Huangqin decoction disrupts energy metabolism of Trichophyton rubrum, with isocitrate lyase as a potential target

The dermatophyte Trichophyton rubrum (T. rubrum) is a highly specialized filamentous fungus that primarily infects keratinized tissues and is the most common pathogen isolated from human dermatophytosis. Huangqin decoction (HQD), a classical traditional Chinese medicine (TCM) formula, has been shown to exhibit inhibitory effects against T. rubrum in our previous study. However, the underlying mechanisms responsible for these effects remain poorly understood. This study aimed to elucidate the comprehensive mode of action of Huangqin decoction (HQD) against T. rubrum as a whole by integrating transcriptome sequencing validated by quantitative real-time PCR (qRT-PCR) and enzymatic activity assays. By treating T. rubrum with HQD at minimum inhibitory concentration (MIC), a total of 338 differentially expressed genes (DEGs) were detected in T. rubrum after HQD exposure (q-value < 0.05). Gene function and Encyclopedia of Genes and Genomes (KEGG) enrichment analyses indicated that DEGs were significantly related to energy metabolism. The expression levels of six DEGs by the involvement of energy metabolism, including the degradation of branched-chain amino acids and the glyoxylate cycle, were verified by qRT-PCR. Three key enzymes in the glyoxylate cycle were further examined by enzymatic activity assays. The results showed that compared to the control group, activities of citrate synthase (CS), aconitate hydratase (ACO), and isocitrate lyase (ICL) in T. rubrum were predominantly affected by HQD (p-value < 0.05). The overall evidence suggested that the interference with energy metabolism contributed to the mode of action of HQD against T. rubrum. Given that the glyoxylate cycle represents an important specific metabolic process in fungi, and the involved enzyme ICL is absent in humans, ICL emerges as a potential antifungal target of HQD against T. rubrum. In summary, our study provides a theoretical basis for the mechanisms of HQD upon T. rubrum infections and makes contributions to the clinical application of HQD against fungi.