"Green" synthesized versus chemically synthesized zinc oxide nanoparticles: In vivo antihyperglycemic activity and pharmacokinetics

Zinc is one of the most studied trace elements, commonly used as supplement in diabetes treatment. By its involvement in the synthesis, secretion of insulin, promotion of insulin sensitivity and its multiple enzymatic functions it is known to contribute to reduce hyperglycemia. Researchers have shown that zinc administered under the form of zinc oxide nanoparticles (ZnONPs) is more effective than under its ionic form. Studies eval-uating the antihyperglycemic activity of these nanocarriers include both ZnONPs synthesised using plants (i.e. green synthesized) or chemically synthesized. The present work aims to compare green synthesized ZnONPs with the marketed chemically synthesized ones. Green ZnONPs were synthesized using the aqueous extract of the stem bark of the medicinal plant Panda oleosa and zinc nitrate hexahydrate. Both nanocarriers were compared in terms of optical properties, morphology, composition, chemical functions, resistance to oxidation, in vivo anti-hyperglycemic activity via oral glucose tolerance test (OGTT) and pharmacokinetics in relation to zinc in C57BL/ 6J mice. A UV absorption peak was observed at 354 nm and 374 nm for the green and marketed ZnONPs, respectively. The shape and hydrodynamic diameters were anisotropic and of 228.8 +/- 3.0 nm for the green ZnONPs and spherical and of 225.6 +/- 0.9 nm for the marketed ZnONPs. Phenolic compounds accounted for 2.58 +/- 0.04% of the green ZnONPs and allowed them to be more stable and unaffected by an oxidizing agent during the experiment, while the marketed chemically synthesized ZnONPs aggregated with or without contact with an oxidizing agent. No significant differences were observed on the amounts of zinc absorbed when comparing green ZnONPs, chemically synthesized ZnONPs and zinc sulfate in a pharmacokinetics study in normoglycemic mice. When evaluating the in vivo hypoglycemic activity of the nanocarriers in obese/diabetic mice, green synthesized ZnONPs displayed a significant hypoglycemic effect compared with the chemically synthesized nanoparticles following an OGTT. Altogether, these data indicate that phytocompounds, as catechin derivatives and polyphenols, attached to the green synthesized ZnONPs' surface, could contribute to their hypoglycemic activity. The comparison thus demonstrated that green synthesized ZnONPs are significantly more efficient than chemically ones at reducing hyperglycemia regardless of their absorption.