Core tracing: depicting connections between features in electron density

Core tracing is a threshold-independent method of determining connectivity (long chains of high-density values) in electron-density maps. It gives visually sparse pictures of large volumes which are useful for initial fitting and for molecular-boundary determination. New methods for visual presentation of the traces are suggested by the way that the connectivity is parameterized in terms of local connections between maxima and the saddle (lowest) points along the connecting paths. The algorithm also partitions the density into small compact volumes containing the maxima. These volumes are useful for localization and statistical analysis.

Toxicity of uranium mine receiving waters to early life stage fathead minnows (Pimephales promelas) in the laboratory

Elevated concentrations of arsenic, nickel, and molybdenum in aquatic systems around northern Saskatchewan uranium mines are an environmental concern. Early life stage fathead minnows were used to assess toxicity from several aquatic systems near the Key Lake and Rabbit Lake uranium operations. Hatching success of fish embryos exposed to waters receiving contaminants associated with uranium ore milling was reduced by 32-61% relative to controls. Mortality differed in two lakes receiving mill effluents because of opposing factors influencing metal toxicity (i.e. low pH and high hardness). In one mill receiving water (Fox Lake), larval mortality was 0%, whereas mortality was 85% in water collected from a downstream location (Unknown Lake). Fish embryos exposed to open-pit dewatering effluent receiving waters, or water from a flooded open pit (i.e. pit waters), hatched 26-39% earlier than those exposed to reference or control water. The combination of low water hardness and elevated nickel concentrations in pit waters contributed to the early hatching. Egg hatchability and hatching time were more sensitive indicators of toxicity than 'standard' endpoints, like larval mortality and growth. Current regulatory emphasis on single contaminants and standard toxicological endpoints should be re-evaluated in light of the complex interaction among confounding variables such as pH, hardness. conductivity, and multi-metal mixtures.

Equine estrogen metabolite 4-hydroxyequilenin induces DNA damage in the rat mammary tissues: formation of single-strand breaks, apurinic sites, stable adducts, and oxidized bases

Epidemiological data strongly suggest that a woman's risk of developing breast cancer is directly related to her lifetime estrogen exposure. Estrogen replacement therapy in particular has been correlated with an increased cancer risk. Previously we showed that the equine estrogens equilin and equilenin, which are major components of the estrogen replacement formulation Premarin (Wyeth-Ayerst), are metabolized to the catechol, 4-hydroxyequilenin which autoxidizes to an o-quinone causing oxidation and alkylation of DNA in vitro [Bolton, J. L., Pisha, E., Zhang, F., and Qiu, S. (1998) Chem. Res. Toxicol. 11, 1113-1227]. In the present study, we injected 4-hydroxyequilenin into the mammary fat pads of Sprague-Dawley rats. Analysis of cells isolated from the mammary tissue for DNA single-strand breaks and oxidized bases using the comet assay showed a dose-dependent increase in both types of lesions. In addition, LC-MS-MS analysis of extracted mammary tissue showed the formation of an alkylated depurinating guanine adduct. Finally, extraction of mammary tissue DNA, hydrolysis to deoxynucleosides, and analysis by LC-MS-MS showed the formation of stable cyclic deoxyguanosine and deoxyadenosine adducts as well as oxidized bases. This is the first report showing that 4-hydroxyequilenin is capable of causing DNA damage in vivo. In addition, the data showed that 4-hydroxyequilenin induced four different types of DNA damage that must be repaired by different mechanisms. This is in contrast to the endogenous estrogen 4-hydroxyestrone where only depurinating guanine adducts have been detected in vivo. These results suggest that 4-hydroxyequilenin has the potential to be a potent carcinogen through the formation of variety of DNA lesions in vivo.

Toxicity of uranium mine-receiving waters to caged fathead minnows, Pimephales promelas

Larval fathead minnows (Pimephales promelas) were placed at four exposure sites for 7 days in each of five lakes surrounding the Key Lake uranium mine in northern Saskatchewan, Canada. Fish placed in lakes receiving Mo-contaminated mill effluent demonstrated higher mortalities than those placed in lakes receiving Ni-contaminated mine-dewatering effluent, which was not significantly different from reference sites. No significant differences were detected in fish growth among the study lakes because of the high (90%) mortality in Fox and Unknown lakes. Principal components analysis characterized exposure sites by total and dissolved metal concentration. Stepwise multiple regression of fish mortality on principal components generated from total metal data revealed that principal component 1 could account for 84% of the variance associated with fish mortality. Careful examination of the metals that correlated strongly with principal component 1 and with fish mortality suggested that dietary Se toxicity probably resulted in the differential fathead minnow mortality observed among study lakes.

The structure of an insect chymotrypsin

The South American imported fire ant (Solenopsis invicta), without natural enemies in the United States, widely infests the southern United States, causing more than a half billion dollars in health and agriculture-related damage annually in Texas alone. Fire ants are resistant to most insecticides, so control will require a more fundamental understanding of their biochemistry and metabolism leading to the design of selective, ecologically safe insecticides. The 4th instar larvae play a crucial role in the nutrition of the colony by secreting proteinases (especially chymotrypsin) which digest food products for the entire colony. The first structure of an ant proteolytic enzyme, fire ant chymotrypsin, was determined to atomic resolution (1.7 A). A structural comparison of the ant and mammalian structures confirms the "universality" of the serine proteinase motif and reveals a difference at residues 147-148, which are proteolytically removed in the bovine enzyme but are firmly intact in the ant chymotrypsin, suggesting a different activation mechanism for the latter. Likewise, the absence of the covalently attached propeptide domain (1-15) further suggests an uncharacteristic activation mechanism. The presence of Gly189 in the S1 site is an atypical feature of this chymotrypsin and is comparable only to human leukocyte elastase, hornet chymotrypsin and fiddler crab collagenase. Binding studies confirm the chymotrypsin nature of this novel enzyme.

