Sensitivity of multifrequency magnetic resonance elastography and diffusion-weighted imaging to cellular and stromal integrity of liver tissue

Microscopic structural alterations of liver tissue induced by freeze-thaw cycles give rise to palpable property changes. However, the underlying damage to tissue architecture is difficult to quantify histologically, and published data on macroscopic changes in biophysical properties are sparse.To better understand the influence of hepatic cells and stroma on global biophysical parameters, we studied rat liver specimens freshly taken (within 30 min after death) and treated by freeze-thaw cycles overnight at either −20 °C or –80 °C using diffusion-weighted imaging (DWI) and multifrequency magnetic resonance elastography (MRE) performed at 0.5 T in a tabletop MRE scanner. Tissue structure was analyzed histologically and rheologic data were analyzed using fractional order derivatives conceptualized by a called spring-pot component that interpolates between pure elastic and viscous responses.Overnight freezing and thawing induced membrane disruptions and cell detachment in the space of Disse, resulting in a markedly lower shear modulus μ and apparent diffusion coefficient (ADC) (μ[−20 °C] = 1.23 ± 0.73 kPa, μ[−80 °C] = 0.66 ± 0.75 kPa; ADC[–20 °C] = 0.649 ± 0.028 μm²/s, ADC[−80 °C] = 0.626 ± 0.025 μm²/s) compared to normal tissue (μ = 9.92 ± 3.30 kPa, ADC = 0.770 ± 0.023 μm²/s, all p < 0.001). Furthermore, we analyzed the springpot-powerlaw coefficient and observed a reduction in −20 °C specimens (0.22 ± 0.14) compared to native tissue (0.40 ± 0.10, p = 0.033) and −80 °C specimens (0.54 ± 0.22, p = 0.002), that correlated with histological observations of sinusoidal dilation and collagen distortion within the space of Disse. Overall, the results suggest that shear modulus and water diffusion in liver tissue markedly decrease due to cell membrane degradation and cell detachment while viscosity-related properties appear to be more sensitive to distorted stromal and microvascular architecture.     

Residue Histidine 50 Plays a Key Role in Protecting α-Synuclein from Aggregation at Physiological pH

α-Synuclein (αSyn) aggregation is involved in the pathogenesis of Parkinson disease (PD). Recently, substitution of histidine 50 in αSyn with a glutamine, H50Q, was identified as a new familial PD mutant. Here, nuclear magnetic resonance (NMR) studies revealed that the H50Q substitution causes an increase of the flexibility of the C-terminal region. This finding provides direct evidence that this PD-causing mutant can mediate long range effects on the sampling of αSyn conformations. In vitro aggregation assays showed that substitution of His-50 with Gln, Asp, or Ala promotes αSyn aggregation, whereas substitution with the positively charged Arg suppresses αSyn aggregation. Histidine carries a partial positive charge at neutral pH, and so our result suggests that positively charged His-50 plays a role in protecting αSyn from aggregation under physiological conditions.     

Low-temperature magnetic circular dichroism evidence for the conversion of four-iron-sulphur clusters in a ferredoxin from Clostridium pasteurianum into three-iron-sulphur clusters

Oxidation of the 8Fe ferredoxin from Clostridium pasteurianum with potassium ferricyanide, followed by purification on Sephadex G-25 and DE-23 cellulose columns, gives a protein with an intense EPR signal at g 2.01. The low-temperature magnetic circular dichroism (MCD) spectra of this species are different from those of the oxidized high-potential iron protein from Chromatium but identical with the spectra of ferredoxin II from Desulphovibrio gigas. On reduction of the ferricyanide-treated ferredoxin with sodium dithionite only a weak EPR signal with g factors of 2.05, 1.94 and 1.89 is obtained. The low-temperature MCD spectra are strongly temperature dependent with a form similar to those of dithionite-reduced D. gigas ferredoxin II. The MCD magnetization curves are dominated by a species with ground-state effective g factors of $\text{g}{}_{\mathrm{?}}$ 8.0 and g_⊥ 0.0, which are also similar to those determined recently by low-temperature MCD spectroscopy for D. gigas ferredoxin II. The MCD characteristics are quite different from those of dithionite-reduced ferredoxin from Cl. pasteurianum, untreated with ferricyanide. This establishes the close similarity of the iron-sulphur clusters in ferricyanide-treated Cl. pasteurianum ferredoxin and in D. gigas ferredoxin II. The latter is known to contain a single 3Fe centre, similar to that observed in ferredoxin I from Azotobacter vinelandii by X-ray crystallography. Therefore, it is concluded that the [4Fe-4S] clusters of Cl. pasteurianum ferredoxin are converted to 3Fe clusters on oxidation with ferricyanide.     

