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Biomedical subjects

S A Masten

Publications and source records attributed to S A Masten.

8 recordsLinked to original sources
PubMed2000

Levels of methyleugenol in a subset of adults in the general U.S. population as determined by high resolution mass spectrometry.

We developed a sensitive and accurate analytical method for quantifying methyleugenol (ME) in human serum. Our method uses a simple solid-phase extraction followed by a highly specific analysis using isotope dilution gas chromatography-high resolution mass spectrometry. Our method is very accurate; its limit of detection is 3.1 pg/g and its average coefficient of variation is 14% over a 200-pg/g range. We applied this method to measure serum ME concentrations in adults in the general U.S. population. ME was detected in 98% of our samples, with a mean ME concentration of 24 pg/g (range < 3.1-390 pg/g). Lipid adjustment of the data did not alter the distribution. Bivariate and multivariate analyses using selected demographic variables showed only marginal relationships between race/ethnicity and sex/fasting status with serum ME concentrations. Although no demographic variable was a good predictor of ME exposure or dose, our data indicate prevalent exposure of U.S. adults to ME. Detailed pharmacokinetic studies are required to determine the relationship between ME intake and human serum ME concentrations.

Adolescent↗
PubMed1999

Quantitative analysis of constitutive and 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced cytochrome P450 1B1 expression in human lymphocytes.

Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD or dioxin) results in a broad spectrum of biological responses, including altered metabolism, disruption of normal hormone signaling pathways, reproductive and developmental effects, and cancer. Cytochrome P450 1B1 (CYP1B1) is a dioxin-inducible gene that is active in the formation of 4-hydroxyestradiol, a potentially genotoxic catechol estrogen. Therefore, the analysis of CYP1B1 in humans may be useful in establishing relationships between dioxin exposure and adverse health effects. In this study, we examined the expression of CYP1B1 in human peripheral blood lymphocytes of unexposed individuals using a quantitative reverse transcription-PCR method. Absolute CYP1B1 RNA levels varied more than 30-fold in uncultured mononuclear cells obtained from 10 individuals. In vitro treatment of mitogen-stimulated lymphocytes with TCDD for 1-5 days of culture resulted in a peak induction of CYP1B1 after 3 days. The induction of CYP1B1 RNA levels after 3 days of culture was dose-dependent, exhibited a maximum response above 10 nM TCDD, and varied greatly among different individuals. However, the half maximal dose required for this induction was similar between individuals and comparable to that observed in the MCF-7 and HepG2 human cell lines. These observations indicate that CYP1B1 exhibits variable constitutive expression and is inducible in vitro by TCDD in human lymphocytes and that the magnitude of induction varies within the population. These data define the suitability of CYP1B1 for use as a mechanistically based biomarker in ongoing molecular epidemiological studies of human populations exposed to dioxins and related chemicals that bind the aromatic hydrocarbon receptor.

Adult↗
PubMed1998

Animal models of human response to dioxins.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is the most potent member of a class of chlorinated hydrocarbons that interact with the aryl hydrocarbon receptor (AhR). TCDD and dioxinlike compounds are environmentally and biologically stable and as a result, human exposure is chronic and widespread. Studies of highly exposed human populations show that dioxins produce developmental effects, chloracne, and an increase in all cancers and suggest that they may also alter immune and endocrine function. In contrast, the health effects of low-level environmental exposure have not been established. Experimental animal models can enhance the understanding of the effects of low-level dioxin exposure, particularly when there is evidence that humans respond similarly to the animal models. Although there are species differences in pharmacokinetics, experimental animal models demonstrate AhR-dependent health effects that are similar to those found in exposed human populations. Comparisons of biochemical changes show that humans and animal models have similar degrees of sensitivity to dioxin-induced effects. The information gained from animal models is important for developing mechanistic models of dioxin toxicity and critical for assessing the risks to human populations under different circumstances of exposure.

Animals↗
PubMed1997

Evidence that a mitogen-inducible prolactin-immunoreactive protein in rat spleen lymphocytes is aldolase A.

This study characterizes several proteins in rat spleen lymphocyte lysates and conditioned medium that are recognized by antiserum to purified rat pituitary prolactin (PRL). One of these proteins, rat prolactin-immunoreactive protein (rPIP-43), has a relative molecular mass (Mr) of 43,000 and is strongly induced by mitogenic stimulation in spleen lymphocytes. A constitutively expressed protein of this size also was detected in the IM-9 human B lymphoblastoid cell line and the Nb2 rat T lymphoma cell line. The N-terminal amino acid sequence of rPIP-43 in spleen lymphocyte lysate was analysed and found to be identical with 25 residues at the N-terminus of the glycolytic enzyme aldolase A. In further experiments, the rPRL antiserum was evaluated for cross-reactivity with an aldolase A preparation and recognized a Mr 43,000 protein in rabbit muscle. Preabsorption of rPRL antiserum with rPRL was found to greatly decrease the intensity of staining of rPRL, aldolase A and rPIP-43. Preabsorption of antiserum with aldolase A had a similar, but less pronounced effect, with the aldolase A band and rPIP-43 being stained less intensely, while there was no effect on the intensity of staining of purified rPRL. Thus, data indicate that rPIP-43 is not a structural variant of PRL, but appears to be a different protein. These results have implications for the use of PRL antiserum to detect PRL in biological samples insofar as aldolase A is a ubiquitously expressed protein.

