Candidate genes and sensory functions in health and irritable bowel syndrome

Adrenergic and serotonergic (ADR-SER) mechanisms alter gut (GI) function; these effects are mediated through G protein transduction. Candidate genetic variations in ADR-SER were significantly associated with somatic scores in irritable bowel syndrome (IBS) and gastric emptying but not small bowel or colonic transit. Our aim was to assess whether candidate ADR-SER genes are associated with motor and sensory GI functions in IBS and subgroups on the basis of bowel dysfunction. In 122 patients with IBS and 39 healthy controls, we assessed gastrointestinal somatic symptoms and affect by validated questionnaires. We measured: gastric volume (GV), maximum tolerated volume, rectal compliance, sensation thresholds and ratings, and genetic variations including alpha2A (C-1291G), alpha2C (Del 332-325), GNbeta3 (C825T), and 5-HTTLPR. Demographics and genotype distributions were similar in the patients with IBS subgrouped on bowel function. There were significant associations between 5-HTTLPR SS genotype and absence of IBS symptoms and between 5-HTTLPR LS/SS genotype and increased rectal compliance and increased pain ratings, particularly at 12 and 24 mmHg distensions. GNbeta3 was associated only with fasting GV; we did not detect associations between alpha2A genotype and the gastrointestinal sensory or motor functions tested. We concluded that 5-HTTLPR LS/SS genotype is associated with both increased pain sensation and increased rectal compliance though the latter effect is unlikely to contribute to increased pain sensation ratings with LS/SS genotype. The data suggest the hypotheses that the endophenotype of visceral hypersensitivity in IBS may be partly related to genetic factors, and the association of GNbeta3 with fasting GV may explain, in part, the reported association of GNbeta3 with dyspepsia.     

Serotonin transporter gene variation, infant abuse, and responsiveness to stress in rhesus macaque mothers and infants

A functional polymorphism in the promoter region of the serotonin transporter (5-HTTLPR) gene has been associated with variation in anxiety and hypothalamus-pituitary-adrenal (HPA) axis function in humans and rhesus macaques. Individuals carrying the short allele are at a higher risk for developmental psychopathology, and this risk is magnified in short allele carriers who have experienced early life stress. This study investigated the relationship between 5-HTTLPR allelic variation, infant abuse, and behavioral and hormonal responses to stress in rhesus macaques. Subjects were 10 abusive mothers and their infants, and 10 nonabusive mother-infant pairs. Mothers and infants were genotyped for the rh5-HTTLPR, and studied in the first 6 months of infant life. For mothers and infants, we measured social group behavior, behavioral responses to handling procedures, and plasma concentrations of ACTH and cortisol under basal conditions and in response to stress tests. The proportion of individuals carrying the short rh5-HTTLPR allele was significantly higher among abusive mothers than controls. Among mothers and infants, the short allele was associated with higher basal cortisol levels and greater hormonal stress responses in the infants. In addition, infants who carried the short rh5-HTTLPR allele had higher anxiety scores than infants homozygous for the long allele. The rh5-HTTLPR genotype also interacted with early adverse experience to impact HPA axis function in the infants. These results are consistent with those of previous studies which demonstrate associations between serotonergic activity and anxiety and stress reactivity, and add additional evidence suggesting that genetic variation in serotonergic function may contribute to the occurrence of abusive parenting in rhesus macaques and modulate emotional behavior and HPA axis function.     

Association Study of Serotonin Transporter SLC6A4 Gene with Chinese Han Irritable Bowel Syndrome

Objective

Irritable bowel syndrome (IBS) is a common clinical gastrointestinal dysfunction disorders. 5-sertonon (5-hydroxytryptamine, 5-HT) is a very important neurotransmitter, which is involved in gastrointestinal motion and sensation. Solute carrier family 6 member 4 (SLC6A4) gene encode serotonin transporter (SERT) which function is to rapidly reuptake the most of 5-HT. Therefore, it is needed to explore the association between SLC6A4 gene polymorphisms and IBS.

Methods

119 patients and 238 healthy controls were administrated to detect the SLC6A4 gene polymorphisms including 5-HT-transporter-gene-linked polymorphic region (5-HTTLPR), variable number of tandem repeats (VNTRs) and three selected tag Single Nucleotide Polymorphisms (SNPs) rs1042173, rs3794808, rs2020936 by using polymerase chain reaction (PCR) and TaqMan® SNP Genotyping.

