Resuscitating effect of melanocortin peptides after prolonged respiratory arrest

Therapeutic Effects of Stimulating the Melanocortin Pathway in Regulating Ocular Inflammation and Cell Death

Alpha-melanocyte-stimulating hormone (α-MSH) and its binding receptors (the melanocortin receptors) play important roles in maintaining ocular tissue integrity and immune homeostasis. Particularly extensive studies have demonstrated the biological functions of α-MSH in both immunoregulation and cyto-protection. This review summarizes the current knowledge of both the physiological and pathological roles of α-MSH and its receptors in the eye. We focus on recent developments in the biology of α-MSH and the relevant clinical implications in treating ocular diseases.

Epinephrine increases contextual learning through activation of peripheral β2-adrenoceptors

RATIONALE

Phenylethanolamine-N-methyltransferase knockout (Pnmt-KO) mice are unable to synthesize epinephrine and display reduced contextual fear. However, the precise mechanism responsible for impaired contextual fear learning in these mice is unknown.

OBJECTIVES

Our aim was to study the mechanism of epinephrine-dependent contextual learning.

METHODS

Wild-type (WT) or Pnmt-KO (129x1/SvJ) mice were submitted to a fear conditioning test either in the absence or in the presence of epinephrine, isoprenaline (non-selective β-adrenoceptor agonist), fenoterol (selective β2-adrenoceptor agonist), epinephrine plus sotalol (non-selective β-adrenoceptor antagonist), and dobutamine (selective β1-adrenoceptor agonist). Catecholamines were separated by reverse-phase HPLC and quantified by electrochemical detection. Blood glucose was measured by coulometry.

RESULTS

Re-exposure to shock context induced higher freezing in WT and Pnmt-KO mice treated with epinephrine and fenoterol than in mice treated with vehicle. In addition, freezing response in Pnmt-KO mice was much lower than in WT mice. Freezing induced by epinephrine was blocked by sotalol in Pnmt-KO mice. Epinephrine and fenoterol treatment restored glycemic response in Pnmt-KO mice. Re-exposure to shock context did not induce a significant difference in freezing in Pnmt-KO mice treated with dobutamine and vehicle.

CONCLUSIONS

Aversive memories are best retained if moderately high plasma epinephrine concentrations occur at the same moment as the aversive stimulus. In addition, epinephrine increases context fear learning by acting on peripheral β2-adrenoceptors, which may induce high levels of blood glucose. Since glucose crosses the blood-brain barrier, it may enhance hippocampal-dependent contextual learning.

Protective effects of the melanocortin analog NDP-α-MSH in rats undergoing cardiac arrest

We previously reported that melanocortins afford cardioprotection in conditions of experimental myocardial ischemia/reperfusion, with involvement of the janus kinases (JAK), extracellular signal-regulated kinases (ERK) and signal transducers and activators of transcription (STAT) signalings. We investigated the influence of the melanocortin analog [Nle(4), D-Phe(7)]α-melanocyte-stimulating hormone (NDP-α-MSH) on short-term detrimental responses to cardiac arrest (CA) induced in rats by intravenous (i.v.) administration of potassium chloride, followed by cardiopulmonary resuscitation (CPR) plus epinephrine treatment. In CA/CPR rats i.v. treated with epinephrine (0.1 mg/kg) and returned to spontaneous circulation (48%) we recorded low values of mean arterial pressure (MAP) and heart rate (HR), alteration of hemogasanalysis parameters, left ventricle low expression of the cardioprotective transcription factors pJAK2 and pTyr-STAT3 (JAK-dependent), increased oxidative stress, up-regulation of the inflammatory mediators tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), and down-regulation of the anti-inflammatory cytokine IL-10, as assessed at 1h and 3h after CPR. On the other hand, i.v. treatment during CPR with epinephrine plus NDP-α-MSH (340 μg/kg) almost completely restored the basal conditions of MAP and HR, reversed metabolic acidosis, induced left ventricle up-regulation of pJAK2, pTyr-STAT3 and IL-10, attenuated oxidative stress, down-regulated TNF-α and IL-6 levels, and improved survival rate by 81%. CA/CPR plus epinephrine alone or in combination with NDP-α-MSH did not affect left ventricle pSer-STAT3 (ERK1/2-dependent) and pERK1/2 levels. These results indicate that melanocortins improve return to spontaneous circulation, reverse metabolic acidosis, and inhibit heart oxidative stress and inflammatory cascade triggered by CA/CPR, likely via activation of the JAK/STAT signaling pathway.

