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Biomedical subjects

J Ashby

Publications and source records attributed to J Ashby.

At least 37 records · Page 2Linked to original sources
PubMed2001

The uterotrophic activity of nonylphenol in the rat is not mediated by aromatase enzyme induction.

p-Nonylphenol (NP) is weakly estrogenic to rodents and to some species of fish. All evidence to date has indicated that the estrogenic effects of NP are due to the interaction of NP with the estrogen receptor. Recent findings of increased plasma estradiol in fish exposed to NP have, however, led to the proposal of an alternative mechanism for NP-induced estrogenicity in this species, possibly via induction of aromatase enzymes. In the present studies, this hypothesis was investigated in rats using the aromatase inhibitor anastrozole. The results indicated that the uterotrophic action of NP, as with estradiol used as a positive control, is mediated directly by its interaction with uterine ER, rather than an indirect effect via aromatase enzyme induction. Circulating levels of estradiol were unchanged after NP treatment and the aromatase inhibitor anastrozole failed to inhibit NP-induced uterine growth. These results are consistent with previous published data on NP in rodents.

Anastrozole↗
PubMed2001

Glucuronidation of nonylphenol and octylphenol eliminates their ability to activate transcription via the estrogen receptor.

Both p-nonylphenol (NP) and p-octylphenol (OP) exhibit weak estrogen-like activity in in vitro and in some rodent assays. To help understand the biochemical and molecular basis for these effects, and thus to permit extrapolation of risk to human health, it is important to establish whether these activities are retained by their metabolites. These data are particularly important in light of the knowledge that both NP and OP are rapidly and extensively metabolized to their glucuronide conjugates in rats. The activity of these glucuronide metabolites, however, is unknown. These studies investigated the intrinsic ability of NP, OP, and their principal mammalian metabolites, nonylphenol glucuronide (NPG) and octylphenol glucuronide (OPG), to affect estrogen receptor (ER)- or androgen receptor (AR)-mediated transcription in a yeast transcriptional activation system. Specifically, the estrogen-, anti-estrogen-, androgen-, and anti-androgen-like activities of NP, OP, NPG, and OPG have been assessed using recombinant yeast strains that express either human ER or AR. The two parent compounds, NP (EC(50) 110 nM) and OP (EC(50) 700 nM), exhibited intrinsic estrogen-like activity in this system, and consistent with numerous studies with these chemicals, they were 3-4 orders of magnitude less potent than 17beta-estradiol (EC(50) 500 pM). However, in contrast to the parent molecules, neither NPG nor OPG exhibited any evidence of estrogen-, antiestrogen-, androgen-, or anti-androgen-like activity in these recombinant yeast strains. Therefore, the weak estrogen-like activity noted for NP and OP in vivo at high doses is likely to reflect saturation of parent molecule glucuronidation. At anticipated levels of human exposure to NP and OP such a saturation of detoxification is highly unlikely; therefore, these in vitro data support the conclusion that the potential endocrine hazard posed by NP and OP to humans is likely to be negligible.

Androgen Antagonists↗
PubMed2001

Replacement of surgical castration by GnRH-inhibition or Leydig cell ablation in the male rat Hershberger antiandrogen assay.

An obstacle to the widespread adoption of the Hershberger antiandrogen assay is the surgical castration procedure required to produce androgen deficiency in the test animals. Here we describe two chemical treatments that produce similar effects to surgical castration. The first is use of ethane dimethane sulphonate (EDS), a specific toxin to the testosterone-producing Leydig cells of the mature testes. The second class of compound is the decapeptide inhibitors of the gonadotrophin-releasing hormone (GnRH), compounds such as Antarelix and Antide. Administration of either EDS or the GnRH inhibitors results in loss of weight of the testes, epididymides, and sex-associated tissues. Co-administration of testosterone to these animals leads to reversal of the induced effects. The basic test protocol for both of these assay modifications is described. Flutamide was used as a representative potent antiandrogen, and DDE as an example of a weakly active antiandrogen. The 5alpha-reductase inhibitor finasteride was used to inhibit the transformation of testosterone to dihydrotestosterone. It is shown that the EDS assay is sensitive to the antiandrogen flutamide, but that it fails to detect the weaker antiandrogen DDE. In contrast, the Antarelix assay performs as well as does the classical castration assay, leading to the detection as antiandrogens of flutamide, DDE, and finasteride. It is concluded that the GnRH inhibition Hershberger assay is more convenient to conduct than the original surgical castration assay, and it involves less stress to the test animals.

