Risk Factors for Treatment Failure in Neonates With Skin and Soft Tissue Infection: A Retrospective Cohort Study

We aimed to describe the frequency of treatment failure and associated risk factors for treatment failure amongst neonates with skin and soft tissue infections (SSTIs). We conducted a retrospective cohort study of neonates 0 to 28 days old with uncomplicated SSTIs presenting to the emergency department of a quaternary care children's hospital from 2009 to 2017. Data were collected via chart review. Skin and soft tissue infections included the following: cellulitis, abscess, mastitis, perirectal SSTI, carbuncle, and furuncle. Of the 202 neonates in the study, most were term, afebrile with mastitis, or perirectal SSTI. Treatment failure occurred in 8% (17/202) of neonates receiving oral antibiotics; 10 of these neonates had perirectal SSTIs and 2 had clindamycin and methicillin-resistant Staphylococcus aureus. Neonates with treatment failure had increased odds of having perirectal SSTIs (odds ratio [OR] = 4.08, 95% confidence interval [CI] = 1.46-11.31). Further studies are needed to identify strategies to prevent treatment failure in neonates with perirectal SSTIs.

Frequency of Treatment Failure of UTIs in Children With Congenital Urinary Tract Anomalies

OBJECTIVES

Children with certain congenital anomalies of the kidney and urinary tract and neurogenic bladder (CAKUT/NGB) are at higher risk of treatment failure for urinary tract infections (UTIs) than children with normal genitourinary anatomy, but the literature describing treatment and outcomes is limited. The objectives of this study were to describe the rate of treatment failure in children with CAKUT/NGB and compare duration of antibiotics between those with and without treatment failure.

METHODS

Multicenter retrospective cohort of children 0 to 17 years old with CAKUT/NGB who presented to the emergency department with fever or hypothermia and were diagnosed with UTI between 2017 and 2018. The outcome of interest was treatment failure, defined as subsequent emergency department visit or hospitalization for UTI because of the same pathogen within 30 days of the index encounter. Descriptive statistics and univariates analyses were used to compare covariates between groups.

RESULTS

Of the 2014 patient encounters identified, 482 were included. Twenty-nine (6.0%) of the 482 included encounters had treatment failure. There was no difference in the mean duration of intravenous antibiotics (3.4 ± 2.5 days, 3.5 ± 2.8 days, P = .87) or total antibiotics between children with and without treatment failure (10.2 ± 3.8 days, 10.8 ± 4.0 days, P = .39) Of note, there was a higher rate of bacteremia in children with treatment failure (P = .04).

CONCLUSIONS

In children with CAKUT/NGB and UTI, 6.0% of encounters had treatment failure. Duration of antibiotics was not associated with treatment failure. Larger studies are needed to assess whether bacteremia modifies the risk of treatment failure.

Viral Coinfections in Kawasaki Disease: A Meta-analysis

CONTEXT

Viral infections are suspected triggers in Kawasaki disease (KD); however, a specific viral trigger has not been identified.

OBJECTIVES

In children with KD, to identify (1) overall prevalence of viral infections; (2) prevalence of specific viruses; and (3) whether viral positivity was associated with coronary artery aneurysms (CAAs) or refractoriness to intravenous immunoglobin (IVIG).

DATA SOURCES

We searched Embase, Medline, and Cochrane databases and gray literature.

STUDY SELECTION

Eligible studies were conducted between 1999 and 2019, and included children diagnosed with KD who underwent viral testing.

DATA EXTRACTION

Two investigators independently reviewed full-text articles to confirm eligibility, extract data, appraise for bias, and assess evidence quality for outcomes using the Grading of Recommendations Assessment Development and Evaluation criteria. We defined viral positivity as number of children with a positive viral test divided by total tested. Secondary outcomes were CAA (z score ≥2.5) and IVIG refractoriness (fever ≥36 hours after IVIG).

RESULTS

Of 3189 unique articles identified, 54 full-text articles were reviewed, and 18 observational studies were included. Viral positivity weighted mean prevalence was 30% (95% confidence interval [CI], 14-51) and varied from 5% to 66%, with significant between-study heterogeneity. Individual virus positivity was highest for rhinovirus (19%), adenovirus (10%), and coronavirus (7%). Odds of CAA (odds ratio, 1.08; 95% CI, 0.75-1.56) or IVIG refractoriness (odds ratio, 0.88; 95% CI, 0.58-1.35) did not differ on the basis of viral status.

LIMITATIONS

Low or very low evidence quality.

CONCLUSIONS

Viral infection was common with KD but without a predominant virus. Viral positivity was not associated with CAAs or IVIG refractoriness.

Hierarchy of Evidence Within the Medical Literature

The quality of evidence from medical research is partially deemed by the hierarchy of study designs. On the lowest level, the hierarchy of study designs begins with animal and translational studies and expert opinion, and then ascends to descriptive case reports or case series, followed by analytic observational designs such as cohort studies, then randomized controlled trials, and finally systematic reviews and meta-analyses as the highest quality evidence. This hierarchy of evidence in the medical literature is a foundational concept for pediatric hospitalists, given its relevance to key steps of evidence-based practice, including efficient literature searches and prioritization of the highest-quality designs for critical appraisal, to address clinical questions. Consideration of the hierarchy of evidence can also aid researchers in designing new studies by helping them determine the next level of evidence needed to improve upon the quality of currently available evidence. Although the concept of the hierarchy of evidence should be taken into consideration for clinical and research purposes, it is important to put this into context of individual study limitations through meticulous critical appraisal of individual articles.

Association of Models of Care for Kawasaki Disease With Utilization and Cardiac Outcomes

OBJECTIVES

Describe the prevalence of different care models for children with Kawasaki disease (KD) and evaluate utilization and cardiac outcomes by care model.

METHODS

Multicenter, retrospective cohort study of children aged 0 to 18 hospitalized with KD in US children's hospitals from 2017 to 2018. We classified hospital model of care via survey: hospitalist primary service with as-needed consultation (Model 1), hospitalist primary service with automatic consultation (Model 2), or subspecialist primary service (Model 3). Additional data sources included administrative data from the Pediatric Health Information System database supplemented by a 6-site chart review. Utilization outcomes included laboratory, medication and imaging usage, length of stay, and readmission rates. We measured the frequency of coronary artery aneurysms (CAAs) in the full cohort and new CAAs within 12 weeks in the 6-site chart review subset.

RESULTS

We included 2080 children from 44 children's hospitals; 21 hospitals (48%) identified as Model 1, 19 (43%) as Model 2, and 4 (9%) as Model 3. Model 1 institutions obtained more laboratory tests and had lower overall costs (P < .001), whereas echocardiogram (P < .001) and immune modulator use (P < .001) were more frequent in Model 3. Secondary outcomes, including length of stay, readmission rates, emergency department revisits, CAA frequency, receipt of anticoagulation, and postdischarge CAA development, did not differ among models.

CONCLUSIONS

Modest cost and utilization differences exist among different models of care for KD without significant differences in outcomes. Further research is needed to investigate primary service and consultation practices for KD to optimize health care value and outcomes.

Investigation of discordant sibling pairs from hereditary breast cancer families and analysis of a rare PMS1 variant

BACKGROUND

It is likely that additional genes for hereditary breast cancer can be identified using a discordant sib pair design. Using this design we identified individuals harboring a rare PMS1 c.605G>A variant previously predicted to result in loss of function.

OBJECTIVES

A family-based design and predictive algorithms were used to prioritize candidate variants possibly associated with an increased risk of hereditary breast cancer. Functional analyses were performed for one of the candidate variants, PMS1 c.605G>A.

METHODS

1) 14 discordant sister-pairs from hereditary breast cancer families were identified. 2) Whole exome sequencing was performed and candidate risk variants identified. 3) A rare PMS variant was identified in 2 unrelated affected sisters but no unaffected siblings. 4) Functional analysis of this variant was carried out using targeted mRNA sequencing.

RESULTS

Genotype-phenotype correlation did not demonstrate tracking of the variant with cancer in the family. Functional analysis revealed no difference in exon 6 incorporation, which was validated by analyzing PMS1 allele specific expression.

CONCLUSIONS

The PMS1 c.605G>A variant did not segregate with disease, and there was no variant-dependent impact on PMS1 exon 6 splicing, supporting this variant is likely benign. Functional analyses are imperative to understanding the clinical significance of predictive algorithms.

