Jeroen Aerssens

Genetic and physiological data implicating the new human gene G72 and the gene for d-amino acid oxidase in schizophrenia

A map of 191 single-nucleotide polymorphism (SNPs) was built across a 5-Mb segment from chromosome 13q34 that has been genetically linked to schizophrenia. DNA from 213 schizophrenic patients and 241 normal individuals from Canada were genotyped with this marker set. Two 1,400- and 65-kb regions contained markers associated with the disease. Two markers from the 65-kb region were also found to be associated to schizophrenia in a Russian sample. Two overlapping genes G72 and G30 transcribed in brain were experimentally annotated in this 65-kb region. Transfection experiments point to the existence of a 153-aa protein coded by the G72 gene. This protein is rapidly evolving in primates, is localized to endoplasmic reticulum/Golgi in transfected cells, is able to form multimers and specifically binds to carbohydrates. Yeast two-hybrid experiments with the G72 protein identified the enzyme d-amino acid oxidase (DAAO) as an interacting partner. DAAO is expressed in human brain where it oxidizes d-serine, a potent activator of N-methyl-D-aspartate type glutamate receptor. The interaction between G72 and DAAO was confirmed in vitro and resulted in activation of DAAO. Four SNP markers from DAAO were found to be associated with schizophrenia in the Canadian samples. Logistic regression revealed genetic interaction between associated SNPs in vicinity of two genes. The association of both DAAO and a new gene G72 from 13q34 with schizophrenia together with activation of DAAO activity by a G72 protein product points to the involvement of this N-methyl-d-aspartate receptor regulation pathway in schizophrenia.

Genetic variations of KCNQ1, KCNH2, SCN5A, KCNE1, and KCNE2 in drug-induced long QT syndrome patients.

Administration of specific drugs may occasionally induce acquired long QT syndrome (aLQTS), a disorder that predisposes to ventricular arrhythmias, typically of the torsade de pointes (TdP) type, and sudden cardiac death. “Forme fruste” mutations in congenital LQTS (cLQTS) genes have been reported repeatedly as the underlying cause of aLQTS, and are therefore considered as an important risk factor. We evaluated the impact of genetic susceptibility for aLQTS through mutations in cLQTS genes. Five cLQTS genes (KCNH2, KCNQ1, SCN5A, KCNE1, KCNE2) were thoroughly screened for genetic variations in 32 drug-induced aLQTS patients with confirmed TdP and 32 healthy individuals. Missense forme frust mutations were identified in four aLQTS patients: D85N in KCNE1 (two cases), T8A in KCNE2, and P347S in KCNH2. Three other missense variations were found both in patients and controls, and are thus unlikely to significantly influence aLQTS susceptibility. In addition, 13 silent and six intronic variations were detected, four of which were found in a single aLQTS patient but not in the controls. We conclude that missense mutations in the examined cLQTS genes explain only a minority of aLQTS cases.

Alterations in Mucosal Immunity Identified in the Colon of Patients With Irritable Bowel Syndrome

BACKGROUND & AIMS Irritable bowel syndrome (IBS) has been associated with mucosal dysfunction, mild inflammation, and altered colonic bacteria. We used microarray expression profiling of sigmoid colon mucosa to assess whether there are stably expressed sets of genes that suggest there are objective molecular biomarkers associated with IBS. METHODS Gene expression profiling was performed using Human Genome U133 Plus 2.0 (Affymetrix) GeneChips with RNA from sigmoid colon mucosal biopsy specimens from 36 IBS patients and 25 healthy control subjects. Real-time quantitative polymerase chain reaction was used to confirm the data in 12 genes of interest. Statistical methods for microarray data were applied to search for differentially expressed genes, and to assess the stability of molecular signatures in IBS patients. RESULTS Mucosal gene expression profiles were consistent across different sites within the sigmoid colon and were stable on repeat biopsy over approximately 3 months. Differentially expressed genes suggest functional alterations of several components of the host mucosal immune response to microbial pathogens. The most strikingly increased expression involved a yet uncharacterized gene, DKFZP564O0823. Identified specific genes suggest the hypothesis that molecular signatures may enable distinction of a subset of IBS patients from healthy controls. By using 75% of the biopsy specimens as a validation set to develop a gene profile, the test set (25%) was predicted correctly with approximately 70% accuracy. CONCLUSIONS Mucosal gene expression analysis shows there are relatively stable alterations in colonic mucosal immunity in IBS. These molecular alterations provide the basis to test the hypothesis that objective biomarkers may be identified in IBS and enhance understanding of the disease.

