Community-Based Knowledge Translation Strategies for Maternal, Neonatal, and Perinatal Outcomes: A Systematic Review of Quantitative and Qualitative Data.

Objective: To identify and assess the effect of community-based Knowledge Translation Strategies (KTS) on maternal, neonatal, and perinatal outcomes. Methods: We conducted systematic searches in Medline, Embase, CENTRAL, CINAHL, PsycInfo, LILACS, Wholis, Web of Science, ERIC, Jstor, and Epistemonikos. We assessed the certainty of the evidence of the studies using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) framework. Results: We identified seven quantitative and seven qualitative studies. Quantitative findings suggest that there is a possible effect on reducing maternal mortality (RR 0.65; 95% CI, 0.48-0.87; moderate evidence certainty); neonatal mortality (RR 0.79; 95% CI 0.70-0.90; moderate evidence certainty); and perinatal mortality (RR 0.84; 95% CI 0.77-0.91; moderate evidence certainty) in women exposed to KTS compared to those who received conventional interventions or no intervention at all. Analysis of qualitative studies identified elements that allowed to generate benefit effects in improving maternal, neonatal, and perinatal outcomes. Conclusion: The KTS in maternal, neonatal, and perinatal outcomes might encourage the autonomy of communities despite that the certainty of evidence was moderate.

Clinical Proof of Concept for Stabilization of Tracheostomy Tubes Using Novel DYNAtraq Device.

Introduction: Tracheostomy is one of the most common surgical strategies in intensive care units (ICU) and provides relevant clinical benefit for multiple indications. However, the complications associated with its use range from 5 to 40% according to different series. The risk of these complications could be reduced if fixation strategies and alignment of the tracheostomy tube with respect to the tracheal axis are improved. Aim: To build a functional device of technological innovation in respiratory medicine for the fixation and alignment of tracheostomy cannula (acronym DYNAtraq) and to evaluate its feasibility and safety in a pilot study in mechanically ventilated patients. Methods: Study carried out in four phases: (1) design engineering and functional prototyping of the device; (2) study of cytotoxicity and tolerance to the force of traction and push; (3) pilot study of feasibility and safety of its use in tracheostomized and mechanically ventilated patients; and (4) health workers satisfaction study. Results: The design of the innovative DYNAtraq device included, on the one hand, a connector with very little additional dead space to be inserted between the cannula and the ventilation tubes, and, on the other hand, a shaft with two supports for adhesion to the skin of the thorax with very high tolerance (several kilograms) to pull and push. In patients, the device corrected the malpositioned tracheostomy tubes for the latero-lateral (p < 0.001) and cephalo-caudal angles (p < 0.001). Its effect was maintained throughout the follow-up time (p < 0.001). The use of DYNAtraq did not induce serious adverse events and showed a 70% protective effect for complications (RR = 0.3, p < 0.001) in patients. Conclusion: DYNAtraq is a new device for respiratory medicine that allows the stabilization, alignment and fixation of tracheostomy tubes in mechanically ventilated patients. Its use provides additional benefits to traditional forms of support as it corrects misalignment and increases tolerance to habitual or forced movements. DYNAtraq is a safe element and can reduce the complications of tracheostomy tubes.

Métodos de investigación empleados para el análisis del acceso a los servicios de salud en contextos rurales / Research methods used for the analysis of access to health services in rural contexts

Introducción: La ruralidad y los sistemas de salud a nivel global constituyen un campo de fuerzas marcado por la pervivencia de la ruralidad y las condiciones de inequidad y desigualdad en el acceso a los servicios de salud. Objetivo: Identificar los métodos de investigación utilizados en el contexto internacional para analizar los servicios de salud en poblaciones rurales. Métodos: Se realizó un estudio de revisión sistemática que incluyó los reportes de investigación relacionados con el tema, publicados hasta diciembre de 2014. El proceso de selección de los estudios se realizó en cuatro etapas: identificación, cribado, elegibilidad e inclusión. Se recuperaron 253 referencias que muestran la diversidad metodológica de aproximación al acceso a servicios de salud en poblaciones rurales. Conclusiones: Se necesita una mirada diferenciada a la ruralidad para elaborar políticas públicas eficientes, que estén en concordancia con los contextos y necesidades de las comunidades que demandan los servicios de salud(AU)

