Covalent modification of GABAA receptor isoforms by a diazepam analogue provides evidence for a novel benzodiazepine binding site that prevents modulation by these drugs

Classical benzodiazepines, for example diazepam, interact with alpha(x)beta(2)gamma(2) GABA(A) receptors, x = 1, 2, 3, 5. Little is known about effects of alpha subunits on the structure of the binding pocket. We studied here the interaction of the covalently reacting diazepam analog 7-Isothiocyanato-5-phenyl-1,3-dihydro-2H-1,4-benzodiazepin-2-one (NCS compound) with alpha(1)H101Cbeta(2)gamma(2) and with receptors containing the homologous mutation, alpha(2)H101Cbeta(2)gamma(2), alpha(3)H126Cbeta(2)gamma(2) and alpha(5)H105Cbeta(2)gamma(2). This comparison was extended to alpha(6)R100Cbeta(2)gamma(2) receptors as this mutation conveys to these receptors high affinity towards classical benzodiazepines. The interaction was studied at the ligand binding level and at the functional level using electrophysiological techniques. Results indicate that the geometry of alpha(6)R100Cbeta(2)gamma(2) enables best interaction with NCS compound, followed by alpha(3)H126Cbeta(2)gamma(2), alpha(1)H101Cbeta(2)gamma(2) and alpha(2)H101Cbeta(2)gamma(2), while alpha(5)H105Cbeta(2)gamma(2) receptors show little interaction. Our results allow conclusions about the relative apposition of alpha(1)H101 and homologous positions in alpha(2), alpha(3), alpha(5) and alpha(6) with the position occupied by -Cl in diazepam. During this study we found evidence for the presence of a novel site for benzodiazepines that prevents modulation of GABA(A) receptors via the classical benzodiazepine site. The novel site potentially contributes to the high degree of safety to some of these drugs. Our results indicate that this site may be located at the alpha/beta subunit interface pseudo-symmetrically to the site for classical benzodiazepines located at the alpha/gamma interface.

Relative positioning of diazepam in the benzodiazepine-binding-pocket of GABA receptors

GABA(A) receptors are the major inhibitory neurotransmitter receptors in the brain. Some of them are targets of benzodiazepines that are widely used in clinical practice for their sedative/hypnotic, anxiolytic, muscle relaxant and anticonvulsant effects. In order to rationally separate these different drug actions, we need to understand the interaction of such compounds with the benzodiazepine-binding pocket. With this aim, we mutated residues located in the benzodiazepine-binding site individually to cysteine. These mutated receptors were combined with benzodiazepine site ligands carrying a cysteine reactive group in a defined position. Proximal apposition of reaction partners will lead to a covalent reaction. We describe here such proximity-accelerated chemical coupling reactions of alpha(1)S205C and alpha(1)T206C with a diazepam derivative modified at the C-3 position with a reactive isothiocyanate group (-NCS). We also provide new data that identify alpha(1)H101C and alpha(1)N102C as exclusive sites of the reaction of a diazepam derivative where the -Cl atom is replaced by a -NCS group. Based on these observations we propose a relative positioning of diazepam within the benzodiazepine-binding site of alpha(1)beta(2)gamma(2) receptors.

Drug-related emergency department visits by elderly patients presenting with non-specific complaints

BACKGROUND Since drug-related emergency department (ED) visits are common among older adults, the objectives of our study were to identify the frequency of drug-related problems (DRPs) among patients presenting to the ED with non-specific complaints (NSC), such as generalized weakness and to evaluate responsible drug classes. METHODS Delayed type cross-sectional diagnostic study with a prospective 30 day follow-up in the ED of the University Hospital Basel, Switzerland. From May 2007 until April 2009, all non-trauma patients presenting to the ED with an Emergency Severity Index (ESI) of 2 or 3 were screened and included, if they presented with non-specific complaints. After having obtained complete 30-day follow-up, two outcome assessors reviewed all available information, judged whether the initial presentation was a DRP and compared their judgment with the initial ED diagnosis. Acute morbidity ("serious condition") was allocated to individual cases according to predefined criteria. RESULTS The study population consisted of 633 patients with NSC. Median age was 81 years (IQR 72/87), and the mean Charlson comorbidity index was 2.5 (IQR 1/4). DRPs were identified in 77 of the 633 cases (12.2%). At the initial assessment, only 40% of the DRPs were correctly identified. 64 of the 77 identified DRPs (83%) fulfilled the criteria "serious condition". Polypharmacy and certain drug classes (thiazides, antidepressants, benzodiazepines, anticonvulsants) were associated with DRPs. CONCLUSION Elderly patients with non-specific complaints need to be screened systematically for drug-related problems. TRIAL REGISTRATION ClinicalTrials.gov: NCT00920491.

