Hydrolysis enhances bioavailability of proanthocyanidin-derived metabolites and improves β-cell function in glucose intolerant rats.

Proanthocyanidins (PAC) are a highly consumed class of flavonoids and their consumption has been linked to beneficial effects in type 2 diabetes. However, limited gastrointestinal absorption occurs due to the polymeric structure of PAC. We hypothesized that hydrolysis of the PAC polymer would increase bioavailability, thus leading to enhanced beneficial effects on glucose homeostasis and pancreatic β-cell function. PAC-rich pea seed coats (PSC) were supplemented to a high-fat diet (HFD) either in native (PAC) or hydrolyzed (HPAC) form fed to rats for 4 weeks. HFD or low-fat diet groups were controls. PAC-derived compounds were characterized in both PSC and serum. Glucose and insulin tolerance tests were conducted. Pancreatic α-cell and β-cell areas and glucose-stimulated insulin secretion (GSIS) from isolated islets were measured. Increased PAC-derived metabolites were detected in the serum of HPAC-fed rats compared to PAC-fed rats, suggesting hydrolysis of PSC-enhanced PAC bioavailability. This was associated with ~18% less (P<.05) weight gain compared to HFD without affecting food intake, as well as improvement in glucose disposal in vivo. There was a 2-fold decrease of α/β-cell area ratio and a 2.5-fold increase in GSIS from isolated islets of HPAC-fed rats. These results demonstrate that hydrolysis of PSC-derived PAC increased the bioavailability of PAC-derived products, which is critical for enhancing beneficial effects on glucose homeostasis and pancreatic β-cell function.