Identifying the Causes of Unexplained Dyspnea at High Altitude Using Normobaric Hypoxia with Echocardiography

Exposure to high altitude results in hypobaric hypoxia, leading to physiological changes in the cardiovascular system that may result in limiting symptoms, including dyspnea, fatigue, and exercise intolerance. However, it is still unclear why some patients are more susceptible to high-altitude symptoms than others. Hypoxic simulation testing (HST) simulates changes in physiology that occur at a specific altitude by asking the patients to breathe a mixture of gases with decreased oxygen content. This study aimed to determine whether the use of transthoracic echocardiography (TTE) during HST can detect the rise in right-sided pressures and the impact of hypoxia on right ventricle (RV) hemodynamics and right to left shunts, thus revealing the underlying causes of high-altitude signs and symptoms. A retrospective study was performed including consecutive patients with unexplained dyspnea at high altitude. HSTs were performed by administrating reduced FiO2 to simulate altitude levels specific to patients' history. Echocardiography images were obtained at baseline and during hypoxia. The study included 27 patients, with a mean age of 65 years, 14 patients (51.9%) were female. RV systolic pressure increased at peak hypoxia, while RV systolic function declined as shown by a significant decrease in the tricuspid annular plane systolic excursion (TAPSE), the maximum velocity achieved by the lateral tricuspid annulus during systole (S' wave), and the RV free wall longitudinal strain. Additionally, right-to-left shunt was present in 19 (70.4%) patients as identified by bubble contrast injections. Among these, the severity of the shunt increased at peak hypoxia in eight cases (42.1%), and the shunt was only evident during hypoxia in seven patients (36.8%). In conclusion, the use of TTE during HST provides valuable information by revealing the presence of symptomatic, sustained shunts and confirming the decline in RV hemodynamics, thus potentially explaining dyspnea at high altitude. Further studies are needed to establish the optimal clinical role of this physiologic method.

Efficacy and Safety of Oral Small Molecule Glucagon-Like Peptide 1 Receptor Agonist Danuglipron for Glycemic Control Among Patients With Type 2 Diabetes: A Randomized Clinical Trial

Importance

Currently available glucagon-like peptide 1 receptor (GLP-1R) agonists for treating type 2 diabetes (T2D) are peptide agonists that require subcutaneous administration or strict fasting requirements before and after oral administration.

Objective

To investigate the efficacy, safety, and tolerability of multiple dose levels of the novel, oral, small molecule GLP-1R agonist danuglipron over 16 weeks.

Design, Setting, and Participants

A phase 2b, double-blind, placebo-controlled, parallel-group, 6-group randomized clinical trial with 16-week double-blind treatment period and 4-week follow-up was conducted from July 7, 2020, to July 7, 2021. Adults with T2D inadequately controlled by diet and exercise, with or without metformin treatment, were enrolled from 97 clinical research sites in 8 countries or regions.

Interventions

Participants received placebo or danuglipron, 2.5, 10, 40, 80, or 120 mg, all orally administered twice daily with food for 16 weeks. Weekly dose escalation steps were incorporated to achieve danuglipron doses of 40 mg or more twice daily.

Main Outcomes and Measures

Change from baseline in glycated hemoglobin (HbA1c, primary end point), fasting plasma glucose (FPG), and body weight were assessed at week 16. Safety was monitored throughout the study period, including a 4-week follow-up period.

Results

Of 411 participants randomized and treated (mean [SD] age, 58.6 [9.3] years; 209 [51%] male), 316 (77%) completed treatment. For all danuglipron doses, HbA1c and FPG were statistically significantly reduced at week 16 vs placebo, with HbA1c reductions up to a least squares mean difference vs placebo of -1.16% (90% CI, -1.47% to -0.86%) for the 120-mg twice daily group and FPG reductions up to a least squares mean difference vs placebo of -33.24 mg/dL (90% CI, -45.63 to -20.84 mg/dL). Body weight was statistically significantly reduced at week 16 compared with placebo in the 80-mg twice daily and 120-mg twice daily groups only, with a least squares mean difference vs placebo of -2.04 kg (90% CI, -3.01 to -1.07 kg) for the 80-mg twice daily group and -4.17 kg (90% CI, -5.15 to -3.18 kg) for the 120-mg twice daily group. The most commonly reported adverse events were nausea, diarrhea, and vomiting.

Conclusions and Relevance

In adults with T2D, danuglipron reduced HbA1c, FPG, and body weight at week 16 compared with placebo, with a tolerability profile consistent with the mechanism of action.

Trial Registration

ClinicalTrials.gov Identifier: NCT03985293.

Peripherally inserted central cathether migration in neonates: Incidence, timing and risk factors

BACKGROUND

PICC line use is a common practice in neonatal units, but it is associated with various complications. Catheter migration is the most common complication in neonates. Periodic imaging is recommended to monitor the tip position of the PICCs, but the optimal frequency is undetermined. The incidence, timing and risk factors that are associated with PICC migration have not been fully investigated beyond 24 hrs in neonates. The aim of the study was to determine the incidence, timing and risk factors that are associated with peripherally inserted central venous catheter (PICC) migration in neonates.

METHODS

This was a single center, retrospective study of 168 PICCs placed in 141 neonates in the neonatal intensive care unit (NICU) between 2015 and 2016. The incidence of catheter migration was determined radiographically at 12-24 hrs and every third day after insertion until it was removed.

RESULTS

Overall incidence of PICC migration was 28%and most commonly was detected within the first three days after PICC placement (83%). The incidence of PICC migration was higher in males. The PICC migration was associated with difficulty advancing the PICC at the time of insertion and PICC dressing change.

CONCLUSION

Serial evaluation of PICC placement in neonates is required to maintain proper position. Based on our experience in our unit, we recommend periodic imaging at 12-24 hrs and on the third day after PICC placement as most migration occurred within three days after insertion.

First-in-human, randomized dose-escalation study of the safety, tolerability, pharmacokinetics, pharmacodynamics and immunogenicity of PF-06480605 in healthy subjects

AIMS

Human genetic, tissue expression, proteomics, transcriptomics and nonclinical studies implicate tumour necrosis factor α-like ligand 1A (TL1A) as a novel target in inflammatory bowel disease (IBD). PF-06480605, a fully human immunoglobulin G1 monoclonal antibody, targets TL1A. This first-in-human, Phase 1, dose-escalation study assessed safety, tolerability, pharmacokinetics, pharmacodynamics and immunogenicity of intravenous (IV) and subcutaneous (SC) PF-06480605 in healthy subjects (NCT01989143).

METHODS

Ninety-two subjects were randomized to single ascending doses (SAD), PF-06480605 1 mg, 3 mg, 10 mg, 30 mg, 100 mg, 300 mg, 600 mg or 800 mg IV, or multiple ascending doses (MAD), PF-06480605 3 × 500 mg IV, or 3 × 30 mg, 3 × 100 mg, or 3 × 300 mg SC every 2 weeks for three doses, or placebo. Safety, tolerability, pharmacokinetics, immunogenicity profiles and total TL1A, anti-drug antibody (ADA) and neutralizing antibody (NAb) levels were assessed at pre-determined times.

