Are Target Urate and Remission Possible in Severe Gout? A Five-year Cohort Study

OBJECTIVE

Determine the proportion of patients achieving target serum urate (SU), defined as < 6 mg/dl for patients with non-severe gout and < 5 mg/dl for patients with severe gout, as well as the proportion of patients achieving remission after 5 years of followup.

METHODS

Patients from the Gout Study Group (GRESGO) cohort were evaluated at 6-month intervals. Demographic and clinical data were obtained at baseline. Visits included assessments of serum urate, flares, tophus burden, health-related quality of life using the EQ-5D, activity limitations using the Health Assessment Questionnaire adapted for gout, and pain level and patient's global assessment using visual analog scales. Treatment for gout and associated diseases was prescribed according to guidelines and available drugs.

RESULTS

Of 500 patients studied, 221 had severe gout (44%) and 279 had non-severe gout (56%) at baseline. No significant differences were observed across the study in percentages of severe gout versus non-severe gout patients achieving SU 6 mg/dl or 5 mg/dl. The highest proportion of patients achieving target SU (50-70%) and remission (39%) were found after 3-4 years of followup. In the fifth year, these proportions decreased and 28% of the patients were in remission, but only 40 patients remained in the study. None of the patients with severe gout achieved remission.

CONCLUSION

In patients with severe gout, target SU was hard to achieve and remission was not possible. The main obstacles for target SU and gout remission include poor medication adherence, persistent tophi, and loss to followup.

Precipitation of Soluble Uric Acid Is Necessary for In Vitro Activation of the NLRP3 Inflammasome in Primary Human Monocytes

OBJECTIVE

To investigate the effects of soluble uric acid (UA) on expression and activation of the NOD-like receptor (NLR) pyrin domain containing protein 3 (NLRP3) inflammasome in human monocytes to elucidate the role of hyperuricemia in the pathogenesis of gout.

METHODS

Primary human monocytes and the THP-1 human monocyte cell line were used to determine the effects of short- and longterm exposure to UA on activation of the NLRP3 inflammasome and subsequent interleukin 1β (IL-1β) secretion by ELISA and cell-based assays. Expression of key NLRP3 components in monocytes from patients with a history of gout were analyzed by quantitative PCR.

RESULTS

Precipitation of UA was required for activation of the NLRP3 inflammasome and subsequent release of IL-1β in human monocytes. Neither monosodium urate (MSU) crystals nor soluble UA had any effect on activation of the transcription factor, nuclear factor-κB. Prolonged exposure of monocytes to soluble UA did not alter these responses. However, both MSU crystals and soluble UA did result in a 2-fold increase in reactive oxygen species. Patients with gout (n = 15) had significantly elevated serum UA concentrations compared to healthy individuals (n = 16), yet secretion of IL-1β and expression of NLRP3 inflammasome components in monocytes isolated from these patients were not different from those of healthy controls.

CONCLUSION

Despite reports indicating that soluble UA can prime and activate the NLRP3 inflammasome in human peripheral blood mononuclear cells, precipitation of soluble UA into MSU crystals is essential for in vitro NLRP3 signaling in primary human monocytes.

Gout and the Risk of Non-vertebral Fracture

Prior studies suggest an association between osteoporosis, systemic inflammation, and pro-inflammatory cytokines such as interleukin (IL)-1 and IL-6. Conflicting findings exist on the association between hyperuricemia and osteoporosis. Furthermore, it remains unknown whether gout, a common inflammatory arthritis, affects fracture risk. Using data from a US commercial health plan (2004-2013), we evaluated the risk of non-vertebral fracture (ie, forearm, wrist, hip, and pelvis) in patients with gout versus those without. Gout patients were identified with ≥2 diagnosis codes and ≥1 dispensing for a gout-related drug. Non-gout patients, identified with ≥2 visits coded for any diagnosis and ≥1 dispensing for any prescription drugs, were free of gout diagnosis and received no gout-related drugs. Hip fracture was the secondary outcome. Fractures were identified with a combination of diagnosis and procedure codes. Cox proportional hazards models compared the risk of non-vertebral fracture in gout patients versus non-gout, adjusting for more than 40 risk factors for osteoporotic fracture. Among gout patients with baseline serum uric acid (sUA) measurements available, we assessed the risk of non-vertebral fracture associated with sUA. We identified 73,202 gout and 219,606 non-gout patients, matched on age, sex, and the date of study entry. The mean age was 60 years and 82% were men. Over the mean 2-year follow-up, the incidence rate of non-vertebral fracture per 1,000 person-years was 2.92 in gout and 2.66 in non-gout. The adjusted hazard ratio (HR) was 0.98 (95% confidence interval [CI] 0.85-1.12) for non-vertebral fracture and 0.83 (95% CI 0.65-1.07) for hip fracture in gout versus non-gout. Subgroup analysis (n = 15,079) showed no association between baseline sUA and non-vertebral fracture (HR = 1.03, 95% CI 0.93-1.15), adjusted for age, sex, comorbidity score, and number of any prescription drugs. Gout was not associated with a risk of non-vertebral fracture. Among patients with gout, sUA was not associated with the risk of non-vertebral fracture. © 2016 American Society for Bone and Mineral Research.

