Adrenocorticotropin reverses vascular dysfunction and protects against splanchnic artery occlusion shock

Altered levels of α-melanocyte stimulating hormone in cerebrospinal fluid and plasma of patients with traumatic brain injury

Traumatic brain injury (TBI) is closely associated with marked inflammation. Although alpha-Melanocyte-Stimulating Hormone (α-MSH) exerts powerful anti-inflammatory effects, changes in endogenous α-MSH levels following TBI remain poorly understood. We investigated the changes of α-MSH levels in the cerebrospinal fluid (CSF) and plasma of post-TBI patients and the association of these changes with the severity of TBI and inflammation. TBI severity was assessed by the GCS coma scale from which, patients were separated into three groups. Clinical data were collected on days 1, 3, 5, and 7 including levels of α-MSH, tumor necrosis factor (TNF-α), and intracranial pressure (ICP). α-MSH levels in CSF steadily increased for one week (peak at day 5) but plasma α-MSH decreased and remained low. These changes were more substantial in the Severe Group of TBI with lower GCS. TNF-α levels were similarly increased in both CSF and plasma (peak at day 3). In the early phase of TBI elevated TNF-α and ICP dominated, and CSF α-MSH displayed a slow and insufficient increase. In later phases of TBI, TNF-α and ICP levels were alleviated concordantly with sustained increases in central α-MSH, wherein an anti-inflammatory environment might predominate. The relationship between plasma α-MSH and TNF-α showed significant negative correlation, and the relationship between CSF α-MSH and TNF-α showed significant positive correlation with a two-day lag. In conclusion, plasma α-MSH levels decreased, but CSF levels increased slowly following TBI. These changes were more substantial in severe patients with a lower GCS. Increases in central α-MSH paralleled alleviation of inflammation.

Effects of etomidate in the adrenal and cytokine responses to hemorrhagic shock in rats

Hemorrhagic shock (HS) induces a compensatory endocrine and cytokine response which aims to restore homeostasis. This response can be modulated by general anesthetics. To our knowledge, no studies have evaluated if etomidate modulates this response in experimental HS. After being premedicated with buprenorphine (0.05 mg/kg subcutaneously), male Wistar rats were anaesthetized with 5% isoflurane and divided into three groups: G1 (control, n = 16), G2 (n = 13), and G3 (n = 14). G2 and G3 were subjected to HS by collecting 30% of their blood volume and resuscitated 90 min later with the collected blood and normal saline, in a 1:3 ratio, respectively. G3 received etomidate (1 mg/kg IV) before HS. Blood gas analysis, adrenocorticotropic hormone (ACTH), corticosterone, and plasma levels of tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-10 and of TNF-α, IL-6, and IL-10 mRNA obtained through real-time polymerase chain reaction (RT-PCR) were measured at 0, 90, 150, and 240 min after HS induction. Compared with G2, etomidate-treated animals had significantly lower corticosterone, PO2, PO2/FiO2, base excess and HCO3, and higher TNF-α, IL-6, IL-10, and TNF-α mRNA levels ( P <0.05). Etomidate-treated rats showed impaired adrenal and increased cytokine response to HS and evidence of worse tissue oxygenation and lung dysfunction. Based on these results, and until further studies are performed to confirm if these findings occur in clinical patients, we suggest that etomidate should be used cautiously in HS.

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.

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.

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.

Melanocortins counteract inflammatory and apoptotic responses to prolonged myocardial ischemia/reperfusion through a vagus nerve-mediated mechanism