Melanocortins and the cholinergic anti-inflammatory pathway

Experimental evidence indicates that small concentrations of inflammatory molecules produced by damaged tissues activate afferent signals through ascending vagus nerve fibers, that act as the sensory arm of an "inflammatory reflex". The subsequent activation of vagal efferent fibers, which represent the motor arm of the inflammatory reflex, rapidly leads to acetylcholine release in organs of the reticuloendothelial system. Acetylcholine interacts with α7 subunit-containing nicotinic receptors in tissue macrophages and other immune cells and rapidly inhibits the synthesis/release of tumor necrosis factor-α and other inflammatory cytokines. This neural anti-inflammatory response called "cholinergic anti-inflammatory pathway" is fast and integrated through the central nervous system. Preclinical studies are in progress, with the aim to develop therapeutic agents able to activate the cholinergic anti-inflammatory pathway. Melanocortin peptides bearing the adrenocorticotropin/α-melanocyte-stimulating hormone sequences exert a protective and life-saving effect in animals and humans in conditions of circulatory shock. These neuropeptides are likewise protective in other severe hypoxic conditions, such as prolonged respiratory arrest, myocardial ischemia, renal ischemia and ischemic stroke, as well as in experimental heart transplantation. Moreover, experimental evidence indicates that melanocortins reverse circulatory shock, prevent myocardial ischemia/reperfusion damage and exert neuroprotection against ischemic stroke through activation of the cholinergic anti-inflammatory pathway. This action occurs via stimulation of brain melanocortin MC3/MC4 receptors. Investigations that determine the molecular mechanisms of the cholinergic anti-inflammatory pathway activation could help design of superselective activators of this pathway.

Melanocortins as potential therapeutic agents in severe hypoxic conditions

Melanocortin peptides with the adrenocorticotropin/melanocyte-stimulating hormone (ACTH/MSH) sequences and synthetic analogs have protective and life-saving effects in experimental conditions of circulatory shock, myocardial ischemia, ischemic stroke, traumatic brain injury, respiratory arrest, renal ischemia, intestinal ischemia and testicular ischemia, as well as in experimental heart transplantation. Moreover, melanocortins improve functional recovery and stimulate neurogenesis in experimental models of cerebral ischemia. These beneficial effects of ACTH/MSH-like peptides are mostly mediated by brain melanocortin MC(3)/MC(4) receptors, whose activation triggers protective pathways that counteract the main ischemia/reperfusion-related mechanisms of damage. Induction of signaling pathways and other molecular regulators of neural stem/progenitor cell proliferation, differentiation and integration seems to be the key mechanism of neurogenesis stimulation. Synthesis of stable and highly selective agonists at MC(3) and MC(4) receptors could provide the potential for development of a new class of drugs for a novel approach to management of severe ischemic diseases.

Protective effects of melanocortins on short-term changes in a rat model of traumatic brain injury*

OBJECTIVE

Treatment for traumatic brain injury remains elusive despite compelling evidence from animal models for a variety of therapeutic targets. Melanocortins have established neuroprotective effects against experimental ischemic stroke. We investigated whether melanocortin treatment of traumatic brain injury induces neuroprotection and promotes functional recovery.

DESIGN

Randomized experiment.

SETTING

Research laboratory at a university hospital.

SUBJECTS

Male Sprague-Dawley rats (n = 215).

INTERVENTIONS

Experimental rat model of diffuse traumatic brain injury, the impact-acceleration model.

MEASUREMENT AND MAIN RESULTS

Brain tissue nitrites, phosphorylation level of extracellular signal-regulated kinases, and c-jun N-terminal kinases; and expression of active caspase-3, tumor necrosis factor-α, BAX, and Bcl-2 as well as serum levels of interleukin-6, high mobility group box-1, interleukin-10, and brain histologic damage were evaluated 24 or 48 hrs after the insult. Sensorimotor orientation and limb use were evaluated at day 7 and learning and memory at days 23-30 after injury. Posttraumatic treatment every 12 hrs with the melanocortin analog [Nle, D-Phe]-α-melanocyte-stimulating hormone (starting 3 or 6 hrs after injury) inhibited traumatic brain injury-induced upregulation of nitric oxide synthesis, phosphorylation level of extracellular signal-regulated kinases, phosphorylation level of c-jun N-terminal kinases, and active caspase-3; reduced expressions/levels of tumor necrosis factor-α, BAX, interleukin-6, and high mobility group box-1; and increased those of Bcl-2 and interleukin-10. These molecular changes were associated with a reduction in brain tissue damage, as highlighted by histopathological findings and improved functional recovery. Pretreatment with the melanocortin MC4 receptor antagonist HS024 abated the positive effects of [Nle, D-Phe]-α-melanocyte-stimulating hormone.

CONCLUSIONS

Our data indicate that melanocortins protect against traumatic brain injury, in a broad time window and through activation of MC4 receptors, by counteracting the main traumatic brain injury-related mechanisms of damage. These findings could have major clinical implications.

