Crystal engineering optimizes emodin-tetramethylpyrazine combination: From cocrystal design to in vivo anti-colitis efficacy assessment

Emodin (EMO) shows therapeutic promise for ulcerative colitis (UC), yet its clinical utility is hampered by low bioavailability. To rationally overcome this limitation, this study employed cocrystal engineering, strategically selecting tetramethylpyrazine (TMP)-a natural compound from traditional Chinese medicine-as the cocrystal coformer (CCF). The selection of TMP was guided by a systematic CCF screening strategy, incorporating extensive literature analysis of natural compound CCF candidates, computational chemistry methods to predict favorable hydrogen-bonding interactions and interaction sites with EMO, and machine learning assessment of cocrystallization propensity. Utilizing this rational design approach, we successfully synthesized and characterized a novel EMO-TMP cocrystal through comprehensive solid-state characterization techniques. The resulting cocrystal significantly enhanced the aqueous solubility of EMO while preserving its intrinsic bioactivity. Pharmacokinetic studies confirmed that the cocrystal formulation markedly improved the oral bioavailability of EMO. In a dextran sulfate sodium (DSS)-induced ulcerative colitis (UC) model, the EMO-TMP cocrystal demonstrated superior efficacy compared to EMO alone, effectively alleviating colitis symptoms and associated pathological markers. This enhanced <i>in vivo</i> efficacy is attributed to the significantly improved systemic exposure achieved through the rationally designed cocrystal. Our findings establish the EMO-TMP cocrystal as a highly promising strategy to surmount the physicochemical barriers of EMO, unlocking its full clinical potential for UC treatment. Critically, this work not only validates TMP as an efficient and safe CCF specifically suited for active pharmaceutical ingredients (APIs) rich in hydrogen-bond donors, but also exemplifies the value of leveraging formulation principles and compatible components inherent in traditional Chinese medicine through advanced crystal engineering approaches.