Accelerated weight histogram method for exploring free energy landscapes.

Calculating free energies is an important and notoriously difficult task for molecular simulations. The rapid increase in computational power has made it possible to probe increasingly complex systems, yet extracting accurate free energies from these simulations remains a major challenge. Fully exploring the free energy landscape of, say, a biological macromolecule typically requires sampling large conformational changes and slow transitions. Often, the only feasible way to study such a system is to simulate it using an enhanced sampling method. The accelerated weight histogram (AWH) method is a new, efficient extended ensemble sampling technique which adaptively biases the simulation to promote exploration of the free energy landscape. The AWH method uses a probability weight histogram which allows for efficient free energy updates and results in an easy discretization procedure. A major advantage of the method is its general formulation, making it a powerful platform for developing further extensions and analyzing its relation to already existing methods. Here, we demonstrate its efficiency and general applicability by calculating the potential of mean force along a reaction coordinate for both a single dimension and multiple dimensions. We make use of a non-uniform, free energy dependent target distribution in reaction coordinate space so that computational efforts are not wasted on physically irrelevant regions. We present numerical results for molecular dynamics simulations of lithium acetate in solution and chignolin, a 10-residue long peptide that folds into a ß-hairpin. We further present practical guidelines for setting up and running an AWH simulation.

Prevalence of suicidality during pregnancy and the postpartum.

This review examined the available prevalence estimates of suicidality (suicide deaths, attempts, and ideation including thoughts of self harm) in pregnancy and the postpartum. Studies that used defined community or clinic samples were identified through multiple electronic databases and contacts with primary authors. Definitions of and measurement of suicide deaths, intentional self-harming behavior, suicide attempts, and thoughts of death and self-harm were varied and are described with each study. While suicide deaths and attempts are lower during pregnancy and the postpartum than in the general population of women, when deaths do occur, suicides account for up to 20% of postpartum deaths. Self-harm ideation is more common than attempts or deaths, with thoughts of self-harm during pregnancy and the postpartum ranging from 5 to 14%. The risk for suicidality is significantly elevated among depressed women during the perinatal period, and suicide has been found to be the second or leading cause of death in this depressed population.

ECT stimulus intensity: are present ECT devices too limited?

OBJECTIVE: The maximum output charge for ECT devices is limited to 576 millicoulombs in the United States, although there are no data ensuring that this limit will allow consistently effective treatments. The authors examined whether this limit has a negative impact on therapeutic response and, therefore, whether a higher stimulus charge should be available. METHOD: They retrospectively reviewed the records of 471 patients who received a clinical index course of ECT at Duke University between 1991 and 1998. These patients received conservative stimulus dosing of 2.25 times seizure threshold for unilateral ECT and 1.5 times seizure threshold for bilateral ECT. RESULTS: Seventy-two (15%) of the 471 patients required the maximum stimulus intensity during their index ECT course. Of these, 24 (5% of the total) had either a short EEG seizure (less than 25 seconds) or had no seizure at the maximum level. Strategies to augment therapeutic response with caffeine, ketamine, or hyperventilation were used in 14 of the 24 patients, and data on therapeutic response were available for 22 of the 24. Only seven (32%) of these 22 patients were considered ECT responders, compared with 242 (66%) of the remaining 364 patients for whom data on response to ECT were available. Older age and pre-ECT course EEG slowing were predictors of requiring the maximum stimulus level. CONCLUSIONS: The maximum available stimulus output was therapeutically insufficient for 5% of the patients studied even when available means to augment response were instituted. This percentage would likely be even larger with the use of a less conservative dosing protocol for unilateral ECT. Increases in maximum stimulus output for ECT devices should be considered as a means to ensure adequate treatment response.

The development and retrospective testing of an electroencephalographic seizure quality-based stimulus dosing paradigm with ECT.

