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Biomedical subjects

L Pardo

Publications and source records attributed to L Pardo.

At least 19 recordsLinked to original sources
PubMed2004

Multiple sclerosis gender issues: clinical practices of women neurologists.

Substantially more women than men develop multiple sclerosis (MS), but information about the effects of MS and gender-specific issues such as pregnancy, breastfeeding, menstruation and hormone use is lacking. A survey study of neurologists' practice patterns was undertaken to elicit information about gender-specific topics and the use of disease-modifying MS therapies (DMT) including the interferons and glatiramer acetate (GA). A total of 147 surveys were returned. Half of respondents require patients to discontinue DMT during pregnancy, while 35% encourage discontinuation. Among those who allow patients to continue therapy, half consider GA to be safer during pregnancy than the interferons. Nearly 86% of respondents do not use DMT in patients who are breastfeeding. Among the 11% who actually prescribe during breastfeeding, most recommend GA. Neurologists generally leave the decision to breastfeed up to patients, and most refer patients to obstetrician/gynaecologists for counselling about contraception or hormone replacement therapy. The survey results described here provide insight into how neurologists manage reproductive health issues among women with MS.

Breast Feeding↗
PubMed2001

3-D-QSAR/CoMFA and recognition models of benzimidazole derivatives at the 5-HT(4) receptor.

3-D-QSAR/CoMFA methodology and computational simulation of ligand recognition have been successfully applied to explain the binding affinities of a series of benzimidazole derivatives 1-24 acting at serotonin 5-HT(4)Rs. Both derived computational models have facilitated the identification of the structural elements of the ligands that are key to high 5-HT(4)R affinity. The results provide the tools for predicting the affinity of related compounds, and for guiding the design and synthesis of new ligands with predetermined affinities and selectivity.

Benzimidazoles↗
PubMed2001

A conserved Asn in transmembrane helix 7 is an on/off switch in the activation of the thyrotropin receptor.

The thyrotropin (TSH) receptor is an interesting model to study G protein-coupled receptor activation as many point mutations can significantly increase its basal activity. Here, we identified a molecular interaction between Asp(633) in transmembrane helix 6 (TM6) and Asn(674) in TM7 of the TSHr that is crucial to maintain the inactive state through conformational constraint of the Asn. We show that these residues are perfectly conserved in the glycohormone receptor family, except in one case, where they are exchanged, suggesting a direct interaction. Molecular modeling of the TSHr, based on the high resolution structure of rhodopsin, strongly favors this hypothesis. Our approach combining site-directed mutagenesis with molecular modeling shows that mutations disrupting this interaction, like the D633A mutation in TM6, lead to high constitutive activation. The strongly activating N674D (TM7) mutation, which in our modeling breaks the TM6-TM7 link, is reverted to wild type-like behavior by an additional D633N mutation (TM6), which would restore this link. Moreover, we show that the Asn of TM7 (conserved in most G protein-coupled receptors) is mandatory for ligand-induced cAMP accumulation, suggesting an active role of this residue in activation. In the TSHr, the conformation of this Asn residue of TM7 would be constrained, in the inactive state, by its Asp partner in TM6.

Animals↗
PubMed2001

The TXP motif in the second transmembrane helix of CCR5. A structural determinant of chemokine-induced activation.

CCR5 is a G-protein-coupled receptor activated by the chemokines RANTES (regulated on activation normal T cell expressed and secreted), macrophage inflammatory protein 1alpha and 1beta, and monocyte chemotactic protein 2 and is the main co-receptor for the macrophage-tropic human immunodeficiency virus strains. We have identified a sequence motif (TXP) in the second transmembrane helix of chemokine receptors and investigated its role by theoretical and experimental approaches. Molecular dynamics simulations of model alpha-helices in a nonpolar environment were used to show that a TXP motif strongly bends these helices, due to the coordinated action of the proline, which kinks the helix, and of the threonine, which further accentuates this structural deformation. Site-directed mutagenesis of the corresponding Pro and Thr residues in CCR5 allowed us to probe the consequences of these structural findings in the context of the whole receptor. The P84A mutation leads to a decreased binding affinity for chemokines and nearly abolishes the functional response of the receptor. In contrast, mutation of Thr-82(2.56) into Val, Ala, Cys, or Ser does not affect chemokine binding. However, the functional response was found to depend strongly on the nature of the substituted side chain. The rank order of impairment of receptor activation is P84A > T82V > T82A > T82C > T82S. This ranking of impairment parallels the bending of the alpha-helix observed in the molecular simulation study.

