The inhibitory effect of flaxseed on the growth and metastasis of estrogen receptor negative human breast cancer xenograftsis attributed to both its lignan and oil components

Our previous studies have shown that dietary flaxseed (FS) can reduce the growth and metastasis of human estrogen receptor negative (ER-) breast cancer in nude mice. The aims of our study were to determine (i) whether the tumor inhibitory effect of FS was due to its oil (FO), lignan secoisolariciresinol diglycoside (SDG), or both components, and (ii) whether the effect on tumor growth was related to increased lipid peroxidation. Athymic nude mice were orthotopically injected with ER- breast cancer cells (MDA-MB-435) and 8 weeks later were fed either the basal diet (BD) or BD supplemented with 10% FS, SDG, FO, or combined SDG and FO (SDG + FO) for 6 weeks. The SDG and FO levels were equivalent to the amounts in the 10% FS. Compared to the BD group, the tumor growth rate was significantly lower (p < 0.05) in the FS, FO, and SDG + FO groups, in concordance with decreased cell proliferation and increased apoptosis; however, these did not significantly relate to the lipid peroxidation, indexed as malonaldehyde (MDA), in the primary tumors. Lung metastasis incidence was reduced (16-70%) by all treatments, significantly in the FS and SDG + FO groups. The distant lymph node metastasis was significantly decreased (52%) only in the FO group. Although the total metastasis incidence was lowered (42%) significantly only in the SDG + FO group, all treatment groups did not differ significantly. In conclusion, FS reduced the growth and metastasis of established ER- human breast cancer in part due to its lignan and FO components, and not to lipid peroxidation.     

The effect of flaxseed supplementation on early risk markers for mammary carcinogenesis.

Since lignans have been suggested to have some cancer-protective effects, flaxseed, the most abundant source of lignan precursors, was tested for its effect on early markers of risk for mammary carcinogenesis. Supplementation of a high-fat diet with flaxseed flour (FF) or defatted flaxseed meal (FM) (5% or 10%) reduced the epithelial cell proliferation by 38.8-55.4% and nuclear aberrations by 58.8-65.9% in female rat mammary gland, with optimum effects seen with the 5% FF. These protective effects were accompanied by increases in urinary lignan excretion indicating that they may be related to the ability of flaxseed to provide lignan precursors.     

The influence of flaxseed and lignans on colon carcinogenesis and {beta}-glucuronidase activity

Flaxseed, the richest source of mammalian lignan precursors,such as secoisolariciresinol diglycoside (SD), has been shownover the short term to decrease some early markers of coloncancer risk. This study determined whether over the long termflaxseed still experts a colon cancer protective effect, whetherits effect may, in part, be due to its high content of SD andwhether any change in ß-glucuronidase activity playsa role in the protective effect. Six groups of male Sprague-Dawleyrats were fed for 100 days either a basal high fat (20%) diet(BD), BD supplemented with 2.5 or 5% flaxseed or 2.5 or 5% defattedfaxseed (equivalent to the respective flaxseed diets) or BDwith a daily gavageof 1.5 mg SD. All rats were injected witha single dose of azoxymethane (15 mg/kg body wt) 1 week priorto commencing the dietary treatments. Urinary lignan excretion,which is an indicator of mammalian lignan production, was significantlyincreased in the flaxseed and defatted flaxseed groups. Thetotal activity of cecal ß-glucuronidase was significantlyincreased in a dose-dependent manner by the flaxseed and defattedflaxseed diet groups. Compared with the control the number ofaberrant crypts per focus was significantly reduced in the distalcolon of the treated rats. Four microadenomas and two polypswere observed in the control group, but not in the treated groups.The total activity of ß-glucuronidase was positivelycorrelated with total urinary lignan excretion and negativelywith the total number of aberrant crypts and the total numberof aberrant crypt foci in the distal colon. There were no significantdifferences between the flaxseed and the corresponding defattedflaxseed groups. It is concluded that flaxseed has a colon cancerprotective effect, that it is due, in part, to SD and that theprotective effect of flaxseed is associated with increased ß-glucuronidaseactivity.     