5-alpha Reductase Inhibitors↗
PubMed2001

Lack of binding to isolated estrogen or androgen receptors, and inactivity in the immature rat uterotrophic assay, of the ultraviolet sunscreen filters Tinosorb M-active and Tinosorb S.

The presence of structurally diverse chemicals as contaminants in the environment has led to concerns regarding their possible endocrine disturbing effects. Recently, some ultraviolet absorbing components of sunscreen preparations have given positive responses in assays monitoring estrogen-like activity both in vitro and in vivo. Consequently, two recently developed sunscreen components, Tinosorb M-active and Tinosorb S, were evaluated using the in vitro estrogen and androgen receptor competitive binding assays. Neither compound gave a positive response in either of the assays, consistent with the large molecular dimensions of each chemical disfavoring binding to the hormone receptors. Both of the chemicals were inactive in immature rat uterotrophic assays conducted using the subcutaneous route of administration. It is concluded that neither of these agents possess intrinsic estrogenic/antiestrogenic or androgenic/antiandrogenic activity. The several positive control chemicals evaluated gave the expected positive responses in the assays used.

Animals↗
PubMed2001

Eye movement control in reading: word predictability has little influence on initial landing positions in words.

We examined the initial landing position of the eyes in target words that were either predictable or unpredictable from the preceding sentence context. Although readers skipped over predictable words more than unpredictable words and spent less time on predictable words when they did fixate on them, there was no difference in the launch site of the saccade to the target word. Moreover, there was only a very small difference in the initial landing position on the target word as a function of predictability when the target words were fixated which is most parsimoniously explained by positing that a few programmed skips of the target word fell short of their intended target. These results suggest that low-level processing is primarily responsible for landing position effects in reading.

Eye Movements↗
PubMed2001

Effects of testosterone replacement on a male professional singer.

Testosterone has been known to play an important role in the development of the postpubertal male voice for many centuries. In fact, the prevention of pubertal development of the voice by castrating young male singers was a well-known practice, especially in Italy beginning in the sixteenth century. The "castrati" were well known for their clear, high-pitched voices. Because of the resulting small larynx and vocal folds, castrati apparently produced a distinctive resonance as well as the high pitch, which cannot be matched even by the counter tenors of today. Busy voice labs occasionally see males with sex hormone deficiencies secondary to chromosomal or gonadal problems. This is a presentation of an unusual patient who was a trained tenor singer and was found to have hypogonadism on a premarital health examination. Administration of replacement testosterone resulted in significant vocal register and voice quality changes.

Adolescent↗
PubMed2001

Expectations for transgenic rodent cancer bioassay models.

The results of the present study have advanced dramatically the database on transgenic mouse abbreviated carcinogenicity bioassay models. As such, it will provide a secure foundation for future evaluations of these assays and for their eventual validation as models for the prediction of possible human carcinogens. Based upon the results derived from the present study, it is suggested that 5 areas require discussion as a prelude to the further evaluation of existing models and the future evaluation of new models. First, there is the need to agree a standard list of calibration chemicals to be studied and to derive agreement on optimal bioassay group sizes, statistical methods, and exposure periods. Second, general agreement must be reached regarding the classes/types of known rodent carcinogens so that it is acceptable for the new models to find negative, by implication, those rodent carcinogens considered not to pose a carcinogenic hazard to humans. Third, current understanding of mechanisms of carcinogenesis should be integrated into the evaluation of new bioassay models. Fourth, any changes made to the standard rodent carcinogenicity bioassay protocol will require compromises being made, and these should be commonly owned between interested parties in order to reduce the number of regional/agency-specific carcinogenicity testing schemes. Fifth, a mechanism needs to be developed by which assays can be adopted or rejected for use in the routine bioassay of chemicals. In the absence of such initiatives the increasing number of new bioassay models will come to exist along side of the standard 2-species bioassay, and this may potentially lead to confusion regarding the true future role of these assays.

