Influence of postprinting cleaning methods on the cleaning efficiency and surface and mechanical properties of three-dimensionally printed resins

STATEMENT OF PROBLEM

The outcome of photopolymerized 3-dimensional (3D) printing is influenced by the methods used for postprinting cleaning, yet information on postprinting cleaning is sparse.

PURPOSE

The purpose of this in vitro study was to assess the cleaning efficiency and surface and mechanical properties of 3D printed resin according to postprinting cleaning methods.

MATERIAL AND METHODS

Specimens were fabricated from a 3D model using resin materials (NextDent C&B MFH and DIOnavi-P. MAX) and were tested for postprinting cleaning methods for 5 minutes with isopropyl alcohol, isopropyl alcohol + ultrasonic, ethyl alcohol, ethyl alcohol + ultrasonic, and ultrasonic alone. Postpolymerization was followed for 5 minutes. The cleaning efficiency, microcomputed tomography (µCT), surface roughness, Vickers hardness, and flexural strength of the specimens were evaluated. The 1-way ANOVA test was performed after considering normality. A post hoc analysis with Bonferroni was also performed (α=.008 or.005).

RESULTS

Ultrasonic in addition to cleaning solutions significantly improved the cleaning efficiency in NextDent C&B MFH specimens (P<.005), whereas ultrasonic did not affect the efficiency in DIOnavi-P. MAX specimens. No significant differences were found in surface roughness by postprinting cleaning methods in either NextDent C&B MFH or DIOnavi-P. MAX (P>.005). No significant changes in surface hardness were observed by postprinting cleaning methods (P>.008). In the NextDent C&B MFH, ethyl alcohol + ultrasonic significantly decreased the flexural strength (P<.005). There were no significant differences in the flexural strength in the DIOnavi-P. MAX (P>.005).

CONCLUSIONS

Ethyl alcohol was comparable with isopropyl alcohol for use as a postprinting cleaning solution for both NextDent C&B MFH and DIOnavi-P. MAX. The addition of ultrasonic to cleaning solutions should be applied with caution. These findings suggest that different postprinting cleaning methods can be recommended depending on the 3D printed resin materials.

Effect of intra-alveolar delivery of Frondoside A on inflammatory response of delayed tooth replantation

BACKGROUND/AIM

Frondoside A is a sea cucumber extract which is well known for its anti-inflammatory and immunomodulatory properties. The purpose of this study was to evaluate the effect of Frondoside A application in the alveolar socket on inflammatory responses after delayed replantation in rat teeth.

MATERIALS AND METHODS

Human periodontal ligament cells were cultured and exposed to Frondoside A. Cell-counting kit-8 assay was performed to evaluate the cell viability and nitric oxide assay was performed to assess the anti-inflammatory effect of Frondoside A. Molars were extracted from 32 Sprague-Dawley rats and randomly divided into control and Frondoside A groups. After 30 min of extra-oral dry time, molars were replanted. In the Frondoside A group, Frondoside A solution was applied in the alveolar socket before replantation. The animals were sacrificed after 28 days and histologically and immunohistochemically evaluated.

RESULTS

0.5 μM Frondoside A showed higher cellular viability at 6 h and lower production of nitric oxide compared with other Frondoside A solutions (p < .05). The Frondoside A group demonstrated lower inflammatory resorption scores in both middle 1/3 and apical 1/3 of root compared to the control group (p < .05). The Frondoside A group showed lower levels of expression in both cathepsin K and CD45 compared with the control group (p < .05).

CONCLUSIONS

Within the limits of this study, intra-alveolar delivery of Frondoside A alleviates inflammatory root resorption in delayed replantation of rat teeth.

Effects of Doxycycline-Loaded NO-Releasing Nanomatrix Gel on Delayed Replanted of Rat Molar

BACKGROUND/AIM

Tooth avulsion and delayed replantation may cause inflammatory responses and root resorption of the tooth. The aim of this study is to investigate the effect of a doxycycline-loaded nitric oxide-releasing nanomatrix (DN) gel on the delayed replantation of avulsed rat teeth, with a focus on assessing the gel's potential to promote regeneration and inhibit complications associated with the replantation process.

MATERIALS AND METHODS

Twenty-four right maxillary first molars from male Sprague-Dawley rats were atraumatically extracted using sterile extraction forceps. The molars were dried for 1 h at room temperature (approximately 23 °C) and divided into four groups according to the root conditioning methods after extra-alveolar 60-min drying: Group 1, no root conditioning treatment prior to replantation; Group 2, soaking in 2% NaF solution for 5 min before replantation; Group 3, 5-min soaking in NO gel and injection of the gel into the alveolar socket; Group 4, 5-min soaking in DN gel and injection of the gel into the alveolar socket before replantation. The animals were euthanized four weeks after the operation and the specimens were evaluated histologically.

RESULTS

The use of NO gel alone showed better anti-inflammatory and periodontal effects than the control group, but it did not show a significant effect compared to the group using NaF. When using NO gel loaded with doxycycline, it showed a significant anti-inflammatory effect compared to the control group and showed a similar inhibitory effect to the group using NaF.

CONCLUSIONS

Within the limits of this study, in delayed replantation situations, the control of inflammatory resorption and replacement resorption is an important factor for achieving a better prognosis of replanted teeth. Root surface treatment with DN gel decreased root resorption after delayed replantation.

Ginsenoside Rb1 alleviates lipopolysaccharide-induced inflammation in human dental pulp cells via the PI3K/Akt, NF-κB, and MAPK signalling pathways

AIM

Among numerous constituents of Panax ginseng, a constituent named Ginsenoside Rb1 (G-Rb1) has been studied to diminish inflammation associated with diseases. This study investigated the anti-inflammatory properties of G-Rb1 on human dental pulp cells (hDPCs) exposed to lipopolysaccharide (LPS) and aimed to determine the underlying molecular mechanisms.

METHODOLOGY

The KEGG pathway analysis was performed after RNA sequencing in G-Rb1- and LPS-treated hDPCs. Reverse-transcription polymerase chain reaction (RT-PCR) and western blot analysis were used for the assessment of cell adhesion molecules and inflammatory cytokines. Statistical analysis was performed with one-way ANOVA and the Student-Newman-Keuls test.

RESULTS

G-Rb1 did not exhibit any cytotoxicity within the range of concentrations tested. However, it affected the levels of TNF-α, IL-6 and IL-8, as these showed reduced levels with exposure to LPS. Additionally, less mRNA and protein expressions of vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) were shown. With the presence of G-Rb1, decreased levels of PI3K/Akt, phosphorylated IκBα and p65 were also observed. Furthermore, phosphorylated ERK and JNK by LPS were diminished within 15, 30 and 60 min of G-Rb1 exposure; however, the expression of non-phosphorylated ERK and JNK remained unchanged.

CONCLUSIONS

G-Rb1 suppressed the LPS-induced increase of cell adhesion molecules and inflammatory cytokines, while also inhibiting PI3K/Akt, phosphorylation of NF-κB transcription factors, ERK and JNK of MAPK signalling in hDPCs.

Effect of orodispersible hyaluronic acid film on palatal mucosa wound healing

OBJECTIVE

The objective of the study was to evaluate the healing effect of hyaluronic acid films on palatal wounds.

MATERIALS AND METHODS

After making 5-mm diameter palatal wounds, 72 rats were randomly assigned to three groups: control, hyaluronic acid gel, and hyaluronic acid film. The animals were sacrificed at 3, 7, and 21 days after the experiment. Clinical, histological, and RT-PCR analyses were performed. Human ex vivo oral mucosa models were used. Histological analysis and pan-cytokeratin staining were performed at 5 days after wound creation.

RESULTS

In rat model, both gels and films showed favorable healing on Days 3 and 7 compared with healing in the control (p < 0.05). Film showed remarkable VEGF and α-SMA expression than did the others (p < 0.05). Immunohistochemical analysis showed that film exhibited significantly lower CD68 and greater α-SMA and vimentin expression levels than those in the others (p < 0.05). In human model, re-epithelialization rate of film group was significantly higher than that of the others. Complete epithelial regeneration was confirmed only in film group using pan-cytokeratin staining.

