The severities and causes of hyperuricemia and gout Hyperuricemia is defined in humans as a serum urate level of greater than or equal to 6.8 milligrams per deciliter (mg / dL). As uric acid (UA) is slightly soluble in water, it is easily crystallized. As a result, 20% of the hyperuricemia patients suffer from gout, which occurs when uric acid builds up in blood and causes inflammation in the joints. These crystals cause the joint to become inflamed, which then causes pain, swelling and warmth. Moreover, hyperuricemia can also cause other complications, such as angiocardiopathy, chronic renal failure and hypertension. According to the questionnaire, the bad life experiences of some patients are likely to cause psychological problems. UA is the metabolite of purine. People who produce overmuch UA because of metabolic disorder, fail to excrete enough UA, or uptake overmuch purine by diet, have a huge possibility to get hyperuricemia. Unfortunately, by interviewing doctors, we know that as people's diets and lifestyles change, more and more people suffer from hyperuricemia. From related reports, the morbidity of gout was about 1%. However, we interviewed Yuxiang Yan, the CTO of a company aiming at the treatment of gout, who told us that as many gout patients at underdeveloped area tend to not go to the hospital, the actual morbidity could reach 4% to 6%. Obviously, hyperuricemia and gout are potential threats that everyone is likely to encounter. Current limitations of gout treatment Surgery can easily remove UA crystals, but it does not make sense without reducing the UA concentration. Anti-inflammatory drugs and analgetics, such as colchicine, can effectively relieve pain. Therefore, according to our research in human practices , many patients are mad about these drugs. However, as they cannot reduce the UA concentration, it is also not a long-term effective method. As a result, at present, the only method to solve gout via reduce UA concentration is to use drugs that can restrain UA generation or promote UA excretion. Allopurinol is a representative drug in this category. However, patients need to use the drug for the rest of their lives, which we find is very hard for the patients to stick to it. The drugs may have hepatotoxicity or nephrotoxicity. What’s more, the drugs, especially allopurinol, are highly allergenic to the Asians. At last, the drugs cannot quantitatively control the UA concentration in real time, which means the UA level might be excessive low after the patients take medicine. According to the doctors, a low concentration of UA can cause dementia.
Our design: a smart cell that can control UA level Due to the trend of cell therapy, which could better solve the diseases that people had little possibility to cure before, we decided to develop a cell to control the UA level steadily for a long time. By literature review , we constructed a gene circuit which mainly contains two parts: detection module and UA degradation module. For detection module, the core is HucR, which is a protein that binds hucO sequence and suppresses the expression of the downstream genes only when there is not much UA. For the degradation module, uricase gene was used to convert UA into soluble and non-toxic allantoin. As a result, the uricase gene is expressed and the UA level is decreased only when the UA concentration is higher than designed threshold. Moreover, the threshold can be changed optionally by debugging the promoters and other parts, so as to satisfy the requirements of different people. As the cell should enter the internal environment, human cell should be used as chassis. Here, we used human HeLa cells as proof of concept.
Appendant: a portable device to detect UA level During the research, we found the patients needed to test their UA level frequently. But it is not convenient to go to hospital that often. Nowadays, a kind of household UA detector appears. However, the test paper for the detector is a little expensive. What's more, the existing detection methods mainly based on uricase. H2O2 is a by-product during UA degradation catalyzed by uricase. The detector detects H2O2 and calculates the corresponding UA level. As a result, the system is highly unstable because H2O2 is an unstable substance and the system is impressionable by the redox property of the samples and the environment. By literature review , we realized that we can use the gene circuit similar to the one in the smart cell. However, a reporter gene should be used to replace uricase gene. We chose Escherichia coli (E. coli) as chassis. A hardware, which is similar to a simple fluorescence reader, is designed to convert the signal released by the bacteria to the UA level of the users’ samples.
 Kemmer, C., Gitzinger, M., Daoud-El Baba, M., Djonov, V., Stelling, J., & Fussenegger, M. (2010). Self-sufficient control of urate homeostasis in mice by a synthetic circuit. Nature biotechnology, 28(4), 355.  Liang, C., Xiong, D., Zhang, Y., Mu, S., & Tang, S. Y. (2015). Development of a novel uric-acid-responsive regulatory system in Escherichia coli. Applied microbiology and biotechnology, 99(5), 2267-2275.