Effects of Uric Acid Lowering Therapy in Patients With Essential Arterial Hypertension

Asymptomatic hyperuricemia (AHU) is dened as elevated serum uric acid (UA) concentration without symptoms. This study aimed to determine the effects of AHU treatment with allopurinol on selected hypertension mediated organ damage (HMOD) indices in patients with uncomplicated essential arterial hypertension (AH). p=0.044), and hs-CRP level (3.36±2.73 mg/l vs 2.74±1.91 mg/l, p=0.028) compared to controls. The decrease in UA concentration was signicantly related to the reduction in IMT (R=0.37, p<0.001), central SBP (R=0.26, p=0.015) and hs-CRP concentration (R=0.30, p=0.004). Multivariate regression analysis revealed the independent relationship between reduction in IMT and UA lowering (R=0.3234, R2=0.0722, p<0.026).


Background
Asymptomatic hyperuricemia (AHU) is traditionally de ned as elevated serum uric acid (UA) concentration but in which neither symptoms of monosodium urate crystal deposition disease, such as gout, nor uric acid renal disease have occurred [1]. The prevalence of AHU has increased over several decades and nowadays it affects 16.9% of the adult population [2]. AHU is more common in subjects with arterial hypertension (AH) than in the general population [3,4]. High UA concentration is one of the important factors associated with the development of AH and promotes vascular and renal organ damage [5]. Experimental and epidemiological data reveal associations between hyperuricemia and hypertension, cardiovascular risk, chronic kidney disease (CKD), and metabolic syndrome [6][7][8]. The risk of coronary artery disease mortality increases by 13% for each 1 mg/dl (60 μmol/L) increase in UA concentration [9]. However, it is still debatable whether hyperuricemia is an independent cardiovascular risk factor. Numerous clinical disorders associated with high UA serum level support the decision to treat AHU to reduce cardiovascular risk. Some results of previous studies showed bene cial effects of AHU pharmacological treatment such as: decreased concentration of in ammation markers (high-sensitivity C-reactive protein, hs-CRP), reduced carotid intima-media thickness (IMT) [10], reduced levels of oxidative stress markers, improved endothelial function [11], reduced serum creatinine and increased estimated glomerular ltration rate (eGFR) [12] as well as reduced blood pressure (BP) [13]. Allopurinol mainly is used to treat AHU, especially in patients at high cardiovascular risk, but there is no evidence for its effect on hard end-points, and this topic still needs further investigations [14][15][16]. Nevertheless, Borghi at al. [15] in the "Expert consensus for the diagnosis and treatment of patient with hyperuricemia and high cardiovascular risk" recommend considering treatment of AHU as a part of cardiovascular events prevention when serum UA concentration is ≥5 mg/dl (300 μmol/l) in patients with high cardiovascular risk and when serum UA concentration is ≥6 mg/dl (360 μmol/l) in other patients. Generally, treatment of AHU as a component of cardiovascular prevention is not a gold standard due to the lack of su cient evidence from clinical studies.
The aim of the study was to determine the effects of AHU treatment with allopurinol on selected Hypertension Mediated Organ Damage (HMOD) indices in patients with uncomplicated essential AH.

Methods
The study population consisted of 562 patients aged 30-70 years, both women and men consecutively admitted to the hypertension outpatient department between September 2017 and March 2018 with: diagnosed AHU de ned as a serum UA ≥ 6 mg/dl (360 μmol/l) [15,17] and with essential hypertension grade 1 or 2 (BP ≥140/90 and <180/110 mmHg) in accordance with the 2018 ESH/ESC guidelines [18] with previously con rmed adequate BP control on antihypertensive treatment (below 140/90 mmHg in o ce measurements). Patients, who received allopurinol (100-300 mg/day) according to Expert consensus [15] comprised urate lowering therapy (ULT) group (n=50). Then, within 5 days from recruitment of the ULT patient, a control patient with AHU and AH who did not receive allopurinol treatment, with age±3 years and preferably the same gender was recruited in a ratio of 1:1 (n=50 cases and n =50 controls). All patients were given the same dietary advice recommended for AH and AHU. All examinations were performed prior to treatment initiation and after 6 months of follow-up.
The exclusion criteria included: any symptoms of monosodium urate crystal deposition disease, especially gout; coronary heart disease (previous myocardial infarction, coronary angioplasty procedure or coronary artery bypass surgery); symptomatic heart failure more than New York Heart Association (NYHA) class I or reduced ejection fraction < 50%; kidney or liver failure; in ammatory diseases; history of allergy to allopurinol or other serious drug reactions (e.g. Lyell's syndrome); or treatment change during follow-up. Study owchart is presented in Figure 1.
The study was performed in accordance with the 1975 Declaration of Helsinki for Human Research and approved by the Jagiellonian University Bioethical Committee (No. 122.6120.94.2017 of April 27th, 2017).
A written informed consent was obtained from all patients.

