Monitoring dynamic alterations in calcium homeostasis by T1‐mapping manganese‐enhanced MRI (MEMRI) in the early stage of small intestinal ischemia–reperfusion injury

Manganese‐enhanced MRI studies have proven to be useful in monitoring physiological activities associated with calcium ions (Ca²⁺) due to the paramagnetic property of the manganese ion (Mn²⁺), which makes it an excellent probe of Ca²⁺. In this study, we developed a method in which a Mn²⁺‐enhanced T₁‐map MRI could enable the monitoring of Ca²⁺ influx during the early stages of intestinal ischemia–reperfusion (I/R) injury. The Mn²⁺ infusion protocol was optimized by obtaining dose‐dependent and time‐course wash‐out curves using a Mn²⁺‐enhanced T₁‐map MRI of rabbit abdomens following an intravenous infusion of 50 mmol/l MnCl₂ (5–10 nmol/g body weight (BW)). In the rabbit model of intestinal I/R injury, T₁ values were derived from the T₁ maps in the intestinal wall region and revealed a relationship between the dose of the infused MnCl₂ and the intestinal wall relaxation time. Significant Mn²⁺ clearance was also observed over time in control animals after the infusion of Mn²⁺ at a dose of 10 nmol/g BW. This technique was also shown to be sensitive enough to monitor variations in calcium ion homeostasis in vivo after small intestinal I/R injury. The T₁ values of the intestinal I/R group were significantly lower (P < 0.05) than that of the control group at 5, 10, and 15 min after Mn²⁺ infusion. Our data suggest that MnCl₂ has the potential to be an MRI contrast agent that can be effectively used to monitor changes in intracellular Ca²⁺ homeostasis during the early stages of intestinal I/R injury. Copyright © 2015 John Wiley & Sons, Ltd.     

Inhibition of the sodium–calcium exchanger via SEA0400 altered manganese‐induced T1 changes in isolated perfused rat hearts

Manganese (Mn²⁺)‐enhanced MRI (MEMRI) provides the potential for the in vivo evaluation of calcium (Ca²⁺) uptake in the heart. Recent studies have also suggested the role of the sodium–calcium (Na⁺–Ca²⁺) exchanger (NCX) in Mn²⁺ retention, which may have an impact on MEMRI signals. In this study, we investigated whether MEMRI with fast T₁ mapping allowed the sensitive detection of changes in NCX activity. We quantified the dynamics of the Mn²⁺‐induced T₁ changes in isolated perfused rat hearts in response to SEA0400, an NCX inhibitor. The experimental protocol comprised 30 min of Mn²⁺ perfusion (wash‐in), followed by a 30‐min wash‐out period. There were three experimental groups: 1, NCX inhibition by 1 µ m SEA0400 during Mn²⁺ wash‐in only (SEAin, n = 6); 2, NCX inhibition by 1 µ m SEA0400 during Mn²⁺ wash‐out only (SEAout, n = 6); 3, no NCX inhibition during both wash‐in and wash‐out to serve as the control group (CNTL, n = 5). Rapid T₁ mapping at a temporal resolution of 3 min was performed throughout the perfusion protocol using a triggered saturation–recovery Look–Locker sequence. Our results showed that NCX inhibition during Mn²⁺ wash‐in caused a significant increase in relaxation rate (R₁) at the end of Mn²⁺ perfusion. During the wash‐out period, NCX inhibition led to less reduction in R₁. Further analysis of Mn²⁺ content in myocardium with flame atomic absorption spectroscopy was consistent with the MRI findings. These results suggest that Mn²⁺ accumulation and retention in rat hearts are, in part, dependent on NCX activity. Hence, MEMRI may provide an imaging method that is also sensitive to changes in NCX activity. Copyright © 2012 John Wiley & Sons, Ltd.     

