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Biomedical subjects

M E Anderson

Publications and source records attributed to M E Anderson.

At least 91 records · Page 5Linked to original sources
PubMed1995

Controlling influence of phosphocitrate in vitro and in vivo on calcium oxalate crystal formation and growth.

Calcium oxalate (CaOx) crystallization in the presence of phosphocitrate (PC) was studied by both in vitro and in vivo techniques. Crystals of the monohydrate (COM) and the dihydrate (COD) forms were generated under controlled conditions in a silica gel matrix. Our data indicated only COD crystals formed when PC was present, inferring that the COD to COM transformation was being impeded. COD crystals were smaller in size than controls and there was evidence of interpenetral twinning. An in vivo study using a rat bladder implant model noted similar findings. Scanning electron microscopy (SEM) revealed that implants recovered from PC treated rats had primarily COD crystals deposited, whereas both the surface and inner layers of encrusted implants from normal rats contained predominantly COM crystals. Infrared (IR) analysis confirmed the visual findings indicating quantitatively that there was a higher proportion of COD present on the implants recovered from the treated rats than in the controls. It is concluded that although total CaOx crystallization cannot be eliminated by PC, its action could assist in reducing the harmful nature of such crystallites in the urine.

Animals↗
PubMed1994

Features of targeted arm movement after unilateral excisions that included the supplementary motor area in humans.

The strategies used to make rapid targeted flexion movements at the elbow were assessed for the right and left arms of ten neurologically normal subjects and seven patients who had unilateral cortical resections that included all or part of one supplementary motor area (SMA). Visual targets were displaced either a constant distance (fixed step task) or a variable distance (variable step task). The reaction time (RT) for SMA patients as a group did not differ significantly from normal, although for some patients, RT exceeded the normal range bilaterally. Total movement time (TMT) was longer than normal for the SMA group, and again, increased TMTs tended to occur bilaterally. Both groups of subjects used a combination of duration and velocity scaling to adjust movement amplitude. In normal subjects, however, velocity scaling predominated, whereas in SMA patients, duration scaling was increased bilaterally. Our data indicate that the initiation of rapid elbow movement to a target presented visually is not consistently delayed after lesions that include part of the SMA, but the movement speed and strategy used to adjust movement amplitude may be changed bilaterally.

Adult↗
PubMed1994

Organization of clusters and internal electron pathways in CO dehydrogenase from Clostridium thermoaceticum: relevance to the mechanism of catalysis and cyanide inhibition.

Cyanide inhibits the CO oxidation activity of carbon monoxide dehydrogenase from Clostridium thermoaceticum by binding tightly to the form of the C-cluster yielding the gav = 1.82 signal (the C1.82 form). CN- dissociates and the enzyme reactivates upon addition of CO, CO2 plus dithionite, or CS2 plus dithionite. Dithionite slows the inhibition of the enzyme by CN-, but it cannot reactivate the enzyme. This behavior is explained by assuming that binding of CO, CO2, or CS2 at a modulator site accelerates the dissociation of CN- from the C-cluster. With CN- bound at the C-cluster, dithionite, but not CO, can reduce those Fe-S clusters in the enzyme whose redox status can be monitored at 420 nm. The electron pathway used for CO oxidation appears to be as follows: C-cluster-->Fe-S Clusters-->external electron acceptors. The electron used to reduce the NiFe complex originates predominantly from the C-cluster, and this reduction is inhibited when CN- is bound at the C-cluster. The NiFe complex is reduced more slowly (in the absence of CN-) than CO is catalytically oxidized, indicating that this reduction is not part of the catalytic mechanism for CO oxidation. The form of the C-cluster yielding the g(av) = 1.86 signal (C1.86) is proposed to be two electrons more reduced than C1.82 and able to bind and reduce CO2. CO is proposed to be oxidized by C1.82. Neither CO or CN- appears to bind C1.86.

Aldehyde Oxidoreductases↗
PubMed1994

Presence of Epstein-Barr virus in many types of benign and malignant lymphoid lesions. Detection by polymerase chain reaction and in situ hybridization.