Introduction: Rurality and health systems represent globally a field of forces marked by the survival of rurality and the inequity and inequality conditions in the access to health services. Objective: Identify the research methods used in the international context to analyze health services in rural populations. Methods: It was carried out an study of systematic review that included research reports related with the topic published until December, 2014. The selection process of the studies was conducted in four stages: identification, sieving, elegibility and inclusion. 253 references were recovered and those show the methodological diversity of approaches in the access to health services in rural populations. Conclusions: It is needed a different view to rurality for creating efficient public policies that are in accordance with the contexts and needs of communities that demand health services(AU)

Immunomodulatory, trypanocide, and antioxidant properties of essential oil fractions of Lippia alba (Verbenaceae).

BACKGROUND: Parasite persistence, exacerbated and sustained immune response, and continuous oxidative stress have been described to contribute to the development of the cardiac manifestations in Chronic Chagas Disease. Nevertheless, there are no efficient therapies to resolve the Trypanosoma cruzi infection and prevent the disease progression. Interestingly, trypanocide, antioxidant, and immunodulatory properties have been reported separately for some major terpenes, as citral (neral plus geranial), limonene, and caryophyllene oxide, presents in essential oils (EO) extracted from two chemotypes (Citral and Carvone) of Lippia alba. The aim of this study was to obtain L. alba essential oil fractions enriched with the aforementioned bioactive terpenes and to evaluate the impact of these therapies on trypanocide, oxidative stress, mitochondrial bioenergetics, genotoxicity, and inflammatory markers on T. cruzi-infected macrophages. METHODS: T. cruzi-infected J774A.1 macrophage were treated with limonene-enriched (ACT1) and citral/caryophyllene oxide-enriched (ACT2) essential oils fractions derived from Carvone and Citral-L. alba chemotypes, respectively. RESULTS: ACT1 (IC50 = 45 ± 1.7 µg/mL) and ACT2 (IC50 = 80 ± 1.9 µg/mL) exhibit similar trypanocidal effects to Benznidazole (BZN) (IC50 = 48 ± 2.5 µg/mL), against amastigotes. Synergistic antiparasitic activity was observed when ACT1 was combined with BZN (∑FIC = 0.52 ± 0.13 µg/mL) or ACT2 (∑FIC = 0.46 ± 1.7 µg/mL). ACT1 also decreased the oxidative stress, mitochondrial metabolism, and genotoxicity of the therapies. The ACT1 + ACT2 and ACT1 + BZN experimental treatments reduced the pro-inflammatory cytokines (IFN-γ, IL-2, and TNF-α) and increased the anti-inflammatory cytokines (IL-4 and IL-10). CONCLUSION: Due to its highly trypanocidal and immunomodulatory properties, ACT1 (whether alone or in combination with BZN or ACT2) represents a promising L. alba essential oil fraction for further studies in drug development towards the Chagas disease control.

The challenge of asymptomatic carriers of COVID-19: A rapid review of literature / El desafío de los portadores asintomáticos de COVID-19: una revisión rápida de la literatura

ABSTRACT Objectives To describe the epidemiological and sociodemographic characteristics of asymptomatic carriers reported in the literature, and to review the strategies used for diagnosis and control. Methods Systematic literature review approach. As inclusion criteria, all studies published between January 1 and June 26, 2020, conducted in humans, that reported people who remained asymptomatic of COVID-19. Descriptors were adapted to the interfaces of eight bibliographic databases were configured: PubMed, Ovid, SciELO, Ebsco, Scopus, LILACS, Epistemonikos and Embase. Results About 45% of the articles reported adult population, thirteen reported mixed population (adult and pediatric). 3 525 asymptomatic people were reported, with an average of 37,1 years [0.5-82 years]. Although the effectiveness of the control and prevention measures was not reported, the identification, isolation and follow-up of contacts stands out as a potential effective mechanism to prevent the transmission. Conclusions The use of this information could be relevant to guide evidence-based public health policies and the protection of populations and the improvement of health care that contributes to stopping this pandemic.

