Biomedical subjects

P Regueiro

Publications and source records attributed to P Regueiro.

11 recordsLinked to original sources

PubMed2004

Phase II study of capecitabine in combination with paclitaxel in patients with anthracycline-pretreated advanced/metastatic breast cancer.

The addition of oral capecitabine to docetaxel improves response rate, time to progression (TTP) and overall survival in anthracycline-pretreated metastatic breast cancer (MBC). This phase II study evaluates the efficacy and safety of a 21-day cycle of oral capecitabine (1000 mg m(-2) twice daily, days 1-14) plus i.v. paclitaxel (175 mg m(-2), day 1) in anthracycline-pretreated advanced/MBC. In all, 73 patients were enrolled at 13 Swedish and Spanish centres. The objective response rate was 52% (95% confidence interval (CI): 40-63%) in the intent-to-treat population, including complete responses in 11%. Disease was stabilised in a further 29%. The median time to disease progression (TTP) was 8.1 months and the median overall survival was 16.5 months. The combination was generally well tolerated with a predictable safety profile. The most common treatment-related nonhaematological adverse events were hand-foot syndrome (42%), alopecia (30%) and diarrhoea (26%). The only treatment-related Grade 3/4 adverse events occurring in >5% of patients were alopecia (22%) and hand-foot syndrome (11%). Grade 3/4 neutropenia and lymphocytopenia were reported in 12 and 14% of patients, respectively. Capecitabine plus paclitaxel is highly active with a favourable safety profile in anthracycline-pretreated MBC.

Adolescent↗

PubMed2002

Capecitabine (Xeloda) in combination with oxaliplatin: a phase I, dose-escalation study in patients with advanced or metastatic solid tumors.

OBJECTIVES: This phase I, dose-escalation study was conducted to determine the recommended dose of intermittent oral capecitabine in combination with a fixed dose of i.v. oxaliplatin. Secondary objectives included evaluation of the safety profile and antitumor activity. PATIENTS AND METHODS: Twenty-three patients with advanced or metastatic solid tumors received a 21-day regimen of oral capecitabine (500, 825, 1000 or 1250 mg/m2 twice daily, days 1-14) in combination with oxaliplatin (130 mg/m2, 2-h i.v. infusion, day 1). Dose-limiting toxicities were determined during the first treatment cycle, and safety and efficacy were evaluated throughout treatment. RESULTS: The recommended dosing schedule is oral capecitabine 1000 mg/m2 twice daily (days 1-14) with i.v. oxaliplatin 130 mg/m2 (day 1) in a 21-day treatment cycle. The principal dose-limiting toxicity was diarrhea. The most frequent treatment-related adverse events occurring during the study were gastrointestinal (nausea/vomiting, diarrhea) and neurological (dysesthesia, paresthesia). The majority of treatment-related adverse events were mild to moderate in intensity, and no grade 4 adverse events occurred in the 15 patients treated at or below the recommended dose. The most common grade 3/4 laboratory abnormalities were lymphocytopenia (52% of patients), thrombocytopenia (22%; grade 3 only), neutropenia (17%) and hyperbilirubinemia (17%). Among patients treated at or below the recommended dose level (n = 15), only two patients experienced grade 3 neutropenia and no patients experienced grade 4 neutropenia. Partial tumor responses occurred in six patients (26%), including five of nine patients (55%) with colorectal cancer. All responding patients were pretreated with 5-fluorouracil and four responders had received prior irinotecan. CONCLUSIONS: Oral capecitabine with i.v. oxaliplatin is a feasible combination regimen that shows promising antitumor activity in patients with colorectal cancer. There is an ongoing, phase II study to further characterize the safety and efficacy of this combination as first-line therapy for metastatic colorectal cancer, using the recommended dose identified in this study.

Administration, Oral↗

PubMed1996

Preparation of giant myelin vesicles and proteoliposomes to register ionic channels.

Myelin vesicles, reconstituted liposomes with proteolipid protein (PLP), the main protein component of myelin, and electrophysiological patch-clamp are potentially powerful tools to study the role of myelin in functional ionic channels. However, technical difficulties in the vesiculation of myelin and the small size of the vesicles obtained do not permit the application of micropipettes for current recordings. From a suspension of purified myelin we have prepared oligolamellar vesicles (mean diameter of 144 nm) using the so-called French pressure system. From this preparation we obtained giant myelin vesicles approximately 10 microns in mean diameter, using a dehydration-rehydration procedure. Qualitative analysis of proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed no significant loss of any component in these vesicles due to pressure, in comparison with non-vesiculated myelin. A way of preparing giant liposomes of approximately 80-100 microns and proteoliposomes of approximately 30 microns in mean diameter, using the same dehydration-rehydration procedure, is also reported. Reconstitution of purified PLP in giant liposomes was confirmed by fluorescent labeling of PLP and by fluorescence microscopy. The current recordings from these vesicles prove the validity of these methods and provide significant evidence of the existence of ionic channels in myelin membranes and the possibility that PLP functions as a channel. The physiological significance and characterization of these channels remain yet unresolved. These results have a special significance for elucidating the molecular role of myelin in the regulation of neural activity and in the brain ion microenvironment.