Epstein-Barr virus (EBV) has been detected in African Burkitt's lymphoma, posttransplant lymphoproliferative disease, and a variable fraction of Hodgkin's lymphomas. To assess if EBV is associated with other lymphoid proliferations, we evaluated a wide variety of benign and malignant lymphoid lesions, using polymerase chain reaction and a sensitive in situ hybridization method. Abundant EBV+ cells were seen in posttransplant lymphomas, some B cell immunoblastic lymphomas, and in tonsils from patients with infectious mononucleosis. Intermediate numbers of EBV+ cells were seen in a mixed B cell lymphoma, peripheral T cell lymphomas, and in syncytial variants of Hodgkin's disease as well as a lymph node from a patient with infectious mononucleosis. Low numbers of EBV+ cells were detected in normal and reactive lymph nodes, B and T cell lymphomas, and Hodgkin's lymphomas. The variable extent of EBV infection in lymphoid lesions suggests that EBV may play a variety of roles in the development of malignant and nonmalignant lymphoid lesions.

Base Sequence↗
PubMed1994

p53 domains: structure, oligomerization, and transformation.

Wild-type p53 forms tetramers and multiples of tetramers. Friedman et al. (P. N. Friedman, X. B. Chen, J. Bargonetti, and C. Prives, Proc. Natl. Acad. Sci. USA 90:3319-3323, 1993) have reported that human p53 behaves as a larger molecule during gel filtration than it does during sucrose gradient sedimentation. These differences argue that wild-type p53 has a nonglobular shape. To identify structural and oligomerization domains in p53, we have investigated the physical properties of purified segments of p53. The central, specific DNA-binding domain within murine amino acids 80 to 320 and human amino acids 83 to 323 behaves predominantly as monomers during analysis by sedimentation, gel filtration, and gel electrophoresis. This consistent behavior argues that the central region of p53 is globular in shape. Under appropriate conditions, however, this segment can form transient oligomers without apparent preference for a single oligomeric structure. This region does not enhance transformation by other oncogenes. The biological implications of transient oligomerization by this central segment, therefore, remain to be demonstrated. Like wild-type p53, the C terminus, consisting of murine amino acids 280 to 390 and human amino acids 283 to 393, behaves anomalously during gel filtration and apparently has a nonglobular shape. Within this region, murine amino acids 315 to 350 and human amino acids 323 to 355 are sufficient for assembly of stable tetramers. The finding that murine amino acids 315 to 360 enhance transformation by other oncogenes strongly supports the role of p53 tetramerization in oncogenesis. Amino acids 330 to 390 of murine p53 and amino acids 340 to 393 of human p53, which have been implicated by Sturzbecher et al. in tetramerization (H.-W. Sturzbecher, R. Brain, C. Addison, K. Rudge, M. Remm, M. Grimaldi, E. Keenan, and J. R. Jenkins, Oncogene 7:1513-1523, 1992), do not form stable tetramers under our conditions. Our findings indicate that p53 has at least two autonomous oligomerization domains: a strong tetramerization domain in its C-terminal region and a weaker oligomerization domain in the central DNA binding region of p53. Together, these domains account for the formation of tetramers and multiples of tetramers by wild-type p53. The tetramerization domain is the major determinant of the dominant negative phenotype leading to transformation by mutant p53s.

Animals↗
PubMed1994

Magnesium attenuates pulmonary hypertension due to hypoxia and group B streptococci.

