Large protein organelles form a new iron sequestration system with high storage capacity.

Iron storage proteins are essential for cellular iron homeostasis and redox balance. Ferritin proteins are the major storage units for bioavailable forms of iron. Some organisms lack ferritins, and it is not known how they store iron. Encapsulins, a class of protein-based organelles, have recently been implicated in microbial iron and redox metabolism. Here, we report the structural and mechanistic characterization of a 42 nm two-component encapsulin-based iron storage compartment from Quasibacillus thermotolerans. Using cryo-electron microscopy and x-ray crystallography, we reveal the assembly principles of a thermostable T = 4 shell topology and its catalytic ferroxidase cargo and show interactions underlying cargo-shell co-assembly. This compartment has an exceptionally large iron storage capacity storing over 23,000 iron atoms. Our results reveal a new approach for survival in diverse habitats with limited or fluctuating iron availability via an iron storage system able to store 10 to 20 times more iron than ferritin.

Influence of iron doping on tetravalent nickel content in catalytic oxygen evolving films.

Iron doping of nickel oxide films results in enhanced activity for promoting the oxygen evolution reaction (OER). Whereas this enhanced activity has been ascribed to a unique iron site within the nickel oxide matrix, we show here that Fe doping influences the Ni valency. The percent of Fe3+ doping promotes the formation of formal Ni4+, which in turn directly correlates with an enhanced activity of the catalyst in promoting OER. The role of Fe3+ is consistent with its behavior as a superior Lewis acid.

Mammographic microcalcifications and breast cancer tumorigenesis: a radiologic-pathologic analysis.

BACKGROUND: Microcalcifications (MCs) are tiny deposits of calcium in breast soft tissue. Approximately 30% of early invasive breast cancers have fine, granular MCs detectable on mammography; however, their significance in breast tumorigenesis is controversial. This study had two objectives: (1) to find associations between mammographic MCs and tumor pathology, and (2) to compare the diagnostic value of mammograms and breast biopsies in identifying malignant MCs. METHODS: A retrospective chart review was performed for 937 women treated for breast cancer during 2000-2012 at St. Michael's Hospital. Demographic information (age and menopausal status), tumor pathology (size, histology, grade, nodal status and lymphovascular invasion), hormonal status (ER and PR), HER-2 over-expression and presence of MCs were collected. Chi-square tests were performed for categorical variables and t-tests were performed for continuous variables. All p-values less than 0.05 were considered statistically significant. RESULTS: A total of 937 patient charts were included. About 38.3% of the patients presented with mammographic MCs on routine mammographic screening. Patients were more likely to have MCs if they were HER-2 positive (52.9%; p < 0.001). There was a significant association between MCs and peri-menopausal status with a mean age of 50 (64%; p = 0.012). Patients with invasive ductal carcinomas (40.9%; p = 0.001) were more likely to present with MCs than were patients with other tumor histologies. Patients with a heterogeneous breast density (p = 0.031) and multifocal breast disease (p = 0.044) were more likely to have MCs on mammograms. There was a positive correlation between MCs and tumor grade (p = 0.057), with grade III tumors presenting with the most MCs (41.3%). A total of 52.2% of MCs were missed on mammograms which were visible on pathology (p < 0.001). CONCLUSION: This is the largest study suggesting the appearance of MCs on mammograms is strongly associated with HER-2 over-expression, invasive ductal carcinomas, peri-menopausal status, heterogeneous breast density and multifocal disease.

Probing the low-temperature water-gas shift activity of alkali-promoted platinum catalysts stabilized on carbon supports.

We report on the direct promotional effect of sodium on the water-gas shift activity of platinum supported on oxygen-free multiwalled carbon nanotubes. Whereas the Na-free Pt catalysts are shown to be completely inactive, the addition of sodium is found to improve the water-gas shift activity to levels comparable to those obtained with highly active Pt catalysts on metal oxide supports. The structure and morphology of the catalyst surface was followed using aberration-corrected HAADF-STEM, which showed that atomically dispersed platinum species are stabilized by the addition of sodium. In situ atmospheric-pressure X-ray photoelectron spectroscopy (AP-XPS) experiments demonstrated that oxidized platinum Pt-OHx contributions in the Pt 4f signal are higher in the presence of sodium, providing evidence for a previously reported active-site structure of the form Pt-Nax-Oy-(OH)z. Pt remained oxidized in all redox experiments, even when a H2-rich gas mixture was used, but the extent of its oxidation followed the oxidation potential of the gas. These findings offer new insights into the nature of the active platinum-based site for the water-gas shift reaction. A strong inhibitory effect of hydrogen was observed on the reaction kinetics, effectively raising the apparent activation energy from 70 ± 5 kJ/mol (in product-free gas) to 105 ± 7 kJ/mol (in full reformate gas). Increased hydrogen uptake was observed on these materials when both Pt and Na were present on the catalyst, suggesting that hydrogen desorption might limit the water-gas shift reaction rate under such conditions.

