Thrombin rapidly digests adrenomedullin: Synthesis of adrenomedullin analogs resistant to thrombin.

Human adrenomedullin (AM) functions as a circulating hormone and as a local paracrine mediator with multiple biological activities. We investigated the metabolism of AM by examining its fragmentation in human serum. Adrenomedullin was rapidly cleaved in human serum, but was relatively stable in plasma. We showed that AM was rapidly digested by thrombin in serum, with AM(13-44) as the main product. On the basis of these data, we prepared AM analogs in which Arg-44 was replaced by Ala, Lys, and D-Arg, respectively. These analogs were resistant to thrombin and showed comparable biological activity to native AM. Furthermore, the bioavailabilities of these peptides were improved after subcutaneous administration in rats. These AM analogs may be promising drug candidates for clinical applications.

Plasma Clearance of Intravenously Infused Adrenomedullin in Rats with Acute Renal Failure.

Plasma adrenomedullin concentrations are reportedly elevated in patients with renal failure; however, the underlying mechanism is unclear. In this study, we investigated the plasma clearance of synthetic human adrenomedullin (AM) in two models of rats with renal dysfunction; one was induced by subcutaneous injection of mercury chloride (RD-Ag) and the other by completely blocking bilateral renal blood flow (RD-Bl). Sixty minutes after starting intravenous AM infusion, AM levels in RD-Ag, RD-Bl, and rats with normal renal function (NF) were still increased slightly; however, plasma AM levels in RD-Ag rats were approximately three times as high as in RD-Bl and NF rats. Plasma AM disappearance after the end of treatment was similar among the three groups. Pharmacokinetic analysis revealed that elevated plasma AM in RD-Ag rats may be caused by a reduced volume of distribution. The adrenomedullin functional receptor is composed of heterodimers, including GPCR, CLR (calcitonin receptor-like receptor, CALCRL), and the single transmembrane proteins, RAMP2 or RAMP3 (receptor activity modifying protein). Calcrl expression was downregulated in the lungs and kidneys of RD-Ag rats. Furthermore, the plasma concentration of exogenous AM was elevated in mice deficient in vascular endothelium-specific Ramp2. These results suggest that decreased plasma AM clearance in RD-Ag is not due to impaired renal excretion but to a decreased volume of distribution caused by a reduction in adrenomedullin receptors.

Development of a novel human adrenomedullin derivative: human serum albumin-conjugated adrenomedullin.

Adrenomedullin is a biologically active peptide with multiple functions. Here, we have developed a novel human serum albumin-adrenomedullin (HSA-AM) conjugate, which was synthesized by the covalent attachment of a maleimide derivative of adrenomedullin to the 34th cysteine residue of HSA via a linker. Denaturing gel electrophoresis and western blotting for HSA-AM yielded a single band with adrenomedullin immunoreactivity at the position corresponding to a molecular weight (MW) of 73 kDa. Following gel-filtration chromatography, the purified HSA-AM showed a single main peak corresponding with an MW of 73 kDa, indicating that HSA-AM is a monomer. Both adrenomedullin and HSA-AM stimulated the intracellular accumulation of cyclic AMP (cAMP) in HEK-293 cells stably expressing the adrenomedullin 1 receptor. The pEC50 values for adrenomedullin and HSA-AM were 8.660 and 7.208 (equivalent to 2.19 and 61.9 nM as EC50), respectively. The bioavailability of HSA-AM compared with that of adrenomedullin was much improved after subcutaneous administration in the rat, which was probably due to the superior resistance of HSA-AM towards endogenous proteases and its reduced clearance from the blood. HSA-AM may be a promising drug candidate for clinical application.

Safety, Tolerability, and Pharmacokinetics of Adrenomedullin in Healthy Males: A Randomized, Double-Blind, Phase 1 Clinical Trial.

