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Biomedical subjects

B A Brown

Publications and source records attributed to B A Brown.

At least 19 recordsLinked to original sources
PubMed1999

Proteolytic dissection of Zab, the Z-DNA-binding domain of human ADAR1.

Zalpha is a peptide motif that binds to Z-DNA with high affinity. This motif binds to alternating dC-dG sequences stabilized in the Z-conformation by means of bromination or supercoiling, but not to B-DNA. Zalpha is part of the N-terminal region of double-stranded RNA adenosine deaminase (ADAR1), a candidate enzyme for nuclear pre-mRNA editing in mammals. Zalpha is conserved in ADAR1 from many species; in each case, there is a second similar motif, Zbeta, separated from Zalpha by a more divergent linker. To investigate the structure-function relationship of Zalpha, its domain structure was studied by limited proteolysis. Proteolytic profiles indicated that Zalpha is part of a domain, Zab, of 229 amino acids (residues 133-361 in human ADAR1). This domain contains both Zalpha and Zbeta as well as a tandem repeat of a 49-amino acid linker module. Prolonged proteolysis revealed a minimal core domain of 77 amino acids (positions 133-209), containing only Zalpha, which is sufficient to bind left-handed Z-DNA; however, the substrate binding is strikingly different from that of Zab. The second motif, Zbeta, retains its structural integrity only in the context of Zab and does not bind Z-DNA as a separate entity. These results suggest that Zalpha and Zbeta act as a single bipartite domain. In the presence of substrate DNA, Zab becomes more resistant to proteases, suggesting that it adopts a more rigid structure when bound to its substrate, possibly with conformational changes in parts of the protein.

Adenosine Deaminase↗
PubMed1999

Folding of pyrimidine-enriched RNA fragments from the vicinity of the internal ribosomal entry site of hepatitis A virus.

Two RNA fragments from the region just upstream of the internal ribosome entry site of Hepatitis A virus (HAV) were studied, a 35mer (HAV-35), 5'U4C3U3C3U4C3U3C2UAU2C3U33(4), and a 23mer (HAV-23), 5(4)U4C3U3C3U4C3U33(4). Secondary structural predictions and nuclease digestion patterns obtained with genomic RNAs suggested that they link two stable Watson-Crick (WC) hairpins in the genomic RNA and do not form conventional WC secondary structure, but do fold to form a condensed, stacked 'domain'. To obtain more information, folding of HAV-23 and -35 RNA fragments was characterized using 1H nuclear magnetic resonance, in H2O as a function of pH and temperature, circular dichroism as a function of NaCl concentration, pH and temperature, and square-wave voltammetry as a function of pH. The results indicate that these oligo-nucleotides form intramolecular structures that contain transient U*U base pairs at pH 7 and moderate ionic strength (100 mM NaCl). This folded structure becomes destabilized and loses the U*U base pairs above and below neutral pH, especially at ionic strengths above 0.1. All of the cytidine protons exchange relatively rapidly with solvent protons (exchange lifetimes shorter than 1 ms), so the structure contains few if any C*CH+base pairs at neutral pH, but can apparently form them at pH values below 6. We present a series of possible models in which chain folding draws the strand termini closer together, possibly serving to pull the attached WC hairpin domains together and providing a functional advantage by nucleating reversible formation of a more viable RNA substrate.

Base Pairing↗
PubMed1998

Isolation and characterization of a monoclonal anti-quadruplex DNA antibody from autoimmune "viable motheaten" mice.

