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Biomedical subjects

A R Clark

Publications and source records attributed to A R Clark.

At least 91 records · Page 5Linked to original sources
PubMed1993

Human insulin gene enhancer-binding proteins in pancreatic alpha and beta cell lines.

Electrophoretic mobility shift assays were performed using oligonucleotides corresponding to known protein binding sites within the human insulin gene enhancer and nuclear extracts from mouse pancreatic alpha and beta cell lines. The results demonstrate that a previously described factor, IUF-1, binds to three sites at -82 (the CT1 box), -215 (the CT2 box), and -319 (the CT3 box) in the human insulin gene enhancer. IUF-1 was present only in beta but not in alpha cells, while all other DNA-binding proteins were present in both cell lines. IUF-1 may therefore be an important determinant of insulin gene beta cell-specific expression.

Animals↗
PubMed1993

The relationship between powder inhaler resistance and peak inspiratory conditions in healthy volunteers--implications for in vitro testing.

Despite the fact that powder inhaler devices have been available for over 3 decades there is still very little fundamental information as to how powder inhaler design interacts with the airway dynamics of patients. This paper documents the results of human volunteer investigations designed to elucidate this interaction. These data indicates that if 'maximum' inhalation effort is employed the flow rate attained through an inhaler is controlled by the maximum pressure drop developed by the chest muscles. If a moderate or 'comfortable' effort is used, however, the relationship is more complex. An equation for defining the 'respirable fraction' of an inhalation aerosol cloud as a function of inhalation flow rate is also proposed.

Administration, Inhalation↗
PubMed1992

Drug delivery from holding chambers with attached facemask.

There is much interest in the use of holding chambers with an attached facemask to deliver aerosols from metered dose inhalers to infants. In order to study the influence of various design factors on the dose inhaled at different tidal volumes, a model was constructed in which a Starling ventilator was used to generate an inspiratory/expiratory cycle across a filter. Sodium cromoglycate was administered via a Nebuhaler and mask, Aerochamber and mask, and a coffee cup using tidal volumes of 25, 50, and 150 ml and the dose deposited upon the filter after six breaths was assayed using an ultraviolet spectrophotometric method. At the lowest tidal volume the high aerosol concentration in the smaller chamber enhanced drug delivery while at the highest tidal volume delivery was greatest from the larger chamber reflecting the larger dose available. Multiple breaths ensured that the dose inhaled per kilogram from each chamber was relatively large and also permitted significant drug delivery despite the introduction of a relatively large dead space between valve and filter. The dose delivered was increased by increasing the dose introduced into the chamber though not proportionately. These devices appear likely to deliver significant quantities of aerosol to infants, though drug delivery may be enhanced by the use of an appropriate valve.

Aerosols↗
PubMed1992

Drug delivery from jet nebulisers.

Maximising the rate of drug delivered in particles small enough to reach the lower respiratory tract from jet nebulisers may allow treatment times to be reduced and thus improve the acceptability of this form of treatment, particularly in very young patients. The role of various technical factors such as driving gas flow (DGF) in determining the rate of drug delivery was studied by constructing a model to simulate the respiratory pattern of individuals with different tidal volumes using a Starling ventilator and filter. Sodium cromoglycate was nebulised under a variety of operating conditions and the dose deposited on the filter was assayed. Tidal volumes of 50 and 400 ml were used at a frequency of 32 breaths per minute. Increasing the DGF from 4 to 8 l/minute produced a 264% increase in the rate of drug output but only a 32% increase in aerosol concentration. The mass of drug contained within droplets less than 5 microns increased from 26.8% to 70.8% of the total. The resultant increase in rate of drug delivery to the filter was 34% for a tidal volume of 50 ml and 79% for a tidal volume of 400 ml though the dose contained within droplets less than 5 microns increased by 4-fold at 50 ml tidal volume and by more than 5-fold at the higher tidal volume. Halving the solution concentration halved the rate of drug delivery. Increasing the tidal volume 8-fold from 50 to 400 ml resulted in an increase in the rate of drug deposition upon the filter of only 2.2 to 3-fold depending upon the DGF so that substantially more drug per ml inhaled was delivered at the lower tidal volume. These results are explained by considering factors that influence the rate of drug delivery. At low tidal volumes the rate of drug delivery at a given respiratory rate is dependent on the tidal volume and aerosol concentration. At high tidal volumes it is dependent upon aerosol concentration and volume of available aerosol and is essentially independent of tidal volume.

