Modulation of Neuroinflammation by Low-Dose Radiation Therapy in an Animal Model of Alzheimer's Disease.

PURPOSE: Recently, several studies have reported that low-dose radiation therapy (RT) suppresses the release of proinflammatory cytokines in inflammatory-degenerative disorders, including Alzheimer disease (AD). AD is the most common cause of dementia, and neuroinflammation is one of the major contributing factors in AD pathogenesis. Therefore, low-dose RT may be used clinically for treating AD. However, the appropriate doses, effects, and underlying mechanisms of RT in AD have not been determined. In this study, we aimed to determine the appropriate RT dose and schedule for AD treatment and to investigate the therapeutic effects and mechanisms of low-dose RT in AD. METHODS AND MATERIALS: We first determined the proper dose and schedule for RT in late-stage AD using 8- to 9-month-old 5x Familial AD (5xFAD) mice, a well-known animal model of AD, by comparing the effects of a low total dose with low dose per fraction (LD-LDRT, 5 × 0.6 Gy) with those of a low moderate total dose with conventional dose per fraction (LMD-CDRT, 5 × 2 Gy). RESULTS: LD-LDRT and LMD-CDRT were found to reduce the levels of the proinflammatory cytokines CD54, IL-3, CXCL9/10, and CCL2/4 in the hippocampus of 5xFAD mice. Furthermore, increased microgliosis assessed using Iba-1 and CD68 dual immunostaining was significantly reduced by LD-LDRT and LMD-CDRT in the hippocampus of 5xFAD mice. Moreover, LD-LDRT and LMD-CDRT decreased the amyloid plaque burden in the hippocampus of 5xFAD mice and attenuated their cognitive impairment; these effects persisted for 4 to 5 weeks. CONCLUSIONS: The present study showed that LD-LDRT alleviates cognitive impairments and prevents the accumulation of amyloid plaques by regulating neuroinflammation in the late stage of AD in 5xFAD mice, with an efficacy equivalent to that of LMD-CDRT. Furthermore, the findings suggest that compared with LMD-CDRT, LD-LDRT may facilitate accessible and convenient treatment in clinical trials.

Reliability of the Patient and Observer Scar Assessment Scale in Evaluating Linear Scars after Thyroidectomy.

OBJECTIVE: To compare the reliability of the Patient and Observer Scar Assessment Scale (POSAS) with the Vancouver Scar Scale (VSS) in evaluating thyroidectomy scars. METHODS: At 6 months after the operation, 112 patients who underwent thyroid surgery via collar neck incision were evaluated by two blinded plastic surgeons and two senior residents using the VSS and the observer component of the POSAS. In addition, the observer-reported VAS score and patient-reported Likert score were evaluated. Internal consistency, interobserver reliability, and correlations between the patient- and observer-reported outcomes were examined. RESULTS: The observer component of POSAS scores demonstrated higher internal consistency and interobserver reliability than the VSS. However, the correlations between the observer-reported VAS score and the patient-reported Likert score (0.450) and between the total sum of patient and observer component scores (0.551) were low to moderate. CONCLUSIONS: The POSAS is more consistent over repeated measurements; accordingly, it may be considered a more objective and reliable scar assessment tool than the VSS. However, a clinician's perspective may not exactly match the patient's perception of the same scar.

Current Protocol for Aesthetic Scar Management in Thyroid Surgery.

