Subcutaneous tissue mechanical behavior is linear and viscoelastic under uniaxial tension

Subcutaneous tissue is part of a bodywide network of "loose" connective tissue including interstitial connective tissues separating muscles and surrounding all nerves and blood vessels. Despite its ubiquitous presence in the body and its potential importance in a variety of therapies utilizing mechanical stretch, as well as normal movement and exercise, very little is known about loose connective tissue's biomechanical behavior. This study aimed to determine elastic and viscoelastic mechanical properties of ex-vivo rat subcutaneous tissue in uniaxial tension with incremental stress relaxation experiments. The elastic response of the tissue was linear, with instantaneous and equilibrium tensile moduli of 4.77 kPa and 2.75 kPa, respectively. Using a 5 parameter Maxwell solid model, material parameters micro(1) = 0.95 +/- 0.24 Ns/m and micro(2) = 8.49 +/- 2.42 Ns/m defined coefficients of viscosity related to time constants tau(1M) = 3.83 +/- 0.15 sec and tau(2M) = 30.15 +/- 3.16 sec, respectively. Using a continuous relaxation function, parameters C = 0.25 +/- 0.12, tau(1C) = 1.86 +/- 0.34 sec, and tau(2C) = 110.40 +/- 25.59 sec defined the magnitude and frequency limits of the relaxation spectrum. This study provides baseline information for the stress-strain behaviors of subcutaneous connective tissue. Our results underscore the differences in mechanical behaviors between loose and high-load bearing connective tissues and suggest that loose connective tissues may function to transmit mechanical signals to and from the abundant fibroblasts, immune, vascular, and neural cells present within these tissues.     

Measuring anisotropic muscle stiffness properties using elastography

Physiological and pathological changes to the anisotropic mechanical properties of skeletal muscle are still largely unknown, with only a few studies quantifying changes in vivo. This study used the noninvasive MR elastography (MRE) technique, in combination with diffusion tensor imaging (DTI), to measure shear modulus anisotropy in the human skeletal muscle in the lower leg. Shear modulus measurements parallel and perpendicular to the fibre direction were made in 10 healthy subjects in the medial gastrocnemius, soleus and tibialis anterior muscles. The results showed significant differences in the medial gastrocnemius (μ_‖ =0.86 ± 0.15 kPa; μ_⊥ = 0.66 ± 0.19 kPa, P < 0.001), soleus (μ_‖ = 0.83 ± 0.22 kPa; μ_⊥ = 0.65 ± 0.13 kPa, P < 0.001) and the tibialis anterior (μ_‖ = 0.78 ± 0.24 kPa; μ_⊥ = 0.66 ± 0.16 kPa, P = 0.03) muscles, where the shear modulus measured in the direction parallel is greater than that measured in the direction perpendicular to the muscle fibres. No significant differences were measured across muscle groups. This study provides the first direct estimates of the anisotropic shear modulus in the triceps surae muscle group, and shows that the technique may be useful for the probing of mechanical anisotropy changes caused by disease, aging and injury. Copyright © 2013 John Wiley & Sons, Ltd.     

Segmental motions of spin-labelled poly(ethylene oxide) in dilute solution

The rotational correlation times (τ) of spin-labelled poly(ethylene oxide), (M_w=20 000) were measured in benzene, pyridine and water. It was found that τ is independent of polymer concentration (c) when c<0,15 g/(ml solvent). In dilute solutions τ values of 49 ps, 43 ps and 100 ps in benzene, pyridine and water at 293 K were obtained. A comparison with results of dielectric relaxation and nuclear magnetic resonance measurements indicated that τ_diel. < τ¹³_CNMR < τ_{spin-labelling} < τ¹_{H NMR}. Values 17.7±2,2 kJ/mol and 17,3kJ/mol for the potential barrier of local conformational changes of PEO in pyridine and water solutions were obtained. The apparent hydrodynamic radii (0,35–0,46 nm) indicated the loosely arranged random coil state of the polymer molecules in solution at 293 K.     