Recently we reported that an efferent vagal fibre-mediated cholinergic protective pathway, activated by melanocortins acting at brain melanocortin MC(3) receptors, is operative in a condition of short-term myocardial ischemia/reperfusion associated with a high incidence of severe arrhythmias and death. Here we investigated melanocortin effects, and the role of the vagus nerve-mediated cholinergic protective pathway, in a rat model of prolonged myocardial ischemia/reperfusion associated with marked inflammatory and apoptotic reactions, and a large infarct size. Ischemia was produced in rats by ligature of the left anterior descending coronary artery for 30 min. At the end of the 2-h reperfusion, western blot analysis of the inflammatory and apoptotic markers tumor necrosis factor-alpha (TNF-alpha), c-jun N-terminal kinases (JNK) and caspase-3, as well as of the anti-apoptotic extracellular signal-regulated kinases (ERK 1/2), was performed in the left ventricle. In saline-treated ischemic rats there was an increase in TNF-alpha levels and in the activity of JNK and caspase-3 accompanied, despite an appreciable ERK 1/2 activation, by a large infarct size. Intravenous treatment, during coronary artery occlusion, with the melanocortin analog [Nle(4), D-Phe(7)]alpha-melanocyte-stimulating hormone (NDP-alpha-MSH) produced a reduction in TNF-alpha levels and in the activity of JNK and caspase-3, associated with marked activation of the pro-survival kinases ERK 1/2, and consequent attenuation of infarct size. Bilateral cervical vagotomy blunted the protective effects of NDP-alpha-MSH. These results indicate that melanocortins modulate the inflammatory and apoptotic cascades triggered by prolonged myocardial ischemia/reperfusion, and reduce infarct size, seemingly by activation of the vagus nerve-mediated cholinergic protective pathway.

Inflamed phenotype of the mesenteric microcirculation of melanocortin type 3 receptor-null mice after ischemia-reperfusion

The existence of anti-inflammatory circuits centered on melanocortin receptors (MCRs) has been supported by the inhibitory properties displayed by melanocortin peptides in models of inflammation and tissue injury. Here we addressed the pathophysiological effect that one MCR, MCR type 3 (MC3R), might have on vascular inflammation. After occlusion (35 min) and reopening of the superior mesenteric artery, MC3R-null mice displayed a higher degree of plasma extravasation (45 min postreperfusion) and cell adhesion and emigration (90 min postreperfusion). These cellular alterations were complemented by higher expression of mesenteric tissue CCL2 and CXCL1 (mRNA and protein) and myeloperoxydase, as compared with wild-type animals. MC1R and MC3R mRNA and protein were both expressed in the inflamed mesenteric tissue; however, no changes in vascular responses were observed in a mouse colony bearing an inactive MC1R. Pharmacological treatment of animals with a selective MC3R agonist ([d-Trp⁸]-γ-melanocyte-stimulating hormone; 10 μg i.v.) produced marked attenuation of cell adhesion, emigration, and chemokine generation; such effects were absent in MC3R-null mice. These new data reveal the existence of a tonic inhibitory signal provided by MC3R in the mesenteric microcirculation of the mouse, acting to down-regulate cell trafficking and local mediator generation.—Leoni, G., Patel, H. B., Sampaio, A. L. F., Gavins, F. N. E., Murray, J. F., Grieco, P., Getting, S. J., Perretti, M. Inflamed phenotype of the mesenteric microcirculation of melanocortin type 3 receptor-null mice after ischemia-reperfusion.

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.

N-acetylcysteine attenuates TNF-alpha-induced human vascular endothelial cell apoptosis and restores eNOS expression

The circulatory inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) is increased in pathological conditions, such as diabetes, which initiate or exacerbate vascular endothelial injury. Both nitric oxide (NO) and reactive oxygen species may play a dual role (i.e., inhibiting or promoting) in TNF-alpha-induced endothelial cell apoptosis. We investigated the effects of the antioxidant N-acetylcysteine on TNF-alpha-induced apoptosis in human vascular endothelial cell (cell line ECV304) apoptosis, NO production and lipid peroxidation. Cultured vascular endothelial cell (ECV304) were either not treated (control), or treated with TNF-alpha (40 ng/ml) alone or TNF-alpha in the presence of N-acetylcysteine at 30 mmol/l or 1 mmol/l, respectively, for 24 h. Cell viability was measured by MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay. Cell apoptosis was assessed by flow cytometry. TNF-alpha-induced endothelial cell apoptosis was associated with increased inducible NO synthase but reduced endothelial NO synthase (eNOS) protein expression. NO production and the levels of the lipid peroxidation product malondialdehyde were concomitantly increased. Treatment with NAC at 30 mmol/l restored eNOS expression and further increased NO production as compared to TNF-alpha alone, resulting in improved cell viability and reduced apoptosis. This was accompanied by increased superoxide dismutase activity, increased glutathione peroxidase production and reduced malondialdehyde levels. N-acetylcysteine at 1 mmol/l, however, did not have significant effects on TNF-alpha-induced endothelial cell apoptosis and cell viability despite it slightly enhanced glutathione peroxidase production. N-acetylcysteine attenuation of TNF-alpha-induced human vascular endothelial cell apoptosis is associated with the restoration of eNOS expression.

