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Biomedical subjects

J P Lee

Publications and source records attributed to J P Lee.

At least 19 recordsLinked to original sources
PubMed1996

In vitro growth of Alzheimer's disease beta-amyloid plaques displays first-order kinetics.

A salient pathological feature of Alzheimer's disease (AD) is the presence of amyloid plaques in the brains of affected patients. The plaques are predominantly composed of human beta-amyloid peptide (A beta). Although the aggregation of synthetic A beta has been extensively studied, the mechanism of AD plaque growth is poorly understood. In order to address this question, we used an in vitro model of plaque growth to determine if assembly or aggregation of A beta is required for deposition. Labeled A beta at physiological concentrations readily deposited onto both neuritic and diffuse plaques and cerebrovascular amyloid in unfixed AD brain tissue, whereas essentially no deposition was detected in tissue without performed amyloid. Using this in vitro model of plaque growth, the kinetics of A beta deposition onto plaques was examined in two independent but complementary systems. Intact sections of unfixed AD brain cortex (analyzed by autoradiographic densitometry) allowed definitive morphological analysis of the site of deposition, while homogenates of the same tissue (analyzed by radioisotope counting) allowed precise quantitation of deposition over a wide range of conditions. Essentially identical results were obtained for both systems. Growth of preexisting tissue plaques by deposition of A beta was found to follow first-order dependence on A beta concentration and exhibited a pH optimum of 7. In sharp contrast, A beta aggregation in the absence of template follows higher order kinetics and shows a pH optimum of 5. On the basis of criteria of kinetic order, pH dependence, and structure-activity relationships, we conclude that aggregation of A beta (template-independent initial nidus formation) and deposition of A beta (template-dependent subsequent plaque growth) are fundamentally distinct biochemical processes. The process of plaque growth and maturation by A beta deposition may be an important target for therapeutic intervention to block the progression of AD.

Alzheimer Disease↗
PubMed1996

Dentin ablation with three infrared lasers.

BACKGROUND AND OBJECTIVE: Lasers are used for caries removal in enamel and dentin, but are currently limited in their ability to remove sound tooth structure. In this study plasma interaction regimes are investigated as the principal factor determining the ablation characteristics. STUDY DESIGN/MATERIALS AND METHODS: Three ablation parameters are considered: ablation rates (AR), surface temperatures (ST), and surface morphological characteristics. The three lasers investigated were Er:YSGG with wavelength (WL) of 2.94 mu m and pulse duration (PD) of 250 mu s, Ho:YSGG at 2.1 mu m and 250 mu s and an Nd:YAG with WL of 1.06 mu M and PD of 15ns. RESULTS: The highest surface temperatures were observed during Er:YSGG treatment (> 300 degrees C), moderate temperatures with the Ho:YSGG (150 degrees C), and lowest with the Nd:YAG (with highest surface temperature generally lower than 80 degrees C). Ablation rates were also compared and were shown to be highest with the Er:YSGG and Ho:YSGG, and lower with the Nd:YAG (< 3 mu m). In all systems, efficient ablation was observed only in the presence of plasma. In spite of their different wavelengths, for similar spot sizes, energy, and pulse duration, ablation rates of Ho:YSGG and Er:YSGG were found to be comparable. These were an order of magnitude larger than the ablation rates observed with the nanosecond system. CONCLUSION: Possible explanation for these observations is given in terms of plasma characteristics.

Dentin↗
PubMed1995

Intragenic suppression of a luxR mutation: characterization of an autoinducer-independent LuxR.

