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Biomedical subjects

I R Tebbett

Publications and source records attributed to I R Tebbett.

At least 19 recordsLinked to original sources
PubMed2001

High mass clearance of autoantibodies from a murine model of lupus nephritis by immunoadsorption using star-configured polyethylene glycols.

The extracorporeal immunoadsorption of antibodies as part of the therapy for human autoimmune diseases has been limited by technology with inadequate and nonselective mass clearance or problems with bioincompatibility. To overcome these shortcomings, we designed a method utilizing star-configured polyethylene glycols (star-PEGs) having up to 63 free arms with immunoreactive (tresylate ester) end-groups for each arm immobilized to a polymer support substrate. The flexibility and length of the arms are thought to allow optimization of epitope presentation and to permit interaction with immunoligands on adjacent arms. To demonstrate efficacy we used an in vitro murine antibody model of human lupus nephritis, wherein we could study the kinetics and mass clearance of hybridoma derived antihistone antibodies from human plasma. Histones were covalently bound to the star-PEG end-groups and the kinetics of antibody adsorption were assessed using a surface plasmon resonance technique. The equilibrium constants of antihistone antibody binding to histone-star-PEGs that were linked to a support grid demonstrated high affinity with a KA of 3.56E + 07 and a KD of 2.81E - 08. The optimum reaction conditions were determined to accomplish the hydrophilization of polysulfone (PS; by an aqueous nitration method) and polymethylmethacrylate substrates (PMMA; by hydrazine), using sheet casts of both polymer substances. Hollow fiber devices of these polymers (commercial hemodialyzers) were modified so that histone-bound star-PEGs were linked to their intracapillary luminal surfaces, using a process which we have shown retains their immunoadsorption properties for antihistone antibodies. A closed loop recirculating model was constructed to measure mass clearance of antibodies from a reservoir. After optimizing conditions using extraction from saline solutions, the removal of antibody from human plasma by control and surface-modified devices was assessed over 4 h. There was no measurable antibody clearance by the control fibers over this time interval. The 2.1 m2 luminal surface area PMMA devices removed 5.0 +/- 1.1 mg, with a maximum of 7.0 mg. The 1.8 m2 PS device cleared 11.3 +/- 6.2 mg with a maximum of 17.5 mg. In summary, star-PEG immunoadsorption is a promising technique for the treatment of human autoimmune disease because it can achieve very high-mass clearance of autoantibodies using modified biocompatible hollow-fiber polymer devices.

Animals↗
PubMed2001

Elimination of cocaine by pregnant sheep following single or multiple exposures.

To test the hypothesis that chronic exposure to cocaine would alter drug elimination in pregnant and fetal sheep compared to a single exposure, we administered intravenous cocaine HCl to 8 pregnant sheep daily as a bolus, followed by a 2-h infusion beginning at gestational age 75 days. Eight additional animals received an equivalent volume of saline. Three days after maternal and fetal catheter placement on day 125, ewes in both groups received cocaine HCl, 2 mg/kg, as a bolus. Maternal and fetal plasma samples were serially obtained and analyzed for cocaine and benzoylecognine. Cocaine half-life in the ewes and fetuses exposed to cocaine was no different from that in animals exposed to saline. We conclude that cocaine is rapidly metabolized in pregnant sheep and that chronic administration does not alter drug clearance.

Animals↗
PubMed2001

Detection of cocaine and its metabolites in breast milk.

A method was developed for measuring cocaine and its metabolites, benzoylecgonine, ecgonine methyl ester, norcocaine, ecgonine ethyl ester, cocaethylene, and m-hydroxybenzoylecgonine, in breast milk by gas chromatography/mass spectrometry. Limits of detection for this method ranged from 2.5 to 10 ng/mL, and limits of quantitation ranged from 5 to 50 ng/mL. For each of the compounds measured by this method, linear response was demonstrated to 750 ng/mL. Breast milk was collected from 11 mothers who admitted to drug use during pregnancy and ten drug-free volunteers serving as control subjects. Cocaine was detected in six of the specimens obtained from drug-exposed subjects, and in none of the drug-free control subjects. In breast milk specimens where cocaine and one or more of its metabolites were detected, the concentration of parent compound was greater than any of the metabolites. The highest cocaine concentration found was over 12 microg/mL. Breast-fed infants of cocaine abusing mothers may be exposed to significant amounts of drug orally.

Adult↗
PubMed2000

Lead content of calcium supplements.

