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Biomedical subjects

M A Gallo

Publications and source records attributed to M A Gallo.

At least 55 records · Page 3Linked to original sources
PubMed1995

Polyamine-mediated conformational perturbations in DNA alter the binding of estrogen receptor to poly(dG-m5dC).poly(dG-m5dC) and a plasmid containing the estrogen response element.

The binding estrogen receptor (ER) to the upstream regions of estrogen-responsive genes, the estrogen response elements (ERE), is of fundamental importance in the regulation of gene expression by estradiol. Multiple cell-specific factors affect ER-ERE binding and modulate the responses of estradiol. We studied the role of polyamines in the recognition of ER, a ligand-activated transcription factor, with a left-handed Z-DNA forming polynucleotide as well as with a plasmid containing ERE. Polyamines are cellular organic cations with multiple functions in cell growth and differentiation. Polyamines induce Z-DNA conformation in alternating purine-pyrimidine sequences. To understand the role of polyamine-induced DNA conformational transition in ER-DNA interaction, we studied the binding of partially purified rabbit uterine ER to poly(dG-m5dC).poly(dG-m5dC). The induction of Z-DNA in the polynucleotide was monitored by circular dichroism and ultraviolet spectroscopic measurements. Binding of ER to poly(dG-m5dC).poly(dG-m5dC) increased from 15% to approx. 50-60% in the presence of 7.5 mM putrescine, 0.5 mM spermidine or 0.25 mM spermine. Maximal binding of ER to the polynucleotide was observed near the midpoint of the B-DNA to Z-DNA transition of the polynucleotide. N1-acetyl spermidine and N1-acetyl spermine facilitated the B-DNA to Z-DNA transition and the binding of ER although they were less effective than the unacetylated analog. Co(NH3)6(3+), a trivalent inorganic cation, also provoked the B-DNA to Z-DNA transition of the polynucleotide and increased its binding to ER. At higher polyamine concentrations, there was an inhibition of ER binding to the polynucleotide. In the presence of polyamines, the binding of ER to a plasmid containing ERE was 2-3-fold higher than that to a control plasmid devoid of ERE. Polyamine-induced facilitation of ER-ERE binding was also confirmed by gel mobility shift assay. Our data indicate that conformational perturbations, similar to that of the early stages of B-DNA to Z-DNA transition, are important in the recognition of ER and ERE.

Animals↗
PubMed1994

Polyamine-induced changes in the sedimentation profile and DNA binding of aryl hydrocarbon receptor.

Aryl hydrocarbon (Ah) receptor mediates the toxic action of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). We studied the effects of polyamines--putrescine, spermidine and spermine--on the physical chemical properties of Ah receptor from A431 cells. Spermidine and spermine caused the precipitation of 9S oligomeric receptor with a gradual decrease in the receptor peak during density gradient sedimentation. RNase A treatment transformed the 9S Ah receptor to a 6S form and DNA binding increased by 2-fold. Following partial purification of transformed Ah receptor by preparative sucrose gradient centrifugation, it lost the ability to bind to DNA, but addition of spermidine increased DNA binding in a concentration-dependent manner. These data show that polyamines modulate the structure and DNA binding of Ah receptor and suggest that cellular polyamine levels might be important in the tissue specific toxicity of TCDD.

Binding Sites↗
PubMed1993

Receptor mechanisms and dose-response models for the effects of dioxins.

There is increasing evidence that receptor-mediated events impact one or more stages responsible for tumor development in experimental animals and humans. Although many chemicals and endogenous hormones require receptor interactions as a necessary event in their carcinogenic activity, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and its structural analogs are the most visible examples of receptor-mediated carcinogens. TCDD, or dioxin as it is frequently called, interacts with the Ah receptor (AhR), which functions in a manner analogous to receptors for steroids. TCDD produces a wide spectrum of biochemical and toxic responses in in vitro and in vivo systems, and the Ah receptor is generally considered necessary for most if not all of these responses. Risk assessments for dioxin made by the United States and other countries throughout the world have been based on its carcinogenecity in experimental animals. Recently, epidemiology studies have indicated that TCDD is a human carcinogen at high doses. Because TCDD appears to be acting like a potent and persistent hormone agonist, it appears reasonable to incorporate mechanistic information on receptor-mediated events in risk assessments for TCDD. This information may be obtained from steroid receptor action and from molecular data on the Ah receptor. In this paper, we evaluate the scientific foundation on which mechanistic models for estimating dioxin's risks should be based. These models need to recognize the mechanisms possible for the diversity of biological responses that are initiated by a single receptor interacting with a single ligand. The U.S. EPA is currently reevaluating dioxin's risks by examining the possibility of developing biologically based models.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Progesterone withdrawal decreases latency to and increases duration of electrified prod burial: a possible rat model of PMS anxiety.

