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Biomedical subjects

D W Roberts

Publications and source records attributed to D W Roberts.

At least 109 records · Page 6Linked to original sources
PubMed1991

Corpus callosotomy for intractable seizures in the pediatric age group.

The results of corpus callosotomy in 18 patients 16 years old and younger are presented. Eighty-three percent of our patients have had a significant improvement from the surgery (a decrease in seizure frequency of greater than 80% or no longer having generalized atonic, tonic, or tonic-clonic seizures). The procedure seems to be well tolerated in young patients, and we have not noted a postoperative deterioration in behavior, memory, or language function in our patients. One of our patients died in status epilepticus 3 months after surgery. Nevertheless, we have not encountered any serious morbidity in our other patients. Corpus callosotomy can be considered for children with intractable seizures, especially when generalized atonic, tonic, or tonic-clonic (whether primary or secondary) seizures are the major seizure type.

Adolescent↗
PubMed1991

Refinement of the relative alkylation index (RAI) model for skin sensitization and application to mouse and guinea-pig test data for alkyl alkanesulphonates.

A derivation, more rigorous than hitherto, of the Relative Alkylation Index (RAI) as a quantifier of carrier protein haptenation in skin sensitization tests is presented. It is shown that the RAI, which is a composite parameter made up of dose, reactivity and lipophilicity terms, is likely to require a higher weighting for the reactivity term in the case of non-adjuvant tests than in the case of Freund's adjuvant-based tests. Methyl alkane-sulphonates, RSO3Me with R ranging from n-C6H13 to n-C16H33, were found to be skin sensitizers in a mouse ear swelling test, in agreement with published findings in a guinea-pig adjuvant model. A structure-activity relationship consistent with the published RAI model was observed whereby, in tests at fixed molar induction (0.1 mM) and challenge concentrations (0.025 mM), the level of sensitization response at first increased with increasing chain length of R, then showed a reversal of this trend at the highest chain length (R = n-C16H33). That this is a genuine 'over-load effect', as reported for several other series of compounds examined in guinea-pig adjuvant models, is indicated by the finding that on reducing the induction concentration for the R = n-C16H33 compound the sensitization response was increased. Alkyl and alkenyl methane-sulphonates, MeSO3R (R = n-C12H25, n-C18H37 and R = oleyl) did not give significant sensitization in the mouse ear test. Although they are chemically less reactive than methyl alkanesulphonates, these compounds are reported to be strong sensitizers in guinea-pig adjuvant tests and to fit a common quantitative sensitization-structure-dose relationship with the methyl alkanesulphonates.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkanesulfonates↗
PubMed1991

Application of QSAR to biodegradation of linear alkylbenzene sulphonate (LAS) isomers and homologues.

An approach of initially testing various structure descriptors on a trial and error basis, followed by mechanistic hypothesis and simple mathematical modelling to refine the choice of descriptor, is applied to develop a quantitative structure-activity relationship (QSAR) correlating initial biodegradation relative rate constants with carbon number and substitution position for (4-sulphophenyl)-substituted alkanes (linear alkyl benzene sulphonates, LAS). The relative rate constants are found to be linearly correlated with a composite descriptor, [(0.5 + L-1)-12 + (0.5 + S-1)-12]1/2 where L and S are the carbon numbers of the longer and shorter chains, respectively, counting from the (4-sulphophenyl) substitution position.

Benzenesulfonates↗
PubMed1991

QSAR issues in aquatic toxicity of surfactants.

Acute lethal toxicity data for a range of anionic and non-ionic surfactants are analysed with the aim of determining whether QSARs can be developed relating toxicity to calculated log P (octanol/water) values. Approaches have been developed for dealing with deficiencies in the fragment method for calculation of log P when applied to surfactants, and when these are applied it is found that log P-based QSARs for surfactants can be developed and are very similar to QSARs established for non-surfactant organic compounds with non-specific modes of action.

Animals↗
PubMed1991

Experimental brain hyperthermia: techniques for heat delivery and thermometry.