Shaking head means "no"

A 45-year-old man was admitted to the emergency department because of twitching of the head. The patient took a tablet of sumatriptan every 3-4 h because of increasing head pain after a car accident. Owing to depression, the patient was on long-term treatment with venlafaxine. The patient presented as hypertensive, tachycardic, with dyskinesia and spontaneous myoclonic movements of the right sternocleidomastoid muscle. In a CT scan of the head and cervical spine any fractures, bleeding or damage of the vessels after the accident could be ruled out. After discontinuation of all serotonergic agents, administration of lorazepam symptoms resolved 24 h after the last intake of sumatriptan. Serotonin syndrome is a clinical diagnosis, which requires a high-index of diagnostic suspicion. Clinical features include a broad spectrum of symptoms ranging from mild to life-threatening manifestations. Management is based on removal of precipitating drugs and symptomatic care including benzodiazepines.

Impact of Acetazolamide and CPAP on Cortical Activity in Obstructive Sleep Apnea Patients

STUDY OBJECTIVES 1) To investigate the impact of acetazolamide, a drug commonly prescribed for altitude sickness, on cortical oscillations in patients with obstructive sleep apnea syndrome (OSAS). 2) To examine alterations in the sleep EEG after short-term discontinuation of continuous positive airway pressure (CPAP) therapy. DESIGN Data from two double-blind, placebo-controlled randomized cross-over design studies were analyzed. SETTING Polysomnographic recordings in sleep laboratory at 490 m and at moderate altitudes in the Swiss Alps: 1630 or 1860 m and 2590 m. PATIENTS Study 1: 39 OSAS patients. Study 2: 41 OSAS patients. INTERVENTIONS Study 1: OSAS patients withdrawn from treatment with CPAP. Study 2: OSAS patients treated with autoCPAP. Treatment with acetazolamide (500-750 mg) or placebo at moderate altitudes. MEASUREMENTS AND RESULTS An evening dose of 500 mg acetazolamide reduced slow-wave activity (SWA; approximately 10%) and increased spindle activity (approximately 10%) during non-REM sleep. In addition, alpha activity during wake after lights out was increased. An evening dose of 250 mg did not affect these cortical oscillations. Discontinuation of CPAP therapy revealed a reduction in SWA (5-10%) and increase in beta activity (approximately 25%). CONCLUSIONS The higher evening dose of 500 mg acetazolamide showed the "spectral fingerprint" of Benzodiazepines, while 250 mg acetazolamide had no impact on cortical oscillations. However, both doses had beneficial effects on oxygen saturation and sleep quality.

Suicidal ideation in a European Huntington's disease population.

BACKGROUND Previous studies indicate increased prevalences of suicidal ideation, suicide attempts, and completed suicide in Huntington's disease (HD) compared with the general population. This study investigates correlates and predictors of suicidal ideation in HD. METHODS The study cohort consisted of 2106 HD mutation carriers, all participating in the REGISTRY study of the European Huntington's Disease Network. Of the 1937 participants without suicidal ideation at baseline, 945 had one or more follow-up measurements. Participants were assessed for suicidal ideation by the behavioural subscale of the Unified Huntington's Disease Rating Scale (UHDRS). Correlates of suicidal ideation were analyzed using logistic regression analysis and predictors were analyzed using Cox regression analysis. RESULTS At baseline, 169 (8.0%) mutation carriers endorsed suicidal ideation. Disease duration (odds ratio [OR]=0.96; 95% confidence interval [CI]: 0.9-1.0), anxiety (OR=2.14; 95%CI: 1.4-3.3), aggression (OR=2.41; 95%CI: 1.5-3.8), a previous suicide attempt (OR=3.95; 95%CI: 2.4-6.6), and a depressed mood (OR=13.71; 95%CI: 6.7-28.0) were independently correlated to suicidal ideation at baseline. The 4-year cumulative incidence of suicidal ideation was 9.9%. Longitudinally, the presence of a depressed mood (hazard ratio [HR]=2.05; 95%CI: 1.1-4.0) and use of benzodiazepines (HR=2.44; 95%CI: 1.2-5.0) at baseline were independent predictors of incident suicidal ideation, whereas a previous suicide attempt was not predictive. LIMITATIONS As suicidal ideation was assessed by only one item, and participants were a selection of all HD mutation carriers, the prevalence of suicidal ideation was likely underestimated. CONCLUSIONS Suicidal ideation in HD frequently occurs. Assessment of suicidal ideation is a priority in mutation carriers with a depressed mood and in those using benzodiazepines.

