Metabolic syndrome (MetS) is a complex disorder defined by a cluster of interconnected factors that increase the risk of cardiovascular atherosclerotic diseases and diabetes mellitus type 2. Currently, several different definitions of MetS exist, causing substantial confusion as to whether they identify the same individuals or represent a surrogate of risk factors. Recently, a number of other factors besides those traditionally used to define MetS that are also linked to the syndrome have been identified. In this review, we critically consider existing definitions and evolving information, and conclude that there is still a need to develop uniform criteria to define MetS, so as to enable comparisons between different studies and to better identify patients at risk. As the application of the MetS model has not been fully validated in children and adolescents as yet, and because of its alarmingly increasing prevalence in this population, we suggest that diagnosis, prevention and treatment in this age group should better focus on established risk factors rather than the diagnosis of MetS.

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Early life stressors display a high universal prevalence and constitute a major public health problem. Prolonged psychoneurobiological alterations as sequelae of early life stress (ELS) could represent a developmental risk factor and mediate risk for disease, leading to higher physical and mental morbidity rates in later life. ELS could exert a programming effect on sensitive neuronal brain networks related to the stress response during critical periods of development and thus lead to enduring hyper- or hypo-activation of the stress system and altered glucocorticoid signaling. In addition, alterations in emotional and autonomic reactivity, circadian rhythm disruption, functional and structural changes in the brain, as well as immune and metabolic dysregulation have been lately identified as important risk factors for a chronically impaired homeostatic balance after ELS. Furthermore, human genetic background and epigenetic modifications through stress-related gene expression could interact with these alterations and explain inter-individual variation in vulnerability or resilience to stress. This narrative review presents relevant evidence from mainly human research on the ten most acknowledged neurobiological allostatic pathways exerting enduring adverse effects of ELS even decades later (hypothalamic-pituitary-adrenal axis, autonomic nervous system, immune system and inflammation, oxidative stress, cardiovascular system, gut microbiome, sleep and circadian system, genetics, epigenetics, structural, and functional brain correlates). Although most findings back a causal relation between ELS and psychobiological maladjustment in later life, the precise developmental trajectories and their temporal coincidence has not been elucidated as yet. Future studies should prospectively investigate putative mediators and their temporal sequence, while considering the potentially delayed time-frame for their phenotypical expression. Better screening strategies for ELS are needed for a better individual prevention and treatment.

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Chronic distress contributes to the development of obesity and comorbid states. Stress is the disturbance of the complex dynamic equilibrium that all organisms must maintain, and is associated with activation of the Stress system comprising of the hypothalamic-pituitary-adrenal axis and the arousal/sympathetic nervous systems. The stress system functions in a baseline circadian fashion and interacts with other systems of the organism to regulate a variety of behavioral, endocrine, metabolic, immune and cardiovascular functions. The experience of perceived or real uncontrollable intense and/or chronic stress (distress) may lead to several psychopathologic conditions, including anxiety, depressive and psychosomatic disorders, substance abuse, obesity and the metabolic syndrome, and osteoporosis, as well as impaired reproductive and immune functions. Developing children and adolescents are particularly vulnerable to the effects of chronic stress. Both behavioral and biological pathways are involved in the connection between chronic stress and obesity in adults and children. Emotional "comfort" eating, lack of sleep, impulsive behaviours and selection of specific foods often characterize stressed individuals. In addition to specific behaviours, dysregulation of the stress system through increased secretion of cortisol and catecholamines, especially in the evening hours, and in concert with concurrently elevated insulin concentrations, leads to development of central obesity, insulin resistance and the metabolic syndrome. In children, chronic alterations in cortisol secretion may have additional effects on cognitive and emotional development, timing of puberty and final stature. Obese children and adolescents are frequently entangled in a vicious cycle between distress, impairing self-image and distorted self-image, maintaining and worsening distress.

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Diverse patterns of cortisol secretion with consistently high circulating catecholamines have been reported in post-traumatic stress disorder (PTSD), an anxiety state that develops after exposure to traumatic life events. Indeed, peripheral cortisol levels have been reported to be low or normal in the majority of adult chronic PTSD studies, whereas, in most paediatric studies, high cortisol values have been documented. Longitudinal studies on PTSD biology, including the transition from childhood to adulthood, may shed light on these discrepancies. In children, elevated evening salivary cortisol in the aftermath of the trauma was predictive of PTSD development 6 months later, whereas plasma interleukin-6 correlated positively with evening cortisol and was equally predictive of later PTSD. Longitudinal assessment of PTSD children 1 and 6 months later revealed progressive normalisation of cortisol levels, whereas noradrenaline concentrations became gradually higher. We hypothesise that, in adults with chronic PTSD, low cortisol levels, together with high catecholamines, may reflect a late event in the natural history of the disorder, months or years after the trauma. The progressive divergence of cortisol and noradrenaline concentrations over time may be responsible for PTSD maintenance in children and explain the differences between the child and adult PTSD endophenotypes. In adults studied immediately after the trauma, and by contrast to children, low cortisol levels are predictive of later PTSD development. Our hypothesis that low cortisol levels may reflect a previous trauma, earlier in development, is supported by the well established observation that prior trauma is a risk factor for a new PTSD diagnosis. The developmental stage of an individual in relation to previous exposure to trauma and PTSD vulnerability are crucial variables that may determine clinical and biological PTSD phenotypes and explain the discrepancies between adults and children in reported cortisol levels.

Glucocorticoids play central roles in the regulation of energy metabolism by shifting it toward catabolism, whereas AMP-activated protein kinase (AMPK) is the master regulator of energy homeostasis, sensing energy depletion and stimulating pathways of increasing fuel uptake and saving on peripheral supplies. We showed here that AMPK regulates glucocorticoid actions on carbohydrate metabolism by targeting the glucocorticoid receptor (GR) and modifying transcription of glucocorticoid-responsive genes in a tissue- and promoter-specific fashion. Activation of AMPK in rats reversed glucocorticoid-induced hepatic steatosis and suppressed glucocorticoid-mediated stimulation of glucose metabolism. Transcriptomic analysis in the liver suggested marked overlaps between the AMPK and glucocorticoid signaling pathways directed mostly from AMPK to glucocorticoid actions. AMPK accomplishes this by phosphorylating serine 211 of the human GR indirectly through phosphorylation and consequent activation of p38 MAPK and by altering attraction of transcriptional coregulators to DNA-bound GR. In human peripheral mononuclear cells, AMPK mRNA expression positively correlated with that of glucocorticoid-responsive glucocorticoid-inducible leucine zipper protein, which correlated also positively with the body mass index of subjects. These results indicate that the AMPK-mediated energy control system modulates glucocorticoid action at target tissues. Because increased action of glucocorticoids is associated with the development of metabolic disorders, activation of AMPK could be a promising target for developing pharmacological interventions to these pathologies.