An experimental canine brain model was developed to assess the effects of hyperthermia for a range of time and temperature endpoints, delivered within a specified distance of an interstitial microwave antenna in normal brain. The target temperature location was defined radially at 5.0 or 7.5 mm from the microwave source at the longitudinal location of maximum heating along the antenna in the left cerebral cortex. Temperatures were measured with fiberoptic probes in a coronal plane at this location in an orthogonal catheter at 1.0 mm intervals. Six antennas were evaluated, including dipole, modified dipole, and four shorted helical antennas with coil lengths from 0.5 to 3.9 cm. Antenna performance evaluated in tissue equivalent phantom by adjusting frequency at a fixed insertion depth of 7.8 cm or adjusting insertion depth at 915 MHz showed dipoles to be much more sensitive to insertion depth and frequency change than helical antennas. Specific absorption rate (SAR) was measured in a brain/skull phantom and isoSAR contours were plotted. In vivo temperature studies were also used to evaluate antenna performance in large and small canine brain tissues. A helical antenna with a 2.0 cm coil length driven at 915 MHz was chosen for the beagle experiments because of tip heating characteristics, well-localized heating along the coil length, and heating pattern appropriate to the smaller beagle cranial vault. Verification of lesion dimensions in 3-D was obtained by orthogonal MRI scans and histology to document the desired heat effect, which was to obtain an imagable lesion with well-defined blood-brain-barrier breakdown and necrotic zones. The desired lesion size was between 1.5 to 2.5 cm diameter radially, in the coronal plane with the greatest diameter.

Animals↗
PubMed1991

Critical considerations in the immunochemical detection and quantitation of antigenic biomarkers.

The formation of covalent adducts as a result of the interaction of metabolically activated chemicals with host macromolecules is a common critical event in mutagenic, carcinogenic, and immunologic phenomena. Because of their antigenicity and their immunogenicity, covalent adducts may be detected using sensitive immunochemical techniques. The immunochemical approaches to biomonitoring and molecular dosimetry of DNA damage are particularly attractive because they allow sensitive quantitation of specific DNA adducts present in small samples and do not rely on the use of radiolabeled adducts. Two examples of biomarker immunoassay development are presented: an avidin/biotin-amplified ELISA for the major DNA adduct of the human bladder carcinogen 4-aminobiphenyl (ABP), and a particle concentration fluorescent immunoassay (PCFIA) for the major protein adduct associated with toxicity by the prototype hepatotoxin acetaminophen. The examples illustrate critical steps in the development of biomarker immunoassays which include selection of the relevant adduct, preparation of an appropriate immunogen, immunization, characterization of antisera, and development of application-specific sample processing techniques for biomarker quantitation. Immunochemical procedures may be combined with other analytical techniques to form hybrid systems which take advantage of both the antigenicity and the physical or chemical properties of a biomarker to achieve greater specificity and/or sensitivity. The future usefulness of these new tools of molecular epidemiology will depend on a compound-by-compound validation of methods and critical evaluation of the biologic importance of the particular antigenic biomarker as an indicator of exposure and as an indicator of risk.

Acetaminophen↗
PubMed1991

Immunohistochemical localization and quantification of the 3-(cystein-S-yl)-acetaminophen protein adduct in acetaminophen hepatotoxicity.

Acetaminophen overdose causes severe hepatotoxicity in humans and laboratory animals, presumably by metabolism to N-acetyl-p-benzoquinone imine: and binding to cysteine groups as 3-(cystein-S-yl)acetaminophen-protein adduct. Antiserum specific for the adduct was used immunohistochemically to demonstrate the formation, distribution, and concentration of this specific adduct in livers of treated mice and was correlated with cell injury as a function of dose and time. Within the liver lobule, immunohistochemically demonstrable adduct occurred in a temporally progressive, central-to-peripheral pattern. There was concordance between immunohistochemical staining and quantification of the adduct in hepatic 10,000g supernate, using a quantitative particle concentration fluorescence immunoassay. Findings include: 1) immunochemically detectable adduct before the appearance of centrilobular necrosis, 2) distinctive lobular zones of adduct localization with subsequent depletion during the progression of toxicity, 3) drug-protein binding in hepatocytes at subhepatotoxic doses and before depletion of total hepatic glutathione, 4) immunohistochemical evidence of drug binding in the nucleus, and 5) adduct in metabolically active and dividing hepatocytes and in macrophagelike cells in the regenerating liver.

Acetaminophen↗
PubMed1990

Immunochemical quantitation of 3-(cystein-S-yl)acetaminophen protein adducts in subcellular liver fractions following a hepatotoxic dose of acetaminophen.