OBJECTIVES/HYPOTHESIS: We compared the scar quality when different protocols were applied, and eventually aim to find the optimal scar management protocol. STUDY DESIGN: We conducted a prospective, randomized, and blinded comparison of different scar management protocols in a single center. METHODS: We allocated 126 patients who underwent thyroidectomy via collar neck incision randomly into three groups. Patients in group A were treated with tissue adhesive only. Patients in group B were treated by means of subcuticular suturing and early scar management with a non-ablative fractional laser (NAFL) and intralesional triamcinolone injection (ILI). Patients in group C had skin closure with tissue adhesive and early scar management. At 6 months after the operation, the Patient and Observer Scar Assessment Scale (POSAS) and the width of the final scar were compared. RESULTS: Comparing the sum of PSAS, groups B and C showed significant higher satisfaction than did group A (22.81 ± 11.66 in group A, 10.9 ± 5.14 in group B, and 15.19 ± 9.98 in group C). In the sum of OSAS, group B also showed a significant difference than did groups A and C (17.74 ± 6.75 in group A, 10.26 ± 3.60 in group B, and 14.52 ± 6.48 in group C). Also, group B showed a narrower scar width than did groups A and C. CONCLUSIONS: Our finding suggests that subcuticular suturing using barbed suture material and early treatment with a combination therapy using NAFL and ILI showed a favorable aesthetic outcome for both patients and operators. Based on our algorithmic approach for thyroidectomy scar, we anticipate an optimal aesthetic outcome. LEVEL OF EVIDENCE: II Laryngoscope, 131:E2188-E2195, 2021.

Dose assessment in dental cone-beam computed tomography: Comparison of optically stimulated luminescence dosimetry with Monte Carlo method.

The variety of cone-beam computed tomography (CBCT) machines and their applications has rapidly increased in recent years, making the dose evaluation of individual devices an important issue. Patient doses from CBCT were assessed with two different methods: optically stimulated luminescence dosimeter (OSLD) measurements and Monte Carlo (MC) simulations, in four different examination modes. Based on an analysis of the measurement process and the obtained values, a recommendation is made regarding which method is more practical and efficient for acquiring the effective dose of CBCT. Twenty-two OSLDs were calibrated and equipped in human phantoms of head and neck organs. They were exposed to radiation from two CBCT units-CS9300 (Carestream Dental LLC, Atlanta, Georgia) and RAYSCAN α+ (Ray Co. Ltd, Hwaseong-si, Korea)-using two different examination modes. The dose recorded using the OSLDs was used to calculate the organ dose and the effective dose for each unit in each examination mode. These values were also calculated using MC software, PCXMC (STUK, Helsinki, Finland). The organ doses and effective doses obtained using both methods were compared for each examination mode of the individual units. The OSLD-measured effective dose value was higher than that obtained using the MC method for each examination mode, except the dual jaw mode of CS9300. The percent difference of the effective dose between the two methods ranged from 4.0% to 14.3%. The dose difference between the methods decreased as the field of view became smaller. The organ dose values varied according to the method, although the overall trend was similar for both methods. The organs showing high doses were mostly consistent for both methods. In this study, the effective dose obtained by OSLD measurements and MC simulations were compared, and both methods were described in detail. As a relatively efficient and easy-to-perform method, we cautiously suggest using MC simulations for dose evaluations in the future.

Characteristics of the Exradin W1 scintillator in the magnetic field.

To investigate the angular dependency of the W1 scintillator with and without a magnetic field, the beam incidence angles to the detector varied from 0° to 360° at intervals of 30° when the detector was pointed in both the craniocaudal and right-to-left directions. The beam incidence angles also varied from 0° to 360° at intervals of 45° when the W1 scintillator was in the anterior-to-posterior direction. To investigate the field size dependency of the W1 scintillator with and without a magnetic field, the doses by an identical beam-on time were measured at various square field sizes and the measured doses were normalized to the dose at the field of 10.5 cm × 10.5 cm (FS10.5). With and without a magnetic field, the deviations of the doses to the dose at the beam incident angle of 0° were always less than 1% regardless of the dosimeter positioning relative to the magnetic field direction. When the field sizes were equal to or less than FS10.5, the differences in the output factors with and without a magnetic field were less than 0.7%. However, those were larger than 1% at fields larger than FS10.5, and up to 3.1%. The W1 scintillator showed no angular dependency to the magnetic field. Differences larger than 1% in the output factors with and without a magnetic field were observed at field sizes larger than 10.5 cm × 10.5 cm.

Dose perturbation by metallic biliary stent in external beam radiotherapy of pancreato-biliary cancers.

