Potential of rooibos, its major C-glucosyl flavonoids, and Z-2-(β-D-glucopyranosyloxy)-3-phenylpropenoic acid in prevention of metabolic syndrome

ABSTRACT

Risk factors of type 2 diabetes mellitus (T2D) and cardiovascular disease (CVD) cluster together and are termed the metabolic syndrome. Key factors driving the metabolic syndrome are inflammation, oxidative stress, insulin resistance (IR), and obesity. IR is defined as the impairment of insulin to achieve its physiological effects, resulting in glucose and lipid metabolic dysfunction in tissues such as muscle, fat, kidney, liver, and pancreatic β-cells. The potential of rooibos extract and its major C-glucosyl flavonoids, in particular aspalathin, a C-glucoside dihydrochalcone, as well as the phenolic precursor, Z-2-(β-D-glucopyranosyloxy)-3-phenylpropenoic acid, to prevent the metabolic syndrome, will be highlighted. The mechanisms whereby these phenolic compounds elicit positive effects on inflammation, cellular oxidative stress and transcription factors that regulate the expression of genes involved in glucose and lipid metabolism will be discussed in terms of their potential in ameliorating features of the metabolic syndrome and the development of serious metabolic disease. An overview of the phenolic composition of rooibos and the changes during processing will provide relevant background on this herbal tea, while a discussion of the bioavailability of the major rooibos C-glucosyl flavonoids will give insight into a key aspect of the bioefficacy of rooibos.

KEYWORDS:

• Dihydrochalcone
• aspalathin
• flavones
• orientin
• isoorientin
• diabetes
• obesity
• bioavailability

Acknowledgments

Funding for collaboration was provided by the National Research Foundation (NRF) of South Africa (grants 75425, 85105 and 95520 to E. Joubert.) and the Japanese Society for the Promotion of Science (grants to K. Yagasaki and Y. Miura). The NRF grant holder (EJ) acknowledges that opinions, findings, and conclusions or recommendations expressed in any publication generated by the NRF supported research are those of the authors, and that the NRF accepts no liability whatsoever in this regard. The funding bodies had no involvement in the study design, collection, analysis and interpretation of data, writing of the manuscript, or decision to publish the work.