Infection of endovascular stents: an uncommon but important complication.

In this review article, four cases of peripheral endovascular stent infection (including a case presented in this issue of the journal) reported in the medical literature are reported. While the actual incidence of endovascular stent infection is probably low, when it occurs it can have serious consequences. This complication may result in the death of a patient, as seen in two of the case reports. The presentation of this complication, the site of stent deployment, the treatment given and the outcome in each of these cases are discussed. Stent infection should be recognized early to avoid the high morbidity and mortality of this complication.

Duodenal obstruction in thyroid storm.

A 35-year-old, previously healthy woman, known to be thyrotoxic, was transferred from a community hospital for "acute abdomen." Abdominal pain, distention, and hyperemesis resolved with placement of nasogastric tube (NGT) and return of 2,600 mL of bilious fluid. Continued high NGT output made oral or NGT administration of antithyroid drugs impossible. We gave propylthiouracil (PTU) by retention enemas with therapeutic serum levels and sublingual saturated solution of potassium iodide (SSKI) with 70% absorption based on 24-hour free iodine urinary excretion. The patient's thyroxine (T4) and triiodothyronine (T3) radioimmunoassays were normal on hospital days 10 and 12, respectively. However, free T4 and T3 resin uptake did not normalize until hospital day 31. On hospital day 32, she tolerated removal of NGT without nausea and 4 days later was taking a regular diet. We conclude that our patient's gastrointestinal symptoms were a prominent feature of her thyrotoxicosis and that rectal PTU and sublingual SSKI are effective in administration of antithyroid drugs.

Perforation of the esophagus secondary to insertion of covered wallstent endoprostheses.

Perforation of the esophagus is a very rare complication of metallic esophageal stent insertion. Two cases are presented in which esophageal perforations were caused by the sharp ends of metallic stents impinging on the esophageal wall. In retrospect, both perforations might have been prevented by additional stent insertion.

The application of a modified nucleotide in aptamer selection: novel thrombin aptamers containing 5-(1-pentynyl)-2'-deoxyuridine.

Combinatorial libraries of nucleic acids are developing into novel sources for lead compounds in drug development. In order to diversify the pool of ss DNA sequences, we have used a modified nucleotide, 5-(1-pentynyl)-2'-deoxyuridine, in place of thymidine in a random nucleic acid library and screened this library against human thrombin. Previously, we described this screening method to identify a novel structural inhibitor (an aptamer) of the coagulation protease thrombin (Bock, L. et. al. (1992) Nature 355 564-566). Using the modified nucleic acid library, we have now isolated a second pool of thrombin inhibitors with strikingly different sequence composition compared to the selection using natural bases. This second class of aptamers is dependent on the presence of the modified nucleotide for protein binding and clotting inhibition. Our method represents a potential strategy to enhance the diversity of libraries for in vitro selection, and thereby increasing the utility of this technique in the identification of molecules with novel biochemical properties.

Rapid onset of chronic granulocytic leukaemia after treatment for Hodgkin's disease.

A 17-year-old white female presented with stage IVB Hodgkin's disease. After chemotherapy and radiotherapy she achieved a complete clinical remission and underwent an autologous bone marrow transplant (ABMT). 22 months later she developed chronic granulocytic leukaemia (CGL). Polymerase chain reaction (PCR) analysis of bone marrow harvested at the time of ABMT did not show any evidence of the bcr-abl sequence that was detectable at the diagnosis of CGL. This case provides further information on the kinetics of the development of CGL and adds to the small pool of data on CGL developing after treatment for Hodgkin's disease.

Molecular heterogeneity of variant Philadelphia translocations in childhood acute lymphoblastic leukaemia.

