The hypoglycemic potency of guava leaf extract has been reported repeatedly by many research groups. This research was carried out with a focus on purifying the hypoglycemic compounds that reside in the aqueous partition of guava leaf extract, since our laboratory has identified the aqueous partition possesses the most potent hypoglycemic properties in in vivo. The chemical properties, phenol/flavonoid contents and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging ability, of those partitions were similar to other reports. The aqueous partition has the lowest contents in phenolic and DPPH scavenging contents, while its flavonoid content is among the lower groups along with butanol and hot water extracts.
The hypoglycemic compounds in the aqueous partition were further purified by LH -20 (hydroxypropyl dextran) columns with PTP1B inhibition as the screening method. The most potent PTP1B inhibitory fraction comes out after the main peak that suggests the hypoglycemic compound is a small molecule.
The HPLC can further purified the compound to near homogeneity but the acetonitrile inactivate the active compounds. The LC/MS method identified one major species in each of the electron spray, a 428 Da in the negative spray and a 516 Da in the positive spray.
A time course study reveals the aqueous partition has a unique slow inactivation property on PTP 1B enzyme activity. This slow inactivation is much less significant with hot water extract and not observed in other organic partitions. Therefore, it is suggested the inactivation of PTP 1B enzymatic activity is probably through a covalent bond inactivation, such as oxidation of cysteine reside.
