Search PubMed⌕ Search

Biomedical subjects

J A Milner

Publications and source records attributed to J A Milner.

At least 73 records · Page 4Linked to original sources
PubMed1991

Inhibition of 7,12-dimethylbenz(a)anthracene-induced mammary tumors and DNA adducts by dietary selenite.

The present studies were designed to examine the influence of dietary selenite supplementation on the initiation phase of 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary carcinogenesis and to correlate selenite-induced changes in the binding of DMBA metabolites to rat mammary cell DNA with the ultimate tumor incidence. Diets formulated to contain selenium, as sodium selenite at 0.1, 0.5, 1, 2, or 4 micrograms/g were fed for 2 weeks prior to and 2 weeks following treatment with DMBA (5 mg/kg body weight). Food intake and weight gain did not differ among treatments. Tumor incidence correlated inversely to the quantity of selenium consumed (r = -0.99). Final tumor incidences were 52, 32, 24, 14, and 10% for rats fed 0.1, 0.5, 1, and 4 micrograms selenium/g, respectively. In a separate group of rats fed a diet containing 4 micrograms selenium/g during both the initiation and promotion stages the final tumor incidence was 4.8%. Selenite supplementation for 2 weeks markedly depressed the occurrence of individual and total DMBA-DNA adducts. The final mammary tumor incidence correlated positively with total DMBA-DNA adducts (r = 0.99). These studies clearly demonstrate that selenite can inhibit the initiation stage of mammary carcinogenesis. This reduction in tumor incidence is likely due to a reduction in carcinogen metabolism and ultimately adduct formation.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1991

Influence of supplemental glutathione on selenite-mediated growth inhibition of canine mammary cells.

Present studies show the in vitro addition of glutathione (GSH) can significantly alter selenite induced growth inhibition of mammary tumor cell line 13 (CMT-13). Preincubation with 100 microM GSH for 24 h partially prevented the growth inhibition caused by 12.6 microM selenite. Pre-incubation with 100 microM GSH for 48 h completely prevented the growth inhibition caused by 12.6 microM selenite. In marked contrast, simultaneous addition of GSH and selenite dramatically increased the severity of selenite-mediated growth inhibition and resulted in cell death. Exposure to selenite (12.6 microM) increased intracellular GSH throughout the 3 day incubation period. Addition of GSH to the medium also led to an approximate 25% increase in intracellular GSH that persisted for 72 h. Cellular retention of selenium following selenite supplementation was decreased up to 70% by GSH preincubation yet increased markedly (greater than or equal to 240%) by the simultaneous addition of GSH and selenite. The rate of selenite uptake was not consistently altered by GSH pretreatment. However, the simultaneous addition of GSH and selenite resulted in a dramatically increased rate of selenium uptake. These data indicate that extracellular GSH can alter the toxicity of supplemental selenite. The protective effect of GSH pre-incubation against selenite toxicity appears to relate to altered selenium retention.

Animals↗
PubMed1991

The role of selenium nutrition in the development of neonatal rat lung.

Our study was designed to assess the role of selenium (Se) in development of neonatal lungs under conditions of normoxia and hyperoxia. Thirty-six female Sprague Dawley rats were bred and fed a Se-deficient (0.03 ppm Se) or a Se-adequate (0.5 ppm Se) diet during pregnancy and lactation. At d 2 postpartum, 24 litters were randomly assigned to either high oxygen (greater than 95%) or air and were cross-fostered for 4 d. Lung weight was significantly enhanced in Se-adequate pups and was not related to high oxygen or air exposure of either the pups or dams. Two types of histologic lesions were observed in the lungs of the pups: septal attenuation and interstitial inflammation. When reared in oxygen, all (17 of 17) Se-deficient pups had lesions. In contrast, only 60% (9 of 15) of Se-adequate pups were affected (p less than 0.01). Lung lesions also were more severe in Se-deficient pups. Se-deficient pups also displayed a significant degree of septal attenuation when reared in air. Se-dependent glutathione peroxidase activity in the pup lung was significantly elevated in response to hyperoxia and was unrelated to Se nutriture. No differences in activities of lung superoxide dismutase, catalase, and glutathione s-transferase were noted between Se-deficient and Se-adequate pups reared in air or high oxygen environments. These data indicate that Se has an important role in the development of neonatal lungs, a role that is even more pronounced during conditions of hyperoxia. The protective role of Se in developing lung tissue cannot be completely explained by enhanced glutathione peroxidase activity.

