Tetracenomycin X sequesters peptidyl-tRNA during translation of QK motifs.

As antimicrobial resistance threatens our ability to treat common bacterial infections, new antibiotics with limited cross-resistance are urgently needed. In this regard, natural products that target the bacterial ribosome have the potential to be developed into potent drugs through structure-guided design, provided their mechanisms of action are well understood. Here we use inverse toeprinting coupled to next-generation sequencing to show that the aromatic polyketide tetracenomycin X primarily inhibits peptide bond formation between an incoming aminoacyl-tRNA and a terminal Gln-Lys (QK) motif in the nascent polypeptide. Using cryogenic electron microscopy, we reveal that translation inhibition at QK motifs occurs via an unusual mechanism involving sequestration of the 3' adenosine of peptidyl-tRNALys in the drug-occupied nascent polypeptide exit tunnel of the ribosome. Our study provides mechanistic insights into the mode of action of tetracenomycin X on the bacterial ribosome and suggests a path forward for the development of novel aromatic polyketide antibiotics.

Assembly mechanism and cryoEM structure of RecA recombination nucleofilaments from Streptococcus pneumoniae.

RecA-mediated homologous recombination (HR) is a key mechanism for genome maintenance and plasticity in bacteria. It proceeds through RecA assembly into a dynamic filament on ssDNA, the presynaptic filament, which mediates DNA homology search and ordered DNA strand exchange. Here, we combined structural, single molecule and biochemical approaches to characterize the ATP-dependent assembly mechanism of the presynaptic filament of RecA from Streptococcus pneumoniae (SpRecA), in comparison to the Escherichia coli RecA (EcRecA) paradigm. EcRecA polymerization on ssDNA is assisted by the Single-Stranded DNA Binding (SSB) protein, which unwinds ssDNA secondary structures that block EcRecA nucleofilament growth. We report by direct microscopic analysis of SpRecA filamentation on ssDNA that neither of the two paralogous pneumococcal SSBs could assist the extension of SpRecA nucleopolymers. Instead, we found that the conserved RadA helicase promotes SpRecA nucleofilamentation in an ATP-dependent manner. This allowed us to solve the atomic structure of such a long native SpRecA nucleopolymer by cryoEM stabilized with ATPγS. It was found to be equivalent to the crystal structure of the EcRecA filament with a marked difference in how RecA mediates nucleotide orientation in the stretched ssDNA. Then, our results show that SpRecA and EcRecA HR activities are different, in correlation with their distinct ATP-dependent ssDNA binding modes.

Impact of an Ultrasound Demonstration on Vascular Surgery Interest in Preclinical Medical Students.

BACKGROUND: One strategy to address the impending shortage of vascular surgeons is to augment interest in the trainee pipeline. Endovascular procedures are unique to vascular surgery (VS) and endovascular simulations have proven effective at generating VS interest in the past. Like endovascular techniques, the use of ultrasound (US) testing in VS is unique among medical specialties. We hypothesized that an interactive US demonstration would increase VS interest in preclinical medical students. METHODS: We created a 5-point Likert scale survey assessing interest in VS, understanding of VS, likelihood to further investigate VS, choosing VS as a rotational elective, and pursuing VS shadowing and research opportunities. This survey was administered 1 day before and 1 day after the demonstration. Results were compared via paired t-test. A VS attending assisted by a senior registered vascular technologist covered physics, B-mode, continuous, pulsed wave, and color Doppler in an interactive, hands-on experience. Our dedicated US simulation laboratory enabled simultaneous interactive virtual broadcast and in-person learning. All first-year and second-year students at our medical school were invited via e-mail. RESULTS: Five hundred twelve students were invited, 39 attended, and 19 students who completed surveys were included. Sixty eight percent were female. Attendance at the US demonstration resulted in a significant increase in students' interest in vascular surgery (P = 0.012), understanding of vascular surgery (P < 0.001), likelihood to further investigate vascular surgery (P < 0.001), likelihood to choose a vascular surgery rotation (P < 0.001), and likelihood to pursue vascular surgery shadowing and research opportunities (P < 0.001). Although only 2 of 6 in-person attendees returned surveys, their increase in average response to all questions was higher than virtual attendees (+1.80 vs. +0.91, P = 0.043). CONCLUSIONS: Attending an interactive US demonstration significantly increased preclinical medical students' interest in understanding of VS. In-person and virtual attendance both had a positive impact. Such a demonstration may be an effective tool to recruit students. It is imperative that we continue innovating to address the future shortage of vascular surgeons.