CONCLUSIONS

Within the limits of this study, hyaluronic acid film outperformed gels in terms of palatal wound healing in both models.

Three-dimensional analysis of the alveolar ridge profiles of maxillary central incisors in children for autotransplantation

BACKGROUND

Sufficient alveolar housing is fundamental to ensure the favorable prognosis of autotransplanted teeth. However, little is known about the alveolar ridge profiles of the anterior maxilla in children. Therefore, this study aimed to investigate the alveolar ridge profiles of the anterior maxilla in growing children.

METHODS

A total of 169 Korean children aged 10-13 years old were included in this retrospective study. Demographic data and cone-beam computed tomography scans of 244 maxillary central incisors were collected. For each tooth, the alveolar ridge thickness was determined at 1-, 3-, and 5-mm levels below the cemento-enamel junction. The alveolar process height and labial concavity were also evaluated. Statistical analyses were performed to evaluate differences according to age and sex.

RESULTS

The alveolar ridge thickness did not differ according to age. The alveolar ridge thickness in males was significantly greater than that in females among those aged 10 and 11 years. The average alveolar process height was 17.43 ± 2.22 mm. The alveolar process height hardly changed with age from 10-13 years, whereas the alveolar process height of males was significantly greater compared with that of females among those aged 10 years. The labial concavity was approximately 150˚, with no significant differences between age and sex.

CONCLUSIONS

Within the limits of this study, the anatomy of the alveolar ridge in the maxillary central incisors showed sufficient capacity as a recipient site for autotransplantation using mandibular premolars, especially in males. These findings serve as a valuable resource for facilitating autotransplantation in children.

Biocompatibility and Bioactivity of a Dual-Cured Resin-Based Calcium Silicate Cement: In Vitro and in vivo Evaluation

INTRODUCTION

This study aimed to assess the biocompatibility and bioactivity of a dual-cured resin-based calcium silicate cement in vitro and in vivo.

METHODS

For in vitro analyses, standardized samples were prepared using TheraCal LC, TheraCal PT, and ProRoot MTA. The amount of residual monomer released from TheraCal LC and TheraCal PT was assessed using liquid chromatography/mass spectrometry. Calcium ion release from the materials was evaluated using inductively coupled plasma-optical emission spectroscopy. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to determine the calcium weight volume in the materials. For in vivo analysis, a rat direct pulp capping model with TheraCal LC, TheraCal PT, and ProRoot MTA groups (n = 16 per group) was used. The rats were euthanized after 7 or 28 days, and histological and immunohistochemical analyses (CD68 and DSPP) were performed.

RESULTS

Bisphenol A-glycidyl methacrylate and polyethylene glycol dimethacrylate release from TheraCal PT was lower than that from TheraCal LC (P < .05). Similar results were obtained for calcium-ion release and calcium weight volume, with ProRoot MTA showing the highest values. In the in vivo evaluation, TheraCal PT showed significantly greater hard tissue formation than TheraCal LC (P < .017). TheraCal PT showed lower CD68 expression and greater DSPP expression than TheraCal LC (P < .017). There were no significant differences in the expression of CD68 or DSPP between the TheraCal PT and ProRoot MTA groups.

CONCLUSIONS

Within the limitations of this study, the biocompatibility and bioactivity of TheraCal PT could be comparable to those of ProRoot MTA.

Accelerated Oral Healing by Angelica gigas Nakai from Hot Melt Extrusion Technology: An In Vitro Study

Background and Objectives: In spite of the oral environment being healing-prone, its dynamic changes may affect wound healing. The purpose of this study was to assess the oral wound healing effect of Angelica gigas Nakai (AG) prepared by hot-melt extrusion. Materials and Methods: Human gingival fibroblast (HGF) cells were treated with AG or AG via hot-melt extrusion (AGH) for 24 h to determine the optimal concentration. For evaluating the anti-inflammatory effect of AG and AGH, a nitric oxide assay was performed under lipopolysaccharide (LPS) stimulation. The wound-healing effects of AG and AGH were evaluated using cell proliferation/migration assays and wound-healing marker expression through qRT-PCR. Results: Both AG and AGH showed no cytotoxicity on HGH cells. Regarding nitric oxide production, AGH significantly decreased LPS-induced nitric oxide production (p < 0.05). AGH showed a significantly positive result in the cell proliferation/cell migration assay compared with that in AG and the control. Regarding wound healing marker expression, AGH showed significantly greater VEGF and COL1α1 expression levels than those in the others (p < 0.05), whereas α-SMA expression was significantly different among the groups. Conclusions: Within the limits of this study, AGH accelerated oral wound healing in vitro.

Bisphenol A release from commercially available 3-dimensionally printed resins and human cell apoptosis to bisphenol A: an in-vitro study

Bisphenol A (BPA) from dental materials may be linked to children's health issues. This study aimed to assess the release of BPA from commercially available 3-dimensional (3D)-printed resin materials and evaluate BPA-related apoptotic effects on human periodontal ligament cells and gingival fibroblasts. Commercially available 3D-printed resin materials for prosthodontic use were selected as follows: NextDent C&B MFH (3D Systems, Rock Hill, SC, USA), DIOnavi-P. MAX (Dio Co., Busan, Korea), and DIOnavi-Denture02 (Dio Co., Busan, Korea). Identical cuboidal samples (1 cm × 1 cm × 0.5 cm) were printed from the materials and cured. BPA release was assessed using liquid chromatography/mass spectrometry (LC/MS). In addition, human gingival fibroblasts and periodontal ligament cells were exposed to various BPA solutions based on the LC/MS results. Cell Counting kit-8 (CCK-8) and real-time polymerase chain reaction analyses were performed to evaluate BPA-related apoptotic effects. The LC/MS analysis confirmed that none of the 3D-printed resin materials released BPA after curing. Both human gingival fibroblasts and periodontal ligament cells showed lower viability after BPA exposure. Regarding apoptosis-related gene expression, Caspase10 (CASP10) expression in periodontal ligament cells was significantly different in the BPA solutions (p < 0.05). The expression of BAX and Capspase8 (CASP8) in gingival fibroblasts was significantly increased by BPA in a dose-dependent manner (p < 0.05). Within the limitations of this study, the 3D-printed resin materials were not found to release BPA. This finding implies that 3D-printed resin materials are not associated with potential BPA-related risks in children.

Determination of the range of intervention timing for supernumerary teeth using the Korean health insurance review and assessment service database

This study aimed to identify the frequency of complications during the diagnosis, observation, and treatment of supernumerary teeth or odontomas and evaluate the relationship between complications and the timing of surgical intervention. This study was conducted based on data from the Korea Health Insurance Review and Assessment Service between January 2008 and December 2019. A 2-year washout period was applied, and a follow-up period of at least 2 years was also included. During the observation period, the age at diagnosis of supernumerary teeth and odontomas was analyzed using major diagnostic codes, and the treatment codes were used to determine the interval between diagnosis and surgical intervention. The incidence rates of supernumerary teeth (1.21%) and odontomas (0.36%) were comparable to that reported in previous studies. The frequency of supernumerary teeth was the highest in the anterior region, followed by the premolar and molar regions. The average ages at diagnosis according to the location of the supernumerary teeth were 7.25, 13.98, and 16.11 years in the anterior, premolar, and molar regions, respectively. The age at diagnosis correlated with the maturity period of the teeth at the corresponding location. For the supernumerary tooth group, surgical intervention was more likely to occur when malocclusion (p < 0.0001) or tooth eruption disturbances (p < 0.0001) were present or dentigerous cysts were absent (p = 0.006). For the odontoma group, malocclusion (p = 0.251) was not correlated with surgical intervention. When tooth eruption disturbances (p = 0.002) and dentigerous cysts (p < 0.0001) were present, surgical intervention was more likely to occur. Pediatric dentists should conduct timely clinical checks and periodic follow-ups to prevent complications and unnecessary orthodontic treatments in patients with supernumerary teeth or odontomas.

Stress distribution in pediatric zirconia crowns depending on different tooth preparation and cement type: a finite element analysis

BACKGROUND

In clinical settings, tooth preparation for prefabricated zirconia crowns (PZCs) in the primary dentition varies widely. However, knowledge about the biomechanical behavior of PZCs in various clinical settings is limited. This study was conducted to evaluate the biomechanical behavior of PZCs in different clinical settings using 3-dimensional finite element analysis.

