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Biomedical subjects

D S Miller

Publications and source records attributed to D S Miller.

At least 91 records · Page 5Linked to original sources
PubMed1996

Renal secretion of organic anions and cations.

The renal proximal tubule actively transports charged, potentially toxic xenobiotics from blood to lumen. Basolateral uptake of organic anions is indirectly coupled to the sodium gradient through Na-dicarboxylate cotransport and dicarboxylate-organic anion exchange. Upon entry, a significant fraction of intracellular organic anion is sequestered within vesicles. Disruption of the cellular microtubular network can lead to both diminished vesicular movement and reduced transepithelial secretion. Luminal efflux of organic anions is energetically downhill, but carrier mediated. Both anion exchange and potential driven transport are present, but neither completely accounts for transport from cell to lumen. For organic cations, basolateral entry is downhill via potential driven facilitated diffusion. Intracellular sequestration of organic cations in vesicles is substantial, but its role in secretion is uncertain. Multiple carriers are available to drive organic cations uphill into the tubular lumen. The classical system indirectly taps the energy of the luminal Na gradient to drive organic cation efflux via Na(+)-H+ and proton-organic cation exchange. In addition, the multidrug resistance ATPase can pump organic cations into the tubular lumen. Thus, although much detailed information has been added over the last 50 years, it is not yet possible to provide a detailed, quantitative understanding of these important excretory systems.

Animals↗
PubMed1996

Secondary prevention of cancer.

In recent years prevention has become extremely important in the war against cancer. For many cancers, major risk factors are not amenable to change and, therefore, secondary prevention through screening and early detection is the major type of intervention. Furthermore, with the discovery of cancer genes and tumor markers, which make it easier than ever before to identify people with increased risk of developing certain types of cancers, the role of secondary prevention has assumed an even greater value. This paper reviews recent advances in secondary prevention of those cancers for which overall efficacy of screening to reduce mortality has been demonstrated but for which some residual controversies exist: breast, cervical, and colorectal cancers.

Breast Neoplasms↗
PubMed1996

Active microtubule-dependent secretion of a fluorescent bile salt derivative in skate hepatocyte clusters.

Fluorescence microscopy and video image analysis were used to study the transport of a fluorescent bile acid derivative [N-[7-(4-nitrobenzo-2-oxa-1,3-diazol)]-7 beta-amino-3 alpha, 12 alpha-dihydroxy-5 beta-cholan-24-oyl-2-aminoethanesulfonate (NBD-TC)] in isolated clusters of hepatocytes from the little skate Raja erinacea. Analysis of images of hepatocyte clusters that were incubated in medium with 0.5-1 microM NBD-TC showed that the fluorescent derivative accumulated in the cells and that the clusters retained a patent canalicular lumen as well as the ability to actively transport the bile acid derivative from the cells into the lumen; i.e., the lumen-to-cell fluorescence ratio greatly exceeded unity. NBD-TC uptake by hepatocytes was inhibited by several organic anions, of which taurocholate was the most effective. Uptake was also blocked by metabolic inhibitors and by incubation in the cold. Neither Na replacement nor increased medium K, which depolarizes the membrane electrical potential [potential difference (PD)], affected NBD-TC accumulation by hepatocytes. Transport of NBD-TC into the canalicular lumen was inhibited by incubation in the cold and was substantially reduced by high-K medium; these blocks were removed by warming and transfer to normal-K medium, respectively. Treatment of hepatocytes with 20-40 microM nocodazole, a drug that reversibly depolymerizes microtubules, reduced cellular NBD-TC accumulation and blocked its secretion into the canalicular lumen; nocodazole effects were reversed by washing the hepatocyte clusters in drug-free medium. Thus uptake of NBD-TC by skate hepatocytes is active and carrier mediated but not dependent on the PD or Na gradient. NBD-TC secretion from cell to canalicular lumen also appears to be active and carrier mediated. Canalicular secretion appears to be driven at least in part by the PD and is highly dependent on an intact microtubular system in this marine species.

Alkanesulfonates↗
PubMed1996

Fluorescence imaging study of organic anion transport from renal proximal tubule cell to lumen.

