Biomedical subjects
Publications and source records attributed to S Lehmann.
This first of two articles on enteral nutrition focuses on the formulas that contain special nutrients to enhance immune system function and digestion. We'll review the specific nutrients in enhanced formulas, what researchers have found about their effects on the critically ill, and whether they're worth using.
This second of two articles on enteral nutrition discusses the basics of tube feedings, including the types of tubes that are used, when to start a feeding, and some common complications that develop in patients--aspiration and diarrhea chief among them.
The health care system is a complex and demanding environment requiring an acculturation process for all those who provide services under its aegis. Social workers new to a medical setting, are faced with difficulties relating to all aspects of their role: bureaucratic, professional and clinical. In an attempt to ease their entry into the health care system, five social work administrators, employed by the largest HMO in Israel, structured and facilitated an off-site orientation program for new workers. A core group of 22 social workers participated in the program, and in the final session, the participants evaluated the course verbally and in an anonymous closed questionnaire. Feedback was mixed and included the participants dissatisfaction with the reduction of the experiential component of the sessions.
Inherited prion diseases are linked to autosomal dominant mutations in the gene that encodes the prion protein (PrP). These mutations are thought to induce PrP to undergo a conformational alteration that converts it to a pathogenic form designated PrP(Sc). In patients who are heterozygous for PrP mutations, the protein encoded by the wild-type allele might influence the conversion of the mutant protein to the PrP(Sc) state, and might itself be converted into PrP(Sc). To test these possibilities, we have constructed stably transfected lines of CHO cells that express both wild-type mouse PrP and mouse PrP carrying an insertional mutation that is homologous to one associated with familial Creutzfeldt-Jakob disease. We find that wild-type PrP in these cells does not acquire any of four different biochemical properties characteristic of PrP(Sc) that we have previously documented in mutant PrPs expressed in CHO cells. We also observe that conversion of the mutant protein to a PrP(Sc)-like state is not impaired by coexpression of the wild-type protein. These results are consistent with the idea that sequence homology between PrP molecules has an important influence on PrP(Sc) generation, and they provide insight into the metabolism of PrP in patients who are heterozygous at the PrP locus.
The conformational conversion of the prion protein, a sialoglycoprotein containing two N-linked oligosaccharide chains, from its normal form (PrPC) to a pathogenic form (PrPSc) is the central causative event in prion diseases. Although PrPSc can be generated in the absence of glycosylation, there is evidence that oligosaccharide chains may modulate the efficiency of the conversion process, and may also serve as molecular markers of diverse prion strains. In addition, mutational inactivation of one of the N-glycosylation sites has recently been associated with a familial spongiform encephalopathy. To investigate the role of N-glycans in determining the properties of PrP, we have expressed in transfected Chinese hamster ovary cells mouse PrP molecules in which N-glycosylation has been blocked either by treatment with the drug tunicamycin, or by substitution of alanine for threonine at one or both of the N-X-T consensus sites. We report that PrP molecules mutated at Thr182 alone or at both Thr182 and Thr198 [corrected] fail to reach the cell surface after synthesis, but that those mutated at Thr198 [corrected] or synthesized in the presence of tunicamycin can be detected on the plasma membrane. We also find that all three mutant PrPs, and to a limited extent wild-type PrP synthesized in the presence of inhibitor, acquire biochemical attributes reminiscent of PrPSc. We suggest that the PrP molecule has an intrinsic tendency to acquire some PrPSc-like properties, and that N-glycan chains protect against this change. However, pathogenic mutations, or presumably contact with exogenous prions, are necessary to fully convert the protein to a PrPSc state.
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Mutations in genes encoding presenilin 1 and presenilin 2 account for the majority of cases of early-onset familial Alzheimer's disease. The presenilins have been localized to the endoplasmic reticulum and Golgi, but which of the multiple hydrophobic segments of the polypeptide chain span the lipid bilayer is unclear. To address this question, we have constructed a series of chimeric molecules in which a topologically neutral reporter protein (a C-terminal fragment of prolactin) containing three artificial glycosylation sites is fused to presenilin 1 following each of the 10 potential transmembrane domains identified in hydrophobicity plots. We have expressed these chimeras by translation in reticulocyte lysate containing canine pancreatic microsomes and by synthesis in transfected COS cells. Based on utilization of the glycosylation sites and sensitivity of the reporter to protease digestion, we provide evidence that presenilin 1 has six transmembrane segments with the N and C termini in the cytoplasm. This model provides important clues to the potential functions of different parts of the presenilin molecule and how these might relate to the pathogenesis of Alzheimer's disease.
The central causative event in infectious, familial, and sporadic forms of prion disease is thought to be a conformational change that converts the cellular isoform of the prion protein (PrPC) into the scrapie isoform (PrPSc) that is the primary constituent of infectious prion particles. To provide a model system for analyzing the mechanistic details of this critical transformation, we have previously prepared cultured Chinese hamster ovary cells that stably express mouse PrP molecules carrying mutations homologous to those seen in familial prion diseases of humans. In the present work, we have analyzed the kinetics with which a PrP molecule containing an insertional mutation associated with Creutzfeldt-Jakob disease acquires several biochemical properties characteristic of PrPSc. Within 10 min of pulse labeling, the mutant protein undergoes a molecular alteration that is detectable by a change in Triton X-114 phase partitioning and phenyl-Sepharose binding. After 30 min of labeling, a detergent-insoluble and protease-sensitive form of the protein appears. After a chase period of several hours, the protein becomes protease-resistant. Incubation of cells at 18 degrees C or treatment with brefeldin A inhibits acquisition of detergent insolubility and protease resistance but does not affect Triton X-114 partitioning and phenyl-Sepharose binding. Our results support a model in which conversion of mutant PrPs to a PrPSc-like state proceeds in a stepwise fashion via a series of identifiable biochemical intermediates, with the earliest step occurring during or very soon after synthesis of the polypeptide in the endoplasmic reticulum.
