PubMed Health⌕ Search

Biomedical subjects

A Kallio

Publications and source records attributed to A Kallio.

At least 55 records · Page 3Linked to original sources
PubMed1989

Human ornithine decarboxylase(ODC)-encoding gene: cloning and expression in ODC-deficient CHO cells.

We have cloned a full-length human ornithine decarboxylase (ODC)-encoding gene from a genomic library of human myeloma cells which overproduce ODC due to a selective gene amplification. Correct expression of the cloned gene was assessed by transfecting it into a Chinese hamster ovary (CHO) cell mutant devoid of ODC activity. Transfection with a 10-kb BamHI DNA fragment of the genomic clone, conferred ODC activity to the recipient cells and relieved them of dependence on exogenous polyamines for growth. A set of 40 transformants was isolated, eight of which were further characterized. The transfected ODC gene appeared to be hypomethylated at the cytosine residues in the sequence CpG. The transfectants were all responsive to serum stimulation, but showed different levels of ODC expression depending on both copy number and integration site of the transfected ODC gene. ODC serum induction in the transfectants was sensitive to cycloheximide and polyamine additions, and the half-life of the enzyme was very short, like that in normal CHO cells. These results suggest that the human ODC gene we transfected contains all the elements needed for normal control of ODC expression.

Animals↗
PubMed1989

Efficient synthesis of influenza virus hemagglutinin in mammalian cells with an extrachromosomal Epstein-Barr virus vector.

The capability of an Epstein-Barr virus hybrid vector (EBV-CMV), containing the cytomegalovirus (CMV) immediate early enhancer and simian virus 40 promoter, to produce large amounts of authentic mammalian proteins was studied. The cDNA of influenza virus hemagglutinin (HA), a cell surface glycoprotein, was inserted into this vector and the EBV-CMV-HA plasmid was transfected into two human and two monkey cell lines. Southern-blot analysis revealed that the EBV-CMV-HA plasmid was maintained in extrachromosomal state and the recombinant cell clones contained on the average three copies (range 1-24) of the transfected DNA. The recombinant HA polypeptides from different cell clones, selected either randomly or by fluorescence-activated cell sorter, were analysed using immunological techniques. Three of the four cell lines expressed recombinant HA on the cell surface in glycosylated form. The highest production levels, 11.5 micrograms/10(6) cells, were obtained in HeLa cells containing only two copies of EBV-CMV-HA DNA per cell. The protein levels correlated with the mRNA levels in Northern-blot analysis. A corresponding vector, containing the same regulatory signals for HA expression, but lacking the EBV sequences, yielded clones with significantly lower expression levels. The results confirm that the extrachromosomal EBV-CMV vector is very useful in the production of apparently authentic mammalian glycoproteins.

Animals↗
PubMed1989

Effects of dexmedetomidine, a selective alpha 2-adrenoceptor agonist, on hemodynamic control mechanisms.

Dexmedetomidine, a selective alpha 2-adrenoceptor agonist, was administered to five healthy male volunteers in single intravenous doses of 12.5, 25, 50, and 75 micrograms as part of a placebo-controlled study. The drug caused dose-dependent decreases in systolic and diastolic blood pressure. A small initial hypertensive response was observed after injection of the two highest doses. Heart rate was decreased. The concentration of norepinephrine in plasma was decreased significantly (by up to 92%), and the decrease was dose-dependent. No significant drug-induced alterations were observed in plasma renin activity or in the concentrations of atrial natriuretic peptide and arginine vasopressin in plasma. Other drug effects included dose-dependent impairment of vigilance and stimulation of growth hormone secretion. Plasma cortisol levels were unaffected. Dexmedetomidine is a potentially useful tool for studies of the physiology and pharmacology of alpha 2-adrenoceptors in human beings and may have therapeutic applications in clinical conditions in which sedative and sympatholytic effects are considered beneficial, such as premedication for anesthesia and surgery.

Adrenergic alpha-Agonists↗
PubMed1989

Pharmacological effects of medetomidine in humans.

Single i.v. doses of medetomidine have been administered to healthy male volunteers in three clinical phase I studies. After an initial open dose-finding study, double-blind, placebocontrolled designs were used. The highest dose tested was 120 micrograms. Medetomidine was well tolerated. It caused dose-dependent decreases of blood pressure (max 22/14 mmHg), heart rate (max 14/min) and cardiac output (max 21%) without subjective sensations of hemodynamic changes or other unexpected side-effects. However, a clear dose-dependent sedative effect, both subjective and objective, and a decrease in salivation was seen after single i.v. doses. Medetomidine had a powerful and dose-dependent effect in reducing noradrenaline (by a maximum of 75%) and increasing human growth hormone levels in plasma. All the observed pharmacological effects are well compatible with an alpha 2-agonistic action of the drug and resemble those seen after i.v. administration of clonidine. However, medetomidine appeared to be more potent and short-acting than clonidine.