Molecular modelling and drug design

Drug design is a creative act of the same magnitude as composing, sculpting, or writing. The results can touch the lives of millions, but the creator is rarely one scientist and the rewards are distributed differently in the arts than in the sciences. The mechanisms of creativity are the same, i.e., incremental (plodding from darkness to dawn) or sudden (the "Eureka" effect) realization, but both are poorly understood. Creativity remains a human characteristic, but it is directly related to the tools available, especially computer software and hardware. While modelling software continues to mature, very little new has evolved in terms of hardware. Here, we discuss the history of molecular modelling and describe two novel modelling tools, a haptic device and a program, SCULPT, to generate solid molecular models at atomic resolution.

Structure of recombinant mouse collagenase-3 (MMP-13)

The matrix metalloproteinases are crucial in the physiological and pathological degradation of the mammalian extracellular matrix, including breast tumours, and osteoarthritic cartilage. These enzymes are classified according to their matrix substrate specificity. Collagenase-3 (MMP-13) is a member of this family and preferentially cleaves type II collagen, cartilage, fibronectin and aggrecan. Collagenase-3 is normally expressed in hypertrophic chondrocytes, periosteal cells, and osteoblasts during bone development. The structure of the catalytic domain of recombinant mouse collagenase-3, complexed to the hydroxamate inhibitor (RS-113456), is reported at 2.0 A resolution. Molecular replacement and weak phasing information from a single derivative determined the structure. Neither molecular replacement nor derivative methods had a sufficient radius of convergence to yield a refinable structure. The structure illuminates the atomic zinc ion interactions with functional groups in the active site, emphasizing zinc ligation and the very voluminous hydrophobic P1' group for the inhibitor potency. The structure provides insight into the specificity of this enzyme, facilitating design of specific inhibitors to target various diseases.

Induction of mammary carcinomas by N-methyl-N-nitrosourea in ovariectomized rats treated with epidermal growth factor

The importance of epidermal growth factor (EGF) in both normal and malignant mammary gland development are presented in these studies. Initial findings demonstrated that in the absence of ovarian hormones, EGF had a significant proliferative effect on mammary epithelial cells. To determine whether mammary epithelial cells grown with EGF, in the absence of ovarian hormones, could be transformed by N-methyl-N-nitrosourea (MNU), female ovariectomized Lewis rats were implanted with pellets containing EGF for 1 week and then treated with MNU for initiation. Two days after MNU treatment, ovaries were implanted and EGF pellets were removed from all ovariectomized groups in order to promote carcinogenesis. The mammary carcinoma incidence of the EGF-stimulated group (90%) was not significantly different from the intact group (100%). The mammary cancer morphology of EGF-treated carcinomas was either ductal carcinoma or cribriform adenocarcinoma, whereas intact animals developed mainly papillary and occasional cribriform carcinomas. Fifty-eight percent of the carcinomas from the EGF group were ovarian hormone-independent compared with 10% of carcinomas from the intact group. These results demonstrate that EGF-induced proliferation during initiation with MNU was sufficient to induce the transformation of mammary carcinomas in the absence of ovarian hormones. The hormonal dependency of these EGF-induced carcinomas were different compared with MNU-initiated mammary carcinomas in intact rats.

Changes in the parous rat mammary gland environment are involved in parity-associated protection against mammary carcinogenesis

Parity in rats results in protection from methylnitrosourea (MNU)-induced mammary cancer. Our goal was to determine if systemic alterations in the mammary gland environment after a full-term pregnancy rendered the parous rat an inadequate host for promotion of initiated mammary epithelial cells to become cancerous. Lewis rat MNU-treated mammary epithelial cells were transplanted into uniparous (UP), age-matched virgin (AMV) (both 130-150 d), or young virgin (YV) (50-60 d) syngeneic hosts to examine if differences in the systemic environments of the three hosts had an effect on hyperplasia and cancer formation. More transplants in YV and AMV hosts contained hyperplasias and adenocarcinomas as compared to transplants in UP hosts. In addition, UP host transplants had significantly fewer numbers of hyperplastic lesions than transplants from the virgin hosts. The evidence presented here shows that the uniparous host environment is less supportive than that of the virgin host for hyperplasia and cancer development.

Hormone levels and mammary epithelial cell proliferation in rats treated with a regimen of estradiol and progesterone that mimics the preventive effect of pregnancy against mammary cancer

Women who bear their first child by their late teens have about half the risk of developing breast cancer relative to nulliparous women. The rat is a good model for studying the role of hormones in breast cancer since, for example, young rats become nearly refractory to mammary carcinogenesis after delivering a litter of pups. Short term administration of estradiol and progesterone (E & P) provides virgin rats protection from mammary carcinogenesis as effectively as pregnancy. The purpose of these studies were twofold: first, to evaluate potential long-term toxicity of the E & P treatments and second, to compare hormone treated rats and pregnant rats with respect to circulating E & P levels as well as mammary epithelial cell proliferation and differentiation. To test for toxicity, rats were treated with E & P (20 micrograms and 4 mg, respectively) or vehicle by s.c. injections 5 times per week for 5 weeks beginning at 40 days of age. The animals were weighed biweekly and sacrificed at 500 days of age when detailed necropsies were performed. No significant difference in weight gain was observed between the two groups nor was any toxicity grossly observable in the hormone-treated rats. Furthermore, there was no increase in the number of spontaneous mammary or pituitary tumors in the E & P treated group relative to controls. To evaluate serum hormone titers and mammary proliferation, rats were treated with steroids or vehicle daily beginning at 65 days of age. At 6 and 24 hours after the 1st, 14th and 35th injection, serum E & P were measured by RIA and mammary epithelial cell proliferation by immunohistochemistry (PCNA). At 6 hours after each injection, E & P levels were 3 to 5 fold those observed late in pregnancy. By 24 hours, however, E & P levels subsided to late pregnancy levels or lower. The mammary epithelial cell proliferation index in either E & P treated or late pregnant rats was 6 to 14%. Histologic sections and wholemounts of mammary glands showed a similar degree of differentiation between rats treated with E & P for 14 days or longer and late pregnant rats. These data further suggest that E & P treatments are a non-toxic means of mimicking the protective effect of pregnancy against mammary cancer and that pregnancy or hormone treatments may achieve this prophylaxis through a differentiation mechanism.