The hepatotoxicity of acetaminophen correlates with the formation of 3-(cystein-S-yl)acetaminophen protein adducts. Using a sensitive and specific immunochemical assay, we quantitated the formation of these protein adducts in liver fractions and serum after administration of a hepatotoxic dose of acetaminophen (400 mg/kg) to B6C3F1 mice. Adducts in the cytosolic fraction increased to 3.6 nmol/mg protein at 2 hr and then decreased to 1.1 nmol/mg protein by 8 hr. Concomitant with the decrease in adducts in the cytosol, 3-(cystein-S-yl)acetaminophen protein adducts appeared in serum and their levels paralleled increases in serum alanine aminotransferase. Microsomal protein adducts peaked at 1 hr (0.7 nmol/mg protein) and subsequently decreased to 0.2 nmol/mg at 8 hr. The 4000 g pellet (nuclei, plasma membranes, and cell debris) had the highest level of adducts (3.5 nmol/mg protein), which remained constant from 1 to 8 hr. Evaluation of fractions purified from a 960 g pellet indicated that the highest concentration of 3-(cystein-S-yl)acetaminophen protein adducts was located in plasma membranes and mitochondria; peak levels were 10.3 and 5.1 nmol/mg respectively. 3-(Cystein-S-yl)acetaminophen protein adducts were detected in nuclei only after enzymatic hydrolysis of the proteins. The localization of high levels of 3-(cystein-S-yl)acetaminophen protein adducts in plasma membranes and mitochondria may play a critical role in acetaminophen toxicity.

Acetaminophen↗
PubMed1990

Acetaminophen-induced alterations in pancreatic beta cells and serum insulin concentrations in B6C3F1 mice.

Administration of acetaminophen (500 mg/kg) to male B6C3F1 mice resulted in alterations of pancreatic beta cell ultrastructure. These alterations were characterized by pronounced intercellular spaces, cytoplasmic vacuolization, damaged membranes of cytoplasm, secretory granules, and other organelles, and pyknotic nuclei with disrupted membranes. Concomitant with these changes, acetaminophen also caused increaes in serum insulin concentrations from 24 microU/ml at 0 time to 160 microU/ml at 8 hr and increases in serum alanine aminotransferase (ALT) concentrations from 42 to 13,279 U/liter, which indicated hepatic damage. Quantitation of 3-(cystein-S-yl)acetaminophen adducts in hepatic 10,000g supernatant protein using a particle concentration fluorescence immunochemical assay indicated a positive correlation between binding and the occurrence of the hepatotoxicity consistent with what has been previously reported; however, 3-(cystein-S-yl)acetaminophen protein adducts were not detected in pancreatic 10,000g supernatant. Immunohistochemical analysis of the liver and pancreas from acetaminophen-treated mice revealed acetaminophen-protein adducts in the centrilobular regions of the liver but not in the pancreatic islets. Doses of 100 and 200 mg/kg produced no evidence of hepatotoxicity and no increase in serum insulin; 300 mg/kg and higher doses produced both hepatotoxicity and increased serum insulin concentrations. A comparison of the time course for the increase in serum levels of ALT and insulin following a toxic dose of acetaminophen indicated that the increase in ALT preceded the increase in insulin. Thus the hepatotoxicity of acetaminophen correlates with the formation of 3-(cystein-S-yl)acetaminophen protein adducts in liver, which supports the concept that this toxicity is mediated by the reactive metabolite N-acetyl-p-benzoquinone imine; however, the toxicity of acetaminophen to beta cells in the pancreas is apparently not mediated by this mechanism.

Acetaminophen↗
PubMed1990

Immunoblot analysis of protein containing 3-(cystein-S-yl)acetaminophen adducts in serum and subcellular liver fractions from acetaminophen-treated mice.

