ABSTRACT
Infection with a high dose of the intracellular parasitic protozoan Leishmania major induces a sustained hyperalgesia in susceptible BALB/c mice accompanied by up-regulation of the pro-inflammatory cytokines IL-1ß and IL-6. Interleukin-13 (IL-13) has been shown to reduce this hyperalgesia (despite increased levels of IL-6) and the levels of IL-1ß during and after the treatment period. These findings favor the cytokine cascade leading to the production of sympathetic amines (involving TNF-α and KC) over prostaglandins (involving IL-lß and IL-6) as the final mediators of hyperalgesia. The aim of this study was to investigate the effect of daily treatment with the ß-blockers atenolol on L. major-induced inflammation in mice with respect to hyperalgesia as well as the levels of TNF-α and KC (the analog of IL-8 in mice). Our data demonstrates that atenolol is able to reduce the L. major induced sustained peripheral hyperalgesia, which does not seem to involve a direct role for neither IL-lß nor KC. Moreover, our results show that TNF-α may play a pivotal and direct role in sensitizing the peripheral nerve endings (nociceptors) since its level was reduced during the period of atenolol treatment, which correlates well with the reduction of the observed peripheral, but not central, hyperalgesia. These findings contribute to a better understanding of the cytokine cascade leading to hyperalgesia and may lead to the development of new and more efficient medications for many types of pain.
ABSTRACT
Infection with high dose Leishmania major induces a sustained hyperalgesia in BALB/c mice while low dose induces a short lived hyperalgesia both accompanied with the upregulation of IL-1ß and IL-6. Although IL-13 was shown to reduce the high dose L. major hyperalgesia during the treatment period, this effect was accompanied by a significant decrease in the levels of IL-1ß and a significant increase in the levels of IL-6 in the paws of mice even beyond this period. Those results suggest that IL-13 exerts those effects via the induction of another mediator, IL-4 being a potential candidate due to its known hypoalgesic effects in other models and to its close functional closeness to IL-13 especially at the level of receptors. In this study we correlated the pain thresholds and the levels of IL-1ß, IL-6 and IL-4 with the period of IL-13 treatment and beyond it in mice infected with high and low dose of L. major. The results of both models show that IL-1ß plays no direct role in provoking the observed hyperalgesia after stopping the treatment with IL-13 which is in contrary to IL-6 which might be a key player after the treatment period. Furthermore we demonstrate that there is no correlation between the levels of IL-4, hyperalgesia, the decreased IL-1ß levels and the increased levels of IL-6 in the paws of IL-13 treated and L. major (high and low dose) infected BALB/c mice.
