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Biomedical subjects

J G Howe

Publications and source records attributed to J G Howe.

At least 37 records · Page 2Linked to original sources
PubMed1991

Longitudinal crack propagation in bone around femoral prosthesis.

Intraoperative femoral fracture is a well-recognized technical complication of cementless total hip arthroplasty. This study was designed to establish an in vitro model for initiation and propagation of fractures of the proximal femur in cementless THA and to assess the effect of fracture fixation in the form of cerclage wiring and drilling a hole in the distal extent of the fracture line. Fourteen human anatomic femur specimens were studied. Longitudinal cracks were made and propagation was performed on a materials testing system machine. A drill hole at the tip of a longitudinal crack does not prevent crack propagation. However, cerclage wiring has a statistically significant effect (p less than 0.025) on the ability of the fractured femur to withstand increased load.

Aged↗
PubMed1990

Arthroscopic strain gauge measurement of the normal anterior cruciate ligament.

This article describes a new arthroscopic technique to study the anterior cruciate ligament (ACL) in vivo. A Hall effect strain transducer (HEST) is inserted arthroscopically into the anterior medial band (AMB) of the ACL. The strain is calculated from HEST displacement data. This method determines a reference length of the AMB when it becomes taut and load bearing. Data from HEST implantation in five patients with normal ACLs are reported. The HEST was implanted in the AMB with patients under local anesthesia. Strain was calculated during anterior-posterior shear testing and isometric quadriceps contractions at 30 and 90 degrees of knee flexion. The results demonstrate that this technique is safe and reliable. Lachman testing (anterior shear testing at 30 degrees) caused significantly higher strain in comparison to the drawer tests (anterior shear testing at 90 degrees). A significant increase in strain occurred during isometric quadriceps contraction when the knee was flexed at 30 degrees. No significant change in strain was measured, however, during isometric quadriceps contraction at 90 degrees of flexion. These results confirm previous studies showing that the Lachman test is a more sensitive clinical method for evaluating the AMB. They suggest that isometric quadriceps activity at 90 degrees of knee flexion can be prescribed for rehabilitation without risk of increased strain of the AMB.

Adult↗
PubMed1989

Epstein-Barr virus small RNA (EBER) genes: unique transcription units that combine RNA polymerase II and III promoter elements.

The Epstein-Barr virus-encoded small RNA (EBER) genes appear to comprise an interesting subset of class III genes different from any previously identified, including U6 and 7SK. EBER genes have functional A and B box intragenic control regions. In addition, they contain three upstream elements that together stimulate in vivo expression 50-fold and resemble sites associated with typical class II promoters. DNAase I footprinting analyses using purified proteins or oligonucleotide competition demonstrate that nucleotides -40 to -55 bind activating transcription factor (ATF) or a related protein, while nucleotides -56 to -77 bind Sp1 protein or a related protein. The element between positions -23 and -28 resembles a TATA box. EBERs are unusual RNA polymerase III transcripts shown to be controlled by ATF- and Sp1-like promoter elements, suggesting mechanisms for their high level expression in EBV-transformed lymphocytes.

Base Sequence↗
PubMed1989

Influence of Burkitt's lymphoma and primary B cells on latent gene expression by the nonimmortalizing P3J-HR-1 strain of Epstein-Barr virus.

