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Biomedical subjects

D Pham

Publications and source records attributed to D Pham.

At least 19 recordsLinked to original sources
PubMed1998

Polymorphic tetranucleotide repeat site within intron 7 of the beta-amyloid precursor protein gene and its lack of association with Alzheimer's disease.

Mutations found in the beta-amyloid precursor protein (APP) gene in a small subset of patients with Alzheimer's disease (AD) are associated with the development of the disease. Several lines of evidence indicate that specific isoforms of APP generated by alternative splicing of the primary transcript may contribute to the etiology of AD. One of the isoforms, APP695, lacks the Kunitz protease inhibitor (KPI) domain and is produced predominantly in neurons by skipping exon 7 of the APP gene. Previous studies imply that the controlling elements for exon 7 skipping exist in the flanking sequences of the exon. Therefore, we have sequenced the human intron 7 of the APP gene and found a polymorphic tetranucleotide (ATTT)n repeat site within the intron 7. In 183 genetically unrelated subjects (97 AD patients and 86 controls), we found four alleles by polymerase chain reaction (PCR) amplification of the repeat site. Although no particular alleles are associated with AD, this newly identified polymorphic site may be useful in other genetic analyses since preliminary evidence suggests allele frequency differences between African Americans and Caucasians.

Age of Onset↗
PubMed1998

Amyloid-beta deposition in skeletal muscle of transgenic mice: possible model of inclusion body myopathy.

Inclusion body myopathy is a progressive muscle disorder characterized by nuclear and cytoplasmic inclusions and vacuolation of muscle fibers. Affected muscle fibers contain deposits of congophilic amyloid, amyloid-beta immunoreactive filaments, and paired helical filaments, all of which are pathological hallmarks of Alzheimer's disease in brain. Accumulations of amyloid-beta and its precursor are thought to play important roles in the pathogenesis of both inclusion body myopathy and Alzheimer's disease. Overexpression of mutant forms of beta protein precursor in transgenic mice by neuron-specific promoters has been reported to cause amyloid deposits in the brain. Here we report that overexpression in transgenic mice of the signal plus 99-amino acid carboxyl-terminal sequences of beta protein precursor, under the control of a cytomegalovirus enhancer/beta-actin promoter, resulted in vacuolation and increasing accumulation of the 4-kd amyloid-beta and the carboxyl-terminus in skeletal muscle fibers during aging. These deposits in transgenic muscle only rarely showed Congo red birefringence. Thus, overexpression of part of beta protein precursor in transgenic mice led to development of some of the characteristic features of inclusion body myopathy. These mice may be a useful model of inclusion body myopathy, which shares a number of pathological markers with Alzheimer's disease.

Age Factors↗
PubMed1997

Non-invasive measurements of breast tissue optical properties using frequency-domain photon migration.

A multiwavelength, high bandwidth (1 GHz) frequency-domain photon migration (FDPM) instrument has been developed for quantitative, non-invasive measurements of tissue optical and physiological properties. The instrument produces 300 kHz to 1 GHz photon density waves (PDWs) in optically turbid media using a network analyser, an avalanche photodiode detector and four amplitude-modulated diode lasers (674 nm, 811 nm, 849 nm, and 956 nm). The frequency of PDW phase and amplitude is measured and compared to analytically derived model functions in order to calculate absorption, mu a, and reduced scattering, mu s, parameters. The wavelength-dependence of absorption is used to determine tissue haemoglobin concentration (total, oxy- and deoxy- forms), oxygen saturation and water concentration. We present preliminary results of non-invasive FDPM measurements obtained from normal and tumour-containing human breast tissue. Our data clearly demonstrate that physiological changes caused by the presence of small (about 1 cm diameter) palpable lesions can be detected using a handheld FDPM probe.

Adult↗
PubMed1997

Chlamydia pneumoniae in acute otitis media.

