Search PubMed⌕ Search

Biomedical subjects

A Ansari

Publications and source records attributed to A Ansari.

At least 37 records · Page 2Linked to original sources
PubMed2001

Increased expression of mXBP-1 (TREB-5) in thymic B cells in New Zealand mice.

New Zealand Black mice as well as several other murine models of murine lupus are well known for premature degeneration of thymus and development of autoimmunity. To focus on molecular events unique to murine lupus, we performed differential display using arbitrary primer pairs to distinguish NZB versus BALB/c thymus at 5 weeks of age. Following an extensive analysis of DNA bands that were either consistently up or downregulated and from studies of expression pattern of thymic genes by in situ nucleic acid hybridization, we focused on one clone that was consistently differentially expressed between NZB and BALB/c thymus. This clone was isolated, sequenced, and identified as the murine homologue of the human X box binding protein (hXBP-1), also known as TREB 5. mXBP-1 was found to be consistently upregulated in B cells in the thymic cortex of NZB and (NZBxNZW)F1, but not BALB/c, C3H/HeJ or C57BL/6 mice. In addition, it was dramatically elevated in MRL/ lpr but not MRL/++ mice; similarly, it was increased in BXSB/ Yaa male but not BXSB female thymic cortex. Of particular interest was an absence of mXBP-1 expression in the thymus of NZB/ Bln- Igh6(null)homozygotes. mXBP-1 has several putative functions, including the regulation of MHC class II expression and by virtue of its ability to recognize CRE-like elements shown to be involved in HTLV-1 transcription.

Animals↗
PubMed2001

The greening of engineers: a cross-cultural experience.

Experience with a group of mechanical engineering seniors at the University of Colorado led to an informal experiment with engineering students in India. An attempt was made to qualitatively gauge the students' ability to appreciate a worldview different from the standard engineering worldview--that of a mechanical universe. Qualitative differences between organic and mechanical systems were used as a point of discussion. Both groups were found to exhibit distinct thought and behavior patterns which provide important clues for sensitizing engineers to environmental issues in future educational initiatives. Cross-cultural and global dimensions of these initiatives are discussed.

Colorado↗
PubMed2001

A semiflexible polymer model applied to loop formation in DNA hairpins.

A statistical mechanical "zipper" model is applied to describe the equilibrium melting of short DNA hairpins with poly(dT) loops ranging from 4 to 12 bases in the loop. The free energy of loop formation is expressed in terms of the persistence length of the chain. This method provides a new measurement of the persistence length of single-stranded DNA, which is found to be approximately 1.4 nm for poly(dT) strands in 100 mM NaCl. The free energy of the hairpin relative to the random coil state is found to scale with the loop size with an apparent exponent of > or = 7, much larger than the exponent of approximately 1.5-1.8 expected from considerations of loop entropy alone. This result indicates a strong dependence of the excess stability of the hairpins, from stacking interactions of the bases within the loop, on the size of the loop. We interpret this excess stability as arising from favorable hydrophobic interactions among the bases in tight loops and which diminish as the loops get larger. Free energy profiles along a generalized reaction coordinate are calculated from the equilibrium zipper model. The transition state for hairpin formation is identified as an ensemble of looped conformations with one basepair closing the loop, and with a lower enthalpy than the random coil state. The equilibrium model predicts apparent activation energy of approximately -11 kcal/mol for the hairpin closing step, in remarkable agreement with the value obtained from kinetics measurements.

Base Composition↗
PubMed2000

Peripartum cardiomyopathy: National Heart, Lung, and Blood Institute and Office of Rare Diseases (National Institutes of Health) workshop recommendations and review.

OBJECTIVE: Peripartum cardiomyopathy (PPCM) is a rare life-threatening cardiomyopathy of unknown cause that occurs in the peripartum period in previously healthy women. In April 1997, the National Heart, Lung, and Blood Institute (NHLBI) and the Office of Rare Diseases of the National Institutes of Health (NIH) convened a Workshop on Peripartum Cardiomyopathy to foster a systematic review of information and to develop recommendations for research and education. PARTICIPANTS: Fourteen workshop participants were selected by NHLBI staff and represented cardiovascular medicine, obstetrics, immunology, and pathology. A representative subgroup of 8 participants and NHLBI staff formed the writing group for this article and updated the literature on which the conclusions were based. The workshop was an open meeting, consistent with NIH policy. EVIDENCE: Data presented at the workshop were augmented by a MEDLINE search for English-language articles published from 1966 to July 1999, using the terms peripartum cardiomyopathy, cardiomyopathy, and pregnancy. Articles on the epidemiology, pathogenesis, pathophysiology, diagnosis, treatment, and prognosis of PPCM were included. RECOMMENDATION PROCESS: After discussion of data presented, workshop participants agreed on a standardized definition of PPCM, a general clinical approach, and the need for a registry to provide an infrastructure for future research. CONCLUSIONS: Peripartum cardiomyopathy is a rare lethal disease about which little is known. Diagnosis is confined to a narrow period and requires echocardiographic evidence of left ventricular systolic dysfunction. Symptomatic patients should receive standard therapy for heart failure, managed by a multidisciplinary team. If subsequent pregnancies occur, they should be managed in collaboration with a high-risk perinatal center. Systematic data collection is required to answer important questions about incidence, treatment, and prognosis.