Amino Acid Sequence↗
PubMed2001

Synthesis and structure-activity relationships of a new model of arylpiperazines. Study of the 5-HT(1a)/alpha(1)-adrenergic receptor affinity by classical hansch analysis, artificial neural networks, and computational simulation of ligand recognition.

A classical quantitative structure-activity relationship (Hansch) study and artificial neural networks (ANNs) have been applied to a training set of 32 substituted phenylpiperazines with affinity for 5-HT(1A) and alpha(1)-adrenergic receptors, to evaluate the structural requirements that are responsible for 5-HT(1A)/alpha(1) selectivity. The resulting models provide a significant correlation of electronic, steric, and hydrophobic parameters with the biological affinities. Although the derived linear Hansch correlations give good statistics and acceptable predictions, the introduction of nonlinear relationships in the analysis gives more solid models and more accurate predictions. In the ANN models on the basis of the obtained 3D plots, the 5-HT(1A) affinity has a nonlinear dependence on F, V(o), V(m), and pi(o), although the nonlinear relationship is not far from a planar one. The alpha(1)-adrenergic receptor affinity has a clear nonlinear dependence on F, V(o), V(m), pi(o), and pi(m). A comparison of both analyses gives an additional understanding for 5-HT(1A)/alpha(1) selectivity: (a) high F values increase the binding affinity for 5-HT(1A) receptors and decrease the affinity for alpha(1) sites; (b) the hydrophobicity at the meta-position has only influence for the alpha(1)-adrenergic receptor; (c) the meta-position seems to be implicated in the 5-HT(1A)/alpha(1) selectivity. While the 5-HT(1A) receptor is able to accommodate bulky substituents in the region of its active site, the steric requirements of the alpha(1)-adrenergic receptor at this position are more restricted. This information was used for the design of the new ligand EF-7412 (33) (5-HT(1A): K(i exptl) = 27 nM, alpha(1): K(i exptl) > 1000 nM; 5-HT(1A): K(i pred) (ANN) = 36 nM, alpha(1): K(i pred ANN) = 2745 nM) which was characterized as an antagonist in vivo in pre- and postsynaptic 5-HT(1A)R sites. Computational simulations of the complex between EF-7412 (33) and a 3D model of the transmembrane domain of the 5-HT(1A) receptor allowed us to define the molecular details of the ligand-receptor interaction that includes: (i) the ionic interaction between the protonated amine of the ligand and Asp 3.32; (ii) the hydrogen bonds between the m-NHSO(2)Et group of the ligand and Asn 7.39; and the hydrogen bonds between the hydantoin moiety of the ligand and (iii) Thr 3.37, (iv) Ser 5.42, and (v) Thr 5.43. These QSAR and ANN results in combination with computational simulations of ligand recognition will be useful for the design of potent selective 5-HT(1A) ligands.

Animals↗
PubMed2001

Computational model of the complex between GR113808 and the 5-HT4 receptor guided by site-directed mutagenesis and the crystal structure of rhodopsin.

A computational model of the transmembrane domain of the human 5-HT4 receptorcomplexed with the GR113808 antagonist was constructed from the crystal structure of rhodopsin and the putative residues of the ligand-binding site, experimentally determined by site-directed mutagenesis. The recognition mode of GR113808 consist of: (i) the ionic interaction between the protonated amine and Asp3.32; (ii) the hydrogen bond between the carbonylic oxygen and Ser5.43; (iii) the hydrogen bond between the ether oxygen and Asn6.55; (iv) the hydrogen bond between the C-H groups adjacent to the protonated piperidine nitrogen and the pi electrons of Phe6.51; and (v) the pi-sigma aromatic-aromatic interaction between the indole ring and Phe6.52. This computational model offers structural indications about the role of Asp3.32, Ser5.43, Phe6.51, Phe6.52, and Asn6.55 in the experimental binding affinities. Asp3.32Asn mutation does not affect the binding of GR113808 because the loss of binding affinity from an ion pair to a charged hydrogen bond is compensated by the larger energetical penalty of Asp to disrupt its side chain environment in the ligand-free form, and the larger interaction between Phe6.51 and the piperidine ring of the ligand in the mutant receptor. In the Phe6.52Val mutant the indole ring of the ligand replaces the interaction with Phe6.52 by a similarly intense interaction with Tyr5.38, with no significant effect in the binding of GR113808. The mutation of Asn6.55 to Leu replaces the hydrogen bond of the ether oxygen of the ligand from Asn6.55 to Cys5.42, with a decrease of binding affinity that approximately equals the free energy difference between the SH...O and NH...O hydrogen bonds. Because these residues are also present in the other members of the neurotransmitter family of G protein-coupled receptors, these findings will also serve for our understanding of the binding of related ligands to their cognate receptors.

