ACTH-related peptides: receptors and signal transduction systems involved in their neurotrophic and neuroprotective actions

Non-Canonical Effects of ACTH: Insights Into Adrenal Insufficiency

Introduction

Adrenocorticotropic hormone (ACTH) is produced from proopiomelanocortin, which is predominantly synthetized in the corticotroph and melanotroph cells of the anterior and intermediate lobes of the pituitary gland and the arcuate nucleus of the hypothalamus. Although ACTH clearly has an effect on adrenal homeostasis and maintenance of steroid hormone production, it also has extra-adrenal effects that require further elucidation.

Methods

We comprehensively reviewed English language articles, regardless of whether they reported the presence or absence of adrenal and extra-adrenal ACTH effects.

Results

In the present review, we provide an overview on the current knowledge on adrenal and extra-adrenal effects of ACTH. In the section on adrenal ACTH effects, we focused on corticosteroid rhythmicity and effects on steroidogenesis, mineralocorticoids and adrenal growth. In the section on extra-adrenal effects, we have analyzed the effects of ACTH on the osteoarticular and reproductive systems, adipocytes, immune system, brain and skin. Finally, we focused on adrenal insufficiency.

Conclusions

The role of ACTH in maintaining the function of the hypothalamic-pituitary-adrenal axis is well known. Conversely, if we broaden our vision and analyze its role as a potential treatment strategy in other conditions, it will be evident in the literature that researchers seem to have abandoned this aspect in studies conducted several years ago. We believe it is worth re-evaluating the role of ACTH considering its noncanonical effects on the adrenal gland itself and on extra-adrenal organs and tissues; however, this would not have been possible without the recent advances in the pertinent technologies.

Neuroprotective effect of ACTH on collagenase-induced peri-intraventricular hemorrhage in newborn male rats

Peri-intraventricular hemorrhage (PIVH) is a common and serious prematurity-related complication in neonates. Adrenocorticotropic hormone (ACTH) has neuroprotective actions and is a candidate to ameliorate brain damage following PIVH. Here, we tested the efficacy of ACTH1-24 on a collagenase-induced lesion of the germinal matrix (GM) in newborn male rats. Animals received microinjection of the vehicle (PBS, 2 µl) or collagenase type VII (0.3 IU) into the GM/periventricular tissue on postnatal day (PN) 2. Twelve hours later pups received microinjection of either the agonist ACTH1-24 (0.048 mg/kg), or the antagonist SHU9119 (antagonist of MCR3/MCR4 receptors, 0.01 mg/kg), or their combination. Morphological outcomes included striatal injury extension, neuronal and glial cells counting, and immunohistochemical expression of brain lesion biomarkers ipsilateral and contralateral to the hemorrhagic site. Data were evaluated on PN 8. Collagenase induced PIVH and severe ipsilateral striatal lesion. ACTH1-24 dampened the deleterious effects of collagenase-induced hemorrhage in significantly reducing the extension of the damaged area, the striatal neuronal and glial losses, and the immunoreactive expression of the GFAP, S100β, and NG2-glia biomarkers in the affected periventricular area. SHU9119 blocked the glial density rescuing effect of ACTH1-24. ACTH1-24 could be further evaluated to determine its suitability for preclinical models of PVH in premature infants.

Influence of the N-terminus acetylation of Semax, a synthetic analog of ACTH(4-10), on copper(II) and zinc(II) coordination and biological properties

Semax is a heptapeptide (Met-Glu-His-Phe-Pro-Gly-Pro) that encompasses the sequence 4-7 of N-terminal domain of the adrenocorticotropic hormone and a C-terminal Pro-Gly-Pro tripeptide. N-terminal amino group acetylation (Ac-Semax) modulates the chemical and biological properties of parental peptide, modifying the ability of Semax to form complex species with Cu(II) ion. At physiological pH, the main complex species formed by Ac-Semax, [CuLH_-2]^2-, consists in a distorted CuN₃O chromophore with a weak apical interaction of the methionine sulphur. Such a complex differs from the Cu(II)-Semax complex system, which exhibits a CuN₄ chromophore. The reduced ligand field affects the [CuLH_-2]^2- formal redox potential, which is more positive than that of Cu(II)-Semax corresponding species. In the amino-free form, the resulting complex species is redox-stable and unreactive against ascorbic acid, unlike the acetylated form. Semax acetylation did not protect from Cu(II) induced toxicity on a SH-SY5Y neuroblastoma cell line, thus demonstrating the crucial role played by the free NH₂ terminus in the cell protection. Since several brain diseases are associated either to Cu(II) or Zn(II) dyshomeostasis, here we characterized also the complex species formed by Zn(II) with Semax and Ac-Semax. Both peptides were able to form Zn(II) complex species with comparable strength. Confocal microscopy imaging confirmed that peptide group acetylation does not affect the Zn(II) influx in neuroblastoma cells. Moreover, a punctuate distribution of Zn(II) within the cells suggests a preferred subcellular localization that might explain the zinc toxic effect. A future perspective can be the use of Ac-Semax as ionophore in antibody drug conjugates to produce a dysmetallostasis in tumor cells.

Investigation of the effect of α-melanocyte-stimulating hormone on proliferation and early stages of differentiation of human induced pluripotent stem cells

We have studied the influence of α-melanocyte-stimulating hormone (α-MSH) on proliferation and early stages of differentiation of human induced pluripotent stem cells (iPSc). We have demonstrated that α-MSH receptor genes are expressed in undifferentiated iPSc. The expression levels of MCR1, MCR2, and MCR3 increased at the embryoid body (EB) formation stage. The formation of neural progenitors was accompanied by elevation of MCR2, MCR3, and MCR4 expression. α-MSH had no effect on EB generation and iPSc proliferation at concentrations ranging from 1 nM to 10 μM. At the same time, α-MSH increased the generation of neural rosettes in human iPSc cultures more than twice.

Evaluation of Cisplatin Neurotoxicity in Cultured Rat Dorsal Root Ganglia via Cytosolic Calcium Accumulation

BACKGROUND

Calcium homeostasis is considered to be important in antineoplastic as well as in neurotoxic adverse effects of cisplatin.

AIMS

This study aimed to investigate the role of Ca(2+) in cisplatin neurotoxicity in cultured rat dorsal root ganglia (DRG) cells.

STUDY DESIGN

Cell culture study.

METHODS

DRG cells prepared from 1-day old Sprague-Dawley rats were used to determine the role of Ca(2+) in the cisplatin (10-600 μM) neurotoxicity. The cells were incubated with cisplatin plus nimodipine (1-3 μM), dizocilpine (MK-801) (1-3 μM) or thapsigargin (100-300 nM). Toxicity of cisplatinon DRG cells was determined by the MTT assay.

RESULTS

The neurotoxicity of cisplatin was significant when used in high concentrations (100-600 μM). Nimodipine (1 μM) but not MK-801 or thapsigargin prevented the neurotoxic effects of 200 μM of cisplatin.

CONCLUSION

Voltage-dependent calcium channels may play a role in cisplatin neurotoxicity.

