Search PubMed⌕ Search

Biomedical subjects

K Clark

Publications and source records attributed to K Clark.

At least 37 records · Page 2Linked to original sources
PubMed1999

Risk factors for sleep-disordered breathing in children. Associations with obesity, race, and respiratory problems.

This study examined risk factors for sleep-disordered breathing (SDB) in children and adolescents; specifically, quantifying risk associated with obesity, race, and upper and lower respiratory problems. Subjects were participants in a genetic-epidemiologic study of SDB and included 399 children and adolescents 2 to 18 yr of age, recruited as members of families with a member (a proband) with known sleep apnea (31 index families) or as members of neighborhood control families (30 families). SDB was assessed with home overnight multichannel monitoring and SDB was defined based on an apneahypopnea index >/= 10 (moderately affected) or < 5 (unaffected). SDB of moderate level was significantly associated with obesity (odds ratio, 4.59; 95% confidence interval [CI], 1.58 to 13.33) and African-American race (odds ratio, 3.49; 95% CI, 1.56 to 8.32) but not with sex or age. After adjusting for obesity, proband sampling, race and familial clustering, sinus problems and persistent wheeze each independently (of the other) predicted SDB. These data suggest the importance of upper and lower respiratory problems and obesity as risk factors for SDB in children and adolescents. Increased risk in African Americans appears to be independent of the effects of obesity or respiratory problems.

Adolescent↗
PubMed1998

Regulation of the extracellular ligand binding activity of integrins.

Integrins are a large heterodimeric family of cell surface adhesion receptors that bind extracellular matrix and cell surface ligands. The extracellular ligand binding activity of integrins is a dynamic and highly regulated event involving the induction of conformational changes within the integrin structure. The adhesive properties of integrins can be controlled by altering the activation state of the integrin, either through conformational change or receptor clustering, using mechanisms that are regulated by intracellular proteins. In this review, we will discuss what is currently known about integrin structure and the ligand binding sites present within the receptor. In addition, the mechanisms by which the ligand binding event is regulated through conformational change will be addressed, and the potential role of intracellular cytoplasmic proteins will be discussed.

Animals↗
PubMed1998

Analysis of ligand-induced and ligand-attenuated epitopes on the leukocyte integrin alpha4beta1: VCAM-1, mucosal addressin cell adhesion molecule-1, and fibronectin induce distinct conformational changes.

The leukocyte integrin alpha4beta1 is a receptor for both cell surface ligands (VCAM-1 and mucosal addressin cell adhesion molecule-1 (MAdCAM-1)) and extracellular matrix components (fibronectin). Through regulated interactions with these molecules, alpha4beta1 mediates leukocyte migration from the vasculature at sites of inflammation. Regulation of integrin activity plays a key role in controlling leukocyte-adhesive events and appears to be partly determined by changes in integrin conformation. Several mAbs that recognize ligand-induced binding site epitopes on integrins have been characterized, and a subset of these mAbs are capable of stimulating integrin-ligand binding. Conversely, some mAbs recognize epitopes that are attenuated by ligand engagement and allosterically inhibit ligand binding. To gain insight into ligand-specific effects on integrin conformation, we have examined the ability of different ligands to modulate the binding of four distinct classes (A, B1, B2, and C) of anti-alpha4 Abs to alpha4beta1. VCAM-1 attenuated B (antifunctional) class epitopes via an allosteric mechanism and also allosterically inhibited the binding of the function-blocking anti-beta1 mAb 13. Additional alpha4beta1 ligands (fibronectin fragments, MAdCAM-1, and the CS1 peptide) also inhibited mAb 13-integrin binding; however, the epitopes of the class B anti-alpha4 mAbs were attenuated by the fibronectin fragments, but not by MAdCAM-1 or the CS1 peptide. Of the two anti-alpha4 class A mAbs examined, one recognized an epitope that was induced uniquely by VCAM-1. Taken together, these data suggest that overlapping but distinct binding mechanisms exist for different alpha4beta1 ligands and that distinct conformational changes are induced upon integrin engagement by different ligands.

Animals↗
PubMed1998

Transfer of a protein binding epitope to a minimal designed peptide.