Exposure to flaxseed or its lignan component during different developmental stages influences rat mammary gland structures.

Reduction of the highly proliferative terminal end bud (TEB) structures in the developing mammary gland by differentiation to alveolar buds (ABs) and lobules has been suggested to be protective against mammary cancer. Flaxseed is high in alpha-linolenic acid (ALA) and secoisolariciresinol diglycoside (SDG). SDG is the precursor of mammalian lignans, which can affect mammary gland structures. Thus, the objective of this study was to determine the effect of lifetime, gestation and lactation or after-weaning exposure to 5 or 10% flaxseed or SDG and flaxseed oil components on the mammary gland structures of virgin female rat offspring at post-natal day 50. Lifetime or gestation and lactation exposure to flaxseed altered mammary gland structure development, whereas exposure to flaxseed after weaning had no effect. Lifetime or gestation and lactation exposure to 5% flaxseed caused endocrine changes, as suggested by delayed puberty onset and reduced number of estrous cycles. These changes reduced exposure to endogenous estrogens, leading to atrophy of mammary TEB structures. SDG, but not flaxseed oil, at the level found in 5% flaxseed produced similar effects as 5% flaxseed. This suggested that the lignans were the component in flaxseed responsible for the observed effects. Lifetime or gestation and lactation exposure to 10% flaxseed also caused endocrine changes, as suggested by early puberty onset and lengthened cycles due to prolonged estrus. This increased exposure to endogenous estrogens and stimulated mammary gland differentiation, as indicated by fewer TEBs and more ABs. Thus, lifetime or gestation and lactation exposure to 5 or 10% flaxseed induced structural changes in the mammary gland that may potentially reduce mammary cancer risk.     

The effect of endocrine therapy with medroxyprogesterone acetate, 4-hydroxyandrostenedione or tamoxifen on plasma concentrations of insulin-like growth factor (IGF)-I, IGF-II and IGFBP-1 in women with advanced breast cancer.

Tamoxifen treatment of women with advanced breast cancer has previously been reported to reduce plasma insulin-like growth factor-type I (IGF-I) concentrations. In this study we have examined the effect of treatment with Tamoxifen, medroxyprogesterone acetate (MPA) or 4-hydroxyandrostenedione (4-OHA) on plasma IGF-I and IGF-II concentrations. As IGF-binding proteins (IGFBPs) can modulate the biological effects of IGF-I, plasma IGFBP-I levels were also measured. Treatment with Tamoxifen for 2 weeks resulted in a small, but significant, decrease in IGF-I levels, but increase in the plasma concentration of IGFBP-I. In contrast, treatment with MPA increased levels of IGF-I, but significantly reduced plasma IGFBP-I concentrations. Treatment with 4-OHA had no significant overall effect on plasma IGF-I or IGFBP-I levels, although changes were detected for some subjects. Plasma IGF-II concentrations were not altered by treatment with Tamoxifen, MPA or 4-OHA. It is concluded that although treatment with Tamoxifen or MPA produced significant changes in plasma IGF-I concentrations, any physiological effects of such changes are likely to be modulated by the corresponding alterations in plasma IGFBP-I concentrations.     

Lignan transformation by gut bacteria lowers tumor burden in a gnotobiotic rat model of breast cancer

High dietary lignan exposure is implicated in a reduced breast cancer risk in women. The bacterial transformation of plant lignans to enterolignans is thought to be essential for this effect. To provide evidence for this assumption, gnotobiotic rats were colonized with the lignan-converting bacteria Clostridium saccharogumia, Eggerthella lenta, Blautia producta and Lactonifactor longoviformis (LCC rats). Germ-free rats were used as the control. All animals were fed a lignan-rich flaxseed diet and breast cancer was induced with 7,12-dimethylbenz(a)anthracene. The lignan secoisolariciresinol diglucoside was converted into the enterolignans enterodiol and enterolactone in the LCC but not in the germ-free rats. This transformation did not influence cancer incidence at the end of the 13 weeks experimental period but significantly decreased tumor numbers per tumor-bearing rat, tumor size, tumor cell proliferation and increased tumor cell apoptosis in LCC rats. No differences between LCC and control rats were observed in the expression of the genes encoding the estrogen receptors (ERs) α, ERβ and G-coupled protein 30. The same was true for IGF-1 and EGFR involved in tumor growth. The activity of selected enzymes involved in the degradation of oxidants in plasma and liver was significantly increased in the LCC rats. However, plasma and liver concentrations of reduced glutathione and malondialdehyde, considered as oxidative stress markers, did not differ between the groups. In conclusion, our results show that the bacterial conversion of plant lignans to enterolignans beneficially influences their anticancer effects.     

