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Biomedical subjects

G Hamilton

Publications and source records attributed to G Hamilton.

At least 145 records · Page 8Linked to original sources
PubMed1996

Effects of extracellular pH on intracellular pH-regulation and growth in a human colon carcinoma cell-line.

Mechanisms of intracellular pH (pHi) regulation seem to be involved in cellular growth and cell division. Little is known about how extracellular acidosis, known to occur in central regions of solid tumors, or alkaline conditions affect pHi regulation in colonic tumors. pHi changes in the colonic adenocarcinoma cell-line SW-620 were recorded by spectrofluorimetric monitoring of the pH-sensitive, fluorescent dye BCECF, and proliferative activity was assessed by [3H]thymidine uptake. Resting pHi in Hepes-buffered solution was 7.53 +/- 0.01 (n = 36). Both 1 mM amiloride and Na(+)-free solution inhibited pHi recovery from acidification and decreased pHi in resting cells. In HCO3-/CO2-buffered media resting pH1 was 7.42 +/- 0.01 (n = 36). Recovery from acidification was Na(+)-dependent, CI(-)-independent, and only partially blocked by 1 mM amiloride. In the presence of amiloride and 200 microM H2DIDS pHi recovery was completely inhibited. In Na(+)-free solution pHi decreased from 7.44 +/- 0.04 to 7.29 +/- 0.03 (n = 6) and no alkalinization was observed in CI(-)-free medium. Addition of 5 microM tributyltin bromide (an anion/OH-exchange ionophore) caused pHi to decrease from 7.43 +/- 0.05 to 7.17 +/- 0.08 (n = 5). The effects of pH0 on steady-state pHi, pHi recovery from acidification and proliferative activity after 48 h were investigated by changing buffer [CO2] and [HCO3-]. In general, increases in pH0 between 6.7 and 7.4 increased pHi recovery, steady-state pHi and growth rates. In summary, SW-620 cells have a resting pHi > 7.4 at 25 degrees C, which is higher than other intestinal cells. Acid extrusion in physiological bicarbonate media is accomplished by a pHi-sensitive Na+/H+ exchanger and a pHi-insensitive Na(+)-HCO3-cotransporter, both of which are operational in control cells at the resting pHi. No evidence for activity of a CI-/HCO3- exchanger was found in these cells, which could account for the high pHi observed and may explain why the cells continue to grow in acidic tumor environments.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1996

Epidermal growth factor promotes rapid response to epithelial injury in rabbit duodenum in vitro.

BACKGROUND & AIMS: Growth factors are mainly involved in the regulation of intestinal epithelial barrier function. This study investigated the effect of epidermal growth factor (EGF) and insulin-like growth factor 1 (IGF-1) on epithelial restitution of rabbit duodenum in vitro. METHODS: Rabbit duodenal mucosal strips mounted in an Ussing chamber were luminally exposed to 10 mmol/L HCl for 10 minutes and then incubated with buffer alone or luminal buffer containing various concentrations of EGF and IGF-1 for 3 hours. Resistance was calculated from potential difference and short-circuit current. Damage was assessed by morphometry on H&E-stained sections. RESULTS: HCl caused resistance to decrease from 112 +/- 2 to 51 +/- 4 ohms x cm2 10 minutes after injury (n = 6; P < 0.05). Postinjury treatment with 25 or 50 ng/mL luminal EGF for 3 hours stimulated resistance to recover to 94 +/- 3 and 104 +/- 3 ohms x cm2, respectively, vs. 81 +/- 3 omega x cm2 in controls (P < 0.05). Ten minutes after injury, 62% of the mucosa was damaged; 3 hours after injury, damage was reduced to 24% +/- 1.09% and 10% +/- 1.42% in the 25 and 50 ng/mL EGF group, respectively, vs. 38% +/- 0.93% in controls (n = 6 per group). EGF stimulated enterocyte migration. IGF-1 did not impair epithelial restitution. CONCLUSIONS: EGF, but not IGF-1, promoted epithelial restitution of rabbit duodenum in vitro.

Animals↗
PubMed1996

Fatigue effects on muscle excitability.

