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Biomedical subjects

J A Fox

Publications and source records attributed to J A Fox.

At least 19 recordsLinked to original sources
PubMed2001

Natural selection for grazer resistance to toxic cyanobacteria: evolution of phenotypic plasticity?

We studied the selection response of the freshwater grazing zooplankter, Daphnia galeata, to increased abundance of cyanobacteria in its environment. Cyanobacteria are a poor-quality and often toxic food. Distinct genotypes of D. galeata were hatched from diapausing eggs extracted from three time horizons in the sediments of Lake Constance, Europe, covering the period 1962 to 1997, a time of change in both the prevalence of planktonic cyanobacteria and levels of phosphorus pollution. We assessed whether the grazers evolved to become more resistant to dietary cyanobacteria by exposing genetically distinct clones to two diets, one composed only of the nutritious green alga, Scenedesmus obliquus (good food), and the other a mixture of S. obliquus and the toxic cyanobacterium Microcvstis aeruginosa (poor food). Genotype performance was measured as the specific rate of weight gain from neonate to maturity (gj). We evaluated evolutionary change in the Daphnia population using an analysis of reaction norms based on relative (log-transformed) changes in gj. Log(gj) is a measure of the proportional effect of dietary cyanobacteria on other fitness components of the Daphnia phenotype. For comparison, we also analyze absolute (i.e., nontransformed) changes in gj and discuss the interpretations of the two approaches. Statistical results using a general linear model demonstrate a significant effect of genotype (showing differences in gj among genotypes), a significant genotype x food-type interaction (showing differences in phenotypic plasticity among genotypes), and, in the case of log-transformed data, a significant sediment-genotype-age x food-type interaction. The latter shows that phenotypic plasticity evolved over the period studied. Two constraints act on response to selection in the D. galeata-Lake Constance system. First, gj on a diet containing poor food is highly correlated with gj on a diet of good food, thus evolving resistance also meant evolving an increase in gj on both diets. Second, because genotypes with a high gj also grow to a large adult body size, which in turn increases Daphnia vulnerability to fish predation, we suggest that selection only acted to favor genotypes possessing a high potential gj after cyanobacteria became prevalent. The presence of cyanobacteria depressed realized gj and led to animals of small adult body size even if their genotypes had the potential for high gj and large size. With realized gj reduced, genotypes with an inherently high value could be selected even in the presence of predatory fish. The joint action of selection by dietary cyanobacteria and vulnerability to fish predation provides an explanation for the observed evolution of resistance to poor food through reduced phenotypic plasticity.

Animals↗
PubMed2001

Composite stentless valve with graft extension for combined replacement of the aortic valve, root and ascending aorta.

OBJECTIVE: The composite mechanical valve conduit has been most commonly used for patients who require combined aortic valve, root, and ascending aorta replacement, but is limited, especially in the elderly, because of the need for long-term anticoagulation. We report the first consecutive series of patients in whom a composite stentless valve with graft extension, which does not require long-term anticoagulation, was performed. METHODS: Between April 1998 and July 2000, eight patients with severe aortic root and ascending aortic pathology underwent a combined aortic valve, root, and ascending aorta replacement with a Freestyle stentless porcine valve with a Hemashield graft extension. Mean age was 74 (range 56--82), three were males. Concomitant procedures included coronary artery bypass graft (CABG) alone (n=2), mitral valve replacement with atrial septal defect repair (n=1) and CABG with septal myomectomy (n=1). RESULTS: Operative mortality was zero. Median aortic cross-clamp and cardiopulmonary bypass times were 150 and 203 min, respectively. Two patients returned to the operating room for bleeding. Median blood transfusions and hospital length of stay were 4 units and 11 days, respectively. CONCLUSIONS: The composite stentless valve with graft extension is a reasonable alternative to a mechanical valve conduit for patients who require a combined aortic valve, root, and ascending aorta replacement, in whom anticoagulation is not desirable or contraindicated.

Aged↗
PubMed2001

The safety of intraoperative transesophageal echocardiography: a case series of 7200 cardiac surgical patients.

