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Biomedical subjects

B R Clark

Publications and source records attributed to B R Clark.

At least 19 recordsLinked to original sources
PubMed2006

Elastic scattering spectroscopy accurately detects high grade dysplasia and cancer in Barrett's oesophagus.

BACKGROUND AND AIMS: Endoscopic surveillance of Barrett's oesophagus currently relies on multiple random biopsies. This approach is time consuming, has a poor diagnostic yield, and significant interobserver variability. Elastic scattering spectroscopy is a real time in vivo optical technique which detects changes in the physical properties of cells. The aim of this study was to assess the potential for elastic scattering to detect high grade dysplasia or cancer within Barrett's oesophagus. METHODS: Elastic scattering spectroscopy measurements collected in vivo were matched with histological specimens taken from identical sites within Barrett's oesophagus. All biopsies were reviewed by three gastrointestinal pathologists and defined as either "low risk" (non-dysplastic or low grade dysplasia) or "high risk" (high grade dysplasia or cancer). Two different statistical approaches (leave one out and block validation) were used to validate the model. RESULTS: A total of 181 matched biopsy sites from 81 patients, where histopathological consensus was reached, were analysed. There was good pathologist agreement in differentiating high grade dysplasia and cancer from other pathology (kappa = 0.72). Elastic scattering spectroscopy detected high risk sites with 92% sensitivity and 60% specificity and differentiated high risk sites from inflammation with a sensitivity and specificity of 79%. If used to target biopsies during endoscopy, the number of low risk biopsies taken would decrease by 60% with minimal loss of accuracy. A negative spectroscopy result would exclude high grade dysplasia or cancer with an accuracy of >99.5%. CONCLUSIONS: These preliminary results show that elastic scattering spectroscopy has the potential to target conventional biopsies in Barrett's surveillance saving significant endoscopist and pathologist time with consequent financial savings. This technique now requires validation in prospective studies.

Adenocarcinoma↗
PubMed2002

W/Wv marrow stromal cells engraft and enhance early erythropoietic progenitors in unconditioned Sl/Sld murine recipients.

Transplantation of marrow stromal cells may provide a means of modulating hematopoiesis and serve as a form of cell therapy. We employed a murine transplant model using Sl/Sl(d) mice, which have macrocytic anemia due to defective expression of stem cell factor (SCF) on bone marrow stromal cells. Donor cells were derived from the complementary mutant strain W/W(v), which also exhibit anemia, due to mutations in c-kit, the SCF receptor expressed on hematopoietic stem cells. The strength of this model is that any correction of the Sl/Sl(d) anemia from the infusion of W/W(v) stromal cells can be attributed to the effect of the stromal cells and not to contaminating W/W(v) hematopoietic stem cells, a major concern in experiments involving wild-type animals. Cultured stromal cells were infused into unconditioned non-splenectomized Sl/Sl(d) mice. Engraftment of donor stromal cells reached levels of up to 1.0% of total marrow cells 4 months post transplant. However, stromal engraftment was not detectable in the spleen. Recipients of W/W(v) stroma showed a significant increase in the committed erythroid progenitors compared with those receiving Sl/Sl(d) stromal cells: 109 +/- 26 vs 68 +/- 5 CFU-E per 10(5) BMC, P = 0.002; 25 +/- 10 vs 15 +/- 5 BFU-E per 10(5) BMC, P = 0.037, for W/W(v) and Sl/Sl(d) stroma recipients, respectively. Despite this increase in erythroid progenitors, the anemia was not corrected. Our data suggest that in this murine model, splenic erythropoiesis may influence stromal cell therapy, and that higher levels of marrow engraftment may be necessary to obtain a clinically significant effect.

Anemia, Macrocytic↗
PubMed2001

Chronic intraventricular infusion of glial cell line-derived neurotrophic factor (GDNF) rescues some cerebellar Purkinje cells from heredodegeneration.

Cerebellar Purkinje cells degenerate in shaker mutant rats. Glia cell line-derived neurotrophic factor (GDNF) was chronically infused intraventricularly in an attempt to rescue mutant Purkinje cells from dying. Four weeks of chronic GDNF infusion delayed the degeneration of many but not all Purkinje cells. Surviving Purkinje cells formed spatially related groups interrupted by other groups of degenerated Purkinje cells. There was a positive correlation in GDNF-supported Purkinje cell survival and persistence of normal motor behaviors.

Animals↗
PubMed2000

X-linked transmission of the shaker mutation in rats with hereditary Purkinje cell degeneration and ataxia.

