A Two-Week Quercetin Supplementation in Horses Results in Moderate Accumulation of Plasma Flavonol Concentrations

Quercetin is a plant-derived flavonoid with strong anti-inflammatory properties. Previously, systemic availability of quercetin was documented in horses. We investigated effects of a daily quercetin supplementation on plasma concentrations of quercetin and its metabolites over two weeks. Additionally, plasma concentrations of selected proinflammatory and anti-inflammatory cytokines were analyzed before and immediately after the experiment. Four adult Warmblood horses with a mean body weight ± standard error of the mean of 551 ± 46 kg were used. During a two-week pre-experimental phase and also during the experiment, the use of dietary supplements, apples, or any form of medication was excluded; the horses were offered hay ad libitum, concentrated feed individually (7 AM and PM), and 8 hours access to pasture. During the experiment, quercetin (10 mg/kg body weight) was administrated within the evening meals. Blood samples were collected (jugular vein) three times during the pre-experimental phase and on days 4, 8, 11, and 14 after the start of the experiment. Flavonols in plasma and feed were analyzed by high-performance liquid chromatography; plasma concentrations of cytokines were measured using commercial enzyme-linked immunosorbent assay kits. Daily quercetin supplementations for two weeks increased kaempferol and thus total plasma flavonol concentrations time dependently without accumulation of quercetin or its methylated metabolite isorhamnetin. Although proinflammatory cytokines stayed below detection limit, plasma concentrations of anti-inflammatory cytokines (interleukin-10, interleukin-1 receptor antagonist) were enhanced by quercetin feeding. The study indicates that dietary quercetin supplementation moderately induces total plasma flavonols and thus may be useful in controlling inflammatory disorders in horses. However, anti-inflammatory effects of quercetin must be confirmed in controlled trials.