A clinical trial evaluated the correlation between serum ornithine levels in RA patients and their degree of remission after the administration of sinomenine (SIN, 120 mg, twice daily), and revealed the potential therapeutic mechanism by which SIN could upregulate the gene expression level of Arg1, thereby inducing a reduction in arginine and further downregulation of ornithine (Shi et al., 2022). Here, ARG1 is linked to rheumatoid arthritis.