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Biomedical subjects

F J Medrano

Publications and source records attributed to F J Medrano.

At least 55 records · Page 3Linked to original sources
PubMed1996

Acquisition of syncytium-inducing HIV-1 strains during therapy with zidovudine alone or combined with alpha interferon or didanosine.

The effect of antiretroviral treatment on HIV-1 phenotype was studied in a group of 83 nucleoside-naive patients. These initially nonsyncytium-inducing HIV-1 positive patients were followed prospectively for their HIV-1 phenotype. Syncytium-inducing variants were detected by cocultivation of peripheral blood mononuclear cells with the MT-2 T-cell line. Overall, 16 of 83 (19%) patients underwent a shift to syncytium-inducing phenotype: 11 of 67 during zidovudine treatment, 3 of 10 during zidovudine plus alpha interferon treatment, and 2 of 6 under initial zidovudine plus didanosine therapy. The results of this study demonstrate that neither zidovudine therapy alone nor combined with interferon or didanosine prevents the acquisition of syncytium-inducing strains.

Adult↗
PubMed1996

HIV-1 viraemia changes in patients with and without syncytium-inducing phenotype treated with nucleoside analogues: a case-control study.

The objective of the present study was to investigate the effect of the nucleoside analogue treatment on serum viraemia, CD4+ cell count and disease progression in patients with and without syncytium-inducing (SI) HIV-1 variants. To achieve this in a case-control study, 11 nucleoside-naive patients harbouring SI variants who started treatment with zidovudine or zidovudine plus didanosine were matched with 11 control patients who never formed SI variants during a follow-up of 48 weeks. The matching criteria were age, CD4+ cell count and CDC clinical category at the start of the study and exposure to the same antiretroviral treatment. During the follow-up there were no significant differences in the changes of serum HIV-1 RNA viral load and CD4+ cell counts between the two groups. In contrast, AIDS or new AIDS-defining events were observed in five SI cases but in none of the non-SI controls (P = 0.002). The emergence of a zidovudine-resistant mutation at codon 215 was observed in all the patients harbouring SI strains and in six of the subjects with non-SI variants (P = 0.03). The results of the present study show that in patients carrying SI virus, measurements of CD4+ count or RNA viral burden are neither related to the virulence of the virus strains nor able to predict the clinical course of the disease, at least under anti-retroviral drug conditions. Thus, determination of SI phenotype should be considered in the evaluation and monitoring of HIV-1 therapies.

Acquired Immunodeficiency Syndrome↗
PubMed1995

The effect of temperature on the structure of vinblastine-induced polymers of purified tubulin: detection of a reversible conformational change.

Addition of the antimitotic drug vinblastine to solutions of purified tubulin induces the formation of helical polymers whose structure and type of aggregation is determined by the concentration of magnesium. While paracrystalline arrangements of single coils are observed at low concentrations of the ion, for concentrations higher than 6 mM free double-coiled spirals are obtained, which are indistinguishable from those obtained in the presence of microtubule-associated proteins (MAPs). This result is consistent with a similar effect of magnesium and MAPs in neutralizing negative charges on the tubulin molecule and so allowing for lateral contacts between protofilaments. The effects that temperature has on the structure of both types of polymers, free spirals or paracrystals, have been monitored using time-resolved X-ray solution scattering. This study shows that a temperature increase: (1) affects the length and lateral aggregation of the spirals in the paracrystalline sample; (2) induces a reversible increase of the helical pitch in both types of polymers that closely follows the temperature change; (3) produces an irreversible aggregation of some of the protein in both types of polymers; and (4) can induce a reversible transformation from one type of structure to the other when the concentration of Mg2+ is in the boundary between the two ranges. We suggest that the changes in pitch are due to a temperature-induced conformational change of the tubulin molecule. This effect may be related to the structural modifications that result in the temperature-induced assembly of microtubules in vitro under normal conditions of assembly.

Animals↗
PubMed1995

Prevalence of infection by human T-cell leukemia virus types I and II in southern Spain.