Aerosols↗
PubMed1991

Two proteins act as the IUF1 insulin gene enhancer binding factor.

IUF1 is a pancreatic beta cell-specific factor which binds to the sequence 5'-CPyCTAATG-3' (CT box) within the human insulin gene enhancer. Here we show that IUF1 is composed of 2 binding activities that can be separated by DEAE ion exchange chromatography. South Western blot analysis indicates that these distinct binding activities have apparent molecular weights of 115 kDa and 46 kDa.

Animals↗
PubMed1991

Delivery of aerosolized medication to intubated babies.

We studied the delivery of aerosolized cromolyn sodium to intubated babies, and evaluated the effect of changes in delivery techniques. In addition, we compared these results with an in vitro model of aerosol delivery. Cromolyn sodium was used as a marker because once the drug is absorbed, it is excreted unchanged, approximately 50% in urine and 50% in bile. We demonstrated that, in vitro, a conventional, jet-type nebulizer aerosolized 20.5% of a test dose of cromolyn, and only 5.5% of the dose was recovered after passage through 60 cm of ventilator tubing and an endotracheal tube adapter. This increased to 44.5% nebulized and 19% recovered when the volume nebulized was increased from 2 mL to 5 mL. A submicronic nebulizer aerosolized 40% and delivered 33.5% of the test dose. A 20 mg dose of nebulized cromolyn sodium was used as a test dose in infants, after which urine was collected for 4 hours. Forty-three urine samples were collected, after the delivery of cromolyn test doses, from nine babies (16-128 days old) intubated for bronchopulmonary dysplasia. Both the jet and submicronic nebulizers were tested in two positions: 1) in place of the ventilator humidifier, and 2) at the endotracheal tube adapter. There were no statistically significant differences in cromolyn delivery for any system configuration. In all situations, means of less than 0.1% of the test dose were recovered in the urine. We estimated that in all cases, less than 1% of the test dose (approximately 50-100 micrograms of cromolyn) had been deposited in the lung. These results show that although the submicronic nebulizer aerosolized cromolyn more efficiently, no additional cromolyn could be detected in infants. We speculate that a significant portion of the smaller particles are exhaled.

Administration, Inhalation↗
PubMed1990

Positive and negative regulation of the human insulin gene by multiple trans-acting factors.

Tissue-specific expression of the human insulin gene is regulated by cis-acting DNA elements 5' to the transcription start site. Deletion of the 5' region of the human insulin gene between nucleotides -279 and -258 caused a 25-fold rise in transcriptional activity whereas further deletion to nucleotide -229 reduced transcription activity 25-fold. In vitro analysis of protein binding in the 5' regulatory region revealed: (i) the major positive regulatory region (-258 to -229) contains a protein-binding site (GC-II) with 75% sequence identity to a motif in the rat insulin I gene, shown to be a powerful transcriptional activator. GC-II motif-binding factors are not restricted to insulin-producing cell lines. (ii) An islet cell-specific factor binds between nucleotides -217 to -210 (CT-II motif). (iii) A region between nucleotides -153 and -127, containing two identical motifs, GG-I and GG-II was also revealed. GG-I-binding factors are ubiquitous, whereas binding to the GG-II motif is beta cell-specific. (iv) A ubiquitous factor binds to a motif between nucleotides -179 and -183, identical to a half-site for the cyclic nucleotide regulatory element. (v) The negative regulatory element between -279 and -258 contains overlapping binding sites for at least 3 protein factors, with differing cell-specific distributions and can independently down-regulate thymidine kinase promoter activity in a beta cell line.