The mechanisms driving organic anion transport from cell to lumen were studied in intact killifish proximal tubules using fluorescence microscopy. Three fluorescent substrates were used as follows: 1) fluorescein (FL); 2) carboxyfluorescein (CF), generated intracellularly from carboxyfluorescein diacetate (CFDA); and 3) bimane-S conjugates, generated intracellularly by conjugation of monochlorobimane (MCB) with glutathione (GSH) and subsequent metabolism. The latter two substrates bypassed the basolateral uptake mechanism, allowing direct study of luminal transport mechanisms. At steady state, for all three substrates, luminal fluorescence was two to three times higher than cellular fluorescence. With FL as substrate, addition of p-aminohippurate (PAH) or probenecid to the incubation medium reduced cellular and luminal fluorescence to roughly the same extent. With CFDA or MCB as substrate, PAH and probenecid only slightly reduced cellular fluorescence but greatly reduced luminal fluorescence. MCB blocked transport of FL from cell to lumen; CFDA blocked transport of bimane-S conjugates from cell to lumen. Finally, depolarizing tubule cells with high-potassium medium did not affect the steady-state lumen-to-cell distribution of FL, CF, or bimane-S conjugates. These results show that organic anion transport from cell to lumen is mediated and uphill but not sensitive to the electrical potential difference across the luminal membrane.

Animals↗
PubMed1996

Multiple pathways of organic anion secretion in renal proximal tubule revealed by confocal microscopy.

Previous studies with p-aminohippurate (PAH) and fluorescein (FL) have shown that cellular uptake and tubular secretion of organic anions is driven by indirect coupling to sodium. Here we used killifish proximal tubules and laser-scanning confocal microscopy to study the transport of a larger organic anion, fluorescein-methotrexate (FL-MTX, mol mass 923 Da). When tubules were incubated in medium containing 2 microM FL-MTX, dye accumulated in both cells and tubular lumens. At steady state, luminal fluorescence was 4-5 times higher than cellular fluorescence. Ouabain (0.1 mM) did not affect cellular or luminal fluorescence, and replacement of medium sodium by N-methylglucamine had only a modest effect; preincubation with glutarate had no effect. KCN did not affect cellular uptake but abolished secretion into the lumen. Uptake and secretion of FL-MTX were inhibited by micromolar concentrations of other organic anions (MTX, folate, probenecid, bromocresol green, bromosulfophthalein), but 1 mM PAH had a relatively small effect. FL-MTX secretion into the lumen was inhibited by leukotriene C4, cyclosporine A, and verapamil, none of which affected FL transport. Thus a substantial component of FL-MTX secretion is Na independent and ouabain insensitive. Both the basolateral and luminal steps in the Na-independent pathway differ from those usually associated with FL and PAH secretion.

Animals↗
PubMed1996

Interaction of fluorescein with the dicarboxylate carrier in rat kidney cortex mitochondria.

The interaction of the organic anion, fluorescein (FL), with mitochondria in renal proximal tubule cells was investigated. Confocal microscopy was used to demonstrate FL accumulation in mitochondria of intact cells. Phenylsuccinate inhibited the mitochondrial accumulation of the FL analog, carboxyfluorescein (CF) indicating that the dicarboxylate carrier may be involved in the intracellular compartmentation of organic anions. To characterize the interaction, radio-tracer uptake and respiration studies with renal mitochondria were carried out using succinate as a substrate. Respiration measurements in freshly isolated kidney cortex mitochondria revealed that FL inhibited ADP-stimulated and uncoupled respiratory rate, indicating that the organic anion inhibited the availability of succinate as a reducing agent. A similar effect on mitochondrial respiration was found for PAH and phenylsuccinate. FL inhibited 14C-succinate uptake concentration-dependently, and Dixon analysis revealed that the nature of interaction between FL and succinate was competitive, Ki values of 0.5 +/- 0.2 and 1.1 +/- 0.8 mM were calculated for respiration experiments and tracer uptake studies, respectively. The data demonstrate that FL competitively interacts with a mitochondrial dicarboxylate transporter.

Animals↗
PubMed1995

Effects of variations in flow on aortic valve area in aortic stenosis based on in vivo planimetry of aortic valve area by multiplane transesophageal echocardiography.

This study provides evidence that acute changes in stroke volume and cardiac output do not result in significant alterations in the anatomic AVA measured with multiplane TEE in patients with AS of moderate or severe degree. Thus, TEE could be useful in the assessment of severity of AS in both low- and high-output states.