Relationship between blood and myocardium manganese levels during manganese‐enhanced MRI (MEMRI) with T1 mapping in rats

Manganese ions (Mn²⁺) enter viable myocardial cells via voltage‐gated calcium channels. Because of its shortening of T₁ and its relatively long half‐life in cells, Mn²⁺ can serve as an intracellular molecular contrast agent to study indirect calcium influx into the myocardium. One major concern in using Mn²⁺ is its sensitivity over a limited range of concentrations employing T₁‐weighted images for visualization, which limits its potential in quantitative techniques. Therefore, this study assessed the implementation of a T₁ mapping method for cardiac manganese‐enhanced MRI to enable a quantitative estimate of the influx of Mn²⁺ over a wide range of concentrations in male Sprague‐Dawley rats. This MRI method was used to compare the relationship between T₁ changes in the heart as a function of myocardium and blood Mn²⁺ levels. Results showed a biphasic relationship between ΔR₁ and the total Mn²⁺ infusion dose. Nonlinear relationships were observed between the total Mn²⁺ infusion dose versus blood levels and left ventricular free wall ΔR₁. At low blood levels of Mn²⁺, there was proportionally less cardiac enhancement seen than at higher levels of blood Mn²⁺. We hypothesize that Mn²⁺ blood levels increase as a result of rate‐limiting excretion by the liver and kidneys at these higher Mn²⁺ doses. Copyright © 2010 John Wiley & Sons, Ltd.     

Assessing manganese efflux using SEA0400 and cardiac T1‐mapping manganese‐enhanced MRI in a murine model

The sodium–calcium exchanger (NCX) is one of the transporters contributing to the control of intracellular calcium (Ca²⁺) concentration by normally mediating net Ca²⁺ efflux. However, the reverse mode of the NCX can cause intracellular Ca²⁺ concentration overload, which exacerbates the myocardial tissue injury resulting from ischemia. Although the NCX inhibitor SEA0400 has been shown to therapeutically reduce myocardial injury, no in vivo technique exists to monitor intracellular Ca²⁺ fluctuations produced by this drug. Cardiac manganese‐enhanced MRI (MEMRI) may indirectly assess Ca²⁺ efflux by estimating changes in manganese (Mn²⁺) content in vivo, since Mn²⁺ has been suggested as a surrogate marker for Ca²⁺. This study used the MEMRI technique to examine the temporal features of cardiac Mn²⁺ efflux by implementing a T₁‐mapping method and inhibiting the NCX with SEA0400. The change in ¹H₂O longitudinal relaxation rate, ΔR₁, in the left ventricular free wall, was calculated at different time points following infusion of 190 nmol/g manganese chloride (MnCl₂) in healthy adult male mice. The results showed 50% MEMRI signal attenuation at 3.4 ± 0.6 h post‐MnCl₂ infusion without drug intervention. Furthermore, treatment with 50 ± 0.2 mg/kg of SEA0400 significantly reduced the rate of decrease in ΔR₁. At 4.9–5.9 h post‐MnCl₂ infusion, the average ΔR₁ values for the two groups treated with SEA0400 were 2.46 ± 0.29 and 1.72 ± 0.24 s^?1 for 50 and 20 mg/kg doses, respectively, as compared to the value of 1.27 ± 0.28 s^?1 for the control group. When this in vivo data were compared to ex vivo absolute manganese content data, the MEMRI T₁‐mapping technique was shown to effectively quantify Mn²⁺ efflux rates in the myocardium. Therefore, combining an NCX inhibitor with MEMRI may be a useful technique for assessing Mn²⁺ transport mechanisms and rates in vivo, which may reflect changes in Ca²⁺ transport. Copyright © 2009 John Wiley & Sons, Ltd.     