Amino Acid Sequence↗
PubMed2001

Patients' answers to a postoperative questionnaire related to laser resurfacing.

To date there is no information that evaluates, from the patient's point of view, the experience of undergoing CO(2) laser skin resurfacing. This article investigates the outcome of laser resurfacing for various cutaneous problems with respect to the patient's expectations and experiences and the surgeon's opinions. Patients were entered into the study prospectively and presented with a questionnaire, at 12 months after treatment, to evaluate the patient's skin resurfacing experience. All patients received standardized preoperative counseling and underwent a standardized surgical protocol, conducted by the same surgeon. Eighty-eight percent of patients considered the result of the laser resurfacing to be very good, and 97% indicated that they had experienced little pain or discomfort. Nevertheless, 77% of patients stated that they would be unwilling to undergo another resurfacing procedure. This discrepancy is most likely the result of the patients' experiences in relation to the degree of erythema afterward. Most patients stated a desire to have more information regarding the procedure, particularly with respect to their experiences concerning postoperative erythema and exudates in the treated area. From the study it can be concluded that patients require extensive preoperative counseling, including a full explanation of all possible sequelae of these procedures to improve the patient's experience.

Aged↗
PubMed2001

[Prognostic factors in colorectal neoplasm. Multivariate analysis in 224 patients].

BACKGROUND: Staging of colorectal carcinoma has prognostic value and allows to take decisions about adjuvant therapy and follow up. Prognostic factors are not universally accepted and there are different staging classifications. AIM: To assess the prognostic value of clinical and pathological variables in 224 patients subjected to a curative resection of a colorectal carcinoma. PATIENTS AND METHODS: A retrospective analysis of 99 men and 125 women, aged 23 to 91 years old subjected to a curative resection of a colorectal carcinoma and followed up for a mean of 72 months. RESULTS: Global survival at 60 months was 72%. Univariate analysis showed that tumor localization, vascular permeation, wall infiltration and number of involved lymph nodes had an influence on survival. A Cox regression model disclosed tumor localization (colon versus rectum), a carcino-embryonic antigen over 30 ng/ml, vascular permeation, presence of 1 to 4 involved lymph nodes, or 5 or more lymph nodes and the presence of an apical lymph node as variables with significant prognostic value. CONCLUSIONS: Our series confirms the prognostic importance of lymph node involvement. This parameter is incorporated in Jass, GITSG (both modifications of Dukes classIfication) and TNM staging scores.

Adenocarcinoma↗
PubMed2000

Molecular determinants of MAO selectivity in a series of indolylmethylamine derivatives: biological activities, 3D-QSAR/CoMFA analysis, and computational simulation of ligand recognition.

A series of indolylmethylamine derivatives were assayed toward MAO-A and MAO-B inhibition. The K(i) values of these compounds are in the range from 0.8 to >10(6) nM for MAO-A or from 0.75 to 476000 nM for MAO-B. The most selective MAO-A or MAO-B inhibitors elicit a ratio of K(i) in the order of 1500 or 1000, respectively. Comparison of MAO-A and MAO-B CoMFA models showed that both the steric and electrostatic properties at the 5 position of the indole ring are determinant for MAO selectivity. Computational simulations of the complex between this part of the ligand and Phe-208 of MAO-A or Ile-199 of MAO-B, experimentally identified as responsible for substrate selectivity, allowed us to further characterize the nature of these enzyme-inhibitor interactions.

Amines↗
PubMed2000

Serine and threonine residues bend alpha-helices in the chi(1) = g(-) conformation.

