Extracellular post-translational modifications of collagen are major determinants of biomechanical properties of fetal bovine cortical bone

Mechanical behavior of bone depends on its mass and architecture, and on the material properties of the matrix, which is composed of a mineral phase and an organic component mainly constituted of type I collagen. Mineral accounts largely for the stiffness of bone, whereas type I collagen provides bone its ductility and toughness, i.e., its ability to undergo deformation and absorb energy after it begins to yield. The molecular mechanisms underlying the effect of alterations in type I collagen on bone mechanical properties are unclear. We used an in vitro model of fetal bovine cortical bone specimens (n = 44), where the extent of type I collagen cross-linking was modified by incubation at 37 degrees C for 0, 60, 90 and 120 days, keeping constant the architecture and the mineral content. At each incubation time, the following parameters were determined: (1) the bone concentration of enzymatic (pyridinoline; PYD and deoxypyridinoline, DPD) and non-enzymatic (pentosidine) crosslinks by HPLC, (2) the extent of aspartic acid isomerization of the type I collagen C-telopeptide (CTX) by ELISA of native (alpha CTX) and isomerized (beta CTX) forms, (3) the mineral density by DXA, (4) the porosity by micro-computed tomography and (5) the bending and compressive mechanical properties. Incubation of bone specimens at 37 degrees C for 60 days increased the level (per molecule of collagen) of PYD (+98%, P = 0.005), DPD (+42%, P = 0.013), pentosidine (+55-fold, P = 0.005), and the degree of type I collagen C-telopeptide isomerization (+4.9-fold, P = 0.005). These biochemical changes of collagen were associated with a 30% decrease in bending and compressive yield stress and a 2.5-fold increase in compressive post-yield energy absorption (P < 0.02 for all), with no significant change of bone stiffness. In multivariate analyses, the level of collagen cross-linking was associated with yield stress and post-yield energy absorption independently of bone mineral density, explaining up to 25% of their variance. We conclude that the extent and nature of collagen cross-linking contribute to the mechanical properties of fetal bovine cortical bone independently of bone mineral density.     

Follow-up and follow-through of depressed patients in primary care: the critical missing components of quality care

Certainly we could improve our identification, diagnosis, and initial treatment approaches to the large numbers of depressed patients we see in primary care. However, until we have established the kind of systematic follow-up and follow-through that the US Preventive Services Task Force said is a prerequisite for its recommendation to routinely screen for depression, none of these earlier actions will make much difference. Recently, a number of controlled trials of innovative approaches to care management have demonstrated clearly how much patient outcomes are improved when systematic follow-up is in place. The problem is that there are few examples of such systems in real clinical practices. This article describes the main components of such a systematic approach.     

Tobacco-cessation services and patient satisfaction in nine nonprofit HMOs

BACKGROUND: The U.S. Public Health Service clinical practice guideline calls for clinicians and healthcare organizations to identify and treat every tobacco user seen in a healthcare setting. There is little information on the extent of compliance with the guideline's treatment model described by the "5A's" (Ask, Advise, Assess, Assist, Arrange). METHODS: In 1999-2000 a survey was mailed to 64,764 members aged 25 to 75 years, of nine nonprofit HMOs participating in the National Cancer Institute-funded Cancer Research Network. These plans provide medical care to more than 8 million Americans including a minority enrollment of 30%. Smokers were asked about tobacco-cessation treatments received during primary care visits in the past year. RESULTS: A 70% response rate identified a smoking prevalence of 10% (n=4207). Results indicated that 90% of smokers were asked about smoking, 71% were advised to quit, 56% were assessed for their willingness to quit, 49% received assistance interventions, and 9% had follow-up arranged. Treatment was provided more often to smokers who asked for help and/or intended to quit. Few and only modest associations were found between other patient characteristics and receipt of 5A's cessation services. In contrast to widely reported concerns about smokers' resistance to tobacco interventions, smokers who received treatment were more satisfied with health plan services. CONCLUSIONS: Results demonstrate substantial clinician compliance with the first two steps-Ask and Advise. Greater efforts are needed in providing the more effective tobacco treatments-Assist and Arrange. Compliance with the guideline is associated with greater patient satisfaction.     

