PubMed Health⌕ Search

Biomedical subjects

B Lefebvre

Publications and source records attributed to B Lefebvre.

At least 19 recordsLinked to original sources
PubMed2004

Chronic intermittent hypoxia increases infarction in the isolated rat heart.

Coronary heart disease is frequently associated with obstructive sleep apnea syndrome and treating obstructive sleep apnea appears to significantly improve the outcome in coronary heart disease. Thus we have developed a rat model of chronic intermittent hypoxia (IH) to study the influence of this condition on myocardial ischemia-reperfusion tolerance and on functional vascular reactivity. Wistar male rats were divided in three experimental groups (n = 12 each) subjected to chronic IH (IH group), normoxia (N group), or control conditions (control group). IH consisted of repetitive cycles of 1 min (40 s with inspired O(2) fraction 5% followed by 20 s normoxia) and was applied for 8 h during daytime, for 35 days. Normoxic cycles were applied in the same conditions, inspired O(2) fraction remaining constant at 21%. On day 36, mean arterial blood pressure (MABP) was measured before isolated hearts were submitted to an ischemia-reperfusion protocol. The thoracic aorta and left carotid artery were also excised for functional reactivity studies. MABP was not significantly different between the three experimental groups. Infarct sizes (in percent of ventricles) were significantly higher in IH group (46.9 +/- 3.6%) compared with N (26.1 +/- 2.8%) and control (21.7 +/- 2.1%) groups. Vascular smooth muscle function was similar in aorta and carotid arteries from all groups. The endothelium-dependent relaxation in response to acetylcholine was also similar in aorta and carotid arteries from all groups. Chronic IH increased heart sensitivity to infarction, independently of a significant increase in MABP, and did not affect vascular reactivity of aorta and carotid arteries.

Animals↗
PubMed2004

Significance of hepatitis C virus coinfection with persistently normal alanine aminotransferase levels in HIV-1-infected patients.

OBJECTIVES: To assess the prevalence of chronic hepatitis C virus (HCV) infection with persistently normal alanine aminotransferase (ALT) levels in HIV-1-infected patients, together with its clinical, biological and histological characteristics and predictive factors. METHODS: We retrospectively studied all HCV/HIV-coinfected patients treated in our Infectious Diseases Department, for whom data on both HIV and HCV infection were available. We compared the demographic characteristics and parameters of HIV and HCV infection between cases, defined by persistently normal ALT levels (<45 IU/L) and detectable serum HCV-RNA (determined by PCR), and controls with high ALT levels and HCV PCR positivity during the previous 3 years. RESULTS: Among the 815 HIV-infected patients assessed for this study, 179 (22%) were HCV-coinfected, of whom 155 were eligible for this analysis. Of these 155 HCV-coinfected patients, 137 (88%) were HCV-PCR-positive, of whom 39 (28.5%) had persistently normal ALT levels (cases) and 98 (71.5%) had high ALT levels (controls). Relative to controls, cases had a significantly lower fibrosis score and a lower fibrosis progression rate (2.2 vs. 1.3, P=0.004; 0.3 vs. 0.2, P=0.006, respectively). Three factors associated with persistently normal ALT levels were identified, namely: HBsAg negativity (P=0.003), HCV genotype 4 (P=0.01) and female sex (P=0.05). CONCLUSION: Persistently normal ALT levels may be considered as a marker of slow HCV disease progression in HIV-coinfected patients, with significantly less severe hepatic lesions.

Adult↗
PubMed2003

Impact of highly active antiretroviral therapy on the occurrence of bacteraemia in HIV-infected patients and their epidemiologic characteristics.