Measurement of peripheral blood pressure
All participants underwent physical examination and o ce BP measurements (mean of three measurements at one-minute intervals) in standard conditions, after 10 minutes rest, in sitting position on the non-dominant arm with the use of the validated Omron M5-I oscillometric device (Omron Healthcare Co., Japan).
24-hour ambulatory BP monitoring (ABPM) was performed using a SpaceLabs 90207 recorder (SpaceLabs Inc, Richmond, Washington, USA) to con rm BP control. Measurements were taken every 15 minutes during daily activity (06:00-22:00h) and every 20 minutes at night-time (22:00-06:00 h). For further analyses the mean values of the 24-hour, daytime, and night-time systolic (SBP) and diastolic blood pressure (DBP), and heart rate were calculated. BP measurements were performed according to the ESH/ESC guidelines for the management of hypertension [18].

Echocardiographic measurements
Echocardiographic examination using the Vivid®E95 (GE-Healthcare Chicago, IL, USA) device and 2,7-3,6 MHz transducer was performed. Left ventricular mass (LVM) was calculated according to the ASE formula [19,20]. Left ventricular mass index (LVMI) was calculated LVM/height 2.7 [21]. Left atrium volume (LAV) was assessed using the modi ed Simpson's method [22]. Left atrium volume index (LAVI) was calculated as LAV/body surface area. Global longitudinal strain (GLS) by speckle tracking echocardiography was measured as the average value of 18 segments, based on three apical imaging planes [23].
Central blood pressure, pulse wave velocity and intima-media thickness measurements SphygmoCor (AtCor Medical, Sydney, Australia) device was used to examine arterial stiffness. Carotidfemoral pulse wave velocity (PWV) and central BP in the aorta were measured according to the recommendations of ESH experts [24,25].
Intima-media thickness (IMT) measurement of common carotid artery was carried out in accordance with the Mannheim consensus with the use of the Vivid®E95 (GE-Healthcare Chicago, IL, USA) and a 10 MHz linear transducer. After at least 10 minutes of patient rest in supine position, good-quality B-mode ultrasound images of left and right common carotid arteries were recorded during ve consecutive heart cycles. The intima -media thickness (IMT) of the far wall was measured o ine using EchoPAC workstation software. Automatic IMT measurement was based on tracing of 1 cm (starting about 1 cm proximally from bifurcation) of the leading edge of the intima surface and the leading edge of the adventitia surface followed by multiple measurements between pairs of pixels located on both traces. Mean IMT was calculated as the average of the left and right IMT [26].

Other measurements
In all patients medical history was collected including concomitant diseases, smoking and drinking habits and the use of medications. Laboratory tests: serum concentrations of uric acid, creatinine, total cholesterol, high-density lipoprotein cholesterol (HDL), low-density lipoprotein cholesterol (LDL), triglycerides, N-terminal prohormone of brain natriuretic peptide (NT-proBNP) and hs-CRP were also obtained at the initial visit.
All performed examinations and laboratory tests were then repeated after 6 months of follow-up.

Statistical analyses
Data are presented as means and standard deviations (SD) and medians and interquartile ranges in cases where nonparametric tests were used. To determine the study sample, we chose as optimal parameter the IMT because of the association with atherosclerosis, BP and potential reversibility during ULT. The analysis showed that to determine a 0.1 mm difference in IMT with mean value of 0.9 and SD of 0.16 mm [27,28] with a power of 80% and with a signi cance of p=0.05, using the two-tailed test, the population of 42 people in each group is required. Normality of variables distribution was tested and, if con rmed, parametric tests were used. When studied variables did not have normal distribution nonparametric tests were used. Between group differences were evaluated using Student's t-test, Mann-Whitney U test or chi-squared test, as appropriate. To assess the effects of the therapy the repeatedmeasures t-test, Wilcoxon signed-rank test, ANCOVA and the association between variables using the Spearman rank correlation were used. Univariate and multivariate regression analyses were used to determine the in uence of independent factors on IMT. P-values <0.05 were considered statistically signi cant for all tests. Statistical analyses were performed using STATISTICA software (StatSoft, Poland), version 13.1.

