Development of Novel Focal Irradiation Tool for High-Precision Irradiation Using Clinical Brachytherapy System

PURPOSE/OBJECTIVE(S)

Several small animals, including mice, are used to conduct research on state-of-the-art radiation therapy techniques or treatment-related toxicity. However, it is difficult to conduct the focal irradiation to a shallow depth on small animals, because irradiation using LINAC has limitations in energy and field size. The purpose of this paper was to develop a focal irradiation tool for high-precision irradiation and to evaluate beam characteristics.

MATERIALS/METHODS

We designed the collimator of 1 mm diameter consisting of tungsten material for high-precision irradiation applied to the clinical brachytherapy system and the percent depth dose and horizontal profile were measured. We compared the depth dose and horizontal profile with 4 mm diameter SRS cone for 6 MV in LINAC. We measured the PDD and horizontal profile using EBT3 film for high-precision irradiation of 1 mm diameter using Ir-192 source. In case of 4 mm diameter, the beam was measured using edge detector. In addition, all measurements were compared with the results of planning tool simulation.

RESULTS

In case of focal irradiation tool, the maximum dose showed at the surface for both measurement and simulation, and 26% and 32% doses at 1 mm depth, respectively. In addition, FWHM at a 1 mm depth showed that high-precision irradiation was possible with measurement and simulation results of 1.86 and 1.28 mm. In case of LINAC, the maximum dose was showed at a depth of 1 cm and 0.8 cm in the measurement and simulation, respectively. Even if the smallest cone is used, the FWHM at a dmax depth was 4.0 mm in both simulation and measurement.

CONCLUSION

We overcame the limitation for energy and field size through the focal irradiation tool for high-precision irradiation. The focal irradiation tool enables high dose delivery to the shallow depth. In addition, small FWHM reduced dose delivery to the periphery at a specific depth and enabled accurate dose delivery. These results mean that the focal irradiation tool can be useful in small animal experiments that require accurate doses near the shallow depth.

A Photograph-Based Visualization and Prediction Framework for Radiation-Induced Dermatitis

PURPOSE/OBJECTIVE(S)

This study aimed to suggest a photograph-based prediction system for acute radiation-induced dermatitis (RID), which can be applied to notify patients about the risk of the development of skin discomfort during radiotherapy.

MATERIALS/METHODS

The proposed system compared the spatial dose distribution with the RID region using the following methods. Skin photographs of patients were taken using an RGB-depth camera to acquire the shape information of RID. The skin surface data measured from the camera was registered with the shape of the external body contour using an iterative closest point algorithm. Spatial dose distribution of skin was extracted from the external body contour to a depth of 2 mm and projected onto the plane of the skin photograph using a transformation matrix for skin depth data. To compare the spatial distribution of skin dose with the shape of RID, the region of RID in patients' skin was delineated on photographs into three toxicity symptoms referring to the CTCAE criteria grade 1 (skin redness), grade 2 (dry desquamation), and grade 3 (moist desquamation). The degree of overlap between the shape of each RID and skin dose distribution was evaluated using the dice similarity coefficient (DSC). Threshold doses for predicting RID occurrence were estimated by skin isodose lines with the highest DSC. The developed system was validated using data from 19 patients who received volumetric modulated arc therapy for head-neck cancer at a single institution.

RESULTS

Threshold doses for RID grades 1, 2, and 3 were estimated using 18, 18, and 2 individual RID labels delineated on skin photographs, respectively. Isodose lines with the highest DSC for RID grades 1, 2, and 3 were calculated as 26.0 Gy, 36.5 Gy, and 54.0 Gy, respectively. A strong overlap (average DSC > 0.6) was observed between isodose skin lines and the shape of RID labels in all RID grades.

CONCLUSION

Assessing the spatial information of skin dose can be helpful in predicting acute RID. The region of RID shows a strong similarity with the skin dose distribution in head-neck patients. Visualization of skin dose on the patient photograph is potent to patient education for preparing the cosmetic discomfort during radiotherapy, which may lead to the improvement of the patient satisfaction in treatment.

Control of fibrosis with enhanced safety via asymmetric inhibition of prolyl-tRNA synthetase 1

Prolyl-tRNA synthetase 1 (PARS1) has attracted much interest in controlling pathologic accumulation of collagen containing high amounts of proline in fibrotic diseases. However, there are concerns about its catalytic inhibition for potential adverse effects on global protein synthesis. We developed a novel compound, DWN12088, whose safety was validated by clinical phase 1 studies, and therapeutic efficacy was shown in idiopathic pulmonary fibrosis model. Structural and kinetic analyses revealed that DWN12088 binds to catalytic site of each protomer of PARS1 dimer in an asymmetric mode with different affinity, resulting in decreased responsiveness at higher doses, thereby expanding safety window. The mutations disrupting PARS1 homodimerization restored the sensitivity to DWN12088, validating negative communication between PARS1 promoters for the DWN12088 binding. Thus, this work suggests that DWN12088, an asymmetric catalytic inhibitor of PARS1 as a novel therapeutic agent against fibrosis with enhanced safety.

