Action of glucagon-like peptide 1 and glucose levels on corticotropin-releasing factor and vasopressin gene expression in rat hypothalamic 4B cells

Hypothalamic Regulation of Corticotropin-Releasing Factor under Stress and Stress Resilience

This review addresses the molecular mechanisms of corticotropin-releasing factor (CRF) regulation in the hypothalamus under stress and stress resilience. CRF in the hypothalamus plays a central role in regulating the stress response. CRF stimulates adrenocorticotropic hormone (ACTH) release from the anterior pituitary. ACTH stimulates glucocorticoid secretion from the adrenal glands. Glucocorticoids are essential for stress coping, stress resilience, and homeostasis. The activated hypothalamic-pituitary-adrenal axis is suppressed by the negative feedback from glucocorticoids. Glucocorticoid-dependent repression of cAMP-stimulated Crf promoter activity is mediated by both the negative glucocorticoid response element and the serum response element. Conversely, the inducible cAMP-early repressor can suppress the stress response via inhibition of the cAMP-dependent Crf gene, as can the suppressor of cytokine signaling-3 in the hypothalamus. CRF receptor type 1 is mainly involved in a stress response, depression, anorexia, and seizure, while CRF receptor type 2 mediates “stress coping” mechanisms such as anxiolysis in the brain. Differential effects of FK506-binding immunophilins, FKBP4 and FKBP5, contribute to the efficiency of glucocorticoids under stress resilience. Together, a variety of factors contribute to stress resilience. All these factors would have the differential roles under stress resilience.

Insights into a possible role of glucagon-like peptide-1 receptor agonists in the treatment of depression

Depression is a highly prevalent mood disorder and one of the major health concerns in modern society. Moreover, it is characterized by a high prevalence of coexistence with many other diseases including metabolic disorders such as type 2 diabetes mellitus (T2DM) and obesity. Currently used antidepressant drugs, which mostly target brain monoaminergic neurotransmission, have limited clinical efficacy. Although the etiology of depression has not been fully elucidated, current scientific data emphasize the role of neurotrophic factors deficiencies, disturbed homeostasis between the nervous system and the immune and endocrine systems, as well as disturbances in brain energy metabolism and dysfunctions in the gut-brain axis as important factors in the pathogenesis of this neuropsychiatric disorder. Therefore, therapeutic options that could work in a way other than classic antidepressants are being sought to increase the effectiveness of the treatment. Interestingly, glucagon-like peptide-1 receptor agonists (GLP-1RAs), used in the treatment of T2DM and obesity, are known to show pro-cognitive and neuroprotective properties, and exert modulatory effects on immune, endocrine and metabolic processes in the central nervous system. This review article discusses the potential antidepressant effects of GLP-1RAs, especially in the context of their action on the processes related to neuroprotection, inflammation, stress response, energy metabolism, gut-brain crosstalk and the stability of the gut microbiota.

GLP-1 receptor agonists do not affect sodium intake: Exploratory analyses from two randomized clinical trials

OBJECTIVES

Excessive sodium intake, despite current dietary advice, remains a global issue with cardiovascular and renal consequences. The aim of this study was to determine whether glucagon-like peptide receptor agonists (GLP-1 RAs), used as antihyperglycemic agents for type 2 diabetes (T2DM) management, may reduce salt cravings as they are known to reduce hedonic feeding behavior and are involved in sodium homeostasis by increasing renal sodium excretion.

METHODS

We performed exploratory analyses using data from two randomized, clinical crossover trials, which primarily aimed to assess the effects of GLP-1 RAs on central satiety and reward circuits and subsequent related feeding behavior. In study A, healthy, obese individuals and patients with T2DM were randomly assigned to receive intravenous administration of placebo or GLP-1 RA exenatide with or without concurrent GLP-1 receptor blockade, on separate testing days. In study B, individuals with T2DM randomly received GLP-1 RA liraglutide (titrated up to 1.8 mg daily) or titrated insulin glargine for 12 wk. In both studies, participants received an ad libitum mixed meal that served to calculate sodium intake. Moreover, salt craving was scored using a Likert scale.