Veno-occlusive disease of the liver after blood and marrow transplantation: analysis of pre- and post-transplant risk factors associated with severity and results of therapy with tissue plasminogen activator

We reviewed our blood and marrow transplantation (BMT) database from April 1982 to July 1996 and identified 111 of 474 patients with serum bilirubin concentration (SBR) > or = 34 micromol/l for two consecutive days within the first 20 days after related allogeneic or autologous BMT. Of the 111, 73 fulfilled the Seattle criteria for veno-occlusive disease of the liver (VOD) and had no other obvious cause for liver dysfunction. The patients were 16-60 years old (median, 39 years), and 41 were male (56%). Fourteen patients (19%) had autologous BMT, and 59 (81%) had allogeneic BMT. Twenty-eight (38%), 12 (16%), and 33 (45%) patients had severe, moderate, and mild VOD, respectively, by Seattle criteria. None of 23 patients with maximum (max) SBR > or = 257 micromol/l survived, all patients with max SBR < or = 128 micromol/l survived, and 7 of 15 patients (47%) with max SBR 128-257 micromol/l survived. The only pre-transplantation risk factor predictive of severe VOD was advanced disease state (P = 0.035), and the only transplant factors that predicted severe VOD were max SBR (P = 0.01) and maximum blood urea level (P = 0.03). Ten patients (all with creatinine levels > or = 150 micromol/l) were treated with tissue plasminogen activator; only two had a significant response and only one survived beyond day 120.     

Initial clinical results of stereotactic radiotherapy for the treatment of craniopharyngiomas

The efficacy and toxicity of stereotactic radiotherapy (SRT) for the treatment of craniopharyngioma has been retrospectively evaluated in 16 patients. The median tumor diameter was 2.8 cm (range 1.5-6.1) and the median tumor volume was 7.7 cc (range 0.7-62.8). SRT was delivered to a single isocenter using a dedicated 6 MV linear accelerator to patients immobilized with a relocatable stereotactic head frame. The three-year actuarial overall survival was 93% and the rate of survival free of any imaging evidence of progressive disease was 75%. The three-year actuarial survival rates free of solid tumor growth or cyst enlargement were 94% and 81% respectively. Our results suggest that SRT is a safe and effective treatment approach for patients with craniopharyngioma. Long-term follow-up is required to determine whether the normal tissue-sparing inherent with SRT results in reduction of the neurocognitive effects of conventional radiotherapy for craniopharyngioma. SRT can be delivered to craniopharyngioma that may be difficult to treat with stereotactic radiosurgery due to proximity of the optic chiasm. Further clinical experience is necessary to determine the clinical utility of beam shaping in the setting of SRT.     

Dynamic arc radiosurgery field shaping: a comparison with static field conformal and noncoplanar circular arcs

Purpose: Recent advances in field-shaping technology and linac multileaf collimator (MLC) integration have resulted in new approaches to performing stereotactic radiosurgery. We present a modeling study comparing the absolute dose distributions from three radiosurgery delivery techniques: a conventional approach utilizing noncoplanar circular arcs, a static field conformal approach, and a dynamic arc field-shaping approach. In the latter, the MLC leaves more in a continuous fashion, conforming to the beam’s-eye-view projection of the target at every increment along the path of an arc.

