Synergistic Protective Effects of Oleaster Fruit and Sophora japonica L. Fruit Extracts Against IL-1β-Induced Inflammation in Human Chondrocytes

Osteoarthritis (OA) is a degenerative joint disease characterized by chronic inflammation and progressive cartilage breakdown. This study investigated the synergistic protective effects of oleaster fruit extract (OE) and <i>Sophora japonica</i> L. fruit extract (SJE) against interleukin-1β (IL-1β) -induced inflammation in human chondrocytes. OE and SJE were tested individually and in combination at various ratios (3:1, 2:1, 1:1, 1:2, and 1:3). Among the tested mixtures, the 3:1 OE:SJE ratio exhibited the most pronounced synergistic effect. When used individually, the concentrations required to achieve 90% cell viability were 313.6 µg/mL for OE and 4135.8 µg/mL for SJE. In contrast, the same viability level was achieved with a combined treatment of 26.4 µg/mL OE and 8.8 µg/mL SJE, yielding a combination index of 0.25, indicative of strong synergy. The 3:1 OE:SJE combination also significantly suppressed inflammatory mediators, including nitric oxide, interleukin-6, and tumor necrosis factor-α. This treatment also led to the downregulation of matrix-degrading enzymes, such as matrix metalloproteinase (MMP)-9 and MMP-13, and it promoted the preservation of hyaluronan, a key extracellular matrix component. These findings suggest that the 3:1 OE:SJE combination exerts a synergistic protective effect by modulating both inflammatory and catabolic pathways and may represent a promising therapeutic strategy for OA prevention or treatment.