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F Eckstein

Publications and source records attributed to F Eckstein.

At least 127 records · Page 7Linked to original sources
PubMed1998

In vitro selection of a purine nucleotide-specific hammerheadlike ribozyme.

The in vitro selection for an intramolecular AUG-cleaving hammerhead-like ribozyme is described. One of the ribozymes selected was found to cleave after this triplet, both intramolecularly and intermolecularly, with rates comparable to the rate of the native GUC-cleaving hammerhead ribozyme. Although the selection was designed for cleavage 3' of the AUG triplet, the ribozyme also cleaves 3' of the AUA triplet. AUU and AUC triplets are, however, not cleaved, and thus the selected ribozyme is purine-specific for the third position in the triplet. In addition, cleavage 3' of the AAG triplet has been observed, thus the central U is not essential. Nuclease digestion indicates that the selected ribozyme has a secondary structure similar to that of the native hammerhead ribozyme, although with an altered core and stem-loop II sequence. All nucleotides in the core, except one, are essential for activity. The nucleotides in loop II are sensitive to changes and cannot, as in the hammerhead ribozyme, be replaced by other sequences or a nonnucleotide linker. Thus there are differences between these two ribozymes even though they have similar two-dimensional structures. The new ribozyme enlarges the application of hammerhead ribozymes for the inhibition of gene expression by extending the range of cleavable triplets.

Base Sequence↗
PubMed1998

An MR-based technique for quantifying the deformation of articular cartilage during mechanical loading in an intact cadaver joint.

The objective of this study was to develop an MR-based technique for quantifying the deformation of articular cartilage during mechanical loading in an intact cadaver joint at high spatial and temporal resolution. A nonmetallic pressure device was constructed for applying loads of >1000 N to a femoro-patellar articulation within an extremity coil of a clinical 1.5 T MRI scanner. Digital image processing methods were used to determine the location- and time-dependent cartilage deformation in consecutive 2D fat-suppressed FLASH images. Additionally, three-dimensional reconstruction of the cartilage was performed from 3D fat-suppressed FLASH image data. During the first 10 min of static compression, thickness changes between 10 and 30% were observed. Thickness changes greater than 50% and volume changes of 20% were recorded after 3 h. The technique permits analysis of the load and time-dependent mechanical behavior of articular cartilage in its natural environment.

Adult↗
PubMed1998

A technique for determining the spatial relationship between the rotator cuff and the subacromial space in arm abduction using MRI and 3D image processing.

An MR imaging-based technique for three-dimensional determination of subacromial space width in relation to the rotator cuff in arm abduction is presented. Five volunteers were examined in an open MRI in seven arm positions, and coronal images were obtained with a gradient-echo sequence. 3D reconstruction of the bones and the supraspinatus was performed, and the minimal spatial distances between acromion, clavicle, and humerus were calculated. The closest contact between the supraspinatus and the anterior inferior part of the acromion occurred at 90 degrees abduction in internal rotation. The technique presented allows investigation of the morphological basis of the impingement syndrome.

Acromion↗
PubMed1998

Correlation of femoral and lumbar DXA and calcaneal ultrasound, measured in situ with intact soft tissues, with the in vitro failure loads of the proximal femur.

The objective of this study was to determine experimentally the sex-specific correlation of femoral and lumbar DXA and calcaneal ultrasound, measured in situ, with the in vitro failure loads of the proximal femur. Fifty-eight cadavers with intact skin and soft tissues (34 male, aged 81.2 +/- 8.7 years; 24 female, aged 83.7 +/- 10.6 years) were examined. The bone mass of the proximal femur and the lumbar spine were determined using dual-energy X-ray absorptiometry and the ultrasonic properties of the calcaneus with quantitative ultrasound. Afterwards, the right femora were excised 18 cm distal to the minor trochanter, and their load to failure determined with a material testing machine. Femoral fracture loads were significantly higher in males than in females, both before and after correcting for body height and weight. Femoral neck bone mineral density (BMD) was significantly correlated with femoral failure loads (r = 0.65 all specimens, 0.57 males (0.64 after excluding trochanteric fractures) and 0.77 females; p < 0.001). The correlations with the ultrasonic Stiffness Index of the calcaneus were in a similar range (r = 0.67 all specimens, 0.48 males (0.64 after excluding trochanteric fractures) and 0.65 females; p < 0.001). The correlations between femoral failure loads and the spinal BMD were lower (r = 0.40, p < 0.01), particularly in males (r = 0.30, not significant). In contrast to previous experimental investigations on excised bones, our results are consistent with clinical studies that have reported that ultrasound and femoral DXA have a similar ability to predict the risk of hip fracture.

