Intracoronary Imaging in left main stent percutaneous coronary intervention has a clear survival benefit particularly in more complex patients

Background

Left Main Stem Disease (LMS) is prognostically important coronary artery disease that is managed either with coronary artery bypass surgery (CABG) or percutaneous coronary intervention (PCI). Use of intracoronary imaging (ICI) modalities such as intravascular ultrasound (IVUS) and optical coherence tomography (OCT) have been shown to improve outcomes with PCI revascularization.

The primary objective of this study was to evaluate the impact of ICI on outcomes following LMS PCI.

Methods

Retrospective observation study of 498 (5.1% of all PCI cases) patients who had undergone LMS PCI at our tertiary primary PCI centre hospital over a 11-year period between July 2010-July 2021. Data was collected from electronic medical records. Follow-up was also obtained through linkage with the Office of National Statistics.

Results

The mean age at the time of enrolment was 70.7±11.5 years. Majority of the patients were male 351 (70.5%). 353 (70.9%) of cases had acute coronary syndrome (ACS) presentation while the remainder were elective procedures. Mean follow-up duration was 3.75±3.06 years. Survival calculated by Kaplan-Meier was 70%. 87 patients (17.5%) deceased during first year of enrolment. 344 (69.1%) patients had ICI, with IVUS in 316 (63.5%) and OCT in 28 (5.6%) patients. IVUS comprised 91.9% of ICI procedures. Protected LMS (OR 0.175, 95% CI: 0.037–0.833, P-value=0.029) and the use of left ventricular mechanical support device (OR 0.324, 95% CI: 0.122–0.859, P-value=0.024) were associated with decreased odds of undergoing an ICI.

Patients undergoing ICI had significantly better survival compared to those without ICI (HR: 0.54, P<0.001). Moreover, OCT showed significantly better survival compared with IVUS (HR: 0.181, P=0.017). Use of ICI was associated with better survival in patients who had Rotablation (HR: 0.455, 95% CI: 0.232–0.892, P=0.022), ACS (HR: 0.523, 95% CI: 0.383–0.714, P<0.001) or comorbidities of diabetes and stroke (HR: 0.551, 95% CI: 0.337–0.807, P=0.002).

Conclusion

ICI in LMS PCI has a significant survival benefit in our dataset. This is especially the case in patients presenting with ACS, those with comorbidities of Diabetes mellitus and stroke and those undergoing rotablation.

Funding Acknowledgement

Type of funding sources: None.

The 11-year outcome of PCI for treatment of left main stem disease

Background

Left Main Stem Disease (LMS) has historically been treated with coronary artery bypass surgery (CABG). However, not all patents with LMS are candidates for CABG due to co-morbidities. There is limited long-term follow-up of patients undergoing PCI in the real world. The primary objective of this study was to investigate the long-term mortality following LMS PCI.

Methods

We conducted a retrospective study of patients who had undergone PCI for LMS disease at our hospital over a 11-year period between July 2010-July 2021. Data was collected from electronic medical records and analyzed using Kaplain-Meier survival analysis. Follow-up was obtained through linkage with the Office of National Statistics.

Results

498 patients underwent LMS PCI (5.1% of the total PCI cases). The overall survival rate was 70%. Median survival following PCI was 1,196 days (IQR = 1,796). The mean age of the patients was 70.7 years; 70.5% were males. 70.9% of patients underwent PCI for Acute Coronary Syndrome (ACS), and 15.3% had STEMI. 33.7% of patients had a history of diabetes, 8% had stroke, 8.2% had COPD, and 8.8% had PVD. 51 patients went into cardiogenic shock, and 25 died prior to discharge.

