Zinc supplementation during pregnancy against mercury toxicity

Abstract

Objective To investigate the protective effect of zinc supplementation during pregnancy against mercury toxicity to mothers and newborns and the possible mechanism. Methods According to the maternal blood mercury levels at middle and late pregnancy, 90 pregnant women were equally divided into a case group (blood mercury5. 8 jug/L at middle and late pregnancy), a treatment group (blood mercury^5. 8 ug/L at middle pregnancy, daily supplementation of 10. 6 mg zinc till delivery), and a control group (normal blood mercury level at middle and late pregnancy). The levels of maternal blood mercury and zinc, and pregnancy outcomewere observed in the three groups. The expression of apoptosis-associated protein Bel-2 and Bax in the placenta tissue wasdetected by Western blotting analysis, and the apoptosis rate of cells in placenta tissue was detected by TUNEL assay in each group. Results The maternal blood mercury level at late pregnancy in the treatment group ([3. 42±0. 52] jug/L) was significantly lower than that in the case group ([6. 16±0. 32] /ng/L, P<0. 05) and that at middle pregnancy ([6. 15 ± 0. 26 ] ug/L, P < 0. 05) in the treatment group; the blood zinc level in the treatment group ([671. 34±44. 65] fg/L) was significantly higher than that in the case group ([483. 25 ±62. 20] fg/L, P<0. 05) and that at middle pregnancy ([480. 73±60. 64] fg/L, P<0. 05) in the treatment group. The incidence rates of premature labour, premature rupture of membranes (PROM), and small for gestational age (SGA) in the case group were significantly higher than those in the treatment group (P<0. 05). The apoptosis rate of cells in the placenta of the case group ([35. 20±4. 96]%) was significantlyhigher than those of the treatment group ([13. 47±2. 43]%) and the control group ([13. 27±2. 21]%, P< 0. 05). The expression level of Bax protein in the placenta of the case group (3 110. 38± 136. 09) was significantly higher than those in the treatment group (2 015. 76± 177. 63) and the control group (2 009. 90±152. 61, P<0. 05). The expression level of Bel-2 protein in the placenta of the case group (2 055. 97±280. 82) was significantly lower than that in the treatment group (5 187. 93 ± 247. 89) and the control group (5 308. 83 ± 259. 97, P < 0. 05). Conclusion Zinc supplementation during pregnancy has protective effect against mercury toxicity to mothers and newborns, which might be associatedwith up-regulation of Bcl-2 protein and down-regulation of Bax protein and the subsequent inhibition of cell apoptosis.