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Biomedical subjects

B A Levine

Publications and source records attributed to B A Levine.

At least 37 records · Page 2Linked to original sources
PubMed1996

Polyps and polypoid lesions of the jejunum and ileum. Clinical aspects.

Polyps and polypoid lesion of the small intestine present a major challenge to the surgeon. In contrast to similar lesions in the large intestine, small bowel polyps present late in their course and are difficult to diagnose. Small bowel tumors produce vague symptoms and screening tests are poor. Most of these polyps are found at autopsy or during exploration for another cause. In this article, the authors outline the problem as well as discuss the diagnosis and treatment options.

Adenomatous Polyposis Coli↗
PubMed1995

Conformational studies of osteocalcin in solution.

1H-NMR and circular dichroism studies have been carried out on osteocalcin, a 49-residue, calcium-binding protein, the sequence of which contains a disulphide bridge, a proline-rich segment and three gamma-carboxyglutamic acid (Gla) residues. These latter residues have been proposed to lie on one face of an alpha helix and interact with the mineral phase, leading to incorporation of the protein into the bone matrix. Circular dichroism shows an increase in the alpha-helical structure on Ca2+ binding to bovine osteocalcin. This induced structure is lost on heating the protein, giving a spectrum close to that of the Ca(2+)-free protein. 1H-NMR studies of rabbit osteocalcin gave a set of resonance assignments and NOEs which could be interpreted in terms of distance constraints. These did not allow a single conformation to be defined for the protein in solution but reflect rather a flexible structure which may be essential for the function of the protein. The calculated structures contain a hydrophobic core (comprising Leu2, Leu32, Val36 and Tyr42, seen to be slowly flipping in the Ca(2+)-bound form) and have the gamma-carboxyglutamic acid side chains exposed on one face of the molecule.

Amino Acid Sequence↗
PubMed1995

Sequential phosphorylation of adjacent serine residues on the N-terminal region of cardiac troponin-I: structure-activity implications of ordered phosphorylation.

We have used NMR spectroscopy to monitor the phosphorylation of a peptide corresponding to the N-terminal region of human cardiac troponin-I (residues 17-30), encompassing the two adjacent serine residues of the dual phosphorylation site. An ordered incorporation of phosphate catalysed by PKA was observed, with phosphorylation of Ser-24 preceding that of Ser-23. Diphosphorylation induced a conformational transition in this region, involving the specific association of the Arg-22 and Ser-24P side-chains, and maximally stabilised when both phosphoserines were in the di-anionic form. The results suggest that the second phosphorylation at Ser-23 of cardiac troponin-I is of particular significance in the mechanism by which adrenaline regulates the calcium sensitivity of the myofibrillar actomyosin Mg-ATPase.

Amino Acid Sequence↗
PubMed1995

The binding of distinct segments of actin to multiple sites in the C-terminus of caldesmon: comparative aspects of actin interaction with troponin-I and caldesmon.

Thin-filament-based regulation of the contractile response is considered to involve the interaction of actin with troponin-I in striated muscle and the interaction of actin with caldesmon in smooth muscle. The nature of the interaction with actin of these inhibitory proteins has been studied by proton magnetic resonance spectroscopy using segments of caldesmon and troponin-I which mimic their functional properties. Caldesmon is shown to interact with two distinct sites on the N-terminal residues 1-44 of actin subdomain 1 with corresponding contacts on caldesmon domain 3 and domain 4 at its C-terminus. We demonstrate that, whereas inhibition by the troponin-I fragment (residues 96-117) is effected by its interaction with the N-terminal region of actin, the separate inhibitory ability of different regions of the C-terminus of caldesmon (domains 4a and 4b) is mediated by interaction with noncontiguous segments on subdomain 1 of actin. Our studies of the spatial relationship of these actin contacts on caldesmon further suggest that one molecule of caldesmon may associate with two actin monomers. The demonstrated interactive nature of these caldesmon attachments to distinct regions of actin is relevant to the mechanism of calcium modulation of inhibition of actomyosin ATPase by caldesmon.

Actins↗
PubMed1995

Vocal cord injection in children with unilateral vocal cord paralysis.

