Co-amorphous systems of sulfasalazine with matrine-type alkaloids: Enhanced solubility behaviors and synergistic therapeutic potential

Sulfasalazine (SULF), a sulfonamide antibiotic, has been utilized in the treatment of rheumatoid arthritis (RA) and inflammatory bowel disease (IBD) since its discovery. However, its poor water solubility causes the high daily doses (1---3 g) for patients, which may lead to the intolerable toxic and side effects for their lifelong treatment for RA and IBD. In this work, two water-soluble natural anti-inflammatory alkaloids, matrine (MAR) and sophoridine (SPD), were employed to construct the co-amorphous systems of SULF for addressing its solubility issue. These newly obtained co-amorphous forms of SULF were comprehensively characterized by powder X-ray diffraction (PXRD), temperature-modulated differential scanning calorimetry (mDSC), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). We also investigated their dissolution behavior, including powder dissolution, in vitro release, and intrinsic dissolution rate. Both co-amorphous systems exhibited superior dissolution performance compared to crystalline SULF. The underlying mechanism responsible for the enhanced dissolution behaviors in co-amorphous systems were also elucidated. These mechanisms include the inhibition of nucleation, complexation, increased hydrophilicity, and robust intermolecular interactions in aqueous solutions. Importantly, these co-amorphous systems demonstrated satisfactory physical stability under various storage conditions. Network pharmacological analysis was utilized to investigate the potential therapeutic targets of both co-amorphous systems against RA, revealing similar yet distinct multitarget synergistic therapeutic mechanisms in the treatment of this condition. Our study suggests these drug-drug co-amorphous systems hold promise for optimizing SULF dosage in the future and providing a potential drug combination strategy.