BACKGROUND: Adrenomedullin (AM), an endogenous vasodilative peptide, has immunomodulative effects and acts as an accelerator of mucosal regeneration in the digestive tract. AM has shown beneficial effects in rodent models of inflammatory bowel disease and patients with ulcerative colitis. The present study aimed to evaluate the pharmacodynamic properties and safety of AM in healthy male adults in a phase 1 clinical trial. METHODS: This phase 1, randomized, double-blind, single-center study was conducted on healthy males aged 20-65 years. Subjects received either a placebo, 3 ng/kg/min AM, 9 ng/kg/min AM, or 15 ng/kg/min AM via continuous 12-h intravenous infusion. Other subjects received either placebo or 15 ng/kg/min AM for 8 h per day for 7 days. Adverse events (AEs), vital signs, physical examinations, laboratory tests, electrocardiograms (ECG), and pharmacokinetics were assessed. FINDINGS: All 24 subjects in the single-dose test completed the study. Of the 12 subjects in multiple dosing test, one from the AM group withdrew owing to a headache. No serious AEs were reported. Hemodynamic parameters were well maintained in all subjects. Slight ECG abnormalities were observed in the single-dose test. The plasma concentration of AM progressively increased in a dose-dependent manner and reached Cmax at the end of administration. Plasma AM rapidly returned to baseline concentrations after termination, with a T1/2 of under 60 min. INTERPRETATION: This is the first phase 1 trial in healthy men evaluating the safety of AM. Our results demonstrate the safety and tolerability of AM for subsequent Phase 2 trials.

Molecular imaging of monocrotaline-induced pulmonary vascular disease with radiolabeled linear adrenomedullin.

UNLABELLED: No test currently exists for molecular imaging of pulmonary arterial hypertension (PAH). Adrenomedullin is a vasodilator peptide predominantly cleared by pulmonary endothelial receptors. We developed a linear adrenomedullin derivative radiolabeled with (99m)Tc ((99m)Tc-AM-L) for imaging of pulmonary circulation and tested its capacity to detect anomalies of pulmonary circulation caused by PAH. METHODS: PAH was induced by monocrotaline in rats and compared with controls. After 5 wk, (99m)Tc-AM-L was injected intravenously. Plasma kinetics were measured, lung activity was determined in vivo after 30 min using a nuclear camera, and lung activity was determined ex vivo in explanted lungs. Expression of adrenomedullin receptors was measured in lung homogenates. RESULTS: The plasma levels of (99m)Tc-AM-L significantly increased in PAH by approximately 2-fold. Uptake by the lungs was homogeneous but greatly reduced in PAH by about 70%. In vivo retention was 14% +/- 1% (mean +/- SD) of the injected dose in controls and 4% +/- 1% in PAH (P < 0.0001). A similar reduction was measured ex vivo (6.0 +/- 1.6 percentage injected dose per gram [%ID/g] vs. 0.95 +/- 0.21 %ID/g, P < 0.0001). The expression of the heterodimeric component of the adrenomedullin receptor, receptor activity modifying protein 2, was also greatly reduced in PAH lungs (P < 0.001). Interestingly, right ventricular uptake of (99m)Tc-AM-L was increased by PAH (P = 0.02) and correlated with the degree of right ventricular hypertrophy (r = 0.83, P = 0.001). CONCLUSION: Pulmonary uptake of (99m)Tc-AM-L is greatly reduced in monocrotaline-induced PAH. This novel molecular imaging agent may be useful in the diagnosis and follow-up of pulmonary vascular disorders.

Effect of adrenomedullin on the cerebral circulation: relevance to primary headache disorders.

Adrenomedullin (ADM) is closely related to calcitonin gene-related peptide, which has a known causative role in migraine. Animal studies have strongly suggested that ADM has a vasodilatory effect within the cerebral circulation. For these reasons, ADM is also likely to be involved in migraine. However, the hypothetical migraine-inducing property and effect on human cerebral circulation of ADM have not previously been investigated. Human ADM (0.08 microg kg(-1) min(-1)) or placebo (saline 0.9%) was administered as a 20-min intravenous infusion to 12 patients suffering from migraine without aura in a crossover double-blind study. The occurrence of headache and associated symptoms were registered regularly 24 h post infusion. Cerebral blood flow (CBF) was measured by (133)Xenon single-photon emission computed tomography, mean blood flow velocity in the middle cerebral artery (V(MCA)) by transcranial Doppler and the diameter of peripheral arteries by transdermal ultrasound (C-scan). ADM did not induce significantly more headache or migraine compared with placebo (P = 0.58). CBF was unaffected by ADM infusion (global CBF, P = 0.32 and rCBF(MCA), P = 0.38) and the same applied for the V(MCA) (P = 0.18). The superficial temporal artery dilated compared with placebo (P < 0.001), and facial flushing was seen after ADM administration (P = 0.001). In conclusion, intravenous ADM is not a mediator of migraine headache and does not dilate intracranial arteries.

Polyethylene glycol-conjugated human adrenomedullin as a possible treatment for vascular dementia.