CONTEXT: Substantial quantities of lead have been reported in some over-the-counter calcium supplement preparations, including not only bone-meal and dolomite, but also over-the-counter natural and refined calcium carbonate formulations. Examination of this issue is warranted given recent increases in physician recommendations for calcium supplements for prevention and treatment of osteoporosis. OBJECTIVES: To determine the lead content of calcium supplements and to quantify the lead exposure from popular brands of calcium in dosages used for childhood recommended daily allowance, osteoporosis, and phosphate binding in dialysis patients. DESIGN AND SETTING: Analysis of lead content in 21 formulations of nonprescription calcium carbonate (including 7 natural [ie, oyster shell] and 14 refined), 1 brand of prescription-only calcium acetate, and 1 noncalcium synthetic phosphate binder conducted in March 2000. MAIN OUTCOME MEASURES: Lead content, assayed using electrothermal atomic absorption, expressed as micrograms of lead per 800 mg/d of elemental calcium, per 1500 mg/d of calcium, and for a range of dosages for patients with renal failure. Six microg/d of lead was considered the absolute dietary limit, with no more than 1 microg/d being the goal for supplements. RESULTS: Four of 7 natural products had measurable lead content, amounting to approximately 1 microg/d for 800 mg/d of calcium, between 1 and 2 microg/d for 1500 mg/d of calcium, and up to 10 microg/d for renal dosages. Four of the 14 refined products had similar lead content, including up to 3 microg/d of lead in osteoporosis calcium dosages and up to 20 microg/d in high renal dosages. No lead was detected in the calcium acetate or polymer products. Lead was present even in some brand name products from major pharmaceutical companies not of natural oyster shell derivation. CONCLUSIONS: Despite increasingly stringent limits of lead exposure, many calcium supplement formulations contain lead and thereby may pose an easily avoidable public health concern. JAMA. 2000;284:1425-1429.

Calcium↗
PubMed2000

Optimization of ligand presentation for immunoadsorption using star-configured polyethylene glycols.

Medical, pharmaceutical, and industrial applications of immunoadsorption are frequently limited by the technologic problems of low affinity, inadequate capacity, hydrophobicity, and bioincompatibility. To overcome these difficulties we studied the use of star-burst configured polyethylene glycols (star-PEGs) with immunoreactive molecules covalently bound to the end of each of the multiple flexible arms. The optimum pH ranges were determined to maintain stability of the tresyl chloride modified star reagents, and the chemistry was designed for their subsequent linkage to the immunoadsorbent moiety. We then devised the chemical reactions using nitration or hydrazine activation to tether these 64-arm structures to polymer supports made of polysulfone or polymethylmethacrylate, respectively. Transmission, scanning, and atomic force microscopy confirmed the preservation of the star configuration, even after linkage to the luminal surface of hollow fiber devices. To establish that these modified devices also maintained immunoadsorption reactivity, we used a model having relevance for human autoimmune disease and demonstrated the clearance of antihistone antibodies by tethered histones. This novel approach to increasing the capacity of immunoadsorption benefits from the star configuration which provides a high density of ligand, improved hydrophilicity of the surface, spacing of reactive molecules away from the support structure, and possible optimization of epitope immunoreactivity by arm-to-arm interaction of the bound molecules.

Adsorption↗
PubMed2000

The effects of pyridostigmine bromide and permethrin, alone or in combination, on response acquisition in male and female rats.

It has been hypothesized that concurrent exposure to pyridostigmine bromide and permethrin may have contributed to the development of neurocognitive symptoms in Gulf War veterans. The present experiment was designed to investigate the effects of pyridostigmine bromide and permethrin alone, or in combination, on the acquisition of a novel response, one measure of normal cognitive functioning. Male and female Sprague-Dawley rats were treated with pyridostigmine bromide (1.5 mg/kg/day, by gavage in a volume of 5 ml/kg) or its vehicle for 7 consecutive days. They then also received an intraperitoneal injection of permethrin (0, 15, or 60 mg/kg) before they were exposed to an experimental session during which they could earn food by pressing a lever in an operant chamber. Serum permethrin levels increased as a function of its dose, and were higher in rats treated with pyridostigmine bromide. Sex differences were observed as permethrin levels were higher in female rats than in male rats following the highest dose. Pyridostigmine bromide delayed response acquisition in male and female rats, and resulted in higher response rates on the inactive lever in female rats than in male rats. Although permethrin levels were higher in subjects treated with pyridostigmine bromide than in those treated with vehicle, there were no differences in the behavioral effects of permethrin. Whether or not these behavioral effects of pyridostigmine bromide are of central or peripheral origin will need to be determined in future studies, as its effects on motor activity and/or gastro-intestinal motility may have affected response acquisition.