Adult↗
PubMed1995

Cytoskeletal organization in clusters of isolated polarized skate hepatocytes: structural and functional evidence for microtubule-dependent transcytosis.

Isolated hepatocytes from the marine vertebrate Raja erinacea (the little skate) retain their structural and functional integrity as clusters of cells formed around a single tubular bile canaliculus, and therefore can be used as a model of polarized hepatocytes in situ. In this study we used confocal and conventional epifluorescence microscopy in conjunction with fluorescent markers and immunocytochemistry to examine the structure and function of the cytoskeleton in these cells. Actin filaments in the hepatocyte clusters were found cortically and also concentrated in a pericanalicular array, while microtubules appeared to radiate away from a concentration near the apical membrane of the biliary pole towards the basolateral sinusoidal surfaces. Treatment of clusters with the microtubule disrupting agent, nocodazole, resulted in the microtubules depolymerizing from the basolateral surfaces towards the apical surface, indicating that the microtubules were oriented with their plus ends at the basolateral surface and their minus ends at the apical surface. Nocodazole was also found to disrupt the ability of clusters to transcytose a fluorescent bile salt derivative into their canalicular lumens. We detected cytoplasmic dynein in skate hepatocyte homogenates by Western blotting using an anti-dynein intermediate chain antibody, and immunofluorescent staining of intact hepatocytes revealed a punctate vesicular pattern. The polarized arrangement of microtubules, the presence of cytoplasmic dynein, and the inhibition of bile salt secretion by nocodozole are consistent with the microtubule cytoskeleton playing a fundamental role in the mediation of transcytosis, endocytosis, and bile excretory function in these hepatocytes. These polarized isolated skate hepatocytes represent an excellent experimental model for the in vitro study of hepatic transport, and allow for important comparative studies aimed at elucidating the evolutionarily conserved nature of various hepatocyte structures amongst the vertebrates.

Actins↗
PubMed1995

Multiple sites of vanadate and peroxovanadate action in Xenopus oocytes.

In Xenopus laevis oocytes, the insulin mimics, vanadate and peroxovanadates (PV), stimulated the uptake of 3H-2-deoxyglucose and incorporation of 35S-methionine into protein. For both hexose transport and protein synthesis, peroxovanadates (produced by reacting vanadate and H2O2) were at least as potent as vanadate. Microinjection of peroxovanadates into the oocytes stimulated 2-deoxyglucose uptake. However, methionine incorporation was not stimulated by microinjection of peroxovanadate or vanadate solutions. Consistent with these results and with the possibility that vanadate and peroxovanadates enter the cell on a phosphate transporter, raising the medium phosphate concentration from 1 mM to 10 mM blocked vanadate-stimulated hexose transport and partially reduced peroxovanadates stimulation of hexose transport. Increased medium phosphate did not reduce stimulation of protein synthesis by either effector. Taken together, these data indicate that vanadate/peroxovanadates act at both intracellular and extracellular sites. Action at the former stimulates hexose uptake and action at the latter, protein synthesis.

Animals↗
PubMed1995

Magnesium-dependent stimulation of protein synthesis by the insulin mimic, pervanadate.

The insulin mimic, peroxide of vanadate (pervanadate), stimulated 35S-methionine incorporation into Xenopus oocyte protein in a Mg(2+)-dependent manner. Reducing the extracellular Mg2+ concentration from 1.0 to 0.1 mM decreased the pervanadate-stimulated component of incorporation by 35%; with 0.01 mM Mg2+ or lower, the pervanadate-stimulated component was abolished. In addition, reducing extracellular Mg2+ to 0.01 mM inhibited about 50% of the insulin-stimulated component of methionine incorporation. Mg2+ depletion had no effects on incorporation in controls or when protein synthesis was stimulated by Zn2+ or bovine growth hormone. Thus, not all substances that stimulated protein synthesis showed a dependence on extracellular Mg2+. Reducing extracellular Ca2+ had no effects on methionine incorporation in control cells or in cells stimulated by pervanadate or insulin. When oocytes maintained in a paraffin oil medium were brought into contact with a 0.5 microliter droplet of buffer containing the Mg2+ indicator dye, mag-fura-2, and pervanadate, apparent droplet Mg2+ decreased rapidly, indicating net uptake by the cells. Insulin also caused a net uptake of Mg2+. In contrast, apparent extracellular Mg2+ was constant when cells were in contact with droplets containing no effectors. Together, these data indicate that extracellular Mg2+, but not Ca2+, is involved in the stimulation of protein synthesis by pervanadate, and to a lesser extent by insulin. Pervanadate appears to induce a net uptake of Mg2+, and this change in membrane transport may be an early event in signalling the increase in translation.