Adrenergic alpha-Agonists↗
PubMed1988

An EBV-based mammalian cell expression vector for efficient expression of cloned coding sequences.

The construction of a mammalian cell expression vector using human cytomegalovirus immediate early gene enhancer to initiate transcription of inserted coding sequences is described. The vector also carries Epstein-Barr virus EBNA-1 nuclear antigen gene, ori-P sequences and hygromycin B resistance gene hph from E. coli. The expression capacity of this construct was tested by inserting the chloramphenicol acetyltransferase (CAT) gene into the vector. The EBV-CAT construct was transfected into various cell lines and high levels of CAT activity were obtained in human and monkey cells. In these cells, the vector DNA also replicates as an extrachromosomal element having 1 to 20 copies per cell. In most cases, the vector copy number and the expression level of inserted gene was in positive correlation in different cell clones.

Acetyltransferases↗
PubMed1988

Comparison of mammalian cell expression vectors with and without an EBV-replicon.

We have characterized the properties of an Epstein-Barr virus vector (EBV-CMV) and compared its expression potential with a respective integrating vector (CMV). These vectors were used to express chloramphenicol acetyltransferase (CAT) gene in human HeLa, 293, monkey CV-1, dog MDCK, and hamster R 1610 cells. The EBV-CMV-cat DNA replicates extrachromosomally in HeLa, 293 and CV-1 cells, where also high expression of CAT gene was observed. The EBV-CMV vector integrated in MDCK and R 1610 cells and the CMV vector integrated in all cells tested. Integration yielded mostly clones with low CAT expression. In all cell lines, except HeLa cells, the existence of the extrachromosomal but not the integrated vector DNA is strictly dependent on the Hygromycin B selection pressure. The extrachromosomal state of the EBV vector is a prerequisite for good expression particularly in human and monkey cells.

Animals↗
PubMed1988

Acute effects of medetomidine, a selective alpha 2-adrenoceptor agonist, on anterior pituitary hormone and cortisol secretion in man.

Single iv doses (25, 50 and 100 micrograms) of medetomidine, a selective alpha 2-adrenoceptor agonist of the imidazole type, were administered to 8 healthy male volunteers in a randomized, double-blind, placebo-controlled study. The concentration of hGH in plasma was powerfully and dose-dependently increased. The plasma level of cortisol was dose-dependently decreased, whereas TSH showed a slight but statistically significant increase. Plasma levels of PRL, FSH and LH were unaffected by the drug. Medetomidine appears to resemble other alpha 2-adrenoceptor agonists, notably clonidine, in its endocrine effects. Its high selectivity and short duration of action make it a suitable tool for studies of the physiology and pharmacology of alpha 2-adrenoceptors in man.

Adrenergic alpha-Agonists↗
PubMed1987

Sedative and cardiovascular effects of medetomidine, a novel selective alpha 2-adrenoceptor agonist, in healthy volunteers.

1. Single intravenous doses (25, 50 and 100 micrograms) of medetomidine (MPV-785, an imidazole derivative), a selective alpha 2-adrenoceptor agonist, were administered to eight healthy male volunteers in a double-blind, placebo-controlled study. 2. The following dose-related effects, all of which were compatible with an agonistic action of the drug at alpha 2-adrenoceptors, were noted: reductions of systolic and diastolic blood pressure (maximum 18/11 mm Hg), heart rate (maximum 10 beats min-1), saliva secretion (maximum 84%) and noradrenaline levels in plasma (maximum 70%). 3. Dose-dependent sedation or impairment of vigilance was also observed, both by subjective and objective (critical flicker fusion threshold) assessments, with the highest dose actually inducing sleep in five of the subjects. 4. The observed effects were in general agreement with those previously seen after intravenous administration of the centrally acting antihypertensive alpha 2-adrenoceptor activating drug, clonidine, but of a shorter duration. 5. The relative importance of alpha 2-adrenoceptors located in peripheral tissues and in the central nervous system for the drug's cardiovascular effects could not be determined, but the high lipid solubility of the compound and the rapid onset of sedation are in favour of a major central component. 6. Medetomidine may be a useful tool for the investigation of the physiology and pharmacology of alpha 2-adrenoceptors in man. In addition, the therapeutic and diagnostic uses of the compound should be investigated in pathological conditions related to increased sympathetic neuronal activity.

Adrenergic alpha-Agonists↗
PubMed1985

Tumourigenicity, cell-surface glycoprotein changes and ornithine decarboxylase gene pattern in Ehrlich ascites-carcinoma cells.