Results from protein mutagenesis and x-ray crystallographic studies of the multidomain protein Vascular Cell Adhesion Molecule (VCAM) were used to design cyclic octapeptides that retain the critical structural and binding elements of the epitope of VCAM in the interaction with the integrin alpha 4 beta 1 (VLA-4). Changes in the activities of peptide analogues correlated with the relative activities of protein mutants of VCAM, and predicted the properties of two new mutants that bound alpha 4 beta 1 with improved affinity vs wild type protein. The nmr structures of two peptides revealed a high degree of similarity to the structure of the VCAM binding epitope. These results demonstrate that a compact binding epitope identified via protein structure-function studies may be transferred to a synthetically accessible small peptide with the key structure-activity relationships intact.

Binding Sites↗
PubMed1998

Normal postexercise facilitation and depression of motor evoked potentials in postpolio patients.

We studied the effects of exercise on motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation in healthy subjects and postpolio patients. Subjects performed repeated sets of isometric exercise until the muscle fatigued. In both groups, the mean MEP amplitude immediately after each exercise set was approximately twice that of the baseline amplitude, indicating similar postexercise facilitation, and after fatigue was approximately half that of the baseline amplitude, indicating similar postexercise depression. We conclude that the intracortical component of central fatigue is normal in postpolio patients.

Adult↗
PubMed1998

Characterization of recombinant human cathepsin B expressed at high levels in baculovirus.

The lysosomal cysteine protease cathepsin B has been studied intensely for many years because of its unique characteristics and its potential involvement in disease states. A reproducible, high yield expression system for active recombinant protein is key to biochemical and biophysical studies as well as rational drug design. Although several microbial and mammalian expression systems for recombinant human cathepsin B have been described, these have been limited by low or variable yields. Further, in some of these systems hyper-glycosylation of the enzyme near the active site affects its activity. We describe a baculovirus expression system and purification scheme that solve all of these problems. Yields of active, protected enzyme were reproducibly in excess of 25 mg/L. Since this protein was not hyper-glycosylated, it had greater activity than cathepsin B produced in yeast systems as indicated by a threefold increase in Kcat. In addition, the biophysical properties of the baculovirus-expressed cathepsin B, as measured by dynamic light scattering, were more amenable to crystallographic study since the data indicated proteins of more uniform size. Therefore, this system for the production of recombinant human cathepsin B constitutes a major improvement in both quantity and quality over those previously reported. Further, we demonstrate that the manner of expression and purification of this enzyme has profound effects on its kinetic and physical parameters.

Baculoviridae↗
PubMed1998

A population-based study of abdominal wall defects in South Australia and Western Australia.

The purpose of this study was to determine the prevalence, clinical characteristics, prenatal diagnosis and occurrence of other birth defects with abdominal wall defects in births and terminations of pregnancy in South Australia (SA) and Western Australia (WA) over the period 1980-90. Cases of gastroschisis, exomphalos, bladder exstrophy, cloacal exstrophy and body stalk anomaly were ascertained from the WA Birth Defects Registry (1980-90) and the SA Birth Defects Register (1986-90). The registers are comparable population-based data collections with information on livebirths and stillbirths of at least 400 g birthweight or 20 weeks' gestation, and terminations of pregnancy for fetal abnormality. The prevalence of gastroschisis was 1.65/10,000 births (59 cases) and of exomphalos 2.90/10,000 births (104 cases). There was no significant difference in prevalence of exomphalos or gastroschisis between SA and WA for the years 1986-90. However, if data from WA for the years 1980-85 were included, SA had a significantly higher prevalence of exomphalos (prevalence ratio 1.71, confidence interval [CI] 1.16-2.55), although not of gastroschisis (prevalence ratio 1.35, CI 0.79-2.32). Exomphalos was significantly more common in mothers < 20 years (odds ratio [OR] 2.45, CI 1.22-4.86) and in mothers of 40 years or older (OR 5.65, CI 1.69-16.77). Gastroschisis was more common in younger mothers (OR 8.76, CI 4.02-19.32). Both exomphalos and gastroschisis were associated with low birthweight, prematurity, intrauterine growth retardation and caesarean section. The reason for the higher prevalence of exomphalos in SA than WA was not clear, but may be related to differences in prenatal diagnosis. The association between maternal age < 20 years and exomphalos raises the possibility of common factors in the aetiology of gastroschisis and exomphalos.

