UBC Theses and Dissertations
Dietary proteins as precursors of dipeptidyl-peptidase IV inhibitors — allies to complement pharmacotherapy in the management of type 2 diabetes Lacroix, Isabelle Marie Estelle
Inhibition of the enzyme dipeptidyl-peptidase IV (DPP-IV) is a promising approach for managing hyperglycemia in type 2 diabetes. The overall objective of this study was to produce, from dietary proteins, peptides able to inhibit the activity of DPP-IV and study their mechanisms of action. The potential of proteins from various food commodities to serve as precursors of DPP-IV inhibitors was first investigated using an in silico approach. Peptide sequences reported to have DPP-IV inhibitory activity were found in all proteins studied, including those from milk, a food product shown in several studies to have beneficial effects on glycemic regulation. Therefore, milk proteins were selected for hydrolysis using different proteases to release the active fragments. Fractionation of the most active hydrolysates, the peptic digests of whey protein isolate and α-lactalbumin, revealed a number of peptides with varying effectiveness and modes of inhibition. Among the sequences identified, the β-lactoglobulin-derived peptides ⁴⁶LKPTPEGDL⁵⁴ and ⁴⁶LKPTPEGDLEIL⁵⁷ displayed the greatest potency (IC₅₀ = 54 and 57 µM, respectively) and inhibited DPP-IV in an un-competitive manner. Peptide arrays were investigated as an alternative strategy to screen food proteins for the presence of DPP-IV inhibitory peptides within their sequences. Using SPOT technology, 114 deca-peptides spanning the entire sequence of α-lactalbumin were synthesized on cellulose membranes and their binding to and inhibition of DPP-IV were studied. SPOT- and traditionally-synthesized peptides displayed consistent trends in DPP-IV inhibitory activity, confirming that peptide arrays can be used to complement or support the traditional methods currently used to identify DPP-IV inhibitors. Lastly, the effect of protein-derived peptides on the activity of porcine and human DPP-IV, the two most commonly used species to assess DPP-IV activity in vitro, was compared. The enzymes differed in their susceptibility to inhibition by 43 of the 62 peptides investigated. Generally, porcine DPP-IV was inhibited more strongly than the human enzyme. Findings from this research showed that DPP-IV inhibitory peptides can be generated from dairy proteins. These natural inhibitors, although less effective than synthetic drugs, could be used to complement pharmacotherapy in the management of type 2 diabetes. Additional research to evaluate their efficacy in humans is, however, needed.
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