Targeting Unique Epitopes on Highly Similar Proteins GDF-11 and GDF-8 with Modified DNA Aptamers

The mature forms of the TGF-β family members GDF-11 and GDF-8 are highly similar 25 kDa homodimers with 90% amino acid sequence identity and 99% similarity. Cross-reactivity of GDF-11 and GDF-8 binding reagents is common, making it difficult to attribute distinct roles of these two proteins in biology. We report the selection of GDF-11 and GDF-8 specific SOMAmer (Slow Off-rate Modified Aptamer) reagents aided by a combination of positive selection for one protein coupled with counter-selection against the other. We identified GDF-11 specific SOMAmer reagents from four modified DNA libraries that showed a high affinity (K_d range 0.05-1.2 nM) for GDF-11 but did not bind to GDF-8 (K_d > 1 μM). Conversely, we identified one SOMAmer reagent for GDF-8 from one of the modified libraries that demonstrated excellent affinity (K_d = 0.23 nM) and specificity. In contrast, standard protocols that utilized only positive selection produced binding reagents with similar affinity for both proteins. High affinity and specificity were efficiently encoded in minimal sequences of 21 nucleotides for GDF-11 and 24 nucleotides for GDF-8. Further characterization in pull-down, competition, sandwich-binding, and kinetic studies revealed robust binding under a wide range of buffer and assay conditions. For highly similar proteins like GDF-11 and GDF-8, our method of selection coupled with counter-selection was essential for identification of high-affinity, specific reagents that have the potential to elucidate the fundamental distinction of these growth factors in biology.

Fit for the Eye: Aptamers in Ocular Disorders

For any new class of therapeutics, there are certain types of indications that represent a natural fit. For nucleic acid ligands in general, and aptamers in particular, the eye has historically been an attractive site for therapeutic intervention. In this review, we recount the discovery and early development of three aptamers designated for use in ophthalmology, one approved (Macugen), and two in late-stage development (Fovista and Zimura). Every one of these molecules was originally intended for other indications. Key improvements in technology, specifically with regard to libraries used for in vitro selection and subsequent chemical optimization of aptamers, have played an important role in allowing the identification of development candidates with suitable properties. The lessons learned from the selection of these molecules are valuable for informing us about the many remaining opportunities for aptamer-based therapeutics in ophthalmology as well as for identifying additional indications for which aptamers as a class of therapeutics have distinct advantages.

Mechanism of inhibition for N6022, a first-in-class drug targeting S-nitrosoglutathione reductase

N6022 is a novel, first-in-class drug with potent inhibitory activity against S-nitrosoglutathione reductase (GSNOR), an enzyme important in the metabolism of S-nitrosoglutathione (GSNO) and in the maintenance of nitric oxide (NO) homeostasis. Inhibition of GSNOR by N6022 and related compounds has shown safety and efficacy in animal models of asthma, chronic obstructive pulmonary disease, and inflammatory bowel disease [Sun, X., et al. (2011) ACS Med. Chem. Lett. 2, 402-406]. N6022 is currently in early phase clinical studies in humans. We show here that N6022 is a tight-binding, specific, and fully reversible inhibitor of GSNOR with an IC(50) of 8 nM and a K(i) of 2.5 nM. We accounted for the fact that the NAD(+)- and NADH-dependent oxidation and reduction reactions, catalyzed by GSNOR are bisubstrate in nature in our calculations. N6022 binds in the GSNO substrate binding pocket like a competitive inhibitor, although in kinetic assays it behaves with a mixed uncompetitive mode of inhibition (MOI) toward the GSNO substrate and a mixed competitive MOI toward the formaldehyde adduct, S-hydroxymethylglutathione (HMGSH). N6022 is uncompetitive with cofactors NAD(+) and NADH. The potency, specificity, and MOI of related GSNOR inhibitor compounds are also reported.

Structure-activity relationship of pyrrole based S-nitrosoglutathione reductase inhibitors: carboxamide modification

The enzyme S-nitrosoglutathione reductase (GSNOR) is a member of the alcohol dehydrogenase family (ADH) that regulates the levels of S-nitrosothiols (SNOs) through catabolism of S-nitrosoglutathione (GSNO). GSNO and SNOs are implicated in the pathogenesis of many diseases including those in respiratory, gastrointestinal, and cardiovascular systems. The pyrrole based N6022 was recently identified as a potent, selective, reversible, and efficacious GSNOR inhibitor which is currently in clinical development for acute asthma. We describe here the synthesis and structure-activity relationships (SAR) of novel pyrrole based analogs of N6022 focusing on carboxamide modifications on the pendant N-phenyl moiety. We have identified potent and novel GSNOR inhibitors that demonstrate efficacy in an ovalbumin (OVA) induced asthma model in mice.

Discovery of s-nitrosoglutathione reductase inhibitors: potential agents for the treatment of asthma and other inflammatory diseases

S-Nitrosoglutathione reductase (GSNOR) regulates S-nitrosothiols (SNOs) and nitric oxide (NO) in vivo through catabolism of S-nitrosoglutathione (GSNO). GSNOR and the anti-inflammatory and smooth muscle relaxant activities of SNOs, GSNO, and NO play significant roles in pulmonary, cardiovascular, and gastrointestinal function. In GSNOR knockout mice, basal airway tone is reduced and the response to challenge with bronchoconstrictors or airway allergens is attenuated. Consequently, GSNOR has emerged as an attractive therapeutic target for several clinically important human diseases. As such, small molecule inhibitors of GSNOR were developed. These GSNOR inhibitors were potent, selective, and efficacious in animal models of inflammatory disease characterized by reduced levels of GSNO and bioavailable NO. N6022, a potent and reversible GSNOR inhibitor, reduced bronchoconstriction and pulmonary inflammation in a mouse model of asthma and demonstrated an acceptable safety profile. N6022 is currently in clinical development as a potential agent for the treatment of acute asthma.

Structure-activity relationships of pyrrole based S-nitrosoglutathione reductase inhibitors: pyrrole regioisomers and propionic acid replacement

S-Nitrosoglutathione reductase (GSNOR) is a member of the alcohol dehydrogenase family (ADH) that regulates the levels of S-nitrosothiols (SNOs) through catabolism of S-nitrosoglutathione (GSNO). GSNO and SNOs are implicated in the pathogenesis of many diseases including those in respiratory, cardiovascular, and gastrointestinal systems. The pyrrole based N6022 was recently identified as a potent, selective, reversible, and efficacious GSNOR inhibitor which is currently undergoing clinical development. We describe here the synthesis and structure-activity relationships (SAR) of novel pyrrole based analogues of N6022 focusing on scaffold modification and propionic acid replacement. We identified equally potent and novel GSNOR inhibitors having pyrrole regioisomers as scaffolds using a structure based approach.

Spectrum of activity and mode of action of REP3123, a new antibiotic to treat Clostridium difficile infections

OBJECTIVES

The aim of this study was to characterize the antimicrobial profile of REP3123, a novel inhibitor of methionyl-tRNA synthetase (MetRS) in development for the treatment of Clostridium difficile infection.

METHODS

The spectrum of activity of REP3123 was determined by susceptibility testing of C. difficile and non-target organisms. The mode of action was studied by enzyme inhibition assays, macromolecular synthesis assays, target overexpression and selection of spontaneous resistant mutants.

