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Biomedical subjects

S Malik

Publications and source records attributed to S Malik.

At least 109 records · Page 6Linked to original sources
PubMed1995

Zinc heparin introduces a preanalytical error in the measurement of ionized calcium concentration.

In this study we determined how zinc heparin affected ionized calcium concentration determinations. Zinc heparin produced a positive bias (0.020-0.067 mmol l-1) in ionized calcium measurement in serum/whole blood and a negative bias (-0.035 to -0.110 mmol l-1) with aqueous ionized calcium standards. To test if the positive bias was due to zinc ions displacing calcium from its protein-calcium complexes, we reproduced the effect by adding ZnCl2 to pooled serum. Changes in [ZnCl2] (0.1-0.5 mmol l-1) caused a dose-dependent increase, a constant bias ([ZnCl2], 0.5-1.25 mmol l-1) or a dose-dependent decrease ([ZnCl2] > 1.25 mmol l-1) in ionized calcium concentration, independent of pH. Similar results were obtained when zinc concentration of the specimen was changed by varying the volume of blood collected into syringes containing zinc heparin. We conclude that zinc heparin produces a positive bias in ionized calcium measurement in protein-based matrices.

Binding Sites↗
PubMed1995

Orbital neurofibrosarcoma: a case report.

Malignant peripheral nerve sheath tumours of orbit is rare entity. Only sixteen cases are reported in world literature. Bengin schwannomas of the orbit are found in 1.5 to 18 percent of patients with von Recklinghausen's disease (VRD) and form 1 percent of all orbital tumours1. The incidence of malignant transformation in VRD is varies from 5-15 percent of all the cases1.

Female↗
PubMed1995

Simultaneous medullary carcinoma, occult papillary carcinoma and lymphocytic thyroiditis.

A 55-year-old female underwent total thyroidectomy for medullary carcinoma of the left lobe of the thyroid. The right lobe showed an incidental occult papillary carcinoma. There was also diffuse lymphocytic thyroiditis. Immunohistochemistry for calcitonin and thyroglobin confirmed the separate histogenesis for both carcinomas. The coexistence of medullarry and papillary carcinoma of the thyroid is rare and the literature usually documents mixed tumours with features of both carcinomas, rather than independent tumours, as in our case.

Carcinoma, Medullary↗
PubMed1994

Activation of apolipoprotein AI gene transcription by the liver-enriched factor HNF-3.

Liver-specific expression of the apolipoprotein AI (apoA-I) gene is controlled by the coordinate action of transcription factors bound to three sites (A, B, and C) located within a powerful liver-specific enhancer which spans the -222 to -110 region upstream of the apoA-I gene transcription start site (+1). Sites A and C bind various members of the nuclear receptor superfamily including the liver-enriched factor HNF-4. In the current report, enhancer derivatives with mutagenized protein-binding sites were tested for their ability to stimulate the apoA-I basal promoter in hepatoblastoma HepG2 cells. The results revealed that occupation of both sites A and B, but not C is essential for high level expression. Electrophoretic mobility shift assays showed that in HepG2 cells site B is occupied by the liver-enriched factor HNF-3 beta. Binding of HNF-3 beta to site B transactivates the apoA-I basal promoter in hepatic and nonhepatic cells. HNF-3 beta binding and transactivation were dependent upon the close proximity of two HNF-3 beta binding motifs within site B. Furthermore, HNF-3 beta and HNF-4, bound to their cognate sites within the apoA-I enhancer exhibited strong synergy in transactivation of the apoA-I basal promoter in nonhepatic cells, highlighting the central role of HNF-3 beta in liver-specific transcription of the apoA-I gene. It is concluded that cooperative binding of HNF-3 beta to site B and synergistic interactions between HNF-4 and HNF-3 beta bound to their cognate sites in the apoA-I enhancer may play a fundamental role in apoA-I gene expression in liver.

Animals↗
PubMed1994

Transcriptional repression of apolipoprotein AI gene expression by orphan receptor ARP-1.

Expression of the apolipoprotein AI (apoAI) gene in the liver is controlled by a liver-specific enhancer. The function of this enhancer depends on synergistic interactions between transcription factors bound to at least three sites (designated A, B, and C) located within this enhancer. We have previously shown that an apoAI gene reporter construct containing the entire enhancer is expressed efficiently in a hepatoma cell line and that its activity is repressed by the orphan receptor ARP-1. Moreover, repression by ARP-1 is overcome by the retinoid X receptor RXR alpha in the presence of retinoic acid. In this study, we show that ARP-1 represses the apoAI promoter by binding to site A of the apoAI liver-specific enhancer, the repression being a promoter context-specific event. Mapping analysis of ARP-1 indicated that its DNA binding domain is essential but not sufficient for repression. Two separate repression domains located at the amino- and carboxyl-terminal halves of ARP-1 were found to individually complement the DNA binding domain for efficient repression. We also demonstrate the reversibility of ARP-1 repression by transcription factors C/EBP and Egr-1, which might also be involved in apoAI gene expression. Significantly, repression by ARP-1 was found to be a prerequisite for C/EBP-mediated transactivation. We interpret our results in terms of a model in which ARP-1 repression via its interaction with site A is an obligatory intermediate step in switching from one activated state of the apoAI gene to another.

