<p>  </p> <p>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 <em>in vitro </em>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 (<em>C. elegans</em>) 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 <em>in vitro</em> 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 <em>in silico</em> 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.</p> <p>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 <em>C. elegans</em>, 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.</p>

La prévalence de l’obésité, du diabète de type 2, et du syndrome métabolique, sont à la hausse chez les Cris d’Eeyou Istchee (CEI-Nord du Québec). Ces problèmes sont aggravés par leur diète non traditionnelle, leur sédentarité, ainsi que par une résistance culturelle aux produits pharmaceutiques. Afin de développer des traitements antidiabétiques culturellement adaptés, notre équipe a effectué une enquête ethnobotanique qui a identifié 17 plantes provenant de la pharmacopée traditionnelle des CEI. À partir des études de criblage effectuées in vitro, deux plantes parmi les 17 ont attiré notre attention. Populus balsamifera L. (Salicaceae) pour ses propriétés anti-obésité et Larix laricina K. Koch (Pinaceae) pour ses propriétés antidiabétiques. P. balsamifera et son composé actif salicortin ont inhibé l’accumulation de triglycérides durant l’adipogénèse dans les adipocytes 3T3-L1. L. laricina a augmenté le transport de glucose et l’activation de l’AMPK dans les cellules musculaires C2C12, l’adipogénèse dans les 3T3-L1 et a démontré un fort potentiel découpleur (propriété anti-obésité). Les objectifs de cette thèse sont d'évaluer les potentiels anti-obésité et antidiabétique et d’élucider les mécanismes d'action de P. balsamifera, salicortin, et L. laricina chez la souris C57BL/6 rendue obèse par une diète riche en gras (HFD). Les souris ont été soumises pendant huit (étude préventive) ou seize semaines (étude traitement) à une HFD, ou à une HFD dans laquelle P. balsamifera, salicortin, ou L. laricina a été incorporé soit dès le départ (prévention), ou dans les 8 dernières des 16 semaines d'administration de HFD (traitement). iv Les résultats démontrent que P. balsamifera (dans les deux études) et salicortin (évalué dans l’étude traitement) diminuent: le poids corporel, le gras rétropéritonéal, la sévérité de la stéatose et l’accumulation de triglycérides hépatique (ERK impliqué), les niveaux de glycémie et d'insuline, et le ratio leptine/adiponectine. Dans les deux études, P. balsamifera a significativement réduit la consommation de nourriture mais cet effet coupe-faim nécessite d’être approfondi. Dans l'étude préventive, P. balsamifera a augmenté la dépense énergétique (hausse de la température à la surface de la peau et de l’activation de la protéine découplante-1; UCP-1). Les voies de signalisation activées par P. balsamifera et par salicortin (de façon plus modeste) sont impliquées dans: la production de glucose hépatique (Akt), l’expression de Glut4 dans le muscle squelettique, la captation du glucose et du métabolisme des lipides (Akt dans le tissu adipeux), la différenciation des adipocytes (ERK et PPARg), l’inflammation dans le foie (IKKαβ), et l'oxydation des acides gras dans le muscle, le foie, ou le tissu adipeux (PPARa et CPT-1). D’autre part, L. laricina a également diminué les niveaux de glycémie et d’insuline, le ratio leptine/adiponectine, le gras rétropéritonéal et le poids corporel. Ces effets ont été observés en conjonction avec une augmentation de la dépense énergétique: hausse de température à la surface de la peau (prévention) et amélioration de la fonction mitochondriale et de la synthèse d'ATP (traitement). En conclusion, l’utilisation de P. balsamifera, salicortin et L. laricina comme des traitements alternatifs et culturellement adaptés aux CEI représente une contribution importante dans la prévention et le traitement de l’obésité et du diabète. / The prevalence of obesity, insulin resistance, and the metabolic syndrome is increasing among the Cree of Eeyou Istchee (CEI - Northern Quebec). Non-traditional diet and sedentary lifestyle along with cultural disconnect of modern type 2 diabetes (T2D) therapies are involved. In order to establish culturally adapted antidiabetic treatments, our research team conducted an ethnobotanical survey, where 17 plants were identified from the CEI traditional pharmacopoeia. Based on data obtained from in vitro screening studies, two plant species out of 17 were of particular interest for their properties as antiobesity, namely Populus balsamifera L. (Salicaceae), and antidiabetic agents, namely Larix laricina K. Koch (Pinaceae). P. balsamifera and its active salicortin inhibited triglyceride accumulation during adipogenesis in 3T3-L1 adipocytes. L. laricina increased glucose uptake and AMPK activation in C2C12 myotubes, adipogenesis in the 3T3-L1 adipocyte cell line, and was observed as one of the strongest uncouplers, severely disrupting mitochondrial function (increasing fuel consumption/metabolic rate; antiobesity property). The purpose of this PhD thesis is to evaluate the antiobesity and antidiabetic potential of P. balsamifera, salicortin, and L. laricina, in an in vivo model of diet-induced obese (DIO) C57BL/6 mice, as well as to investigate their possible mechanisms of action. Mice were subjected for eight (prevention study) or sixteen weeks (treatment study) to a high fat diet (HFD), or HFD to which P. balsamifera, salicortin, or L. laricina were incorporated either at onset (prevention), or in the last 8 of the 16 weeks of administration of the HFD (treatment). The results showed that P. balsamifera (in either study) and salicortin (incorporated in HFD only in treatment study) decreased the weight of whole vii body, retroperitoneal fat pad, reduced the severity of hepatic macrovesicular steatosis and triglyceride accumulation (ERK pathway implicated). They also decreased glycemia and improved insulin sensitivity by diminishing insulin levels, and altering adipokine secretion whereby reducing the leptin/adiponectin ratio. In both studies, P. balsamifera significantly reduced food intake. This appetite-reducing effect needs to be investigated further. In the prevention study this was accompanied by an increase in energy expenditure (increase in skin temperature and tends to increase expression of uncoupling protein-1; UCP-1). The signaling pathways activated by P. balsamifera and slightly by salicortin are implicated in either controlling hepatic glucose output (Akt), skeletal muscle Glut4 expression, glucose uptake and lipid metabolism in adipose tissue (Akt), adipocyte differentiation (ERK pathway and PPARg), decreasing the hepatic inflammatory state (IKKab), and increasing muscular, hepatic, or adipose tissue fatty acid oxidation (PPARa, CPT-1). As for L. laricina, it effectively decreased glycemia levels, insulin levels and the leptin/adiponectin ratio, improved insulin sensitivity and slightly decreased abdominal fat pad and body weights. This occurred in conjunction with increased energy expenditure as demonstrated by elevated skin temperature in the prevention study, and tendency to improve mitochondrial function and ATP synthesis in the treatment protocol. In conclusion, these results represent a major contribution, identifying P. balsamifera, salicortin, and L. laricina, as promising alternative, and culturally adapted therapies for the prevention and treatment care of obesity and diabetes among the CEI.

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