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K Weaver

Publications and source records attributed to K Weaver.

At least 19 recordsLinked to original sources
PubMed2001

Structural mechanisms of drug resistance for mutations at codons 181 and 188 in HIV-1 reverse transcriptase and the improved resilience of second generation non-nucleoside inhibitors.

Mutations at either Tyr181 or Tyr188 within HIV-1 reverse transcriptase (RT) give high level resistance to many first generation non-nucleoside inhibitors (NNRTIs) such as the anti-AIDS drug nevirapine. By comparison second generation inhibitors, for instance the drug efavirenz, show much greater resilience to these mutations. In order to understand the structural basis for these differences we have determined a series of seven crystal structures of mutant RTs in complexes with first and second generation NNRTIs as well as one example of an unliganded mutant RT. These are Tyr181Cys RT (TNK-651) to 2.4 A, Tyr181Cys RT (efavirenz) to 2.6 A, Tyr181Cys RT (nevirapine) to 3.0 A, Tyr181Cys RT (PETT-2) to 3.0 A, Tyr188Cys RT (nevirapine) to 2.6 A, Tyr188Cys RT (UC-781) to 2.6 A and Tyr188Cys RT (unliganded) to 2.8 A resolution. In the two previously published structures of HIV-1 reverse transcriptase with mutations at 181 or 188 no side-chain electron density was observed within the p66 subunit (which contains the inhibitor binding pocket) for the mutated residues. In contrast the mutated side-chains can be seen in the NNRTI pocket for all seven structures reported here, eliminating the possibility that disordering contributes to the mechanism of resistance. In the case of the second generation compounds efavirenz with Tyr181Cys RT and UC-781 with Tyr188Cys RT there are only small rearrangements of either inhibitor within the binding site compared to wild-type RT and also for the first generation compounds TNK-651, PETT-2 and nevirapine with Tyr181Cys RT. For nevirapine with the Tyr188Cys RT there is however a more substantial movement of the drug molecule. We conclude that protein conformational changes and rearrangements of drug molecules within the mutated sites are not general features of these particular inhibitor/mutant combinations. The main contribution to drug resistance for Tyr181Cys and Tyr188Cys RT mutations is the loss of aromatic ring stacking interactions for first generation compounds, providing a simple explanation for the resilience of second generation NNRTIs, as such interactions make much less significant contribution to their binding.

Binding Sites↗
PubMed2001

2-Amino-6-arylsulfonylbenzonitriles as non-nucleoside reverse transcriptase inhibitors of HIV-1.

A series of 2-amino-5-arylthiobenzonitriles (1) was found to be active against HIV-1. Structural modifications led to the sulfoxides (2) and sulfones (3). The sulfoxides generally showed antiviral activity against HIV-1 similar to that of 1. The sulfones, however, were the most potent series of analogues, a number having activity against HIV-1 in the nanomolar range. Structural-activity relationship (SAR) studies suggested that a meta substituent, particularly a meta methyl substituent, invariably increased antiviral activities. However, optimal antiviral activities were manifested by compounds where both meta groups in the arylsulfonyl moiety were substituted and one of the substituents was a methyl group. Such a disubstitution led to compounds 3v, 3w, 3x, and 3y having IC50 values against HIV-1 in the low nanomolar range. When gauged for their broad-spectrum antiviral activity against key non-nucleoside reverse transcriptase inhibitor (NNRTI) related mutants, all the di-meta-substituted sulfones 3u-z and the 2-naphthyl analogue 3ee generally showed single-digit nanomolar activity against the V106A and P236L strains and submicromolar to low nanomolar activity against strains E138K, V108I, and Y188C. However, they showed a lack of activity against the K103N and Y181C mutant viruses. The elucidation of the X-ray crystal structure of the complex of 3v (739W94) in HIV-1 reverse transcriptase showed an overlap in the binding domain when compared with the complex of nevirapine in HIV-1 reverse transcriptase. The X-ray structure allowed for the rationalization of SAR data and potencies of the compounds against the mutants.