To assess the spread of human T-cell leukemia virus (HTLV) type I and II in different population groups at potential risk of infection in Spain, a total of 756 subjects were studied: 453 belonging to groups at risk for retrovirus infection, 255 with diseases potentially linked to HTLV-I/II infection and 48 immigrants from endemic areas. An HTLV-I viral-lysate enzyme immunoassay (EIA) with a recombinant transmembrane envelope protein incorporated was used to screen serum samples. Reactive specimens were confirmed by Western blot strips spiked with recombinant proteins that differentiated HTLV-I from HTLV-II. Infection was then verified by the polymerase chain reaction (PCR). Serum samples from 19 of the 756 subjects analyzed (2.5%) were reactive for HTLV by EIA. One of these was from an intravenous drug user (IVDU) in whom HTLV-II infection was confirmed by Western blot and PCR; a specimen from another IVDU showed Western blot reactivity for both retroviruses, but PCR results were negative. Lastly, Western blot confirmed the presence of HTLV in one of the immigrant subjects. Western blot did not verify HTLV infection in the remaining 16 cases, indicating a high rate of nonspecific anti-HTLV reactivity when a second-generation EIA screening test was applied. These results suggest that HTLV is present in Spain among populations at high risk for HTLV, although at a very low rate and restricted to intravenous drug users and individuals immigrating from endemic areas.

Blotting, Western↗
PubMed1995

Emergence and clinical relevance of mutations associated with zidovudine resistance in asymptomatic HIV-1 infected patients.

The dynamics leading to the emergence of a zidovudine-resistant mutation at codon 215 of the reverse transcriptase coding region was investigated in a cohort of HIV-infected individuals who received early zidovudine therapy. Clinical implications and the role of the resistance mutation at codon 41 were also assessed. Thirty-eight initially asymptomatic HIV-infected patients with a CD4+ cell count above 400 cells/mm3 were followed for a mean period of 121 weeks (20 received zidovudine and 18 matching placebo). Specific mutations in the HIV-1 reverse transcriptase coding region conferring resistance to zidovudine were detected using a selective polymerase chain reaction. During the follow-up period a mutation at codon 215 was detected in eight (40%) of the individuals in the zidovudine group, and in two of these eight subjects, a mutation at codon 41 was found. During the study, disease progression occurred in seven of the eight (88%) patients with a mutation at codon 215, compared with 7 of 18 (39%) patients assigned to the placebo group and 3 of the 12 (25%) patients receiving zidovudine treatment who did not develop a 215-mutant strain (p < 0.05). At entry, none of the patients harbored MT-2 tropic virus. Therefore, the emergence of a zidovudine-resistant mutation at codon 215 is associated with subsequent disease progression in asymptomatic HIV-infected patients who receive zidovudine monotherapy. This association suggests that the mutation at codon 215 is involved in a loss of therapeutic efficacy and, therefore, patients should be monitored during treatment with zidovudine.

Adult↗
PubMed1994

Predictive value of IgM antibodies to hepatitis C virus in patients with chronic hepatitis C undergoing interferon-alpha therapy. Analysis by two different methods.

To determine the predictive value of IgM anti-hepatitis C virus (HCV) testing in patients with chronic hepatitis C infections undergoing interferon-alpha (IFN-alpha) therapy, IgM anti-HCV reactivity was analysed by two different methods (non-commercial and commercial) in 19 patients and monitored at times 0 (pretreatment), 3, 6, 12, and 24 months during follow-up. Eight patients were non-responders, five remained in sustained response 1 year after stopping treatment, and six had a relapse. No correlation between alanine transaminase (ALT) levels and IgM anti-HCV reactivity was found by either method in baseline samples. In addition, neither the presence nor absence of IgM anti-HCV in baseline samples, nor the loss of specific IgM reactivity during treatment, had any predictive value. Finally, no other parameters analysed (age, sex, risk group and histological diagnosis), were significantly associated with IgM anti-HCV reactivity in our study. In summary, these results suggest that baseline detection and monitoring of IgM anti-HCV reactivity are not useful in predicting the sustained response to IFN-alpha therapy in chronic hepatitis C infection.

Adult↗
PubMed1992

Low resolution structure of microtubules in solution. Synchrotron X-ray scattering and electron microscopy of taxol-induced microtubules assembled from purified tubulin in comparison with glycerol and MAP-induced microtubules.

