Serum uric acid to high‐density lipoprotein ratio as a novel indicator of inflammation is correlated with the presence and severity of metabolic syndrome: A large‐scale study

Abstract Introduction We investigated the association of serum uric acid to high‐density lipoprotein ratio (UHR) with the presence and severity of metabolic syndrome (MetS) among MASHAD cohort participants. Methods In this cross‐sectional study, according to International Diabetes Federation criteria, the cohort participants were divided into MetS (+) and MetS (−) groups. MetS (+) were classified into Group 1 (those with 3 MetS criteria), Group 2 (those with 4 MetS criteria) and Group 3 (those with 5 MetS criteria). UHR was compared among the groups. Results Data related to 9637 subjects including 3824 MetS (+) and 5813 MetS (−) were analysed. The mean UHR was significantly higher (p < .001) in the MetS (+) group compared with the MetS (−) group. UHR increased as the MetS severity increased (p < .001). ROC analysis revealed that UHR greater than 9.5% has 89.07% sensitivity and 77.03% specificity in differentiating MetS (−) from MetS (+) subjects. Conclusion Among MASHAD cohort study participants, a significant association between UHR and MetS was found. Furthermore, there is an increase in UHR as the severity of MetS increases. Registration number of MASHAD cohort study: 85134.

the production of nitric oxide, endothelial dysfunction and oxidative metabolism.Studies showed that increased insulin secretion increases serum UA levels due to a decline in renal function and serum UA concentration is independently correlated with MetS risk factors, HTN, kidney disease and cardiovascular events. 4,5 can also induce inflammatory and oxidative changes in adipocytes. 6,7On the contrary, high-density lipoprotein (HDL) known as 'good' cholesterol is a cardioprotective biomarker, which removes excess cholesterol from peripheral tissues and transports it to the liver; for HDL, a spectrum of antiapoptotic, antithrombotic, antiinflammatory and antioxidative activities have been shown. 8A low concentration of HDL is identified as an independent predictor of CVD risk.On the contrary, it was discovered that depending on the presence or absence of inflammation, HDL may act both as an antiinflammatory or pro-inflammatory factor for multiple metabolic disorders.[11][12] Investigations suggest that combination of HDL and serum UA may be a better predictor of CVD morbidity and mortality than either alone. 11Recently, serum UA to HDL ratio (UHR) has been reported as a novel inflammatory and metabolic marker, which increases in inflammatory conditions such as steatohepatitis and Hashimoto's thyroiditis. 13The predictive value of UHR has also been validated in DM and MetS. 14,15However, whether UHR is associated with MetS severity remains unclear.
Since the prevalence of hyperuricaemia and MetS has been increasing not only in advanced countries but also in developing countries, 16 the early diagnosis is a crucial issue.Also, due to both anti-inflammatory and pro-inflammatory properties of total HDL and since few studies assessed the relationship between UHR as a novel and easy-to-assess metabolic marker and MetS in a large-scale population so far, the present study intended to compare the UHR between MetS patients and non-MetS ones enrolled in MASHAD cohort study 17 and examine correlations between UHR and of MetS severity.

| Study design and population
The target population was recruited from the Mashhad Stroke and Heart Atherosclerotic Disorder (MASHAD) study, a 10-year prospective cohort from Mashhad city, northeast of Iran.The methodology and sampling details have been published elsewhere. 17In brief, 9704 individuals aged 35-65 years were recruited using stratified cluster random sampling technique.The socio-demographic, hematologic, anthropometric and biochemical data were collected.Those whose biochemical data was not available were excluded from the present study.
In our study, MetS is defined based on the International Diabetes Federation (IDF). 18According to the IDF definition, someone has MetS if she or he has central obesity (≥94 cm for men and ≥80 cm for women) plus two or more of the following four factors:

| Ethical consideration
All participants included in the study were informed about the study, and signed a written informed consent form before inclusion.The study was approved by the Ethic Committee of Mashhad University of Medical Sciences.

| Anthropometric measurements
Anthropometric measurements including height, weight and waist circumference (WC) were obtained.Height was measured by a standard wall height meter.Weight was measured by an analogue scale, which was kept on a firm horizontal surface.WC was measured with a non-stretchable fibre measuring tape.The body mass index (BMI) was calculated as the weight (kg) divided by the square of the height (m).

| Blood pressure
Participants were requested to relax for at least 15 min.Then, blood pressure of the right arm was measured and repeated after 10 and 20 min (a total of three times).If taking the blood pressure from the right arm was not successful, the left arm was considered.The mean of the three measurements was recorded as the participant's final blood pressure.