Repeated isometric or shortening contractions of skeletal muscle cause muscle fatigue but several prior studies have reported an apparent absence of muscle fatigue when humans performed up to 70 lengthening contractions. We pursued the hypothesis that perhaps muscle excitability is a factor that aids force preservation with repeated eccentric actions. Soleus compound muscle action potential (M-wave) latency, peak-to-peak amplitude (PPA), duration, and area under the curve were examined in 12 subjects (mean age 24.3 y) over 4 testing days that included: no exercise, isometric exercise (neutral ankle angle), isokinetic (0.5 rad.s-1) concentric and eccentric exercise of the plantar flexors in the seated position on a Biodex dynamometer. Supramaximal shocks were delivered to the tibial nerve in the popliteal fossa at baseline (3 shocks, 1 min apart), during exercise (1 shock-after each of 5 bouts/10 contractions), and during 10-min recovery. From initial to final contractions, concentric, isometric, and eccentric fatigue was -32, -41 and + 2% (Condition by Trial Interaction, F2,22 = 25.1, p = 0.000). No changes occurred in latency or duration (p > 0.05), but PPA (Condition by Time interaction, F51,561 = 3.7, p = 0.000) increased during isometric and eccentric exercise and remained elevated during recovery. Area increased (F51,561 = 3.1, p = 0.000) significantly during all three exercise conditions and approximated baseline by minute 8 of recovery. It was concluded that although the potentiation of the action potential of individual muscle fibers seems to be the common mechanism underlying the increase in muscle excitability during plantar flexion exercise, it is possible that different factors could cause such a non-specific response.

Action Potentials↗
PubMed1996

Laminin stimulates rapid epithelial restitution of rabbit duodenal mucosa in vitro.

BACKGROUND: This study investigated the effect of the basal lamina constituents fibronectin, collagen IV, and laminin on epithelial restitution of rabbit duodenum in vitro. METHODS: Rabbit duodenal mucosal sheets were mounted in Ussing chambers, luminally exposed to 10 mM HCI for 10 min, and incubated with buffer or luminal buffer containing 25-100 micrograms/ml of collagen IV, fibronectin, laminin, or polyclonal antisera directed against these proteins (diluted 1:50-1:20) for 3 h. Resistance was calculated from potential difference and short-circuit current. Mucosal damage was assessed by morphometry on hematoxylin- and eosin-stained sections. RESULTS: Acid exposure caused a 40% drop in resistance (119 +/- 5 versus 71 +/- 5 Ohm.cm2 before versus after injury; P < 0.05, n = 6) and mucosal damage of 58 +/- 4% (n = 6). Three hours after injury resistance was 102 +/- 6, 117 +/- 4, and 48 +/- 5 Ohm.cm2 in the control, laminin, and anti-laminin groups, respectively. Furthermore, 36 +/- 2%, 16 +/- 2%, and 64 +/- 5% of the mucosa was damaged in the control, laminin, and anti-laminin groups, respectively, 3 h after injury (P < 0.05 versus controls). Laminin promoted epithelial wound closure by stimulation of enterocyte migration, which was inhibited by anti-laminin. Fibronectin, collagen IV, anti-fibronectin, and anti-collagen IV did not impair restitution. CONCLUSION: Our results show that laminin promotes electrophysiologic restoration and epithelial restitution of rabbit duodenum in vitro. We therefore suggest that laminin plays an important part in the orchestration of epithelial integrity and barrier function.

Animals↗
PubMed1996

A decision support system for prevention and treatment of pressure ulcers based on AHCPR guidelines.

We have developed a Pressure Ulcer Prevention and Management System to assist clinicians with patient-specific decision making. The system captures coded data about assessment, diagnosis and interventions using a point-and-click interface. Guideline-based knowledge is imbedded into the system, and is accessible in several ways: 1) via hypertext links from the data entry screens; 2) via explicit entry into an indexed version of the guideline; 3) via imbedded knowledge-based rules that critique the diagnosis and offer guidance for treatment; and 4) via explicit entry into interactive algorithms. The system has been implemented experimentally on one care unit at our hospital, where its impact will be assessed in comparison with a control unit. Preliminary usage data are provided. Issues with rendering guideline material useful for patient-specific decision support are discussed. In our setting, these issues had to do with a) incongruity with local standards; b) insufficient specificity; and 3) insufficient comprehensiveness. Issues of use and dissemination in the context of today's health care environment are also addressed.

