Piperine Improves Hyperuricemic Nephropathy by Inhibiting URAT1/GLUT9 and the AKT-mTOR Pathway

Uncontrolled hyperuricemia often leads to the development of hyperuricemic nephropathy (HN), characterized by excessive inflammation and oxidative stress. Piperine, a cinnamic acid alkaloid, possesses various pharmacological activities, such as antioxidant and anti-inflammatory effects. In this study, we intended to investigate the protective effects of piperine on adenine and potassium oxonate-induced HN mice and a uric-acid-induced injury model in renal tubular epithelial cells (mRTECs). We observed that treatment with piperine for 3 weeks significantly reduced serum uric acid levels and reversed kidney function impairment in mice with HN. Piperine (5 μM) alleviated uric acid-induced damage in mRTECs. Moreover, piperine inhibited transporter expression and dose-dependently inhibited the activity of both transporters. The results revealed that piperine regulated the AKT/mTOR signaling pathway both in vivo and in vitro. Overall, piperine inhibits URAT1/GLUT9 and ameliorates HN by inhibiting the AKT/mTOR pathway, making it a promising candidate for patients with HN.

New SLC22A12 (URAT1) Variant Associated with Renal Hypouricemia Identified by Whole-Exome Sequencing Analysis and Bioinformatics Predictions

Renal hypouricemia (RHUC) is a rare hereditary disorder caused by loss-of-function mutations in the SLC22A12 (RHUC type 1) or SLC2A9 (RHUC type 2) genes, encoding urate transporters URAT1 and GLUT9, respectively, that reabsorb urate in the renal proximal tubule. The characteristics of this disorder are low serum urate levels, high renal fractional excretion of urate, and occasional severe complications such as nephrolithiasis and exercise-induced acute renal failure. In this study, we report two Spanish (Caucasian) siblings and a Pakistani boy with clinical characteristics compatible with RHUC. Whole-exome sequencing (WES) analysis identified two homozygous variants: a novel pathogenic SLC22A12 variant, c.1523G>A; p.(S508N), in the two Caucasian siblings and a previously reported SLC2A9 variant, c.646G>A; p.(G216R), in the Pakistani boy. Our findings suggest that these two mutations cause RHUC through loss of urate reabsorption and extend the SLC22A12 mutation spectrum. In addition, this work further emphasizes the importance of WES analysis in clinical settings.

Hyperuricemia during Pregnancy Leads to a Preeclampsia-Like Phenotype in Mice

Hyperuricemia is a common feature in pregnancies compromised by pre-eclampsia, a pregnancy disease characterized by hypertension and proteinuria. The role of uric acid in the pathogenesis of pre-eclampsia remains largely unclear. The aim of this study was to investigate the effect of elevated uric acid serum levels during pregnancy on maternal blood pressure and neonatal outcome using two different murine knockout models. Non-pregnant liver-specific GLUT9 knockout (LG9KO) mice showed elevated uric acid serum concentrations but no hypertensive blood pressure levels. During pregnancy, however, blood pressure levels of these animals increased in the second and third trimester, and circadian blood pressure dipping was severely altered when compared to non-pregnant LG9KO mice. The impact of hyperuricemia on fetal development was investigated using a systemic GLUT9 knockout (G9KO) mouse model. Fetal hyperuricemia caused distinctive renal tissue injuries and, subsequently an impaired neonatal growth pattern. These findings provide strong evidence that hyperuricemia plays a major role in the pathogenesis of hypertensive pregnancy disorders such as pre-eclampsia. These novel insights may enable the development of preventive and therapeutic strategies for hyperuricemia-related diseases.

Fucoidan from Laminaria japonica Inhibits Expression of GLUT9 and URAT1 via PI3K/Akt, JNK and NF-κB Pathways in Uric Acid-Exposed HK-2 Cells

This work aimed to investigate the effect of fucoidan (FPS) on urate transporters induced by uric acid (UA). The results showed that UA stimulated the expression of glucose transporter 9 (GLUT9) and urate transporter 1 (URAT1) in HK-2 cells, and FPS could reverse the effect. Moreover, UA could activate NF-κB, JNK and PI3K/Akt pathways, but both pathway inhibitors and FPS inhibited the UA-induced activation of these three pathways. These data suggested that FPS effectively inhibited the expression induction of reabsorption transporters URAT1 and GLUT9 by UA, through repressing the activation of NF-κB, JNK and PI3K/Akt signal pathways in HK-2 cells. The in vitro research findings support the in vivo results that FPS reduces serum uric acid content in hyperuricemia mice and rats through inhibiting the expression of URAT1 and GLUT9 in renal tubular epithelial cells. This study provides a theoretical basis for the application of FPS in the treatment of hyperuricemia.

Lycium barbarum polysaccharides protect mice from hyperuricaemia through promoting kidney excretion of uric acid and inhibiting liver xanthine oxidase

CONTEXT

Lycium barbarum L. (Solanaceae) polysaccharides (LBPs) are important active constituents that have demonstrated kidney protection.

OBJECTIVE

This study investigated the effect of LBPs on hyperuricaemia and explored the underlying mechanism in mice.

