Novel insights into diminished cardiac reserve in non-obstructive hypertrophic cardiomyopathy from four-dimensional flow cardiac magnetic resonance component analysis

AIMS

Hypertrophic cardiomyopathy (HCM) is characterized by hypercontractility and diastolic dysfunction, which alter blood flow haemodynamics and are linked with increased risk of adverse clinical events. Four-dimensional flow cardiac magnetic resonance (4D-flow CMR) enables comprehensive characterization of ventricular blood flow patterns. We characterized flow component changes in non-obstructive HCM and assessed their relationship with phenotypic severity and sudden cardiac death (SCD) risk.

METHODS AND RESULTS

Fifty-one participants (37 non-obstructive HCM and 14 matched controls) underwent 4D-flow CMR. Left-ventricular (LV) end-diastolic volume was separated into four components: direct flow (blood transiting the ventricle within one cycle), retained inflow (blood entering the ventricle and retained for one cycle), delayed ejection flow (retained ventricular blood ejected during systole), and residual volume (ventricular blood retained for >two cycles). Flow component distribution and component end-diastolic kinetic energy/mL were estimated. HCM patients demonstrated greater direct flow proportions compared with controls (47.9 ± 9% vs. 39.4 ± 6%, P = 0.002), with reduction in other components. Direct flow proportions correlated with LV mass index (r = 0.40, P = 0.004), end-diastolic volume index (r = -0.40, P = 0.017), and SCD risk (r = 0.34, P = 0.039). In contrast to controls, in HCM, stroke volume decreased with increasing direct flow proportions, indicating diminished volumetric reserve. There was no difference in component end-diastolic kinetic energy/mL.

CONCLUSION

Non-obstructive HCM possesses a distinctive flow component distribution pattern characterised by greater direct flow proportions, and direct flow-stroke volume uncoupling indicative of diminished cardiac reserve. The correlation of direct flow proportion with phenotypic severity and SCD risk highlight its potential as a novel and sensitive haemodynamic measure of cardiovascular risk in HCM.

Clinical characteristics with inflammation profiling of long COVID and association with 1-year recovery following hospitalisation in the UK: a prospective observational study

BACKGROUND

No effective pharmacological or non-pharmacological interventions exist for patients with long COVID. We aimed to describe recovery 1 year after hospital discharge for COVID-19, identify factors associated with patient-perceived recovery, and identify potential therapeutic targets by describing the underlying inflammatory profiles of the previously described recovery clusters at 5 months after hospital discharge.

METHODS

The Post-hospitalisation COVID-19 study (PHOSP-COVID) is a prospective, longitudinal cohort study recruiting adults (aged ≥18 years) discharged from hospital with COVID-19 across the UK. Recovery was assessed using patient-reported outcome measures, physical performance, and organ function at 5 months and 1 year after hospital discharge, and stratified by both patient-perceived recovery and recovery cluster. Hierarchical logistic regression modelling was performed for patient-perceived recovery at 1 year. Cluster analysis was done using the clustering large applications k-medoids approach using clinical outcomes at 5 months. Inflammatory protein profiling was analysed from plasma at the 5-month visit. This study is registered on the ISRCTN Registry, ISRCTN10980107, and recruitment is ongoing.

FINDINGS

2320 participants discharged from hospital between March 7, 2020, and April 18, 2021, were assessed at 5 months after discharge and 807 (32·7%) participants completed both the 5-month and 1-year visits. 279 (35·6%) of these 807 patients were women and 505 (64·4%) were men, with a mean age of 58·7 (SD 12·5) years, and 224 (27·8%) had received invasive mechanical ventilation (WHO class 7-9). The proportion of patients reporting full recovery was unchanged between 5 months (501 [25·5%] of 1965) and 1 year (232 [28·9%] of 804). Factors associated with being less likely to report full recovery at 1 year were female sex (odds ratio 0·68 [95% CI 0·46-0·99]), obesity (0·50 [0·34-0·74]) and invasive mechanical ventilation (0·42 [0·23-0·76]). Cluster analysis (n=1636) corroborated the previously reported four clusters: very severe, severe, moderate with cognitive impairment, and mild, relating to the severity of physical health, mental health, and cognitive impairment at 5 months. We found increased inflammatory mediators of tissue damage and repair in both the very severe and the moderate with cognitive impairment clusters compared with the mild cluster, including IL-6 concentration, which was increased in both comparisons (n=626 participants). We found a substantial deficit in median EQ-5D-5L utility index from before COVID-19 (retrospective assessment; 0·88 [IQR 0·74-1·00]), at 5 months (0·74 [0·64-0·88]) to 1 year (0·75 [0·62-0·88]), with minimal improvements across all outcome measures at 1 year after discharge in the whole cohort and within each of the four clusters.

INTERPRETATION

The sequelae of a hospital admission with COVID-19 were substantial 1 year after discharge across a range of health domains, with the minority in our cohort feeling fully recovered. Patient-perceived health-related quality of life was reduced at 1 year compared with before hospital admission. Systematic inflammation and obesity are potential treatable traits that warrant further investigation in clinical trials.

FUNDING

UK Research and Innovation and National Institute for Health Research.

Longitudinal trajectory of cardiac magnetic resonance and cardiopulmonary exercise testing findings in moderate to severe COVID-19 and association with symptoms

Background

Cardiac magnetic resonance (CMR) and cardiopulmonary exercise testing (CPET) have provided important insights into the prevalence of early cardiopulmonary abnormalities in COVID-19 patients. It is currently unknown whether such abnormalities persist over time and relate to ongoing symptoms.

Purpose

To describe the longitudinal trajectory of cardiopulmonary abnormalities on CMR and CPET in moderate to severe COVID-19 patients and assess their relationship with ongoing symptoms.

Methods

Fifty-eight previously hospitalised COVID-19 patients and 30 age, sex, body mass index, comorbidity-matched controls underwent CMR, CPET and a symptom-based questionnaire at 2–3 months (2–3m). Repeat assessments (including gas transfer) were performed in 46 patients at 6 months (6m).

Results

During admission, 1/3rd of patients needed ventilation or intensive care (Table 1) and three (5%) had a raised troponin.

On CMR, patients had preserved left (LV) and right ventricular (RV) volumes and function at 2–3m from infection. By 6m, LV function did not change but RV end diastolic volume decreased (mean difference −4.3 mls/m2, p=0.005) and RV function increased (mean difference +3.2%, p<0.001, Fig. 1A).

