MeCP2 binds to methylated DNA independently of phase separation and heterochromatin organisation

Correlative evidence has suggested that the methyl-CpG-binding protein MeCP2 contributes to the formation of heterochromatin condensates via liquid-liquid phase separation. This interpretation has been reinforced by the observation that heterochromatin, DNA methylation and MeCP2 co-localise within prominent foci in mouse cells. The findings presented here revise this view. MeCP2 localisation is independent of heterochromatin as MeCP2 foci persist even when heterochromatin organisation is disrupted. Additionally, MeCP2 foci fail to show hallmarks of phase separation in live cells. Importantly, we find that mouse cellular models are highly atypical as MeCP2 distribution is diffuse in most mammalian species, including humans. Notably, MeCP2 foci are absent in Mus spretus which is a mouse subspecies lacking methylated satellite DNA repeats. We conclude that MeCP2 has no intrinsic tendency to form condensates and its localisation is independent of heterochromatin. Instead, the distribution of MeCP2 in the nucleus is primarily determined by global DNA methylation patterns.

Phosphorylation controls spatial and temporal activities of motor-PRC1 complexes to complete mitosis

During mitosis, spindle architecture alters as chromosomes segregate into daughter cells. The microtubule crosslinker protein regulator of cytokinesis 1 (PRC1) is essential for spindle stability, chromosome segregation and completion of cytokinesis, but how it recruits motors to the central spindle to coordinate the segregation of chromosomes is unknown. Here, we combine structural and cell biology approaches to show that the human CENP-E motor, which is essential for chromosome capture and alignment by microtubules, binds to PRC1 through a conserved hydrophobic motif. This binding mechanism is also used by Kinesin-4 Kif4A:PRC1. Using in vitro reconstitution, we demonstrate that CENP-E slides antiparallel PRC1-crosslinked microtubules. We find that the regulation of CENP-E -PRC1 interaction is spatially and temporally coupled with relocalization to overlapping microtubules in anaphase. Finally, we demonstrate that the PRC1-microtubule motor interaction is essential in anaphase to control chromosome partitioning, retain central spindle integrity and ensure cytokinesis. Taken together our findings reveal the molecular basis for the cell cycle regulation of motor-PRC1 complexes to couple chromosome segregation and cytokinesis.

Potent microtubule-depolymerizing activity of a mitotic Kif18b-MCAK-EB network

The precise regulation of microtubule length during mitosis is essential to assemble and position the mitotic spindle and segregate chromosomes. The kinesin-13 Kif2C or MCAK acts as a potent microtubule depolymerase that diffuses short distances on microtubules, whereas the kinesin-8 Kif18b is a processive motor with weak depolymerase activity. However, the individual activities of these factors cannot explain the dramatic increase in microtubule dynamics in mitosis. Using in vitro reconstitution and single-molecule imaging, we demonstrate that Kif18b, MCAK and the plus-end tracking protein EB3 (also known as MAPRE3) act in an integrated manner to potently promote microtubule depolymerization at very low concentrations. We find that Kif18b can transport EB3 and MCAK and promotes their accumulation to microtubule plus ends through multivalent weak interactions. Together, our work defines the mechanistic basis for a cooperative Kif18b-MCAK-EB network at microtubule plus ends, that acts to efficiently shorten and regulate microtubules in mitosis, essential for correct chromosome segregation.

Mechanistic basis for Sgo1-mediated centromere localization and function of the CPC

Centromere association of the chromosomal passenger complex (CPC; Borealin-Survivin-INCENP-Aurora B) and Sgo1 is crucial for chromosome biorientation, a process essential for error-free chromosome segregation. Phosphorylated histone H3 Thr3 (H3T3ph; directly recognized by Survivin) and histone H2A Thr120 (H2AT120ph; indirectly recognized via Sgo1), together with CPC’s intrinsic nucleosome-binding ability, facilitate CPC centromere recruitment. However, the molecular basis for CPC–Sgo1 binding and how their physical interaction influences CPC centromere localization are lacking. Here, using an integrative structure-function approach, we show that the “histone H3-like” Sgo1 N-terminal tail-Survivin BIR domain interaction acts as a hotspot essential for CPC–Sgo1 assembly, while downstream Sgo1 residues and Borealin contribute for high-affinity binding. Disrupting Sgo1–Survivin interaction abolished CPC–Sgo1 assembly and perturbed CPC centromere localization and function. Our findings reveal that Sgo1 and H3T3ph use the same surface on Survivin to bind CPC. Hence, it is likely that these interactions take place in a spatiotemporally restricted manner, providing a rationale for the Sgo1-mediated “kinetochore-proximal” CPC centromere pool.

Establishment of centromere identity is dependent on nuclear spatial organization

The establishment of centromere-specific CENP-A chromatin is influenced by epigenetic and genetic processes. Central domain sequences from fission yeast centromeres are preferred substrates for CENP-A^Cnp1 incorporation, but their use is context dependent, requiring adjacent heterochromatin. CENP-A^Cnp1 overexpression bypasses heterochromatin dependency, suggesting that heterochromatin ensures exposure to conditions or locations permissive for CENP-A^Cnp1 assembly. Centromeres cluster around spindle-pole bodies (SPBs). We show that heterochromatin-bearing minichromosomes localize close to SPBs, consistent with this location promoting CENP-A^Cnp1 incorporation. We demonstrate that heterochromatin-independent de novo CENP-A^Cnp1 chromatin assembly occurs when central domain DNA is placed near, but not far from, endogenous centromeres or neocentromeres. Moreover, direct tethering of central domain DNA at SPBs permits CENP-A^Cnp1 assembly, suggesting that the nuclear compartment surrounding SPBs is permissive for CENP-A^Cnp1 incorporation because target sequences are exposed to high levels of CENP-A^Cnp1 and associated assembly factors. Thus, nuclear spatial organization is a key epigenetic factor that influences centromere identity.

Image guidance system use amongst Canadian otolaryngologists: a nationwide survey

Background

The use of image guidance systems has gained widespread acceptance as an adjunctive tool for endoscopic sinus surgery. However, the accessibility and usage of this technology is variable across hospitals in Canada.

Study objective

The aim of this study is to investigate the availability, usage, and related issues surrounding the use of image guidance systems in endoscopic sinus surgery across Canadian otolaryngology practice settings.

Methods

An online survey was electronically distributed to practicing otolaryngologists across Canada. The survey contained 27 questions pertaining to the availability, usage, barriers and overall experience of image guidance systems.

