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OBJECTIVE: Thrombotic changes in fibrin networks contribute to increased cardiovascular risk in patients with abdominal aortic aneurysm (AAA). Given that aspirin modulates the fibrin network, we aimed to determine if aspirin therapy is associated with changes in ex-vivo fibrin clot characteristics in AAA patients and also conducted an exploratory analysis of 5-year mortality in these individuals. METHODS: We recruited 145 male patients, divided into controls (aortic diameter < 3 cm, n = 49), AAA not taking aspirin (AAA-Asp, n = 50) and AAA on 75 mg day(-1) aspirin (AAA+Asp, n = 46), matched for aneurysm size. Characteristics of clots made from plasma and plasma-purified fibrinogen were investigated using turbidimetric analysis, permeation studies, and confocal and electron microscopy. Plasma fibrinogen, D-dimer and inflammatory marker levels were also measured. RESULTS: Maximum absorbance (MA) of plasma clots from controls was lower than that of AAA patients not on aspirin (AAA-Asp) at 0.30 ± 0.01 and 0.38 ± 0.02 au, respectively (P = 0.002), whereas aspirin-treated subjects had MA similar to controls (0.31 ± 0.02 P = 0.9). Plasma clot lysis time displayed an identical pattern at 482 ± 15, 597 ± 24 and 517 ± 27 s for control, AAA-Asp and AAA+Asp (P = 0.001 and P = 0.8). The lysis time of clots made from purified fibrinogen of AAA-Asp was longer than that of AAA+Asp patients (756 ± 47 and 592 ± 52 s, respectively; P = 0.041). Permeation studies and confocal and electron microscopy showed increased clot density in AAA-Asp compared with the AAA+Asp group. Mortality in AAA-Asp and AAA+Asp was similar, despite increased cardiovascular risk in the latter group, and both exhibited higher mortality than controls. CONCLUSION: Aspirin improves fibrin clot characteristics in patients with AAA, which may have important clinical implications.
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Aneurisma de la Aorta Abdominal/complicaciones , Aspirina/uso terapéutico , Fibrina/metabolismo , Fibrinólisis , Anciano , Estudios de Casos y Controles , Humanos , Masculino , Persona de Mediana EdadRESUMEN
INTRODUCTION: Catheter-directed thrombolysis (CDT) for iliofemoral deep vein thrombosis (DVT) restores venous patency, reduces the risk of the post-thrombotic syndrome and may reduce longer term treatment costs. This study assessed the potential role of CDT in patients with DVT with regard to representation following the index event. METHODS: A retrospective review of all patients with a positive lower limb DVT scan. Potential suitability of each patient to undergo CDT was based on well-recognized inclusion/exclusion criteria. RESULTS: In total, 1689 patients underwent a DVT-specific lower limb venous duplex. A total of 269 were found to have a DVT. Fifty-three of these patients met the inclusion criteria for CDT (only 2 underwent CDT). Fifty-nine of the 269 patients with an index DVT re-presented to our institution with a venous thromboembolism-related clinical event. These patients were significantly younger than those who did not reattend. A higher proportion of patients who represented were deemed suitable for CDT for the index DVT compared with those who did not represent (17/59 versus 36/210; P = 0.04). CONCLUSION: This pragmatic study highlights the fact that significant number of patients return to secondary care with actual/perceived complications following initial diagnosis and treatment of a DVT which may have been amenable to CDT.
