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Biomedical subjects

A Siddiqui

Publications and source records attributed to A Siddiqui.

At least 19 recordsLinked to original sources
PubMed2000

Human La antigen is required for the hepatitis C virus internal ribosome entry site-mediated translation.

The 5'-noncoding region (5'-NCR) of the hepatitis C virus (HCV) RNA genome serves as an internal ribosome entry site (IRES) and mediates translation initiation in a cap-independent manner. Previously, we reported the interaction between La antigen and the HCV IRES, which appeared to occur in the context of initiator AUG. It was further shown that HCV IRES-mediated translation was stimulated in the presence of human La antigen. In this study, we have defined the cis- and trans-acting elements responsible for La-5'-NCR interactions and established the dependence of the HCV IRES efficiency on cellular La antigen. During the La-IRES interaction, initiator AUG but not the neighboring codons was found to be the direct target of La binding. The C terminus effector domain-dependent modulation of La binding to the HCV IRES is demonstrated by deletion and substitution mutagenesis of the protein. An RNA systematic evolution of ligands by exponential enrichment (SELEX), generated against La protein that selectively binds La in HeLa lysates and competes for the protein binding to the 5'-NCR, was used to demonstrate the requirement of La for the HCV IRES function in the context of mono- and dicistronic mRNAs. Sequestration of La antigen by the RNA SELEX in HeLa translation lysates blocked the HCV and poliovirus IRES-mediated translation in vitro. The functional requirement of La protein for the HCV IRES activity was further established in a liver-derived cell line and in an add-back experiment in which the inhibited IRES was rescued by recombinant human La. These results strongly argue for the novel role of La protein during selection of the initiator AUG and its participation during internal initiation of translation of the HCV RNA genome.

5' Untranslated Regions↗
PubMed2000

Enhancing the aqueous solubility of d4T-based phosphoramidate prodrugs.

A range of polyether para-substituted phosphoramidates were synthesised and found to have substantially elevated aqueous solubilities compared to the underivatised parent prodrug. A 30-fold increase in aqueous solubility could be achieved without a substantial decrease of in vitro activity against HIV-1. Replacement of the aryl (i.e. phenolic) moiety by tyrosine led to a substantial enhancement in aqueous solubility but also to a decrease in antiviral potency. A previously unobserved trend was identified, relating increased aryl substituent steric bulk to decreased antiviral activity.

Amides↗
PubMed2000

Incidence of neurapraxia in digital nerve injuries.

Hand surgeons presented with a hand or finger laceration and an abnormal static two-point discrimination (> or =10 mm) must determine which patients require surgical exploration. There appears to be a paucity of data in the literature defining the incidence and nature of neurapraxia in this setting. A study was conducted in a busy urban practice to better understand this problem. To determine the incidence of intact nerves (i.e., neurapraxia) in digital nerve injury patients, the authors reviewed experience with 152 patients who presented with isolated digital nerve injuries over a 33-month period. Preoperative return of sensation and negative exploration cases were combined and referred to as the trauma-induced neurapraxia (TIN) group. There were 18 non-repair cases among the 152 isolated digital nerve injuries, giving a 12 percent incidence of TIN. Sensory recovery among the TIN patients ranged from 12 days to 6 months. In this study, the authors defined a group of patients who did not require surgical repair for isolated digital nerve injury as TIN cases. The TIN group represented 12 percent of the digital nerve trauma patients and required long follow-up for sensory recovery. This information is an important part of patient education and informed consent.

Fingers↗
PubMed2000

Allergic reaction to spinal cord stimulator.

OBJECTIVE: The objective was to report on the possibility of allergic reaction to the components of a spinal cord stimulator. DESIGN: We describe a severe allergic reaction after the insertion of a spinal cord stimulator in a patient with complex regional pain syndrome type 1. SETTING: The patient was being followed in an office-based pain management practice. PATIENT: The patient is a 41-year-old woman with complex regional pain syndrome type 1, posttrauma. INTERVENTION: Insertion of a cervical and lumbar spinal cord stimulator. OUTCOME MEASURES: The outcome measures were a numerical scale of pain intensity and the ability to perform the activities of daily living. RESULTS: Adequate pain control complicated by allergic reaction. CONCLUSIONS: There exists a possibility that a patient may experience an allergic reaction to spinal cord stimulator components. Recognition of such contact sensitivity is important for physicians implanting such devices. Patients may be misdiagnosed as having infections, which can delay appropriate management; definitive diagnosis can be confirmed with a patch test. Treatment consists of removal of such devices.

