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Uric acid is the end product of purine metabolism in humans, and its excessive accumulation leads to hyperuricemia and urate crystal deposition in tissues including joints and kidneys. Hyperuricemia is considered an independent risk factor for cardiovascular and renal diseases. Although the symptoms of hyperuricemia-induced renal injury have long been known, the pathophysiological molecular mechanisms are not completely understood. In this review, we focus on the research advances in the mechanisms of hyperuricemia-caused renal injury, primarily on oxidative stress, endothelial dysfunction, renal fibrosis, and inflammation. Furthermore, we discuss the progress in hyperuricemia management.

Hyperuricemia is highly prevalent and especially common in subjects with metabolic, cardiovascular and renal diseases. In chronic kidney disease, hyperuricemia is extremely common, and uric acid (UA) excretion relies on gut uricolysis by gut microbiota. Current therapy for lowering serum UA includes drugs that may produce undesired secondary effects. Therefore, this pilot study was designed to evaluate the potential of two probiotic supplements to reduce systemic uric acid concentrations. Secondary objectives were to assess whether the hypouricemic effect related to a therapeutic benefit on the hyperuricemia-induced renal damage and hypertension. Analysis of fecal microbiota was also performed. Groups of 6 rats each were followed for 5 weeks and allocated in the following treatment groups: C = Control; HU-ND = Oxonic acid-induced hyperuricemia (HU) +regular diet; HU-P = HU+placebo; HU-F1 = HU+ probiotics formula 1 and HU-F2 = HU+ probiotics formula 2. We confirmed that oxonic acid-induced hyperuricemia produced hypertension and renal functional and structural changes, along with modest changes in the overall composition of fecal microbiota. Both probiotic-containing diets prevented HU, elevated UA urinary excretion and intrarenal UA accumulation induced by oxonic acid. The hypouricemic effect conferred by probiotic supplementation also prevented the renal changes and hypertension caused by hyperuricemia. However, probiotic treatment did not restore the fecal microbiota. In conclusion, we demonstrated for the first time the ability of probiotics containing uricolytic bacteria to lower serum uric acid in hyperuricemic animals with beneficial consequences on blood pressure and renal disease. As probiotics supplements are innocuous for human health, we recommend clinical studies to test if probiotic supplements could benefit hyperuricemic individuals.

Since the publication of the Framingham Heart Study, which suggested that uric acid should no longer be associated with coronary heart disease after additional adjustment for cardiovascular disease risk factors, the number of publications challenging this statement has dramatically increased. The aim of this paper was to review and discuss the most recent studies addressing the possible relation between sustained elevated serum uric acid levels and the onset or worsening of cardiovascular and renal diseases. Original studies involving American teenagers clearly showed that serum uric acid levels were directly correlated with systolic and diastolic pressures, which has been confirmed in adult cohorts revealing a 2.21-fold increased risk of hypertension. Several studies involving patients with coronary artery disease support a role for serum uric acid level as a marker and/or predictor for future cardiovascular mortality and long-term adverse events in patients with coronary artery disease. Retrospective analyses have shown an inverse relationship between serum uric acid levels and renal function, and even a mild hyperuricemia has been shown to be associated with chronic kidney disease in patients with type 2 diabetes. Interventional studies, although of small size, showed that uric acid (UA)-lowering therapies induced a reduction of blood pressure in teenagers and a protective effect on renal function. Taken together, these studies support a role for high serum uric acid levels (>6 mg/dL or 60 mg/L) in hypertension-associated morbidities and should bring awareness to physicians with regards to patients with chronic hyperuricemia.

Serum uric acid (SUA) level has been suggested to be associated with cardiovascular disease, diabetes and metabolic syndrome. However, little is known about the relationship between SUA and liver enzymes activity in the general population. The present study aimed to assess the relationship between SUA and serum liver enzymes in an adult population in Bangladesh. In this cross-sectional study, a total of 410 blood samples were collected from apparently healthy adults aged > 18 years. SUA, liver enzymes, lipid profile and other biochemical markers were measured in the collected samples by using standard methods. Multinomial logistic regression model was used to assess the relationship between SUA and elevated levels of liver enzymes among the participants. Overall, the prevalence of hyperuricemia was 30.1% with 32.2% in male and 18.6% in female participants. About 33% of the participants had at least one or more elevated levels of liver enzymes. The mean level of SUA was significantly higher in males (389.3 ± 96.9 µmol/L) than in the female (290.4 ± 89.8 µmol/L) subjects (p < 0.001). There was a significant difference in the mean levels of serum ALT and GGT between the male (34.5 ± 16.0 U/L and 26.7 ± 19.5 U/L, respectively) and female (25.0 ± 13.0 U/L and 19.5 ± 13.2 U/L, respectively) participants (p < 0.001 and p < 0.01, respectively). An increasing trend was observed in the mean levels of serum ALT and GGT across the SUA quartile groups (p < 0.001 and p < 0.01, respectively). SUA showed a positive and significant correlation with serum ALT (p < 0.001) and GGT (p < 0.01). In further statistical analysis after adjustment for potential confounders, SUA showed an independent and significant association with serum ALT and GGT in all regression models. In conclusion, SUA was strongly associated with serum levels of ALT and GGT after adjustment for potential confounders. More prospective studies are needed to clarify the complex relationship between SUA and liver enzymes in the general population.

