A specific carrier substance for human corticotrophin releasing factor in late gestational maternal plasma which could mask the ACTH-releasing activity

Corticotropin Releasing Factor Binding Protein as a Novel Target to Restore Brain Homeostasis: Lessons Learned From Alcohol Use Disorder Research

Stress is well-known to contribute to the development of many psychiatric illnesses including alcohol and substance use disorder (AUD and SUD). The deleterious effects of stress have also been implicated in the acceleration of biological age, and age-related neurodegenerative disease. The physio-pathology of stress is regulated by the corticotropin-releasing factor (CRF) system, the upstream component of the hypothalamic-pituitary-adrenal (HPA) axis. Extensive literature has shown that dysregulation of the CRF neuroendocrine system contributes to escalation of alcohol consumption and, similarly, chronic alcohol consumption contributes to disruption of the stress system. The CRF system also represents the central switchboard for regulating homeostasis, and more recent studies have found that stress and aberrations in the CRF pathway are implicated in accelerated aging and age-related neurodegenerative disease. Corticotropin releasing factor binding protein (CRFBP) is a secreted glycoprotein distributed in peripheral tissues and in specific brain regions. It neutralizes the effects of CRF by sequestering free CRF, but may also possess excitatory function by interacting with CRF receptors. CRFBP’s dual role in influencing CRF bioavailability and CRF receptor signaling has been shown to have a major part in the HPA axis response. Therefore, CRFBP may represent a valuable target to treat stress-related illness, including: development of novel medications to treat AUD and restore homeostasis in the aging brain. This narrative review focuses on molecular mechanisms related to the role of CRFBP in the progression of addictive and psychiatric disorders, biological aging, and age-related neurodegenerative disease. We provide an overview of recent studies investigating modulation of this pathway as a potential therapeutic target for AUD and age-related neurodegenerative disease.

Stress-related endogenous neuropeptides induce neuronal excitation in the Laterodorsal Tegmentum

Stress is a physiological response that promotes maintenance of balance against harmful stimuli. Unfortunately, chronic activation of stress systems facilitates the development of psychiatric disorders. A stress-mediated hypercholinergic state could underlie this facilitation, as cholinergic mechanisms have been suggested to play a role in anxiety, depression, and substance use disorder (SUD). Stimulation by stress hormones, urocortin (Ucn1) or corticotropin-releasing factor (CRF), of the CRF receptor type 1 (CRFR1) of acetylcholine-containing neurons of the laterodorsal tegmental nucleus (LDT) could be involved in modulation of cholinergic transmission during periods of stress hormone activation, which could play a role in psychiatric disorders as cholinergic LDT neurons project to, and control activity in, mood-, arousal- and SUD-controlling regions. The present study investigated for the first time the membrane effects and intracellular outcomes of CRFR1 activation by endogenous stress hormones on LDT neurons. Patch clamp recordings of immunohistochemically-identified cholinergic and non-cholinergic LDT neurons with concurrent calcium imaging were used to monitor cellular responses to CRFR1 stimulation with Ucn1 and CRF. Postsynaptically-mediated excitatory currents were elicited in LDT cholinergic neurons, accompanied by an enhancement in synaptic events. In addition, CRFR1 activation resulted in rises in intracellular calcium levels. CRFR1 stimulation recruited MAPK/ERK and SERCA-ATPase involved pathways. The data presented here provide the first evidence that Ucn1 and CRF exert pre and postsynaptic excitatory membrane actions on LDT cholinergic neurons that could underlie the hypercholinergic state associated with stress which could play a role in the heightened risk of psychiatric disorders associated with a chronic stress state.

Molecular Modeling of Structures and Interaction of Human Corticotropin-Releasing Factor (CRF) Binding Protein and CRF Type-2 Receptor

The corticotropin-releasing factor (CRF) system is a key mediator of the stress response and addictive behavior. The CRF system includes four peptides: The CRF system includes four peptides: CRF, urocortins I-III, CRF binding protein (CRF-BP) that binds CRF with high affinity, and two class B G-protein coupled receptors CRF₁R and CRF₂R. CRF-BP is a secreted protein without significant sequence homology to CRF receptors or to any other known class of protein. Recently, it has been described a potentiation role of CRF-BP over CRF signaling through CRF₂R in addictive-related neuronal plasticity and behavior. In addition, it has been described that CRF-BP is capable to physically interact specifically with the α isoform of CRF₂R and acts like an escort protein increasing the amount of the receptor in the plasma membrane. At present, there are no available structures for CRF-BP or for full-length CRFR. Knowing and studying the structure of these proteins could be beneficial in order to characterize the CRF-BP/CRF_2αR interaction. In this work, we report the modeling of CRF-BP and of full-length CRF_2αR and CRF_2βR based on the recently solved crystal structures of the transmembrane domains of the human glucagon receptor and human CRF₁R, in addition with the resolved N-terminal extracellular domain of CRFRs. These models were further studied using molecular dynamics simulations and protein-protein docking. The results predicted a higher possibility of interaction of CRF-BP with CRF_2αR than CRF_2βR and yielded the possible residues conforming the interacting interface. Thus, the present study provides a framework for further investigation of the CRF-BP/CRF_2αR interaction.

CRF binding protein facilitates the presence of CRF type 2α receptor on the cell surface

Corticotropin releasing factor binding protein (CRF-BP) was originally recognized as CRF sequestering protein. However, its differential subcellular localization in different brain nuclei suggests that CRF-BP may have additional functions. There is evidence that CRF-BP potentiates CRF and urocortin 1 actions through CRF type 2 receptors (CRF2R). CRF2R is a G protein-coupled receptor (GPCR) that is found mainly intracellularly as most GPCRs. The access of GPCRs to the cell surface is tightly regulated by escort proteins. We hypothesized that CRF-BP binds to CRF2R, exerting an escort protein role. We analyzed the colocalization of CRF-BP and CRF2R in cultured rat mesencephalic neurons, and the localization and interaction of heterologous expressed CRF-BP and CRF2αR in yeast, human embryonic kidney 293, and rat pheochromocytoma 12 cells. Our results showed that CRF-BP and CRF2R naturally colocalize in the neurites of cultured mesencephalic neurons. Heterologous expression of each protein showed that CRF-BP was localized mainly in secretory granules and CRF2αR in the endoplasmic reticulum. In contrast, CRF-BP and CRF2αR colocalized when both proteins are coexpressed. Here we show that CRF-BP physically interacts with the CRF2αR but not the CRF2βR isoform, increasing CRF2αR on the cell surface. Thus, CRF-BP emerges as a GPCR escort protein increasing the understanding of GPCR trafficking.

Corticotropin-releasing factor-binding protein (CRF-BP) inhibits CRF- and urotensin-I-mediated activation of CRF receptor-1 and -2 in common carp

Corticotropin-releasing factor-binding protein (CRF-BP) is considered a key determinant for CRF receptor (CRF-R) activation by CRF and several related peptides. Earlier studies have shown that the CRF system is highly conserved in gene structures throughout evolution, yet little is known about the evolutionary conservation of its biological functions. Therefore, we address the functional properties of CRF-BP and CRF-Rs in a teleost fish (common carp; Cyprinus carpio L.). We report the finding of two similar, yet distinct, genes for both CRF-R1 and CRF-R2 in this species. The four receptors are differentially responsive to CRF, urotensin-I (UI), sauvagine, and urocortin-2 (Ucn-2) and -3 (Ucn-3) as shown by luciferase assays. In vitro, carp CRF-BP inhibits CRF- and UI-mediated activation of the newfound CRF-Rs, but its potency to do so varies between receptor and peptide ligand. This is the first paper to establish the functionality and physiological interplay between CRF-BP, CRF-Rs and CRF-family peptides in a teleostean species.

The physiological roles of placental corticotropin releasing hormone in pregnancy and childbirth

In response to stress, the hypothalamus releases cortiticotropin releasing hormone (CRH) that travels to the anterior pituitary, where it stimulates the release of adrenocorticotropic hormone (ACTH). ACTH travels to the adrenal cortex, where it stimulates the release of cortisol and other steroids that liberate energy stores to cope with the stress. During pregnancy, the placenta synthesises CRH and releases it into the bloodstream at increasing levels to reach concentrations 1,000 to 10, 000 times of that found in the non-pregnant individual. Urocortins, which are CRH analogues are also secreted by the placenta. Desensitisation of the maternal pituitary to CRH and resetting after birth may be a factor in post-partum depression. Recently, CRH has been found to modulate glucose transporter (GLUT) proteins in placental tissue, and therefore there may be a link between CRH levels and foetal growth. Evidence suggests CRH is involved in the timing of birth by modulating signalling systems that control the contractile properties of the myometrium. In the placenta, cortisol stimulates CRH synthesis via activation of nuclear factor kappa B (NF-κB), a component in a cellular messenger system that may also be triggered by stressors such as hypoxia and infection, indicating that intrauterine stress could bring forward childbirth and cause low birth weight infants. Such infants could suffer health issues into their adult life as a result of foetal programming. Future treatment of these problems with CRH antagonists is an exciting possibility.

