Diabetes, one of the major metabolic diseases, has become a major public health concern worldwide leading to chronic lesions in various organs such as kidney and cardiovascular disease, severely impacting quality of life and life expectancy. Current drug treatments for diabetes have varying degrees of side effects. Therefore, finding natural, safe, and effective functional foods to prevent and control diabetes and its complications has become a research hotspot. Coreopsis tinctoria Nutt. (C. tinctoria) is rich in polyphenols (e.g. flavonoids), polysaccharides, and other bioactive components, possessing various health benefits. Studies have shown that C. tinctoria flavonoids lower blood sugar levels through multiple pathways, including suppressing oxidative stress, decreasing the inflammatory cascade, regulating glucose and lipid metabolism, increasing insulin sensitivity and improving insulin resistance. This review briefly summarizes the research progress on diabetes and its complications, and details the mechanisms of action of C. tinctoria bioactives in prevention and treatment of diabetes and its complications. The aim is to provide the molecular mechanisms of C. tinctoria and its bioactives for a potential application of C. tinctoria in controlling diabetes and its complications.

Polymethoxyflavones (PMFs) including 5,6,7,4′-tetramethoxyflavone (TMF), tangeretin, sinensetin, nobiletin, and 3,5,6,7,8,3′,4′-heptamethoxyflavone (HMF), possess multiple significant health-promoting activities. They have drawn increasing attention in recent years. However, the supply of pure singlemers of these PMFs, even the major content of tangeretin, nobiletin, HMF and TMF has been a limiting factor for their in vivo study and human testing, due to the difficulties in large scale preparation. Due to the close structural and configurational similarities of these PMFs in plants such as citrus peels, the purification to obtain single PMFs for in-depth efficacy evaluation has been an enormous challenge, preventing further large scale and broad study for their potential excellent biological properties. In this review, we summarized the up to date reported purification methods chiefly from citrus peel extract using various chromatography techniques to obtain singlemers of these PMFs. These methods including normal phase and reversed phase liquid chromatography, macroporous gel separation, counter current chromatography, and supercritical fluid chromatography as well as the combination of those isolation techniques. The aim of this review is to provide key references to establish an efficient and scalable separation method in acquiring single polymethoxyflavone isomers which will enable further investigations on the health-promoting and medicinal properties of these PMFs and associated mechanisms.