AMP-activated protein kinase: a physiological off switch for murine gastric acid secretion

Adenosine monophosphate (AMP)-activated protein kinase (AMPK) has been shown to be a metabolic energy regulator in various cells. Activation is a direct result of rising AMP concentration coupled with falling adenosine triphosphate (ATP). AMPK activation during metabolic stress consequently reduces cellular ATP consumption. The gastric parietal cell has a large abundance of mitochondria per cell volume due to the numerous energy-dependent transporters and channels responsible for acid secretion. We identified AMPK in the parietal cell as a metabolic energy regulator that can switch acid secretion off as cellular ATP levels fall. AMPK presence in murine gastric glands was evaluated by immunofluorescent localization. We used a digital imaging system to monitor acid secretion as observed by proton efflux from parietal cells in hand-dissected gastric glands loaded with the pH-sensitive dye 2′,7′-bis-(2-carboxyethyl)-5-(and 6)-carboxyfluorescein. Individual murine gastric glands were exposed to histamine, pentagastrin, or carbachol. AMPK was pharmacologically activated with 5-aminoimidazole-4-carboxamide-1-β-d-riboside (AICAR) monophosphate or inhibited with 6-[4-(2-piperidin-1-yl-ethoxy)-phenyl)]-3-pyridin-4-yl-pyyrazolo[1,5-a] pyrimidine (compound C) or ATP. Acid secretion was evaluated under these conditions as the rate of intracellular pH recovery. In addition, whole-stomach pH measurements were performed. Immunofluorescent localization confirmed the presence of AMPK in gastric mucosa. Exposure to AICAR monophosphate significantly reduced secretagogue-induced acid secretion; addition of compound C or ATP restored acid secretion. Our results indicate that secretagogue-induced acid secretion could be significantly reduced with AMPK activation and restored with its deactivation. We therefore propose the AMPK as a cellular metabolic off switch for gastric acid secretion.     

The novel marker LTBP2 predicts all-cause and pulmonary death in patients with acute dyspnoea

The risk stratification in patients presenting with acute dyspnoea remains a challenge. We therefore conducted a prospective, observational cohort study enrolling 292 patients presenting to the emergency department with acute dyspnoea. A proteomic approach for antibody-free targeted protein quantification based on high-end MS was used to measure LTBP2 [latent TGF (transforming growth factor)-binding protein 2] levels. Final diagnosis and death during follow-up were adjudicated blinded to LTBP2 levels. AHF (acute heart failure) was the final diagnosis in 54% of patients. In both AHF (P<0.001) and non-AHF (P=0.015) patients, LTBP2 levels at presentation were significantly higher in non-survivors compared with survivors with differences on median levels being 2.2- and 1.5-fold respectively. When assessing the cause of death, LTBP2 levels were significantly higher in patients dying from pulmonary causes (P=0.0005). Overall, LTBP2 powerfully predicted early pulmonary death {AUC (area under the curve), 0.95 [95% CI (confidence interval), 0.91-0.98]}. In ROC (receiver operating characteristic) curve analyses for the prediction of 1-year mortality LTBP2 achieved an AUC of 0.77 (95% CI, 0.71-0.84); comparable with the predictive potential of NT-proBNP [N-terminal pro-B-type natriuruetic peptide; 0.77 (95% CI, 0.72-0.82)]. Importantly, the predictive potential of LTBP2 persisted in patients with AHF as the cause of dypnea (AUC 0.78) and was independent of renal dysfunction (AUC 0.77). In a multivariate Cox regression analysis, LTBP2 was the strongest independent predictor of death [HR (hazard ratio), 3.76 (95% CI, 2.13-6.64); P<0.0001]. In conclusion, plasma levels of LTBP2 present a novel and powerful predictor of all-cause mortality, and particularly pulmonary death. Cause-specific prediction of death would enable targeted prevention, e.g. with pre-emptive antibiotic therapy.     

Effect and clinical prediction of worsening renal function in acute decompensated heart failure

We aimed to establish the prevalence and effect of worsening renal function (WRF) on survival among patients with acute decompensated heart failure. Furthermore, we sought to establish a risk score for the prediction of WRF and externally validate the previously established Forman risk score. A total of 657 consecutive patients with acute decompensated heart failure presenting to the emergency department and undergoing serial creatinine measurements were enrolled. The potential of the clinical parameters at admission to predict WRF was assessed as the primary end point. The secondary end point was all-cause mortality at 360 days. Of the 657 patients, 136 (21%) developed WRF, and 220 patients had died during the first year. WRF was more common in the nonsurvivors (30% vs 41%, p = 0.03). Multivariate regression analysis found WRF to independently predict mortality (hazard ratio 1.92, p <0.01). In a single parameter model, previously diagnosed chronic kidney disease was the only independent predictor of WRF and achieved an area under the receiver operating characteristic curve of 0.60. After the inclusion of the blood gas analysis parameters into the model history of chronic kidney disease (hazard ratio 2.13, p = 0.03), outpatient diuretics (hazard ratio 5.75, p <0.01), and bicarbonate (hazard ratio 0.91, p <0.01) were all predictive of WRF. A risk score was developed using these predictors. On receiver operating characteristic curve analysis, the Forman and Basel prediction rules achieved an area under the curve of 0.65 and 0.71, respectively. In conclusion, WRF was common in patients with acute decompensated heart failure and was linked to significantly worse outcomes. However, the clinical parameters failed to adequately predict its occurrence, making a tailored therapy approach impossible.     

