Functionally gene-linked polymorphic regions and genetically controlled neurotransmitters metabolism

Evaluation of Platelet Parameters in Children with Autism Spectrum Disorder: Elongated Collagen-Adenosine Diphosphate and Collagen-Epinephrine Closure Times

Changes related to the serotonin system play a key role in the etiology of autism spectrum disorder (ASD). Although we know that platelets are associated with the serotonin system, their relation to ASD has not yet been elucidated. In this study, we aim to investigate platelet parameters in children with ASD. Forty patients with ASD according to Diagnostic and Statistical Manual of Mental Disorders 5 (DSM-5) and 30 healthy controls were included in the study. A complete blood count was done to measure parameters relating to platelet morphology. Moreover, prothrombin time (PT) and activated partial thromboplastin time (aPTT) were evaluated. Lastly, platelet functions were assessed with a platelet functions analyzer 100 (PFA-100) device by measuring collagen-ADP and collagen-epinephrine (EPI) closure times. There was not a significant difference between the groups in terms of platelet count, mean platelet volume (MPV), platelet distribution width, plateletcrit, PT, or aPTT parameters for ASD patients when compared to the control group (P > 0.05). However, MPV in severe ASD, as quantified by the Childhood Autism Rating Scale, was found to be significantly lower when compared to mild to moderate ASD (P = 0.047). Moreover, in terms of platelet functions, the elongation in collagen-ADP and collagen-EPI closure times were significantly higher for the ASD group (P = 0.044). These results may suggest an impairment in platelet functions rather than in platelet morphology for children with ASD. Considering these results, further investigation of thrombocyte functions in the ASD may lead to a better understanding of the pathogenesis of ASD and to the development of our limited knowledge of this disorder. Autism Res 2019, 12: 1069-1076. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Serotonin is a chemical that is found in brain as wells as in blood cells that function in blood clotting in the human body. There are problems related to serotonin in brains of people who have autism. Thus, blood clotting cells may also be affected in people who have autism. In this study, we compare blood clotting functions of children with autism with that of healthy controls.

Effects of high-tryptophan diet on pre- and postnatal development in rats: a morphological study

PURPOSE

Tryptophan is an essential amino acid, precursor of serotonin. Serotonin (5HT) regulates the secretion of pituitary growth hormone (GH), which in turn stimulates the liver to produce insulin-like growth factor-I (IGF-I) that is necessary for development and growth. The aim of our study was to investigate the effects of an excess of tryptophan in the diet of pregnant rats on the differentiation of skeletal muscle tissue.

METHODS

We conducted an immunohistochemical study on the IGF-I expression in hepatic and muscle tissues in offspring, and then, we associated this molecular data with morphological effects on the structure of the muscle fibers and hepatic tissue at different postnatal weeks, from birth to sexual maturity. Measurements of 5HT, GH in blood, and of tryptophan hydroxylase (Tph) activity in gastrointestinal tracts tissue were also taken.

RESULTS

Hyperserotonemia and higher values of Tph activity were detected in both pregnant rats and pups. Very low levels of GH were detected in experimental pups. Morphological alterations of the muscle fibers and lower IGF-I expression in hepatic and muscle tissue in pups were found.

CONCLUSIONS

Our data suggest that an excess of tryptophan in the diet causes hyperserotonemia in fetus. Hyperserotonemia results in an excess of serotonin in the brain where it has an adverse effect on the development of serotonergic neurons. The affected neurons do not regulate optimally the secretion of pituitary GH that consequently decreases. This limits stimulation in the liver to produce IGF-I, crucial for development and growth of pups.