Influence of sildenafil on lung diffusion during exposure to acute hypoxia at rest and during exercise in healthy humans

We sought to determine the influence of sildenafil on the diffusing capacity of the lungs for carbon monoxide (DL_CO) and the components of DL_CO (pulmonary capillary blood volume V _c, and alveolar–capillary membrane conductance D _M) at rest and following exercise with normoxia and hypoxia. This double-blind placebo-controlled, cross-over study included 14 healthy subjects (age = 33 ± 11 years, ht = 181 ± 8 cm, weight = 85 ± 14 kg, BMI = 26 ± 3 kg/m², peak normoxic VO₂ = 36 ± 6 ml/kg, mean ± SD). Subjects were randomized to placebo or 100 mg sildenafil 1 h prior to entering a hypoxic tent with an FiO₂ of 12.5% for 90 min. DLCO, V _c, and D _M were assessed at rest, every 3 min during exercise, at peak exercise, and 10 and 30 min post exercise. Sildenafil attenuated the elevation in PAP at rest and during recovery with exposure to hypoxia, but pulmonary arterial pressure immediately post exercise was not different between sildenafil and placebo. Systemic O₂ saturation and VO_2peak did not differ between the two conditions. DL_CO was not different between groups at any time point. V _C was higher with exercise in the placebo group, and the difference in D _M between sildenafil and placebo was significant only when corrected for changes in V _c (D _M/V _c = 0.57 ± 0.29 vs. 0.41 ± 0.16, P = 0.04). These results suggest no effect of sildenafil on DLCO, but an improvement in D _M when corrected for changes in V _c during short-term hypoxic exposure with exercise.     

Estimation of chain molecular dimension of poly(2-methylpent-1-ene sulfone) at critical polymer contents by dielectric measurements

Dielectric measurements were made in the frequency range from 30 Hz to 3 MHz for a series of the solutions of poly(2-methylpent-1-ene sulfone) (PMPS) having two different molecular weights in benzene at 30°C. The unperturbed chain molecular dimension was estimated from dielectric relaxation time at the critical polymer contents, C_cr. This value of the unperturbed dimension was much higher than that from the intrinsic viscosity measurement. The dielectric motion at C_cr involves simultaneous co-operative reorientations of about three spheres. The number of the spheres of reorientation may be related to the flexibility of the molecular chain of the polymer. The ratio of two effective volumes of the polymer obtained from the unperturbed chain molecular dimension and from the dielectric relaxation time, τ_m agreed with that of the two effective volumes obtained from the K value in Onogi's treatment and from the τ_m value.     

Lactoferrin and anti‐lactoferrin antibodies: Effects of ironloading of lactoferrin on albumin extravasation in different tissues in rats

Lactoferrin is a cationic iron‐binding protein, which is released from activated neutrophils in concert with reactive oxygen species. In vitro, lactoferrin has both anti‐ and proinflammatory effects; many of them dependent on iron‐binding. In vivo, only iron‐free lactoferrin reduced inflammatory hyperpermeability in the lung. We therefore examined whether 1 mg iron‐free (Apo‐Lf) or iron‐saturated lactoferrin (Holo‐Lf) alone or followed by anti‐lactoferrin antibodies (aLf) affected permeability evaluated by extravasation of radiolabelled bovine serum albumin (C_BSA) in different tissues of anaesthetized rats. Fifteen minutes after i.v. injection of Lf, aLf or saline was given and circulatory arrest was induced 20 min thereafter. Measurements were performed in control, after Apo‐Lf, Holo‐Lf, Apo‐Lf + aLf, Holo‐Lf + aLf and aLf alone (n=6–8 in each group). No intergroup differences were found for plasma volume and haematocrit at the start and end of the 37 min extravasation period or for total tissue water in any of the six different tissues studied, excluding larger transcapillary fluid shifts. However, increases in C_BSA were seen without differences in tissue intravascular volume. Iron‐free lactoferrin and aLf alone did not change C_BSA significantly. Iron‐saturated lactoferrin significantly increased C_BSA in skin (neck), trachea and left ventricle of the heart to 249 ± 9, 284 ± 16 and 160 ± 7% of control, respectively. When followed by aLf, both Apo‐ and Holo‐Lf increased C_BSA significantly in four and five of the tissues studied, respectively. However, no significant effect was seen for Holo‐Lf + aLf compared with Holo‐Lf alone. In conclusion, iron‐saturated, but not iron‐free lactoferrin increased C_BSA, whereas antilactoferrin increased C_BSA compared with lactoferrin alone only when following iron‐free lactoferrin.     

