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Biomedical subjects

R Lopez

Publications and source records attributed to R Lopez.

At least 109 records · Page 6Linked to original sources
PubMed1993

Local secretory IgA in dogs with low systemic IgA levels.

Low plasma IgA concentrations are commonly found in clinically normal dogs. In order to ascertain the relative importance of local and systemic IgA concentrations as factors determining the absence of clinical signs, IgA concentrations in plasma and tears were assayed in clinically normal dogs with a deficiency of IgA (10.33 +/- 0.63 mg/dl). The IgA levels in tears (25.28 +/- 1.91 mg/dl) did not differ significantly from those of control dogs or from previously published data for dogs. Thus, low systemic levels did not imply a significant reduction in local IgA levels. The absence of clinical signs in dogs with low plasma IgA concentrations may therefore be explained by the presence of normal secretory levels and an effective immune response against local pathogens.

Age Factors↗
PubMed1993

Parental smoking and risk of childhood brain tumors.

Data from a large, population-based, case-control study were analyzed to assess the role of parental smoking in childhood brain tumors. Parents of 361 cases, newly diagnosed between January 1, 1977 and December 31, 1981 and ascertained from eight Surveillance, Epidemiology, and End Results (SEER) program registries, and 1,083 controls had been interviewed. No significant differences in risks were found to be associated with maternal or paternal smoking at any time (odds ratio (OR) = 0.92 for mothers and 1.06 for fathers), during the year of birth of the child (which included both the prenatal and postnatal periods) (ORs = 0.84 for < 1 pack/day and 1.0 for > or = 1 pack/day for mothers, and 0.68 for < 1 pack/day and 1.07 for > or = 1 pack/day for fathers), or 2 years before the child was born, i.e., the pre-conception period (ORs = 0.75 for < 1 pack/day and 1.01 for > or = 1 pack/day for mothers, and 0.90 for < 1 pack/day and 1.15 for > or = 1 pack/day for fathers). Mothers were also specifically asked if they smoked during the pregnancy, and no association was found compared with never smokers (OR = 1.08, 95% confidence interval (CI) 0.80-1.45) or for ever-smokers who continued to smoke during pregnancy compared with those who stopped smoking during pregnancy (OR = 1.15, 95% CI 0.75-1.78). Finally, no significant increase in risk of brain tumors was found for the child's passive exposure to parental smoking during the period from birth to diagnosis of the brain tumor in the case. The lack of an effect of parental smoking was observed for both the major histologic types and locations of brain tumors. These findings and those from earlier studies provide no support for the hypothesis that parental cigarette smoking influences the risk of brain tumors in children.

Adult↗
PubMed1993

Effect of anthelmintic treatment on the allergic reactivity of children in a tropical slum.

It is well known that helminthic infection can cause a polyclonal stimulation of the synthesis of IgE, which is dependent on interleukin-4 (IL-4) production, and it has been suggested that this can modulate the expression of allergic reactivity in tropical populations. We evaluated the effect of regular anthelmintic treatment, for a period of 22 months, on certain aspects of the allergic reactivity of children in a slum area of Caracas, Venezuela, where helminths are endemic. The treatment (Oxantel-Pyrantel; Quantrel) effectively eliminated intestinal helminthic infection and resulted in a significant decrease in the initially elevated total serum IgE levels. IL-4 was detectable in the serum, and a significant reduction in IL-4 was also observed after treatment. In contrast, both the immediate-hypersensitivity skin-test reactivity and serum levels of specific IgE antibody against environmental allergens were markedly increased in the treated children. In a group of children who were also evaluated in the same slum, but who declined treatment, a substantial increase in helminthic infection occurred, which was related to an acute deterioration of the socioeconomic conditions of Venezuela over the course of our study period. This was paralleled by a considerable increase in total IgE levels in these children and a decrease in the skin-test reactivities and specific IgE levels. The application of Prausnitz-Küstner passive transfer tests and analysis of specific IgE antibody levels indicated that the polyclonal stimulation of IgE synthesis by helminthic parasites results in mast cell Fc epsilon receptor saturation and suppression of specific IgE antibody synthesis. This inhibition of allergic reactivity is reversible by anthelmintic treatment.