Bulk manufacture of concentrated oxygen gas-filled microparticles for intravenous oxygen delivery.

Self-assembling, concentrated, lipid-based oxygen microparticles (LOMs) have been developed to administer oxygen gas when injected intravenously, preventing organ injury and death from systemic hypoxemia in animal models. Distinct from blood substitutes, LOMs are a one-way oxygen carrier designed to rescue patients who experience life-threatening hypoxemia, as caused by airway obstruction or severe lung injury. Here, we describe methods to manufacture large quantities of LOMs using an in-line, recycling, high-shear homogenizer, which can create up to 4 liters of microparticle emulsion in 10 minutes, with particles containing a median diameter of 0.93 microns and 60 volume% of gas phase. Using this process, we screen 30 combinations of commonly used excipients for their ability to form stable LOMs. LOMs composed of DSPC and cholesterol in a 1:1 molar ratio are stable for a 100 day observation period, and the number of particles exceeding 10 microns in diameter does not increase over time. When mixed with blood in vitro, LOMs fully oxygenate blood within 3.95 seconds of contact, and do not cause hemolysis or complement activation. LOMs can be manufactured in bulk by high shear homogenization, and appear to have a stability and size profile which merit further testing.

DNA base identification by electron microscopy.

Advances in DNA sequencing, based on fluorescent microscopy, have transformed many areas of biological research. However, only relatively short molecules can be sequenced by these technologies. Dramatic improvements in genomic research will require accurate sequencing of long (>10,000 base-pairs), intact DNA molecules. Our approach directly visualizes the sequence of DNA molecules using electron microscopy. This report represents the first identification of DNA base pairs within intact DNA molecules by electron microscopy. By enzymatically incorporating modified bases, which contain atoms of increased atomic number, direct visualization and identification of individually labeled bases within a synthetic 3,272 base-pair DNA molecule and a 7,249 base-pair viral genome have been accomplished. This proof of principle is made possible by the use of a dUTP nucleotide, substituted with a single mercury atom attached to the nitrogenous base. One of these contrast-enhanced, heavy-atom-labeled bases is paired with each adenosine base in the template molecule and then built into a double-stranded DNA molecule by a template-directed DNA polymerase enzyme. This modification is small enough to allow very long molecules with labels at each A-U position. Image contrast is further enhanced by using annular dark-field scanning transmission electron microscopy (ADF-STEM). Further refinements to identify additional base types and more precisely determine the location of identified bases would allow full sequencing of long, intact DNA molecules, significantly improving the pace of complex genomic discoveries.

Nanocomposite gold-silk nanofibers.

Cell-biomaterial interactions can be controlled by modifying the surface chemistry or nanotopography of the material, to induce cell proliferation and differentiation if desired. Here we combine both approaches in forming silk nanofibers (SNFs) containing gold nanoparticles (AuNPs) and subsequently chemically modifying the fibers. Silk fibroin mixed with gold seed nanoparticles was electrospun to form SNFs doped with gold seed nanoparticles (SNF(seed)). Following gold reduction, there was a 2-fold increase in particle diameter confirmed by the appearance of a strong absorption peak at 525 nm. AuNPs were dispersed throughout the AuNP-doped silk nanofibers (SNFs(Au)). The Young's modulus of the SNFs(Au) was almost 70% higher than that of SNFs. SNFs(Au) were modified with the arginine-glycine-aspartic acid (RGD) peptide. Human mesenchymal stem cells that were cultured on RGD-modified SNF(Au) had a more than 2-fold larger cell area compared to the cells cultured on bare SNFs; SNF(Au) also increased cell size. This approach may be used to alter the cell-material interface in tissue engineering and other applications.

Oxygen gas-filled microparticles provide intravenous oxygen delivery.

We have developed an injectable foam suspension containing self-assembling, lipid-based microparticles encapsulating a core of pure oxygen gas for intravenous injection. Prototype suspensions were manufactured to contain between 50 and 90 ml of oxygen gas per deciliter of suspension. Particle size was polydisperse, with a mean particle diameter between 2 and 4 µm. When mixed with human blood ex vivo, oxygen transfer from 70 volume % microparticles was complete within 4 s. When the microparticles were infused by intravenous injection into hypoxemic rabbits, arterial saturations increased within seconds to near-normal levels; this was followed by a decrease in oxygen tensions after stopping the infusions. The particles were also infused into rabbits undergoing 15 min of complete tracheal occlusion. Oxygen microparticles significantly decreased the degree of hypoxemia in these rabbits, and the incidence of cardiac arrest and organ injury was reduced compared to controls. The ability to administer oxygen and other gases directly to the bloodstream may represent a technique for short-term rescue of profoundly hypoxemic patients, to selectively augment oxygen delivery to at-risk organs, or for novel diagnostic techniques. Furthermore, the ability to titrate gas infusions rapidly may minimize oxygen-related toxicity.

