Sexual dimorphism in the effect of maternal obesity on antioxidant defense mechanisms in the human placenta

Abstract

Introduction: Maternal obesity creates an adverse intrauterine environment, negatively impacts placental respiration, is associated with a higher incidence of pregnancy complications and programs the offspring for disease in adult life in a sexually dimorphic manner. We defined the effect of maternal obesity and fetal sex on pro- and anti-oxidant status in placenta and placental mitochondria.

Methods: Placental villous tissue was collected at term via c-section prior to labor from four groups of patients based on fetal sex and prepregnancy/1st trimester body mass index: lean - BMI 22.1 ± 0.3 (6 male, 6 female) and obese - BMI 36.3 ± 0.4 (6 male, 6 female). Antioxidant enzyme activity, mitochondrial protein carbonyls, nitrotyrosine residues, total and nitrated superoxide dismutase (SOD) and nitric oxide synthesis were measured.

Results: Maternal obesity was associated with decreased SOD and catalase activity, and total antioxidant capacity (TAC), but increased oxidative (protein carbonyls) and nitrative (nitrotyrosine) stress in a sexually dimorphic manner. Placentas of lean women with a male fetus had higher SOD activity and TAC (p < 0.05) than other groups whereas obese women with a male fetus had highest carbonyls and nitrotyrosine (p < 0.05). Glutathione peroxidase and thioredoxin reductase activity increased with obesity, significantly with a male fetus, perhaps as a compensatory response.

Conclusion: Maternal obesity affects oxidative stress and antioxidant activity in the placenta in a sexually dimorphic manner. The male fetus of a lean women has the highest antioxidant activity, a protection which is lost with obesity perhaps contributing to the increased incidence of adverse outcomes with a male fetus.

Keywords: Antioxidants; Mitochondria; Obesity; Oxidative stress; Placenta.

Figure 1

Effect of obesity on antioxidant activity in the placenta of lean and obese women. A. Superoxide dismutase (SOD) activity was expressed as SOD U/mg protein. Values are mean ± SEM. (a = p<0.05 vs lean male, n=5). B. Catalase (CAT) activity was measured as nmol formaldehyde (FCOH)/min/mg protein. Values are mean ± SEM. (* = p<0.05 vs lean, a = p<0.05 vs lean male, n=5). C. Total antioxidant capacity (TAC) was measured as μmole Trolox/mg protein in lean and obese women. Values are mean ± SEM. (a = p<0.05 vs lean male, b = p<0.05 vs obese male, n=5).

Figure 2

Effect of obesity on selenoproteins in placenta of lean and obese women. A. Glutathione peroxidase (GPx) activity was measured as nmol NADP⁺/min/mg protein. Values are mean ± SEM. (a = p<0.05 vs obese male, n=6). B. Thioredoxin reductase (TrxR) activity was measured as nmol 2-nitro-5-thiobenzoate (NTB)/min/mg protein. Values are mean ± SEM. (a = p<0.05 vs lean male, b = p<0.05 vs obese female, n=5)

Figure 3

Effect of obesity on oxidative stress in placental mitochondria. Protein carbonyls were measured as mmol/mg protein in lean and obese women. Values are mean ± SEM. (a = p<0.05 vs lean male, n=5)

Figure 4

Effect of obesity on placental nitric oxide (NO) generation and mitochondrial nitrative stress. A. NO generation was measured as Total nitrate/nitrite levels (pmol/mg protein) in lean and obese women. Values are mean ± SEM. (* = p<0.05 vs lean, a = p<0.05 vs obese male, n=5). B. Western analysis of placental mitochondrial nitrotyrosine (3-NT) residues. Density for each band was normalized to its loading control (VDAC). Values are mean ± SEM. (* = p<0.05 vs lean, a = p<0.05 vs lean female, b = p<0.05 vs lean male).

Figure 5

Effect of obesity induced nitrative stress on mitochondrial manganese superoxide dismutase (MnSOD). A. Western analysis of placental mitochondrial MnSOD. Density of each band was normalized to its loading control voltage-dependent anion channel (VDAC). Values are mean ± SEM. (a = p<0.05 vs obese male, n=6). B. Western analysis following immunoprecipitation of placental mitochondrial nitrated MnSOD. Density of each band was normalized to its loading control IgG from the immunoprecipitation. Values are mean ± SEM. (a = p<0.05 vs lean female, b = p<0.05 vs lean male, n=6). C. Ratio of nitrated MnSOD to Total MnSOD. Values are mean ± SEM. (n=6)