EPRS1 Controls the TGF- Signaling Pathway via Interaction with TβRI in Hepatic Stellate Cell

Glutamyl-prolyl-tRNA synthetase 1 (EPRS1) is known to associated with fibrosis through its catalytic activity to produce prolyl-tRNA. Although its catalytic inhibitor halofuginone (HF) has been known to inhibit the TGF-β pathway as well as to reduce prolyl-tRNA production for the control of fibrosis, the underlying mechanism how EPRS1 regulates the TGF-β pathway was not fully understood. Here, we show a noncatalytic function of EPRS1 in controlling the TGF-β pathway and hepatic stellate cell activation via its interaction with TGF-β receptor I (TβRI). Upon stimulation with TGF-β, EPRS1 is phosphorylated by TGF-β-activated kinase 1 (TAK1), leading to its dissociation from the multi-tRNA synthetase complex and subsequent binding with TβRI. This interaction increases the association of TβRI with SMAD2/3 while decreases that of TβRI with SMAD7. Accordingly, EPRS1 stabilizes TβRI by preventing the ubiquitin-mediated degradation of TβRI. HF disrupts the interaction between EPRS1 and TβRI, and reduces TβRI protein levels, leading to inhibition of the TGF-β pathway. In conclusion, this work suggests the novel function of EPRS1 involved in the development of fibrosis by regulating the TGF-β pathway and the antifibrotic effects of HF by controlling both of EPRS1 functions.

Structural and biochemical insights into PsEst3, a new GHSR-type esterase obtained from Paenibacillus sp. R4

PsEst3, a psychrophilic esterase obtained from Paenibacillus sp. R4, which was isolated from the permafrost of Alaska, exhibits relatively high activity at low temperatures. Here, crystal structures of PsEst3 complexed with various ligands were generated and studied at atomic resolution, and biochemical studies were performed to analyze the structure-function relationship of PsEst3. Certain unique characteristics of PsEst3 distinct from those of other classes of lipases/esterases were identified. Firstly, PsEst3 contains a conserved GHSRA/G pentapeptide sequence in the GxSxG motif around the nucleophilic serine. Additionally, it contains a conserved HGFR/K consensus sequence in the oxyanion hole, which is distinct from that in other lipase/esterase families, as well as a specific domain composition (for example a helix-turn-helix motif) and a degenerative lid domain that exposes the active site to the solvent. Secondly, the electrostatic potential of the active site in PsEst3 is positive, which may cause unintended binding of negatively charged chemicals in the active site. Thirdly, the last residue of the oxyanion hole-forming sequence, Arg44, separates the active site from the solvent by sealing the acyl-binding pocket, suggesting that PsEst3 is an enzyme that is customized to sense an unidentified substrate that is distinct from those of classical lipases/esterases. Collectively, this evidence strongly suggests that PsEst3 belongs to a distinct family of esterases.

A New Approach to Quantify and Grade Radiation Dermatitis Using Deep-Learning Segmentation in Skin Photographs

AIMS

Objective evaluation of radiation dermatitis is important for analysing the correlation between the severity of radiation dermatitis and dose distribution in clinical practice and for reliable reporting in clinical trials. We developed a novel radiation dermatitis segmentation system based on convolutional neural networks (CNNs) to consistently evaluate radiation dermatitis.

MATERIALS AND METHODS

The radiation dermatitis segmentation system is designed to segment the radiation dermatitis occurrence area using skin photographs and skin-dose distribution. A CNN architecture with a dilated convolution layer and skip connection was designed to estimate the radiation dermatitis area. Seventy-three skin photographs obtained from patients undergoing radiotherapy were collected for training and testing. The ground truth of radiation dermatitis segmentation is manually delineated from the skin photograph by an experienced radiation oncologist and medical physicist. We converted the skin photographs to RGB (red-green-blue) and CIELAB (lightness (L^∗), red-green (a^∗) and blue-yellow (b^∗)) colour information and trained the network to segment faint and severe radiation dermatitis using three different input combinations: RGB, RGB + CIELAB (RGBLAB) and RGB + CIELAB + skin-dose distribution (RGBLAB_D). The proposed system was evaluated using the Dice similarity coefficient (DSC), sensitivity, specificity and normalised Matthews correlation coefficient (nMCC). A paired t-test was used to compare the results of different segmentation performances.