Cardiomyopathies↗
PubMed2000

Fetal microchimerisms in the mother: immunologic implications.

The previously held concept that the fetus is completely separated from the mother, especially by trophoblasts that line the outer layer of the placenta, has recently been questioned. It has recently been shown that fetal cells are detectable not only in the peripheral blood, but also in maternal skin and liver. Although the migration of fetal cells into the maternal circulation has been given a great deal of attention because of its implication in the prenatal diagnosis of genetic diseases, the potential role of such placental transfer of fetal cells in the pathogenesis of autoimmune diseases has only recently been considered. In patients with scleroderma, fetal cell-derived DNA was detected more frequently in the peripheral blood of patients than controls. This finding of a limited number of fetal cells in maternal tissues leading to microchimerism has been proposed to have a role in the induction of scleroderma. Although evidence for microchimerism has also been confirmed in a high frequency of liver tissues from patients with primary biliary cirrhosis (PBC), a similar high frequency was noted in control patients, which suggests that microchimerism by itself is unlikely to fully account for the pathogenesis of PBC. The finding of such a high frequency of fetal microchimerism in the liver suggests that this is a very common event, raising the possibility that the migration of fetal cells may be important in the induction and subsequent maintenance of tolerance against the fetus during pregnancy. In addition, it is clearly possible that such microchimerism could contribute to the pathogenesis of select autoimmune diseases.

Autoimmunity↗
PubMed2000

Comparative immunoreactivity of anti-trifluoroacetyl (TFA) antibody and anti-lipoic acid antibody in primary biliary cirrhosis: searching for a mimic.

Previous studies documenting the existence of cross-reactivity between the lipoated (but not unlipoated) forms of the inner lipoyl domain (E2L2) of PDC-E2 [the major autoantigen in Primary biliary cirrhosis (PBC)] and trifluoroacetylated (TFA) proteins, led us to hypothesize that PBC may be due to an initial insult with an environmental agent that cross-reacts with TFA. Therefore, we performed a comparative study of the reactivity of rabbit anti-TFA antibody and anti-lipoic acid (LA) antibody against the mitochondrial autoantigens of human PBC and various TFA and LA conjugated proteins. Whereas both anti-TFA and anti-LA reacted with PDC-E2, the wild-type lipoated form of E2L2, OGDC-E2, E3-BP and LA-KLH, neither reacted with BCOADC-E2 or the non-lipoated form of E2L2. Of interest was that while anti-TFA reacted with PDC-E2, TFA-RSA and LA-KLH, it failed to inhibit PDC-E2 enzyme function. In contrast, anti-LA demonstrated cytoplasmic and mitochondrial staining, and inhibited PDC enzyme activity. Hence, although considerable cross reactivity exists between anti-TFA and anti-LA, the molecular nature of the interaction is clearly different. One of 14 PBC sera reacted weakly with TFA-albumin, whereas four of 14 PBC sera reacted with LA-KLH. Immunohistochemically, both anti-TFA and anti-LA antibodies reacted focally with periportal hepatocytes and bile ducts in both PBC and controls. However, anti-LA produced much stronger focalized staining of the bile ducts of diseased liver. This study suggests that while anti-TFA antibody recognizes lipoic acid-linked enzymes and proteins, the epitope recognized differs from that of anti-LA antibody and PBC autoantibodies. It is unlikely that a response to TFA is the triggering event in PBC. Anti-LA antibodies share a higher degree of similarity to PBC sera providing suggestive evidence that anti-LA antibodies or anti-LA like antibodies (mimotopes) may help define the initiator of the autoimmune response.

Animals↗
PubMed2000

Genotypic analysis of hepatitis C virus in blood donors in Indonesia.

