Changes In Transverse Relaxation Time Research Articles

Aerobic exercise and metformin on intermuscular adipose tissue (IMAT): insights from multimodal MRI and histological changes in prediabetic rats

BackgroundPhysical exercise is the first-line intervention for prediabetes, and metformin is the most widely used oral insulin-sensitizing agent. Moreover, intermuscular adipose tissue (IMAT) directly affects insulin resistance by helping maintain glucose homeostasis. Here, we evaluated the effects of moderate aerobic exercise and/or metformin on histological IMAT parameters in non-streptozotocin-induced prediabetes.MethodsMale Wistar rats with prediabetes fed a high-fat diet and high-sugar drinks were randomly assigned to high-fat diet (PRE), metformin (MET), moderate aerobic exercise (EXE), combined therapy (EMC), or EMC + compound-c (EMA) groups for 4 weeks. Multimodal magnetic resonance imaging (MRI) was then performed, and tissue-specific inflammation and energy and lipid metabolism were evaluated in IMAT.ResultsThe EXE group had lower inflammatory factor levels, lipid metabolism, and mitochondrial oxidative stress, and shorter IMAT adipocyte diameters than the MET group. The MET group exhibited lower IL-1β and Plin5 expression than the PRE group. Furthermore, the IMAT of the EMC group had lower TNF-α and phosphorylated NF-κB levels and higher GLUT1 and GLUT4 expression than the PRE group. Multimodal MRI revealed significant changes in transverse-relaxation time 2, apparent diffusion coefficient, and fractional anisotropy values in the IMAT and muscles, as well as lower IMAT% values in the EXE and EMC groups than in the MET and PRE groups.ConclusionModerate aerobic exercise training can effectively improve IMAT function and structure via the AMP-activated protein kinase pathway in prediabetes. Combining metformin with moderate aerobic exercise might elicit modest synergy, and metformin does not counterbalance the beneficial effects of exercise.

Enhanced magnetic relaxation switching immunoassay for chlorpyrifos based on tyramine signal amplification

AbstractChlorpyrifos, an organophosphorus pesticide, is widely used in agriculture to protect crops from insects. However, the presence of its residues in food has caused widespread concern due to the serious risks to human health. Traditional detection methods suffer from limitations, such as low sensitivity, long detection time, and complicated operations. Herein, based on the tyramine signal amplification (TSA) strategy, we developed a sensitive and rapid magnetic relaxation switching (MRS) immunosensor for the detection of chlorpyrifos. Wherein, magnetic Fe3O4 nanoparticles modified with tyramine (MNP150‐tyramine) acted as magnetic probes for magnetic relaxation signal output. In the presence of hydrogen peroxide (H2O2) and horseradish peroxidase (HRP), tyramine can be converted to the highly reactive intermediate that covalently binds with the nearby proteins, such as HRP and antibody, thus assembling MNPs to magnetic clusters and showing changes in transverse relaxation time (T2) signals. Based on the “antibody–antigen” immunoreaction, chlorpyrifos could make a connection of HRP/antibody‐modified MNPs and MNP150‐tyramine with a result of MNPs aggregation and strong T2 signals. In this study, the TSA‐MRS method showed sensitive detection of chlorpyrifos with a limit of detection of 0.54 ng/mL, a 4.5‐fold enhancement in the sensitivity compared with the ELISA method, providing an alternative method for the detection of harmful substances in food samples.

Win-Win Cooperation: Magnetic relaxation switching biosensor for chloramphenicol detection based on the pipet platform and antigen-driven enzyme-free dual signal amplification strategy

Herein, we developed an enzyme-free dual signal amplification magnetic relaxation switching biosensor to detect the high hazard chloramphenicol based on the significant advantages of the pipet platform (low cost and easy operation). The competitive immunoassay was carried out by coating the polydopamine-modified pipets with the antibody, causing a content change of trigger DNA-chloramphenicol-antigen conjugate (the first signal amplification) in the supernatant. This triggered the aggregation of magnetic nanoparticles with three-dimensional DNA network structures (the second signal amplification) for chloramphenicol quantitative analysis by changes in transverse relaxation time (T2). The pipet platform can simplify the sample pretreatment process to eliminate the potential interference with magnetic probes. Its low-cost combined with the enzyme-free strategy greatly reduces the overall detection expenses. The antigen-driven dual signal amplification strategy not only has high sensitivity (1.37 pg/mL), but also provides an alternative path for the efficient combination of immunoassay and DNA signal amplification.

