Quercetin and Thyroid

Abstract

Quercetin is the most abundant flavonoid present in fruits and vegetables. For its antiproliferative, antiviral, anti-inflammatory and antioxidants activities, it is an active ingredient of several herbal remedies and is available as a nutraceutical. Experimental studies performed in vitro have demonstrated that quercetin inhibits growth and function in normal thyroid cells and may act as a thyroid disruptor. These effects have also been confirmed in vivo using rodent models. Some studies have reported the ability of quercetin to interfere with the metabolism of thyroid hormones, since it inhibits the 5'-deiodinase type 1 (D1) activity in the thyroid, as well as in the liver. Besides the effects on normal thyroid cells, several experiments performed in vitro have shown a potential therapeutic role of quercetin in thyroid cancer. Indeed, quercetin inhibits the growth, the adhesion and the migration of thyroid cancer cells, and it also has redifferentiation properties in some thyroid cancer cell lines. In conclusion, these data suggest that, although its effects can be of benefit in hyperthyroidism and thyroid cancer, caution is required in the use of high doses of quercetin due to its anti-thyroid properties. Further in vivo studies are certainly needed to confirm these hypotheses.

Keywords: FRTL-5 cells; endocrine disruptors; flavonoids; quercetin; thyroid.

Figure 1

Chemical structures of the flavonols subgroup (A) and quercetin (B).

Figure 2

Inhibition of tritiated thymidine incorporation into DNA in FRTL-5 cells by quercetin. Cells were treated with various concentrations of quercetin (2.5 μM, grey line; 5 μM, orange line; 10 μM, light blue line) for the indicated time. Data points represent the mean ± SD of three separate experiments performed in triplicate and are expressed as percentages relative to the control (set to 100%). Comparable data were observed with the cell proliferation assay. * p < 0.05. From Reference [18].

Figure 3

Inhibition of the thyroid-specific genes NIS, TSHR, TG and TPO RNA expression by quercetin 10 μM after 48 h of treatment in the FRTL-5 cells. Data are expressed as percentages relative to the control (set to 100%) and represent the normalized (against actin) mean ± SD of three separate experiments. * p < 0.05. Data from References [4,18].