Inhibition of protein phosphatase-2B (calcineurin) activity towards Alzheimer abnormally phosphorylated tau by neuroleptics

Abnormally hyperphosphorylated tau is the major protein component of neurofibrillary tangles, the characteristic lesion of Alzheimer's disease (AD). Protein phosphatases (PP) type 1 (PP-1), type 2A (PP-2A) and type 2B (PP-2B) appear to be involved in the regulation of tau phosphorylation. The incidence of neurofibrillary tangles is higher in brains of schizophrenic patients treated with neuroleptics than in those without this treatment. We have found that the commonly used neuroleptics chlorpromazine, trifluoperazine and clozapine inhibit PP-2B but not PP-1 or PP-2A activity towards [32P]phosphorylase kinase as a substrate. When AD abnormally hyperphosphorylated tau is used as a substrate, PP-2B activity is inhibited by trifluoperazine > chlorpromazine > clozapine. Using phosphorylation-dependent monoclonal antibodies, tau-1, AT8 and PHF-1, we have found that the dephosphorylation of the abnormal tau by PP-2B is inhibited at all the sites recognized by these antibodies. The IC50 of the inhibition of dephosphorylation at tau-1 site is approximately 20 microM for trifluoperazine and approximately 120 microM for chlorpromazine. These two neuroleptics inhibit tau dephosphorylation by PP-2B through antagonizing calmodulin as well as directly interacting with PP-2B. The inhibition of the dephosphorylation of abnormally hyperphosphorylated tau by neuroleptics raises an intriguing possibility that the chronic use of these drugs might contribute to neurofibrillary degeneration in schizophrenic and AD patients.

Allelic association between a Ser-9-Gly polymorphism in the dopamine D3 receptor gene and schizophrenia

We examined a Ser-9-Gly polymorphism in the dopamine D3 receptor gene for allelic association with schizophrenia in 133 patients currently treated with clozapine and 109 controls. Allele 1 (Ser-9) was significantly more frequent in the patients (69%) than in the controls (56%) (P = 0.004). The 1-1 genotype was more common (43% vs 30%) and the 2-2 genotype less common (5% vs 18%) in patients than in controls. When the patient group was subdivided on the basis of clinical response to clozapine, using a 20-point improvement in the global assessment scale as cut-off, genotype 1-1 was found to be more frequent among the non-responders (53% vs 36%, P = 0.04). To place our results in the context of previous studies of this polymorphism and schizophrenia, we performed a meta-analysis of all published data including the present sample. The combined analysis shows evidence for a modest association between genotype 1-1 and schizophrenia (odds ratio 1.25, 95% confidence interval 1.05-1.49, P = 0.01). These results suggest that the Ser-9 allele, or a nearby polymorphism in linkage disequilibrium, results in a small increase in susceptibility to schizophrenia.

Analysis of clozapine response and polymorphisms of the dopamine D4 receptor gene (DRD4) in schizophrenic patients

We have examined the hypothesis that a variable number of tandem repeats in the third cytoplasmic loop of the dopamine D4 receptor influences clinical response to clozapine using a sample of 189 schizophrenic patients. Alleles of the 48-bp repeat, which range from two to ten copies in the normal human population, were analysed by the polymerase chain reaction using genomic DNA as template. Association between these alleles and response to clozapine was tested using the difference in pre- and post-treatment GAS scores as a measure of response. We found no statistically significant variation between genotypic groups and response by analysis of variance. We conclude that the variation of the number of 48-bp repeats alone does not determine response to clozapine. Larger studies are underway to determine if there is a more subtle relationship with sequence variation within the repeats or at other polymorphic sites within the gene that may provide evidence for a component of clozapine's action being at D4 receptors.

Systematic search for major genes in schizophrenia: methodological issues and results from chromosome 12

We describe a method of systematically searching for major genes in disorders of unknown mode of inheritance, using linkage analysis. Our method is designed to minimize the probability of missing linkage due to inadequate exploration of data. We illustrate this method with the results of a search for a locus for schizophrenia on chromosome 12 using 22 highly polymorphic markers in 23 high density pedigrees. The markers span approximately 85-90% of the chromosome and are on average 9.35 cM apart. We have analysed the data using the most plausible current genetic models and allowing for the presence of genetic heterogeneity. None of the markers was supportive of linkage and the distribution of the heterogeneity statistics was in accordance with the null hypothesis.

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.

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.

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.

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.

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.

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.

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.

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.

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.

A continuous linkage map of 22 short tandem repeat polymorphisms on human chromosome 12

A continuous linkage map consisting of 22 short tandem repeat polymorphisms has been constructed for human chromosome 12 using 23 non-CEPH pedigrees. The markers were distributed at an average distance of 9.35 cM (3.1-33.9 cM). Eighteen of the markers could be positioned uniquely with a likelihood of > 1000:1. The physical locations of some of the markers suggest that the map covers 85-95% of the chromosome. This framework map of 18 markers has a female length of 213 cM and a male length of 131 cM. Female recombination frequencies were greater than male recombination frequencies except in the distal portion of the short arm. The map provides confirmatory evidence for orders established previously on CEPH pedigrees and uniquely positions 4 additional markers (CD4, ATPSB, D12S56, PLA2).

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.

A linkage study of schizophrenia with DNA markers from the long arm of chromosome 11

We report the results of a collaborative linkage study using 12 polymorphic markers (9 loci) from the long arm of chromosome 11, and 24 families multiply affected with schizophrenia and other closely related disorders. This region is of interest because several families have been reported in which balanced translocations involving 11q apparently co-segregate with psychotic illness. In addition, the dopamine D2 receptor, porphobilinogen deaminase, and tyrosinase genes map within the region studied and may be aetiologically involved in schizophrenia. We have primarily analysed genotypic data by the LOD score method using a range of single gene models. In order to minimize error due to mis-specification of genetic parameters we have analysed data from markers at candidate gene loci by the non-parametric extended sib-pair method in addition to the LOD score method. Our results suggest that most of the region can be excluded from containing a gene of major effect in the aetiology of this disease.

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.

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.

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.

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.

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.