A study was conducted to describe the genetic diversity of hepatitis C virus (HCV) in a population of positive blood donors from throughout Indonesia. Repeat analysis by reverse transcription-polymerase chain reaction (RT-PCR) of 102 anti-HCV positive samples showed that 67 gave HCV-specific positive signals by the PCR for the 5'-untranslated genomic region of HCV. Further genotypic analysis on 64 HCV RNA-positive samples indicated that 57 belonged to the following individual genotypes: 1a, 1b, 2a, 2b, and 3b. The predominant HCV genotypes in this donor population were 1b (57.8%), 2a (17.2%), and 3b (10.9%). The core sequences of the 4 indeterminate samples when aligned with published sequences of various HCV genotypes showed a range of homology from 16.16% to 78.67%. Comparative analysis of genotypic representation from other anti-HCV-positive study populations, including polytransfused pediatric and adult renal dialysis groups, is now being carried out to determine the potential genotypic association with mechanistic HCV spread.

5' Untranslated Regions↗
PubMed1999

Persistence of an alternate chromatin structure at silenced loci in vitro.

In Saccharomyces cerevisiae, transcriptional repression at the HM mating-type loci and telomeres results from the formation of a heterochromatin-like structure. Silencing requires at least three Sir proteins (Sir2p-4p), which are recruited to chromatin by silencers at the HM loci and TG1-3 tracts at telomeres. Sir proteins and telomeres colocalize at the nuclear periphery, suggesting that this subnuclear position may also contribute to transcriptional repression. To evaluate the contribution of nuclear context to silencing, we developed methodology to isolate silent chromatin for analysis in vitro. Site-specific recombination was used in vivo to produce DNA rings from the silent HMR locus, and differential centrifugation was used to isolate the rings from whole-cell lysate. The partially purified rings retained many of the intracellular hallmarks of transcriptionally repressed domains. Specifically, rings from repressed strains were resistant to restriction endonuclease digestion, bore an altered DNA topology, and were associated with Sir3p. The recombination approach also was used to form rings from HMR that lacked silencers. Despite the uncoupling of these cis-acting regulatory elements, similar but nonidentical results were obtained. We conclude that an alternate chromatin structure at silent loci can persist in vitro in the absence of silencers and nuclear compartmentalization.

Chromatin↗
PubMed1999

Distribution of the Purkinje fibres in the sheep heart.

The aim of the present study was to advance our knowledge regarding the anatomy of the purkinje fibres from their origin, at the bundle branches, till their termination within the myocardium. Indian ink injections of the purkinje fibres were carried out in the left ventricle of 25 fresh sheep hearts and in the right ventricle of 20 hearts. Numerous samples were taken from the walls and papillary muscles of the two ventricles for histological analysis and determination of the mode of termination of the fibres. The ventricular conduction system could be injected as far proximally as the bundle branches, thus illustrating the bifascicular nature of the left bundle branch, with numerous interfascicular communications. The purkinje fibres were observed to form an extensive subendocardial network, forming a polygonal arrangement in the left ventricle with a characteristic pattern around the papillary muscles. Deep myocardial branches took origin from this network which penetrated the ventricular wall to reach the epicardium. Histological analysis demonstrated the characteristic features of the purkinje cells, and confirmed the presence ofa perifascicular sheath of connective tissue which surrounded the purkinje fibres until their transition with working cardiomyocytes. The perifascicular connective tissue sheath is important in organising the contraction of the myocardium by preventing lateral spread of conduction and by permitting transmission of the impulse only at the termination of the purkinje fibre. The sheath may also protect the fibres from the stresses and strains originating from contraction of the surrounding myocardium.

Animals↗
PubMed1999

Autoepitope mapping and reactivity of autoantibodies to the dihydrolipoamide dehydrogenase-binding protein (E3BP) and the glycine cleavage proteins in primary biliary cirrhosis.