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Extremidad Inferior , Trombolisis Mecánica , Trombosis de la Vena/diagnóstico , Trombosis de la Vena/terapia , Adulto , Anciano , Femenino , Humanos , Masculino , Persona de Mediana Edad , Síndrome Postrombótico/diagnóstico , Síndrome Postrombótico/prevención & control , Estudios RetrospectivosRESUMEN
Paradoxical embolus through a patent foramen ovale is a well-reported phenomenon. Clinical consequences include stroke, intestinal infarction, lower limb ischaemia, and even acute myocardial infarction (MI), via embolisation to the coronary arteries. We present a case of acute MI, cardiogenic shock, and cardiac arrest caused not by this mechanism, but by embolisation of thrombotic material to the aortic root with transient complete occlusion of the left main stem (LMS) coronary artery. During percutaneous coronary intervention to treat this occlusion the thrombus became lodged at the aortic bifurcation causing lower limb ischaemia. Despite successful treatment of this via bilateral groin exploration and thromboembolectomy the patient became increasingly acidotic and an abdominal and pelvic CT scan was performed. This revealed the source of the thrombus to be the patient's congested and compressed pelvic veins which were the result of a large, previously undiagnosed ovarian malignancy with metastatic spread. Although very unusual we feel this case highlights an important differential in the diagnosis of anterolateral MI and images similar to those presented here are previously unreported in the literature.
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Blue toe syndrome (BTS) is an important vascular condition characterized by painful blue discoloration of one or more digits. It is frequently due to emboli and is important because of the risk of progressive ischemia and tissue loss. A 53-year-old male presented with recurrent episodes of painful blue discoloration and blistering of the skin of the right hallux. On examination, the patient was found to have a cool, blue-purple great toe; all peripheral pulses were present. The patient was investigated for coagulopathy and potential sources of emboli, but the only abnormality was significant stenosis of the dorsalis pedis artery due to extrinsic compression by the extensor hallucis brevis tendon. In the absence of any other embolic source or abnormality, we believe that this case presents a novel and potentially remediable cause of BTS and indicates the need for a careful search for an underlying lesion when common causes of BTS have been excluded.
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Arteriopatías Oclusivas/etiología , Síndrome del Dedo Azul/etiología , Embolia/etiología , Pie/irrigación sanguínea , Tendones/anomalías , Angiografía de Substracción Digital , Arteriopatías Oclusivas/diagnóstico , Arteriopatías Oclusivas/terapia , Síndrome del Dedo Azul/diagnóstico , Síndrome del Dedo Azul/terapia , Constricción Patológica , Embolia/diagnóstico , Embolia/terapia , Humanos , Imagen por Resonancia Magnética , Masculino , Persona de Mediana Edad , Inhibidores de Agregación Plaquetaria/uso terapéutico , Recurrencia , Tendones/cirugía , Tenotomía , Resultado del Tratamiento , Ultrasonografía Doppler DúplexRESUMEN
Isolated popliteal venous entrapment is unusual and often caused by variation or aberrant origins of the gastrocnemius muscle, thickened perivenous fascia or an abnormal vascular bundle. We report a unique case of a fit and well 35-year-old man with popliteal venous entrapment after presenting to the vascular unit with symptomatic varicose veins. The cause of the entrapment was found to be an aberrant medial sural artery on operative exploration. The artery was ligated, releasing the entrapped vein. The patient made an uneventful recovery with resolution of symptoms of venous insufficiency without evidence of muscle ischaemia.
