Forsythiaside A Alleviates Kidney Injury and Intestinal Epithelium Dysfunction in <scp>IgA</scp> Nephropathy by Inhibiting <scp>TLR4</scp> / <scp>NF</scp> ‐ <scp>κB</scp> Signaling

IgA nephropathy (IgAN), the most common form of glomerulonephritis, is a major and growing public health issue. It results from intestinal barrier dysfunction that leads to mesangial deposition of pathogenic galactose-deficient IgA1 (Gd-IgA1) and renal inflammation. This study aimed to investigate the therapeutic effects and associated mechanisms of forsythiaside A on intestinal barrier injury in IgAN in animal models. Rats were treated with bovine serum albumin (BSA), carbon tetrachloride (CCl₄), and lipopolysaccharide (LPS) to induce IgAN, followed by intragastric administration of forsythiaside A once daily from weeks 15 to 20 after model establishment. Biochemical markers, including 24-h urinary protein, blood urea nitrogen (BUN), serum creatinine (SCr), renal and intestinal tissue pathology, and levels of pro-inflammatory cytokines in the serum, kidney, and intestine, intestinal tight junction proteins, and TLR4/NF-κB pathway components were examined. The results showed that forsythiaside A decreased 24-h urinary protein, BUN, and SCr levels, alleviated renal damage, and attenuated glomerular and tubular lesions, collagen deposition, and glomerular IgA deposition in IgAN rats. Forsythiaside A treatment inhibited CD68-positive macrophage infiltration in renal tissues and downregulated serum and renal levels of IL-1β, IL-6, and TNF-α, while also alleviating intestinal barrier injury and intestinal inflammation, as shown by reduced levels of IL-1β, IL-6, and TNF-α and increased expression of the intestinal tight junction proteins occludin and ZO-1. Lastly, forsythiaside A treatment lowered serum LPS concentrations, as well as renal and intestinal levels of TLR4, p-NF-κB p65, and p-IκBα, and raised both renal and intestinal levels of IκBα. Collectively, forsythiaside A was found to ameliorate the progression of IgAN in rats by alleviating inflammation and intestinal barrier injury by suppression of TLR4/NF-κB signaling.