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December 2001

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Inhibition of cigarette smoke-related DNA adducts in rat tissues by indole-3-carbinol.

Indole-3-carbinol (I3C) found in various cruciferous vegetables has been shown to exert anti-carcinogenic activity in several target organs. In this study, we have investigated the effects of I3C on cigarette smoke-related lipophilic DNA adduct formation, potentially a key step in chemical carcinogenesis. Female Sprague-Dawley rats were exposed to sidestream cigarette smoke in a whole-body exposure chamber for 6 h per day, 7 days a week for 4 weeks. Control animals received only vehicle while the intervention groups received I3C (1. 36 or 3.40 mmol/kg, b.wt.) daily by gavage starting from 1 week prior to smoke initiation until the end of the experiment. Analysis of tissue DNA by nuclease P1-mediated 32P-postlabeling showed one major and several minor smoke-related adducts in lung, trachea, heart and bladder. The high dose of I3C significantly inhibited the major adducts in lung (#5) and trachea (#3) by 55% each; minor adducts were slightly inhibited (20-40%). The low dose of I3C showed lesser degree of inhibition (30-40%) in both lung and trachea; however, it was found statistically significant in lung only. The major smoke-related adduct in bladder (#2) was strongly inhibited (>65%) by high dose of I3C approaching adduct levels achieved in sham-exposed rats. A small but statistically significant decrease in the smoke-related DNA adduct (#5) in heart tissue was also observed by intervention with high dose I3C. Low levels (30-50 adducts/10(10) nucleotides) of I3C-derived DNA adducts were also found in all the tissues examined although their significance remains unknown. These data show significant inhibition of cigarette smoke-related DNA adducts by I3C, particularly in the lung, trachea and bladder.

Mutat Res 2000 Jul 20;452(1):11-18

Placebo-controlled trial of indole-3-carbinol in the treatment of CIN.

OBJECTIVE: Most precancerous lesions of the cervix are treated with surgery or ablative therapy. Chemoprevention, using natural and synthetic compounds, may intervene in the early precancerous stages of carcinogenesis and prevent the development of invasive disease. Our trial used indole-3-carbinol (I-3-C) administered orally to treat women with CIN as a therapeutic for cervical CIN. METHODS: Thirty patients with biopsy proven CIN II-III were randomized to receive placebo or 200, or 400 mg/day I-3-C administered orally for 12 weeks. If persistent CIN was diagnosed by cervical biopsy at the end of the trial, loop electrocautery excision procedure of the transformation zone was performed. HPV status was assessed in all patients. RESULTS: None (0 of 10) of the patients in the placebo group had complete regression of CIN. In contrast 4 of 8 patients in the 200 mg/day arm and 4 of 9 patients in the 400 mg/day arm had complete regression based on their 12-week biopsy. This protective effect of I-3-C is shown by a relative risk (RR) of 0.50 ((95% CI, 0. 25 to 0.99) P = 0.023) for the 200 mg/day group and a RR of 0.55 ((95% CI, 0.31 to 0.99) P = 0.032) for the 400 mg/day group. HPV was detected in 7 of 10 placebo patients, in 7 of 8 in the 200 mg/day group, and in 8 of 9 in the 400 mg/day group. CONCLUSIONS: There was a statistically significant regression of CIN in patients treated with I-3-C orally compared with placebo. The 2/16 alpha-hydroxyestrone ratio changed in a dose-dependent fashion.

Gynecol Oncol 2000 Aug;78(2):123-129

Effects of dietary indole-3-carbinol on estradiol metabolism and spontaneous mammary tumors in mice.

Indole-3-carbinol (I3C) is a potent inducer of cytochrome P450 enzymes in many species, including humans. We therefore studied alterations in the cytochrome P450-dependent metabolism of estradiol in different strains of mice consuming I3C in semisynthetic powdered diets at doses ranging from 250 to 5000 p.p.m. (34-700 mg/kg/day) for different periods of time. In short-term metabolic studies (3 weeks), wet liver weight increased in SW and C3H/OuJ mice in a dose-responsive manner. Dietary I3C increased the cytochrome P450 content measured in hepatic microsomes, as well as the extent of estradiol 2-hydroxylation, up to 5-fold. In a long-term feeding experiment (8 months), female C3H/OuJ mice consumed synthetic diets containing I3C at 0, 500 or 2000 p.p.m. Mammary tumor incidence and multiplicity were significantly lower at both doses of I3C, and tumor latency was prolonged in the high-dose group. We conclude that I3C is an inducer of hepatic P450-dependent estrogen metabolism in mice, and that it is chemopreventive in the C3H/OuJ mouse mammary tumor model. This protective effect may be mediated in part by the increased 2-hydroxylation and consequent inactivation of endogenous estrogens.

