abundant phenolic antioxidants in the human diet. Many studies have documented its beneficial properties. It is therefore essential to understand the absorption and metabolism of FA in detail. The purpose of this study was to confirm the hypothesis that FA is absorbed in rat stomach and metabolized mainly in the liver. We determined the recovery of FA and its metabolites (FA sulfate/glucuronides) in rat gastric contents, gastric mucosa, portal vein plasma, celiac arterial plasma, bile, and urine after 2.25 micromol FA was administered in 0.5 mL physiological saline and incubated for 25 min in situ in the stomach of rats. Within 25 min, 74 +/- 11% of the administered FA disappeared from the stomach; later, FA was recovered in both free and conjugated forms in plasma, bile, and urine. On the other hand, only free FA was detected in the gastric contents and mucosa; it was also detected in the portal vein plasma as 49 +/- 5% of the total FA (all forms of FA). However, the proportion of free FA in the celiac arterial plasma, bile, and urine decreased to 5-8%. These results indicate that FA can be quickly absorbed from the rat stomach, and then is likely metabolized mainly in the liver. Such novel information would be helpful in the use of FA as a nutrient supplement. For example, oral administration of FA in capsule form or in a form bonded with sugar esters may provide a more appropriate concentration of FA in the circulation, which may improve its proposed efficacy in preventing chronic disease.

Inhibitory effects of beer on heterocyclic amine-induced mutagenesis and PhIP-induced aberrant crypt foci in rat colon

Anti-mutagenic and anti-carcinogenic effects of beer on heterocyclic amine (HCA)-induced carcinogenesis were studied in vitro and in vivo. Four commercial beers (two pilsner-type, black, and stout) showed inhibitory effects against five HCAs, 2-amino-3,8-dimethylimidazo [4,5-f]quinoxaline (MeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2), 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (Glu-P-1) and 2-amino-3-methylimidazo[4,5-f]-quinoline (IQ), in the Ames assay using Salmonella typhimurium TA98 in the presence of rat S9 mix. The inhibitory effects of dark-colored beers (stout and black beer) were greater than those of pilsner-type beers. Dark-colored beers suppressed CYP1A2 activity in a dose-dependent manner, suggesting that inhibition of HCA activation is partly responsible for their strong anti-mutagenic effects. Anti-mutagenic effects were also observed when the pooled human S9 mix or activated IQ was used in the assay. The micronucleus test using Chinese hamster lung CHL/IU cells showed that the addition of freeze-dried samples of pilsner-type and stout beer to the culture medium significantly reduced the number of cells with micronuclei induced with PhIP or Trp-P-2. Single-cell gel electrophoresis assay (comet assay) revealed that oral ingestion of pilsner-type and stout beers for 1 week significantly inhibited DNA damage in the liver cells of male ICR mice exposed to MeIQx (13 mg/kg, i.p.). A decrease in the formation of DNA adducts was also observed using a 32P-postlabeling method. Male Fischer 344 rats orally received PhIP (75 mg/kg, five times a week for 2 weeks) and aberrant crypt foci (ACF) formation in the colon was analyzed after 5 weeks. The number of ACF was significantly reduced in rats fed a diet containing freeze-dried beer. These results suggest that beer inhibits the genotoxic effects of HCAs and may reduce the risk of carcinogenesis caused by food borne carcinogens.

The tumor suppressor adenomatous polyposis coli and caudal related homeodomain protein regulate expression of retinol dehydrogenase L

Development of normal colon epithelial cells proceeds through a systematic differentiation of cells that emerge from stem cells within the base of colon crypts. Genetic mutations in the adenomatous polyposis coli (APC) gene are thought to cause colon adenoma and carcinoma formation by enhancing colonocyte proliferation and impairing differentiation. We currently have a limited understanding of the cellular mechanisms that promote colonocyte differentiation. Herein, we present evidence supporting a lack of retinoic acid biosynthesis as a mechanism contributing to the development of colon adenomas and carcinomas. Microarray and reverse transcriptase-PCR analyses revealed reduced expression of two retinoid biosynthesis genes: retinol dehydrogenase 5 (RDH5) and retinol dehydrogenase L (RDHL) in colon adenomas and carcinomas as compared with normal colon. Consistent with the adenoma and carcinomas samples, seven colon carcinoma cell lines also lacked expression of RDH5 and RDHL. Assessment of RDH enzymatic activity within these seven cell lines showed poor conversion of retinol into retinoic acid when compared with normal cells such as normal human mammary epithelial cells. Reintroduction of wild type APC into an APC-deficient colon carcinoma cell line (HT29) resulted in increased expression of RDHL without affecting RDH5. APC-mediated induction of RDHL was paralleled by increased production of retinoic acid. Investigations into the mechanism responsible for APC induction of RDHL indicated that beta-catenin fails to repress RDHL. The colon-specific transcription factor CDX2, however, activated an RDHL promoter construct and induced endogenous RDHL. Finally, the induction of RDHL by APC appears dependent on the presence of CDX2. We propose a novel role for APC and CDX2 in controlling retinoic acid biosynthesis and in promoting a retinoid-induced program of colonocyte differentiation.

