Is urate crystal precipitation a predictor of cardiovascular risk in hyperuricemic patients? A Danish cohort study

The biology of urate

Urate is the end-product of the purine metabolism in humans. The dominant source of urate is endogenous purines and the remainder comes through diet. Approximately two thirds of urate is eliminated via the kidney with the rest excreted in the feces. While the transporter BCRP, encoded by ABCG2, has been found to play a role in both the gut and kidney, SLC22A12 and SLC2A9 encoding URAT1 and GLUT9, respectively, are the two transporters best characterized. Only 8-12% of the filtered urate is excreted by the kidney. Renal elimination of urate depends substantially on specific transporters, including URAT1, GLUT9 and BCRP. Studies that have assessed the biologic effects of urate have produced highly variable results. Although there is a suggestion that urate may have anti-oxidant properties in some circumstances, the majority of evidence indicates that urate is pro-inflammatory. Hyperuricemia can result in the formation of monosodium urate (MSU) crystals that may be recognized as danger signals by the immune system. This immune response results in the activation of the NLRP3 inflammasome and ultimately in the production and release of interleukin-1β, and IL-18, that mediate both inflammation, pyroptotic cell death, and necroinflammation. It has also been demonstrated that soluble urate mediates effects on the kidney to induce hypertension and can induce long term epigenetic reprogramming in myeloid cells to induce "trained immunity." Together, these sequelae of urate are thought to mediate most of the physiological effects of hyperuricemia and gout, illustrating this biologically active molecule is more than just an "end-product" of purine metabolism.

Is increased uric acid a risk factor or a defensive response? The Campania Salute Network

BACKGROUND AND AIMS

Circulating uric acid (UA) is positively associated with body mass index (BMI), blood glucose, blood pressure (BP), markers of inflammation, and altered lipid profile. UA has also anti-oxidative properties which might be beneficial for cardiovascular (CV) system. It is still debated whether or not UA is independently associated with increased CV morbidity and/or mortality.

METHODS AND RESULTS

We studied prognostic impact of UA in 8833 hypertensive adults (mean age 53 ± 12 yrs, 3857 women) from the Campania Salute Network, without prevalent CV disease and more than stage 3 CKD. We calculated standardized UA Z-score, adjusted for age, sex, glomerular filtration rate, and BMI. Low and high UA and UA Z-score quartiles were compared to the 2 middle quartiles assumed to be "normal". Prevalence of obesity and diabetes was higher in low and high than in normal UA Z-score group (all p < 0.001). Systolic BP, left ventricular mass, carotid intima thickness were significantly higher and ejection fraction was reduced in the presence of high UA Z-score (all p < 0.001). Over 33-months average follow-up, incident major CV end-points (MACE) were not significantly different among low, normal and high UA or UA Z-score. In the latter analysis, however, incident MACE tended to be more frequent in the low than the high UA Z-score. Despite the results of multivariable analyses, the effect of less aggressive therapy in low UA Z-score cannot be excluded with certainty.

CONCLUSION

In treated hypertensive patients, high levels of UA normalized for major biological determinants do not independently predict CV outcome. CLINICALTRIALS.

GOV IDENTIFIER

NCT02211365.

Physiology of Hyperuricemia and Urate-Lowering Treatments

Gout is the most common form of inflammatory arthritis and is a multifactorial disease typically characterized by hyperuricemia and monosodium urate crystal deposition predominantly in, but not limited to, the joints and the urinary tract. The prevalence of gout and hyperuricemia has increased in developed countries over the past two decades and research into the area has become progressively more active. We review the current field of knowledge with emphasis on active areas of hyperuricemia research including the underlying physiology, genetics and epidemiology, with a focus on studies which suggest association of hyperuricemia with common comorbidities including cardiovascular disease, renal insufficiency, metabolic syndrome and diabetes. Finally, we discuss current therapies and emerging drug discovery efforts aimed at delivering an optimized clinical treatment strategy.

Evaluation of the Relationship Between Serum Uric Acid Levels and Cardiovascular Events in Patients With Gout: A Retrospective Analysis Using Electronic Medical Record Data

OBJECTIVES

The aim of this study was to evaluate relationships between serum uric acid (SUA) and newly emergent acute myocardial infarction (AMI), congestive heart failure (CHF), coronary artery disease (CAD), composite cardiovascular (CV) events (AMI, CHF, CAD), hypertension, hyperlipidemia, and renal disease in gout patients.

METHODS

Retrospective analysis of electronic medical records from Humedica identified adults (≥18 years) with 2 or more International Classification of Diseases, Ninth Revision, Clinical Modification codes for gout 30 days or more apart (first diagnosis = index event) having 1 or more SUA assessment on or after the index date, and at least 6 months preindex and at least 12 months postindex enrollment. Outcomes were measured during 12 months postindex; patients with preindex events were excluded from analysis of those events. The SUA level (0.01-4.00 mg/dL, 4.01-6.00 mg/dL, 6.01-8.00 mg/dL, and ≥8.01 mg/dL) was determined using the closest laboratory assessment before or on the date of the CV event. Tukey-Kramer comparisons were performed for pairs of SUA strata and Cox proportional model estimated hazard ratios.

RESULTS

A significantly higher incidence of AMI, CHF, and renal disease was observed for patients with 8.01 mg/dL or greater relative to other SUA levels (P < 0.0001), and a significantly higher incidence of composite CV events (AMI, CHF, and CAD) was observed for hypouricemia (SUA, 0.01-4.00 mg/dL) compared with other SUA levels (P < 0.0001). Cox models confirmed the increased risk associated with SUA 8.01 mg/dL or greater; hazard ratios ranged from 1.16 for hypertension to 2.04 for renal disease. Hyperlipidemia and hypertension were diagnosed concurrently with gout in 24% and 28% of patients, respectively.

CONCLUSIONS

Hyperuricemia and hypouricemia were associated with an increased risk of CV events.