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Biomedical subjects

G A Gibson

Publications and source records attributed to G A Gibson.

At least 19 recordsLinked to original sources
PubMed2000

Overexpression of frequenin, a modulator of phosphatidylinositol 4-kinase, inhibits biosynthetic delivery of an apical protein in polarized madin-darby canine kidney cells.

Polyphosphoinositides regulate numerous steps in membrane transport. The levels of individual phosphatidylinositols are controlled by specific lipid kinases, whose activities and localization are in turn regulated by a variety of effectors. Here we have examined the effect of overexpression of frequenin, a modulator of phosphatidylinositol 4-kinase activity, on biosynthetic and postendocytic traffic in polarized Madin-Darby canine kidney cells. Endogenous frequenin was identified in these cells by polymerase chain reaction, Western blotting, and indirect immunofluorescence. Adenoviral-mediated overexpression of frequenin had no effect on early Golgi transport of membrane proteins, as assessed by acquisition of resistance to endoglycosidase H. However, delivery of newly synthesized influenza hemagglutinin from the trans-Golgi network to the apical cell surface was severely inhibited in cells overexpressing frequenin, whereas basolateral delivery of the polymeric immunoglobulin receptor was unaffected. Overexpression of frequenin did not affect postendocytic trafficking steps including apical and basolateral recycling and basal-to-apical transcytosis. We conclude that frequenin, and by inference, phosphatidylinositol 4-kinase, plays an important and selective role in apical delivery in polarized cells.

1-Phosphatidylinositol 4-Kinase↗
PubMed2000

Influenza M2 proton channel activity selectively inhibits trans-Golgi network release of apical membrane and secreted proteins in polarized Madin-Darby canine kidney cells.

The function of acidification in protein sorting along the biosynthetic pathway has been difficult to elucidate, in part because reagents used to alter organelle pH affect all acidified compartments and are poorly reversible. We have used a novel approach to examine the role of acidification in protein sorting in polarized Madin-Darby canine kidney (MDCK) cells. We expressed the influenza virus M2 protein, an acid-activated ion channel that equilibrates lumenal and cytosolic pH, in polarized MDCK cells and examined the consequences on the targeting and delivery of apical and basolateral proteins. M2 activity affects the pH of only a subset of acidified organelles, and its activity can be rapidly reversed using ion channel blockers (Henkel, J.R., G. Apodaca, Y. Altschuler, S. Hardy, and O.A. Weisz. 1998. Mol. Biol. Cell. 8:2477-2490; Henkel, J.R., J.L. Popovich, G.A. Gibson, S.C. Watkins, and O.A. Weisz. 1999. J. Biol. Chem. 274:9854-9860). M2 expression significantly decreased the kinetics of cell surface delivery of the apical membrane protein influenza hemagglutinin, but not of the basolaterally delivered polymeric immunoglobulin receptor. Similarly, the kinetics of apical secretion of a soluble form of gamma-glutamyltranspeptidase were reduced with no effect on the basolaterally secreted fraction. Interestingly, M2 activity had no effect on the rate of secretion of a nonglycosylated protein (human growth hormone [hGH]) that was secreted equally from both surfaces. However, M2 slowed apical secretion of a glycosylated mutant of hGH that was secreted predominantly apically. Our results suggest a role for acidic trans-Golgi network pH in signal-mediated loading of apical cargo into forming vesicles.

Animals↗
PubMed2000

Evidence against the acidification hypothesis in cystic fibrosis.