This study aims to investigate dose perturbations caused by a metallic biliary stent (MBS) in patients undergoing external beam radiotherapy for cancers in the pancreato-biliary region. Four MBSs with nitinol mesh were examined in the EasyCube® phantom including a custom stent holder fabricated by a 3D printer. For experimental models, three-dimensional conformal radiotherapy plans using a single anterior-posterior (AP) and four-field box (4FB) as well as volumetric modulated arc therapy (VMAT) plan were prepared to deliver the photon beam of 8 Gy to the stent holder. EBT3 film was used to measure dose distributions at four sides surrounding MBS. All MBSs in the AP beam demonstrated mean dose enhancements of 2.3-8.2% at the proximal, left, and right sides. Maximum dose enhancements of 12.3-19.5% appeared at regions surrounding the radiopaque markers. At the location distal to the source, there were mean dose reductions of - 3.6 to - 10.9% and minimum doses of - 11.1 to - 9.5%. The mean and maximum doses with the 4FB plan were in the ranges of - 0.1 to 3.6% and 6.7-14.9%, respectively. The VMAT produced mean doses of - 0.9 to 4.8% and maximum doses of 6.0-15.3%. Dose perturbations were observed with maximum and minimum spots near the stent surface. The use of multiple beams including parallel-opposed pairs reduced dose perturbations caused by the nitinol and radiopaque components within the stent. Special attention is required for patients in whom the radiopaque markers are closely located near critical structures or the target volume.

Anti-vasospastic effects of botulinum toxin B pretreatment in animal models.

BACKGROUND: Botulinum toxin has been recently known for its vasodilatory effect. The main purpose of our study was to demonstrate the anti-vasospastic effect of botulinum toxin B in animal models. METHOD: In this prospective experimental rat study, we used 10 male Sprague-Dawley rats. The right and left inguinal areas (femoral vessels) served as the experimental and control groups, respectively. Three days prior to the experimental procedure, botulinum toxin B and normal saline were subcutaneously injected in the experimental and control groups, respectively. After three days, the vascular diameter and flow were measured. Then, phenylephrine was injected, and after one hour the same parameters were measured. RESULTS: The changes in arterial diameter in the experimental and control group were 30.83 ± 10.43% and 40.00 ± 8.61%, respectively. The vein diameter decreased by 22.98 ± 10.08% in the experimental group compared to 49.05 ± 10.08% for the control group. Furthermore, the arterial flow change in the control group was 8.28 ± 2.10% compared to 1.16 ± 0.65% in the experimental group. In addition, the venous flow in the control group decreased by 9.27 ± 2.75% compared to 0.92 ± 0.56% in the experimental group. Both arterial and venous diameters and flows showed statistical significance between the experimental and control groups (p < .05). CONCLUSIONS: Our study demonstrated that pretreatment with botulinum toxin B led to significantly reduced change in vascular diameters and flows compared with the control group, supporting the anti-vasospastic effects of botulinum toxin B.

"Radiological morphometric analysis of the zygomatic arch: Application of osteosynthesis on the upper arch border for rigid fixation".

BACKGROUND: This study was designed to introduce a novel method of applying osteosynthetic materials to the upper zygomatic arch border for fracture fixation through a temporal incision, and analyze the radiologic morphometric dimensions of the arch to verify its validity. METHODS: Radiological morphometry was analyzed in 51 adult patients with unilateral isolated zygomatic arch fractures. Frequent fracture sites, sites of minimal thickness and height, and their correlation were evaluated, as were the locations and dimensions of fixation vantage points. The novel surgical method based on the results was implemented in 17 clinical cases. RESULTS: Frequent fracture sites, occurring 4.40, 16.47 and 30.48 mm posterior to the arch origin, did not correlate to sites of minimal height and thickness. Arch minimal thickness and height locations were 12.23 and 27.09 mm behind its origin, respectively. Fixation vantage point dimensions varied from point to point, with upper thickness ranging from 1.67 to 4.86 mm and mid-portion thickness ranging from 2.06 to 7.36 mm, and height ranging from 8.99 to 22.53 mm. Arch vertical axis inclination ranged from 6.51° to 16.47°, which increased as the arch stretches posteriorly. These results suggested the use of 1.5 mm-wide plates and 1 mm-diameter screws with 6-8 mm length. Patients received surgery based on these morphometry results for satisfactory stabilization. CONCLUSIONS: This study introduces a new method for open reduction and internal fixation of arch fractures, with morphometric analysis of the arch verifying the validity of tangential plate application to the upper border.