Unilateral vocal cord paralysis (UVCP) in children is uncommon and rarely leads to serious sequelae. However, on rare occasions, it can present with severe aspiration and dysphonia. Several therapeutic techniques have been used in adults with UVCP, but the reported alternatives in children have been much more limited. Observation and speech therapy are the standard treatment. We describe three children with UVCP and severe aspiration who were treated with vocal cord injection. The treatment indications, clinical courses, and outcomes of the three cases are detailed. The injection of vocal cords in children is discussed, with an emphasis on those aspects unique to the management of UVCP in pediatric patients. Alternative surgical treatment modalities are also presented. Vocal cord injection is an effective and viable therapeutic option for the management of UVCP in certain pediatric patients with severe aspiration and dysphonia.

Bronchiolitis↗
PubMed1995

Phase II trial of chemotherapy, external and intraluminal radiation plus surgery for oesophageal cancer.

A pilot study was performed to assess the feasibility of combining 5-fluorouracil, recombinant alpha-2b-interferon, external radiation therapy and intraluminal high dose rate brachytherapy with surgery in patients with locally advanced esophageal carcinoma. 5-fluorouracil, 750 mg m-2, was administered via continuous 5-day infusion beginning day 1 and weekly thereafter; interferon, 10 mu subcutaneously, was administered three times per week beginning day 1 and sargramostin, 5 micrograms kg-1, was administered on days without 5-fluorouracil. External radiation began on day one using 1.5 daily fractions to 55.5 Gy. Intraluminal brachytherapy was delivered concomitantly once each week for 5 fractions of 4 Gy. None of the first eight patients went to surgery. The external radiation was changed to 1.5 Gy BID to 45 Gy followed by BID intraluminal radiation to 15 Gy. Of the last four patients, there was one case of radiation myelitis. It was found that successful surgery was not possible and excessive toxicities, including radiation myelitis, occurred with this aggressive regimen.

Aged↗
PubMed1995

Initial experience with transluminally placed endovascular grafts for the treatment of complex vascular lesions.

OBJECTIVES: Complex arterial occlusive, traumatic, and aneurysmal lesions may be difficult or impossible to treat successfully by standard surgical techniques when severe medical or surgical comorbidities exist. The authors describe a single center's experience over a 2 1/2-year period with 96 endovascular graft procedures performed to treat 100 arterial lesions in 92 patients. PATIENTS AND METHODS: Thirty-three patients had 36 large aortic and/or peripheral artery aneurysms, 48 had 53 multilevel limb-threatening aortoiliac and/or femoropopliteal occlusive lesions, and 11 had traumatic arterial injuries (false aneurysms and arteriovenous fistulas). Endovascular grafts were placed through remote arteriotomies under local (16[17%]), epidural (42[43%]), or general (38[40%]) anesthesia. RESULTS: Technical and clinical successes were achieved in 91% of the patients with aneurysms, 91% with occlusive lesions, and 100% with traumatic arterial lesions. These patients and grafts have been followed from 1 to 30 months (mean, 13 months). The primary and secondary patency rates at 18 months for aortoiliac occlusions were 77% and 95%, respectively. The 18-month limb salvage rate was 98%. Immediately after aortic aneurysm exclusion, a total of 6 (33%) perigraft channels were detected; 3 of these closed within 8 weeks. Endovascular stented graft procedures were associated with a 10% major and a 14% minor complication rate. The overall 30-day mortality rate for this entire series was 6%. CONCLUSIONS: This initial experience with endovascular graft repair of complex arterial lesions justifies further use and careful evaluation of this technique for major arterial reconstruction.

Adolescent↗
PubMed1994

Structural determinants of substrate selection by the human insulin-receptor protein-tyrosine kinase.

Using NMR spectroscopy to visualise tyrosine phosphorylation kinetics in real time, we have investigated the sequence-dependent determinants of the selectivity of the human insulin receptor protein-tyrosine kinase for different tyrosine residues. The peptides used encompass the multiple-tyrosine-containing autophosphorylation site sequences from the insulin receptor kinase core domain (Tyr1158, Tyr1162 and Tyr1163) and from its specific C-terminal tail domain (Tyr1328 and Tyr1334). Comparison of the phosphorylation kinetics with those found for the tyrosine residues on a peptide comprising the regulatory tyrosine phosphorylation site of cdc2 points to the role of the primary sequence context of the phosphate acceptor. The particularly deleterious influence of a basic residue immediately C-terminal to the tyrosine is discussed in relation to the autophosphorylation properties of the regulatory loop regions of the insulin and epidermal growth factor receptor kinases. The data further suggest that receptor tyrosine kinase active sites and their substrate targets act in concert to ensure that specific downstream effects are activated.

Amino Acid Sequence↗
PubMed1994

Anti-CD38-blocked ricin: an immunotoxin for the treatment of multiple myeloma.