Extra-Anatomic Bypass and Excision is Superior to Graft Salvage Attempts with Antibiotic Beads to Treat Vascular Graft Infections in the Groin.

BACKGROUND: This study aimed to determine if conventional extra-anatomic bypass and graft removal versus aggressive attempts at graft preservation have better survival and limb salvage in patients with localized groin wound infections of vascular grafts. METHODS: We conducted a retrospective review of 53 consecutive patients with vascular graft infections presenting in the groin. Treatment groups consisted of group 1 (extra-anatomic bypass and graft excision, n = 22) and group 2 (initial graft preservation attempts with utilization of antibiotic beads, n = 31). In group 2, patients underwent serial debridement and placement of antibiotic beads until culture-negative wounds were achieved. Significantly more patients underwent muscle flap coverage in group 2 (27/31) compared with group 1 (7/22; P < 0.001). Data collected included demographics, comorbidities, intraoperative details, and outcomes, including patency, limb salvage, mortality, and number of procedures. Continuous variables were examined with Student's t-test, and dichotomous variables were examined with chi-squared test. Linear and logistic regressions were used to analyze factors associated with outcomes, in addition to Kaplan-Meier analysis with log rank for actuarial analysis. RESULTS: Both groups were similar with respect to demographics. The overall Kaplan-Meier 1- and 3-year survival rates were 66.2% and 34.1%, with no statistically significant difference between groups. The Kaplan-Meier 1- and 3-year limb salvage rates were 68.8% and 36.6% for group 1 vs. 58.5% and 38.7% for group 2 (P = not significant [NS]). The 1- and 3-year primary patency rates were 71% and 71% in traditional group 1 vs. 72% and 56% in group 2 (P = NS). One-year and 3-year secondary patency rates in traditional group 1 were 83% and 71% vs. 85% and 61% in group 2 (P = NS). Patients in group 1 underwent fewer total procedures when compared with group 2 (2.3 ± 0.2 vs. 5.1 ± 0.7, P = 0.03). The late reinfection rate was significantly less in group 1 (4.5%) compared with group 2 (26%; P = 0.04). Freedom from reinfection at 1 and 3 years were 94% and 94% in traditional group 1 vs. 74% and 62% in group 2 (P = 0.03). Multivariable analysis showed a higher incidence of amputation in patients who suffered reinfection (n = 13, P = 0.049). There was a higher mortality in patients with septic shock (n = 10, P = 0.007) and reinfection (n = 13, P = 0.036). Reinfection was associated with the highest mortality (P = 0.03). CONCLUSIONS: Conventional graft excision with extra-anatomic bypass resulted in similar mortality when compared with aggressive attempts at graft preservation and trended toward improved limb salvage and patency. However, attempts at graft preservation with antibiotic beads resulted in a significantly higher reinfection rate and greater number of procedures, and therefore, this approach should be used very selectively.

Surgical versus transcatheter palliation for insufficient pulmonary blood supply in infants with cyanotic CHD.

Infants with complex cyanotic CHD can become symptomatic from insufficient pulmonary blood supply following either ductal closure or due to outflow tract obstruction. Blalock-Taussig shunt mortality remains significant and recent studies have highlighted the advantages of using transcatheter alternatives. We present here our experience in changing our primary choice of palliation from the Blalock-Taussig shunt to transcatheter palliation with either a ductal stent or, if antegrade flow is present, a right ventricular outflow tract stent.This is a retrospective, single-unit cohort study. Eighty-seven infants underwent palliation for insufficient pulmonary blood flow at under 3 months of age between 2012 and 2019. On an intention-to-treat basis, 29 underwent insertion of a Blalock-Taussig shunt, 36 duct stents, and 22 right ventricular outflow tract stents at median ages of 15, 9, and 32 days, respectively, and median weights of 3.3, 3.1, and 3.1 kg, respectively. No primary Blalock-Taussig shunts have been performed in our institution since 2017.At 30-days there had been one death in each group (univariable p = 0.93) and deaths prior to repair totalled three in the shunt group, four in the ductal stent group, and two in the right ventricular outflow tract stent group (univariable p = 0.93). Reintervention on the pulmonary circuit prior to next stage of surgery was more frequent in those undergoing transcatheter intervention, reaching statistical significance by logrank (p = 0.012).In conclusion, within this work we provide further evidence of the safety and efficacy of transition from a primary surgical to primary transcatheter palliation pathway in infants with insufficient pulmonary blood supply.