A novel open channel blocker of GABA-A receptors

GABA-A receptors are chloride ion channels composed of five subunits, mediating fast synaptic and tonic inhibition in the mammalian brain. 19 different subunit isoforms have been identified, with the major receptor type in mammalian adult brain consisting of α1, β2, and γ2 subunits. GABA-A receptors are the target of numerous sedating and anxiolytic drugs such as benzodiazepines. The currently known endogenous ligands are GABA, neurosteroids and the endocannabinoid 2- arachidonoyl glycerol (2-AG). The pharmacological properties of this chloride ion channel strictly depend on receptor subunit composition and arrangement. GABA-A receptors bind and are inhibited by epileptogenic agents such as picrotoxin, and cyclodiene insecticides such as dieldrin. We screened aromatic monovalent anions with five-fold symmetry for inhibition of GABA-A receptors. One of the anions, PCCPinhibited currents elicited by GABA with comparable potency as picrotoxin. This inhibition showed all characteristics of an open channel block. The GABA-A receptor ion channel is lined by residues from the M2 membrane-spanning segment. To identify important residues of the pore involved in the interaction with the blocking molecules PCCP-, a mutation scan was performed in combination with subsequent analysis of the expressed mutant proteins using electrophysiological techniques. In a second project we characterised a light-switchable modulator of GABA-A receptors based on propofol. It was my responsibility to investigate the switching kinetics in patch clamp experiments. After its discovery in 1980, propofol has become the most widely used intravenous general anaesthetic. It is commonly accepted that the anaesthesia induced by this unusually lipophilic drug mostly results from potentiation of GABA induced currents. While GABA-A receptors respond to a variety of ligands, they are normally not sensitive towards light. This light sensitivity could be indirectly achieved by using modulators that can be optically switched between an active and an inactive form. We tested an azobenzene derivative of propofol where an aryldiazene unit is directly coupled to the pharmacophore. This molecule was termed azopropofol (AP2). The effect of AP2 on Cl- currents was investigated with electrophysiological techniques using α1β2γ2 GABA-A receptors expressed in Xenopus oocytes and HEK-cells. In the third project we wanted to investigate the functional role of GABA-A receptors in the liver, and their possible involvement in cell proliferation. GABA-A receptors are also found in a wide range of peripheral tissues, including parts of the peripheral nervous system and non-neural tissues such as smooth muscle, the female reproductive system, liver and several cancer tissues. However their precise function in non neuronal or cancerous cells is still unknown. For this purpose we investigated expression, localization and function of the hepatocytes GABA-A receptors in model cell lines and healthy and cancerous hepatocytes.

Structural analogues of the natural products magnolol and honokiol as potent allosteric potentiators of GABA(A) receptors.

Biphenylic compounds related to the natural products magnolol and 4'-O-methylhonokiol were synthesized, evaluated and optimized as positive allosteric modulators (PAMs) of GABA(A) receptors. The most efficacious compounds were the magnolol analog 5-ethyl-5'-hexylbiphenyl-2,2'-diol (45) and the honokiol analogs 4'-methoxy-5-propylbiphenyl-2-ol (61), 5-butyl-4'-methoxybiphenyl-2-ol (62) and 5-hexyl-4'-methoxybiphenyl-2-ol (64), which showed a most powerful potentiation of GABA-induced currents (up to 20-fold at a GABA concentration of 3μM). They were found not to interfere with the allosteric sites occupied by known allosteric modulators, such as benzodiazepines and N-arachidonoylglycerol. These new PAMs will be useful as pharmacological tools and may have therapeutic potential for mono-therapy, or in combination, for example, with GABA(A) receptor agonists.

Association between intraoperative electroencephalographic suppression and postoperative mortality

BACKGROUND Low bispectral index values frequently reflect EEG suppression and have been associated with postoperative mortality. This study investigated whether intraoperative EEG suppression was an independent predictor of 90 day postoperative mortality and explored risk factors for EEG suppression. METHODS This observational study included 2662 adults enrolled in the B-Unaware or BAG-RECALL trials. A cohort was defined with >5 cumulative minutes of EEG suppression, and 1:2 propensity-matched to a non-suppressed cohort (≤5 min suppression). We evaluated the association between EEG suppression and mortality using multivariable logistic regression, and examined risk factors for EEG suppression using zero-inflated mixed effects analysis. RESULTS Ninety day postoperative mortality was 3.9% overall, 6.3% in the suppressed cohort, and 3.0% in the non-suppressed cohort {odds ratio (OR) [95% confidence interval (CI)]=2.19 (1.48-3.26)}. After matching and multivariable adjustment, EEG suppression was not associated with mortality [OR (95% CI)=0.83 (0.55-1.25)]; however, the interaction between EEG suppression and mean arterial pressure (MAP) <55 mm Hg was [OR (95% CI)=2.96 (1.34-6.52)]. Risk factors for EEG suppression were older age, number of comorbidities, chronic obstructive pulmonary disease, and higher intraoperative doses of benzodiazepines, opioids, or volatile anaesthetics. EEG suppression was less likely in patients with cancer, preoperative alcohol, opioid or benzodiazepine consumption, and intraoperative nitrous oxide exposure. CONCLUSIONS Although EEG suppression was associated with increasing anaesthetic administration and comorbidities, the hypothesis that intraoperative EEG suppression is a predictor of postoperative mortality was only supported if it was coincident with low MAP. CLINICAL TRIAL REGISTRATION NCT00281489 and NCT00682825.

