Discovery of TRPM8 Antagonist ( S)-6-(((3-Fluoro-4-(trifluoromethoxy)phenyl)(3-fluoropyridin-2-yl)methyl)carbamoyl)nicotinic Acid (AMG 333), a Clinical Candidate for the Treatment of Migraine

Transient-receptor-potential melastatin 8 (TRPM8), the predominant mammalian cold-temperature thermosensor, is a nonselective cation channel expressed in a subpopulation of sensory neurons in the peripheral nervous system, including nerve circuitry implicated in migraine pathogenesis: the trigeminal and pterygopalatine ganglia. Genomewide association studies have identified an association between TRPM8 and reduced risk of migraine. This disclosure focuses on medicinal-chemistry efforts to improve the druglike properties of initial leads, particularly removal of CYP3A4-induction liability and improvement of pharmacokinetic properties. A novel series of biarylmethanamide TRPM8 antagonists was developed, and a subset of leads were evaluated in preclinical toxicology studies to identify a clinical candidate with an acceptable preclinical safety profile leading to clinical candidate AMG 333, a potent and highly selective antagonist of TRPM8 that was evaluated in human clinical trials.

Discovery of Indazoles as Potent, Orally Active Dual Neurokinin 1 Receptor Antagonists and Serotonin Transporter Inhibitors for the Treatment of Depression

Combination studies of neurokinin 1 (NK1) receptor antagonists and serotonin-selective reuptake inhibitors (SSRIs) have shown promise in preclinical models of depression. Such a combination may offer important advantages over the current standard of care. Herein we describe the discovery and optimization of an indazole-based chemotype to provide a series of potent dual NK1 receptor antagonists/serotonin transporter (SERT) inhibitors to overcome issues of ion channel blockade. This effort culminated in the identification of compound 9, an analogue that demonstrated favorable oral bioavailability, excellent brain uptake, and robust in vivo efficacy in a validated depression model. Over the course of this work, a novel heterocycle-directed asymmetric hydrogenation was developed to facilitate installation of the key stereogenic center.

Optimization of potency and pharmacokinetic properties of tetrahydroisoquinoline transient receptor potential melastatin 8 (TRPM8) antagonists

Transient receptor potential melastatin 8 (TRPM8) is a nonselective cation channel expressed in a subpopulation of sensory neurons in the peripheral nervous system. TRPM8 is the predominant mammalian cold temperature thermosensor and is activated by cold temperatures ranging from 8 to 25 °C and cooling compounds such as menthol or icilin. TRPM8 antagonists are being pursued as potential therapeutics for treatment of pain and bladder disorders. This manuscript outlines new developments in the SAR of a lead series of 1,2,3,4-tetrahydroisoquinoline derivatives with emphasis on strategies to improve pharmacokinetic properties and potency. Selected compounds were profiled in two TRPM8 target-specific in vivo coverage models in rats (the icilin-induced wet dog shake model and the cold pressor test). Compound 45 demonstrated robust efficacy in both pharmacodynamic models with ED90 values <3 mg/kg.

Discovery of (S,E)-3-(2-fluorophenyl)-N-(1-(3-(pyridin-3-yloxy)phenyl)ethyl)-acrylamide as a potent and efficacious KCNQ2 (Kv7.2) opener for the treatment of neuropathic pain

Acrylamide (S)-6, a potent and efficacious KCNQ2 (Kv7.2) opener, demonstrated significant activity in two models of neuropathic pain and in the formalin test, suggesting that KCNQ2 openers may be useful in the treatment of neuropathic pain including diabetic neuropathy.

Preparation of imidazoles as potent calcitonin gene-related peptide (CGRP) antagonists

Several new potent CGRP receptor antagonists have been prepared in which the amide bond of lead compound 1 has been replaced by bioisosteric imidazole moieties. Substitution at N-1 of the imidazole was optimized to afford compounds with comparable potency to that of lead 1. Conformational restraint of the imidazole to form tetrahydroimidazo[1,5-a]pyrazine 43 gave substantially improved permeability.

Discovery of (R)-4-(8-fluoro-2-oxo-1,2-dihydroquinazolin-3(4H)-yl)-N-(3-(7-methyl-1H-indazol-5-yl)-1-oxo-1-(4-(piperidin-1-yl)piperidin-1-yl)propan-2-yl)piperidine-1-carboxamide (BMS-694153): a potent antagonist of the human calcitonin gene-related peptide receptor for migraine with rapid and efficient intranasal exposure

Calcitonin gene-related peptide (CGRP) has been implicated in the pathogenesis of migraine. Early chemistry leads suffered from modest potency, significant CYP3A4 inhibition, and poor aqueous solubility. Herein, we describe the optimization of these leads to give 4 (BMS-694153), a molecule with outstanding potency, a favorable predictive toxicology profile, and remarkable aqueous solubility. Compound 4 has good intranasal bioavailability in rabbits and shows dose-dependent activity in validated in vivo and ex vivo migraine models.

Cytochrome P450 reaction-phenotyping: an industrial perspective

It is now widely accepted that the fraction of the dose metabolized by a given drug-metabolizing enzyme is one of the major factors governing the magnitude of a drug interaction and the impact of a polymorphism on (total) drug clearance. Therefore, most pharmaceutical companies determine the enzymes involved in the metabolism of a new chemical entity (NCE) in vitro, in conjunction with human data on absorption, distribution, metabolism and excretion. This so called reaction-phenotyping, or isozyme-mapping, usually involves the use of multiple reagents (e.g., recombinant proteins, liver subcellular fractions, enzyme-selective chemical inhibitors and antibodies). For the human CYPs, reagents are readily available and in vitro reaction-phenotyping data are now routinely included in most regulatory documents. Ideally, the various metabolites have been definitively identified, incubation conditions have afforded robust kinetic analyses, and well characterized (high quality) reagents and human tissues have been employed. It is also important that the various in vitro data are consistent (e.g., scaled turnover with recombinant CYP proteins, CYP inhibition and correlation data with human liver microsomes) and enable an integrated in vitro CYP reaction-phenotype. Results of the in vitro CYP reaction-phenotyping are integrated with clinical data (e.g., human radiolabel and drug interaction studies) and a complete package is then submitted for regulatory review. If the NCE receives market approval, information on key routes of clearance and their associated potential for drug-drug interactions are included in the product label. The present review focuses on in vitro CYP reaction-phenotyping and the integration of data. Relatively simple strategies enabling the design and prioritization of follow up clinical studies are also discussed.

Involvement of Multiple Cytochrome P450 and UDP-Glucuronosyltransferase Enzymes in the in Vitro Metabolism of Muraglitazar

Muraglitazar (Pargluva), a dual alpha/gamma peroxisome proliferator-activated receptor activator, has both glucose- and lipid-lowering effects in animal models and in patients with diabetes. The human major primary metabolic pathways of muraglitazar include acylglucuronidation, aliphatic/aryl hydroxylation, and O-demethylation. This study describes the identification of human cytochrome P450 (P450) and UDP-glucuronosyltransferase (UGT) enzymes involved in the in vitro metabolism of muraglitazar. [(14)C]Muraglitazar was metabolized by cDNA-expressed CYP2C8, 2C9, 2C19, 2D6, and 3A4, but to a very minimal extent by CYP1A2, 2A6, 2B6, 2C18, 2E1, and 3A5. Inhibition of the in vitro metabolism of muraglitazar in human liver microsomes, at a clinically efficacious concentration, by chemical inhibitors and monoclonal antibodies further supported involvement of CYP2C8, 2C9, 2C19, 2D6, and 3A4 in its oxidation. A combination of intrinsic clearance (V(max)/K(m)) and relative concentrations of each P450 enzyme in the human liver was used to predict the contribution of CYP2C8, 2C9, 2C19, 2D6, and 3A4 to the formation of each primary oxidative metabolite and to the overall oxidative metabolism of muraglitazar. Glucuronidation of [(14)C]muraglitazar was catalyzed by cDNA-expressed UGT1A1, 1A3, and 1A9, but not by UGT1A6, 1A8, 1A10, 2B4, 2B7, and 2B15. The K(m) values for muraglitazar glucuronidation by the three active UGT enzymes were similar (2-4 muM). In summary, muraglitazar was metabolized by multiple P450 and UGT enzymes to form multiple metabolites. This characteristic predicts a low potential for the alteration of the pharmacokinetic parameters of muraglitazar via polymorphic drug metabolism enzymes responsible for clearance of the compound or by coadministration of drugs that inhibit or induce relevant metabolic enzymes.