The Epstein-Barr virus (EBV) genes expressed in B lymphocytes immortalized in vitro or in Burkitt's lymphoma (BL) cells infected in vivo have been characterized previously; however, the viral products which are essential for immortalization or for establishment of EBV latency are still not known. To approach this question, we compared the kinetics of expression of EBV nuclear antigens and the two EBV-encoded small RNAs, EBER1 and EBER2, after infection of primary B cells or EBV genome-negative BL cells with either an immortalizing EBV strain (B95-8) or the nonimmortalizing deletion mutant (HR-1). Following infection of primary cells with B95-8 virus, EBV nuclear antigen (EBNA)-2 was expressed first, followed by EBNA-1, -3, and -4 (also called leader protein [LP]) and the two small RNAs. Infection of EBV genome-negative BL cells with the same strain of virus resulted in a similar pattern of gene expression, except that the EBNAs appeared together and more rapidly. EBERs were not apparent in one BL cell line converted by B95-8. The only products detected after infection of primary B lymphocytes with the HR-1 deletion mutant were the EBNA-4 (LP) family and trace amounts of EBER1. Although HR-1 could express neither EBNA-1, EBNA-3, nor EBER2 in primary cells, all these products were expressed rapidly after HR-1 infection of EBV genome-negative BL cell lines. The results indicate that the mutation in HR-1 virus affects immortalization not only through failure to express EBNA-2, a gene which is deleted, but also indirectly by curtailing expression of several other EBV genes whose coding regions are intact in the HR-1 virus and normally expressed during latency. The pattern of latent EBV gene expression after HR-1 infection is dependent on the host cell, perhaps through products specific for the cell cycle or the state of B-cell differentiation.

Antigens, Viral↗
PubMed1988

Total knee arthroplasty kinematics. An in vivo evaluation of four different designs.

Thirty-four patients who had 42 total knee arthroplasties during the past 5 years were examined. Four types of total knee arthroplasties (Tricon-M, PCA, Variable Axis, and Anametric) were evaluated, using a computerized knee evaluation system. The patients and 10 controls with normal knees were tested for anteroposterior stability with the Lachman test, medial/lateral stability at 20 degrees, varus/valgus stability at 20 degrees, internal/external rotation at 80 degrees and 20 degrees of flexion, and internal/lateral rotation (screw home) over the active range of motion. At 30 degrees of flexion, the Variable Axis prosthesis was 54% more constrained than the normal knee to anterior/posterior shear. The Anametric and the Variable Axis were more lax under varus/valgus stress than the normal knee by 85% and 71%, respectively. There were no statistical differences for any of the other tests.

Aged↗
PubMed1988

Structural analyses of EBER1 and EBER2 ribonucleoprotein particles present in Epstein-Barr virus-infected cells.

The ribonucleoprotein (RNP) particles containing the Epstein-Barr virus-associated small RNAs EBER1 and EBER2 were analyzed to determine their RNA secondary structures and sites of RNA-protein interaction. The secondary structures were probed with nucleases and by chemical modification with single-strand-specific reagents, and the sites of modification or cleavage were mapped by primer extension. These data were used to develop secondary structures for the two RNAs, and likely sites of close RNA-protein contact were identified by comparing modification patterns for naked RNA and RNA in RNP particles. In addition, sites of interaction between each Epstein-Barr virus-encoded RNA (EBER) and the La antigen were identified by analyzing RNA fragments resistant to digestion by RNase A or T1 after immunoprecipitation by an anti-La serum sample from a lupus patient. Our results confirm earlier findings that the La protein binds to the 3' terminus of each molecule. Possible functions for the EBER RNPs are discussed.

Autoantigens↗
PubMed1988

Isolation and characterization of the genes for two small RNAs of herpesvirus papio and their comparison with Epstein-Barr virus-encoded EBER RNAs.

Genes for the Epstein-Barr virus-encoded RNAs (EBERs), two low-molecular-weight RNAs encoded by the human gammaherpesvirus Epstein-Barr virus (EBV), hybridize to two small RNAs in a baboon cell line that contains a similar virus, herpesvirus papio (HVP). The genes for the HVP RNAs (HVP-1 and HVP-2) are located together in the small unique region at the left end of the viral genome and are transcribed by RNA polymerase III in a rightward direction, similar to the EBERs. There is significant similarity between EBER1 and HVP-1 RNA, except for an insert of 22 nucleotides which increases the length of HVP-1 RNA to 190 nucleotides. There is less similarity between the sequences of EBER2 and HVP-2 RNA, but both have a length of about 170 nucleotides. The predicted secondary structure of each HVP RNA is remarkably similar to that of the respective EBER, implying that the secondary structures are important for function. Upstream from the initiation sites of all four RNA genes are several highly conserved sequences which may function in the regulation of transcription. The HVP RNAs, together with the EBERs, are highly abundant in transformed cells and are efficiently bound by the cellular La protein.