The structure of microtubules has been characterized to 3 nm resolution employing time-resolved X-ray scattering. This has revealed detailed structural features of microtubules not observed before in solution. The polymerization of highly purified tubulin, induced by the antitumour drug taxol, has been employed as a microtubule model system. This assembly reaction requires Mg2+, is optimal at a 1:1 taxol to tubulin heterodimer molar ratio, proceeds with GTP or GDP and is intrinsically reversible. The X-ray scattering profiles are consistent with identical non-globular alpha and beta-tubulin monomers ordered within the known helical surface lattice of microtubules. Purified tubulin-taxol microtubules have a smaller mean diameter (approx. 22 nm) than those induced by microtubule associated proteins or glycerol (approx. 24 nm), but nearly identical wall substructure to the resolution of the measurements. This is because the majority of the former consist of only 12 protofilaments instead of the typical 13 protofilaments, as confirmed by electron microscopy of thin-sectioned, negatively stained and ice-embedded taxol microtubules. It may be concluded that taxol induces a slight reduction of the lateral contact curvature between tubulin monomers. The main fringe pattern observed in cryo-electron micrographs is consistent with a simple 12 protofilament 3-start skewed lattice model. Cylindrical closure of this lattice can be achieved by tilting the lattice 0.8 degrees with respect to the microtubule axis. The closure implies a discontinuity in the type of lateral contacts between the tubulin monomers (regardless of whether these are of the -alpha-beta- or the -alpha-alpha-/-beta-beta- type), which indicates that lateral contacts and the subunit specificity of taxol binding are, to a large degree, equivalent.

Alkaloids↗
PubMed1992

Visceral leishmaniasis in HIV-1-infected individuals: a common opportunistic infection in Spain?

OBJECTIVE: To investigate the epidemiological, clinical and biological features of visceral leishmaniasis (VL) in patients with HIV-1 infection. DESIGN: Retrospective study. SETTING: Three university hospitals in southern Spain. PATIENTS: Forty-seven adult patients with VL and HIV-1 infection diagnosed between January 1986 and November 1991. RESULTS: Forty-five out of the 47 (96%) cases were diagnosed in the last 2 years. Fever (87%), hepatomegaly (74%), splenomegaly (72%) and pancytopenia (77%) were the most common presenting features. Most patients (79%) were strongly immunocompromised when VL was diagnosed, and were in stage IV of the Centers for Disease Control classification; 87% had a CD4 lymphocyte count < 200 x 10(6)/l. However, VL was the first severe infection diagnosed in 10 cases. Significant titres (> 1:40) of antileishmanial antibodies were detected by indirect immunofluorescence in five out of 16 (31%) cases only. Clinical response to the therapy was difficult to assess. Microbiological response was achieved in only 38% of the patients evaluated. CONCLUSIONS: Leishmaniasis is a relatively common infection in HIV-1-infected individuals in southern Spain. Its clinical picture is quite uniform and it can be the first opportunistic infection in individuals with HIV-1. In endemic areas, a high index of clinical suspicion should be maintained in order to avoid underdiagnosis of leishmaniasis.

AIDS-Related Opportunistic Infections↗
PubMed1991

Roles of ring C oxygens in the binding of colchicine to tubulin.

The roles of the oxygens in ring C of colchicine in its binding to tubulin were probed by a study of the interactions of two allocolchicine biphenyl analogues, 2,3,4,4'-tetramethoxy-1,1'-biphenyl (TMB) and 2,3,4-trimethoxy-4'-acetyl-1,1'-biphenyl (TKB), the first one containing a methoxy group in position 4', the second a keto group. Both analogues were found to bind specifically to the colchicine-binding site on tubulin in a rapidly reversible equilibrium. The standard free energies of binding at 25 degrees C were delta G zero (TKB) = 7.19 +/- 0.11 kcal mol-1 and delta G zero (TMB) = -6.76 +/- 0.22 kcal mol-1. The binding of TKB induced the same perturbation in protein circular dichroism at 220 nm as colchicine and allocolchicine, as well as quenching of protein tryptophan fluorescence. Binding of TMB did not affect the protein CD spectrum within experimental error and induced only a marginal quenching of protein fluorescence. Comparison with the binding properties of allocolchicine and its des(ring B) analogue 2,3,4-trimethoxy-4'-carbomethoxy-1,1'-biphenyl (TCB) [Medrano et al. (1989) Biochemistry 28, 5589-5599] has shown that the binding properties of the 4'-keto analogue (TKB) were closer to those of allocolchicine, even though the substituent in the 4'-position of TCB is identical with that of allocolchicine. It has been proposed that binding in the ring C subsite on tubulin, which is stabilized thermodynamically by stacking interactions, can be modulated in a nonidentical fashion by the carbonyl and the ether oxygens in the para position of ring C.