RESULTS

In study A, acute exenatide, parallel to reduced total food intake, reduced sodium intake in all studied groups by up to 30%. In study B, prolonged liraglutide treatment did not affect sodium or total caloric intake. Neither acute exenatide nor prolonged liraglutide treatment affected salt craving as measured by the Likert scale.

CONCLUSION

Acute exenatide reduced sodium intake in light of a generalized reduction in food ingestion, while prolonged intervention with liraglutide did not lower sodium intake. Neither intervention affected salt craving. Given the known effects of these drugs on renal sodium excretion, blood pressure, and renal and cardiovascular outcome, it seems plausible to perform dedicated mechanistic studies in humans to assess the effects of GLP-1 RA administration on sodium balance.

Chronic Suppression of Glucagon-Like Peptide-1 Receptor (GLP1R) mRNA Translation in the Rat Bed Nucleus of the Stria Terminalis Reduces Anxiety-Like Behavior and Stress-Induced Hypophagia, But Prolongs Stress-Induced Elevation of Plasma Corticosterone

The anterior lateral bed nucleus of the stria terminalis (alBST) expresses glucagon-like peptide-1 receptors (GLP1Rs) and receives input from caudal brainstem GLP1 neurons. GLP1 administered centrally reduces food intake and increases anxiety-like behavior and plasma corticosterone (cort) levels in rats, whereas central GLP1R antagonism has opposite effects. Anxiogenic threats and other stressors robustly activate c-fos expression in both GLP1-producing neurons and also in neurons within alBST subregions expressing GLP1R. To examine the functional role of GLP1R signaling within the alBST, adult male Sprague Dawley rats received bilateral alBST-targeted injections of an adeno-associated virus (AAV) vector expressing short hairpin RNA (shRNA) to knock down the translation of GLP1R mRNA (GLP1R-KD rats), or similar injections of a control AAV (CTRL rats). In situ hybridization revealed that GLP1R mRNA is expressed in a subset of GABAergic alBST neurons, and quantitative real-time PCR confirmed that GLP1R-KD rats displayed a significant 60% reduction in translatable GLP1R mRNA. Compared with CTRL rats, GLP1R-KD rats gained more body weight over time and displayed less anxiety-like behavior, including a loss of light-enhanced acoustic startle and less stress-induced hypophagia. Conversely, while baseline plasma cort levels were similar in GLP1R-KD and CTRL rats, GLP1R-KD rats displayed a prolonged stress-induced elevation of plasma cort levels. GLP1R-KD and CTRL rats displayed similar home cage food intake and a similar hypophagic response to systemic Exendin-4, a GLP1R agonist that crosses the blood-brain barrier. We conclude that GLP1R expressed within the alBST contributes to multiple behavioral responses to anxiogenic threats, yet also serves to limit the plasma cort response to acute stress.SIGNIFICANCE STATEMENT Anxiety is an affective and physiological state that supports threat avoidance. Identifying the neural bases of anxiety-like behaviors in animal models is essential for understanding mechanisms that contribute to normative and pathological anxiety in humans. In rats, anxiety/avoidance behaviors can be elicited or enhanced by visceral or cognitive threats that increase glucagon-like peptide-1 (GLP1) signaling from the caudal brainstem to the hypothalamus and limbic forebrain. Data reported here support a role for limbic GLP1 receptor signaling to enhance anxiety-like behavior and to attenuate stress-induced elevations in plasma cort levels in rats. Improved understanding of central GLP1 neural pathways that impact emotional responses to stress could expand potential therapeutic options for anxiety and other stress-related disorders in humans.

Hypothalamic insulin and glucagon-like peptide-1 levels in an animal model of depression and their effect on corticotropin-releasing hormone promoter gene activity in a hypothalamic cell line

BACKGROUND

In depression, excessive glucocorticoid action may cause maladaptive brain changes, including in the pathways controlling energy metabolism. Insulin and glucagon-like peptide-1 (GLP-1), besides regulation of glucose homeostasis, also possess neurotrophic properties. Current study was aimed at investigating the influence of prenatal stress (PS) on insulin, GLP-1 and their receptor (IR and GLP-1R) levels in the hypothalamus. GLP-1 and GLP-1R were assayed also in the hippocampus and frontal cortex - brain regions mainly affected in depression. The second objective was to determine the influence of exendin-4 and insulin on CRH promoter gene activity in in vitro conditions.