Identification and characterization of a novel corticotropin-releasing hormone-binding protein (CRH-BP) gene from Chinese honeybee (Apis cerana cerana)

Corticotropin-releasing hormone-binding protein (CRH-BP) is an essential secreted glycoprotein for coordinating the neuroendocrine responses to stress by binding either CRHs or its related peptides. A novel CRH-BP gene AccCRH-BP from Apis cerana cerana was identified and characterized. Its genomic DNA was consisted of seven exons and six introns, and shared high similarity with the homologous members from other insects and vertebrates. Homologous and phylogenetic analysis indicated that AccCRH-BP was highly conserved, suggesting the maintenance of conservative structure might be necessary for its biological function. Real-time quantitative PCR revealed that AccCRH-BP was highly expressed in pupa and adult, especially in the head of pupa. However, there was no expression in larval stage. Furthermore, the transcripts of AccCRH-BP in the brain of honeybees were induced by exposure to environmental stresses including UV-light, heat, and cold. The expression level of AccCRH-BP in workers or queens was significantly higher than that of drones. Additionally, analysis of 5'-flanking region of AccCRH-BP revealed a number of putative development and stress transcription factor-binding sites. These data suggest that AccCRH-BP may play important roles in the regulation of honeybee development, and in the central nervous system of the brain to regulate the neuroendocrine stress responses.

Lipopolysaccharide increases plasma levels of corticotropin-releasing hormone in rats

BACKGROUND

Corticotropin-releasing hormone (CRH) is expressed in the brain, immune cells and the gut, where gene expression is upregulated by lipopolysaccharide (LPS) 6 h after injection. Whether these changes are reflected by increased circulating levels of CRH and adrenocorticotropic hormone (ACTH) is unknown.

METHODS

LPS (100 μg/kg) was injected intraperitoneally in conscious rats, and blood processed for CRH using the new RAPID (reduced temperatures, acidification, protease inhibition, isotopic exogenous controls and dilution) method compared with EDTA blood with or without plasma methanol extraction. Hormone levels were measured by commercial radioimmunoassay.

RESULTS

The RAPID method improved blood recovery of ¹²⁵I-CRH in vitro compared to EDTA only added to the blood without or with methanol extraction (90.8 ± 2.0 vs. 66.9 ± 2.6 and 47.5 ± 2.0%, respectively; p < 0.001 vs. RAPID). Basal CRH levels from blood processed by the RAPID method were 28.9 ± 2.8 pg/ml, and by other methods below the radioimmunoassay detection limit (<10 pg/ml). At 6 h after LPS, CRH plasma levels increased significantly by 2.9 times, and in the proximal colon tended to decrease (-27.6 ± 5.7%; p > 0.05), while circulating levels were unchanged at 3 or 4 h. ACTH levels rose compared to control rats (135.3 ± 13.8 vs. 101.4 ± 6.0 pg/ml; p < 0.05) 30 min after the increase in CRH, while at 3 or 6 h after LPS, the levels were not changed.

CONCLUSION

Intraperitoneal LPS induces a delayed rise in plasma CRH levels associated with an elevation in ACTH plasma levels 30 min later, suggesting that under conditions of immune challenge, CRH of peripheral origin may also contribute to pituitary activation, as detected using the RAPID method of blood processing, which improves CRH recovery.

Neuroendocrine mechanisms in pregnancy and parturition

The complex mechanisms controlling human parturition involves mother, fetus, and placenta, and stress is a key element activating a series of physiological adaptive responses. Preterm birth is a clinical syndrome that shares several characteristics with term birth. A major role for the neuroendocrine mechanisms has been proposed, and placenta/membranes are sources for neurohormones and peptides. Oxytocin (OT) is the neurohormone whose major target is uterine contractility and placenta represents a novel source that contributes to the mechanisms of parturition. The CRH/urocortin (Ucn) family is another important neuroendocrine pathway involved in term and preterm birth. The CRH/Ucn family consists of four ligands: CRH, Ucn, Ucn2, and Ucn3. These peptides have a pleyotropic function and are expressed by human placenta and fetal membranes. Uterine contractility, blood vessel tone, and immune function are influenced by CRH/Ucns during pregnancy and undergo major changes at parturition. Among the others, neurohormones, relaxin, parathyroid hormone-related protein, opioids, neurosteroids, and monoamines are expressed and secreted from placental tissues at parturition. Preterm birth is the consequence of a premature and sustained activation of endocrine and immune responses. A preterm birth evidence for a premature activation of OT secretion as well as increased maternal plasma CRH levels suggests a pathogenic role of these neurohormones. A decrease of maternal serum CRH-binding protein is a concurrent event. At midgestation, placental hypersecretion of CRH or Ucn has been proposed as a predictive marker of subsequent preterm delivery. While placenta represents the major source for CRH, fetus abundantly secretes Ucn and adrenal dehydroepiandrosterone in women with preterm birth. The relevant role of neuroendocrine mechanisms in preterm birth is sustained by basic and clinic implications.

Long-term hypoxia enhances ACTH response to arginine vasopressin but not corticotropin-releasing hormone in the near-term ovine fetus

This study tested the hypothesis that long-term hypoxia (LTH) results in enhanced fetal corticotrope sensitivity to the ACTH secretagogues, corticotropin-releasing hormone (CRH), and AVP. Ewes were maintained at high altitude (3,820 m) from 40 to 130-131 days of gestation. Upon return to the laboratory, hypoxia was maintained by maternal nitrogen infusion. Vascular catheters were placed in both LTH (n = 4) and normoxic controls (n = 4). Each fetus received a 15-min infusion of either saline, 100 ng/kg of ovine CRH, or 20 ng/kg of AVP/min over 3 consecutive days in a randomized order. Fetal blood samples were collected at 0, 15, 30, 60, and 90 min after the start of infusion and analyzed for ACTH(1-39), ACTH precursors, and cortisol. Anterior pituitaries were collected from additional noninstrumented fetuses for analysis of vasopressin receptor 1b (V1b) mRNA and protein. Basal plasma concentrations of both ACTH(1-39) and ACTH precursors were higher in LTH fetuses and were not altered by saline infusion. In response to CRH, ACTH(1-39) increased in both groups and was higher in the LTH group compared with control (P < 0.05). When analyzed as sum of ACTH(1-39) released (Delta0-90 min) above basal, CRH released equal amounts of ACTH(1-39) in both groups. In LTH fetuses, AVP evoked a greater ACTH(1-39) release (P < 0.05) when analyzed as an increased sum of ACTH(1-39) (Delta0-90 min) above basal. Both CRH and AVP elicited a release of ACTH precursors with no differences observed between LTH and control. AVP and CRH elicited significant increases in cortisol, which were higher in response to AVP than CRH. V1b mRNA and protein were elevated in the anterior pituitary of LTH fetuses compared with control. LTH significantly increases pituitary sensitivity to AVP. This enhanced sensitivity may be a mechanism of our previously observed enhanced corticotrope function.

Amniotic fluid and umbilical cord plasma corticotropin-releasing factor (CRF), CRF-binding protein, adrenocorticotropin, and cortisol concentrations in intraamniotic infection and inflammation at term

CONTEXT

Pregnant tissues express corticotropin-releasing factor (CRF), a peptide modulating fetal and placental ACTH and cortisol secretion. These actions are modulated by the locally expressed CRF-binding protein (CRF-BP).

OBJECTIVE

The objective of the study was to determine whether CRF, CRF-BP, ACTH, and cortisol concentrations change in amniotic fluid and umbilical cord plasma in the presence of intraamniotic infection/inflammation (IAI) in women with spontaneous labor at term.

DESIGN

This was a cross-sectional study.

SETTING

The study was conducted at a tertiary referral center for obstetric care.

PATIENTS

Patients included women in active labor at term with (n = 39) and without (controls; n = 78) IAI.

MAIN OUTCOME MEASURES

Amniotic fluid and umbilical cord plasma concentrations of CRF, CRF-BP, ACTH, and cortisol measured by RIA and immunoradiometric assays were measured.

