FAP and type 2 diabetes mellitus: A 2024 randomized, placebo-controlled trial in type 2 diabetes patients (1000 mg twice daily for 12 weeks) found that, while circulating FGF-21 levels remained unchanged, metformin significantly suppressed fibroblast activation protein (FAP) activity and upregulated FGFR1c and β-klotho expression in adipose tissue.