Jacob Urbach

Transfer and accumulation of cadmium, and the level of metallothionein in perfused human placentae

The purpose of the present study was to investigate the effect of perfusion with a medium containing 12 or 24 μg Cadmium (as CdCl2) per ml on this metals accumulation, transfer rate and metallothionein (MT) level. The experiments were performed with an isolated lobule of a dually-perfused human term placenta. Placental cell integrity and viability were characterised by their morphology and metabolic function, manifested in the tissues electron microscopic structure and glucose and oxygen (O2) consumption, respectively. Perfusion with 24 μg Cd/ml medium for 5 h resulted in significant elevation in MT. The transfer rate of Cd to the fetal side of the placenta was very slow, and not until 40 min after the addition of Cd into the maternal side was a significant increase in the metals level observed in the fetal perfusate. Thereafter, the level of the metal increased gradually and reached a steady state about 1 h later, at a level which was less than 1/20th of its concentration in the maternal perfusate. There was a 60-fold increase in Cd level in the cytosolic fraction obtained from the Cd-treated samples. At 12 μg Cd/ml no significant changes were noted in morphology, metabolic function and MT content. None of the Cd levels caused a signicant change in O2 and glucose consumption, in spite of the fact that with the higher Cd dose the microstructure of the tissue showed some pathological changes. The observed elevation in MT may provide the fetus some protection against the harmful effects of the metal.

In vitro exposure to mercury and cadmium alters term human placental membrane fluidity

The effect of incubation with mercury (Hg) as HgCl2 and cadmium (Cd) as CdCl2, at levels of 6 or 12 micrograms/ml of medium, on explants of term human placental microvillus membrane fluidity were studied. After incubation for 6 or 24 hr explants for each dose level were pooled and washed with fresh medium to remove any unbound metal. Placental membranes were separated by differential centrifugation and fluidity was studied by steady-state fluorescence polarization, expressed as the fluorescence anisotropy, r, with 1,6-diphenyl-1,3,5-hexatriene as a probe. The results show that membranes derived from explants incubated for 24 hr with either 6 or 12 micrograms/ml medium of either metal showed fluorescence anisotropy values (i.e., decreased fluidity) significantly higher than that of their respective controls. With 6 micrograms/ml of either metal the decrease in fluidity was highly significant for both metals and with 12 micrograms/ml a further decrease in membrane fluidity was observed with either metal. Both metals accumulated in placental membranes in proportion to their level in the medium. Membrane accumulation of Cd was higher than that of Hg. The cholesterol, phospholipid, and cholesterol-to-phospholipid mole ratios in membranes derived from metal-treated explants were unchanged, compared to their respective controls. However, no changes in membrane fluidity were observed in the samples incubated for 6 hr. In conclusion, exposure of placental cells to Hg and Cd caused accumulation of the metals in the membranes and lowered the membrane fluidity, which may affect membrane function and cause damage to the developing fetus.

Effect of inorganic mercury on in vitro placental nutrient transfer and oxygen consumption

The effect of mercury (HgCl2) on placental amino acid and glucose transfer as determined by the use of their nonmetabolizable radioactive analogues, aminoisobutyric acid (AIB) and 3-o-methyl glucose (3MG), respectively, was studied in an in vitro perfusion model of a term human placenta. Hg2+ was found to decrease the transfer and accumulation of AIB without affecting 3MG transfer. It was also found to decrease the placental oxygen consumption rate. Placental circulation and tissue morphology remained intact, as demonstrated by the antipyrine transfer rate, and by electron microscopy, respectively. The mechanism by which Hg2+ may interfere with placental amino acid transfer and accumulation is discussed. Although much higher concentrations than those found in the ordinary polluted environment were used, this is the first report showing that Hg2+ interferes with an essential human placental function in a system employing a whole human placental cotyledon. This finding may indicate the possible involvement of Hg2+ in impaired organogenesis in early pregnancy or deranged fetal growth during the last trimester.

In vitro effect of mercury on enzyme activities and its accumulation in the first-trimester human placenta

The effect of incubating young placental explants with HgCl2 on the activities of aryl hydrocarbon hydroxylase (AHH) (a phase I enzyme), quinone reductase (QR), catecholamine-O-methyltransferase (COMT) (both phase II enzymes), and glucose-6-phosphate dehydrogenase (G-6-PD) is described. Mercury (Hg) at low doses significantly elevated placental phase I and phase II enzyme activities, but decreased the activity of G-6-PD. The increase in activities, which was time- and dose-dependent, was higher in explants incubated for 24 hr than in those incubated for 6 hr. The decrease in placental G-6-PD activity was drastic at low Hg dose levels but at higher levels the inhibitory effect was milder for both incubation periods. Placental explants accumulated Hg in amounts proportional to its concentration in the incubation medium and this accumulation was greater in explants incubated for 24 hr. The data suggest that contamination with low Hg levels from the environment during pregnancy may affect placental enzymatic activity. The accumulation of Hg during short incubation indicates a strong placental cell affinity for Hg, which could affect its other metabolic functions. The system used in sensitive, as it shows alteration in enzyme activity even with relatively low concentrations of the metal and the response is dose-related.