The purpose of this study was to determine whether withdrawal from chronic exposure to the female sex steroid progesterone (P) alters response of female rats to an electrified prod using the defensive burying paradigm, considered a rat model of anxiety. Withdrawal from chronic exposure to 500 micrograms P (daily, SC, for four days) resulted in a significant decrease in the latency (77%, P < 0.05) to prod burial and an increase in duration (75%, P < 0.05) of this reflexive response, compared with the behavior of oil-injected controls. These results are consistent with the idea that withdrawal from chronic exposure to P increases behaviors that accompany anxiety. At a lower dose (50 micrograms), withdrawal from chronically administered P produced significant changes in response to this paradigm only when the steroid was given concomitantly with estradiol (2 micrograms, SC, for two days). Prior exposure to indomethacin, which blocks the conversion of P to its metabolite 3 alpha,5 alpha-tetrahydroprogesterone (3-alpha-hydroxy-5-alpha-pregnan-20-one), prevented P withdrawal from altering response in the defensive burying paradigm. This finding suggests that it may be withdrawal from this metabolite, rather than P, which increases behaviors associated with increased anxiety.

Animals↗
PubMed1992

Antiestrogenic action of 2,3,7,8-tetrachlorodibenzo-p-dioxin: tissue-specific regulation of estrogen receptor in CD1 mice.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a polychlorinated aromatic hydrocarbon with teratogenic and carcinogenic properties. Previous studies in our and other laboratories have demonstrated that TCDD has antiestrogenic properties. In order to elucidate the mechanism of action of TCDD on estrogen sensitive tissues, we studied its effects on serum estradiol and estrogen receptor (ER) levels in liver and uteri of CD1 mice. Treatment with TCDD did not result in alterations of serum estradiol levels at any of the doses tested (1.0-30 micrograms/kg). In contrast, TCDD treatment induced a dose-dependent decrease in hepatic and uterine ER protein as determined by an enzyme immunoassay and equilibrium binding assays. A decrease in cytosolic and nuclear ER levels in uteri occurred as early as 24 hr after initial treatment with 30 micrograms/kg TCDD and recovery occurred by 14 days. Hepatic cytosolic and nuclear ER also decreased at a dose of 30 micrograms/kg TCDD at 24 hr after treatment, but recovery occurred only by 21 days. Studies in ovariectomized mice indicate that the regulation of hepatic ER by TCDD is independent of ovarian factors, but ovariectomy inhibited the downregulation of uterine ER by TCDD. Furthermore, determination of TCDD-induced cytochrome P-450 levels indicates that the downregulation of uterine ER is uncoupled from induction of hepatic cytochrome P-450. This study indicates that the antiestrogenic effects of low doses of TCDD are mediated through its ability to decrease hepatic and uterine ER and are not due to alterations in serum estradiol levels. Our results on ovariectomized mice indicate that TCDD-induced downregulation of ER is tissue specific and may involve different mechanisms at transcriptional or posttranscriptional levels.

Animals↗
PubMed1992

The potentiation of 2,3,7,8-tetrachlorodibenzo-p-dioxin toxicity by tamoxifen in female CD1 mice.

