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Biomedical subjects

Alejandro Perez

Publications and source records attributed to Alejandro Perez.

6 recordsLinked to original sources
PubMed2006

The mammographic appearance of breast carcinomas of invasive ductal type: relationship with clinicopathological parameters, biological features and prognosis.

OBJECTIVES: To evaluate the clinical significance of the mammographic appearance of tumors in 411 patients with infiltrating ductal carcinoma of the breast. STUDY DESIGN: Tumors were classified into five radiographic subgroups: spiculated mass (A-type), diffuse changes with or without suspicious microcalcifications (B-type), microcalcifications with a mass (C-type), circumscribed (D-type), and not visible (E-type). Intratumoral levels of estrogen (ER) and progesterone (PR) receptors, c-erbB-2, EGFR, pS2, cathepsin D and tPA, ploidy and S-phase fraction, were analysed in a significant number of cases. RESULTS: A-type A radiographic pattern was detected in 234 patients (57%), B-type in 46 (11%), C-type in 46 (11%), D-type in 68 (17%), and E-type in 17 patients (4%). On the other hand, a total of 155 tumors (37.8%) showed microcalcifications. The percentage of tumors showing A-type pattern was more frequent in postmenopausal women, in well-differentiated tumors, and in those showing higher levels of ER, pS2 of tPA. However, B-type pattern was detected in a high percentage of premenopausal women and in those showing larger tumors, positive nodes, poor differentiation or high S-phase fraction. Cox multivariate analysis showed that B-type pattern and the absence of microcalcifications were factors significantly associated to high risk for relapse. CONCLUSIONS: Our results suggest that the mammographic appearance of tumor may to provide useful clinical information in addition to classical prognostic factor in infiltrating ductal carcinoma of the breast.

Adult↗
PubMed2005

Density functional theory study of water activation and COads + OHads reaction on pure platinum and bimetallic platinum/ruthenium nanoclusters.

A density functional theory study of the elementary steps that lead to the removal of CO(ads(Pt)) over alloyed and sequentially deposited Pt/Ru bimetallic nanoclusters is presented. The reaction energies and activation barriers for the H2O(ads(Ru)) dissociation and CO(ads(Pt)) + OH(ads(Ru)) reaction are estimated in solid-gas interface and in a microsolvated environment to determine which surface morphology is more tolerant to COads poisoning. On the basis of the energetics, the sequentially deposited Pt/Ru nanocluster is predicted to be a much more promising anode catalyst than the alloy cluster surface in fuel cell applications.

Journal Article↗
PubMed2004

Lorentz invariance and quantum gravity: an additional fine-tuning problem?

Trying to combine standard quantum field theories with gravity leads to a breakdown of the usual structure of space time at around the Planck length, 1.6x10(-35) m, with possible violations of Lorentz invariance. Calculations of preferred-frame effects in quantum gravity have further motivated high precision searches for Lorentz violation. Here, we explain that combining known elementary particle interactions with a Planck-scale preferred frame gives rise to Lorentz violation at the percent level, some 20 orders of magnitude higher than earlier estimates, unless the bare parameters of the theory are unnaturally strongly fine tuned. Therefore an important task is not just the improvement of the precision of searches for violations of Lorentz invariance, but also the search for theoretical mechanisms for automatically preserving Lorentz invariance.

Journal Article↗
PubMed2004

Beneficial effect of retinoic acid on the outcome of experimental acute renal failure.

BACKGROUND: Retinoic acid (RA) exerts beneficial effects on vascular remodelling and experimental nephritis, and plays a role in kidney development. Pathological changes caused by acute renal failure (ARF) result in high mortality. We determined whether RA ameliorates ARF-induced pathology caused by potassium dichromate (PD). METHODS: Adult Wistar female rats (210-250 g) were randomly allocated to four groups: (i) an ARF group that received PD [15 mg/kg body weight (bw), single dose subcutaneously]; (ii) a group that received PD plus RA (1 mg/kg bw) beginning at 5 days before PD and that continued for 14 additional days; (iii) a group that received PD plus thyroxine (T(4); 8 micro g/100 g bw) with RA; and (iv) a group that received only the vehicle for PD (saline solution). We evaluated functional, biochemical and morphological characteristics of the kidneys. RESULTS: PD-induced alterations in serum creatinine, creatinine clearance (C(cr)) and fractional excretion of sodium (FeNa) were less severe when rats received RA. PD increased lipoperoxidation and this alteration was partially blocked by RA. Animals undergoing ARF showed severe histological injury (brush border loss, acidophilia, oedema, pyknosis, karyorhexis, cell detachment and disruption of the basement membrane). These alterations were less severe in RA-treated rats, indicating a protective effect on functional and morphological alterations. Alterations in urinary sediment were reduced by RA. The simultaneous administration of T(4) with RA did not produce additional protection. CONCLUSION: RA exerted beneficial effects on the duration and severity of renal damage induced by PD in a model of renal failure resembling ARF in humans. The protective effect of RA may be mediated by diminished lipoperoxidative damage.

Acute Kidney Injury↗
PubMed2003

The structure of tri-proline in water probed by polarized Raman, Fourier transform infrared, vibrational circular dichroism, and electric ultraviolet circular dichroism spectroscopy.

Tripeptidesserve as model systems for understanding the so-called random-coil state of peptides and proteins. While it is well known that polyproline or proline-rich polypeptides adopt the very regular polyproline-II (PPII) or left-handed 3(1)-helix conformation, it was thus far not clear whether this is also the predominant structure adopted by proline-containing tripeptides. To clarify this issue, we have investigated the amide I' band profile in the ir, isotropic, and anisotropic Raman, and vibrational circular dichroism (VCD) spectrum of cationic and zwitterionic tri-proline in D(2)O. The data were analyzed by modifying a recently developed algorithm, which allows one to obtain the central dihedral angles of tripeptides from the amide I' band intensities (R. Schweitzer-Stenner, Biophysical Journal, 2002, Vol. 83, pp. 523-532). Our analysis revealed that the peptide adopts a nearly canonical PPII structure in water with psi and phi values in the range of 175 degrees -165 degrees and -70 degrees -(-80 degrees ), respectively. This is fully confirmed by the respective electronic ultraviolet-CD spectra. Our result indicates that the strong PPII propensity of trans proline results from local interactions between the pyrrolidine ring and the backbone and is not due to any long-range interactions.

Alanine↗