Functional analyses of Toxoplasma gondii dihydroorotase reveal a promising anti-parasitic target.

Toxoplasma gondii relies heavily on the de novo pyrimidine biosynthesis pathway for fueling the high uridine-5'-monophosphate (UMP) demand during parasite growth. The third step of de novo pyrimidine biosynthesis is catalyzed by dihydroorotase (DHO), a metalloenzyme that catalyzes the reversible condensation of carbamoyl aspartate to dihydroorotate. Here, functional analyses of TgDHO reveal that tachyzoites lacking DHO are impaired in overall growth due to decreased levels of UMP, and the noticeably growth restriction could be partially rescued after supplementation with uracil or high concentrations of L-dihydroorotate in vitro. When pyrimidine salvage pathway is disrupted, both DHOH35A and DHOD284E mutant strains proliferated much slower than DHO-expressing parasites, suggesting an essential role of both TgDHO His35 and Asp284 residues in parasite growth. Additionally, DHO deletion causes the limitation of bradyzoite growth under the condition of uracil supplementation or uracil deprivation. During the infection in mice, the DHO-deficient parasites are avirulent, despite the generation of smaller tissue cysts. The results reveal that TgDHO contributes to parasite growth both in vitro and in vivo. The significantly differences between TgDHO and mammalian DHO reflect that DHO can be exploited to produce specific inhibitors targeting apicomplexan parasites. Moreover, potential DHO inhibitors exert beneficial effects on enzymatic activity of TgDHO and T. gondii growth in vitro. In conclusion, these data highlight the important role of TgDHO in parasite growth and reveal that it is a promising anti-parasitic target for future control of toxoplasmosis.

In Vitro Evaluation Reveals Effect and Mechanism of Artemether against Toxoplasma gondii.

Due to the limited effectiveness of existing drugs for the treatment of toxoplasmosis, there is a dire need for the discovery of new therapeutic options. Artemether is an important drug for malaria and several studies have indicated that it also exhibits anti-T. gondii activity. However, its specific effect and mechanisms are still not clear. To elucidate its specific role and potential mechanism, we first evaluated its cytotoxicity and anti-Toxoplasma effect on human foreskin fibroblast cells, and then analyzed its inhibitory activity during T. gondii invasion and intracellular proliferation. Finally, we examined its effect on mitochondrial membrane potential and reactive oxygen species (ROS) in T. gondii. The CC50 value of artemether was found to be 866.4 µM, and IC50 was 9.035 µM. It exhibited anti-T. gondii activity and inhibited the growth of T. gondii in a dose-dependent manner. We also found that the inhibition occurred primarily in intracellular proliferation, achieved by reducing the mitochondrial membrane integrity of T. gondii and stimulating ROS production. These findings suggest that the mechanism of artemether against T. gondii is related to a change in the mitochondrial membrane and the increase in ROS production, which may provide a theoretical basis for optimizing artemether derivatives and further improving their anti-Toxoplasma efficacy.

[Expression and significance of JNK1, Raf-1 and Livin in the carcinogenesis of sporadic colorectal tubular adenoma].

OBJECTIVE: To study the possible role of JNK1, Raf-1 and Livin in the carcinogenesis of sporadic colorectal tubular adenoma. METHODS: Immunohistochemical staining was used to detect the expression of JNK1, Raf-1 and Livin proteins in 65 sporadic colorectal tubular adenomas with dysplasia of varying degrees and 22 colorectal tubular adenoma with cancerous area. RESULTS: In normal colorectal mucosa, colorectal tubular adenoma with dysplasia and colorectal tubular adenoma with cancerous area, the positive rate of JNK1, Raf-1 and Livin expression was increased gradually. The positive expression of JNK1, Raf-1 and Livin was all significantly higher in the cases of colorectal tubular adenoma with dysplasia or with cancerous area than that in normal colorectal mucosa (P < 0.05), and the positive expression of JNK1, Raf-1 and Livin was significantly higher in colorectal tubular adenoma with cancerous area than that in colorectal tubular adenoma with dysplasia of different degrees (P < 0.05). In the cases of colorectal tubular adenoma with dysplasia of varying degrees, the positive expression of Raf-1 was increased along with the increasing dysplasia degree of colorectal tubular adenoma (P < 0.05). Coexpression of JNK1, Raf-1 and Livin increased gradually in the carcinogenesis of sporadic colorectal tubular adenoma, while positive correlation was found among the expressions of JNK1, Raf-1 and Livin. CONCLUSION: JNK1, Raf-1 and Livin may be involved in the carcinogenesis of sporadic colorectal tubular adenoma.