Metabolic conversion of retinol to retinoic acid mediates the biological responsiveness of human mammary epithelial cells to retinol.

The biological effects of vitamin A are mediated in part by retinoic acid (RA) modulation of gene transcription. In this study, we examined whether normal human mammary epithelial cells (HMECs) are biologically responsive to retinol (ROH), the metabolic precursor of RA. While both ROH and tRA resulted in time- and dose-dependent decreases in total cell number, tRA was markedly more potent. Metabolically, treatment of HMECs with physiological doses of ROH resulted in rapid uptake and subsequent production of both retinyl esters and tRA. Although a comparatively minor metabolite, tRA levels peaked at 6 h and remained above endogenous levels for up to 72 h in proportion to cellular ROH concentrations. In HMECs transfected with an RA-responsive luciferase reporter gene, treatment with 3 microM ROH resulted in an increase in luciferase activity to a level intermediate between that observed with 0.001 and 0.01 microM tRA. Citral, an RA-synthesis inhibitor, was also used to examine the biological activity of ROH. Compared to ROH alone, ROH plus citral treatment resulted in three-fold less tRA synthesis and a > 65% attentuation of RA-responsive reporter gene activity which persisted through 72 h. Citral also significantly attenuated the extent of ROH-mediated reductions in total HMEC number. Thus, treatment with physiological concentrations of ROH results in fewer total numbers of HMECs and this response is a consequence of cellular tRA synthesis which can induce RA-responsive gene expression.

Rat embryos cultured under copper-deficient conditions develop abnormally and are characterized by an impaired oxidant defense system.

Rat embryos (gestation days 9.0 and 10.0) obtained from dams that were fed a Cu-adequate (8 micrograms Cu/g) or Cu-deficient (< 0.5 micrograms Cu/g diet were cultured for 48 hr in Cu-adequate (16.2 microM) or Cu-deficient (1.0 microM) rat serum. Control embryos cultured in control serum were morphologically normal. Embryos from Cu-deficient dams developed abnormally when cultured in Cu-deficient serum; the abnormalities included distended hindbrains, blisters, blood pooling, and cardiac defects. Control embryos cultured in Cu-deficient serum and Cu-deficient embryos cultured in control serum also showed abnormal development, but to a lesser degree than that of the Cu-deficient embryos cultured in Cu-deficient serum. To test the idea that the above abnormalities were due in part to free radical induced damage occurring secondary to an impaired oxidant defense system, a chemiluminescence assay was used to detect superoxide dismutase (SOD) activity in the cultured embryos. SOD activity was lowest in embryos cultured in Cu-deficient serum. When the Cu-deficient serum was supplemented with antioxidants (CuZnSOD or glutathione peroxidase), its teratogenicity was reduced. These data support the idea that an impaired oxidant defense system contributes to the dysmorphology associated with Cu deficiency. However, the Cu-deficient embryos also had low cytochrome c oxidase activity compared to control embryos--thus, multiple factors are likely contributing to Cu deficiency-induced abnormalities.

Effect of copper deficiency on prenatal development and pregnancy outcome.

Copper deficiency during embryonic and fetal development can result in numerous gross structural and biochemical abnormalities. Such a deficiency can arise through a variety of mechanisms, including low maternal dietary copper intake, disease-induced or drug-induced changes in maternal and conceptus copper metabolism, or both. These issues are discussed in this article along with the use of in vitro embryo culture models to study the mechanisms underlying copper deficiency-induced teratogenesis. Current data suggest that changes in free radical defense mechanisms, connective tissue metabolism, and energy production can all contribute to the dysmorphogenesis associated with developmental copper deficiency.

Restricting oxygen supply to the prospective dorsal side does not reverse axis polarity in embryos of Xenopus laevis.

During the first cell cycle, the prospective dorsal side of the embryo of Xenopus laevis becomes enriched in mitochondria relative to the ventral side. This differential distribution of mitochondria persists throughout early development, but it is not known if it is of functional significance, since there do not appear to be dorsal-ventral differences in metabolic rate. However, the unilateral anaerobiosis experiments of Landström and Løvtrup do suggest a role for energy metabolism in determining axis polarity. These experiments apparently show that restricting oxygen supply to the prospective dorsal side causes a reversal of dorsal-ventral axis polarity. We have reinvestigated this point using cell-marking techniques. We find that although gastrulation is initiated at the open end of the tube, the polarity of neural plate development is unaffected. Thus, definitive dorsal-ventral polarity is not affected by the experimental treatment, and it is unlikely that gradients of energy metabolism have a role in specifying axis polarity in X. laevis.