Animals↗

PubMed1992

Renaturation of the brain myelin proteins by octyl glucoside detergent.

The secondary structure of myelin proteins undergoes a deep change when the membrane is delipidated and suspended in an aqueous buffer containing phosphate and sulfate anions. However, when increasing concentrations of octyl glucoside are dissolved in this saline medium, proteins recover gradually its native secondary structure, reaching a maximum for a detergent/protein ratio which, in addition, is optimal for maximal membrane solubilization. Larger amounts of detergent, however, reverted the effect. Results are explained in terms of anion-lipid and detergent-lipid interactions. Quantitative estimates on the spectral profiles let us find the optimal detergent-protein stoichiometry for preserving almost completely the native secondary structure of myelin proteins while keeping maximal solubilization. These findings are of great importance for reconstitution experiments designed with the goal of determining the biological functions of myelin proteins.

Animals↗

PubMed1992

Protein conformational changes and myelin solubilization by anion-detergent solutions.

The addition of sodium sulfate to a myelin suspension in sodium phosphate buffer at neutral pH, containing octyl glucoside detergent (OG), increases the membrane solubility more than 5-fold by an unknown structural mechanism. FTIR spectroscopy has been applied to investigate anion effects on the conformational structure of myelin proteins. Sulfate and sulfate-phosphate media, but not phosphate alone, induce a great conformational protein disorder. The addition of the detergent to the anion mixture solution prevents the myelin from protein denaturation. The conformational transitions have also been quantified through the amide I region. Explanations of these changes and their connections with myelin solubility are also included.

Animals↗

PubMed1992

Preparation of a protein-free total brain white matter lipid fraction: characterization of liposomes.

A method of preparing a total lipid extract (TLE), free of protein, by extracting brain white matter with tetrahydrofuran is presented. The optimal conditions of extraction were found to be 50 ml of THF per gram of lyophilized tissue, though fresh tissue can also be used if larger volumes of solvent are employed. The method allowed, in a short time and in a single step, a yield of TLE of 50% on a dry weight basis. Its analytical characterization revealed a qualitative and quantitative composition very similar to the lipid composition of CNS myelin, including all the phospholipid and galactolipid species, cholesterol and gangliosides, but it contained only traces (0.1%) of protein. TLE has been used to prepare liposomes, either multilamellar (MLVs) or unilamellar (LUVs, SUVs), characterized by freeze-fracture electron microscopy. A multilayered, heterogeneous population of liposomes is observed in the MLVs preparation. When these samples were submitted to a freezing and thawing procedure the resulting liposomes were single-walled, and their intravesicular volume was increased. They were quite impermeable to the monovalent cation 86Rb+ and, by contrast, rather permeable to 45Ca+ +. Their complex lipid composition, together with their permeability properties and their response to ionophores, make them very useful to study protein-lipid interactions occurring within the myelin membrane as well as the functional properties of myelin proteins in reconstitution experiments.

Animals↗

PubMed1991

Selective extraction, solubilization, and reversed-phase high-performance liquid chromatography separation of the main proteins from myelin using tetrahydrofuran/water mixtures.

The number of solvents capable of dissolving myelin and proteolipid protein (PLP) and of being used as a mobile phase for the separation of myelin proteins by reversed-phase high-performance liquid chromatography (RP-HPLC) is very limited. In a thorough study, we found that aqueous tetrahydrofuran (THF) fulfilled such a requirement. The maximal amount of protein extracted corresponded to a THF/water ratio of 4:1 v/v and a polarity index of 5.16. This mixture dissolved a purified PLP preparation completely, 60% of proteins from fresh myelin, and 20% of white matter total proteins. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of those extracts, followed by densitometric analysis, showed that the amount and type of proteins dissolved depended on the polarity (i.e., the content of water) of the solvent mixture used. This selective effect was greater for basic protein in myelin preparations. Crude extracts highly enriched in basic protein can be prepared. In addition, the solvent system THF/water proved to be very useful as a mobile phase in RP-HPLC for separating myelin proteins. Using a C3 column and a linear gradient from 30% to 100% THF in water, both containing 0.1% trifluoroacetic acid (TFA), we separated completely the three main protein fractions of central nervous system (CNS) myelin in a short period of time. The high solubility power of THF/water mixtures prolonged greatly the life of the column.

Animals↗

PubMed1991

Solubilization of myelin membranes by detergents.