Serum Uric Acid and the Risk of Incident and Recurrent Gout: A Systematic Review

OBJECTIVE

Lowering serum uric acid (SUA) levels can essentially cure gout; however, this is not widely practiced. To summarize epidemiologic evidence related to this causal link, we conducted a systematic review of the published literature reporting the association between SUA level and incident and recurrent gout (i.e., gout flares).

METHODS

We systematically searched Medline, EMBASE, and the Cochrane Database of Systematic Reviews using separate search strategies for incident gout and recurrent gout. We screened 646 abstracts to identify 8 eligible articles reporting gout incidence and 913 abstracts to identify 18 articles reporting recurrent gout.

RESULTS

For both gout incidence and recurrence, a graded trend was observed where the risk was increased with higher SUA levels. Gout incidence rates per 1000 person-years from population-based studies ranged from 0.8 (SUA ≤ 6 mg/dl) to 70.2 cases (SUA ≥ 10 mg/dl). Recurrent gout risk in clinical cohorts ranged from 12% (SUA ≤ 6 mg/dl) to 61% (SUA ≥ 9 mg/dl) among those receiving urate-lowering therapy (ULT), and 3.7% (SUA 6-7 mg/dl) to 61% (SUA > 9.3 mg/dl) after successful ULT. Retrospective database studies also showed a graded relationship, although the strength of the association was weaker. Studies reporting mean flares or time-to-flare according to SUA showed similar findings.

CONCLUSION

This systematic review confirms that higher SUA levels are associated with increased risk of incident and recurrent gout in a graded manner. Although few prospective cohorts have evaluated incident and recurrent gout according to SUA, the existing evidence underscores the need to treat to SUA targets, as recommended by the American College of Rheumatology and the European League Against Rheumatism.

Sex-specific Relationship of Serum Uric Acid with All-cause Mortality in Adults with Normal Kidney Function: An Observational Study

OBJECTIVE

To explain the clinical effect of serum uric acid (SUA) levels as a risk factor for mortality, considering exclusion of kidney function.

METHODS

Participants aged over 40 years who underwent health checkups were recruited. Individuals with estimated glomerular filtrations rates < 60 ml/min/1.73 m² and who received laboratory study and colonoscopy on the same day were excluded.

RESULTS

SUA levels were higher in men than in women (5.7 ± 1.2 mg/dl for men and 4.2 ± 0.9 mg/dl for women, p < 0.001). During 12.3 ± 3.6 years of followup, 1402 deaths occurred among 27,490 participants. About 6.9% of men and 3.1% of women died. The overall mortality rate had a U-shaped association with SUA levels, a U-shaped association in men, and no association in women. There was a significant interaction of sex for the SUA-mortality association (p for interaction = 0.049); therefore, survival analysis was conducted by sex. In men, the lower SUA group had a higher mortality rate after adjustment (SUA ≤ 4.0 mg/dl, adjusted HR 1.413, 95% CI 1.158-1.724, p = 0.001) compared with the reference group (SUA 4.1-6.0 mg/dl). A higher SUA contributed to an insignificant increased mortality in men (> 8.0 mg/dl, adjusted HR 1.140, 95% CI 0.794-1.636, p = 0.479). Women failed to show any significant association between SUA and mortality.

CONCLUSION

This study provided novel evidence that SUA-mortality association differed by sex. We demonstrated that a lower SUA was an independent risk factor for all-cause mortality in men with normal kidney function.

Low levels of serum uric Acid increase the risk of low bone mineral density in young male patients with ankylosing spondylitis

OBJECTIVE

Uric acid (UA) has antiosteoporotic effects in postmenopausal women. This study investigated the association between serum UA levels and bone mineral density (BMD) in young male patients with ankylosing spondylitis (AS).

METHODS

One hundred fifty patients who fulfilled the modified New York criteria for the classification of AS were analyzed. All patients were male and under 50 years of age. BMD, serum UA concentrations, clinical variables, and radiographic progression were assessed. The associations between UA and BMD at the lumbar spine and hip were evaluated using multiple linear regression analysis. Multivariate logistic regression analyses were performed to identify risk factors associated with low BMD.

