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Biomedical subjects

G A Thompson

Publications and source records attributed to G A Thompson.

At least 91 records · Page 5Linked to original sources
PubMed1991

Pharmacokinetics and bioavailability of a new formulation of teicoplanin following intravenous and intramuscular administration to humans.

Pharmacokinetics, bioavailability, and local tolerance (at the site of intramuscular administration) of a new formulation of teicoplanin (400 mg/3 mL) were investigated in 24 normal, healthy, male volunteers. A single dose of 6 mg/kg was administered intravenously and intramuscularly using a randomized crossover design. Volunteers and investigator were blinded as to the route of administration; placebo was administered by the other route. Blood and urine samples were collected for 21 days and were analyzed for microbiological activity. The median (range) pharmacokinetic parameters of teicoplanin following single-dose iv administration were as follows: steady-state volume of distribution of 1.6 (1.2-2.8) L/kg; total clearance of 10.2 (8.6-15.1) mL/h/kg; renal clearance of 10.0 (7.9-13.8) mL/h/kg; and terminal disposition half-life of 168 (111-278) h. Following single-dose im administration, significantly more subjects complained of pain following administration of teicoplanin (58%) compared with placebo (4%). Teicoplanin was completely absorbed with a median (range) peak serum concentration of 12.3 (6.6-37.5) micrograms/mL occurring at a median (range) time of 4.1 (0.7-6.1) h. Since the 90% confidence interval for the ratio of areas under the serum concentration-time curve falls within the range of 80 to 120%, the extent of systemic absorption of teicoplanin following im administration is equivalent to that following iv administration.

Adult↗
PubMed1991

Normal and lysine-containing zeins are unstable in transgenic tobacco seeds.

Chimeric genes composed of the beta-phaseolin promoter, an alpha-zein coding sequence and its modified versions containing lysine codons, and a beta-zein polyadenylation signal were inserted into the genome of tobacco by Agrobacterium-mediated transformation. alpha-Zein mRNA levels in the transgenic tobacco seeds 20 days after self-pollination varied between 1.0% and 2.5% of the total mRNA population. At 25 days after pollination the 19 kDa alpha-zein was immunologically detected with a polyclonal antiserum in protein extracts from the seeds of transgenic plants. The transgenic plant with the highest level of zein gene expression had an alpha-zein content that was approximately 0.003% of the total seed protein. The amount of alpha-zein in other transgenic plants varied between 1 x 10(-4)% and 1 x 10(-5)% of the total seed protein. The differences in the amounts of mRNA and protein did not correlate with the lysine substitutions introduced into the alpha-zein protein. Polysomes translating alpha-zein mRNA isolated from tobacco seeds contained fever ribosomes than those from maize endosperm, but this did not appear to be the cause of the inefficient protein synthesis. In vivo labelling and immunoprecipitation indicated that newly synthesized alpha-zein was degraded in tobacco seeds with a half-life of less than 1 hour.

Lysine↗
PubMed1991

Diacylglycerol Metabolism in the Green Alga Dunaliella salina under Osmotic Stress : Possible Role of Diacylglycerols in Phospholipase C-Mediated Signal Transduction.

The sn-1,2-diacylglycerol (DAG) content and molecular species composition of Dunaliella salina whole cells and cell fractions were measured by complementary high performance liquid chromatography and gas chromatography techniques. At 4.2 nanomoles per 100 nanomoles lipid phosphorus, the whole cell DAG level was high in comparison with most animal tissues. The DAG concentration was highest in the microsome-enriched fraction, followed by that in the chloroplast and in the plasma membrane fractions. The predominant DAG molecular species in all cell fractions contained oleic (18:1), linoleic (18:2), or linolenic (18:3) acid in the sn-1 position and palmitate (16:0) in the sn-2 position. Recent studies have raised the possibility of DAG serving a signal transducing function in osmotically stressed D. salina cells. During the first 30 seconds following hypoosmotic shock, there was a 40% increase in the plasma membrane DAG content, whereas the DAG content of the microsome-enriched fraction was unchanged. On a nanomole per 100 nanomoles phospholipid basis, the rise in plasma membrane DAG nearly matched the previously reported (KJ Einspahr, TC Peeler, GA Thompson Jr [1988] J Biol Chem 263: 5775-5779) transient fall in phosphatidylinositol 4,5-bisphosphate. Furthermore, 18:1/16:0 DAG, one of the major plasma membrane DAG molecular species increasing in amount after hypoosmotic shock, was the characteristic molecular species of plasma membrane phosphatidylinositol, phosphatidylinositol 4-phosphate, and phosphatidylinositol 4,5-bisphosphate, but no other lipid of that membrane. Evidence was found for a rise in 16:0/18:2 and 16:0/18:3 DAG as well following hypoosmotic shock. This pattern suggested that phosphatidylcholine hydrolysis also contributed to the stress-induced production of DAG in the D. salina plasma membrane. The extent of the sudden DAG increase was sufficient to consider it a potential second messenger in phospholipase C-mediated signal transduction.

