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Biomedical subjects

G D Bennett

Publications and source records attributed to G D Bennett.

At least 19 recordsLinked to original sources
PubMed1996

Arsenic-induced alterations in embryonic transcription factor gene expression: implications for abnormal neural development.

We examined the morphological and molecular consequences of acute in utero exposure to teratogenic concentrations of arsenate. The treatment produced a dose-related increase in neural tube defects, along with a significant alteration in the pattern of gene expression for several transcription factors (creb, Hox 3.1, Pax3, and Emx-1) that were examined using in situ transcription and antisense RNA amplification procedures. On gestational day 9:0, there was a significant delay in the embryos progression through neural tube closure, accompanied by a significant downregulation of Hox 3.1 expression and a significant upregulation of Pax3, Emx-1, and creb. As both Hox 3.1 and Pax3 serve to regulate N-CAM expression, it is possible that abnormalities associated with N-CAM may compromise neural crest cell migration and normal neural tube closure.

Animals↗
PubMed1996

Protein-reactive metabolites of carbamazepine in mouse liver microsomes.

The character of reactive metabolites formed from carbamazepine (CBZ) was sought in incubations of [14C]CBZ in hepatic microsomes prepared from adult female mice of a strain (SWV/Fnn) susceptible to CBZ-induced teratogenicity. The formation of radio-labeled protein adducts was used as an index of reactive metabolite exposure. A dependence on cytochrome P450 was shown by a requirement for NADPH and inhibition by carbon monoxide, 1-aminobenzotriazole, piperonyl butoxide, and stiripentol. The addition of ascorbic acid, caffeic acid, N-acetylcysteine, and glutathione decreased the rate of binding of the radiolabel from [14C]CBZ to microsomal protein by more than 50%. The addition of glutathione transferases diminished protein adduct formation beyond that seen with glutathione alone. Evidence for the formation of an arene oxide was sought through the use of inhibitors of epoxide hydrolases, including cyclohexene oxide, chalcone oxides (with the addition of cytosol as appropriate), and by the addition of recombinant human soluble and microsomal epoxide hydrolases and recombinant rat microsomal epoxide hydrolase. The microsomal epoxide hydrolases decreased the velocity of 14C-labeled protein adduct formation by approximately 23%, whereas inhibitors had no effect, most likely because of the low native activity of microsomal epoxide hydrolase in mice. Both DT-diaphorase and catechol-O-methyltransferase diminished 14C-labeled protein adduct formation by 54% and 45%, respectively. The data suggest that the major reactive metabolites formed from CBZ by adult female SWV/Fnn liver microsomes are quinones and arene oxides.

Animals↗
PubMed1995

Effect of treatment with phenobarbital and stiripentol on carbamazepine-induced teratogenicity and reactive metabolite formation.

A model using SWV mice was developed to investigate the mechanistic basis of carbamazepine (CBZ)-related fetotoxicity. Drug administration was initiated prior to conception and continued until day 18 of gestation. The incidence of malformation was 33% following CBZ exposure (1,500 mg/kg/day), compared with a 5% incidence in pair-fed control animals (P < 0.05). Coadministration of nonteratogenic doses of phenobarbital (PB; a cytochrome P-450 inducer) (45 mg/kg/day) and CBZ (1,000 mg/kg/day) increased the frequency of malformation from 10% to 26% (P < 0.05), compared with mice dosed with CBZ alone (1,000 mg/kg/day). Coadministration of stiripentol (STP; a cytochrome P-450 inhibitor) (300 mg/kg/day) decreased the incidence of malformations produced by CBZ (1,500 mg/kg/day) from 33% to 16.7% (P < 0.05). The effect of PB administration on the binding of 14C in maternal and fetal tissue was assessed in dams that received CBZ (1,000 mg/kg/day) with or without PB (45 mg/kg/day) or STP (300 mg/kg/day) chronically and a single i.p. dose of 14C-CBZ on day 12 of gestation. In all instances, binding was greatest in maternal liver, then in the placenta, fetal head and body, and maternal thigh muscle. In all tissues, PB caused a two-to threefold increase in binding, compared with binding in mice exposed to CBZ alone. STP administration decreased protein adduct formation only in maternal liver. The binding of 14C was also assessed in hepatic microsomes prepared from female mice exposed to CBZ and PB or STP as in the in vivo study of 14C binding. The extent of irreversible binding was 67% greater in microsomes prepared from mice pretreated with PB and CBZ than with CBZ alone, while STP resulted in only 21% inhibition of 14C adduct formation (P < 0.05). The results are consistent with the formation of a chemically reactive teratogenic metabolite of CBZ in mice by cytochrome(s) P-450.