OBJECTIVE: 1. to assess the impact of highly active antiretroviral therapy (HAART) on the occurrence of bacteraemia in HIV-infected patients and their clinical and microbiological characteristics. 2. to identify risk factors for bacteraemia in this setting. METHODS: The files of all HIV-infected patients hospitalized for an episode of bacteraemia in a 28-bed infectious diseases unit between January 1995 and December 1998 were reviewed. Cases occurring during HAART were compared to cases occurring in patients not receiving HAART. Furthermore, in a case-control study, patients with bacteraemia occurring during HAART were compared with other patients receiving HAART. RESULTS: There were 74 episodes of bacteraemia in patients not receiving HAART and 31 episodes in patients receiving HAART. The occurrence of bacteraemia fell from 10.5/100 hospitalizations in 1995 to 5.5/100 in 1998 (P = 0.02 trend test). The occurence of P. aeruginosa bacteraemia fell sharply (9/398 vs 1/273, P = 0.05). A significant fall in catheter-related infections was observed between 1995 and 1998 (5.5% vs 1.8%). The two-thirds/one-third distribution of hospital-acquired and community-acquired infections remained stable throughout the period study. In patients receiving HAART, the case-control study showed by multivariate analysis, that a CD4 cell count of less than 100/ micro L [OR = 7.3 (1.9-49.7)], and the use of exogenous devices [OR = 13.3 (2.5-71)] were significantly associated with the risk of bacteraemia. CONCLUSION: The introduction of HAART has been associated with a significant fall in the occurrence of bacteraemia. However, patients with a low CD4 cell count remain at risk of bacteraemia with similar microbiological and epidemiological characteristics than in the pre-HAART era.

Adult↗
PubMed2000

Scintimammography with 11beta-methoxy-(17alpha,20Z)-[123I]iodovinylestrad iol: a complementary role to 99mTc-methoxyisobutyl isonitrile in the characterization of breast tumors.

UNLABELLED: The aim of this study was to investigate a possible relationship between 99mTc-methoxyisobutyl isonitrile (MIBI) uptake and the estrogen receptor (ER) status of breast tumors as determined by 11beta-methoxy-(17alpha,20Z)-[123I]iodovinylestradi ol (MIVE) scintimammography. METHODS: Thirteen patients referred for MIVE scintimammography after abnormal mammography or finding of a suspect mass on physical examination were injected intravenously with MIVE. Planar images of the breasts and axillary region were taken with both radiopharmaceuticals and compared with pathologic examination of the tumor tissue and in vitro ER quantification. RESULTS: The presence of cancerous tissue, as indicated by MIBI uptake, is a prerequisite for the accumulation of MIVE by the breast tumors. There was no statistically significant correlation between the MIBI and MIVE tumor uptake ratios. However, the latter correlate well with the presence of ER, as determined by an in vitro assay. CONCLUSION: MIVE scans add unique information concerning the tumor ER status in breast cancer patients, which could contribute to a better characterization of the tumor and aid in the selection of the most appropriate treatment protocol.

Adult↗
PubMed1999

The histone acetylase PCAF is a phorbol-ester-inducible coactivator of the IRF family that confers enhanced interferon responsiveness.

Transcription factors of the interferon regulatory factor (IRF) family bind to the type I interferon (IFN)-responsive element (ISRE) and activate transcription from IFN-inducible genes. To identify cofactors that associate with IRF proteins, DNA affinity binding assays were performed with nuclear extracts prepared from tissue culture cells. The results demonstrated that the endogenous IRFs bound to the ISRE are complexed with the histone acetylases, PCAF, GCN5, and p300/CREB binding protein and that histone acetylase activities are accumulated on the IRF-ISRE complexes. By testing recombinant proteins, we show that PCAF directly binds to some but not all members of the IRF family through distinct domains of the two proteins. This interaction was functionally significant, since transfection of PCAF strongly enhanced IRF-1- and IRF-2-dependent promoter activities. Further studies showed that expression of PCAF and other histone acetylases was markedly induced in U937 cells upon phorbol ester treatment, which led to increased recruitment of PCAF to the IRF-ISRE complexes. Coinciding with the induction of histone acetylases, phorbol ester markedly enhanced IFN-alpha-stimulated gene expression in U937 cells. Supporting the role for PCAF in conferring IFN responsiveness, transfection of PCAF into U937 cells led to a large increase in IFN-alpha-inducible promoter activity. These results demonstrate that PCAF is a phorbol ester-inducible coactivator of the IRF proteins which contributes to the establishment of type I IFN responsiveness.

Acetyltransferases↗
PubMed1999

Biodistribution, dosimetry and metabolism of 11beta-methoxy-(17alpha,20E/Z)-[123I]iodovinylestradiol in healthy women and breast cancer patients.

