Search PubMed⌕ Search

Biomedical subjects

L Rojas

Publications and source records attributed to L Rojas.

At least 19 recordsLinked to original sources
PubMed2005

Human immunodeficiency virus and other sexually transmitted diseases in Cuban women.

A cross-sectional study was performed in 60 Cuban women of child-bearing age who were seropositive for human immunodeficiency virus (HIV) and 60 controls. Human papillomavirus (HPV) was identified most frequently, with oncogenic HPV serotypes 16, 33 and 58 detected in HIV-positive patients, and serotypes 11, 33 and 51 in the controls (relative risk 4.41; 95% CI 2.21-8.29). Syphilis and hepatitis B and C viruses were detected exclusively in HIV-seropositive women (p<0.05). Sexually transmitted diseases (STDs) appeared to pose a substantial health problem, especially for HIV-positive women. Clinics should consider screening and treatment for STDs as part of their HIV prevention programmes.

Adolescent↗
PubMed1999

Inhibition of angiogenesis and breast cancer xenograft tumor growth by VEGI, a novel cytokine of the TNF superfamily.

Recently, we reported a novel protein of the tumor necrosis factor (TNF) superfamily, named vascular endothelial cell growth inhibitor (VEGI), which is expressed predominantly in endothelial cells. When a secreted form of this new protein was overexpressed in mouse colon cancer cells, the growth of tumors formed by these cells in black mice was inhibited. We now report that recombinant VEGI inhibits the proliferation of endothelial cells but not that of other types of cells examined. The protein also inhibits formation of capillary-like structures by endothelial cells in collagen gels, and the growth of capillaries into collagen gels placed on the chick chorioallantoic membrane. The anticancer potential of VEGI was examined in a breast cancer xenograft tumor model in which the cancer cells were co-injected with Chinese hamster ovary cells overexpressing a secreted form of the protein. The co-injection resulted in potent inhibition of xenograft tumor growth. Our findings are consistent with the view that VEGI is an endothelial cell-specific negative regulator of angiogenesis.

Animals↗
PubMed1999

K+ Channel density increases selectively in the endfoot of retinal glial cells during development of Rana catesbiana.

The radial glial cells that span the retina, described by Müller in 1851, have a remarkable distribution of ion channels in adult amphibia that mediate extracellular K+ spatial buffering. 94% of the total membrane conductance of these cells resides in inward rectifier K+ channels in the endfoot processes apposed to the vitreous humour. We now report that this regional specialization is found in Müller cells isolated from adult (>120 day old) bullfrogs but to a far less extent in those from 10-20 day old tadpoles (stages 34-36). Using the cell attached configuration of the patch-clamp technique, we found, in agreement with previous studies in salamanders, that the endfoot of adult cells had 19.2+/-2.4 (mean +/- S.E., n = 81) channels/patch, whereas the soma had 1.81+/-0.28 (n = 21) channels/patch. In the tadpole, the respective values were 4.29+/-0.26 (n = 79) for the endfoot and 2.26+/-0.24 (n = 27) for the soma. The slope conductance of the inward rectifier K+ channel in 115 mM K+, 19.2+/-0.25 pS (n = 205), channel kinetics and the resting membrane potential (-69+/-2.7 mV, n = 224) were similar at both the endfoot and soma of both adults and embryos. We conclude that during development, the K+ conductance of the Müller cell endfoot, but not of the soma, increases due to a selective clustering of inwardly rectifying K+ channels in that specific region of the cell membrane. The properties of the channels change little during the transformation from tadpole to adult bullfrog.

Animals↗
PubMed1999

VEGI, a novel cytokine of the tumor necrosis factor family, is an angiogenesis inhibitor that suppresses the growth of colon carcinomas in vivo.

A novel member of the tumor necrosis factor (TNF) family has been identified from the human umbilical vein endothelial cell cDNA library, named vascular endothelial growth inhibitor (VEGI). The VEGI gene was mapped to human chromosome 9q32. The cDNA for VEGI encodes a protein of 174 amino acid residues with the characteristics of a type II transmembrane protein. Its amino acid sequence is 20-30% identical to other members of the TNF family. Unlike other members of the TNF family, VEGI is expressed predominantly in endothelial cells. Local production of a secreted form of VEGI via gene transfer caused complete suppression of the growth of MC-38 murine colon cancers in syngeneic C57BL/6 mice. Histological examination showed marked reduction of vascularization in MC-38 tumors that expressed soluble but not membrane-bound VEGI or were transfected with control vector. The conditioned media from soluble VEGI-expressing cells showed marked inhibitory effect on in vitro proliferation of adult bovine aortic endothelial cells. Our data suggest that VEGI is a novel angiogenesis inhibitor of the TNF family and functions in part by directly inhibiting endothelial cell proliferation. The results further suggest that VEGI maybe highly valuable toward angiogenesis-based cancer therapy.