Absorptiometry, Photon↗
PubMed1998

Quantitative relationships of normal cartilage volumes of the human knee joint--assessment by magnetic resonance imaging.

The objective of this study was to assess the normal range of cartilage volumes in the knee joints of healthy adults, the ratio between the patellar, femoral, and tibial cartilages, and the correlation of the volumes with age, body weight, height, body mass index (obesity), patellar bone size, and the diameter of the tibial head. We examined the knee joints of nine healthy volunteers and eleven normal post-mortem specimens with an age range of 24 to 82 years. The cartilage volumes of the patella, femur, medial tibia and the lateral tibia were quantified, using a fat-suppressed FLASH-3D sequence (resolution 2x0.31x0.31 mm3) and digital postprocessing, involving three-dimensional reconstruction. The mean total volume of the knee joint cartilage was 23,245 mm3, the relative standard deviation (CV%) 19%, and the range 16,341 to 33,988 mm3. In the patella, femur and tibia, the CV% amounted to between 22 and 25%. These joint surfaces occupied a relatively variable proportion of the total knee joint volume, the percentage of the patella being 11 to 22%, that of the femur 54 to 69%, that of the medial tibia 7 to 12%, and that of lateral tibia 11 to 16%. The volumes of the lateral tibia were systematically higher than those of the medial tibia (P<0.001). There was no significant correlation of the knee joint cartilage volume with age (r=+0.05), body weight (r=+0.38), height (r=+0.39) or body mass index (r=+0.29), but a relatively high correlation with the diameter of the tibial head (r=+0.78, P<0.001). After normalising the volumes to this diameter, the CV% of the total knee joint cartilage volume was reduced to 13%, its variation being 12 to 21% in the patella, femur and tibia. MRI is available for measuring cartilage volume during growth, functional adaptation, and tissue loss in degenerative joint disease. The study shows that a wide variation of cartilage volumes exists in the knee joints of normal adults. To reduce the variability between individuals, the cartilage volumes may be normalised to the head of the tibial diameter.

Adult↗
PubMed1998

Designing ribozymes for the inhibition of gene expression.

Ribozymes are being increasingly used for the sequence-specific inhibition of gene expression by the cleavage of mRNAs encoding proteins of interest. However, particular attention must be paid to the following points: the identification of regions on the mRNA accessible to the ribozyme; the delivery of ribozymes to cells by either exogenous or endogenous delivery; colocalization of the ribozyme with the target RNA in the cell; and differentiation between closely related sequences. This field is advancing rapidly, and results obtained with transgenic animals demonstrate the power of this strategy for the inhibition of gene expression.

Animals↗
PubMed1998

The distribution of cartilage thickness in the knee-joints of old-aged individuals -- measurement by A-mode ultrasound.