The Vibrio fischeri luminescence genes are activated by the LuxR protein and a diffusible signal termed the autoinducer. LuxR consists of two domains, a C-terminal transcriptional activator domain, and an N-terminal autoinducer-binding domain, which serves to regulate the function of the C-terminal domain. We have isolated and characterized an intragenic suppressor of a mutation that maps to the N-terminal domain and blocks autoinducer binding. The suppressor changes an alanine residue at position-221 in the C-terminal domain to a valine. In Escherichia coli, the suppressor allows partial activation of the V. fischeri luminescence genes although E. coli containing this protein remains unable to bind autoinducer. To further analyze the influence of the second-site mutation on luxR function, we constructed a luxR gene that coded for a protein with a wild-type N-terminal domain and with the ala-221 to val substitution in the C-terminal domain. This protein activated the luminescence genes in the presence or absence of autoinducer, and it bound autoinducer at levels comparable to the wild-type LuxR protein. Apparently, the alanine to valine substitution at position-221 allows activity of the C-terminal domain in a fashion independent of whether autoinducer is bound to the N-terminal domain.

Bacterial Proteins↗
PubMed1995

1H NMR of A beta amyloid peptide congeners in water solution. Conformational changes correlate with plaque competence.

To begin to examine the structural basis for the deposition of soluble A beta amyloid peptide onto senile plaques in Alzheimer's disease, we have prepared A beta congeners and measured their activity in an in vitro plaque growth assay. The N-terminal fragment, A beta (1-28)-OH, was inactive at all pH values tested. While the central fragment, A beta (10-35)-NH2, and the full length peptide, A beta (1-40)-OH, were inactive below pH 4, both were active (plaque competent) between pH 5 and 9. The active and inactive fragments were studied by nuclear magnetic resonance spectroscopy in water at submillimolar concentrations at pH 2.1 and 5.6. Changes in chemical shifts, coupling constants, and nuclear Overhauser enhancements indicate a pH dependent folding transition in A beta (10-35)-NH2 as it becomes active. The conformation of the active fragment is not helical, and preliminary data indicate the presence of several turns and at least two short strands. In contrast, the inactive fragment A beta (1-28)-OH did not undergo a similar folding transition. Earlier nuclear magnetic resonance studies of amyloid peptides in fluorinated alcohols or detergent micelles at low pH described a helical conformation and proposed a helix to sheet transition in plaque formation; the present study demonstrates that no such conformations are present in water under conditions where the peptides can adhere to authentic amyloid plaques.

Alzheimer Disease↗
PubMed1995

Variation in portal and hepatic venous anatomy as shown by magnetic resonance imaging: implication for transjugular intrahepatic portosystemic shunt.

Magnetic resonance imaging (MRI) is able to show the portal and hepatic venous anatomy. Variation in the relative position of the right portal vein and the right hepatic vein is shown in three parasagittal planes in three different cases and accounts for the different appearances of the transjugular intrahepatic portosystemic shunt (TIPS) in three patients. MRI shows that the optimal plane of exit from the right portal vein is 1-2.5 cm from the lateral wall of the inferior vena cava but individual variation does occur: a right portal vein with a more anterior and craniad location may not be accessible to the Colapinto needle; a parenchymal tract which is directed too far inferomedially risks puncturing the portal vein outside the liver capsule.

Hepatic Veins↗
PubMed1995

Management of strabismus due to orbital myositis.

We report on 5 consecutive patients seen at the botulinum toxin clinic at Moorfields Eye Hospital with an ocular motility disorder secondary to orbital myositis. CT scans demonstrated involvement of one or both of the medial recti in the inflammatory process in all 5 patients. In addition 1 patient had involvement of both the lateral recti and the right superior rectus. Two patients had been treated with oral steroids, 3 with non-steroidal anti-inflammatory agents, and 1 with orbital radiotherapy. Prior to toxin injection 3 patients had an esotropia (ranging from 4 delta to 30 delta) and two an exotropia (52 delta and 85 delta). A vertical imbalance was present in 3, and all 5 patients had symptomatic diplopia. A total of six injections were given to 5 patients, 2 of whom later went on to have surgery. Toxin injection reduced the angle of the deviation to less than 10 delta in 4 patients, all of whom are now asymptomatic. The fifth patient has persistent diplopia despite two operations to correct a large exotropia. We discuss the role of botulinum toxin and surgery in the management of strabismus due to orbital myositis.

