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S Swenson

Publications and source records attributed to S Swenson.

18 recordsLinked to original sources
PubMed2005

Snake venom fibrin(ogen)olytic enzymes.

Snake venoms contain a number of serine and metalloproteinases and included among these are the fibrin(ogen)olytic proteinases. Some years ago it was postulated that the fibrin(ogen)olytic enzymes may be clinically useful. Over the past 150 years a substantial body of literature has been generated on the identification and characterization of fibrin(ogen)olytic enzymes from a broad spectrum of snake species. In this review we describe the two different classes of fibrin(ogen)olytic enzymes isolated from snake venom and we summarize a number of studies aimed at characterizing the purified enzymes and/or their derivatives. Two distinct classes of venom fibrin(ogen)olytic enzymes have been previously identified, the metalloproteinases and serine proteinases. These two classes of proteinases differ in their mechanism of action and they target different amino acid sequences in fibrin(ogen), but each perform the same role in nature. When a snake envenomates its prey it needs a mechanism to facilitate the spread of the toxic components throughout the circulation. Fibrin(ogen)olytic enzymes break down fibrin rich clots and help to prevent further clot formation by their action on fibrinogen. This characteristic feature has led to development of fibrin(ogen)olytic snake venom enzymes as potential clinical agents to treat occlusive thrombi. Fibrolase, a fibrinolytic metalloproteinase isolated from Agkistrodon contortrix contortrix venom and the serine beta-fibrinogenolytic proteinase from Vipera lebetina have been chosen as representative enzymes from the two classes, and their biochemical and physiochemical properties will be described in detail. Finally, the characterization and development of alfimeprase, a recombinant fibrinolytic enzyme derived from fibrolase, as a clinical agent is described citing the progression from the laboratory bench to its current status as having successfully completed Phase II clinical trials.

Amino Acid Sequence↗
PubMed2004

Alpha-fibrinogenases.

Snake venoms contain a number of serine and metalloproteinases, included among these are the fibrinolytic metalloproteinases. When the fibrinolytic enzymes were first isolated from viper venoms it was postulated that there may be a clinical application for these enzymes in the treatment of occlusive thrombi, such as those occurring in the great arteries and veins of cardiac and cerebral circulation as well as peripheral arteries and veins. In the ensuing years a substantial body of literature has been generated on the identification and characterization of the fibrinolytic enzymes from a broad spectrum of snake species. In this report we describe the biological properties and positive clinical features of the class of enzymes known as alpha-fibrinogenases. Fibrolase, a fibrinolytic metalloproteinase originally isolated from Agkistrodon contortrix contortrix venom, is the representative fibrinolytic enzyme used for the description and characterization of the alpha-fibrinogenases in this chapter. The biochemical and physiochemical properties and in vivo activity of the enzyme are described as well as in vitro studies using a platelet avid chimera of fibrolase. The chimera was formed by coupling fibrolase to an Arg-Gly-Asp (RGD) like peptide imparting inhibitory activity on platelet aggregation and thrombus formation, while maintaining full fibrinolytic activity. Fibrolase has also been modified through the adduction of polyethylene glycol to reduce the rate of clearance from the circulation. In this review we also include a description of alfimeprase, a recombinant fibrinolytic enzyme derived from fibrolase, and follow the development of the enzyme as a potential clinical agent in the clearance of occlusive thrombi. Alfimeprase is presently in clinical trials for two indications: the treatment of peripheral arterial occlusions (in which phase II is nearing successful completion), and for use in the clearance of occluded vascular access catheters in direct competition with plasminogen activators.

Agkistrodon↗
PubMed2001

Three-dimensional structure of fibrolase, the fibrinolytic enzyme from southern copperhead venom, modeled from the X-ray structure of adamalysin II and atrolysin C.

The fibrinolytic enzyme from southern copperhead snake venom, fibrolase, contains 1 mole of zinc per mole of protein, belongs to the major family of metalloproteinases known as the metzincins, and has been shown to degrade fibrin clots in vitro and in vivo. The purpose of this study was to develop a 3-dimensional model of fibrolase to investigate the geometry of conserved and variable sequences between members of the snake venom metalloproteinases. When compared to atrolysin C (form D) or adamalysin II (metzincins with completely different substrate specificity), fibrolase has approximately 60% overall sequence identity and nearly 100% sequence similarity in the active site. We used the crystal structure of adamalysin II to build a 3-dimensional homology model of fibrolase. Three disulfide bonds were constructed (the highly conserved disulfide bond [118-198] was maintained from the adamalysin II structure and 2 new disulfide bonds were introduced between residues 158-182 and 160-165). We used Sculpt 2.5 and HyperChem 5.0 to "dock" a substrate fragment octapeptide (HTEKLVTS), and a water molecule into the active site cleft. We calculated the differential average homology profile for fibrolase compared to 8 hemorrhagic and 5 nonhemorrhagic metzincins. We then determined the sequence regions that might be responsible for their substrate specificity. Our 3-dimensional homology model shows that the variable sequences lie on the periphery of the identified active site region containing the His triangle; this indicates that substrate specificity may depend on surface residues that are not directly associated with the active site.

