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J Eck

Publications and source records attributed to J Eck.

18 recordsLinked to original sources
PubMed2001

A biomechanical comparison of modern anterior and posterior plate fixation of the cervical spine.

STUDY DESIGN: A biomechanical study was designed to assess relative rigidity provided by anterior, posterior, or combined cervical fixation using cadaveric cervical spine models for flexion-distraction injury and burst fracture. OBJECTIVES: To compare the construct stability provided by anterior plating with locked fixation screws, posterior plating with lateral mass screws, and combined anterior-posterior fixation in clinically simulated 3-column injury or corpectomy models. SUMMARY OF BACKGROUND DATA: Anterior plating with locked fixation screws is the most recent design and is found to provide better stability than the conventional unlocked anterior plating. However, there are few data on the direct comparison of biomechanical stability provided by anterior plating with locked fixation screws versus posterior plating with lateral mass screws. Biomechanical advantages of using combined anterior-posterior fixation compared with that of using either anterior or posterior fixation alone also have not been well investigated yet. METHODS: Biomechanical flexibility tests were performed using cervical spines (C2-T1) obtained from 10 fresh human cadavers. In group I (5 specimens), one-level, 3-column injury was created at C4-C5 by removing the ligamentum flavum and bilateral facet capsules, the posterior longitudinal ligament, and the posterior half of the intervertebral disc. In group II (5 specimens), complete corpectomy of C5 was performed to simulate burst injury. In each specimen, the intact spine underwent flexibility tests, and the following constructs were tested: (1) posterior lateral mass screw fixation (Axis plate) after injury; (2) polymethylmethacrylate anterior fusion block plus posterior fixation; (3) polymethylmethacrylate block plus anterior (Orion plate) and posterior plate fixation; and (4) polymethylmethacrylate block plus anterior fixation. Rotational angles of the C4-C5 (or C4-C6) segment were measured and normalized by the corresponding angles of the intact specimen to study the overall stabilizing effects. RESULTS: Posterior plating with an interbody graft showed effective stabilization of the unstable cervical segments in all loading modes in all cases. There was no significant stability improvement by the use of combined fixation compared with the posterior fixation with interbody grafting, although combined anterior-posterior fixation tended to provide greater stability than both anterior and posterior fixation alone. Anterior fixation alone was found to fail in stabilizing the cervical spine, particularly in the flexion-distraction injury model in which no contribution of posterior ligaments is available. Anterior plating fixation provided much greater fixation in the corpectomy model than in the flexion-distraction injury model. This finding suggests that preservation of the posterior ligaments may be an important factor in anterior plating fixation. CONCLUSIONS: This study showed that the posterior plating with interbody grafting is biomechanically superior to anterior plating with locked fixation screws for stabilizing the one-level flexion-distraction injury or burst injury. More rigid postoperative external orthoses should be considered if the anterior plating is used alone for the treatment of unstable cervical injuries. It was also found that combined anterior and posterior fixation may not improve the stability significantly as compared with posterior grafting with lateral mass screws and interbody grafting.

Aged↗
PubMed2001

Cervical spine: postmortem assessment of accident injuries--comparison of radiographic, MR imaging, anatomic, and pathologic findings.

PURPOSE: To assess the ability of postmortem radiography and magnetic resonance (MR) imaging to depict occult cervical spine injuries as compared with anatomic and pathologic findings. MATERIALS AND METHODS: The cervical spines of 10 adult accident victims underwent radiography and MR imaging, with T1-weighted, fast spin-echo T2-weighted, and four gradient-echo pulse sequences. The frozen specimens were cut into 3-mm-thick slices (sagittal plane) and photographed, and microfocus radiographs were obtained. Imaging findings were compared with the anatomic and pathologic findings. RESULTS: Eight of the 10 specimens had 28 posttraumatic lesions: three fractures (two missed at the initial MR imaging reading), 10 facet joint capsule lesions with bleeding, five soft-tissue and ligament lesions, eight disk lesions, and two spinal cord lesions. Radiography depicted one lesion (4%). Two partial ruptures of the anterior annulus fibrosus were depicted at only MR imaging. Initially, 11 of 28 lesions were detected on MR images; retrospectively, 17 of 28 lesions were correlated with anatomic findings. CONCLUSION: Soft-tissue and intervertebral disk and ligament injuries account for 89% (25 of 28) of posttraumatic cervical spine lesions detected on postmortem images. Occult lesions, including apophyseal joint injuries, were found in clinically noninjured cervical spines. MR imaging was limited in the depiction of discrete lesions when T1-weighted non-fat-saturated, fast spin-echo T2-weighted, and gradient-echo pulse sequences were used.

