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Biomedical subjects

J Preston

Publications and source records attributed to J Preston.

At least 19 recordsLinked to original sources
PubMed1999

A retrospective analysis of Hickman line-associated complications in patients with solid tumours undergoing infusional chemotherapy.

We present a retrospective analysis of Hickman line use and associated complications in patients with solid tumours undergoing treatment with infusional chemotherapy. One hundred and ten lines were inserted in 94 patients (55 females and 39 males, median age 51), of whom 107 were placed under radiological screening, the remainder by a surgical approach. Catheters were in situ for a total of 9670 days (median 101 days, range 1-278). Fifty-five complications occurred during the lifespan of 39 catheters (35.5%), giving an overall complication rate of 4.03/1000 catheter days. Early complications included pneumothorax (4%), arterial puncture (1%) and failure of placement (1%). Late complications included sepsis (superficial and systemic) (24.5%), venous thrombosis (9%), line displacement (10%) and catheter blockage (1%). Fifteen episodes of systemic sepsis occurred in 12 patients, giving an overall sepsis rate of 1.55/1000 catheter days, while complications requiring catheter removal occurred in 20 cases (18% of insertions, 2.07/1000 catheter days). We conclude that the use of Hickman catheters as a means of long-term venous access in infusional chemotherapy patients is generally safe, but is associated with significant morbidity.

Aged↗
PubMed1998

Genotoxicity of radiofrequency radiation. DNA/Genetox Expert Panel.

During the past several years, concerns have been raised regarding the potential adverse effects of exposures to nonionizing radiation, particularly in the extremely low frequency (ELF) range (50 to 60 MHz) and radiofrequency radiation (RFR) with frequencies ranging from 30 KHz to 30,000 MHz. One focus of concern has been potential DNA interactions. Publications reviewing the genotoxicity of ELF radiation [McCann et al. (1993): Mutat Res 297(1):61-95; Murphy et al. (1993): Mutat Res 296:221-240; NAS (1997)], have been uniform in concluding that the weight of evidence does not indicate any genotoxic risk from exposure to this type of radiation. Concern that RFR may be associated with adverse biological effects [WHO, 1993], including recent allegations that they may be involved in the production of brain tumors in humans [Elmer-Dewit (1993): Time, February 8:42], has resulted in the production of a large number of publications describing the effects of RFR on the integrity of nucleic acids. Data from studies conducted in a frequency range from 800 to 3,000 MHz were reviewed and subjected to a weight-of-evidence evaluation. The evaluation focused on direct toxicological effects of RFR as well as on studies addressing basic biological responses to RFR at the cellular and molecular level. The data from over 100 studies suggest that RFR is not directly mutagenic and that adverse effects from exposure of organisms to high frequencies and high power intensities of RFR are predominantly the result of hyperthermia; however, there may be some subtle indirect effects on the replication and/or transcription of genes under relatively restricted exposure conditions.

Animals↗
PubMed1996

IPCS harmonization of methods for the prediction and quantification of human carcinogenic/mutagenic hazard, and for indicating the probable mechanism of action of carcinogens.

A flow chart is presented as a recommended sequence of tests to predict the carcinogenic hazard, and to predict and quantify the mutagenic hazard to germ cells of chemicals to humans. Ten associated principles of testing for these endpoints are also suggested. These recommendations are the result of a meeting convened under the auspices of the International Programme on Chemical Safety (IPCS), as part of their project on 'Harmonization of Approaches to the Assessment of Risk from Exposure to Chemicals'. The meeting was held at Carshalton, Surrey, from 13-17 February 1995.

Animals↗
PubMed1996

Performance of CAD/CAM crown restorations.

This research paper documents the current performance of an advanced CAD/CAM system. Patients with CAD/CAM Empress glass-ceramic or Aristeé composite machined complete crowns were retrospectively evaluated using U. S. Public Health Service criteria at least two years after placement. The composite restorations had unacceptable wear and surface loss. Development continues.

Adolescent↗
PubMed1995

Kinetic characteristics of ZENECA ZD5522, a potent inhibitor of human and bovine lens aldose reductase.