Fluorine substitution can block CYP3A4 metabolism-dependent inhibition: identification of (S)-N-[1-(4-fluoro-3- morpholin-4-ylphenyl)ethyl]-3- (4-fluorophenyl)acrylamide as an orally bioavailable KCNQ2 opener devoid of CYP3A4 metabolism-dependent inhibition

The formation of a reactive intermediate was found to be responsible for CYP3A4 metabolism-dependent inhibition (MDI) observed with (S)-N-[1-(3-morpholin-4-ylphenyl)ethyl]-3-phenyl-acrylamide (1). Structure-3A4 MDI relationship studies culminated in the discovery of a difluoro analogue, (S)-N-[1-(4-fluoro-3-morpholin-4-ylphenyl)ethyl]-3-(4-fluoro-phenyl)acrylamide (2), as an orally bioavailable KCNQ2 opener free of CYP3A4 MDI.

Selenium deficiency in Fisher-344 rats decreases plasma and tissue homocysteine concentrations and alters plasma homocysteine and cysteine redox status

The purpose of the present study was to determine the effect of graded amounts of dietary selenium on plasma and tissue parameters of methionine metabolism including homocysteine. Male weanling Fisher-344 rats (n = 7-8/group) were fed a selenium-deficient, torula yeast-based diet, supplemented with 0 (selenium deficient), 0.02, 0.05 or 0.1 microg (adequate) selenium (as selenite)/g diet. After 61 d, plasma total homocysteine and cysteine were decreased (P < 0.0001) and glutathione increased (P < 0.0001) by selenium deficiency. The concentrations of homocysteine in kidney and heart were decreased (P = 0.02) by selenium deficiency. The activities of liver betaine homocysteine methyltransferase, methionine synthase, S-adenosylmethionine synthase, cystathionine synthase and cystathionase were determined; selenium deficiency affected only betaine homocysteine methyltransferase, which was decreased (P < 0.0001). The ratios of plasma free reduced homocysteine (or cysteine) to free oxidized homocysteine (or cysteine) or to total homocysteine (or cysteine) were increased by selenium deficiency, suggesting that selenium status affects the normally tightly controlled redox status of these thiols. Most differences due to dietary selenium were between rats fed 0 or 0.02 microg selenium/g diet and those fed 0.05 or 0.1 microg selenium/g diet. The metabolic consequences of a marked decrease in plasma homocysteine and smaller but significant decreases in tissue homocysteine are not known.

Low dietary zinc alters indices of copper function and status in postmenopausal women

OBJECTIVES

To better define the relationship between dietary zinc and copper for humans so that sound recommendations for intakes of these elements can be made.

METHODS

A study was conducted to ascertain the effect of moderately excessive and deficient intakes of zinc on copper metabolism and use in humans fed low and luxuriant amounts of copper. Twenty-one postmenopausal women housed in a metabolic unit completed the study as designed. After a 10-d equilibration period in which they were fed a diet providing 31.5 micromol (2 mg) Cu and 91.8 micromol (9 mg) Zn/8.4 MJ (2000 kcal), the women were divided into two groups. One group was fed a diet containing 15.7 micromol (1 mg) Cu/8.4 MJ (2000 kcal), and the other group was fed a diet containing 47.2 micromol (3 mg) Cu/8.4 MJ (2000 kcal). After equilibration, both groups were fed the basal diet providing 45.9 micromol (3 mg) Zn/8.4 MJ (2000 kcal) for 90 d; this was followed by another 10-d equilibration period before dietary zinc was increased to 811 micromol (53 mg)/8.4 MJ (2000 kcal) for 90 d.

RESULTS

The women were in positive copper balance only when the diet provided 47.2 micromol (3 mg) Cu and 811 micromol (53 mg) Zn/d. Immunoreactive ceruloplasmin concentrations and platelet cytochrome-c oxidase activity on a platelet number basis were significantly lower and the ratio between enzymatic and immunoreactive ceruloplasmin was significantly higher during low dietary than during high dietary zinc intake. Serum cholesterol was higher in subjects fed 15.7 micromol (1 mg) Cu/d than in those fed 47.2 micromol (3 mg) Cu/d. Total and low-density lipoprotein cholesterol concentrations decreased with zinc supplementation. Whole-blood glutathione concentration and erythrocyte glutathione peroxidase activity were lower during high than during low dietary zinc intake.

CONCLUSIONS

The findings indicate that an inadequate intake of zinc (45.9 micromol/d; 3 mg/d) was more effective than a moderately high intake of zinc (811 micromol/d; 53 mg/d) in inducing changes associated with a decreased copper status in postmenopausal women. Furthermore, the findings indicate that copper status indicators might be useful in evaluating changes in zinc status in humans, and an intake of 15.7 micromol (1 mg)/d of copper may be inadequate for postmenopausal women.

Cancer-protective properties of high-selenium broccoli

Selenium (Se) from high-Se garlic reduces the incidence of chemically induced mammary tumors, and Se from high-Se broccoli reduces colon cancer. However, the ability of Se from high-Se broccoli to protect against mammary cancer has not been tested. Also, the sprout form of broccoli contains many secondary plant compounds that are known to reduce cancer risk, but the anticarcinogenic activity of broccoli sprouts has not been investigated. The present studies examined the ability of high-Se broccoli or high-Se broccoli sprouts to protect against chemically induced mammary or colon cancer. In one experiment, Sprague--Dawley rats that consumed diets containing 3.0 microg of Se/g supplied as high-Se broccoli had significantly fewer mammary tumors than rats fed 0.1 microg of Se as selenite with or without the addition of regular broccoli. In the second experiment, Fisher F-344 rats fed 2.0 microg of Se/g of diet supplied as either high-Se broccoli florets or high-Se broccoli sprouts had significantly fewer aberrant colon crypts than rats fed 0.1 or 2 microg of Se/g of diet supplied as selenite with or without the addition of low-Se broccoli. These data demonstrate that the cancer-protective effect of Se in high-Se broccoli extends to mammary cancer and the protective forms of broccoli against colon cancer include high-Se broccoli sprouts.

Dietary copper and dimethylhydrazine affect protein kinase C isozyme protein and mRNA expression and the formation of aberrant crypts in colon of rats

Low dietary copper has been shown to decrease the expression of various protein kinase C (PKC) isozymes and increase the risk of colon cancer development in experimental animals. The purpose of this study was to investigate the relationship between dietary copper and carcinogen administration on PKC isozyme accumulation and aberrant crypt foci (ACF) formation in rats fed 0.9 and 7.7 microg Cu/g diet. After 24 and 31 d on the diets, the rats were injected with either dimethylhydrazine (DMH) (25 mg/kg i.p.) or saline and killed at two time points (2 wk and 8 wk after DMH). Rats fed low dietary copper had significantly lower (p<0.0001) hematocrits, hemoglobin, ceruloplasmin activity and plasma and liver copper concentrations than rats fed adequate dietary copper. Ingestion of low dietary copper significantly (p<0.005) increased the formation of DMH-induced ACF (116.8 vs 59.6). Low dietary copper significantly (p<0.05) decreased the concentration of PKC alpha, delta, and zeta in the colon at 2 wk but not at 8 wk. Thus, changes in PKC isoform protein concentration may be related to increased susceptibility of copper-deficient animals to colon cancer.

Manganese absorption and retention in rats is affected by the type of dietary fat

There is evidence that manganese (Mn) metabolism may be altered by the form and amount of dietary fat. Also, iron (Fe) absorption is greater with saturated fats, as compared to polyunsaturated fatty acids (PUFAs). The absorption of Fe and Mn are interrelated in many aspects; therefore, the form of dietary fat may indirectly alter Mn absorption. The reported studies were conducted to determine whether saturated fat, as compared to unsaturated fat, affected Mn absorption, retention, and metabolism. In experiment I, adult rats were fed diets containing either 0.7 or 100.4 microg/g Mn with the fat source as high-linoleic safflower oil or stearic acid. After 2 wk of equilibration, the animals were fed a test meal of 54Mn followed by whole-body counting for 10 d. Manganese absorption was significantly (p < 0.05) lower in the stearic acid group (0.9-4.8%) than in the safflower oil group (20-33.8%); however, the biological half-life was shorter in the safflower oil group. Retention of 54Mn and total Mn was always significantly (p < 0.05) greater in the safflower oil group when dietary Mn was low, but it was the same when dietary Mn was high. In experiment II, weanling rats were fed 1.3, 39.3, or 174.6 microg Mn/g and either stearate, high-oleic safflower oil or high-linoleic safflower oil for 8 wk. Long-term feeding of the stearate and low Mn-containing diet resulted in a significant (p < 0.0001) reduction in heart superoxide dismutase activity and kidney and liver Mn concentrations compared to the other diets. These data show that stearic acid inhibitits Mn absorption, but it may not inhibit Mn retention when dietary Mn is high.