Dietary flaxseed alters tumor biological markers in postmenopausal breast cancer.

PURPOSE: Flaxseed, the richest source of mammalian lignan precursors, has previously been shown to reduce the growth of tumors in rats. This study examined, in a randomized double-blind placebo-controlled clinical trial, the effects of dietary flaxseed on tumor biological markers and urinary lignan excretion in postmenopausal patients with newly diagnosed breast cancer. EXPERIMENTAL DESIGN: Patients were randomized to daily intake of either a 25 g flaxseed-containing muffin (n = 19) or a control (placebo) muffin (n = 13). At the time of diagnosis and again at definitive surgery, tumor tissue was analyzed for the rate of tumor cell proliferation (Ki-67 labeling index, primary end point), apoptosis, c-erbB2 expression, and estrogen and progesterone receptor levels. Twenty-four-hour urine samples were analyzed for lignans, and 3-day diet records were evaluated for macronutrient and caloric intake. Mean treatment times were 39 and 32 days in the placebo and flaxseed groups, respectively. RESULTS: Reductions in Ki-67 labeling index (34.2%; P = 0.001) and in c-erbB2 expression (71.0%; P = 0.003) and an increase in apoptosis (30.7%; P = 0.007) were observed in the flaxseed, but not in the placebo group. No significant differences in caloric and macronutrient intake were seen between groups and between pre- and posttreatment periods. A significant increase in mean urinary lignan excretion was observed in the flaxseed group (1,300%; P < 0.01) compared with placebo controls. The total intake of flaxseed was correlated with changes in c-erbB2 score (r = -0.373; P = 0.036) and apoptotic index (r = 0.495; P < 0.004). CONCLUSION: Dietary flaxseed has the potential to reduce tumor growth in patients with breast cancer.     

Flaxseed and its components reduce metastasis after surgical excision of solid human breast tumor in nude mice

This study determined the effect of 10% flaxseed (FS) and its components, secoisolariciresinol diglycoside (SDG) and flaxseed oil (FO) alone or in combination (SDG+FO), on the metastasis and recurrence of human breast tumor after excision in nude mice. Mice were injected orthotopically with human breast cancer cells (MDA-MB-435) and fed basal diet (BD). When the tumors reached an average size of 110 mm(2) (0.9 g), surgical excisions were performed, and the mice were assigned to one of five diet groups for 7 weeks. The total incidence of metastasis was significantly lower in the FS, SDG, and SDG+FO groups. Reduced lung and lymph node metastases were observed in the FS and SDG+FO groups. In the FS and FO groups, a greater reduction in lung and total metastases was found when excised tumors were 0.9 g. There was no significant difference in tumor recurrence among groups. In conclusion, FS and its components inhibited tumor metastasis but not tumor recurrence after surgical excision of the primary tumor.     

Flaxseed influences urinary lignan excretion in a dose-dependent manner in postmenopausal women.

