Pekka Leinonen

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.

Fetal Hypoxia Is Associated with Elevated Cord Serum C-Reactive Protein Levels in Diabetic Pregnancies

Maternal diabetes increases the risk of intrauterine hypoxia. Inflammation may play a role in the pathogenesis of hypoxia-related neonatal complications. We studied correlations between levels of cord serum C-reactive protein (CRP), measured by a highly sensitive immunofluorometric assay, and indices of fetal hypoxia in diabetic pregnancies. Cord serum CRP correlated positively with amniotic fluid erythropoietin and umbilical artery pCO2. A negative correlation existed between cord serum CRP and umbilical artery pH and pO2. Amniotic fluid erythropoietin showed an independent effect on cord serum CRP in multiple regression analysis. These data suggest that the fetus responds to hypoxia by an inflammatory reaction.

Diabetic pregnancy associated with increased epidermal growth factor in cord serum at term.

OBJECTIVE: Epidermal growth factor is a ubiquitous mitogen that also possesses insulin-like properties. Fetal malgrowth is associated with altered epidermal growth factor levels. Maternal diabetes is frequently complicated by macrosomia, but the effect of maternal diabetes on fetal epidermal growth factor levels is not known. We studied cord serum epidermal growth factor concentrations in pregnancies complicated by diabetes and in normal pregnancies. METHODS: Cord serum epidermal growth factor concentrations were measured at birth by a sandwich-type time-resolved immunofluorometric assay in 63 pregnancies complicated by insulin-dependent diabetes mellitus, in 25 pregnancies complicated by insulin-treated gestational diabetes, and in 56 normal pregnancies. RESULTS: Cord serum epidermal growth factor correlated positively with the duration of pregnancy in diabetic and normal pregnancies. In a subgroup of women at similar gestational ages (38–39 weeks), cord serum epidermal growth factor concentrations were higher in pregnancies complicated by insulin-dependent diabetes mellitus (962 ± 211 ng/L, P = .047; n = 9) and in pregnancies complicated by gestational diabetes (1133 ± 115 ng/L, P = .001; n = 9) than in controls (564 ± 75 ng/L; n = 22). In multiple regression analysis, only umbilical artery hemoglobin in diabetic pregnancies and vaginal delivery in normal pregnancies were associated with cord serum epidermal growth factor. CONCLUSION: Epidermal growth factor concentrations are higher than normal in fetuses of diabetic mothers at term. Pregnancy complications, such as hypertensive disorders, fetal hypoxia and fetal malgrowth, may not explain the rise in epidermal growth factor levels. We hypothesize that the rise in epidermal growth factor levels is a metabolic response of the fetoplacental unit to diabetes-related hyperglycemia. LEVEL OF EVIDENCE: III

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.

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 C⨍oI, 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.

Increased thromboxane production in women with a history of venous thromboembolic event: effect of heparins

We investigated the production of prostacyclin and thromboxane in pregnant women with a previous venous thromboembolic event before, during and after the use of unfractionated heparin and low molecular weight heparin (dalteparin). Twenty women were studied before starting heparin prophylaxis (before 20u2003weeks of gestation), during heparin prophylaxis (at 30u2003weeks of gestation) and after heparin prophylaxis (16u2003weeks after delivery). Ten pregnant women with no history of thromboembolism were studied as the control group. Urinary output of the stable metabolite of prostacyclin (2,3‐dinor‐6‐keto‐PGF1α) and that of thromboxane A2 (2,3‐dinor‐TxB2), as well as a number of markers of thrombophilia were measured and expressed as mean (±SEM). Women with a history of thromboembolism were characterized by normal prostacyclin production but elevated thromboxane production (44·0u2003±u20034·1 versus 19·0u2003±u20033·6u2003ng/mmol creatinine, Pu2003<u20030·001) at 12u2003weeks of pregnancy. Heparin prophylaxis (regardless of the type) had abolished elevated thromboxane concentrations at 30u2003weeks of gestation. Four months after delivery, thromboxane dominance had returned (25·2u2003±u20033·5 versus 13·6u2003±u20032·1u2003ng/mmol creatinine, Pu2003<u20030·01). The presence of hereditary thrombophilia (9/20) was not associated with any changes in prostanoid concentrations. Thus, women with a history of venous thromboembolic events have thromboxane dominance during and after pregnancy, but this dominance can be eliminated through the use of heparins.