Results

There were significant difference for 5-HTTLPR between IBS and control groups (X2 = 106.168, P<0.0001). In control group, genotypes were mainly L/L (58.4%), however, the genotypes in IBS were S/S (37.8%). The significant difference was shown in D-IBS subjects when compared to the controls (X² = 50.850, P<0.0001) for 5-HTTLPR. For STin2 VNTR, rs1042173, rs3794808, and rs2020936 polymorphisms, there were no any significant differences between IBS and control groups. There were no statistical significantly haplotypes for 5-HTTLPR, VNTRs and the three SNPs between IBS and controls.

Conclusion

The S allele in 5-HTTLPR was a susceptible allele with Chinese Han IBS, but other associations of VNTRs, three selected Tag SNPs and positive haplotype with IBS were not found. It is indicated that much research are needed to study the relationship between other polymorphisms in SLC6A4 gene and IBS.     

Serotonin transporter function is modulated by brain-derived neurotrophic factor (BDNF) but not nerve growth factor (NGF)

The serotonin transporter (5-HTT) regulates serotonergic neurotransmission by determining the magnitude and duration of serotonergic responses. We have recently described a polymorphism in the 5-HTT gene promoter (5-HTTLPR) which influences the function of the 5-HTT and is associated with several psychiatric disorders. Immortalized B lymphocytes express the 5-HTT, and a B lymphocyte line has been shown to express the receptor for brain-derived neurotrophic factor, trkB. Since brain-derived neurotrophic factor (BDNF) is a specific growth and differentiation factor for serotonergic neurons, we assessed whether BDNF is able to modulate 5-HTT function in B lymphoblasts. Nerve growth factor (NGF), another neurotrophin which acts via the trkA receptor, was also studied. Eight immortalized B lymphoblast lines were generated and genotyped for the 5-HTTLPR. After treatment with BDNF or NGF, 5-HT uptake and proliferation of the cell lines were assessed. Two of the B cell lines showed a dose-dependent reduction of 5-HT uptake after exposure to BDNF. Both of these cell lines were homozygous for the long allele of the 5-HTTLPR. NGF did not influence 5-HT uptake or cellular proliferation in any of the cell lines. Thus, BDNF but not NGF may influence 5-HT uptake in some B lymphocytes. The fact that regulation of the 5-HTT was observed preferentially in cells of the long/long genotype indicates that presence of a short allele confers reduced regulatory capacity on the 5-HTT. In conclusion, B lymphoblasts represent a practical model for functional regulation of the 5-HTT by neurotrophins in serotonergic neurons.     

Influences of COMT and 5-HTTLPR Polymorphisms on Cognitive Flexibility in Healthy Women: Inhibition of Prepotent Responses and Memory Updating

Understanding genetic factors that affect monoamine neurotransmitters flux in prefrontal cortex may help to further specify the complex neurobiological processes that underlie cognitive function and dysfunction in health and illness. The current study examined the associations between the polymorphisms of dopaminergic (COMT Met158Val) and serotoninergic (5-HTTLPR) genes and the sequential pattern of responses in a motor random generation task providing well-established indexes for executive functioning in a large sample of 255 healthy women. Participants homozygous for the Met allele of the COMT polymorphism showed impaired inhibition of prepotent responses, whereas individuals homozygous for the s-allele of the 5-HTTLPR showed a restricted ability to update information in working memory. Taken together the results indicate differentiated influences of dopaminergic and serotonergic genes on important and definite executive sub-processes related to cognitive flexibility.     