Chemoprevention of Colorectal Cancer by Grape Seed Proanthocyanidin Is Accompanied by a Decrease in Proliferation and Increase in Apoptosis

Effects of proanthocyanidin (PA), procyanidin B-2 (B-2), and epigallocatechin gallate (EGCG) on azoxymethane (AOM)-induced colonic preneoplastic aberrant crypt foci (ACF) formation were investigated using F344 rats. The numbers of total ACF in rats treated with 0.002% PA and 0.05% B-2 were significantly decreased compared with the AOM alone group (control). Cell proliferation in the colon, as shown by proliferating cells nuclear antigen (PCNA), was also reduced in those treatments. The single-stranded DNA (ssDNA) labeling index, a marker for apoptosis, was significantly increased in 0.002% PA and 0.05% B-2 groups compared with control. Moreover, the numbers of CD11b/c+ cells (macrophages) and NKR-P1A+ cells (NK cells) in the all groups were significantly increased compared with control. In an in vitro study using rat colon cancer cell line RCN-9, PA, especially 5-10mer of PA (PA5/10), strong growth inhibition was shown. PA5/10 caused the most remarkable apoptosis as cleared by FACS analysis. These cells showed significantly increased caspase-3 activity. The results would suggest that the PA, especially PA5/10, might strongly enhance caspase-3 activity and cause apoptosis in cancer cells. PA at fairly low doses in the long term might serve as an effective means for preventing colon carcinogenesis.

Farnesyl-O-acetylhydroquinone and geranyl-O-acetylhydroquinone suppress the proliferation of murine B16 melanoma cells, human prostate and colon adenocarcinoma cells, human lung carcinoma cells, and human leukemia cells

Farnesyl-O-acetylhydroquinone (IC(50)=2.5 microM/l) suppressed the proliferation of murine B16F10 melanoma cells with a potency much greater than those of farnesol (IC(50)=45 microM/l) and farnesyl anthranilate (IC(50)=46 microM/l), its alcohol, and ester counterparts with proven anti-tumor activities in vivo. Geranyl-O-acetylhydroquinone (IC(50)=5.1 microM/l) also had a much-improved activity compared to geraniol (IC(50)=160 microM/l) and geranyl anthranilate (IC(50)=30 microM/l). The suppression by farnesyl-O-acetylhydroquinone was concentration- and time-dependent and was accompanied by arrest of cell cycle at G1 and G2/M phases as shown by flow cytometry. Farnesyl-O-acetylhydroquinone and lovastatin had additive impact on B16 cell proliferation. Farnesyl-O-acetylhydroquinone also suppressed the proliferations of human cancer cells HL-60, DU145, PC-3, LNCaP, Caco-2, and A549. Our results suggested that farnesyl derivatives, suppressors of tumor 3-hydroxy-3-methylglutaryl coenzyme A reductase activities, have potential as chemopreventive or chemotherapeutic agents.

Chemomodulatory influence of Ferula asafoetida on mammary epithelial differentiation, hepatic drug metabolizing enzymes, antioxidant profiles and N-methyl-N-nitrosourea-induced mammary carcinogenesis in rats

