Mechanism of Action and Interactions between Thyroid Peroxidase and Lipoxygenase Inhibitors Derived from Plant Sources

Abstract

This study focused on the effect of kaempferol, catechin, apigenin, sinapinic acid, and extracts from plants (i.e., parsley, cumin, mustard, green tea, and green coffee) on thyroid peroxidase (TPO) and lipoxygenase (LOX) activity, antiradical potential, as well as the result of interactions among them. Catechin, sinapinic acid, and kaempferol acted as a competitive TPO inhibitors, while apigenin demonstrated an uncompetitive mode of inhibitory action. Ethanol extracts from all plants acted as competitive TPO inhibitors, while, after in vitro digestion, TPO activation was found especially in the case of mustard (24%) and cumin (19.85%). Most importantly, TPO activators acted synergistically. The TPO effectors acted as LOX inhibitors. The most effective were potentially bioaccessible compounds from green tea and green coffee (IC₅₀ = 29.73 mg DW/mL and 30.43 mg DW/mL, respectively). The highest free radical scavenging ability was determined for catechin and sinapinic acid (IC₅₀ = 78.37 µg/mL and 84.33 µg/mL, respectively) and potentially bioaccessible compounds from mustard (0.42 mg DW/mL) and green coffee (0.87 mg DW/mL). Green coffee, green tea, cumin, and mustard contain potentially bioaccessible TPO activators that also act as effective LOX inhibitors, which indicate their potentially health-promoting effects for people suffering from Hashimoto's disease.

Keywords: antioxidant activity; dietary polyphenols; inhibition; lipoxygenase; thyroid peroxidase.

Figure 1

Mode of TPO inhibition by pure polyphenols: apigenin (A), catechin (B), kaempferol (C), and sinapinic acid (D).

Figure 2

Mode of TPO inhibition by ethanol extracts from parsley (A), green coffee (B), green tea (C), cumin (D), and mustard (E).

Figure 3

Mode of TPO influence by digested extracts of parsley (A), green coffee (B), green tea (C), cumin (D), and mustard (E).

Figure 4

Mode of LOX inhibition by ethanol extracts from parsley (A), green coffee (B), green tea (C), cumin (D), and mustard (E).

Figure 5

Mode of LOX inhibition by digested extracts from parsley (A), green coffee (B), green tea (C), cumin (D), and mustard (E).

Figure 6

Dose-normalized isobolograms for digested extracts from green tea and green coffee (A), cumin and green coffee (B), mustard and green tea (C), cumin and green tea (D), mustard and green coffee(E), mustard and cumin (F) affecting TPO activity.