UNLABELLED: Transesophageal echocardiography (TEE) is an invaluable intraoperative diagnostic monitor that is considered to be relatively safe and noninvasive. Insertion and manipulation of the TEE probe, however, may cause oropharyngeal, esophageal, or gastric trauma. We report the incidence of intraoperative TEE-associated complications in a single-center series of 7200 adult cardiac surgical patients. Information related to intraoperative TEE-associated complications was obtained retrospectively from the intraoperative TEE data form, routine postoperative visits, and cardiac surgical morbidity and mortality data. The overall incidences of TEE-associated morbidity and mortality in the study population were 0.2% and 0%, respectively. The most common TEE-associated complication was severe odynophagia, which occurred in 0.1% of the study population. Other complications included dental injury (0.03%), endotracheal tube malpositioning (0.03%), upper gastrointestinal hemorrhage (0.03%), and esophageal perforation (0.01%). TEE probe insertion was unsuccessful or contraindicated in 0.18% and 0.5% of the study population, respectively. These data suggest that intraoperative TEE is a relatively safe diagnostic monitor for the management of cardiac surgical patients. IMPLICATIONS: The overall morbidity (0.2%) and mortality (0%) rates of intraoperative transesophageal echocardiography (TEE) were determined in a retrospective case series of 7200 adult, anesthetized cardiac surgical patients. The most common source of TEE-associated morbidity was odynophagia (0.1%), which resolved with conservative management. These results suggest that TEE is a safe diagnostic tool for the management of cardiac surgical patients.

Adult↗
PubMed2001

Preclinical studies to predict the disposition of Apo2L/tumor necrosis factor-related apoptosis-inducing ligand in humans: characterization of in vivo efficacy, pharmacokinetics, and safety.

Apo2L/TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) is a member of the tumor necrosis factor gene family known to induce apoptosis in a number of cancer cell lines and may have broad-spectrum activity against human malignancies. These studies have evaluated the potency of recombinant soluble human Apo2L/TRAIL in a mouse xenograft model and the disposition and safety of Apo2L/TRAIL in rodents and nonhuman primates. Mice with established COLO205 tumors were given daily i.v. injections of Apo2L/TRAIL (30-120 mg/kg/day). Control tumors doubled in size every 2 to 3 days, while time to tumor doubling in the treatment groups was significantly longer and related to dose (14-21 days). For pharmacokinetic studies, Apo2L/TRAIL was given as an i.v. bolus to mice (10 mg/kg), rats (10 mg/kg), cynomolgus monkeys (1, 5, and 50 mg/kg), and chimpanzees (1 and 5 mg/kg). Apo2L/TRAIL was rapidly eliminated from the serum of all species studied. Half-lives were approximately 3 to 5 min in rodents and approximately 23 to 31 min in nonhuman primates. Allometric scaling provided estimates of Apo2L/TRAIL kinetics in humans, suggesting that on a milligram per kilogram basis, doses significantly lower than those used in xenograft studies could be effective in humans. Apo2L/TRAIL clearance was highly correlated with glomerular filtration rate across species, indicating that the kidneys play a critical role in the elimination of this molecule. Safety evaluations in cynomolgus monkeys and chimpanzees revealed no abnormalities associated with Apo2L/TRAIL exposure. In conclusion, these studies have characterized the disposition of Apo2L/TRAIL in rodents and primates and provide information that will be used to predict the pharmacokinetics of Apo2L/TRAIL in humans.

Algorithms↗
PubMed2000

High resolution mapping of the binding site on human IgG1 for Fc gamma RI, Fc gamma RII, Fc gamma RIII, and FcRn and design of IgG1 variants with improved binding to the Fc gamma R.

Immunoglobulin G (IgG) Fc receptors play a critical role in linking IgG antibody-mediated immune responses with cellular effector functions. A high resolution map of the binding site on human IgG1 for human Fc gamma RI, Fc gamma RIIA, Fc gamma RIIB, Fc gamma RIIIA, and FcRn receptors has been determined. A common set of IgG1 residues is involved in binding to all Fc gamma R; Fc gamma RII and Fc gamma RIII also utilize residues outside this common set. In addition to residues which, when altered, abrogated binding to one or more of the receptors, several residues were found that improved binding only to specific receptors or simultaneously improved binding to one type of receptor and reduced binding to another type. Select IgG1 variants with improved binding to Fc gamma RIIIA exhibited up to 100% enhancement in antibody-dependent cell cytotoxicity using human effector cells; these variants included changes at residues not found at the binding interface in the IgG/Fc gamma RIIIA co-crystal structure (Sondermann, P., Huber, R., Oosthuizen, V., and Jacob, U. (2000) Nature 406, 267-273). These engineered antibodies may have important implications for improving antibody therapeutic efficacy.