Functional characterization of the mouse melanocortin 3 receptor gene promoter

Melanocortin receptor 3 (MC3R) is expressed in the hypothalamus and pituitary in humans and rodents, and is involved in the control of feeding, energy metabolism, and pituitary function. In the mouse pituitary, MC3R is detected in mammotrophs. This study aimed to clarify the regulatory mechanism for Mc3r expression in the mouse pituitary. The promoter activities of reporter constructs for the MC3R gene 5'-flanking region up to -4000 bp (transcription initiation site designated as +1) were analyzed. The promoter activity significantly increased in the -86/+109 construct, but decreased in the -38/+109 construct, indicating that the minimal promoter required for basal expression of Mc3r is located in the -86/+109 region. Putative binding sites for transcription factors AP-1 and ATF4 were found in the 5'-flanking region of Mc3r. Site-directed mutation or deletion of these sites affected the promoter activities. In gel-shift assays with a nuclear extract of mouse anterior pituitary cells, band-shifts were detected for both sites after the addition of the nuclear extract, and were decreased in the presence of excess unlabeled probe competitors. These results indicated that both sites were involved in the regulation of Mc3r expression in anterior pituitary cells. Estradiol-17β treatment increased the Mc3r promoter activity, indicating that the gene is regulated by estradiol-17β. In conclusion, we have demonstrated the minimum promoter region required for Mc3r expression, and identified two binding sites for AP-1 and ATF4 and in the 5' upstream-flanking region of Mc3r that are essential for Mc3r expression.

Predicting mechanism of biphasic growth factor action on tumor growth using a multi-species model with feedback control

A large number of growth factors and drugs are known to act in a biphasic manner: at lower concentrations they cause increased division of target cells, whereas at higher concentrations the mitogenic effect is inhibited. Often, the molecular details of the mitogenic effect of the growth factor are known, whereas the inhibitory effect is not. Hepatoctyte Growth Factor, HGF, has recently been recognized as a strong mitogen that is present in the microenvironment of solid tumors. Recent evidence suggests that HGF acts in a biphasic manner on tumor growth. We build a multi-species model of HGF action on tumor cells using different hypotheses for high dose-HGF activation of a growth inhibitor and show that the shape of the dose-response curve is directly related to the mechanism of inhibitor activation. We thus hypothesize that the shape of a dose-response curve is informative of the molecular action of the growth factor on the growth inhibitor.

Effects of the COOH-terminal tripeptide alpha-MSH(11-13) on corneal epithelial wound healing: role of nitric oxide

It is known that alpha-melanocyte stimulating hormone (alpha-MSH) may exert anti-inflammatory effects and facilitate reparative processes in different tissues. The effective message sequence of alpha-MSH resides in the COOH-terminal tripeptide alpha-MSH(11-13). This study was undertaken to investigate the effects of topical administration of the COOH-terminal tripeptide sequence of alpha-MSH (alpha-MSH(11-13), KPV) on corneal epithelial wound healing in rabbits and the possible role of nitric oxide (NO) in these effects. The whole corneal epithelium was denuded in both eyes by mechanical abrasion. The area of the corneal epithelial defect was stained with fluorescein, photographed, and then measured before the treatment and every 12 h by a computerized software. The mean epithelial wound area and the mean percent of epithelial defect remaining at each follow-up control were compared between experimental groups. Rabbits were topically treated with KPV 1, 5 or 10 mg/ml (30 microl), two drops four times in a day, for 4 days, starting immediately after corneal abrasion, while control animals received topical phosphate-buffered saline as vehicle. In order to study the role of NO in corneal repair processes, the NO donor, sodium nitroprusside (SP, 10 mg/ml, 30 microl) was administered in both eyes, two drops four times in a day, for 4 days. The effects of KPV or SP were challenged by pre-treatment with the nitric oxide synthase inhibitor, N omega-nitro-L-arginine methyl ester (L-NAME, 10 mg/ml, 30 microl) 30 min prior to KPV or SP instillation. The mean percent epithelial defect remaining each time was significantly smaller in animals treated with KPV or SP in comparison to controls. Sixty hours later, eight out of eight (100%) corneas treated with KPV or SP were completely re-epithelized (P<0.05) while none of the corneas treated with placebo were re-epithelized. Pre-treatment with L-NAME inhibited the facilitating effect of KPV on corneal epithelial wound healing process and totally prevented the effect of SP. Rabbit corneal epithelial cells (RCE) in culture were exposed for 1, 6 and 24 h to different KPV concentrations (0.1, 1 and 10 microM) in medium containing 15% foetal bovine serum (FBS). Cell viability was stimulated by 1 and 10 microM concentrations of the substance. Thus, KPV may facilitate corneal epithelial wound healing in rabbits with a mechanism that may involve NO disposition in corneal tissue. However, it is not known whether this mechanism is likely to depend on a direct stimulating repairing activity shared by the entire molecule of alpha-MSH.

Degradation of the ACTH(4-10) analog Semax in the presence of rat basal forebrain cell cultures and plasma membranes

Here a new approach of the elucidation of paths of proteolytic biodegradation of physiologically active peptides, based on the use of a peptide with isotopic label at all amino acid residues and the enrichment of HPLC samples with unlabeled peptide fragments in UV-detectable concentration, has been proposed. The method has been applied for the investigation of degradation dynamics of the neuroactive heptapeptide MEHFPGP (Semax) in the presence of plasma membranes, and cultures of glial and neuronal cells obtained from the rat basal forebrain. The splitting away of ME and GP, and formation of pentapeptides are the predominant processes in the presence of all tested objects, whereas the difference in patterns of resulting peptide products for glial and neuronal cells has been detected. In conclusion, the approach applied allows analyzing physiologically active peptide concentrations in biological tissues and degradation pathways of peptides in the presence of targets of their action.

Semax, an analogue of adrenocorticotropin (4-10), binds specifically and increases levels of brain-derived neurotrophic factor protein in rat basal forebrain

The heptapeptide Semax (Met-Glu-His-Phe-Pro-Gly-Pro) is an analogue of the N-terminal fragment (4-10) of adrenocorticotropic hormone which, after intranasal application, has profound effects on learning and memory formation in rodents and humans, and also exerts marked neuroprotective effects. A clue to the molecular mechanism underlying this neurotropic action was recently given by the observation that Semax stimulates the synthesis of brain-derived neurotrophic factor (BDNF), a potent modulator of synaptic plasticity, in astrocytes cultured from rat basal forebrain. In the present study, we investigated whether Semax affects BDNF levels in rat basal forebrain upon intranasal application of the peptide. In addition, we examined whether cell membranes isolated from this brain region contained binding sites for Semax. The binding of tritium-labelled Semax was found to be time dependent, specific and reversible. Specific Semax binding required calcium ions and was characterized by a mean+/-SEM dissociation constant (KD) of 2.4+/-1.0 nm and a BMAX value of 33.5+/-7.9 fmol/mg protein. Sandwich immunoenzymatic analysis revealed that Semax applied intranasally at 50 and 250 microg/kg bodyweight resulted in a rapid increase in BDNF levels after 3 h in the basal forebrain, but not in the cerebellum. These results point to the presence of specific binding sites for Semax in the rat basal forebrain. In addition, these findings indicate that the cognitive effects exerted by Semax might be associated, at least in part, with increased BDNF protein levels in this brain region.

