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D J Roberts

Publications and source records attributed to D J Roberts.

At least 109 records · Page 6Linked to original sources
PubMed1993

Protection, pathogenesis and phenotypic plasticity in Plasmodium falciparum malaria.

Why does Plasmodium falciparum cause severe illness in some but not all infections? How is clinical immunity acquired? These questions have intrigued investigators since the clinical epidemiology of malaria was first described. The search for answers to both questions has highlighted the changes that take place at the surface of infected red blood cells during the last half of the erythrocytic cycle. These changes specify the antigenic and adhesive or cytoadherence phenotypes for the infected cell. Now the antigenic and adhesive phenotypes appear to be linked and together undergo clonal variation. In this article David Roberts, Beverley-Ann Biggs, Graham Brown and Christopher Newbold explain how clonal phenotypic variation and the linkage between adhesive and antigenic types contribute to our understanding of naturally acquired immunity and of pathogenesis of severe malaria.

Journal Article↗
PubMed1993

An unusual variant of congenital dyserythropoietic anaemia with mild maternal and lethal fetal disease.

An unusual variant of congenital dyserythropoietic anaemia is described presenting as mild haemolytic anaemia with multinucleated erythroblasts in the marrow of the proband. The outcome of her non-consanguineous pregnancy was a third trimester, in utero, fetal demise. The hydropic fetus had dyserythropoiesis with circulating multinucleated erythroblasts, and haemosiderosis. Re-evaluation of the proband revealed a variant of congenital dyserythropoietic anaemia with an inheritance pattern, and with morphological, serological and biochemical features which are not consistent with any of the three described variants of congenital dyserythropoietic anaemias.

Adolescent↗
PubMed1993

Initial-phase optimization for bioremediation of munition compound-contaminated soils.

We examined the bioremediation of soils contaminated with the munition compounds 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine, and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetraazocine by a procedure that produced anaerobic conditions in the soils and promoted the biodegradation of nitroaromatic contaminants. This procedure consisted of flooding the soils with 50 mM phosphate buffer, adding starch as a supplemental carbon substrate, and incubating under static conditions. Aerobic heterotrophs, present naturally in the soil or added as an inoculum, quickly removed the oxygen from the static cultures, creating anaerobic conditions. Removal of parent TNT molecules from the soil cultures by the strictly anaerobic microflora occurred within 4 days. The reduced intermediates formed from TNT and hexahydro-1,3,5-trinitro-1,3,5-triazine were removed from the cultures within 24 days, completing the first stage of remediation. The procedure was effective over a range of incubation temperatures, 20 to 37 degrees C, and was improved when 25 mM ammonium was added to cultures buffered with 50 mM potassium phosphate. Ammonium phosphate buffer (50 mM), however, completely inhibited TNT reduction. The optimal pH for the first stage of remediation was between 6.5 and 7.0. When soils were incubated under aerobic conditions or under anaerobic conditions at alkaline pHs, the TNT biodegradation intermediates polymerized. Polymerization was not observed at neutral to slightly acidic pHs under anaerobic conditions. Completion of the first stage of remediation of munition compound-contaminated soils resulted in aqueous supernatants that contained no munition residues or aminoaromatic compounds.

Ammonia↗
PubMed1993

GABA mediation of the dual effects of somatostatin on guinea pig ileal myenteric cholinergic transmission.

Somatostatin (SS) has both excitatory and inhibitory actions on myenteric cholinergic transmission, which are mimicked by gamma-aminobutyric acid (GABA). We hypothesized that both effects of SS are mediated by neural GABA pathways. In guinea pig ileal longitudinal muscle-myenteric plexus, SS evoked [3H]-GABA release verifying GABA neural activation. SS (10(-9)-10(-5) M) stimulation of atropine-sensitive ileal contraction and evocation of tetrodotoxin-sensitive [3H]acetylcholine (ACh) release was mimicked by the GABAA agonist muscimol but not the GABAB agonist baclofen. SS (10(-7) M)-evoked contraction and [3H]ACh release were markedly reduced by the GABAA antagonist bicuculline (10(-5) M) but not the GABAB antagonist phaclofen. Cholecystokinin (CCK) evokes ileal contraction via an atropine-sensitive pathway and stimulates ACh release via adenylate cyclase activation. SS inhibited contraction and release evoked by CCK (10(-7) M). These inhibitory actions were reversed by phaclofen but not bicuculline and were mimicked by baclofen but not muscimol. Pertussis toxin (200 ng/ml for 3 h) reversed the inhibitory effects of SS and baclofen on CCK-stimulated contraction and release. In conclusion, SS modulates ileal cholinergic pathways by stimulation of GABA neural pathways. The excitatory action of SS is mediated by GABAA receptors, whereas the inhibitory action utilizes GABAB receptors via a pertussis toxin-sensitive G protein.