Carcinogenesis 1991 Sep;12(9):1571-1574

Cigarette smoking and the risk of endometrial cancer.

Because of evidence of reduced estrogen excretion in the urine of women who smoke cigarettes and evidence linking estrogen levels to the risk of cancer of the female reproductive system, we evaluated the risk of endometrial cancer in relation to cigarette use in a hospital-based case-control study of 510 women with endometrial cancer (cases) and 727 women with other cancers (controls). The rate-ratio estimate (relative risk) for current smokers as compared with women who had never smoked was 0.7 (95 per cent confidence interval, 0.5 to 1.0), and for former smokers the estimate was 0.9 (0.6 to 1.2). For women currently smoking 25 or more cigarettes per day, the rate-ratio estimate was 0.5 (0.3 to 0.8). The effect of current smoking of at least 25 cigarettes per day appeared to be confined to postmenopausal women, among whom the estimate was 0.5 (0.2 to 0.9). Among premenopausal women the estimate was 0.9 (0.4 to 2.2), but the difference between these two estimates could have been due to chance. The data suggest that women who smoke heavily may have a lower risk of endometrial cancer than nonsmokers. The present findings do not have direct public health importance since cigarettes, overall, have serious deleterious effects. However, if these results are confirmed, elucidation of the underlying mechanisms whereby smoking reduces the risk would be of interest and might be useful in the development of strategies for preventing endometrial cancer.

N Engl J Med 1985 Sep 5;313(10):593-596

Changes in levels of urinary estrogen metabolites after oral indole-3-carbinol treatment in humans.

BACKGROUND: The oxidative metabolism of estrogens in humans is mediated primarily by cytochrome P450, many isoenzymes of which are inducible by dietary and pharmacologic agents. One major pathway, 2-hydroxylation, is induced by dietary indole-3-carbinol (I3C), which is present in cruciferous vegetables (e.g., cabbage and broccoli). PURPOSE: Because the pool of available estrogen substrates for all pathways is limited, we hypothesized that increased 2-hydroxylation of estrogens would lead to decreased activity in competing metabolic pathways. METHODS: Urine samples were collected from subjects before and after oral ingestion of I3C (6-7 mg/kg per day). In the first study, seven men received I3C for 1 week; in the second study, 10 women received I3C for 2 months. A profile of 13 estrogens was measured in each sample by gas chromatography-mass spectrometry. RESULTS: In both men and women, I3C significantly increased the urinary excretion of C-2 estrogens. The urinary concentrations of nearly all other estrogen metabolites, including levels of estradiol, estrone, estriol, and 16alpha-hydroxyestrone, were lower after I3C treatment. CONCLUSIONS: These findings support the hypothesis that I3C-induced estrogen 2-hydroxylation results in decreased concentrations of several metabolites known to activate the estrogen receptor. This effect may lower estrogenic stimulation in women. IMPLICATIONS: I3C may have chemopreventive activity against breast cancer in humans, although the long-term effects of higher catechol estrogen levels in women require further investigation.

J Natl Cancer Inst 1997 May 21;89(10):718-723

Screening of potential chemopreventive agents using biochemical markers of carcinogenesis.

Ninety potential chemopreventive agents were screened using 6 chemoprevention-associated biochemical end points. These compounds were tested using rodent (tracheal epithelial or liver) cells and human cells [neonatal foreskin fibroblasts, bronchial epithelial cells, or human leukemic cells (HL-60)]. The effects measured were: (a) inhibition of 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced tyrosine kinase activity in HL-60 cells; (b) inhibition of TPA-induced ornithine decarboxylase (ODC) activity in rat tracheal epithelial cells; (c) inhibition of poly(ADP-ribose)polymerase in propane sultone-treated primary human fibroblasts; (d) inhibition of benzo[a]pyrene(B[a]P)-DNA binding in human bronchial epithelial cells; (e) induction of reduced glutathione in Buffalo rat liver cells; and (f) inhibition of TPA-induced free radical formation in primary human fibroblasts or HL-60 cells. Fifty compounds were highly effective in inhibiting TPA-induced tyrosine kinase activity. This assay identified compounds from a wide variety of chemical classes as effective inhibitors, including all the vitamins, retinoic acid analogues, protein kinase C inhibitors, and chemicals belonging to the amino acid category. Fifty-two chemicals were classified as highly positive compounds when examined for their ability to inhibit TPA-induced ODC activity. These agents showed a dose-dependent inhibition or inhibition at all doses. Retinoids, in general, exhibited strong inhibition of ODC activity. A category of compounds showing dose-dependent inhibition were the sulfur compounds, especially the thiols and thiones. Among the natural products, terpenes were strong inhibitors of ODC. Forty-seven compounds were classified as strong inhibitors of poly(ADP-ribose)polymerase. In the carcinogen-DNA binding inhibition assay, 21 compounds were identified as strong inhibitors, which include phenolic compounds as well as sulfur compounds. Vitamins and their analogues were also good inhibitors. Testing for induced glutathione yielded 19 compounds that were good inducers. Sulfur-containing compounds and most of the phenolic compounds were also inducers of glutathione. Twenty compounds were highly positive for inhibition of TPA-induced free radical formation. A significant number of phenolic and sulfur compounds were again strong oxygen radical scavengers. Some antiinflammatory agents were also identified as free radical inhibitors. In general, retinoids were quite active in all the assays. Eight compounds were positive in all of the six assays; these were vitamin C (ascorbic acid), bismuththiol, esculetin, etoperidone, folic acid, hydrocortisone, indole-3-carbinol, and tocopherol succinate. Agents that were positive in these assays may inhibit the carcinogenesis process by similar mechanisms in humans and are identified as candidates for development as chemopreventive agents.

