CDK5 and metabolic disease: Because the polypharmacological effects of butyrolactone I on both CDK5 and PPARγ can offer new therapeutic opportunities to treat metabolic diseases and cancers, further studies should be directed to elucidate the polypharmacological outcome of butyrolactone I in various in vivo disease models, especially associated with its additive or synergistic effects on both metabolic diseases and human cancers.