Finite element analysis of wall stress in the equine pulmonary artery.

REASONS FOR PERFORMING STUDY: Arterial calcification is found frequently in the pulmonary artery of racehorses, but the aetiology is unknown. Calcification might be associated with increased wall stress due to arterial geometry (shape) and exercise-induced hypertension. HYPOTHESIS: High wall stress levels are found in the regions associated with calcified lesion formation, exacerbated as transluminal pressure increases to levels associated with exercise. METHODS: The pulmonary arteries of 5 horses, unaffected by calcification, were dissected and pressurised to resting and exercising physiological transluminal pressures and scanned with MRI. Arterial geometries were reconstructed to form 3D computer models and finite element analyses performed. Wall stress levels were measured in 4 regions of interest: the arterial trunk and bifurcation, the wall ipsilateral and contralateral to the bifurcation. Measurements were made for arterial transluminal pressures of 25, 50 and 100 mmHg. RESULTS: High wall stress levels were consistently found at the pulmonary artery bifurcation and wall ipsilateral to the bifurcation, where calcified lesions typically form. Lower wall stress levels were found along the trunk and the wall contralateral to the bifurcation where lesions are less frequently found. Wall stress levels increased 5-fold over a 4-fold increase in pressure. The wall stress levels ranged 10 kPa in the wall of the branch contralateral to the bifurcation at 25 mmHg to 400 kPa in the bifurcation at 100 mmHg. CONCLUSIONS: Wall stress from arterial geometry and increased pulmonary artery transluminal pressure are factors that may be associated with calcification of the equine pulmonary artery. POTENTIAL RELEVANCE: Arterial calcification may increase the risk of arterial wall failure in racing horses.

Revision total knee arthroplasty using a novel 3D printed titanium augment: A biomechanical cadaveric study.

BACKGROUND: During revision total knee arthroplasty (rTKA), proximal tibial bone loss is frequently encountered and can result in a less-stable bone-implant fixation. A 3D printed titanium revision augment that conforms to the irregular shape of the proximal tibia was recently developed. The purpose of this study was to evaluate the fixation stability of rTKA with this augment in comparison to conventional cemented rTKA. METHODS: Primary total knee arthroplasty (pTKA) surgery was performed on 11 pairs of thawed fresh-frozen cadaveric tibias (22 tibias). Fixation stability testing was conducted using a three-stage eccentric loading protocol. Bone-implant micromotion was measured using a high-resolution optical system. The pTKA were removed. Revision TKA was performed using a 3D printed titanium augment or a standard fully cemented stem. The three-stage eccentric loading protocol was repeated and micromotion was measured for the revision implants. RESULTS: After rTKA, the mean vertical micromotion was 28.1 µm ± (SD) 20.3 µm in the control group and 17.5 µm ± 18.7 µm in the experimental group. There was significantly less micromotion in the experimental group (p = 0.029). CONCLUSIONS: This study suggests that early fixation stability of revision TKA with the novel 3D printed titanium augment is better then the conventional fully cemented rTKA. The early press-fit fixation of the augment is likely sufficient for promoting bony ingrowth of the augment in vivo. Further studies are needed to investigate the long-term in-vivo fixation of the novel 3D printed augment.

Solution of a protein crystal structure with a model obtained from NMR interproton distance restraints.

Model calculations were performed to test the possibility of solving crystal structures of proteins by Patterson search techniques with three-dimensional structures obtained from nuclear magnetic resonance (NMR) interproton distance restraints. Structures for crambin obtained from simulated NMR data were used as the test system; the root-mean-square deviations of the NMR structures from the x-ray structure were 1.5 to 2.2 A for backbone atoms and 2.0 to 2.8 A for side-chain atoms. Patterson searches were made to determine the orientation and position of the NMR structures in the unit cell. The correct solution was obtained by comparing the rotation function results of several of the NMR structures and the average structure derived from them. Conventional refinement techniques reduced the R factor from 0.43 at 4 A resolution to 0.27 at 2 A resolution without inclusion of water molecules. The partially refined structure has root-mean-square backbone and side-chain atom deviations from the x-ray structure of 0.5 and 1.3 A, respectively.

Repeatability of measuring knee flexion angles with wearable inertial sensors.