Expression of 5HT-related genes after perinatal treatment with 5HT agonists

Serotonin (5HT) is a biologically active amine with diverse roles in the mammalian organism. Developmental alterations in 5HT homeostasis could lead to exposure of the developing brain to non-optimal serotonin concentrations that may result in developmental and behavioral deficits. In order to explore the molecular basis of the effects of developmental disturbances on 5HT metabolism on adult central 5HT homeostasis, observed in our previous studies, we measured changes in gene expression of the neuronal 5HT-regulating proteins in adult animals after perinatal treatment with the immediate 5HT precursor 5-hydroxytryptophan (5HTP, 25 mg/kg), or monoamine oxidase (MAO) inhibitor tranylcypromine (TCP 2 mg/kg), during the period of the most intensive development of 5HT neurons — from gestational day 12 until postnatal day 21. Adult animals were sacrificed and the relative mRNA levels for tryptophan hydroxylase 2, MAO A, MAO B, receptors 5HT1A and 5HT2A, 5HT transporter (5HTT) and vesicular monoamine transporter (VMAT) were determined in the raphe nuclei region and prefrontal cortex using Real-Time Relative qRT-PCR. In comparison to the saline treated animals, treatment with 5HTP caused mild but significant increase in MAO A and MAO B mRNA abundance. TCP-treated animals, besides an increase in mRNA abundance for both MAO genes, displayed significantly increased 5HTT and VMAT2 mRNA levels and significantly decreased 5HT1A receptor mRNA levels. Our results suggest that perinatal exposure of rats to 5HTP, and especially TCP, induces long-lasting/permanent changes in the expression of 5HT-regulating genes, that presumably underlie 5HT-related neurochemical and behavioral changes in adult animals.

Anxiety-like behavior and cognitive flexibility in adult rats perinatally exposed to increased serotonin concentrations

Serotonin (5-hydroxytryptamine, 5HT) is a biologically active amine that regulates the development of 5HT neurons and target tissues during neurogenesis, while later it assumes the function of a neurotransmitter. Serotonin mediates many essential behaviors common to all mammals, and is held responsible for anxiety-like behavior and cognitive rigidity. Proper serotonin levels, controlled through 5HT synthesis and metabolism, are crucial for normal brain development. In this study we investigated anxiety-like behavior and cognitive flexibility in adult animals after exposing their developing brains to increased 5HT concentrations. Wistar rats were treated subcutaneously from gestational day 12 to post-natal day 21 with the immediate 5HT precursor 5-hydroxytryptophan (5HTP, 25mg/kg), a non-selective MAO inhibitor tranylcypromine (TCP, 2mg/kg), or saline. After reaching adulthood, animals were tested for anxiety-like behavior (exploratory behavior, thigmotactic behavior, social contact, and reaction to stressful stimulus) and cognitive flexibility (ability for reversal learning). Results of the behavioral studies corresponded with our previous neurochemical findings. Treatment with 5HTP, which has induced mild reduction in cortical 5HT concentrations, caused reduction in only one aspect of anxiety-like behavior (increased exploratory activity). Treatment with TCP, which lead to drastic reduction in 5HT concentration/function, resulted in a highly anxiolytic phenotype (reduced thigmotaxis, reaction to stress, and social anxiety) with improved cognitive flexibility. Although further neurochemical, anatomical and gene-expression studies are needed to elucidate the mechanisms underlying the observed behavior, we hope that our results will contribute to the understanding of the role of serotonin in anxiety-like behavior and cognitive rigidity.

The effects of the perinatal treatment with 5-hydroxytryptophan or tranylcypromine on the peripheral and central serotonin homeostasis in adult rats

Serotonin (5HT) is a biologically active amine present in mammals in the brain and the peripheral tissues. Autism is a neurodevelopmental disorder in which 5HT homeostasis is disturbed both centrally and peripherally, but the relationship between the 5HT disturbances in the two compartments is not understood. In an attempt to explore the relationship between the disturbed peripheral 5HT homeostasis and central 5HT functioning, we exposed the developing rat brain to increased 5HT concentrations, by treatment of rats with subcutaneous injections of the immediate 5HT precursor 5-hydroxy-L-tryptophan (5HTP, 25 mg/kg), or the non-selective MAO inhibitor tranylcypromine (TCP, 2 mg/kg), during the period of the most intensive development of 5HT neurons--from gestational day 13 to post-natal day 21. The effects of the mentioned treatments on peripheral and central 5HT levels were then studied in adult rats. Platelet and plasma 5HT concentrations (measured by ELISA), as well as cortical and midbrain 5HT, tryptophan and 5-hydroxyindoleacetic acid levels (measured by HPLC) were determined in twelve 5HTP treated and eight TCP treated rats, and compared with the values measured in 10 control, saline treated rats. Treatment with 5HTP significantly raised peripheral but not central 5HT concentrations. At adult age, peripheral 5HT homeostasis was re-established, while modest decrease in 5HT concentration was observed in frontal cortex, presumably due to hyperserotonemia-induced loss of 5HT terminals during brain development. Treatment with TCP induced significant 5HT elevations in both compartments. At adult age, permanent changes in 5HT homeostasis were observed, both peripherally (as hyperserotonemia) and centrally (as altered 5HT metabolism with decreased 5HT concentrations). Further studies are planned in order to explore the nature of the different disturbances of 5HT homeostasis induced by the two compounds, and their results are expected to shed some light on the role of hyperserotonemia in autism.