A novel mutation (T65P) in the PAS domain of the human potassium channel HERG results in the long QT syndrome by trafficking deficiency

The congenital long QT syndrome is a cardiac disease characterized by an increased susceptibility to ventricular arrhythmias. The clinical hallmark is a prolongation of the QT interval, which reflects a delay in repolarization caused by mutations in cardiac ion channel genes. Mutations in the HERG (human e ther-à-go-go-relatedgene KCNH2 can cause a reduction in IKr, one of the currents responsible for cardiac repolarization. We describe the identification and characterization of a novel missense mutation T65P in the PAS (Per-Arnt-Sim) domain of HERG, resulting in defective trafficking of the protein to the cell membrane. Defective folding of the mutant protein could be restored by decreased cell incubation temperature and pharmacologically by cisapride and E-4031. When trafficking was restored by growing cells at 27 °C, the kinetics of the mutated channel resembled that of wild-type channels although the rate of activation, deactivation, and recovery from inactivation were accelerated. No positive evidence for the formation of heterotetramers was obtained by co-expression of wild-type with mutant subunits at 37 °C. As a consequence the clinical symptoms may be explained rather by haploinsufficiency than by dominant negative effects. This study is the first to relate a PAS domain mutation in HERG to a trafficking deficiency at body temperature, apart from effects on channel deactivation.

Essential role for TRPV1 in stress‐induced (mast cell‐dependent) colonic hypersensitivity in maternally separated rats

Abstract  Irritable bowel syndrome is in part characterized by an increased sensitivity to colonic distension. Stress is an important trigger factor for symptom generation. We hypothesized that stress induces visceral hypersensitivity via mast cell degranulation and transient receptor ion channel 1 (TRPV1) modulation. We used the rat model of neonatal maternal separation (MS) to investigate this hypothesis. The visceromotor response to colonic distention was assessed in adult MS and non‐handled (NH) rats before and after acute water avoidance (WA) stress. We evaluated the effect of the mast cell stabilizer doxantrazole, neutralizing antiserum against the mast cell mediator nerve growth factor (NGF) and two different TRPV1 antagonists; capsazepine (non‐specific) and SB‐705498 (TRPV1‐specific). Immunohistochemistry was used to assess post‐WA TRPV1 expression in dorsal root ganglia and the presence of immunocytes in proximal and distal colon. Retrograde labelled and microdissected dorsal root ganglia sensory neurons were used to evaluate TRPV1 gene transcription. Results showed that acute stress induces colonic hypersensitivity in MS but not in NH rats. Hypersensitivity was prevented by prestress administration of doxantrazole and anti‐NGF. Capsazepine inhibited and SB‐705498 reversed poststress hypersensitivity. In MS rats, acute stress induced a slight increase in colonic mast cell numbers without further signs of inflammation. Post‐WA TRPV1 transcription and expression was not higher in MS than NH rats. In conclusion, the present data on stress‐induced visceral hypersensitivity confirm earlier reports on the essential role of mast cells and NGF. Moreover, the results also suggest that TRPV1 modulation (in the absence of overt inflammation) is involved in this response. Thus, mast cells and TRPV1 are potential targets to treat stress‐induced visceral hypersensitivity.

Dissecting the role of sodium currents in visceral sensory neurons in a model of chronic hyperexcitability using Nav1.8 and Nav1.9 null mice.