Survival of the ACS group was significantly lower than the stable group (67% vs 77%, p<0.01); the STEMI group did not significantly differ from rest of the ACS group (62% vs 66%, p=0.87). Survival in those <60 years of age was significantly higher than in those >60 years (80% vs 68%; p<0.01). The presence of one or more co-morbidities was associated with higher survival compared to zero co-morbidities (74% vs 65%, p<0.01). Patients with a history of diabetes had a significantly lower survival rate than those without diabetes (63% vs 73%, p<0.01). Patients with an LV ejection fraction ≤35% had a significantly lower survival than those with an ejection fraction >35% (22% vs 29%, p<0.01); only 259 patients had data on LV function. Patients who developed cardiogenic shock had a significantly lower survival rate than those who did not develop shock (38% vs 70%; p<0.01). When these patients were excluded from the data set, the overall survival rate increased from 70% to 74%. Lastly, a multinomial analysis showed that the only independent predictors of mortality were age (p<0.01) and cardiogenic shock (p<0.01).

Conclusion

Our results show that the real world 10-year mortality rate following LMS PCI is influenced by multiple factors including age, shock, and LV function. The high mortality rate was potentially due to the significant number of acute cases (70.1%) in non-operable patients. While factors such as age and past medical history are considered in the decision-making process regarding CABG vs PCI, we saw that specific subgroups within these factors may have decreased the effectiveness of PCI as a treatment for LMS disease, suggesting that deeper analysis into these risk factors is required when deciding between CABG and PCI for LMS disease management.

Funding Acknowledgement

Type of funding sources: None.

Performance of the C2HEST score to predict sustained atrial high-rate episodes in patients implanted with cardiac implantable electronic device

Funding Acknowledgements

Type of funding sources: None.

Background

Sustained atrial high-rate episodes (SAHRE), which are considered ‘subclinical atrial fibrillation’ (AF), increase the risk of adverse outcomes in patients with a cardiac implantable electronic device (CIED). Risk stratification for the development of SAHREs has never been investigated.

Purpose

To assess test the performance of the C2HEST score (coronary artery disease or chronic obstructive pulmonary disease [1 point each]; hypertension [1 point]; elderly [age ≥75 years, 2 points]; systolic heart failure [2 points]; thyroid disease [1 point]) in predicting SAHRE in patients implanted with CIED without AF.

Methods

Retrospective study including 500 consecutive patients implanted with CIEDs in the West Birmingham in the UK. Patients were followed after implantation to record the development of SAHRE lasting >24h. Risk factors and incidence of SAHRE were analyzed. The predictive value of the C2HEST score for SAHRE prediction was evaluated.

Results

During 53.1 months of follow-up, 44 (8.8%) patients developed SAHRE. SAHRE was associated with higher all-cause mortality (P < 0.001) and ischemic stroke (P = 0.001). Age and heart failure were associated with SAHRE occurrence. The incidence of SAHRE increased by the C2HEST score (39% higher risk per point increase)(table). Among those with C2HEST score ≥4, the incidence of SAHRE was 3.62%/year (95%CI 2.14-5.16). The C2HEST score had a moderate predictive capability (area under the curve 0.73 [95%CI 0.64-0.81]) and discriminative ability (log-rank P = 0.003), which was better than other clinical scores (CHA2DS2-VASc, CHADS2, HATCH).

Conclusions

The C2HEST score predicted SAHRE incidence in non-AF subjects with CIED, with the highest risk seen in patients with C2HEST score ≥4 The benefit of using the C2HEST score in clinical practice in this patient population needs further investigation. C2HEST score Subjects n (%) SAHRE (n) Incident rate (95%CI) Hazard Ratio (95% CI) P 0-1 144 (28.5%) 5 0.85 (0.27-1.94) Reference Reference 2-3 211 (42.2%) 17 1.87 (1.06-2.91) 2.06 (0.76-5.59) 0.159 ≥4 145 (29.0%) 22 3.62 (2.14-5.16) 4.25 (1.61-11.22) 0.004

Thymoquinone supplementation ameliorates cisplatin-induced hepatic pathophysiology