We report the development of a potent anti-CD38 immunotoxin capable of killing human myeloma and lymphoma cell lines. The immunotoxin is composed of an anti-CD38 antibody HB7 conjugated to a chemically modified ricin molecule wherein the binding sites of the B chain have been blocked by covalent attachment of affinity ligands (blocked ricin). Conjugation of blocked ricin to the HB7 antibody has minimal effect on the apparent affinity of the antibody and no effect on the ribosome-inactivating activity of the ricin A-chain moiety. Four to six logs of CD38+ tumor cell line kill was achieved at concentrations of HB7-blocked ricin in the range of 0.1 to 3 nmol/L. Low level of toxicity for normal bone marrow (BM) granulocyte-macrophage colony-forming units (CFU-GM), burst-forming units-erythroid (BFU-E), colony-forming units-granulocyte/erythroid/monocyte/macrophage (CFU-GEMM) cells was observed. Greater than two logs of CD38+ multiple myeloma cells were depleted from a 10-fold excess of normal BM mononuclear cells (BMMCs) after an exposure to HB7-blocked ricin under conditions (0.3 nmol/L) that were not very toxic for the normal BM precursors. HB7-blocked ricin was tested for its ability to inhibit protein synthesis in fresh patients' multiple myeloma cells and in normal BMMCs isolated from two healthy volunteers; tumor cells from four of five patients were 100-fold to 500-fold more sensitive to the inhibitory effect of HB7-blocked ricin than the normal BM cells. HB7 antibody does not activate normal resting peripheral blood lymphocytes, and HB7-blocked ricin is not cytotoxic toward these cells at concentrations of up to 1 nmol/L. The potent killing of antigen-bearing tumor cells coupled with a lack of effects on peripheral blood T cells or on hematopoietic progenitor cells suggests that HB7-blocked ricin may have clinical utility for the in vivo or in vitro purging of human multiple myeloma cells.

ADP-ribosyl Cyclase↗
PubMed1994

Phosphorylation effects on flanking charged residues. Structural implications for signal transduction in protein kinases.

1H-NMR and 31P-NMR spectroscopy were employed to assess the electrostatic consequences of phosphorylation of single and multiple tyrosine residues in peptides derived from the core and tail autophosphorylation regions of the human insulin receptor tyrosine-kinase domain. In both peptides, phosphorylation was accompanied by changes in the resonances from basic side-chains; those from acidic residues were unaffected. Tyrosine phosphorylation caused increases of up to one in the pKa values of histidine residues situated up to eight residues away in the primary sequence. Titration curve analysis by Hill plots suggested some cooperativity of histidine and phosphate ionizations. Behaviour closely analogous to that of the insulin receptor tail peptide was observed during changes in phosphorylation of the intact insulin receptor kinase domain, suggesting that the electrostatic dissemination effects seen for the isolated peptide are retained by the peptide sequence in the context of the much larger protein. Similar changes in the behaviour of basic residues were also observed upon tyrosine phosphorylation of a cdc2-derived peptide, suggesting that this potential of phosphorylation events to propagate directed structural changes may find a widespread utility in the activation of protein kinases and in the transduction of phosphorylation-based signalling.

Amino Acid Sequence↗
PubMed1994

Lipid mediator production in acute and chronic pancreatitis in the rat.

Pancreatic production of lipid mediators of inflammation, including eicosanoids and platelet-activating factor (PAF), was examined in two models of pancreatitis in the rat. Chronic pancreatitis was induced by ligation of the pancreatic duct and acute pancreatitis by infusion of sodium taurocholate into the pancreatic duct. In the model of chronic pancreatitis, prostaglandin E2 (PGE2), PGD2, 6-keto PGF1 alpha, thromboxane B2 (TXB2), and PAF increased significantly in the pancreas in a similar fashion, whereas leukotriene B4 (LTB4) remained unchanged. BN52021, a PAF antagonist, reduced the accumulation of pancreatic TXB2, 6-keto PGF1 alpha, and PGD2, and did not affect PGE2. In the model of acute pancreatitis, LTB4 increased, whereas PGE2, TXB2, and 6-keto PGF1 alpha decreased significantly; PGD2 changed slightly; and PAF was undetectable. The present results indicate that mild chronic pancreatitis is accompanied by the production and accumulation of a wide spectrum of lipid mediators while LTB4 was the only lipid mediator detected at biologically active concentrations in the model of severe acute pancreatitis. It is suggested that various mediators are involved in establishing a balance between inflammation and the repair of the inflamed pancreatic tissue observed in mild chronic pancreatitis. While both eicosanoids and PAF are involved in such self-limiting responses to inflammatory challenge, PAF seems to play a central role in instigating the production of the various other mediators detected in the model of chronic pancreatitis. In the model of acute pancreatitis while the deficiency of various lipid mediators may render the pancreatic tissue more susceptible to acute damage, enhanced LTB4 appears to contribute to the destructive pathology observed.(ABSTRACT TRUNCATED AT 250 WORDS)