Animals↗
PubMed2000

Interactions of pyridostigmine bromide, DEET and permethrin alter locomotor behavior of rats.

Drug interactions have been suggested as a cause of Gulf War Syndrome. Pyridostigmine bromide (PB), a prophylactic treatment against potential nerve gas attack, the insect repellent DEET, and permethrin (PERM) impregnated in soldiers' uniforms may have interacted and caused greater than expected toxicity. We tested those 3 drugs singly and in combinations on male and female Sprague-Dawley rats in open field arenas to find the effects on rate of locomotion and thigmotaxis. Administration rates were 10 mg PB/kg; 50, 200, or 500 mg DEET/kg; 15, 30, or 60 mg PERM/kg; 5 mg PB/kg + 100 mg DEET/kg; 5 mg PB/kg + 15 mg PERM/kg; 100 mg DEET/kg + 15 mg PERM/kg; or vehicle by gavage and i.p. injection. Locomotor behavior was quantified by video-computer analysis for 2 h post-treatment. Female rats were tested in either pro- or metestrus. Drug interactions were determined by the isobolographic method. Blood serum drug concentrations were estimated by high performance liquid chromatography or gas chromatography-mass spectrometry. Single drug effects were very limited within the ranges tested. Double-drug administrations at half the single-drug rates resulted in statistically significant interactions in male rats for both locomotion rate and thigmotaxis. Combination of PB + PERM and DEET + PERM significantly affected speed, whereas only the combination of DEET + PERM significantly affected thigmotaxis. Female rats did not show significant interactions. Our data suggest that serum concentrations of PB and DEET may have been higher in females than males. Administration of PB + DEET may have reduced the serum concentration of DEET, and administration of PB + PERM may have increased the serum concentration of PERM.

Animals↗
PubMed2000

Repeated coadministrations of pyridostigmine bromide, DEET, and permethrin alter locomotor behavior of rats.

Interactions of pyridostigmine bromide (PB), permethrin (PERM), and the insect repellent DEET (DEET) have been suggested as possible causes of Gulf War Syndrome (GWS) in humans. Open field locomotor studies have long been used in behavioral toxicology. Using male and female Sprague-Dawley rats, video-computer analyses, and the isobolographic method we have determined the effects on locomotor speed and thigmotaxis following repeated administration of single-, double-, or triple-drug or vehicle controls in an open field. The effects were measured 24 hours after 7 daily drug administrations. Single-drug administrations caused no significant effects. Double-drug administrations resulted in significant effects in the following cases: males given PB + DEET had a significantly slower locomotion rate; males given DEET + PERM had a significantly faster locomotion rate; females given PB + DEET had a significantly slower locomotion rate; and females given PB + PERM spent significantly more time in the center zone (less thigmotaxis). Triple-drug administration caused no significant effect. These results in comparison with behavioral studies in chickens and insects show certain similarities. The implications of the lasting effects on animal models are relevant to GWS in humans.

Animals↗
PubMed1999

The effects of acute and repeated pyridostigmine bromide administration on response acquisition with immediate and delayed reinforcement.

This experiment was designed to assess the effects of acute and repeated administration of pyridostigmine bromide (a carbamate with prophylactic and therapeutic uses) on response acquisition. Experimentally naïve, male Sprague-Dawley rats were exposed to a situation in which lever presses were either immediately followed by food-pellet presentation or after a 16-s resetting delay. Different groups of rats received either one acute administration of pyridostigmine bromide (10 mg/kg, by gavage) or repeated pyridostigmine administration for 7 days (1.5 mg/kg/day, by gavage). Other groups were treated with distilled water for the same period of time. Both acute and repeated pyridostigmine bromide administration decreased serum cholinesterase levels by approximately 50%, but neither treatment affected brain cholinesterase levels in our assay. Acute and repeated drug administration produced the same behavioral effects. Subjects exposed to the 0-s delay conditions obtained many more food pellets than those exposed to the 16-s delay conditions. Administration of pyridostigmine bromide delayed the onset of responding in some, but not all, of the subjects in the treated groups, independent of the delay condition to which they were exposed. Many more responses were observed on an inoperative lever during the 16-s delay conditions than during the 0-s delay conditions, especially during the 16-s delay condition in which subjects had received acute vehicle administration. Whether or not these effects of small doses of pyridostigmine bromide on response acquisition are of central or peripheral origin will need to be determined in future studies, as response acquisition in the present experiment may have been affected by pyridostigmine's effects on gastrointestinal functioning and/or motor activity.