Abnormalities, Drug-Induced↗
PubMed1993

Structure of 1,8-bis(hydroxymethyl)naphthalene.

1,8-Naphthalenedimethanol, C12H12O2, M(r) = 188.24, monoclinic, P2(1)/n, a = 8.549(4), b = 4.856(3), c = 22.604(4) A, beta = 94.24(3) degrees, V = 935.8(7) A 3, Z = 4, Dx = 1.34 g cm-3, lambda(Mo K alpha) = 0.71073 A, mu = 0.84 cm-1, F(000) = 400, T = 295 K, R = 0.042 for 1455 unique reflections having I > 3 sigma I. In the title structure the exterior angles at ring atoms C(1), C(8) and C(9) deviate significantly from 120 degrees as a result of the steric interactions of the hydroxymethyl substituents. The ten C atoms comprising the naphthalene core have an average deviation of 0.012 (7) A from the best least-squares plane describing the core. The conformation of the title compound is compared to those of other 1,8-disubstituted naphthalenes. Each hydroxy group is involved in hydrogen bonding as both acceptor and donor, creating infinite chains that propagate in the [010] directions. The neutron-adjusted parameters for the two H...O(acceptor) distances are 1.78 (3) and 1.80 (3) A and for the two O--H...O(acceptor) angles are 165 (2) and 170 (2) degrees. The packing arrangement can be described as a modified herringbone structure with the shortest crystallographic axis coinciding with the b axis of the standard monoclinic setting.

Molecular Structure↗
PubMed1993

Lack of concordance between heat shock proteins and the development of tolerance to teratogen-induced neural tube defects.

The present study was undertaken to examine the role of heat shock response in the development of tolerance and cross-tolerance in an in vivo murine model of teratogen-induced neural tube defects. The experimental paradigm designed to address this question was to utilize inbred mouse strains that differed in their sensitivity to hyperthermia and valproic acid induced neural tube defects, subjecting the dams to subteratogenic pretreatments with either heat or valproic acid at two different timepoints during development prior to the administration of the teratogenic insult. A statistically significant reduction in the frequency of neural tube defects and/or embryolethality following a pretreatment in dams subsequently exposed to a teratogenic treatment was considered evidence for the induction of tolerance. This was observed in the SWV embryos exposed to the 38 degrees C pretreatment at 8:06 and to embryos exposed to either pretreatment temperature at 8:10 prior to a teratogenic heat shock at 8:12. In the LM/Bc embryos, only the 41 degrees C pretreatment at 8:06 induced thermotolerance. There was no evidence of tolerance induced in either mouse strain using valproic acid. On the other hand, cross-tolerance was clearly demonstrated in this study, with a low temperature (41 degrees C) pretreatment successfully protecting SWV fetuses from a subsequent teratogenic treatment with valproic acid, while valproic acid (200 mg/kg) was effective in reducing the risk of hyperthermia-induced neural tube defects in the LM/Bc fetuses. In all instances, tolerance was induced in the absence of significant induction of hsp synthesis. The lack of concordance between hsps and thermotolerance suggests that some other factor(s) is involved in conferring thermotolerance on developing murine embryos.

Animals↗
PubMed1992

The heat shock response: potential to screen teratogens.

The embryonic stress hypothesis of teratogenesis suggests that a proportion of all human congenital defects is due to a failure in essential gene transcription along with translational pre-emption by the heat shock response (HSR). We sought to determine the potential usefulness of the murine HSR to screen agents suspected of being human teratogens. The teratogenic potential of a selected group of known teratogenic (hyperthermia, insulin, retinoic acid and valproic acid) or non-teratogenic (cycloheximide, dinitrophenol and tetracycline) agents were administered to pregnant SWV mice at critical periods of neural tube closure. Following exposure to either teratogenic doses or at the highest dose possible that did not induce maternal toxicity for those compounds that were not teratogenic, the induction of heat shock protein (hsp) synthesis and changes in total protein synthesis were determined in lymphocytes isolated from murine spleens. The varied results obtained in these studies cast doubt on the value of the murine HSR to screen teratogens.