OBJECTIVE: To provide data on the normal distribution of cartilage thickness in the knee joints of old-aged individuals. DESIGN: The accuracy and reproducibility of cartilage thickness measurements were evaluated with A-mode ultrasound, and the cartilage thickness distribution was examined throughout both knee joints of nine individuals aged between 62 and 94 yr. BACKGROUND: Data on the variation of cartilage thickness in the joint surfaces are relevant for the design of computer models of diathrodial joints and for surgical and arthroscopic procedures, particularly the calculation of cartilage material properties from indentation tests. METHODS: A 12.5 MHz A-mode ultrasound transducer was used, and after determining the accuracy and reproducibility of the system in comparison with CT arthrography and anatomical sections, the cartilage thickness was measured throughout the knee at 256 coordinate points. RESULTS: A-mode ultrasound yields results consistent with established methods. The cartilage thickness is distributed regularly in the knee-joint of older individuals. However, the absolute values are considerably lower than those previously reported for younger people, the mean (and maximal) thickness being 2.0 mm (3.3 mm) in the patella, 1.9 mm (3.3 mm) in the femur, and 1.9 mm (3.5 mm) in the tibia. CONCLUSION: If the results of computer models or surgical strategies are to be applied to the demographically important group of older individuals, the typical distribution of articular cartilage thickness in this group should be taken into consideration.

Journal Article↗
PubMed1998

A method for quantifying time dependent changes in MR signal intensity of articular cartilage as a function of tissue deformation in intact joints.

A method is proposed to determine accurately the signal intensity changes of the articular cartilage from sectional MR images and its related cartilage deformation under compression in an intact joint. Image processing methods are developed to delineate and register the cartilage boundaries in consecutive MR images in order to track corresponding tissue sectors during the loading experiment. Regions of interest can then be defined and traced during the compression, making a spatial and temporal analysis of signal intensity changes possible. In addition, the cartilage deformation is calculated in the respective tissue sectors and is related to the MR signal changes. Using a fat-suppressed FLASH 3D sequence, the preliminary results showed location-dependent slight changes of the signal intensity varying from individual to individual. The quantitative analysis of the signal intensity changes as a function of cartilage deformation with magnetic resonance imaging (MRI) aims to characterize microstructural properties of the articular cartilage that may lead to a better understanding of degenerative joint disease.

Adult↗
PubMed1998

Prediction of vertebral failure loads from spinal and femoral dual-energy X-ray absorptiometry, and calcaneal ultrasound: an in situ analysis with intact soft tissues.

The objective of the current study was to determine the correlation of spinal and femoral dual-energy X-ray absorptiometry (DXA) and calcaneal ultrasound, measured in situ with intact soft tissues, with the in vitro failure loads of lumbar vertebral bodies. Forty-nine cadavers with intact skin and soft tissues (32 men aged 82.1 +/- 9.0 years, 17 women aged 83.1 +/- 10.1 years) were examined. The bone mineral content (BMC), the projectional area, and the bone mineral density (BMD) of the lumbar spine and proximal femur were determined with DXA, and the ultrasonic properties of the calcaneus with quantitative calcaneal ultrasound. The fourth lumbar vertebra was then excised with adjacent intervertebral disks and its mechanical failure load determined, using a materials testing machine. Absolute fracture loads were significantly higher in men than in women, but they were similar after adjusting for body weight and height. Spinal DXA was significantly associated with vertebral failure load (r = 0.62 combined; r = 0.54 men; r = 0.58 women). Femoral DXA (r = 0.46) and calcaneal ultrasound (r = 0.48) showed somewhat lower correlation coefficients, with the speed of sound (SOS) being able to add predictive information in a stepwise regression model. Normalizing the vertebral failure loads to body weight and height reduced the correlations, with only spinal DXA yielding a significant relationship. Our data suggest that previous in vitro studies may have overestimated the association between spinal DXA and vertebral failure loads, presumably because measurements were performed on excised bones, but not in situ in the presence of soft tissue inhomogeneity. The results indicate that, even in a population of old age and under in situ conditions, spinal DXA may still be somewhat better than femoral DXA and calcaneal ultrasound in predicting vertebral failure loads.

Absorptiometry, Photon↗
PubMed1998

Determination of 2'-hydroxyl and phosphate groups important for aminoacylation of Escherichia coli tRNAAsp: a nucleotide analogue interference study.

