The role of the disulfide bond in the interaction of islet amyloid polypeptide with membranes

Human islet amyloid polypeptide (hIAPP) forms amyloid fibrils in pancreatic islets of patients with type 2 diabetes mellitus. It has been suggested that the N-terminal part, which contains a conserved intramolecular disulfide bond between residues 2 and 7, interacts with membranes, ultimately leading to membrane damage and β-cell death. Here, we used variants of the hIAPP1–19 fragment and model membranes of phosphatidylcholine and phosphatidylserine (7:3, molar ratio) to examine the role of this disulfide in membrane interactions. We found that the disulfide bond has a minor effect on membrane insertion properties and peptide conformational behavior, as studied by monolayer techniques, 2H NMR, ThT-fluorescence, membrane leakage, and CD spectroscopy. The results suggest that the disulfide bond does not play a significant role in hIAPP–membrane interactions. Hence, the fact that this bond is conserved is most likely related exclusively to the biological activity of IAPP as a hormone

An AFM study of solid-phase bilayers of unsaturated PC lipids and the lateral distribution of the transmembrane model peptide WALP23 in these bilayers

An altered lipid packing can have a large influence on the properties of the membrane and the lateral distribution of proteins and/or peptides that are associated with the bilayer. Here, it is shown by contact-mode atomic force microscopy that the surface topography of solid-phase bilayers of PC lipids with an unsaturated cis bond in their acyl chains shows surfaces with a large number of line-type packing defects, in contrast to the much smoother surfaces observed for saturated PC lipids. Di-n:1-PC (n = 20, 22, 24) and (16:0,18:1)-PC (POPC) were used. Next, the influence of an altered lipid environment on the lateral distribution of the single α-helical model peptide WALP23 was studied by incorporating the peptide in the bilayers of di-n:1-PC (n = 20, 22, 24) and (16:0,18:1)-PC unsaturated lipids. The presence of WALP23 leads to an increase in the number of packing defects but does not lead to the formation of the striated domains that were previously observed in bilayers of saturated PC lipids and WALP. This is ascribed to the less efficient lateral lipid packing of the unsaturated lipids, while the increase in packing defects is probably an indirect effect of the peptide. Finally, the fact that an altered lipid packing affects the distribution of WALP23 is also confirmed in an additional experiment where the solvent TFE (2,2,2-trifluorethanol) is added to bilayers of di-16:0-PC/WALP23. At 3.5 vol% TFE, the previous striated ordering of the peptide is abolished and replaced by loose lines

Reversal of rocuronium-induced neuromuscular block by sugammadex is independent of renal perfusion in anesthetized cats

Item does not contain fulltextPURPOSE: Sugammadex is a selective relaxant binding agent designed to encapsulate the aminosteroidal neuromuscular blocking agent rocuronium, thereby reversing its effect. Both sugammadex and the sugammadex-rocuronium complex are eliminated by the kidneys. This study investigated the effect of sugammadex on recovery of rocuronium-induced neuromuscular block in cats with clamped renal pedicles, as a model for acute renal failure. METHODS: Twelve male cats were divided into two groups and anesthetized with medetomidine, ketamine, and alpha-chloralose. The cats were intubated and ventilated with a mixture of oxygen and air. Neuromuscular monitoring was performed by single twitch monitoring. Rocuronium 0.5 mg/kg i.v. was administered. After spontaneous recovery from neuromuscular block, both renal pedicles were ligated. A second dose of rocuronium 0.5 mg/kg i.v. was given. One minute after disappearance of the twitches, in Group 1 placebo (0.9% saline) and in Group 2 sugammadex 5.0 mg/kg i.v. was administered. Onset time, duration of neuromuscular block, and time to recovery to 25, 50, 75, and 90% were determined. Results : After renal pedicle ligation, sugammadex reversed rocuronium-induced neuromuscular block significantly faster than spontaneous recovery. Mean time (SEM) to 90% recovery of the twitch response was 4.7 (0.25) min (Group 2) versus 31.1 (5.0) min (Group 1) (p < 0.0001). No signs of recurrence of neuromuscular block were observed for 90 min after complete twitch restoration. Sugammadex caused no significant cardiovascular effects. CONCLUSION: Sugammadex rapidly and effectively reversed rocuronium-induced neuromuscular block in anesthetized cats, even when both renal pedicles were ligated and renal elimination of the drugs was no longer possible