BACKGROUND: As assessment with inertial-measurement-units (IMUs) increases in research and in clinics, it is important to be aware of the repeatability of these sensors. The objectives of this experiment were to evaluate the measurement repeatability of IMU joint angles using a repeatable robot controller and an anthropomorphic leg phantom and to determine effects of joint speed and sensor positioning on the angles collected by these sensors. Comparisons to an electro-goniometer and three-dimensional (3D) motion capture cameras were also completed. METHODS: Two dual-IMU setups (posterior and lateral) were tested concurrently with an electro-goniometer and 3D motion capture cameras using a repeatable robot controller and a leg phantom. All modalities were attached to the phantom, which was flexed 10 times using a pre-programmed motion pathway during each test. Mean angles were compared across tests. Effects of joint speed, sensor re-positioning, and anatomical placement of the sensors on repeatability were assessed. RESULTS: Re-positioning caused greater deviation to the maximum and minimum angles than differences in speed. Overall, the means ±â€¯standard deviations, and 95% confidence intervals of the maximum angles across all tests for the 3D camera markers, electro-goniometer, posterior IMUs, and lateral IMUs were 119.4 ±â€¯0.3° (119.4, 119.5), 112.4 ±â€¯0.5° (112.3, 112.5), 116.2 ±â€¯2.4° (115.7, 116.7), and 118.3 ±â€¯1.1° (118.1, 118.6). CONCLUSIONS: Both posterior and lateral IMU setups demonstrated acceptable repeatability in measurement of range of motion that was advantageous to manual goniometer methods. Posterior and lateral IMU setups demonstrated overlapping standard deviations about their means.

A randomized controlled trial investigating the value of patient-specific instrumentation for total knee arthroplasty in the Canadian healthcare system.

AIMS: The purpose of the present study was to compare patient-specific instrumentation (PSI) and conventional surgical instrumentation (CSI) for total knee arthroplasty (TKA) in terms of early implant migration, alignment, surgical resources, patient outcomes, and costs. PATIENTS AND METHODS: The study was a prospective, randomized controlled trial of 50 patients undergoing TKA. There were 25 patients in each of the PSI and CSI groups. There were 12 male patients in the PSI group and seven male patients in the CSI group. The patients had a mean age of 69.0 years (sd 8.4) in the PSI group and 69.4 years (sd 8.4) in the CSI group. All patients received the same TKA implant. Intraoperative surgical resources and any surgical waste generated were recorded. Patients underwent radiostereometric analysis (RSA) studies to measure femoral and tibial component migration over two years. Outcome measures were recorded pre- and postoperatively. Overall costs were calculated for each group. RESULTS: There were no differences (p > 0.05) in any measurement of migration at two years for either the tibial or femoral components. Movement between one and two years was < 0.2 mm, indicating stable fixation. There were no differences in coronal or sagittal alignment between the two groups. The PSI group took a mean 6.1 minutes longer (p = 0.04) and used a mean 3.4 less trays (p < 0.0001). Total waste generated was similar (10 kg) between the two groups. The PSI group cost a mean CAD$1787 more per case (p < 0.01). CONCLUSION: RSA criteria suggest that both groups will have revision rates of approximately 3% at five years. The advantages of PSI were minimal or absent for surgical resources used and waste eliminated, and for meeting target alignment, yet had significantly greater costs. Therefore, we conclude that PSI may not offer any advantage over CSI for routine primary TKA cases. Cite this article: Bone Joint J 2019;101-B:565-572.

Highly crosslinked polyethylene wear rates and acetabular component orientation: a minimum ten-year follow-up.

