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S Shaikh

Publications and source records attributed to S Shaikh.

18 recordsLinked to original sources
PubMed1995

Phosphatase activity toward abnormally phosphorylated tau: decrease in Alzheimer disease brain.

Microtubule-associated protein tau is abnormally hyperphosphorylated and aggregated in affected neurons of Alzheimer disease brain. This hyperphosphorylated tau can be dephosphorylated at some of the abnormal phosphorylated sites by purified protein phosphatase-1, 2A, and 2B in vitro. In the present study, we have developed an assay to measure protein phosphatase activity toward tau-1 sites (Ser199/Ser202) using the hyperphosphorylated tau isolated from Alzheimer disease brain as substrate. Using this assay, we have identified that in normal brain, protein phosphatase-2A and 2B and, to a lesser extent, 1 are involved in the dephosphorylation of tau. The Km values of dephosphorylation of the hyperphosphorylated tau by protein phosphatase-2A and 2B are similar. The tau phosphatase activity is decreased by approximately 30% in brain of Alzheimer disease patients compared with those of age-matched controls. These findings suggest that a defect of protein phosphatase could be the cause of the abnormal hyperphosphorylation of tau in Alzheimer disease.

Aged↗
PubMed1995

Cytochrome P4502D6 genotype does not determine response to clozapine.

1. The atypical antipsychotic drug clozapine, used in the treatment of resistant schizophrenia, is metabolized partly by the hepatic cytochrome P450 enzyme CYP2D6. Two phenotypes with respect to the activity of the enzyme are recognized (extensive metabolisers (EM) and poor metabolisers (PM)), resulting from allelic variation in the gene, CYP2D6. 2. Genotype was determined in 123 schizophrenic patients currently being treated with clozapine, in order to determine if EM or PM status influences response to this drug. Patients were divided into responders and non-responders using the Global Assessment Scale, and genotyped for the A and B poor metaboliser mutations by digesting PCR products with HpaII or BstNI. 3. Fifty-nine patients were heterozygous for allele B and for allele A. Eight patients were determined as poor metabolisers since they were homozygous either for A and B. Poor metabolisers were equally distributed between responders and nonresponders and no correlation between CYP2D6 alleles and response to clozapine was found. 4. The results are consistent with recent findings showing that CYP1A2, rather than CYP2D6, is the major enzyme responsible for the metabolism of clozapine.

Alleles↗
PubMed1994

Failure to find linkage between a functional polymorphism in the dopamine D4 receptor gene and schizophrenia.

We report the results of a linkage study in 24 families multiply affected with schizophrenia using a polymorphic DNA sequence encoding the third cytoplasmic loop of the dopamine D4 receptor. Two-point LOD score analyses with a range of single gene models ranging from near dominant to near recessive revealed no evidence for linkage. In addition, we examined the data by non-parametric sib-pair analysis and found no excess sharing of alleles between affected sib-pairs. We therefore conclude that mutations within the dopamine D4 receptor gene do not have a major aetiological role in schizophrenia in our collection of pedigrees.

Alleles↗
PubMed1994

Analysis of the conserved Asp(114) residue of the dopamine D2 receptor in schizophrenic patients.

The factors that influence response to antipsychotics treatment in chlorpromazine remain difficult to delineate but are thought to include genetic factors. Site-directed mutagenesis studies have demonstrated that substitution of the conserved residues Asp(113) to an Asn or Glu greatly reduces the binding affinity of propranolol in the beta-adrenergic receptor and the substitution of an Asp(114) has similar effects in the dopamine D2 receptor. In this study we have found the Asp(114) in the dopamine D2 receptor to be unaltered in 72 unrelated schizophrenic individuals including 12 patients classified according to their response to chlorpromazine.

Aspartic Acid↗
PubMed1994

Platelet-derived growth factor-AA and -BB (PDGF-AA and -BB) enhance the synthesis of PDGF-AA in bone cell cultures.