This study reports on the mode of inheritance of the shaker mutation and the development of an inbred strain of the shaker rat mutation from Sprague Dawley outbred stock onto a Wistar Furth background. Neuroanatomical and behavioral expression of the affected phenotype, through seven generations of backcross and intercross breeding, has confirmed the mode of inheritance to be X-linked. Behaviorally, affected mutants present with a wide-based ataxic gait and whole body tremor. In affected mutants calbindin immunostaining for surviving cerebellar Purkinje cells revealed widespread degeneration in the anterior lobe and in limited areas of the posterior lobe. Fast Fourier transform analysis of the tremor revealed a frequency of 3-5 Hz. As predicted by X-linked inheritance, female descendants of an affected male are carriers for the genotype and the phenotype is expressed in one-half of her male offspring. There was spatially random and limited degeneration of Purkinje cells in carrier females, but they did not display overt clinical signs of ataxia and tremor. These data provide further support for using the shaker mutant rat as an animal model for studies of mechanisms underlying human heredodegenerative diseases.

Animals↗
PubMed2000

Olivocerebellar projections modify hereditary Purkinje cell degeneration.

Brainstem inferior olivary neurons, through their olivocerebellar efferent projections, dynamically regulate the structure and function of Purkinje neurons. To test the hypothesis that the inferior olive can epigenetically modify adult-onset hereditary Purkinje cell death, olivocerebellar projections were destroyed by 3-acetylpyridine chemoablation of the inferior olive in Shaker mutant rats. Starting around seven weeks of age, mutant Purkinje cells degenerate in a highly predictable spatial and temporal pattern. Chemoablation of the inferior olive at the onset of hereditary Purkinje cell degeneration accelerated the temporal pattern of Purkinje cell death from a natural phenotypic course of six to eight weeks to one and two weeks. When chemoablation of the inferior olive was performed three and a half weeks earlier, the onset of Purkinje cell death was accelerated by seven to 10days, but the spatial pattern and natural rate of temporal degeneration was maintained. Chemoablation of the inferior olive in normal rats did not result in any apparent death of Purkinje cells. These findings indicate that the olivocerebellar system can markedly modify hereditary Purkinje cell death. The accelerated death of Purkinje cells following chemoablation of the inferior olive can result from either the interruption of a trophic signal by climbing fiber deafferentation or parallel fiber excitotoxicity due to cortical disinhibition, but not due to olivocerebellar excitotoxicity.

Animals↗
PubMed1999

Genetically corrected autologous stem cells engraft, but host immune responses limit their utility in canine alpha-L-iduronidase deficiency.

Canine alpha-L-iduronidase (alpha-ID) deficiency, a model of the human storage disorder mucopolysaccharidosis type I (MPS I), is an ideal system in which to evaluate the clinical benefit of genetically corrected hematopoietic stem cells. We performed adoptive transfer of genetically corrected autologous hematopoietic cells in dogs with alpha-ID deficiency. Large volume marrow collections were performed on five alpha-ID-deficient dogs. Marrow mononuclear cells in long-term marrow cultures (LTMCs) were exposed on three occasions during 3 weeks of culture to retroviral vectors bearing the normal canine alpha-ID cDNA. Transduced LTMC cells from deficient dogs expressed enzymatically active alpha-ID at 10 to 200 times the levels seen in normal dogs. An average of 32% of LTMC-derived clonogenic hematopoietic cells were provirus positive by polymerase chain reaction and about half of these expressed alpha-ID. Approximately 10(7) autologous gene-modified LTMC cells/kg were infused into nonmyeloablated recipients. Proviral DNA was detected in up to 10% of individual marrow-derived hematopoietic colonies and in 0.01% to 1% of blood and marrow leukocytes at up to 2 to 3 years postinfusion. Despite good evidence for engraftment of provirally marked cells, neither alpha-ID enzyme nor alpha-ID transcripts were detected in any dog. We evaluated immune responses against alpha-ID and transduced cells. Humoral responses to alpha-ID and serum components of the culture media (fetal bovine and horse sera and bovine serum albumin) were identified by enzyme-linked immunosorbent assay. Cellular immune responses to autologous alpha-ID but not neo(r) transduced cells were demonstrated by lymphocyte proliferation assays. To abrogate potential immune phenomena, four affected dogs received posttransplant cyclosporine A. Whereas immune responses were dampened in these dogs, alpha-ID activity remained undetectable. In none of the dogs engrafted with genetically corrected cells was there evidence for clinical improvement. Our data suggest that, whereas the alpha-ID cDNA may be transferred and maintained in approximately 5% of hematopoietic progenitors, the potential of this approach appears limited by the levels of provirally derived enzyme that are expressed in vivo and by the host's response to cultured and transduced hematopoietic cells expressing foreign proteins.