Cancer Res 1994 Nov 15;54(22):5848-5855

Influence of smoking on the development of lung metastases from breast cancer.

BACKGROUND. This study examined the association between cigarette smoking status and the development of lung metastases in a group of 835 women diagnosed with primary malignant unilateral breast cancer. METHOD. Female patients with breast cancer diagnosed between 1982 and 1991 at Roswell Park Cancer Institute (RPCI) in Buffalo, New York, who provided information on their cigarette smoking history at the time of their diagnosis were included. The subsequent disease status of patients was monitored by the RPCI Tumor Registry. The Cox regression model was used to estimate the relationship between smoking status and the development of lung metastases, adjusting for the patient's age, stage of disease at diagnosis, and body weight. RESULTS. Of those patients who developed lung metastases, 8.7% were nonsmokers, 14.1% were former smokers and 14.3% were current smokers. Tests showed that nonsmokers had significantly fewer lung metastases than either of the two smoking groups (P < 0.01). The estimated relative rates of lung metastases developing adjusting for age, stage, and body weight in women who smoked less than 10,000, between 10,001 and 20,000, and more than 20,000 packs over their lifetimes compared with nonsmokers were 1.06 (95% CI, 0.51-2.20), 3.10 (95% CI, 1.5-6.3), and 3.73 (95% CI, 1.6-8.9) respectively. The Cox regression model showed that every 1000 packs of cigarettes consumed over a lifetime increased a woman's risk of developing lung metastases by about 3% to 7% (P < 0.001). CONCLUSION. This study found a significant association between cigarette smoking history and risk of lung metastases developing in women diagnosed with primary invasive unilateral breast cancer. The risk of lung metastases developing increased as the number of cigarettes smoked in a lifetime increased.

Cancer 1995 Jun 1;75(11):2693-2699

Induction by estrogen metabolite 16 alpha-hydroxyestrone of genotoxic damage and aberrant proliferation in mouse mammary epithelial cells.

BACKGROUND: Estrogens are potent mammary tumor promoters influencing post-initiation events via epigenetic mechanisms. The upregulation (i.e., induction) of the C16 alpha-hydroxylation pathway during 17 beta-estradiol (E2) biotransformation has been associated with mammary cell transformation. The action of E2 metabolites on tumorigenic transformation, however, is poorly understood. PURPOSE: The newly established mammary epithelial cell line C57/MG, derived from the C57BL mouse strain, was used to examine whether E2 or its metabolites, 16-hydroxyestrone (16 alpha-OHE1) and estriol (E3), function as initiators of mammary cell transformation. METHODS: DNA repair (hydroxyurea-insensitive thymidine uptake), estrogen metabolism (3H exchange to form 3H2O), hyperproliferation (increased cell number), and acquisition of anchorage-independent growth (soft-agar colonies) were used as quantitative end points to measure the relative extent of transformation. RESULTS: Treatment of cells with 200 ng/mL 16 alpha-OHE1 resulted in a 55.2% increase in DNA repair synthesis, a 23.09% increase in proliferative activity, and a 18-fold increase in the number of soft-agar colonies, relative to the solvent controls (P less than .0001). The extent of upregulation of the three end points was similar to that induced by the genotoxic mammary carcinogen 7, 12-dimethylbenz[a]anthracene (DMBA, positive control). DMBA treatment also upregulated the ratio of 16 alpha/C2 hydroxylation of E2 leading to increased formation of 16 alpha-OHE1. E2 and E3 were not effective in upregulating these markers for transformation. CONCLUSION: These results demonstrate that in nontransformed C57/MG cells, 16 alpha-OHE1 may function as an initiator, perturbing the intermediate biomarkers for preneoplastic transformation.

J Natl Cancer Inst 1992 Apr 15;84(8):634-638

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