Selenium (Se) from high-selenium broccoli is utilized differently than selenite, selenate and selenomethionine, but is more effective in inhibiting colon carcinogenesis

The reduction in incidence of chemically-induced colon cancer by foods high in selenium (Se) was investigated in Fisher-344 rats. The foods used were high-Se broccoli (produced in a greenhouse by addition of selenate to the media surrounding the plant roots) and a processed high-Se wheat product (made by milling high-Se wheat purchased from a seleniferous area). Weanling rats were fed diets containing different amounts of Se from these foods or from selenium salts (selenite and selenate). Early in the experiment the animals were injected with a chemical carcinogen. After 11 weeks on diets animals were killed and the colons examined for preneoplastic lesions (aberrant crypts foci, ACF). ACF were significantly reduced in animals fed supra-nutritional amounts of Se from broccoli, despite the finding that Se from broccoli was poorly bioavailable. Supra-nutritional amounts of Se from high-Se processed wheat also significantly reduced aberrant crypts (AC), although pure selenomethionine, (the predominant chemical form of Se in wheat), did not significantly reduce AC. These results emphasize the need to study Se in food forms, and not extrapolate from previous studies using pure chemical forms in cancer inhibition studies. They also demonstrate that foods with high Se bioavailability are not necessarily the most efficacious for cancer incidence reduction.

Dietary selenium and arsenic affect DNA methylation in vitro in Caco-2 cells and in vivo in rat liver and colon

Selenium is an essential trace element for human health, and it has received considerable attention for its possible role as an anticarcinogenic agent. The purpose of the present study was to determine whether changes in the amount and the chemical form of selenium would affect DNA methylation and whether this effect would be modified by arsenic. Caco-2 cells, a human colon cancer cell line, were exposed to 0, 1 or 2 micromol supplemental selenite/L and 0, 1 or 2 micromol supplemental arsenite/L for 7 d. DNA isolated from Caco-2 cells not treated with selenite was significantly (P: < 0. 0001) hypomethylated compared with that from cells treated with 1 or 2 micromol selenite/L. DNA isolated from Caco-2 cells not treated with arsenite was significantly (P: < 0.0001) hypomethylated compared with DNA isolated from cells treated with 1 or 2 micromol arsenite/L. In addition, methylation of the p53 promoter region of Caco-2 cells decreased when cells were cultured in the absence of selenite and in the absence of arsenite. Sixty weanling male Fischer 344 rats were fed a torula yeast-based diet supplemented with 0, 0.1 or 2 mg selenium/kg diet as either selenite or selenomethionine in the presence or absence of 5 mg arsenic/kg diet as arsenite for 6 wk. Similar to the results with Caco-2 cells, rats fed selenium-deficient diets had significantly (P: < 0.0001) hypomethylated liver and colon DNA compared with rats fed 0.1 or 2.0 microg selenium/g diets as either selenite or selenomethionine. Thus, alterations in DNA methylation may be a potential mechanism, whereby deficient dietary selenium increases liver and colon tumorigenesis.

Inadequate dietary copper increases tumorigenesis in the Min mouse

Multiple intestinal neoplasia (Min) mice are a good model for the investigation of the effects of dietary alterations on genetic susceptibility for intestinal cancer. In the current study, nursing dams and their pups were placed on an AIN-93G diet containing either 1 or 6 ppm copper. The pups were maintained on the same concentration of dietary copper after weanling until they were 13-weeks-old. Animals fed copper deficient diets had a significantly (P<0.0003) higher small intestine tumor incidence and a significantly (P<0.04) higher small intestine tumor burden than animals fed adequate dietary copper. Therefore, inadequate dietary copper can increase the spontaneous tumorigenesis that occurs in the Min mouse.

Selenium from high selenium broccoli protects rats from colon cancer

Colon cancer is the third most common newly diagnosed cancer in the United States and the third most common cause of cancer-related deaths. Previous supplementation studies have demonstrated the efficacy of selenium (Se) for prevention of colon cancer in humans. The metabolism of Se depends on its chemical form, and studies have shown that the chemical form of Se in broccoli does not accumulate in the body as fast as other forms of Se and may be especially beneficial for prevention of cancer. In the first experiment of the present study, Fisher F-344 rats (n = 45) were allotted randomly to torula yeast-based diets supplemented with the following: 1) no Se; 2) 0.1 microg Se/g diet as selenate; 3) 1.0 microg Se/g diet as selenate; 4) 0.1 microg Se/g diet as selenized broccoli (Se concentration of approximately 500 microg/g); or 5) 1.0 microg Se/g diet as selenized broccoli. In Experiment 2, rats (n = 80) were allotted randomly to the same basal diet supplemented with the following: 1) no added Se; 2) 2.0 microg Se/g diet as selenite; 3) 2. 0 microg Se/g diet as selenite + low Se broccoli; and 4) 2.0 microg Se/g diet as selenized broccoli. Rats were fed the diets for 2 wk and injected with a chemical carcinogen (3,2 dimethyl 4-amino biphenyl or dimethyl-hydrazine in Experiment 1 or dimethyl hydrazine in Experiment 2; 2 rats/treatment were used as vehicle controls). Supranutritional amounts of Se supplied as high Se broccoli significantly decreased (P: < 0.05) the incidence of aberrant crypts (AC) and aberrant crypt foci (ACF; preneoplastic lesions indicative of colon cancer) compared with other dietary treatments. Diets were controlled for the presence or absence of broccoli and for the total amount of Se. The reduction in AC and ACF was a function of Se in high Se broccoli and not a result of broccoli alone or Se alone. Adequate dietary Se supplied as high Se broccoli did not accumulate in tissues or increase glutathione peroxidase activity as well as other forms and amounts of Se. Thus, Se from high Se broccoli may be metabolized in a manner that diverts much of the Se into a pool that provides protection against colon cancer.

Case study using descriptive analysis to estimate hidden costs in processing third party prescriptions

OBJECTIVE

To identify and quantify additional hidden costs associated with processing third party prescriptions.

DESIGN/SETTING

Using time and motion techniques, the frequency of rejected third party prescriptions and the time involved to resolve those rejections were measured in one supermarket chain pharmacy and one independent pharmacy. From this information, additional costs attributed to processing third party prescriptions were calculated.

RESULTS

In a market where almost 95% of all prescriptions are third party reimbursed, payers rejected 18.7% and 22.3% of the prescriptions submitted by the supermarket chain and independent pharmacies, respectively. Additional or hidden costs for rejected prescriptions averaged $1.10 at the supermarket chain pharmacy and $1.54 at the independent pharmacy, with the difference attributable to the higher level of pharmacy staff involvement in resolving rejections at the independent pharmacy. When additional costs for all third party prescriptions were calculated, the average additional cost per third party prescription dropped to $0.44 for the supermarket chain pharmacy and $0.61 for the independent pharmacy.

CONCLUSION

Increasing pharmacist availability for pharmaceutical care requires decreasing time spent in the dispensing process, especially resolving third party problems. Systems analysis and time and motion techniques were effectively used to more accurately measure the time and costs associated with processing third party prescriptions. Actual costs found in this study were considerable, but significantly less than those reported previously in studies using estimates and surveys.

Changes in dietary zinc and copper affect zinc-status indicators of postmenopausal women, notably, extracellular superoxide dismutase and amyloid precursor proteins

BACKGROUND

Zinc is an essential trace element for human health and well-being; however, methods currently available for the assessment of zinc status in humans are unsatisfactory.

OBJECTIVE

The objective was to critically evaluate the use of various indicators of zinc status in humans in a controlled metabolic ward study.

DESIGN

Indicators of zinc status were measured in 25 healthy postmenopausal women aged 64.9 +/- 6.7 y. After a 10-d equilibration period, volunteers consumed a diet with either a low (1 mg/d; n = 12) or a high (3 mg/d; n = 13) copper content based on a total energy content of 8.4 MJ. They received the same amount of copper throughout the study. Both groups were fed the basal diet (3 mg Zn/d) with no zinc supplement for one 90-d period, and the diet supplemented with 50 mg Zn/d for another 90-d period.

RESULTS

Zinc supplementation significantly increased (P < 0.0001) extracellular but not erythrocyte superoxide dismutase activity. This increase was more apparent when subjects were fed the low-copper diet. Zinc supplementation in combination with the low-copper diet significantly decreased (P < 0.01) amyloid precursor protein expression in platelets. Other indicators of zinc status that were significantly elevated after zinc supplementation were as follows: plasma zinc and free thyroxine concentrations and mononuclear 5'-nucleotidase activity.

CONCLUSION

The measurement of serum extracellular superoxide dismutase activity may be useful as a marker for the functional assessment of zinc status in humans.