Journal Article↗
PubMed1991

Teicoplanin pharmacokinetics in intravenous drug abusers being treated for bacterial endocarditis.

The pharmacokinetics of teicoplanin were determined after multiple 30-min intravenous infusions of 10 to 15 mg/kg every 12 to 24 h in 11 intravenous drug abuse (IVDA) patients being treated for bacterial endocarditis. Multiple serum samples were obtained over 7 to 14 days. Twenty-four-hour urine collections were obtained on days 1 and 5. Serum concentration-time data were analyzed by using multiple-dose pharmacokinetic analysis (NONLIN84). Results were compared with pharmacokinetic parameters derived from previous studies in normal healthy volunteers following multiple intravenous infusions of teicoplanin (3 to 6 mg/kg/day). Total and renal clearances of teicoplanin in IVDA patients were found to be significantly greater and more highly variable than those observed previously in normal healthy volunteers. As a result, predicted steady-state trough concentrations in serum may vary up to fivefold. The mechanism responsible for this variation appears to be related to the glomerular filtration rate. In IVDA patients, individualized teicoplanin dosage may be required in the treatment of bacterial endocarditis.

Adult↗
PubMed1991

Diphenoxylate-atropine (Lomotil) overdose in children: an update (report of eight cases and review of the literature)

Eight pediatric accidental overdoses of diphenoxylate-atropine (Lomotil) are reported, and 28 literature cases are reviewed. This overdose is primarily an opioid intoxication, occasionally associated with atropine toxicity. Only 6 of 36 children showed signs of atropine overdose (central nervous system excitement, hypertension, fever, flushed dry skin). Contrary to popular belief, atropine effects occur before, during, or after opioid effects. Opioid overdose (central nervous system and respiratory depression with miosis) predominated or occurred without any signs of atropine toxicity in 33 cases (92%). Diphenoxylate-induced hypoxia was the major problem and was associated with slow or fast respirations, hypotonia or rigidity, cardiac arrest, and in 3 cases cerebral edema and death. Respiratory depression recurred 13 to 24 hours after the ingestion in 7 cases and was probably due to accumulation of difenoxine, an active metabolite of diphenoxylate. Recommended treatment is intravenous naloxone for depressed or inadequate respirations, followed by continuous intravenous naloxone infusion, prompt gastric lavage, repeated administration of activated charcoal, and close monitoring for 24 hours.

Atropine↗
PubMed1990

Action of a homogeneous hydrogenation catalyst on living Tetrahymena mimbres cells.

Various conditions were tested in an attempt to hydrogenate the unsaturated fatty acids of living Tetrahymena mimbres with the homogeneous catalyst palladium di-(sodium alizarine monosulfonate) without causing serious damage to the cells. Using a low (20 micrograms/ml) catalyst concentration in the external medium, hydrogenation of greater than 20% of surface membrane lipid double bonds were obtained, but hydrogenation of intracellular membranes was minimal. When exposed to H2, cells preincubated with inactive catalyst for several hours and visibly loaded with the catalyst lost viability as soon as hydrogenation exceeded trace levels. Material secreted by Tetrahymena into their medium effectively inhibited hydrogenation of added oleic acid, normally a good substrate. Mucus secreted by the cells, soluble proteins isolated from cell homogenates, bovine serum albumin, and cysteine were also inhibitory, but the inhibition could be overcome by employing higher catalyst concentrations. Although some enzymatic retroconversion of saturated lipids back to unsaturated lipids appeared to take place, the scale of the conversion was small, and further experimentation will be required to understand the mechanism involved. The selective hydrogenation of surface membranes achieved by these methods may be especially useful to those interested in fluidity effects on plasma membrane properties.