The inotropic mechanism of the phosphodiesterase inhibitor OPC 3911 alone and in combination with rolipram,studied in papillary muscles of ferret and guinea–pig and isolated myocytes of guinea–pig ventricular muscle

OPC 3911 is a potent inhibitor and PDE III is a specific inhibitor in cardiac muscle. The effects of the drug alone and in combination with the non–inotropic PDE IV inhibitor rolipram were analysed using hearts from guinea–pigs and ferrets. OPC 3911 had an EC₅₀ value of 0.1μM. At 0.1 fiM peak force was increased by 50.7 ± 7.6% (n = 6, P< 0.001), time to peak tension (TPT) reduced by 18,7±5.6% (n = 6, P < 0.05). Time to half relaxation (THR) was prolonged by 19±4.2% (n= 6, P < 0.001). After addition of rolipram (30 μM) there was a potentiation of peak force at all concentrations of OPC 3911. At 0.1 μM OPC rolipram increased peak force by 82.8±8.9% (n= 6, P < 0.001), reduced TPT by 73 ± 6% (n = 6, P < 0.005) and increased THR by 27±5% (P<0.01). OPC 3911 shortened action potential duration (APD) at 50% repolarization by 5.3 ±2.5% (n= 6, P < 0.05). Addition of rolipram prolonged APD by 3.7 ± 2.5% (n = 6, P < 0.05). Second inward current (I_8l) was increased at 3μM OPC 3911 by 46 ± 6% (n = 6, P< 0.05). The combination of OPC 3911 and rolipram intensified the I_8l to 101 ± 5% (n= 3). Rolipram slowed the rate of restitution and the onset of restitution was prolonged. Relative maximum post–extrasystolic potentiation was reduced in the presence of OPC 3911 from 67 ± 5% to 45 ±6%. Adding rolipram caused potentiation of 55 ± 6%. OPC 3911 increased the recirculation fraction of activator calcium from 0.36 to 0.42 (n = 10, P < 0.05). After addition of rolipram the recirculation fraction was 0.41 ± 0.04 (n =10, P < 0.05). The results suggest that rolipram exerts its potentiating effect on OPC 3911 via an increased I_sl.     

Measurement of the mechanical properties of the human gallbladder

Gallbladder is a small organ of the body which is located in the right side of the liver. It is responsible of storing the bile and releasing it to the intestine. The gallbladder can subject to the mechanical deformation/loading as a result of the cholecystitis, cholesterolosis of the gallbladder, etc. However, so far the mechanical properties of the human gallbladder have not been measured. This study was aimed at conducting an experimental study to measure the mechanical properties of the human gallbladder under the axial and transversal tensile loadings. To do that, the gallbladder tissue of 16 male individuals was excised during the autopsy and subjected to a series of axial and transversal loadings under the strain rate of 5?mm/min. The amount of elastic modulus as well as the maximum/failure stress of the tissues were calculated via the resulted stress–strain diagrams and reported. The results revealed that the axial and transversal elastic modulus were 641.20?±?28.12 (mean?±?SD) and 255?±?24.55?kPa, respectively. The amount of maximum stresses was also 1240?±?99.94 and 348?±?66.75?kPa under the axial and transversal loadings, respectively. The results revealed a significantly higher axial stiffness (p?post hoc Scheffe method) compared to the transversal one. These findings have implications not only for understanding the axial and transversal mechanical properties of the human gallbladder tissue, but also for providing a diagnosis tool for the doctors to have a suitable threshold value of the healthy gallbladder tissue.     

T1 and T2 temperature dependence of female human breast adipose tissue at 1.5 T: groundwork for monitoring thermal therapies in the breast

