Correlations between plasma-neuropeptides and temperament dimensions differ between suicidal patients and healthy controls

Effect of depression and suicidal behavior on neuropeptide Y (NPY) and its receptors in the adult human brain: A postmortem study

Neuropeptides are small proteinaceous molecules (3-100 amino acids) that are secreted by neurons and act on both neuronal and non-neuronal cells. Neuropeptide Y (NPY), a highly conserved and expressed neuropeptide in the central nervous system of mammals, plays a major role in stress response and resilience. Increasing evidence suggests that NPY and its receptors are altered in depression and suicide, pointing to their antidepressant-like nature. The objective of this study was to examine the role of NPY system in depression and suicidal behavior. Expression of NPY and its four receptors, NPY1R, NPY2R, NPY4R, and NPY5R was studied at the transcriptional and translational levels in the prefrontal cortex (PFC) and hippocampus regions of the postmortem brain of normal control (NC) (n = 24) and depressed suicide (DS) (n = 24) subjects. We observed a significant decrease in NPY mRNA and upregulation in NPY1R and NPY2R mRNA in both brain regions of DS subjects compared with NC subjects. We also observed a significant decrease in NPY protein expression in the PFC of subjects with DS. This study provides the first detailed evidence of alterations in the NPY system and the associated stress response in depression and suicidal behavior in humans. The outcomes of this study could be applied in the development of novel NPY system-targeted approaches for the treatment of depression.

Differential associations of phasic and tonic irritability to suicidality among U.S. adults

Research on the relations between irritability and suicidality among adults has rarely compared or differentiated between tonic versus phasic irritability. The current cross-sectional study investigated the role of both tonic and phasic irritability in relation to lifetime suicidal ideation, plans, and attempts. The study included adult participants who completed the suicidality module from the National Comorbidity Survey - Replication (NCS-R) (N = 7683 for suicidal ideation and N = 1223 for suicidal plan and attempt). The NCS-R used lay-administered, standardized diagnostic interviews. Phasic and tonic irritability were assessed with individual screener items from the World Health Organization Composite International Diagnostic Interviews (CIDI). The current study used logistic regression, weighted Cox proportional hazard model, and multinomial logit regression, adjusting for sex, race/ethnicity, age, education, and marital status. Both types of irritability were included simultaneously in the models. Results indicated that both types of irritability were significantly associated with increased odds of suicidal ideation (phasic: Odds Ratio 2.72 [2.35,3.14]); tonic: OR 2.34 [2.04,2.68]), age of first-time suicidal ideation (phasic: Adjusted Hazard Ratio 2.87 [2.27, 3.63]; tonic: AHR 2.12 [1.76,2.54]), and suicide attempt (phasic: OR 1.53 [1.13,2.07]); tonic: OR 1.44 [1.11,1.89]). Only tonic but not phasic irritability was associated with suicide plans (OR 1.39 [1.08,1.79]). When suicide attempts were divided into those that were impulsive versus planned and compared them to no suicide attempt, both types of irritability were associated planned attempts, (phasic: OR 1.53 [1.13,2.07]); tonic: OR 1.44 [1.11,1.89]) but only phasic irritability was related to impulsive attempts (OR 1.70 [1.10,2.64]). Phasic and tonic irritability show differential relations to and can serve as differential markers for suicide-related outcomes in adults.

Neuropeptide Y plasma levels and suicidal behavior in combat veterans

War veterans are at increased risk of suicide that may be related to deployment and/or post-deployment stressors and to adjustment-related factors. The aim of this study was to examine whether levels of plasma neuropeptide Y (NPY) might distinguish combat veterans who have made a post-deployment suicide attempt from those who have never made a suicide attempt. We focused on NPY because of prior findings linking NPY with the neurobiology of resilience, stress-related and other disorders, and suicidal behavior. Demographic and clinical parameters of suicide attempters and non-attempters were assessed and plasma NPY was determined by radioimmunoassay. NPY levels were higher among attempters in comparison to non-attempters, controlling for sex and body-mass index. Suicide attempters had higher Scale for Suicidal Ideation (SSI) scores than non-attempters. There was a positive correlation between NPY levels and SSI scores among non-attempters but not among attempters. Likewise, NPY levels positively correlated with Brown-Goodwin Aggression Scale scores among suicide attempters but not among non-attempters. This is the first demonstration of altered plasma NPY levels in association with suicide attempt history and suicidal ideation in veterans. Our findings suggest that clinical differences between combat veterans with or without a history of suicide attempt may have a neurobiological origin.