Anti-HIV Agents↗
PubMed2001

Idiopathic shoulder girdle neuropathy.

Idiopathic shoulder girdle neuropathy is the syndrome of acute upper extremity pain located primarily in the shoulder, which is subsequently replaced by painless neurologic weakness and sensation loss. The disease is self-limited and generally carries with it a favorable prognosis. The clinical presentation, electrodiagnostic picture and natural history are discussed.

Electromyography↗
PubMed2000

Monoclonal antibody B9-2 recognizes an 8 amino acid sequence that spans an autocatalytic cleavage site between the two subunits of human procaspase 8.

Caspase 8 is synthesized in a zymogen form and must be proteolytically cleaved to be activated. The catalytically active enzyme is composed of two of the four cleavage products. We have determined that the monoclonal antibody B9-2 recognizes the octomer EMDLSSPQ. This sequence is shared by two of the cleavage products: a decamer linker region released after autocatalysis and the smaller subunit of the active enzyme.

Amino Acid Sequence↗
PubMed1999

Five year results of LINAC radiosurgery for arteriovenous malformations: outcome for large AVMS.

PURPOSE: For radiosurgery of large arteriovenous malformations (AVMs), the optimal relationship of dose and volume to obliteration, complications, and hemorrhage is not well defined. Multivariate analysis was performed to assess the relationship of multiple AVM and treatment factors to the outcome of AVMs significantly larger than previously reported in the literature. METHODS AND MATERIALS: 73 patients with intracranial AVMs underwent LINAC radiosurgery. Over 50% of the AVMs were larger than 3 cm in diameter and the median and mean treatment volumes were 8.4 cc and 15.3 cc, respectively (range 0.4-143.4 cc). Minimum AVM treatment doses varied between 1000-2200 cGy (median: 1600 cGy). RESULTS: The obliteration rates for treatment volumes < 4 cc, 4-13.9 cc, and > or = 14 cc were 67%, 58%, and 23%, respectively. AVM obliteration was significantly associated with higher minimum treatment dose and negatively associated with a history of prior embolization with particulate materials. No AVM receiving < 1400 cGy was obliterated. The incidence of post-radiosurgical imaging abnormalities and clinical complications rose with increasing treatment volume. For treatment volumes > 14 cc receiving > or = 1600 cGy, the incidence of post-radiosurgical MRI T2 abnormalities was 72% and the incidence of radiation necrosis requiring resection was 22%. The rate of post-radiosurgical hemorrhage was 2.7% per person-year for AVMs with treatment volumes < 14 cc and 7.5% per person-year for AVMs > or = 14 cc. CONCLUSION: As AVM size increases, the dose-volume range for the optimal balance between successful obliteration and the risk of complications and post-radiosurgical hemorrhage narrows.

Adolescent↗
PubMed1999

Interaction between broad-spectrum antibiotics and the combined oral contraceptive pill. A literature review.

There is considerable variation in opinion about the importance of drug interactions between the combined oral contraceptive pill (COCP) and broad-spectrum antibiotics. Clinical practice varies widely, especially between doctors in Europe and those in the US. Rifampicin and griseofulvin induce hepatic enzymes and do appear to have a genuine interaction with the COCP, leading to reduced efficacy. The situation with the broad-spectrum antibiotics is less clear. There are relatively few prospective studies of the pharmacokinetics of concurrent COCP and antibiotic use and few, if any, demonstrate a convincing basis for any reduced contraceptive efficacy. There is evidence, however, that variable contraceptive steroid handling could make some women, at some times, more susceptible to COCP failure. Given the serious consequences of unwanted pregnancy, the cautious approach of using additional or alternative contraception during short courses of broad-spectrum antibiotics and the initial weeks of long-term antibiotic administration may be justified to safeguard the few unidentifiable women who may be at risk. Conflicting opinion and advice is potentially confusing to both professionals and patients, and instructions for additional precautions during and after concurrent COCP and antibiotic use are complicated. Many women are ignorant of, or confused about, the circumstances that can cause OC to fail. Health professionals who prescribe the COCP must continue to strive to educate women about the mode of action and about the times when there is the greatest danger of failure. Professionals who feel that concurrent antibiotic use represents a real threat to contraceptive efficacy of the COCP should be prepared to present the advice for additional contraceptive precautions in a simple and consistent way, backed up with written information and reinforced at regular intervals.

