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D L Lee

Publications and source records attributed to D L Lee.

At least 19 recordsLinked to original sources
PubMed2004

Effects of single D-amino acid substitutions on disruption of beta-sheet structure and hydrophobicity in cyclic 14-residue antimicrobial peptide analogs related to gramicidin S.

Gramicidin S (GS) is a 10-residue cyclic beta-sheet peptide with lytic activity against the membranes of both microbial and human cells, i.e. it possesses little to no biologic specificity for either cell type. Structure-activity studies of de novo-designed 14-residue cyclic peptides based on GS have previously shown that higher specificity against microbial membranes, i.e. a high therapeutic index (TI), can be achieved by the replacement of a single L-amino acid with its corresponding D-enantiomer [Kondejewski, L.H. et al. (1999) J. Biol. Chem. 274, 13181]. The diastereomer with a D-Lys substituted at position 4 caused the greatest improvement in specificity vs. other L to D substitutions within the cyclic 14-residue peptide GS14, through a combination of decreased peptide amphipathicity and disrupted beta-sheet structure in aqueous conditions [McInnes, C. et al. (2000) J. Biol. Chem. 275, 14287]. Based on this information, we have created a series of peptide diastereomers substituted only at position 4 by a D- or L-amino acid (Leu, Phe, Tyr, Asn, Lys, and achiral Gly). The amino acids chosen in this study represent a range of hydrophobicities/hydrophilicities as a subset of the 20 naturally occurring amino acids. While the D- and L-substitutions of Leu, Phe, and Tyr all resulted in strong hemolytic activity, the substitutions of hydrophilic D-amino acids D-Lys and D-Asn in GS14 at position 4 resulted in weaker hemolytic activity than in the L-diastereomers, which demonstrated strong hemolysis. All of the L-substitutions also resulted in poor antimicrobial activity and an extremely low TI, while the antimicrobial activity of the D-substituted peptides tended to improve based on the hydrophilicity of the residue. D-Lys was the most polar and most efficacious substitution, resulting in the highest TI. Interestingly, the hydrophobic D-amino acid substitutions had superior antimicrobial activity vs. the L-enantiomers although substitution of a hydrophobic D-amino acid increases the nonpolar face hydrophobicity. These results further support the role of hydrophobicity of the nonpolar face as a major influence on microbial specificity, but also highlights the importance of a disrupted beta-sheet structure on antimicrobial activity.

1-Naphthylamine↗
PubMed2003

Increased endothelin-induced Ca2+ signaling, tyrosine phosphorylation, and coronary artery disease in diabetic dyslipidemic Swine are prevented by atorvastatin.

Endothelin-1 (ET-1) signaling mechanisms have been implicated in the pathogenesis of excess coronary artery disease in diabetic dyslipidemia. We hypothesized that in diabetic dyslipidemia ET-1-induced coronary smooth muscle calcium (Ca2+m) and tyrosine phosphorylation would be increased, and the lipid lowering agent, atorvastatin, would inhibit these increases. Male Yucatan miniature swine groups were treated for 20 weeks: normal low-fat fed control, high-fat/cholesterol fed (hyperlipidemic), hyperlipidemic made diabetic with alloxan (diabetic dyslipidemic), and diabetic dyslipidemic treated with atorvastatin (atorvastatin-treated). Blood glucose values were 5-fold greater in diabetic dyslipidemic and atorvastatin-treated versus control and hyperlipidemic. Total and low-density lipoprotein (LDL) plasma cholesterol in hyperlipidemic, diabetic dyslipidemic, and atorvastatin-treated were approximately 5-fold greater than control. Intravascular ultrasound detectable coronary disease and hypertriglyceridemia were only observed in diabetic dyslipidemic and were abolished by atorvastatin. In freshly isolated cells, the Ca2+m response to ET-1 in diabetic dyslipidemic was greater than in control, hyperlipidemic, and atorvastatin-treated groups. Selective ET-1 receptor antagonists showed in the control group that the ETB subtype inhibits ETA regulation of Ca2+m. There was almost a complete switch of receptor subtype regulation of Ca2+m from largely ETA in control to an increased inhibitory interaction between ETA and ETB in hyperlipidemic and diabetic dyslipidemic groups, such that neither ETA nor ETB antagonist alone could block the ET-1-induced Ca2+m response. The inhibitory interaction was attenuated in the atorvastatin-treated group. In single cells, basal and ET-1-induced tyrosine phosphorylation in diabetic dyslipidemic were more than 3- and 6-fold greater, respectively, than in control, hyperlipidemic, and atorvastatin-treated. Attenuation by atorvastatin of coronary disease and ET-1-induced Ca2+m and tyrosine phosphorylation signaling with no change in cholesterol provides strong evidence for direct actions of atorvastatin and/or triglycerides on the vascular wall.

