Biomedical subjects

A Larkin

Publications and source records attributed to A Larkin.

At least 19 recordsLinked to original sources

PubMed2004

Weak dynamical localization in periodically kicked cold atomic gases.

Quantum kicked rotor was recently realized in experiments with cold atomic gases and standing optical waves. As predicted, it exhibits dynamical localization in the momentum space. Here we consider the weak-localization regime concentrating on the Ehrenfest time scale. The latter accounts for the spread time of a minimal wave packet and is proportional to the logarithm of the Planck constant. We show that the onset of the dynamical localization is essentially delayed by four Ehrenfest times, and give quantitative predictions suitable for an experimental verification.

Journal Article↗

PubMed2004

Exposure variations under error conditions in automatic exposure controlled film-screen projection radiography.

Improper automatic exposure control (AEC) termination may result in high overexposures on some radiographic systems. Under AEC, X-ray factors are adjusted automatically to compensate for differences in patient thickness and density. In radiography, AEC is implemented using ionization chambers placed in the film bucky. In this study we deliberately chose incorrect set-up conditions and assessed the response of the AEC system. Two types of incorrect set-up were studied: (1) incorrect selection of bucky radiation detector and (2) simulated misalignment between the X-ray field and light field. The systems tested varied in age from 1 year to in excess of 10 years. In the first test, overexposures of 90 mGy were recorded. Two systems did not meet EC guidelines for improper AEC termination. The second test, misalignment of the X-ray field, was observed to affect the exposure delivered by approximately +/-22%. The maximum dose increase observed, with a chest phantom in the beam, was 165 microGy. Misalignments also resulted in reduced exposures, which may impact on image quality.

Humans↗

PubMed2003

Lymphoproliferative disease in antibody deficiency: a multi-centre study.

We have undertaken a retrospective study of antibody deficient patients, with and without lymphoma, and assessed the ability of specific polymerase chain reaction (PCR) primers to determine if the detection of clonal lymphocyte populations correlates with clinical and immunohistochemical diagnosis of lymphoma. We identified 158 cases with antibody deficiency presenting during the past 20 years. Paraffin-embedded biopsy specimens or slides were available for analysis in a cohort of 34 patients. Of these patients, 29 had common variable immunodeficiency, one X-linked agammaglobulinaemia, one X-linked immunoglobulin deficiency of uncertain cause and three isolated IgG subclass deficiency. We have confirmed that lymphoma in antibody deficiency is predominantly B cell in origin. Clonal lymphocyte populations were demonstrated in biopsies irrespective of histology (16/19 with lymphoma and 11/15 without). Isolated evidence of clonality in biopsy material is therefore an insufficient diagnostic criterion to determine malignancy. Furthermore, our data suggest that clonal expansions are rarely the result of Epstein-Barr virus-driven disease.

Adult↗

PubMed2001

A new monoclonal antibody, P2A8(6), that specifically recognizes a novel epitope on the multidrug resistance-associated protein 1 (MRP1), but not on MRP2 nor MRP3.

Multidrug resistance (MDR) is a major problem in the chemotherapeutic treatment of cancer. Overexpression of the multidrug resistance-associated protein 1 (MRP1), is associated with MDR in certain tumors. A number of MRP1-specific MAbs, which facilitate both clinical and experimental investigations of this protein, are available. To add to this panel of existing antibodies, we have now generated an additional MRP1-specific monoclonal antibody (MAb), P2A8(6), which detects a unique heat stable epitope on the MRP1 molecule. Female Wistar rats were immunized via footpad injections with a combination of two short synthetic peptides corresponding to amino acids 235-246 (peptide A) and 246-260 (peptide B) of the MRP1 protein. Immune reactive B cells were then isolated from the popliteal lymph nodes for fusion with SP2/O-Ag14 myeloma cells. Resultant hybridoma supernatants were screened for MRP1-specific antibody production. Antibody P2A8(6) was characterized by Western blotting and immunocytochemistry on paired multidrug resistant (MRP1 overexpressing) and sensitive parental cell lines. The antibody detects a protein of 190 kDa in MRP1-expressing cell lines but not in MRP2- or MRP3-transfected cell lines. P2A8(6) stains drug-selected and MRP1-transfected cell lines homogeneously by immunocytochemistry and recognizes MRP1 by immunohistochemistry on formalin-fixed paraffin wax-embedded tissue sections. Peptide inhibition studies confirm that P2A8(6) reacts with peptide B (amino acids 246-260), therefore recognizing a different epitope from that of all currently available MRP1 MAbs. This new MAb, chosen for its specificity to the MRP1 protein, may be a useful addition to the currently available range of MRP1-specific MAbs.

