4-Chloromethylbiphenyl (4CMB): a novel mutagen and potential carcinogen

The bacterial mutagenicity and cell transforming propertiesof the monocyclic alkylating agent benzyl chloride have beencompared with those of its biphenyl analogue, 4-chloromethylbiphenyl(4CMB), and it is apparent that the addition of the second benzenering greatly enhances biological activity. The possible reasonsfor this enhancement are discussed in relation to similar effectsobserved when comparing the activities of aniline with its biphenylanalogue, 4-aminobiphenyl (4AB). The marked activity observedfor 4CMB, a stable and crystalline solid, suggests that it couldprove useful as a direct-acting positive control test chemicalfor use in short-term mutagenicity tests.     

Identification of aprt gene mutations induced in repair-deficient and P450-expressing CHO cells by the food-related mutagen/carcinogen, PhIP

We investigated the specific sequence changes produced by thedietary mutagen 2-amino-l-methyl-6-phenylimidazo-[4,5-b]pyridine(PhIP) in UV5P3 cells [a Chinese hamster ovary (CHO) cell line].Sequence analysis of the PhIP induced mutations in the adeninephosphoribosyltransferase (aprt) gene, which is heterozygousin the UV5P3 cells, can provide insight into the mutagenic mechanismin these repair-deficient cells expressing P4501A2. Two allelespecific 20 mer oligonucleotide primer pairs were used in thepolymerase chain reaction and the allele of interest was amplified.Single-base transversions occurred in 31/32 PhIP-induced mutants;of these, 6 were A·T     

Effects of dietary fats and butylated hydroxytoluene on mutagen activation in rats

The effects of hydrogenated fats and butylated hydroxytoluene (BHT) in the diets of rats on the hepatic activation of benzo(a)pyrene, 2-acetylaminofluorene (AAF), and 2-aminofluorene by liver homogenates (S-9 fraction) were evaluated. The Salmonella/microsomal mutagenicity assay (Strain TA 98) was utilized to determine the mutagenic potential of the activated compounds. The S-9 fraction was obtained from animals fed a 15% fat diet consisting of hydrogenated fats (43% trans-fatty acids) or unsaturated fats (0% trans-fatty acids). BHT was administered orally (0.5%) 6 days prior to sacrifice in both groups. The incorporation of BHT in the diet of rats enhanced the mutagenic potential of AAF and 2-aminofluorene but not of benzo(a)pyrene. This effect was independent of the lipid composition of the diet. The most significant increment in the production of mutagenic metabolites was observed with AAF when BHT and hydrogenated fats were included in the diet of rats. Dietary hydrogenated fats appeared to potentiate the effects of BHT on AAF mutagenicity. Further studies to elucidate the mechanisms by which BHT and hydrogenated fats enhance AAF mutagenicity are warranted.     

化学合成P6对小鼠正常淋巴细胞损伤作用及其机制的观察

目的:在证实化学合成2'-氧-甲基鸟嘌呤核苷(P6)具有抑制肿瘤细胞增殖及诱导肿瘤细胞凋亡作用的基础上,观察其对正常免疫细胞的损伤作用.方法:Balb/c小鼠断颈处死后.制备脾脏T淋巴细胞并分为对照组、50μtg/mL P6组、100μtg/mL P6组及150 μg/mL P6组.采用细胞形态学观察、MTT实验、流式细胞术等方法检测P6对细胞的增殖抑制作用;流式细胞术、RT-PCR技术检测P6对细胞的凋亡诱导作用.结果:形态学观察表明,P6作用72 h后,小鼠淋巴细胞的活化程度和密度随P6浓度的增高逐渐降低;MTT检测表明,与空白对照组相比,P6各浓度组均可抑制活化小鼠淋巴细胞的增殖(P<0.05),该抑制作用具有剂量依赖性;流式细胞术检测细胞周期发现,与空白对照组相比,P6各浓度组G1、G2期细胞减少,S、sub-G1期(凋亡峰)细胞增多(P<0.05),呈剂量依赖性.表明P6可抑制淋巴细胞增殖,使其阻滞于细胞周期中的S期,并促进其凋亡.RT-PCR法检测淋巴细胞促凋亡基因Bax和抗凋亡基因Bc1-2的表达发现,P6可促进Bax mRNA的表达,并抑制Bc1-2 mR-NA的表达.结论:化学合成P6除抑制肿瘤细胞增殖并诱导其凋亡以外,同样具有抑制正常免疫细胞增殖及促进凋亡的作用.P6作为新的抗肿瘤药其药效及毒副反应尚需进一步研究.     

Effects of temperature and time on mutagen formation in pan-fried hamburger.

