David Kitts
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Graduate Student Supervision
Doctoral Student Supervision
Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.
Phenolic compounds derived from the diet are typically sourced from cereals, fruits and vegetables and also beverages. They are documented to have biological functions that include antioxidant and anti-inflammatory activities, and can mitigate gastrointestinal disorders. This thesis focused on looking at mechanism(s) of phenolic acid induced intracellular hydrogen peroxide (H₂O₂) level and effects on intestinal epithelial cell signaling that are related to intestinal epithelial functionality. The first experiment showed that different phenolic acids varied specifically in relative stability and capacity to produce H₂O₂ when incubated in cell culture media for 24 hr. Phenolic acids varied in affinity to induce apoptosis and inhibit proliferation in non-differentiated Caco-2 cells.Subsequent studies demonstrated the effect of selective phenolic acids on extracellular/intracellular redox by controlling H₂O₂ influx activity and to relate this event to cell signaling and control of oxidative stress in differentiated Caco-2 cells. HyPer-3, a genetically encoded fluorescent H₂O₂ sensitive indicator was constructed to monitor intracellular H₂O₂ in differentiated Caco-2 cells. Results showed that extracellular generation of H₂O₂ occurred from autoxidation of phenolic acids in culture and subsequent disappearance corresponded to intracellular uptake in differentiated Caco-2 cells. Phenolic acid specific pro-oxidant activity was sufficient to activate intracellular nuclear factor-erythroid factor 2-related factor 2 (Nrf2) cell signaling; the degree of which was dependent on both the source of the phenolic acid and concentration used in culture. A Caco-2/RAW 264.7 co-culture model enabled intercellular cell signaling measurements in response to an inflammatory response by inflamed macrophage. The capacity of specific phenolic acids to regulate the inflammatory status of activated RAW 264.7 cells was dependent on the type of phenolic acid which influenced Nrf2 cell signaling, monolayer integrity, and cytokine production in Caco-2 cells. It is concluded from these experiments that phenolic acids regulate extracellular/intracellular redox due to a susceptibility for pro-oxidant activity that is specific for individual phenolic acids. The pro-oxidant activity was related to capacity to produce H₂O₂, or its cellular influx, which in turn had a role in cell signaling, cytokine production and intestinal epithelial cell functionality.
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Chlorogenic acid (CGA) is a general term used to describe the most abundant group of phenolic acids in coffee. 3-CQA, 4-CQA, 5-CQA, 3,4-diCQA, 3,5-diCQA, and 4,5-diCQA are major CGAs in coffee; but only 5-CQA has been thoroughly studied. The first objective of this thesis was to study interactions between major CGA isomers and chemical changes in coffee brew that affect antioxidant activity noted for coffee. The second overall objective was to study the potential of these six major CGA isomers in modulating oxidative stress and inflammation using a human intestinal Caco-2 cell line. The findings from Chapter 2 suggested that the other five CGA isomers (4-CQA, 5-CQA, 3,4-diCQA, 3,5-diCQA, and 4,5-diCQA) together account for more than 50% of the total CGA in coffee and contributed to the antioxidant activity of coffee brew. Chapter 3 and 4 addressed the research question of whether these major CGA isomers have a modulating effect on oxidative stress and inflammation in human intestinal Caco-2 cell line. Caco-2 cells were first incubated with, or without, individual CGA isomers, followed by a phorbol 12-myristate 13-acetate plus human interferon gamma challenge. Biomarkers of oxidative stress (intracellular ROS and GSH/GSSG) and inflammation (IL-8) were measured. The results demonstrated that CGA isomers scavenged intracellular ROS in inflamed Caco-2 cells, mitigated the drop in GSH/GSSG ratio and attenuated IL-8 secretion. Dicaffeoylquinic acids (3,4-diCQA, 3,5-diCQA, and 4,5-diCQA) had a relatively stronger capacity to evoke protection compared to caffeoylquinic acids (3-CQA, 4-CQA, and 5-CQA). To elucidate the possible mechanism underlying these actions, the effects of CGA isomers on the nuclear factor kappa B signaling pathway, mitogen-activated protein kinase cascades, and nuclear factor (erythroid-derived 2)-like 2 signaling pathway were further investigated. In conclusion, structural differences in six CGA isomers were found to correspond to differences in antioxidant and anti-inflammation activities. CGA isomers attenuate oxidative stress and inflammation in Caco-2 cells by triggering changes in redox biology parameters, lead to an up-regulation of nuclear factor kappa B signaling at very early stage, mitigation of p38 phosphorylation and up-regulation of antioxidant genes in an intermediate stage, and activation of Nrf2 signaling at a much later stage.
