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Biomedical subjects

J Ramírez

Publications and source records attributed to J Ramírez.

At least 37 records · Page 2Linked to original sources
PubMed2000

Regulation of monovalent ion homeostasis and pH by the Ser-Thr protein phosphatase SIT4 in Saccharomyces cerevisiae.

A gene, SIT4, was identified as corresponding to a serine/threonine protein phosphatase and when overexpressed confers lithium tolerance in galactose medium to the budding yeast Saccharomyces cerevisiae. This gene has been previously identified as a regulator of the cell cycle and involved in nitrogen sensing. It is shown that the transcription levels of SIT4 are induced by low concentrations of Li(+) in a time-dependent manner. Na(+) and K(+) at high concentrations, but not sorbitol, also induce transcription. As a response to Na(+) or Li(+) stress, yeast cells lower the intracellular K(+) content. This effect is enhanced in cells overexpressing SIT4, which also increase (86)Rb efflux after the addition of Na(+) or Li(+) to the extracellular medium. Another feature of SIT4-overexpressing cells is that they maintain a more alkaline pH of 6.64 compared with 6.17 in the wild type cells. It has been proposed that the main pathway of salt tolerance in yeast is mediated by a P-type ATPase, encoded by PMR2A/ENA1. However, our results show that in a sit4 strain, expression of ENA1 is still induced by monovalent cations, and overexpression of SIT4 does not alter the amount of ENA1 transcript. These results show that SIT4 acts in a parallel pathway not involving induction of transcription of ENA1 and suggest a novel function for SIT4 in response to salt stress.

Adenosine Triphosphatases↗
PubMed2000

Occupation and risk of malignant pleural mesothelioma: A case-control study in Spain.

BACKGROUND: The association of mesothelioma and asbestos exposure is well known, but some data suggest that probably many people are still being exposed to asbestos without knowing it. METHODS: Between 1993 and 1996, 132 cases (77% males) of histologically confirmed malignant pleural mesothelioma and 257 controls, residents in two provinces of Spain (Barcelona and C¿adiz), were interviewed. They were classified according to their probability and intensity of occupational asbestos exposure by a panel of industrial hygienists, based on a detailed occupational history. RESULTS: Age and sex-adjusted odds ratio (OR) for the highest probability of exposure to asbestos was 13.2 (95% confidence interval 6.4-27.3), and 27.1 (9. 28-79.3) for high intensity. A dose-response trend was observed for both, probability and intensity. Overall, 61% of cases and 42% of controls had ever worked in an occupation with risk of asbestos exposure, with an OR of 2.59 (1.60-4.22). In our population 62% of cases could be attributed to occupational asbestos exposure. CONCLUSIONS: A high risk of pleural mesothelioma due to occupational asbestos exposure is confirmed, but there is still a sizeable proportion for which no evidence of occupational exposure was found. Most of these cases could be due to other sources of asbestos exposure, mainly domestic or environmental.

Adult↗
PubMed2000

Inactivation of mitochondrial permeability transition pore by octylguanidine and octylamine.

Mitochondrial permeability transition occurs through a Ca2+-dependent opening of a transmembrane pore, whose identity has been attributed to that of the adenine nucleotide translocase (ANT). In this work, we induced permeability transition by adding 0.5 microM carboxyatractyloside. The process was evaluated analyzing Ca2+ efflux, a drop in transmembrane electric gradient, and swelling. We found that the amphiphyllic cations octylguanidine and octylamine, at the concentration of 100 microM, inhibited, almost completely, nonspecific membrane permeability. Hexylguanidine, hexylamine, as well as guanidine chloride and hydroxylamine failed to do so. The inhibition was reversed after the addition of 40 mM Li+, Na+ K+, Rb+, or Cs+; K+ was the most effective. We propose that the positive charge of the amines interact with negative charges of membrane proteins, more likely the ADP/ATP carrier, while the alkyl chain penetrates into the hydrophobic milieu of the inner membrane, fixing the reagent.

Adenosine Diphosphate↗
PubMed2000

Polytomella spp. growth on ethanol. Extracellular pH affects the accumulation of mitochondrial cytochrome c550.