Analysis of the structure of HIV-1 protease complexed with a hexapeptide inhibitor. Part II: Molecular dynamic studies of the active site region

Six models of the catalytic site of HIV-1 protease complexed with a reduced peptide inhibitor, MVT-101, were investigated. These studies focused on the details of protonation of the active site, its total net charge and hydrogen bonding pattern, which was consistent with both the observed coplanar configuration of the acidic groups of the catalytic aspartates (Asp-25 and Asp-125) and the observed binding mode of the inhibitor. Molecular dynamic simulations using AMBER 4.0 indicated that the active site should be neutral. The planarity of the aspartate dyad may be due to the formation of two hydrogen bonds: one between the inner O delta 1 oxygen atoms of the two catalytic aspartates and another between the O delta 2 atom of Asp-125 and the nitrogen atom of the reduced peptide bond of the bound inhibitor. This would require two additional protonations, either of both aspartates, or of one Asp and the amido nitrogen atom of Nle-204. Our results favor the Asp-inhibitor protonation but the other one is not excluded. Implications of these findings for the mechanism of enzymatic catalysis are discussed. Dynamic properties of the hydrogen bond network in the active site and an analysis of the interaction energy between the inhibitor and the protease are presented.

Cell proliferation and apoptosis during mammary carcinogenesis in pituitary isografted mice

In the present study, pituitary isografted animals serve as a model for evaluating the changes in differentiation, cell proliferation and programmed cell death (apoptosis) in mammary epithelial cells during carcinogenesis. The percentage of bromodeoxyuridine (BrdU)-labeled ductal and alveolar cells was significantly higher in pituitary isografted animals than in non-isografted control animals. BrdU-labeled cells increased in lobular hyperplastic nodules, keratinized nodules and mammary carcinomas; similar changes were observed with apoptotic cells, which were rare in mammary glands of adult non-isografted animals (one to three apoptotic cells per 2000 mammary epithelial cells), but their number increased in hyperplastic lesions and mammary carcinomas. Among hyperplastic nodular lesions, variants with high, moderate and low proliferative activity and/or apoptotic cell death were identified, which suggests that they may have different growth potentials and different propensities for malignant transformation. After removing pituitary isografts, apoptosis occurs in hyperplastic lesions but not in mammary carcinomas-implying that malignant tumors are hormone-independent. The dynamics of the changes in apoptotic cell death among various hyperplastic lesions after removal of pituitary isografts suggests that these lesions are composed of heterogeneous cell populations, as far as the initiation of apoptosis is concerned. Our data indicate that apoptosis can be used together with cell proliferation as a potential marker in characterizing the growth potential and phenotypic diversity of hyperplastic, premalignant and malignant mammary gland lesions.

N-Ethyl-N-nitrosourea induces mammary cancers in the pituitary-isografted mouse which are histologically and genotypically distinct from those induced by N-methyl-N-nitrosourea

N-Ethyl-N-nitrosourea (ENU) and N-methyl-N-nitrosourea (MNU) are alkylating agents which respectively ethylate or methylate nucleophilic centers in the cell such as DNA. In vitro studies with naked DNA and bacterial mutagenesis assays suggest that these two compounds induce different spectra of genetic lesions. In addition, the ethyl-DNA adducts induced by ENU persist longer than the methyl-DNA adducts induced by MNU. Since MNU is a known mammary carcinogen in the pituitary-isografted mouse, these data suggest that ENU may be an even more potent carcinogen than MNU. The purpose of this study was to determine whether ENU was a mammary carcinogen in the pituitary-isografted mouse and if so, to compare the genotype and phenotype of ENU-induced mammary tumors with those induced by MNU. Fifteen adult female virgin BALB/c mice were isografted with two pituitaries and subsequently treated with a single intravenous injection of ENU (50 micrograms/g body weight). Mammary adenocarcinomas arose in all of the survivors (n=12) with a median latency of 27 weeks and a mean frequency of 1.4 cancers per mouse. When tumor DNA was analyzed for mutations in the 12th and 61st codons of c-Ki-ras or c-Ha-ras protooncogenes, only wild type sequences were found. This is in contrast to MNU which causes a G to A transition mutation in the 12th codon of the c-Ha-ras proto-oncogene in about one of five mammary cancers induced in pituitary-isografted mice. Furthermore, the ENU-induced tumors were solid viable papillary adenocarcinomas, whereas MNU induced tumors are highly necrotic adenocarcinomas with squamous metaplasia. These results demonstrate that, in the pituitary-isografted mouse, ENU is as potent a mammary carcinogen as MNU and suggest that oncogenes other than c-Ki-ras or c-Ha-ras may be involved in ENU-induced mammary cancers.

Hormone dependent and independent mammary tumor development form N-methyl-N-nitrosourea-treated rat mammary epithelial cell xenografts in the nude mouse: multiple pathways and H-ras activation

A nude mouse mammary fat pad xenograft system was developed to examine hormone dependent and independent mammary tumorigenesis and progression from N-methyl-N-nitrosourea (MNU)-induced hyperplastic lesions. Ninety-one percent of transplanted mammary tumors grew, with an orthotopic preference, and maintained their hormone dependence, histopathology, and H-ras mutation frequency. Grafted mammary epithelial cells, from MNU-treated rats, developed normal; and hyperplastic outgrowths, representative of those found in the rat mammary gland after MNU-treatment. Hyperplasias developed into neoplasias that were both hormone dependent and independent. We demonstrate that hormone independent tumors can develop directly either from lobuloalveolar or ductal hyperplasias or from hormone dependent tumors. H-ras mutation was detected in mammary preneoplasias (4 lines) before they developed into tumors and was associated with an elevated tumorigenic potential. Our observations suggest that there are multiple histopathogenic pathways in the development and progression to hormone independent rat mammary tumors.

Refractoriness to mammary tumorigenesis in parous rats: is it caused by persistent changes in the hormonal environment or permanent biochemical alterations in the mammary epithelia?