RESULTS

REP3123 was active against a collection of 108 clinical isolates of C. difficile and against epidemic, moxifloxacin-resistant BI/NAP1/027 strains (MIC range=0.5-1 mg/L and MIC(90) = 1 mg/L). The spectrum of activity included clinically important aerobic Gram-positive cocci such as Staphylococcus aureus, Streptococcus pyogenes, Enterococcus faecalis and Enterococcus faecium (MIC(90)s < 1 mg/L), but REP3123 was not active against most Gram-negative bacteria. REP3123 targeted C. difficile MetRS with a calculated inhibition constant (K(i)) of 0.020 nM, and selectivity was >1000-fold over human mitochondrial and cytoplasmic MetRS. The specific mode of action within bacterial cells was demonstrated by macromolecular synthesis assays that showed inhibition of protein synthesis by REP3123, and by metS overexpression, which resulted in a 16-fold increase in MIC for REP3123. Spontaneous REP3123-resistant mutants of C. difficile (MICs, 4-128 mg/L) arose with frequencies of 10(-8)-10(-9) and harboured distinct point mutations within the metS gene, resulting in 13 different amino acid substitutions. Most of the MetRS substitutions caused reduced catalytic efficiency and a growth fitness burden.

CONCLUSIONS

REP3123 demonstrated a favourable microbiological profile and was found to target C. difficile with high specificity and selectivity.

Inhibition of methionyl-tRNA synthetase by REP8839 and effects of resistance mutations on enzyme activity

REP8839 is a selective inhibitor of methionyl-tRNA synthetase (MetRS) with antibacterial activity against a variety of gram-positive organisms. We determined REP8839 potency against Staphylococcus aureus MetRS and assessed its selectivity for bacterial versus human orthologs of MetRS. The inhibition constant (K(i)) of REP8839 was 10 pM for Staphylococcus aureus MetRS. Inhibition of MetRS by REP8839 was competitive with methionine and uncompetitive with ATP. Thus, high physiological ATP levels would actually facilitate optimal binding of the inhibitor. While many gram-positive bacteria, such as Staphylococcus aureus, express exclusively the MetRS1 subtype, many gram-negative bacteria express an alternative homolog called MetRS2. Some gram-positive bacteria, such as Streptococcus pneumoniae and Bacillus anthracis, express both MetRS1 and MetRS2. MetRS2 orthologs were considerably less susceptible to REP8839 inhibition. REP8839 inhibition of human mitochondrial MetRS was 1,000-fold weaker than inhibition of Staphylococcus aureus MetRS; inhibition of human cytoplasmic MetRS was not detectable, corresponding to >1,000,000-fold selectivity for the bacterial target relative to its cytoplasmic counterpart. Mutations in MetRS that confer reduced susceptibility to REP8839 were examined. The mutant MetRS enzymes generally exhibited substantially impaired catalytic activity, particularly in aminoacylation turnover rates. REP8839 K(i) values ranged from 4- to 190,000-fold higher for the mutant enzymes than for wild-type MetRS. These observations provide a potential mechanistic explanation for the reduced growth fitness observed with MetRS mutant strains relative to that with wild-type Staphylococcus aureus.

Aptamers as reagents for high-throughput screening

The identification of new drug candidates from chemical libraries is a major component of discovery research in many pharmaceutical companies. Given the large size of many conventional and combinatorial libraries and the rapid increase in the number of possible therapeutic targets, the speed with which efficient high-throughput screening (HTS) assays can be developed can be a rate-limiting step in the discovery process. We show here that aptamers, nucleic acids that bind other molecules with high affinity, can be used as versatile reagents in competition binding HTS assays to identify and optimize small-molecule ligands to protein targets. To illustrate this application, we have used labeled aptamers to platelet-derived growth factor B-chain and wheat germ agglutinin to screen two sets of potential small-molecule ligands. In both cases, binding affinities of all ligands tested (small molecules and aptamers) were strongly correlated with their inhibitory potencies in functional assays. The major advantages of using aptamers in HTS assays are speed of aptamer identification, high affinity of aptamers for protein targets, relatively large aptamer-protein interaction surfaces, and compatibility with various labeling/detection strategies. Aptamers may be particularly useful in HTS assays with protein targets that have no known binding partners such as orphan receptors. Since aptamers that bind to proteins are often specific and potent antagonists of protein function, the use of aptamers for target validation can be coupled with their subsequent use in HTS.

Intimal hyperplasia recurs after removal of PDGF-AB and -BB inhibition in the rat carotid artery injury model

Several antagonists specific for platelet-derived growth factor (PDGF) or its receptors have recently been developed and shown to inhibit intimal hyperplasia formation in various animal models, but data investigating the durability of this intervention is limited. The present study was designed to investigate the potency of PDGF B-chain aptamer, a novel type of PDGF-AB and -BB antagonist, in the rat carotid model and to characterize intermediate-term effects on lesion formation. One hundred thirty-four animals were randomized to aptamer treatment or placebo. Daily treatment with the antagonist resulted in a 50% reduction in lesion size at 2 weeks (P<0.001). The beneficial effect involved increased apoptosis and possibly an interference with smooth muscle cell migration. Discontinuing administration 1 week earlier did not give any significant benefit compared with phosphate-buffered saline-treated controls. When the antagonist was administered for 2 weeks and the vessels analyzed 6 weeks later, the beneficial effect was lost and the treated lesions had a higher intima-media and area-cell ratio compared with the treated lesions in the 2-week-endpoint study. Our findings confirm a role of PDGF B-chain in intimal hyperplasia, but the successful use of PDGF antagonists may require either prolonged treatment or combination therapy with other agents.

Estimates of repolarization dispersion from electrocardiographic measurements

BACKGROUND

Repolarization dispersion (Rd) is frequently mentioned as a predictor of cardiac abnormalities. We present a new measure of Rd based on the root-mean-square (RMS) curve of an ECG lead set and compare its performance with that of the commonly used QT dispersion (QTd) measure with the use of recovery times measured from directly recorded canine electrograms.

METHODS AND RESULTS

Using isolated, perfused canine hearts suspended in a torso-shaped electrolytic tank, we simultaneously recorded electrograms from 64 epicardial sites and ECGs from 192 "body surface" sites. RMS curves were derived from 4 lead sets: epicardial, body surface, precordial, and a 6-lead optimal set. Repolarization was altered by changing cycle length, temperature, and activation sequence. Rd, calculated directly from recovery times of the 64 epicardial potentials, was then compared with the width of the T wave of the RMS curve and with QTd for each of these 4 lead sets. The correlation between T-wave width and Rd for each lead set, respectively, was epicardium, 0.91; body surface, 0.84; precordial, 0.72; and optimal leads, 0.81. The correlation between QTd and Rd for each lead set was epicardium, 0.46; body surface, 0.47; precordial, 0.17; and optimal leads, 0.11.

CONCLUSIONS

RMS curve analysis provides an accurate method of estimating Rd from the body surface. In contrast, QTd analysis provides a poor estimate of Rd.