Amino Acid Sequence↗
PubMed1998

LIGHT, a novel ligand for lymphotoxin beta receptor and TR2/HVEM induces apoptosis and suppresses in vivo tumor formation via gene transfer.

LIGHT is a new member of tumor necrosis factor (TNF) cytokine family derived from an activated T cell cDNA library. LIGHT mRNA is highly expressed in splenocytes, activated PBL, CD8(+) tumor infiltrating lymphocytes, granulocytes, and monocytes but not in the thymus and the tumor cells examined. Introduction of LIGHT cDNA into MDA-MB-231 human breast carcinoma caused complete tumor suppression in vivo. Histological examination showed marked neutrophil infiltration and necrosis in LIGHT expressing but not in the parental or the Neo-transfected MDA-MB-231 tumors. Interferon gamma (IFNgamma) dramatically enhances LIGHT-mediated apoptosis. LIGHT protein triggers apoptosis of various tumor cells expressing both lymphotoxin beta receptor (LTbetaR) and TR2/HVEM receptors, and its cytotoxicity can be blocked specifically by addition of a LTbetaR-Fc or a TR2/HVEM-Fc fusion protein. However, LIGHT was not cytolytic to the tumor cells that express only the LTbetaR or the TR2/HVEM or hematopoietic cells examined that express only the TR2/HVEM, such as PBL, Jurkat cells, or CD8(+) TIL cells. In contrast, treatment of the activated PBL with LIGHT resulted in release of IFNgamma. Our data suggest that LIGHT triggers distinct biological responses based on the expression patterns of its receptors on the target cells. Thus, LIGHT may play a role in the immune modulation and have a potential value in cancer therapy.

Apoptosis↗
PubMed1998

Development of a pediatric liver transplantation program in Argentina.

This article describes the preliminary experimental steps and clinical implementation of a purely pediatric liver transplantation (LT) program in a large public children's hospital in Buenos Aires, Argentina, a city with well over 10 million inhabitants and a referral population of over 30 million. Between 1993 and 1997, 84 LTs were performed in 81 patients, of which one-fourth weighed below 10 kg. The main indications were biliary atresia (n = 25, 30%) and fulminant liver failure (n = 23, 27%), followed by autoimmune cirrhosis (n = 14, 16%) and other liver diseases. Shortage of organs due to local conditions led to the use of liver-reduction techniques in 48 cases (57%), split liver in 2, and living-related donor (LRD) in 2. Retransplantation was necessary in 3 instances. Seventy-eight percent of the recipients survived for more than 1 year and 71% were alive after 4 years. The authors comment on the need for adaptation to local conditioning factors when developing a pediatric LT program in any country in which demographics and economic, medical, and sociological environments have a decisive influence on organ procurement, the actual performance of the operation, and the lifelong postoperative medication. In Buenos Aires, where the hospital setting is well-developed, the indications are in part determined by the high incidence of hepatitis A. Organ shortages in our area led to liberal use of liver reduction, split-liver, and LRD techniques. The overall results of the first years of such a program were largely satisfactory.

Argentina↗
PubMed1998

Venezuelan hemorrhagic fever: clinical and epidemiological studies of 165 cases.

Epidemiological and clinical data are presented on 165 cases of Venezuelan hemorrhagic fever (VHF), a newly emerging viral zoonosis caused by Guanarito virus (of the family Arenaviridae). The disease is endemic in a relatively circumscribed area of central Venezuela. Since its first recognition in 1989, the incidence of VHF has peaked each year between November and January, during the period of major agricultural activity in the region of endemicity. The majority of cases have involved male agricultural workers. Principal symptoms among the patients with VHF included fever, malaise, headache, arthralgia, sore throat, vomiting, abdominal pain, diarrhea, convulsions, and a variety of hemorrhagic manifestations. The majority of patients also had leukopenia and thrombocytopenia. The overall fatality rate among the 165 cases was 33.3%, despite hospitalization and vigorous supportive care.

