Nucleic acid binding properties of the nucleic acid chaperone domain of hepatitis delta antigen.

The N terminal region of hepatitis delta antigen (HDAg), referred to here as NdAg, has a nucleic acid chaperone activity that modulates the ribozyme activity of hepatitis delta virus (HDV) RNA and stimulates hammerhead ribozyme catalysis. We characterized the nucleic acid binding properties of NdAg, identified the structural and sequence domains important for nucleic acid binding, and studied the correlation between the nucleic acid binding ability and the nucleic acid chaperone activity. NdAg does not recognize the catalytic core of HDV ribozyme specifically. Instead, NdAg interacts with a variety of nucleic acids and has higher affinities to longer nucleic acids. The studies with RNA homopolymers reveal that the binding site size of NdAg is around nine nucleotides long. The extreme N terminal portion of NdAg, the following coiled-coil domain and the basic amino acid clusters in these regions are important for nucleic acid binding. The nucleic acid-NdAg complex is stabilized largely by electrostatic interactions. The formation of RNA-protein complex appears to be a prerequisite for facilitating hammerhead ribozyme catalysis of NdAg and its derivatives. Mutations that reduce the RNA binding activity or high ionic strength that destabilizes the RNA-protein complex, reduce the nucleic acid chaperone activity of NdAg.

Disposition of inhaled 1,1,1,2-tetrafluoroethane (HFA134A) in healthy subjects and in patients with chronic airflow limitation. Measurement by 18F-labeling and whole-body gamma-counting.

HFA134a (1,1,1,2-tetrafluoroethane) is a nonozone-depleting candidate to replace the chlorofluorocarbons used as propellants in metered-dose inhalers (MDIs) for pharmaceuticals that are widely used in the treatment of respiratory tract disease. As a means for ensuring the safety of such a compound for human use, it is necessary to establish that there is no excessive or unexpected accumulation in the body and in selected regions. A sensitive whole-body gamma-counting technique has been used with 18F-labeled HFA134a to measure the whole-body and regional absorption, distribution, and retention of HFA134a after administration in humans by single-breath inhalation. In seven healthy subjects, labeled HFA134a was rapidly eliminated by ventilation during the first few minutes, with an average of 9.6% of the radioactivity retained in the body at 5 min. This radioactivity cleared with an apparent terminal half-life of 1.5-4.2 hr to leave, on average, < 1% of the administered dose (< 750 micrograms, approximately 0.2 microCi) retained in the body at 5.8 hr. Disposition of radioactivity was independent of the position of label. Thus, there was no evidence of any significant degradative metabolism. On average, only 0.0056% of the administered dose appeared in the urine within the first 2 hr. Later samples contained no significant radioactivity. Inhaled HFA134a first distributed to all regions of the body and then cleared without evident accumulation in any specific region.(ABSTRACT TRUNCATED AT 250 WORDS)

Retrospective analysis of calls to poison control centers resulting from exposure to the insect repellent N,N-diethyl-m-toluamide (DEET) from 1985-1989.

This study analyzed 9,086 human exposures involving N,N-diethyl-m-toluamide--containing insect repellents that were reported to Poison Control Centers from 1985-1989. Nearly two-thirds of those exposed had no adverse effects or only experienced minor symptoms that resolved rapidly. Symptoms were more likely to occur after ocular or inhalation exposures and least likely to occur if the product was ingested. The only reported death occurred in a patient who suicidally ingested 8 oz of an insect repellent containing N,N-diethyl-m-toluamide. Five patients may have experienced a serious or potentially life-threatening effect but the poison center record did not provide unequivocal substantiation of the effect or clearly establish N,N-diethyl-m-toluamide as the causative agent. From the analysis of those patients calling Poison Control Centers, it appears the risk of serious medical effects with the labeled use of N,N-diethyl-m-toluamide-containing insect repellents is low in comparison with its reported annual use by about 30% of Americans. For patients contacting Poison Control Centers, the occurrence of adverse effects appears to be related to the route of exposure rather than age or gender of the patient or the concentration of N,N-diethyl-m-toluamide in the product.