Patients had higher native T1 (a marker of fibroinflammation) at 2–3m compared to controls (Table 1, Fig. 1B), which normalised by 6m. Extracellular volume was normal and improved by 6m. Native T2, a marker of myocardial oedema, did not differ between patients and controls on serial CMR. At 2–3m, late gadolinium enhancement (LGE) was higher in patients (p=0.023) but became comparable to controls by 6m (p=0.62). Six (12%) patients had LGE in a myocarditis pattern and one (2%) had myocardial infarction. None had active myocarditis using the Modified Lake Louise Criteria.

Lung imaging (T2-weighted) revealed parenchymal abnormalities in 2/3rds of patients at 2–3 and 6 months. The extent of abnormalities improved on serial imaging (Table 1). Gas transfer (DLco) was worse in those with lung abnormalities (77% vs 91% of predicted, p=0.009).

CPET revealed reduced peak oxygen consumption (pVO2) in patients at 2–3m, which normalised by 6m (80.5% to 93.3% of predicted, p=0.001) (Table 1, Fig. 1C). At 2–3m, 49% of patients had submaximal tests (respiratory exchange ratio <1.1), reducing to 25% by 6m (p=0.057). VE/VCO2 slope, a marker of lung efficiency, was abnormal in patients but improved on serial CPET (Table 1, Fig. 1D).

Cardiac symptoms (chest pain, dyspnoea, palpitations, dizziness or syncope) were present in 83% of patients at 2–3m, reducing to 52% by 6m (p<0.001). There was no significant association between CMR or CPET parameters and persistent cardiac symptoms at 6m (Fig. 1E).

Conclusions

Cardiopulmonary parameters (on CMR and CPET) improved in moderate-severe COVID-19 patients from 2–3 to 6 months post infection. Despite this, patients continued to experience cardiac symptoms which had no relationship with measured parameters.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): 1. NIHR Oxford and Oxford Health Biomedical Research Centre, Oxford British Heart Foundation (BHF) Centre of Research Excellence (RE/18/3/34214), United Kingdom Research Innovation and Wellcome Trust2. Medical Research Council and Department of Health and Social Care/National Institute for Health Research Grant (MR/V027859/1) ISRCTN number 10980107 Table 1Figure 1

2378Blunted stress myocardial oxygenation and not myocardial perfusion reserve is associated with arrhythmic risk in hypertrophic cardiomyopathy

Background

In hypertrophic cardiomyopathy (HCM), myocardial ischaemia is believed to play a role in fatal life-threatening ventricular arrhythmias and caused by microvascular dysfunction manifesting as impaired myocardial perfusion. However, previous studies suggest that myocardial oxygenation during vasodilator stress may also be blunted when perfusion is normal, due to increased metabolic demands conferred by energy-costly sarcomeric mutations, left ventricular hypertrophy and outflow obstruction. Whether or not impaired myocardial perfusion reserve or blunted stress oxygenation on cardiac magnetic resonance (CMR) predict the risk of ventricular arrhythmia in HCM is unknown.

Purpose

We sought to investigate if impaired myocardial perfusion reserve or stress oxygenation is associated with an increased risk of ventricular arrhythmia in HCM.

Methods

103 genotyped HCM patients (mean age 47±15 years) and 32 age- and sex-matched healthy controls underwent adenosine stress blood oxygen level dependent (BOLD) imaging, first pass perfusion and late gadolinium imaging (LGE) on CMR to assess stress oxygenation (BOLD ΔSI), myocardial perfusion reserve index (MPRI), and fibrosis respectively. All HCM patients were monitored for ventricular tachycardia (≥3 beats, ≥120 beats per minute) on a 24-hour Holter.

Results

As expected, MPRI was significantly reduced in HCM (1.5±0.4 vs 2.0±0.3, p<0.0001) compared to controls. Stress oxygenation response was blunted in HCM versus controls (9.1±4.1% vs 17.0±1.6%, p<0.0001, Figure 1B). Twenty-six (25%) patients developed ventricular tachycardia on Holter monitoring. On univariate analysis, only stress oxygenation and not MPRI associated with ventricular tachycardia. The prevalence of ventricular tachycardia in HCM increased with decreasing quartiles of stress oxygenation (Figure 1D). HCM patients in the lowest quartile of oxygenation (BOLD ΔSI <6.5%) were at a three-fold risk of ventricular tachycardia (OR 3.04, 95% confidence interval 1.02–9.05, p=0.04) on multivariable analysis (after adjusting for sudden cardiac death risk factors and LGE mass) compared to other patients. Sarcomeric mutation status was an independent determinant of stress oxygenation on multivariable analysis. Stress oxygenation was impaired in phenotype-negative sarcomeric mutation carriers (Sarc+P-, n=16) despite normal perfusion (Figure 1C, E). Sarcomeric HCM (Sarc+HCM) had more severe impairment in stress oxygenation than genotype negative HCM (G-HCM) and controls (Figure 1E).

Figure 1

Conclusion

In HCM, blunted stress-induced oxygenation is associated with an increased risk of ventricular arrhythmia and may represent a novel biomarker of arrhythmic risk. Sarcomeric mutation status is an important determinant of stress oxygenation response.

Acknowledgement/Funding

National Institute for Health Research Oxford Biomedical Centre and British Heart Foundation.

A toolbox for tuberculosis (TB) diagnosis: an Indian multi-centric study (2006-2008); evaluation of serological assays based on PGL-Tb1 and ESAT-6/CFP10 antigens for TB diagnosis

BACKGROUND

The aim of this multi-centric prospective study in India was to assess the accuracy of a serological test as an additional tool for diagnosing active tuberculosis (ATB). In particular, an assay based on ELISA using a phenolic glycolipid (PGL-Tb1) or a fusion protein (ESAT-6/CFP10) was compared to the tuberculin skin test (TST) and the microbiological results according to HIV status.

METHODS

Individuals with and without ATB and HIV infection were enrolled. Serology and TST results were analyzed per se and in combination with the microbiological data.

RESULTS

Among the 778 ATB patients, 102 were HIV-infected, 316 HIV-uninfected and 360 had an HIV-unknown status. Of the 945 non-ATB subjects, 559 were at low risk (community adults) and 386 at high risk of M. tuberculosis exposure. Among those with ATB, the sensitivity of ELISA-PGL-Tb1 for ATB was higher than that of ELISA-ESAT-6/CFP10, both in HIV-infected (72.3% versus 63.7%, p = 0.29) and HIV-uninfected/HIV-unknown groups (40.5% versus 28.6%; p<0.0001), whereas the specificity was around 91% for both tests. Sensitivity for ATB increased when the results of the two ELISA were combined, reaching 75.5% in the HIV-infected and 50.9% in the group of HIV-uninfected/HIV-unknown ATB, with a significant decrease of the global specificity (83.9%). Analyzing the ELISA results with the microbiological results, we observed that the sensitivity of both serology tests was independent of the ATB patients' smear microscopy (SM) status and grade. Combining the results of SM with both ELISA, the detection of ATB patients significantly increased (p<0.0001), particularly in those with extrapulmonary TB (up to 45.1%) or HIV infection (up to 83.3%). No significant association was observed between TST and serology results.