2'-Deoxynucleoside 5'-a-thiotriphosphates have been incorporated randomly, replacing any of the four nucleotides separately and at a low level in Escherichia colitRNA(AsP)transcripts. After some tRNAs were charged with the cognate aminoacyl-tRNA synthetase and biotinylated, charged and uncharged tRNAs were separated by binding to Streptavidin. A comparison of the iodine cleavage pattern of charged and uncharged tRNAs indicated positions of 2'-deoxyphosphorothioate interference with charging. To separate the 2'-deoxy from the phosphorothioate effect, the same sequence of reactions was performed with the corresponding NTPalphaS. Several positions were identified with a 2'-deoxy or a phosphorothioate effect. tRNAs with single deoxy substitutions at the identified positions were prepared by enzymatic ligation of chemically synthesized halves. The kinetics of charging these tRNAs were determined. The 2'-deoxy effects identified by the interference assay were confirmed, showing a reduction in charging efficiency of between 2.5-6-fold, except for the terminal A76 with a 25-fold reduction. Inspection of the X-ray structure of the tRNA-synthetase complex showed consistency of most of these findings. Critical 2'-deoxy groups are localized mainly on the proposed contact surface with the synthetase or at the interface of the two tRNA domains. The same overall picture emerged for critical phosphorothioates. With the exception of 2'-deoxy-adenosine-containing tRNAs, multiple 2'-deoxy-substituted tRNAs, prepared by ligation of halves, showed a much larger reduction in charging efficiency than the mono-substituted tRNAs, indicating an additive effect.

Adenosine↗
PubMed1998

Thickness of the subchondral mineralised tissue zone (SMZ) in normal male and female and pathological human patellae.

The objective of this paper was to analyse sex differences of the thickness of the subchondral mineralised tissue zone (SMZ), and to find out whether systematic changes of SMZ thickness are associated with naturally occurring, non-full-thickness cartilage lesions of human patellae. In 32 methyl-methacrylate-embedded specimens (16 normal, 8 with focal medial, and 8 with lateral lesions) the SMZ thickness was determined, using a binocular macroscope and an image analysing system. In each case, the thickness distribution was reconstructed throughout the entire joint surface. The maximal and mean SMZ thicknesses were significantly higher in males than in females (P < 0.01). In normal patellae and those with lateral lesions, the thickness was significantly thicker laterally than medially (P < 0.05), but it was not in specimens with medial damage. Patellae with medial damage exhibited a significantly lower total mean and lateral mean (P < 0.05). A lower SMZ thickness was found directly beneath medial lesions than beneath lateral ones, but the local thickness was always in the range of that observed in normal specimens. We conclude that differences of patellar SMZ thickness exist between males and females. Naturally occurring cartilage lesions appear, however, not to be associated with local changes of SMZ thickness, but they may be associated with an altered regional distribution pattern within the joint surface.

Aged↗
PubMed1998

The distribution of cartilage thickness within the joints of the lower limb of elderly individuals.

The objective of this study was to investigate the normal distribution of cartilage thickness in the major joints of the lower limb in elderly individuals. A 12.5 MHz ultrasound transducer was used to measure the cartilage thickness in the right and left hip, knee and ankle joint of 10 individuals aged between 62 and 99 y. Distribution patterns of cartilage thickness were derived by b-spline interpolation and the average distribution computed in each surface. The maximum cartilage thickness in the hip joint was 2.6 (+/-0.36) mm and the mean thickness 1.3 (+/-0.17) mm. The CV% (a measure of thickness inhomogeneity within the joint surface) was 32%. In the knee, the maximal and mean values were 3.8 (+/-0.46) mm and 1.9 mm (+/-0.24) mm, respectively (CV% = 34%), and in the ankle 1.7 (+/-0.25) mm and 1.0 (+/-0.16) mm (CV% = 32%). Systematic differences existed between both sides in the knee, the distal femur showing a significantly greater thickness on the right. While the mean and maximal thicknesses were systematically higher in the knee than in the hip, and in the hip higher than in the ankle (P < 0.05), there were no systematic differences in the thickness inhomogeneity of the 3 joints. Only the malleolus showed a somewhat more uniform thickness than the other joint surfaces. The variability between individuals was similar for all joints for mean thickness, but the interindividual variability of the maximal thickness values was highest in the knee and lowest in the ankle. Whereas the cartilage thickness distributions in the joints of the lower limb have been suggested to reflect the pressure distribution within the articular surface, the absolute thickness is proposed to be a function of dynamic loading (range of motion) during gait, rather than being a reflection of the static articular pressure.