Regulation of fast skeletal muscle activity by SERCA1 vicinal-cysteines

During prolonged skeletal muscle contractions free radicals are produced that may lead to fatigue. Vicinal cysteines, known as a Vicinal-thiol groups react preferentially among them depending on redox potential. Therefore, we examined the role of VT groups on the activity and conformational changes of sarcoplasmic reticulum (SR) Ca²⁺-ATPase (SERCA1) from rabbit skeletal muscle isolated SR, by selective oxidation–reduction of VT-groups. After Ca²⁺ is released from the SR to start contraction, SERCA1 pumps this cytosolic Ca²⁺ back to the SR leading to muscle relaxation. Phenylarsine oxide (PAO) reacts selectively with VT-proteins forming dithioarsines, which are stable but exchanges rapidly with 2,3-dimercaptopropanol (BAL). When 0.1 mM PAO is added to isolated SR, 60 and 67% inhibition of SERCA1 hydrolytic and Ca²⁺ uptake activities, respectively is observed. ATPase activity was fully reversible with 1 mM BAL. The SERCA1 thermal inactivation determined from isolated SR from muscle at rest showed a single transition for inactivation (T _i) at 49 ± 1.12°C. In the presence of 0.1 mM PAO, SERCA1 shows two transitions at T _i 34 ±0.9°C and at 27 ±1.2°C. The thermal denaturation profile of SERCA1 from muscle at rest, showed two transitions at T _m = 51.5 ±1.3°C and 63 ±1.02°C related to nucleotide and Ca²⁺ binding domains, respectively. Whereas isolated SR obtained after a protocol of tetanic stimulation to produce muscle fatigue, showed three transitions in the SERCA1 denaturation profile similar to the effect of PAO, addition of 1 mM BAL reverted the effect of fatigue on SERCA1 denaturation profile. These results indicate a mechanism relating VT group’s oxidation to muscle fatigue.     

Structural variations of DNA + Mn2+ complexes during helix-coil transition

The helix-coil transition in Phage T2 DNA in the presence of 6,4 · 10^?3 mol/l Mn²⁺ is studied using light scattering and UV spectroscopy. The transition range is about 0,5°C. Near the temperature of the end of melting T_f the molecular weight M_w and the radius of gyration R_z of the complex are observed to decrease to about one half. At a temperature 0,1–0,25°C higher than T_f, M_w and R_z pass through a minimum, which implies that aggregation is preceded by unwinding of DNA strands. Thus, rise in temperature rather than Mn²⁺ -induced aggregation causes DNA + Mn²⁺ melting.     

MEMRI and tumors: a method for the evaluation of the contribution of Mn(II) ions in the extracellular compartment

The purpose of the work was to set‐up a simple method to evaluate the contribution of Mn²⁺ ions in the intra‐ and extracellular tumor compartments in a MEMRI experiment. This task has been tackled by “silencing” the relaxation enhancement arising from Mn²⁺ ions in the extracellular space. In vitro relaxometric measurements allowed assessment of the sequestering activity of DO2A (1,4,7,10‐tetraazacyclododecane‐1,7‐diacetic acid) towards Mn²⁺ ions, as the addition of Ca‐DO2A to a solution of MnCl₂ causes a drop of relaxivity upon the formation of the highly stable and low‐relaxivity Mn‐DO2A. It has been proved that the sequestering ability of DO2A towards Mn²⁺ ions is also fully effective in the presence of serum albumin. Moreover, it has been shown that Mn‐DO2A does not enter cell membranes, nor does the presence of Ca‐DO2A in the extracellular space prompt migration of Mn ions from the intracellular compartment. On this basis the in vivo, instantaneous, drop in SE% (percent signal enhancement) in T₁‐weighted images is taken as evidence of the sequestration of extracellular Mn²⁺ ions upon addition of Ca‐DO2A. By applying the method to B16F10 tumor bearing mice, T₁ decrease is readily detected in the tumor region, whereas a negligible change in SE% is observed in kidneys, liver and muscle. The relaxometric MRI results have been validated by ICP‐MS measurements. Copyright © 2015 John Wiley & Sons, Ltd.     