RESULTS

PF-06480605 SAD up to 800 mg IV and MAD up to 300 mg ×3 SC and 500 mg ×3 IV were well tolerated. Overall, there were 45 and 44 treatment-emergent adverse events in SAD and MAD cohorts, respectively, and no deaths or serious adverse events. PF-06480605 exposure generally increased dose-dependently. ADA and NAb levels did not impact safety, pharmacokinetics, or pharmacodynamics at higher doses. Target engagement was demonstrated through dose-dependent differences in serum total soluble TL1A concentrations for PF-06480605 vs placebo cohorts.

CONCLUSIONS

PF-06480605 was generally well tolerated, and binding of soluble TL1A was maintained throughout the dose interval, supporting further study of PF-06480605 in patients with IBD and other inflammatory conditions.

Phase II evaluation of anti-MAdCAM antibody PF-00547659 in the treatment of Crohn's disease: report of the OPERA study

OBJECTIVE

This phase II, randomised, double-blind, placebo-controlled clinical trial was designed to evaluate the efficacy and safety of PF-00547659, a fully human monoclonal antibody that binds to human mucosal addressin cell adhesion molecule (MAdCAM) to selectively reduce lymphocyte homing to the intestinal tract, in patients with moderate-to-severe Crohn's disease (CD).

DESIGN

Eligible adults were aged 18-75 years, with active moderate-to-severe CD (Crohn's Disease Activity Index (CDAI) 220-450), a history of failure or intolerance to antitumour necrosis factor and/or immunosuppressive agents, high-sensitivity C reactive protein >3.0 mg/L and ulcers on colonoscopy. Patients were randomised to PF-00547659 22.5 mg, 75 mg or 225 mg or placebo. The primary endpoint was CDAI 70-point decrease from baseline (CDAI-70) at week 8 or 12.

RESULTS

In all, 265 patients were eligible for study entry. Although CDAI-70 response was not significantly different with placebo versus PF-00547659 treatment at weeks 8 or 12, remission rate was greater in patients with higher baseline C reactive protein (>5 mg/L vs >18.8 mg/L, respectively). Soluble MAdCAM decreased significantly from baseline to week 2 in a dose-related manner and remained low during the study in PF-00547659-treated patients. Circulating β7+ CD4+ central memory T-lymphocytes increased at weeks 8 and 12 with PF-00547659 treatment. No safety signal was seen.

CONCLUSIONS

Clinical endpoint differences between PF-00547659 and placebo did not reach statistical significance in patients with moderate-to-severe CD. PF-00547659 was pharmacologically active, as shown by a sustained dose-related decrease in soluble MAdCAM and a dose-related increase in circulating β7+ central memory T cells.

TRIAL REGISTRATION NUMBER

NCT01276509; Results.

Dietary Patterns and Colorectal Cancer Risk: A Review of 17 Years of Evidence (2000-2016)

PURPOSE OF REVIEW

Colorectal cancer (CRC) is a global public health problem, with an estimated 1.4 million cases diagnosed worldwide in 2012. Evidence suggests that diet may be important for primary prevention.

RECENT FINDINGS

The 2017 WCRF/AICR Continuous Update Project on colorectal cancer concluded that there is convincing evidence linking several individual dietary factors with CRC risk but the evidence for dietary patterns was limited and inconclusive. Also, previous reviews and meta-analyses have not critically synthesized various dietary patterns. This review synthesized data from dietary patterns studies over a 17-year period from 2000 to 2016.

SUMMARY

We included 49 studies (28 cohort and 21 case-control) that examined the association of index-based and empirically-derived dietary patterns and CRC risk. A synthesis of food group components comprising the different index-based and empirically-derived patterns revealed two distinct dietary patterns associated with CRC risk. A "healthy" pattern, generally characterized by high intake of fruits and vegetables, wholegrains, nuts and legumes, fish and other seafood, milk and other dairy products, was associated with lower CRC risk. In contrast, the "unhealthy" pattern, characterized by high intakes of red meat, processed meat, sugar-sweetened beverages, refined grains, desserts and potatoes was associated with higher CRC risk. It is notable that the number of food groups, the intake quantity, the exact types of foods in each food group, differed between populations, yet the two dietary patterns remained consistent across regions, especially in empirically-derived patterns, an indication of the high reproducibility of these patterns. However, findings for CRC risk in both index-based and empirically-derived patterns, differed by sex, with stronger associations among men than women; study design, a higher proportion of case-control studies reported significant findings compared to prospective studies. Consuming a dietary pattern high in fruits and vegetables and low in meats and sweets is protective against CRC risk. However, important questions remain about mechanisms underlying differences by sex; life-course timing of exposure to dietary patterns; interaction of dietary patterns with the microbiome or with lifestyle factors including physical activity; and elucidation of subsite differences.

Pharmacist independent prescribing in critical care: results of a national questionnaire to establish the 2014 UK position

OBJECTIVES

Clinical pharmacist practice is well established in the safe and effective use of medicines in the critically ill patient. In the UK, independent pharmacist prescribers are generally recognised as a valuable and desirable resource. However, currently, there are only anecdotal reports of pharmacist-independent prescribing in critical care. The aim of this questionnaire was to determine the current and proposed future independent prescribing practice of UK clinical pharmacists working in adult critical care.

METHODS

The questionnaire was distributed electronically to UK Clinical Pharmacy Association members (closed August 2014).

KEY FINDINGS

There were 134 responses to the questionnaire (response rate at least 33%). Over a third of critical care pharmacists were practising independent prescribers in the specialty, and 70% intended to be prescribers within the next 3 years. Pharmacists with ≥5 years critical care experience (P < 0.001) or worked in a team (P = 0.005) were more likely to be practising independent prescribers. Pharmacists reported significant positives to the use of independent prescribing in critical care both in patient care and job satisfaction. Independently, prescribing was routine in: dose adjustment for multi-organ failure, change in route or formulation, correction prescribing errors, therapeutic drug monitoring and chronic medication. The majority of pharmacist prescribers reported they spent ≤5% of their clinical time prescribing and accounted for ≤5% of new prescriptions in critical care patients.

CONCLUSIONS

Most critical care pharmacists intend to be practising as independent prescribers within the next 3 years. The extent and scope of critical care pharmacist prescribing appear to be of relatively low volume and within niche prescribing areas.

Do food blogs serve as a source of nutritionally balanced recipes? An analysis of 6 popular food blogs

OBJECTIVE

To determine whether sampled food blogs provide nutritionally balanced recipes.