Abdominal Muscles↗
PubMed1998

An oligo-screening strategy to fill gaps found during shotgun sequencing projects.

During the course of projects to sequence human and nematode cosmids we encountered great difficulties generating contiguous sequence in regions with repetitive DNA (Alu repeats in humans and tandem or inverted repeats in the nematode). We have developed a simple and efficient strategy to fill gaps. By screening M13, plasmid or phagemid libraries with oligonucleotides flanking the gap, clones are identified that contiguate the cosmid sequence. Our method has been integrated into the GAP4 sequence assembly program. The strategy reduces both time and costs in large scale sequencing projects.

Animals↗
PubMed1998

'Two-component' ethylene signaling in Arabidopsis.

The Arabidopsis ETR1 gene codes for an ethylene hormone receptor that has striking sequence similarity with bacterial two-component regulators. This finding predicts that the ETR1 receptor transduces the ethylene signal through the phosphotransfer mechanisms established for a number of the bacterial regulators. To test this hypothesis, we have performed in vitro assays for ETR1 autokinase activity as well as for transfer of phosphate to the ETR1 receiver. So far, we have not detected either of these activities. Another question we are focusing on is the identity of protein substrates of the ETR1 receptor. Using the yeast two-hybrid system, we have obtained several clones to be subsequently characterized as potential interactors with ETR1.

Arabidopsis↗
PubMed1998

Manual versus mechanical compression for femoral artery hemostasis after cardiac catheterization.

BACKGROUND: Most cardiac catheterizations are performed via femoral artery access. Reported rates of both peripheral vascular complications and success rates for the use of manual and mechanical compression techniques to achieve femoral artery hemostasis after cardiac catheterization vary. OBJECTIVE: To determine is use of a mechanical clamp is as effective as standard manual pressure for femoral artery hemostasis after cardiac catheterization. METHODS: Subjects consisted of 720 patients from 2 community hospitals who had elective diagnostic cardiac catheterization via the femoral artery. The control group (n=343) received manual compression for hemostasis; the study group (n=377) received mechanical compression. Standard protocols were used for the 2 compression techniques. Pressure was applied for a minimum of 10 minutes for 5F and 6F sheaths and catheters and for a minimum of 15 minutes for 7F and 8F sheaths and catheters. Prospective data were collected and analyzed for each patients, including sheath or catheter size, blood pressure, height, weight, age, time from administration of local anesthetic to successful cannulation of the femoral artery, anticoagulation status, total compression time, physician performing the catheterization procedure, nurse or technician who obtained hemostasis, and complications. In follow-up, patients were asked site-specific and functional status questions 1 to 2 days after the catheterization procedure and again 3 days after the catheterization procedure. RESULTS: Data were analyzed by using frequency distributions, measures of central tendency, and measures of variability. Only 1 difference between the 2 groups was significant: manual compression time was 14.93 +/- minutes, whereas mechanical compression time was 17.13 +/- minutes. CONCLUSION: Mechanical compression is as effective as manual compression for femoral artery hemostasis after cardiac catheterization.

Cardiac Catheterization↗
PubMed1998

The effect of intrathecal and epidural narcotic analgesia on the length of labor.

A number of studies have shown conflicting results on the effect of epidural (EPI) analgesia on the length of labor. Combined spinal-epidural (CSE) and intrathecal analgesia (ITA) techniques have been used to provide pain relief for parturients, but currently there are few studies comparing EPI, CSE, and ITA techniques and their effect on the length of labor. Intrathecal opioids provide immediate pain relief for the parturient without autonomic, sensory, or motor blockade. The purpose of this retrospective study is to identify the effects of ITA on the length of labor compared with other regional anesthesia techniques. A total of 213 uncomplicated obstetric charts were reviewed in a 70-bed Air Force hospital that provided EPI, CSE, and ITA for obstetrical patients. The study consisted of the following four groups: (1) CSE (n = 76), (2) EPI(n = 41), (3) ITA (n = 49), and (4) no regional analgesia (NR) (n = 47). The results showed that the length of first-stage labor was statistically significantly less for those who received ITA compared with those who received CSE, EPI, and NR (P < .001). Second-stage labor was statistically significantly shorter for the NR group compared with the CSE and EPI groups (P < .01). No statistically significant difference was found between the length of second stage for ITA and NR groups. ITA analgesia shortened the first stage significantly in both primipara and multipara patients (P < .01). These results imply that the use of intrathecal opioids in the obstetrical patient does not prolong labor and seems to shorten the first stage of labor in both the primipara and multipara patients.