The T₁ and T₂ temperature dependence of female breast adipose tissue was investigated at 1.5 T in order to evaluate the applicability of relaxation‐based MR thermometry in fat for the monitoring of thermal therapies in the breast. Relaxation times T₁, T₂ and T_2TSE (the apparent T₂ measured using a turbo spin echo readout sequence) were measured in seven fresh adipose breast samples for temperatures from 25 to 65 °C. Spectral water suppression was used to reduce the influence of the residual water signal. The temperature dependence of the relaxation times was characterized. The expected maximum temperature measurement errors based on average calibration lines were calculated. In addition, the heating–cooling reversibility was investigated for two samples. The T₁ and T_2TSE temperature (T) dependence could be fitted well with an exponential function of 1/T. A linear relationship between T₂ and temperature was found. The temperature coefficients (mean ± inter‐sample standard deviation) of T₁ and T_2TSE increased from 25 °C (dT₁/dT = 5.35 ± 0.08 ms/°C, dT_2TSE/dT = 3.82 ± 0.06 ms/°C) to 65 °C (dT₁/dT = 9.50 ± 0.16 ms/°C, dT_2TSE/dT = 7.99 ± 0.38 ms/°C). The temperature coefficient of T₂ was 0.90 ± 0.03 ms/°C. The temperature‐induced changes in the relaxation times were found to be reversible after heating to 65 °C. Given the small inter‐sample variation of the temperature coefficients, relaxation‐based MR thermometry appears to be feasible in breast adipose tissue, and may be used as an adjunct to proton resonance frequency shift (PRFS) thermometry in aqueous tissue (glandular + tumor). Copyright © 2015 John Wiley & Sons, Ltd.     

Quantification of regional myocardial mean intracellular water lifetime: A nonhuman primate study in myocardial stress

Heart failure with preserved ejection fraction (HFpEF) is typically associated with early metabolic remodeling. Noninvasive imaging biomarkers that reflect these changes will be crucial in determining responses to early drug interventions in these patients. Mean intracellular water lifetime (τ_i) has been shown to be partially inversely related to Na, K‐ATPase transporter activity and may thus provide insight into the metabolic status in HFpEF patients. Here, we aim to perform regional quantification of τ_i using dynamic contrast‐enhanced (DCE) magnetic resonance imaging (MRI) in the nonhuman primate (NHP) heart and evaluate its region‐specific variations under conditions of myocardial stress in the context of perturbed myocardial function. Cardiac stress was induced in seven naïve cynomolgus macaques using a dobutamine stepwise infusion protocol. All animals underwent 3 T cardiac dual‐bolus DCE and tagging MRI experiments. The shutter‐speed model was employed to quantify regional τ_i from the DCE‐MR images. Additionally, τ_i values were correlated with myocardial strains. During cardiac stress, there was a significant decrease in global τ_i (192.9 ± 76.3 ms vs 321.6 ± 70 ms at rest, P < 0.05) in the left ventricle, together with an increase in global peak circumferential strain (?15.4% ± 2.7% vs ?10.1% ± 2.9% at rest, P < 0.05). Specifically, slice‐level analysis further revealed that a greater significant decrease in mean τ_i was observed in the apical region (Δτ_I = 182.4 ms) compared with the basal (Δτ_i = 113.2 ms) and midventricular regions (Δτ_i = 108.4 ms). Regional analysis revealed that there was a greater significant decrease in mean τ_i in the anterior (Δτ_i = 243.9 ms) and antero‐lateral (Δτ_i = 177.2 ms) regions. In the inferior and infero‐septal regions, although a decrease in τ_i was observed, it was not significant. Whole heart regional quantification of τ_i is feasible using DCE‐MRI. τ_i is sensitive to regional changes in metabolic state during cardiac stress, and its value correlates with strain.     

Long‐TE 1H MRS suggests that liver fat is more saturated than subcutaneous and visceral fat

Cross‐talk between adipose tissue and liver is disturbed in the metabolic syndrome. Moreover, the relative fatty acid composition of adipose and liver fat is poorly characterized. Long‐TE ¹H MRS can determine the unsaturation and polyunsaturation of adipose tissue. The aim of this study was to use long‐TE ¹H MRS to determine the composition of liver fat and its relation to adipose tissue composition. Sixteen subjects with increased liver fat (>5%) were recruited for the study. Using TE = 200 ms, we were able to resolve the olefinic (?CH, 5.3 ppm) and water (H₂O, 4.7 ppm) resonances in liver spectra and to obtain a repeatable estimate of liver fat unsaturation (coefficient of variation, 2.3%). With TE = 135 ms, the diallylic (?C? CH₂? C?, 2.8 ppm) resonance was detectable in subjects with a liver fat content above 15%. Long‐TE ¹H MRS was also used to determine the unsaturation in subcutaneous (n = 16) and visceral (n = 11) adipose tissue in the same subjects. Liver fat was more saturated (double bonds per fatty acid chain, 0.812 ± 0.022) than subcutaneous (double bonds per fatty acid chain, 0.862 ± 0.022, p < 0.0004) or visceral (double bonds per fatty acid chain, 0.865 ± 0.033, p < 0.0004) fat. Liver fat unsaturation correlated with subcutaneous unsaturation (R = 0.837, p < 0.0001) and visceral unsaturation (R = 0.879, p < 0.0004). The present study introduces a new noninvasive method for the assessment of the composition of liver fat. The results suggest that liver fat is more saturated than subcutaneous or visceral adipose tissue, which may be attributed to differences in de novo lipogenesis. Copyright © 2010 John Wiley & Sons, Ltd.     