Natural and hybrid (“chimeric”) stable regulatory glyproline peptides

The present concept of relative instability of regulatory peptides (RPs) in organisms must be amended. The recently characterized family of glyprolines and some other prolyl-glycyl-proline (PGP)-containing oligopeptides show the stability quite comparable with those of major pharmacological preparations. The ability of glyprolines to pass gastro-enteric tract barriers opens ways to per-oral administration of this new group of drugs such as semax, selank and their fragments. The most interesting approach is the creation of hybrid ("chimeric") peptide drugs combining the unmodified representatives of various natural RPs that distinctly manifest their inherent physiological activities and cooperate with each other in stabilization of whole peptide in vivo. As the result, the activity of such peptides as semax and selank may have value in a vide variety of pathological processes.

Basic science behind the catastrophic epilepsies

The major catastrophic epileptic syndromes of childhood include infantile spasms, Lennox-Gastaut syndrome, and the progressive myoclonus epilepsies (PMEs). Although each of these syndromes manifests in an age-specific manner and is defined by distinct electroclinical features, they are all refractory to medical therapy and are invariably associated with psychomotor deficits, and in the most severe cases, either epileptic encephalopathy or progressive neurodegeneration. While much has been written about the clinical features and natural history of the catastrophic epilepsies, very little is known about the underlying pathophysiology. Progress in our understanding and treatment of these conditions has been hampered by the lack of suitable animal models in which putative mechanisms and novel targets for intervention could be rigorously studied. Nevertheless, recent clinical and basic investigations have identified certain mechanisms that may be relevant to their pathogenesis. In this review, three major hypotheses regarding the pathophysiology of infantile spasms are highlighted: the corticotropin-releasing hormone (CRH) hypothesis, the N-methyl-D-aspartate (NMDA) hypothesis, and the serotonin-kynurenine hypothesis. One or more of these mechanisms may be relevant in part to later-onset catastrophic epilepsies since infantile spasms can persist into later childhood and, like Lennox-Gastaut syndrome, well into adulthood. There is a profound need to develop more relevant animal models of the developmental encephalopathic epilepsies to truly develop better therapeutic strategies for these catastrophic disorders.

Proopiomelanocortin and melanocortin receptors in the adult rat retino-tectal system and their regulation after optic nerve transection

The aim of this study was to characterise the expression of the melanocortin system in the normal and injured rat visual system. Using real-time polymerase chain reaction and immunohistochemistry, we detected melanocortin MC(3), MC(4) and MC(5) receptors and proopiomelanocortin in adult retina and superior colliculus. Melanocortin MC(4) receptor mRNA was the most abundant receptor. Melanocortin MC(3), MC(4) and MC(5) receptors were localised to the ganglion cell and inner nuclear layers and the melanocortin MC(3) and MC(4) receptors were localised to retinal ganglion cells. Transection of the optic nerve leads to ganglion cell death and both melanocortin receptor and proopiomelanocortin expression decreased in superior colliculus after transection whereas the expression was unchanged or even increased in the retina. alpha-Melanocyte-stimulating hormone elicited neurite outgrowth from embryonic retinal explants. Together, these data implicate a role for the melanocortin system in the adult rat retina and that melanocortins can stimulate neurite growth from retinal neurons.

The role of melanocortins and their receptors in inflammatory processes, nerve regeneration and nociception

The melanocortins are a family of bioactive peptides derived from proopiomelanocortin. Those peptides, included among hormones and comprising ACTH, alpha-MSH, beta-MSH and gamma-MSH, are best known mainly for their physiological effects, such as the control of skin pigmentation by alpha-MSH, and ACTH effects on pigmentation and steroidogenesis. Melanocortins are released in various sites in the central nervous system and in peripheral tissues, and participate in the regulation of multiple physiological functions. They are involved in grooming behavior, food intake and thermoregulation processes, and can also modulate the response of the immune system in inflammatory states. Research of the past decade provided evidence that melanocortins could elicit their diverse biological effects by binding to a distinct family of G protein-coupled receptors with seven transmembrane domains. To date, five melanocortin receptor genes have been cloned and characterized. Those receptors differ in their tissue distribution and in their ability to recognize various melanocortins. These advances have opened up new horizons for exploring the significance of melanocortins, their ligands and their receptors for a variety of important physiological functions. We reviewed the origin of MSH peptides, the function and distribution of melanocortin receptors and their endogenous and exogenous ligands and the role of melanocortins and their receptors in inflammatory processes, nerve regeneration and nociception. Moreover, we analyzed their interaction with opioid peptides and finally, we discussed the postulated role of the melanocortin system in pain transmission at the spinal cord level.

Action of metyrapone and tetracosactrin to modify cisplatin-induced acute and delayed emesis in the ferret

Cisplatin 5 mg/kg, i.p., induced an acute (day 1) and delayed (days 2 and 3) emetic response in the ferret that was used to investigate the potential anti-emetic activity of metyrapone and tetracosactrin and their potential interaction. The 11beta-hydroxylase enzymes inhibitor metyrapone 10-30 mg/kg, i.p., dose dependently potentiated the acute cisplatin-induce retching+vomiting response by up to 219% at the highest dose (P<0.001) but failed to affect significantly delayed emesis (P>0.05). The adrenocorticotropic hormone (ACTH) mimetic tetracosactrin 0.1 mg/kg, i.m., antagonised significantly the acute and delayed emetic response by 98% (P<0.01) and 75% (P<0.001), respectively. The anti-emetic action of tetracosactrin on acute but not delayed emesis was prevented by combination with metyrapone 10 mg/kg, i.p. Tetracosactrin 0.1 mg/kg, i.m., failed to modify apomorphine (0.25 mg/kg, s.c.)-induced emesis. The potential anti-emetic mechanism of action of metyrapone and tetracosactrin to modulate emesis is discussed.

2,3-Diaryl-5-anilino[1,2,4]thiadiazoles as melanocortin MC4 receptor agonists and their effects on feeding behavior in rats

The melanocortin-4 receptor (MC4) modulates physiological functions such as feeding behavior, nerve regeneration, and drug addiction. Using a high throughput screen based on (125)I-NDP-MSH binding to the human MC4 receptor, we discovered 2,3-diaryl-5-anilino[1,2,4]thiadiazoles 3 as potent and selective MC4 receptor agonists. Through SAR development on the three attached aryl rings, we improved the binding affinity from 174 nM to 4.4 nM IC(50). When delivered intraperitoneally, compounds 3a, 3b, and 3c induced significant inhibition of food intake in a fasting-induced feeding model in rats. When delivered orally, these compounds lost activity, mainly due to rapid metabolism to inactive imidoylthiourea reduction products.

ACTH(1-24) down-regulates expression of ciliary neurotrophic factor mRNA in cultured rat astrocyte

We examined the effects on astrocytes of ACTH, which is used to treat West syndrome. We stimulated cultured rat astrocytes with ACTH(1-24), corticotropin-releasing factor, and dexamethasone, and examined changes in neurotrophic factor mRNAs by reverse transcription-PCR. Down-regulation of ciliary neurotrophic factor mRNA expression was observed by stimulation with ACTH(1-24), but the expression of nerve growth factor, brain-derived neurotrophic factor, and nerotrophin-3 mRNAs was unaffected. Northern blot analysis revealed that the decrease in ciliary neurotrophic factor mRNA occurred 4 h after stimulation with more than 10 nM of ACTH(1-24). Up-regulation of nerotrophin-3 mRNA expression was found after stimulation with 1 mM dexamethasone. These results suggest that ACTH(1-24) administrated in West syndrome may influence the expression of neurotrophic factors in astrocytes in vivo.