Adrenomedullin (AM) is a multifunctional bioactive peptide. Recent studies have shown that AM has protective effects against ischemic brain damage. We recently prepared a long-acting human AM derivative that was conjugated with a 60 kDa polyethylene glycol (PEG-AM), which had an effect similar to that of native AM. In this study, we examined the effect of PEG-AM on four-vessel occlusion model rats, which exhibit vascular dementia. From day 10 to day 14 after surgery, the learning and memory abilities of the rats were examined using a Morris water maze. The rats were treated with a single subcutaneous injection of 1.0 or 10.0 nmol/kg of PEG-AM. PEG-AM treatment reduced the escape latency in the hidden platform test. Furthermore, the treatment increased the time spent in the platform quadrant in the probe test. The data showed that PEG-AM injection prevented memory loss and learning disorders in dose-dependent manner. On day 14, the immunoreactive AM concentration in plasma was 9.749 ±â€¯2.167 pM in the high-dose group (10.0 nmol/kg) and 0.334 ±â€¯0.073 pM in the low-dose group (1.0 nmol/kg). However, even in the low-dose group, a significant effect was observed in both tests. The present data indicate that PEG-AM is a possible therapeutic agent for the treatment of ischemic brain injury or vascular dementia.

Use of adrenomedullin derivatives for molecular imaging of pulmonary circulation.

UNLABELLED: Currently, there is no low-molecular-weight agent for imaging of the pulmonary circulation. Adrenomedullin (AM) is a peptide predominantly cleared by the pulmonary circulation through specific endothelial receptors. We developed human AM derivatives radiolabeled with 99mTc and evaluated their biodistribution, plasma kinetics, and utility as pulmonary vascular imaging agents. METHODS: Two derivatives radiolabeled with 99mTc were evaluated: the natural cyclic form of the peptide, to which the chelator diethylenetriaminepentaacetic acid was added (C-DTPA-AM), and the linear form, which allows direct labeling (L-AM). The compounds were injected into dogs, and the activities of the tracers in blood and in organs were determined with a nuclear medicine camera. Single-pass pulmonary clearance was measured by the indicator dilution technique. The capacity to image perfusion defects was evaluated after surgical pulmonary artery ligation. RESULTS: Both derivatives were rapidly cleared from plasma, with elimination half-lives of 42 and 32 min for C-DTPA-AM and L-AM, respectively. The lungs retained most of the activity after 30 min; this activity was higher (P = 0.02) for L-AM (42% +/- 5% [mean +/- SEM]) than for C-DTPA-AM (27% +/- 1%). Lung activity slowly declined over time but was maintained after 2 h at approximately 20% for both tracers. The single-pass pulmonary clearance of plasma L-AM was 414 +/- 85 mL/min. There was a higher level of urinary excretion of L-AM than of C-DTPA-AM. After pulmonary artery ligation, perfusion defects were easily detectable by external imaging. CONCLUSION: AM derivatives are promising compounds for molecular imaging of the pulmonary circulation. L-AM displayed higher levels of initial lung retention and of kidney excretion.

Al[18F]F-complexation of DFH17, a NOTA-conjugated adrenomedullin analog, for PET imaging of pulmonary circulation.

INTRODUCTION: Adrenomedullin receptors are highly expressed in human alveolar capillaries and provide a molecular target for imaging the integrity of pulmonary microcirculation. In this work, we aimed to develop a NOTA-derivatized adrenomedullin analog (DFH17), radiolabeled with [18F]AlF, for PET imaging of pulmonary microcirculation. METHODS: Highly concentrated [18F](AlF)2+ (15 µL) was produced from purified fluorine-18 in NaCl 0.9%. Various complexation experiments were carried out at Al-to-NOTA molar ratios ranging from 1:1 to 1:40 to assess optimal radiolabeling conditions before using the peptide. DFH17 peptide (2 mM, pH 4) was radiolabeled with [18F](AlF)2+ for 15 min at 100 °C in a total volume of 60 µL. As part of the radiolabeling process, parameters such as fluorine-18 activity (~37 and 1480 MBq), concentration of AlCl3 (0.75, 2, 3, 6 or 10 mM) and the effects of hydrophilic organic solvent (aqueous vs ethanol 50%) were studied. The final formulation was tested for purity, identity and stability in saline. Initial in vivo evaluation of [18F]AlF-DFH17 was performed in normal rats by PET/CT. RESULTS: The scaled-up production of [18F]AlF-DFH17 was performed in high radiochemical and chemical purities in an overall radiochemical yield of 22-38% (at end-of-synthesis) within 60 min. The final formulation was stable in saline at different radioactive concentrations for 8 h. PET evaluation in rats revealed high lung-to-background ratios and no defluorination in vivo up to 1 h post-injection. CONCLUSION: The novel radioconjugate [18F]AlF-DFH17 appears to be a promising PET ligand for pulmonary microcirculation imaging.

