Apple and banana displayed better inhibition of dipeptidyl peptidase IV activity than vildagliptin

[Speaker] Idowu M Kazeem:1
[Co-author] Naomi O Awenegieme:1
1:Department of Biochemistry, Lagos State University, Ojo, Lagos, Nigeria

Background: The inhibition of dipeptidyl peptidase-IV (DPP-IV) activity increases the level of glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), which in turn reduces diabetes-induced hyperglycemia. A group of synthetic drugs known as gliptins have been developed to inhibit the activity of this enzyme. However, these drugs are bedevilled with many drawbacks including deleterious side effect and safety concerns. Therefore this study is aimed at evaluating the inhibitory effect of some tropical fruits on the activity of DPP-IV since they are part of human diet.

Methods: Appropriate concentrations of the fruit juices were incubated with the enzyme and substrate (Gly-Pro-p-nitroanilide) for 30 minutes at 37 degrees Celsius. The reactions were stopped with the addition of glacial acetic acid and absorbance measured. Modes of inhibition of the enzyme were tested by varying the concentrations of the substrate. The percentage inhibition, concentration of samples required to inhibit 50% of the enzyme activity (IC50) and modes of inhibition were determined using Microsoft Excel and GraphPad Prism 6.0.

Results: All the fruits exhibited concentration-dependent inhibition of DPP-IV. However from the IC50 calculated, apple and banana displayed the strongest inhibition of the enzyme with IC50 55.84 and 76.49 microgram/mL respectively. These values are also significantly lower than the standard, vildagliptin (IC50: 110.95 microgram/mL), making them more potent than it. Lineweaver-Burk plot revealed that the apple and banana juice inhibited the enzyme in a non-competitive and competitive manner respectively.

Conclusions: Out of the fruits tested, apple and banana exhibited the most effective inhibition of DPP-IV and their activities were better than the standard drug, vildagliptin. It can, therefore, be concluded that fruits, especially apple and banana, are potent inhibitors of DPP-IV activity. Their consumption can also help in the management of diabetes mellitus and its associated complications. Further studies are required to isolate the bioactive compounds responsible for these activities.

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