Tayfun Dalbasti

Detection of Interaction Between Metal Complex Indicator and DNA by Using Electrochemical Biosensor

There has been extensive research on binding of transition metal complexes to DNA via electrostatic and hydrophobic interactions. Most indicator based electrochemical DNA biosensors have used cationic metal complexes that interact in a different way with single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). Described here are the electrochemical parameters for a mixed-ligand complex, [Co(phen)33+] (phen: 1,10-phenanthroline), on binding to DNA. The milimolar quantities of [Co(phen)33+], which associates reversibly with immobilized calf thymus DNA was detected by using dsDNA-modified carbon paste electrode (dsDNA-modified CPE), ssDNA-modified carbon paste electrode (ssDNA-modified CPE) and bare carbon paste electrode (bare CPE), voltammetrically and the decreased peak currents were observed, respectively. The extend of hybridization between the complementary sequences is determined by the enhancement of the voltammetric peak of the [Co(phen)33+] indicator. Numerous factors affecting the DNA immobilization and indicator were investigated. Experiments were also performed at various salt concentrations and the optimum salt concentration was determined. The difference between the peak currents of denaturated calf thymus DNA (ssDNA)-modified CPE and dsDNA-modified CPE was also observed. These results demonstrated the use of the electroactive hybridization indicator, [Co(phen)33+] for DNA biosensors.

Buttermilk Based Cobalt Phthalocyanine Dispersed Ferricyanide Mediated Amperometric Biosensor for the Determination of Xanthine

A tissue-based amperometric biosensor for xanthine determination has been developed. The biosensor uses a carbon paste electrode (CPE) which contains buttermilk (BTM) as source of xanthine oxidase (XOD) (EC.1.1.3.2.2.) and cobalt phthalocyanine (CoPc) as mediator. The system is also mediated with ferricyanide in solution to obtain a double-mediated biosensor. The effect of various variables upon the response was studied. Linearity was observed over the concentration range of 1–15 mM xanthine. The optimum operational pH range for the electrode is 8.0–9.0. Reproducibility was studied and a relative standard deviation (rsd) of 10.26 % was found. After 60 days the normalized response of the BTM-modified electrode was 60 % of the first day.

Linezolid in the treatment of methicillin-resistant staphylococcal post-neurosurgical meningitis: A series of 17 cases

Abstract Background: Linezolid is a bacteriostatic antibiotic with good cerebrospinal fluid penetration. The aim of this study was to evaluate the efficacy of linezolid in methicillin-resistant staphylococcal (methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase-negative Staphylococcus (MRCoNS)) meningitis. Methods: We extracted data and outcomes for all adult patients (age > 18 y) with culture-proven MRSA or MRCoNS meningitis treated with linezolid between January 2006 and September 2010 in our hospital. Demographic, clinical, and laboratory data and predisposing factors, as well as information on response to treatment and outcome were obtained by regular visits. Results: A total of 17 cases (9 MRCoNS, 7 MRSA, and 1 MRCoNS and MRSA mixed) fulfilled the inclusion criteria. All patients had hospital-acquired meningitis and had undergone neurosurgery. Cumulative microbiological success on day 5 was 88%. There was 1 staphylococcal meningitis-related death. There were no severe adverse events. Conclusions: Our experience with linezolid suggests that it can be an alternative for the treatment of MRCoNS- and MRSA-related meningitis.

Online electrochemical monitoring of nitric oxide during photodynamic therapy

Photodynamic therapy (PDT), as a novel treatment modality, is based on the use of a photosensitizing agent with an excitation light source for the treatment of various malignancies. Its effect is mediated through reactive oxygen species and nitric oxide (NO), which are shown to be present in apoptosis. Individual differences among patients and even in different areas of the same tumor in one patient may cause a major problem with PDT: dose calculation during application of the light. An electrochemical sensor is proposed for online monitoring of NO generation as a solution of this problem. 5-Aminolevulinic acid (ALA) was administered as the photosensitizer in rat cerebellum. An amperometric sensor, selective to NO, was designed and tested both in vitro and in vivo during PDT. ALA-mediated PDT resulted in rapid generation of NO, starting as early as the application of light on the tissue. Simultaneous amperometric recordings have been carried out for 5 min during PDT. The progressive increase in NO concentration peaked at 1.10 min and then the response current began to decrease until it reached a plateau at around 70% of its peak value. This study, for the first time, electrochemically demonstrates the generation of NO during PDT. Rapid and stable responses obtained by the experimental setup confirmed that this method could be used as an online monitoring system for PDT-mediated apoptosis.