Agkistrodon↗
PubMed2000

Chimeric derivative of fibrolase, a fibrinolytic enzyme from southern copperhead venom, possesses inhibitory activity on platelet aggregation.

Fibrolase, a metalloproteinase isolated from the venom of Agkistrodon contortrix contortrix (southern copperhead snake), is a direct acting fibrinolytic enzyme that has been used to digest occlusive blood clots in animal models. The snake venom enzyme directly degrades fibrin associated with platelet rich blood clots and does not rely on plasminogen activation. Rethrombosis is a serious complication that is experienced in a significant percentage of patients treated with thrombolytic agents to remove occlusive vascular thrombi. The involvement of platelets in the initiation of rethrombosis is well known. Arg-Gly-Asp-(RGD)-containing agents have been shown to inhibit rethrombosis following thrombus dissolution by plasminogen activators. In an effort to create a more effective fibrinolytic enzyme and to target the enzyme to platelet-rich thrombi, thereby decreasing the potential for rethrombosis, a chimeric derivative of fibrolase has been produced. This report describes the construction and biochemical characterization of the chimeric enzyme and an evaluation of its in vitro activities. The chimera was formed by covalently incorporating an RGD-like peptide into fibrolase. The site of peptide attachment was determined to be a single lysine residue remote from the enzymes active site. Covalent modification of fibrolase with the RGD-like peptide did not inhibit either fibrinolytic activity of the enzyme nor platelet aggregation inhibitory activity of the peptide. The chimera not only retained the same level of enzymatic activity as native fibrolase, but also acquired the ability to inhibit platelet aggregation by binding to the fibrinogen receptor (integrin alphaIIbbeta3) on platelets.

Agkistrodon↗
PubMed1999

Thymidylate synthase inhibitors.

Thymidylate synthase (TS) is a critical enzyme for DNA replication and cell growth because it is the only de novo source of thymine nucleotide precursors for DNA synthesis. TS is the primary target of 5-fluorouracil (5-FU), which has been used for cancer treatment for more than 40 years. However, dissatisfaction with the overall activity of 5-FU against the major cancers, and the recognition that TS still remains an attractive target for anticancer drugs because of its central position in the pathway of DNA synthesis, led to a search for new inhibitors of TS structurally analogous to 5,10-methylenetetrahydrofolate, the second substrate of TS. TS inhibitory antifolates developed to date that are in various stages of clinical evaluation are ZD 1694 and ZD9331 (Astra-Zeneca, London, UK), (Eli Lilly, Indianapolis, IN), LY231514 (BW1843U89 (Glaxo-Wellcome, Research Triangle Park, NC), and AG337 and AG331 (Agouron, La Jolla, CA). Although each of these compounds has TS as its major intracellular site of action, they differ in propensity for polyglutamylation and for transport by the reduced folate carrier. LY231514 also has secondary target enzymes. As a result, each compound is likely to have a different spectrum of antitumor activity and toxicity. This review will summarize the development and properties of this new class of TS inhibitors.

Animals↗
PubMed1997

Chimeric fibrolase: covalent attachment of an RGD-like peptide to create a potentially more effective thrombolytic agent.

We have prepared an agent possessing both thrombolytic and antiplatelet properties, by conjugating fibrolase, a direct-acting fibrinolytic enzyme isolated from southern copperhead venom, to a peptide which inhibits platelet aggregation. Heterobifunctional coupling reagents, N-succinimidyl 3-(2-pyridyldithio) propionate (SPDP) or sulfosuccinimidyl 6-[alpha-methyl-alpha-(2-pyridyldithio)-toluamido]hexanoate (Sulfo-LC-SMPT), were used in a molar ratio of 10:1 (coupling agent/fibrolase). The N-hydroxy-succinimide of the coupling agent reacts with surface epsilon-amino groups of lysine residues on fibrolase and provides a dithio group that is highly reactive with small thiol compounds. The derivatives obtained in the first reaction contain approximately two moles of 2-pyridyl disulphide per mole of enzyme. These derivatives were then reacted with the free thiol group in an antiplatelet peptide at a molar ratio of 2:1 (peptide/fibrolase). The peptide-fibrolase conjugate was purified by cation exchange HPLC and analyzed by amino acid analysis. The conjugate contains one mole peptide per mole of fibrolase and retains approximately 85% fibrinolytic activity. The IC50 for inhibition of platelet aggregation in human PRP is 300 nM for the conjugate and 67 nM for the antiplatelet peptide. These results demonstrate the successful formation of a novel chimeric protein with bifunctional activity.