RESULTS

Optimal data composition was observed in the network trained for radiation dermatitis segmentation using skin photographs and skin-dose distribution. The average DSC, sensitivity, specificity and nMCC values of RGBLAB_D were 0.62, 0.61, 0.91 and 0.77, respectively, in faint radiation dermatitis, and 0.69, 0.78, 0.96 and 0.83, respectively, in severe radiation dermatitis.

CONCLUSION

Our study showed that CNN-based radiation dermatitis segmentation in skin photographs of patients undergoing radiotherapy can describe radiation dermatitis severity and pattern. Our study could aid in objectifying the radiation dermatitis grading and analysing the reliable correlation between dosimetric factors and the morphology of radiation dermatitis.

Leucine-sensing mechanism of leucyl-tRNA synthetase 1 for mTORC1 activation

Leucyl-tRNA synthetase 1 (LARS1) mediates activation of leucine-dependent mechanistic target of rapamycin complex 1 (mTORC1) as well as ligation of leucine to its cognate tRNAs, yet its mechanism of leucine sensing is poorly understood. Here we describe leucine binding-induced conformational changes of LARS1. We determine different crystal structures of LARS1 complexed with leucine, ATP, and a reaction intermediate analog, leucyl-sulfamoyl-adenylate (Leu-AMS), and find two distinct functional states of LARS1 for mTORC1 activation. Upon leucine binding to the synthetic site, H251 and R517 in the connective polypeptide and ⁵⁰FPYPY⁵⁴ in the catalytic domain change the hydrogen bond network, leading to conformational change in the C-terminal domain, correlating with RagD association. Leucine binding to LARS1 is increased in the presence of ATP, further augmenting leucine-dependent interaction of LARS1 and RagD. Thus, this work unveils the structural basis for leucine-dependent long-range communication between the catalytic and RagD-binding domains of LARS1 for mTORC1 activation.

Phospho-dependent signaling during the general stress response by the atypical response regulator and ClpXP adaptor RssB

In the model organism Escherichia coli and related species, the general stress response relies on tight regulation of the intracellular levels of the promoter specificity subunit RpoS. RpoS turnover is exclusively dependent on RssB, a two-domain response regulator that functions as an adaptor that delivers RpoS to ClpXP for proteolysis. Here, we report crystal structures of the receiver domain of RssB both in its unphosphorylated form and bound to the phosphomimic BeF₃ ^- . Surprisingly, we find only modest differences between these two structures, suggesting that truncating RssB may partially activate the receiver domain to a "meta-active" state. Our structural and sequence analysis points to RssB proteins not conforming to either the Y-T coupling scheme for signaling seen in prototypical response regulators, such as CheY, or to the signaling model of the less understood FATGUY proteins.

Screening and Genetic Network Analysis of Genes Involved in Freezing and Thawing Resistance in DaMDHAR-Expressing Saccharomyces cerevisiae Using Gene Expression Profiling

The cryoprotection of cell activity is a key determinant in frozen-dough technology. Although several factors that contribute to freezing tolerance have been reported, the mechanism underlying the manner in which yeast cells respond to freezing and thawing (FT) stress is not well established. Therefore, the present study demonstrated the relationship between DaMDHAR encoding monodehydroascorbate reductase from Antarctic hairgrass Deschampsia antarctica and stress tolerance to repeated FT cycles (FT2) in transgenic yeast Saccharomyces cerevisiae. DaMDHAR-expressing yeast (DM) cells identified by immunoblotting analysis showed high tolerance to FT stress conditions, thereby causing lower damage for yeast cells than wild-type (WT) cells with empty vector alone. To detect FT2 tolerance-associated genes, 3′-quant RNA sequencing was employed using mRNA isolated from DM and WT cells exposed to FT (FT2) conditions. Approximately 332 genes showed ≥2-fold changes in DM cells and were classified into various groups according to their gene expression. The expressions of the changed genes were further confirmed using western blot analysis and biochemical assay. The upregulated expression of 197 genes was associated with pentose phosphate pathway, NADP metabolic process, metal ion homeostasis, sulfate assimilation, β-alanine metabolism, glycerol synthesis, and integral component of mitochondrial and plasma membrane (PM) in DM cells under FT2 stress, whereas the expression of the remaining 135 genes was partially related to protein processing, selenocompound metabolism, cell cycle arrest, oxidative phosphorylation, and α-glucoside transport under the same condition. With regard to transcription factors in DM cells, MSN4 and CIN5 were activated, but MSN2 and MGA1 were not. Regarding antioxidant systems and protein kinases in DM cells under FT stress, CTT1, GTO, GEX1, and YOL024W were upregulated, whereas AIF1, COX2, and TRX3 were not. Gene activation represented by transcription factors and enzymatic antioxidants appears to be associated with FT2-stress tolerance in transgenic yeast cells. RCK1, MET14, and SIP18, but not YPK2, have been known to be involved in the protein kinase-mediated signalling pathway and glycogen synthesis. Moreover, SPI18 and HSP12 encoding hydrophilin in the PM were detected. Therefore, it was concluded that the genetic network via the change of gene expression levels of multiple genes contributing to the stabilization and functionality of the mitochondria and PM, not of a single gene, might be the crucial determinant for FT tolerance in DaMDAHR-expressing transgenic yeast. These findings provide a foundation for elucidating the DaMDHAR-dependent molecular mechanism of the complex functional resistance in the cellular response to FT stress.