Thrombosis of a Drainage Vein in Developmental Venous Anomaly (DVA) Leading Venous Infarction: A Case Report and Review of the Literature

Developmental venous anomalies (DVAs) are common congenital venous drainage anomalies. Although they typically have a benign clinical course and a low symptomatic rate, thrombosis of a drainage vein may occur, leading to potentially debilitating complications. We report imaging findings of posterior fossa DVA with a thrombosed drainage vein in a patient with nonhemorrhagic cerebellar infarct. We also review the relevant literature on the subject.

Vancomycin versus linezolid in the treatment of methicillin-resistant Staphylococcus aureus meningitis.

BACKGROUND Vancomycin is the mainstay of treatment for methicillin-resistant Staphylococcus aureus (MRSA) meningitis. However, successful outcomes with linezolid have not been reported in a large series of patients. We conducted a single-center retrospective cohort study to compare vancomycin with linezolid in the treatment of MRSA meningitis. METHODS We extracted data and outcomes for all adult patients (age >18 years) with culture-proved MRSA meningitis who received vancomycin or linezolid between January 2006 and June 2011. A definite diagnosis of meningitis was based on the isolation of MRSA in at least one cerebrospinal fluid (CSF) culture and findings in CSF that are typical of the infection. Linezolid was given intravenously (IV) at a dosage of 600 mg q12h and vancomycin IV at 500 mg q6h. RESULTS A total of 8 patients with MRSA meningitis (5 male, 3 female; age [mean±SD] 61.6±13.2 years) received vancomycin and 9 patients (7 male, 2 female; age 59.1±15.6 years) received linezolid. All isolated strains of MRSA were susceptible to both vancomycin and linezolid. The rates of microbiologic success with linezolid or vancomycin, in terms of clearance of MRSA from CSF on day 5, were 7/9 and 2/8 (p=0.044, Fisher exact test). No severe adverse events occurred in either treatment arm of the study. One-month survival of the patients in whom treatment was successful microbiologically was 2/2 in the vancomycin-treated group and 4/7 in the linezolid-treated group. Minimum inhibitory concentration (MIC) data for vancomycin were available for 5/6 treatment failures with vancomycin, and vancomycin MIC values of these five strains were 2 mg/L. CONCLUSION Analysis of the findings in the limited cohorts in our study suggests that linezolid is superior to vancomycin for treating MRSA meningitis, especially in cases in which there is a high MIC (2 mg/L) for vancomycin. A clinical study involving larger cohorts may increase the evidence available in relation to this question.

Microelectrode for in vivo real-time detection of NO.

Nitric oxide (NO) is gaining importance with its diverse spectrum of clinic effects. However, there is still a need for an ideal sensor to monitor its concentration in tissue. An ideal sensor should not interfere with the ongoing physiological process, while making fast, reliable, and repeatable measurements. We have designed a microelectrode for electrochemical NO measurement from tissue with relatively low interference and reliable results upon calibration. Details of electrode preparation and calibration procedure are explained along with an experiment to monitor effects of photodynamic therapy.

Comparison of electrochemical detection of acetylcholine-induced nitric oxide release (NO) and contractile force measurement of rabbit isolated carotid artery endothelium

