General properties of PQQ: (A) Antioxidant function: PQQ in its reduced state acts as a potent antioxidant, efficiently catalyzing electron transfer reactions. (B) Enzyme cofactor: PQQ serves as an enzyme cofactor in lactate dehydrogenase. (C) Role in cellular pathways: PQQ influences mitochondrial biogenesis and fat metabolism (by regulating PGC-1α, PPAR-α, and PPAR-γ), cell regulation (by regulating MAPK and JAK pathways), and inflammation (through the modulation of NF-κB). (ArO(•)): aroxyl radicals; NAD+/NADH: nicotinamide adenine dinucleotide oxidized and reduced; JAK: Janus kinase; LDH: Lactate dehydrogenase; MAPK: mitogen-activated protein kinase; NF-κB: nuclear factor kappa-light-chain-enhancer of activated B cells; PGC-1α: proliferator-activated receptor gamma coactivator 1-alpha; PPAR-α and PPAR-γ: Peroxisome proliferator-activated receptors alpha and gamma; PQQox: pyrroloquinoline quinone; PQQred: pyrroloquinoline quinol; (ROO(•)):Peroxyl radicals. Created with BioRender.com, accessed on 10 August 2024.