RESULTS

In patients with IAI, amniotic fluid CRF (0.97 +/- 0.18 ng/ml) and CRF-BP (33.06 +/- 5.54 nmol/liter) concentrations were significantly (P < 0.001) higher than in controls (CRF: 0.32 +/- 0.04 ng/ml; CRF-BP: 14.69 +/- 2.79 ml). The umbilical cord plasma CRF and CRF-BP concentrations were significantly (P < 0.001 for all) higher in women with IAI than in controls (CRF: 2.96 +/- 0.35 ng/ml vs. 0.38 +/- 0.18 ng/ml; CRF-BP: 152.12 +/- 5.94 nmol/liter vs. 106.9 +/- 5.97 nmol/liter). In contrast, amniotic fluid and umbilical cord plasma ACTH and cortisol concentrations did not differ between groups.

CONCLUSIONS

Amniotic fluid and umbilical cord plasma CRF and CRF-BP concentrations are increased in women with spontaneous labor at term and IAI. CRF-BP may modulate CRF actions on ACTH and cortisol secretion, playing a pivotal role in limiting the inflammatory process and thus avoiding an overactivation of the fetal/placental hypothalamus-pituitary-adrenal axis at birth.

A corticotropin-releasing hormone binding protein (CRH-BP) gene from the intertidal copepod, Tigriopus japonicus

The corticotropin-releasing hormone (CRH) plays a critical role in stress-response regulation in vertebrates. The activity of CRH depends on CRH-binding protein (CRH-BP). CRH-BP is considered to play a chaperoning role in stress. Limited information mainly from the insects is available on the molecular structure and functions of invertebrate CRH and CRH-BP. We cloned and sequenced a CRH-BP gene from the intertidal copepod, Tigriopus japonicus which was expressed at all the stages of development. Molecular phylogenetic analysis showed that T. japonicus CRH-BP was closely related to CRH-BP of honeybee and other insects. The highest level of CRH-BP transcripts was expressed in adult males followed by nauplius stage 1. The expression of CRH-BP was upregulated when T. japonicus was subjected to temperature or salinity stress. This study demonstrates that CRH-BP in T. japonicus might play a role in stress-response. However, establishing such a role demands further studies on CRH-BP from other invertebrates and their expression under stress.

Corticotropin-releasing factor binding protein within the ventral tegmental area is expressed in a subset of dopaminergic neurons

Corticotropin-releasing factor (CRF) and related peptides play a role in mediating neuronal effects of stress. These peptides mediate stress responses by their interactions with the CRF receptors and the CRF-binding protein (CRF-BP). Because the CRF-BP is implicated in neurotransmission within the ventral tegmental area (VTA), we investigated whether the CRF-BP is expressed in VTA neurons. By in situ hybridization, we detected cellular expression of CRF-BP mRNA in the VTA; no such expression was seen in neighboring substantia nigra pars compacta (SNC) or substantia nigra pars reticulata. By double in situ hybridization, we determined that VTA neurons with CRF-BP mRNA coexpressed transcripts encoding either tyrosine hydroxylase [TH; a marker for dopamine (DA) neurons] or glutamic acid decarboxylase [GAD; synthesizing enzyme of gamma-aminobutyric acid (GABA)]. Neurons with CRF-BP mRNA represented 25% of the total population of TH-expressing neurons and 28% of the total population of GAD-expressing neurons, indicating that discrete subpopulations of dopaminergic and GABAergic neurons are present in the VTA. Within the total population of neurons containing CRF-BP mRNA, 70% coexpressed TH mRNA and only 27% coexpressed GAD mRNA. As far as we are aware, we provide the first anatomical evidence that a molecule, CRF-BP, is encoded by DAergic neurons of the VTA but not by those of the SNC. We propose, based on the observation that the majority of VTA neurons expressing CRF-BP mRNA are DAergic, that in the VTA interactions of CRF-BP with CRF, or with CRF-related peptides, are likely to be mediated predominantly by DAergic neurons.

Residues of corticotropin releasing factor-binding protein (CRF-BP) that selectively abrogate binding to CRF but not to urocortin 1

Corticotropin releasing factor-binding protein (CRF-BP) binds CRF and urocortin 1 (Ucn 1) with high affinity, thus preventing CRF receptor (CRFR) activation. Despite recent progress on the molecular details that govern interactions between CRF family neuropeptides and their cognate receptors, little is known concerning the mechanisms that allow CRF-BP to bind CRF and Ucn 1 with picomolar affinity. We conducted a comprehensive alanine scan of 76 evolutionarily conserved residues of CRF-BP and identified several residues that differentially affected the affinity for CRF over Ucn 1. We determined that both neuropeptides derive their similarly high affinity from distinct binding surfaces on CRF-BP. Alanine substitutions of arginine 56 (R56A) and aspartic acid 62 (D62A) reduce the affinity for CRF by approximately 100-fold, while only marginally affecting the affinity for Ucn 1. The selective reduction in affinity for CRF depends on glutamic acid 25 in the CRF peptide, as substitution of Glu(25) reduces the affinity for CRF-BP by approximately 2 orders of magnitude, but only in the presence of both Arg(56) and Asp(62) in human CRF-BP. We show that CRF-BP(R56A) and CRF-BP(D62A) have lost the ability to inhibit CRFR1-mediated responses to CRF that activate luciferase induction in HEK293T cells and ACTH release from cultured rat anterior pituitary cells. In contrast, both CRF-BP mutants retain the ability to inhibit Ucn 1-induced CRFR1 activation. Collectively our findings demonstrate that CRF-BP has distinct and separable binding surfaces for CRF and Ucn 1, opening new avenues for the design of ligand-specific antagonists based on CRF-BP.

The regulation of adrenocorticotrophic hormone receptor by corticotropin-releasing hormone in human fetal adrenal definitive/transitional zone cells

As gestation progresses, human fetal adrenals (HFA) initiate the production of cortisol, which increases placental corticotropin-releasing hormone (CRH) biosynthesis. While adrenocorticotrophic hormone (ACTH) is important for the onset of cortisol production, the late gestational surge in cortisol production occurs despite falling ACTH levels in the fetal circulation. The authors determine if CRH directly regulates the expression of the ACTH receptor (ACTHR) in HFA definitive/transitional zone (DZ/TZ) cells. DZ/TZ cells isolated from midgestation HFA were cultured before treatment with 0.01 nM to 100 nM CRH or ACTH. Cortisol was measured by radioimmunoassay. Real-time reverse-transcriptase polymerase chain reaction was used to measure ACTHR mRNA. Whole-cell ACTH binding studies were performed using I(125) (Tyr-23) ACTH. CRH produced a dose-dependent rise in cortisol production and caused a time-dependent increase in ACTHR mRNA levels between 12 and 24 hours. As little as 0.1 nM CRH induced ACTHR transcript by 12-fold at 24 hours. Together with ACTH 0.01 nM, 0.03 or 0.1 nM CRH increased ACTHR expression more than ACTH alone. Binding assays demonstrated a 3.5-fold increase in ACTHR protein at 48 hours with combined CRH and ACTH treatment. Physiologic levels of CRH seen in the late-gestation fetus stimulate DZ/TZ ACTHR expression. Since placental CRH production increases strikingly near the end of gestation, the authors suggest that CRH-induced ACTH receptor expression may increase TZ responsiveness to circulating ACTH and contribute to the late gestational rise in cortisol secretion by the HFA, participating in an endocrine cascade that is involved in fetal organ maturation and potentially in the timing of human parturition.

The role of corticotropin-releasing factor in the investigation of endocrine diseases

Since the discovery and structural elucidation of corticotropin-releasing factor (CRF) synthetic ovine and human CRF have become useful tools for the diagnosis of pituitary and adrenocortical disorders. The stimulation of release of adrenocorticotropic hormone (ACTH) after a dose of 100 micrograms CRF allows differentiation of the various causes of secondary adrenal insufficiency. In patients with specific autoimmune corticotroph disorders or general inflammatory or tumorous destruction of the anterior pituitary there is no rise of ACTH after intravenous administration of CRF. In contrast, patients with secondary adrenal failure due to suprasellar lesions show a rise of ACTH from a low or unmeasurable basal level without an accompanying cortisol response, demonstrating the integrity of the corticotroph and the atrophy of the cRF neuron and the adrenocortical cell. Similar observations are made in patients with secondary adrenal failure resulting from long-term glucocorticoid treatment. This demonstrates that the main reason for adrenal insufficiency after glucocorticoid treatment is the persisting suppression of the activity of CRF neurons. In patients with adrenocortical hyperfunction (Cushing's syndrome) the CRF stimulation test differentiates unequivocally between autonomous adrenal hypercortisolism and ACTH-dependent bilateral adrenal hyperplasia. However, the differential diagnosis between eutopic pituitary (Cushing's disease) and paraneoplastic ACTH secretion (ectopic ACTH syndrome) is difficult. Recent results show that catheterization of the sinus petrous inferior and measurement of ACTH in central and peripheral blood before and after CRF injection allows this differential diagnosis to be made with confidence. The usefulness of measuring CRF plasma levels is not established. The only exception to this is in cases of ectopic CRF syndrome, which is a rare cause of Cushing's syndrome.