The hepatotoxicity of acetaminophen is believed to be mediated by the metabolic activation of acetaminophen to N-acetyl-p-benzoquinone imine which covalently binds to cysteinyl residues on proteins as 3-(cystein-S-yl)acetaminophen adducts. The formation of these adducts in hepatic protein correlates with the hepatotoxicity. In this study, the formation of 3-(cystein-S-yl)acetaminophen adducts in specific cellular proteins was investigated using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and detected using affinity-purified antisera specific for 3-(cystein-S-yl)acetaminophen adducts on immunoblots. These techniques were used to investigate the liver 10,000g supernatant and serum from B6C3F1 mice that received hepatotoxic doses of acetaminophen. More than 15 proteins containing 3-(cystein-S-yl)acetaminophen adducts were detected in the liver 10,000g supernatant. The most prominent protein containing 3-(cystein-S-yl)acetaminophen adducts in the hepatic 10,000g supernatant had a relative molecular mass of 55 kDa. Serum proteins containing 3-(cystein-S-yl)acetaminophen adducts had molecular masses similar to those found in the liver 10,000g supernatant (55, 87, and approximately 102 kDa). These data, combined with our previous findings describing the temporal relationship between the appearance of 3-(cystein-S-yl)acetaminophen adducts in protein in the serum and the decrease in the levels of 3-(cystein-S-yl)acetaminophen adducts in protein in the liver, suggested that liver adducts were released into the serum following lysis of hepatocytes. The temporal relationship between the formation of specific adducts and hepatotoxicity in mice following a hepatotoxic dose of acetaminophen was examined using immunoblots of mitochondria, microsomes, cytosol, and plasma membranes. Hepatotoxicity indicated by serum alanine aminotransferase levels was increased at 2 and 4 hr after dosing. The cytosolic fraction contained numerous proteins with 3-(cystein-S-yl)acetaminophen adducts, the most intensely stained of which was a 55-kDa protein. 3-(Cystein-S-yl)acetaminophen adducts were detected in the 55-kDa liver protein 30 min after dosing and prior to the development of significant toxicity. Examination of gels suggested that maximal levels of immunochemically detectable adducts in the 55-kDa protein occurred at 1-2 hr, with a decrease in intensity 4 hr after dosing. The presence of 3-(cystein-S-yl)acetaminophen adducts in proteins prior to hepatotoxicity suggests a threshold for adduct formation in the development of toxicity. Protein in microsomes which contained 3-(cystein-S-yl)acetaminophen adducts ranged in molecular weight from 38 to approximately 106 kDa. The major proteins containing 3-(cystein-S-yl)acetaminophen adducts in the mitochondria had molecular masses of 39, 50, 68, and 79 kDa.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetaminophen↗
PubMed1990

Effects of lithium and rubidium on immune responses of rats.

Rats were treated with LiCl or RbCl in drinking water for 65 days. Spleen cells from both treated groups exhibited significantly greater proliferative responses to lipopolysaccharide (LPS) than those from untreated controls. Responses to concanavalin A (Con A) were not affected. Cytotoxic activities of natural killer (NK) cells from both treated groups were significantly less than those from untreated controls. In vitro, Li augmented responses of spleen cells to LPS, but the same doses of Rb suppressed the responses. Effects on responses to Con A were variable. Both Li and Rb alone had a small mitogenic effect on spleen cells.

Animals↗
PubMed1990

A quantitative structure activity/dose response relationship for contact allergic potential of alkyl group transfer agents.

As part of the investigation of structure activity relationships in contact allergy, it has been shown that methyl transfer agents are capable of acting as skin sensitizers. This work has now been extended to a more general examination of alkyl transfer reactions. The modified single injection adjuvant test has been used to investigate the sensitization potential of C12, C16 and unsaturated C18 alkyl transfer agents. Dose responses to challenge and the patterns of cross-reactivity between these materials and methyl transfer agents have been studied. All alkyl transfer agents examined were potent sensitizers in the guinea pig. There was evidence of mutual cross-reactivity between all alkyl transfer agents examined (including methyl transfer agents). Analysis of the data in terms of a modified relative alkylation index showed evidence of an overload effect. The sensitization data has been accurately modelled using a mathematical equation. These results emphasize the possibilities for relating physicochemical parameters and skin sensitization potential. Further studies with alkyl transfer agents are in progress of amplify the observations and conclusions presented in this report. No in vitro model is available for the prediction of skin sensitization potential. Therefore an approach based on a model using physicochemical criteria is the most likely route to a reduced requirement for animal testing.

Animals↗
PubMed1990

Improvement of central auditory function after partial temporal lobectomy in a patient with seizure disorder.