Serotonergic genes and amygdala activity in response to negative affective facial stimuli in Korean women

Serotonergic genes have been implicated in mood disorders, alcoholism and certain personality traits. We investigated the possible relationship between several polymorphisms in the serotonin (5-HT) system and amygdala responses to negative facial stimuli in Korean women using functional magnetic resonance imaging. All participants were genotyped with regard to the following polymorphisms: the serotonin transporter-gene-linked polymorphic region (5-HTTLPR), tryptophan hydroxylase 2 (TPH2) G(-703)T, 5-HT(1A) C(-1019)G and 5-HT(2A) single nucleotide polymorphism (SNP) rs6311. We found increased activations in response to angry facial stimuli in the bilateral amygdala of subjects with the long allele of 5-HTTLPR compared with those with two copies of the short allele. Higher activations in response to sad facial stimuli were found in the bilateral amygdala of subjects with the T/T genotype of 5-HT(2A) SNP rs6311, compared with C allele carriers, and in subjects with the G/G genotype of TPH2 G(-703)T, compared with those with T/T and G/T genotypes. Our results for individuals from an Asian population countered a previous finding for a Caucasian population and identified the moderating role of genetic background in the relationships between these serotonergic gene polymorphisms and amygdala function elicited by negative emotional stimuli.     

Effects of neonatal maternal separation on neurochemical and sensory response to colonic distension in a rat model of irritable bowel syndrome

Early life stress has been implicated as a risk factor for irritable bowel syndrome (IBS). We studied the effect of neonatal maternal separation on the visceromotor response and the expression of c-fos, 5-HT, and its receptors/transporters along the brain-gut axis in an animal model of IBS. Male neonatal Sprague-Dawley rats were randomly assigned to a 3-h daily maternal separation (MS) or nonhandling (NH) on postnatal days 2-21. Colorectal balloon distention (CRD) was performed for assessment of abdominal withdrawal reflex as a surrogate marker of visceral pain. Tissues from dorsal raphe nucleus in midbrain, lumbar-sacral cord, and distal colon were harvested for semiquantitative analysis of c-fos and 5-HT. The expression of 5-HT expression, 5-HT3 receptors, and 5-HT transporter were analyzed by RT-PCR. Pain threshold was significantly lower in MS than NH rats. The abdominal withdrawal reflex score in response to CRD in MS rats was significantly higher with distension pressures of 40, 60, and 80 mmHg. In MS rats, the number of c-fos-like immunoreactive nuclei at dorsal horn of lumbar-sacral spinal cord increased significantly after CRD. 5-HT content in the spinal cord of MS rats was significant higher. In the colon, both 5-HT-positive cell number and 5-HT content were comparable between MS and NH groups before CRD. Post-CRD only MS rats had significant increase in 5-HT content. Protein and mRNA expression levels of 5-HT3 receptors and 5-HT transporter were similar in MS and NH rats. Neonatal maternal separation stress predisposes rats to exaggerated neurochemical responses and visceral hyperalgesia in colon mimicking IBS.     

Peppermint oil in irritable bowel syndrome

In a literature search 16 clinical trials investigating 180-200 mg enteric-coated peppermint oil (PO) in irritable bowel syndrome (IBS) or recurrent abdominal pain in children (1 study) with 651 patients enrolled were identified. Nine out of 16 studies were randomized double blind cross over trials with (n = 5) or without (n = 4) run in and/or wash out periods, five had a randomized double blind parallel group design and two were open labeled studies. Placebo served in 12 and anticholinergics in three studies as comparator. Eight out of 12 placebo controlled studies show statistically significant effects in favor of PO. Average response rates in terms of "overall success" are 58% (range 39-79%) for PO and 29% (range 10-52%) for placebo. The three studies versus smooth muscle relaxants did not show differences between treatments hinting for equivalence of treatments. Adverse events reported were generally mild and transient, but very specific. PO caused the typical GI effects like heartburn and anal/perianal burning or discomfort sensations, whereas the anticholinergics caused dry mouth and blurred vision. Anticholinergics and 5HT3/4-ant/agonists do not offer superior improvement rates, placebo responses cover the range as in PO trials. Taking into account the currently available drug treatments for IBS PO (1-2 capsules t.i.d. over 24 weeks) may be the drug of first choice in IBS patients with non-serious constipation or diarrhea to alleviate general symptoms and to improve quality of life.     

