Objective: A preliminary study showed that geraniin extracted from Nephelium lappaceum L. at 50 mg/kg caused reduction in blood glucose and insulin resistance. The present study serves to further investigate the effects of geraniin at increasing doses between 3.125 and 100 mg/kg in high-fat diet-treated rats.
Methods: Geraniin (95% purity) was extracted and purified from rambutan rind. Two groups of male Sprague-Dawley rats were fed with 60% high-fat diet and standard rat chow, respectively, for 12 weeks. High-fat diet-treated rats were then administered geraniin at different doses. Body weight, blood pressure and blood glucose readings were measured. At the end of treatment, blood was collected for analysis of glycated haemoglobin A1c (HbA1c), insulin, advanced glycation end-product (AGE) levels, renin, aldosterone and electrolytes.
Results: Within the first week of treatment, even the lowest dose of geraniin caused a significant reduction in blood pressure, which was comparable to control diet-treated rats. There were no changes in serum electrolytes, renin or aldosterone. Similarly, there was a significant reduction in serum insulin, insulin resistance and AGE levels at the lowest dose. However, there was no significant decrease in fasting blood glucose or HbA1c. The effects of decreasing insulin, insulin resistance and AGEs were observed only at the lower doses, unlike the results observed for blood pressure reduction.
Conclusion: Geraniin at lower doses improved blood pressure and other metabolic parameters. Secondary metabolites of geraniin, associated with antihypertensive activity, are relatively different to those involved in inhibiting AGE formation and increasing insulin sensitivity. The secondary metabolites of geraniin may be individually responsible for the bioactivities demonstrated.
Keywords: Advanced glycation end-product levels; Geraniin; Hyperglycemia; Hypertension; Insulin resistance; Metabolic syndrome.
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