Aldose reductase (aldehyde reductase 2) catalyses the conversion of glucose to sorbitol, and methylglyoxal to acetol. Treatment with aldose reductase inhibitors (ARIs) is a potential approach to decrease the development of diabetic complications. The sulphonylnitromethanes are a recently discovered class of aldose reductase inhibitors, first exemplified by ICI215918. We now describe enzyme kinetic characterization of a second sulphonylnitromethane, 3',5'-dimethyl-4'-nitromethylsulphonyl-2-(2-tolyl)acetanilide (ZD5522), which is at least 10-fold more potent against bovine lens aldose reductase in vitro and which also has a greater efficacy for reduction of rat nerve sorbitol levels in vivo (ED95 = 2.8 mg kg-1 for ZD5522 and 20 mg kg-1 for ICI 215918). ZD5522 follows pure noncompetitive kinetics against bovine lens aldose reductase when either glucose or methylglyoxal is varied (K(is) = K(ii) = 7.2 and 4.3 nM, respectively). This contrasts with ICI 215918 which is an uncompetitive inhibitor (K(ii) = 100 nM) of bovine lens aldose reductase when glucose is varied. Against human recombinant aldose reductase, ZD5522 displays mixed noncompetitive kinetics with respect to both substrates (K(is) = 41 nM, K(ii) = 8 nM with glucose and K(is) = 52 nM, K(ii) = 3.8 nM with methylglyoxal). This is the first report of the effects of a sulphonylnitromethane on either human aldose reductase or utilization of methylglyoxal. These results are discussed with reference to a Di Iso Ordered Bi Bi mechanism for aldose reductase, where the inhibitors compete with binding of both the aldehyde substrate and alcohol product. This model may explain why aldose reductase inhibitors follow noncompetitive or uncompetitive kinetics with respect to aldehyde substrates, and X-ray crystallography paradoxically locates an ARI within the substrate binding site. Aldehyde reductase (aldehyde reductase 1) is closely related to aldose reductase. Inhibition of bovine kidney aldehyde reductase by ZD5522 follows uncompetitive kinetics with respect to glucuronate (K(ii) = 39 nM), indicating a selectivity greater than 5-fold for bovine aldose reductase relative to aldehyde reductase.

Acetanilides↗
PubMed1995

Texas Telemedicine Project: a viability study.

OBJECTIVE: The purpose of this research was to investigate viability factors in the implementation of telemedicine systems. The Texas Telemedicine Project examined the viability of a rural network where multiple facilities shared a switchable long-distance network rather than using fixed point-to-point connections. METHODS: During Phase I, conducted in 1989, staff at participating institutions analyzed applications for the proposed network and developed methodologies for data collection. The capital costs and potential savings of a telemedicine network linking institutions in Austin and Giddings, Texas, were estimated. In April of 1991, Phase II of the system was implemented, and the first year's actual capital expenditures and savings (e.g., trips avoided, salaries of traveling specialists saved, reduced mileage and patient transport expenses, redundant tests avoided, reduced long distance telephone charges) attributed to the network were calculated. RESULTS: On the basis of the data collected in Phase I, it was projected that each $1.00 applied toward installation and operation of the network should yield $1.50 in benefits, with return on investment (break-even) within 1 year. In practice, there was a net deficit during the first year, although linear extrapolation predicted return on investment in 2.7 years. CONCLUSION: Linking multiple users over a shared infrastructure has the benefit of distributing cost among the participants and achieving an economy of scale for telecommunications services. The chief barriers to greater savings were the failure of five of the six network sites to design mission-oriented telemedicine policies and the absence of Medicare reimbursement.

Cost-Benefit Analysis↗
PubMed1995

Calmodulin inhibitors and calcium channel blockers influence dideoxycytidine renal excretion.

Renal handling of 2',3'-dideoxycytidine (ddC), a new anti-HIV dideoxynucleoside which undergoes renal and non-renal clearance, was determined in CF-1 male mice. Since calmodulin inhibitors (CIs) and calcium channel blockers (CCBs) have been shown to influence the flux of pyrimidine nucleosides across mammalian membranes and since the plasma concentration (and hence the efficacy) of therapeutic nucleosides is usually affected by the rate of renal elimination, we decided to determine the impact of the CIs loperamide (LOP) and trifluoperazine (TFP) as well as the CCB verapamil (VER) on the renal excretion of ddC. The ratio of ddC clearance to inulin clearance suggests that ddC undergoes secretion into renal tubules. Pre-exposure of mice to the calmodulin inhibitors loperamide (LOP) and trifluoperazine (TFP) resulted in a decrease in ddC renal secretion while pre-treatment with the calcium channel blocker verapamil increased ddC secretion.

Animals↗
PubMed1994

Characterization of and the influence of calcium channel blockers on the renal excretion of pyrimidine anticancer agents.

The renal handling of two anticancer (a-Ca) pyrimidines 5-fluorodeoxyuridine (FUdR) and 5-fluorouracil (5-FU) was investigated in clearance experiments in CF-1 mice using specific inhibitors of classical renal transport systems. The 5-FU was derived from the metabolism of FUdR. Based on the FUdR:inulin clearance ratio and 5-FU:inulin clearance ratio, it was determined that FUdR was secreted into renal tubules while 5-FU underwent reabsorption. The secretion of FUdR was inhibited by cimetidine and dipyridamole but not by probenecid or phloridzin. While the clearance ratio of 5-FU:inulin was significantly reduced by phloridzin, it (i.e., the ratio) was not affected by cimetidine, dipyridamole, or probenecid. The impact of two calcium channel blockers, diltiazem (DZM) and verapamil (VER), on the renal handling of FUdR and 5-FU was also examined. VER increased the secretion of FUdR without affecting the reabsorption of 5-FU while DZM slightly decreased the secretion of FUdR and prevented the reabsorption of 5-FU. These data suggest that the organic cation carrier and a dipyridamole-sensitive nucleoside transporter are involved in the renal excretion of FUdR; that the renal transport of both FUdR and 5-FU is associated with the calcium channel; and that 5-FU utilizes, at least in part, the glucose transporter for its reabsorption.