Structural and kinetic insights into flavin-containing monooxygenase and calponin-homology domains in human MICAL3

MICAL is an oxidoreductase that participates in cytoskeleton reorganization via actin disassembly in the presence of NADPH. Although three MICALs (MICAL1, MICAL2 and MICAL3) have been identified in mammals, only the structure of mouse MICAL1 has been reported. Here, the first crystal structure of human MICAL3, which contains the flavin-containing monooxygenase (FMO) and calponin-homology (CH) domains, is reported. MICAL3 has an FAD/NADP-binding Rossmann-fold domain for mono-oxygenase activity like MICAL1. The FMO and CH domains of both MICAL3 and MICAL1 are highly similar in structure, but superimposition of the two structures shows a different relative position of the CH domain in the asymmetric unit. Based on kinetic analyses, the catalytic efficiency of MICAL3 dramatically increased on adding F-actin only when the CH domain was available. However, this did not occur when two residues, Glu213 and Arg530, were mutated in the FMO and CH domains, respectively. Overall, MICAL3 is structurally highly similar to MICAL1, which suggests that they may adopt the same catalytic mechanism, but the difference in the relative position of the CH domain produces a difference in F-actin substrate specificity.

Structural Analysis of an Epitope Candidate of Triosephosphate Isomerase in Opisthorchis viverrini

Opisthorchis viverrini, a parasitic trematode, was recategorized as a group 1 biological carcinogen because it causes opisthorchiasis, which may result in cholangiocarcinoma. A new strategy for controlling opisthorchiasis is needed because of issues such as drug resistance and reinfection. Triosephosphate isomerase (TIM), a key enzyme in energy metabolism, is regarded as a potential drug target and vaccine candidate against various pathogens. Here, we determined the crystal structures of wild-type and 3 variants of TIMs from O. viverrini (OvTIM) at high resolution. The unique tripeptide of parasite trematodes, the SAD motif, was located on the surface of OvTIM and contributed to forming a 3₁₀-helix of the following loop in a sequence-independent manner. Through thermal stability and structural analyses of OvTIM variants, we found that the SAD motif induced local structural alterations of the surface and was involved in the overall stability of OvTIM in a complementary manner with another parasite-specific residue, N115. Comparison of the surface characteristics between OvTIM and Homo sapiens TIM (HsTIM) and structure-based epitope prediction suggested that the SAD motif functions as an epitope.

Long-term outcomes of laparoscopic large hiatus hernia repair with nonabsorbable mesh

The use of mesh to augment suture repair of large hiatus hernias remains controversial. Repair with mesh may help reduce the recurrence rate of primary repair, but concerns about the potential for serious complications, such as mesh erosion or stricturing, continue to limit its use. We aim to evaluate the long-term outcome of primary hiatus hernia repair with lightweight polypropylene mesh (TiMesh) specifically looking at rates of clinical recurrence, dysphagia, and mesh-related complications. From a prospectively maintained database, 50 consecutive patients who underwent elective primary laparoscopic hiatal hernia repair with TiMesh between January 2005 and December 2007 were identified. Case notes and postoperative endoscopy reports were reviewed. Clinical outcomes were evaluated using a structured questionnaire, including a validated dysphagia score. Of the 50 patients identified, 36 (72%) were contactable for follow-up. At a median follow-up of 9 years, the majority of patients (97%) regarded their surgery as successful. Twelve patients (33%) reported a recurrence of their symptoms, but only 4 (11%) reported that their symptoms were as severe as prior to the surgery. There was no significant difference between pre- and postoperative dysphagia scores. Postoperative endoscopy reports were available for 32 patients at a median time point of 4 years postoperatively, none of which revealed any mesh-related complications. One patient had undergone a revision procedure for a recurrent hernia at another institution. In this series, primary repair of large hiatus hernia with nonabsorbable mesh was not associated with any adverse effects over time. Patient satisfaction with symptomatic outcome remained high in the long term.