Animals↗
PubMed1990

Consequences of selenite supplementation on the growth and metabolism of cultures of canine mammary cells.

Previous studies with cultures of canine mammary cells revealed differences in the degree of growth inhibition caused by selenite supplementation, with canine mammary tumor cell line 13 > 11 >> non-neoplastic canine mammary cells. The present studies show this variation in growth retardation cannot be explained by selenium retention. Intracellular glutathione related inversely to the degree of growth inhibition resulting from the addition of selenite. Dimethyl selenide formation by S-9 preparations corresponded to the sensitivity of the culture to supplemental selenite. DL-buthionine-SR-sulfoximine, a specific inhibitor of glutathione biosynthesis, accentuated the growth inhibition and prevented the increase in intracellular glutathione caused by supplemental selenite. Treatment of canine mammary tumor cell line 13 cultures with DL-buthionine-SR-sulfoximine resulted in a persistent depletion of intracellular glutathione without affecting growth. Glutathione reductase activity, before and following selenite, was inversely related to the degree of growth inhibition, with canine mammary tumor cell line 13 > 11 > non-neoplastic canine mammary tumor cell line. Selenite addition increased the activity of gamma-glutamylcysteine synthetase in canine mammary tumor cell line 11 and non-neoplastic canine mammary cells, but not in canine mammary tumor cell line 13 cells. The present data suggest the differences in the growth inhibition caused by selenite among these mammary cells is related to glutathione regulation and ultimately to selenium detoxification.

Journal Article↗
PubMed1990

Trace minerals in the nutrition of children.

Trace elements perform important functions in growth and development. However, little information exists about their dietary requirements during the demanding period of infancy. Opportunities to add to knowledge of the physiologic significance and dietary adequacy of trace elements in human nutrition are provided by recent analytic advances. Specific, sensitive, and reliable methods for the detection of trace element imbalances are sorely needed. Although several factors influence the dietary needs of these essential elements, the basis for establishing dietary needs in infants is hindered by the death of studies that have assessed their bioavailability in this age group. Thus until it has been conclusively shown otherwise, the physiologic response to human milk is used as the standard for infant feeding practices. This review is limited primarily to the physiologic significance and bioavailability of zinc, copper, manganese, molybdenum, chromium, fluoride, and selenium. The space devoted to each trace element is not meant to represent the element's importance but, rather, to reflect some of the present understanding of its metabolism and utilization.

Biological Availability↗
PubMed1990

Milk selenium of rural African women: influence of maternal nutrition, parity, and length of lactation.

The selenium content of milk samples from rural Gambian women (n = 55) was evaluated as a function of parity, stage of lactation, and maternal nutrition. Samples were collected during periods of relative food abundance (dry season) and food scarcity (rainy season). Milk selenium was lower (p less than 0.01) in the rainy than in the dry season (208 vs 256 nmol/L, respectively). Milk selenium was similar in samples from women in early (1-6 mo postpartum) and late (13-19 mo postpartum) lactation. During late lactation, parity, which ranged from 1 to 11, was negatively correlated with milk selenium regardless of plane of maternal nutrition (p less than 0.02). Measures of protein, glutathione peroxidase, and total peroxidase were not affected by stage of lactation or parity. Glutathione peroxidase activity accounted for 38% of the peroxidase activity in milk. Results show that although length of lactation alone had little impact, milk selenium secretion was influenced by both maternal nutritional adequacy and parity of rural Gambian women.

Chromatography, Gas↗
PubMed1990

Identification and in vivo formation of 32P-postlabeled rat mammary DMBA-DNA adducts.

