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Biomedical subjects

A Ortiz

Publications and source records attributed to A Ortiz.

At least 73 records · Page 4Linked to original sources
PubMed2000

Isolation and biochemical characterization of a new topoisomerase I inhibitor from Ocotea leucoxylon.

In a continuation of our search for potential tumor inhibitors from plants, we found that a crude extract from Ocotea leucoxylon showed selective activity typical of inhibitors of the enzyme topoisomerase I in a yeast assay for DNA-damaging agents. Using a bioassay-directed fractionation approach, the major bioactive compound was isolated and identified as the known aporphine alkaloid dicentrinone (4); the inactive alkaloid dicentrine (3) was also isolated. Compound 4 showed selective bioactivity against the rad52 repair-deficient yeast strain RS322 (IC(12) 49 microg/mL) and was inactive against the rad52- and topo1-deficient strain RS321 (IC(12) > 2000 microg/mL) and against the repair-proficient strain RJ03 (IC(12) > 2000 microg/mL). Biochemical studies with recombinant human topoisomerase I indicated that dicentrinone (4) is an inhibitor of the human enzyme. Colony formation studies suggest that it is weakly cytotoxic, but that its mechanism of toxicity differs from that of camptothecin and its derivatives.

Aporphines↗
PubMed2000

Hepatitis C virus RNA in kidney biopsies from infected patients with renal diseases.

Hepatitis C virus (HCV) infection has been associated with several renal pathologies, including membranoproliferative and membranous glomerulonephritis. Although the presence of HCV proteins has been reported, there are no data concerning detection of the viral RNA in renal cells from HCV-infected patients with kidney disease. In this report we analysed, by in situ hybridization, the presence of HCV RNA in renal biopsies from 10 patients who were positive for antibodies to HCV (anti-HCV) and serum HCV RNA positive, and from four patients without HCV infection, with different renal disease. HCV RNA was detected in the renal biopsies from all of the 10 HCV-infected patients. Hybridization signals were detected in the tubular and capillary endothelial cells. No hybridization signals were found in the renal biopsies of the four anti-HCV-negative patients. In conclusion, our results demonstrate that HCV RNA is common in kidney cells of patients with renal diseases who are infected with HCV. The presence of HCV RNA is not necessarily associated with a pathogenetic consequence.

Adult↗
PubMed2000

Expression of apoptosis regulatory proteins in tubular epithelium stressed in culture or following acute renal failure.

BACKGROUND: While tubular cell death is a characteristic of acute renal failure (ARF), the molecular mechanisms that modulate this cell death are unclear. Cell fate in acute renal failure hinges on a balance of survival and mortality factors in a changing environment. We further explored this issue by studying selected cell death-related proteins in experimental renal failure. METHOD: The expression of genes that promote (c-myc, Bax, BclxS) or protect (Bcl2, BclxL) from cell death was studied by Northern blot, Western blot, and immunohistochemistry in murine kidneys following ARF induced by folic acid or in renal tubular epithelial cells (MCT) stressed in culture. RESULTS: Renal mRNA levels encoding for c-myc and BclxL were elevated in ARF while the Bcl2/Bax ratio was decreased (Bcl2 decreased and Bax increased; P < 0.05). Protein levels of BclxL increased and Bcl2 protein decreased. Expression of tumor necrosis factor (TNF-alpha), a mediator of ARF, was also increased. Immunohistochemistry further demonstrated that BclxL was increased in some tubuli and absent in others, while Bcl2 expression decreased diffusely. Bax staining was also patchy among tubuli and individual cells in the tubular wall and lumen. As a relative deficit of survival factors is present in ARF, MCT epithelium were deprived of serum survival factors. This resulted in apoptosis, decreased Bcl2/Bax and BclxL/Bax ratios (P < 0.05) and sensitization to TNF-alpha-induced apoptosis (P < 0.05). The latter was prevented by enforced overexpression of BclxL (P < 0.01). TNF-alpha increased the mRNA levels encoding for c-myc and decreased BclxL expression. Neither MCT cells nor the kidney expressed BclxS. CONCLUSIONS: A relative deficit of survival factors likely contributes to changes in levels of BclxL and Bax in ARF. These deficits predispose to cell death induced by persistent lethal factors such as TNF-alpha that is increased in ARF and a potential source of increased c-myc, a downstream facilitator of cell death. These findings implicate members of the Bcl2 family of proteins as regulators of tubular cell death in ARF and single them out as potential therapeutic targets.