RESUMEN Objetivos Describir las características epidemiológicas y sociodemográficas de los portadores asintomáticos reportadas en la literatura y revisar las estrategias utilizadas para el diagnóstico y control. Métodos Se realizó una revisión sistemática de la literatura. Se incluyeron todos los estudios publicados entre el 1.° de enero y el 26 de junio de 2020 realizados en humanos que informaron personas que permanecieron asintomáticas por COVID-19. Se adaptaron descriptores a las interfaces de ocho bases de datos bibliográficas: Pub-Med, Ovid, SciELO, Ebsco, Scopus, LILACS, Epistemonikos y Embase. Resultados Aproximadamente el 45% de los artículos reportaron población adulta, trece estudios informaron población mixta (adultos y pediátricos). Se identificaron 3 525 personas asintomáticas, con un promedio de 37,1 años [0,5-82 años]. Si bien no se reportó efectividad de medidas de control y prevención, la identificación, aislamiento y seguimiento de los contactos se destaca como un potencial mecanismo efectivo para prevenir la transmisión. Conclusiones El uso de esta información podría ser relevante para orientar las políticas de salud pública basadas en la evidencia y la protección de las poblaciones y la mejora de la atención médica que contribuya a detener esta pandemia.

Rurality as an analytic category: implications for public health / Ruralidad como una categoría analítica: implicaciones para la salud pública

ABSTRACT Rurality as a concept was originated within the framework of the migration phenomena of the nineteenth century. During the post-war period, a dichotomic approach was established for this concept, along with the emerging notion of growth, which influenced the economic models of multiple countries worldwide. However, during the last 50 years, the rurality concept acquired a polysemic nature. Thus, the main objective of this article is analyzing several definitions of rurality from the perspective of some subdisciplines of the social sciences and their lines of thought to evaluate their implications for public health within different contexts.

RESUMEN El concepto de ruralidad surgió en el marco de los fenómenos migratorios ocurridos durante el siglo XIX. Para el periodo posguerra, con la emergente noción de desarrollo, se configuró una aproximación dicotómica al concepto, que influyó en los modelos económicos de distintos países del mundo. No obstante, durante los últimos 50 años la ruralidad adquirió un carácter polisémico. En consecuencia, el objetivo del artículo es analizar las definiciones de ruralidad desde algunas disciplinas de las ciencias sociales y sus corrientes de pensamiento, con el fin de inferir sus implicaciones para la salud pública en distintos contextos.

The challenge of asymptomatic carriers of COVID-19: A rapid review of literature / El desafío de los portadores asintomáticos de COVID-19: una revisión rápida de la literatura

ABSTRACT Objectives To describe the epidemiological and sociodemographic characteristics of asymptomatic carriers reported in the literature, and to review the strategies used for diagnosis and control. Methods Systematic literature review approach. As inclusion criteria, all studies published between January 1 and June 26, 2020, conducted in humans, that reported people who remained asymptomatic of COVID-19. Descriptors were adapted to the interfaces of eight bibliographic databases were configured: PubMed, Ovid, SciELO, Ebsco, Scopus, LILACS, Epistemonikos and Embase. Results About 45% of the articles reported adult population, thirteen reported mixed population (adult and pediatric). 3 525 asymptomatic people were reported, with an average of 37,1 years [0.5-82 years]. Although the effectiveness of the control and prevention measures was not reported, the identification, isolation and follow-up of contacts stands out as a potential effective mechanism to prevent the transmission. Conclusions The use of this information could be relevant to guide evidence-based public health policies and the protection of populations and the improvement of health care that contributes to stopping this pandemic.