The pleiotropic effects of cystic fibrosis (CF) result from the mislocalization or inactivity of an apical membrane chloride channel, the cystic fibrosis transmembrane conductance regulator (CFTR). CFTR may also modulate intracellular chloride conductances and thus affect organelle pH. To test the role of CFTR in organelle pH regulation, we developed a model system to selectively perturb the pH of a subset of acidified compartments in polarized cells and determined the effects on various protein trafficking steps. We then tested whether these effects were observed in cells lacking wild-type CFTR and whether reintroduction of CFTR affected trafficking in these cells. Our model system involves adenovirus-mediated expression of the influenza virus M2 protein, an acid-activated ion channel. M2 expression selectively slows traffic through the trans-Golgi network (TGN) and apical endocytic compartments in polarized Madin-Darby canine kidney (MDCK) cells. Expression of M2 or treatment with other pH perturbants also slowed protein traffic in the CF cell line CFPAC, suggesting that the TGN in this cell line is normally acidified. Expression of functional CFTR had no effect on traffic and failed to rescue the effect of M2. Our results argue against a role for CFTR in the regulation of organelle pH and protein trafficking in epithelial cells.

Acids↗
PubMed2000

Economic and humanistic impact of adverse events associated with CSFs.

The current economic health care environment is causing considerable challenges for hospital pharmacy. As pharmacy managers attempt to deal with managing the costs associated with pharmaceuticals, there is considerable pressure to account for the clinical outcomes associated with drug therapy. Particularly in cancer treatment as high-cost biopharmaceuticals have infiltrated the care of these patients, pharmacy managers must account for reimbursement issues, clinical outcomes, patient satisfaction and demands, budgetary costs, and appropriate use of costly resources. Consequently, managers need to develop strategies to address these concerns. Ideally, pharmacoeconomics should be used to incorporate the costs of clinical outcomes and drug costs into the overall evaluation of drug therapy. Unfortunately, for a variety of reasons, the practical application of pharmacoeconomics is not universally employed and, as a result, most evaluations rely on only drug costs. A method to assess the economic impact of clinical outcomes associated with adverse drug events and cancer chemotherapy is described.

Antineoplastic Agents↗
PubMed2000

Comparative safety of filgrastim versus sargramostim in patients receiving myelosuppressive chemotherapy.

STUDY OBJECTIVE: To compare rates of adverse events with filgrastim versus sargramostim when given prophylactically to patients receiving myelosuppressive chemotherapy. DESIGN: Retrospective review with center crossover. SETTING: Ten United States outpatient chemotherapy centers. PATIENTS: Four hundred ninety patients treated for lung, breast, lymphatic system, or ovarian tumors. INTERVENTION: Prophylactic use of filgrastim or sargramostim, with dosages at investigator discretion. MEASUREMENTS AND MAIN RESULTS: The frequency and severity of adverse events and the frequency of switching to the alternative CSF were assessed. There was no difference in infectious fever. Fever unexplained by infection was more common with sargramostim (7% vs 1%, p<0.001), as were fatigue, diarrhea, injection site reactions, other dermatologic disorders, and edema (all p<0.05). Skeletal pain was more frequent with filgrastim (p=0.06). Patients treated with sargramostim switched to the alternative agent more often (p<0.001). CONCLUSION: Adverse events were less frequent with filgrastim than with sargramostim, suggesting that quality of life and treatment costs also may differ.

Antineoplastic Agents↗
PubMed1999

Selective perturbation of early endosome and/or trans-Golgi network pH but not lysosome pH by dose-dependent expression of influenza M2 protein.

Many sorting stations along the biosynthetic and endocytic pathways are acidified, suggesting a role for pH regulation in protein traffic. However, the function of acidification in individual compartments has been difficult to examine because global pH perturbants affect all acidified organelles in the cell and also have numerous side effects. To circumvent this problem, we have developed a method to selectively perturb the pH of a subset of acidified compartments. We infected HeLa cells with a recombinant adenovirus encoding influenza virus M2 protein (an acid-activated ion channel that dissipates proton gradients across membranes) and measured the effects on various steps in protein transport. At low multiplicity of infection (m.o.i.), delivery of influenza hemagglutinin from the trans-Golgi network to the cell surface was blocked, but there was almost no effect on the rate of recycling of internalized transferrin. At higher m.o.i., transferrin recycling was inhibited, suggesting increased accumulation of M2 in endosomes. Interestingly, even at the higher m.o.i., M2 expression had no effect on lysosome morphology or on EGF degradation, suggesting that lysosomal pH was not compromised by M2 expression. However, delivery of newly synthesized cathepsin D to lysosomes was slowed in cells expressing active M2, suggesting that acidification of the TGN and endosomes is important for efficient delivery of lysosomal hydrolases. Fluorescence labeling using a pH-sensitive dye confirmed the reversible effect of M2 on the pH of a subset of acidified compartments in the cell. The ability to dissect the role of acidification in individual steps of a complex pathway should be useful for numerous other studies on protein processing and transport.