Structural Basis for Inhibitor-Induced Hydrogen Peroxide Production by Kynurenine 3-Monooxygenase

Kynurenine 3-monooxygenase (KMO) inhibitors have been developed for the treatment of neurodegenerative disorders. The mechanisms of flavin reduction and hydrogen peroxide production by KMO inhibitors are unknown. Herein, we report the structure of human KMO and crystal structures of Saccharomyces cerevisiae (sc) and Pseudomonas fluorescens (pf) KMO with Ro 61-8048. Proton transfer in the hydrogen bond network triggers flavin reduction in p-hydroxybenzoate hydroxylase, but the mechanism triggering flavin reduction in KMO is different. Conformational changes via π-π interactions between the loop above the flavin and substrate or non-substrate effectors lead to disorder of the C-terminal α helix in scKMO and shifts of domain III in pfKMO, stimulating flavin reduction. Interestingly, Ro 61-8048 has two different binding modes. It acts as a competitive inhibitor in scKMO and as a non-substrate effector in pfKMO. These findings provide understanding of the catalytic cycle of KMO and insight for structure-based drug design of KMO inhibitors.

Patient-specific medial unicompartmental knee arthroplasty has a greater protective effect on articular cartilage in the lateral compartment: A Finite Element Analysis

OBJECTIVES

Patient-specific (PS) implantation surgical technology has been introduced in recent years and a gradual increase in the associated number of surgical cases has been observed. PS technology uses a patient's own geometry in designing a medical device to provide minimal bone resection with improvement in the prosthetic bone coverage. However, whether PS unicompartmental knee arthroplasty (UKA) provides a better biomechanical effect than standard off-the-shelf prostheses for UKA has not yet been determined, and still remains controversial in both biomechanical and clinical fields. Therefore, the aim of this study was to compare the biomechanical effect between PS and standard off-the-shelf prostheses for UKA.

METHODS

The contact stresses on the polyethylene (PE) insert, articular cartilage and lateral meniscus were evaluated in PS and standard off-the-shelf prostheses for UKA using a validated finite element model. Gait cycle loading was applied to evaluate the biomechanical effect in the PS and standard UKAs.

RESULTS

The contact stresses on the PE insert were similar for both the PS and standard UKAs. Compared with the standard UKA, the PS UKA did not show any biomechanical effect on the medial PE insert. However, the contact stresses on the articular cartilage and the meniscus in the lateral compartment following the PS UKA exhibited closer values to the healthy knee joint compared with the standard UKA.

CONCLUSION

The PS UKA provided mechanics closer to those of the normal knee joint. The decreased contact stress on the opposite compartment may reduce the overall risk of progressive osteoarthritis.Cite this article: K-T. Kang, J. Son, D-S. Suh, S. K. Kwon, O-R. Kwon, Y-G. Koh. Patient-specific medial unicompartmental knee arthroplasty has a greater protective effect on articular cartilage in the lateral compartment: A Finite Element Analysis. Bone Joint Res 2018;7:20-27. DOI: 10.1302/2046-3758.71.BJR-2017-0115.R2.

A computational simulation study to determine the biomechanical influence of posterior condylar offset and tibial slope in cruciate retaining total knee arthroplasty

Objectives

Posterior condylar offset (PCO) and posterior tibial slope (PTS) are critical factors in total knee arthroplasty (TKA). A computational simulation was performed to evaluate the biomechanical effect of PCO and PTS on cruciate retaining TKA.

Methods

We generated a subject-specific computational model followed by the development of ± 1 mm, ± 2 mm and ± 3 mm PCO models in the posterior direction, and -3°, 0°, 3° and 6° PTS models with each of the PCO models. Using a validated finite element (FE) model, we investigated the influence of the changes in PCO and PTS on the contact stress in the patellar button and the forces on the posterior cruciate ligament (PCL), patellar tendon and quadriceps muscles under the deep knee-bend loading conditions.

Results

Contact stress on the patellar button increased and decreased as PCO translated to the anterior and posterior directions, respectively. In addition, contact stress on the patellar button decreased as PTS increased. These trends were consistent in the FE models with altered PCO. Higher quadriceps muscle and patellar tendon force are required as PCO translated in the anterior direction with an equivalent flexion angle. However, as PTS increased, quadriceps muscle and patellar tendon force reduced in each PCO condition. The forces exerted on the PCL increased as PCO translated to the posterior direction and decreased as PTS increased.