Activation of the cholinergic anti-inflammatory pathway reduces NF-kappab activation, blunts TNF-alpha production, and protects againts splanchic artery occlusion shock

The cholinergic anti-inflammatory pathway has not yet been studied in splanchnic artery occlusion (SAO) shock. We investigated whether electrical stimulation (STIM) of efferent vagus nerves suppresses the inflammatory cascade in SAO shock. Animals were subjected to clamping of the splanchnic arteries for 45 min, followed by reperfusion. This surgical procedure resulted in an irreversible state of shock (SAO shock). Sham-operated animals were used as controls. Two minutes before the start of reperfusion, rats were subjected to bilateral cervical vagotomy (VGX) or sham surgical procedures. Application of constant voltage pulses to the caudal vagus ends (STIM: 5 V, 2 ms, 6 Hz for 15 min, 5 min after the beginning of reperfusion) increased survival rate (VGX + SAO + Sham STIM = 0% at 4 h of reperfusion; VGX + SAO + STIM = 90% at 4 h of reperfusion), reverted the marked hypotension, inhibited IkappaBalpha liver loss, blunted the augmented nuclear factor-kappaB activity, decreased hepatic tumor necrosis factor (TNF)-alpha mRNA (VGX + SAO + Sham STIM = 1.0 +/- 1.9 TNF-alpha/glyceraldehyde-3-phosphate dehydrogenase ratio; VGX + SAO + STIM = 0.3 +/- 0.2 TNF-alpha/glyceraldehyde-3-phosphate dehydrogenase ratio), reduced plasma TNF-alpha (VGX + SAO + Sham STIM = 118 +/- 19 pg/mL; VGX + SAO + STIM = 39 +/- 8 pg/mL), ameliorated leukopenia, and decreased leukocyte accumulation, as revealed by means of myeloperoxidase activity in the ileum (VGX + SAO + Sham STIM = 7.9 +/- 1 U/g tissue; VGX + SAO + STIM = 3.1 +/- 0.7 U/g tissue) and in the lung (VGX + SAO + Sham STIM = 8.0 +/- 1.0 U/g tissue; VGX + SAO + STIM = 3.2 +/- 0.6 U/g tissue). Chlorisondamine, a nicotinic receptor antagonist, abated the effects of vagal stimulation. Our results show a parasympathetic inhibition of nuclear factor-kappaB and TNF-alpha in SAO 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.

Activation of an efferent cholinergic pathway produces strong protection against myocardial ischemia/reperfusion injury in rats

OBJECTIVE

A vagus nerve-mediated, brain cholinergic protective mechanism activated by melanocortin peptides is operative in conditions of circulatory shock; moreover, there is anatomical evidence of dual vagal-cardiac efferent pathways in rats, which could play different roles in controlling heart function. Therefore, we investigated the role and functional mechanism of such vagal efferent pathway(s) in an experimental model of ischemic heart disease.

DESIGN

Randomized experimental study.

SETTING

Research laboratory.

SUBJECTS

Adult Wistar rats of either sex.

INTERVENTIONS

After bilateral cervical vagotomy (with or without pretreatment with atropine), efferent vagal fibers were electrically stimulated in rats subjected to coronary artery occlusion (5 mins) followed by reperfusion (5 mins). Other rats (intact, vagotomized, or pretreated with atropine) were treated with nanomolar doses of melanocortin peptides.