A cell line that produces an autoantibody specific for DNA quadruplex structures has been isolated and cloned from a hybridoma library derived from 3-month-old nonimmunized autoimmune, immunodeficient "viable motheaten" mice. This antibody has been tested extensively in vitro and found to bind specifically to DNA quadruplex structures formed by two biologically relevant sequence motifs. Scatchard and nonlinear regression analyses using both one- and two-site models were used to derive association constants for the antibody-DNA binding reactions. In both cases, quadruplexes had higher association constants than triplex and duplex molecules. The anti-quadruplex antibody binds to the quadruplex formed by the promoter-region-derived oligonucleotide d(CGCG4GCG) (Ka = 3.3 x 10(6) M-1), and has enhanced affinity for telomere-derived quadruplexes formed by the oligonucleotides d(TG4) and d(T2G4T2G4T2G4T2G4) (Ka = 5.38 x 10(6) and 1.66 x 10(7) M-1, respectively). The antibody binds both types of quadruplexes but has preferential affinity for the parallel four-stranded structure. In vitro radioimmunofilter binding experiments demonstrated that purified anti-DNA quadruplex antibodies from anti-quadruplex antibody-producing tissue culture supernatants have at least 10-fold higher affinity for quadruplexes than for triplex and duplex DNA structures of similar base composition and length. The antibody binds intramolecular DNA triplexes formed by d(G4T3G4T3C4) and d(C4T3G4T3G4), and the duplex d(CGCGCGCGCG)2 with an affinities of 6. 76 x 10(5), 5.59 x 10(5), and 8.26 x 10(5) M-1, respectively. Competition experiments showed that melted quadruplexes are not effective competitors for antibody binding when compared to native structures, confirming that the quadruplex is bound structure-specifically. To our knowledge, this is the first immunological reagent known to specifically recognize quadruplex structures. Subsequent sequence analysis demonstrates homologies between the antibody complementarity determining regions and sequences from Myb family telomere binding proteins, which are hypothesized to control cell aging via telomeric DNA interactions. The presence of this antibody in the autoimmune repertoire suggests a possible linkage between autoimmunity, telomeric DNA binding proteins, and aging.

Animals↗
PubMed1998

Construction and characterization of a quadruplex DNA selective single-chain autoantibody from a viable motheaten mouse hybridoma with homology to telomeric DNA binding proteins.

An autoantibody produced by a hybridoma derived from a viable motheaten mouse was isolated and found to have moderately high binding affinity for nucleic acids and specific preference for quadruplex DNAs. Polymerase chain reaction primers were designed to link the cloned parental antibody variable region fragments together in a subcloning vector. This single-chain variable fragment construct was then subcloned into the T7 promoter-driven expression vector pET22b(+). The construct contains (N- to C-terminal) a pelB leader sequence, variable heavy chain, glycine-serine polylinker, variable light chain, and biotin mimic peptide "strep-tag" sequence (pelB-VH-linker-VL-strep-tag). The ca. 29 kDa protein was expressed, exported to the periplasmic space of NovaBlue (DE) Escherichia coli, and purified by streptavidin affinity chromatography by binding the fused strep-tag peptide. The specificity of the purified single-chain variable fragment (scFv) for quadruplex and duplex DNAs was evaluated by a radioimmunofilterbinding assay. It retained about 10-fold higher affinity for quadruplexes relative to duplex DNA, a reduction of ca. 4-fold from the relative preferences of the parent IgG. The complementary-determining regions contain sequences that are homologous to or conservatively divergent from the key DNA-binding helix-turn-helix-forming motifs of Myb/RAP1 family telomeric DNA-binding proteins (1-3). The presence of this antibody in the autoimmune repertoire suggests a possible linkage between autoimmunity, telomeric DNA binding proteins, and aging.

Amino Acid Sequence↗
PubMed1998

Results of operation in Mycobacterium avium-intracellulare lung disease.

BACKGROUND: Although operation remains part of the management of Mycobacterium avium-intracellulare lung disease, few series have assessed operation in the era of better therapeutic drugs (especially clarithromycin). METHODS: From January 1, 1989, through June 30, 1997, 28 patients with M avirum-intracellulare lung disease underwent pulmonary resection. All were receiving multidrug therapy (17 of 28 were receiving clarithromycin) before and after operation. Eight patients underwent pneumonectomy (6 right, 2 left); 20 patients underwent partial resections including 18 with upper lobe lobectomies (14 right, 4 left). The most common indications for operation were medical treatment failure (15) and as part of initial therapy (9). RESULTS: Mean postoperative follow-up was 39 months. Complications occurred in 9 of 28 patients (32%), and included persistent air leak requiring surgical correction (5), early postoperative death (2), and late bronchopleural fistulae (1 patient). Twenty-three of 26 patients were known to be acid fast bacilli culture negative within 1 month of operation. Only 1 of 26 patients who survived 2 years is known to have had a relapse. CONCLUSIONS: Operation continues to play an important role in treatment of M avium-intracellulare lung disease. More than 90% of patients become culture negative and remain so when they continue to receive drugs. Although morbidity is relatively high, it is manageable and the 12-month mortality in the current series was low (7%).

Adult↗
PubMed1998

Evaluation of a disk diffusion method for determining susceptibility of Mycobacterium avium complex to clarithromycin.

