Biomedical subjects

K Farrell

Publications and source records attributed to K Farrell.

At least 73 records · Page 4Linked to original sources

PubMed1990

Metabolic profiling of valproic acid in patients using negative-ion chemical ionization gas chromatography-mass spectrometry.

A negative-ion chemical ionization gas chromatographic-mass spectrometric method for the determination of valproic acid (VPA) and fourteen of its metabolites in a single chromatographic run is reported. The assay features the use of four internal standards and is applicable to the analysis of small serum and urine volumes. A combination of pentafluorobenzyl and trimethylsilyl derivatization resulted in the [M - 181]- ion as the base peak for all the metabolites measured. When these ions were monitored sensitivities in the low picogram levels were achieved. The VPA metabolite profile was determined in pediatric patients on VPA monotherapy and on combined VPA therapy with either carbamazepine or clobazam. The recently characterized diene metabolite, (E,E)-2,3'-diene-VPA, was found to be a major serum metabolite of VPA. In the patient groups taking VPA in combination with carbamazepine, the induction of omega and omega-1 pathways of VPA metabolism was apparent, while the levels of the beta-oxidation products were significantly decreased.

Adolescent↗

PubMed1990

Electrophysiologic studies, computed tomography, and neurologic outcome in acute bacterial meningitis.

To determine the value of computed tomography and electrophysiologic studies in predicting neurologic outcome, we prospectively studied 41 children with acute bacterial meningitis, using clinical examination, computed tomography of the head, electroencephalography, brain-stem auditory evoked response, and visual evoked potential mapping during the acute illness. Two children died; 32 of the remaining 39 children were reviewed clinically, electrophysiologically, and with computed tomography between 5 and 38 months after the illness. The electrophysiologic data obtained during the illness were not found to alter the acute-stage management. Focal or generalized suppression, demonstrated on the electroencephalogram, was associated with a poor outcome. Cerebral infarction and edema, demonstrated by computed tomography of the head, were predictive of a poor outcome, but enlarged ventricular and subarachnoid spaces and increased subdural effusions were of no predictive value. Neither computed tomographic scans nor electrophysiologic data were better indicators of neurologic prognosis than the clinical examination.

Acute Disease↗

PubMed1990

The high incidence of valproate hepatotoxicity in infants may relate to familial metabolic defects.

The incidence of fatal hepatic failure associated with valproic acid (VPA) therapy is highest in children under the age of three years, particularly in those with developmental delay. The pathogenesis of VPA hepatotoxicity is unclear but may relate to the accumulation of a toxic metabolite of VPA which impairs fatty-acid oxidation. We describe two unrelated infants with developmental delay who developed hepatic failure while receiving VPA. Siblings of both children subsequently developed hepatic steatosis and intractable seizures without being exposed to VPA. This suggests that the two children who developed liver failure when receiving VPA may have had a familial metabolic disorder. Familial metabolic disorders may account partly for the higher incidence of fatal hepatotoxicity described in infants receiving VPA.

Chemical and Drug Induced Liver Injury↗

PubMed1990

Decline in head growth and cognitive impairment in survivors of acute lymphoblastic leukaemia.

Twenty five children in remission, who were asymptomatic and who had last been treated at least two years before for acute lymphoblastic leukaemia, were examined neurologically and neuropsychologically. Their treatment included early cranial irradiation (24 Gy or 18 Gy), intrathecal methotrexate, and systemic chemotherapy. One half of the children demonstrated a decline in head circumference centile, which occurred in all patients treated with 24 Gy and in those patients treated with 18 Gy under the age of 3 years. In those children whose head growth was reduced, performance was significantly impaired in neuropsychological tests designed to assess concentration and short term memory. These children also developed clinically important learning difficulties in the classroom. Minor neurological dysfunction was present in almost half of the entire group. These data suggest that the treatment employed to prevent central nervous system leukaemia (primarily cranial irradiation) has a deleterious effect on head and brain growth and intellectual function.

Adolescent↗

PubMed1989

Routine screening of blood and urine for severe reactions to anticonvulsant drugs in asymptomatic patients is of doubtful value.