Hemorrhagic Fevers, Viral↗
PubMed1996

Action of protein kinase A activators on the caudal neuromuscular junction of toad tadpoles, recorded on synaptic spots.

Miniature end-plate currents (MEPCS), from synaptic spots on the caudal muscles of Bufo marinus tadpoles, were analyzed in both pre- and postsynaptic domains, when protein kinase A (PKA) activity modificators were used. Sp-cAMPS diasteromer induced an increase in MEPC frequency, which was completely reversed by Rp-cAMPS. However, changes in the decay time of MEPCS were not detected. Dibutyryl-cAMP produced a similar presynaptic action, but its postsynaptic action was similar to butyrate. Presynaptic effect of forskolin (FSK), if any, is masked by the increase of MEPC frequency produced by dimethylsulfoxide (DMSO), the solvent used.

Administration, Topical↗
PubMed1996

An empirical study of the psychodynamics of suicide: a preliminary report.

Preliminary results from a study of psychodynamic constructs are presented based on data from inpatients following a suicide attempt. The study examines the association between four psychodynamic constructs, severity of suicidal intent, and severity of depressive symptomatology in a sample of hospitalized suicide attempters. Higher levels of suicidal intent were associated with less differentiated self and object representations and less emotional investment in relationships. More severe depressive symptoms in suicide attempters were correlated with more self-targeted anger, less eternally directed anger, higher levels of shame and guilt, more affectively negative views of relationships, greater use of maladaptive and self-sacrificing defenses, and more impaired reality testing. These findings offer some preliminary empirical support for the validity of psychodynamic theories of suicidal behavior.

Adult↗
PubMed1995

The role of pulse oximetry. Its use as an indicator of severe respiratory disease in Peruvian children living at sea level. Respiratory Group in Peru.

OBJECTIVE: To evaluate pulse oximetry as a technique for diagnosing pneumonic and nonpneumonic acute lower respiratory tract infection (ALRI) in Peruvian children. DESIGN: Children with acute respiratory infection were diagnosed with hypoxemia by pulse oximetry, with ALRI by the World Health Organization (WHO) algorithm and clinical examination, and with pneumonia by radiographic examination. Diagnoses were compared using kappa analysis. SETTING: Pediatric emergency department. PATIENTS: Peruvian pediatric patients with acute respiratory infection (n = 269) and well children (n = 162). MAIN OUTCOME MEASURES: Hypoxemia (arterial oxygen saturation < 96.6% of the mean arterial oxygen saturation of well children -2 SD). RESULTS: Children with pneumonic and nonpneumonic ALRI (59%, 160/269) had a mean (+/- SD) arterial oxygen saturation significantly lower than well children (93.8% +/- 3.5% vs 98.7% +/- 1.51%; P < .01). Pulse oximetry detected 88% and the WHO algorithm 90% of cases of pneumonic ALRI. The WHO algorithm and pulse oximetry detected 72% of radiologic pneumonia. Pulse oximetry misclassified notably fewer well children than did the WHO algorithm (4% vs 35%). Pulse oximetry and the WHO algorithm together (SATWHO) detected 99% and 87% of pneumonic ALRI and radiologic pneumonias, respectively, and both methods detected 94% of all cases of pneumonic and nonpneumonic ALRI diagnosed clinically. CONCLUSIONS: Pulse oximetry and the WHO algorithm are practical, helpful, and appropriate for use in developing countries to identify children with pneumonic and non-pneumonic ALRI who require treatment. The SATWHO is highly sensitive for detecting children with ALRI.

Acute Disease↗
PubMed1995

[The action of an aqueous extract of Aloe barbadensis Miller in an in-vitro culture of Trichomonas vaginalis].

The antiparasitic action of an aqueous extract of Aloe barbadensis Miller against and in vitro culture of Trichomonas vaginalis was studied for the first time. Three strains of this parasite were used for the study. Taking an initial concentration of 400 mg/mL of the extract, double serial dilutions were performed, and final concentrations based on the dried weight of the extract were 10.4, 20.8, 41, 83, and 160 mg/mL. Within 24 hours, percentages of inhibition greater than 50% were obtained from concentrations of 20.8 micrograms/mL. Similar results were obtained at 48, and 72 hours, with a lower concentration, the inhibition of growth was greater than 50%.