Animals↗
PubMed1990

Analysis of promoter activity from an alpha-zein gene 5' flanking sequence in transient expression assays.

Three DNA regions required for high levels of transcription were identified by transient gene expression analysis of the 5' flanking region of a 19 kDa alpha-zein gene. For these analyses, the zein promoter region was fused to the beta-glucuronidase (GUS) gene and assayed by transient expression in carrot protoplasts. A 107-bp sequence (-114/-8) containing the TATA box resulted in low levels of GUS activity. Addition of the proximal 75 bp (-189/-114) doubled the level of GUS expression, and a further increase in expression was obtained when additional upstream sequences (-483/-226) were placed 5' of the zein promoters. Zein upstream sequences enhanced transcription independently of the -189/-114 region. Although the -189/-114 region was not essential for transcription, it was important to obtain maximum GUS activity. A 121 bp upstream sequence (-347/-226) that contains the conserved TGTAAAG sequence gave high levels of GUS activity when placed in either orientation 5' of the zein promoter sequences. However, nucleotides -347 to -309, containing the TGTAAAG sequence, could be deleted from this fragment without a significant change in GUS activity. Zein upstream sequences did not promote transcription of the GUS gene in somatic maize protoplasts. The upstream activating sequence from the cauliflower mosaic virus (CaMV) 35S promoter placed 5' of deletion mutants of the zein promoter also failed to produce GUS activity above background.

Base Sequence↗
PubMed1990

Characterization and sequencing of the active site of 1-aminocyclopropane-1-carboxylate synthase.

The pyridoxal phosphate (PLP)-dependent 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (S-adenosyl-L-methionine methylthioadenosine-lyase, EC 4.4.1.14), the key enzyme in ethylene biosynthesis, is inactivated by its substrate S-adenosylmethionine (AdoMet). Apple ACC synthase was purified with an immunoaffinity gel, and its active site was probed with NaB3H4 or Ado[14C]Met. HPLC separation of the trypsin digest yielded a single radioactive peptide. Peptide sequencing of both 3H- and 14C-labeled peptides revealed a common dodecapeptide of Ser-Leu-Ser-Xaa-Asp-Leu-Gly-Leu-Pro-Gly-Phe-Arg, where Xaa was the modified, radioactive residue in each case. Acid hydrolysis of the 3H-labeled enzyme released radioactive N-pyridoxyllysine, indicating that the active-site peptide contained lysine at position 4. Mass spectrometry of the 14C-labeled peptide indicated a protonated molecular ion at m/z 1390.6, from which the mass of Xaa was calculated to be 229, a number that is equivalent to the mass of a lysine residue alkylated by the 2-aminobutyrate portion of AdoMet, as we previously proposed. These results indicate that the same active-site lysine binds the PLP and convalently links to the 2-aminobutyrate portion of AdoMet during inactivation. The active site of tomato ACC synthase was probed in the same manner with Ado[14C]Met. Sequencing of the tomato active-site peptide revealed two highly conserved dodecapeptides; the minor peptide possessed a sequence identical to that of the apple enzyme, whereas the major peptide differed from the minor peptide in that methionine replaced leucine at position 6.

Amino Acid Sequence↗
PubMed1990

Transmembrane Signaling via Phosphatidylinositol 4,5-Bisphosphate Hydrolysis in Plants.

Recent investigations have confirmed the presence of the polyphosphoinositides, phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate (PIP(2)), as well as inositol phospholipid-specific phospholipase C in higher plant and microalgal cells. In addition, it has been shown that stimulation of some photosynthetic cell types by environmental or hormonal challenge is accompanied by degradation of the polyphosphoinositides. The products of phospholipase C-catalyzed PIP(2) hydrolysis, inositol 1,4,5-trisphosphate and diacylglycerol, appear to be capable of releasing organelle-bound Ca(2+) and stimulating protein kinase C-like activity in vitro. However, a direct cause and effect relationship between stimulated PIP(2) breakdown and changes in intracellular calcium, protein phosphorylation, or cell function has not yet been unequivocally established. Despite a number of technical difficulties slowing progress in this field, it is likely that photosynthetic organisms will soon be shown to transmit physiologically significant extracellular signals across their plasma membranes by a PIP(2)-mediated transduction mechanism.

Journal Article↗
PubMed1990

Biphasic mortality response of chipmunks in the wild to single doses of ionizing radiation: toxicity and longevity hormesis.