Invasive Bacterial Infections in Infants Younger Than 60 Days With Skin and Soft Tissue Infections

OBJECTIVE

The objective of this study was to describe the frequency of invasive bacterial infections (IBIs) in young infants with skin and soft tissue infections (SSTIs) and the impact of IBI evaluation on disposition, length of stay (LOS), and cost.

METHODS

This retrospective (2009-2014) cohort study used data from 35 children's hospitals in the Pediatric Health Information System. We included infants younger than 60 days who presented to an emergency department (ED) with SSTI. Invasive bacterial infection was defined as bacteremia/sepsis, bone/joint infection, or bacterial meningitis. Readmission and return ED visits within 30 days were evaluated to identify missed IBIs for infants.

RESULTS

A total of 2734 infants were included (median age, 33 days; interquartile range [IQR], 21-44); 62% were hospitalized. Invasive bacterial infection was identified in 2%: bacteremia (1.8%), osteomyelitis (0.1%), and bacterial meningitis (0.1%). Hospitalization occurred in 78% of infants with blood cultures, 95% with cerebrospinal fluid cultures, and 23% without cultures. Median hospitalization LOS was 2 days (IQR, 1-3). Median cost was US $4943 for infants with cerebrospinal fluid cultures (IQR, US $3475-6780) compared with US $419 (IQR, US $215-1149) for infants without IBI evaluations (P < 0.001). Five infants (0.2%) returned to the ED within 30 days with new IBI diagnoses (4 bacteremia, 1 meningitis).

CONCLUSIONS

Invasive bacterial infection occurs infrequently in infants younger than 60 days who present to children's hospital EDs with SSTI. Bacteremia is the most common IBI. More extensive evaluation for IBI is associated with increased rate of admission, LOS, and cost. Further studies are needed to evaluate the safety of a limited IBI evaluation in young infants with SSTI.

Antibiotic Regimens and Associated Outcomes in Children Hospitalized With Staphylococcal Scalded Skin Syndrome

BACKGROUND

Controversy exists regarding the optimal antibiotic regimen for use in hospitalized children with staphylococcal scalded skin syndrome (SSSS). Various regimens may confer toxin suppression and/or additional coverage for methicillin-susceptible Staphylococcus aureus (MSSA) or methicillin-resistant S aureus (MRSA).

OBJECTIVES

To describe antibiotic regimens in hospitalized children with SSSS and examine the association between antistaphylococcal antibiotic regimens and patient outcomes.

DESIGN/METHODS

Retrospective cohort study of children hospitalized with SSSS using the Pediatric Health Information System database (2011-2016). Children who received clindamycin monotherapy, clindamycin plus MSSA coverage (eg, nafcillin), or clindamycin plus MRSA coverage (eg, vancomycin) were included. The primary outcome was hospital length of stay (LOS); secondary outcomes were treatment failure and cost. Generalized linear mixed-effects models were used to compare outcomes among antibiotic groups.

RESULTS

Of 1,259 children included, 828 children received the most common antistaphylococcal antibiotic regimens: clindamycin monotherapy (47%), clindamycin plus MSSA coverage (33%), and clindamycin plus MRSA coverage (20%). Children receiving clindamycin plus MRSA coverage had higher illness severity (44%) compared with clindamycin monotherapy (28%) and clindamycin plus MSSA (32%) (P =.001). In adjusted analyses, LOS and treatment failure did not differ among the 3 regimens (P =.42 and P =.26, respectively). Cost was significantly lower for children receiving clindamycin monotherapy and highest in those receiving clindamycin plus MRSA coverage (mean, $4,839 vs $5,348, respectively; P <.001).

CONCLUSIONS

In children with SSSS, the addition of MSSA or MRSA coverage to clindamycin monotherapy was associated with increased cost and no incremental difference in clinical outcomes.

Effectiveness of Modalities to Teach Evidence Based Medicine to Pediatric Clerkship Students: A Randomized Controlled Trial

OBJECTIVE

To evaluate the effectiveness of a traditional didactic session (TDS) as compared to a self-paced, interactive, multimedia module (SPM) on the application of evidence-based medicine (EBM) skills among medical students during their inpatient pediatric rotation.

METHODS

We conducted a randomized controlled trial from June, 2017 to June, 2018 at a quaternary care children's hospital. Students were randomized to TDS or SPM during each 2-week block. All students completed a critical appraisal tool (CAT) of evidence related to a clinical question in a standardized appraisal form and self-reflected about the EBM process. The primary outcome was the numeric score of the CAT derived by using the validated Fresno tool. Secondary outcomes of knowledge, attitudes, confidence, and self-reported behaviors related to EBM were measured using validated surveys. Statistical analysis was performed using Student's t test for CAT scores and mixed-model procedure (PROC MIXED), with subject as random effect and time as repeated measure for the secondary outcomes.

RESULTS

One hundred twenty-seven clerkship students were included. Overall, there was no significant difference in mean CAT scores for TDS (n = 59) versus SPM (n = 66) groups (90.3 vs 92.0, P = .65). There were no significant differences between SPM and TDS groups for knowledge (P = .66), attitudes (P = .97), confidence (P  = .55), and accessing evidence (P = .27). Both groups showed significant gains in knowledge, attitudes, confidence, and accessing evidence from baseline to postcourse. Improvements in knowledge and confidence were sustained at 3-months.

CONCLUSION

A SPM learning module is as effective as a TDS module for application of EBM concepts and knowledge to patient care.

Clinical Predictors for Abnormal Renal Bladder Ultrasound in Hospitalized Young Children With a First Febrile Urinary Tract Infection

BACKGROUND

Physicians often obtain a routine renal bladder ultrasound (RBUS) for young children with a first febrile urinary tract infection (UTI). However, few children are diagnosed with serious anatomic anomalies, and opportunity may exist to take a focused approach to ultrasonography. We aimed to identify characteristics of the child, prenatal ultrasound (PNUS), and illness that could be used to predict an abnormal RBUS and measure the impact of RBUS on management.

METHODS

We conducted a single-center prospective cohort study of hospitalized children 0 to 24 months of age with a first febrile UTI from October 1, 2016, to December 23, 2018. Independent variables included characteristics of the child, PNUS, and illness. The primary outcome, abnormal RBUS, was defined through consensus of a multidisciplinary team on the severity of ultrasound findings important to identify during a first UTI.

RESULTS

A total of 211 children were included; the median age was 1.0 month (interquartile range 0-2), and 55% were uncircumcised boys. All mothers had a PNUS with 10% being abnormal. Escherichia coli was the pathogen in 85% of UTIs, 20% (n = 39 of 197) had bacteremia, and 7% required intensive care. Abnormal RBUS was found in 36% (n = 76 of 211) of children; of these, 47% (n = 36 of 76) had moderately severe findings and 53% (n = 40 of 76) had severe findings. No significant difference in clinical characteristics was seen among children with and without an abnormal RBUS. One child had Foley catheter placement, and 33% received voiding cystourethrograms, 15% antibiotic prophylaxis, and 16% subspecialty referrals.

CONCLUSIONS

No clinical predictors were identified to support a focused approach to RBUS examinations. Future studies should investigate the optimal timing for RBUS.

Caregivers' Perceptions and Hospital Experience After a Brief Resolved Unexplained Event: A Qualitative Study

BACKGROUND AND OBJECTIVES

The American Academy of Pediatrics published guidelines for evaluation and management of lower-risk infants for a brief resolved unexplained event (BRUE). The guideline identified gaps in knowledge related to caregiver satisfaction, anxiety, and family-centered educational strategies to improve caregiver experience and patient outcomes. The objective of this study was to understand caregivers' experience with hospitalization for infants with BRUE, including their perception of the hospital stay, the diagnosis of BRUE, and their feelings toward the upcoming discharge from the hospital.

METHODS

We conducted a qualitative study using semistructured interviews with caregivers of infants aged 0 to 12 months who were admitted to a quaternary care children's hospital for a BRUE. Interviews were conducted within 24 hours of discharge. Two investigators coded transcripts and identified themes using consensus.

