Forsythiaside A Alleviates Kidney Injury and Intestinal Epithelium Dysfunction in IgA Nephropathy by Inhibiting TLR4/NF-κB 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.