<i>d</i>₄-Cystamine: A Deuterated Cystamine Derivative with Improved Anti-Inflammatory and Anti-Fibrotic Activities in a Murine Model of Fibrosing Steatohepatitis

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a multifactorial chronic disease that can progress to metabolic dysfunction-associated steatohepatitis (MASH) and liver fibrosis, ultimately leading to liver cirrhosis and hepatocellular carcinoma. Oxidative stress is believed to play an important role in the development of MASH. Small aminothiol compounds such as cysteamine and its oxidized precursor, cystamine, are known pleiotropic compounds that exhibit relatively potent antioxidant and other effects. Herein, we evaluate the efficacy of cystamine, as well as two deuterated derivatives, in a choline-deficient, L-amino acid-defined, high-fat-diet (CDAA-HFD) mouse model of rapidly progressing liver fibrosis. Compared to control mice, daily oral administration of isotopically reinforced cystamine derivatives (200 mg/kg) led to a significant reduction of liver fibrosis and inflammation as well as oxidative stress. Moreover, the efficacy of treatment appeared to increase with the deuteration state of cystamine, with the tetradeuterated derivative, <i>d</i> _<i>4</i> -cystamine, being the most effective. These results indicate that deuterated cystamine derivatives hold promise as potential candidates for the treatment of MASH.