Animals↗

PubMed2000

Shot noise in chaotic systems: "classical" to quantum crossover.

This paper is devoted to study of the classical-to-quantum crossover of the shot noise in chaotic systems. This crossover is determined by the ratio of the particle dwell time in the system, tau(d), to the characteristic time for diffraction t(E) approximately lambda(-1)|lnh, where lambda is the Lyapunov exponent. The shot noise vanishes when t(E)>>tau(d), while it reaches a universal value in the opposite limit. Thus, the Lyapunov exponent of chaotic mesoscopic systems may be found by shot noise measurements.

Journal Article↗

PubMed2000

p38 MAPK and NF-kappa B collaborate to induce interleukin-6 gene expression and release. Evidence for a cytoprotective autocrine signaling pathway in a cardiac myocyte model system.

In cardiac myocytes, the stimulation of p38 MAPK by the MAPKK, MKK6, activates the transcription factor, NF-kappaB, and protects cells from apoptosis. In the present study in primary neonatal rat cardiac myocytes, constitutively active MKK6, MKK6(Glu), bound to IkappaB kinase (IKK)-beta and stimulated its abilities to phosphorylate IkappaB and to activate NF-kappaB. MKK6(Glu) induced NF-kappaB-dependent interleukin (IL)-6 transcription and IL-6 release in a p38-dependent manner. IL-6 protected myocardial cells against apoptosis. Like IL-6, TNF-alpha, which activates both NF-kappaB and p38, also induced p38-dependent IL-6 expression and release and protected myocytes from apoptotis. While TNF-alpha was relatively ineffective, IL-6 activated myocardial cell STAT3 by about 8-fold, indicating a probable role for this transcription factor in IL-6-mediated protection from apoptosis. TNF-alpha-mediated IL-6 induction was inhibited by a kinase-inactive form of the MAPKKK, TGF-beta activated protein kinase (Tak1), which is known to activate p38 and NF-kappaB in other cell types. Thus, by stimulating both p38 and NF-kappaB, Tak1-activating cytokines, like TNF-alpha, can induce IL-6 expression and release. Moreover, the myocyte-derived IL-6 may then function in an autocrine and/or paracrine fashion to augment myocardial cell survival during stresses that activate p38.

Animals↗

PubMed2000

Appropriateness of a Resuscitation Council (UK) advanced life support course for primary care dentists.

OBJECTIVES: To investigate whether a standard Resuscitation Council (UK) ALS course is appropriate for primary care dentists or whether a course should be specifically designed for dentists. DESIGN: Opinions canvassed by pre-course expectation and post-course evaluation questionnaires. SUBJECTS: 23 West Pennine primary care dentists providing a general anaesthetic or conscious sedation service who attended an ALS course. RESULTS: Knowledge and skills were rated on a 5-point scale from 1 (not important at all) to 5 (extremely important). Basic airway management (mean = 5) and anaphylaxis (mean = 4.9) scored the highest on the 'expectation' questionnaire. Rhythm recognition (P < 0.001), defibrillation (P = 0.007) and arrest algorithms (P = 0.047) were rated as significantly more important after the course than before. Knowledge about rhythm disorder management, cardiac pacing, post-resuscitation care, blood gas interpretation and bereavement were not considered to be so important either before or after the course. CONCLUSIONS: Despite rating some aspects as unimportant, all dentists stated that this course had been appropriate. They did not want a specially designed ALS course for dentistry. Taking exactly the same recognised course and assessments as other healthcare professionals and gaining the same certification was felt to be important to this group of dentists.

Adult↗

PubMed2000

Low-dose twice-daily fractionated X-irradiation of ovarian tumor cells in vitro generates drug-resistant cells overexpressing two multidrug resistance-associated proteins, P-glycoprotein and MRP1.

Failure of chemotherapy is frequently observed in patients previously treated with radiotherapy. To establish a cellular model for examining this resistance phenotype a series of mammalian tumor cell lines were exposed in vitro to fractionated X-irradiation and were then shown to express resistance to multiple antitumor drugs, including vincristine, etoposide and cisplatin. In these experiments the radiation was delivered as 10 fractions of 5 Gy (dose resulting in 1 log cell kill) given intermittently over several months. We now report that a comparable multidrug-resistance profile is expressed by human SK-OV-3 human ovarian tumor cells exposed in vitro to low dose (2 Gy) twice-daily fractions of X-rays given for 5 days on two consecutive weeks, essentially mimicking clinical practice, involving an overexpression of two MDR-associated proteins, P-glycoprotein and the multidrug resistance protein 1 (MRP1), with the latter being readily detectable by immunocytochemistry.

ATP Binding Cassette Transporter, Subfamily B↗

PubMed1999

A new monoclonal antibody that specifically recognises the MDR-3-encoded gene product.