RESULTS

Eighteen caregivers of 13 infants were interviewed. No infants met criteria for being low risk according to the American Academy of Pediatrics guidelines. The coding scheme produced 3 major themes. First, parents felt reassured by hospital monitoring, diagnostic evaluation, and staff support in the hospital. Second, parents felt unsettled by the uncertainty of the child's condition and whether BRUE's "unexplainable" quality is understood as being part of normal infant behavior. Third, these themes manifested as conflicting emotions about caregivers' readiness for discharge.

CONCLUSIONS

Although hospital monitoring may provide reassurance for some caregivers, they continue to struggle with the uncertainty of the diagnosis. Caregiver perspectives can inform physicians' strategies to improve hospital experience and discharge readiness.

Variation in Antibiotic Selection and Clinical Outcomes in Infants <60 Days Hospitalized With Skin and Soft Tissue Infections

OBJECTIVES

To describe variation in empirical antibiotic selection in infants <60 days old who are hospitalized with skin and soft-tissue infections (SSTIs) and to determine associations with outcomes, including length of stay (LOS), 30-day returns (emergency department revisit or readmission), and standardized cost.

METHODS

Using the Pediatric Health Information System, we conducted a retrospective study of infants hospitalized with SSTI from 2009 to 2014. We analyzed empirical antibiotic selection in the first 2 days of hospitalization and categorized antibiotics as those typically administered for (1) staphylococcal infection, (2) neonatal sepsis, or (3) combination therapy (staphylococcal infection and neonatal sepsis). We examined the association of antibiotic selection and outcomes using generalized linear mixed-effects models.

RESULTS

A total of 1319 infants across 36 hospitals were included; the median age was 30 days (interquartile range [IQR]: 17-42 days). We observed substantial variation in empirical antibiotic choice, with 134 unique combinations observed before categorization. The most frequently used antibiotics included staphylococcal therapy (50.0% [IQR: 39.2-58.1]) and combination therapy (45.4% [IQR: 36.0-56.0]). Returns occurred in 9.2% of infants. Compared with administration of staphylococcal antibiotics, use of combination therapy was associated with increased LOS (adjusted rate ratio: 1.35; 95% confidence interval: 1.17-1.53) and cost (adjusted rate ratio: 1.39; 95% confidence interval: 1.21-1.58), but not with 30-day returns.

CONCLUSIONS

Infants who are hospitalized with SSTI experience wide variation in empirical antibiotic selection. Combination therapy was associated with increased LOS and cost, with no difference in returns. Our findings reveal the need to identify treatment strategies that can be used to optimize resource use for infants with SSTI.

Variation in Diagnostic Test Use and Associated Outcomes in Staphylococcal Scalded Skin Syndrome at Children's Hospitals

OBJECTIVES

The incidence of staphylococcal scalded skin syndrome (SSSS) is rising, but current practice variation in diagnostic test use is not well described. Our aim was to describe the variation in diagnostic test use in children hospitalized with SSSS and to determine associations with patient outcomes.

METHODS

We performed a retrospective (2011-2016) cohort study of children aged 0 to 18 years from 35 children's hospitals in the Pediatric Health Information System database. Tests included blood culture, complete blood count, erythrocyte sedimentation rate, C-reactive protein level, serum chemistries, and group A streptococcal testing. K-means clustering was used to stratify hospitals into groups of high (cluster 1) and low (cluster 2) test use. Associations between clusters and patient outcomes (length of stay, cost, readmissions, and emergency department revisits) were assessed with generalized linear mixed-effects modeling.

RESULTS

We included 1259 hospitalized children with SSSS; 84% were ≤4 years old. Substantial interhospital variation was seen in diagnostic testing. Blood culture was the most commonly obtained test (range 62%-100%), with the most variation seen in inflammatory markers (14%-100%). Between hospital clusters 1 and 2, respectively, there was no significant difference in adjusted length of stay (2.6 vs 2.5 days; P = .235), cost ($4752 vs $4453; P = .591), same-cause 7-day readmission rate (0.8% vs 0.4%; P = .349), or emergency department revisit rates (0.1% vs 0.6%; P = .148).

CONCLUSIONS

For children hospitalized with SSSS, lower use of diagnostic tests was not associated with changes in outcomes. Hospitals with high diagnostic test use may be able to reduce testing without adversely affecting patient outcomes.

Human cells contain a factor that facilitates the DNA glycosylase-mediated excision of oxidized bases from occluded sites in nucleosomes

Reactive oxygen species generate some 20,000 base lesions per human cell per day. The vast majority of these potentially mutagenic or cytotoxic lesions are subject to base excision repair (BER). Although chromatin remodelers have been shown to enhance the excision of oxidized bases from nucleosomes in vitro, it is not clear that they are recruited to and act at sites of BER in vivo. To test the hypothesis that cells possess factors that enhance BER in chromatin, we assessed the capacity of nuclear extracts from human cells to excise thymine glycol (Tg) lesions from exogenously added, model nucleosomes. The DNA glycosylase NTHL1 in these extracts was able to excise Tg from both naked DNA and sites in nucleosomes that earlier studies had shown to be sterically accessible. However, the same extracts were able to excise lesions from sterically-occluded sites in nucleosomes only after the addition of Mg²⁺/ATP. Gel mobility shift assays indicated that nucleosomes remain largely intact following the Mg²⁺/ATP -dependent excision reaction. Size exclusion chromatography indicated that the NTHL1-stimulating activity has a relatively low molecular weight, close to that of NTHL1 and other BER glycosylases; column fractions that contained the very large chromatin remodeling complexes did not exhibit this same stimulatory activity. These results indicate that cells possess a factor(s) that promotes the initiation of BER in chromatin, but differs from most known chromatin remodeling complexes.

Prevalence of Concomitant Acute Bacterial Meningitis in Neonates with Febrile Urinary Tract Infection: A Retrospective Cross-Sectional Study

OBJECTIVE

To describe the frequency of concomitant acute bacterial meningitis (ABM) in neonates with febrile urinary tract infection (UTI).

STUDY DESIGN

This was a retrospective cross-sectional study from 2005 to 2013 of infants ≤30 days old evaluated in the emergency department of a quaternary care children's hospital with fever and laboratory-confirmed UTI. Definite ABM was defined as cerebrospinal fluid (CSF) culture with growth of pathogenic bacteria and probable ABM if pleocytosis with ≥ 20 white blood cell was present in an antibiotic-pretreated patient. The timing of lumbar puncture and first antibiotic dose was recorded to assess for antibiotic pretreatment.

RESULTS

A total of 236 neonates with UTI were included. Mean age was 18.6 days (SD 6.2); 79% were male infants. Twenty-three (9.7%) had bacteremia. Fourteen (6%) were pretreated. No neonate (0%; 95% CI 0%-1.6%) had definite ABM and 2 (0.8%; 95% CI 0.1%-3.0%) neonates with bloody CSF had probable ABM. CSF white blood cell count was 25 and 183 for these 2 infants, and CSF red blood cell count was 3100 and 61 932, respectively. Another neonate had herpes simplex virus meningoencephalitis.

CONCLUSIONS

The frequency of ABM in neonates with febrile UTI is low. Further prospective studies are needed to evaluate the safety of a tiered approach to evaluate for serious bacterial infection, in which lumbar puncture potentially could be avoided in well-appearing febrile neonates with suspected UTI.

Periprosthetic fractures of the distal femur after total knee arthroplasty : Plate versus nail fixation

The incidence of periprosthetic fractures about a TKA is increasing. Traditionally, these fractures are classified by their location and prosthesis integrity. In the setting of a supracondyar fracture about a well-fixed prosthesis, both plate and nail fixation of the fracture present themselves as options, each with unique benefits and pitfalls. Through review and discussion of the literature, we aim to describe some of the patient, fracture, and implant related factors that should be considered when planning fixation of periprosthetic fractures about a TKA. Additionally, we present several technical pearls that may be useful in the successful treatment of these difficult injuries.

LEVEL OF EVIDENCE

4.

Impact of Enterovirus Testing on Resource Use in Febrile Young Infants: A Systematic Review

CONTEXT

Enterovirus infection commonly causes fever in infants aged 0 to 90 days and, without testing, is difficult to differentiate from serious bacterial infection.

OBJECTIVE

To determine the cost savings of routine enterovirus testing and identify subgroups of infants with greater potential impact from testing among infants 0 to 90 days old with fever.

DATA SOURCES

Studies were identified systematically from published and unpublished literature by using Embase, Medline, the Cochrane database, and conference proceedings.