Metabolic cost, mechanical work, and efficiency during walking in young and older men

Aim: To investigate mechanical work, efficiency, and antagonist muscle co‐activation with a view to better understand the cause of the elevated metabolic cost of walking (C_W) in older adults. Methods: Metabolic, mechanical and electromyographic measurements were made as healthy young (YOU; n = 12, age = 27 ± 3 years) and older (OLD; n = 20, age = 74 ± 3 years) men of equivalent body mass and leg length walked on a treadmill at four speeds (ranging from 0.83 to 1.67 m s^?1). Results: Net (above resting) C_W, determined by indirect calorimetry was 31% higher (average across speeds) in OLD (P < 0.05). The integrity of the passive pendulum like interchange of mechanical energies of the centre of mass (COM_B), an energy‐saving mechanism, was maintained in OLD. Furthermore, total mechanical work, determined from fluctuations in mechanical energy of COM_B and of body segments relative to COM_B, was not significantly elevated in OLD. This resulted in a lower efficiency in OLD (?17%, P < 0.05). Co‐activation, temporally quantified from electromyography recordings, was 31% higher in OLD for antagonist muscles of the thigh (P < 0.05). Thigh co‐activation was moderately correlated with C_W at three speeds (r = 0.38–0.52, P < 0.05). Conclusion: Healthy septuagenarians with no gait impairment have an elevated C_W which is not explained by an elevation in whole body mechanical work. Increased antagonist muscle co‐activation (possibly an adaptation to ensure adequate joint stability) may offer partial explanation of the elevated C_W.     

Glycemic control influences lung membrane diffusion and oxygen saturation in exercise-trained subjects with type 1 diabetes: alveolar-capillary membrane conductance in type 1 diabetes

Lung diffusing capacity (DLCO) is influenced by alveolar-capillary membrane conductance (D _M) and pulmonary capillary blood volume (V _C), both of which can be impaired in sedentary type 1 diabetes mellitus (T1DM) subjects due to hyperglycemia. We sought to determine if T1DM, and glycemic control, affected DLNO, DLCO, D _M, V _C and SaO₂ during maximal exercise in aerobically fit T1DM subjects. We recruited 12 T1DM subjects and 18 non-diabetic subjects measuring DLNO, DLCO, D _M, and V _C along with SaO₂ and cardiac output (Q) at peak exercise. The T1DM subjects had significantly lower DLCO/Q and D _M/Q with no difference in Q, DLNO, DLCO, D _M, or V _C (DLCO/Q = 2.1 ± 0.4 vs. 1.7 ± 0.3, D _M/Q = 2.8 ± 0.6 vs. 2.4 ± 0.5, non-diabetic and T1DM, p < 0.05). In addition, when considering all subjects there was a relationship between DLCO/Q and SaO₂ at peak exercise (r = 0.46, p = 0.01). Within the T1DM group, the optimal glycemic control group (HbA1c <7%, n = 6) had higher DLNO, DLCO, and D _M/Q than the poor glycemic control subjects (HbA1c ≥7%, n = 6) at peak exercise (DLCO = 38.3 ± 8.0 vs. 28.5 ± 6.9 ml/min/mmHg, DLNO = 120.3 ± 24.3 vs. 89.1 ± 21.0 ml/min/mmHg, D _M/Q = 3.8 ± 0.8 vs. 2.7 ± 0.2, optimal vs. poor control, p < 0.05). There was a negative correlation between HbA1c with DLCO, D _M and D _M/Q at peak exercise (DLCO: r = −0.70, p = 0.01; D _M: r = −0.70, p = 0.01; D _M/Q: r = −0.68, p = 0.02). These results demonstrate that there is a reduction in lung diffusing capacity in aerobically fit athletes with T1DM at peak exercise, but suggests that maintaining near-normoglycemia potentially averts lung diffusion impairments.     