Animals↗
PubMed1995

Adenovirus-based p53 gene therapy in ovarian cancer.

Mutations of the p53 tumor suppressor gene are the most common molecular genetic abnormality to be described in ovarian cancer. To determine the feasibility of mutant p53 as a molecular target for gene therapy in ovarian cancer, we constructed an adenovirus vector containing the wild-type p53 gene. The ability of this adenovirus construct (Ad-CMV-p53) to express p53 protein was examined by Western blot analysis in the H358 lung cancer cell line, which has a homozygous deletion of the p53 gene. The ability of the adenovirus vector system to infect ovarian cancer cells was tested using an adenovirus containing the beta-galactosidase reporter gene under the control of the CMV promoter (Ad-CMV-beta gal). The ovarian cancer cell line 2774, which contains an Arg273His p53 mutation, was infected with Ad-CMV-beta gal, and the infected cells were assayed for beta-galactosidase activity after 24 hr. To test the ability of wild-type p53 to inhibit cell growth, the 2774 cell line was infected with Ad-CMV-p53 or Ad-CMV-beta gal, and the effect of these agents on the growth of 2774 cells was determined using an in vitro growth inhibition assay. Western blot analysis of lysates from H358 cells infected with Ad-CMV-p53 showed expression of wild-type p53 protein. When 2774 cells were infected with Ad-CMV-beta gal at a multiplicity of infection (m.o.i.) of 10 PFU/cell, > 90% of cells showed beta-galactosidase activity, demonstrating that these cells are capable of efficient infection by the adenovirus vector. Growth of 2774 cells infected with Ad-CMV-p53 was inhibited by > 90% compared to noninfected cells. The ability of the adenovirus vector to mediate high-level expression of infected genes and the inhibitory effect of Ad-CMV-p53 on the 2774 cell line suggests that the Ad-CMV-p53 could be further developed into a therapeutic agent for ovarian cancer.

Adenoviridae↗
PubMed1995

The effect of naproxen on fever in patients with advanced gynecologic malignancies.

The antipyretic action of naproxen has been reported as sufficiently selective for neoplasm-related fever such that the use of this agent has been recommended to distinguish neoplastic from infectious fever. The antipyretic effect of naproxen was evaluated in gynecologic oncology patients with advanced pelvic malignancies and fever without obvious source of infection (suspected neoplastic fever). Naproxen (250 mg orally every 8 hr) was given to 12 patients with (i) a daily temperature greater than 38.3 degrees C, (ii) fever for at least 3 days, (iii) no evidence of infection on physical exam, (iv) negative results of blood and urine cultures, and (v) a chest roentgenogram negative for pneumonia. Ten of the 12 patients initially received a minimum of 3 days of empiric antibiotic therapy without resolution of fever. Within 24 hr of starting naproxen therapy, 10 patients' (83%) fever responded: Eight patients (80%) had a complete lysis of fever and two had partial lysis (20%). Temperature response was accompanied by subjective improvement in patient malaise and fatigue. Naproxen therapy was continued for 5-7 days in these patients, and chemotherapy was administered to those patients scheduled to receive it. Two patients did not respond to naproxen therapy in 24 hr; thus, it was stopped and the fever workup was continued. Of these two patients, one was eventually diagnosed with bacteremia after multiple negative blood cultures and initially no response to antibiotics. Naproxen is clinically useful in the palliation of fever-related symptoms in gynecologic oncology patients with suspected neoplastic fever. Naproxen may also allow the limitation of extensive fever workups and prolonged empiric antibiotic therapy in these patients, and prevent delays in systemic therapy or supportive care.

Adult↗
PubMed1995

Transfusion medicine in obstetrics and gynecology.