Acute Kidney Injury↗
PubMed2000

Antiplatelet therapy alters iron requirements in hemodialysis patients.

Hemodialysis (HD) patients are prone to develop iron deficiency because of consumption of iron stores during erythropoietin (EPO) therapy. Data are needed to establish the factors involved in the different iron needs among these patients. Sixty-five HD patients were prospectively studied during a year. The subjects were dialyzed through polytetrafluoroethylene (PTFE) grafts (n = 23), arteriovenous native fistulae (n = 41), and a Permcath (n = 1). Twenty-four patients were administered aspirin; 23 patients, ticlopidine; 1 patient, dipyridamole; and 4 patients, anticoagulation with acenocoumarol. Iron supplementation (oral or parenteral) and laboratory parameters were recorded monthly. Significant differences in iron requirements, depending on the use of antiplatelet and/or anticoagulation agents, were found. Total parenteral iron supplements were greater in patients on antiplatelet therapy with either native or graft vascular accesses compared with the rest (2,406 +/- 1,445 versus 1,562 +/- 858 mg; P = 0.0081). Twelve of 52 patients on antiplatelet therapy required oral iron and only 1 of 13 patients not on antiplatelet therapy was administered oral iron supplements (P < 0.05). Patients on antiplatelet therapy were administered more transfusions (1.9 +/- 3.8 transfusions/y) than individuals not on antiplatelet therapy (0.15 +/- 0.3 transfusions/y; P = 0.0015). However, only patients with PTFE grafts on antiplatelet therapy had a post-HD bleeding time longer than patients not on antiplatelet therapy (9.1 +/- 3.6 versus 5.7 +/- 3.9 minutes; P < 0.0001). Multiple logistic regression analysis showed that the use of antiplatelet agents (P < 0.05) is an independent factor that increased the probability of requiring greater parenteral iron supplements (>2.5 g/y). Patients with PTFE grafts required more EPO than those with autologous fistulae (160 +/- 93 versus 100 +/- 63 U/kg/wk; P = 0.012). No differences between groups were found that could explain this finding. Antiplatelet and/or anticoagulation therapy implied the use of greater amounts of iron supplements in HD patients. Although these greater requirements of iron occurred in parallel with bleeding from the vascular access, additional data favor the existence of other factors, eg, interdialytic blood losses. The present study suggests that antiplatelet therapy may be an important factor in determining iron requirements in HD patients. Moreover, our data relate for the first time the use of prosthetic grafts with increased EPO requirements, an issue of great potential importance in the debate about vascular access policy in dialysis units.

Administration, Oral↗
PubMed2000

Riboflavin uptake by human-derived colonic epithelial NCM460 cells.