Aged↗
PubMed1995

Drug-protein conjugates: haptenation of 1-methyl-10 alpha-methoxydihydrolysergol and 5-bromonicotinic acid to albumin for the production of epitope-specific monoclonal antibodies against nicergoline.

Two types of monoclonal antibodies were used for the determination of nicergoline in biological matrices. The antibodies were prepared with the hydrolysis products 5-bromonicotinic acid and 1-methyl-10 alpha-methoxydihydrolysergol after hemisuccinoylation to haptens. The current amide bond-generating methods (mixed anhydride-, carbodiimide-, carbodiimide/sulfo-N-hydroxysuccinimide-, and dicyclohexylcarbodiimide/N-hydroxysuccinimide methods) were used in bovine serum albumin (BSA)-coupling techniques and yielded conjugates that were haptenated to varying extents. The conjugates exhibiting 23 mol of 1-methyl-10 alpha-methoxydihydrolysergol (MMD) or 41 mol of 5-bromonicotinic acid (BNA) per mole of BSA were used for both immunization of mice and for coating the wells of the microtiter plates to select hybridomas and investigate specificity of the obtained antibodies. The results of hapten-inhibition ELISA using antigen-coated wells indicate that the supernatant of MMD-specific hybridoma exhibited 50% inhibition of antibody binding at 17 +/- 2 micrograms of MMD and at 24.5 +/- 2 micrograms of nicergoline, and the BNA-specific hybridoma exhibited similar inhibition at 147 +/- 6 micrograms of BNA and 500 +/- 30 micrograms of nicergoline. A main requirement for analytical purposes is that two different types of monoclonal antibodies recognize two different epitopes on nicergoline and its main metabolite, as shown by hapten-inhibition ELISA.

Alkaloids↗
PubMed1995

Biomechanical properties of normal tendons, normal palmar aponeuroses, and tissues from patients with Dupuytren's disease subjected to elastase and chondroitinase treatment.

Normal tendons, normal palmar aponeuroses and palmar aponeuroses from patients with Dupuytren's disease were subjected to elastase or chondroitinase treatment. Young's modulus was derived from the linear portion of stress-strain graph. It showed the lowest value for the apparently normal palmar aponeuroses and the highest value for tendon samples. Elastase treatment caused an increase of extensibility and a reduction of Young's modulus of normal palmar aponeuroses and tendons, but not of contracture bands. In normal tendons, normal palmar aponeuroses and apparently normal palmar aponeuroses residual strain and hysteresis loop increased significantly as a linear function of the amount of digested elastin. In contrast these biomechanical parameters were not affected significantly in contracture bands. In normal and apparently normal areas incubation with chondroitinase ABC resulted in a significant increase of residual strain and, as opposed to elastase, a decrease of normalized hysteresis loop. In contracture bands, however, these biomechanical parameters remained unchanged. RELEVANCE: The increasing evidence of a correlation between morphological changes of palmar elastin and ground substance with the progress of Dupuytren's disease emphasizes the need to determine the relative importance of these connective tissue components for the pathogenesis of Dupuytren's disease.

Journal Article↗
PubMed1995

Clostridium difficile toxin B is more potent than toxin A in damaging human colonic epithelium in vitro.

Toxin A but not toxin B, appears to mediate intestinal damage in animal models of Clostridium difficile enteritis. The purpose of this study was to investigate the electrophysiologic and morphologic effects of purified C. difficile toxins A and B on human colonic mucosa in Ussing chambers. Luminal exposure of tissues to 16-65 nM of toxin A and 0.2-29 nM of toxin B for 5 h caused dose-dependent epithelial damage. Potential difference, short-circuit current and resistance decreased by 76, 58, and 46%, respectively, with 32 nM of toxin A and by 76, 55, and 47%, respectively, with 3 nM of toxin B, when compared with baseline (P < 0.05). 3 nM of toxin A did not cause electrophysiologic changes. Permeability to [3H]mannitol increased 16-fold after exposure to 32 nM of toxin A and to 3 nM of toxin B when compared with controls (P < 0.05). Light and scanning electron microscopy after exposure to either toxin revealed patchy damage and exfoliation of superficial epithelial cells, while crypt epithelium remained intact. Fluorescent microscopy of phalloidin-stained sections showed that both toxins caused disruption and condensation of cellular F-actin. Our results demonstrate that the human colon is approximately 10 times more sensitive to the damaging effects of toxin B than toxin A, suggesting that toxin B may be more important than toxin A in the pathogenesis of C. difficile colitis in man.