METHODS

Two entree recipes per season, per year (2010-2011) were selected from 6 highly ranked food blogs (n = 96). Food Processor Nutrition and Fitness software was used to analyze sodium, saturated fat, and energy content. Analysis was separated by protein type (vegetarian, poultry, red meat, and seafood).

RESULTS

Recipes met energy recommendations but were excessive in saturated fat and sodium. Vegetarian and seafood recipes were significantly lower in risk nutrients compared with red meat and poultry recipes. Red meat recipes were not significantly different from poultry recipes for risk nutrients studied; poultry recipes were higher in sodium and energy compared with red meat recipes.

CONCLUSIONS AND IMPLICATIONS

The public should be aware of the nutritional limitations of popular food blogs; dietitians could assist in modifying blog recipes for individuals and partner with bloggers to improve the nutritional profile of recipes.

Methodology for adding glycemic index to the National Health and Nutrition Examination Survey nutrient database

Generating valid estimates of dietary glycemic index (GI) and glycemic load (GL) has been a challenge in nutritional epidemiology. The methodologic issues may have contributed to the wide variation of GI/GL associations with health outcomes observed in existing literature. We describe a standardized methodology for assigning GI values to items in the National Health and Nutrition Examination Survey (NHANES) nutrient database using the new International Tables to develop research-driven, systematic procedures and strategies to estimate dietary GI/GL exposures of a nationally representative population sample. Nutrient databases for NHANES 2003-2006 contain information on 3,155 unique foods derived from the US Department of Agriculture National Nutrient Database for Standard Reference versions 18 and 20. Assignment of GI values were made to a subset of 2,078 carbohydrate-containing foods using systematic food item matching procedures applied to 2008 international GI tables and online data sources. Matching protocols indicated that 45.4% of foods had identical matches with existing data sources, 31.9% had similar matches, 2.5% derived GI values calculated with the formula for combination foods, 13.6% were assigned a default GI value based on low carbohydrate content, and 6.7% of GI values were based on data extrapolation. Most GI values were derived from international sources; 36.1% were from North American product information. To confirm data assignments, dietary GI and GL intakes of the NHANES 2003-2006 adult participants were estimated from two 24-hour recalls and compared with published studies. Among the 3,689 men and 4,112 women studied, mean dietary GI was 56.2 (men 56.9, women 55.5), mean dietary GL was 138.1 (men 162.1, women 116.4); the distribution of dietary GI was approximately normal. Estimates of population GI and GL compare favorably with other published literature. This methodology of adding GI values to an existing population nutrient database utilized systematic matching protocols and the latest comprehensive data sources on food composition. The database can be applied in clinical and survey research settings where there is interest in estimating individual and population dietary exposures and relating them to health outcomes.

Dietary Patterns and the Risk of Colorectal Cancer

Diet and lifestyle play a significant role in the development of colorectal cancer, but the full complexity of the association is not yet understood. Dietary pattern analysis is an important new technique that may help to elucidate the relationship. This review examines the most common techniques for extrapolating dietary patterns and reviews dietary pattern/colorectal cancer studies published between September 2011 and August 2012. The studies reviewed are consistent with prior research but include a more diverse international population. Results from investigations using a priori dietary patterns (i.e., diet quality scores) and a posteriori methods, which identify existing eating patterns (i.e., principal component analysis), continue to support the benefits of a plant-based diet with some dairy as a means to lower the risk of colorectal cancer, whereas a diet high in meats, refined grains, and added sugar appears to increase risk. The association between colorectal cancer and alcohol remains unclear.

Dietary patterns of women are associated with incident abdominal obesity but not metabolic syndrome

Data on the relationship between empirical dietary patterns and metabolic syndrome (MetS) and its components in prospective study designs are limited. In addition, demographic and lifestyle determinants of MetS may modify the association between dietary patterns and the syndrome. We prospectively examined the relationship between empirically derived patterns and MetS and MetS components among 1146 women in the Framingham Offspring/Spouse cohort. They were aged 25-77 y with BMI ≥18.5 kg/m(2) and free of cardiovascular disease, diabetes, cancer, and MetS at baseline, and followed for a mean of 7 y. Five dietary patterns, Heart Healthier, Lighter Eating, Wine and Moderate Eating, Higher Fat, and Empty Calorie, were previously identified using cluster analysis from food intake collected using a FFQ. After adjusting for potential confounders, we observed lower odds for abdominal obesity for Higher Fat [OR = 0.48 (95% CI: 0.25, 0.91)] and Wine and Moderate Eating clusters [OR = 0.28 (95% CI: 0.11, 0.72)] compared with the Empty Calorie cluster. Additional adjustment for BMI somewhat attenuated these OR [Higher Fat OR = 0.52 (95% CI: 0.27, 1.00); Wine and Moderate Eating OR = 0.34 (95% CI: 0.13, 0.89)]. None of the clusters was associated with MetS or other MetS components. Baseline smoking status and age did not modify the relation between dietary patterns and MetS. The Higher Fat and Wine and Moderate Eating patterns showed an inverse association with abdominal obesity; certain foods might be targeted in these habitual patterns to achieve optimal dietary patterns for MetS prevention.

Associations of carotid artery intima-media thickness (IMT) with risk factors and prevalent cardiovascular disease: comparison of mean common carotid artery IMT with maximum internal carotid artery IMT

OBJECTIVE

The goal of this study was to compare internal carotid artery (ICA) intima-media thickness (IMT) with common carotid artery (CCA) IMT as global markers of cardiovascular disease (CVD).

METHODS

Cross-sectional measurements of the mean CCA IMT and maximum ICA IMT were made on ultrasound images acquired from the Framingham Offspring cohort (n = 3316; mean age, 58 years; 52.7% women). Linear regression models were used to study the associations of the Framingham risk factors with CCA and ICA IMT. Multivariate logistic regression models and receiver operating characteristic (ROC) curve analysis were used to compare the associations of prevalent CVD with CCA and ICA IMT and determine sensitivity and specificity.

RESULTS

The association between age and the mean CCA IMT corresponded to an increase of 0.007 mm/y; the increase was 0.037 mm/y for the ICA IMT. Framingham risk factors accounted for 28.6% and 27.5% of the variability in the CCA and ICA IMT, respectively. Age and gender contributed 23.5% to the variability of the CCA IMT and 22.5% to that of the ICA IMT, with the next most important factor being systolic blood pressure (1.9%) for the CCA IMT and smoking (1.6%) for the ICA IMT. The CCA IMT and ICA IMT were statistically significant predictors of prevalent CVD, with the ICA IMT having a larger area under the ROC curve (0.756 versus 0.695).

CONCLUSIONS

Associations of risk factors with CCA and ICA IMT are slightly different, and both are independently associated with prevalent CVD. Their value for predicting incident cardiovascular events needs to be compared in outcome studies.

Proton transport mechanism of bacteriorhodopsin as revealed by site-specific mutagenesis and protein sequence variability

A large share of the current ideas about the mechanism of proton transport by bacteriorhodopsin has emerged from studies of site-specific mutants. This review is an attempt to check some of these ideas against the natural variability in the primary structure of the protein.