Hyperserotonemia in autism: activity of 5HT-associated platelet proteins

Disturbances in serotonin (5HT) neurotransmission have been indicated as biological substrates in several neuropsychiatric disorders including autism. Blood 5HT concentrations, elevated in about one-third of autistic subjects, are regulated through the action of peripheral 5HT-associated proteins. We have measured the activity of two platelet 5HT-associated proteins: 5HT transporter (5HTT) and monoamine oxidase B (MAOB), and indirectly studied the activity of 5HT(2A) receptor (5HT(2A)r) in 15 hyperserotonemic (HS) and 17 normoserotonemic (NS) autistic subjects, and 15 healthy controls (C). While mean velocities of 5HTT kinetics did not significantly differ among the groups, significant elevation in the mean velocity of MAOB kinetics was observed in NS subjects and was even more pronounced in HS subjects in comparison to controls. Also, a decrease in adenosine 5'-diphosphate-induced platelet aggregation of borderline significance was observed in NS subjects, compared to C subjects. The results suggest a possibility of upregulation of monoaminergic synthesis/degradation and, probably consequential, downregulation of 5HT(2A)r in autistic subjects.

Serotonergic candidate genes and puerperal psychosis: an association study

BACKGROUND

Altered serotonergic function is implicated in the aetiology and pathogenesis of a host of psychiatric disorders, and structural variations/polymorphisms in genes encoding the serotonin transporter and various serotonin receptor subtypes are attractive candidates to investigate the biological component underlying these disorders. Specific phenotypic subtypes, that perhaps represent homogeneous forms of the disorder, may increase the power to detect genes in complex diseases.

OBJECTIVE

We investigated regulatory and functional polymorphic DNA markers of serotonergic candidate genes using a case-control approach in puerperal psychosis and bipolar affective disorder probands.

METHODS

We genotyped 320 female participants (104 puerperal psychosis probands, 102 bipolar disorder participants and 114 controls) at the serotonin transporter SERT (5-HTT) 5-HTTVNTR and 5-HTTLPR locus; serotonin receptor 2A (5-HT2A)-T102C and His452Tyr loci, the serotonin receptor 2C (5-HT2C)-Cys23Ser locus, and seven unrelated Alu polymorphic markers.

RESULTS

We observed an association of the puerperal psychosis phenotype with the allele 10 of 5-HTTVNTR of SERT (P=0.004) and a modest association with the genotypic frequencies of the 5-HTTLPR (P=0.036). A nominal P value of 0.006 was observed with the S-10 haplotype in the PP group as compared with bipolar affective disorder probands. Significant association was observed with bipolar affective disorder phenotype with Tyr allele of the 5-HT2A His452Tyr gene polymorphism (P=0.00043) even after a conservative multiple test correction. No association was observed, however, with the 5-HT2A T102C locus, and the distribution of the other seven Alu markers did not differ between the groups.

CONCLUSION

The association between polymorphisms in serotonergic genes (SERT and 5-HT2A, 5-HT2C) suggests that these genetic factors can modulate vulnerability to puerperal psychosis in female bipolar participants.

Serotonin transporter gene (5-Htt): association analysis with temporal lobe epilepsy

Two functional polymorphisms, a 44bp insertion/deletion polymorphism in the 5' regulatory region and a variable number of tandem repeat polymorphisms in the second intron of the serotonin transporter gene (5-HTT), were previously identified and suggested to modulate transcription. The current study was designed to determine the contribution of these polymorphisms in the 5-HTT gene to susceptibility to temporal lobe epilepsy (TLE). Two hundred and seventy six patients with TLE, and 309 age- and sex-matched healthy controls from Calabria (Southern Italy) were studied. Patients and controls were genotyped using the WAVE TM DNA Fragment Analysis System for the insertion/deletion polymorphism in the promoter region (5-HTTLPR), and the GENESCAN TM System for the variable number tandem repeat (VNTR) in the second intron of the 5-HTT gene (5-HTTVNTR). The program UNPHASED was used to compare genotype, allele and haplotype frequencies between cases and controls, including age and gender as covariates in the model. No significant differences between cases and controls were observed for 5-HTTLPR, but a significant association was obtained for the 5-HTTVNTR polymorphism, both modeling genotypes (P-value=0.0145) or alleles (P-value=0.0086). Patients with TLE showed lower frequencies of the 10 repeat at 5-HTTVNTR than the controls (26.2% in patients versus 40.8% in controls). The frequency of homozygous individuals for the 10 allele was observed to be lower among patients than the controls (5.2% of patients were 10/10 versus 18.8% of controls). Haplotype analysis did not increase the evidence for association. These results suggest that the serotonin transporter gene may play a role in the etiology of TLE.