CONCLUSIONS

In this prospective multi-centric study, the combination of two rapid tests, such as SM and serology, might be useful in detecting ATB, especially in HIV-infected patients.

Randomized clinical trial of thrice-weekly 4-month moxifloxacin or gatifloxacin containing regimens in the treatment of new sputum positive pulmonary tuberculosis patients

BACKGROUND

Shortening tuberculosis (TB) treatment duration is a research priority. This paper presents data from a prematurely terminated randomized clinical trial, of 4-month moxifloxacin or gatifloxacin regimens, in South India.

METHODS

Newly diagnosed, sputum-positive HIV-negative pulmonary TB patients were randomly allocated to receive gatifloxacin or moxifloxacin, along with isoniazid and rifampicin for 4 months with pyrazinamide for first 2 months (G or M) or isoniazid and rifampicin for 6 months with ethambutol and pyrazinamide for first 2 months (C). All regimens were administered thrice-weekly. Clinical and bacteriological assessments were done monthly during treatment and for 24 months post-treatment. The Data and Safety Monitoring Board recommended termination of the trial due to high TB recurrence rates in the G and M regimens.

RESULTS

Of 416 patients in intent-to-treat analysis, 6 (5%) of 124, 2 (2%) of 110 and 2 (2%) of 137 patients with drug-susceptible TB in the G, M and C arms respectively had unfavorable response at the end of treatment; during the next 24 months, 17 (15%) of 115, 11 (11%) of 104 and 8 (6%) of 132 patients respectively, had TB recurrence. Of 38 drug-resistant patients 1 of 8 and 3 of 26 in the G and C arms respectively had unfavourable response at the end of treatment; and TB recurrence occurred in 2 of 7 and 2 of 23 patients, respectively. The differences in TB recurrence rates between the G and C arms was statistically significant (p = 0.02). Gastro-intestinal symptoms occurred in 23%, 22% and 9% of patients in the G, M and C arms respectively, but most reactions were mild and manageable with symptomatic measures; 1% required regimen modification.

CONCLUSIONS

4-month thrice-weekly regimens of gatifloxacin or moxifloxacin with isoniazid, rifampicin and pyrazinamide, were inferior to standard 6-month treatment, in patients with newly diagnosed sputum positive pulmonary TB.

TRIAL REGISTRATION

Clinical Trials Registry of India CTRI/2012/10/003060.

A toolbox for tuberculosis (TB) diagnosis: an Indian multicentric study (2006-2008). Evaluation of QuantiFERON-TB gold in tube for TB diagnosis

BACKGROUND

The aim of this multicentric prospective study in India was to assess the performance of the QuantiFERON TB-Gold in tube (QFT-GIT), Tuberculin Skin Test (TST) and microbiological results as additional tools for diagnosing active tuberculosis (TB) and latent infection (LTBI) according to Human Immunodeficiency Virus (HIV) status.

METHODS

Individuals with and without active TB and HIV infection were enrolled between 2006-2008. QFT-GIT and TST results were analyzed per se and in combination with microbiological data.

RESULTS

Among the 276 individuals (96 active pulmonary TB and 180 no active TB) tested by QFT-GIT, 18 indeterminate results (6.5%) were found, more significantly numerous in the HIV-infected (15/92; 16.3%) than the HIV-uninfected (3/184; 1.6%)(p<0.0001). QFT-GIT sensitivity for active TB was 82.3% and 92.9% respectively after including or excluding indeterminate results. Clinical sensitivity was significantly lower in the HIV-infected (68.4%) than the HIV-uninfected (91.4%) patients (p = 0.0059). LTBI was detected in 49.3% of subjects without active TB but varied according to TB exposure. When the TST and QFT-GIT were concomitantly performed, the respective sensitivity for active TB diagnosis was 95.0% and 85.0% in the HIV-uninfected (p = 0.60), and 66.7% and 51.5% in the HIV-infected patients (p = 0.32). QFT-GIT and TST respective specificity for active TB in the HIV-uninfected was 25.0% and 57.1% (p = 0.028), and 64.8% and 83.3% in the HIV-infected (p = 0.047). In those with active TB, QFT-GIT results were not associated with microbiological parameters (smear grade, liquid culture status, time-to-positivity of culture) or clinical suspicion of active TB score (provided by the clinicians at enrollment). Combining microbiological tests with both immunological tests significantly increased sensitivity for active TB diagnosis (p = 0.0002), especially in the HIV-infected individuals (p = 0.0016).

CONCLUSION

QFT-GIT and TST have similar diagnostic value for active TB diagnosis. In HIV-infected patients, combining microbiological tests with both immunological tests significantly increases the sensitivity for active TB diagnosis.

A toolbox for tuberculosis diagnosis: an Indian multicentric study (2006-2008): microbiological results

BACKGROUND

The aim of this multicentric prospective study in India was to assess the value of several microbiological tools that contribute to the diagnosis of tuberculosis (TB) according to HIV status.

METHODS

Standard microbiological tools on individual specimens were analyzed.

RESULTS

Among the 807 patients with active TB, 131 were HIV-infected, 316 HIV-uninfected and 360 had HIV-unknown status. Among the 980 non-active TB subjects, 559 were at low risk and 421 were at high risk of M. tuberculosis (Mtb) exposure. Sensitivity of smear microscopy (SM) was significantly lower in HIV-infected (42.2%) than HIV-uninfected (75.9%) (p = 0.0001) and HIV-unknown pulmonary TB patients (61.4%) (p = 0.004). Specificity was 94.5% in non-TB patients and 100% in health care workers (HCW) and healthy family contacts. Automated liquid culture has significantly higher diagnostic performances than solid culture, measured by sensitivity (74.7% vs. 55.9%) (p = 0.0001) and shorter median time to detection (TTD) (12.0 vs. 34.0 days) (p = 0.0001). Specificity was 100% in HCW and cured-TB patients, but was lower in non-TB patients (89%) due to isolation of Mycobacteria other than tuberculosis (MOTT). TTD by both methods was related to AFB score. Contamination rate was low (1.4%). AccuProbe hybridization technique detected Mtb in almost all culture-positive specimens, but MOTT were found in 4.7% with a significantly higher frequency in HIV-infected (15%) than HIV-uninfected TB patients (0.5%) (p = 0.0007). Pre-test classification significantly increased the diagnostic value of all microbiological tests in pulmonary TB patients (p<0.0001) but to a lesser degree in extrapulmonary TB patients.

