FC 003HYPERURICEMIA HAS VASOACTIVE EFFECTS IN CHOLESTEROL CRYSTAL-INDUCED ACUTE KIDNEY INJURY
Authors: Yang Luying , Mammadova-Bach Elmina , Braun Attila , Gudermann Thomas , Anders Hans-Joachim , Steiger Stefanie 
Published: May 2021

Abstract

Background and Aims
Numerous observational studies have reported an association between hyperuricemia (HU) and cardiovascular disease where atherosclerosis is a leading cause. In advanced atherosclerosis, cholesterol crystal (CC) embolism is a life-threatening complication with an average mortality of 62.8%. Clinical manifestations include skin necrosis, intestinal injury and acute kidney injury (AKI). Autopsies and tissue biopsies reveal CC inside the arterial lumen. In a new model of CC-induced AKI, we recently found that fibrin clots formed around CC obstruct peripheral arteries and cause tissue infarction and organ failure. However, the role of asymptomatic HU in CC-induced AKI is currently unknown. Thus, we hypothesized that asymptomatic HU improves the outcomes after CC-induced AKI.

Method
In vivo, 6 weeks old Alb-creERT2;Glut9lox/lox and Glut9lox/lox control mice were intraperitoneally injected with tamoxifen to deplete hepatic Glut9 expression. Both groups of mice were placed on a standard chow diet enriched with inosine for two weeks. Afterward, a solution of CCs was injected into the left kidney arteries of mice to induce AKI. Serum and kidneys were collected 24 hours later, and kidney function, infarct size and kidney injury evaluated using GFR measurement, colorimetric assays, ELISA and immunohistochemistry of kidney sections. For in vitro studies, we isolated platelets from healthy mice and cultured them in the presence or absence of soluble uric acid (sUA) prior to CC activation. After stimulation, platelet aggregation assays and flow cytometry were performed.

Results
Our in vivo data showed that Alb-creERT2;Glut9lox/lox mice developed asymptomatic HU without kidney impairment (serum UA levels 9-15 mg/dL), while Glut9lox/lox control mice remained healthy. HU mice displayed a rapid decline in GFR of approx. 80% as compared to only 30% in healthy mice after CC-induced AKI, which was in line with increased serum BUN and IL-6 levels. The rapid GFR decline was due to vasoconstriction in arteries of the contralateral kidney as determined by αSMA/fibrin staining and a reduced ratio of lumen versus artery area in mice with HU after AKI. HU mice also had significantly less kidney infarct size as well as reduced kidney injury (necrosis and edema) and arterial occlusion. The in vitro data showed that sUA had no impact on platelet aggregation, activation and degranulation as compared to medium control in response to CCs.

Conclusion
We now show that HU has vasoconstrictive effects in the contralateral kidney by reducing GFR, while at the same time protects mice from CC-induced AKI suggesting a compensatory physiological mechanism of autoregulation to protect nephrons. On the other hand, in patients with chronic kidney disease, HU-related vasoconstriction might lead to increased arterial blood pressure; thus, increasing the risk for cardiovascular complications due to platelet activation and aggregation.