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Biomedical subjects

H Buck

Publications and source records attributed to H Buck.

14 recordsLinked to original sources
PubMed2005

Biocompatibility of an electrochemical sensor for continuous glucose monitoring in subcutaneous tissue.

BACKGROUND: The continuous monitoring of glucose allows for tighter control of the glucose concentration and thus may prevent hyper- and hypoglycemia as well as long-term complications of diabetes. While most current systems depend on the transport of fluid to a glucose sensor outside the body, we investigate the possibility of implanting a reagent-based sensor directly into the skin. In this manuscript, the biocompatibility of an electrochemical sensor for continuous glucose monitoring was assessed in vitro and in vivo. METHODS: Cytotoxicity was investigated in vitro using agar diffusion testing. In vivo biocompatibility was assessed by means of histomorphological examination of the surrounding tissue 10 days after sensor implantation in rats. RESULTS: The grade of cytotoxicity of the individual sensor components in vitro was between none and mild based on agar diffusion testing. The complete sensor also showed no cytotoxic effects when coated with the co-polymer MPC (2-methacryloyloxyethyl phosphorylcholine, Lipidure CM 5206, NOF Corp., Tokyo, Japan) and when assessed under working conditions, i.e., when a bias voltage was applied to the sensor. Additionally, the hydrogen peroxide-which is inherently generated by the enzymatic glucose detection process using glucose oxidase (GOD)-is likely to have been sufficiently decomposed under these working conditions. Finally, no toxic leachable substances were found during the cytotoxicity testing of sensors and its extracts in vitro. In the in vivo experiments, the strongest foreign body reaction (FBR) was found near the GOD-electrode using a sensor without MPC coating and without a porous membrane. Covering the sensor with MPC, a porous membrane, or both led to a gradual decrease of the FBR down to the level of the negative control. CONCLUSIONS: The electrochemical, reagent-based sensor with MPC coating and/or a porous membrane is suitable for continuous monitoring of glucose from a biocompatibility standpoint.

Animals↗
PubMed2004

Acute radiation toxicity assessment of a 3-D conformal head and neck radiation treatment technique.

Patients undergoing radiation treatment for head and neck cancer have many critical structures within or adjacent to the treatment area. Avoiding these critical structures is more efficient and easier using 3-D conformal planning. At Sir Charles Gairdner Hospital an investigation into the acute radiation toxicity was undertaken when the head and neck treatment technique was changed from the conventional 2-D plan to the conformal 3-D plan. Although the primary target volume (PTV), fraction size and overall dose remain the same for the two techniques, differing beam configurations mean that treatment fields enter and exit through different parts of the head and neck. Ten patients were initially assessed to gain a baseline appearance of their head and neck region, and then graded weekly according to the toxicity criteria during treatment and at 4, 8 and 12 weeks after treatment. The results of the assessment indicate that there is no increase in toxicity as a result of treating using the conformal head and neck technique.

Acute Disease↗
PubMed2003

Assessment of adrenal suppression from two new dry powder inhaler formulations of budesonide delivered by Clickhaler compared with the Pulmicort Turbuhaler.

Assessment of adrenal suppression via systemic cortisol levels provides an indirect measure of the lung delivery of inhaled corticosteroids. This randomized, placebo-controlled, double-blind, double-dummy crossover study compared urinary and plasma cortisol levels in healthy adult volunteers following single 1,000-microg doses of budesonide from two multiple dose dry powder inhalers (DPIs). Two new formulations of budesonide (lactose and PassCal) delivered from the Clickhaler were compared with Pulmicort from the Turbuhaler. An open dose (2,000 microg) of Pulmicort Turbuhaler was included to validate the experimental model. Overnight (22:00-07:00 h) and early morning (07:00-08:00 h) urine and 08:00 h plasma samples were collected after each treatment and cortisol levels analyzed by radioimmunoassay. Combined overnight and early morning urinary cortisol values for PassCal Clickhaler and Pulmicort Turbuhaler (1,000 microg) were statistically significantly lower than placebo (p < 0.05). The lactose budesonide Clickhaler showed a non-significant urinary cortisol reduction compared with placebo. Differences between the three 1,000-microg budesonide treatments were not significant. The Pulmicort Turbuhaler 2,000 microg showed significant urinary cortisol suppression compared with placebo. Plasma cortisol showed similar effects, with significance between the two Pulmicort doses. These results suggest that adrenal suppression can be used to assess the pulmonary bioavailability of different formulation.

Adrenal Glands↗
PubMed2001

Combinatorial discovery of alloy electrocatalysts for amperometric glucose sensors.