Hepatotoxicity is a major dose-limiting side effect of CP chemotherapy besides nephrotoxicity and gastrointestinal dysfunction. TQ, a principal Nigella sativa seed oil constituent, has been shown to improve hepatic functions in various in vivo models of acute hepatic injury. In view of this, the present study aimed to evaluate the effect of TQ against CP-induced hepatotoxicity. Rats were divided into four experimental groups; control, CP, CP+TQ and TQ. Animals in CP+TQ and TQ groups were administered TQ (1.5 mg/kg bwt, orally), with or without a single hepatotoxic dose of CP (6 mg/kg bwt, i.p.) respectively, for 14 days before and four days following the CP treatment. CP induced an upsurge in serum ALT and AST activities, indicating liver injury, as also confirmed by the histopathological findings. CP caused significant alterations in the activities of membrane marker enzymes, carbohydrate metabolic enzymes, and the enzymatic and nonenzymatic components of the antioxidant defense system. TQ supplementation ameliorated all these adverse biochemical and histological changes in CP-treated rats. Thus, TQ may have excellent scope for clinical applications in combating CP-induced hepatic pathophysiology.

Identifying at-risk subjects for sustained atrial high-rate episodes using the C2HEST score: the West Birmingham AF project

Background

Sustained atrial high-rate episodes (SAHREs) (lasting >24h) was associated with unfavorable pragnosis.

Objectives

To evaluate the performance of the C2HEST score in assessing individuals' risk of SAHRE.

Methods

The West Birminghan Atrial Fibrillation (AF) Project included 500 consecutive non-AF patients with implantable cardiac electronic device. The role of the C2HEST score for SAHRE risk stratification was evaluated.

Results

SAHRE was detected in 8.8% of patients (2.09%/year, 95% CI 1.47–2.71) over a mean 4.4 years of follow-up. SAHRE was associated with increased all-cause mortality (P<0.001). The risk of SAHRE increased by C2HEST score (39% higher risk per point increase). The C2HEST score had moderate predictive capability (c-index 0.706 [0.615–0.798], log-rank P=0.003) for SAHRE, which was better than other clinical scores (CHA2DS2-VASc, CHADS2, HATCH).

Conclusions

The C2HEST score was predictive of SAHRE, which may help to identify at-risk subjects who may need intensive device review.

Central Illustration

Funding Acknowledgement

Type of funding source: None

Barriers and enablers for practicing kangaroo mother care (KMC) in rural Sindh, Pakistan

Background

More than 2.5 million newborns die each year, contributing to 47% of under 5 mortality worldwide. Globally, Every Newborn Action Plan has emphasized on Kangaroo Mother Care (KMC) as an essential component of neonatal health initiatives. An international joint policy statement and endorsement from health professional associations also recommended practicing KMC for newborn care.

Methods

We conducted a qualitative study with 12 in-depth interviews (IDIs) and 14 focus group discussion (FGD) sessions, in two health facilities of Sindh, Pakistan during October-December 2016, to understand the key barriers and enablers to a mother’s ability to practice KMC and the feasibility of implementing and improving these practices.

Results

Our study findings revealed that community stakeholders were generally aware of health issues especially related to maternal and neonatal health. Both the health care providers and managers were supportive of implementing KMC in their respective health facilities as well as for continuous use of KMC at household level. In order to initiate KMC at facility level, study respondents emphasized on strengthening of availability and quality of services as well as training of health providers as critical prerequisites. Also in order to continue practicing KMC at household level, engaging the community and establishing functional referral linkage between community and facilities were focused issues in facility and community level FGDs and IDIs. The study participants considered it feasible to initiate KMC practice at health facility and to continue practicing at home after returning from facility.

Conclusions

Ensuring facility readiness to initiate KMC, improving capacity of health providers, coupled with strengthened community mobilization, and targeting specific audiences may help policy makers and program planners to initiate KMC practice at health facility and keep KMC practice continued at household level.