Adolescent↗
PubMed1993

Analysis of the c-FOS gene on chromosome 14 and the promoter of the amyloid precursor protein gene in familial Alzheimer's disease.

The c-FOS gene product, a putative transacting transcriptional regulator of the amyloid precursor protein (APP) gene, is a candidate locus for the familial Alzheimer's disease (FAD) mutation on chromosome 14 (FAD14). In light of this functional relationship, we investigated the nucleotide sequence and segregation of c-FOS and the nucleotide sequence of the 5' APP promoter. Single-stranded conformational polymorphisms (SSCPs) in the c-FOS gene revealed that c-FOS closely cosegregates with the FAD14 gene but does not show allelic association with FAD. A conservative third-position T-->C mutation was demonstrated in exon 2 (codon 84) of c-FOS, and a C-->G substitution was detected at -209 bp in the 5' promoter of APP. Neither were unique to FAD and are unlikely to be pathogenic or secondary modifiers of the FAD phenotype. We conclude that the c-FOS open reading frame is probably not the site of the FAD14 locus, but we cannot exclude the existence of modifier loci on chromosome 21.

Adult↗
PubMed1992

Cloning of a gene from Bacillus cereus with homology to the mreB gene from Escherichia coli.

We have cloned and sequenced a gene coding for a putative shape-determining protein (MreB) highly homologous to the mreB gene product of Escherichia coli. The amino acid (aa) identity was 53% and the similarity 72%. The gene is expressed early in the logarithmic phase. The aa sequence comparison showed that the protein, like the E. coli MreB, has structural similarity to actin and heat-shock protein Hsc70 encoded by a new super-gene family.

Amino Acid Sequence↗
PubMed1992

Long-term results of vitrectomy and perfluorocarbon gas for the treatment of severe proliferative vitreoretinopathy.

The results of 87 patients who underwent vitrectomy, scleral buckling, and injection of perfluorocarbon gas in one eye each for proliferative vitreoretinopathy of grade C3 (marked, involving three quadrants) or worse were studied. The retinas of 60 of the 87 patients (69%) were attached posterior to the scleral buckle one month after disappearance of the gas, with the initial reattachment rate being inversely proportional to the severity of proliferative vitreoretinopathy. Follow-up data ranging from six to 106 months were available on 54 eyes with attached retinas. Final visual acuity in those patients ranged from light perception to 20/40 and was not related to severity of proliferative vitreoretinopathy or duration of reattachment. Thirty-eight of the 54 patients (70%) had a visual acuity of 20/400 or better. Twenty-nine of the 37 patients (78%) with retinas attached 24 months or longer had the same or better visual acuity than at six months postoperatively. Macular pucker was observed in 16 of the 54 eyes (30%) and was the most frequently seen long-term retinal complication affecting visual acuity.

Adolescent↗
PubMed1992

Granulocyte Fc gamma receptor recognition of cell bound and aggregated IgG: effect of gamma-interferon.

