The potential of oxytocin as a therapeutic target for psychiatric disorders

Genetic Variations in Elements of the Oxytocinergic Pathway are Associated with Attention/Hyperactivity Problems and Anxiety Problems in Childhood

Genetic alterations related to oxytocin system seem to influence the neurobiology of attention-deficit hyperactivity disorder and anxiety problems leading to greater functional, social and emotional impairment. Here, we analyzed the association of OXTR rs2254298 and CD38 rs6449182 variants with attention/hyperactivity problems and anxiety problems in children. The study enrolled 292 children and adjusted regression model revealed OXTR rs2254298 AA genotype as a risk factor for attention deficit/hyperactivity problems (PR: 2.37; PadjFDR = 0.006), attention problems (PR: 2.71; PadjFDR = 0.003) and anxiety problems (PR: 1.92; PadjFDR = 0.018). CD38 rs6449182 G allele showed as a risk factor for attention deficit/hyperactivity problems (PR: 1.56; PadjFDR = 0.028). Moreover, in silico approach for regulatory roles found markers that influence chromatin accessibility and transcription capacity. Together, these data provide genetic information of oxytocin in developmental and behavioral disorders opening a range of opportunities for future studies that clarify their neurobiology in childhood.

Structure-function relationships of the disease-linked A218T oxytocin receptor variant

Various single nucleotide polymorphisms (SNPs) in the oxytocin receptor (OXTR) gene have been associated with behavioral traits, autism spectrum disorder (ASD) and other diseases. The non-synonymous SNP rs4686302 results in the OXTR variant A218T and has been linked to core characteristics of ASD, trait empathy and preterm birth. However, the molecular and intracellular mechanisms underlying those associations are still elusive. Here, we uncovered the molecular and intracellular consequences of this mutation that may affect the psychological or behavioral outcome of oxytocin (OXT)-treatment regimens in clinical studies, and provide a mechanistic explanation for an altered receptor function. We created two monoclonal HEK293 cell lines, stably expressing either the wild-type or A218T OXTR. We detected an increased OXTR protein stability, accompanied by a shift in Ca²⁺ dynamics and reduced MAPK pathway activation in the A218T cells. Combined whole-genome and RNA sequencing analyses in OXT-treated cells revealed 7823 differentially regulated genes in A218T compared to wild-type cells, including 429 genes being associated with ASD. Furthermore, computational modeling provided a molecular basis for the observed change in OXTR stability suggesting that the OXTR mutation affects downstream events by altering receptor activation and signaling, in agreement with our in vitro results. In summary, our study provides the cellular mechanism that links the OXTR rs4686302 SNP with genetic dysregulations associated with aspects of ASD.

Intranasal Oxytocin Restores Maternal Behavior and Oxytocin Neuronal Activity in the Supraoptic Nucleus in Rat Dams with Cesarean Delivery

Oxytocin (OT) is a key factor for maternal behavior. However, neurochemical regulation of OT neurons, the major source of OT, remains incompletely understood. Here we report the effect of intranasally-applied OT (IAO) on OT neuronal activity in the supraoptic nucleus (SON) and on maternal behavior in a rat model of cesarean delivery (CD) at day 4-5 (stage I) and day 8-9 (stage II) following delivery. We found that at stage I, CD dams exhibited significantly longer latency of pup retrieval, lower number of anogenital licks and smaller acinar area of the mammary glands. In the SON, the number of OT neurons expressing phosphorylated extracellular signal-regulated protein kinase 1/2 (pERK 1/2) decreased significantly. IAO reversed the depressive-like maternal behavior and involution-like change in the mammary glands, and restored the number of pERK1/2-positive OT neurons in CD dams. At stage II, CD did not significantly influence the latency of retrieval and pERK1/2 expression in the SON. However, CD still reduced the number of anogenital licks during suckling, which was reversed by IAO. Notably, IAO but not hypodermic OT application in CD dams significantly increased litter's body weight gains. In brain slices, CD but not CD plus IAO significantly depolarized membrane potential and increased spike duration in OT neurons. In vasopressin neurons, CD, but not CD plus IAO, significantly depolarized membrane potential and increased the firing rate. Thus, decreased OT neuronal activity and increased vasopressin neuronal activity impair maternal behavior in CD dams, which can be prevented by IAO .