Antibody-Dependent Cell Cytotoxicity↗
PubMed2000

Immunotherapy approach to allergic disease.

The causal role of immunoglobulin E (IgE) in triggering the cascade of biochemical events leading to allergic disease is well established. Treatments that selectively inhibit IgE activity are a logical approach in managing the allergic response. One such strategy utilizes rhuMAb-E25, a recombinant humanized IgG(1) monoclonal anti-IgE antibody, which binds to IgE. This anti-IgE antibody binds at the same epitope site of IgE that binds to FcvarepsilonRI and is thus non-anaphylactogenic. By binding to IgE and removing it via immune complex formation, the pool of IgE available to interact with mast cells and basophils is thereby reduced and the allergic response is attenuated. The clinical safety and efficacy of rhuMAb-E25 demonstrated in phase II studies of allergic asthma will be outlined.

Allergens↗
PubMed1999

Secretion of glycosylation site mutants can be rescued by the signal/pro sequence of tissue plasminogen activator.

Strategies that prevent the attachment of N-linked carbohydrates to nascent glycoproteins often impair intracellular transport and secretion. In the present study, we describe a method to rescue the intracellular transport and secretion of glycoproteins mutagenized to delete N-linked glycosylation sites. Site-directed mutagenesis was used to delete N-linked glycosylation sites from a chimeric protein, TNFR-IgG1. Deletion of any of the three glycosylation sites in the TNFR portion of the molecule, alone or in combination, resulted in a moderate or near total blockade of TNFR-IgG1 intracellular transport and secretion. Pulse chase experiments suggested that the glycosylation site mutants accumulated in the endoplasmic reticulum (ER) and were inefficiently exported to the Golgi apparatus (GA). Replacement of the TNFR signal sequence with the signal/pro sequence of human tissue plasminogen activator (tPA) overcame the blockade to intracellular transport, and restored secretion to levels comparable to those achieved with the fully glycosylated molecule. Ligand binding studies suggested that the secreted glycosylation variants possessed binding characteristics similar to the fully glycosylated protein. This study demonstrates that N-terminal sequences of tPA are unexpectedly efficient in facilitating transport from the ER to the GA and suggests that these sequences contain a previously unrecognized structural element that promotes intracellular transport.

Amino Acid Sequence↗
PubMed1999

Nonclinical studies addressing the mechanism of action of trastuzumab (Herceptin).

HER2 is a ligand-less member of the human epidermal growth factor receptor or ErbB family of tyrosine kinases. In normal biological systems, HER2 functions as a co-receptor for a multitude of epidermal growth factor-like ligands that bind and activate other HER family members. HER2 overexpression is observed in a number of human adenocarcinomas and results in constitutive HER2 activation. Specific targeting of these tumors can be accomplished with antibodies directed against the extracellular domain of the HER2 protein. One of these antibodies, 4D5, has been fully humanized and is termed trastuzumab (Herceptin; Genentech, San Francisco, CA). Treatment of HER2-overexpressing breast cancer cell lines with trastuzumab results in induction of p27KIP1 and the Rb-related protein, p130, which in turn significantly reduces the number of cells undergoing S-phase. A number of other phenotypic changes are observed in vitro as a consequence of trastuzumab binding to HER2-overexpressing cells. These phenotypic changes include downmodulation of the HER2 receptor, inhibition of tumor cell growth, reversed cytokine resistance, restored E-cadherin expression levels, and reduced vascular endothelial growth factor production. Interaction of trastuzumab with the human immune system via its human immunoglobulin G1 Fc domain may potentiate its antitumor activities. In vitro studies demonstrate that trastuzumab is very effective in mediating antibody-dependent cell-mediated cytotoxicity against HER2-overexpressing tumor targets. Trastuzumab treatment of mouse xenograft models results in marked suppression of tumor growth. When given in combination with standard cytotoxic chemotherapeutic agents, trastuzumab treatment generally results in statistically superior antitumor efficacy compared with either agent given alone. Taken together, these studies suggest that the mechanism of action of trastuzumab includes antagonizing the constitutive growth-signaling properties of the HER2 system, enlisting immune cells to attack and kill the tumor target, and augmenting chemotherapy-induced cytotoxicity.