Adult↗
PubMed2000

Cytotoxic activity of recombinant bFGF-rViscumin fusion proteins.

A fusion protein (bFGF-rMLA), containing the mitogen basic fibroblast growth factor (bFGF) and the cytotoxic component of rViscumin (recombinant mistletoe lectin), the enzymatic A-chain (rMLA), was expressed in Escherichia coli, purified, and functionally characterized. bFGF-rMLA is cytotoxic for mouse B16 melanoma cells expressing the FGF receptor with an IC(50) value of approximately 1 nM. rMLA shows no significant effect on the viability of the B16 cells up to a concentration of 141 nM. Additionally, bFGF-rMLA was associated with the rViscumin B-chain (rMLB) in an in vitro folding procedure. The IC(50) value of bFGF-rMLA/rMLB to B16 cells in the presence of lactose-to block rMLB lectin activity-was 134 pM. Thus, it was possible to enhance the efficacy of a rViscumin A-chain mitotoxin through addition of rMLB. We conclude that rViscumin fusion proteins may be generally applicable for the receptor-specific inactivation of target cells and point out their potential in drug development.

Animals↗
PubMed1999

Site-specific mutagenesis of mistletoe lectin: the role of RIP activity in apoptosis.

Recombinant mistletoe lectin (rML) belongs to the class of type II ribosome-inactivating proteins (RIP) composed of a catalytically active A-chain with rRNA N-glycosidase activity and a B-chain with carbohydrate binding properties. To investigate the contribution of the enzymatic activity of the rML A-chain to the observed cytotoxic and apoptotic effects, an rMLA E166Q R169Q molecule was developed by means of site-specific mutagenesis. Following heterologous expression, the activity of mutant rMLA was measured in a cell-free assay for rRNA-N-glycosidase activity. Moreover, after generation of heterodimer, the activities of mutant rML E166Q R169Q and rML wild type were determined in a cytotoxicity and apoptosis assay. Although the reduction of activity as measured in the cell-free RIP assay was more pronounced (factor 237) than in both cellular assays (factors 20-22), the data clearly indicate a close correlation between cytotoxicity, apoptosis, and the enzymatic activity of the rML A-chain. Thus, RIP activity is an essential feature of rML and therefore a prerequisite for its biological function as an anticancer agent.

Apoptosis↗
PubMed1999

Functional expression of an inactivating potassium channel (Kv4.3) in a mammalian cell line.

OBJECTIVE: The goal of this study was to characterize the electrophysiological properties of the Kv4.3 channels expressed in a mammalian cell line. METHODS: Currents were recorded using the whole-cell voltage clamp technique. RESULTS: The threshold for activation of the expressed Kv4.3 current was approximately -30 mV. The dominant time constant for activation was 1.71 +/- 0.16 ms (n = 10) at +60 mV. The current inactivated, this process being incomplete, resulting in a sustained level which contributed 15 +/- 2% (n = 25) of the total current. The time course of inactivation was fit by a biexponential function, the fast component contributing 74 +/- 5% (n = 9) to the overall inactivation. The fast time constant was voltage-dependent [27.6 +/- 2.0 ms at +60 mV (n = 10) versus 64.0 +/- 3.6 ms at 0 mV (n = 10); P < 0.01], whereas the slow was voltage-independent [142 +/- 15 ms at +60 mV (n = 10) versus 129 +/- 33 ms at 0 mV (n = 6) P > 0.05]. The voltage-dependence of inactivation exhibited midpoint and slope values of -26.9 +/- 1.5 mV and 5.9 +/- 0.3 mV (n = 21). Recovery from inactivation was faster at more negative membrane potentials [203 +/- 17 ms (n = 13) and 170 +/- 19 ms (n = 4), at -90 and -100 mV]. Bupivacaine block of Kv4.3 channels was not stereoselective (KD approximately 31 microM). CONCLUSIONS: The functional profile of Kv4.3 channels expressed in Ltk- cells corresponds closely to rat ITO, although differences in recovery do not rule out association with accessory subunits. Nevertheless, the sustained component needs to be considered with respect to native ITO.