Adult↗
PubMed2000

Characterization of Mycobacterium tuberculosis isolates from patients in Houston, Texas, by spoligotyping.

Mycobacterium tuberculosis isolates (n = 1,429) from 1,283 patients collected as part of an ongoing population-based tuberculosis epidemiology study in Houston, Texas, were analyzed by spoligotyping and IS6110 profiling. The isolates were also assigned to one of three major genetic groups on the basis of nucleotide polymorphisms located at codons 463 and 95 in the genes (katG and gyrA) encoding catalase-peroxidase and the A subunit of DNA gyrase, respectively. A total of 225 spoligotypes were identified in the 1,429 isolates. There were 54 spoligotypes identified among 713 isolates (n = 623 patients) assigned to 73 IS6110 clusters. In addition, among 716 isolates (n = 660 patients) with unique IS6110 profiles, 200 spoligotypes were identified. No changes were observed either in the IS6110 profile or in the spoligotype for the 281 isolates collected sequentially from 133 patients. Five instances in which isolates with slightly different spoligotypes had the same IS6110 profile were identified, suggesting that in rare cases isolates with different spoligotypes can be clonally related. Spoligotypes correlated extremely well with major genetic group designations. Only three very similar spoligotypes were shared by isolates from genetic groups 2 and 3, and none was shared by group 1 and group 2 organisms or by group 1 and group 3 organisms. All organisms belonging to genetic groups 2 and 3 failed to hybridize with spacer probes 33 to 36. Taken together, the results support the existence of three distinct genetic groups of M. tuberculosis organisms and provide new information about the relationship between IS6110 profiles, spoligotypes, and major genetic groups of M. tuberculosis.

Bacterial Proteins↗
PubMed2000

Hepatitis B virus X protein colocalizes to mitochondria with a human voltage-dependent anion channel, HVDAC3, and alters its transmembrane potential.

Understanding the mechanism(s) of action of the hepatitis B virus (HBV)-encoded protein HBx is fundamental to elucidating the underlying mechanisms of chronic liver disease and hepatocellular carcinoma caused by HBV infection. In our continued attempts to identify cellular targets of HBx, we have previously reported the identification of a novel cellular protein with the aid of a yeast two-hybrid assay. This cellular gene was identified as a third member of the family of human genes that encode the voltage-dependent anion channel (HVDAC3). In the present study, physical interaction between HBx and HVDAC3 was established by standard in vitro and in vivo methods. Confocal laser microscopy of transfected cells with respective expression vectors colocalized HVDAC3 and HBx to mitochondria. This novel, heretofore unreported subcellular distribution of HBx in mitochondria implies a functional role of HBx in functions associated with mitochondria. Using a stable cationic fluorophore dye, CMXRos, we show that HBx expression in cultured human hepatoma cells leads to alteration of mitochondrial transmembrane potential. Such functional roles of HBx in affecting mitochondrial physiology have implications for HBV-induced liver injury and the development of hepatocellular carcinoma.

Animals↗
PubMed1999

Expression of hepatitis B virus polymerase in Ty1-his3AI retroelement of Saccharomyces cerevisiae.