The major proteins of myelin have classically been extracted in organic solvents. Here we investigated some of the characteristics of brain myelin solubilization in aqueous detergent solutions. At comparable molar concentrations, two nonionic detergents, i.e., octyl glucoside and Lubrol PX, proved relatively better myelin solubilizers than the detergents related to the bile salts, i.e., cholate and CHAPS. The two former detergents solubilized more protein than lipid and the two latter ones more lipid than protein from myelin membranes. All four detergents solubilized the phospholipid more efficiently than the cholesterol component of myelin. The detergent concentrations required for myelin solubilization were reduced substantially if the temperature and the salt concentration of the media were increased. As much as 3 mg of lyophilized myelin (about 1 mg of protein) were solubilized readily per milliliter of a solution containing 30 mM octyl glucoside and 0.1 M sodium sulfate in 0.1 M sodium phosphate buffer, pH 6.7. Each of the detergents studied, including the above four, sodium dodecyl sulfate (SDS). Triton X-100, and Zwittergent 3-14, had its own advantages and drawbacks as myelin protein extractors. The nonionic amphiphiles and CHAPS left a small residue mainly composed of proteins of the Wolfgram fraction, as revealed by SDS-polyacrylamide gel electrophoresis. Octyl glucoside was preferred, given its versatility as solubilizer, ultraviolet transparency, and high critical micellar concentration. Observations on possible difficulties that may be encountered are also included.

Animals↗

PubMed1990

Pre-replicative phase-related changes in bile acid-induced choleresis in the regenerating rat liver.

1. During the pre-replicative phase of the regenerating rat liver some interesting changes occur, which might selectively modify some mechanisms involved in bile formation, such as those responsible for the hypercholeretic effect of ursodeoxycholic acid. The aim of the present work was to gain information on this point. 2. Anaesthetized male Wistar rats (approximately 250 g) were used. The animals underwent two-thirds hepatectomy 1, 6 or 12 h before collection of bile samples was begun. Very early after hepatectomy (1 h) spontaneous bile flow and bile acid output were increased. Both returned to values not significantly different from those of the controls at 6 h. Bile flow increased again at the end of the pre-replicative phase. Taurocholate infusion (200 nmol min-1 g-1 calculated liver weight) induced increases in bile flow and bile acid output that were similar in both the control and hepatectomized rats, regardless of the time of the pre-replicative phase considered. 3. Cholic acid and ursodeoxycholic acid were infused (300 nmol min-1 g-1 calculated liver weight) into control and partially hepatectomized rats (at the mid-point of the pre-replicative phase, i.e. 6 h after surgical liver resection). Cholic acid-induced bile flow, bile acid and bicarbonate output expressed per g of remaining liver were similar in control and in hepatectomized rats. By contrast, ursodeoxycholic acid-induced choleresis were profoundly altered during the pre-replicative phase. As expressed per g of remaining liver, bile flow was markedly reduced (-17%, P less than 0.05), in spite of total bile acid output being greatly increased (+ 148%, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Biliary lipid secretion during the prereplicative phase of rat liver regeneration.

The prereplicative phase-related changes in spontaneous and taurocholate-induced biliary lipid secretion were studied in anaesthetized male Wistar rats (250 g). Rats underwent two-thirds hepatectomy 1, 6 or 12 h before starting to collect bile samples. As compared with non-hepatectomized rats, biliary lipid secretion was increased at 1 h after hepatectomy and then restored to values similar to the control group up to 12 h after hepatectomy. In separate experiments, taurocholate was infused (200 nmol/min/g calculated liver weight) through the jugular vein over 80 min. Both taurocholate-induced bile flow and bile acid output were similar in control and hepatectomized rats, regardless of the time of the prereplicative phase considered. By contrast, taurocholate-induced lecithin and cholesterol outputs were markedly modified. The former was lowered throughout the prereplicative phase, whereas the latter increased at 6 h and decreased at 12 h. In summary, these results indicate that shortly after hepatectomy bile acid-induced biliary lipid secretion is profoundly modified, probably due to changes in the plasma membrane involved in preparing the hepatocyte to enter the cell cycle.

Animals↗

PubMed1988

Evidence for the presence of carbonic anhydrase in the plasma membrane of rat hepatocytes.

The cellular distribution of carbonic anhydrase is a key characteristic for the role of the enzyme in cell function. In several epithelia involved in bicarbonate transport this enzyme is located in the plasma membrane. Because bicarbonate secretion is an important mechanism in bile formation by the liver, we investigated the presence of carbonic anhydrase activity in isolated plasma membranes from rat hepatocytes. Carbonic anhydrase activity was enriched 1.79-fold in plasma membrane preparations. This activity was inhibited by acetazolamide and activated by Triton X-100, but was insensitive to Cl- or CNO-. It is highly unlikely that the low contamination of cytoplasm and intracellular membranes could account for the presence of carbonic anhydrase activity in plasma membrane preparations. Moreover, the results from resuspension/washing of plasma membrane fractions in ionic media suggest an absence of soluble carbonic anhydrase adsorption upon plasma membrane. Accordingly, the present findings provide strong evidence for the presence of carbonic anhydrase in the plasma membrane of rat hepatocytes.

Animals↗