Stress-induced relapse to cocaine seeking: roles for the CRF(2) receptor and CRF-binding protein in the ventral tegmental area of the rat

RATIONALE

Footshock reinstates cocaine seeking in cocaine-experienced rats by inducing corticotropin-releasing factor (CRF) and glutamate release in the ventral tegmental area (VTA) and thus activating VTA dopaminergic neurons. Footshock-induced VTA glutamate release, dopamine activation and reinstatements are blocked by VTA administration of a alpha-helical CRF, a nonselective CRF receptor antagonist. The effects of selective CRF antagonists have not yet been reported.

OBJECTIVE

The present studies were designed to explore the roles of VTA CRF receptor subtypes and CRF-BP in these effects induced by footshock.

METHODS

Rats were first trained to lever-press for intravenous cocaine (1 mg/infusion/0.13 ml, FR-1 schedule), and then tested under extinction conditions until response rates returned to the pretraining baseline. Reinstatements, VTA glutamate and dopamine levels [microdialysis with high performance liquid chromatography (HPLC)] were then assessed, under various pharmacological conditions, after mild inescapable footshock.

RESULTS

Footshock-induced reinstatement of cocaine seeking and release of VTA glutamate and dopamine were blocked by selective blockade of VTA CRF(2) receptors (CRF(2)Rs) but not CRF(1)Rs. VTA perfusion of CRF or CRF(2)R agonists that have strong affinity for CRF-BP mimicked the effects induced by footshock while CRFR agonists that do not bind CRF-BP were ineffective. CRF(6-33), which competes for the CRF binding site on CRF-BP, attenuated the effects of CRF or urocortin I on VTA glutamate and dopamine release and on reinstatement of cocaine seeking.

CONCLUSIONS

The present studies revealed a role of VTA CRF-BP and suggest an involvement of CRF(2)R in the effectiveness of stress in triggering glutamate and dopamine release and cocaine seeking in drug-experienced animals.

The role of the hypothalamic-pituitary-adrenal axis in neuroendocrine responses to stress

Animals respond to stress by activating a wide array of behavioral and physiological responses that are collectively referred to as the stress response. Corticotropin-releasing factor (CRF) plays a central role in the stress response by regulating the hypothalamic-pituitary-adrenal (HPA) axis. In response to stress, CRF initiates a cascade of events that culminate in the release of glucocorticoids from the adrenal cortex. As a result of the great number of physiological and behavioral effects exerted by glucocorticoids, several mechanisms have evolved to control HPA axis activation and integrate the stress response. Glucocorticoid feedback inhibition plays a prominent role in regulating the magnitude and duration of glucocorticoid release. In addition to glucocorticoid feedback, the HPA axis is regulated at the level of the hypothalamus by a diverse group of afferent projections from limbic, mid-brain, and brain stem nuclei. The stress response is also mediated in part by brain stem noradrenergic neurons, sympathetic andrenornedullary circuits, and parasympathetic systems. In summary, the aim of this review is to discuss the role of the HPA axis in the integration of adaptive responses to stress. We also identify and briefly describe the major neuronal and endocrine systems that contribute to the regulation of the HPA axis and the maintenance of homeostasis in the face of aversive stimuli.

The remarkable conservation of corticotropin-releasing hormone (CRH)-binding protein in the honeybee (Apis mellifera) dates the CRH system to a common ancestor of insects and vertebrates

CRH-binding protein (CRH-BP) is a key factor in the regulation of CRH signaling; it modulates the bioactivity and bioavailability of CRH and its related peptides. The conservation of CRH-BP throughout vertebrates was only recently demonstrated. Here we report the presence of CRH-BP in the honeybee (Apis mellifera) and other insects. Honeybee CRH-BP resembles previously characterized vertebrate CRH-BP sequences with respect to conserved cysteine residues, gene organization, and overall sequence identity. Phylogenetic analyses confirm the unambiguous orthology of insect and vertebrate CRH-BP sequences. Soon after their discovery, it was noted that insect diuretic hormone-I (DH-I) and its receptor share similarities with the vertebrate CRH family and their receptors. Despite these similarities, demonstration of common ancestry of DH-I and the vertebrate CRH family is still speculative: the mature neuropeptides are short, and their genes differ substantially with regard to the number of coding exons. Moreover, DH and CRH receptors belong to the much larger family of G protein-coupled receptors. In contrast, the unique and conspicuous features of CRH-BP greatly facilitate the establishment of orthology over much larger evolutionary distances. The identification of CRH-BP in insects clearly indicates that this gene predates vertebrates by at least several hundred million years. Moreover, our findings imply that a CRH system is shared by insects and vertebrates alike and, consequently, that it has been present at least since the common ancestor to both phylogenetic lines of proto- and deuterostomians.

The role of corticotropin-releasing factor-like peptides in cannabis, nicotine, and alcohol dependence

The corticotropin-releasing factor (CRF)-like peptides, which include the mammalian peptides CRF, urocortin 1, urocortin 2, and urocortin 3, play an important role in orchestrating behavioral and physiological responses that may increase an organism's chance of survival when confronted with internal or external stressors. There is, however, evidence that a chronic overactivity of brain CRF systems under basal conditions may play a role in the etiology and maintenance of psychiatric disorders such as depression and anxiety disorders. In addition, there is evidence of a role for CRF-like peptides in acute and protracted drug abstinence syndromes and relapse to drug-taking behavior. This review focuses on the role of CRF-like peptides in the negative affective state associated with acute and protracted withdrawal from three widely abused drugs, cannabis, nicotine, and alcohol. In addition, we discuss the high comorbidity between stress-associated psychiatric disorders and drug dependence. A better understanding of the brain stress systems that may underlie psychiatric disorders, acute and protracted drug withdrawal, and relapse to drug-taking behavior may help in the development of new and improved pharmacotherapies for these widespread psychiatric disorders.

Maternal and fetal hypothalamic-pituitary-adrenal axes during pregnancy and postpartum

The principal modulators of the hypothalamic-pituitary-adrenal (HPA) axis are corticotropin-releasing hormone (CRH) and arginine-vasopressin (AVP). Corticotropin-releasing hormone is not exclusively produced in the hypothalamus. Its presence has been demonstrated at peripheral inflammatory sites. Ovulation and luteolysis bear characteristics of an aseptic inflammation. CRH was found in the theca and stromal cells as well as in cells of the corpora lutea of human and rat ovaries. The cytoplasm of the glandular epithelial cells of the endometrium has been shown to contain CRH and the myometrium contains specific CRH receptors. It has been suggested that CRH of fetal and maternal origin regulates FasL production, thus affecting the invasion (implantation) process through a local auto-paracrine regulatory loop involving the cytotrophoblast cells. Thus, the latter may regulate their own apoptosis. During pregnancy, the plasma level of circulating maternal immunoreactive CRH increases exponentially from the first trimester of gestation due to the CRH production in the placenta, decidua, and fetal membranes. The presence in plasma and amniotic fluid of a CRH-binding protein (CRHbp) that reduces the bioactivity of circulating CRH by binding is unique to humans. Maternal pituitary ACTH secretion and plasma ACTH levels rise during pregnancy-though remaining within normal limits-paralleling the rise of plasma cortisol levels. The maternal adrenal glands during pregnancy gradually become hypertrophic. Pregnancy is a transient, but physiologic, period of hypercortisolism. The diurnal variation of plasma cortisol levels is maintained in pregnancy, probably due to the secretion of AVP from the parvicellular paraventricular nuclei. CRH is detected in the fetal hypothalamus as early as the 12th week of gestation. CRH levels in fetal plasma are 50% less than in maternal plasma. The circulating fetal CRH is almost exclusively of placental origin. The placenta secretes CRH at a slower rate in the fetal compartment. AVP is detected in some neurons of the fetal hypothalamus together with CRH. AVP is usually detectable in the human fetal neurohypophysis at 11 to 12 weeks gestation and increases over 1000-fold over the next 12 to 16 weeks. The role of fetal AVP is unclear. Labor appears to be a stimulus for AVP release by the fetus. The processing of POMC differs in the anterior and intermediate lobes of the fetal pituitary gland. Corticotropin (ACTH) is detectable by radioimmunoassay in fetal plasma at 12 weeks gestation. Concentrations are higher before 34 weeks gestation, with a significant fall in late gestation. The human fetal adrenal is enormous relative to that of the adult organ. Adrenal steroid synthesis is increased in the fetus. The major steroid produced by the fetal adrenal zone is sulfoconjugated dehydroepiandrosterone (DHEAS). The majority of cortisol present in the fetal circulation appears to be of maternal origin, at least in the nonhuman primate. The fetal adrenal uses the large amounts of progesterone supplied by the placenta to make cortisol. Another source of cortisol for the fetus is the amniotic fluid where cortisol converted from cortisone by the choriodecidua, is found. In humans, maternal plasma CRH, ACTH, and cortisol levels increase during normal labor and drop at about four days postpartum; however, maternal ACTH and cortisol levels at this stage are not correlated. In sheep, placental CRH stimulates the fetal production of ACTH, which in turn leads to a surge of fetal cortisol secretion that precipitates parturition. The 10-day-long intravenous administration of antalarmin, a CRH receptor antagonist, significantly prolonged gestation compared to the control group of animals. Thus, CRH receptor antagonism in the fetus can also delay parturition. The HPA axis during the postpartum period gradually recovers from its activated state during pregnancy. The adrenals are mildly suppressed in a way analogous to postcure Cushing's syndrome. Provocation testing has shown that hypothalamic CRH secretion is transiently suppriently suppressed at three and six weeks postpartum, normalizing at 12 weeks.