Tamoxifen, an antiestrogen commonly used in breast cancer therapy, potentiated the lethality of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) when coadministered to female CD1 mice, despite the virtual lack of toxicity associated with the administration of tamoxifen alone. The 58-day ip LD50 of TCDD was reduced from 330 to 185 micrograms/kg by sc administration of 1 mg/kg/day tamoxifen. A significant dose-response relationship was observed for the potentiating effect of tamoxifen on TCDD lethality. All mice receiving TCDD developed a centrilobular pattern of hepatocellular degeneration and necrosis with perivascular infiltration of inflammatory cells. Clinical chemistry parameters were indicative of liver disease. Abnormalities in mice receiving tamoxifen plus TCDD were similar to, but more severe than, those in mice receiving TCDD only. Seven days after administration of [14C]TCDD, liver retention of radioactivity was increased 80-100% by coadministration of tamoxifen. This elevated retention was associated with a 50 and 37% decrease in excretion of radioactivity by the urinary and fecal routes, respectively. Our results suggest that the potentiation of TCDD toxicity by tamoxifen is associated with decreased excretion of TCDD, leading to elevated liver retention and enhanced severity of liver pathology.

Animals↗
PubMed1992

Pulmonary bioavailability and fine particle enrichment of 2,3,7,8-tetrachlorodibenzo-p-dioxin in respirable soil particles.

The pulmonary bioavailability of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and the enrichment of polychlorinated dioxins (PCDDs) and furans (PCDFs) in fine particles were evaluated to assess the implications that these factors have on risk and exposure assessments. Respirable subfractions of PCDD-contaminated soil from a former 2,4,5-trichlorophenoxyacetic acid manufacturing site were isolated by chemical dispersion and gravity sedimentation. Analysis of the subfractions revealed that there was a size-dependent enrichment of PCDDs and PCDFs, with smaller particles more highly contaminated. TCDD was enriched up to 33-fold as compared to unfractionated soil. Soil and laboratory-recontaminated gallium oxide, which served as the positive control, were administered by intratracheal instillation to female Sprague-Dawley rats. Animals were terminated up to 28 days following treatment and pulmonary bioavailability of TCDD was assessed by hepatic enzyme induction and TCDD concentration. Enzyme induction was dependent on the duration of exposure with up to 56 and 918% increases in cytochrome P450 and aryl hydrocarbon hydroxylase (AHH) activity, respectively, following exposure to PCDD-contaminated soil. There was no significant difference in AHH induction between animals which received contaminated soil and those treated with the positive control. Hepatic concentration of TCDD in soil-exposed rats was 115, 101, and 179% of positive controls at 1, 7, and 28 days post-treatment, suggesting that the soil or cocontaminants influenced retention of TCDD in the liver. These data indicate that the relative pulmonary bioavailability of TCDD on respirable soil particles is 100% as compared to laboratory-recontaminated gallium oxide and that PCDDs and PCDFs are highly enriched on respirable particles.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Inhalation↗
PubMed1991

Ionic and ligand-specific effects on the DNA binding of progesterone receptor bound to the synthetic progestin R5020 and the antiprogestin RU486.

Antiprogestin and other antihormones are valuable therapeutic agents in hormone-responsive cancers. A fundamental mechanism in the action of antiprogestin is its binding to PR,3 an intracellular protein that mediates the action of progesterone by direct interaction at the regulatory sites of responsive genes. To elucidate the mechanism of action of PR bound to agonistic and antagonistic ligands, we determined the binding affinity of rabbit uterine PR bound to R5020 and RU486, respectively, with different DNA sequences. We used 2 recombinant plasmid DNAs, pDHf14 and pDHf2, with 60- and 23-base pair inserts of potential Z-DNA-forming (dA-dC)n.(dG-dT)n sequences, respectively, parental plasmid pDPL6 with no insert, calf thymus DNA, and several synthetic polynucleotides in this study. The concentration of DNA required to elute 50% of the receptor bound to DNA-cellulose (EC50) was used as a measure of the relative binding affinity of the receptor for DNA. EC50 values of plasmids pDHf14 and pDHf2 were 1.2 +/- 0.5 (SD) and 2.5 +/- 0.6 micrograms/ml, respectively, for PR bound to R5020. In contrast, EC50 for control plasmid was 350 micrograms/ml. PR.R5020 had lower affinity for calf thymus DNA and polynucleotides compared with pDHf2 and pDHf14. Receptors complexed with the antiprogestin RU486 had lower affinity for the plasmids; EC50 values were 2.4 +/- 0.4 and 10 +/- 1 microgram/ml, respectively, for pDHf14 and pDHf2. This ligand-specific difference in DNA binding was amplified by the presence of 5 mM Mg2+ or Ca2+. The relative binding affinity of PR.R5020 to pDHf14 was 6- and 7-fold higher than that of PR.RU486, in the presence of 5 mM Mg2+ and Ca2+, respectively. These results show that PR.RU486 has lower binding affinity for specific DNA sequences than PR.R5020, but the binding affinity of both receptors is in a range that cannot preclude competitive interactions at the DNA recognition site. The effects of Mg2+ and Ca2+ on PR binding to DNA further suggest that these cations could affect PR recognition of DNA in a ligand-specific manner.