Local administration of vasoactive intestinal peptide after nerve transection accelerates early myelination and growth of regenerating axons

Our goal was to determine whether local injections of vasoactive intestinal peptide (VIP) promote early stages of regeneration after nerve transection. Sciatic nerves were transected bilaterally in 2 groups of 10 adult mice. In the first group, 15 microg (20 microL) of VIP were injected twice daily into the gap between transected ends of the right sciatic nerve for 7 days (4 mice) or 14 days (6 mice). The same number of mice in the second group received placebo injections (20 microL of 0.9% sterile saline) in the same site, twice daily, for the same periods. After 7 days, axon sizes, relationships with Schwann cells and degree of myelination were compared in electron micrographs of transversely sectioned distal ends of proximal stumps. Fourteen days after transection, light and electron microscopy were used to compare and measure axons and myelin sheaths in the transection gap, 2-mm distal to the ends of proximal stumps. Distal ends of VIP-treated proximal stumps contained larger axons 7 days after transection. More axons were in 1:1 relationships with Schwann cells and some of them were surrounded by thin myelin sheaths. In placebo-treated proximal stumps, axons were smaller, few were in 1:1 relationships with Schwann cells and no myelin sheaths were observed. In VIP-treated transection gaps, measurements 14 days after transection showed that larger axons were more numerous and their myelin sheaths were thicker. Our results suggest that in this nerve transection model, local administration of VIP promotes and accelerates early myelination and growth of regenerating axons.

Rapid induction of neurotrophin mRNAs in rat glial cell cultures by Semax, an adrenocorticotropic hormone analog

The proliferation, differentiation and survival of neuronal and glial cells are affected by a number of neurotrophic factors, such as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and others. In a previous study, we observed the effects of 'Semax' (Met-Glu-His-Phe-Pro-Gly-Pro), the physiologically active analogue of adrenocorticotropic hormone(4--10), on neuronal cell survival in vitro. We hypothesized that these effects may be mediated by the regulation of expression of some neurotrophic factors. To test this hypothesis we analyzed NGF and BDNF gene expression in glial cells obtained from the basal forebrain of newborn rats, following in vitro treatment with 'Semax'. We observed changes in mRNA levels for both the NGF and BDNF genes. The greatest increase in expression was found after 30 min of 'Semax' administration. At this time, BDNF mRNA level was increased eight-fold in comparison with control, and NGF mRNA level was increased five-fold.

Delta-sleep inducing peptide (DSIP) and ACTH (4-10) analogue influence fos-induction in the limbic structures of the rat brain under emotional stress

The effects of the ACTH (4-10) analogue, ACTH (4-7)-Pro-Gly-Pro, and delta-sleep inducing peptide (DSIP) on the induction of Fos immunoreactivity in the hypothalamic parvocellular paraventricular nucleus (pPVN) and limbic brain regions were studied in Wistar rats with high (resistant) or low (predisposed) resistance to emotional stress, predicted from differences in their open-field behaviour. Fos-immunoreactive (Fos-IR) cells were counted in brain sections automatically with a computer-based image analyser. Under basal conditions, Fos-IR cell numbers were greater in the pPVN in the predisposed rats, but were lower than in the resistant rats in the basolateral amygdala and medial and lateral septum. Intraperitoneal DSIP injection (30 μg/kg) increased basal Fos-IR cell number in the pPVN and lateral septum in resistant rats, with no effects in predisposed rats. ACTH (4-10) analogue (50 μg/kg)increased Fos expression in the pPVN in both resistant and predisposed rats, with essentially no effects in the basolateral amygdala or medial and lateral septum. Emotional stress (60 min restraint and intermittent subcutaneous electrical shocks) increased Fos expression in the pPVN and medial and lateral septum similarly in predisposed and resistant rats, but in the basolateral amygdala in only the predisposed rats. Intraperitoneal DSIP injection reduced the increases in Fos-IR cell number after emotional stress, particularly in predisposed rats. In predisposed rats DSIP decreased the number of Fos-IR cells in the pPVN and the medial and lateral septum, with no change in the basolateral amygdala. In resistant rats, DSIP decreased Fos expression only in the lateral septum. ACTH (4-10) analogue injection inhibited stress-induced Fos expression in the pPVN and the medial septum, but only in predisposed rats. The experiments indicate that DSIP and ACTH (4-10) analogue reduce pPVN and limbic neurone responses to emotional stress in the rats predisposed to emotional stress; the effects on Fos expression may play a role in the biological activities of these peptides.

Age-dependent changes in HCNP-related antigen expression in the human hippocampus

Hippocampal cholinergic neurostimulating peptide (HCNP), originally purified from the young rat hippocampus, enhances the cholinergic phenotype development of the medial septal nucleus in vitro. In this study, we examined the HCNP-antigen distribution and the age-related changes in the number of positive cells in the hippocampus (obtained at autopsy from 74 subjects with no known neurological disorders). Immunohistochemical assay revealed that the immunopositive cells were GABAergic neurons and oligodendrocytes. They were first identified in the fetus at around 25 to 30 weeks and their number increased rapidly with advancing postconceptional age to reach maximal at the perinatal stage and in early postnatal life; it then decreased to the adult level by 10 years old. These results suggest that HCNP-related antigen may play important roles in the development and/or differentiation of the human hippocampus.

Ectopic and abnormal hormone receptors in adrenal Cushing's syndrome

The mechanism by which cortisol is produced in adrenal Cushing's syndrome, when ACTH is suppressed, was previously unknown and was referred to as being "autonomous." More recently, several investigators have shown that some cortisol and other steroid-producing adrenal tumors or hyperplasias are under the control of ectopic (or aberrant, illicit, inappropriate) membrane hormone receptors. These include ectopic receptors for gastric inhibitory polypeptide (GIP), beta-adrenergic agonists, or LH/hCG; a similar outcome can result from altered activity of eutopic receptors, such as those for vasopressin (V1-AVPR), serotonin (5-HT4), or possibly leptin. The presence of aberrant receptors places adrenal cells under stimulation by a trophic factor not negatively regulated by glucocorticoids, leading to increased steroidogenesis and possibly to the proliferative phenotype. The molecular mechanisms responsible for the abnormal expression and function of membrane hormone receptors are still largely unknown. Identification of the presence of these illicit receptors can eventually lead to new pharmacological therapies as alternatives to adrenalectomy, now demonstrated by the long-term control of ectopic P-AR- and LH/hCGR-dependent Cushing's syndrome by propanolol and leuprolide acetate. Further studies will potentially identify a larger diversity of hormone receptors capable of coupling to G proteins, adenylyl cyclase, and steroidogenesis in functional adrenal tumors and probably in other endocrine and nonendocrine tumors.