Abnormalities, Drug-Induced↗
PubMed1990

Embryonic and maternal heat shock responses to a teratogenic hyperthermic insult.

Exposing embryos to elevated temperatures both in vivo and in vitro has been shown to result in the production of offspring with severe congenital abnormalities. While a direct effect of heat cannot be excluded, recent interest has been focused on the possible role that the induction of the heat shock response may have in the etiology of the observed congenital defects. In the present study, mouse embryos from inbred strains known to differ in terms of their sensitivity to heat-induced exencephaly were treated in vivo and their heat shock response determined using SDS-PAGE electrophoretic techniques. Further, the embryonic responses were compared with a maternal cell type. We observed excellent agreement between the two test systems following exposure to a teratogenic hyperthermic insult. Both the embryonic and maternal cells underwent a reduction in total protein synthesis and an enhanced synthesis of four heat shock proteins migrating with the molecular weights of 68, 70, 97, and 110 kDa. The results failed to indicate any strong correlation between the heat shock response and enhanced genetic sensitivity to hyperthermia-induced neural tube defects.

Animals↗
PubMed1990

Genetic differences in the duration of the lymphocyte heat shock response in mice.

Lymphocytes from adult mice bearing a known difference in genetic susceptibility to teratogen-induced exencephaly (SWV/SD, and DBA/2J) were evaluated for changes in protein synthesis following an in vivo heat treatment. Particular attention was paid to changes indicative of the heat shock response, a highly conserved response to environmental insult consisting of induction of a few, highly conserved proteins with simultaneous decreases in normal protein synthesis. The duration of heat shock protein induction in lymphocytes was found to be increased by 1 hr in the teratogen-sensitive SWV/SD strain as compared to the resistant DBA/2J strain. Densitometric analysis revealed a significant decrease in the relative synthesis of at least two non-heat shock proteins (36 kD and 45 kD) in the SWV/SD lymphocytes as compared to DBA/2J cells. The increased sensitivity of protein synthesis to hyperthermia in the SWV/SD lymphocytes were lost in the F1 progeny of reciprocal crosses between SWV/SD and DBA/2J mouse strains. Sensitivity to hyperthermia-induced exencephaly is recessive to resistance in these crosses. The relationship between altered protein synthesis and teratogen susceptibility is discussed.

Animals↗
PubMed1988

Common hierarchies of susceptibility to the induction of neural tube defects in mouse embryos by valproic acid and its 4-propyl-4-pentenoic acid metabolite.

The teratogenic effects of valproic acid and its 4-propyl-4-pentenoic acid (4-en) metabolite were investigated in three inbred mouse strains that were known to possess differing sensitivity to heat-induced neural tube defects. In the heat-resistant DBA/2J strain, administration of either valproic acid or the metabolite during the critical period of neural tube development failed to produce any abnormal offspring. Similar treatment in the moderately heat-sensitive LM/Bc strain resulted in up to 19.8% exencephalic fetuses. The highly heat-sensitive SWV strain was also very susceptible to the induction of neural tube defects by either valproic acid or its 4-en metabolite. When administered on gestational day 8 plus 12 hours, the parent compound produced 35% exencephalic fetuses, while the metabolite had a response frequency of 32.4%. Thus, the hierarchy of susceptibility for the induction of neural tube defects in these inbred mouse strains was exactly the same whether the teratogen was a physical agent such as hyperthermia or a chemical compound such as valproic acid. If such diverse agents as these should interact to produce malformations, then it is possible that a wide variety of other agents might interact in a similar manner to produce neural tube defects.

Animals↗
PubMed1987

Genetic markers in Australian Caucasian subjects with coeliac disease.

A group of 69 unrelated Australian coeliac subjects (41 adult onset and 28 childhood onset) were typed for for HLA-A, B, DR and DQ antigens. Immunoglobulin allotypes were also determined in 36 of these patients. An association between coeliac disease and the antigens DR3, DR7 and DQw2 was confirmed in this population. There was no significant difference in antigen frequencies between childhood and adult onset coeliac disease, although the association with DR7 was stronger in the childhood group. All coeliac patients who did not carry DR3 or DR7 were found to be DR4 positive. No association was demonstrated between coeliac disease and any immunoglobulin allotype, either in the absence of HLA antigens B8 and DR3 or in male coeliac patients.