Dietary estrogens, such as lignans, are similar in structure to endogenous sex steroid hormones and may act in vivo to alter hormone metabolism and subsequent cancer risk. The objective of this study was to examine the effect of dietary intake of a lignan-rich plant food (flaxseed) on urinary lignan excretion in postmenopausal women. This randomized, cross-over trial consisted of three 7-week feeding periods during which 31 healthy postmenopausal women, ages 52-82 years, consumed their habitual diets plus 0, 5, or 10 grams of ground flaxseed per day. Urine samples collected for 2 consecutive days during the last week of each feeding period were analyzed for lignan content (enterodiol, enterolactone, and matairesinol) by isotope dilution gas chromatography/mass spectrometry. Compared with the 0-gram flaxseed diet, consumption of 5 or 10 grams of flaxseed significantly increased excretion of enterodiol by 1,009 and 2,867 nmol/day, respectively; significantly increased excretion of enterolactone by 21,242 and 52,826 nmol/day, respectively; and significantly increased excretion of total lignans (enterodiol + enterolactone + matairesinol) by 24,333 and 60,640 nmol/day, respectively. Excretion of matairesinol was not significantly altered by flaxseed consumption. Consumption of flax, a significant source of dietary estrogens, in addition to their habitual diets increased excretion of enterodiol and enterolactone, but not matairesinol, in a dose-dependent manner in this group of postmenopausal women. Urinary excretion of lignan metabolites is a dose-dependent biomarker of flaxseed intake within the context of a habitual diet.     

Prospective study of IGF-I,IGF-binding proteins,and breast cancer risk,in northern and southern Sweden

Objective: To examine the possible relationships of breast cancer risk to prediagnostic plasma levels of insulin; insulin-like growth factor-I (IGF-I); and IGF-binding proteins -1, -2, and -3. Methods: Within two prospective cohorts in Umeå and Malmö we measured plasma concentrations of insulin, IGF-I, and IGFBPs for a total of 513 incident breast cancer cases and 987 matched controls. Results: Globally, risk was unassociated with levels of IGF-I, IGFBP-3, or IGF-I adjusted for IGFBP-3. When breaking down the analysis by subgroups of age at blood donation, an increase in risk was observed for increasing levels of IGF-I in women aged 55 or older, in the Umeå cohort only (odds ratios of 1.00, 1.73, 1.76, 1.90; p _trend = 0.05). This effect weakened, however, when the analysis was restricted to subjects who did not use exogenous hormones for the treatment of menopausal symptoms. Levels of IGF-I and IGFBP-3 were not related to risk in younger women, recruited before age 50, contrary to observations from previous studies. In a subcohort where blood samples had been collected after at least four hours of fasting, breast cancer risk showed no clear associations with levels of insulin, IGFBP-1, or IGFBP-2. Conclusions: Our results do not confirm earlier findings of an association of plasma IGF-I levels with breast cancer risk especially in young women, but suggest a possible association with postmenopausal breast cancer risk, possibly among ERT/HRT users only. Our results do not support the hypothesis that elevated plasma insulin levels, and reduced levels of IGFBP-1 and IGFBP-2, are associated with increased breast cancer risk.     

Plasma insulin-like growth factor-I and serum IGF-binding protein 3 can be associated with the progression of breast cancer, and predict the risk of recurrence and the probability of survival in African-American and Hispanic women

In vitro studies have shown that insulin-like growth factor (IGF) is a mitogen for breast cancer cells. However, the associations of plasma IGF-I with tumor histopathology in high-risk groups need further investigation. We hypothesize that plasma IGF-I and serum IGFBP3 concentrations in breast cancer patients may provide useful information on the progression of their disease, and determine the probability of recurrence and survival. We have carried out a retrospective study on 130 minority breast cancer patients. Plasma IGF-I and serum IGFBP3 were correlated with tumor histopathology, menopausal status, treatment modality, recurrence rates, and probability of survival. Plasma IGF-I and serum IGFBP3 were measured by radioimmunoassay. Our studies show that breast cancer patients have elevated plasma IGF-I and serum IGFBP3 levels. In addition we observed the following: IGF-I did not correlate with age and nodal stage. IGF-I and IGFBP3 increased with tumor size (T4). IGF-I did not correlate with estrogen receptor status, but did increase in progesterone-receptor-positive patients. IGF-I levels were higher in premenopausal patients and in women with cancer recurrence. Tamoxifen reduced IGF-I levels significantly and reduced the risk of recurrence. The survival probability was greater in patients with plasma IGF-I levels <120 ng/ml. In conclusion, lowering of plasma IGF-I may offer the following benefits: (a) reduce the risk of developing breast cancer in high-risk groups; (b) slow the progression of breast cancer in patients at early stages of cancer; (c) lower the risk of recurrence, and (d) increase the probability of survival. Copyright Copyright 1999 S. Karger AG, Basel     