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Arterias/anomalías , Arterias/cirugía , Extremidad Inferior , Músculo Esquelético , Vena Poplítea/anomalías , Vena Poplítea/cirugía , Várices/cirugía , Adulto , Humanos , Extremidad Inferior/irrigación sanguínea , Extremidad Inferior/cirugía , Masculino , Músculo Esquelético/irrigación sanguínea , Músculo Esquelético/cirugía , Inducción de RemisiónAsunto(s)
Aneurisma de la Aorta Abdominal , Inhibidores de Hidroximetilglutaril-CoA Reductasas , Humanos , Aneurisma de la Aorta Abdominal/tratamiento farmacológico , Aneurisma de la Aorta Abdominal/patología , Inhibidores de Hidroximetilglutaril-CoA Reductasas/uso terapéutico , Metaanálisis como Asunto , Revisiones Sistemáticas como AsuntoRESUMEN
BACKGROUND: Trans-abdominal laparoscopic inguinal hernia repair allows rapid assessment and exploration of the contralateral groin and repair of an occult hernia. Although previous studies have shown that the totally extra-peritoneal (TEP) hernia repair can be used to assess the contralateral groin, there is little data pertaining to the trans-abdominal pre-peritoneal (TAPP) approach. The aim of this study was to document the incidence of occult contralateral hernia at the time of TAPP hernia repair. METHODS: Data were collected prospectively from all patients undergoing laparoscopic TAPP hernia repair in a District General Hospital over a three-year period. Two specialist laparoscopic/upper gastrointestinal surgeons undertook all of the operations and telephone follow-up was carried out by a dedicated laparoscopic specialist nurse. RESULTS: A total of 310 patients underwent hernia surgery. Four cases were excluded, leaving 306 patients in the study. The male:female ratio was 10.5:1, with a median age of 59 years. Two hundred and six (67%) patients were booked for a unilateral hernia repair; of these, a contralateral hernia was found and repaired in 45 (22%). In 76 cases where a bilateral repair was planned, 61 (80%) went on to have both groin defects repaired. In the remaining 20%, the clinical suspicion of bilateral hernia was revised at the time of surgery to unilateral only. Twenty (7%) patients were booked to undergo a unilateral repair with the possibility of a contralateral hernia--in this group, the suspected contralateral defect was confirmed in 6 (30%) cases. Four (1%) cases were booked as femoral repairs, one of which was found to be an inguinal hernia. The clinical diagnostic accuracy was 78%. CONCLUSION: Accurate incidence figures of an occult contralateral inguinal hernia will enhance the pre-operative information given to patients and may impact on resource allocation and planning theatre logistics. Finding and repairing an occult contralateral hernia at the time of TAPP has the distinct advantage that it saves the patient from further symptoms and from another operation with its associated potential morbidity.
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Hernia Femoral/epidemiología , Hernia Femoral/cirugía , Hernia Inguinal/epidemiología , Hernia Inguinal/cirugía , Femenino , Hernia Femoral/diagnóstico , Hernia Inguinal/diagnóstico , Humanos , Incidencia , Laparoscopía , Masculino , Persona de Mediana Edad , Estudios ProspectivosRESUMEN
Supracondylar fractures of the humerus are the commonest upper limb fractures in children, accounting for up to 70% of all paediatric elbow fractures [Wilson MJ, Hunter JB. Supracondylar fractures of the humerus in children--wire removal in the outpatient setting. Injury Extra 2006 Aug;37(8):313-315] and are often complicated by neurovascular injury. Much confusion surrounds the management of the child with a "pink pulseless hand" post-fracture reduction and several treatment options have been proposed including observation, immediate exploration and angiography. The literature contains a number of case series with variable follow-up. Both angiography and colour duplex ultrasound provide little benefit in the management of these patients. A child with a pink pulseless hand post-fracture reduction can be managed expectantly unless additional signs of vascular compromise develop, in which case exploration should be undertaken.
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Vasos Sanguíneos/lesiones , Mano/irrigación sanguínea , Fracturas del Húmero/complicaciones , Niño , Humanos , Pulso Arterial , Heridas y Lesiones/diagnóstico , Heridas y Lesiones/terapiaRESUMEN
BACKGROUND: Inactivation of the human type Ialpha regulatory subunit (RIalpha) of cyclic AMP dependent protein kinase (PKA) (PRKAR1A) leads to altered kinase activity, primary pigmented nodular adrenocortical disease (PPNAD), and sporadic adrenal and other tumours. METHODS AND RESULTS: A transgenic mouse carrying an antisense transgene for Prkar1a exon 2 (X2AS) under the control of a tetracycline responsive promoter (the Tg(Prkar1a*x2as)1Stra, Tg(tTAhCMV)3Uh or tTA/X2AS line) developed thyroid follicular hyperplasia and adenomas, adrenocortical hyperplasia and other features reminiscent of PPNAD, including late onset weight gain, visceral adiposity, and non-dexamethasone suppressible hypercorticosteronaemia, with histiocytic, epithelial hyperplasias, lymphomas, and other mesenchymal tumours. These lesions were associated with allelic losses of the mouse chromosome 11 Prkar1a locus, an increase in total type II PKA activity, and higher RIIbeta protein levels; the latter biochemical and protein changes were also documented in Carney complex tumours associated with PRKAR1A inactivating mutations and chromosome 17 PRKAR1A locus changes. CONCLUSION: We conclude that the tTA/X2AS mouse line with a downregulated Prkar1a gene replicates several of the findings in Carney complex patients and their affected tissues, supporting the role of RIalpha as a candidate tumour suppressor gene.
