Urinary Chromium Excretion in Response to an Insulin Challenge Is Not a Biomarker for Chromium Status

Over 50 years ago, chromium (Cr) was proposed to be an essential trace element; however, recent studies indicate that this status should be removed as the effects of Cr supplementation appear to be pharmacological rather than nutritional. The pharmacological basis for Cr's effects can explain the inability of investigators to discover a biomarker for Cr status. One potential biomarker has not been examined to date. Cr is known to be mobilized in the body in response to insulin (or insulin release in response to a glucose challenge), resulting in an increase in urinary Cr excretion. The magnitude of increase in urinary Cr loss as a function of dietary Cr intake was tested as a potential biomarker for Cr. Zucker lean rats housed in carefully controlled metal-free conditions were provided a series of purified diets containing variable Cr contents (from 16 μg/kg diet to 2,000 μg/kg) for 23 weeks. The 16 μg/kg diet contained less Cr than any diet examined to date. Urine samples were collected before and after insulin and glucose challenges (0, 2, 6, and 12 h postinjection). Urinary Cr levels were analyzed by the standard method of addition using graphite furnace atomic absorption. The rate of urinary Cr loss after a glucose or insulin challenge was found to not be dependent on the Cr content of the rats' diets. Blood iron levels of the rats were also measured to determine if the addition of Cr to the diet altered iron status. The Cr content of the diet was found to have no affect on blood iron levels. Overall, the study demonstrated that insulin-stimulated urinary Cr excretion cannot be used as a biomarker for Cr status.     

37 A comparative study of ribosomal proteins: linkage between amino acid distribution and ribosomal assembly

Assembly of the ribosome from its protein and RNA constituents has been studied extensively over the past 50?years, and here we utilize a comparative analysis approach to relate the composition of ribosomal proteins (r-proteins) to their role in the assembly process. We computed the amino acid distributions for the 30S subunit r-protein sequences from 560 bacterial species and compared this composition to those of other house-keeping proteins from the same species. We found that r-proteins have a significantly higher content of positively charged residues (Lysine, K, and Arginine, R) than do nonribosomal proteins (10% for R and 11% for K in r-proteins, vs. 4.7% R and 5.9% K in non-ribosomal proteins), which is consistent with prior knowledge of net positive charges carried by r-proteins (Baker et al., 2001; Klein et al., 2004; Burton et al., 2012). Furthermore, these two residues are also highly represented at contact sites along the protein/RNA interface (contact enrichment factor (CEF)?>?1). These results provide further evidence of the importance of electrostatic interactions between the positively charged proteins and negatively charged ribosomal RNA (rRNA) during ribosome assembly. Other highly represented contact residues include polar and aromatic residues, which are likely to interact with rRNA via hydrogen bonds and base stacking interactions, respectively. Interestingly, the proportion of K residues generally decreases with r-protein size, reflecting a negative correlation between protein lengths and the proportion of K (Spearman’s rank correlation, ρ?=??0.802, p?=?2.60e???5). We suggest that this trend helps the smaller r-proteins, which experience higher translational entropy than large proteins, overcome the increased free energy barrier during assembly. When the r-protein sequences were categorized according to the species’ optimal growth temperature, we found that thermophiles show increased R, Isoleucine (I), and Tyrosine (Y) content, whereas mesophiles have increased proportions of Serine (S) and Threonine (T). These results reflect one typical distinction between thermophiles and mesophiles (Kumar and Nussinov 2001), yet these differences in amino acid distributions do not extend to their respective contact sites. That is, the makeup of thermophilic and mesophilic r-protein contact residues are not significantly different (p?>?0.01). This indicates that, while the percent compositions of amino acids relating to qualities such as thermostability and protein folding are expected to vary with environmental temperature, the distributions of residues in contact with rRNA are comparable for all bacterial species. From this, we conclude that the electrostatic interactions that guide ribosome assembly are independent of temperature.     

Disruption and eradication of P. aeruginosa biofilms using nitric oxide-releasing chitosan oligosaccharides

Biofilm disruption and eradication were investigated as a function of nitric oxide- (NO) releasing chitosan oligosaccharide dose and the results compared with control (ie non-NO-releasing) chitosan oligosaccharides and tobramycin. Quantification of biofilm expansion/contraction and multiple-particle tracking microrheology were used to assess the structural integrity of the biofilm before and after antibacterial treatment. While tobramycin had no effect on the physical properties of the biofilm, NO-releasing chitosan oligosaccharides exhibited dose-dependent behavior with biofilm degradation. Control chitosan oligosaccharides increased biofilm elasticity, indicating that the scaffold may mitigate the biofilm disrupting power of nitric oxide somewhat. The results from this study indicate that nitric oxide-releasing chitosan oligosaccharides act as dual-action therapeutics capable of eradicating and physically disrupting P. aeruginosa biofilms.     