Serotonin transporter gene polymorphisms and sertraline response in major depression patients

Major depression (MD) has a complex multifactorial etiology with genetic and environmental factors contributing to the disorder. As with all antidepressant treatments, there is variability in drug response due to heredity, generally focusing on genetic polymorphism of the drug-metabolizing transporter genes. The serotonin transporter (5-HTT) gene is a particularly important candidate for genetic involvement in MD disorders owing to its key role in the regulation of serotonergic transmission and is therefore considered to be an interesting candidate in the mechanism of antidepressant drugs. In this study, we have focused on the associations between genetic polymorphisms in two regions of the 5-HTT gene (5-HTTLPR and VNTR) related to sertraline responses. Our sample consisted of 64 unrelated Turkish subjects who strictly met DSM-IV and CGI scores. There was no significant difference between the frequency of the SS, LS, LL, 9/10, 10/10, 9/12, 10/12, and 12/12 genotypes and responses to sertraline. However, the number of patients can be increased and different drugs can be studied in order to find a specific pharmacogenetic relation.     

Modulation of serotonin transporter function by interleukin-4

Serotonin (5-HT) is an important mediator of interactions between the nervous and immune systems. 5-HT signaling is regulated by the 5-HT transporter (5-HTT), which determines the magnitude and duration of serotonergic responses. Due to this important role, regulation of the 5-HTT by cytokines has been the focus of recent interest. A number of proinflammatory cytokines, including interleukin-1beta, tumor necrosis factor-alpha, and interferon-gamma, have been shown to upregulate the 5-HTT. In the present study we investigated the influence of interleukin-4 (IL-4), which acts as an anti-inflammatory cytokine in the central nervous system, on the 5-HTT. As a model system we used immortalized B lymphocytes, which not only express the 5-HTT, but also allow testing the co-modulatory influence of a recently described polymorphism in the 5-HTT gene promoter (5-HTTLPR) that is associated with anxiety- and depression-related behavioral traits. The results show that IL-4 induces a dose-dependent reduction of 5-HT uptake. This effect is preferentially seen in cell lines homozygous for the long, high-activity allele of the 5-HTTLPR. In conclusion, a picture of differential modulation of the 5-HTT by proinflammatory and anti-inflammatory cytokines is emerging, which may represent a fine-tuned mechanism to communicate the state of an immune response to the central nervous system.     

Serotonin transporter gene-linked polymorphic region: Allele distributions in relationship to body weight and in anorexia nervosa

Several lines of evidence implicate a role for the serotonergic system in body weight regulation and eating disorders. The magnitude and duration of postsynaptic responses to serotonin (5-HT) is directed by the transport into and release from the presynaptic neuron. Recently, a common polymorphism of a repetitive element in the region of the serotonin transporter (5-HTT) gene-linked polymorphic region (5-HTTLPR) was identified that results in a system of two common alleles. The activity of the 5-HTT, as measured in in vitro assays and in human lymphoblastoid cell lines, is dependent on the respective genotype. We thus hypothesized that this polymorphism is relevant for weight regulation in general and is possibly involved in the etiology of anorexia nervosa (AN). Allele frequencies and genotypes were determined in a total of 385 unrelated obese children, adolescents and adults, 112 underweight subjects and 96 patients with AN. Furthermore, both parents of 98 obese children and adolescents and of 55 patients with AN, respectively, were genotyped, thus allowing to test for both association and linkage. The comparison of allele frequencies between obese and underweight probands provided no evidence for a major role of the 5-HTTLPR in weight regulation. Patients with AN had allele frequencies not significantly different to those observed for obese and underweight individuals.     

Lack of CB1 receptor activity impairs serotonergic negative feedback

Serotonergic and endocannabinoid systems are important substrates for the control of emotional behaviour and growing evidence show an involvement in the pathophysiology of mood disorders. In the present study, the absence of the activity of the CB₁ cannabinoid receptor impaired serotonergic negative feedback in mice. Thus, in vivo microdialysis experiments revealed increased basal 5-HT extracellular levels and attenuated fluoxetine-induced increase of 5-HT extracellular levels in the prefrontal cortex of CB₁ knockout compared with wild-type mice. These observations could be related to the significant reduction in the 5-HT transporter binding site density detected in frontal cortex and hippocampus of CB₁ knockout mice. The lack of CB₁ receptor also altered some 5-HT receptors related to the 5-HT feedback. Extracellular recordings in the dorsal raphe nucleus (DRN) revealed that the genetic and pharmacological blockade of CB₁ receptor induced a 5-HT_1A autoreceptor functional desensitization. In situ hybridization studies showed a reduction in the expression of the 5-HT_2C receptor within several brain areas related to the control of the emotional responses, such as the DRN, the nucleus accumbens and the paraventricular nucleus of the hypothalamus, whereas an over-expression was observed in the CA3 area of the ventral hippocampus. These results reveal that the lack of CB₁ receptor induces a facilitation of the activity of serotonergic neurons in the DRN by altering different components of the 5-HT feedback as well as an increase in 5-HT extracellular levels in the prefrontal cortex in mice.     