The relationship between the Ser, Thr, and Cys side-chain conformation (chi(1) = g(-), t, g(+)) and the main-chain conformation (phi and psi angles) has been studied in a selection of protein structures that contain alpha-helices. The statistical results show that the g(-) conformation of both Ser and Thr residues decreases their phi angles and increases their psi angles relative to Ala, used as a control. The additional hydrogen bond formed between the O(gamma) atom of Ser and Thr and the i-3 or i-4 peptide carbonyl oxygen induces or stabilizes a bending angle in the helix 3-4 degrees larger than for Ala. This is of particular significance for membrane proteins. Incorporation of this small bending angle in the transmembrane alpha-helix at one side of the cell membrane results in a significant displacement of the residues located at the other side of the membrane. We hypothesize that local alterations of the rotamer configurations of these Ser and Thr residues may result in significant conformational changes across transmembrane helices, and thus participate in the molecular mechanisms underlying transmembrane signaling. This finding has provided the structural basis to understand the experimentally observed influence of Ser residues on the conformational equilibrium between inactive and active states of the receptor, in the neurotransmitter subfamily of G protein-coupled receptors.

Animals↗
PubMed2000

Binding mechanisms of TATA box-binding proteins: DNA kinking is stabilized by specific hydrogen bonds.

One of the common mechanisms of DNA bending by minor groove-binding proteins is the insertion of protein side chains between basepair steps, exemplified in TBP (TATA box-binding protein)/DNA complexes. At the central basepair step of the TATA box TBP produces a noticeable decrease in twist and an increase in roll, while engaging in hydrogen bonds with the bases and sugars. This suggests a mechanism for the stabilization of DNA kinks that was explored here with ab initio quantum mechanical calculations and molecular dynamics/potential of mean force calculations. The hydrogen bonds are found to contribute the energy necessary to drive the conformational transition at the central basepair step. The Asn, Thr, and Gly residues involved in hydrogen bonding to the DNA bases and sugar oxygens form a relatively rigid motif in TBP. The interaction of this motif with DNA is found to be responsible for inducing the untwisting and rolling of the central basepair step. Notably, direct readout is shown not to be capable of discriminating between AA and AT steps, as the strength of the hydrogen bonds between TBP and the DNA are the same for both sequences. Rather, the calculated free energy cost for an equivalent conformational transition is found to be sequence-dependent, and is calculated to be higher for AA steps than for AT steps.

Biophysical Phenomena↗
PubMed2000

The significance of orbital anatomy and periocular wrinkling when performing laser skin resurfacing.

Knowledge of orbital anatomy and the interaction of muscle contractions, gravitational forces and photoagingis fundamental in understanding the limitations of carbon dioxide (CO2) laser skin resurfacing when rejuvenating the skin of the periocular area. Laser resurfacing does not change the mimetic behavior of the facial muscles nor does it influence gravitational forces. When resurfacing periocular tissue, the creation of scleral show and ectropion are a potential consequence when there is an over zealous attempt at improving the sagging malar fat pad and eyelid laxity by performing an excess amount of laser passes at the lateral portion of the lower eyelid. This results in an inadvertent widening of the palpebral fissure due to the lateral pull of the Orbicularis oculi. Retrospectively, 85 patients were studied, who had undergone periorbital resurfacing with a CO2 laser using anew treatment approach. The Sharplan 40C CO2 Feather Touchlaser was programmed with a circular scanning pattern and used just for the shoulders of the wrinkles. A final laser pass was performed with the same program over the entire lower eyelid skin surface, excluding the outer lateral portion (e.g. a truncated triangle-like area),corresponding to the lateral canthus. Only a single laser pass was delivered to the lateral canthal triangle to avoid widening the lateral opening of the eyelid, which might lead to the potential complications of scleral show and ectropion. When the area of the crows' feet is to be treated, three passes on the skin of this entire lateral orbital surface are completed by moving laterally and upward toward the hairline. Patients examined on days 1, 7, 15, 30, 60, and one year after laser resurfacing showed good results. At two months after treatment, the clinical improvement was rated by the patient and physician as being "very good" in 81 of the 85 patients reviewed. These patients underwent laser resurfacing without complications. The proposed technique of periocular resurfacing prevents complications of scleral show and laxity in the lateral eyelid opening and even ectropion, because treatment conforms to the osseo-muscular anatomical relationship of eyelid structures.

