In vitro activity of nicotinamide adenine dinucleotide- and nicotinamide adenine dinucleotide phosphate-linked 15-hydroxyprostaglandin dehydrogenases in placentas from normotensive and preeclamptic/eclamptic pregnancies

Gene expression profiling of placentas affected by pre-eclampsia

Several studies point to the placenta as the primary cause of pre-eclampsia. Our objective was to identify placental genes that may contribute to the development of pre-eclampsia. RNA was purified from tissue biopsies from eleven pre-eclamptic placentas and eighteen normal controls. Messenger RNA expression from pooled samples was analysed by microarrays. Verification of the expression of selected genes was performed using real-time PCR. A surprisingly low number of genes (21 out of 15,000) were identified as differentially expressed. Among these were genes not previously associated with pre-eclampsia as bradykinin B1 receptor and a 14-3-3 protein, but also genes that have already been connected with pre-eclampsia, for example, inhibin beta A subunit and leptin. A low number of genes were repeatedly identified as differentially expressed, because they may represent the endpoint of a cascade of events effectuated throughout gestation. They were associated with transcriptional regulation and vasoregulative pathways, along with a number of hypothetical proteins and gene sequences with unknown functions.

Prostaglandin-metabolizing enzymes during pregnancy: characterization of NAD(+)-dependent prostaglandin dehydrogenase, carbonyl reductase, and cytochrome P450-dependent prostaglandin omega-hydroxylase

Prostaglandins E2 and F2 alpha regulate a number of physiological functions in reproductive tissues, and concentrations of these bioactive modulators increase during pregnancy. Corresponding to the increase in circulating levels of prostaglandins during pregnancy is an increase in enzymes that metabolize these agents. Three prostaglandin-metabolizing enzymes induced during pregnancy are NAD(+)-dependent 15-hydroxyprostaglandin dehydrogenase (PGDH), NADPH-dependent carbonyl reductase, and cytochrome P450-dependent prostaglandin omega- or 20-hydroxylase. This review discusses the biochemical properties, regulation, and possible functions of these three enzymes.

Placental localization of 15-hydroxy-prostaglandin dehydrogenase in early and term human pregnancy

The human placenta possesses a large capacity for inactivation of prostanoids. This is due to the presence of large quantities of the NAD(+)-linked 15-hydroxy-prostaglandin dehydrogenase (PGDH type I; EC 1.1.1.141). In order to investigate whether a specific localization of PGDH is at the origin of the increasing placental PGDH activity during early pregnancy, PGDH activity was localized histochemically in placental tissue obtained in early pregnancy and at term. Intracellular PGDH activity was present in three distinct compartments in the placenta. First, the syncytiotrophoblast and second, the underlying cytotrophoblast layer of placental terminal villi contained PGDH. Third, scattered throughout the sections, we found chorion-like cells which showed strong staining for PGDH activity. The intensity of staining in samples before 12 weeks of gestation was much less than in samples after 12 weeks of gestation, which were comparable to those at term. Thus, the fetal cell layers at the boundary between the fetal tissues and the maternal blood have a great potential to inactivate prostanoids suggesting that the fetus protects itself against prostanoids of maternal origin.

Nifedipine increases urinary excretion of prostacyclin metabolite in hypertensive pregnancy

Renal prostanoid excretion was investigated in nine hypertensive pregnant patients before and during treatment with nifedipine 10 mg orally t.i.d. Urinary excretion of prostacyclin (measured as 6-ketoprostaglandin F1 alpha, 6-keto-PGF1 alpha) increased by 77% during nifedipine treatment (P less than 0.05). No changes were found in prostaglandin E2 (PGE2) and thromboxane A2 (as thromboxane B2, TXB2) excretions. A significant reduction in blood pressure did not correlate with an increase in 6-keto-PGF1 alpha excretion. Plasma prekallikrein and urinary kallikrein and catecholamine excretions remained unaltered. In six normotensive non-pregnant women, increase in 6-keto-PGF1 alpha excretion during nifedipine treatment was not significant. No changes in PGE2 and TXB2 excretions were found, whereas plasma prekallikrein was reduced (P less than 0.05) and urinary excretion of kallikrein (P less than 0.05) and noradrenaline (P = 0.06) increased under nifedipine. The results suggest that nifedipine enhances the renal 6-keto-PGF1 alpha excretion in hypertensive pregnancy.