A defined medium with ethanol as sole carbon source was devised for growth of the colorless, unicellular alga Polytomella spp. Cell density on this carbon source was related to extracellular pH. An acidic pH was required for ethanol utilization; best yields were obtained at pH 3.7. Spectroscopic analysis of the cells showed that the concentration of cytochrome c per cell was 40% higher than at pH 6.0; the concentrations of cytochrome a606 (cytochrome c oxidase) and b566 (cytochrome bc1 complex) were the same. A soluble cytochrome c550 was purified from cells grown at pH 3.7 and characterized by peptide sequencing as the 12-kDa cytochrome c550 of the mitochondrial respiratory chain. Immunoblots of total cell proteins showed higher accumulation of cytochrome c550 at pH 3.7 than at pH 6.0. RNA blot analysis gave clear evidence of the abundance of c550 transcript in cells grown at pH 3.7. The amount of mitochondrial proteins obtained from cells grown at pH 3.7 was twofold higher than that of cells grown at pH 6.0. Mitochondria isolated from both cell types readily oxidized succinate, malate or ethanol. The rates of oxygen uptake were 20-25% higher in mitochondria from cells grown at pH 3.7. Cyanide and antimycin A inhibited respiration with succinate up to 95% in both types of mitochondria. The participation of cytochrome c550 in mitochondrial electron transport from succinate to oxygen was shown by spectral measurements.

Amino Acid Sequence↗
PubMed2000

Iron bioavailability in humans from breakfasts enriched with iron bis-glycine chelate, phytates and polyphenols.

This study was conducted to determine the bioavailability of iron amino acid chelate (ferrochel) added to fortify breads prepared from either precooked corn flour or white wheat flour + cheese and margarine compared with the same basal breakfast enriched with either ferrous sulfate or iron-EDTA. The inhibitory effect of phytate and polyphenols on iron absorption from ferrochel was also tested. A total of 74 subjects were studied in five experiments. Iron absorption from ferrochel was about twice the absorption from ferrous sulfate (P: < 0.05). When ferrous sulfate and ferrochel were administered together or in different meals, absorption from ferrochel was about twice the absorption from ferrous sulfate (P: < 0.05). Polyphenols present in coffee and tea inhibited iron absorption in a dose-dependent manner. American-type coffee did not modify iron absorption significantly, whereas both espresso-type coffee and tea reduced iron absorption from ferrochel by 50% (P: < 0. 05). Ferrochel partially prevented the inhibitory effect of phytates. Because of its high solubility in aqueous solutions even at pH 6, its low interactions with food and high absorption, ferrochel is a suitable compound for food fortification.

Adolescent↗
PubMed2000

Flavopiridol metabolism in cancer patients is associated with the occurrence of diarrhea.

Flavopiridol, a cyclin-dependent kinase inhibitor currently undergoing clinical evaluation, has a dose-limiting toxicity of diarrhea. Preclinical data on flavopiridol metabolism indicate that flavopiridol undergoes hepatic glucuronidation. The purpose of this study is to evaluate whether the occurrence of diarrhea is related to the systemic glucuronidation of flavopiridol. Parent drug and metabolite concentrations in plasma were measured by high-pressure liquid chromatography in 22 metastatic renal cancer patients treated on a Phase II trial of 50 mg/m2/day of flavopiridol administered every 2 weeks as a 72-h continuous infusion. Pharmacokinetics of flavopiridol and its glucuronide were assessed during the first cycle at 23, 47, and 71 h during the infusion. Flavopiridol concentrations at 23, 47, and 71 h were 389 nM (296-567 nM), 412 nM (297-566 nM), and 397 nM (303-597 nM) [median (interquartile range)], respectively. Flavopiridol glucuronide reached a plateau of 358 nM (196-553 nM) at 47 h. Metabolic ratios of flavopiridol glucuronide:flavopiridol at 71 h showed an apparent bimodal distribution with an antimode of 1.2. Thirteen patients experienced diarrhea and had lower metabolic ratios [0.72 (0.53-0.86)] than patients without diarrhea [2.24 (1.76-2.3); P = 0.002]. Eight of 11 extensive glucuronidators (ratio > 1.2) did not develop diarrhea, whereas 10 of 11 poor glucuronidators (ratio < 1.2) developed diarrhea (P = 0.008). The glucuronidation of flavopiridol is apparently polymorphic, suggesting a genetic etiology. The systemic glucuronidation of flavopiridol is inversely associated with the risk of developing diarrhea.

Antineoplastic Agents↗
PubMed2000

New property of vitamin A and beta-carotene on human iron absorption: effect on phytate and polyphenols as inhibitors of iron absorption.