Analysis of Variance↗
PubMed1999

Pyridostigmine bromide alters locomotion and thigmotaxis of rats: gender effects.

Male rats and female rats in the proestrous and metestrous stages of estrus were tested to determine the effects of pyridostigmine bromide on locomotion rate and thigmotactic response using doses of 3.0, 10.0, and 30.0 mg/kg. Thirty minutes after administration of the pyridostigmine bromide the rats were videorecorded for 2 h in a 1 m2 open-field arena. The rats' activities were analyzed for the drug's effect on speed throughout the 2 h and during six 20-min segments. Also, the times that the rats were observed moving through the central 50% of the arena were determined. Locomotion rates decreased significantly, and thigmotaxses increased significantly in all groups of rats as a dose response to pyridostigmine bromide. Habituation occurred over 2 h for both responses, primarily during the first 40 min. Female rats were more affected than males, but metestrous and proestrous females did not differ significantly in their responses. At the 30 mg/kg the effect was persistent throughout the test period. Proestrous females dosed at 30 mg/kg had much higher pyridostigmine bromide serum levels than metestrous females and males.

Animals↗
PubMed1998

Cocaine suppresses fetal immune system.

The effects of cocaine are well documented in the CNS; however, recent evidence suggests that cocaine may suppress the immune system. Maternal cocaine use essentially exposes the fetus to a continuous exposure of cocaine. The objective of this study was to investigate the immunomodulatory effects of cocaine and its metabolites on maternal and fetal immune systems. Subjects were recruited from an Investigational Review Board approved protocol, and biologic specimens were collected. For each subject peripheral blood mononuclear cells (PBMCs) were isolated by density gradient. Each PBMC sample was stimulated in separate wells with phytohemagglutinin and phrobol 12-myristate 13-acetate. Samples were radiolabeled and stimulation was measured. Cytokine measurements were made on the serum via ELISA assay techniques. In both the phorbol 12-myrisate 13-acetate and the phytohemagglutinin group, the PBMCs isolated from fetal cord blood in the cocaine-using group had significantly (p < 0.05) decreased responses compared with control subjects. IL 1 and IL 2 concentrations were suppressed in the cocaine-exposed fetal serum compared with controls (p < 0.005 and p < 0.05, respectively). We have shown that in utero cocaine exposure results in a nonspecific suppression of fetal T lymphocyte response. The clinical consequences of prenatal cocaine-induced immunosuppression need to be further explored.

Adult↗
PubMed1997

Cocaine and benzoylecgonine in serum microsamples of intact and gonadectomized male and female Wistar rats.

Tail-tip plasma samples of intact and gonadectomized male and female Wistar rats were analyzed for cocaine and benzoylecgonine. The samples were obtained from immobilized subjects 10 and 30 min following the 1st and 22nd intraperitoneal injections of 10 mg/kg cocaine hydrochloride. Gender differences in plasma cocaine or benzoylecgonine levels were not observed after the first injection of cocaine because many of the samples were below the detection limit. Cocaine plasma levels were much higher after the 22nd injection, but gender differences were not observed either 10 or 30 min following cocaine administration. Plasma levels of benzoylecgonine were higher 30 min than 10 min after cocaine administration in intact and castrated male rats and ovariectomized female rats but not in intact female rats. These data show that, in rats, gender differences in cocaine metabolism may be observed after repeated cocaine administration, but the exact mechanism remains to be elucidated.

Animals↗
PubMed1996

In vitro-in vivo myotoxicity of intramuscular liposomal formulations.

PURPOSE: The first objective was to study the in vitro myotoxicity of empty liposomes and to examine whether liposome size, charge and fluidity affect of liposomal myotoxicity. The second objective was to investigate the effect of liposomal encapsulation on the in vitro and in vivo myotoxicity of loxapine compared to the loxapine commercial preparation (Loxitane). METHODS: The in vitro myotoxicity of empty liposomes and loxapine liposomes was evaluated by the cumulative efflux of the cytosolic enzyme creatine kinase (CK) from the isolated rat extensor digitorum longus (EDL) muscle over a 2 hour period. In the in vivo studies, the area under plasma CK curve over 12 hours was used to evaluate muscle damage. RESULTS: The in vitro myotoxicity for all empty liposomal formulations was not statistically different from negative controls (untreated control muscles and normal saline injected muscles). However, these empty liposomal formulations were significantly less myotoxic than the positive controls (muscles injected with phenytoin and muscle sliced in half). In vitro-in-vivo studies showed that the liposomal encapsulation of loxapine resulted in significant (P < 0.05) reduction in myotoxicity (80% in vitro and 60% in vivo) compared to the commercially available formulation which contains propylene glycol (70% V/V) and polysorbate 80 (5% W/V) prepared at equal concentration. CONCLUSIONS: Results indicate that empty liposomes do not induce myotoxicity. Furthermore, liposomal size, charge and fluidity do not affect myotoxicity. In addition, in vitro and in vivo studies have demonstrated that liposomal encapsulation of loxapine can reduce myotoxicity compared to a formulation containing organic cosolvents.