Base Sequence↗
PubMed1990

The use of reservoir devices for the simultaneous delivery of two metered-dose aerosols.

Many patients benefit from using metered-dose inhalers (MDIs) with spacer or reservoir devices. Concomitant therapy with separate MDI doses of cromolyn sodium and a beta-agonist is common practice. If two puffs from each drug could be placed into a chamber, the patient could administer both medications at once, enhancing compliance. A multistage liquid impinger (a four-stage inertial impaction device incorporating an inlet bend and an absolute filter, which separates an aerosol cloud into six fractions) was used to investigate such a possibility. Cromolyn sodium and albuterol MDIs were used with an Aerochamber (Monaghan Medical Corp., Plattsburgh, N.Y.) and an Inspirease (Schering Corp., Kenilworth, N.J.). Results are reported by analyzing milligrams of cromolyn sodium per actuation retrieved. With the Aerochamber, two puffs of cromolyn sodium followed by two puffs of albuterol resulted in the total "dose to patient" being reduced by 75% (0.19 versus 0.05 mg) and the effective dose of fine particles (less than 6.5 microns) being reduced by 80% (0.13 versus 0.03 mg) compared to two puffs of cromolyn sodium alone. With the Inspirease, total dose was decreased by 80% (0.32 versus 0.06 mg), whereas the effective dose of fine particles was reduced by 60% (0.19 versus 0.05 mg) compared to one puff of cromolyn sodium alone. The use of cromolyn sodium and albuterol MDIs in a multipuff combination with the Aerochamber or the Inspirease is not recommended because this leads to a loss of the dose delivered compared to a single administration.

Aerosols↗
PubMed1989

In vitro performance of the small particle aerosol generator (SPAG-2).

The anti-viral drug ribavirin primarily used for the treatment of respiratory syncytial virus (RSV) infection in infants is delivered by continuous nebulization with the Small Particle Aerosol Generator (SPAG). Clinical data suggest that the SPAG is an efficient nebulizer for ribavirin; it is also being used for the delivery of other pulmonary agents. The efficiency of a nebulizer can be defined in large part by delivering a major proportion of its output with a particle size of 1 to 5 microns which is small enough to penetrate the tracheobronchial tree. We assessed both the quality and quantity of the SPAG aerosol cloud with the aid of a multistage liquid impinger, utilizing 2% ribavirin and 1% cromolyn sodium solutions. The aerosol of either solution had a mass median aerodynamic diamter (MMAD) of approximately 1.2 microns, and this seemed insensitive to solution strength and nebulization period. Of the solutions of ribavirin and cromolyn sodium 92.3% and 95.0%, respectively, by weight of delivered particles, had aerodynamic diameters less than 5 microns and about 70-75% of the aerosol particles had an aerodynamic diameter in the 1-5 microns range. This implies that the aerosol cloud is adequate for delivery through a ventilator circuit. Performance was maintained over long (16 hours), continuous periods of delivery. The SPAG could be useful for delivery of other respiratory drugs by continuous nebulization.

Aerosols↗
PubMed1989

Does 99Tcm human serum albumin alter the characteristics of nebulized pentamidine isethionate?

Nebulized pentamidine has been used as therapy for Pneumocystis carinii pneumonia. The lung dose delivered using different nebulizer systems and doses of pentamidine from 50-600 mg is unknown. To measure this a marker which does not alter the characteristics of the nebulized pentamidine solution must be found. We have assessed the aerosol characteristics of four jet nebulizers (System 22, System 22 Mizer, Optimist, Respigard II) and one ultrasonic device (Pulmosonic) using two concentrations of pentamidine isethionate (50 mg and 300 mg) in 3 ml of solution. The jet nebulizers were operated at a flow rate of 6 l min-1, a rate suitable for home use. These measurements were repeated with 99Tcm labelled human serum albumin (HSA) added to the solutions. A linear relationship between 99Tcm-HSA activity and pentamidine concentration was demonstrated by using a nine stage cascade impactor. The Respigard II and Optimist produced the best results in terms of particle size (96% less than 5 microns), but the addition of the tracer to the latter led to a smaller particle size range and a reduction in the amount of aerosol present at the mouthpiece. The Mizer system had 52% of particles less than 5 microns, the Pulmosonic 46%. The Respigard II had a total output of 8.7 mg for the 50 mg concentration and 30.9 mg for the 300 mg concentration. The System 22 produced corresponding outputs of 18.0 mg and 67.1 mg with 54% of the aerosol particles less than 5 microns.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerosols↗
PubMed1989

Why nebulise for more than five minutes?