Actins↗
PubMed1995

Biomechanical properties of normal tendons, normal palmar aponeuroses and palmar aponeuroses from patients with Dupuytren's disease subjected to elastase and chondroitinase treatment.

Normal tendons, normal palmar aponeuroses and specimens from patients with Dupuytren's disease, namely apparently normal palmar aponeuroses and contracture bands were subjected to elastase and chondroitinase ABC digestion. Maximum Young's modulus, normalized hysteresis loop and residual elongation were determined before and after enzyme treatment. In normal tendons, normal and apparently normal palmar aponeuroses both normalized hysteresis loop and residual elongation increased significantly after elastase treatment, whereas the stiffness decreased. Normalized hysteresis loop and residual elongation display changes corresponding to the amount of digested elastin. The increased viscosity of untreated contracture bands containing less elastin, as compared to normal palmar aponeurosis, was not affected by elastase. Obviously, the elastic fibers in normal shape and distribution are responsible for maintaining an elastic status with a low viscous stress component. With the exception of contracture bands chondroitinase ABC caused a minor increase of residual elongation and as opposed to elastase a decrease of normalized hysteresis loop indicating an increased mobility of the tissue fibers.

Animals↗
PubMed1994

Low-dose intra-arterial thrombolysis in the treatment of phlegmasia caerulea dolens.

Three patients with phlegmasia caerulea dolens treated successfully by low-dose intra-arterial thrombolysis are presented. In all patients a rapid improvement was observed and amputation avoided. The risk of pulmonary embolus was reduced by the use of a retrievable vena cava filter in one patient and thrombolytic therapy in the presence of a previously inserted cava filter in the other two.

Adult↗
PubMed1994

Dental infection in vascular surgical patients.

Seventy patients, 18 women and 52 men of mean age 68 (range 52-81) years, with vascular disease were studied using the Community Periodontal Index of Treatment Needs (CPITN). Twenty-six were edentulous and 44 dentate; 32 dentate patients were wearing partial dentures. All had occlusive peripheral arterial disease (ankle:brachial pressure index less than 0.9) or aortic aneurysm. No significant periodontal pathology was found in edentulous patients. Of the dentate patients, 28 were in the significant pathology range (CPITN 4) and 12 were in the moderate pathology group (CPITN 3); only four had no significant pathology (CPITN 0-2). As a proportion of prosthetic vascular graft infections may be due to dental sepsis, surgeons should consider referral for dental assessment before elective bypass grafting and patients should be warned about the importance of dental care after operation.

Aged↗
PubMed1994

Endothelial seeding of compliant polyurethane vascular graft material.

Compliance was measured in a new compliant polyurethane vascular graft material and in polytetrafluoroethylene (PTFE) graft material using an ultrasonic device; attachment of indium-111 oxine-labelled human endothelial cells to both surfaces with a range of surface coatings was assessed. Compliant polyurethane was six to eight times more compliant than PTFE (P < 0.01) at all pressures in the range 50-120 mmHg, and endothelial cell attachment to uncoated polyurethane was three times better than to uncoated PTFE at times up to 90 min (P < 0.01). Attachment to polyurethane was also better after blood clot, collagen and fibronectin treatment at times up to 30 min (P < 0.05). Endothelial seeding of compliant graft material may provide a prosthetic vascular substitute with characteristics similar to those of autologous vein.

Aged↗
PubMed1994

Intracellular pH regulation of human colonic crypt cells.