Aims: The aim of this study was to determine whether there is a difference in the rate of wear between acetabular components positioned within and outside the 'safe zones' of anteversion and inclination angle. Patients and Methods: We reviewed 100 hips in 94 patients who had undergone primary total hip arthroplasty (THA) at least ten years previously. Patients all had the same type of acetabular component with a bearing couple which consisted of a 28 mm cobalt-chromium head on a highly crosslinked polyethylene (HXLPE) liner. A supine radiostereometric analysis (RSA) examination was carried out which acquired anteroposterior (AP) and lateral paired images. Acetabular component anteversion and inclination angles were measured as well as total femoral head penetration, which was divided by the length of implantation to determine the rate of polyethylene wear. Results: The mean anteversion angle was 19.4° (-15.2° to 48°, sd 11.4°), the mean inclination angle 43.4° (27.3° to 60.5°, sd 6.6°), and the mean wear rate 0.055 mm/year (sd 0.060). Exactly half of the hips were positioned inside the 'safe zone'. There was no difference (median difference, 0.012 mm/year; p = 0.091) in the rate of wear between acetabular components located within or outside the 'safe zone'. When compared to acetabular components located inside the 'safe zone', the wear rate was no different for acetabular components that only achieved the target anteversion angle (median difference, 0.012 mm/year; p = 0.138), target inclination angle (median difference, 0.013 mm/year; p = 0.354), or neither target (median difference, 0.012 mm/year; p = 0.322). Conclusion: Placing the acetabular component within or outside the 'safe zone' did not alter the wear rate of HXLPE at long-term follow-up to a level that risked osteolysis. HXLPE appears to be a forgiving bearing material in terms of articular surface wear, but care must still be taken to position the acetabular component correctly so that the implant is stable. Cite this article: Bone Joint J 2018;100-B:891-7.

Inducible displacement of cemented tibial components ten years after total knee arthroplasty.

AIMS: The aim of this study was to evaluate the long-term inducible displacement of cemented tibial components ten years after total knee arthroplasty (TKA). PATIENTS AND METHODS: A total of 15 patients from a previously reported prospective trial of fixation using radiostereometric analysis (RSA) were examined at a mean of 11 years (10 to 11) postoperatively. Longitudinal supine RSA examinations were acquired at one week, one year, and two years postoperatively and at final follow-up. Weight-bearing RSA examinations were also undertaken with the operated lower limb in neutral and in maximum internal rotation positions. Maximum total point motion (MTPM) was calculated for the longitudinal and inducible displacement examinations (supine versus standing, standing versus internal rotation, and supine versus standing with internal rotation). RESULTS: All patients showed some inducible displacement. Two patients with radiolucent lines had greater mean standing-supine MTPM displacement (1.35; sd 0.38) compared with the remaining patients (0.68; sd 0.36). These two patients also had a greater mean longitudinal MTPM at ten years (0.64; sd 0.50) compared with the remaining patients (0.39; sd 0.13 mm). CONCLUSION: Small inducible displacements in well-fixed cemented tibial components were seen ten years postoperatively, of a similar magnitude to that which has been reported for well-fixed components one to two years postoperatively. Greater displacements were found in components with radiolucent lines. Cite this article: Bone Joint J 2018;100-B:170-5.

Migration of a cemented fixed-bearing, polished titanium tibial baseplate (Genesis II) at ten years : a radiostereometric analysis.

AIMS: The purpose of the present study was to examine the long-term fixation of a cemented fixed-bearing polished titanium tibial baseplate (Genesis ll). PATIENTS AND METHODS: Patients enrolled in a previous two-year prospective trial (n = 35) were recalled at ten years. Available patients (n = 15) underwent radiostereometric analysis (RSA) imaging in a supine position using a conventional RSA protocol. Migration of the tibial component in all planes was compared between initial and ten-year follow-up. Outcome scores including the Knee Society Score, Western Ontario and McMaster Universities Arthritis Index, 12-item Short Form Health Survey, Forgotten Joint Score, and University of California, Los Angeles Activity Score were recorded. RESULTS: At ten years, the mean migration of the tibial component was less than 0.1 mm and 0.1° in all planes relative to the post-operative RSA exam. Maximum total point movement increased with time (p = 0.002) from 0.23 mm (sd 0.18) at six weeks to 0.42 mm (sd 0.20) at ten years. CONCLUSION: The low level of tibial baseplate migration found in the present study correlates to the low rate of revision for this implant as reported in individual studies and in joint replacement registries. TAKE HOME MESSAGE: Overall, the implant was found to be well fixed at ten years, supporting its continued clinical use and the predictive power of RSA for determining long-term fixation of implants. Cite this article: Bone Joint J 2016;98-B:616-21.

Patterns for prediction of hydration around polar residues in proteins.