STUDY SELECTION

Inclusion criteria were original studies, in any language, of enterovirus infection including the outcomes of interest in infants aged 0 to 90 days.

DATA EXTRACTION

Standardized instruments were used to appraise each study. The evidence quality was evaluated using Grading of Recommendations Assessment, Development, and Evaluation criteria. Two investigators independently searched the literature, screened and critically appraised the studies, extracted the data, and applied the Grading of Recommendations Assessment, Development, and Evaluation criteria.

RESULTS

Of the 257 unique studies identified and screened, 32 were completely reviewed and 8 were included. Routine enterovirus testing was associated with reduced hospital length of stay and cost savings during peak enterovirus season. Cerebrospinal fluid pleocytosis was a poor predictor of enterovirus meningitis. The studies were all observational and the evidence was of low quality.

CONCLUSIONS

Enterovirus polymerase chain reaction testing, independent of cerebrospinal fluid pleocytosis, can reduce length of stay and achieve cost savings, especially during times of high enterovirus prevalence. Additional study is needed to identify subgroups that may achieve greater cost savings from testing to additionally enhance the efficiency of testing.

Current Evidence on the Evaluation and Management of Fever Without a Source in Infants Aged 0-90 Days: A Review

BACKGROUND

Despite development of risk stratification tools decades ago, the best strategy for evaluation and management of young infants with fever without a clear source remains uncertain.

OBJECTIVE

To describe the variability in current practice and review recently published evidence in three key areas: inflammatory markers were used as a tool for risk stratification, impact of viral testing, and optimal observation time on antibiotics.

METHOD

Articles were identified using PubMed, Scopus, and Cochrane databases and via experts. Abstracts were screened and potential articles underwent full review if they focused on febrile infants 0- 90 days with fever without a source and outcomes for key topics.

RESULTS

Thirty-two articles were included. Recent studies show that variability exists for most aspects of evaluation and management. C reactive protein and procalcitonin (PCT) perform poorly for identification of serious bacterial infections (SBIs). However, PCT has good diagnostic accuracy for detection of invasive bacterial infections (IBIs), such as bacteremia and meningitis. When PCT is combined with urinalysis and clinical appearance in the Step-by-Step method, the sensitivity for detection of IBI is 92% for infants &gt; 21 days of age. Infants with lab-confirmed viral infection were found to have reduced risk for SBI. Blood culture yield for true pathogens was the highest in the first 12-36 hours after incubation.

CONCLUSION

Recent studies suggest viral testing and inflammatory markers (specifically PCT) can help better stratify young febrile infants at risk for IBIs. Infants who are deemed low risk may benefit from shorter observation times and tailored or discontinued antibiotic therapy.

An Examination of Physician-, Caregiver-, and Disease-Related Factors Associated With Readmission From a Pediatric Hospital Medicine Service

OBJECTIVES

The purpose of this study was to describe the characteristics and reasons for pediatric hospital medicine readmissions. We also aimed to describe characteristics of potentially preventable cases and the reliability of classification.

METHODS

Retrospective descriptive study from December 2008 through June 2010 in a large academic tertiary care children's hospital in Houston, Texas. Children were included if they were readmitted to the hospital within 30 days of discharge from the pediatric hospital medicine service. Reasons for readmission were grouped into three categories: physician-related, caretaker-related, and disease-related. Readmissions with physician- or caretaker-related reasons were considered potentially preventable.

RESULTS

The overall readmission rate was 3.1%, and a total of 204 subjects were included in the analysis. Lymphadenitis and failure to thrive had the highest readmission rates with 21%, and 13%, respectively. Twenty percent (n=41/204) of readmissions were preventable with 24% (n=10/41) being physician-related, 12% (n=5/41) caregiver-related, and 63% (n=26/41) for mixed reasons. When comparing classification of readmissions into preventable status, there was moderate agreement between 2 reviewers (K=0.44, 95% confidence interval: 0.28-0.60). Among patients with preventable readmission, the probability of having had a readmission by 7 days and 15 days was 73% and 78%, respectively.

CONCLUSIONS

Reliable identification of preventable pediatric readmissions using individual reviewers remains a challenge. Additional studies are needed to develop a reliable approach to identify preventable readmissions and underlying modifiable factors. A focused review of 7-day readmissions and diagnoses with high readmission rates may allow use of fewer resources.

Risk factors for complications in hospitalized young infants presenting with uncomplicated pertussis

OBJECTIVE

We sought to identify risk factors for complications in hospitalized young infants with uncomplicated pertussis.

METHODS

Retrospective cohort study of hospitalized infants 0 to 6 months of age with confirmed pertussis from 2005 to 2009. Subjects presenting without complications or need for initial intensive care admission were deemed to have uncomplicated pertussis. Complications during hospitalization were defined as apnea, pneumonia, seizures, or encephalopathy. Univariate analysis was performed by estimating odds ratios (OR) and 95% confidence intervals (CI) for the association between each variable and the occurrence of complications. Multivariable analysis was performed using logistic regression. Clinical variables included demographics, historical, laboratory, and imaging data.

RESULTS

Of 126 study subjects, 46 (36.5%) developed complications in the hospital: 43 with apnea (two required endotracheal intubation), seven with pneumonia, and three with seizures; there were no cases of encephalopathy and no deaths. Age less than 60 days (OR, 2.71; 95% CI, 1.08-6.82), cough duration less than 7 days (OR, 5.38; 95% CI, 1.79-16.18), history of color change (OR, 5.24; 95% CI, 1.14-24.07), parental intervention (OR, 10.05; 95% CI, 1.67-60.39), and need for oxygen in the emergency department (OR. 3.94; 95% CI. 1.37-11.36) were associated with development of complications. The median duration of cough at the time of complication was 9 days (range 2-30 days). Initial complete blood cell count and radiographic findings were not associated with complications.

CONCLUSIONS

Infants with uncomplicated pertussis may be at low risk for developing respiratory failure or death. Historical information may assist practitioners in determining risk for serious complications.

Expression of the oxidative base excision repair enzymes is not induced in TK6 human lymphoblastoid cells after low doses of ionizing radiation

Most of the DNA damage produced by ionizing radiation is repaired by the base excision repair (BER) pathway. To determine whether the BER genes were up-regulated by low doses of ionizing radiation, we investigated their expression in TK6 human lymphoblastoid cells by measuring mRNA levels using real-time quantitative PCR. No induction at the transcriptional level of any of the base excision repair genes, NTH1 (NTHL1), OGG1, NEIL1, NEIL2, NEIL3, APE1, POLB, or accessory protein genes, LIG3, XRCC1 or XPG, was found at gamma-radiation doses ranging from 1 cGy to 2 Gy in a 24-h period. As has been measured in other cell lines, a dose-dependent induction of CDKN1A (WAF1) mRNA levels was observed in TK6 cells in the dose range of 0.5 to 2.0 Gy. We also examined BER enzyme activity on 8-oxoguanine-, dihydrouracil- and furan-containing oligonucleotide substrates and found no increase in extracts of TK6 cells after gamma-ray doses of 0.5-2.0 Gy. These data were corroborated by Western blot analysis of APE1 and NTH1, suggesting that the BER enzymes are also not up-regulated at the post-transcriptional level after ionizing radiation exposure.

Abortive base-excision repair of radiation-induced clustered DNA lesions in Escherichia coli

It has been postulated that ionizing radiation produces a unique form of cellular DNA damage called "clustered damages" or "multiply damaged sites". Here, we show that clustered DNA damages are indeed formed in Escherichia coli by ionizing radiation and are converted to lethal double-strand breaks during attempted base-excision repair. In wild-type cells possessing the oxidative DNA glycosylases that cleave DNA at repairable single damages, double-strand breaks are formed at radiation-induced clusters during postirradiation incubation and also in a dose-dependent fashion. E. coli mutants lacking these enzymes do not form double-strand breaks postirradiation and are substantially more radioresistant than wild-type cells. Furthermore, overproduction of one of the oxidative DNA glycosylases in mutant cells confers a radiosensitive phenotype and an increase in the number of double-strand breaks. Thus, the effect of the oxidative DNA glycosylases in potentiating DNA damage must be considered when estimating radiation risk.