RESUMEN Objetivos Describir las características epidemiológicas y sociodemográficas de los portadores asintomáticos reportadas en la literatura y revisar las estrategias utilizadas para el diagnóstico y control. Métodos Se realizó una revisión sistemática de la literatura. Se incluyeron todos los estudios publicados entre el 1.° de enero y el 26 de junio de 2020 realizados en humanos que informaron personas que permanecieron asintomáticas por COVID-19. Se adaptaron descriptores a las interfaces de ocho bases de datos bibliográficas: Pub-Med, Ovid, SciELO, Ebsco, Scopus, LILACS, Epistemonikos y Embase. Resultados Aproximadamente el 45% de los artículos reportaron población adulta, trece estudios informaron población mixta (adultos y pediátricos). Se identificaron 3 525 personas asintomáticas, con un promedio de 37,1 años [0,5-82 años]. Si bien no se reportó efectividad de medidas de control y prevención, la identificación, aislamiento y seguimiento de los contactos se destaca como un potencial mecanismo efectivo para prevenir la transmisión. Conclusiones El uso de esta información podría ser relevante para orientar las políticas de salud pública basadas en la evidencia y la protección de las poblaciones y la mejora de la atención médica que contribuya a detener esta pandemia.

Rurality as an analytic category: implications for public health.

Rurality as a concept was originated within the framework of the migration phenomena of the nineteenth century. During the post-war period, a dichotomic approach was established for this concept, along with the emerging notion of growth, which influenced the economic models of multiple countries worldwide. However, during the last 50 years, the rurality concept acquired a polysemic nature. Thus, the main objective of this article is analyzing several definitions of rurality from the perspective of some subdisciplines of the social sciences and their lines of thought to evaluate their implications for public health within different contexts.

The challenge of asymptomatic carriers of COVID-19: A rapid review of literature.

OBJECTIVES: To describe the epidemiological and sociodemographic characteristics of asymptomatic carriers reported in the literature, and to review the strategies used for diagnosis and control. METHODS: Systematic literature review approach. As inclusion criteria, all studies published between January 1 and June 26, 2020, conducted in humans, that reported people who remained asymptomatic of COVID-19. Descriptors were adapted to the interfaces of eight bibliographic databases were configured: PubMed, Ovid, SciELO, Ebsco, Scopus, LILACS, Epistemonikos and Embase. RESULTS: About 45% of the articles reported adult population, thirteen reported mixed population (adult and pediatric). 3 525 asymptomatic people were reported, with an average of 37,1 years [0.5-82 years]. Although the effectiveness of the control and prevention measures was not reported, the identification, isolation and follow-up of contacts stands out as a potential effective mechanism to prevent the transmission. CONCLUSIONS: The use of this information could be relevant to guide evidence-based public health policies and the protection of populations and the improvement of health care that contributes to stopping this pandemic.

Phase I study of the anti-endothelin B receptor antibody-drug conjugate DEDN6526A in patients with metastatic or unresectable cutaneous, mucosal, or uveal melanoma.