Granulocyte Fc gamma receptors are important components in the recognition of IgG-coated cells and immune complexes. Two proteins have been identified on resting human granulocytes which function as Fc gamma receptors, Fc gamma RII (CD32) and Fc gamma RIII (CD16). A third protein, Fc gamma RI (CD64), is not constitutively expressed on resting granulocytes, but can be induced by activation with gamma-interferon. We examined the role of these three Fc gamma receptors on human granulocytes in the binding of both IgG-sensitized erythrocytes and soluble oligomeric IgG. In these studies we employed anti-Fc gamma receptor antibodies which complete for the Fc gamma RII and Fc gamma RIII ligand binding sites. Preincubation of granulocytes with saturating concentrations of high-affinity anti-Fc gamma RII monoclonal antibody did not alter the recognition of IgG sensitized human cells by granulocytes. Furthermore, ligand binding studies demonstrated that anti-Fc gamma RII antibody altered neither the number nor the affinity of granulocyte binding sites for human trimeric IgG. In contrast, Fab anti-Fc gamma RIII inhibited the binding of both IgG (anti-D) sensitized human RBCs and IgG sensitized sheep RBCs. Similarly, a reduction in the expression of Fc gamma RIII by treatment with phosphatidyl-inositol specific phospholipase C reduced PMN recognition of IgG-sensitized cells. Also, anti-Fc gamma RIII decreased the number of granulocyte binding sites for human IgG trimer without a change in receptor affinity. Fc gamma RI, which was induced by gamma-IFN, increased granulocyte recognition of both IgG sensitized RBCs and IgG trimer. These data suggest that Fc gamma RIII is the primary Fc gamma receptor on granulocytes which recognizes IgG sensitized RBCs and low molecular weight complexes of IgG. With gamma-interferon activated granulocytes, Fc gamma RI appears to enhance this recognition process.

Antibodies, Monoclonal↗
PubMed1992

High-performance liquid chromatographic determination of the pi values of azol-N-yl substituents.

The pi (hydrophobic constant) values for 16 parent azoles (pyrrole, imidazole, pyrazole, four triazoles, two tetrazoles, indole, benzimidazole, 1H- and 2H-indazoles, 1H- and 2H-benzotriazoles, and carbazole) were calculated from the logarithms of the capacity factors (log k') determined by HPLC. The values thus obtained are discussed according to an additive model in which the number and position of pyridinelike nitrogen atoms and the annelation effect are considered.

Azoles↗
PubMed1992

The ultrastructure of transplanted rabbit retinal epithelium.

Retinal epithelial cells from pigmented rabbits have been cultured and radiolabelled during division with 3H-thymidine and transplanted to the subretinal space of albino rabbits using a pars plana transvitreal approach. The host rabbits were maintained on cyclosporine immunosuppression after transplantation surgery. The transplant cells survive and maintain a morphologically normal appearance for at least 5 months. The pigmented epithelial cells retain their pigmentation and become integrated with the host retinal epithelium forming junctional complexes with both the host and other transplant cells. The transplant cells contact host photoreceptors with their apical processes and phagocytize outer segments. There appears to be no significant cell division among the transplant cells.

Albinism↗
PubMed1992

Monitoring photoreceptor transplants with nuclear and cytoplasmic markers.

Two methods are described for identifying transplanted photoreceptors in a foreign host retina. One involves the use of [3H]thymidine to label the nuclei of photoreceptors which are dividing for 1 week after birth in myomorphic retina. These photoreceptors can be identified by autoradiography. The second involves the use of a transgenic mouse carrying a bovine rhodopsin promoter in tandem with the bacterial LacZ gene. These mice express beta-galactosidase in their rods. X-gal reaction allows these rods to be identified by routine light and electron microscopy. These methods have been used to follow photoreceptor transplants in adult Royal College of Surgeons strain rat and C3H mouse mutants which have lost virtually all their photoreceptors. Dissociated photoreceptors transplanted to the subretinal space of these animals survive for at least 3 months. The inner segment, cell body, and synaptic terminal of these transplanted photoreceptors remain morphologically normal; the outer segment, however, becomes rudimentary.

Animals↗
PubMed1992

CpG islands as gene markers in the human genome.

CpG islands are short, dispersed regions of unmethylated DNA with a high frequency of CpG dinucleotides relative to the bulk genome. We have analyzed 375 genes and 58 pseudogenes from the human entries in the EMBL Database for the presence of CpG islands. All 240 islands identified are associated with genes, and almost all cover at least a part of one exon; i.e., they are useful landmarks in the genome for identifying genes. More than half of the genes analyzed were associated with islands. All housekeeping and widely expressed genes have a CpG island covering the transcription start, whereas 40% of the genes with a tissue-specific or limited expression are associated with islands. In this latter group of genes, the position of the islands was not biased toward the 5' end of the transcription unit.