Acetylcholine↗
PubMed1993

Extrarenal Wilms' tumors. A study of their relationship with classical renal Wilms' tumor using expression of WT1 as a molecular marker.

BACKGROUND: Wilms' tumors (WT) are renal malignancies typically of childhood with classic histopathologic features. A candidate WT gene (WT1) has been described, expression of which is largely restricted to the developing genitourinary system. WT1 is highly expressed in most sporadic childhood renal WT, and inactivating mutations have been described, consistent with its role as a tumor suppressor gene. WT1, therefore, may be used as a molecular marker for renal WT in most cases. Rarely, do tumors, that histologically resemble WT, develop in adult kidneys or exceptionally at nonrenal sites. This study addresses the question, are extrarenal tumors that have the morphology of renal WT really a type of WT? We investigated this question by using WT1 expression as a molecular marker for WT. EXPERIMENTAL DESIGN: We studied WT1 expression in eight well-documented cases of extra-renal WT by RNA-RNA in situ hybridization using an 35S-labeled probe derived from a cloned WT1 gene sequence. RESULTS: WT1 mRNA expression was detected in 5 of 5 childhood cases of sporadic childhood renal WT and 2 of 8 extrarenal WT. Both WT1-positive extrarenal WT were endometrial primaries. The WT1-negative extrarenal WT included retroperitoneal (3), pararenal or paravesical (2), and paraspinal (1) primaries. The seven non-WT uterine malignancies (carcinomas and sarcomas) studied were WT1-negative. CONCLUSIONS: These findings suggest that some cases of extrarenal WT are related to classical renal WT by more than mere morphologic resemblance, as indicated by the detection of WT1 mRNA expression in at least a subset of these rare tumors. Furthermore, the results suggest different pathogeneses of subsets of extrarenal WT.

Adult↗
PubMed1993

Choriocarcinoma in a term placenta: pathologic diagnosis of tumor in an asymptomatic patient with metastatic disease.

A clinically unsuspected choriocarcinoma arose in a term placenta. The patient was hospitalized for 3 weeks antepartum with preterm labor. She was delivered of a normal female infant at 36 weeks' gestation. Mother and infant were discharged after 3 days. The placenta, 465 g, contained multiple white nodules, a single infarct, and retroplacental hemorrhage. By microscopy, there was multifocal choriocarcinoma. No villous stromal invasion was found. The patient was readmitted 6 days postpartum with a serum beta human chorionic gonadotropin (hCG) value of 741,640 mIU/ml and lung metastases. She received 9 courses of multiagent chemotherapy and is currently free of tumor 1 year after diagnosis. The infant, 46,XX, remained clinically free of tumor although she had a serum beta hCG of 37 mIU/ml at 1 week of life. This placenta provides evidence of choriocarcinoma developing directly from mature placental villi in a chromosomally normal gestation and depicts a situation wherein choriocarcinoma is diagnosed correctly in the presence of villous tissue. It also demonstrates the utility of placental examination in clinically abnormal gestations.

Adult↗
PubMed1992

Pancopride, a potent and long-acting 5-HT3 receptor antagonist, is orally effective against anticancer drug-evoked emesis.

Pancopride ((+-)N-(1-azabicyclo-[2,2,2]-oct-3-yl)-2-cyclopropylmethoxy-4-ami no-5-chlorobenzamide) is a new potent and selective 5-HT3 receptor antagonist, orally and parenterally effective against cytotoxic drug-induced emesis. In vitro, pancopride displayed high affinity (Ki = 0.40 nM) for [3H]GR65630-labelled 5-HT3 recognition sites in membranes from the cortex of rat brains. In vivo, pancopride antagonized 5-HT-induced bradycardia in anaesthetized rats when administered i.v. 5 min (ID50 = 0.56 microgram/kg) or p.o. 60 min (ID50 = 8.7 micrograms/kg) before 5-HT challenge. A single oral dose (10 micrograms/kg) of pancopride produced a significant inhibition of the bradycardic reflex over an 8-h period. Pancopride dose dependently inhibited the number of vomiting episodes and delayed the onset of vomiting induced by cisplatin in dogs (ID50 = 3.6 micrograms/kg i.v. and 7.1 micrograms/kg p.o.). Pancopride was also effective in blocking mechlorethamine- and dacarbazine-induced emesis. Unlike metoclopramide, pancopride was shown to lack any measurable antidopaminergic activity both in vitro and in vivo. These results support clinical data, indicating that pancopride will be a useful drug for treating cytostatic-induced emesis in humans.

Animals↗
PubMed1992

Rapid switching to multiple antigenic and adhesive phenotypes in malaria.