Animals↗
PubMed2001

Are trigger sequences essential in the folding of two-stranded alpha-helical coiled-coils?

The amino acid residues comprising the interface between strands of the coiled-coil motif are usually hydrophobic and make a major contribution to coiled-coil folding and stability. However, in some cases the presence of excellent hydrophobic residues at the coiled-coil interface is insufficient for folding. It has been proposed that a "consensus trigger sequence" exists that is necessary within the coiled-coil domains of various proteins to trigger folding. Therefore, in this study we designed a 31-residue hybrid sequence based on sequences from the two-stranded parallel coiled-coil domains of the yeast transcriptional activator GCN4 and the actin-bundling protein Dictyostelium discoideum cortexillin I. The hybrid and its analogs were studied by CD spectroscopy and analytical ultracentrifugation. The hybrid had stable residues in the core "a" and "d" positions in the 3-4 hydrophobic repeat, denoted (abcdefg)n, but did not have a consensus trigger sequence and did not possess appreciable secondary structure as determined by CD spectroscopy. The substitutions in the parent peptide were introduced at positions other than "a" and "d", altering a variety of interactions including alpha-helical propensity, interchain and intrachain electrostatics, and hydrophobicity. Although the substitutions did not bring the overall sequence in closer agreement to the consensus trigger sequence, they increased coiled-coil folding and stability. Therefore, our results suggest that the combination of stabilizing effects along a protein sequence is a more general indicator of protein folding in coiled-coils than the identification of a specific trigger sequence. We propose that surpassing a critical threshold stability value using any type or combination of stabilizing effects will allow coiled-coils to fold, in the absence of a specific trigger sequence per se.

Amino Acid Sequence↗
PubMed2001

Investigation of a direct conversion flat panel imager for portal imaging.

Flat-panel based x-ray imaging is an emerging new technology that could be used to significantly improve the quality of on-line portal imagers. There are two types of flat panel imagers: direct and indirect conversion. Previous experimental work on flat panel detectors for portal imaging application used indirect-conversion imagers. In this paper, a direct-conversion amorphous-selenium flat panel imager is investigated for application in portal imaging. The imager has an active imaging area of 14 in. X 17 in., i.e., 3072 X 2560 pixels each with dimensions 139 microm X 139 microm. The spatial frequency dependent detective quantum efficiency of the imager has been measured for a 6 MV beam and found to be amongst the best area detectors investigated for on-line portal imaging. Effects of changing pixel size, as well as possible improvements to both the image quality and convenience of operation are discussed. Comparison with an indirect conversion flat panel imager is also included.

Diagnostic Imaging↗
PubMed2000

Chronic unloading by left ventricular assist device reverses contractile dysfunction and alters gene expression in end-stage heart failure.

BACKGROUND: Left ventricular (LV) assist devices (LVADs) can improve contractile strength and normalize characteristics of the Ca(2+) transient in myocytes isolated from failing human hearts. The purpose of the present study was to determine whether LVAD support also improves contractile strength at different frequencies of contraction (the force-frequency relationship [FFR]) of intact myocardium and alters the expression of genes encoding for proteins involved in Ca(2+) handling. METHODS AND RESULTS: The isometric FFRs of LV trabeculae isolated from 15 patients with end-stage heart failure were compared with those of 7 LVAD-supported patients and demonstrated improved contractile force at 1-Hz stimulation, with reversal of a negative FFR after LVAD implantation. In 20 failing hearts, Northern blot analysis for sarcoplasmic endoreticular Ca(2+)-ATPase subtype 2a (SERCA2a), the ryanodine receptor, and the sarcolemmal Na(+)-Ca(2+) exchanger was performed on LV tissue obtained before and after LVAD implantation. These paired data demonstrated an upregulation of all 3 genes after LVAD support. In tissue obtained from subsets of these patients, Western blot analysis was performed, and oxalate-supported Ca(2+) uptake by isolated sarcoplasmic reticular membranes was determined. Despite higher mRNA for all genes after LVAD support, only SERCA2a protein was increased. Functional significance of increased SERCA2a was confirmed by augmented Ca(2+) uptake by sarcoplasmic reticular membranes isolated from LVAD-supported hearts. CONCLUSIONS: LVAD support can improve contractile strength of intact myocardium and reverse the negative FFR associated with end-stage heart failure. The expression of genes encoding for proteins involved in Ca(2+) cycling is upregulated (reverse molecular remodeling), but only the protein content of SERCA2a is increased.