We evaluated an agar disk diffusion method for determining the susceptibility of Mycobacterium avium complex to clarithromycin. Isolates were inoculated onto the surface of a Middlebrook 7H11 plate, followed by the application of a 15-microgram clarithromycin disk. Zone sizes were read after 5-7 days of incubation. Zone sizes had a bimodal distribution; 40 isolates (10%) had no zone of inhibition, whereas the zone sizes for the remaining isolates ranged from 11 to 60 mm. Most isolates (37/40) having no zone of inhibition came from patients who had been treated previously with clarithromycin. Fifty-one isolates were also tested for clarithromycin susceptibility using a microdilution broth method. Defining susceptibility as a zone size of > 10 mm, disk diffusion test results agreed with the results by the microdilution broth method for 50 of 51 (98%) isolates tested by both methods. Agar disk diffusion is a promising method for the determination of clarithromycin susceptibility testing for M. avium complex.

Animals↗
PubMed1998

AIDS-related Mycobacterium kansasii infection with initial resistance to clarithromycin.

Clarithromycin is a promising drug for the treatment of Mycobacterium kansasii infection. We report a patient with AIDS and severe M. kansasii infection who had previously received a short course of clarithromycin for sinusitis. He had clinical failure of treatment using clarithromycin plus ethambutol, and the initial isolate was found to be highly resistant to clarithromycin. Nucleotide sequencing of the 23S rRNA gene of this isolate demonstrated a single base mutation at position 2058, the same as that found in clarithromycin-resistant Mycobacterium avium.

AIDS-Related Opportunistic Infections↗
PubMed1998

Long-term laboratory contamination by Mycobacterium abscessus resulting in two pseudo-outbreaks: recognition with use of random amplified polymorphic DNA (RAPD) polymerase chain reaction.

Beginning in 1993, an increase in clinical isolates of Mycobacterium abscessus was observed in a single hospital microbiology laboratory. This involved a cluster of four patients in June 1993 and five patients and a quality-control culture of distilled water in May 1994. Twenty-three M. abscessus isolates recovered between 1991 and 1996 were compared by random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR). Sixteen of 21 clinical isolates recovered over a 6-year period and the distilled water isolate had identical RAPD-PCR patterns consistent with a single strain or clone. Only six of 15 patients had findings suggestive of clinical disease. Since the use of in-house-prepared distilled water was discontinued, no further laboratory contamination of clinical specimens has been observed. Molecular typing was the key to defining distilled water as the source of this pseudo-outbreak. Recognition of such outbreaks is important for prevention of unnecessary therapeutic and diagnostic interventions.

Adolescent↗
PubMed1998

A single 16S ribosomal RNA substitution is responsible for resistance to amikacin and other 2-deoxystreptamine aminoglycosides in Mycobacterium abscessus and Mycobacterium chelonae.

Twenty-six clinical isolates of Mycobacterium abscessus resistant to amikacin were identified. Most isolates were from patients with posttympanostomy tube placement otitis media or patients with cystic fibrosis who had received aminoglycoside therapy. Isolates were highly resistant (MICs > 1024 microg/mL) to amikacin, kanamycin, gentamicin, tobramycin, and neomycin (all 2-deoxystreptamine aminoglycosides) but not to streptomycin. Sequencing of their 16S ribosomal (r) RNA revealed that 16 (94%) of 17 had an A-->G mutation at position 1408. In vitro-selected amikacin-resistant mutants of M. abscessus and Mycobacterium chelonae had the same resistance phenotype, and 15 mutants all had the same A-->G substitution at position 1408. Introducing an rRNA operon from Mycobacterium smegmatis with a mutated A-->G at this position into a single functional allelic rRNA mutant of M. smegmatis produced the same aminoglycoside resistance phenotype. These studies demonstrate this 16S rRNA mutation is responsible for amikacin resistance in M. abscessus, which has only one copy of the rRNA operon.

Alleles↗
PubMed1998

Initial (6-month) results of three-times-weekly azithromycin in treatment regimens for Mycobacterium avium complex lung disease in human immunodeficiency virus-negative patients.