Association between current medication use and progression of radiographic knee osteoarthritis: data from the osteoarthritis initiative.

OBJECTIVE: Use of specific medications may accelerate the progression of radiographic knee OA (RKOA). Our aim was to examine the effect of medication use on the progression of RKOA. METHODS: We used longitudinal data from the Osteoarthritis Initiative (OAI), an observational study of risk factors for knee OA. At baseline, we selected participants with RKOA (Kellgren-Lawrence grade ≥2) and excluded those with a history of knee-related injury/surgery and other musculoskeletal disorders. Current medication use (use/non-use in the previous 30 days) and radiographic medial minimum joint space width (mJSW) data were available at baseline and annually up to 96 months follow-up. We used random effects, panel regression to assess the association between current medication use (non-users as reference group) and change in mJSW. RESULTS: Of 2054 eligible participants, 2003 participants with baseline mJSW data were included [55.7% female, mean age 63.3 (s.d. 8.98) years]. Of seven medication classes, at baseline NSAIDs were the most frequently used analgesia (14.7%), anti-histamine (10.4%) use was frequent and the following comorbidity medications were used most frequently: statins (27.4%), anti-hypertensives (up to 15.0%), anti-depressant/anxiolytics/psychotropics (14.0%), osteoporosis-related medication (10.9%) and diabetes-related medication (6.9%). Compared with current non-users, current use of NSAIDs was associated with a loss of mJSW (b = -0.042, 95% CI -0.08, -0.0004). No other associations were observed. CONCLUSIONS: In current users of NSAIDs, mJSW loss was increased compared with current non-users in participants with RKOA. Clinical trials are required to assess the potential disease-modifying effects of these medications.

Quantitative and semi-quantitative assessment of synovitis on MRI and the relationship with symptoms in symptomatic knee osteoarthritis.

OBJECTIVES: Synovitis in symptomatic knee OA (KOA) is common and is associated with joint symptoms. Optimal synovial measurement on MRI is, however, unclear. Our aims were to examine the relationship between MRI measures of synovitis and knee symptoms in symptomatic KOA. METHODS: Data from a randomized, multicentre, placebo-controlled trial (UK-VIDEO) of vitamin-D therapy in symptomatic KOA were utilized. Participants reported knee symptoms using WOMAC at baseline and annually. On contrast-enhanced (CE) MRI, synovial thickness was measured using established, semi-quantitative methods whilst synovial tissue volume (STV) was assessed as absolute STV (aSTV) and relative to the width of femoral condyle (rSTV). STV of the infrapatellar region was also assessed. Associations between synovial measures and symptoms were analysed using multiple linear regression modelling. RESULTS: No linear association was observed between knee symptoms and synovitis thickness scores. Whole-joint aSTV (0.88, 95% CI: 0.17, 1.59) and infrapatellar aSTV (5.96, 95% CI: 1.22, 10.7) were positively associated with knee pain. Whole-joint rSTV had a stronger association with pain (7.96, 95% CI: 2.60, 13.33) and total scores (5.63, 95% CI: 0.32, 10.94). Even stronger associations were found for infrapatellar rSTV with pain (55.47, 95% CI: 19.99, 90.96), function (38.59, 95% CI: 2.1, 75.07) and total scores (41.64, 95% CI: 6.56, 76.72). CONCLUSIONS: Whole-joint and site-specific infrapatellar STV measures on CE-MRI were associated with knee pain, respectively. Volumes relative to the size of the femoral condyle may be promising outcome measures in KOA trials.

Monitoring work-related physical activity and estimating lower-limb loading: a proof-of-concept study.

