Sprint interval running increases insulin sensitivity in young healthy subjects

High intensity cycling training increases oxidative capacity in skeletal muscles and improves insulin sensitivity. The present study compared the effect of eight weeks of sprint interval running (SIT) and continuous running at moderate intensity (CT) on insulin sensitivity and cholesterol profile in young healthy subjects (age 25.2 ± 0.7; VO(2max) 49.3 ± 1.2 ml·kg(-1)·min(-1)). SIT and CT increased maximal oxygen uptake by 5.3 ± 1.8 and 3.8 ± 1.6%, respectively (p < 0.05 for both). Oral glucose tolerance test (OGTT) was performed before and 60 h after the last training session. SIT, but not CT, reduced glucose area under curve and improved HOMA β-cell index (p < 0.05). Insulin area under curve did not decrease significantly in any group. SIT, but not CT, reduced LDL and total cholesterol. In conclusion, sprint interval running improves insulin sensitivity and cholesterol profile in healthy subjects, and sprint interval running may be more effective to improve insulin sensitivity than continuous running at moderate intensity.     

Membrane effects of lysozyme amyloid fibrils

The influence of mature lysozyme fibrils on the structural and physical properties of model membranes composed of phosphatidylcholine (PC) and its mixtures with cardiolipin (CL) (10 mol%) and cholesterol (Chol) (30 mol%) was studied using fluorescent probes DPH, pyrene, Laurdan and MBA. Analysis of pyrene fluorescence spectra along with the measurements of DPH fluorescence anisotropy revealed that the structure of hydrocarbon chains region of lipid bilayer is not affected by the fibrillar aggregates of lysozyme. In contrast, probing the membrane effects by Laurdan and MBA showed the rise of both the generalized polarization of Laurdan and the MBA fluorescence anisotropy, suggesting that amyloid protein induces reduction of bilayer hydration and increase of lipid packing in the interfacial region of model membranes.     

Imaging of subchondral bone by optical coherence tomography upon optical clearing of articular cartilage

Optical clearing is an effective method to reduce light scattering of biological tissues that provides significant enhancement of light penetration into the biological tissues making non‐invasive diagnosis more feasible. In current report Optical Coherence Tomography (OCT) in conjunction with optical clearing is applied for assessment of deep cartilage layers and cartilage‐bone interface. The solution of Iohexol in water has been used as an optical clearing agent. The cartilage‐bone boundary becomes visible after 15 min of optical clearing that enabling non‐invasive estimation of its roughness: S_a = 10 ± 1 µm. The results show that for 0.9 mm thick cartilage optical clearing is stopped after 50 min with an increase of refractive index from 1.386 ± 0.008 to 1.510 ± 0.009. Current approach enables more reliable detection of arthroscopically inaccessible regions, including cartilage‐bone boundary and subchondral bone, and potentially improves accuracy of the osteoarthritis diagnosis.

     

Pulsed-laser creation and characterization of giant plasma membrane vesicles from cells

Femtosecond-pulsed laser irradiation was found to initiate giant plasma membrane vesicle (GPMV) formation on individual cells. Laser-induced GPMV formation resulted from intracellular cavitation and did not require the addition of chemical stressors to the cellular environment. The viscosity, structure, and contents of laser-induced GPMVs were measured with fluorescence microscopy and single-particle tracking. These GPMVs exhibit the following properties: (1) GPMVs grow fastest immediately after laser irradiation; (2) GPMVs contain barriers to free diffusion of incorporated fluorescent beads; (3) materials from both the cytoplasm and surrounding media flow into the growing GPMVs; (4) the GPMVs are surrounded by phospholipids, including phosphatidylserine; (5) F-actin is incorporated into the vesicles; and (6) caspase activity is not essential for GPMV formation. The effective viscosity of 65 nm polystyrene nanoparticles within GPMVs ranged from 32 to 434 cP. The nanoparticle diffusion was commonly affected by relatively large, macromolecular structures within the bleb.     