Hippocampal cholinergic neurostimulating peptides (HCNP)

Neuronal development and differentiation require a variety of cell interactions. Diffusible molecules from target neurons play an important part in mediating such interactions. Our early studies used explant culture technique to examine the factors that enhance the differentiation of septo-hippocampal cholinergic neurons, and they revealed that several components resident in the hippocampus are involved in the differentiation of presynaptic cholinergic neurons in the medial septal nucleus. One of these components, originally purified from young rat hippocampus, is a novel undecapeptide (hippocampal cholinergic neurostimulating peptide; HCNP); this enhances the production of ChAT, but not of AchE. Later experiments revealed that: (1) a specific receptor appears to mediate this effect; (2) NGF and HCNP act cooperatively to regulate cholinergic phenotype development in the medial septal nucleus in culture; and (3) these two molecules differ both in their mechanism of release from the hippocampus and their mechanism of action on cholinergic neurons. The amino acid sequence deduced from base sequence analysis of cloned HCNP-precursor protein cDNA shows that HCNP is located at the N-terminal domain of its precursor protein. The 21 kDa HCNP precursor protein shows homology with other proteins, and it functions not only as an HCNP precursor, but also as a binding protein for ATP, opioids and phosphatidylethanolamine. The distribution and localization of HCNP-related components and the expression of their mRNAs support the notion that the precursor protein is multifunctional. In keeping with its multiple functions, the multiple enhancers and promoters found in the genomic DNA for HCNP precursor protein may be involved in the regulation of its gene in a variety of cells and at different stages of development. Furthermore, several lines of evidence obtained from studies of humans and animal models suggest that certain types of memory and learning disorders are associated with abnormal accumulation and expression of HCNP analogue peptide and/or its precursor protein mRNA in the hippocampus.

Melanocortins and the treatment of nervous system disease. Potential relevance to the skin?

For several decades melanocortins have been implicated in the modulation of brain function. More recently, this idea has been supported by the identification and cloning of melanocortin (MC) receptors in the nervous system. MCs stimulate axonal growth in fetal neural tissue or in neural cell lines in culture. This feature was utilized in screening their neurotrophic or neuroprotection potential in animal studies of nervous system disease (peripheral nerve and spinal cord trauma, toxic and metabolic neuropathies, EAN, EAE, etc.). Some of these effects may be mediated by MC4 receptor activation, although as yet unknown receptors may also be involved (for instance, protection by Org 2766). To what extent MC-nervous system effects are related to known effects of MCs in skin- and neuro-immune systems, remains to be discovered. Nevertheless, it is of interest to note that activation of brain MC4 receptors profoundly affects care behavior for the body surface (skin and fur). The excessive grooming response in rodents exhibits a remarkable functional correlation with MSH activity in a brain-skin axis.

Receptor-Mediated Modulation of Murine Mast Cell Function by α-Melanocyte Stimulating Hormone

The proopiomelanocortin (POMC)-derived neuropeptide α-melanocyte stimulating hormone (α-MSH) is known to modulate some aspects of inflammation through direct effects on T cells, B cells, and monocytes. To determine whether α-MSH might similarly influence mast cell responsiveness, mast cells were examined to see if they expressed the receptor for α-MSH, melanocortin-1 (MC-1), and whether α-MSH altered mast cell function. We thus first identified MC-1 on bone marrow cultured murine mast cells (BMCMC) and a murine mast cell line (MCP-5) employing flow cytometry and through detection of specific binding. Subsequent treatment of mast cells with α-MSH increased the cAMP concentration in a characteristic biphasic pattern, demonstrating that α-MSH could affect intracellular processes. We next examined the effect of α-MSH on mediator release and cytokine expression. IgE/DNP-human serum albumin-stimulated histamine release from mast cells was inhibited by ∼60% in the presence of α-MSH. Although activation of BMCMC induced the expression of mRNAs for the inflammatory cytokines IL-1β, IL-4, IL-6, TNF-α, and the chemokine lymphotactin, mRNAs for IL-1β, TNF-α, and lymphotactin were down-modulated in the presence of α-MSH. Finally, IL-3-dependent proliferative activity of BMCMC was slightly but significantly augmented by α-MSH. Taken together, these observations suggest that α-MSH may exert an inhibitory effect on the mast cell-dependent component of a specific inflammatory response.

Alpha-melanocyte stimulating hormone promotes regrowth of injured axons in the adult rat spinal cord

Peptides related to melanotropin (alphaMSH) and corticotropin (ACTH), collectively termed melanocortins, are known to improve the postlesion repair of injured peripheral nerves. In addition, melanocortins exert trophic effects on the outgrowth of neurites from central nervous system neurons in vitro. Here we report, for the first time, the stimulation by alpha-MSH of spinal neurite outgrowth in vivo after injury. In the in vivo model, spinal cord trauma was produced at lower thoracic spinal levels of adult rats. Under a surgical microscope a laminectomy was performed exposing the dorsum of the spinal cord. Then the dura was cut longitudinally and the dorsal columns were identified. Iridectomy scissors were used to transect the dorsal half of the spinal cord bilaterally, thereby completely lesioning the main corticospinal tract component. Then the lesion gap was immediately filled with a solid collagen matrix. Ingrowth of fibers was quantified using an advanced image analyser using a video image of sections transmitted by a camera. In the control situation virtually no ingrowth of sprouting injured fibers into the collagen implant in the lesion gap was seen. However, when the collagen matrix contained 10(-8) M alpha-MSH, a profound and significant stimulation of fiber ingrowth into the implant was observed (alpha-MSH, 21.5 +/- 2.9%; control, 1.4 +/- 0.6% p < 0.01). A small percentage of these ingrowing fibers was CGRP-immunoreactive (17.0 +/- 4%), whereas no serotonergic ingrowth was observed. Furthermore, we found that local application of alpha-MSH directs a substantial amount of lesioned anterogradely labelled corticospinal tract axons to regrow into the collagen implant (alpha-MSH, 15.2 +/- 5.2%; control, 0.5 +/- 0.3%, p < 0.01). The observed fiber ingrowth is not accompanied by an invasion of astroglial or reactive microglial cells into the implant. In conclusion, inclusion of alpha-MSH in the collagen implant stimulates the regrowth of injured axons in the adult rat spinal cord.

Melanocortin-4 receptor messenger RNA expression is up-regulated in the non-damaged striatum following unilateral hypoxic-ischaemic brain injury

Melanocortin peptides (alpha-melanocyte-stimulating hormone, adrenocorticotropin and fragments thereof) have been shown to have numerous effects on the central nervous system, including recovery from nerve injury and retention of learned behaviour, but the mechanism of action of these peptides is unknown. A family of five melanocortin receptors have recently been discovered, two of which (melanocortin-3 and melanocortin-4 receptors) have been mapped in the rat brain. We have tested the hypothesis that the expression of one or more of the messenger RNAs for three melanocortin receptors (melanocortin-3, melanocortin-4 and melanocortin-5 receptors) would be altered in rat brain following unilateral transient hypoxic-ischaemic brain injury. In this study, using in situ hybridization, we show that melanocortin-4 receptor messenger RNA was up-regulated in the striatum in the non-damaged hemisphere within 24 h after severe hypoxic-ischaemic injury compared with control brains (P<0.05). In a small group of animals, this induction was not blocked by treatment with the anticonvulsant, carbamazepine. Expression of melanocortin-3 receptor messenger RNA in the brain was not altered in this hypoxic-ischaemic injury model and melanocortin-5 receptor messenger RNA was not detected in either control or hypoxic-ischaemic injured rat brains. We hypothesize that the up-regulation of melanocortin-4 receptor messenger RNA expression in the contralateral striatum may be involved in transfer of function to the uninjured hemisphere following unilateral brain injury.