The atomic co-ordinates of seven very high resolution (< 1.4 A) proteins have been used to define a water-hydrogen bond template for five polar side-chains (arginine, aspartic acid, glutamic acid, asparagine and glutamine). The average water molecule positions determined were consistent with the hydrogen bonding stereochemistry expected for each side-chain. Hydrogen bonding geometry around nitrogen atoms was significantly better localized than around oxygen atoms, perhaps because of the proton on nitrogen. A prediction algorithm written to locate water molecule sites around these side-chains from the protein co-ordinates only was tested for crambin as well as for two high resolution protein structures not included in the hydrogen bond data base. The root-mean-square deviation of the predicted positions from the crystallographically determined ones for these structures was better than the resolution of these structures. The method also successfully predicted water positions for X-ray refinement of two proteins, indicating that predicted water molecules are within the radius of convergence of refinement. This method has utility for X-ray models as well as for analysis of enzyme hydration and function.

Atomic resolution (0.83 A) crystal structure of the hydrophobic protein crambin at 130 K.

To enhance the already high quality of diffraction data for crystals of the hydrophobic protein crambin, X-ray data were collected at 130 K by the method of H. Hope to 0.83 A resolution. Refinement with PROLSQ yields a model with an R value of 10.5%. The final model had three parameter anisotropic vibration factors for all atoms, which included 367 protein heavy atoms, 372 hydrogen atoms and 144 solvent atoms with one ethanol molecule. Dihedral angles and hydrogen-bonding distances generally agree with earlier studies of high-resolution protein structures, but some new patterns are noted. Solvent-related helix distortions are reminiscent of those described by others. Helix and beta-sheet regions show distinct patterns in their side-chain conformations. Despite crambin's hydrophobic nature, its accessible surface area in the crystal is surprisingly close to that of water-soluble proteins like myoglobin and carboxypeptidase A. More of crambin's hydrophobic surface is buried in the crystal, perhaps accounting for its high order of diffraction. A total of 24% of the 46 residues show discrete disorder at 130 K. This includes five side-chains at both 300 and 130 K, and six more side-chains and an ethanol molecule at 130 K. Disorder is associated with the sequence microheterogeneity at Pro/Ser22 and Leu/Ile25, with space filling or with solvent disorder. Correlated conformations extend over three to five residues. The patterns of disorder in this structure reveal important principles of protein structure and its dynamics. Finding disordered groups correlated over 5 to 8 A suggests that co-ordinated motion extends in groups rather than simply as uncorrelated movement around an atom center. Thermal diffuse scattering experiments on insulin and lysozyme are consistent with this interpretation. Nearly all of the protein-bound solvent has been located. Less than 1% of protein accessible surface area remains uncovered by solvent or crystal contacts. Preliminary analysis of the solvent network reveals two main networks in each of four solvent regions.

Nuclear magnetic resonance study of the solution structure of alpha 1-purothionin. Sequential resonance assignment, secondary structure and low resolution tertiary structure.

The solution structure of the 45-residue plant protein, alpha 1-purothionin, is investigated by nuclear magnetic resonance (n.m.r.) spectroscopy. Using a combination of two-dimensional n.m.r. techniques to demonstrate through-bond and through-space (less than 5 A) connectivities, the 1H n.m.r. spectrum of alpha 1-purothionin is assigned in a sequential manner. The secondary structure elements are then delineated on the basis of a qualitative interpretation of short-range nuclear Overhauser effects (NOE) involving the NH, C alpha H and C beta H protons. There are two helices extending from residues 10 to 19 and 23 to 28, two short beta-strands from residues 3 to 5 and 31 to 34 which form a mini anti-parallel beta-sheet, and five turns. In addition, a number of long-range NOE connectivities are assigned and a low resolution tertiary structure is proposed.

Taperosis: Does head length affect fretting and corrosion in total hip arthroplasty?

Tribocorrosion at the head-neck taper interface - so-called 'taperosis' - may be a source of metal ions and particulate debris in metal-on-polyethylene total hip arthroplasty (THA). We examined the effect of femoral head length on fretting and corrosion in retrieved head-neck tapers in vivo for a minimum of two years (mean 8.7 years; 2.6 to 15.9). A total of 56 femoral heads ranging from 28 mm to 3 mm to 28 mm + 8 mm, and 17 femoral stems featuring a single taper design were included in the study. Fretting and corrosion were scored in three horizontally oriented concentric zones of each taper by stereomicroscopy. Head length was observed to affect fretting (p = 0.03), with 28 mm + 8 mm femoral heads showing greater total fretting scores than all other head lengths. The central zone of the femoral head bore taper was subject to increased fretting damage (p = 0.01), regardless of head length or stem offset. High-offset femoral stems were associated with greater total fretting of the bore taper (p = 0.04). Increased fretting damage is seen with longer head lengths and high-offset femoral stems, and occurs within a central concentric zone of the femoral head bore taper. Further investigation is required to determine the effect of increased head size, and variations in head-neck taper design.

