Uric Acid Effects on Endothelium and Oxydative Stress
Condition: Oxidative Stress; Endothelial Function; Cardiovascular System; Hypertension
MeSH terms: Hypertension
Study type: Interventional

Summary: 
      Cardiovascular disease is the leading cause of mortality worldwide. Endothelial dysfunction
      (ED) is the main mechanism which leads to atherosclerosis, where the balance between pro and
      antioxidant factors results in a decreased nitric oxide (NO) bioavailability. Xanthine
      OxidoReductase (XOR) is one of the main generators of reactive oxygen species (ROS). Uric
      acid (UA), a major antioxidant in human plasma and end product of purine metabolism, is
      associated with cardiovascular diseases since many years; however the precise mechanisms
      which relate UA to ED are still not well understood.

      The purpose of this study is to unravel the XOR and UA pathways involved in ED. Three groups
      of participants (young (< 40 y) male healthy participants [1] ; male and female helthy
      participants (40 to 65 y) [2] and patients with primary hypertension [3]) will be exposed to
      febuxostat (a strong and selective XOR inhibitor), or recombinant uricase (which oxidizes UA
      into allantoin) to vary UA levels and concomitantly control for confounding changes in XOR
      activity. Oxidative stress will be estimated by several markers. Endothelial function will be
      assessed by a laser Doppler imager in the presence of hyperthermia and endothelium
      stimulators. This study is specifically designed to untie the respective effects of UA and
      XOR pathways on oxidative stress and endothelial function in humans.

      The investigators will test the following hypothesis:

        1. An extremely low level of uric acid after uricase administration induces endothelial
           dysfunction and oxydative stress,

        2. A specific XO inhibitor limits unfavourable effects of the serum UA reduction elicited
           by uricase administration,

        3. Endothelial function and oxydative stress are further improved with febuxostat as
           compared to placebo,

        4. All these observations are more marked in hypertensives then in older participants than
           in young healthy subjects.
    

Detailed description: 
      The goals of the research protocol are to clearly untie the respective roles of uric acid
      (UA) and xanthine oxidoreductase (XOR) pathways on endothelial function and oxidative stress
      in humans.

      UA represents the end-product of purine metabolism due to the loss of uricase 15 million
      years ago in humans. The selective advantage of this mutation could be the strong antioxidant
      effect of UA (which represents more than 60% of the antioxidant plasmatic capacity). Many
      recent epidemiological studies have showed a J-shape association between UA levels and
      cardiovascular risk. An UA level lower than 3 mg/dl could be damageable due to the loss of
      the antioxidant properties of UA. In contrast, hyperuricemia is associated with an increased
      inflammation, insulin resistance, ED, platelet aggregation, left ventricle hypertrophy,
      arterial vasodilatation impairment, aortic stiffness and intima-media thickness. However, the
      association between UA and cardiovascular disease remains controversial because whether UA is
      an independent risk factor for these illnesses is unclear.

      Interventional studies:

      Because the above-mentioned associations do not prove causation, several authors designed
      interventional studies with the purpose to modify UA levels and determine if this affected
      endothelial function and oxidative stress. The main limitation of these studies is that they
      were unable to untie the effects of the synthesis of UA, of UA itself and of the activity of
      XOR, on ROS production and endothelial function in humans.

      This is because:

        1. serum UA is a powerful plasmatic antioxidant,

        2. but transformation of hypoxanthine to xanthine and xanthine to UA by XO generates
           intracellular ROS,

        3. moreover, in endothelial cells, UA reduces NO bioavailability by many ways (L-arginine
           blockade and degradation, increased superoxide anion production, NOS inhibition, reduced
           NOS genes expression and direct NO scavenging),

        4. in addition, UA forms crystals in the endothelium wall which create a pro-inflammatory
           and thrombotic state, increases smooth muscle cells proliferation and also insulin
           resistance and inflammation in adipocytes,

        5. finally, and most importantly, XO is inhibited by physiologic levels of UA (which acts
           as an uncompetitive XO inhibitor).

      In summary, the present protocol aims at testing the following hypothesis:

        1. Experimental serum UA variations are correlated with endothelial function and oxydative
           stress markers : an extremely low level after uricase administration induces ED and
           oxydative stress,

        2. A specific XO inhibitor (FX) limits unfavourable effects of the serum UA reduction
           elicited by uricase administration, since this will hamper the feedback activation of XO
           by a low UA level,

        3. Endothelial function and oxydative stress are further improved with FX as compared to
           placebo, because the first experimental condition results in a XO blockade,

        4. All these observations are more marked in hypertensive patients then in older
           participants than in young healthy subjects.

      Data collection

      Data collection from the participants will be collected informatically through a case report
      form. The names and personnal data from the patients will be kept in a secret place or in a
      password-protected file. All the data will be destroyed at the end of the study (including
      blood and urine samples).

      Statistical analysis

      Statistical analysis will be performed using SPSS. Baseline characteristics will be compared
      using a Student t test. Two-way repeated-measures ANOVAs will be used to detect significant
      changes between sessions and groups. Statistical significance is assumed when p is <0.05.
      Sample size is not possible due to the lack of data of the effect of acute hypouricemia. We
      estimate a minimum of 15 participants in each group.

      Specific test will be used for non gaussian variables. Correlation test will be used if
      necessary according the results of the first test.

      Placebo-corrected values and comparisons of the delta will be used too.

      Subgroups analyses will be performed for the study of population 2 and 3 (enrolled together).
    

Intervention name(s): Placebos; Febuxostat; Rasburicase
Intervention type(s): Drug; Drug; Drug
Intervention description(s): Lactose placebo for pills and saline for perfusion.; Febuxostat tablet.; Rasburicase injectable solution.
Other intervention name(s): Placebo; Adenuric; Fasturtec
Intervention MeSH terms: Febuxostat; Rasburicase
Allocation: Randomized
Intervention model: Crossover Assignment
Intervention model description: This is a prospective, randomized, placebo-controlled, double-blinded and 3 ways cross-over study.
Three populations : healthy male subjects under 40 y [1] ; healthy male and female participants between 40 and 65 years [2] and subjects with hypertension [3]. Minimum 15 participants in each group are needed.
The populations 2 and 3 will be studied together with subgroups analyses of the results for the status of hypertension, of treatment, age and gender.
For 5 subjects in each group, we will perform a fourth session with Placebo PO and Rasburicase IV. That session will be non-randomized and blinded only for the subject.
Masking: Double (Participant, Investigator)
Primary purpose: Basic Science
Keywords: uric acid; xanthin oxydoreductase; febuxostat; uricase