The emerging role of peripheral corticotropin-releasing hormone (CRH)

Corticotropin-releasing hormone (CRH) is distributed in the brain and spinal cord and it has also been found in the myometrium, the endometrium, the placenta and diverse inflammatory sites. Traditionally, hypothalamic CRH has been considered to act indirectly in an anti-inflammatory fashion, since the end product of the hypothalamic-pituitary-adrenal axis is cortisol, a well-known anti-inflammatory compound. However, CRH produced at peripheral inflammatory sites may participate in an auto-/paracrine stimulation of inflammation. CRH in inflammatory sites seems to be involved in the activation of the Fas/Fas ligand system. Furthermore, locally produced embryonic and endometrial CRH plays a role in both the aseptic inflammatory process of implantation and the anti-rejection process that protects the fetus from the maternal immune system. There are two types of G protein-coupled CRH receptors, type 1 and 2. Pyrrolopyrimidine compounds, such as antalarmin, have been developed as CRH receptor antagonists. The systemic administration of antalarmin blocks pituitary CRH receptors and the CRH-induced secretion of adrenocorticotropin. Additonally, antalarmin has been shown to reduce the inflammatory-like reaction of the endometrium to the invading blastocyst, with a possible therapeutic potential as a non-steroidal inhibitor of pregnancy at its early stages.

Predicting risk of preterm birth: the roles of stress, clinical risk factors, and corticotropin-releasing hormone

The relationships and predictive abilities of perceived stress, selected clinical risk factors, and corticotropin-releasing hormone (CRH) levels in maternal plasma were investigated for their association with preterm labor (PTL), preterm birth, and gestational age at delivery. An exploratory, prospective, longitudinal research design was used to measure CRH 4 times over pregnancy, perceived stress at 24 and 32 weeks of pregnancy, clinical risk factors, and genitourinary infections in low-income women. Multiple regression analyses revealed that a model of measurement ofperceived stress at 24 or 32 weeks, CRH at 24 or 32 weeks, and PTL (indicated by a diagnosis by the physicians on the medical record and greater than 5 contractions per hour on the fetal monitor) was predictive of as much as 0.23 to 0.27 of the variance in gestational age at birth. Entering ethnicity as a variable into a model did not improve the predictive value. An analysis of variance between Caucasian and Hispanic ethnic groups revealed differences in CRH levels. However, simple regression analysis of ethnicity as a predictor showed a weak r2 with no significance for prediction. There was some evidence of an association of smoking with stress and both PTL and preterm birth. The measurement of stress combined with the measurement of CRHfrom maternal plasma may improve the prediction of which pregnant women are at riskfor pretern birth. The measurement of CRH has potential as an early biological marker of preterm birth.

The corticotropin-releasing factor family of peptides and CRF receptors: their roles in the regulation of energy balance

The corticotropin-releasing factor (CRF) system could play a significant role in the regulation of energy balance. This system, which includes CRF, CRF-related peptides and CRF receptors, is part of a huge network of cells connected to central and peripheral pathways modulating energy metabolism. CRF and CRF-related peptides, which elicit their effects through G-protein-coupled receptors known in mammals as CRF(1) receptor and CRF(2) receptor, are capable of strong anorectic and thermogenic effects. Also supporting a role for the CRF system in the regulation of energy balance are findings demonstrating alterations in this system in obese and food-deprived animals that concur to facilitate energy deposition. In recent years, great progress has been made in understanding the specific physiological roles of the CRF system. In that respect, the discovery of urocortins II and III, two endogenous ligands of the CRF(2) receptor, and the development of selective and long-acting antagonists for the CRF receptors, have led to a better comprehension of the role of the CRF system in the regulation of energy balance. Although there are still important unresolved issues in the field of CRF research, the progress made recently warrants investigations aimed at evaluating the CRF system as a potential target for anti-obesity drugs.

Paradoxical activational effects of a corticotropin-releasing factor-binding protein "ligand inhibitor" in rat brain

The corticotropin-releasing factor-binding protein is distinct from known corticotropin-releasing factor receptors, but can bind the peptide and neutralize its biological actions. Recent interest has centered about the therapeutic potential of "ligand inhibitors" of binding protein action, synthetic corticotropin-releasing factor fragments which are inactive at corticotropin-releasing factor receptors, but can displace the peptide from the binding protein, thereby increasing levels of free corticotropin-releasing factor. To identify sites of action of such ligands, the distribution of Fos expression seen following intracerebroventricular administration of rat/human corticotropin-releasing factor(6-33) (5-50 microg) was charted in relation to corticotropin-releasing factor-binding protein and receptor expression. It was expected that Fos induction would mimic aspects of the distribution of the two known corticotropin-releasing factor receptors, but the far greater correspondence was seen with that of the binding protein itself. This included neurons in the isocortex, the olfactory system, amygdala and a number of discrete brainstem cell groups; many Fos-immunoreactive neurons in each were found to co-express corticotropin-releasing factor-binding protein messenger RNA. Subsets of activated neurons co-expressed Type 1 corticotropin-releasing factor receptor messenger RNA, though these were largely limited to cell groups that also express the corticotropin-releasing factor-binding protein, and where binding protein immunoreactivity and Type 1 receptor transcripts were found to co-exist. Responsive neurons displaying Type 2 corticotropin-releasing factor receptor message were seen reliably only in the lateral septal nucleus. These findings support only a limited capacity of the ligand inhibitor to activate neurons bearing corticotropin-releasing factor receptors. The more pervasive activation seen among neurons that express the corticotropin-releasing factor-binding protein may be indicative of an unexpected role for this protein in signaling by corticotropin-releasing factor-related peptides.

Biological mechanisms that might underlie iron's effects on fetal growth and preterm birth

A negative association between anemia and duration of gestation and low birth weight has been reported in the majority of studies, although a causal link remains to be proven. This paper explores potential biological mechanisms that might explain how anemia, iron deficiency or both could cause low birth weight and preterm delivery. The risk factors for preterm delivery and intrauterine growth retardation are quite similar, although relatively little is understood about the influence of maternal nutritional status on risk of preterm delivery. Several potential biological mechanisms were identified through which anemia or iron deficiency could affect pregnancy outcome. Anemia (by causing hypoxia) and iron deficiency (by increasing serum norepinephrine concentrations) can induce maternal and fetal stress, which stimulates the synthesis of corticotropin-releasing hormone (CRH). Elevated CRH concentrations are a major risk factor for preterm labor, pregnancy-induced hypertension and eclampsia, and premature rupture of the membranes. CRH also increases fetal cortisol production, and cortisol may inhibit longitudinal growth of the fetus. An alternative mechanism could be that iron deficiency increases oxidative damage to erythrocytes and the fetoplacental unit. Iron deficiency may also increase the risk of maternal infections, which can stimulate the production of CRH and are a major risk factor for preterm delivery. It would be useful to explore these potential biological mechanisms in randomized, controlled iron supplementation trials in anemic and iron-deficient pregnant women.

