Antipsychotic drugs activate SREBP-regulated expression of lipid biosynthetic genes in cultured human glioma cells: a novel mechanism of action?

Several studies have reported on structural abnormalities, decreased myelination and oligodendrocyte dysfunction in post-mortem brains from schizophrenic patients. Glia-derived cholesterol is essential for both myelination and synaptogenesis in the CNS. Lipogenesis and myelin synthesis are thus interesting etiological candidate targets in schizophrenia. Using a microarray approach, we here demonstrate that the antipsychotic drugs clozapine and haloperidol upregulate several genes involved in cholesterol and fatty acid biosynthesis in cultured human glioma cells, including HMGCR (3-hydroxy-3-methylglutaryl-coenzyme A reductase), HMGCS1 (3-hydroxy-3-methylglutaryl-coenzyme A synthase-1), FASN (fatty acid synthase) and SCD (stearoyl-CoA desaturase). The changes in gene expression were followed by enhanced HMGCR-enzyme activity and elevated cellular levels of cholesterol and triglycerides. The upregulated genes are all known to be controlled by the sterol regulatory element-binding protein (SREBP) transcription factors. We show that clozapine and haloperidol both activate the SREBP system. The antipsychotic-induced SREBP-mediated increase in glial cell lipogenesis could represent a novel mechanism of action, and may also be relevant for the metabolic side effects of antipsychotics.

The phospholipase C-gamma1 gene (PLCG1) and lithium-responsive bipolar disorder: re-examination of an intronic dinucleotide repeat polymorphism.

Twin, family and adoption studies have indicated that genetic susceptibility plays an important role in the etiology of bipolar disorder. Turecki et al. (1998) recently published preliminary evidence suggesting that bipolar patients with an excellent response to lithium treatment have a higher frequency of a specific dinucleotide repeat allele in the phospholipase Cgamma-1 (PLCG1) genomic region. The present work was undertaken to re-examine the finding by Turecki et al. in a sample of Norwegian lithium-treated bipolar patients sub-classified as lithium responders, non-responders, or partial responders/unclassified. The overall distribution of the PLCG1 dinucleotide repeat alleles was not significantly different between different categories of subjects. When analyzed according to presence or absence of different dinucleotide alleles, a PLCG1-8 repeat was more frequent among lithium responders vs controls. In line with Turecki et al., we also noticed a moderately over-representation of the PLCG1-5 repeat among the bipolar patients as compared to the controls.

Polymorphisms in CYP2D6 duplication-negative individuals with the ultrarapid metabolizer phenotype: a role for the CYP2D6*35 allele in ultrarapid metabolism?

Ultrarapid drug metabolism mediated by CYP2D6 is associated with inheritance of alleles with duplicated or amplified functional CYP2D6 genes. However, genotyping for duplicated CYP2D6 alleles only explains a fraction (10-30%) of the ultrarapid metabolizer phenotypes observed in Caucasian populations. Using a sample of CYP2D6 duplication-negative ultrarapid metabolizer subjects and selected control subjects with extensive metabolism, we examined parts of the CYP2D7 pseudogene, and the promoter region and 5'-coding sequence of CYP2D6 for polymorphisms possibly associated with the ultrarapid metabolizer phenotype. In an initial screening of 17 subjects (13 ultrarapid metabolizers and four extensive metabolizers), we identified three DNA variants in the 5'-end of the CYP2D7 pseudogene and 29 variants in the 5'-end of the CYP2D6 gene. Five variants were then selected for examination in a larger sample of subjects having the ultrarapid metabolizer (n = 27) or extensive metabolizer phenotype (n = 77). Subsequent statistical analyses of allele, genotype and estimated haplotype distributions showed that the 31A allele of the 31G > A (Val(II)Met) polymorphism was significantly more frequent in ultrarapid metabolizer subjects than in extensive metabolizer subjects (P = 0.04). Also, estimation of haplotype frequencies suggested that one of the haplotypes with the 31A variant was significantly more frequent among the ultrarapid metabolizers compared with the extensive metabolizers (P = 0.03). The average metabolic ratio was significantly lower in subjects possessing the 31A allele compared with subjects homozygous for the 31G allele (P = 0.02). We also observed a nonsignificant over-representation of the G-allele of a - 1584 C > G promoter polymorphism in the ultrarapid metabolizer group. Since our results are based on a relatively low number of subjects, further studies on larger samples and functional analyses of the polymorphisms detected are necessary to determine the role of the 31G > A and - 1584C > 6 variants in CYP2D6 duplication-negative ultrarapid metabolizer subjects.

