| Author: | Shum, Tim Fat |
| Title: | Evaluation of probiotics and food contaminants on the gastrointestinal tract integrity and immune homeostasis via alteration of gut microbiome |
| Advisors: | Chiou, Amber (ABCT) Wong, Man Sau (ABCT) |
| Degree: | Ph.D. |
| Year: | 2022 |
| Subject: | Intestines -- Microbiology Probiotics Microplastics Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Applied Biology and Chemical Technology |
| Pages: | 236 pages : color illustrations |
| Language: | English |
| Abstract: | Gut microbiota is considered as a "forgotten organ" which plays important roles on the health and disease status of human. The composition of microbiota could be affected by various factors such as probiotics, antibiotics, diet, and personal living style. This study aims to determine (1) the beneficial effect of in-house probiotic isolates on the gut integrity and immune homeostasis; and (2) the potential impact of food contaminants on the intestinal epithelium and its subsequent influence on the immune response. Probiotics have been known to modulate the gut microbiota and involve in promoting barrier function and immunomodulation of gastrointestinal (GI) tract. The first part of this study aims to characterize the ability of GI colonization of probiotics isolated in our laboratory, demonstrate the protective effects on the GI epithelial integrity and ability of immunomodulation from intestinal to systemic regions by the selected novel probiotic isolates. With full length 16S rDNA sequence matching with Lactobacillus rhamnosus, S1 was selected for the mentioned investigation using Simulator of Human Intestinal Microbial Ecosystem (SHIME) and Sprague Dawley (SD) rat model. 16S rDNA analyses showed that, S1 treatment to both SHIME and SD rats promoted the relative abundance of commensal genus Bacteroides. Several taxa that have been reported associated with inflammatory diseases were reduced by S1 treatment. Megasphaera spp. was reduced in distal colon of SHIME, whereas an unclassified genus under family Prevotellaceae (f_Prevotellaceae), Clostridia UCG-014 and Streptococcus were decreased in SD rats after S1 treatment. These mentioned taxa have been reported associated with inflammatory diseases. The extract of S1-treated SHIME distal colon promoted the trans-epithelial electrical resistance (TEER) (up to 26%) and occludin expression (+39%) of cultural enterocyte (Caco-2), suggesting the enhancement of epithelial integrity. Meanwhile, S1-treated SD rats expressed higher anti-inflammatory cytokine IL-10 in their colonic tissue, mesenteric lymph node cells, and splenic mononuclear cells in ex-vivo cultures. The results showed that L. rhamnosus S1 can modify the gut original microbiota of both human and murine. S1 protects intestinal epithelial integrity and modulates immunity, which could serve as a promising probiotic for human health. Another part of the study was related to food contaminants, microplastics (MP) and plasticizers. Use of plasticware in the daily life has become one of the inevitable essentials for many modern societies due to the convenience and economic reasons. Recent studies have demonstrated that microplastic and plasticizers are present in different food products and drinking water, in which some of those have been shown to interfere the GI microbiota, immunity, endocrine system and reproductive organ developments in the animal models. However, the studies to investigate the impacts of MP and plasticizer on human-origin gut microbiota, and the subsequent influences on the gut barrier function and immunomodulation are rather limited. The second part of this study is to investigate the impact of plasticizers including di(2-ethylhexyl) phthalate (DEHP) and di-iso-nonyl phthalate (DINP), and MPs including polyvinyl chloride (PVC) and polyethylene (PE) on the human gut microbiota. DINP promoted the relative abundance of Escherichia-Shigella spp. and Streptococcus spp., whereas Megasphaera spp. was reduced in the human in vitro GI tract. Extracts from the treatment of high DINP dosages (1.68 μg/ml and 16.8 μg/ml) reduced the expression levels of anti-inflammatory genes of RAW264.7, claudin-4, JAM-A and E-cadherin of HT-29, yet the same treatment enriched claudin-2. By contrast, extract from the treatment of DEHP promoted pore-forming claudin-2 in HT-29, and induced microbiota compositional changes similar to those observed in the patients of inflammatory bowel diseases (IBDs). Since plasticizers are commonly used in PVC softening, assessment was expanded to PVC and DEHP/PVC. The distal colon with PVC treatment had a relatively comparable microbiota to that of the control. Augmented relative abundance of pro-inflammatory taxon Collinsella spp. was observed in both DEHP and DEHP/PVC fermenters, whereas health-associated short-chain fatty acid producer Coprococcus spp. was reduced the most in the gut microbiota treated with PVC or DEHP. Furthermore, the extract of high dosage of DEHP/PVC decreased occludin by and trans epithelial electrical resistance (TEER) by 13% in Caco-2. Finally, another MP selected for study is PE as it is widely used in multiple plasticware which leads to high exposure frequency to human. Consistently, the occludin expression was reduced by 23% in the Caco-2 cells treated with the extract from PE batch culture. The SHIME was further adopted to study the effect of PE on the human gut microbiota in this part of study. Though gene expressions of major tight junction and adherens junction remained stable, the extract of PE-treated SHIME distal colon promoted the enterocyte barrier permeability (26%) of cultured Caco-2. The detailed relationships and mechanisms between the biochemical alterations and particular bacterial taxon remains to be elucidated in the future. |
| Rights: | All rights reserved |
| Access: | open access |
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