Retrospective Cohort Study of the Incidence of Acute Kidney Injury with Vancomycin Area under the Curve-Based Dosing with Concomitant Piperacillin-Tazobactam Compared to Meropenem or Cefepime.

Acute kidney injury (AKI) is a complication associated with vancomycin. Previous studies demonstrated that the combination of vancomycin and piperacillin-tazobactam increases the risk of AKI compared to vancomycin with meropenem or cefepime. These studies did not utilize area under the curve (AUC)-based dosing, which reduces vancomycin exposure and may decrease nephrotoxicity compared with trough-based dosing. This study evaluated the incidence of AKI in patients receiving AUC-dosed vancomycin with either concomitant piperacillin-tazobactam (VPT) or meropenem or cefepime (VMC). This retrospective cohort study included patients admitted to Sentara Norfolk General Hospital between October 2019 and September 2020 who received AUC-dosed vancomycin and concomitant piperacillin-tazobactam, meropenem, or cefepime for at least 48 h. The primary outcome was the incidence of AKI during treatment or within 24 h of discontinuation. A total of 435 patients (VPT, n = 331; VMC, n = 104) who received a median duration of 4 days of treatment were included. The incidence of AKI was significantly higher with VPT than with VMC (13.6% versus 4.8% [P = 0.014]). Multivariable analysis showed VPT to be an independent risk factor for the development of AKI (odds ratio [OR], 3.00 [95% confidence interval {CI}, 1.15 to 7.76]). VPT was associated with more frequent AKI than VMC, even with the relatively short courses of antimicrobial therapy administered in this population. In comparison with the precedent in the literature for trough-based vancomycin dosing, our results suggest that the use of AUC-based vancomycin dosing in combination with piperacillin-tazobactam, meropenem, or cefepime may result in a lower overall incidence of AKI.

Ancient proteins resolve the evolutionary history of Darwin's South American ungulates.

No large group of recently extinct placental mammals remains as evolutionarily cryptic as the approximately 280 genera grouped as 'South American native ungulates'. To Charles Darwin, who first collected their remains, they included perhaps the 'strangest animal[s] ever discovered'. Today, much like 180 years ago, it is no clearer whether they had one origin or several, arose before or after the Cretaceous/Palaeogene transition 66.2 million years ago, or are more likely to belong with the elephants and sirenians of superorder Afrotheria than with the euungulates (cattle, horses, and allies) of superorder Laurasiatheria. Morphology-based analyses have proved unconvincing because convergences are pervasive among unrelated ungulate-like placentals. Approaches using ancient DNA have also been unsuccessful, probably because of rapid DNA degradation in semitropical and temperate deposits. Here we apply proteomic analysis to screen bone samples of the Late Quaternary South American native ungulate taxa Toxodon (Notoungulata) and Macrauchenia (Litopterna) for phylogenetically informative protein sequences. For each ungulate, we obtain approximately 90% direct sequence coverage of type I collagen α1- and α2-chains, representing approximately 900 of 1,140 amino-acid residues for each subunit. A phylogeny is estimated from an alignment of these fossil sequences with collagen (I) gene transcripts from available mammalian genomes or mass spectrometrically derived sequence data obtained for this study. The resulting consensus tree agrees well with recent higher-level mammalian phylogenies. Toxodon and Macrauchenia form a monophyletic group whose sister taxon is not Afrotheria or any of its constituent clades as recently claimed, but instead crown Perissodactyla (horses, tapirs, and rhinoceroses). These results are consistent with the origin of at least some South American native ungulates from 'condylarths', a paraphyletic assembly of archaic placentals. With ongoing improvements in instrumentation and analytical procedures, proteomics may produce a revolution in systematics such as that achieved by genomics, but with the possibility of reaching much further back in time.

Investigating the effect of pH on the aggregation of two surfactant-like octapeptides.