Human histologic and histomorphometric analysis comparing OsteoGraf/N with PepGen P-15 in the maxillary sinus elevation procedure: a case report

The use of the anorganic bovine bone mineral OsteoGraf/N combined with demineralized freeze-dried bone allograft has received widespread use in sinus elevations. This composite graft material has proven to be suitable, predictable, and successful for the placement and integration of endosseous implants in the edentulous, atrophic maxilla. In this case study, the current materials and accepted methodology were compared with the latest tissue-engineered bone replacement graft material, PepGen P-15. PepGen P-15 is a combination of OsteoGraf/N and a synthetic peptide (P-15) that mimics the cell-binding domain of Type-I collagen responsible for cell migration, differentiation, and proliferation. The radiographic, histologic, and histomorphometric evaluations of the sinus grafted with PepGen P-15 showed enhanced bone formation within a shorter time interval compared with the composite graft material of OsteoGraf/N and demineralized freeze-dried bone allograft.

Inhibition of oxidative DNA repair in cadmium-adapted alveolar epithelial cells and the potential involvement of metallothionein

This study evaluated the effects of cadmium (Cd) adaptation in cultured alveolar epithelial cells on oxidant-induced DNA damage and its subsequent repair. Using the comet assay, we determined that lower levels of DNA damage occurred in Cd-adapted cells compared with non-adapted cells following treatment of cells with hydrogen peroxide (H(2)O(2)). This may be a consequence of increased thiol-containing antioxidants that were observed in adapted cells, including metallothionein and glutathione. Cd-adapted cells were, however, less efficient at repairing total oxidative DNA damage compared with non-adapted cells. Subsequently, we investigated the effect of Cd adaptation on the repair of particular oxidized DNA lesions by employing lesion-specific enzymes in the comet assay, namely formamidopyrimidine DNA glycosylase (Fpg), an enzyme that predominantly repairs 8-oxoguanine (8-oxoG), and endonuclease III, that is capable of repairing oxidized pyrimidines. The data demonstrated that adaptation to Cd results in significantly impaired repair of both Fpg- and endonuclease III-sensitive lesions. In addition, in situ detection of 8-oxoG using a recombinant monoclonal antibody showed that Cd-adaptation reduces the repair of this oxidative lesion after exposure of cells to H(2)O(2). Activities of 8-oxoG-DNA glycosylase and endonuclease III were determined in whole cell extracts using 32P-labeled synthetic oligonucleotides containing 8-oxoG and dihydrouracil sites, respectively. Cd adaptation was associated with an inhibition of 8-oxoG-DNA glycosylase and endonuclease III enzyme activity compared with non-adapted cells. In summary, this study has shown that Cd adaptation: (1) reduces oxidant-induced DNA damage; (2) increases the levels of key intracellular antioxidants; (3) inhibits the repair of oxidative DNA damage.

Base excision repair processing of radiation-induced clustered DNA lesions

Energy from low LET ionising radiation, such as X rays and gamma rays, is deposited in the water surrounding the DNA molecule such that between 2 to 5 radical pairs are generated within a radius of I to 4 nm. As a result, multiple single lesions, including oxidised purine or pyrimidine bases, sites of base loss, and single-strand breaks, can be formed in DNA from the same radiation energy deposition event. The single lesions in these so-called multiply damaged sites or clustered lesions are repaired by base excision repair. Here we show that clustered DNA damages are formed in bacterial cells by ionising radiation and are converted to lethal double-strand breaks during attempted repair. In wild type cells possessing the oxidative DNA glycosylases that recognise and cleave DNA at repairable single damages, double-strand breaks are formed at radiation-induced clusters during post-irradiation incubation and in a dose-dependent fashion. Mutant cells lacking these enzymes do not form double-strand breaks post-irradiation and are substantially more radioresistant than wild type cells. These radioresistant mutant cells can be made radiosensitive by overexpressing one of the oxidative DNA glycosylases. Thus the effect of the oxidative DNA glycosylases in potentiating DNA damage must be considered when estimating radiation risk.

Spectroscopic studies of zinc(II)- and cobalt(II)-associated Escherichia coli formamidopyrimidine-DNA glycosylase: extended X-ray absorption fine structure evidence for a metal-binding domain

Formamidopyrimidine-DNA glycosylase (Fpg) is a 30.2 kDa protein that plays an important role in the base excision repair of oxidatively damaged DNA in Escherichia coli. Sequence analysis and genetic evidence suggest that zinc is associated with a C4-type motif, C(244)-X(2)-C(247)-X(16)-C(264)-X(2)-C(267), located at the C-terminus of the protein. The zinc-associated motif has been shown to be essential for damaged DNA recognition. Extended X-ray absorption fine structure (EXAFS) spectra collected on the zinc-associated protein (ZnFpg) in the lyophilized state and in 10% frozen aqueous glycerol solution show directly that the metal is coordinated to the sulfur atom of four cysteine residues. The average Zn-S bond length is 2.33 +/- 0.01 and 2.34 +/- 0.01 A, respectively, in the lyophilized state and in 10% frozen aqueous glycerol solution. Fpg was also expressed in minimal medium supplemented with cobalt nitrate to yield a blue-colored protein that was primarily cobalt-associated (CoFpg). The profiles of the circular dichroism spectra for CoFpg and ZnFpg are identical, suggesting that the substitution of Co(2+) for Zn(2+) does not alter the structure of Fpg. A similar conclusion is reached upon the analysis of two-dimensional (15)N/(1)H HSQC spectra of uniformly (15)N-labeled samples of ZnFpg and CoFpg; the spectra are similar and display features characteristic of a structured protein. Biochemical assays with a 54 nt DNA oligomer containing 7, 8-dihydro-8-oxoguanine at a specific location show that CoFpg and ZnFpg are equally active at cleaving the DNA at the site of the oxidized guanine. EXAFS spectra of CoFpg indicate that the cobalt is coordinated to the sulfur atom of four cysteine residues with an average Co-S bond length of 2.28 +/- 0.01 and 2.29 +/- 0.01 A, respectively, in the lyophilized state and in 10% frozen aqueous glycerol solution. The structural similarity between CoFpg and ZnFpg suggests that it is biologically relevant to use the paramagnetic properties of Co(2+) as a structural probe.

Multiprobe RNase protection assay analysis of mRNA levels for the Escherichia coli oxidative DNA glycosylase genes under conditions of oxidative stress

Escherichia coli formamidopyrimidine DNA glycosylase (Fpg), MutY DNA glycosylase, endonuclease VIII, and endonuclease III are oxidative base excision repair DNA glycosylases that remove oxidized bases from DNA, or an incorrect base paired with an oxidized base in the case of MutY. Since genes encoding other base excision repair proteins have been shown to be part of adaptive responses in E. coli, we wanted to determine whether the oxidative DNA glycosylase genes are induced in response to conditions that cause the type of damage their encoded proteins remove. The genes fpg, mutY, nei, and nth encode Fpg, MutY, endonuclease VIII, and endonuclease III, respectively. Multiprobe RNase protection assays were used to examine the transcript levels of these genes under conditions that induce the SoxRS, OxyR, and SOS regulons after a shift from anaerobic to aerobic growth and at different stages along the growth curve. Transcript levels for all four genes decreased as cells progressed from log-phase growth to stationary phase and increased after cells were shifted from anaerobic to aerobic growth. None of the genes were induced by hydrogen peroxide, paraquat, X rays, or conditions that induce the SOS response.

Histologic and clinical comparison of bilateral sinus floor elevations with and without barrier membrane placement in 12 patients: Part 3 of an ongoing prospective study

In 1993 the Department of Implant Dentistry at New York University College of Dentistry began a long-term clinical, histologic, histomorphometric, and radiographic study of the sinus elevation procedure. One of the parameters under evaluation in this study is the effect of barrier membrane placement on the creation of vital bone in the grafted sinus cavity. This report presents a histologic and histomorphometric evaluation of healing with and without the placement of an expanded polytetrafluoroethylene (e-PTFE) barrier membrane over the lateral window at the time of sinus grafting. The data were collected from 12 patients who underwent bilateral sinus elevation surgery. In each of these 12 patients the same grafting material was used in both sinuses, making the presence or absence of an e-PTFE barrier membrane the only controlled variable. Under the conditions of this study, the results indicate that (1) placement of the barrier membrane tends to increase vital bone formation; (2) placement of a barrier membrane has a positive effect on implant survival; and (3) membrane placement should be considered for all sinus elevation procedures.