Background Endothelin B receptor (ETBR) is involved in melanoma pathogenesis and is overexpressed in metastatic melanoma. The antibody-drug conjugate DEDN6526A targets ETBR and is comprised of the humanized anti-ETBR monoclonal antibody conjugated to the anti-mitotic agent monomethyl auristatin E (MMAE). Methods This Phase I study evaluated the safety, pharmacokinetics, pharmacodynamics, and anti-tumor activity of DEDN6526A (0.3-2.8 mg/kg) given every 3 weeks (q3w) in patients with metastatic or unresectable cutaneous, mucosal, or uveal melanoma. Results Fifty-three patients received a median of 6 doses of DEDN6526A (range 1-49). The most common drug-related adverse events (>25% across dose levels) were fatigue, peripheral neuropathy, nausea, diarrhea, alopecia, and chills. Three patients in dose-escalation experienced a dose-limiting toxicity (infusion-related reaction, increased ALT/AST, and drug-induced liver injury). Based on cumulative safety data across all dose levels, the recommended Phase II dose (RP2D) for DEDN6526A was 2.4 mg/kg intravenous (IV) q3w. The pharmacokinetics of antibody-conjugated MMAE and total antibody were dose-proportional at doses ranging from 1.8-2.8 mg/kg. A trend toward faster clearance was observed at doses of 0.3-1.2 mg/kg. There were 6 partial responses (11%) in patients with metastatic cutaneous or mucosal melanoma, and 17 patients (32%) had prolonged stable disease ≥6 months. Responses were independent of BRAF mutation status but did correlate with ETBR expression. Conclusion DEDN6526A administered at the RP2D of 2.4 mg/kg q3w had an acceptable safety profile and showed evidence of anti-tumor activity in patients with cutaneous, mucosal, and uveal melanoma. ClinicalTrials.gov identifier: NCT01522664.

Kinetic Modeling of the Tau PET Tracer 18F-AV-1451 in Human Healthy Volunteers and Alzheimer Disease Subjects.

18F-AV-1451 is currently the most widely used of several experimental tau PET tracers. The objective of this study was to evaluate 18F-AV-1451 binding with full kinetic analysis using a metabolite-corrected arterial input function and to compare parameters derived from kinetic analysis with SUV ratio (SUVR) calculated over different imaging time intervals. Methods:18F-AV-1451 PET brain imaging was completed in 16 subjects: 4 young healthy volunteers (YHV), 4 aged healthy volunteers (AHV), and 8 Alzheimer disease (AD) subjects. Subjects were imaged for 3.5 h, with arterial blood samples obtained throughout. PET data were analyzed using plasma and reference tissue-based methods to estimate the distribution volume, binding potential (BPND), and SUVR. BPND and SUVR were calculated using the cerebellar cortex as a reference region and were compared across the different methods and across the 3 groups (YHV, AHV, and AD). Results: AD demonstrated increased 18F-AV-1451 retention compared with YHV and AHV based on both invasive and noninvasive analyses in cortical regions in which paired helical filament tau accumulation is expected in AD. A correlation of R2 > 0.93 was found between BPND (130 min) and SUVR-1 at all time intervals. Cortical SUVR curves reached a relative plateau around 1.0-1.2 for YHV and AHV by approximately 50 min, but increased in AD by up to approximately 20% at 110-130 min and approximately 30% at 160-180 min relative to 80-100 min. Distribution volume (130 min) was lower by 30%-35% in the YHV than AHV. Conclusion: Our data suggest that although 18F-AV-1451 SUVR curves do not reach a plateau and are still increasing in AD, an SUVR calculated over an imaging window of 80-100 min (as currently used in clinical studies) provides estimates of paired helical filament tau burden in good correlation with BPND, whereas SUVR sensitivity to regional cerebral blood changes needs further investigation.

Evidencias para la prevención y control de lesiones en motociclistas / Evidence for the prevention and control of injuries in motorcyclists

Los accidentes del tránsito representan una de las principales causas de mortalidad, lesiones y discapacidad en personas a nivel mundial. Este fenómeno no es ajeno al contexto colombiano, con la particularidad del aumento del parque automotor durante las últimas dos décadas con mayor número de motocicletas, que representan más del 50 por ciento de las lesiones y muertes en los accidentes de tránsito. El trabajo fue autorizado por el comité de ética e investigación, su propósito es identificar las estrategias más efectivas que contribuyan a la prevención y control de las lesiones causadas por el tránsito de motocicletas. Se realizó una revisión sistemática de la literatura que incluyó estudios observacionales, investigación cualitativa y estudios econométricos. Se recopilaron 30 artículos publicados entre el 2002 y el 2013. Estos estudios muestran la implementación del uso del casco, de medidas de visibilidad, control de comportamientos de riesgo y la aplicación de leyes donde se restringe la ingesta de alcohol, como las principales prácticas orientadas a la prevención de accidentes en los motociclistas. El presente estudio resalta la robustez del uso del casco como la principal medida para la prevención y control de estos accidentes, reconoce la complejidad del fenómeno y la necesidad en consecuencia de la sinergia entre métodos cualitativos y cuantitativos para darleuna mayor explicación; supone una base conceptual sólida para la generación de políticas públicas pertinentes que busquen la disminución de la morbilidad, mortalidad y discapacidad asociada a este tipo de siniestros viales(AU).