Drug-induced activation of the nervous control of inflammation: a novel possibility for the treatment of hypoxic damage

Together with undernutrition and, on the opposite, overeating and obesity, sudden tissue hypoperfusion is the most important cause of mortality and disability worldwide. Tissue hypoperfusion/hypoxia rapidly triggers an unrestrained inflammatory cascade that is the main responsible for the severity of the eventual outcome. The brain plays a key role in inflammation, either through activation of the hypothalamic-pituitary-adrenal humoral response or through activation of the vagal "cholinergic anti-inflammatory pathway". Both humoral and nervous brain responses to inflammation are under the regulatory control of melanocortins, which have moreover a direct anti-inflammatory effect on inflammatory cells. Abundant experimental and clinical evidence indicates that MC(3)/MC(4) melanocortin receptor agonists and cholinergic receptor agonists (mainly at the α7-nicotinic subtype) should by now be considered as completely innovative, effective drugs for the treatment of hypoxic conditions; melanocortin agonists being practically devoid of harmful side effects.

Treatment of cerebral ischemia with melanocortins acting at MC4 receptors induces marked neurogenesis and long-lasting functional recovery

Melanocortins produce neuroprotection against ischemic stroke with subsequent long-lasting functional recovery, through melanocortin MC(4) receptor activation. Here we investigated whether the long-lasting beneficial effect of melanocortins in stroke conditions is associated with a stimulation of neurogenesis. Gerbils were subjected to transient global cerebral ischemia by occluding both common carotid arteries for 10 min; then, they were prepared for 5-bromo-2'-deoxyuridine (BrdU) labeling of proliferating cells. Delayed treatment (up to 9 h after the ischemic injury) for 11 days with the melanocortin analog [Nle(4),D-Phe(7)]α-melanocyte-stimulating hormone (NDP-α-MSH) improved learning and memory throughout the 50-day observation period. Immunohistochemical examination of the hippocampus on day 50 showed, in the dentate gyrus, an elevated number of BrdU immunoreactive cells colocalized with NeuN (used as indicator of mature neurons) and Zif268 (used as indicator of functionally integrated neurons). Retrospective analysis during the early stage of neural stem/progenitor cell development (days 3 and 4 after stroke) showed, in NDP-α-MSH-treated gerbils, a high degree of daily cell proliferation and revealed that NDP-α-MSH favorably affects Wnt-3A signaling pathways and doublecortin expression. Pharmacologic blockade of MC(4) receptors prevented all effects of NDP-α-MSH. These data indicate that treatment of cerebral ischemia with MC(4) receptor agonists induces, with a broad window of therapeutic opportunity, long-lasting functional recovery associated with a large number of mature and likely functional newborn neurons in brain injured areas. Our findings reveal previously undescribed effects of melanocortins which might have major clinical implications.

Melanocortins protect against multiple organ dysfunction syndrome in mice

BACKGROUND AND PURPOSE

Melanocortins reverse circulatory shock and improve survival by counteracting the systemic inflammatory response, and through the activation of the vagus nerve-mediated cholinergic anti-inflammatory pathway. To gain insight into the potential therapeutic value of melanocortins against multiple organ damage following systemic inflammatory response, here we investigated the effects of the melanocortin analogue [Nle⁴ D-Phe⁷]α-MSH (NDP-α-MSH) in a widely used murine model of multiple organ dysfunction syndrome (MODS).

EXPERIMENTAL APPROACH

MODS was induced in mice by a single intraperitoneal injection of lipopolysaccharide followed, 6 days later (= day 0), by zymosan. After MODS or sham MODS induction, animals were randomized to receive intraperitoneally NDP-α-MSH (340 µg·kg⁻¹ day) or saline for up to 16 days. Additional groups of MODS mice were concomitantly treated with the melanocortin MC₄ receptor antagonist HS024, or the nicotinic acetylcholine receptor antagonist chlorisondamine, and NDP-α-MSH.

KEY RESULTS

At day 7, in the liver and lung NDP-α-MSH, significantly reduced mRNA expression of tumour necrosis factor-α (TNF-α), increased mRNA expression of interleukin-10 and improved the histological picture, as well as reduced TNF-α plasma levels; furthermore, NDP-α-MSH dose-dependently increased survival rate, as assessed throughout the 16 day observation period. HS024 and chlorisondamine prevented all the beneficial effects of NDP-α-MSH in MODS mice.

CONCLUSIONS AND IMPLICATIONS

These data indicate that NDP-α-MSH protects against experimental MODS by counteracting the systemic inflammatory response, probably through brain MC₄ receptor-triggered activation of the cholinergic anti-inflammatory pathway. These findings reveal previously undescribed effects of melanocortins and could have clinical relevance in the MODS setting.

