Molecular determinants of benzodiazepine receptor affinities and anticonvulsant activities

In vivo convulsant activities profiles and receptor binding studies together with the techniques of theoretical chemistry were used to characterize 15 compounds, from five different chemical families, known to bind to the BDZ receptor. The experimental goals of this study were to determine the affinity of these analogs for this receptor, the effect of gamma-aminobutyric acid on the affinity, and, in a self-consistent manner, the nature of the activity, agonist (anticonvulsant), antagonist, or inverse agonist (proconvulsant, convulsant), elicited by binding to this receptor. To these ends, in vivo studies were made to determine the proconvulsant, convulsant, and anticonvulsant activities and antagonism to anticonvulsant activities of the 15 analogs. Their receptor affinities at 25 degrees were also determined by competitive inhibition of [3H] flunitrazepam and [3H]Ro 15-1788 in the absence and presence of gamma-aminobutyric acid. The goal of the theoretical studies was to identify and calculate molecular properties that modulate these affinities and types of activities and from them to develop a model of receptor recognition and activation that could consistently explain observed behavior and predict new results. Thus, molecular orbital calculations were carried out for all analogs, using semiempirical quantum mechanical methods. In addition to the optimization of structures, a number of electronic properties, such as polarizations, partition coefficients, and proton and electron affinities were computed and examined for their ability to modulate relative affinities and modes of activation of the receptor. From these studies, a model for receptor recognition involving two anchoring hydrogen bond-acceptor sites and for activation involving interaction of the most lipophilic aromatic region of each compound with the receptor was developed, which could systematically account for the three different types of behavior, agonist, antagonist, and inverse agonist, observed for these analogs. Electronic rather than structural properties were found to be the principal modulator of both recognition and activation. A possible mechanism of agonist activation of the receptor involving electron transfer to the agonist, as well as a possible induced conformational change in the receptor, is also suggested by these results. Finally, by complementarity, some steric and electronic characteristics of the receptor binding site could be deduced.     

Technical Note: A comparison of a novel direct ophthalmoscope, the OptyseTM, to conventional direct ophthalmoscopes

Despite the current popularity of binocular indirect ophthalmoscopy, direct ophthalmoscopes are still commonly used by clinicians for fundus examination. They are considered to be expensive, however, and it has been suggested that this cost can prevent their use by healthcare professionals in developing countries. The Optyse Lens Free Ophthalmoscope is a novel direct ophthalmoscope, without a lens focus system, that allows for comparatively inexpensive manufacture and supply. We compared the clarity of view with the Optyse to that with standard direct ophthalmoscopes, over a sequential cohort of patients with a variety of refractive errors and ocular conditions. The grade of clarity of view with the Optyse Lens Free Ophthalmoscope was less than conventional ophthalmoscopes (Wilcoxon signed rank test, p < 0.0001). This grade of clarity of view was not associated with the ametropia of the ophthalmoscopic observation (Spearman r < or = 0.03, p > or = 0.28) but was with the presence of cataracts (chi2 test, p < 0.0001) with both the Optyse and the conventional ophthalmoscopes. Despite its limitations, the retinal view with Optyse was often within acceptable clinical limits suggesting that this relatively inexpensive ophthalmoscope may have a place when cost prohibits any other type of ophthalmoscope use.     

[3H]Ketanserin labels 5-HT2 receptors and α1-adrenoceptors in human and pig brain membranes

The binding characteristics of [3H]ketanserin (a reported selective radioligand for serotonin 5-HT2 receptors) and [125I]BE 2254 (which labels selectively alpha 1-adrenoceptors) were characterized in brain frontal cortex membranes of pig and man. Saturation experiments indicated that both radioligands label apparently a homogeneous class of binding sites in human and pig fontal cortex membranes. Competition experiments with [125I]BE 2254 using 17 agonists and antagonists showed monophasic and steep curves in human and pig frontal cortex membranes. The pharmacological profile of these sites is typical of alpha 1-adrenoceptors. In competition experiments with [3H]ketanserin, most of the tested compounds displayed shallow or biphasic curves. In particular, alpha 1-adrenoceptor-selective antagonists (prazosin, WB 4101, BE 2254...) displaced with nanomolar affinity about 15 and 40% of the specific [3H]ketanserin binding in human and pig frontal cortex membranes, respectively. The minor component of [3H]ketanserin binding correlated highly significantly with [125I]BE 2254 binding in both membrane preparations. The major component of [3H]ketanserin binding to pig and human frontal cortex membranes correlated significantly with [3H]ketanserin binding in rat brain cortex membranes (which is essentially to 5-HT2 receptors). The present data demonstrate that [3H]ketanserin in nanomolar concentrations binds significantly to alpha 1-adrenoceptors in human and pig frontal cortex membranes; this suggests a rather limited degree of selectivity of ketanserin for 5-HT2 receptors in pig and human tissues.     