Results
The ow of participants in the study is presented in Figure 1.
The nal analysis included 87 patients: 44 in the ULT group (20 females and 24 males) and 43 in the control group (23 females, 20 males). During the study follow-up, 13 patients (n=6 in the ULT group, n=7 in the control group) were withdrawn from the study due to the need of antihypertensive therapy modi cation or lack of follow-up appointment There were no signi cant differences in studied parameters at baseline visit between patients who dropped out and those who completed the study.

Baseline characteristics
Baseline characteristics of the study patients are presented in Table 1.
There were no signi cant differences between the ULT group and the control group in age, sex distribution, and baseline serum UA concentration (p=0.054). However, they did differ in BMI and total cholesterol (see Tables 1 and 2).
The effects of uric acid lowering therapy In this study, ULT was safe and no treatment-related adverse effects were observed.

Biochemistry
Changes in laboratory parameters from baseline to 6 months follow-up in both groups are summarized in Table 2. Urate-lowering therapy with the use of allopurinol 100-300 mg daily (mean 184 ± 91.3 mg, median 150 (100; 300) mg) in the ULT group was associated with a signi cant reduction in serum uric acid concentration level (464 ± 68.8 vs. 314 ± 55.6 µmol/l; p<0.001). In the control group a small albeit statistically signi cant reduction in serum UA concentration was observed (437 ± 61.1 vs. 426 ± 56.9 µmol/l, p=0.044). Compared to controls, there was a signi cant reduction in hs-CRP levels in the ULT group at 6 months follow-up.
Blood pressure .
Baseline o ce and central BPs were higher in the ULT group than in the control group, however the unadjusted decline in DBP at 6 months follow-up in the ULT group was signi cantly higher compared to controls ( Figure 2).
The ANCOVA analysis corrected for baseline BP values showed no differences between study groups in observed BP decrease after 6 months observation.

HMOD
Among the assessed echocardiographic parameters, signi cant reductions in LAV and LAVI were noticed in the ULT group at 6 months follow-up (Table 4). There were no comparable changes in the echocardiographic parameters in the control group at follow-up.
Compared to the control group, there was a signi cant reduction in carotid IMT in the ULT group at 6 months follow-up ( Figure 3, Table 4).
In our study, UA lowering therapy had no effect on the change in arterial stiffness determined by PWV ( Table 4).
The magnitude of reduction in IMT, CRP, LAVI, and UA was greater in the ULT group than in the control group ( Figure 2).
In all patients, the amount of reduction in serum UA concentration was related to the reduction in IMT The multivariate regression analyses showed a signi cant association between UA lowering and IMT reduction in the entire study group after adjustment for changes in LDL and PP values (the known pathophysiological factors in uencing IMT) (R=0.3234, R2=0.0722, p<0.026).