Severe or fatal reactions to anticonvulsant agents are fortunately rare. We examined the value of routine screening of blood and urine to detect early signs of such reactions in asymptomatic patients. The basic assumptions of this type of screening program have been faulty or unproven, and the results of studies, although not definitive, have not supported the value of such programs. Our recommendations, approved by the Canadian Association for Child Neurology, suggest that asymptomatic patients not undergo routine screening of blood and urine but, rather, be informed of the early symptoms of severe toxic reactions and be asked to report them immediately to a physician.

Adult↗

PubMed1989

The effect of carbamazepine on valproic acid disposition in adult volunteers.

1. Pharmacokinetic parameters for valproic acid (VPA) were determined before and following 2 weeks of carbamazepine (CBZ) administration in five healthy male volunteers. Mean VPA dosage was 16.4 mg kg-1 day-1. CBZ dosage was started at 100 mg twice daily and increased after 1 week to a total daily dose of 300 mg. 2. After CBZ administration, mean VPA plasma clearance increased from 0.90 +/- 0.18 s.d. to 1.26 +/- 0.24 l h-1 (P less than 0.05) as did clearance of free VPA (20.8 +/- 7.6 to 37.0 +/- 13.6 l h-1). Mean VPA elimination rate constant increased from 0.051 +/- 0.011 to 0.067 +/- 0.011 h-1 (P less than 0.05) after CBZ administration. 3. Mean area under the serum concentration vs time curve decreased from 675.0 +/- 130.5 to 475.7 +/- 75.7 mg l-1 h (P less than 0.05) after CBZ administration. Mean serum VPA half-life decreased from 14.0 +/- 2.4 to 10.6 +/- 1.4 h (P less than 0.05). Mean serum VPA trough concentrations decreased from 44.0 +/- 16.7 to 27.0 +/- 10.4 micrograms ml-1 (P less than 0.05). 4. A significant change was not observed in the mean VPA volume of distribution after CBZ coadministration suggesting that enzyme induction rather than a competition for plasma protein binding sites was involved in this interaction. 5. Despite the increased clearance of VPA, the urinary recovery of VPA or conjugate did not increase after CBZ administration.

Adult↗

PubMed1989

Complex partial status epilepticus associated with cyclosporin A therapy.

Significant neurotoxicity including seizures, encephalopathy and coma may complicate the use of cyclosporin A (CyA). Two patients are described, receiving CyA, who presented with abnormal behaviour, stupor, focal motor activity and were shown to be in complex partial status epilepticus (CPSE). Abnormalities of behaviour and/or stupor in patients receiving CyA may be a manifestation of CPSE. Patients receiving CyA who develop an encephalopathy should have electroencephalography performed at the time of the abnormal behaviour.

Adult↗

PubMed1989

Development and validation of in vitro induction assays for toxic halogenated aromatic mixtures: a review.

Halogenated aromatic industrial compounds, typified by the polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and biphenyls (PCBs) have been identified as residues in almost every component of the global ecosystem. Risk assessment of the complex mixtures of halogenated aromatics found in environmental samples is complicated by analytical problems and the lack of toxicological information on individual compounds and mixtures. Research in our laboratory has focused on the development and vadidation of the in vitro aryl hydrocarbon hydroxylase (AHH) induction assay in rat hepatoma H-4-II E cells in culture for quantitating individual toxic halogenated aryl hydrocarbons and their mixtures. For several PCB, PCDD, PCDF congeners, their mixed bromo/chloro analogs and reconstituted mixtures there was an excellent linear correlation between their -log ED50 values for AHH induction in rat hepatoma cells and their -log ED50 values for in vivo hepatic microsomal AHH induction, inhibition of body weight gain and thymic atrophy in the rat. It has also been shown for selected compounds that there was a good correlation between their in vitro AHH induction potencies and their effects in guinea pigs (AHH induction, inhibition of body weight gain) and mice (immunotoxicity). This assay system has been utilized to quantitative the "2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) equivalents" present in extracts from diverse sources including fly ash from a municipal incinerator and pyrolyzed brominated flame retardants which contain a complex mixture of halogenated dibenzo-p-dioxins and dibenzofurans.

Animals↗

PubMed1988

Amaurosis fugax in teenagers. A migraine variant.

