Cholesterol-rich clusters of SNARE (soluble NSF attachment protein receptor) proteins have been implicated as being important for exocytosis. Here we demonstrate the significance of cholesterol for normal biphasic insulin secretion in mouse beta cells by removal of cholesterol from the plasma membrane using methyl-beta-cyclodextrin (MBCD). Maximal inhibition of insulin secretion in static incubations was achieved using 0.1 mM MBCD. In in situ pancreatic perfusion measurements, both first and second phase insulin secretions were reduced by approximately 50% (P<0.05). This was accompanied by a reduced number of docked large dense core vesicles (LDCVs) (approximately 40%; P<0.01) and a reduced exocytotic response (>50%; P<0.01). Further, subcellular fractionations demonstrated movement of the synaptosomal protein of 25 kDa (SNAP-25) from the plasma membrane to the cytosol after MBCD treatment. The inhibitory actions of MBCD were counteracted by subsequent addition of cholesterol. We hypothesize that desorption of cholesterol leads to the disturbance of a basic exocytotic mechanism partly due to migration of SNAP-25, and we conclude that insulin secretion is highly sensitive to changes in plasma membrane cholesterol.

BackgroundThe combination of the new high sensitivity troponin T (hsTnT) assays and copeptin, a biomarker of endogenous stress, has been suggested to have the potential of early rule-out of acute coronary syndrome (ACS). The aim of this study was to examine the ability of this combination to rule out ACS in patients presenting with chest pain and to compare the diagnostic performance to hsTnT alone.MethodIn this prospective observational study, patients with chest pain admitted for observation were consecutively included. Patients presenting with ST elevation were excluded. Copeptin and hsTnT were analyzed at admission and hsTnT was thereafter determined approximately every 3rd hour as long as clinically indicated. The follow-up period was 60 days. A combined primary endpoint of ACS, non-elective percutanous coronary intervention, non-elective coronary artery bypass surgery and death of all causes was used.Results478 patients were included. 107 (22%) patients were diagnosed with ACS during hospital stay. 70 (14%) had non-ST-segment elevation myocardial infarction (NSTEMI) and 37 (8%) had unstable angina pectoris (UAP).The combination of hsTnT >14 ng/L or copeptin ≥14 pmol/L at admission identified ACS with a higher sensitivity than hsTnT alone: 0.83 (95% confidence interval (CI): 0.74-0.89) versus 0.69 (95% CI: 0.59-0.77), p <0.001. Negative predictive values (NPV) 91% (95% CI: 86-94) versus 89% (95% CI: 84-92). A repeated hsTnT analyzed 3-4 hours after admission resulted in a sensitivity of: 0.77 (95% CI: 0.65-0.86), p =0.031 for comparison with the combination analyzed at admission.ConclusionsIn patients presenting with chest pain admitted for observation, the combination of hsTnT and copeptin analyzed at admission had a significantly higher sensitivity to diagnose ACS than hsTnT alone. We report a sensitivity of 83% and a NPV of 91% for the combination of hsTnT and copeptin and we conclude that biomarkers alone are not sufficient to rule out ACS. However, the combination of hsTnT and copeptin seems to have a significantly higher sensitivity to identify ACS than a repeated hsTnT test, and thus enables an earlier risk stratification of chest pain patients. This can be time-saving and beneficial for the individual patient by contributing to early decisions on treatment, need of further assessment and level of care.

Aims: To examine whether undetectable high sensitivity troponin T (hsTnT) can be used to safely rule out non-STelevation acute coronary syndrome (NSTE-ACS) (using the limit of detection (LOD) as the cut-off) and to compare this strategy to serial hsTnT and the use of combined hsTnT and copeptin. Methods: In this prospective observational study, 478 patients presenting with chest pain were consecutively included. A combined primary endpoint of ACS, non-elective revascularization and/or death of all causes was used. The follow-up period was 60 days. Results: NSTE-ACS was diagnosed in 107 (22%) patients during hospital stay. Undetectable hsTnT at admission ruled out NSTE-ACS with a negative predictive value of 94% (95% confidence interval (CI): 88-97) giving a sensitivity of 0.90 (95% CI: 0.80-0.95) versus 0.78 (95% CI: 0.66-0.87) for serial hsTnT testing, p=0.008. The combination of hsTnT and copeptin analysed at admission resulted in a sensitivity of 0.83 (95% CI: 0.74-0.89), p=0.07 for comparison with undetectable hsTnT. Conclusion: A single hsTnT test at presentation, using the LOD as the cut-off, appears to be a safe and time-saving strategy to rule out NSTE-ACS. Further, undetectable levels of hsTnT were associated with an excellent prognosis and none of the patients with undetectable hsTnT were diagnosed with NSTEMI. Together with ECG and clinical assessment this biomarker strategy might permit outpatient treatment of almost one third of the patients we currently admit for observation.