Periplasmic superoxide dismutases in Aquaspirillum magnetotacticum

Aquaspirillum magnetotacticum MS-1 cells cultured microaerobically (dissolved O₂ tension 1% of saturation), expressed proteins with superoxide dismutase (SOD) activity. The majority (roughly 95%) of total cell superoxide dismutase activity was located in the cell periplasm with little or no activity in the cell cytoplasm. Irontype SOD (FeSOD) contributed 88% of the total activity activity detected, although a manganese-type SOD (MnSOD) was present in the periplasm as well. Cells cultured at a higher dissolved O₂ tension (10% of saturation) expressed increased activity of the MnSOD relative to that of the FeSOD.     

Immobilization of amyloglucosidase from SSF of Aspergillus niger by crosslinked enzyme aggregate onto magnetic nanoparticles using minimum amount of carrier and characterizations

Immobilizations of enzymes are done for operational stability, recovery and re-use of the enzymes and easy separation of products. Amyloglucosidase (AMG) obtained from solid state fermentation (SSF) of Aspergillus niger was directly immobilized by novel technique of crosslinked enzyme aggregate onto magnetic nanoparticles. AMG was covalently linked to the magnetic nanoparticle (MNP) to form a monolayer of AMG (MNP–AMG), followed by crosslinked aggregates with free AMG (which was not immobilized) to yield MNP with high enzyme loading (MNP–AMG_n). Under optimized conditions, very high recovery (92.8%) of enzyme activity was obtained in MNP–AMG_n using 14 times less carrier compared to the quantity of carrier required by conventional method. MNP–AMG_n showed enhanced affinity for substrate, thermal stability, storage stability and reusability.     

Application of nuclear magnetic resonance spectroscopy to analysis of ethanol fermentation kinetics in yeasts and bacteria

Nuclear Magnetic Resonance (NMR) spectroscopy is proving to be a very valuable technique for characterizing the metabolic status of a range of microbial fermentations. This non-invasive method allows us not only to determine the presence of particular metabolites, but also to monitor reaction rates, enzyme activities and transport mechanisms in vivo. Despite the low levels of the carbon-13 isotope (1.1%), natural-abundance ¹³C-NMR studies have proven useful in monitoring the progress of various fermentation processes. Furthermore, ³¹P-NMR can provide noninvasive information relating to cellular metabolism, and on the energy status of the cells. This results from the facility with NMR to identify various nucleotide phosphates and other energy-rich compounds in the cell, as well as to characterize changes in the intracellular pH from the chemical shifts of internal phosphate and other phosphorylated intermediates. In this review, we will summarize the use of NMR as an analytical tool in biotechnology and also discuss examples that illustrate how NMR can be used to obtain significant information on the characteristics of ethanol fermentations in both yeasts and bacteria.     

Historical record of human impact in a lake of northern China: Magnetic susceptibility,nutrients, heavy metals and OCPs

The historical record (1859–2011) of magnetic susceptibility, total organic carbon, total nitrogen, δ¹³C_org, δ¹⁵N, As, Cd, Hg, Pb, and organochlorine pesticide (OCP) signatures in Baiyangdian Lake was used to analyze the water environmental changes due to human activities. The results indicate the following: the status of the lake approaches the background condition in 1859–1950s; the lake suffered increasing anthropogenic effects from the 1950s because of increasing human activities such as coal-fired power plant operations since 1958, fertilizer use in the agriculture and land transformation since the 1950s, steelmaking between the 1960s and 1970s, machinery manufacturing since the 1970s, use of petrol containing alky-lead since 1990; the lake has been in a contaminated condition since the 2000s. This study confirms that OCPs have been effectively controlled in the area, the level of nutrient and heavy metal pollution is increasing, coal-fired power plants are an important source of Hg, and the use of petrol containing alky-lead has accelerated the accumulation of Pb in the environment. The study indicates that magnetic susceptibility can be used as a rapid, simple, and non-destructive tool for assessment of organic and heavy metal pollution in the lake.     

Phylogenetic analysis of a novel sulfate-reducing magnetic bacterium, RS-1, demonstrates its membership of the δ-Proteobacteria

Abstract Most of the 16S ribosomal RNA gene of a sulfate-reducing magnetic bacterium, RS-1, was sequenced, and phylogenetic analysis was carried out. The results suggest that RS-1 is a member of the δ-Proteobacteria, and it appears to represent a new genus. RS-1 is the first bacterium reported outside the α-Proteobacteria that contains magnetite inclusions. RS-1 therefore disrupts the correlation between the α-Proteobacteria and possession of magnetite inclusions, and that between the δ-Proteobacteria and possession of greigite inclusions. The existence of RS-1 also suggests that intracellular magnetite biomineralization is of multiple evolutionary origins.