The effect of inter-implant distance on the height of inter-implant bone crest

BACKGROUND

The biologic width around implants has been well documented in the literature. Once an implant is uncovered, vertical bone loss of 1.5 to 2 mm is evidenced apical to the newly established implant-abutment interface. The purpose of this study was to evaluate the lateral dimension of the bone loss at the implant-abutment interface and to determine if this lateral dimension has an effect on the height of the crest of bone between adjacent implants separated by different distances.

METHODS

Radiographic measurements were taken in 36 patients who had 2 adjacent implants present. Lateral bone loss was measured from the crest of bone to the implant surface. In addition, the crestal bone loss was also measured from a line drawn between the tops of the adjacent implants. The data were divided into 2 groups, based on the inter-implant distance at the implant shoulder.

RESULTS

The results demonstrated that the lateral bone loss was 1.34 mm from the mesial implant shoulder and 1.40 mm from the distal implant shoulder between the adjacent implants. In addition, the crestal bone loss for implants with a greater than 3 mm distance between them was 0.45 mm, while the implants that had a distance of 3 mm or less between them had a crestal bone loss of 1.04 mm.

CONCLUSIONS

This study demonstrates that there is a lateral component to the bone loss around implants in addition to the more commonly discussed vertical component. The clinical significance of this phenomenon is that the increased crestal bone loss would result in an increase in the distance between the base of the contact point of the adjacent crowns and the crest of bone. This could determine whether the papilla was present or absent between 2 implants as has previously been reported between 2 teeth. Selective utilization of implants with a smaller diameter at the implant-abutment interface may be beneficial when multiple implants are to be placed in the esthetic zone so that a minimum of 3 mm of bone can be retained between them at the implant-abutment level.

Fluorescence detection of 8-oxoguanine in nuclear and mitochondrial DNA of cultured cells using a recombinant Fab and confocal scanning laser microscopy

The presence of 8-oxoguanine (8-oxoG) in DNA is considered a marker of oxidative stress and DNA damage. We describe a multifluorescence technique to detect the localization of 8-oxoG in both nuclear and mitochondrial DNA using a mouse recombinant Fab 166. The Fab was generated by repertoire cloning and combinatorial phage display, and specifically recognized 8-oxoG in DNA, as determined by competitive enzyme-linked immunosorbent assays (ELISAs). In situ detection of 8-oxoG was accomplished using rat lung epithelial (RLE) cells and human B lymphoblastoid (TK6) cells treated with hydrogen peroxide (H(2)O(2)) or ionizing radiation, respectively. Using confocal scanning laser microscopy, we observed nuclear and perinuclear immunoreactivity of 8-oxoG in control cultures. The simultaneous use of a nuclear DNA stain, propidium iodide, or the mitochondrial dye, MitoTracker (Molecular Probes, Eugene, OR, USA), confirmed that 8-oxoG immunofluorescence occurred in nuclear and mitochondrial DNA. Marked increases in the presence of 8-oxoG in nuclear DNA were apparent after treatment with H(2)O(2) or ionizing radiation. In control experiments, Fab 166 was incubated with 200 microM purified 8-oxodG or with formamidopyrimidine DNA-glycosylase (Fpg) to remove 8-oxoG lesions in DNA. These protocols attenuated both nuclear and mitochondrial staining. We conclude that both nuclear and mitochondrial oxidative DNA damages can be simultaneously detected in situ using immunofluorescence labeling with Fab 166 and confocal microscopy.

The genes encoding endonuclease VIII and endonuclease III in Escherichia coli are transcribed as the terminal genes in operons

Escherichia coli endonuclease VIII and endo-nuclease III are oxidative base excision repair DNA glycosylases that remove oxidized pyrimidines from DNA. The genes encoding these proteins, nei and nth, are both co-transcribed as the terminal genes in operons. nei is the terminal gene in an operon with four open reading frames that encode proteins of unknown function. This operon has two confirmed transcription initiation sites upstream of the first open reading frame and two transcript termination sites downstream of nei. nth is the terminal gene in an operon with seven open reading frames that encode proteins of unknown function. The six open reading frames immediately upstream of nth show homology to the genes rnfA, rnfB, rnfC, rnfD, rnfG and rnfE from Rhodobacter capsulatis. The rnf genes are required for nitrogen fixation in R.capsulatis and have been predicted to make up a membrane complex involved in electron transport to nitrogenase. The nth operon has transcription initiation sites upstream of the first and second open reading frames and a single transcript termination site downstream of nth. The order of genes in these operons has been conserved or partially conserved in other bacteria, although it is not known whether the genes are co-transcribed in these other organisms.

Fabs specific for 8-oxoguanine: control of DNA binding

Free radicals produce a broad spectrum of DNA base modifications including 7,8-dihydro-8-oxoguanine (8-oxoG). Since free radicals have been implicated in many pathologies and in aging, 8-oxoG has become a benchmark for factors that influence free radical production. Fab g37 is a monoclonal antibody that was isolated by phage display in an effort to create a reagent for detecting 8-oxoG in DNA. Although this antibody exhibited a high degree of specificity for the 8-oxoG base, it did not appear to recognize 8-oxoG when present in DNA. Fab g37 was modified using HCDR1 and HCDR2 segment shuffling and light chain shuffling. Fab 166 and Fab 366 which bound to 8-oxoG in single-stranded DNA were isolated. Fab 166 binds more selectively to single-stranded oligonucleotides containing 8-oxoG versus control oligonucleotides than does Fab 366 which binds DNA with reduced dependency on 8-oxoG. Numerous other clones were also isolated and characterized that contained a spectrum of specificities for 8-oxoG and for DNA. Analysis of the primary sequences of these clones and comparison with their binding properties suggested the importance of different complementarity determining regions and residues in determining the observed binding phenotypes. Subsequent chain shuffling experiments demonstrated that mutation of SerH53 to ArgH53 in the Fab g37 heavy chain slightly decreased the Fab's affinity for 8-oxoG but significantly improved its binding to DNA in an 8-oxoG-dependent manner. The light chain shuffling experiments also demonstrated that numerous promiscuous light chains could enhance DNA binding when paired with either the Fab g37 or Fab 166 heavy chains; however, only the Fab 166 light chain did so in an additive manner when combined with the Fab 166 heavy chain that contains ArgH53. A three-point model for Fab 166 binding to oligonucleotides containing 8-oxoG is proposed. We describe a successful attempt to generate a desired antibody specificity, which was not present in the animal's original immune response.

A novel role for Escherichia coli endonuclease VIII in prevention of spontaneous G-->T transversions

In the bacterium Escherichia coli, oxidized pyrimidines are removed by two DNA glycosylases, endonuclease III and endonuclease VIII (endo VIII), encoded by the nth and nei genes, respectively. Double mutants lacking both of these activities exhibit a high spontaneous mutation frequency, and here we show that all of the mutations observed in the double mutants were G:C-->A:T transitions; no thymine mutations were found. These findings are in agreement with the preponderance of C-->T transitions in the oxidative and spontaneous mutational databases. The major oxidized purine lesion in DNA, 7,8-dihydro-8-oxoguanine (8-oxoG), is processed by two DNA glycosylases, formamidopyrimidine DNA glycosylase (Fpg), which removes 8-oxoG opposite C, and MutY DNA glycosylase, which removes misincorporated A opposite 8-oxoG. The high spontaneous mutation frequency previously observed in fpg mutY double mutants was significantly enhanced by the addition of the nei mutation, suggesting an overlap in the substrate specificities between endo VIII and Fpg/MutY. When the mutational specificity was examined, all of the mutations observed were G:C-->T:A transversions, indicating that in the absence of Fpg and MutY, endo VIII serves as a backup activity to remove 8-oxoG. This was confirmed by showing that, indeed, endo VIII can recognize 8-oxoG in vitro.