Animals↗
PubMed1999

Development of young children's understanding that the recent past is causally bound to the present.

The results of 6 studies (involving 304 children) suggested that 4- and 5-year-olds, but not 3-year-olds, understand that very recent past events determine the present. In Studies 1-3, 3- and 4-year-old children were introduced to 2 empty hiding locations. With children's backs to these locations, a camera recorded an experimenter secretly hiding a puppet in one of them. Children then viewed the videotape of what had just happened, along with another tape that depicted identical events except with a different child and with the puppet hidden in the other location. Only 4-year-olds were subsequently able to locate the puppet, even though 3-year-olds remembered the contents of the tapes and understood the equivalence between the video events and the real world. In Study 4, similar effects were obtained when a verbal analog of the test was presented to 3-5-year-olds. Studies 5 and 6 showed that when children observed 2 events in which they had just participated, only 5-year-olds understood that the most recent events were relevant.

Child Development↗
PubMed1997

What is the role of the HIV liaison psychiatrist?

In this article we review the field of HIV liaison psychiatry and illustrate the manner in which psychiatric care can contribute to the health and quality of life of this group of patients. To illustrate our discussion we review experience and findings in relation to affective illness, cognitive impairments, and personality disorder in HIV infection. We also highlight some of the areas where psychiatric care of people with HIV infection is unique from other types of psychiatric liaison work.

AIDS Dementia Complex↗
PubMed1996

Human hematopoiesis in SCID mice implanted with human adult cancellous bone.

The persistence of hematopoietic cells from human adult cancellous bone fragments implanted subcutaneously into CB-17 scid/scid mice was studied. Recipient mice received either no pretreatment (control group) or pretreatment with 3 Gy total-body irradiation and anti-asialo GM1 sera (ASGM1; pretreated group) before implantation. Pretreated severe combined immunodeficient (SCID) mice implanted with human bone were subsequently given ASGM1 every 7 days for the duration of the experiments. At 12 weeks postimplantation, flow cytometry of cells from pretreated and control animal tissues detected human CD45+ cells in the mouse spleen (mean, 7.8% and 3.4% positive cells, pretreated and control animals, respectively), bone marrow (BM; mean, 16.5% and 4.8% positive cells, respectively), and blood (mean, 5.5% and < 2% positive cells, respectively), and in the implanted human bone (73% and 8.9% positive cells, respectively). At 12 weeks, pretreated mice had human granulocyte-macrophage colony-forming cells (GM-CFC) and burst-forming units-erythrocyte (BFU-E) in the implanted human bone in the murine BM and in some of the spleens. The spleens also had extensive infiltration of human B cells and macrophages. Mean serum levels of human IgG in pretreated animals were 14 micrograms/mL during weeks 6 to 12, compared with trace levels (< 1 microgram/mL) in control mice. Bone from patients with acute myeloblastic leukemia (AML) was also implanted in pretreated SCID mice, and retrieved at 8 weeks for analysis. Comparison of preimplantation and implanted samples showed that the original histology was maintained, and massive infiltration of human CD68+ cells was observed in the mice spleens and BM. Implantation of AML bone in SCID mice facilitates analysis of in situ AML cell interaction with stromal cells in the leukemic state, and therapies against AML can be tested in this system, especially the selective killing of AML cells in the presence of other BM cells. Furthermore, this model requires no exogenous administration of cytokines to maintain human hematopoiesis with both normal or AML bone. Because the structure and function of both normal and diseased human adult bone is maintained, this animal model should facilitate investigation of both normal human hematopoiesis and hematopoietic malignancies.

Acute Disease↗
PubMed1995

Biology of bone marrow stroma.

The marrow microenvironment is a complex, three-dimensional structure composed of many cell types and abundant extracellular matrix. Much of the data are derived from analysis of the adherent layer of murine and, especially, human long-term marrow cultures. An essential feature of this in vitro counterpart to the marrow microenvironment is the presence of flat angulated cells functionally defined as marrow stromal cells with the following phenotype: type IV collagen(+), laminin(+), vimentin(+), CD10(+), muscle actin(+), Stro-1(+), and negative for CD45, Mac-1, and HLA-DR. Stromal precursors are Stro-1(+) and CD34(+). Regulation of hematopoietic precursors by the microenvironment occurs by elaboration of regulatory molecules such as hematopoietic cytokines, by cell-cell contact via adhesion molecules such as alpha 4 beta 1 integrin, and by interactions with components of the extracellular matrix as in the case of the glycosaminoglycan hyaluronic acid with cell-associated CD44. Although little about the regulation of stromal cell development itself is known, several studies indicate the transplantability of marrow stromal cells under specific conditions. These developments suggest a potential role of stromal cells in cell therapy. Transfected stromal cells may serve as suitable vehicles for gene delivery to correct single gene disorders in which the product of the target gene does not require stringent regulation as, for example, in the correction of Factor VIII and Factor IX deficiency. Further studies are warranted to investigate marrow stromal cell physiology and regulation to better understand hematopoiesis and to explore the possible use of stroma in therapy.