Oxygen consumption and vital organ masses in young growing quail (Coturnix coturnix japonica)

Increased negativity of interstitial fluid pressure (P_if) occurs concomitantly with oedema formation in acute airway inflammation. This observation is principally important because the loose connective tissues become `active' and provide the driving force for the rapid oedema formation via P_if. The present study reports P_if in acute airway inflammation in alloxan diabetic rats. The basis for the study was, firstly, that inflammation is important in the pathogenesis of asthma. Secondly, that clinically there is almost a mutual exclusion between diabetes and asthma and, lastly, that the inflammatory response is attenuated in alloxan diabetic rats. P_if was measured on the ventral side of the trachea with sharpened glass capillaries (3–6 μm) connected to a servocontrolled counterpressure system. Measurements and nerve stimulation were performed after circulatory arrest, since oedema formation associated with inflammation will increase P_if, causing an underestimation of a potentially increased negativity of P_if. Control or diabetic rats (alloxan 45 mg kg^?1 i.v. 5 days earlier) received either the mast cell degranulating substance compound 48/80 (100 μg), dextran 70 (60 mg) i.v. or vagal nerve stimulation. After dextran, P_if was ?4.7 ± 0.9 (SD) mmHg (n = 6) and ?1.3 ± 0.3 mmHg (n = 6) (P < 0.01) in normal and diabetic rats, respectively. Corresponding values after vagal nerve stimulation were ?5.3 ± 1.8 mmHg (n = 5) and ?0.7 ± 0.2 mmHg (P < 0.01). Insulin treatment restored the P_if response to dextran and vagal stimulation. P_if after Compound 48/80 did not differ between control and diabetic rats. Interstitial volume, total tissue water and transcapillary albumin extravasation increased significantly in controls after vagal nerve stimulation, but was attenuated in diabetic rats.     

Magnetic resonance elastography of skeletal muscle deep tissue injury

The current state‐of‐the‐art diagnosis method for deep tissue injury in muscle, a subcategory of pressure ulcers, is palpation. It is recognized that deep tissue injury is frequently preceded by altered biomechanical properties. A quantitative understanding of the changes in biomechanical properties preceding and during deep tissue injury development is therefore highly desired. In this paper we quantified the spatial–temporal changes in mechanical properties upon damage development and recovery in a rat model of deep tissue injury. Deep tissue injury was induced in nine rats by two hours of sustained deformation of the tibialis anterior muscle. Magnetic resonance elastography (MRE), T₂‐weighted, and T₂‐mapping measurements were performed before, directly after indentation, and at several timepoints during a 14‐day follow‐up. The results revealed a local hotspot of elevated shear modulus (from 3.30 ± 0.14 kPa before to 4.22 ± 0.90 kPa after) near the center of deformation at Day 0, whereas the T₂ was elevated in a larger area. During recovery there was a clear difference in the time course of the shear modulus and T₂. Whereas T₂ showed a gradual normalization towards baseline, the shear modulus dropped below baseline from Day 3 up to Day 10 (from 3.29 ± 0.07 kPa before to 2.68 ± 0.23 kPa at Day 10, P < 0.001), followed by a normalization at Day 14. In conclusion, we found an initial increase in shear modulus directly after two hours of damage‐inducing deformation, which was followed by decreased shear modulus from Day 3 up to Day 10, and subsequent normalization. The lower shear modulus originates from the moderate to severe degeneration of the muscle. MRE stiffness values were affected in a smaller area as compared with T₂. Since T₂ elevation is related to edema, distributing along the muscle fibers proximally and distally from the injury, we suggest that MRE is more specific than T₂ for localization of the actual damaged area.     