Antibody response to heat shock proteins and histopathology in mice infected with Trypanosoma cruzi and maintained at elevated temperature

Highly susceptible C3HeB/FeJ mice survive an otherwise lethal infection with a Brazil strain of Trypanosoma cruzi when held at an elevated environmental temperature of 36 C. The body temperature of these mice has been shown to increase 3-4 C to levels typical of a febrile response. In the present study, the synthesis of parasite heat shock proteins (hsp60, hsp70, and hsp90) was shown to be enhanced at a temperature of 39 C and the results of immunoprecipitation analysis indicated that parasite HSPs are highly immunogenic in T. cruzi-infected mice maintained at 36 C or room temperature (RT). Differences in the histopathology of cardiac and skeletal muscle in C3HeB/FeJ mice maintained at RT or 36 C at different times postinfection also were investigated in this study. The lower numbers of circulating parasites observed in mice maintained at 36 C were correlated with lower levels of tissue parasitism, inflammation, and tissue destruction. Finally, the transfer of infected mice from RT to an environment of 36 C at various times during infection was shown to increase the survival rate of infected mice and also resulted in a dramatic reduction in parasitemia levels. In light of the growing evidence for a beneficial effect of elevated temperature during experimental Chagas' disease, further studies seem warranted to determine if hyperthermia or fever therapy might also be beneficial in the treatment of humans infected with T. cruzi.

In vivo mutagenicity and hepatocarcinogenicity of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) in bitransgenic c-myc/lambda lacZ mice

2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) is a mutagenic and carcinogenic heterocyclic amine found in cooked meat. Hepatic DNA adduct formation, in vivo mutagenicity, and hepatocarcinogenicity of MeIQx were examined in mice harboring the lacZ mutation reporter gene (Muta mice) and bitransgenic mice overexpressing the c-myc oncogene. C57Bl/lambda lacZ and bitransgenic c-myc (albumin promoter)/lambda lacZ mice were bred and weaned onto an American Institute of Nutrition-76-based diet containing 0.06% (w/w) MeIQx or onto control diet. After 30 weeks on diet, only male bitransgenic mice on MeIQx developed hepatocellular carcinoma (100% incidence). By 40 weeks, hepatic tumor incidence was 100%/75% (17%/0%) and 44%/17% (0%/0%) in male c-myc/lambda lacZ and C57Bl/lambda lacZ mice who were given MeIQx (or control) diet, respectively, supporting a synergism between MeIQx and c-myc overexpression in hepatocarcinogenesis. At either time point, mutant frequency in the lacZ gene was at least 40-fold higher in MeIQx-treated mice than in control mice of either strain. These findings suggest that MeIQx-induced hepatocarcinogenesis is associated with MeIQx-induced mutations. Elevated mutant frequency in MeIQx-treated mice also occurred concomitant with the formation of MeIQx-guanine adducts, as detected by the 32P-postlabeling assay. Irrespective of strain or diet, sequence analysis of the lacZ mutants from male mouse liver showed that the principal sequence alterations were base substitutions at guanine bases. Adenine mutations, however, were detected only in animals on control diet. MeIQx-fed mice harboring the c-myc oncogene showed a 1.4-2.6-fold higher mutant frequency in the lacZ gene than mice not carrying the transgene. Although there was a trend toward higher adduct levels in c-myc mice, MeIQx-DNA adduct levels were not significantly different between c-myc/lambda lacZ and C57Bl/lambda lacZ mice after 30 weeks on diet. Thus, it seemed that factors in addition to MeIQx-DNA adduct levels, such as the enhanced rate of proliferation associated with c-myc overexpression, may have accounted for a higher mutant frequency in c-myc mice. In the control diet groups, the lacZ mutant frequency was significantly higher in c-myc/lambda lacZ mice than in C57Bl/lambda lacZ mice. The findings are consistent with the notion that c-myc overexpression is associated with an increase in mutagenesis. The mechanism for the synergistic effects of c-myc overexpression on MeIQx hepatocarcinogenicity seems to involve an enhanced expression of MeIQx-induced mutations.

Dietary selenium reduces the formation of aberrant crypts in rats administered 3,2'-dimethyl-4-aminobiphenyl

Human epidemiologic studies suggest that low selenium status is associated with increased cancer risk and that selenium supplementation is associated with reduction in the incidence of several cancers, including colorectal cancer. Aromatic and heterocyclic amine carcinogens are thought to be important in the etiology of human colorectal cancer, but no information is available on the effects of selenium on aromatic amine-induced colon cancer. In order to investigate this effect, aberrant crypt foci (ACF), the putative preneoplastic lesions of colon cancer in humans and rodents, were used as a biomarker to test the hypothesis that selenium supplementation can reduce aromatic amine-induced colon carcinogenesis. Male weanling F344 inbred rats were fed a basal torula yeast selenium-deficient diet supplemented with 0, 0.1, or 2. 0 mg selenium/kg diet as selenite, selenate, or selenomethionine (SeMet). Animals were fed the diets for 4 weeks and then administered 1 sc injection/week for 2 weeks of 3, 2'-dimethyl-4-aminobiphenyl (DMABP; 100 mg/kg) or vehicle (peanut oil). At 12 weeks, the rats were euthanized and the colon and rectum were removed, opened longitudinally, and fixed in 70% ethanol. Glutathione peroxidase activities in erythrocytes and liver cytosol and selenium concentrations in the colon/rectum and kidney increased significantly (p < 0.05) and in a dose-dependent manner with each of the three selenium diets. No ACF were identified in vehicle-treated rats. In DMABP-treated rats, ACF frequencies decreased significantly (p < 0.05) in groups supplemented with 0.1 or 2.0 mg selenium/kg diet as selenite and selenate but not SeMet. There were no significant differences in ACF and aberrant crypts between rats fed 0.1 vs 2.0 mg selenium/kg diet. These results suggest that dietary selenium, depending on chemical form, can reduce aromatic amine-induced colon carcinogenesis.

Dietary copper, manganese and iron affect the formation of aberrant crypts in colon of rats administered 3,2'-dimethyl-4-aminobiphenyl

Aberrant crypt foci (ACF) are preneoplastic lesions for colon cancer. Altered amounts of copper-zinc (CuZnSOD) and manganese (MnSOD) superoxide dismutases have been implicated in multistage carcinogesis of both rodents and humans. Dietary factors are potential modulators of both CuZnSOD and MnSOD activity. The purpose of this study was to investigate the interactive effects of dietary copper, manganese, and iron on 3,2'-dimethyl-4-aminobiphenyl (DMABP)-induced ACF and superoxide dismutase activities in weanling rats fed low or adequate copper (0.8 or 5.1 microg Cu/g diet), low or adequate manganese (0.6 or 17 microg Mn/g diet), and adequate or high iron (37 or 140 microg Fe/g diet). Twelve rats were allowed free access to each of these eight diets for 3.5 wk prior to DMABP administration and for an additional 8 wk after the first DMABP injection. Rats fed low dietary copper had 105% (P < 0.0001) higher formation of DMABP-induced ACF than those fed adequate dietary copper. Rats ingesting low rather than adequate dietary manganese had 23% higher formation of ACF, and rats ingesting high rather than adequate dietary iron had 18% higher formation of ACF. Heart total superoxide dismutase activity was significantly correlated with the number of ACF (r = -0.43, P < 0.0001) in rats administered DMABP. These results suggest that dietary alterations that affect superoxide dismutase activity may affect cancer susceptibility.

Manganese deficiency and toxicity: are high or low dietary amounts of manganese cause for concern?

Manganese is an essential trace element that is required for the activity of several enzymes. Manganese is also quite toxic when ingested in large amounts, such as the inhalation of Mn-laden dust by miners. This review examines Mn intake by way of the food supply and poses the question: Is there reason to be concerned with Mn toxicity or deficiency in free-living populations in North America? Although much remains to be learned of the functions of Mn, at present there are only a few vaguely described cases of Mn deficiency in the medical literature. Given the heterogeneity of the North American food supply, it is difficult to see the possibility of more than greatly isolated and unique instances of Mn deficiency. However, low Mn-dependent superoxide dismutase activity may be associated with cancer susceptibility, and deserves further study. There may be reasons, however, to be concerned about Mn toxicity under some very specialized conditions. Increasing numbers of young people are adopting a vegetarian lifestyle which may greatly increase Mn intake. Iron deficiency may increase Mn absorption and further increase the body-burden of Mn, especially in vegetarians. Mn is eliminated primarily through the bile, and hepatic dysfunction could depress Mn excretion and further contribute to the body burden. Would such a combination of events predispose substantial numbers of people to chronic Mn toxicity? At present, there is no definite proof of this occurring, but given the state of knowledge at the present time, more studies with longer time-frames and more sensitive methods of analysis are needed.