RESULTS

Mean serum UA concentration in the 150 patients with AS was 5.5 ± 1.3 mg/dl. BMD at the lumbar spine, but not at the total hip and femoral neck, increased with increasing serum UA tertiles (p = 0.033). The significant positive association between serum UA and BMD at the lumbar spine remained after adjustment for confounding factors (β = 0.185, p = 0.014, adjusted R(2) = 0.310). Multiple logistic regression analyses showed that lower UA concentrations (OR 4.02, 95% CI 1.34-12.3) and body mass index and increased erythrocyte sedimentation rate were independently associated with the risk of low BMD.

CONCLUSION

Lower serum UA levels are associated with lower BMD in young male patients with AS. UA may be a novel predictive marker or therapeutic target in patients with AS.

Relationship between serum uric acid levels and hepatic steatosis in non-obese postmenopausal women

OBJECTIVE

Serum uric acid levels have been reported to be associated with non-alcoholic fatty liver disease (NAFLD). However, very few studies specifically examining the relationship between serum uric acid (SUA) levels and NAFLD in postmenopausal women have been reported in China, especially in postmenopausal women with normal body mass index (BMI) in whom NAFLD is not uncommon.

METHODS

A cross-sectional study was employed of 528 Chinese normal-BMI postmenopausal women (aged 41-79 years) who participated in annual health check-ups. NAFLD is defined as a hepatic steatosis observed on liver ultrasonography in the absence of a second cause. Of all the participants, 121 women were diagnosed with hepatic steatosis (NAFLD group) and the others were without (non-NAFLD group). SUA quartiles were defined as follows: Q1, < 3.8 mg/dl; Q2, 3.8-4.4 mg/dl; Q3, 4.5-5.0 mg/dl; Q4, 5.1-6.0 mg/dl. Stepwise multivariable regression analysis was used to assess the relationships between SUA level and other variables. The association between SUA quartiles and hepatic steatosis was assessed using binary logistic regression.

RESULTS

Compared to the non-NAFLD group, the mean level of SUA was significantly higher in the NAFLD group (p < 0.01). The adjusted odds ratio (95% confidence interval) for the presence of hepatic steatosis in the highest SUA quartile vs. the lowest quartile was 2.774 (1.396-5.513) for all women (p < 0.01) after adjusting for the factors which were independently associated with uric acid level including waist circumference, high blood pressure, blood urea nitrogen, creatinine, γ-glutamyltransferase, and triglycerides. Most estimates changed little after further adjustment for age, metabolic syndrome, drinking status, and smoking status. The presence of hepatic steatosis significantly increased in the third and fourth quartiles of SUA. The prevalence of hepatic steatosis increased gradually with an increasing SUA quartile (p for trend < 0.01).

CONCLUSION

Higher SUA levels even within the normal range are positively and independently associated with the presence of hepatic steatosis in Chinese postmenopausal women with normal BMI.

Common variants of cGKII/PRKG2 are not associated with gout susceptibility

OBJECTIVE

Recently, genetic analyses indicated the association between gout and cGMP-dependent protein kinase 2 (cGKII/PRKG2) gene in a Fukien-Taiwanese heritage population. However, no replication study has been reported in other ancestries. Therefore, we investigated this association in a Japanese population.

METHODS

Genotyping of 4 variants (rs11736177, rs10033237, rs7688672, and rs6837293) of cGKII was performed in 741 male gout patients and 1302 male controls.

RESULTS

cGKII variants have no association with gout.

CONCLUSION

Our replication study suggests that cGKII is not involved in gout susceptibility.

Effect of urate-lowering therapies on renal disease progression in patients with hyperuricemia

OBJECTIVE

To evaluate the association between hyperuricemia and renal disease progression in a real-world, large observational database study.

METHODS

We conducted a population-based retrospective cohort study identifying 111,992 patients with hyperuricemia (> 7 mg/dl) from a large medical group. The final cohort were ≥ 18 years old, urate-lowering therapy (ULT)-naïve, and had the following laboratory results available: at least 1 glomerular filtration rate (GFR) level before the index date and at least 1 serum uric acid (sUA) level and GFR in the followup 36-month period. The cohort was categorized into 3 groups: never treated (NoTx), ULT time receiving therapy of < 80% (< 80%), and ULT time receiving therapy of ≥ 80% (≥ 80%). Outcomes were defined as a ≥ 30% reduction in GFR from baseline, dialysis, or GFR of ≤ 15 ml/min. A subanalysis of patients with sUA < 6 mg/dl at study conclusion was performed. Cox proportional hazards regression model determined factors associated with renal function decline.