Adhesion of parasitized erythrocytes to post-capillary venular endothelium or uninfected red cells is strongly implicated in the pathogenesis of severe Plasmodium falciparum malaria. Neoantigens at the infected red-cell surface adhere to a variety of host receptors, demonstrate serological diversity in field isolates and may also be a target of the host-protective immune response. Here we use sequential cloning of P. falciparum by micromanipulation to investigate the ability of a parasite to switch antigenic and cytoadherence phenotypes. Our data show that antigens at the parasitized cell surface undergo clonal variation in vitro in the absence of immune pressure at the rate of 2% per generation with concomitant modulations of the adhesive phenotype. A clone has the potential to switch at high frequency to a variety of antigenic and adhesive phenotypes, including a new type of cytoadherence behaviour, 'auto-agglutination' of infected erythrocytes. This rapid appearance of antigenic and functional heterogeneity has important implications for pathogenesis and acquired immunity.

Animals↗
PubMed1992

Plasmodium falciparum: the human agglutinating antibody response to the infected red cell surface is predominantly variant specific.

There is mounting evidence that an important component of the host-protective immune response to Plasmodium falciparum is the antibody response to the altered surface of the infected erythrocyte. The nature of these surface changes and the responses to them have been difficult to analyse because of the diverse nature of the parasite-derived neoantigens (PDN) expressed, because of the additional presence of modified host determinants, and because of the lack of monospecific reagents. We have studied the reactivity of field isolates and laboratory clones with pooled or individual sera using a novel approach which obviates the need for specific antibody. We see marked diversity in PDN but in contrast to previous studies, we also find that the predominant agglutinating antibody response in humans is variant specific. Antibodies which cross-react between different serotypes are rare and react only with a subset of PDN types. These results have implications for mechanisms underlying the development of acquired immunity to P. falciparum.

Agglutination↗
PubMed1992

Cardiac histologic pathology characteristic of trisomies 13 and 21.

To identify fetal histologic features characteristic of specific chromosomal anomalies, we reviewed histologic slides of 415 cases, including therapeutic and spontaneous abortuses, stillbirths, and perinatal deaths. These included 126 cases (30%) with karyotypically confirmed trisomy 21 and 23 cases (5.5%) with trisomy 13. Two histologic abnormalities of the fetal heart were identified that correlated with specific karyotypic abnormalities: (1) a discrete central papillary muscle calcification was present in 14 of 85 (16%) cases with trisomy 21, in seven of 18 (39%) cases with trisomy 13, and in six of 255 (2%) controls (P less than .001); and (2) a focal ventricular epicardial lymphocytic infiltrate was present in 22 of 93 (24%) cases with trisomy 21 versus nine of 284 (3%) controls (P less than .001). When both histologic abnormalities coexisted, trisomy 21 was present in five of six cases (83%). Neither histologic finding was significantly associated with fetal or maternal infection or congenital heart defects. In a restricted prospective study of the hearts of fetuses with trisomy 21, papillary muscle calcification was demonstrated by specimen radiographs in four of six (67%) cases; one case was studied by specimen ultrasonogram, which identified a papillary muscle echodensity. We conclude that (1) a focal ventricular epicardial lymphocytic infiltrate is characteristic of trisomy 21, (2) papillary muscle microcalcifications are characteristic of trisomies 13 and 21, and (3) further studies are needed to determine whether papillary muscle calcification might be useful in antenatal ultrasonographic screening for chromosomal anomalies.

Calcification, Physiologic↗
PubMed1992

A flow cytometric study of 137 fresh hydropic placentas: correlation between types of hydatidiform moles and nuclear DNA ploidy.

Hydropic placentas may be classified by histopathology into hydropic abortus, partial hydatidiform mole, and complete hydatidiform mole. We studied 142 hydropic placentas: 39% were complete hydatidiform moles, 35% partial hydatidiform moles, and 26% hydropic abortuses. Villous vesicle size was predictive of histologic diagnosis. We determined DNA ploidy in 137 cases. Seventy-three percent of hydropic abortuses were diploid and 11% were triploid. Ninety percent of partial moles were triploid or near-triploid; one partial mole was haploid and one diploid. Of the complete moles, 50% were diploid, 43% were tetraploid, 3.6% polyploid, and 1.7% triploid. Partial moles had lower pre-evacuation beta-hCG levels than complete moles. Persistent tumor followed 33% of complete moles and 12% of partial moles. Although the numbers were small, no patient with a diploid, tetraploid, aneuploid, or haploid partial mole developed persistent disease. Among complete moles, the pre-evacuation beta-hCG level was not predictive of persistence (P = .15). Subdividing complete moles by ploidy, we found that tetraploid moles were associated with higher pre-evacuation beta-hCG levels than were diploid moles. However, tetraploidy was not associated with increased persistent tumor among complete moles. Although most partial moles were triploid and most complete moles were diploid or tetraploid, there was wider DNA heterogeneity among molar gestations than previously reported. In this series, DNA ploidy was not an independent predictor of persistence in complete moles.