Animals↗
PubMed1999

Cloning of the mistletoe lectin gene and characterization of the recombinant A-chain.

Mistletoe lectin I (MLI) is the major active constituent of mistletoe extracts, which are widely used for adjuvant tumour therapy. The 66-kDa heterodimeric disulphide-linked glycoprotein is classified as type II ribosome-inactivating protein (RIP) due to the rRNA-cleaving enzyme activity of the A-subunit, also referred to as toxic entity. MLI and the close relative ricin both belong to the family of the two-chain plant type II RIP proteins. Isolation of the glycosylated proteins from plant material yield inhomogeneous material probably due to post-translational modifications. The aim of this study was to prepare pure and homogeneous protein as a prerequisite for structural and mechanistic studies in order to gain insight into the mode of action of this cytotoxic plant protein on tumour and immune cells. Of particular interest was to explain whether the differences in toxicity of ML and ricin are the result of variations of their enzymatic activities. By investigating the sequence homologies between the active sites of different RIPs we were able to deduce a set of primers which were suitable for specific amplification of the mistletoe lectin gene. Applying this PCR strategy the full-length 1923 nucleotide DNA sequence coding for the prepro-protein was obtained showing the existence of a single intron-free gene. In order to elucidate the molecular basis for the observed differences in cytotoxicity within the family of RIP the enzymatic A-subunit was expressed in a heterologous system. Expression of the A-chain in E. coli BL21/pT7 resulted in production of insoluble inclusion bodies constituting 20-30% of total protein. Refolding led to a pure and homogeneous protein species with an apparent molecular mass of 27 kDa and a pI value of 6.4. The ribosome-inactivating activity of the unglycosylated recombinant A-chain (IC50 20.5 pM) protein was in the same range as that of the glycosylated plant-derived ML A-chain (IC50 3.7 pM), which was very similar to that of ricin A-chain (IC50 4.9 pM). Thus, the higher cytotoxicity of ricin cannot be accountable for differences in the enzymatic activities of the type II RIP A-chains.

Amino Acid Sequence↗
PubMed1999

Characterization of recombinant and plant-derived mistletoe lectin and their B-chains.

Mistletoe lectin I (pML) and its isoforms ML II and III constitute the active principle in extract preparations from mistletoe, commonly used as immunomodulator in adjuvant tumour therapy. The heterodimeric disulfide-linked cytotoxic protein is classified as type II ribosome inactivating protein (RIP). Recently, the sequence coding for the mistletoe lectin prepro-protein was identified and the existence of a single intron-free gene was shown [Eck, J., Langer, M., Möckel, B., Baur, A., Rothe, M., Zinke, H. & Lentzen, H. (1999) Eur. J. Biochem. 264, 775-784]. The aim of this study was to prepare pure and homogeneous rMLB-chain as well as rML heterodimer for studying the carbohydrate binding specificity of recombinant versus natural protein and its contribution to the observed cytotoxic effect. Expression in E. coli resulted in the production of insoluble protein (inclusion bodies). A procedure for generating correctly folded, biochemically and biologically active rMLB was established starting from the insoluble single chain. Carbohydrate binding and specificity of pMLB and rMLB were analysed by a competitive enzyme linked lectin assay (ELLA). Asialofetuin was able to compete with binding of both chains (50% at 0.8 microM). The specificity of the B-chains to lactose was more distinct with halfmaximal competition at 4.9 mM (pMLB) and > 90 mM (rMLB), respectively. Furthermore, in a coassociation process rMLA- and rMLB inclusion bodies were associated in one step by defined dilution yielding active rML-heterodimer. The activities of recombinant (rML) and plant derived mistletoe lectin (pML) were compared. Cytotoxicity was determined using MOLT-4 cells and enzymatic rRNA N-glycosidase activity was measured in a coupled transcription/translation assay. The IC50 values of the two heterodimers were similar in both assays; rMLB-chain did not show any cytotoxic effect. In the ELLA with lactose as a competitor 50% competition of binding to asialofetuin was achieved at 1.6 mM (rML) and 1.8 mM (pML). Hence, using three different assays we found no significant differences between the recombinant protein and the glycosylated form of ML. Comparing the biological activities of the single chains with those of the heterodimer we conclude, that both, lectin activity and the rRNA N-glycosidase activity, are prerequisites for the cytotoxic effects on target cells.