Sudden, transient loss of vision in one eye (amaurosis fugax) is associated frequently with atherosclerosis of the internal carotid artery in adults and may herald a stroke. Thus, cerebral angiography is often performed. Amaurosis fugax in children is uncommon and an underlying cause is rarely demonstrated. Recurrent episodes of amaurosis fugax occurred in five adolescents. A characteristic evolution and pattern of visual loss, consistent with choroidal ischemia as the underlying mechanism, was described by four of them. Although none of the episodes were accompanied by headache, four patients had a history of common migraine at other times or a family history of migraine. These episodes of visual loss may represent a migraine variant, and cerebral angiography is not indicated in adolescents with such a history.

Adolescent↗

PubMed1988

Congenital abnormalities in two sibs exposed to valproic acid in utero.

Neural tube, craniofacial, and other congenital abnormalities have been described in infants born to mothers with epilepsy who were treated with valproic acid (VPA) during pregnancy. The pathogenetic relationship between the congenital abnormalities and exposure to VPA is not clear. We describe 3 sibs born to a mother with epilepsy. Only the 2 sibs who were exposed to VPA in utero had certain of the characteristic craniofacial changes described in previous reports of children with similar exposure. In addition, the 2 affected children had other craniofacial and skeletal abnormalities which have not been reported previously as teratogenic sequelae of VPA exposure. Many of the minor anomalies present in the 2 affected patients resemble those observed in rhesus monkeys exposed to VPA in utero. This suggests that the abnormalities observed in the 2 children may have been a consequence of intrauterine exposure to VPA.

Abnormalities, Drug-Induced↗

PubMed1988

Recognition memory of item, associative and serial-order information after temporal lobectomy for seizure disorder.

Children, adolescents, and young adults with temporal lobectomy judged the context of their encounters with a word (by deciding about its prior occurrence or familiarity) and also identified word attributes involving associative content and serial order (by indicating word meanings and reconstructing word sequences). Laterality of temporal lobectomy was important for identifying familiarity: individuals with right-sided temporal lobectomies made better judgements than those with left resections about the prior occurrence of target words, with the more successful performance depending on enhanced sensitivity to the familiarity or non-familiarity of what was heard. Identifying the attributes of an item, as contrasted with its prior occurrence, depended on aspects of temporal lobe disorder in conjunction with laterality: deficits of brain structure involving histopathology and significant tissue loss disrupted content memory; compromised brain function resulting from certain post-infantile seizures impaired memory for serial order. In the young brain after temporal lobectomy, there exists a functional dissociation between judging the familiarity of an event and identifying its attributes, a dissociation that depends, not only on laterality of surgery, but also on the structural and functional intactness of the residual brain.

Adolescent↗

PubMed1988

Envelope sequences of two new United States HIV-1 isolates.

One of the striking molecular aspects of the human T-cell lymphotropic virus type III (HTLV-III) (now called HIV-1) is an unusually large variability in the env genes of different isolates. These differences are clustered primarily within the coding sequences for the large envelope protein and are interspersed among regions within the env gene of relative constancy. Differences among the envelopes of isolates from Africa are so far greater than those among U.S. isolates, but few U.S. isolates have been characterized to date. We report the sequence of the env gene of two U.S. isolates [HTLV-III(MN) and (SC)] and compare them with previously characterized isolates. These two isolates differ substantially from all previously described isolates, especially in the region coding for the large envelope proteins. The env genes of the two new HIV-1 isolates contain conserved and hypervariable regions similar to what has been reported for other isolates, helping to further define those regions. A comparison of the envelope sequences of all the U.S. isolates shows that the similarity between any two ranges from 81 to 85% [except for LAV(BRU) and HTLV-III(BH10) which are 97% similar]. Similar analyses of the African (Zairean) isolates give significantly lower values [71 to 78%, except for 88% between LAV(ELI) and Z6]. This suggests that the African isolates diverged earlier than the U.S. isolates or that transmission of the virus has been more rapid in Africa. Two previous presumptive Haitian isolates are similar to each other and to the U.S. isolates to the same degree as are other U.S. isolates, but differ more markedly from the African isolates suggesting a common lineage of Haitian and U.S. HIV-1 isolates.

Amino Acid Sequence↗

PubMed1987

Synthesis and aryl hydrocarbon receptor binding properties of radiolabeled polychlorinated dibenzofuran congeners.