BACKGROUND: Physical activity (PA) is important to general health and knee osteoarthritis (OA). Excessive workplace PA is an established risk factor for knee OA however, appropriate methods of measurement are unclear. There is a need to examine and assess the utility of new methods of measuring workplace PA and estimating knee load prior to application to large-scale, knee OA cohorts. Our aims, therefore, were to monitor workplace PA and estimate lower-limb loading across different occupations in health participants. METHODS: Twenty-four healthy adults, currently working full-time in a single occupation (≥ 35 h/week) and free of musculoskeletal disease, comorbidity and had no history of lower-limb injury/surgery (past 12-months) were recruited across New South Wales (Australia). A convenience sample was recruited with occupations assigned to levels of workload; sedentary, light manual and heavy manual. Metrics of workplace PA including tasks performed (i.e., sitting), step-count and lower-limb loading were monitored over 10 working days using a daily survey, smartwatch, and a smartphone. RESULTS: Participants of light manual occupations had the greatest between-person variations in mean lower-limb load (from 2 to 59 kg*m/s3). Lower-limb load for most participants of the light manual group was similar to a single participant in heavy manual work (30 kg*m/s3) and was at least three times greater than the sedentary group (2 kg*m/s3). The trends of workplace PA over working hours were largely consistent, per individual, but rare events of extreme loads were observed across all participants (up to 760 kg*m/s3). CONCLUSIONS: There are large interpersonal variations in metrics of workplace PA, particularly among light and heavy manual occupations. Our estimates of lower-limb loading were largely consistent with pre-conceived levels of physical demand. We present a new approach to monitoring PA and estimating lower-limb loading, which could be applied to future occupational studies of knee OA.

Multivalent Ligand Binding to Cell Membrane Antigens: Defining the Interplay of Affinity, Valency, and Expression Density.

Nature uses multivalency to govern many biological processes. The development of macromolecular and cellular therapies has largely been dependent on engineering similar polyvalent interactions to enable effective targeting. Such therapeutics typically utilize high-affinity binding domains that have the propensity to recognize both antigen-overexpressing tumors and normal-expressing tissues, leading to "on-target, off-tumor" toxicities. One strategy to improve these agents' selectivity is to reduce the binding affinity, such that biologically relevant interactions between the therapeutic and target cell will only exist under conditions of high avidity. Preclinical studies have validated this principle of avidity optimization in the context of chimeric antigen receptor (CAR) T cells; however, a rigorous analysis of this approach in the context of soluble multivalent targeting scaffolds has yet to be undertaken. Using a modular protein nanoring capable of displaying ≤8 fibronectin domains with engineered specificity for a model antigen, epithelial cell adhesion molecule (EpCAM), this study demonstrates that binding affinity and ligand valency can be optimized to afford discrimination between EpCAMHigh (2.8-3.8 × 106 antigens/cell) and EpCAMLow (5.2 × 104 to 2.2 × 105 antigens/cell) tissues both in vitro and in vivo.

Measurement of synovial tissue volume in knee osteoarthritis using a semiautomated MRI-based quantitative approach.

PURPOSE: Synovitis is common in knee osteoarthritis and is associated with both knee pain and progression of disease. Semiautomated methods have been developed for quantitative assessment of structure in knee osteoarthritis. Our aims were to apply a novel semiautomated assessment method using 3D active appearance modeling for the quantification of synovial tissue volume (STV) and to compare its performance with conventional manual segmentation. METHODS: Thirty-two sagittal T1 -weighted fat-suppressed contrast-enhanced MRIs were assessed for STV by a single observer using 1) manual segmentation and 2) a semiautomated approach. We compared the STV analysis using the semiautomated and manual segmentation methods, including the time taken to complete the assessments. We also examined the reliability of STV assessment using the semiautomated method in a subset of 12 patients who had participated in a clinical trial of vitamin D therapy in knee osteoarthritis. RESULTS: There was no significant difference in STV using the semiautomated quantitative method compared to manual segmentation, mean difference = 207.2 mm3 (95% confidence interval -895.2 to 1309.7). The semiautomated method was significantly quicker than manual segmentation (18 vs. 71 min). For the semiautomated method, intraobserver agreement was excellent (intraclass correlation coefficient (3,1) = 0.99) and interobserver agreement was very good (intraclass correlation coefficient (3,1) = 0.83). CONCLUSION: We describe the application of a semiautomated method that is accurate, reliable, and quicker than manual segmentation for assessment of STV. The method may help increase efficiency of image assessment in large imaging studies and may also assist investigation of treatment efficacy in knee osteoarthritis.

