The Protective Effect of Exogenous 17β-Estradiol against Experimentally Induced Oxidative Damage to Membrane Lipids Is Stronger in Male vs. Female Porcine Thyroids: Preliminary Results

Abstract

It is well-known that thyroid diseases are more prevalent in women than in men. The contribution of sex hormones may explain such disparity. The aim of this study was to check if there are any differences between sexes concerning the effects of 17β-estradiol on oxidative damage to membrane lipids (lipid peroxidation) in porcine thyroid homogenates under basal conditions and in the presence of Fenton reaction (Fe²⁺ + H₂O₂→Fe³⁺ + ^•OH + OH^-) substrates. We observed that 17β-estradiol did not change the basal level of lipid peroxidation (measured spectrophotometrically as concentrations of malondialdehyde + 4-hydroxyalkenals) in thyroid homogenates, and no differences were found between sexes. The lipid peroxidation level in response to Fe²⁺ + H₂O₂ plus 17β-estradiol was lower in male thyroids. In turn, in male thyroids, 17β-estradiol reduced experimentally induced lipid peroxidation in as low of a concentration as 0.1 μM, whereas in female thyroids the lowest effective concentration of 17β-estradiol was 10 μM, i.e., 100 times higher than in males. In conclusion, the protective effects of exogenous 17β-estradiol against experimentally induced oxidative damage to membrane lipids is stronger in male than in female thyroids. Our observation suggests that female tissue is less sensitive to the protective effects of exogenous 17β-estradiol. This sexual dimorphism of oxidative processes in the thyroid may constitute one of the mechanisms of the different prevalence of thyroid diseases in women and in men.

Keywords: 17β-estradiol; Fenton reaction; oxidative stress; sexual dimorphism; thyroid.

Figure 1

Lipid peroxidation, measured as MDA + 4-HDA level, and expressed in nmol per mg protein (A) or in nmol per mg tissue (B) in male (black bars) and female (striped bars) porcine thyroid homogenates. Homogenates were incubated in the presence of 17β-estradiol alone (1 mM; 100 μM; 10 μM; 1 μM; 100 nM; 10 nM; 1 nM; 100 pM; 10 pM; 1 pM). Bars represent the mean ± SE of three independent experiments run in duplicates. No significant differences were found.

Figure 2

Lipid peroxidation, measured as MDA + 4-HDA level, and expressed in nmol per mg protein (A) or in nmol per mg tissue (B) in male (black bars) and female (striped bars) porcine thyroid homogenates. Homogenates were incubated in the presence of 17β-estradiol (1 mM; 100 μM; 10 μM; 1 μM; 100 nM; 10 nM; 1 nM; 100 pM; 10 pM; 1 pM) together with Fenton reaction substrates [FeSO₄ (30 μM) + H₂O₂ (0.5 mM)]. Bars represent the mean ± SE of three independent experiments run in duplicates. ^■ p < 0.05 vs. Fe²⁺ + H₂O₂ (in the absence of 17β-estradiol) in male thyroid; * p < 0.05 vs. Fe²⁺ + H₂O₂ (in the absence of 17β-estradiol) in female thyroid; ^▲ p < 0.05 vs. the same concentration of 17β-estradiol in male thyroid.