Microchlorination of 1,4,9[3H]dibenzofuran gave several polychlorinated dibenzofuran (PCDF) products and 2,3,7,8-[3H]tetrachlorodibenzofuran (TCDF), 1,2,3,7,8-[3H]pentachlorodibenzofuran (PeCDF), and 1,2,3,6,7,8-/1,2,3,4,7,8-hexachlorodibenzofuran (HCDF) of high specific activity (57, 34, and 32.5 Ci/mmol, respectively) were purified by preparative high-pressure liquid chromatography. These compounds were investigated as radioligands for the rat liver cytosolic aryl hydrocarbon (Ah) receptor protein. Like 2,3,7,8-[3H]tetrachlorodibenzo-p-dioxin (TCDD), the radiolabeled PCDF congeners exhibited saturable binding with the receptor protein and sucrose density gradient analysis of the radiolabeled ligand-receptor complexes gave specific binding peaks with comparable sedimentation profiles. The rank order of radioligand binding affinities (Kd values) was 2,3,7,8-TCDD greater than 2,3,7,8-TCDF greater than 1,2,3,6,7,8-HCDF greater than 1,2,3,7,8-PeCDF and the maximum difference in Kd values for the four radioligands was less than 13-fold (0.44-5.9 nM). The interactions of the PCDF radioligands with the cytosolic receptor all exhibited saturable binding curves and linear Scatchard plots and the slopes of their Hill plots were in the range 1.0-1.1, thus indicating that cooperativity was not a factor in these binding interactions. The relative stabilities and dissociation kinetics of the radioligand-receptor complexes were highly dependent on the structure of the radioligand. The dissociation curves of the 2,3,7,8-[3H]TCDD and PCDF receptor complexes were biphasic and this suggests that there may be a temporal shift in ligand binding affinities. However, the rates of dissociation did not correlate with the rank order of ligand binding affinities. The stabilities of the radioligand-receptor complexes were also dependent on the structures of the radioligands; for example, the 2,3,7,8-[3H]TCDD-receptor complex degraded more rapidly than the PCDF-receptor complex and these relative stabilities were clearly not related to the Kd values or the relative in vivo or in vitro biologic potencies of these halogenated aryl hydrocarbons.

Animals↗

PubMed1987

Absence of positive co-operativity in the binding of 2,3,7,8-tetrachlorodibenzo-p-dioxin to its cytosolic receptor protein.

The role of positive co-operativity in stabilizing the binding of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to the rat hepatic cytosolic TCDD receptor protein (Ah receptor) was investigated. The binding mechanism of TCDD was determined by kinetic means through equilibrium and saturation binding studies, and Scatchard and Hill plot analysis. In all studies, the slope of the Hill plot was close to 1.0, indicating the absence of positive co-operativity. Interpretation of the Scatchard plot was however complicated by the fact that both linear and nonlinear plots were experimentally obtained. The nonlinearity was shown to be an experimental artifact and a consequence not of co-operativity, but of high levels of nonspecific binding. The high level of nonspecific binding could be attributed to: (1) lipophilicity of the TCDD ligand, and (2) inefficient competition of receptor-bound [3H]TCDD. When nonspecific binding was minimized, the Scatchard slope was linear and in agreement with the Hill coefficient, thus indicating the lack of positive co-operativity in the binding of TCDD to the Ah receptor.

Animals↗

PubMed1987

Characterization of argininosuccinate lyase (EC 4.3.2.1) from Chlamydomonas reinhardtii.

We have isolated and characterized argininosuccinate lyase (ASL; EC 4.3.2.1) from the photosynthetic green alga, Chlamydomonas reinhardtii. The general properties of Chlamydomonas ASL are very similar to those described previously for ASLs from phylogenetically diverse organisms. The algal ASL has a native Mr, determined by gel-filtration chromatography, of 218,000 +/- 25,000, and a pI of 5.4-5.6. The Km for argininosuccinate at 37 degrees C and pH 7.5 is 0.26 mM. The subunit Mr of Chlamydomonas ASL is approx. 50,000, determined by SDS/polyacrylamide-gel electrophoresis, in contrast with a previously reported value of 39,000. Rabbit antisera prepared against the Mr-50,000 protein completely abolished ASL activity in vitro. In contrast, serum prepared against the Mr-39,000 protein was ineffective in inhibiting ASL activity. Despite the general similarity of the physical properties of Chlamydomonas ASL and those of other ASLs, antiserum raised against the algal ASL did not cross-react with ASL preparations from Escherichia coli, Saccharomyces cerevisiae or bovine liver.