UNLABELLED: The biodistribution and dosimetry of the 20E and 20Z stereoisomers of 11 beta-methoxy-(17alpha,20)-[123I]iodovinylestradiol (MIVE) were evaluated in six healthy women. Tumor uptake and metabolism of the 20Z isomer were evaluated in 13 women referred after abnormal mammography or after discovery of a suspect mass at physical examination. METHODS: The radiopharmaceuticals were prepared from their corresponding stannyl intermediates and administrated intravenously. Blood samples were drawn at different time intervals and urine was collected for up to 24 h. Metabolites were detected by radiochromatography. Tissue distribution was followed for up to 24 h by scintigraphic imaging. The dosimetry was computed according to the Medical Internal Radiation Dose scheme. RESULTS: The 20E and 20Z isomers exhibit similar biodistribution and dosimetry patterns. Chromatographic analysis of plasma samples of healthy volunteers and cancer patients, as well as in vitro plasma incubations, confirmed the in vivo stability of (20Z)-[123I]MIVE. Radioactivity was rapidly cleared from the blood by the liver and excreted through the gut, which received the highest radiation dose (0.211 mGy/MBq). The effective doses for the adult female and male phantom were 0.054 and 0.046 mSv/MBq, respectively. Among the 13 patients imaged with (20Z)-[123I]MIVE, 3 had fibrocystic disease with no focal uptake, 8 had good agreement with in vitro estrogen receptor determination and 2 were false-positive. CONCLUSION: The radiation dose after intravenous administration of 20E- or (20Z)-[123I]MIVE at imaging dose levels is within acceptable limits. There was a good correlation between uptake of (20Z)-[123I]MIVE and the presence of estrogen receptors in breast cancer patients.

Adult↗
PubMed1998

H11-H12 loop retinoic acid receptor mutants exhibit distinct trans-activating and trans-repressing activities in the presence of natural or synthetic retinoids.

Retinoids, such as the naturally occurring all-trans-retinoic acid (atRA) and synthetic ligand CD367 modulate ligand-dependent transcription through retinoic acid receptors (RARs). Retinoid binding to RAR is believed to trigger structural transitions in the ligand-binding domain (LBD), leading to helix H1 and helix H12 repositioning and coactivator recruitment and corepressor release. Here, we carried out a detailed mutagenesis analysis of the H11-H12 loop (designated the L box) to study its contribution to hRARalpha activation process. Point mutations that reduced transactivation by atRA also reduced atRA-induced transrepression of AP1 transcription, correlating ligand-induced activation and repression. However, a correlation was not observed with these mutations when tested with another ligand CD367, a synthetic agonist with binding properties identical to those of atRA. Transcription was strongly inhibited in the presence of CD367 for some mutants, thus leading to an inverse agonist activity of this ligand. None of these mutations significantly altered binding affinity for either ligand, indicating that altered transcription was not caused by altered ligand binding by these mutations. Although simple correlations with transcriptional activities were not found, these mutations were also characterized by altered ligand-induced structural transitions, which were distinct for the atRA-hRARalpha or CD367-hRARalpha complexes. These results indicate that amino acids in the L box are involved in specifying trans-repressive and trans-activating properties of the hRARalpha, and support the notion that different agonists induce distinct conformations in the LBD of the receptor.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Binding of retinoic acid receptor heterodimers to DNA. A role for histones NH2 termini.

The retinoic acid signaling pathway is controlled essentially through two types of nuclear receptors, RARs and RXRs. Ligand dependent activation or repression of retinoid-regulated genes is dependent on the binding of retinoic acid receptor (RAR)/9-cis-retinoic acid receptor (RXR) heterodimers to retinoic acid response element (RARE). Although unliganded RXR/RAR heterodimers bind constitutively to DNA in vitro, a clear in vivo ligand-dependent occupancy of the RARE present in the RARbeta2 gene promoter has been reported (Dey, A., Minucci, S., and Ozato, K. (1994) Mol. Cell. Biol. 14, 8191-8201). Nucleosomes are viewed as general repressors of the transcriptional machinery, in part by preventing the access of transcription factors to DNA. The ability of hRXRalpha/hRARalpha heterodimers to bind to a nucleosomal template in vitro has therefore been examined. The assembly of a fragment from the RARbeta2 gene promoter, which contains a canonical DR5 RARE, into a nucleosome core prevented hRXRalpha/hRARalpha binding to this DNA, in conditions where a strong interaction is observed with a linear DNA template. However, histone tails removal by limited proteolysis and histone hyperacetylation yielded nucleosomal RAREs able to bind to hRXRalpha/hRARalpha heterodimers. These data establish therefore the role of histones NH2 termini as a major impediment to retinoid receptors access to DNA, and identify histone hyperacetylation as a potential physiological regulator of retinoid-induced transcription.