Cisplatin ototoxicity and the possibly protective effect of alpha-melanocyte stimulating hormone

It is known that adrenocorticotrophic hormone (ACTH)-derived peptides, the so-called melanocortins, can reduce cisplatin-induced neurotoxicity. Recently, our group has found that cisplatin-induced ototoxicity can also be reduced or prevented by treatment with the synthetic melanocortin-like peptide, ORG 2766 (Hamers et al., 1994; De Groot et al., 1997). The present study was designed to investigate the possibly ameliorating effects of the physiologically more relevant naturally occurring neuropeptide alpha-melanocyte stimulating hormone (alpha-MSH) upon cisplatin ototoxicity and to compare its protective effects to those of ORG 2766. For eight consecutive days guinea pigs were treated with cisplatin at a concentration of either 1.5 mg/kg/day or 2 mg/kg/day. Animals were co-treated with either alpha-MSH (75 microg/kg/day), ORG 2766 (75 microg/kg/day), or a sham injection containing physiological saline. Electrocochleography and hair cell counts were performed. Treatment with 1.5 mg/kg/day cisplatin resulted in a large variability of the morphological and electrophysiological data, a variability that might have masked possible effects of ORG 2766 and alpha-MSH. Treatment with 2 mg/kg/day cisplatin caused less variable, severe reductions in the compound action potentials and cochlear microphonics combined with basal and middle-turn outer hair cell loss in five out of six animals. However, in the alpha-MSH co-treated groups, two out of six animals could be classified as normal, two animals as moderately affected and two animals as severely affected. In the ORG 2766 co-treated group we found three animals that were not affected and three animals that were severely affected. We conclude that the protective effects of alpha-MSH and ORG 2766 co-treatment are comparable and that alpha-MSH might be clinically useful in protecting against cisplatin-induced ototoxicity.

Expression of melanocortin receptors and pro-opiomelanocortin in the rat spinal cord in relation to neurotrophic effects of melanocortins

Although neurotrophic effects of alpha-melanocyte-stimulating hormone (alpha-MSH) are well established, the mechanism underlying these effects is unknown. To identify candidate components of the signaling system that may mediate these effects, in the present study rat spinal cord, dorsal root ganglia, sciatic nerve and soleus muscle were analysed for the expression of the neural MC3, MC4 and MC5 receptors and for the expression of the melanocortin precursor pro-opiomelanocortin (POMC). In rat lumbar spinal cord, the MC4 receptor was the only MC receptor subtype for which mRNA was detectable using RNAse protection assays. In situ binding studies using 125I-NDP-MSH, a synthetic alpha-MSH analogue, demonstrated MC receptor protein in the rat spinal cord, predominantly localised in substantia gelatinosa and area X, surrounding the central canal. Furthermore, POMC mRNA was demonstrated in rat spinal cord and dorsal root ganglia. These findings suggest a functional melanocortin system in the rat spinal cord, that might be involved in peripheral nerve repair. Regulation of POMC or MC receptor transcripts does not appear to be involved in the response to peripheral nerve crush in rats, since no change in mRNA expression patterns was detected after sciatic nerve crush, using quantitative RNAse protection assays. Nevertheless, subtle changes in melanocortin receptor binding did occur postsurgically in several regions of the spinal cord in both sham-operated and sciatic nerve-lesioned rats. The robust expression of MC receptor protein in spinal cord regions that are generally associated with nociception suggests a potentially broader involvement of endogenous melanocortins in spinal pathways which mediate the responses to peripheral injury, in addition to any direct melanocortin effects on sprouting and neurite outgrowth.

Cisplatin-induced apoptosis in rat dorsal root ganglion neurons is associated with attempted entry into the cell cycle

Platinum compounds induce apoptosis in malignant cells and are used extensively in the treatment of cancer. Total dose is limited by development of a sensory neuropathy. We now demonstrate that when rats are administered cisplatin (2 mg/kg i.p. for 5 d), primary sensory neurons in the dorsal root ganglion die by apoptosis. This was reproduced by exposure of dorsal root ganglion neurons and PC12 cells to cisplatin (3 microg/ml) in vitro. Apoptosis was confirmed by electron microscopy, DNA laddering, and inhibition by the caspase inhibitor z-VAD.fmk (100 microM). Cell death in vitro was preceded by upregulation of cyclin D1, cdk4, and increased phosphorylation of retinoblastoma protein; all are indicators of cell cycle advancement. The level of p16(INK4a), an endogenous inhibitor of the cyclin D1/cdk4 complex decreased. Exposure of PC12 cells and dorsal root ganglion neurons to increased levels of nerve growth factor (100 ng/ ml) prevented both apoptosis and upregulation of the cell cycle markers. Cancer cells without nerve growth factor receptors (gp140TrkA) were not protected by the neurotrophin. This indicated that cisplatin may kill cancer cells and neurons by a similar mechanism. In postmitotic neurons, this involves an attempt to re-enter the cell cycle resulting in apoptosis which is specifically prevented by nerve growth factor.

Effects of the peptide HP228 on nerve disorders in diabetic rats

Motor and sensory nerve conduction velocities (MNCV and SNCV) were reduced in the sciatic nerve of rats after 4 weeks of untreated streptozotocin-induced diabetes, and declined further during the following 4 weeks. Treating diabetic rats with the novel peptide HP228 had no effect on the decline of MNCV after the first 4 weeks of diabetes but attenuated the decline in SNCV. HP228 treatment also prevented any further decline in MNCV or SNCV between weeks 4 and 8 of diabetes. Consequently, at the conclusion of the study, the nerve conduction velocities (NCVs) in treated rats were significantly (both P < .001) higher than in untreated diabetic rats. Reduced nerve homogenate Na+,K+-adenosine triphosphatase (ATPase) activity in diabetic rats was significantly (P < .05) increased by HP228 but remained significantly (P < .05) lower than in untreated controls. HP228 treatment also reduced nerve Na+,K+-ATPase activity of control rats compared with untreated controls (P < .05). There was no effect of HP228 on the hyperglycemia, nerve polyol accumulation, myo-inositol depletion, reduced nerve laser Doppler blood flow, thermal hypoalgesia, or reduced mean axonal caliber in diabetic rats or on any of these parameters in control rats. These data demonstrate that a novel peptide may protect against the slowing of nerve conduction in prolonged diabetes and that the mechanism of action is unrelated to aldose reductase inhibition, prevention of nerve ischemia, or axonal atrophy. HP228 may prove a potential therapeutic agent for the treatment of prolonged diabetic neuropathy.