Functional recovery after delayed treatment of ischemic stroke with melanocortins is associated with overexpression of the activity-dependent gene Zif268

Melanocortin peptides afford strong neuroprotection and improve functional recovery in experimental ischemic stroke; they also have established neurotrophic actions. The expression of the immediate early gene Zif268 is dependent on synaptic activity and is involved in injury repair and memory formation. Here, we investigated the role of Zif268 in learning and memory recovery after delayed treatment of ischemic stroke with the melanocortin analog [Nle(4), D-Phe(7)]alpha-MSH (NDP-alpha-MSH). A 10-min period of global cerebral ischemia was induced by occluding both common carotid arteries in gerbils. Treatment with a nanomolar dose of NDP-alpha-MSH (every 12h for 11 days) was performed starting 3h or 9h after stroke induction; where indicated, gerbils were pretreated with the melanocortin MC(4) receptor antagonist HS024. Animals were subjected to the Morris water-maze test (four sessions from 4 to 50 days after the ischemic episode). Fifty days after stroke, histological damage and Zif268 expression were investigated in the hippocampus. Treatment with NDP-alpha-MSH significantly reduced hippocampal damage, including neuronal death, and improved learning and memory recovery. This protective effect was long-lasting (50 days, at least) and associated with Zif268 overexpression, with both schedules of NDP-alpha-MSH treatment. Pharmacological blockade of MC(4) receptors prevented these effects. Our data indicate that MC(4) receptor-mediated actions of melanocortins could trigger repair mechanisms able to improve neuronal functionality and synaptic plasticity, and to promote long-lasting functional recovery from ischemic stroke with Zif268 gene involvement.

Role of alpha-melanocyte stimulating hormone and melanocortin 4 receptor in brain inflammation

Inflammatory processes contribute widely to the development of neurodegenerative diseases. The expression of many inflammatory mediators was found to be increased in central nervous system (CNS) disorders suggesting that these molecules are major contributors to neuronal damage. Melanocortins are neuropeptides that have been implicated in a wide range of physiological processes. The melanocortin alpha-melanocyte stimulating hormone (alpha-MSH) has pleiotropic functions and exerts potent anti-inflammatory actions by antagonizing the effects of pro-inflammatory cytokines and by decreasing important inflammatory mediators. Five subtypes of melanocortin receptors (MC1R-MC5R) have been identified. Of these, the MC4 receptor is expressed predominantly throughout the CNS. Evidence of effectiveness of selective MC4R agonists in modulating inflammatory processes and their low toxicity suggest that these molecules may be useful in the treatment of CNS disorders with an inflammatory component. This review describes the involvement of the MC4R in central anti-inflammatory effects of melanocortins and discusses the potential value of MC4R agonists for the treatment of inflammatory-related disorders.

Neuroprotection in focal cerebral ischemia owing to delayed treatment with melanocortins

In gerbils subjected to transient global cerebral ischemia, melanocortin peptides produce long-lasting protection with a broad time window, and through the activation of central nervous system melanocortin MC(4) receptors. Here we aimed to investigate whether melanocortins are neuroprotective also in a rat model of focal cerebral ischemia induced by intrastriatal microinjection of endothelin-1. The vasoconstrictor agent endothelin-1 caused a significant impairment in spatial learning and memory, as well as in sensory-motor orientation and limb use, associated with severe striatal morphological damage including intense neuronal death and an almost complete myelin degradation. Treatment of ischemic rats with a nanomolar dose (340 microg/kg/day i.p. for 11 days, beginning 3 h or 9 h after endothelin-1 microinjection) of the melanocortin analog [Nle(4), D-Phe(7)]alpha-melanocyte-stimulating hormone (NDP-alpha-MSH) significantly reduced striatal damage, and improved subsequent functional recovery, with all scheduled NDP-alpha-MSH treatments. Pharmacological blockade of melanocortin MC(4) receptors prevented the protective effect of NDP-alpha-MSH. Our findings give evidence that melanocortins are neuroprotective, with a broad time window, also in a severe model of focal cerebral ischemia, and suggest that melanocortin MC(4) receptor agonists could produce neuroprotection in different experimental models of ischemic stroke.

Selective melanocortin MC4 receptor agonists reverse haemorrhagic shock and prevent multiple organ damage

BACKGROUND AND PURPOSE

In circulatory shock, melanocortins have life-saving effects likely to be mediated by MC4 receptors. To gain direct insight into the role of melanocortin MC4 receptors in haemorrhagic shock, we investigated the effects of two novel selective MC4 receptor agonists.

EXPERIMENTAL APPROACH

Severe haemorrhagic shock was produced in rats under general anaesthesia. Rats were then treated with either the non-selective agonist [Nle4, D-Phe7]-melanocyte-stimulating hormone (NDP--MSH) or with the selective MC4 agonists RO27-3225 and PG-931. Cardiovascular and respiratory functions were continuously monitored for 2 h; survival rate was recorded up to 24 h. Free radicals in blood were measured using electron spin resonance spectrometry; tissue damage was evaluated histologically 25 min or 24 h after treatment.