Based on survivalship data from Tryon and Snyder, wild chipmunks (Tamias striatus), captured, exposed to single doses of either 200 or 400 rad ionizing radiation, and subsequently returned to their natural habitat, exhibited a biphasic response in age-specific mortality rate (omega x). On the one hand, a residuum of unrepaired toxicity (injury) appeared to persist and manifest itself throughout life (enhancement of omega x values). A second response, termed longevity hormesis (of unknown mechanism), was also observed. This phenomenon initially reduced omega x values but was reversible. A relatively simple mathematical model characterizing differences in mortality experience between control and irradiated populations was formulated and tested. Although there were some shortcomings, the model characterized the data reasonably well.

Aging↗
PubMed1989

Effect of catalytic hydrogenation of Tetrahymena ciliary phospholipid fatty acids on ciliary phospholipase A activity.

Detached Tetrahymena cilia were treated for increasing periods of time with the homogeneous hydrogenation catalyst palladium di(sodium alizarine monosulphonate). This caused a 4-70% reduction in the number of double bonds in phospholipid-bound fatty acids and a concurrent decrease in membrane fluidity as detected by ESR measurements. Ciliary phospholipase A activity was markedly inhibited when as little as 13% of the fatty acid double bonds had been hydrogenated, suggesting that the enzyme activity is very sensitive to changes in membrane fluidity.

Animals↗
PubMed1989

Structural elements regulating zein gene expression.

Zeins are a group of alcohol-soluble proteins that are synthesized in the endosperm of developing maize seeds. These proteins are encoded by a large number of genes located on several chromosomes; based upon the number of mutants that have been isolated, zein gene regulation is complex. Comparisons of gene flanking regions reveal conserved sequences that may be important for their regulation. Studies of transformed plant tissues support the assertion that cis-acting elements with the 5' flanking regions of zein genes are required for accurate transcription. Although the genes are transcribed in transgenic tobacco and petunia plants, they are not properly regulated. This appears to be due to transcriptional effects rather than protein or mRNA instability.

Base Sequence↗
PubMed1989

Membrane acclimation by unicellular organisms in response to temperature change.

Unicellular organisms possess a wide variety of molecular mechanisms for altering the lipid composition (and thereby the physical properties) of their membranes in response to changes in environmental temperature. These are discussed with a view to establish which of the mechanisms are of more importance to bacteria, algae, and protozoa in coping with extremes of temperature.

Animals↗
PubMed1989

Lipid Characterization of an Enriched Plasma Membrane Fraction of Dunaliella salina Grown in Media of Varying Salinity.

We have developed a rapid procedure for isolating a fraction enriched in plasma membrane from Dunaliella salina using an aqueous two-phase system (dextran/polyethylene glycol, 6.7%/6.7%). An enriched plasma membrane fraction, free of chloroplast and mitochondrial contamination, could be obtained in 2.5 hours. Plasma membrane proteins, which accounted for approximately 1% of the total membrane protein, contained a number of unique proteins compared with the other cell fractions, as shown by gel electrophoresis. The lipids of the plasma membrane fraction from 1.7 molar NaCl-grown cells were extracted and characterized. Phosphatidylethanolamine and phosphatidylcholine were the two most prevalent phospholipids, at 20.6% and 6.0% of the total lipid, respectively. In addition, inositol phospholipids were a significant component of the D. salina plasma membrane fraction. Phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate accounted for 5.2% and 1.5% of the plasma membrane phospholipid, respectively. Diacylglyceryltrimethylhomoserine accounted for 7.9% of the plasma membrane total lipid. Free sterols were the major component of the plasma membrane fraction, at 55% of the total lipid, and consisted of ergosterol and 7-dehydroporiferasterol. Sterol peroxides were not present in the plasma membrane fraction. The lipid composition of enriched plasma membrane fractions from cells grown at 0.85 molar NaCl and 3.4 molar NaCl were compared with those grown at 1.7 molar NaCl. The concentration of diacylglyceryltrimethylhomoserine and the degree of plasma membrane fatty acid saturation increased in 3.4 molar plasma membranes. The relative concentration of sterols in the plasma membrane fraction was similar in all three NaCl concentrations tested.

Journal Article↗
PubMed1989

Fatty Acid Acylated Proteins of the Halotolerant Alga Dunaliella salina.