Epidemiological research has shown that elevated serum urate concentration is a risk factor for the development of kidney disease; however, the mechanisms underlying this process have not yet been elucidated. To examine the role of urate in the kidney, we used Wistar rats to functionally disrupt expression of urate oxidase (UOX) by using the CRISPR/Cas9 system. In comparison to wild-type (WT) rats, serum urate levels spontaneously and persistently increased in UOX-KO rats, without showing a significant decrease in survival rate. Architecture and function of the kidneys in UOX-KO rats were impaired. Injury to the kidney resulted in increased interstitial fibrosis, macrophage infiltration, increased expression of NLRP3 and IL-1β, and activation of multiple cell-signaling pathways associated with autophagy, such as AMPK, p38 MAPK, ERK and JNK pathways. Inhibition of autophagy with the PI3K inhibitor 3-MA abrogated the development of kidney damage and attenuated renal fibrosis, macrophage infiltration, and expression of NLRP3 and IL-1β in injured kidneys. In conclusion, the UOX-KO rat is a great model to study hyperuricemia-related diseases. Hyperuricemia-induced autophagy and NLRP3-dependent inflammation are critically involved in the development of renal damage and, therefore, highlight the inhibition of autophagy and inflammation in search of therapeutic strategies to treat uric acid nephropathy.

This study aimed to assess the anti-hyperuricemia efficacy of Zhejiang psyllium polysaccharides (ZPP) in rats and to explore its underlying mechanism. Hyperuricemia was induced by intragastric administration of potassium oxonate, hypoxanthine, and adenine. The serum levels of uric acid (UA), creatinine (Cr), and blood urea nitrogen (BUN) were measured, and kidney pathology was examined. Serum metabolomics was employed to monitor metabolic alterations following ZPP intervention. Metagenomic analysis was conducted to investigate the impact of ZPP on the intestinal flora of hyperuricemia rats. The results showed that ZPP could significantly reduce the serum UA level in hyperuricemia rats and exhibited a certain renal protective effect. The metabolomics results indicated that ZPP regulates uric acid levels in rats with hyperuricemia and ameliorates renal pathological changes by modulating biomarkers associated with purine metabolism, amino acid metabolism, and lipid metabolism. Metagenomic research also found that ZPP could increase the relative abundance of uric acid metabolism-related probiotics, such as Limosilactobacillus reuteri and Lactobacillus murinus , thereby improving intestinal flora imbalance in rats with hyperuricemia.

Hyperuricemia has been linked to kidney problems including hyperuricemic nephropathy (HN), which is characterised by inflammation and fibrosis in the kidneys. HN is frequently observed in patients with chronic gout. However, the causes of HN are not fully understood and effective treatments are limited. The status of RNA m6A, expression, and location of METTL3 in the kidney was evaluated in mice with HN. The mechanism of the METTL3‐associated ABCG2 downregulation was further studied in mTEC cells and a potassium oxazinate + adenine‐induced mice model and adeno‐associated virus 9 (AAV9)‐mediated METTL3 silencing mice. Expressions of ABCG2, α‐SMA, collagen‐1, TGF‐β1, IL‐1β, IL‐6, and TNF‐α were analysed using real‐time PCR and western blotting. Hyperuricemia led to elevated m6A levels and METTL3 expression in mouse kidneys. METTL3 was mainly located in mTEC cells. METTL3‐specific inhibitor STM2457 alleviated uric acid‐induced inflammatory and fibrotic responses in mTEC cells. Mechanistically, ABCG2 was identified as a target of METTL3 by RNA sequencing. The stability of ABCG2 was decreased through the binding of IGF2BP2 (insulin‐like growth factor 2 binding protein 2) to its m6A‐modified stop codon regions. Silencing or inhibition of METTL3 significantly reduced uric acid‐induced cell injury and increased ABCG2 expression, leading to uric acid excretion. In vivo data showed that AAV9‐mediated METTL3 silencing significantly alleviated renal dysfunction and fibrosis in HN mice. Our study provides the first evidence that METTL3 regulates uric acid excretion by controlling the m6A levels of ABCG2 through the binding of IGF2BP2, and inhibiting METTL3 can effectively alleviate kidney damage caused by hyperuricemia, showing potential as a therapy for HN.