Normal microflora of the large intestine synthesize a number of water-soluble vitamins including riboflavin (RF). Recent studies have shown that colonic epithelial cells possess an efficient carrier-mediated mechanism for absorbing some of these micronutrients. The aim of the present study was to determine whether colonic cells also possess a carrier-mediated mechanism for RF uptake and, if so, to characterize this mechanism and study its cellular regulation. Confluent monolayers of the human-derived nontransformed colonic epithelial cells NCM460 and [(3)H]RF were used in the study. Uptake of RF was found to be 1) appreciable and temperature and energy dependent; 2) Na(+) independent; 3) saturable as a function of concentration with an apparent K(m) of 0.14 microM and V(max) of 3.29 pmol x mg protein(-1) x 3 min(-1); 4) inhibited by the structural analogs lumiflavin and lumichrome (K(i) of 1.8 and 14.1 microM, respectively) but not by the unrelated biotin; 5) inhibited in a competitive manner by the membrane transport inhibitor amiloride (K(i) = 0.86 mM) but not by furosemide, DIDS, or probenecid; 6) adaptively regulated by extracellular RF levels with a significant and specific upregulation and downregulation in RF uptake in RF-deficient and oversupplemented conditions, respectively; and 7) modulated by an intracellular Ca(2+)/calmodulin-mediated pathway. These studies demonstrate for the first time the existence of a specialized carrier-mediated mechanism for RF uptake in an in vitro cellular model system of human colonocytes. This mechanism appears to be regulated by extracellular substrate level and by an intracellular Ca(2+)/calmodulin-mediated pathway. It is suggested that the identified transport system may be involved in the absorption of bacterially synthesized RF in the large intestine and that this source of RF may contribute toward RF homeostasis, especially that of colonocytes.

Biological Transport↗
PubMed2000

Adaptive regulation of intestinal folate uptake: effect of dietary folate deficiency.

Folate is an essential micronutrient that, in mammals, must be obtained from exogenous sources via intestinal absorption. Previous studies have characterized different aspects of the mechanism of the intestinal folate uptake process. Much less, however, is known about regulation of this process. In this study, we examined the effect of dietary folate deficiency on intestinal folate uptake using the rat as an animal model. The results showed that dietary folate deficiency leads to a significant (P < 0.01) and specific upregulation in the transepithelial transport of folic acid. The upregulation in transepithelial folate transport 1) was found to be due to an induction in carrier-mediated folate uptake across the brush-border membrane (BBM) and was mediated via a significant (P < 0.01) increase in the maximal velocity but not the apparent Michaelis constant of the uptake process, 2) was associated with a marked increase in the steady-state mRNA level of reduced folate carrier-1 and in the level of the expressed protein at the intestinal BBM, and 3) was associated with a marked (>10-fold) increase in the activity of the intestinal BBM form of folate hydrolase. Results of this study demonstrate, for the first time, that dietary folate deficiency leads to a marked upregulation in intestinal folate uptake and in the activity of folate hydrolase. Furthermore, the upregulation in folate uptake is associated with an increase in mRNA and protein levels of folate carrier, suggesting possible involvement of a transcriptional regulatory mechanism(s) in the upregulation.

Adaptation, Physiological↗
PubMed2000

Photosensitizing properties of palladium-tetraphenylporphycene on cultured tumour cells.

In this study we describe photokilling properties and effects on the mitotic index (MI) of cultured HeLa cells induced by palladium(II)-tetraphenylporphycene (PdTPP(0)). The drug was synthesized by refluxing tetraphenylporphycene (TPP(0)) and PdCl2 in dimethylformamide, followed by evaporation and purification by chromatography. Cells were treated with different concentrations of PdTPPo incorporated into dipalmitoylphosphatidylcholine liposomes, and red light irradiation (lambda > 600 nm) was performed at 21 mW/cm2. No dark toxicity was found when the drug was applied under our experimental conditions. Using lethal (LD(100)) treatments, cells showed the immediate occurrence of bubbles on the plasma membrane, whereas homogeneous nuclear condensation and loss of cytoplasm appeared 3-24 h later. An increased MI was found 6-8 h after sublethal LD(25) and LD(40) treatments as well as a high proportion of abnormal metaphases with altered spindle microtubules. Chromatin condensation and fragmentation were observed 8 h after LD(75) treatments. These results show that in comparison with TPP(0), the new sensitizer PdTPPo has more efficient photokilling properties which could be very valuable for the photodynamic therapy of cancer.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1999

The novel Cer-like protein Caronte mediates the establishment of embryonic left-right asymmetry.