Base Sequence↗
PubMed1998

Distinct modes of interaction of the retinoic acid receptor alpha with natural and synthetic retinoids.

Retinoids regulate key cellular processes through their binding to their cognate nuclear receptors, RARs and RXRs. Synthetic ligands mimic most of their biological effects and alteration of their chemical structure confers selectivity for RAR isotypes alpha, beta or gamma. In this study, we have examined the contribution of a domain (L box) of hRARalpha located at the C-terminus of the ligand binding domain (LBD), between helices H11 and H12, to the ligand binding activity of this receptor. By site-directed mutagenesis, we demonstrate that, in the absence of the ligand-dependent activation domain 2 (AF2-AD), the receptor discriminates between classes of structurally distinct retinoids. This property was lost in the presence of the AF2-AD domain, evidencing major structural transitions in this part of the receptor. We propose that ligand binding occurs in two steps: first, the ligand interacts with the LBD in its opened, holo-receptor conformation in which the L box plays a crucial role in defining the ligand binding repertoire of hRARalpha; secondly, the LBD adopts its closed conformation in which the ligand interacts with the receptor mostly through its carboxylic moiety.

Amino Acid Sequence↗
PubMed1998

Preoperative localization of parathyroid lesions in hyperparathyroidism: relationship between technetium-99m-MIBI uptake and oxyphil cell content.

UNLABELLED: The aim of this study was to assess the relationship between parathyroid oxyphil cell content and early or late phases of uptake of 99mTc-MIBI, a radioisotope preferentially retained in mitochondria-rich cells. METHODS: This study is a retrospective, single-blind analysis of all double-phase 99mTc-MIBI parathyroid scintigraphy studies performed before surgery in our institution between 1990 and 1995. A total of 18 parathyroid lesions in 14 patients were reviewed. This sample included 11 cases of primary hyperparathyroidism (8 adenomas, 1 adenocarcinoma and 2 hyperplasias) and 3 cases of tertiary hyperparathyroidism secondary to chronic renal failure. RESULTS: Uptake of 99mTc-MIBI in the early phase of scintigraphy was associated with larger parathyroid lesions (1.61 +/- 1.61 ml versus 0.33 +/- 0.27 ml; p < 0.02) and higher serum calcium levels (3.00 +/- 0.41 mM versus 2.67 +/- 0.14 mM; p < 0.02). More importantly, we found that a parathyroid oxyphil cell content greater than 25% was more often associated with a positive uptake of 99mTc-MIBI in the late phase of the test (positive late uptake in 78% of lesions with a high oxyphil cell content versus 33% in lesions with an oxyphil cell content between 1% and 25% and 0% in lesions with no oxyphil cells; p < 0.04). CONCLUSION: These findings suggest that the late retention of 99mTc-MIBI in double-phase scintigraphy is related to parathyroid oxyphil cell content.

Adenoma↗
PubMed1997

Limited proteolysis for assaying ligand binding affinities of nuclear receptors.

The binding of natural or synthetic ligands to nuclear receptors is the triggering event leading to gene transcription activation or repression. Ligand binding to the ligand binding domain of these receptors induces conformational changes that are evidenced by an increased resistance of this domain to proteases. In vitro labeled receptors were incubated with various synthetic or natural agonists or antagonists and submitted to trypsin digestion. Proteolysis products were separated by SDS-PAGE and quantified. The amount of trypsin-resistant fragments was proportional to receptor occupancy by the ligand, and allowed the determination of dissociation constants (kDa). Using the wild-type or mutated human retinoic acid receptor alpha as a model, kDa values determined by classical competition binding assays using tritiated ligands are in agreement with those measured by the proteolytic assay. This method was successfully extended to human retinoic X receptor alpha, glucocorticoid receptor, and progesterone receptor, thus providing a basis for a new, faster assay to determine simultaneously the affinity and conformation of receptors when bound to a given ligand.

Animals↗
PubMed1995

Structural determinants of the ligand-binding site of the human retinoic acid receptor alpha.

