Effect of folic acid on homocysteine-induced trophoblast apoptosis.

In trophoblast cells exposed to homocysteine (Hcy) we observed cellular apoptosis and the inhibition of trophoblast functions. Because folate and Hcy, linked in the same metabolic pathway, are inversely related, we investigated the role of folic acid in reversing the Hcy effect in human placenta. In primary trophoblast cells we examined the cytosolic release of cytochrome c, both M30 and terminal deoxynucleotidyl transferase-mediated dUDP nick-end labelling (TUNEL) and DNA laddering. Hcy (20 micromol/l) treatment resulted in cytochrome c release from mitochondria to the cytosol, and an increased number of M30-positive trophoblast cells and TUNEL positive nuclei. Furthermore, DNA cleavage in agarose gel and the determination of histone-associated DNA fragments have been investigated. Homocysteine induced DNA fragmentation and significantly reduced hCG secretion. The addition of folic acid (20 nmol/l) resulted in inhibition of the effects of Hcy on human trophoblast. These results suggest a protective role of folic acid in the prevention of trophoblast apoptosis linked to Hcy.

Retinoic acid modulates the cell-cycle in fetal rat hepatocytes and HepG2 cells by regulating cyclin-cdk activities.

Retinoic acid (RA), the most biologically active metabolite of vitamin A, is known to modulate cell proliferation, apoptosis and differentiation, with different effects depending on the cellular context. Retinoic acid can exert its effects by directly or indirectly influencing the expression of genes involved in the control of cell proliferation. In the present report we investigate the possible correlation between the antiproliferative, differentiative and apoptotic effects previously observed on rat hepatocytes and HepG2 cells, with a possible modulation of cell-cycle regulators. We demonstrate that RA induces growth arrest and differentiation in HepG2 cells by influencing the activities of cyclin-cdk complexes involved in the regulation of G1/S transition and S-phase progression, in particular by modifying the binding of these complexes to p21 and p27 inhibitors. In fetal cells, however, the induction of apoptosis and differentiation by RA was obtained via inhibition of cyclin D1-cdk4 activity, as result of an increased binding to the p16 inhibitor. Retinoic acid also modulates c-myc and Bcl-2 expression. In conclusion, our data suggest that RA could be useful to regulate the reversion of transformed phenotype and could also be utilized as a chemiopreventive agent in cells of hepatic origin.