Mechanisms of antiinflammatory action of the neuroimmunomodulatory peptide alpha-MSH

The antiinflammatory effects of alpha-melanocyte-stimulating hormone (alpha-MSH) molecules, specifically alpha-MSH(1-13) and its COOH-terminal tripeptide alpha-MSH(11-13), are well established. The peptides have been effective in tests of all major models of inflammation, and more recent tests have been extended to include experimental inflammatory bowel disease, CNS ischemia/reperfusion injury, and bacterial endotoxin-induced inflammation within the brain. The broad effectiveness of alpha-MSH molecules in all major types of inflammation indicates that the peptides exert actions that are very basic to the inflammatory process. Three general mechanisms of antiinflammatory action of alpha-MSH molecules have been identified: inhibition of production of inflammatory mediators by, or inhibition of inflammatory actions of, peripheral host cells; inhibition of peripheral inflammation induced by actions on melanocortin receptors within the brain; inhibition of CNS inflammation by local action of the peptides. It appears that alpha-MSH molecules have multiple actions that modulate the primitive inflammatory response.

Interactions of signaling pathways in ACTH (1-24)-induced cell shape changes in invertebrate immunocytes

ACTH (1-24) induces cell shape changes in the immunocytes of the bivalve mollusc, Mytilus galloprovincialis. Using computer-assisted microscopic image analysis, we have found that the G protein antagonist suramin sodium, the adenylate cyclase inhibitor 2',5'-dideoxyadenosine, and the protein kinase inhibitor staurosporine inhibit this effect. The highly specific inhibitors H-89 (for protein kinase A) and calphostin C (for protein kinase C) only inhibited partially the morphological alterations. In contrast, the simultaneous action of H-89 and calphostin C completely blocked these changes. The above findings indicate that ACTH (1-24) induces cell shape changes in molluscan immunocytes via adenylate cyclase/cAMP/protein kinase A pathway, as well as the activation of protein kinase C.

FK506 and the role of immunophilins in nerve regeneration

FK506 is a new FDA-approved immunosuppressant used for prevention of allograft rejection in, for example, liver and kidney transplantations. FK506 is inactive by itself and requires binding to an FK506 binding protein-12 (FKBP-12), or immunophilin, for activation. In this regard, FK506 is analogous to cyclosporin A, which must bind to its immunophilin (cyclophilin A) to display activity. This FK506-FKBP complex inhibits the activity of the serine/threonine protein phosphatase 2B (calcineurin), the basis for the immunosuppressant action of FK506. The discovery that immunophilins are also present in the nervous system introduces a new level of complexity in the regulation of neuronal function. Two important calcineurin targets in brain are the growth-associated protein GAP-43 and nitric oxide (NO) synthase (NOS). This review focuses on studies showing that systemic administration of FK506 dose-dependently speeds nerve regeneration and functional recovery in rats following a sciatic-nerve crush injury. The effect appears to result from an increased rate of axonal regeneration. The nerve regenerative property of this class of agents is separate from their immunosuppressant action because FK506-related compounds that bind to FKBP-12 but do not inhibit calcineurin are also able to increase nerve regeneration. Thus, FK506's ability to increase nerve regeneration arises via a calcineurin-independent mechanism (i.e., one not involving an increase in GAP-43 phosphorylation). Possible mechanisms of action are discussed in relation to known actions of FKBPs: the interaction of FKBP-12 with two Ca2+ release-channels (the ryanodine and inositol 1,4,5-triphosphate receptors) which is disrupted by FK506, thereby increasing Ca2+ flux; the type 1 receptor for the transforming growth factor-beta (TGF-beta 1), which stimulates nerve growth factor (NGF) synthesis by glial cells, and is a natural ligand for FKBP-12; and the immunophilin FKBP-52/FKBP-59, which has also been identified as a heat-shock protein (HSP-56) and is a component of the nontransformed glucocorticoid receptor. Taken together, studies of FK506 indicate broad functional roles for the immunophilins in the nervous system. Both calcineurin-dependent (e.g., neuroprotection via reduced NO formation) and calcineurin-independent mechanisms (i.e., nerve regeneration) need to be invoked to explain the many different neuronal effects of FK506. This suggests that multiple immunophilins mediate FK506's neuronal effects. Novel, nonimmunosuppressant ligands for FKBPs may represent important new drugs for the treatment of a variety of neurological disorders.

Resuscitating effect of melanocortin peptides after prolonged respiratory arrest

1. The resuscitating activity of melanocortin peptides (MSH-ACTH peptides) was tested in an experimental model of prolonged respiratory arrest. 2. Anaesthetized, endotracheally intubated rats subjected to a 5 min period of ventilation interruption, invariably died from cardiac arrest within 6-9 min of resumption of ventilation. 3. When resumption of ventilation was associated with the simultaneous intravenous (i.v.) injection of a melanocortin peptide (alpha-MSH or ACTH-(1-24)) (160 microg kg(-1) there was an almost immediate (within 1 min), impressive increase in cardiac output, heart rate, mean arterial pressure (+ 560% of the before-treatment value) and pulse pressure (+356% of the before-treatment value), with full recovery of electroencephalogram after 30-45 min. Blood gases and pH were normalized within 15-60 min after treatment, and all treated animals eventually recovered completely and survived indefinitely (= more than 15 days). 4. The same response was observed in adrenalectomized animals, as well as in animals pretreated with a beta1-adrenoceptor blocking agent (atenolol, 3 mg kg(-1), i.v.), or with an alpha1-adrenoceptor blocking agent (prazosin, 0.1 mg kg(-1), i.v.), or with an adrenergic neurone blocking agent (guanethidine, 10 mg kg(-1), intraperitoneally). 5. An effect quite similar to that produced by melanocortins was obtained with ouabain (0.1 mg kg(-1), i.v.); the antioxidant drug, glutathione (75 mg kg(-1), i.v.) also produced 100% resuscitation, but the effect was slower in onset. On the other hand, adrenaline (0.005 mg kg(-1), i.v.) was able to resuscitate only 1 out of 8 rats and dobutamine (0.02 mg kg(-1), i.v.) resuscitated 4 out of 8 rats; moreover, the effect of both catecholamines was much slower in onset than that of melanocortins and the initial, impressive stimulation of cardiovascular function was absent. 6. These results show that melanocortin peptides have a resuscitating effect in a pre-terminal condition produced in rats by prolonged asphyxia. This effect seems primarily due to the restoration of cardiac function, not mediated by catecholamines. These data also suggest that these peptides may have potential therapeutic value in conditions of transient cardiac hypoxia and re-oxygenation such as occur in coronary artery disease.

alpha-MSH modulates local and circulating tumor necrosis factor-alpha in experimental brain inflammation

Tumor necrosis factor (TNF-alpha) underlies pathological processes and functional disturbances in acute and chronic neurological disease and injury. The neuroimmunomodulatory peptide alpha-MSH modulates actions and production of proinflammatory cytokines including TNF-alpha, but there is no prior evidence that it alters TNF-alpha induced within the brain. To test for this potential influence of the peptide, TNF-alpha was induced centrally by local injection of bacterial lipopolysaccharide (LPS). alpha-MSH given once i.c.v. with LPS challenge, twice daily intraperitoneally (i.p.) for 5 d between central LPS injections, or both i.p. and centrally, inhibited production of TNF-alpha within brain tissue. Inhibition of TNF-alpha protein formation by alpha-MSH was confirmed by inhibition of TNF-alpha mRNA. Plasma TNF-alpha concentration was elevated markedly after central LPS, indicative of an augmented peripheral host response induced by the CNS signal. The increase was inhibited by alpha-MSH treatments, in relation to inhibition of central TNF-alpha. Presence within normal mouse brain of mRNA for the alpha-MSH receptor MC-1 suggests that the inhibitory effects of alpha-MSH on brain and plasma TNF-alpha might be mediated by this receptor subtype. The inhibitory effect of alpha-MSH on brain TNF-alpha did not depend on circulating factors because the effect also occurred in brain tissue in vitro. This indicates that alpha-MSH can act directly on brain cells to inhibit their production of TNF-alpha. If central TNF-alpha contributes to pathology in CNS disease and injury, and promotes inflammation in the periphery, agents that act on brain alpha-MSH receptors should decrease the pathological TNF-alpha reaction and promote tissue survival.