Animals↗
PubMed1996

Humanization of an anti-lymphocyte function-associated antigen (LFA)-1 monoclonal antibody and reengineering of the humanized antibody for binding to rhesus LFA-1.

Lymphocyte function-associated antigen 1 (LFA-1; CD11a/CD18) is involved in leukocyte adhesion during cellular interactions essential for immunologic responses and inflammation. mAbs against LFA-1 have been shown to inhibit several T cell-dependent immune functions in vitro and prevent graft failure after bone marrow transplantation in vivo. A murine anti-human CD11a mAb, MHM24, has been humanized and shown to prevent adhesion of human T cells to human keratinocytes and the proliferation of T cells in response to nonautologous leukocytes in the mixed lymphocyte response assay. However, of the nonhuman primate CD11a that we tested, the murine and humanized mAbs cross-reacted only with chimpanzee CD11a. To have a mAb available for preclinical studies in rhesus monkeys, the humanized mAb was reengineered to bind to rhesus CD11a by changing four residues in one of the complementarity-determining regions, CDR-H2, in the variable heavy domain. Cloning and molecular modeling of rhesus CD11a I-domain suggested that the changes from Lys197 and/or Arg189 in human CD11a I-domain to Glu197 and Gln189 in rhesus CD11a I-domain may be the reason that rhesus CD11a does not bind to the murine and humanized mAbs.

Amino Acid Sequence↗
PubMed1996

Detection of intravenous fluid extravasation using resistance measurements.

Resistance to fluid infusion can be derived from measurements of pressure at two or more flow rates. We measured resistance in 31 patients using a pressure-monitoring infusion pump (Model 560, IVAC) by recording pressure at five flow rates (0, 50, 100, 200, and 300 mL/hr), and computing resistance as the slope of the pressure versus flow curve. Resistance was measured subcutaneously (Rtissue) and intravenously (Rvein) immediately after unsuccessful or successful IV catheter placement. In all patients, Rtissue was always greater than Rvein. The difference ranged from 23 resistance units (RU) to 4166 RU, with a mean difference of 1147 RU (p < 0.0001, Student's t-test). Unpaired analysis of the data was performed to assess the ability of resistance to indicate extravasation in the absence of prior Rvein measurement. The median value for Rvein was 62 RU (range -13.6 to 420 RU), and for Rtissue, 544 RU (range 65.7 to 4170 RU). Receiver operating characteristic (ROC) analysis revealed that a 200-RU threshold detected infiltration with 0.90 sensitivity and 0.91 specificity. We conclude that elevated resistance during fluid infusion is an important early and easily measurable finding in fluid extravasation.

Extravasation of Diagnostic and Therapeutic Materi↗
PubMed1996

Resistance to fluid flow in veins.

We evaluated the resistance to fluid infusion in the veins of 118 adult patients after intravenous catheter insertion prior to elective surgery. Hydraulic resistance in veins was defined as the slope of the pressure-flow relationship obtained by measuring venous pressure at several fluid flow rates. A resistance unit (RU) was defined as 1 mmHg/L/hr. Resistance in veins ranged from -12.1 to 732 RU, with 50th and 95th percentiles being 22 and 198 RU, respectively. Venous resistance was not significantly affected by site of catheter insertion, tissue characteristics at the insertion site, age, sex, patient anxiety, American Society of Anesthesiologists physical status, or catheter size. This report provides a distribution of resistance to fluid infusion in arm veins of adult patients.

Adult↗
PubMed1996

Anti-CD18 antibodies improve cardiac function following cardiopulmonary bypass in dogs.