The output of the drug and the particle size produced by various nebulisers were assessed, and sensible nebulisation times for sodium cromoglycate calculated. Three of the four nebuliser systems tested produced over 80% of total drug output within the first five minutes of nebulisation. We suggest that five minutes is an optimum nebulisation time for sodium cromoglycate using these nebuliser combinations.

Cromolyn Sodium↗
PubMed1989

Pressurised aerosol deposition in the human lung with and without an "open" spacer device.

A radiotracer technique has been used to assess aerosol delivery from a pressurised metered dose inhaler, used both with and without a 10 cm cylindrical spacer attachment (Syncroner), which has an open section in its upper surface. The radionuclide technetium-99m (99mTc) was added to sodium cromoglycate in a canister (Intal inhaler; 1 mg/puff); in vitro studies with a multistage liquid impinger showed that the radiolabel acted as a marker for the presence of drug over a wide range of particle sizes. Ten healthy volunteers were studied after they had inhaled from (1) a metered dose inhaler alone (slow inhaled flow rate, about 25 l/min); (2) metered dose inhaler plus spacer (slow flow rate); and (3) metered dose inhaler plus spacer (fast inhaled flow rate, about 100 l/min). Inhalation was coordinated with firing the spray and was followed by 10 seconds' breath holding. With the metered dose inhaler alone a mean 11.0% (SEM 1.4%) of the dose reached the lungs, compared with significantly higher doses for slow (16.1% (2.2%] and fast (13.3% (1.7%] inhalations through the spacer. The distribution pattern within the lungs was significantly more peripheral after slow inhalation. Oropharyngeal deposition was halved by the spacer. The open spacer should teach patients good coordination and delivers more aerosol to the lungs than a correctly used metered dose inhaler.

Adolescent↗
PubMed1988

Tests of genetic markers on aborted fetal material.

Women who conceive as a result of rape often elect to abort the fetus. We describe twelve cases where genetic markers were tested on the aborted fetal material to provide evidence of the genetic constitution of the rapist. Two cases are presented in detail, and the problems encountered with the testing are discussed.

Abortion, Induced↗
PubMed1986

An isolated perfused rat lung preparation for the study of aerosolized drug deposition and absorption.

The isolated, perfused rat lung preparation was modified to allow characterized solid aerosol delivery. Deposition and airway-to-perfusate transfer of disodium fluorescein from 3-4 micron dae solid aerosols were studied under different ventilatory regimes. The lungs inhaled from an aerosol stream of constant concentration via a tracheal cannula. Air displacement from a sealed artificial thorax housing the lungs provided the driving force for inhalation. The lungs were suspended in a physiologically normal position and both left and right sides of the heart were cannulated for constant rate perfusate flow. Fractional deposition was inversely proportional to respiratory frequency implying that sedimentation was the primary deposition mechanism. Increasing tidal volumes similarly enhanced the ratio of amount deposited/amount administered. Fluorescein transfer to the perfusate occurred from the lung regions containing intact vasculature, was apparent first-order, and independent of perfusate flow. The average rate constant for transfer was 0.057 +/- 0.02 min-1 (t1/2 = 12.2 +/- 4.2 min-1). The ratio of transferable amount/amount deposited appeared to indicate the depth of aerosol penetration. This increased at high respiratory frequency and tidal volume, while decreasing with increasing aerosol particle size. Potential applications of the model are discussed in the light of these results.

Absorption↗