Absorption↗
PubMed1993

Hydrocephalus decreases chloride efflux from the choroid plexus epithelium.

To explore the novel concept of intrinsic brain regulation of the choroid plexus (CP), we studied the function of the CP exposed to increased intracranial pressure (ICP). The function of the CP was evaluated by in vitro chloride (Cl-) efflux from isolated CP 21 days after kaolin induced hydrocephalus. The Cl- efflux was significantly decreased in animals with elevated intracranial pressure (rate constant, K = 0.024 +/- 0.001 s-1) and enlarged ventricles (K = 0.023 +/- 0.001 s-1) compared to sham animals (K = 0.031 +/- 0.001 s-1). In contrast, the Cl- efflux of CP from animals with normal ICP and ventricular size did not differ from sham animals. These results illustrate the first demonstration of regulation of the CP epithelial function with elevated ICP; they also suggest a brain-CP regulatory mechanism that alters CP function.

Animals↗
PubMed1993

Inhibition of aldose reductase by (2,6-dimethylphenylsulphonyl)nitromethane: possible implications for the nature of an inhibitor binding site and a cause of biphasic kinetics.

Aldose reductase (aldehyde reductase 2, ALR2) is often isolated as a mixture of two forms which are sensitive (ALR2S), or insensitive (ALR2I), to inhibitors. We show that ICI 215918 ((2-6-dimethylphenylsulphonyl)-nitromethane) follows either noncompetitive, or uncompetitive kinetics with respect to aldehyde for ALR2S, or the closely related enzyme, aldehyde reductase (aldehyde reductase 1, ALR1). Similar behaviour is exhibited by two other structural types of aldose reductase inhibitor (ARI), spirohydantoins and acetic acids, when either aldehyde, or NADPH is varied. For ALR2S, we have demonstrated kinetic competition between a sulphonylnitromethane, an acetic acid and a spirohydantoin. Thus, different ARIs probably have overlapping binding sites. Published studies imply that ALR2 follows an ordered mechanism where coenzyme binds first and induces a reversible conformation change (E.NADPH-->E*.NADPH). Reduction of aldehyde appears rate-limited by the step E*.NADP+-->E.NADP+. Spontaneous activation converts ALR2S into ALR2I and increases kcat. This must be associated with acceleration of the rate-determining step. We now propose the following hypothesis to explain characteristics of ARIs. (1) Inhibitors preferentially bind to the E* conformation. (2) The ARI binding site contains residues in common with that for aldehyde substrates. When aldehyde is varied, uncompetitive inhibition arises from association at the site for alcohol product in the E*.NADP+ complex which has little affinity for the substrate. Any competitive inhibition arises from use of the aldehyde site in the E*.NADPH complex. (3) Acceleration of the E*.NADP+-->E.NADP+ step upon activation of ALR2 reduces steady state levels of E* and so decreases sensitivity to ARIs.

Acetates↗
PubMed1993

Reconstruction of the hard and soft tissues for optimal placement of osseointegrated implants.

Success, as it is usually defined for osseointegrated implants, may leave much to be desired in terms of esthetics, phonetics, and function. Optimal occlusal function demands that the implant-supported restoration be placed in a position that will permit the desired cusp-fossae relations with axial loading. In the partially edentulous patient, the implant-supported restoration also should blend into the arch form of the adjacent and opposing teeth. From a phonetic viewpoint, the natural contour and position of the anterior teeth must be maintained. To achieve these goals, it may be necessary to restore the hard and soft tissue anatomy vertically and horizontally and to augment or reconstruct the sinus. Depending on the circumstances, these measures may be carried out before, during, or after implant placement. In this paper, the considerations involved in diagnosis and selection of reconstructive technique are outlined.

Alveolar Bone Loss↗
PubMed1992

Using telemedicine to improve health care in distant areas.

Many users consider telemedicine a partial solution to problems of delivering health care to remote areas or areas underserved by clinicians. Current telemedical technology benefits from recent developments such as the decreased cost and improved quality of the coder-decoder (codec) equipment used in interactive digital video systems and the expansion of fiber-optic cable networks. The authors outline some pioneering telemedicine programs of the 1960s and 1970s and describe two recently activated systems in Texas. One network, serving the western two-fifths of the state, links faculty members from four campuses of Texas Tech University Health Sciences Center with almost 40 rural communities. The other connects the state hospital and three other facilities in Austin with four health care sites in the town of Giddings, 65 miles away. Besides serving patients, the systems provide continuing medical education and support to reduce the isolation of rural health care professionals. Primary goals include evaluation and certification of telemedical training and analysis of the cost feasibility of telemedical services.

Delivery of Health Care↗