Intranasal oxytocin has sympathoexcitatory effects on vascular tone in healthy males

Oxytocin appears to be involved in the neuroendocrine regulation of sympathetic blood pressure (BP) homeostasis. In animals, intracerebral administration of oxytocin induces BP-relevant sympathetic activation. In humans, central nervous effects of oxytocin on BP regulation remain unclear. Intranasal administration supposedly delivers oligopeptides such as oxytocin directly to the brain. We investigated the effects of intranasal oxytocin on sympathetic vascular baroreflex function in humans using microneurographic techniques. In a balanced, double-blind crossover design, oxytocin or placebo was administered intranasally to 12 lean, healthy males (age 25 ± 4 yr). Muscle sympathetic nerve activity (MSNA) was assessed microneurographically before (presubstance), 30-45 min (postsubstance I), and 105-120 min (postsubstance II) after oxytocin administration. Baroreflex was challenged via graded infusions of vasoactive drugs, and correlation of BP with MSNA and heart rate (HR) defined baroreflex function. Experiments were conducted in the afternoon after a 5-h fasting period. After oxytocin, resting MSNA (burst rate and total activity) showed significant net increases from pre to postsubstance II compared with placebo [Δincrease = +4.3 ± 1.2 (oxytocin) vs. +2.2 ± 1.4 bursts/min (placebo), ANOVA; P < 0.05; total activity = 184 ± 11.5% (oxytocin) vs. 121 ± 14.3% (placebo), ANOVA; P = 0.01). This was combined with a small but significant net increase in resting diastolic BP, whereas systolic and mean arterial BP or HR as well as baroreflex sensitivity at vasoactive drug challenge were not altered. Intranasally administered oxytocin induced vasoconstrictory sympathoactivation in healthy male humans. The concomitant increase of diastolic BP was most likely attributable to increased vascular tone. This suggests oxytocin-mediated upward resetting of the vascular baroreflex set point at centers superordinate to the mere baroreflex-feedback loop.

Oxytocin may have a therapeutical potential against cardiovascular disease. Possible pharmaceutical and behavioral approaches

Based on the ancient role of oxytocin and its homologues as amplifiers of reproduction we argue for an evolutionary coupling of oxytocin to signaling pathway which support restorative mechanisms of cells and tissue. In particular, the survival and function of different categories of stem cells and primordial cells are enhanced by mitogen-activated protein kinase (MAPK) pathways. Furthermore, oxytocin stimulates the AMP-activated protein kinase pathway (AMPK) in numerous of cell types which promotes the maintenance of different cell structures. This involves autophagic processes and, in particular, may support the renewal of mitochondria. Mitochondrial fitness may protect against oxidative and inflammatory stress - a well-documented effect of oxytocin. The combined specific trophic and protective effects oxytocin may delay several degenerative phenomena including sarcopenia, type-2 diabetes and atherosclerosis. These effects may be exerted both on a central level supporting the function and integrity of the hypothalamus and peripherally acting directly on blood vessels, pancreas, heart, skeletal muscles and adipose tissue etc. Furthermore, in the capacity of being both a hormone and neuromodulator, oxytocin interacts with numerous of regulatory mechanisms particularly the autonomic nervous system and HPA-axis which may reduce blood pressure and affect the immune function. The potential of the oxytocin system as a behavioral and molecular target for the prevention and treatment of cardiovascular disease is discussed. Focus is put on the affiliative and sexual significance and the different options and limitations associated with a pharmaceutical approach. MeSH: Aging, Atherosclerosis, Heart, Hypothalamus, Inflammation, Love, Orgasm, Oxytocin.

De Novo Protein Synthesis Mediated by the Eukaryotic Elongation Factor 2 Is Required for the Anxiolytic Effect of Oxytocin

BACKGROUND

The neuropeptide oxytocin (OXT) mediates its actions, including anxiolysis, via its G protein-coupled OXT receptor. Within the paraventricular nucleus of the hypothalamus (PVN), OXT-induced anxiolysis is mediated, at least in part, via activation of the mitogen-activated protein kinase pathway following calcium influx through transient receptor potential cation channel subfamily V member 2 channels. In the periphery, OXT activates eukaryotic elongation factor 2 (eEF2), an essential mediator of protein synthesis.