Aging↗
PubMed1999

Electron microscopy comparison of CO2 laser flash scanning and pulse technology one year after skin resurfacing.

BACKGROUND: The recent adaptation of laser technology in plastic and dermatologic surgery has provided a means to reduce efficiently the irregularities of the surface of the skin. Previous studies have analyzed the short- and medium-term clinical and histologic results of two laser systems: the Sharplan 40C SilkTouch and the 5000C Coherent Ultrapulse with Computer Pattern Generator (CPG). This paper contains the long-term ultrastructural findings observed with the aid of transmission electron microscopy (TEM). MATERIALS AND METHODS: Twenty skin biopsy specimens were taken from ten Caucasion patients, between 54 and 72 years of age, who had undergone facial skin resurfacing with a CO2 laser 1 year previously. The treated areas of the face were divided into two equal parts. One half of the face was treated with the Sharplan SilkTouch laser and the other half with the Coherent Ultrapulse laser. Using TEM, the cell composition of the epidermis was studied ultrastructurally, as were the dermal-epidermal junction (DEJ) and the different fibers and cells in the superficial and middle dermis. RESULTS: On the side treated by the Sharplan laser, little melanin was observed, the DEJ was thicker, and there were abundant collagen fibers well compacted in the dermis. Also present was abundant elastin fiber with scarce interstitial spaces. On the side treated by the Coherent, the melanin was abundant and the DEJ was well structured. There were fibroblasts with lax chromatin in the dermis and collagen fibers in the papillary dermis oriented in a vertical and horizontal manner in relation to the epidermis. There was little elastin. The interstitial spaces were abundant. CONCLUSIONS: The Sharplan laser system seems to provoke a significantly more intense tissue response, with abundant dermal collagen and elastic fibers. This indicates that the Sharplan 40C SilkTouch might produce longer lasting clinical effects.

Aged↗
PubMed1998

Experimental and theoretical characterization of the high-affinity cation-binding site of the purple membrane.

Binding of Mn2+ or Mg2+ to the high-affinity site of the purple membrane from Halobacterium salinarium has been studied by superconducting quantum interference device magnetometry or by ab initio quantum mechanical calculations, respectively. The binding of Mn2+ cation, in a low-spin state, to the high-affinity site occurs through a major octahedral local symmetry character with a minor rhombic distortion and a coordination number of six. A molecular model of this binding site in the Schiff base vicinity is proposed. In this model, a Mg2+ cation interacts with one oxygen atom of the side chain of Asp85, with both oxygen atoms of Asp212 and with three water molecules. One of these water molecules is hydrogen bonded to both the nitrogen of the protonated Schiff base and the Asp85 oxygen. It could serve as a shuttle for the Schiff base proton to move to Asp85 in the L-M transition.

Aspartic Acid↗
PubMed1998

Selective binding of the TATA box-binding protein to the TATA box-containing promoter: analysis of structural and energetic factors.

We report the results of an energy-based exploration of the components of selective recognition of the TATA box-binding protein (TBP) to a TATA box sequence that includes 1) the interaction between the hydrophobic Leu, Pro, and Phe residues of TBP with the TA, AT, AA, TT, and CG steps, by ab initio quantum mechanical calculations; and 2) the free energy penalty, calculated from molecular dynamics/potential of mean force simulations, for the conformational transition from A-DNA and B-DNA into the TA-DNA form of DNA observed in a complex with TBP. The GTAT, GATT, GAAT, and GTTT tetramers were explored. The results show that 1) the discrimination of TA, AT, AA, TT, or CG steps by TBP cannot rest on their interaction with the inserting Phe side chains; 2) the steric clash between the bulky and hydrophobic Pro and Leu residues and the protruding -NH2 group of guanine is responsible for the observed selectivity against any Gua-containing basepair; 3) the Pro and Leu residues cannot selectively discriminate among TA, AT, AA, or TT steps; and 4) the calculated energy required to achieve the TA-DNA conformation of DNA that is observed in the complex with TBP appears to be a key determinant for the observed selectivity against the AT, AA, and TT steps. The simulations also indicate that only the TA step can form a very efficient interbase hydrogen bond network in the TA-DNA conformation. Such an energetically stabilizing network is not achievable in the AA and TT steps. While it is viable in the AT step, structural constraints render the hydrogen bonding network energetically ineffective there.

DNA-Binding Proteins↗