Adult↗
PubMed1997

Potent alpha 4 beta 1 peptide antagonists as potential anti-inflammatory agents.

The migration, adhesion, and subsequent extravasation of leukocytes into inflamed tissues contribute to the pathogenesis of a variety of inflammatory diseases including asthma, rheumatoid arthritis, inflammatory bowel disease, and multiple sclerosis. The integrin adhesion receptor alpha 4 beta 1 expressed on leukocytes binds to the extracellular matrix protein fibronectin and to the cytokine inducible vascular cell adhesion molecule-1 (VCAM-1) at inflamed sites. Binding of alpha 4 beta 1 to VCAM-1 initiates firm adhesion of the leukocyte to the vascular endothelium followed by extravasation into the tissue. Monoclonal antibodies generated against either alpha 4 beta 1 or VCAM-1 can moderate this inflammatory response in a variety of animal models. Recently peptides containing a consensus LDV sequence based on the connecting segment-1 (CS-1) of fibronectin and cyclic peptides containing an RCD motif have shown promise in modulating leukocyte migration and inflammation presumably by blocking the interaction of alpha 4 beta 1 with VCAM-1. Here we describe novel, highly potent, cyclic peptides that competitively inhibit alpha 4 beta 1 binding to VCAM-1 and fibronectin at sub nanomolar concentrations. The structure of a representative analog was determined via NMR spectroscopy and used to facilitate optimization of peptide leads. The peptides discussed here utilize similar functional groups as the binding epitope of VCAM-1, inhibit lymphocyte migration in vivo, and are highly selective for alpha 4 beta 1. Furthermore the structure--activity relationships described here have provided a template for the structure-based design of small molecule antagonists of alpha 4 beta 1-mediated cell adhesion processes.

Animals↗
PubMed1997

Novel cytokine-independent induction of endothelial adhesion molecules regulated by platelet/endothelial cell adhesion molecule (CD31).

Tumor necrosis factor-alpha, interleukin-1, and endotoxin stimulate the expression of vascular endothelial cell (EC) adhesion molecules. Here we describe a novel pathway of adhesion molecule induction that is independent of exogenous factors, but which is dependent on integrin signaling and cell-cell interactions. Cells plated onto gelatin, fibronectin, collagen or fibrinogen, or anti-integrin antibodies, expressed increased amounts of E-selectin, vascular cell adhesion molecule-1, and intercellular adhesion molecule-1. In contrast, ECs failed to express E-selectin when plated on poly-L-lysine or when plated on fibrinogen in the presence of attachment-inhibiting, cyclic Arg-Gly-Asp peptides. The duration and magnitude of adhesion molecule expression was dependent on EC density. Induction of E-selectin on ECs plated at confluent density was transient and returned to basal levels by 15 h after plating when only 7 +/- 2% (n = 5) of cells were positive. In contrast, cells plated at low density displayed a 17-fold greater expression of E-selectin than did high density ECs with 57 +/- 4% (n = 5) positive for E-selectin expression 15 h after plating, and significant expression still evident 72 h after plating. The confluency-dependent inhibition of expression of E-selectin was at least partly mediated through the cell junctional protein, platelet/endothelial cell adhesion molecule-1 (PECAM-1). Antibodies against PECAM-1, but not against VE-cadherin, increased E-selectin expression on confluent ECs. Co- culture of subconfluent ECs with PECAM-1- coated beads or with L cells transfected with full-length PECAM-1 or with a cytoplasmic truncation PECAM-1 mutant, inhibited E-selectin expression. In contrast, untransfected L cells or L cells transfected with an adhesion-defective domain 2 deletion PECAM-1 mutant failed to regulate E-selectin expression. In an in vitro model of wounding the wound front displayed an increase in the number of E-selectin-expressing cells, and also an increase in the intensity of expression of E-selectin positive cells compared to the nonwounded monolayer. Thus we propose that the EC junction, and in particular, the junctional molecule PECAM-1, is a powerful regulator of endothelial adhesiveness.

Blood Platelets↗