We investigated whether hypermagnesemia alleviates hypoxic or group B streptococcal (GBS) pulmonary hypertension (PH). Hypoxic PH was induced and maintained in 14 lambs by continuous ventilation with 12% oxygen. GBS PH was induced and maintained in 16 lambs by the continuous infusion of 5-10 x 10(8) colony-forming units.kg-1.h-1 of GBS. After the onset of PH, lambs were randomized to receive either magnesium sulfate (MgSO4, intermittent boluses of 0.38 mmol/kg, with a continuous infusion of 0.15 mmol.kg-1.h-1) or a similar volume of normal saline. Hypermagnesemia lowered pulmonary arterial pressure (PAP) and delayed the fall in systemic arterial pressure and stroke volume index seen in the control animals (each P < 0.05). At a serum magnesium concentration ([Mg]) of 2.75 +/- 0.25 mmol/l, PAP was 27 +/- 3 compared with 40 +/- 4 Torr in the control animals ([Mg] = 0.87 +/- 0.06 mmol/l; P < 0.05). In the GBS PH trial, hypermagnesemia prevented the continued increase in PAP seen in the control animals. At [Mg] = 2.15 +/- 0.07 mmol/l, PAP fell 2 +/- 1 Torr from prerandomization values, whereas it rose 4 +/- 2 Torr in the control animals ([Mg] = 0.59 +/- 0.07 mmol/l; P < 0.05). However, during the same time the systemic arterial pressure fell further in the magnesium-treated animals (-19 +/- 1 vs. -2 +/- 5 Torr). MgSO4 attenuates PH in both models but may cause systemic hypotension in sepsis.

Animals↗
PubMed1994

Nitrate tolerance in vivo is not associated with depletion of arterial or venous thiol levels.

Results from in vitro experiments suggest that development of nitrate tolerance is due to a depletion of vascular thiol compounds (ie, cysteine and glutathione [GSH]) necessary for the bioconversion of organic nitrates. However, it is unknown whether in vivo tolerance development is associated with changes in thiol levels. This study measures plasma and vessel tissue GSH and cysteine levels in nontolerant rats, nitrate-tolerant rats, and rats treated with the two characteristically different thiol donors N-acetyl-L-cysteine and L-2-oxothiazolidine-4-carboxylic acid (OXO). Chronically catheterized conscious rats received an intravenous infusion of either nitroglycerin (NTG, 0.2 mg/h) or matching placebo for 3 days. At day 3, the hypotensive effect of 2.5 mg NTG/kg was decreased by 74 +/- 6% (mean +/- SEM, P < .05) in the NTG-treated group (n = 7), indicating the development of tolerance. No change in the hypotensive effect of NTG was seen in the placebo group (n = 6, P > .05). Hemodynamic tolerance is not associated with changes in aorta cysteine or GSH levels as compared with the placebo group (cysteine, 77 +/- 14 versus 57 +/- 11 [mean + SEM] nmol/g; GSH, 414 +/- 62 versus 399 +/- 89 nmol/g; P > .05). However, the increase in vascular thiol levels seen after OXO treatment in nontolerant rats is completely absent in nitrate-tolerant animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcysteine↗
PubMed1994

Multifunctional Ca2+/calmodulin-dependent protein kinase mediates Ca(2+)-induced enhancement of the L-type Ca2+ current in rabbit ventricular myocytes.

The intracellular mechanism underlying the Ca(2+)-induced enhancement of the L-type Ca2+ current (ICa) was examined in adult rabbit cardiac ventricular myocytes by using patch-clamp methodology. Internal Ca2+ was elevated by flash photolysis of the Ca2+ chelator Nitr 5, and intracellular Ca2+ levels were simultaneously monitored by Fluo 3 fluorescence. Flash photolysis of Nitr 5 produced a rapid (< 1-second) elevation of internal Ca2+, which led to enhancement (39% to 51% above control) of the peak inward Ca2+ current after a delay of 20 to 120 seconds. Internal dialysis of myocytes with synthetic inhibitory peptides derived from the pseudosubstrate (peptide 273-302) and calmodulin binding (peptide 291-317) regions within the regulatory domain of multifunctional Ca2+/calmodulin-dependent protein kinase (CaM kinase) blocked enhancement of ICa produced by elevation of internal Ca2+ but not that produced by beta-adrenergic stimulation. These inhibitory peptides also had no effect on the elevation of internal Ca2+ produced by flash photolysis of Nitr 5. A pseudosubstrate inhibitory peptide derived from protein kinase C had no significant effect on Ca(2+)-dependent enhancement of ICa. We conclude that CaM kinase mediates the Ca(2+)-induced enhancement of ICa in mammalian cardiac myocytes by a mechanism likely involving direct phosphorylation of the L-type Ca2+ channel complex or an associated regulatory protein.

