Search PubMed⌕ Search

Biomedical subjects

P Leinonen

Publications and source records attributed to P Leinonen.

At least 37 records · Page 2Linked to original sources
PubMed1993

Thyroxine withdrawal is accompanied by decreased circulating levels of insulin-like growth factor-binding protein-1 in thyroidectomized patients.

We carried out a study on the effect of T4 withdrawal on serum insulin-like growth factor-binding protein-1 (IGFBP-1) levels in 10 thyroidectomized patients with papillary thyroid cancer receiving T4 replacement therapy. As controls we also measured serum sex hormone-binding globulin (SHBG) levels, known to be regulated by T4. Each patient acted as his/her own control, studied both before and 30 days after T4 withdrawal. On the average, the IGFBP-1 level decreased by 36% from 66 +/- 9 to 44 +/- 8 micrograms/L (mean +/- SE; P = 0.0007) during T4 withdrawal. The SHBG level decreased by 47% from 78 +/- 17 to 46 +/- 13 nmol/L (P = 0.0001). The fasting insulin levels were unaffected by T4 withdrawal. There also was an 18% decline in the serum IGF-I concentration after T4 withdrawal (P = 0.011). It is concluded that in athyreotic patients receiving T4, withdrawal of the drug decreases serum IGFBP-1 and SHBG concentrations and IGF-I levels. In view of the possible role of IGFBP-1 in glucose counterregulation, these results indicate a novel mechanism by which T4 may exert its metabolic action on liver carbohydrate metabolism.

Adult↗
PubMed1993

Tri-iodothyronine and cycloheximide enhance insulin-like growth factor-binding protein-1 gene expression in human hepatoma cells.

The growth-regulating actions of IGFs are modulated by their binding proteins (IGFBPs). The serum concentration of IGFBP-1 is down-regulated by insulin, and in-vitro studies have demonstrated that IGFBP-1 secretion from various tissues and cells can be stimulated by theophylline, forskolin, oestrogen and progesterone. We have studied the effects and mechanisms of thyroid hormone action on IGFBP-1 gene expression and secretion by human hepatoma cells in vitro. Tri-iodothyronine dose-dependently enhanced IGFBP-1 secretion in serum-free HepG2 cell cultures after 24-48 h of exposure, as measured by a specific immunofluorometric assay. This was accompanied by an increase (+ 50%) in the amount of IGFBP-1 mRNA, which could be prevented by cycloheximide, a protein synthesis inhibitor. Cycloheximide transiently enhanced (+ 200%) the accumulation of IGFBP-1 mRNA at 3-12 h of incubation, when no effect of tri-iodothyronine was observed. It is concluded that thyroid hormone stimulates IGFBP-1 secretion slowly by enhancing IGFBP-1 gene expression by a protein mediator. The acute stimulation of IGFBP-1 gene transcription by cycloheximide associates this gene with a number of growth-related genes encoding growth- and tumour-associated peptides.

Carrier Proteins↗
PubMed1993

Phosphorylation of insulin-like growth factor-binding protein-1 from different sources.

During purification, insulin-like growth factor binding protein-1 from amniotic fluid was separated into five different peaks by anion exchange chromatography. These peaks represent differently phosphorylated forms of IGFBP-1. The major peak (peak 1) is non-phosphorylated. Peaks 3, 4, and 5 are more phosphorylated and, in native polyacrylamide gel electrophoresis (PAGE), they migrate faster than peaks 1 and 2. The more phosphorylated forms have higher IGF-I-binding affinity. Both dephosphorylated and phosphorylated peaks enhanced IGF-I stimulated DNA-synthesis in fetal skin fibroblast cell culture. They, however, inhibited the binding of IGF-I to the same cells. The phosphorylation of IGFBP-1 was changed during pregnancy. In decidua and in amniotic fluid the degree of phosphorylation increased from early to late pregnancy, as indicated by faster mobility of IGFBP-1 in native PAGE and increased relative amount of the more phosphorylated peaks in anion exchange chromatography. Human ovarian follicular fluid, culture media from human granulosa cells and endometrial adenocarcinoma cells (HEC-1-B) consisted mostly of the non-phosphorylated form of IGFBP-1.

