Plasma proadrenomedullin N-terminal 20 peptide (PAMP) in patients with congestive heart failure

Genetic loss of proadrenomedullin N-terminal 20 peptide (PAMP) in mice is compatible with survival

Adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP) are small peptides derived from a common precursor, pre-proadrenomedullin. Although AM and PAMP share hypotensive effects in the cardiovascular system, the peptides also exert diverse and distinct effects on endocrine physiology, innate immunity, cytoskeletal biology and receptor signaling pathways. Tremendous knowledge has been gleaned from the study of several genetic animal models of AM deletion or overexpression, some of which also simultaneously delete the coding region for PAMP peptide. However, deletion of PAMP without concurrent deletion of AM in an animal model is not currently available for the study of PAMP function. Here, we present the generation of Adm^{ΔPAMP/ΔPAMP} and Adm^ΔPAMP/- mice, which lack the coding sequence for PAMP while preserving the coding sequence for AM. Adm^{ΔPAMP/ΔPAMP} mice survive to adulthood without any obvious abnormalities and are fertile, though Adm^ΔPAMP/- females have small litters. Interestingly, these animals express lower levels of Adm mRNA and AM peptide than wild type animals, but these levels are still compatible with survival. Importantly, despite reduced levels, the spatiotemporal expression of AM peptide within the hearts of Adm^ΔPAMP/- mice remains similar to wild type animals. Adm^{ΔPAMP/ΔPAMP} mice are now a publicly available tool for future investigations of PAMP function.

NMR conformational analysis of proadrenomedullin N-terminal 20 peptide, a proangiogenic factor involved in tumor growth

The preferred conformation of Proadrenomedullin N-Terminal 20 Peptide (PAMP; ARLDVASEFRKKWNKWALSR-amide) has been determined using 1H and 13C two-dimensional nuclear magnetic resonance (NMR) spectroscopy and molecular modeling. PAMP is a peptide that has various physiological functions, including its role as a proangiogenic factor in facilitating tumor growth and its inhibitory effect on catecholamine secretion at nicotinic receptors. The preferred conformation of PAMP was determined in a helix-inducing trifluoroethanol and water (TFE/H2O) solution, and in a membrane-mimetic sodium dodecylsulfate-d25 (SDS) micellar solution. The secondary structure consists of an alpha-helix for residues Arg2 to Arg20 in TFE/H2O solution and an alpha-helix for residues Arg2 to Ala17 in SDS solution. We postulate that the polar charged residues Arg2, Lys12, and Arg20 are responsible for the initial interaction of the peptide with the micelle, and that this is followed by the binding of the hydrophobic residues Leu3, Val5, Phe9, Trp13, and Trp16 to the micellar core. The three C-terminal amino acid residues adopt an extended structure in SDS, suggesting that they are important in receptor recognition and binding. This is supported by truncation studies done by Mahata et al. (Hypertension, 1998, Vol. 32, pp. 907-916), which show the importance of the C-terminal in physiological activity. Furthermore, Belloni et al. (Hypertension, 1999, Vol. 33, pp. 1185-1189), and Martinez et al. (Cancer Research, 2004, Vol. 64, pp. 6489-6494) suggested that the N-terminal was also important in PAMP activity. However, no differences in conformational preference of the N-terminal were observed between the two solvent systems.

The clinical relevance of adrenomedullin: a promising profile?

Adrenomedullin (AM) is a peptide that possesses potentially beneficial properties. Since the initial discovery of the peptide by Kitamura et al. in 1993, the literature has been awash with reports describing its novel mechanisms of action and huge potential as a therapeutic target. Strong evidence now exists that AM is able to act as an autocrine, paracrine, or endocrine mediator in a number of biologically significant functions, including the endothelial regulation of blood pressure, protection against organ damage in sepsis or hypoxia, and the control of blood volume through the regulation of thirst. Its early promise as a potential mediator/modulator of disease was not, however, entirely as a result of the discovery of physiological functions but due more to the observation of increasing levels measured in plasma in direct correlation with disease progression. In health, AM circulates at low picomolar concentrations in plasma in 2 forms, a mature 52-amino acid peptide and an immature 53-amino acid peptide. Plasma levels of AM have now been shown to be increased in a number of pathological states, including congestive heart failure, sepsis, essential hypertension, acute myocardial infarction, and renal impairment. These earliest associations have been further supplemented with evidence of a role for AM in other pathologies including, most intriguingly, cancer. In this review, we offer a timely review of our current knowledge on AM and give a detailed account of the putative role of AM in those clinical areas in which the best therapeutic opportunities might exist.