This study explored the uric acid-lowering effects of hederagenin (HD) through molecular docking analysis and a chronic hyperuricemia (HUA) mouse model. Molecular docking was performed to evaluate HD’s interactions key urate-regulating proteins, including xanthine oxidase (XOD), ABCG2, OAT1, URAT1, and GLUT9. To establish a chronic HUA model, mice were fed a yeast-adenine diet supplemented with potassium oxonate. The mice were randomly assigned to six groups: normal control, HUA model control, benzbromarone (BEN) group, and three HD treatment groups at doses of 50, 100, and 200 mg/kg. Serum uric acid (UA) levels, liver and kidney function indicators, XOD activity, and oxidative stress markers were assessed. Histopathological analyses of the liver and kidney were also conducted. In addition, gene and protein expression levels of urate transporters and inflammatory markers were assessed using RT-PCR and Western blotting. The results showed that HD interacts with XOD and urate transporters, significantly reducing serum UA levels and inhibiting XOD activity in HUA model. It also modulated the expression of urate transporter to enhance UA excretion. Moreover, HD protected liver and kidney function by reducing pro-inflammatory cytokine levels and inhibiting the TLR4/Myd88/NF-κB and NLRP3 signaling pathways. These findings suggest HD may serve as a promising therapeutic agent for lowing uric acid and preventing organ damage associated with HUA.

Previous studies have demonstrated the effects of hyperuricemia on the damage to target organs, including the kidneys, joints and the heart. However, it is unclear whether hyperuricemia results in damage to the intestines. The aim of the present study was to investigate intestinal barrier dysfunction in a mouse model of hyperuricemia constructed by knocking out the urate oxidase (Uox) gene. The morphology of the intestine was assessed via hematoxylin and eosin, and alcian blue staining. The serum and intestinal tissue levels of uric acid, tumor necrosis factor (TNF)-α and interleukin (IL)-6, in addition to the presence of uremic toxins in the serum, were assessed. The levels of diamine oxidase (DAO), D-lactate (D-LAC) and endotoxins in the serum, which are markers of the intestinal permeability, were measured using ELISA. The expression of the intestinal tight junction proteins zona occludens-1 (ZO-1) and occludin were detected by reverse transcription-quantitative polymerase chain reaction, western blotting and immunohistochemical analysis. The Uox-knockout mice spontaneously developed hyperuricemia. Histopathological analysis indicated notable intestinal defects including sparse villi, mucosal edema and a declining mucus layer in hyperuricemic mice. The expression levels of ZO-1 and occludin in the intestines were downregulated, and the serum levels of DAO, D-LAC and endotoxins were higher in the hyperuricemic mice, compared with control mice. The serum and intestinal tissue levels of IL-6 and TNF-α were significantly increased. Additionally, the expression levels of the serum uremic toxins, serum creatinine, blood urea nitrogen were significantly increased in hyperuricemic mice compared with the control mice, while only a marked increase in indoxyl sulfate (IS) and p-cresol sulfate was reported. Collectively, the results of the present study suggested that intestinal barrier dysfunction and subsequent enhanced intestinal permeability may occur as a result of hyperuricemia in mice. Furthermore, we proposed that the loss of intestinal epithelium barrier function may be associated with uric acid-induced inflammatory responses; however, further investigation is required.

The Japan Chronic Kidney Disease Database (J-CKD-DB) is a nationwide clinical database of patients with chronic kidney disease (CKD) based on electronic health records. The objective of this study was to assess the prevalences of hyperuricemia and electrolyte abnormalities in Japanese patients with CKD. In total, 35,508 adult outpatients with estimated glomerular filtration rates of 5-60 ml/min/1.73 m2 in seven university hospitals were included this analysis. The proportions of patients with CKD stages G3b, G4, and G5 were 23.5%, 7.6%, and 3.1%, respectively. Logistic regression analysis showed that prevalence of hyperuricemia was associated with CKD stages G3b (adjusted odds ratio [95% confidence interval]: 2.12 [1.90-2.37]), G4 (4.57 [3.92-5.32]), and G5 (2.25 [1.80-2.80]). The respective prevalences of hyponatremia, hypercalcemia, hyperphosphatemia, and narrower difference between serum sodium and chloride concentrations were elevated in patients with CKD stages G3b, G4, and G5, compared with those prevalences in patients with CKD stage G3a. The prevalences of hyperkalemia were 8.3% and 11.6% in patients with CKD stages G4 and G5, respectively. In patients with CKD stage G5, the proportions of patients with optimal ranges of serum uric acid, potassium, corrected calcium, and phosphate were 49.6%, 73.5%, 81.9%, and 56.1%, respectively. We determined the prevalences of hyperuricemia and electrolyte abnormalities in Japanese patients with CKD using data from a nationwide cohort study.