Key messages

Introducing KMC at health facility followed by continuing practice at household level is feasible, even in a religiously conservative setting like Pakistan. Facility readiness, improved health workers’ capacity coupled with strengthened community mobilization targeting specific audiences could help scaling up this public health intervention in Pakistan.

Intra-aortic balloon pump counterpulsation: are we optimizing the management of cardiogenic shock?

Intra-aortic balloon pump counterpulsation (IABPC) has been used in various forms for decades. The change in physiology brought about by their use is conceptually appealing in managing cardiogenic shock and mechanical complications of myocardial infarction. A common myth is that this method of managing acute cardiological emergencies is to be limited to the realms of this specialist field. However, as medical physicians an appreciation and understanding of this novel therapy is essential not only as a lifesaving measure but also as a bridging therapy to more definitive management in the acute medical setting. IABPC is a safe and under-utilized technique despite featuring in all major international guidelines (ESC and ACC) for the management of cardiogenic shock secondary to acute coronary syndromes. Without awareness of this intervention we may be suboptimally managing patients in the first instance. To improve awareness we examine the evidence supporting the use of the IABPC therapy and the contraindications to their use. Complications and advances in technology are also addressed.

Aspirin treatment failure: is this a real phenomenon? A review of the aetiology and how to treat it

Multiple clinical trials have shown that aspirin can reduce all cardiovascular events in primary and secondary prevention and yet there is a large population in whom aspirin fails. This review brings together the evidence and controversies surrounding the definition of ‘aspirin treatment failure’, its clinical significance and the possible approaches to managing such patients. Several different assays have been developed to measure the biochemical action of aspirin. At present there is no ‘gold standard’ and there is massive disparity between methods. Studies thus far have shown inconsistent results and to date the treatment of aspirin therapy failure is left to the discretion of the leading physician.

Dynamic changes in biomarker profiles associated with clinical and subclinical tuberculosis in a high transmission setting: a four-year follow-up study

Mycobacterium tuberculosis (MTB) is a slow growing bacterium. Therefore, the immune responses associated with resolution of infection or development of disease post-exposure may take several months to evolve. We have carried out a prospective longitudinal study in a high TB transmission setting to determine the evolution of biomarkers in a recently exposed household contact (HC = 77) and their respective sputum positive index cases (TB = 17). Mycobacterium-induced cytokines [interferon-gamma (IFN-gamma), tumour necrosis factor-alpha, interleukin-6 (IL-6) and IL-10)] were assessed in whole blood cultures and immunoglobulin G (IgG1) antibodies in plasma. When compared with non-exposed community controls (endemic controls = 59) the HC group at intake showed changes in biomarkers commensurate with recent exposure. The HC group showed significant increases in IFN-gamma between 0 and 6 months (paired t-test; P = 0.001) and IL-0 between 6 and 12 months (P = 0.001), most likely reflecting the role of these cytokines in resolution and immune recovery from infection as this HC cohort remained symptom-free for 4 years without prophylactic treatment. When the TB group post-treatment was compared with the HC group, the best discriminators (ANOVA; repeated measures) were IL-10 responses at 0 (P = 0.004) and 6 months (P = 0.001) and IgG1 at 6 (P = 0.004) and 12 months (P = 0.014) with a 3-4 fold higher responses in the TB group. Therefore, within each group, biomarkers show unique profile of responses. These studies highlighted the importance of assessing multiple biomarkers in longitudinal studies for providing better understanding of protective biomarker profiles associated with resolution of clinical and subclinical infections in TB.