Adrenomedullin: potential in physiology and pathophysiology

Adrenomedullin (ADM), a 52-amino acid ringed-structure peptide with C-terminal amidation, was originally isolated from human pheochromocytoma. ADM mediates vasodilatory and natriuretic properties through the second messenger cyclic adenosine 3',5'-monophosphate (cAMP), nitric oxide and the renal prostaglandin system. ADM immunoreactivity and its gene are widely distributed in cardiovascular, pulmonary, renal, gastrointestinal, cerebral and endocrine tissues. ADM is also synthesized and secreted from vascular endothelial and smooth muscle cells. When injected intravenously, ADM increases flow rates predominantly in organs in which the ADM gene is highly expressed, suggesting that ADM acts as a local autocrine and/or paracrine vasoactive hormone. In addition, ADM is a circulating hormone and its plasma concentration is increased in various cardiorenal diseases such as hypertension, chronic renal failure and congestive heart failure. Current evidence suggests that ADM plays an important role in fluid and electrolyte homeostasis and cardiorenal regulation, however further investigations are required to address the importance of ADM under various physiological and pathophysiological conditions.

Comparison of vasodilator potency of adrenomedulling and proadrenomedullin N-terminal 20 peptide in human

Adrenomedullin (ADM) and proadrenomedullin N-terminal peptide (PAMP), both of which are derived from preproadrenomedullin, are reported to have a potent hypotensive effect in animals. However, no data are available concerning the vasodilatory potency of PAMP or comparing this potency to that of ADM in human vasculature. We examined the effects of intra-arterial infusion of graded doses of ADM (1.25, 2.5, 5.0 and 7.5 pmol/min per 100 ml of tissue) and PAMP (125, 250, 500, 750 and 1000 pmol/min per 100 ml of tissue) on total forearm blood flow and forearm skin blood flow in 11 healthy subjects. ADM increased total forearm blood flow from 2.9 +/- 0.4 to 8.6 +/- 1.1 ml/min per 100 ml (p < 0.01), and skin blood flow from 0.07 +/- 0.02 to 0.14 +/- 0.03 volts (p < 0.01). In contrast to this potent vasodilatory effect, a significant rise in forearm skeletal blood flow was seen only in response to the maximum dose of PAMP (from 2.7 +/- 0.5 to 5.3 +/- 1.0 ml/min per 100 ml; p < 0.01). In addition, PAMP had no significant vasoactive effect on skin blood flow (from 0.06 +/- 0.02 to 0.09 +/- 0.03 volts; NS). In conclusion, the skeletal muscle vasodilator potency of PAMP is less than one hundredth of that of ADM in human forearm. Given its weak dilator potency, it seems unlikely that PAMP alone could significantly regulate resistance vessel tone as a circulating hormone in humans.

Increased plasma proadrenomedullin N-terminal 20 peptide in patients with essential hypertension

The novel hypotensive peptide, proadrenomedullin N-terminal 20 peptide (PAMP), is processed from the adrenomedullin precursor. Recently, we identified PAMP-12 [PAMP(9-20)] from the porcine adrenal medulla as a major endogenous and biologically active peptide. Using a new, sensitive radioimmunoassay which recognizes the C-terminal region of PAMP-20 [PAMP(1-20)], we investigated the role of PAMP in patients with essential hypertension who had normal renal function, and whether PAMP-12 is present in humans. The mean PAMP plasma concentration, like that of adrenomedullin, was significantly higher in hypertensive [1.51 fmol/mL, standard error of the mean (SEM) 0.09 fmol/mL] than normotensive participants (1.08 fmol/mL, SEM 0.05). The increase in plasma PAMP concentration in patients with organ damage accompanied by hypertension was significantly higher than that in patients without organ damage. The PAMP concentration had a significant positive correlation with mean blood pressure and adrenomedullin concentration. The immunoreactive PAMP in human tissue and plasma was characterized by reverse-phase high-performance liquid chromatography. PAMP-12, as well as PAMP-20, was abundant in the phaeochromocytoma tissue. These findings suggest that PAMP plays some pathophysiological role against the development of essential hypertension.

Short-term modulation of the renin-angiotensin system does not alter plasma adrenomedullin concentration in humans

OBJECTIVE

Adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP) are novel hypotensive peptides produced from the same precursor. A relationship between AM and the renin-angiotensin-aldosterone (RAA) axis was reported in several studies, but the response of the above two peptides to short-term modulation of the RAA axis in humans is not yet clear. Here, we assessed the responses of AM and PAMP in patients with varying RAA system status, including renovascular hypertension (RVH) and primary aldosteronism (PA).

DESIGN AND METHODS

Essential hypertension (EHT), RVH and PA patients were hospitalized and maintained on a standard diet (NaCl 10 g/day). The patients underwent a captopril (25 mg) loading test. A renin-secretion stimulating test (furosemide 1 mg/kg, i.v. +2 h of walking) and an ACTH loading test were performed for the PA patients. The plasma renin activity (PRA), plasma aldosterone concentration (PAC), and plasma AM and PAMP levels were monitored before and after the loadings.

