A processive versus a distributive mechanism of action correlates with differences in ability of normal and xeroderma pigmentosum group A endonucleases to incise damaged nucleosomal DNA

A DNA endonuclease, isolated from the nuclei of normal human and xeroderma pigmentosum complementation group A (XPA) cells, which recognizes predominately pyrimidine dimers, was examined for the mechanism by which it locates sites of damage on UVC-irradiated DNA. In reaction mixtures with low ionic strengths (i.e. lacking KCl), the normal and XPA endonuclease locate sites of UV damage on both naked and reconstituted nucleosomal DNA by different mechanisms. On both of these substrates, the normal endonuclease acts by a processive mechanism, meaning that it binds non-specifically to DNA and scans the DNA for sites of damage, whereas the XPA endonuclease acts by a distributive one, meaning that it randomly locates sites of damage on DNA. However, while both the normal and XPA endonucleases can incise UVC irradiated naked DNA, they differ in ability to incise damaged nucleosomal DNA. The normal endonuclease showed increased activity on UVC treated nucleosomal DNA compared with naked DNA, whereas the XPA endonuclease showed decreased activity on the damaged nucleosomal substrate. Since a processive mechanism of action is sensitive to the ionic strength of the micro-environment, the KCl concentration of the reaction was increased. At 70 mM KCI, the normal endonuclease switched to a distributive mechanism of action and its ability to incise damaged nucleosomal DNA also decreased. These studies show that there is a correlation between the ability of these endonucleases to act by a processive mechanism and their ability to incise damaged nucleosomal DNA; the normal endonuclease, which acts processively, can incise damaged nucleosomal DNA, whereas the XPA endonuclease, which acts distributively, is defective in ability to incise this substrate.      

Palpable lymph nodes of the neck in Swedish schoolchildren

We studied 3592 Swedish schoolchildren, 8 or 9 years old, examined for palpable submandibular, cervical and supraclavicular lymph nodes. All children were skin tested with 2 TU PPD RT23 and with 0.1 μ g of Mycobacterium avium sensitin or 0.1 μ g of M. scrofulaceum sensitin. A total of 991 children had palpable lymph nodes in any of the three locations. Among them, 811 had lymph nodes in one location, 162 in two locations and 18 in three. In 312 children, the lymph nodes were ± 5 mm in size in any location. The most common location was submandibular. Boys had a significantly higher prevalence of palpable lymph nodes than girls. There was also seasonal variation. Children infected by atypical mycobacteria (sensitin reaction ±6 mm) did not have a higher prevalence of palpable lymph nodes than those not infected.     

The rationale for nonsteroidal anti-inflammatory drug therapy for inflammatory myofibroblastic tumors: a Children's Oncology Group study

Background

Inflammatory myofibroblastic tumors (IMTs) are neoplasms that are highly vascularized, have an intermediate prognosis, and are associated with infiltration, obstruction, local recurrence, and rare metastasis. Resection of large IMTs can lead to substantial morbidity and even mortality. Anecdotal experience suggests that nonsteroidal anti-inflammatory drugs may eradicate large IMTs or shrink them to a more readily resectable size and configuration. To support the hypothesis that nonsteroidal anti-inflammatory drugs are antiangiogenic for IMTs by interfering with vascular endothelial growth factor (VEGF) signaling via cyclooxygenase 2 (COX-2) inhibition, IMT specimens were immunohistochemically examined for expression of COX-2 enzyme and VEGF.

Methods

The diagnosis of IMT was confirmed in all 18 cases comprising the study. Intensity of COX-2 and VEGF staining was graded, and staining uniformity was examined. ALK-1 protein expression, found in up to two thirds of IMTs, was also determined.

Results

COX-2 and VEGF expression were identified in all tissue examined, with staining intensity varying independently. ALK-1 protein expression was identified in 33% of specimens. Its presence was not related to the intensity of COX-2 or VEGF staining.

Conclusions

Our data suggest that the mediators of angiogenesis, VEGF and COX-2, are present and may play an important role in the growth of IMTs.     