METHODS

Adult male PS rats were subjected to acute stress and/or received orally glucose. Levels of hormones and their receptors were assayed with ELISA method. In vitro studies were performed on mHypoA-2/12 hypothalamic cell line, stably transfected with CRH promoter coupled with luciferase.

RESULTS

PS has reduced GLP-1 and GLP-1R levels, attenuated glucose-induced increase in insulin concentration and increased the amount of phosphorylated IR in the hypothalamus of animals subjected to additional stress stimuli, and also decreased the GLP-1R level in the hippocampus. In vitro studies demonstrated that insulin is capable of increasing CRH promoter activity in the condition of stimulation of the cAMP/PKA pathway in the applied cellular model.

CONCLUSION

Prenatal stress may act as a preconditioning factor, affecting the concentrations of hormones such as insulin and GLP-1 in the hypothalamus in response to adverse stimuli. The decreased GLP-1R level in the hippocampus could be linked with the disturbances in neuronal plasticity.

Vasopressin: physiology, assessment and osmosensation

Vasopressin (AVP) plays a major role in the regulation of water and sodium homeostasis by its antidiuretic action on the kidney, mediated by V2 receptors. AVP secretion is stimulated by a rise in plasma osmolality, a decline in blood volume or stress. V1a receptors are expressed in vascular smooth muscle cells, but the role of vasopressin in blood pressure regulation is still a matter of debate. AVP may also play a role in some metabolic pathways, including gluconeogenesis, through its action on V1a receptors expressed in the liver. It is now understood that thirst and arginine vasopressin (AVP) release are regulated not only by the classical homeostatic, intero-sensory plasma osmolality negative feedback, but also by novel, extero-sensory, anticipatory signals. AVP measurement is time-consuming, and AVP level in the blood in the physiological range is often below the detection limit of the assays. Recently, an immunoassay has been developed for the measurement of copeptin, a fragment of the pre-provasopressin molecule that is easier to measure. It has been shown to be a good surrogate marker of AVP.

Copeptin, insulin-like growth factor binding protein-1 and sitagliptin: A report from the BEta-cell function in Glucose abnormalities and Acute Myocardial Infarction study

PURPOSE

To investigate whether sitagliptin affects copeptin and osmolality, suggesting arginine vasopressin activation and a potential for fluid retention, compared with placebo, in patients with a recent acute coronary syndrome and newly discovered type 2 diabetes or impaired glucose tolerance. A second aim was to confirm whether copeptin correlated with insulin-like growth factor binding protein-1.

METHODS

Fasting blood samples were used from the BEta-cell function in Glucose abnormalities and Acute Myocardial Infarction trial, in which patients recently hospitalized due to acute coronary syndrome and with newly detected abnormal glucose tolerance were randomized to sitagliptin 100 mg once daily (n = 34) or placebo (n = 37). Copeptin, osmolality and insulin-like growth factor binding protein-1 were analysed at baseline and after 12 weeks.

RESULTS

Copeptin and osmolality were unaffected by sitagliptin. There was no correlation between copeptin and insulin-like growth factor binding protein-1.

CONCLUSION

Sitagliptin therapy does not appear to be related to activation of the arginine vasopressin system.