Animals↗
PubMed1991

Syntheses of psoralen analogues and evaluation of their inhibition of epidermal growth factor binding.

An exchange hydrogenation reaction on trioxsalen yields two isomeric dihydro analogues for which a combined HPLC-supercritical fluid chromatography method supplies purified materials. These reduced compounds and a related benzodipyranone are biologically active and inhibit the binding of epidermal growth factor on HeLa cells to an even greater extent than trioxsalen. This observation suggests a non-DNA target may play a role in the overall effects of psoralens on cells.

Binding, Competitive↗
PubMed1991

Evaluation of the relative contribution of exposure routes in a health risk assessment of dioxin emissions from a municipal waste incinerator.

Polychlorinated dioxins (PCDDs) and furans (PCDFs) are perceived by the public as the most hazardous materials emitted from municipal waste incinerators. These compounds disperse in the atmosphere and deposit on environmental media, where they may bioconcentrate in the food chain, resulting in a number of potential sources for human exposure. We performed a cancer risk assessment of PCDD/PCDF emissions from a municipal waste incinerator to evaluate the relative contribution of various exposure routes. Three scenarios were examined, all of which predicted ingestion of fish to be a significant source of exposure. In the common case, representative of the general population consuming mainly foods from commercial sources, inhalation was predicted to be the source of greatest exposure, followed by ingestion of fish, beef, milk, vegetation, and soil. In addition to fish, milk and beef ingestion contributed significantly to total exposure under the highly-exposed and worst case scenarios. Life-time cancer risk from the emitted PCDD/PCDFs was assessed for each scenario and was estimated as 1.8 x 10(-7) (common case), 2.5 x 10(-6) (highly-exposed case), and 6.7 x 10(-6) (worst case). In view of the conservative assumptions used in the assessment, the relatively low magnitude of these risks suggests that the PCDD/PCDF emissions from this incinerator should not be considered a significant public health concern.

Air Pollutants↗
PubMed1990

Release of chemotactic factors by veins during preparation for arterial bypass.

With the use of arterial bypass release neutrophil chemotactic factors, saphenous veins were removed from dogs by means of standard surgical technique and were distended to a pressure of 200 mm Hg for 15 minutes with cold (4 degrees C) plasmalyte solution. Veins cannulated in situ and flushed with cold (4 degrees C) plasmalyte solution served as negative controls. Experimental and control flush solutions were assayed for the presence of neutrophil chemotactic factors with the use of modified Boyden chambers. Chemotactic activity from the distended vein grafts was 2.2 to 7.2 times the control value. Biologic chemotactic activity was demonstrated as well. These results suggest a role for the vein graft itself in the recruitment of neutrophils to implanted veins by releasing chemoattractants.

Animals↗
PubMed1990

A novel succinyl dipeptide stimulates directed cell migration by modulating protein kinase C activity.