Administration of a single i.v. injection of 50 mg N-methyl-N-nitrosourea (MNU)/kg body wt to 50- to 60-day old virgin rats, 120-day-old virgin rats, and 120-day-old parous rats (Sprague-Dawley; n = 18-37) resulted in a high incidence of mammary carcinomas in the virgin animals (97.3% in 50- to 60-day-old virgin rats; 75.0% in 120-day-old virgin rats), but mammary carcinomas did not develop in the parous rats. The concentrations in serum of various mammotropic hormones were measured in identical groups of rats at the time of MNU treatment. Growth hormone (GH) concentration was significantly reduced in parous rats, as compared with young or age-matched virgin rats. The concentrations of prolactin, 17 beta-estradiol, progesterone, corticosterone and thyroxine were not significantly altered in the parous rats compared to the two groups of virgin animals. Histological examination of the mammary glands from the three groups of rats showed that the epithelia of the parous animals were in a stage of regression, whereas the mammae of the young virgin rats showed the highest degree of lobulo-alveolar development. The levels of estrogen receptor (ER), epidermal growth factor (EGF) receptor (EGF-R) and GH receptor (GHR) in the mammary glands of the animals were also measured. We found a reduction in the receptor levels for both estrogen and EGF in mammary tissues from parous animals. Receptors for GH were present in normal mammary tissues from both virgin and parous rats. We hypothesize that the reduction in the circulating concentration of GH caused the reduced susceptibility of parous rats to mammary carcinogenesis possibly by decreasing the levels of ER and/or EGF-R in the mammary gland.

Refractoriness to mammary carcinogenesis in the parous mouse is reversible by hormonal stimulation induced by pituitary isografts

We have previously reported that mouse mammary epithelial cells transformed in vitro yield tumors which vary qualitatively and quantitatively as a function of the mitogenic environment in which the cells are propagated at the time of carcinogen treatment. One milieu supportive of transformation in vitro was medium supplemented with progesterone and prolactin as the mitogens. We have performed parallel studies in which virgin mice were isografted with pituitaries resulting in elevated serum titers of progesterone and prolactin. After carcinogen treatment, these mice developed mammary tumors which included those identical genotypically and phenotypically to tumors induced in vitro in cells grown in progesterone and prolactin during carcinogen exposure. Our current working hypothesis is that the mitogenic environment around the time of carcinogen administration can modulate the incidence and phenotype of the resultant tumors. To further test this hypothesis, we have evaluated the susceptibility of hormonally-stimulated parous mice to chemically induced mammary carcinogenesis since parity is known to significantly reduce the susceptibility of the mouse mammary gland to carcinogenesis. Virgin or multiparous BALB/c mice were isografted with two pituitaries. Five weeks after surgery, the mice were injected with N-methyl-N-nitrosourea (MNU; 50 micrograms/g i.v.). Mammary carcinomas arose in 85% (11/13) with a median latency of 22.8 weeks and 1.9 tumors per virgin mouse and 80% (24/30) with a median latency of 22.1 weeks at a frequency of 1.9 tumors per parous mouse. Only 14% (2/14) of the non-isografted, age-matched parous controls developed tumors when injected with MNU. Fourteen parous mice receiving only pituitary isografts (no MNU), did not develop mammary carcinomas within the 7-month period of the study. These results demonstrate that parous BALB/c mice are refractory to MNU-induced mammary carcinogenesis and that this refractoriness is not permanent, but can be overcome by hormonal stimulation mediated by pituitary isografts.

In vivo growth stimulation of collagen gel embedded normal human and mouse primary mammary epithelial cells

A new system for studying growth of normal human mammary epithelial cells in an in vivo environment using athymic nude mice is described. Human mammary epithelial cells dissociated from reduction mammoplasty specimens were embedded within collagen gels and subsequently transplanted subcutaneously into nude mice. Histological sections of recovered collagen gels showed epithelial cells arranged as short tubules with some branching. Proliferation of mammary epithelial cells was quantitated in vivo by 3 days' continuous infusion with 5 bromo-2'-deoxy-uridine followed by immunostaining of sections from recovered gels. Ovarian steroids administered to the host animals, resulting in blood serum levels normally found in the human female, had little or no effect on the proliferation of human mammary epithelial cells. Collagen gel embedded mouse mammary epithelial cells, mouse mammary explants, and host mammary glands all responded similarly to ovarian steroids, suggesting that the unresponsiveness of the human mammary epithelial cells under these conditions was not due to dissociation per se. However, an increased dose of 17 beta-estradiol or a growth factor combination containing epidermal growth factor, cholera toxin, and cortisol significantly stimulated the proliferation of human outgrowths. The growth factor response was dependent on the location of the cells, with the greatest response seen in the part of the gel proximal to the osmotic pump delivering the growth factors and the effect gradually waning in area more distal to the pump. The effect was especially striking since the mitotic figures could be easily identified and the labeling index was as high as 75%. The host mouse mammary gland also responded to growth factors, resulting in ductal hyperplasia. The proliferative and morphogenetic effects of various agents on normal human mammary epithelial cells embedded in collagen gel can be studied in vivo in nude mice.

Pituitary-isografted mice are highly susceptible to MNU-induced mammary carcinogenesis irrespective of the level of alveolar differentiation

We have recently developed a mammary tumorigenesis system in which adult female BALB/c mice are grafted with two pituitaries from isologous donors and subsequently treated with a single i.v. injection of N-methyl-N-nitrosourea (MNU, 50 mg/kg). Mice bearing isografts have elevated serum titers of prolactin and progesterone which act on the mammary glands to produce a highly differentiated morphology resembling that of late pregnancy. MNU treatment of the mouse mammary gland in this differentiated state results in tumors in > 90% of tested animals. Since the mammary gland is believed to be particularly vulnerable to chemically induced carcinogenesis during alveolar morphogenesis, we chose to assess the susceptibility of the mammary gland during the initial weeks after pituitary isografting when they are ostensibly undergoing marked cell proliferation and differentiation. To this end, mice were isografted with pituitaries and subsequently analyzed at 1, 3, 5, 8 and 12 weeks for epithelial cell differentiation and susceptibility to MNU-induced tumorigenesis. By 3 weeks after isografting, the glands showed marked lobuloalveolar development and highest casein production. Tumor latency and frequency paralleled parenchymal differentiation for the first 3 weeks. By 5 weeks, and thereafter, the mice continued to be extremely susceptible to MNU-induced mammary carcinogenesis despite the highly differentiated state of the glands. Since tumors generated in this system are not dependent on pituitary isografts for their growth when transplanted to isologous recipients, and since the pituitary isograft does not act as a classical promoter but is required at the time of carcinogen treatment, we conclude that the pituitary isograft maintains a condition permissive for transformation to occur and a level of proliferation sufficient for the expression of the transformed phenotype.