The in vivo formation of 32P-postlabeled mammary 7,12-dimethylbenz[a]anthracene (DMBA)-DNA adducts was evaluated for female Sprague-Dawley rats following administration of DMBA (i.g.) at 1, 3, 5, 10 and 20 mg/rat. Adduct formation was also measured as a function of time following DMBA intubation. At least eight adducts were formed in vivo in mammary epithelial cells. The identities of four of these nucleoside bisphosphate adduct spots were determined by cross-referencing with previously characterized 3H-labeled nucleoside DMBA adducts. These identified adducts constitute four of the five major adducts formed in vivo. Two adducts were identified as the anti-dihydrodiolepoxide of DMBA reacted with deoxyguanosine (dGuo). Two other major adducts were derived from the syn-dihydrodiolepoxide and bound to dGuo and to deoxyadenosine (dAdo). Total DMBA-DNA binding increased at all DMBA doses investigated (r = 0.94). Total binding values were (mean +/- SEM) 39.3 +/- 6.1, 158.0 +/- 16.9, 194.7 +/- 9.9, 326.9 +/- 21.5 and 443.2 +/- 20.8 nmol DMBA/mol DNA for rats administered DMBA at 1, 3, 5, 10 and 20 mg/rat respectively. The anti-dGuo adduct predominated at all doses and times evaluated, contributing to approximately 52% of total binding. The occurrence of anti-derived adducts was greater than that of syn-derived adducts. Binding of DMBA to dGuo substantially exceeded binding to dAdo. The 32P-postlabeling procedure represents a sensitive technique for detecting specific DMBA-DNA adducts formed in vivo in the rat mammary gland.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1989

In vitro and in vivo effects of sodium selenite on 7,12-dimethylbenz[a]anthracene--DNA adduct formation in isolated rat mammary epithelial cells.

Supplementation with increasing quantities of selenium (Se), as sodium selenite, to cultures of rat mammary epithelial cells resulted in a proportional depression in 7,12-dimethylbenz[a]anthracene (DMBA) binding to DNA. A depression in the two major anti bay-region dihydrodiol epoxide-deoxyribonucleoside adducts largely accounted for the reduced binding. DMBA-DNA binding in freshly isolated mammary cells from rats fed a diet containing 2.0 p.p.m. Se and incubated in culture with DMBA for 24 h was decreased 32% compared to binding in cells obtained from rats fed 0.1 p.p.m. Se. DMBA-DNA binding in mammary cells obtained from rats fed supplemental Se for 2 weeks or more was depressed compared to that occurring in cells from unsupplemented rats. The reduced ability of cells obtained from rats previously fed a 2.0 p.p.m. Se diet to activate DMBA to intermediates capable of binding to DNA became increasingly apparent with the duration of exposure to the carcinogen. Consistent with the in vitro supplementation study, cells isolated from rats previously fed a diet containing 2.0 p.p.m. Se had a reduced occurrence of the two major anti dihydrodiol epoxide adducts. The depression in DMBA binding following selenite supplementation, both in vitro and in vivo, supports the ability of Se to inhibit the initiation phase of carcinogenesis.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1989

Lack of effect of selenium on induction of tumors of esophagus and bladder in rats by two nitrosamines.

The effect of differences in level of dietary selenium on the induction of esophageal and bladder tumors in rats by two nitrosamines was investigated. Groups of 20 female F344 rats were given a synthetic diet containing less than 0.05 ppm Se to which selenium (as sodium selenite) was added at the concentration of 0.35, 0.7, 1.4 and 2.1 ppm selenium. These four groups, plus one without added Se, were treated with 20 ml per rat per day, 5 days a week, of a solution of nitrosomethylcyclohexylamine containing 5 mg/liter. A parallel five groups were treated in the same way with a solution of nitrosomethyl-3-carboxypropylamine in drinking water containing 600 mg per liter, as drinking water. Treatment lasted 28 weeks, at which time some animals had developed tumors. A group of 20 rats fed 0, 1.4 and 2.1 ppm Se was not treated with carcinogen. Rats consuming 1.4 ppm or 2.1 ppm Se gained weight more slowly than other groups. There was no significant difference in survival between the five groups treated with each carcinogen but receiving different dietary levels of selenium. Neither was there any significant difference between groups receiving each carcinogen in the incidence of tumors of the esophagus induced by nitrosomethylcyclohexylamine or of tumors of the urinary bladder induced by nitrosomethylcarboxypropylamine. Control rats on the synthetic diets did not survive as well as untreated rats eating regular chow diet. In these conditions there was no effect of dietary selenium levels on the induction of tumors in female rats by the two carcinogenic nitrosamines we used.

Animals↗
PubMed1988

Characteristics of human milk glutathione peroxidase.

