The systemic inflammatory response in heart failure

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.

Aberrant central nervous system responses to the Valsalva maneuver in heart failure

Heart failure (HF) is associated with aberrant autonomic nervous system (ANS) activity, with altered responses to blood pressure and breathing challenges that appear to reflect abnormal central nervous system function. The authors used functional magnetic resonance imaging (fMRI) to determine whether the Valsalva maneuver, an ANS challenge, would show abnormal responses in ANS regulatory areas of the brain in HF. Brain fMRI signal changes in 5 HF patients (left ventricular ejection fraction, 0.15+/-0.08; age, 50+/-10 years) and 14 controls (age, 47+/-11 years) were assessed during 3 successive Valsalva maneuvers. The hypothalamus, hippocampus, putamen, amygdala, mid-cingulate, right insula, and cerebellar cortex showed exaggerated and phase-shifted fMRI responses in HF; other areas showed inverted signals from those found in controls. Central ANS control areas have altered phase, extent, and direction of responses to Valsalva maneuvers in a small sample of HF patients. These findings suggest that therapeutics that address neuroprotective aspects may be useful interventions for the condition.

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.