Background: Thioredoxin reductase (E.C 18.104.22.168.; TrxR) is a widely distributed flavoprotein that
catalyzes the NADPH-dependent reduction of thioredoxin (Trx) in many cellular events such as DNA synthesis,
DNA repair, angiogenesis, antioxidative defense, and regulating apoptosis. Although TrxR is indispensible in
protecting cells against oxidative stress, the overexpression of TrxR is seen in many aggressive tumors. Therefore,
targeted inhibition of TrxR has been accepted as a new approach for chemotherapy.
Objective: In this study, in vitro inhibition effect of the lichen acids (diffractaic, evernic, lobaric, lecanoric, and
vulpinic acid) on mitochondrial TrxR purified from rat lung was investigated.
Method: It was the first time the enzyme was purified from rat lungs by using 2’, 5’-ADP Sepharose 4B affinity
chromatography. The purity of the enzyme was checked with SDS-PAGE. In vitro inhibition effect of the lichen
acids was investigated spectrophotometrically. To emphasize the importance of the obtained data, the commercial
anticancer drugs cisplatin and doxorubicin were used as positive controls.
Results: Molecular mass of the enzyme was calculated as approximately 52.4 kDa. The enzyme was purified
with a 63.6% yield, 208.3 fold, and 0.5 EU/mg proteins specific activity. The IC50 values of five lichen acids
were significantly lower than IC50 values of anticancer drugs.
Conclusion: All of the lichen acids, especially lecanoric and vulpinic acid, exhibited much stronger inhibitory
effect on TrxR than the anticancer drugs cisplatin and doxorubicin. These lichen acids have pharmacological
potential as effective natural antioxidants, antimicrobials, and anticancer agents.