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Biomedical subjects

F Ahmad

Publications and source records attributed to F Ahmad.

At least 91 records · Page 5Linked to original sources
PubMed1995

Increased abundance of the receptor-type protein-tyrosine phosphatase LAR accounts for the elevated insulin receptor dephosphorylating activity in adipose tissue of obese human subjects.

Protein-tyrosine phosphatases (PTPases) have an essential role in the regulation of the steady-state phosphorylation of the insulin receptor and other proteins in the insulin signalling pathway. To examine whether increased PTPase activity is associated with adipose tissue insulin resistance in human obesity we measured PTPase enzyme activity towards the insulin receptor in homogenates of subcutaneous adipose tissue from a series of six lean and six nondiabetic, obese (body mass index > 30) subjects. The obese subjects had a mean 1.74-fold increase in PTPase activity (P < 0.0001) with a striking positive correlation by linear regression analysis between PTPase activity and body mass index among all of the samples (R = 0.918; P < 0.0001). The abundance of three candidate insulin receptor PTPases in adipose tissue was also estimated by immunoblot analysis. The most prominent increase was a 2.03-fold rise in the transmembrane PTPase LAR (P < 0.001). Of the three PTPase examined, only immunodepletion of LAR protein from the homogenates with neutralizing antibodies resulted in normalization of the PTPase activity towards the insulin receptor, demonstrating that the increase in LAR was responsible for the enhanced PTPase activity in the adipose tissue from obese subjects. These studies suggest that increased PTPase activity towards the insulin receptor is a pathogenetic factor in the insulin resistance of adipose tissue in human obesity and provide evidence for a potential role of the LAR PTPase in the regulation of insulin signalling in disease states.

Adipose Tissue↗
PubMed1995

Sickle cell anaemia in Saudi-Arabian children.

Forty-one Saudi Arabian children aged between six months and 13 years had a total of 68 admissions for complications of sickle cell anaemia during 1992. Review of their in-patient records and the relevant out-patient notes revealed a change in the clinical profile as compared to previous years. Hand-foot syndrome is virtually non-existent and vaso-occlusive crisis remains the commonest cause of admission. Introduction of pneumococcal vaccine and prophylactic oral penicillin has had no effect on the frequency of admissions and the admission rate per patient year. We have not seen any septicaemia/meningitis due to pneumococci. No death occurred during 1992.

Adolescent↗
PubMed1995

Urinary tract infection at a specialist hospital in Saudi Arabia.

Midstream specimens of urine from inpatients and out patients at King Fahd Specialist Hospital in Buraidah, Saudi Arabia, were collected over a period of 12 months to determine prospectively the frequencies of different causative organisms and their antimicrobial susceptibility. A total of 854 from 4157 specimens (20.54%) gave significant bacterial counts i.e., counts greater than 10(5) organisms per millilitre. Escherichia coli was the commonest organism (50.11%) followed by Klebsiella spp. (28.33%) Pseudomonas spp. (7.84%) and Proteus spp. (4.91%). Other bacterial pathogens were Enterococcus spp. (3.98%), Acinetobacter spp. (1.84%), Staphylococcus aureus (1.63%), Enterobacter spp. (0.35), Staphylococcus epidermidis (0.30%), Haemolytic streptococci B (0.47%) and Salmonella paratyphi A (0.12%). In vitro drug sensitivity tests showed norfloxacin and nalidixic acid to be very effective for most of the strains of the bacterial pathogens. A very high proportion of strains of Escherichia coli (86%) and Klebsiella spp. (94.6%) were found to be resistant to ampicillin.

Drug Resistance, Microbial↗
PubMed1995

Antibiotic sensitivity of isolates of Pseudomonas aeruginosa in Buraidah, Saudi Arabia.

A study was carried out to determine the pattern of in vitro antibiotic sensitivity of a cross section of the isolates of Pseudomonas aeruginosa recovered from diverse clinical sources during a one year period. One hundred and eighty-six isolates were investigated by disc diffusion method employing multidiscs. Majority of the isolates were sensitive to amikacin (89.7%), tobramycin (75.81%), norfloxacin (68.48%), piperacillin (68.25%), and ceftazidime (58.81%). Other antibiotics were effective for a lesser number of isolates. A few isolates were simultaneously resistant to several antibiotics, viz. gentamicin, carbenicillin, tobramycin, ceftazidime and augmentin. The significance of the findings is discussed.

Adult↗
PubMed1994

Increased thermal stability of proteins in the presence of amino acids.