Two consecutive, open, prospective trials of intermittent azithromycin (600 mg), usually given Monday, Wednesday, and Friday (TIW) for Mycobacterium avium complex (MAC) lung disease were initiated in human immunodeficiency virus-negative patients. Regimen A consisted of TIW azithromycin and daily ethambutol (15 mg/kg/day), daily rifabutin (300 mg/day), and initial twice weekly (BIW) streptomycin. Regimen B consisted of TIW azithromycin, TIW ethambutol (25 mg/kg/dose), TIW rifabutin (600 mg/dose), and initial BIW streptomycin. Of 19 patients enrolled in regimen A who completed at least 6 months of therapy, 14 (74%) had sputum samples become culture-negative. Of 39 patients enrolled in regimen B who completed at least 6 months of therapy, 24 (62%) had sputum conversion. These sputum conversion rates are comparable to previous rates at 6 months in patients receiving daily clarithromycin- or azithromycin-containing regimens. No resistance to azithromycin emerged with either regimen. This is the first study to demonstrate the efficacy of intermittent administration of medication for MAC lung disease.

Anti-Bacterial Agents↗
PubMed1998

Urge incontinence: the patient's perspective.

Urge incontinence has a profound effect on the day-to-day lives of women. The purpose of this study was to identify specific aspects of functioning and well-being affected by urge incontinence or mixed incontinence with a primary urge component. We conducted six focus groups of 65 racially and age diverse, community-dwelling women with urge incontinence. Transcripts of the focus groups were quantitatively analyzed for word use frequency with QSR NUD*IST software. Demographics, symptomatology, and the impact of incontinence on daily activities and feelings were assessed by questionnaire. Participants in the focus groups were on average 62 years of age; 52% were nonwhite, and 26% had a high school or less education. In the three identified broad domains, 52% of domain-related words were associated with feelings, 40% with activities, and 8% with relationships. Frequently identified references were bathroom availability (24%), loss of control (14%), anxiety (11%), and sleep disturbance (10%). Women under the age of 70 compared with older women more commonly identified feeling unattractive and low self-esteem (12% versus 2%, p < 0.007) and adverse effects on dating and sexual activity (45% versus 0%, p < 0.02). The effect of incontinence on quality of life correlated with frequency, nocturia, and pad use (Kendall's tau beta 0.02-0.32, p < 0.05). Urge incontinence affects many quality of life issues and contributes to limitation of activities, loss of control, and negative self-perception. Focus groups of diverse women with urge incontinence symptomatology are useful in understanding these effects.

Activities of Daily Living↗
PubMed1998

Clinical application of PCR-restriction enzyme pattern analysis for rapid identification of aerobic actinomycete isolates.

The accuracy and practicality of PCR-restriction enzyme pattern analysis (PRA) for routine identification of aerobic actinomycete clinical isolates were evaluated for 299 cultures submitted to the Mycobacteria/Nocardia Laboratory at the University of Texas Health Center at Tyler. PRA identification using an amplified 439-bp segment (amplicon) of the 65-kDa heat shock protein gene was compared to identification by traditional methods, including growth characteristics, susceptibility patterns, biochemical testing, and high-performance liquid chromatography analysis. Microbiological examination of six cultures ruled out aerobic actinomycetes, and they were omitted from the study. Amplicons were analyzed with BstEII, HaeIII, MspI, HinfI, and BsaHI. When necessary, AciI, HhaI, and NarI were also used. From March 1995 through May 1997 (27 months), 274 of the remaining 293 (93.5%) isolates were accurately identified by PRA. Major diagnostic groups included 170 mycobacteria, 93 nocardiae, and 30 other aerobic actinomycetes. Mixed cultures were readily recognized by PRA, including a wound culture that contained two Nocardia taxa that were indistinguishable morphologically. Mycobacterium mucogenicum was identified in three cultures heavily contaminated with gram-positive cocci. The 19 isolates that produced PRA patterns that did not match those in the current PRA database were differentiated into 8 Mycobacterium species and 11 other aerobic actinomycetes by the presence or absence of BstEII recognition sites. Identification of 15 of these 19 isolates was also equivocal by traditional methods. PRA results were reportable within 2 to 5 working days and were as accurate as and faster and less expensive to obtain than those of traditional methods.

Actinomycetales↗
PubMed1998

Sensitivity of fluorochrome microscopy for detection of Mycobacterium tuberculosis versus nontuberculous mycobacteria.

