Outcomes for people admitted to Australian and New Zealand intensive care units with primary, exacerbating, or incidental SARS-CoV-2 infections, 2022-23: a retrospective analysis of ANZICS data.

OBJECTIVES: To compare in-hospital mortality and intensive care unit (ICU) length of stay for people admitted to Australian and New Zealand ICUs during 2022-23 with coronavirus disease 2019 (COVID-19) pneumonitis, incidental or exacerbating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections, or without SAR-CoV-2 infections. STUDY DESIGN: Retrospective cohort study; analysis of Australian and New Zealand Intensive Care Society (ANZICS) Adult Patient Database data. SETTING, PARTICIPANTS: Adults (16 years or older) admitted to participating ICUs in Australia or New Zealand, 1 January 2022 - 30 June 2023. MAJOR OUTCOME MEASURES: The primary outcome was in-hospital mortality, the secondary outcome ICU length of stay, each by SARS-CoV-2 infection attribution classification: primary COVID-19; exacerbating SARS-CoV-2 infection (SARS-CoV-2 infection was a contributing factor to the primary cause of ICU admission); incidental SARS-CoV-2 infections (SARS-CoV-2 infection detected during ICU admission but did not contribute to admission diagnosis); no SARS-CoV-2 infection. RESULTS: A total of 207 684 adults were admitted to 195 Australian and New Zealand ICUs during 2022-23; 2674 people (1.3%) had incidental SARS-CoV-2 infections, 4923 (2.4%) exacerbating infections, and 3620 (1.7%) primary COVID-19. Unadjusted in-hospital mortality for people with incidental SARS-CoV-2 infections (288 deaths, 10.8%) was lower than for those with exacerbating infections (928 deaths, 18.8%) or primary COVID-19 (830 deaths, 22.9%), but higher than for patients without SARS-CoV-2 infections (15 486 deaths, 7.9%). After adjusting for illness severity, frailty, geographic region, and type of hospital, mortality was higher for patients with incidental SARS-CoV-2 infections (adjusted odds ratio [aOR], 1.28; 95% confidence interval [CI], 1.10-1.50), exacerbating infections (aOR, 1.35; 95% CI, 1.22-1.48), or primary COVID-19 (aOR, 2.54; 95% CI, 2.30-2.81) than for patients without SARS-CoV-2 infections. After adjusting for diagnosis and illness severity, ICU stays were longer for people with incidental (mean difference, 3.3 hours; 95% CI, 2.4-4.2 hours) or exacerbating infections (0.8 hours; 95% CI, 0.2-1.5 hours) than for those without SARS-CoV-2 infections. CONCLUSION: Risk-adjusted in-hospital mortality and ICU length of stay are higher for people admitted to intensive care who have concomitant SARS-CoV-2 infections than for people who do not.

Beta-blockade for the treatment of refractory hypoxaemia during venovenous extracorporeal membrane oxygenation: An in-silico study.

INTRODUCTION: Venovenous extracorporeal membrane oxygenation (VV ECMO) is used for refractory hypoxemia, although despite this, in high cardiac output states, hypoxaemia may persist. The administration of beta-blockers has been suggested as an approach in this scenario, however the physiological consequences of this intervention are not clear. METHODS: We performed an in-silico study using a previously described mathematical model to evaluate the effect of beta-blockade on mixed venous and arterial saturations (Sv¯O2, SaO2), in three different clinical scenarios and considered the potential effects of beta-blockers on, cardiac output, oxygen consumption and recirculation. Additionally we assessed the interaction of beta-blockade with haemoglobin concentration. RESULTS: In scenario 1: simulating a patient with high cardiac output and partial lung shunt Sv¯O2 decreased from increased 53.5% to 44.7% despite SaO2 rising from 74.2% to 79.2%. In scenario 2 simulating a patient with high cardiac output and complete lung shunt Sv¯O2 remained unchanged at 52.2% and SaO2 rose from 71.9% to 85%. In scenario 3 a patient with normal cardiac output and high recirculation Sv¯O2 fell from 50.8% to 25.5% and also fell from 82.4% to to 78.3%. Across the remaining modelling examples the effect on Sv¯O2 varied but oxygen delivery was consistently reduced across all scenarios. CONCLUSION: The administration of beta-blockers for refractory hypoxemia during VV ECMO are unpredictable and may reduce oxygen delivery, although this will vary with patient and circuit features. This study does not support the use of beta-blockers for this indication.