The present study was conducted to ascertain the modulatory influences of Ferula asafoetida L. (asafoetida, flavoring agent) on the mammary epithelial tissue differentiation, hepatic drug metabolizing enzymes, antioxidant profiles and N-methyl-N-nitrosourea (MNU)-induced mammary carcinogenesis in Sprague-Dawley rats. Feeding with two doses of asafoetida (1.25 and 2.5% w/w in diet) showed a remarkable increase in the development and differentiation of ducts/ductules (p < 0.01-0.005), lobules (p < 0.005) and a decrease in terminal end buds (p < 0.05-0.005) as compared to both normal and MNU-treated control animals. To assess the biochemical parameters, effect of asafoetida on drug-metabolizing enzymes was evaluated in the liver of rats. Asafoetida treatment significantly reduced (p < 0.05) the levels of cytochrome P450 and b5. There was an enhancement in the activities of glutathione S-transferase (p < 0.05-0.005), DT-diaphorase (p < 0.05-0.01), superoxide dismutase (p < 0.01-0.005) and catalase (p < 0.05-0.005) and in the level of reduced glutathione (p < 0.05-0.005), followed by asafoetida treatment. Also, asafoetida significantly restored the level of antioxidant system, depleted by MNU-treatment. The strengthening of antioxidant system by the lower and higher doses of asafoetida in the presence and absence of MNU was further substantiated by a significant inhibition (p < 0.005) in lipid peroxidation as measured by thiobarbituric acid-reactive substances (TBARS) in the liver of rat. Further, in long-term animal studies, where MNU was used to induce mammary carcinogenesis, asafoetida treatment resulted in a significant reduction in the multiplicity (p < 0.001) and size of palpable mammary tumors (p < 0.005-0.001) and a delay in mean latency period of tumor appearance (p < 0.005). Together, these findings indicate the chemopreventive potential of asafoetida against MNU-induced mammary carcinogenesis. Thus, asafoetida needs further investigation with regard to identification and characterization of its active principle(s) and mechanism of action, for this compound to be developed as a potential chemopreventive agent for human cancers.

Folic acid mediated attenuation of loss of heterozygosity of DCC tumor suppressor gene in the colonic mucosa of patients with colorectal adenomas

Loss of heterozygosity (LOH) and/or inactivation of tumor suppressor genes are implicated in the initiation and progression of many malignancies, including colorectal cancer. Although accumulating evidence suggests a chemopreventive role for folate in colorectal cancer, regulatory mechanisms are poorly understood. The primary objective of the current investigation was to determine whether folic acid would prevent LOH of the three tumor suppressor genes, deleted in colorectal cancer (DCC), adenomatous polyposis coli (APC) and p53 in macroscopically normal appearing rectal mucosa of patients with adenomatous polyps. In addition, the effect of folic acid on rectal mucosal proliferation was determined. Twenty patients were randomized in a double-blind study to receive either folic acid 5mg once daily or identical placebo tablets for 1 year. Genomic DNA and total protein were extracted from the rectal mucosa at baseline and after 1 year of treatment and analyzed for LOH and protein levels of APC, DCC and p53 genes. In addition, paraffin-embedded mucosal specimens were analyzed for proliferating cell nuclear antigen (PCNA) immunoreactivity, as a measure of cellular proliferative activity. Folate supplementation prevented LOH of DCC gene in five out of five (100%) patients who demonstrated baseline heterozygosity, whereas two out of four (50%) placebo-treated patients with baseline heterozygosity demonstrated allelic loss. Mucosal protein levels of DCC were also reduced in 7 of 10 (70%) placebo-treated patients compared to only 2 of 10 (20%) of patients treated with folate. Levels increased, however, in eight and three patients in the folic acid and placebo groups, respectively (P<0.02). Folic acid caused no change in allelic status of either APC or p53 gene. Folate supplementation caused a small, but not statistically significant, 16% reduction in mucosal proliferation, whereas placebo treatment resulted in a 88% (P<0.05) increase in this parameter, when compared with the corresponding baseline values. Our results indicate that folic acid prevents an increase in proliferation and arrests LOH of DCC gene and also stabilizes its protein in normal appearing rectal mucosa of patients with colorectal adenomas. Taken together, our data suggest that one of the ways folate may exert its chemopreventive effect is by stabilizing certain tumor suppressor gene(s) and preventing further increases in proliferation.