Coupling of the reisomerization of the retinal, proton uptake, and reprotonation of Asp-96 in the N photointermediate of bacteriorhodopsin

In the N to O reaction of the bacteriorhodopsin photocycle, Asp-96 is protonated from the cytoplasmic surface, and coupled to this, the retinal isomerizes from 13-cis,15-anti back to the initial all-trans configuration. To dissect the two steps, and to better understand how and why they occur, we describe the properties of two groups of site-specific mutants in which the N intermediate has greatly increased lifetime. In the first group, with the mutations near the retinal, an unusual N state is produced in which the retinal is 13-cis,15-anti but Asp-96 has a protonated carboxyl group. The apparent pK(a) for the protonation is 7.5, as in the wild-type. It is likely that here the interference with N decay is the result of steric conflict of side-chains with the retinal or with the side-chain of Lys-216 connected to the retinal, which delays the reisomerization after protonation of Asp-96. In the second group, with the mutations located near Asp-96 or between Asp-96 and the cytoplasmic surface, reprotonation of Asp-96 is strongly perturbed. The reisomerization of the retinal occurs only after recovery from a long-living protein conformation in which reprotonation of Asp-96 is either entirely blocked or blocked at low pH.

The validity of the interviewer severity ratings in groups of ASI interviewers with varying training

AIMS

This study evaluated the hypothesis that the subjective interviewer severity rating (ISR) summary indices of the intake Addiction Severity Index (ASI) of less trained interviewers are less valid than those of more highly trained interviewers.

DESIGN

Baseline ASIs from three completed studies whose interviewers varied in degree of initial ASI training and subsequent quality assurance monitoring were examined. Associations between baseline ISRs and three other sets of ASI summary indices not based on interviewer ratings-composite scores, clinical indices and evaluation indices-were compared for three groups of interviewers with varying amounts of training. The assumption underlying these analyses was that more reliable ISRs, found in more trained interviewers, would be more highly associated with the other more objective indices.

SETTING

Methadone maintenance patients in the Philadelphia and New York City areas.

PARTICIPANTS

Thirty-five interviewers with the most intense training who administered 295 interviews; 10 interviewers with an intermediate level of training who administered 763 interviews; and eight identified (and other unidentified) least trained interviewers who administered a total of 276 interviews. Measurements and methods. Four sets of summary indices from the above ASIs. Both bivariate and multivariate analyses were performed.

FINDINGS

The study found that the validity of the validity of ISRs was greater in more trained interviewers.

CONCLUSIONS

Greater training and subsequent monitoring of ASI interviewers generally appears to be associated with increased ISR validity.

Photochemical reaction cycle and proton transfers in Neurospora rhodopsin

It was recently found that NOP-1, a membrane protein of Neurospora crassa, shows homology to haloarchaeal rhodopsins and binds retinal after heterologous expression in Pichia pastoris. We report on spectroscopic properties of the Neurospora rhodopsin (NR). The photocycle was studied with flash photolysis and time-resolved Fourier-transform infrared spectroscopy in the pH range 5-8. Proton release and uptake during the photocycle were monitored with the pH-sensitive dye, pyranine. Kinetic and spectral analysis revealed six distinct states in the NR photocycle, and we describe their spectral properties and pH-dependent kinetics in the visible and infrared ranges. The phenotypes of the mutant NR proteins, D131E and E142Q, in which the homologues of the key carboxylic acids of the light-driven proton pump bacteriorhodopsin, Asp-85 and Asp-96, were replaced, show that Glu-142 is not involved in reprotonation of the Schiff base but Asp-131 may be. This implies that, if the NR photocycle is associated with proton transport, it has a low efficiency, similar to that of haloarchaeal sensory rhodopsin II. Fourier-transform Raman spectroscopy revealed unexpected differences between NR and bacteriorhodopsin in the configuration of the retinal chromophore, which may contribute to the less effective reprotonation switch of NR.

Feelings in context: countertransference and the real world in feminist therapy

The concept of countertransference has been seen as problematic by feminist therapists. However, feminist therapy theory is intensely interested in the symbolic levels of the relationships between therapists and clients, with an emphasis on how the here and now social context informs and transforms those symbols. This article describes a feminist perspective on the therapist's symbolic relationships to clients, and the positive and challenging ramifications of those symbolic encounters.

Light-induced rotation of a transmembrane alpha-helix in bacteriorhodopsin

Spin labeling EPR spectroscopy has been used to characterize light-induced conformational changes of bacteriorhodopsin (bR). Pairs of nitroxide spin labels were attached to engineered cysteine residues at strategic positions near the cytoplasmic ends of transmembrane alpha-helices B, F, and G in order to monitor distance changes upon light activation. The EPR analysis of six doubly labeled bR mutants indicates that the cytoplasmic end of helix F not only tilts outwards, but also rotates counter-clockwise during the photocycle. The direction of the rotation of helix F is the opposite of the clockwise rotation previously reported for bovine rhodopsin. The opposite chirality of the F helix rotation in the two systems is perhaps related to the differences in the cis-trans photoisomerization of the retinal in the two proteins. Using time-resolved EPR, we monitored the rotation of helix F also in real time, and found that the signal from the rotation arises concurrently with the reprotonation of the retinal Schiff base.

Reconciling crystallography and mutagenesis: a synthetic approach to the creation of a comprehensive model for proton pumping by bacteriorhodopsin

As a result of the number of new high-resolution structures of the pigment and some of its photointermediates, a realistic model for the functioning of bacteriorhodopsin seems to be finally emerging. However, lack of structural information for some of the key functional states, and contradictions between some published structural models, argue for the use of the synthetic approach, one that includes use of data from both crystallographic and mutagenesis studies. The role of mutagenesis in this synthetic approach falls into two categories. First, to provide additional structural information, and second, to test the predictions of structural models by studying mutant phenotypes. This review urges critical comparisons of the structural and mutagenesis data, as there are problems with their selective and indiscriminate use.

Origins of deuterium kinetic isotope effects on the proton transfers of the bacteriorhodopsin photocycle

Deuterium kinetic isotope effects (KIE) were measured, and proton inventory plots were constructed, for the rates of reactions in the photocycles of wild-type bacteriorhodopsin and several site-specific mutants. Consistent with earlier reports from many groups, very large KIEs were observed for the third (and largest) rise component for the M state and for the decay of the O state, processes both linked to proton transfers in the extracellular region. The proton inventory plots (ratio of reaction rates in mixtures of H(2)O and D(2)O to that in H(2)O vs mole fraction of D(2)O) were approximately linear for the first and second M rise components and for M decay, as well as for O decay, indicating that the rates of these reactions are limited by simple proton transfer. Uniquely, the third rise component of M (and in the D96N mutant also a fourth rise component) exhibited a strongly curved proton inventory plot, suggesting that its rate, which largely accounts for the rate of deprotonation of the retinal Schiff base, depends on a complex multiproton process. This curvature is observed also in the E194Q, E204Q, and Y57F mutants but not in the R82A mutant. From these findings, and from the locations of bound water in the extracellular region in the crystal structure of the protein [Luecke, Schobert, Richter, Cartailler, and Lanyi (1999) J. Mol. Biol. 291, 899-911], we suspect that the effects of deuterium substitution on the formation of the M state originate from cooperative rearrangements of the extensively hydrogen-bonded water molecules 401, 402, and 406 near Asp-85 and Arg-82.