We selected a 2-difluoromethylornithine-resistant Ehrlich ascites-carcinoma cell line that grows in the presence of 20 mM-difluoromethylornithine. These cells contain 10-20 times the normal amount of hybridizable sequences for ornithine decarboxylase (EC 4.1.1.17) in their genomic DNA. We used these gene-amplified cells, their revertant counterparts (grown in the absence of the drug after an established gene amplification) and tumour cells grown in the presence of putrescine to investigate the changes of ornithine decarboxylase gene pattern and simultaneously occurring phenotypic changes, such as tumourigenicity and the expression of cell-surface glycoproteins. In the tumour cells reverted back to the normal gene frequency, not only did the amplified sequences disappear, but there were also signs of gene re-arrangements seen as a "gene jump', when a signal evidently moved to a heavier restriction fragment. Similar gene re-arrangement likewise occurred in cells exposed to putrescine. Although the wild-type tumour cells and the gene-amplified cells readily grew in the peritoneal cavity of mice, the revertant cells and the putrescine-treated cells had lost their tumourigenicity in mice. Gene-amplified tumour cells and the revertant cells showed distinct changes in their surface glycoprotein pattern in comparison with the parental cell line. These findings indicate that alterations of ornithine decarboxylase gene pattern/dosage may be associated with phenotypic changes possibly related to the tumourigenicity of these carcinoma cells.

Animals↗
PubMed1985

Difluoromethylornithine-induced amplification of ornithine decarboxylase genes in Ehrlich ascites carcinoma cells.

Stepwise increments of the concentration of 2-difluoromethylornithine, a mechanism-based irreversible inhibitor of mammalian ornithine decarboxylase (EC 4.1.1.17), resulted in a selection of cultured Ehrlich ascites carcinoma cells capable of growing in the presence of up to 50 mM difluoromethylornithine. Dialyzed extracts of drug-resistant tumor cells exhibited a very high ornithine decarboxylase activity and contained large excess of immunoreactive ornithine decarboxylase protein. Hybridization analyses with cloned complementary DNA revealed that the difluoromethylornithine-resistant tumor cells also expressed mRNA of the enzyme at greatly enhanced rate. The overproduction of ornithine decarboxylase by the tumor cells grown under the pressure of difluoromethylornithine was at least partly attributable to a 10 to 20-fold increase in the total gene dosage of ornithine decarboxylase involving an amplification of several genes of the gene family. The gene amplification developed appeared to be stable, as the gene dosage only slowly (during a period of several months) returned towards the normal level upon the removal of difluoromethylornithine. The overproduction of ornithine decarboxylase was accompanied by an enhanced resistance of the enzyme towards difluoromethylornithine in vitro.

Animals↗
PubMed1984

Differential effects of 2-difluoromethylornithine and methylglyoxal bis(guanylhydrazone) on the testosterone-induced growth of ventral prostate and seminal vesicles of castrated rats.

2-Difluoromethylornithine totally prevented any increases in putrescine and spermidine concentrations in the ventral prostate of castrated rats during a 6-day testosterone treatment. Prostatic ornithine decarboxylase activity was inhibited by 80%, whereas S-adenosylmethionine decarboxylase was stimulated by more than 9-fold. In seminal vesicle, the inhibition of putrescine and spermidine accumulation, as well as of ornithine decarboxylase activity, was only minimal, and no stimulation of S-adenosylmethionine decarboxylase was observed. Administration of methylglyoxal bis(guanylhydrazone) to castrated androgen-treated rats resulted in a marked increase in concentrations of all prostatic polyamines. Prostatic ornithine decarboxylase activity was nearly 2 times and adenosylmethionine decarboxylase activity 9 times higher than that of the testosterone-treated animals. In contrast with ventral prostate, methylglyoxal bis(guanylhydrazone) treatment inhibited moderately the accumulation of spermidine and spermine in seminal vesicle, although both ornithine decarboxylase and S-adenosylmethionine decarboxylase activities were stimulated. Difluoromethylornithine inhibited significantly the weight gain of ventral prostate, but methylglyoxal bis(guanylhydrazone) produced a substantial increase in prostatic weight. These changes were largely due to the fact that the volume of prostatic secretion was greatly decreased by difluoromethylornithine, whereas methylglyoxal bis(guanylhydrazone) increased the amount of secretion. Treatment with difluoromethylornithine strikingly increased the methylglyoxal bis(guanylhydrazone) content of both ventral prostate and seminal vesicle, but even under these conditions the drug concentration remained low in comparison with other tissues. The results indicate that a combined use of these two polyamine anti-metabolites does not necessarily result in a synergistic growth inhibition of the androgen-induced growth of male accessory sexual glands.