肠道微生物代谢物在肠易激综合征中的研究进展

肠易激综合征(irritable bowel syndrome, IBS)是常见的胃肠道功能障碍疾病,以腹痛、腹胀、排便习惯改变等为典型临床症状。尽管IBS病因复杂且发病机制并未完全阐明,但越来越多的文献报道其发病与微生物-肠-脑轴调控失常密切相关。本文以肠道微生物衍生的代谢物神经递质、短链脂肪酸和胆汁酸代谢物为切入点,对其在内脏敏感、腹痛、腹泻和精神心理障碍等IBS症状发展中的作用进行系统综述,为以代谢物转化细菌为靶点治疗IBS提供理论支撑。     

CB1-cannabinoid receptors are involved in the modulation of non-synaptic [3H]serotonin release from the rat hippocampus

In the present study we investigated whether serotonin release in the hippocampus is subject to regulation via cannabinoid receptors. Both rat and mouse hippocampal slices were preincubated with [3H]serotonin ([3H]5-HT) and superfused with medium containing serotonin reuptake inhibitor citalopram hydrobromide (300 nM). The cannabinoid receptor agonist R(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolo[1,2,3-de]-1,4-benzoxazinyl]-(1-naphthalenyl) methanone mesylate (WIN55,212-2, 1 microM) did not affect either the resting or the electrically evoked [3H]5-HT release. In the presence of the ionotropic glutamate receptor antagonists D(-)-2-amino-5-phosphonopentanoic acid (AP-5, 50 microM) and 6-cyano-7-nitroquinoxaline-2,3-dione-disodium (CNQX, 10 microM) the evoked [3H]5-HT release was decreased significantly. Similar findings were obtained when CNQX (10 microM) was applied alone with WIN55,212-2. This effect was abolished by the selective cannabinoid receptor subtype 1 (CB1) antagonists N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (SR141716, 1 microM) and 1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-1-piperidinyl-1H-pyrazole-3-carboxamide trifluoroacetate salt (AM251, 1 microM). Similarly to that observed in rats, WIN55,212-2 (1 microM) decreased the evoked [3H]5-HT efflux in wild-type mice (CB1+/+). The inhibitory effect of WIN55,212-2 (1 microM) was completely absent in hippocampal slices derived from mice genetically deficient in CB1 cannabinoid receptors (CB1-/-). Relatively selective degeneration of fine serotonergic axons by the neurotoxin parachloramphetamine (PCA) reduced significantly the tritium uptake and the evoked [3H]5-HT release. In addition, PCA, eliminated the effect of WIN55,212-2 (1 microM) on the stimulation-evoked [3H]5-HT efflux. In contrast to the PCA-treated animals, WIN55,212-2 (1 microM) reduced the [3H]5-HT efflux in the saline-treated group. Our data suggest that a subpopulation of non-synaptic serotonergic afferents express CB1 receptors and activation of these CB1 receptors leads to a decrease in 5-HT release.     

Multitrait GWAS to connect disease variants and biological mechanisms

Genome-wide association studies (GWASs) have uncovered a wealth of associations between common variants and human phenotypes. Here, we present an integrative analysis of GWAS summary statistics from 36 phenotypes to decipher multitrait genetic architecture and its link with biological mechanisms. Our framework incorporates multitrait association mapping along with an investigation of the breakdown of genetic associations into clusters of variants harboring similar multitrait association profiles. Focusing on two subsets of immunity and metabolism phenotypes, we then demonstrate how genetic variants within clusters can be mapped to biological pathways and disease mechanisms. Finally, for the metabolism set, we investigate the link between gene cluster assignment and the success of drug targets in randomized controlled trials.     