Diagnostic assays for leprosy based on T-cell epitopes

To date, only a limited number of antigens have been described as specific for Mycobacterium leprae, and in many cases, homologues have subsequently been shown to exist in mycobacteria such as M. avium and M. intracellulare. A Leprosy Synthetic Peptide Skin Test Initiative was established by the Steering Committee on the Immunology of Mycobacteria of the UNDP/World Bank/WHO Special Programme for Research and Training in Tropical Diseases, to investigate the potential of synthetic peptides that encode T-cell epitopes as diagnostic tools, which could be used to develop a skin-test reagent specific for leprosy. Such M. leprae-specific peptides should have unique amino acid sequences, or significant sequence-dissimilarity from those in other mycobacteria. Synthetic peptides, 15 amino acids long, were synthesised from 33 genes or open reading frames within the M. leprae genome. Tuberculoid leprosy patients from four leprosy-endemic countries, Brazil, Ethiopia, Nepal and Pakistan, were tested as subjects known to have been infected with M. leprae, and to make good T-cell responses to antigens of M. leprae; UK blood donors were used as non-exposed or non-infected subjects. Peptides inducing potentially specific responses in leprosy patients and not in UK controls, and those inducing cross-reaction responses, present in both leprosy patients and non-exposed, non-infected controls, were identified. A difference from the equivalent M. tuberculosis sequence of five or more amino acid residues did not, by itself, identify peptides that were M. leprae-specific, suggesting that many of these peptides may have homologues in environmental mycobacteria. To date, this approach has identified a number of peptides with greater than 90% specificity and 19-47% sensitivity, which are undergoing further specificity-testing. Such peptides would have great potential as T-cell reagents with which to monitor exposure to M. leprae within communities, formulated either as skin-test reagents, or as antigens for tests in vitro.

A postgenomic approach to identification of Mycobacterium leprae-specific peptides as T-cell reagents

To identify Mycobacterium leprae-specific human T-cell epitopes, which could be used to distinguish exposure to M. leprae from exposure to Mycobacterium tuberculosis or to environmental mycobacteria or from immune responses following Mycobacterium bovis BCG vaccination, 15-mer synthetic peptides were synthesized based on data from the M. leprae genome, each peptide containing three or more predicted HLA-DR binding motifs. Eighty-one peptides from 33 genes were tested for their ability to induce T-cell responses, using peripheral blood mononuclear cells (PBMC) from tuberculoid leprosy patients (n = 59) and healthy leprosy contacts (n = 53) from Brazil, Ethiopia, Nepal, and Pakistan and 20 United Kingdom blood bank donors. Gamma interferon (IFN-gamma) secretion proved more sensitive for detection of PBMC responses to peptides than did lymphocyte proliferation. Many of the peptides giving the strongest responses in leprosy donors compared to subjects from the United Kingdom, where leprosy is not endemic, have identical, or almost identical, sequences in M. leprae and M. tuberculosis and would not be suitable as diagnostic tools. Most of the peptides recognized by United Kingdom donors showed promiscuous recognition by subjects expressing differing HLA-DR types. The majority of the novel T-cell epitopes identified came from proteins not previously recognized as immune targets, many of which are cytosolic enzymes. Fifteen of the tested peptides had > or =5 of 15 amino acid mismatches between the equivalent M. leprae and M. tuberculosis sequences; of these, eight gave specificities of > or =90% (percentage of United Kingdom donors who were nonresponders for IFN-gamma secretion), with sensitivities (percentage of responders) ranging from 19 to 47% for tuberculoid leprosy patients and 21 to 64% for healthy leprosy contacts. A pool of such peptides, formulated as a skin test reagent, could be used to monitor exposure to leprosy or as an aid to early diagnosis.

Leprosy patients with lepromatous disease recognize cross-reactive T cell epitopes in the Mycobacterium leprae 10-kD antigen