Adaptation, Physiological↗
PubMed1998

Modified oligonucleotides: synthesis and strategy for users.

Synthetic oligonucleotide analogs have greatly aided our understanding of several biochemical processes. Efficient solid-phase and enzyme-assisted synthetic methods and the availability of modified base analogs have added to the utility of such oligonucleotides. In this review, we discuss the applications of synthetic oligonucleotides that contain backbone, base, and sugar modifications to investigate the mechanism and stereochemical aspects of biochemical reactions. We also discuss interference mapping of nucleic acid-protein interactions; spectroscopic analysis of biochemical reactions and nucleic acid structures; and nucleic acid cross-linking studies. The automation of oligonucleotide synthesis, the development of versatile phosphoramidite reagents, and efficient scale-up have expanded the application of modified oligonucleotides to diverse areas of fundamental and applied biological research. Numerous reports have covered oligonucleotides for which modifications have been made of the phosphodiester backbone, of the purine and pyrimidine heterocyclic bases, and of the sugar moiety; these modifications serve as structural and mechanistic probes. In this chapter, we review the range, scope, and practical utility of such chemically modified oligonucleotides. Because of space limitations, we discuss only those oligonucleotides that contain phosphate and phosphate analogs as internucleotidic linkages.

Deoxyribose↗
PubMed1998

Effect of physical exercise on cartilage volume and thickness in vivo: MR imaging study.

PURPOSE: To quantify, with magnetic resonance (MR) imaging, the in vivo changes in cartilage volume and thickness after physical exercise. MATERIALS AND METHODS: The patellae of eight volunteers were imaged six times at physical test by using a spoiled fat-suppressed gradient-echo sequence with an acquisition time of 4.10 minutes. The volunteers then performed 50 knee bends, and two more data sets were acquired 3-7 minutes and 8-12 minutes after exercise. The patellar cartilage volume was determined after three-dimensional reconstruction, and the thickness was assessed with a three-dimensional minimal-distance algorithm. RESULTS: Whereas repositioning had a small effect on the measurements (mean coefficient of variation, 1.4%), a statistically significant decrease in cartilage volume was observed 3-7 minutes (mean decrease, 6.0%; P < .05) and 8-12 minutes (mean decrease, 5.2%; P < .05) after exercise. The deformation was homogeneous throughout the joint surface. In one asymptomatic volunteer, a cartilage lesion became more pronounced after exercise. CONCLUSIONS: MR imaging can be used to investigate the response of articular cartilage to physical exercise in vivo. Patients or volunteers should be allowed a sufficient period of physical rest if quantitative measurements of cartilage volume and thickness are to be undertaken in longitudinal studies.

Adult↗
PubMed1998

[Relevance of susceptibility-induced geometrical distortion for validity of MRI-based cartilage volume and density measurements of the knee joint].