BACKGROUND: Aerobic bacterial pathogens are recovered from 65 to 85% of patients with acute otitis media (AOM). Although Chlamydia pneumoniae is a common pathogen of pediatric pneumonia, it has rarely been cultured from children with chronic otitis media and its role in AOM is unknown. METHODS: We cultured for C. pneumoniae in tympanocentesis aspirates and nasopharyngeal swabs from 101 consecutive, otherwise healthy children with AOM or refractory AOM. A control group of 50 similarly aged, healthy children was evaluated for nasopharyngeal carriage of C. pneumoniae. Specimens were also evaluated by PCR for C. pneumoniae. RESULTS: C. pneumoniae was recovered by tympanocentesis in 8 (8%) of 101 children with AOM. Among the 8 children with C. pneumoniae-positive-AOM, 5 had C. pneumoniae detected by PCR in middle ear fluid, none had C. pneumoniae recovered by nasopharyngeal culture or PCR and 5 were younger than 16 months. C. pneumoniae was the sole pathogen isolated in 2 patients. Copathogens included beta-lactamase-positive positive Haemophilus influenzae (2), beta-lactamase positive Moraxella catarrhalis (1), penicillin-resistant Streptococcus pneumoniae (2) and penicillin-susceptible S. pneumoniae (1). C. pneumoniae was recovered from nasopharyngeal culture in 2 additional patients with C. pneumoniae-negative AOM and in none of 50 healthy control children, although 2 controls were positive by PCR from the nasopharynx. CONCLUSIONS: This is the first study to report the isolation of C. pneumoniae in middle ear fluid of children with AOM.

Acute Disease↗
PubMed1997

A novel human T-leukemia virus type 1 cell-to-cell transmission assay permits definition of SU glycoprotein amino acids important for infectivity.

Human T-leukemia virus type 1 (HTLV-1) envelope glycoproteins play a major role in viral transmission, which in the case of this virus occurs almost exclusively via cell-to-cell contact. Until very recently, the lack of an HTLV-1 infectivity assay precluded the determination of the HTLV-1 protein domains required for infectivity. Here, we describe an assay which allows the quantitative evaluation of HTLV-1 cell-to-cell transmission in a single round of infection. Using this assay, we demonstrate that in this system, cell-to-cell transmission is at least 100 times more efficient than transmission with free viral particles. We have examined 46 surface (SU) glycoprotein mutants in order to define the amino acids of the HTLV-1 SU glycoprotein required for full infectivity. We demonstrate that these amino acids are distributed along the entire length of the SU glycoprotein, including the N-terminus and C-terminus regions, which have not been previously defined as being important for HTLV-1 glycoprotein function. For most of the mutated glycoproteins, the capacity to mediate cell-to-cell transmission is correlated with the ability to induce formation of syncytia. This result indicates that the fusion capacity is the main factor responsible for infectivity mediated by the HTLV-1 SU envelope glycoprotein, as is the case for other retroviral glycoproteins. However, other factors must also intervene, since two of the mutated glycoproteins were correctly fusogenic but could not mediate cell-to-cell transmission. Existence of this phenotype shows that capacity for fusion is not sufficient to confer infectivity, even in cell-to-cell transmission, and could suggest that postfusion events involve the SU.

Animals↗
PubMed1997

The ectodomain of the human T-cell leukemia virus type 1 TM glycoprotein is involved in postfusion events.

To examine the contribution of the transmembrane envelope glycoprotein (TM) to the infectivity of the human T-cell leukemia virus type 1 (HTLV-1), single amino acid substitutions were introduced throughout its ectodomain. The mutated envelopes were tested for intracellular maturation and for functions, including ability to elicit syncytium formation and ability to mediate cell-to-cell transmission of the virus. Three major phenotypes, defining three functionally distinct regions, were identified. (i) Mutations causing defects in intracellular maturation of the envelope precursor are mostly distributed in the central portion of the TM ectodomain, containing the immunosuppressive peptide. This region, which includes vicinal cysteines thought to form an intramolecular disulfide bridge, is probably essential for correct folding of the protein. (ii) Mutations resulting in reduced syncytium-forming ability despite correct intracellular maturation are clustered in the amino-terminal part of the TM ectodomain, within the leucine zipper-like motif. Similar motifs with a propensity to form coiled-coil structures have been implicated in the fusion process driven by other viral envelope proteins, and HTLV-1 may thus conform to this general rule for viral fusion. (iii) Mutants with increased syncytium-forming ability define a region immediately amino-terminal to the membrane-spanning domain. Surprisingly, these mutants exhibited severe defects in infectivity, despite competence for fusion. Existence of this phenotype indicates that capacity for cell-to-cell fusion is not sufficient to ensure viral entry, even in cell-to-cell transmission. The ectodomain of the TM glycoprotein thus may be involved in postfusion events required for full infectivity of HTLV-1, which perhaps represents a unique feature of this poorly infectious retrovirus.