Obstetricians and Gynecologists care for many patients with conditions potentially requiring blood transfusions. Cesarean section and hysterectomy are the two surgeries performed most frequently and both have the potential for blood loss requiring transfusion. Other examples include postpartum hemorrhage, placenta previa, and ruptured ectopic pregnancy. Obstetricians and gynecologists need to become knowledgeable about the ever-changing aspects of blood transfusion and apply it in their clinical practice. This review intends to update obstetricians and gynecologists and other health care professionals about the basic as well as the latest technologies of blood transfusion. The different types of blood components are discussed including their preparation, indications, risks, and benefits. The complications of blood transfusion and their management are reviewed, including infections, noninfectious, and immunological etiologies. HIV and hepatitis are explored, these being the most serious infectious risks of transfusion. Autologous blood transfusion, an underutilized option, is examined. Hemodilution and intraoperative blood salvage, other techniques for using the patient's own blood, are discussed. Finally, synthetic agents such as erythropoietin, granulocyte colony-stimulating factors, factors, desmopressin acetate, gonadotropin-releasing hormone agonists, and new products are introduced as potential replacements to blood transfusion in the future.

Blood Transfusion↗
PubMed1995

The heart of aging: special challenges of cardiac ischemic disease and failure in the elderly.

The elderly are the fastest-growing segment of society, and heart disease is the single-most common cause of death in this population. In this article, age-related structural and functional changes that occur in the heart are discussed, including changes in the heart muscle, valves, conduction system and major arteries. Coronary artery disease affects half of those older than 65, resulting in acute myocardial infarction, angina pectoris, dysrhythmias, congestive heart failure and sudden death. Each of these is discussed, including altered presentation in the elderly and implications for practice derived from national and international studies.

Age Factors↗
PubMed1995

Daunomycin secretion by killfish renal proximal tubules.

Epifluorescence microscopy and video-image analysis were used to measure the uptake of the fluorescent anthracycline daunomycin by intact killifish renal proximal tubules. When tubules were incubated in medium containing 2-5 microM daunomycin, the drug accumulated in the cells and the tubular lumen. At steady state, luminal fluorescence was two to three times greater than cellular fluorescence. Luminal accumulation of daunomycin was reduced when tubules were exposed to the multidrug-resistance (MDR) transporter modifiers verapamil and cyclosporin A (CSA), but not tetraethylammonium (TEA), a model substrate for the renal organic cation transport system. NaCN and vanadate reduced luminal drug accumulation. In contrast, cellular daunomycin accumulation was not affected by verapamil, CSA, TEA, or vanadate and was only slightly reduced by NaCN. When the pH of the buffer solution was decreased from 8.25 to 7.25, luminal, but not cellular, accumulation of daunomycin was again reduced by CSA; however, TEA now reduced cellular and luminal accumulation. These findings are consistent with daunomycin being actively secreted in killifish proximal tubule by two mechanisms. At pH 8.25, daunomycin crossed the basolateral membrane by simple diffusion and was secreted into the tubular lumen by the MDR transporter. At pH 7.25, daunomycin was transported across the basolateral membrane by simple diffusion and carrier-mediated uptake on the organic cation transporter and was secreted into the lumen by the MDR transporter and the organic cation/H+ exchanger.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1995

P-glycoprotein-mediated secretion of a fluorescent cyclosporin analogue by teleost renal proximal tubules.

The transport of a fluorescent cyclosporin analogue was measured in killifish (Fundulus heteroclitus) proximal tubules by means of epifluorescence microscopy and digital image analysis. Renal cells rapidly accumulated the cyclosporin analogue from the medium and attained steady state within 60 min; luminal fluorescence increased over the first 60-90 min. At steady state, luminal fluorescence intensity was two to three times higher than cellular. Cellular fluorescence intensity was a linear function of medium substrate concentration and was not affected by any treatment used. In contrast, luminal fluorescence exhibited a saturable component as the medium concentration of the cyclosporin was increased. Secretion into the lumen was blocked by metabolic inhibitors, vanadate, other cyclosporins, such as cyclosporin A and cyclosporin G, and substrates for P-glycoprotein (verapamil, vinblastine, and quinine) but not by substrates for the renal organic anion or organic cation transport systems, such as p-aminohippurate or tetraethylammonium. The data are consistent with the fluorescent cyclosporin analogue entering proximal tubule cells by simple diffusion and then being pumped into the tubular lumen by P-glycoprotein.

ATP Binding Cassette Transporter, Subfamily B, Mem↗