Environmental monitoring of bleached kraft pulp mill chlorophenolic compounds in a northern Canadian river system

The environmental transport of pulp mill effluent compounds and the exposure of two fish species has been monitored by parallel analyses of effluent, water column and suspended sediment samples, and fish bile and muscle. Compounds analyzed included over 20 chlorophenolic compounds and 12 fatty and resin acids. The concentration of chlorophenols varied with seasonal river flows and mill process changes such as the substitution of chlorine dioxide (ClO2) for chlorine gas (Cl2) in the bleach plant. At 100% (ClO2) substitution, the effluent and the water column concentrations of most chlorophenolics approached the analytical detection limits of 0.1-1 parts per billion. Chlorophenolic and fatty/resin acid compounds were detected in the bile of both mountain whitefish (Prosopium williamsoni) and longnose sucker (Catostomus catostomus), but were rarely detected in fillets. Fish bile concentrations were observed in an apparent spatial gradient as far as 230 km downstream of the mill. A depuration experiment with fish held in uncontaminated water for eight days indicated a rapid decrease in chlorophenol levels. These observations corroborate previous investigations that chlorophenolic compounds are rapidly excreted and can be used as sensitive markers for recent exposure to mill effluents.

In situ localization of prolactin receptor message in the mammary glands of pituitary-isografted mice

The receptors for prolactin (PRLR) are expressed in many tissues including the mammary gland, a classical target tissue for prolactin (PRL), but the cellular localization of expression of the PRLR gene in mammary gland has not yet been identified. PRL is known to up regulate its own receptor. We therefore employed the pituitary isografted mouse as a model to distinguish the cells expressing PRLR since PRL blood levels are known to be constitutively elevated in these animals. Mammary glands of virgin or pituitary isografted mice were analyzed by northern blot or in situ hybridization with a digoxygenin-labeled cRNA probe. Northern analysis revealed the expression of 1.3 kb and 2.5 kb forms of PRLR corroborating the results of various laboratories studying other tissues. PRLR was barely detectable by in situ hybridization in non-isografted mice. Two weeks after pituitary isografting, however, PRLR expression was substantially increased in the epithelial cells of mammary ducts and alveoli. No signal was ever detected in the mammary stromal compartment of either virgin or pituitary-isografted mice. The localization of PRL-responsive cells to the parenchyma of the mammary gland suggests that epithelial cells are the mediators of PRL action and that the transcriptional regulation of PRLR expression by PRL is direct in the epithelial cell.

Kinetics of mammary epithelial cell proliferation in pituitary isografted BALB/c mice

Recently, we have published that treatment of pituitary isografted BALB/c mice with a single injection of N-methyl-N-nitrosourea (MNU) leads to the rapid development of mammary tumors in over 90% of the animals (Guzman et al., Cancer Res., 52, 5732-5737). In the present study, we characterized the changes in proliferative activity and lobulo-alveolar differentiation of MECs at different time intervals after isografting animals with pituitary glands. Virgin BALB/c mice 1, 3, 5 or 8 weeks after pituitary isografting were either pulse-labeled for 2 h or continuously infused with bromodeoxyuridine (BrdU) and the percentage of BrdU-labeled MECs was assessed. The S-phase duration (TS) of MECs was evaluated by double labeling with [3H]thymidine and BrdU. The population potential doubling time (TP) was calculated from the values of BrdU-LI and TS. Three stages of proliferation and differentiation of MECs in pituitary isografted virgin BALB/c mice were observed: (i) A sharp increase in the percentage of proliferating MECs of the terminal ducts and ductal branchings in the first 1-2 weeks, (ii) Development of lobulo-alveolar structures from the terminal ductal and alveolar buds, between weeks 3 and 5 with the highest BrdU-LI in week 3 and (iii) Multiplication of the alveolar structures and decrease in the BrdU-LI between weeks 5 and 8. The BrdU-LIs of alveolar cells 5 weeks after isografting the animals were significantly higher than those of the ductal cells. The continuous administration of BrdU for 3, 5 or 7 days by using osmotic pumps revealed zones in the ducts where almost all MECs were labeled as well as zones lacking proliferate activity. When the BrdU administration was extended for 10-14 days, almost all (> 95%) ductal and lobular epithelial cells were labeled. A small percentage (< 5%), of ductal and lobulo-alveolar MECs cells, remained unlabeled even after 14 days infusion of BrdU. The TS and TP values were shorter in pituitary isografted animals than in controls, but no significant difference was found for either values between the ductal and alveolar cells in either isografted or control mice. Changes in proliferation kinetics of mouse MECs in pituitary isografted animals correlated with the circulating concentrations of prolactin, progesterone and 17 beta-estradiol, but not with corticosterone, growth hormone or thyroxin.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of noise on entropy

A complementary relationship between the entropy (S) and the variance (sigma(2)) of an electron-density map is derived by approximating the logarithmic term in the entropy expression by a series expansion around the average map density. The resulting expression is S approximately ln N - 1/2sigma(2), where N is the number of grid points and sigma is the r.m.s. deviation from the mean in a map normalized to unit mean. The algebraic expression is of interest because it is consistent with and allows numerical evaluation of the surprising argument that noise decreases the entropy of a map. The argument is that a noise contribution by itself generates a certain variance that is independent of the atomic structure and that adds to the variance due to the structure. Increased variance corresponds to decreased entropy. This property of noise provides an intuitively reasonable justification for maximizing the entropy of an electron-density map in the quest for more readily interpretable maps of macromolecules. The entropy-variance relationship also extends the range of applicability of the entropy concept to maps with a limited amount of negative density. The approximation which leads to the entropy-variance relationship is most applicable where it is most likely to be useful - in experimental maps of relatively low structure definition.