Animals↗
PubMed1984

Transfer of intestine-derived diamines into tumour cells during treatment of Ehrlich-ascites--carcinoma-bearing mice with polyamine anti-metabolites.

Treatment of Ehrlich-ascites-carcinoma-bearing mice with methylglyoxal bis(guanylhydrazone) alone or in combination with 2-difluoromethylornithine greatly enhanced the transfer of intragastrically administered radioactive putrescine and cadaverine into the carcinoma cells. Difluoromethylornithine alone did not have any effect on the accumulation of intestine-derived diamines in the tumour cells. The frequently reported restoration of difluoromethylornithine-induced polyamine depletion on administration of methylglyoxal bis(guanylhydrazone) is in all likelihood attributable to a profound inhibition of intestinal diamine oxidase (EC 1.4.3.6), resulting in an enhanced entry of intestinal (bacterial) diamines into general circulation and finally into tumour cells.

Animals↗
PubMed1983

Role of diamine oxidase during the treatment of tumour-bearing mice with combinations of polyamine anti-metabolites.

Treatment of mice bearing L1210 leukaemia with 2-difluoromethylornithine, a specific inhibitor of ornithine decarboxylase (EC 4.1.1.17), produced a profound depletion of putrescine and spermidine in the tumour cells. Sequential combination of methylglyoxal bis(guanylhydrazone), an inhibitor of adenosylmethionine decarboxylase (EC 4.1.1.50), with difluoromethylornithine largely reversed the polyamine depletion and led to a marked accumulation of cadaverine in the tumour cells. Experiments carried out with the combination of difluoromethylornithine and aminoguanidine, a potent inhibitor of diamine oxidase (EC 1.4.3.6), indicated that the methylglyoxal bis(guanylhydrazone)-induced reversal of polyamine depletion was mediated by the known inhibition of diamine oxidase by the diguanidine. In spite of the normalization of the tumour cell polyamine pattern upon administration of methylglyoxal bis(guanylhydrazone) to difluoromethylornithine-treated animals, the combination of these two drugs produced a growth-inhibitory effect not achievable with either of the compounds alone.

Amine Oxidase (Copper-Containing)↗
PubMed1983

Role of polyamines and their antimetabolites in clinical medicine.

Polyamine research, which began with a clinical observation more than 300 years ago, has progressed for several decades as pure basic research, sometimes considered as an academic triviality. The role of polyamines in clinical medicine is coming of age. The fruits of polyamine research are just now entering into the realm of practical application and in a very multidisciplinary manner. Basic research on polyamine metabolism and the elucidation of their physiologic functions has involved many academically interesting, even revolutionary, aspects, but the imagination of biochemists and cell biologists may no longer be sufficient to discover the best ways to translate the results of this basic research into clinical practice. It is almost certain that polyamine antimetabolites will soon find their place among the drug regimens used for the treatment of human malignancies and, possibly, also of hyperproliferative skin diseases. The elucidation of the role of polyamines in cell differentiation may offer fundamental applications regarding the regulation of cell cycle events. The discovery of the antiparasitic properties of polyamine antimetabolites may have a major impact on the well-being of millions of people in the developing world. The potential application of polyamine research in microbial and viral diseases is an area in which investigational insight is just beginning. Finally, the clinical chemistry of extracellular polyamines, although initially disappointing, has not yet been explored in depth and may offer applications useful for the diagnosis or follow-up of a variety of common diseases.

Animals↗
PubMed1983

Modulation of the tissue disposition of methylglyoxal bis(guanylhydrazone) in mice by polyamine depletion and by polyamine administration.

Treatment of mice with DL-alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase (EC 4.1.1.17), produced a significant spermidine depletion in liver, small intestine, and bone marrow among eight tissues studied. The accumulation of methylglyoxal bis(guanylhydrazone) (MGBG) was selectively enhanced in small intestine and in bone marrow cells in response to a prior DFMO treatment. In other tissues studied, i.e., brain, skeletal and cardiac muscle, liver, kidney, and spleen, a preceding treatment with DFMO had no effect on the accumulation of subsequently injected MGBG. When mice, primed with DFMO and then treated with a single injection of MGBG, were given nontoxic doses of spermidine or putrescine through a gastric tube, high concentrations of MGBG in the small intestine and in bone marrow cells were effectively reduced. In spite of the route of administration, bone marrow cells appeared to be more sensitive than intestinal tissue as regards the prevention of the tissue accumulation of MGBG by the polyamines. The different sensitivity of various tissues to the natural polyamines in this respect may offer a means to develop a tissue-specific "polyamine rescue concept" to be used in connection with MGBG treatment.

Animals↗