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Biomedical subjects

M Rivera

Publications and source records attributed to M Rivera.

At least 73 records · Page 4Linked to original sources
PubMed1999

Complete isomer-specific 1H and 13C NMR assignments of the heme resonances of rat liver outer mitochondrial membrane cytochrome b5.

Singly and doubly labeled delta-aminolevulinic acid derivatives were used to prepare rat liver outer mitochondrial membrane (OM) cytochrome b5 containing a 13C-labeled heme active site. A variety of NMR experiments, including HMBC and INADEQUATE in conjunction with the more commonly used HMQC, NOESY, and COSY, were conducted to make unambiguous assignments of protonated carbons and the quaternary pyrrole-alpha and -beta carbons in both isomeric forms of the paramagnetic active center of OM cytochrome b5. Because the long interpulse delays in the HMBC experiment have a detrimental effect on the detectability of fast relaxing paramagnetically affected resonances. INADEQUATE is proposed as the experiment of choice for assigning quaternary carbons in paramagnetic hemes with carefully chosen macrocycle labeling patterns. Furthermore, the applicability of the INADEQUATE experiment to paramagnetic heme active sites should be facilitated greatly by the availability of biosynthetic methods for producing isotopically labeled b-hemes and, more recently, isotopically labeled c-hemes.

Aminolevulinic Acid↗
PubMed1999

An electrochemical study of the factors responsible for modulating the reduction potential of putidaredoxin.

The gene coding for putidaredoxin has been synthesized using a combination of chemical and enzymatic methods and subsequently expressed in Escherichia coli. The recombinant protein characterized by electronic spectroscopy, mass spectrometry, and electrochemistry was found to be identical to putidaredoxin obtained from Pseudomonas putida. Polylysine was found to promote the fast and reversible electrochemistry of putidaredoxin at negatively charged electrodes such as indium-doped tin oxide or gold surfaces modified with mercaptoalkanoate groups. The value of the heterogeneous electron transfer rate constant obtained from solutions containing a mixture of putidaredoxin and polylysine (k(s) = 1.3 x 10(-3) cm/s) is one order of magnitude larger than the values reported previously at gold electrodes modified with mercaptoethylamine or at antimony-doped tin oxide semiconductor electrodes. It was observed that when the reduction potential of putidaredoxin is measured by cyclic voltammetry, the resultant value is consistently more positive (64 mV) than the reduction potential measured with potentiometric titrations. A comparison between the electrochemical responses of putidaredoxin and spinach ferredoxin, combined with the examination of their corresponding three-dimensional structures, indicates that the positive shift in the reduction potential of putidaredoxin originates from the formation of a transient complex between putidaredoxin and polylysine at the electrode surface. The formation of this transient complex modulates the reduction potential of putidaredoxin by lowering the value of the dielectric constant around its iron-sulfur cluster microenvironment, specifically by neutralizing negative charges surrounding the active site and by excluding water from the solvent exposed iron sulfur cluster. The observed positive shift in E degrees ', which is induced by complexation with polylysine at the electrode-surface, suggests that similar factors are likely to contribute to the anodic shift in the E degrees ' of cytochrome P450(cam)-bound putidaredoxin (+44 mV) with respect to the E degrees ' measured for free putidaredoxin.

Amino Acid Sequence↗
PubMed1999

Differences in curable STDs between HIV and non-HIV populations in Spain.