The aggregation of two de novo designed surfactant-like peptides, with sequences Ac-IIKKEENN-OH (P1) and Ac-IIEENNDD-OH (P2), has been studied in aqueous solution at various pH values using titration, Circular dichroism (CD), Fourier transform infrared spectroscopy (FTIR), and atomic force microscopy (AFM). It was found that aggregates of P1 and P2 both display 5 pK(a)'s, some of which differ considerably from the tabulated values for those amino acids. In particular, a lysine of P1 titrated to 4.939 +/- 0.066. CD spectra of P1 were insensitive to pH, while CD spectra of P2 demonstrated a random coil-to-beta-sheet transition as pH was decreased. AFM images confirmed that P1 aggregates were spheres at all pH values and ranged in size from 3 to 20 nm. On the other hand, P2 aggregates were twisted ribbons below pH 4 but spheres less than 10 nm above pH 4. In addition, AFM images demonstrated the partial breakup of these twisted ribbons upon elevating the pH from 3.03 to 3.46 and the virtual disappearance of ribbons at pH 3.82. FTIR spectra of P2 indicate a structural transition from random coil to beta-sheet as pH was decreased. The role of backbone hydrogen bonding as well as charge is discussed.

High throughput production of single-wall carbon nanotube fibres independent of sulfur-source.

Floating catalyst chemical vapor deposition (FC-CVD) methods offer a highly scalable strategy for single-step synthesis and assembly of carbon nanotubes (CNTs) into macroscopic textiles. However, the non-uniform axial temperature profile of a typical reactor, and differing precursor breakdown temperatures, result in a broad distribution of catalyst particle sizes. Spun CNT fibres therefore contain nanotubes with varying diameters and wall numbers. Herein, we describe a general FC-CVD approach to obtain relatively large yields of predominantly single-wall CNT fibres, irrespective of the growth promoter (usually a sulfur compound). By increasing carrier gas (hydrogen) flow rate beyond a threshold whilst maintaining a constant C : H2 mole ratio, CNTs with narrower diameters, a high degree of graphitization (G : D ratio ∼100) and a large throughput are produced, provided S : Fe ratio is sufficiently low. Analysis of the intense Raman radial breathing modes and asymmetric G bands, and a shift in the main nanotube population from thermogravimetric data, show that with increasing flow rate, the fibres are enriched with small diameter, metallic CNTs. Transmission electron microscopy corraborates our primary observation from Raman spectroscopy that with high total flow rates, the fibres produced consist of predominantly small diameter SWCNTs.

Self-assembling peptide detergents stabilize isolated photosystem I on a dry surface for an extended time.

We used a class of designed peptide detergents to stabilize photosystem I (PS-I) upon extended drying under N2 on a gold-coated-Ni-NTA glass surface. PS-I is a chlorophyll-containing membrane protein complex that is the primary reducer of ferredoxin and the electron acceptor of plastocyanin. We isolated the complex from the thylakoids of spinach chloroplasts using a chemical detergent. The chlorophyll molecules associated with the PS-I complex provide an intrinsic steady-state emission spectrum between 650 and 800 nm at -196.15 degrees C that reflects the organization of the pigment-protein interactions. In the absence of detergents, a large blue shift of the fluorescence maxima from approximately 735 nm to approximately 685 nm indicates a disruption in light-harvesting subunit organization, thus revealing chlorophyll-protein interactions. The commonly used membrane protein-stabilizing detergents, N-dodecyl-beta-D-maltoside and N-octyl-beta-D-glucoside, only partially stabilized the approximately 735-nm complex with approximately 685-nm spectroscopic shift. However, prior to drying, addition of the peptide detergent acetyl-AAAAAAK at increasing concentration significantly stabilized the PS-I complex. Moreover, in the presence of acetyl-AAAAAAK, the PS-I complex is stable in a dried form at room temperature for at least 3 wk. Another peptide detergent, acetyl-VVVVVVD, also stabilized the complex but to a lesser extent. These observations suggest that the peptide detergents may effectively stabilize membrane proteins in the solid-state. These designed peptide detergents may facilitate the study of diverse types of membrane proteins.