Tetrodotoxin‐resistant (TTX‐R) sodium currents have been proposed to underlie sensory neuronal hyperexcitability in acute inflammatory models, but their role in chronic models is unknown. Since no pharmacological tools to separate TTX‐R currents are available, this study employs Nav1.8 and Nav1.9 null mice to evaluate these currents roles in a chronic hyperexcitability model after the resolution of an inflammatory insult. Transient jejunitis was induced by infection with Nippostrongylus brasiliensis (Nb) in Nav1.9 and Nav1.8 null, wild‐type and naïve mice. Retrogradely labelled dorsal root ganglia (DRG) neurons were harvested on day 20–24 post‐infection for patch clamp recording. Rheobase and action potential (AP) parameters were recorded as measures of excitability, and Nav1.9 and Nav1.8 currents were recorded. DRG neuronal excitability was significantly increased in post‐infected mice compared to sham animals, despite the absence of ongoing inflammation (sham = 1.9 ± 0.3, infected = 3.6 ± 0.7 APs at 2× rheobase, P= 0.02). Hyperexcitability was associated with a significantly increased amplitude of TTX‐R currents. Hyperexcitability was maintained in Nav1.9−/− mice, but hyperexcitability was absent and APs were blunted in Nav1.8−/− mice. This study identifies a critical role for Nav1.8 in chronic post‐infectious visceral hyperexcitability, with no contribution from Nav1.9. Nb infection‐induced hyperexcitability is not observed in Nav1.8−/− mice, but is still present in Nav1.9−/− mice. It is not clear whether hyperexcitability is due to a change in the function of Nav1.8 channels or a change in the number of Nav1.8 channels.

Activation of the cannabinoid 2 (CB2) receptor inhibits murine mesenteric afferent nerve activity

Abstract  Cannabinoid 2 (CB2) receptors have both antinociceptive and antihypersensitivity effects, although the precise mechanisms of action are still unclear. In this study, the modulatory role of CB2 receptors on the mesenteric afferent response to the endogenous immunogenic agent bradykinin (BK) was investigated. Mesenteric afferent recordings were obtained from anaesthetized wild‐type and CB2−/− mice using conventional extracellular recording techniques. Control responses to BK were obtained in all experiments prior to administration of either CB2 receptor agonist AM1241, or AM1241 plus the CB2 receptor antagonist AM630. Bradykinin consistently evoked activation of mesenteric afferents (n = 32). AM1241 inhibited the BK response in a dose dependent manner. In the presence of AM630 (10 mg kg−1), however, AM1241 (10 mg kg−1) had no significant effect on the BK response. Moreover, AM1241 had also no significant effect on the BK response in CB2−/− mice. Activation of the CB2 receptor inhibits the BK response in mesenteric afferents, demonstrating that the CB2 receptor is an important regulator of neuroimmune function. This may be a mechanism of action for the antinociceptive and antihypersensitive effects of CB2 receptor agonists.

Validation of 16S rDNA sequencing in microdissected bowel biopsies from Crohn's disease patients to assess bacterial flora diversity