RESULTS

In the basal state, significantly higher concentrations of AM and PAMP were shown in the RVH patients compared to the other groups. AM and PAMP were significantly correlated with PRA but not PAC in all patients. The AM and PAMP levels were not affected by the captopril loading with or without a hypotensive reaction. The AM and PAMP levels were increased only slightly despite the large increase in PAC induced in the PA patients by the renin-secretion stimulating and ACTH loading tests.

CONCLUSION

The responses of plasma AM and PAMP to a short-term modulation of the RAA system were relatively small, despite the correlations observed between PRA and AM or PAMP.

Proadrenomedullin N-terminal 20 peptide: minimal active region to regulate nicotinic receptors

Proadrenomedullin N-terminal 20 peptide (PAMP-[1-20]; ARLDVASEFRKKWNKWALSR-amide) is a potent hypotensive and catecholamine release-inhibitory peptide released from chromaffin cells. We studied the mechanism of PAMP action and how its function is linked to structure. We tested human PAMP-[1-20] on catecholamine secretion in PC12 pheochromocytoma cells and found it to be a potent, dose-dependent (IC50 approximately 350 nmol/L) secretory inhibitor. Inhibition was specific for nicotinic cholinergic stimulation since PAMP-[1-20] failed to inhibit release by agents that bypass the nicotinic receptor. Nicotinic cationic (22Na+,45Ca2+) signal transduction was disrupted by this peptide, and potencies for inhibition of 22Na+ uptake and catecholamine secretion were comparable. Even high-dose nicotine failed to overcome the inhibition, suggesting noncompetitive nicotinic antagonism. N- and C-terminal PAMP truncation peptides indicated a role for the C-terminal amide and refined the minimal active region to the C-terminal 8 amino acids (WNKWALSR-amide), a region likely to be alpha-helical. PAMP also blocked (EC50 approximately 270 nmol/L) nicotinic cholinergic agonist desensitization of catecholamine release, as well as desensitization of nicotinic signal transduction (22Na+ uptake). Thus, PAMP may exert both inhibitory and facilitatory effects on nicotinic signaling, depending on the prior state of nicotinic stimulation. PAMP may therefore contribute to a novel, autocrine, homeostatic (negative-feedback) mechanism controlling catecholamine release.

Cardiovascular and sympathetic effects of proadrenomedullin NH2-terminal 20 peptide in conscious rats

Proadrenomedullin NH2-terminal 20 peptide (PAMP) and adrenomedullin (AM), which are derived from the same gene, are novel vasodilative peptides and have been shown to exhibit hypotensive action in anesthetized animals. To avoid the modification via anesthesia, we investigated the effects of intravenously administered PAMP on mean arterial pressure, heart rate (HR), and renal sympathetic nerve activity (RSNA) relative to those of AM in conscious unrestrained rats. We also examined whether the arterial baroreceptor reflex was altered with the two peptides. Intravenous injection of rat PAMP (rPAMP) (10, 20 and 50 nmol/kg) and rat AM (rAM) (0.3, 1.0 and 3.0 nmol/kg) similarly elicited dose-related hypotension accompanied by increases in HR and RSNA. However, the responses to rPAMP were less potent in magnitude and shorter in duration than those to rAM. Moreover, rAM facilitated baroreflex control, whereas rPAMP attenuated it. These findings indicate that although PAMP, as well as AM, may play an important role as a circulating hormone in the systemic circulation of conscious rats, the two peptides derived from an identical origin might have different mechanisms responsible for their cardiovascular and RSNA actions.

Purification and characterization of PAMP-12 (PAMP[9-20]) in porcine adrenal medulla as a major endogenous biologically active peptide

Proadrenomedullin N-terminal 20 peptide (PAMP-20) is a potent hypotensive peptide processed from the adrenomedullin (AM) precursor. We developed a specific radioimmunoassay which recognizes the C-terminal region of PAMP-20. Using this radioimmunoassay, the distribution of immunoreactive (ir-) PAMP was determined in porcine tissues. High concentrations of ir-PAMP were observed in the adrenal medulla and in the atrium, and these values were comparable to the corresponding concentrations of ir-AM. The concentration of ir-PAMP was almost the same as that of ir-AM in the kidney, while ir-PAMP was significantly lower than ir-AM in the ventricle, lung, and aorta. Reversed-phase high performance liquid chromatography in each porcine tissue sample revealed that two major peaks of ir-PAMP existed: one emerged at a position identical to that of authentic porcine PAMP-20; the other unknown peak was eluted earlier. The unknown peptide was purified to homogeneity from porcine adrenal medulla, and its complete amino acid sequence was determined. This peptide was found to be PAMP[9-20] with a C-terminal amide structure, and was named PAMP-12. Intravenous injections of PAMP-12 in anesthetized rats showed a significant hypotensive effect in a dose-dependent fashion, and the effect was comparable to that of PAMP-20. These data indicate that PAMP-12, a major component of ir-PAMP, is processed from the AM precursor, as is PAMP-20, and may participate in cardiovascular control.