The chemical form of selenium influences 3,2'-dimethyl-4-aminobiphenyl-DNA adduct formation in rat colon

There is increasing evidence that selenium can protect against tumorigenesis or preneoplastic lesion development induced by chemical carcinogens. This study examined whether selenite, selenate or selenomethionine would be protective against 3, 2'-dimethyl-4-aminobiphenyl (DMABP)-DNA adduct formation in the liver and colon of rats and sought to delineate the mechanism for the protective effects of the different chemical forms of selenium against aberrant crypt formation, a preneoplastic lesion for colon cancer. After injection of DMABP, two DNA adducts were identified in the liver and colon of rats. Supplementation with either 0.1 or 2.0 mg selenium/kg diet as either selenite or selenate but not selenomethionine resulted in significantly fewer (53-70%; P < 0.05) N-(deoxyguanosin-8-yl)-(deoxyguanosin-8-yl)-3, 2'-dimethyl-4-aminobiphenyl (C8-DMABP)-DNA adducts in the colon but not the liver than in rats fed a selenium-deficient diet. Rats supplemented with selenomethionine had greater (P < 0.05) plasma and liver selenium concentrations and glutathione peroxidase activity than those supplemented with selenite or selenate; however, they also had more DMABP-DNA adducts. The protective effect of selenite and selenate against DMABP-DNA adduct formation apparently is not a result of alterations in plasma or liver selenium concentrations or altered glutathione peroxidase or glutathione transferase activities but may be related to differences in the metabolism of the different forms of selenium.

Beneficial effect of selenium supplementation during murine infection with Trypanosoma cruzi

Selenium (Se) has been shown to function as an antioxidant that may enhance immunity during microbial infection. To investigate the effect of elevated levels of Se on the course of experimental Chagas' disease, 5 groups of C3HeB/FeJ mice were infected with 10(3) bloodform trypomastigotes of a Brazil strain of Trypanosoma cruzi while receiving supplements of 0 ppm, 2 ppm, 4 ppm, 8 ppm, or 16 ppm Se as sodium selenate in drinking water. After 64 days of infection, survival ranged from 0 to 60%, with groups receiving 4 ppm and 8 ppm Se exhibiting 60% survival and the group without Se exhibiting 0% survival. In addition, parasitemia levels of mice supplemented with Se were significantly lower (P<0.01) than in nonsupplemented mice. The results of the present study suggest that Se supplementation does have a beneficial effect during murine infection with T. cruzi, resulting in decreased parasitemias and increased longevity.

Proliferation, development and DNA adduct levels in the mammary gland of rats given 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and a high fat diet

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a heterocyclic amine derived from cooked meat that is a mammary gland carcinogen in rats. A carcinogenic dose-regimen of PhIP (75 mg/kg, p.o., 10 doses, once per day) was administered to 43-day old female Sprague-Dawley rats, and the rats were then placed on a defined high fat (23.5% corn oil) or low fat (5% corn oil) diet for up to 6 weeks. At various times after carcinogen and diet, and prior to carcinogenesis, we examined the percentage of proliferating cells in terminal end bud (TEB) epithelial structures of the rat mammary gland by proliferating cell nuclear antigen staining, mammary gland architecture by whole mounting, and PhIP-DNA adduct levels in mammary epithelial cells by the 32P-post-labeling assay. Immediately after dosing, the percentage of proliferating epithelial cells in TEBs was significantly higher in PhIP-treated rats than in control rats receiving vehicle only [7.5 +/- 0.9% (n = 99) versus 4.2 +/- 0.6% (n = 127), respectively]. The mammary glands of PhIP-treated rats showed a significantly lower density of alveolar buds (ABs) and a higher density of TEBs than control rats, which suggests that PhIP exposure partially inhibited the normal glandular differentiation of TEBs to ABs. After 6 weeks on the diet, proliferation in TEBs was statistically higher in rats given PhIP plus a high fat diet than in rats given vehicle plus a low fat diet. The mammary glands from rats on a high fat diet also showed a statistically higher density of TEBs when compared with rats on a low fat diet [2.08 +/- 0.34% versus 1.04 +/- 0.20%, respectively (n = 6)]. PhIP-DNA adduct levels were relatively high in mammary epithelial cells of treated rats. At 3 h after the last dose of PhIP, DNA adduct levels [relative adduct labeling (RAL) x 10(7), mean +/- SE] were 10.5 +/- 1.7 (n = 8) and 0.9 +/- 0.2 (n = 7) in epithelial cells isolated from mammary gland and in the liver, respectively. DNA adduct removal rates from the mammary gland were not different between rats on the high fat and low fat diets. Adducts were still detected after 6 weeks on either diet. Thus, events that occurred prior to neoplasia in the mammary glands of PhIP-treated rats include formation of PhIP-DNA adducts at relatively high levels, and enhanced proliferation in TEBs (putative sites of origin of mammary gland carcinomas) and partial inhibition of TEB differentiation. The high fat diet, a promoter of PhIP-induced mammary gland carcinogenesis, appeared to sustain the proliferative effect of PhIP in mammary gland TEBs at a time when PhIP-DNA adducts are still detectable. These early events may contribute to the targeting and carcinogenicity of PhIP to the mammary gland of rats.

Effect of biliary ligation on manganese accumulation in rat brain

Neurologic and radiologic disorders have been reported to occur in miners inhaling manganese (Mn)-laden dust and in humans receiving long-term parenteral nutrition. These abnormalities have been attributed to Mn intoxication because of elevated serum Mn concentrations. Because the liver, by way of the bile, is the major route of Mn excretion, it is possible that anything that decreases biliary excretion could increase accumulation of Mn in the brain. The purpose of this study was to determine whether biliary ligation would increase Mn accumulation in the brain of rats that were exposed to deficient or adequate amounts of dietary manganese. The first experiment had a 2 x 3 factorial design, two levels of Mn (0 or 45 microg/g diet) and three surgical treatments (control, sham, or bile-ligation). Animals were sacrificed 10 d after being fed 54Mn. In experiment 2, animals that had a sham operation or bile-ligation were sacrificed at 8 time points after being injected intraportally with 54Mn complexed to albumin. The biliary-ligated animals had a significantly (p < 0.001) smaller percentage of the 54Mn in their brains (when expressed as a percentage of whole animal 54Mn) than the sham-operated animals. Mn deficiency had a similar effect. However, we did observe an increased accumulation of the radioisotope in the brain over time. Therefore, in short-term studies, biliary-ligated rats do not appear to be a good model for Mn accumulation in the brains of people with cholestatic liver disease.

Metabolism of food-derived heterocyclic amines in nonhuman primates

During the cooking of meats, several highly mutagenic heterocyclic amines (HCAs) are produced. Three HCAs, IQ, MeIQx, and PhIP have been under study for carcinogenicity in cynomolgus monkeys, and to date, IQ has been shown to be a potent hepatocarcinogen. Concomitantly, the metabolic processing of these HCAs has been examined. Metabolism studies show that the potent hepatocarcinogenicity of IQ is associated with the in vivo metabolic activation of IQ via N-hydroxylation and the formation of DNA adducts. In monkeys undergoing carcinogen bioassay with IQ, N-hydroxylation was confirmed by the presence of the N-hydroxy-N-glucuronide conjugate of IQ in urine. The N-hydroxylation of IQ appears to be carried out largely by hepatic CYP3A4 and/or CYP2C9/10, and not by CYP1A2, an isoform not expressed in liver of this species. Notably MeIQx is poorly activated in cynomolgus monkeys and lacks the potency of IQ to induce hepatocellular carcinoma after a 5-year dosing period. The poor activation of MeIQx appears to be due to the lack of constitutive expression of CYP1A2 and an inability of other cytochromes P450, such as CYP3A4 and CYP2C9/10, to N-hydroxylate the quinoxalines. MeIQx is detoxified in monkeys largely by conjugation with glucuronide at the N-1 position. Although the carcinogenicity of PhIP is not yet known, the metabolic data suggest that PhIP will be carcinogenic in this species. PhIP is metabolically activated in vivo in monkeys by N-hydroxylation, as discerned by the presence of the N-hydroxy-N-glucuronide conjugate in urine, bile, and plasma. PhIP also produces DNA adducts that are widely distributed in tissues. The results from these studies support the importance of N-hydroxylation in the carcinogenicity of HCAs in nonhuman primates and by analogy, the importance of this metabolic activation step in the possible carcinogenicity of dietary HCAs in humans.