The dexamethasone suppression test and DSM-III-R diagnoses in suicide attempters

Previous research on hypothalamic-pituitary adrenal (HPA) axis-activity in suicide attempter research has shown conflicting outcomes. The design of the present study was to test the influence of personality disorders and concominant axis I diagnoses on the dexamethasone suppression diagnostic test by use of multiple regression analyses. The sample consisted of 184 patients with a recent suicide attempt and 42 healthy controls. As expected, the lowest pre- and postdexamethasone cortisol levels were found in patients with personality disorders axis II, cluster B as compared to the other patients. The results remained significant when analysed for covariance with DSM-III-R axis I diagnoses, age or sex. Whether these low cortisol levels are due to previous experience of extreme stressful events or long-lasting burden, or whether they may be a consequence of biogenetic or psychological predisposal of interest, remains to be elucidated. Axis I comorbidity needs to be further examined.

Association between irritability and suicide-related outcomes across the life-course. Systematic review of both community and clinical studies

BACKGROUND

Irritability is gaining considerable attention as a risk factor for suicide-related outcomes (suicide mortality, attempt, and ideation). However, the evidence of this association is scant. We conducted a systematic review of the evidence regarding the associations between irritability and suicide-related outcomes across the life-course.

METHODS

We conducted a systematic search on Medline and PsycINFO (up to January 2018) for original articles published in English investigating the association between irritability and suicide-related outcomes. Two researchers independently screened the articles, assessed the quality of the evidence (New-Castle-Ottawa Scale) and extracted study characteristics.

RESULTS

Thirty-nine studies were retrieved, most were of low/medium quality. Twelve assessed irritability in childhood/adolescence (6 in community samples, 6 in clinical samples) and 27 in adulthood (7 in community samples, 20 in clinical samples). In both childhood/adolescence and adult samples, most community-based studies reported a positive association between irritability and suicidal ideation and/or attempt, while clinical studies reported mixed findings. More specifically, in clinical studies, the association of irritability with suicide-related outcomes (i) was not supported among adult depressed patients, (ii) findings were inconsistent in adult bipolar patients, (iii) for inpatients/outpatients with various psychiatric disorders/conditions, association was observed in adulthood but not in childhood/adolescence.

LIMITATIONS

Differences in methodology and definition/measurement of irritability limited the comparability of included studies.

CONCLUSIONS

Although irritability has been proposed as a promising transdiagnostic factor associated with suicide-related outcomes, the absence of consensus in the definition of irritability (vs anger or reactive/impulsive aggression), the poor methodological quality, and the lack of developmental considerations mitigate the conclusions.

Identifying neuropeptide Y (NPY) as the main stress-related substrate of dipeptidyl peptidase 4 (DPP4) in blood circulation

BACKGROUND

Dipeptidyl peptidase 4 (DPP4; EC 3.4.14.5; CD26) is a membrane-bound or shedded serine protease that hydrolyzes dipeptides from the N-terminus of peptides with either proline or alanine at the penultimate position. Substrates of DPP4 include several stress-related neuropeptides implicated in anxiety, depression and schizophrenia. A decline of DPP4-like activity has been reported in sera from depressed patient, but not fully characterized regarding DPP4-like enzymes, therapeutic interventions and protein.

