Uric acid indicates a high cardiovascular risk profile but is not closely associated with insulin resistance in obese adolescents

The relationship between serum uric acid and homocysteine is influenced by kidney function

BACKGROUND AND AIM

Prior research has established a relationship between homocysteine (Hcy) and serum uric acid (SUA) levels; however, the precise mechanisms underlying this association remain unclear. The objective of this research was to explore the correlation between SUA and Hcy and to evaluate the possible role of kidney function as a mediator in the connection between SUA and Hcy.

METHODS AND RESULTS

Consecutive enrollment of 16870 participants aged 20-60 years was conducted at the Third Xiangya Hospital of Central South University. Self-reported health questionnaires were used to gather information on health behaviors and medical backgrounds. Trained personnel performed laboratory examinations using standard methods. A mediation analysis was performed to explore the possible effect of renal function on the association between SUA and Hcy levels. Estimated glomerular filtration rate (eGFR) was used to assess kidney function. Logistic regression analysis showed that SUA levels were positively correlated with Hcy levels and hyperhomocysteinemia (HHcy) risk (p < 0.01). Subgroup analysis showed the robustness of the results. Significant mediation effects of eGFR were found in the relationship between SUA and Hcy, as demonstrated by the subsequent mediation analysis. In the overall study group, the percentage of eGFR mediated in the association between SUA and Hcy was 63.36 %, with 41.59 % and 57.59 % in women and men, respectively.

CONCLUSIONS

SUA was positively correlated with Hcy and HHcy risks, and the effects of SUA on Hcy may be mediated by renal function indicators (eGFR).

Uric acid, impaired fasting glucose and impaired glucose tolerance in youth with overweight and obesity

BACKGROUND AND AIM

The relationships between uric acid (UA) and prediabetes is poorly explored in youth. We investigated the association between UA, impaired fasting glucose (IFG), impaired glucose tolerance (IGT), insulin resistance (IR) and low insulin sensitivity (IS) in youth with overweight/obesity (OW/OB).

METHODS AND RESULTS

A cross-sectional study was performed in 2248 youths with OW/OB (age 5-17 years). The sample was stratified in sex-specific quintiles (Q1 to Q5) of UA and the associations with fasting (FG), 2-h post-load glucose (2H-PG), IR and low IS were investigated. IR and low IS were estimated by assessment model of insulin resistance (HOMA-IR) and whole-body IS index (WBISI), respectively. IFG was defined as FG ≥ 100 < 126 mg/dL, IGT as 2H-PG ≥140 < 200 mg/dL, IR as HOMA-IR ≥75th percentile and low IS as WBISI ≤25th percentile by sex. Age, body mass index z-score, 2H-PG, HOMA-IR and WBISI, increased across sex-quintiles of UA while FG did not. The prevalence of IFG and IR were significantly increased in Q5 vs Q1 (reference quartile, P < 0.025). The prevalence of IGT increased from Q3 to Q5 vs Q1 (P < 0.025-0.0001) and that of low IS from Q2 to Q5 vs Q1 (P < 0.005-0.0001).

CONCLUSIONS

In youth with OW/OB, rates of IGT and low IS increased progressively across quintiles of UA. On the contrary, IFG and IR were associated only with the highest quintile of UA. Our data suggest that UA is a biomarker of impaired glucose metabolism prevalently in post-challenge condition rather than in fasting state.

Body mass index and serum uric acid level: Individual and combined effects on blood pressure in middle-aged and older individuals in China