Incidence of c-Ki-ras activation in N-methyl-N-nitrosourea-induced mammary carcinomas in pituitary-isografted mice

We found previously that mouse mammary epithelial cells cultured in the presence of the mammogenic hormones progesterone and prolactin and treated with the carcinogen N-methyl-N-nitrosourea produced a high frequency of hyperplastic alveolar nodules and carcinomas with squamous metaplasia upon transplantation to syngeneic mice. The majority of these mammary transformants had an activated c-Ki-ras proto-oncogene with a specific point mutation in codon 12 (G35 to A35). To determine whether these in vitro findings parallel mammary carcinogenesis in vivo, virgin female mice were pituitary isografted to increase their circulating levels of progesterone and prolactin. The pituitary isograft results in an increase in proliferation, leading to lobulo-alveolar development and differentiation of the mammary epithelial cells. Five weeks after pituitary isografting, the mice were treated with a single injection of N-methyl-N-nitrosourea (50 micrograms/g body weight). Greater than 90% of the N-methyl-N-nitrosourea-treated mice developed mammary carcinomas between 3 and 7 months after treatment. The majority (75%) of the carcinomas had histopathology identical to that of tumors induced in vitro in the presence of progesterone and prolactin. A number of the mammary cancers (17%) induced in pituitary-isografted mice also had the identical point mutation in the c-Ki-ras proto-oncogene found in the in vitro studies. These results suggest that the hormonal milieu around the time of carcinogen exposure affects not only the incidence and phenotype of the mammary transformants but also the molecular events associated with mammary carcinogenesis.

Simulations of dynamical properties of a Michaelis complex: porcine pancreatic elastase and the hexapeptide, Thr-Pro-n Val-Leu-Tyr-Thr

Molecular dynamic simulations (30ps) of the Michaelis complex of hexapeptide (Thr-Pro-nVal-Leu-Tyr-Thr) bound to porcine pancreatic elastase (PPE) hydrated by about 2000 water molecules have been performed using the AMBER 3.0 program package. Dynamical properties of the conformation of the active site have been examined. A comparison with previously reported simulations of native PPE shows that after the substrate is bound, the catalytically crucial H-bond between O gamma-H group of (Ser 195) and nitrogen N epsilon (His 57) is more readily formed. These results show, however, that the H-bond does not adopt the most favorable conformation. The O gamma-H group of Ser 195 has a statistical preference for an attractive interaction with the O = C carbonyl (Ser 214) rather than the nitrogen N epsilon (His 57).

Dynamic properties of the first enzymatic reaction steps of porcine pancreatic elastase. How rigid is the active site of the native enzyme? Molecular dynamics simulation

Two molecular dynamics simulations (100 and 50 ps) of native porcine pancreatic elastase i.e., without bound substrate and with the active site hydrated by a dome of water (630 molecules) have been performed. Dynamical properties of the catalytic tetrad have been examined. While relative conformations of the Asp 102, His 57, and Ser 214 are rather stable in time, the side chain of Ser 195 undergoes several conformational changes. No preferences are observed for the formation of a hydrogen bond between the O gamma-H group (Ser 195) and nitrogen N, (His 57). A cluster of ordered water molecules effectively competes with the H-O gamma group (Ser 195) and thereby prevents the formation of this H bond, which is generally agreed to be crucial for catalysis.

Animation: a useful tool for protein molecular dynamicists, applied to hydrogen bonds in the active site of elastase

Massive amounts of coordinate data result from molecular dynamics calculations. The animation program MDKINO is a simple but powerful tool for previewing or reviewing the results. In recent simulations of elastase, we have examined hydrogen bonding patterns, conformational changes involving shifts in ring positions and rotations of amino acid side chains, electric fields in interatomic space, and electric forces acting on chosen nuclei. Animation is also useful for checking on the stability of calculations in progress. Simple programming techniques achieve acceptable levels of animation with readily available hardware (PS330 or PS390 display with a serial interface to a laboratory VAX). In about half an hour, it is possible to make and watch a color stereo "movie" of a selected subsystem of a simulation (up to 1,000 frames of about 100 atoms each).

Evaluation of the mutagenic and cytostatic potential of aristolochic acid (3,4-methylenedioxy-8-methoxy-10-nitrophenanthrene-1-carboxylic acid) and several of its derivatives

Aristolochic acid (1), a constituent of Aristolochia species, has been used for medicinal purposes since the Graeco-Roman period. Following the observation that the compound was mutagenic and carcinogenic, it was removed from pharmaceutical products. Consistent with previous reports, we have found that 1 serves as a direct-acting mutagen in Salmonella typhimurium strains TA100, TA102, TA1537 and TM677, but was not active in the nitroreductase-deficient strains TA98NR and TA100NR. However, aristolic acid (2), a compound that differs in structure only by the absence of the nitro group, was also found to be a direct-acting mutagen in Salmonella strains TA98, TA100, TA102, TA1537, and TM677, as well as strains TA98NR and TA100NR. Both compounds (1 and 2) were active mutagens when evaluated with cultured Chinese hamster ovary cells. Thus, in contrast to previous suggestions, the nitro group at position 10 is not required to induce a mutagenic response. Also, a series of structural relatives (the methyl esters of 1 and 2 (3 and 4, respectively), aristolochic acid-D (5), aristolactam (6), aristolactam A-II (7), and aristolactam-N-beta-D-glucoside (8)) were evaluated for mutagenic potential with Salmonella typhimurium strain TM677 and found to be inactive. Since compounds 3 and 4 were found to be active mutagens with Salmonella typhimurium strains TA98, TA100, TA102 and TA1537 (sufficient quantities of compounds 5-8 were not available for testing), differential sensitivity of the tester strains unrelated to mutagenic potential is suggested. Further, compounds 1, 2, and 6-8 were evaluated for potential to inhibit growth with cultured KB or P388 cells. P388 cells were substantially more sensitive, and compound 1 was the most active of the materials tested (ED5 = 0.58 microM). Compound 6 also demonstrated appreciable activity (ED50 = 4.2 microM), as did compound 8 (ED50 = 6.0 microM). It therefore appears that phenanthrene-ring substituents, in addition to the nitro group at position 10, serve important roles for biological potential. In considering the carcinogenic event induced by aristolochic acid, these functionalities should also be taken into account.