The MDR-3-encoded P-glycoprotein (Pgp) is highly expressed in liver and is thought to function as a hepatic transporter of phospholipids into bile. However its role, if any, in other tissues remains undefined. Although transfection experiments have indicated that it may be unable to confer drug resistance, there is evidence that it may be involved in drug resistance in certain B-cell leukaemias. To date, most work on clinical samples has been performed at the mRNA level; limited work has been performed using polyclonal antibodies raised to MDR-3 and mdr-2 (the murine equivalent of MDR-3). We have generated a new monoclonal antibody, termed 6/1G, which specifically recognises the human MDR-3 gene-encoded product. Antibody 6/1G was produced by in vitro immunisation of spleen cells from BALB/c mice with a synthetic 12-amino acid peptide. Cells from MDR-3 transgenic mice showed consistent membranous staining with antibody 6/1G. Immunoblotting with 6/1G identified a band at 170 kDa on lysates of MDR-3 transgenic cells. Preliminary results with a range of B-cell leukaemias suggest that MDR-3 Pgp positivity may be a marker for a more malignant phenotype in B-CLL. Antibody 6/1G may be useful in defining a role for MDR-3 in malignancy and drug resistance, as well as in certain liver diseases such as progressive familial intracholeostasis.

ATP Binding Cassette Transporter, Subfamily B↗

PubMed1999

Preliminary immunocytochemical studies of MDR-1 and MDR-3 Pgp expression in B-cell leukaemias.

P-glycoproteins (Pgps) belong to the family of ATP binding cassette (ABC) transporter proteins. In humans two Pgp genes have been identified; mdr-1 and mdr-3. Classical Multiple Drug Resistance (MDR) is associated with over expression of the mdr-1 gene product, P-170. No role for mdr-3 in MDR has yet been proven. However there is evidence that mdr-3 overexpression may be associated with drug resistance in certain B-cell lymphocytic leukaemias. In an immunocytochemical study we have looked at a selection of B-cell leukaemias for mdr-1 and mdr-3 encoded Pgp expression using monoclonal antibodies specific for the mdr-1 and mdr-3 encoded gene products. In B-CLL patients a differential pattern of MDR-3 positive staining was observed; suggesting that MDR-3 positivity may be associated with a more malignant phenotype in B-CLL. This pattern was not observed with MDR-1 positivity. We also observed MDR-3 positivity in an AML stage M5a patient which is the first report of MDR-3 Pgp expression being detected in AML; suggesting that MDR-3 Pgp expression may be limited to particular subtypes of this disease. Results from B-NHL cases were inconclusive with varying expression of MDR-1 and MDR-3 Pgps observed. Work is currently underway to further explain the significance of these findings.

ATP Binding Cassette Transporter, Subfamily B↗

PubMed1999

An improved method for STR analysis of bloodstained denim.

Indigo dye is used to dye denim and other fabrics. It is now accepted that if this is co-extracted with the DNA, it may inhibit PCR amplification. A simple, improved method is described for the extraction of DNA from bloodstained denim for PCR amplification and short tandem repeat (STR) analysis. The DNA was extracted by constructing a blotting system using capillary action to draw a saline solution through the denim. The transferred material was collected onto nylon membranes and these were processed by chelex extraction. A variety of coloured denim substrates and other heavily dyed fabrics, including case work samples were used. In all cases the DNA was extracted, amplified and typed correctly.

Alleles↗

PubMed1998

Monoclonal antibodies raised to paraffin wax embedded archival tissue; feasibility study of their potential to detect novel antigenic markers.

A study to determine the feasibility of using archival paraffin wax embedded tissue to generate monoclonal antibodies is described. Specifically, monoclonal antibodies were raised to paraffin wax embedded normal human kidney tissue to test the possibility of producing antibodies to such tissue samples prior to attempting generation of antibodies to valuable archival tissue. Multiple sections (10 x 5 microm) were pooled and dewaxed as for immunohistochemical procedures and combined with Freund's adjuvant for immunization of BALB/c mice in vivo. Immunized spleen cells were fused with SP2 myeloma cells and subsequent clones screened on paraffin wax embedded normal human kidney sections, a range of cell lines and normal mouse tissue. Supernatants from 11 wells (from a total of 90 wells screened) showed different staining patterns on sections of paraffin wax embedded kidney. One clone, 1/11C, (isotype IgG1) which exhibited strong staining on all kidney tubules by immunohistochemical studies (glomeruli interstitium and vessels were unstained) and identified a band at 52 kDa on immunoblots of dewaxed kidney tissue (as used for immunogen) was chosen for further characterization. Immunoblotting of five mammalian cell lines showed differential expression of this 52 kDa band (distinct expression on 3/5, weak expression on 2/5 cell lines) whereas, all cell lines displayed a band at 44 kDa and a third band at 70 kDa was observed on 2/5 cell lines. In mouse tissue extracts, the 52 kDa band was identified in kidney tissue only (not in the lung, liver or spleen) with the 44 kDa and 70 kDa bands weakly expressed in all tissues. This preliminary investigation of a novel approach to identifying possible new antigenic markers or producing monoclonal antibodies which react better to known antigens on sections of paraffin wax embedded tissue showed that this method is feasible. The need to have a comprehensive screening system in place and the ability to identify potentially useful clones after the initial screening is paramount due to the relative scarcity of screening material (archival tissue sections) and the tedious nature of the screening method.