METHODS

Sera from 16 melancholic- and 16 non-melancholic-depressed patients were evaluated for DPP4-like activities and the concentration of soluble DPP4 protein before and after treatment by anti-depressive therapies. Post-translational modification of DPP4-isoforms and degradation of NPY, Peptide YY (PYY), Galanin-like peptide (GALP), Orexin B (OrxB), OrxA, pituitary adenylate cyclase-activating polypeptide (PACAP) and substance P (SP) were studied in serum and in ex vivo human blood. N-terminal truncation of biotinylated NPY by endothelial membrane-bound DPP4 versus soluble DPP4 was determined in rat brain perfusates and spiked sera.

RESULTS

Lower DPP4 activities in depressed patients were reversed by anti-depressive treatment. In sera, DPP4 contributed to more than 90% of the overall DPP4-like activity and correlated with its protein concentration. NPY displayed equal degradation in serum and blood, and was equally truncated by serum and endothelial DPP4. In addition, GALP and rat OrxB were identified as novel substrates of DPP4.

CONCLUSION

NPY is the best DPP4-substrate in blood, being truncated by soluble and membrane DPP4, respectively. The decline of soluble DPP4 in acute depression could be reversed upon anti-depressive treatment. Peptidases from three functional compartments regulate the bioactivity of NPY in blood.

Neuropeptide Y, social function and long-term outcome in schizophrenia

There is a lack of biomarkers in schizophrenia and the mechanisms underlying the observed deficits in social functioning are poorly understood. This cohort study aimed to explore whether neurotransmitter neuropeptide Y (NPY) in cerebrospinal fluid (CSF) from patients with schizophrenia is correlated to social function and clinical variables. A further aim was to determine whether baseline levels of NPY were associated with subsequent 3-year outcome. Fifty-six consecutively admitted patients with schizophrenia were included and underwent lumbar puncture and symptom ratings before antipsychotic treatment. NPY levels in CSF were determined by radioimmunoassay. Social function (Social Competence and Social Interest) was assessed by Nurses' Observation Scale for Inpatient Evaluation while psychiatric symptoms were rated using the Comprehensive Psychopathological Rating Scale. Three-year outcome was assessed with the Strauss-Carpenter Outcome Scale. Cross-sectional analysis showed a correlation between level of NPY and Social Competence at index admission (r(s)=0.37, p<0.05). The longitudinal analysis (i.e., at the 3-year follow-up) indicated that, for each standard deviation increase in baseline NPY, there was an increased risk of being unemployed (odds ratio [OR] 2.02, 95% confidence interval [CI] 1.07-3.82), having moderate or severe symptoms (OR 3.09, CI 1.30-7.32) or being hospitalized at least 6 months the previous year (OR 3.24, CI 1.09-9.64). However, NPY was not correlated to Social Interest or clinical variables at index admission. In conclusion, NPY levels in CSF are correlated to Social Competence and seem to predict some aspects of longitudinal outcome in schizophrenia.

The role of neuropeptides in suicidal behavior: a systematic review

There is a growing evidence that neuropeptides may be involved in the pathophysiology of suicidal behavior. A critical review of the literature was conducted to investigate the association between neuropeptides and suicidal behavior. Only articles from peer-reviewed journals were selected for the inclusion in the present review. Twenty-six articles were assessed for eligibility but only 22 studies were included. Most studies have documented an association between suicidality and some neuropeptides such as corticotropin-releasing factor (CRF), VGF, cholecystokinin, substance P, and neuropeptide Y (NPY), which have been demonstrated to act as key neuromodulators of emotional processing. Significant differences in neuropeptides levels have been found in those who have attempted or completed suicide compared with healthy controls or those dying from other causes. Despite cross-sectional associations between neuropeptides levels and suicidal behavior, causality may not be inferred. The implications of the mentioned studies were discussed in this review paper.

Suicide risk markers in major depressive disorder: a study of electrodermal activity and event-related potentials

BACKGROUND

Globally approximately 1 million people die annually by suicide. We studied both Electrodermal Activity (EDA) and Event-Related Potential (ERP) P3, together with an assessment of expressed anger as potential suicide risk predictors in Major Depressive Disorder (MDD) patients.