Results

The survey was electronically sent to a total of 654 Canadian otolaryngologists of which 158 responded (response rate 24.2%). Image guidance was available to 56.3% of respondents. Of the respondents without access to IGS, 85.5% indicated they would use it if it was available. Financial (capital cost) was identified as the most important barrier in obtaining IGS by 76.3% of respondents.

Conclusion

Over half of Canadian otolaryngologists have access to IGS with over 85% of those without access interested in using it if it was made available. A multitude of different factors contribute to this disparity. We hope that the results of this study will help support Canadian otolaryngologists to access IGS.

Graphical Abstract

Predictors and Outcomes for COVID-19 Re-Admissions in the Anticipate Cohort

Aims To describe readmissions of hospitalised patients with COVID-19, define predictors of readmission and explore the long term outcomes using the SF-12 score compared to patients who were not readmitted and those not hospitalised. Methods A single centre retrospective in North Inner-City Dublin. Recruitment was done through a COVID follow up clinic. Predictors of readmission and SF-12 scores at two timepoints post follow up at median 3 months and 12 months. Results Seventy (45%) participants were admitted, with a median age of 49.5 years (IQR 41.3-56.9), 36(51%) of whom were female. Unscheduled readmissions at ≤30 days in COVID-19 patients were 9(12.9%) and length of stay was four days (IQR 2-5). Readmissions were due to ongoing symptoms(n=9(64.3%)) or new complications(n=5(35.7%)). Mechanical ventilation and having symptoms of nausea and vomiting on index admission were predictive of readmission. (p=0.002). SF-12 scores at one year of readmitted patients were not different to patients who were never admitted at median one year follow up, p=.089. Conclusions Most readmissions were of short duration. Early follow up of patients post MV or who had nausea and vomiting on index admission should be prioritised. Wellbeing of readmitted patients was not different to those never hospitalised, at one year.

COVID-19: Extensive epithelial damage and ciliary dyskinesia in hospitalised patients

Infection with SARS-CoV-2 can cause severe respiratory disease and it is predicted that the COVID-19 pandemic will leave a substantial number of patients with long-term respiratory complications (1).

Hepatitis C virus infection in Irish drug users and prisoners - a scoping review

BACKGROUND

Hepatitis C infection is a major public health concern globally. In Ireland, like other European countries, people who use drugs (PWUD) and prisoners carry a larger HCV disease burden than the general population. Recent advances in HCV management have made HCV elimination across Europe a realistic goal. Engaging these two marginalised and underserved populations remains a challenge. The aim of this review was to map key findings and identify gaps in the literature (published and unpublished) on HCV infection in Irish PWUD and prisoners.

METHODS

A scoping review guided by the methodological framework set out by Levac and colleagues (based on previous work by Arksey & O'Malley).

RESULTS

A total of 58 studies were identified and divided into the following categories; Epidemiology, Guidelines and Policy, Treatment Outcomes, HCV-related Health Issues and qualitative research reporting on Patients' and Health Providers' Experiences. This review identified significantly higher rates of HCV infection among Irish prisoners and PWUD than the general population. There are high levels of undiagnosed and untreated HCV infection in both groups. There is poor engagement by Irish PWUD with HCV services and barriers have been identified. Prison hepatology nurse services have a positive impact on treatment uptake and outcomes. Identified gaps in the literature include; lack of accurate epidemiological data on incident infection, untreated chronic HCV infection particularly in PWUD living outside Dublin and those not engaged with OST.

CONCLUSION

Ireland like other European countries has high levels of undiagnosed and untreated HCV infection. Collecting, synthesising and identifying gaps in the available literature is timely and will inform national HCV screening, treatment and prevention strategies.

The depolymerase activity of MCAK shows a graded response to Aurora B kinase phosphorylation through allosteric regulation

Kinesin-13 motors regulate precise microtubule dynamics and limit microtubule length throughout metazoans by depolymerizing microtubule ends. Recently, the kinesin-13 motor family member MCAK (also known Kif2C) has been proposed to undergo large conformational changes during its catalytic cycle, as it switches from being in solution to being bound to microtubules. Here, we reveal that MCAK has a compact conformation in solution through crosslinking and electron microscopy experiments. When MCAK is bound to the microtubule ends, it adopts an extended conformation with the N-terminus and neck region of MCAK interacting with the microtubule. Interestingly, the region of MCAK that interacts with the microtubule is the region phosphorylated by Aurora B and contains an end binding (EB) protein-binding motif. The level of phosphorylation of the N-terminus results in a graded microtubule depolymerase activity. Here, we show that the N-terminus of MCAK forms a platform to integrate Aurora B kinase downstream signals and in response fine-tunes its depolymerase activity during mitosis. We propose that this allosteric control mechanism allows decoupling of the N-terminus from the motor domain of MCAK to allow MCAK depolymerase activity at kinetochores.

Summary: The kinesin-13 MCAK has a compact conformation in solution but is extended when bound to microtubules. Aurora B phosphorylation of MCAK inhibits depolymerase activity by disrupting its extended conformation.

Microtubule end tethering of a processive kinesin-8 motor Kif18b is required for spindle positioning

Mitotic spindle positioning specifies the plane of cell division during anaphase. Spindle orientation and positioning are therefore critical to ensure symmetric division in mitosis and asymmetric division during development. The control of astral microtubule length plays an essential role in positioning the spindle. In this study, using gene knockout, we show that the kinesin-8 Kif18b controls microtubule length to center the mitotic spindle at metaphase. Using in vitro reconstitution, we reveal that Kif18b is a highly processive plus end-directed motor that uses a C-terminal nonmotor microtubule-binding region to accumulate at growing microtubule plus ends. This region is regulated by phosphorylation to spatially control Kif18b accumulation at plus ends and is essential for Kif18b-dependent spindle positioning and regulation of microtubule length. Finally, we demonstrate that Kif18b shortens microtubules by increasing the catastrophe rate of dynamic microtubules. Overall, our work reveals that Kif18b uses its motile properties to reach microtubule ends, where it regulates astral microtubule length to ensure spindle centering.

Kif15 functions as an active mechanical ratchet

Kif15 is a kinesin-12 that contributes critically to bipolar spindle assembly in humans. Here we use force-ramp experiments in an optical trap to probe the mechanics of single Kif15 molecules under hindering or assisting loads and in a variety of nucleotide states. While unloaded Kif15 is established to be highly processive, we find that under hindering loads, Kif15 takes <∼10 steps. As hindering load is increased, Kif15 forestep:backstep ratio decreases exponentially, with stall occurring at 6 pN. In contrast, under assisting loads, Kif15 detaches readily and rapidly, even from its AMPPNP state. Kif15 mechanics thus depend markedly on the loading direction. Kif15 interacts with a binding partner, Tpx2, and we show that Tpx2 locks Kif15 to microtubules under both hindering and assisting loads. Overall, our data predict that Kif15 in the central spindle will act as a mechanical ratchet, supporting spindle extension but resisting spindle compression.