Insulin-like Growth Factor (IGF)-I, IGF-binding Protein-3 and Colorectal Adenomas in Japanese Men

Several epidemiological studies have found that high levels of plasma insulin-like growth factor (IGF)-I and low levels of IGF-binding protein (IGFBP)-3 are related to an increased risk of colorectal cancer or late-stage adenomas. We examined the relation of body mass index, fasting and 2-h postload plasma glucose levels and plasma concentrations of IGF-I and IGFBP-3 to colorectal adenomas in middle-aged Japanese men. The study subjects comprised 157 cases of histologically diagnosed colorectal adenomas and 311 controls with normal colonoscopy or non-polyp benign lesions in a consecutive series of 803 men receiving a preretirement health examination at two hospitals of the Self Defense Forces (SDF). After adjustment for rank in the SDF, hospital, smoking and IGFBP-3, a statistically nonsignificant modest increase in the prevalence odds of colorectal adenomas was observed for the highest versus the lowest quartile level of IGF-I. The increase was slightly greater with further adjustment for 2-h glucose concentrations (adjusted odds ratio 1.8, 95% confidence interval 1.0–4.5, trend P =0.06). Men with high levels of IGFBP-3 showed only a minimal decrease in risk after adjustment for IGF-I. The association with IGF-I was less evident for advanced adenomas (≥5 mm in size or tubulovillous/villous). Fasting and 2-h glucose and body mass index were more strongly positively associated with colorectal adenomas than IGF-I, especially with advanced adenomas, independently of IGF-I and IGFBP-3. The findings suggest that plasma IGF-I and IGFBP-3 may be involved in colorectal tumorigenesis regardless of the stage in growth of adenoma, but not as a mediator for the effects of being overweight or of hyperglycemia.     

Insulin-like growth factor (IGF)-I, IGF-binding protein-3 and colorectal adenomas in Japanese men.

Several epidemiological studies have found that high levels of plasma insulin-like growth factor (IGF)-I and low levels of IGF-binding protein (IGFBP)-3 are related to an increased risk of colorectal cancer or late-stage adenomas. We examined the relation of body mass index, fasting and 2-h postload plasma glucose levels and plasma concentrations of IGF-I and IGFBP-3 to colorectal adenomas in middle-aged Japanese men. The study subjects comprised 157 cases of histologically diagnosed colorectal adenomas and 311 controls with normal colonoscopy or non-polyp benign lesions in a consecutive series of 803 men receiving a preretirement health examination at two hospitals of the Self Defense Forces (SDF). After adjustment for rank in the SDF, hospital, smoking and IGFBP-3, a statistically nonsignificant modest increase in the prevalence odds of colorectal adenomas was observed for the highest versus the lowest quartile level of IGF-I. The increase was slightly greater with further adjustment for 2-h glucose concentrations (adjusted odds ratio 1.8, 95% confidence interval 1.0-4.5, trend P=0.06). Men with high levels of IGFBP-3 showed only a minimal decrease in risk after adjustment for IGF-I. The association with IGF-I was less evident for advanced adenomas (>5 mm in size or tubulovillous/villous). Fasting and 2-h glucose and body mass index were more strongly positively associated with colorectal adenomas than IGF-I, especially with advanced adenomas, independently of IGF-I and IGFBP-3. The findings suggest that plasma IGF-I and IGFBP-3 may be involved in colorectal tumorigenesis regardless of the stage in growth of adenoma, but not as a mediator for the effects of being overweight or of hyperglycemia.     

Flaxseed supplementation and early markers of colon carcinogenesis.