Catabolism of alpha-ketoglutarate by a sucA mutant of Bradyrhizobium japonicum: evidence for an alternative tricarboxylic acid cycle

A complete tricarboxylic acid (TCA) cycle is generally considered necessary for energy production from the dicarboxylic acid substrates malate, succinate, and fumarate. However, a Bradyrhizobium japonicum sucA mutant that is missing alpha-ketoglutarate dehydrogenase is able to grow on malate as its sole source of carbon. This mutant also fixes nitrogen in symbiosis with soybean, where dicarboxylic acids are its principal carbon substrate. Using a flow chamber system to make direct measurements of oxygen consumption and ammonium excretion, we confirmed that bacteroids formed by the sucA mutant displayed wild-type rates of respiration and nitrogen fixation. Despite the absence of alpha-ketoglutarate dehydrogenase activity, whole cells of the mutant were able to decarboxylate alpha-[U-(14)C]ketoglutarate and [U-(14)C]glutamate at rates similar to those of wild-type B. japonicum, indicating that there was an alternative route for alpha-ketoglutarate catabolism. Because cell extracts from B. japonicum decarboxylated [U-(14)C]glutamate very slowly, the gamma-aminobutyrate shunt is unlikely to be the pathway responsible for alpha-ketoglutarate catabolism in the mutant. In contrast, cell extracts from both the wild type and mutant showed a coenzyme A (CoA)-independent alpha-ketoglutarate decarboxylation activity. This activity was independent of pyridine nucleotides and was stimulated by thiamine PP(i). Thin-layer chromatography showed that the product of alpha-ketoglutarate decarboxylation was succinic semialdehyde. The CoA-independent alpha-ketoglutarate decarboxylase, along with succinate semialdehyde dehydrogenase, may form an alternative pathway for alpha-ketoglutarate catabolism, and this pathway may enhance TCA cycle function during symbiotic nitrogen fixation.

Estimates of repolarization and its dispersion from electrocardiographic measurements: direct epicardial assessment in the canine heart

This study investigates a technique to estimate dispersion based on the root mean square (RMS) signal of multiple electrocardiographic leads. Activation and recovery times were measured from 64 sites on the epicardium of canine hearts using acute in situ or Langendorff perfused isolated heart preparations. Repolarization and its dispersion were altered by varying cycle length, myocardial temperature, or ventricular pacing site. Mean and dispersion of activation and recovery times, and activation-recovery interval (ARI) were calculated for each beat. The waveform was then calculated from all leads. Estimates of mean and dispersion of activation and recovery times and mean ARI were derived using only inflection points from the RMS waveform. QT intervals were also measured and QT dispersion was determined. Estimates determined from the RMS waveform provided accurate estimates of repolarization and were, in particular, a better measure of repolarization dispersion than QT dispersion.

Novel approach to specific growth factor inhibition in vivo: antagonism of platelet-derived growth factor in glomerulonephritis by aptamers

Mesangial cell proliferation and matrix accumulation, driven by platelet-derived growth factor (PDGF), contribute to many progressive renal diseases. In a novel approach to antagonize PDGF, we investigated the effects of a nuclease-resistant high-affinity oligonucleotide aptamer in vitro and in vivo. In cultured mesangial cells, the aptamer markedly suppressed PDGF-BB but not epidermal- or fibroblast-growth-factor-2-induced proliferation. In vivo effects of the aptamer were evaluated in a rat mesangioproliferative glomerulonephritis model. Twice-daily intravenous (i.v.) injections from days 3 to 8 after disease induction of 2.2 mg/kg PDGF-B aptamer, coupled to 40-kd polyethylene glycol (PEG), led to 1) a reduction of glomerular mitoses by 64% on day 6 and by 78% on day 9, 2) a reduction of proliferating mesangial cells by 95% on day 9, 3) markedly reduced glomerular expression of endogenous PDGF B-chain, 4) reduced glomerular monocyte/macrophage influx on day 6 after disease induction, and 5) a marked reduction of glomerular extracellular matrix overproduction (as assessed by analysis of fibronectin and type IV collagen) both on the protein and mRNA level. The administration of equivalent amounts of a PEG-coupled aptamer with a scrambled sequence or PEG alone had no beneficial effect on the natural course of the disease. These data show that specific inhibition of growth factors using custom-designed, high-affinity aptamers is feasible and effective.

Liposome-anchored vascular endothelial growth factor aptamers

Nuclease-resistant aptamers identified from randomized nucleic acid libraries represent a novel class of drug candidates. Aptamers are synthesized chemically and therefore can be readily modified with functional groups that modulate their properties. We report here on the preparation, initial characterization, and functional properties of a nuclease-resistant vascular endothelial growth factor (VEGF) aptamer anchored in liposome bilayers through a lipid group on the aptamer. While the high-affinity binding to VEGF is maintained, the plasma residence time of the liposome-anchored aptamer is considerably improved compared with that of the free aptamer. The lipid group attachment and/or liposome anchoring leads to a dramatic improvement in inhibitory activity of the aptamer toward VEGF-induced endothelial cell proliferation in vitro and vascular permeability increase and angiogenesis in vivo.

2'-Fluoropyrimidine RNA-based aptamers to the 165-amino acid form of vascular endothelial growth factor (VEGF165). Inhibition of receptor binding and VEGF-induced vascular permeability through interactions requiring the exon 7-encoded domain

Vascular endothelial growth factor (VEGF) has been implicated in the pathological induction of new blood vessel growth in a variety of proliferative disorders. Using the SELEX process (systematic evolution of ligands by exponential enrichment), we have isolated 2'-F-pyrimidine RNA oligonucleotide ligands (aptamers) to human VEGF165. Representative aptamers from three distinct sequence families were truncated to the minimal sequence capable of high affinity binding to VEGF (23-29 nucleotides) and were further modified by replacement of 2'-O-methyl for 2'-OH at all ribopurine positions where the substitution was tolerated. Equilibrium dissociation constants for the interaction of VEGF with the truncated, 2'-O-methyl-modified aptamers range between 49 and 130 pM. These aptamers bind equally well to murine VEGF164, do not bind to VEGF121 or the smaller isoform of placenta growth factor (PlGF129), and show reduced, but significant affinity for the VEGF165/PlGF129 heterodimer. Cysteine 137 in the exon 7-encoded domain of VEGF165 forms a photo-inducible cross-link to a single uridine residue in each of the three aptamers. The aptamers potently inhibit the binding of VEGF to the human VEGF receptors, KDR and Flt-1, expressed by transfected porcine aortic endothelial cells. Furthermore, one of the aptamers is able to significantly reduce intradermal VEGF-induced vascular permeability in vivo.

Isocitrate dehydrogenase and glyoxylate cycle enzyme activities in Bradyrhizobium japonicum under various growth conditions

Bradyrhizobium japonicum, the nitrogen-fixing symbiotic partner of soybean, was grown on various carbon substrates and assayed for the presence of the glyoxylate cycle enzymes, isocitrate lyase and malate synthase. The highest levels of isocitrate lyase [165-170 nmol min-1 (mg protein)-1] were found in cells grown on acetate or beta-hydroxybutyrate, intermediate activity was found after growth on pyruvate or galactose, and very little activity was found in cells grown on arabinose, malate, or glycerol. Malate synthase activity was present in arabinose- and malate-grown cultures and increased by only 50-80% when cells were grown on acetate. B. japonicum bacteroids, harvested at four different nodule ages, showed very little isocitrate lyase activity, implying that a complete glyoxylate cycle is not functional during symbiosis. The apparent Km of isocitrate lyase for D,L-isocitrate was fourfold higher than that of isocitrate dehydrogenase (61.5 and 15.5 microM, respectively) in desalted crude extracts from acetate-grown B. japonicum. When isocitrate lyase was induced, neither the Vmax nor the D,L-isocitrate Km of isocitrate dehydrogenase changed, implying that isocitrate dehydrogenase is not inhibited by covalent modification to facilitate operation of the glyoxylate cycle in B. japonicum.

QT interval dispersion: dispersion of ventricular repolarization or dispersion of QT interval?

