Early Molecular Insights into Thanatin Analogues Binding to A. baumannii LptA.

The cationic antimicrobial ß-hairpin, thanatin, was recently developed into drug-like analogues active against carbapenem-resistant Enterobacteriaceae (CRE). The analogues represent new antibiotics with a novel mode of action targeting LptA in the periplasm and disrupting LPS transport. The compounds lose antimicrobial efficacy when the sequence identity to E. coli LptA falls below 70%. We wanted to test the thanatin analogues against LptA of a phylogenetic distant organism and investigate the molecular determinants of inactivity. Acinetobacter baumannii (A. baumannii) is a critical Gram-negative pathogen that has gained increasing attention for its multi-drug resistance and hospital burden. A. baumannii LptA shares 28% sequence identity with E. coli LptA and displays an intrinsic resistance to thanatin and thanatin analogues (MIC values > 32 µg/mL) through a mechanism not yet described. We investigated the inactivity further and discovered that these CRE-optimized derivatives can bind to LptA of A. baumannii in vitro, despite the high MIC values. Herein, we present a high-resolution structure of A. baumannii LptAm in complex with a thanatin derivative 7 and binding affinities of selected thanatin derivatives. Together, these data offer structural insights into why thanatin derivatives are inactive against A. baumannii LptA, despite binding events in vitro.

Peptidomimetic antibiotics disrupt the lipopolysaccharide transport bridge of drug-resistant Enterobacteriaceae.

The rise of antimicrobial resistance poses a substantial threat to our health system, and, hence, development of drugs against novel targets is urgently needed. The natural peptide thanatin kills Gram-negative bacteria by targeting proteins of the lipopolysaccharide transport (Lpt) machinery. Using the thanatin scaffold together with phenotypic medicinal chemistry, structural data, and a target-focused approach, we developed antimicrobial peptides with drug-like properties. They exhibit potent activity against Enterobacteriaceae both in vitro and in vivo while eliciting low frequencies of resistance. We show that the peptides bind LptA of both wild-type and thanatin-resistant Escherichia coli and Klebsiella pneumoniae strains with low-nanomolar affinities. Mode of action studies revealed that the antimicrobial activity involves the specific disruption of the Lpt periplasmic protein bridge.

Peptides in BioNMR Research.

Heteronuclear NMR in combination with isotope labelling is used to study folding of polypeptides induced by metals in the case of metallothioneins, binding of the peptidic allosteric modulator ρ-TIA to the human G-protein coupled α1b adrenergic receptor, the development of therapeutic drugs that interfere with the biosynthesis of the outer membrane of Gram-negative bacteria, and a system in which protein assembly is induced upon peptide addition. NMR in these cases is used to derive precise structural data and to study the dynamics.

Biosynthesis of Glycoconjugate Virus-like Particles (VLPs).

The outermost surface of bacterial pathogens consists primarily of complex carbohydrate structures-polysaccharides, glycolipids, and glycoproteins. To raise a long-lasting and effective immune response against carbohydrate antigens, they generally require covalent attachment to an immunogenic carrier protein-a so-called glycoconjugate vaccine. One hurdle to the development of glycoconjugate vaccines is that carbohydrate antigens remain inaccessible to recombinant production. Thus, the carbohydrate antigen is typically purified from the pathogen and then chemically conjugated to an immunogenic protein. Recent developments in the field of bacterial glycoengineering have opened the opportunity for total recombinant production of glycoconjugate vaccines. In this method, we describe the production of proteinaceous, virus-like particles (VLPs) bearing the conserved N-glycan of Actinobacillus pleuropneumoniae, the causative agent of porcine pleuropneumoniae.

Radiographic outcomes of cable-plate versus cable-grip fixation in periprosthetic fractures of the proximal femur.