Human milk glutathione peroxidase (GPx) was purified 4500-fold using acetone precipitation and purification by repetitive ion-exchange and gel filtration chromatography with an overall yield of 34%. Homogeneity was established by gel electrophoresis. Using gel filtration, the molecular weight (mol wt) of the enzyme was estimated to be 92 kdalton (kD). The monomeric molecular weight was estimated to b 23 kD from polyacrylamide gel electrophoresis, indicating that the native enzyme consists of four identical subunits. The molecular weight of each subunit was supported by amino acid analysis. Selenium (Se) content of the purified enzyme was 0.31%, in a stoichiometry of 3.7 g-atoms/mol. Data from these studies reveal that GPx provided approximately 22% of total milk Se, but only 0.025% of the total protein.

Amino Acids↗
PubMed1987

Distribution of selenium in human milk.

The present studies were designed to characterize selenium distribution in human milk. These studies reveal that most selenium in human milk is protein bound. Percentage dialyzable selenium varied proportionally with total selenium content of milk but not with stage of lactation. Neither rate of freezing nor frozen storage of samples for one month influenced distribution profiles. At least nine selenoproteins were detected in dialyzed milk samples following molecular sieve (Sephadex) chromatography. Glutathione peroxidase accounted for approximately 15-30% of selenium found in milk. Approximately half of peroxidase activity in human milk was associated with selenium dependent glutathione peroxidase activity.

Adult↗
PubMed1987

Influence of prior dietary protein intake on metabolism, DNA binding and adduct formation of 7,12-dimethylbenz[a]anthracene in isolated rat mammary epithelial cells.

These studies were designed to examine the influence of prior dietary protein intakes in rats on the ability of their isolated mammary cells to metabolize 7,12-dimethylbenz[a]anthracene (DMBA). Total metabolism of DMBA increased as dietary protein increased. After 6 h of incubation, water-soluble metabolites made only a minor (less than 12%) contribution to total DMBA metabolism. The binding of DMBA to isolated mammary cell DNA after 6 h of incubation from rats fed 15% dietary protein was 20% higher than binding from cells of rats fed 7.5% dietary protein. The increased binding in mammary epithelial cells from rats fed 15% protein was associated with an increase in the syn-dihydrodiol-epoxide adduct. The syn-dihydrodiol-epoxide:deoxyadenosine adduct was the major contributor to binding. The present studies are consistent with a decrease in carcinogen activation in tissues obtained from animals fed diets limiting in protein.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1987

Selenium content and distribution of human, cow and goat milk.

Studies were undertaken to compare the content and distribution of selenium in human, cow and goat milk. Selenium content of cow milk was found to be lower than that of either human or goat milk. Regardless of source, less than 3% of total milk selenium was associated with the lipid fraction. Selenium within the 120,000 X g supernatant accounted for 72, 62 and 30% of the total in cow, human and goat milk, respectively. Glutathione peroxidase occurred in all milk samples with goat greater than human greater than cow. Percent of total peroxidase activity associated with glutathione peroxidase was 29, 27 and 65 for human, cow and goat milk, respectively. Approximately 20-28% of the selenium in milk was removed by dialysis (molecular exclusion of 6-8 kDa). After gel chromatography, 8-12 selenoprotein fractions were detected in undialyzed skim milk from each species. Most of the glutathione peroxidase activity was found in the fractions corresponding to 170 and 96 kDa in milk from all species examined. The diameric form of glutathione peroxidase also appeared in dialyzed and undialyzed milk. Distinct differences in the content and distribution of selenoproteins among these species in fresh and dialyzed milk are discussed.

Animals↗
PubMed1987

Prior dietary protein intake and DNA-binding 7,12-dimethylbenz[a]anthracene metabolites formed by isolated rat hepatocytes.

