Protective Effects of a Polyphenol-Rich Extract from Syzygium cumini (L.)‎ Skeels Leaf on Oxidative Stress-Induced Diabetic Rats

Abstract EN

Syzygium cumini (L.) Skeels has been reported to exert anti-inflammatory and cardiometabolic activities due to its high content of polyphenols.

We characterized the chemical composition and assessed the antidiabetic effects of a novel polyphenol-rich extract (PESc) obtained from S.

cumini leaf.

Rats were injected with alloxan (150 mg/kg, ip, ALX group) and followed up for 7 days.

Some were orally treated with PESc (50 mg/kg/day) for 7 days before and after diabetes induction (ALX-PP) or only for 7 days after alloxan injection (ALX-P).

ALX-P and ALX-PP decreased fasting glycemia in 37 and 43%, respectively, as compared to ALX.

Triglycerides and total cholesterol serum levels were also significantly reduced in comparison to ALX.

PESc presented high polyphenol concentration (71.78 ± 8.57 GAE/100 g), with flavonoid content of 8.21 ± 0.42 QE/100 g.

Upon HPLC-MS/MS and MS/MS studies, five main polyphenols—gallic acid, quercetin, myricetin, and its derivatives—were identified.

Myricetin was predominant (192.70 ± 16.50 μg/mg PESc), followed by measurable amounts of gallic acid (11.15 ± 0.90 μg/mg PESc) and quercetin (4.72 ± 0.06 μg/mg PESc).

Kinetic assessment of total antioxidant capacity revealed PESc high potency, since maximum response was reached within 5 min reaction time in a concentration-dependent manner.

Specific antioxidant activity of PESc was assessed against both DPPH• and ABTS•+, showing strong activity (IC50: 3.88 ± 1.09 and 5.98 ± 1.19 μg/mL, resp.).

PESc also inhibited lipoxygenase activity (IC50: 27.63 ± 8.47), confirming its antioxidant activity also on biologically relevant radicals.

Finally, PESc induced insulin secretion by directly stimulating INS-1E β cells in the absence of any cytotoxic effect.

Overall, our results support that PESc is a potent antioxidant phytocomplex with potential pharmacological use as a preventive antidiabetic natural product.