Lateral diffusion of manganese in the rat brain determined by T<Subscript>1</Subscript> relaxation time measured by <Superscript>1</Superscript>H MRI

In order to optimize manganese ion-enhanced MRI in thalamic and hypothalamic nuclei, we analyzed the diffusion of manganese in the brain followed by the intra-cerebroventricular application of manganese-bicine (Mn-bicine). T₁-weighted MRI intensities, with 9-pixel ROIs in the hypothalamus perpendicular to the third ventricle, were measured during continuous infusion of Mn-bicine solution in the lateral cerebroventricle. Using a relationship between the image intensity of T₁-weighted MRI and T₁ relaxation time, the image intensity was converted into the concentration of manganese. Assuming a simple diffusion process, the apparent diffusion coefficient (D _ap) of manganese (4.2 × 10⁻⁵ mm² s⁻¹) is much lower than that of water (6 × 10⁻⁴ mm² s⁻¹), and the D _ap tended to decrease when the distance from the third ventricle increased. These results suggest (1) the Mn²⁺ ion is trapped by neural cells during diffusion and (2) the manganese efflux is discharged from the brain via veins.     

Manganese‐enhanced MRI (MEMRI) via topical loading of Mn2+ significantly impairs mouse visual acuity: a comparison with intravitreal injection

Manganese‐enhanced MRI (MEMRI) with topical loading of MnCl₂ provides optic nerve enhancement comparable to that seen by intravitreal injection. However, the impact of this novel and non‐invasive Mn²⁺ loading method on visual function requires further assessments. The objective of this study is to determine the optimal topical Mn²⁺ loading dosage for MEMRI and to assess visual function after MnCl₂ loading. Intravitreal administration was performed to compare the two approaches of MnCl₂ loading. Twenty‐four hours after topical loading of 0, 0.5, 0.75, and 1 M MnCl₂, T₁‐weighted, T2‐weighted, diffusion tensor imaging and visual acuity (VA) assessments were performed to determine the best topical loading dosage for MEMRI measurements and to assess the integrity of retinas and optic nerves. Mice were perfusion fixed immediately after in vivo experiments for hematoxylin and eosin and immunohistochemistry staining. Topical loading of 1 M MnCl₂ damaged the retinal photoreceptor layer with no detectable damage to retina ganglion cell layers or prechiasmatic optic nerves. For the topical loading, 0.75 M MnCl₂ was required to see sufficient enhancement of the optic nerve. At this concentration the visual function was significantly affected, followed by a slow recovery. Intravitreal injection (0.25 μL of 0.2 M MnCl₂) slightly affected VA, with full recovery a day later. To conclude, intravitreal MnCl₂injection provides more reproducible results with less adverse side‐effects than topical loading. Copyright © 2014 John Wiley & Sons, Ltd.     

Cell layers and neuropil: contrast‐enhanced MRI of mouse brain in vivo

Contrast‐enhanced T₁‐ and T₂‐weighted MRI at 9.4 T and in‐plane resolutions of 25 and 30 µm has been demonstrated to differentiate between neural tissues in mouse brain in vivo, including granule cell layers, principal cell layers, general neuropil, specialized neuropil and white matter. In T₁‐weighted MRI of the olfactory bulb, hippocampus and cerebellum, contrast obtained by the intracranial administration of gadopentetate dimeglumine (Gd‐DTPA) reflects the extra‐ and intracellular spaces of gray matter in agreement with histological data. General neuropil areas are highlighted, whereas other tissues present with lower signal intensities. The induced contrast is similar to that in plain T₂‐weighted MRI, but offers a 16–30‐fold higher contrast‐to‐noise ratio. Systemic administration of manganese chloride increases the signal‐to‐noise ratio in T₁‐weighted MRI to a significantly greater extent in principal cell layers and specialized neuropil than in granule cell layers, whereas gadolinium‐enhanced MRI indicates no larger intracellular spaces in these tissues. Granule cell layers are enhanced no more than general neuropil by manganese, whereas gadolinium‐enhanced MRI indicates significantly larger intracellular spaces in the cell layers. These discrepancies suggest that the signal increase after manganese administration reflects cellular activity which is disproportionate to the intracellular space. As a result, principal cell layers and specialized neuropil become highlighted, whereas granule cell layers, general neuropil and white matter present with lower signal intensities. Copyright © 2013 John Wiley & Sons, Ltd.     