Factors affecting oral regurgitation by larval spruce budworm

This study evaluated factors that influence the regurgitation behaviour of sixth instar spruce budworm, Choristoneura fumiferana Clemens (Lepidoptera: Tortricidae), reared on balsam fir, Abies balsamea (L.) Mill. (Pinaceae), under various experimental conditions in the laboratory. Upon physical disturbance, larvae discharged a median volume of regurgitant of 0.4 μl when fed and 1.6 μl when food‐deprived. Larvae deprived of food for 24 or 48 h disgorged more regurgitant than larvae feeding on balsam fir foliage, and the effect was consistent for laboratory‐reared and field‐collected larvae. The water content of the foliage fed upon by larvae had no immediate impact on the volume of regurgitant; following a 24‐h period of food deprivation, however, larvae that previously fed on fresh foliage discharged >2.5 times more regurgitant than larvae that previously fed on dry foliage. Self‐regulated regurgitation by larvae, measured using the number of regurgitant stains on filter paper, was >10 times higher when larvae had access to balsam fir foliage than when they were starved. The number of larvae confined inside the Petri dish (one or four individuals) had a relatively small effect on regurgitation. Larvae were deterred from feeding when balsam fir needles were entirely covered with regurgitant, but not when only a portion of the foliage was treated. These results suggest that the regurgitant does not serve as resource marking or spacing pheromone. The high level of regurgitation by larvae after contact with ants suggests that the regurgitant has evolved in part as a defence mechanism against natural enemies.     

Global metabolic profiling to model biological processes of aging in twins

Aging is intimately linked to system‐wide metabolic changes that can be captured in blood. Understanding biological processes of aging in humans could help maintain a healthy aging trajectory and promote longevity. We performed untargeted plasma metabolomics quantifying 770 metabolites on a cross‐sectional cohort of 268 healthy individuals including 125 twin pairs covering human lifespan (from 6 months to 82 years). Unsupervised clustering of metabolic profiles revealed 6 main aging trajectories throughout life that were associated with key metabolic pathways such as progestin steroids, xanthine metabolism, and long‐chain fatty acids. A random forest (RF) model was successful to predict age in adult subjects (≥16 years) using 52 metabolites (R² = .97). Another RF model selected 54 metabolites to classify pediatric and adult participants (out‐of‐bag error = 8.58%). These RF models in combination with correlation network analysis were used to explore biological processes of healthy aging. The models highlighted established metabolites, like steroids, amino acids, and free fatty acids as well as novel metabolites and pathways. Finally, we show that metabolic profiles of twins become more dissimilar with age which provides insights into nongenetic age‐related variability in metabolic profiles in response to environmental exposure.     

Features of wild-type human SOD1 limit interactions with misfolded aggregates of mouse G86R Sod1

Mutations in the gene encoding superoxide dismutase 1 (SOD1) account for about 20% of the cases of familial amyotrophic lateral sclerosis (fALS). It is well established that mutations in SOD1, associated with fALS, heighten the propensity of the protein to misfold and aggregate. Although aggregation appears to be a factor in the toxicity of mutant SOD1s, the precise nature of this toxicity has not been elucidated. A number of other studies have now firmly established that raising the levels of wild-type (WT) human SOD1 (hSOD1) proteins can in some manner augment the toxicity of mutant hSOD1 proteins. However, a recent study demonstrated that raising the levels of WT-hSOD1 did not affect disease in mice that harbor a mouse Sod1 gene (mSod1) encoding a well characterized fALS mutation (G86R). In the present study, we sought a potential explanation for the differing effects with WT-hSOD1 on the toxicity of mutant hSOD1 versus mutant mSod1. In the cell culture models used here, we observe poor interactions between WT-hSOD1 and misfolded G86R-mSod1, possibly explaining why over-expression of WT-hSOD1 does not synergize with mutant mSod1 to accelerate the course of the disease in mice.     

Genomic and Functional Analysis of the Type VI Secretion System in Acinetobacter

The genus Acinetobacter is comprised of a diverse group of species, several of which have raised interest due to potential applications in bioremediation and agricultural purposes. In this work, we show that many species within the genus Acinetobacter possess the genetic requirements to assemble a functional type VI secretion system (T6SS). This secretion system is widespread among Gram negative bacteria, and can be used for toxicity against other bacteria and eukaryotic cells. The most studied species within this genus is A. baumannii, an emerging nosocomial pathogen that has become a significant threat to healthcare systems worldwide. The ability of A. baumannii to develop multidrug resistance has severely reduced treatment options, and strains resistant to most clinically useful antibiotics are frequently being isolated. Despite the widespread dissemination of A. baumannii, little is known about the virulence factors this bacterium utilizes to cause infection. We determined that the T6SS is conserved and syntenic among A. baumannii strains, although expression and secretion of the hallmark protein Hcp varies between strains, and is dependent on TssM, a known structural protein required for T6SS function. Unlike other bacteria, A. baumannii ATCC 17978 does not appear to use its T6SS to kill Escherichia coli or other Acinetobacter species. Deletion of tssM does not affect virulence in several infection models, including mice, and did not alter biofilm formation. These results suggest that the T6SS fulfils an important but as-yet-unidentified role in the various lifestyles of the Acinetobacter spp.