Animals↗
PubMed1994

Fast atom bombardment mass spectrometric determination of the molecular weight range of uremic compounds that displace phenytoin from protein binding: absence of midmolecular uremic toxins.

Uremic compounds are known to displace phenytoin from protein binding, resulting in a higher concentration of the pharmacologically active free fraction of phenytoin. The true chemical identities and molecular weight range of all these compounds are still unknown. We demonstrated that indoxyl sulfate and hippuric acid, which are found at high concentrations in uremic patients, can only partially explain the elevated free phenytoin concentration. Other known uremic compounds, guanidine, methylguanidine, and guanidinosuccinic acid, do not displace phenytoin from the protein-binding sites. Uremic compounds from sera of patients on maintenance hemodialysis were removed using activated charcoal. These compounds were then backextracted from activated charcoal using methanol and analyzed by fast atom bombardment mass spectroscopy. Mass spectra of uremic sera showed no peak over m/z 450, indicating that midmolecular uremic toxins are not involved in displacing phenytoin from protein binding. We also observed additional peaks in the mass spectrum of uremic compounds when compared with the normal serum extract, indicating the presence of several endogenous compounds in uremic sera, as expected.

Drug Interactions↗
PubMed1994

Extraction and detection of sulfamethazine in spray-dried milk.

Processes that reduce moisture content of fluid milk may result in a high concentration of animal drug residues that are undetectable in the fluid milk on the basis of the same weights. The objectives were to determine the amount of sulfamethazine in spray-dried milk powder manufactured from fluid milk contaminated with sulfamethazine and to determine the effectiveness of supercritical fluid extraction as a means to extract sulfamethazine from dry milk powder. Fluid whole (3.25% fat) and skim milks with sulfamethazine added at concentrations of 5, 10, and 100 ppb were spray-dried. Based on total solids, observed concentrations were 493 and 523 ppb in skim and whole dry milk powders, respectively, compared with fluid milk containing 100 ppb of sulfamethazine as determined by HPLC. The increase in sulfamethazine concentration from fluid to dry milk was also measured quantitatively by a microbial receptor assay and an ELISA. Poor recoveries and variability in data were possibly due to binding of sulfamethazine to undetermined milk components. Dry milk powder with measured concentrations of sulfamethazine was treated with supercritical CO2. Sulfamethazine was not detectable in the extracted dry milk powder by microbial receptor assay or ELISA.

Animals↗
PubMed1994

Experience with brain abscesses.

Brain abscesses were studied in 47 patients. Thirty-four (72%) of them were between 5-15 years and 9 were infants. Otogenic source (34%) was the commonest predisposing factor, followed by scalp and face infection (21.3%) and congenital cyanotic heart disease (12.8%). Twenty (42%) patients had multiple abscesses. Supratentorial abscesses were commonest (75.9%). Predominant clinical features were fever (87.2%), raised intracranial tension (78.7%) and altered sensorium (53.2%). A total of 38.3% presented with focal neurological deficit and 34% were admitted in Grade III or IV coma. Diagnosis of abscess and monitoring of its evolution was done principally by CT scanning. Causative organisms were isolated in 54.8% of cases and Staphylococci, Proteus and Pseudomonas were the common pathogens. Therapy was most often a combination of surgical aspiration with or without excision in addition to antimicrobial therapy. The overall mortality in our series was 44.7%. Bad prognostic factors were Grade III/IV of coma at admission, age below 2 years and multiple abscesses.

Adolescent↗
PubMed1993

A role for band 4.2 in human erythrocyte band 3 mediated anion transport.