The pandemic impact of HIV has changed the clinical spectrum of STDs all over the world. The incidence and frequency of STDs in the different global geographic areas demonstrate the diagnostic and treatment capabilities of various local and national health systems and is simultaneously informing about the sexual behaviours of the population. The purpose of this study was to determine the frequency of curable STDs (herpes, chlamydia, gonorrhoea, syphilis, trichomoniasis) in a hospital-based STD clinic in Madrid, Spain during a 4-year period. Patients were referred mainly from the emergency department, gynecological wards, and family planning (61%) as well as from the HIV-hospital unit (31 beds) and outpatient department (39%). The total number of patients seen was 952 (243 men, 709 women) with an annual average of 238 patients per year. Of these, 139 (14.6%) were HIV-patients and 813 (85.4%) non-HIV patients. In non-HIV patients, STDs were identified in 493 cases (54.2%). In HIV-patients, STDs were diagnosed in 108 cases (77.7%; p < or = 0.001). Two or more STDs were more prevalent in HIV than non-HIV patients. The frequency of STDs in both HIV and non-HIV patients were vulvovaginal candidiasis, 47.8%:57.2%; syphilis, 11.7%:1.4% (p < or = 0.05); gonorrhea, 5.3%:3.9%; Gardnerella vaginosis, 6.3%:4.8%; genital chlamydia, 6.3%:9.06%; trichomoniasis, 17%:6.5% (p < or = 0.05); and genital herpes, 20.2%:5.3% (p < or = 0.05).

Adolescent↗
PubMed1999

Increased bone mineral density in dual x-ray densitometry due to gluteal implants.

The results of dual x-ray bone densitometry in a patient with bilateral gluteal implants are presented. The patient underwent three measurements of the spine and hips, and one of them was before surgery. A baseline study showed mild osteopenia. After surgery, bone mineral density increased in both femoral necks, because of the superimposition of the implants. A spine phantom with and without a similar implant reproduced the findings in the patient. It is important to consider this type of surgery as a cause of potential bone mineral density artifact.

Absorptiometry, Photon↗
PubMed1999

Stabilization of unstable steady states and periodic orbits in an electrochemical system using delayed-feedback control.

We report numerical and experimental results indicating successful stabilization of unstable steady states and periodic orbits in an electrochemical system. Applying a continuous delayed-feedback technique not only periodic and chaotic oscillations are suppressed via stabilization of steady-state solutions but also the chaotic dynamics can be converted to periodic behavior. In all cases the feedback perturbation vanishes as a target state is attained.

Journal Article↗
PubMed1999

Role of secondary structure in discrimination between constitutive and inducible activators.

We have examined structural differences between the proto-oncogene c-Myb and the cyclic AMP-responsive factor CREB that underlie their constitutive or signal-dependent activation properties. Both proteins stimulate gene expression via activating regions that articulate with a shallow hydrophobic groove in the KIX domain of the coactivator CREB-binding protein (CBP). Three hydrophobic residues in c-Myb that are conserved in CREB function importantly in cellular gene activation and in complex formation with KIX. These hydrophobic residues are assembled on one face of an amphipathic helix in both proteins, and mutations that disrupt c-Myb or CREB helicity in this region block interaction of either factor with KIX. Binding of the helical c-Myb domain to KIX is accompanied by a substantial increase in entropy that compensates for the comparatively low enthalpy of complex formation. By contrast, binding of CREB to KIX entails a large entropy cost due to a random coil-to-helix transition in CREB that accompanies complex formation. These results indicate that the constitutive and inducible activation properties of c-Myb and CREB reflect secondary structural characteristics of their corresponding activating regions that influence the thermodynamics of formation of a complex with CBP.

Amino Acid Sequence↗
PubMed1999

Treatment of secondary hyperparathyroidism in hemodialyzed patients with high-dose calcium carbonate without vitamin D3 supplements.