6-Ketoprostaglandin F1 alpha↗
PubMed1993

Anti-B4-blocked ricin immunotoxin shows therapeutic efficacy in four different SCID mouse tumor models.

Anti-CD19 monoclonal antibody anti-B4 (IgG1) conjugated to the novel toxin-blocked ricin forms a potent immunotoxin, anti-B4-blocked ricin, that kills greater than 4.5 logs of CD19-positive cells in vitro after a 24-h exposure to a conjugate concentration of 5 x 10(-9) M (1.11 micrograms/ml). The efficacy of anti-B4-blocked ricin in vivo was assessed in survival models of SCID mice bearing either a human B-cell lymphoma (Namalwa), a human non-T and non-B acute lymphoblastic leukemia (Nalm-6), or a murine B-cell lymphoma transfected with the human CD19 gene (300B4). In one model, 5 x 10(7) tumor cells were injected i.p., and 1 h later the mice were treated with i.v. bolus injections of anti-B4-blocked ricin at 100 micrograms/kg/day for 5 days. Controls included similar treatment with anti-B4 antibody (72 micrograms/kg/day or 2 mg/kg/day for 5 days) alone or with the isotype-matched nonspecific immunotoxin, N901-blocked ricin (100 micrograms/kg/day). In a second model, 4 x 10(6) tumor cells were injected i.v., and 7 days later mice were treated i.v. as above. Anti-B4-blocked ricin showed efficacy by killing in vivo up to 3 logs of tumor cells, which was manifested in significant prolongation of the life of the treated animals. Only very limited or no effects were observed in animals treated with either anti-B4 antibody alone or N901-blocked ricin control conjugate. The concentration of anti-B4-blocked ricin in the blood of animals was 150 ng/ml after the first i.v. injection and about 800 ng/ml following the fifth injection of conjugate. This increase may be due to damage to the reticuloendothelial system by anti-B4-blocked ricin, since the rate of clearance of carbon from blood also decreased 5-fold after five injections as compared to the rate after only one injection. These studies indicate that anti-B4-blocked ricin has the potential to increase survival times of hosts with malignant disease.

Animals↗
PubMed1993

Platelet-activating factor: a mediator of pancreatic inflammation during cerulein hyperstimulation.

Hyperstimulation of the exocrine pancreas with cerulein causes acute pancreatitis, characterized by intensive interstitial edema, acinar vacuolization, leukocytic infiltration, and hyperamylasemia. Whereas the pathogenesis of cerulein-induced pancreatitis is not well-defined, a local inflammatory response may contribute to the full expression of acute pancreatitis. Platelet-activating factor (PAF) seems to be an important mediator of the inflammatory response. The present evidence includes: 1) pancreatic PAF levels increased in rats in which cerulein-induced pancreatitis was initiated, concomitant with an increase in calcium concentrations in the pancreatic tissue; 2) treatment of rats exposed to cerulein with WEB2170, a PAF receptor antagonist, was shown to reduce inflammatory injury, as demonstrated by decreases in pancreatic weight, Evan's blue extravasation, and myeloperoxidase activity and an improvement in pancreatic histology. In an idealized in vitro experiment mimicking cerulein-induced acute pancreatitis, in which pancreatic acini were employed, cerulein induced amylase release, an increase in [Ca2+]i, and an increase in PAF synthesis. Whereas amylase release was induced by low concentrations of cerulein (10(-11) mol/L), relatively high concentrations of cerulein (10(-9) mol/L) were required for the observed increases in PAF synthesis and the [Ca2+]i, indicating that these two responses may not occur under physiological conditions. The present study suggests that the pancreatic accumulation of PAF coupled with Ca2+ overload are important biochemical components of the pathophysiology of cerulein-induced acute pancreatitis. In fact, PAF production may serve as a primary mediator of inflammation observed during pancreatic hyperstimulation. This is an important observation that will allow a more detailed characterization of the molecular basis of cerulein-induced acute pancreatitis.

Animals↗