Saccharomyces cerevisiae Ntg1p and Ntg2p: broad specificity N-glycosylases for the repair of oxidative DNA damage in the nucleus and mitochondria

Saccharomyces cerevisiae possesses two functional homologues (Ntg1p and Ntg2p) of the Escherichia coli endonuclease III protein, a DNA base excision repair N-glycosylase with a broad substrate specificity directed primarily against oxidatively damaged pyrimidines. The substrate specificities of Ntg1p and Ntg2p are similar but not identical, and differences in their amino acid sequences as well as inducibility by DNA damaging agents suggest that the two proteins may have different biological roles and subcellular locations. Experiments performed on oligonucleotides containing a variety of oxidative base damages indicated that dihydrothymine, urea, and uracil glycol are substrates for Ntg1p and Ntg2p, although dihydrothymine was a poor substrate for Ntg2p. Vectors encoding Ntg1p-green fluorescent protein (GFP) and Ntg2p-GFP fusions under the control of their respective endogenous promoters were utilized to observe the subcellular targeting of Ntg1p and Ntg2p in S. cerevisiae. Fluorescence microscopy of pNTG1-GFP and pNTG2-GFP transformants revealed that Ntg1p localizes primarily to the mitochondria with some nuclear localization, whereas Ntg2p localizes exclusively to the nucleus. In addition, the subcellular location of Ntg1p and Ntg2p confers differential sensitivities to the alkylating agent MMS. These results expand the known substrate specificities of Ntg1p and Ntg2p, indicating that their base damage recognition ranges show distinct differences and that these proteins mediate different roles in the repair of DNA base damage in the nucleus and mitochondria of yeast.

In vitro repair of synthetic ionizing radiation-induced multiply damaged DNA sites

When ionizing radiation traverses a DNA molecule, a combination of two or more base damages, sites of base loss or single strand breaks can be produced within 1-4 nm on opposite DNA strands, forming a multiply damaged site (MDS). In this study, we reconstituted the base excision repair system to examine the processing of a simple MDS containing the base damage, 8-oxoguanine (8-oxoG), or an abasic (AP) site, situated in close opposition to a single strand break, and asked if a double strand break could be formed. The single strand break, a nucleotide gap containing 3' and 5' phosphate groups, was positioned one, three or six nucleotides 5' or 3' to the damage in the complementary DNA strand. Escherichia coli formamidopyrimidine DNA glycosylase (Fpg), which recognizes both 8-oxoG and AP sites, was able to cleave the 8-oxoG or AP site-containing strand when the strand break was positioned three or six nucleotides away 5' or 3' on the opposing strand. When the strand break was positioned one nucleotide away, the target lesion was a poor substrate for Fpg. Binding studies using a reduced AP (rAP) site in the strand opposite the gap, indicated that Fpg binding was greatly inhibited when the gap was one nucleotide 5' or 3' to the rAP site. To complete the repair of the MDS containing 8-oxoG opposite a single strand break, endonuclease IV DNA polymerase I and Escherichia coli DNA ligase are required to remove 3' phosphate termini, insert the "missing" nucleotide, and ligate the nicks, respectively. In the absence of Fpg, repair of the single strand break by endonuclease IV, DNA polymerase I and DNA ligase occurred and was not greatly affected by the 8-oxoG on the opposite strand. However, the DNA strand containing the single strand break was not ligated if Fpg was present and removed the opposing 8-oxoG. Examination of the complete repair reaction products from this reaction following electrophoresis through a non-denaturing gel, indicated that a double strand break was produced. Repair of the single strand break did occur in the presence of Fpg if the gap was one nucleotide away. Hence, in the in vitro reconstituted system, repair of the MDS did not occur prior to cleavage of the 8-oxoG by Fpg if the opposing single strand break was situated three or six nucleotides away, converting these otherwise repairable lesions into a potentially lethal double strand break.

The genes encoding formamidopyrimidine and MutY DNA glycosylases in Escherichia coli are transcribed as part of complex operons

Escherichia coli formamidopyrimidine (Fpg) DNA glycosylase and MutY DNA glycosylase are base excision repair proteins that work together to protect cells from the mutagenic effects of the commonly oxidized guanine product 7,8-dihydro-8-oxoguanine. The genes encoding these proteins, fpg and mutY, are both cotranscribed as part of complex operons. fpg is the terminal gene in an operon with the gene order radC, rpmB, rpmG, and fpg. This operon has transcription initiation sites upstream of radC, in the radC coding region, and immediately upstream of fpg. There is a strong attenuator in the rpmG-fpg intergenic region and three transcription termination sites downstream of fpg. There is an additional site, in the radC-rpmB intergenic region, that corresponds either to a transcription initiation site or to an RNase E or RNase III cleavage site. mutY is the first gene in an operon with the gene order mutY, yggX, mltC, and nupG. This operon has transcription initiation sites upstream of mutY, in the mutY coding region, and immediately upstream of nupG. There also appear to be attenuators in the yggX-mltC and mltC-nupG intergenic regions. The order of genes in these operons has been conserved or partially conserved only in other closely related gram-negative bacteria, although it is not known whether the genes are cotranscribed in these other organisms.

Radiation-induced DNA base damage detected in individual aerobic and hypoxic cells with endonuclease III and formamidopyrimidine-glycosylase

X-ray-induced DNA base damage can be detected using endonuclease III and formamidopyrimidine-glycosylase, which create DNA strand breaks at enzyme-sensitive sites. Strand breaks can then be measured with excellent sensitivity using the alkaline comet assay, a single-cell gel electrophoresis method that detects DNA damage in individual cells. In using this approach to measure the oxygen enhancement ratio (OER) for radiation-induced base damage, we observed that the number of enzyme-sensitive sites increased with dose up to 4 Gy in air and 12 Gy in hypoxic WIL2NS cells. After rejoining of radiation-induced strand breaks, base damage was detected more easily after higher doses. The number of radiation-induced enzyme-sensitive sites was similar under both air and nitrogen. Base damage produced by hydrogen peroxide and 4-nitroquinoline-N-oxide (4NQO) was also measured. Results with hydrogen peroxide (20 min at 4 degrees C) were similar to those observed for X rays, indicating that enzyme-sensitive sites could be detected most efficiently when few direct strand breaks were present. Removing DNA-associated proteins before irradiation did not affect the ability to detect base damage. Base damage produced by 4NQO (30 min at 37 degrees C) was readily apparent after treatment with low concentrations of the drug when few 4NQO-induced strand breaks were present, but the detection sensitivity decreased rapidly as direct strand breaks increased after treatment with higher concentrations. We conclude that: (1) the OER for base damage is approximately 1.0, and (2) the presence of direct DNA strand breaks (>2000-4000 per cell) prevents accurate detection of base damage measured as enzyme-sensitive sites with the alkaline comet method.

In vitro selection of sequence contexts which enhance bypass of abasic sites and tetrahydrofuran by T4 DNA polymerase holoenzyme

The influence of sequence context on the ability of DNA polymerase to bypass sites of base loss was addressed using an in vitro selection system. Oligonucleotides containing either an aldehydic abasic site or tetrahydrofuran surrounded by four randomized bases on both the 5' and 3' sides were used as templates for synthesis by phage T4 DNA polymerase holoenzyme proficient or deficient in the 3'-->5' proofreading exonuclease activity. Successful bypass products were purified, subcloned and the sequences of approximately 100 subclones were determined for each of the four polymerase/lesion combinations tested. Between 7 and 19 % of the bypass products contained deletions of one to three nucleotides in the randomized region. In bypass products not containing deletions, biases for and against certain nucleotides were readily noticeable across the entire randomized region. Template strands from successful bypass products of abasic sites had a high frequency of T in most of the randomized positions, while those from bypass products of tetrahydrofuran had a high frequency of G at the positions immediately to the 3' and 5' side of the lesion. Consensus sequences were shared by successful bypass products of the same lesion but not between bypass products of the two lesions. The consensus sequence for efficient bypass of tetrahydrofuran was over-represented in several frames relative to the lesion. T4 DNA polymerase inserted A opposite abasic sites 63 % of the time in the presence of proofreading and 79 % of the time in its absence, followed by G>T>C, while the insertion of A opposite tetrahydrofuran ranged between 93 % and 100 % in the presence and absence of proofreading, respectively. Finally, sequence context influenced the choice of nucleotide inserted opposite abasic sites and consensus sequences which favored the incorporation of nucleotides other than A were defined.