Tissue‐ and column‐specific measurements from multi‐parameter mapping of the human cervical spinal cord at 3 T

The aim of this study was to quantify a range of MR parameters [apparent proton density, longitudinal relaxation time T₁, magnetisation transfer (MT) ratio, MT saturation (which represents the additional percentage MT saturation of the longitudinal magnetisation caused by a single MT pulse) and apparent transverse relaxation rate R₂*] in the white matter columns and grey matter of the healthy cervical spinal cord. The cervical cords of 13 healthy volunteers were scanned at 3 T using a protocol optimised for multi‐parameter mapping. Intra‐subject co‐registration was performed using linear registration, and tissue‐ and column‐specific parameter values were calculated. Cervical cord parameter values measured from levels C1–C5 in 13 subjects are: apparent proton density, 4822 ± 718 a.u.; MT ratio, 40.4 ± 1.53 p.u.; MT saturation, 1.40 ± 0.12 p.u.; T₁ = 1848 ± 143 ms; R₂* = 22.6 ± 1.53 s^–1. Inter‐subject coefficients of variation were low in both the cervical cord and tissue‐ and column‐specific measurements, illustrating the potential of this method for the investigation of changes in these parameters caused by pathology. In summary, an optimised cervical cord multi‐parameter mapping protocol was developed, enabling tissue‐ and column‐specific measurements to be made. This technique has the potential to provide insight into the pathological processes occurring in the cervical cord affected by neurological disorders. © 2013 The Authors. NMR in Biomedicine published by John Wiley & Sons, Ltd.     

39K and 23Na relaxation times and MRI of rat head at 21.1 T

At ultrahigh magnetic field strengths (B₀ ≥ 7.0 T), potassium (³⁹K) MRI might evolve into an interesting tool for biomedical research. However, ³⁹K MRI is still challenging because of the low NMR sensitivity and short relaxation times. In this work, we demonstrated the feasibility of ³⁹K MRI at 21.1 T, determined in vivo relaxation times of the rat head at 21.1 T, and compared ³⁹K and sodium (²³Na) relaxation times of model solutions containing different agarose gel concentrations at 7.0 and 21.1 T. ³⁹K relaxation times were markedly shorter than those of ²³Na. Compared with the lower field strength, ³⁹K relaxation times were up to 1.9‐ (T₁), 1.4‐ (T_2S) and 1.9‐fold (T_2L) longer at 21.1 T. The increase in the ²³Na relaxation times was less pronounced (up to 1.2‐fold). Mono‐exponential fits of the ³⁹K longitudinal relaxation time at 21.1 T revealed T₁ = 14.2 ± 0.1 ms for the healthy rat head. The ³⁹K transverse relaxation times were 1.8 ± 0.2 ms and 14.3 ± 0.3 ms for the short (T_2S) and long (T_2L) components, respectively. ²³Na relaxation times were markedly longer (T₁ = 41.6 ± 0.4 ms; T_2S = 4.9 ± 0.2 ms; T_2L = 33.2 ± 0.2 ms). ³⁹K MRI of the healthy rat head could be performed with a nominal spatial resolution of 1 × 1 × 1 mm³ within an acquisition time of 75 min. The increase in the relaxation times with magnetic field strength is beneficial for ²³Na and ³⁹K MRI at ultrahigh magnetic field strength. Our results demonstrate that ³⁹K MRI at 21.1 T enables acceptable image quality for preclinical research. Copyright © 2016 John Wiley & Sons, Ltd.     

Assessment of iron nanoparticle distribution in mouse models using ultrashort-echo-time MRI

Microscopic magnetic field inhomogeneities caused by iron deposition or tissue-air interfaces may result in rapid decay of transverse magnetization in MRI. The aim of this study is to detect and quantify the distribution of iron-based nanoparticles in mouse models by applying ultrashort-echo-time (UTE) sequences in tissues exhibiting extremely fast transverse relaxation. In 24 C57BL/6 mice (two controls), suspensions containing either non-oxidic Fe or AuFeO_x nanoparticles were injected into the tail vein at two doses (200 μg and 600 μg per mouse). Mice underwent MRI using a UTE sequence at 4.7 T field strength with five different echo times between 100 μs and 5000 μs. Transverse relaxation times T₂* were computed for the lung, liver, and spleen by mono-exponential fitting. In UTE imaging, the MRI signal could reliably be detected even in liver parenchyma exhibiting the highest deposition of nanoparticles. In animals treated with Fe nanoparticles (600 μg per mouse), the relaxation time substantially decreased in the liver (3418 ± 1534 μs (control) versus 228 ± 67 μs), the spleen (2170 ± 728 μs versus 299 ± 97 μs), and the lungs (663 ± 101 μs versus 413 ± 99 μs). The change in transverse relaxation was dependent on the number and composition of the nanoparticles. By pixel-wise curve fitting, T₂* maps were calculated showing nanoparticle distribution. In conclusion, UTE sequences may be used to assess and quantify nanoparticle distribution in tissues exhibiting ultrafast signal decay in MRI.     

