###### Abstract  
In the present study, we prepared an ethanol extract from the flowers of _Styphnolobium japonicum_ L. (SJFE) and found that it contains rutin as a major constituent as well as quercetin kaempfer and isonhametism as minor components. In lipopolysaccharide-stimulated RAW 264.7 macrophages, we observed that SJFE significantly inhibited the production of nitric oxide and the expression of major inflammatory biomarkers such as inducible NO synthase, cyclooxygenase-2, interleukin (IL)-6, and IL-1\(\beta\) significantly. Based on these in vitro results, we investigated the anti-inflammatory properties of SJFE on osteoarthritis (OA) of the left hind knee joints induced by monosodium iodoacetate in rats. SJFE was orally administered to the rats with arthritis for 4 weeks, and the following results were obtained. The rats treated with SJFE exhibited a 24% improvement in the weight-bearing index of their affected legs, as well as reductions of 31.5% and 23.2% in serum levels of cartilage oligomeric matrix protein and C-terminal telopeptide 2, respectively. Additionally, [PERSON]'s score, an indicator used to assess the severity of joint cartilage damage, decreased by 2.75 points compared to the control with no treatment. These findings suggest that SJFE possesses anti-inflammatory properties and can alleviate symptoms of OA, indicating its potential to offer relief to individuals suffering from arthritis.  
Styphnolobium japonicum; flavonoids; rutin; HPLC; osteoarthritis; inflammation +
Footnote †: journal: Medical  
and bleeding, hepatotoxicityoxicity, impaired blood coagulation, and immunosuppression [8; 9]. These adverse effects often limit their usage. Consequently, there is a growing demand for medications or functional ingredients with fewer safety concerns, potentially derived from biomaterials like edible herbal plants.  
_Styphnolobium japonicum_ L. has been commonly used in traditional medicine, particularly in Asia, to treat various disorders, such as appendicitis, hematuria, and intestinal bleeding, among other effects [10]. Recently, we have discovered that the fruit extract of this plant alleviates the symptoms of photo-aging by inhibiting the release of inflammatory mediators and tissue-damaging substances in the skin irradiated with UV [11; 12]. Moreover, it has been shown that the flowers of this plant also contain bioactive compounds, such as isoflavoids, and triterpen possessing anti-inflammatory properties [13; 14], suggesting the flowers may also have an anti-inflammatory property.  
Thus, the present study was performed to evaluate the anti-inflammatory properties of the flowers of this plant. For this purpose, we prepared the ethanol extract of the flowers of _S. japonicum_ L. (SJFE) and conducted two experiments to assess its anti-inflammatory activities. In the first preliminary in vitro experiment, SJFE was examined for its effects on the production of nitric oxide and the expression of genes of inflammatory mediators in lipopolysaccharide-stimulated RAW 264.7 murine macrophages. In the subsequent animal experiment, SJFE was orally administered to the rats with osteoarthritis in the knee joints induced by monosodium iodoacetate, and its effects were observed on the weight-bearing power of the affected legs and cartilage degradation parameters. We obtained the positive effects in both cellular and animal experiments. These results suggest that the flower extract of this plant has the potential to provide benefits in managing osteoarthritis.