BACKGROUND: Vitamin D compounds are usually indicated for the treatment of secondary hyperparathyroidism in dialysis patients. The possibility to induce a reversal of hyperparathyroidism with calcium supplementation alone is controversial. The present study was conducted to assess if oral calcium carbonate may constitute a therapeutic option for the control of hyperparathyroidism in patients with high PTH concentrations at the beginning of the treatment with chronic hemodialysis. METHODS: Thirty-one patients with end-stage renal failure with an intact PTH concentration above 250 pg/ml at the beginning of chronic hemodialysis therapy were treated with high doses of calcium carbonate; no patient received either aluminium-containing binders or vitamin D compounds. To minimize hypercalcemia, a calcium dialysate concentration of 2.5 mEq/l was used in all patients. The goal of the study was to reduce the intact PTH concentration to 250 pg/ml with oral calcium carbonate supplements alone. RESULTS: Throughout the first year on hemodialysis treatment, the intact PTH concentration decreased from 538 +/- 256 to 251 +/- 218 pg/ml (p < 0.001). By the end of the study, the therapeutic objective was achieved in 22 patients (71%) ('responder' group). The remaining 9 patients were classified as the 'treatment failure' group. The basal intact PTH concentration was not different between both groups (508 +/- 235 vs. 612 +/- 303 pg/ml, respectively, p = n.s.), but 5 'treatment failure' patients admitted to take a dose of calcium carbonate lower than that prescribed. There were 40 episodes of hyperphosphatemia (11% of all measurements) in 7 of 31 patients, 5 of them belonged to the noncompliance 'treatment failure' patients. Only 15 episodes (4% of all measurements) of transient hypercalcemia (range 11.1 - 11.9 mg/dl) were detected in 8 patients. CONCLUSIONS: Secondary hyperparathyroidism in hemodialysis patients can often be reverted by oral calcium carbonate alone. But a good adherence to treatment is absolutely necessary.

Administration, Oral↗
PubMed1999

Modulation of prohormone convertase 2 in spinal cord during gestation and hormone-simulated pregnancy.

Gestation as well as its hormonal simulation (HSP) is characterized by an enhanced spinal dynorphin/kappa-opioid antinociception. This antinociception is accompanied by decreased content of dynorphin precursor intermediates and increased content of mature dynorphin peptides (1-17 and 1-8) in the lumbar spinal region. This suggests that augmented processing of spinal dynorphin precursor intermediates is an adaptive mechanism used by dynorphin neurons to meet increased synthetic demands necessitated by increased dynorphin neurotransmission. Prohormone convertase (PC) 1 and 2 represent major secretory granule proteolytic processing activities capable of converting neuroendocrine and neurotransmitter peptide (dynorphin) precursor intermediates to their mature, biologically active products. Accordingly, the current investigation was undertaken to assess their potential relevance to peptidergic (dynorphin) neuronal functional plasticity in vivo. In order to evaluate a molecular biological parameter of PC2 synthesis, a solution hybridization assay was developed with which to quantify changes in the spinal lumbar content of its mRNA. This study demonstrates that during gestation and HSP, lumbar PC2 protein content, but not that of PC1, is augmented. The increase in lumbar PC2 during HSP indicates that the pregnancy blood concentration profile of 17beta-estradiol and progesterone is a predominant facet of the pregnant condition responsible for its modulation during this condition. In contrast to the elevated content of lumbar PC2 protein, levels of PC2 mRNA in the lumbar cord of pregnant or HSP rats were essentially unchanged. This indicates that increased transcriptional activity is not, necessarily, a prerequisite for increased PC2 protein content to be manifest. These observations suggest positive modulation of PC2 to be a critical component of the mechanism(s) by which spinal dynorphin neurons adapt to the demand-induced increased production of mature dynorphin peptides.

Animals↗
PubMed1999

[Indication of gastrojejunostomy in unresectable pancreatic cancer].