Bone Marrow Cells↗
PubMed1995

Development and testing of nursing home quality indicators.

In this article, the authors report on the development and testing of a set of indicators of quality of care in nursing homes, using resident-level assessment data. These quality indicators (QIs) have been developed to provide a foundation for both external and internal quality-assurance (QA) and quality-improvement activities. The authors describe the development of the QIs, discuss their nature and characteristics, address the development of a QI-based quality-monitoring system (QMS), report on a pilot test of the QIs and the system, comment on methodological and current QI validation efforts, and conclude by raising further research and development issues.

Accidental Falls↗
PubMed1994

Chronic NMDA receptor blockade or muscimol inhibition of cerebellar cortical neuronal activity alters the development of spinocerebellar afferent topography.

The requirement for cerebellar cortical neuronal activity in the development of spinocerebellar afferent topography was investigated in neonatal rats. In adult rats lower thoracic-upper lumbar spinocerebellar projections are localized to sharply circumscribed patches in the granule cell layer of the cerebellar anterior lobe. In transverse sections these patches appear as sagittally oriented stripes. This pattern develops postnatally as many spinal axons which initially project between the incipient stripes are eliminated thereby sharpening the stripe boundaries. We attempted to alter cerebellar cortical neuronal activity in neonatal animals to study the effects of these changes on the development of spinocerebellar stripes. In some experiments glutaminergic excitatory synaptic transmission was chronically blocked with the N-methyl-D-aspartate (NMDA) receptor antagonist 2-aminophosphovaleric acid (APV). In other experiments postsynaptic activity was directly inhibited by the gamma-aminobutyric acid agonist muscimol. Chronic exposure to APV or to muscimol did not affect the initial development of spinocerebellar projections; many spinal axons were present in the anterior lobe and arranged in incipient stripes. Both the APV and the muscimol appeared to prevent the elimination of interstripe projections; consequently the boundaries of the stripes remained poorly defined. These findings suggest that cerebellar cortical neuronal activity is a necessary requirement for the refinement of spinal afferent topography in the anterior lobe.

2-Amino-5-phosphonovalerate↗
PubMed1994

Antigen-specific deletion of cloned T cells using peptide-toxin conjugate complexed with purified class II major histocompatibility complex antigen.

In a previous report, we showed that cloned T cells incubated with soluble, cognate major histocompatibility complex (MHC) II-peptide complex internalized the peptide moiety of the complex. Here, we report antigen-specific deletion of cloned T cells by treatment with soluble, cognate MHC II-(peptide-toxin) complexes. Toxin (doxorubicin or mycophenolic acid) was attached to synthetic AcMBP(1-14)Ala4 peptide, an analog of the natural acetylated NH2-terminal segment, AcMBP(1-14), of rat myelin basic protein (MBP). IAk-restricted, AcMBP(1-14)-Specific AJ1.2 and 4R3.9 cloned murine T cells were killed by IAk-(AcMBP(1-14)Ala4-toxin). No killing resulted from incubating AJ1.2 and 4R3.9 cells with irrelevant MHC II-(peptide-toxin) or treating IEk-restricted, pigeon cytochrome c-specific A.E7 cloned murine T cells with IAk-(AcMBP(1-14)Ala4-toxin). T cell receptor-mediated T cell uptake of the peptide-toxin moiety of relevant complex was blocked by anti-T cell receptor-alpha/beta antibody and by excess toxin-free complex. LD50 determinations revealed that cognate MHC II-(peptide-toxin) killed T cells much more effectively than did peptide-toxin conjugate alone. Finally, T cell uptake of peptide-toxin and intracellular release of toxin occurred after incubation with relevant MHC II-(peptide-toxin) containing radiolabeled toxin. These findings, which provide the first evidence that cloned T cells can be deleted with soluble, cognate MHC II-(peptide-toxin) complexes, may have significant clinical relevance for antigen-specific therapy of autoimmune or other T cell-mediated diseases.

Amino Acid Sequence↗
PubMed1993

Cloned T cells internalize peptide from bound complexes of peptide and purified class II major histocompatibility complex antigen.