Folate, colorectal carcinogenesis, and DNA methylation: lessons from animal studies

Folate, a water-soluble B vitamin and cofactor in one-carbon transfer, is an important nutritional factor that may modulate the development of colorectal cancer (CRC). Epidemiologic and clinical studies indicate that dietary folate intake and blood folate levels are inversely associated with CRC risk. Collectively, these studies suggest an approximately 40% reduction in the risk of CRC in individuals with the highest dietary folate intake compared with those with the lowest intake. Animal studies using chemical and genetically predisposed rodent models have provided considerable support for a causal relationship between folate depletion and colorectal carcinogenesis as well as a dose-dependent protective effect of folate supplementation. However, animal studies also have shown that the dose and timing of folate intervention are critical in providing safe and effective chemoprevention; exceptionally high supplemental folate levels and folate intervention after microscopic neoplastic foci are established in the colorectal mucosa promote, rather than suppress, colorectal carcinogenesis. These animal studies, in conjunction with clinical observations, suggest that folate possesses dual modulatory effects on carcinogenesis depending on the timing and dose of folate intervention. Folate deficiency has an inhibitory effect, whereas folate supplementation has a promoting effect on the progression of established neoplasms. In contrast, folate deficiency in normal epithelial tissues appears to predispose them to neoplastic transformation, and modest levels of folate supplementation suppress the development of tumors in normal tissues. Notwithstanding the limitations associated with animal models, these studies suggest that the optimal timing and dose of folate intervention must be established for safe and effective chemoprevention in humans. Folate is an important factor in DNA synthesis, stability, and integrity, the repair aberrations of which have been implicated in colorectal carcinogenesis. Folate may also modulate DNA methylation, which is an important epigenetic determinant in gene expression (an inverse relationship), in the maintenance of DNA integrity and stability, in chromosomal modifications, and in the development of mutations. A mechanistic understanding of how folate status modulates colorectal carcinogenesis further strengthens the case for a causal relationship and provides insight into a possible chemopreventive role of folate.

Dietary resveratrol does not affect intestinal tumorigenesis in Apc(Min/+) mice

To determine its effect on intestinal tumorigenesis and the protumorigenic COX pathway in Apc(Min/+) mice, resveratrol was administered as a powdered admixture in the diet at 0, 4, 20, or 90 mg/kg body weight for 7 wk. In two separate experiments, resveratrol did not affect intestinal tumor load. It was stable in the diet under experimental conditions, circulated in the plasma as the glucuronide-conjugated form and reached the tumors as evidenced by significant decreases in PGE2 levels. However, immunohistochemical staining of intestinal tumors revealed no changes in COX-2 expression. This study demonstrates that resveratrol consumed ad libitum in the diet, does not modify tumorigenesis in Apc(Min/+) mice.

Preclinical models for chemoprevention of colon cancer

Colon cancer is the second leading cause of cancer incidence and death in the USA in 2002. Specific genetic defects have been identified which cause hereditary colon cancers in humans. In addition, a number of intestinal luminal risk factors for colon cancer have been described. This information has been exploited to develop experimental cell and rodent models which recapitulate features of human colon cancer. In this chapter, we will discuss the strengths and limitations of these models to further our understanding of basic mechanisms of colon carcinogenesis and to develop strategies for colon cancer chemoprevention.

The synthetic retinoid adapalene inhibits proliferation and induces apoptosis in colorectal cancer cells in vitro

Chemotherapy of advanced stages of colorectal carcinoma is unsatisfactory. Retinoids inhibit cell growth and induce apoptosis in a variety of human malignancies. We compared the effect of the synthetic retinoid adapalene (ADA) and 9-cis-retinoic acid (CRA) on carcinoma cell lines in vitro. Colon carcinoma cell lines CC-531, HT-29 and LOVO as well as human foreskin fibroblasts were exposed to different concentrations of ADA and CRA for 3-72 hr. Proliferation was assessed by BrdU incorporation and apoptosis by FACS analysis. Breakdown of DeltaPsi(m) was determined by JC-1 staining and activity of caspases 3 and 8, by a colorimetric assay. Quantitative Western blots were performed to detect changes in bax, bcl-2 and caspase-3. Both retinoic derivatives suppressed DNA synthesis and induced apoptosis in all tested cell lines time- and dose-dependently. While the natural retinoid CRA showed moderate antiproliferative and proapoptotic effects only at the highest concentration (10(-4) M), the synthetic retinoic ADA was significantly more effective, showing remarkable effects even at 10(-5) M. ADA and CRA disrupt DeltaPsi(m) and induce caspase-3 activity in responsive tumor cells. Quantitative Western blots showed a shift of the bax:bcl-2 ratio toward proapoptotic bax in ADA-treated cells. Our results clearly indicate the superiority of ADA compared to CRA. Therefore, we suggest that ADA may be far more suitable as an adjunctive therapeutic agent for treatment of colon cancer in vivo.

