6 research outputs found
Microscopic Rates of Peptide–Phospholipid Bilayer Interactions from Single-Molecule Residence Times
The binding of glucagon-like peptide-1 (GLP-1) to a planar
phospholipid
bilayer is measured using single-molecule total internal reflection
fluorescence microscopy. From several reports in the literature, GLP-1
has been shown to be a random coil in free solution, adopting a folded,
α-helix conformation when intercalated into membrane environments.
Single-molecule fluorescence measurements of GLP-1 binding to supported
lipid bilayers show evidence of two populations of membrane-associated
molecules having different residence times, suggesting weakly adsorbed
peptides and strongly bound peptides in the lipid bilayer. The path
to and from a strongly bound (folded, intercalated) state would likely
include an adsorbed state as an intermediate, so that the resulting
kinetics would correspond to a consecutive first-order reversible
three-state model. In this work, the relationships between measured
single-molecule residence times and the microscopic rates in a three-state
kinetic model are derived and used to interpret the binding of GLP-1
to a supported lipid bilayer. The system of differential equations
associated with the proposed consecutive-three state kinetics scheme
is solved, and the solution is applied to interpret histograms of
single-molecule, GLP-1 residence times in terms of the microscopic
rates in the sequential two-step model. These microscopic rates are
used to estimate the free energy barrier to adsorption, the fraction
of peptides adsorbing to the membrane surface that successfully intercalate
in the bilayer, the lifetime of inserted peptides in the membrane,
and the free energy change of insertion into the lipid bilayer from
the adsorbed state. The transition from a random coil in solution
to a folded state in a membrane has been recognized as a common motif
for insertion of membrane active peptides. Therefore, the relationships
developed here could have wide application to the kinetic analysis
of peptide–membrane interactions
Unravelling the interplay between hyperkalaemia, renin\u2013angiotensin\u2013aldosterone inhibitor use and clinical outcomes. Data from 9222 chronic heart failure patients of the ESC-HFA-EORP Heart Failure Long-Term Registry
Aims: We assessed the interplay between hyperkalaemia (HK) and renin\u2013angiotensin\u2013aldosterone system inhibitor (RAASi) use, dose and discontinuation, and their association with all-cause or cardiovascular death in patients with chronic heart failure (HF). We hypothesized that HK-associated increased death may be related to RAASi withdrawal. Methods and results: The ESC-HFA-EORP Heart Failure Long-Term Registry was used. Among 9222 outpatients (HF with reduced ejection fraction: 60.6%, HF with mid-range ejection fraction: 22.9%, HF with preserved ejection fraction: 16.5%) from 31 countries, 16.6% had HK ( 655.0 mmol/L) at baseline. Angiotensin-converting enzyme inhibitor (ACEi) or angiotensin receptor blocker (ARB) was used in 88.3%, a mineralocorticoid receptor antagonist (MRA) in 58.7%, or a combination in 53.2%; of these, at 6550% of target dose in ACEi: 61.8%; ARB: 64.7%; and MRA: 90.3%. At a median follow-up of 12.2 months, there were 789 deaths (8.6%). Both hypokalaemia and HK were independently. associated with higher mortality, and ACEi/ARB prescription at baseline with lower mortality. MRA prescription was not retained in the model. In multivariable analyses, HK at baseline was independently associated with MRA non-prescription at baseline and subsequent discontinuation. When considering subsequent discontinuation of RAASi (instead of baseline use), HK was no longer found associated with all-cause deaths. Importantly, all RAASi (ACEi, ARB, or MRA) discontinuations were strongly associated with mortality. Conclusions: In HF, hyper- and hypokalaemia were associated with mortality. However, when adjusting for RAASi discontinuation, HK was no longer associated with mortality, suggesting that HK may be a risk marker for RAASi discontinuation rather than a risk factor for worse outcomes