NMR study of fresh cut salads: Influence of temperature and storage time on leaf structure and water distribution in escarole.

Consumption of fresh-cut vegetables has rapidly increased over the past decades. Among salads, escarole is one of the most popular varieties. Specific packaging limits gas exchange and consequently water loss and bacterial respiration, increasing the shelf life of salads. Although the major cause of quality loss for minimally processed salads is the leaf textural changes, this aspect has rarely been investigated. Therefore, investigating structural changes of leaves during storage is important in order to understand and minimize quality loss of salads. In this study, we focused on the impact of storage duration and temperature on the escarole leaf structure. The complex leaf structure was investigated by relaxation NMR, via transverse relaxation times, which allows the specific description of vacuolar water compartment of the cell. The storage duration (maximum 12days) and temperatures (4°C, 7°C, 10°C, and 12°C) have been chosen in order to represent the conditions registered in factory. The results showed that the temperature did not have significant impact on the salad structure during the first week. During the second week, changes in the water distribution and changes in the relaxation time T2 have been observed. The changes in transverse relaxation times associated with vacuolar water are related to lost of cell membrane and wall integrity. The NMR results confirmed the effect of storage temperature on the degradation process of the cell before visual detection of the salad leaf degradation. The present study confirmed the sensibility of NMR relaxometry for monitoring water changes in the leaf.

Magnetic 3D scaffold: A theranostic tool for tissue regeneration and non-invasive imaging in vivo

We report an osteoconducting magnetic 3D scaffold using Fe2+ doped nano-hydroxyapatite-Alginate-Gelatin (AGHFe1) for Magnetic Resonance Imaging based non-invasive monitoring of bone tissue regeneration. In rat cranial defect model, the scaffold facilitated non-invasive monitoring of cell migration, inflammatory response and matrix deposition by unique changes in transverse relaxation time (T2). Cell infiltration resulted in a considerable increase in T2 from ~37 to ~62 ms, which gradually returned to that of native bone (~23 ms) by 90 days. We used this method to compare in vivo performance of scaffold with bone-morphogenic protein-2 (AGHFe2) or faster degrading (AGHFe3). MRI and histological analysis over 90 days showed non-uniform bone formation in AGHFe1 with ∆T2 (T2Native bone – T2 Regenerated bone) ~13 ms, whereas, AGHFe2 and AGHFe3 showed ∆T2 ~ 09 and 05 ms respectively, suggesting better bone formation in AGHFe3. Thus, we show that MR-contrast enabled scaffold can help better assessment of bone-regeneration non-invasively.

Assessment of Perfusion and Oxygenation of the Human Renal Cortex and Medulla by Quantitative MRI during Handgrip Exercise.

Renal flow abnormalities are believed to play a central role in the pathogenesis of nephropathy and in primary and secondary hypertension, but are difficult to measure in humans. Handgrip exercise is known to reduce renal arterial flow (RAF) by means of increased renal sympathetic nerve activity. To monitor medullary and cortical oxygenation under handgrip exercise-reduced perfusion, we used contrast- and radiation-free magnetic resonance imaging (MRI) to measure regional changes in renal perfusion and blood oxygenation in ten healthy normotensive individuals during handgrip exercise. We used phase-contrast MRI to measure RAF, arterial spin labeling to measure perfusion, and both changes in transverse relaxation time (T2*) and dynamic blood oxygenation level-dependent imaging to measure blood oxygenation. Handgrip exercise induced a significant decrease in RAF. In the renal medulla, this was accompanied by an increase of oxygenation (reflected by an increase in T2*) despite a significant drop in medullary perfusion; the renal cortex showed a significant decrease in both perfusion and oxygenation. We also found a significant correlation (R2=0.8) between resting systolic BP and the decrease in RAF during handgrip exercise. Renal MRI measurements in response to handgrip exercise were consistent with a sympathetically mediated decrease in RAF. In the renal medulla, oxygenation increased despite a reduction in perfusion, which we interpreted as the result of decreased GFR and a subsequently reduced reabsorptive workload. Our results further indicate that the renal flow response's sensitivity to sympathetic activation is correlated with resting BP, even within a normotensive range.