Role of Folate in Colon Cancer Development and Progression

Folate, a water-soluble B vitamin and important cofactor in 1-carbon transfer, is an important nutritional factor that may modulate the development of colorectal cancer. Epidemiologic and clinical studies indicate that dietary folate intake and blood folate levels are inversely associated with colorectal cancer risk. Collectively, these studies suggest an approximately 40% reduction in the risk of colorectal cancer in individuals with the highest dietary folate intake compared with those with the lowest intake. Animal studies using chemical and genetically predisposed rodent models have provided considerable support for a causal relationship between folate depletion and colorectal carcinogenesis as well as a dose-dependent protective effect of folate supplementation. However, animal studies have also shown that the dose and timing of folate intervention are critical in providing safe and effective chemoprevention; exceptionally high supplemental folate levels and folate intervention after microscopic neoplastic foci are established in the colorectal mucosa promote rather than suppress colorectal carcinogenesis. These animal studies in conjunction with clinical observations suggest that folate possesses the dual modulatory effects on carcinogenesis depending on the timing and dose of folate intervention. Folate deficiency has an inhibitory effect whereas folate supplementation has a promoting effect on progression of established neoplasms. In contrast, folate deficiency in normal epithelial tissues appears to predispose them to neoplastic transformation, and modest levels of folate supplementation suppress the development of tumors in normal tissues. Notwithstanding the limitations associated with animal models, these animal studies suggest that the optimal timing and dose of folate intervention need to be established for safe and effective chemoprevention in humans.

Effects of dietary antioxidants and 2-amino-3-methylimidazo[4,5-f]- quinoline (IQ) on preneoplastic lesions and on oxidative damage, hormonal status, and detoxification capacity in the rat

The potential beneficial or adverse affect of prolonged dietary administration of moderate to high doses (1-100 mg/kg diet) of the antioxidants, lycopene, quercetin and resveratrol or a mixture of lycopene and quercetin was investigated in male F344 rats. Selected markers for toxicity and defense mechanisms were assayed in blood, liver and colon and the impact of the antioxidant administrations on putative preneoplastic changes in liver and colon was assessed. The dietary carcinogen, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) (200 mg/kg diet) served as a pro-oxidant, genotoxicity and general toxicity control. IQ increased the levels of protein and DNA oxidation products in plasma, the area of glutathione S-transferase-placental form positive (GST-P) foci in the liver as well as the number of colonic aberrant crypt foci (ACF). All antioxidants and the antioxidant combination significantly increased the level of lymphocytic DNA damage, to an extent comparable with the effect induced by IQ. In contrast to the control group where no GST-P foci were detected, GST-P foci were detected in animals exposed to quercetin, lycopene and the combination of the two. However, the increase in the volume of GST-P foci did not reach statistical significance. The present results indicate that moderate to high doses of common dietary antioxidants can damage lymphocyte DNA and induce low levels of preneoplastic liver lesions in experimental animals. Long-term exposure to moderate to high doses of antioxidants may thus via pro-oxidative mechanisms and non-oxidative mechanisms modulate carcinogenesis.

Chemopreventive effect of farnesol and lanosterol on colon carcinogenesis

Cholesterol metabolites play a several critical roles in regulating cell growth and function. 3-Hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase, the rate-limiting enzyme for this pathway, is down regulated by feedback mechanisms due to increased levels of cholesterol and its premetabolites. Several HMG-CoA metabolites, such as farnesyl pyrophosphate and geranyl pyrophosphate are implicated in oncogene activation and tumorigenesis. Recent studies suggest that inhibition of HMG-CoA reductase by specific inhibitors or by naturally-occurring phytochemicals, such as farnesol or squalene can modulate tumor cell growth. Thus, in this study, we have assessed the chemopreventive efficacy of farnesol and lanosterol on azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) in rats. In addition, we measured the effect of farnesol and lanosterol on serum high denisity lipoprotein (HDL) and cholesterol levels in the rats. Seven-week-old male F344 rats were fed the control diet (modified AIN-76A) or experimental diets containing I or 2% lanosterol or 1.5% farnesol. One week later, all animals except those in vehicle (normal saline)-treatment groups were s.c. injected with AOM (15 mg/kg body weight, once weekly for 2 weeks). At 16 weeks of age, all rats were killed, colons were evaluated for ACF and serum was assayed for HDL and cholesterol levels. Administration of dietary farnesol significantly inhibited ACF formation by about 34% (P < 0.001) and reduced crypt multiplicity by about 44% (P < 0.0001). Also, administration of lanosterol at dose levels of I or 2 % in the diet significantly suppressed AOM-induced colonic ACF as well as multicrypt foci formation. (P < 0.01-0.001). Further, farnesol at 1.5% and lanosterol at 1% did not show any significant effect on serum HDL nor on total cholesterol levels. However, lanosterol at 2% significantly increased serum HDL (P < 0.05) and cholesterol (P < 0.01) levels. That farnesol and lanosterol significantly suppress colonic ACF formation and crypt multiplicity strengthens the hypothesis that these agents possess chemopreventive activity against colon carcinogenesis.