Antipanic efficacy of paroxetine and polymorphism within the promoter of the serotonin transporter gene

Serotonin selective reuptake inhibitors (SSRIs) are the drugs of choice in the treatment of panic disorder (PD). The serotonin transporter (5-HTT) is a prime target for SSRIs. A functional polymorphism within the promoter region of the 5-HTT gene, leading to different transcriptional efficiency, was repeatedly reported to influence the response to SSRIs in mood disorders while the response of patients with OCD seems unrelated. We tested the hypothesis that allelic variation of the 5-HTT promoter could be related to the antipanic response to paroxetine. In total, 92 patients with PD completed a treatment with a variable dose of paroxetine for 12 weeks. The severity of panic-phobic symptomatology was measured before the beginning of the treatment and after 12 weeks. Allelic variation in each subject was determined using a PCR-based method. Both homozygotes for the long variant (l/l) of the 5-HTT promoter and heterozygotes (l/s) showed a better response to paroxetine than homozygotes for the short variant (s/s) (chi(2)=6.9, p<0.03). This result emerged in the whole sample, but was related only to female patients (chi(2)=7.6, p<0.02). The presence of the long allelic variant was associated with a better response of panic attacks while was not significantly associated with the response of anticipatory anxiety or phobic avoidance. In conclusion, paroxetine efficacy in PD seems to be related to allelic variation within the promoter of the 5-HTT gene in female subjects. This gender effect might be related to the genomic effects of sex hormones. Understanding the interaction between gender and genes coding for structures target of psychotropic drugs could help to individualize the pharmacological treatment of PD.

Candidate genes for antidepressant response to selective serotonin reuptake inhibitors

Selective serotonin reuptake inhibitors (SSRIs) can safely and successfully treat major depression, although a substantial number of patients benefit only partially or not at all from treatment. Genetic polymorphisms may play a major role in determining the response to SSRI treatment. Nonetheless, it is likely that efficacy is determined by multiple genes, with individual genetic polymorphisms having a limited effect size. Initial studies have identified the promoter polymorphism in the gene coding for the serotonin reuptake transporter as moderating efficacy for several SSRIs. The goal of this review is to suggest additional plausible polymorphisms that may be involved in antidepressant efficacy. These include genes affecting intracellular transductional cascades; neuronal growth factors; stress-related hormones, such as corticotropin-releasing hormone and glucocorticoid receptors; ion channels and synaptic efficacy; and adaptations of monoaminergic pathways. Association analyses to examine these candidate genes may facilitate identification of patients for targeted alternative therapies. Determining which genes are involved may also assist in identifying future, novel treatments.

Association between serotonin-related genetic polymorphisms and CCK-4-induced panic attacks with or without 5-hydroxytryptophan pretreatment in healthy volunteers

Genetic regulation of the function of serotonin (5-HT) may be important for the neurobiology of panic disorder. In order to evaluate the influence of 5-HT-related gene variants on the vulnerability to panic attacks, we genotyped 32 healthy volunteers who participated in the study of the effect of 5-hydroxytryptophan on panic attacks induced with cholecystokinin tetrapeptide (CCK-4). The polymorphisms of interest included those of 5-HT transporter (5-HTTLPR) and monoamine oxidase A (MAO-A promoter region) genes. The results showed significant associations between certain genotypes and panic rate in females but not in male volunteers. Specifically, there was a significantly lower rate of CCK-4-induced panic attacks in female subjects who had MAO-A longer alleles or 5-HTTLPR short allele gene variants. These data suggest that functional genetic polymorphisms of the 5-HT system may influence the vulnerability to panic attacks and add to the growing evidence of inhibitory function of 5-HT in the neuronal circuitry of panic.