BACKGROUND: Newer generation cable-plate designs are commonly used for periprosthetic proximal femur fractures; however, comparisons relative to cable-grips remain limited. The aim of this study was to compare radiographic healing rates of cable-plate versus cable-grip fixation for periprosthetic proximal femur fractures. PATIENTS AND METHODS: Consecutive patients with an acute or chronic Vancouver A, B1, or B2 periprosthetic proximal femur fracture undergoing trochanteric fixation with a cable-plate (n = 46 cases) or cable-grip (n = 24 cases) system were identified retrospectively from a single-centre hospital database (mean follow-up 28 months [range 6-89 months]). Demographics, radiographic fracture healing, and complications were compared between the 2 groups. Radiographic union rates were not different between the cable-grip versus cable-plate group (67% vs. 76% respectively; p = 0.4). Healing rates of greater trochanteric fractures alone were not different between the cable-plate versus cable-grip groups (75% vs. 71% respectively; p = 0.38). The cable-plates were used for a more diverse range of fracture patterns relative to the cable-grips. RESULTS: An increased number of cables was associated with radiographic healing (odds ratio 14 [95% confidence interval 2-64]; p = 0.01), and body mass index had a negative correlation with radiographic healing (odds ratio -0.4 [95% confidence interval 0.5-0.9]. CONCLUSIONS: Similar rates of periprosthetic fracture healing were seen using a cable-grip versus cable-plate system; however, the cable-plate system could be used for a more diverse range of fracture patterns.

Incidence, indications, outcomes, and survivorship of stems in primary total knee arthroplasty.

PURPOSE: The indications, incidence, outcomes, and survivorship of stems in primary total knee arthroplasty (TKA) are lacking in the contemporary literature. Our hypothesis is stems in primary TKA would result in worse outcomes and survivorship. METHODS: All primary TKAs between 2007 and 2011 with 2-year follow-up were identified. Revision TKA or UKA conversion was excluded. Demographic information (age, sex, race, BMI, primary diagnosis, and Charlson-Deyo comorbidity index), outcome measures including KOOS and WOMAC, and any revisions were identified from the registry. A 2:1 matched cohort of non-stemmed/stemmed primary TKA patients was created to compare revision rates and outcomes at baseline and 2 years post-TKA. Subgroup analyses of long versus short stems, 1 versus 2 stems, and cemented versus hybrid stem fixation were completed. Two-sample t tests and Chi-square tests were used to compare conventional and stemmed TKA groups. RESULTS: The registry review included 13,507 conventional TKA and 318 stemmed TKA resulting in an incidence of 2.3 % in primary TKA. The mean follow-up was approximately 49 months in both groups. No difference was found in revision rates between stemmed TKA (2.5 %) and conventional TKA (2.2 %). Patients with post-traumatic arthritis had an odds ratio of 10.5 (95 % CI 1.2-15.3) of receiving stems. Stem length did not affect revision rates. Patients with two stems had worse KOOS and WOMAC scores at baseline which equalized to single-stem patients at 2 years. CONCLUSIONS: The use of stems may provide a survival benefit in complex primary TKA over the short term and no adverse effect on patient outcomes or satisfaction. LEVEL OF EVIDENCE: III.

Survivorship of Extensor Mechanism Allograft Reconstruction After Total Knee Arthroplasty.

BACKGROUND: Extensor mechanism disruption remains a devastating complication after total knee arthroplasty. The purpose of this study is to describe the outcomes of extensor mechanism allograft (EMA) reconstruction in a large single-center case series. METHODS: Consecutive patients with a previous total knee arthroplasty undergoing extensor mechanism reconstruction using a fresh-frozen EMA tensioned in full extension were identified retrospectively from single-center institutional database (N = 25 patients, 26 knees; mean follow-up 68 months [range 22-113 months]). The primary outcome was initial allograft failure, defined as removal of the allograft or extensor lag >30 degrees at most recent follow-up. RESULTS: Sixty-nine percent (18/26) of knees had retained their initial allograft reconstruction at their latest follow-up despite reoperation rates of 58% (15/26). A younger age was significantly associated with failure of the initial allograft reconstruction. Knee Society Scores increased from 101 (38 standard deviation [SD]) to 116 (40 SD) at most recent follow-up for the group as a whole (P = .4). Patients undergoing a reoperation for any cause had lower Knee Society Scores (101 [SD 38] vs 138 [SD 32], respectively; P = .04) at most recent follow-up. CONCLUSION: EMA reconstruction shows adequate overall intermediate-term survival; however, reoperation rates were high and associated with worse functional outcomes.