Aniline Compounds↗
PubMed1994

The battle for Hue: casualty and disease rates during urban warfare.

Renewed nationalism with the ending of the Cold War has precipitated numerous conflicts between regions or countries that were formerly united. Hostilities between some ethnic and nationalistic factions have reached the point where regional security is threatened and United Nations-sanctioned military operations may be required. Because some U.N. operations could require the forcible removal of an entrenched faction from an urban setting, the present investigation seeks to determine the levels of medical casualties that might be sustained during urban warfare. Casualty rates and illness incidence were examined for U.S. Marine forces participating in the retaking of the city of Hue during the Tet offensive in 1968. The casualty rates were analyzed for different phases of the urban assault and contrasted with a different period of the Vietnam Conflict, and with the high intensity battle for Okinawa during World War II. Rates of casualties during the retaking of Hue were highest during the two phases of the operation that required close-quarter fighting. The house-to-house fighting south of the river yielded a wounded rate of 37.9 per 1,000 strength per day, while the fighting in the inner city yielded a rate of 44.4. Rate of wounded during the "mopping-up" phase was 5.8. The rate of illness incidence was stable over the month-long operation and showed no concomitant increase with battle intensity."

Humans↗
PubMed1993

Transport of glutathione diethyl ester into human cells.

Glutathione monoesters in which the carboxyl group of the glycine residue is esterified were previously found, in contrast to glutathione itself, to be effectively transported into various types of cells and to be converted intracellularly into glutathione. Glutathione monoesters are thus useful for prevention of oxidative stress, certain toxicities, and for treatment of glutathione deficiency. Glutathione diethyl ester is rapidly split to the glutathione monoethyl ester by mouse plasma glutathione diester alpha-esterase activity. Thus, as expected, glutathione mono- and diesters have similar effects on cellular glutathione levels in mice. However, human plasma lacks glutathione diester alpha-esterase; thus, it became of interest to compare the transport properties of glutathione mono- and diesters in human cells. We found that human cells (erythrocytes, peripheral blood mononuclear cells, fibroblasts, ovarian tumor cells, and purified T cells) transport glutathione diethyl ester much more effectively than the corresponding monoethyl (glycyl) ester. Human cells rapidly convert glutathione diethyl ester to the monoester, whose intracellular levels rise to levels that are significantly higher than levels found after application of the monoester to the cells. High levels of the monoester provide the cells with a means of producing glutathione over a period of time. We conclude that glutathione diethyl ester is highly effective as a delivery agent for glutathione monoester, and thus for glutathione, in human cells and therefore could serve to decrease oxidative stress and toxicity. Hamster (and certain other animals) also lack plasma glutathione diester alpha-esterase and therefore would be suitable animal models. Previously reported toxicity of certain glutathione ester preparations appears to reflect the presence of impurities rather than effects of the esters.

Animals↗
PubMed1993

Amino acid sequence and function of the light subunit of rat kidney gamma-glutamylcysteine synthetase.

The heavy subunit (M(r), 72,614) of rat kidney gamma-glutamylcysteine synthetase, the enzyme that catalyzes the first step of glutathione (GSH) synthesis, mediates the catalytic activity of this enzyme and its feedback inhibition by GSH. There is evidence that the light subunit has a regulatory function (Huang, C.-S., Chang, L.-S., Anderson, M.E., and Meister, A. (1993) J. Biol. Chem. 268, 19675-19680). In the present work the cDNA for the light subunit was isolated, sequenced, and expressed in Escherichia coli. The cDNA was found to code for a protein of 274 amino acid residues (M(r) 30, 548). Recombinant holoenzyme was obtained by co-expression of the heavy and light subunits and by mixing of the separately expressed proteins. These recombinant holoenzyme preparations exhibit catalytic and GSH feedback inhibitory properties that are virtually identical to those of the isolated holoenzyme. These studies establish that the light subunit is an integral part of the enzyme and that the light and heavy subunits, are coded for separately. Possibly significant similarity of sequence of amino acids was found between the light subunit and E. coli gamma-glutamylcysteine synthetase, which is a single polypeptide.

