Biomedical subjects

Steven A Barker

Publications and source records attributed to Steven A Barker.

5 recordsLinked to original sources

PubMed2006

Matrix solid phase dispersion (MSPD).

A review of the many uses of matrix solid phase dispersion (MSPD) in the extraction and analysis of a variety of compounds from a range of samples is provided. Matrix solid phase dispersion (MSPD) has found particular application as a somewhat generic analytical process for the preparation, extraction and fractionation of solid, semi-solid and/or highly viscous biological samples. Its simplicity and flexibility contribute to it being chosen over more classical methods for these purposes. MSPD is based on several simple principles of chemistry and physics, involving forces applied to the sample by mechanical blending to produce complete sample disruption and the interactions of the sample matrix with a solid support bonded-phase (SPE) or the surface chemistry of other solid support materials. These principles are discussed as are the factors to be considered in conducting a MSPD extraction.

Solid Phase Extraction↗

PubMed2004

Bupropion (Zyban, Wellbutrin) inhibits nicotine-induced viral reactivation in herpes simplex virus type 1 latent rabbits.

We reported that nicotine applied via a transdermal patch (21 mg/day) induced viral reactivation and ocular shedding in herpes simplex virus type 1 (HSV-1) latent rabbits. One possible mechanism of action involves the release of catecholamines and other similar agents, triggering HSV reactivation. Bupropion (Zyban, Wellbutrin), a non-nicotine aid to smoking cessation, inhibits neuronal uptake of norepinephrine, serotonin, and dopamine. To determine whether bupropion inhibits HSV reactivation, rabbits latent with HSV-1 were grouped (at least 10 rabbits/group) and treated as follows: nicotine patch (transdermal delivery) and bupropion [Zyban sustained-release tablets (150 mg) twice a day (oral)], nicotine patch only, Zyban tablets only [twice a day (oral)], nicotine patch with oral placebo [twice a day (oral)], or no drug treatment. Eyes were swabbed for 22 consecutive days. The appearance of HSV-1 in the tear film was significantly less frequent in the bupropion-treated rabbits, in terms of positive rabbits/total rabbits, positive eyes/total eyes, and positive swabs/total swabs. Nicotine-treated rabbits had 78/440 (17.7%) positive/total swabs, and nicotine/placebo-treated rabbits had 149/792 (18.8%) positive/total swabs, whereas bupropion-treated rabbits had 23/440 (5.2%), and nicotine/bupropion-treated rabbits had 47/792 (5.9%) positive/total swabs. Thus, bupropion significantly reduces nicotine-induced HSV reactivation in latent rabbits.

Animals↗

PubMed2003

Heparanase degrades syndecan-1 and perlecan heparan sulfate: functional implications for tumor cell invasion.

Heparanase (HPSE-1) is involved in the degradation of both cell-surface and extracellular matrix (ECM) heparan sulfate (HS) in normal and neoplastic tissues. Degradation of heparan sulfate proteoglycans (HSPG) in mammalian cells is dependent upon the enzymatic activity of HPSE-1, an endo-beta-d-glucuronidase, which cleaves HS using a specific endoglycosidic hydrolysis rather than an eliminase type of action. Elevated HPSE-1 levels are associated with metastatic cancers, directly implicating HPSE-1 in tumor progression. The mechanism of HPSE-1 action to promote tumor progression may involve multiple substrates because HS is present on both cell-surface and ECM proteoglycans. However, the specific targets of HPSE-1 action are not known. Of particular interest is the relationship between HPSE-1 and HSPG, known for their involvement in tumor progression. Syndecan-1, an HSPG, is ubiquitously expressed at the cell surface, and its role in cancer progression may depend upon its degradation. Conversely, another HSPG, perlecan, is an important component of basement membranes and ECM, which can promote invasive behavior. Down-regulation of perlecan expression suppresses the invasive behavior of neoplastic cells in vitro and inhibits tumor growth and angiogenesis in vivo. In this work we demonstrate the following. 1) HPSE-1 cleaves HS present on the cell surface of metastatic melanoma cells. 2) HPSE-1 specifically degrades HS chains of purified syndecan-1 or perlecan HS. 3) Syndecan-1 does not directly inhibit HPSE-1 enzymatic activity. 4) The presence of exogenous syndecan-1 inhibits HPSE-1-mediated invasive behavior of melanoma cells by in vitro chemoinvasion assays. 5) Inhibition of HPSE-1-induced invasion requires syndecan-1 HS chains. These results demonstrate that cell-surface syndecan-1 and ECM perlecan are degradative targets of HPSE-1, and syndecan-1 regulates HPSE-1 biological activity. This suggest that expression of syndecan-1 on the melanoma cell surface and its degradation by HPSE-1 are important determinants in the control of tumor cell invasion and metastasis.