The bowel flora is implicated in Crohns disease (CD) pathogenesis but its precise role is still unclear. Several non‐mutually exclusive hypotheses have been proposed: an unidentified persistent pathogen; excessive bacterial translocation; an immune system abnormality in response to normal bacteria; or a breakdown in the balance between protective and harmful bacteria. These hypotheses can be tested by identifying bacteria in specific microscopic bowel structures or lesions. The present paper describes a novel technique to assess bacterial flora diversity in bowel biopsies, by combining laser capture microdissection with broad‐range 16S rDNA sequencing. Fifty‐four samples comprising histologically normal and pathological mucosa, MALT, ulcers, submucosal lymphangiectasias, epithelioid granulomas, and lymph nodes were microdissected out of 30 bowel biopsies from five CD patients. Bacterial 16S rDNA was successfully amplified by PCR in all samples, and PCR products from 15 samples were selected for cloning and sequence analysis. A total of 729 bacterial DNA sequences were analysed, which could be attributed to six different phyla (Proteobacteria, Firmicutes, Bacteroidetes, Actinobacteria, Fusobacteria, and Planctomycetes). DNA from typical bowel bacteria (Enterobacteriaceae, Clostridiales, Bacteroidetes, Fusobacteria) was detected in all microdissected areas. It was thus convincingly demonstrated that 16S rDNA sequencing can be combined with microdissection to study the bowel flora. However, no specific persistent pathogen causal for CD was identified. The results suggest that Enterobacteriaceae may initiate or colonize ulcers in CD. Translocation of bacteria through established mucosal lesions or as a result of increased permeability may be involved in the evolution towards chronic inflammation and in the establishment of persistent lesions. Further study is needed to confirm these preliminary findings. Copyright

Potential ethnic modifiers in the assessment and treatment of Alzheimer's disease: challenges for the future

OBJECTIVE Despite numerous clinical trials, it is unknown whether ethnicity affects treatment response to cognitive enhancers in Alzheimers disease (AD). There is convincing evidence of ethnic and genetic variability in drug metabolism. This article reviews the available data on ethnicity in clinical trials for AD to answer two questions: (1) what are the challenges to diagnose and treat AD across different ethnic groups, and (2) are there differences in response to pharmacologic interventions for AD across these different ethnic groups? METHOD Available data from Alzheimers Disease Cooperative Study (ADCS) randomized controlled clinical trials and from randomized controlled industry-sponsored trials for four cognitive enhancers (donepezil, galantamine, rivastigmine and sabeluzole) were pooled to assess the numbers of non-Caucasian participants. RESULTS The participation of ethnic minority subjects in clinical trials for AD was dependent on the funding source, although Caucasian participants were over-represented and non-Caucasian participants were under-represented in the clinical trials. Because of the low participation rate of ethnic minorities, there were insufficient data to assess any differences in treatment outcome among different ethnic groups. Strategies to improve diversity in clinical trials are discussed. CONCLUSION Greater participation of ethnically diverse participants in clinical trials for AD would generate additional information on possible differences in metabolism, treatment response, adverse events to therapeutic agents, and could foster the investigation of genetic variability among ethnic groups.

Galantamine Population Pharmacokinetics in Patients with Alzheimer's Disease: Modeling and Simulations

Galantamine is a reversible, competitive inhibitor of acetylcholinesterase and an allosteric modulator of nicotinic acetylcholine receptors. It is cleared by renal and hepatic mechanisms, including metabolism by the CYP 450 2D6 and 3A4 isoenzymes. The authors estimated the population pharmacokinetics of galantamine using nonlinear mixed‐effects modeling as implemented in NONMEM software. Data from 15 clinical studies (1089 individuals, 7480 concentration measurements in total) were used to examine the effect of body size, demographic characteristics, and concomitant disease status on galantamine pharmacokinetic parameters. Galantamine clearance was shown to decrease with age and increase with body weight and creatinine clearance of individuals. Median clearance in male and female patients with Alzheimers disease (AD) was 14.8 and 12.4 L/h, respectively. The dissimilarity was related to the body weight difference, not to the real gender effect. Metabolic clearance was reduced by 60% in patients with moderate or severe hepatic dysfunction (Pugh score 7 or higher). Simulations were performed to assess the impact of hepatic impairment and renal insufficiency on peak plasma concentration of galantamine. Simulations confirmed the need for slower dose titration in patients with hepatic impairment: 4 mg daily during 1 week followed by 4, 8, and 12 mg bid, with each dose level during 1 week compared to the standard titration scheme 4–8–12–16 mg bid. However, no significant differences between plasma levels in AD patients with and without severe renal insufficiency were found. CYP 450 2D6 genotype also influenced galantamine clearance but not to the extent that dose adjustment is required.