Composite outcome measures in high-impact critical care randomised controlled trials: a systematic review.

BACKGROUND: The use of composite outcome measures (COM) in clinical trials is increasing. Whilst their use is associated with benefits, several limitations have been highlighted and there is limited literature exploring their use within critical care. The primary aim of this study was to evaluate the use of COM in high-impact critical care trials, and compare study parameters (including sample size, statistical significance, and consistency of effect estimates) in trials using composite versus non-composite outcomes. METHODS: A systematic review of 16 high-impact journals was conducted. Randomised controlled trials published between 2012 and 2022 reporting a patient important outcome and involving critical care patients, were included. RESULTS: 8271 trials were screened, and 194 included. 39.1% of all trials used a COM and this increased over time. Of those using a COM, only 52.6% explicitly described the outcome as composite. The median number of components was 2 (IQR 2-3). Trials using a COM recruited fewer participants (409 (198.8-851.5) vs 584 (300-1566, p = 0.004), and their use was not associated with increased rates of statistical significance (19.7% vs 17.8%, p = 0.380). Predicted effect sizes were overestimated in all but 6 trials. For studies using a COM the effect estimates were consistent across all components in 43.4% of trials. 93% of COM included components that were not patient important. CONCLUSIONS: COM are increasingly used in critical care trials; however effect estimates are frequently inconsistent across COM components confounding outcome interpretations. The use of COM was associated with smaller sample sizes, and no increased likelihood of statistically significant results. Many of the limitations inherent to the use of COM are relevant to critical care research.

The Australian Traumatic Brain Injury Initiative: Systematic Review of the Effect of Acute Interventions on Outcome for People With Moderate-Severe Traumatic Brain Injury.

The Australian Traumatic Brain Injury Initiative (AUS-TBI) is developing a data resource to enable improved outcome prediction for people with moderate-severe TBI (msTBI) across Australia. Fundamental to this resource is the collaboratively designed data dictionary. This systematic review and consultation aimed to identify acute interventions with potential to modify clinical outcomes for people after msTBI, for inclusion in a data dictionary. Standardized searches were implemented across bibliographic databases from inception through April 2022. English-language reports of randomized controlled trials (RCTs) evaluating any association between any acute intervention and clinical outcome in at least 100 patients with msTBI, were included. A predefined algorithm was used to assign a value to each observed association. Consultation with AUS-TBI clinicians and researchers formed the consensus process for interventions to be included in a single data dictionary. Searches retrieved 14,455 records, of which 124 full-length RCTs were screened, with 35 studies included. These studies evaluated 26 unique acute interventions across 21 unique clinical outcomes. Only 4 interventions were considered to have medium modifying value for any outcome from the review, with an additional 8 interventions agreed upon through the consensus process. The interventions with medium value were tranexamic acid and phenytoin, which had a positive effect on an outcome; and decompressive craniectomy surgery and hypothermia, which negatively affected outcomes. From the systematic review and consensus process, 12 interventions were identified as potential modifiers to be included in the AUS-TBI national data resource.

Frequency of and associations with alterations of medical emergency team calling criteria in a teaching hospital emergency department.

BACKGROUND: Medical emergency team (METs), activated by vital sign-based calling criteria respond to deteriorating patients in the hospital setting. Calling criteria may be altered where clinicians feel this is appropriate. Altered calling criteria (ACC) has not previously been evaluated in the emergency department (ED) setting. OBJECTIVES: The objectives of this study were to (i) describe the frequency of ACC in a teaching hospital ED and the number and type of vital signs that were modified and (ii) associations between ACC in the ED and differences in the baseline patient characteristics and adverse outcomes including subsequent MET activations, unplanned intensive care unit (ICU) admissions and death within 72 h of admission. METHODS: Retrospective observational study of patients presenting to an academic, tertiary hospital ED in Melbourne, Australia between January 1st, 2019 and December 31st, 2019. The primary outcome was frequency and nature of ACC in the ED. Secondary outcomes included differences in baseline patient characteristics, frequency of MET activation, unplanned ICU admission, and mortality in the first 72 h of admission between those with and without ACC in the ED. RESULTS: Amongst 14 159 ED admissions, 725 (5.1%) had ACC, most frequently for increased heart or respiratory rate. ACC was associated with older age and increased comorbidity. Such patients had a higher adjusted risk of MET activation (odds ratio [OR]: 3.14, 95% confidence interval [CI]: 2.50-3.91, p = <0.001), unplanned ICU admission (OR: 1.97, 95% CI: 1.17-3.14, p = 0.016), and death (OR: 3.87, 95% CI: 2.08-6.70, p = 0.020) within 72 h. CONCLUSIONS: ACC occurs commonly in the ED, most frequently for elevated heart and respiratory rates and is associated with worse patient outcomes. In some cases, ACC requires consultant involvement, more frequent vital sign monitoring, expeditious inpatient team review, or ICU referral.