Asialoglycoproteins↗
PubMed1998

Mistletoe lectin I forms a double trefoil structure.

The quaternary structure of mistletoe lectin I (MLI), a type II ribosome inactivating protein, has been determined by X-ray crystallography. A definitive molecular replacement solution was determined for MLI using the co-ordinates of the homologue ricin as a search model. MLI exists as an [AB]2 dimer with internal crystallographic two-fold symmetry. Domain I of the B chains is non-covalently associated through interactions involving three looped chains (alpha, beta, gamma) in each molecule of the dimer, forming a double trefoil structure. The ricin molecule which shares 52% sequence homology with MLI has a disulphide bridge between Cys20 and Cys39 in the alpha loop. An evolutionary mutation has replaced Cys39 with serine in MLI. This mutation appears to allow the alpha loop the flexibility required to take up its place at the dimer interface, and also suggests a rationale for why ricin does not form dimers. Measurement of retention times using FPLC gel filtration confirms that dimerisation also occurs in solution between MLI B chains with an association constant Ka = 10(6) M.

Amino Acid Sequence↗
PubMed1997

Biomechanical evaluation of anterior and posterior fixations in an unstable calf spine model.

STUDY DESIGN: Fresh calf lumbar spines were used to perform flexibility tests in multiple loading directions to compare the stabilizing effects of anterior and posterior rigid instrumentations. OBJECTIVE: To compare the biomechanical flexibility of anterior and posterior instrumentation constructs using an unstable calf spine model. SUMMARY OF BACKGROUND DATA: Unstable burst fractures of the thoracolumbar spine can be managed anteriorly or posteriorly. Controversy persists, however, on the merit of anterior fixation versus that of posterior fixation in terms of how much stability can be achieved. METHODS: Fifteen fresh calf spines (L2-L5) were loaded with pure unconstrained moments in flexion, extension, axial rotation, and lateral bending directions. After removal of L3-L4 disc and endplates to create an 1.5-cm anterior and middle column defect, testing was performed on five specimens after anterior Kaneda rod fixation, anterior University Plate fixation, or posterior ISOLA pedicle screw fixation (AcroMed, Cleveland, OH). Testing was repeated after inserting a polymethylmethacrylate block to stimulate an interbody anterior graft with instrumentation. RESULTS: All fixation devices provided a significant stabilizing effect in flexion and lateral bending. In extension, all constructs except ISOLA (AcroMed) without graft were stiffer than the intact specimen. In axial rotation with no graft, only the Kaneda device significantly reduced the flexibility from that of the intact specimen. The interbody graft provided additional rigidity to the ISOLA (AcroMed) instrumentation construct in flexion and extension and to the Kaneda construct in lateral bending. There was no significant effect of grafting in axial rotation. CONCLUSIONS: A short, transpedicular instrumentation, such as ISOLA (AcroMed), provided less rigid fixation in flexion and extension without the anterior structural graft. The Kaneda rod and University plate with grafting provided a significant stabilizing effect in all directions compared with the intact specimen. When no graft was inserted, the Kaneda device was more effective in preventing axial rotation than the other devices. In lateral bending, the University plate provided more rigid fixation than the Kaneda device without grafting.

Animals↗
PubMed1997

High relaxivity linear Gd(DTPA)-polymer conjugates: the role of hydrophobic interactions.

A series of linear copolymers of DTPA-class Gd3+ conjugates, linked by alpha, omega-alkyldiamides with a varying number (n) of methylenes separating the amide function, were synthesized. Surprisingly, their relaxivities at all fields increased with increasing n. At MRI fields and 35 degrees C, the relaxivities of the n = 10 and n = 12 polymers were unexpectedly high, similar to those of rigid dendrimer-based Gd3+ chelates. The magnetic field dependence of solvent proton 1/T1 was measured for aqueous urea-free and urea-containing polymer solutions. The results for urea-free solutions imply an increase of rigidity (required for high relaxivities) with increasing n, arising from hydrophobic interactions of the methylene groups with solvent. This hypothesis is supported by a large decrease in the relaxivities upon addition of urea, which is known to weaken hydrophobic interactions. The relaxivities are also independent of polymer concentration, indicating that the hydrophobic interactions are intramolecular.