This study is a systematic attempt to understand the roles of osmolytes in protecting proteins against denaturing stress. Thermal denaturation of cytochrome c has been studied in the presence of various concentrations of all L-amino acids that are more hydrophobic than glycine and have a solubility of 0.1 M or higher in water at 25 degrees C. The basic observations are as follows. (1) Arginine and histidine destabilize the native protein; both Tm (the midpoint of thermal transition) and delta GDH2O (25 degrees C) (the Gibbs energy of stabilization) decrease with increasing amino acid concentration. (2) Isoleucine, leucine and phenylalanine have no effect on Tm and deltaGDH2O (25 degrees C). (3) Valine and less hydrophobic amino acids stabilize the protein in terms of Tm but deltaGDH2O (25 degrees C) is unchanged. This observation was confirmed by the study of isothermal denaturation of cytochrome c by guanidinium chloride which suggested that delta GDH2O is independent of osmolyte concentration, but Cm (the midpoint of transition) is increased in their presence. (4) In the case of stabilizers, change in Tm/mol of amino acid decreases with increasing hydrophobicity of these osmolytes.

Amino Acids↗
PubMed1994

Physico-chemical characterization of products of unfolding of cytochrome c by calcium chloride.

Cytochrome c (cyt c) denaturation by calcium chloride (CaCl2) and guanidine hydrochloride (GdnHCl) denaturation in presence of low fixed concentrations of CaCl2 has been carried out by UV/Vis spectrophotometry at pH 7.0 and 25 degrees C. The unfolding process was followed by measuring changes in difference molar extinction coefficient around 400 nm and delta epsilon 290. The products of denaturation were further characterized by intrinsic viscosity ([eta]) measurements. It has been observed that the reversible unfolding of cyt c by CaCl2 occurs in two distinct stages or involves three species (or states) namely N<-->X<-->D. Characterization of the native state, N intermediate state, X and the end product, D suggests that (i) During N<-->X only heme is exposed and no secondary structure unfolding occurs so that X state remains as compact as the native state. (ii) Stage X<-->D shows the melting of secondary structure. (iii) The end product corresponds to a random coil. and (iv) Thermodynamic characterization of the end product shows that heme plays an important role in the stability of the protein and removal of heme will lead to the unfolding of cyt c. Mixed denaturation shows a highly cooperative reversible transition between the native and denatured conformation. Analysis of the mixed results shows that (1) Gdn+ does not have any binding site (s) on the native cyt c, (2) there is one binding site for Ca2+ which stabilizes the protein, and (3) the binding constant, ks, is 5 M-1 for Ca2+.

Calcium Chloride↗
PubMed1994

Molecular cloning and expression of a unique receptor-like protein-tyrosine-phosphatase in the leucocyte-common-antigen-related phosphate family.

Protein-tyrosine-phosphatases (PTPases) have been implicated in the regulation of certain tyrosine kinase growth factor receptors in that they dephosphorylate the activated (autophosphorylated) form of the receptors. In order to identify PTPases that potentially act on receptor targets in liver, we used the human leucocyte common antigen-related PTPase (LAR) cDNA [Streuli, Krueger, Hall, Schlossman and Saito (1988) J. Exp. Med. 168, 1523-1530] and isolated two closely related transmembrane PTPase homologues from a rat hepatic cDNA library. Both PTPases had large extracellular domains that contained three immunoglobulin-like repeats and eight type-III fibronectin repeats. Both enzymes had tandem homologous PTPase domains following a single hydrophobic transmembrane domain. One sequence encoded the rat homologue of LAR. The second PTPase, designated LAR-PTP2, had 79 and 90% identity with rat LAR in the respective cytoplasmic PTPase domains, with only 57% sequence similarity in the extracellular domain. The catalytic domains of LAR and LAR-PTP2 prepared by bacterial expression were active in dephosphorylating a variety of phosphotyrosyl substrates but did not hydrolyse phosphoserine or phosphothreonine residues of labelled casein. Both enzymes exhibited rapid turnover numbers of 4-7 s-1 for myelin basic protein and 78-150 s-1 for derivatized lysozyme. LAR and LAR-PTP2 displayed similar PTPase activity towards the simultaneous dephosphorylation of receptors of intact insulin and epidermal growth factor from liver membranes. These data indicate that there is a family of LAR-related PTPases that may regulate the phosphorylation state of receptor tyrosine kinases in liver and other tissues.

Amino Acid Sequence↗
PubMed1994

Preliminary screening of methanolic extracts of Celastrus paniculatus and Tecomella undulata for analgesic and anti-inflammatory activities.

Flowers of Celastrus paniculatus and whole plant of Tecomella undulata were extracted individually in absolute methanol. Using the hot water tail immersion test in mice and carrageenan induced pedal edema in rats, both extracts were tested for their oral analgesic and anti-inflammatory potentials. Results showed that C. paniculatus had both analgesic and anti-inflammatory activities, while T. undulata had only analgesic potential when compared with aspirin.

Analgesics↗
PubMed1994

A new method for testing the functional dependence of unfolding free energy changes on denaturant concentration.