T cell responses play a critical role in determining protective responses to leprosy. Patients with self-limiting tuberculoid leprosy show high T cell reactivity, while patients with disseminated lepromatous form of the disease show absent to low levels of T cell reactivity. Since the T cell reactivity of lepromatous patients to purified protein derivative (PPD), a highly cross-reactive antigen, is similar to that of tuberculoid patients, we queried if lepromatous patients could recognize cross-reactive epitopes in Mycobacterium leprae antigens as well. T cell responses were analysed to a recombinant antigen 10-kD (a heat shock cognate protein) which is available from both M. tuberculosis (MT) and M. leprae (ML) and displays 90% identity in its amino acid sequence. Lymphoproliferative responses were assessed to ML and MT 10 kD in newly diagnosed leprosy patients (lepromatous, n = 23; tuberculoid, n = 65). Lepromatous patients showed similar, but low, lymphoproliferative responses to ML and MT 10 kD, while tuberculoid patients showed much higher responses to ML 10 kD. This suggests that the tuberculoid patients may be recognizing both species-specific and cross-reactive epitopes in ML 10 kD, while lepromatous patients may be recognizing only cross-reactive epitopes. This was further supported by linear regression analysis. Lepromatous patients showed a high concordance in T cell responses between ML and MT 10 kD (r=0.658; P<0.0006) not observed in tuberculoid patients (r=0.203; P>0.1). Identification of cross-reactive T cell epitopes in M. leprae which could induce protective responses should prove valuable in designing second generation peptide-based vaccines.

Low serum HDL-cholesterol is associated with raised tumor necrosis factor-alpha during ENL reactions

The concentrations of serum lipids and tumor necrosis factor (TNF) were measured in leprosy patients across the spectrum of the disease and in erythema nodosum leprosum (ENL) patients at the onset of the reaction and after the reaction had clinically subsided. Lepromatous/borderline lepromatous (LL/BL) patients had significantly higher serum triglyceride and lower HDL-cholesterol levels; there was no such change in the tuberculoid/borderline tuberculoid (TT/BT) patients. The household contacts (HC) of the LL/BL patients also had significantly lower serum HDL levels. ENL patients during the acute phase of the reaction had significantly lower total, LDL-, HDL-cholesterol levels compared to the stable LL/BL patients, and these changes were reversible to pre-ENL levels after the reaction had subsided. Serum TNF levels were significantly higher in household contacts and in LL/BL patients but were not statistically different in TT/BT patients. Serum TNF levels were also significantly higher during the acute phase of ENL, and declined after the clinical remission of the reaction to levels comparable with those of LL/BL patients. There was a significant negative correlation between serum TNF and HDL-cholesterol levels during and after ENL reaction. However, there was no such correlation between TNF and total or LDL-cholesterol levels in ENL patients. Our results suggest that the changes in HDL-cholesterol metabolism are a specific part of the host response to lepromatous leprosy and to the ENL reaction and may be mediated by increased TNF production.

Erythema nodosum leprosum is associated with up-regulation of polyclonal IgG1 antibody synthesis

Erythema nodosum leprosum (ENL) is a serious complication of lepromatous (L) disease in leprosy. We have previously shown that of the four IgG subclasses, IgG1 and IgG3 Mycobacterium leprae-specific antibodies are significantly lower in leprosy patients during ENL reaction compared with untreated L patients. To see if this decrease results from a down-regulation of antibody synthesis during ENL, the frequency of antibody-secreting B cells (ABSC) in the blood compartment was determined by ELISPOT and related to serum immunoglobulin concentrations (microgram/ABSC). Control groups consisted of 16 patients with stable L disease and 32 healthy endemic controls (EC). Paired samples were analysed during acute ENLS (n = 13) and after the reaction had subsided to identify changes associated with ENL. Polyclonal (PC) IgG1 was elevated in L patients compared with EC (325 micrograms versus 180 micrograms). Interestingly, patients during acute ENL showed concentrations higher than L patients (419 micrograms), which decreased after the reaction had subsided (260 micrograms), indicating the transient nature of the antibody response. IgG2 antibodies showed the reverse trend and were lower during ENL and increased after the reaction had subsided. The mean concentrations for PC IgG3 and IgG4 antibodies were similar during ENL and after the reaction had subsided. Thus, decrease in M. leprae-specific IgG1 and IgG3 antibodies is not related to down-regulation of B cell responses. Identification of factors which regulate PC IgG1 antibody synthesis may provide additional insights into determinants of ENL reactions.