Homology modeling of the dopamine D2 receptor and its testing by docking of agonists and tricyclic antagonists.

We present the first model of dopamine D2 receptor transmembrane helices constructed directly from the bacteriorhodopsin (bR) coordinates derived from two-dimensional electron diffraction experiments. We have tested this model by its ability to accommodate rigid agonist and semirigid antagonist molecules which were docked into the putative binding pocket with stabilizing interactions. The model is consistent with structure-activity relationships of agonists and antagonists that interact with the receptor. It also illuminates data on a Na+ site for regulation of receptor function. The plausibility of the model is increased by its consistency with many mutagenesis studies on G protein-coupled receptors. Further, this model provides a basis to suggest testable molecular mechanisms for changes in the D2 conformational states for high- and low-affinity binding and signal transduction. Changes in the conformational state of the receptor are hypothesized to be due partly to movement of helix 7. In contrast to the model presented here, other published models were built using ideal helical structures or following the sense of the bacteriorhodopsin structure rather than the actual available coordinates. The presented model for the dopamine G protein-coupled receptor can be reconciled with the recent rhodopsin projection structure (Schertler, G. F. X.; Villa, C.; Henderson, R. Projection Structure of Rhodopsin.

CoMFA-based prediction of agonist affinities at recombinant D1 vs D2 dopamine receptors.

We have previously shown that using agonist affinity at recombinant receptors selectively expressed in clonal cells as the dependent variable in three-dimensional quantitative structure-activity relationship studies (3D-QSAR) presents a unique opportunity for accuracy and precision in measurement. Thus, a comparison of affinity's structural determinants for a set of compounds at two different recombinant dopamine receptors represents an attainable goal for 3D-QSAR. A molecular database of bound conformations of 16 structurally diverse agonists was established by alignment with a high-affinity template compound for the D1 receptor, 3-allyl-6-bromo-7,8-dihydroxy-1-phenyl-2,3,4, 5-tetrahydro-1H-benzazepin. A second molecular database of the bound conformations of the same compounds was established against a second template for the D2 receptor, bromocriptine. These aligned structures suggested three-point pharmacophore maps (one cationic nitrogen and two electronegative centers) for the two dopamine receptors, which differed primarily in the height of the nitrogen above the plane of the catechol ring and in the nature of the hydrogen-bonding region. The ln(1/KL) values for the low-affinity agonist binding conformation at recombinant D1 and D2 dopamine receptors stably expressed in C6 glioma cells were used as the target property for the CoMFA (comparative molecular field analysis) of the 16 aligned structures. The resulting CoMFA models yielded cross-validated R2 (q2) values (standard error of prediction) of 0. 879 (1.471, with five principal components) and 0.834 (1.652, with five principal components) for D1 and D2 affinity, respectively. The simple R2 values (standard error of the estimate) were 0.994 (0.323) and 0.999 (0.116), respectively, for D1 and D2 receptor. F values were 341 and 2465 for D1 and D2 models, respectively, with 5 and 10 df. The predictive utility of the CoMFA model was evaluated at both receptors using the dopamine agonists, apomorphine and 7-OH-DPAT. Predictions of KL were accurate at both receptors. Flexible 3D searches of several chemical databases (NCI, MDDR, CMC, ACD, and Maybridge) were done using basic pharmacophore models at each receptor to determine the similarity of hit lists between the two models. The D1 and D2 models yielded different lists of lead compounds. Several of the lead compounds closely resembled high-affinity training set compounds. Finally, homology modeling of agonist binding to the D2 receptor revealed some consistencies and inconsistencies with the CoMFA-derived D2 model and provided a possible rationale for features of the D2 CoMFA contour map. Together these results suggest that CoMFA-homology based models may provide useful insights concerning differential agonist-receptor interactions at related receptors. The results also suggest that comparisons of CoMFA models for two structurally related receptors may be a fruitful approach for differential QSAR.

CoMFA-based prediction of agonist affinities at recombinant wild type versus serine to alanine point mutated D2 dopamine receptors.