The unicellular, wall-less alga Dunaliella salina has been shown to contain an array of proteins modified by the covalent attachment of fatty acids. Myristic acid (14:0) comprised approximately 80% by weight of the protein-linked acyl groups in samples derived from cells cultured in medium containing 1.7 molar NaCl and 93% in samples from cells grown in medium containing 3.0 molar NaCl. Palmitic and stearic acids accounted for most of the remaining protein-bound acyl chains. Approximately 0.2% of the incorporated radioactivity was estimated to be in linkage with protein. The bulk of acyl chains (about 99%) were resistant to cleavage by alkali, indicating a preponderance of amide bonding. The sodium dodecyl sulfate-polyacrylamide electrophoresis labeling pattern of proteins from [(3)H]myristic-labeled cells was significantly different from that of proteins from cells exposed to [(3)H]palmitate. The appearance of radioactivity in certain proteins was also influenced by the salinity of the culture medium. Thus growth in moderate (1.7 molar) salt favored the acylation of a 48-kilodalton polypeptide whereas in high (3.0 molar) salt, a 17-kilodalton polypeptide was more heavily labeled.

Journal Article↗
PubMed1989

Galactolipids of Thylakoid Pigment Protein Complexes Separated Electrophoretically from Thylakoids of Dunaliella salina Labeled with Radioactive Fatty Acids.

Experiments have been conducted to determine whether mono- and digalactosyldiacylglycerols (MGDG and DGDG) labeled by short term exposure of the green alga Dunaliella salina to exogenous radioactive lauric, myristic, or palmitic acids are preferentially recovered in one or more thylakoid protein complexes separated by electrophoresis on nondenaturing gels. A selective retention of certain lipid classes and molecular species by the major electrophoretically separable fractions, oligomeric form (LHCP-1) and monomeric form (LHCP-3) of hight-harvesting chlorophyll a/b protein complex, and major photosystem I protein complex (CPla), and nonprotein-bound lipids, was indicated. After 5 min of labeling with (3)H-palmitate the specific radioactivities of MGDG and DGDG molecular species recovered from LHCP-3 and CPla were slightly higher and lower, respectively, than specific radioactivities of equivalent molecular species from LHCP-1 and nonprotein-bound lipid. However, the differences were smaller than those which have been observed between whole thylakoids and the more highly labeled chloroplast envelopes from briefly labeled cells.

Journal Article↗
PubMed1989

Phosphatidylinositol 4,5-Bisphosphate Phospholipase C and Phosphomonoesterase in Dunaliella salina Membranes.

In comparison with other cell organelles, the Dunaliella salina plasma membrane was found to be highly enriched in phospholipase C activity toward exogenous [(3)H]phosphatidylinositol 4,5-bisphosphate (PIP(2)). Based on release of [(3)H]inositol phosphates, the plasma membrane exhibited a PIP(2)-phospholipase C activity nearly tenfold higher than the nonplasmalemmal, nonchloroplast ;bottom phase' (BP) membrane fraction and 47 times higher than the chloroplast membrane fraction. The majority of phospholipase activity was clearly of a phospholipase C nature since over 80% of [(3)H]inositol phosphates released were recovered as [(3)H]inositol trisphosphate (IP(3)). These results suggest a plausible mechanism for the rapid breakdown of PIP(2) and phosphatidylinositol 4-phosphate (PIP) following hypoosmotic shock. Quantitative analysis of major [(3)H]inositol phospholipids during these assays revealed that some of the [(3)H]-PIP(2) was converted to [(3)H]phosphatidylinositol 4-monophosphate (PIP) and to [(3)H]phosphatidyl-inositol (PI) in the BP fraction of membrane remaining after removal of plasmalemma and chloroplasts. This latter fraction is enriched more than fivefold in PIP(2)/PIP phosphomonoesterase activity when compared to the plasmalemma or chloroplast membrane fractions. We have also examined some of the in vitro characteristics of the plasma membrane phospholipase C activity and have found it to be calcium sensitive, reaching maximal activity at 10 micromolar free [Ca(2+)]. We also report here that 100 micromolar GTPgammaS stimulates phosphospholipase C activity over a range of free [Ca(2+)]. Together, these results provide evidence that the plasma membrane PIP(2)-phospholipase C of D. salina may be subject to Ca(2+) and G-protein regulation.

Journal Article↗