Mn-doped silica nanoparticles for hepatocyte-targeted detection of liver cancer in T1-weighted MRI

With an aim to examine the possibility of developing a liver-specific MRI contrast agent that takes advantages of brightly enhanced MR images by Mn²⁺ whilst making up the limitations of the pre-developed contrast agent, the Mn²⁺-doped SiO₂ nanoparticles (Mn–SiO₂) were synthesized and their characteristics as MR contrast agents were investigated. The in vitro and in vivo investigations showed that Mn–SiO₂ has unique MR contrast-enhancing characteristics that activate positive contrast enhancement in T₁-weighted MR images only under low pH conditions by liberating Mn²⁺ ions from MR inactive nanoparticles. The administration of Mn–SiO₂ to an orthotopic xenograft model of human hepatocellular carcinoma (HCC) resulted in a differentiation of enhancement periods between HCC and normal parenchyma tissues on T₁-weighted MR images and consequently presented the duplicates of the highly contrast-enhanced liver image with an equal liver-to-HCC contrast ratio but opposite contrast. The Mn–SiO₂-enhanced MR imaging therefore allowed for the repetitive detection of the HCC within a single MR imaging session, which can help us to achieve more reliable diagnosis and characterization of liver lesions than is possible with any currently used Mn²⁺-based contrast agent. In addition, the in vivo biodistribution study also supported the effectiveness of Mn–SiO₂ nanoparticles as a liver-specific MRI contrast agent, which efficiently delivers and releases the T₁-contrasting Mn²⁺ ions to targeted hepatocytes.     

The distribution of Mn2+ in rabbit eyes after topical administration for manganese-enhanced MRI

Purpose: To analyze the distribution of Mn²⁺ in rabbit eyes after topical administration of Mncl₂ for manganese-enhanced MRI. Methods: Forty-eight Chinese white rabbits were divided into three groups. In group 1 (n = 4), the baseline concentration of Mn²⁺ in aqueous, vitreous and serum samples were analyzed. In group 2 and 3, the rabbits received one topical instillation (20 μL) of Mncl₂ (1 mol•L^-1). In group 2 (n = 40), aqueous, vitreous and serum samples were collected and analyzed at predetermined time points (0.5, 1, 2, 4, 6, 12, 24, 48, 72 and 168 hours postdose). Assays were performed using inductively coupled plasma-mass spectrometer (ICP-MS). In group 3 (n = 4), after topical administration of Mncl₂, dynamic manganese-enhanced MRI (MEMRI) was performed at predetermined time points. The signal-to-noise ratio (SNR) was calculated to evaluate the enhancements of eyes. Results: After topical administration, the maximum concentrations of Mn²⁺ in the aqueous and vitreous samples were 11.1641 ± 0.7202 (2 hours) and 1.5622 ± 0.1567 (12 hours). In group 3, the maximum enhancement of aqueous humor (SNR = 108.81 ± 10.65) appeared at 2 hours postdose, whereas, no significant changes were detected in vitreous. Conclusion: Mn²⁺ could distribute into aqueous humor rapidly after topical administration of Mncl₂, whereas, the concentration of Mn²⁺ in vitreous body fluctuated in a narrow range over the course. The uptake of Mn²⁺ in retina may involve several different pathways.     

Simulated dive in rats lead to acute changes in cerebral blood flow on MRI, but no cerebral injuries to grey or white matter

In this study, the effect of a simulated dive on rat brain was investigated using several magnetic resonance imaging (MRI)-methods and immunohistochemistry. Rats were randomly assigned to a dive- or a control group. The dive group was exposed to a simulated air dive to 600 kPa for 45 min. Pulmonary artery was monitored for vascular gas bubbles by ultrasound. MRI was performed 1 h after decompression and at one and 2 weeks after the dive with a different combination of MRI sequences at each time point. Two weeks after decompression, rats were sacrificed and brains were prepared for histology. Dived rats had a different time-curve for the dynamic contrast-enhanced MRI signal than controls with higher relative signal intensity, a tendency towards longer time to peak and a larger area under the curve for the whole brain on the acute MRI scan. On MRI, 1 and 2 weeks after dive, T₂-maps showed no signal abnormalities or morphological changes. However, region of interest based measurements of T₂ showed higher T₂ in the brain stem among decompressed animals than controls after one and 2 weeks. Microscopical examination including immunohistochemistry did not reveal apparent structural or cellular injuries in any part of the rat brains. These observations indicate that severe decompression does not seem to cause any structural or cellular injury to the brain tissue of the rat, but may cause circulatory changes in the brain perfusion in the acute phase.     