METHODS

3-dimensional models of the PZC, cement, and tooth with six different conditions were simulated in primary molar teeth, incorporating cement thickness (100, 500, and 1000 μm) and cement type (resin-modified glass ionomer cement and resin cement). A total of 200 N of occlusal force was applied to the models, both vertically and obliquely as representative cases. A general linear model univariate analysis with partial eta-squared (ηp²) was performed to evaluate the relative effects of the variables.

RESULTS

The overall stress of tooth was increased as the cement space increases under oblique loading. The von Mises stress values of the resin cements were significantly higher than those of the resin-modified glass ionomer cements for all cement thicknesses (p < .05). The effect size of the cement type (η_p² = .519) was more dominant than the cement thickness (η_p² = .132) in the cement layer.

CONCLUSIONS

Within the limits of this study, cement type has a greater influence on the biomechanical behavior of PZCs than cement thickness.

Treatment of impacted double teeth using 3D surgical simulation in a school-age child: a case report

This report presents the therapeutic approach and results of a case of impacted undeveloped double teeth using 3D simulation in a school-age child. A 10-year-old girl was referred to hospital for the evaluation and treatment of fully impacted premolar double teeth in the left maxillary area. After evaluation, the double teeth were surgically removed, hemisected, and replanted after modification. For accurate surgery, replicas were made of the double teeth using CBCT and a 3D printer, and several mock surgeries were performed. Although remarkable signs for clinical and radiologic pathology were not found at the 5-month follow-up, short root with infraocclusion was found at the 30-month follow-up. This treatment widened the treatment spectrum with modern diagnostic approaches and preparation in large double teeth in children.

Correlations between skeletal maturity and dental calcification stages in Korean children

AIM

To evaluate the relationship between dental calcification and skeletal maturity and to identify the tooth with the highest correlation with skeletal maturity index in Korean children.

MATERIALS

For 447 children (205 boys and 242 girls) aged between 5 and 13 years, hand-wrist and lateral cephalometric radiographs were taken to assess skeletal maturity by Fishman's skeletal maturity indicators (SMI) and Baccetti's cervical vertebrae maturation (CVM) stages. Dental panoramic radiographs were taken to assess dental maturity of the permanent mandibular canine, first and second premolar, and second molar using the method devised by Dermirjian.

CONCLUSION

Dental calcification stages determined by panoramic radiographs can be clinically used as useful indices to predict skeletal maturity in Korean children.

Three-dimensional evaluation of tooth preparation forms in paediatric zirconia crowns: An in vitro study

BACKGROUND

Though prefabricated zirconia crowns (PZCs) differ from stainless steel crowns and have different preparation guidelines for optimal crown adaptation, little is known about how clinicians prepare teeth for PZCs.

AIM

To investigate the prepared tooth forms for PZCs and identify the shared patterns of tooth preparation.

DESIGN

Twenty participants prepared primary maxillary first molars and mandibular second molars for PZCs. A model with ideally prepared tooth was digitally generated as a reference. The prepared teeth were digitally scanned and superimposed on the reference. Three-dimensional analysis software was used to evaluate the discrepancy between ideal and prepared surface for overall surface and subdivided area.

RESULTS

Half of the surfaces received excessive reduction, and 24% showed error within 0.2 mm (p < .001) in maxilla. 41.6% of surfaces showed error within 0.2 mm, and 20% were excessively prepared (p = .002) in mandible. The highest discrepancies were found at the mesiopalatal line angles (maxillary) and at the distobuccal line angles (mandibular). Significant discrepancies were observed on the occlusal surfaces, especially at the cusps.

CONCLUSIONS

Tooth preparations for PZCs showed wide variations related to depth among the participants.

Orodispersible hyaluronic acid film delivery for oral wound healing in rats

Background/purpose

Oral wound healing undergoes a dynamic process of oral environment. This study aimed to investigate the effects of hyaluronic acid (HA) film on oral wound healing in a rat model.

Materials and methods

A total of 60 rats with tongue wounds (5 mm in diameter) were randomly divided into control (n = 20), HA gel (n = 20), and HA film groups (n = 20). The animals were sacrificed on either 3 or 7 days after the experiment. Clinical, histological, and quantitative reverse transcriptase-polymerase chain reaction analysis were performed to evaluate the healing rate, inflammation, re-epithelialization, and gene expression of wound healing biomarkers.

Results

The healing rates of HA gel (84.4 ± 9.2%) and HA film (74.0 ± 15.0%) were significantly higher than that of the control (51.7 ± 16.9%) on day 7 (P < 0.001 and P = 0.002, respectively). Histological analysis revealed no significant differences between the groups on day 3. On day 7, only the HA film showed significant improvement in inflammation (P = 0.038) and re-epithelialization (P = 0.011) compared to the control. Regarding wound healing biomarkers, both HA gel and HA film groups showed lower level of COL1α1 expression on day 3 compared to the control.

Conclusion

Within the limits of this study, HA film was found to be effective for oral wound healing, particularly for re-epithelialization. This finding suggests that HA film delivery can be beneficial not only for clinical convenience but also for promoting oral wound healing.

Void characteristics and tortuosity of calcium silicate-based cements for regenerative endodontics: a micro-computed tomography analysis

Background

Internal voids of materials can serve a hub for microorganism and affect the sealing ability. This study aimed to evaluate the sealing performance of calcium silicate-based cements in immature teeth treated with regenerative endodontics.

Methods

Twenty single root canals from immature permanent premolars were prepared using regenerative endodontic protocols. The root canals were randomly divided into two groups and sealed with mineral trioxide aggregate (MTA) and Biodentine (BD). The teeth were kept in humid environment for 7 days and scanned using micro-computed tomography. The voids within the cements were segmented and visualized using image processing, incorporating the modified Otsu algorithm. The porosity of each sample was also calculated as the ratio between the number of voxels of voids and the volume of the cements. Tortuosity was also calculated using the A-star algorithm.

Results

Voids larger than 70 μm were predominantly observed in the top and interfacial surface of cements. The others were evenly distributed. MTA and BD showed the same level of porosity and tortuosity at interfacial surfaces. In inner surfaces, MTA showed more less porosity and tortuosity compared to BD (p < 0.05).

Conclusions

There were no differences in sealing performance between MTA and BD.

The perspective of undergraduate dental students on web-based learning in pediatric dentistry during the COVID-19 pandemic: a Korean multicenter cross-sectional survey

BACKGROUND

The COVID-19 pandemic changed the world and created a shift in the dental education program. This sudden change in the dental education program may have affected the academic standards of dental students. This study aimed to evaluate the overall satisfaction and effectiveness of online learning in pediatric dentistry of undergraduate dental students' during the COVID-19 pandemic in South Korea.

METHODS

An anonymous online survey was sent to three dental schools, and responses were collected from dental school students. Questions included the demographics, perspectives of online classes, comparison of online and offline pediatric dentistry classes and opinions on how dental schools are handling the pandemic. Students' perspectives on online classes were evaluated based on satisfaction with online education. Data were analyzed using the Kruskal-Wallis test and the Mann-Whitney U test.

RESULTS

Most students took online classes from home (80.9%) using Zoom (50.4%). The majority reported overall program satisfaction (74.1%) and agreed that universities implemented online classes well (55%). Students who were in favor of online classes responded more positively to questions on the effectiveness and safety of online learning (p < 0.05). Regardless of satisfaction with online education, the students agreed that the online education shift was the right decision in pandemic outbreak.

CONCLUSIONS

Dental students in South Korea preferred and adapted well to the web-based learning program in pediatric dentistry during COVID-19 pandemic.

A Digital Fabrication of Dental Prosthesis for Preventing Self-Injurious Behavior Related to Autism Spectrum Disorder: A Case Report

This case report aimed to demonstrate the prosthetic solution of an autism patient with self-injurious behavior using digital dentistry. A 24-year-old male visited our clinic with chief complaints of severe gingival recession associated with self-injurious behavior. Bilateral fixed prosthesis with denture flange were delivered using a digital workflow for the protection of the gingiva. The patient showed healed gingival tissue, behavioral modification, and acceptable oral hygiene during the follow-up period. Also, his caregivers reported no recurrence of the self-injurious behavior. Autism patients usually show self-injurious behavior, which can damage their oral tissue. With adoption of this prosthesis, behavior modification as well as healing of oral tissue was achieved.

