According to one of the top medical journals THE LANCET, by 2017, the number of CKD patients in the world had reached 697.5 million, among which there are 132.3 million of Chinese patients with 9.5% incidence rate of CKD. With a global prevalence of 9.1%, chronic kidney disease (CKD) affects 10.8% of adult population in China. Provided the severe health problems that accompanies CKD such as heart disease and stroke, however, 9 in 10 people with CKD are not aware of the disease. Prior to the design of our experiment, we conducted a survey in our community in Shanghai, China. We received valid results from 274 participants. Only 16.06% of them claimed that they have heard about CKD and the harm behind it, and about 71.9% of them have not paid attention to their kidney health. Therefore, these findings inspired us to focus on spreading the awareness of CKD and the harm of uremic toxin, as well as aiming to design engineered probiotics to target this issue.
Due to the damage on kidney, metabolites and waste products fail to be filtered out into urine. Uremic toxins such as p-cresol sulfate (pCS) will hence accumulate inside the organ, further exacerbating the harm. Therefore, the we aim to engineer probiotics that can be consumed by the patient, express the target gene into enzymes to degrade p-cresol, the precursor of pCS. Since p-cresol is produced from phenylalanine and tyrosine in diet, we created tyrosine inducer gene, which controls the expression of polyphenol oxidase (PPO) – an enzyme that can degrade p-cresol. This system was tested with the green fluorescent protein gene on the p15A plasmid. We also extracted the pchC – pchF – pchA operon gene segment from Pseudomonas citronellolis and connected onto the p15A plasmid skeleton to assist PPO degrading p-cresol under oxygen-deficient environment (intestine). Lastly, the plasmid was converted onto Escherichia coli Nissle 1917, an edible and harmless probiotic, while high performance liquid chromatography was used to examine the ability of our finished product in degradation of p-cresol.
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