Table 3.
Anti-inflammatory, antioxidant, and hypouricemic effects of quercetin.
| Author | Study | Treatment | Findings | Comments |
|---|---|---|---|---|
| In vitro studies | ||||
| Kirakosyan et al.20 | In vitro study examining the effects of tart cherry on enzymes related to cardiovascular disease and diabetes | Quercetin (0.1 mg/ml) extracted from tart cherry powder | Enzymatic activity inhibition: COX-I by 52.8%; COX-II by 42.3%; XO by 10%; lipoxygenase by 67% |
Tart cherry extract with 65.1% and 37.8% inhibition on COX-I and II, XO by 26% |
| O’Leary et al.73 | Examine the effect of flavonoids and vitamin E on COX-II transcription and COX activity in vitro | Quercetin and quercetin conjugates at 0.1, 1.0, and 10 µmol/l concentrations | Quercetin and its conjugates reduced COX-II expression in both unstimulated and IL-1β stimulated colon cancer cells; COX-II activity inhibited by up to 85% | Effect was not dose dependent |
| Wilms et al.72 | Examine the protective effects of quercetin against oxidative DNA damage and formation of bulky DNA adducts in vitro and in vivo/ex vivo in human lymphocytes |
In vitro: quercetin at various concentrations (0–100 μmol/l) In vivo, 8 female volunteers consumed 1 l of quercetin-rich juice daily for 4 weeks |
In vitro: significant (p < 0.01) dose-dependent protection against formation of oxidative damage and BPDE-DNA adducts (p < 0.05). In vivo: TEAC increased from 773 to 855 μmol/l TE (p = 0.04) at 4 weeks |
Ex vivo: oxidative damage nonsignificantly (p = 0.07) decreased by 41%, BPDE-DNA adduct level nonsignificantly (p = 0.24) decreased by 11% |
| Zhang et al.74 | In vitro study exploring the inhibitory action of quercetin on xanthine oxidase | Quercetin dissolved in absolute ethanol and diluted to different concentrations | Quercetin reversibly inhibited the generation of urate and superoxide radicals Concentration of quercetin resulting in 50% loss of enzyme activity was 2.74 ± 0.04 × 10−6 mol/l |
Inhibition was dose dependent Allopurinol concentration resulting in 50% loss of enzyme activity was 2.69 ± 0.02 × 10−6 mol/l |
| Animal studies | ||||
| Jingqun-Huang et al.70 | Animal model examining the effects of quercetin on MSU crystal-induced inflammation in rats | Quercetin at 100, 200, and 400 mg/kg given orally daily for 7 days. | Dose-dependent improvement in joint circumference, decreased synovitis at 200 or 400 mg/kg, and significantly decreased levels of TNF-α (p < 0.01), IL1-β (p < 0.01), and COX-II (p < 0.05) | Similar effect seen in rats treated with indomethacin at 3 mg/kg Statistically significant improvement in antioxidant status (SOD, catalase, malondialdehyde) |
| Mamani-Matsuda et al.71 | In vivo and in vivo/ex vivo study examining the effects of quercetin on macrophage activation and inflammatory mediators in chronic adjuvant-induced arthritis in rats | Quercetin 150 mg/rat by gavage; 25 and 50 mg/rat IC, every 2 days x5 doses | Oral quercetin at 150 mg/rat (p < 0.0004) and IC quercetin at 50 >25 mg/rat significantly reduced arthritis scores, and significantly decreased levels of TNF-α (p < 0.02), IL1-β (p < 0.003), and MCP1 (p < 0.014) | PGE₂ production unchanged |
| Human studies | ||||
| Shi et al.75 | Randomized, double-blinded, placebo-controlled, crossover trial examining the effects of quercetin on plasma urate, BP, and fasting glucose in 22 healthy males without gout | One tablet containing 500 mg quercetin daily for 4 weeks | After 4 weeks, plasma urate levels decreased from baseline of 330 ± 56 μmol/l (5.55 ± 0.94 mg/dl) to 304 ± 48 μmol/l (5.11 ± 0.81 mg/dl), p < 0.008 | Fasting glucose, urinary excretion of urate, and BP were unchanged |
BPDE, benzo(a)pyrene [B(a)P] diolepoxide; COX, cyclooxygenase; DNA, deoxyribonucleic acid; MCP1, monocyte chemoattractant protein-1; MSU, monosodium urate; BP, blood pressure; TE, Trolox equivalent; TEAC, Trolox-equivalent antioxidant capacity; XO, xanthine oxidase; IL, interleukin; TNF, tumor necrosis factor; SOD, superoxide dismutase; PGE2, prostaglandin E2; IC, intracutaneous.