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Biomedical subjects

O López

Publications and source records attributed to O López.

At least 19 recordsLinked to original sources
PubMed2006

Effect of sodium dodecyl sulfate at different hydration conditions on dioleoyl phosphatidylcholine bilayers studied by grazing incidence X-ray diffraction.

The effect of the surfactant content and hydration conditions in the phases of dioleoyl phosphatidylcoline (DOPC)/sodium dodecyl sulfate (SDS) mixtures was studied. To this end, surface X-ray diffraction experiments have been performed on bilayers of the mixtures deposited on hydrophobic silicon wafers by dip coating. To investigate the effect of relative humidity (RH) on bilayer organization, a humidity chamber with dry-wet air control was used, and RH values were fixed between 1 and 65%. Our results showed, in addition to the lamellar phase, a rhombohedral phase in mixtures at low hydration conditions (RH < 30%). The d spacing between lamellae increased with the RH and SDS content. This fact could be associated with a swelling effect that is probably due to the localization of water molecules between the polar headgroups of the DOPC and SDS forming the bilayers. The electron-density profiles calculated by Fourier reconstruction of the lamellar stacking for the different samples also confirmed this fact. In addition, the increase in d spacing could be related to the increase in the hydrophilic character of the mixture when the SDS content increases. The rhombohedral phase was more clearly observed in mixtures with high SDS content. Thus, the stalk structure of the rhombohedral phase could be facilitated because of the SDS contribution to inverse structures.

Lipid Bilayers↗
PubMed2006

Study and formation of vesicle systems with low polydispersity index by ultrasound method.

The formation of liposomes with low polydispersity index by application of ultrasounds was investigated considering methodology specifications such as sonication time and sonication power. Phosphatidylcholine (PC) liposomes were formed by the evaporation-hydration method. The vesicles were sonicated using several sonication conditions. The liposomes were then characterized by dynamic light scattering (DLS) and freeze-fracture electron microscopy (FFEM). Correlation functions from DLS were treated by cumulants method and GENDIST to obtain the mean radius and polydispersity index. These calculations allowed to fix an optimal sonication time (3000 s) and a useful interval of ultrasound power between 39 and 91 W. DLS and FFEM results confirmed that vesicle size, lamellarity and the polydispersity index decreased with the increase of sonication power. Thus, we propose a systematic method to form liposomes in which the physical characteristics of the vesicles may be controlled as a function of sonication time and power.

Chemical Phenomena↗
PubMed2006

First 100 liver transplants at the medico-surgical research center (CIMEQ).

In July 1999 we began a liver transplant program that to October 2005 has included 100 liver transplants in 92 patients, eight retransplants, and two combined liver and kidney grafts. Twelve transplants were in pediatric patients, who showed a 92% survival rate in the first year. Fifty-four percent of the patients were male and 46% female. The most frequent etiologies of cirrhosis were 27% hepatitis virus C, 18% alcoholic, 13% cryptogenic, and 11% autoimmune. In 95% of the patients, we preserved the retrohepatic vena cava. The bile duct was reconstructed with a Kehr tube in 46% of patients with 31% using end-to-end suture with a tutor and 15% an end-to-end suture without a tutor. A hepaticojejunostomy was performed in 8%. The immunosuppression included cyclosporine (Neoral) or Prograf combined with mycophenolate mofetil or mycophenolate sodium and steroids. The most frequent biliary complications were local anastomosis leaks (6%) and stenosis (10%). The overall 1-year survival rate was 72%.

Cuba↗
PubMed2006

Solid mesenchymal hamartoma in an adult: a case report.

Mesenchymal hamartoma of the liver (MHL) is an uncommon tumour composed of architecturally abnormal bile ducts in an uncommitted myxoid stroma. Most MHL are diagnosed in childhood and few cases have been reported in adults. This report describes a case of a well defined solid mass in the right lobe of the liver in a 51 year old man. Preoperative radiological examination revealed a large completely solid mass. Biopsy showed a dense fibrous stroma with hyalinisation and some bile ducts. A provisional diagnosis of MHL was made. Surgical excision was impossible and liver transplantation was undertaken. Definitive pathology confirmed the diagnosis. Review of published reports shows this to be the fourth case of MHL treated by liver transplantation.