The Influence of Dissection Range of the Facial Nerve on Transient Postoperative Facial Palsy in Mandibular Condyle Fractures.

PURPOSE: This study examined the relation between dissection range of facial nerve branches and transient postoperative facial palsy caused by nerve traction for open treatment of mandibular condyle fractures using a preauricular approach. MATERIALS AND METHODS: This retrospective study included 58 patients who underwent rigid fixation of condylar head and upper neck fractures. Patients were divided into 3 groups based on dissection range of the frontal and zygomatic branches. For group 1 (n = 22), the dissection range was extended anteriorly and posteriorly from the condylar borders through the retroparotid approach. The transparotid approach was used in groups 2 (n = 19) and 3 (n = 17) in which nerve dissection was limited to the condylar borders and was extended only anteriorly, respectively. Using multivariate correlation and multiple regression analyses, differences in duration of nerve traction and angle difference by traction from the natural course of the nerve were analyzed according to dissection range, and the recovery period for facial palsy was evaluated. RESULTS: The duration of nerve traction for group 2 was 77.53 minutes, which was longer than that for groups 1 (66.00 minutes) and 3 (65.41 minutes). The angle differences by traction were 62.42° and 58.00° for the frontal and zygomatic branches in group 2, respectively, which were considerably greater than those in groups 1 (23.32° and 20.14°) and 3 (37.24° and 28.88°). In consequence, group 2 showed the longest recovery, requiring 64.47 days for the frontal branch and 51.63 days for the zygomatic branch. The angle difference by traction had a greater influence on the recovery period than duration of nerve traction. CONCLUSIONS: Duration of nerve traction and angle difference by traction were quantitatively dependent on the dissection range of facial nerve branches and were related to the recovery period for transient facial palsy.

Bacterial profile of suction drains and the relationship thereof to surgical-site infections in prosthetic breast reconstruction.

BACKGROUND: Despite the increasing popularity of prosthetic breast reconstruction, scant data exist on the microbiological profile of drainage fluid from closed-suction drains and the relationship thereof to surgical-site infections (SSIs) in breast reconstruction surgery. This study aimed to determine whether bacteria isolated from drainage fluid were associated with the development of SSIs, and whether the bacterial profile of drainage fluid could be a clinically useful predictor of SSIs. METHODS: We performed a retrospective chart review of 61 women who underwent tissue expander/implant or direct-to-implant reconstructions. Patient demographics and culture studies of drainage fluid from suction drains collected on postoperative day 7 were evaluated. RESULTS: Sixteen patients (26.23%) were culture-positive, and 45 patients (73.77%) were culture-negative. The most frequently isolated bacteria were coagulase-negative staphylococci, followed by Staphylococcus aureus. SSIs were diagnosed in seven patients and were mostly resolved by systemic antibiotics; however, the tissue expander or implant was explanted in two patients. Positive culture of drainage fluid from closed-suction drains was significantly associated with the development of SSIs (P<0.05). The positive predictive value was 37.50%, and the negative predictive value was 97.78%. CONCLUSIONS: To our knowledge, this study is the first to demonstrate a significant association between the microbiological profile of drainage fluid from closed-suction drains and the development of SSIs in patients with prosthetic breast reconstructions. The high negative predictive value suggests that microbial testing of drainage fluid from closed-suction drains may have clinical utility. Further prospective studies with larger sample sizes are required to confirm our findings.

Pulmonary thromboembolism in patient with coexistence of Behçet's disease and antiphospholipid syndrome.