A human myo-inositol monophosphatase gene (IMPA2) localized in a putative susceptibility region for bipolar disorder on chromosome 18p11.2: genomic structure and polymorphism screening in manic-depressive patients.

For several decades, lithium has been the drug of choice in the long-term treatment of manic-depressive illness, but the molecular mechanism(s) mediating its therapeutic effects remain to be determined. The enzyme myo-inositol monophosphatase (IMPase) in the phospholipase C signaling system is inhibited by lithium at therapeutically relevant concentrations, and is a candidate target of lithium's mood-stabilizing action. Two genes encoding human IMPases have so far been isolated, namely IMPA1 on chromosome 8q21. 13-21.3 and IMPA2 on chromosome 18p11.2. Interestingly, several studies have indicated the presence of a susceptibility locus for bipolar disorder on chromosome 18p11.2. IMPA2 is therefore a candidate for genetic studies on both etiology and lithium treatment of manic-depressive illness. Here we report that the genomic structure of IMPA2 is composed of eight exons, ranging in size from 46 bp to 535 bp. The promoter region contains several Sp1 elements and lacks a TATA-box, features typical for housekeeping genes. By a preliminary polymorphism screening of exons 2-8 in a sample of 23 Norwegian bipolar patients, we have identified nine single nucleotide polymorphisms (SNPs). Seven of the polymorphisms were located in the introns, one was a silent transition in exon 2 (159T>C) and one was a transition in exon 5 (443G>A) resulting in a predicted amino acid substitution (R148Q). Our data show that even in a small sample of bipolar patients, several variants of the IMPA2 gene can be identified. IMPA2 is therefore an intriguing candidate gene for future association studies of manic-depressive illness.

[Creatinine and calcium in urine and blood after brief exposure to magnetic fields]. / Kreatinin og kalsium i urin og blod etter kortvarig eksponering for magnetfelter.

In this experimental study, 35 males were exposed to artificial magnetic fields. The fields were produced by a set of Helmholz coils internally isolated by a Faraday cage which effectively eliminated electrical fields. Each participant stayed inside the coils for 40 minutes on two occasions with an interval of seven days, but was actually only once exposed to a static magnetic field (9.6 mT) and oscillating magnetic fields of variable frequency and strength. Urine and blood samples were taken before and after exposure, and before and after non-exposure. Analysis detected significant changes in serum creatinine level after exposure (p < 0.0001). The changes in serum creatinine level in the nonexposed situation were significantly smaller than the changes found in the exposed situation (p < 0.0001). The changes i urine creatinine after 40 minutes of exposure was also found to be significant (p < 0.01). Exposure to magnetic fields may induce biological reactions.

Genomic structure and sequence analysis of a human inositol polyphosphate 1-phosphatase gene (INPP1).