Effect of Vitamin D supplementation on synovial tissue volume and subchondral bone marrow lesion volume in symptomatic knee osteoarthritis.

BACKGROUND: Data from a recent clinical trial of vitamin D therapy in knee OA suggests that, compared to placebo, vitamin D therapy may be associated with a reduction in effusion-synovitis. Our aim was, using contrast-enhanced (CE) magnetic resonance imaging (MRI), to examine the effect of vitamin D therapy on synovial tissue volume (STV) and also subchondral bone marrow lesion (BML) volume in men and women with symptomatic knee OA. METHODS: Data was acquired from participants who took part in a randomised placebo-controlled trial (UK VIDEO) investigating the effect of vitamin D therapy (800 IU cholecalciferol daily) on radiographic joint space narrowing. A subsample had serial CE MRI scans acquired during the trial. Subjects with serial images were assessed (N = 50) for STV and subchondral BML volume. The difference in the mean change from baseline in these structural outcomes between intervention and placebo groups was assessed using random-effects modelling. RESULTS: The mean age of the 50 subjects (24 active group, 26 placebo group) who contributed data to the analysis was 63.3 years (SD 6.5) and 74% were female. There was no significant difference at 2 years follow-up between the vitamin D and placebo groups in the mean change from baseline for STV (93.9 mm3, 95% CI -1605.0 to 1792.7) and subchondral BML volume (- 313.5 mm3, 95% CI -4244.7 to 3617.7). CONCLUSIONS: Vitamin D supplementation does not appear to have an effect on synovitis or BML volume in patients with symptomatic knee OA. TRIAL REGISTRATION: VIDEO was registered with EudraCT: ref. 2004-000169-37. The protocol for the trial can be accessed at https://www.ctu.mrc.ac.uk/studies/all-studies/v/video/.

Bacterial transformation: ComFA is a DNA-dependent ATPase that forms complexes with ComFC and DprA.

Pneumococcal natural transformation contributes to genomic plasticity, antibiotic resistance development and vaccine escape. Streptococcus pneumoniae, like many other naturally transformable species, has evolved sophisticated protein machinery for the binding and uptake of DNA. Two proteins encoded by the comF operon, ComFA and ComFC, are involved in transformation but their exact molecular roles remain unknown. In this study, we provide experimental evidence that ComFA binds to single stranded DNA (ssDNA) and has ssDNA-dependent ATPase activity. We show that both ComFA and ComFC are essential for the transformation process in pneumococci. Moreover, we show that these proteins interact with each other and with other proteins involved in homologous recombination, such as DprA, thus placing the ComFA-ComFC duo at the interface between DNA uptake and DNA recombination during transformation.

Density-dependent resource selection by a terrestrial herbivore in response to sea-to-land nutrient transfer by seals.

Sea-to-land nutrient transfers can connect marine food webs to those on land, creating a dependence on marine webs by opportunistic species. We show how nitrogen, imported by gray seals, Halichoerus grypus, and traced through stable isotope (δ15 N) measurements in marram grass, Ammophila breviligulata, significantly alters foraging behavior of a free-roaming megaherbivore (feral horses, Equus ferus caballus) on Sable Island, Canada. Values of δ15 N correlated with protein content of marram and strongly related to pupping-seal densities, and positively influenced selective foraging by horses. The latter was density dependent, consistent with optimal foraging theory. We present the first demonstration of how sea-to-land nutrient transfers can affect the behavioral process of resource selection (resource use relative to availability) of terrestrial consumers. We hypothesize that persistence of horses on Sable Island is being facilitated by N subsidies. Our results have relevance to advancing theory on trophic dynamics in island biogeography and metaecosystem ecology.

Formyl Group Activation of a Bromopyrrole Ester in Suzuki Cross-Coupling Reactions: Application to a Formal Synthesis of Polycitone A and B and Polycitrin A.