Potassium loss from skeletal muscle during exercise in man: a radioisotope study.

Muscle potassium (K+) content decreases during exercise. Previous studies, in humans, have used measurements of arteriovenous plasma potassium concentration differences (AV delta[K+]) and/or muscle biopsy to measure the loss of muscle K+ during exercise. In the current study a non-invasive method was developed to measure skeletal muscle K+ before and after exercise, using an isotope of K+, potassium-43 (43K+). Twelve subjects performed single-leg extension exercise for 2 h at 50% of their maximum predicted heart rate. The level of radioactivity from the quadriceps femoris was determined before exercise and during two periods post-exercise. After correction for counts arising outside the exercised muscle, we estimate a decrease in muscle K+ content of 3.2 +/- 1.55% (mean +/- S.E.M.) following exercise. The muscle K+ was not restored following 75 min of recovery. The decrease in muscle K+ following exercise in our study is considerably less than that suggested by previous studies using AV delta[K+] measurements but not so dissimilar from results obtained using muscle biopsy. We conclude that a small but significant loss of K+ occurs following prolonged dynamic exercise, and that complete recovery of muscle K+ is slow.

A method of studying pharmacokinetics in man at picomolar drug concentrations.

1. We describe a new method that enables the tissue kinetics of picomolar concentrations of drugs to be measured in man. The method is based on the administration of a drug, labelled with a short-lived positron-emitting radioisotope, such as carbon-11 (t1/2 = 20.4 min, beta + = 99.8%) or fluorine-18 (t1/2 = 109.8 min, beta + = 96.9%), which is then detected in vivo by an array of 10 large uncollimated sodium iodide scintillation detectors, arranged as five opposing pairs, with each pair collecting data over one major organ or region of the body. 2. To illustrate the scope of the new method we report the results of administering [O-methyl-11C]-diprenorphine, an established radioligand for central opiate (mu, kappa, and delta) receptors and L-6-[18F]-fluoro-DOPA, a marker for dopaminergic neurons. 3. Only 2-10 muCi (74-370 kBq) of radioactivity are used and, as a consequence of the high specific activities with which carbon-11 and fluorine-18 labelled compounds can be prepared, the method requires less than a nanomole of drug to be administered. In many cases, this amount of drug might be considered low enough to avoid any adverse biological effect. Furthermore repeat studies are possible in many without delivering unacceptable radiation burdens. 4. The high sensitivity realised for both radioactivity and mass suggests a mean for determining the human biodistribution of a new drug at a very early stage in its development. This has potential benefit to drug discovery programmes and to ensuing drug therapies.

New neutron sources for radiotherapy.

All existing neutron sources suffer from disadvantages which would not be tolerated in modern megavoltage X-ray equipment. Experimental work with 30-60 MeV protons on beryllium and other elements has shown how these difficulties can to a large extent be overcome. Angular distributions and kerma rates as a function of proton energy are presented for various targets. Thin targets are found to be a better method than filtration for improving the penetration of the beam. A 237Np fission counter and a GM counter have been used to decompose stray radiation into its neutron and gamma-ray components. A model of a treatment head was found to attenuate the neutron component to less than 1% of its value in the useful beam.

Analysis of information provided by clinical pharmacists.

Data were collected to characterize the interactions between clinical pharmacists and other health professionals in a university hospital with decentralized pharmaceutical services. A self-report data collection form was developed. Six faculty pharmacists participated in the study. Each pharmacist collected data by recording all clinical interactions that occurred in his normal activities for a one-month period. the pharmacists' practice sites were inpatient internal medicine, inpatient pediatrics (two pharmacists), family practice clinic, pediatric clinic, and inpatient physical medicine and rehabilitation. A computer program was written to provide correlation data among the locations, contents, and participants of the interactions. Data were collected on the time required for a literature search and on the outcomes of the interactions. Four hundred ninety-nine interactions were documented. Work rounds were the most common location for these interactions, and the housestaff physicians were the most frequent participants. Patients' dosage schedule was the most common topic discussed (17%). Pharmacokinetics accounted for only 6% of the communications; drug interactions, only 3%. Ninety-six percent of the pharmacists' recommendations were adopted within 24 hours. More than half of the interactions (56%) required no literature search by the pharmacists and nearly half (249) required less than one minute of pharmacist time.