Primary biliary cirrhosis (PBC) is an autoimmune liver disease characterized by the presence of antimitochondrial antibodies (AMA) directed primarily against the E2 subunits of the pyruvate dehydrogenase complex, the branched chain 2-oxo-acid dehydrogenase complex, the 2-oxoglutarate dehydrogenase complex, as well as the dihydrolipoamide dehydrogenase-binding protein (E3BP) of pyruvate dehydrogenase complex. The autoantibody response to each E2 subunit is directed to the lipoic acid binding domain. However, hitherto, the epitope recognized by autoantibodies to E3BP has not been mapped. In this study, we have taken advantage of the recently available full-length human E3BP complementary DNA (cDNA) to map this epitope. In addition, another lipoic binding protein, the H-protein of the glycine cleavage complex, was also studied as a potential autoantigen recognized by AMA. Firstly, the sequence corresponding to the lipoic domain of E3BP (E3BP-LD) was amplified by polymerase chain reaction and recombinant protein and then purified. Immunoreactivity of 45 PBC sera (and 52 control sera) against the purified recombinant E3BP-LD was analyzed by enzyme-linked immunosorbent assay (ELISA) and immunoblotting. Secondly, reactivity of PBC sera was similarly analyzed by immunoblotting against H-protein. It is interesting that preabsorption of patient sera with the lipoic acid binding domain of E3BP completely removed all reactivity with the entire protein by immunoblotting analysis, suggesting that autoantibodies to E3BP are directed solely to its lipoic acid binding domain. Fifty-three percent of PBC sera reacted with E3BP-LD, with the majority of the response being of the immunoglobulin G (IgG) isotype (95%). Surprisingly, there was little IgM response to the E3BP-LD suggesting that the immune response was secondary because of determinant spreading. In contrast, H-protein does not appear to possess (or expose) autoepitopes recognized by PBC sera. This observation is consistent with structural data on this moiety.

Amino Acid Oxidoreductases↗
PubMed1999

Fetal microchimerism alone does not contribute to the induction of primary biliary cirrhosis.

Microchimerism has been implicated in the etiology of autoimmune diseases. It has also been implicated in the induction/maintenance of fetal tolerance. We used polymerase chain reaction (PCR) analysis to determine whether microchimerism occurred in patients who subsequently developed primary biliary cirrhosis (PBC), and thus may be involved in its etiology. We performed PCR amplification of sequences unique to both the X and Y chromosomes from the livers of 37 women with PBC and 39 female controls using WAVE technology; a very sensitive technology based on an ion-pair reverse-phase high-performance liquid chromatography system. All patients were known to have had at least 1 son and it was confirmed that PBC was diagnosed after the birth of the son. Data were analyzed for both detection of the Y chromosome gene and the ratio of the yield of the Y chromosome PCR products to the X chromosome. The prevalence of Y chromosome detection in PBC was 26 of 37 (70%) compared with 28 of 39 (72%) in controls, and the ratio of Y chromosome to X chromosome was similar between the PBC and control groups, 0.402 +/- 0.143 vs. 0.271 +/- 0.055, respectively. Our results, using our more sensitive technology, showed that microchimerism is a very common event in human liver and supported the thesis that this may contribute to the induction/maintenance of fetal tolerance. However, although we cannot exclude the possibility that select fetal major histocompatibility complex (MHC) haplotypes might contribute to disease susceptibility, our data suggest that microchimerism by itself does not play a significant role in the development of PBC.

Adult↗
PubMed1999

Autoantibodies in human chronic graft-versus-host disease after hematopoietic cell transplantation.

Primary biliary cirrhosis (PBC) and graft-versus-host disease (GVHD) are thought to have common immunopathologic features and previous studies have reported that 5.2 to 81% of patients with chronic GVHD after allogeneic hematopoietic cell transplant have antimitochondrial antibodies (AMA). We studied a total of 89 patients with chronic GVHD and 60 controls for AMA reactivity by ELISA and immunoblotting using recombinant PDC-E2, BCOADC-E2, and OGDC-E2, immunoblotting of beef heart mitochondrial proteins, and reactivity to nuclei, smooth muscle (ASMA), ribonucleoprotein JO-1, extractable nuclear antigen, nuclear proteins SSA/ SSB, ribonucleic P proteinase III, cardiolipin (ACA), liver kidney microsomal, thyroid microsomal, myeloperoxidase, and the reactivity of rheumatoid factor. A subset of 60 chronic GVHD sera were tested for reactivity to gp210 and LBR. Finally, liver tissue from patients with chronic GVHD and PBC was studied by immunohistochemistry to determine whether there was comparable abnormal apical staining of biliary epithelial cells using PDC-E2-specific monoclonal antibodies. Surprisingly, there were no AMA found in the sera from the 89 patients with chronic GVHD. Review of published data on AMA in GVHD suggests that previous results were primarily false positives. In contrast, sera from the patients with GVHD did have a variety of other autoantibodies and, in particular, 20/89 (22.4%) positive ANA, 23/89 (25.8%) positive ASMA, and 9/89 (10.1%) positive ACA. The other autoantibodies assayed were not statistically different from controls. Finally, abnormal biliary epithelial luminal staining of bile ducts was found, as expected, in liver tissue of patients with PBC but was absent in chronic GVHD.

Adult↗
PubMed1999

Isolation of selected chromatin fragments from yeast by site-specific recombination in vivo.