Agonist affinity changes dramatically as a result of serine to alanine mutations (S193A, S194A, and S197A) within the fifth transmembrane region of D2 dopamine receptors and other receptors for monoamine neurotransmitters. However, agonist 2D-structure does not predict which drugs will be sensitive to which point mutations. Modeling drug-receptor interactions at the 3D level offers considerably more promise in this regard. In particular, a comparison of the same test set of agonists across receptors differing minimally (point mutations) offers promise to enhance the understanding of the structural bases for drug-receptor interactions. We have previously shown that comparative molecular field analysis (CoMFA) can be applied to comparisons of affinity at recombinant D1 and D2 dopamine receptors for the same set of agonists, a differential QSAR. Here, we predicted agonist K(L) for the same set of agonists at wild type D2 vs S193A, S194A, and S197A receptors using CoMFA. Each model used bromocriptine as the template. ln(1/K(L)) values for the low-affinity agonist binding conformation at recombinant wild type and mutant D2 dopamine receptors stably expressed in C6 glioma cells were used as the target property for the CoMFA of the 16 aligned agonist structures. The resulting CoMFA models yielded cross-validated R(2) (q(2)) values ranging from 0.835 to 0.864 and simple R(2) values ranging from 0.999 to 1.000. Predictions of test compound affinities at WT and each mutant receptor were close to measured affinity values. This finding confirmed the predictive ability of the models and their differences from one another. The results strongly support the idea that CoMFA models of the same training set of compounds applied to WT vs mutant receptors can accurately predict differences in drug affinity at each. Furthermore, in a "proof of principle", two different templates were used to derive the CoMFA model for the WT and S193A mutant receptors. Pergolide was chosen as an alternate template because it showed a significant increase in affinity as a result of the S193A mutation. In this instance both the bromocriptine- and pergolide-based CoMFA models were similar to one another but different from those for the WT receptor using bromocriptine- or pergolide- as templates. The pergolide-based S193A model was more strikingly different from that of the WT receptor than was the bromocriptine-based S193A model. This suggests that a "dual-template" approach to differential CoMFA may have special value in elucidating key differences across related receptor types and in determining important elements of the drug-receptor interaction.

Energy minimization for tertiary structure prediction of homologous proteins: alpha 1-purothionin and viscotoxin A3 models from crambin.

Homologous proteins may fold into similar three-dimensional structures. Spectroscopic evidence suggests this is true for the cereal grain thionins, the mistletoe toxins, and for crambin, three classes of plant proteins. We have combined primary sequence homology and energy minimization to predict the structures alpha 1-purothionin (from Durum wheat) and viscotoxin A3 (from Viscum album, European mistletoe) from the high resolution (0.945 A) crystal structure of crambin (from Crambe abyssinica). Our predictions will be verifiable because we have diffraction-quality crystals of alpha 1-purothionin whose structure we are have predicted. The potential energy minimizations for each protein were performed both with and without harmonic constraints to its initial backbone to explore the existence of local minima for the predicted proteins. Crambin was run as a control to examine the effects of the potential energy minimization on a protein with a well-known structure. Only alpha 1-purothionin which has one fewer residue in a turn region shows a significant difference for the two minimization paths. The results of these predictions suggest that alpha 1-purothionin and viscotoxin are amphipathic proteins, and this character may relate to the mechanism of action for these proteins. Both are mildly membrane-active and their amphipatic character is well suited for interaction with a lipid bilayer.

Mapping the binding site of aflatoxin B1 in DNA: molecular modeling of the binding sites for the N(7)-guanine adduct of aflatoxin B1 in different DNA sequences.