Autoantigens↗
PubMed1986

Localization of Epstein-Barr virus-encoded small RNAs by in situ hybridization.

Human B lymphocytes latently infected with Epstein-Barr virus (EBV) synthesize two low molecular weight RNAs designated EBER 1 and 2. Using an in situ hybridization technique we have localized EBER 1 and 2 within the nucleus of single EBV-harboring B lymphocytes from established and recently transformed cell lines. As controls, the locations of the small nuclear RNA, U1, and the small cytoplasmic RNA, 7SL, were examined in HeLa and EBV-harboring cells. Because of possible functional similarities between EBERs and the adenovirus-associated (VA) RNAs, VAI was also localized; it appeared to be in the nucleus and cytoplasm, implying that VAI may have a different role than that of the nuclear-localized EBERs.

Cell Nucleus↗
PubMed1986

Preparation and release characteristics of tobramycin-impregnated polymethylmethacrylate beads.

Preparation of tobramycin-impregnated polymethylmethacrylate (PMMA) bone cement beads and release of tobramycin from the beads in vitro and after implantation in a patient are described. Tobramycin sulfate powder 1.2 g was mixed with Palacos PMMA bone cement 40 g in a custom-made mold to produce 25 beads containing 3.26 mg tobramycin (as the sulfate salt) per bead. Chains of the beads, strung on stainless-steel suture, were sterilized with ethylene oxide. Three single beads were each placed in multiple-electrolyte solution (pH 7.4); the solution was removed and replaced with fresh solution every 24 hours for 28 days. The tobramycin content of each day's solution was determined by fluorescence polarization immunoassay. After day 28, solution was removed weekly for assay until day 84. Tobramycin concentrations were measured in drainage from the surgical wound after six chains of tobramycin-PMMA bone cement beads were implanted in the right acetabulum and femur of a patient whose hip prosthesis had been removed because of infection. Tobramycin concentrations in the dissolution medium averaged 34.3 micrograms/mL initially, and 7.5 micrograms/mL on day 2, gradually decreasing to 0.6 microgram/mL on day 28. Release of tobramycin followed a predictable pattern, and variation among samples was small. Over 12 weeks, less than 20% of the theoretically available tobramycin from a single bead was released. Tobramycin concentration in wound drainage was 90.0 micrograms/mL during the first 24 hours after surgery, while serum tobramycin concentrations were less than 0.5 microgram/mL. Extemporaneously prepared beads of bone cement are effective for delivering high concentrations of tobramycin to an infection site.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone Cements↗
PubMed1984

The rate of evolutionary divergence of initiation factors IF2 and IF3 in various bacterial species determined quantitatively by immunoblotting.

Antibodies to Escherichia coli translational initiation factors IF2 and IF3 were used for an immunological comparison of unpurified proteins from the following genera: Salmonella, Serratia, Proteus, Aeromonas, Pseudomonas, Streptococcus, Sarcina and Bacillus. Immunological relatedness was compared by Ouchterlony double diffusion experiments and immunoblotting analysis. Immunoblotting is a quantitative technique for measuring levels of specific proteins in crude cell lysates. We have used this technique to measure immunological distance with the assumption that the levels of the various translational components are essentially the same in the different bacterial cells examined. Both immunodiffusion and immunoblotting analysis showed a similar evolutionary relationship between the various species for the two initiation factors examined: (Escherichia = Salmonella greater than Serratia greater than Proteus greater than Aeromonas greater than Pseudomonas). Little or no crossreactivity was found using either analysis with genera: Streptococcus, Sarcina and Bacillus. Using the immunoblot distance, the two initiation factors were shown to diverge at similar rates. One advantage the immunoblotting analysis has over other immunological techniques is that the antigens can be analyzed structurally. We found, for example, that the two forms of IF2 were present in all bacterial species which cross-reacted with anti-IF2, suggesting that both forms are functionally important. Because of its sensitivity, the immunoblot analysis may be more useful than other immunological techniques in studying species that are more distantly related.

Antibodies, Bacterial↗
PubMed1984

Translational initiation factor and ribosome association with the cytoskeletal framework fraction from HeLa cells.