Does insulin affect placental glucose metabolism and transfer

An in vitro recycled perfusion of the human placenta was used to investigate the effect of insulin on placental metabolism and transfer of glucose. Human insulin, 1000 microU/ml, was introduced into either maternal or maternal and fetal compartments. In one series of experiments placentas were used as either a control group or study group, whereas in the other series each placenta served as its own control. Metabolic effects were determined by measuring placental glucose and oxygen consumption and lactate production rate. The effect of insulin on transfer was studied by the use of 3-O-methylglucose labeled with tritium; this effect was expressed as the slope of maternal minus fetal concentrations on a natural logarithmic scale and compared with the antipyrine tagged with carbon 14. The stability of perfusate volume was used as an index for placental integrity, whereas absence of tissue edema demonstrated adequacy of perfusion. Neither of the metabolic parameters studied was significantly affected by insulin, and insulin did not have an effect on 3-O-methylglucose transfer rate. It was concluded that, in contrast to other tissues in the body, placental glucose metabolism and transfer are not sensitive to the action of insulin.

Effect of cadmium on some enzyme activities in first-trimester human placentae

Explants from first-trimester placentae obtained from non-smoking women were incubated with doses of 0, 0.75, 1.5, 3, 6 and 12 micrograms of cadmium (Cd) as CdCl2 for 6 or 24 h. At the end of the incubation period, the activities of placental aryl hydrocarbon hydroxylase (AHH) (a phase I enzyme), quinone reductase (QR) and catecholamine-O-methyltransferase (COMT) (both phase II enzymes) and glucose-6-phosphate dehydrogenase (G-6-PD) were determined. Cd at low dose levels increased significantly the activities of placental phases I and II enzymes in a time- and dose-dependent manner. Of the first 3 enzymes, only AHH showed a biphasic response for the two time periods, with the activities of QR and COMT continually increasing at all the dose levels tested for the two incubation periods. However, the G-6-PD activity was inhibited at all the dose levels of Cd, the effect being very drastic after exposure to 0.75 ppm Cd for both incubation periods.

Secretion of human chorionic gonadotropin in superfused young placental tissue exposed to cadmium

The effect of various concentrations of cadmium (Cd) in levels ranging from 0.75 to 12 μg/ml medium, on the secretion of human chorionic gonadotropin (hCG) in first-trimester placental expiants, after 6 or 24 h incubation, employing both static and dynamic systems was examined. Later the unbound Cd was washed for 45 min with fresh medium devoid of Cd, followed by superfusion with the latter medium for 75 min, during which time samples were collected for hCG assay. For the superfusion experiments the parameters used for evaluating the hCG secretion pattern were: mean peak amplitude (MPA), pulse frequency (PF) and the area under the hCG secretion curve (AUC). The results indicate that in the dynamic system the hCG secretion increased significantly, and this increase was dose dependent. There was also a dose-related increase in mean total hCG secreted by the explants exposed to Cd. Maximal hCG secretion was observed after 24 h exposure of explants to 6 μg of the metal/ml. Both the MPA and AUC parameters showed a statistically significant increase for this dose level. At 12 μg/ml, the pulsatile secretion of hCG decreased, the value for the mean hCG secretion being comparable to that observed for 0.75 μg/ml. After 6 h incubation, however, there were no significant changes from the control, as judged by all of the above parameters. The levels of hCG secreted by the explants into the media in the static system were not significantly different from their respective controls, for both incubation periods and Cd levels. These results indicate that Cd may affect the normal placental function, as reflected in its hCG secretion pattern.

Transplacental Transfer of Ritodrine and Its Effect on Placental Glucose and Oxygen Consumption in an in vitro Human Placental Cotyledon Perfusion

Maternofetal transfer of ritodrine and its effect on placental glucose and oxygen consumption were studied using a recycling perfusion of maternal and fetal circulations of an isolated cotyledon of a term human placenta. 3H-labeled ritodrine was introduced into the maternal side of the perfusion system. Transfer was calculated from the linear rise of ritodrine concentrations on the fetal side and was found to be 7.31 +/- 1.02 ng/g placental wet weight/min (SEM) when 1.4 micrograms/ml of ritodrine was used (n = 3) and 14.7 +/- 1.06 ng/g placental wet weight/min when the concentration was 2.8 micrograms/ml (n = 5). The antipyrine transfer rate, 4.1 +/- 0.51 mg/kg/min (n = 8), was used to demonstrate perfusion adequacy and served as an internal standard. Upon computing the mass balance of ritodrine and antipyrine at the end of the experiment, it was found that 17% of ritodrine disappeared from the perfusion system compared to 0.7% of antipyrine (p less than 0.01). The introduction of ritodrine into the perfusion system did not affect placental glucose and oxygen consumption rates of 0.35 +/- 0.01 mumol/g/min (n = 7) and 0.19 +/- 0.013 mumol/g/min (n = 5), respectively.