The QT interval (QTI) has long been useful as a clinical index of the duration of ventricular repolarization, particularly as a marker of prolonged repolarization and its well-established association with arrhythmogenic cardiac states. Likewise, inhomogeneity (dispersion) of repolarization has been linked definitively to increased susceptibility to reentrant arrhythmias. Recent studies have reported the use of QTI dispersion as a meaningful clinical index to identify patients at risk, but the interpretation of the measurement has been controversial. A Langendorff-perfused, isolated canine heart suspended in a torso-shaped, electrolytic tank filled with NaCl-sucrose solution was used to investigate the relationship between body surface QTIs and ventricular repolarization measured directly from the cardiac surface by using activation-recovery intervals, which have been documented to reflect the duration of local action potentials as well as local refractory periods. The data showed poor correlation between cardiac surface activation-recovery intervals and QTIs, as well as the insensitivity of QTIs to regional repolarization shortening in the presence of prolonged repolarization elsewhere. Furthermore, the data confirmed that torso tank QTI dispersion does not reflect directly the full range of measured ventricular repolarization inhomogeneity. It is concluded that body surface QTI dispersion is not a reliable index of repolarization dispersion.

Three-dimensional distribution of ST-T wave alternans during acute ischemia

INTRODUCTION

A canine model of reversible ischemia was used to measure the magnitude and transmural distribution of repolarization alternans.

METHODS AND RESULTS

Twenty-four multielectrode needles were inserted into a reversibly ischemic region created by 8 minutes of coronary occlusion. One hundred ninety-two unipolar electrograms were simultaneously recorded at 1-minute intervals for 8 minutes of ischemia and 3 minutes of reflow recovery. Beat-to-beat repolarization alternans was quantified for all electrograms using the standard deviation of QRST integrals. When alternans from animals that fibrillated was compared with alternans from animals that did not, the magnitude of alternans in the fibrillation group was an average standard deviation of 1125 +/- 99.7 mV-msec at the time of fibrillation and 409 +/- 183 mV-msec at 8 minutes of ischemia in the animals that did not fibrillate. The increase in alternans occurred mainly in the mid-myocardial and epicardial regions in the animals that fibrillated. QRS morphology of sequential electrograms did not differ in beat-to-beat comparison, suggesting that repolarization alternans measured was not due to alternating conduction block in the region of reversible ischemia.

CONCLUSION

During acute ischemia, the magnitude and distribution of repolarization alternans are greater and differ in hearts that experience ventricular fibrillation. This observation may have clinical utility in arrhythmia prediction. It also is consistent with the possibility there may be multiple mechanisms for repolarization alternans.

Bradyrhizobium japonicum does not require alpha-ketoglutarate dehydrogenase for growth on succinate or malate

The sucA gene, encoding the E1 component of alpha-ketoglutarate dehydrogenase, was cloned from Bradyrhizobium japonicum USDA110, and its nucleotide sequence was determined. The gene shows a codon usage bias typical of non-nif and non-fix genes from this bacterium, with 89.1% of the codons being G or C in the third position. A mutant strain of B. japonicum, LSG184, was constructed with the sucA gene interrupted by a kanamycin resistance marker. LSG184 is devoid of alpha-ketoglutarate dehydrogenase activity, indicating that there is only one copy of sucA in B. japonicum and that it is completely inactivated in the mutant. Batch culture experiments on minimal medium revealed that LSG184 grows well on a variety of carbon substrates, including arabinose, malate, succinate, beta-hydroxybutyrate, glycerol, formate, and galactose. The sucA mutant is not a succinate auxotroph but has a reduced ability to use glutamate as a carbon or nitrogen source and an increased sensitivity to growth inhibition by acetate, relative to the parental strain. Because LSG184 grows well on malate or succinate as its sole carbon source, we conclude that B. japonicum, unlike most other bacteria, does not require an intact tricarboxylic acid (TCA) cycle to meet its energy needs when growing on the four-carbon TCA cycle intermediates. Our data support the idea that B. japonicum has alternate energy-yielding pathways that could potentially compensate for inhibition of alpha-ketoglutarate dehydrogenase during symbiotic nitrogen fixation under oxygen-limiting conditions.

Inhibitory DNA ligands to platelet-derived growth factor B-chain

We have identified a group of DNA molecules that bind to platelet-derived growth factor (PDGF)-AB with subnanomolar affinity from a randomized DNA library using in vitro selection. Individual ligands cloned from the affinity-enriched pool bind to PDGF-AB and PDGF-BB with comparably high affinity (Kd approximately 10(-10) M) and to PDGF-AA with lower affinity (> 10(-8) M), indicating specific recognition of the PDGF B-chain in the context of the hetero- or homodimer. The consensus secondary structure motif for most of the high-affinity ligands is a three-way helix junction with a three-nucleotide loop at the branch point. Photo-cross-linking experiments with 5-iodo-2'-deoxyuridine-substituted ligands establish a point contact between a thymidine nucleotide in the helix junction loop region and phenylalanine 84 of the PDGF-B chain. Representative minimal DNA ligands inhibit the binding of 125I-PDGF-BB but not of 125I-PDGF-AA to PDGF alpha- or beta-receptors expressed in porcine aortic endothelial (PAE) cells in a concentration-dependent manner with half-maximal effects of approximately 1 nM. The same ligands also exhibit a similar inhibitory effect on PDGF-BB-dependent [3H]thymidine incorporation in PAE cells expressing the PDGF beta-receptors. These DNA ligands represent a novel class of specific and potent antagonists of PDGF-BB and, by inference, PDGF-AB.

Inhibitory DNA ligands to platelet-derived growth factor B-chain

We have identified a group of DNA molecules that bind to platelet-derived growth factor (PDGF)-AB with subnanomolar affinity from a randomized DNA library using in vitro selection. Individual ligands cloned from the affinity-enriched pool bind to PDGF-AB and PDGF-BB with comparably high affinity (Kd approximately 10(-10) M) and to PDGF-AA with lower affinity (> 10(-8) M), indicating specific recognition of the PDGF B-chain in the context of the hetero- or homodimer. The consensus secondary structure motif for most of the high-affinity ligands is a three-way helix junction with a three-nucleotide loop at the branch point. Photo-cross-linking experiments with 5-iodo-2'-deoxyuridine-substituted ligands establish a point contact between a thymidine nucleotide in the helix junction loop region and phenylalanine 84 of the PDGF-B chain. Representative minimal DNA ligands inhibit the binding of 125I-PDGF-BB but not of 125I-PDGF-AA to PDGF alpha- or beta-receptors expressed in porcine aortic endothelial (PAE) cells in a concentration-dependent manner with half-maximal effects of approximately 1 nM. The same ligands also exhibit a similar inhibitory effect on PDGF-BB-dependent [3H]thymidine incorporation in PAE cells expressing the PDGF beta-receptors. These DNA ligands represent a novel class of specific and potent antagonists of PDGF-BB and, by inference, PDGF-AB.

Genetically defined therapy of inherited long-QT syndrome. Correction of abnormal repolarization by potassium

BACKGROUND

Many members of families with inherited long-QT (LQT) syndrome have mutations in HERG, a gene encoding a cardiac potassium channel that is modulated by extracellular potassium. We hypothesized that an increase in serum potassium would normalize repolarization in these patients.