Oxygenation During Venoarterial Extracorporeal Membrane Oxygenation: Physiology, Current Evidence, and a Pragmatic Approach to Oxygen Titration.

OBJECTIVES: This review aims to: 1) identify the key circuit and patient factors affecting systemic oxygenation, 2) summarize the literature reporting the association between hyperoxia and patient outcomes, and 3) provide a pragmatic approach to oxygen titration, in patients undergoing peripheral venoarterial extracorporeal membrane oxygenation (ECMO). DATA SOURCES: Searches were performed using PubMed, SCOPUS, Medline, and Google Scholar. STUDY SELECTION: All observational and interventional studies investigating the association between hyperoxia, and clinical outcomes were included, as well as guidelines from the Extracorporeal Life Support Organization. DATA EXTRACTION: Data from relevant literature was extracted, summarized, and integrated into a concise narrative review. For ease of reference a summary of relevant studies was also produced. DATA SYNTHESIS: The extracorporeal circuit and the native cardiorespiratory circuit both contribute to systemic oxygenation during venoarterial ECMO. The ECMO circuit's contribution to systemic oxygenation is, in practice, largely determined by the ECMO blood flow, whereas the native component of systemic oxygenation derives from native cardiac output and residual respiratory function. Interactions between ECMO outflow and native cardiac output (as in differential hypoxia), the presence of respiratory support, and physiologic parameters affecting blood oxygen carriage also modulate overall oxygen exposure during venoarterial ECMO. Physiologically those requiring venoarterial ECMO are prone to hyperoxia. Hyperoxia has a variety of definitions, most commonly Pa o2 greater than 150 mm Hg. Severe hypoxia (Pa o2 > 300 mm Hg) is common, seen in 20%. Early severe hyperoxia, as well as cumulative hyperoxia exposure was associated with in-hospital mortality, even after adjustment for disease severity in both venoarterial ECMO and extracorporeal cardiopulmonary resuscitation. A pragmatic approach to oxygenation during peripheral venoarterial ECMO involves targeting a right radial oxygen saturation target of 94-98%, and in selected patients, titration of the fraction of oxygen in the mixture via the air-oxygen blender to target postoxygenator Pa o2 of 150-300 mm Hg. CONCLUSIONS: Hyperoxia results from a range of ECMO circuit and patient-related factors. It is common during peripheral venoarterial ECMO, and its presence is associated with poor outcome. A pragmatic approach that avoids hyperoxia, while also preventing hypoxia has been described for patients receiving peripheral venoarterial ECMO.

A novel somatostatin receptor ligand for human ACTH - and GH -secreting pituitary adenomas.

OBJECTIVE: Somatostatin receptor ligands have come to play a pivotal role in the treatment of both ACTH- and GH-secreting pituitary adenomas. Clinical efficacy averages 30-50%, thus a considerable number of patients with Cushing's disease or acromegaly remain unresponsive to this therapeutic approach. HTL0030310 is a new somatostatin receptor ligand selective for subtype 5 over subtype 2, thus with a different receptor profile compared to clinical somatostatin receptor ligands. DESIGN: Assessment of the effect of HTL0030310 on hormone secretion in human ACTH- and GH-secreting pituitary adenomas in vitro. METHODS: Primary cultures from 3 ACTH-secreting and 5 GH-secreting pituitary adenomas were treated with 1, 10 and 100 nM HTL0030310 alone or with 10 nM CRH or GHRH, respectively. Parallel incubations with 10 nM pasireotide were also carried out. ACTH and GH secretion were assessed after 4 and 24 hour incubation; SSTR2, SSTR3, SSTR5, GH and POMC expression were evaluated after 24 hours. RESULTS: HTL0030310 reduced unchallenged ACTH and POMC levels up to 50% in 2 ACTH-secreting adenomas and blunted CRH-stimulated ACTH/POMC by 20-70% in all 3 specimens. A reduction in spontaneous GH secretion was observed in 4 GH-secreting adenomas and in 2 specimens during GHRH co-incubation. SSTRs expression was detected in all specimens. CONCLUSIONS: This first study on a novel somatostatin receptor 5-preferring ligand indicates that HTL0030310 can inhibit hormonal secretion in human ACTH- and GH-secreting pituitary adenomas. These findings suggest a potential new avenue for somatostatin ligands in the treatment of Cushing's disease and acromegaly.