MATERIALS AND METHODS

Thirty-six C57BL/6 mice were randomly divided into the control group, hyperuricaemia group, allopurinol group (5 mg/kg) and three LBP groups (n = 6). The LBP groups were treated orally with LBPs at 50, 100 and 200 mg/kg body weight for 7 days. We examined the levels of serum uric acid (S_UA) and urinary uric acid (U_UA), as well as xanthine oxidase (XOD) activities. mRNA and protein were quantified by quantitative real-time PCR and Western blotting, respectively.

RESULTS

LBPs treatment (100 and 200 mg/kg) significantly reduced the S_UA levels to 4.83 and 4.48 mg/dL, and markedly elevated the U_UA levels to 4.68 and 5.18 mg/dL (p < 0.05), respectively, while significantly increased the mRNA and protein expression levels of renal organic anti-transporter 1 (OAT1) and organic anti-transporter 3 (OAT3), and markedly decreased the levels of glucose transporter 9 (GLUT9) (p < 0.05). Additionally, the serum XOD activities were reduced to 31.5 and 31.1 mU/mL, and the liver XOD activities were reduced to 80.6 and 75.6 mU/mL after treatment with 100 and 200 mg/kg LBPs (p < 0.01), respectively.

DISCUSSION AND CONCLUSIONS

This study demonstrated the potential role of LBPs in reducing the uric acid level in hyperuricemic mice. A border study population should be evaluated. These results are valuable for the development of new anti-hyperuricaemia agents from LBPs.

Molecular mechanistic insight into the anti-hyperuricemic effect of Eucommia ulmoides in mice and rats

CONTEXT

Eucommia ulmoides Oliver (Eucommiaceae) has various medicinal properties. Our previous studies revealed that Eucommia ulmoides has a protective effect on hyperuricaemia.

OBJECTIVE

This study investigates the effect of Eucommia ulmoides cortex ethanol extract (EU) on hyperuricaemia and explores the underlying mechanism in Kunming mice and Sprague-Dawley rats.

MATERIAL AND METHODS

Sixty mice and sixty rats were divided into normal control, hyperuricaemia, allopurinol (10 mg/kg) and three EU groups. The EU groups received intragastric EU at 80, 160, 320 mg/kg in mice and 100, 200, 400 mg/kg in rats for 7 days. Serum uric acid (SUA) was measured using a kit. mRNA and proteins were quantified by RT-qPCR and immunohistochemical assays (IHC), respectively.

RESULTS

The Maximal Tolerable Dose (MTD) of EU administered intragastrically was 18 g/kg in mice. The intermediate (160 mg/kg) and high (320 mg/kg) EU treatment significantly reduced (p < 0.05) SUA levels to 130.16 μmol/L and 109.29 μmol/L, respectively, and markedly elevated the mRNA expression of organic anion transporters 1 (OAT1) and organic anion transporters 3 (OAT3), while significantly deceasing the mRNA levels of glucose transporter 9 (GLUT9) and uric acid transporter 1 (URAT1) in the mouse kidney (p < 0.05). In hyperuricemic rats, high EU (400 mg/kg) significantly reduced SUA levels to 253.85 μmol/L, and increased OAT1 and OAT3 levels, but decreased URAT1 and GLUT9, compared to the hyperuricaemia group (p < 0.05).

DISCUSSION AND CONCLUSIONS

This study demonstrated the potential hyperuricaemia ameliorating effect of EU. Specific active ingredients in EU should be evaluated. These results are valuable for the development of antihyperuritic agents from EU.

Hypouricemic Effects of Ganoderma applanatum in Hyperuricemia Mice through OAT1 and GLUT9

Ganoderma applanatum (G. applanatum) dispels wind to eliminate dampness and exhibited nephron- and liver-protective effects as noted in Chinese herbal classic literature; it might also affect hyperuricemia. Therefore, we examined the hypouricemia effects and mechanisms underlying G. applanatum on chemical-induced hyperuricemia in mice. Ethanol (GAE) and water (GAW) extracts were prepared by extracting G. applanatum in ethanol (GAE), followed by bathing the remains in water to yield GAW. GAE and GAW were administered orally at different doses to hyperuricemia mice, while allopurinol and benzbromarone served as positive controls. Both GAE and GAW showed remarkable hypouricemia activities, rendering a substantial decline in the SUA (serum uric acid) level in hyperuricemia control (P < 0.01). Moreover, the urine uric acid (UUA) levels were enhanced by GAE and GAW. In contrast to the evident renal toxicity of allopurinol, GAE and GAW did not show a distinct renal toxicity. Almost no suppressing effect was observed on the XOD activities. However, compared to the hyperuricemia control, OAT1 was elevated remarkably in mice drugged with GAE and GAW, while GLUT9 was significantly decreased. Similar to benzbromarone, GAE decreased the URAT1 protein levels significantly (P < 0.01), while GAW did not display a similar effect. GAE and GAW downregulated the level of CNT2 proteins in the gastrointestinal tract of hyperuricemia mice. Thus, G. applanatum produced outstanding hypouricemic effects, mediated by renal OAT1, GLUT9, and URAT1 and gastrointestinal CNT2 that might elevate urine uric secretions and decline in the absorption of purine in the gastrointestinal tracts. G. applanatum showed little negative influence on inner organs. By docking screening, four top-ranked compounds were identified that necessitated further investigation. Compounds: potassium oxonate, hypoxanthine, allopurinol, benzbromarone.