Neutron beams from protons on beryllium.

Measurements of dose rate and penetration in water have been made for neutron beams produced by 30--75 MeV protons on beryllium. The effects of Polythene filters added on the target side of the collimator have also been studied. A neutron beam comparable with a photon beam from a 4--8 MeV linear accelerator can be produced with p/Be neutrons plus 5 cm Polythene filtrations, with protons in the range 50--75 MeV. This is a more economical method than use of the d/Be reaction.

Lidocaine anesthesia: comparison of iontophoresis, injection, and swabbing.

The duration and depth of anesthesia produced by lidocaine with three methods of administration were studied. To test duration of anesthesia, either lidocaine or placebo was administered by iontophoresis, subcutaneous infiltration, or swabbing to each of three sites 3 cm apart on the flexor surface of each forearm of 27 subjects. To test for feeling, the tip of a 21-gauge hypodermic needle was pressed on each application site every five minutes until feeling returned. The depth of anesthesia achieved with iontophoresis or infiltration of lidocaine was tested on the flexor surface of each forearm of 12 subjects, with a random assignment of application methods to each arm. Lidocaine iontophoresis produced local anesthesia of significantly longer duration (p less than 0.001) than topical application of lidocaine or placebo by any route of administration, but of significatnly shorter duration (p less tahn 0.001) than lidocaine infiltration. The results showed that lidocaine iontophoresis is an effective method of producing local anesthesia for about five minutes without requiring the use of a hypodermic needle and syringe.

The use of 10B to enhance the tumour dose in fast-neutron therapy.

Incorporation of 10B in tumours treated by fast-neutron therapy would increase the tumour dose via the reaction 10B(n, alpha)7Li which occurs with partially thermalised neutrons. The extent of the dose enhancement was measured for neutron beams with median energies of 2.4, 3.3, 7.0 and 9.0 MeV by two techniques: with a BF3 proportional counter in three beams and activation of 23Na in the fourth. The results obtained with the two techniques are in good agreement. The magnitude of the dose enhancement depends upon the depth, field size and neutron beam energy. The dose enhancement at a depth of 8 cm varied from 0.32% with the lowest-energy beam to 0.07% with the highest-energy beam for each microgram of 10B uptake per gram of tissue. The products of the reaction in 10B would, however, have an RBE about twice that of the fast-neutron dose in the absence of boron. The method may be useful if drugs providing adequate uptake of 10B can be synthesised.

On the nature and significance of the radiation outside the beam in neutron therapy.

Measurements have been made of beam profiles at 10 cm deep for the neutron beam of mean energy 7.5 MeV produced by the MRC cyclotron at Hammersmith Hospital. Neutron and gamma-ray doses in water were measured with a tissue-equivalent chamber and a Geiger-Müller counter. Far outside the beam the radiation consists mostly of gamma rays penetrating the shielding. Perfect shielding would reduce this but the profile of biologically effective dose would still be worse than that from conventional X- and gamma-ray generators owing to the high RBE of small doses of neutrons. The main hazard to the patient is probably that of carcinogenesis. An approximate assessment is made of this hazard which is compared with that estimated in previous publications.

A comparison for use in radiotherapy of neutron beams generated with 16 and 42 MeV deuterons on beryllium.

The physical and radiobiological properties of two neutron beams have been compared. The beams were generated by deuterons of 16 MeV at Hammersmith Hospital and 42 MeV at Harwell, in both cases falling on a Be/Cu target. The dose-rate and depth-dose characteristics at the higher energy were found to be superior to those at the lower energy. Collimation and shielding at the higher energy are facilitated by the greater degree of forward-peaking and by the fact that a higher dose-rate allows longer collimators to be used. Attenuation in iron was found to be similar at the two energies. The radiobiological properties of the two neutron beams are very similar. There is a difference of about 20 per cent in RBE for effects on mammalian tissues for doses between 300 and 2,000 rad of neutrons. The OER and the sparing effect of two large fractions are the same for the two beams.