In order to investigate the regulation of intracellular pH (pHi) in freshly isolated human colonocytes, we have used a newly developed technique for the rapid isolation and covalent attachment of these cells to glass surfaces and microspectrofluorimetric measurement of the pH-sensitive fluorescence of 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF)-loaded specimens in a perfusion chamber (37 degrees C). In N-2-hydroxyethylpiperazine-N'-2-ethanesulphonic-acid-(HEPES)-buffered Ringer solution (HBS) a baseline pHi of 7.35 +/- 0.03 (mean +/- SD; n = 42) was found for human colonocytes and in HBS, NH4Cl-prepulse-induced intracellular acidification in colonocytes is reversed rapidly by the ubiquitous amiloride-sensitive (1 mmol/l) Na+/H+ exchanger. Switching from HBS to HCO(3-)-buffered solution (BBS) led to a transient intracellular acification (7.29 +/- 0.09), followed by a recovery to a final resting pHi of 7.43 +/- 0.03. One-third of the acid extrusion in BBS is amiloridesensitive; the remaining two-thirds are caused by the dihydroderivative of 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (H2DIDS)-sensitive HCO(3-)-dependent mechanisms. The functional activity of an acid-extruding Na+/HCO3- cotransporter in human colonocytes was observed in response to the reintroduction of Na+ into amiloride-containing Na+/Cl(-)-free BBS. In addition, the mechanism leading to alkalinization (7.56 +/- 0.05) in Cl(-)-free BBS was identified as Na(+)-dependent Cl-/HCO3- exchange, by its H2DIDS sensitivity and the specific requirement for Cl- and Na+. The intrinsic buffering capacity (beta i) of the human colonocytes was calculated from pH changes induced by sequential NH4Cl-loading steps during blockage of acid/base transporters.(ABSTRACT TRUNCATED AT 250 WORDS)

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1994

Inhibition of P-glycoprotein-mediated vinblastine transport across HCT-8 intestinal carcinoma monolayers by verapamil, cyclosporine A and SDZ PSC 833 in dependence on extracellular pH.

The ability of the multidrug resistance modifiers R- and R,S-verapamil (VPL), cyclosporine A (CsA) and its non-immunosuppressive derivative SDZ PSC 833 (PSC 833) to inhibit P-glycoprotein (P-gp)-mediated transepithelial flux of tritiated vinblastine was investigated using tight and highly resistant (R > 1,400 omega cm2) monolayer cultures of intestinal adenocarcinoma-derived HCT-8 cells grown on permeable tissue-culture inserts. Apical addition of these chemosensitizers inhibited drug flux (137 pmol h-1 cm-2; range, 133-142 pmol h-1 cm-2) in the basal to apical secretory direction at clinically relevant concentrations, with PSC 833 showing the highest activity, exhibiting inhibition at concentrations as low as 10 ng/ml (9 nM). Acidification of the modulator-containing apical compartment to an extracellular pH (pHo) of 6.8 had no influence on MDR reversal by CsA at 1 microgram/ml (0.9 microM; flux inhibition, 52%) or by PSC 833 at 100 ng/ml (0.09 microM; flux inhibition, 60%), in contrast to R,S- and R-VPL, which showed decreased inhibition and caused less accumulation of vinblastine in HCT-8 cells under this condition (flux inhibition of 35% and 23%, respectively, at pHo 6.8 vs 50% and 43%, respectively, at pHo 7.5). P-gp-mediated rhodamine 123 efflux from dye-loaded single-cell suspensions of HCT-8 cells as measured by flow cytometry was not impeded at pHo 6.8 in comparison with pHo 7.5 in standard medium, but at low pHo the inhibitory activity of R-VPL (29% vs 60% rhodamine 123 efflux inhibition) was diminished significantly, again without a reduction in the effect of PSC 833 (rhodamine 123 flux inhibition, 75%). In conclusion, drug extrusion across polarised monolayers, which offer a relevant model for normal epithelia and tumour border areas, is inhibited by the apical presence of R,S- and R-VPL, CsA and PSC 833 at similar concentrations described for single-cell suspensions, resulting in increased (2.2- to 3.7-fold) intracellular drug accumulation. Functional apical P-gp expression, the absence of paracellular leakage and modulator-sensitive rhodamine 123 efflux in single HCT-8 cells indicate a P-gp-mediated transcellular efflux in HCT-8 monolayers. In addition to its high MDR-reversing capacity, the inhibitory activity of PSC 833 is not affected by acidic extracellular conditions, which reduce the VPL-induced drug retention significantly. As far as MDR contributes to the overall cellular drug resistance of solid tumours with hypoxic and acidic microenvironments, PSC 833 holds the greatest promise for clinical reversal of unresponsiveness to the respective group of chemotherapeutics.

ATP Binding Cassette Transporter, Subfamily B, Mem↗