Amniotic Fluid↗
PubMed1991

Testosterone-secreting virilizing adrenal adenoma with human chorionic gonadotrophin receptors and 21-hydroxylase deficiency.

A 60-year-old woman was evaluated for persistently elevated serum testosterone concentrations after bilateral ovariectomy. Her serum cortisol, androstenedione, dehydroepiandrosterone sulphate and 17-hydroxyprogesterone levels were normal, and decreased after dexamethasone administration. Those of testosterone (17.8-18.4 nmol/l) were remarkably high (normal range 0.7-2.8 nmol/l), were not suppressed by dexamethasone, but clearly increased after hCG administration (up to 128 nmol/l). Computed tomography revealed an adenoma in the right adrenal gland and adrenal scintigraphy under dexamethasone suppression visualized this adenoma. A right adrenalectomy was performed. (1) The tumour was histologically and ultrastructurally adrenocortical adenoma of zona reticularis cell type. (2) The adenoma tissue contained hCG receptors (198 fmol/g). (3) During tissue culture both ACTH and hCG were capable of maintaining its testosterone production, which was attenuated with time without stimulation. (4) The adenoma tissue did not elaborate 21-hydroxylated steroids in contrast to normal adrenal tissue. Thus the aberrant endocrine behaviour of this gonadotrophin-responsive testosterone-secreting adenoma of adrenal zona reticularis cell origin can be explained by ectopic functional hCG receptors and the lack of 21-hydroxylase activity.

Adenoma↗
PubMed1991

Polyamines: from molecular biology to clinical applications.

The polyamines putrescine, spermidine and spermine represent a group of naturally occurring compounds exerting a bewildering number of biological effects, yet despite several decades of intensive research work, their exact physiological function remains obscure. Chemically these compounds are organic aliphatic cations with two (putrescine), three (spermidine) or four (spermine) amino or amino groups that are fully protonated at physiological pH values. Early studies showed that the polyamines are closely connected to the proliferation of animal cells. Their biosynthesis is accomplished by a concerted action of four different enzymes: ornithine decarboxylase, adenosylmethionine decarboxylase, spermidine synthase and spermine synthase. Out of these four enzyme, the two decarboxylases represent unique mammalian enzymes with an extremely short half life and dramatic inducibility in response to growth promoting stimuli. The regulation of ornithine decarboxylase, and to some extent also that of adenosylmethionine decarboxylase, is complex, showing features that do not always fit into the generally accepted rules of molecular biology. The development and introduction of specific inhibitors to the biosynthetic enzymes of the polyamines have revealed that an undisturbed synthesis of the polyamines is a prerequisite for animal cell proliferation to occur. The biosynthesis of the polyamines thus offers a meaningful target for the treatment of certain hyperproliferative diseases, most notably cancer. Although most experimental cancer models responds strikingly to treatment with polyamine antimetabolites--namely, inhibitors of various polyamine synthesizing enzymes--a real breakthrough in the treatment of human cancer has not yet occurred. It is, however, highly likely that the concept is viable. An especially interesting approach is the chemoprevention of cancer with polyamine antimetabolites, a process that appears to work in many experimental animal models. Meanwhile, the inhibition of polyamine accumulation has shown great promise in the treatment of human parasitic diseases, such as African trypanosomiasis.

Adenosylmethionine Decarboxylase↗
PubMed1988

Effect of dexamethasone on the activity and expression of ornithine decarboxylase in rat liver and thymus.