Induction of Th1 cytokine responses by mycobacterial antigens in leprosy

Twelve mycobacterial antigens were compared for induction of gamma interferon (IFN-gamma) secretion by human blood mononuclear cells of patients with leprosy. Fractionated Mycobacterium leprae antigens containing cell wall proteins or cytosolic and membrane proteins induced good IFN-gamma responses in tuberculoid leprosy patients. Lipoarabinomannan from M. tuberculosis Erdman and M. leprae mycolylarabinogalactan peptidoglycan were the poorest IFN-gamma inducers.

Cross-modulation by transforming growth factor beta in human tuberculosis: suppression of antigen-driven blastogenesis and interferon gamma production

In tuberculosis, Mycobacterium tuberculosis (MTB)-stimulated T-cell responses are depressed transiently, whereas antibody levels are increased. Lymphoproliferative responses of peripheral blood mononuclear cells (PBMCs) from Pakistani tuberculosis (TB) patients to both mycobacterial and candidal antigens were suppressed by approximately 50% when compared to healthy purified protein derivative (PPD)-positive household contacts. Production of interferon gamma (IFN-gamma) in response to PPD also was depressed by 78%. Stimulation with PPD and the 30-kDa alpha antigen of MTB (30-kDa antigen) induced greater secretion of transforming growth factor beta (TGF-beta), but not interleukin 10 (IL-10) or tumor necrosis factor alpha (TNF-alpha), by PBMCs from TB patients compared to healthy contacts. The degree of suppression correlated with the duration of treatment; patients treated for <1 month had significantly lower T-cell blastogenesis and IFN-gamma production and higher levels of TGF-beta than did patients treated for >1 month. Neutralizing antibody to TGF-beta normalized lymphocyte proliferation in response to PPD, partially restored blastogenesis to candidal antigen, and significantly increased PPD-stimulated production of IFN-gamma in TB patients but not in contacts. Neutralizing antibody to IL-10 augmented, but did not normalize, T-cell responses to both PPD and candida in TB patients and candidal antigen in contacts. TGF-beta, produced in response to MTB antigens, therefore plays a prominent role in down-regulating potentially protective host effector mechanisms and looms as an important mediator of immunosuppression in TB.

Resonance energy transfer between cysteine-34 and tryptophan-214 in human serum albumin. Distance measurements as a function of pH

The single cysteine residue (Cys-34) of human serum albumin was modified with the organic mercurial [4-[p-(dimethylamino)phenyl]azo]phenyl]mercuric acetate. Introduction of this chromophore into the protein results in the quenching of the protein tryptophan fluorescence spectrum due to energy transfer from the tryptophan residue to the mercurial. Since human albumin contains only a single tryptophan, it was then possible to calculate distances between the mercurial bound at Cys-34 and Trp-214 under various conditions. This distance contracted during the course of the N leads to F transition, being 34-35 A in the N conformation (pH 6-7.5) and 29.9 A in the F conformation (pH 3.6). The distance increased substantially during the course of the F leads to E transition occurring between pH 3.6 and pH 1.9 and was found to be nearly 37 A at pH 1.9. The distance between Cys-34 and Trp-214 was found to undergo a slight contraction during the N leads to B transition occurring between pH 7.0 and pH 9.0. At pH 8.5-9 where the protein is predominately in the B form, the distance was found to be slightly more than 31 A.

The lanthanide-induced N = to F transition and acid expansion of serum albumin

Serum albumin exists in the native or N conformation between pH 5 and 7. As the pH is lowered from 5 to 3.5, the protein undergoes a conformational change resulting in expansion, known as the N = to F (partially acid expanded) transition. As the pH is lowered still further to 2, the protein continues to expand. In the present study, using the techniques of circular dichroism, fluorescence, and UV difference spectroscopy, lanthanide ions at concentrations between 1-30 mM have been shown to produce both changes in the albumin structure analogous to the N = to F transition and acid expansion of bovine serum albumin at a constant pH near 6.