Dynein at kinetochores: Making the connection

McHugh and Welburn highlight Mosalaganti et al.’s and Gama et al.’s work revealing the molecular mechanism of dynein recruitment to kinetochores.​

Dynein removes the checkpoint proteins from kinetochores once chromosomes are bioriented. In this issue, Gama et al. (2017. J. Cell Biol.https://doi.org/10.1083/jcb.201610108) and Mosalaganti et al. (2017. J. Cell Biol.https://doi.org/10.1083/jcb.201611060) reveal the molecular basis for how dynein and its adaptor protein Spindly are recruited to the ROD–Zw10–Zwilch complex in the fibrous corona of unattached kinetochores.

Using Social Media to Increase Accessibility to Online Teaching Resources

The key learning points of Surgical Grand Rounds (SGR) are often not accessible at times of exam revision for students. We sought to use Twitter as an online teaching repository. A SGR Twitter profile was created. 23 SGR presentations were made accessible on Twitter over a 3 month period. 93 students were invited to complete a questionnaire assessing usage of the repository. 84 (90%) in total responded, of these, 25 (80.6%) felt that the online provision of SGR through twitter was "useful". The majority (71%) felt that the online content was easily accessible. The novel use of social media is a useful adjunctive educational tool in accessing an online repository of SGR presentations.

The Kinesin-12 Kif15 is a processive track-switching tetramer

Kinesin-12 motors are a little studied branch of the kinesin superfamily with the human protein (Kif15) implicated in spindle mechanics and chromosome movement. In this study, we reconstitute full-length hKif15 and its microtubule-targeting factor hTpx2 in vitro to gain insight into the motors mode of operation. We reveal that hKif15 is a plus-end-directed processive homotetramer that can step against loads of up to 3.5 pN. We further show that hKif15 is the first kinesin that effectively switches microtubule tracks at intersections, enabling it to navigate microtubule networks, such as the spindle. hKif15 tetramers are also capable of cross-linking microtubules, but unexpectedly, this does not depend on hTpx2. Instead, we find that hTpx2 inhibits hKif15 stepping when microtubule-bound. Our data reveal that hKif15 is a second tetrameric spindle motor in addition to the kinesin-5 Eg5 and provides insight into the mechanisms by which hKif15 and its inhibitor hTpx2 modulate spindle microtubule architecture.

DOI:http://dx.doi.org/10.7554/eLife.01724.001

Before a cell can divide, it produces an extra copy of all its chromosomes, and it must then ensure that each daughter cell ends up with one copy of each chromosome. During the division process, a structure called the spindle forms in the cell. This spindle is made of thread-like extensions called microtubules that grow from two poles at opposite ends of the cell. These microtubules are responsible for getting the chromosomes to line up in the middle of the cell, and then pulling half of the chromosomes to one end of the cell, and half to the other end. The cell then divides into two daughter cells.

Two motor proteins—so-called because they consume chemical energy to ‘walk’ along the microtubules—have important roles in this process: Kif11 motor proteins mainly drive the formation of the spindle and thus division of the chromosomes. A cell that does not contain Kif11 can only divide if it contains extra copies of a second motor protein called Kif15: this suggests that Kif15 can serve as some sort of back up for Kif11.

Normal cells only divide when new cells are needed for growth or to replace old cells that have died. Cancer cells, on the other hand, divide in a way that is not controlled. Drugs that interfere with Kif11 have been developed in the hope that they will stop cancer cells dividing, but these drugs have not been very effective in clinical tests, possibly due to the Kif15 back up. Scientists hope, therefore, that a better understanding of the role of Kif15 may lead to improved cancer treatments.

Drechsler et al. have isolated individual Kif15 motor proteins and used advanced microscopy techniques to study them in action. These experiments showed that Kif15 motor proteins can travel long distances along a single microtubule, and can also switch to a different microtubule at intersections. This movement of Kif15 is stopped when they bump into Tpx2 proteins, which are sitting on the microtubules. Together, these proteins can also form links between microtubules that can withstand high forces. These properties provide a starting point to understand how Kif15 can act as a back up for Kif11 in cells. In the future, it will be important to work out how Kif11 and Kif15 motor proteins work together in teams to build the spindle.

DOI:http://dx.doi.org/10.7554/eLife.01724.002

Socioeconomic Factors Influencing BRCA 1/2 Mutation Carriers To Choose Risk Reduction Surgery in Community Cancer Genetics Program

Background: Mutations in the BRCA 1/2 genes predispose women to increased risk of breast and ovarian cancer. Prophylactic mastectomy (PM) reduces the risk of breast cancer by approximately 90% while prophylactic salpingo-oophorectomy (PSO) reduces the risk of both breast and ovarian cancer. Yet, there is a paucity of data to determine if mutation carriers avail themselves of these risk reducing surgeries in the community setting.Purpose: This study evaluates if particular socioeconomic factors influence BRCA 1/2 mutation carriers to elect risk reduction surgery (RRS), either PM or PSO or both.Method: Of 129 BRCA1/2 positive patients identified by a community-based cancer genetics program outside Philadelphia from 1998 to 2008, 44 were excluded due to personal history of ovarian cancer, loss of follow-up, male gender, or deceased status. The 85 remaining patients were asked to complete a questionnaire addressing: age at diagnosis, ethnicity, religion, parity, education level, marital status, occupation, number of first degree relatives with breast or ovarian cancer, personal history of breast cancer, and use of oral contraceptives, tobacco, and alcohol. A chart review was performed on all responders.Results: Forty-nine patients (58%) completed the questionnaire. Of these, 68% (34/49) had RRS. Of those who did not have RRS, 63% (10/15) stated they definitely plan for RRS in the future. More than half of the women planning RRS in the future (6/10) were younger than 30 years old. Therefore, of all responders, 90% (44/49) stated they had or definitely plan to have RRS. The mean age of women with RRS versus those without was 43.9 and 35.6 years, respectively (p=.0102). Women age 40-64 had the highest rate of RRS (26/34; 84%; p=0.004). Most women (88%) with RRS had children (30/34; p=0.0493). Sixty-five percent (32/49) of women responders were college graduates; 24% were high school graduates (12/49). Of women who had RRS, 68% were college graduates. College graduates age &gt; 40 were the group most likely to have RRS (17/18; 94%; p= .00029). Only 63% of high school graduates age &gt; 40 (5/8; p=1.0) had RRS. Eight-five percent (11/13) of Ashkenazi Jewish women had RRS versus 67% (18/27) of non-Jewish Caucasian women. This was not statistically significant (p=0.2925). There was also no statistical difference for women choosing RRS with respect to occupation, birth control pill use, history of breast cancer, or family history of breast or ovarian cancer. Only 3/49 smoked cigarettes (&gt;more than 1 pack per week) and none drank alcohol (&gt;1 drink/day).Discussion: Women who presented to this community based genetics program had a high rate of RRS, were likely to be college educated, non-smokers, and non-drinkers. Age older than 40, completion of child bearing, and attainment of a college degree were the most significant factors associated with BRCA 1/2 mutation carriers having RRS. Further studies should explore barriers to genetic testing services, as well as evaluate reasons why BRCA1/2 mutation carriers decline RRS.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 4076.