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Neoplasias de las Glándulas Endocrinas/enzimología , Proteínas/fisiología , Enfermedades de la Corteza Suprarrenal/enzimología , Enfermedades de la Corteza Suprarrenal/genética , Neoplasias de las Glándulas Suprarrenales/enzimología , Neoplasias de las Glándulas Suprarrenales/genética , Alelos , Animales , Subunidad RIalfa de la Proteína Quinasa Dependiente de AMP Cíclico , Proteína Quinasa Tipo II Dependiente de AMP Cíclico , Proteínas Quinasas Dependientes de AMP Cíclico/metabolismo , Regulación hacia Abajo , Neoplasias de las Glándulas Endocrinas/genética , Eliminación de Gen , Genes Supresores de Tumor , Humanos , Pérdida de Heterocigocidad , Ratones , Ratones Transgénicos , Mutación , Síndromes Neoplásicos Hereditarios/enzimología , Síndromes Neoplásicos Hereditarios/genética , Fenotipo , Proteínas/genética , Neoplasias de la Tiroides/enzimología , Neoplasias de la Tiroides/genéticaRESUMEN
Carney complex (CNC) is a familial multiple endocrine neoplasia syndrome associated with GH-producing pituitary tumours and transmitted as an autosomal dominant trait. Mutations of the PRKAR1A gene are responsible for approximately half the known CNC cases but have never found in sporadic pituitary tumours. Pituitary tissue was obtained from an acromegalic CNC patient heterozygote for a common (PRKARIA)i-inactivating mutation. Both immunohistochemistry and electron microscopy showed a highly pleiomorphic pituitary adenoma. The cell culture population appeared morphologically heterogeneous and remained so after more than 30 passages. The mixture was comprised of cells strongly immunostained for GH, spindle-shaped myofibroblast-like cells, and cuboid cells with large axonal projections (negative for GH). The population appeared to have both epithelial and mesenchymal cells. Both at baseline and at passage 30, cytogenetic analysis indicated the presence of normal 46, XY diploid karyotype, whereas losses of the PRKARIA(i) locus were demonstrated in more than 98% of the cells by fluorescent in situ hybridisation, supporting this gene's involvement in pituitary tumorigenesis. Allelic loss may have occurred in a single precursor cell type that differentiated and clonally expanded into several phenotypes. Epithelial-to-mesenchymal transition may also occur in CNC-associated pleiomorphic pituitary adenomas.