Vascular Effects of Adrenomedullin and the Anti-Adrenomedullin Antibody Adrecizumab in Sepsis.

Sepsis remains a major scientific and medical challenge, for which, apart from significant refinements in supportive therapy, treatment has barely changed over the last few decades. During sepsis, both vascular tone and vascular integrity are compromised, and contribute to the development of shock. The free circulating peptide adrenomedullin (ADM) is involved in the regulation of the endothelial barrier function and tone of blood vessels. Several animal studies have shown that ADM administration improves outcome of sepsis. However, in higher dosages, ADM administration may cause hypotension, limiting its clinical applicability. Moreover, ADM has a very short half-life and easily adheres to surfaces, further hampering its clinical use. The non-neutralizing anti-ADM antibody Adrecizumab (HAM8101) which causes a long-lasting increase of plasma ADM has shown promising results in animal models of systemic inflammation and sepsis; it reduced inflammation, attenuated vascular leakage, and improved hemodynamics, kidney function, and survival. Combined with an excellent safety profile derived from animal and phase I human studies, Adrecizumab represents a promising candidate drug for the adjunctive treatment of sepsis. In this review, we first provide a brief overview of the currently available data on the role of adrenomedullin in sepsis and describe its effects on endothelial barrier function and vasodilation. Furthermore, we provide a novel hypothesis concerning the mechanisms of action through which Adrecizumab may exert its beneficial effects in sepsis.

Adrenomedullin reduces gender-dependent loss of hypotensive cerebrovasodilation after newborn brain injury through activation of ATP-dependent K channels.

Cerebrovascular dysregulation during hypotension occurs after fluid percussion brain injury (FPI) in the newborn pig owing to impaired K channel function. This study was designed to (1) determine the role of gender and K channel activation in adrenomedullin (ADM) cerebrovasodilation, (2) characterize the role of gender in the loss of hypotensive cerebrovasodilation after FPI, and (3) determine the role of gender in the ability of exogenous ADM to modulate hypotensive dysregulation after FPI. Lateral FPI (2 atm) was induced in newborn male and female newborn pigs (1 to 5 days old) equipped with a closed cranial window, n=6 for each protocol. Adrenomedullin-induced pial artery dilation was significantly greater in female than male piglets and blocked by the K(ATP) channel antagonist glibenclamide, but not by the K(ca) channel antagonist iberiotoxin. Cerebrospinal fluid ADM was increased from 3.8+/-0.7 to 14.6+/-3.0 fmol/mL after FPI in female but was unchanged in male piglets. Hypotensive pial artery dilation was blunted to a significantly greater degree in male versus female piglets after FPI. Topical pretreatment with a subthreshold vascular concentration of ADM (10(-10) mol/L) before FPI reduced the loss of hypotensive pial artery dilation in both genders, but protection was significantly greater in male versus female piglets. These data show that hypotensive pial artery dilation is impaired after FPI in a gender-dependent manner. By unmasking a gender-dependent endogenous protectant, these data suggest novel gender-dependent approaches for clinical intervention in the treatment of perinatal traumatic brain injury.

Biological properties of adrenomedullin conjugated with polyethylene glycol.

Adrenomedullin (AM) is a vasodilator peptide with pleiotropic effects, including cardiovascular protection and anti-inflammation. Because of these beneficial effects, AM appears to be a promising therapeutic tool for human diseases, while intravenous injection of AM stimulates sympathetic nerve activity due to short-acting potent vasodilation, resulting in increased heart rate and renin secretion. To lessen these acute reactions, we conjugated the N-terminal of human AM peptide with polyethylene glycol (PEG), and examined the biological properties of PEGylated AM in the present study. PEGylated AM stimulated cAMP production, an intracellular second messenger of AM, in cultured human embryonic kidney cells expressing a specific AM receptor in a dose-dependent manner, as did native human AM. The pEC50 value of PEGylated AM was lower than human AM, but no difference was noted in maximum response (Emax) between the PEGylated and native peptides. Intravenous bolus injection of 10nmol/kg PEGylated AM lowered blood pressure in anesthetized rats, but the acute reduction became significantly smaller by PEGylation as compared with native AM. Plasma half-life of PEGylated AM was significantly longer than native AM both in the first and second phases in rats. In summary, N-terminal PEGylated AM stimulated cAMP production in vitro, showing lessened acute hypotensive action and a prolonged plasma half-life in comparison with native AM peptide in vivo.