In the chick embryo, left-right asymmetric patterns of gene expression in the lateral plate mesoderm are initiated by signals located in and around Hensen's node. Here we show that Caronte (Car), a secreted protein encoded by a member of the Cerberus/Dan gene family, mediates the Sonic hedgehog (Shh)-dependent induction of left-specific genes in the lateral plate mesoderm. Car is induced by Shh and repressed by fibroblast growth factor-8 (FGF-8). Car activates the expression of Nodal by antagonizing a repressive activity of bone morphogenic proteins (BMPs). Our results define a complex network of antagonistic molecular interactions between Activin, FGF-8, Lefty-1, Nodal, BMPs and Car that cooperate to control left-right asymmetry in the chick embryo.

Amino Acid Sequence↗
PubMed1999

A study on the interactions of surfactin with phospholipid vesicles.

Surfactin, an acidic lipopeptide produced by various strains of Bacillus subtilis, behaves as a very powerful biosurfactant and posses several other interesting biological activities. By means of differential scanning calorimetry and X-ray diffraction the effect of surfactin on the phase transition properties of bilayers composed of different phospholipids, including lipids forming hexagonal-HII phases, has been studied. The interactions of surfactin with phosphatidylcholine and phosphatidylglycerol seem to be optimal in the case of myristoyl acyl chains, which have a similar length to the surfactin hydrocarbon tail. Data are shown that support formation of complexes of surfactin with phospholipids. The ionized form of surfactin seems to be more deeply inserted into negatively charged bilayers when Ca2+ is present, also supporting the formation of surfactin-Ca2+ complexes. In mixtures with dielaidoylphosphatidylethanolamine, a hexagonal-HII phase forming lipid, surfactin displays a bilayer stabilizing effect. Our results are compatible with the marked amphiphilic nature of surfactin and may contribute to explain some of its interesting biological actions; for instance the formation of ion-conducting pores in membranes.

Bacterial Proteins↗
PubMed1999

The influence of vitamin K1 on the structure and phase behaviour of model membrane systems.

Vitamin K1 is a component of the Photosystem I of plants which constitutes the major dietary form of vitamin K. The major function of this vitamin is to be cofactor of the microsomal gamma-glutamylcarboxylase. Recently, novel roles for this vitamin in the membrane have been postulated. To get insight into the influence of vitamin K1 on the phospholipid component of the membrane, we have studied the interaction between vitamin K1 and model membranes composed of dimyristoylphosphatidylcholine (DMPC) and dielaidoylphosphatidylethanolamine (DEPE). We utilized high-sensitivity differential scanning calorimetry and small-angle X-ray diffraction techniques. Vitamin K1 affected the thermotropic properties of the phospholipids, broadened and shifted the transitions to lower temperatures, and produced the appearance of several peaks in the thermograms. The presence of the vitamin gave rise to the formation of vitamin-rich domains which were immiscible with the bulk phospholipid in both the gel and the liquid-crystalline phases. Vitamin K1 was unable to alter the lamellar organization of DMPC, but we found that it produced an increase in the interlamellar repeat spacing of DMPC at 10 degrees C. Interestingly, vitamin K1 promoted the formation of inverted hexagonal HII structures in the DEPE system. We discuss the possible implications that these vitamin K1-phospholipid interactions might have with respect to the biological function of the vitamin.

Calorimetry, Differential Scanning↗
PubMed1999

Membrane fusion and the lamellar-to-inverted-hexagonal phase transition in cardiolipin vesicle systems induced by divalent cations.