Inflammation and iron deficiency in the hypoferremia of obesity

CONTEXT

Obesity is associated with hypoferremia, but it is unclear if this condition is caused by insufficient iron stores or diminished iron availability related to inflammation-induced iron sequestration.

OBJECTIVE

To examine the relationships between obesity, serum iron, measures of iron intake, iron stores and inflammation. We hypothesized that both inflammation-induced sequestration of iron and true iron deficiency were involved in the hypoferremia of obesity.

DESIGN

Cross-sectional analysis of factors anticipated to affect serum iron.

SETTING

Outpatient clinic visits.

PATIENTS

Convenience sample of 234 obese and 172 non-obese adults.

MAIN OUTCOME MEASURES

Relationships between serum iron, adiposity, and serum transferrin receptor, C-reactive protein, ferritin, and iron intake analyzed by analysis of covariance and multiple linear regression.

RESULTS

Serum iron was lower (75.8+/-35.2 vs 86.5+/-34.2 g/dl, P=0.002), whereas transferrin receptor (22.6+/-7.1 vs 21.0+/-7.2 nmol/l, P=0.026), C-reactive protein (0.75+/-0.67 vs 0.34+/-0.67 mg/dl, P<0.0001) and ferritin (81.1+/-88.8 vs 57.6+/-88.7 microg/l, P=0.009) were higher in obese than non-obese subjects. Obese subjects had a higher prevalence of iron deficiency defined by serum iron (24.3%, confidence intervals (CI) 19.3-30.2 vs 15.7%, CI 11.0-21.9%, P=0.03) and transferrin receptor (26.9%, CI 21.6-33.0 vs 15.7%, CI 11.0-21.9%, P=0.0078) but not by ferritin (9.8%, CI 6.6-14.4 vs 9.3%, CI 5.7-14.7%, P=0.99). Transferrin receptor, ferritin and C-reactive protein contributed independently as predictors of serum iron.

CONCLUSIONS

The hypoferremia of obesity appears to be explained both by true iron deficiency and by inflammatory-mediated functional iron deficiency.

Natural history of the long-term cognitive, affective, and physical sequelae of mild traumatic brain injury

Mild traumatic brain injury (MTBI) is associated with cognitive,affective, and physical sequelae. When symptoms persist for more than 3 months, a diagnosis of Post-Concussion Syndrome (PCS) is often given. The current study tracked symptom development to explore the natural sequelae of MTBI. Twenty-six MTBI patients received a comprehensive neuropsychological assessment at three intervals: within 1 week, at 4 months and at 7 months post-concussion. Based on DSMIV criteria and clinical judgment, two external raters diagnosed five MTBI participants with PCS. Results suggested that aspects of cognitive functioning of the symptomatic MTBI (i.e., PCS) participants were different from matched normal control (NC) subjects, and from the 21 MTBI patients who were asymptomatic, at 4 months. Asymptomatic MTBI participants improved in overall level of functioning from 4 to 7 months, but remained significantly different from NC participants in their reduced verbal fluency and working memory functioning.

Effects of radiotherapy and of differences in the extent of surgery for early breast cancer on local recurrence and 15-year survival: an overview of the randomised trials

BACKGROUND

In early breast cancer, variations in local treatment that substantially affect the risk of locoregional recurrence could also affect long-term breast cancer mortality. To examine this relationship, collaborative meta-analyses were undertaken, based on individual patient data, of the relevant randomised trials that began by 1995.

METHODS

Information was available on 42,000 women in 78 randomised treatment comparisons (radiotherapy vs no radiotherapy, 23,500; more vs less surgery, 9300; more surgery vs radiotherapy, 9300). 24 types of local treatment comparison were identified. To help relate the effect on local (ie, locoregional) recurrence to that on breast cancer mortality, these were grouped according to whether or not the 5-year local recurrence risk exceeded 10% (<10%, 17,000 women; >10%, 25,000 women).

FINDINGS

About three-quarters of the eventual local recurrence risk occurred during the first 5 years. In the comparisons that involved little (<10%) difference in 5-year local recurrence risk there was little difference in 15-year breast cancer mortality. Among the 25,000 women in the comparisons that involved substantial (>10%) differences, however, 5-year local recurrence risks were 7% active versus 26% control (absolute reduction 19%), and 15-year breast cancer mortality risks were 44.6% versus 49.5% (absolute reduction 5.0%, SE 0.8, 2p<0.00001). These 25,000 women included 7300 with breast-conserving surgery (BCS) in trials of radiotherapy (generally just to the conserved breast), with 5-year local recurrence risks (mainly in the conserved breast, as most had axillary clearance and node-negative disease) 7% versus 26% (reduction 19%), and 15-year breast cancer mortality risks 30.5% versus 35.9% (reduction 5.4%, SE 1.7, 2p=0.0002; overall mortality reduction 5.3%, SE 1.8, 2p=0.005). They also included 8500 with mastectomy, axillary clearance, and node-positive disease in trials of radiotherapy (generally to the chest wall and regional lymph nodes), with similar absolute gains from radiotherapy; 5-year local recurrence risks (mainly at these sites) 6% versus 23% (reduction 17%), and 15-year breast cancer mortality risks 54.7% versus 60.1% (reduction 5.4%, SE 1.3, 2p=0.0002; overall mortality reduction 4.4%, SE 1.2, 2p=0.0009). Radiotherapy produced similar proportional reductions in local recurrence in all women (irrespective of age or tumour characteristics) and in all major trials of radiotherapy versus not (recent or older; with or without systemic therapy), so large absolute reductions in local recurrence were seen only if the control risk was large. To help assess the life-threatening side-effects of radiotherapy, the trials of radiotherapy versus not were combined with those of radiotherapy versus more surgery. There was, at least with some of the older radiotherapy regimens, a significant excess incidence of contralateral breast cancer (rate ratio 1.18, SE 0.06, 2p=0.002) and a significant excess of non-breast-cancer mortality in irradiated women (rate ratio 1.12, SE 0.04, 2p=0.001). Both were slight during the first 5 years, but continued after year 15. The excess mortality was mainly from heart disease (rate ratio 1.27, SE 0.07, 2p=0.0001) and lung cancer (rate ratio 1.78, SE 0.22, 2p=0.0004).