Reduction in myocardial high energy phosphate spin lattice relaxation times using manganese

Paramagnetic contrast agents are being widely used in proton magnetic resonance imaging. The present study demonstrates the potential usefulness of paramagnetic contrast agents in ³¹P NMR spectroscopy. Using the Langendorff perfused rat heart, manganese chloride (Mn²⁺) at a concentration of 50 μM /L was added to the perfusate for 10 or 30 min. ³¹P NMR T_i relaxation times were subsequently measured at 121.5 MHz. After the 10 min exposure to Mn²⁺, ³¹P NMR T_i measurements of phosphocreatine and ATP were reduced by ca 25 and 50%, respectively, with no significant change in linewidths. A small additional decrease in T_i relaxation times after infusion of Mn²⁺ for 30 min was not significantly different from the values at 10 min. Potential uses of Mn²⁺ in ³¹P NMR spectroscopy include improving the S/N ratio of spectra and assessment of calcium ion channel activity.     

Fractionated manganese injections: effects on MRI contrast enhancement and physiological measures in C57BL/6 mice

Manganese‐enhanced MRI (MEMRI) is an increasingly used imaging method in animal research, which enables improved T₁‐weighted tissue contrast. Furthermore accumulation of manganese in activated neurons allows visualization of neuronal activity. However, at higher concentrations manganese (Mn²⁺) exhibits toxic side effects that interfere with the animals' behaviour and well‐being. Therefore, when optimizing MEMRI protocols, a compromise has to be found between minimizing side effects and intensifying image contrast. Recently, a low concentrated fractionated Mn²⁺ application scheme has been proposed as a promising alternative. In this study, we investigated effects of different fractionated Mn²⁺ dosing schemes on vegetative, behavioural and endocrine markers, and MEMRI signal contrast in C57BL/6N mice. Measurements of the animals' well‐being included telemetric monitoring of body temperature and locomotion, control of weight and observation of behavioural parameters during the time course of the injection protocols. Corticosterone levels after Mn²⁺ application served as endocrine marker of the stress response. We compared three MnCl₂ · 4H₂O application protocols: 3 times 60 mg/kg with an inter‐injection interval of 48 h, six times 30 mg/kg with an inter‐injection interval of 48 h, and 8 times 30 mg/kg with an inter‐injection interval of 24 h (referred to as 3 × 60/48, 6 × 30/48 and 8 × 30/24, respectively). Both the 6 × 30/48 and the 8 × 30/24 protocols showed attenuated effects on animals' well‐being as compared to the 3 × 60/48 scheme. Best MEMRI signal contrast was observed for the 8 × 30/24 protocol. Together, these results argue for a fractionated application scheme such as 30 mg/kg every 24 h for 8 days to provide sufficient MEMRI signal contrast while minimizing toxic side effects and distress. Copyright © 2010 John Wiley & Sons, Ltd.     

Treatment of exertional heat stress developed during low or moderate physical work

Purpose

We examined whether treatment for exertional heat stress via ice water immersion (IWI) or natural recovery is affected by the intensity of physical work performed and, thus, the time taken to reach hyperthermia.

Methods

Nine adults (18–45 years; 17.9 ± 2.8 percent body fat; 57.0 ± 2.0 mL kg^?1 min^?1 peak oxygen uptake) completed four conditions incorporating either walking or jogging at 40 °C (20 % relative humidity) while wearing a non-permeable rain poncho. Upon reaching 39.5 °C rectal temperature (T _re), participants recovered either via IWI in 2 °C water or via natural recovery (seated in a ~29 °C environment) until T _re returned to 38 °C.