Animals↗
PubMed1996

The HTLV-I envelope glycoproteins: structure and functions.

The human T-cell lymphotropic virus type I (HTLV-I) envelope has a structural organization shared by all retroviral envelopes, which contain two mature viral glycoproteins deriving from a common precursor: an external surface protein (SU), associated with a transmembrane protein (TM) responsible for anchoring the SU-TM complex at the cell surface or in the viral envelope. Our understanding of the tertiary structure of these proteins is extremely poor. The intracellular maturation follows the normal cellular secretory pathway, resulting in expression of the mature glycoproteins at the cell surface. The five potential N-glycosylation sites are glycosylated. Most mutations artificially introduced into the glycoproteins result in loss of function, mostly due to abnormal intracellular maturation. This probably indicates a very compact structure of these proteins, where the entire structure is involved in correct conformation. Studies using neutralizing antibodies or mutagenesis have defined functional domains in the SU protein, which is responsible for receptor binding. These domains occur throughout the SU glycoprotein. Sequence analysis of the HTLV-I TM predicts a structure, and probably functions, similar to other retrovirus TMs: involvement of this glycoprotein in the different oligomerization steps leading to a fusogenic SU-TM complex and in the fusion process itself. These features remain to be proven, and it is not yet understood why the free HTLV-I viral particle is not infectious.

Amino Acid Sequence↗
PubMed1996

What can angiotensin antagonists do that converting-enzyme inhibition can't: the case of post-angioplastic restenosis.

The introduction of nonpeptide angiotensin II antagonists in clinical use has necessarily led to comparison with the various and clinically established angiotensin converting enzyme inhibitors. In essence, losartan, the first approved angiotensin receptor antagonist, has a clinical profile highly similar to that of the converting-enzyme inhibitors, although much higher doses are required but with the advantage of no dry cough. On the other hand, the emergence of the concept of inverse agonism on other receptor systems has led to the search for pathological situations mediated through constitutive receptor activity as well as antagonists with inverse agonistic properties on the angiotensin receptor. Basic research on angiotensin peptide antagonists has led to the identification of molecular characteristics that produce antagonism. The combination of these characteristics then led to angiotensin antagonists that possessed a long in vivo duration of action. Studies with angiotensin converting enzyme inhibitors and nonpeptide antagonists on animal models of post-angioplastic restenosis revealed that both classes of compounds have similar partial efficacy on the inhibition of neointima formation. A peptide antagonist produced on the rat carotid model a complete inhibition of neointima formation. This increased efficacy is now tentatively attributed to potential inverse agonistic activity of this peptide antagonist. This concept would give angiotensin antagonists therapeutic opportunities where convertase inhibitors should be ineffective.

Angioplasty, Balloon↗
PubMed1995

Optimization of MR pulse sequences for Bayesian image segmentation.

A method for optimizing MR imaging pulse sequence parameters in a statistical framework is presented. Parameters are defined to be optimal when the resulting scalar images yield optimal image segmentations using Bayesian pixel classification. Thus, Bayes risk is used as the objective function to minimize. Approximations are made to give a tractable solution in a four-step procedure. A sample calculation is carried out to determine the optimal TR and flip angle for scalar SPGR imaging of the brain. Overall, this paper gives a new approach to optimize MRI pulse sequences for the specific objective of improved image segmentation.

Bayes Theorem↗
PubMed1994

Alterations of the three-phase bone scan after sympathectomy.