INTERPRETATION

In these trials, avoidance of a local recurrence in the conserved breast after BCS and avoidance of a local recurrence elsewhere (eg, the chest wall or regional nodes) after mastectomy were of comparable relevance to 15-year breast cancer mortality. Differences in local treatment that substantially affect local recurrence rates would, in the hypothetical absence of any other causes of death, avoid about one breast cancer death over the next 15 years for every four local recurrences avoided, and should reduce 15-year overall mortality.

Subtle developmental abnormalities in the inferior olive: an indicator of prenatal brainstem injury in the sudden infant death syndrome

Subtle quantitative abnormalities in neuronal populations derived from the rhombic lip (i.e. arcuate nucleus at the ventral medullary surface, external granular layer of the cerebellum) have been reported in victims of the sudden infant death syndrome (SIDS). In this study, we examined the inferior olive, a major rhombic lip derivative, to determine if subtle rhombic lip abnormalities also involve this nucleus in SIDS. We analyzed the number and density of neurons and reactive astrocytes in the inferior olive in 29 SIDS cases and 29 controls. Computer-assisted cell counting procedures were used in sections stained with hematoxylin and eosin/Luxol fast blue. There was a significant difference in the postconceptionally age-adjusted mean for neuronal density between SIDS cases (7,687 +/- 255 neurons/mm(3)) and controls (8,889 +/- 255 neurons/mm(3)) (p = 0.002). The difference in age-adjusted mean neuronal number between SIDS cases (1,932 +/- 89 neurons/2 sections) and controls (2,172 +/- 89 neurons/2 sections) was marginally significant (p = 0.063). Reactive astrocytes were present in the inferior olive in SIDS cases, but their number, density, and developmental profile were not significantly different from that of control infants dying of diverse known causes. SIDS victims found dead in cribs, beds, and sofas, prone or supine had subtle olivary abnormalities, suggesting that affected infants are at risk in various sleeping situations. We propose that at least some SIDS victims experience intrauterine brainstem injury including the olivo-arcuato-cerebellar circuitry derived from the rhombic lip. These observations provide future directions for SIDS research concerning the role of early insults in pregnancy, the rhombic lip, and the interactions of the ventral medulla and cerebellum in cardioventilatory control.

The effect of prone positioning on intraocular pressure in anesthetized patients

BACKGROUND

Ocular perfusion pressure is commonly defined as mean arterial pressure minus intraocular pressure (IOP). Changes in mean arterial pressure or IOP can affect ocular perfusion pressure. IOP has not been studied in this context in the prone anesthetized patient.

METHODS

After institutional human studies committee approval and informed consent, 20 patients (American Society of Anesthesiologists physical status I-III) without eye disease who were scheduled for spine surgery in the prone position were enrolled. IOP was measured with a Tono-pen XL handheld tonometer at five time points: awake supine (baseline), anesthetized (supine 1), anesthetized prone (prone 1), anesthetized prone at conclusion of case (prone 2), and anesthetized supine before wake-up (supine 2). Anesthetic protocol was standardized. The head was positioned with a pinned head-holder. Data were analyzed with repeated-measures analysis of variance and paired t test.

RESULTS

Supine 1 IOP (13 +/- 1 mmHg) decreased from baseline (19 +/- 1 mmHg) (P < 0.05). Prone 1 IOP (27 +/- 2 mmHg) increased in comparison with baseline (P < 0.05) and supine 1 (P < 0.05). Prone 2 IOP (40 +/- 2 mmHg) was measured after 320 +/- 107 min in the prone position and was significantly increased in comparison with all previous measurements (P < 0.05). Supine 2 IOP (31 +/- 2 mmHg) decreased in comparison with prone 2 IOP (P < 0.05) but was relatively elevated in comparison with supine 1 and baseline (P < 0.05). Hemodynamic and ventilatory parameters remained unchanged during the prone period.

CONCLUSIONS

Prone positioning increases IOP during anesthesia. Ocular perfusion pressure could therefore decrease, despite maintenance of normotension.

Clinical sensitivity of p53 mutation detection in matched bladder tumor, bladder wash, and voided urine specimens

BACKGROUND

Mutations in the p53 tumor suppressor gene may correlate with an increased risk of recurrence and disease progression in patients with bladder carcinoma. The ability to accurately and sensitively detect p53 mutations in cytology specimens may be of benefit in the treatment of bladder carcinoma patients with superficial, minimally invasive disease.

METHODS

Genomic DNA was isolated from 49 cases, each of which was comprised of matched bladder tumor tissue, bladder wash, and voided urine specimens obtained concurrently at a single institution. The genomic DNA was analyzed for mutations in the p53 tumor suppressor gene using a p53 mutation detection assay. Automated dideoxy sequencing of mutant specimens also was performed.

RESULTS

Of the 49 cases, 29 (59%) showed no evidence of p53 mutations in the tumor, bladder wash, or voided urine specimens. Of the remaining 20 cases, 19 showed evidence of mutations in the tumor. Of these 19 p53 mutant bladder tumors, 16 (84%) were detected in the matched bladder wash and 16 (84%) were detected in the matched voided urine specimens. One case resulted in the detection of mutant p53 in the voided urine and the bladder wash, but not in the tumor. Analysis of the results between tumor tissue and bladder wash or tumor and voided urine showed 84.2% sensitivity, 96.8% specificity, and 91.8% accuracy. Sequence analysis of the mutant cases showed that the mutations detected in the tumor tissue were the same mutations detected in the bladder wash and the voided urine specimens.

CONCLUSIONS

Both voided urine and bladder wash specimens from patients with bladder carcinoma were found to provide a high rate of clinical accuracy for the determination of the p53 gene status in patients with bladder tumors.