Animals↗
PubMed1996

Associations of individual genomic heterozygosity, estimated by molecular fingerprinting, and of dam major histocompatibility complex with growth and egg production traits in layer chickens.

Growth and egg production data from F2 layer chickens produced from a mating of MHC-heterozygous B15B44 sires to B15B44 and B15B43 dams were analyzed for associations with the level of the individual's genomic heterozygosity and dam MHC. The F1 sires and dams were produced from mating of birds from two genetically distinct, highly inbred lines. Genomic heterozygosity (expressed as composite band frequency, CBF) was estimated based on the average proportion of shared bands of individual birds compared to a composite pool of Hinf I-digested DNA samples from the two inbred lines. Birds from dams of genotype B15B43 had significantly greater BW than progeny from B15B44 dams at 6 wk and thereafter. Dam MHC genotype differences were also significant for number of eggs laid from 20 to 28 wk of age, with B15B43 progeny being superior. Negative regression coefficients at hatch, 32 and 44 wk were observed for the effect of CBF on BW of progeny from B15B43 dams and at hatch and 32 wk from progeny of pooled dam genotypes. Similarly, negative regression coefficients were observed for the association of CBF with number of eggs within progeny from the B15B44 dam MHC genotypes at 20 to 28 wk and total period recorded, and at 28 to 36 wk for progeny from B15B43 dams. The CBF regression coefficients and the differences among progeny based on dam MHC genotypes suggest that individual heterozygosity and MHC genotype may be associated with BW and egg production in chickens.

Animals↗
PubMed1993

Direct observation of UV-crosslinked protein-nucleic acid complexes by matrix-assisted laser desorption ionization mass spectrometry.

Interactions between proteins and nucleic acids are important in the fundamental cellular processes that drive replication, recombination, dynamic alteration and repair of DNA, transcription and processing of RNA, synthesis of proteins, and regulation of enzyme activities. As part of an effort to develop a general, sensitive mass spectrometric strategy for the characterization of protein-nucleic acid interactions, we have used matrix-assisted laser desorption-ionization (MALDI) time-of-flight mass spectrometry to analyze protein-nucleic acid complexes that have been covalently crosslinked by ultraviolet (UV) light. In general, the application of MALDI mass spectrometric techniques to studies of UV-induced crosslinking of nucleoprotein complexes is demonstrated to be feasible. Specifically, MALDI mass analysis was used to determine the molecular weights of the phage T4 gene 32 protein (gp32) crosslinked to the oligonucleotide (dT)20, and the Escherichia coli transcription termination factor rho, photoaffinity labeled with 4-thio-uridine-diphosphate (4sUDP). The covalent gp32:(dT)20 complex is readily detected at a concentration of 1-2 microM in 1 microL of an unpurified solution of reactants that has been exposed to a single, 266 nm UV laser pulse. Mass spectrometric molecular weight determinations of the covalent rho:4sUDP complex add directness and specificity to the ATPase inactivation assay normally used to monitor the formation of 4sUDP photoaffinity labeled rho. It is found that successful MALDI mass spectrometry of protein-nucleic acid complexes is as critically dependent on the choice of solvents and additives as it is on the primary matrix compound.

Mass Spectrometry↗
PubMed1991

Serologic distinction between human T-lymphotropic virus (HTLV) type I and HTLV type II.