Australia↗
PubMed1986

Failure of epoxide formation to influence carbamazepine-induced teratogenesis in a mouse model.

The teratogenic potential of the anticonvulsant drug carbamazepine was determined following chronic oral administration in two inbred mouse strains (SWR/J and LM/Bc). The drug was administered in the animal's diet in concentrations equivalent to 0, 1,000, 1,500, or 2,000 mg/kg body weight, with treatment starting 2 wks prior to mating and continuing throughout gestation. Fetal examination failed to reveal a significant pattern of malformation in either strain at any treatment level. Levels of plasma carbamazepine and its metabolite, carbamazepine-10,11-epoxide, were determined by high pressure liquid chromatography. There was no correlation with either of these compounds and the incidence of fetal abnormality. The inherent teratogenicity of carbamazepine is significantly lower than that of other anticonvulsant drugs that have been similarly tested in an animal model.

Animals↗
PubMed1985

Seizure control following administration of anticonvulsant drugs in the quaking mouse.

The effectiveness of a variety of clinical anticonvulsant drugs was evaluated in the quaking mutant mouse model of epilepsy. In this model, tonic-clonic seizures are easily elicited by handling and the effects of administration of carbamazepine (CBZ), phenytoin (DPH), phenobarbital (PB), diazepam, valproic acid (VPA) and ethosuximide were quantitatively evaluated. Chronic oral administration of CBZ, DPH and PB reduced the frequency of seizures and this was positively correlated with plasma levels of the drugs. The plasma levels of the 10,11-epoxide metabolite of CBZ were found to be approximately 3-5 times that of the parent compound with chronic oral administration. Acute intraperitoneal administration of the other drugs revealed VPA to be an effective anticonvulsant agent, whereas ethosuximide and diazepam were ineffective at dosage levels that are normally effective in mice as determined by classical testing methods such as electroshock and chemoshock. The results of the present study suggest that the quaking mouse may be a simple, reliable and inexpensive animal model for the evaluation of agents effective against focal motor seizures in humans.

Animals↗
PubMed1982

Is there an HLA antigen association with duodenal ulcer?

To assess the influence of ethnic origin on the incidence of HLA antigens in duodenal ulcer, we typed 160 white Australian patients (including 22 born in Greece or Italy) and 320 blood donor controls for the HLA-A and -B loci. 5 of the 22 (22.7%) southern European patients, but only 19 of the 138 (13.8%) of the remaining duodenal ulcer patients were found to have antigen B5 compared with 27 (8.4%) of the controls. HLA-B12 was found in 55 (34.4%) duodenal ulcer patients (including 6 of the 22 southern European patients) and 117 (36.6%) controls. No significant association of duodenal ulcer with HLA-B5 or HLA-B12 was found when differences in racial origin of patients were taken into account.

Adult↗
PubMed1981

Homeostatic removal of senescent murine erythrocytes by splenic macrophages.

Removal of senescent erythrocytes (RBC) from the circulation was investigated both in vivo and in vitro using inbred BALB/C mice as a model. Murine RBC were pulse-labeled in situ with 59Fe, and young and old peripheral blood RBC were separated by density gradient centrifugation on Percoll gradients. 59Fe labeled young RBC were found at a density of p 1.09. Forty days after 59Fe pulse labeling, 59Fe labeled RBC were found at p = 1.11 and 1.12, 59Fe labeled young or old cells were transfused into mice. Peripheral blood and spleen cell populations (i.e., macrophages, lymphocytes, polymorphonuclear leukocytes, and RBC) were assessed for radioactivity at varying time intervals after young or old RBC injection. Spleen cell populations were separated by density gradient centrifugation. The results revealed that senescent RBC were cleared more rapidly from the peripheral blood than were young RBC. and that the rate was related to the incorporation of senescent RBC by splenic macrophages. Studies performed in vitro revealed that splenic macrophages phagocytized autologous senescent RBC but not autologous young RBC. Thus, splenic macrophages can function as homeostatic regulators by selectively phagocytizing senescent cells in situ. Development of a murine model for RBC clearance studies should facilitate further studies on mechanisms of macrophage recognition of effete self RBC and other somatic cells.

Animals↗