METHODS AND RESULTS

We studied seven subjects with chromosome 7-linked LQT syndrome and five normal control subjects. Repolarization was measured by ECG and body surface potential mapping during sinus rhythm, exercise, and atrial pacing, before and after serum potassium increase. Potassium administration improved repolarization in the LQT syndrome. At baseline, LQT subjects differed from control subjects: resting corrected QT interval (QTc, 627 +/- 90 versus 425 +/- 25 ms, P = .0007), QTc dispersion (133 +/- 62 versus 36 +/- 9 ms, P = .009), QT/RR slope (0.35 +/- 0.08 versus 0.24 +/- 0.07, P = .04), and global root-mean-square QT interval (RMS-QTc; 525 +/- 68 versus 393 +/- 22, P = .002). All LQT subjects had biphasic or notched T waves. After administration of potassium, the LQT group had a 24% reduction in resting QTc interval (from 617 +/- 92 to 469 +/- 23 ms, P = .004) compared with a 4% reduction among control subjects (from 425 +/- 25 to 410 +/- 45 ms, P > .05). The reduction was significantly greater in LQT subjects (P = .018). QT dispersion became normal in LQT subjects and did not change in control subjects. The slope of the relation between QT interval and cycle length (QT/RR slope) decreased toward normal. T-wave morphology improved in six of seven LQT subjects. The LQT group had a greater reduction in RMS-QTc than control subjects (P = .04).

CONCLUSIONS

An increase in serum potassium corrects abnormalities of repolarization duration, T-wave morphology, QT/ RR slope, and QT dispersion in patients with chromosome 7-linked LQT.

Optimal lead selection for detection of ST segment shifts

A comparison was made to determine the ability of optimal sets of 2-6 unipolar leads and a normal Holter lead set to estimate ST potential distributions changes induced by balloon inflation during angioplasty. The performance of these lead sets was compared to measurements observed in recorded 32-lead body surface maps. Unipolar lead potentials were estimated using a linear, least mean squared error estimator of the total body surface map. The correlation between maximum ST potential change in the body surface map and that predicted by the unipolar lead sets ranged from 0.84-0.93. The correlation between maximum ST segment change measured from the body surface map and measured from the Holter leads was 0.29. Therefore, shifts in ST segment potentials can accurately be estimated from a small number of unipolar leads. In contrast, current bipolar ambulatory recording techniques may introduce significant bias to such estimates.

Amino acid sequences of heterotrophic and photosynthetic ferredoxins from the tomato plant (Lycopersicon esculentum Mill.)

Several forms (isoproteins) of ferredoxin in roots, leaves, and green and red pericarps in tomato plants (Lycopersicon esculentum Mill.) were earlier identified on the basis of N-terminal amino acid sequence and chromatographic behavior (Green et al. 1991). In the present study, a large scale preparation made possible determination of the full length amino acid sequence of the two ferredoxins from leaves. The ferredoxins characteristic of fruit and root were sequenced from the amino terminus to the 30th residue or beyond. The leaf ferredoxins were confirmed to be expressed in pericarp of both green and red fruit. The ferredoxins characteristic of fruit and root appeared to be restricted to those tissue. The results extend earlier findings in demonstrating that ferredoxin occurs in the major organs of the tomato plant where it appears to function irrespective of photosynthetic competence.

Nuclease-resistant nucleic acid ligands to vascular permeability factor/vascular endothelial growth factor

BACKGROUND

Vascular permeability factor/vascular endothelial growth factor (VPF/VEGF) is a potent inducer of new blood vessel growth (angiogenesis) that contributes to the pathology of many angiogenesis-associated disease states such as psoriasis, rheumatoid arthritis and cancer. Few molecular entities capable of binding to VPF/VEGF with high affinity and specificity have been described to date.

RESULTS

Nuclease-resistant 2'-amino-2'-deoxypyrimidine nucleotide RNA (2'-aminopyrimidine RNA) ligands that bind to VPF/VEGF with high affinity have been identified by iterative rounds of affinity-selection/amplification from two independent random libraries. The sequence information that confers high affinity binding to VPF/VEGF is contained in a contiguous stretch of 24 nucleotides, 5'-CCCUGAUGGUAGACGCCGGGGUG-3' (2'-aminopyrimidine nucleotides are designated with italic letters). Of the 14 ribopurines in this minimal ligand, 10 can be substituted with the corresponding 2'-O-methylpurine nucleotides without a reduction in binding affinity to VPF/VEGF. In fact, the 2'-O-methyl substitution at permissive positions leads to a approximately 17-fold improvement in the binding affinity to VPF/VEGF. The higher affinity results from the reduction in the dissociation rate constant of the 2'-O-methyl-substituted RNA ligand from the protein compared to the unsubstituted ligand. The 2'-O-methyl-substituted minimal ligand, which folds into a bulged hairpin motif, is also more thermally stable than the unsubstituted ligand. Nuclease resistance of the ligand is further improved by the 2'-O-methyl substitutions and the addition of short phosphorothioate caps to the 3'- and 5'-ends.

CONCLUSIONS

We have used the SELEX (systematic evolution of ligands by exponential enrichment) process in conjunction with post-SELEX modifications to define a highly nuclease-resistant oligonucleotide that binds to VPF/VEGF with high affinity and specificity.

Potent 2'-amino-2'-deoxypyrimidine RNA inhibitors of basic fibroblast growth factor

Screening of random oligonucleotide libraries with SELEX [systematic evolution of ligands by exponential enrichment; Tuerk, C., & Gold, L. (1990) Science 249, 505-510] has emerged as a powerful method for identifying high-affinity nucleic acid ligands for a wide range of molecular targets. Nuclease sensitivity of unmodified RNA and DNA, however, imposes considerable restrictions on their use as therapeutics or diagnostics. Modified RNA in which pyrimidine 2'-hydroxy groups have been substituted with 2'-amino groups (2'-aminopyrimidine RNA) is known to be substantially more resistant to serum nucleases. We report here on the use of SELEX to identify high-affinity 2'-aminopyrimidine RNA ligands to a potent angiogenic factor, basic fibroblast growth factor (bFGF). High-affinity ligands with the same consensus primary structure have been isolated from two independent libraries of approximately 6 x 10(14) molecules containing 30 or 50 randomized positions. Compared to unmodified RNA with the same sequence, 2'-aminopyrimidine ligands are at least 1000-fold more stable in 90% human serum. The sequence information required for high-affinity binding to bFGF is contained within 24-26 nucleotides. The minimal ligand m21A (5'-GGUGUGUGGAAGACAGCGGGUGGUUC-3'; G = guanosine, A = adenosine, C = 2'-amino-2'-deoxycytidine, U = 2'-amino-2'-deoxyuridine, and C = 2'-amino-2'-deoxycytidine or deoxycytidine) binds to bFGF with an apparent dissociation constant (Kd) of 3.5 +/- 0.3) x 10(-10) M at 37 degrees C in phosphate-buffered saline (pH 7.4). Disassociation of m21A from bFGF is adequately described with a first-order rate constant of (1.96 +/- 0.08) x 10(-3) s-1 (t1/2 = 5.9 min). The calculated value for the association rate constant (kon = k(off)/Kd) was 5.6 x 10(6) M-1 s-1. Highly specific binding of m21A to bFGF was observed: binding to denatured bFGF, five proteins from the FGF family (acidic FGF, FGF-4, FGF-5, FGF-6, and FGF-7), and four other heparin binding proteins is substantially weaker under the same conditions with KdbFGF/Kdprotein values ranging from (4.1 +/- 1.4) x 10(-2) to > 10(-6). Heparin but not chondroitin sulfate competed for binding of m21A to bFGF. In cell culture, m21A inhibited [125I]bFGF binding to both low-affinity sites (ED50 approximately 1 nM) and high-affinity sites (ED50 approximately 3 nM) on CHO cells expressing transfected FGF receptor-1.(ABSTRACT TRUNCATED AT 400 WORDS)

Clinical applications of body surface potential mapping

Accumulated evidence suggests that the electrocardiographic information provided by the standard 12-lead electrocardiogram can be improved by use of multilead electrocardiograms. The clinical utility of body surface potential mapping is related to the selective regional information provided by the increased number of leads. That clinical utility includes such things as improved localization of accessory pathways in preexcitation syndromes, improved localization of pacing sites within the ventricles, localization of late potentials, and improved recognition of acute myocardial ischemia. Recording equipment and interpretation schemes are available to make possible more widespread application of potential mapping.