Animals↗

PubMed1998

The utility of patch tests using larger screening series of allergens.

BACKGROUND: The number of patch test allergens available within the United States for routine commercial purchase is limited. Allergens chosen for inclusion in routine screening series or patch test trays vary, and the degree of information obtained from any series may or may not serve a patient's needs. OBJECTIVE: Knowledge of how well the allergens chosen for inclusion in the two commercially available sources perform compared with a more expansive panel of tests can help physicians select the more appropriate tests. METHODS: From 1994 to mid-1997, 554 patients were tested with allergens recommended by the North American Contact Dermatitis Group (NACDG). This included all allergens currently available from both current domestic sources, although not in the identical form used by the Thin-layer Rapid Use Epicutaneous Test (TRUE) test (Glaxo Dermatology, Research Triangle Park, NC). Another 185 patients were tested with supplemental series of allergens. RESULTS: The larger the series of allergens used, the more positive tests were found and the more relevant tests as well. Hermal patch test allergens identified about 55% of the information found by the NACDG series; the TRUE test allergens (but not in the TRUE test system) identified 65%. Of the 103 reactions to supplemental allergens not found by the NACDG series, 59 were relevant. CONCLUSION: Larger series of allergens can enhance accurate diagnosis of allergic contact dermatitis. No single arbitrary series of allergens can adequately survey the contemporary environment of individual patients. Selection of allergens for testing requires consideration of the patient's history and access to appropriate environmental contactants.

Acrolein↗

PubMed1997

A new mdr-1 encoded P-170 specific monoclonal antibody: (6/1C) on paraffin wax embedded tissue without pretreatment of sections.

AIMS: The generation and characterisation of a monoclonal antibody that specifically recognises the mdr-1 encoded protein, P-glycoprotein (P-170), on routinely processed formalin fixed, paraffin wax embedded tissue sections. METHODS: The monoclonal antibody, designated 6/1C, was produced following a combination of in vivo and in vitro immunisation regimens in Balb/c mice with a synthetic 12 amino acid peptide that corresponds to amino acids 21-32 (believed to be intracellularly located) of P-170 and has insignificant homology with the mdr-3 encoded P-170. Antibody 6/1C was characterised by western blotting and immunocytochemistry on cytospins of paired multidrug resistant or sensitive cell lines, including mdr-1 and mdr-3 transfected cells, and by immunohistochemistry on normal and malignant formalin fixed paraffin wax embedded tissue sections. RESULTS: Antibody 6/1C showed a single band at 170 kDa on western blots of multidrug resistant cell lysates and mdr-1 transfected cell lysates that was absent on similar preparations of drug sensitive cells and mdr-3 transfected cells. Immunocytochemical studies on cytospins of multidrug resistant cells and mdr-1 transfected cells revealed strong inner plasma membrane/cytoplasmic staining. Staining was negligible on drug sensitive cells and cells transfected with the mdr-3 gene. Immunohistochemical studies on formalin fixed, paraffin wax embedded normal adult kidney, liver, and breast tissue and a range of fetal tissues exhibited staining patterns of a variety of secretory surfaces consistent with documented mdr-1 specific staining. Specific staining of malignant cells in similarly treated sections of breast tumours was seen also with antibody 6/1C. Staining on paraffin wax embedded tissue with this antibody did not require any pretreatment of tissue sections. CONCLUSIONS: This new monoclonal antibody, chosen for its specificity with the mdr-1 encoded P-170 and its reactivity on routinely fixed paraffin wax embedded tissue samples without pretreatment, appears to be useful for the investigation of P-170 in archival material. It is especially useful for retrospective studies on pretreatment and post-treatment tissue sections, and could help establish when and how rapidly mdr-1 associated drug resistance develops during chemotherapeutic regimens. Immunohistochemical assessment of P-170 expression in many cancers has potential for diagnostic purposes and may influence the choice of chemotherapeutic drugs used in the treatment of refractory tumours.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1996