Aflatoxin B1 (AFB1), a potent mutagen and carcinogen, forms an adduct exclusively at the N(7) position of guanine, but the structure of this adduct in double stranded DNA is not known. Molecular modeling (using the program, PSFRODO) in conjunction with molecular mechanical calculation (using the program, AMBER) are used to assess the binding modes available to this AFB1 adduct. Two modes appear reasonable; in one the AFB1 moiety is intercalated between the base pair containing the adducted guanine and the adjacent base pair on the 5'-side in reference to the adducted guanine, while in the second it is bound externally in the major groove of DNA. Rotational flexibility appears feasible in the latter providing four, potential binding sites. Molecular modeling reveals that the binding sites around the reactive guanine in different sequences are not uniformly compatible for interaction with AFB1. As the sequence is changed, one particular external binding site would be expected to give a pattern of reactivities that is reasonably consistent with the observed sequence specificity of binding that AFB1 shows in its reaction with DNA (Benasutti, M., Ejadi, S., Whitlow, M. D. and Loechler, E. L. (1988) Biochemistry 27, 472-481). The AFB1 moiety is face-stacked in the major groove with its long axis approximately perpendicular to the helix axis. Favorable interactions are formed between exocyclic amino groups that project into the major groove on cytosines and adenines surrounding the reactive guanine, and oxygens in AFB1; unfavorable interactions involve van der Waals contacts between the methyl group on thymine and the AFB1 moiety. "Some of the sequence specificity of binding data can be rationalized more readily if it is assumed that 5'-GG-3' sequences adopt an A-DNA structure." Based upon molecular modeling/potential energy minimization calculation, it is difficult to predict how reactivity would change in different DNA sequences in the case of the intercalative binding mode; however, several arguments suggest that intercalation might not be favored. From these considerations a model of the structure for the transition state in reaction of AFB1 with DNA is proposed involving one particular external binding site.

A-DNA accommodates adducts derived from diol epoxides of polycyclic aromatic hydrocarbons bound in a "side-stacking" mode.

The minor groove of undistorted A-DNA provides a good binding site for planar, hydrophobic moieties such as unmetabolized polycyclic aromatic hydrocarbons (PAHs), and the base pairs at the ends of short oligodeoxynucleotide helices. It also accommodates the chief adduct derived from the metabolically activated form of the carcinogen benzo[a]pyrene. B-DNA lacks such a site. Computerized models have been generated for the major (N2-guanine-linked) adducts formed at this site by both + and - enantiomers of anti-benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide (anti-BPDE) with poly(dG).poly(dC) in the A-DNA conformation. The BPDE adducts lie in the shallow, relatively hydrophobic minor groove of the A-DNA after empirical potential energy minimization using the program AMBER. We term this binding mode "side-stacking." The side-stacked + anti-BPDE may constitute the chief carcinogenic lesion derived from benzo[a]pyrene.

Cholecystokinin octapeptide and lithium produce different effects on feeding and taste aversion learning.

The strengths of taste aversion induced by sulphated cholecystokinin 26-33 (CCK-8; 1,2,4 and 8 micrograms/kg IP) and lithium chloride (LiCl; 7.5, 15, 30 and 60 mg/kg IP) were determined in order to assess the relative aversiveness of the two compounds. All doses of LiCl induced strong aversion, but only the highest dose of CCK-8 induced aversion, which was mild. Effects of CCK-8 and LiCl on food intake were then compared in the hour (hr) following 8 hr of food deprivation; rats were on this food deprivation schedule for a relatively long time (78 days) throughout testing. All doses of CCK-8 reduced food intake significantly. Most doses of LiCl either did not affect or significantly increased food intake. Although 60 mg/kg LiCl did not affect food intake when administered 15 or 30 min before food presentation, it significantly increased food intake when administered 1, 2 or 3 hr before food presentation. Overeating of solid food may be an illness-induced behavior. Although a very high dose of LiCl (120 mg/kg) decreased food intake markedly, the rats were obviously distressed, not satiated. Failure of CCK-8 to affect feeding behavior like LiCl is indirect evidence that the reduction of food intake by CCK-8 is not merely the result of aversiveness, but is an extremely potent and specific behavioral effect.

Damage of an Oxinium femoral head and polyethylene liner following 'routine' total hip replacement.

We present a case of early retrieval of an Oxinium femoral head and corresponding polyethylene liner where there was significant surface damage to the head and polyethylene. The implants were retrieved at the time of revision surgery to correct leg-length discrepancy just 48 hours after the primary hip replacement. Appropriate analysis of the retrieved femoral head demonstrated loss of the Oxinium layer with exposure of the underlying substrate and transfer of titanium from the acetabular shell at the time of a reduction of the index total hip replacement. In addition, the level of damage to the polyethylene was extensive despite only 48 hours in situ. The purpose of this report is to highlight the care that is required at the time of reduction, especially with these hard femoral counter-faces such as Oxinium. To our knowledge, the damage occurring at the time of reduction has not been previously reported following the retrieval of an otherwise well-functioning hip replacement.