CONCLUSIONS

Conventional microbiological tools led to results similar to those already described in India special features for HIV-infected TB patients included lower detection by SM and culture. New microbiological assays, such as the automated liquid culture system, showed increased accuracy and speed of detection.

IP-10 response to RD1 antigens might be a useful biomarker for monitoring tuberculosis therapy

Background

There is an urgent need of prognosis markers for tuberculosis (TB) to improve treatment strategies. The results of several studies show that the Interferon (IFN)-γ-specific response to the TB antigens of the QuantiFERON TB Gold (QFT-IT antigens) decreases after successful TB therapy. The objective of this study was to evaluate whether there are factors other than IFN-γ [such as IFN-γ inducible protein (IP)-10 which has also been associated with TB] in response to QFT-IT antigens that can be used as biomarkers for monitoring TB treatment.

Methods

In this exploratory study we assessed the changes in IP-10 secretion in response to QFT-IT antigens and RD1 peptides selected by computational analysis in 17 patients with active TB at the time of diagnosis and after 6 months of treatment. The IFN-γ response to QFT-IT antigens and RD1 selected peptides was evaluated as a control. A non-parametric Wilcoxon signed-rank test for paired comparisons was used to compare the continuous variables at the time of diagnosis and at therapy completion. A Chi-square test was used to compare proportions.

Results

We did not observe significant IP-10 changes in whole blood from either NIL or QFT-IT antigen tubes, after 1-day stimulation, between baseline and therapy completion (p = 0.08 and p = 0.7 respectively). Conversely, the level of IP-10 release to RD1 selected peptides was significantly different (p = 0.006). Similar results were obtained when we detected the IFN-γ in response to the QFT-IT antigens (p = 0.06) and RD1 selected peptides (p = 0.0003). The proportion of the IP-10 responders to the QFT-IT antigens did not significantly change between baseline and therapy completion (p = 0.6), whereas it significantly changed in response to RD1 selected peptides (p = 0.002). The proportion of IFN-γ responders between baseline and therapy completion was not significant for QFT-IT antigens (p = 0.2), whereas it was significant for the RD1 selected peptides (p = 0.002), confirming previous observations.

Conclusions

Our preliminary study provides an interesting hypothesis: IP-10 response to RD1 selected peptides (similar to IFN-γ) might be a useful biomarker for monitoring therapy efficacy in patients with active TB. However, further studies in larger cohorts are needed to confirm the consistency of these study results.

Outcome of standardized treatment for patients with MDR-TB from Tamil Nadu, India

BACKGROUND & OBJECTIVES

Programmatic management of MDR-TB using a standardized treatment regimen (STR) is being implemented under the Revised National Tuberculosis Control Programme (RNTCP) in India. This study was undertaken to analyse the outcomes of MDR-TB patients treated at the Tuberculosis Research Centre, Chennai, with the RNTCP recommended 24 months STR, under programmatic conditions.

METHODS

Patients failed to the category II re-treatment regimen and confirmed to have MDR-TB, were treated with the RNTCP's STR in a prospective field trial on a predominantly ambulatory basis. Thirty eight patients were enrolled to the trial from June 2006 to September 2007.

RESULTS

Time to culture conversion was two months or less for 82 per cent of patients. Culture conversion rates at 3 and 6 months were 84 and 87 per cent respectively. At the end of treatment, 25 (66%) were cured, 5 defaulted, 3 died and 5 failed. At 24 months, 30 (79%) patients, including 5 defaulters, remained culture negative for more than 18 months. Twenty two (58%) patients reported adverse drug reactions (ADRs) which required dose reduction or termination of the offending drug. No patient had XDR-TB initially, but 2 failure cases emerged as XDR-TB during treatment.

INTERPRETATION & CONCLUSIONS

Outcomes of this small group of MDR-TB patients treated with the RNTCP's STR is encouraging in this setting. Close attention needs to be paid to ensure adherence, and to the timely recognition and treatment of ADRs.

Role of QuantiFERON-TB gold, interferon gamma inducible protein-10 and tuberculin skin test in active tuberculosis diagnosis

Background

The measurement of Interferon gamma or Interferon gamma inducible protein (IP)-10 in antigen stimulated blood samples is suggested as an alternative method for latent tuberculosis (TB) diagnosis. Nonetheless, their role in active TB diagnosis, particularly in TB endemic settings is yet to be defined. In this study, the sensitivities and specificities of Interferon gamma release assay (IGRA), IP-10 assay and tuberculin skin test (TST) in detecting active TB cases were assessed in human immunodeficiency virus (HIV) sero-negative TB patients and healthy controls respectively.

Methods/Principal Findings

A total of 177 adult TB patients and 100 healthy controls were included for this study. QuantiFERON-TB Gold In-tube (QFT-IT) method was used to analyze the sensitivity and specificity of IGRA. QFT-IT, IP-10 and TST yielded the diagnostic sensitivities of 90.6% (95%CI: 86.3%–94.9%), 92.5% (95%CI: 88.6%–96.4%) and 68.9% (95%CI: 60.6%–77.2%) and specificities of 55% (95% CI: 35.2%–54.8%), 48% (95% CI: 38.2%–57.8%) and 75.5% (95% CI: 66.8%–84.2%), respectively. The extent of pulmonary involvement or presence of diabetes mellitus did not appear to influence the sensitivities of any of these tests. The combination of any of the two tests among QFT-IT, IP-10 and TST showed >98% sensitivity among smear negative cases and particularly the combination of IP-10, TST and smear microscopy showed 100% sensitivity, however, the specificity was decreased to 44.8%.

Conclusions/Significance

QFT-IT and IP-10 were highly sensitive in detecting active TB cases. The combination with TST improved the sensitivity of QFT-IT and IP-10 significantly. Although the higher sensitivity of combination of QFT-IT/IP-10 and TST may be useful in active TB diagnosis, they are limited by their poor specificity due to the high prevalence of latent TB in our settings.

Arginine hydrochloride enhances the dynamics of subunit assembly and the chaperone-like activity of alpha-crystallin

PURPOSE

Alpha-crystallin, a major eye lens protein, bears homology with small heat shock proteins (sHsps) and exhibits molecular chaperone-like activity. Structural perturbation by temperature or low concentrations of denaturants leads to enhancement of its chaperone-like activity. We have earlier demonstrated similar enhancement of chaperone-like activity using biologically compatible solutes such as arginine hydrochloride and aminoguanidine. The purpose of the present study is to get an insight into the mechanism of the arginine induced enhancement of chaperone-like activity of alpha-crystallin.