Hepatitis B virus (HBV), although a DNA virus, replicates using reverse transcriptase encoded by the HBV polymerase (pol) gene. The biochemical dissection of HBV pol has been hampered by failure to liberate enzymatically active protein from nucleocapsids. Here, we have employed a yeast-based genetic approach to express the HBV reverse transcriptase. In this strategy, the reverse transcriptase of yeast retrotransposon Ty1 element is replaced with the HBV pol gene to produce the hybrid Ty1/HBV element. Additionally, the indicator gene his3AI is combined in an antisense orientation to the transcripts of the hybrid Ty1/HBVRT element. The splicing of his3AI, cDNA synthesis of the Ty1/HBVRT RNA and subsequent integration relies on the reverse transcriptase activity. The production of histidine prototrophs results from the successful reverse transcription of Ty1/HBVRThis3AI transcripts followed by either homologous recombination or integrase-mediated insertion and subsequent expression of HIS3 gene. Using this approach we successfully detected the reverse transcriptase activity of HBV in yeast strains defective in endogenous Ty1 expression. Consistent with the unique priming activity associated with HBV pol, the minus strand DNA synthesis was protein-primed. Deletion of HBV reverse transcriptase (RT) or RNase H domains resulted in a dramatic drop in histidine prototrophs. The addition of HBV encoded HBx protein in virus-like particles during in vitro RT reaction stimulated the RT reaction by severalfold. Furthermore, in the presence of 3TC, a known inhibitor of HBV reverse transcriptase, yeast His(+) growth of His protrophs was not observed. Thus, this approach, which is based on genetic selection in yeast, is safe, economic, and a reliable strategy with a potential for large scale screening of cofactors and inhibitors of HBV polymerase functions.

Genetic Markers↗
PubMed1999

Biochemical and functional properties of a palindromic sequence motif within the hepatitis B virus enhancer 1.

The hepatitis B virus (HBV) enhancer 1 is a transcriptional element that contributes to the liver-specific regulation of HBV gene expression. We previously identified a novel protein binding site within the enhancer that contains an 8-bp palindromic sequence motif. This motif partially overlaps the binding sites for nuclear factor 1 and hepatocyte nuclear factor 3beta (HNF3beta). Moreover, we demonstrated that this novel site is recognized by a protein or proteins, tentatively designated as palindrome-binding factor (PBF), that cooperatively interact with HNF3beta. In the present work, we have further examined the biochemical and functional attributes of PBF. Protein-DNA interaction studies indicate that three thymidine residues located at the 3'-end of the palindromic sequence motif are important for maximal PBF-binding activity. When protein-DNA complexes were photocrosslinked by exposure to ultraviolet (UV) light, a prominent polypeptide with an apparent molecular mass of 50 kDa was found to associate with the PBF-binding site. Furthermore, transient transfection studies support the hypothesis that PBF contributes to enhancer 1 activity by a combinatorial mechanism that involves at least one other cis-acting sequence motif, the HNF3beta-binding site.

Enhancer Elements, Genetic↗
PubMed1999

Co-activation of Gi and Gq proteins exerts synergistic effect on human platelet aggregation through activation of phospholipase C and Ca2+ signalling pathways.

Our previous studies have shown that subthreshold concentrations of two platelet agonists exert synergistic effects on platelet aggregation. Here we studied the mechanism of synergistic interaction of 5-hydroxytryptamine (5-HT) and epinephrine mediated platelet aggregation. We show that 5-HT had no or little effect on aggregation but it did potentiate the aggregation response of epinephrine. The synergistic interaction of 5-HT (1-5 microM) and epinephrine (0.5-2 microM) was inhibited by alpha2-adrenoceptor blocker (yohimbine; IC50= 0.4 microM), calcium channel blockers (verapamil and diltiazem with IC50 of 10 and 48 mM, respectively), PLC inhibitor (U73122; IC50=6 microM) and nitric oxide (NO) donor, SNAP (IC50=1.6 microM)). The data suggest that synergistic effects of platelet agonists are receptor-mediated and occur through multiple signalling pathways including the activation PLC/Ca2+ signalling cascades.

Blotting, Western↗
PubMed1999

Vascular endothelial growth factor is more important than basic fibroblastic growth factor during ischemic wound healing.