Hamartoma↗
PubMed2005

Real-time deformable models for surgery simulation: a survey.

Simulating the behaviour of elastic objects in real time is one of the current objectives of computer graphics. One of its fields of application lies in virtual reality, mainly in surgery simulation systems. In computer graphics, the models used for the construction of objects with deformable behaviour are known as deformable models. These have two conflicting characteristics: interactivity and motion realism. The different deformable models developed to date have promoted only one of these (usually interactivity) to the detriment of the other (biomechanical realism). In this paper, we present a classification of the different deformable models that have been developed. We present the advantages and disadvantages of each one. Finally, we make a comparison of deformable models and perform an evaluation of the state of the art and the future of deformable models.

Biomechanical Phenomena↗
PubMed2005

Liver transplantation at the Cuban Center for Medical and Surgical Research.

From July 4, 1999, when a liver transplantation program was started in Cuba, to October 2003, 66 procedures had been performed in 60 patients. The most frequent reason was cirrhosis caused by hepatitis C virus (29%), and alcoholic cirrhosis (22%). Two patients received simultaneous liver-kidney transplants. Half of the patients were men. Patient ages ranged from 12 to 62 years; the average surgical time was 6 hours; and cold ischemia time was 4 to 14 hours. The average blood consumption was 2033 mL; 2900 mL of plasma and 8 units of platelets were used in 7 cases. Immunosuppression was mainly cyclosporine (Neoral), mycophenolate mofetil or azathioprine, and prednisone. Acute cellular rejections were treated in almost all cases with 3 doses of methylprednisolone. The most frequent complications were biliary (24%), hepatic arterial thrombosis (12%), post-surgical bleeding (10%), acute cellular rejection (24%), and ductopenic rejection (2%). The overall 1-year survival rate was 73.7%.

Cuba↗
PubMed2005

Cystic echinococcosis: analysis of the serological profile related to the risk factors in individuals without ultrasound liver changes living in an endemic area of Tacuarembó, Uruguay.

Cystic echinococcosis (CE) is a high prevalence zoonosis among the rural population of Tacuarembó (Uruguay). The correlation between serological data and the incidence of risk factors was studied in a survey carried out in 1998 among rural communities where 480 individuals were examined by means of abdominal sonography (local prevalence = 0.8%). Serum samples (305) were analysed by ELISA to determine specific IgG against crude antigens from Echinococcus granulosus. A total of 27 individuals exhibiting no detectable changes in abdominal sonographic examination were found to be seropositive ('ultrasound normal group'). Of these individuals 9 were seroreactive against purified antigen B. A significant degree of correlation was found between seroreactivity and the incidence of some risk factors (CE antecedent in the family, P < 0.005 and use of rural water, P < 0.0001) among this group. Follow-up of individuals of the 'ultrasound normal group' was carried out after 2 years to evaluate the implications of this serological reactivity. No predictive value for cyst development was assessed with complementary image study; in contrast transient antibodies were observed with both crude and purified antigen as approximately 60% of individuals became negative when re-sampled.

Adult↗
PubMed2004

Effect of the electrostatic charge on the mechanism inducing liposome solubilization: a kinetic study by synchrotron radiation SAXS.

The anionic surfactant sodium dodecyl sulfate (SDS) was used to induce the initial steps of the solubilization of liposomes. The structural transformations as well as the kinetics associated with this initial period were studied by means of time-resolved small-angle X-ray scattering (SAXS) using a synchrotron radiation source. Neutral and electrically charged (anionic and cationic) liposomes were used to investigate the effect of the electrostatic charges on the kinetics of these initial steps. The mechanism that induces the solubilization process consisted of adsorption of surfactant on the bilayers and desorption of mixed micelles from the liposomes surface to the aqueous medium. In all cases the time needed for desorption of the first mixed micelles was shorter than that for complete adsorption of the surfactant on the liposomes surface. The present work demonstrates that adsorption of the SDS molecules on negatively charged liposomes was slower and release of mixed micelles from the surface of these liposomes was faster than for neutral liposomes. In contrast, in the case of positively charged liposomes, the adsorption and release processes were, respectively, faster and slower than those for neutral vesicles.