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Prion diseases are a group of fatal neurodegenerative disorders that are unique in being infectious, genetic, and sporadic in origin. Infectious cases are caused by prions, which are composed primarily of PrPSc, a posttranslationally modified isoform of the normal cellular prion protein PrPC. Inherited cases are linked to insertional or point mutations in the host gene encoding PrPC. To investigate the molecular mechanisms underlying inherited prion diseases, we have constructed stably transfected Chinese hamster ovary cells that express mouse PrPs homologous to two human PrPs associated with familial Creutzfeldt-Jakob disease. One mouse PrP molecule carries a Glu-->Lys substitution at codon 199, and the other carries an insertion of six additional octapeptide repeats between codons 51 and 90. We find that both of these mutant PrPs display several biochemical hallmarks of PrPSc when synthesized in cell culture. Unlike wild-type PrP, the mutant proteins are detergent insoluble and are relatively resistant to digestion by proteinase K, yielding an N-terminally truncated core fragment of 27-30 kDa. Pulse-chase labeling experiments demonstrate that these properties are acquired posttranslationally, and are accompanied by increased metabolic stability of the protein. Our results provide the first evidence that a molecule with properties reminiscent of PrPSc can be generated de novo in cultured cells.
Prion diseases are unusual neurodegenerative disorders that can be both infectious and inherited. Both forms are hypothesized to result from a posttranslational structural alteration in the cell surface glycoprotein PrPc (cellular isoform of the prion protein) that converts it into the protease-resistant isoform PrPSc (scrapie isoform of the prion protein). However, a direct comparison of molecular events underlying these two manifestations of prion diseases has not been possible, because there has been no cell culture model for the familial forms. We report here that when mutant prion proteins associated with three different inherited prion disorders of humans are expressed as their murine homologues in cultured Chinese hamster ovary cells, the proteins are protease-resistant and detergent-insoluble, two biochemical properties characteristic of infectious PrPSc. In addition, each mutant protein remains tightly associated with the plasma membrane after enzymatic cleavage of its glycosylphosphatidylinositol anchor, a property that we now show is also typical of infectious PrPSc. The cell culture system described here is the first in vitro model for familial prion diseases and provides compelling evidence that infectious and genetic cases share common molecular features.
The prognosis of operated patients with non-small cell lung cancer (NSCLC) is poor despite thorough pre-operative staging. An improved preselection is needed of patients likely to profit from surgery. This study was undertaken to evaluate the prognostic significance of nuclear p53 overexpression in a cohort of 247 surgically treated patients with NSCLC. It showed that the prevalence of immunohistochemically detectable p53 overexpression varied between different tumour types. p53 overexpression was equally frequent in large cell carcinoma (53 per cent) and in squamous cell carcinoma (54 per cent), but significantly less frequent in adenocarcinoma (34 per cent; P = 0.009). p53 overexpression was particularly rare in bronchioloalveolar carcinoma (positivity in 1 of 17 cases). These variations may reflect aetiological differences between the histological subtypes. p53 overexpression was also associated with high tumour grade (P = 0.0157) and the presence of lymph node metastasis (P = 0.0259), but not with advanced tumour stage. Survival analysis showed no difference in clinical outcome between p53-positive and p53-negative tumours within 101 node-positive tumours. In contrast, survival time was significantly better in p53-negative tumours than in p53-positive tumours within the group of 113 node-negative tumours (P = 0.032). Stepwise regression analysis showed that p53 overexpression is an independent prognostic factor in node-negative NSCLC.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
There is currently no effective therapy for human prion diseases. However, several polyanionic glycans, including pentosan sulfate and dextran sulfate, prolong the incubation time of scrapie in rodents, and inhibit the production of the scrapie isoform of the prion protein (PrPSc), the major component of infectious prions, in cultured neuroblastoma cells. We report here that pentosan sulfate and related compounds rapidly and dramatically reduce the amount of PrPC, the non-infectious precursor of PrPSc, present on the cell surface. This effect results primarily from the ability of these agents to stimulate endocytosis of PrPC, thereby causing a redistribution of the protein from the plasma membrane to the cell interior. Pentosan sulfate also causes a change in the ultrastructural localization of PrPC, such that a portion of the protein molecules are shifted into late endosomes and/or lysosomes. In addition, we demonstrate, using PrP-containing bacterial fusion proteins, that cultured cells express saturable and specific surface binding sites for PrP, many of which are glycosaminoglycan molecules. Our results raise the possibility that sulfated glycans inhibit prion production by altering the cellular localization of PrPC precursor, and they indicate that endogenous proteoglycans are likely to play an important role in the cellular metabolism of both PrPC and PrPSc.