Mutagenic activity generated in hamburger during pan-frying is dependent upon both temperature and time, with temperature appearing to be the more important variable. Uniformly prepared frozen hamburger pattie (115 g; 19% fat) were fried under carefully controlled conditions at 143 degrees C, 191 degrees C and 210 degrees C. Mutagenic activity assayed with the Ames test was not detected in uncooked hamburger, and in hamburger fried at 143 degrees C mutagenic activity remained low at all times studied (4--20 min). In contrast, frying at 191 degrees C or 210 degrees C for up to 10 min resulted in the generation of considerably higher levels of mutagenic activity. Mutagenic activity in fried hamburgers sold at selected restaurants ranged from very low to moderately high. Evidence is also presented for mutagenic inhibitory activity in uncooked and fried hamburger. Mutagenic inhibitory activity decreased mutagenesis mediated by liver S-9 from normal rats but not from Aroclor 1254-treated rats.     

Effects of carcinogen dosage on experimental colonic carcinogenesis by azoxymethane: an ultrastructural study of grossly normal colonic mucosa

The transmission electron microscopic features of grossly normal colonic mucosa in the azoxymethane [(AOM) CAS: 25843-45-2]-treated rat model of colonic carcinogenesis were studied by the method of concomitant variation. Ten-week-old male F344 rats were given 10 weekly sc injections of AOM at doses of 3, 7, or 14 mg/kg body weight and were killed 1 week or 15 weeks after the last AOM dose. Grossly normal distal left colon was examined using transmission electron microscopy. Three transient dose-dependent features of colonic epithelial cells were identified: a) mitochondrial injury, b) nuclear pleomorphism and loss of polarity, and c) increased numbers of mitotic figures in the lower third of the crypts. Because these dose-dependent features were present only shortly after AOM administration, they appeared to be manifestations of carcinogen toxicity and associated reactive, regenerative epithelial changes. By contrast, four persistent dose-dependent features were identified: a) increased numbers of epithelial cells with enlarged nucleoli, b) increased numbers of mitotic figures in the middle third of crypts, c) reduced numbers of goblet cells, and d) reduced numbers of apical cytoplasmic vacuoles in the upper third of the crypts. Because these features persisted in a dose-dependent manner for many weeks after the last dose of AOM and were present after the latent period to tumor formation, they appear to be morphologic precursors to colonic carcinogenesis in the model.     

Effects of astragali radix extract on carcinogenesis, cytokine production, and cytotoxicity in mice treated with a carcinogen, N-butyl-N'-butanolnitrosoamine

We studied the effects of astragali radix extract, a Chinese herb and one of eight components in Shikaron, on carcinogenesis, natural killer (NK) cell activity, and the cytokine production of lymphocytes in mice treated with a carcinogen, N-butyl-N'-butanolnitrosoamine (BBN). We found a significantly lower incidence of urinary bladder carcinoma in mice treated with BBN plus 10 mg/kg/day or more of Astragalus extract (7, 2, and 3 mice among 15 mice in 10, 20, and 40 mg/kg/day group, respectively, vs. 14 of 15 mice treated with BBN alone). Astragalus extract prevented the cytotoxic activity of lymphocytes against YAC-1 cells from the depression by BBN. It also protected the production of interleukin-2 and gamma-interferon of lymphocytes from the depression by BBN. These results, including our previous findings, suggest that the Astragalus extract exerts an anticarcinogenic effect in carcinogen-treated mice through activation of cytotoxic activity and the production of cytokines.     

Arrest and retention of multilamellar liposomes in the brain of normal mice or mice bearing experimental brain metastases

The blood-brain barrier presents a major obstacle to the systemic treatment of malignant brain tumors and brain metastases. We investigated whether the direct injection of liposomes into the internal carotid artery of normal mice or mice with experimental brain-melanoma metastases could allow delivery of anticancer drugs across this barrier. Liposomes of different sizes (greater than 5 microns, less than 1 micron, 40-80 nm) and lipid compositions were injected i.v. or into the internal carotid artery. The retention of liposomes in the brain of normal C3H/HeN mice was similar to that observed in mice with experimental brain cancer metastasis. The highest accumulation of liposomes in the brain occurred with large multilamellar vesicles, which also produced severe toxicity presumably due to embolism. Smaller liposomes were not toxic but did not accumulate in the brain. Liposomes injected i.v. did not accumulate in the brain, either. Thus, neither i.v. nor intracarotid administration of liposomes produce results suitable for therapy of brain tumors/metastases.     

Binding of the food mutagen PhIP in pigmented tissues of mice.