Anti-inflammatory actions of the neuroimmunomodulator alpha-MSH

alpha-melanocyte-stimulating hormone (alpha-MSH) is an endogenous neuroimmunomodulatory peptide that inhibits fever and all major forms of experimental inflammation. In humans, concentrations of alpha-MSH are increased at sites of inflammation, and in plasma in inflammatory disorders and after infection of endotoxin. The effects of this 'anti-cytokine' peptide are mediated through alpha-MSH receptors and regulatory circuits in macrophages and neutrophils, and through descending neural anti-inflammatory pathways that originate from alpha-MSH receptors on neurons within the brain.

Melanocortins and opiate addiction

Adrenocorticotropic hormone (ACTH) and alpha-melanocyte stimulating hormone (alpha-MSH) are centrally acting melanocortin peptides with numerous reported functions, including induction of excessive grooming and antipyresis, among others. Also reported is a role for melanocortins in aspects of opiate action. Although early work examined the effects of ACTH and MSH on opiate-induced behaviors, further progress has been limited. Recently, however, advances in the identification and characterization of melanocortin receptor (MC-R) subtypes have provided novel tools with which to study interactions between melanocortins and addiction. The present review discusses the effects of ACTH and MSH on opiate-induced behaviors and relates these findings to more recent reports on the regulation of melanocortin systems by exogenous opiates. Emerging from these data is the possibility that melanocortin receptor activation, specifically at the MC4-R subtype, may act to antagonize certain properties of exogenous opiates, including perhaps addiction.

Alpha-MSH stimulates neurite outgrowth of neonatal rat corticospinal neurons in vitro

Peptides related to melanocortin (alpha MSH) and corticotropin (ACTH), collectively termed melanocortins, exert trophic effects on the outgrowth of neurites from peripheral and central nervous system in vitro. Here we study the neurite outgrowth promoting effect of alpha-MSH on corticospinal (CS) neurons in vitro. Corticospinal neurons were identified in cell culture of neonatal rat cortex by immunostaining of cholera toxin subunit B (CTB), retrogradely transported from the cervical parts of the spinal cord. The CTB-immunoreactive neurons represent a small percentage (3-5%) of the total cell population after 72 h in vitro. The axons or dendrites of cortical and CTB-labelled layer V neurons were visualized using antibodies against axon- or dendrite-specific markers and measured using a semi-automatic quantification device. Here we report that alpha-MSH stimulates axonal as well as dendrite outgrowth from both total and CTB-labelled neurons with a bell-shape response curve. Axonal outgrowth of CTB-labelled neurons was dose-dependently stimulated with a maximal effect of 50% at 10(-10) M alpha-MSH. The maximal effect for stimulation of axon outgrowth for the total cortex population was observed at 10(-8) M alpha-MSH. In addition dendrite outgrowth of both total and CTB-labelled neurons is stimulated in a dose-dependent manner with maximal effects (varying between 46 and 48%) at 10(-8) M alpha-MSH. Explanations in the shift for the optimal alpha-MSH concentration for stimulation of axonal outgrowth of CTB-labelled layer V neurons as compared to total cortex neurons are discussed.

Melanocortin receptors mediate alpha-MSH-induced stimulation of neurite outgrowth in neuro 2A cells

Melanocortins (MC), neuropeptides derived from pro-opiomelanocortin, have been implicated in enhancing neurite outgrowth via an as yet unknown mechanism. Recently, five MC receptors have been identified, three of which, the MC3-R, the MC4-R and the MC5-R, are expressed in the nervous system. In this study, alpha-MSH and the melanocortin analog [D-Phe7]ACTH (4-10) were able to stimulate neurite outgrowth in the neuroblastoma cell line Neuro 2A. ACTH (4-10), gamma2-MSH and ORG2766 were inactive. In addition, the MC4-R antagonist [D-Arg8]ACTH (4-10), inhibited the alpha-MSH effect, indicating that the MC4-R mediated stimulation of neurite outgrowth by alpha-MSH. Indeed, the presence of MC4-R mRNA in Neuro 2A cells was demonstrated by a RNase protection assay. Heterologous expression of the MC5-R in Neuro 2A cells lead to the recruitment of a responsiveness to gamma2-MSH, but did not increase the effect of alpha-MSH on neurite outgrowth. This finding indicated that the function of MC4-R can also be exerted by another MC receptor, suggesting that the coupling to Gs, which they have in common, plays an essential role in the neurite outgrowth promoting effect. This was further substantiated by the fact that forskolin treatment per se induced neurite outgrowth in a similar fashion. These data imply that the neurotrophic properties of alpha-MSH are likely to result from Gs-coupled MC receptor activity in neuronal cells.

Cardiovascular effects of gamma-MSH/ACTH-like peptides: structure-activity relationship

Intravenous administration of gamma2-melanocyte-stimulating hormone (gamma2-MSH) to conscious rats causes a dose-dependent increase in blood pressure and heart rate, while the structurally related peptide adrenocorticotropic hormone-(4-10) (ACTH-(4-10)) is 5-10 times less potent in this respect. This prompted us to investigate which amino acid sequence is determinant for the cardiovascular selectivity of peptides of the gamma-MSH family. Lys-gamma2-MSH, most likely the endogenously occurring gamma-MSH analog, was as potent as gamma2-MSH in inducing increases in blood pressure and heart rate. Removal of C-terminal amino acids resulted in gamma-MSH-fragments which were devoid of cardiovascular activities. Removal of amino acids from the N-terminal side of gamma2-MSH resulted in fragments which were less potent, but had an intrinsic activity not different from that of gamma-MSH. Surprisingly, gamma-MSH-(6-12) was more potent than gamma2-MSH. The shortest fragment which displayed pressor and tachycardiac responses was the MSH 'core', His-Phe-Arg-Trp (= gamma-MSH-(5-8)), which is identical to ACTH-(6-9). This was corroborated by testing fragments of ACTH-(4-10). We conclude that the message essential for cardiovascular effects resides in the gamma-MSH-(5-8)/ACTH-(6-9) sequence. Proper C-terminal elongation is required for full expression of cardiovascular activity of gamma2-MSH, as the sequence of Asp9-Arg10-Phe11 appears to play an important role in establishing intrinsic activity. The amino acids N-terminal to the MSH 'core' sequence appear to be essential for the potency of the peptides.