Adenoviridae↗
PubMed1999

Economic impact of a drug information service.

OBJECTIVE: A cost-avoidance model was developed to determine potential cost savings or "avoidance" that results from a drug information service (DIS) responding to drug information requests. DESIGN: Patient-specific questions received by the DIS were reviewed and evaluated. A panel determined whether a drug misadventure event may have occurred if the DIS had not been consulted. Potential outcomes from drug information requests were classified using a decision-tree model. A severity rating was then attached to each applicable request to predict potential cost savings of the DIS. RESULTS: Seventy-seven of the 570 drug information responses received in the six-week study period had assessable potential cost savings to the institution. During the study interval, potential cost savings were estimated to be $195,000. Projected to one year, potential cost savings reached $1.7 million. Of the savings noted, most were attributable to prevention of increased monitoring or additional treatment. Using a sensitivity analysis, annual potential cost savings ranged from $417,792 to $2,052,740 per year. Based on the estimated annual costs related to maintaining a DIS of $145,950, the resultant range of benefit/cost ratio is 2.9:1 to 13.2:1. CONCLUSIONS: This model demonstrates that the DIS at our institution provides potential cost savings. This model may be modified to evaluate potential cost savings in other areas of pharmacy practice.

Cost Savings↗
PubMed1993

Management of postoperative paralysis of diaphragm in infants and children.

During an 8-month period, 86 consecutive infants and children under 2 years of age underwent palliative or corrective cardiac surgery, of whom 11 subsequently developed phrenic nerve injury (PNI). This was seen most frequently following classic or modified Blalock-Taussig shunts. The diagnosis was established by ultrasound screening of the diaphragm, and patients were initially managed expectantly with ventilatory support. In nine patients no further management was necessary with demonstrated return of diaphragmatic function. The remaining two patients underwent plication of the diaphragm. The mean time to diaphragmatic recovery was 40.8 days and was more prolonged in patients with paradoxical, as opposed to absent, diaphragmatic movement. There were no deaths in the series. A further retrospective review of 241 patients of similar age undergoing similar surgery over the preceding 2 years revealed evidence of PNI in 11 (4.6%). Recovery of diaphragmatic function was documented in all except one patient who died. Based on these results we believe that although PNI is associated with considerable morbidity, and frequently a long stay in Intensive Care, there is evidence of spontaneous recovery of diaphragmatic function in 90% of the patients. Consequently, plication of the diaphragm can usually be avoided. Ultrasound scanning is extremely useful in establishing the diagnosis and offers assistance in predicting prognosis and deciding management.

Algorithms↗
PubMed1991

Gentamicin pharmacokinetics in postpartum women with endomyometritis.