Combinatorial methods were used to search for active alloy electrocatalysts for use in enzyme-free amperometric glucose sensors. Electrode arrays (715-member) containing combinations of Pt, Pb, Au, Pd, and Rh were prepared and screened by converting anodic current to visible fluorescence. The most active compositions contained both Pt and Pb. Bulk quantities of catalysts with compositions corresponding to those identified in the screening experiments were prepared and characterized. The best alloy electrocatalysts catalyzed glucose oxidation at substantially more negative potentials than pure platinum in enzyme-free voltammetric measurements. They were also insensitive to potential interfering agents (ascorbic and uric acids, and 4-acetamidophenol), which are oxidized at slightly more positive potentials. Rotating disk electrode (RDE) experiments were carried out to study the catalytic mechanism. The improvement in catalytic performance was attributed to the inhibition of adsorption of oxidation products, which poison Pt electrodes.

Alloys↗
PubMed2001

The ideal inhaler for asthma therapy.

Innovations in multidose nebulisers and dry-powder inhalation devices have been stimulated by the development of new chemical entities and the availability of generic drugs. In addition, conventional pressurised inhalers are being replaced because of the phasing-out of chlorofluorocarbon gases. This article highlights the key features that constitute the ideal inhaler.

Administration, Inhalation↗
PubMed1998

College health needs to participate in the national STD debate.

We have a window of opportunity in which events are coming together, and we in ACHA can make a significant impact on STDs/STIs. College health professionals can choose to become actively involved or we can be bystanders. Our population, our tradition, and our moral imperatives all urge us to become engaged at all levels. We work with one of the most highly educated of all groups--a group that also shows some of the highest rates of risky behaviour--and we should be able to demonstrate the highest levels of successful intervention.

Health Priorities↗
PubMed1998

Triage of women with ASCUS and LSIL on Pap smear reports: management by repeat Pap smear, HPV DNA testing, or colposcopy?

BACKGROUND: The purpose of this study was to determine the efficacy of a repeat Papanicolaou (Pap) smear and the Hybrid Capture tube-based (HCT) HPV DNA test for detecting cervical intraepithelial neoplasia (CIN) grade 2 or 3 in women with recent atypical squamous cells of undetermined significance (ASCUS) or low-grade squamous intraepithelial lesion (LSIL) Pap smear reports. METHODS: Women with a recent Pap smear report of ASCUS (n = 169) or LSIL (n = 110) had a repeat Pap smear, sampling of the cervix for HCT HPV DNA assay and a colposcopy examination. Data were evaluated using three different triage thresholds for colposcopy examination: a repeat Pap smear of persistent ASCUS or more severe dysplasia, a finding of persistent LSIL or more severe dysplasia, and a carcinogenic HPV test result. RESULTS: The sensitivity, specificity, and positive and negative predictive values for detecting CIN 2/3 were 70%, 45%, 7%, and 96% for a repeat Pap smear using an ASCUS-positive threshold and 20%, 86%, 8%, and 94% for a repeat Pap smear using an LSIL-positive threshold, respectively, when women with an initial ASCUS Pap smear were considered. HPV testing for carcinogenic viruses alone or in combination with a repeat Pap smear (using ASCUS as a positive threshold) yielded results of 50%, 67%, 9%, and 96%, respectively, and 70%, 37%, 7%, and 95%, respectively, for detecting CIN 2/3. In women with an initial LSIL Pap smear, respective values for detecting CIN 2/3 by a repeat Pap smear with an ASCUS threshold were 92%, 26%, 14%, and 96%, and for an LSIL threshold 23%, 64%, 8%, and 86%, respectively. Hybrid Capture HPV testing alone or in combination with a repeat Pap smear yielded 69%, 43%, 14%, and 91%, respectively, and 100%, 21%, 14%, and 100%, respectively. CONCLUSIONS: A Pap smear triage threshold restricted to LSIL or more severe dysplasia for women with prior ASCUS or LSIL Pap smear results was clearly ineffective for detecting high-grade cervical precancerous lesions. In contrast, when the repeat Pap smear triage threshold was expanded to include persistent ASCUS as abnormal, 83% of the women with CIN 2/3 were detected. Detection of carcinogenic HPV DNA using the HCT test was almost as sensitive for detecting CIN 2/3 as a solitary repeat Pap smear using an ASCUS or more severe positive threshold. Combining the HPV test with a repeat Pap smear did not significantly improve the sensitivity of cytology for detecting high-grade CIN. This study suggests that women with ASCUS and particularly LSIL Pap smears should be referred for a colposcopy examination until better triage methods become available.

Adult↗
PubMed1996

K252a modulates the expression of nerve growth factor-dependent capsaicin sensitivity and substance P levels in cultured adult rat dorsal root ganglion neurones.