A new pyrrole building block is described, which allows for the regiospecific synthesis of 2,3,5-trisubstituted pyrroles and 2,3,4,5- tetrasubstituted pyrroles. Optimization studies are presented for the preparation of the pyrrole building block along with the evaluation of various cross-coupling conditions and cross-coupling agents. A short, formal synthesis of the natural products Polycitone A, Polycitone B and Polycitrin A from the pyrrole building block is also described.

Cholinergic mu-opioid receptor deletion alters reward preference and aversion-resistance.

The endogenous opioid system has been implicated in alcohol consumption and preference in both humans and animals. The mu opioid receptor (MOR) is expressed on multiple cells in the striatum, however little is known about the contributions of specific MOR populations to alcohol drinking behaviors. The current study used mice with a genetic deletion of MOR in cholinergic cells (ChAT-Cre/Oprm1fl/fl) to examine the role of MORs expressed in cholinergic interneurons (CINs) in home cage self-administration paradigms. Male and female ChAT-Cre/Oprm1fl/fl mice were generated and heterozygous Cre+ (knockout) and Cre- (control) mice were tested for alcohol consumption in two drinking paradigms: limited access "Drinking in the Dark" and intermittent access. Quinine was added to the drinking bottles in the DID experiment to test aversion-resistant, "compulsive" drinking. Nicotine and sucrose drinking were also assessed so comparisons could be made with other rewarding substances. Cholinergic MOR deletion did not influence consumption or preference for ethanol (EtOH) in either drinking task. Differences were observed in aversion-resistance in males with Cre + mice tolerating lower concentrations of quinine than Cre-. In contrast to EtOH, preference for nicotine was reduced following cholinergic MOR deletion while sucrose consumption and preference was increased in Cre+ (vs. Cre-) females. Locomotor activity was also greater in females following the deletion. These results suggest that cholinergic MORs participate in preference for rewarding substances. Further, while they are not required for consumption of alcohol alone, cholinergic MORs may influence the tendency to drink despite negative consequences.

Sex, but not early life stress, effects on two-bottle choice alcohol drinking behaviors in mice.

In humans, early life stress (ELS) is associated with an increased risk for developing both alcohol use disorder (AUD) and post-traumatic stress disorder (PTSD). We have previously used an infant footshock model to explore this shared predisposition. Infant footshock produces stress-enhanced fear learning (SEFL) in rats and mice and increases aversion-resistant alcohol drinking in rats. The goal of the current study was to extend this model of comorbid PTSD and AUD to male and female C57BL/6J mice. Acute ELS was induced using 15 foot-shocks on postnatal day 17. In adulthood, after PND 90, ethanol drinking behavior was tested in one of three two-bottle choice drinking paradigms: continuous access, limited access drinking in the dark, or intermittent access. In continuous access, mice were given 24 h access to 5% or 10% ethanol and water. Each ethanol concentration was provided for five consecutive drinking sessions. In limited access drinking in the dark, mice were given 2 h of access to 15% ethanol and water across 15 sessions. Ethanol was provided 3 h into the dark cycle to maximize task engagement when mice are most active. In intermittent access, mice were presented with 20% ethanol and water Monday, Wednesday, and Friday, for four consecutive weeks. In a fifth week of intermittent access drinking, increasing concentrations of quinine (10 mg/L, 100 mg/L, and 200 mg/L) were added to the ethanol to test aversion-resistant drinking. Our results indicate that infant footshock does not influence adult ethanol consumption in mice. Infant footshock did not affect ethanol-only consumption or preference in any of the three drinking paradigms. Further, and in contrast to our previous results in rats, infant footshock did not appear to influence consumption of quinine-adulterated ethanol. The biological sex of the mice did affect ethanol-only consumption in all three drinking paradigms, with females consuming more ethanol than males. Preference for ethanol vs. water was higher in females only under continuous access conditions. Our results suggest that infant footshock alone may not be sufficient to increase drinking levels in mice. We hypothesize that infant footshock may require a secondary, adolescent stress exposure to influence ethanol drinking behavior. Further research is needed to create a valid model of PTSD-AUD comorbidity in male and female mice.