Since flaxseed ingestion produces potentially anticarcinogenic lignans in the colon, this study determined whether flaxseed decreases the risk for colon carcinogenesis. Following a single injection of azoxymethane (15 mg/kg body wt.), five groups of male Sprague-Dawley rats were fed a high-fat (20% corn oil) basal diet with or without supplementation with 5% or 10% flaxseed meal (FM) or flaxseed flour (FF) for four weeks. Upon sacrifice, colons were examined for aberrant morphology and cell proliferation. In the descending colon of supplemented groups, the total number of aberrant crypts and foci were significantly reduced by 41-53% and 48-57%, respectively. The labeling index (LI) was also 10-22% lower in these groups, except for the 5% FM group. While these effects are not linearly related to the level of flaxseed fed, it suggests that flaxseed feeding may reduce the risk for colon carcinogenesis.     

Dietary Determinants of Circulating Insulin-like Growth Factor (IGF)-I and IGF Binding Proteins 1, -2 and -3 in Women in the Netherlands

OBJECTIVE: Epidemiological studies suggest that individuals with elevated plasma concentrations of insulin-like growth factor (IGF-I) are at increased risk of developing cancer. We assessed whether dietary intake of total energy, protein, alcohol, phytoestrogens and related foods, and tomatoes and lycopene was associated with plasma levels of IGF-I and IGF binding proteins (IGFBPs) in Dutch women. METHODS: A cross-sectional study was conducted in 224 premenopausal and 162 postmenopausal women, aged 49-69, participating in the Prospect-EPIC study in the Netherlands. Diet was assessed using a food frequency questionnaire. RESULTS: In postmenopausal women, higher alcohol intake was associated with lower plasma IGFBP-1 concentrations (alcohol 1.4 to 20 g/day: 20% decrease in IGFBP-1; p = 0.04), and higher intake of plant lignans was associated with higher IGFBP-1 concentrations (plant lignans 0 to 1 mg/day: 59% increase in IGFBP-1; p =0.02). Higher soy intake was associated with higher plasma IGFBP-2 concentrations in premenopausal women (soy 0 to 2.5 g/day: 3% increase in IGFBP-2; p = 0.04). No independent associations of dietary factors with IGF-I or IGFBP-3 concentrations were observed. However, in premenopausal women alcohol intake was inversely associated with IGF-I and positively associated with IGFBP-3 after mutual adjustment. CONCLUSIONS: In this study population, with limited variation in dietary intake, total energy, protein, phytoestrogens and lycopene were not associated with IGF-I and IGFBP-3. Alcohol was inversely, and some measures of phytoestrogen intake were positively associated with plasma IGFBP-1 or -2 concentrations. The roles of IGFBP-1 and -2 in relation to IGF-I bioactivity and cancer deserve further investigation.     

Effect of tamoxifen on plasma insulin-like growth factor I in patients with breast cancer

Human breast cancer cells secrete and have membrane receptors for insulin-like growth factor I (IGF-I), a growth hormone-dependent peptide that stimulates cell replication. However, little is known about plasma concentrations of IGF-I in breast cancer patients. Plasma IGF-I levels are decreased in malnutrition, decline with advancing age, and are influenced by estrogen. We evaluated the effect of the antiestrogen agent tamoxifen on plasma IGF-I in 32 ambulatory breast cancer patients. Treatment with tamoxifen was associated with lower concentrations of plasma IGF-I (0.48 +/- 0.3 unit/ml in treated versus 1.03 +/- 0.6 units/ml in nontreated patients, P less than 0.01). However, patients treated with tamoxifen did not differ from nontreated patients in age, menopause, duration since diagnosis, metastatic disease, recent weight loss, or measures of nutritional status. We conclude that tamoxifen therapy results in a reduction of plasma IGF-I concentration. We speculate that the antitumor action of tamoxifen in breast cancer is due in part to suppression of IGF-I.     