Adolescent↗
PubMed1992

Bioremediation of soils contaminated with the herbicide 2-sec-butyl-4,6-dinitrophenol (dinoseb).

A novel soil treatment method for achieving the removal of dinoseb (2-sec-butyl-4,6-dinitrophenol) from contaminated soils was investigated. One soil contained dinoseb as the major contaminant, although several other hazardous compounds were also present. A second soil was highly contaminated with dinoseb. Dinoseb was not degraded in these soils under the aerobic conditions at each site. Pretreatment of the soils by the addition of a starchy potato-processing by-product and flooding with phosphate buffer stimulated the consumption of oxygen and nitrate from the soils, thereby lowering the redox potential and creating anaerobic conditions. Anaerobiosis (Eh less than -200 mV) promoted the establishment of an anaerobic microbial consortium that degraded dinoseb completely, without the formation of the polymerization products seen under aerobic or microaerophilic conditions. When dinoseb was present at low concentrations in a chronically contaminated soil, the natural microflora was capable of establishing anaerobic conditions and degrading dinoseb as a result of starch degradation. Inoculation of this soil with an aerobic starch-degrading microorganism and then an acclimated, anaerobic, dinoseb-degrading consortium did not improve dinoseb degradation. In a second acutely contaminated soil, these inoculations improved dinoseb degradation rates over those of uninoculated controls.

2,4-Dinitrophenol↗
PubMed1992

Effect of ropivacaine and bupivacaine on uterine blood flow in pregnant ewes.

The effects of ropivacaine, a new amide local anesthetic, on uterine blood flow and fetal well-being were compared with those of bupivacaine in 10 chronically instrumented pregnant ewes. In random sequence, animals received two intravenous infusions of each drug. The low infusion rate regimens were chosen to result in clinically relevant maternal plasma concentrations of local anesthetics, whereas the more rapid rates of infusions were given to assess the safety of higher maternal drug concentrations. An epinephrine infusion was given to demonstrate the appropriateness of the animal model for the measurement of uterine blood flow. Maternal and fetal heart rates, arterial blood pressure, and the ewe's central venous pressure, intraamniotic pressure, and uterine blood flow were recorded continuously. Arterial blood samples were taken from mother and fetus at frequent intervals to determine acid-base status and local anesthetic concentrations. A total of 39 studies were performed. None of the infusions of either local anesthetic resulted in a significant decrease in uterine blood flow or deterioration in fetal condition. The mean maternal plasma concentrations at the end of infusions were as follows: ropivacaine low dose, 1.60 +/- 0.35 micrograms/mL; bupivacaine low dose, 1.55 +/- 0.15 micrograms/mL; ropivacaine high dose, 2.50 +/- 0.37 micrograms/mL; and bupivacaine high dose, 1.83 +/- 0.19 micrograms/mL. Epinephrine infusion resulted in a 25% decrease in uterine blood flow without adverse fetal effects. We conclude that neither ropivacaine nor bupivacaine, as administered in this study, led to any ill effects on uterine artery blood flow or fetal well-being.

Amides↗
PubMed1992

Placenta increta complicating a first-trimester abortion. A case report.

Placenta increta complicating pregnancy in the first trimester is rare. A patient with risk factors for placenta increta required a hysterectomy to control a hemorrhage after a first-trimester abortion. Pathologic study confirmed the preoperative diagnosis of placenta increta.

Abortion, Induced↗
PubMed1990

CO(2) Incorporation and 4-Hydroxy-2-Methylbenzoic Acid Formation during Anaerobic Metabolism of m-Cresol by a Methanogenic Consortium.

The metabolism of m-cresol by methanogenic cultures enriched from domestic sewage sludge was investigated. In the initial studies, bromoethanesulfonic acid was used to inhibit methane production. This led to the accumulation of 4.0 +/- 0.8 mol of acetate per mol of m-cresol metabolized. These results suggested that CO(2) incorporation occurred because each molecule of m-cresol contained seven carbon atoms, whereas four molecules of acetate product contained a total of eight carbon atoms. To verify this, [C]bicarbonate was added to bromoethanesulfonic acid-inhibited cultures, and those cultures yielded [C]acetate. Of the label recovered as acetate, 89% was found in the carboxyl position. Similar cultures fed [methyl-C]m-cresol yielded methyl-labeled acetate. A C-labeled transient intermediate was detected in cultures given either m-cresol and [C]bicarbonate or bicarbonate and [methyl-C]m-cresol. The intermediate was identified as 4-hydroxy-2-methylbenzoic acid. In addition, another metabolite was detected and identified as 2-methylbenzoic acid. This compound appeared to be produced only sporadically, and it accumulated in the medium, suggesting that the dehydroxylation of 4-hydroxy-2-methylbenzoic acid led to an apparent dead-end product.

Journal Article↗