Adolescent↗
PubMed1994

Detection and characterization of a phospholactoyl-enzyme adduct in the reaction catalyzed by UDP-N-acetylglucosamine enolpyruvoyl transferase, MurZ.

The MurZ enzyme catalyzes enolpyruvoyl transfer from phosphoenolpyruvate to the 3-OH of UDP-N-acetylglucosamine (UDP-GlcNAc) in Escherichia coli peptidoglycan biosynthesis. The kinetic mechanism of MurZ has been shown to involve the generation of a non-covalently bound tetrahedral phospholactoyl-UDP-GlcNAc intermediate [Marquardt, J.L., et al. (1993) J. Am. Chem. Soc. 115, 10398-10399]. In the work described here, MurZ overproduced in E. coli copurified with 1 equiv of bound PEP. Enzyme free of bound PEP was prepared by incubation of purified MurZ with UDP-GlcNAc followed by removal of small molecules. Addition of either [14C]PEP or [32P]PEP to PEP-free enzyme led to stoichiometric labeling. The MurZ-PEP complex was stable to 6.7 M urea, and digestion of the [32P]PEP-labeled protein followed by SDS-PAGE generated a labeled peptide of molecular weight 5000. Solution NMR of MurZ incubated with [2-13C]PEP suggested a tetrahedral phospholactoyl enzyme adduct attached via C-2 to an enzyme nucleophile. The kon for generation of the phospholactoyl enzyme in the absence of UDP-GlcNAc was 0.24 microM-1 s-1, too slow to represent the binding order of the kinetically preferred pathway since the lower limit of the second-order binding constant for PEP (kcat/Km) is 15 microM-1 s-1. Rapid chemical quench analysis under single-turnover conditions using [32P]PEP in the presence of UDP-GlcNAc demonstrated that the covalent enzyme-phospholactoyl adduct appeared and decayed on a time scale consistent with catalysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkyl and Aryl Transferases↗
PubMed1994

The use of botulinum toxin for treatment of acquired nystagmus and oscillopsia.

PURPOSE: To evaluate the role of botulinum toxin A (BTA) in treating patients with diminished visual acuity secondary to acquired nystagmus and oscillopsia. METHODS: Twelve patients with acquired nystagmus causing oscillopsia and reduced vision were treated with injection of BTA. Botulinum toxin A was injected directly into the horizontal recti in three patients, and in nine patients retrobulbar BTA was administered. Injections were given at 3- to 4-month intervals and repeated as long as patients noted improvement in their quality of life. RESULTS: Improvement in visual function varied, and not all patients benefited from the procedure. However, 8 of 12 patients demonstrated a measurable improvement in visual acuity. Transient ptosis was the most common side effect. CONCLUSION: Retrobulbar BTA provides a simple and safe alternative in managing a condition for which alternative treatments are typically unsatisfactory.

Adult↗
PubMed1994

Persisting hypotropias following protective ptosis induced by botulinum neurotoxin.

Botulinum toxin A induced ptosis (BTXAP) has become an established method for producing a temporary ptosis for corneal protection. Adams et al1 reported from an initial series of 15 patients and observed that the ptosis lasted for a mean period of 2.5 weeks and that full recovery was achieved after a mean of 8.1 weeks. They noted that in 80% of cases there was a temporary superior rectus weakness which lasted for a mean of 6 weeks. We present three cases in which the superior rectus weakness was permanent and required corrective strabismus surgery. We believe that these are the first cases reported. We propose two possible mechanisms which may be acting together: firstly that a prolonged period of occlusion may have led to a breakdown of fusion, and secondly that following botulinum toxin induced superior rectus weakness there was contracture of the ipsilateral antagonist muscle further disrupting fusional mechanisms.

Botulinum Toxins↗
PubMed1993

Apolipoprotein A-I domains involved in lecithin-cholesterol acyltransferase activation. Structure:function relationships.