The results for 6,532 consecutive mycobacterial respiratory specimens collected from 1,040 patients from 1993 to 1995 in a Texas hospital were studied to determine the sensitivity of fluorescence microscopy for detection of Mycobacterium tuberculosis and nontuberculous mycobacteria (NTM). Smears were positive for acid-fast bacilli (AFB) in 63% (677 of 1,082) of specimens growing M. tuberculosis and 56% (638 of 1,148) of specimens growing the four most common species of NTM. Smear positivity by species was 58% (446 of 776) for M. avium complex, 51% (154 of 300) for rapidly growing mycobacteria (98% were M. abscessus), 78% (29 of 37) for M. kansasii, and 26% (9 of 35) for M. gordonae. Definite or probable disease by clinical criteria was present in 79% of patients with M. avium complex, 93% of patients with rapidly growing mycobacteria, 100% of patients with M. kansasii, and 0% of patients with M. gordonae. Patients with M. avium complex had a low incidence of AIDS (7%), and approximately 50% of non-AIDS patients had upper-lobe cavitary disease and 50% had nodular bronchiectasis. Only 23 of 6,532 (0.35%) of AFB smears were positive with a negative culture excluding patients on therapy for established mycobacterial disease. These studies suggest that NTM are as likely as M. tuberculosis to be detected by fluorescent microscopy in specimens from patients from areas endemic for NTM lung disease and at low risk for AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Nosocomial outbreaks/pseudo-outbreaks caused by nontuberculous mycobacteria.

Nosocomial outbreaks and pseudo-outbreaks caused by the nontuberculous mycobacteria (NTM) have been recognized for more than 20 years and continue to be a problem. Most of these outbreaks have involved the rapidly growing mycobacterial species Mycobacterium fortuitum and M. abscessus. The reservoir for these outbreaks is generally municipal and (often separate) hospital water supplies. These mycobacterial species and others are incredibly hardy, able to grow in municipal and distilled water, thrive at temperatures of 45 degrees C or above (M. xenopi and M. avium complex), and resist the activity of organomercurials, chlorine, 2% concentrations of formaldehyde and alkaline glutaraldehyde, and other commonly used disinfectants. Disease outbreaks usually involve sternal wound infections, plastic surgery wound infections, or postinjection abscesses. Pseudo-outbreaks most commonly relate to contaminated bronchoscopes and endoscopic cleaning machines (M. abscessus) and contaminated hospital water supplies (M. xenopi). Knowledge of the reservoir of these species, their great survival capabilities within the hospital, and newer molecular techniques for strain comparison have helped control and more quickly identify current nosocomial outbreaks or pseudo-outbreaks caused by the NTM.

Bronchoscopy↗
PubMed1998

Polyclonal Mycobacterium avium complex infections in patients with nodular bronchiectasis.

Mycobacterium avium complex (MAC) isolates among patients with chronic lung disease were studied for their heterogeneity using genetic identification methods, pulsed field gel electrophoresis (PFGE) and seroagglutination. A mean of 7.3 cultures per patient were collected from 17 patients with nodular bronchiectasis who were elderly (mean age 66 yr), predominantly female (76%), had smoked a mean of only 5 pack-years, and had multifocal bronchiectasis. A mean of 7.7 cultures per patient were collected from nine patients with upper lobe cavitary disease who were younger (mean age 52 yr), predominantly male (78%), and heavy smokers (mean 56 pack-yr). A mean of 2.9 PFGE types (genotypes) per patient (range, 1 to 9) were identified in the nodular bronchiectasis group, with 15 of 17 patients (88%) having two or more genotypes and 9 of 17 (53%) having three or more genotypes. In contrast a mean of 1.2 genotypes were identified in the patients with cavitary disease, with only 1 of 9 (11%) having two or more genotypes. Mycobacterium intracellulare was the most frequently recovered genotype in both groups and most isolates were rough or nontypable by seroagglutination. Some genotypes from the same patient considered different by current PFGE criteria had the same serotype and shared 11 to 20 common PFGE bands, suggesting they were related. These data demonstrate that patients with nodular bronchiectasis have multiple and/or repeated infections due to MAC whereas patients with upper lobe cavitary disease are usually infected with only a single strain.

Adult↗
PubMed1998

Porous hip replacement in Paget's disease. An 8-2/3-year followup.

An 8-year 8-month followup of a now 78-year-old active woman with a painful, severe varus deformity of the femur and arthritis of the right hip associated with monostotic Paget's disease of the hip is presented. Treatment consisted of multiple osteotomies, followed by implantation of a long stemmed cobalt chrome fully coated porous ingrowth hip system. The patient had an excellent outcome, including relief of pain and restoration of excellent function, despite ongoing severe osteolytic changes that did not appear to influence the healing of the osteotomies or the clinical stability of the implant.

Aged↗