Diurnal salivary cortisol, glycemia and insulin resistance: The multi-ethnic study of atherosclerosis

Hypercortisolism is associated with insulin resistance (IR) and diabetes mellitus (DM); however, to our knowledge prior studies have not examined the association of diurnal cortisol curve features with measures of glycemia or IR in a population-based setting. Using log-transformed salivary cortisol data on 850 ethnically diverse men and women from the Multi-Ethnic Study of Atherosclerosis, we investigated the cross-sectional association of cortisol curve features with (1) glycemia in those with and without DM and (2) IR, in non-diabetic subjects. The log-transformed salivary cortisol curve features included wake-up cortisol, cortisol awakening response (CAR), early decline slope (30min to 2h post-awakening), late decline slope (2h post-awakening to bedtime), overall decline slope (0min to bedtime, excluding 30min cortisol), bedtime cortisol and total area under the curve (AUC). Overall, following multivariable adjustment, among those with diabetes mellitus (DM), early decline slope, overall decline slope, bedtime cortisol, and AUC were significantly and positively associated with a 5.4% (95% CI: 1.3, 9.7), 54.7% (95% CI: 12.4, 112.9), 4.0% (95% CI: 1.6,6.4), and 6.8% (95% CI: 3.3,10.4) higher HbA1c per 1 unit increase in log cortisol feature, respectively. Cortisol curve features were not associated with HbA1c among non-diabetic participants; however, wake-up cortisol and AUC were associated with a 8.2% lower (95% CI: -13.3,-2.7) and 7.9% lower (95% CI: -14.6, -0.6) log HOMA-IR, respectively. This was attenuated by adjustment for waist circumference. Among participants with DM, cortisol curve parameters suggestive of higher hypothalamic-pituitary-adrenal (HPA) axis activity and dysfunction were associated with higher HbA1c. In non-diabetic participants, greater HPA activity was paradoxically associated with lower insulin resistance.

Gonadal steroid hormones and the hypothalamo-pituitary-adrenal axis

The hypothalamo-pituitary-adrenal (HPA) axis represents a complex neuroendocrine feedback loop controlling the secretion of adrenal glucocorticoid hormones. Central to its function is the paraventricular nucleus of the hypothalamus (PVN) where neurons expressing corticotropin releasing factor reside. These HPA motor neurons are a primary site of integration leading to graded endocrine responses to physical and psychological stressors. An important regulatory factor that must be considered, prior to generating an appropriate response is the animal's reproductive status. Thus, PVN neurons express androgen and estrogen receptors and receive input from sites that also express these receptors. Consequently, changes in reproduction and gonadal steroid levels modulate the stress response and this underlies sex differences in HPA axis function. This review examines the make up of the HPA axis and hypothalamo-pituitary-gonadal (HPG) axis and the interactions between the two that should be considered when exploring normal and pathological responses to environmental stressors.

Evaluation of the diagnostic criteria for Cushing's disease in Japan

Adrenocorticotropic hormone (ACTH)-dependent Cushing's syndrome is caused by an ACTH-producing tumor, as is the case with Cushing's disease and ectopic ACTH syndrome (EAS). Diagnosis and differential diagnosis of Cushing's disease from EAS in ACTH-dependent Cushing's syndrome are thus challenging problems in clinical endocrinology. The diagnostic criteria for Cushing's disease in Japan, established by the working group of the Japan Ministry of Health, Labour and Welfare, were originally reported in 2003 and revised in 2007 and 2010. In addition, criteria for subclinical Cushing's disease were established in Japan in 2010. In this review, we evaluate the usefulness and accuracy of the most recent diagnostic criteria. Previous data suggest that as an initial test of Cushing's syndrome, 0.5 mg dexamethasone is more sensitive than 1 mg in the overnight dexamethasone suppression test (DST). Here, we recommend 0.5 mg plus a plasma cortisol cut-off level of 3 µg/dL as a suitable low-dose overnight DST for screening of all cases of ACTH-dependent Cushing's syndrome in Japan. Recently, standardization of cortisol measurements by the ID-LC/MS/MS method using seven assay kits with standard plasma material containing synthetic hydrocortisone-d4 was carried out in Japan. The resulting relative standard deviation was within 10%. The cut-off value remains valid even after standardization of plasma cortisol measurements. Although the recent diagnostic criteria achieve higher diagnostic specificity, care should be taken since data for Cushing's disease partially overlaps with some cases of EAS. Overall, therefore, this review suggests that the accuracy of each diagnostic test should be considered.