Ethanol decreases zinc transfer to the fetus in normal but not metallothionein-null mice

BackgroundEthanol causes significant teratogenicity in normal (MT+/+) but not metallothionein-null (MT-/-) fetuses. Impaired maternal fetal zinc (Zn) transfer is indicated, because ethanol significantly reduces plasma Zn concentrations in MT+/+ dams while increasing concentrations in MT-/- dams. In this study we examined maternal-fetal Zn homeostasis in response to ethanol in MT+/+ and MT-/- mice and the origins of the increase in plasma Zn in MT-/- mice.Methods and resultsMice were treated with saline or ethanol (0.015 ml/g intraperitoneally at 0 and 4 hr) on day 12 of gestation. An additional subcutaneous injection of 65Zn tracer was administered after the second ethanol injection before mice were killed 3 hr later. Maternal liver MT levels were not different between ethanol and saline MT+/+ mice. Both liver Zn and 65Zn levels were higher in MT+/+ mice. Plasma Zn concentrations were higher in MT-/- mice, with MT-/- ethanol-treated mice having levels greater than those of MT-/- saline-treated controls. MT+/+ ethanol-treated fetuses exhibited lower 65Zn transfer and whole Zn concentrations compared with MT+/+ and MT-/- saline and MT-/- ethanol fetuses. So we could examine changes in plasma Zn after ethanol treatment, MT+/+ and MT-/- mice were injected with 65Zn 3 days before they received ethanol treatment. Muscle and skin showed a decrease in 65Zn retention in both genotypes over 3 hr. There was a trend toward greater 65Zn release from skin and muscle at an earlier time in MT-/- mice: 24% vs. 2% decrease (MT-/- vs. MT+/+) for muscle and 28% vs. 15% decrease (MT-/- vs. MT+/+) for skin at 2 hr.ConclusionsThe results show (a) that ethanol interferes with the transfer of Zn to the fetus, and that this is MT dependent, and (b) that the increase in plasma Zn seen in MT-/- mice after ethanol administration is a result of Zn release from the skin and muscle, in the absence of hepatic Zn sequestration.Carey, Luke C. ; Coyle, Peter ; Philcox, Jeffrey C. ; Rofe, Allan M

Maternal ethanol exposure is associated with decreased plasma zinc and increased fetal abnormalities in normal but not metallothionein-null mice

BackgroundEthanol profoundly affects fetal development, and this is proposed to be due primarily to a transient fetal zinc (Zn) deficiency that arises from the binding of Zn by metallothionein (MT) in the maternal liver. Zn homeostasis and fetal outcome were investigated in normal (MT+/+) and metallothionein-null (MT-/-) mice in response to ethanol exposure.Methods/resultsMice were treated with saline or ethanol (0.015 m/g intraperitoneally at 0 and 4 hr) on day 8 of gestation (Gd8), and the degree of fetal dysmorphology was assessed on Gd18. The incidence of external abnormalities was significantly increased in offspring from MT+/+ dams exposed to ethanol, where 27.4% of fetuses were affected. MT-/- ethanol-, MT+/+ saline-, and MT-/- saline-treated dams had fetuses in which the frequencies of abnormalities were 2.2, 6.4, and 6.9%, respectively. To investigate Zn homeostasis, nonpregnant mice were killed at intervals over 16 hr after ethanol injection. Liver MT concentrations in MT+/+ mice were increased 20-fold by 16 hr, with a significant elevation evident by 4 hr, whereas liver Zn levels were also significantly increased by 2 hr and maintained for 16 hr. In parallel with these changes, plasma Zn concentrations in MT+/+ mice decreased by 65%, with minimum levels of 4.5+/-0.3 micromol/liter at 8 hr. Conversely, MT-/- mice exhibited increased plasma Zn concentrations, with peak values of 20.8+/-0.3 observed at 4 hr.ConclusionThese findings link the teratogenic effect of ethanol to the induction of maternal MT and the limitation of fetal Zn supply from the plasma.Carey, Luke C. ; Coyle, Peter ; Philcox, Jeffrey C. ; Rofe, Allan M