This case study reports the auditory findings in one patient with left temporal lobectomy. Behavioral and electrophysiologic central auditory tests were administered just before and 1 week after surgical removal of the left anterior temporal lobe, including the amygdala and portions of the hippocampus. The dichotic digits test and late auditory evoked potentials with P-300 showed marked improvement postoperatively, consistent with improved central auditory function. Postoperative behavioral results on the dichotic digits test are consistent with anatomic evidence that there are few, if any, auditory connections to the anterior temporal lobe. Although electrophysiologic recordings improved postoperatively, they are still considered abnormal. This case study illustrates the use of both behavioral and electrophysiologic procedures for monitoring central auditory function.

Adult↗
PubMed1989

Novel GTP-binding proteins in plasma membranes of the fungus Metarhizium anisopliae.

We report the existence of several families of GTP-binding proteins in plasma membranes of Metarhizium anisopliae. Two proteins (18.4 and 24 kDa) resemble mammalian Gn-proteins in their being toxin insensitive, binding [alpha-32P]GTP on nitrocellulose blots of sodium dodecyl sulfate (SDS)-polyacrylamide gels, and also in their immunological properties. Four other proteins (31-38.2 kDa) were similar except that they did not bind [alpha-32P]GTP after treatment with sodium dodecyl sulfate. An 18.2 kDa cholera toxin substrate and three toxin insensitive bands (18.6, 18.8, and 24 kDa) are novel proteins antigenically related both to mammalian G-proteins and ras gene products. An additional 23 kDa pertussis toxin substrate (the major G-protein in a crude mycelial extract) reacted strongly with antisera to G-proteins but not with anti-ras serum. Other substrates ADP ribosylated by cholera toxin or botulinum D toxin were immunologically unreactive. Analysis of the structural and functional characteristics of these multiple GTP-binding proteins will promote a better understanding of signal transduction in fungi.

Adenosine Diphosphate Ribose↗
PubMed1989

Arachidonic acid-dependent peroxidative activation of carcinogenic arylamines by extrahepatic human tissue microsomes.

Prostaglandin H synthase (PHS), an arachidonic acid-dependent peroxidase, has been implicated in the peroxidative activation of carcinogenic aromatic amines in extrahepatic carcinogen target tissues of experimental animals. We have examined the arachidonic acid-dependent activation of [3H]benzidine to DNA-bound products by microsomal preparations from 75 normal human tissues obtained during necessary surgical procedures. For several samples of urinary bladder epithelium, prostatic epithelium, colonic mucosa, and peripheral lung tissue, an arachidonic acid-dependent, microsomal-catalyzed activation of benzidine was observed; and the activity could be inhibited appreciably by indomethacin, a known inhibitor of PHS. Little or no arachidonic acid-dependent activity was detected in human placenta, breast, or liver microsomes or the majority of colon microsomes. Substrate specificity was also examined with purified ram PHS and with human bladder and with active colon preparations. Purified PHS catalyzed the activation of benzidine much greater than 2-naphthylamine, 2-amino-6-methyldipyrido[1,2-alpha:3',2'-d]imidazole greater than 4-aminobiphenyl greater than 2-amino-3-methylimidazo[4,5-f]quinoline greater than 3-amino-1-methyl-5H-pyrido[4,3-b] indole. In comparison, human bladder and colon microsomes catalyzed the activation of benzidine greater than 4-aminobiphenyl, 2-amino-6-methyldipyrido[1,2-alpha:3',2'-d]imidazole, 2-naphthylamine greater than 2-amino-3-methylimidazo[4,5-f]quinoline, 3-amino-1-methyl-5H-pyrido[4,3-b]indole. To confirm the occurrence of PHS antigen in human extrahepatic tissues, an avidin/biotin-amplified competitive enzyme-linked immunoabsorbent assay was developed with purified ram PHS and a commercially available monoclonal antibody known to cross-react with human platelet PHS. The avidin/biotin-amplified enzyme-linked immunosorbent assay, which detected ng quantities of ram PHS, clearly established the presence of the PHS protein in human bladder, prostate, and lung microsomes. In contrast, PHS antigen was not detected in the liver or placental microsomes. The interindividual and tissue-dependent variability of PHS and its role in aromatic amine carcinogenesis are discussed.

Arachidonic Acid↗