Therapeutic Hypothermia for Refractory Hypoxemia on Venovenous Extracorporeal Membrane Oxygenation: An In Silico Study.

Patients with respiratory failure may remain hypoxemic despite treatment with venovenous extracorporeal membrane oxygenation (VV-ECMO). Therapeutic hypothermia is a potential treatment for such hypoxia as it reduces cardiac output ( ) and oxygen consumption. We modified a previously published mathematical model of gas exchange to investigate the effects of hypothermia during VV-ECMO. Partial pressures were expressed as measured at 37°C (α-stat). The effect of hypothermia on gas exchange was examined in four clinical scenarios of hypoxemia on VV-ECMO, each with different physiological derangements. All scenarios had arterial partial pressure of oxygen (PaO 2 ) ≤ 46 mm Hg and arterial oxygen saturation of hemoglobin (SaO 2 ) ≤ 81%. Three had high with low extracorporeal blood flow to ratio ( ). The problem in the fourth scenario was recirculation, with normal . Cooling to 33°C increased SaO 2 to > 89% and PaO 2 to > 50 mm Hg in all scenarios. Mixed venous oxygen saturation of hemoglobin as % ( ) increased to > 70% and mixed venous partial pressure of oxygen in mm Hg ( ) increased to > 34 mm Hg in scenarios with low . In the scenario with high recirculation, and increased, but to < 50% and < 27 mm Hg, respectively. This in silico study predicted cooling to 33°C will improve oxygenation in refractory hypoxemia on VV-ECMO, but the improvement will be less when the problem is recirculation.

Regional characterisation of TRPV1 and TRPA1 signalling in the mouse colon mucosa.

Capsaicin and allyl isothiocyanate (AITC) activate transient receptor potential (TRP) vanilloid-1 (TRPV1) and TRP ankyrin-1 (TRPA1), respectively. TRPV1 and TRPA1 expression have been identified in the gastrointestinal (GI) tract. GI mucosal functions remain largely undefined for TRPV1 and TRPA1 with side-dependence and regional differences in signalling unclear. Here we investigated TRPV1- and TRPA1-induced vectorial ion transport as changes in short-circuit current (ΔIsc), in defined segments of mouse colon mucosa (ascending, transverse and descending) under voltage-clamp conditions in Ussing chambers. Drugs were applied basolaterally (bl) or apically (ap). Capsaicin responses were biphasic, with primary secretory and secondary anti-secretory phases, observed with bl application only, which predominated in descending colon. AITC responses were monophasic and secretory, with ΔIsc dependent on colonic region (ascending vs. descending) and sidedness (bl vs. ap). Aprepitant (neurokinin-1 (NK1) antagonist, bl) and tetrodotoxin (Na+ channel blocker, bl) significantly inhibited capsaicin primary responses in descending colon, while GW627368 (EP4 receptor antagonist, bl) and piroxicam (cyclooxygenase inhibitor, bl) inhibited AITC responses in ascending and descending colonic mucosae. Antagonism of the calcitonin gene-related peptide (CGRP) receptor had no effect on mucosal TRPV1 signalling, while tetrodotoxin and antagonists of the 5-hydroxytryptamine-3 and 4 receptors, CGRP receptor, and EP1/2/3 receptors had no effect on mucosal TRPA1 signalling. Our data demonstrates the regional-specificity and side-dependence of colonic TRPV1 and TRPA1 signalling, with involvement of submucosal neurons and mediation by epithelial NK1 receptor activation for TRPV1, and endogenous prostaglandins and EP4 receptor activation for TRPA1 mucosal responses.

A growing understanding of the role of muscarinic receptors in the molecular pathology and treatment of schizophrenia.

