Determination of the Effects of Different Maillard Reaction Products on the Taxonomic Composition of the Gut Microbiota

The Maillard Reaction (MR) is a non-enzymatic chemical reaction which results in linkage between the amino group of amino acids and the carbonyl group of reduced sugars. This reaction generates Maillard reaction products (MRPs) which are not present naturally in foods, and are responsible for a range of colors, odors, flavors, and other sensory properties. Conflicting reports of MRPs impacts on human health are probably due to the fact that bioconversion of these digestible molecules by the gut microbiota has been marginally taken into account. This study aimed to determine the effects of different MRPs on rodent’s gut microbiota through16S rRNA amplicon sequencing over three different studies. Study 1 focused on the impact of NCarboxymethyllysine (CML) on the composition of mice gut microbiota and potential association with severity of experimental colitis. Study 2 focused on the impact of bread melanoidins on the composition of healthy and experimental colitis mice gut microbiota. Study 3 focused on the impact of consumption of increasing amounts of malt melanoidins on mice gut microbiota. It was found that CML induced limited changes in gut microbiota profiles of healthy mice, but was found to significantly relieve the bacterial dysbiosis imparted by one (but not the other) inflammation-inducing chemical, especially the Proteobacteria bloom. Bread crust model (high in melanoidins) showed significant decreases of Bacteroides spp. and Enterobacteriaceae, while it increased Faecalibacterium spp. Also, bread crust model limited to increase Enterobacteriaceae in colitis model. High amounts of malts rich melanoidins rapidly and persistently led to significantly different gut microbiota profiles. There was a trend for decrease of Lactobacillus and Ruminococcus and increase of Akkermansia and Bifidobacterium with higher amounts of dietary melanoidins. We concluded that CML and melanoidins are not detrimental in terms of their impact on the gut microbiota, and that they may even have prebiotic properties. ACKNOWLEDGEMENTS: I would like to express my special thanks of gratitude to my advisor Dr. Franck Carbonero who gave me the opportunity to work on this project and welcomed me in his lab and office. His knowledge and experiences are always invaluable to increase my knowledge and success in my educational pursuits. He is always willing to assist me with scheduling, research, and guidance over the years. I could not have been as successful as I am right now without his help through every step. I would also like to thank Dr. Pauline Anton-Gay and Dr. Pascale Gadonna at LaSalle University for constructive discussions that helped me to do this wonderful project on the topic of Maillard Reaction Products and for the valuable information provided by them in their respective fields. I would also like to thank my advisory committee members: Professor Steve Ricke, Dr. Sami Dridi, and Dr. Charles Rosenkrans for supporting my career. I would like to thank Dr. Ricke’s lab for providing equipment, especially Dr. Peter Rubinelli and Thomas Flecker. I would also like to thank the Cell and Molecular Biology program for providing me with an outstanding education throughout my PhD degree. I also extend my gratitude to all people at University of Arkansas for their advice and guidance without which this project would not have been possible. My thanks and appreciations also go to King Abdul Aziz University in Saudi Arabia for supporting and encouraging which helped me in completion of my degree. Lastly, I thank almighty, my family, friends, and lab members for their constant encouragement without which this assignment would not be possible. TABLE OF CONTENT: General Introduction.1 References.5 Chapter one: Review of the Literature.7 1.1 Abstract.8 1.2 Introduction.9 1.3 The Chemistry of Maillard Reaction Products.10 1.3.1 Maillard reaction in food.10 1.3.2 Generation of Maillard Reaction Products in vivo.11 1.3.3 Important Maillard Reaction Product Molecules.12 1.4 Maillard Reaction Products Impact on Nutrition and Health.18 1.4.1 Consequences of the Maillard Reaction in Nutrition.18 1.4.2 Effect of Maillard Reaction Products on Health.20 1.5 MRPs and Gut Microbiome and Metabolome.26 1.5. 1 Human Gut Microbiome and Metabolome.26 1.5. 2 Known Microbial Interactions between Microbes and MRPs.27 1.6 Conclusions and Perspectives.33 1.7 References.35 Chapter Two: Research Article.55 2-1 Abstract.56 2.2 Introduction.58 2.3 Materials and Methods.60 2.3.1 Chemicals.60 2.3.2 Animals and Study design.60 2.3.3 Experimental Colitis.61 2.3.4 DNA Extraction and Amplicon Sequencing Strategy.63 2.3.5 Library Preparation and Quality Control.64 2.3.6 Bioinformatics and Statistical Analyses.64 2.4 Results.65 2.4.1 Effect of CML on Weight Change and Food Intake in Healthy and Colitic Mice.65 2.4.2 Effect of CML on Macroscopic Lesions and Neutrophil Infiltration in Healthy and Colitic Mice.65 2.4.3 Gut Microbiota Analyses.66 2.4.3.1 Impact of CML on the Gut Microbiota of Healthy Mice.66 2.4.3.2 Impact of TNBS and DSS on the Gut Microbiota.66 2.4.3.3 Impact of CML on the Gut Microbiota of DSS and TNBS-Treated Mice.68 2.5 Discussion and Conclusion.68 2.6 References.74 Chapter Three: Research Article.93 3.1 Abstract.94 3.2 Introduction.95 3.3 Material and Methods.96 3.3.1 Bread Preparation.96 3.3.2 Animals and Study design.97 3.3.3 DNA Extraction and PCR Amplifications (Polymerase Chain Reaction). 98 3.3.4 Library Preparation.98 3.3.5 Sequencing, Bioinformatics and Statistical Analyses.99 3.4 Results and Discussion.100 3.4.1 Impact of TNBS treatment on the gut microbiota.101 3.4.2 Impact of MFC on the rats gut microbiota.102 3.4.3 Impact of BCM on the rats gut microbiota.104 3.5 Conclusions.107 3.6 References.108 Chapter Four: Research Article.126 4.1 Abstract.127 4.2 Introduction.128 4.3 Material and Methods.130 4.3.1 Experimental Animals.130 4.3.2 Experimenta