PURPOSE: Cardiopulmonary bypass is associated with activation of neutrophils, which may adhere to vascular endothelium causing lung, heart, and brain injury. We tested whether blocking neutrophil adherence would improve organ function following cardiopulmonary bypass in dogs. MATERIALS AND METHODS: All dogs received a standard anesthetic, and then one group (n = 6) received 2 hours of cardiopulmonary bypass followed by 4 hours of observation. A second group (n = 6) received a monoclonal antibody (6 mg/kg) to CD18, a neutrophil adherence factor, immediately before cardiopulmonary bypass. A third group (n = 6) did not receive cardiopulmonary bypass or antibody. RESULTS: Using flow cytometry we found that the antibody bound essentially all neutrophil CD18 sites. All three groups had similar gas exchange and hemodynamics. Lung and heart histology results were similar between groups. By echocardiography, five animals receiving cardiopulmonary bypass alone showed regional wall abnormalities, whereas only one receiving antibody showed wall motion abnormality (P < .05). Following cardiopulmonary bypass, intracellular myocardial pH was higher (P < .05) in the antibody-treated group compared with the group that had cardiopulmonary bypass alone (7.23 +/- 0.05 v 7.07 +/- 0.07 respectively). CONCLUSION: Monoclonal antibodies to CD18 can prevent the deterioration in cardiac function routinely observed following cardiopulmonary bypass.

Analysis of Variance↗
PubMed1996

Tissue distribution and complex formation with IgE of an anti-IgE antibody after intravenous administration in cynomolgus monkeys.

A humanized antihuman IgE antibody, rhuMAb-E25, was designed to form complexes with free IgE, blocking its interaction with mast cells and basophils and thereby preventing the initiation of the allergic cascade. To characterize the rhuMAb-E25: IgE complexes formed in vivo and to examine the disposition of the antibody in a relevant animal model, 125I-rhuMAb-E25 was administered as an intravenous bolus dose to cynomolgus monkeys that have high levels of IgE. The pharmacokinetic values of unlabeled and radiolabeled antibody were similar, which indicated that the disposition of 125I-rhuMAb-E25 reflected that of rhuMAb-E25. Size-exclusion chromatography of serum samples showed that the rhuMAb-E25:IgE complexes were of limited size and were similar to the small complexes formed in vitro with human IgE. Pharmacokinetic analysis revealed that both rhuMAb-E25 and rhuMAb-E25:IgE complexes cleared the serum compartment, albeit slowly. No specific uptake of radioactivity was seen in any of the tissues collected from the cynomolgus monkeys at 1 hr and 96 hr postadministration; no association was observed between 125I-rhuMAb-E25, or the complexes, and blood cells. Urinary excretion was the primary route of elimination of radioactivity; > 90% of the radioactivity found in urine was not associated with protein. The lack of specific tissue uptake and blood cell association and the slow clearance of rhuMAb-E25:IgE complexes were consistent with low-avidity interaction of small complexes with Fc gamma receptors of leukocytes and the reticuloendothelial system.

Animals↗
PubMed1996

Hepatitis B and the theatre nurse.

On 1st July 1995, an important change was made in DOH policy which affects all staff employed in the operating theatre. It was from this date that staff were required to declare their hepatitis B status. As workers who undertake exposure prone procedures (EPP workers), theatre staff are required to be immunised against this disease and to have their vaccination dates and immunity recorded by their employer's Occupational Health Department. Job applicants will not be offered a post unless they can provide proof of immunisation. This important change has been in force for medical EPP workers since July 1994. Other staff are also recommended to have been immunised against hepatitis B although failure to do so should not preclude them from employment in non-EPP areas. This means that any person working in the operating theatre will be required to prove that he or she: has been successfully immunised has attempted immunisation but failed to respond is not a carrier of the hepatitis B virus (i.e. that they are surface antigen negative) The document issued by the DOH1 states that: 'no-one involved in exposure prone procedures can refuse to be immunised or show that they are not infectious carriers of hepatitis B: refusers will not be allowed to continue EPP work' Non-responders to immunisation will be required to provide fresh blood tests every six months in order to prove their continuing non-carrier status.

Hepatitis B↗
PubMed1995

Irreversible and reversible blockade of IMR32 calcium channel currents by synthetic MVIIA and iodinated MVIIC omega-conopeptides.

The actions of two omega-conopeptides on high-voltage-activated calcium channel currents in differentiated human neuroblastoma IMR32 cells were investigated. Similar to the previously reported action of omega-conopeptide GVIA, omega-conopeptide MVIIA irreversibly blocks IMR32 HVA calcium channel currents at low concentrations. Unlike GVIA action, however, novel omega-conopeptide SNX-260 (iodinated MVIIC) reversibly blocks these currents, also at low concentrations, with an IC50 near 50 nM. Different omega-conopeptides may be potent blockers of HVA calcium channel currents yet act either reversibly or irreversibly in a single cell.

Calcium Channel Blockers↗