One hundred and seventy four human subjects were studied to find out the interaction of vitamin A or beta-carotene with the inhibitors of iron absorption, from a basal breakfast containing bread from either 100 g of precooked corn flour or 100 g of white wheat flour, 50 g of cheese and 10 g of margarine. Bread was labeled with either 55Fe or 59Fe. This bread was made from commercially flours fortified with iron as ferrous fumarate and vitamins. It was noticed that the percentage of iron absorption from the breakfast prepared with precooked corn flour given alone and with different concentrations of coffee was practically the same, while the iron absorption from the breakfast prepared from wheat flour decreased from 6% when the breakfast was given alone, to less than 2% when it was given with different concentrations of coffee. The only ingredient present in precooked corn flour and not in wheat flour was vitamin A. This difference encouraged the authors to perform further experiments using precooked corn and wheat flours fortified only with ferrous fumarate. These studies demonstrated that vitamin A inhibits the effect of the polyphenol and partially inhibits the effect phytate on iron absorption. HPLC and spectrophotometric studies demonstrated an interaction between vitamin A and iron. Other experiments, which included 100 volunteers, were performed to test the effect of vitamin A and beta-carotene on iron absorption from corn, wheat and rice. The presence of vitamin A increased iron absorption up to 3 times for rice, 2.4 times for wheat and 1.8 times for corn. beta-carotene increased absorption almost 3 times for the three cereals tested, showing that both compounds were capable of preventing the inhibitory effect of phytates on iron absorption. This information suggest that vitamin A and beta-carotene form a complex with iron keeping it soluble in the intestinal lumen and preventing the inhibitory effect of phytates and polyphenols on iron absorption.

Antioxidants↗
PubMed1999

Involvement of Nha1 antiporter in regulation of intracellular pH in Saccharomyces cerevisiae.

The Nha1 antiporter is involved in regulation of intracellular pH in Saccharomyces cerevisiae. We report that deletion of the NHA1 gene resulted in an increase of cytoplasmic pH in cells suspended in water or acidic buffers. Addition of KCl or NaCl to exponentially growing cells lowered the internal pH but the difference between cells with or without NHA1 was maintained. Addition of KCl to starved cells resulted in much higher alkalinization of cytoplasmic pH in a strain lacking Nha1p compared to the wild-type or Nha1p-overexpressing strains. The H+/K+(Na+) exchange mechanism of Nha1p was confirmed in reconstituted plasma membrane vesicles.

Biological Transport↗
PubMed1999

Phenotype-genotype correlation of in vitro SN-38 (active metabolite of irinotecan) and bilirubin glucuronidation in human liver tissue with UGT1A1 promoter polymorphism.

BACKGROUND: Hepatic uridine diphosphate glucuronosyltransferase (UGT) isoform 1A1 (UGT1A1) is primarily responsible for the glucuronidation of SN-38 (7-ethyl-10-hydroxycamptothecin), the active metabolite of the anticancer agent irinotecan. UGT1A1, also catalyzing the glucuronidation of bilirubin, has been shown to have reduced activity in Gilbert's syndrome. The presence of an additional TA repeat [(TA)7TAA] in the TATA sequence of UGT1A1 has been associated with Gilbert's syndrome. OBJECTIVE: To evaluate the relationship between UGT1A1 phenotypic activity and UGT1A1 promoter polymorphism. METHODS: Phenotypic measurements included in vitro SN-38 and bilirubin glucuronidation in human liver microsomes (n = 44). A recently developed genotyping test was used to determine TATA sequence polymorphisms in UGT1A1. Genotypes were assigned as follows: 7/7, homozygous for the (TA)7TAA allele; 6/6, homozygous for the (TA)6TAA allele; and 6/7, heterozygous with 1 of each allele. RESULTS: Nine percent of screened liver samples were found to be homozygous for allele 7 (7/7), 43% were homozygous for allele 6 (6/6), and 48% were heterozygous (6/7). Frequencies of (TA)7TAA and (TA)6TAA alleles were 0.33 and 0.67, respectively. A significant trend toward a decrease in SN-38 and bilirubin glucuronidation rates was found as the number of TA repeats increased (6/6 > 6/7 > 7/7). Glucuronidation rates of both substrates were significantly lower in the 7/7 and 6/7 groups compared with the 6/6 group. CONCLUSIONS: The results indicate a significant association of UGT1A1 phenotype and genotype based on in vitro phenotypic measurements. The clinical significance of our finding remains to be established.

Antineoplastic Agents, Phytogenic↗
PubMed1999

Synthesis of steroids in pancreas: evidence of cytochrome P-450scc activity.