C1q binding by a high affinity anti-fluorescein murine monoclonal IgM antibody and monomeric subunits

Comparative interactions of purified rabbit C1q with 18-2-3, a high affinity (2-3 X 10(10) M-1) anti-fluorescein (anti-F1) murine monoclonal IgM antibody (pentamer) and constitutive monomeric subunits (IgMs) were studied. Using a solid phase radioimmunoassay (SPRIA), based on immobilized polyvalent antigen, it was shown that the mechanism of C1q binding to IgM was characteristically multiphasic while IgMs yielded monophasic binding curves. The latter compared qualitatively and quantitatively with a monoclonal IgG2a anti-fluorescein antibody with the same intrinsic affinity of 2-3 X 10(10) M-1. C1q binding efficiency to antibodies was significantly enhanced when the immunoglobulins interacted with immobilized multivalent antigen. Monoclonal IgM antibody bind identically to six F1-carrier protein conjugates independent of epitope (F1) density. In contrast, the C1q-antibody interaction binding was dependent upon epitope density. An average distance between F1 epitopes of 80 A was optimal for C1q binding by IgM. At low concn of IgM, when fluorescein was bound by antigen-binding sites on adjacent subunits of an intact pentamer, C1q appeared to bind IgM intramolecularly.

Evaluation of the cytotoxic potential of catechols and quinones structurally related to butylated hydroxyanisole

The cytotoxicity of 2- and 3-butylated hydroxyanisole (BHA) and 18 related aromatic compounds has been determined employing cultured P388 and KB cells. The phenolic compounds, 3-BHA and 2-BHA, had moderately low cytotoxic activity. Their corresponding catechols had ED50 values that were much lower than those of the parent compounds. This substantial increase in the cytotoxic activity is attributed to the presence of the catechol group, which is known to undergo one-electron oxidation readily to give the corresponding semiquinone radical. Other related catechols had similar cytotoxic activity. In general, derivatization of the catechol functionality resulted in a decrease of the cytotoxic potential of the compounds. Monoacetylation or monomethylation of the catechols gave products that were less potent cytotoxic agents than the parent compounds. Further loss of activity was observed when both hydroxy groups of the catechol function were blocked. Substitution of a methoxy group in place of a hydrogen atom in these compounds resulted in a significant increase of cytotoxicity, whereas the replacement of a methoxy group with a methyl group reduced the cytotoxicity. The catechols and quinones derived from 2-BHA were more active when compared with those derived from 3-BHA. The t-butyl group adjacent to the catechol or quinone moiety in the 3-BHA derivatives appeared to exert a significant steric effect toward the cytotoxic potential of these compounds. These results suggest the potential use of o-quinones and catechols as cytotoxic and antitumor agents.

Characterization of bacterial mutagenicity mediated by 13-hydroxy-ent-kaurenoic acid (steviol) and several structurally-related derivatives and evaluation of potential to induce glutathione S-transferase in mice

Stevioside is a sweet-tasting diterpene glycoside that is derived from Stevia rebaudiana (Bertoni) Bertoni (Compositae). It is used commercially in Japan and other parts of the world as a sucrose substitute. Whereas stevioside demonstrates no mutagenic activity in a variety of test systems, the aglycone, steviol (13-hydroxy-ent-kaurenoic acid), is mutagenic toward Salmonella typhimurium strain TM677 in the presence of a metabolic activating system derived from the liver of Aroclor 1254-pretreated rats. The required activating component is localized in the microsomal fraction of rat liver, suggestive of a cytochrome P-450-mediated reaction. Partially purified epoxide hydrolase does not inhibit steviol-induced mutagenicity, indicating that an active metabolite is not an epoxide that serves as a substrate for this enzyme preparation. The 13-hydroxy group of steviol is required for the expression of mutagenicity since ent-kaurenoic acid is nonmutagenic, and acetylation of steviol at this position negates mutagenicity. Similarly, diterpenes bearing a strong structural resemblance to steviol, cafestol and kahweol, were found to demonstrate no mutagenic activity toward Salmonella typhimurium TM677, as were their respective acetates and palmitic acid esters. Conversely, 19-O-beta-D-glucopyranosyl steviol, a potential hydrolysis product of stevioside, is mutagenic and bactericidal in the presence of a metabolic activating system. Additionally, in contrast to the nonmutagenic diterpenes cafestol and kahweol that are effective as inducers of glutathione S-transferase activity, evaluation by administration to mice proved steviol, isosteviol and various steviol glycosides to be inactive in this process. Thus, structural differences among these naturally occurring and semi-synthetic diterpenes appear to impart major differences in biological activity that may relate to human health upon dietary ingestion.