Fourier transform infrared study of fully hydrated dimyristoylphosphatidylglycerol. Effects of Na+ on the sn-1' and sn-3' headgroup stereoisomers

Molecular packing and the thermotropic phase behavior of fully hydrated ammonium salts of 1,2-dimyristoyl-sn-glycero-3-phosphatidyl-sn-1'-glycerol (1'-DMPG) and the corresponding 3' stereoisomer (3'-DMPG) as well as the effects of 300 mM NaCl on these lipids were studied by Fourier transform infrared (FTIR) spectroscopy. The ammonium salts of both stereoisomer show similar thermotropic phase behavior and have an order-disorder phase transition at approximately 21 degrees C. While complexing with Na+, however, an incubation of liposomes at +6 degrees C for 3 days results in significant structural differences between liposomes of 1'-DMPG and 3'-DMPG. In the presence of 300 mM NaCl the infrared spectra for 3'-DMPG reveal the appearance of a more solidified lipid nominated here as the highly crystalline phase with a transition into the liquid-crystalline state at a significantly higher temperature (approximately at 33 degrees C) than that for 1'-DMPG (approximately at 23 degrees C). Crystal field splitting resulting from interchain vibrational coupling is observed in the CH2 scissoring mode of the 3'-DMPG(Na+) complex in the highly crystalline phase (T less than 33 degrees C); i.e., the acyl chains are packed in a rigid orthorhombic- or monoclinic-like crystal lattice. At temperatures above the transition at 33 degrees C the acyl chains of 3'-DMPG(Na+) give rise to infrared spectra indicative of hexagonal packing. The latter type of hydrocarbon chain packing is also found for the ammonium salts of 1'-DMPG and 3'-DMPG without Na+ as well as for 1'-DMPG with Na+. In addition, the binding of Na+ to 3'-DMPG causes narrowing of the bands associated with the interfacial and polar headgroup regions of 3'-DMPG and thus reveals reduced motional freedom. This demonstrates that Na+ binds tightly to 3'-DMPG, leading to the immobilization of the entire phospholipid polar headgroup. Such effects by Na+ are not observed for 1'-DMPG.     

Chemical modification of acyl-CoA:cholesterol O-acyltransferase. 1. Identification of acyl-CoA:cholesterol O-acyltransferase subtypes by differential diethyl pyrocarbonate sensitivity

Acyl-CoA:cholesterol O-acyltransferase (EC 2.3.1.26) (ACAT) catalyzes the intracellular synthesis of cholesteryl esters from cholesterol and fatty acyl-CoA at neutral pH. Despite the probable pathophysiologic role of ACAT in vascular cholesteryl ester accumulation during atherogenesis, its mechanism of action and its regulation remain to be elucidated because the enzyme polypeptide has never been identified or purified. Present chemical modification results identify two distinct tissue types of ACAT, based on marked differences in reactivity of an active-site histidine residue toward diethyl pyrocarbonate (DEP) and acetic anhydride. The apparent Ki of the DEP-sensitive ACAT subtype, typified by aortic ACAT, was 40 microM, but the apparent Ki of the DEP-resistant ACAT subtype, typified by liver ACAT, was 1500 microM, indicating a 38-fold difference in sensitivity to DEP. Apparent Ki's of aortic and liver ACAT for inhibition by acetic anhydride were also discordant (less than 500 microM and greater than 5 mM, respectively). On the basis of the reversibility of inhibition by hydroxylamine, a neutral pKa for maximal modification, and acetic anhydride protection against DEP inactivation, DEP and acetic anhydride appear to modify a common histidine residue. Oleoyl-CoA provided partial protection against inactivation by DEP and acetic anhydride, suggesting that the modified histidine is at or near the active site of ACAT. Systematic investigation of ACAT activity from 14 different organs confirmed the existence of 2 subtypes of ACAT on the basis of their different reactivities toward DEP and acetic anhydride.(ABSTRACT TRUNCATED AT 250 WORDS)     

Binding of cytochrome c to liposomes as revealed by the quenching of fluorescence from pyrene-labeled phospholipids

