Silychristin, a Flavonolignan Derived From the Milk Thistle, Is a Potent Inhibitor of the Thyroid Hormone Transporter MCT8

[helvella]

We have seen many claims for Milk Thistle over the years. Often suggested for people with liver-related issues.

But the only person I know who tried it felt unwell from taking it. So I have long been cautious.

This paper identifies a potentially significant issue with a constituent of Milk Thistle.

I have already posted about its possible impact in pregnancy:

healthunlocked.com/thyroidu...

Endocrinology . 2016 Apr;157(4):1694-701.

doi: 10.1210/en.2015-1933. Epub 2016 Feb 24.

Silychristin, a Flavonolignan Derived From the Milk Thistle, Is a Potent Inhibitor of the Thyroid Hormone Transporter MCT8

Jörg Johannes 1 , Roopa Jayarama-Naidu 1 , Franziska Meyer 1 , Eva Katrin Wirth 1 , Ulrich Schweizer 1 , Lutz Schomburg 1 , Josef Köhrle 1 , Kostja Renko 1

Affiliations

• PMID: 26910310

• DOI: 10.1210/en.2015-1933

Abstract

Thyroid hormones (THs) are charged and iodinated amino acid derivatives that need to pass the cell membrane facilitated by thyroid hormone transmembrane transporters (THTT) to exert their biological function. The importance of functional THTT is affirmed by the devastating effects of mutations in the human monocarboxylate transporter (MCT) 8, leading to a severe form of psychomotor retardation. Modulation of THTT function by pharmacological or environmental compounds might disturb TH action on a tissue-specific level. Therefore, it is important to identify compounds with relevant environmental exposure and THTT-modulating activity. Based on a nonradioactive TH uptake assay, we performed a screening of 13 chemicals, suspicious for TH receptor interaction, to test their potential effects on THTT in MCT8-overexpressing MDCK1-cells. We identified silymarin, an extract of the milk thistle, to be a potent inhibitor of T3 uptake by MCT8. Because silymarin is a complex mixture of flavonolignan substances, we further tested its individual components and identified silychristin as the most effective one with an IC50 of approximately 100 nM. The measured IC50 value is at least 1 order of magnitude below those of other known THTT inhibitors. This finding was confirmed by T3 uptake in primary murine astrocytes expressing endogenous Mct8 but not in MCT10-overexpressing MDCK1-cells, indicating a remarkable specificity of the inhibitor toward MCT8. Because silymarin is a frequently used adjuvant therapeutic for hepatitis C infection and chronic liver disease, our observations raise questions regarding its safety with respect to unwanted effects on the TH axis.

Full paper accessible here:

academic.oup.com/endo/artic...

[helbell]

I have been considering milk thistle, many thanks gor this information.

[carorueil]

Thank you for this - I've occasionally used this from what I've read it doesn't seem to include Milk Thistle avogel.co.za/products/herba... but perhaps I'll give it a miss just in case it has similar effects!

[Marz]

healthunlocked.com/thyroidu...

...and then there's your earlier 'blockbuster' in Related Posts 🥰

[LindaC]

Fascinating - thank you helvella.