Fourier transform infrared spectra of a late intermediate of the bacteriorhodopsin photocycle suggest transient protonation of Asp-212

We measured time-resolved difference spectra, in the visible and the infrared, for the Glu-194 and Glu-204 mutants of bacteriorhodopsin and detected an anomalous O state, labeled O', in addition to the authentic O intermediate, before recovery of the initial state in the photocycle. The O' intermediate exhibits prominent bands at 1712 cm(-1) (positive) and 1387 cm(-1) (negative). These bands arise with the same time constant as the deprotonation of Asp-85. Both bands are shifted to lower frequency upon labeling of the protein with [4-(13)C]aspartic acid. The former band, but not the latter, is shifted in D2O. These shifts identify the two bands as the carboxyl stretch of a protonated aspartic acid and the symmetric carbonyl stretch of an unprotonated aspartate, respectively, and suggest that in O' an initially anionic aspartate enters into protonation equilibrium with Asp-85. Elimination of the few other candidates, on various grounds, identifies Asp-212 as the unknown residue. It is possible, therefore, that in the last step of the photocycle of the mutants studied the proton released from Asp-85 is conducted to the extracellular surface via Asp-212. An earlier report of a weak band at 1712 cm(-1) late in the wild-type photocycle [Zscherp and Heberle (1997) J. Phys. Chem. B 101, 10542-10547] suggests that Asp-212 might play this role in the wild-type protein also.

Binding of calcium ions to bacteriorhodopsin

Adding Ca2+ or other cations to deionized bacteriorhodopsin causes a blue to purple color shift, a result of deprotonation of Asp85. It has been proposed by different groups that the protonation state of Asp85 responds to the binding of Ca2+ either 1) directly at a specific site in the protein or 2) indirectly through the rise of the surface pH. We tested the idea of specific binding of Ca2+ and found that the surface pH, as determined from the ionization state of eosin covalently linked to engineered cysteine residues, rises about equally at both extracellular and cytoplasmic surfaces when only one Ca2+ is added. This precludes binding to a specific site and suggests that rather than decreasing the pKa of Asp85 by direct interaction, Ca2+ increases the surface pH by binding to anionic lipid groups. As Ca2+ is added the surface pH rises, but deprotonation of Asp85 occurs only when the surface pH approaches its pKa. The nonlinear relationship between Ca2+ binding and deprotonation of Asp85 from this effect is different in the wild-type protein and in various mutants and explains the observed complex and varied spectral titration curves.

Functional roles of aspartic acid residues at the cytoplasmic surface of bacteriorhodopsin

The functions of the four aspartic acid residues in interhelical loops at the cytoplasmic surface of bacteriorhodopsin, Asp-36, Asp-38, Asp-102, and Asp-104, were investigated by studying single and multiple aspartic acid to asparagine mutants. The same mutants were examined also with the additional D96N residue replacement. The kinetics of the M and N intermediates of the photochemical cycles of these recombinant proteins were affected only in a minor, although self-consistent, way. When residue 38 is an aspartate and anionic, it makes the internal proton exchange between the retinal Schiff base and Asp-96 about 3 times more rapid, and events associated with the reisomerization of retinal to all-trans about 3 times slower. Asp-36 has the opposite effect on these processes, but to a smaller extent. Asp-102 and Asp-104 have even less or none of these effects. Of the four aspartates, only Asp-36 could play a direct role in proton uptake at the cytoplasmic surface. In the 13 bacterioopsin sequences now available, only this surface aspartate is conserved.

Methadone-maintenance outcomes for Hispanic and African-American men and women

Six-month methadone-maintenance response and outcome were examined for African-American and Hispanic men and women in a large urban sample. A consistent pattern of improvement was indicated for both races and genders on the addiction severity index (ASI). There were virtually no statistically significant differences in ASI outcomes between Hispanics and African-Americans and men and women using conventional analysis of variance (ANOVA) procedures. Results from an additional equivalence analysis, however, indicated that baseline to 6-month changes for the different groups were generally not similar enough to consider them equivalent. Urine toxicologies obtained during the 6-month treatment period were also not statistically equivalent by race and gender. Evaluating outcomes by gender and race are discussed, as are the implications of using equivalence tests when examining group differences.

Rates of tuberculosis infection in healthcare workers providing services to HIV-infected populations. Terry Beirn Community Programs for Clinical Research on AIDS

OBJECTIVE

To assess the prevalence of tuberculosis (TB) or a positive skin test in healthcare workers (HCWs) providing services to human immunodeficiency virus (HIV)-infected individuals and to determine prospectively the incidence of new infections in this population.

DESIGN

This prospective cohort study enrolled 1,014 HCWs working with HIV-infected populations from 10 metropolitan areas. Purified protein derivative (PPD) tuberculin skin tests were placed at baseline and every 6 months afterwards on those without a history of TB or a positive PPD. Demographic, occupational, and TB exposure data also were collected.

SETTING

Outpatient clinics, hospitals, private practice offices, and drug treatment programs providing HIV-related healthcare and research programs.

PARTICIPANTS

A voluntary sample of staff and volunteers from 16 Community Programs for Clinical Research on AIDS units.

RESULTS

Factors related to prior TB or a positive skin test at baseline included being foreign-born, increased length of time in health care, living in New York City, or previous bacille Calmette-Guerin vaccination. The rate of PPD conversion was 1.8 per 100 person years of follow-up. No independent relation was found between the amount or type of contact with HIV-infected populations and the risk of TB infection.

CONCLUSION

These data provide some reassurance that caring for HIV-infected patients is not related to an increased rate of TB infection among HCWs in these settings.