In acute lymphoblastic leukemia (ALL), it is unclear whether variant Philadelphia (Ph) translocations have the same molecular and clinical implications as the classical translocation. Two children with Ph+ ALL with variant translocations are described. One, in whom cytogenetic remission was not achieved, had evidence of translocation of c-abl to chromosome 22, rearrangement of minor breakpoint cluster region (mBCR) and expression of hybrid bcr/abl transcripts. In the other case, no gene rearrangement was found and complete remission was achieved. Variant Ph translocations in childhood ALL are heterogeneous at the molecular level. Molecular studies coupled with observations of clinical outcome are needed in larger numbers of such children to determine whether poor clinical response correlates with bcr/abl involvement and to allow planning of appropriate therapeutic strategies.

Selection of single-stranded DNA molecules that bind and inhibit human thrombin.

Aptamers are double-stranded DNA or single-stranded RNA molecules that bind specific molecular targets. Large randomly generated populations can be enriched in aptamers by in vitro selection and polymerase chain reaction. But so far single-stranded DNA has not been investigated for aptamer properties, nor has a target protein been considered that does not interact physiologically with nucleic acid. Here we describe the isolation of single-stranded DNA aptamers to the protease thrombin of the blood coagulation cascade and report binding affinities in the range 25-200 nM. Sequence data from 32 thrombin aptamers, selected from a pool of DNA containing 60 nucleotides of random sequence, displayed a highly conserved 14-17-base region. Several of these aptamers at nanomolar concentrations inhibited thrombin-catalysed fibrin-clot formation in vitro using either purified fibrinogen or human plasma.

The biological activity of retinoids in melanoma cells. Induction of expression of retinoic acid receptor-beta by retinoic acid in S91 melanoma cells.

The expression of mRNA for retinoic acid receptor beta (RAR-beta) was induced by all trans-retinoic acid in murine S91 melanoma cells. The induction of RAR-beta was dose-dependent, rapid and insensitive to cycloheximide. Both 13-cis-retinoic acid and 3,4-didehydro-all trans-retinoic acid also induced expression of RAR-beta but were only effective at concentrations 100-fold greater than all trans-retinoic acid. The expression of RAR-alpha and RAR-gamma was unaffected by retinoic acid.

Defining the inside and outside of a catalytic RNA molecule.

Ribozymes are RNA molecules that catalyze biochemical reactions. Fe(II)-EDTA, a solvent-based reagent which cleaves both double- and single-stranded RNA, was used to investigate the structure of the Tetrahymena ribozyme. Regions of cleavage alternate with regions of substantial protection along the entire RNA molecule. In particular, most of the catalytic core shows greatly reduced cleavage. These data constitute experimental evidence that an RNA enzyme, like a protein enzyme, has an interior and an exterior. Determination of positions where the phosphodiester backbone of the RNA is on the inside or on the outside of the molecule provides major constraints for modeling the three-dimensional structure of the Tetrahymena ribozyme. This approach should be generally informative for structured RNA molecules.

Immunohistochemical markers of human sebaceous gland differentiation.

Cryostat sections of human skin were stained with monoclonal antibodies to involucrin, a range of cytokeratins, epithelial membrane antigen (EMA), and an ovarian cystadenocarcinoma antibody (OM1) to identify combinations of antibodies that could be used to discriminate between basal and differentiated sebocytes and other cell types present in the pilosebaceous unit. Both the EMA and OM1 monoclonal antibodies specifically recognized differentiated sebocytes. No staining of basal sebocytes or other epidermal cell types was seen. Differentiated (but not basal) sebocytes were also stained by a cytokeratin 10 antibody (LH2). Conversely, the basal sebocytes were recognized by an antibody specific to basal keratinocytes (LH6). Cells of the sebaceous duct stained with both LH2 and LH6 and also with the anti-involucrin monoclonal antibody. Cytokeratin 4 has been detected in sebaceous glands by protein analysis but has not previously been detectable immunohistochemically. We show by immunofluorescence after limited proteolysis that cytokeratin 4 epitopes are distributed in all sebaceous gland cells, including the duct cells.