Contrast Media↗
PubMed1997

Effects of mistletoe lectin I on human blood cell lines and peripheral blood cells. Cytotoxicity, apoptosis and induction of cytokines.

The effects of mistletoe lectin I (ML I) on the human T-cell leukemia line MOLT-4, the monocytic line THP-1 and on human peripheral blood mononuclear cells (PBMC) were investigated with regard to general cell viability and induction of apoptosis. Using a sensitive serum-free cytotoxicity assay, the time- and concentration-dependent direct toxicity towards MOLT-4 cells was determined with IC50-values ranging from 20-40 pg/ml (300-600 fmol/l). Investigations on the time course of the toxic effect using selected concentrations of ML I revealed distinct response curves for concentrations of high, low and intermediate toxicity, respectively. The ratio of apoptotic to viable MOLT-4 cells was determined after treatment with ML I for 24 h. Apoptosis and cytotoxicity were correlated at low and intermediate concentrations, whereas at long intervals and high concentrations of ML I mostly necrotic effects were observed. The data showed that in the concentration range of low cytotoxicity ML I-induced cell death is quantitatively due to apoptotic processes. The immunomodulatory activity of ML I was investigated in vitro by measuring cytokine release. At concentrations of low cytotoxicity ML I showed immunostimulatory activity on PBMC and THP-1. RT-PCR with THP-1 cells confirmed that cytokine induction by ML I is regulated on the transcriptional level. These findings suggest that in the blood cells investigated both apoptosis and cellular signalling are induced by the same concentration range of ML I.

Apoptosis↗
PubMed1996

A nonradioactive assay for ribosome-inactivating proteins.

A sensitive nonradioactive method to determine the activity of ribosome-inactivating proteins (RIPs) based on a combined transcription/translation in vitro assay was established. Using this assay we investigated the RIP activities of the heterodimeric toxic plant lectins ricin and mistletoe lectin I (ML-I). The enzymatic activities of the holoproteins were compared to that of the RIP-active chain of ML-I (ML-I A-chain) and recombinant ML-I A-chain expressed in Escherichia coli. The IC50 values determined for the plant toxins showed that the translation-inactivating activity of ML-I (39.8 pM) is about four times higher than that of ricin (176.0 pM). The plant-derived ML-I A-chain is more toxic (3.4 pM) in the cell-free translation system than the respective holoprotein. The recombinant ML-I A-chain was found to be about three times less active (IC50 10.6 pM) than the A-chain from plant. The in vitro assay described here is a convenient method for the fast determination of RIP activity with a 1000-fold lower detection limit than that of commonly used RIP assays.

Animals↗
PubMed1995

Biomechanical evaluation of anterior thoracolumbar spinal instrumentation.

STUDY DESIGN: A biomechanical study was designed to assess relative construct stabilities of modern anterior thoracolumbar instrumentations in a calf spine model with an anterior and middle column defect. OBJECTIVES: The purpose is to compare the biomechanical stability of various anterior fixation devices in an unstable calf spine model. SUMMARY OF BACKGROUND DATA: Modern types of anterior thoracolumbar instrumentations evolved to either rods or plates. Biomechanical properties and comparative studies of these instrumentations are lacking. METHODS: Twenty fresh calf spines (L2-L5) were used for the biomechanical tests. L2 and L5 vertebrae were used to attach the loading and base frames, respectively. Specimens underwent nondestructive biomechanical tests performed using a three-dimensional motion measuring system. In each specimen, three different cases were tested: intact spine, anterior fixation with an interbody graft after total discectomy and endplate excision of L3-L4 disc, anterior fixation only without the graft. Four anterior fixators, University Anterior Plating System, the Kaneda device, the Z-plate, and Texas Scottish Rite Hospital system were used. Each device was tested on five specimens. A polymethylmethacrylate block was inserted into the disc space to simulate the interbody grafting, and a fixation device was implanted with axial compression. Rotational angles of the L3-L4 segment stabilized by a fixation device and graft were normalized by the corresponding angles of the intact specimen to study the overall stabilizing effects. RESULTS: With the interbody graft and fixation devices, all showed significant stabilizing effects in flexion, extension, and lateral bending. All devices restored axial rotation stability to intact specimen, but only the Kaneda device restored the torsional stability beyond the intact specimen. No statistical differences in stabilizing effects in axial rotation were found between any of the tested devices. When the graft was removed, the Kaneda device significantly decreased the motions in all directions compared with the intact motion, whereas the University plate decreased the motions in flexion, extension, and lateral bending. The Texas Scottish Rite Hospital system was found to reduce the flexion and lateral bending motions significantly, and Z-plate decreased lateral bending motions only. Stabilizing effects of the interbody graft were significant in lateral bendings for all devices. Additionally, the significant stabilizing role of the graft was noted in flexion and extension in Z-plate only. The graft did not significantly reduce the axial rotation motion in any instrumentations. CONCLUSIONS: Modern anterior instrumentations for the thoracolumbar spine, such as the Kaneda device, Texas Scottish Rite Hospital system, Z-plate, and University plate, restored the stability in all motions when an interbody graft was inserted. The stability of fixation devices revealed that the Kaneda device is the best, particularly in restoring the torsional stability. The information on the relative stability provided by different instrumentations should help the spine surgeon in choosing the appropriate instrumentation for the particular circumstance.

