Human case studies have described pleural effusions and the presence of a widened mediastinum onchest x-rays as the most common clinical features of anthrax disease. Of the 11 people who developed acuteanthrax disease in 2001, 6 survived due to the intensive care received at hospitals that included fluid drainagefrom the lung, and treatment with antibiotics. Increased vascular permeability has been strongly implicated inanthrax toxin induced tissue edema in a large number of mammalian models (non-human primates, rabbits,guinea pigs, rats, mice). The importance of blood vessels and endothelial cells in anthrax toxicity has beendifficult to investigate due to the inability to observe progressive vascular changes without sacrificing themammalian host. Therefore, we developed the transparent zebrafish embryo as a model to facilitate liveimaging of anthrax lethal toxin action on intact blood vessels. We observed that lethal toxin induced increasedvascular permeability as an early consequence leading to progressive defects in cardiovascular function. Sincevascular permeability is regulated by the vascular endothelial growth factor, also called the vascularpermeability factor (VEGFNPF), we employed chemical inhibitors to block this pathway to reduce toxin effects,achieving remarkable levels of attenuation. These data were confirmed using an established vascularpermeability assay in adult mouse skin microvasculature termed the Miles Assay. Here, inhibition of theVEGFNPF pathway reduced lethal toxin induced vascular leakage as measured by a colorimetric dye. Sincethe Fischer 344 rat is an established anthrax toxin model where vascular defects have been observed, we arecurrently employing this model to test the hypothesis that blocking the VEGF pathway can yield protectiveeffects against lethal toxin action as measured by increased survival time. This model is extremely sensitive tolethal toxin challenge, typically inducing death in about 45-60 minutes. In our experiments, we observevascular defects in multiple organs and extensive pleural effusions at late stages during toxin challenge.Analysis of VEGFR phosphorylation levels in the lung demonstrated increased activation of this pathway posttoxin injection, suggesting that inhibitors of the VEGF pathway could attenuate toxin effects. Since anti-VEGFtherapies are already in clinical use for cancer therapy and for the treatment of age-related vascularizedmacula degeneration, further testing of their usefulness as an anti-anthrax therapeutic could be expedited. Thisapproach may be combined with antibiotics or anti-toxins to increase the therapeutic window for the effectivetreatment of anthrax disease.
Showing the most recent 10 out of 417 publications