Endovascular management of a patient after SAH

Treatment of acute aneurysmal subarachnoid hemorrhages consists of occluding the aneurysm to prevent rebleed, attempting to prevent vasospasm, and maintaining blood flow to the brain through vessels in vasospasm. Endovascular treatment has been shown to be as safe as, or safer, than surgical clipping for patients with SAH. Engineering solutions to our clinical problems continue to improve endovascular outcomes. This article reviews the current state of endovascular therapy.     

Gastrointestinal stromal tumors: insights from a new familial GIST kindred with unusual genetic and pathologic features

Familial gastrointestinal stromal tumor (GIST) is a rare autosomal dominant genetic disorder. We report the second family to date with a germline point mutation in exon 17 of the KIT gene that leads to substitution of aspartic acid at position 820 with tyrosine (D820Y). One or more GISTs was documented in three generations of this kindred, and there was associated hyperplasia of the interstitial cells of Cajal (ICC). One affected family member complained of dysphagia and another suffered small intestinal diverticulosis with perforation, which may represent additional consequences of ICC hyperplasia. Diffuse and nodular ICC hyperplasia associated with the latter family member's small intestinal diverticulosis is illustrated, providing supportive functional and morphologic evidence for the ICC being the cell of origin of GISTs. Skin hyperpigmentation was not observed. Analysis of a 17-cm malignant GIST in the index patient revealed that it was hemi/homozygous for the germline D820Y mutation, indicating loss of the remaining wild-type KIT allele with tumor progression. Two smaller lesions from this patient were heterozygous for the mutation. This phenomenon has been observed in up to 8% of sporadic malignant GISTs but has not been documented in familial disease.     

Multispectral analysis of magnetic resonance images

Magnetic resonance (MR) imaging systems produce spatial distribution estimates of proton density, relaxation time, and flow, in a two dimensional matrix form that is analogous to that of the image data obtained from multispectral imaging satellites. Advanced NASA satellite image processing offers sophisticated multispectral analysis of MR images. Spin echo and inversion recovery pulse sequence images were entered in a digital format compatible with satellite images and accurately registered pixel by pixel. Signatures of each tissue class were automatically determined using both supervised and unsupervised classification. Overall tissue classification was obtained in the form of a theme map. In MR images of the brain, for example, the classes included CSF, gray matter, white matter, subcutaneous fat, muscle, and bone. These methods provide an efficient means of identifying subtle relationships in a multi-image MR study.     

Heart failure care in a hospital unit: a comparison of standard 3-month and extended 6-month programs

BACKGROUND: We have previously shown that a structured in-hospital and outpatient heart failure (HF) program reduces clinical events over a 3-month period following hospital discharge. AIMS: This prospective randomized controlled study examines the additional benefits of extending the standard 3-month HF program to 6 months on death and readmission over a 2-year follow-up period. METHODS: Of 161 patients admitted with NYHA class IV HF who completed the standard 3-month HF program, 130 consenting patients (mean age 69.9+/-12.2 years, 65% male) were randomized to the extended 6-month HF program (EP; n=62) or standard care (SP; n=68). The primary endpoint was death and/or unplanned rehospitalization for HF at 2 years postrandomization. RESULTS: In the 2-year follow-up period, there were eight people with unplanned hospitalizations for HF and 16 deaths in the EP group (event rate 38.7%) compared to seven people with unplanned HF readmissions and 14 deaths in the SP group (event rate 30.9%, p=0.348 versus EP). Kaplan-Meier survival analysis demonstrated no difference in outcome between standard and extended program (p=0.315). There were no differences between the groups in terms of unscheduled clinic visits or non-HF-related readmissions in the 2-year follow-up period. CONCLUSIONS: There is no measured clinical advantage in terms of death and/or HF readmission in extending a structured hospital-based disease management program for HF beyond 3 months postdischarge. However, it appears that patients continue to need access to the service to help abort clinical deteriorations, and this may have implication for the optimal organisation of such programs.