Platelet-derived growth factor (PDGF), an agent with important mitogenic effects for bone cells, exists in three isoforms, PDGF-AA, -BB, and -AB. PDGF-AB and -BB are the prevalent circulating isoforms, whereas normal unstimulated cells of the osteoblast lineage synthesize primarily PDGF-AA. We examined the effects of PDGF-BB on PDGF-A mRNA expression and PDGF-AA polypeptide concentrations in cultures of osteoblast-enriched cells from 22-day-old fetal rat calvariae (Ob cells). In a selected number of experiments we compared the effects of PDGF-BB with those of PDGF-AA on PDGF-A mRNA levels. Steady state PDGF-A mRNA levels were determined by Northern blot analysis, and PDGF-AA concentrations were determined in acidified and fractionated culture medium by a specific RIA for PDGF-A chains. Treatment of Ob cells with PDGF-AA or -BB at 0.3-3.3 nM caused a dose-dependent increase in steady state PDGF-A mRNA, an effect that was initially observed after 2 h. Treatment with PDGF-BB at 1-3.3 nM for 24 h increased PDGF-AA polypeptide concentrations by 2- to 5-fold. The effects of PDGF on PDGF-A mRNA and polypeptide levels were prevented by the protein synthesis inhibitor cycloheximide at 3.6 microM. Phorbol 12-myristate 13-acetate at 1 microM increased PDGF-A mRNA after 2-6 h and PDGF-AA polypeptide levels after 24 h by 2-fold. However, the protein kinase-C inhibitor staurosporine at 50 nM did not modify basal PDGF-A mRNA levels and did not prevent the stimulatory effect of PDGF-AA or -BB on PDGF-A mRNA or PDGF-AA polypeptide levels. In conclusion, PDGF-BB and -AA increase skeletal PDGF-A synthesis, an effect that reveals autoinduction of PDGF in bone cells.

Alkaloids↗
PubMed1994

Functional neuroimaging and pharmacogenetic studies of clozapine's action at dopamine receptors.

The factors that influence response to neuroleptic drugs are poorly understood. These factors may include clinical variables such as length of illness before treatment, age at onset, and the presence of negative symptoms; and pharmacologic factors such as rates of drug metabolism. For example, pharmacodynamic differences in therapeutic response to haloperidol have been observed between Chinese and Caucasian patients. Response rates may also reflect clinical heterogeneity, although familiality, history of obstetric trauma, or ventricular enlargement have been not shown to be significant factors. It is also possible that genetic differences in receptors that are targets for these drugs may influence response.

Adult↗
PubMed1993

Microtubule-associated protein tau. Abnormal phosphorylation of a non-paired helical filament pool in Alzheimer disease.

The major protein subunit of the paired helical filaments (PHF) of Alzheimer disease (AD) is the microtubule-associated protein tau. Tau is a family of phosphopolypeptides that are abnormally phosphorylated in PHF. In this study, a non-PHF pool of tau abnormally phosphorylated at Ser-199/202, and tau not phosphorylated at this site (AD P-tau and AD tau, respectively) were isolated from the 27,000 x g to 200,000 x g fraction of AD brain homogenate by extraction in 8 M urea, followed by dialysis against Tris buffer. AD P-tau and AD tau were further purified and separated from each other by acid precipitation, glial fibrillary acidic protein affinity chromatography, and phosphocellulose chromatography. The resulting AD P-tau and AD tau preparations were free of cytoskeletal proteins, ubiquitin, and beta-amyloid peptide. Immunochemical and morphological analysis of AD P-tau preparations revealed that most of the protein was of non-PHF origin. The AD P-tau was about 3-4-fold (approximately 8 mol P04/mol protein, M(r) 41,318) more phosphorylated than cytosolic tau from AD and control brains. Unlike PHF, the AD P-tau lacked ubiquitin. In AD brain the levels of cytosolic tau were about half of those in control aged cases. These findings suggest that the abnormal phosphorylation of tau in AD occurs in the cytosol.

Aged↗
PubMed1993

RFLP analysis of the MHC class III region defines unique haplotypes for the non-obese diabetic, cataract Shionogi and the non-obese non-diabetic mouse strains.