Animal Testing Alternatives↗
PubMed2001

The application of the restriction site mutation assay to compare 1-ethyl-1-nitrosourea-induced mutations between the endogenous p53 gene and the transgenic LacZ gene in MutaMouse testes.

Transgenic mouse modelling has provided a new approach to study the various steps involved in spontaneous and induced mutagenesis in rodent somatic and germline tissues in vivo. However, the important question arises as to whether mutations occur at the same rate in transgenes as in endogenous genes. Here, the restriction site mutation (RSM) assay was used to study mutations induced in the endogenous p53 gene and LacZ transgene of MutaMouse testes treated with 1-ethyl-1-nitrosourea (ENU). The aim of these experiments was to compare mutation susceptibility between the endogenous p53 gene and the integrated LacZ gene in the transgenic mouse. ENU-treated and control testes were analysed 102 days after treatment; a total of 297 RSM analyses were performed on ENU-treated and untreated testis DNA. Ten mutational events were detected in the p53 gene (exon 5 and intron 8), two of which occurred in untreated animals and probably represent spontaneous events. Only a single mutation was detected in the LacZ gene of an ENU-treated animal by the RSM assay. Thus the RSM assay can readily detect ENU-induced mutations in the p53 gene, but not in the LacZ transgene. Comparison of the LacZ RSM mutation data with results from a previous study of identically dosed MutaMice in the transgenic selection assay [Ashby, J., Gorelick,N.J. and Shelby,M.D. (1997) Mutat. Res., 388, 111-122] showed that LacZ mutations were far more readily recovered with the MutaMouse transgenic selection assay than by RSM analysis. The reason for the relative inability of the RSM assay to detect LacZ mutations may be the smaller target size of the RSM analysis compared with the transgenic selection assay (16 bases compared with 3000 bases). Taking into account the different target sizes by calculating the mutation frequency per base allowed the RSM data regarding p53 and LacZ to be compared with previously published data from transgenic selection assays. These studies demonstrated that the p53 mutations were present at mutation frequencies (per base) 5- to 70-fold higher than the LacZ gene mutations. In addition, the LacZ mutation frequency per base found in the RSM was an order of magnitude higher than that found in the transgenic selection assay. The transgenic selection assay is more sensitive per locus (due to the larger target of the LacZ gene), as evidenced by ability to detect ENU-induced testes mutations readily.

Alkylating Agents↗
PubMed2001

The male rat carcinogens limonene and sodium saccharin are not mutagenic to male Big Blue rats.

Limonene and sodium saccharin are male rat specific carcinogens giving rise to renal and bladder tumours, respectively. Both compounds give negative results in genetic toxicity assays suggesting a non-genotoxic mode of action for their carcinogenicity. The alpha 2U-globulin accumulation theory has been invoked to explain the renal carcinogenicity of limonene: the accumulation of micro masses of calcium phosphate in the bladder, coupled with a high pH environment in the male rat bladder, has been suggested to be responsible for the bladder carcinogenicity of sodium saccharin. The implication of these proposed mechanisms is that limonene and sodium saccharin will not be mutagenic to the rat kidney and bladder, respectively. This proposal has been evaluated by assessing the mutagenic potential of the two chemicals to male lacI transgenic (Big Blue) rats. Male Big Blue rats were exposed for 10 consecutive days to either limonene in diet, at a dose level in excess of that used in the original National Toxicology Program gavage carcinogenicity bioassay, or to sodium saccharin in diet at the dose known to induce bladder tumours. The multi-site rat carcinogen 4-aminobiphenyl was used as a positive control for the experiment. Limonene failed to increase the mutant frequency in the liver or kidney of the rats, and sodium saccharin failed to increase the mutant frequency in the liver or bladder of the rats. 4-Aminobiphenyl was mutagenic to all three of these tissues. These results add further support to a non-genotoxic mechanism of carcinogenic action for both limonene and sodium saccharin.

