The Role of Hyperuricemia in the Pathogenesis and Progressivity of Chronic Kidney Disease

In humans, the end product of purine metabolism is uric acid. Over 70% of uric acid is excreted through the kidneys. When renal function is impaired, uric acid secretion is also impaired. This directly correlates the prevalence of hyperuricemia with the severity of chronic kidney disease (CKD). It has been reported that the prevalence of hyperuricemia in patients with Stage I-III CKD is 40–60% and up to 70% in patients with Stage IV-V CKD. Some studies found a link between serum uric acid levels and decreased glomerular filtration rate (GFR), an independent risk factor for CKD development. Because CKD and serum uric acid levels are related, the relationship between the two frequently generates controversy. As such, this review of the literature discusses the role of uric acid in the pathogenesis and progression of CKD.

Regulation of Catechins in Uric Acid Metabolism Disorder Related Human Diseases

Uric acid is the end product of purine metabolism in humans. High uric acid levels form sodium urate crystals that trigger biological processes, which lead to the development of several diseases, including diabetes, hyperuricemia, gout, inflammatory disease, kidney disease, cardiovascular disease and hypertension. Catechins have been suggested to be beneficial for the regulation of uric acid metabolic disorders due to their powerful antioxidant and anti-inflammatory properties. To identify an effective and safe natural substance that can decrease levels of serum uric acid to improve uric acid metabolism disorders. A search was performed on PubMed, Web of Science and Google Scholar to identify comprehensive studies that presented summarized data on the use of catechins in lowering uric acid levels in diseases. This review details the role of catechins in inhibiting the activity of xanthine oxidase to decrease uric acid overproduction in the liver and in regulating expressions of uric acid transporters, URAT1, OAT1, OAT3, ABCG2 and GLUT9, to balance levels of uric acid secretion and reabsorption through the kidney and intestine. Additionally, Catechins were also found to prevent monosodium urate-induced inflammatory reactions. In vivo, catechins can be used to decrease high uric acid levels that result from hyperuricemia and related diseases. Catechins can be used to maintain the balance of uric acid metabolism.

Bioactive Compounds from Plant-Based Functional Foods: A Promising Choice for the Prevention and Management of Hyperuricemia

Hyperuricemia is a common metabolic disease that is caused by high serum uric acid levels. It is considered to be closely associated with the development of many chronic diseases, such as obesity, hypertension, hyperlipemia, diabetes, and cardiovascular disorders. While pharmaceutical drugs have been shown to exhibit serious side effects, and bioactive compounds from plant-based functional foods have been demonstrated to be active in the treatment of hyperuricemia with only minimal side effects. Indeed, previous reports have revealed the significant impact of bioactive compounds from plant-based functional foods on hyperuricemia. This review focuses on plant-based functional foods that exhibit a hypouricemic function and discusses the different bioactive compounds and their pharmacological effects. More specifically, the bioactive compounds of plant-based functional foods are divided into six categories, namely flavonoids, phenolic acids, alkaloids, saponins, polysaccharides, and others. In addition, the mechanism by which these bioactive compounds exhibit a hypouricemic effect is summarized into three classes, namely the inhibition of uric acid production, improved renal uric acid elimination, and improved intestinal uric acid secretion. Overall, this current and comprehensive review examines the use of bioactive compounds from plant-based functional foods as natural remedies for the management of hyperuricemia.

Cellular Processing of the ABCG2 Transporter—Potential Effects on Gout and Drug Metabolism

The human ABCG2 is an important plasma membrane multidrug transporter, involved in uric acid secretion, modulation of absorption of drugs, and in drug resistance of cancer cells. Variants of the ABCG2 transporter, affecting cellular processing and trafficking, have been shown to cause gout and increased drug toxicity. In this paper, we overview the key cellular pathways involved in the processing and trafficking of large membrane proteins, focusing on ABC transporters. We discuss the information available for disease-causing polymorphic variants and selected mutations of ABCG2, causing increased degradation and impaired travelling of the transporter to the plasma membrane. In addition, we provide a detailed in silico analysis of an as yet unrecognized loop region of the ABCG2 protein, in which a recently discovered mutation may actually promote ABCG2 membrane expression. We suggest that post-translational modifications in this unstructured loop at the cytoplasmic surface of the protein may have special influence on ABCG2 processing and trafficking.

Uric Acid Secretion from Adipose Tissue and Its Increase in Obesity

Obesity is often accompanied by hyperuricemia. However, purine metabolism in various tissues, especially regarding uric acid production, has not been fully elucidated. Here we report, using mouse models, that adipose tissue could produce and secrete uric acid through xanthine oxidoreductase (XOR) and that the production was enhanced in obesity. Plasma uric acid was elevated in obese mice and attenuated by administration of the XOR inhibitor febuxostat. Adipose tissue was one of major organs that had abundant expression and activities of XOR, and adipose tissues in obese mice had higher XOR activities than those in control mice. 3T3-L1 and mouse primary mature adipocytes produced and secreted uric acid into culture medium. The secretion was inhibited by febuxostat in a dose-dependent manner or by gene knockdown of XOR. Surgical ischemia in adipose tissue increased local uric acid production and secretion via XOR, with a subsequent increase in circulating uric acid levels. Uric acid secretion from whole adipose tissue was increased in obese mice, and uric acid secretion from 3T3-L1 adipocytes was increased under hypoxia. Our results suggest that purine catabolism in adipose tissue could be enhanced in obesity.