The distribution of the 14C-labelled food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in the tissues of C57B1/6 and NMRI mice was studied. The results showed a high and selective binding of radioactivity in the pigment epithelium of the eye and in the fur following a single dose (0.3-4 mg/kg) of [14C]PhIP in the pigmented C57B1/6 mice whereas no such localization of radioactivity was present in the albino NMRI mice. A low but selective covalent binding of radioactivity was observed in the liver, inner cortex of the kidney and in the tracheal mucosa of [14C]PhIP-injected mice. PhIP was firmly bound to synthetic melanin pigment in vitro; only 3% was released by extraction with a phosphate buffer (pH 7) whereas 72% was released by extraction by methanol:conc. NH3 (15:1). Three hours to 7 days following a single injection of [14C]PhIP in C57B1/6 mice the radioactivity in the eye was 3- to 6-fold higher than that in the liver or kidney. Almost 60% of the radioactive material present in the pigmented epithelium of the eye 3 and 24 h following injection could be extracted by basic methanol and identified as unchanged PhIP. The residual radioactivity in the pigmented epithelium of the eyes may represent a covalent binding of [14C]PhIP metabolites to cellular constituents or to a basic methanol-resistant binding of [14C]PhIP to melanin. The results indicate that pigmented tissues may be potential target tissues for the toxic effects of PhIP and suggest that the use of hair for biological monitoring of PhIP should be examined.     

Metabolism of the food-derived mutagen/carcinogen 2-amino-1-methyl-6-phenylimidazo[4, 5-b]pyridine (PhIP) in nonhuman primates

Metabolism of the food-derived heterocyclic amine mutagen/carcinogen2-amino-1-methy1–6-phenylimidazo[4, 5-b]pyridine (PhIP)was examined in cynomolgus monkeys. [3H]PhiP (50µmol/kg,p.o.) was extensively metabolized, with only 1% of the doseexcreted into the urine as parent compound. Four metaboliteswere isolated by HPLC and identified: PhIP-4–0-glucuronide,PhIP-4‘-sulfate, 4’-hydroxy-PhIP and a glucur-onideconjugate of N-hydroxy-PhIP. All four metabolites were detectedin urine, bile and plasma of monkeys. 4‘-Hydroxy-PhIPand PhIP were found in feces. The major PhIP metabolite in urine,bile and plasma was PhIP-4’-sulfate. Inurine this metaboliteconstituted -64–72% of the radioactivity excreted. Theclearance of PhIP and PhIP metabolites from plasma was rapid,with the largest elimination occurring within 8 h. Administrationof nine consecutive daily doses of unlabeled PhIP (50 µmol/kg,p.o.) prior to administration of [3H]PhIP (50 µmol/kg,p.o.) did not alter the plasma clearance of radiolabeled PhIPor PhIP metabolites, suggesting that this multiple-dose regimendid not induce or alter PhIP metabolism. PhIP formed DNA adductsin white blood cells, as determined by the 32P-postlabelingmethod. The levels of PhIP-DNA adducts in blood appeared topeak 3 h after administering a single dose of PhIP (50µmol/kg,p.o.) and were still detected 1 week after dosing. The presenceof the glucuronide conjugate of N-hydroxy-PhIP in urine, bileand plasma, and the presence of PhIP-DNA adducts in white bloodcells indicate that PhIP undergoes metabolic activation viaN-hydroxylation in cynomolgus monkeys. The results suggest thatPhIP is activated in vivo to genotoxic metabolites in nonhumanprimates and thus is a potential carcinogen in this species.     

The fractionation of isolated liver cells from normal and carcinogen treated rats.

Suspensions of isolated cells were obtained from livers of normal rats and rats treated with the hepatocarcinogen N,N-dimethyl-4-aminoazobenzene. Differential centrifugation of dispersed cells yielded a large parenchymal cell fraction and a small non-parencymal cell fraction. By means of rate sedimentation through different concnetrations of Ficoll, parenchymal cells were separated into cells with fast, intermediate and slow rates of sedimentation. Periods of sedimentation were brief and centrifugal forces low in order to retain the best possible state of preservation of cells. DNA, RNA and protein contents, acid phosphatase activity, cell size and nucleocytoplasmic ratios of parenchymal cells sedimenting at fast, intermediate and slow rates were measured. Cell fractions from normal livers had properties suggesting that faster sedimenting cells were derived from the centre and middle of the lobule whereas slowly sedimenting cells were periportal; however, much of the periportal cell population remained in a residue of undissociated tissue. Compared with normal cells, carcinogen treated cells appeared to fractionate according to different physical and chemical criteria and could not be related to their origin within the liver lobule. They were smaller, slower sedimenting, lower in protein and RNA content and acid phosphatase activity. The tissue residue contained abnromal histological structures.     

Effects of high-fat diet and/or body weight on mammary tumor leptin and apoptosis signaling pathways in MMTV-TGF-α mice

Introduction  

Obesity is a risk factor for postmenopausal breast cancer and is associated with shortened mammary tumor (MT) latency in MMTV-TGF-α mice with dietary-induced obesity. One link between obesity and breast cancer is the adipokine, leptin. Here, the focus is on diet-induced obesity and MT and mammary fat pad (MFP) leptin and apoptotic signaling proteins.