Temperature-dependent expression of a 95 kD protein in rat testis

Testicular tissue from mature male Sprague-Dawley rats was maintained in culture at 33 degrees C or 37 degrees C. Detergent-extracted proteins were separated by polyacrylamide gel electrophoresis (PAGE) followed by staining or fluorography. Unilateral surgical cryptorchidism was performed as an in vivo model for testicular exposure to abdominal temperature. Testes were harvested at various time points, followed by protein analysis as performed for in vitro studies. Tissue incubated in vitro for 48 h at 37 degrees C demonstrated loss of a prominent actively synthesized 95 kD protein (p95) seen at 33 degrees C. No other temperature-dependent protein changes were observed. Liver, kidney, spleen and thymus failed to reveal p95 or any other temperature-sensitive proteins when incubated at 33 degrees C and 37 degrees C. Surgical cryptorchidism resulted in loss of p95 by 1 week in abdominal testes and normal p95 expression in sham-operated scrotal testes. p95 appears to be a temperature-sensitive protein in rat testis, with increased degradation accounting for its loss at abdominal temperature. The failure to identify similar protein changes in other tissues suggests a role for p95 in the temperature-dependent function of the testis.

The Churg-Strauss syndrome. A case report with angiographically documented coronary involvement and a review of the literature

The Churg-Strauss syndrome (CSS) is an unusual disease that presents as a systemic vasculitis and peripheral eosinophilia in a patient with chronic atopic disease. Although often not prominent on initial presentation, cardiac involvement is a major cause of morbidity and mortality in patients with CSS. We report a case of a young woman with CSS who had a myocardial infarction. Coronary arteriography was performed for recurrent chest pain and demonstrated diffuse vasculopathy consistent with vasculitis in CSS. We have also included a review of the literature on cardiac involvement in CSS.

Estimating ECG distributions from small numbers of leads

The utility of body surface potential mapping to improve interpretation of electrocardiographic information lies in the presentation of thoracic surface distributions to characterize underlying electrophysiology less ambiguously than that afforded by conventional electrocardiography. Localized cardiac disease or abnormal electrophysiology presents itself electrocardiographically on the body surface in a manner in which pattern plays an important role for identifying or characterizing these abnormalities. Thus, in myocardial infarction, transient myocardial ischemia, Wolff-Parkinson-White syndrome, or ventricular ectopy, observation of electrocardiographic potential patterns, their extrema, and their magnitudes permits localization and quantization of the abnormal activity. Conventional electrocardiography assesses pattern information incompletely and does not use information of distribution extrema locations or magnitudes. Thus, increases or decreases in the magnitudes of electrocardiographic features (ST-segment potential displacement, amplitude, or morphology of Q, R, S, or T waves) associated with changes in cardiac sources (ischemia, infarction, conduction abnormalities, etc.) as measured from fixed leads have a high likelihood of being misinterpreted if the distribution itself is changing. In this study, the authors demonstrate the utility of estimating distributions from small numbers of optimally selected leads, including conventional leads, to reduce uncertainty in the interpretation of electrocardiographic information. This issue is highly relevant when thresholds are used to detect significance of potential levels (exercise testing, detection of myocardial infarction, and continuous monitoring to assess ST-segment changes). Significance of this work lies in improved detection and characterization of abnormal electrophysiology using conventional or enhanced leadsets and methods to estimate thoracic potential distributions.

Inhibition of receptor binding by high-affinity RNA ligands to vascular endothelial growth factor

The proliferation of new blood vessels (angiogenesis) is a process that accompanies many pathological conditions including rheumatoid arthritis and solid tumor growth. Among angiogenic cytokines that have been identified to date, vascular endothelial growth factor (VEGF) is one of the most potent. We used SELEX [systematic evolution of ligands by exponential enrichment; Tuerk, C., & Gold, L. (1990) Science 249, 505-510] to identify RNA ligands that bind to VEGF in a specific manner with affinities in the low nanomolar range. Ligands were selected from a starting pool of about 10(14) RNA molecules containing 30 randomized positions. Isolates from the affinity-enriched pool were grouped into six distinct families on the basis of primary and secondary structure similarities. Minimal sequence information required for high-affinity binding to VEGF is contained in 29-36-nucleotide motifs. Binding of truncated (minimal) high-affinity ligands to VEGF is competitive with that of other truncated ligands and heparin. Furthermore, truncated ligands from the six ligand families inhibit binding of [125I]VEGF to its cell-surface receptors. Oligonucleotide ligands described here represent an initial set of lead compounds in our ongoing effort toward the development of potent and specific VEGF antagonists.

Resolution of pace mapping stimulus site separation using body surface potentials

BACKGROUND

Several studies have related 12-lead ECG waveform during ventricular tachycardia to ECG waveform during ventricular pacing to identify ablation sites for therapy of ventricular tachycardia. QRS isopotential maps and QRS isointegral maps derived from body surface isopotential maps have also been correlated with left ventricular pacing sites with the same objective. The comparison process used is subjective and only semiquantitative. Improved accuracy of catheter placement may improve success rates of ablation therapy.

METHODS AND RESULTS

This animal study was performed to determine the spatial resolution with which left ventricular pacing sites could be distinguished by body surface isopotential mapping. Potentials were recorded from 64 evenly spaced thoracic leads. Hexapolar or octapolar pacing catheters with 2-mm interelectrode spacing were placed percutaneously in the left ventricle in each of six dogs, and bipolar endocardial pacing was performed using each pair of adjacent electrodes. QRS isopotential maps of each pacing site for each catheter placement were cross-correlated by computer. Difference maps for each pair of pacing sites were calculated lead by lead and time instant by time instant, and root-mean-square voltage differences were calculated. Results indicated that correlation coefficients and root-mean-square error of voltage differences monotonically decrease and increase, respectively, with stimulus site separation. Both measures were significantly different (P < .05) for separations of 4 mm or more.

CONCLUSIONS

A method of quantitative comparison of body surface potential maps can be used in normal hearts to localize ventricular pacing sites within a 4-mm range. The method may have utility in determining potential ablation sites for therapy of ventricular tachycardia or preexcitation syndromes.

Assessment of spatial and temporal characteristics of ventricular repolarization

Measurement of dynamics and spatial characteristics of ventricular repolarization is of interest in assessing patients with ischemic heart disease, particularly in relation to the detection and characterization of ischemic events, identification of patients at risk of ventricular arrhythmias, or determination of the efficacy of drugs intended to alter repolarization. The QT interval (QTI) has been the index of choice for assessing repolarization abnormalities. It is a general measure of repolarization duration but lacks the power to assess the spatial aspects of repolarization and the ability to detect localized shortening in the setting of global prolongation. For direct cardiac surface measurement, QRST integrals and activation recovery intervals (ARIs) were used to assess repolarization and its disparity. The use of similar measurements from the body surface was proposed to provide better characterization of repolarization, its disparity, and its dynamics than is possible using the QTI. In one open-chest experiment using an intact canine heart and two experiments using isolated canine hearts suspended in a torso-shaped electrolytic tank, 64 epicardial electrograms and 192 torso surface electrocardiograms were measured simultaneously. Ventricular repolarization was globally altered by varying pacing cycle lengths or tank temperature. Atrial and ventricular pacing were used to assess sensitivity of repolarization indices to activation sequence. At the cardiac surface, (1) QTI tracks global repolarization changes but is affected by activation sequence and insensitive to localized shortening of repolarization; (2) distribution of QRST integrals reflects disparity of repolarization and is largely independent of activation sequence; and (3) ARI measures local repolarization duration and is only weakly affected by activation sequence.(ABSTRACT TRUNCATED AT 250 WORDS)