The polymorphic phase behavior of bovine heart cardiolipin (CL) in the presence of different divalent cations and the kinetics of CL vesicle fusion induced by these cations have been investigated. (31)P-NMR measurements of equilibrium cation-CL complexes showed the lamellar-to-hexagonal (L(alpha)-H(II)) transition temperature (T(H)) to be 20-25 degrees C for the Sr(2+) and Ba(2+) complexes, whereas in the presence of Ca(2+) or Mg(2+) the T(H) was below 0 degrees C. In the presence of Sr(2+) or Ba(2+), CL large unilamellar vesicles (LUVs) (0.1 microm diameter) showed kinetics of destabilization, as assessed by determination of the release of an aqueous fluorescent dye, which strongly correlated with the L(alpha)-H(II) transition of the final complex: at temperatures above the T(H), fast and extensive leakage, mediated by vesicle-vesicle contact, was observed. On the other hand, mixing of vesicle contents was limited and of a highly transient nature. A different behavior was observed with Ca(2+) or Mg(2+): in the temperature range of 0-50 degrees C, where the H(II) configuration is the thermodynamically favored phase, relatively nonleaky fusion of the vesicles occurred. Furthermore, with increasing temperature the rate and extent of leakage decreased, with a concomitant increase in fusion. Fluorescence measurements, involving incorporation of N-NBD-phosphatidylethanolamine in the vesicle bilayer, demonstrated a relative delay in the L(alpha)-H(II) phase transition of the CL vesicle system in the presence of Ca(2+). Freeze-fracture electron microscopy of CL LUV interaction products revealed the exclusive formation of H(II) tubes in the case of Sr(2+), whereas with Ca(2+) large fused vesicles next to H(II) tubes were seen. The extent of binding of Ca(2+) to CL in the lamellar phase, saturating at a binding ratio of 0.35 Ca(2+) per CL, was close to that observed for Sr(2+) and Ba(2+). It is concluded that CL LUVs in the presence of Ca(2+) undergo a transition that favors nonleaky fusion of the vesicles over rapid collapse into H(II) structures, despite the fact that the equilibrium Ca(2+)-CL complex is in the H(II) phase. On the other hand, in the presence of Sr(2+) or Ba(2+) at temperatures above the T(H) of the respective cation-CL complexes, CL LUVs rapidly convert to H(II) structures with a concomitant loss of vesicular integrity. This suggests that the nature of the final cation-lipid complex does not primarily determine whether CL vesicles exposed to the cation will initially undergo a nonleaky fusion event or collapse into nonvesicular structures.

4-Chloro-7-nitrobenzofurazan↗
PubMed1999

Locations of remorse and homelands of resilience: notes on grief and sense of loss of place of Latino and Irish-American caregivers of demented elders.

In this essay, based on qualitative research with Latino and Irish-American caregivers of demented elders, we argue that spatially and culturally constituted definitions of personhood, the moral life, and justice shape perceptions of normative aging, the agency of the demented persons and their place in the community, the appropriate care of the aged and demented, as well as partially determine the concrete resources which will be available to elders and their families. We review how ties to homelands and neighborhood institutions act as mediators and shapers of anticipatory grief, caregiver burdens, and caregiver resources, serving as a buffer against exhaustion and despair for some families (primarily the Irish-American sample), and as an additional site of loss or stress for others (primarily the Latino sample).

Attitude↗
PubMed1999

24-h pH monitoring is necessary to assess acid reflux suppression in patients with Barrett's oesophagus undergoing treatment with proton pump inhibitors.

BACKGROUND: Control of acid reflux is the main objective of treatment for Barrett's oesophagus. However, as these patients have a reduced sensitivity to acid reflux, disappearance of symptoms may not correlate with efficient control of acid reflux. The aim of this study was to determine in a group of patients with Barrett's oesophagus whether treatment with proton pump inhibitors suppressed pathological acid reflux once the symptoms of reflux had been controlled and the associated inflammatory lesions cured. METHODS: Eighteen consecutive patients with Barrett's oesophagus were studied, all of whom presented with heartburn. Twenty-four-hour oesophageal pH monitoring before treatment showed pathological acid reflux in all cases: median percentage of total time with pH less than 4, 22 (range 8-52) per cent. All patients received proton pump inhibitors (dose 20-60 mg/day) until symptoms were controlled. RESULTS: While on therapy, pH was reduced (median percentage of total time with pH less than 4, 3 versus 22 per cent; P < 0.001). However, three patients had persistent pathological rates of acid reflux. CONCLUSION: Disappearance of symptoms is not a good indicator of control of pathological acid reflux in patients with Barrett's oesophagus. Twenty-four-hour pH monitoring should be performed for proper adjustment of the dose of medication.

Adolescent↗