Background: Toxocara canis, a globally distributed roundworm, can cause debilitating disease in dogs and humans; however, little is known about the metabolomic response of the hosts to T. canis infection. There is an increasing need to understand the metabolic mechanisms underlying the pathogenesis of T. canis infection in dogs. Here, we examined the metabolomic changes in Beagle dogsʼ serum following T. canis infection using LC-MS/MS. Results: The metabolic profiles of Beagle dogsʼ serum were determined at 12 h, 24 h, 10 d and 36 d after oral infection with 300 infectious T. canis eggs by LC-MS/MS. We tested whether the T. canis-associated differentially abundant metabolites could distinguish the serum of infected dogs from controls, as measured by the area under the receiver operating characteristic (ROC) curve (AUC). The differentially expressed metabolites were further evaluated by principal components analysis and pathway enrichment analysis. A total of 5756 and 5299 ions were detected in ESI+ and ESI− mode, respectively. ROC curve analysis revealed nine and five metabolite markers, at 12 hpi and 24 hpi to 36 dpi, respectively, with potential diagnostic value for toxocariasis. The levels of taurocholate, estradiol, prostaglandins and leukotriene were significantly changed. Primary bile acid biosynthesis pathway, steroid hormone biosynthesis pathway and biosynthesis of unsaturated fatty acids pathway were significantly altered by T. canis infection. Conclusions: These findings show that T. canis infection can induce several changes in the dog serum metabolome and that the metabolic signature associated with T. canis infection in dogs has potential for toxocariasis diagnosis.

Diphtheria toxin A (DTA), a segment of the diphtheria toxin (tox), inhibits protein synthesis in cells. When released from a cell, DTA is nontoxic and cannot enter other cells independently without the help of diphtheria toxin B. In this study, we artificially synthesized the DTA gene sequence and cloned it into pEGFP-N1 to generate the recombinant vector pEGFP-N1-DTA. This recombinant vector was then transfected into 293T cells to observe the effect of DTA protein expression on enhanced green fluorescent protein (EGFP) protein expression and the proliferation of 293T cells. After 48 h, high levels of EGFP expression were seen in control pEGFP-N1-transfected cells, whereas very low levels were seen in cells transfected with pEGFP-N1-DTA. Reverse transcription polymerase chain reaction confirmed the expression of the DTA gene in cells transfected with pEGFP-N1-DTA. Further, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay revealed a significant difference in cell proliferation between the control group and the pEGFP-N1-DTA-transfected group. Using the expression of EGFP expression as an indicator, this study revealed that DTA expression can inhibit intracellular protein synthesis and cell proliferation.