Importance of TNF-a independent effects on the development of a vascular dysfunction in chronic inflammatory diseases
Final Report Abstract
Chronic inflammation is an important and independent risk factor for the development of cardiovascular events in patients suffering from chronic inflammatory diseases. While the treatment of the primary symptoms of, for example, rheumatoid arthritis has incredibly improved with the current therapy options, the secondary symptoms like cardiovascular events are problematic to treat. Even though many inflammatory events are mediated by or through TNF-a, the use of TNF-a antagonists together with methotrexate does not robustly decrease the risk for cardiovascular events in these patients, indicating that TNF-a independent effects may play an important role. Chronically inflamed TTP KO mice develop an endothelial dysfunction, one of the first clinical signs of vascular changes, that is independent of TNF-a, resembling the paradox observed in patients suffering from chronic inflammatory diseases. The endothelial dysfunction in these mice seems to be caused in part by a NADPH oxidase (Nox)2- mediated increase in reactive oxygen and nitrogen species, leading to a reduction of bioactive nitric oxide. It was hypothesized that the additional knock out of Nox2 in TTP KO mice will improve the vascular function of these mice in comparison to the single TTP KO. Surprisingly, the double-KO mice developed arthritis symptoms such severe and early in their lives that almost 85% of them had to be euthanized around day 63. Unfortunately, with mice that young it was not possible to measure any type of difference in endothelial function using the initially proposed methods, since occurrence of an endothelial dysfunction is a process that takes time. Ongoing studies using conscious echocardiography in mice at an age of 7 and 10 weeks may be able to shed light upon the impact of Nox2 deficiency on cardiovascular disease. The unexpectedly severe phenotype in the double-KO mice with massive swelling of the talocalcaneal joints, a joint that was not affected in any of the single knock out mice used, may be in part due to issues with inflammatory responses, as well as B cell, basophile, and eosinophil differentiation and dysfunction. However, here I report evidence that a decrease in ROS can actually increase the severity of an inflammatory syndrome, in contrast to the prevailing opinion about the harmfulness of ROS. To bypass the problems of a general Nox2 knock out, pharmacological inhibition of Nox2 activity was tried; I treated mice with 0.36 mg/kg/day of the Nox inhibitor VAS2870. While time-constraints only allowed a first pilot study in WT mice, the mice tolerated the 6-week long injections well and future studies could focus on using VAS2870 in TTP KO vs. WT mice to determine whether the compound is able to reduce or abolish the vascular dysfunction in the TTP KO mice and could have any future implications in the treatment of cardiovascular disease. Molecular studies revealed that TTP, contrary to the initial hypothesis, does not directly bind the Nox2 mRNA in order to lead to the observed increase in mRNA stability and activity in TTP KO mice. Indirect effects that are linked to the chronic inflammation in TTP KO mice may very likely lead to the observed effects.