A series of mutant apolipoprotein (apoA-I) constructs were designed and then expressed in cell culture to identify structural domains within the mature native apoA-I protein that participate in the activation of the plasma enzyme, lecithin-cholesterol acyltransferase (LCAT). Evolutionary conservation analysis has shown previously that apoA-I contains eight repeats containing 22 amino acids and two repeats containing 11 amino acids that are highly conserved among species as well as within the apolipoprotein supergene family. These tandem repeats begin at residue 44 and are usually marked by a proline residue, with six of the 22-mer repeats showing high amphipathic alpha-helical character. To determine if specific 11- or 22-amino acid domains are essential for maximal LCAT activation within the entire native protein, each of the 10 repeats was sequentially deleted using a polymerase chain reaction based method of mutagenesis. The wild-type and mutant apoA-I gene constructs were expressed in Chinese hamster ovary (CHO) cells and stable lines established. Wild-type and mutant apoA-I protein were purified from 48-96-h conditioned serum-free medium and characterized by SDS-polyacrylamide gel electrophoresis and Western blot analysis. Wild-type apoA-I showed a single migrating band of 28,000 daltons that corresponded to the mobility of human plasma apoA-I, whereas apoA-I deletion mutants (lacking 22- or 11-mer repeats) showed the corresponding shift to lower molecular size. To measure the relative LCAT activation of all deletion mutant apoA-I proteins relative to wild-type apoA-I, an assay system utilizing small unilamellar vesicles as the lipid substrate was used. The results of these studies suggest that several central amphipathic alpha-helical regions within the mature protein are critical in LCAT activation.

Animals↗
PubMed1993

Orbitozygomatic infratemporal approach to lateral skull base tumors.

An orbitozygomatic infratemporal approach for the removal of large neoplasms involving the lateral skull base is described. This approach, involves a unilateral frontotemporal incision extended inferiorly to the neck, a lateral facial flap reflected anteriorly. Transection of the zygoma is followed by its reflection inferolaterally with the temporalis muscle. This exposure provides excellent visualization of both the intradural and extradural aspects of the anterior portion of the cavernous sinus, allowing an aggressive resection of neoplasms in this region. Experience with this procedure in the management of 15 patients is reported here. There was one postoperative death due to pneumonia and septicemia. The morbidities included wound infection, meningitis, CSF leakage and cranial nerve palsy. All the surviving patients, are living independently and have returned to their previous occupations.

Adolescent↗
PubMed1993

Surgical treatment of thalamic arteriovenous malformations.

The microsurgical excision of arteriovenous malformations located in the thalamic region in eight patients is reported. Six were located in the posterior aspect of the thalamus and two were located in the anterior. Hemorrhage occurred in all of the cases. Hemiparesis, hemianesthesia, and consciousness disturbance were the most typical clinical features. The supine position with the anterior transcallosal approach was used for anterior dorsal lesions, and the sitting position with the posterior interhemispheric approach was used for posterior dorsal lesions. Total removal was confirmed by angiography in seven patients, and incomplete removal was noted in one patient. There was one death in this group of patients. Memory disturbance was the most common postoperative complication. This complication showed considerable improvement with time. Other complications included homonymous hemianopsia (three patients), hemisensory loss (six patients), and transient hemiparesis (one patient). All survivors (seven patients) were able to return to their occupation after surgery. The vascular input, the location of the malformation, and clinical history are the contributory factors concerning operability. With the modern neurosurgical and anesthesiological facilities, surgical removal of thalamic malformations in selected cases is advisable.

Adolescent↗
PubMed1992

Aromatic-aromatic interactions in the zinc finger motif. Analysis of the two-dimensional nuclear magnetic resonance structure of a mutant domain.

The folding and stability of globular proteins are determined by a variety of chemical mechanisms, including hydrogen bonds, salt bridges and the hydrophobic effect. Of particular interest are weakly polar interactions involving aromatic rings, which are proposed to regulate the geometry of closely packed protein interiors. Such interactions reflect the electrostatic contribution of pi-electrons and, unlike van der Waals' interactions and the hydrophobic effect, may, in principle, introduce a directional force in a protein's hydrophobic core. Although the weakly polar hypothesis is supported by a statistical analysis of protein structures, the general importance of such contributions to protein folding and stability is unclear. Here, we show the presence of alternative aromatic-aromatic interactions in the two-dimensional nuclear magnetic resonance structure of a mutant Zn finger. Changes in aromatic packing lead in turn to local and non-local differences between the structures of a wild-type and mutant domain. The results provide insight into the evolution of Zn finger sequences and have implications for understanding how geometric relationships may be chemically encoded in a simple sequence template.