Anti-Bacterial Agents↗
PubMed1998

Purification and characterization of a membrane bound neutral pH optimum magnesium-dependent and phosphatidylserine-stimulated sphingomyelinase from rat brain.

Sphingomyelin hydrolysis and ceramide generation catalyzed by sphingomyelinases (SMase) are key components of the signaling pathways in cytokine- and stress-induced cellular responses. In this study, we report the partial purification and characterization of the membrane bound, neutral pH optimal, and magnesium-dependent SMase (N-SMase) from rat brain. Proteins from Triton X-100 extract of brain membrane were purified sequentially with DEAE-Sephacel, heparin-Sepharose, ceramic hydroxyapatite, Mono Q, phenyl-Superose, and Superose 12 column chromatography. After eight purification steps, the specific activity of the enzyme increased by 3030-fold over the brain homogenate. The enzyme hydrolyzed sphingomyelin but not phosphatidylcholine and its activity was dependent upon magnesium with an optimal pH of 7.5 and a native pI of 5.2. Delipidation of the enzyme through chromatographic purification or by extraction with 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid followed by gel filtration revealed that the enzyme became increasingly dependent on phosphatidylserine (PS). Up to 20-fold stimulation was observed with PS whereas other lipids examined were either ineffective or only mildly stimulatory. The Km of the enzyme for substrate sphingomyelin (3.4 mol %) was not affected by PS. The highly purified enzyme was inhibited by glutathione with a >95% inhibition observed with 3 mM glutathione and with a Hill number calculated at approximately 8. The significance of these results to the regulation of N-SMase is discussed.

Animals↗
PubMed1998

MALDI-TOF analysis of polymerase chain reaction products from methanotrophic bacteria.

Polymerase chain reaction (PCR) assays were designed to amplify 56- and 99-base regions of the pmoA gene from Methylosinus trichosporium OB3b and Methylomicrobium albus BG8, two species of methanotrophic bacteria that are of interest for monitoring bioremediation activity. The PCR product sizes are in a mass range that is accessible to analysis by MALDI-TOF mass spectrometry. A rapid purification procedure using commercially available reversed-phase cartridges was applied prior to MALDI-TOF analysis. A small aliquot (1.5%, 1.5 microL) from a single 100-microL PCR reaction was sufficient for reliable detection. No cross-amplification products were observed when primers designed for one bacterial species were used with genomic DNA of the other species. The methodology described here has potential to allow less expensive and faster characterization of the ability of microbial populations to destroy pollutants in groundwater and soil at contaminated industrial sites.

Biodegradation, Environmental↗
PubMed1998

Anisotropy functions for 125I and 103Pd sources.

The anisotropy function was defined by AAPM Task Group 43 in a recent report, and reference data were provided. However, some of the data appeared to have large experimental errors. In this work, anisotropy functions are presented for three low-energy photon-emitting sources commonly used for brachytherapy: 125I source models 6702 and 6711, and the model 200 103Pd source. The data were generated via a two-step process: the sources' intrinsic radiation emission pattern was determined from in-air measurements, and these data were used as input to Monte Carlo calculations of the fluence distribution in water. The new anisotropy function values for iodine compare well with earlier data from diode measurements, and seem more physically realistic than some data provided by TG43. Previous palladium data measured with TLDs are more variable, but on the average are similar to the data presented here. The new data have estimated uncertainties of 3%-6%; this level of accuracy should be completely adequate for clinical calculations.

Anisotropy↗
PubMed1996

Nursing the peace.

Explore the source record for details and available documents.

Bosnia and Herzegovina↗
PubMed1996

Mechanical work adaptations of above-knee amputee ambulation.