Lithium remains the most widely used long-term treatment for bipolar affective disorder, but the molecular mechanisms underlying its therapeutic efficacy have not been fully elucidated. Two enzymes involved in the phospholipase C signalling system, namely the myo-inositol monophosphatase (IMPase) and the inositol polyphosphate 1-phosphatase (IPPase), have been postulated as targets for the therapeutic action of lithium in manic-depressive illness. Intriguingly, Drosophila mutants lacking IPPase activity display a defect in synaptic transmission, and this alteration could be phenocopied by lithium exposure. We recently demonstrated the presence of several polymorphisms in the IPPase-encoding inositol polyphosphate 1-phosphatase gene (INPP1) cDNA and suggested that polymorphic variants of the human IPPase might be associated with the striking difference in lithium response among bipolar patients. We report the genomic structure and organization of the INPP1 gene on chromosome 2q32. Based on DNA sequencing of the entire genomic region containing INPP1, we found that the gene consists of six exons and spans more than 25 kb. Expression analysis showed that INPP1 is present as a 1.9 kb mRNA transcript in all organs and tissues examined, including the central nervous system. The level of expression varies, with at least a fourfold higher transcript level in testis compared with other tissues with high expression. A highly polymorphic dinucleotide repeat, (CA)18-25, with an observed heterozygosity of 0.86 was detected immediately downstream of the gene. The present sequence information will be used to further investigate the possible role of the INPP1 gene in lithium-treated bipolar illness.

The polymorphic inositol polyphosphate 1-phosphatase gene as a candidate for pharmacogenetic prediction of lithium-responsive manic-depressive illness.

Long-term treatment with lithium salts has been established as an effective prophylactic therapy in manic-depressive (bipolar) illness. Many patients, however, display a lack of (or partial) treatment response. We recently proposed that pharmacogenetic factors may influence and determine the therapeutic efficacy of lithium in bipolar disorder. The lithium-blockable enzyme inositol polyphosphate 1-phosphatase in the phospholipase C signaling pathway is a putative target for the mood-stabilizing effects of lithium. In the present study, we searched for DNA variations in the human INPP1 gene encoding the inositol polyphosphate 1-phosphatase enzyme. We report the existence of four common polymorphisms in the coding region of the gene. The DNA alterations were all single base substitutions, of which one (A682G) predicted an amino acid change (Thr228Ala), whereas the remaining three (G153T, G348A and C973A) were silent, In a Norwegian pilot sample the frequencies of the four single base substitutions were not significantly different between lithium-treated bipolar patients and healthy control individuals. When subdivided with respect to drug response, however, the C973A transversion was present in six out of nine lithium responders (67%) versus one out of nine non-responders (11%) In contrast, the C973A polymorphism was equally common among lithium responders and non-responders in an independent sample of bipolar patients from Israel. Future studies are therefore need to determine whether allelic variants of the INPP1 gene are associated with a favourable efficacy of lithium in manic-depressive illness.

Genomic structure and chromosomal localization of a human myo-inositol monophosphatase gene (IMPA).

Manic-depressive illness is a serious psychiatric disorder that in many, but far from all, patients can be treated with lithium. The main causes for discontinuation of lithium therapy are unpleasant or serious side effects and lack of response. The reason for the striking variation in clinical efficacy of lithium treatment among bipolar patients is not known. The enzyme myo-inositol monophosphatase (IMPase) has been postulated as a target for the mood-stabilizing effects of lithium, but variation in the coding region of the human IMPA gene encoding IMPase activity has not been observed in manic-depressive patients (Steen et al., Pharmacogenetics, 1996, 6, 113-116). It is nevertheless conceivable that polymorphisms or mutations in the noncoding regions of this gene could influence the lithium response in psychiatric patients. As a first step in investigating this possibility, we here report the genomic structure of the human IMPA gene. The gene is composed of at least nine exons and covers more than 20 kb of sequence on chromosome 8q21.13-q21.3. In the 3'-untranslated part of the gene, we observed a polymorphism (a G to A transition) and also two short sequences similar to the inositol/cholin-responsive element consensus. Finally, we postulate that two additional IMPA-like transcripts originate from the human genome, one from a position close to IMPA itself on chromosome 8 and the other from chromosome 18p. Our data may contribute to the identification of genetic factors involved in the pathogenesis and determination of treatment response in manic-depressive illness.