The pharmacokinetics of gentamicin in postpartum women with endomyometritis were characterized and models for predicting patient pharmacokinetic parameters were developed using multiple regression analysis. Fifty-one women 13-34 years of age received gentamicin in combination with either ampicillin or clindamycin to treat endomyometritis. Forty-three women delivered by cesarean section and 8 women had vaginal deliveries. Gentamicin serum concentrations were determined at steady-state to compute the elimination rate constant (Kc), half-life (t1/2), apparent volume of distribution (Vd), and total body clearance (Cl). Gentamicin dosages were individualized using a one-compartment intermittent infusion model to achieve steady-state peak and trough concentrations of 6.5 and less than 2 micrograms/mL, respectively. The mean gentamicin t1/2 was 2.8 +/- 0.9 h; the mean apparent Vd was 21 +/- 8 L; and the mean total body Cl was 89.5 +/- 31.7 mL/min. Multiple regression analysis revealed that total body weight (TBW) was the best predictor for the apparent Vd, described by the equation Vd = 0.146 TBW + 8.153 (r = 0.56, p = 0.00005). Total body weight and creatinine clearance (Clcr) were included as predictors for total body Cl, described by the equation Cl = 0.264 TBW + 0.337 Clcr + 3.416 (r = 0.68, p = 0.00005). Age and serum creatinine (SCr) were included in the models for the Ke, described by the equation Ke = -3.770 x 10(-3) age -0.115 SCr + 0.449 (r = 0.42, p less than 0.004). Additional patient factors need to be identified to explain the variance in these pharmacokinetic parameters.

Adolescent↗
PubMed1990

Lack of probenecid effect on nonrenal excretion of ceftriaxone in anephric patients.

Probenecid has been shown to decrease renal and biliary excretion of organic acids. In a randomized crossover study, the effect of coadministered probenecid on nonrenal excretion of ceftriaxone was studied in six functionally anephric patients in whom ceftriaxone is eliminated exclusively by nonrenal or presumably by biliary excretion. Each patient received 0.5 g IV ceftriaxone without and with probenecid (0.5 g at 10 and 2 hours prior to ceftriaxone and 0.5 g q12h X 3 doses post ceftriaxone). Serial blood samples were collected over 48 hours and plasma analyzed for ceftriaxone by high performance liquid chromatography (HPLC). Pharmacokinetic analysis was based on a model-independent approach. Probenecid did not significantly affect the disposition of ceftriaxone in this study, thus suggesting that nonrenal excretion of ceftriaxone is not inhibited by probenecid.

Adult↗
PubMed1989

Comparison of gentamicin immunoassays using univariate and multivariate analyses.

Gentamicin concentrations, pharmacokinetic parameters, and calculated doses from enzyme multiplied immunoassay (EMI) and fluorescence polarization immunoassay (FPIA) were compared in 79 samples from 39 patients. Associations between patient factors and the differences between assay results were also assessed. Concentrations were lower when measured by EMI than by FPIA in 71 of the 79 samples (p less than 0.001). Mean EMI values for elimination rate constant, volume of distribution, clearance, dose, and daily dose were 10-20% higher than mean FPIA values (p less than or equal to 0.01). Dosing intervals calculated from EMI and FPIA data were different in 20 pairs of intervals and varied depending on the length of calculated interval. Univariate and multivariate analyses revealed that renal function and the presence or absence of cardiovascular disease, cimetidine, or ranitidine, and heparin were related to differences between the assay results. EMI and FPIA yielded different results for gentamicin concentrations, pharmacokinetic parameters, and calculated daily doses in the clinical setting. Such differences could result in toxic or subtherapeutic doses being administered and may be related, in part, to various patient factors.

Adult↗
PubMed1988

Vancomycin concentrations in infected and noninfected human bone.

Concentrations of vancomycin in bones of 14 patients undergoing total hip arthroplasty (group 1) and 5 patients with osteomyelitis (group 2) were studied. Group 1 received vancomycin, 15 mg/kg intravenously, 1 h prior to anesthesia. Group 2 received doses adjusted to achieve peak levels in serum of 20 to 30 micrograms/ml and trough levels of less than 12 micrograms/ml; bone specimens were collected during surgical debridement. The specimens were pulverized and eluted into phosphate buffer, and the supernatants were analyzed for vancomycin content by fluorescence polarization immunoassay. In group 1, vancomycin was detectable in all cancellous specimens with a mean concentration of 2.3 +/- 4.0 micrograms/g (range, 0.5 to 16 micrograms/g); 10 of 14 cortical specimens had detectable vancomycin; the mean cortical concentration was 1.1 +/- 0.8 micrograms/g (range, not detectable to 2.6 micrograms/g). In group 2, vancomycin was detectable in only two of five cortical bone specimens (mean concentration, 5.9 +/- 3.5 micrograms/g). Cancellous bone was obtained in one patient; the vancomycin concentration was 3.6 micrograms/g. In most patients the vancomycin levels in bones were higher than the MIC for susceptible staphylococci following single prophylactic doses. In the few infected patients studied, penetration was variable and deserves further study.

