Acute Effects of Tart Cherry on Uric Acid and Biomarkers of CVD Risk in Healthy Individuals

This study aims to provide evidence as to whether consumption of tart cherry juice can reduce the risk of gout and cardiovascular disease (CVD) in an acute context. The proposed study is a 2-way cross-over, randomised, placebo-controlled trial and aims to answer the following research questions:

1. What effect does a single 30mL serving of tart cherry concentrate have on serum uric acid and urinary excretion of uric acid in healthy individuals, when compared with water?
2. What effect does a single 30mL serving of tart cherry concentrate have on markers of cardiovascular disease risk and oxidative stress in healthy individuals, when compared with water?

By measuring acute changes in serum urate, fractional urinary urate excretion, inflammatory markers, oxidative stress markers and CVD risk markers (namely central and brachial blood pressure, and arterial stiffness), it will highlight possible mechanisms through which tart cherry may reduce risk of gout and/or CVD.

Healthy, non-smoking, adult volunteers (n = 15) will be recruited to a 2-way cross-over, randomized, placebo-controlled study.

A sample size of 13 has been calculated using data from White et al. (2018), using the primary outcome of change in serum uric acid level. Between-person variations in serum urate was established at approximately 50 µmol/L. Within-subject variation to apple juice was approximately 35 µmol/L. It has been estimated that cherry juice will produce a fall in serum urate of approximately 15 µmol/L (Jacob et al., 2003). Therefore, 13 participants will be needed to detect this change with 80% power at an alpha level of 0.05.

Participants will avoid strenuous exercise for 72-hours prior to the study until 24-hours post-consumption of the test drinks; compliance will be assessed through completion of a physical activity diary. They will also follow a low-polyphenolic diet for 48-hours prior to the study until 24-hours post-consumption of the test drinks; participants will be provided with a list of foods/drinks to avoid and compliance will be assessed through completion of a food diary. Participants will be provided with instructions of foods to avoid and a low polyphenolic pasta ready-meal, dessert and low nitrate water to consume the evening preceding the study day.

Participants will attend the laboratory following an overnight fast. Blood pressure (central and brachial) and arterial stiffness will be measured using a non-invasive Vicorder device. A venepuncture blood sample will be collected by a researcher trained in phlebotomy before consumption of the test drink. Approximately 10 ml of blood will be taken during each venepuncture. A urine sample will also be collected. Participants will consume 250 ml of tart cherry juice or neutral control (water) on two occasions, at least one week apart; the sequence order will be random. The cherry juice comprises 30 mL tart cherry concentrate diluted with 220 mL water. Further venous blood samples will be taken at 1 and 2 hours post-consumption. These will be supplemented with finger-prick samples collected at 3, 5 and 24 hours post drink. Post-drink measures of arterial stiffness will be taken at 1, 2, 3, 5 and 24-hours post-consumption. Additional urine samples will also be collected between 0-2, 2-4, 4-5, 5-8, 8-11, and 11-24 hours, post-consumption of the test drinks. Participants' water intake during each laboratory visit will be standardised at 500 ml. Participants will be provided with a low-polyphenolic sandwich lunch, pasta ready-meal dinner, dessert, snacks and low nitrate water to consume following the 5-hour measurements. Participants will return to the laboratory the next morning following a 12-hour fast for their 24-hour measurements.

Blood will be analysed for serum uric acid and creatinine concentrations at all time points and for CRP (a measure of inflammation) at baseline, 2, and 5 hours, post-drink. White blood cells (lymphocytes) will be separated from whole venous blood samples collected at baseline, 1 and 2-hours post-drink consumption for the analysis of oxidative DNA damage. Urine samples will be analysed for uric acid and creatinine to calculate fractional excretion of urinary uric acid (using a commercial colorimetric assay). Polyphenolic metabolites from the test drink will also be analysed in urine samples.

Data analysis: The effect of the treatment (tart cherry versus water) on all outcome variables will be analysed with 2-way repeated measures ANOVAs. A statistical significance level of P≤ 0.05 will be set.

Eligibility Criteria:
Inclusion Criteria:

* aged 18 years or over
* able and willing to participate in the study and provide written informed consent

Exclusion Criteria:

* current smoker
* any known food allergies/intolerances
* history of medical conditions, including gastrointestinal disease, severe renal impairment (estimated glomerular filtration rate of \<30ml/min) or renal disease, cardiovascular disease, diabetes (type 1 or type 2) and gout