Hepatocytes were isolated from noninbred Sprague-Dawley rats previously fed diets containing 7.5 or 15% protein. These hepatocytes were incubated in the presence of exogenous DNA for examination of their ability to metabolize 7,12-dimethylbenz[a]anthracene [(DMBA) CAS: 57-97-6] and release reactive DNA-binding metabolites to the medium. An increased formation of extracellular water-soluble metabolites of DMBA was observed in hepatocyte cultures from rats fed a 15% protein diet compared with that in cells from rats fed 7.5% protein. As dietary protein increased, there was a reduction in the release of DNA-binding metabolites by isolated hepatocytes. Bay-region dihydrodiol-epoxide adducts were formed with extracellular calf thymus DNA and hepatic DNA. However, most of the binding of DMBA with extracellular and intracellular DNA was due to unidentified DMBA-DNA adducts that eluted, upon reversed-phase chromatography, after the bay-region dihydrodiol-epoxide DMBA adducts were formed. The present studies show that feeding animals diets that are limiting in protein results in a decrease in DMBA detoxification and an increase in excretion of reactive DMBA metabolites from the liver. These results may explain the previously observed influence of dietary protein on the initiation of DMBA-induced mammary carcinogenesis in the rat.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1986

Inhibition of chemical carcinogenesis and tumorigenesis by selenium.

Selenium is effective in inhibiting the incidence and total number of tumors resulting from treatment with various chemical carcinogens. This inhibition occurs both at the initiation and promotion phases of chemical carcinogenesis. At least part of the inhibition of the initiation stage is associated with changes in the metabolism of the parent carcinogen. Studies with 7,12-dimethylbenz(a)anthracene suggest that selenium specifically blocks the enzyme(s) responsible for the formation of anti-dihydrodiol epoxide adducts to DNA. Selenium is also effective in reducing the in vitro and in vivo growth of numerous neoplastic cells. However, differences in the sensitivity to selenium are evident in the various tumor cell lines that have been examined. Continuous selenium intake appears to be necessary to maximal inhibition in both models of carcinogenesis. Evidence suggests that selenodiglutathione or some other intermediate in selenium metabolism is responsible for the anticarcinogenic and antitumorigenic properties of this trace element. The mechanism by which selenium produces these effects is unknown, but it may relate to alterations in either RNA transcription or translation. These and other data strongly suggest that selenium is a naturally occurring anticarcinogenic and antitumorigenic agent.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1986

DNA binding and adduct formation of 7,12-dimethylbenz[a]-anthracene by rat mammary epithelial cell aggregates in vitro.

Freshly isolated mammary epithelial cell aggregates from female Sprague-Dawley rats metabolized 7,12-dimethylbenz-[a]anthracene (DMBA) to bay-region anti- and syn-dihydrodiolepoxides that bound to deoxyguanosine and deoxyadenosine residues in cellular DNA. After 24 h of incubation 68% of the DMBA (0.4 micrograms/ml) was metabolized and 58% of the extracellular metabolites were water-soluble. DMBA-DNA binding increased rapidly during the initial 24 h of incubation. Formation of the bay-region syn-dihydrodiolepoxide:deoxyadenosine adduct increased linearly throughout the 24 h, whereas formation of deoxyadenosine and deoxyguanosine adducts with the bay-region anti-dihydrodiolepoxide increased rapidly following a delay of 12 h.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1986

Differential effects of selenium on normal and neoplastic canine mammary cells.

Four different canine mammary tumor (CMT) cell lines and a nonneoplastic primary culture of mammary cells were examined for their in vitro responsiveness to selenium supplementation. These cell lines were found to vary in their metabolic response to increasing concentrations of selenium. Sensitivity to selenium, as sodium selenite, increased with increasing concentrations of this trace element in all of the neoplastic lines. These data also suggest that increasing the plating density of tumor cells further increases the sensitivity to selenium. A relatively selenium-sensitive cell line (CMT-13) and relatively insensitive cell line (CMT-11) were characterized on the basis of reduced growth resulting from selenium supplementation. Increasing the concentration of selenium to 0.75 microgram/ml depressed the growth of CMT-13 and CMT-11 cells by 75% and 11%, respectively, while no inhibition was observed in nonneoplastic cells. These cell lines also varied in their sensitivity to different forms of selenium. Selenodiglutathione was the most effective form of selenium examined that inhibited tumor cell growth. The sensitivity of the neoplastic lines was selenodiglutathione much greater than sodium selenite much greater than selenocystine greater than selenomethionine. None of the forms of selenium examined inhibited the growth of the nonneoplastic mammary cells in culture. Supplementation with sodium selenite (1 microgram Se per ml) for 60 min resulted in a dramatic depression in RNA biosynthesis in CMT-13, but not CMT-11 or nonneoplastic cells.

Animals↗