| Biochemical parameters
In our laboratory unit, a 20-mL blood sample was taken from each participant.Blood samples were taken between 8 and 10 a.m. by venipuncture of an antecubital vein after 14 h of overnight fasting.
According to standard protocol, samples were collected in vacuum tubes (20 mL) from subjects in a sitting position and immediately centrifuged at room temperature to separate the plasma and serum into six aliquots (0.5 mL) and then sent to the MA-SHAD study biobank.BT3000 biochemical analyser was used for determination of biochemical parameters levels including: fasting blood glucose (FBG), UA, high-sensitivity C-reactive protein (hs-CRP), Low-density lipoprotein (LDL), total cholesterol (TC), TGs and HDL.All devices were daily checked by a laboratory technician.UHR was calculated as the ratio of serum UA (mg/dL) to HDL (mg/dL).

| Statistical analysis and model building
To describe the quantitative and qualitative variables, mean ± SD and frequency (%) are reported, respectively.The Chi-squared test and Fisher's exact test were applied to measure the association between categorical variables.Also, the mean of quantitative variables between the MetS (+) and MetS (−) groups were compared by independent t test.In addition, logistic regression (LR) algorithm was used to analyse data.In fact, we applied the algorithm to deduce the association between MetS and related factors.All analysis was performed using SPSS version 22 (IBM Corp.).

| Logistic regression (LR) modelling
LR is a popular model to evaluate the relationship between various predictor variables (either categorical or continuous) and binary outcomes in medicine, public health, etc. [19][20][21][22][23] Let Y i denotes the response variable and takes the values of 0 or 1 depending on whether response occurs or not.Also, X be vectors of covariates associated with response variable, is the corresponding vectors of regression coefficients.So, the association between the covariates and binary response variable can be investigated as follows:

| RE SULTS
A total of 9704 subjects were enrolled to the MASHAD cohort study.After applying exclusion criteria, data related to 9637 eligible patients were analysed (3824 with MetS and 5813 without MetS) (Figure 1).Comparisons of the basic characteristics of the MetS (+) and MetS (−) groups are shown in Table 1
LR technique was used to investigate the relationship between predictors and binary response variables (MetS [+] and MetS [−]).So, the main objective was to anticipate MetS using the LR model and to determine MetS associated factors.

| LR model
Results from the multiple LR model revealed that variables including sex, TG, WC, HDL, glucose, SBP, DBP, HTN, UA, TC, DM and UHR were significantly associated with of the presence of MetS (p < .002)(Table 3).In other words, our findings after adjusting the effect of other variables in the model, presented that the odds of having MetS in males is 0.14 times than that of females (p < .001).Also, after adjusting the effect of other variables for each increasing in UA, the odds of having MetS raised by 31% (p < .001)and for a 10-unit increase in UHR, the odds of having MetS decreased by 54% (p < .001).Among the analysed variables, UHR ( 95% CI 1.70-2.37)had the greatest associations with MetS.In addition, Figure 2 shows the comparison between UHR, UA, HDL and hs-CRP and group 1, 2 and 3 of MetS (+) population.Moreover, in order to determine the sensitivity and specificity of UHR, receiver operating characteristic (ROC) curve analysis was performed.The optimum cutoff was 9.5% with sensitivity 89.07%, specificity 77.03% and accuracy 84.30% (area under ROC [AUC] 92.17%) (Figure 3).We summarize the concept of the paper in graphical abstract (Figure 4).