METHODS

The effect of arginine hydrochloride on the chaperone-like activity of alpha-crystallin at 25 degrees C was studied using DTT induced aggregation of insulin as a model system. Changes in the accessibility of the thiol group near the end of the alpha-crystallin domain in the absence and the presence of arginine hydrochloride were studied using dithiobisnitrobenzoic acid. Fluorescence resonance energy transfer studies were performed to investigate changes in the dynamics of the subunit assembly. Urea induced denaturation studies of alpha-crystallin were carried out to investigate structural destabilization of alpha-crystallin, if any, in the presence of arginine hydrochloride.

RESULTS

Arginine hydrochloride increases the chaperone-like activity of alpha-crystallin several fold towards DTT induced aggregation of insulin at room temperature. Our study shows that both the extent and the rate of accessibility of the thiol group are increased in the presence of arginine. Fluorescence resonance energy transfer experiments show that arginine hydrochloride significantly increases the subunit exchange between the oligomers of alpha-crystallin. Arginine induced structural perturbation and loosening of subunit assembly of alpha-crystallin leads to overall destabilization of the protein as reflected by the urea denaturation study.

CONCLUSIONS

Arginine perturbs the tertiary and quaternary structure of alpha-crystallin and enhances the dynamics of the subunit assembly leading to enhanced chaperone-like activity. Thus, in addition to size, surface hydrophobicity, and charge distribution, the dynamics of the subunit assembly appears to be one of the critical factors that can modulate the chaperone activity.

Aortoiliac angulation and the need for secondary procedures to secure stent graft fixation: which angle is important?

BACKGROUND

The purpose of this study was to quantify the degree of aortoiliac tortuosity and determine the relationship between aortoiliac angulation and the need for a secondary procedure following endovascular repair.

METHODS

Among 206 patients treated with the AneuRx stent graft, 3-year follow up data were available in 71 patients. Twenty eight patients without duplex and CT angiograms (CT angiography) on follow-up were excluded. The anatomy of the preoperative proximal aortic neck was evaluated using 3D-CT angiography reconstructed images in: a) Group I: 15 patients who required secondary procedures and b) Group II: 18 patients without any endovascular leak during follow up. The groups did not differ in age (72.9+/-6.1 versus 73.3+/-9.1) or aneurysm diameter (60.1+/-9.1 versus 60.5+/-10.1). In order to determine the aortoiliac tortuosity, we measured: a) the suprarenal aorta-infrarenal aortic neck angle: angle of the aorta at the level of the renal arteries, b) infrarenal aortic neck-aneurysm angle: angle of the aorta at the start of aneurysm, c) right iliac angle, d) left iliac angle, e) aortic neck length, f) aortic neck diameter.

RESULTS

Computer-based measurements on 3D-CT angiography reconstructed images were: a) suprarenal aorta-infrarenal aortic neck angle: group I: (22.6+/-16.2), group II: (11.9+/-6.9), p<0.05; b) infrarenal aortic neck-aneurysm angle: group I: 17.6+/-12.4, group II: 18.8+/-9.4, p=NS; c) right iliac angle: group I: 22.9+/-12.6, group II: 20.4+/-9.5, p=NS; d) left iliac angle: group I: 22.4+/-10.5, group II: 19.1+/-12.2, p=NS; e) aortic neck length: group I: 18.9+/-5.3 mm, group II: 20.4+/-5.3 mm, p=NS; f) aortic neck diameter: group I: 24.1+/-1.0 mm, group II: 23.3+/-1.6, p=NS.

CONCLUSIONS

Aortoiliac angulation can be defined and quantified. In patients requiring secondary procedures, there is an increased angulation at the proximal aortic neck angle.

Unfolding and refolding of a quinone oxidoreductase: alpha-crystallin, a molecular chaperone, assists its reactivation

alpha-Crystallin, a member of the small heat-shock protein family and present in vertebrate eye lens, is known to prevent the aggregation of other proteins under conditions of stress. However, its role in the reactivation of enzymes from their non-native inactive states has not been clearly demonstrated. We have studied the effect of alpha-crystallin on the refolding of zeta-crystallin, a quinone oxidoreductase, from its different urea-denatured states. Co-refolding zeta-crystallin from its denatured state in 2.5 M urea with either calf eye lens alpha-crystallin or recombinant human alpha B-crystallin could significantly enhance its reactivation yield. alpha B-crystallin was found to be more efficient than alpha A-crystallin in chaperoning the refolding of zeta-crystallin. In order to understand the nature of the denatured state(s) of zeta-crystallin that can interact with alpha-crystallin, we have investigated the unfolding pathway of zeta-crystallin. We find that it unfolds through three distinct intermediates: an altered tetramer, a partially unfolded dimer, which is competent to fold back to its active state, and a partially unfolded monomer. The partially unfolded monomer is inactive, exhibits highly exposed hydrophobic surfaces and has significant secondary structural elements with little or no tertiary structure. This intermediate does not refold into the active state without assistance. alpha-Crystallin provides the required assistance and improves the reactivation yield several-fold.

N(omega)-arginine dimethylation modulates the interaction between a Gly/Arg-rich peptide from human nucleolin and nucleic acids

We studied the interaction between a synthetic peptide (sequence Ac-GXGGFGGXGGFXGGXGG-NH(2), where X = arginine, N(omega),N(omega)-dimethylarginine, DMA, or lysine) corresponding to residues 676-692 of human nucleolin and several DNA and RNA substrates using double filter binding, melting curve analysis and circular dichroism spectroscopy. We found that despite the reduced capability of DMA in forming hydrogen bonds, N(omega),N(omega)-dimethylation does not affect the strength of the binding to nucleic acids nor does it have any effect on stabilization of a double-stranded DNA substrate. However, circular dichroism studies show that unmethylated peptide can perturb the helical structure, especially in RNA, to a much larger extent than the DMA peptide.

Interaction of human recombinant αA- and αB-crystallins with early and late unfolding intermediates of citrate synthase on its thermal denaturation

We have investigated the role of recombinant human alphaA- and alphaB-crystallins in the heat-induced inactivation and aggregation of citrate synthase. Homo-multimers of both alphaA- and alphaB-crystallins confer protection against heat-induced inactivation in a concentration-dependent manner and also prevent aggregation. Interaction of crystallins with early unfolding intermediates of citrate synthase reduces their partitioning into aggregation-prone intermediates. This appears to result in enhanced population of early unfolding intermediates that can be reactivated by its substrate, oxaloacetate. Both these homo-multimers do not form a stable complex with the early unfolding intermediates. However, they can form a soluble, stable complex with aggregation-prone late unfolding intermediates. This soluble complex formation prevents aggregation. Thus, it appears that the chaperone activity of alpha-crystallin involves both transient and stable interactions depending on the nature of intermediates on the unfolding pathway; one leads to reactivation of the enzyme activity while the other prevents aggregation.