Volume homeostasis and osmoregulation in human pregnancy

This chapter reviews alterations in volume and sodium homeostasis and osmoregulation during human pregnancy. Pregnant women undergo extracellular and plasma volume increases of 50-70%, and these changes accompany marked cumulative sodium retention shared by both mother and fetus. Pregnancy alters several factors with opposing effects on renal salt handling; however, mechanisms by which gestational sodium accumulation and volume expansion are achieved remain obscure. Furthermore, despite substantial increases in absolute blood volume, considerable uncertainty exists as to how this volume is sensed, particularly in late pregnancy when a rapid increase in volume is associated with decreases in peripheral resistance and blood pressure. Attempts to assess 'effective' intravascular volume suggest that pregnant women sense their volume as normal. Osmoregulation is also changed. Body tonicity and the osmotic thresholds for AVP release and thirst decrease by about 10 mosm/kg. The mechanisms responsible for the osmoregulatory changes are obscure. Haemodynamic stimuli such as decrements in blood pressure and of 'effective circulating volume' do not seem to account for them. Of the many increments in hormone levels known to accompany gestation, only hCG has so far been implicated in these changes. Pregnant women experience three- to fourfold increments in AVP disposal rates between early and mid pregnancy; this may be caused by the striking rise in circulating cystine-aminopeptidase (vasopressinase) which also occurs during this period. The increments in MCR may be one reason why the hormonal response to a given osmotic stimulus appears to decrease in late pregnancy. All these alterations permit speculation on the manner in which the decrease in Posm occurs and is maintained within narrow limits. Lowering the osmotic threshold to drink stimulates a rise in water intake and dilution of body fluids. Since AVP release is not suppressed at the usual level of hypotonicity, AVP continues to circulate at levels sufficient to permit water retention. Posm continues to decline until it decreases below the new osmotic thirst threshold, when a new steady state is established. At this point water turnover, too, resembles that in the non-pregnant state. The change in MCR and the marked increment in plasma vasopressinase may explain certain observations regarding disordered water metabolism during late pregnancy. These are the transient DI syndromes due either to subclinical hypothalamic disease or to a disorder peculiar to pregnancy which is AVP-resistant but dDAVP-responsive; the latter analogue resists degradation by vasopressinase.

Trans-placental transport and metabolism of carbacyclin by perfused human placental in vitro

When carbacyclin (5E-6a-carba-prostaglandin I2) was added to the maternal afferent circulation of in vitro perfused placentae from normal term pregnancies, relatively little carbacyclin was found in either the maternal or fetal efferent circulations. When carbacyclin was added to the perfusate at 1.0 microM, the peak level in the maternal effluent was only 0.06 microM and in the fetal effluent, 0.026 microM. When infused at 10 microM, 0.77 microM carbacyclin was measured in the maternal effluent and 0.13 in the fetal effluent. These findings demonstrate that carbacyclin is transferred across the placenta from the maternal side to the fetal, but that the net transfer is small. The assay procedure employed HPLC resolution, followed by capillary gas chromatography and selected ion monitoring using PGB as an internal standard. The low levels of carbacyclin detected in the effluents did not result from poor recovery in the analyses. When carbacyclin was added to maternal or fetal effluents at 1 microM, the recovery averaged 85.4 +/- 14.1% (SD); at 10 microM recovery averaged 97.3 +/- 4.2%. Much of the loss of carbacyclin on passage through placental circulation resulted from metabolism. Extracts of both fetal and maternal effluents from placenta perfused with carbacyclin contained a component which on reverse phase HPLC appeared less polar than carbacyclin. When analyzed by GC/MS as the methyl ester-trimethylsilyl ether, this component had a mass spectrum expected for 15-dehydro-carbacyclin. When the presumed metabolite was further converted to the methoxime, the mass spectrum was identical to published spectra for that derivative of 15-dehydro-carbacyclin. When extracts of fetal effluents were analyzed for 15-dehydro-carbacyclin metabolite as well as carbacyclin, it appeared that the metabolite accounted for the majority of the carbacyclin recovered. Most of the metabolite was apparently not formed in the fetal circulation, since when carbacyclin was added to the fetal afferent circulation, little 15-dehydro-carbacyclin was observed in either efferent fluid, and most of the perfused carbacyclin was recovered unaltered in the fetal effluent.

Purification of the human placental NAD-linked 15-hydroxyprostaglandin dehydrogenase

An NAD-linked 15-hydroxyprostaglandin dehydrogenase has been purified 13,100-fold from human placental tissue. The specific activity of the purified enzyme ranges from 6900 to 8300 mU/mg protein depending on the method used to determine the protein concentration. On discontinuous electrophoresis in sodium dodecyl sulfate more than 95% of the protein migrates as a single band; its estimated molecular weight is 25.5-26.0 kDa. This is half the value obtained when the molecular weight is estimated under non-denaturing conditions and suggests that the enzyme is composed of two identical or nearly identical subunits.

Inhibition of the human placental NAD- and NADP-linked 15-hydroxyprostaglandin dehydrogenases by nonsteroidal anti-inflammatory drugs

A number of nonsteroidal anti-inflammatory drugs are non-competitive or mixed inhibitors of human placental NAD- and NADP-linked 15-hydroxyprostaglandin dehydrogenases. Cis- and trans-sulindac sulfide and cis- and trans-sulindac inhibit the NAD-linked enzyme as well or better than they inhibit various cyclooxygenases in vitro. The remainder of the compounds tested are at least one order of magnitude less effective as inhibitors of the 15-hydroxyprostaglandin dehydrogenases than they are as inhibitors of cyclooxygenases. Cis- and trans-sulindac sulfide are sufficiently strong inhibitors of the NAD-linked enzyme (Kis of 7.8 microM and 6.8 microM respectively) to raise the possibility that they might also inhibit this enzyme in vivo.