Dinucleoside Phosphates↗
PubMed1992

Analgesia for tonic pain by self-administered lateral hypothalamic stimulation.

The present study was designed to determine if analgesia for tonic pain could be induced with self-administered lateral hypothalamic (LH) stimulation. The majority of studies of LH stimulation employed behaviorally non-contingent stimulation. According to some investigators behaviorally non-contingent LH stimulation might be aversive and consequently yield stress-induced analgesia rather than a primary analgesic effect. Other investigators have reported that non-contingent LH stimulation can be rewarding. Our findings indicate that LH analgesia for tonic pain can be obtained with self-administered LH stimulation. These findings indicate that the analgesia we have obtained in previous work is a primary effect and not dependent on stress induced by behaviorally non-contingent LH stimulation.

Analgesia↗
PubMed1992

The insertion site of the temperate phage HB-746 is located near the phage remnant in the pneumococcal host chromosome.

Combined Southern blot hybridization analyses of DNA digests of several clinical strains of Streptococcus pneumoniae have revealed the presence of a gene (hblR), or part of it, similar to the hbl7 gene coding for the cell wall lytic enzyme of the temperate HB-746 phage. The results confirmed that the genome of HB-746, which contains protein covalently linked to the 5' ends of its DNA, becomes integrated into the host strain 8R1 and showed that both the host and phage attachment sites, attB and attP, lie downstream of the 3' end of the structural region of the hblR and hbl7 genes, respectively. The data reported also highlight some evolutionary relationships between phage and bacteria.

Bacteriophages↗
PubMed1992

Suramin: rapid loading and weekly maintenance regimens for cancer patients.

PURPOSE: Suramin is an anticancer agent with a narrow therapeutic window and a terminal half-life of 45 to 55 days. These characteristics make it necessary to control accurately the serum concentrations of the drug. Therefore, the aim of the present study was to develop a rapid loading regimen, followed by weekly administration of suramin to maintain serum concentrations of between 150 and 300 micrograms/mL for 8 weeks. PATIENTS AND METHODS: Eligible patients were treated with five different loading regimens. Initially, weekly maintenance doses were estimated manually by the treating physician. Subsequently, computer-assisted dosing that used Bayesian pharmacokinetic modeling was used. RESULTS: Thirty-eight courses of suramin that were administered to 35 patients were studied. The optimal loading regimen consisted of a continuous infusion of 600 mg/m2 during a 24-hour period, which resulted in a mean serum concentration of 319 micrograms/mL. Potentially toxic concentrations that were observed with shorter infusions were avoided. Maintenance treatment, which used the weekly administration of suramin during a 6-hour period, seemed to be able to maintain mean suramin serum trough concentrations of 150 micrograms/mL, while preventing mean peak concentrations of more than 300 micrograms/mL. The use of Bayesian pharmacokinetics was superior to manual estimation in tailoring the optimal dose to the therapeutic window. CONCLUSIONS: Continuous infusion is the optimal way of delivering suramin during the loading phase. To maintain trough levels and peak levels within a narrower therapeutic window, suramin will have to be administered more frequently than once a week. Bayesian modeling based on individual serum levels and population pharmacokinetics allows accurate dosing to maintain suramin levels within the therapeutic window.

Adult↗
PubMed1992

An estimate of the sequencing error frequency in the DNA sequence databases.

We have examined vector sequences fortuitously present in the EMBL sequence database as contaminating parts of submitted sequences, and found a sequencing error frequency of 3.55% in this subset of release 27 of the database. We discuss the possibility that this value may be representative for corresponding errors in the database as a whole.

Base Sequence↗