Methods and Materials: For the analysis, we devised a simulated target consisting of three overlapping spheres. This was chosen because it offered a straightforward planning approach for all three techniques, primarily the multiple isocenter approach. In addition, three representative cases were selected from the prior radiosurgery experience. These range in increasing size, from 0.50 to 9.79 cm³, and in complexity, requiring from 3 isocenters to 16 in the case of circular arcs. In each situation, the goals were twofold: (1) to cover the entire volume with as high an appropriate isodose level (90% in the case of the conformal and dynamic arc techniques, 50% in the case of circular collimators) while (2) minimizing the dose to normal brain and where applicable, any adjacent radiation-sensitive structures. Because of the latter requirement, a single isocenter circular arc approach was ruled out for the analysis.

Results: In the case of large or irregularly shaped lesions, the circular arc technique requires multiple isocenters, producing a high level of dose heterogeneity within the target volume. Both the static field and dynamic arc conformal techniques, as with all single isocenter approaches, produce a highly homogeneous dose throughout the target region. For a given large dose, peripheral dose is decreased as additional beams or arc degrees are added with either of the conformal approaches. Dose–volume histogram analysis evaluating the peripheral dose shows that, in many cases, dose to surrounding structures can be reduced through the use of a conformal static or dynamic arc approach over the conventional multiple isocenter, circular arc techniques.

Conclusions: Dynamic arc shaping is an efficient and effective method for accurately delivering a homogeneous target dose while simultaneously minimizing peripheral dose in radiosurgery applications.     

Multilocus genotypes of two strains of Neisseria meningitidis and their presumed variants obtained upon subcultivation

Loss of sulfonamide resistance and endotoxin liberation have been described in two strains of Neisseria meningitidis serogroup B, upon subcultivation every 1 to 2 months over an 18-month period. Subsequently, the two laboratory variants, designated 270E- and 840E-, were also found to differ from the parent strains, 270E+ and 840E+, in serotype, outer membrane protein pattern, and virulence in mice. We report here the multilocus genotypes determined by enzyme electrophoresis, of the four isolates 270E+, 270E-, 840E+, and 840E-, and demonstrate that 270E- and 840E- strains could not have originated from subcultivation of 270E+ and 840E+, respectively, but that a mix-up of strains has occurred.     

Differential rates of metabolic activation and detoxication of the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine by different cytochrome P450 enzymes

Rat liver microsomes metabolized the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) to the genotoxic metabolite 2-hydroxamino-1-methyl-6-phenylimidazo[4,5-b]pyridine (2-hydroxamino-PhIP) and to the detoxified product 2-amino-4'-hydroxy-1-methyl-6-phenylimidazo[4,5-b]pyridine (4'-hydroxy-PhIP). A 25-fold higher rate of metabolism was measured in microsomes from polychlorinated-biphenyl-treated rats (94 nmol/mg proteins/30 min) in comparison with those from untreated rats. Other effective inducers of PhIP metabolism were beta-naphthoflavone and isosafrole (ISF), whereas phenobarbital was ineffective. About twice as much 2-hydroxamino-PhIP as 4'-hydroxy-PhIP was formed in microsomes irrespective of the inducer the rats had been treated with. The metabolism was dependent on NADPH and was abolished by the cytochrome P450 inhibitor alpha-naphthoflavone. In a reconstituted enzyme system purified rat cytochrome P450 IA2 (P450ISF-G) had the highest N-hydroxylation rate (30 nmol/nmol P450/30 min) closely followed by the rat cytochrome P450 IA1 (P450BNF-B). Less activity was seen with rat P450 IIC11 (P450UT-A) and rabbit P450 IA2 (P450 LM4). Rat P450 IIE1 (P450j), P450 IIB1 (P450PB-B) and rabbit P450 IIB4 (P450 LM-2) and P450 IIE1 (P450 LM3a) were essentially inactive. Rat P450 IA1 (P450BNF-B) produced five times more 4'-hydroxy-PhIP (32 +/- 2 nmol/nmol P450/30 min) than did P450 IA2 (P450ISF-G). Hence, the measured ratio of activation to detoxication for rat P450 IA2 (P450ISF-G) enzyme was 7-fold higher than that of the other active P450 enzymes.