Compound Tufuling Granules ([characters: see text]) regulate glucose transporter 9 expression in kidney to influence serum uric acid level in hyperuricemia mice

OBJECTIVE

To explore the effect of Compound Tufuling Granules ([characters: see text], CTG) on regulating glucose transporter 9 (GLUT9) expression in the kidney to influence the uric acid excretion by the kidney and serum uric acid (SUA) level in hyperuricemia mice.

METHODS

Sixty Kunming male mice were randomly divided into the control group, model group, benzbromarone group, and CTG high-, middle- and low-dose groups. The yeast extract and uricase inhibition method were used to build hyperuricemia model, and the corresponding drugs were administrated on the 7th day. On the 21st day the 24-h urine was collected, on the 22nd day the blood was collected, the SUA level was detected by uricase colorimetry, and the mRNA and protein expressions of GLUT9 were detected by quantitative real-time polymerase chain reaction and Western blot, respectively.

RESULTS

Compared with the model group, the levels of SUA and the mRNA and protein expressions of GLUT9 were significantly decreased, and the fraction excretion of uric acid (FEUA) was significantly increased in the CTG groups and benzbromarone group (all P<0.05). There was no significant difference in the above indicators between the CTG high-dose group and benzbromarone group (P>0.05). SUA is positively related to the GLUT9 mRNA and protein expressions in the kidney (P<0.05 or P<0.01).

CONCLUSIONS

CTG can significantly reduce the SUA and increase the FEUA. In addition, CTG can effectively inhibit the mRNA and protein expressions of GLUT9 in the kidney of hyperuricemia mice to inhibit the uric acid re-absorption, promote uric acid excretion and reduce SUA.

Urate-induced acute renal failure and chronic inflammation in liver-specific Glut9 knockout mice

Plasma urate levels are higher in humans than rodents (240-360 vs. ∼30 μM) because humans lack the liver enzyme uricase. High uricemia in humans may protect against oxidative stress, but hyperuricemia also associates with the metabolic syndrome, and urate and uric acid can crystallize to cause gout and renal dysfunctions. Thus, hyperuricemic animal models to study urate-induced pathologies are needed. We recently generated mice with liver-specific ablation of Glut9, a urate transporter providing access of urate to uricase (LG9KO mice). LG9KO mice had moderately high uricemia (∼120 μM). To further increase their uricemia, here we gavaged LG9KO mice for 3 days with inosine, a urate precursor; this treatment was applied in both chow- and high-fat-fed mice. In chow-fed LG9KO mice, uricemia peaked at 300 μM 2 h after the first gavage and normalized 24 h after the last gavage. In contrast, in high-fat-fed LG9KO mice, uricemia further rose to 500 μM. Plasma creatinine strongly increased, indicating acute renal failure. Kidneys showed tubule dilation, macrophage infiltration, and urate and uric acid crystals, associated with a more acidic urine. Six weeks after inosine gavage, plasma urate and creatinine had normalized. However, renal inflammation, fibrosis, and organ remodeling had developed despite the disappearance of urate and uric acid crystals. Thus, hyperuricemia and high-fat diet feeding combined to induce acute renal failure. Furthermore, a sterile inflammation caused by the initial crystal-induced lesions developed despite the disappearance of urate and uric acid crystals.

Serum uric acid in relation to serum 1,5-anhydroglucitol levels in patients with and without type 2 diabetes mellitus

OBJECTIVES

The aim of this study was to examine the relationship between serum levels of uric acid (UA) and 1,5-anhydroglucitol (1,5-AG) in elderly subjects (60 years or older; mean age, 73.0±7.2 years) with and without type 2 diabetes mellitus (DM).

METHODS

Subjects with DM (n=97) and without DM (n=360) were recruited from among our outpatients (estimated glomerular filtration rate≥45 mL min⁻¹ 1.73 m⁻², and urine protein equivalent to <1.0 g/L), and a cross-sectional study was performed with simple linear regression and stepwise multiple linear regression analyses.

RESULTS

The mean serum UA levels of men were significantly higher than those of women in both groups. The mean serum 1,5-AG levels of men were significantly higher than those of women in the non-DM group. There were positive correlations (indicated by Pearson's correlation coefficients) between serum UA levels and 1,5-anhydroglucitol levels in all patients and in both men and women. Simple linear regression and multiple linear regression analyses showed that the serum 1,5-AG levels were significantly and positively correlated with the serum UA level in both the non-DM group and the DM group. In the non-DM group, HbA1c levels, as well as 1,5-AG levels, were positively correlated with serum UA levels. Furthermore, the correlation between 1,5-AG and UA levels was stronger in subjects with DM than in subjects without DM.

CONCLUSIONS

These results suggest that the serum 1,5-AG level is an independent factor associated with serum UA levels in the nondiabetic state, as in DM.