Deguelin suppresses the formation of carcinogen-induced aberrant crypt foci in the colon of CF-1 mice

Deguelin [(7aS,BaS)-13,13a-dihydro-9,10-dimethoxy-3,3-dimethyl-3H-Bis[1]benzopyrano[3,4-b:6',5'-e]pyran-7(7aH)-one], a naturally occurring rotenone, has shown chemopreventive efficacy in several in vivo and in vitro models. In this report, the effectiveness of deguelin at inhibiting the development of AOM-induced colonic ACF was investigated in CF-1 mice. Loss of hex activity was assessed as a second biomarker. In an initial experiment, animals were given s.c. injections of AOM (10 mg/kg body weight) once a week for 2 weeks to induce ACF. Deguelin and vehicle (corn oil) were administered i.g. 7 days a week. Treatment was initiated 2 weeks prior to the first dose of carcinogen and continued for the duration of the study. The mean number of ACF for the control group was 29.0 +/- 4.3, whereas the mean numbers of ACF in the deguelin groups were 24.8 +/- 2.7, 7.2 +/- 1.5 and 4.6 +/- 1.4 at doses of 2.5, 5.0 and 10.0 mg/kg body weight, respectively. In a similar manner, treatment with deguelin significantly (p < 0.001) suppressed the appearance of hex(-) crypts in a dose-dependent manner. In a second study, the ability of deguelin to block the initiation and promotion stages of colon carcinogenesis was investigated. Greatest inhibition was observed when deguelin was administered during the promotional stage (73.3%, p < 0.001). These results demonstrate that deguelin is an efficacious chemopreventive agent against colon carcinogenesis.

Intake of beer inhibits azoxymethane-induced colonic carcinogenesis in male Fischer 344 rats

Modulatory effects of beer consumption on azoxymethane (AOM)-induced rat colonic carcinogenesis in male Fischer 344 rats were investigated. Single cell gel electrophoresis assay indicated that DNA damage of colonocytes, induced by a single AOM injection (15 mg/kg body weight), was significantly reduced in rats fed beer or malt extract for 2 weeks. Examination of aberrant crypt foci (ACF) formation in colonic mucosa, induced by AOM (15 mg/kg body weight; twice weekly), revealed that feeding of beer during the whole experimental period of 5 weeks significantly reduced the number of ACF by 35%. In the post-initiation protocol, a reduction in ACF formation by 26% was not significant. The efficacy in inhibition of ACF formation varied with the brand of beer. ACF formation was significantly reduced in rats treated with freeze-dried beer (FD Beer), but not with ethanol, suggesting that nonvolatile components of beer are responsible for the reduction. Significant suppression of ACF formation was observed in groups treated with hot water extract of malt, especially with extracts of colored malts, although no reduction was observed by feeding with hops extract. A long-term experiment of 42 weeks indicated that intake of beer decreased tumor incidence by 22% and decreased the number of neoplastic lesions, including adenocarcinomas and adenomas, by 44%. These results suggest that components of beer have chemopreventive effects on colonic carcinogenesis induced by AOM and that intake of beer may contribute to a reduction in the risk of cancer susceptibility.

The combination of 1alpha,25(OH2)-vitamin D3, calcium and acetylsalicylic acid affects azoxymethane-induced aberrant crypt foci and colorectal tumours in rats

Effects of 1alpha,25(OH)(2)-vitamin D(3) and acetylsalicylic acid at various dietary levels of calcium (CaCO(3)) on development of aberrant crypt foci (ACF) and tumours in colon were examined in groups of 16 male F344 rats initiated with azoxymethane and observed for 16 weeks. Calcium was the most potent modulator of ACF development. The total number of ACF increased with low calcium and decreased with high calcium. The number of large ACF decreased with any addition of calcium, acetylsalicylic acid and 1alpha,25(OH)(2)-vitamin D(3). High levels of calcium alone or in combination with 1alpha,25(OH)(2)-vitamin D(3) increased the incidence of tumour-bearing animals. 1alpha,25(OH)(2)-vitamin D(3) and acetylsalicylic acid at 5,000 ppm calcium increased the incidence as well.