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Adenoma/enzimología , Adenoma/genética , Proteínas Quinasas Dependientes de AMP Cíclico/genética , Hormona Liberadora de Hormona del Crecimiento/genética , Pérdida de Heterocigocidad/genética , Neoplasia Endocrina Múltiple/enzimología , Neoplasia Endocrina Múltiple/genética , Neoplasias Hipofisarias/enzimología , Neoplasias Hipofisarias/genética , Adenoma/patología , Adenoma/ultraestructura , Adulto , Hormona Liberadora de Hormona del Crecimiento/inmunología , Humanos , Inmunohistoquímica/métodos , Hibridación Fluorescente in Situ/métodos , Masculino , Microscopía Electrónica/métodos , Neoplasia Endocrina Múltiple/patología , Neoplasia Endocrina Múltiple/ultraestructura , Neoplasias Hipofisarias/patología , Neoplasias Hipofisarias/ultraestructura , Células Tumorales CultivadasRESUMEN
The type 1 alpha regulatory subunit (R1alpha) of cAMP-dependent protein kinase A (PKA) (PRKAR1A) is an important regulator of the serine-threonine kinase activity catalyzed by the PKA holoenzyme. Carney complex (CNC) describes the association 'of spotty skin pigmentation, myxomas, and endocrine overactivity'; CNC is in essence the latest form of multiple endocrine neoplasia to be described and affects the pituitary, thyroid, adrenal and gonadal glands. Primary pigmented nodular adrenocortical disease (PPNAD), a micronodular form of bilateral adrenal hyperplasia that causes a unique, inherited form of Cushing syndrome, is also the most common endocrine manifestation of CNC. CNC and PPNAD are genetically heterogeneous but one of the responsible genes is PRKAR1A, at least for those families that map to 17q22-24 (the chromosomal region that harbors PRKAR1A). CNC and/or PPNAD are the first human diseases to be caused by mutations in one of the subunits of the PKA holoenzyme. Despite the extensive literature on R1alpha and PKA, little is known about their potential involvement in cell cycle regulation, growth and/or proliferation. The presence of inactivating germline mutations and the loss of its wild-type allele in CNC lesions indicated that PRKAR1A could function as a tumor-suppressor gene in these tissues. However, there are conflicting data in the literature about PRKAR1A's role in human neoplasms, cancer cell lines and animal models. In this report, we review briefly the genetics of CNC and focus on the involvement of PRKAR1A in human tumorigenesis in an effort to reconcile the often diametrically opposite reports on R1alpha.
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Neoplasia Endocrina Múltiple/enzimología , Proteínas/fisiología , Animales , Subunidad RIalfa de la Proteína Quinasa Dependiente de AMP Cíclico , Proteínas Quinasas Dependientes de AMP Cíclico , HumanosRESUMEN
The degree of medical adherence in pediatric solid-organ transplant recipients frequently correlates with the degree of psychological distress, family functioning, and the physiological side-effects of immunosuppressant medications. This article examines the current literature regarding each of these factors and proposes recommendations for increasing the medical compliance among childhood transplant recipients.
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Trasplante de Órganos/psicología , Cooperación del Paciente , Pediatría , Relaciones Familiares , Conocimientos, Actitudes y Práctica en Salud , Humanos , Terapia de Inmunosupresión/psicología , Apoyo SocialRESUMEN
In mice and other sensitive species, PPARalpha mediates the induction of mitochondrial, microsomal, and peroxisomal fatty acid oxidation, peroxisome proliferation, liver enlargement, and tumors by peroxisome proliferators. In order to identify PPARalpha-responsive human genes, HepG2 cells were engineered to express PPARalpha at concentrations similar to mouse liver. This resulted in the dramatic induction of mRNAs encoding the mitochondrial HMG-CoA synthase and increases in fatty acyl-CoA synthetase (3-8-fold) and carnitine palmitoyl-CoA transferase IA (2-4-fold) mRNAs that were dependent on PPARalpha expression and enhanced by exposure to the PPARalpha agonist Wy14643. A PPAR response element was identified in the proximal promoter of the human HMG-CoA synthase gene that is functional in its native context. These data suggest that humans retain a capacity for PPARalpha regulation of mitochondrial fatty acid oxidation and ketogenesis. Human liver is refractory to peroxisome proliferation, and increased expression of mRNAs for the peroxisomal fatty acyl-CoA oxidase, bifunctional enzyme, or thiolase, which accompanies peroxisome proliferation in responsive species, was not evident following Wy14643 treatment of cells expressing elevated levels of PPARalpha. Additionally, no significant differences were seen for the expression of apolipoprotein AI, AII, or CIII; medium chain acyl-CoA dehydrogenase; or stearoyl-CoA desaturase mRNAs.