Analysis of Variance↗
PubMed1989

[An activated charcoal filter for eliminating volatile anesthetics. A contribution to the management of malignant hyperthermia].

Anesthesia machines may not be contaminated with anesthetic vapors when a patient susceptible to malignant hyperthermia (MHS) is to be anesthetized. A clean machine may not always be available, and recommended protocols for preparing a contaminated machine are cumbersome and time-consuming. We suggest the use of an activated charcoal filter that is easily assembled from spare parts available in many anesthesiology departments (Fig. 2). It consists of an HME container (Servo-Humidifier 150, Siemens-Elema), a sieve set from an anesthesia circuit (7a/8-ISO, Dräger, Lübeck), and grained activated charcoal (2.5 mm, Merck, Darmstadt). All parts are autoclavable. The filter adsorbs anesthetic vapors quantitatively (Fig. 3) without affecting humidity, nitrous oxide concentration, or circuit resistance. Storage of such a filter may obviate the need to keep a clean anesthesia machine available for MHS patients.

Anesthesiology↗
PubMed1986

Effects of selected softball bat loading strategies on impact reaction impulse.

Interior loading strategies to modify the location and size of the effective hitting area of aluminum softball bats were identified. The effects of these strategies on theoretically derived and empirically determined relevant mechanical parameters were compared. Loading strategies consisted of adding 315 g to the interior of three similar (790 g) aluminum softball bats: at the center of mass of the original bat (bat C); at the ends of the bat and distributed so that the center of mass was unchanged, (bat A); and at the ends of the bat and distributed so that the moment of inertia about the swing axis (I1) was the same as that of bat C (bat B). The following parameters were derived theoretically by considering the bat as a physical pendulum and empirically by observing the impact reaction impulse on the axis of suspension: moment of inertia about the suspension axis (I0); moment of inertia about the swing axis; distance from the suspension axis to the center of percussion; and the slope of the impact reaction impulse (P1) relative to the impact impulse (P) as a function of impact location. These values for each bat were compared. Both empirical and theoretically derived data indicated that: the center of percussion of bat B was farther away from the axis than bats A and C; the moment of inertia about the swing axis of bat A was much greater than that of bats B and C; and the slope of the impact reaction regression line as a function of impact location for bat B was significantly less than that of the other bats. Thus, the effective hitting area of bat B was moved toward the barrel end of the bat and enlarged without a substantial increase in the moment of inertia about the swing axis.

Baseball↗
PubMedDate not supplied

Polymeric gadolinium chelate magnetic resonance imaging contrast agents: design, synthesis, and properties.

We have synthesized and evaluated five series of polymeric gadolinium chelates which are of interest as potential MRI blood pool contrast agents. The polymers were designed so that important physical properties including molecular weight, relaxivity, metal content, viscosity, and chelate stability could be varied. We have shown that, by selecting polymers of the appropriate MW, extended blood pool retention can be achieved. In addition, relaxivity can be manipulated by changing the polymer rigidity, metal content affected by monomer selection, viscosity by polymer shape, and chelate stability by chelator selection.

Animals↗