Differential gene expression profiles of periodontal soft tissue from rat teeth after immediate and delayed replantation: a pilot study

Purpose

In dental avulsion, delayed replantation usually has an uncertain prognosis. After tooth replantation, complex inflammatory responses promote a return to periodontal tissue homeostasis. Various types of cytokines are produced in the inflammatory microenvironment, and these cytokines determine the periodontal tissue response. This study aimed to identify the gene expression profiles of replanted teeth and evaluate the functional differences between immediate and delayed replantation.

Methods

Maxillary molars from Sprague-Dawley rats were extracted, exposed to a dry environment, and then replanted. The animals were divided into 2 groups according to the extra-oral time: immediate replantation (dry for 5 minutes) and delayed replantation (dry for 60 minutes). Either 3 or 7 days after replantation, the animals were sacrificed. Periodontal soft tissues were harvested for mRNA sequencing. Hallmark gene set enrichment analysis was performed to predict the function of gene-gene interactions. The normalized enrichment score (NES) was calculated to determine functional differences.

Results

The hallmark gene sets enriched in delayed replantation at 3 days were oxidative phosphorylation (NES=2.82, Q<0.001) and tumor necrosis factor-alpha (TNF-α) signaling via the nuclear factor kappa light chain enhancer of activated B cells (NF-κB) pathway (NES=1.52, Q=0.034). At 7 days after delayed replantation, TNF-α signaling via the NF-κB pathway (NES=–1.82, Q=0.002), angiogenesis (NES=–1.66, Q=0.01), and the transforming growth factor-beta signaling pathway (NES=–1.46, Q=0.051) were negatively highlighted.

Conclusions

Differentially expressed gene profiles were significantly different between immediate and delayed replantation. TNF-α signaling via the NF-κB pathway was marked during the healing process. However, the enrichment score of this pathway changed in a time-dependent manner between immediate and delayed replantation.

Postpartum haemorrhage requiring transfusion and risk of cardiovascular disease later in life: a retrospective cohort study

OBJECTIVE

To determine whether postpartum haemorrhage (PPH) is associated with cardiovascular disease (CVD), including cerebrovascular and ischaemic heart disease beyond the peripartum period.

DESIGN

Population-based cohort study.

SETTING

Merged databases of the Korea National Health Insurance (KNHI) claims, National Health Screening Examination and National Health Screening Program for Infants and Children.

POPULATION

Women who gave birth in 2007 in the Republic of Korea and who were tracked through to 2015 for the occurrence of CVD.

METHODS

Patients were identified and the occurrences of PPH and transfusion were determined using the KNHI claims database. The occurrence of CVD was tracked through 2015 using codes from the International Classification of Diseases, tenth revision (ICD-10).

MAIN OUTCOME MEASURES

The risk of CVD after PPH.

RESULTS

Among 150 381 women who gave birth during the study period, 9107 were diagnosed with PPH and 899 were treated with transfusion. The risk of CVD in women with PPH was no different than in women without PPH, after adjustment (HR 1.03, 95% CI 0.93-1.13). The risk of CVD in women with PPH requiring transfusion was significantly increased compared with women without PPH, after adjustment (HR 1.60, 95% CI 1.25-2.06). The risk of CVD in women with PPH without transfusion was not significantly different compared with women without PPH (HR 0.96, 95% CI 0.86-1.07).

CONCLUSIONS

Postpartum haemorrhage (PPH) requiring transfusion is associated with an increased risk of CVD. Guidelines for management should be established, and further studies on the mechanisms involved should be conducted.

TWEETABLE ABSTRACT

PPH requiring transfusion is associated with an increased risk of CVD.

Validation of a three-dimensional printed model for training of surgical extraction of supernumerary teeth

INTRODUCTION

This study aimed to validate a three-dimensional (3D) printed model to provide training for supernumerary teeth (SNTs) extraction.

MATERIALS AND METHODS

Each of the 30 participants, grouped as experienced and without experience, conducted two identically simulated surgeries on a 3D-printed replica of human mixed dentition with a SNT. The surgery time, area of bony window and volume of removed material were measured; subsequently, responses to a five-item questionnaire were recorded. The collected data were statistically analysed.

RESULTS

The surgery time was 228.37 ± 141.53 seconds and 125.47 ± 53.03 seconds in the first and second surgery, respectively. The training significantly decreased the surgery time in the participants without experience (P = .000). However, there were no significant differences in the area of window opening (P = .271) and volume of removed material between the two surgeries (P = .075). The participants who perceived educational benefits accounted for more than 60% of the respondents for every question. Participants without experience in SNT extraction showed a tendency to rate a higher score than did those with experience.

CONCLUSIONS

A 3D-printed model for surgical extraction of a SNT can improve surgical skill and, especially, shorten the learning curve in beginners.

Differential Gene Expression Changes in Human Primary Dental Pulp Cells Treated with Biodentine and TheraCal LC Compared to MTA

This study aimed to analyze the effects of pulp capping materials on gene expression changes in primary tooth-derived dental pulp cells using next-generation sequencing. Dental pulp cells were extracted and treated with mineral trioxide aggregate (MTA), Biodentine (BD), or TheraCal LC (TC). Cell viability assays were performed. Total RNA was extracted and analyzed through mRNA sequencing. Bioinformatic analysis of differential gene expression in dental pulp cells exposed to BD or TC versus MTA was performed. MTA, BD, and TC exposure had no significant effect on pulp cell viability (p > 0.05). Gene sets associated with inflammatory response (p = 2.94 × 10⁻⁵) and tumor necrosis factor alpha (TNF-α) signaling via the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway (p = 2.94 × 10⁻⁵) were enriched in all materials. In BD-treated cells, Wnt/β-catenin signaling (p = 3.15 × 10⁻⁴) gene sets were enriched, whereas enrichment of interferon gamma (IFN-γ) response (p = 3 × 10⁻³) was observed in TC-treated cells. In gene plot analysis, marked increases in receptor activator of nuclear factor kappa-Β ligand (RANKL) expression were seen in TC-treated cells over time. Despite the similar cell viabilities exhibited among MTA-, BD-, and TC-treated cells, patterns of gene networks differed, suggesting that diverse functional gene differences may be associated with treatment using these materials.

Customized surgical guide with a bite block and retraction arm for a deeply impacted odontoma; a technical note

Odontomas can cause impaction of permanent teeth. During the removal of odontomas associated with an impacted tooth, minimally-invasive surgical approaches are necessary. We present a technical note highlighting easy extraction of a deeply impacted odontoma using a patient-specific computer-aided design/computer-aided manufacturing (CAD/CAM) surgical guide. Its use and advantages are described.

An easy way to secure catheter in position during marsupialization procedure

Marsupialization is the conservative treatment for cystic lesion in children. This technique requires maintaining the patency between the cyst and oral cavity to allow spontaneous healing of cystic lesion. There have been various fixation methods for securing the patency. However, the previous fixation methods have limitation of being invasive and inability to retain catheter firmly during the treatment. In this technical note, we adopted a novel and easy fixation method to obtain firm stability of catheter without damage to intraoral tissues during marsupialization technique.

Systematic analysis of early phase clinical studies for patients with breast cancer: Inclusion of patients with brain metastasis

PURPOSE

This systematic review aims to better define the limitations and patterns with which patients with MBC and CNS metastasis are enrolled into early phase developmental therapeutics trials.

METHODS

In June 2016, PubMed search was conducted using the following keywords: "Breast cancer". Drug-development phase 1, phase 2 or phase 1/2 trials for patients with MBC were included. Multiple-histology trials and trials without an efficacy endpoint were excluded.

RESULTS

In total, 1474 studies were included; Inclusion criteria for 423 (29%) allowed for CNS metastasis, 770 (52%) either excluded or did not document eligibility of patients with CNS disease. Trials accruing patients with HER2-positive MBC and including targeted therapies had higher odds of allowing for patients with CNS disease (adjusted OR 1.56, 95% CI 1.08-2.2.6; p=0.019 and 1.49, 95% 1.08-2.06; p=0.014, respectively). There were also higher odds of accrual of patients with CNS involvement into clinical trials over time (odds ratio=1.10, 95% CI 1.07-1.12; p<0.0001).