OBJECTIVE: To quantify the muscular adaptations of above-knee amputee patients' ambulation using an experimental and modeling approach. DESIGN: Nonrandomized controlled study. SETTING: A referral center for treatment of veterans with amputation. SUBJECTS: Eight normal ambulators and 8 nondysvascular above-knee amputee subjects wearing the same lightweight prostheses were studied with a gait analysis system, walking at self-selected speeds. MAIN OUTCOME MEASURES: Using an inverse dynamics linked segment model, the mechanical torque, power output, and work done were calculated at the hip, knee, and ankle joints. RESULTS: The mean concentric ankle plantarflexor work done was much greater for the normal subjects compared to the prosthetic limb in pushoff (25.2 +/- 3.7 J vs 4.9 +/- 2.1 J), but greatest for the intact limb of the amputee subjects (34.2 +/- 6.6 J). Also, the concentric hip extensor work done in early stance was greater for the intact limb of the amputee subjects than for normal subjects (9.9 +/- 5.5 J vs 3.6 +/- 2.6 J), presumably compensating for the coincident decreased pushoff of the prosthetic limb. Other compensatory mechanisms are also discussed. CONCLUSIONS: Increased joint torques and power outputs of the amputee subjects' intact limb compared to normal ambulation may be viewed as providing additional gait progression and upright stance during parts of the gait cycle when the amputated limb lacks needed active muscle support.

Adaptation, Physiological↗
PubMed1996

Safety and efficacy of ethylene oxide sterilized polyethylene in total knee arthroplasty.

Eleven unassembled metal backed patellar interfaces were inoculated with 0.1 ml of Sportol (Bacillus subtilis variety niger spore) and then assembled. Ten of the 11 implants were exposed to 1/2 of a standard ethylene oxide sterilization cycle. The remaining implant was left unsterilized as a control. All the implants were separately incubated in soybean casein digest broth for 7 days at 30 degrees to 35 degrees C and tested for positive growth of Bacillus subtilis. To measure residual ethylene oxide content, 4 ultrahigh molecular weight polyethylene tibial inserts were exposed to a full ethylene oxide sterilization cycle. The implants were removed from the sterilization chamber and tested for residual ethylene oxide at 3, 5, 8, and 9 days after sterilization using an exhaustive extraction headspace technique. Residual ethylene oxide was measured in 3 additional implants 26 days after sterilization. No growth of Bacillus subtilis occurred on any of the 10 inoculated and ethylene oxide sterilized metal backed patellar components, whereas positive growth occurred on the inoculated, unsterilized control implant. Residual ethylene oxide measured in the tibial inserts at 3, 5, 8, and 9 days after sterilization was 23, 15, 12, and 9 ppm, respectively. Twenty-six days after sterilization, residual ethylene oxide was below the minimum detectable level of the measurement technique (5 ppm).

Bacillus subtilis↗
PubMed1996

A source model for efficient brachytherapy computations with Monte Carlo.

Monte Carlo techniques have the potential for producing accurate brachytherapy dose distributions in heterogeneous finite geometries. However, for routine clinical use, computational speed must be adequate. A fast, all-particle, CT-based Monte Carlo code called PEREGRINE is being developed at Lawrence Livermore National Laboratory for radiation treatment planning. As one feature, the code will produce accurate dose distributions from brachytherapy sources in heterogeneous geometries. For efficiency, brachytherapy sources in this model are treated as points or line segments. Radiation is emitted with the proper energy spectrum and (perhaps anisotropic) angular distribution. In particular, for anisotropic emission the polar angle is determined by a random-number driven empirical function constructed from a source's measured or precomputed fluence emission pattern. Source model parameters are presented for iodine and iridium sources. While designed for the PEREGRINE program, this source model can be used in any Monte Carlo code.

Biophysical Phenomena↗
PubMed1996

Fatigue strength of polyethylene after sterilization by gamma irradiation or ethylene oxide.