The association of mRNA and ribosomes with the cytoskeleton of eucaryotic cells may be important for protein synthesis and its regulation. HeLa cells were gently lysed with detergent, and soluble and cytoskeletal framework subfractions were prepared by centrifugation. We analyzed these fractions for ribosomes and confirmed earlier findings that polysomes are preferentially associated with the cytoskeletal fraction. The levels of initiation factors eIF-2, eIF-3, eIF-4A, and eIF-4B were quantitated by immunoblotting; all are enriched in the cytoskeletal fraction relative to the soluble fraction. Heat shock, fluoride, pactamycin , and cytochalasin caused the release of both ribosomes and initiation factors into the soluble fraction. However, treatment of the cytoskeletal fraction with EDTA or low levels of ribonuclease resulted in polysome degradation but no release. Therefore initiation factor association with the cytoskeletal framework correlates with the presence of ribosomes, whereas ribosome association does not require intact mRNA.

Electrophoresis, Polyacrylamide Gel↗
PubMed1983

Initiation factor and ribosome levels are coordinately controlled in Escherichia coli growing at different rates.

The levels of initiation factors and other translational components were compared in crude lysates of Escherichia coli grown at different rates. Cells were grown in media containing [35S]sulfate and different carbon sources, and harvested during mid-exponential phase after about 10 generations of balanced growth. Initiation factors (IF), elongation factors (EF), and a number of ribosomal proteins were identified unambiguously in gel patterns following two-dimensional polyacrylamide gel electrophoresis. The molar concentration of each protein was calculated from measurements of the radioactivity in excised gel spots and knowledge of the sulfur content of each protein. We found that the ribosomal proteins and elongation factors were present in equimolar amounts except for L7/L12 and EF-Tu which were 4-fold and 5-fold more abundant, respectively, and that the levels of each protein increased in proportion to growth rate. These results are similar to ones obtained previously by other methods, and serve to confirm the validity of our method. We found that the levels of IF2a and IF3 also were approximately proportional to growth rate. We also measured the levels of all three initiation factors using a radioimmune assay, showed that the factors are present in equimolar amounts, and confirmed that their abundance increased in parallel with ribosomes. We conclude that initiation factor levels are coordinately regulated with one another and with ribosome and elongation factor levels.

Electrophoresis, Polyacrylamide Gel↗
PubMed1983

Thirst, resetting of the osmostat, and water intoxication following encephalitis.

A young man developed pathological thirst and hyperdipsia, hyperphagia, disordered temperature regulation, a lowered threshold for aggressive behavior, apathy, impaired memory, and seizures following encephalitis. He had marked hyponatremia. Bouts of water drinking produced water intoxication and precipitated status epilepticus. Studies of water handling with measurements of plasma osmolality and arginine vasopressin (AVP) revealed a very low thirst threshold (below 242 mOsm/kg) with resetting of the osmostat to a new level (255 mOsm/kg) but normal control of plasma osmolality at that level with adequate AVP release.

Adult↗
PubMed1983

Levels of ribosomal protein S1 and elongation factor G in the growth cycle of Escherichia coli.

The relative levels of ribosomes, ribosomal protein S1, and elongation factor G in the growth cycle of Escherichia coli were examined with two-dimensional polyacrylamide gel electrophoresis. Nonequilibrium pH gradient polyacrylamide gel electrophoresis was used in the first dimension, and polyacrylamide gradient-sodium dodecyl sulfate gel electrophoresis was used in the second dimension. The identities of protein spots containing S1 and elongation factor G were confirmed by radioiodination of the proteins and peptide mapping of the radiolabeled peptides. The levels of ribosomes and ribosomal protein S1 were coordinately reduced during transition from exponential phase to stationary phase. There was no accumulation of S1 in the stationary phase. In marked contrast, the level of elongation factor G showed no significant change from exponential phase to stationary phase. The relative level of elongation factor G compared with ribosomes or S1 increased by about 2.5-fold during transition from exponential phase to stationary phase. The results show that there are differences between the regulation of the levels of elongation factor G and of ribosomal proteins, including S1, apparent during the transition from exponential to stationary phase.

Bacterial Proteins↗