Denaturations of ribonuclease A, lysozyme, and cytochrome c by guanidine hydrochloride (GdnHCl), urea, and GdnHCl-urea mixture were studied at constant temperature and pH to assess the functional dependence of denaturational free energy change (delta GD) on denaturant concentration over an extended GdnHCl concentration range. Conventional analysis of GdnHCl-induced transition curve exhibits a linear plot of delta GD versus [GdnHCl] in the transition zone. To extend delta GD measurements beyond this narrow concentration range, GdnHCl-induced unfolding was measured in the presence of different concentrations of urea. delta GD values from these measurements were corrected for the effect of urea on the free energy change using the appropriate relation. The corrected delta GD data were mapped onto the delta GD versus [GdnHCl] plot. For each protein, the dependence of free energy change on denaturation was found to be linear over the full GdnHCl concentration.

Animals↗
PubMed1994

Vanadate augments insulin-stimulated insulin receptor kinase activity and prolongs insulin action in rat adipocytes. Evidence for transduction of amplitude of signaling into duration of response.

Vanadate, a protein tyrosine phosphatase inhibitor, preserves insulin-stimulated lipogenesis after removal of insulin. To investigate the mechanism of this action of vanadate, lipogenesis was studied in isolated rat adipocytes exposed to vanadate for 60 min followed by insulin for 15 min at 37 degrees C. Vanadate (10-50 microM) prolonged insulin-stimulated lipogenesis. The half-time (t1/2) of the decay in insulin (0.34 nM)-stimulated lipogenesis after removal of insulin by washing in pH 7.0 followed by pH 7.6 buffer was 21 min in the absence and 59 min in the presence of vanadate. During these conditions, vanadate did not alter insulin binding nor the removal of insulin by the series of washes. In contrast to lipogenesis, the t1/2 of the decay in insulin receptor tyrosine kinase (IRK) activity, assayed with the artificial substrate Poly[Glu:Tyr] (4:1), was not significantly prolonged by vanadate (6 vs. 6.8 min). However, insulin-stimulated IRK activity was markedly augmented by vanadate to 319 +/- 19% of insulin alone, associated with a similar augmentation of phosphotyrosine incorporation into the insulin receptor beta-subunit determined by Western blotting with antiphosphotyrosine antibodies. To determine the relationship between prolongation of lipogenesis and the increase in IRK, adipocytes were exposed to 17.2 nM insulin to activate the IRK to the same extent as insulin (0.34 nM) plus vanadate (maximum activation). During these two conditions, the decay of lipogenesis was similar and after stimulation with 17.2 nM insulin was not prolonged by vanadate. We conclude that vanadate prolongs insulin action at insulin concentrations that do not maximally activate the IRK by augmenting IRK activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipocytes↗
PubMed1994

Biotin holocarboxylase synthetase: purification from rat liver cytosol and some properties.

The purification of biotin holocarboxylase synthetase (EC 6.3.4.10) from rat liver cytosol to a much higher degree of purity than previously reported, is described. The specific enzymatic activity of the final preparation is increased about 7,000 fold over the starting material. The purified preparation elutes from a gel-filtration column in a volume consistent with a molecular size of 100 kDa and examination by SDS-PAGE reveals one major band of M(r) 50 kDa. This suggests that the native synthetase may exist as a dimer of similar weight subunits.

Animals↗
PubMed1993

Interactions of glutathione S-transferase-pi with ethacrynic acid and its glutathione conjugate.

Ethacrynic acid, a diuretic drug known to be an inhibitor of glutathione S-transferases (GSTs), has been shown to enhance the cytotoxicity of the alkylating agent class of chemotherapeutic drugs in cultured cancer cells resistant to alkylating agents. This action of ethacrynic acid is presumably mediated by inhibition of GSTs which are implicated in detoxification of alkylating agents. In addition to being an inhibitor of GSTs, ethacrynic acid also interacts with GSTs as a substrate for conjugation with GSH to yield an ethacrynic acid-GSH conjugate. This conjugate is formed both enzymatically and non-enzymatically and itself is a GST inhibitor. Since ethacrynic acid-GSH conjugate is itself likely to be able to mediate reversal of alkylating agents through GST inhibition, we have synthesized and purified the ethacrynic acid-GSH conjugate, studied the kinetics of inhibition of human lung pi-class GST by ethacrynic acid and the conjugate, and compared the kinetics of the enzymatic and non-enzymatic formation of the conjugate using an HPLC method. Results of our studies showed that the ethacrynic acid-GSH conjugate was a more potent inhibitor of human lung GST-pi than ethacrynic acid (Ki = 1.5 vs. 11.5 microM, respectively) and that their mechanisms for GST inhibition were distinct (competitive and non-competitive, respectively). Comparison of enzymatic and non-enzymatic rates of conjugate formation in vitro indicated that GST-pi catalyzed a rapid conjugation of ethacrynic acid with GSH at a concentration of ethacrynic acid an order of magnitude above that required to nearly completely inhibit GST catalyzed conjugation of 1-chloro-2,4-dinitrobenzene. However, because of the rapid non-enzymatic reaction, and the inhibition of GST-pi with the accumulation of the conjugate in the reaction mixture, the overall quantity of the conjugate formed after 150 min was nearly identical in the presence or absence of GST-pi. Results of these studies suggest that inhibition of GSTs by ethacrynic acid-GSH conjugate may be the main mechanism through which ethacrynic acid reverses alkylating agent resistance.