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The presence of Listeria spp. and L. monocytogenes (Lm) was investigated in provincially inspected food processing and retail facilities in British Columbia. Lm (n=56) was recovered in food processing environment (FPE) of dairy, meat and fish facilities, and in ready-to-eat fish products. The majority of Lm belonged to listeriosis causing serotypes 1/2a and 4b. Isolate fingerprinting revealed 14 sequence types, and 38 pulsotypes, with 66% of Lm possessing the full-length inlA, a causally linked virulence determinant. Unexpectedly, 4b serotypes more readily acquired point mutations leading to rifampicin resistance compared to other serotypes (p
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Vitamin (vit) E comprises 8 isoforms, of which only α-tocopherol (Toc) has been thoroughly investigated. Other vit E isoforms, particularly γ-Toc and δ-Toc, however are present in significant amounts in the North American diet. The effect of α-Toc, γ-Toc and δ-Toc in modulating oxidative status and inflammatory responses in adult-derived Caco-2 and fetal-derived FHs 74 Int intestinal cell lines were thus determined. Toc isoforms were effective antioxidants that protected against peroxyl radical-induced membrane oxidation in both cell lines in an isoform-dependent manner (δ-Toc>γ-To>α-Toc). Nevertheless, Toc isoforms exhibited differential modulation of inflammatory response in the two cell lines, in that Toc isoforms suppressed IFNγ/PMA-induced IL8 expression in Caco-2 cells, but promoted an inflammatory response in FHs 74 Int cells. Modulation of IL8 expression by Toc isoforms corresponded with an efficacy of Toc to modulate NfκB pro-inflammatory and Nrf-2 antioxidant enzyme signaling pathways. Non-α-Toc isoforms promoted Nrf-2 activation in both cell lines. Alpha-Toc and γ-Toc mitigated IFNγ/PMA-induced NfκB activation in Caco-2 cells while non-α-Toc isoforms promoted NfκB activation in FHs 74 Int cells. The pro-oxidant activity of δ-Toc corresponded to its lower ability to suppress IFNγ/PMA-induced IL8 expression and NfκB activation, but enhanced the Nrf-2 signal in Caco-2 cells. One key difference between the effect of Toc isoforms on modulation of NfκB and Nrf-2 signaling was that non-α-Toc isoforms down-regulated the gene expression of glutamate cysteine ligase, the rate-limiting enzyme in glutathione biosynthesis, in FHs 74 Int, but not in Caco-2 cells. This was supported by a reduced (P
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Maillard reaction products (MRPs) are produced when reducing sugars react with amino acids, peptides or proteins in heat-processed foods. The overall objective of this research was to isolate and identify MRPs that exhibit antioxidant and anti-inflammatory activities, from different sugar-amino acid model systems comprised of fructose, glucose or ribose, each with glycine (Fru-Gly, Glu-Gly and Rib-Gly) or lysine (Fru-Lys, Glu-Lys and Rib-Lys), respectively. The development of peroxyl radical scavenging activity was found to be positively correlated (r = 0.893-0.905, P
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Master's Student Supervision
Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.
The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.
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Using a carrot processing line in a fresh-cut produce processing plant, it was found that Failure Mode and Effects Analysis (FMEA) provided a more accurate portrayal of the risk that is associated with a fresh-cut processing line than that provided by a conventional Hazard Analysis. This conclusion is based on the fact that FMEA clearly indicates the residual risk that is left after risk-mitigating activities are in place, and identifies the variables responsible for the remaining risk factor. This methodology also requires examination of the risk associated with all product and process changes that are involved in processing, with an integral part of this approach being the need for continuous improvement. FMEA, therefore, has the potential to decrease the likelihood that food processors will sell contaminated food to consumers because they have not detected when their biological hazards are not being adequately controlled, a classical type 2 error.It was also demonstrated that FMEA required a rating of the hazard detection method which drives the need to examine detection methods for hazards. In this example, a Run Chart was used to indicate changes in the microbiological status of a fresh-cut processing line. While the Run Chart successfully indicated this change, the information gained was not useful for showing the presence of a significant biological hazard. It was determined that this occurred because the information was not provided sufficiently in time to prevent the sale of contaminated carrots to customers. Use of a Defect Opportunity Checklist (DOC) was assessed to detect defects in a sanitation process; in effect, whether or not planned activities were being followed. This information was subsequently analyzed and an improvement plan was developed. While the DOC successfully performed this function, it was not adopted by the processing site because the current methods for verifying the sanitation indicated that the process was acceptable. This suggests that there may be limited acceptance of FMEA and DOC by food processors if it is perceived they perceive that their hazards are fully controlled by their existing food safety methodologies.
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Coffee contains biologically active components which may affect chronic disease risk.These biologically active components include caffeine, cafestol and kahweol, andantioxidants such as chlorogenic acids and Maillard reaction products (MRPs) that aregenerated during roasting. Although MRPs are regarded as being the most abundantgroup of antioxidants present in coffee, the mechanism underlying the antioxidant effectsof coffee MRPs in both in vitro and in biological systems has yet to be elucidated.In this study, the in vitro antioxidant properties of roasted and non-roasted coffee extracts(Coffea arabica L.) were tested using oxygen radical absorbance capacity (ORAC),Trolox equivalent antioxidant capacity (TEAC) and reducing power assays. MRPs wereshown to be the prevailing antioxidants in roasted coffee extracts. The mechanisms of theantioxidant action associated with coffee MRPs involve the hydrogen atom transfer (HAT)mechanism and the single electron transfer (SET) mechanism.The biological effects of MRPs derived from coffee extracts on the enzymatic antioxidantdefense in human colon adenocarcinoma Caco-2 cells were also investigated. Noinduction of antioxidant enzyme activities of catalase, glutathione peroxidase, glutathionereductase and superoxide dismutase were observed in Caco-2 cells after exposure tocoffee MRPs, except for an increased glutathione peroxidase activity after 24 h exposure.In contrast, significantly decreased activities of catalase and glutathione peroxidase, and areduced glutathione content were observed in Caco-2 cells after treatment with coffeeMRPs (p
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