Treatment of combat-related nightmares using imagery rehearsal: a pilot study

Posttraumatic nightmares are a hallmark of PTSD and distinct from general nightmares as they are often repetitive and faithful representations of the traumatic event. This paper presents data from a pilot study that examined the use of Imagery Rehearsal in treating combat-related nightmares of 12 Vietnam veterans with PTSD. Three treatment groups, comprising 4 veterans in each, completed standardised treatment across 6 sessions. Treatment effects were investigated using nightmare diaries and established instruments, including the IES-R, BDI, BAI, and SCL-90-R. The data demonstrate significant reductions in nightmares targeted, and improvements in PTSD and comorbid symptomatology. The paper recommends that, on the basis of the promising preliminary data, a randomised control trial be established to assess imagery ability and attitude toward nightmares.

Mooren ulcer in South India: serology and clinical risk factors

PURPOSE

To investigate the rate of undiagnosed rheumatologic diseases and hepatitis C infection among patients with the clinical diagnosis of Mooren ulcer seen at Aravind Eye Hospital, Madurai, South India.

METHODS

Twenty-one patients with the clinical diagnosis of Mooren ulcer and 44 control patients underwent a complete ophthalmic history and examination, as well as serologic testing for antinuclear antibodies, rheumatoid factor, antineutrophil cytoplasmic antibodies, herpes simplex virus 1 antibodies, and hepatitis C virus antibodies.

RESULTS

There were no statistically significant differences in the rates of seropositivity for antinuclear antibodies, rheumatoid factor, antineutrophil cytoplasmic antibodies, herpes simplex virus 1 antibodies, and hepatitis C virus antibodies between patients with Mooren ulcer and control patients. Two patients with Mooren ulcer and four control patients were found to have a rheumatoid factor titer of greater than 1:20. One of the control patients, but none of the patients with Mooren ulcer, was found to have serologic evidence of hepatitis C infection. A history of corneal trauma, surgery, or infection was reported by 68% of patients with Mooren ulcer, compared with 20% of control patients (P < .001). Among patients with Mooren ulcer, bilateral disease occurred in 37% of patients, visual acuity was reduced to light perception in 15% of eyes, and perforation occurred in 19% of eyes.

CONCLUSIONS

Nineteen (90%) of 21 patients with the clinical diagnosis of Mooren ulcer were found to have no evidence of an underlying rheumatologic disease by history, examination, or serologic testing, and none was seropositive for hepatitis C. However, patients with Mooren ulcer were more likely than control patients to report a history of corneal trauma, surgery, or infection.

Cleavage of double-stranded copy RNA by RNase 1 and RNase T1 provides a robust means to detect p53 gene mutations in clinical specimens

Detecting somatic mutations in patient specimens is challenging because of the wide variation in quality and quantity of genomic DNA in clinically derived material. In cancer specimens, the challenge of detecting mutations is usually compounded by the presence of large numbers of nonmutated normal cells that dampen the relative signal that can be obtained from employing any mutation detection strategy. In the case of somatic mutations in the gene encoding the tumor suppressor, p53, a clinically useful mutation detection assay must be able to detect a wide variety of types of mutations scattered over five coding exons and their flanking intron sequences. This study examined the ability of a mutation detection strategy, termed NIRCA, to identify single-base mutations in the clinically relevant domain of the p53 gene. This strategy relies on RNase digestion-mediated cleavage of double-stranded copy RNA transcribed in vitro from polymerase chain reaction (PCR)-amplified genomic templates to detect mismatched base pairs resulting from hybridization of complimenting mutant and wild-type copy RNA strands. This assay system was found to robustly detect all twelve possible mismatches and the plus one and minus one frame shifts. Furthermore, the assay could detect mutations in clinical specimens when the mutant alleles composed as few as 4% of the total population of alleles isolated in bulk specimen genomic DNA. This mutation detection strategy worked efficiently in bladder, breast, colon and lung tumors as well as sediments from bladder cytology specimens.

MMPI-2 data for Australian Vietnam Veterans with combat-related PTSD

Considerable attention has been devoted to the MMPI in the assessment of combat-related PTSD. To date, published data have focused almost exclusively on American Vietnam veterans. This study investigated MMPI-2 profiles of 100 Australian Vietnam veterans admitted to an intensive PTSD treatment program. Comparisons with United States (U.S.) data suggested strong similarities between the American and Australian populations in terms of F-scale elevations and typical 3-point code types (8-7-2). However, the American samples showed relatively higher elevations of Scales 4 and 6, suggesting social alienation and a tendency to externalize, while a subgroup of Australian veterans showed a greater propensity for somatization (Scale 1). The results provide overall support for the generalizability of American MMPI data to an alternative cultural group of combat veterans.

Malignant paraganglioma of the prostate: case report, depiction by meta-iodobenzylguanidine scintigraphy and review of the literature

OBJECTIVE

To describe the 123-I-MIBG scintigraphic, CT, MRI, operative and pathological findings in a case of malignant prostatic paraganglioma and to review the literature on this very rare tumor.

EXPERIMENTAL DESIGN

Clinical imaging and pathological correlation of data in a referred patient.

SETTING

Regional referral center and tertiary referral academic medical center.

PATIENT

17 year old man presenting with painless hematuria and a large prostatic mass. Interventions and measures. Renal ultrasound, transrectal ultrasound, ultrasound guided prostatic biopsy, pelvic CT and MRI, planar and SPECT 123-I-MIBG scintigraphy, and surgical exploration.

RESULTS

The patient had a significant hydronephrosis of the left kidney and marked enlargement (120 ml) of the prostate gland by ultrasound. Ultrasound guided biopsies of the prostate and a left pelvic lymph node revealed a neuroendocrine tumor staining positive for chromogranin. CT and MRI revealed a large tumor of the prostate invading the seminal vesicles, bladder and rectum with extensive pelvic lymph node spread. The primary tumor and one of the nodes were shown to be 123-I-MIBG avid confirming the neuroendocrine nature of the tumor. The lesion was unresponsive to chemotherapy and unresectable at surgical exploration.

CONCLUSIONS

To date there have only been 5 reports of prostatic paragangliomas. To our knowledge this is the first to have been studied by MIBG scintigraphy and like most paragangliomas it was MIBG-avid.

The light intensity dependence of protochlorophyllide photoconversion and its significance to the catalytic mechanism of protochlorophyllide reductase

The light-dependent step in chlorophyll synthesis by higher plants involves hydrogen transfer from NADPH+ to the porphyrin protochlorophyllide catalysed by the photoenzyme protochlorophyllide reductase. The light intensity dependence of the process has been studied in vitro using wheat etioplast membranes. The results suggest that a single photochemical event is involved in the photoconversion. In support of this conclusion we also demonstrate that illumination of these membranes with a train of ultrashort (150 fs) flashes resulted in chlorophyll accumulation. The significance of the findings in terms of possible mechanisms for the reductase are discussed.