RESULTS

A total of 16,186 patients met inclusion criteria. There were 11,192 NoTx patients, 3902 with < 80% time receiving ULT, and 1092 with ≥ 80% time receiving ULT. Factors associated with renal disease progression were age, sex, hypertension, diabetes, congestive heart failure, hospitalizations, rheumatoid arthritis, and higher sUA at baseline. Time receiving therapy was not associated with renal outcomes. Patients who achieved sUA < 6 mg/dl had a 37% reduction in outcome events (p < 0.0001; HR 0.63, 95% CI: 0.5-0.78).

CONCLUSION

Hyperuricemia is an independent risk factor for renal function decline. Patients treated with ULT who achieved sUA < 6 mg/dl on ULT showed a 37% reduction in outcome events.

Serum urate and incidence of kidney disease among veterans with gout

OBJECTIVE

To study the association between serum urate level (sUA) and the risk of incident kidney disease among US veterans with gouty arthritis.

METHODS

From 2002 through 2011 adult male patients with gout who were free of kidney disease were identified in the data from the Veterans Administration VISN 16 database and were followed until incidence of kidney disease, death, or the last available observation. Accumulated hazard curves for time to kidney disease were estimated for patients with average sUA levels > 7 mg/dl (high) versus ≤ 7 mg/dl (low) based on Kaplan-Meier analyses; and statistical comparison was conducted using a log-rank test. A Cox proportional hazard model with time-varying covariates was used to estimate the unadjusted and adjusted hazard ratios for kidney disease.

RESULTS

Eligible patients (n = 2116) were mostly white (53%), with average age 62.6 years, mean body mass index 31.2 kg/m(2), and high baseline prevalence of hypertension (93%), hyperlipidemia (67%), and diabetes (20%). Mean followup time was 6.5 years. The estimated rates of all incident kidney disease in the overall low versus high sUA groups were 2% versus 4% at Year 1, 3% versus 6% at Year 2, and 5% versus 9% at Year 3, respectively (p < 0.0001). After adjustment, high sUA continued to predict a significantly higher risk of kidney disease development (HR 1.43, 95% CI 1.20-1.70).

CONCLUSION

Male veterans with gout and sUA levels > 7 mg/dl had an increased incidence of kidney disease.

The renal mechanism for urate excretion in the Dalmatian coach-hound

1. The renal mechanism for urate excretion in the Dalmatian dog resembles that in birds. Urate is cleared at a rate considerably greater than the glomerular filtration rate, indicating that its excretion is the result of both glomerular filtration and active tubular secretion. The basic physiological mechanisms involved in the anomalous purine metabolism of the Dalmatian are indicated and their possible biological significance briefly discussed. 2. A new enzymatic method for the direct estimation of true urate in biological fluids is described, which does not require the estimation of total urate and urate chromogen, followed by the calculation of true urate as a difference.

HYPERTRIGLYCERIDEMIA IN GOUT

Serum triglyceride levels were significantly higher in 34 patients with gout (42 mg. per 100 ml.) in comparison to the levels in 28 healthy men over 35 years of age (100 mg. per 100 ml.). There was no significant predictive relation between levels of serum uric acid and triglycerides in either group. No significant difference in serum cholesterol levels nor lipoprotein profile was apparent between the two groups. The patients with gout had been selected to exclude any manifestations of atherosclerosis or other disease known to be associated with abnormalities in circulating lipids. The results provide support for possible linkage of genetic factors influencing uric acid and triglyceride metabolism. The presence of hypertriglyceridemia in gout may be correlated with the increased incidence of arteriosclerosis.

ROLE OF FERREDOXIN IN THE METABOLISM OF MOLECULAR HYDROGEN

Valentine, R. C. (University of Illinois, Urbana) and R. S. Wolfe. Role of ferredoxin in the metabolism of molecular hydrogen. J. Bacteriol. 85:1114-1120. 1963.-The metabolism of molecular hydrogen by Clostridium pasteurianum, Micrococcus lactilyticus (Veillonella alcalescens), and several other anaerobic bacteria was studied. Oxidation of hydrogen, using several electron-accepting substrates including triphosphopyridine nucleotide, uric acid, xanthine, nitrite, and hydroxylamine, required ferredoxin in conjunction with hydrogenase. Evolution of hydrogen from pyruvate, alpha-ketoglutarate, hypoxanthine, and dithionite was mediated by ferredoxin. On the basis of these findings, a unitary hypothesis for biological hydrogen evolution is proposed in which ferredoxin plays a key role.