The ligand-dependent transactivating properties of retinoic acid receptors are controlled through a complex structure at the C-terminus of these proteins, commonly referred to as the hormone binding domain. This domain is involved not only in ligand recognition but also in protein-protein interactions such as homo- and heterodimerization processes. To identify more precisely regions of the human all-trans-retinoic acid receptor alpha (hRAR alpha) that are involved in ligand binding, we constructed a series of deletion mutants of this molecule and overexpressed them in bacteria. We found that the C-terminal part of the D domain (amino acids 186-198) was necessary for ligand binding. The F domain and the 10 C-terminal amino acids of the E domain were dispensable for high-affinity binding of various natural and synthetic retinoids. A further deletion to position 403 resulted in a moderate decrease in affinity for all-trans-(ATRA) and 9-cis-retinoic acids, whereas the binding of two RAR alpha-specific ligands (Am80 and Am580) was abolished. In addition, hRAR alpha and the minimal hormone binding domain (amino acids 186-410) bound ATRA with a positive, cooperative mechanism. This behavior was not observed with CD367, a conformationally restricted synthetic retinoid. The positive cooperativity could be correlated with stable ATRA binding to RAR homodimers, whose formation was triggered by ligand. In the same conditions, only monomeric CD367-RAR alpha complexes were detected. These data indicate that ligand binding to hRAR alpha requires the presence of part of the D domain, whereas the C-terminal end of the E domain is involved in more subtle ligand recognition processes.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1995

The use of Japanese and bobwhite quail as indicator species in avian toxicity test. ECPA/GIFAP Environmental Round Table.

A comparative analysis was made between the toxicity of plant protection products to two species of quail used in regulatory testing. It was shown that in general differences in the sensitivity between bobwhite quail and Japanese quail were small, and not statistically significant. It was therefore concluded that both species should be seen as equally suitable models for avian safety assessment. The mutual acceptance of studies carried out on either of these species for US and EC registration procedures, would lead to a reduction in vertebrate sacrifice and resource spending.

Animals↗
PubMed1995

A physiologic approach to renal scintigraphy. Application to evaluation of hypertension.

The aim of this study was to define the use of the triple radiopharmaceutical renal study (TRRS) for renal scintigraphy as a physiological tool for renal evaluation, and to determine if the sensitivity and/or specificity of a renal study for the diagnosis of renovascular hypertension (RVH) could be improved by the combination of three radiopharmaceuticals (i.e., I-131 OIH, Tc-99m DTPA, and Tc-99m glucoheptonate). One hundred ninety-five patients with suspected RVH underwent TRRS, standard Tc-99m DTPA renal studies, and renal angiography. One hundred eighty-nine patients were hypertensive and ischemic nephropathy was suspected in six. Ninety-one, including three patients with ischemic nephropathy, had a renal artery stenosis of 70% or more (66 unilateral, 25 bilateral). Effective renal plasma flow (ERPF), glomerular filtration rate (GFR) (from plasma clearance of I-131 OIH and Tc-99m DTPA), and geometric renal masses (from Tc-99m glucoheptonate study) were compared to normal values corrected for body surface, to determine the severity of renal dysfunction. For the TRSS, RVH criteria included: 1) differential Tc-99m DTPA function minus differential Tc-99m glucoheptonate function of affected kidney ( < -5% or > 5%) and 2) functional parameters: ERPF = 1.6-2.0 ml/g/minute, GFR = 0.25-0.4 ml/g/minute, and filtration fraction (i.e., GFR/ERPF = 0.15-0.20) on the affected side.

Aged↗
PubMed1995

Rapid washout of technetium-99m-MIBI from a large parathyroid adenoma.

We report a case of rapid 99mTc-methoxyisobutylisonitrile (MIBI) clearance from a parathyroid adenoma. A double-phase 99mTc-MIBI parathyroid scintigraphy was performed on a 62-yr-old female evaluated for primary hyperparathyroidism. A large parathyroid adenoma was visualized caudal to the left lobe of the thyroid gland with an unusually rapid washout of the tracer from tumor tissue. Histologic tissue examination confirmed the presence of a parathyroid adenoma and the absence of oxyphil cells. Care should be taken in interpretation of 99mTc-MIBI parathyroid scintigrams because some adenomas can present a rapid release of the radiotracer in a double-phase study. Technetium-99m-MIBI retention could be related to the number of mitochondria-rich cells in parathyroid adenomas or to hyperplasia.

Adenoma↗