CONCLUSION

Most published early phase clinical trials either did not clearly document or did not allow for accrual of patients with CNS disease. Early phase trials with targeted agents or enrolling HER2+ MBC had higher odds of permitting CNS metastases.

Abstract P6-06-47: The association between EGFR and cMET expression and phosphorylation and its prognostic implication in patients with breast cancer

Background: It has been shown that EGFR, cMET and their cross-talk play an important role in the progression of breast cancer and development of resistance to different targeted therapies. cMET expression and phosphorylation is linked with poor survival outcome in breast cancer. Recently, EGFR and cMET dual blockade has been proposed as an attractive targeted therapy for breast cancer. However, little is known about the co-expression patterns of EGFR and cMET in human breast cancer and its prognostic significance. We hypothesized that co-expression or co-activation of EGFR and cMET is linked with adverse survival outcome.

Methods: We measured protein levels of EGFR, cMET and their phosphorylated proteins in 825 breast cancers using reverse phase protein array. Given unimodal distribution of proteins, median was selected as a cut-off after sensitivity analyses. Kaplan-Meier survival curves were used to estimate relapse-free (RFS) and overall survival (OS). Cox proportional hazards models were fit to determine associations of EGFR and cMET with outcomes after adjustment for other clinical characteristics such as age, tumor stage, nodal status, receptor subtype and histologic grade.

Results: Mean age was 58 years. There were 457 (55%) hormone receptor (HR) positive, 211 (26%) triple-negative (TN) and 148 (18%) HER2 positive tumors. HER2 subgroup showed higher EGFR expression and phosphorylation compared to HR and TN subtypes (p&lt;0.05).

High EGFR expression group was associated with higher phosho-cMET (pcMET) but not cMET compared to low expression group (ANOVA pcMET p&lt;0.001, MET p = 0.34). The same association was found with High phospho-EGFR (pEGFR) group at Try 992 and Tyr1068 (both p&lt;0.001). In HR subtype, similar association was observed between EGFR/pEGFRs and pcMET (all p&lt;0.01). High expression groups in either of two pEGFRs were linked with higher cMET as well (all p&lt;0.001). In TN subtype, High expression group in EGFR and pEGFR at Tyr992 but not at Tyr1068 was associated with higher pcMET (p&lt;0.00, p = 0.012, p = 0.4, respectively). Only high expression group in pEGFR at Tyr 992 was linked with higher expression of cMET (p = 0.02). In contrast, among HER2 subtype, high expression group in pEGFR at Tyr 1068 but not at Tyr992 was associated with higher cMET and pcMET (cMET p = 0.023, pcMET p&lt;0.001).

Four subgroups of patients defined by dichotomized EGFR (or pEGFR) and cMET (or pcMET) level demonstrated no significant differences in RFS and OS. In multivariate analyses, only cMET expression level was associated with adverse survival (RFS p = 0.06, OS p = 0.035) while levels of pcMET, EGFR, and pEGFRs did not show significant association with outcomes.

Conclusion: We report that EGFR and cMET are either frequently co-expressed or co-activated in human breast cancer. HER2 subtype showed higher EGFR expression and activation compared to other subtypes. cMET protein expression level was found to be an independent prognostic factor irrespective of the EGFR expression or phosphorylation status.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P6-06-47.

Abstract P6-10-01: The Association between the Use of Selective COX-2 Inhibitors and Breast Cancer Recurrence

Introduction:

There have been biological findings alluding to the role of selective COX-2 inhibitors in reducing the risk of developing cancers including breast cancer. Epidemiological data suggest that COX-2 inhibitors may prevent the development of cancers, including colorectal, esophageal and lung cancer. To date, there exists no study that reported any relationship between their use and the risk of breast cancer recurrence. Thus, we investigated the associations between the use of COX-2 inhibitors and the risk of tumor recurrence among breast cancer patients.

Methods: We reviewed the medical records of female patients diagnosed with stage II/III breast cancer in Albert Einstein Medical Center between 1999 and 2005 and later reached no evident disease (NED) stage. Follow up period was from 1999 to 2008 with mean and maximum being 4.4 years and 9.8 years, respectively. COX-2 inhibitor user was defined as patients taking the medication in NED stage for at least 6 months. Age, race, family history, smoking history, menopausal status, diabetes, HER2/Neu status, hormone receptor status, TNM stage, histology, and treatment received were compared between COX-2 inhibitor users and nonusers. The primary outcome was disease free survival. The secondary outcome was overall survival. Multivariate analyses were performed using Cox proportional hazard model.

Results: Of 682 cancer patients, 7.3 % (n=50) were prescribed COX-2 inhibitor; 10.0 % (5/50) of patients developed recurrence among COX-2 inhibitor users, while 22.0% (139/632) did among nonusers (chi-square test: P&lt;0.05). COX-2 inhibitor use was negatively associated with cancer recurrence (hazard ratio [HR], 0.41; 95% confidence interval[CI], 0.17-1.00; P=0.05). Variables associated with recurrence in multivariate model were race (Caucasian vs. non-Caucasian; adjusted hazard ratio [AHR], 1.83; 95% CI, 1.20-1.84; P&lt;0.01) and number of nodes ≥3 (AHR, 2.22; 95% CI, 1.24-3.98; P&lt;0.01). In multivariate analysis, the association between COX-2 inhibitor use and cancer recurrence only suggestive (AHR, 0.35; 95% CI; 0.11-1.12; P=0.07). Kaplan-Meier survival analysis revealed that COX-2 inhibitor use was related to disease-free survival benefit (log-rank test P&lt;0.05). 5 year survival was 0.88 for COX-2 inhibitor users, and 0.77 for non-users. However, COX-2 inhibitor use was not associated with reduced overall mortality in breast cancer patients (AHR, 0.49; 95% CI: 0.15-1.58; P=0.23; log-rank test P=0.12) K-M Survival Curve of Breast Cancer Recurrence

Conclusions: The use of COX-2 inhibitors seems to be related to a reduced risk of developing recurrence in patients with breast cancer. This result provides the clinical evidence, in accordance with existing biological data, that COX-2 inhibitor use in breast cancer patients may be inversely associated with tumor recurrence. However, prospective randomized trials are required to validate our finding.

Solution structure of the toluene 4-monooxygenase effector protein (T4moD)

Toluene 4-monooxygenase (T4MO) from Pseudomonas mendocina catalyzes the NADH- and O(2)-dependent hydroxylation of toluene to form p-cresol. The complex consists of an NADH oxidoreductase (T4moF), a Rieske ferredoxin (T4moC), a diiron hydroxylase [T4moH, with (alphabetagamma)(2) quaternary structure], and a catalytic effector protein (T4moD). The solution structure of the 102-amino acid T4moD effector protein has been determined from 2D and 3D (1)H, (13)C, and (15)N NMR spectroscopic data. The structural model was refined through simulated annealing by molecular dynamics in torsion angle space (DYANA software) with input from 1467 experimental constraints, comprising 1259 distance constraints obtained from NOEs, 128 dihedral angle constraints from J-couplings, and 80 hydrogen bond constraints. Of 60 conformers that met the acceptance criteria, the 20 that best satisfied the input constraints were selected to represent the solution structure. With exclusion of the ill-defined N- and C-terminal segments (Ser1-Asn11 and Asp99-Met102), the atomic root-mean-square deviation for the 20 conformers with respect to the mean coordinates was 0.71 A for the backbone and 1.24 A for all non-hydrogen atoms. The secondary structure of T4moD consists of three alpha-helices and seven beta-strands arranged in an N-terminal betaalphabetabeta and a C-terminal betaalphaalphabetabetabeta domain topology. Although the published NMR structures of the methane monooxygenase effector proteins from Methylosinus trichosporium OB3b and Methylococcus capsulatus (Bath) have a similar secondary structure topology, their three-dimensional structures differ from that of T4moD. The major differences in the structures of the three effector proteins are in the relative orientations of the two beta-sheets and the interactions between the alpha-helices in the two domains. The structure of T4moD is closer to that of the methane monooxygenase effector protein from M. capsulatus (Bath) than that from M. trichosporium OB3b. The specificity of T4moD as an effector protein was investigated by replacing it in reconstituted T4MO complexes with effector proteins from monooxygenases from other bacterial species: Pseudomonas pickettii PKO1 (TbuV, toluene 3-monooxygenase); Pseudomonas species JS150 (TbmC, toluene 2-monooxygenase); and Burkeholderia cepacia G4 (S1, toluene 2-monooxygenase). The results showed that the closely related TbuV effector protein (55% sequence identity) provided partial activation of the complex, whereas the more distantly related TbmC (34% sequence identity) and S1 (29% sequence identity) did not. The (1)H NMR chemical shifts of the side-chain amide protons of Asn34, a conserved, structurally relevant amino acid, were found to be similar in spectra of effector proteins T4moD and TbuV but not in the spectrum of TbmC. This suggests that the region around Asn34 may be involved in structural aspects contributing to functional specificity.