Administration, Oral↗
PubMed2001

Effect of rodent diets on the sexual development of the rat.

Five rodent diets have been evaluated for their possible effect on the sexual development of the rat. Groups of 12 pregnant Alpk rats were fed one of the following combinations of diets during pregnancy and postnatally: RM3/RM1, AIN-76A/AIN-76A, RM3/AIN-76A, Teklad Global 2016 (Global)/Global and Purina 5001/Purina 5001. AIN-76A is phytoestrogen-free while the other diets contained varying amounts of phytoestrogens. The phytoestrogens genistein and daidzein were determined in the diets studied, and the concentrations found agreed with earlier estimates. RM3/RM1 was selected as the control group, as this has been used routinely in this laboratory for the past decade. Determinations were made in offspring of the times of vaginal opening and first estrus among the females, and of prepuce separation and testes descent among the males. At postnatal day (PND) 26 the females from 6 of the 12 litters were terminated and tissue weights measured. Males from 6 of the 12 litters were similarly studied at PND 68. Animals from the remaining litters were transferred to RM1 diet at PND 70. Termination of the study was at PND 128 (males) and PND 140 (females) when body weights and tissue weights were determined. Marked differences in body weight, sexual development, and reproductive tissue weights were observed for rats maintained on AIN-76A or Purina 5001, with only minimal effects among rats maintained on the Global diet. These comparisons were against RM3/RM1 as the reference diet. However, using Purina 5001 as the reference diet reversed the direction of the differences seen when using RM3/RM1 as the reference diet. The differences observed when using RM3/RM1 as reference diet occurred mainly postnatally. In addition, the fact that similar differences were seen for the phytoestrogen-free diet, AIN-76A, and the phytoestrogen-rich diet, Purina 5001, indicate that these effects are more likely to be caused by nutritional differences between the diets that then have centrally mediated effects on rodent sexual development, rather than individual dietary components affecting peripheral estrogen receptors (ER). This proposal is supported by abolition of the uterotrophic activity of AIN-76A and Purina 5001 (relative to RM3/RM1) in the immature rat by coadministration of the gonadotrophin-releasing hormone (GnRH) antagonist ANTARELIX: The present data indicate that choice of diet may influence the timing of sexual development in the rat, and consequently, that when evaluating the potential endocrine toxicity of chemicals, the components of rodent diets used should be known, and as far as is possible, controlled.

Age Factors↗
PubMed2001

Pharmacokinetics and tissue penetration of linezolid following multiple oral doses.

The pharmacokinetics of multiple-dose linezolid were determined following administration of five 600-mg oral doses given every 12 h to each of six healthy male volunteers. Concentrations of the drug were determined in plasma and inflammatory blister fluid using high-pressure liquid chromatography. A mean peak concentration in plasma of 18.3 microg/ml (standard deviation [SD], 6.0) was attained at a mean time of 0.7 h (SD, 0.3) after the final dose. The penetration into the inflammatory fluid was 104% (SD, 20.7). A mean peak concentration of 16.4 microg/ml (SD, 10.6) was attained in the inflammatory fluid at 3 h (SD, 0.6) after the final dose. The elimination half-life from serum and inflammatory fluid was 4.9 (SD, 1.8) and 5.7 (SD, 1.7) h, respectively. The area under the concentration-time curve in plasma and blister fluid was 140.3 (SD, 73.1) and 155.3 (SD, 80.1) microg x h/ml, respectively. These data suggest that linezolid has good tissue penetration, and we can predict that it will be successful in the treatment of a variety of gram-positive infections.

Acetamides↗
PubMed2001

Increasing the sensitivity of the rodent uterotrophic assay to estrogens, with particular reference to bisphenol A.