Few studies on the individual and combined analysis between serum uric acid (SUA) and body mass index (BMI) and blood pressure (BP) were conducted in individuals aged ≥45 years. We aimed to assess the extent to which BMI and SUA and their interaction affect BP in Chinese middle-aged and older adults.Data were selected from the China Health and Retirement Longitudinal Study (CHARLS). A total of 5888 individuals aged 45 to 96 was included. Differences between BMI, or between categories of blood pressure were evaluated by t test or chi-square test. The trend of related variables according to four BMI categories was also tested using contrast analysis. The adjusted associations between various characteristics and BP status were first compared using linear regression models, as appropriate. Then, general linear models adjusting for related potential confounders were used to examine the synergistic effect of SUA and BMI level on BP for middle-aged and elderly individuals in China.Age-adjusted partial Pearson correlation coefficient showed that BMI was significantly and positively correlated with BP both in male and female, SUA positively correlated with both systolic blood pressure (SBP) and diastolic blood pressure (DBP) in males with BMI <24.0 kg/m and females with BMI <24.0 kg/m. However, SUA level significantly and positively correlated with DBP, but not with SBP, in females with BMI ≥24.0 kg/m. Multiple linear regression analysis showed that BMI was independently associated with BP both in male and female, SUA significantly and positively associated with SBP in both males and females with BMI <24.0 kg/m, However, SUA level positively correlated with DBP in females with BMI <24.0 kg/m, but not with males with BMI <24.0 kg/m, independent of other confounding factors. A general linear model analysis adjusted for confounding factors did not reveal interaction between BMI, SUA levels and SBP (β=-1.404, P = .686 in males; β=-2.583, P = .575 in females) and DBP (β=-2.544, P = .263 in males; β=-2.619, P = .622 in females).No interaction between BMI, SUA levels, and BP was observed in either males or females; However, BMI was independently associated with BP both in male and female, SUA independently associated with SBP both in males and females with BMI <24.0 kg/m, and SUA independently associated with DBP in females with BMI ≥24.0 kg/m.

Knockout of the urate oxidase gene provides a stable mouse model of hyperuricemia associated with metabolic disorders

The urate oxidase (Uox) gene encodes uricase that in the rodent liver degrades uric acid into allantoin, forming an obstacle for establishing stable mouse models of hyperuricemia. The loss of uricase in humans during primate evolution causes their vulnerability to hyperuricemia. Thus, we generated a Uox-knockout mouse model on a pure C57BL/6J background using the transcription activator-like effector nuclease (TALEN) technique. These Uox-knockout mice spontaneously developed hyperuricemia (over 420 μmol/l) with about 40% survival up to 62 weeks. Renal dysfunction (elevated serum creatinine and blood urea nitrogen) and glomerular/tubular lesions were observed in these Uox-knockout mice. Male Uox-knockout mice developed glycol-metabolic disorders associated with compromised insulin secretion and elevated vulnerability to streptozotocin-induced diabetes, whereas female mice developed hypertension accompanied by aberrant lipo-metabolism. Urate-lowering drugs reduced serum uric acid and improved hyperuricemia-induced disorders. Thus, uricase knockout provides a suitable mouse model to investigate hyperuricemia and associated disorders mimicking the human condition, suggesting that hyperuricemia has a causal role in the development of metabolic disorders and hypertension.

Gender-specific association of serum uric acid with metabolic syndrome and its components in juvenile obesity

BACKGROUND

Hyperuricemia has been implicated in the pathogenesis of obesity and related metabolic abnormalities. Studies on the association between serum uric acid (sUA) and metabolic syndrome (MetS) in juvenile obesity are scant. The effect of gender has not been evaluated.

METHODS

sUA (uricase method), anthropometric and biochemical indices were measured in gender-stratified children/adolescents consisting of 113 overweight/obese and 71 lean individuals.

RESULTS

In males, sUA was significantly elevated in overweight as well as obese patients. sUA was strongly associated with obesity indices and reflected sexual development, decreases in high density lipoprotein-cholesterol, and moderately, the number of MetS components. Waist circumference (WC) and Tanner stage explained 40% of sUA variability. Controlling for body mass index (BMI) and other MetS components, sUA was associated with abdominal obesity, explaining 30% of variability in WC. In females, sUA was significantly increased in obesity, high blood pressure (BP), and MetS and corresponded with the number of MetS components, indices of glucose metabolism, triglycerides (TG), and the atherogenecity index. Insulin-resistance (IR) (homeostasis model assessment; HOMA) and high BP explained 29% of sUA variability, whereas sUA, while controlling for BMI, age, and other MetS components, was associated with hypertriglyceridemia, hyperglycemia, high BP, and abdominal obesity. IR mediated the associations with high TG and glucose.

CONCLUSIONS

The association between sUA and MetS components in juvenile obesity is gender-specific, with females being related more closely and to more metabolic abnormalities. It may explain why, despite its lower concentrations, sUA is an independent predictor of mortality from all causes and from vascular diseases exclusively in females. Our findings may help in identifying metabolic abnormalities which may possibly be targeted by reducing sUA in males and females.