Connectivity of the retinal Schiff base to Asp85 and Asp96 during the bacteriorhodopsin photocycle: the local-access model

In the recently proposed local-access model for proton transfers in the bacteriorhodopsin transport cycle (Brown et al. 1998. Biochemistry. 37:3982-3993), connection between the retinal Schiff base and Asp85 (in the extracellular direction) and Asp96 (in the cytoplasmic direction)is maintained as long as the retinal is in its photoisomerized state. The directionality of the proton translocation is determined by influences in the protein that make Asp85 a proton acceptor and, subsequently, Asp96 a proton donor. The idea of concurrent local access of the Schiff base in the two directions is now put to a test in the photocycle of the D115N/D96N mutant. The kinetics had suggested that there is a single sequence of intermediates, L<-->M1<-->M2<-->N, and the M2-->M1 reaction depends on whether a proton is released to the extracellular surface. This is now confirmed. We find that at pH 5, where proton release does not occur, but not at higher pH, the photostationary state created by illumination with yellow light contains not only the M1 and M2 states, but also the L and the N intermediates. Because the L and M1 states decay rapidly, they can be present only if they are in equilibrium with later intermediates of the photocycle. Perturbation of this mixture with a blue flash caused depletion of the M intermediate, followed by its partial recovery at the expense of the L state. The change in the amplitude of the C=O stretch band at 1759 cm-1 demonstrated protonation of Asp85 in this process. Thus, during the reequilibration the Schiff base lost its proton to Asp85. Because the N state, also present in the mixture, arises by protonation of the Schiff base from the cytoplasmic surface, these results fulfill the expectation that under the conditions tested the extracellular access of the Schiff base would not be lost at the time when there is access in the cytoplasmic direction. Instead, the connectivity of the Schiff base flickers rapidly (with the time constant of the M1<-->M2 equilibration) between the two directions during the entire L-to-N segment of the photocycle.

Partitioning of free energy gain between the photoisomerized retinal and the protein in bacteriorhodopsin

Photoisomerization of the all-trans-retinal of bacteriorhodopsin to 13-cis,15-anti initiates a sequence of thermal reactions in which relaxation of the polyene chain back to all-trans is coupled to various changes in the protein and the translocation of a proton across the membrane. We investigated the nature of this high-energy state in a genetically modified bacteriorhodopsin. When the electric charges of residues 85 and 96, the two aspartic acids critical for proton transport, are both changed to what they become after photoexcitation of the wild-type protein, i.e., neutral and anionic, respectively, the retinal assumes a thermally stable 13-cis,15-anti configuration. Thus, we have reversed cause and effect in the photocycle. It follows that when the 13-cis,15-anti isomeric state is produced by illumination, in the wild type it is unstable initially only because of conflicts with the retinal binding pocket. Later in the photocycle, the free energy gain is transferred from the chromophore to the protein. Before recovery of the initial state, it will come to be represented entirely by the free energy of the changed protonation states of aspartic acids 85 and 96.

The effect of fluconazole on the clinical pharmacokinetics of methadone

A randomized, double-blinded, placebo-controlled pharmacokinetic and safety trial was conducted to determine the effect of fluconazole on methadone disposition. Volunteers receiving methadone maintenance therapy were randomized to receive either 200 mg/day oral fluconazole (n = 13) or placebo (n = 12). After 14 days there was a 35% average increase in serum methadone area under the curve relative to baseline among patients receiving fluconazole (p = 0.0008). At the same time, mean serum methadone peak and trough concentrations increased by 27% (p = 0.0076) and 48% (p = 0.0023), respectively, and oral clearance of methadone was reduced by 24% (p = 0.0007). In contrast, the pharmacokinetics of methadone were unaltered in the placebo group. Renal clearance of methadone was not significantly affected by fluconazole or placebo therapy. Although exposed to increased concentrations of methadone, patients treated with fluconazole did not exhibit signs or symptoms of significant narcotic overdose.

Buprenorphine maintenance treatment of opiate dependence: a multicenter, randomized clinical trial

AIMS

To evaluate the safety and efficacy of an 8 mg/day sublingual dose of buprenorphine in the maintenance treatment of heroin addicts by comparison with a 1 mg/day dose over a 16-week treatment period. As a secondary objective, outcomes were determined concurrently for patients treated with two other dose levels.

DESIGN

Patients were randomized to four dosage groups and treated double-blind.

SETTING

Twelve outpatient opiate maintenance treatment centers throughout the United States.

PARTICIPANTS

Two hundred and thirty-nine women and 497 men who met the DSM-III-R criteria for opioid dependence and were seeking treatment.

INTERVENTION

Patients received either 1, 4, 8 or 16 mg/day of buprenorphine and were treated in the usual clinical context, including a 1-hour weekly clinical counseling session.

MEASUREMENT

Retention in treatment, illicit opioid use as determined by urine toxicology, opioid craving and global ratings by patient and staff. Safety outcome measures were provided by clinical monitoring and by analysis of the reported adverse events.

FINDINGS

Outcomes in the 8 mg group were significantly better than in the 1 mg group in all four efficacy domains. No deaths occurred in either group. The 8 mg group did not show an increase in the frequency of adverse events. Most reported adverse effects were those commonly seen in patients treated with opioids.

CONCLUSIONS

The findings support the safety and efficacy of buprenorphine and suggest that an adequate dose of buprenorphine will be a useful addition to pharmacotherapy.

Local-access model for proton transfer in bacteriorhodopsin

The accessibility of the retinal Schiff base in bacteriorhodopsin was studied in the D85N/D96N mutant where the proton acceptor and donor are absent. Protonation and deprotonation of the Schiff base after pH jump without illumination and in the photocycle of the unprotonated Schiff base were measured in the visible and the infrared. Whether access is extracellular (EC) or cytoplasmic (CP) was decided from the effect of millimolar concentrations of azide on the rates of proton transfers. The results, together with earlier work on the wild-type protein, suggest a new hypothesis for the proton-transfer switch: (i) In the metastable 13-cis, 15-anti and all-trans, 15-syn photoproducts, but not in the stable isomeric states, access flickers between the EC and CP directions. (ii) The direction of proton transfer is decided both by this local access and by the presence of a suitable donor or acceptor group (in the wild type), or the proton conductivity in the EC and CP half-channels (in D85N/D96N). (iii) Thermal reisomerization of the retinal can occur only when the Schiff base is protonated, as is well-known. In the wild-type transport cycle, the concurrent local EC and CP access during the lifetime of the metastable 13-cis, 15-anti state enables the changing pKa's of the proton acceptor and donor to determine the direction of proton transfer. Proton transfer from the Schiff base to Asp-85 in the EC direction is followed by reprotonation by Asp-96 from the CP direction because proton release to the EC surface raises the pKa of Asp-85 and a large-scale protein conformation change lowers the pKa of Asp-96. The unexpected finding we report here for D85N/D96N, that when the retinal is in the stable all-trans, 15-anti and 13-cis, 15-syn isomeric forms access of the Schiff base is locked (in the EC and CP directions, respectively), suggests that in this protein reisomerization, rather than changes in the proton conductivities of the EC and CP half-channels, provides the switch function. With this mechanism, the various modes of transport reported for Asp-85 mutants (CP to EC direction with blue light, and EC to CP direction with blue plus green light) are understood also in terms of rules i-iii.