Positive modulation of synaptic and extrasynaptic GABAA receptors by an antagonist of the high affinity benzodiazepine binding site.

GABAA receptors are the major inhibitory neurotransmitter receptors in the brain and are the target for many clinically important drugs such as the benzodiazepines. Benzodiazepines act at the high-affinity binding site at the α+/γ- subunit interface. Previously, an additional low affinity binding site for diazepam located in the transmembrane (TM) domain has been described. The compound SJM-3 was recently identified in a prospective screening of ligands for the benzodiazepine binding site and investigated for its site of action. We determined the binding properties of SJM-3 at GABAA receptors recombinantly expressed in HEK-cells using radioactive ligand binding assays. Impact on function was assessed in Xenopus laevis oocytes with electrophysiological experiments using the two-electrode voltage clamp method. SJM-3 was shown to act as an antagonist at the α+/γ- site. At the same time it strongly potentiated GABA currents via the binding site for diazepam in the transmembrane domain. Mutation of a residue in M2 of the α subunit strongly reduced receptor modulation by SJM-3 and a homologous mutation in the β subunit abolished potentiation. SJM-3 acts as a more efficient modulator than diazepam at the site in the trans-membrane domain. In contrast to low concentrations of benzodiazepines, SJM-3 modulates both synaptic and extrasynaptic receptors. A detailed exploration of the membrane site may provide the basis for the design and identification of subtype-selective modulatory drugs.

Physician and patient determinants of the treatment of sleep difficulties in U.S. outpatient settings

The prevalence of sleep difficulties among the patients seen in the primary care settings is about 30%. This problem increases with age and is more common among females than males. Variations are noticed in prescription choices for different patients with sleep difficulties. Many factors affect a physician's prescription decision while chosen from a wide array of available medications. Both pharmacological and behavioral therapies are available for the treatment of sleep difficulties. It is important to know the impact of use of different types of prescriptions on health outcomes related to sleep difficulties. Thus the knowledge of prescription patterns among different types of patients (e.g. age, gender, race, insurance type etc.) becomes important for determining a clinical guideline. This study is designed to assist in evidence-based policymaking on understanding the variations in physician prescriptions for sleep difficulties and reasons for such variations. ^ A modified version of the model suggested by Eisenberg was used as a theoretical framework for this study to predict the factors influencing treatment of sleep difficulties. Multivariate logistic regression methods were used to analyze the 1996–2001 National Ambulatory Medical Care Survey data. ^ This study found that increased age, female gender, white race, established patients, and mental comorbidity were associated with significantly increased likelihood for prescription of some type of therapy for sleep difficulties in US outpatient settings. Patients with private insurance were associated with lower likelihood of receipt of many therapies. Psychiatrists were more likely to prescribe some kind of treatment as well as more expensive therapies for sleep difficulty as compared to other physician specialties. HMO enrolled patient visits were more likely to be associated with receipt of behavioral therapy. This study also found that 32% of patients with sleep difficulties received no type of therapy during their visits. Only 5% of the patients received behavioral therapy only. Almost three-quarters of the patients receiving some kind of medication prescription were prescribed benzodiazepines. The study results also suggest a need for wider coverage of behavioral therapy by payers in US outpatient settings. ^

Culminating experience: Initiation of cholinesterase inhibitors in an inpatient setting

We examined the practice of initiating Cholinesterase Inhibitors (ChEI) in a Veterans Affairs Medical Center. Patients hospitalized in FY 2008 and prescribed ChEI were identified. We reviewed electronic medical records, comparing those started on ChEI during hospitalization with those continuing ChEI from outpatient status. Of 282 patients receiving ChEI during hospitalization, 15.6% (44) were new-starts and 84.3% (238) were continuing medication. Median length of stay was 16 days in new-starts vs. 6 days in continuation patients (P<0.05). 38.6% new-starts were also treated for infection, which is a delirium risk factor. Chart review also suggested possible treatment for delirium by initiation of benzodiazepines and antipsychotics in 11.4% and 22.7% new-starts respectively. We observed a substantive practice of initiating ChEIs in hospitalized elderly who were at risk of delirium. Though there was no difference in 30-day mortality and readmission rates, new-starts were more likely to have a prolonged hospital stay than continuation patients.^

Consumo de drogas adictivas en alumnos de la UNCuyo, Mendoza, Argentina.