Amino Acid Sequence↗
PubMed1992

NMR analysis of regioselectivity in dephosphorylation of a triphosphotyrosyl dodecapeptide autophosphorylation site of the insulin receptor by a catalytic fragment of LAR phosphotyrosine phosphatase.

An autophosphorylation site in the activated insulin receptor tyrosine kinase domain has three tyrosines phosphorylated when fully activated. To begin to examine recognition of triphosphotyrosyl sites by protein tyrosine phosphatases in possible control of signal transduction a triphosphotyrosyl dodecapeptide TRDIpYETDpYpYRK corresponding to residues 1,142-1,153 of the insulin receptor was prepared and incubated with the 40-kDa catalytic domain of the human PTPase LAR. To assess regioselectivity of recognition, the three diphosphotyrosyl regioisomers, and the three monophosphotyrosyl regioisomers were prepared and assayed. All seven peptides were PTPase substrates. To identify any preferences in dephosphorylation at pY5, pY9, or pY10, 1H-NMR analyses were conducted during enzyme incubations and distinguishing fingerprint regions determined for each of the seven phosphotyrosyl peptides. LAR PTPase shows strong preference for dephosphorylation first at pY5 (at tri-, di-, and monophosphotyrosyl levels). Initially this regioselectivity gives the Y5(pY9)(pY10) diphospho regioisomer, followed by equal dephosphorylation at pY9 or pY10 to give the corresponding monophosphoryl species on the way to fully dephosphorylated product. The NMR methodology is applicable to other peptides with multiple sites of phosphorylation that undergo attack by any phosphatase.

Amino Acid Sequence↗
PubMed1992

Segmental colonic dilatation in a neonate.

Segmental dilatation of the colon is rare, usually affecting older children, and may mimic Hirschsprung's disease. A neonate with Down's syndrome and malrotation presented with this condition and was cured by segmental resection.

Colon↗
PubMed1992

Recovery of anterior segment circulation after strabismus surgery in adult patients.

The effects of vertical rectus muscle surgery on the anterior segment and iris fluorescein angiogram were documented in 43 eyes of 41 adult patients. Characteristic iris sector perfusion defects were seen in 33 of 37 eyes (89%) after primary vertical rectus muscle surgery (no previous surgery on these muscles). Although iris perfusion defects were commonly present, associated clinical signs were mild. Two patients developed permanent pupillary changes after simultaneous surgery on two rectus muscles (superior/inferior rectus muscles and contiguous inferior/medial rectus muscles). In most patients, clinical findings resolved and the iris circulation recovered during the first 2 weeks after surgery. In 3 of 8 patients with grade 3 anterior segment ischemia (pupil dysfunction and cells) or early "postoperative uveitis," recovery of iris circulation took up to 12 weeks. These findings indicate that the time course of recovery of the anterior segment circulation after vertical rectus muscle surgery may be shorter than previously assumed.

Adolescent↗
PubMed1992

A scoring method for Hess charts.

A new scoring system for Hess charts is described. Scores for both horizontal and vertical deviations are calculated from the displacement of individual points on the Hess chart, using weighting factors for the centre, inner and outer zones. The scoring system was validated in a group of 24 patients undergoing surgery for paralytic or restrictive strabismus. Subjective scores were obtained from patients both before and after corrective surgery, and corresponding Hess charts were scored using the new system. There was a good correlation between the changes in subjective and objective score. Our scoring system has applications in both research and clinical practice, allowing objective analysis of changes in muscle balance in a variety of motility disorders.

Diplopia↗