Functional polymorphisms in dopamine and serotonin pathway genes

There is mounting evidence on the functional significance of single nucleotide and simple repeat sequence polymorphisms in both the coding and regulatory regions of genes in the monoamine neurotransmitter pathways. Many of these gene variants have been associated with human behavioral disorders and traits, and thus have important clinical relevance. This review summarizes the literature on the published functional studies from a molecular, cellular, and neurobiological perspective, and notes their possible behavioral consequences. Functional studies have adopted a variety of strategies. Pharmacological studies have focused on the effects of gene variation at the protein level in terms of binding to ligands or drugs. Other key investigations have determined effects on gene expression at the level of transcription in mammalian cell cultures, lymphoblasts, and/or human postmortem brain tissue. This has enabled the comparison of in vitro and in vivo data, and furthermore provides an improved perceptive of their respective advantages. Additionally, molecular biological approaches have identified transcription factors (DNA-binding proteins) that interact with the motifs within the polymorphisms themselves. Various neuroimaging studies have further determined the relationship of genotype with protein availability in the brain, and thus have contributed to our understanding of the in vivo functional significance of gene variants. Finally, there is growing evidence from both human and animal studies on the interaction of functional polymorphisms with the environment in determining a behavioral outcome. Taken together, these findings have contributed to a greater understanding of the plausible molecular mechanisms that underpin the functional significance of polymorphisms in monoamine neurotransmitter pathway genes, and how they may influence behavioral phenotypes.

Serotonin transporter promoter and intron 2 polymorphisms: relationship between allelic variants and gene expression

BACKGROUND

Two polymorphic regions of serotonin transporter (5-HTT) gene: a 44 base pair (bp) insertion/deletion in the promoter region (5-HTTLPR) and a 17 bp variable number of tandem repeats in second intron (VNTR-2), seem to modulate the gene's transcription in allele-dependent manner.

METHODS

We have earlier demonstrated association with 5-HTT gene in families multiply affected by schizophrenia. Here, we investigated separate and combined effects of VNTR-2 and 5-HTTLPR on the rate of peripheral 5-HTT transcription in a sample of offspring from those families. Relative 5-HTT mRNA levels were determined in 53 permanent lymphoblast cell lines by semiquantitative real-time polymerase chain reaction using beta-actin as reference.

RESULTS

Since the low-expressing alleles (short [S], 10) appeared to act dominantly, genotypes were grouped as "high-expressing" (long [L]/L, 12/12) versus "low-expressing" (S, 10). At both loci, nonsignificant differences in 5-HTT mRNA levels ( approximately 30%) were observed between "high"- and "low-expressing" genotypes. In order to search for the potential combined effect of 5-HTTLPR and VNTR-2, levels of 5-HTT mRNA were compared among three groups of samples having "low-expressing" genotype at none, one, or both loci. Increase in number of "low-expressing" genotypes significantly reduced relative 5-HTT gene expression (p <.02).

CONCLUSIONS

Our results indicate weak individual influence, but possible combined effect, of 5-HTTLPR and VNTR-2 polymorphisms on 5-HTT gene expression.

Genetic Predictors of the Clinical Response to Opioid Analgesics

This review uses a candidate gene approach to identify possible pharmacogenetic modulators of opioid therapy, and discusses these modulators together with demonstrated genetic causes for the variability in clinical effects of opioids. Genetically caused inactivity of cytochrome P450 (CYP) 2D6 renders codeine ineffective (lack of morphine formation), slightly decreases the efficacy of tramadol (lack of formation of the active O-desmethyl-tramadol) and slightly decreases the clearance of methadone. MDR1 mutations often demonstrate pharmacogenetic consequences, and since opioids are among the P-glycoprotein substrates, opioid pharmacology may be affected by MDR1 mutations. The single nucleotide polymorphism A118G of the mu opioid receptor gene has been associated with decreased potency of morphine and morphine-6-glucuronide, and with decreased analgesic effects and higher alfentanil dose demands in carriers of the mutated G118 allele. Genetic causes may also trigger or modify drug interactions, which in turn can alter the clinical response to opioid therapy. For example, by inhibiting CYP2D6, paroxetine increases the steady-state plasma concentrations of (R)-methadone in extensive but not in poor metabolisers of debrisoquine/sparteine. So far, the clinical consequences of the pharmacogenetics of opioids are limited to codeine, which should not be administered to poor metabolisers of debrisoquine/sparteine. Genetically precipitated drug interactions might render a standard opioid dose toxic and should, therefore, be taken into consideration. Mutations affecting opioid receptors and pain perception/processing are of interest for the study of opioid actions, but with modern practice of on-demand administration of opioids their utility may be limited to explaining why some patients need higher opioid doses; however, the adverse effects profile may be modified by these mutations. Nonetheless, at a limited level, pharmacogenetics can be expected to facilitate individualised opioid therapy.