Serotoninergic polymorphisms (5-HTTLPR and 5-HT2A): association studies with psychosis in Alzheimer disease

Patients with Alzheimer disease (AD) often exhibit psychotic symptoms associated with cognitive impairment. A few association studies have been carried out to determine if the serotonin transporter and receptor genes are potential risk factors for AD and/or associated psychopathology. The aim of this study was to investigate the association of a serotonin transporter gene-linked polymorphic region (5-HTTLPR) and the 5-HT2A receptor T102C polymorphism with the risk of developing dementia and/or psychotic symptoms in a group of sporadic AD patients from Italy. No significant differences in the distribution of allele and genotype frequencies of 5-HTTLPR and 5-HT2A T102C were found between patient and control groups. However, a significant association between the C102/C102 5-HT2A genotype and psychotic symptoms (p < 0.001) was observed. Our data strongly confirm results from previous studies suggesting that the C102 allele of the 5-HT2A receptor is associated with the occurrence of psychotic symptoms in AD. On the contrary, the serotonin transporter does not appear to be a major susceptibility factor in the pathophysiology of the disease.     

The Association of 5-HT2A, 5-HTT,and LEPR Polymorphisms with Obstructive Sleep Apnea Syndrome: A Systematic Review and Meta-Analysis

Objective

A consensus has not been reached regarding the association of several different gene polymorphisms and susceptibility to obstructive sleep apnea syndrome (OSAS). We performed a meta-analysis to better evaluate the associations between 5-HT2A, 5-HTT, and LEPR polymorphisms, and OSAS.

Method

5-HT2A, 5-HTT, and LEPR polymorphisms and OSAS were identified in PubMed and EMBASE. The pooled odd rates (ORs) with 95%CIs were estimated using a fixed-effect or random-effect models. The associations between these polymorphisms and OSAS risk were assessed using dominant, recessive and additive models.

Results

Twelve publications were included in this study. The -1438 “A” allele of 5-HT2A was identified as a candidate genetic risk factor for OSAS (OR: 2.33, 95%CI 1.49–3.66). Individuals carrying the -1438 “G” allele had a nearly 70% reduced risk of OSAS when compared with AA homozygotes (OR: 0.30, 95%CI 0.23–0.40). There was no significant association between 5-HT2A 102C/T and OSAS risk, using any model. The “S” allele of 5-HTTLPR conferred protection against OSAS (OR: 0.80, 95%CI 0.67–0.95), while the “10” allele of 5-HTTVNTR contributed to the risk of OSAS (OR: 2.08, 95%CI: 1.58–2.73). The “GG” genotype of LEPR was associated with a reduced risk of OSAS (OR: 0.39, 95%CI 0.17–0.88).

Conclusion

The meta-analysis demonstrated that 5-HTR-1438 “A” and 5-HTTVNTR “10” alleles were significantly associated with OSAS. The “S” allele of 5-HTTLPR and the “GG” genotype of LEPR conferred protection against OSAS. Further studies, such as Genome-Wide Association study (GWAS), should be conducted in a large cohort of OSAS patients to confirm our findings.     

肠易激综合征患者肠道菌群分布和炎症因子及血清NPY、SP、5\|HT水平的变化

目的 探究肠易激综合征(IBS)患者肠道菌群分布、相关炎症因子和血清神经肽Y(NPY)、P物质(SP)、5\|羟色胺(5\|HT)水平的变化。 方法 选择2017年1月至2018年12月我院收治的80例IBS患者为研究对象,入选对象分为腹泻组(IBS\|D组,40例)和便秘组(IBS\|C组,40例)。以40例结肠息肉或胃息肉切除术后复查者作为对照组。检测3组患者肠道菌群数量与定植抗力(B/E值)。利用酶联免疫吸附法(ELISA)检测血清IL\|6、IL\|8、TNF\|α水平及血清NPY、SP、5\|HT水平变化。 结果 IBS\|D组患者肠道双歧杆菌、乳杆菌、类杆菌数量及B/E值均低于对照组(均P结论 IBS会导致患者肠道定植抗力下降,进而发生肠道菌群失调并伴随炎症因子水平与血清NPY、SP、5\|HT水平升高。不同亚型的肠易激综合征患者各指标变化情况不同。