Placental corticotropin-releasing factor. An update

Corticotropin-releasing factor (CRF) produced in placenta has paracrine effects within placenta, decidua, and myometrium and endocrine effects on mother and fetus. CRF is a potent local regulator of myometrial contractility and of prostaglandin release, Recently, urocortin, a new member of the CRF family, has been localized in human placenta and membranes. Urocortin mimics some of the local effects of CRF in intrauterine tissues, that is, increase of adrenocorticotrophic hormone (ACTH) and prostagiandin release and myometrial contractility. A local CRF-BP modulates the paracrine effects of CRF and urocortin. The various CRF receptor subtypes are well distributed in placenta and membranes. CRH also acts on placental blood vasculature and has an action on fetal adrenal gland to stimulate the production of the steroid DHEA-S. In nonpregnant women, plasma CRF levels are low; they become higher during the first and second trimesters of pregnancy. A clear increase is evident at term and when CRF-BP levels decrease. Women with preterm labor show high CRF and low CRF-BP levels, supporting an involvement of this pathway in mechanism of parturition.

Corticotrophin-releasing hormone and CRH-binding protein. Differences between patients at risk for preterm birth and hypertension

BACKGROUND

During pregnancy in the second and third trimester there is a progressive rise in plasma CRH thought to be secreted by the placenta. Plasma CRH-BP inactivates CRH, which may prevent its peripheral action on the maternal pituitary and myometrium. In the last few weeks of pregnancy CRH-BP decreases, thereby causing an increase in free CRH or a CRH/CRH-BP complex available to play a role in the onset of parturition.

OBJECTIVE

We tested the hypothesis that differences in CRH, CRH-BP, or a CRH/CRH-BP complex in patients at risk for preterm birth (PTB) and hypertension (HYP) account for the differences in the timing of parturition.

METHODS

From a Behavior in Pregnancy Study database, we identified 18 patients who had spontaneous PTB and 23 patients who developed HYP. Both groups were case controlled and matched with patients who delivered at term (Normal). Maternal plasma samples had been appropriately collected from these patients at 18-20, 28-30, and 35-36 weeks gestational age. CRH levels were measured by double antibody RIA kit and the CRH-BP by a immunoradiometric technique. A CRH-BP/CRH dimer complex index was calculated. Statistical analysis was done using Kruskal-Wallis test for two cases.

RESULTS

Maternal CRH (pg/ml) in the PTB cases compared to the HYP cases was significantly elevated at all three time periods. Maternal CRH-BP (pg/ml) in the PTB versus HYP cases was significantly lower at all three time periods in the PTB cases compared to the HYP cases. Maternal CRH-BP/CRH dimer complex index was significantly lower in the PTB cases at all three time periods than either the controls or the HYP cases, suggesting excessive CRH. The mean GA at delivery for the PTB cases was significantly lower than the control or HYP cases.

CONCLUSIONS

These results suggest that those patients at risk for PTB have significantly elevated CRH, lower CRH-BP, and a reduced CRH-BP/CRH dimer complex index at all three time periods of assessment.

Urocortin: slower dissociation than corticotropin releasing factor from the CRF binding protein

We report on a comparison of the kinetics of [125I][Tyr0]corticotropin releasing factor (CRF) and [125I][Tyr0]urocortin binding to the CRF binding protein (CRF-BP) at physiological temperature. The association rates of [125I][Tyr0]urocortin or [125I][Tyr0]CRF binding to the CRF-BP were similar. The half time of association for [125I][Tyr0]urocortin was 3.2 min and for [125I][Tyr0]CRF, 2.6 min. [125I][Tyr0]urocortin dissociated from the CRF-BP but the rate of dissociation was slower than for [125I][Tyr0]CRF. The half time for dissociation of [125I][Tyr0]urocortin was 131 min and for [125I][Tyr0]CRF, 64 min. This slower dissociation indicates that the CRF-BP may be more effective in clearing urocortin than CRF.

Evolution and physiology of the corticotropin-releasing factor (CRF) family of neuropeptides in vertebrates

Corticotropin-releasing factor (CRF), urotensin-I, urocortin and sauvagine belong to a family of related neuropeptides found throughout chordate taxa and likely stem from an ancestral peptide precursor early in metazoan ancestry. In vertebrates, current evidence suggests that CRF on one hand, and urotensin-I, urocortin and sauvagine, on the other, form paralogous lineages. Urocortin and sauvagine appear to represent tetrapod orthologues of fish urotensin-I. Sauvagine's unique structure may reflect the distinctly derived evolutionary history of the anura and the amphibia in general. The physiological actions of these peptides are mediated by at least two receptor subtypes and a soluble binding protein. Although the earliest functions of these peptides may have been associated with osmoregulation and diuresis, a constellation of physiological effects associated with stress and anxiety, vasoregulation, thermoregulation, growth and metabolism, metamorphosis and reproduction have been identified in various vertebrate species. The elaboration of neural circuitry for each of the two paralogous neuropeptide systems appears to have followed distinct pathways in the actinopterygian and sarcopterygian lineages of vertebrates. A comparision of the functional differences between these two lineages predicts additional functions of these peptides.

Maternal plasma corticotropin-releasing hormone associated with stress at 20 weeks' gestation in pregnancies ending in preterm delivery

OBJECTIVE

This study tested the hypothesis that maternal stress is associated with elevated maternal levels of corticotropin releasing hormone and activation of the placental-adrenal axis before preterm birth.

STUDY DESIGN

In a behavior in pregnancy study, 524 ethnically and socioeconomically diverse women were followed up prospectively and evaluated at 3 gestational ages: 18 to 20 weeks, 28 to 30 weeks, and 35 to 36 weeks. Maternal variables included demographic data, medical conditions, perceived stress level, and state anxiety. Maternal plasma samples were collected at each gestational age. Eighteen case patients with spontaneous onset of preterm labor were matched against 18 control subjects who were delivered at term, and their samples were assayed for corticotropin-releasing hormone, adrenocorticotropic hormone, and cortisol by means of radioimmunoassay. Statistical tests were used to examine mean differences in these hormones. In addition, the relationship between stress level and each hormone was tested with a Pearson correlation coefficient and hierarchic multiple regressions in each group.

RESULTS

Patients who had preterm delivery had significantly higher plasma corticotropin-releasing hormone levels than did control subjects at all 3 gestational ages (P <.0001). Analyses did not find any differences in reported levels of stress between 18 to 20 weeks' gestation and 28 to 30 weeks' gestation. A hierarchic multiple regression indicated that maternal stress level at 18 to 20 weeks' gestation and maternal age accounted for a significant amount of variance in corticotropin-releasing hormone at 28 to 30 weeks' gestation, after controlling for corticotropin-releasing hormone at 18 to 20 weeks' gestation (P <. 001). In addition, patients who were delivered preterm had significantly elevated plasma levels of adrenocorticotropic hormone at all 3 gestational ages (P <.001) and significantly elevated cortisol levels at 18 to 20 weeks' gestation and 28 to 30 weeks' gestation (P <.001).

CONCLUSION

Maternal plasma levels of corticotropin-releasing hormone are significantly elevated at as early as 18 to 20 weeks' gestation in women who are subsequently delivered preterm. Changes in corticotropin-releasing hormone between 18 to 20 weeks' gestation and 28 to 30 weeks' gestation are associated with maternal age and stress level at 18 to 20 weeks' gestation. Maternal stress and corticotropin-releasing hormone levels may be potential markers for the patient at risk for preterm birth. Activation of the placental maternal pituitary-adrenal axis is consistent with the classic endocrine response to stress.

Characterization of [125I-Tyr0]-corticotropin releasing factor (CRF) binding to the CRF binding protein using a scintillation proximity assay

We describe the characterization of high affinity [125I-Tyr0]-human CRF binding to purified recombinant human CRF-binding protein (CRF-BP) using a scintillation proximity assay (SPA). For this stable nonseparation technique developed in 96 well microtiter plates, biotinylated CRF-BP is captured by streptavidin-coated SPA beads for the detection of bound [125I-Tyr0]-CRF. Unbound [125I-Tyr0]-CRF represented little or no signal in the assay. Total binding observed was greater than 5000 cpm with a nonspecific signal of < 100 cpm determined in the presence of excess unlabeled human CRF. A comparison of the SPA method with a charcoal precipitation method confirmed that the biotinylation procedure did not adversely affect affinity of the CRF-BP for [125I-Tyr0]-CRF. Saturation binding analysis yielded an apparent equilibrium dissociation constant (Kd) of 208 +/- 5.0 pM (+/- S.D., n = 3). An inhibition constant (Ki) for unlabeled CRF was calculated to be 0.22 +/- 0.03 nM (+/- S.D., n = 8) and a pharmacological profile for eight CRF-related neuropeptides gave a rank potency similar to previously reported results. Finally, the assay variability was assessed with intra- and inter-plate coefficients of variation which were less than 5% each.