Bioactivation and inactivation of aflatoxin B1 by human, mouse and rat liver preparations: effect on SCE in human mononuclear leucocytes

The purpose of this study was to investigate the use of human and animal subcellular liver fractions in an in vitro evaluation of carcinogenic risk. The bioactivation and bioinactivation of the known genotoxic carcinogen aflatoxin B1 by human, mouse and rat liver preparations was investigated using the SCE assay in human lymphocytes as a genotoxic endpoint. There was a 10-fold variation in SCE response (1.1-11.6 SCE/Cell) in human mononuclear leucocytes (MNLs) after aflatoxin B1 was activated by human liver microsomes (n = 6). Activation correlated with the CYP1A2 phenotype of livers (r = 0.8; p < 0.05), but there was no correlation with either GST M1 genotype or epoxide hydrolase phenotype. Mouse liver microsomes activated aflatoxin B1 to a greater extent [(1 micro M) 12.8 +/- 2.51 SCE/Cell] than either rat [(10 micro M) 12.0 +/- 3.84 SCE/Cell or human (L25) [(10 micro M) 8.8 +/- 2.00 SCE/Cell liver microsomes. The addition of mouse liver cytosol and reduced glutathione (GSH) significantly (p < 0.001) reduced aflatoxin B1-dependent genotoxicity, whereas the addition of either human or rat cytosol (+GSH) was without effect. These data indicate that species variation in both bioactivation and bioinactivation can exist. Therefore there is a necessity for careful selection of activation systems from species whose biochemical profile reflects that of man.

Hepatic tumor induction in c-myc mono-transgenic and TGF-alpha/c-myc double-transgenic mice

Double transgenic mice bearing fusion genes consisting of mouse albumin enhancer/promoter-mouse c-myc cDNA and mouse metallothionein 1 promoter-human TGF-alpha cDNA were generated to investigate the interaction of these genes in hepatic oncogenesis and to provide a general paradigm for characterizing both the interaction of nuclear oncogenes and growth factors in tumorigenesis as well as to produce an experimental model to test how environmental chemicals might interact with these genes during the neoplastic process. Coexpression of c-myc and TGF-alpha as transgenes in the mouse liver resulted in a tremendous acceleration of neoplastic development in this organ as compared to expression of either of these transgenes alone. The two distinct cellular reactions that occurred in the liver of the double transgenic mice prior to the appearance of liver tumors were dysplastic and apoptotic changes in the existing hepatocytes followed by emergence of multiple focal lesions composed of both hyperplastic and dysplastic cell populations. These observations suggest that the interaction of c-myc and TGF-alpha, during development of hepatic neoplasia contributes to the selection and expansion of the preneoplastic cell populations which consequently increases the probability of malignant conversion. Treatment of the double transgenic mice with both genotoxic agents such as diethylnitrosamine and IQ as well as the tumor promoter phenobarbital greatly accelerated the neoplastic process. These results suggest that selective transgenic mouse models may provide important tools for testing both the carcinogenic potential of environmental chemicals and the interaction/cooperation of these compounds with specific genes during the neoplastic process.

Characterisation of the toxic metabolite(s) of naphthalene

The toxicity of naphthalene and its metabolites has been investigated in vitro. Both naphthalene and its metabolite 1-naphthol were bioactivated by human hepatic microsomes to metabolite(s) which were toxic to mononuclear leucocytes (MNL). However 1-naphthol was more cytotoxic than naphthalene (49.8 +/- 13.9% vs. 19.0 +/- 10.0% cell death; P < 0.01), indicating that the toxicity of naphthalene is dependent on the bioactivation of 1-naphthol. CYP2E1-induced rat liver microsomes increased metabolism of naphthalene by 13% compared to control microsomes with a concomitant increase in both 1-naphthol and dihydrodiol formation. The cytotoxicity of naphthalene but not of 1-naphthol was increased by CYP2E1 induction, indicating that separate enzymes are involved in the bioactivation of 1-naphthol. The metabolites of 1-naphthol, 1,2-naphthoquinone (51.4 +/- 6.6% cell death) and 1,4-naphthoquinone (49.1 +/- 3.4% cell death) were directly toxic to MNL and depleted glutathione to 1.0% of the control levels. Both quinones were also genotoxic to human lymphocytes. In contrast, the primary metabolite of naphthalene, the 1,2-epoxide (0-100 microM) was neither cytotoxic nor genotoxic, and did not deplete glutathione. In conclusion, our data suggests that the cytotoxicity and genotoxicity of naphthalene is associated with the formation of quinones from 1-naphthol rather than naphthalene-1,2-epoxide.

In vivo mutagenicity and DNA adduct levels of heterocyclic amines in Muta mice and c-myc/lacZ double transgenic mice

The cooked meat derived heterocyclic amines (HCAs) 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), and 2-amino-9H-pyrido[2,3-b]indole (A alpha C) are established mutagens in the Salmonella assay and hepatocarcinogens in mice. The current study uses transgenic mice to examine hepatic HCA-DNA adduct formation and mutagenesis in vivo and the impact of hepatic overexpression of the c-myc oncogene on HCA-induced mutagenesis. C57B1/lacZ and c-myc/lacZ mice strains, produced by crossbreeding Muta Mice (carrying the lacZ mutation target gene) with either C57B1 control or c-myc transgenic mice, respectively, were treated with 10 daily doses of IQ, MelQx or A alpha C (20 micrograms/g, p.o.). Four weeks after dosing, the frequency of mutations in the lacZ gene in liver of either C57B1/lacZ or c-myc/lacZ mice was significantly higher in mice treated with any one of the three HCAs than in mice given vehicle only. In addition, all three HCAs formed hepatic DNA adducts, as measured by the 32P-postlabeling analysis 24 h after dosing. In both strains of mice, hepatic DNA adduct levels were 2-3-fold higher with A alpha C than with either IQ or MeIQx, although the mutant frequencies in the lacZ gene were 30-40% lower in mice dosed with A alpha C. These results suggest that A alpha C-DNA adducts may be less mutagenic in vivo than either IQ- or MeIQx-DNA adducts. The lacZ mutant frequencies observed with all three HCAs appeared to be influenced by c-myc transgene expression: after HCA treatment, transgenic mice carrying the c-myc gene showed a 30-40% higher lacZ mutant frequency than mice not carrying this transgene. Notably, lacZ mutant frequencies were not different among C57B1/lacZ and c-myc/lacZ mice that received vehicle control. DNA adduct studies showed that the levels of IQ- and MeIQx-DNA adducts were 2-3-fold higher in c-myc/lacZ mice than in C57B1/lacZ mice; however, A alpha C DNA adducts were not statistically different between the two strains. In addition, phase 1 metabolic activation of these HCAs, as assessed by hepatic microsomal mutagenic activation, was also similar in both strains of mice. These results support the notion that overexpression of the c-myc oncogene cooperates with the HCAs to enhance in vivo mutagenicity. Further studies are needed to assess the mechanisms of this cooperative effect.

N-acetyltransferase expression and metabolic activation of the food-derived heterocyclic amines in the human mammary gland

The heterocyclic amines (HCAs) found in cooked meat are procarcinogens that are metabolically activated by N-hydroxylation followed by O-acetylation by the N-acetyltransferases NAT1 and NAT2. Despite the importance of metabolic activation in HCA carcinogenicity and the finding that several HCAs are rodent mammary gland carcinogens, nothing was known about O-acetylation activity in the human mammary gland. The current study examines the expression and catalytic activity of NAT toward the N-hydroxy-HCAs 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-hydroxy-PhIP) and 2-hydroxy-amino-3-methylimidazo[4,5-f]quinoline (N-hydroxy-IQ) in the human mammary gland. Mammary gland cytosol from 10 women and lysates from a primary culture of human mammary epithelial cells metabolically activated 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine and 2-hydroxyamino-3-methylimidazo[4,5-f]quinoline by NAT-mediated 0-acetyltransferase, as measured by the acetyl CoA-enhanced binding of the N-hydroxylamines to calf thymus DNA in vitro. N-acetylation of p-aminosalicylic, an activity specific to NAT1, but not N-acetylation of sulfamethazine, an activity specific to NAT2, was detected in the mammary gland cytosols and human mammary epithelial cell lysates. Immunohistochemical analysis of human mammary gland sections showed positive staining for NAT1 protein in the epithelial cells lining the mammary gland ducts. Reverse transcription-PCR analysis showed that mRNA transcripts for both NAT1 and NAT2 were present in human mammary gland; however, no NAT2 catalytic activity was detectable. Our data demonstrate for the first time that the human mammary gland is catalytically active toward the metabolic activation of HCA food mutagens, and that this activity is most likely contributed by NAT1 expressed in the ductular epithelial cells of the mammary gland.