Adenocarcinoma↗

PubMed2002

Analysis of fenbendazole residues in bovine milk by ELISA.

Fenbendazole residues in bovine milk were analyzed by ELISAs using two monoclonal antibodies. One monoclonal antibody (MAb 587) bound the major benzimidazole anthelmintic drugs, including fenbendazole, oxfendazole, and fenbendazole sulfone. The other (MAb 591) was more specific for fenbendazole, with 13% cross-reactivity with the sulfone and no significant binding to the sulfoxide metabolite. The limit of detection of the ELISA method in the milk matrix was 7 ppb for MAb 587 and 3 ppb for MAb 591. Fenbendazole was administered in feed, drench, and paste form to three groups of dairy cattle. Milk was collected immediately before dosing and then every 12 h for 5 days. The ELISA indicated that residue levels varied widely among individual cows in each group. Fenbendazole levels peaked at approximately 12-24 h and declined rapidly thereafter. Metabolites were detected at much higher levels than the parent compound, peaked at approximately 24-36 h, and declined gradually. Residue levels were undetectable by 72 h. The ELISA data correlated well with the total residues determined by chromatographic analysis, but the use of the two separate ELISAs did not afford an advantage over ELISA with the single, broadly reactive MAb 587. The ELISA method could be used to flag high-residue samples in on-site monitoring of fenbendazole in milk and is a potential tool for studying drug pharmacokinetics.

Animals↗

PubMed2002

Plasma concentrations of endothelin-like immunoreactivity in healthy horses and horses with naturally acquired gastrointestinal tract disorders.

OBJECTIVE: To compare plasma endothelin (ET)- like immunoreactivity between healthy horses and those with naturally acquired gastrointestinal tract disorders. ANIMALS: 29 healthy horses and 142 horses with gastrointestinal tract disorders. PROCEDURE: Blood samples were collected from healthy horses and from horses with gastrointestinal tract disorders prior to treatment. Magnitude and duration of abnormal clinical signs were recorded, and clinical variables were assessed via thorough physical examinations. Plasma concentrations of ET-like immunoreactivity were measured by use of a radioimmunoassay for human endothelin-1, and CBC and plasma biochemical analyses were performed. RESULTS: Plasma ET-like immunoreactivity concentration was significantly increased in horses with gastrointestinal tract disorders, compared with healthy horses. Median plasma concentration of ET-like immunoreactivity was 1.80 pg/ml (range, 1.09 to 3.2 pg/ml) in healthy horses. Plasma ET-like immunoreactivity was greatest in horses with strangulating large-intestinal obstruction (median, 10.02 pg/ml; range, 3.8 to 22.62 pg/ml), peritonitis (9.19 pg/ml; 789 to 25.83 pg/ml), and enterocolitis (8.89 pg/mI; 6.30 to 18.36 pg/ml). Concentration of ET-like immunoreactivity was significantly associated with survival, PCV, and duration of signs of pain. However, correlations for associations with PCV and duration of pain were low. CONCLUSIONS AND CLINICAL RELEVANCE: Horses with gastrointestinal tract disorders have increased plasma concentrations of ET-like immunoreactivity, compared with healthy horses. The greatest values were detected in horses with large-intestinal strangulating obstructions, peritonitis, and enterocolitis. This suggests a potential involvement of ET in the pathogenesis of certain gastrointestinal tract disorders in horses.

Animals↗