Indole-3-Butyric Acid, a Natural Auxin, Protects against Fenton Reaction-Induced Oxidative Damage in Porcine Thyroid

Abstract

We present results on the potential protective antioxidant properties of indole-3-butyric acid. Indole-3-butyric acid is an indole derivative defined as an auxin and widely known as a plant growth regulator. It naturally occurs in Arabidopsis thaliana, which is applied as a model plant in genetic studies. Oxidative damage to membrane lipids (lipid peroxidation; LPO) in porcine thyroid homogenates was induced by Fenton reaction substrates (Fe²⁺ + H₂O₂). Iron (Fe²⁺) was used in very high concentrations of 1200, 600, 300, 150, 75, 37.5, 18.75, 9.375, 4.687, and 2.343 µM. Indole-3-butyric acid (10.0, 5.0, 2.5, 1.25, and 0.625 mM) was applied to check whether it prevents the above process. The LPO level, expressed as malondialdehyde + 4-hydroxyalkenals (MDA + 4-HDA) concentration, was measured spectrophotometrically. Expectedly, Fenton reaction substrates, in a Fe²⁺ concentration-dependent manner, increased LPO level, with the lowest effective concentration of iron being 9.375 µM. In the case of almost all concentrations of indole-3-butyric acid, this auxin has exhibited very promising antioxidant protection, with the most effective concentrations being 10.0 and 5.0 mM; however, as low concentrations of indole-3-butyric acid at 1.25 mM was still effective. Indole-3-butyric acid used alone did not change the basal level of LPO, which is a favourable effect. To summarise, indole-3-butyric acid has protective antioxidant properties against experimentally induced oxidative damage to membrane lipids in the thyroid, and this is for the first time documented in the literature. This compound can be considered a natural protective agent present in plants, which can serve as a dietary nutrient.

Keywords: Fenton reaction; antioxidant; indole-3-butyric acid; iron; lipid peroxidation; porcine thyroid; reactive oxygen species.

Figure 1

Concentration of malondialdehyde and 4-hydroxyalkenals (MDA + 4-HDA) in porcine thyroid homogenates. Homogenates were incubated in the presence of FeSO₄·6H₂O (0.0, 1200, 600, 300, 150, 75, 37.5, 18.75, 9.375, 4.687, 2.343 µM) plus H₂O₂ (5.0 mM) used to induce LPO. Data are expressed as the amount of MDA + 4-HDA (nmol) per mg protein. Bars represent the mean ± SE of three independent experiments run in duplicates. ^a p < 0.05 vs. control ‘0’.

Figure 2

Concentration of malondialdehyde + 4-hydroxyalkenals (MDA + 4-HDA) in the porcine thyroid homogenates, which were incubated in the presence of different concentrations of FeSO₄·6H₂O (0.0, 1200, 600, 300, 150, 75, 37.5, 18.75, 9.375, 4.687, 2.343 µM) plus H₂O₂ (5.0 mM) and, additionally, in the presence of indole-3-butyric acid (0.0, 10.0, 5.0, 2.5, 1.25, 0.625 mM). Data are expressed as the amount of MDA + 4-HDA (nmol) per mg of protein. Bars represent the mean ± SE of three independent experiments run in duplicate. ^a p < 0.05 vs. control ‘0’; ^b p < 0.05 vs. respective concentration of Fe²⁺ ions with addition of H₂O₂ (without indole-3-butyric acid).

Figure 3

The concentrations of malondialdehyde + 4-hydroxyalkenals (MDA + 4-HDA) in porcine thyroid homogenates. Homogenates were incubated in the presence of FeSO₄·6H₂O and H₂O₂ used to induce LPO and, additionally, in the presence of indole-3-butyric acid (0.0, 10.0, 5.0, 2.5, 1.25, 0.625 mM). Data are expressed as the amount of MDA + 4-HDA (nmol) per mg of protein. Bars represent the mean ± SE of three independent experiments run in duplicates. ^a p < 0.05 vs. control ‘0’; ^b p < 0.05 vs. respective concentration of Fe²⁺ plus H₂O₂ (without indole-3-butyric acid).

Figure 4

Concentration of malondialdehyde and 4-hydroxyalkenals (MDA + 4-HDA) in porcine thyroid homogenates. Homogenates were incubated in the presence of indole-3-butyric acid (0.0, 10.0, 5.0, 2.5, 1.25, 0.625 mM). Data are expressed as the amount of MDA + 4-HDA (nmol) per mg protein. Bars represent the mean ± SE of three independent experiments run in duplicates.