KEY RESULTS

All shocked rats treated with saline died within 30-35 min. Treatment with NDP--MSH, RO27-3225 and PG-931 produced a dose-dependent (13-108 nmol kg-1 i.v.) restoration of cardiovascular and respiratory functions, and improved survival. The three melanocortin agonists also markedly reduced circulating free radicals relative to saline-treated shocked rats. All these effects were prevented by i.p. pretreatment with the selective MC4 receptor antagonist HS024. Moreover, treatment with RO27-3225 prevented morphological and immunocytochemical changes in heart, lung, liver, and kidney, at both early (25 min) and late (24 h) intervals.

CONCLUSIONS AND IMPLICATIONS

Stimulation of MC4 receptors reversed haemorrhagic shock, reduced multiple organ damage and improved survival. Our findings suggest that selective MC4 receptor agonists could have a protective role against multiple organ failure following circulatory shock.

Broad therapeutic treatment window of [Nle(4), D-Phe(7)]alpha-melanocyte-stimulating hormone for long-lasting protection against ischemic stroke, in Mongolian gerbils

Melanocortin peptides have been shown to produce neuroprotection in experimental ischemic stroke. The aim of the present investigation was to identify the therapeutic treatment window of melanocortins, and to determine whether these neuropeptides chronically protect against damage consequent to brain ischemia. A 10-min period of global cerebral ischemia in gerbils, induced by occluding both common carotid arteries, caused impairment in spatial learning and memory (Morris test: four sessions from 4 to 67 days after the ischemic episode), associated with neuronal death in the hippocampus. Treatment with a nanomolar dose (340 microg/kg i.p., every 12 h for 11 days) of the melanocortin analog [Nle(4), D-Phe(7)]alpha-melanocyte-stimulating hormone (NDP-alpha-MSH), starting 3-18 h after the ischemic episode, reduced hippocampal damage with improvement in subsequent functional recovery. The protective effect was long-lasting (67 days, at least) with all schedules of NDP-alpha-MSH treatment; however, in the latest treated (18 h) gerbils, some spatial memory deficits were detected. Pharmacological blockade of melanocortin MC(4) receptors prevented the protective effects of NDP-alpha-MSH. Our findings indicate that, in conditions of brain ischemia, melanocortins can provide strong and long-lasting protection with a broad therapeutic treatment window, and with involvement of melanocortin MC(4) receptors, 18 h being the approximately time-limit for stroke late treatment to be effective.

Further evidence that melanocortins prevent myocardial reperfusion injury by activating melanocortin MC3 receptors

In rats subjected to myocardial ischemia/reperfusion, melanocortin peptides, including gamma(1)-melanocyte-stimulating hormone (gamma(1)-MSH), are able to exert a protective effect by stimulating brain melanocortin MC(3) receptors. A non-melanocortin receptor belonging to a group of receptors for Phe-Met-Arg-Phe-NH(2) (FMRFamide)-like peptides may be involved in some of the cardiovascular effects of the gamma-MSHs. FMRFamide-like peptides and gamma(1)-/gamma(2)-MSH share, among other things, the C-terminal Arg-Phe sequence, which seems to be essential for cardiovascular effects in normal animals. So we aimed to further investigate which receptor and which structure are involved in the protective effects of melanocortins in anesthetized rats subjected to myocardial ischemia by ligature of the left anterior descending coronary artery (5 min), followed by reperfusion. In saline-treated rats, reperfusion induced, within a few seconds, a high incidence of ventricular tachycardia and ventricular fibrillation, and a high percentage of death within the 5 min of observation period. Reperfusion was associated with a massive increase in free radical blood levels and with an abrupt and marked fall in systemic arterial pressure. The i.v. treatment (162 nmol/kg) during the ischemic period with the adrenocorticotropin fragment 1-24 [ACTH-(1-24): the reference protective melanocortin which binds all melanocortin receptors], as well as with both the melanocortin MC(3) receptor agonists gamma(2)-MSH and [D-Trp(8)]gamma(2)-MSH, reduced the incidence of ventricular tachycardia, ventricular fibrillation and death, the increase in free radical blood levels and the fall in arterial pressure. On the contrary, gamma(2)-MSH-(6-12) (a fragment unable to bind melanocortin receptors) was ineffective. Such protective effect was prevented by the melanocortin MC(3)/MC(4) receptor antagonist SHU 9119. In normal (i.e., not subjected to myocardial ischemia/reperfusion) rats, the same i.v. dose (162 nmol/kg) of gamma(2)-MSH, [D-Trp(8)]gamma(2)-MSH and gamma(2)-MSH-(6-12) provoked a prompt and transient increase in arterial pressure; on the other hand, ACTH-(1-24), which lacks the C-terminal Arg-Phe sequence, decreased arterial pressure, but only at higher doses. Heart rate of normal rats was not affected by any of the assayed peptides. The present data confirm and extend our previous findings that melanocortins prevent myocardial reperfusion injury by activating melanocortin MC(3) receptors. Moreover, they further support the notion that, in normal rats, cardiovascular effects of gamma-MSHs are mediated by receptors for FMRFamide-like peptides, for whose activation, but not for that of melanocortin MC(3) receptors, the C-terminal Arg-Phe structure being relevant.