Dopamine D3-receptor gene variant and susceptibility to tardive dyskinesia in schizophrenic patients.

Schizophrenia is a serious psychiatric illness with a life-time risk of approximately one percent. Many of the patients, but not all, benefit from treatment with anti-psychotic drugs known to block dopamine D2-like receptors. The use of conventional neuroleptics is, however, hampered by the risk of extrapyramidal side-effects. Tardive dyskinesia (TD) is usually regarded as the most serious of these drug-induced movement disorders due to its high prevalence and potentially irreversible nature. In this study, we have investigated the genetic variation of the dopamine D3 receptor gene (DRD3) as a putative risk factor for TD in schizophrenic patients receiving long-term anti-psychotic drug therapy. We found a high frequency (22-24%) of homozygosity for the Ser9Gly variant (allele 2) of the DRD3 gene among subjects with TD in both a cross-sectional and a longitudinal evaluation, as compared with the relative under-representation (4-6%) of this genotype in patients with no or fluctuating TD. This result indicates that autosomal inheritance of two polymorphic Ser9Gly alleles (2-2 genotype), but not homozygosity for the wild-type allele (1-1 genotype), is a susceptibility factor for the development of TD, an observation which may improve the understanding of the pathophysiological mechanisms of TD and influence the design and choice of future anti-psychotic drugs. The correlation between a serious motor side-effect and a genetic marker could lead to selection bias in the sampling of schizophrenic patients for genetic studies, and may therefore explain the apparent association reported between susceptibility for schizophrenia per se and homozygosity for the DRD3 gene.

Ultrarapid metabolizers of debrisoquine: characterization and PCR-based detection of alleles with duplication of the CYP2D6 gene.

Up to 7% of Caucasians may demonstrate ultrarapid metabolism of debrisoquine due to inheritance of alleles with duplicated functional CYP2D6 genes. Here we describe the genomic organization of the duplicated CYP2D6 genes in the 42 kb XbaI allele. We postulate that this duplication originates from a homologous, unequal cross-over event which involved two 29 kb XbaI wild-type alleles, and had break points within a 2.8 kb direct repeat (CYP-REP) flanking the CYP2D6 gene. Moreover, we have designed two different PCR assays for detection of alleles with duplicated CYP2D6 genes. Both assays correctly identified 29 out of 29 subjects positive for the 42 kb XbaI allele. No false negative or false positive reactions were observed.

The Ca(2+)-sensing receptor gene (PCAR1) mutation T151M in isolated autosomal dominant hypoparathyroidism.

Isolated autosomal dominant hypoparathyroidism is a heterogeneous disorder characterized by parathyroid hormone (PTH) deficiency, hypocalcemia and hyperphosphatemia. The candidate gene approach was used to study a large Norwegian family. The loci for the PTH gene, PTH receptor gene and RET protooncogene were excluded using dinucleotide markers and restriction fragment length polymorphism analysis. Complete cosegregation of this trait was found with the chromosomal region 3q13, using the short tandem repeat markers D3S1267, D3S1269, D3S1303, D3S1518, and RHO. This region contains the candidate locus for the Ca(2+)-sensing receptor (PCAR1). By single-strand conformation polymorphism (SSCP) analysis of all PCAR1 exons followed by automated sequencing, we identified a C to T transition in exon 2 (cDNA position 452) on the mutant allele in the family. The mutation predicts a substitution of Thr to Met in amino acid position 151 (T151M). A StyI restriction site created by the nucleotide substitution was used to confirm the mutation on all alleles, as well as to exclude it among 100 normal alleles (blood donors). SSCP analysis also identified a novel polymorphism of PCAR1 intron 4 (1609-88t --> c) on normal alleles. The T151M mutation is located in the extracellular N-terminal domain of PCAR1, which belongs to the superfamily of G protein-coupled receptors. We suggest that this is a gain-of-function mutation that increases the sensitivity of the receptor to [Ca2+], thereby decreasing the calcium set point.