Conclusion

The change in PCO alternatively provided positive and negative biomechanical effects, but it led to a reduction in a negative biomechanical effect as PTS increased.

Cite this article: K-T. Kang, Y-G. Koh, J. Son, O-R. Kwon, J-S. Lee, S. K. Kwon. A computational simulation study to determine the biomechanical influence of posterior condylar offset and tibial slope in cruciate retaining total knee arthroplasty. Bone Joint Res 2018;7:69–78. DOI: 10.1302/2046-3758.71.BJR-2017-0143.R1.

Spin-Orbit Coupling and Interband Transitions in the Optical Conductivity of Sr_{2}RhO_{4}

The prototypical correlated metal Sr_{2}RhO_{4} was studied using optical and photoemission spectroscopy. At low energies and temperatures, the optical data reveal a complex, multicomponent response that on the surface points to an unconventional metallic state in this material. Via a comparison with photoemission, the anomalous optical response may be attributed to an unexpectedly strong interband transition near 180 meV between spin-orbit coupled bands that are nearly parallel along ΓX. This spin-orbit coupling effect is shown to occur in a number of related metallic ruthenates and explains the previously puzzling optical properties reported for these materials.

Computational study on the effect of malalignment of the tibial component on the biomechanics of total knee arthroplasty: A Finite Element Analysis

Objectives

Malalignment of the tibial component could influence the long-term survival of a total knee arthroplasty (TKA). The object of this study was to investigate the biomechanical effect of varus and valgus malalignment on the tibial component under stance-phase gait cycle loading conditions.

Methods

Validated finite element models for varus and valgus malalignment by 3° and 5° were developed to evaluate the effect of malalignment on the tibial component in TKA. Maximum contact stress and contact area on a polyethylene insert, maximum contact stress on patellar button and the collateral ligament force were investigated.

Results

There was greater total contact stress in the varus alignment than in the valgus, with more marked difference on the medial side. An increase in ligament force was clearly demonstrated, especially in the valgus alignment and force exerted on the medial collateral ligament also increased.

Conclusion

These results highlight the importance of accurate surgical reconstruction of the coronal tibial alignment of the knee joint. Varus and valgus alignments will influence wear and ligament stability, respectively in TKA.

Cite this article: D-S. Suh, K-T. Kang, J. Son, O-R. Kwon, C. Baek, Y-G. Koh. Computational study on the effect of malalignment of the tibial component on the biomechanics of total knee arthroplasty: A Finite Element Analysis. Bone Joint Res 2017;6:623–630. DOI: 10.1302/2046-3758.611.BJR-2016-0088.R2.

Preservation of kinematics with posterior cruciate-, bicruciate- and patient-specific bicruciate-retaining prostheses in total knee arthroplasty by using computational simulation with normal knee model

Objectives

Preservation of both anterior and posterior cruciate ligaments in total knee arthroplasty (TKA) can lead to near-normal post-operative joint mechanics and improved knee function. We hypothesised that a patient-specific bicruciate-retaining prosthesis preserves near-normal kinematics better than standard off-the-shelf posterior cruciate-retaining and bicruciate-retaining prostheses in TKA.

Methods

We developed the validated models to evaluate the post-operative kinematics in patient-specific bicruciate-retaining, standard off-the-shelf bicruciate-retaining and posterior cruciate-retaining TKA under gait and deep knee bend loading conditions using numerical simulation.

Results

Tibial posterior translation and internal rotation in patient-specific bicruciate-retaining prostheses preserved near-normal kinematics better than other standard off-the-shelf prostheses under gait loading conditions. Differences from normal kinematics were minimised for femoral rollback and internal-external rotation in patient-specific bicruciate-retaining, followed by standard off-the-shelf bicruciate-retaining and posterior cruciate-retaining TKA under deep knee bend loading conditions. Moreover, the standard off-the-shelf posterior cruciate-retaining TKA in this study showed the most abnormal performance in kinematics under gait and deep knee bend loading conditions, whereas patient-specific bicruciate-retaining TKA led to near-normal kinematics.

Conclusion

This study showed that restoration of the normal geometry of the knee joint in patient-specific bicruciate-retaining TKA and preservation of the anterior cruciate ligament can lead to improvement in kinematics compared with the standard off-the-shelf posterior cruciate-retaining and bicruciate-retaining TKA.

Cite this article: Y-G. Koh, J. Son, S-K. Kwon, H-J. Kim, O-R. Kwon, K-T. Kang. Preservation of kinematics with posterior cruciate-, bicruciate- and patient-specific bicruciate-retaining prostheses in total knee arthroplasty by using computational simulation with normal knee model. Bone Joint Res 2017;6:557–565. DOI: 10.1302/2046-3758.69.BJR-2016-0250.R1.