Adult↗
PubMed1987

Relationship of steady-state serum concentrations of amiodarone and desethylamiodarone to therapeutic efficacy and adverse effects.

The relationship of steady-state serum levels of amiodarone and its major metabolite, desethylamiodarone, to therapeutic and toxic effects was evaluated in 111 patients treated for supraventricular and ventricular arrhythmias. All patients were treated for more than two months (mean 10 +/- 7), and repeated serum levels determined at least two months apart were within 0.5 mg/liter of each other. Effective control of arrhythmias during steady-state therapy was achieved in 91 patients (82 percent of the study populations); recurrent arrhythmias or sudden death did not correlate with levels. An adverse drug effect necessitating cessation of therapy and/or concomitant medical therapy for the adverse effect occurred in 12 patients (11 percent); an additional 33 patients (30 percent) had an adverse effect that did not require change in therapy. The mean serum concentrations of amiodarone and desethylamiodarone associated with adverse drug effects were higher (2.6 +/- 1.2 mg/liter and 2.0 +/- 0.8 mg/liter) than those in patients without adverse effects (2.1 +/- 1.0 mg/liter and 1.5 +/- 0.7 mg/liter), p less than 0.05. An amiodarone serum concentration of 2.5 mg/liter or more had a positive predictive value of 76 percent for identifying patients with an adverse effect. The level of desethyl metabolite of amiodarone correlated directly with the serum amiodarone concentration (r = 0.82). Measurement of desethylamiodarone did not increase the sensitivity or specificity of the amiodarone level alone in the identification of patients at risk for adverse drug effects.

Adult↗
PubMed1987

Biliary excretion of imipenem-cilastatin in hospitalized patients.

Imipenem-cilastatin concentrations in bile were measured in 12 cholecystectomy patients (group 1) and 12 patients with common duct drainage (group 2). Six patients in each group received 0.5 g, and six received 1.0 g intravenously over 30 to 60 min. In group 1, bile was collected a mean of 85 min postinfusion. The mean concentrations of imipenem in bile were 1.3 microgram/ml after the 0.5-g dose and 3.5 micrograms/ml after the 1.0-g dose. The mean concentrations of cilastatin in bile were 9.0 micrograms/ml after the 0.5-g dose and 38.0 micrograms/ml after the 1.0-g dose. In patients with common duct drainage, bile was collected predose and 0 to 2, 2 to 3, 3 to 4, and 4 to 6 h postinfusion. Peak imipenem concentrations in bile were 4.4 micrograms/ml after the 0.5-g dose and 8.6 micrograms/ml after the 1.0-g dose. Peak cilastatin concentrations in bile were 4.6 micrograms/ml for the 0.5-g dose and 10.9 micrograms/ml for the 1.0-g dose. Peak imipenem concentrations in bile occurred a mean of 2.3 h after administration of the drug; cilastatin peak concentrations occurred at a mean of 2.4 h. Less than 0.3% of each drug was recovered in the bile. Our results suggest that imipenem enters bile by simple diffusion and in most patients attains concentrations sufficient to inhibit susceptible organisms. In contrast, cilastatin had a bimodal entry into bile. Some patients had very high concentrations in bile, whereas others had very low or undetectable concentrations, suggesting that cilastatin may be actively secreted into the bile.

Adult↗