HAIRLESS CANARY SEED (PHALARIS CANARIENSIS L.) PEPTIDES AND THEIR USE AS NUTRACEUTICALS COMPOUNDS
The ever-growing interest in novel food ingredients and their dietary influence on human health and wellbeing has driven the study of bioactive peptides (BAP). BAP are protein-derived fragments composed of (2-20 amino acids) that could positively affect bodily function and chronic diseases. This dissertation explores the health-promoting properties of a novel source of BAPs, namely canary seed, by encompassing three specific aims: 1) evaluate the in vitro potential of hairless canary seed peptides (CSP) as a nutraceutical ingredient, 2) develop an understanding of CSP's bioavailability and molecular interactions with its biological targets, and 3) evaluate CSP's antioxidant and antiobesity activity at the organism level using a nematode (C. elegans) and murine (C57BL/6J mice) model, respectively. First, CSP were generated by implementing mechanical oil extraction followed by commercial enzymatic hydrolysis with Alcalase™. In addition, CSP were also subject to simulated gastrointestinal digestion (SGD) to assess their gastric stability and in vitro bioavailability. The results showed that canary seed proteins were mainly composed of prolamins fractions followed by glutelins, globulins, and albumins. CSP extracts with low molecular weight (< 3 kDa and 3–10 kDa) showed the highest bioactivity. Furthermore, after SGD, CSP inhibitory activity remained stable toward angiotensin-converting enzyme (ACE), dipeptidyl peptidase IV (DPP-IV), and pancreatic lipase but unstable for α-glucosidase. The digested peptides were transported efficiently (>10%) through the Caco-2 monolayer, indicating a potential high absorption capacity through the intestinal epithelium. During kinetic analysis by Lineweaver-Burk plots, it was observed that CSP-SGD interacted by mixed-type inhibition for DPP-IV and α-glucosidase, non-competitive inhibition for ACE, and uncompetitive inhibitor for pancreatic lipase. Furthermore, CSP-SGD were especially potent as antihypertensive (ACE inhibitors) and antiobesity (pancreatic lipase) agents. Consequently, molecular docking and in silico analyses were targeted to understand CSP-SGD interactions with ACE and pancreatic lipase. CSP-SGD with ACE inhibitory activity were found to be rich in proline, glutamine, and cationic residues and could have inhibited ACE by destabilizing the tetrahedral transition state and zinc ions interaction leading to conformational changes in the enzyme structure. For peptides with antiobesity properties, it was also found that arginine, glycine, and hydrophobic amino acids from CSP-SGD hold critical interactions with the lid domain (CYS238-CYS262) of pancreatic lipase, disrupting its proper function and preventing fat hydrolysis.
In the second part of this dissertation, the relevant health-promoting properties of CSP were further investigated by testing the effects of peptide supplementation on obesity and oxidative stress animal models. The studies showed that exposure to CSP significantly mitigated the acute and chronic oxidative damage in C. elegans, extending the lifespan of the nematodes by 88 and 61%, respectively. Furthermore, it was established that the CSP prevented oxidative stress by scavenging free radicals and antioxidant gene upregulation. Concerning this, CSP caused a drop in reactive oxygen species (ROS) to safe levels and induce the upregulation of the GST-4 gene encoding antioxidant enzyme Glutathione S-transferase. Concerning antiobesity properties, the daily supplementation with CSP successfully prevented metabolic implications of western diet-induced obesity in C57BL/6J mice, including preventing weight gain by up to 20%, increasing glucose tolerance, and reducing insulin, leptin, and LDL/VLDL levels in plasma. Likewise, CSP promoted a drop in fatty acid uptake gene, LPL, and fatty acid biosynthesis genes FAS and ACC while unaffecting lipid oxidation genes PPAR-α and ACO in the liver. While both moderate and high CSP supplementation levels exhibit hypolipidemic effects, only moderate levels induce satiety and significantly prevent weight gain. Together, these results suggest that CSP's weight gain prevention depended on a dual mechanism involving lipid metabolism retardation to modulate satiety. Overall, the results presented in this dissertation establish the effectiveness of canary seed peptides as nutraceutical ingredients for antioxidant and antiobesity functional food applications.
This work is supported by the USDA National Institute of Food and Agriculture, Hatch Act formula funds project 1019794
- Doctor of Philosophy
- Food Science
- West Lafayette