Ions↗
PubMed2004

Influence of chemical and freezing fixation methods in the freeze-fracture of stratum corneum.

A comparison between two fixation techniques for freeze-fracture was established. Stratum corneum (SC) samples from pig epidermis were fixed using high-pressure freezing (HPF) and using plunging in propane freezing; the latter after chemical fixation. Then, frozen samples were freeze-fractured, coated with platinum-carbon, and visualized using a high-resolution low-temperature scanning electron microscope and a transmission electron microscope. Our results indicate that the plane of freeze-fracture was different depending on the fixation and freezing methodology used. In the samples frozen by HPF without chemical fixation, the fracture plane laid mainly between the lipid lamellae. However, when chemical fixation and plunging in propane freezing was used, the fracture plane did not show preference to a specific way. Plunging in propane freezing of chemically fixed samples, on the other hand, provides a more homogeneous fracture behaviour. Thus, depending on the methodology used, we can favour a visualization of either lipid or protein domains of the SC. These results could be very useful in future ultrastructural studies in order to facilitate the microscopic visualization and interpretation of the complex images such as those of SC and even of other samples in which different domains coexist.

Animals↗
PubMed2004

Monoclonal antibodies against a 62 kDa proteinase of Trichomonas vaginalis decrease parasite cytoadherence to epithelial cells and confer protection in mice.

Trichomonas vaginalis infects the epithelium of the genital tract. The mechanism by which it invades the tissue leading to the disease is not thoroughly understood. However, results of several studies seem to agree that parasite adhesion to epithelium cells is the initial step leading to infection in women. T. vaginalis is associated with high levels of proteolytic activity. The role of some of these proteinases in the development of infection has been demonstrated. The current study establishes the role of a 62 kDa excretion-secretion proteinase in parasite cytoadherence. Monoclonal antibodies (MAbs) against this enzyme were tested for their ability to inhibit this process. Three stable hybrid producers of IgG(1)class MAbs (4D8, 1A8, 3C11) against the 62 kDa proteinase were obtained. Two of them (4D8 and 1A8) showed parasite recognition by immunofluorescence. Parasite cytoadherence to a monolayer of HeLa cells was inhibited by the 4D8, 1A8 and 3C11 antibodies. MAb 4D8 administered 24 h before a challenge with T. vaginalis by the intraperitoneal route was able to protect the majority of mice. Nitric oxide levels in the serum of animals inoculated with MAb 4D8 and challenged with the parasite were significantly different from those recorded in mice treated with an unrelated MAb. These studies show that an appropriate antibody against 62 kDa proteinase can help the host resist a challenge by the intraperitoneal route with T. vaginalis.

Animals↗
PubMed2004

Environmental enrichment-behavior-oxidative stress interactions in the aged rat: issues for a therapeutic approach in human aging.

The effects of environment enrichment on motor activity, exploration, and cognitive performances were studied in aged rats. Both nonimpaired (NI) and impaired (I) rats were submitted to daily training in a complex-enriched environment (cEE) for 60 days. Animals were examined at spatial water maze task, passive avoidance test, open-field test, and sensorimotor coordination tasks (bridges test and Marshall scales). At the end of experiments, animals were killed for brain biochemical determinations (gluthatione content and specific-ChAT activity). Results after the first evaluation (before training) corroborate that the aged rat population showed a heterogeneity in behavioral patterns like that observed in humans. Also, cEE modified exploration activity, cognition, motor functions, and biochemical markers in both NI and I groups, but changes reached significant relevance for the last group. It is significant that neurotrophins, "novo" synthesis of neurotransmitters, and oxidative stress levels may mediate the observed changes, indicating that the aged brain still has appreciable plasticity in response to well-manipulated environmental stimulation. Finally, our results also support the novel concepts and programs in prevention/reduction both in incidence/severity and outcome of age-associated neurodegenerative conditions.