Interrelationships between dietary restriction, the IGF-I axis, and expression of vascular endothelial growth factor by prostate adenocarcinoma in rats

Human studies suggest that excessive energy intake and obesity may influence prostate cancer progression. Rodent experiments demonstrate that diet restriction attenuates tumor growth in parallel with reduced vascular density. The present study examines changes in the insulin-like growth factor I (IGF-I) axis caused by dietary restriction and their association with the expression of vascular endothelial growth factor (VEGF) in prostate cancer. Weanling male Copenhagen rats were randomized into control or 40% dietary restricted groups (n = 5). After 8 wk, rats were implanted with rat AT6.3 prostate adenocarcinoma cells. Two weeks later, the animals were sacrificed and serum, normal prostate, liver, and prostate tumor samples were collected for analyses. Dietary restriction reduced serum concentrations of IGF-I by 35% (P < 0.05) and increased IGF-binding protein-3 (IGFBP3) by sevenfold (P < 0.0001). Lower circulating IGF-I concentrations were correlated with reduced IGF-I mRNA expression in the liver, the primary source of circulating IGF-I. Dietary restriction also lowered mRNA expression of IGF-I (45%, P = 0.0242) and its receptor IGFIR (40%, P = 0.0083) in prostate tumors. Similarly, reduced VEGF mRNA (30%, P = 0.0176) and secreted VEGF protein (33%, P = 0.0003) were observed in prostate cancer of restricted rats. An in vitro study employing AT6.3 prostate cancer cells demonstrated dose- and time-dependent stimulation of VEGF expression by IGF-I. These results suggest that dietary restriction reduces endocrine and prostate tumor autocrine/paracrine IGF-I expression, which contributes to reduced VEGF expression and signaling, to inhibit tumor angiogenesis associated with prostate tumorigenesis.     

Enhanced sensitivity of human oral carcinomas to induction of apoptosis by selenium compounds: involvement of mitogen-activated protein kinase and Fas pathways

Prospective studies and recent intervention trials suggest that the risk of some cancers, including respiratory tract cancers, may be inversely related to selenium (SE) intake, and this is supported by strong experimental evidence with chemical-induced animal cancer models. How this cancer-protective effect is mediated is unclear, but interference with the balance of growth/apoptosis during tumor outgrowth is one plausible hypothesis. In general, there is a correlation between the effectiveness of SE compounds as chemopreventive agents in vivo and their ability to inhibit cell growth and induce apoptosis in vitro. This study has investigated the signal transduction pathways affected by SE compounds in biopsies of normal human oral mucosa cells and human oral squamous carcinoma cells (SCCs), using a primary culture system. Two SE compounds were tested: selenodiglutathione (SDG), the primary metabolite of selenite and the most commonly used cancer-protective SE compound in animal models, and the synthetic SE compound, 1,4-phenylenebis(methylene)selenocyanate (p-XSC), one of the most potent chemopreventive pharmacological SE compounds. Three novel findings are reported: (a) SCCs were found to be significantly more sensitive to induction of apo ptosis by SDG than normal human oral mucosa cells, though the differences were marginal with p-XSC; (b) both SE compounds induced the expression of Fas ligand (Fas-L) in oral cells to a degree that correlated with the extent of apoptosis induction; and (c) both SDG and p-XSC induced the stress pathway kinases, Jun NH2-terminal kinase (JNK) and p38 kinase, at concentrations causing apoptosis; p-XSC, and to a lesser extent SDG, also activated extracellular regulated kinases 1&2 (ERKs 1&2) and protein kinase-B or Akt. To test their functional involvement, the effect of inhibiting each of these pathways on induction of apoptosis by SDG and p-XSC was determined in SCCs. Inhibiting the ERKs 1&2 or Akt pathways with specific chemical inhibitors (PD98059 or LY294002, respectively) did not affect the extent of apoptosis induced by SDG or p-XSC (with the exception of LY294002, which actually enhanced the level of induction of apoptosis by SDG). The JNK pathway appeared to be most important for induction of Fas-L and apoptosis because concentrations of SB202190 that inhibited activation of both the JNK and p38 kinase (but not ERKs 1&2) in SCC reduced the extent of induction of Fas-L and apoptosis by SDG and p-XSC, whereas lower concentrations that inhibited activation only of p38 kinase did not. This was confirmed by the fact that exogenous expression of a dominant negative deletion mutant of c-Jun (TAM67) reduced the induction of both apoptosis and Fas-L by SDG.     