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Receptores Citoplasmáticos y Nucleares/biosíntesis , Factores de Transcripción/biosíntesis , Acilcoenzima A/metabolismo , Secuencia de Aminoácidos , Animales , Apolipoproteína A-I/metabolismo , Apolipoproteína A-II/metabolismo , Apolipoproteína C-III , Apolipoproteínas C/metabolismo , Western Blotting , Carnitina O-Palmitoiltransferasa/metabolismo , División Celular , Línea Celular , Ácidos Grasos/metabolismo , Humanos , Hígado/metabolismo , Luciferasas/metabolismo , Ratones , Mitocondrias/enzimología , Datos de Secuencia Molecular , Oxígeno/metabolismo , Peroxisomas/metabolismo , Regiones Promotoras Genéticas , Pirimidinas/metabolismo , ARN Mensajero/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Ribonucleasas/metabolismo , Timidina Quinasa/genética , Transfección , Células Tumorales CultivadasRESUMEN
Many of the key molecular events underlying the induction and patterning of the vertebrate mesoderm and endoderm have recently been elucidated. T-box transcription factors and TGF-beta and Wnt signaling pathways play crucial roles in the initial induction of the mesendoderm and the subdivision of the posterior mesoderm into rostral and caudal domains.
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Tipificación del Cuerpo/fisiología , Inducción Embrionaria/fisiología , Endodermo/fisiología , Mesodermo/fisiología , Animales , Vertebrados/embriología , Xenopus/embriología , Pez Cebra/embriologíaRESUMEN
Reverse transcriptase-polymerase chain reaction was used to amplify a partial cDNA from rabbit lung mRNA that shared 77% protein sequence identity with the mouse pregnane X receptor (PXR). Rapid amplification of cDNA ends from a rabbit kidney lambdaZAP expression library resulted in the isolation of overlapping cDNAs spanning the complete coding sequence. The deduced amino acid sequence of 411 residues exhibited 79% overall amino acid identity with human PXR and 77% identity with mouse PXR. Based on this protein sequence relationship and a similar degree of conservation exhibited by the mouse and human PXR orthologs, the cDNA appears to encode the rabbit PXR ortholog. 5'-rapid amplification of cDNA ends performed on an adaptor-ligated cDNA library from rabbit liver revealed the presence of an alternate mRNA, which differed at the 5'-terminus. RNase protection assays indicated that the alternate mRNA was expressed at >50-fold lower levels in rabbit kidney and liver. Rifampicin treatment of CV-1 cells cotransfected with a rabbit PXR expression plasmid and a luciferase reporter construct containing two copies of the DR3 enhancer from CYP3A23 produced a 6-fold induction of luciferase activity. In contrast, rat PXR was not responsive to this antibiotic under the same conditions. Pregnenolone 16alpha-carbonitrile was an efficacious activator of rat PXR, but failed to significantly activate rabbit PXR at equivalent concentrations. These results indicate that the ligand activation profile of rabbit PXR is distinct from rat PXR and more closely resembles that of human PXR. The rabbit PXR activation profile is consistent with the cytochrome P450 (P450) 3A6 induction profile in rabbits.
