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

Gliclazide may have an antiapoptotic effect related to its antioxidant properties in human normal and cancer cells

Experimental and clinical studies suggest that gliclazide may protect pancreatic β-cells from apoptosis induced by an oxidative stress. However, the precise mechanism(s) of this action are not fully understood and requires further clarification. Therefore, using human normal and cancer cells we examined whether the anti-apoptotic effects of this sulfonylurea is due to its free radical scavenger properties. Hydrogen peroxide (H2O2) as a model trigger of oxidative stress was used to induce cell death. Our experiments were performed on human normal cell line (human umbilical vein endothelial cell line, HUVEC-c) and human cancer cell lines (human mammary gland cell line, Hs578T; human pancreatic duct epithelioid carcinoma cell line, PANC-1). To assess the effect of gliclazide the cells were pre-treated with the drug. The 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay was employed to measure the impact of gliclazide on cell viability. Generation of reactive oxygen species, mitochondrial membrane potential (∆Ψm), and intracellular Ca2+ concentration [Ca2+] were monitored. Furthermore, the morphological changes associated with apoptosis were determined using double staining with Hoechst 33258-propidium iodide (PI). Gliclazide protects the tested cells from H2O2-induced cell death most likely throughout the inhibition of ROS production. Moreover, the drug restored loss of ΔΨm and diminished intracellular [Ca2+] evoked by H2O2. Double staining with Hoechst 33258-PI revealed that pre-treatment with gliclazide diminished the number of apoptotic cells. Our findings indicate that gliclazide may protect both normal and cancer human cells against apoptosis induced by H2O2. It appears that the anti-apoptotic effect of the drug is most likely associated with reduction of oxidative stress

A comparison of angiographic CT and multisection CT in lumbar myelographic imaging

BACKGROUND AND PURPOSE: The purpose of this work was to provide an intraindividual comparison of angiographic CT (ACT) and multisection CT (MSCT) in lumbar myelographic imaging and to evaluate possible benefits of ACT, which is a further development of rotational angiography providing image data of high spatial and CT-like contrast resolution. MATERIALS AND METHODS: In 26 patients with degenerative lumbar spine disease a lumbar ACT was performed in combination with conventional lumbar myelography and followed by postmyelographic. MSCT. Conventional lumbar myelography and lumbar ACT were performed with a flat panel detector-equipped angiographic device. Postmyelographic MSCT was performed with a 16-section CT scanner. Three experienced neuroradiologists rated anonymized sets of multiplanar reformatted CT and ACT images regarding diagnostic and technical parameters. The ratings were repeated after 2 months. Weighted K Statistics were calculated to describe the levels of intraobserver and interobserver agreement. RESULTS: The analysis shows that MSCT achieves higher ratings than ACT in all of the parameters asked. An adequate diagnostic quality was only assigned to 80% of the ACT acquisitions compared with 97% of the MSCT acquisitions. All of the mean K values were above 0.60, demonstrating a substantial intraobserver and interobserver agreement for MSCT, as well as for ACT. CONCLUSION: Using ACT, radiographic myelography and myelographic CT can be performed at the same imaging system. However, the results of our study show that the current myelographic ACT image quality fails to apply diagnostic standards. We, therefore, cannot recommend ACT as a general alternative to postmyelographic MSCT

Diagnosis of a multifocal B cell lymphoma with preceding demyelinating central nervous system lesions by single voxel proton MR spectroscopy

Single voxel proton magnetic resonance spectroscopy (MRS) provides a rapid non-invasive fingerprint of tissue chemistry. A case history is presented in which a B cell lymphoma with antecedent demyelinating lesions of the CNS was suspected by MRS and confirmed by neuropathological examination and immunoglobulin gene rearrangement.


Membrane damage by human islet amyloid polypeptide through fibril growth at the membrane

Fibrillar protein deposits (amyloid) in the pancreatic islets of Langerhans are thought to be involved in death of the insulin-producing islet β cells in type 2 diabetes mellitus. It has been suggested that the mechanism of this β cell death involves membrane disruption by human islet amyloid polypeptide (hIAPP), the major constituent of islet amyloid. However, the molecular mechanism of hIAPP-induced membrane disruption is not known. Here, we propose a hypothesis that growth of hIAPP fibrils at the membrane causes membrane damage. We studied the kinetics of hIAPP-induced membrane damage in relation to hIAPP fibril growth and found that the kinetic profile of hIAPP-induced membrane damage is characterized by a lag phase and a sigmoidal transition, which matches the kinetic profile of hIAPP fibril growth. The observation that seeding accelerates membrane damage supports the hypothesis. In addition, variables that are well known to affect hIAPP fibril formation, i.e., the presence of a fibril formation inhibitor, hIAPP concentration, and lipid composition, were found to have the same effect on hIAPP-induced membrane damage. Furthermore, electron microscopy analysis showed that hIAPP fibrils line the surface of distorted phospholipid vesicles, in agreement with the notion that hIAPP fibril growth at the membrane and membrane damage are physically connected. Together, these observations point toward a mechanism in which growth of hIAPP fibrils, rather than a particular hIAPP species, is responsible for the observed membrane damage. This hypothesis provides an additional mechanism next to the previously proposed role of oligomers as the main cytotoxic species of amyloidogenic proteins