Amino Acid Sequence↗
PubMed1993

Catalytic and regulatory properties of the heavy subunit of rat kidney gamma-glutamylcysteine synthetase.

gamma-Glutamylcysteine synthetase (rat kidney), which catalyzes the first step of GSH synthesis, can be dissociated into subunits (M(r) 73,000 and 27,700) by native gel electrophoresis after treatment with dithiothreitol (DTT); the heavy subunit, which exhibits catalytic activity and feedback inhibition by GSH (Seelig, G. F., Simondsen, R. P., and Meister, A. (1984) J. Biol. Chem. 259, 9345-9347), was cloned and sequenced (Yan, N., and Meister, A. (1990) J. Biol. Chem. 265, 1588-1593). Here, the cDNA for the heavy sub unit was expressed in Escherichia coli, and the recombinant enzyme was separated from E. coli gamma-glutamylcysteine synthetase and purified. The recombinant enzyme and the isolated heavy subunit have much lower affinity for glutamate and higher sensitivity to GSH inhibition than the holoenzyme, suggesting that the heavy subunit alone would not be very active in vivo. A GSH analog, gamma-Glu-alpha-aminobutyryl-Gly (ophthalmic acid), inhibits only slightly, but inhibits much more after treatment of the holoenzyme with DTT. In contrast, ophthalmic acid inhibits the recombinant and isolated heavy subunit enzymes substantially without DTT treatment. We conclude that (a) the light subunit has a regulatory function affecting the affinity of the enzyme for glutamate and GSH and (b) feedback inhibition by GSH involves reduction of the enzyme and also competition between GSH and glutamate for the glutamate site.

Animals↗
PubMed1993

A perifusion loop-gap resonator NMR probe for aerobic cell suspensions.

NMR studies of aerobic cell metabolism require that spectral data of high sensitivity and resolution be acquired from samples maintained under suitable conditions. The loop-gap resonator 31P NMR probe described here was designed for investigations of highly aerobic-dependent renal proximal tubules in an environment similar to those of conventional incubation flasks. The inherently higher sensitivity of the loop-gap resonator design and associated circuitry made it possible to obtain adequate spectra in short periods of time with small amounts of sample. Cellular physiological properties of perifused aerobic renal proximal tubule cell suspensions in the loop-gap resonator probe were found to be similar to equivalent tissue samples incubated in conventional flasks. Furthermore, the loop-gap perifusion probe was found to provide useful 31P NMR spectra of the kidney tubule system after acquisition times as short as 3 min.

Aerobiosis↗
PubMed1993

On the synthesis and characterization of N-formyl glutathione and N-acetyl glutathione.

Treatment of glutathione (GSH) with formic acid and acetic anhydride leads to preparation of crystalline N-formyl GSH. This is the first characterized preparation of N-formyl GSH; this product was previously erroneously thought to be N-acetyl GSH. Authentic N-acetyl GSH (crystalline) was prepared by treating GSH with acetic acid and acetic anhydride. The N-acylated derivatives were characterized by 1H NMR and mass spectroscopy.

Acetic Anhydrides↗
PubMed1993

A versatile perifusion system for the NMR spectroscopy of bovine retina. Assignment of resonances and effect of ischemia.

A perifusion system has been designed for metabolic nuclear magnetic resonance (NMR) spectroscopy studies of the bovine retina. This system, which allows the use of unmodified commercial probes for multinuclear studies, is shown here to maintain the perifused retina in a metabolic steady state at 25 degrees C, as deduced from its 31P and 1H NMR spectra. The 31P NMR ex vivo spectrum of the retina has been characterized, and its major resonances have been assigned in tissue extracts. We have found that excised retinal tissue subjected to 2 hr of ischemia is capable, upon perifusion with oxygenated medium, of recovering its resting spectral pattern. Thus, this system offers a versatile model for studies of physiological events related with ischemia in a neural tissue, without associated systemic effects.

Animals↗