Since the identification of nitric oxide (NO) as an endothelial-derived relaxing factor, it became very important to quantify NO in biological models eventhough it is present in very low concentrations with a very short half-life. The use of electrochemistry as an alternative detection method is quite promising and electrochemical probes are now being developed to detect NO. This paper consists of an amperometric, bi-polymer modified, platinum-iridium microelectrode (Pt 90%-Ir 10% alloy, multistranded, total diameter 130 microm) design and its application for NO detection in acetylcholine (Ach) introduced, rabbit isolated carotid artery endothelium model. In a pH range of 3.0-10.0. pH 3.0 was found to be the optimum pH. As the pH values increased up to 10.0, the response current decreased as the oxidation of NO is catalyzed by H(+) in the acidic media. Temperature effect was checked at 25 degrees C (room temperature), 30 and 40 degrees C. An increasing trend was observed in sensor response with the increasing temperature. Most common biological interferences as ascorbic acid, uric acid and glucose were eliminated via bi-polymer coatings of four layers of Nafion and a layer of 50 mM o-phenylenediamine (OPD). When S/N ratio was accepted as 3, limit of detection was calculated as 15 nM. NO release from carotid artery endothelium was also determined by measuring response force in thermostatic isolated organel baths. Obtained force responses (mg) were compared with the electrochemical (nA) sensor responses.

Local interstitial chemotherapy with sustained release bucladesine in de novo glioblastoma multiforme: a preliminary study.

This clinical study was designed to evaluate the safety and efficacy of the sustained release form of dibutryl adenosine-3′,5′-cyclic monophosphate (dB-cAMP, bucladesine) placed in the tumor resection cavity at the time of recurrence of the de novo glioblastoma multiforme (GBM) patients.In a randomized prospective manner, 40 patients who were diagnosed as GBM in their first operations were included in this study. Four different therapy protocols were used: First group of 10 patients had tumor resection only. Second group assessed had only systemic chemotherapy as six i.v. infusions of fotémustine after tumor resection. Third group had implantation of bucladesine-loaded biodegradable polymeric sustained release (bcl-SR) pellets while the last group received six i.v. infusions of systemic fotémustine as in the second group in addition to local implantation of bcl-SR pellets. A biodegradable polymer, poly-dl-lactide-co-glycolide with molecular weight of 80 000, was used as carrier matrix for the drug with an approximately 4–5 months of release time. Maximal doses of 20 mg of bucladesine with a mean dose of 15.5 mg were implanted. No bone marrow suppression occurred and there were no wound infections as far as the local bucladesine-loaded polymer therapy is concerned.In this randomized prospective trial of local interstitial chemotherapy with long acting bcl-SR did show a statistically significant delay of recurrence on the treatment of GBM patients. Best treatment results obtained from the local bcl-SR + systemic fotémustine treated group in which survival rate estimated by the Kaplan–Meier method was 70% in de novo GBM at 12 months.

Assessment of genetic markers and glioblastoma stem-like cells in activation of dendritic cells

Glioblastoma (GBM) is the most common and aggressive intraparenchymal primary brain tumor in adults. The principal reasons for the poor outcomes of GBM are the high rates of recurrence and resistance to chemotherapy. The aim of this study was to determine the role of tailored cellular therapy for GBM with a poor prognosis and compare the activity of dendritic cells (DCs) that have encountered GBM cells. Detecting the correlations between methylation and expression of MGMT and PTEN genes and GBM cancer stem cells (CSCs) markers after co-cultures with a mononuclear cell cocktail are also aims for this study. Allogenic umbilical cord blood (UCB)-derived DCs were labeled with the CD11a and CD123 for immature DCs, and CD80 and CD11c for mature DCs. CD34, CD45, and CD56 cells were isolated from allogenic UCB for using in DCs maturation. GBM CSCs were detected with CD133/1 and CD111 antibodies after co-culture studies. DC activation was carried out via GBM cells including CD133 and CD111 cells and a mononuclear cells cocktail including CD34, CD45, and CD56 natural killer cells. Real-time PCR was performed to detect the expression and promoter methylation status of PTEN and MGMT genes. The expression of CSCs markers was found in all GBM cases, and a statistically significant correlation was found among them after co-culture studies. The most pronounced affinity of DCs to GBM cells was observed at dilutions between 1/4 and 1/256 in co-cultures. There was a statistically significant correlation between cellularity and granularity ratios for CD123 and CD11c. PTEN and MGMT gene expression and methylation values were evaluated with respect to CSCs expression and no statistical significance was found. Activation of DCs might associate with CSCs and the mononuclear cells cocktail including CD34, CD45, and CD56 cells which were obtained from allogenic UCB.