Alkylating Agents↗
PubMed1993

Adipose pyruvate carboxylase: amino acid sequence and domain structure deduced from cDNA sequencing.

The complete amino acid sequence of 3T3-L1 adipocyte pyruvate carboxylase (PC) [pyruvate:carbon-dioxide ligase (ADP-forming), EC 6.4.1.1] has been deduced from sequencing overlapping cDNA clones obtained from an adipocyte cDNA library constructed in the lambda Zap vector. The encoding mRNA for PC promoter contains 4067 nt, including a 3534-nt coding sequence and noncoding regions of 100 and 433 nt at the 5' and 3' ends, respectively. The biotinylated lysine of the encoded PC promoter (1178 amino acids with a calculated M(r) of apocarboxylase = 129,784) is located 35 residues from the COOH-terminal end and, as in most other biotin enzymes, is in the consensus sequence AMKM. The adipocyte PC is closely similar (53% identity) to the yeast enzyme and contains different segments that are homologous with regions from the biotin carboxylase component of Escherichia coli acetyl-CoA carboxylase, the keto acid-binding subunits of Propionibacterium shermanii oxaloacetate transcarboxylase and Klebsiella pneumoniae oxaloacetate decarboxylase, and to the biotin carboxyl-carrier protein of the bacterial biotin enzymes. In addition to the putative mitochondrial targeting signal, functional domains are readily identifiable in the sequence and are in the following order: biotin carboxylase-carboxyltransferase-biotin carboxyl-carrier protein, as proposed for yeast PC.

3T3 Cells↗
PubMed1993

Evidence for locus heterogeneity in autosomal dominant torsion dystonia.

Idiopathic torsion dystonia (ITD) is most commonly an autosomal dominant disorder with reduced penetrance and variable expression. A locus on the distal long arm of chromosome 9 has been identified in one large non-Jewish and several Jewish families in the United States. Linkage analysis in a large Australian kindred with ITD, also containing two patients with Wilson's disease, excludes a locus for ITD in chromosome 9q34 or the region of chromosome 13 containing the Wilson disease gene. This study provides evidence for locus heterogeneity in autosomal dominant ITD and also gives additional information on gene order in chromosome 9q.

Adolescent↗
PubMed1993

Cerebral vein thrombosis due to hereditary antithrombin III deficiency.

Cerebral vein thrombosis, also called superior sagittal sinus thrombosis, is a well recognized clinical and radiologic entity associated with a variety of medical disorders. We report a patient with fatal cerebral vein thrombosis following myelography, in whom the cause was familial antithrombin III (AT3) deficiency. Unsuspected AT3 deficiency should be considered in cases of unexplained cerebral venous thromboses.

Adult↗
PubMed1993

Linkage analysis in British and French families with idiopathic torsion dystonia.

Idiopathic torsion dystonia is most commonly caused by an autosomal dominant gene or genes with reduced penetrance. An idiopathic torsion dystonia locus has been mapped to chromosome 9q34 in one large non-Jewish and several Jewish kindreds in the USA. Linkage analysis was performed in 27 (26 British, one French) small families with idiopathic torsion dystonia, three of which were Ashkenazi Jewish, using the highly polymorphic loci argininosuccinate synthetase (ASS) and Abelson oncogene (ABL) which map to 9q34. The cumulative lod score for the more informative ASS locus at a recombination fraction of 0.001 was -6.72. A large component of this score was derived from three non-Jewish families, indistinguishable clinically from the others, in which individual lod scores excluded a disease locus tightly linked to ASS. Analysis of all the data using HOMOG showed significant heterogeneity, but evidence for linkage of an idiopathic torsion dystonia gene to 9q34 in a subset of families. The allelic association observed between ASS/ABL and idiopathic torsion dystonia in Ashkenazi families in the USA was also present in British Jewish kindreds. These data suggest genetic heterogeneity in idiopathic torsion dystonia but indicate the existence of a locus for idiopathic torsion dystonia at 9q34 in both Jewish and non-Jewish kindreds in the UK.

Argininosuccinate Synthase↗