| DISCUSS ION
To the best of our knowledge, this is the first study conducted on possible association between UHR and severity of MetS in a large population.Our study showed that UHR was significantly higher in the MetS (+) group compared to the MetS (−) population.Subgroup analysis showed a correlation between the increases in the number of MetS criteria along with the increase in the UHR, serum UA and hs-CRP.
MetS is a tremendously growing public health problem, which is comprised of interconnected and heterogeneous metabolic origin risk factors that appear to be directly promoting the development of type 2 DM, adverse cardiovascular events and all-cause mortality. 24MetS induces low-grade chronic systemic inflammation in the circulation and peripheral metabolic tissues, defined as 'metabolic inflammation', which is different from classical inflammation. 25,26merous studies confirmed that CRP as a conventional marker of systemic inflammation is correlated with the number of MetS components (i.e.MetS severity) and a higher CRP level was associated with an increased incidence of cardiovascular events. 27In accordance with previous studies, our study showed that serum hs-CPR level was significantly higher in the MetS (+) group and it was also significantly increased with the number of MetS components.Nevertheless, we found no statistically significant difference in term of smoking status between the MetS (+) and MetS (−) groups.A study by Daniel et al. reported that not former smokers had significantly greater insulin resistance compared to non-smokers in a native American population. 28Hughes et al. reported that fasting insulin levels did not significantly differ between smokers and non-smokers in a random sample of males aged 30-69 years from the general population of Singapore. 29This could be in agreement with the finding that smoking less than 10 cigarettes per day was not an independent risk factor for MetS in either gender. 30e relationship between serum UA levels and MetS has been well demonstrated in the literature.According to numerous studies, there is a positive association between serum UA and the prevalence of MetS.Furthermore, serum UA level was elevated significantly as the number of metabolic components increased. 4,6,31,32,33A higher level of serum UA is also an independent and strong factor for developing and predicting MetS in healthy middle-aged population of both gender. 34,35In subjects with elevated serum UA levels, the risk of incident type 2 DM is also increased. 36,37In Iran, it has been reported that those with MetS have higher serum UA levels compared to those without MetS. 33,38  cholesterol transport. 39HDL functionality has been reported to be negatively and independently associated with the risk of developing CVD. 12 Our study showed that people with low HDL level were more likely to develop MetS than with normal HDL cholesterol, which is consistent with previous studies. 40,41Furthermore, mean level of HDL significantly decreased as the number of components (severity) of MetS increase.As mentioned before, UHR is a novel inflammatory and metabolic marker, which increases in inflammatory conditions. 13e diagnostic role of UHR was first described by Kocak et al. in patients with MetS. 15Then, an increased UHR levels has been discussed in other metabolic and inflammatory conditions.Zhang et al.
showed that UHR was an independent risk factor of non-alcoholic fatty liver disease (NAFLD) among lean adults population who had normal range of HDL and UA. 42 In a study on 4551 patients diagnosed with type 2 DM in Shanghai, a positive correlation between UHR and diabetic macrovascular and microvascular complications such as CVD and chronic kidney disease (CKD) was observed in men and postmenopausal women, which may show the importance of measuring and lowering UHR level in a timely manner to prevent diabetic nephropathy.However, no correlation was observed between the prevalence of diabetic retinopathy and UHR level. 46e relationship between UHR and MetS has been investigated in few studies before.Kocak et al. pointed out that UHR could predict MetS better than all five MetS criteria and could use as a new a inflammatory marker. 15Then, Aktas et al. reported that UHR was significantly and positively associated with fasting plasma glucose (FPG) and HbA 1 c in men with type2 DM, so the study suggested that UHR could serve as a promising predictor of diabetic control. 14A study conducted on 817 people in 2021, reported that UHR is useful in diagnosis of MetS and can also be used to screen subjects at risk of MetS. 40However, in that study, the relationship between UHR and MetS severity was not evaluated.In the present study, we found a significant positive association between UHR and MetS.Furthermore, we identified that the mean levels of UHR in subgroups of the MetS (+) group increased with increasing MetS components, indicating that patients with MetS generally have higher serum UA level and lower HDL cholesterol level.This study is the first clinical study, which demonstrates a significant positive association between UHR and MetS severity.Another strength of present study is the large population included.One of the limitations of the present study is its retrospective design, which could cause selection bias.We also did not exclude patients with comorbidities such as DM.Nevertheless, The primary findings of present study.

1 . 2 .
Raised concentration of triglycerides (TGs): ≥150 mg/dL (1.7 mmol/L) or receives specific treatment for this lipid abnormality; Reduced concentration of HDL cholesterol: <40 mg/dL (1.03 mmol/L) in men and <50 mg/dL (1.29 mmol/L) in women or receives specific treatment for this lipid abnormality; 3. Raised fasting plasma glucose concentration: ≥100 mg/dL (5.6 mmol/L) or previously diagnosed with DMII; 4. Raised blood pressure: systolic blood pressure (SBP) ≥130 mmHg or diastolic blood pressure (DBP) ≥85 mmHg or receives treatment for previously diagnosed HTN.Then, subjects classified as MetS (+) group were divided into three subgroups based on the number of MetS criteria they had as follows: group 1 (patients with three MetS criteria), group 2 (patients with four MetS criteria) and group 3 (patients with five MetS criteria).Rest of the population was selected as MetS (−) group.The flowchart of current study design outlined in Figure 1.

F I G U R E 1
Flowchart of the present study participants and grouping.Those whose biochemical data was not available A total of 9637 subjects were included in the study Subgroup analysis demonstrated that in the MetS (+) group, there was a positive relationship between increasing number of MetS components (i.e. the severity of MetS) and serum UA levels

F I G U R E 2
Comparison between UHR (A), UA (B), HDL (C) and hs-CRP (D) and group 1, 2 and 3 of MetS (+) population.hs-CRP, high-sensitive C-reactive protein; HDL, high-density lipoprotein; UA, uric acid; UHR, uric acid to HDL ratio.F I G U R E 3 ROC curve of UHR in determining MetS.ROC, receiver operating characteristic; UHR, uric acid to HDL ratio.
Safiri et al. reported that the association of serum UA with some components of MetS may indicate that serum UA might be an additional component of MetS in adolescents.The results of multiple LR model for the MetS (+) group.
38Our results are confirmatory to previous findings.In our study, serum UA level was significantly higher in those with MetS; moreover, serum UA increased as the number of criteria (severity) of MetS increased.HDL has anti-inflammatory, antioxidant and atheroprotective properties with mitigates endothelial dysfunction through reverse