In pancreas, the activities of several sex steroid-transforming enzymes have been reported. Data have been obtained in perfused organs, total tissue homogenates, and subcellular organelles. These data, concurrent with the description of the presence of ligand-regulated steroid receptors, as well as the sexually dimorphic behavior of some pancreatic tumors, are clear evidence in support of the participation of steroid hormones in the pancreatic function. In this study, the steroidogenic ability of the pancreas was demonstrated by two different methods: (a) in tissue homogenates, by the identification of cytochrome P-450scc gene (CYP11A) transcripts after reverse transcription-polymerase chain reaction amplification (RT-PCR); and (b) in isolated mitochondria by the glutethimide-dependent inhibition of cholesterol-pregnenolone biotransformation. The results obtained in a series of independent experiments showed that (a) the pancreatic tissue possessed transcriptional activity of the CYP11A gene, although to a lesser extent than the typical steroidogenic tissues, and (b) isolated mitochondria obtained from the pancreas were able consistently to synthesize pregnenolone; furthermore, the addition of the specific inhibitor aminoglutethimide (AMG) blocked its synthesis. On the whole, these findings are interpreted as clear evidences of the activity of the cytochrome P-450scc enzymatic complex (P450scc), responsible for the transformation of cholesterol into pregnenolone and considered the first and limiting step in steroid biosynthesis.

Aminoglutethimide↗
PubMed1999

Inflammatory reaction in pulmonary muscular arteries of patients with mild chronic obstructive pulmonary disease.

Endothelial dysfunction and intimal thickening have been shown in pulmonary arteries (PA) of patients with mild chronic obstructive pulmonary disease (COPD). To investigate whether an inflammatory process related to tobacco smoking might be involved in the development of pulmonary vascular abnormalities in COPD, we characterized the inflammatory cell infiltrate and the endothelium-dependent relaxation in PA of 39 patients who underwent lung resection, divided into three groups: "nonsmokers" (n = 7); "smokers," with normal lung function (n = 12); and "COPD" (n = 20). Endothelium-dependent relaxation was assessed in vitro by exposing PA rings to adenosine diphosphate (ADP). Inflammatory cell types were identified by immunohistochemistry. PA of COPD patients developed lower relaxation in response to ADP than nonsmokers and smokers. The number of inflammatory cells was increased in PA of COPD compared with the other two groups. This cell infiltrate was largely constituted by T lymphocytes. The CD8(+) T-cell subset was increased in both smokers and COPD compared with nonsmokers, yielding a reduction of the CD4(+)/CD8(+) ratio. The intensity of the inflammatory infiltrate correlated with both the endothelium-dependent relaxation and the intimal thickness. We conclude that cigarette smoking induces a CD8(+) T-lymphocyte infiltrate in PA, which is associated with the impairment of the vessel's structure and function, suggesting the potential involvement of an inflammatory process in the pathogenesis of pulmonary vascular abnormalities in the early stage of COPD.

Aged↗
PubMed1998

Simultaneous determination of 5-fluorouracil and uracil by high-performance liquid chromatography using four serial columns.

A sensitive assay was developed for the quantitation of 5-fluorouracil (5-FU) and uracil using liquid-liquid extraction (LLE) and HPLC with UV detection. Analyses were performed with four microBondapak C18 columns connected in series using 20 mM acetic acid with 1% ACN as mobile phase. The calibration curves were linear across the range of 26-1000 ng ml(-1) (0.21-7.8 microM) for 5-FU and 1.0-14.0 microg ml(-1) (0.01-110 microM) for uracil. This assay has been implemented to determine the plasma concentrations for pharmacokinetic studies for 5-FU and uracil in conjunction with clinical trials.

Chromatography, High Pressure Liquid↗
PubMed1998

Hypothyroidism renders liver mitochondria resistant to the opening of membrane permeability transition pore.

Membrane permeability was examined in liver mitochondria isolated from hypothyroid rats. It was found that such a thyroid status provides substantial protection from membrane leakiness as induced by Ca2+ loading. Thus, these mitochondria are less prone to undergoing permeability transition than mitochondria from euthyroid rats. The above conclusion was reached on the basis of the following two facts: (1) hypothyroid mitochondria are not strictly dependent on the addition of ADP to retain high matrix Ca2+ concentrations, and (2) carboxyatractyloside, antimycin A or carbonyl cyanide-m-chlorophenyl hydrazone failed to promote Ca2+ efflux. We discuss the possible relevance of the low content of membrane cardiolipin as well as the low expression of the adenine nucleotide translocase as responsible for the resistance to membrane damage.

Adenosine Diphosphate↗