Alkali-stabilized Pt-OHx species catalyze low-temperature water-gas shift reactions.

We report that alkali ions (sodium or potassium) added in small amounts activate platinum adsorbed on alumina or silica for the low-temperature water-gas shift (WGS) reaction (H(2)O + CO → H(2) + CO(2)) used for producing H(2). The alkali ion-associated surface OH groups are activated by CO at low temperatures (~100°C) in the presence of atomically dispersed platinum. Both experimental evidence and density functional theory calculations suggest that a partially oxidized Pt-alkali-O(x)(OH)(y) species is the active site for the low-temperature Pt-catalyzed WGS reaction. These findings are useful for the design of highly active and stable WGS catalysts that contain only trace amounts of a precious metal without the need for a reducible oxide support such as ceria.

Rab3B immunoexpression in human pituitary adenomas.

Rab3B, a member of the Rab family is a low molecular weight GTP-binding protein that has been implicated in the regulation of exocytosis. To shed light on its presence in the normal human pituitary and in adenomas, a detailed immunohistochemical study of 130 surgically removed human pituitary adenomas was undertaken, including 23 somatotroph, 32 lactotroph, 19 functional corticotroph, 10 silent subtype 1 and 8 silent subtype 2 corticotroph adenomas, 12 gonadotroph hormone producing, 10 thyrotroph, 7 silent subtype 3 adenomas, and 9 null cell adenomas, 5 of the latter being of oncocytic type. Among the 32 prolactin lactotroph adenomas, 10 had been treated preoperatively with bromocriptine, a dopamine agonist. Among the 23 somatotroph adenomas, 10 were pretreated with octreotide, a long acting somatostatin analog. In addition, 10 nontumorous adenohypophyses were also examined. As used by the World Health Organization, the tumors were classified on the basis of their histologic, immunohistochemical, and ultrastructural characteristics. The results showed Rab3B immunopositivity to be strongest in corticotroph adenomas followed by thyrotroph, lactotroph, gonadotroph, null cell, and somatotroph adenomas. No difference was noted between endocrinologically active and silent corticotroph adenomas. Bromocriptine therapy was associated with decreased Rab3B immunoexpression, whereas pretreatment with octreotide induced no significant reduction. Immunopositivity was cytoplasmic and was evenly distributed. No staining was noted in normal adenohypophyses. Our results add new information to the view that Rab3B is involved in the regulation of pituitary hormone secretion.

Expression of caveolin-1 and caveolin-2 in the human pituitary: an immunohistochemical study.

Caveolins are coat proteins of caveolae, the plasmalemmal transport vesicles. To our knowledge their presence in the human pituitary and various types of hypophysial adenomas has not been investigated. In the present work, expression of caveolin-1 and caveolin-2 was studied by immunohistochemistry using the streptavidin-biotin-peroxidase complex method. The material included 7 autopsy obtained, 5 surgically removed non-tumorous pituitaries, and 97 hypophysial adenomas classified on the basis of histologic immunohistochemical and ultrastructural features. No immunoreactivity was seen for caveolin-1 and caveolin-2 in non-tumorous adenohypophysial and neurohypophysial cells and in the tumor cells, indicating that caveolins are not involved in the initiation and progression of pituitary adenomas. The expression of caveolin-1 and caveolin-2 in the endothelial cells did not depend on age, gender, endocrine status of the patients, morphologic features, and type of pituitary tumors. Scattered endothelial cells were immunopositive for both caveolins showing similar cytoplasmic localization. Evidence that the two caveolins were indeed localized to the same endothelial cell was demonstrated on consecutive sections using Factor-8 and CD-34, two reliable endothelial cell markers. Not every endothelial cell was immunoreactive for the two caveolins, suggesting that the functional status of endothelial cells is not the same within the adenomas, not even in the same capillary.

Protecting oneself from human immunodeficiency virus: are prevention messages being heard?

The transmission of human immunodeficiency virus (HIV) and other communicable diseases is socially organized. Public health attempts to reduce HIV transmission have admonished persons to reduce their risks--in effect, to act as if their partners are or could be HIV-seropositive. Therefore, a good test of the effectiveness of public health messages is to compare the riskiness of behaviors among HIV-seronegative persons with the riskiness of the behavior of serodiscordant partners. Data were collected for a network study of 267 drug users and nonusers in an urban inner city. Results show that in most of the domains studied, persons with HIV-seronegative partners engaged in less risky behavior than did persons whose partners were HIV-seropositive. This result suggests that risk reduction messages have been relatively successful in convincing most persons to treat their partner as if he or she were HIV-seropositive.