MEASUREMENTS AND MAIN RESULTS

Electrical stimulation of efferent vagal fibers (5 V, 2 m secs, 1-9 Hz, for the whole period of ischemia/reperfusion) strongly reduced the high incidence of severe arrhythmias and lethality, reduced the increase in free radical blood levels and left-ventricle histologic alterations, and augmented the extracellular signal-regulated kinase activation. Treatment with the melanocortin peptides adrenocorticotropin and gamma2-melanocyte-stimulating hormone (162 nmol/kg intravenously or 16.2 nmol/kg intracerebroventricularly, during coronary occlusion) produced the same protective effects of electrical stimulation and with the same muscarinic acetylcholine receptor-dependent mechanism, seemingly through brain activation (mediated by melanocortin MC3 receptors, as previously described) of such efferent vagal pathway.

CONCLUSIONS

The present results give evidence for the identification of a protective, melanocortin-activated, efferent vagal cholinergic pathway, operative in conditions of myocardial ischemia/reperfusion. These data suggest that melanocortins and pertinent compounds able to activate such a pathway could provide the potential for development of a new class of drugs for a novel approach to management of ischemic heart disease.

MC-3 receptor and the inflammatory mechanisms activated in acute myocardial infarct

Investigation of the mechanisms activated by endogenous inhibitory pathways can lead to identification of novel targets for cardiovascular inflammatory pathologies. Here we exploited the potential protective role that melanocortin receptor type 3 (MC3-R) activation might play in a myocardial ischemia-reperfusion injury model. In resting conditions, mouse and rat heart extracts expressed MC3-R mRNA and protein, without changes following ischemia-reperfusion. At the cellular level heart macrophages, but not fibroblasts or cardiomyocytes, expressed this receptor, as demonstrated by immunogold labeling. In vivo, administration of the melanocortin agonist MTII (10 microg per mouse equivalent to 9.3 nmol) 30 min prior to ischemia (25 min) attenuated mouse heart 2 h reperfusion injury by approximately 40%, an effect prevented by the mixed MC3/4-R antagonist SHU9119 but not by the selective MC4-R antagonist HS204. Similar results were obtained when the compound was given at the beginning of the reperfusion period. Importantly, delayed myocardial damage as measured 24 h post-reperfusion was equally protected by administration of 10 microg MTII. The focus on MC3-R was also substantiated by analysis of the recessive yellow (e/e) mouse, bearing a mutated (inactive) MC1-R, in which MTII was fully protective. Myocardial protection was associated with reduced markers of systemic and local inflammation, including cytokine contents (interleukin-1 and KC) and myeloperoxidase activity. In conclusion, this study has highlighted a previously unrecognized protective role for MC3-R activation on acute and delayed heart reperfusion injury. These data may open new avenues for therapeutic intervention against heart and possibly other organ ischemia-reperfusion injury.

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.

Cannabinoid CB(1) receptor blockade enhances the protective effect of melanocortins in hemorrhagic shock in the rat

