The flavonoid quercetin inhibits titanium dioxide (TiO 2 )-induced chronic arthritis in mice.

Titanium dioxide (TiO ₂ ) is a common component of orthopedic prosthesis. However, prosthesis wear releases TiO ₂ , which induces inflammation and osteolysis in peri-prosthetic tissues. Quercetin is a flavonoid widely present in human diet, which presents biological activities such as antinociceptive, anti-inflammatory and antioxidant effects. Therefore, the effect of intraperitoneal treatment with quercetin in TiO ₂ -induced arthritis model was evaluated. In the first set of experiments, mice received injection of TiO ₂ (0.1-3 mg/knee joint) and articular mechanical hyperalgesia, edema and histopathology analysis were performed in a 30 days protocol. The dose of 3 mg of TiO ₂ showed the most harmful effect, and was chosen to the following experiments. Subsequently, mice received 3 mg of TiO ₂ followed by post-treatment with quercetin during 30 days. Quercetin (10-100 mg/kg) inhibited in a dose-dependent manner TiO ₂ -induced knee joint mechanical hyperalgesia, edema and leukocyte recruitment and did not induce damage in major organs such as liver, kidney and stomach. The dose of 30 mg/kg was chosen for the subsequent analysis, and reduced histopathological changes such as leukocyte infiltration, vascular proliferation and synovial hyperplasia (pannus formation) on day 30 after TiO ₂ challenge. The protective analgesic and anti-inflammatory mechanisms of quercetin included the inhibition of TiO ₂ -induced neutrophil and macrophage recruitment, proteoglycan degradation, oxidative stress, cytokine production (TNF-α, IL-1β, IL-6, and IL-10), COX-2 mRNA expression, and bone resorption as well as activation of Nrf2/HO-1 signaling pathway. These results demonstrate the potential therapeutic applicability of the dietary flavonoid quercetin to reduce pain and inflammatory damages associated with prosthesis wear process-induced arthritis.
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