Proanthocyanidins in immune-mediated inflammatory diseases: molecular mechanisms and therapeutic potential

Immune-mediated inflammatory diseases (IMIDs), a heterogeneous group of disorders, are characterized by chronic inflammation and subsequent organ damage, encompassing diverse conditions like atopic dermatitis (AD), inflammatory bowel disease (IBD) - which includes Crohn's disease (CD) and ulcerative colitis (UC), psoriasis, rheumatoid arthritis (RA), and systemic lupus erythematosus (SLE). These chronic diseases mainly stem from inappropriate or excessive immune responses. In recent years, the incidence of IMIDs has been increasing. Considering their frequent association with various complications, such as cardiovascular diseases, cognitive impairment, metabolic disorders, and high-level disabilities, IMIDs have emerged as a major medical challenge. Proanthocyanidins (PCs), also known as condensed tannins, are among the most abundant polyphenols in the human diet. Owing to their health-protective activities, they have attracted extensive research interest. These compounds are commonly found in plants, including fruits, nuts, bark, chocolate, wine, as well as some plant seeds and flowers. A multitude of studies have demonstrated that PCs possess a wide range of pharmacological properties, such as antioxidant effects, anti-inflammatory action, immune regulation, cardiovascular benefits, and antineoplastic effects. It has been demonstrated that PCs, as natural plant compounds, are safe and rare of notable adverse effects. Their extensive range of biological activities has facilitated their applications in treating various IMIDs. In this review, we provide a comprehensive overview of the diverse biological activities of PCs and their favorable roles in common IMIDs, while also elucidating the underlying mechanisms involved in IMIDs.