OBJECTIVES: To test the influence of vascular endothelial growth factor (VEGF) on normal and ischemic wounds in a noncontractive dermal ulcer standardized model in the rabbit ear and to assay the levels of both VEGF and basic fibroblastic growth factor messenger RNA levels in normal and ischemic wounds at different intervals during the healing process. DESIGN AND INTERVENTIONS: Dermal ulcers were created in the normal and ischemic ears of 20 anesthetized young female New Zealand white rabbits. Either VEGF 121, VEGF 165 (30 microg per wound), or buffered saline solution alone was applied to each wound and covered. Wounds were harvested at day 7 or 10 and evaluated histologically. Twenty-four similar rabbits were wounded in the same manner and their untreated wounds were harvested at 1, 3, 7, and 10 days after wounding. The wounds were analyzed with reverse transcriptase polymerase chain reaction. MAIN OUTCOME MEASURES: Histologic specimens were measured for amount of new epithelium and granulation tissue. Reverse transcriptase polymerase chain reaction was used to determine basic fibroblastic growth factor and VEGF messenger RNA expression. RESULTS: Both isoforms of VEGF improved granulation tissue formation in both normal and ischemic wounds with a magnitude similar to other vulnerary agents tested in the past. Vascular endothelial growth factor application had no effect on new epithelium formation. In contrast to basic fibroblastic growth factor, VEGF messenger RNA levels were induced 4 fold by ischemia alone and 6 fold by wounding in both ischemic and normal wounds. CONCLUSION: Vascular endothelial growth factor seems to be more important than basic fibroblastic growth factor during ischemic wound healing. Treatment of ischemic wounds with VEGF improves the deficit in wound healing produced by ischemia.

Animals↗
PubMed1999

The mitochondrial DNA G13513A transition in ND5 is associated with a LHON/MELAS overlap syndrome and may be a frequent cause of MELAS.

We report on 4 male patients with clinical, radiological, and muscle biopsy findings typical of the mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) phenotype. Skeletal muscle mitochondrial DNA (mtDNA) analysis showed that all patients harbored a heteroplasmic G13513A mutation in the ND5 subunit gene. One of these cases (Patient 1) presented with symptoms characteristic of Leber's hereditary optic neuropathy (LHON) 2 years before the first stroke-like episode. Quantitative analysis in several postmortem tissue sections showed that the relative proportions of mutant mtDNA were generally lower than those reported with other pathogenic mtDNA mutations. Single-fiber polymerase chain reaction studies demonstrated significantly higher amounts of mutant mtDNA in ragged red fibers (RRFs) compared with non-RRFs. This study indicates that the G13513A transition is likely to be pathogenic, that it can cause an LHON/MELAS overlap syndrome, and that it may be a more frequent cause of MELAS than previously recognized.

Adult↗
PubMed1999

Characterization of the bile acid profile in developing male and female hamsters in response to dietary cholesterol challenge.

The Syrian golden hamster is a frequently used model to study cholesterol and bile acid metabolism as well as cholesterol-induced cholelithiasis. However, diet-induced gallstones seem limited to young male hamsters of certain strains that develop depressed cholate/chenodeoxycholate bile acid ratios. To further elucidate gender and age specific aspects of cholesterol and bile acid metabolism, i.e. a possible age-related bile acid/gallstone relationship, plasma and biliary lipids and bile acid composition were analyzed in male and female hamsters under various physiological conditions of age and diet, the latter formulated with and without dietary cholesterol. During normal development (no cholesterol challenge) the percentage of cholic acid decreased while chenodeoxycholate increased, the shift being more pronounced in males. Furthermore, female hamsters had higher total plasma cholesterol than in males, while hepatic and biliary lipids did not differ. When challenged with excessive dietary cholesterol, female hamsters again developed significantly higher total plasma and hepatic cholesterol concentrations. Biliary lipids and cholesterol gallstone incidence revealed a significant gender effect with male hamsters developing a higher lithogenic index and more gallstones (cholesterol and pigment stones) than females. Female hamsters revealed a lower percentage of chenodeoxycholate and a higher percentage of cholate resulting in a more protective, higher cholate/cheno ratio (1.5 +/- 1.0) than in males (1.0 +/- 0.2). In summary, the bile acid pattern in developing and cholesterol-fed hamsters renders females less susceptible to gallstones, in part because they maintain more favorable biliary lipid and bile acid profiles, characterized by lower molar percentages of biliary cholesterol and chenodeoxycholate.

Animals↗
PubMed1999

Monocular and binocular depth discrimination thresholds.