Pulmonary thromboembolism (PTE) is rarely reported in Behçet's disease (BD) due to its distinctive thrombus-forming mechanism. In BD, the inflammation on vessel walls causes venous thrombosis. The thrombi are considered to be tethered to the inflamed walls making embolization less frequent. Thus, immunosuppressive agents are the mainstay of treatment. However, the necessity of anticoagulation therapy is controversial because of its uncertain efficacy of resolving thrombi and the possibility of fatal side effects of hemorrhage. A 25-year-old man with recurrent oral aphthae visited with abrupt onset of dyspnea and chest pain. Based on history, imaging studies and laboratory results, he was diagnosed with BD with vascular involvement and antiphospholipid syndrome (APS), causing PTE from deep vein thrombosis. The co-existing APS may have further promoted the thrombosis, shifting his blood profile toward the hypercoagulable state. Immunosuppressive therapy with glucocorticoid and azathioprine, and concomitant anticoagulation with warfarin were achieved successfully without any fatal complications. When atypical features of vascular involvement in BD develop, other coexisting diseases should be considered to design an optimal therapeutic plan.

Individual case review in a phase 3 randomized trial to investigate the role of internal mammary lymph node irradiation for breast cancer: Korean Radiation Oncology Group 08-06 study.

PURPOSE/OBJECTIVE: This study aimed to assess protocol compliance based on an individual case review (ICR) of the Korean Radiation Oncology Group-0806 trial. METHODS AND MATERIALS: For the ICR, 747 participants were divided into eight subgroups based on internal mammary node irradiation (IMNI), tumor laterality, and surgery type. Next, 15% of patients were randomly selected within each subgroup, and corresponding hospitals were subsequently requested to upload information related to radiation therapy (RT) planning. We reviewed the dose distributions of targets and organs at risk to determine protocol compliance. RESULTS: Data of 102 patients were collected. Overall, RT plans were found to be mostly protocol-compliant, with acceptability rates of 60-80% despite deviations in the ipsilateral lung in Arm 2 (IMNI group). However, despite few deviations, a subgroup analysis revealed significant differences in protocol compliance. Among RT techniques, plans using standard and partial wide tangents were most compliant in both Arms. In this ICR, the estimated survival benefits based on IMN doses were 7.7%, 8.4%, and 7.2% for all, breast-conserving surgery, and mastectomy cases, respectively. CONCLUSION: This ICR demonstrated overall protocol compliance, despite significant differences with regard to IMN irradiation and organs at risk according to subgroups and adopted field arrangements.

Mechanical quality assurance using light field for linear accelerators with camera calibration.

Mechanical Quality Assurance (QA) is important to assure spatially precise delivery of external-beam radiation therapy. As an alternative to the conventional-film based method, we have developed a new tool for mechanical QA of LINACs which uses a light field rather than radiation. When light passes through the collimator, a shadow is projected onto a piece of translucent paper and the resulting image is captured by a digital camera via a mirror. With this method, we evaluated the position of the LINAC isocenter and the accuracy of the gantry, collimator, and couch rotation. We also evaluated the accuracy of the digital readouts of the gantry, collimator, and couch rotation. In addition, the treatment couch position indicator was tested. We performed camera calibration as an essential pre-requisite for quantitative measurements of the position of isocenter, the linear motion of the couch, and the rotation angles of the gantry and collimator. Camera calibration reduced the measurement error to submillimeter based on uncertainty in pixel size of the image, while, without calibration, the measurement error of up to 2 mm could occur for an object with a length of 5 cm.

Effects of the interleukin-1ß-511 C/T gene polymorphism on the risk of gastric cancer in the context of the relationship between race and H. pylori infection: a meta-analysis of 20,000 subjects.

