Chuanjiang Dong,1,* Yueqing Wang,2,3,* Yi Cai,4,* Yuhuang Wu,2,3 Wei Chen,2,3 Lu Wang,2,3 Xiaowen Liu,2 Lili Zou,2,3 Jun Wang5 

1Department of Urology, The First Dongguan Affiliated Hospital, Guangdong Medical University, Dongguan, Guangdong province, 523718, People’s Republic of China; 2Hubei Key Laboratory of Tumor Microenvironment and Immunotherapy, College of Basic Medical Science, China Three Gorges University, Yichang, Hubei Province, 443002, People’s Republic of China; 3Yichang Key Laboratory of Infection and Inflammation, College of Basic Medical Science, China Three Gorges University, Yichang, Hubei Province, 443002, People’s Republic of China; 4Department of Laboratory Medicine, Xiaogan Central Hospital, Xiaogan, Hubei Province, 432099, People’s Republic of China; 5The Second People’s Hospital of China Three Gorges University, Yichang, Hubei Province, 443002, People’s Republic of China

*These authors contributed equally to this work

Correspondence: Lili Zou; Jun Wang, Email zoulili@ctgu.edu.cn; wangjfox@ctgu.edu.cn

Purpose: Tuberculosis (TB) remains a major health threat worldwide, and the spread of drug-resistant (DR) TB impedes the reduction of the global disease burden. Ebselen (EbSe) targets bacterial thioredoxin reductase (bTrxR) and causes an imbalance in the redox status of bacteria. Previous work has shown that the synergistic action of bTrxR and sensitization to common antibiotics by EbSe is a promising strategy for the treatment of DR pathogens. Thus, we aimed to evaluate whether EbSe could enhance anti-TB drugs against Mycobacterium marinum (M. marinum) which is genetically related to Mycobacterium tuberculosis (Mtb) and resistant to many antituberculosis drugs.
Methods: Minimum inhibitory concentrations (MIC) of isoniazid (INH), rifampicin (RFP), and streptomycin (SM) against M. marinum were determined by microdilution. The Bliss Independence Model was used to determine the adjuvant effects of EbSe over the anti-TB drugs. Thioredoxin reductase activity was measured using the DTNB assay, and its effects on bacterial redox homeostasis were verified by the elevation of intracellular ROS levels and intracellular GSH levels. The adjuvant efficacy of EbSe as an anti-TB drug was further evaluated in a mouse model of M. marinum infection. Cytotoxicity was observed in the macrophage cells Raw264.7 and mice model.
Results: The results reveal that EbSe acts as an antibiotic adjuvant over SM on M. marinum. EbSe + SM disrupted the intracellular redox microenvironment of M. marinum by inhibiting bTrxR activity, which could rescue mice from the high bacterial load, and accelerated recovery from tail injury with low mammalian toxicity.
Conclusion: The above studies suggest that EbSe significantly enhanced the anti-Mtb effect of SM, and its synergistic combination showed low mammalian toxicity in vitro and in vivo. Further efforts are required to study the underlying mechanisms of EbSe as an antibiotic adjuvant in combination with anti-TB drug MS.

Keywords: Ebselen, antibiotic adjuvant, thioredoxin reductase, reactive oxygen species