Patient and Perioperative Variables Affecting 30-Day Readmission for Surgical Complications After Hip and Knee Arthroplasties: A Matched Cohort Study.

BACKGROUND: Changes in reimbursement for total hip and knee arthroplasties (THA and TKA) have placed increased financial burden of early readmission on hospitals and surgeons. Our purpose was to characterize factors of 30-day readmission for surgical complications after THA and TKA at a single, high-volume orthopedic specialty hospital. METHODS: Patients with a diagnosis of osteoarthritis and who were readmitted within 30 days of their unilateral primary THA or TKA procedure between 2010 and 2014. Readmitted patients were matched to nonreadmitted patients 1:2. Patient and perioperative variables were collected for both cohorts. A conditional logistic regression was performed to assess both the patient and perioperative factors and their predictive value toward 30-day readmission. RESULTS: Twenty-one thousand eight hundred sixty-four arthroplasties (THA = 11,105; TKA = 10,759) were performed between 2010 and 2014 at our institution, in which 60 patients (THA = 37, TKA = 23) were readmitted during this 5-year period. The most common reasons for readmission were fracture (N = 14), infection (N = 14), and dislocation (N = 9). Thirty-day readmission for THA was associated with increased procedure time (P = .05), length of stay (LOS) shorter than 2 days (P = .04), discharge to a skilled nursing facility (P = .05), and anticoagulation use other than aspirin (P = .02). Thirty-day readmission for TKA was associated with increased tourniquet time (P = .02), LOS <3 days (P < .01), and preoperative depression (P = .02). In the combined THA/TKA model, a diagnosis of depression increased 30-day readmission (odds ratio 3.5 [1.4-8.5]; P < .01). CONCLUSION: Risk factors for 30-day readmission for surgical complications included short LOS, discharge destination, increased procedure/tourniquet time, potent anticoagulation use, and preoperative diagnosis of depression. A focus on risk factor modification and improved risk stratification models are necessary to optimize patient care using readmission rates as a quality benchmark.

Outcomes of Custom Flange Acetabular Components in Revision Total Hip Arthroplasty and Predictors of Failure.

BACKGROUND: Custom triflange acetabular components (CTAC) have become more popular in the treatment of Paprosky type IIIB defects with an average survivorship of 80% at 4 years. Many studies report survivorship of CTAC, but radiographic parameters of CTAC success or failure have not been previously reported. The purpose of the study was to assess radiographic and patient factors predictive of failure in CTAC. METHODS: A retrospective review of 63 patients with >24 months of follow-up was completed. Continuous and categorical variables were compared between failed vs successful CTAC using Wilcoxon rank-sum test and Fisher exact test, respectively. RESULTS: The failure rate of the CTAC was 13.5% over an average follow-up of 4.32 years (±2.94). Patients had a mean of 2 revisions (range, 0-11) before CTAC implantation. Compared with the contralateral hip center of rotation, the failed CTAC group tended to lateralize the hip center by a mean of 18.29 mm (±11.90 mm) compared to a mean of 9.86 mm (±11.89) in the intact group, although this did not reach statistical significance (P = .1029). The Western Ontario and McMaster Universities Osteoarthritis Index function score improved from 38.94 (±14.23) to 71.35 (±21.96) at most recent follow-up (P = .0002). The Western Ontario and MacMaster Universities Osteoarthritis Index scores were not significantly different between intact and failed CTAC groups. CONCLUSIONS: CTAC tends to lateralize the hip center by approximately 1 cm, and there is a trend toward nearly 2 cm of lateralization in the small subset of failed CTAC. Future efforts should focus on medializing the hip center in CTAC to improve ingrowth and survivorship.