Discussion
The 2018 ESC/ESH Guidelines for the management of arterial hypertension recommend routine measurement of serum UA as part of the screening in hypertensive patients, because elevated UA level is independently associated with increased cardiovascular risk in both hypertensive patients and general population [18]. Reduction in serum UA concentration with ULT may have an impact on the reduction in parameters related to cardiovascular risk such as IMT, LAVI or serum hs-CRP level. In a three-year randomized parallel-controlled study in patients with type 2 diabetes and AHU, Liu et al. found that effective control of the serum UA level with allopurinol therapy decreases the serum hs-CRP level and carotid IMT [10]. Our study demonstrates that UA lowering therapy is associated with a signi cant reduction in hs-CRP and IMT in patients with hypertension, however in a substantially shorter duration (i.e. 6 months). Based on these results, the reduction in hs-CRP indicates that ULT has an antiin ammatory effect likely to explain the accompanying reduction in carotid IMT which is a surrogate marker for atherosclerosis, commonly known as a chronic in ammatory disease.
In a study by Higgins et al. one-year treatment with allopurinol at a dose of 300 mg daily resulted in a decrease in central SBP and augmentation index, and prevented progression in IMT in patients following ischemic stroke or transient ischemic attack (TIA) [27].
Carotid IMT has been shown to predict cardiovascular risk in multiple large studies [29], however its reproducibility and usefulness in daily practice is limited [18]. In our study we used an automatic IMT measuring technique (using multiple measurement points) to increase the accuracy and repeatability of measurements according to the Mannheim consensus [26].
Our study found a signi cant reduction in o ce (SBP, DBP, PP) and central (SBP, PP) BP values but not in ambulatory BP values in the ULT group. Our ndings suggest that treatment with allopurinol is safe and despite the minor impact on ambulatory BP levels (Table 3), UA lowering therapy signi cantly improves HMOD even after a relatively short time of treatment. Limited o ce BP changes following allopurinol therapy in our study may result from adequate BP control at baseline and short study duration in the ULT group (6 months) compared to a longer (3 years) study by Liu et al. [10].
While most available data indicate that allopurinol reduces BP regardless of antihypertensive drugs, the underlying mechanism is not clear [13]. In the meta-analysis of 15 randomized controlled trials performed in patients with hyperuricemia, with length of follow-up from 2 to 23 months, allopurinol decreased BP and creatinine level [30]. A sub-analysis revealed that allopurinol signi cantly decreased SBP irrespective of antihypertensive drug therapy, however a decrease in DBP was only observed in patients receiving antihypertensive drugs. In patients receiving combination of antihypertensive drugs and allopurinol in a dose ≤300 mg/day the reduction in SBP was larger compared to patients receiving allopurinol at higher dose (>300 mg/day) [30].
A further interesting nding derived from our study is a signi cant reduction in left atrium volume index, likely as a result of the decrease in central BP (afterload) following ULT.
The noticeable decrease in UA concentration in the ULT group is comparable to previous studies [10], con rming the adherence to drug therapy. Interestingly, a slight, but signi cant decrease in UA concentration was also present in the control group indicating that patients follow a dietary advice which previously has proven its e cacy. In the study by Rai  Findings related to BP changes following allopurinol therapy are inconsistent. A study by Jalal et al. conducted in chronic kidney disease (CKD) patients found that a 3-month therapy with allopurinol had no effects on BP levels, in ammation and oxidative stress markers compared to placebo [35]. In contrast, a study by Kanbay et al. has shown that a 4-month treatment with allopurinol led to a decrease in SBP and an increase in ow-mediated dilation and eGFR in patients without CKD [36]. Different results in both studies on BP changes during allopurinol treatment are likely to be explained by advanced and irreversible atherosclerotic changes in the arteries in high risk CKD patients. In line with this observation, our study population was limited to patients with essential hypertension grade 1 or 2 without previous history of coronary heart disease, CKD or symptomatic heart failure. In our opinion patients with potentially reversible cardiovascular changes are most likely to receive the greatest bene ts from intensive ULT used in parallel with the modi cation of other cardiovascular risk factors as part of primary prevention of ischemic heart disease. We have previously shown that a higher UA concentration via higher serum matrix metalloproteinase (MMP) 3 enhances selected HMOD, especially carotid IMT in patients with AH [37]. Extracellular MMPs are part of in ammation leading to the degradation of collagen, vessel remodelling and atherosclerotic plaque rupture [38,39]. It is still the matter of controversy whether hyperuricemia is only a biomarker of cardiovascular risk or a direct factor attributable to the harmful effects on cardiovascular system [40].

The study limitations
A small sample size could be viewed as a study limitation. However, all patients enrolled in this study were comprehensively phenotyped concerning BP levels and associated HMOD to determine the true effects of allopurinol therapy. Secondly, the short length of follow-up may limit our ndings, however the study duration was planned based on available data and allopurinol e cacy.

Conclusions
Allopurinol in patients with arterial hypertension and hyperuricemia decreases blood pressure and, in a relatively short time, seems to favourably in uence hypertension-mediated organ damage, in particular intima-media thickness. Our ndings indicate that the bene cial effects of urate lowering therapy with allopurinol on blood pressure and organ damage may result from anti-in ammatory and antiatherosclerotic actions, with a potential impact on long-term patient outcomes Further prospective studies in larger patient groups are required to support our ndings.

Declarations Ethics approval and consent to participate
The study was performed in accordance with the 1975 Declaration of Helsinki for Human Research and approved by the Jagiellonian University Bioethical Committee (No. 122.6120.94.2017 of April 27th, 2017). A written informed consent was obtained from all patients.

Consent for publication
Not applicable.

Availability of data and materials
The datasets used and/or analysed during the current study are available from the corresponding author upon reasonable request.

Competing interests
The authors declare that they have no con ict of interest.

Funding
Not applicable.  Intima-media thickness (IMT) changes in the urate-lowering therapy (ULT) group [1] and in the control group [0] at 6 months follow-up.