BACKGROUND: Up to 20% of patients with pancreatic carcinoma subjected to a bilio digestive diversion, develop a delayed gastric emptying due to duodenal infiltration. However the role of prophylactic gastrojejunoanastomosis is not well defined. AIM: To compare the effects of gastrojejunoanastomosis performed as prophylaxis or as treatment for duodenal infiltration, in patients with unresectable pancreatic carcinoma. PATIENTS AND METHODS: Between 1983 and 1994, 44 gastrojejunoanastomosis were performed in patients with pancreatic carcinoma. In 24 patients the procedure was done as prophylaxis and in 20 as treatment of duodenal infiltration. Of these, three had been subjected previously to a bilio digestive diversion. Postoperative outcome and mortality of both groups of patients were compared. RESULTS: Both groups of patients had similar sex and age. Operative morbidity and mortality were 33% and 0% in the group with the prophylactic procedure and 35 and 10% in the group with duodenal infiltration. Oral feeding was started 6.5 and 6.9 days after operation, and hospital stay was 10.7 and 11.4 days in either group. At the moment of the analysis, 95.5% of patients had died. Survival was significantly longer in the group with the prophylactic procedure (337.2 and 116.9 days respectively, p < 0.01). Thirty eight percent of patients required a further admission to the hospital, but only 4.8% due to gastric retention. CONCLUSIONS: Gastrojejunoanastomosis is a good palliative procedure in patients with unresectable pancreatic carcinoma. It should be performed in every such patient who is subjected to a bilio digestive diversion and in whom a survival of some months can be predicted.

Adult↗
PubMed1999

[Measure of the slow phase angular speed by the trigonometric method].

We compare trigonometric and traditional systems for nystagmus slow phase speed measures. Results are detailed in Table I. Mean difference between both procedures is 0.88 +/- 0.51 degree/sec. so we conclude that trigonometric system is a reliable method for these measures.

Electronystagmography↗
PubMed1998

Enzyme-linked immunosorbent assay (ELISA) for detection of anti-Trypanosoma evansi equine antibodies.

The standardization of ELISA for the detection of anti-Trypanosoma evansi antibodies in naturally and experimentally infected horses is described. Bayesian analysis was used to establish the cutoff between positive and negative sera. In order to determine the assessment of the ELISA test, the results obtained were compared with those from an IFA. A relative sensibility of 98.39%, a specificity of 95.12% and a predictive value of 96.83% were determined. The standardized technique was used to evaluate the antibody production against trypanosome in an experimentally infected equine, in which the sera converted 15 days after infection. The test was also used for a study of sera prevalence in a non-random sample from two different populations. A prevalence of 81.7% in workhorse and 57.14% in stable horses was found.

Animals↗
PubMed1998

Conversion of mitochondrial cytochrome b5 into a species capable of performing the efficient coupled oxidation of heme.

Histidine-63, one of the heme axial ligands in outer mitochondrial membrane cytochrome b5 (OM cyt b5) has been replaced by a methionine. The H63M variant performs the efficient and regioselective coupled oxidation of heme in order to produce >90% of the alpha-isomer of verdoheme. The variant was characterized by electronic, EPR, and NMR spectroscopic studies which indicate that the ferric form is a high-spin species whose heme is coordinated by histidine-39 in the proximal site and likely by water in the distal site. The coordination of methionine to the ferric heme was ruled out on the basis of NMR spectroscopic studies. Addition of imidazole to a solution of the ferric variant results in the formation of a species axially coordinated by imidazole and histidine-63. The reduction potential of the variant was found to be +110 mV in the absence of exogenous imidazole and -92 mV in the presence of imidazole. These values compare well with the reduction potential of myoglobin (50 mV) and wild-type OM cyt b5 (-102 mV), respectively, consistent with the axial ligation described above. The ferrous variant, on the other hand, is a low-spin species coordinated by histidine-39 and methionine-63. Carbon monoxide (CO) readily displaces Met-63 from its coordination site on the ferrous heme, whereas CO cannot completely displace Met-63 from its coordination site on verdoheme. Consequently, the mechanism of inhibition for the oxidation of verdoheme to iron-biliverdin in the H63M variant appears to be similar to that observed for the heme-heme oxygenase complex in the presence of CO.

Cytochromes b5↗
PubMed1998

The reduction potential of cytochrome b5 is modulated by its exposed heme edge.