Amino Acid Sequence↗
PubMed1996

Characterization of the aryl hydrocarbon receptor complex in human B lymphocytes: evidence for a distinct nuclear DNA-binding form.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) suppresses B lymphocyte proliferation and immunoglobulin production. We previously reported that the aryl hydrocarbon receptor (AhR) complex, composed of the AhR ligand binding subunit and the Ah receptor nuclear translocator (ARNT), was constitutively present in nuclear extracts from two human B lymphocyte cell lines (Biochem. Biophys. Res. Commun. 212, 27-34, 1995). The present study compared the AhR complex in the IM-9 and PJS-91 human B lymphocyte and HepG2 human hepatoma cell lines. AhR mRNA levels in the two lymphocyte cell lines were substantially lower than those in HepG2 cells, as was immunoreactive AhR protein. In contrast, ARNT mRNA and protein were expressed at a high level in all three cell lines. TCDD induction of cytochrome P450 1A1 mRNA and protein was detected in only the PJS-91 lymphocyte cell line, and at a markedly lower level than that in HepG2 cells. In gel shift assays, the cytosolic DNA-binding AhR complex in IM-9 and PJS-91 cells was indistinguishable from that in HepG2 cells. In contrast, the nuclear DNA-binding AhR complex in IM-9 and PJS-91 cells consisted of several closely migrating species, one being recognized by an AhR antibody, while an ARNT antibody reacted with all species. Protein:DNA cross-linking analysis revealed the presence of a novel Mr 100,000 DNA-binding protein in nuclear extracts from IM-9 and PJS-91, but not HepG2, cells that was not recognized by either AhR or ARNT antibodies. These results show that IM-9 and PJS-91 human B cells constitutively express a distinct nuclear DNA-binding form of the AhR complex that may result from the presence of an additional protein or a structural variant of the AhR.

Aryl Hydrocarbon Receptor Nuclear Translocator↗
PubMed1996

Evaluation of immune parameters and lymphocyte production of prolactin-immunoreactive proteins after chronic administration of cocaine to pregnant rats.

This study examined the effect of chronic cocaine exposure on selected immune parameters in pregnant rats. Cocaine hydrochloride, 60 mg/kg, was administered by i.p. injection as a divided daily dose on gestation days 8 to 19. This cocaine treatment regimen did not result in any change in maternal body weight, spleen and thymus body weight ratios or lymphocyte recovery from these organs. Cocaine treatment had no effect on the plasma levels of prolactin, growth hormone and insulin-like growth factor-1; hormones with immunoregulatory potential. In contrast, the plasma immunoglobulin G concentration in cocaine-treated animals was 48% higher (P < .05) than in control animals. Spleen lymphocytes and thymocytes were isolated and evaluated for their proliferative responses in vitro to a panel of T and B cell mitogens. Lymphocytes from cocaine-treated animals showed no significant differences in proliferative responses to concanavalin A (conA), phytohemagglutinin, pokeweed mitogen, interleukin-2 or lipopolysaccharide. The ability of conA-stimulated spleen lymphocytes to synthesize and secrete prolactin-immunoreactive proteins was further assessed by Western immunoblotting. We found that conA-stimulated spleen lymphocytes from cocaine-treated animals showed significantly decreased levels of intracellular and secreted 44,000-mw prolactin-immunoreactive proteins. In contrast, conA-stimulated spleen lymphocytes from control and cocaine-treated groups secreted equivalent amounts of the cytokine interleukin-2. In conclusion, chronic administration of cocaine to female rats during pregnancy significantly altered serum immunoglobulin G levels and lymphocyte production of prolactin-immunoreactive proteins in the absence of changes in lymphocyte proliferation in response to mitogens.

Animals↗
PubMed1995

The Ah receptor recognizes DNA binding sites for the B cell transcription factor, BSAP: a possible mechanism for dioxin-mediated alteration of CD19 gene expression in human B lymphocytes.

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) inhibits murine and human B lymphocyte immunoglobulin production through an unknown mechanism. This study investigated the effect of TCDD on expression of the CD19 gene in a human B lymphocyte cell line. Northern blot analysis showed that TCDD treatment decreased steady state levels of CD19 mRNA by 67% in the IM-9 cell line. Using a gel mobility shift assay, we identified a DNA-binding complex in IM-9 nuclear extracts that by several criteria appears to be the Ah receptor. In addition, the Ah receptor complex recognized a DNA binding site for B cell lineage-specific activator protein (BSAP) in the promoter region of the human CD19 gene which is similar to the consensus Ah receptor DNA binding site. These results suggest that the AhR could interfere with BSAP-stimulated CD19 gene transcription by competition for a common DNA binding site.

Animals↗