Animals↗
PubMed1996

Comparison of HPLC and GC-MS for measurement cocaine and metabolites in human urine.

High-performance liquid chromatography (HPLC) was compared with gas chromatography-mass spectrometry (GC-MS) for quantitation of cocaine, benzoylecgonine, norcocaine, and cocaethylene in urine. Calibration standards were prepared in human urine, and bupivacaine was added as the internal standard for quantitation. After solid-phase extraction, the reconstituted samples were divided into aliquots for analysis by HPLC and GC-MS. The analytical performance of the two methods were compared with regard to sensitivity, precision, and dynamic range. Results of GC-MS and HPLC analyses of nine urine specimens previously confirmed as positive for benzoylecgonine were compared. Analytical results by HPLC were comparable to GC-MS. Therefore, for many laboratories, HPLC is a useful alternative to GC-MS for measuring cocaine and metabolites in urine.

Chromatography, High Pressure Liquid↗
PubMed1995

Effect of chronic cocaine administration on amino acid uptake in rat placental membrane vesicles.

This study evaluated the effects of chronic exposure to cocaine during pregnancy on amino acid uptake in placental membrane vesicles. Pregnant rats received 62 mg/kg of cocaine hydrochloride by intraperitoneal (IP) injection as a divided daily dose on gestation days 8-19 inclusive. Fetal body weights were significantly decreased by 19% in the cocaine group, while placental weights were unchanged. Placental apical membrane vesicles were prepared from control and cocaine-treated animals, and marker enzyme enrichments for alkaline phosphatase and [3H]-dihydroalprenolol binding did not differ between cocaine and control groups. Rates of uptake (10 sec) of selected radiolabeled amino acids were measured utilizing a rapid filtration technique. Na(+)-dependent apical membrane [3H]-glutamine transport (50 microM) was reduced by 95% (p < 0.05) in cocaine-treated compared to control placentas. Uptake of 50 microM [3H]-methyl aminoisobutyric acid (MeAIB) into apical membranes was also decreased by 43% (p < 0.05) in cocaine membranes. Na(+)-independent [3H]-arginine transport (10 microM), however, did not differ between control or cocaine-treated groups. In summary, chronic cocaine administration selectively inhibited the transport of glutamine and MeAIB into apical membrane vesicles, but had minimal effect on arginine transport. We postulate that this diminution in uptake may contribute to the fetal growth retardation noted in our model.

Aminoisobutyric Acids↗
PubMed1995

Stimulatory effects of cocaine and its metabolites on IM-9 human B-lymphoblastoid cells.

This study examined the effect of cocaine and its metabolites benzoylecgonine, norcocaine, and cocaethylene on human B-cell proliferation using IM-9 cells. Cells were incubated with 0.01-10 micrograms/ml of cocaine or metabolite in serum-free medium or medium containing 2% FBS for 24 and 48 h, and [3H] thymidine incorporation into DNA was measured using liquid scintillation counting. Results showed incubation with cocaine and metabolites significantly increased IM-9 cell proliferation. With cocaine, maximal stimulation of 148% (compared to drug-free control) occurred at 1.0 micrograms/ml in serum-free medium at 48 h. Benzoylecgonine and norcocaine showed maximal stimulation at 0.1 micrograms/ml with 170% and 150% stimulation, respectively. Cocaethylene showed maximal stimulation of 146% at 10 micrograms/ml. Drug stability was monitored under incubation conditions using high-performance liquid chromatography (HPLC). We have shown that cocaine and its major metabolites have an immunomodulatory effect on B-cell proliferation at concentrations equivalent to serum levels produced during cocaine use in humans. Since the cocaine metabolites also show an immunomodulatory effect, the immune consequences of cocaine use may be significantly prolonged.

B-Lymphocytes↗