Adult↗
PubMed2000

Vaccination of young lambs against infection with Nematodirus battus using gamma irradiated larvae.

Helminthologically naIve 6-week-old Suffolk lambs were given 1-3 doses of 20000 gamma-irradiated infective larvae (L3) of the nematode Nematodirus battus at weekly intervals. Following an anthelmintic drench they were challenged with 50000 viable L3 at 10 weeks of age. Nematode worm burdens 14 days post-challenge showed a significant (P<0.01) 66% reduction in the single vaccine dose group. The two and three dose groups had mean worm burdens which were 30 and 42% lower than controls, respectively, although these were not statistically significant. There was little measurable stimulation of the immune system in the vaccinated lambs, suggesting that the repeatedly dosed animals may have developed immunological unresponsiveness to the parasite.

Animals↗
PubMed2000

An anteromedial internal jugular vein successfully cannulated using the assistance of ultrasonography.

The internal jugular vein usually is found either lateral or anterolateral to the carotid artery when it is cannulated for central vein access using external anatomical landmarks. We report a case in which the carotid artery was inadvertently punctured, but the right internal jugular vein could not be found. We used ultrasonic guidance to determine that the right internal jugular vein was anteromedial to the carotid artery. A figure showing the ultrasound of this rare anatomical variation is provided. The advantages and utility of ultrasound when used for the placement of internal jugular central vein catheters are reviewed.

Aged↗
PubMed2000

Neonicotinoid insecticides: molecular features conferring selectivity for insect versus mammalian nicotinic receptors.

The favorable selective toxicity of neonicotinoid insecticides (represented here by imidacloprid, thiacloprid, and a nitromethylene analogue) for insects versus mammals is not shared by three of their N-unsubstituted imine derivatives or by nicotine or epibatidine. The same selectivity pattern is evident at the receptor level, i.e., the insect nicotinic acetylcholine receptor (nAChR) versus mammalian nAChR subtypes (alpha1, alpha3, alpha4, and alpha7) assayed independently. The insect-selective compounds are not protonated with a nitroimine, cyanoimine, or nitromethylene group and the mammalian-selective compounds are ionized at physiological pH. We propose that the negatively charged tip of the nitro or cyano group (not a partial positive charge at imidazolidine N-1 as suggested earlier) interacts with a putative cationic subsite of the insect nAChR. This contrasts with the mammalian nAChRs where the iminium cation (+C-NH2 <--> C =+NH2) of the neonicotinoid imine derivatives or ammonium nitrogen of nicotine or epibatidine interacts with the anionic subsite.

Animals↗
PubMed1999

Role of C3 cleavage in monocyte activation during extracorporeal circulation.

BACKGROUND: We previously demonstrated that inhibiting formation of terminal complement components (C5a and C5b-9) prevents platelet and neutrophil (PMN) but not monocyte activation during simulated extracorporeal circulation (SECC). This study examined whether earlier complement inhibition during SECC, blocking C3a formation, would additionally prevent monocyte activation. METHODS AND RESULTS: SECC was established by recirculating heparinized whole blood from human volunteers on a membrane oxygenator. CAB-2, a chimeric protein constructed from genes encoding the complement regulatory proteins CD46 and CD55, inactivates the C3/C5 convertases and blocks in vitro generation of C3a, C5a, and C5b-9. CAB-2 was used in 4 experiments at a final concentration of 300 micrograms/mL and 4 experiments at 30 micrograms/mL; 4 control runs used vehicle alone. Samples were assayed for C3a and C5b-9, monocyte activation (CD11b upregulation), PMN activation (CD11b upregulation and elastase release), and platelet activation (P-selectin expression and monocyte-platelet conjugate formation). CAB-2 at both doses significantly inhibited formation of C3a and C5b-9 during SECC. High-dose CAB-2 significantly blocked monocyte and PMN CD11b upregulation and PMN elastase release. CAB-2 also inhibited formation of platelet activation-dependent monocyte-platelet conjugates. CONCLUSIONS: Blockade of complement activation early in the common pathway inhibited monocyte CD11b upregulation during SECC, suggesting that early complement components contribute most to monocyte activation during SECC. As expected, PMN and platelet activation were blocked by terminal complement inhibition. This investigation further elucidates the relation between complement and blood cell activation during simulated cardiopulmonary bypass.