Protective effect of adrenomedullin on contrast induced nephropathy in rats / Efecto protector de la adrenomedulina en la nefropatía inducida por contraste en ratas

Background and aims: Contrast-induced nephropathy (CIN) has a growing incidence in which renal vasoconstriction and medullary hypoxia are important mechanisms. Therapeutic approaches are very restricted and there is a considerable interest in advancing preventive strategies. Adrenomedullin is a relatively novel peptide having antioxidant, vasoactive and vasodilatory properties. We aimed to investigate whether adrenomedullin might have a preventive role against the development of experimental CIN. Methods: Wistar albino rats (n=24) were allocated randomly into four equal groups of 6 each; Control (C), Adrenomedullin (A), Contrast Media (CM) and Adrenomedullin plus Contrast Media (ACM). All rats were deprived of water from day 1 to day 4 during 72 hours. Then, intravenous administrations of chemicals were performed. Adrenomedullin was given at dose of 12µg/kg to groups A and ACM. A single dose of high-osmolar contrast media; diatrizoate (Urografin 76%, Schering AG, Germany) was injected to groups CM and ACM at dose of 10mL/kg. On day 1 and 6 blood samples were drawn for renal function tests and inflammatory markers including TNF-α IL-1β, IL-6 and IL-18. After sacrification, kidney histologies were examined with hematoxylin-eosin staining. Results: Compared to CM group, serum cystatin-C levels on 6th day were found significantly lower in ACM group (p<0.05). Additionally, daily protein excretion rates, absolute changes in daily urine output and creatinine clearance values were significantly lower in ACM group than those in CM group (p<0.05). In histopathological evaluation, regarding the degree of tubular damage and medullary congestion scores, ACM group had slightly better scores compared to CM group; however the differences did not reach significance as shown in inflammatory markers. Conclusion: This study demonstrated a beneficial impact of adrenomedullin on deteriorated renal function tests in an experimental CIN model. Adrenomedullin might be a candidate agent for prophylaxis of CIN. However, further studies are needed to shed more light on this issue

Antecedentes y objetivos: La incidencia de la nefropatía inducida por contraste (NIC) está aumentando y la vasoconstricción renal y la hipoxia medular son mecanismos importantes. Los enfoques terapéuticos son muy limitados y existe un gran interés en avanzar en las estrategias preventivas. La adrenomedulina es un péptido relativamente nuevo con propiedades antioxidantes, vasoactivas y vasodilatadoras. Nuestro objetivo es investigar si la adrenomedulina puede jugar un papel preventivo frente al desarrollo de la NIC experimental. Métodos: Se distribuyeron ratas Wistar albinas (n = 24) de forma aleatoria en cuatro grupos de 6: control (C), adrenomedulina (A), medio de contraste (MC) y adrenomedulina más medio de contraste (AMC). Las ratas no ingirieron agua desde el día 1 al día 4 (durante 72 horas). Posteriormente, se les administraron las sustancias de forma intravenosa. Los grupos A y AMC recibieron una dosis de adrenomedulina de 12 µg/kg. Los grupos MC y AMC recibieron una única dosis de medio de contraste de alta osmolaridad: 10 ml/kg de diatrizoato (Urografin 76 %, Schering AG, Alemania). Los días 1 y 6 se tomaron muestras de sangre para realizar análisis de función renal y de marcadores inflamatorios, incluidos el TNF-α, IL-1β, IL-6 e IL-18. Tras el sacrificio, se examinaron las histologías renales con tinción hematoxilina-eosina. Resultados: En comparación con el grupo MC, los niveles de cistatina C sérica fueron significativamente inferiores en el grupo AMC (P < 0,05). Además, la tasa de excreción diaria de proteínas, los cambios absolutos en el gasto urinario diario y los valores de aclaramiento de la creatinina fueron significativamente inferiores en el grupo AMC que en el grupo MC (P < 0,05). En la evaluación histopatológica, en lo que respecta al grado de daño tubular y los valores de congestión medular, el grupo AMC presentaba niveles ligeramente mejores en comparación con el grupo MC. Sin embargo, según los marcadores inflamatorios, las diferencias no presentaron significación estadística. Conclusión: El estudio ha demostrado que la adrenomedulina resulta beneficiosa en los análisis de función renal deteriorada en un modelo experimental de NIC. Por lo tanto, la adrenomedulina puede ser un candidato para la profilaxis de la NIC. No obstante, se necesitan más estudios que arrojen luz sobre este tema