Bronchogenic cancer in patients under 40 years old. The experience of a Latin American country

Lung cancer in young patients is increasing in frequency, as documented by data from the United States, Canada, Japan, and European countries. However, to date and to our knowledge, there have not been any reports from Latin America on this topic. The published reports show that lung cancer in young patients is associated with smoking habit and family history of lung cancer. Its clinical course seems to be more aggressive than in older patients and the histologic type is less often squamous type. We describe 48 patients, aged 40 years or younger, who were diagnosed as having lung cancer in the Instituto Nacional de Cancerología from 1980 to 1990. The patients were equally divided between men and women. Smoking was documented for only 46 percent of the cases. The histologic type most frequently diagnosed was adenocarcinoma (N = 26) followed by squamous cell carcinoma (N = 12). Almost all the cases (46 cases) were staged IV according to the TNM classification. A group of 33 patients older than 40 years (56 to 82 years) were used for comparison. The differences in sex ratio that were higher for men in the elder (m/f, 2.7:1) were family history for cancer in six patients elder; positive smoking habit in all the aged patients (100 percent) compared with only 43.7 percent in the younger group; histologic type (26 adenocarcinomas and 4 squamous in the younger compared with 14 and 12, respectively, in the elder).

On-line coupling of supercritical fluid extraction with multidimensional microcolumn liquid chromatography/gas chromatography

An on-line multidimensional supercritical fluid extraction/microcolumn liquid chromatography/capillary gas chromatography system (SFE/LC/GC) has been developed and applied to the quantitative determination of trace levels (parts per billion) of chlorpyrifos insecticide in grass field samples. This system provides all the advantages of an on-line multidimensional system, including increased resolving power, high sensitivity, quantitation, precision, and automation potential. Off-line analysis of the grass extracts by GC with an electron capture detector yielded a complex chromatogram from which it was difficult to quantitate the chlorpyrifos, but analysis of the extract by LC/GC yielded a simple chromatogram from which chlorpyrifos could be quantitated. On-line SFE/LC/GC resulted in reduced sample preparation with the grass extract being deposited directly on the LC microcolumn via an impactor interface, followed by the LC/GC separation. The reproducibility of the on-line SFE/LC/GC procedure was studied and found to yield a relative standard deviation of 10.8% for the determination of chlorpyrifos insecticide in grass field samples at a concentration of 160 ng/g. Using this method, the entire analysis including extraction, clean-up, and gas chromatography required less than 0.1 mL of organic solvent.

Epicardial potential mapping. Effects of conducting media on isopotential and isochrone distributions

BACKGROUND

Epicardial excitation sequences, recovery sequences, and potential distributions are recorded from patients during surgery and from animals in the research laboratory for a variety of purposes. During such recordings, a portion of the cardiac surface is exposed to air, and the remainder of the epicardial surface variably is in contact with conductive tissue. No systematic studies document the degree to which these different conditions affect measured excitation times, potential distributions, and/or the configuration of epicardial electrograms.

METHODS AND RESULTS

Epicardial potential distribution was recorded from five isolated, perfused hearts using a 64-unipolar-lead sock. Data were recorded first with the heart suspended in air and then with the heart immersed in a heated tank filled sequentially to full and half-full levels with conductive Tyrode's solution and then NaCl-sucrose solution. These solutions had resistivity less than and more than that of blood, respectively, and air was assumed to have infinite resistivity. Epicardial potentials were recorded from two hearts before removal from the chest, both with and without a latex sheet insulating the heart from the pericardial cradle. Amplitude of recorded potentials from both intact and isolated hearts was markedly higher when the heart was surrounded by an insulating medium, but locations of positive and negative regions were less affected by surrounding medium. Isochrone activation maps calculated using the minimum derivative of the QRS (intrinsic deflection) were not affected by the conductivity of media surrounding the heart.

CONCLUSIONS

The present study provides evidence that isochrone maps recorded at surgery are not distorted by exposure of the cardiac surface to insulating air. Results suggest that epicardial isochrones recorded during cardiac surgery could be used in patients to assess the accuracy of "inverse" procedures that noninvasively compute epicardial electrograms and isochrones from body surface potentials.

Nonparametric identification of discriminative information in body surface maps

A nonparametric method, based on the Kolmogorov-Smirnov (K-S) test was used to detect significant differences between classes of body surface maps (BSPM's). By systematic application of the method throughout the cardiac cycle, discriminative spatio-temporal information can be identified. In a second method, a Sebestyen linear transformation (SLT) was derived to give estimates of pairwise, linear separability of clinical classes. The utility of the method was illustrated by the pairwise comparison of 40 normal subjects (NOR), 40 patients with anterior myocardial infarction (AMI), and 40 with inferior myocardial infarction (IMI). The application examples demonstrated that: a) diagnostic information in low potential amplitude regions may surpass that in high amplitude regions, b) probability distributions of characteristic features showed small overlap in NOR versus AMI and NOR versus IMI dichotomies although they were not linearly separable, and c) the single best separating potential sample in the K-S sense for NOR versus AMI or NOR versus IMI dichotomies recovered 88 and 73% of the SLT performance, respectively.

Detection and localization of prolonged epicardial electrograms with 64-lead body surface signal-averaged electrocardiography

BACKGROUND

Prolonged, fractionated ventricular electrograms often are detectable after myocardial infarction and are a marker for an arrhythmia-prone state. QRS late potentials detected on the body surface with signal-averaged electrocardiography (SAECG) are thought to arise from the diseased tissue that generates prolonged ventricular electrograms and as such are also a marker for arrhythmias. A limitation of the current SAECG technique is that recordings are obtained from only three bipolar lead pairs. Because late potentials probably arise from multiple small sources in the heart, more extensive sampling of the body surface may contribute additional information to the SAECG: The present study investigates the additional sensitivity of SAECG using 64 body surface leads in detecting prolonged epicardial electrograms and examines its use in determining the epicardial location of prolonged electrograms.

METHODS AND RESULTS

Dogs were studied before and 5-10 days after either lateral left ventricular (n = 13) or right ventricular (n = 8) myocardial infarction. Greater prolongation of signal-averaged QRS duration was detected with 64-lead SAECG (postinfarction QRS duration, 100.3 +/- 16.3 msec) than with three-lead SAECG (postinfarction QRS duration, 89.4 +/- 10.1, p = 0.0005). Nineteen of the 21 dogs (90%) had prolonged epicardial electrograms detected over the infarct. The correlation between epicardial electrogram duration and signal-averaged QRS duration calculated from individual leads was much better for 64-lead SAECG (r = 0.88, p less than 0.0001) than for three-lead SAECG (r = 0.53, p = 0.01), and the difference was most marked in cases with longer electrogram durations (more than 100 msec). Local late potential maxima on the thorax after lateral left ventricular infarction were located to the left and inferior compared with those after right ventricular infarction (p = 0.006).

CONCLUSIONS

SAECG with more extensive recording from the body surface using 64 leads detects greater QRS prolongation than three-lead SAECG, and the longer QRS durations detected correspond to the duration of prolonged epicardial electrograms. Body surface location of late potentials corresponds to the epicardial location of the prolonged electrograms. This application of body surface mapping techniques to SAECG may permit more sensitive detection of arrhythmia-prone states and may aid in identifying arrhythmia sources.