Aging↗
PubMed2003

Influence of the temperature in the adsorption of sodium dodecyl sulfate on phosphatidylcholine liposomes.

The influence of the temperature on the adsorption of monomeric and micellar solutions of the anionic surfactant sodium dodecyl sulfate (SDS) on phosphatidylcholine (PC) liposomes was investigated using the fluorescent probe 2-(p-toluidinyl)-naphthalene-6-sodium sulfonate (TNS). The number of adsorbed molecules was quantified by measuring changes in the electrostatic potential (Psi(o)) of the liposomes/probe during an incubation with SDS at varying temperatures. At low surfactant concentrations (from 0.05 to 0.25 mM), the increase in temperature reduced the number of surfactant molecules incorporated per vesicle regardless of the incubation time, whereas at high surfactant concentrations (from 0.50 to 1.0 mM) the incubation time has an opposite effect on this process. Thus, after 10s, the surfactant adsorption decreased with temperature, yet it increased progressively with time. The adsorption was linear with temperature below critical micellar concentration (CMC) of SDS and this linear tendency did not change above CMC. This suggests an adsorption of SDS monomers regardless of the surfactant concentration.

Adsorption↗
PubMed2003

Transcranial Doppler sonography in fulminant hepatic failure.

UNLABELLED: The clinical course of patients with fulminant hepatic failure (FHF) is often worsened by the presence of cerebral edema and endocranial hypertension. In spite of the multiple studies using Transcranial Doppler Sonography (TCDS), few have shown the cerebral blood flow (CBF) pattern among patients with encephalopathy resulting from FHF. OBJECTIVE: Our objective was to characterize the CBF pattern in these patients through the use of TCDS to provide therapeutic strategies. METHOD: The TCDS pattern was assessed in five patients diagnosed with FHF and compared with a control group who displayed critical neurologic conditions not associated with FHF. Pulsatile index, systolic, diastolic, and mean velocity of the middle cerebral artery were measured. RESULTS: The mean age of patients with FHF was 45.4 years. One hundred percent were women, with viral hepatitis as the predominant etiology. A cerebral hypoperfusion pattern was found in 80% of the FHF group and 40% of the control group. In the former group there was no evidence of hyperemia, as there was among 20% of the control group. The mean values of velocity and pulsatile index were 36.6 cm/sec and 2.4, respectively, in the FHF group and 47.8 cm/s and 1.8 in the control group (P=0.268, P=0.402). CONCLUSIONS: FHF patients show a predominance of cerebral hypoperfusion pattern with mean velocities lower than normal values and an increased pulsatile index. We recommend that clinicians take appropriate measures to improve cerebral perfusion and avoid hypoxia. Hyperventilation as a first level measure is contraindicated.

Adult↗
PubMed2003

The transplantation donation process in the Centro de Investigaciones Medico Quirurgicas of Cuba: 1999-2002.

OBJECTIVE: In 1998 in the Centro de Investigaciones Medico Quirurgicas the Transplant Coordination Office (TCO) was created, with the aim to organize a system to support a hepatic transplantation program. This organization, which changed the transplantation-donation process not only in our center but in the whole country, is described in this article. METHOD: The files of donors generated in our hospital were studied together with the transplant coordination records, from 1999 till the first half of 2002. RESULTS: In the period studied, 21 potential donors were diagnosed with brain death, yielding a donation rate of 71.4%. Brain death was most frequently caused by vascular brain disease; however, in the realized donor group, the cranioencephalic trauma predominated. The typical donor was a man of average age 39.2 years (range, 18-86 years). Among the potential donors, 24% were excluded based on medical criteria, and 5% due to family objections. Forty liver transplantation were performed in 36 patients including 1 liver-kidney simultaneous procedure. The principal etiologies for transplant included hepatitis C virus cirrhosis, 22%; alcoholic, 19%; and acute hepatic failure, 13%. Kidney transplantations were performed in 70 patients, including 41 from cadaveric donors (53.6%) and 29 from living related donors (41.4%). In 2001, a pancreas-kidney transplantation program was started. CONCLUSION: The creation of the TCO has been of paramount importance to optimize transplantation program functions.