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Antibióticos Antituberculosos/farmacología , Hidrocarburo de Aril Hidroxilasas , Receptores Citoplasmáticos y Nucleares/agonistas , Receptores de Esteroides/agonistas , Rifampin/farmacología , Secuencia de Aminoácidos , Animales , Antiinflamatorios/farmacología , Núcleo Celular/efectos de los fármacos , Sistema Enzimático del Citocromo P-450/biosíntesis , Sistema Enzimático del Citocromo P-450/metabolismo , ADN/biosíntesis , ADN/genética , Dexametasona/farmacología , Inducción Enzimática/efectos de los fármacos , Humanos , Riñón/efectos de los fármacos , Riñón/enzimología , Hígado/efectos de los fármacos , Hígado/enzimología , Ratones , Oxigenasas de Función Mixta/metabolismo , Datos de Secuencia Molecular , Poli A/biosíntesis , Poli A/genética , Receptor X de Pregnano , ARN/biosíntesis , ARN/genética , Conejos , Ratas , Receptores Citoplasmáticos y Nucleares/genética , Receptores de Esteroides/genética , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Transfección/genéticaRESUMEN
T-box transcription factors are critical regulators of early embryonic development. We have characterized a novel zebrafish T-box transcription factor, hrT (H15-related T box) that is a close relative of Drosophila H15 and a recently identified human gene. We show that Drosophila H15 and zebrafish hrT are both expressed early during heart formation, in strong support of previous work postulating that vertebrate and arthropod hearts are homologous structures with conserved regulatory mechanisms. The timing and regulation of zebrafish hrT expression in anterior lateral plate mesoderm suggest a very early role for hrT in the differentiation of the cardiac precursors. hrT is coexpressed with gata4 and nkx2.5 not only in anterior lateral plate mesoderm but also in noncardiac mesoderm adjacent to the tail bud, suggesting that a conserved regulatory pathway links expression of these three genes in cardiac and noncardiac tissues. Finally, we analyzed hrT expression in pandora mutant embryos, since these have defects in many of the tissues that express hrT, including the heart. hrT expression is much reduced in the early heart fields of pandora mutants, whereas it is ectopically expressed subsequently. Using hrT expression as a marker, we describe a midline patterning defect in pandora affecting the anterior hindbrain and associated midline mesendodermal derivatives. We discuss the possibility that the cardiac ventricular defect previously described in pandora and the midline defects described here are related.
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Drosophila/embriología , Corazón/embriología , Factores de Transcripción/fisiología , Pez Cebra/embriología , Secuencia de Aminoácidos , Animales , Regulación del Desarrollo de la Expresión Génica , Humanos , Datos de Secuencia Molecular , Homología de Secuencia de Aminoácido , Factores de Transcripción/químicaAsunto(s)
Sistema Enzimático del Citocromo P-450/biosíntesis , Receptores Citoplasmáticos y Nucleares/fisiología , Xenobióticos/farmacología , Secuencia de Aminoácidos , Animales , Sistema Enzimático del Citocromo P-450/genética , ADN/metabolismo , Inducción Enzimática , Hormonas/fisiología , Humanos , Datos de Secuencia Molecular , Especificidad de la Especie , Activación TranscripcionalRESUMEN
Human cytochrome P450s 2C9 and 2C19 metabolize many important drugs including tolbutamide, phenytoin, and (S)-warfarin. Although they differ at only 43 of 490 amino acids, sulfaphenazole (SFZ) is a potent and selective inhibitor of P450 2C9 with an IC50 and a spectrally determined binding constant, KS, of <1 microM. P450 2C19 is not affected by SFZ at concentrations up to 100 microM. A panel of CYP2C9/2C19 chimeric proteins was constructed in order to identify the sequence differences that underlie this difference in SFZ binding. Replacement of amino acids 227-338 in 2C19 with the corresponding region of 2C9 resulted in high-affinity SFZ binding (KS approximately 4 microM) that was not seen when a shorter fragment of 2C9 was substituted (227-282). However, replacement of amino acids 283-338 resulted in extremely low holoenzyme expression levels in Escherichia coli, indicating protein instability. A single mutation, E241K, which homology modeling indicated would restore a favorable charge pair interaction between K241 in helix G and E288 in helix I, led to successful expression of this chimera that exhibited a KS < 10 microM for SFZ. Systematic replacement of the remaining differing amino acids revealed that two amino acid substitutions in 2C19 (N286S, I289N) confer high-affinity SFZ binding (KS < 5 microM). When combined with a third substitution, E241K, the resulting 2C19 triple mutant exhibited a high cataltyic efficiency for warfarin metabolism with the relaxed stereo- and regiospecificity of 2C19 and a lower KM for (S)-warfarin metabolism (<10 microM) typical of 2C9.