[Lipid, protein oxidation and antioxidant status in menopausal women with different levels of vitamin D in blood].

Abstract

The relevance of this study is due to the high prevalence of vitamin D deficiency in menopausal women, as vitamin D is a modulator of free-radical oxidation and antioxidant defense processes. However, the mechanisms by which vitamin D regulates free-radical homeostasis remain poorly understood and have not been definitively interpreted. The aim of the study was to evaluate the nature of changes in the parameters of free-radical oxidation of lipids, proteins, and the state of antioxidant protection in women of the menopausal period with different levels of 25-OH vitamin D in blood serum.

Material and methods: 98 menopausal women were divided into three groups depending on their 25-OH vitamin D serum levels: control (30-50 ng/mL, n=20), 25-OH vitamin D insufficiency (20-29.9 ng/ml, n=31), and 25-OH vitamin D deficiency (˂20 ng/ ml, n=47). The 25-OH vitamin D deficiency group was additionally stratified into moderate (15-19.9 ng/ml, n=20) and severe (<15 ng/ ml, n=27) deficit. Free radical oxidation parameters were determined in all women by spectophotometry, including level of lipid peroxidation substrates with isolated double bonds, conjugated dienes (CD), ketodienes and conjugated trienes (KD-CT), thiobarbituric acid reactive substances (TBARS), Schiff bases and advanced oxidation protein products (AOPP). The assessment of the components of the antioxidant defense system included the determination of the total antioxidant activity (TAA) of blood plasma using spectophotometry, the activity of superoxide dismutase (SOD) in erythrocyte lysate using photometry, the level of α-tocopherol and retinol in plasma using fluorometric methods, the level of reduced (GSH) and oxidized glutathione (GSSG) in erythrocyte lysate using fluorometric method with the calculation of their ratio (GSH/GSSG) and the content of glutathione-Stransferase π in serum (GSTP) using ELISA.

Results: In menopausal women with insufficient 25-OH vitamin D levels, SOD activity (p=0.016) and α-tocopherol levels (p=0.018) increased, while GSTP concentration decreased (р=0.023) relative to the control group. In 25-OH vitamin D deficiency α-tocopherol level (p=0.042) increased while TBARS (p=0.013) and Schiff bases (p=0.002) levels decreased relative to the control group and group with micronutrient deficiency (р=0.049 and р=0.025 accordingly). Positive correlations were found between the level of 25-OH vitamin D and the TBARS (ρ=0.20, p=0.05) and Schiff bases (ρ=0.31, p=0.002). Under moderate 25(OH)D deficiency an increase in ТАА (p=0.049), α-tocopherol (p=0.003) and retinol (p=0.026) levels and a decrease in the levels of TBARS (p=0.021), Schiff bases (p=0.024), AOPP (p=0.043), GSH (p=0.043) and GSH/GSSG (p=0.030) were observed compared to the control. In severe 25(OH) D deficit a decrease in the levels of TBARS (p=0.041) and Schiff bases (p=0.002) relative to the control was revealed. Comparison of subgroups with different levels of 25(OH)D deficiency showed an increase in the content of CD (p=0.05), KD-CT (p=0.048) and a decrease in α-tocopherol (p=0.033) and retinol (p=0.05) level with increasing vitamin D deficiency.

Conclusion: Changes in the parameters of free radical oxidation of lipids, proteins and the state of antioxidant protection in women during menopause are most likely nonlinear, stage-by-stage in nature and are associated with the degree of vitamin D supply. As the deficiency worsens, redox-adaptive reactions give way to depletion of antioxidant potential and the prevalence of maladaptive processes, confirming the regulatory role of vitamin D in maintaining redox homeostasis.