Existence of a proton transfer chain in bacteriorhodopsin: participation of Glu-194 in the release of protons to the extracellular surface

Glu-194 near the extracellular surface of bacteriorhodopsin is indispensable for proton release to the medium upon protonation of Asp-85 during light-driven transport. As for Glu-204, its replacement with glutamine (but not aspartate) abolishes both proton release and the anomalous titration of Asp-85 that originates from coupling between the pKa of this buried aspartate and those of the other acidic groups. Unlike the case of Glu-204, however, replacement of Glu-194 with aspartate raises the pKa for proton release. In Fourier transform infrared spectra of the E194D mutant a prominent positive band is observed at 1720 cm-1. It can be assigned from [4-13C]aspartate and D2O isotope shifts to the C&dbd;O stretch of protonated Asp-194. Its rise correlates with proton transfer from the retinal Schiff base to Asp-85. Its decay coincides with the appearance of a proton at the surface, detected under similar conditions with fluorescein covalently bound to Lys-129 and with pyranine. Its amplitude decreases with increasing pH, with a pKa of about 9. We show that this pKa is likely to be that of the internal proton donor to Asp-194, the Glu-204 site, before photoexcitation, while 13C NMR titration indicates that Asp-194 has an initial pKa of about 3. We propose that there is a chain of interacting residues between the retinal Schiff base and the extracellular surface. After photoisomerization of the retinal the pKa's change so as to allow (i) Asp-85 to become protonated by the Schiff base, (ii) the Glu-204 site to transfer its proton to Asp-194 in E194D, and therefore to Glu-194 in the wild type, and (iii) residue 194 to release the proton to the medium.

Sexual risk behaviour among subgroups of heterosexual HIV infected patients in an urban setting

OBJECTIVE

To determine the frequency of characteristics associated with unprotected heterosexual intercourse in HIV infected adults in an urban area.

DESIGN

Retrospective comparison of sexual risk transmission behaviour between HIV infected men and women from a drug treatment site and between women from the drug site and HIV infected women from an urban medical centre.

METHODS

HIV infected women and men were asked questions on sexual behaviour for a 1 year period before enrollment. The outcome variable was heterosexual risk behaviour (HRB) defined as having vaginal sex at least once in the previous year and not always using condoms.

RESULTS

73% of the drug clinic females, 72% of the drug clinic males, and 42% of the medical centre female engaged in HRB. Using logistic regression analysis, women and men in drug treatment engaged in similar rates of HRB; however, women in drug treatment were four times (95% CI = 2.0-8.3) more likely to engage in HRB risk behaviour than women from the medical centre.

CONCLUSION

The data suggest that a surprisingly large portion of HIV infected patients under treatment engaged in HRB, especially former drug users. Without specifically targeted interventions, the heterosexual spread of HIV in urban areas will continue to be a serious problem.

Transient channel-opening in bacteriorhodopsin: an EPR study

Active translocation of ions across membranes requires alternating access of the ion binding site inside the pump to the two membrane surfaces. Proton translocation by bacteriorhodopsin (bR), the light-driven proton pump in Halobacterium salinarium, involves this kind of a change in the accessibility of the centrally located retinal Schiff base. This key event in bR's photocycle ensures that proton release occurs to the extracellular side and proton uptake from the cytoplasmic side. To study the role of protein conformational changes in this reprotonation switch, spin labels were attached to pairs of engineered cysteine residues in the cytoplasmic interhelical loops of bR. Light-induced changes in the distance between a spin label on the EF interhelical loop and a label on either the AB or the CD interhelical loop were observed, and the changes were monitored following photoactivation with time-resolved electron paramagnetic resonance (EPR) spectroscopy. Both distances increase transiently by about 5 A during the photocycle. This opening occurs between proton release and uptake, and may be the conformational switch that changes the accessibility of the retinal Schiff base to the cytoplasmic surface after proton release to the extracellular side.

Guanidinium restores the chromophore but not rapid proton release in bacteriorhodopsin mutant R82Q

Replacement of the Arg residue at position 82 in bacteriorhodopsin by Gln or Ala was previously shown to slow the rate of proton release and raise the pK of Asp 85, indicating that R82 is involved both in the proton release reaction and in stabilizing the purple form of the chromophore. We now find that guanidinium chloride lowers the pK of D85, as monitored by the shift of the 587-nm absorbance maximum to 570 nm (blue to purple transition) and increased yield of photointermediate M. The absorbance shift follows a simple binding curve, with an apparent dissociation constant of 20 mM. When membrane surface charge is taken into account, an intrinsic dissociation constant of 0.3 M fits the data over a range of 0.2-1.0 M cation concentration (Na+ plus guanidinium) and pH 5.4-6.7. A chloride counterion is not involved in the observed spectral changes, as chloride up to 0.2 M has little effect on the R82Q chromophore at pH 6, whereas guanidinium sulfate has a similar effect to guanidinium chloride. Furthermore, guanidinium does not affect the chromophore of the double mutant R82Q/D85N. Taken together, these observations suggest that guanidinium binds to a specific site near D85 and restores the purple chromophore. Surprisingly, guanidinium does not restore rapid proton release in the photocycle of R82Q. This result suggests either that guanidinium dissociates during the pump cycle or that it binds with a different hydrogen-bonding geometry than the Arg side chain of the wild type.

A controlled trial of isoniazid in persons with anergy and human immunodeficiency virus infection who are at high risk for tuberculosis. Terry Beirn Community Programs for Clinical Research on AIDS

BACKGROUND

Patients with human immunodeficiency virus (HIV) infection and latent tuberculosis are at substantial risk for the development of active tuberculosis. As a public health measure, prophylactic treatment with isoniazid has been suggested for HIV-infected persons who have anergy and are in groups with a high prevalence of tuberculosis.

METHODS

We conducted a multicenter, randomized, double-blind, placebo-controlled trial of six months of prophylactic isoniazid treatment in HIV-infected patients with anergy who have risk factors for tuberculosis infection. The primary end point was culture-confirmed tuberculosis.

RESULTS

The study was conducted from November 1991 through June 1996. Over 90 percent of the patients had two or more risk factors for tuberculosis infection, and nearly 75 percent of patients were from greater New York City. After a mean follow-up of 33 months, tuberculosis was diagnosed in only 6 of 257 patients in the placebo group and 3 of 260 patients in the isoniazid group (risk ratio, 0.48; 95 percent confidence interval, 0.12 to 1.91; P=0.30). There were no significant differences between the two groups with regard to death, death or the progression of HIV disease, or adverse events.

CONCLUSIONS

Even in HIV-infected patients with anergy and multiple risk factors for latent tuberculosis infection, the rate of development of active tuberculosis is low. This finding does not support the use of isoniazid prophylaxis in high-risk patients with HIV infection and anergy unless they have been exposed to active tuberculosis.