The non-obese diabetic (NOD) mouse strain which spontaneously develops diabetes is a model for human Type 1 (insulin-dependent) diabetes mellitus. At least one of several genes controlling diabetes in the NOD mouse has been mapped to the MHC. Although previous experiments have implicated the MHC class II genes in the development of the disease, the existence of other MHC linked susceptibility genes has not been ruled out. In order to identify these susceptibility genes we have further characterized the MHC haplotype of the NOD mouse and two non-diabetic sister strains, the non-obese non-diabetic (NON) and cataract Shionogi (CTS). We have examined the mouse MHC class III region for the presence of homologous genes to 17 newly isolated human MHC class III region genes (G1, G2, G4, G6, G7a/valyl-tRNA synthetase, HSP70, G8, G9, G10, G12, G13, G14, G15, G16, G17 and G18). We detect unique hybridizing DNA fragments for 16 of the 17 genes in six inbred mouse strains (NOD, NON, CTS, B10, BALB/c and CBA/J) indicating that this part of the H-2 region is similar to the human MHC class III region. Using a panel of restriction enzymes we have defined RFLPs for 6 (G2, G6, HSP70, G12, G16, G18) of the 16 cross-hybridizing probes. The RFLPs demonstrate that NOD, NON and CTS mouse strains each have a distinct MHC haplotype in the MHC class III region.

Animals↗
PubMed1993

The dopamine D3 receptor gene: no association with bipolar affective disorder.

Bipolar affective disorder and schizophrenia share many clinical and genetic characteristics, and are thought by some to be different expressions of the same underlying disorder. A recent study showed an excess of homozygosity at a BalI polymorphism in the dopamine D3 receptor gene in schizophrenic patients compared with controls, from two independent centres. We have found no evidence of such an excess in a comparable sample of patients with bipolar affective disorder compared with matched controls. If these findings are confirmed then at least one genetic distinction between these two disorders will have been ascertained and doubt cast upon theories of a common genetic aetiology.

Alleles↗
PubMed1992

Analysis of the T cell receptor (TcR) regions in the NOD, NON and CTS mouse strains define new TcR V alpha haplotypes and new deletions in the TcR V beta region.

We have analyzed the T cell receptor (TcR) V alpha and TcR V beta regions in the spontaneous mouse model for insulin-dependent diabetes mellitus, the NOD mouse, and compared it to the regions in the two sister strains, the NON and CTS strains. Based on restriction fragment length polymorphism analysis the TcR V alpha region in the NOD mouse is essentially identical to that of the SJL/J strain. In contrast both the NON and CTS strains have a unique TcR V alpha haplotype. Whereas the NOD and NON strains apparently contains all the TcR V beta genes, the CTS mouse has three deletions in the V beta region. Our analysis does not give any indications for the diabetic phenotype of the NOD mouse.

Animals↗
PubMed1991

Dietary risk factors associated with acute and persistent diarrhea in children in Karachi, Pakistan.

Feeding practices may have an important impact on diarrheal diseases in developing countries. This study evaluated feeding practices in three groups of male children aged 6-36 mo: 100 with persistent diarrhea (PD), 79 with acute diarrhea (AD), and 86 in a comparison group (CG). The children came from comparably poor socioeconomic settings in Karachi, Pakistan, except that the literacy rates were higher in mothers of the CG (P = 0.0001). Although greater than 95% of all infants were breast-fed, delayed initiation of breast-feeding was more common in the diarrhea groups. Children with diarrhea were also more likely to receive supplemental milk (PD = 92%, AD = 87%) than were children in the CG (69%, P less than 0.05). Feedings were not withheld during diarrhea but changes were made in the nature of foods given. These results indicate that several feeding practices may be important risk factors for diarrhea in Pakistan.

Acute Disease↗
PubMed1991

A traditional diet as part of oral rehydration therapy in severe acute diarrhoea in young children.

Recently, the role of feeding as treatment of acute diarrhoea has received increasing attention. To assess the efficacy of early feeding in acute diarrhoea, we conducted a randomised, clinical trial of a traditional legume-based weaning diet khitchri in boys 9 to 48 months old with moderate to severe dehydration. Khitchri is composed of rice and lentils cooked with cottonseed oil. Children were randomly allocated to 2 groups: group A received only WHO ORS but no food for the first 24 hours and then khitchri and half-strength cow's milk formula freely; group B received khitchri and the half-strength formula in addition to ORS after the initial rehydration period of 4 to 6 hours. The mean period of evaluation was 3 days. 69 patients were admitted into the study, 33 in group A and 36 in group B. The initial mean purging rate for the children was greater than 200 g/kg/day. Six children did not complete the study because they developed intercurrent infections or were removed by their parents for non-medical reasons. Of the 63 patients who were evaluated, 44 (70%) were successfully treated, 21 in group A and 23 in group B. There were no significant differences in the 2 groups in mean stool output, number of stools, or weight gain, although a trend toward earlier improvement was seen in group B. These data indicate that early feeding of khitchri and WHO/ORS may be as well tolerated as WHO/ORS alone in the first 24 hours treatment of severe acute diarrhoea in young children.

