Spectroscopic and Molecular Docking Study on Specific Binding and Inhibition of Isoniazid to Human Serum Albumin and Catalase.

Isonicotinic acid hydrazide (Isoniazid, INH) is one of the most commonly used first-line anti-tuberculosis drugs, which has been reported that the high concentration of INH in human body can lead to epilepsy, liver function failure, and even death. Therefore, studying the potential binding effects of INH on the structure and activity of human serum albumin (HSA) and catalase (CAT) is very essential for evaluating its toxicity and side effect. In this paper, multi-spectroscopic and molecular docking methods were used to elucidate the patterns of INH to HSA and CAT under imitated physiological conditions. The inner filter effect of all fluorescence data in the paper was eliminated to get accurate binding parameters. The Stern-Volmer quenching constants (KSV) of both HSA-INH system and CAT-INH system inversely correlated with temperatures, demonstrating that INH quench the intrinsic fluorescence of HSA and CAT via static quenching. The conformational investigation of HSA and CAT through UV-visible absorption spectroscopy, synchronous fluorescence and circular dichroism (CD) showed that INH could change the micro-environment of tryptophan residues and reduced the α-helix content of protein. These results demonstrated that the binding of INH may lead to the loosening of protein skeleton, which which may affect its physiological function. The results of molecular docking revealed that the INH was located in Sudlow’s site I of HSA. And INH bound to CAT at a cavity among the wrapping domain helical domain and β-barrel, which resulted in the inhibition of CAT activity. In addition, Levofloxacin (LVFX) is a new effective and safe second-line anti-tuberculosis drugs and can improve the curative effect on anti-TB by using with other anti-TB drugs, the result of Hill’s coefficients (nH) about synergy between INH and proved that LVFX promoted the interaction of HSA with INH. Moreover, according to the CD spectra, synergy between INH and LVFX changed the conformation of HSA and the amount of α-helix decreased about 7.9%. This work will provide important insights into the binding and toxicity mechanism of INH to HSA and CAT in vivo and is expected to be helpful in evaluating the essential information for using the INH safely.