The interleukin (IL)-1ß-511 C/T polymorphism has been shown to be functional and to contribute to the risk of gastric cancer. However, the relationship between the IL-1ß-511 C/T polymorphism and gastric carcinogenesis remains inconclusive. A systematical electronic search was conducted of the MEDLINE, EMBASE, and CENTRAL databases. A random and a fixed effects model were exploited to estimate summary odds ratios and 95 % confidence intervals. Subgroup and sensitivity analyses were carried out with respect to ethnicity, quality assessment scores, control sources, genotyping methods, cancer histopathology and location, and Helicobacter pylori (H. pylori) infection. A total of 45 studies containing 9,066 cases of gastric cancer and 11,192 control subjects satisfied the inclusion criteria. The IL-1ß-511 C/T polymorphism was found to enhance the risk of stomach cancer for overall and HWE-satisfying studies. Asians showed a positive relationship in both the overall and HWE-satisfying groups, whereas Caucasians did not. Based on subgroup analysis, H. pylori infection and genotype analysis using PCR-RFLP methods increase the association between IL-1ß-511 T allele carrier and risk of stomach cancer. A positive relationship was found between the IL-1ß-511 C/T SNP and stomach carcinoma susceptibility, and the results suggest that Asian ethnicity, H. pylori infection and methodologically, PCR-RFLP genotyping strengthen this relationship. Reflecting on prevalence of H. pylori in Asian countries, additional studies on the IL-1ß-511 C/T SNP in the context of ethnicity and H. pylori infection may provide key insights into the mechanism underlying gastric cancer carcinogenesis. It was found PCR-RFLP is the most reliable genotyping method, and thus, it is recommendable to adopt it to determine the presence of the IL-1ß-511 C/T SNP.

Association between TNF-α-308 G/A gene polymorphism and gastric cancer risk: a systematic review and meta-analysis.

OBJECTIVE: Tumor necrosis factor-alpha (TNF-α) has been found to be associated with gastric carcinogenesis, but individually published results have been inconclusive. The aim of this study was to explore the relationship between the TNF-α-308 G/A polymorphism and gastric cancer risk. METHODS: MEDLINE, EMBASE and the COCHRANE library databases were searched for relevant articles to identify all available data. The odds ratios (ORs) with 95% confidence intervals (95% CIs) from each study were used to assess the association between the TNF-α-308 G/A polymorphism and gastric cancer risk. RESULTS: This meta-analysis included 30 studies (32 datasets) involving 7009 gastric cancer cases and 12,119 control subjects. Overall, a significant association was found between the TNF-α-308 G/A polymorphism and gastric cancer in AA+GA vs. GG (dominant contrast model) (OR=1.20, 95% CI=1.07-1.34, p=0.001). With stratification based on ethnicity, the TNF-α-308 G/A polymorphism was correlated with gastric cancer risk in Caucasians, using the dominant contrast model (OR=0.74, 95% CI=0.57-0.96, p=0.02), but not in East Asians and other ethnic groups. In the comprehensive subgroup analysis, a significant association was also found in recent articles (published after 2005), population-based high-quality studies, hospital-based high-quality studies, studies using the TaqMan method and non-cardia subgroups. However, the TNF-α-308 G/A polymorphism was not associated with specific histological types of gastric cancer risk. CONCLUSIONS: The TNF-α-308 G/A polymorphism may contribute to susceptibility to gastric cancer in Caucasians, especially for non-cardia gastric cancer, as most strongly demonstrated in high-quality studies and in studies using the TaqMan genotyping method. Furthermore, we recommend the TaqMan method as the preferred genotyping method in DNA polymorphism studies.

Ethnic differences in the association of the glutathione S-transferase T1 (GSTT1) null genotype and risk of gastric carcinoma: a systematic review and meta-analysis.