The oxidation level of ultrahigh molecular weight polyethylene specimens sterilized by gamma irradiation in either air or Ar gas was compared with that of unsterilized and ethylene oxide sterilized ultrahigh molecular weight polyethylene. The fatigue strength of ultrahigh molecular weight polyethylene specimens sterilized by gamma irradiation in air was compared with that of unsterilized and ethylene oxide sterilized ultrahigh molecular weight polyethylene. At the specimen surface, oxidation was highest for ultrahigh molecular weight polyethylene gamma irradiated in air, lower for ultrahigh molecular weight polyethylene gamma irradiated in Ar gas, and absent in unsterilized and ethylene oxide sterilized ultrahigh molecular weight polyethylene. At a depth of 3.5 mm below the specimen surface, oxidation levels were equivalent for ultrahigh molecular weight polyethylene gamma irradiated in either air or Ar gas whereas unsterilized and ethylene oxide sterilized specimens were again unoxidized. Thus, even in an inert atmosphere, oxidative degradation of gamma irradiated ultrahigh molecular weight polyethylene occurs. The 10 million cycle fatigue strength was similar for unsterilized and ethylene oxide sterilized ultrahigh molecular weight polyethylene whereas the fatigue strength of gamma irradiated in air ultrahigh molecular weight polyethylene was lower. Results of this study show that ethylene oxide gas does not degrade ultrahigh molecular weight polyethylene whereas gamma radiation in air causes changes in the polymer that adversely affect its mechanical properties. Ethylene oxide gas is a viable alternative to gamma radiation in air that avoids oxidation and fatigue strength degradation known to accompany irradiation of ultrahigh molecular weight polyethylene polymer bearing surfaces in total joint implants.

Biophysical Phenomena↗
PubMed1995

Quantification of inhibin pro-alpha C-containing forms in human serum by a new ultrasensitive two-site enzyme-linked immunosorbent assay.

Precursor forms of the alpha-subunit of inhibin are abundant in human follicular fluid and possibly plasma, although their function is uncertain. We now describe the development of a new enzyme-linked immunosorbent assay to measure inhibin forms containing both the pro and alpha C regions of the alpha-subunit. The assay has a detection limit for purified human pro-alpha C of 0.5 pg/mL and less than 0.02% cross-reaction with recombinant forms of inhibin, activin, and follistatin. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting of follicular fluid extracts demonstrated that the assay is likely to detect pro-containing precursor forms of both the free alpha-subunit and intact dimeric inhibin. The serum concentration was measured in normal men (446 +/- 28 pg/mL), postmenopausal women (45.8 +/- 3.8 pg/mL), and women treated with FSH before in vitro fertilization (1827 pg/mL). Pooled human follicular fluid contained 488 ng/mL. The mean serum concentration in the female menstrual cycle rose from 150.6 +/- 26.1 pg/mL in the early follicular phase to 692.2 +/- 113 pg/mL in the midluteal phase. This assay offers a useful tool for investigation of the role of inhibin-related proteins in human reproduction. There may be particular clinical value under circumstances in which other assays for inhibin forms have insufficient sensitivity.

Activins↗
PubMed1994

Enzymatic synthesis of folate and antifolate polyglutamates with Escherichia coli folylpolyglutamate synthetase.

Escherichia coli folylpolyglutamate synthetase was used to synthesize micromole quantities of polyglutamyl conjugates of folic acid, methotrexate, and other analogs of folic acid. The products of the enzymatic reactions were purified by semipreparative C18 HPLC. The position of each amide linkage (gamma or alpha carboxyl) in the polyglutamated products was determined by limited and exhaustive hydrolyses with hog kidney folylpolyglutamate hydrolase and with yeast carboxypeptidase Y. Under standard reaction conditions, the E. coli enzyme added up to five glutamyl residues to each monoglutamated substrate, primarily at the gamma carboxyl position. Thus, an enzyme which naturally adds only two glutamates to naturally occurring folates can be used synthetically to make higher polyglutamates of a wide range of synthetic substrates. The products of the reactions are valuable tools for the study of the metabolism of antifolate drugs as well as metabolic reactions involving folate cofactors.

Escherichia coli↗