A burgeoning interest in the role of chromatin structure in a wide variety of chromosome functions has established a need for methods to obtain chromatin in its native form. Here we describe a simple and efficient method for biochemical isolation of selected chromatin fragments from yeast chromosomes. The approach involves three steps. First, site-specific recombination in vivo is used to excise a chromosomal domain of interest in the form of a small extrachromosomal ring. Second, whole cell lysate is prepared from cultures in which recombination has been induced. Third, differential centrifugation is used to separate excised chromatin rings from chromosomes and other cellular debris. Using this methodology, we show that rings containing the transcriptionally repressed HMR mating-type locus can be formed and isolated in high yield. Furthermore, we show that the isolation procedure results in significant enrichment of recombinant rings. Finally, we show that the nucleosomal organization of the recombined material is not altered during isolation.

Cell Fractionation↗
PubMed1999

Are infectious agents involved in primary biliary cirrhosis? A PCR approach.

BACKGROUND/AIMS: A variety of data suggest that microbial infections and, in particular, atypical mycobacteria infections, may either initiate and/or be associated with the pathogenesis of primary biliary cirrhosis. METHODS: To address this hypothesis, use was made of polymerase chain reaction techniques and primers specific for the 16s rRNA gene of Eubacteria, Archaeabacteria, Mycobacteria and Helicobacter to determine if such sequences were detectable in liver tissue specimens from 29 patients with primary biliary cirrhosis. Similar liver tissues from patients with primary sclerosing cholangitis, chronic hepatitis, alcoholic liver disease and otherwise normal donors were analyzed in parallel. Genomic DNA was extracted from each of these liver tissue specimens using sterile techniques to avoid possible laboratory contamination. The DNA was subjected to polymerase chain reaction amplification using bacterial genus specific primers and the amplified products cloned and sequenced. Sequence data were analyzed by searching for homology to existing genes. RESULTS: Sequences from primary biliary cirrhosis and control livers corresponded to those found in a variety of bacteria, but no consensus sequence was found in primary biliary cirrhosis specimens. Neither Archaeabacteria nor Mycobacteria products were detected in liver specimens of patients with primary biliary cirrhosis, and Helicobacter pylori DNA was detected in only one primary biliary cirrhosis patient. CONCLUSIONS: Although bacterial infection, particularly with intracellular organisms, has been suggested to play a role in the initiation of primary biliary cirrhosis, there is no evidence from this study to suggest an ongoing chronic infectious process.

Archaea↗
PubMed1999

Abzyme prodrugs

Explore the source record for details and available documents.

Journal Article↗
PubMed1999

The U69 gene of human herpesvirus 6 encodes a protein kinase which can confer ganciclovir sensitivity to baculoviruses.

The protein encoded by the U69 open reading frame (ORF) of human herpesvirus 6 (HHV-6) has been predicted to be a protein kinase. To investigate its functional properties, we have expressed the U69 ORFs from both HHV-6 variants, A and B, by using recombinant baculoviruses (BV6AU69 and BV6BU69). Nickel agarose and antibody affinity chromatography was used to purify the proteins to homogeneity and when incubated with [gamma-32P]ATP, both U69 proteins became phosphorylated on predominantly serine residues. These data strongly suggest that U69 is a protein kinase which autophosphorylates. The phosphorylation reaction was optimal at physiological pH and low NaCl concentrations. It required the presence of Mg2+ or Mn2+, and Mg2+ was able to support phosphorylation over a wider range of concentrations than Mn2+. Both ATP and GTP could donate phosphate in the protein kinase assay and the former was more efficient. U69 was capable of phosphorylating histone and casein (serine/threonine kinase substrates) but not enolase (a tyrosine kinase substrate). For the autophosphorylation reaction, the Michaelis constants for ATP of baculovirus-expressed HHV-6A and HHV-6B U69 were calculated to be 44 and 11 microM, respectively. U69 is a homologue of the UL97 gene encoded by human cytomegalovirus which has been shown to phosphorylate the antiviral drug ganciclovir (GCV). We analyzed whether the U69 ORF alone was capable of conferring GCV sensitivity on baculoviruses BV6AU69 and BV6BU69. In plaque reduction experiments, these baculoviruses displayed a GCV-sensitive phenotype compared to a control baculovirus (BVLacZ). The 50% inhibitory concentrations (IC50) of BV6AU69 and BV6BU69 were calculated to be 0.35 and 0.26 mM, respectively, whereas the control baculovirus had an IC50 of >1.4 mM. This shows that the U69 gene product is the only one required to confer GCV sensitivity on baculovirus.

Antiviral Agents↗