Pre-clinical models, postmortem and neuroimaging studies all support a role for muscarinic receptors in the molecular pathology of schizophrenia. From these data it was proposed that activation of the muscarinic M1 and/or M4 receptor would reduce the severity of the symptoms of schizophrenia. This hypothesis is now supported by results from two clinical trials which indicate that activating central muscarinic M1 and M4 receptors can reduce the severity of positive, negative and cognitive symptoms of the disorder. This review will provide an update on a growing body of evidence that argues the muscarinic M1 and M4 receptors have critical roles in CNS functions that are dysregulated by the pathophysiology of schizophrenia. This realization has been made possible, in part, by the growing ability to visualize and quantify muscarinic M1 and M4 receptors in the human CNS using molecular neuroimaging. We will discuss how these advances have provided evidence to support the notion that there is a sub-group of patients within the syndrome of schizophrenia that have a unique molecular pathology driven by a marked loss of muscarinic M1 receptors. This review is timely, as drugs targeting muscarinic receptors approach clinical use for the treatment of schizophrenia and here we outline the background biology that supported development of such drugs to treat the disorder.

Expanding the apelin receptor pharmacological toolbox using novel fluorescent ligands.

Introduction: The apelin receptor binds two distinct endogenous peptides, apelin and ELA, which act in an autocrine/paracrine manner to regulate the human cardiovascular system. As a class A GPCR, targeting the apelin receptor is an attractive therapeutic strategy. With improvements in imaging techniques, and the stability and brightness of dyes, fluorescent ligands are becoming increasingly useful in studying protein targets. Here, we describe the design and validation of four novel fluorescent ligands; two based on [Pyr1]apelin-13 (apelin488 and apelin647), and two based on ELA-14 (ELA488 and ELA647). Methods: Fluorescent ligands were pharmacologically assessed using radioligand and functional in vitro assays. Apelin647 was validated in high content imaging and internalisation studies, and in a clinically relevant human embryonic stem cell-derived cardiomyocyte model. Apelin488 and ELA488 were used to visualise apelin receptor binding in human renal tissue. Results: All four fluorescent ligands retained the ability to bind and activate the apelin receptor and, crucially, triggered receptor internalisation. In high content imaging studies, apelin647 bound specifically to CHO-K1 cells stably expressing apelin receptor, providing proof-of-principle for a platform that could screen novel hits targeting this GPCR. The ligand also bound specifically to endogenous apelin receptor in stem cell-derived cardiomyocytes. Apelin488 and ELA488 bound specifically to apelin receptor, localising to blood vessels and tubules of the renal cortex. Discussion: Our data indicate that the described novel fluorescent ligands expand the pharmacological toolbox for studying the apelin receptor across multiple platforms to facilitate drug discovery.

A phase 1b/2a multicenter study of the safety and preliminary pharmacodynamic effects of selective muscarinic M1 receptor agonist HTL0018318 in patients with mild-to-moderate Alzheimer's disease.

INTRODUCTION: This study examined the safety and pharmacodynamic effects of selective muscarinic M1 receptor orthosteric agonist HTL0018318 in 60 patients with mild-to-moderate Alzheimer's disease (AD) on background donepezil 10 mg/day. METHODS: A randomized, double-blind, placebo-controlled 4-week safety study of HTL0018318 with up-titration and maintenance phases, observing exploratory effects on electrophysiological biomarkers and cognition. RESULTS: Treatment-emergent adverse events (TEAEs) were mild and less frequently reported during maintenance versus titration. Headache was most commonly reported (7-21%); 0 to 13% reported cholinergic TEAEs (abdominal pain, diarrhea, fatigue, nausea) and two patients discontinued due to TEAEs. At 1 to 2 hours post-dose, HTL0018318-related mean maximum elevations in systolic and diastolic blood pressure of 5 to 10 mmHg above placebo were observed during up-titration but not maintenance. Postive effects of HTL0018318 were found on specific attention and memory endpoints. DISCUSSION: HTL0018318 was well tolerated in mild-to-moderate AD patients and showed positive effects on attention and episodic memory on top of therapeutic doses of donepezil.

A pilot, feasibility, randomised controlled trial of midodrine as adjunctive vasopressor for low-dose vasopressor-dependent hypotension in intensive care patients: The MAVERIC study.

PURPOSE: To assess the feasibility and physiological efficacy of adjunctive midodrine in patients with vasopressor-dependent hypotension. MATERIALS AND METHODS: This was a pilot, open label, randomised controlled trial. Patients were enrolled from two tertiary intensive care units on low dose intravenous vasopressor therapy for more than 24 h. We randomly assigned patients to receive either adjunctive midodrine (10 mg every 8 h) or usual care. The primary efficacy outcome was time to cessation of intravenous vasopressor therapy. Secondary outcomes included protocol compliance, ICU and hospital length of stay. RESULTS: We screened 381 patients over 22-months and enrolled 62 (32 in midodrine group, 30 in usual care group). Median time to cessation of vasopressor infusion was 16.5 h for midodrine vs 19 h for usual care (p = 0.22). Time in ICU (50 [25.50, 74.00] hours for midodrine v 59 [38.50, 93.25] hours for usual care, p = 0.14) and hospital length of stay (9 days vs. 7.5 days, p = 0.92) were similar. Protocol compliance was 96.9%. One patient ceased midodrine early due to symptomatic bradycardia. CONCLUSIONS: Adjunctive midodrine therapy was feasible with acceptable compliance, duration of therapy, and safety profile. However, at the chosen dose, there was no evidence of physiological or clinical efficacy.