Traffic accidents represent one of the main causes of mortality, injuries and disabilities worldwide. This phenomenon is also present in the Colombian setting where its main feature is related to the significant increase of the car fleet over the past two decades, with greater number of motorcycles, accounting for more than 50 percent of the lesions and deaths from road traffic accidents. The ethics and research committee authorized the presentation of this paper. Its objective was to identify the more effective strategies that will contribute to the prevention and control of injures from motorcycle traffic accidents. A systematic literature review including observational, qualitative and econometric studies was made. Thirty studies published from 2002 to 2013 were gathered. These studies showed the implementation of the use of helmet provisions, visibility measures, control of risky behaviors and application of laws on alcohol consumption as the main practices aimed at the prevention of motorcycle accidents. The present study underlined the soundness of the helmet use as the main measure for the prevention and control of accidents. It also recognized the complexity of this phenomenon and the need of synergy between qualitative and quantitative methods to provide broader explanation. This paper represents a sound conceptual basis for the generation of relevant public policies in search of the reduction of morbidity, mortality and disability associated to this type of road disasters(AU).

Structures reveal details of small molecule binding to cardiac troponin.

In cardiac and skeletal muscle, the troponin complex turns muscle contraction on and off in a calcium-dependent manner. Many small molecules are known to bind to the troponin complex to modulate its calcium binding affinity, and this may be useful in a broad range of conditions in which striated muscle function is compromised, such as congestive heart failure. As a tool for developing drugs specific for the cardiac isoform of troponin, we have designed a chimeric construct (cChimera) consisting of the regulatory N-terminal domain of cardiac troponin C (cNTnC) fused to the switch region of cardiac troponin I (cTnI), mimicking the key binding event that turns on muscle contraction. We demonstrate by solution NMR spectroscopy that cChimera faithfully reproduces the native interface between cTnI and cNTnC. We determined that small molecules based on diphenylamine can bind to cChimera with a KD as low as 10µM. Solution NMR structures show that minimal structural perturbations in cChimera are needed to accommodate 3-methyldiphenylamine (3-mDPA), which is probably why it binds with higher affinity than previously studied compounds like bepridil, despite its significantly smaller size. The unsubstituted aromatic ring of 3-mDPA binds to an inner hydrophobic pocket adjacent to the central beta sheet of cNTnC. However, the methyl-substituted ring is able to bind in two different orientations, either inserting into the cNTnC-cTnI interface or "flipping out" to form contacts primarily with helix C of cNTnC. Our work suggests that preservation of the native interaction between cNTnC and cTnI is key to the development of a high affinity cardiac troponin-specific drug.

Reversible Covalent Binding to Cardiac Troponin C by the Ca2+-Sensitizer Levosimendan.

The binding of Ca2+ to cardiac troponin C (cTnC) triggers contraction in heart muscle. In the diseased heart, the myocardium is often desensitized to Ca2+, which leads to impaired contractility. Therefore, compounds that sensitize cardiac muscle to Ca2+ (Ca2+-sensitizers) have therapeutic promise. The only Ca2+-sensitizer used regularly in clinical settings is levosimendan. While the primary target of levosimendan is thought to be cTnC, the molecular details of this interaction are not well understood. In this study, we used mass spectrometry, computational chemistry, and nuclear magnetic resonance spectroscopy to demonstrate that levosimendan reacts specifically with cysteine 84 of cTnC to form a reversible thioimidate bond. We also showed that levosimendan only reacts with the active, Ca2+-bound conformation of cTnC. Finally, we propose a structural model of levosimendan bound to cTnC, which suggests that the Ca2+-sensitizing function of levosimendan is due to stabilization of the Ca2+-bound conformation of cTnC.