Human erythrocyte band 3 was purified essentially free of peripheral proteins, in particular band 4.2, using affinity chromatography. Band 3 protein was then reconstituted into liposomes of lipid type and ratio approximating that of erythrocyte membranes. Stilbenedisulfonate inhibition of band 3 mediated efflux of radiolabeled sulfate from preloaded liposomes was used to test the functionality and correct orientation of the protein. When sulfate efflux, mediated by purified band 3, was compared with partially purified band 3, which contained detectable amounts of bands 4.1 and 4.2, a clear difference in efflux was measured. Sulfate efflux was approximately 30% faster from liposomes containing purified band 3 compared with those containing partially purified protein. In order to investigate further any specific effect of band 4.2 protein on band 3 mediated anion transport, band 4.2 was purified. Increasing amounts of band 4.2 were complexed with purified band 3 and then reconstituted into liposomes. Increasing amounts of band 4.2 complexed with band 3 caused a decrease in band 3 mediated anion transport. The effect of band 4.2 on band 3 mediated anion transport appears to be specific since increasing concentrations of band 4.2 added exogenously to band 3 in reconstituted vesicles (rather than complexed with band 3 before reconstitution) produced no significant changes in sulfate efflux. Further, when increasing amounts of band 4.2 were added to the functionally active transmembrane domain of band 3 and then reconstituted into vesicles, there was also no significant change in sulfate efflux.(ABSTRACT TRUNCATED AT 250 WORDS)

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1993

An alternative pathway for transcription initiation involving TFII-I.

The minimal promoter elements required for initiation by RNA polymerase II include the TATA box and/or an initiator element (Inr) at or near the transcription start site. Studies of the adenovirus major late core promoter (containing both elements) have demonstrated an initiation pathway that involves binding of the transcription factor TFIID (or the derived subunit, the TATA-binding protein TBP (TFIID tau)) to the TATA element, which is facilitated by transcription factor TFIIA, followed by sequential interactions of other general factors. Here we describe a novel pathway that requires an intact Inr and the Inr-binding factor TFII-I (ref. 3). Sequential addition of the general factors generated TFII-I-dependent preinitiation complexes different from those formed with TFIIA. Furthermore, TBP bound cooperatively (with only TFII-I) to an Inr-containing TATA-less promoter, suggesting a means for activation of TATA-less promoters, which nonetheless require TFIID (refs 9-11). These observations provide support for functionally distinct pathways which could be subject to differential regulation by specific activators or repressors.

Adenoviridae↗
PubMed1993

Evaluation of vero cell lysate antigen for the ELISA of flaviviruses.

The vero cell lysate antigen for the enzyme-linked immunosorbent assay (ELISA) of flaviviruses was evaluated for sensitivity, specificity including cross-reactions, and background by comparing with the standard ELISA. Human sera, in serial dilutions, were taken from subjects 14, 35, and 210 days postvaccination with 17D antigen. Early after injection, high sensitivity (82.9%) was shown by the cell lysate antigen method. Late after infection, high sensitivity was achieved by the standard method (96.2% and 94%), with significant difference (P = 0.0001). However, sensitivity achieved by the cell lysate antigen method was also acceptable (91.7% & 88.9%). The cell lysate antigen method showed high specificity and low cross reactivity early after infection. At 35 days postvaccination, no difference in specificity was observed between the two methods, but higher cross-reactions were observed for the standard method. This pattern continued at 210 days postvaccination, with significantly higher cross-reactions with the standard ELISA. The optical density differences by the two methods did not show significant relationship with the serial dilutions of human sera. No difference was observed in early and late infections in the background values of the negative control (Western equine encephalitis) between the two methods. The ELISA by the cell lysate antigen, within the limits of the experiments done, was found to be a good replacement for the ELISA by the standard method.

Animals↗
PubMed1993

A saturation threshold for taxol cytotoxicity in human glial and neuroblastoma cells.

The cytotoxic effects of taxol at concentrations of 0.001-1.0 microgram/ml were determined in two human glioblastoma multiforme, two neuroblastoma and two primitive neuroectodermal tumor cell lines. The neuroectodermal cell lines were established from previously treated patients, while the glioblastomas were from untreated patients. At exposure durations of 1, 4 and 24 h there was an inverse taxol concentration-survival relationship for all six cell lines as measured by the MTT method. Significant differences in sensitivity to taxol among these cell lines were observed; the most resistant cell line SK-N-FI is characterized by very high levels of MDR1 expression and the most sensitive SK-N-AS by very low levels. An additional level of complexity concerns a saturation threshold for taxol-induced cytotoxic effects which when reached precludes additional effects of prolonged or additional exposure. Tumors of the brain and peripheral nervous system appear to be sensitive to taxol. However, dosage necessary to maximize cytocidal effects in tumors requires knowledge of at least the range of each tumors constitutive sensitivity to taxol and a way to optimize drug delivery.

Brain Neoplasms↗
PubMed1993

Potential RNA polymerase II-induced interactions of transcription factor TFIIB.