OBJECTIVE: To evaluate alterations of the three-phase bone scan (TPBS) in patients with the clinical diagnosis of reflex sympathetic dystrophy (RSD) before and after surgical or chemical sympathectomy. DESIGN: The TPBS was done after i.v. administration of 99technetium dimethylphosphonate. Scans were read by one blinded and one nonblinded reviewer (as to site of symptoms and procedure), using a visual grading system devised in our institution. Since there were no statistically significant differences between the two examiners' scores for blood flow, pool, and delayed phases, all scores were averaged and used for comparison before and after sympathectomy. SUBJECTS: Ten women and four men with RSD were observed with 17 TPBSs before and 30 TPBSs after surgical (n = 6) or chemical (n = 8) sympathectomy. RESULTS: All three phases of TPBS were significantly enhanced after sympathectomy in 11 of 14 patients in a pattern indistinguishable from that very commonly reported in florid RSD. The increased uptake occurred within 24 h after the procedure, normalized as early as 3 months in some scans, and remained abnormal in some patients in the 12-month follow-up period. In total, only 33% of all sympathectomies performed led to long-term symptom relief. CONCLUSIONS: The data demonstrated that alterations in TPBS after sympathectomy are identical to those reported in early RSD and these alterations bear no relationship to the success of sympathectomy regarding pain relief. The mechanisms underlying alterations of TPBS as well as the potential mechanisms of sympathectomy failures are discussed.

Adolescent↗
PubMed1994

The open reading frame I (ORF I)/ORF II part of the human T-cell leukemia virus type I X region is dispensable for p40tax, p27rex, or envelope expression.

The X region of the human T-cell leukemia virus type I contains the second coding exon of the tax and rex regulatory proteins (open reading frame IV [ORF IV] and ORF III, respectively), as well as coding regions for more recently described proteins, p30II (or the tof protein) and p13II in ORF II and the putative rof protein and p12I in ORF I. Deletions and transcomplementation experiments showed that expression of the envelope, as well as that of the tax and rex proteins, was independent of the proteins encoded in the ORF I/ORF II region. Furthermore, p30II and p12I proteins could not replace the rex protein in a rex-dependent envelope or Gag protein expression system.

Gene Expression↗
PubMed1994

Identification of functional regions in the human T-cell leukemia virus type I SU glycoprotein.

Single conservative and nonconservative amino acid substitutions were introduced into the gp45 external envelope protein (SU) of human T-cell leukemia virus type I (HTLV-I). The mutated amino acids were those identified as being conserved in HTLV-I, HTLV-II, and simian T-cell leukemia virus type I (but not in bovine leukemia virus). The mutated envelopes were tested for intracellular maturation and for function. Mutants with three major phenotypes could be defined: (i) 9 mutants with a wild-type phenotype, which included most of the conservative amino acid changes (five of seven) distributed throughout the SU protein; (ii) 8 mutants with affected intracellular maturation, 6 of which define a region in the central part of the SU protein essential for correct folding of the protein; and (iii) 13 mutants with normal intracellular maturation but impaired syncytium formation. These mutations likely affect the receptor binding step or postbinding events required for fusion. Five of these mutations are located between amino acids 75 and 101 of the SU protein, in the amino-terminal third of the molecule. The other mutations involve positions 170, 181, 195, 197, 208, 233, and 286, suggesting that two other domains, one central and one carboxy terminal, are involved in HTLV-I envelope functions.

Animals↗
PubMed1994

Functional comparison between HTLV-I envelopes originating from TSP/HAM or ATL cell lines.

The human T-cell leukemia type I (HTLV-I) virus is associated with two different diseases, adult T-cell leukemia (ATL) and tropical spastic paraparesis/HTLV-I-associated myelopathy (TSP/HAM). We have compared the viral envelopes originating from TSP/HAM and ATL patients, using the capacity of infected cells to form syncytia with receptor-expressing cells. We show that like the ATL cell lines, the TSP/HAM ones can form syncytia with a large panel of human target cells, including a variety of hematopoietic cell lines, as well as cell lines of neuroectodermal origin. None of the target cell lines tested was able to discriminate between TSP/HAM- and ATL-infected cell lines. When infected cells of TSP/HAM origin are cocultivated with cells of ATL origins, syncytia are never observed. This interference phenomenon suggests that the viruses expressed by the different cell lines utilize the same receptor.