We performed a systematic review and meta-analysis of the association between the glutathione S-transferase T1 (GSTT1) deletion polymorphism and gastric cancer risk in populations from different ethnic backgrounds, based on a comprehensive literature search of the MEDLINE, EMBASE, and COCHRANE libraries. Thirty-six individual case-control studies comprising 7,689 gastric cancer cases and 12,445 controls were included in our meta-analysis. Overall, the GSTT1 null genotype appeared to increase gastric cancer risk (OR 1.17, 95% CI 1.06-1.31, p = 0.003). While Caucasian populations showed an association between the GSTT1 deletion polymorphism and gastric cancer risk (OR 1.27, 95% CI 1.05-1.52, p = 0.01), Asian populations did not show such an association (p = 0.11). When stratified by quality assessment scores, a significant association between the GSTT1 deletion polymorphism and gastric cancer risk was observed only in the Caucasian high quality subgroup (OR 1.27 95% CI 1.01-1.60, p = 0.05). Null genotypes for both GSTT1 and GSTM1 deletion polymorphisms also increased gastric cancer risk (OR 1.37, 95% CI 1.04-1.80, p = 0.03). Our study suggests that the GSTT1 null genotype is associated with a significant increase in gastric cancer risk in Caucasians, but not in Asians. Further well-designed studies are required to confirm the association between GSTT1 polymorphisms and gastric cancer risk in relation to various clinicopathological factors in different ethnic groups, especially Caucasians.

Structural diversity and extreme stability of unimolecular Oxytricha nova telomeric G-quadruplex.

Oxytricha nova telomeric DNA contains guanine-rich short-tandem repeat sequences (GGGGTTTT) n and terminates as a single strand at the 3'-end. This single-stranded overhang forms a novel DNA structure, namely, G-quadruplex, comprising four quartets. In this study, we investigated the structures and dynamics of unimolecular Oxytricha nova ( O. nova) telomeric G-quadruplexes by performing single molecule fluorescence resonance energy transfer (FRET) spectroscopy and bulk circular dichroism (CD) measurements. We observed that unimolecular O. nova G-quadruplexes exhibit structural polymorphism according to monovalent cations. In the presence of Na (+), only antiparallel conformation is detected, which was demonstrated in previous studies; however, in the presence of K (+), they fold into two different conformations, a parallel conformation and an antiparallel one different from that induced by Na (+). Furthermore, these G-quadruplexes show extremely high stability in their dynamics when compared with human G-quadruplexes. While human telomeric G-quadruplexes that possess three quartets display fast dynamic behavior (<100 s) at low K (+) concentrations or high temperatures, O. nova G-quadruplexes maintain their conformational state for a long time (>1000 s), even at the lowest K (+) concentration and the highest temperature investigated. This high stability is primarily due to an extra quartet that results in additional cation coordination. In addition to cation coordination, we propose that other factors such as base stacking and the size of the thymine loop may contribute to the stability of O. nova G-quadruplexes; this is based on the fact that the O. nova G-quadruplexes were observed to be more stable than the human ones in the presence of Li (+), which is known to greatly destabilize G-quadruplexes because of imprecise coordination. This extreme stability of four-quartet G-quadruplexes enables telomere protection even in the absence of protective proteins or in the case of abrupt environmental changes, although only a single G-quadruplex structure can be derived from the short single-stranded overhang.

Molecular basis for the local conformational rearrangement of human phosphoserine phosphatase.

Human phosphoserine phosphatase (HPSP) regulates the levels of glycine and d-serine, the putative co-agonists for the glycine site of the NMDA receptor in the brain. Here, we describe the first crystal structures of the HPSP in complexes with the competitive inhibitor 2-amino-3-phosphonopropionic acid (AP3) at 2.5 A, and the phosphate ion (Pi) and the product uncompetitive inhibitor l-serine (HPSP.l-Ser.Pi) at 2.8 A. The complex structures reveal that the open-closed environmental change of the active site, generated by local rearrangement of the alpha-helical bundle domain, is important to substrate recognition and hydrolysis. The maximal extent of this structural rearrangement is shown to be about 13 A at the L4 loop and about 25 degrees at the helix alpha3. Both the structural change and mutagenesis data suggest that Arg-65 and Glu-29 play an important role in the binding of the substrate. Interestingly, the AP3 binding mode turns out to be significantly different from that of the natural substrate, phospho-l-serine, and the HPSP.l-Ser.Pi structure provides a structural basis for the feedback control mechanism of serine. These analyses allow us to provide a clear model for the mechanism of HPSP and a framework for structure-based drug development.