In determining the mechanism of the chemokinetic action of the thiol protease inhibitor, E-64, in endothelial cell monolayers subjected to wounding, we synthesized succinyl-leucyl-agmatine (SLA), an analogue of E-64 that lacked the epoxy group and protease inhibitory effect. We observed that this analogue retained its chemokinetic effect on wounded endothelial cells. Its stimulatory action on endothelial cell polarization response to wounding was rapid and associated with directed cell migration. Furthermore, its effect on cellular polarization was blocked by protein kinase C (PKC) inhibitors and mimicked by pharmacologic agents that stimulated PKC activity. To determine if SLA's chemokinetic action was mediated by protein kinase C activation, we compared the effects of SLA and the tumor promoter phorbol myristate acetate (PMA) on the translocation of PKC activity in endothelial cells. We observed that both SLA and PMA induced the translocation of PKC activity from the cytosolic to the particulate fraction of the cells. We also observed that both SLA and PMA induced the phosphorylation of two proteins (Mr 23.4 and 36.5 kDa) in intact 32P-labeled cells. Thus, SLA stimulates the endothelial cell locomotor response to wounding by stimulating PKC activity.

Amino Acid Sequence↗
PubMed1990

Hepatic aryl hydrocarbon hydroxylase and cytochrome P450 induction following the transpulmonary absorption of TCDD from intratracheally instilled particles.

Inhalation of particles contaminated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) will be an increasingly important route of human exposure in light of the increased utilization of municipal waste incineration and the resultant emission of contaminated materials into the environment. The potential for pulmonary absorption of the compound from respirable particles was assessed in the present study following the intratracheal instillation of TCDD (1) as a contaminant of gallium oxide particles and (2) in a corn oil vehicle. Groups of five female Sprague-Dawley rats received 0, 0.005, 0.055, 0.55, or 5.5 micrograms/kg TCDD in a single instillation and were euthanized 4 days later. Absorption was characterized by enzyme induction [aryl hydrocarbon hydroxylase (AHH) activity and total cytochrome P450] and histopathological examination of the liver. Induction of hepatic enzymes was dose-dependent with both treatment regimes. Up to an 18-fold increase in AHH and an 80% increase in cytochrome P450 were observed in treated animals. Induction was slightly higher when animals received TCDD in corn oil than when animals received TCDD-contaminated particles and was relatively comparable to induction following oral exposure. Similar results were obtained when animals were treated with particles contaminated up to 4 weeks prior to instillation. Characteristics of TCDD-induced hepatotoxicity, including enlarged hepatocytes and fatty infiltration, were apparent in treated rats, but were not present in vehicle-instilled animals. These results indicate that systemic effects occur following pulmonary exposure to TCDD and that inhalation may be an important route of exposure for TCDD.

Absorption↗
PubMed1990

Regulation of polyamine biosynthesis by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD).

We have examined the effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on tissue polyamine concentrations in CD1 mice. Two days after a low dose treatment with TCDD, polyamine content of the liver and thymus of treated mice showed a 49-82% decrease, but that of spleen was not affected. Based on this finding, we examined the role of alterations in polyamine levels in the toxicity of TCDD. We administered the polyamine biosynthetic inhibitor difluoromethylornithine (DFMO) to animals treated with a toxic dose of TCDD. DFMO dramatically increased the toxicity of TCDD as measured by mortality, ascites and changes in organ weights. In addition, administration of the polyamine putrescine was able to reduce the toxicity of TCDD. These results suggest that a decrease in polyamine concentrations in critical organs may play an important role in the toxic effects of TCDD.

Animals↗
PubMed1990

The fallacy of ranking possible carcinogen hazards using the TD50.

Ames et al. have proposed a new model for evaluating carcinogenic hazards in the environment. They advocate ranking possible carcinogens on the basis of the TD50, the estimated dose at which 50% of the test animals would get tumors, and extrapolating that ranking to all other doses. We argue that implicit in this methodology is a simplistic and inappropriate statistical model. All carcinogens are assumed to act similarly and to have dose-response curves of the same shape that differ only in the value of one parameter. We show by counterexample that the rank order of cancer potencies for two chemicals can change over a reasonable range of doses. Ames et al.'s use of these TD50 ranks to compare the hazards from low level exposures to contaminants in our food and environment is wholly inappropriate and inaccurate. Their dismissal of public health concern for environmental exposures, in general, based on these comparisons, is not supported by the data.

Animals↗