The ubiquitous transcription factor TFIIB is required for initiation by RNA polymerase II and serves as a target of some regulatory factors. The carboxy-terminal portion of TFIIB contains a large imperfect direct repeat reminiscent of the structural organization of the TATA-binding component (TBP) of TFIID, as well as sequence homology to conserved regions of bacterial sigma factors. The present study shows that the carboxy-terminal portion of TFIIB, like that of TBP, is folded into a compact protease-resistant core. The TFIIB core, unlike the TBP core, is inactive in transcription but retains structural features that enable it to form a complex with promoter-bound TFIID. The protease-susceptible amino terminus appears to contain components responsible for direct interaction with RNA polymerase II (in association with TFIIF) either on the promoter (in association with TFIID) or independently. In addition, core TFIIB (but not intact TFIIB) extends the footprint of TBP on promoter DNA, suggesting that TFIIB has a cryptic DNA-binding potential. These results are consistent with a model in which TFIIB, in a manner functionally analogous to that of bacterial sigma factors, undergoes an RNA polymerase II-dependent conformational change with resultant DNA interactions during the pathway leading to a functional preinitiation complex.

Amino Acids↗
PubMed1992

Isolation and characterization of a cDNA encoding Drosophila transcription factor TFIIB.

A Drosophila cDNA encoding a human transcription factor TFIIB homologue was isolated by PCR methods. The deduced amino acid sequence indicates 85% sequence similarity with human TFIIB, and the corresponding cDNA product expressed in Escherichia coli is interchangeable with human TFIIB for both basal and GAL4-VP16-induced transcription. Structural motifs including the direct repeats, basic repeats, and sigma sequence similarities are well conserved among Drosophila, human, and Xenopus TFIIB. However, the N-terminal region of each direct repeat is less conserved among the three species, suggesting the presence of two structural subdomains in the direct repeat. Moreover, the amino acid changes in the N-terminal subdomain produce altered positions of the conserved amino acids between the direct repeats. An overall similarity in general structural features between TFIIB and TFIID tau (the TATA-binding subunit of TFIID) was previously noted. However, in contrast to the sequence divergence reported for the N-terminal domains of TFIID tau from different species, the N-terminal sequence of TFIIB was highly conserved among the species. This suggests that TFIIB has a more rigid structure, consistent with its function as a "bridging" protein between TFIID and RNA polymerase II. Further implications of the TFIIB structure are discussed.

Amino Acid Sequence↗
PubMed1992

Structural stability of the erythrocyte anion transporter, band 3, in native membranes and in detergent micelles.

The exothermic thermal denaturation transition of band 3, the anion transporter of the human erythrocyte membranes, has been studied by differential scanning calorimetry, in ghost membranes and in nonionic detergent micelles. In detergent micelles the transmembrane domain of band 3 gave an irreversible denaturation transition (C transition). However, no thermal transition was observed for the N-terminal cytoplasmic domain when band 3 was solubilised in detergent micelles. A reduction in enthalpy (190-300 kcal mol-1) with an accompanying decrease in thermal denaturation temperatures (48-60 degrees C) for the C transition was observed in detergent solubilised band 3 when compared with ghost membranes. Unlike ghost membranes, two thermal transitions for band 3 in detergent micelles were observed for the C transition when in the presence of excess covalent inhibitor, 4,4'-diisothiocyanostilbene-2,2'-disulphonate (DIDS), which derive from the thermal unfolding of a single protein with two different thermal stabilities; DIDS-stabilised (75 degrees C) and DIDS-insensitive (62 degrees C). A reduction in the denaturation temperature for the transmembrane domain of band 3 was observed when compared with intact band 3 although no significant differences was observed in the corresponding enthalpy values. This indicates some cooperativity of the two domains of band 3 in maintaining the transmembrane conformation. The results presented in this study show that detergents of intermediate micelle size (e.g. Triton X-100 and C12E8) are required for optimal thermal stability of band 3.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1992

Progressive vision loss. A rare manifestation of familial cavernous angiomas.

We studied four generations of a family in which the index case had progressive loss of vision secondary to a cavernous angioma of the optic nerve and chiasm. Magnetic resonance imaging of the brain revealed multiple, asymptomatic intracerebral cavernous angiomas. Brain magnetic resonance imaging scans of the family members revealed multiple cavernous angiomas in the brother and paternal grandfather, but none in the father or his siblings. Autopsy reports of the paternal great grandfather noted multiple cavernous angiomas in the brain and abdominal viscera. We believe our patient to be the sixth reported case in which a cavernous angioma involved the optic chiasm and optic nerve. Magnetic resonance imaging is a sensitive and specific method of detecting cavernous angiomas. Cavernous angiomas have an autosomal dominant pattern of inheritance with variable penetrance. Surgical intervention in patients with symptomatic cavernous angiomas depends on the location and size of the lesion and associated surgical risks.

Adolescent↗