Temperature‐Induced Phase Transition Characterization of Responsive Polymer Brushes Grafted onto Nanoparticles

Temperature‐induced phase transition parameters of responsive free polymer and brushes onto nanoparticles are measured using high‐resolution magic‐angle sample spinning (HRMAS) NMR spectroscopy. To this purpose, a two‐state statistical model of temperature dependence of thermodynamic observables is developed and applied to obtain parameters which characterize the process of temperature‐induced phase transition of stimuli‐sensitive polymers. In this investigation the thermodynamic observable is the integral intensity of the 1H HRMAS NMR spectrum peaks and the derived thermodynamic parameters are transition temperature and transition entropy. This approach is applied to investigate the dependence of temperature‐induced coil‐to‐globule transition of poly(N‐isopropylacrylamide), (PNIPAm), asymmetric end functionalized with benzyl and thiol groups (Bn–PNIPAm–SH) on molecular weight in the range 3600–30 000 g mol–1 in aqueous solutions. The characteristics of the phase transition represented by transition temperature, and transition entropy are compared to that of Bn–PNIPAm–SH brushes onto gold nanorods in the same range of molecular weight. The method used for measuring the characteristics of phase transition is based on transverse magnetization relaxation (T2) spin‐echo enhance editing of the integral intensities of the 1H HRMAS NMR spectra. This NMR observable reflects changes in transverse relaxation times as an indicative of the polymer chains conformations and dynamics reached in the process of temperature‐induced phase transition. image

Changes in transverse relaxation time of quadriceps femoris muscles after active recovery exercises with different intensities

The purpose of this study was to examine the changes in the metabolic state of quadriceps femoris muscles using transverse relaxation time (T2), measured by muscle functional magnetic resonance (MR) imaging, after inactive or active recovery exercises with different intensities following high-intensity knee-extension exercise. Eight healthy men performed recovery sessions with four different conditions for 20 min after high-intensity knee-extension exercise on separate days. During the recovery session, the participants conducted a light cycle exercise for 20 min using a cycle (50%, 70% and 100% of the lactate threshold (LT), respectively: active recovery), and inactive recovery. The MR images of quadriceps femoris muscles were taken before the trial and after the recovery session every 30 min for 120 min. The percentage changes in T2 for the rectus femoris and vastus medialis muscles after the recovery session in 50%LT and 70%LT were significantly lower than those in either inactive recovery or 100%LT. There were no significant differences in those for vastus lateralis and vastus intermedius muscles among the four trials. The percentage changes in T2 of rectus femoris and vastus medialis muscles after the recovery session in 50%LT and 70%LT decreased to the values before the trial faster than those in either inactive recovery or 100%LT. Those of vastus lateralis and vastus intermedius muscles after the recovery session in 50%LT and 70%LT decreased to the values before the trial faster than those in 100%LT. Although the changes in T2 after active recovery exercises were not uniform in exercised muscles, the results of this study suggest that active recovery exercise with the intensities below LT are more effective to recover the metabolic state of quadriceps femoris muscles after intense exercise than with either intensity at LT or inactive recovery.

Lumbar Muscle Activity During Common Lifts: A Preliminary Study Using Magnetic Resonance Imaging

The purpose of this preliminary study was to assess lumbar multifidus, erector spinae, and quadratus lumborum muscle activity during lifts as measured by changes in transverse relaxation time (T2) from magnetic resonance imaging (MRI). Thirteen healthy adults performed dynamic squat, stoop, and asymmetric stoop lifts at a standard load, with each lift followed by MRI. Increase in T2 for the multifidus and erector spinae was greater for the stoop than squat. No difference in T2 increase was noted between the multifidus and erector spinae for the squat or stoop. Increase in T2 for the contralateral multifidus was less for the asymmetric stoop than stoop. Future research using MRI and other biomechanical techniques is needed to fully characterize lumbar muscle activity during lifts for various populations, settings, postures, and loads.

