Mammalian cells have two major isoforms—a cytosolic thioredoxin 1 and a mitochondrial thioredoxin 2 that pair up with thioredoxin reductases 1 and 2 (TXNRD1 and TXNRD2), respectively.34,35 Auranofin inhibits both isoforms of thioredoxin reductase36 and is also an approved drug (Ridaura®) for the treatment of rheumatoid arthritis. This evidence concerns the gene TXNRD2 and rheumatoid arthritis.