Plasma neutrophil gelatinase-associated lipocalin for the prediction of acute kidney injury in acute heart failure

Introduction

The accurate prediction of acute kidney injury (AKI) in patients with acute heart failure (AHF) is an unmet clinical need. Neutrophil gelatinase-associated lipocalin (NGAL) is a novel sensitive and specific marker of AKI.

Methods

A total of 207 consecutive patients presenting to the emergency department with AHF were enrolled. Plasma NGAL was measured in a blinded fashion at presentation and serially thereafter. The potential of plasma NGAL levels to predict AKI was assessed as the primary endpoint. We defined AKI according to the AKI Network classification.

Results

Overall 60 patients (29%) experienced AKI. These patients were more likely to suffer from pre-existing chronic cardiac or kidney disease. At presentation, creatinine (median 140 (interquartile range (IQR), 91 to 203) umol/L versus 97 (76 to 132) umol/L, P < 0.01) and NGAL (114.5 (IQR, 67.1 to 201.5) ng/ml versus 74.5 (60 to 113.9) ng/ml, P < 0.01) levels were significantly higher in AKI compared to non-AKI patients. The prognostic accuracy for measurements obtained at presentation, as quantified by the area under the receiver operating characteristic curve was mediocre and comparable for the two markers (creatinine 0.69; 95%CI 0.59 to 0.79 versus NGAL 0.67; 95%CI 0.57 to 0.77). Serial measurements of NGAL did not further increase the prognostic accuracy for AKI. Creatinine, but not NGAL, remained an independent predictor of AKI (hazard ratio (HR) 1.12; 95%CI 1.00 to 1.25; P = 0.04) in multivariable regression analysis.

Conclusions

Plasma NGAL levels do not adequately predict AKI in patients with AHF.     

Copeptin and risk stratification in patients with acute dyspnea

Introduction

The identification of patients at highest risk for adverse outcome who are presenting with acute dyspnea to the emergency department remains a challenge. This study investigates the prognostic value of Copeptin, the C-terminal part of the vasopressin prohormone alone and combined to N-terminal pro B-type natriuretic peptide (NT-proBNP) in patients with acute dyspnea.

Methods

We conducted a prospective, observational cohort study in the emergency department of a university hospital and enrolled 287 patients with acute dyspnea.

Results

Copeptin levels were elevated in non-survivors (n = 29) compared to survivors at 30 days (108 pmol/l, interquartile range (IQR) 37 to 197 pmol/l) vs. 18 pmol/l, IQR 7 to 43 pmol/l; P < 0.0001). The areas under the receiver operating characteristic curve (AUC) to predict 30-day mortality were 0.83 (95% confidence interval (CI) 0.76 to 0.90), 0.76 (95% CI 0.67 to 0.84) and 0.63 (95% CI 0.53 to 0.74) for Copeptin, NT-proBNP and BNP, respectively (Copeptin vs. NTproBNP P = 0.21; Copeptin vs. BNP P = 0.002). When adjusted for common cardiovascular risk factors and NT-proBNP, Copeptin was the strongest independent predictor for short-term mortality in all patients (HR 3.88 (1.94 to 7.77); P < 0.001) and especially in patients with acute decompensated heart failure (ADHF) (HR 5.99 (2.55 to 14.07); P < 0.0001). With the inclusion of Copeptin to the adjusted model including NTproBNP, the net reclassification improvement (NRI) was 0.37 (P < 0.001). An additional 30% of those who experienced events were reclassified as high risk, and an additional 26% without events were reclassified as low risk.

Conclusions

Copeptin is a new promising prognostic marker for short-term mortality independently and additive to natriuretic peptide levels in patients with acute dyspnea.     

A model for early failure prediction of blood pressure measurement devices in a stepped validation approach

Blood pressure monitoring (BPM) devices have to be validated according to strict international validation protocols. Each protocol requests a specific number of participants to be included. All protocols use vast amounts of resources, as three people have to be present for every measurement, making trials costly, especially when the manufacturer has no intention to execute a validation study, reflected in the low share of validated in the commercially available BPM devices. The aim of our study was to develop criteria, which could detect low accuracy devices that could not pass a validation protocol early in the course of the validation process. The 2010 European Society of Hypertension International Protocol (ESH‐IP) and the Universal Standard for Validation of BPM devices (AAMI/ESH/ISO) were scrutinized for criteria which can be used for preclusion of passing. Based on this, we developed a fail model. We found that a BPM device cannot pass the ESH‐IP protocol, if there are ≥27, 13, or 4 single measurements differing more than 5, 10, or 15 mmHg, respectively, from the reference. For the AAMI/ESH/ISO protocol, we developed a model, which calculates best‐case standard deviations (SDs) to detect SDs which would prevent the passing of the protocol before its completion, making a stepwise validation process possible. In conclusion, we found that our model is able to predict failure of low‐accuracy BPM devices early during a validation protocol if used in a stepwise‐approach. This can be useful to keep costs of validation studies low and to enable investigator‐initiated trials.