A review of animal model studies of tomato carotenoids, lycopene, and cancer chemoprevention

There are relatively few reports on the cancer chemopreventive effects of lycopene or tomato carotenoids in animal models. The majority, but not all, of these studies indicate a protective effect. Inhibitory effects were reported in two studies using aberrant crypt foci, an intermediate lesion leading to colon cancer, as an end point and in two mammary tumor studies, one using the dimethylbenz(a)anthracene model, and the other the spontaneous mouse model. Inhibitory effects were also reported in mouse lung and rat hepatocarcinoma and bladder cancer models. However, a report from the author's laboratory found no effect in the N-nitrosomethylurea-induced mammary tumor model when crystalline lycopene or a lycopene-rich tomato carotenoid oleoresin was administered in the diet. Unfortunately, because of differences in routes of administration (gavage, intraperitoneal injection, intra-rectal instillation, drinking water, and diet supplementation), species and strain differences, form of lycopene (pure crystalline, beadlet, mixed carotenoid suspension), varying diets (grain-based, casein based) and dose ranges (0.5-500 ppm), no two studies are comparable. It is clear that the majority of ingested lycopene is excreted in the feces and that 1000-fold more lycopene is absorbed and stored in the liver than accumulates in other target organs. Nonetheless, physiologically significant (nanogram) levels of lycopene are assimilated by key organs such as breast, prostate, lung, and colon, and there is a rough dose-response relationship between lycopene intake and blood levels. Pure lycopene was absorbed less efficiently than the lycopene-rich tomato carotenoid oleoresin and blood levels of lycopene in rats fed a grain-based diet were consistently lower than those in rats fed lycopene in a casein-based diet. The latter suggests that the matrix in which lycopene is incorporated is an important determinant of lycopene uptake. A number of issues remain to be resolved before any definitive conclusions can be drawn concerning the anticancer effects of lycopene. These include the following: the optimal dose and form of lycopene, interactions among lycopene and other carotenoids and fat soluble vitamins such as vitamin E and D, the role of dietary fat in regulating lycopene uptake and disposition, organ and tissue specificity, and the problem of extrapolation from rodent models to human populations.

A critical review of the toxicological effects of carrageenan and processed eucheuma seaweed on the gastrointestinal tract

Carrageenan is a high-molecular-weight, strongly anionic polymer derived from several species of red seaweed that is used for the textural stabilization of foods. Processed Eucheuma Seaweed (PES) is a form of carrageenan with a higher cellulose content. Food-grade carrageenan has a weight average molecular weight greater than 100,000 Da, with a low percentage of smaller fragments. Carrageenan is not degraded to any extent in the gastrointestinal tract and is not absorbed from it in species examined, such as rodents, dogs, and non-human primates. Systemically administered carrageenan has been reported to have a variety of effects, particularly on the immune system, but these are not pertinent to orally administered carrageenan. The substance poligeenan (formerly referred to as degraded carrageenan) is not a food additive. It exhibits toxicological properties at high doses that do not occur with the food additive carrageenan. In-long term bioassays, carrageenan has not been found to be carcinogenic, and there is no credible evidence supporting a carcinogenic effect or a tumor-promoting effect on the colon in rodents. Also, like many dietary fibers, there is significant cecal enlargement in rodents when it is administered at high doses, but this does not appear to be associated with any toxicological consequences to the rodent. Many toxicological studies on carrageenan have involved administration at doses in excess of today's standards for dietary feeding levels in bioassays, and they are orders of magnitude in excess of those to which humans are exposed. Previous reviews of carrageenan and PES by the Joint Food and Agriculture Organization/World Health Organization Expert Committee on Food Additives (JECFA) have recommended a group allowable daily intake (ADI) of "not specified". The lack of carcinogenic, genotoxic, or tumor-promoting activity with carrageenan strongly supports continuing such an ADI, and JECFA, during its most recent review in 2001, continued this recommendation. The various toxicological studies related to orally administered food-grade carrageenan are summarized along with a brief discussion of critical factors in intestinal carcinogenesis.