Blood Platelets↗
PubMed1999

Intestinal helminth infections amongst school children in the Serian District of Sarawak.

School children from 3 primary and 2 secondary schools in Sarawak were examined for the presence of gastrointestinal helminths. One primary school and 1 secondary school were located in a town (Serian), the other primary and secondary schools were in the countryside outside Serian. The intestinal helminths detected were Ascaris lumbricoides, Trichuris trichiura, Enterobius vermicularis and hookworm. Children from the rural schools had higher numbers of eggs in their faeces than those from the Serian schools. Children from the rural primary schools had higher number of eggs than those from the rural secondary school. The prevalence of Ascaris, Trichuris and hookworms in male and female and in primary and secondary school children was recorded.

Adolescent↗
PubMed1998

From toxicological problem to therapeutic use: the discovery of the mode of action of 2-(2-nitro-4-trifluoromethylbenzoyl)-1,3-cyclohexanedione (NTBC), its toxicology and development as a drug.

NTBC is a triketone with herbicidal activity that has been shown to have a novel mode of action by inhibiting the enzyme 4-hydroxyphenylpyruvate dioxygenase in plants. Early studies on the toxicity of this compound found that rats treated with NTBC developed corneal lesions. Investigations aimed at understanding the mechanistic basis for the ocular toxicity discovered that the rats developed tyrosinaemia and excreted large amounts of 4-hydroxyphenylpyruvate and 4-hydroxyphenyllactate, owing to inhibition of the hepatic enzyme 4-hydroxyphenylpyruvate dioxygenase. The corneal lesions resemble those seen when rats are fed a diet supplemented with tyrosine, leading us to conclude that the ocular toxicity seen with NTBC is a consequence of a marked and sustained tyrosinaemia. Studies in collaboration with Professor Sven Lindstedt showed that NTBC was a potent inhibitor of purified human liver 4-hydroxyphenylpyruvate dioxygenase. This interaction lead to the concept of using NTBC to treat patients with tyrosinaemia type 1, to block or reduce the formation of toxic metabolites such as succinylacetoacetate in the liver. Zeneca Agrochemicals and Zeneca Pharmaceuticals made NTBC available for clinical use and, with the approval of the Swedish Medical Products Agency, a seriously ill child with an acute form of tyrosinaemia type 1 was successfully treated in February 1991. Subsequently, other children with this inborn error of metabolism in Sweden and other countries have been treated with NTBC. The drug is now available to those in need via Swedish Orphan AB.

4-Hydroxyphenylpyruvate Dioxygenase↗
PubMed1998

Attentional focus of students with hyperactivity during a word-search task.

Mirrors have been used to focus attention to aspects of the self (e.g., to known strategies, standards). We hypothesized that this could be important for students with hyperactivity/inattention, who typically direct attention outward to external novelty. In this study, we administered a partially solvable word puzzle to 43 middle school students, with and without hyperactivity/inattention, in the presence and absence of a mirror, counterbalanced for condition and form order. Differences between students with hyperactivity/inattention and comparisons in accuracy were found only in the no mirror condition. Furthermore, the beneficial effect of the mirror for children with hyperactivity/inattention was most pronounced for those who looked at the mirror. Findings were interpreted in terms of their potential to remedy the production deficits of these children.

Adolescent↗
PubMed1998

The development of a new direct digital extra-oral radiographic system prototype using a thin-film transistor panel.

OBJECTIVE: To develop a new method of direct digital image acquisition for extra-oral radiography. METHODS: A selenium detector was combined with a thin-film transistor sensor and integrated with current technology for computed radiography in a system named Direct Radiography (DR). The effective image area of the prototype is 178 mm x 213.5 mm, and consists of a 1280 x 1536 pixel matrix with a pixel pitch of 139 microns x 139 microns. The electrical characteristics were evaluated and image quality was tested with a dried human mandible and half-skull phantom. The resultant images were subjectively reviewed by seven oral and maxillofacial radiologists. RESULTS: The prototype had a signal-to-noise ratio of 400:1 when the exposure was 250 x 10(-8) C/Kg. Spatial resolution was equal to the Nyquist frequency of 3.55 cycles/mm. The images of the phantoms were considered to be of equivalent quality to conventional screen-film images and demonstrated the normal anatomical structures used for clinical evaluation. Three to four images per minute were generated with this system. CONCLUSION: The DR system has an X-ray sensitivity comparable with a 400-speed film-screen system and appears suitable for clinical radiography. Further evaluation is therefore planned.