No effect of red clover-derived isoflavone intervention on the insulin-like growth factor system in women at increased risk of colorectal cancer

BACKGROUND: Increased insulin-like growth factor (IGF)-I and IGF-II concentrations are related to increased colorectal cancer risk. Isoflavones have been associated with reduced colorectal cancer risk, and may affect the IGF system because of their weak estrogenic activity. The aim of the study was to investigate the effect of isolated isoflavones on serum concentrations of IGF system components. MATERIALS AND METHODS: We conducted a randomized, placebo-controlled, double-blinded, crossover trial in four hospitals in the Netherlands to investigate the effect of an 8-week supplementation with red clover-derived isoflavones (84 mg/d) on serum IGF-I concentrations. In addition, serum concentrations of IGF-II and IGF binding proteins (IGFBP)-1, IGFBP-2, and IGFBP-3 were assessed. Normal colorectal tissue biopsies were obtained after the first intervention period and mRNA expression of IGF-I, IGF-II, IGFBP-3, and IGF-IR was evaluated. Our study population consisted of 34 postmenopausal women with a family history of colorectal cancer or a personal history of colorectal adenomas. RESULTS: Isoflavone supplementation did not significantly affect serum concentrations of total IGF-I (mean relative within-person difference; IGF-I, -2.0%; 95% confidence interval, -8.0% to 3.9%). IGF-II and IGFBPs were also not significantly altered after isoflavone supplementation. Colorectal tissue mRNA expression of IGF system components did not significantly differ between individuals on isoflavone supplementation and those who received placebo. CONCLUSIONS: The results of our trial, supported by a qualitative review of soy trials published to date, suggest that isoflavones do not significantly affect circulating levels of IGF system components. Increased levels of IGF-I, as observed in most of these trials, are likely due to simultaneous protein supplementation.     

Effect of energy restriction on cell cycle machinery in 1-methyl-1-nitrosourea-induced mammary carcinomas in rats

Energy restriction (ER) results in a profound inhibition of chemically induced mammary carcinogenesis. The cancer inhibitory activity of ER has been shown to be associated with lower rates of cell proliferation during both premalignant and malignant stages of this disease process. Moreover, inhibition of carcinogenesis and suppression of cell proliferation occur in animals in which plasma concentrations of insulin-like growth factor (IGF)-I are reduced, and plasma corticosterone levels are increased concomitantly. Given the role of both hormones in signal transduction pathways that can modulate cell cycle progression, albeit via different regulatory mechanisms, we report experiments conducted to determine whether hypothesized effects of changes in plasma levels of IGF-I and corticosterone on cell cycle regulation could be detected in mammary carcinomas occurring in 40% ER rats in comparison to ad libitum fed control rats or 40% ER rats that were energy repleted for 7 days (ER-REP). As determined by appropriate combinations of immunoprecipitations, Western blots, and kinase activity assays, it was found that levels of phosphorylated retinoblastoma and E2F-1 were significantly reduced by ER (approximately 40 and 75%, respectively; P < 0.01), an effect that was partially reversed by ER-REP. Reductions in cyclin-dependent kinase (CDK)2 (82%) and CDK4 (77%) kinase activity in ER carcinomas were likely to account for the observed effects on retinoblastoma and E2F-1. Both Cip1/p21 and Kip1/p27 and levels of these proteins complexed with CDK2 were significantly elevated in ER carcinomas (P < 0.01), and levels of cyclin E were reduced. On the other hand, regulation of CDK4 kinase activity by ER was likely attributable to effects on cyclin D1 as well as increased binding of P16 and P19 to CDK4. The majority of changes induced by ER were reversed by ER-REP. These observations are consistent with the hypothesis that ER exerts its profound cancer inhibitory activity, in part, by multifaceted regulation of cell cycle machinery, possibly via concomitant changes in corticosterone and IGF-1 metabolism, although the role of other hormones and growth factors should not be dismissed.