Enhanced ordering reduces electric susceptibility of liquids confined to graphene slit pores.

The behaviours of a range of polar and non-polar organic liquids (acetone, ethanol, methanol, N-methyl-2-pyrrolidone (NMP), carbon tetrachloride and water) confined to 2D graphene nanochannels with thicknesses in the range of 4.5 Å to 40 Å were studied using classical molecular dynamics and hybrid density functional theory. All liquids were found to organise spontaneously into ordered layers parallel to the confining surfaces, with those containing polar molecules having their electric dipoles aligned parallel to such surfaces. In particular, monolayers of NMP showed remarkable in-plane ordering and low molecular mobility, suggesting the existence of a previously unknown 2D solid-like phase. Calculations for polar liquids showed dramatically reduced static permittivities normal to the confining surfaces; these changes are expected to improve electron tunnelling across the liquid films, modifying the DC electrical properties of immersed assemblies of carbon nanomaterials.

Designer short peptide surfactants stabilize G protein-coupled receptor bovine rhodopsin.

Membrane proteins play vital roles in every aspect of cellular activities. To study diverse membrane proteins, it is crucial to select the right surfactants to stabilize them for analysis. Despite much effort, little progress has been made in elucidating their structure and function, largely because of a lack of suitable surfactants. Here we report the stabilization of a G protein-coupled receptor bovine rhodopsin in solution, using a new class of designer short and simple peptide surfactants. These surfactants consist of seven amino acids with a hydrophilic head, aspartic acid or lysine, and a hydrophobic tail with six consecutive alanines. These peptide surfactants not only enhance the stability of bovine rhodopsin in the presence of lipids and the common surfactants n-dodecyl-beta-D-maltoside and octyl-D-glucoside, but they also significantly stabilize rhodopsin under thermal denaturation conditions, even after lipids are removed. These peptide surfactants are simple, versatile, effective, and affordable. They represent a designer molecular nanomaterial for use in studies of diverse elusive membrane proteins.

Biochemical characterization of the chondroitinase B active site.

Chondroitinase B from Flavobacterium heparinum is the only known lyase that cleaves the glycosaminoglycan, dermatan sulfate (DS), as its sole substrate. A recent co-crystal structure of chondroitinase B with a disaccharide product of DS depolymerization has provided some insight into the location of the active site and suggested potential roles of some active site residues in substrate binding and catalysis. However, this co-crystal structure was not representative of the actual enzyme-substrate complex, because the disaccharide product did not have the right length or the chemical structure of the minimal substrate (tetrasaccharide) involved in catalysis. Therefore, only a limited picture of the functional role of active site residues in DS depolymerization was presented in previous structural studies. In this study, by docking a DS tetrasaccharide into the proposed active site of the enzyme, we have identified novel roles of specific active site amino acids in the catalytic function of chondroitinase B. Our conformational analysis also revealed a unique, symmetrical arrangement of active site amino acids that may impinge on the catalytic mechanism of action of chondroitinase B. The catalytic residues Lys-250, Arg-271, His-272, and Glu-333 along with the substrate binding residues Arg-363 and Arg-364 were mutated using site-directed mutagenesis, and the kinetics and product profile of each mutant were compared with recombinant chondroitinase B. Mutating Lys-250 to alanine resulted in inactivation of the enzyme, potentially attributable to the role of the residue in stabilizing the carbanion intermediate formed during enzymatic catalysis. The His-272 and Glu-333 mutants showed diminished enzymatic activity that could be indicative of a possible role for one or both residues in the abstraction of the C-5 proton from the galactosamine. In addition, the Arg-364 mutant had an altered product profile after exhaustive digestion of DS, suggesting a role for this residue in defining the substrate specificity of chondroitinase B.