Humans↗
PubMed1997

Ureteral duplication with lower pole ectopia to the vas: a case report of an exception to the Weigert-Meyer law.

We report an unusual case of ureteral duplication with lower-pole ectopia and ureterolithiasis, which violates the Weigert-Meyer law. The duplicated ureter arose from a lower-pole calyx and drained inferiorly into the ipsilateral vas. A presentation of the case is followed by a comparison to the only known similar one, reported in 1988. A possible embryologic hypothesis for this anomaly is discussed.

Abnormalities, Multiple↗
PubMed1997

Neurologic findings in coronary artery bypass patients: perioperative or preexisting?

OBJECTIVES/DESIGN: This prospective study compares the incidence of preexisting neurologic findings in elective cardiac surgery patients presenting with and without coronary atherosclerosis. SETTING: This single-center study was conducted at a tertiary care hospital. PARTICIPANTS/INTERVENTIONS: After Review Board approval and obtaining written informed consent, 11 patients undergoing valvular heart surgery, 9 patients undergoing similar valvular procedures with concomitant coronary artery bypass surgery, and 4 patients undergoing coronary artery bypass surgery alone were enrolled. Preoperatively, all patients underwent a structured neurologic assessment, and the latter four additionally had preoperative magnetic resonance imaging. MEASUREMENTS AND MAIN RESULTS: The patients, 9 of 24 of whom were female, were aged 46 to 78 years and, other than ischemic heart disease, had medical histories that were similar between groups, with the exception of one patient having scleroderma. None of the patients had a clinical history of neurologic or cerebrovascular disease. Nine percent (1 of 11) of the valve-only patients showed subtle preoperative neurologic abnormalities, compared with 89% (eight of nine) of the valve patients having concomitant coronary surgery and 100% (four of four) of coronary artery bypass-only patients. Additionally, brain imaging scans of all four coronary bypass patients showed nonspecific changes reported as scattered punctate areas of high signal less than 3 to 4 mm in diameter. CONCLUSION: This survey shows that both subtle neurological abnormalities and magnetic resonance imaging lesions can be found in a high percentage of patients with coronary atherosclerosis. Furthermore, this study indicates that without a standardized preoperative neurological examination, postoperative neurologic dysfunction cannot necessarily be ascribed to perioperative events.

Aged↗
PubMed1997

The effect of dexamethasone on resistance of older lambs to infection with Nematodirus battus.

Old lambs (8 months of age) infected with 50,000 L3 of Nematodirus battus had larvae developing normally in their tissues on day 4 post-infection (P.I.), but by day 8 P.I. there were only 4105 +/- 1044 worms left in the alimentary tract. Some of these worms contained crystals in their intestine. Eight-month-old lambs treated with dexamethasone and infected with 50,000 L3 of N. battus contained a mean worm burden of 7878 +/- 1262 on 18 days P.I. Untreated 8-month-old lambs similarly infected were virtually worm free by day 18 P.I. Peripheral eosinophilia became elevated in the untreated lambs over the course of infection and, at post-mortem, the tissue mast cell and eosinophil counts were much higher than in the dexamethasone treated group. Although the phenomenon of age resistance is thought to have a strong immunological component, there may also be other physiological factors, resulting in fewer nematodes and lower fecundity of the worms.

Aging↗
PubMed1997

The mast cell and eosinophil response of young lambs to a primary infection with Nematodirus battus.

Helminthologically naive 8-week-old lambs were administered 50,000 infective-stage larvae of the trichostrongyle nematode Nematodirus battus. Initial mean adult worm burdens were significantly reduced (P < 0.01) at day 21 post-infection (p.i.). Peripheral blood eosinophil counts showed a significant increase (P < 0.001) by day 25 p.i. when compared with uninfected control animals. Sections of small intestine taken at post-mortem from the area of adult worm establishment over the course of infection showed a significant increase in mucosal eosinophil and mast cell numbers during the period of adult worm rejection, when compared with uninfected control animals. These results show that young lambs develop significant increases in the numbers of cells associated with an inflammatory reaction in the intestine during the development of a partially protective immune response to this parasitic nematode.

Animals↗