The aim of the present study was to analyze the relevance of susceptibility-induced geometrical distortion to the accuracy of MR-based cartilage volume and thickness measurement in the human knee joint. Nine cadaveric knee joints were imaged in the sagittal plane with MRI at a resolution of 2 x 0.31 x 0.31 mm3, using a fat-suppressed gradient echo sequence, with a normal gradient orientation and also with the frequency- and phase-encoding directions changed. CT arthrographic data sets were then obtained. On the basis of 3-D constructions, we determined the cartilage volume and, with a 3-D minimal distance algorithm, the thickness distribution, of the patella, femur and tibia. Irrespective of the gradient orientation, good agreement was observed between MRI and CT arthrography in terms of cartilage volumes and maximum cartilage thickness. With a normal gradient orientation the volume was overestimated by 2.5% in MRI, and 2.3% when the gradients were changed. The maximum cartilage thickness was underestimated by 0.24 intervals (interval = 0.5 mm) with a normal gradient orientation, and by 0.22 intervals when the gradient orientation was changed. In none of the joint surfaces was a relevant difference between the two methods observed. It can be shown that, using high-resolution, fat-suppressed gradient-echo sequences--susceptibility-induced geometrical distortion has no significant effect on the accuracy of MR-based cartilage volume and thickness measurements. MRI would therefore appear suitable for the design of patient-specific finite element models with the aim of analysing load transmission in diarthrodial joints and planning surgical interventions.

Adult↗
PubMed1998

In vivo reproducibility of three-dimensional cartilage volume and thickness measurements with MR imaging.

OBJECTIVE: Previous studies suggest that MR imaging is capable of providing accurate data on knee joint cartilage volume and thickness in vitro, but the reproducibility of these data in living subjects has not been analyzed rigorously. Our aim was therefore to determine the in vivo reproducibility of volume and thickness measurements from replicated data sets, applying three-dimensional (3D) postprocessing methods. SUBJECTS AND METHODS: Eight healthy volunteers were imaged six times at a resolution of 2 x 0.31 x 0.31 mm with a fat-suppressed fast low-angle shot 3D sequence, the knee being repositioned in between replicated examinations. Three-dimensional reconstructions of the articular cartilage surfaces were obtained from sagittal data sets, and the cartilage volumes were calculated. The thickness distribution was analyzed throughout the joint surfaces independent of the section orientation, using a previously validated 3D minimal-distance algorithm. RESULTS: In the volunteers, the coefficient of variation for replicated volume measurements ranged from 1.3% (patella) to 3.4% (lateral tibia), and the standard deviation of the individual cartilage volumes ranged from +/- 16% (lateral tibia) to +/- 22% (femur). The intraclass correlation coefficient ranged from .959 (lateral tibia) to .995 (patella). The interobserver evaluation was similar to the interscan reproducibility. The mean interscan deviation of the maximal cartilage thickness interval ranged from 0.1 to 0.3 cartilage thickness intervals (of 0.5 mm); only in rare cases did we record deviations greater than one thickness interval. CONCLUSION: MR imaging can be used to determine cartilage volume and thickness in the knee joints of living subjects with high precision, provided that a fat-suppressed gradient-echo sequence with adequate resolution and 3D digital image processing are used.

Adult↗
PubMed1998

Accuracy of cartilage volume and thickness measurements with magnetic resonance imaging.

A noninvasive imaging technique for quantifying articular cartilage is needed for diagnosis, monitoring, and therapy control in osteoarthritis. In this study the accuracy of three-dimensional cartilage volume and thickness measurements in the knee with magnetic resonance imaging was analyzed. Eight cadaveric specimens had sagittal imaging with a fat suppressed gradient echo sequence. After a contrast agent was injected, two sagittal computed tomography data sets were obtained, with the knees being repositioned between the examinations. The cartilage thickness was determined, after three-dimensional reconstruction, using a minimal distance algorithm. The mean absolute volume deviation between magnetic resonance imaging and computed tomography arthrography was 3.3% and that between the two computed tomography data sets was 3.6%. The absolute error in determining the maximal cartilage thickness with magnetic resonance imaging was on average 0.6 intervals (of 0.5-mm thickness) and that between the computed tomography examinations was 0.5 intervals. In a patient with anterior knee pain, a focal cartilage defect was seen with magnetic resonance imaging, and this was verified by arthroscopic examination. Using three-dimensional image processing, magnetic resonance imaging can provide accurate data on cartilage volume and thickness in the human knee joint surfaces. This imaging technique potentially may be valuable in the treatment of patients with joint disease.

Adult↗