A single intraperitoneal injection of the synthetic glucocorticoid dexamethasone into rats resulted in a marked stimulation (more than 60-fold) of hepatic ornithine decarboxylase (ODC) at 4 h after the injection, whereas the enzyme activity in thymus was almost totally (about 95%) depressed at the same time. The stimulation of ODC activity in liver was in all likelihood attributable to a greatly enhanced accumulation of mRNA species for the enzyme as revealed by Northern blot and dot-blot hybridization analyses. ODC activity in thymus, in response to dexamethasone, was only 5% of that found in control animals, but this decrease was apparently not accompanied by similar reductions of the levels of ODC message, which was in fact decreased only by 50% at the maximum. In addition to two mRNA species (2.1 and 2.6 kilobases; kb), typical to mouse cells, rat tissues seemed to contain a third hybridizable message for ODC, smaller (1.6 kb) than the above-mentioned species and not seen in samples obtained from mouse or human cells. Interestingly, these smaller poly(A)+ RNA sequences, hybridizable with cDNA complementary to mouse ODC mRNA, were apparently constitutively expressed, as the treatment with glucocorticoid altered the amount of these sequences only slightly.

Age Factors↗
PubMed1988

Hypomethylation of ornithine decarboxylase gene and erb-A1 oncogene in human chronic lymphatic leukemia.

The methylation state of CCGG sites in and around the human ornithine decarboxylase gene, oncogenes c-myc and erb-A1, and actin genes were determined in human malignant leucocytes from patients with acute and chronic myeloid leukemia, chronic lymphatic leukemia, polycythemia vera, and multiple myeloma by means of isoschizomeric restriction endonuclease analysis. When compared with DNA from leucocytes of healthy controls, the ornithine decarboxylase and erb-A1 genes were substantially hypomethylated in all samples obtained from patients with chronic lymphatic leukemia. Hypomethylation of genes, particularly growth-related sequences, might be a crucial fact in the malignant transformation of human leucocytes. Its relatively simple detection from blood samples may prove clinically applicable in monitoring patients with chronic lymphatic leukemia.

B-Lymphocytes↗
PubMed1987

Chronic exposure to dexamethasone induces hypomethylation of ornithine decarboxylase genes in a human myeloma cell line.

Chronic exposure of a human myeloma cell line to dexamethasone resulted in a selection of cells resistant to the growth-inhibitory action of the glucocorticoid. Upon acute exposure of the parental myeloma cells to dexamethasone growth inhibition was associated with depression of ornithine decarboxylase (ODC, EC 4.1.1.17) activity. However, in cells adapted to grow in the presence of micromolar concentrations of dexamethasone, ODC activity was fully comparable to that in the parental cells. Restriction enzyme analyses with the two isoschizomers HpaII and MspI as well as with the methylation-sensitive CfoI, indicated that the otherwise heavily methylated ODC gene(s) were rendered hypomethylated in the myeloma cells resistant to dexamethasone. This hypomethylation within and/or around ODC genes was associated with a 2-4-fold enhancement of accumulation of ODC mRNA.

Cell Line↗
PubMed1987

Human myeloma cells acquire resistance to difluoromethylornithine without overproducing ornithine decarboxylase.

An exposure of a human myeloma cell line to 2-difluoromethylornithine the mechanism-based inhibitor of ornithine decarboxylase (EC 4.1.1.17), resulted in a selection of tumor cells readily growing in the presence of 4 mM difluoromethylornithine, a concentration that swiftly halted the growth of the parental cells. Determination of the intracellular polyamines revealed that there were measurable amounts of putrescine and spermidine in the resistant cells. Restriction enzyme analyses of genomic DNA isolated from the resistant cells indicated that the gene dosage for ornithine decarboxylase was not increased to any appreciable extent. Similarly, the accumulation of mRNA was unaltered. The resistant myeloma cells, however, displayed arginase (EC 3.5.3.1) activity that was roughly ten times higher than that in the parental cells.

Arginase↗
PubMed1987

Human myeloma cells acquire resistance to difluoromethylornithine by amplification of ornithine decarboxylase gene.