Probing the mechanism of cardiovascular drugs using a covalent levosimendan analog.

One approach to improve contraction in the failing heart is the administration of calcium (Ca(2+)) sensitizers. Although it is known that levosimendan and other sensitizers bind to troponin C (cTnC), their in vivo mechanism is not fully understood. Based on levosimendan, we designed a covalent Ca(2+) sensitizer (i9) that targets C84 of cTnC and exchanged this complex into cardiac muscle. The NMR structure of the covalent complex showed that i9 binds deep in the hydrophobic pocket of cTnC. Despite slightly reducing troponin I affinity, i9 enhanced the Ca(2+) sensitivity of cardiac muscle. We conclude that i9 enhances Ca(2+) sensitivity by stabilizing the open conformation of cTnC. These findings provide new insights into the in vivo mechanism of Ca(2+) sensitization and demonstrate that directly targeting cTnC has significant potential in cardiovascular therapy.

Structure and Dynamics of the Acidosis-Resistant A162H Mutant of the Switch Region of Troponin I Bound to the Regulatory Domain of Troponin C.

Intracellular acidosis lowers the Ca²âº sensitivity of cardiac muscle, which results in decreased force generation, decreased cardiac output, and, eventually, heart failure. The A162H mutant of cardiac troponin I in the thin filament turns the heart acidosis-resistant. Physiological and structural studies have provided insights into the mechanism of protection by the A162H substitution; however, the effect of other native residues of cardiac troponin I is not fully understood. In this study, we determined the structure of the A162H mutant of the switch region of cardiac troponin I bound to the regulatory domain of troponin C at pH 6.1, and the dynamics as a function of pH, by NMR spectroscopy to evaluate the changes induced by protonation of A162H. The results indicate that A162H induces a transitory curved conformation on troponin I that promotes contraction, but it is countered by residue E164 to ensure proper relaxation. Our model explains the absence of diastolic impairment in the gain-of-function phenotype induced by the A162H substitution as well as the effects of a variety of mutants studied previously. The description of this mechanism underlines the fine quality of regulation on cardiac muscle contraction and anticipates pharmacological agents that induce modest changes in the contraction-relaxation equilibrium to produce marked effects in cardiac performance.

The cardiac-specific N-terminal region of troponin I positions the regulatory domain of troponin C.

The cardiac isoform of troponin I (cTnI) has a unique 31-residue N-terminal region that binds cardiac troponin C (cTnC) to increase the calcium sensitivity of the sarcomere. The interaction can be abolished by cTnI phosphorylation at Ser22 and Ser23, an important mechanism for regulating cardiac contractility. cTnC contains two EF-hand domains (the N and C domain of cTnC, cNTnC and cCTnC) connected by a flexible linker. Calcium binding to either domain favors an "open" conformation, exposing a large hydrophobic surface that is stabilized by target binding, cTnI[148-158] for cNTnC and cTnI[39-60] for cCTnC. We used multinuclear multidimensional solution NMR spectroscopy to study cTnI[1-73] in complex with cTnC. cTnI[39-60] binds to the hydrophobic face of cCTnC, stabilizing an alpha helix in cTnI[41-67] and a type VIII turn in cTnI[38-41]. In contrast, cTnI[1-37] remains disordered, although cTnI[19-37] is electrostatically tethered to the negatively charged surface of cNTnC (opposite its hydrophobic surface). The interaction does not directly affect the calcium binding affinity of cNTnC. However, it does fix the positioning of cNTnC relative to the rest of the troponin complex, similar to what was previously observed in an X-ray structure [Takeda S, et al. (2003) Nature 424(6944):35-41]. Domain positioning impacts the effective concentration of cTnI[148-158] presented to cNTnC, and this is how cTnI[19-37] indirectly modulates the calcium affinity of cNTnC within the context of the cardiac thin filament. Phosphorylation of cTnI at Ser22/23 disrupts domain positioning, explaining how it impacts many other cardiac regulatory mechanisms, like the Frank-Starling law of the heart.