Argininosuccinate Lyase↗

PubMed1987

Prospective study of computed tomography in acute bacterial meningitis.

We performed serial CT scans at the time of admission and discharge, and again after 6 to 18 months, in children older than 2 months of age with bacterial meningitis. During the 2-year study period, 60 patients with bacterial meningitis were admitted to British Columbia's Children's Hospital. Forty-one were included in the study, two of whom died soon after admission. The infecting organism was Haemophilus influenzae in 29, Neisseria meningitidis in six, and Streptococcus pneumoniae in six. Abnormalities on the first two CT scans included subdural effusion in eight patients, focal infarction in five, and pus in the basal cisterns in one. All patients with focal infarction or cisternal pus had hemiparesis. Marked cerebral edema was seen in the two patients who died. Transient mild dilation of the subarachnoid space was a common finding; the size of the ventricles or subarachnoid space was increased on the second scan in 29 of 36 patients, and decreased to normal on the third scan in 30 of 33 patients. Clinical management was not influenced by the CT findings, which failed to reveal any clinically significant abnormalities that were not suspected on neurologic examination.

Acute Disease↗

PubMed1986

Capillary gas chromatography-mass spectrometry of valproic acid metabolites in serum and urine using tert.-butyldimethylsilyl derivatives.

A quantitative method has been developed for valproic acid and twelve of its metabolites using capillary gas chromatography--mass spectrometry with selected-ion monitoring. The method is applicable to serum or urine and all metabolites are measured in a single run. Ions selected for quantitative purposes were the characteristic (M-57)+ ions of the tert.-butyldimethylsilyl (tBDMS) derivatives. The 4-hydroxyvalproic acid was measured as the gamma-lactone. Calibration curves were found to be linear and the sensitivities in the order of 0.1 microgram/ml. Patient data are presented. A comparison of tBDMS and trimethylsilyl (TMS) derivatives showed that tBDMS gave superior sensitivity for the unsaturated metabolites and a shorter analysis time. Mixed tBDMS-TMS derivatives were also investigated.

Gas Chromatography-Mass Spectrometry↗

PubMed1986

Polychlorinated dibenzo-p-dioxins: quantitative in vitro and in vivo structure-activity relationships.

There were marked effects of structure on the activities of 14 polychlorinated dibenzo-p-dioxins (PCDDs) as competitive ligands for the 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) receptor and as inducers of aryl hydrocarbon hydroxylase (AHH) and ethoxyresorufin O-deethylase (EROD) in rat hepatoma H-4-II E cells in culture. 2,3,7,8-TCDD was the most active compound in both assays and several PCDD congeners which were fully substituted in the lateral 2, 3, 7 and 8 positions but also contained additional chlorosubstituents in non-lateral 1, 4, 6 and 9 positions were less active. It was also evident that there was a decrease in in vitro binding and induction activities with decreasing lateral chlorine substitution. Although comparable structure-activity relationships (SARs) for the PCDDs were observed for the induction and receptor binding assays, there was not a linear or rank order correlation between the 2 sets of data. Several in vivo biologic and toxic activities of 2,3,7-trichloro-, 2,3,7,8- and 1,3,7,8-tetrachloro-, 1,2,4,7,8- and 1,2,3,7,8-pentachloro- and 1,2,3,4,7,8-hexachlorodibenzo-p-dioxin were determined in a dose-response fashion in immature male Wistar rats. The ED50 values for hepatic microsomal AHH and EROD induction, body weight loss and thymic atrophy were obtained. There was an excellent linear correlation between the -log EC50 values for AHH or EROD induction in cell culture and the -log ED50 values for enzyme induction, body weight loss and thymic atrophy in the rat. The in vitro enzyme induction data could be used to quantitatively estimate the toxicity of the PCDD congeners in the rat: this latter correlation has previously been observed for a series of polychlorinated dibenzofurans.

Animals↗