Functional recombinant rabbit muscle phosphoglucomutase from Escherichia coli

The gene coding for phosphoglucomutase (PGM) from Oryctolagus cuniculus (rabbit) has been expressed in Escherichia coli under a T7 expression system with a His-tag. About half of the expressed PGM protein was present in inclusion bodies, but this protein was inactive when solubilized. The protein in the soluble cell fraction was isolated and purified in one step on a Ni-NTA column. The eluate from this column was adjusted to 95% saturated ammonium sulfate, and the resulting protein precipitate was resuspended in sodium phosphate buffer and dialyzed against 2.5 M ammonium sulfate. The final yield of protein was about 10 mg per liter of LB medium. The protein was judged to be greater than 90% pure on the basis of gel electrophoresis and activity measurements (128 U per milligram). Our motivation for developing this bacterial production system for PGM has been to prepare sufficient quantities of stable-isotope-labeled protein for experiments that utilize recently developed NMR technologies suitable for proteins the size of PGM (61.6 kDa). Preliminary NMR studies indicate that the current level of purity is adequate for this work. The construct described here was designed to incorporate an N-terminal His-tag for ease of isolation. Although PGM is a metalloprotein, the His-tag does not appear to interfere with activity. The presence of the His-tag should not pose a problem for proposed (31)P NMR investigations of the protein and its complexes in aqueous solution or incorporated into reverse micelles. However, we plan to design a cleavable His-tag for later (1)H, (13)C, (15)N studies of the active site, which includes essential histidine residues.

Oligomerization of the EK18 mutant of the trp repressor of Escherichia coli as observed by NMR spectroscopy

The regulation of the trp repressor system of Escherichia coli is frequently modeled by a single equilibrium, that between the aporepressor (TR) and the corepressor, l-tryptophan (Trp), at their intracellular concentrations. The actual mechanism, which is much more complex and more finely tuned, involves multiple equilibria: TR and Trp association, TR oligomerization, specific and nonspecific binding of various states of TR to DNA, and interactions between these various species and ions. TR in isolation exists primarily as a homodimer, but the state of oligomerization increases as the TR concentration goes up and/or the salt concentration goes down, leading to species with lower affinity for DNA. We have used multinuclear, multidimensional NMR spectroscopy to investigate structural changes that accompany the oligomerization of TR. For these investigations, the superrepressor mutant EK18 (TR with Glu 18 replaced by Lys) was chosen because it exhibits less severe oligomerization at higher protein concentration than other known variants; this made it possible to study the dimer to tetramer oligomerization step by NMR. The NMR results suggest that the interaction between TR dimers is structurally linked to folding of the DNA binding domain and that it likely involves direct contacts between the C-terminal residues of the C-helix of one dimer with the next dimer. This implies that oligomerization can compete with DNA binding and thus serves as a factor in the fine-tuning of gene expression.

Detection and classification of hyperfine-shifted 1H, 2H, and 15N resonances of the Rieske ferredoxin component of toluene 4-monooxygenase

T4MOC is a 12.3 kDa soluble Rieske ferredoxin that is obligately required for electron transfer between the oxidoreductase and diiron hydroxylase components of toluene 4-monooxygenase from Pseudomonas mendocina KR1. Our preliminary 1H NMR studies of oxidized and reduced T4MOC [Markley, J. L., Xia, B., Chae, Y. K., Cheng, H., Westler, W. M., Pikus, J. D., and Fox, B. G. (1996) in Protein Structure Function Relationships (Zaidi, Z., and Smith, D., Eds.) pp 135-146, Plenum Press, London] revealed the presence of hyperfine-shifted 1H resonances whose short relaxation times made it impractical to use nuclear Overhauser effect (NOE) measurements for assignment purposes. We report here the use of selective isotopic labeling to analyze the hyperfine-shifted 1H, 2H, and 15N signals from T4MOC. Selective deuteration led to identification of signals from the four Hbeta atoms of cluster ligands C45 and C64 in the oxidized and reduced forms of T4MOC. In the reduced state, the Curie temperature dependence of the Hbeta protons corresponded to that predicted from the simple vector spin-coupling model for nuclei associated with the localized ferric site. The signal at 25.5 ppm in the 1H spectrum of reduced T4MOC was assigned on the basis of selective 2H labeling to the His Hepsilon1 atom of one of the cluster ligands (H47 or H67). This assignment was corroborated by a one bond 1H-13C correlation (at 25.39 ppm 1H and 136.11 ppm 13C) observed in spectra of [U-13C]T4MOC with a 1H-13C coupling constant of approximately 192 Hz. The carbon chemical shift and one bond coupling constant are those expected for 1Hepsilon1-13Cepsilon1 in the imidazolium ring of histidine and are inconsistent with values expected for cysteine 1Halpha-13Calpha. The His Hepsilon1 proton exhibited weak Curie temperature dependence from 283 to 303 K, contrary to the anti-Curie temperature dependence predicted from the spin coupling model for nuclei associated with the localized ferrous site. A 1H peak at -12.3 ppm was observed in spectra of reduced T4MOC; this signal was found to correspond to a hydrogen (probably in an H-bond to the cluster) that exchanged with solvent with a half-time of about 2 days in the oxidized state but with a much longer (undetectable) half-time in the reduced state. These results with T4MOC call into question certain 1H assignments recently reported on the basis of NOE measurements for the comparable Rieske ferredoxin component of an evolutionarily related alkene monooxygenase from Xanthobacter sp. Py2 [Holz, R. C., Small, F. J., and Ensign, S. A, (1997) Biochemistry 36, 14690-14696]. Selective 15N labeling was used to identify hyperfine-shifted 15N NMR signals from the backbone nitrogens of all four cluster ligands (C45, H47, C64, and H67), from the Nepsilon2 atoms of the two histidine ligands (H47 and H67), and from nonligand Gln and Ala residues (Q48 and A66) present in the cluster-binding motif of T4MOC in the oxidized and reduced states. The results indicate that the Ndelta1 of each of the two ligand histidines of T4MOC are ligated to an iron atom and reveal a pattern of H-bonding to the Rieske [2Fe-2S] center involving four (H47, Q48, A66, and H67 of T4MOC) of the five backbone amide H-bonds expected on the basis of comparison with the crystal structures of other related Rieske proteins; the fifth backbone amide (I50 of T4MOC) failed to exhibit a hyperfine shift. This anomaly may arise from the lack of an associated disulfide in T4MOC, a fundamental structural difference between the three types of Rieske proteins that may be related to functional diversity in this protein family.

Lipid binding ridge on loops 2 and 3 of the C2A domain of synaptotagmin I as revealed by NMR spectroscopy

The C2A domain of synaptotagmin I, which binds Ca2+ and anionic phospholipids, serves as a Ca2+ sensor during excitation-secretion coupling. We have used multidimensional NMR to locate the region of C2A from rat synaptotagmin I that interacts, in the presence of Ca2+, with phosphatidylserine. Untagged, recombinant C2A was double-labeled with 13C and 15N, and triple-resonance NMR data were collected from C2A samples containing either Ca2+ alone or Ca2+ plus 6:0 phosphatidylserine. Phospholipid binding led to changes in chemical shifts of backbone atoms in residues Arg233 and Phe234 of loop 3 (a loop that also binds Ca2+) and His198, Val205, and Phe206 of loop 2. These residues lie along a straight line on a surface ridge of the C2A domain. The only other residue that exhibited appreciable chemical shift changes upon adding lipid was His254; however, because His254 is located on the other side of the molecule from the phospholipid docking site defined by the other residues, its shifts may result from nonspecific interactions. The results show that the "docking ridge" responsible for Ca2+-dependent membrane association is localized on the opposite side of the C2A domain from the transmembrane and C2B domains of synaptotagmin.