Redox-regulated chaperone function and conformational changes of Escherichia coli Hsp33

We have studied the chaperone activity and conformation of Escherichia coli heat shock protein (Hsp)33, whose activity is known to be switched on by oxidative conditions. While oxidized Hsp33 completely prevents the heat-induced aggregation of zeta-crystallin at 42 degrees C at a ratio of 1:1 (w/w), the reduced form exhibits only a marginal effect on the aggregation. Far UV-circular dichroism (CD) spectra show that reduced Hsp33 contains a significant alpha-helical component. Oxidation results in significant changes in the far UV-CD spectrum. Near UV-CD spectra show changes in tertiary structural packing upon oxidation. Polarity-sensitive fluorescent probes report enhanced hydrophobic surfaces in the oxidized Hsp33. Our studies show that the oxidative activation of the chaperone function of Hsp33 involves observable conformational changes accompanying increased exposure of hydrophobic pockets.

Detection and assay of proteases using calf lens beta-crystallin aggregate as substrate

The eye lens protein, betaL-crystallin, aggregates and yields a turbid solution upon refolding from its denatured state. We have observed that the addition of trace amounts of protease results in clearing of this turbidity. Based on this observation, we have developed a simple and rapid method for the detection and assay of proteases. This assay can be performed in the pH range of 6.0-9.0. We could assay the activity of trypsin at a concentration as low as 5 microg/ml.

Artificial chaperoning of insulin, human carbonic anhydrase and hen egg lysozyme using linear dextrin chains--a sweet route to the native state of globular proteins

Linear dextrins (alpha-1,4-D-glucopyranoside chains) are known to possess amphiphilic surfaces and solubilize lipophilic compounds. We have assessed the ability of this amphiphilic surface of dextrin to inhibit the self-aggregation and assist the refolding of proteins. Addition of decameric dextrin, or dextrin-10, in the renaturation buffer improves the refolding yield of human carbonic anhydrase from its guanidinium chloride-induced denatured state. It is also seen to inhibit the self-aggregation of insulin. The ability of dextrin-10 to interact with cetyltrimethylammonium bromide and postpone its critical micellar concentration allows the use of dextrin-10 as a 'detergent stripping agent' in a novel artificial chaperoning process described earlier. The aggregation of human carbonic anhydrase and lysozyme upon refolding is prevented by cetyltrimethylammonium bromide due to the formation of a protein-detergent complex; dextrin-10 strips off the detergent from the complex and allow the proteins to fold, thus increasing the renaturation yield. Dextran-4 (the alpha-1,6-D-glucopyranoside chain), which does not exhibit amphiphilic properties, does not help in such artificial chaperoning.

The chaperone-like alpha-crystallin forms a complex only with the aggregation-prone molten globule state of alpha-lactalbumin

The chaperone-like alpha-crystallin prevents aggregation of several proteins by interacting with their non-native states. Alpha-Lactalbumin adopts different non-native states under different experimental conditions. We have investigated the interaction of alpha-crystallin with three non-identical non-native states, using fluorescence, circular dichroism, and gel filtration chromatography. The compact molten globule state of apo-alpha-lactalbumin in tris buffer does not interact with alpha-crystallin. The expanded, flexible molten globule-like state of reduced apo-alpha-lactalbumin (formed at pH 7.2) also does not interact with alpha-crystallin. Only the aggregation-prone non-native state of reduced apo-alpha-lactalbumin formed at pH 6.0 interacts with alpha-crystallin to form a stable complex. The alpha-crystallin bound reduced apo-alpha-lactalbumin exhibits properties similar to those of a molten globule. Our results show that alpha-crystallin interacts only with the aggregation prone molten globule state of reduced apo-alpha-lactalbumin but not with the other non-aggregating molten globule states of the protein.

Separation and estimation of seven vasodilators using packed column supercritical fluid chromatography

This paper reports a method for an isocratic separation and simultaneous estimation of seven vasodilators: isosorbide mononitrate (ISMN), isosorbide dinitrate (ISDN), cyclandelate, nimodipine, amlodipine, pentifylline and pentoxifylline using packed column supercritical fluid chromatography (SFC). An arbitrary choice of vasodilatory compounds with respect to their chemical structures was made to examine the viability of this technique for analysis of drugs and pharmaceuticals. Elution was performed on a RP-C18 column. SFC offers several degrees of freedom: temperature, pressure and modifier concentration to attain optimum resolution and sensitivity. The effects of these parameters on retention time have been studied using methanol modified carbon dioxide. The analytes were identified and measured by UV-detection. The chromatographic points of merit have been listed. Detection limits appear to be similar to those found in liquid chromatography. Modifier concentration does generally make major changes in retention and selectivity. A full scale validation for the seven vasodilators has been attempted and the statistical quality evaluated.

Structural perturbation of alpha-crystallin and its chaperone-like activity

alpha-Crystallin is a multimeric lenticular protein that has recently been shown to be expressed in several non-lenticular tissues as well. It is shown to prevent aggregation of non-native proteins as a molecular chaperone. By using a non-thermal aggregation model, we could show that this process is temperature-dependent. We investigated the chaperone-like activity of alpha-crystallin towards photo-induced aggregation of gamma-crystallin, aggregation of insulin and on the refolding induced aggregation of beta- and gamma-crystallins. We observed that alpha-crystallin could prevent photo-aggregation of gamma-crystallin and this chaperone-like activity of alpha-crystallin is enhanced several fold at temperatures above 30 degrees C. This enhancement parallels the exposure of its hydrophobic surfaces as a function of temperature, probed using hydrophobic fluorescent probes such as pyrene and 8-anilinonaphthalene-1-sulfonate. We, therefore, concluded that alpha-crystallin prevents the aggregation of other proteins by providing appropriately placed hydrophobic surfaces; a structural transition above 30 degrees C involving enhanced or re-organized hydrophobic surfaces of alpha-crystallin is important for its chaperone-like activity. We also addressed the issue of conformational aspects of target proteins and found that their aggregation prone molten globule states bind to alpha-crystallin. We trace these developments and discuss some new lines that suggest the role of tertiary structural aspects in the chaperone process.