Resonance energy transfer from pyrene-fatty acid containing phospholipid derivatives to the heme of cytochrome c (cyt c) was used to observe the binding of this protein to liposomal membranes. Liposomes were formed of egg yolk phosphatidic acid (PA) and either egg yolk phosphatidylcholine or dipalmitoylphosphatidylcholine with 1 mol % of the fluorescent lipid. Binding of cyt c to liposomes was monitored by measuring the decrease either in the fluorescence intensity or in the lifetime of pyrene emission. The requirement for the presence of the acidic phospholipid in the membrane for the binding of cyt c could be reconfirmed. Below 5 mol % of phosphatidic acid in the membrane, no significant attachment of cyt c to liquid-crystalline bilayers was evident whereas upon increasing the concentration of PA further the association of cyt c progressively increased until a saturation was reached at about 30 mol % of phosphatidic acid. Addition of NaCl caused the fluorescence intensity and lifetimes to return to values observed in the absence of cyt c, thus revealing the dissociation of the protein from the membrane. The pyrene-labeled phosphatidic acid derivatives PPHPA and PPDPA were quenched more effectively than the corresponding phosphatidylcholines, apparently due to the direct involvement of the acidic head group in binding cyt c. When dipalmitoylphosphatidylcholine (DPPC) with 5 mol % of phosphatidic acid was used, no binding of cyt c to the liposomes above the phase transition temperature of the former lipid could be demonstrated whereas below the transition temperature (Tm) binding did take place.(ABSTRACT TRUNCATED AT 250 WORDS)     

Poly(ethylene glycol)-induced and temperature-dependent phase separation in fluid binary phospholipid membranes.

Exclusion of the strongly hygroscopic polymer, poly(ethylene glycol) (PEG), from the surface of phosphatidylcholine liposomes results in an osmotic imbalance between the hydration layer of the liposome surface and the bulk polymer solution, thus causing a partial dehydration of the phospholipid polar headgroups. PEG (average molecular weight of 6000 and in concentrations ranging from 5 to 20%, w/w) was added to the outside of large unilamellar liposomes (LUVs). This leads to, in addition to the dehydration of the outer monolayer, an osmotically driven water outflow and shrinkage of liposomes. Under these conditions phase separation of the fluorescent lipid 1-palmitoyl-2[6-(pyren-1-yl)]decanoyl-sn-glycero-3-phosphocholine (PPDPC) embedded in various phosphatidylcholine matrices was observed, evident as an increase in the excimer-to-monomer fluorescence intensity ratio (IE/IM). Enhanced segregation of the fluorescent lipid was seen upon increasing and equal concentrations of PEG both inside and outside of the LUVs, revealing that osmotic gradient across the membrane is not required, and phase separation results from the dehydration of the lipid. Importantly, phase separation of PPDPC could be induced by PEG also in binary mixtures with 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC), and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), for which temperature-induced phase segregation of the fluorescent lipid below Tm was otherwise not achieved. In the different lipid matrices the segregation of PPDPC caused by PEG was abolished above characteristic temperatures T0 well above their respective main phase transition temperatures Tm. For 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), DMPC, SOPC, and POPC, T0 was observed at approximately 50, 32, 24, and 20 degrees C, respectively. Notably, the observed phase separation of PPDPC cannot be accounted for the 1 degree C increase in Tm for DMPC or for the increase by 0.5 degrees C for DPPC observed in the presence of 20% (w/w) PEG. At a given PEG concentration maximal increase in IE/IM (correlating to the extent of segregation of PPDPC in the different lipid matrices) decreased in the sequence 1,2-dihexadecyl-sn-glycero-3-phosphocholine (DHPC) > DPPC > DMPC > SOPC > POPC, whereas no evidence for phase separation in 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) LUV was observed (Lehtonen and Kinnunen, 1994, Biophys. J. 66: 1981-1990). Our results indicate that PEG-induced dehydration of liposomal membranes provides the driving force for the segregation of the pyrene lipid.(ABSTRACT TRUNCATED AT 400 WORDS)