METHODS

In this controlled cross-sectional study, MDD inpatients were allocated to one of three groups: 1. history of 'hard attempted suicide' (e.g., hanging, stabbing; HAS), 2. 'soft attempted suicide' (poisoning; SAS) or 3. no attempted suicide (NAS), respectively. Patients were tested using both an auditory habituation paradigm (study 1) and an 'oddball task' (study 2). EDA Habituation Rate (HabR) and P3 amplitude differences evoked by both 'novel' and 'target' stimuli were computed between the first and second halves of the two studies. 'Anger' was assessed using State Trait Anger Expression Inventory (STAXI) subscales.

RESULTS

HabRs in both HAS (n=16) and SAS (n=16) were significantly lower than in NAS (n=18), in both study 1 and study 2, condition 'novel'. Decreases in P3 were also more pronounced in the HAS and SAS groups in study 1 and in the HAS group in study 2, 'novel' and 'target' condition. STAXI Anger In score was higher in HAS than in NAS.

LIMITATIONS

The sample size is small; medication may influence EDA.

CONCLUSIONS

Both EDA and P3 habituated faster in MDD patients with a history of attempted suicide, and were associated with higher 'anger' scores. Our data is a starting point for developing further neurobiological assessments of suicide risk in clinical practice.

A possible role of neuropeptide Y in depression and stress

Neuropeptide Y (NPY) mediates its physiological effects through at least four receptors known as Y(1), Y(2), Y(4), and Y(5). This peptide is one of the most abundant peptides in the central nervous system and is highly conserved throughout evolution. The most abundant receptors of the NPY family, the Y(1) and Y(2) receptors, are densely expressed in the cortex, hippocampus, and amygdala. These brain regions are particularly associated with mood disorders, stress responses, and memory processing. With this in mind, researchers suggested the involvement of NPY as well as the Y(1) and Y(2) receptors in affective disorders. Earlier studies showed that NPY and the Y(1) and Y(2) receptors mediate some aspects of depression-like disorders and stress responses in rodents. Recent research also suggests the involvement of the Y(4) and Y(5) receptors in emotion-related processes in rodents. In addition, human studies have consistently suggested a role for NPY in stress responses, whereas conflicting data have been obtained in relation to the role of NPY in depression-related illnesses. However, novel evidence from polymorphisms in the prepro-NPY gene has shed new light on the potential clinical relevance of NPY in depression. In this article, we review the literature from both animal and human studies regarding the contribution of NPY and its receptors in depression and stress.

HPA system regulation and adult attachment anxiety: individual differences in reactive and awakening cortisol

Early life experiences can influence hypothalamus-pituitary-adrenal (HPA) axis regulation in adulthood, in both animals and humans. In humans, they have also been shown to influence adult attachment styles. However, the relationship between adult attachment styles and HPA axis regulation is largely unexplored. The present study investigated the relationship among varying levels of attachment anxiety and avoidance with both the cortisol response to acute stress (CRS) and the cortisol response to awakening (CRA) in 48 adult women. Attachment-unrelated stress was induced by a laboratory stress task. Saliva for free cortisol assessment was sampled before and after the stress task in the laboratory and at home on 2 consecutive days in the morning after awakening. We found that attachment anxiety but not attachment avoidance was associated with cortisol measures. Attachment anxiety was positively correlated with CRS and negatively with CRA. Finally, the two cortisol parameters were negatively associated with one another. The results are discussed with respect to (1) recent findings suggesting that the HPA system and hippocampus are programmed during critical development periods, establishing a certain trajectory of physiological responsiveness throughout life, and (2) a model that links development of the hippocampus with self development.

Towards a possible aetiology for depressions?

BACKGROUND

Since a genetic disposition for depression is probable, there ought to be biochemical changes. Increased peptide levels with relevant bioactivities have been found in urine in a previous investigation, which may be such changes.

METHODS

Urine from patients with severe depression according to ICD 10 have been run on reversed phase High Performance Liquid Chromatography, and off line mass spectrometry was performed on some of these peptides.