Aloe↗
PubMed1994

Mutations in the M4 domain of Torpedo californica acetylcholine receptor dramatically alter ion channel function.

Site-directed mutagenesis was used to mutate alpha Cys418 and beta Cys447 in the M4 domain of Torpedo californica acetylcholine receptor expressed in Xenopus laevis oocytes. The M4 region is a transmembrane domain thought to be located at the lipid-protein interface. By whole-cell voltage clamp analysis, mutation of both alpha subunits to alpha Trp418 increased maximal channel activity approximately threefold, increased the desensitization rate compared with wild-type receptor, and shifted the EC50 for acetylcholine from 32 microM to 13 microM. Patch measurements of single-channel currents revealed that the alpha Trp418 increased channel open times approximately 28-fold at 13 degrees C with no effect on channel conductance. All of our measured functional changes in the alpha Trp418 mutant are consistent with a simple kinetic model of the acetylcholine receptor in which only the channel closing rate is altered by the mutation. Our results show that changes in protein structure at the putative lipid-protein interface can dramatically affect receptor function.

Acetylcholine↗
PubMed1994

[Desensitization of the nicotinic acetylcholine receptor].

In biological membranes, ionic channels act speeding up ion movements. Each ionic channel is excited by a specific stimulus (i.e. electric, mechanical, chemical, etc.). Chemically activated ionic channels (CAIC), such as the nicotinic acetylcholine receptor (nAChR), suffer desensitization when the receptor site is still occupied by the agonist molecule. The desensitized CAIC is a non functional channel state regarded as a particular case of receptors rundown. CAIC desensitization only involve reduced activity and not their membrane elimination. Desensitization is important to control synaptic transmission and the development of the nervous system. In this review we discuss results related to its production, modulation and some aspects associated to models that consider it. Finally, an approach combining molecular biology and electrophysiology techniques to understand desensitization and its importance in biological systems is presented.

Animals↗
PubMed1993

[Modulation of transmitter release and its interaction with the receptor in the neuromuscular junction].

New techniques to control the potential in membrane patches are giving in detail important characteristics of the pre- and post-synaptic channels. When used to assess the quantal size regulation during synchronous (evoked) or asynchronous (spontaneous) release of neurotransmitter can provide valuable information above this process. The macropatch technique (a version of the original patch clamp technique), has advantages in comparison with other macroscopic voltage clamp techniques to record the miniature end-plate current, mepc. During this focal recording, the puzzle size variation of mepc's amplitudes produced, from events generated over distant parts of the cell, are removed. The quantal response is an important feature during synaptic plasticity. Therefore, in this review we focus on pre- and post-synaptic aspects from the quantal asynchronous release of neurotransmitter, that occurs in the neuromuscular junction. We take emphasis on the caudal muscle of tadpoles from amphibian.

Acetylcholine↗
PubMed1992

The effect of ATP on Ca(2+)-dependent K+ channels of human red cells.

The action of ATP on Ca(2+)-dependent K+ channels was studied in fresh human erythrocytes using patch-clamp techniques. Single-channel current was recorded at pH 6.5 from inside-out patches in the presence of symmetrical K+ gluconate solutions, containing both 1 microM free Ca2+ in the bath and 0.5 mM LaCl3 on the pipette side. With no ATP, the electrical activity revealed low-conductance K+ channels (25 pS), which showed inward rectification and an opening kinetics dependent on membrane potential. When ATP (1 mM) and Mg2+ (2 mM) were added together and a depolarizing potential was simultaneously applied, only a high-conductance channel (about 75 pS) was observed. This channel showed no rectifying properties and it was not found if ATP was added in the absence of Mg2+. Channel activity was enhanced by adding fluoride (10 mM) or trifluoperazine (50 microM) whilst it was reduced after incubating with dibutyryl cAMP (50 microM) or alkaline phosphatase (250 U/ml). On the other hand, when fragmented membranes from inside-out vesicles were incubated with gamma-32 P-ATP and 1 microM free Ca2+ under above conditions, only two high-molecular weight polypeptides (235 and 320 kDa) were labelled with 32P. The results suggest that ATP-mediated phosphorylation of Ca(2+)-dependent K+ channels leads to a high-conductance state.

Adenosine Triphosphate↗