Results

Cooling rates were greater in the IWI [T _re: 0.24 °C min^?1; esophageal temperature (T _es): 0.24 °C min^?1] than the natural recovery (T _re and T _es: 0.03 °C min^?1) conditions (p < 0.001) with no differences between the two moderate and the two low intensity conditions (p > 0.05). Cooling rates for T _re and T _es were greater in the 39.0–38.5 °C (T _re: 0.19 °C min^?1; T _es: 0.31 °C min^?1) compared with the 39.5–39.0 °C (T _re: 0.11 °C min^?1; T _es: 0.13 °C min^?1) period across conditions (p < 0.05). Similar reductions in heart rate and mean arterial pressure were observed during recovery across conditions (p > 0.05), albeit occurred faster during IWI. Percent change in plasma volume at the end of natural recovery and IWI was 5.96 and 9.58 %, respectively (p < 0.001).

Conclusion

The intensity of physical work performed and, thus, the time taken to reach hyperthermia does not affect the effectiveness of either IWI treatment or natural recovery. Therefore, while the path to hyperthermia may be different for each patient, the path to recovery must always be immediate IWI treatment.     

Predictive accuracy of single‐ and multi‐slice MRI for the estimation of total visceral adipose tissue in overweight to severely obese patients

The quantification of visceral adipose tissue (VAT) is increasingly being considered for risk assessment and treatment monitoring in obese patients, but is generally time‐consuming. The goals of this work were to semi‐automatically segment and quantify VAT areas of MRI slices at previously proposed anatomical landmarks and to evaluate their predictive power for whole‐abdominal VAT volumes on a relatively large number of patients. One‐hundred and ninety‐seven overweight to severely obese patients (65 males; body mass index, 33.3 ± 3.5 kg/m²; 132 females; body mass index, 34.3 ± 3.2 kg/m²) underwent MRI examination. Total VAT volumes (V_VAT‐T) of the abdominopelvic cavity were quantified by retrospective analysis of two‐point Dixon MRI data (active‐contour segmentation, visual correction and histogram analysis). V_VAT‐T was then compared with VAT areas determined on one or five slices defined at seven anatomical landmarks (lumbar intervertebral spaces, umbilicus and femoral heads) and corresponding conversion factors were determined. Statistical measures were the coefficients of variation and standard deviations σ₁ and σ₅ of the difference between predicted and measured VAT volumes (Bland–Altman analysis). V_VAT‐T was 6.0 ± 2.0 L (2.5–11.2 L) for males and 3.2 ± 1.4 L (0.9–7.7 L) for females. The analysis of five slices yielded a better agreement than the analysis of single slices, required only a little extra time (4 min versus 2 min) and was substantially faster than whole‐abdominal assessment (24 min). Best agreements were found at intervertebral spaces L3–L4 for females (σ_5/1 = 523/608 mL) and L2–L3 for males (σ_5/1 = 613/706 mL). Five‐slice VAT volume estimates at the level of lumbar disc L3–L4 for females and L2–L3 for males can be obtained within 4 min and were a reliable predictor for abdominopelvic VAT volume in overweight to severely adipose patients. One‐slice estimates took only 2 min and were slightly less accurate. These findings may contribute to the implementation of analytical methods for fast and reliable (routine) estimation of VAT volumes in obese patients. Copyright © 2015 John Wiley & Sons, Ltd.     