Acute Disease↗
PubMed1984

The specificity of ketanserin in the inhibition of serotonin-induced steroidogenesis in the rat adrenal zona glomerulosa.

Although the biological effects of ketanserin were originally attributed to its specific interaction with serotonin type 2 (5HT2) receptors, at high doses (greater than 10(-8)M) it also appears to act as an alpha 1-antagonist in some tissues. This in vitro study examines the possibility that Ketanserin may inhibit serotonin-induced steroidogenesis by blockade of alpha 1-receptors. Rat zona glomerulosa cells prepared by collagenase digestion of adrenal capsular tissue were incubated at 37 degrees C in Krebs-Ringer bicarbonate buffer (0.2% glucose, 0.2% bovine serum albumin) for 30 min with increasing doses of serotonin (10(-9)-10(-6)M) alone or in the presence of ketanserin (10(-6)M), methysergide (a 5HT-receptor antagonist) 10(-6)M) or prazosin (an alpha 1-antagonist)(10(-6)M). Cyclic AMP, Corticosterone and aldosterone outputs were measured by radioimmunoassay. Serotonin produced correlative sigmoidal dose responses for cyclic AMP, corticosterone and aldosterone which were inhibited by ketanserin and methysergide but not by prazosin. These results suggest that ketanserin does not act by alpha 1-blockade in the adrenal zona glomerulosa but rather as a specific 5HT-receptor antagonist.

Adrenal Cortex↗
PubMed1982

Effects of taxol and nocodazole on insulin secretion from isolated rat islets of Langerhans.

Taxol, a promotor of microtubule polymerization, and nocodazole, which induces microtubule depolymerization, used at concentrations known to be specific for these effects in other cell types, were each shown to inhibit glucose-stimulated insulin secretion from isolated rat islets of Langerhans. These findings suggest that the dynamic regulation of microtubule polymerization-depolymerization in pancreatic B cells may be important for insulin secretion via the microtubule-microfilamentous system.

Alkaloids↗
PubMedDate not supplied

Differential effects of ozone on lung epithelial lining fluid volume and protein content.

Urea dilution has been used to estimate the volume of epithelial lining fluid (ELF) in the respiratory tract. However, ELF volume may be overestimated as the result of rapid net diffusion of urea from tissues into the bronchoalveolar lavage (BAL) fluid. This study established a protocol for rat BAL in a manner that minimizes this problem and then used this procedure to examine the edemagenic effects of ozone (O3) exposure on ELF volume and the concentrations of ELF protein and albumin. One passage lavage with variable dwell times up to 30 s showed no difference in recovered urea, protein, and albumin and ELF volume between 0 and 4 s, but a progressive increase of each thereafter. The calculated concentrations of protein and albumin in ELF did not vary significantly with dwell time. By increasing the number of lavage passages from one to three, the amounts of recovered urea, protein, and albumin and estimated ELF volume were increased with each passage. Again, the calculated concentrations of protein and albumin in ELF did not vary appreciably. When a single lavage passage and no added dwell time were used, it was observed that exposure of rats to 2 but not 0.5 and 1 ppm O3 increased urea, protein, and albumin in the BAL immediately after 6 h exposure. In addition, at 18 h postexposure to 1 ppm O3, ELF volume increased only 21%, but protein and albumin concentrations in ELF were 2.3- and 4.5-fold of control values, respectively. A higher O3 concentration (2 ppm) moderately increased ELF volume (+83%) and exerted even greater effects on concentrations of ELF protein (7.8-fold) and albumin (19-fold) while lower O3 dosage (0.5 ppm) had no significant effect. SDS-PAGE analysis showed that small serum proteins including albumin were greatly enriched in lung BAL fluid of 1 ppm O3-exposed rats. These results demonstrate that movement of water and protein into the airspaces after O3 exposure is not strictly coupled, and that protein recovery by BAL should cautiously be used to indicate airspace edema as a result of O3 injury.

Albumins↗