Kynurenic Acid in Kidney Fibrosis: Exploring Therapeutic Potential

Background: Kidney injury of various origins leads to TGF-β1 activation and progressive fibrosis. In this study, we investigated the antifibrotic potential of immunomodulatory metabolites kynurenine (KYN) and kynurenic acid (KYNA). Methods: Mouse fibroblasts were stimulated with recombinant TGF-β1 (5 ng/ml) and treated with KYN (3 or 10 µmol/l) or KYNA (50 or 150 µmol/l) for 24, 48, or 72 hours. Treatments were applied at initiation and at 24-hour intervals for longer timepoints. Cells were analysed by Western blotting. Wistar rats were divided into four groups (n=10): sham-operated rats (SHAM), rats underwent unilateral ureteral obstruction (UUO), and UUO rats treated with KYNA p.o. (100 mg/kg every 24 hours; KYNA100, and 200 mg/kg every 12 hours; KYNA400) for 7 days. On day 8, kidneys were collected for histological and protein expression analysis. Results: In vitro, KYN and KYNA treatments attenuated expression of TGF-β1-fibrotic pathway proteins. The most significant decrease was found in the KYNA150 group at all timepoints: 24h (pSMAD2 -31%±7% vs.TGF, p<0.05), 48h (Collagen I -33%±11%; αSMA -76%±14%; pSMAD2 -59%±21%; pp38 -52%±12%; pERK/ERK -58%±15%; pJNK/JNK -69%±13%; pMEK/MEK -84%±21%; all vs.TGF, p<0.05) and 72h (Collagen I -67%±11%; Vimentin -59%±5%; αSMA -85%±20%; pSMAD2 -70%±38%; pp38 -68%±30%; pJNK/JNK -52%±28% all vs.TGF, p<0.05). In animal model, we observed a reduction in fibrotic area (-45%±6%; vs.UUO; p<0.05), α-SMA-positive area (-22%±5%; vs.UUO; p<0.05) and the expression of pp38 (-51%±14%; vs.UUO p<0.05) in KYNA100 group. The treatment reduced cortical (-14%±5%; vs. UUO p<0.05) and medullary (-17%±7%; vs. UUO p<0.05) distal tubule dilatation. We observed decrease in Collagen III (-49%±17%; vs.UUO; p<0.05) and Vimentin expression (-32%±14%; vs. UUO; p<0.05) in KYNA400 group. KYNA also modulated oxidative stress markers (MnSOD +12%±4%; iNOS -31%±10%; all vs.UUO, p<0.05). Conclusion: Our study demonstrates, for the first time, an antifibrotic potential of KYN and KYNA by reducing the expression of fibrotic markers and signaling proteins in in vitro and in vivo fibrotic model. KYNA also exerts antioxidant effects, supporting its therapeutic potential. Funding: Project was supported by APVV-23-0399, VEGA 1/0121/2022, VEGA 1/0513/2024. Funding: Government Support – Non-U.S.