Physiological and neurochemical aspects of corticotropin-releasing factor actions in the brain: the role of the locus coeruleus

Corticotropin-releasing factor (CRF) is both a major regulator of the hypothalamo-pituitary-adrenal (HPA) axis and the activity of the autonomic nervous system. Besides, it exerts numerous effects on other physiological functions such as appetite control, motor and cognitive behavior and immune function. The basis for these effects is constituted by its distribution in hypothalamic and extra-hypothalamic brain areas, the latter being represented by limbic structures such as the central nucleus of the amygdala or by brain stem neurons such as the locus coeruleus (LC) or nucleus of the solitary tract (NTS). The effects of CRF are mediated through recently described CRF-receptor subtypes, whose molecular biology, biochemistry and pharmacological regulation are discussed in detail. In the second part of this review, we will focus on the physiology of CRF-systems in the brain, with a particular emphasis on cardiovascular regulation, respiration, appetite control and stress-related behavior. Finally, the role of the locus coeruleus in the control of CRF-mediated behavioral activities is discussed. The interaction of noradrenergic and CRF-neurons clearly implies that CRF appears to directly activate LC neurons in a stressful situation, thus ultimately coordinating the bodily response to a stressful stimulus.

Ectopic expression of the CRF-binding protein: minor impact on HPA axis regulation but induction of sexually dimorphic weight gain

Corticotrophin-releasing factor (CRF) and urocortin possess a high-affinity binding protein. Although the CRF binding protein (BP) can sequester these ligands and inhibit their activity, the endogenous activity of this protein is not understood. Therefore, transgenic mouse lines that over-express the CRF-BP were created. The transgene was constructed by ligating rat CRF-BP cDNA (1.1 kb) between a mouse metallothionein-I promoter (1.8 kb) and a nonfunctional human growth hormone gene sequence (2.1 kb) in a modified pBR322 plasmid and microinjecting the transgene into C57BL/6 x SJL hybrid ova. The transgene was expressed in 50% in both male and female progeny. All transgenic lines were maintained by crossing transgenic animals with wild-type C57BL/6 mates. Reverse-transcriptase (RT) PCR of the CRF-BP transgene showed that it is widely expressed not only in the brain and pituitary, but also peripheral tissues including the liver, kidney and spleen. Transgenic animals of both sexes showed significant increases in weight gain as established by analysis of variance; however, the weight gain profiles for each sex were distinct. High levels of circulating CRF-BP were detected in the transgenic animals, but the basal ACTH and corticosterone levels were not significantly decreased compared to wild-type littermates. The hypothalamopituitary-adrenal (HPA) axis was stimulated by systemic inflammation induced with lipopolysaccharide (LPS). An expected increase in transgene expression was observed and was accompanied by a significant attenuation of ACTH secretion at 3 h after LPS injection in the transgenic males but not the females. These data suggest that HPA axis regulation is significantly affected only with very high circulating levels of CRF-BP. Moreover, this work supports previous studies that implicate CRF and urocortin in the regulation of appetite and the binding protein expression may play a sexually dimorphic role in regulating this and other responses.

ACTH responses to CRF and AVP in pregnant and nonpregnant ewes

During both ovine and human pregnancy plasma cortisol is increased. In human pregnancy the placenta secretes corticotropin-releasing factor (CRF), but pituitary responses to CRF are decreased. However, in ovine pregnancy there is no measurable placental secretion of CRF. This study tests for changes in pituitary responsiveness to CRF or AVP. Pregnant and nonpregnant ewes were infused with saline or CRF at three doses (3, 9, 45 microg/h), with or without coinfusion of AVP (9 microg/h). AVP infusion increased plasma AVP to approximately 250 pg/ml. CRF infusions increased plasma CRF from approximately 25 to 50, 150, and 850 pg/ml. ACTH was significantly increased by the infusion of AVP and by all infusions of CRF. Within-animal comparisons revealed a potentiation of the ACTH response to CRF in the presence of AVP. The ACTH responses to AVP and/or CRF were During both ovine and human pregnancy plasma cortisol is increased. In human pregnancy the placenta secretes corticotropin-releasing factor (CRF), but pituitary responses to CRF are decreased. However, in ovine pregnancy there is no measurable placental secretion of CRF. This study tests for changes in pituitary responsiveness to CRF or AVP. Pregnant and nonpregnant ewes were infused with saline or CRF at three doses (3, 9, 45 microg/h), with or without coinfusion of AVP (9 microg/h). AVP infusion increased plasma AVP to approximately 250 pg/ml. CRF infusions increased plasma CRF from approximately 25 to 50, 150, and 850 pg/ml. ACTH was significantly increased by the infusion of AVP and by all infusions of CRF. Within-animal comparisons revealed a potentiation of the ACTH response to CRF in the presence of AVP. The ACTH responses to AVP and/or CRF were

Excess corticotropin releasing hormone-binding protein in the hypothalamic-pituitary-adrenal axis in transgenic mice

Corticotropin-releasing hormone (CRH) is the primary hypothalamic releasing factor that mediates the mammalian stress response. The CRH-binding protein (CRH-BP) is secreted from corticotropes, the pituitary CRH target cells, suggesting that the CRH-BP may modulate hypothalamic-pituitary-adrenal (HPA) axis activity by preventing CRH receptor stimulation. Transgenic mice were generated that constitutively express elevated levels of CRH-BP in the anterior pituitary gland. RNA and protein analyses confirmed the elevation of pituitary CRH-BP. Basal plasma concentrations of corticosterone and adrenocorticotropin hormone (ACTH) are unchanged, and a normal pattern of increased corticosterone and ACTH was observed after restraint stress. However, CRH and vasopressin (AVP) mRNA levels in the transgenic mice are increased by 82 and 35%, respectively, to compensate for the excess CRH-BP, consistent with the idea that CRH-BP levels are important for homeostasis. The transgenic mice exhibit increased activity in standard behavioral tests, and an altered circadian pattern of food intake which may be due to transgene expression in the brain. Alterations in CRH and AVP in response to elevated pituitary CRH-BP clearly demonstrate that regulation of CRH-BP is important in the function of the HPA axis.

Pharmacological characterisation of the recombinant human CRF binding protein using a simple assay

We present the pharmacological characterisation of the recombinant human corticotropin releasing factor binding protein (hCRF-BP) using a simple assay. In this assay we employed [3H]urocortin as the radioligand and, as a means to separate bound and free ligand, adsorption to activated charcoal. Using this method, approximately 60-70% of total binding was specific. Kinetic analysis revealed that association of specific [3H]urocortin binding was monophasic and slow and that the binding was irreversible. Saturation analysis showed a single saturable site of relatively high density (94 fmol per 10 microl of medium from cells transfected with the recombinant CRF binding protein). The apparent Kd for [3H]urocortin binding of 0.25 nM is similar to previously reported affinities of rat urocortin for hCRF-BP. A range of CRF-related peptides potently competed for specific [3H]urocortin binding. The rank order of potency of these agents was human/rat CRF = urotensin 1 > human urocortin > CRF6-33 > sauvagine > ovine CRF. The non-peptide CRF1 receptor antagonists CP 154,526 (N-butyl-N-[2,5-dimethyl-7-(2,4,6-trimethylphenyl)-7H-pyrrolo[2,3-d]p yri midin-4-yl]-N-ethylamine) and SC 241 ([3-(2-bromo-4-isopropyl-phenyl)-5-methyl-3H-[1,2,3]triazo lo[4,5-d]pyrimidin-7-yl]-bis-(2-methoxy-ethyl)-amine) were not active at the highest concentration tested (10(-6) M). We conclude that this is a simple and accurate assay for characterisation of the pharmacology of the recombinant CRF-BP. This assay should assist with further study of the pharmacology and function of the CRF-BP.

The corticotrophin-releasing factor-binding protein: an act of several parts

Previously the function of hormone binding proteins has been viewed entirely as one of either sequestering ligand activity or of delivering ligand to target tissues. However, some binding proteins have the ability when complexed with ligand to interact directly with target tissues and can undergo considerable post-translational and post-secretional modifications that serve to modify their action. We propose that for the corticotrophin-releasing factor-binding protein (CRF-BP), this adds a further level at which hormonal action may be regulated. This contrasts with previous concepts of a passive role and shows them as important regulators of hormonal action in their own right.