When the reduction potential of cytochrome b5 is measured with the aid of several different surface-modified electrodes that function on the basis of electrostatic interactions with the protein, the resultant values have been consistently more positive (40-100 mV) than the reduction potentials measured with potentiometric methods. In this paper, we report that the heme edge containing the exposed heme propionate, a heme methyl, and a heme vinyl, and which constitutes part of the surface of cytochrome b5, modulates its reduction potential. The positive shifts observed in the voltammetric measurements appear to originate from the formation of a complex between cytochrome b5 and the modified electrode surface which (a) neutralizes the charge on the heme propionate located on the exposed heme edge and (b) lowers the dielectric of the exposed heme microenvironment by excluding water from the complex interface, factors which result in the destabilization of the positive charge on the ferric heme with respect to the neutral ferrous heme. The observed positive shift, which is induced by complexation at the electrode surface, may indicate that similar shifts in the reduction potential of cytochrome b5 occur when it forms a complex with physiological partners, prior to electron transfer. The effect of the value of the dielectric constant on the reduction potential of cytochrome b5 was corroborated by preparing the V45L/V61L double mutant whose reduction potential was measured to be 50 mV more negative than the value measured for the wild type protein. The negative shift in the reduction potential of the mutant protein was explained by the increased accessibility of water to the heme binding site, as observed in its X-ray crystal structure.

Amino Acid Substitution↗
PubMed1998

An 1H-13C-13C-edited 1H NMR experiment for making resonance assignments in the active site of heme proteins.

In paramagnetic heme proteins, it is often problematic to make proton resonance assignments for heme substituents that do not have large isotropic shifts and consequently lie under the large envelope of polypeptide resonances. Furthermore, assignments that would normally be performed with the aid of HMBC experiments in diamagnetic molecules can prove difficult in the active site of paramagnetic heme proteins if T2(-1) > 2JCH. To circumvent this problem, a new method is presented to selectively detect 1H in 1Hn-13C-13C fragments biosynthetically introduced into the active site of heme proteins. The pulse sequence combines well-known building blocks such as INEPT to transfer 1H spin magnetization to bonded 13C nuclei, followed by INADEQUATE to generate 13C-13C double-quantum coherence that is selected with pulsed field gradients, and finally reverse-INEPT to transfer magnetization back to 1H nuclei for subsequent observation. The new 1Hn-13C-13C edited experiment takes advantage of the relatively large values of 1JCH and 1JCC, avoiding the long interpulse delays in HMBC that compromise the detectability of rapidly relaxing nuclei. The potential applicability of the pulse sequence is demonstrated by its contribution to the unambiguous assignment of the carbonyl carbons in the heme propionates of ferricytochrome b5.

Fourier Analysis↗
PubMed1998

Differential effect of chronic morphine on mRNA encoding adenylyl cyclase isoforms: relevance to physiological sequela of tolerance/dependence.

In opiate naive longitudinal muscle myenteric plexus tissue, facilitation (GS-mediated) and inhibition (Gi-mediated) of adenylyl cyclase (AC) activity is observed in response to low (nM) and high (microM) concentrations of sufentanil, respectively. Following chronic in vivo exposure to morphine, previously inhibitory concentrations produce excitatory effects. The present study was undertaken to explore the potential relevance of AC isoform-specific regulation to the qualitative change in opioid responsiveness following chronic morphine. Following persistent activation of opiate receptors, levels of AC I mRNA remain unchanged but that of AC IV is significantly augmented (approximately 37%, P < 0.05). AC I and IV are differentially regulated by G alpha i and G beta gamma. The former is inhibited by G alpha i and G beta gamma whereas the latter is relatively insensitive to G alpha i and is stimulated by G beta gamma. Thus, an increase in AC IV mRNA could represent a shift from inhibitory to stimulatory opiate receptor-G protein signalling, as has been observed following chronic morphine. These results indicate that persistent activation of opiate receptors can induce selective changes in the abundance (activity) of AC isoforms. This could explain, in part, some of the adaptations that occur following chronic in vivo morphine exposure.

Adenylyl Cyclases↗