In November 1988, the Food and Drug Administration approved reagents for serologic screening for human T-lymphotropic virus type I (HTLV-I) infection in blood donors and patients suspected of having HTLV-I-related illnesses. These reagents are able to detect HTLV type II (HTLV-II), a close relative of HTLV-I with no known pathologic effect. The distinction between the two forms of HTLV is important to the donor and to any recipient of blood containing HTLV. The application to sera from 38 seropositive blood donors and 2 recipients (37 "confirmed" positive and 3 indeterminate by Western blot) of two methods (Western blot and peptide enzyme immunoassay) for serologic distinction between HTLV-I and -II is described. These results were compared to those from polymerase chain reaction (PCR) analysis of HTLV proviral DNA obtained from donor peripheral blood mononuclear cells. The peptide enzyme immunoassay was found to be less sensitive than the Western blot, but completely concordant with PCR results when differential reactivity could be established. The Western blot pattern showed complete diagnostic concordance with the samples with confirmed-positive serologic tests, but was incorrect in two HTLV-II-infected donors with indeterminate serologic tests. Thirty-three (89%) of the 37 individuals from this predominantly Native American and Hispanic group of blood donors were found to have HTLV-II. These findings confirm and extend previous reports that HTLV-I infection may be less common, and HTLV-II infection more common, than previously believed. The peptide enzyme immunoassay can provide most individuals who have positive results with the HTLV-I/II screening test with serologic distinction between HTLV-I and HTLV-II.

Blood Donors↗
PubMed1991

Incidence of hairy cell leukemia, mycosis fungoides, and chronic lymphocytic leukemia in first known HTLV-II-endemic population.

Unlike human T cell leukemia-lymphoma virus type I (HTLV-I), HTLV-II has not been convincingly linked to a malignancy. In the first 10 months of serologic screening for HTLV-I/II among blood donors in New Mexico in 1988-1989, HTLV-I/II infection was found in 27 donors. HTLV-I/II infection was present in 1.0%-1.6% of American Indian and 0.16%-0.27% of Hispanic donors compared with 0.009%-0.06% of non-Hispanic white donors. HTLV-II was identified by DNA amplification in 12 of 13 samples from Indian and Hispanic seropositive donors. Despite apparent endemic HTLV-II infection in these populations, New Mexico Tumor Registry data showed that the incidences of hairy cell leukemia, mycosis fungoides, and chronic lymphocytic leukemia were comparable among the three ethnic groups. A population with endemic HTLV-II infection has been identified, and there is no evidence of increased risk for these three malignancies in the endemic groups.

Blood Donors↗
PubMed1991

Prediction of steady-state plasma levels of doxepin and imipramine from single dose levels in depressed outpatients.

We have investigated the predictive value of single dose levels for steady state levels of two commonly used antidepressants, doxepin (DOX) and imipramine (IMI) in a population of 40 outpatients with unipolar depression. After a wash-out period, patients were given 75 mg of either doxepin or imipramine and blood samples were drawn 16 h after the dose. Treatment was continued for 2 weeks on a fixed 100 mg/day dose and after that the dose was adjusted according to patients' response. Drugs and their demethylated metabolites were determined weekly using a GC technique. There was a large (more than 5-fold) inter-individual variation in both the single dose and steady-state levels of the two drugs. However, a significant correlation was found between the single-dose levels and initial steady-state levels for both. The respective linear regression equations were: DOX (parent drug & demethylated metabolite): y = 1.4x + 16.8; r = 0.75, p less than 0.001; IMI (parent drug & demethylated metabolite): y = 3.1x + 4.9; r = 0.85; p less than 0.001. These results confirm, in a population of depressed outpatients, previous findings of a significant correlation between single dose and steady state plasma levels of imipramine, and indicate for the first time that such a correlation also exists for another commonly used tricyclic antidepressant, doxepin. From this relationship, dose requirement can be estimated for individual patients to achieve a desired steady-state concentration of total tricyclics (parent drug & metabolite).

Adolescent↗
PubMed1990

High frequency of human T-cell leukemia-lymphoma virus type II infection in New Mexico blood donors: determination by sequence-specific oligonucleotide hybridization.

The Albuquerque branch of the United Blood Services system was found to have an unusually high blood donor human T-cell leukemia/lymphoma virus (HTLV) seroprevalence (0.72 per 1,000). Many studies investigating HTLV seroprevalence and transmission have assumed that all seropositivity is due to HTLV type I (HTLV-I); recent data dispute this conclusion. We investigated the high prevalence of HTLV seropositivity in New Mexico by determining whether HTLV-I or HTLV-II is predominant in our donors. Using polymerase chain reaction (PCR) amplification of proviral DNA from peripheral blood, followed by sequence-specific hybridization with oligonucleotide probes to distinguish the two viruses, we demonstrate that 9 of 10 Western blot-confirmed HTLV-seropositive blood donors from New Mexico are infected with HTLV-II. Implications of this finding for donors and the safety of the blood supply are discussed.

Base Sequence↗
PubMed1990

Cis- and trans-isomers of doxepin and desmethyldoxepin in the plasma of depressed patients treated with doxepin.