From structure to clinic: Design of a muscarinic M1 receptor agonist with potential to treatment of Alzheimer's disease.

Current therapies for Alzheimer's disease seek to correct for defective cholinergic transmission by preventing the breakdown of acetylcholine through inhibition of acetylcholinesterase, these however have limited clinical efficacy. An alternative approach is to directly activate cholinergic receptors responsible for learning and memory. The M1-muscarinic acetylcholine (M1) receptor is the target of choice but has been hampered by adverse effects. Here we aimed to design the drug properties needed for a well-tolerated M1-agonist with the potential to alleviate cognitive loss by taking a stepwise translational approach from atomic structure, cell/tissue-based assays, evaluation in preclinical species, clinical safety testing, and finally establishing activity in memory centers in humans. Through this approach, we rationally designed the optimal properties, including selectivity and partial agonism, into HTL9936-a potential candidate for the treatment of memory loss in Alzheimer's disease. More broadly, this demonstrates a strategy for targeting difficult GPCR targets from structure to clinic.

Acetylcholine prioritises direct synaptic inputs from entorhinal cortex to CA1 by differential modulation of feedforward inhibitory circuits.

Acetylcholine release in the hippocampus plays a central role in the formation of new memory representations. An influential but largely untested theory proposes that memory formation requires acetylcholine to enhance responses in CA1 to new sensory information from entorhinal cortex whilst depressing inputs from previously encoded representations in CA3. Here, we show that excitatory inputs from entorhinal cortex and CA3 are depressed equally by synaptic release of acetylcholine in CA1. However, feedforward inhibition from entorhinal cortex exhibits greater depression than CA3 resulting in a selective enhancement of excitatory-inhibitory balance and CA1 activation by entorhinal inputs. Entorhinal and CA3 pathways engage different feedforward interneuron subpopulations and cholinergic modulation of presynaptic function is mediated differentially by muscarinic M3 and M4 receptors, respectively. Thus, our data support a role and mechanisms for acetylcholine to prioritise novel information inputs to CA1 during memory formation.

In vitro metabolism of synthetic Elabela/Toddler (ELA-32) peptide in human plasma and kidney homogenates analyzed with mass spectrometry and validation of endogenous peptide quantification in tissues by ELISA.

BACKGROUND: Elabela/Toddler (ELA) is a novel endogenous ligand of the apelin receptor, whose signalling has emerged as a therapeutic target, for example, in cardiovascular disease and cancer. Shorter forms of ELA-32 have been predicted, including ELA-21 and ELA-11, but metabolism and stability of ELA-32 in humans is poorly understood. We, therefore, developed an LC-MS/MS assay to identify ELA-32 metabolites in human plasma and tissues. METHOD: Human kidney homogenates or plasma were incubated at 37 °C with ELA-32 and aliquots withdrawn over 2-4 h into guanidine hydrochloride. Proteins were precipitated and supernatant solid-phase extracted. Peptides were extracted from coronary artery, brain and kidney by immunoprecipitation or solid-phase extraction following acidification. All samples were reduced and alkylated before analysis on an Orbitrap mass spectrometer in high and nano flow mode. RESULTS: The half-life of ELA-32 in plasma and kidney were 47.2 ±â€¯5.7 min and 44.2 ±â€¯3 s, respectively. Using PEAKS Studio and manual data analysis, the most important fragments of ELA-32 with potential biological activity identified were ELA-11, ELA-16, ELA-19 and ELA-20. The corresponding fragments resulting from the loss of C-terminal amino acids were also identified. Endogenous levels of these peptides could not be measured, as ELA peptides are prone to oxidation and poor chromatographic peaks. CONCLUSIONS: The relatively long ELA plasma half-life observed and identification of a potentially more stable fragment, ELA-16, may suggest that ELA could be a better tool compound and novel template for the development of new drugs acting at the apelin receptor.