A local electrostatic change is the cause of the large-scale protein conformation shift in bacteriorhodopsin

During light-driven proton transport bacteriorhodopsin shuttles between two protein conformations. A large-scale structural change similar to that in the photochemical cycle is produced in the D85N mutant upon raising the pH, even without illumination. We report here that (i) the pKa values for the change in crystallographic parameters and for deprotonation of the retinal Schiff base are the same, (ii) the retinal isomeric configuration is nearly unaffected by the protein conformation, and (iii) preventing rotation of the C13-C14 double bond by replacing the retinal with an all-trans locked analogue makes little difference to the Schiff base pKa. We conclude that the direct cause of the conformational shift is destabilization of the structure upon loss of interaction of the positively charged Schiff base with anionic residues that form its counter-ion.

Time-resolved fourier transform infrared study of structural changes in the last steps of the photocycles of Glu-204 and Leu-93 mutants of bacteriorhodopsin

The last intermediate in the photocycle of the light-driven proton pump bacteriorhodopsin is the red-shifted O state. The structure and dynamics of the last step in the photocycle were characterized with time-resolved Fourier transform infrared spectroscopy of the mutants of Glu-204 and Leu-93, which accumulate this intermediate in much larger amounts than the wild type. The results show that E204Q and E204D give distorted all-trans-retinal chromophore like the O intermediate of the wild type. This is simply due to the perturbation of the proton acceptor function of Glu-204 in the O-to-BR transition in the Glu-204 mutants. The corresponding red-shifted intermediates of L93M, L93T, and L93S have a 13-cis chromophore like the N intermediate of the wild type, as reported from analysis of extracted retinal [Delaney, J. K., Schweiger, U., & Subramaniam, S. (1995) Proc. Natl. Acad. Sci. U.S.A. 92, 11120-11124]. In spite of their different chromophore structures from the O intermediate, the red-shifted intermediates are similar to the O intermediate but not to the N intermediate of the wild type with respect to structural changes in the peptide carbonyls. The structural changes around Asp-96 in the N intermediate are completely restored also in the red-shifted intermediates of the Leu-93 mutants like in the O intermediate. These results imply that the protein structural changes in the last step proceed regardless of thermal isomerization of the chromophore. Time-resolved Fourier transform infrared spectroscopy with the Glu-204 mutants suggests that the response of Asp-204 (Glu-204 in the wild type) to the protonation of Asp-85 during formation of the M intermediate, which results in proton release, is slow and may occur through structural changes.

Interaction of proton and chloride transfer pathways in recombinant bacteriorhodopsin with chloride transport activity: implications for the chloride translocation mechanism

When the protonated retinal Schiff base dissociates in the photocycle of the proton pump bacteriorhodopsin, asp-85 is the proton acceptor. Replacing this residue with threonine confers halorhodopsin-like properties on the protein, including chloride transport [Sasaki, J., Brown, L.S., Chon, Y.-S., Kandori, H., Maeda, A., Needleman, R., & Lanyi, J.K. (1995) Science 269, 73-75]. However, the electrostatic interaction between the vicinity of residue 85 and glu-204, a residue located about 10 A away near the extracellular surface, that is a part of the proton transport mechanism, should still exist. We find that in the D85T mutant glu-204 becomes protonated when chloride is added. This indicates that the binding of chloride at thr-85 must be equivalent to deprotonation of asp-85. The protonation state of glu-204 reports therefore on the presence or absence of chloride bound at thr-85. During the chloride-transport cycle of D85T, but not D85T/E204Q, fluorescein and pyranine detect the transient release of protons from the protein to the surface and the bulk. The release and the subsequent uptake of the protons occur during the rise and decay of a red-shifted photointermediate, respectively, and confirm the earlier suggestion that this state has the same role in the chloride transport as the M intermediate in the proton transport. Consistent with the red-shift of the absorption maximum, the chloride bound near the Schiff base had already moved away, presumably to be released at the cytoplasmic surface, but another chloride ion has not yet been taken up from the extracellular surface. The switch of the connectivity of the chloride binding site from the cytoplasmic to the extracellular membrane surface must occur therefore during the lifetime of this photointermediate.

Lack of a pharmacologic interaction between rifabutin and methadone in HIV-infected former injecting drug users

Rifampin, an agent known to decrease the half-life of methadone, and rifabutin are two rifamycins that are structurally similar and share mechanisms of action. Hence the possibility of a drug-drug interaction between rifabutin and methadone was evaluated in 24 methadone-maintained, former injecting drug users infected with the human immunodeficiency virus. The study was an open-label, drug-drug interaction and safety trial in which patients were followed for 15 days. Each patient received rifabutin 300 mg as a single dose concomitantly with their individualized methadone dosage. No significant differences in methadone peak plasma concentration, time to peak plasma concentration, area under the plasma concentration-time curve, systemic clearance or renal clearance was observed in the presence of rifabutin. Seventy-five percent of the patients reported at least one symptom of narcotic withdrawal during the study, however, these symptoms were mild. A relationship between the development of narcotic withdrawal and methadone systemic exposure could not be established. Concurrent administration of rifabutin and methadone appeared to be safe in human immunodeficiency virus-infected injecting drug users maintained on stable doses of methadone and is not expected to produce any significant changes in the pharmacokinetics of methadone in these patients.

Nicotine dependence and depression among methadone maintenance patients

There recently has been increasing interest at substance abuse treatment centers in smoking cessation treatment. Because a history of depression has been shown in other populations to complicate cessation efforts, the relationship between depression and nicotine dependence was tested in 726 methadone patients. Elevated odds of nicotine dependence given depression were found with three of four depression measures. Additional research is recommended to determine whether smoking cessation treatment will be more successful for methadone patients with a history of depression if it also addresses depression.

Hydration of the counterion of the Schiff base in the chloride-transporting mutant of bacteriorhodopsin: FTIR and FT-raman studies of the effects of anion binding when Asp85 is replaced with a neutral residue

The chromophores of the D85T and D85N mutants of bacteriorhodopsin are blue but become purple like the wild type when chloride or bromide binds near the Schiff base. In D85T this occurs near neutral pH, but in D85N only at pH < 4. The structures of the L and the unphotolyzed states of these proteins were examined with Fourier transform infrared spectroscopy. The difference spectra of the purple forms, but not the blue forms in the absence of these anions, resembled the spectrum of the wild-type protein. Shift of the ethylenic band toward lower frequency upon replacing chloride by bromide confirmed the contribution of the negative charge of the anions to the Schiff base counterion. These anions restored the change of water, which is bound near the protonated Schiff base but is absent in the blue form of the D85N mutant, though with stronger H-bonding than in the wild type. The C = N stretching vibration of the Schiff base in H2O and 2H2O was detected by Fourier transform Raman spectroscopy. The H-bonding strength of the Schiff base in the unphotolyzed state was weaker when chloride or bromide was bound to the mutants than with Asp85 as the counterion in the wild type. Thus, although the geometry of the environment is different, there is at least one water molecule coordinated to the bound halide in these mutants, in a way similar to water bound to Asp85 in the wild type.