1H‐NMR Study of the Impact of High Pressure and Thermal Processing on Cell Membrane Integrity of Onions

Proton nuclear magnetic resonance (¹H-NMR) relaxometry was used to study the effects of high pressure and thermal processing on membrane permeability and cell compartmentalization, important components of plant tissue texture. High pressure treated onions were subjected to pressure levels from 20 to 200 MPa at 5 min hold time at initial temperatures of 5 and 20 °C. Thermally treated onions were exposed for 30 min at temperatures from 40 to 90 °C. Loss of membrane integrity was clearly shown by changes in transverse relaxation time (T(2)) of water at temperatures of 60 °C and above. Destabilization effects on membranes exposed to high pressure were observed at 200 MPa as indicated by T(2) measurements and cryo-scanning electron microscopy (Cryo-SEM). T(2) relaxation successfully discriminated different degrees of membrane damage based on the T(2) shift of the vacuolar component. Analyses of the average water self-diffusion coefficient indicated less restricted diffusion after membrane rupture occurred in cases of severe thermal treatments. Milder processing treatments yielded lower average diffusion coefficients than the controls. ¹H-NMR proved to be an effective method for quantification of cell membrane damage in onions and allowed for the comparison of different food processes based on their impact on tissue integrity.

Characterization of water status in primed seeds of tomato (Lycopersicon esculentum Mill.) by sorption properties and NMR relaxation times

The enhanced laboratory and field emergence characteristics of osmo- and halo-primed tomato seeds (cv. Pusa Ruby) were related to changes in hydration–dehydration kinetics, modified sorption properties and nuclear magnetic resonance (NMR) relaxation behaviour of humidified and imbibed seeds. Water sorption isotherms were constructed for primed and unprimed seeds by equilibrating to different water activities (aw) at 25°C. Analysis of the isotherms by the D'Arcy–Watt equation revealed that priming reduced the number of strong binding sites and the associated water content, and increased significantly the number of weak binding sites and the associated water content. This redistribution of water, which increased the availability of seed water, may be the reason for the higher speed of germination of primed seeds. The changes in transverse relaxation time (T2) of seed water and its components, measuredin vivousing nuclear magnetic resonance spectroscopy, showed interesting differences between primed and unprimed seeds. With an increase in humidification time, the T2of primed seeds could be resolved into three components with varying mobilities, while the control seeds had only two components until 10 d of humidification. During imbibition, the third component appeared after 2 and 6 h in primed and control seeds, respectively. This component disappeared after the germination process started in all treatments. The third fraction, with very low molecular mobility, which accounted for about 40% of the proton population, was assigned to hydration water of macromolecules. Hence, we propose that better performance of primed seeds may be attributed to the modifications of seed water-binding properties and reorganization of seed water during imbibition, so as to increase the macromolecular hydration water required for various metabolic activities related to the germination process.

Residual dipolar coupling for the assessment of cross-link density changes in γ-irradiated silica-PDMS composite materials

We have measured changes in transverse relaxation times (T2e), residual dipolar couplings (〈Ωd2〉), and the mean-squared fluctuations in the residual dipolar couplings (〈δΩd2〉), associated with cross-link density changes in a complex silica-filled polydiphenylpolysiloxane/polydimethylsiloxane (PDPS/PDMS) block copolymer composite material. The crosslinks were induced by both chemical modification of the base polymer and by radiolytic aging. We have detected H1 NMR responses from polymer chains directly interacting with the silica filler (〈δΩd2〉≫2×106 rad2 sec−2), network polymer chains not directly interacting with the silica filler (〈Ωd2〉∼2×106 rad2 sec−2 and 〈δΩd2〉∼2×106 rad2 sec−2) and non-network, low molecular weight chains and chain ends (〈δΩd2〉∼1×105 rad2 sec−2). The network domain and the non-network domain were observed to exchange spin magnetization with a correlation time of 1 sec. No evidence of spin-exchange effects on the stimulated echo were observed between the PDMS and PDPS blocks, although the blocks were observed to be in spatial proximity by double quantum NMR methods. The residual dipolar couplings change in a straightforward manner with radiation and chemically induced cross-linking of the polymer network. The strength of the filler-polymer interaction was seen to affect only the residual dipolar couplings and the transverse relaxation times and not directly the mean-squared fluctuations of the residual dipolar couplings. Dipolar correlation effect NMR shows direct evidence for surface adsorbed species, however, and has measured changes in the amount of surface adsorption due to irradiation. The results suggest that siloxane polymer cross-linking was preceded by an initial disruption of the hydrogen bond interaction between the polymer backbone and the silica silanol groups at the polymer/silica interface and that noticeable radiation induced cross-linking then occurs at dosages above 100 kGray. The work reported here shows that detailed characterization of the relaxation processes of the various nuclei in the siloxane polymers under static conditions has the potential to provide detailed insight into changes in the mechanisms and energetics of motional processes brought about by polymer aging processes.