The optimization of electroconvulsive therapy (ECT) stimulus dosing remains uncertain. Previous work suggests the potential utility of ictal EEG models of seizure adequacy, but such models have never been tested for their ability to improve the clinical dosing of ECT treatments. Using data from 149 depressed patients, the authors developed an ictal electroencephalographic (EEG) model that can discriminate seizures produced by more therapeutically effective and less efficacious types of stimuli. They retrospectively determined how stimulus dosing according to this seizure adequacy-based model would have differed from that actually used in an additional 61 patients who received ECT according to a standard clinical dose-titration and EEG seizure duration-based dosing strategy. Although the model indicated an increase in stimulus intensity at some point during the ECT treatment course in 23 of 61 patients, only 5 of these 23 actually received a clinical increase in stimulus intensity. The patients who did not receive this increase had a significantly diminished therapeutic response compared with the other patients. Conversely, the model also indicated that an increase in stimulus intensity that occurred clinically might have been unnecessary to achieve therapeutic efficacy in 11% of the patients. This study provides preliminary evidence that ictal EEG models have the potential to make clinically relevant seizure adequacy distinctions among ECT treatments. Further prospective work is indicated to determine the clinical utility of such models.

The use of flumazenil in the anxious and benzodiazepine-dependent ECT patient.

Many patients who receive electroconvulsive therapy (ECT) are benzodiazepine dependent or are anxious and require benzodiazepine drugs. Because these agents may diminish the therapeutic effectiveness of ECT, we explored the dosing, safety, and efficacy of pre-ECT flumazenil administration, a benzodiazepine-competitive antagonist, in patients receiving benzodiazepine medications. We report our experience with 35 patients who received both flumazenil and benzodiazepine drugs during their ECT course. We compared seizure duration with and without flumazenil and compared treatment efficacy to 49 patients who received ECT without either of these medications. Flumazenil could be safely administered with ECT. A few subjects taking higher chronic benzodiazepine dosages experienced breakthrough anxiety or withdrawal symptoms, which were well managed by dosing flumazenil immediately before the anesthetic agent and by immediate posttreatment benzodiazepine administration. A dose of 0.4-0.5 mg was adequate for all but those taking the highest benzodiazepine dosages, where 0.8-1.0 mg resulted in a clinically more effective reversal. No differences in efficacy or seizure duration were found as a function of flumazenil administration. Flumazenil offers the promise of safe and effective ECT in patients receiving benzodiazepine drugs. Follow-up outcome investigation on a random assignment basis will be necessary for definitive assessment of the value of flumazenil. In addition, the direct effect of benzodiazepine drugs and the flumazenil/benzodiazepine combination on ECT seizures remains to be determined.

Characterization of production and enzyme properties of an endo-beta-1,4- glucanase from Bacillus subtilis CK-2 isolated from compost soil.

Bacillus subtilis CK-2, isolated from garden organic waste compost, was found to have high hydrolytic activity against carboxymethylcellulose (CMC) due to the secretion of an endo-beta-1,4- glucanase. Enzyme production was related to the sporulation process, and was regulated by the concentration of readily metabolizable carbohydrate in growth medium. Enzyme production did not require CMC or other cellulose containing materials. The endo-beta-1,4-glucanase activity was optimal at pH 5.6-5.8 and at 65 degrees C, and achieved thermal stability up to 55 degrees C. The activity was inhibited by Hg2+. The purified enzyme gave a single band corresponding to a MW of 35.5 kDa on SDS-PAGE, while the Sephadex G-75 chromatography revealed a molecular weight of the active enzyme around 70 kDa, indicating a dimeric form of the active enzyme. The enzyme activity was irreversibly inhibited by SDS. Native PAGE and IEF revealed three different isoelectric forms of the enzyme, all with an identical N-terminal amino-acid sequence.

Nucleotide sequence of an endo-beta-1,4-glucanase gene from Bacillus subtilis CK-2.

The gene encoding endo-beta-1,4-glucanase in Bacillus subtilis CK-2 was cloned into Escherichia coli DH5 alpha, and the nucleotide sequence determined. The 1500 bp gene encodes a protein of 499 amino-acid residues with a calculated molecular mass of 55,261, and is equipped with a typical B. subtilis signal peptide. Nucleotide sequence comparison revealed only 2 basepairs deviation between this gene and the endo-beta-1,4-glucanase gene of B. subtilis PAP115, and 93% to 95% homology was found between the amino acid sequences of these enzymes and other B. subtilis endo-beta-1,4-glucanases. Regions of similarity were also observed between the carboxy-terminal part of these enzymes and the part of the B. lautus PL236 celA enzyme constituting the cellulose-binding domain.