Versatile cardiac troponin chimera for muscle protein structural biology and drug discovery.

Investigation of the molecular interactions within and between subunits of the heterotrimeric troponin complex, and with other proteins in the sarcomere, has revealed salient structural elements involved in regulation of muscle contraction. The discovery of new cardiotonic drugs and structural studies utilizing intact troponin, or regulatory complexes formed between the key regions identified in troponin C and troponin I, face intrinsic and technical difficulties associated with weak protein-protein interactions and with solubility, aggregation, stability of the overall architecture, isotope labeling, and size, respectively. We have designed and characterized a chimeric troponin C-troponin I hybrid protein with a cleavable linker that is useful for producing isotopically labeled troponin peptides, stabilizes their interaction, and has proven to be a faithful representation of the original complex in the systolic state, but lacking its disadvantages, making it particularly suitable for drug screening and structural studies.

Conformation of the critical pH sensitive region of troponin depends upon a single residue in troponin I.

The calcium sensitivity of cardiac and skeletal muscle is reduced during cytosolic acidosis, and this inhibition is more pronounced in cardiac muscle. Replacing cardiac troponin I with skeletal troponin I reduces the pH sensitivity of cardiac muscle. This diminished pH sensitivity depends on a single amino acid difference in troponin I: an alanine in cardiac and a histidine in skeletal. Studies suggested that when this histidine is protonated, it forms an electrostatic interaction with glutamate 19 on the surface of cardiac troponin C. Structures of the skeletal and cardiac troponin complexes show very different conformations for the region of troponin I surrounding this residue. In this study, we determined the structure of skeletal troponin I bound to cardiac troponin C. Skeletal troponin I is found to bind to cardiac troponin C with histidine 130 in close proximity to glutamate 19. This conformation is homologous to the crystal structure of the skeletal troponin complex; but different than in the cardiac complex. We show that an A162H variant of cardiac troponin I adopts a conformation similar to the skeletal structure. The implications of these structural differences in the context of cardiac muscle regulation are discussed.

Interaction between the regulatory domain of cardiac troponin C and the acidosis-resistant cardiac troponin I A162H.

AIMS: Ischaemic heart disease is the leading cause of mortality worldwide. Acidosis is the main mediator of ischaemia and shielding against it might be possible. In this study, we characterize the nature of interaction between the regulatory domain of cardiac troponin C and the A162H-substituted cardiac troponin I (cTnI) that confers protection against acidosis. METHODS AND RESULTS: We used nuclear magnetic resonance spectroscopy to study the interaction of the Ca(2+)-saturated N-domain of cardiac troponin C with the switch region of cTnI containing the A162H substitution under normal and acidic conditions. Our results show that H162 increases the affinity of TnI for troponin C at pH 7 and this affinity is further enhanced at pH 6. To investigate the nature of the interactions responsible for such improvement, we determined the acid dissociation constants of the glutamate residues in troponin C. The results show that E15 and E19 exhibit deviations in their acid dissociation constant (pK(a)) profiles and reflect a common high pK(a) value of 6.8, indicating electrostatic interactions with H162. Residue H171 in wild-type cTnI does not play a similar role. CONCLUSION: This work provides evidence for the mechanism by which cTnI A162H improves myocardial performance during acidosis. The electrostatic interaction between residues E15 and E19 in troponin C and H162 in TnI at low pH is responsible for stabilizing the conformation of troponin C that leads to contraction, thus partially ablating the decreased Ca(2+)-sensitivity caused by acidosis.