RESULTS

We find overlapping patterns of peptide peaks in severe depression, but with considerable individuality. Mass spectrometry shows that some of these peptides are probably of dietary origin, because their sequences are found only in certain dietary proteins. Opioids from casein and gliadin are typical examples.

CONCLUSION

Our data show that the disposition must be polygenetic because some peptide peaks with the same bioactivity are of different length in different patients, but with the same diagnosis. However, some of the peaks are common Peptide increase in urine is found when break down is deficient, and the data presented agree with reports on peptidase deficiencies in depression. Antidepressant drugs decrease the peptide level after about 3 weeks.

The Role of Alcohol and Steroid Hormones in Human Aggression

The association between alcohol and aggressive behavior is well established although a direct causal relationship has proven hard to demonstrate. There are, however, indications that alcohol facilitates aggression in individuals who already have a predisposition to behave aggressively. Aggressive personality disorders have in turn been explained by elevated testosterone level. A one-to-one relation between increased levels of testosterone and aggression has been, nevertheless, difficult to reveal. Two metabolites of testosterone, estradiol and 5alpha-dihydrotestosterone (DHT), have been studied much less in human aggressive behavior. Estradiol might reduce androgenic effects and have a counterbalancing influence on aggression. DHT, again, has a much higher affinity than testosterone to androgen receptors, and there are indications that some of the effects of testosterone-mediating aggressive behavior occur after aromatization. Disregard of seasonal and circadian fluctuations in male testosterone production might be responsible for some of the inconclusive testosterone-aggression results. In addition, increasing age decreases both aggressive behavior and testosterone production in males. Cortisol has yielded conflicting results as a mediator in aggressive behavior. Both higher and lower levels have been reported in aggressive and abusive men. Finally, the acute and chronic effects of alcohol influence the steroid hormone levels in various ways. The present understanding of the etiology of aggression is still vague. It is clear that a multidimensional approach, combining both biological and psychosocial factors, will be necessary for the development of a more general concept of human aggression in the future.

The NPY system in stress, anxiety and depression

NPY antagonizes behavioral consequences of stress through actions within the brain. Behavioral anti-stress actions of NPY are noteworthy in that (1) their magnitude surpasses that of other endogenous compounds; (2) they are produced across a wide range of animal models, normally thought to reflect different aspects of emotionality. This suggests that NPY acts with a high potency on a common core mechanism of emotionality and behavioral stress responses. Behavioral studies in genetically modified animals support this hypothesis. Increased emotionality is seen upon inactivation of NPY transmission, while the opposite is found when NPY signalling is made overactive. Several brain structures are involved in mediating anti-stress actions of NPY, with the most extensive evidence available for amygdala and hippocampus, and some evidence for regions within the septum, and locus coeruleus. Antistress actions of NPY are mimicked by Y1-receptor agonists, and blocked by Y1 antagonists, although Y5 receptors may substitute for Y1 actions in some cases. Blockade of Y2 receptors produces anti-stress effects indistinguishable from those produced by Y1 agonism, presumably through potentiation of presynaptic release of endogenous NPY. Together, available data point to the potential of the NPY system as a target for novel pharmacological treatments of stress-related disorders, including anxiety and depression. Development of Y2 antagonists presently appears to offer the most promising strategy for developing these clinical treatments.

Neuropeptide Y (NPY) and depression: from animal studies to the human condition

Neuropeptide Y (NPY) is widely distributed throughout the central nervous system (CNS) and is one of the most conserved peptides in evolution, suggesting an important role in the regulation of basic physiological functions. In addition, both pre-clinical and clinical evidence have suggested that NPY, together with its receptors, may have a direct implication in several psychiatric disorders, including depression and related illnesses. NPY-like immunoreactivity and NPY receptors are expressed throughout the brain, with varying concentrations being found throughout the limbic system. Such brain structures have been repeatedly implicated in the modulation of emotional processing, as well as in the pathogenesis of depressive disorders. This review will concentrate on the distribution of NPY, its receptors, and the putative role played by this peptide in depressive illness based on both pre-clinical and clinical evidence.