Evidence that a nereistoxin metabolite, and not nereistoxin itself, reduces neuronal nicotinic receptors: studies in the whole chick ciliary ganglion, on isolated neurons and immunoprecipitated receptors

Nereistoxin (100 microM, 2-10 min) blocks nicotinic receptors in the intact chick ciliary ganglion. This effect mimics blockade by the reducing agent dithiothreitol (2 mM, 20 min), which is not reversed until oxidation with dithiobisnitrobenzoic acid (1 mM, 5 min). After treating intact ganglia with either nereistoxin or dithiothreitol, the affinity alkylating agent bromoacetylcholine causes irreversible blockade that cannot be reversed by dithiobisnitrobenzoic acid. These data suggest that nereistoxin, or a metabolite, acts to reduce nicotinic receptors, although nereistoxin differs from dithiothreitol in that agonists only partially protect against nereistoxin reduction. In studies on chick retina, we previously proposed that a metabolite of nereistoxin (such as dihydronereistoxin) is the actual reducing agent for neuronal nicotinic receptors. Current findings in chick ciliary ganglion supporting this hypothesis include: 1) changing pH alters the minimal nereistoxin concentration needed for blockade in intact ganglia, but has little effect on the minimal concentration needed for dithiothreitol, 2) application of a quaternary analog of nereistoxin has little effect on intact ganglion, but a quaternary analog of dihydronereistoxin blocks nicotinic receptors by reduction, 3) nereistoxin weakly oxidizes rather than reduces immunoprecipitated receptors from chick brain and 4) in whole-cell patch-clamp studies, nereistoxin clearly does not reduce receptors on chick ciliary neurons, although dihydronereistoxin mimics receptor blockade by dithiothreitol, and requires oxidation by dithiobisnitrobenzoic acid for reactivation. Together, these data suggest that nereistoxin is not a direct reducing agent for neuronal nicotinic receptors.

IL-10 production in cutaneous basal and squamous cell carcinomas. A mechanism for evading the local T cell immune response

Cytokines play a vital role in the host immune response by regulating the development and function of immunocompetent cells. To explore the possibility that tumors may alter the host response via release of immunomodulatory cytokines, we studied two different skin cancers, basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) as models. By RT-PCR, we found that the type 2 cytokines, IL-4 and IL-10, were strongly expressed in BCC compared with matched PBMC. Furthermore, IL-10 was more strongly expressed in SCC compared with benign growths. To identify the cell types responsible for production of these cytokines, tumor and tumor-infiltrating lymphocyte (TIL) cell lines were derived from BCC and SCC biopsy specimens. IL-2 and IFN-gamma mRNAs were expressed in TIL, while IL-10 mRNA were strongly expressed in BCC lines. In addition, IL-10 was detected in culture supernatants from BCC and SCC cell lines by ELISA and in tissue sections by immunohistology. TIL lines derived from these tumors demonstrated proliferative activity to autologous tumor cells in the presence of APCs, dependent on the addition of low concentrations of rIL-2 or neutralizing anti-IL-10 mAb in the culture medium. Furthermore, treatment of BCC with intralesional IFN-alpha induced tumor regression with concomitant up-regulation of IL-2 and down-regulation of IL-10 mRNA expression in lesions. These data suggest that tumor production of the cytokine, IL-10, may provide a mechanism for evading the local T cell-mediated immune response.

IL-10 production in cutaneous basal and squamous cell carcinomas. A mechanism for evading the local T cell immune response

Cytokines play a vital role in the host immune response by regulating the development and function of immunocompetent cells. To explore the possibility that tumors may alter the host response via release of immunomodulatory cytokines, we studied two different skin cancers, basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) as models. By RT-PCR, we found that the type 2 cytokines, IL-4 and IL-10, were strongly expressed in BCC compared with matched PBMC. Furthermore, IL-10 was more strongly expressed in SCC compared with benign growths. To identify the cell types responsible for production of these cytokines, tumor and tumor-infiltrating lymphocyte (TIL) cell lines were derived from BCC and SCC biopsy specimens. IL-2 and IFN-gamma mRNAs were expressed in TIL, while IL-10 mRNA were strongly expressed in BCC lines. In addition, IL-10 was detected in culture supernatants from BCC and SCC cell lines by ELISA and in tissue sections by immunohistology. TIL lines derived from these tumors demonstrated proliferative activity to autologous tumor cells in the presence of APCs, dependent on the addition of low concentrations of rIL-2 or neutralizing anti-IL-10 mAb in the culture medium. Furthermore, treatment of BCC with intralesional IFN-alpha induced tumor regression with concomitant up-regulation of IL-2 and down-regulation of IL-10 mRNA expression in lesions. These data suggest that tumor production of the cytokine, IL-10, may provide a mechanism for evading the local T cell-mediated immune response.

Overexpression of IL-10 in atopic dermatitis. Contrasting cytokine patterns with delayed-type hypersensitivity reactions

The skin lesions of patients with atopic dermatitis provide a model to study immunoregulation in human allergy. To determine the local cytokine pattern of cells present (both endogenous and recruited) at the site of disease, we extracted RNA from skin biopsy specimens from patients with atopic dermatitis, allergic contract dermatitis, and positive tuberculin reactions and used PCR to assay for cytokine mRNA. cDNAs were normalized to the intensity of the CD3 delta PCR product as a marker of T cell mRNA. We found overexpression of IL-10 mRNA in atopic dermatitis lesions, in comparison with allergic contact dermatitis lesions and tuberculin reactions. In contrast, IL-4 mRNA was most strongly expressed in allergic contact dermatitis lesions and IFN-gamma mRNA was the predominant cytokine in tuberculin reactions. Using an anti-IL-10 mAb with immunoperoxidase, we localized IL-10 protein to large mononuclear cells in the dermal infiltrate of atopic lesions. After immunomagnetic sorting of mononuclear cell populations from PBMC of atopic dermatitis subjects, IL-10 mRNA as measured by PCR was found to be strongly expressed in CD14+ cells. Spontaneous release of IL-10 from PBMC-derived adherent cells was greater in atopic dermatitis donors than normal controls. We therefore renormalized skin biopsy cDNA according to the level of beta-actin PCR product, as a marker of total cellular mRNA, and found by PCR that IL-10 was nevertheless greatest in atopic dermatitis subjects. We conclude that the relative overexpression of IL-10 in atopic dermatitis greatest in atopic dermatitis subjects. We conclude that the relative overexpression of IL-10 in atopic dermatitis may contribute to the up-regulation of humoral responses and the down-regulation of Th1 responses.