An electrochemical, kinetic, and spectroscopic characterization of [2Fe-2S] vegetative and heterocyst ferredoxins from Anabaena 7120 with mutations in the cluster binding loop

Residues within the cluster binding loops of plant-type [2Fe-2S] ferredoxins are highly conserved and serve to structurally stabilize this unique region of the protein. We have investigated the influence of these residues on the thermodynamic reduction potentials and rate constants of electron transfer to ferredoxin:NADP+ reductase (FNR) by characterizing various single and multiple site-specific mutants of both the vegetative (VFd) and the heterocyst (HFd) [2Fe-2S] ferredoxins from Anabaena. Incorporation of residues from one isoform into the polypeptide backbone of the other created hybrid mutants whose reduction potentials either were not significantly altered or were shifted, but did not reconcile the 33-mV potential difference between VFd and HFd. The reduction potential of VFd appears relatively insensitive to mutations in the binding loop, excepting nonconservative variations at position 78 (T78A/I) which resulted in approximately 40- to 50-mV positive shifts compared to wild type. These perturbations may be linked to the role of the T78 side chain in stabilizing an ordered water channel between the iron-sulfur cluster and the surface of the wild-type protein. While no thermodynamic barrier to electron transfer to FNR is created by these potential shifts, the electron-transfer reactivities of mutants T78A/I (as well as T48A which has a wild-type-like potential) are reduced to approximately 55-75% that of wild type. These studies suggest that residues 48 and 78 are involved in the pathway of electron transfer between VFd and FNR and/or that mutations at these positions induce a unique, but unproductive orientation of the two proteins within the protein-protein complex.

Structure-function relationships in Anabaena ferredoxin: correlations between X-ray crystal structures, reduction potentials, and rate constants of electron transfer to ferredoxin:NADP+ reductase for site-specific ferredoxin mutants

A combination of structural, thermodynamic, and transient kinetic data on wild-type and mutant Anabaena vegetative cell ferredoxins has been used to investigate the nature of the protein-protein interactions leading to electron transfer from reduced ferredoxin to oxidized ferredoxin:NADP+ reductase (FNR). We have determined the reduction potentials of wild-type vegetative ferredoxin, heterocyst ferredoxin, and 12 site-specific mutants at seven surface residues of vegetative ferredoxin, as well as the one- and two-electron reduction potentials of FNR, both alone and in complexes with wild-type and three mutant ferredoxins. X-ray crystallographic structure determinations have been carried out for six of the ferredoxin mutants. None of the mutants showed significant structural changes in the immediate vicinity of the [2Fe-2S] cluster, despite large decreases in electron-transfer reactivity (for E94K and S47A) and sizable increases in reduction potential (80 mV for E94K and 47 mV for S47A). Furthermore, the relatively small changes in Calpha backbone atom positions which were observed in these mutants do not correlate with the kinetic and thermodynamic properties. In sharp contrast to the S47A mutant, S47T retains electron-transfer activity, and its reduction potential is 100 mV more negative than that of the S47A mutant, implicating the importance of the hydrogen bond which exists between the side chain hydroxyl group of S47 and the side chain carboxyl oxygen of E94. Other ferredoxin mutations that alter both reduction potential and electron-transfer reactivity are E94Q, F65A, and F65I, whereas D62K, D68K, Q70K, E94D, and F65Y have reduction potentials and electron-transfer reactivity that are similar to those of wild-type ferredoxin. In electrostatic complexes with recombinant FNR, three of the kinetically impaired ferredoxin mutants, as did wild-type ferredoxin, induced large (approximately 40 mV) positive shifts in the reduction potential of the flavoprotein, thereby making electron transfer thermodynamically feasible. On the basis of these observations, we conclude that nonconservative mutations of three critical residues (S47, F65, and E94) on the surface of ferredoxin have large parallel effects on both the reduction potential and the electron-transfer reactivity of the [2Fe-2S] cluster and that the reduction potential changes are not the principal factor governing electron-transfer reactivity. Rather, the kinetic properties are most likely controlled by the specific orientations of the proteins within the transient electron-transfer complex.

Site-specific mutagenesis demonstrates that the structural requirements for efficient electron transfer in Anabaena ferredoxin and flavodoxin are highly dependent on the reaction partner: kinetic studies with photosystem I, ferredoxin:NADP+ reductase, and cytochrome c

Electron transfer reactions involving site-specific mutants of Anabaena ferredoxin (Fd) and flavodoxin (Fld) modified at surface residues close to the prosthetic groups, with photoexcited P700 in spinach photosystem I (PSI) particles, ferredoxin:NADP+ reductase (FNR), and horse cytochrome c (cytc), have been investigated by laser flash photolysis and stopped-flow spectrophotometry. Nonconservative mutations in Fd at F65 and E94, which have been shown to result in very large inhibitions of electron transfer to FNR, were found to yield wild-type behavior in reactions with PSI and cytc. In general, the effects of Fd mutagenesis on the PSI reactions were considerably smaller than those observed for the FNR reaction. In the case of Fld, mutagenesis was found to have only small effects on both the FNR and PSI reactions, although the specific sites whose mutation caused changes in electron transfer properties differed for the two systems. In contrast, several of the Fld mutants showed appreciably larger effects on the nonphysiological reaction with cytc. We conclude from these studies that the structural requirements for efficient electron transfer involving the Fd and Fld molecules differ, depending upon the reactant with which these redox proteins interact. This is consistent with the multiple roles that these proteins have in vivo in biological electron transfer and implies that different conserved residues in these proteins have evolved to satisfy varying requirements of particular reaction partners.

Analysis of the hyperfine-shifted nitrogen-15 resonances of the oxidized form of Anabaena 7120 heterocyst ferredoxin

Hyperfine-shifted nitrogen signals have been detected in one-dimensional 15N NMR spectra of oxidized Anabaena 7120 heterocyst ferredoxin labeled uniformly with 15N. Several of these have been classified by amino acid type by reference to results from selective 15N-labeling studies. Remarkable agreement is seen between a dipole-dipole analysis of the 15N T1 relaxation and the distances of several of the nitrogens from the irons of the cluster as derived from the X-ray structure of this protein [Jacobson, B. L., Chae, Y. K., Markley, J. L., Rayment, I., & Holden, H. M. (1993) Biochemistry 32, 6788-6793]. The agreement is within experimental error for hyperfine-shifted nitrogens that are at least 4.2 A distant from either of the irons of the cluster; however, the simple model appears to fail for hyperfine-shifted nitrogens that are closer to the cluster. The failure of the model for short distances may stem either from a breakdown of the point-dipole approximation and/or from neglect of delocalization of unpaired electron density from the iron ions to other atoms. Even with the above limitations, dipolar analysis of 15N relaxation should provide useful distance constraints for solution-state studies of iron-sulfur proteins.