Stepwise increments of the concentration of 2-difluoromethylornithine (DFMO), a mechanism-based irreversible inhibitor of mammalian ornithine decarboxylase (ODC), resulted in a selection of cultured human IgG-myeloma cells (Sultan cell line) capable of growing in the presence of up to 3 mM-DFMO. This capacity was associated with 10-fold increase in ODC activity in the dialysed extracts of drug-resistant myeloma cells, markedly enhanced synthesis rate for ODC enzyme molecules, as revealed by a 20 min [35S]methionine labelling of cellular proteins, followed by specific immunoprecipitation and SDS/polyacrylamide-gel electrophoresis, dose-dependently increased expression of ODC mRNA in resistant cells (effective dose causing 50% inhibition), dose-dependent amplification of ODC gene sequences in a 9-kilobase-pairs EcoRI genomic DNA fragment, and (v) a 10-fold increase in the ED50 (effective dose causing 50% inhibition) for the anti-proliferative action of DFMO in these myeloma cells. These results represent one of the few gene amplifications described in cultured human cells.

Cell Line↗
PubMed1987

Mouse and human ornithine decarboxylase genes. Methylation polymorphism and amplification.

With the use of the isoschizomeric restriction endonucleases HpaII and MspI, we found that mouse tumour ornithine decarboxylase (ODC; EC 4.1.1.17) genes are extensively methylated. ODC genes in L1210 mouse leukaemia cells were apparently more methylated than in Ehrlich ascites carcinoma, as revealed by the use of HpaII endonuclease, yet the digestion of genomic DNA isolated from these two murine tumour cell lines with MspI, which cleaves at a CCGG sequence, also with internally methylated cytosine, resulted in an apparently identical restriction pattern. It is possible that the amplification of ODC genes in Ehrlich ascites-carcinoma cells in response to 2-difluoromethylornithine (DFMO) was associated with hypomethylation, or that less-methylated genes were amplified. A human myeloma (Sultan) cell line only revealed three separate hybridization signals when cleaved with HpaII. One of these signals was amplified under the pressure of DFMO. When cleaved with MspI, these three HpaII fragments disappeared and were replaced by a double signal of 2.3-2.4 kilobase-pairs (kbp) in size. The amplified ODC sequences in the Sultan myeloma cell line apparently originated from chromosome 2, as indicated by a unique hybridization signal in a 5.8 kbp HindIII fragment specific for the human ODC locus on chromosome 2. A comparison of different human cells, the Sultan myeloma, a lymphocytic B-cell leukaemia (Ball), normal mononuclear leucocytes and leucocytes obtained from leukaemia patients, revealed interesting differences in the methylation of ODC genes. The use of two restriction endonucleases (HpaII and CfoI), the cleavage site for both of which contains a CG sequence and which only cleave when cytosine is unmethylated, indicated that ODC genes in the lymphocytic leukaemia cells were much less methylated than those in the normal leucocytes or in the Sultan cells.

Animals↗
PubMed1985

Effects of long-term administration of tamoxifen on steroid metabolism in prostatic carcinoma patients.

Six patients with advanced prostatic carcinoma were treated with tamoxifen (2 X 20 mg daily) for up to 3 months before orchiectomy. Blood samples for gonadotropin, sex steroid, and prostate-specific acid phosphatase (PAP) determinations were taken before tamoxifen treatment, daily for 1 week, and at monthly intervals. Steroid concentrations in the testis tissue and spermatic vein blood were assayed from samples taken at orchiectomy. No consistent changes were observed during tamoxifen treatment, although there was a transient drop in the mean concentrations of LH on days 3 and 4 of treatment. The circulating concentrations of estradiol tended to be increased at 1, 2, and 3 months of treatment. The spermatic vein concentrations of testosterone and its precursors tended to be higher than those in nontreated prostatic carcinoma patients previously reported from this laboratory, indicating slight stimulation of testicular steroidogenesis. There were no changes in circulating levels of PAP and no improvement in clinical condition, indicating that long-term tamoxifen administration is not effective in the treatment of prostate carcinoma.

Aged↗