Sensitivity of somatic mutations in human umbilical cord blood to maternal environments

To assess the potential effect of maternal environments on human embryonic/fetal somatic mutation, we measured the frequencies of hypoxanthine-guanine phosphoribosyltransferase (HPRT, hprt gene), mutant T lymphocytes (M_f), and glycophorin A (GPA) variant erythrocytes (V_f) of both allele-loss (ø/N) and allele-loss-and-duplication (N/N) phenotypes in umbilical cord blood. The mean hprt M_f (1.40 ± 1.11 × 10^?6, N = 66) and GPA V_f (ø/N 4.0 ± 2.2 × 10^?6, N = 114; N/N 2.7 ± 2.0 × 10^?6, N = 91) were significantly lower than those previously reported for adult populations. In addition, the hprt M_f was significantly higher than that of a published study of newborn cord blood samples from a geographically distant population (0.64 ± 0.41 × 10^?6, N = 45, P < 0.01; t test, P < 0.01, Mann-Whitney U test). An examination of the demographic data from these two populations led to the sampling of 10 additional newborns specifically matched to the published study for maternal socioeconomic status. The hprt M_f (0.70 ± 0.49 × 10^?6) of this selected population was consistent with the published report and significantly lower than that of our initial population (P < 0.03, t test; P < 0.01, Mann-Whitney U test). These results indicate that there is an environmental effect related to maternal socioeconomic status on the frequency of embryonic/fetal somatic mutations. Molecular analyses of hprt mutants from this cohort with elevated M_f revealed a significant decrease in the relative contribution of gross structural mutations to the overall M_f (25 of 38, 66% vs. 34 of 41, 83%, P = 0.024, x² test), suggesting that the higher M_f resulted from an elevated level of “point” mutations. No individual maternal demographic or environmental factor was identified as contributing more significantly than other any factor to the observed variability in hprt M_f or GPA V_f. © 1995 Wiley-Liss, Inc.     

Purification and characterization of lactate dehydrogenase isoenzymes 1 and 2 from Molinema dessetae (Nematoda: Filarioidea)

 High levels of lactate dehydrogenase (LDH; EC 1. 1. 1. 27) activity have been detected in the filarial worm Molinema dessetae. The two major LDH isoenzymes (LDH1 and LDH2) from female worms were purified by successive chromatography on diethylaminoethyl (DEAE)-Sepharose, carboxymethyl (CM)-Sepharose, and hydroxyapatite columns followed by fast protein liquid chromatography (FPLC)-gel filtration. LDH1 and LDH2 isoenzymes were found to be dimers with subunits of 58 kDa. They had similar properties with regard to substrate and coenzyme affinity. The apparent Michaelis constants (K _m values; mean ± SEM, n = 10) were 0.34 ± 0.04 mM for pyruvate, 0.25 ± 0.02 mM for reduced nicotinamide adenine dinucleotide (NADH), 2.5 ± 0.21 mM for lactate, and 0.18 ± 0.02 mM for NAD, which suggested that pyruvate reduction was the favored reaction. LDH1 and LDH2 were affected by p-chloromercuribenzoate and Hg²⁺, and such inhibitory effects could be reversed by the addition of thiol compounds (L-cysteine or β-mercaptoethanol) as observed for mammalian LDH. Oxalate acted as a noncompetitive inhibitor of pyruvate reduction (K _i = 4.7 ± 0.35 mM; mean ± SEM, n = 10) and as a competitive inhibitor with lactate (K _i = 2.3 ± 0.21 mM), whereas oxamate acted as a competitive inhibitor with pyruvate (K _i = 3.3 ± 0.28 mM) and was noncompetitive with lactate (K _i = 19 ± 1.2 mM). These substrate analogues exerted similar effects on mammalian LDH, but the inhibition constants were significantly different. The existence of structural and kinetic differences between mammal and filarial LDH isoenzymes prompted us to evaluate them as targets for chemotherapeutic attack. Received: 10 January 1996 / Accepted: 30 May 1996