Este trabajo muestra los resultados de una encuesta realizada en 2010 sobre consumo de drogas adictivas en alumnos de 7 Facultades de la UNCUYO y los compara con los resultados obtenidos 12 años antes con una encuesta equivalente. La encuesta fue semiestructurada, con 17 preguntas, autocumplimentada, individual y anónima, con una muestra de 1108 alumnos de ambos sexos. De esa encuesta se utilizaron 7 preguntas específicas sobre drogas adictivas y una pregunta sobre consumo de medicamentos en general, con 46 opciones entre las que figuraban 10 denominaciones comerciales de benzodiacepinas, como drogas adictivas de prescripción. Para las comparaciones estadísticas se utilizó Chi cuadrado. El ranking de drogas utilizadas fue relativamente similar en 1998 y 2010 pero, exceptuando tabaco y “otras drogas" que se mantuvieron estables, el resto aumentó alrededor de 4 veces en el periodo. El 82,8% de los alumnos manifestó consumir alcohol (siempre + a veces); de 1 a 5 vasos semanales el 79%. En todas las Facultades, cerveza y Fernet encabezaron el ranquing de preferencias por bebidas alcohólicas. La prevalencia del consumo de tabaco en el total de la muestra se mantuvo constante en 1998 y 2010 (alrededor del 28%) pero el consumo entre Facultades fue variable y en Artes fue significativamente más elevado (42%). Siguen en el ranking marihuana con 10% de prevalencia, tranquilizantes con alrededor del 6% y cocaína con poco más del 1%. Finalmente “otras drogas" (Hachis, LSD, extasis, anabólicos, anfetaminas, “hongos") representaron solamente un 3% de prevalencia. Artes y Ciencias Políticas mostraron las mayores prevalencias de consumo y Derecho e Ingeniería las menores. Esto indica implementar acciones preventivas y correctivas particulares para cada Facultad.

A point mutation in the γ2 subunit of γ-aminobutyric acid type A receptors results in altered benzodiazepine binding site specificity

Benzodiazepines allosterically modulate γ-aminobutyric acid (GABA) evoked chloride currents of γ-aminobutyric acid type A (GABAA) receptors. Coexpression of either rat γ2 or γ3, in combination with α1 and β2 subunits, results both in receptors displaying high [3H]Ro 15-1788 affinity. However, receptors containing a γ3 subunit display a 178-fold reduced affinity to zolpidem as compared with γ2-containing receptors. Eight chimeras between γ2 and γ3 were constructed followed by nine different point mutations in γ2, each to the homologous amino acid residue found in γ3. Chimeric or mutant γ subunits were coexpressed with α1 and β2 in human embryonic kidney 293 cells to localize amino acid residues responsible for the reduced zolpidem affinity. Substitution of a methionine-to-leucine at position 130 of γ2 (γ2M130L) resulted in a 51-fold reduction in zolpidem affinity whereas the affinity to [3H]Ro 15-1788 remained unchanged. The affinity for diazepam was only decreased by about 2-fold. The same mutation resulted in a 9-fold increase in Cl 218872 affinity. A second mutation (γ2M57I) was found to reduce zolpidem affinity by about 4-fold. Wild-type and γ2M130L-containing receptors were functionally expressed in Xenopus oocytes. Upon mutation allosteric coupling between agonist and modulatory sites is preserved. Dose–response curves for zolpidem and for diazepam showed that the zolpidem but not the diazepam apparent affinity is drastically reduced. The apparent GABA affinity is not significantly affected by the γ2M130L mutation. The identified amino acid residues may define part of the benzodiazepine binding pocket of GABAA receptors. As the modulatory site in the GABAA receptor is homologous to the GABA site, and to all agonist sites of related receptors, γ2M130 may either point to a homologous region important for agonist binding in all receptors or define a new region not underlying this principle.

Benzodiazepine use in pregnancy and major malformations or oral cleft: meta-analysis of cohort and case-control studies

Objective: To determine if exposure to benzodiazepines during the first trimester of pregnancy increases risk of major malformations or cleft lip or palate.