Co-refolding denatured-reduced hen egg white lysozyme with acidic and basic proteins

Refolding of denatured-reduced lysozyme and the effect of co-refolding it with other proteins such as RNase A, bovine serum albumin, histone, myelin basic protein, alcohol dehydrogenase and DNase I on the renaturation yield and the aggregation of lysozyme have been studied. Basic proteins consistently increase the renaturation yield of the basic protein lysozyme (10-20% more than in their absence) with little or no aggregation. On the other hand, co-refolding of lysozyme with acidic proteins leads to aggregation and a significant decrease in renaturation yields. Our results show that hetero-interchain interactions (non-specific interactions) occur when the basic protein lysozyme is refolded together with acidic proteins such as bovine serum albumin, alcohol dehydrogenase or DNase I. Our results also suggest that the net charge on proteins plays a significant role in such non-specific aggregation. These results should prove useful in understanding the hetero-interchain interactions between folding polypeptide chains.

Effect of the chaperone-like alpha-crystallin on the refolding of lysozyme and ribonuclease A

Alpha-crystallin exhibits chaperone-like properties in preventing aggregation of proteins. We have studied the effect of alpha-crystallin on the refolding of denatured-disulfide intact and denatured-reduced lysozyme and RNase A. Alpha-crystallin does not have any effect on the refolding of both the denatured-disulfide intact enzymes. However, it inhibits the aggregation and oxidative renaturation of denatured-reduced lysozyme. Interestingly, it has no effect on the refolding of denatured-reduced RNase A. In order to probe the molecular basis of this differential behavior of alpha-crystallin towards lysozyme and RNase A, we have carried out circular dichroism and fluorescence studies on the refolding of denatured-reduced RNase A. It exhibits an extended conformation with little difference in the exposed hydrophobicity during the refolding process. We have earlier shown the presence of an aggregation-prone, refolding-competent, molten-globule-like intermediate on the refolding pathway of lysozyme. Alpha-crystallin binds to this intermediate, prevents its aggregation and inhibits its oxidative refolding. It was earlier believed that alpha-crystallin, unlike other chaperones, does not recognize intermediates on the refolding pathway but only recognizes intermediates on the unfolding pathway of proteins. Our present study clearly shows that it recognizes the refolding intermediates as well.

Chaperone-like activity and temperature-induced structural changes of alpha-crystallin

alpha-Crystallin is known to exhibit chaperone-like activity. We have studied its chaperone-like activity toward the aggregation of betaL-crystallin upon refolding of this protein from its unfolded state in guanidinium chloride. The chaperone-like activity of alpha-crystallin is less pronounced below 30 degrees C and is enhanced above this temperature. The plot of percentage protection as a function of temperature shows two transitions; one at 30 degrees C and another at around 55 degrees C. We have performed steady state fluorescence, fluorescence polarization, fluorescence quenching, circular dichroism, sedimentation analysis, and gel filtration chromatography to probe the temperature-induced structural changes of alpha-crystallin. Our results show that at above 50 degrees C, alpha-crystallin undergoes a transition to a multimeric molten globule-like state. Above 30 degrees C, a minor but detectable perturbation in its tertiary structure occurs that might lead to the observed exposure of its hydrophobic surfaces. These results support our earlier hypothesis that alpha-crystallin prevents the aggregation of other proteins by providing appropriately placed hydrophobic surfaces; a structural transition above 30 degrees C involving enhanced or reorganized hydrophobic surfaces of alpha-crystallin is important for its chaperone-like activity. It is possible that a structural alteration induced by temperature forms a part of the general mechanism of chaperone function, because they are required to function more effectively at nonpermissible temperatures.

Molten-globule state of carbonic anhydrase binds to the chaperone-like alpha-crystallin

alpha-Crystallin, a multimeric protein, exhibits chaperone-like activity in preventing aggregation of several proteins. We have studied the chaperone-like activity of alpha-crystallin toward heat-induced aggregation of bovine and human carbonic anhydrase. Human carbonic anhydrase aggregates at 60 degrees C, while bovine carbonic anhydrase does not aggregate significantly at this temperature. Removal of the enzyme-bound metal ion, Zn2+, by EDTA modulates the aggregation behavior of bovine carbonic anhydrase. Fluorescence and circular dichroism studies show that removal of the metal ion from the bovine carbonic anhydrase by a chelator such as EDTA enhances the propensity of the enzyme to adopt the molten-globule state. alpha-Crystallin binds to this state of the enzyme and prevents aggregation. Fluorescence and circular dichroism studies on the alpha-crystallin-enzyme complexes show that the enzymes in the complex are in the molten-globule state. These results are of relevance to the interaction of chaperones with the partially unfolded states of target proteins.

Refolding of denatured and denatured/reduced lysozyme at high concentrations

Refolding of proteins at high concentrations often results in aggregation. To gain insight into the molecular aspects of refolding and to improve the yield of active protein, we have studied the refolding of lysozyme either from its denatured state or from its denatured/reduced state. Refolding of denatured lysozyme, even at 1 mg/ml, yields fully active enzyme without aggregation. However, refolding of denatured/reduced lysozyme into buffer that lacks thiol/disulfide reagents leads to aggregation. Thiol/disulfide redox reagents such as cysteine/cystine and reduced/oxidized glutathione facilitate the renaturation, with the yield depending on their absolute concentrations. We have obtained an approximately 70% renaturation yield upon refolding of lysozyme at 150 microgram/ml. The cysteine/cystine redox system is more efficient compared with the glutathione redox system. When lysozyme is refolded in the absence of redox reagents, a transient intermediate that has regained a significant amount of secondary structure is formed. The tryptophans in this intermediate are as exposed to water as in the fully unfolded protein. It shows increased exposure of hydrophobic surfaces compared with the native or completely unfolded enzyme. This aggregation-prone intermediate folds to active enzyme upon addition of oxidized glutathione before the aggregation process starts. These properties of the intermediate in the refolding pathway of lysozyme are similar to those proposed for the molten globule.

Rapid refolding studies on the chaperone-like alpha-crystallin. Effect of alpha-crystallin on refolding of beta- and gamma-crystallins

alpha-Crystallin, a multimeric protein present in the eye lens, is shown to have chaperone-like activity in preventing thermally induced aggregation of enzymes and other crystallins. We have studied the rapid refolding of alpha-crystallin, and compared it with other calf eye lens proteins, namely beta- and gamma-crystallins. alpha-Crystallin forms a clear solution upon rapid refolding from 8 M urea. The refolded alpha-crystallin has native-like secondary, tertiary, and quaternary structures as revealed by circular dichroism and fluorescence characteristics as well as gel filtration and sedimentation velocity measurements. On rapid refolding, beta- and gamma-crystallins aggregate and form turbid solutions. The presence of alpha-crystallin in the refolding buffer marginally increases the recovery of beta- and gamma-crystallins in the soluble form. However, unfolding of these crystallins together with alpha-crystallin using 8 M urea and subsequent refolding significantly increases the recovery of these proteins in the soluble form. These results indicate that an intermediate of alpha-crystallin formed during refolding is more effective in preventing the aggregation of beta- and gamma-crystallins. This supports our earlier hypothesis (Raman, B., and Rao, C. M. (1994) J. Biol. Chem. 269, 27264-27268) that the chaperone-like activity of alpha-crystallin is more pronounced in its structurally perturbed state.

