A Comparative Study on Improving Streptozotocin-Induced Type 2 Diabetes in Rats by Hydrosol, Extract and Nanoemulsion Prepared from Cinnamon Leaves

Cinnamomoum osmophloeum Kanehira (C. osmophloeum) contains various biologically active antioxidant compounds such as flavonoids, phenolic acids and cinnamaldehyde. Type 2 diabetes mellitus is a chronic disease of metabolic abnormality caused by insulin deficiency or resistance. The objectives of this study were to analyze various bioactive compounds in C. osmophloeum leaves by ultra-high-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS), and compare the effects of hydrosol, extract and nanoemulsion prepared from C. osmophloeum leaves on improving type 2 diabetes in rats. Our results show that a total of 15 bioactive compounds in C. osmophloeum leaves, including quercetin, quercetin-3-O-galactoside, quercetin-3-O-glucoside, rutin, caffeic acid, benzoic acid, 5-O-caffeoylquinic acid, kaempferol 3-β-D-glucopyranoside, trans-cinnamic acid, coumarin, cinnamyl alcohol, p-coumaric acid, eugenol, kaempferol and cinnamaldehyde, were separated within 14 min for subsequent identification and quantitation by UPLC-MS/MS. The nanoemulsion was successfully prepared by mixing C. osmophloeum leaf extract, soybean oil, lecithin, Tween 80 and deionized water in an appropriate proportion with a mean particle size, polydispersity index, zeta potential and encapsulation efficiency of 36.58 nm, 0.222, −42.6 mV and 91.22%, respectively, while a high storage and heating stability was obtained. The animal experiment results reveal that the high-dose nanoemulsion was the most effective in reducing both fasting blood glucose and oral glucose tolerance test value, followed by low-dose nanoemulsion, high-dose extract, low-dose extract and leaf powder in hydrosol. A similar trend was shown in reducing serum insulin and the homeostatic model assessment of insulin resistance index. In addition, the contents of serum biochemical parameters, including total cholesterol, triglyceride, aspartate aminotransferase, alanine aminotransferase, uric acid, urea nitrogen and creatinine, were reduced, with the high-dose nanoemulsion showing the most pronounced effect. Collectively, the high-dose nanoemulsion may possess great potential to be developed into a hypoglycemic health food or botanic drug.