Antigen presentation to helper T cells involves the formation of a trimolecular complex consisting of a class II major histocompatibility complex (MHC) antigen combined with an antigenic peptide on the surface of an antigen-presenting cell and a T cell receptor (TCR) on the T cell. The fate of the MHC class II, peptide, or TCR moieties of the ternary complex following antigen presentation is unknown. Using radiolabeled complexes of affinity-purified murine MHC class II molecules and peptides corresponding to T cell epitopes of myelin basic protein (MBP), this report presents evidence that the binding of preformed relevant MHC class II-peptide complexes to cloned T cells in vitro results in internalization of the peptide moiety. Neither the restricting MHC class II molecule nor the TCR moiety of the trimolecular complex was internalized by T cells. The specificity of peptide internalization was demonstrated using complexes of syngeneic MHC class II with an irrelevant MBP peptide analog and by cloned T cells restricted for a different epitope of the same MBP antigen. Furthermore, the peptide translocation mediated by MHC class II and TCR was demonstrated by antibody-blocking experiments using anti-class and anti-TCR monoclonal antibodies. The peptide internalization by T cells was markedly reduced when binding was performed at 4 degrees C as compared with 37 degrees C. In addition, a significant inhibition of peptide translocation was observed in the presence of a metabolic inhibitor (sodium azide) but not in the presence of cytochalasin B. These results together demonstrate that the in vitro interaction of soluble MHC II-peptide complexes with cloned T cells is an active process associated with uptake of the antigenic peptide.

Amino Acid Sequence↗
PubMed1993

Stimulation of T cells by antigenic peptide complexed with isolated chains of major histocompatibility complex class II molecules.

Major histocompatibility complex (MHC) class II molecules are heterodimeric glycoproteins with one alpha and one beta polypeptide chain of similar molecular size. In this report, we describe the binding of an acetylated N-terminal peptide of myelin basic protein, [Ala4]MBP-(1-14), to purified individual alpha and beta chains of murine I-Ak molecules. Purified complexes of isolated single chains and antigenic peptide bind to cloned T cells restricted by I-Ak and [Ala4]MBP-(1-14) tetradecapeptide. The binding is blocked by alpha/beta anti-T-cell receptor (TCR) monoclonal antibody. Cell triggering as measured by an increase in extracellular acidification rate is observed when cloned T cells are exposed to purified complexes of isolated chains and antigenic peptide. This increase in the extracellular acidification rate is antigen specific and MHC-restricted, as chains alone or irrelevant chain-peptide complexes do not trigger an increase in the metabolic acidification rate. These results together demonstrate that in vitro cloned T cells are triggered by complexes of specific antigenic peptides and isolated individual chains of their cognate MHC proteins.

Amino Acid Sequence↗
PubMed1993

Purified beta-chain of MHC class II binds to CD4 molecules on transfected HeLa cells.

The initial event triggering the activation of Th cells occurs when the TCR interacts with antigenic peptide in the context of the MHC II on APC. Various T cell accessory molecules including CD4, CD28, and LFA-1 participate and facilitate the activation event. Although some evidence for the interaction of MHC II and CD4 is available, the site of MHC class II (alpha-chain, beta-chain, or both chains) for CD4 interaction has not yet been clearly defined. Results from different laboratories had indicated the involvement of alpha 1, beta 1, and beta 2 domains of MHC class II molecules in CD4 interaction. Recently, a conserved site of DR beta 2 domain has been identified that involves CD4 interaction that is analogous to MHC class I binding site for CD8 molecule. In this report, direct binding of affinity-purified HLA-DR2 dimer and its isolated alpha- and beta-chains to CD4 was studied using a CD4-transfected HeLa cell line. Preferential binding of the beta-chain and intact MHC II dimer to the CD4-transfected cells was observed and found to be specifically inhibited by anti-CD4 mAb. In contrast, the isolated alpha-chain of HLA DR2 did not show significant binding to CD4-transfected cells. Complexes of radiolabeled DR2 dimer or beta-chain alone with an immunodominant epitope from myelin basic protein (83-102) did not show any further increase in binding of these molecules. Binding of the beta-chain to CD4+ cells was markedly inhibited by a DR beta 1 peptide (35-46) and was partially inhibited by a DR beta 2 peptide (134-148) of MHC class II molecule. These results suggest the involvement of at least two conserved regions of the beta polypeptide chain of MHC class II in CD4 interaction. Because in our experiments transfected cells lack TCR molecules and the binding of DR2 to the CD4-transfected cells was unaffected by added antigenic peptide, it is possible that the interaction of MHC class II to CD4 is independent of TCR occupancy.

Amino Acid Sequence↗