Protein-protein interactions with the acidic COOH terminus of the single-stranded DNA-binding protein of the bacteriophage T4

The single-stranded DNA-binding protein of the bacteriophage T4 is encoded by gene 32. Monoclonal antibodies were raised against intact gene 32 protein (gp32). We mapped the epitopes recognized by 12 of these monoclonal antibodies; the epitopes are all within the COOH-terminal region of gp32. As shown by others, removal of the COOH terminus of gp32 abolishes the ability of the intact protein to bind to many T4 proteins involved in replication, recombination, repair, and late transcription. These results suggest that the COOH terminus of gp32 is a protein-binding domain. The COOH terminus is attached to a DNA-binding domain that includes a zinc finger. We propose a model in which the DNA-binding and protein-binding domains are used in T4 replication, recombination, repair, and late transcription. The COOH terminus of gp32 is very acidic and may form four negatively charged amphipathic alpha-helices, which could fold into a four-helix bundle when associated with other proteins. At least six of the monoclonal anti-gp32 antibodies bind to the COOH terminus of gp32 and to DNA. Similarities between the COOH terminus of gp32 and DNA are explored.

Ferredoxin and ferredoxin-NADP reductase from photosynthetic and nonphotosynthetic tissues of tomato

Ferredoxin and ferredoxin-NADP+ oxidoreductase (FNR) were purified from leaves, roots, and red and green pericarp of tomato (Lycopersicon esculentum, cv VFNT and cv Momotaro). Four different ferredoxins were identified on the basis of N-terminal amino acid sequence and charge. Ferredoxins I and II were the most prevalent forms in leaves and green pericarp, and ferredoxin III was the most prevalent in roots. Red pericarp of the VFNT cv yielded variable amounts of ferredoxins II and III plus a unique form, ferredoxin IV. Red pericarp of the Momotaro cv contained ferredoxins I, II, and IV. This represents the first demonstration of ferredoxin in a chromoplast-containing tissue. There were no major differences among the tomato ferredoxins in absorption spectrum or cytochrome c reduction activity. Two forms of FNR were present in tomato as judged by anion exchange chromatography and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. FNR II had a lower apparent relative molecular weight, a slightly altered absorption spectrum, and a lower specific activity for cytochrome c reduction than FNR I. FNR II could be a partially degraded form of FNR I. The FNRs from the different tissues of tomato plants all showed diaphorase activity, with FNR II being more active than FNR I. The presence of ferredoxin and FNR in heterotrophic tissues of tomato is consistent with the existence of a nonphotosynthetic ferredoxin/FNR redox pathway to support the function of ferredoxin-dependent enzymes.

Sources of variability in normal body surface potential maps

Within-group variability of body surface potential maps was assessed on data from 685 carefully validated normal subjects (348 men and 337 women). Sources of within-group variability were evaluated by subgrouping maps by patient sex, age, height, and weight. Contribution of reproducibility error to total variance was assessed in a separate group of 52 normal subjects in whom multiple maps were recorded. Total variance was significantly lower in women than in men. Total variance tended to decrease with age, and the greatest decrease occurred in men during the 3rd decade. The ratio of total variance to mean signal energy showed a slow decrease with age for each group. Results suggest that the dominant source of within-group variability arises from variability of cardiac electric sources while the influence of volume conductor variability is significantly less. Variability due to measurement reproducibility was approximately half of the total variance.

A region of a cyanobacterial genome required for sulfate transport

Using the cysA locus of Salmonella typhimurium as a heterologous probe, we have cloned a region of the Anacystis nidulans R2 (Synechococcus PCC 7942) genome involved in sulfate assimilation. The 8.3-kilobase-pair region encodes at least five transcripts that cannot be detected unless the cells are deprived of sulfur. One of the genes in this region has been sequenced, and the protein that it encodes is homologous to a polypeptide component of other permease systems of Escherichia coli and Salmonella. Insertional inactivation of the putative sulfate permease gene, designated cysA, as well as of other genes within this region, results in cysteine auxotrophy, reduced sulfate uptake, and altered expression of soluble and cytoplasmic-membrane polypeptides associated with sulfur starvation.

Instrumentation and practice standards for electrocardiographic monitoring in special care units. A report for health professionals by a Task Force of the Council on Clinical Cardiology, American Heart Association

The proposed recommendations for continuous electrocardiographic monitoring systems represent goals for future development. Description of a technique in the report does not constitute an endorsement of its clinical use. Lead systems for ECG monitoring must adequately sense the cardiac electrical field and the leads should be standardized. Future monitors should be capable of simultaneously displaying and analyzing multiple leads. Recommendations for electrode placement and position of patient are made. Important parameters in each category of standards for instrumentation published in 1983 in the American National Standard for Cardiac Monitors, Heart Rate Meters, and Alarms are listed. Selected procedures proposed by the Association for the Advancement of Medical Instrumentation to inform users of minimally acceptable accuracy of computerized systems in a standardized manner are presented. Emphasis is placed on the importance of nursing and medical staff capabilities. Personnel qualifications and training as well as systems to assure and maintain quality of immediate ECG diagnosis are highlighted.

Changes in sulfate transport characteristics and protein composition of Anacystis nidulans R2 during sulfur deprivation

Sulfur-starved cells of Anacystis nidulans have an increased capacity to take up sulfate. The apparent Vmax for sulfate uptake increased at least 10-fold after 24 h of sulfur deprivation, whereas the K1/2 remained unchanged at approximately 1.35 microM. The initial rate of sulfate uptake increased between 2 and 6 h after transfer of the cells to sulfur-free medium, in concert with elevated levels of three cytoplasmic membrane polypeptides with molecular masses of 43, 42, and 36 kilodaltons (kDa). The amounts of these polypeptides did not increase in response to nitrogen or phosphorus deprivation. A fourth cytoplasmic membrane polypeptide of 17 kDa did not appear until 24 h after transfer to sulfur-deficient medium. In the total soluble fraction, three polypeptides with masses of 36.5, 33.5, and 28.5 kDa increased dramatically in response to sulfur deprivation, but not in response to nitrogen or phosphorus deprivation. The specificity and abundance of these polypeptides indicate that they could play an important role in the response of A. nidulans to sulfur deprivation.

Detection and localization of coronary artery disease with body surface mapping in patients with normal electrocardiograms

Patients with clinically significant coronary artery disease often have normal resting electrocardiograms. Clinical and experimental studies have shown that body surface potential maps provide improved recognition of some disease states and more regionally selective information than standard electrocardiograms. Body surface maps were recorded at rest from 41 symptomatic patients with angiographically documented coronary artery disease and normal electrocardiograms. Patient maps were statistically compared with maps recorded from 644 normal subjects with the use of previously reported data representation technique. By this technique, maps from patients with symptomatic coronary artery disease and normal electrocardiograms were separated from maps of normal subjects with a sensitivity and specificity greater than 94%. The majority of discriminating information was present in the QRS interval. Fifteen of the 41 symptomatic patients had documented single-vessel coronary disease and their maps were separately compared with normal maps. Average maps from each of three patient groups with single-vessel disease contained abnormal patterns during the QRS interval that were unique to the vessel affected. In comparison with a average map from normal subjects, the average map from the group with left anterior descending coronary disease showed lower potentials over the anterior and inferolateral thorax during the early to mid QRS interval, the average map from the circumflex disease group showed decreased potentials around the entire inferior thorax in the mid to late QRS interval, and the average map from the right coronary disease group showed decreased potentials over the right anterior thorax during the mid to late QRS interval.(ABSTRACT TRUNCATED AT 250 WORDS)