Liver tumorigenesis by Helicobacter hepaticus: considerations of mechanism

A new animal model for the causation of liver tumors via a bacterial infection presented itself fortuitously in the form of a new species, Helicobacter hepaticus. This species of Helicobacter colonizes the hepatic bile canaliculi in susceptible strains of mice, resulting in hepatitis and hepatocellular and hepatocholangiolar adenomas and carcinomas. The mechanism by which this infection leads to cancer is unknown. Tests with Helicobacter hepaticus have revealed thus far that the bacteria do not secrete a mutagen which is capable of detection by the Ames Assay. Measurement of oxidatively damaged bases in the liver DNA of hepaticus infected mice have shown accumulation of 8-oxodeoxyguanosine with disease progression. Other promutagenic DNA lesions, 7-methylguanine and O6-methylguanine, indicative of nitrosation of endogenous amines by nitric oxide, were not detected. Analysis of carcinomas and adenomas taken from H. hepaticus infected A/JCr mice revealed no mutations in ras oncogenes or in exons 5-8 of the p53 gene. These preliminary results indicate that a non-genotoxic tumor promotion mechanism, possibly implemented by reactive oxygen species from the immune response, is more likely than a genotoxic mechanism.

Ahr locus phenotype in congenic mice influences hepatic and pulmonary DNA adduct levels of 2-amino-3-methylimidazo[4,5-f]quinoline in the absence of cytochrome P450 induction

The potent food mutagen/carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) undergoes metabolic N-hydroxylation by cytochromes P450, including cytochrome P450 1A2, followed by generation of an unstable ester catalyzed by acetyltransferases; promutagenic DNA adducts result. Genetic polymorphisms in these enzymes have been implicated in human cancer risk related to arylamine exposure. We investigated the effects of Ahr locus and acetylator polymorphisms on 32P-postlabeled IQ/DNA adducts in lungs and livers of female C57BL/6 mice congenic for slow acetylation and/or Ahr-nonresponsiveness; some groups were pretreated with beta-naphthoflavone (beta NF), a cytochrome P450 1A inducer. Total adducts in lung were doubled by beta NF pretreatment in Ahr-responsive mice only and consisted of < or = 30% adduct 2 and < or = 60% adduct 3. In contrast, in Ahr-nonresponsive mice, adducts 2 and 3 were each < or= 7% of the total. Livers of noninduced Ahr-responsive mice formed 6-18-fold more adducts than those of nonresponsive mice. This striking difference was not due to altered levels of cyp1a-2, as indicated by specific enzyme assays and immunoblotting, and was not accompanied by a comparable increase in the ability of liver preparations to activate IQ to a mutagen in the Ames test. Pretreatment of responsive mice with beta NF to induce cyp1a-1 and cyp1a-2 led to a reduction in liver adduct levels. Acetylation phenotype also had a significant effect in Ahr-responsive mice, with 3-fold more adducts in slow than in rapid acetylators. These results indicate that in uninduced mice, the normal Ah receptor facilitates formation of IQ/DNA adducts in liver and alters the profile of adducts in lung, via an unknown mechanism, whereas the Ah receptor-dependent enzyme induction reduces adducts in liver, probably due to increased detoxification, but increases them in lung.

Protection by chlorophyllin and indole-3-carbinol against 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-induced DNA adducts and colonic aberrant crypts in the F344 rat

The most abundant heterocyclic amine in fried ground beef, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), induces colon carcinomas in the male F344 rat. The potential chemopreventive effects of two compounds, namely, the 'interceptor molecule' chlorophyllin (CHL) and a modulator of carcinogen activation, indole-3-carbinol (I3C), were examined in a PhIP colon carcinogenesis model. During weeks 3 and 4 of a 16-week study, F344 rats were given PhIP by oral gavage (50 mg/kg body weight, alternating days). Inhibitors were given either before and during PhIP exposure, after PhIP treatment, or continuously for 16 weeks. Treatment of rats with 0.1% CHL in the drinking water inhibited the formation of aberrant crypt foci (ACF) with > or = 4 crypts/focus, from 1.4 +/- 0.9 in controls to 0.7 +/- 0.3 following post-initiation CHL treatment, and to 0.3 +/- 0.5 in rats given CHL continuously for 16 weeks (mean +/- SD; P < 0.05). Potent inhibition of PhIP-induced ACF occurred following initiation, post-initiation and continuous exposure to 0.1% I3C in the diet. Using the initiation protocol, I3C completely inhibited the induction of the ACF with > or = 4 crypts/focus. In a separate experiment, rats were given 0.1% CHL in the drinking water or 0.1% I3C in the diet for 4 weeks. At the end of week 3, animals received 50 mg PhIP/kg body weight by single oral gavage and PhIP-DNA adducts were quantified in the colon and several other tissues by 32P-postlabeling analysis. In addition, the urine and feces were collected to study the effects of inhibitor treatment on PhIP metabolism and excretion. No significant protection against PhIP-DNA adduct formation was detected in the colon after CHL dosing, nor was a consistent pattern of CHL inhibition observed in several other tissues. In contrast, I3C shifted the time-course of adducts in all tissue; compared with controls, adducts were increased by I3C at 6 h but decreased at 24 h and 7 days following PhIP treatment. Analysis of urine metabolites revealed that I3C and CHL decreased the excretion of unmetabolized PhIP and 4'-hydroxy- << PhIP but increased the phase II detoxification products PhIP-4'-O-glucuronide and PhIP-4'- sulfate. In the feces, the elimination of unmetabolized PhIP was increased from 54.5% in controls to approximately 67% in CHL-treated rats and decreased to 28% in rats given I3C (P < 0.05). These results support a protective role for CHL and I3C against PhIP-induced colon carcinogenesis through mechanisms which alter the uptake or metabolism of the carcinogen, and by suppression in the post-initiation phase.

Analysis of EGFR, TGF-alpha, neu and c-myc in 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine-induced mammary tumors using RT-PCR

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), a mutagen found in cooked meat, has been shown to induce mammary gland tumors in rats. Our laboratory recently observed that a high fat diet enhances the incidence and severity of PhIP-induced mammary gland cancer in rats. In the current study, reverse transcription followed by polymerase chain reaction amplification was used to determine whether EGFR, TGF-alpha, neu and c-myc are differentially expressed in PhIP-induced mammary gland tumors classified histologically as benign or malignant and to evaluate whether dietary fat intake influences the expression of these genes. Of 23 total PhIP-induced mammary tumors examined, 43%, 57% and 74% had increased expression of EGFR, TGF-alpha and neu mRNA respectively. Increased expression of these genes appeared to be consistently present in tumors displaying papillomatosis. In contrast, to the other three genes, c-myc mRNA levels were infrequently elevated. The percentage of dietary fat did not appear to influence the expression of EGFR, TGF-alpha or neu in either tumors or mammary gland from control rats. However, the levels of c-myc mRNA were 1.8- and 2.9-fold higher in the control mammary gland and benign PhIP-induced tumors respectively in rats fed the high-fat diet than in rats fed the low-fat diet, suggesting a slight effect of dietary fat (P < 0.08) on c-myc expression. These results suggest that increased expression of EGFR, TGF-alpha and especially neu is associated with PhIP-induced mammary gland cancer in rats.

Possible mechanisms for PhIP-DNA adduct formation in the mammary gland of female Sprague-Dawley rats

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), the most abundant heterocyclic amine in fried beef, is mammary gland carcinogen in rats. Using the 32P-postlabeling method, PhIP-DNA adduct levels were measured in mammary epithelial cells isolated from female Sprague-Dawley rats given 10 daily doses of PhIP (75 mg/kg, p.o.) according to a protocol previously shown to induce mammary gland cancer. At 24 h, 48 h, 1 week and 5 weeks after the last dose of PhIP, PhIP-DNA adduct levels [relative adduct labeling (RAL) x 10(7), mean +/- SD] were 10.2 +/- 0.7, 7.9 +/- 2.7, 2.2 +/- 0.6 and 0.9 +/- 0.03 respectively. When isolated rat mammary epithelial cells (from untreated rats) were incubated in vitro with N-hydroxy-PhIP (45 microM, 1 h, 37 degrees C), PhIP-DNA adducts were detected in cell DNA (RAL = approximately 97 x 10(7); however, no adducts were detected in cells incubated with PhIP (200 microM, 15 h, 37 degrees C). Incubating cells with pentachlorophenol, an inhibitor of acetyltransferase, or incubating cells at 0-4 degrees C, reduced N-hydroxy-PhIP adduct levels by 45 and 75% respectively, indicating that formation of N-hydroxy-PhIP adducts was largely due to metabolic activation. Further studies showed that rat mammary gland microsomes had little capacity to N-hydroxylate PhIP, as assayed by the mutagenic activation of PhIP in the Ames Salmonella assay. In contrast, N-hydroxy-PhIP was metabolically activated by cytosol-catalyzed PhIP-DNA adduct formation to calf thymus DNA incubated in vitro with N-hydroxy-PhIP (2 microM) in the presence of acetyl CoA. Notably, mammary cytosolic O-acetyltransferase activation of N-hydroxy-IQ or N-hydroxy-MeIQx. All three N-hydroxylamines were activated via cytosolic proline aminoacyl-tRNA synthetase and phosphorylase, although the activities of these enzymes were approximately 100-fold lower than O-acetyltransferase. No mammary cytosolic sulfotransferase activation could be detected with any of the N-hydroxylamines. Our results are consistent with the notion that PhIP-DNA adduct formation and initiation of carcinogenesis in the rat mammary gland may be associated with N-hydroxylation of PhIP outside the mammary gland, transport of the N-hydroxylamine to the mammary gland and subsequent in situ O-acetyltransferase-catalyzed activation of N-hydroxy-PhIP.