Overexpression of IL-10 in atopic dermatitis. Contrasting cytokine patterns with delayed-type hypersensitivity reactions

The skin lesions of patients with atopic dermatitis provide a model to study immunoregulation in human allergy. To determine the local cytokine pattern of cells present (both endogenous and recruited) at the site of disease, we extracted RNA from skin biopsy specimens from patients with atopic dermatitis, allergic contract dermatitis, and positive tuberculin reactions and used PCR to assay for cytokine mRNA. cDNAs were normalized to the intensity of the CD3 delta PCR product as a marker of T cell mRNA. We found overexpression of IL-10 mRNA in atopic dermatitis lesions, in comparison with allergic contact dermatitis lesions and tuberculin reactions. In contrast, IL-4 mRNA was most strongly expressed in allergic contact dermatitis lesions and IFN-gamma mRNA was the predominant cytokine in tuberculin reactions. Using an anti-IL-10 mAb with immunoperoxidase, we localized IL-10 protein to large mononuclear cells in the dermal infiltrate of atopic lesions. After immunomagnetic sorting of mononuclear cell populations from PBMC of atopic dermatitis subjects, IL-10 mRNA as measured by PCR was found to be strongly expressed in CD14+ cells. Spontaneous release of IL-10 from PBMC-derived adherent cells was greater in atopic dermatitis donors than normal controls. We therefore renormalized skin biopsy cDNA according to the level of beta-actin PCR product, as a marker of total cellular mRNA, and found by PCR that IL-10 was nevertheless greatest in atopic dermatitis subjects. We conclude that the relative overexpression of IL-10 in atopic dermatitis greatest in atopic dermatitis subjects. We conclude that the relative overexpression of IL-10 in atopic dermatitis may contribute to the up-regulation of humoral responses and the down-regulation of Th1 responses.

IL-12 regulates T helper type 1 cytokine responses in human infectious disease

We investigated the role of IL-12 in regulating T cell and cytokine responses in human infectious disease by using the spectrum of leprosy as a model. Tuberculoid patients mount strong T cell responses to Mycobacterium leprae, with production of the type 1 cytokines IL-2 and IFN-gamma in lesions; whereas lepromatous patients manifest weak T cell responses to M. leprae, with production of the type 2 cytokines IL-4 and IL-10 in lesions. We found expression of IL-12 p40 mRNA, as measured by PCR amplification, and IL-12 p70, as measured by immunohistochemistry, to be 10-fold greater in tuberculoid lesions than in lepromatous lesions. The ability of M. leprae to stimulate release of IL-12 from monocytes was inhibited by rIL-4 and rIL-10. M. leprae-induced T cell proliferation in tuberculoid patients was blocked by the addition of neutralizing Abs to IL-12. Furthermore, rIL-12 stimulated proliferation of CD4+ type 1 T cell clones from tuberculoid lesions, but not CD8+ type 2 T cell clones from lepromatous lesions; however, both responded to rIL-2, rIL-12 augmented M. leprae-specific T cell proliferation in lepromatous patients, thereby causing the selective expansion of CD4+ T cells and increasing T cell IFN-gamma production. These data indicate that IL-12 is an important mediator in the generation of the type 1 cytokine response in human infectious disease.

IL-12 regulates T helper type 1 cytokine responses in human infectious disease

We investigated the role of IL-12 in regulating T cell and cytokine responses in human infectious disease by using the spectrum of leprosy as a model. Tuberculoid patients mount strong T cell responses to Mycobacterium leprae, with production of the type 1 cytokines IL-2 and IFN-gamma in lesions; whereas lepromatous patients manifest weak T cell responses to M. leprae, with production of the type 2 cytokines IL-4 and IL-10 in lesions. We found expression of IL-12 p40 mRNA, as measured by PCR amplification, and IL-12 p70, as measured by immunohistochemistry, to be 10-fold greater in tuberculoid lesions than in lepromatous lesions. The ability of M. leprae to stimulate release of IL-12 from monocytes was inhibited by rIL-4 and rIL-10. M. leprae-induced T cell proliferation in tuberculoid patients was blocked by the addition of neutralizing Abs to IL-12. Furthermore, rIL-12 stimulated proliferation of CD4+ type 1 T cell clones from tuberculoid lesions, but not CD8+ type 2 T cell clones from lepromatous lesions; however, both responded to rIL-2, rIL-12 augmented M. leprae-specific T cell proliferation in lepromatous patients, thereby causing the selective expansion of CD4+ T cells and increasing T cell IFN-gamma production. These data indicate that IL-12 is an important mediator in the generation of the type 1 cytokine response in human infectious disease.

Interactions of dithiols with p-aminophenyldichloroarsine and nicotinic acetylcholine receptors

Interactions of dithiols with p-aminophenyldichloroarsine (APA) and with Torpedo nicotinic receptors were studied using two approaches. First, the stability of dithiol-APA complexes in solution was studied based on quenching thiol reactions with dithiobis-(nitrobenzoic acid). A peptide corresponding to a portion of the Torpedo alpha-subunit and various 1,2-dithiols such as 2,3-dimercaptopropanesulfonic acid (DMPS), 2,3-dimercaptosuccinic acid formed stable complexes with APA, while 1,4-dithiols, such as dithiothreitol (DTT) and 2,5 dimercapto-N,N,N'N'-tetradipamide (DTA) did not. The Kd of APA association with DTT in Tris buffer is 2 microM. These data suggest that APA has greater affinity for reduced nicotinic receptors than for either DTT or DTA, a prediction that was experimentally confirmed, since these reagents do not reverse the effects of APA on nicotinic receptors. Second, application of DMPS and BAL, but not 2,3-dimercaptosuccinic acid, to DTT-treated receptors both reversed the effects of APA-receptor complexes and prevented alkylation by bromoacetylcholine, suggesting that DMPS and BAL "oxidize" reduced nicotinic receptors. The presence of air is required for this "oxidizing" effect, but no clear mechanism was discovered, since prevention of formation of the reactive oxygen species superoxide, hydrogen peroxide, or hydroxyl radicals failed to block oxidation. These data suggest that oxygen reacts with dithiols to produce unknown reactive species that directly oxidize reduced nicotinic receptors, although other interpretations are still possible.