Nuclear magnetic resonance relaxation studies of poly(hydroxybutyrate) in whole cells and in artificial granules

The physical state of poly(hydroxybutyrate) (PHB) in whole cells and in the form of artificial biomimetic granules has been probed using 13C nuclear magnetic resonance (NMR) spectroscopy. Studies on varying concentrations of whole cells of Alcaligenes eutrophus show that changes in the line widths of PHB in whole cells do not correlate with changes in transverse relaxation times. Solid-state magic-angle spinning NMR studies demonstrate that the line broadening results from a reduction in the static field homogeneity rather than from intrinsic properties of the PHB within the cells. Transverse and longitudinal relaxation times of PHB in whole cells and in artificial granules are similar, indicating similarities in structure and mobility.

Changes in magnetic resonance images in human skeletal muscle after eccentric exercise.

To investigate the time-course of changes in transverse relaxation time (T2) and cross-sectional area (CSA) of the quadriceps muscle after a single session of eccentric exercise, magnetic resonance imaging was performed on six healthy male volunteers before and at 0, 7, 15, 20, 30 and 60 min and 12, 24, 36, 48, 72 and 168 h after exercise. Although there was almost no muscle soreness immediately after exercise, it started to increase 1 day after, peaking 1-2 days after the exercise (P < 0.01). Immediately after exercise, T2 increased significantly in the rectus femoris, vastus lateralis and intermedius muscles (P < 0.05) and decreased quickly continuing until 60 min after exercise. At and after the 12th h, a significant increase was perceived again in the T2 values of the vastus lateralis and intermedius muscles (P < 0.01) [maximum 9.3 (SEM 2.8)% and 10.9 (SEM 2.2)%, respectively]. The maximal values were exhibited at 24-36 h after exercise. In contrast, the rectus femoris muscle showed no delayed-stage increase. Also, in CSA, an increase after 12 h was observed in addition to the one immediately after exercise in the vastus lateralis, intermedius and medialis and quadriceps muscles as a whole (P < 0.01), reaching the maximal values at 12-24 h after exercise. The plasma creatine kinase activity remained unchanged up to 24 h after and then increased significantly 48 h after exercise (P < 0.05). Beginning 12 h after exercise, the subjects whose T2 and CSA increased less than the others displayed a faster decrease in muscle soreness.(ABSTRACT TRUNCATED AT 250 WORDS)

Nuclear Relaxation Studies of Lecithin Bilayers

BILAYER phases of lipids have broad proton magnetic resonance (PMR) spectra, which have been attributed to incomplete averaging of the dipole–dipole interactions between various protons as a result of slow molecular motion1,2. Two pulsed nuclear magnetic resonance (NMR) studies, however, have proposed internal magnetic field gradients as the source of spectral broadening. Kaufman et al. concluded that these gradients led to inhomogeneity broadening3, whereas Hansen and Lawson proposed molecular diffusion through them4. These conclusions were based on the apparent dependence of the spectral width on the applied magnetic field5 as well as abrupt changes in transverse relaxation time (T2) without concomitant changes in the longitudinal relaxation time (T1) at the bilayer phase boundaries4,5. The dependence of T2 on pulse spacing in a Carr–Purcell experiment6 has also been taken as evidence for molecular diffusion through internal magnetic field gradients4.