Kinetic parameters of lymphocyte microsomal epoxide hydrolase in carbamazepine hypersensitive patients. Assessment by radiometric HPLC

Idiosyncratic hypersensitivity reactions with carbamazepine have been postulated to be due to a deficiency of microsomal epoxide hydrolase (HYL1), although this is based on indirect evidence. Using 3H-cis stilbene oxide (0.5 Ci/mmol) as a substrate, we have developed a radiometric HPLC assay sensitive enough to measure the kinetic parameters of HYL1 in lymphocytes. The intra-assay coefficient of variation was 8%. Enzyme activity has been measured in lymphocytes from six carbamazepine hypersensitive patients, six patients on carbamazepine without any adverse effects, and twelve drug-naive healthy volunteers. No significant difference was observed in three kinetic parameters of the enzyme among these three groups. The values for Km, Vmax, and intrinsic clearance ranged from 6.1-89.9 microM, 3.0-23.2 pmoles diol formed/min/mg protein, and 0.147-0.493 microliter/min/mg protein. There was no difference in enzyme activity between patients currently on carbamazepine and healthy volunteers, indicating a lack of induction of lymphocyte HYL1 by carbamazepine. Co-incubation of lymphocytes with 1,1,1-trichloropropene oxide, an inhibitor of hepatic HYL1, resulted in an 82% inhibition of activity, similar to that observed with the hepatic enzyme. The healthy volunteers were genotyped as being either GSTM1 positive (n = 6) or GSTM1 negative (n = 6). This did not affect the kinetic parameters of lymphocyte microsomal epoxide hydrolase. Our results suggest that there is normal HYL1 activity in lymphocytes of hypersensitive patients using cis-stilbene oxide as a substrate.

Protective effect of N-acetylcysteine against heterocyclic amine-induced cardiotoxicity in cultured myocytes and in rats

Cooked meat contains many mutagenic/carcinogenic heterocyclic amines (HAs), including 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). The reactive N-hydroxylamine metabolites N-hydroxy-IQ and N-hydroxy-PhIP are toxic to isolated rat cardiomyocytes. This study examined whether antioxidant agents protect against N-hydroxylamine-induced cardiotoxicity. In isolated rat cardiomyocytes, N-acetylcysteine, alpha-tocopherol and glutathione were protective against N-hydroxylamine-mediated lactate dehydrogenase release into the medium, suggesting that a free radical mechanism may be partly involved in HA-induced cardiotoxicity. Since N-acetylcysteine was by far the most protective of the agents investigated, the effects of N-acetylcysteine on HA-induced ultrastructural damage were further examined both in vitro and in vivo. Isolated cardiomyocytes treated with 1.2 mM N-acetylcysteine before and during exposure to N-hydroxy-IQ or N-hydroxy-PhIP showed a smaller percentage of ultrastructural abnormalities, such as myofilament loss, sarcoplasmic reticulum swelling and abnormal mitochondria. N-Acetylcysteine pretreatment also significantly reduced the percentage of cardiac cells with T-tubule dilation and myelin figures in adult rats dosed with IQ. The protective effect of N-acetylcysteine was not associated with a reduction in HA-DNA adducts, as assessed by 32P-postlabelling analysis of DNA from isolated cardiomyocytes treated with N-hydroxylamines. DNA adduct formation per se, therefore, may not be associated with the observed cardiotoxic effects of the HAs. Further studies are required to confirm the involvement of a free radical mechanism in HA cardiotoxicity.

Metabolism of the food-derived carcinogen 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) in nonhuman primates

The metabolism and disposition of the food mutagen and rodent carcinogen 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline was investigated in cynomolgus monkeys. Monkeys were administered a single dose of radiolabeled [14C]MeIQx (2.2 or 50 mumol/kg). Peak blood levels of radioactivity were observed within 1-3 h after dosing and declined rapidly thereafter. By 72 h after dosing, approximately 50% and 70% of the 2.2 mumol/kg, and 50 mumol/kg dose, respectively, was excreted in the urine. Approximately 15-20% of either dose was recovered in the feces. Eight metabolites and the parent compound were detected in urine by HPLC. The parent compound accounted for approximately 15-25% of the dose excreted in the urine. Seven MeIQx urinary metabolites were identified. Five metabolites were identical to MeIQx metabolites previously found in rats: MeIQx-N2-glucuronide, MeIQx-N2-sulfamate, MeIQx-5-sulfate, MeIQx-5-O-glucuronide, and 8-CH2OH-MeIQx-5-sulfate. Cynomolgus monkeys, however, metabolized MeIQx to a novel glucuronide conjugate of MeIQx not found in rats. Based upon mass spectroscopy and proton NMR analyses, the structure of this metabolite was consistent with an N1-glucuronide of MeIQx. This metabolite was the major urinary metabolite found in monkeys, accounting for 31-37% of the dose excreted in the urine over a 24 h period. One additional metabolite identified in urine and feces of MeIQx treated cynomolgus monkeys, that has not been found previously in any other animal model, was 7-oxo-MeIQx, a likely enteric bacterial metabolite of MeIQx. 7-Oxo-MeIQx accounted for 20-25% of the dose of MeIQx found in the urine and was the major fecal metabolite. The N2-glucuronide conjugate of the carcinogenic metabolite 2-hydroxyamino-3,8-dimethylimidazo[4,5-f]quinoxaline (NHOH-MeIQx) was not detected in urine or bile of monkeys, even after 10 daily doses of MeIQx (100 mumol/kg) were given. The results indicate that MeIQx is metabolically processed in monkeys via multiple pathways of detoxification. However, MeIQx is poorly metabolically activated via cytochrome P450 mediated N-oxidation. The in vivo metabolism of MeIQx in cynomolgus monkeys is different from that of the structurally related food-derived mutagen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), which is readily metabolically activated by this species and in contrast to MeIQx, has been shown to be a powerful hepatic carcinogen.

Tissue manganese concentrations and antioxidant enzyme activities in rats given total parenteral nutrition with and without supplemental manganese

BACKGROUND

Manganese is an essential but potentially toxic mineral. Parenteral administration of manganese via total parenteral nutrition (TPN) bypasses homeostatic mechanisms (intestinal absorption and presystemic hepatic elimination). Our objective in this study was to determine the effect of supplemental manganese in TPN solutions on manganese status in a rat model.

METHODS

Male Sprague-Dawley rats underwent jugular catheterization and were given 61.0 +/- 0.4 g/d TPN solution providing 0.5 +/- 0.2 nmol manganese/g (Mn-; n = 6) or 16 +/- 3 nmol manganese/g (Mn+; n = 7) for 7 days. Reference rats (RF; n = 8) were fed a purified diet containing 1.3 mmol manganese/g.

RESULTS

Liver manganese decreased in both TPN groups, but tibia, spleen, and pancreas manganese concentrations were greater in Mn+ rats than in Mn- or RF rats. Although no treatment differences were seen in heart or liver manganese superoxide dismutase activity, heart copper-zinc superoxide dismutase activity was lower in the Mn+ rats than in Mn- or RF rats (p < .05). Glutathione peroxidase activity was depressed in livers of both Mn- and Mn+ rats relative to RF rats (p < .0001), which was not due to selenium deficiency.

CONCLUSIONS

Supplemental parenteral manganese is taken up to a greater extent by peripheral tissues than the liver. In this first report of antioxidant enzyme activities in animals maintained with TPN, we found that TPN as well as supplemental manganese can influence antioxidant enzyme activities. We conclude that it is generally unnecessary and potentially toxic to supplement TPN solutions with manganese during short-term usage.