Crystal structure of tRNAHis guanylyltransferase from Saccharomyces cerevisiae

tRNA maturation involves several steps, including processing, splicing, CCA addition, and posttranscriptional modifications. tRNA^His guanylyltransferase (Thg1) is the only enzyme known to catalyze templated nucleotide addition in the 3'-5' direction, unlike other DNA and RNA polymerases. For a better understanding of its unique catalytic mechanism at the molecular level, we determined the crystal structure of GTP-bound Thg1 from Saccharomyces cerevisiae at the maximum resolution of 3.0 Å. The structure revealed the enzyme to have a tetrameric conformation that is well conserved among different species, and the GTP molecule was clearly bound at the active site, coordinating with two magnesium ions. In addition, two flexible protomers at the potential binding site (PBS) for tRNA^His were observed. We suggest that the PBS of the tetramer could also be one of the sites for interaction with partner proteins.

The effects of posterior cruciate ligament deficiency on posterolateral corner structures under gait- and squat-loading conditions: A computational knee model

Objectives

The aim of the current study was to analyse the effects of posterior cruciate ligament (PCL) deficiency on forces of the posterolateral corner structure and on tibiofemoral (TF) and patellofemoral (PF) contact force under dynamic-loading conditions.

Methods

A subject-specific knee model was validated using a passive flexion experiment, electromyography data, muscle activation, and previous experimental studies. The simulation was performed on the musculoskeletal models with and without PCL deficiency using a novel force-dependent kinematics method under gait- and squat-loading conditions, followed by probabilistic analysis for material uncertain to be considered.

Results

Comparison of predicted passive flexion, posterior drawer kinematics and muscle activation with experimental measurements showed good agreement. Forces of the posterolateral corner structure, and TF and PF contact forces increased with PCL deficiency under gait- and squat-loading conditions. The rate of increase in PF contact force was the greatest during the squat-loading condition. The TF contact forces increased on both medial and lateral compartments during gait-loading conditions. However, during the squat-loading condition, the medial TF contact force tended to increase, while the lateral TF contact forces decreased. The posterolateral corner structure, which showed the greatest increase in force with deficiency of PCL under both gait- and squat-loading conditions, was the popliteus tendon (PT).

Conclusion

PCL deficiency is a factor affecting the variability of force on the PT in dynamic-loading conditions, and it could lead to degeneration of the PF joint.

Cite this article: K-T. Kang, Y-G. Koh, M. Jung, J-H. Nam, J. Son, Y.H. Lee, S-J. Kim, S-H. Kim. The effects of posterior cruciate ligament deficiency on posterolateral corner structures under gait- and squat-loading conditions: A computational knee model. Bone Joint Res 2017;6:31–42. DOI: 10.1302/2046-3758.61.BJR-2016-0184.R1.

Measuring the effect of femoral malrotation on knee joint biomechanics for total knee arthroplasty using computational simulation

Objectives

Malrotation of the femoral component can result in post-operative complications in total knee arthroplasty (TKA), including patellar maltracking. Therefore, we used computational simulation to investigate the influence of femoral malrotation on contact stresses on the polyethylene (PE) insert and on the patellar button as well as on the forces on the collateral ligaments.

Materials and Methods

Validated finite element (FE) models, for internal and external malrotations from 0° to 10° with regard to the neutral position, were developed to evaluate the effect of malrotation on the femoral component in TKA. Femoral malrotation in TKA on the knee joint was simulated in walking stance-phase gait and squat loading conditions.

Results

Contact stress on the medial side of the PE insert increased with internal femoral malrotation and decreased with external femoral malrotation in both stance-phase gait and squat loading conditions. There was an opposite trend in the lateral side of the PE insert case. Contact stress on the patellar button increased with internal femoral malrotation and decreased with external femoral malrotation in both stance-phase gait and squat loading conditions. In particular, contact stress on the patellar button increased by 98% with internal malrotation of 10° in the squat loading condition. The force on the medial collateral ligament (MCL) and the lateral collateral ligament (LCL) increased with internal and external femoral malrotations, respectively.

Conclusions

These findings provide support for orthopaedic surgeons to determine a more accurate femoral component alignment in order to reduce post-operative PE problems.

Cite this article: K-T. Kang, Y-G. Koh, J. Son, O-R. Kwon, C. Baek, S. H. Jung, K. K. Park. Measuring the effect of femoral malrotation on knee joint biomechanics for total knee arthroplasty using computational simulation. Bone Joint Res 2016;5:552–559. DOI: 10.1302/2046-3758.511.BJR-2016-0107.R1.