The gravimetric uterotrophic assay is currently the most well-established, short-term rodent estrogenicity assay. Increasing attention is being paid to the extent to which use of morphometric or molecular changes in the uterus could act as surrogates for the gravimetric end point of the assay, thereby perhaps increasing the sensitivity of the assay. In this paper I discuss the available data, paying particular attention to studies on bisphenol A (BPA) because it offers the largest database for consideration. I conclude that the case has yet to be made for augmenting the gravimetric end point of the uterotrophic assay. To resolve this important question, it will be necessary to conduct detailed dose-response studies where the no-observed-effect level (NOEL) for the proposed surrogate end points are compared with the NOEL for the gravimetric end point. Currently, few such studies exist, and among those that do no clear message emerges. The general trend to increasing use of molecular assays in toxicology (multigene microarrays and real-time polymerase chain reaction) emphasizes the need for clear criteria for comparing the performance of individual markers of toxicity.

Animals↗
PubMed2001

The OECD program to validate the rat uterotrophic bioassay to screen compounds for in vivo estrogenic responses: phase 1.

The Organisation for Economic Co-operation and Development has completed the first phase of an international validation program for the rodent uterotrophic bioassay. This uterotrophic bioassay is intended to identify the in vivo activity of compounds that are suspected agonists or antagonists of estrogen. This information could, for example, be used to help prioritize positive compounds for further testing. Using draft protocols, we tested and compared two model systems, the immature female rat and the adult ovariectomized rat. Data from 19 participating laboratories using a high-potency reference agonist, ethinyl estradiol (EE), and an antagonist, ZM 189,154, indicate no substantive performance differences between models. All laboratories and all protocols successfully detected increases in uterine weights using EE in phase 1. These significant uterine weight increases were achieved under a variety of experimental conditions (e.g., strain, diet, housing protocol, bedding, vehicle). For each protocol, there was generally good agreement among laboratories with regard to the actual EE doses both in producing the first significant increase in uterine weights and achieving the maximum uterine response. Furthermore, the Hill equation appears to model the dose response satisfactorily and indicates general agreement based on calculated effective dose (ED)(10) and ED(50) within and among laboratories. The feasibility of an antagonist assay was also successfully demonstrated. Therefore, both models appear robust, reproducible, and transferable across laboratories for high-potency estrogen agonists such as EE. For the next phase of the OECD validation program, both models will be tested against a battery of weak, partial estrogen agonists.

Animals↗
PubMed2001

Assessment of the effects of metabolism on the estrogenic activity of xenoestrogens: a two-stage approach coupling human liver microsomes and a yeast estrogenicity assay.

Concern that the reproductive health of humans is being affected by exposure to xenoestrogens has led to the development of various in vitro and in vivo screening assays for the identification of suspected xenoestrogens. However, the estrogenic activity of a chemical determined in vitro may not necessarily predict its activity in vivo if the chemical is metabolized during the assay and/or in vivo. Therefore, to investigate the role of metabolism in modulating the estrogenic activity of suspected xenoestrogens, we have devised a two-stage approach coupling incubations with either human or rat hepatic microsomes with a yeast estrogenicity (transcription) assay. We have assessed the activity of the proestrogenic pesticide 99.5% methoxychlor [1,1,1-trichloro-2,2-bis-(4-methoxyphenyl)ethane, MXC] (EC(50) = 4.45 +/- 1.9 ,icroM, n = 6) and a structural analog, methoxybisphenol A [2,2-bis-(4-methoxyphenyl) propane, MBPA], in the yeast estrogenicity assay and also established that yeast (Saccharomyces cerevisiae), unlike human liver microsomes, are not able to demethylate MXC or MBPA to estrogenic metabolites. This indicates that the proestrogen MXC has weak intrinsic estrogenic activity. Using 99.5% MXC and 17beta-estradiol as paradigms, we have demonstrated how metabolism can enhance or suppress, respectively, estrogenic activity. The effect of metabolism on the activities of the weak xenoestrogens 3,17beta-bisdesoxyestradiol [1,3,5(10)-estratriene] and 6-hydroxytetralin (5,6,7,8-tetrahydro-2-naphthol) was also assessed. This two-stage approach can distinguish the estrogenic activity of a suspect chemical from the activity due to its more, or less, active metabolites and will aid in the evaluation of novel xenoestrogens and, more importantly, proestrogens.

Animals↗