BACKGROUND: Measurement of stereoacuity at varying distances, by real or simulated depth stereoacuity tests, is helpful in the evaluation of patients with binocular imbalance or strabismus. Although the cue of binocular disparity underpins stereoacuity tests, there may be variable amounts of other binocular and monocular cues inherent in a stereoacuity test. In such circumstances, a combined monocular and binocular threshold of depth discrimination may be measured--stereoacuity conventionally referring to the situation where binocular disparity giving rise to retinal disparity is the only cue present. A child-friendly variable distance stereoacuity test (VDS) was developed, with a method for determining the binocular depth threshold from the combined monocular and binocular threshold of depth of discrimination (CT). METHODS: Subjects with normal binocular function, reduced binocular function, and apparently absent binocularity were included. To measure the threshold of depth discrimination, subjects were required by means of a hand control to align two electronically controlled spheres at viewing distances of 1, 3, and 6m. Stereoacuity was also measured using the TNO, Frisby, and Titmus stereoacuity tests. BTs were calculated according to the function BT= arctan (1/tan alphaC - 1/tan alphaM)(-1), where alphaC and alphaM are the angles subtended at the nodal points by objects situated at the monocular threshold (alphaM) and the combined monocular-binocular threshold (alphaC) of discrimination. RESULTS: In subjects with good binocularity, BTs were similar to their combined thresholds, whereas subjects with reduced and apparently absent binocularity had binocular thresholds 4 and 10 times higher than their combined thresholds (CT). The VDS binocular thresholds showed significantly higher correlation and agreement with the TNO test and the binocular thresholds of the Frisby and Titmus tests, than the corresponding combined thresholds (p = 0.0019). CONCLUSION: The VDS was found to be an easy to use real depth (distance) stereoacuity test. The method described for calculating the BT provides one simple nonlinear solution for determining the respective contributions of binocular and monocular (MT) depth discrimination to the combined depth threshold.

Adolescent↗
PubMed1999

Physiology teaching in the developing world: models for quality learning.

An important initiative to develop higher education and physiology teaching was launched when recommendations were deliberated at the concluding session of a four-day international workshop, Physiology Teaching in the Developing World: Models for Quality Learning, held April 5-8, 1999, at the Aga Khan University, Karachi, Pakistan. The event was organized under the auspices of the International Union of Physiological Sciences (IUPS), Pakistan Physiological Society, and Aga Khan University. Among other major sponsors, the Islamic Development Bank, Islamic Educational Science and Cultural Organization. Third World Academy of Sciences, and Pakistan Science Foundation were prominent.

Developing Countries↗
PubMed1999

Punch technique for preservation of interdental papillae at nonsubmerged implant placement.

Surgical flap procedures currently used for the placement of endosseous implants often can result in damage to the interdental papilla with subsequent poor esthetics. A simple technique is presented whereby the implants are placed by using a tissue punch and without raising a full thickness flap. At no time is the subperiosteal soft tissue flap raised, and the integrity of the interdental papilla is never disrupted. There is no discontinuation of the alveolar blood supply of the surrounding osseous tissue. In the authors' experience, there has been a significant reduction in postoperative discomfort. It is proposed that this technique warrants further evaluation, especially to compare the rate of bone resorption, because it is hypothesized that because of lack of discontinuation of the blood supply, there might be reduced bone resorption compared with conventional flap procedures.

Adult↗
PubMed1998

Lactate cannot substitute for alanine in d4T-based anti-HIV nucleotide prodrugs--despite efficient esterase-mediated hydrolysis.

As part of our on-going effort to deliver masked phosphates of antiviral nucleosides inside living cells we have previously discovered that amino acid-derived phosphoramidates are particularly effective. Here we report that lactate analogues, with a simple change of bridging nitrogen for oxygen, are virtually inactive as antiviral agents and apparently do not achieve intracellular nucleoside phosphate delivery.

Alanine↗
PubMed1998

The inter-relationship between gonadal steroids and POMC peptides, beta-endorphin and alpha-MSH, in the control of sexual behavior in the female rat.

Estradiol benzoate (10 microg EB) given to ovariectomized-adrenalectomized rats induced sexual receptivity in half the animals and increased alpha-MSH in the preoptic area, ventromedial nucleus (VMN) and arcuate nucleus (ARC), in all the animals, although levels were significantly higher in the VMN and ARC of the receptive (R) subgroup. EB also raised levels of beta-endorphin in the VMN and ARC in the R rats only. POMC expression was not altered. EB did not affect alphaMSH in extra-hypothalamic areas, but addition of progesterone, raised levels in the septum, amygdala, hippocampus and caudate putamen. Only in the VMN, ARC and septum were the steroid-induced increases correlated with onset of sexual behavior.

Animals↗