Noncrystalline uric acid inhibits proteoglycan and glycosaminoglycan synthesis in distal tubular epithelial cells (MDCK)

Effects of high-dose uric acid on cellular proteome, intracellular ATP, tissue repairing capability and calcium oxalate crystal-binding capability of renal tubular cells: Implications to hyperuricosuria-induced kidney stone disease

Hyperuricosuria is associated with kidney stone disease, especially uric acid (UA) and calcium oxalate (CaOx) types. Nevertheless, detailed mechanisms of hyperuricosuria-induced kidney stone formation remained unclear. This study examined changes in cellular proteome and function of renal tubular cells after treatment with high-dose UA for 48-h. Quantitative proteomics using 2-DE followed by nanoLC-ESI-ETD MS/MS tandem mass spectrometry revealed significant changes in levels of 22 proteins in the UA-treated cells. These proteomic data could be confirmed by Western blotting. Functional assays revealed an increase in intracellular ATP level and enhancement of tissue repairing capability in the UA-treated cells. Interestingly, levels of HSP70 and HSP90 (the known receptors for CaOx crystals) were increased in apical membranes of the UA-treated cells. CaOx crystal-cell adhesion assay revealed significant increase in CaOx-binding capability of the UA-treated cells, whereas neutralization of the surface HSP70 and/or HSP90 using their specific monoclonal antibodies caused significant reduction in such binding capability. These findings highlighted changes in renal tubular cells in response to high-dose UA that may, at least in part, explain the pathogenic mechanisms of hyperuricosuria-induced mixed kidney stone disease.

Mechanistic Insights of Soluble Uric Acid-related Kidney Disease

Hyperuricemia, defined as the presence of elevated serum uric acid (sUA), could lead to urate deposit in joints, tendons, kidney and other tissues. Hyperuricemia as an independent risk factor was common in patients during the causation and progression of kidney disease. Uric acid is a soluble final product of endogenous and dietary purine metabolism, which is freely filtered in kidney glomeruli where approximately 90% of filtered uric acid is reabsorbed. Considerable studies have demonstrated that soluble uric acid was involved in the pathophysiology of renal arteriolopathy, tubule injury, tubulointerstitial fibrosis, as well as glomerular hypertrophy and glomerulosclerosis. In the review, we summarized the mechanistic insights of soluble uric acid related renal diseases.

Serum uric acid and acute kidney injury: A mini review

Acute kidney injury causes great morbidity and mortality in both the community and hospital settings. Understanding the etiological factors and the pathophysiological principles resulting in acute kidney injury is essential in prompting appropriate therapies. Recently hyperuricemia has been recognized as a potentially modifiable risk factor for acute kidney injury, including that associated with cardiovascular surgery, radiocontrast administration, rhabdomyolysis, and associated with heat stress. This review discussed the evidence that repeated episodes of acute kidney injury from heat stress and dehydration may also underlie the pathogenesis of the chronic kidney disease epidemic that is occurring in Central America (Mesoamerican nephropathy). Potential mechanisms for how uric acid might contribute to acute kidney injury are also discussed, including systemic effects on renal microvasculature and hemodynamics, and local crystalline and noncrystalline effects on the renal tubules. Pilot clinical trials also show potential benefits of lowering uric acid on acute kidney injury associated with a variety of insults. In summary, there is mounting evidence that hyperuricemia may have a significant role in the development of acute kidney injury. Prospective, placebo controlled, randomized trials are needed to determine the potential benefit of uric acid lowering therapy on kidney and cardio-metabolic diseases.

Soluble uric acid increases NALP3 inflammasome and interleukin-1β expression in human primary renal proximal tubule epithelial cells through the Toll-like receptor 4-mediated pathway

Urate crystals activate innate immunity through Toll like receptor 4 (TLR4) activation, leading to the formation of the NACHT, LRR and PYD domains-containing protein 3 [NALP3; also known as NOD-like receptor family, pyrin domain containing 3 (NALP3) and cryopyrin] inflammasome, caspase-1 activation and interleukin (IL)-1β expression in gout. However, whether elevated serum uric acid (UA) levels are associated with the development and progression of renal diseases without renal urate crystal deposition remains unknown. In the present study, human primary renal proximal tubule epithelial cells were incubated with soluble UA (100 µg/ml) with or without the TLR4 inhibitor, TAK242 (1 µM). The gene expression and protein synthesis of TLR4, NALP3, caspase-1, IL-1β and intercellular adhesion molecule-1 (ICAM-1) were detected by real-time PCR, ELISA, western blot analysis and fluorescence-activated cell sorting (FACS), respectively. Soluble UA significantly enhanced TLR4, NALP3, caspase-1, IL-1β and ICAM-1 expression in the human primary renal proximal tubule epithelial cells. The TLR4 inhibitor, TAK242 effectively blocked the soluble UA-induced upregulation of TLR4, NALP3, caspase-1, IL-1β and ICAM-1 expression in the human primary renal proximal tubule epithelial cells. Our findings indicate that soluble UA enhances NALP3 expression, caspase-1 activation, IL-1β and ICAM-1 production in renal proximal tubule epithelial cells in a TLR4-dependent manner, suggesting the activation of innate immunity in human primary renal proximal tubule epithelial cells by soluble UA.