The administration of alpha-melanocyte-stimulating hormone protects the ischemic/reperfused myocardium

The contribution of alpha-melanocyte-stimulating hormone (alpha-MSH) treatment, an active fragment of adrenocorticotropic hormone (ACTH), to the recovery of postischemic cardiac function, infarct size, the incidence of reperfusion-induced ventricular fibrillation and apoptotic cell death was studied in ischemic/reperfused isolated rat hearts. Rats were subcutaneously injected with 40, 200 and 400 microg/kg of alpha-MSH, and 12 h later, hearts were isolated, perfused and subjected to 30 min of ischemia followed by 120 min of reperfusion. Thus, after 120 min of reperfusion, with the concentration of 200 microg/kg alpha-MSH, coronary flow, aortic flow and left ventricular developed pressure were significantly improved from their control values of 14.6+/-0.6 ml/min, 7.5+/-0.5 ml/min and 9.1+/-0.4 kPa to 20.2+/-0.4 ml/min (p<0.05), 31.5+/-0.9 ml/min (p<0.05) and 15.9+/-0.6 (p<0.05) kPa, respectively. With the doses of 40, 200 and 400 microg/kg of alpha-MSH, infarct size was reduced from its control value of 38+/-5% to 33+/-6% (NS), 17+/-3% (p<0.05) and 19+/-4% (p<0.05), respectively. The reduction in the incidence of reperfusion-induced ventricular fibrillation followed the same pattern. It is reasonable to assume that a reduction in infarct size, in the alpha-MSH-treated myocardium, resulted in a reduction as well in apoptotic cell death. Although we did not specifically study the exact mechanism(s) of alpha-MSH-afforded postischemic protection, we assume that this protection may be related to alpha-MSH-induced corticosterone release and corticosterone-induced de novo protein synthesis, which reflected in the recovery of postischemic cardiac function in isolated hearts. Thus, interventions that are able to increase plasma corticosterone or glucocorticoid release may prevent the development of ischemia/reperfusion-induced damage.

Involvement of the central nervous system in the protective effect of melanocortins in myocardial ischaemia/reperfusion injury

Melanocortin peptides exert, in rats, a protective effect in myocardial ischaemia followed by reperfusion, or permanent occlusion of a coronary artery. Moreover, melanocortins have an anti-shock effect. Since the mechanism of the life-saving effect of these peptides in haemorrhagic shock includes an essential brain loop, we aimed to determine whether the central nervous system (CNS) is also involved in the protective effect against the outcome of short-term myocardial ischaemia followed by reperfusion. Ischaemia was produced in anaesthetized rats by ligature of the left anterior descending coronary artery for 5 min. Reperfusion-induced ventricular tachycardia (VT), ventricular fibrillation (VF) and lethality, and the time-course of arterial blood pressure over 5 min following reperfusion were evaluated. Groups of 8-14 rats were used. Intravenous (i.v.) injection of ACTH-(1-24) (0.16-0.48 mg/kg) during the ischaemic period dose dependently reduced the incidence of VT, VF and of lethality. In saline-treated rats, coronary reperfusion caused VT in 100% animals, VF in 86%, and death in 86%. The highest dose of ACTH-(1-24) (0.48 mg/kg) completely prevented the occurrence of VT, VF and death in all rats (P<0.005). Moreover, the melanocortin peptide prevented the fall in mean arterial pressure (MAP) occurring during reperfusion. Treatment with ACTH-(1-24) by the intracerebroventricular (i.c.v.) route also reduced the incidence of VT, VF and lethality, and prevented the fall in MAP in a dose dependent manner. Complete (100%) protection occurred with an i.c.v. dose (0.048 mg/kg) 10 times less than that needed by the i.v. route. The present data show that in the protective effect of melanocortin peptides against the injury after myocardial ischaemia/reperfusion, the i.c.v. route of administration is more effective than the i.v. route. They suggest that a CNS mechanism, not yet identified, may be involved.

Asphyxia-induced release of alpha-melanocyte-stimulating hormone in newborn pigs

Asphyxia and reperfusion induced changes in the plasma and cerebrospinal fluid (CSF) concentrations of alpha-melanocyte-stimulating hormone (alpha-MSH) were studied in newborn pigs using a specific radioimmunoassay technique. Cardiovascular and metabolic failure induced by neonatal asphyxia resulted in a 3-fold, significant (P < 0.05) increase in plasma alpha-MSH levels, whereas the hormone concentration in CSF was significantly (P < 0.05) reduced by 50% during postasphyxial reperfusion. Our data indicate an asphyxia-induced release of alpha-MSH, and suggest a discordant regulation of plasma and CSF concentrations in newborn pigs.