Mutations of surface residues in Anabaena vegetative and heterocyst ferredoxin that affect thermodynamic stability as determined by guanidine hydrochloride denaturation

The stability properties of oxidized wild-type (wt) and site-directed mutants in surface residues of vegetative (Vfd) and heterocyst (Hfd) ferredoxins from Anabaena 7120 have been characterized by guanidine hydrochloride (Gdn-HCl) denaturation. For Vfd it was found that mutants E95K, E94Q, F65Y, F65W, and T48A are quite similar to wt in stability. E94K is somewhat less stable, whereas E94D, F65A, F65I, R42A, and R42H are substantially less stable than wt. R42H is a substitution found in all Hfds, and NMR comparison of the Anabaena 7120 Vfd and Hfd showed the latter to be much less stable on the basis of hydrogen exchange rates (Chae YK, Abildgaard F, Mooberry ES, Markley JL, 1994, Biochemistry 33:3287-3295); we also find this to be true with respect to Gdn-HCl denaturation. Strikingly, the Hfd mutant H42R is more stable than the wt Hfd by precisely the amount of stability lost in Vfd upon mutating R42 to H (2.0 kcal/mol). On the basis of comparison of the X-ray crystal structures of wt Anabaena Vfd and Hfd, the decreased stabilities of F65A and F65I can be ascribed to increased solvent exposure of interior hydrophobic groups. In the case of Vfd mutants E94K and E94D, the decreased stabilities may result from disruption of a hydrogen bond between the E94 and S47 side chains. The instability of the R42 mutants is also most probably due to decreased hydrogen bonding capabilities.(ABSTRACT TRUNCATED AT 250 WORDS)

Multinuclear, multidimensional NMR studies of Anabaena 7120 heterocyst ferredoxin. Sequence-specific resonance assignments and secondary structure of the oxidized form in solution

Sequence-specific assignments were determined for the diamagnetic proton resonances from recombinant Anabaena 7120 heterocyst ferredoxin (M(r) = 11,000) produced in Escherichia coli. Several samples selectively labeled with nitrogen-15 were prepared for use in two-dimensional heteronuclear multiple quantum coherence (HMQC) [Müller, L. (1979) J. Am. Chem. Soc. 101, 4481-4484] experiments. A sample uniformly labeled with nitrogen-15 was also prepared and used in two three-dimensional experiments: NOESY-HMQC and TOCSY-HMQC [Zuiderweg, E. R. P., & Fesik, S. W. (1989) Biochemistry 28, 2387-2391; Marion, D., Ikura, M., Tsuchudin, R., & Bax, A. (1989) J. Magn. Reson. 85, 393-399]. The sequential assignment strategy relied on the detection of 15N-edited interresidue 1H alpha i/1HNi+1 NOE connectivities. Starting points and checks were provided by HMQC spectra of the selectively labeled samples. A sample doubly labeled with carbon-13 and nitrogen-15 was also prepared and used in three triple-resonance experiments: HNCA, HNCO, and HN(CO)CA [Ikura, M., Kay, L. E., & Bax, A. (1990) Biochemistry 29, 4659-4667; Kay, L. E., Ikura, M., Tschudin, R., & Bax, A. (1990) J. Magn. Reson. 89, 496-514]. The HNCA and HN(CO)CA spectra, which were used to confirm assignments from NOE connectivities, provided independent sequential assignments from spin couplings. Resonances from 18 residues were not seen in the diamagnetic region of the NMR spectrum. Several of these residues are very close to the [2Fe-2S] cluster, and their absence is explained by paramagnetic broadening and/or shifting.(ABSTRACT TRUNCATED AT 250 WORDS)

Structure-function studies of [2Fe-2S] ferredoxins

The ability to overexpress [2Fe-2S] ferredoxins in Escherichia coli has opened up exciting research opportunities. High-resolution x-ray structures have been determined for the wild-type ferredoxins produced by the vegatative and heterocyst forms of Anabaena strain 7120 (in their oxidized states), and these have been compared to structural information derived from multidimensional, multinuclear NMR spectroscopy. The electron delocalization in in these proteins in their oxidized and reduced states has been studied by 1H, 2H, 13C, and 15N NMR spectroscopy. Site-directed mutagenesis has been used to prepare variants of these ferredoxins. Mutants (over 50) of the vegetative ferredoxin have been designed to explore questions about cluster assembly and stabilization and to determine which residues are important for recognition and electron transfer to the redox partner Anabaena ferredoxin reductase. The results have shown that serine can replace cysteine at each of the four cluster attachment sites and still support cluster assembly. Electron transfer has been demonstrated with three of the four mutants. Although these mutants are less stable than the wild-type ferredoxin, it has been possible to determine the x-ray structure of one (C49S) and to characterize all four by EPR and NMR. Mutagenesis has identified residues 65 and 94 of the vegetative ferredoxin as crucial to interaction with the reductase. Three-dimensional models have been obtained by x-ray diffraction analysis for several additional mutants: T48S, A50V, E94K (four orders of magnitude less active than wild type in functional assays), and A43S/A45S/T48S/A50N (quadruple mutant).

Amino acid residues in Anabaena ferredoxin crucial to interaction with ferredoxin-NADP+ reductase: site-directed mutagenesis and laser flash photolysis

Ferredoxin (Fd) functions in photosynthesis to transfer electrons from photosystem I to ferredoxin-NADP+ reductase (FNR). We have made several site-directed mutants of Anabaena 7120 Fd and have used laser flash photolysis to investigate the effects of these mutations on the kinetics of reduction of oxidized Fd by deazariboflavin semiquinone (dRfH.) and the reduction of oxidized Anabaena FNR by reduced Fd. None of the mutations influenced the second-order rate constant for dRfH. reduction by more than a factor of 2, suggesting that the ability of the [2Fe-2S] cluster to participate in electron transfer was not seriously affected. In contrast, a surface charge reversal mutation, E94K, resulted in a 20,000-fold decrease in the second-order rate constant for electron transfer from Fd to FNR, whereas a similar mutation at an adjacent site, E95K, produced little or no change in reaction rate constant compared to wild-type Fd. Such a dramatic difference between contiguous surface mutations suggests a very precise surface complementarity at the protein-protein interface. Mutations introduced at F65 (F65I and F65A) also decreased the rate constant for the Fd/FNR electron transfer reaction by more than 3 orders of magnitude. Spectroscopic and thermodynamic measurements with both the E94 and F65 mutants indicated that the kinetic differences cannot be ascribed to changes in gross conformation, redox potential, or FNR binding constant but rather reflect the protein-protein interactions that control electron transfer. Several mutations at other sites in the vicinity of E94 and F65 (R42, T48, D68, and D69) resulted in little or no perturbation of the Fd/FNR interaction.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular structure of the oxidized, recombinant, heterocyst [2Fe-2S] ferredoxin from Anabaena 7120 determined to 1.7-A resolution

The [2Fe-2S] ferredoxin produced in the heterocyst cells of Anabaena 7120 plays a key role in nitrogen fixation, where it serves as an electron acceptor from various sources and an electron donor to nitrogenase. The three-dimensional structure of this ferredoxin has now been determined and refined to a crystallographic R value of 16.7%, with all measured X-ray data from 30.0 to 1.7 A. The molecular motif of this ferredoxin is similar to that of other plant-type ferredoxins with the iron-sulfur cluster located toward the outer edge of the molecule and the irons tetrahedrally coordinated by both inorganic sulfurs and sulfurs provided by protein cysteinyl residues. The overall secondary structure of the molecule consists of seven strands of beta-pleated sheet, two alpha-helices, and seven type I turns. It is of special interest that 4 of the 22 amino acid positions thought to be absolutely conserved in nonhalophilic ferredoxins are different in the heterocyst form of the protein. Three of these positions are located in the metal-cluster binding loop.

Crystallization and preliminary analysis of oxidized, recombinant, heterocyst [2Fe-2S] ferredoxin from Anabaena 7120

The [2Fe-2S] ferredoxin produced in the heterocyst cells of Anabaena 7120 plays a key role in nitrogen fixation, where it serves as an electron acceptor from various sources and an electron donor to nitrogenase. Crystals of recombinant heterocyst ferredoxin, coded for by the fdx H gene from Anabaena 7120 and overproduced in Escherichia coli, have been grown from ammonium sulfate solutions and are suitable for high resolution X-ray crystallographic analysis. They belong to the hexagonal space group P6(1) or P6(5) with unit cell dimensions of a = b = 44.2 A and c = 80.6 A. The crystals contain one molecule per asymmetric unit and diffract to a nominal resolution of 1.6 A. The molecular structure of this heterocyst ferredoxin is of special interest in that 4 of the 22 amino acid positions thought to be absolutely conserved in nonhalophilic ferredoxins are different and, based on amino acid sequence alignments, three of these positions are located in the metal-cluster binding loop. Consequently, a high-resolution X-ray analysis of this [2Fe-2S] ferredoxin, and subsequent three-dimensional comparisons with other known ferredoxin models, will provide new insight into structure/function relationships for this class of redox proteins.