Sinus floor elevation using anorganic bovine bone matrix (OsteoGraf/N) with and without autogenous bone: a clinical, histologic, radiographic, and histomorphometric analysis--Part 2 of an ongoing prospective study

One of the goals of the sinus elevation procedure is the creation of vital bone to effect the osseointegration of dental implants placed in the posterior maxilla. With this goal in mind, in 1993 the Department of Implant Dentistry at New York University College of Dentistry began a long-term clinical, histologic, histomorphometric, and radiographic study of the sinus elevation procedure. The primary parameters included the effects of graft material selection, time allowed for graft maturation, and the effect of barrier membrane placement on the creation of vital bone in the sinus cavity. The effects of these and other parameters on implant survival rates were also to be evaluated. This paper reports the data collected on a subgroup of 113 sinus elevations that used anorganic bovine bone matrix (OsteoGraf/N) alone or in combination with autogenous bone and/or demineralized freeze-dried bone as a graft material. This is the second in a proposed series of papers that will result from this ongoing research project. The results of this study indicate that: OsteoGraf/N appears to be an effective graft material with a 98.2% implant survival rate to date: vital bone formation increased with time; vital bone formation increased moderately when demineralized freeze-dried bone allograft was added, and increased substantially when intraoral autogenous bone was added or when an expanded polytetrafluoroethylene membrane was used; and the increased height achieved by the procedure was stable over a 3-year period. Because of the high overall implant survival rate, it was not possible to determine the relationship between vital bone formation or membrane usage and implant survival.

Enzymatic processing of radiation-induced free radical damage in DNA

A significant fraction of DNA damage produced by ionizing radiation comes from free radicals generated during the radiolysis of water, that is, by indirect effects. The hydroxyl radical, the principal damaging species, produces single-strand breaks and a plethora of base and sugar lesions that can be cytotoxic or mutagenic. Free radical-induced DNA damage is repaired by an efficient and ubiquitous process called "base excision repair" which is composed of either three or four enzymatic steps, depending on the initial lesion. The result is an intact DNA molecule with a short repair patch size. If, however, multiply damaged sites similar to those produced by ionizing radiation are processed by base excision repair, a double-strand break can result if the opposing lesions are more than three nucleotides apart. Because base excision repair evolved to protect the genome from endogenous damages, the proteins involved are highly conserved from bacteria to humans, not only at the functional level, but at the level of amino acid sequence.

Molecular Biology to Radiation Oncology: A Model for Translational Research? Opportunities in basic and translational research. From a workshop sponsored by the National Cancer Institute, Radiation Research Program, January 26-28, 1997, Bethesda, Maryland

Many exciting discoveries are being made that are providing new insights into how molecules, cells and tissues respond to ionizing radiation. There remains a need, however, to translate these findings into more effective treatments for cancer patients, including those treated with radiation therapy. This complex task will require the collaboration of scientists studying molecular, cellular and tissue responses, and those performing clinical trials of emerging therapies. The Radiation Research Program of the National Cancer Institute sponsored a workshop entitled "Molecular Biology to Radiation Oncology: A Model for Translational Research?" to bring together basic scientists and clinicians to exchange ideas and fundamental concepts and to identify opportunities for future research and collaboration. Four broad topics were addressed: signal transduction and apoptosis, the cell cycle, repair of radiation damage, and the microenvironment. The development, selection and use of appropriate experimental models is crucial to finding and developing new therapies, and opportunities exist in this area as well. This paper and the accompanying paper by Coleman and Harris that provides the viewpoint of radiation oncologists (Radiat. Res. 150, 134-147, 1998) summarize the background concepts and opportunities for translational research identified by the workshop participants.

In search of a mutational hotspot

In vitro selection was used to define sequence contexts that significantly enhanced the mutagenic potential of 7, 8-dihydro-8-oxoguanine (8-oxoG). Contexts that simultaneously reduced the efficiency of 8-oxoG cleavage by formamidopyrimidine DNA N-glycosylase and increased the efficiency of misincorporating A opposite the lesion by DNA polymerase were isolated from a pool of 4(8) random octanucleotide sequences. Kinetic analysis showed that the combined effects of poor repair and high miscoding resulted in 10(2)- to 10(3)-fold increase in the mutagenic potential of 8-oxoG. Furthermore, the isolated sequence contexts correlated strongly with G --> T transversion hotspots in spontaneous mutational spectra reported for the Escherichia coli lacI and human p53 and factor IX genes. We present an example directly linking the interplay between DNA repair and replication to a "high risk sequence" for base substitution.

Enzymatic processing of uracil glycol, a major oxidative product of DNA cytosine

A major stable oxidation product of DNA cytosine is uracil glycol (Ug). Because of the potential of Ug to be a strong premutagenic lesion, it is important to assess whether it is a blocking lesion to DNA polymerase as is its structural counterpart, thymine glycol (Tg), and to evaluate its pairing properties. Here, a series of oligonucleotides containing Ug or Tg were prepared and used as templates for a model enzyme, Escherichia coli DNA polymerase I Klenow fragment (exo-). During translesion DNA synthesis, Ug was bypassed more efficiently than Tg in all sequence contexts examined. Furthermore, only dAMP was incorporated opposite template Ug and Tg and the kinetic parameters of incorporation showed that dAMP was inserted opposite Ug more efficiently than opposite Tg. Ug opposite G and A was also recognized and removed in vitro by the E. coli DNA repair glycosylases, endonuclease III (endo III), endonuclease VIII (endo VIII), and formamidopyrimidine DNA glycosylase. The steady state kinetic parameters indicated that Ug was a better substrate for endo III and formamidopyrimidine DNA glycosylase than Tg; for endonuclease VIII, however, Tg was a better substrate.

Multiply damaged sites in DNA: interactions with Escherichia coli endonucleases III and VIII

Bursts of free radicals produced by ionization of water in close vicinity to DNA can produce clusters of opposed DNA lesions and these are termed multiply damaged sites (MDS). How MDS are processed by the Escherichia coli DNA glycosylases, endonuclease (endo) III and endo VIII, which recognize oxidized pyrimidines, is the subject of this study. Oligonucleotide substrates were constructed containing a site of pyrimidine damage or an abasic (AP) site in close proximity to a single nucleotide gap, which simulates a free radical-induced single-strand break. The gap was placed in the opposite strand 1, 3 or 6 nt 5' or 3' of the AP site or base lesion. Endos III and VIII were able to cleave an AP site in the MDS, no matter what the position of the opposed strand break, although cleavage at position one 5' or 3' was reduced compared with cleavage at positions three or six 5' or 3'. Neither endo III nor endo VIII was able to remove the base lesion when the gap was positioned 1 nt 5' or 3' in the opposite strand. Cleavage of the modified pyrimidine by endo III increased as the distance increased between the base lesion and the opposed strand break. With endo VIII, however, DNA breakage at the site of the base lesion was equivalent to or less when the gap was positioned 6 nt 3' of the lesion than when the gap was 3 nt 3' of the lesion. Gel mobility shift analysis of the binding of endo VIII to an oligonucleotide containing a reduced AP (rAP) site in close opposition to a single nucleotide gap correlated with cleavage of MDS substrates by endo VIII. If the strand break in the MDS was replaced by an oxidized purine, 7,8-dihydro-8-oxoguanine (8-oxoG), neither endo VIII cleavage nor binding were perturbed. These data show that processing of oxidized pyrimidines by endos III and VIII was strongly influenced by the position and type of lesion in the opposite strand, which could have a significant effect on the biological outcome of the MDS lesion.

Uracil glycol deoxynucleoside triphosphate is a better substrate for DNA polymerase I Klenow fragment than thymine glycol deoxynucleoside triphosphate

A major stable oxidation product of DNA cytosine is 5,6-dihydroxy-5, 6-dihydrouracil (Ug). Ug can be formed directly in DNA or in the cellular nucleotide pools by deamination of the unstable primary product, cytosine glycol. Here, we synthesized dUgTP and showed that dUgTP was incorporated in place of dTTP and was a much better substrate for the model enzyme DNA polymerase I Klenow fragment lacking proofreading activity, Kf (exo-), than deoxythymidine glycol triphosphate (dTgTP). The relative efficiency for dUgTP insertion opposite A was 10 times higher than for dTgTP; however, the extension of a primer with 3' dUg was about 100 times more efficient than the extension of a primer with 3' dTg. At the insertion step, the differences in Vmax appeared to be responsible since the apparent Kms for dUgTP and dTgTP were about the same. In contrast, both the apparent Km and Vmax for elongation of dUg were markedly different from those of dTg. Molecular modeling was performed with both Tg and Ug and provides a rational structural explanation for these observations.