TXN and metabolic disease: Thioredoxin-interacting protein (Txnip), a vitamin D3-upregulated protein in 1α,25-dihydroxyvitamin D3 (1,25[OH]2D3)-treated HL-60 cells (7), acts as an endogenous inhibitor of the antioxidant thioredoxin (Trx), which is involved in a wide variety of cellular processes including the response to oxidative stress, cancer development, metabolic diseases, and inflammatory processes (8–13).