Metabolically activated steviol, the aglycone of stevioside, is mutagenic

Stevioside, a constituent of Stevia rebaudiana, is commonly used as a noncaloric sugar substitute in Japan. Consistent with reports in the literature, we have found that stevioside is not mutagenic as judged by utilization of Salmonella typhimurium strain TM677, either in the presence or in the absence of a metabolic activating system. Similar negative results were obtained with several structurally related sweet-tasting glycosides. However, steviol, the aglycone of stevioside, was found to be highly mutagenic when evaluated in the presence of a 9000 X g supernatant fraction derived from the livers of Aroclor 1254-pretreated rats. Expression of mutagenic activity was dependent on both pretreatment of the rats with Aroclor 1254 and addition of NADPH; unmetabolized steviol was not active. The structurally related species, isosteviol, was not active regardless of metabolic activation. Similarly, chemical reduction of the unsaturated bond linking the carbon-16 and -17 positions of steviol resulted in the generation of two isomeric products, dihydrosteviol A and B, that were not mutagenic. In addition, ent-kaurenoic acid was found to be inactive. It is therefore clear that a metabolite of an integral component of stevioside is mutagenic; structural features of requisite importance for the expression of mutagenic activity include a hydroxy group at position 13 and an unsaturated bond joining the carbon atoms at positions 16 and 17. A potential metabolite of steviol, steviol-16 alpha,17-epoxide, was synthesized chemically and found to be ineffective as a direct-acting mutagen. Thus, although stevioside itself appears innocuous, it would seem prudent to expeditiously and unequivocally establish the human metabolic disposition of this substance.

Evaluation of the mutagenic potential of endod (Phytolacca dodecandra), a molluscicide of potential value for the control of schistosomiasis

Extracts of the fruit of Phytolacca dodecandra (endod) demonstrate molluscicidal and other biological activities. Since this plant is indigenous to some countries where schistosomiasis is a common problem, it has been proposed that it may be socioeconomically feasible to employ endod as an aid in the control of this disease through its use to control the snail vector. As an initial step in the safety assessment of this substance, its mutagenic potential was determined utilizing Salmonella typhimurium strain TM677. The seeds and fruit of Phytolacca americana, also molluscicidal, were additionally evaluated for mutagenic potential. Using a variety of conditions, no mutagenic activity could be demonstrated for any of the extracts tested. Thus, subject to the results of future safety assessment, endod remains a viable candidate as a useful molluscicide.

Levels of 226Ra, 210Pb and total U in fish near a Saskatchewan uranium mine and mill

Radionuclide levels in fish from the Beaverlodge Lake area, Saskatchewan, Canada, varied significantly among lakes, species and tissues, but did not vary with fish sex or age. Fish from lakes affected by an operating uranium mine and mill had radionuclide levels one to two orders of magnitude above levels in fish from an uncontaminated control lake. Concentrations were greatest in white suckers, intermediate in lake whitefish, and low in lake trout. Skin and bone contained the highest radionuclide levels; levels in flesh were much lower. The mean ash-weight concentration of 226Ra in non-control, eviscerated, whole fish was 9.3, 1.8 and 0.8 pCi X g-1 in white suckers, lake whitefish and lake trout respectively. Mean 210Pb levels for those species were 4.0, 1.4 and 0.5 pCi X g-1, while U content was 96.8, 28.2 and 5.8 micrograms X g-1, respectively. Radium-226 content in forage fish ranged from 9.7-70 pCi X g-1. Lead-210 levels ranged from 3.9-55.0 pCi X g-1, while U levels ranged from 15-119 micrograms X g-1. Bioconcentration factors varied among sites, species and tissues. The primary radionuclide transfer pathway appears to be via sediments, either through direct contact or through food organisms. Bottom-feeding species had the highest radionuclide levels while piscivorous fish had the lowest levels. The internal dose rate to non-control fish are comparatively low; any effects are likely to occur at the genetic level.

Comparison of rest/exercise ECG, thallium-201 scans and radionuclide angiography in patients with suspected coronary artery disease

The results of rest and exercise ECG, 201Tl myocardial perfusion imaging and equilibrium radionuclide angiography were analyzed in 71 consecutive patients referred for diagnosis or evaluation of coronary artery disease (CAD). In 45 patients the diagnosis was established either by catheterization or typical history. In this group the overall sensitivity for rest/exercise ECG was 66%, for 201Tl scans 74%, for both combined 79% and for the ejection fraction response to exercise determined by radionuclide angiography 97%. If only the exercise response was considered, the corresponding sensitivity values were 58% (ECG), 50% (201Tl scans), 71% (ECG + 201Tl) and 97% (radionuclide angiography). The specificity for coronary artery disease was determined to be 71% for ECG, 86% for 201Tl scans and 42% for radionuclide angiography. All patients with false-positive results by radionuclide angiography had cardiomyopathies, thus this test has a high specificity for left ventricular dysfunction rather than for CAD alone. Criteria developed from the analysis of the test results in the 45 patients with definite diagnoses were then applied to the evaluation of 26 additional patients with atypical chest pain. A diagnosis could be made in all but 5 of them and radionuclide angiography was again the single most reliable test. Based on this study a new approach for the noninvasive evaluation of patients with suspected coronary artery disease is proposed.

Reproducibility of ejection-fraction determinations by equilibrium radionuclide angiography in response to supine bicycle exercise: concise communication

Sixteen patients with stable, chronic coronary artery disease were studied twice within and average of 15 days to evaluate the reproducibility of ejection fraction (EF) determined by equilibrium radionuclide angiography (EQ) at rest, during supine bicycle exercise (ex), and in the recovery period (rec). Following injection of 20--25 mCi of Tc-99m-tagged human serum albumin, data were analyzed for 2-min periods at rest, during several stages of exercise (submax, max), and during recovery (rec1 = minutes 2 + 3, rec2 = minutes 9 + 10). Each patient reached similar (heart rate) X (blood pressure) products in the two studies: 21280 +/- 5200 compared with 20390 +/- 4140 mmHg/min. Mean EFs for the first and second studies were: at rest (53.0 +/- 10.8)%, 52.5 +/- 10.4)% (r = 0.95; submax ex (51.4 +/- 12.0)%, (52.1 +/- 12.8)%, (r = 0.91); max ex (50.6 +/- 12.6)%, (51.6 +/- 12.9)% (r = 0.97); rec1 (62.7 +/- 11.6)%, (62.4 +/- 12.2)% (r = 0.95); rec2 (55.5 %/- 10.8)%, (57.2 +/- 11.7)% (r = 0.91). In stable patients, the reproducibility of EF determined by EQ is excellent during rest, supine bicycle exercise, and recovery from exercise.