Manganese and the heart: acute cardiodepression and myocardial accumulation of manganese

The aim of study was to assess acute effects of the divalent manganese ion (Mn²⁺) in an intact but isolated heart preparation. Rat hearts were perfused in the Langendorff mode at constant flow rate. Left ventricular (LV) developed pressure (LVDP), LV pressure first derivatives (LVdp/dt max and min), heart rate (HR) and aortic pressure (AoP) were recorded. Ventricular contents of high energy phosphate compounds (HEP) and Mn metal were measured at the end of experiment. Infusion of MnCl₂ for 5 min with perfusate concentrations 1–3000 μM induced an immediate depression of contractile function at and above 30 μM and negative chronotropy at and above 300 μM . These EC₅₀ values were found (μM ): LVDP 250; LVdp/dt max 160; LVdp/dp min 120; HR 1000; and increase in AoP 80. Recovery of function during a 14 min washout period was rapid and extensive, except for Mn²⁺ 3000 μM . Somewhat unexpected, Mn²⁺ 30–1000 μM raised coronary vascular resistance up to about twice the control level, whereas the vasoconstrictory response was overcome at 3000 μM . Mn²⁺ 3000 μM reduced tissue HEP. Ventricular Mn content rose stepwise for perfusate Mn²⁺ above 1 μM up to about 55 times the control level for perfusate Mn²⁺ 3000 μM . It is concluded that: acute effects of Mn²⁺ like depression of contractility and rate is rapidly reversible; and rat hearts accumulate and buffer large amounts of Mn²⁺ without affecting cardiac function or energy metabolism in the acute stage.     

31P NMR relaxation of cortical bone mineral at multiple magnetic field strengths and levels of demineralization

Recent work has shown that solid‐state ¹H and ³¹P MRI can provide detailed insight into bone matrix and mineral properties, thereby potentially enabling differentiation of osteoporosis from osteomalacia. However, ³¹P MRI of bone mineral is hampered by unfavorable relaxation properties. Hence, accurate knowledge of these properties is critical to optimizing MRI of bone phosphorus. In this work, ³¹P MRI signal‐to‐noise ratio (SNR) was predicted on the basis of T₁ and T₂* (effective transverse relaxation time) measured in lamb bone at six field strengths (1.5–11.7 T) and subsequently verified by 3D ultra‐short echo‐time and zero echo‐time imaging. Further, T₁ was measured in deuterium‐exchanged bone and partially demineralized bone. ³¹P T₂* was found to decrease from 220.3 ± 4.3 µs to 98.0 ± 1.4 µs from 1.5 to 11.7 T, and T₁ to increase from 12.8 ± 0.5 s to 97.3 ± 6.4 s. Deuteron substitution of exchangeable water showed that 76% of the ³¹P longitudinal relaxation rate is due to ¹H–³¹P dipolar interactions. Lastly, hypomineralization was found to decrease T₁, which may have implications for ³¹P MRI based mineralization density quantification. Despite the steep decrease in the T₂*/T₁ ratio, SNR should increase with field strength as B₀^0.4 for sample‐dominated noise and as B₀^1.1 for coil‐dominated noise. This was confirmed by imaging experiments. Copyright © 2013 John Wiley & Sons, Ltd.     

Covalent attachment of Mn-porphyrin onto doxorubicin-loaded poly(lactic acid) nanoparticles for potential magnetic resonance imaging and pH-sensitive drug delivery

In this paper, theranostic nanoparticles (MnP-DOX NPs) were fabricated by conjugating Mn-porphyrin onto the surface of doxorubicin (DOX)-loaded poly(lactic acid) (PLA) nanoparticles (DOX NPs) for potential T₁ magnetic resonance imaging and pH-sensitive drug delivery. An in vitro drug release study showed that the release rate of DOX from MnP-DOX NPs was slow at neutral pH but accelerated significantly in acidic conditions. It was found that MnP-DOX NPs could be easily internalized by HeLa cells and effectively suppressed the growth of HeLa cells and HT-29 cells due to the accelerated drug release in acidic lysosomal compartments. Magnetic resonance imaging (MRI) scanning analysis demonstrated that MnP-DOX NPs had much higher longitudinal relaxivity in water (r₁ value of 27.8 mM^?1 s^?1 of Mn³⁺) than Mn-porphyrin (Mn(III)TPPS3NH₂; r₁ value of 6.70 mM^?1 s^?1 of Mn³⁺), behaving as an excellent contrast agent for T₁-weighted MRI both in vitro and in vivo. In summary, such a smart and promising nanoplatform integrates multiple capabilities for effective cancer diagnosis and therapy.