De novo generation of histamine in sputum and the effect of antibiotics

We have performed experiments to test the hypothesis that bacteria may contribute to the presence of histamine in sputum. Sputum samples obtained from 7 patients with exacerbations of chronic bronchitis and 7 patients with cystic fibrosis were incubated at 37 degrees C for 72 hours. Serial sputum histamine estimations, performed by a recently-developed HPLC technique, showed large, progressive increases in both groups of samples. Both the pre-heating of samples at 100 degrees C prior to incubation and the addition of antibiotics to the incubates substantially reduced these increases. These findings strongly suggest that bacteria may contribute to sputum histamine in infective lung disease.     

Urinary output of endogenous monoamine oxidase inhibitor and isatin during acute migraine attacks

Summary Urinary output of endogenous monoamine oxidase (MAO) inhibitory activity, was significantly raised in serial samples collected across a migraine attack compared with collections during attack-free periods and in healthy controls, which did not differ from each other. There was a highly significant correlation in output between isatin, a major fraction of the MAO inhibitory activity, and output of the MAO inhibitory activity itself. However, although there was a tendency towards increased isatin excretion during migraine attacks, it failed to reach statistical significance.     

Sensitisation to Swine Leukocyte Antigens in Patients with Broadly Reactive HLA Specific Antibodies

We have previously shown that IgG HLA specific antibodies in the sera of highly sensitised patients awaiting renal transplantation can cross-react with swine leukocyte antigens (SLA). In this study we determined the frequency of patient serum IgG HLA specific antibody binding to a porcine lymphocyte panel and the likelihood of locating a cross-match negative pig donor for sensitised patients. Serum samples (n = 82) were obtained from 35 sensitised [current IgG panel reactive antibodies (PRA) > 10%] and seven nonsensitised patients awaiting renal transplantation at Addenbrooke's Hospital, Cambridge, UK. Fifty sera had IgG HLA specific PRA of 11-84%, 20 had IgG PRA of >84% and 12 had 0% PRA (negative controls). Sera were absorbed with porcine erythrocytes to remove xenoreactive natural antibodies and tested for cross-reactive IgG HLA specific antibody binding by flow cytometry against a panel of porcine lymphocytes obtained from 23 human decay accelerating factor (hDAF) transgenic pigs. A total of 1,884 cross-match combinations were tested and 369 (20%) gave a positive porcine lymphocyte cross-match. For sera from sensitised patients with IgG PRA (11-64%), only 6 of 805 (0.75%) cross-match tests were positive. In contrast, for sera from patients with high IgG PRA (>64%), 363 of 805 (45%) cross-match tests were positive (p < 0.0001). There was no difference in the frequency of positive cross-matches between patient sera with IgG PRA 65-84% and highly sensitised patient sera with IgG PRA 85-100% [156/345 (45%) vs. 207/460 (45%)]. This study demonstrates that only patient sera with broadly reactive IgG HLA specific PRA (>64%) cross-react with porcine lymphocytes. If future clinical trials of xenotransplantation are undertaken, it may be of value to select a cross-match-negative pig organ donor for such patients.     

Development and implementation of an innovative intern training programme

The quality of medical education during internship is a cause for concern. This paper describes a structured educational programme for interns that was based around learning modules, clinical attachments and bedside teaching. The programme was incorporated into the term rotation of interns within an Area Health Service, and evaluated. Learning modules were timetabled by a Programme Coordinator and interns were reminded to attend. Clinical attachments were organized by the interns from a list of willing supervisors. Attendance at timetabled learning modules averaged 67%, which was greater than the 27% attendance at clinical attachments. Both sessions received high ratings for quality and clinical relevance. This structured education programme was based upon adult learning methods and was both feasible and well received by interns. Intern training programmes need to be programmed into the working week to ensure attendance, and modified following evaluation by interns. Such programmes should be considered by all hospitals to which interns are allocated.