New aspects on the melanocortins and their receptors

Knowledge of melanocortins and their receptors has increased tremendously over the last few years. The cloning of five melanocortin receptors, and the discovery of two endogenous antagonists for these receptors, agouti and agouti-related peptide, have sparked intense interest in the field. Here we give a comprehensive review of the pharmacology, physiology and molecular biology of the melanocortins and their receptors. In particular, we review the roles of the melanocortins in the immune system, behaviour, feeding, the cardiovascular system and melanoma. Moreover, evidence is discussed suggesting that while many of the actions of the melanocortins are mediated via melanocortin receptors, some appear to be mediated via mechanisms distinct from melanocortin receptors.

Alpha-melanocyte-stimulating hormone in normal human physiology and disease states

Over the past two decades, research in animal models has indicated that alpha-melanocyte-stimulating hormone (alpha-MSH) has potent anti-inflammatory properties. Furthermore, recent data show that the peptide has antimicrobial effects and probably contributes to innate immunity. alpha-MSH, which is produced by many extrapituitary human cells, should no longer be considered solely a pituitary hormone; rather, it should be viewed as a ubiquitous modulatory peptide.

Plasma concentrations and anti-L-cytokine effects of alpha-melanocyte stimulating hormone in septic patients

OBJECTIVES

The aim of this research was to investigate endogenous concentrations and anti-cytokine effects of the antiinflammatory peptide alpha-melanocyte stimulating hormone (alpha-MSH) in patients with systemic inflammation. The objectives were to determine the following: changes over time of plasma alpha-MSH and relationship with patient outcome, correlation between plasma alpha-MSH and tumor necrosis factor (TNF)-alpha plasma concentration and production in whole blood samples, and influences of alpha-MSH on production of TNF-alpha and interleukin (IL)-1beta in whole blood samples stimulated with lipopolysaccharide (LPS).

DESIGN

Prospective, nonrandomized, clinical study.

SETTING

Intensive care unit of a university hospital.

PATIENTS

A total of 21 patients with sepsis syndrome/septic shock and an equal number of healthy volunteers.

INTERVENTIONS

Circulating alpha-MSH and TNF-alpha concentrations and TNF-alpha production in supernatants of LPS (1 ng/mL)-stimulated whole blood were measured repeatedly. To determine whether alpha-MSH can modulate production of TNF-alpha and IL-1 beta, these cytokines were measured in whole blood samples stimulated with LPS (1 ng/mL) in the presence or absence of concentrations of the peptide.

MEASUREMENTS AND MAIN RESULTS

Plasma alpha-MSH was low in early samples and gradually increased in patients who recovered but not in those who died. There was a negative correlation between plasma concentrations of alpha-MSH and TNF-alpha. In blood samples taken at early phases of sepsis syndrome, production of TNF-alpha was reduced relative to control values; such production increased in patients who recovered but not in those who died. Addition of alpha-MSH to LPS-stimulated whole blood samples inhibited production of TNF-alpha and IL-1beta in a concentration-dependent manner.

CONCLUSIONS

In patients with systemic inflammation, there are substantial changes over time in plasma concentrations of alpha-MSH that are reduced in early phases of the disease. Reduction of this endogenous modulator of inflammation could be detrimental to the host. Addition of alpha-MSH to LPS-stimulated blood samples reduces production of cytokines involved in development of septic syndrome. This inhibition by alpha-MSH, a peptide that is beneficial in treatment of experimental models of sepsis, might therefore be useful to treat sepsis syndrome in humans.

alpha-MSH in systemic inflammation. Central and peripheral actions

Until recently, inflammation was believed to arise from events taking place exclusively in the periphery. However, it is now clear that central neurogenic influences can either enhance or modulate peripheral inflammation. Therefore, it should be possible to improve treatment of inflammation by use of antiinflammatory agents that reduce peripheral host responses and inhibit proinflammatory signals in the central nervous system (CNS). One such strategy could be based on alpha-melanocyte stimulating hormone (alpha-MSH). Increases in circulating TNF-alpha and nitric oxide (NO), induced by intraperitoneal administration of endotoxin in mice, were modulated by central injection of a small concentration of alpha-MSH. Inducible nitric oxide synthase (iNOS) activity and iNOS mRNA in lungs and liver were likewise modulated by central alpha-MSH. Increase in lung myeloperoxidase (MPO) activity was significantly less in lungs of mice treated with central alpha-MSH. Proinflammatory agents induced by endotoxin were significantly greater after blockade of central alpha-MSH. The results suggest that antiinflammatory influences of neural origin that are triggered by alpha-MSH could be used to treat systemic inflammation. In addition to its central influences, alpha-MSH has inhibitory effects on peripheral host cells, in which it reduces release of proinflammatory mediators. alpha-MSH reduces chemotaxis of human neutrophils and production of TNF-alpha, neopterin, and NO by monocytes. In research on septic patients, alpha-MSH inhibited release of TNF-alpha, interleukin-1 beta (IL-1 beta), and interleukin-8 (IL-8) in whole blood samples in vitro. Combined central and peripheral influences can be beneficial in treatment of sepsis.