METHODS

In order to study whether OXT activates eEF2 also in neurons to exert its anxiolytic properties in the PVN, we performed in vivo and cell culture experiments.

RESULTS

We demonstrate that OXT, in a protein kinase C-dependent manner, activates eEF2 both in a hypothalamic cell line and in vivo within the PVN. Next, we reveal that OXT stimulates de novo protein synthesis, while inhibition of protein synthesis within the PVN prevents the anxiolytic effect of OXT in male rats. Moreover, activation of eEF2 within the PVN conveyed an anxiolytic effect supporting a role of OXT-induced eEF2 activation and protein synthesis for its anxiolysis. Finally, we show that one of the proteins that is upregulated by OXT is the neuropeptide Y receptor 5. Infusion of a specific neuropeptide Y receptor 5 agonist into the PVN consequently led to decreased anxiety-related behavior, while pretreatment with a neuropeptide Y receptor 5 antagonist prevented the anxiolytic effect of OXT.

CONCLUSIONS

Taken together, these results show that OXT recruits several intracellular signaling cascades to induce protein synthesis, which mediates the anxiolytic effects of OXT within the PVN and suggests that eEF2 represents a novel target for anxiety-related disorders.

Prosocial effects of an oxytocin metabolite, but not synthetic oxytocin receptor agonists, in a mouse model of autism

Currently, there are no established pharmaceutical strategies that effectively treat social deficits in autism spectrum disorder (ASD). Oxytocin, a neurohormone that plays a role in multiple types of social behaviors, has been proposed as a possible therapeutic against social impairment and other symptoms in ASD. However, from the standpoint of pharmacotherapy, oxytocin has several liabilities as a standard clinical treatment, including rapid metabolism, low brain penetrance, and activity at the vasopressin (antidiuretic hormone) receptors. The present studies describe findings from a preclinical screening program to evaluate oxytocin receptor (OXTR) agonists and oxytocin metabolites for potential clinical use as more optimal treatments. We first investigated two synthetic oxytocin analogs, TC-OT-39 and carbetocin, using in vitro cell-based assays for pharmacological characterization and behavioral tests in the BALB/cByJ mouse model of ASD-like social deficits. Although both TC-OT-39 and carbetocin selectively activate the OXTR, neither synthetic agonist had prosocial efficacy in the BALB/cByJ model. We next evaluated two oxytocin metabolites: OT(4-9) and OT(5-9). While OT(5-9) failed to affect social deficits, the metabolite OT(4-9) led to significant social preference in the BALB/cByJ model, in a dose-dependent manner. The increased sociability was observed at both 24 h and 12 days following the end of a subchronic regimen with OT(4-9) (2.0 mg/kg). Overall, these results suggest that the prosocial effects of oxytocin could be mediated by downstream activity of oxytocin metabolites, raising the possibility of new pathways to target for drug discovery relevant to ASD.

Oxytocin and Stress-related Disorders: Neurobiological Mechanisms and Treatment Opportunities

Novel pharmacotherapies that improve outcomes for individuals with stress-related psychiatric disorders are needed. The neurohormone oxytocin (OT) is a promising candidate given its influence on the social-emotional brain. In this review, we present an overview of evidence supporting OT's utility for treating major depressive disorder and posttraumatic stress disorder. We first discuss endogenous OT, which research suggests is not yet a reliable biomarker of stress-related disorders. Second, we review effects of intranasal (IN) OT on processes relevant to stress-related disorders in healthy populations (anhedonia, reward processing, psychosocial stress reactivity, fear/anxiety, and social behavior) and their neurobiological mechanisms (e.g., the salience network and hypothalamic-pituitary-adrenal axis). Third, we present the sparse but promising findings from clinical populations, followed by discussion of critical moderating variables to consider in the service of maximizing the therapeutic potential of OT (e.g., patient sex and child maltreatment). We also identify heterogeneous findings and limitations of existing research, including reliance on single-dose studies in psychiatrically healthy samples and unanswered questions regarding the effectiveness of IN drug delivery and dosing schedules. Well-controlled multidose studies including women and measures of potentially moderating variables are sorely needed and would inform our understanding of the utility of OT for preventing and treating stress-related psychiatric disorders.