Binding, Competitive↗
PubMed1991

Mechanism of colchicine binding to tubulin. Tolerance of substituents in ring C' of biphenyl analogues.

The limits of structural variation of the substituent in position 4' of ring C' of biphenyl colchicine analogues (ring C in colchicine) were probed by the synthesis of a number of analogues and the examination of their binding to tubulin and its consequences. Binding was found to require the location in three-dimensional space of the oxygen in the 4'-substituent at a locus not far distant from those of the colchicine ring C oxygens. All those analogues that bind to the colchicine site of tubulin induced the GTPase activity and inhibited microtubule assembly, those containing a carbonyl group substoichiometrically and the others stoichiometrically. A similar relation was found for the induction of the abnormal polymerization of the colchicine analogue-tubulin complex, with methoxy-containing compounds requiring a higher temperature to induce the polymerization. A concerted analysis of the binding thermodynamics of colchicine and its various analogues has shown full consistency with the previously proposed two-step binding pathway that involves two nonidentical binding moieties in the ligand [Andreu, J. M., & Timasheff, S. N. (1982) Biochemistry 21, 534-543]. Comparison of the binding parameters of colchicine, its des(ring B) analogue (MTC), and ring A and C compounds individually with the thermodynamic parameters deduced for the first steps of the bindings of colchicine and MTC [Engelborghs, Y., & Fitzgerald, T. J. (1987) J. Biol. Chem. 262, 5204-5209] have led to the conclusion that binding can occur by two pathways leading to the identical product. In the first pathway, ring A binds first; this is followed by a rate-determining thermodynamically indifferent reaction (protein conformation change), and finally a rapid binding of ring C. In the second pathway, the events are the same except that the order of binding of the rings is reversed. Colchicine, due to the steric hindrance of ring B, can follow only the second pathway. For MTC, both kinetic pathways are open and binding may be initiated by random first contact of either ring A or ring C.

Animals↗
PubMed1989

A thermodynamic study of the interaction of tubulin with colchicine site ligands.

The bicyclic colchicine analogue 2-methoxy-5-(2',3',4'-trimethoxyphenyl)-2,4,6-cycloheptatrien-1-on e (MTC) has been used to study the thermodynamics of specific ligand binding to the colchicine site of tubulin, employing isothermal reaction microcalorimetry. The binding of MTC to purified calf brain tubulin, in 10 mM sodium phosphate buffer, pH 7.0, is characterized by delta H degree = -19 +/- 1 kJ.mol-1, delta G degree = -31.8 +/- 0.6 kJ.mol-1, and delta S degree = 43 +/- 5 J.mol-1.K-1 at 298 K, with a slight variation in the temperature range from 283 to 308 K. The binding thermodynamics of colchicine and allocolchicine are similar to MTC under the conditions examined, suggesting related molecular interactions of the three ligands with the protein binding site. The standard enthalpy changes of binding of colchicine and MTC at 308 K coincide within experimental error. Therefore the more favorable free energy change of binding of colchicine must come from a larger binding entropy change (by about 20 J.mol-1.K-1). This difference could be attributed to the presence of the middle ring of colchicine, which is absent in MTC. Consistently, a similar entropy change is observed by the comparison of allocolchicine to MTC binding at several temperatures. In addition, allocolchicine binding is about 6 kJ.mol-1 less exothermic than MTC binding, which could be attributed to the presence in allocolchicine of a substituted phenyl ring instead of the colchicine-MTC tropolone ring. The present results and analysis are fully compatible with the previously proposed bifunctional binding of colchicine and MTC (through their trimethoxybenzene and tropolone moieties) to a bifocal protein binding site, and also with a partial immobilization of intramolecular rotation of MTC upon binding, which in colchicine is already constrained by its middle ring (Andreu, J. M., Gorbunoff, M. J., Lee, J. C., and Timasheff, S. (1984) Biochemistry 23, 1742-1752).

Animals↗