Activation of peripheral cannabinoid CB(1) receptors contributes to hemorrhagic hypotension, and endocannabinoids produced by macrophages and platelets may be mediators of this effect. A number of studies have provided evidence that functional links exist in the mechanisms of action of cannabinoids and opioid peptides; and opioids too play an important role in the pathophysiology of hemorrhagic hypotension and shock. On the other hand, melanocortin peptides, which are the main endogenous functional antagonists of opioid peptides, have an antishock effect in animals and humans. Thus, we investigated whether an interaction exists between endocannabinoids and the endogenous opioid/antiopioid system also in a condition of hemorrhagic shock and, particularly, whether the blockade of cannabinoid CB(1) receptors potentiates the antishock effect of melanocortins. Urethane-anesthetized rats were stepwise bled until mean arterial pressure decreased to, and stabilized at, 21-23 mm Hg. In this model of hemorrhagic shock, which caused the death of all control rats within 30 min after vehicle (tween 80, 5% in saline) injection, the intravenous (i.v.) bolus injection of the cannabinoid CB(1) receptor antagonist N-piperidino-5-[4-chlorophenyl]-1-[2,4 dichlorophenyl]-4-methyl-3-pyrazolecarboxamide (SR141716A) increased mean arterial pressure, pulse pressure, respiratory rate and survival rate in a dose-related manner (0.1-3 mg/kg), an almost complete recovery of mean arterial pressure, pulse pressure and respiratory rate, and 100% survival at the end of the observation period (2 h), occurring with the dose of 3 mg/kg. The melanocortin ACTH-(1-24) (adrenocorticotropin) also produced in a dose-related manner (0.02-0.16 mg/kg i.v.) a restoration of cardiovascular and respiratory functions, and increased survival rate, an almost complete recovery and 100% survival at the end of the observation period (2 h) occurring with the dose of 0.16 mg/kg. When a subactive dose of SR141716A (0.2 mg/kg; 30% survival) was associated with a subactive dose of ACTH-(1-24) (0.02 mg/kg; 12% survival), a complete reversal of the shock condition was obtained with 100% survival at the end of the 2-h observation period. The present results show that the concurrent inhibition of both endogenous opioid and cannabinoid systems produces a reversal of hemorrhagic shock more effective than that produced by the inhibition of either of them. These data suggest that functional interactions between endocannabinoids and opioid/antiopioid are at work also in the pathophysiology of hemorrhagic shock.

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.

Survival rate after early treatment for acute type-A aortic dissection with ACTH-(1-24)

Haemorrhagic shock, usually as a consequence of major trauma, is the most frequent cause of death among people younger than 40 years. Reports indicate that melanocortin peptides are effective in reversing haemorrhagic shock. We found that in patients with aortic-dissection-induced haemorrhagic shock, the addition of an early intravenous bolus injection of the melanocortin andrenocorticotrophic hormone (ACTH)-(1-24) to standard treatment significantly improved cardiovascular function and increased survival rate. Because administration of ACTH-(1-24) is simple, and because melanocortin peptides have no acute toxicity, their use in the early critical care of patients in shock should be more extensively assessed.

Pregnancy stimulates secretion of adrenocorticotropin and nitric oxide from peripheral bovine lymphocytes

The cross-talk between the endocrine and the immune systems mediated by a wide array of hormones, cytokines, and neuromodulators is heightened during disease, stress, and presumably, during pregnancy. Adrenocorticotropin (ACTH) and nitric oxide (NO) are two immunomodulators that are also produced from lymphocytes and contribute to the immunomodulation. Thus, we investigated whether the heightened bidirectional communication between the immune and the endocrine systems observed during pregnancy is reflected in production of ACTH and NO from peripheral bovine lymphocytes and if any temporal correlation exists between them. Adrenocorticotropin was analyzed using a sandwich immunoradiometric assay, and nitrite and nitrate (a measure of NO) were estimated in supernatants of cultured peripheral blood lymphocytes (PBLs) using a colorimetric assay based on the Griess reaction. A significantly high secretion of ACTH and NO was noticed from PBLs in all stages of pregnancy compared to that in cyclic and cystic cows. Increased secretory capacity was noticed as early as 7 days after conception, which reached as much as 600% that of nonpregnant animals between Days 90-120 of gestation. Adrenocorticotropin and NO decline 1 mo before the expected time of parturition. Unlike those from cyclic animals, PBLs from pregnant cows were refractory to stimulation by PHA-M (Phytohemagglutinin) and corticotropin-releasing hormone. A strong correlation was observed between ACTH and NO secretion from PBLs in pregnant, in cyclic, and in cystic cows. To our knowledge, this is the first evidence elucidating the induction of ACTH and NO from PBLs during pregnancy, and it implies a new role for ACTH and NO secreted from PBLs in recognition and, probably, maintenance of pregnancy.

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.