Adolescent↗
PubMed2002

In vitro susceptibility of Cryptococcus neoformans serotypes to GM 237354 derivative of the sordarin class.

In vitro susceptibility to the sordarin derivative GM 237354 and amphotericin B were tested in a total of 190 Cryptococcus neoformans clinical isolates from different geographical areas of Spain and South American countries. Minimal inhibitory concentrations (MICs) were obtained using the NCCLS reference microbroth dilution method and analysed according the serotypes of Cr. neoformans. The MICs for amphotericin B were lower than 1.0 microg ml(-1) (MIC90% 0.5 microg ml(-1) , MIC50% 0.125 microg ml(-1)) but five isolates showed MICs of 2.0 microg ml(-1) to GM 237354 (MIC90% 1.0 microg ml(-1), MIC50% 0.5 microg ml(-1)). Cryptococcus neoformans var. gattii serotype B, was significantly less susceptible than A and AD serotypes (P = 0.047 and P = 0.022, respectively).

Amphotericin B↗
PubMed2001

Use of a fluorescence spectroscopy technique to study the adsorption of sodium dodecylsulfonate on liposomes.

The fluorescent probe 2-(p-toluidinyl)-naphthalene-6-sodium sulfonate was used to study the surface adsorption of sublytic concentrations of the anionic surfactant sodium dodecylsulfonate (C(12)-SO(3)) on phosphatidylcholine bilayers. The number of adsorbed molecules was quantified by determination of the electrostatic potential (psi(0)) of the bilayers. The abrupt decrease in the fluorescence intensity already detected 10 s after the surfactant addition and the slight fluorescence variations with time indicated that the surfactant adsorption was very fast and almost complete. For a given number of monomers adsorbed, a linear dependence between the lipid and C(12)-SO(3) concentrations was obtained, indicating a similar adsorption mechanism regardless of the surfactant concentration. Hence, a monomeric adsorption is assumed even in systems with a C(12)-SO(3) concentration above its critical micellar concentration (CMC). In addition, this linear correlation allowed us to determine the surfactant/lipid molar ratios (Re) (inversely related to the C(12)-SO(3) ability to be adsorbed on liposomes) and the bilayer/aqueous phase coefficients (K). The fact that the lowest values for Re were always reached after 10 s of incubation corroborates the rapid kinetic of the process. The decrease in the C(12)-SO(3) partitioning (K) when the number of surfactant molecules exceeded 15000 was possibly due to the electrostatic repulsion between the free and the adsorbed monomers, which could hinder the incorporation of new monomers on the charged surface of liposomes.

Adsorption↗
PubMed2001

Use of a fluorescence spectroscopy technique to study the adsorption of sodium dodecylsulfonate on liposomes.

The fluorescent probe 2-(p-toluidinyl)-naphthalene-6-sodium sulfonate (TNS) was used to study the surface adsorption of sublytic concentrations of the anionic surfactant sodium dodecylsulfonate (C(12)-SO(3)) on phosphatidylcholine (PC) bilayers. The number of adsorbed molecules was quantified by determination of the electrostatic potential (psi(o)) of the bilayers. The abrupt decrease in the fluorescence intensity detected even 10 s after the surfactant addition and the slight fluorescence variations with time indicated that the surfactant adsorption was very fast and almost complete. For a given number of monomers adsorbed a linear dependence between the lipid and C12-SO3 concentrations was obtained, indicating similar adsorption mechanism regardless of the surfactant concentration. Hence, a monomeric adsorption is assumed even in systems with a C12-SO3 concentration above its CMC. In addition, this linear correlation allowed us to determine the surfactant/lipid molar ratios (Re) (inversely related to the C12-SO3 ability to be adsorbed on liposomes) and the bilayer/aqueous phase coefficients (K). The fact that the lowest values for Re were always reached after 10 s of incubation corroborates the rapid kinetics of the process. The decrease in the C12-SO3 partitioning (K) when the number of surfactant molecules exceeded 15000 was possibly due to the electrostatic repulsion between the free and the adsorbed monomers, which could hinder the incorporation of new monomers on the charged surface of liposomes.

Adsorption↗