Peritoneal fluid levels of immunoreactive corticotropin-releasing factor (CRF) and CRF-binding protein (CRF-BP) in healthy and endometriosic women

Corticotropin-releasing factor (CRF) is a 41-amino acid neurohormone involved in the neuroendocrine response to stress, also playing a role in cell-mediated immune functions and in inflammation. In the light of recent evidence showing an association between endometriosis and altered cellular immunity factors, the present study investigates immunoreactive (ir) CRF in the peritoneal fluid of healthy women, and in patients with pelvic adhesions and endometriosis. In addition, peritoneal fluid concentrations of CRF-binding protein (CRF-BP), a 37-kDA protein of 322 amino acids able to modulate central and peripheral CRF functions, were evaluated. Peritoneal fluid samples (n = 35) were collected from healthy women (n = 12), from patients with intrapelvic adhesions (n = 8), and from women with endometriosis (n = 15). In the control group a specimen of blood was collected. Peritoneal fluid and plasma CRF levels were measured by a two-site immunoradiometric assay (IRMA), and CRF-BP levels were measured by a specific radioimmunoassay (RIA). CRF and CRF-BP levels in peritoneal fluid were lower than plasma values, and independent of the phase of the menstrual cycle: in particular, in healthy women there was no significant difference between peritoneal fluid and plasma CRF-BP levels during two phases of the menstrual cycle. Peritoneal fluid levels of CRF and CRF-BP were similar in healthy patients and women with pelvic adhesions or with endometriosis, and when patients with adhesions or with endometriosis were considered as single group, no difference in CRF and CRF-BP levels was noted in comparison to the control group. In patients with endometriosis, no significant differences in peritoneal fluid CRF or CRF-BP levels were recorded, although in patients with stage 2 and stage 3 of the disease peritoneal fluid CRF-BP levels were higher than in healthy patients or in those with a lower grade of the disease. These results suggest that the peritoneal concentration of these hormones may reflect the circulating levels: the absence of any significative variations in peritoneal fluid CRF levels according to the degree of the endometriosis, suggests a limited role of CRF in the immunological changes related to the disease

Heterogeneity of the human corticotropin-releasing factor-binding protein

Human corticotropin-releasing factor (hCRF), secreted by the placenta, principally in the third trimester, is specifically bound in the peripheral circulation to a 37-kDa binding protein (CRF-BP). This complex is cleared from the circulation. We postulate that the protein may be returned to the blood in a form that is immunologically altered and not well recognized by the reported RIAs. We report that a stable isoform can result from temporary denaturation of recombinant CRF-BP by 8 mol/L urea. This isoform, urea-treated binding protein, which can bind CRF, has been found to bind to an antibody raised against a synthetic peptide comprising the first 24 amino acid residues of CRF-BP, but not to a second similar N-terminal antibody, although it was closely matched in titer. Urea-treated binding protein also cross-reacts poorly in the RIA with CRF-BP. It is proposed that as a result of in vivo post-ligand binding events, isoforms may be susceptible to cleavage. After affinity purification, which involves denaturation, recombinant CRF-BP was often found to be cleaved after storage in the presence of protease inhibitors. Here we present evidence for a C-terminally truncated form of the native binding protein in the plasma of subjects suffering from rheumatoid arthritis, which may parallel the in vitro truncation.

Cord plasma corticotropin-releasing factor-binding protein (CRF-BP) in term and preterm labour

Corticotropin-releasing factor-binding protein (CRF-BP) in pregnant women is measurable in maternal and fetal plasma as well as in amniotic fluid. The concentration of CRF-BP in maternal plasma and amniotic fluid changes significantly at the time of parturition. The aim of the present study was to evaluate fetal plasma CRF-BP levels in women delivering at term or with preterm labour. CRF-BP levels were measured the in umbilical cord plasma of women subdivided into two groups: (1) healthy pregnant women throughout the last 5 weeks of pregnancy either (a) out of labour (n = 21) or (b) at delivery after spontaneous labour (n = 64); and (2) patients with preterm labour (a) gone to delivery (n = 12) or (b) responding to tocolysis (n = 10). In the group of healthy women at term, CRF-BP levels were also measured in maternal plasma. CRF-BP was measurable in all specimens of umbilical cord plasma. Mean values +/- SEM at 40 weeks (5.85 +/- 0.65 nmol/l) were significantly lower than those obtained at 37 (6.48 +/- 0.47 nmol/l) or 38 (6.95 +/- 1.16 nmol/l) weeks of pregnancy. Similarly, mean +/- SEM maternal plasma CRF-BP levels in women at term out of labour were lowest at 40 weeks (3.57 +/- 0.22 nmol/l). In these women, mean +/- SEM CRF-BP levels in cord plasma (37 weeks: 6.47 +/- 0.47; 38 weeks: 6.95 +/- 1.16; 40 weeks: 5.85 +/- 0.65 nmol/l) were significantly higher than in maternal plasma at the same gestational age (37 weeks: 4.29 +/- 0.2; 38 weeks: 4.35 +/- 0.205; 40 weeks: 3.57 +/- 0.22 nmol/l). Mean +/- SEM levels of cord blood collected at delivery at term (4.93 +/- 0.14 nmol/l) showed lower CRF-BP levels than in women out of labour (6.18 +/- 0.55 nmol/l). Patients with preterm labour, with delivery within 48 h, showed significantly lower levels of cord plasma CRF-BP (4.21 +/- 0.29 nmol/l) than women at term out of labour (6.18 +/- 0.55 nmol/l) and than those at term with labour (4.93 +/- 0.14 nmol/l). Cord plasma CRF-BP levels decreased in the last 5 weeks of pregnancy, similar to maternal plasma CRF-BP levels, the lowest values resulting in women at labour or with preterm labour, thus suggesting that changes of CRF-BP in cord plasma are associated with the events of parturition.

Urocortin interaction with corticotropin-releasing factor (CRF) binding protein (CRF-BP): a novel mechanism for elevating "free' CRF levels in human brain

Here we demonstrate that urocortin, a new mammalian member of the corticotropin-releasing factor (CRF) neuropeptide family has high affinity for both the recombinant human CRF binding protein (CRF-BP) and for a membrane-associated form of the protein solubilized from postmortem human cerebrocortical brain tissue. The rank order of binding potency for both the human recombinant CRF-BP and for the solubilized human brain CRF-BP is: urotensin > hCRF > urocortin > sauvagine. The bound hCRF/hCRF-BP complex was detected in the postmortem human brain tissue using an ELISA assay specific for the hCRF/hCRF-BP complex. A large proportion (65%) of the endogenous hCRF was found to be complexed to the CRF-BP and thus unavailable for CRF receptor activation. Incubation of human brain postmortem tissue extracts with urocortin and urotensin resulted in a dramatic decrease in hCRF/hCRF-BP levels and a concomitant increase in "free' hCRF levels. Thus, urocortin and other putative CRF-related peptides may elevate endogenous levels of "free' hCRF in brain by displacing hCRF from the binding protein. These data define an indirect endogenous mechanism for activation of CRF receptors by new mammalian members of the CRF family of neuropeptides.

Corticotropin releasing factor and its binding protein

Although the lack of ACTH releasing activity of the high peripheral plasma levels of corticotropin releasing factor (CRF) of human placental origin can now be accounted for by the action of a specific sequestering plasma binding protein (pBP), there are many regions of the brain where the BP is found with little or no overlap with CRF. The existence of a mechanism promoting the rapid disappearance of pBP following bolus injection of exogenous CRF into normal individuals, which is triggered by the formation of a dimer complex (BP2/CRF2), and the elevation of pBP levels found in inflammatory disease, coupled with the lack of unequivocal evidence for endogenous CRF in many of these situations, suggests a role for pBP interaction with ligands other than CRF. We have searched for novel BP ligands in the brain and periphery and have found evidence for them in extracts of sheep brain and in synovial fluid collected from the joints of arthritic patients. These novel BP ligands could, thus, be the peptides responsible for many of the roles currently assigned to brain, peripheral, or immune CRF.

Corticotrophin-releasing factor receptors: from molecular biology to drug design

Corticotrophin-releasing factor (CRF) acts within both the brain and the periphery to coordinate the overall response of the body to stress. The involvement of the CRF systems in a variety of both CNS and peripheral disease states has stimulated great interest in this peptide as a potential site of therapeutic intervention. The recent cloning of multiple CRF receptor subtypes has precipitated a new era in CRF research that has allowed precise molecular, pharmacological and anatomical examination of mammalian CRF receptors. In this article, Derek Chalmers and colleagues highlight the major differences between the two classes of CRF receptors, CRF1 and CRF2, and a functionally related CRF-binding protein, and discuss the relevance of these sites to the ongoing development of CRF-based therapeutics.