The structure of the pleiotropic transcription regulator CodY provides insight into its GTP-sensing mechanism

GTP and branched-chain amino acids (BCAAs) are metabolic sensors that are indispensable for the determination of the metabolic status of cells. However, their molecular sensing mechanism remains unclear. CodY is a unique global transcription regulator that recognizes GTP and BCAAs as specific signals and affects expression of more than 100 genes associated with metabolism. Herein, we report the first crystal structures of the full-length CodY complex with sensing molecules and describe their functional states. We observed two different oligomeric states of CodY: a dimeric complex of CodY from Staphylococcus aureus with the two metabolites GTP and isoleucine, and a tetrameric form (apo) of CodY from Bacillus cereus. Notably, the tetrameric state shows in an auto-inhibitory manner by blocking the GTP-binding site, whereas the binding sites of GTP and isoleucine are clearly visible in the dimeric state. The GTP is located at a hinge site between the long helical region and the metabolite-binding site. Together, data from structural and electrophoretic mobility shift assay analyses improve understanding of how CodY senses GTP and operates as a DNA-binding protein and a pleiotropic transcription regulator.

When β-cells fail: lessons from dedifferentiation

Diabetes is caused by a combination of impaired responsiveness to insulin and reduced production of insulin by the pancreas. Until recently, the decline of insulin production had been ascribed to β-cell death. But recent research has shown that β-cells do not die in diabetes, but undergo a silencing process, termed "dedifferentiation." The main implication of this discovery is that β-cells can be revived by appropriate treatments. We have shown that mitochondrial abnormalities are a key step in the progression of β-cell dysfunction towards dedifferentiation. In normal β-cells, mitochondria generate energy required to sustain insulin production and its finely timed release in response to the body's nutritional status. A normal β-cell can adapt its mitochondrial fuel source based on substrate availability, a concept known as "metabolic flexibility." This capability is the first casualty in the progress of β-cell failure. β-Cells lose the ability to select the right fuel for mitochondrial energy production. Mitochondria become overloaded, and accumulate by-products derived from incomplete fuel utilization. Energy production stalls, and insulin production drops, setting the stage for dedifferentiation. The ultimate goal of these investigations is to explore novel treatment paradigms that will benefit people with diabetes.

Essential Role of the Linker Region in the Higher Catalytic Efficiency of a Bifunctional MsrA-MsrB Fusion Protein

Many bacteria, particularly pathogens, possess methionine sulfoxide reductase A (MsrA) and B (MsrB) as a fusion form (MsrAB). However, it is not clear why they possess a fusion MsrAB form rather than the separate enzymes that exist in most organisms. In this study, we performed biochemical and kinetic analyses of MsrAB from Treponema denticola (TdMsrAB), single-domain forms (TdMsrA and TdMsrB), and catalytic Cys mutants (TdMsrAB(C11S) and TdMsrAB(C285S)). We found that the catalytic efficiency of both MsrA and MsrB increased after fusion of the domains and that the linker region (iloop) that connects TdMsrA and TdMsrB is required for the higher catalytic efficiency of TdMsrAB. We also determined the crystal structure of TdMsrAB at 2.3 Å, showing that the iloop mainly interacts with TdMsrB via hydrogen bonds. Further kinetic analysis using the iloop mutants revealed that the iloop-TdMsrB interactions are critical to MsrB and MsrA activities. We also report the structure in which an oxidized form of dithiothreitol, an in vitro reductant for MsrA and MsrB, is present in the active site of TdMsrA. Collectively, the results of this study reveal an essential role of the iloop in maintaining the higher catalytic efficiency of the MsrAB fusion enzyme and provide a better understanding of why the MsrAB enzyme exists as a fused form.

Processing of A-form ssDNA by cryptic RNase H fold exonuclease PF2046

RNase H fold protein PF2046 of Pyrococcus furiosus is a 3'-5' ssDNA exonuclease that cleaves after the second nucleotide from the 3' end of ssDNA and prefers poly-dT over poly-dA as a substrate. In our crystal structure of PF2046 complexed with an oligonucleotide of four thymidine nucleotides (dT4), PF2046 accommodates dT4 tightly in a groove and imposes steric hindrance on dT4 mainly by Phe220 such that dT4 assumes the A-form. As poly-dA prefer B-form due to the stereochemical restrictions, the A-form ssDNA binding by PF2046 should disfavor the processing of poly-dA. Phe220 variants display reduced activity toward poly-dA and the A-form appears to be a prerequisite for the processing by PF2046.