Blotting, Western↗
PubMed1993

Composite kidney-islet transplantation prevents recurrent autoimmune beta-cell destruction.

BACKGROUND: Clinically successful islet transplantation has been rare despite adequate isolation techniques. Reenactment of the original autoimmune beta-cell destruction may contribute to the poor results. Distinguishing autoimmune effects from rejection can be accomplished with isogeneic transplants exchanged between diabetes-prone (BB-DP) and diabetes-resistant (BB-DR) rats. These experiments determine the relative sensitivity of islet, whole pancreas, and composite kidney-islet transplants to recurrent autoimmunity. METHODS: Acutely diabetic (BB-Ac) BB rats served as recipients of vascularized pancreas, intraportal (IPo) or renal capsular (KC) islet transplants, or vascularized composite kidney-islet grafts from BB-DR or BB-DP donors. Graft function was assessed by daily blood glucose level, and the outcome was confirmed on histologic examination. Cyclosporine 5 mg/kg/day intramuscularly was administered to assess its effect on recurrent beta-cell injury. RESULTS: BB-DP pancreases developed recurrent autoimmunity in 55% of cases; cyclosporine afforded complete protection if maintained. Diabetes resistance was transplanted with 23 of 23 BB-DR pancreas grafts; however, islet isolation led to a loss of diabetes resistance for islet grafts to the KC and IPo. Cyclosporine protected KC but not IPo islets. Composite BB-DR kidney-islet transplants functioned indefinitely in all cases. CONCLUSIONS: Transplanted islets initially survive by passive diffusion but are ultimately revascularized by capillary ingrowth. The finding that composite kidney-islet transplants function indefinitely suggests that the revascularizing endothelium may play a role in resistance or susceptibility to autoimmune beta-cell destruction.

Animals↗
PubMed1992

Human T-cell leukemia virus type I envelope protein maturation process: requirements for syncytium formation.

The human T-cell leukemia virus type I (HTLV-I) envelope protein is synthesized as a gp61 precursor product cleaved into two mature proteins, a gp45 exterior protein and a gp20 anchoring the envelope at the cell membrane. Using N-glycosylation inhibitors and site-directed mutagenesis of the potential glycosylation sites, we have studied the HTLV-I envelope intracellular maturation requirements for syncytium formation. We show here that experimental conditions resulting in the absence of precursor cleavage (tunicamycin, monensin treatments, and use of inhibitors of the reticulum steps of the N glycosylations) also result in no cell surface expression of envelope protein. The lack of syncytium formation observed in these cases is thus explained by incorrect intracellular transport. When the precursor is cleaved in the Golgi stack (no treatment or treatment with inhibitors of the Golgi steps of the N glycosylations), it is transported to the cell surface in all the cases examined. Syncytium formation is markedly reduced, however, when Golgi glycosylations are incorrect, which shows that the sugar moieties are involved in the envelope functions. Site-directed mutagenesis demonstrates that each of the five potential glycosylation sites is actually glycosylated. Glycosylation of sites 1 and 5 is required for normal maturation, whereas that of sites 2, 3, and 4 is dispensable. Glycosylation of each site, however, is required for normal syncytium formation. Altogether, the restraints exerted by the cell for the HTLV-I envelope to be transported and functional are very high, which might play a role in the observed conservation of the envelope amino acid sequence between various strains.

1-Deoxynojirimycin↗
PubMed1992

Transient migratory osteoporosis: a variant of reflex sympathetic dystrophy? Report of 3 cases and literature review.

Three cases of transient migratory osteoporosis treated with sympathetic blocks are described. Review of the literature in conjunction with the presentation and treatment of these 3 cases led to the formulation of a hypothesis of a common mechanism (mediated through the sympathetic nervous system) responsible for the profound osteoporosis and pain of reflex sympathetic dystrophy and transient migratory osteoporosis. Arguments are presented supporting transient migratory osteoporosis as a variant of the classical reflex sympathetic dystrophy.

Adolescent↗