Corticotropin-releasing factor (CRF) induced anorexia is not influenced by a melanocortin 4 receptor blockage

CRF and melanocortin (MSH/ACTH) peptides share a number of central effects including anorexia and grooming. The effects of CRF may be secondary, due to CRF's effects on melanocortin peptide release. We investigated if the newly discovered selective melanocortin 4 receptor antagonist HS014 could influence CRF induced anorexia and grooming. The data show that ICV administration of CRF (3 mg/rat), significantly reduced food intake, feeding time and feeding episodes whereas it increased grooming time and grooming episodes. HS014 (5 mg/rat), that previously has been shown to antagonize the anorectic effect and the excessive grooming induced by alpha-MSH, did however not influence any of the behavioral effects induced by CRF when the peptides were administered together. The data indicate that the anorectic and grooming effects of CRF are independent of pathways involving the MC4 receptors. These data suggest that the anorectic and grooming effect of CRF are not due to a secondary effect caused by increase in release of melanocortins acting on the central MC receptors.

Treatment of acute renal failure

Acute renal failure is a life threatening illness whose mortality has remained high since the introduction of hemodialysis 25 years ago, despite advances in supportive care. Acute renal failure is an extremely morbid and costly disorder with a significant proportion of patients progressing to end-stage renal disease requiring dialysis. To the nephrologist, acute renal failure remains an extremely frustrating disease, because the pathophysiology is not well understood and the limited therapeutic options force the nephrologist to sit on the sidelines and wait for renal function to return. For example, dialysis remains the only FDA-approved treatment for acute renal failure, but dialysis may also cause renal injury that prolongs renal failure. The purpose of this perspective is to understand the results of the recent, largely negative, clinical trials in view of recent advances in the epidemiology of ARF. This review will also discuss diagnostic tools, strategies for improved design of clinical trials, and other therapeutic interventions that will be needed to properly treat acute renal failure in the 21st century.

Adrenocorticotropin counteracts the increase in free radical blood levels, detected by electron spin resonance spectrometry, in rats subjected to prolonged asphyxia

We investigated the influence of the adrenocorticotropic fragment 1-24 [ACTH-(1-24)] on the blood levels of highly-reactive free radicals in a rat model of prolonged asphyxia. Anesthetized animals were endotracheally intubated and mechanically ventilated with room air; after a 10 min stabilization period, the ventilator was turned off to induce asphyxia for 5 min; then, the ventilator was turned back on, and, simultaneously, the rats were intravenously treated with either ACTH-(1-24) (160 microg/kg in a volume of 1 ml/kg) or equivolume saline. Free radicals were detected in arterial blood by electron spin resonance spectrometry using an ex vivo method that avoids injection of the spin-trapping agent employed (alpha-phenyl-N-tert-butylnitrone). Arterial pressure, electrocardiogram (ECG) and electroencephalogram (EEG) were monitored for the 60 min observation period, or until prior death. At the end of the 5 min period of respiratory arrest, blood levels of free radicals were about four times higher than those of the basal, pre-asphyxia condition, arterial pressure had dramatically decreased, ECG showed marked bradycardia and signs of ischemic damage and the EEG had become isoelectric. Treatment with ACTH-(1-24) produced an immediate normalization of the blood levels of free radicals, associated with a restoration of cardiovascular function and full recovery of EEG within 30-45 min; all the saline-treated rats, on the other hand, died within 6.89 +/- 0.96 min. These results provide direct evidence that in a severe condition of prolonged asphyxia there is a rapid and massive production of highly-reactive free radicals and suggest that the resuscitating effect of adrenocorticotropin fragments in severe hypoxic conditions may be largely due to the inhibition of free radical overproduction during tissue reoxygenation.

alpha-Melanocyte-stimulating hormone and acute renal failure

alpha-Melanocyte-stimulating hormone (MSH) is an endogenous anti-inflammatory cytokine that inhibits all major forms of inflammation, alpha-MSH level is increased at sites of inflammation in humans, and is produced in the pituitary and in macrophages. The effects of alpha-MSH are mediated by melanocortin receptors found on macrophages, neutrophils, and renal tubules. alpha-MSH inhibited ischemic acute renal failure in mice and rats, even when started 6 h after injury. alpha-MSH acts, in part, by inhibiting the maladaptive activation of genes that cause inflammatory and cytotoxic renal injury. However, alpha-MSH is effective even in the absence of neutrophils, suggesting that alpha-MSH also acts directly on renal tubules.