Plasma levels of doxepin and desmethyldoxepin were measured in split samples of 20 depressed patients treated with doxepin by using a conventional extraction and gas chromatography method on a packed column (method 1) and derivation of secondary amine and gas chromatography on a capillary column, allowing the separation and simultaneous quantitation of the cis- and trans-isomers of the two compounds (method 2). We have found that significantly higher levels of desmethyldoxepin and of total drug are detected in plasma when the two isomers are separated and measured by method 2. We concluded that the plasma levels of doxepin reported in most previous studies were underestimated since the cis- and trans-isomers were not separated and included in the total drug concentration. Because the activity of the two isomers is different and their proportion varies in individual patients, we suggest that in future studies correlating plasma levels and the clinical effects of doxepin, both the cis- and the trans-isomers of doxepin and desmethyldoxepin be determined.

Chromatography, Gas↗
PubMed1990

Transmission of HTLV-II via blood transfusion.

Transmission of HTLV-I by transfusion is well documented in Japan, where HTLV-I is endemic. In non endemic regions such as the United States, HTLV-I/II infection has been transmitted by transfusion as well, but no effort to distinguish HTLV-I from HTLV-II infection was made in these studies. There is a growing body of evidence that a substantial proportion of HTLV-I/II seropositivity in the US is due to infection with HTLV-II. We report 2 cases of apparent transfusion-transmitted HTLV-II infection and discuss the importance of distinguishing between the two viruses in blood donors and recipients.

Adult↗
PubMed1989

Characterization of human adipocyte adenosine receptors.

125I-Hydroxyphenylisopropyl adenosine (125I-HPIA) was used to characterize adenosine receptors in human adipocyte plasma membranes. Steady state binding was achieved after 6 h at 37 degrees. Scatchard plots were linear, with a KD of approx. 2.5 nM, and Bmax of 360-1800 fmol/mg protein. (-)N6-phenylisopropyl adenosine (PIA) was a more potent inhibitor of binding than N-ethyl carboxamido adenosine, and (+)PIA was more than 10-fold less potent than (-)PIA, consistent with A1 adenosine receptor binding. Theophylline was a potent inhibitor of binding (IC50 approx. 10 microM). Photoaffinity cross-linking studies demonstrated that the receptor is a single subunit, Mr approx. 43 kDa. The findings demonstrate that the human adipocyte adenosine receptor is similar to the A1 adenosine receptor of rat adipocytes, although its molecular weight is higher, and its affinity for HPIA is lower than that of the rat.

Adenosine↗
PubMed1987

Whole body leucine, phenylalanine, and tyrosine kinetics in end-stage liver disease before and after hepatic transplantation.

The kinetics of leucine, phenylalanine, and tyrosine metabolism following orthotopic human liver transplantation in end-stage liver disease in hospitalized patients were evaluated and compared to controls. The investigation was carried out by protein turnover studies using 13C leucine, D5-phenylalanine, and [U-14C] tyrosine by continuous infusion and employing a stochastic model in 32 patients with end-stage liver disease, 17 of whom went on to receive an hepatic allograft, and 7 controls without significant liver disease who underwent elective abdominal surgery. Mean tyrosine flux in the liver disease group was 3,242 +/- 811 (n = 32) v 2,899 +/- 688 mumol/h in controls (n = 7) (P less than .001), while the tyrosine oxidation was 328 +/- 179 v 422 +/- 185 mumol/h (P less than .001). Tyrosine clearance in pretransplant patients was 719 +/- 345 (n = 17) v 1,193 +/- 568 mL/min (P less than .005) in posttransplant patients (n = 17) with virtually no overlap. There was a significant correlation between serum albumin levels and the tyrosine clearance (r = .60, P less than .05), but correlations with other conventional liver function tests were of a low order. Leucine and phenylalanine kinetics in liver disease patients did not show any significant differences from controls. Leucine and tyrosine fluxes in controls did exhibit a significant correlation (r = .70, P less than .05), but no correlation was observed in patients with liver disease. These findings indicate that the kinetics of the amino acid tyrosine are substantially altered by end-stage liver disease, with the most profound effect on tyrosine clearance.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbon Isotopes↗
PubMedDate not supplied

New tools, new dilemmas: genetic frontiers.

The powerful new methods, expansive scope, and accelerated pace of human molecular genetics combine to catapult us into ethically unfamiliar territory. These features lend special urgency to questions of genetic ownership and privacy, disease and normalcy, identity and genetic determinism, and early diagnosis and therapy.

Biotechnology↗