Temperature dependent chaperone-like activity of alpha-crystallin

Alpha-crystallin, a multimeric protein present in the eye lens, is known to have chaperone-like activity in preventing the aggregation of enzymes and other crystallins. We have studied the chaperone-like activity of this protein towards the aggregation of insulin B chain, induced by reducing the interchain disulphide bond with dithiothreitol. At room temperature, there is no detectable protection (at a 1:1 (w/w) ratio of insulin: alpha-crystallin) against the aggregation of insulin B chain by alpha-crystallin, whereas it completely prevents this aggregation at 40 degrees C. We have monitored the temperature dependence of the protection of aggregation by alpha-crystallin; the protection increases sharply above 30 degrees C and reaches almost 100% by 41 degrees C. Probing the hydrophobic surfaces of alpha-crystallin with the hydrophobic fluorphore 8-anilino-1 naphthalene sulfonate suggests that the hydrophobic surfaces of alpha-crystallin are exposed to a greater extent above 30 degrees C. A complete prevention of the aggregation is achieved at 27.6 degrees C by increasing the concentration of alpha-crystallin by more than 8 fold. Similar temperature dependent chaperone-like activity of alpha-crystallin is observed towards the aggregation of zeta-crystallin, an enzyme crystallin from guinea pig. We have earlier shown that alpha-crystallin exposes hydrophobic surface(s) at temperatures above 30 degrees C. These results support our earlier hypothesis [Raman, B. and Rao, Ch.M. (1994) J. Biol. Chem. 269, 27264-27268] that the chaperone-like activity of alpha-crystallin is more pronounced in its structurally perturbed state.

Fluorescent staining for proteins on polyacrylamide gels with 5-dimethylamino-1-naphthalenesulfonyl chloride (dansyl chloride)

A simple and sensitive post electrophoresis fluorescent staining technique for proteins on polyacrylamide gels using 5-dimethylamino-1-naphthalene sulfonyl chloride (dansyl chloride) has been developed. Dansyl chloride staining increases the sensitivity, 0.125 micrograms protein per band can be visualised by this technique. The staining method appears to be applicable to all types of proteins including proteoglycans.

Chaperone-like activity and quaternary structure of alpha-crystallin

alpha-Crystallin has been shown to function as a molecular chaperone in preventing thermal aggregation of crystallins and other proteins. The molecular mechanism of this protection is not yet clear. gamma-Crystallin aggregates upon exposure to UV light. We have investigated the effect of the presence of alpha-crystallin in the photoaggregation process and find that alpha-crystallin does not prevent photoaggregation at low temperatures. The protection starts around 30 degrees C and steeply increases with temperature. The plot of protection ability versus temperature is sigmoidal, indicating a structural transition. Perturbation of the quaternary structure of alpha by non-thermal mode, such as 3 M urea, also results in enhanced protection. Pyrene, a hydrophobic fluorophore, is sparingly soluble in water. alpha-Crystallin enhances the solubility of pyrene by severalfold. Temperature dependence of this solubilization shows a transition around 30 degrees C (another at about 50 degrees C). Fluorescence intensity ratio of third and first peaks of pyrene emission (I3/I1,), indicative of hydrophobicity of the reporting area, also shows similar transitions suggesting enhanced hydrophobicity. Gel filtration experiments of irradiated samples indicate the complex formation between gamma- and alpha-crystallins. alpha-Crystallin does not prevent cold precipitation of gamma-crystallin. On the basis of these results, we hypothesize that alpha-crystallin prevents aggregation of non-native structures by providing appropriately placed hydrophobic surfaces. A structural transition above 30 degrees C enhances the protective ability, perhaps by increasing or reorganizing the hydrophobic surfaces. A similar temperature dependence has been reported for GroEL. Whether a structural switch, either activated by temperature, solvent conditions, or small molecule binding, forms a part of the general mechanism of chaperone activity needs to be investigated.

Amphiphilic properties of polysaccharides: dextrin chains as example

Polysaccharide chains are usually considered to be highly hydrophilic, since they contain no obvious apolar moieties. However, it is possible for even these chains to display hydrophobic character, arising out of stereochemical constraints in the chain. We had earlier shown that linear dextrin chains display amphiphilic properties, since all the hydroxyl groups are disposed on one side or face of the chain and the hydrogens disposed on the other. We provide further evidence here for this conclusion that dextrins are amphiphilic chains. In contrast, dextrans and cellulosic chains do not display amphiphilicity. Oligosaccharides that can adopt incipient helical structures might display amphiphilicity. This property might be relevant to intermolecular recognition on cell surfaces, lectin-sugar binding, antigen-antibody interactions and the like, and might be manifested more in a heteromolecular recognition process than as homomolecular self-aggregation.

Aggregation of lasalocid A in membranes: a fluorescence study

The aggregation behavior of the carboxylic ionophore, lasalocid A, has been studied in egg phosphatidylcholine vesicles by monitoring the intrinsic fluorescence of lasalocid A. Self quenching of lasalocid A fluorescence in vesicles of egg phosphatidylcholine suggests aggregation of lasalocid A. When aggregated lasalocid A is treated with increasing concentrations of lipid, there is an increase in fluorescence due to gradual reduction of self quenching on lateral dilution. This confirms the presence of loosely held non-covalent aggregates of lasalocid A in the membrane. This result is relevant in elucidating the molecular mechanism of cation transport by lasalocid A across membranes.

Hydrophobic surfaces in oligosaccharides: linear dextrins are amphiphilic chains

Polysaccharide chains are usually considered to be highly hydrophilic, since they have no obvious nonpolar moieties in them. Yet, it is possible to realise conformations in these chains wherein all the hydroxy groups are disposed in one side or face of the chain and the hydrogens disposed in the other. We experimentally demonstrate that such an amphiphilic surface is present in linear oligomeric dextrins, i.e., alpha-1,4-linked D-glucosides, but not in alpha-1,6-D-glucosides (dextrans) or in beta-1,4-D-glucosides (cellulose). This amphiphilicity is generated as a consequence of the stereochemical constraints, which vary with the structure of the sugar and with the type of linkage. Oligosaccharide chains that can adopt incipient helical structures might display amphiphilicity. This property might be relevant to intermolecular recognition on cell surfaces, lectin-sugar binding, antigen-antibody interactions and the like, and might be manifested more in heteromolecular recognition process than as homomolecular self-aggregation.