K252a, an inhibitor of trk phosphorylation and nerve growth factor signal transduction in PC12 cells, blocked nerve growth factor-induced responses in cultured adult rat dorsal root ganglion sensory neurones. The nerve growth factor-dependent appearance of capsaicin sensitivity and accumulation of the neuropeptide substance P were inhibited when dorsal root ganglion neurones were grown in the presence of low concentrations (100 nM) of K252a. At higher concentrations (3 microM), however, K252a stimulated the development of capsaicin sensitivity and the accumulation of substance P even in the absence of nerve growth factor. By using a wide dose range, therefore, we showed that K252a could either inhibit or mimic nerve growth factor's actions on sensory neurones. These results may explain the apparent paradox in the literature that some groups show a blocking effect of K252a on nerve growth factor-dependent survival of dorsal root ganglion sensory neurones, whereas other report that K252a can substitute for nerve growth factor or other trophic factors and promote neuronal survival.

Animals↗
PubMed1991

Growth factor involvement in the multihormonal regulation of MCF-7 breast cancer cell growth in soft agar.

The hormone dependency of the MCF-7 breast cancer cell line, while extensively tested in liquid culture, has not been previously evaluated under conditions of anchorage-independent growth in serum-free media. Using the soft agar clonogenic assay, we demonstrate that physiologically relevant concentrations of estradiol (E2), progesterone (Pg), and prolactin (PRL) similarly stimulated MCF-7 cell colony formation in the absence of serum. Addition of an anti-insulin-like growth factor-I (IGF-I) antibody inhibited E2- and Pg-stimulated growth, while PRL action was not affected. Similar results were obtained with an anti-IGF-I receptor antibody, except that its inhibitory effect on Pg-induced colony formation was modest and not statistically significant. Administration of either an anti-transforming growth factor-alpha (TGF-alpha) antibody or an anti-epidermal growth factor (EGF) receptor antibody similarly inhibited E2-stimulated MCF-7 cell growth in soft agar, while neither antibody influenced Pg or PRL effects. Addition of TGF-beta 1, -beta 2, -beta 3 similarly suppressed MCF-7 cell colony formation in a dose dependent manner to a degree comparable to that observed with 4-OH-tamoxifen (4-OH-T). Furthermore, the growth inhibitory effect of 4-OH-T was completely reversed by an anti-TGF-beta antibody. We conclude that IGFs and TGF-alpha are important mediators of E2-stimulated MCF-7 cell growth in soft agar. IGFs may also be playing a role in Pg action, while neither growth factor is involved in PRL-stimulated colony formation. Finally, TGF-beta appears to be an important mediator of antiestrogen-induced inhibition of tumor growth.

Agar↗
PubMed1990

Characterization of the African HIV-1 isolate CBL-4 (RUT) by partial sequence analysis and virus neutralization with peptide antibody and antisense phosphate-methylated DNA.

The HIV-1 isolate CBL-4 (RUT), originating from Tanzania, was characterized using a comprehensive virus-typing system. This system included sequence analysis of the region coding for the neutralization domain in the third variable region (V3) of the external envelope and of the tat responsive (TAR) region after polymerase chain reaction (PCR) amplification of these sequences from cellular DNA in the CBL-4 (RUT) producer line. Based on independent cluster analysis of TAR and V3 sequences the CBL-4 (RUT) virus was positioned closest to the Z6 (and ELI) African virus family. The V3 amino acid sequence on the surface of the virus particle was confirmed by the inhibition of neutralization of CBL-4 (RUT) by a synthetic peptide derived from the nucleic acid sequence. Using antisense phosphate-methylated DNA covering the TAR loop region of LAV-1/HTLV-IIIB, inhibition of HTLV-IIIB and HTLV-IIIRF infection was seen, whereas no inhibition was observed for CBL-4 (RUT), indicating two or more mismatches in the TAR loop region, a characteristic shared with Z6 virus, but not with ELI. We propose a virus-typing system based on sequence analysis confirmed by virus neutralization with a peptide binding antibody and inhibition by antisense phosphate-methylated DNA to group viruses for laboratory use and vaccine design.

Acquired Immunodeficiency Syndrome↗
PubMed1987

A new ELISA-based assay for quantitation of human T-lymphocyte subpopulations.

In order to circumvent the problems associated with the available methods, we have developed a simple, reliable ELISA for quantitation of T-cells and their subpopulations, T-helper/inducer and T-suppressor/cytotoxic cells. Standard curves with three concentrations of sheep anti-mouse IgG-coupled beads for each T-cell population were used for the determination of the T-cell content in blood. Enzyme-labelled monoclonal antibodies against T-Pan, T-S and T-H cell surface markers were readily able to bind to such beads and the test system was calibrated with T-lymphocytes by comparing cytofluorographic and enzyme immunometric results. Purified preparations of monocytes and granulocytes were negative in the test. Lymphocytes from 50 healthy blood donors gave results which correlated closely with cytofluorograph determinations.

Antigens, Surface↗